Insulin and the arginine paradox.

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S Kurz, D G Harrison

IFN-gamma, IGIF, and IDDM.

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N Sarvetnick

Correction

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Cell adhesion and angiogenesis.

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J Bischoff

Arthropod- and host-specific gene expression by Borrelia burgdorferi.

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A M de Silva, E Fikrig

High density lipoproteins, but not other lipoproteins, provide a vehicle for sterol transport to bile.

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Unesterified cholesterol (UC) that is taken up by the liver from lipoproteins is rapidly mixed by exchange with liver UC. Thus, it is not possible to quantitate the transport of UC from different lipoproteins into bile using radiolabeled UC. However, plant sterols do not exchange with UC and are secreted in bile with the same kinetics as UC. To compare the contribution to bile of sterols from different lipoproteins, we perfused isolated rat livers with VLDL, LDL, and HDL that were obtained from patients with hereditary phytosterolemia and were rich in plant sterols. After 30-min recirculating perfusions, hepatic concentrations of plant sterols were not different after different lipoproteins were perfused. However, biliary plant sterol secretion was markedly different: with the perfusion of either VLDL or LDL there was no increase in plant sterols in bile, but with perfusion of HDL, the secretion of plant sterols was increased two- to threefold (P = 0.0005). The increase in biliary plant sterols was detected 5-10 min after HDL was added to perfusates and was similarly large for each of three individual plant sterols that was tracked. Results show that when sterol transport from lipoproteins into bile can be determined, only HDL provides a vehicle for UC elimination in bile that is consistent with its putative function in reverse cholesterol transport.

Authors

S J Robins, J M Fasulo

Diet-induced obese mice develop peripheral, but not central, resistance to leptin.

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Leptin administration reduces obesity in leptin-deficient ob/ob mice; its effects in obese humans, who have high circulating leptin levels, remain to be determined. This longitudinal study was designed to determine whether diet-induced obesity in mice produces resistance to peripheral and/or central leptin treatment. Obesity was induced in two strains of mice by exposure to a 45% fat diet. Serum leptin increased in proportion to body weight (P < 0.00001). Whereas C57BL/6 mice initially responded to peripherally administered leptin with a marked decrease in food intake, leptin resistance developed after 16 d on high fat diet; mice on 10% fat diet retained leptin sensitivity. In AKR mice, peripheral leptin significantly decreased food intake in both 10 and 45% fat-fed mice after 16 d of dietary treatment. However, after 56 d, both groups became resistant to peripherally administered leptin. Central administration of leptin to peripherally leptin-resistant AKR mice on 45% fat diet resulted in a robust response to leptin, with a dose-dependent decrease in food intake (P < 0.00001) and body weight (P < 0.0001) after a single intracerebroventricular infusion. These data demonstrate that, in a diet-induced obesity model, mice exhibit resistance to peripherally administered leptin, while retaining sensitivity to centrally administered leptin.

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M Van Heek, D S Compton, C F France, R P Tedesco, A B Fawzi, M P Graziano, E J Sybertz, C D Strader, H R Davis Jr

Leptin accelerates the onset of puberty in normal female mice.

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The fat-derived hormone, leptin, is proposed to serve as an adipostatic signal to the brain to reduce food intake and body weight. In addition to its effects on body weight, chronic leptin treatment restores puberty and fertility to ob/ob mice with total leptin deficiency, and acute treatment substantially corrects hypogonadism in mice starved for 2 d without affecting body weight. Leptin may therefore be a critical signal, linking adiposity and reproduction. Since body weight and adiposity appear to play a critical role in the timing of puberty in humans and rodents, and leptin levels rise with increasing adiposity, we studied the effects of once daily injections of recombinant leptin on the onset of puberty in female mice weaned on day 21 and fed ad libitum. There was a linear increase in body weight during the study period, which was not altered by the dose of leptin used. Mice injected with leptin had an earlier onset of three classic pubertal parameters (i.e., vaginal opening, estrus, and cycling) compared with saline-injected controls. Leptin is the first peripheral molecule demonstrated to accelerate the maturation of the reproductive axis in normal rodents. We propose that leptin is the signal that informs the brain that energy stores are sufficient to support the high energy demands of reproduction, and may be a major determinant of the timing of puberty.

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R S Ahima, J Dushay, S N Flier, D Prabakaran, J S Flier

CD95 ligand (FasL)-induced apoptosis is necessary for corneal allograft survival.

