Characterization of high density lipoprotein binding to human adipocyte plasma membranes

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Tumor products and the hypercalcemia of malignancy.

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G R Mundy, K J Ibbotson, S M D'Souza

Secretion of an articular cartilage proteoglycan-degrading enzyme activity by murine T lymphocytes in vitro.

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Destruction of articular cartilage is the hallmark of inflammatory arthritides. Enzymes elaborated by mononuclear cells infiltrating the synovium mediate, in part, the degradation of the cartilage extracellular matrix. Since mononuclear cells are the dominant cell type found in chronic inflammatory synovitis, we investigated whether interaction of immune mononuclear cells with antigen initiated the synthesis and secretion of a proteoglycan-degrading enzyme activity. Proteoglycan-degrading enzyme activity was monitored by the capacity of murine spleen cell conditioned medium to release [3H]serine/35SO4 incorporated into rabbit cartilage proteoglycan monomer fraction (A1D1), and by the relative change in specific viscosity of bovine nasal cartilage proteoglycan monomer. The results demonstrated that both virgin and immune mononuclear cells spontaneously generated proteoglycan-degrading enzyme activity and that cellular activation and proliferation induced by the antigen keyhole limpet hemocyanin or the mitogen phytohemagglutinin was not required. Kinetic studies demonstrated stable release of the enzyme activity over 72 h. Cell separation studies showed that T lymphocytes, a thymoma line, and macrophages separately produced proteoglycan-degrading enzyme activity. The enzyme activity has been partially characterized and appears to belong to a class of neutral pH metal-dependent proteinases. These observations, the first to demonstrate that T lymphocytes secrete an enzyme capable of degrading cartilage proteoglycan, raise the possibility that this enzyme activity contributes to cartilage extracellular matrix destruction in vivo. Moreover, these data support the conclusion that production of this enzyme by T lymphocytes is independent of an antigen-specific stimulus.

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G M Kammer, A I Sapolsky, C J Malemud

Apolipoprotein B-100 deficiency. Intestinal steatosis despite apolipoprotein B-48 synthesis.

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We describe a child, the issue of phenotypically normal parents, who had fat malabsorption, both intestinal and hepatic steatosis, and serum cholesterol and triglyceride concentrations of 38 and 63 mg/dl, respectively. Lipoprotein electrophoresis, Ouchterlony double diffusion, and electron microscopy demonstrated that normal low density lipoproteins (LDL: 1.006 less than rho less than 1.063 g/ml) were absent. Lipoprotein particles in the rho less than 1.006-g/ml fraction were triglyceride rich, very large (93.2 +/- 35.1 nm), and contained the B-48 but not the B-100 apoprotein; both species of apolipoprotein (apo) B were found in the parents' lipoproteins. These chylomicrons and chylomicron remnants were present even in the patient's fasting plasma, which suggested prolonged dietary fat absorption. Plasma levels of high density lipoprotein lipids and proteins were low, and the phosphatidylcholine/sphingomyelin ratio was reduced as in typical abetalipoproteinemia. The monosialylated form of apo C-III was not identified on polyacrylamide gel electrophoresis, which suggested that this protein was elaborated only with very low density lipoproteins (VLDL). A radioimmunoassay for apo B employing a polyclonal antisera to plasma LDL gave apparent plasma apo B levels of 0.6, 66, and 57 mg/dl in the patient and his father and mother, respectively. The displacement curve generated by the parents' VLDL and LDL did not did not differ from control lipoproteins. The patient's chylomicron-chylomicron remnant fraction displaced normal LDL over the entire radioimmunoassay range, but the efficiency of displacement was strikingly less than with B-100 containing lipoproteins. If the patient's B-48 protein is not qualitatively abnormal, these results confirm very limited immunochemical cross-reactivity between at least one major epitope on B-100 and the epitopes expressed on B-48. The apo B defect in this patient appears to be recessive. It abolishes B-100 production and may additionally limit the formation of B-48.

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P N Herbert, J S Hyams, D N Bernier, M M Berman, A L Saritelli, K M Lynch, A V Nichols, T M Forte

Activation of factor XII-dependent pathways in human plasma by hematin and protoporphyrin.

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Intravenous administration of hematin is effective in the treatment of acute exacerbations of the inducible porphyrias. In the course of such treatment, coagulopathies have occurred that are characterized by prolongation of prothrombin time, partial thromboplastin time, and formation of fibrin split products. In experiments in vitro with normal human plasma, we observed that hematin and protoporphyrin activated Factor XII-dependent pathways of coagulation and fibrinolysis, and that they generated kallikrein activity. Incubation of protoporphyrin with purified Factor XII resulted in activation as measured by amidolysis of a chromogenic substrate. Neither coproporphyrin, uroporphyrin, delta-aminolevulinic acid, porphobilinogen, or bilirubin activated Factor XII-dependent pathways. Exposure of serum containing added uroporphyrin, coproporphyrin, and protoporphyrin, but not hematin, to ultraviolet light (405 nm) resulted in activation of the classical pathway of the complement system. On the other hand, exposure of plasma containing uroporphyrin or coproporphyrin to ultraviolet light did not result in activation of Factor XII-dependent pathways.

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C G Becker, M Wagner, A P Kaplan, M Silverberg, R W Grady, H Liem, U Muller-Eberhard

Pathophysiology of spontaneous hypercalciuria in laboratory rats. Role of deranged vitamin D metabolism.

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Recent data suggest a causal role of deranged 1,25(OH)2D metabolism in the syndrome of idiopathic hypercalciuria. To test this hypothesis, we evaluated if vitamin D availability and/or increased serum 1,25(OH)2D were critical for the expression of hypercalciuria in laboratory rats. Ca balance, serum 25OHD3, and 1,25(OH)2D3 were studied in D-deprived (-D) and D-repleted (+D) male progeny (p) born to normocalciuric (NC) and spontaneously hypercalciuric (SH) rats. 7 of the 14 pSH and 2 of 21 pNC had SH, which was defined as urinary Ca greater than two standard deviations above the mean of values for control animals on days 5 and 6 of a low Ca +D diet (1.19 vs. 0.58 mg/d, P less than 0.001). Fasting serum Ca and 25OHD3 were similar to control. Serum 1,25(OH)2D3 was elevated in these nine SH rats (232 vs. 145 pg/ml, P less than 0.005). However, during vitamin D deprivation, their Ca excretion was also increased (1.53 vs. 0.45 mg/d, P less than 0.001), despite comparably reduced serum 1,25(OH)2D3 (102 vs. 106 pg/ml) and undetectable serum 25OHD3. Net intestinal Ca absorption on a low Ca diet was comparable during D repletion (-0.75 vs. -0.82 mg/d) or D deprivation (-0.80 vs. -2.15 mg/d), excluding primary hyperabsorption as the mediator of the hypercalciuria. Mild hypophosphatemia was present in SH on +D (5.8 vs. 6.9 mg/dl, P less than 0.005) and -D diets (6.2 vs. 7.9 mg/dl, P less than 0.005), and was associated with higher rates of cyclic adenosine monophosphate excretion (32.8 vs. 26.9 and 48.5 vs. 41.0 nmol/mg of creatinine, respectively). Spontaneous hypercalciuria is therefore dissociable from increased Ca absorption, serum levels of 25OHD3, or 1,25(OH)2D3. The data are most compatible with the hypothesis of a renal Ca leak which stimulates parathyroid hormone activity and increases serum 1,25(OH)2D3, if provided adequate 25OHD3 as substrate.

Authors

K Lau, D Thomas, C Langman, B Eby

Evidence for a mouse mesangial cell-derived factor that stimulates lymphocyte proliferation.

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The functions of the glomerular mesangium are served by at least two populations of cells--a cell bearing microfilaments that regulates blood flow, and a phagocytic cell bearing Ia determinants and Fc receptors. We provide evidence that mouse mesangial cells (bearing microfilaments) produce a factor(s) that stimulates spleen cell proliferation. The factor(s) appears to act via monocytes/macrophages, since its stimulatory activity is abrogated by prior depletion of the responding mononuclear cell population of monocytes/macrophages. Confirmation of its action on macrophages was documented by experiments that showed that medium from macrophages incubated with mesangial cell supernatant contained greater amounts of a factor that stimulated [3H]thymidine uptake by macrophage-depleted spleen cell populations. By the cothymocyte proliferation assay, it could be shown that mesangial cell supernatant induced splenic macrophage production of interleukin-1-like activity. Preliminary characterization reveals the factor to have a molecular weight greater than 100,000. Thus, a novel function is delineated for this mesangial cell type that appears capable of modulating the local immune response by providing an amplification signal.

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E P MacCarthy, A Hsu, Y M Ooi, B S Ooi

Phorbol diesters stimulate the development of an early murine progenitor cell. The burst-forming unit-megakaryocyte.

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When murine (C57BL/6) bone marrow cells are cultivated with WEHI-3 conditioned media, a source of megakaryocyte-colony-stimulating activity (Mk-CSA), and phorbol myristate acetate (PMA), a previously undetected population of megakaryocyte (Mk) progenitor cells is observed. These new Mk colonies are reminiscent of erythroid bursts, in that they contain large numbers (40-500) of Mk and multiple foci (2-7) of development. These burst-forming units, Mk (BFU-Mk), are defined as having greater than or equal to 42 cells/colony and, at least, three foci of Mk development (colonies grown in soft agar cultures, all studies done at limiting dilutions; colonies detected by acetylcholinesterase [ACh-E] staining). CFU-Mk and BFU-Mk require two activities for optimal growth: Mk-CSA and PMA. However, the BFU-Mk require a tenfold greater concentration of PMA for optimal development (10(-6) vs. 10(-7) M). BFU-Mk detection is linear (over a range of 25-100 X 10(3) cells/ml), with the regression line passing through the origin. Bone marrow frequencies of these two progenitor cells are CFU-Mk, 36.7 +/- 2.5, and BFU-Mk, 7.3 +/- 0.7 per 10(5) total nucleated cells (mean +/- SEM; n = 28). The BFU-Mk have a restricted velocity sedimentation range (3.3-4.5 mmh-1 vs. 3.3-6.8 mmh-1 for CFU-Mk). Modal buoyant densities are 1.068 +/- 0.0002 and 1.070 +/- 0.002 for BFU-Mk and CFU-Mk, respectively. Thus, these cells are found among the smallest and less dense of the Mk progenitors, and are not clumps or clusters of CFU-Mk. Kinetic analysis indicates that CFU-Mk require 5-7 d for optimal growth, whereas BFU-Mk require 10-12 d. Examination of the proliferative potential (cells per colony) shows 19.3 +/- 1.5 cells per colony (n = 246 colonies) for day 10 CFU-Mk, vs. 118 +/- 6.0 for day 10 BFU-Mk (n = 163). Analysis of the cellularity/subcolony within each burst indicates 37.0 +/- 2.1 (n = 146) Mk/colony and 3.9 +/- 0.1 subcolonies/burst (n = 100). Finally, greater than 90% of the BFU-Mk contain only ACh-E positive cells, indicating that these are not mixed colonies. These results indicate that the BFU-Mk, compared with the CFU-Mk, require an increased amount of stimulation in order to differentiate, show delayed in vitro development, and have a higher proliferative potential. These data are consistent with the hypothesis that these cells are early progenitor cells in the Mk lineage that antedate the CFU-Mk.

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M W Long, L L Gragowski, C H Heffner, L A Boxer

Identification of gallbladder mucin-bilirubin complex in human cholesterol gallstone matrix. Effects of reducing agents on in vitro dissolution of matrix and intact gallstones.

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The goals of this study were to isolate and characterize the nonlipid matrix of human cholesterol gallstones. The lipid portion of gallstones was dissolved in ethanol/ether, leaving an insoluble, granular, brown-black matrix that constituted 12.5% of solitary large stones and 3.5% of multiple small stones. The matrix was partially solubilized by sonication and studied by exclusion gel chromatography and density gradient ultracentrifugation. On Sepharose 2B column chromatography, bile pigment eluted with glycoprotein in the void volume, suggesting the presence of a high molecular weight complex (Mr greater than 2 X 10(6)). The identity of mucin in this complex was confirmed by its typical buoyant density during ultracentrifugation. The major bile pigments in the matrix were identified as bilirubin (84%) and bilirubin monoglucuronide (15%) by thin-layer chromatography. Because of their ability to solubilize mucin-type glycoproteins, we tested the ability of the reducing agents 2-mercaptoethanol (2ME) and N-acetylcysteine (NAcCys) to solubilize gallstone matrix. Both reducing agents caused a two- to threefold enhancement of matrix dissolution after 4 d compared to aqueous buffer alone (P less than 0.01). Sepharose 2B chromatography revealed that 2ME released a high molecular weight mucin-bilirubin complex as well as unbound pigment from the insoluble matrix. We also tested the effect of reducing agents on dissolution of matched cholesterol gallstones by monooctanoin, a cholesterol solvent. Both 2ME and NAcCys significantly accelerated gallstone dissolution in monooctanoin. Matched human cholesterol stones (n = 10) incubated for 4 d in monooctanoin plus either 2ME or NAcCys (1 M final concentration) weighed approximately half as much (P less than 0.01 for each) as stones incubated in monooctanoin alone. This study describes, for the first time, the isolation of a bilirubin-mucin complex in the insoluble matrix of human cholesterol gallstones. The ability of reducing agents to dissolve the matrix and thereby accelerate gallstone dissolution by monooctanoin in vitro may be relevant to gallstone dissolution in humans.

Authors

B F Smith, J T LaMont

Interleukin-2 receptor (Tac antigen) expressed on adult T cell leukemia cells.

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We studied the expression of the interleukin-2 (IL-2) receptor and the proliferative response to exogenous IL-2 of peripheral blood leukemic cells from patients with adult T cell leukemia (ATL) in order to see whether IL-2 receptor expressed on ATL cells is different from normal IL-2 receptor and whether it plays a role in the neoplastic growth in ATL. Peripheral blood leukemic cells from 42 patients with ATL examined expressed IL-2 receptors that were detected by anti-Tac monoclonal antibody when examined immediately after the separation of cells or after the culture for 24 or 48 h. The number of anti-Tac binding sites ranged from 3,100 to 11,400 in fresh cells and from 3,600 to 96,000/cell in short-term cultured leukemic cells, whereas phytohemagglutinin-P (PHA-P)-stimulated normal T cells exhibited 6,900-35,000 anti-Tac binding sites per cell. ATL-derived and human T cell leukemia/lymphoma virus, type I (HTLV-I)-infected cell lines such as MT-1 and Hut102 expressed a much higher number of anti-Tac binding sites. Leukemic cells from 15 patients with ATL examined showed no or very poor proliferative response to various concentrations of immunoaffinity-purified IL-2, although they expressed Tac antigen (Ag). Radiolabeled IL-2 binding experiments demonstrated that ATL leukemic cells could bind IL-2, and they expressed both high and low affinity IL-2 receptors, although the number of high affinity IL-2 receptor was much less than that of low affinity IL-2 receptor and that of anti-Tac binding sites. In contrast, leukemic T cells from a patient with T cell chronic lymphocytic leukemia (CLL), in whom HTLV-I infection was not demonstrated, responded as well as PHA-P-stimulated normal T cells, and their IL-2 receptors, unlike ATL cells, were modulated (down regulated) by anti-Tac antibody. No differences were noted between ATL cells and normal activated T cells in one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of the IL-2 receptor. Thus, leukemic cells in ATL spontaneously and continuously express IL-2 receptor, which appears to be abnormally regulated and unresponsive to IL-2. These results, taken together with those on normal IL-2 receptors on HTLV-I-negative T-CLL cells, suggest that abnormal expression of the IL-2 receptor in ATL is closely associated with HTLV-I infection and may play a role in the neoplastic growth of ATL cells.

