Oxygen sensing, potassium channels, and the ductus arteriosus.

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Authors

S H Abman

Life and death at labor.

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C H Streuli, J D Aplin

Endothelial adherens junctions: implications in the control of vascular permeability and angiogenesis.

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E Dejana

Hyaluronic acid capsule and the role of streptococcal entry into keratinocytes in invasive skin infection.

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It has been suggested that entry of pathogenic bacteria, including streptococci, into epithelial cells may represent an early stage of invasive infections. We found that poorly encapsulated wild-type strains and unencapsulated mutants of group A Streptococcus entered cultured human keratinocytes with high efficiency, while strains that produced large amounts of hyaluronic acid capsule did not, regardless of M-protein type or clinical source of the isolate. However, encapsulated streptococci produced extensive local necrosis and systemic infection in a mouse model of skin infection, while an isogenic acapsular strain did not. The results implicate the hyaluronic acid capsule as a virulence factor in soft tissue infection. Entry of poorly encapsulated group A Streptococcus into human epithelial cells does not appear to represent an initial step in invasive disease; rather, the capacity of encapsulated strains to avoid uptake by epithelial cells is associated with enhanced virulence in skin and soft tissue infection.

Authors

H M Schrager, J G Rheinwald, M R Wessels

Oxygen-induced constriction of rabbit ductus arteriosus occurs via inhibition of a 4-aminopyridine-, voltage-sensitive potassium channel.

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The ductus arteriosus is a vital fetal structure allowing blood ejected from the right ventricle to bypass the pulmonary circulation in utero. Closure of the ductus arteriosus at birth, essential for postnatal adaptation, is initiated by an increase in oxygen (O2) tension. We recently demonstrated the presence of O2-sensitive potassium channels in the fetal and adult pulmonary circulation which regulate vascular tone in response to changes in O2 tension. In this study, we assessed the cellular mechanisms underlying O2-induced constriction of the ductus arteriosus in late-gestation fetal rabbits. We report that O2 reversibly inhibits a 58-pS voltage- and 4-aminopyridine-sensitive potassium channel, causing membrane depolarization, an increase in intracellular calcium through L-type voltage-gated calcium channels, and constriction of the ductus arteriosus. We conclude that the effector mechanism for O2 sensing in the ductus arteriosus involves the coordinated action of delayed rectifier potassium channels and voltage-gated calcium channels.

Authors

M Tristani-Firouzi, H L Reeve, S Tolarova, E K Weir, S L Archer

Vascular damage without hypertension in transgenic rats expressing prorenin exclusively in the liver.

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We have developed a transgenic animal model to investigate the effects of overexpression of rat prorenin on the cardiovascular system. Two transgenic rat lines were generated in which rat prorenin expression was directed to the liver by a human alpha1-antitrypsin promoter. Liver-specific expression was confirmed by RNase protection assay. Plasma prorenin concentrations in transgenic rats were increased 400-fold in the males of both lines but were increased only two- to threefold in the females. Thus, transgene expression exhibited sexual dimorphism. Blood pressures were not significantly higher in transgenic rats than in nontransgenic controls. The ratio of heart weight to body weight was greater in male transgenic rats than in the nontransgenic controls. Histological analysis revealed severe renal lesions and hypertrophic cardiomyocytes in transgenic males only. This transgenic model demonstrates a likely role of prorenin in the development of cardiac and renal pathology independent of hypertension. These animals will facilitate studies of the effects of blockade of the renin-angiotensin system and other pharmacological interventions on the development and treatment of cardiac, vascular, and renal lesions induced by changes in this system in the absence of chronic hypertension.

Authors

M Véniant, J Ménard, P Bruneval, S Morley, M F Gonzales, J Mullins

A program of cell death and extracellular matrix degradation is activated in the amnion before the onset of labor.

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Fetal membranes usually rupture during the process of labor. Premature fetal membrane rupture occurs not infrequently and is associated with significant fetal and maternal morbidity. The mechanisms of normal and pathologic fetal membrane rupture are not well understood. We have examined structural and biochemical changes in the rat amnion as labor approaches in order to characterize this process in normal pregnancy. Here we report that before the onset of active labor the amnion epithelial cells undergo apoptotic cell death which encompasses degradation of 28S ribosomal subunit RNA and associated P proteins and fragmentation of nuclear DNA. Concurrent with these cellular changes, the amnion type I collagen matrix is degraded with the accumulation of three-quarter length type I collagen fragments in extraembryonic fluid, characteristic of the cleavage of fibrillar collagen by interstitial collagenase. Western blot and immunohistochemical analyses confirmed that interstitial collagenase protein appears in association with the loss of amnion type I collagen. We conclude that amnion epithelial cells undergo a process of programmed cell death associated with orchestrated extracellular matrix degradation which begins before the onset of active labor. Thus, fetal membrane rupture is likely to be the result of biochemical changes as well as physical forces.

Authors

H Lei, E E Furth, R Kalluri, T Chiou, K I Tilly, J L Tilly, K B Elkon, J J Jeffrey, J F Strauss 3rd

Apoptosis induced by HIV-1 infection of the central nervous system.