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Although anatomical barriers and soluble mediators have been implicated in immune privilege, it appears that the apoptotic cell death of Fas+ cells by tissue-associated CD95 ligand (Fas ligand, FasL) is an important component. One clinical example of the function of an immune privileged site is the success of human corneal transplants, where a very high percentage of transplants accept without tissue matching or immunosuppressive therapy. Since the mouse cornea expresses abundant Fas ligand and immune privilege has been implicated in the success of these transplants, we examined the role of FasL in corneal transplantation. Our results show that human corneas express functional FasL capable of killing Fas+ lymphoid cells in an in vitro culture system. Using a mouse model for corneal allograft transplantation, FasL+ orthografts were accepted at a rate of 45%, whereas FasL- grafts, or normal grafts transplanted to Fas- mice, were rejected 100% of the time. Histological analysis found that FasL+ grafts contained apoptotic mononuclear cells indicating the induction of apoptosis by the graft, while rejecting FasL- corneas contained numerous inflammatory cells without associated apoptosis. Taken together our results demonstrate that FasL expression on the cornea is a major factor in corneal allograft survival and, thus, we provide an explanation for one of the most successful tissue transplants performed in humans.

Authors

P M Stuart, T S Griffith, N Usui, J Pepose, X Yu, T A Ferguson

Drug-induced apoptosis in hepatoma cells is mediated by the CD95 (APO-1/Fas) receptor/ligand system and involves activation of wild-type p53.

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Chemotherapeutic drugs are cytotoxic by induction of apoptosis in drug-sensitive cells. We investigated the mechanism of bleomycin-induced cytotoxicity in hepatoma cells. At concentrations present in the sera of patients during therapy, bleomycin induced transient accumulation of nuclear wild-type (wt) p53 and upregulated expression of cell surface CD95 (APO-1/Fas) receptor in hepatoma cells carrying wt p53 (HepG2). Bleomycin did not increase CD95 in hepatoma cells with mutated p53 (Huh7) or in hepatoma cells which were p53-/- (Hep3B). In addition, sensitivity towards CD95-mediated apoptosis was also increased in wt p53 positive HepG2 cells. Microinjection of wt p53 cDNA into HepG2 cells had the same effect. In contrast, bleomycin did not enhance susceptibility towards CD95-mediated apoptosis in Huh7 and in Hep3B cells. Furthermore, bleomycin treatment of HepG2 cells increased CD95 ligand (CD95L) mRNA expression. Most notably, bleomycin-induced apoptosis in HepG2 cells was almost completely inhibited by antibodies which interfere with CD95 receptor/ligand interaction. These data suggest that apoptosis induced by bleomycin is mediated, at least in part, by p53-dependent stimulation of the CD95 receptor/ligand system. The same applies to other anti-cancer drugs such as cisplatin and methotrexate. These data may have major consequences for drug treatment of cancer and the explanation of drug sensitivity and resistance.

Authors

M Müller, S Strand, H Hug, E M Heinemann, H Walczak, W J Hofmann, W Stremmel, P H Krammer, P R Galle

Direct glucocorticoid inhibition of insulin secretion. An in vitro study of dexamethasone effects in mouse islets.

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The direct effects of glucocorticoids on pancreatic beta cell function were studied with normal mouse islets. Dexamethasone inhibited insulin secretion from cultured islets in a concentration-dependent manner: maximum of approximately 75% at 250 nM and IC50 at approximately 20 nM dexamethasone. This inhibition was of slow onset (0, 20, and 40% after 1, 2, and 3 h) and only slowly reversible. It was prevented by a blocker of nuclear glucocorticoid receptors, by pertussis toxin, by a phorbol ester, and by dibutyryl cAMP, but was unaffected by an increase in the fuel content of the culture medium. Dexamethasone treatment did not affect islet cAMP levels but slightly reduced inositol phosphate formation. After 18 h of culture with or without 1 microM dexamethasone, the islets were perifused and stimulated by a rise in the glucose concentration from 3 to 15 mM. Both phases of insulin secretion were similarly decreased in dexamethasone-treated islets as compared with control islets. This inhibition could not be ascribed to a lowering of insulin stores (higher in dexamethasone-treated islets), to an alteration of glucose metabolism (glucose oxidation and NAD(P)H changes were unaffected), or to a lesser rise of cytoplasmic Ca2+ in beta cells (only the frequency of the oscillations was modified). Dexamethasone also inhibited insulin secretion induced by arginine, tolbutamide, or high K+. In this case also the inhibition was observed despite a normal rise of cytoplasmic Ca2+. In conclusion, dexamethasone inhibits insulin secretion through a genomic action in beta cells that leads to a decrease in the efficacy of cytoplasmic Ca2+ on the exocytotic process.