Authors

T Uchiyama, T Hori, M Tsudo, Y Wano, H Umadome, S Tamori, J Yodoi, M Maeda, H Sawami, H Uchino

Immunological studies of an organic anion-binding protein isolated from rat liver cell plasma membrane.

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The mechanism of organic anion uptake by hepatocytes has kinetics that suggest facilitated diffusion, and carrier-mediated membrane transport has been postulated. In previous studies, we purified a 55,000-mol wt organic anion-binding protein (OABP) by affinity chromatography on sulfobromophthalein (BSP)-Sepharose of deoxycholate solubilized liver cell plasma membrane preparations. Using specific goat and rabbit antibodies to OABP, we have now investigated the distribution of this protein in liver fractions and other tissues by an enzyme-linked immunosorbent assay and by the immunoblot (Western blot) procedure. These studies indicated that OABP is present in significant amounts in all tissues examined except for blood. Although OABP has not as yet been isolated from each of these tissues and characterized, OABP in heart retained the ability to bind organic anions, and was purified by affinity chromatography on BSP-sepharose. In liver, OABP was membrane bound and remained so after extraction with 0.9 M NaCl, which suggests that it is an intrinsic membrane protein. OABP did not have a ubiquitous subcellular distribution within the hepatocyte. Preparation of subfractions of liver cell plasma membrane revealed that OABP is present in the sinusoidal and absent from the canalicular membrane. Immunofluorescence studies performed in short-term cultured hepatocytes suggest that OABP is associated with the surface of these cells and does not have a significant intracellular distribution.

Authors

A W Wolkoff, A Sosiak, H C Greenblatt, J Van Renswoude, R J Stockert

Regulation of glucose utilization in adipose cells and muscle after long-term experimental hyperinsulinemia in rats.

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The effects of chronic insulin administration on the metabolism of isolated adipose cells and muscle were studied. Adipose cells from 2 and 6 wk insulin-treated and control rats, fed either chow or chow plus sucrose, were prepared, and insulin binding, 3-O-methylglucose transport, glucose metabolism, and lipolysis were measured at various insulin concentrations. After 2 wk of treatment, adipose cell size and basal glucose transport and metabolism were unaltered, but insulin-stimulated transport and glucose metabolism were increased two- to threefold when cells were incubated in either 0.1 mM glucose (transport rate limiting) or 10 mM glucose (maximum glucose metabolism). Insulin binding was increased by 30%, but no shift in the insulin dose-response curve for transport or metabolism occurred. After 6 wk of treatment, the effects of hyperinsulinemia on insulin binding and glucose metabolism persisted and were superimposed on the changes in cell function that occurred with increasing cell size in aging rats. Hyperinsulinemia for 2 or 6 wk did not alter basal or epinephrine-stimulated lipolysis in adipose cells or the antilipolytic effect of insulin. In incubated soleus muscle strips, insulin-stimulated glucose metabolism was significantly increased after 2 wk of hyperinsulinemia, but these increases were not observed after 6 wk of treatment. We conclude that 2 wk of continuous hyperinsulinemia results in increased insulin-stimulated glucose metabolism in both adipose cells and soleus muscle. Despite increased insulin binding to adipose cells, no changes in insulin sensitivity were observed in adipose cells or muscle. In adipose cells, the increased glucose utilization resulted from both increased transport (2 wk only) and intracellular glucose metabolism (2 and 6 wk). In muscle, after 2 wk of treatment, both glycogen synthesis and total glucose metabolism were increased. These effects of hyperinsulinemia were lost in muscle after 6 wk of treatment, when compared with sucrose-supplemented controls.

Authors

L J Wardzala, M Hirshman, E Pofcher, E D Horton, P M Mead, S W Cushman, E S Horton

Evidence for alteration of the vitamin D-endocrine system in blacks.

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As compared with values in white subjects, bone mass is known to be increased and urinary calcium to be diminished in black individuals. To evaluate the possibility that these changes are associated with alterations in the vitamin D-endocrine system, an investigation was performed in 12 black subjects, 7 men and 5 women, and 14 white subjects, 8 men and 6 women, ranging in age from 20 to 35 yr. All of them were hospitalized on a metabolic ward and were given a constant daily diet containing 400 mg of calcium, 900 mg of phosphorus, and 110 meq of sodium. Whereas mean serum calcium, ionized calcium, and phosphate were the same in the two groups, mean serum immunoreactive parathyroid hormone (350 +/- 34 vs. 225 +/- 26 pg/ml, P less than 0.01) and mean serum 1,25-dihydroxyvitamin D (1,25(OH)2D) (41 +/- 3 vs. 29 +/- 2 pg/ml, P less than 0.01) were significantly higher, and mean serum 25-hydroxy-vitamin D (25-OHD) was significantly lower in the blacks than in the whites (6 +/- 1 vs. 20 +/- 2 ng/ml, P less than 0.001). Mean urinary sodium and 24-h creatinine clearance were the same in the two groups, whereas mean urinary calcium was significantly lower (101 +/- 14 vs. 166 +/- 13 mg/d, P less than 0.01) and mean urinary cyclic AMP was significantly higher (3.11 +/- 0.47 vs. 1.84 +/- 0.25 nM/dl glomerular filtrate, P less than 0.01) in the blacks. Further, the blacks excreted an intravenous calcium load, 15 mg/kg body weight, as efficiently as the whites (49 +/- 3 vs. 53 +/- 3%, NS). Mean serum Gla protein was lower in blacks than in whites (14 +/- 2 vs. 24 +/- 3 ng/ml, P less than 0.02), and increased significantly in both groups in response to 1,25(OH)2D3, 4 micrograms/d for 4 d. There was a blunted response of urinary calcium to 1,25(OH)2D3 in the blacks, and mean serum calcium did not change. The results indicate that alteration of the vitamin D-endocrine system with enhanced renal tubular reabsorption of calcium and increased circulating 1,25(OH)2D as a result of secondary hyperparathyroidism may contribute to the increased bone mass in blacks. Their low serum 25-OHD is attributed to diminished synthesis of vitamin D in the skin because of increased pigment.

Authors

N H Bell, A Greene, S Epstein, M J Oexmann, S Shaw, J Shary

Evidence for beta adrenoceptors in proximal tubules. Isoproterenol-sensitive adenylate cyclase in pars recta of canine nephron.

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Observations in vivo suggest that catecholamines modulate reabsorptive functions of proximal tubules by acting on beta-adrenoceptors. However, beta-catecholamine binding sites or beta-adrenoceptor-sensitive adenylate cyclase (AdC) has not been found in segments of proximal tubules of rat, rabbit, or mouse kidney. In the present study, we investigated the responsiveness of AdC to catecholamines, [8-Arg]vasopressin (AVP), and to parathyroid hormone (PTH) in proximal convoluted tubules (PCT), proximal straight tubules (PST), and in late distal convoluted tubules (LDCT) microdissected from canine kidney. Isoproterenol (ISO) caused a marked and dose-dependent stimulation of AdC in PST (maximum: delta + 850%; half maximum stimulation at 10(-7) M ISO), but ISO had no effect on AdC in PCT. The AdC in both PCT and PST was markedly stimulated by PTH; AVP stimulated the AdC in LDCT but not in PST or in PCT. The stimulatory effect of 10(-5) M ISO in PST (delta + 725%) was significantly greater than in LDCT (delta + 307%); norepinephrine and epinephrine had stimulatory effects in PST similar to ISO. The stimulation of AdC in PST by ISO was blocked by propranolol and by beta 2-blocker ICI-118551. On the other hand, alpha-blocker phentolamine and beta 1-blocker metoprolol did not abolish the stimulation of AdC in PST by ISO. The accumulation of cAMP in intact PCT and PST incubated in vitro was stimulated by PTH both in PST and in PCT, but ISO elevated cAMP (delta + 683%) only in PST. Our results show that proximal tubules of canine nephron, PST but not PCT, contain beta-adrenoceptors of beta 2 subtype coupled to AdC. These observations provide direct evidence that the effects of catecholamines, either released from renal nerve endings or arriving from blood supply, can act directly on beta 2-adrenoceptors located in proximal tubules, and also suggest that at least some of the catecholamine effects in proximal tubules are mediated via cAMP generation.

Authors

N Murayama, B T Ruggles, S M Gapstur, J L Werness, T P Dousa

Characterization of a new model of GM2-gangliosidosis (Sandhoff's disease) in Korat cats.

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We have detected a disorder in Korat cats (initially imported from Thailand) that is analogous to human Sandhoff's disease. Pedigree analysis indicates that this disease in an autosomal recessive disorder in the American Korat. Postmortem studies on one affected cat showed hepatomegaly that was not reported in the only other known feline model of GM2-gangliosidosis type II. Histologic and ultra-structural evaluation revealed typical storage vacuoles. There was a marked deficiency in the activity of hexosaminidase (HEX) A and B in affected brain and liver as compared to controls. Electrophoresis of a liver extract revealed a deficiency of normal HEX A and B in the affected animals. The blocking primary enzyme immunoassay verified the presence of antigenically reactive HEX present in affected cat livers in quantities slightly elevated with respect to the normal HEX concentration in control cats. In leukocytes, obligate heterozygotes had intermediate levels of total HEX activity with a slight increase in the percent activity due to HEX A. Indeed, 4 of 11 phenotypically normal animals in addition to four obligate heterozygotes appear to be carriers using this assay. Affected brain and liver compared with control brain and liver contained a great excess of bound N-acetylneuraminic acid in the Folch upper-phase solids; thin-layer chromatography showed a marked increase in GM2-ganglioside. In summary, we have characterized the pedigree, pathology, and biochemistry of a new feline model of GM2-gangliosidosis which is similar to but different from the only other known feline model.

Authors

E A Neuwelt, W G Johnson, N K Blank, M A Pagel, C Maslen-McClure, M J McClure, P M Wu

Interaction of human leukocytes and Entamoeba histolytica. Killing of virulent amebae by the activated macrophage.

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Capable effector mechanisms in the human immune response against the cytolytic, protozoan parasite Entamoeba histolytica have not been described. To identify a competent human effector cell, we studied the in vitro interactions of normal human polymorphonuclear neutrophils, peripheral blood mononuclear cells (PBMC), monocytes (MC), and MC-derived macrophages with virulent axenic amebae (strain HMI-IMSS). Amebae killed neutrophils, PBMC, MC, and MC-derived macrophages (P less than 0.001), without loss of parasite viability. The addition of heat-inactivated immune serum did not enable leukocytes to kill amebae, nor did it protect these host cells from amebae. MC-derived macrophages, activated with lymphokine elicited by the mitogens conconavalin A, phytohemagglutinin, or an amebic soluble protein preparation (strain HK9), killed 55% of amebae by 3 h in a trypan blue exclusion assay (P less than 0.001); during this time, 40% of the activated macrophages died. Lysis of amebae was confirmed using 111Indium oxine radiolabeled parasites and was antibody independent. Macrophage death appeared to be due to the deleterious effect of lysed amebae rather than the contact-dependent effector mechanisms of E. histolytica. Adherence between activated macrophages and amebae was greater than that between other leukocytes and amebae (P less than 0.001). Microscopic observations, kinetic analysis of the killing of amebae by activated macrophages, and suspension of amebae with adherent activated macrophages in a 10% dextran solution indicated that contact by activated macrophages was necessary to initiate the killing of amebae. Catalase but not superoxide dismutase inhibited the amebicidal capacity of activated macrophages (P less than 0.001). However, activated macrophages from an individual with chronic granulomatous disease were able to kill amebae, but not as effectively as normal cells (P less than 0.01). In summary, activated MC-derived macrophages killed virulent E. histolytica trophozoites through a contact-dependent, antibody-independent mechanism involving oxidative-dependent and -independent processes.

Authors

R A Salata, R D Pearson, J I Ravdin

Immunoglobulin G-induced single ionic channels in human alveolar macrophage membranes.

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While it is well known that the engagement of IgG Fc receptors on the macrophage surface triggers a number of cellular responses, including particle ingestion, secretion, and respiratory burst activity, the mechanism of signal transmission following ligand binding remains poorly understood. To acquire more data in this area, we studied the electrical properties of the macrophage membrane and its response to oligomeric immunoglobulin G (IgG) using the patch-clamp technique on human alveolar macrophages that were obtained by bronchoalveolar lavage and maintained in short-term tissue culture. The results showed that cell resting potentials, as determined from whole-cell tight seal recordings, increased from -15 mV on the day of plating to -56 mV after the first day in culture and remained stable at this hyperpolarized level. Macrophages revealed an input resistance of 3.3 G omega, independent of age in culture. Extracellular application of heat-aggregated human IgG to cells voltage-clamped at -70 mV resulted in peak inward currents of approximately 470 pA. We identified an IgG-dependent, nonselective channel in both cell-attached and isolated membrane patches, with a unitary conductance of approximately 350 pS and a predominant subconductance level of 235 pS in symmetrical NaCl solutions. Single channel open times were observed to be in the range of seconds and, in addition, were dependent upon membrane voltage. Channel opening involved transitions between a number of kinetic states and subconductance levels. Channel events recorded in cell-attached patches showed characteristic exponential relaxations, which implied a variation in membrane potential as a result of a single ion channel opening. These data suggest that the IgG-dependent nonselective cation channel that we have characterized may provide the link between Fc receptor engagement and subsequent cellular activation.

Authors

D J Nelson, E R Jacobs, J M Tang, J M Zeller, R C Bone

Virulence of Cryptococcus neoformans. Regulation of capsule synthesis by carbon dioxide.

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Cryptococcus neoformans is variably encapsulated in vitro, whereas in tissues it develops a large capsule. We observed that cells of a strain with thin capsules, when growing in a standard fungal culture medium, became heavily encapsulated when incubated in serum-free cell culture medium (Dulbecco's modified Eagle's medium [DME]). Capsule size was quantitated physically by measuring cell volume, and chemically by determining the content of a capsular monosaccharide, glucuronate. The CO2/HCO-3 couple stimulated capsule development, resulting in visible enlargement by 3 h after exposure to high CO2/HCO-3. The amount of capsule per cell was directly proportional to the total millimolar CO2/HCO-3 concentration between 24 and 2.4 mM at pH 7.35, but at constant PCO2 (40 torr) and varying [HCO-3], the cells were heavily encapsulated down to pH 6.8. Concentration of CO2/HCO-3 in the physiologic range increased elaboration of polysaccharide into the medium and slowed the cell generation time from 2 to 6 h. Four other first-passage clinical isolates were all heavily encapsulated in DME with CO2/HCO-3, but variably encapsulated in DME without CO2/HCO-3. Exposure of yeast to increased CO2/HCO-3 caused a marked reduction in complement-mediated phagocytosis by mouse macrophages. A stable clone was isolated which contained capsular polysaccharide, but lacked the CO2-inducible phenotype. This clone was avirulent for steroid-treated rabbits. Thus, the prevailing CO2 concentration in mammalian tissues may be one stimulus for capsular polysaccharide synthesis. This could serve as an adaptive mechanism favoring parasite survival in the host.