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Apoptosis plays a role in AIDS pathogenesis in the immune system, but its role in HIV-1-induced neurological disease is unknown. In this study, we examine apoptosis induced by HIV-1 infection of the central nervous system (CNS) in an in vitro model and in brain tissue from AIDS patients. HIV-1 infection of primary brain cultures induced apoptosis in neurons and astrocytes in vitro as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and propidium iodide staining and by electron microscopy. Apoptosis was not significantly induced until 1-2 wk after the time of peak virus production, suggesting induction by soluble factors rather than by direct viral infection. Apoptosis of neurons and astrocytes was also detected in brain tissue from 10/11 AIDS patients, including 5/5 patients with HIV-1 dementia and 4/5 nondemented patients. In addition, endothelial cell apoptosis was frequently detected in the brain of AIDS patients and was confirmed by electron microscopy. Most of the apoptotic cells were not localized adjacent to HIV-1-infected cells, providing further evidence for induction by soluble factors. In six non-AIDS control patients with normal brain, apoptotic cells were absent or limited to rare astrocytes. However, TUNEL-positive neurons and astrocytes were frequently detected in seven patients with Alzheimer's disease or abundant senile plaques. These studies suggest that apoptosis is a mechanism of CNS injury in AIDS which is likely to be induced by soluble factors. The apoptosis of endothelial cells in the CNS raises the possibility that some of these factors may be blood-derived.

Authors

B Shi, U De Girolami, J He, S Wang, A Lorenzo, J Busciglio, D Gabuzda

Regulation of extracellular matrix by mechanical stress in rat glomerular mesangial cells.

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Increases in intraglomerular pressure are known to predispose to the development of glomerular sclerosis, which is characterized by accumulation of extracellular matrix within the glomerulus. Glomerular mesangial cells are exposed to pulsatile capillary pressures and are a potential target for mechanical stress. In the present studies, we subjected cultured rat mesangial cells to continuous cycles of stretching and relaxation (stretch/relaxation) and examined alterations in extracellular matrix gene expression. After 48 h of stretch/relaxation, immunofluorescent localization of matrix accumulation indicated increases in types I, III, and IV collagens, fibronectin, and laminin, with the greatest increases seen at the periphery of the culture dish, at the point of the greatest deformation. Northern blot analysis of total RNA revealed time-dependent induction of alpha1(I) collagen, alpha1(III) collagen, alpha1(IV) collagen, fibronectin, and laminin by stretch/relaxation, with maximal increases occurring between 12 and 24 h. Transient transfection of reporter gene constructs of the 5' flanking region of alpha1(I) collagen gene indicated that stimulation of gene transcription was involved in the increased expression of matrix mRNA. Gelatinolytic activity in conditioned media was decreased at 24 and 48 h of stretch/relaxation, in association with a significant decrease in levels of mRNA for matrix metalloproteinase-2 (68-72 kD type IV collagenase) occurring within 6 h of stretch/relaxation. In contrast, expression of tissue inhibitor of metalloproteinase-2 was increased within 12 h of stretch/relaxation. Stretch/relaxation increased immunoreactive TGF-beta at 48 but not 12 h. TGF-beta1 mRNA levels remained unchanged during the initial 12 h of stretch/relaxation, but were significantly elevated at 48 h, and no differences in TGF-beta bioactivity could be detected in conditioned media for up to 12 h of stretch/relaxation. These findings demonstrate that in glomerular mesangial cells, repeated cycles of stretching and relaxation lead to matrix accumulation by stimulating production of extracellular matrix and decreasing activity of degradative enzymes. The observed induction of TGF-beta1 suggests a role in matrix accumulation occurring in response to continued mechanical deformation.

Authors

T Yasuda, S Kondo, T Homma, R C Harris

F(c)gammaRI-targeted fusion proteins result in efficient presentation by human monocytes of antigenic and antagonist T cell epitopes.

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A major challenge for using native or modified T cell epitopes to induce or suppress immunity relates to poor localization of peptides to antigen presenting cells (APCs) in vivo. In this study, we demonstrate enhanced presentation of antigenic and antagonistic peptides by targeting them to the type I Fc receptor for IgG (F(c)gammaRI, CD64) on human monocytes. A Th epitope of tetanus toxoid, TT830, and the antagonistic peptide for TT830, TT833S, were genetically grafted into the constant region of the heavy chain of the humanized anti-CD64 mAb 22 and expressed as monovalent fusion proteins, Fab22-TT830 and Fab22-TT833S. These CD64-targeted peptides were up to 1,000- and 100-fold more efficient than the parent peptides for T cell stimulation and antagonism, respectively, suggesting that such fusion proteins could effectively increase the delivery of peptides to APCs in vivo. Moreover, the F(c)gammaRI-targeted antagonistic peptide inhibited proliferation of TT830-specific T cells even when APCs were first pulsed with native peptide, a situation comparable with that which would be encountered in vivo when attempting to ameliorate an autoimmune response. These data suggest that targeted presentation of antagonistic peptides could lead to promising Ag-specific therapies for T cell-mediated autoimmune diseases.

Authors

C Liu, J Goldstein, R F Graziano, J He, J K O'Shea, Y Deo, P M Guyre

Contributions of de novo synthesis of fatty acids to total VLDL-triglyceride secretion during prolonged hyperglycemia/hyperinsulinemia in normal man.