Authors

C Lambillotte, P Gilon, J C Henquin

Human neutrophils employ the myeloperoxidase-hydrogen peroxide-chloride system to convert hydroxy-amino acids into glycolaldehyde, 2-hydroxypropanal, and acrolein. A mechanism for the generation of highly reactive alpha-hydroxy and alpha,beta-unsaturated aldehydes by phagocytes at sites of inflammation.

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Reactive aldehydes derived from reducing sugars and lipid peroxidation play a critical role in the formation of advanced glycation end (AGE) products and oxidative tissue damage. We have recently proposed another mechanism for aldehyde generation at sites of inflammation that involves myeloperoxidase, a heme enzyme secreted by activated phagocytes. We now demonstrate that human neutrophils employ the myeloperoxidase-H202-chloride system to produce alpha-hydroxy and alpha,beta-unsaturated aldehydes from hydroxy-amino acids in high yield. Identities of the aldehydes were established using mass spectrometry and high performance liquid chromatography. Activated neutrophils converted L-serine to glycolaldehyde, an alpha-hydroxyaldehyde which mediates protein cross-linking and formation of Nepsilon-(carboxymethyl)lysine, an AGE product. L-Threonine was similarly oxidized to 2-hydroxypropanal and its dehydration product, acrolein, an extremely reactive alpha,beta-unsaturated aldehyde which alkylates proteins and nucleic acids. Aldehyde generation required neutrophil activation and a free hydroxy-amino acid; it was inhibited by catalase and heme poisons, implicating H202 and myeloperoxidase in the cellular reaction. Aldehyde production by purified myeloperoxidase required H202 and chloride, and was mimicked by reagent hypochlorous acid (HOCl) in the absence of enzyme, suggesting that the reaction pathway involves a chlorinated intermediate. Collectively, these results indicate that the myeloperoxidase-H202-chloride system of phagocytes converts free hydroxy-amino acids into highly reactive alpha-hydroxy and alpha,beta-unsaturated aldehydes. The generation of glycolaldehyde, 2-hydroxypropanal, and acrolein by activated phagocytes may thus play a role in AGE product formation and tissue damage at sites of inflammation.

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M M Anderson, S L Hazen, F F Hsu, J W Heinecke

The vascular effects of L-Arginine in humans. The role of endogenous insulin.

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This study aimed at evaluating whether increased availability of the natural precursor of nitric oxide, L-arginine, could influence systemic hemodynamic and rheologic parameters in humans and whether the effects of L-arginine are mediated by endogenous insulin. 10 healthy young subjects participated in the following studies: study I, infusion of L-arginine (1 g/min for 30 min); study II, infusion of L-arginine plus octreotide (25 microg as i.v. bolus + 0.5 microg/min) to block endogenous insulin and glucagon secretion, plus replacement of basal insulin and glucagon; study III, infusion of L-arginine plus octreotide plus basal glucagon plus an insulin infusion designed to mimic the insulin response of study I. L-Arginine infusion significantly reduced systolic (11+/-3, mean+/-SE) and diastolic (8+/-2 mmHg, P < 0.001) blood pressure, platelet aggregation (20+/-4%), and blood viscosity (1.6+/-0.2 centipois, P < 0.01), and increased leg blood flow (97+/-16 ml/min), heart rate, and plasma catecholamine levels (P < 0.01). In study II, plasma insulin levels remained suppressed at baseline; in this condition, the vascular responses to L-arginine were significantly reduced, except for plasma catecholamines which did not change significantly. In study III, the plasma insulin response to L-arginine was reestablished; this was associated with hemodynamic and rheologic changes following L-arginine not significantly different from those recorded in study I. These findings show that systemic infusion of L-arginine in healthy subjects induces vasodilation and inhibits platelet aggregation and blood viscosity. These effects are mediated, in part, by endogenous released insulin.

Authors

D Giugliano, R Marfella, G Verrazzo, R Acampora, L Coppola, D Cozzolino, F D'Onofrio

Inhibition of T cell apoptosis in the rheumatoid synovium.