Authors

D L Granger, J R Perfect, D T Durack

Systemic complement activation, lung injury, and products of lipid peroxidation.

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Abstract

Previously we have demonstrated that systemic activation of the complement system after intravenous injection of cobra venom factor (CVF) results in acute lung injury as reflected by increases in the vascular permeability of the lung as well as by morphologic evidence of damage to lung vascular endothelial cells. In using the vascular permeability of the lung as the reference, the current studies show a quantitative correlation between lung injury and the appearance in plasma of lipid peroxidation products (conjugated dienes) as well as increased concentrations of lactic dehydrogenase (LDH) and one of its isoenzymes (LDH-4). After injection of CVF, extracts of lungs also showed elevated levels of conjugated dienes, whereas no elevations were found in extracts of liver, kidney, and spleen. There was no evidence in CVF-injected rats of renal or hepatic injury as reflected by the lack of development of proteinuria and the failure to detect increased serum levels of liver-related enzymes. Other peroxidation products identified in plasma of CVF-injected rats involved hydroperoxides and fluorescent compounds with features of Schiff bases. Not surprisingly, malondialdehyde was not found to be a reliable plasma indicator of lipid peroxidation associated with oxygen radical-mediated lung vascular injury. In using a model of oxygen radical-independent lung injury induced by oleic acid, although large amounts of LDH and LDH-4 were found in the plasma, no increases in plasma levels of conjugated dienes were detected. In CVF-injected animals treated with interventions protective against lung injury (neutrophil depletion, catalase, hydroxyl radical scavengers, or iron chelators), there were striking reductions in the plasma levels of conjugated dienes, hydroperoxides, and fluorochromic products. Morphometric analysis of lung sections revealed that the protective interventions did not interfere with the accumulation of neutrophils in lung interstitial capillaries after systemic activation of complement. In vitro studies with phorbol-stimulated neutrophils failed to demonstrate appearance of conjugated dienes, suggesting that the dienes appearing in plasma of CVF-injected animals are not the result of autotoxic changes in neutrophils. The data presented in this paper suggest that acute lung injury mediated by oxygen radicals derived from phagocytic cells can be monitored by the appearance in plasma of products of lipid peroxidation.

Authors

P A Ward, G O Till, J R Hatherill, T M Annesley, R G Kunkel

Identification of intracellular factor XIII in human monocytes and macrophages.

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Abstract

Factor XIII is a blood protransglutaminase that is distributed in plasma and platelets. The extracellular and intracellular zymogenic forms differ in that the plasma zymogen contains A and B subunits, while the platelet zymogen has A subunits only. Both zymogens form the same enzyme. Erythrocytes, in contrast, contain a tissue transglutaminase that is distinct from Factor XIII. In this study other bone marrow-derived cells were examined for transglutaminase activity. Criteria that were used to differentiate Factor XIII proteins from erythrocyte transglutaminase included: (a) immunochemical and immunohistochemical identification with monospecific polyclonal and monoclonal antibodies to Factor XIII proteins, (b) requirement for thrombin cleavage to express activity, (c) pattern of fibrin cross-linking catalyzed by the enzyme, and (d) different electrophoretic mobilities in nondenaturing gel systems. By these criteria human peripheral blood monocytes, peritoneal macrophages, and monocytes maintained in culture contain an intracellular protransglutaminase that is the same as platelet Factor XIII. The monocyte-macrophage protein is thrombin-sensitive, and under appropriate conditions there is no enzyme expression without activation of the zymogen. Both the monocyte-macrophage zymogen and enzyme have the same electrophoretic mobilities as platelet Factor XIII zymogen and enzyme. Antibody to A protein reacts with the monocyte-macrophage protein. B protein is not associated with this intracellular zymogen. By immunoperoxidase staining monocyte-macrophage protein seems to be localized in the cytoplasm, similar to the known cytoplasmic distribution of platelet and megakaryocyte Factor XIII. These procedures were also used to study populations of human granulocytes and lymphocytes, and protransglutaminase activity was not observed in these cells.

Authors

P Henriksson, S Becker, G Lynch, J McDonagh

Antiadhesive properties of biological surfaces are protective against stimulated granulocytes.

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Abstract

Despite the fact that a series of endogenous and exogenous inflammatory mediators are potent activators of circulating granulocytes, damage of vascular endothelium, a primary target tissue, is a rather unusual event in systemic inflammatory states. Since mediator-induced neutrophil hyperadhesiveness on plastic tissue culture dishes is invariably accompanied by intense release of lysosomal granule constituents and respiratory burst activation, thus representing a powerful model to investigate neutrophil cytotoxic states, comparative studies with neutrophils suspended in autologous plasma in the presence or absence of N-formyl-Met-Leu-Phe (2.5 microM), the most potent adhesion inducer, were performed on different biologic surfaces. On optimally adherent closed monolayers of cultured endothelial cells or fibroblasts we observed poor stimulation of adhesion as well as minimal granule release and hexose monophosphate pathway activation. Functional behavior of neutrophils on single molecular components of basal laminas such as fibronectin and collagen (type IV) coats was intermediate, with positive adhesion promotion but markedly reduced metabolic activation. When tested on endothelial cell-derived extracellular matrices, neutrophils again showed functional nonresponsiveness to N-formyl-Met-Leu-Phe. Scanning electron microscopy revealed an impressive congruency between the degree of cellular spreading and metabolic activation in the presence of N-formyl-Met-Leu-Phe, with maximally flattened neutrophils on plastic vs. nonspread, polarized cells on monolayers. Identical results were obtained by using other adhesion inducers such as complement-activated plasma or endotoxin. Lack of cell injury by N-formyl-Met-Leu-Phe-exposed neutrophils was corroborated by the absence of tracer release from [111In]tropolonate-labeled endothelium. These results indicate that biologic surfaces possess antiadhesive properties that protect them from cytotoxic damage by stimulated angry phagocytes.

Authors

J Fehr, R Moser, D Leppert, P Groscurth

Paradoxical effects of pyrazinoate and nicotinate on urate transport in dog renal microvillus membranes.

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Abstract

The effects of pyrazinoate and nicotinate on urate transport in microvillus membrane vesicles isolated from canine renal cortex were evaluated. An outwardly directed gradient of pyrazinoate stimulated uphill urate accumulation, suggesting urate-pyrazinoate exchange. An inside-alkaline pH gradient stimulated uphill pyrazinoate accumulation, which suggested pyrazinoate-OH- exchange. Pyrazinoate-OH- exchange and urate-OH- exchange were similarly sensitive to inhibitors, implying that both processes occur via the same transport system. In addition, an inward Na+ gradient stimulated uphill pyrazinoate accumulation, suggesting Na+-pyrazinoate cotransport. Inhibitor studies demonstrated that Na+-pyrazinoate cotransport takes place via the same pathway that mediates Na+-lactate cotransport in these membrane vesicles. Previously we found that urate does not share this Na+-dependent cotransport pathway. Nicotinate inhibited transport of pyrazinoate by the anion exchange pathway and the Na+ cotransport pathway, suggesting that it is a substrate for both transport systems. Finally, in the presence of an inward Na+ gradient, low doses of pyrazinoate or nicotinate stimulated urate uptake, and higher doses of pyrazinoate or nicotinate inhibited urate accumulation, thereby mimicking in vitro the paradoxical effects of drugs on renal urate excretion that have been observed in vivo. These findings indicate that the paradoxical effect of uricosuric drugs at low doses to cause urate retention may result at least in part from stimulation of urate reabsorption across the luminal membrane of the proximal tubular cell.

Authors

S E Guggino, P S Aronson

Regulatory roles of T mu and T gamma cells in the collaborative cellular initiation of the extrinsic coagulation pathway by bacterial lipopolysaccharide.

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Abstract

The Shwartzman reaction is a classic biologic response in which the coagulation system is activated in vivo. Cellular initiation of the extrinsic coagulation protease cascade can be mediated by one or more limbs of the lymphoid response to diverse biological stimuli. The T cell-instructed monocyte and macrophage responses that have been implicated are mediated by a number of different cellular pathways and are elicited not only by antigens and allogeneic cells but also by other stimuli such as immune complexes and the lipid A moiety of bacterial lipopolysaccharide (LPS). The latter response has been implicated in the pathogenesis of the disseminated intravascular coagulation associated with bacterial infection. In the rapid collaborative cellular pathway response to LPS, we have described a relatively rigorous requirement for T helper cells in induction of the biosynthesis of tissue factor and Factor VII by monocytes. To elucidate potential regulatory aspects of this cellular procoagulant response, we provide the first evidence for the existence of T suppressor cells for the cellular procoagulant response to LPS by the rapid T cell-instructed pathway. Human peripheral blood lymphocytes were separated by cytoaffinity into Fc gamma-positive and Fc mu-positive cells and were characterized for their functional properties in the procoagulant response. T mu cells mediated the monocyte response, consistent with their identity with instructor cells. T gamma cells suppressed the response of monocytes to LPS in the presence of T mu cells, suggesting that they possess suppressor function for this response. The T gamma suppressor cells required stimulation by LPS to express their suppressor function and they exerted their suppressive effect directly on the monocyte. The existence and participation of LPS-responsive T suppressor cells on the cellular procoagulant response in vitro add a new dimension to the complexity of the rapid pathway of the collaborative cellular procoagulant response and may be important in the pathogenesis of disseminated intravascular coagulation.

Authors

G A Levy, B S Schwartz, L K Curtiss, T S Edgington

Excess purine degradation in exercising muscles of patients with glycogen storage disease types V and VII.

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Abstract

To investigate purine catabolism in exercising muscles of patients with muscle glycogen storage disease, we performed ischemic forearm exercise tests and quantitated metabolites appearing in cubital venous blood. Two patients with glycogen storage disease type V and three with glycogen storage disease type VII participated in this study. Basal lactate concentrations lowered in every patient with glycogen storage disease type V or type VII. Two patients with glycogen storage disease type VII, who had markedly elevated concentrations of serum uric acid (14.3 and 11.9 mg/dl, respectively), showed high basal concentrations of ammonia (118 and 79 mumol/liter, respectively; 23 +/- 4 mumol/liter in healthy controls) and of hypoxanthine (23.4 and 20.4 mumol/liter, respectively; 2.0 +/- 0.4 mumol/liter in healthy controls). Other patients showed near normal measurements of these metabolites. After forearm exercise, ammonia, inosine, and hypoxanthine levels increased greatly in every patient studied, in contrast with the lack of increase in lactate levels. The incremental area under the concentration curves for venous ammonia was 13-fold greater in the glycogen storage disease group than in controls (1,120 +/- 182 vs. 83 +/- 26 mumol X min/liter). The incremental areas of inosine and hypoxanthine were also greater in the glycogen storage disease group (29.2 +/- 7.2 vs. 0.4 +/- 0.1 and 134.6 +/- 23.1 vs. 14.9 +/- 3.2 mumol X min/liter, respectively). The incremental areas of ammonia in controls and in glycogen storage disease patients strongly correlated with those of hypoxanthine (r = 0.984, n = 11, P less than 0.005). These findings indicated that excess purine degradation occurred in the exercising muscles of patients with glycogen storage disease types V and VII, and suggested that the ATP pool in the exercising muscles may be deranged because of defective glycogenolysis or glycolysis.

Authors

I Mineo, N Kono, T Shimizu, N Hara, Y Yamada, S Sumi, K Nonaka, S Tarui

In vivo and in vitro studies of urinary concentrating ability in potassium-depleted rabbits.

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Abstract

The factors responsible for the urinary concentrating defect associated with the potassium-depleted (KD) state are uncertain. The present studies were designed to, first, determine whether a urinary concentrating defect exists in potassium-depleted rabbits and, second, to use the technique of in vitro perfusion to evaluate directly the antidiuretic hormone (ADH) responsiveness of cortical collecting tubules (CCT) in this setting. Feeding female New Zealand White rabbits a potassium-deficient diet for 2 wk caused a significant fall in plasma potassium levels in both the ad-libitum and controlled water intake groups (P less than 0.001). Muscle potassium content after 2 wk of potassium restriction fell from 45.6 +/- 0.9 to 29.0 +/- 1.2 meq/100 g fat-free dry solids (P less than 0.001). Renal papillary sodium content fell significantly from a control value of 234.6 +/- 8.0 to 182.46 +/- 10.0 meq/kg H2O after 2 wk of potassium restriction. Maximal urinary osmolality measured after 12 h of dehydration and 1.25 U pitressin IM was significantly decreased in rabbits after 2 wk of potassium restriction in both the ad-libitum and controlled water intake groups (P less than 0.001). The relationship between plasma potassium concentration and maximum urinary osmolality was significantly correlated in both the ad-libitum and controlled water intake groups, r = 0.73 and 0.68 (P less than 0.001), respectively. In addition, refeeding KD rabbits with normal chow for 1 wk resulted in normalization of both plasma potassium levels and urinary concentrating ability. CCT from control and KD rabbits were perfused in vitro at 25 degrees C. The hydraulic conductivity coefficient, Lp, was significantly reduced at all doses of ADH tested in tubules from KD rabbits when compared with control tubules. In addition, the maximal hydraulic conductivity in tubules from KD rabbits when tested with 200 microU/ml ADH at 37.5 degrees C was only 23% of control values (P less than 0.05). Furthermore, this reduced ADH responsiveness persisted when the bath potassium was elevated from 5 to 20 mM. The reflection coefficient for NaCl when compared with raffinose was 0.91 in tubules from KD animals. Thus, these data suggest that the ADH-resistant urinary concentrating defect associated with potassium depletion is due, at least in part, to a diminished responsiveness of the CCT to ADH. Therefore, further studies were designed to investigate the cellular steps involved in this abnormal response. There was no difference in the 8-para-chlorophenylthio cyclic AMP induced hydroosmotic response between CCT from KD and control rabbits. Since the cAMP-induced hydroosmotic response was similar between KD and control CCT, experiments were performed to evaluate the contribution of phosphodiesterase (PDIE) activity by using the potent PDIE inhibitor isobutylmethylxanthine (10(-4) and 10(-3)M) in the presence of ADH (200 U/ml). Although Lp was increased by PDIE inhibition in CCT from both control and KD animals, the overall hydroosmotic response in CCT from KD rabbits was still significantly reduced when compared with controls. The final experiments used forskolin to evaluate further the adenylate cyclase complex. The resulting hydroosmotic response in CCT from KD rabbits was almost identical to that obtained in controls. In conclusion, these data suggest that the decreased responsiveness of CCT from KD rabbits to ADH involves a step at or proximal to the stimulation of the catalytic subunit of adenylate cyclase, and that PDIE activity makes no contribution to this abnormal hydroosmotic response.

Authors

K H Raymond, K K Davidson, T D McKinney

Hydrogen peroxide from cellular metabolism of cystine. A requirement for lysis of murine tumor cells by vernolepin, a glutathione-depleting antineoplastic.