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Triglycerides (TG) are synthesized in the liver principally from two sources of fatty acids (FA): FA synthesized de novo in the liver and preformed FA. We have measured the rate of secretion of de novo synthesized FA and total secretion of FA bound to VLDL-TG in healthy men (n = 5) in the basal state, and after 1 (day 1) and 4 d (day 4) of a hypercaloric carbohydrate diet (approximately 2.5 times energy expenditure) that generated a moderate endogenous hyperinsulinemia (plasma insulin approximately 60 microU/ml). Prolonged carbohydrate hyperalimentation/hyperinsulinemia increased plasma VLDL-TG approximately 10-fold in part due to a 3.4-fold increase in total VLDL-TG secretion rate (basal state = 72+/-23, day 4 = 242+/-78 micromol TG/kg/d). Although the secretion of de novo synthesized FA increased throughout the study (basal state = 1.1+/-0.4, day 1 = 15.9+/-7.9, day 4 = 50.0+/-18.8 micromol TG/ kg/d), the 2.7-fold increase in secretion rate of preformed FA (basal state = 70+/-23, day 4 = 191+/-57 micromol TG/kg/d) quantitatively contributed the most to total VLDL-TG secretion rate. Decreased catabolism of VLDL-TG also contributed to the hypertriglyceridemia as reflected by an approximately fourfold decrease in both fractional turnover rate (basal state = 9.2+/-3.8, day 1 = 2.1+/-0.2, day 4 = 2.1+/-0.3 pools/d) and rate of clearance (basal state = 0.35+/-0.08, day 1 = 0.11+/-0.01, day 4 = 0.09+/-0.01 liter/kg/d) of VLDL-TG. Thus, the primary difference between 1 and 4 d of hyperinsulinemia in conjunction with carbohydrate hyperalimentation is the increase in hepatic secretion of preformed FA into VLDL-TG.

Authors

A Aarsland, D Chinkes, R R Wolfe

Characterization of vascular endothelial growth factor's effect on the activation of protein kinase C, its isoforms, and endothelial cell growth.

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Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen which mediates its effects by binding to tyrosine kinase receptors. We have characterized the VEGF-activated intracellular signal transduction pathway in bovine aortic endothelial cells and correlated this to its mitogenic effects. VEGF induced concentration- and time-dependent increases in protein kinase C (PKC) activation with a maximum of 2.2-fold above the basal level at 5 x 10(-10) M within 10 min as measured both by in situ and translocation assays. Immunoblotting analysis of PKC isoforms in cytosolic and membrane fractions indicated that after VEGF stimulation the content of Ca(2+)-sensitive PKC isoforms (alpha and betaII) was increased in the membrane fractions, whereas no changes were observed for PKC isoforms delta and epsilon. The stimulation of PKC activity by VEGF was preceded by the activation of phospholipase Cgamma (PLCgamma). This was demonstrated by parallel increases in PLCgamma tyrosine phosphorylation, [3H]inositol phosphate production, and [3H]arachidonic acid-labeled diacylglycerol formation in bovine aortic endothelial cells. In addition, VEGF increased phosphatidylinositol 3-kinase activity 2.1-fold which was inhibited by wortmannin, a phosphatidylinositol 3-kinase inhibitor, without decreasing the VEGF-induced increase in PKC activity or endothelial cell growth. Interestingly, genistein, a tyrosine kinase inhibitor, and GFX or H-7, PKC inhibitors, abolished both VEGF-induced PKC activation and endothelial cell proliferation. VEGF's mitogenic effect was inhibited by a PKC isoform beta-selective inhibitor, LY333531, in a concentration-dependent manner. In contrast, antisense PKC-alpha oligonucleotides enhanced VEGF-stimulated cell growth with a simultaneous decrease of 70% in PKC-alpha protein content. Thus, VEGF appears to mediate its mitogenic effects partly through the activation of the PLCgamma and PKC pathway, involving predominately PKC-beta isoform activation in endothelial cells.

Authors

P Xia, L P Aiello, H Ishii, Z Y Jiang, D J Park, G S Robinson, H Takagi, W P Newsome, M R Jirousek, G L King

The mutation in the mitochondrial aldehyde dehydrogenase (ALDH2) gene responsible for alcohol-induced flushing increases turnover of the enzyme tetramers in a dominant fashion.

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Deficiency in mitochondrial aldehyde dehydrogenase (ALDH2), a tetrameric enzyme, results from inheriting one or two ALDH2*2 alleles. This allele encodes a protein subunit with a lysine for glutamate substitution at position 487 and is dominant over the wild-type allele, ALDH2*1. The ALDH2*2-encoded subunit (ALDH2K) reduces the activity of ALDH2 enzyme in cell lines expressing the wild-type subunit (ALDH2E). In addition to this effect on the enzyme activity, we now report that ALDH2*2 heterozygotes had lower levels of ALDH2 immunoreactive protein in autopsy liver samples. The half-lives of ALDH2 protein in HeLa cell lines expressing ALDH2*1, ALDH2*2, or both were determined by the rate of loss of immunoreactive protein after inhibition of protein synthesis with puromycin and by pulse-chase experiments. By either measure, ALDH2E enzyme was very stable, with a half-life of at least 22 h. ALDH2K enzyme had an enzyme half-life of only 14 h. In cells expressing both subunits, most of the subunits assemble as heterotetramers, and these enzymes had a half-life of 13 h. Thus, the effect of ALDH2K on enzyme turnover is dominant. These studies indicate that the ALDH2*2 allele exerts its dominant effect both by interfering with the catalytic activity of the enzyme and by increasing its turnover. This represents the first example of a dominantly acting allele with this effect on a mitochondrial enzyme's turnover.

Authors

Q Xiao, H Weiner, D W Crabb

Corticotropin-releasing hormone excites adrenocorticotropin-secreting human pituitary adenoma cells by activating a nonselective cation current.