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Synovial T cells in rheumatoid arthritis are highly differentiated and express a phenotype suggesting susceptibility to apoptosis (CD45RB dull, CD45RO bright, Bcl-2 low, Bax high, Fas high). However, no evidence of T cell apoptosis was found in synovial fluid from any of 28 patients studied. In contrast, synovial fluid from 10 patients with crystal arthritis showed substantial levels of T cell apoptosis. The failre of apoptosis was not an intrinsic property of rheumatoid synovial T cells, as they showed rapid spontaneous apoptosis on removal from the joint. Synovial T cells from rheumatoid arthritis and gout patients could be rescued from spontaneous apoptosis in vitro either by IL-2R gamma chain signaling cytokines (which upregulate Bcl-2 and Bcl-XL) or by interaction with synovial fibroblasts (which upregulates Bcl-xL but not Bcl-2). The phenotype of rheumatoid synovial T cells ex vivo (Bcl-2 low, Bcl-xL high) suggested a fibroblast-mediated mechanism in vivo. This was confirmed by in vitro culture of synovial T cells with fibroblasts which maintained the Bcl-xL high Bcl-2 low phenotype. Synovial T cells from gout patients were Bcl-2 low Bcl-xL low and showed clear evidence of apoptosis in vivo. Inhibition experiments suggested that an integrin-ligand interaction incorporating the Arg-Gly-Asp motif is involved in fibroblast-mediated synovial T cell survival. We propose that environmental blockade of cell death resulting from interaction with stromal cells is a major factor in the persistent T cell infiltration of chronically inflamed rheumatoid synovium.

Authors

M Salmon, D Scheel-Toellner, A P Huissoon, D Pilling, N Shamsadeen, H Hyde, A D D'Angeac, P A Bacon, P Emery, A N Akbar

Differential human multiple myeloma cell line responsiveness to interferon-alpha. Analysis of transcription factor activation and interleukin 6 receptor expression.

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Although IFN-alpha is commonly used as maintenance treatment for multiple myeloma patients, its effectiveness is varied. In this study, we have used a panel of IL-6 responsive myeloma cell lines that vary remarkably in responsiveness to IFN-alpha. Three cell lines were growth arrested by IFN-alpha; however, IFN-alpha significantly stimulated growth of the fourth cell line, KAS-6/1. Our studies have focused on elucidating the mechanism of differential IFN-alpha responsiveness. First, we have shown that IFN-alpha-stimulated growth of the KAS-6/1 cells did not result from induction of autocrine IL-6 expression. Second, analysis of Stats 1, 2, and 3 and IFN regulatory factor-1 (IRF-1) and IRF-2 activation failed to reveal differences between the IFN-alpha growth-arrested or growth-stimulated cells. Third, although IFN-alpha treatment of the IFN-alpha growth-inhibited cell lines reduced IL-6 receptor (IL-6R) expression, IFN-alpha also reduced KAS-6/1 IL-6R expression. Finally, although IFN-alpha treatment reduced IL-6R numbers on each cell line, analysis of Stat protein activation revealed that the receptors were still functional. We conclude that myeloma cell responsiveness to IFN-alpha is heterogeneous and that mechanisms of IFN-alpha-mediated growth inhibition other than IL-6R downregulation must exist in myeloma. Identification of these mechanisms may allow development of agents that are more universally effective than IFN-alpha.

Authors

D F Jelinek, K M Aagaard-Tillery, B K Arendt, T Arora, R C Tschumper, J J Westendorf

Increased accumulation of the glycoxidation product N(epsilon)-(carboxymethyl)lysine in human tissues in diabetes and aging.

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N(epsilon)-(Carboxymethyl)lysine (CML), a major product of oxidative modification of glycated proteins, has been suggested to represent a general marker of oxidative stress and long-term damage to proteins in aging, atherosclerosis, and diabetes. To investigate the occurrence and distribution of CML in humans an antiserum specifically recognizing protein-bound CML was generated. The oxidative formation of CML from glycated proteins was reduced by lipoic acid, aminoguanidine, superoxide dismutase, catalase, and particularly vitamin E and desferrioxamine. Immunolocalization of CML in skin, lung, heart, kidney, intestine, intervertebral discs, and particularly in arteries provided evidence for an age-dependent increase in CML accumulation in distinct locations, and acceleration of this process in diabetes. Intense staining of the arterial wall and particularly the elastic membrane was found. High levels of CML modification were observed within atherosclerotic plaques and in foam cells. The preferential location of CML immunoreactivity in lesions may indicate the contribution of glycoxidation to the processes occurring in diabetes and aging. Additionally, we found increased CML content in serum proteins in diabetic patients. The strong dependence of CML formation on oxidative conditions together with the increased occurrence of CML in diabetic serum and tissue proteins suggest a role for CML as endogenous biomarker for oxidative damage.