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Abstract

The sesquiterpene lactone antineoplastic vernolepin acutely depletes murine tumor cell glutathione (GSH), and lyses the cells by an unknown mechanism that is enhanced synergistically by inhibition of GSH synthesis with buthionine sulfoximine (BSO) (Arrick et al. 1983. J. Clin. Invest. 71:258). We found here that lysis of P815 mastocytoma cells by vernolepin, with or without BSO, required cystine in the culture medium. Addition of catalase markedly suppressed vernolepin-mediated cytolysis in cystine-containing media, suggesting the involvement of hydrogen peroxide in the cytolytic action of vernolepin. Consistent with this, inhibition of tumor cell glutathione disulfide reductase with 1,3-bis(2-chloroethyl)-1-nitrosourea or inhibition of endogenous catalase with aminotriazole synergistically augmented cytolysis by vernolepin. Moreover, H2O2 was released by suspensions of P815 cells in cystine-containing buffer (63 pmol/10(6) cells X h). Omission of cystine reduced the rate of H2O2 accumulation 10-fold. No H2O2 was detected without cells. Cytolysis by vernolepin could be restored in cystine-deficient medium by several other disulfides, themselves noncytolytic, such as disulfiram and oxidized Captopril, as well as by cysteine. In contrast, withholding two other essential amino acids (leucine or tryptophan) or adding cycloheximide did not interfere with cytolysis by vernolepin. These results suggest that cellular uptake of disulfides of physiologic and pharmacologic interest may be followed by their intracellular reduction and autooxidation with generation of H2O2. This previously unrecognized source of intracellular oxidant stress may be an important component of injury to GSH-depleted cells.

Authors

B A Arrick, W Griffo, Z Cohn, C Nathan

Development of an integrated model for analysis of the kinetics of apolipoprotein B in plasma very low density lipoproteins, intermediate density lipoproteins, and low density lipoproteins.

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Abstract

To quantify more precisely the metabolism of apolipoprotein B (apo B) in human beings, an integrated model was developed for the analysis of the isotope kinetics of apo B in very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), and low density lipoproteins (LDL). The experimental basis for model development was a series of 30 triple-isotope studies in which patients received autologous 131I-VLDL, 125I-IDL, and [3H]glycerol as a precursor of VLDL triglycerides. The currently proposed model contains the following components: (a) a VLDL delipidation cascade that has a variable number of subcompartments, (b) a slowly catabolized pool of VLDL, (c) an IDL compartment consisting of two closely connected subcompartments, one of which is outside the immediate circulation, and (d) a two-compartment subsystem for LDL. Because mass data indicate that not all VLDL were converted to LDL, the model allows for irreversible removal of apo B from VLDL (or IDL) subsystems. It accounts for apparent "direct" input of LDL by postulating an early, rapidly metabolized compartment of VLDL that is converted directly to IDL. The model appears to be consistent with specific activity curves from the current triple-isotope studies and with present concepts of lipoprotein physiology; it also can be used to quantify pathways of lipoprotein apo B transport in normal and abnormal states.

Authors

W F Beltz, Y A Kesäniemi, B V Howard, S M Grundy

Comparisons of metabolism of apolipoprotein B in normal subjects, obese patients, and patients with coronary heart disease.

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Abstract

This study was designed to examine the integrated metabolism of apolipoprotein B (apo B) in very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), and low density lipoproteins (LDL) in normal subjects, obese patients, and a group of patients with coronary heart disease (CHD). Turnover rates of 131I-VLDL-B, 131I-IDL-B, 125I-LDL-B, and [3H]VLDL-triglycerides (TG) were determined by the multicompartmental analysis that used the model described in the preceding article (Beltz, W.F., et al. 1985. J. Clin. Invest. 76: 575-585). Compared with five normal subjects, four obese subjects had increased synthesis rates of both VLDL-B and VLDL-TG. Production of LDL-B was inconsistently raised in these same patients. Five patients with CHD had enhanced production of both VLDL-B and LDL-B, but secretion rates of VLDL-TG were not increased. Thus, in patients with obesity and in those with CHD, synthesis rates of VLDL particles may be abnormally high. In the obese patients, the VLDL appeared to be of normal composition, but in patients with CHD, the VLDL were relatively poor in TG. The study also showed that a significant fraction of VLDL-B is removed directly from the circulation and never reaches LDL regardless of the type of patients. The fraction that does reach LDL is one factor that determines LDL concentrations.

Authors

Y A Kesäniemi, W F Beltz, S M Grundy

Influence of obesity on the metabolism of apolipoprotein B in humans.

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Abstract

The influence of obesity on the metabolism of apolipoprotein B (apo B) in very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) was investigated in nine obese and seven nonobese Pima Indian men. Kinetics of VLDL-apo B (VLDL-B), VLDL-triglycerides, IDL-B and LDL-B were studied after injection of autologous 131I-VLDL, [3H]glycerol, and autologous 125I-LDL. Specific activities were measured in apo B isolated from all lipoprotein fractions and in triglyceride isolated from VLDL. Transport rates and fractional catabolic rates for apo B in VLDL, IDL, and LDL and triglyceride in VLDL were determined by multicompartmental analysis. This method also allowed the estimation of rates of interconversions of the lipoproteins. The two groups had similar mean ages and heights, but the obese group had a higher total body weight (131 +/- 14 vs. 66 +/- 3 kg +/- SEM) and fat free mass (81 +/- 5 vs. 54 +/- 2 kg) than lean controls. Plasma total lipids were similar for the two groups, and apo B concentrations in VLDL, IDL, and LDL were similar in obese and lean subjects. In spite of similarity in concentrations, obese subjects compared to lean subjects had higher synthetic rates of VLDL-triglyceride (62.6 +/- 15 vs. 26.2 +/- 7 g/d, P less than 0.01), VLDL-B (2,241 +/- 215 vs. 1,113 +/- 72 mg/d, P less than 0.001), and LDL-B (1,234 +/- 87 vs. 802 +/- 83 mg/d, P less than 0.01). Furthermore, in obese subjects, significantly higher amounts of VLDL-B were removed from the circulation without conversion to LDL-B (1,078 +/- 159 vs. 460 +/- 34 mg/d, P less than 0.05), and obese subjects had a higher fractional catabolic rate for LDL than the lean controls (0.48 +/- 0.02 vs. 0.41 +/- 0.02 d-1, P less than 0.05). The rapid catabolism of LDL and increased metabolism of VLDL without conversion to LDL in obese individuals may be mechanisms for maintenance of LDL at normal levels despite the overproduction of its precursor.

Authors

G Egusa, W F Beltz, S M Grundy, B V Howard

Diminished type I collagen synthesis and reduced alpha 1(I) collagen messenger RNA in cultured fibroblasts from patients with dominantly inherited (type I) osteogenesis imperfecta.

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Abstract

Type I osteogenesis imperfecta (OI) is characterized clinically by a moderate fracture frequency with minimal bone deformity and dominant inheritance. Previous studies of the collagenous proteins synthesized by dermal fibroblasts obtained from unrelated patients with this form of OI suggested that the biochemical basis of the disease was reduced production of type I collagen. This study was designed to determine if this biochemical finding segregated with the disease within an individual family. Dermal fibroblast strains were established from three generations of a family having the typical features of type I OI. Analysis of the collagenous proteins made in culture revealed an elevated alpha 1(III) to alpha 1(I) collagen type ratio and an elevated alpha 1(I) to alpha 2(I) collagen chain ratio. The procollagen that accumulated in the medium reflected these ratios to the same degree. Total collagen synthesis was significantly reduced in affected family members. Therefore, the most striking abnormality in affected members was a 50-75% reduction of type I collagen production. Furthermore, the ratio of the alpha 1(I)/alpha 2(I) collagen messenger RNA (mRNA), measured by dot hybridization, was one-half of the value of uninvolved family members and unrelated controls. Since the reduction in the production of type I collagen and the altered alpha 1(I)/alpha 2(I) mRNA ratio clearly segregated with affected individuals within this family, these biochemical measurements may be a useful genetic marker for type I OI.

Authors

D W Rowe, J R Shapiro, M Poirier, S Schlesinger

Control of glomerular hypertension limits glomerular injury in rats with reduced renal mass.

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Abstract

Micropuncture and morphologic studies were performed in four groups of male Munich-Wistar rats after removal of the right kidney and segmental infarction of two-thirds of the left kidney. Groups 1 and 3 received no specific therapy. Groups 2 and 4 were treated with the angiotensin I converting enzyme inhibitor, enalapril, 50 mg/liter of which was put in their drinking water. All rats were fed standard chow. Groups 1 and 2 underwent micropuncture study 4 wk after renal ablation. Untreated group 1 rats exhibited systemic hypertension and elevation of the single nephron glomerular filtration rate (SNGFR) due to high average values for the mean glomerular transcapillary hydraulic pressure difference and glomerular plasma flow rate. In group 2 rats, treatment with enalapril prevented systemic hypertension and maintained the mean glomerular transcapillary hydraulic pressure gradient at near-normal levels without significantly compromising SNGFR and the glomerular capillary plasma flow rate, as compared with untreated group 1 rats. Groups 3 and 4 were studied 8 wk after renal ablation. Untreated group 3 rats demonstrated persistent systemic hypertension, progressive proteinuria, and glomerular structural lesions, including mesangial expansion and segmental sclerosis. In group 4 rats, treatment with enalapril maintained systemic blood pressure at normal levels over the 8-wk period and significantly limited the development of proteinuria and glomerular lesions. These studies suggest that control of glomerular hypertension effectively limits glomerular injury in rats with renal ablation, and further support the view that glomerular hemodynamic changes mediate progressive renal injury when nephron number is reduced.

Authors

S Anderson, T W Meyer, H G Rennke, B M Brenner

Regional alveolar pressure during periodic flow. Dual manifestations of gas inertia.

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Abstract

We measured pressure excursions at the airway opening and at the alveoli (PA) as well as measured the regional distribution of PA during forced oscillations of six excised dog lungs while frequency (f[2-32 Hz]), tidal volume (VT [5-80 ml]), and mean transpulmonary pressure (PL [25, 10, and 6 cm H2O]) were varied. PA's were measured in four alveolar capsules glued to the pleura of different lobes. The apex-to-base ratio of PA's was used as an index of the distribution of dynamic lung distension. At low f, there was slight preferential distension of the lung base which was independent of VT, but at higher f, preferential distension of the lung apex was found when VT's were small, whereas preferential distension of the lung base was found when VT's approached or exceeded dead space. These VT-related changes in distribution at high frequencies seem to depend upon the branching geometry of the central airways and the relative importance of convective momentum flux vs. unsteady inertia of gas residing therein, which, in this study, we showed to be proportional to the ratio VT/VD*, where VD* is an index of dead space. Furthermore, they imply substantial alteration in the distribution of ventilation during high frequency ventilation as f, VT, and PL vary. The data also indicate that alveolar and airway opening pressure costs per unit flow delivered at the airway opening exhibit weakly nonlinear behavior and that resonant amplification of PA's, which has been described previously for the case of very small VT's, persists but is damped as VT's approach dead space values.

Authors

J L Allen, I D Frantz 3rd, J J Fredberg

Modulation of phosphate absorption by calcium in the rabbit proximal convoluted tubule.

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Abstract

Proximal convoluted (S2) and straight (S3) renal tubule segments were studied to determine the effect of Ca on lumen-to-bath phosphate flux (JlbPO4). Increasing bath and perfusate Ca from 1.8 to 3.6 mM enhanced JlbPO4 from 3.3 +/- 0.7 to 6.6 +/- 0.6 pmol/mm per min in S2 segments (P less than 0.001) but had no effect in S3 segments. Decreasing bath and perfusate Ca from 1.8 to 0.2 mM reduced JlbPO4 from 3.7 +/- 0.6 to 2.2 +/- 0.6 in S2 segments. These effects were unrelated to changes in fluid absorption and transepithelial potential difference. Increasing cytosolic Ca with a Ca ionophore, inhibiting the Ca-calmodulin complex with trifluoperazine, or applying the Ca channel blocker nifedipine had no effect on JlBPO4 in S2 segments. Increasing only bath Ca from 1.8 to 3.6 mM did not significantly affect JlbPO4. However, increasing only perfusate Ca enhanced JlbPO4 from 3.4 +/- 0.7 to 6.1 +/- 0.7 pmol/mm per min (P less than 0.005). Inhibition of hydrogen ion secretion, by using a low bicarbonate, low pH perfusate, both depressed base-line JlbPO4 and abolished the stimulatory effect of raising perfusate Ca. Net phosphate efflux (JnetPO4) also increased after ambient calcium levels were raised, ruling out a significant increase in PO4 backflux. When net sodium transport was abolished by reducing the bath temperature to 24 degrees C, JnetPO4 at normal ambient calcium was reduced and increasing ambient calcium failed to increase it, ruling out a simple physicochemical reaction wherein phosphate precipitates out of solution with calcium. The present studies provide direct evidence for a stimulatory effect of Ca on sodium-dependent PO4 absorption in the proximal convoluted tubule, exerted at the luminal membrane. It is postulated that Ca modulates the affinity of the PO4 transporter for the anion.

Authors

D Rouse, W N Suki

Multiple disturbances of free fatty acid metabolism in noninsulin-dependent diabetes. Effect of oral hypoglycemic therapy.

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Abstract

To assess the mechanisms for the elevation of free fatty acids in noninsulin-dependent diabetes, free fatty acid metabolism and lipid and carbohydrate oxidation were compared in 14 obese diabetic Pima Indians and in 13 age-, sex-, and weight-matched nondiabetics. The studies were repeated in 10 of the diabetics after 1 mo of oral hypoglycemic therapy. Fasting plasma glucose concentrations were elevated in diabetics (242 +/- 14 vs. 97 +/- 3 mg/dl, P less than 0.01) and decreased to 142 +/- 12 (P less than 0.01) after therapy. Fasting free fatty acid concentrations were elevated in diabetics (477 +/- 26 vs. 390 +/- 39 mumol/liter, P less than 0.01) and declined to normal values after therapy (336 +/- 32, P less than 0.01). Although free fatty acid transport rate was correlated with obesity (r = 0.75, P less than 0.001), the transport of free fatty acid was not higher in diabetics than in nondiabetics and did not change after therapy. On the other hand, the fractional catabolic rate for free fatty acid was significantly lower in untreated diabetics (0.55 +/- 0.04 vs. 0.71 +/- 0.06 min-1, P less than 0.05); it increased after therapy to 0.80 +/- 0.09 min-1, P less than 0.05, and was inversely correlated with fasting glucose (r = -0.52, P less than 0.01). In diabetics after therapy, lipid oxidation rates fell significantly (from 1.35 +/- 0.06 to 1.05 +/- 0.01 mg/min per kg fat-free mass, P less than 0.01), whereas carbohydrate oxidation increased (from 1.21 +/- 0.10 to 1.73 +/- 0.13 mg/min per kg fat-free mass, P less than 0.01); changes in lipid and carbohydrate oxidation were correlated (r = 0.72, P less than 0.02), and in all subjects lipid oxidation accounted for only approximately 40% of free fatty acid transport. The data suggest that in noninsulin-dependent diabetics, although free fatty acid production may be elevated because of obesity, the elevations in plasma free fatty acid concentrations are also a result of reduced removal, and fractional clearance of free fatty acid appears to be closely related to diabetic control. Furthermore, the increase in fractional clearance rate, despite a marked decrease in lipid oxidation, suggests that the clearance defect in the diabetics is due to an impairment in reesterification, which is restored after therapy.

Authors

M R Taskinen, C Bogardus, A Kennedy, B V Howard

Induction of the insulin proreceptor by hydrocortisone in cultured lymphocytes (IM-9 line).