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The mechanisms of corticotropin-releasing hormone (CRH) induced excitation of ACTH-secreting adenoma cells were investigated using the perforated whole-cell clamp technique and intracellular Ca2+ concentration ([Ca2+]i) measurement. CRH depolarized ACTH-secreting adenoma cells by activating a nonselective cation current that showed slight inward rectification. This channel did not seem to be a member of the Ca(2+)-activated cation currents because it was activated even when the [Ca2+]i was chelated below 50 nM. The activation of the current was induced by protein kinase A-mediated pathways. By [Ca2+]i measurement, CRH increased [Ca2+]i of these cells dependently on voltage-gated Ca2+ current. This CRH-induced [Ca2+]i increase was abolished in Na(+)-free extracellular solution, but was not abolished by the addition of 5 microM tetrodotoxin to the extracellular solution. CRH-induced ACTH secretion from the cultured adenoma cells was also abolished in Na(+)-free extracellular solution, but not in tetrodotoxin-containing extracellular solution. These data indicate that a Na+ current (maybe the nonselective cation current) other than voltage-gated Na+ current plays an important role in CRH-induced [Ca2+]i increase and ACTH secretion. CRH also activated a nonselective cation current in nonadenoma human corticotrophs, suggesting that the activation of a nonselective cation current is a physiological mechanism of CRH-induced excitation in human corticotrophs.

Authors

K Takano, J Yasufuku-Takano, A Teramoto, T Fujita

Bradykinin stimulates NF-kappaB activation and interleukin 1beta gene expression in cultured human fibroblasts.

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Bradykinin (BK), a pluripotent nonameric peptide, is known for its proinflammatory functions in both tissue injury and allergic inflammation of the airway mucosa and submucosa. To understand the mechanisms by which BK serves as an inflammatory mediator, the human lung fibroblast cell line WI-38 was stimulated with BK and the expression of IL-1beta gene was examined. BK at nanomolar concentrations induced a marked increase in immunoreactive IL-1beta, detectable within 2 h in both secreted and cell-associated forms. BK-induced IL-1beta synthesis was inhibited by a B2-type BK receptor antagonist and by treatment of the cells with pertussis toxin, indicating the involvement of a BK receptor that couples to the G(i)/G(o) class of heterotrimeric G proteins. Whereas cycloheximide and actinomycin D both inhibited BK-induced IL-1beta synthesis, results from Northern blot and nuclear run-on assays suggested that BK acted primarily at the transcription level which led to the accumulation of IL-1beta message in stimulated cells. Gel mobility shift assays were used with nuclear extracts from stimulated WI-38 cells to examine the transcription mechanism for BK-induced IL-1beta expression. A DNA binding activity specific for the decameric kappaB enhancer was detected and was found to contain the p50 and p65 subunits of the NF-kappaB/rel protein family. BK-induced NF-kappaB activation correlated with IL-1beta message upregulation with respect to agonist concentration, time course, sensitivity to bacterial toxins, and blockade by the B2 receptor antagonist. After BK stimulation, a significant increase in the activity of chloramphenicol acetyltransferase was observed in WI-38 cells transfected with a reporter plasmid bearing the kappaB enhancers from the IL-1beta gene. Deletion of the kappaB enhancer sequence significantly reduced BK-induced chloramphenicol acetyltransferase activity. These findings suggests a novel function of BK in the activation of NF-kappaB and the induction of cytokine gene expression.

Authors

Z K Pan, B L Zuraw, C C Lung, E R Prossnitz, D D Browning, R D Ye

Asbestos induces apoptosis of human and rabbit pleural mesothelial cells via reactive oxygen species.

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Mesothelial cells, the progenitor cell of the asbestos-induced tumor mesothelioma, are particularly sensitive to the toxic effects of asbestos, although the molecular mechanisms by which asbestos induces injury in mesothelial cells are not known. We asked whether asbestos induced apoptosis in mesothelial cells and whether reactive oxygen species were important. Pleural mesothelial cells (rabbit or human) were exposed to asbestos (crocidolite, amosite, or chrysotile) or control particles at moderate doses (1-10 microg/cm2) over 24 h and evaluated for oligonucleosomal DNA fragmentation, loss of membrane phospholipid asymmetry, and nuclear condensation. Asbestos fibers, not control particles, induced apoptosis in mesothelial cells by all assays and induction of apoptosis was dose dependent for all types of asbestos, with crocidolite (5 microg/cm2) inducing 15.0+/-1.1% (mean+/-SE; n = 12) apoptosis versus control particles < 4%. Apoptosis induced by asbestos, but not by actinomycin D, was inhibited by extracellular catalase, superoxide dismutase in the presence of catalase, hypoxia (8% oxygen), deferoxamine, 3-aminobenzamide [an inhibitor of poly(ADP-ribosyl) polymerase], and cytochalasin B. Only catalase and cytochalasin B decreased fiber uptake. We conclude that asbestos induces apoptosis in mesothelial cells via reactive oxygen species. Escape from this pathway could allow the abnormal survival of mesothelial cells with asbestos-induced mutations.

Authors

V C Broaddus, L Yang, L M Scavo, J D Ernst, A M Boylan

Atrial natriuretic peptide regulation of noradrenaline release in the anterior hypothalamic area of spontaneously hypertensive rats.