Authors

E D Schleicher, E Wagner, A G Nerlich

Active stage of autoimmune diabetes is associated with the expression of a novel cytokine, IGIF, which is located near Idd2.

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Recently, interferon-gamma-inducing-factor (IGIF) has been described as a novel monokine that is a more potent interferon-gamma (IFN-gamma) inducer than IL-12. By cloning IGIF from affected tissue and studying IGIF gene expression, we describe for the first time a close association of this cytokine with an autoimmune disease. The non-obese diabetic (NOD) mouse spontaneously develops autoimmune insulitis and diabetes which can be accelerated and synchronized by a single injection of cyclophosphamide. IGIF mRNA was demonstrated by reverse transcriptase PCR in NOD mouse pancreas during early stages of insulitis. Levels of IGIF mRNA increased rapidly after cyclophosphamide treatment and preceded a rise in IFN-gamma mRNA, and subsequently diabetes. Interestingly, these kinetics mimick that of IL-12p40 mRNA, resulting in a close correlation of individual mRNA levels. Cloning of the IGIF cDNA from pancreas RNA followed by sequencing revealed identity with the IGIF sequence cloned from Kupffer cells and in vivo preactivated macrophages. When extending our study to macrophages of the spleen we observed that NOD mouse macrophages responded to cyclophosphamide with IGIF gene expression while macrophages from Balb/c mice treated in parallel did not. The IGIF gene position is located within the Idd2 interval on mouse chromosome 9 and therefore it is a candidate for the Idd2 susceptible gene. We conclude that IGIF expression is abnormally regulated in autoimmune NOD mice and closely associated with diabetes development.

Authors

H Rothe, N A Jenkins, N G Copeland, H Kolb

Molecular and mutation trends analyses of omp1 alleles for serovar E of Chlamydia trachomatis. Implications for the immunopathogenesis of disease.

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Serovars E, F, and D are the most prevalent Chlamydia trachomatis strains worldwide. This prevalence may relate to epitopes that enhance infectivity and transmission. There are numerous major outer membrane protein (MOMP) gene (omp1) variants described for D and F but few for E. However, omp1 constant regions are rarely sequenced yet, they may contain mutations that affect the structure/function relationship of the protein. Further, differentiating variants that occur as a result of selection from variants that contain random mutations without biologic impact is difficult. We investigated 67 urogenital E serovars and found 11 (16%) variants which contained 16 (53%) nonconservative amino acid changes. Using signature-pattern analysis, 57 amino acids throughout MOMP differentiated the E sequence set from the non-E sequence set, thus defining E strains. Four E variants did not match this signature-pattern, and, by phenetic analyses, formed new phylogenetic branches, suggesting that they may be biologically distinct variants. Our analyses offer for the first time a unique approach for identifying variants that may occur from selection and may affect infectivity and transmission. Understanding the mutation trends, phylogeny, and molecular epidemiology of E variants is essential for designing public health control interventions and a vaccine.

Authors

D Dean, K Millman

Immunologic and hematopoietic effects of CD40 stimulation after syngeneic bone marrow transplantation in mice.

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CD40 is a molecule present on multiple cell types including B lymphocyte lineage cells. CD40 has been shown to play an important role in B cell differentiation and activation in vitro, although little is known concerning the effects of CD40 stimulation in vivo. We therefore examined the effects of CD40 stimulation in mice using a syngeneic bone marrow transplantation (BMT) model in an effort to augment B cell recovery after high dose therapy with hematopoietic reconstitution. After the BMT, mice were treated with or without 2-6 microg of a soluble recombinant murine CD40 ligand (srmCD40L) given intraperitoneally twice a week. A significant increase in B cell progenitors (B220+/ surface IgM-) was observed in the bone marrow of mice receiving the srmCD40L. The treated recipients also demonstrated improved B-cell function with increases in total serum immunoglobulin and increased splenic mitogen responsiveness to LPS being noted. Additionally, srmCD40L treatment promoted secondary lymphoid organ repopulation, accelerating germinal center formation in the lymph nodes. Total B cell numbers in the periphery were not significantly affected even with continuous srmCD40L administration. Lymphocytes obtained from mice treated with the ligand also had increases in T cell mitogen and anti-CD3 mAb responsiveness and acquired the capability to produce IL-4. Surprisingly, treatment with srmCD40L also produced hematopoietic effects in mice, resulting in an increase of BM and splenic hematopoietic progenitor cells in the mice after BMT. Treatment with srmCD40L significantly increased granulocyte and platelet recovery in the peripheral blood. Incubation of BMC with srmCD40L in vitro also resulted in increased progenitor proliferation, demonstrating that the hematopoietic effects of the ligand may be direct. Thus, stimulation of CD40 by its ligand may be beneficial in accelerating both immune and hematopoietic recovery in the setting of bone marrow transplantation.