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Abstract

Hydrocortisone increases the number of insulin receptors at the surface of human cultured lymphocytes (IM-9 line) without altering the degradation of the mature receptor subunits. To elucidate the effect of glucocorticoids on the biosynthesis of the insulin receptor of IM-9 cells, we preincubated cells in the presence or absence of hydrocortisone (1.4 X 10(-6) M) and measured the incorporation of radiolabeled sugars into the insulin receptor components. From 6 to 22 h, there was a progressive increase in the incorporation of [3H]mannose into the insulin proreceptor (190,000 mol wt) and the mature subunits (210,000, 135,000, and 95,000 mol wt). The amount incorporated into hydrocortisone-treated cells was always three to four times higher than in control cells, despite no change in cell number, viability, or radioactive sugar pool. To test directly the earliest effect of hydrocortisone, we undertook pulse-chase studies. The incorporation of [3H]mannose into the insulin receptor precursor and the mature subunits was detectable as early as 30 min of chase and was two to three times higher in hydrocortisone-treated cells at any time point of incubation. In both groups, the increase into the proreceptor (190,000 mol wt) peaked by 60 min and decreased rapidly thereafter (half disappearance rate, 45 min); there was a sustained increase of incorporation into the two major mature subunits (135,000 and 95,000 mol wt) throughout the 4-h chase. Hydrocortisone represents the first pharmacologic agent shown to induce the synthesis of the insulin proreceptor. Further, we present a model system designed to study other agents that may act at a very early step in insulin receptor biosynthesis.

Authors

D G Rouiller, A McElduff, J A Hedo, P Gorden

Accumulation of leukotriene C4 and histamine in human allergic skin reactions.

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Abstract

To determine whether lipoxygenase products of arachidonic acid metabolism are released in vivo during human allergic cutaneous reactions, we serially assayed chamber fluid placed over denuded skin sites for the presence of both C-6 peptide leukotrienes (e.g., LTC4, LTD4, and LTE4) and leukotriene B4 (LTB4), using radioimmune assay and HPLC separation, and compared it to histamine (assayed radioenzymatically) in 13 atopic and two nonatopic volunteers. Skin chamber sites challenged with ragweed or grass pollen antigen (250-750 protein nitrogen units/ml) for the first hour and phosphate-buffered saline (PBS) for the next 3 h were assayed hourly and compared to sites challenged with PBS alone. As assessed by HPLC, LTC4 composed greater than 85% of the C-6 peptide leukotriene released at any skin site, whereas little LTD4 or LTE4 was detected. LTC4 was present in significantly greater concentrations at antigen sites as compared to PBS-challenged sites throughout the 4-h period. Minimal concentrations of LTB4 were found throughout this time period and were not different at antigen or PBS sites. Histamine was present in significantly greater concentrations at antigen rather than PBS sites, but the pattern of release was different from that of LTC4. Peak histamine release invariably occurred during the first hour and decreased progressively thereafter, whereas the greatest amounts of LTC4 were detected during the 2nd to 4th hours. The amount of LTC4 accumulating at the site was dependent upon the dosage of antigen used in the epicutaneous challenge. We have demonstrated in this study that of the leukotrienes assessed LTC4 is released in the greatest quantity in situ during in vivo allergic cutaneous reactions and that it is present at such sites for at least 4 h after antigen challenge. Since intradermal injection of LTC4 in humans induces wheal and flare responses that persist for hours, our findings support the hypothesis that LTC4 is an important mediator of human allergic skin reactions.

Authors

S F Talbot, P C Atkins, E J Goetzl, B Zweiman

Effects of exercise training on in vivo insulin action in individual tissues of the rat.

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Abstract

It has previously been suggested that exercise training leads to increased whole body insulin sensitivity. However, the specific tissues and metabolic pathways involved have not been examined in vivo. By combining the euglycemic clamp with administration of glucose tracers, [3H]2-deoxyglucose (2DG), [14C]glucose, and [3H]glucose, in vivo insulin action at the whole body level and within individual tissues has been assessed in exercise-trained (ET, running 1 h/d for 7 wk) and sedentary control rats at four insulin doses. Whole body insulin sensitivity was significantly increased in ET. In addition, the skeletal muscles, soleus, red and white gastrocnemius, extensor digitorum longus (EDL), and diaphragm all showed increased sensitivity of insulin-stimulated 2DG uptake with training. With the exception of EDL, no significant difference in insulin-mediated glycogen synthesis between control and ET could be found. Therefore, the increased insulin-induced 2DG uptake observed in muscle following training is apparently directed towards glucose oxidation. In ET animals, adipose tissue exhibited a significant increase in insulin-mediated 2DG uptake and [14C]glucose incorporation into free fatty acids but there was no difference from control in any parameters measured in lung or liver. EDL and white gastrocnemius, which are not primarily involved during exercise of this type, also demonstrated increased insulin sensitivity following training. In conclusion, exercise training results in a marked increase in whole body insulin sensitivity related mainly to increased glucose oxidation in skeletal muscle. This effect may be mediated by systemic as well as local factors and is likely to be of therapeutic value in pathological conditions exhibiting insulin resistance.

Authors

D E James, E W Kraegen, D J Chisholm

Pathophysiology of chronic tubulo-interstitial disease in rats. Interactions of dietary acid load, ammonia, and complement component C3.

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Abstract

The human end-stage kidney and its experimental analogue, the remnant kidney in the rat, exhibit widespread tubulo-interstitial disease. We investigated whether the pathogenesis of such tubulo-interstitial injury is dependent upon adaptive changes in tubular function and, in particular, in ammonia production when renal mass is reduced. Dietary acid load was reduced in 1 3/4-nephrectomized rats by dietary supplementation with sodium bicarbonate (NaHCO3), while control rats, paired for serum creatinine after 1 3/4 nephrectomy, were supplemented with equimolar sodium chloride. After 4-6 wk, NaHCO3-supplemented rats demonstrated less impairment of tubular function as measured by urinary excretory rates for total protein and low molecular weight protein and higher transport maximum for para-aminohippurate per unit glomerular filtration rate, less histologic evidence of tubulo-interstitial damage, less deposition of complement components C3 and C5b-9, and a lower renal vein total ammonia concentration. Such differences in tubular function could not be accounted for simply on the basis of systemic alkalinization, and differences in tubular injury could not be ascribed to differences in glomerular function. Because nitrogen nucleophiles such as ammonia react with C3 to form a convertase for the alternative complement pathway, and because increased tissue levels of ammonia are associated with increased tubulo-interstitial injury, we propose that augmented intrarenal levels of ammonia are injurious because of activation of the alternative complement pathway. Chemotactic and cytolytic complement components are thereby generated, leading to tubulo-interstitial inflammation. Thus, alkali supplementation reduces chronic tubulo-interstitial disease in the remnant kidney of the rat, and we propose that this results, at least in part, from reduction in cortical ammonia and its interaction with the alternative complement pathway.

Authors

K A Nath, M K Hostetter, T H Hostetter

Biliary secretion of fluid-phase markers by the isolated perfused rat liver. Role of transcellular vesicular transport.

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Abstract

In these studies, we have used several approaches to systematically explore the contribution of transcellular vesicular transport (transcytosis) to the blood-to-bile movement of inert fluid-phase markers of widely varying molecular weight. First, under steady-state conditions, the perfused rat liver secreted even large markers in appreciable amounts. The bile-to-plasma (B/P) ratio of these different markers, including microperoxidase (B/P ratio = 0.06; mol wt = 1,879), insulin (B/P ratio = 0.09, mol wt = 5,000), horseradish peroxidase (B/P ratio = 0.04, mol wt = 40,000), and dextran (B/P ratio = 0.09, mol wt = 70,000), exhibited no clear ordering based on size alone, and when dextrans of two different sizes (40,000 and 70,000 mol wt) were studied simultaneously, the relative amounts of the two dextran species in bile were the same as in perfusate. Taurocholate administration produced a 71% increase in bile flow but little or no (0-20%) increase in the output of horseradish peroxidase, microperoxidase, inulin, and dextran. Second, under nonsteady-state conditions in which the appearance in or disappearance from bile of selected markers was studied after their abrupt addition to or removal from perfusate, erythritol reached a B/P ratio of 1 within 2 min. Microperoxidase and dextran appeared in bile only after a lag period of approximately 12 min and then slowly approached maximal values, whereas sucrose exhibited kinetically intermediate behavior. A similar pattern was observed after removal of greater than 95% of the marker from the perfusate. Erythritol rapidly reapproached a B/P ratio of 1, whereas the B/P ratio for sucrose, dextran, and microperoxidase fell much more slowly and exceeded 1 for a full 30 min after perfusate washout. Finally, electron microscopy and fluorescence microscopy of cultured hepatocytes demonstrated the presence of horseradish peroxidase and fluorescein-dextran, respectively, in intracellular vesicles, and fractionation of perfused liver homogenates revealed that at least 35-50% of sucrose, inulin, and dextran was associated with subcellular organelles. Collectively, these observations are most compatible with a transcytosis pathway that contributes minimally to the secretion of erythritol, but accounts for a substantial fraction of sucrose secretion and virtually all (greater than 95%) of the blood-to-bile transport of microperoxidase and larger markers. These findings have important implications with respect to current concepts of canalicular bile formation as well as with respect to the conventional use of solutes such as sucrose as markers of canalicular or paracellular pathway permeability.

Authors

J R Lake, V Licko, R W Van Dyke, B F Scharschmidt

Distinct clonotypes of anti-DNA antibodies in mice with lupus nephritis.

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Abstract

Clonotypes of IgG anti-DNA antibodies were studied by isoelectric focusing in various autoimmune mice with or without lethal lupus nephritis. MRL/MpJ-lpr/lpr mice exhibited the most heterogeneous spectrotypes of anti-DNA antibodies in the pH range from 6.5 to 8.5, with marked variation in individual mice. Female (NZB X NZW)F1 mice expressed rather uniform DNA-binding bands composed of at least five to six distinct subgroups, having isoelectric points from 6.5 to 8.0. Male BXSB mice showed major characteristic bands confined to alkaline pH range from 7.8 to 8.5, similar to C57BL/6J-lpr/lpr mice, which showed markedly restricted bands in this region. Both AKR/J-lpr/lpr and C3H/HeJ-lpr/lpr mice expressed DNA-binding bands mostly focused between pH 6.5 and 8.2. The aging study indicated that three autoimmune mice (MRL/MpJ-lpr/lpr, [NZB X NZW]F1, and male BXSB) that developed fatal glomerulonephritis showed clonal expansion of anti-DNA antibodies throughout their life. In contrast, such age-dependent expansion of anti-DNA clonotypes was not evident in three lpr cogenic mice (C57BL/6J-lpr/lpr, AKR/J-lpr/lpr, and C3H/HeJ-lpr/lpr) that developed only mild glomerulonephritis; rather, their expression of anti-DNA spectrotypes diminished as they aged. Anti-DNA activities in renal eluates from nephritic autoimmune mice were mostly distributed in the pH range from 6.5 to 8.0, without significant concentrations in the high alkaline range of more than pH 8.0. These results suggest that there exist distinct anti-DNA clonotypes in each mouse strain and that the development of lupus nephritis does not appear to be associated with particular spectrotypes of anti-DNA antibodies. Rather, the age-dependent expansion of anti-DNA clonotypes may be a feature more characteristic of mice developing lethal lupus nephritis.

Authors

H Yoshida, M Yoshida, S Izui, P H Lambert

Long-term control of plasma calcitriol concentration in dogs and humans. Dominant role of plasma calcium concentration in experimental hyperparathyroidism.

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Abstract

Despite great interest in the elevated circulating levels of calcitriol (1,25-[OH]2D) associated with the clinical syndrome of human primary hyperparathyroidism, the relative potencies of known and potential stimuli/suppressors of long-term calcitriol levels have not been evaluated in either clinical or experimentally induced hyperparathyroid states. Based on reports that aparathyroid animals exhibit suppressed plasma calcitriol concentration and that acute administration of parathyroid hormone (PTH) to both humans and experimental animals or to renal slices in vitro results in increased plasma calcitriol concentration/production rate, it might be predicted that a chronic experimental model of either hypercalcemic primary hyperparathyroidism or hypocalcemic secondary hyperparathyroidism would show increased plasma calcitriol concentration. Chronic alterations in plasma calcium concentration have not been implicated as modulating calcitriol levels in any species. Accordingly, we investigated the long-term response of plasma calcitriol concentration in states of sustained experimental primary and secondary hyperparathyroidism. Intact dogs (group I) undergoing continuous intravenous PTH infusion for 12 d developed sustained hypercalcemia and hypophosphatemia, and plasma calcitriol concentration decreased from 23 +/- 3 to 14 +/- 3 pg/ml (P less than 0.01). Subsequent chelator (EGTA)-induced chronic normalization of hypercalcemia during ongoing PTH infusion resulted in a large and sustained increase in plasma calcitriol concentration to supernormal levels, reversible during subsequent cessation of chelator infusion. In additional intact dogs (group II), chronic chelator-induced hypocalcemic secondary hyperparathyroidism resulted in a sustained increase in plasma calcitriol concentration despite hyperphosphatemia. In normal human subjects undergoing a 12-13-d continuous intravenous PTH infusion to result in sustained moderate hypercalcemia (12.0 +/- 0.2 mg/100 ml) and hypophosphatemia, plasma calcitriol concentration decreased significantly (P less than 0.01) as in group I dogs and was followed by reversal to normal levels in a recovery period. The present results provide strong evidence in both humans and dogs that during experimentally induced chronic PTH excess, alterations in plasma calcium concentration dictate the directional response of circulating calcitriol concentrations. The long-term potency of plasma calcium concentration as a modulator of calcitriol metabolism is sufficient to override opposing modulation by plasma phosphorus concentration and PTH.

Authors

H N Hulter, B P Halloran, R D Toto, J C Peterson

N-Acetylcysteine potentiates inhibition of platelet aggregation by nitroglycerin.

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Abstract

Platelet aggregation is currently felt to play an important role in the pathogenesis of ischemic vascular disorders. The smooth muscle relaxant, nitroglycerin, has been shown to inhibit platelet aggregation in vitro, but at concentrations that were felt to be unattainable in vivo. Because the in vivo action of nitroglycerin on smooth muscle cells has been shown to depend on the presence of reduced cytosolic sulfhydryl groups, the inhibitory effect of nitroglycerin on platelet aggregation was examined in the presence of the reduced thiol, N-acetylcysteine. Millimolar concentrations of N-acetylcysteine potentiated markedly the inhibitory effect of nitroglycerin on platelet aggregation induced by ADP, epinephrine, collagen, and arachidonate, decreasing the 50% inhibitory concentration (IC50) approximately 50-fold for each of these agents. Other guanylate cyclase activators inhibited ADP-induced aggregation similarly and this inhibition was likewise potentiated by N-acetylcysteine. Platelet guanosine 3',5'-cyclic monophosphate content increased fivefold in the presence of nitroglycerin and N-acetylcysteine 2 min before maximal inhibition of ADP-induced aggregation was achieved, while simultaneously measured cyclic AMP did not change relative to base-line levels. In the absence of N-acetylcysteine, nitroglycerin induced a marked decrease in platelet-reduced glutathione content as S-nitroso-thiol adducts were produced. The synthetic S-nitroso-thiol, S-nitroso-N-acetylcysteine, markedly inhibited platelet aggregation with an IC50 of 6 nM. These data show that N-acetylcysteine markedly potentiates the inhibition of platelet aggregation by nitroglycerin and likely does so by inducing the formation of an S-nitrosothiol adduct(s), which activate guanylate cyclase.