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In spontaneously hypertensive rats (SHR), high NaCl diets increase arterial pressure and sympathetic nervous system activity by decreasing noradrenaline release in the anterior hypothalamic area (AHA), thereby reducing the activation of sympathoinhibitory neurons in AHA. Atrial natriuretic peptide (ANP) can inhibit the release of noradrenaline, and ANP concentration is elevated in the AHA of SHR. The present study tests the hypothesis that in SHR, local ANP inhibits noradrenaline release from nerve terminals in AHA. Male SHR fed a basal or high NaCl diet for 2 wk and normotensive Wistar Kyoto rats (WKY) fed a basal NaCl diet were studied. In SHR on the basal diet, microperfusion of exogenous ANP into the AHA elicited a dose-related decrease in the concentration of the major noradrenaline metabolite 3-methoxy-4-hydroxy-phenylglycol (MOPEG) in the AHA; this effect was attenuated in the other two groups. In a subsequent study, the ANP-C (clearance) receptor agonist c-ANP was microperfused into the AHA to increase extracellular concentration of endogenous ANP in AHA. c-ANP reduced AHA MOPEG concentration in SHR on the basal NaCl diet but not in the other two groups. These data support the hypothesis that local ANP inhibits noradrenaline release in the AHA and thereby contributes to NaCl-sensitive hypertension in SHR.

Authors

N Peng, S Oparil, Q C Meng, J M Wyss

The antifungal antibiotic, clotrimazole, inhibits Cl- secretion by polarized monolayers of human colonic epithelial cells.

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Clotrimazole (CLT) prevents dehydration of the human HbSS red cell through inhibition of Ca++-dependent (Gardos) K+ channels in vitro (1993. J. Clin Invest. 92:520-526.) and in patients (1996. J. Clin Invest. 97:1227-1234.). Basolateral membrane K+ channels of intestinal crypt epithelial cells also participate in secretagogue-stimulated Cl- secretion. We examined the ability of CLT to block intestinal Cl- secretion by inhibition of K+ transport. Cl- secretion was measured as short-circuit current (Isc) across monolayers of T84 cells. CLT reversibly inhibited Cl- secretory responses to both cAMP- and Ca2+-dependent agonists with IC50 values of approximately 5 microM. Onset of inhibition was more rapid when CLT was applied to the basolateral cell surface. Apical Cl- channel and basolateral NaK2Cl cotransporter activities were unaffected by CLT treatment as assessed by isotopic flux measurement. In contrast, CLT strongly inhibited basolateral 86Rb efflux. These data provide evidence that CLT reversibly inhibits Cl- secretion elicited by cAMP-, cGMP-, or Ca2+-dependent agonists in T84 cells. CLT acts distal to the generation of cAMP and Ca2+ signals, and appears to inhibit basolateral K+ channels directly. CLT and related drugs may serve as novel antidiarrheal agents in humans and animals.

Authors

P A Rufo, L Jiang, S J Moe, C Brugnara, S L Alper, W I Lencer

Exacerbation of inflammation-associated colonic injury in rat through inhibition of cyclooxygenase-2.

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Cyclooxygenase type 1 is constitutively expressed and accounts for synthesis of prostaglandins in the normal gastrointestinal tract. Cyclooxygenase-2 is expressed at sites of inflammation. Selective inhibitors of cyclooxygenase-2 have been suggested to spare gastrointestinal prostaglandin synthesis, and therefore lack the ulcerogenic effects associated with standard nonsteroidal antiinflammatory drugs. However, the effects of cyclooxygenase-2 inhibitors on inflamed gastrointestinal mucosa have not been examined. We examined cyclooxygenase-2 mRNA and protein expression before and after induction of colitis in the rat, the contribution of cyclooxygenase-2 to colonic prostaglandin synthesis during colitis and the effects of selective inhibitors of cyclooxygenase-2 on colonic injury in this model. Cyclooxygenase-2 mRNA expression increased three to sixfold during the period 24 h to 1 wk after induction of colitis, with marked increases in cyclooxygenase-2 protein expression in the lamina propria and muscularis of the colon during colitis. Cyclooxygenase-1 expression (mRNA and protein) was not affected by the induction of colitis. The prostaglandins produced during colitis were largely derived from cyclooxygenase-2. Treatment with selective cyclooxygenase-2 inhibitors resulted in exacerbation of colitis, with perforation occurring when the compounds were administered for a week. These studies demonstrate that suppression of cyclooxygenase-2 can result in exacerbation of inflammation-associated colonic injury.

Authors

B K Reuter, S Asfaha, A Buret, K A Sharkey, J L Wallace

The Trp64Arg mutation of the beta3 adrenergic receptor gene has no effect on obesity phenotypes in the Québec Family Study and Swedish Obese Subjects cohorts.

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The beta adrenergic system plays a key role in regulating energy balance through the stimulation of both thermogenesis and lipid mobilization in brown and white adipose tissues in human and various animal models. Recent studies have suggested that a missense Trp64Arg mutation in the beta3 adrenergic receptor (ADRB3) gene was involved in obesity and insulin resistance. We have investigated the effect of this mutation on obesity-related phenotypes in two cohorts: the Québec Family Study (QFS) and the Swedish Obese Subjects (SOS). In QFS, no association was found between this mutation and body mass index (BMI), body fat including abdominal visceral fat, resting metabolic rate, various diabetes and cardiovascular risk factors, and changes in body weight and body fat over a 12-yr period. With the exception of RMR (P = 0.04), no evidence of linkage was detected between the mutation and phenotypes of QFS based on sib-pair data. In SOS, the frequency of the Trp64Arg allele was not significantly different between nonobese and obese female subjects and no association was found between the mutation and body weight gain over time. These findings do not support the view that there is an association between the Trp64Arg mutation in the ADRB3 gene and obesity.

Authors

J Gagnon, P Mauriège, S Roy, D Sjöström, Y C Chagnon, F T Dionne, J M Oppert, L Pérusse, L Sjöström, C Bouchard

Cardiac and skeletal muscle insulin resistance in patients with coronary heart disease. A study with positron emission tomography.