Authors

S Funakoshi, D D Taub, M R Anver, A Raziuddin, O Asai, V Reddy, H Rager, W C Fanslow, D L Longo, W J Murphy

Retinoic acid inhibits the regulated expression of vascular cell adhesion molecule-1 by cultured dermal microvascular endothelial cells.

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The regulated expression of cell adhesion molecules (CAM) on endothelial cells is central to the pathogenesis of various inflammatory processes. Retinoic acid and synthetic derivatives have been demonstrated to exert antiinflammatory effects in cutaneous diseases. To determine modes of retinoid action in the modulation of inflammatory responses, we explored effects of all-trans-retinoic acid (t-RA) on the TNFalpha-induced expression of vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin in cultured human dermal microvascular endothelial cells. Pretreatment with t-RA specifically prevented TNFalpha-induced VCAM-1 expression, but not ICAM-1 and E-selectin induction. t-RA significantly reduced VCAM-1-dependent T cell binding to TNFalpha-treated human dermal microvascular endothelial cells as well. This differential modulation of TNFalpha-induced CAM expression by t-RA was reflected at steady state mRNA levels and in nuclear run-on studies. In transcriptional activation studies, the TNFalpha-mediated activation of the human VCAM-1 promoter was inhibited after t-RA treatment, while the ICAM-1 promoter activation was unaffected, indicating that the selective inhibition of CAM expression is regulated in part at the level of gene transcription. Furthermore, the transcriptional inhibition by t-RA appears to be mediated by its effects upon the activation of NF-kappaB-dependent complex formation. Analysis of protein-DNA binding assays revealed marked inhibition of specific NF-kappaB-dependent binding to the tandem NF-KB sites of the VCAM-1 promoter, but not to the functional NF-kappaB motif of the ICAM-1 promoter. The specific inhibition of cytokine-mediated VCAM-1 gene expression in vitro may provide a potential basis by which retinoids exert their biological effects at sites of inflammation in vivo.

Authors

J Gille, L L Paxton, T J Lawley, S W Caughman, R A Swerlick

The exchange between proglycogen and macroglycogen and the metabolic role of the protein-rich glycogen in rat skeletal muscle.

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The aim of this study is to determine if proglycogen and macroglycogen are kinetically related in rat skeletal muscle. Eight groups of anesthetized fasted rats (seven hepatic-occluded and one nonoccluded) were intravenously infused with [3-3H]glucose at a rate of 1.7 microCi x min(-1) for 20 min. At the end of infusion, hindlimb muscles were excised and rapidly frozen in liquid nitrogen. Proglycogen was extracted by precipitation in 10% TCA; and macroglycogen as a part of total glycogen by precipitation in 20% KOH-65% ethanol. Along with the tracer, the occluded rats were also infused with: saline (group 1); insulin at rates ranging from 5 to 50 mU x min(-1) (groups 2 to 5); and insulin at a rate of 10 mU x min(-1) plus glucose at rates of 10.2 and 20.4 micromol x min(-1), respectively (groups 6 and 7). The infusion regimens resulted in up to 30-fold difference in whole-body glucose utilization among the rats. In the rats infused with saline and insulin at a rate of 5 mU x min(-1), [3H]glucose was found to be exclusively incorporated into proglycogen. Incorporation into macroglycogen was found in the rats infused with insulin at rates > 10 mU x min(-1). Supplementary glucose infusion increased the synthesis of [3H]proglycogen (four- to sixfold), and equilibrated the two extractable forms of glycogen in the insulin-infused rats. In the saline-infused nonoccluded rats, only proglycogen was found to be labeled. In conclusion, our data indicate that in the intact and hepatic-occluded rats, proglycogen in the skeletal muscles may undergo synthesis and degradation of its own more readily than exchange between itself and depot macroglycogen.

Authors

M Huang, C Lee, R Lin, R Chen

A cholecystokinin-releasing factor mediates ethanol-induced stimulation of rat pancreatic secretion.