Authors

J Loscalzo

Clonal analysis of T lymphocytes in the acquired immunodeficiency syndrome. Evidence for an abnormality affecting individual helper and suppressor T cells.

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Abstract

Purified helper-inducer (T4+) and suppressor-cytotoxic (T8+) lymphocytes from eight patients with acquired immunodeficiency syndrome (AIDS) and eight healthy heterosexual donors were examined by limiting dilution analysis for their ability to be clonally expanded. It was demonstrated that viable T4+ and T8+ lymphocytes from patients with AIDS had markedly reduced proportions of clonable cells compared to the healthy donors (T4 = 1:255 vs. 1:34, P = 0.06; T8 = 1:355 vs. 1:55, P = 0.01). However, the cloned T cells that were obtained from the patients with AIDS demonstrated normal proliferation in response to phytohemagglutinin and alloantigen, and normal ability to help or suppress pokeweed mitogen-driven IgG synthesis. These results strongly suggest that, in addition to a quantitative diminution of T4+ lymphocytes in AIDS, there is an intrinsic functional defect in the surviving T4+ and T8+ lymphocytes, which is reflected by a severe decrease in their potential for clonal expansion.

Authors

J B Margolick, D J Volkman, H C Lane, A S Fauci

Localization of collagenase in the growth plate of rachitic rats.

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Abstract

In the transition from proliferation to hypertrophic cell zones in the growth plate, there is an increase in chondrocyte volume and a corresponding decrease in collagen content to accommodate the enlarging cells. It is postulated that collagenase accounts for this collagen loss. To test this hypothesis, tibial growth plates were obtained from normal rats, rachitic rats deficient in vitamin D and phosphate, and rats after 48 and 72 h of healing from rickets. Collagenase was quantitated by a pellet assay based on the release of solubilized collagen from the endogenous insoluble collagen in the tissue homogenates. A fourfold greater collagen release and a concomitant sixfold greater hypertrophic cell volume were measured in rachitic growth plates compared with normal age-matched controls. During healing of rickets, collagenase activity and hypertrophic cell volume returned almost to control levels. Rachitic growth plates were dissected into the juxtaepiphyseal 1/3 and the juxtametaphyseal 2/3. The latter portion contained greater than 95% of the hypertrophic cells and 86% of the collagenase. The collagen-degrading activity was extracted from this region and was shown to be a true collagenase by its production of typical A fragments of tropocollagen produced by collagenase action. The enzyme was activated by aminophenylmercuric acetate and trypsin and was inhibited by EDTA, 1,10-phenanthroline, and a tissue inhibitor of metalloproteinases from human articular cartilage. Inhibitors of aspartic, cysteine, and serine proteases had no effect. Micropuncture fluids aspirated from rachitic cartilage contained latent collagenase activity, indicating an extracellular localization. Negative tests for hemoglobin in the rachitic cartilage samples indicated that there was no contamination by capillaries and that this was not a source of collagenase. It is concluded that extracellular collagenase accounts for the loss of cartilage matrix in the hypertrophic zone, and that this process may be distinct from that of capillary invasion.

Authors

D D Dean, O E Muniz, I Berman, J C Pita, M R Carreno, J F Woessner Jr, D S Howell

Anti-Fab antibodies in humans. Predominance of minor immunoglobulin G subclasses in rheumatoid arthritis.

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Abstract

Isoelectric focusing analyses of sera from patients with rheumatoid arthritis (RA) demonstrate two populations of antibodies directed against the Fab portion of pooled human IgG. One population is composed of polyclonal alkaline anti-Fab antibodies (alpha FABA) and the other, acidic alpha FABA which are more clonally restricted. In this study we have identified the immunoglobulin classes and subclasses of these antibodies in RA sera. Enzyme-linked immunosorbent assays (ELISA) demonstrated alpha FABA in RA sera to be predominantly IgG. A large portion of IgG alpha FABA existed as immune complexes, inasmuch as dialysis of RA sera against 6 M urea before ELISA analysis was necessary for maximal detection of alpha FABA activity. Chromatofocusing of RA sera isolated alpha FABA of different charges and revealed the acidic clonally restricted alpha FABA to be IgG4 and IgG3, whereas the polyclonal alkaline group contained IgG1, IgG2, and IgG3. Overall, acidic IgG3 and IgG4 comprised 70% of IgG alpha FABA, and high levels of IgG4 were seen in most RA sera. When alpha FABA were elevated in normal sera, they were primarily of the IgG4 subclass, and also existed as immune complexes. Serum anti-Fab activity was removed by adsorption of sera with Fab fragments. Anti-Fab antibodies of both kappa and lambda light-chain types were present in RA sera, and F(ab')2 fragments of RA serum immunoglobulin were found to possess anti-Fab activity. These studies indicate that alpha FABA in RA sera are limited to the IgG class, and that most of these antibodies exist as immune complexes and display clonal and minor IgG subclass restriction.

Authors

J E Persselin, R H Stevens

Familial systemic lupus erythematosus. Presence of a cross-reactive idiotype in healthy family members.

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Abstract

Sera of 27 members of 3 human kindreds with familial systemic lupus erythematosus (SLE) were examined for expression of a cross-reactive idiotype present on anti-DNA antibodies of SLE patients. By radioimmunoassay, serum samples from 6 of 8 SLE patients and 15 of 19 family members had high-titered reactivity with the antiidiotype, 3I. Isoelectric focusing and Western blot analysis of 3I-reactive bands revealed two patterns of reactivity: either a pattern of bands present at pH 5-7, or bands present at pH 5-7 with additional bands present at pH 7-8.5. Cationic bands were found to correlate with the presence of anti-DNA antibodies, indicating that immunoglobulin charge may be a factor in determining specificity for DNA. Millipore filter analysis revealed anti-DNA antibodies in sera of 4 of 8 SLE patients and 2 of 19 family members without SLE. In 2 additional SLE patients and 2 additional family members, anti-DNA antibodies were revealed when sera were analyzed under conditions that dissociate immune complexes. This study indicates that expression of an idiotype associated with anti-DNA antibodies is significantly increased in relatives of SLE patients and usually occurs in the absence of anti-DNA activity.

Authors

R Halpern, A Davidson, A Lazo, G Solomon, R Lahita, B Diamond

Effect of dietary fat, carbohydrate, and protein on branched-chain amino acid catabolism during caloric restriction.

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Abstract

To assess the effect of each dietary caloric source on the catabolism of branched-chain amino acids, we investigated the rate of leucine oxidation before and after obese volunteers consumed one of the following diets for one week: (a) starvation, (b) 300 or 500 cal of fat/d, (c) 300 or 500 cal of carbohydrate/d, (d) 300 or 500 cal of protein/d, (e) a mixture of carbohydrate (300 cal/d) and fat (200 cal/d), or (f) a mixture of carbohydrate (300 cal/d) and protein (200 cal/d). Starvation significantly increased the rate of leucine oxidation (1.4 +/- 0.11 vs. 1.8 +/- 0.16 mmol/h, P less than 0.01). The same occurred with the fat and protein diets. In sharp contrast, the 500-cal carbohydrate diet significantly decreased the rate of leucine oxidation (1.3 +/- 0.13 vs. 0.6 +/- 0.09 mmol/h, P less than 0.01). The same occurred when a portion of the carbohydrate diet was isocalorically replaced with either fat or protein. The cumulative nitrogen excretion during the fat diet and starvation was not significantly different. As compared with the fat diets, the carbohydrate diets on the average reduced the urinary nitrogen excretion by 12 g/wk. Nitrogen balance was positive during the consumption of the 500-cal protein diet, but negative during the consumption of carbohydrate-protein diet. The fat diets, like the protein diets and starvation, greatly increased plasma leucine (119 +/- 13 vs. 222 +/- 15 microM, P less than 0.01) and beta-hydroxybutyrate (0.12 +/- 0.02 vs. 4.08 +/- 0.43 mM, P less than 0.01) concentrations, and significantly decreased plasma glucose (96 +/- 4 vs. 66 +/- 3 mg/dl, P less than 0.01) and insulin (18 +/- 4 vs. 9 +/- 1 microU/ml, P less than 0.05) concentrations. These changes did not occur, or were greatly attenuated, when subjects consumed carbohydrate alone or in combination with fat or protein. We conclude that during brief caloric restriction, dietary lipid and protein, unlike carbohydrate, do not diminish the catabolism of branched-chain amino acids and the decrease in branched-chain amino acid oxidation is associated with protein sparing.

Authors

J A Vazquez, E L Morse, S A Adibi

Biosynthesis of bile acids in cerebrotendinous xanthomatosis. Relationship of bile acid pool sizes and synthesis rates to hydroxylations at C-12, C-25, and C-26.

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Abstract

To examine the defect in side-chain oxidation during the formation of bile acids in cerebrotendinous xanthomatosis, we measured in vitro hepatic microsomal hydroxylations at C-12 and C-25 and mitochondrial hydroxylation at C-26 and related them to the pool size and synthesis rates of cholic acid and chenodeoxycholic acid as determined by the isotope dilution technique. Hepatic microsomes and mitochondria were prepared from seven subjects with cerebrotendinous xanthomatosis and five controls. Primary bile acid synthesis was markedly reduced in cerebrotendinous xanthomatosis as follows: cholic acid, 133 +/- 30 vs. 260 +/- 60 mg/d in controls; and chenodeoxycholic acid, 22 +/- 10 vs. 150 +/- 30 mg/d in controls. As postulated for chenodeoxycholic acid synthesis, mitochondrial 26-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha-diol was present in all specimens and was 30-fold more active than the corresponding microsomal 25-hydroxylation. However, mean mitochondrial 26-hydroxylation of 5 beta-cholestane-3 alpha,7 alpha-diol was less active in cerebrotendinous xanthomatosis than in controls: 59 +/- 17 compared with 126 +/- 21 pmol/mg protein per min. As for cholic acid synthesis, microsomal 25-hydroxylation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol was substantially higher in cerebrotendinous xanthomatosis and control preparations (620 +/- 103 and 515 +/- 64 pmol/mg protein per min, respectively) than the corresponding control mitochondrial 26-hydroxylation of the same substrate (165 +/- 25 pmol/mg protein per min). Moreover in cerebrotendinous xanthomatosis, mitochondrial 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol-26-hydroxylase activity was one-seventh as great as in controls. Hepatic microsomal 12 alpha-hydroxylation, which may be rate-controlling for the cholic acid pathway, was three times more active in cerebrotendinous xanthomatosis than in controls: 1,600 vs. 500 pmol/mg protein per min. These results demonstrate severely depressed primary bile acid synthesis in cerebrotendinous xanthomatosis with a reduction in chenodeoxycholic acid formation and pool size disproportionately greater than that for cholic acid. The deficiency of chenodeoxycholic acid can be accounted for by hyperactive microsomal 12 alpha-hydroxylation that diverts precursors into the cholic acid pathway combined with decreased side-chain oxidation (mitochondrial 26-hydroxylation). However, side-chain oxidation in cholic acid biosynthesis may be initiated via microsomal 25-hydroxylation of 5beta-cholestane-3alpha,7alpha,12alpha-triol was substantially lower in control and cerebrotendinous xanthomatosis liver. Thus, separate mechanisms may exist for the cleavage of the cholesterol side chain in cholic acid and chenodeoxycholic acid biosynthesis.

Authors

G Salen, S Shefer, G S Tint, G Nicolau, B Dayal, A K Batta

Markedly increased circulating pyridoxal-5'-phosphate levels in hypophosphatasia. Alkaline phosphatase acts in vitamin B6 metabolism.

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Abstract

Markedly increased circulating concentrations of pyridoxal-5'-phosphate (PLP) were found in each of 14 patients representing all clinical forms of hypophosphatasia, an inborn error characterized by deficient activity of the tissue nonspecific (bone/liver/kidney) isoenzyme of alkaline phosphatase (AP). The mean PLP concentration in plasma was 1174 nM (range, 214-3839 nM) in the patients and 57 +/- 26 nM (mean +/- SD) in 38 control subjects. In four affected children, urinary excretion of the PLP degradation product, 4-pyridoxic acid, was unremarkable during consumption of normal quantities of dietary vitamin B6. Our findings identify increased circulating PLP concentration as a marker for hypophosphatasia and provide further evidence that tissue nonspecific AP acts in vitamin B6 metabolism. Tissue nonspecific AP appears to function as an ectoenzyme to regulate extracellular but not intracellular levels of PLP substrate. Performing assays of circulating PLP concentration alone to assess vitamin B6 nutrition may be misleading in disorders associated with altered AP activity.

Authors

M P Whyte, J D Mahuren, L A Vrabel, S P Coburn

Substrate cycling between gluconeogenesis and glycolysis in euthyroid, hypothyroid, and hyperthyroid man.

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Abstract

Substrate, or futile cycles, have been hypothesized to be under hormonal control, and important in metabolic regulation and thermogenesis. To define the role of thyroid hormones in the regulation of substrate cycling in glycolysis and gluconeogenesis, we measured rates of cycling in normal (n = 4), hypothyroid (n = 5), and hyperthyroid (n = 5) subjects employing a stable isotope turnover technique. Glucose labeled with deuterium at different positions (2-D1-, 3-D1-, and 6,6-D2-glucose) was given as a primed-constant infusion in tracer doses, and arterialized plasma samples were obtained and analyzed by gas-chromatography mass-spectrometry for the steady state enrichment of glucose that was labeled at the various positions. The rate of appearance (Ra) was then calculated for each isotopic tracer. The difference between the Ra determined by 2-D1-glucose (Ra2) and the Ra determined by 3-D1-glucose (Ra3) represents the substrate cycling rate (SCR) between glucose and glucose-6-phosphate. The difference between the Ra determined by 3-D1-glucose (Ra3) and the Ra determined by 6,6-D2-glucose (Ra6) represents the SCR between fructose-6-phosphate and fructose-1,6-diphosphate. The difference between Ra2 and Ra6 represents the combined SCR of both cycles. In normal subjects (serum thyroxine [T4] = 8.4 +/- 1.2 microgram/dl (all expressions, mean +/- SD), n = 4), the rates of appearance for Ra2, Ra3, and Ra6 were 3.23 +/- 0.56, 2.64 +/- 0.50, and 2.00 +/- 0.27 mg/kg X min, respectively, whereas those in the hypothyroid subjects (T4 = 1.0 +/- 0.8 microgram/dl; n = 5) were 1.77 +/- 0.56 (P less than 0.01), 1.52, 1.57 +/- 0.31 (P less than 0.05) mg/kg X min, respectively. Conversely, the rates of appearance for Ra2 and Ra6 in the hyperthyroid subjects (T4 = 23.9 +/- 3.6 micrograms/dl) were 3.94 +/- 0.43 (P less than 0.05) and 2.54 +/- 0.22 (P less than 0.02), respectively, compared with the normal subjects. On the basis of these data, we noted that the normal subjects had a combined SCR of 1.23 +/- 0.35 mg/kg X min. In contrast, the hypothyroid patients had a significantly decreased combined SCR, 0.20 +/- 0.54 mg/kg X min (P less than 0.02). The hyperthyroid patients had a combined SCR of 1.39 +/- 0.23 mg/kg X min (P less than NS). To determine whether these cycles responded to thyroid hormone treatment, these same hypothyroid subjects were acutely treated for 1 wk with parenteral 50 micrograms/d sodium L-triiodothyronine and chronically with 100-150 micrograms/d L-thyroxine. After 7 d, their mean oxygen consumption rate and carbon dioxide production rate increased significantly from 102+/-13 micromol/kg.min, to 147+/-34 micromol/kg.min (P<0.05), and from 76+/-13 micromol/kg.min to 111+/-19 micromol/kg.min (P<0.05), respectively. The combined SCR (Ra(2)--Ra(6) remained unchanged at 0.07+/-0.37 mg/kg.min. However, after 6 mo of oral L-thyroxine therapy (T(4)=9.5+/-1.4 microgram/kl) the treated hypothyroid patients had increased their combined SCR (Ra(2)--Ra(6)) to 0.86 +/-0.23 mg/kg.min (P<0.02), a value not significantly different from the combined SCR of normal subjects. We conclude that substrate cycling between glucose and glucose-6-phosphate and between fructose-6-phosphate and fructose-1,6-diphosphate occurs in man and is affected by thyroid hormone. Substrate cycles may represent a mechanism by which thyroid hormone alters the sensitivity of certain reactions to metabolic signals.