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Patients with coronary artery disease or heart failure have been shown to be insulin resistant. Whether in these patients heart muscle participates in the insulin resistance, and whether reduced blood flow is a mechanism for such resistance is not known. We measured heart and skeletal muscle blood flow and glucose uptake during euglycemic hyperinsulinemia (insulin clamp) in 15 male patients with angiographically proven coronary artery disease and chronic regional wall motion abnormalities. Six age- and weight-matched healthy subjects served as controls. Regional glucose uptake was measured by positron emission tomography using [18F]2-fluoro-2-deoxy-D-glucose (FDG), blood flow was measured by the H2(15)O method. Myocardial glucose utilization was measured in regions with normal perfusion and wall motion as assessed by radionuclide ventriculography. Whole-body glucose uptake was 37+/-4 micromol x min(-1) x kg(-1) in controls and 14+/-2 mciromol x min(-1) x kg(-1) in patients (P = 0.001). Myocardial blood flow (1.09+/-0.06 vs. 0.97+/-0.04 ml x min(-1) x g(-1), controls vs. patients) and skeletal muscle (arm) blood flow (0.046+/-0.012 vs. 0.043+/-0.006 ml x min(-1) x g(-1)) were similar in the two groups (P = NS for both). In contrast, in patients both myocardial (0.38+/-0.03 vs. 0.70+/-0.03 micromol x min(-1) x g(-1), P = 0.0005) and muscle glucose uptake (0.026+/-0.004 vs. 0.056+/-0.006 micromol x min(-1) x g(-1), P = 0.005) were markedly reduced in comparison with controls. In the whole dataset, a direct relationship existed between insulin-stimulated glucose uptake in heart and skeletal muscle. Patients with a history of myocardial infarction and a low ejection fraction are insulin resistant. This insulin resistance affects both the myocardium and skeletal muscle and is independent of blood flow.

Authors

G Paternostro, P G Camici, A A Lammerstma, N Marinho, R R Baliga, J S Kooner, G K Radda, E Ferrannini

A carboxy-terminal truncated insulin receptor substrate-1 dominant negative protein reverses the human hepatocellular carcinoma malignant phenotype.

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Insulin receptor substrate-1 (IRS-1), a substrate of various receptor tyrosine kinases transmits mitogenic signals initiated by extracellular ligands. This protein is involved in normal hepatocyte growth and has been found to be overexpressed in human hepatocellular carcinoma. Expression of a carboxy-terminal truncated IRS-1 molecule containing the pleckstrin homology and phosphotyrosine-binding domains associates with the insulin receptor and prevents tyrosyl phosphorylation of endogenous IRS-1 and Shc proteins. Thus, subsequent activation of downstream signaling molecules induced by insulin and IGF-1 such as phosphatidylinositol-3 kinase and mitogen activated protein kinase is inhibited. The morphologic features of transformed human hepatocellular carcinoma cells change to a differentiated hepatocyte appearance and characteristics of the malignant phenotype as manifested by anchorage independent cell growth and tumor formation in nude mice are lost. These studies demonstrate that signal transduction pathways mediated through or by IRS-1 are important in hepatocyte and human hepatocellular carcinoma cell growth.

Authors

S Tanaka, J R Wands

Autoimmunity associated with TGF-beta1-deficiency in mice is dependent on MHC class II antigen expression.

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The progressive inflammatory process found in transforming growth factor beta1 (TGF-beta1)-deficient mice is associated with several manifestations of autoimmunity, including circulating antibodies to nuclear antigens, immune complex deposition, and increased expression of both class I and class II major histocompatibility complex (MHC) antigens. The contribution of MHC class II antigens to the genesis of this phenotype has been determined by crossing the TGF-beta1-null [TGF-beta1(-/-)] genotype into the MHC class II-deficient [MHC-II(-/-)] background. Mice homozygous for both the TGF-beta1 null allele and the class II null allele [TGF-beta1(-/-);MHC-II(-/-)] are without evidence of inflammatory infiltrates, circulating autoantibodies, or glomerular immune complex deposits. Instead, these animals exhibit extensive extramedullary hematopoiesis with progressive splenomegaly and adenopathy, surviving only slightly longer than TGF-beta1(-/-);MHC-II(+/+) mice. The role of CD4+ T cells, which are also absent in MHC class II-deficient mice, is directly demonstrated through the administration of anti-CD4 monoclonal antibodies in class II-positive, TGF-beta1(-/-) mice. The observed reduction in inflammation and improved survival emphasize the significance of CD4+ cells in the pathogenesis of the autoimmune process and suggest that the additional absence of class II antigens in TGF-beta1(-/-);MHC-II(-/-) mice may contribute to their extreme myeloid metaplasia. Thus, MHC class II antigens are essential for the expression of autoimmunity in TGF-beta1-deficient mice, and normally may cooperate with TGF-beta1 to regulate hematopoiesis.

Authors

J J Letterio, A G Geiser, A B Kulkarni, H Dang, L Kong, T Nakabayashi, C L Mackall, R E Gress, A B Roberts

Dynamic effects of acid on Barrett's esophagus. An ex vivo proliferation and differentiation model.