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The mechanisms by which short-term ethanol administration alters pancreatic exocrine function are unknown. We have evaluated the effects of ethanol administration on pancreatic secretion of digestive enzymes. In our studies, anesthetized as well as conscious rats were given ethanol at a rate sufficient to cause the blood ethanol concentration to reach levels associated with clinical intoxication. Ethanol was administered over a 2-h period during which blood ethanol levels remained stably elevated. We report that intravenous administration of ethanol results in a transient increase in pancreatic amylase output and plasma cholecystokinin (CCK) levels. The ethanol-induced increase in amylase output can be completely inhibited by the CCK-A receptor antagonist L-364,718 and partially inhibited by the muscarinic cholinergic antagonist atropine. The ethanol-induced rise in amylase output can be completely prevented by instillation of trypsin into the duodenum or by lavage of the duodenum with saline during ethanol administration. Furthermore, the intraduodenal activity of a CCK-releasing factor is increased by infusion of ethanol. These studies indicate that administration of ethanol causes rat pancreatic exocrine secretion to increase. This phenomenon is mediated by a trypsin-sensitive CCK-releasing factor which is present within the duodenal lumen. These observations lead us to speculate that repeated CCK-mediated ethanol-induced stimulation of pancreatic digestive enzyme secretion may play a role in the events which link ethanol abuse to the development of pancreatic injury.

Authors

A K Saluja, L Lu, Y Yamaguchi, B Hofbauer, M Rünzi, R Dawra, M Bhatia, M L Steer

Activation of large conductance potassium channels inhibits the afferent and efferent function of airway sensory nerves in the guinea pig.

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Sensory nerves play an important role in airway disease by mediating central reflexes such as cough, and local axon reflexes resulting in the peripheral release of neuropeptides. We have tested whether the benzimidazolone compound, NS1619, an opener of large conductance calcium-activated potassium (BK Ca) channels, inhibits the activity of sensory fibers, and central and local airway reflexes in guinea pig airways. In in vitro single fiber recording experiments, NS1619 applied to identified receptive fields in the trachea inhibited the firing of A(delta)-fibers evoked by hypertonic saline and distilled water, and bradykinin-evoked firing of C-fibers. Electrically evoked nonadrenergic noncholinergic contractions of isolated bronchi mediated by the release of neurokinin A (NKA) from C-fibers, but not those elicited by exogenous NKA, were inhibited by NS1619. These effects of NS1619 were prevented by iberiotoxin, a selective blocker of BK Ca channels. In conscious guinea pigs, cough evoked by aerosolized citric acid was also inhibited by NS1619. These data show that BK Ca channel activation inhibits sensory nerve activity, resulting in a reduction of both afferent and efferent function. BK Ca channel openers may therefore be of potential benefit in reducing neurogenic inflammation and central reflexes seen during inflammatory conditions of the airways, and may represent a new class of antitussive drug.

Authors

A J Fox, P J Barnes, P Venkatesan, M G Belvisi

Alternative expression of platelet glycoprotein Ib(beta) mRNA from an adjacent 5' gene with an imperfect polyadenylation signal sequence.

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Glycoprotein (GP) Ib is a major component of the platelet membrane receptor for von Willebrand factor, designated the GP Ib-IX-V complex. GP Ib is composed of two subunits (GP Ib(alpha) and GP Ib(beta)) each synthesized from separate genes. The 206 amino acid precursor of GP Ib(beta) is synthesized from a 1.0-kb mRNA expressed by megakaryocytes and was originally characterized from cDNA clones of human erythroleukemic (HEL) cell mRNA, a cell line exhibiting megakaryocytic-like properties. The cell line CHRF-288-11 also exhibits megakaryocytic-like properties, but synthesizes two related GP Ib(beta) mRNA species of 3.5 and 1.0 kb. We performed cDNA cloning experiments to identify the origin of the 3.5-kb transcript and determine its relationship to the 1.0-kb GP Ib(beta) mRNA found in megakaryocytes, platelets, and HEL cells. Our cloning experiments demonstrate that the longer transcript results from a nonconsensus polyadenylation recognition sequence, 5'AACAAT3', within a separate gene located upstream to the platelet GP Ib(beta) gene. In the absence of normal polyadenylation the more 5' gene uses the polyadenylation site within its 3' neighbor, the platelet GP Ib(beta) gene. This newly identified 5' gene contains an open reading frame encoding 369 amino acids with a high degree of sequence similarity to an expanding family of GTP-binding proteins.

Authors

B Zieger, Y Hashimoto, J Ware

Neutrophil margination, sequestration, and emigration in the lungs of L-selectin-deficient mice.