Authors

G I Shulman, P W Ladenson, M H Wolfe, E C Ridgway, R R Wolfe

Cytoplasmic immunoglobulin content in multiple myeloma.

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Abstract

Bone marrow cells of 82 patients with multiple myeloma were subjected to flow cytometric analysis of DNA and cytoplasmic immunoglobulin (CIg) content using propidium iodide and direct immunofluorescence assays. Except for two patients with nonsecretory myeloma, there was conformity in the immunoglobulin type derived from immunoelectrophoresis and plasma cell CIg staining. One patient with nonsecretory myeloma exhibited monotypic CIg staining, while the second showed no reaction. In eight patients with IgG lambda myeloma, the same tumor cells contained both lambda and kappa light chains, suggesting the productive rearrangement of both light chain genes. 14 patients with previously unrecognized plasma cells of low RNA content, all of whom were resistant to chemotherapy, were identified by CIg staining. By revealing previously unrecognized plasma cells with low RNA content, CIg analysis identified more patients with treatment-refractory myeloma.

Authors

B Barlogie, R Alexanian, M Pershouse, L Smallwood, L Smith

Effect of arginine vasopressin on renal medullary blood flow. A videomicroscopic study in the rat.

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Abstract

The role of arginine vasopressin (AVP) in the regulation of renal medullary blood flow is uncertain. To determine if AVP has a direct vasoconstrictive action on vasa recta, the effect of AVP on erythrocyte velocity (VRBC), diameter, and blood flow (QVR) in descending vasa recta (DVR) and ascending vasa recta (AVR) was studied in the exposed renal papilla of four groups of chronically water diuretic rats using fluorescence videomicroscopy. There were three periods: control (period 1), experimental (period 2), and recovery (period 3). In periods 1 and 3, all groups received hypotonic saline. In period 2, group I rats (AVP) received AVP (45 ng/h per kg body wt); group II (time) received hypotonic saline alone; group III (AVP plus V1-inhibitor) received AVP plus its vascular antagonist, d(CH2)5Tyr(Me)AVP; and group IV (V1-inhibitor) received the vascular antagonist alone. Another group of rats (group V) was employed to demonstrate that the rise in blood pressure induced by a 3- or 10-ng/kg injection of AVP was virtually abolished by the prior infusion of the V1-inhibitor. The urine of group III as well as group I rats was concentrated (Uosm = 721 +/- 62 H2O vs. 670 +/- 39 mosM/kg), while urine remained dilute in groups II and IV. In period 2, VRBC and QVR in DVR and AVR decreased in group I, did not decrease in group III, and increased in groups II and IV. The vascular antagonist thus completely abolished the AVP-induced decrease in QVR in group III. These findings unequivocally establish that AVP in physiological amounts reduces medullary blood flow, at least in part, by a direct vasoconstrictive action on the medullary microcirculation. They also show that an effect of AVP on medullary blood flow is not necessary for its antidiuretic effect.

Authors

B Zimmerhackl, C R Robertson, R L Jamison

Importance of amino acids on vasopressin-stimulated water flow.

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Abstract

The presence of several naturally occurring amino acids in the serosal bath of toad urinary bladder significantly alters the hydrosmotic response of this tissue to vasopressin. We found that histidine, glutamate, and lysine increase vasopressin-stimulated water flow by 75%, 60%, and 43%, respectively. In contrast, alanine did not alter vasopressin-stimulated water flow, whereas glutamine decreased it by 25%. The effect of each amino acid represents intracellular events because their effects on theophylline-stimulated water flow were similar to those found with vasopressin. However, the site of action of amino acids varied, with some operating at steps before and others at steps after cyclic AMP generation. The fact that the metabolically inactive D-histidine and D-glutamate are as effective as their metabolically active L-counterparts suggests that the action of amino acids depends upon some physicochemical properties of their molecules. The ability of amino acids to influence the hydrosmotic effects of vasopressin was shown to be independent of prostaglandin generation, ionic composition, and molecular charge. In the case of histidine, we were able to obtain some understanding of the mechanism responsible for its action. We first showed that the effect of histidine does not depend upon its metabolism. In addition to D-histidine being as effective as the metabolically active L-histidine, we also showed that histidine is effective when its metabolism is abolished by low ambient temperature and also when its incorporation into proteins was prevented by cycloheximide. These findings suggest that histidine operates through some physicochemical property localized on its molecule. We were able to show that this property resides on the imidazole part of histidine. Imidazole, similar to histidine, increases vasopressin-stimulated water flow. Methylation of histidine on the imidazole ring completely abolished its effectiveness in increasing vasopressin-stimulated water flow. In contrast, methylation of histidine at the side chain increased vasopressin action similar to that found for histidine. We provide evidence that the physicochemical property of the imidazole ring of histidine is that of chelating Zn++ intracellularly, and that the intracellular site of action of histidine is closely linked to microtubules formation and/or action.

Authors

C P Carvounis, G Carvounis, B J Wilk

Identification of immunostimulatory dendritic cells in the synovial effusions of patients with rheumatoid arthritis.

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Abstract

Dendritic cells in the circulation are leukocytes that are rich in Ia antigens and that actively stimulate T cell replication. We have identified dendritic cells in the joint effusions of patients with rheumatoid arthritis. By phase-contrast and immunofluorescence microscopy, synovial mononuclear cells contained 1-5% dendritic profiles that were rich in HLA-DR and DQ, had small amounts of C3bi receptor, and lacked a battery of monocyte and lymphocyte markers. These dendritic cells could be enriched to 60-80% purity by cytolytic depletion of monocytes and lymphocytes with a group of monoclonal antibodies (MAb) and complement. By transmission electron microscopy, the dendritic cell processes were bulbous in shape and lacked organelles. The cytoplasm had few lysosomes or endocytic vacuoles but contained a well-developed smooth reticulum that was comparable to that previously described in the Ia-rich interdigitating cells of lymphoid tissues. The growth of sodium periodate-modified T lymphocytes was used as a rapid quantitative assay of accessory cell function. Synovial mononuclear cells were some ten times more active than normal blood cells. Treatment with alpha-Ia MAb and complement ablated stimulatory function. In contrast, removal of monocytes (MAb, 3C10) or monocytes and B (MAb, BA-1) plus T (MAb, OKT3, or T101) lymphocytes did not significantly alter total activity, and the function per viable cell increased four- to eightfold. We conclude that rheumatoid arthritis synovial fluids contain cells that are comparable in function, phenotype, and structure to blood dendritic cells, although the frequency (1-5%) is 10 times greater in joints. The reason for their accumulation in the articular cavity is not known, but dendritic cells may be important in perpetuating the joint inflammation characteristic of this disease.

Authors

N J Zvaifler, R M Steinman, G Kaplan, L L Lau, M Rivelis

Immunologic and structural studies of the lupus/Sjögren's syndrome autoantigen, La/SSB, with a monoclonal antibody.

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Abstract

La/SSB is a small nuclear RNA protein against which precipitating autoantibodies are made in many patients with systemic lupus erythematosus or Sjögren's syndrome. The recent purification of La/SSB has made structural and immunologic studies possible. Consequently, a mouse hybridoma antibody (La1) was raised, after immunization and fusion, that reacted with bovine La/SSB. Results of inhibition tests with tissue extracts and fluorescent antinuclear antibody tests demonstrated that La1 reacted with bovine extracts and cells, but not with those from human, mouse, or rabbit sources. La1 reacted in Western blot and in an adapted anti-La/SSB enzyme-linked immunosorbent assay with only the 41-kD bovine La/SSB peptide and not with the smaller 29-kD bovine La/SSB peptide. RNA gels showed that La1 bound the La/SSB particle that contained the predominant La/SSB RNA species near 90 nucleotides as well as the minor RNA species, both of which were bound by the human autoimmune anti-La/SSB serum. A solid-phase assay for human autoimmune anti-La/SSB antibody using La1 was more sensitive for the detection of human anti-La/SSB than was a comparable assay using purified La/SSB, and showed that anti-La/SSB is present in nearly all Ro/SSA precipitin-positive sera. Thus, this study demonstrates that monoclonal antibody can be raised against La/SSB; that the protein moiety of bovine La/SSB differs from human, mouse, and rabbit at an epitope on the 41-kD La/SSB peptide; that the RNA bound to the La1-reactive particle was as heterogeneous as that binding the anti-La/SSB autoimmune serum; and that anti-Ro/SSA and anti-La/SSB are closely associated.

Authors

J B Harley, M O Rosario, H Yamagata, O F Fox, E Koren

Enhancement of the impaired autologous mixed leukocyte reaction in patients with systemic lupus erythematosus.

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Abstract

The cellular basis of the impaired autologous mixed leukocyte reaction (AMLR) in patients with systemic lupus erythematosus (SLE) was investigated. Non-T cells from normal subjects and from SLE patients were fractionated into low and high density subpopulations. SLE patients were found to have an increased proportion of low density to high density non-T cells when compared to normal subjects. Although normal low-density non-T cells were highly enriched in AMLR stimulatory capacity, SLE low-density non-T cells induced minimal proliferation by autologous T cells. Brief incubation of SLE non-T cells with phorbol myristate acetate or formalin-treated Staphylococcus aureus resulted in marked augmentation of the capacity of those non-T cells to stimulate an AMLR, although the magnitude of the activated non-T cell-induced AMLR did not achieve that observed in normal subjects. No significant alterations in the expression of Ia molecules on the surface of the non-T cells were detected after in vitro activation. These experiments support the hypothesis that the impaired capacity of SLE T lymphocytes to proliferate in response to autologous non-T cells may in part represent a failure of SLE non-T cells to present an appropriate stimulus for the generation of a T cell response.

Authors

M K Crow

Effect of Reye's syndrome serum on isolated chinchilla liver mitochondria.

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Abstract

A general impairment of liver mitochondrial enzymes is central to Reye's syndrome (RS). The respiration of isolated liver mitochondria was measured after the addition of concentrated normal serum or RS serum derived from 12 patients. RS serum stimulates oxygen consumption in isolated rat liver mitochondria. This effect is due to the oxidation of uric acid by peroxisomes contaminating the preparation and a stimulation of mitochondrial respiration (1.05 +/- 0.14 nmol of O2/min X mg of protein; control 0.30 +/- 0.08 nmol O2/min X mg). The stimulation of respiration occurs in the presence of all respiratory substrates, is dependent on the amount of serum added, and represents an uncoupling of oxidative phosphorylation. RS serum reduces ATP formation by 15-76%. The uncoupling effect correlates with the amount of free fatty acid in the serum sample and resembles the effect induced by the addition of a dicarboxylic fatty acid. Dicarboxylic fatty acids, especially long-chain dicarboxylic acids, impair ATP formation. Dicarboxylic acids were found in the serum of all RS patients and comprised as much as 54% of the total serum free fatty acids. 90% of the serum dicarboxylic acids were of 16-18 carbon lengths. The amount of dicarboxylic acids in the RS serum corresponded directly with the reduction in ATP formation by the RS serum. This demonstrates that dicarboxylic acids occur in RS and may be important in the general impairment of mitochondrial function in RS and other disorders where they are present.

Authors

J H Tonsgard, G S Getz

Elevated factor Xa activity in the blood of asymptomatic patients with congenital antithrombin deficiency.

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Abstract

The presence of congenital antithrombin deficiency has been consistently shown to predispose patients to venous thrombosis. We have utilized the prothrombin fragment F1+2 radioimmunoassay to quantitate factor Xa activity in the blood of 22 asymptomatic individuals with this clinical disorder not receiving antithrombotic therapy. The mean level of F1+2 was significantly elevated in these patients as compared to normal controls (3.91 vs. 1.97 nM, P less than 0.001). The metabolic behavior of 131 I-F1+2 was found to be similar in antithrombin-deficient subjects and normal individuals. The hemostatic system hyperactivity as measured by the F1+2 assay could be specifically corrected by raising the plasma antithrombin levels of the above asymptomatic individuals into the normal range. This study provides the first demonstration that the prethrombotic state can be biochemically defined as an imbalance between the production and inhibition of factor Xa enzymatic activity within the human circulation. It is known that antithrombin and alpha 1-proteinase inhibitor (PI) are the major inhibitors of factor Xa in human plasma in the absence of heparin. To further evaluate the mechanism by which antithrombin functions as an inhibitor of factor Xa in humans, we studied five patients who exhibited severe congenital deficiencies of alpha 1-PI. Our results indicated that the plasma of these subjects showed virtually identical decreases in plasma antifactor Xa activity in the absence of heparin when compared to antithrombin-deficient individuals, but the plasma F1+2 levels in the alpha 1-PI deficient population were not significantly different than normal. This data suggests that alpha 1-PI does not function as a major inhibitor of factor Xa in vivo, and that a tonically active heparin-dependent mechanism exists in humans for accelerating the neutralization of this enzyme by antithrombin.

Authors

K A Bauer, T L Goodman, B L Kass, R D Rosenberg

Influences of gamma interferon on synovial fibroblast-like cells. Ia induction and inhibition of collagen synthesis.