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Barrett's esophagus (BE), or specialized intestinal metaplasia, is a premalignant heterogeneous epithelium associated with reflux and an increased risk for adenocarcinoma. Since acid is a major component of refluxate, we investigated its effects ex vivo on cell differentiation as determined by villin expression; and on cell proliferation, as determined by tritiated thymidine incorporation and proliferating cell nuclear antigen expression. To mimic known physiological conditions, endoscopic biopsies of normal esophagus, BE, and duodenum were exposed, in organ culture, to acidified media (pH 3-5) either continuously, or as a 1-h pulse and compared with exposure to pH 7.4 for up to 24 h. Before culture, villin expression was noted in 25% of BE samples, and increased after 6 or 24 h of continuous acid to 50% or 83% of BE samples, respectively. Increased villin expression correlated with ultrastructural maturation of the brush border. In contrast, an acid-pulse followed by culture at pH 7.4, did not alter villin expression in BE. Moreover, continuous acid exposure blocked cell proliferation in BE, whereas, an acid-pulse enhanced cell proliferation, as compared to pH 7.4. Based on our ex vivo findings, we propose a model in which the diverse patterns of acid exposure in vivo may contribute to the observed heterogeneity and unpredictable progression to neoplasia of BE.

Authors

R C Fitzgerald, M B Omary, G Triadafilopoulos

Human cytomegalovirus increases modified low density lipoprotein uptake and scavenger receptor mRNA expression in vascular smooth muscle cells.

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Abstract

Evidence suggests a possible role for human cytomegalovirus (HCMV) in the development of arteriosclerosis. One of the earliest events in plaque formation is the accumulation of lipid-laden foam cells, derived from macrophages and smooth muscle cells (SMCs). The lipid accumulation that occurs depends upon the uptake of oxidized LDL (Ox-LDL), a process in which the scavenger receptor (SR) has been postulated to play an important role. We therefore examined the effects of HCMV on this process. We demonstrate that HCMV infection of human SMCs increases modified LDL uptake and stimulates class A SR gene (SR-A) mRNA expression. In addition, infection of rat SMCs with HCMV, which causes immediate early gene expression (IE72/IE84), but no early or late HCMV gene products and no cytopathic effects, also increases SMC uptake of Ox-LDL and acetylated LDL, with either effect blocked by an excess of either cold Ox-LDL or acetylated-LDL, and by fucoidin, an SR competitor. Cotransfection of an IE72, but not an IE84, expression plasmid and a plasmid containing a Class A SR promoter/reporter gene construct enhances SR promoter activity. Since increased Ox-LDL uptake is believed to play an important role in arteriosclerosis, these results provide a link between HCMV infection and arteriosclerotic plaque formation.

Authors

Y F Zhou, E Guetta, Z X Yu, T Finkel, S E Epstein

Glomerular inflammation induces resistance to tubular injury in the rat. A novel form of acquired, heme oxygenase-dependent resistance to renal injury.

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Abstract

Considerable attention is directed to a surprising biologic phenomenon wherein tissues exposed to one insult acquire resistance to another. We identify a novel example of acquired resistance to acute renal failure and a mechanism that contributes to such resistance. Nephrotoxic serum, administered to rats 24 h before the induction of glycerol-induced acute renal failure, reduces functional and structural injury that occurs in this model. Since heme oxygenase, the rate-limiting enzyme in heme degradation, protects against heme protein-induced renal injury, we questioned whether induction of heme oxygenase underlies the protection afforded by nephrotoxic serum. Kidney heme oxygenase (HO-1) mRNA was induced 6 h after nephrotoxic serum and renal tubules were identified as the site of expression of heme oxygenase protein. Induction of heme oxygenase was accompanied by increased renal content of ferritin but not by induction of other antioxidant enzymes. Inhibition of heme oxygenase prevented the protection afforded by nephrotoxic serum. Nephrotoxic serum did not protect against ischemic acute renal failure, a model in which heme oxygenase is not induced. Thus, nephrotoxic serum protects against glycerol-induced acute renal failure by inducing heme oxygenase in tubules. This study provides the first demonstration of resistance to tubular injury acquired from glomerular inflammation, uncovers a mechanism for such resistance, and exposes the dialogue that occurs between glomeruli and tubules.

Authors

B A Vogt, T P Shanley, A Croatt, J Alam, K J Johnson, K A Nath

Ethanol-induced retention of nascent proteins in rat hepatocytes is accompanied by altered distribution of the small GTP-binding protein rab2.

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Abstract

Chronic ethanol consumption induces hepatocellular retention of nascent proteins leading to hepatomegaly. While the molecular mechanisms behind this impairment are undefined, it has been predicted that protein retention results from a disruption of vesicle-mediated secretory processes. Small GTP-binding proteins (rab proteins) have recently been implicated in the regulation of vesicular trafficking in eukaryotic cells. Our objectives were to identify intracellular sites of ethanol-induced protein retention and to determine whether the distribution of secretory rab proteins was altered by ethanol. Transport of hepatic proteins along the secretory pathway in livers from control and ethanol-fed rats was analyzed using subcellular fractionation and immunoprecipitation in the context of in vivo pulse-chase experiments. We show that pre-Golgi and Golgi compartments, as well as secretory vesicles, are sites of ethanol-induced retention of nascent soluble and transmembrane secretory proteins. These results are supported by immunofluorescence localization of hepatic proteins on liver sections. Further, immunoblot analyses of hepatic subcellular fractions from ethanol-damaged livers indicate a dramatic reduction in the association of rab2 with a Golgi compartment as compared with controls. In contrast, rab6 and alpha-mannosidase II, Golgi marker proteins, appear unchanged. These studies provide a detailed analysis of the intracellular site of ethanol-induced protein retention in the hepatocyte and lend novel insight into a potential mechanism behind this impairment. The effects of ethanol exposure on rab proteins and Golgi function are discussed.