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These studies tested the hypothesis that L-selectin plays a role in neutrophil traffic in the lungs, particularly in neutrophil margination, sequestration, and emigration, using L-selectin-deficient mice. No defect in neutrophil margination within either capillaries or arterioles and venules was observed in uninflamed lungs of L-selectin-deficient mice. The initial rapid sequestration of neutrophils within the pulmonary capillaries 1 min after intravascular injection of complement fragments was not prevented. In contrast, L-selectin did contribute to the prolonged neutrophil sequestration (> or = 5 min). Interestingly, neutrophil accumulation within noncapillary microvessels required L-selectin at both 1 and 5 min after complement injection. During bacterial pneumonias, L-selectin played a role in neutrophil accumulation within noncapillary microvessels in response to either Escherichia coli or Streptococcus pneumoniae and within capillaries in response to E. coli but not S. pneumoniae. However, L-selectin was not required for emigration of neutrophils or edema in response to either organism. These studies demonstrate a role for L-selectin in the prolonged sequestration of neutrophils in response to intravascular complement fragments, in the intracapillary accumulation of neutrophils during E. coli-induced pneumonia, and in the accumulation of neutrophils within noncapillary microvessels when induced by either intravascular complement fragments or

Authors

N A Doyle, S D Bhagwan, B B Meek, G J Kutkoski, D A Steeber, T F Tedder, C M Doerschuk

Differentiation of glucose toxicity from beta cell exhaustion during the evolution of defective insulin gene expression in the pancreatic islet cell line, HIT-T15.

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Abstract

Chronic exposure of HIT-T15 cells to supraphysiologic glucose concentration diminishes insulin gene expression and decreased binding of two critical insulin gene transcription factors, STF-1 and RIPE-3b1 activator. To distinguish whether these changes are caused by glucose toxicity or beta cell exhaustion, HIT-T15 cells grown from passage 75 through 99 in media containing 11.1 mM glucose were switched to 0.8 mM glucose at passage 100. They regained binding of STF-1 and RIPE-3b1 activator and had a partial but minimal return of insulin mRNA expression. In a second study, inclusion of somatostatin in the media-containing 11.1 mM glucose inhibited insulin secretion; however, despite this protection against beta cell exhaustion, dramatic decreases in insulin gene expression, STF-1 and RIPE-3b1 binding, and insulin gene promoter activity still occurred. These data indicate that the glucotoxic effects caused by chronic exposure to supraphysiologic concentration of glucose are only minimally reversible and that they are not due simply to beta cell exhaustion. These observations carry with them the clinical implication that Type II diabetic patients who remain hyperglycemic for prolonged periods may have secondary glucose toxic effects on the beta cell that could lead to defective insulin gene expression and worsening of hyperglycemia.

Authors

A Moran, H J Zhang, L K Olson, J S Harmon, V Poitout, R P Robertson

Nitric oxide (NO) modulates the neurogenic control of blood pressure in rats with chronic renal failure (CRF).

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Abstract

Increased sympathetic nervous system (SNS) activity plays a role in the genesis of hypertension in rats with chronic renal failure (CRF). Because nitric oxide (NO) modulates the activity of the SNS, a deficit of NO synthesis could be responsible for the increased SNS activity in these animals. In the present study, we evaluated the effects of L-arginine and L-NAME on blood pressure and SNS activity-in Sprague Dawley 5/6 nephrectomized or sham-operated rats. SNS activity was determined by measuring norepinephrine turnover rate in several brain nuclei involved in the regulation of blood pressure. In the same brain nuclei, we measured NO content and nitric oxide synthase (NOS) gene expression by semiquantitative measurements of NOS mRNA reverse transcription polymerase chain reaction. In CRF rats, norepinephrine turnover rate was increased in the posterior hypothalamic nuclei, locus coeruleus, paraventricular nuclei, and the rostral ventral medulla, whereas NOS mRNA gene expression and NO2/NO3 content were increased in all brain nuclei tested. L-NAME increased blood pressure and NE turnover rate in several brain nuclei of both control and 5/6 nephrectomized rats. In CRF rats, a significant relationship was present between the percent increment in NOS mRNA gene expression related to the renal failure, and the percent increase in norepinephrine turnover rate caused by L-NAME. This suggests that endogenous NO may partially inhibit the activity of the SNS in brain nuclei involved in the neurogenic regulation of blood pressure, and this inhibition is enhanced in CRF rats. In summary, the increase in SNS activity in the posterior hypothalamic nuclei and in the locus coeruleus of CRF rats is partially mitigated by increased local expression of NOS m-RNA.

Authors

S Ye, S Nosrati, V M Campese