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Abstract

The shape and function of adherent cells cultured from rheumatoid synovial membranes are influenced by immune cells, and their products. The synovial cells produce collagenase and prostaglandin E2 (PGE2), the levels of which are increased when the cells are incubated with the monokine, mononuclear cell factor/interleukin 1. The majority of adherent synovial cells are fibroblastlike in appearance and synthesize collagens and fibronectin; the synthesis of collagens and fibronectins are also increased by a monocyte factor. In the present study we found that the fibroblastlike cells expressed major histocompatibility complex class II (Ia-like) antigens after initial dispersion from the synovial membrane. Monocyte lineage antigens were detected on some round cells in early passage, but no T lymphocytes were identified in established cultures. There was loss of Ia expression on the fibroblastlike cells with age and passage in culture. The addition of the lymphokine, gamma interferon (recombinant), induced class II antigen (DR and DS/DQ) expression in early or late passage cells in a time- and dose-dependent manner and required protein synthesis. Furthermore, the adherent synovial fibroblastlike cells continued to be Ia-positive when examined as long as 10 d after the removal of gamma interferon. Ia expression was also induced by gamma interferon in normal skin fibroblasts. Synovial cells that could be induced to express Ia also bound a monoclonal antibody to type III collagen (a fibroblast marker). Gamma interferon, while inducing Ia expression, decreased the binding of type III collagen antibody on unstimulated as well as monokine-stimulated cells. Analysis of [3H]proline-labeled medium by SDS polyacrylamide gel electrophoresis showed that gamma interferon decreased the synthesis of type I and III collagens and fibronectin by adherent synovial cells in a dose-dependent manner. These findings suggest that Ia expression by synovial tissue cells is not cell-specific, but reflects one or several related events, such as the degree of T lymphocyte infiltration, the presence of factors that stimulate gamma interferon release, or an increased sensitivity of the cells to gamma interferon. Whereas the synthesis of class II antigens is enhanced by the lymphokine gamma interferon, and a monocyte factor(s) stimulates collagen, collagenase and PGE2 synthesis by the same cells, gamma interferon inhibits basal and monokine-induced collagen synthesis. Thus, lymphokines and monokines may influence the extent of fibrosis as contrasted to matrix destruction at various stages of the rheumatoid lesion by affecting the function of fibroblastlike synovial cells.

Authors

E P Amento, A K Bhan, K G McCullagh, S M Krane

Serial studies of autologous antibody reactivity to melanoma. Relationship to clinical course and circulating immune complexes.

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Abstract

The low titer and incidence of autologous antibody to melanoma has hampered its evaluation. Through acid dissociation and ultrafiltration of serum, we have been able to augment the autologous immune response in 9 of 10 patients studied. This result suggests that autologous antibody is present in most patients with melanoma, but is obscured by circulating antigen and the formation of immune complexes. Because native antibody and antibody derived from circulating immune complexes are produced by the host against physiologically relevant antigens, correlations can be made to clinical course. Serological studies of three patients with melanoma were performed with serum samples obtained over many months; these studies demonstrated correlations with tumor progression and clinical course. Serial serologic studies may yet provide one of the better ways to evaluate these relationships. They have the advantage of detecting transient events that may occur with the inception of metastatic disease or autoimmune phenomena, and of avoiding the difficulties encountered in comparing antibody responses between different individuals.

Authors

D R Vlock, J M Kirkwood

Contribution of individual superficial nephron segments to ammonium handling in chronic metabolic acidosis in the rat. Evidence for ammonia disequilibrium in the renal cortex.

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Abstract

Ammonia entry along surface nephron segments of rats was studied with micropuncture techniques under control and chronic metabolic acidosis conditions. Tubule fluid was collected successively from sites at the end and beginning of the distal tubule and at the end of the proximal tubule of the same nephron. During chronic metabolic acidosis, ammonium excretion doubled. As anticipated, the ammonium concentration (TFNH+4) was significantly higher in proximal tubule fluid during acidosis, and ammonium delivery to end proximal sites increased from 19.4 +/- 2.3 to 34.0 +/- 3.2 pmol/min (P less than 0.001). Although chronic acidosis did not affect TFNH+4 at the beginning of the distal tubule, ammonium delivery to the end of the distal tubule increased from 5.72 +/- 0.97 to 9.88 +/- 0.97 pmol/min. In both control and acidotic groups ammonium delivery was lower (P less than 0.001) to end distal sites than to end proximal sites, indicating net loss in the intervening segment. This loss was greater during chronic metabolic acidosis (23.9 +/- 3.3 vs. 13.6 +/- 2.0 pmol/min in controls, P less than 0.025). In both groups net entry of ammonia, in similar amounts, occurred along the distal tubule (P less than 0.05). In situ pH averaged 6.80 +/- 0.05 at end proximal tubule sites and fell to 6.54 +/- 0.08 at the beginning of the distal tubule (P less than 0.005). Chronic metabolic acidosis did not affect these measurements. The calculated free ammonia at the end of the proximal tubule rose from 9.3 +/- 2.2 to 21 +/- 9 microM (P less than 0.005) during chronic metabolic acidosis, and was also higher at beginning distal sites during acidosis (8.8 +/- 2.4 vs. 2.7 +/- 0.7 microM in controls, P less than 0.05). In both groups ammonia values for the beginning distal tubule fluid were lower than for end proximal tubule fluid. Thus, loss of ammonium in the loop segment is enhanced by chronic metabolic acidosis. Distal entry of ammonia is markedly less than along the proximal tubule and does not change in chronic metabolic acidosis, and ammonia permeabilities for the proximal and distal segments of surface nephrons seem different.

Authors

E Simon, D Martin, J Buerkert

Acute intermittent porphyria: characterization of a novel mutation in the structural gene for porphobilinogen deaminase. Demonstration of noncatalytic enzyme intermediates stabilized by bound substrate.

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Abstract

To investigate the molecular pathology in acute intermittent porphyria (AIP), the nature of the defective porphobilinogen (PBG)-deaminase was determined in erythrocyte lysates from 165 AIP heterozygotes from 92 unrelated families representing 20 different ethnic or demographic groups. Immunologic and physicokinetic studies revealed the occurrence of four classes of PBG-deaminase mutations. In the majority of families studied, the amount of immunoreactive enzyme protein corresponded to the amount of enzymatic activity, indicating the absence of cross-reacting immunologic material (CRIM) produced by the mutant allele. In 78 of these CRIM-negative families (designated type 1), the affected heterozygotes had half-normal PBG-deaminase activity. In three families (designated CRIM-negative type 2), symptomatic patients had increased urinary excretion of delta-aminolevulinic acid and PBG, and normal levels of erythrocyte PBG-deaminase activity. In contrast, noncatalytic, immunoreactive protein was expressed in heterozygotes from 11 families, about one-eighth of those studied, consistent with mutations in the structural gene for PBG-deaminase. Two types of CRIM-positive mutations were identified: the type 1 mutation had a CRIM/activity ratio of approximately 1.7 and a crossed-immunoelectrophoretic profile in which all the enzyme intermediates were increased, with the B or monopyrrole-enzyme intermediate predominant (B greater than A much greater than C congruent to D greater than E). The mutation altered both the kinetic and stability properties of the noncatalytic immunoreactive enzyme protein. The second CRIM-positive mutation, type 2, had markedly increased levels of noncatalytic immunoreactive protein (CRIM/activity ratio approximately 5.7). Crossed-immunoelectrophoresis revealed markedly increased amounts of the substrate-bound intermediates, B, C, D, and E (B greater than C greater than D greater than E much greater than A). The accumulation of these noncatalytic enzyme intermediates presumably resulted from the enhanced binding and/or defective release of substrate molecules. The conformation of these enzyme-substrate intermediates apparently rendered the complexes more resistant to intraerythrocyte proteolysis. These findings provide evidence for the presence of different allelic mutations in the structural gene for PBG-deaminase and document molecular genetic heterogeneity in AIP.

Authors

R J Desnick, L T Ostasiewicz, P A Tishler, P Mustajoki

Thermal inactivation of the acquired immunodeficiency syndrome virus, human T lymphotropic virus-III/lymphadenopathy-associated virus, with special reference to antihemophilic factor.

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Abstract

The virus that causes the acquired immunodeficiency syndrome (AIDS), human T lymphotropic virus/lymphadenopathy-associated virus (HTLV-III/LAV), was incubated at temperatures from 37 degrees to 60 degrees C and virus titer (ID-50) was determined over time by a microculture infectivity assay. The rate of thermal decay was consistent with first-order kinetics, and these data were used to construct a linear Arrhenius plot (r = 0.99), which was used to determine inactivation time as a function of temperature. In the liquid state, thermal decay was little affected by matrix (culture media, serum, or liquid Factor VIII). In the lyophilized state, the time required to reduce virus titer 10-fold (1 log) at 60 degrees C was 32 min compared with 24 s in the liquid state. HTLV-III/LAV in liquid antihemophilic Factor VIII or IX was lyophilized and heated according to commercial manufacturers' specifications. Infectious virus was undetectable with these regimens. Heat treatment should reduce or stop transmission of HTLV-III/LAV by commercial antihemophilic Factor VIII or IX.

Authors

J S McDougal, L S Martin, S P Cort, M Mozen, C M Heldebrant, B L Evatt

L6 cells as a tissue culture model for thyroid hormone effects on skeletal muscle metabolism.

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Abstract

L6 cells have been investigated as a potential tissue culture model for the study of thyroid hormone effects on skeletal muscle metabolism. Differentiated L6 myotubes contained high-affinity triiodothyronine (T3) receptors with a Kd of 3 X 10(-10) M and a maximal binding capacity of 24 fmol T3/100 micrograms DNA. Undifferentiated cells contained receptors with the same Kd, but the binding capacity was reduced by at least a factor of three. Sarcoplasmic reticulum vesicle calcium pumping was demonstrated in L6 cell homogenates. The Vmax for calcium pumping was increased 2.5-fold when T3 was present in the culture medium, but the Kd was unchanged. L6 cells contained high affinity thyroid hormone receptors and were thyroid hormone responsive. These cells may be useful as a tissue culture model for studying the effects of thyroid hormones on skeletal muscle metabolism. In addition, the increase in T3 receptor number with the differentiated state suggests this as a model system for studying regulation of T3 receptor number and the role of T3 in the induction or maintenance of the differentiated state.

Authors

R J Koenig, R J Smith

Muscarinic receptors on intact human fibroblasts. Absence of receptor activity in adult skin cells.

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Abstract

The intact human fibroblast has been used in clinical and basic research studies of receptor-mediated control of cell function, however there is little information about the relationship between muscarinic receptor density and the regulation of cyclic AMP (cAMP) accumulation. We have compared the muscarinic receptor characteristics of both lung and skin intact fibroblasts at fetal and adult stages of development using carbachol-mediated inhibition of cAMP accumulation and the binding of [3H]quinuclidinyl benzilate (QNB). Prostaglandin E1 (PGE1) stimulated cAMP accumulation in all four cell lines, while carbachol inhibited cAMP accumulation only in the fetal lung, adult lung, and to a lesser extent, the fetal skin. Adult skin fibroblasts did not display significant evidence of inhibitory muscarinic receptor activity. [3H]QNB binding was saturable for the fetal and adult lung, and the fetal skin, yielding Kd values of approximately 0.5 nM for these cell lines. Bmax values were 360 fmol/mg for fetal skin, 600 fmol/mg for adult lung, and 876 fmol/mg for the fetal lung. Specific binding of [3H]QNB to adult skin fibroblasts was found to be low and variable. Comparisons of the Bmax values and maximal inhibitory capacities showed that the receptor density paralleled receptor activity in all cell lines. The lack of muscarinic receptor activity in the adult skin fibroblast was confirmed in several different adult skin cell lines, indicating that the adult skin fibroblast may not be an appropriate model for muscarinic receptor activity in clinical investigations.

Authors

D A Van Riper, M P Absher, R H Lenox

Treatment with aldose reductase inhibitor or with myo-inositol arrests deterioration of the electroretinogram of diabetic rats.

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Abstract

Biochemical abnormalities in the retinal pigment epithelium of experimentally diabetic animals include increased sorbitol and decreased myo-inositol. Diabetes also causes a progressive reduction in the amplitude of the c-wave of the electroretinogram of the pigmented rat. The c-wave is generated by the retinal pigmented epithelium. Myo-inositol administration or treatment with sorbinil, an inhibitor of aldose reductase, arrested the decline in the c-wave. Therefore, hyperglycemia-associated defects in myo-inositol or sorbitol metabolism may be involved in the pathogenesis of the electrophysiological deficit of the diabetic retina. The homogeneous cell layer of the pigment epithelium may be a useful tissue model for studying the pathogenesis of the complications of diabetes.

Authors

L C MacGregor, F M Matschinsky

Metabolic effect of 3,3',5'-triiodothyronine in cultured growth hormone-producing rat pituitary tumor cells. Evidence for a unique mechanism of thyroid hormone action.

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Abstract

Physiologic levels of 3,3',5'-triiodothyronine (rT3) are generally believed to have minimal metabolic effects in the pituitary gland and other tissues. In the present studies, the regulatory role of rT3 and other thyroid hormones on iodothyronine 5'-deiodinase (I5'D) activity was studied in a growth hormone-producing rat pituitary tumor cell line (GH3 cells). I5'D activity was thiol-dependent and displayed nonlinear reaction kinetics suggesting the presence of two enzymatic processes, one having a low Michaelis constant (Km for thyroxine [T4] of 2 nM) and a second with a high Km value (0.9 microM). Growth of cells in hormone-depleted medium resulted in a two- to 3.5-fold increase in low Km I5'D activity (P less than 0.001). The addition of thyroid hormones to the culture medium resulted in a rapid, dose-dependent inhibition of low Km I5'D activity with the following order of analogue potency: rT3 greater than or equal to T4 greater than 3,5,3'-triiodothyronine (T3). Using serum-free culture conditions, rT3 was approximately 50 times more active than T3. These inhibitory effects were noted within 15 min of hormone addition and could not be attributed to substrate competition with T4. These findings suggest that the control of T4 to T3 conversion by thyroid hormones in the anterior pituitary gland is mediated by a unique cellular mechanism that is independent of the nuclear T3 receptor; and under some circumstances, rT3 may play a regulatory role in controlling this enzymatic process.

Authors

D L St Germain

Identification of a point mutation in the adenosine deaminase gene responsible for immunodeficiency.

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Abstract

Deficiency of adenosine deaminase (ADA) is the cause of an autosomal recessive form of immunodeficiency. We sought to define, at a molecular level, the mutations responsible for ADA deficiency in the cell line GM-1715, derived from an immunodeficient patient. Full-length complementary DNA (cDNA) for ADA was synthesized and cloned from the cell line. Sequence analysis of the clones revealed a point mutation in codon 101 (CGG to CAG) that predicts an amino acid change from arginine to glutamine. Southern blot analysis, based on silent polymorphisms in the cDNA sequence, indicated that only one of the defective alleles of the GM-1715 line had been sequenced. The mutation that was identified appears to be responsible for the loss of function in this allele, since the predicted primary structure of the enzyme is otherwise entirely normal.

Authors

D T Bonthron, A F Markham, D Ginsburg, S H Orkin

Thromboxane synthase is preferentially conserved in activated mouse peritoneal macrophages.

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Abstract

Resident macrophages isolated from uninfected animals produce large quantities of arachidonic acid (AA) metabolites. Immunizing animals with protein antigens or bacteria activates macrophages and causes an 80% reduction in the cyclooxygenase and lipoxygenase metabolites relative to resident cells. Since some products have been shown to modulate immune functions, we examined how the AA metabolic enzyme activities regulate the products that are synthesized. We demonstrate that the cyclooxygenase, 5-lipoxygenase, prostacyclin synthase, and probably prostaglandin (PG) endoperoxide E-isomerase activities were decreased in activated peritoneal macrophages. In sharp contrast, thromboxane synthase activity was selectively unchanged or enhanced in the activated macrophages. Thus the immune response appears to modulate the activity of the AA and PG endoperoxide-dependent enzymes, thus dictating a major shift in the profile of metabolites synthesized by macrophages.

Authors

C S Tripp, K M Leahy, P Needleman