Authors

J M Larkin, B Oswald, M A McNiven

Nitric oxide contributes to estrogen-induced vasodilation of the ovine uterine circulation.

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Abstract

Estradiol-17beta (E2beta), a potent vasodilator, has its greatest effects on the uterine vasculature, blood flow (UBF) increasing > or = 10-fold. The mechanism(s) responsible for E2beta-induced vasodilation is unclear. We determined if nitric oxide (NO)-induced increases in cGMP modulate estrogen-induced increases in UBF, and if cyclooxygenase inhibition modifies E2beta responses. Nonpregnant (n = 15) and pregnant (n = 8) ewes had flow probes implanted on main uterine arteries and catheters in branches of the uterine vein and artery bilaterally for blood sampling and infusion of the NO synthase inhibitor L-nitro-arginine methyl ester (L-NAME), respectively. In nonpregnant ewes E2beta (1 microg/kg) caused parallel increases (P < 0.001) in UBF (15+/-3 to 130+/-16 ml/min) and uterine cGMP secretion (23+/-10 to 291+/-38 pmol/min); uterine venous cGMP also rose (4.98+/-1.4 to 9.43+/-3.2 pmol/ml; P < 0.001). Intra-arterial L-NAME partially inhibited increases in UBF dose-dependently (r = 0.66, n = 18, P < 0.003) while completely inhibiting cGMP secretion (P = 0.025). Indomethacin, 2 mg/kg intravenously, did not alter E2beta-induced responses. After E2beta-induced increases in UBF, intraarterial L-NAME partially decreased UBF dose dependently (r = 0.73, n = 46, P < 0.001) while inhibiting cGMP secretion (178+/-48 to 50+/-24 pmol/min; n = 5, P = 0.006); both were reversed by L-arginine. In pregnant ewes, E2beta increased UBF and venous cGMP (9.1+/-0.96 to 13.2+/-0.96 pmol/ml, P < 0.01); however, intraarterial L-NAME decreased basal cGMP secretion 66% (P = 0.02), but not UBF. Acute estrogen-induced increases in UBF are associated with NO-dependent increases in cGMP synthesis, but other mechanisms may also be involved. However, vasodilating prostanoids do not appear to be important. In ovine pregnancy NO is not essential for maintaining uteroplacental vasodilation.

Authors

C R Rosenfeld, B E Cox, T Roy, R R Magness

In vivo nitrogen metabolism in ornithine transcarbamylase deficiency.

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Abstract

We developed a new technique that monitors metabolic competency in female heterozygotes for ornithine transcarbamylase deficiency (OTCD). The method uses mass spectrometry to measure conversion of (15)NH4Cl to [15N]urea and [5-(15)N]glutamine following an oral load of (15)NH4Cl. We found that heterozygotes converted significantly less NH3 nitrogen to urea, with this difference being particularly obvious for symptomatic carriers, in whom the blood [15N]urea concentration (mM) was significantly less than control values at most time points. The blood concentration of [5-(15)N]-glutamine (microM) was significantly higher in both asymptomatic and symptomatic heterozygotes than it was in the control subjects. The administration of a test dose of sodium phenylbutyrate to the control group did not affect the rate of [15N]urea formation. We conclude: (a) This test effectively monitors in vivo N metabolism and might obviate the need for liver biopsy to measure enzyme activity in OTCD; (b) Asymptomatic OTCD carriers form urea at a normal rate, indicating that ureagenesis can be competent even though enzyme activity is below normal; (c) Although ostensibly asymptomatic OTCD carriers form urea at a normal rate, their nitrogen metabolism is still abnormal, as reflected in their increased production of [5-(15)N]glutamine; and (d) This new test may be important for monitoring the efficacy of novel treatments for OTCD, e.g., liver transplantation and gene therapy.

Authors

M Yudkoff, Y Daikhin, I Nissim, A Jawad, J Wilson, M Batshaw

Determinants and vitamin responsiveness of intermediate hyperhomocysteinemia (> or = 40 micromol/liter). The Hordaland Homocysteine Study.

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Abstract

From 1992-93, we screened 18,043 subjects, aged 40-67 yr, and found 67 cases (0.4%) with total plasma homocysteine (tHcy) > or = 40 micromol/liter. Compared to 329 controls, the cases had lower plasma folate and cobalamin levels, lower intake of vitamin supplements, consumed more coffee, and were more frequently smokers. Homozygosity for the C677T mutation in the methylenetetrahydrofolate reductase gene was observed in 73.1% of the cases and 10.2% of the controls. Only seven cases with cobalamin deficiency and one with homocystinuria received specific therapeutic instructions. 2 yr after the screening, 58 subjects were reinvestigated. 41 still had tHcy > 20 micromol/liter, and in 37 of these, intervention with low dose folic acid (0.2 mg/d) was started. Notably, 34 of 37 (92%) had homozygosity for the C677T mutation. Plasma tHcy was reduced in all but two after 7 wk, and became normal within 7 mo in 21 of 37 subjects. Most of the remaining subjects obtained a normal tHcy level with 5 mg/d of folic acid. We conclude that most subjects with hyperhomocysteinemia > or = 40 micromol/liter in the general population have the C677T mutation combined with low folate status. Daily supplement of low dose folic acid will reduce and often normalize their tHcy level.

Authors

A B Guttormsen, P M Ueland, I Nesthus, O Nygård, J Schneede, S E Vollset, H Refsum