In rat pancreatic islets, hypoxia severely decreased both the oxidation of D-[U-14C]glucose and the release of insulin evoked by D-glucose. The production of [14C]lactate was increased in the hypoxic islets, the relative magnitude of such... more
In rat pancreatic islets, hypoxia severely decreased both the oxidation of D-[U-14C]glucose and the release of insulin evoked by D-glucose. The production of [14C]lactate was increased in the hypoxic islets, the relative magnitude of such an increment being greater at low (2.8 mM) than high (8.3 and 16.7 mM) D-glucose concentrations. Hypoxia increased the detritiation of D-[5-3H]glucose at low glucose concentration (2.8 mM), failed to affect 3H2O production at an intermediate glucose level (8.3 mM), and inhibited the utilization of D-[5-3H]glucose at a higher hexose concentration (16.7 mM). In tumoral islet cells (RINm5F line) exposed to 16.7 mM D-glucose, hypoxia decreased D-[U-14C]glucose oxidation to the same extent as in normal islet cells, but increased the production of [14C]lactate and 3H2O to a greater extent than in normal islets. These findings indicate that the Pasteur effect is operative in islet cells. The experimental data also suggest that, under normal conditions of ...
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Injection of streptozotocin (30-40 mg/kg body weight) to adult rats caused within 4-6 days a sizeable decrease in the activity of FAD-linked glycerophosphate dehydrogenase in pancreatic islets, with little change in either glutamate... more
Injection of streptozotocin (30-40 mg/kg body weight) to adult rats caused within 4-6 days a sizeable decrease in the activity of FAD-linked glycerophosphate dehydrogenase in pancreatic islets, with little change in either glutamate dehydrogenase or 2-oxoglutarate dehydrogenase activity. The severity of the enzymatic defect was related to that of the diabetic state, although a decreased enzymic activity was also observed in islets from virtually normoglycemic animals examined 2-3 weeks after streptozotocin injection. The administration of nicotinamide prior to that of streptozotocin prevented the change in enzymic activity. It is proposed that the enzymatic defect, rather than being attributable to a genomic effect of streptozotocin, may reflect the preferential impairment of a subpopulation of pancreatic B-cells.
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Research Interests: Biology, Biological Chemistry, Apoptosis, Medicine, Signal Transduction, and 13 moreToll like receptor signaling, Biological Sciences, Cell line, Animals, Male, Biological, CHEMICAL SCIENCES, Rats, Wistar Rats, Type 2 Diabetes Mellitus, Antiviral Agents, Interferon gamma, and Medical and Health Sciences
β-Cells under immune attack are destroyed by the aberrant activation of key intracellular signaling cascades. The aim of the present study was to evaluate the contribution of the signal transducer and activator of transcription (STAT)-1... more
β-Cells under immune attack are destroyed by the aberrant activation of key intracellular signaling cascades. The aim of the present study was to evaluate the contribution of the signal transducer and activator of transcription (STAT)-1 pathway for β-cell apoptosis by studying the sensitivity of β-cells from STAT-1 knockout (−/−) mice to immune-mediated cell death in vitro and in vivo. Whole islets from STAT-1−/− mice were completely resistant to interferon (IFN)-γ (studied in combination with interleukin [IL]-1β)-mediated cell death (92 ± 4% viable cells in STAT-1−/− mice vs. 56 ± 3% viable cells in wild-type controls, P ≤ 0.001) and had preserved insulin release after exposure to IL-1β and IFN-γ. Moreover, analysis of cell death in cytokine-exposed purified β-cells confirmed that protection was due to absence of STAT-1 in the β-cells themselves. Deficiency of STAT-1 in islets completely prevented cytokine-induced upregulation of IL-15, interferon inducible protein 10, and inducibl...
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Research Interests: Biology, Cell Adhesion, Medicine, Molecular Mechanics, Diabetes mellitus, and 15 moreExpressed Sequence Tags, Animals, Male, Clinical Sciences, Positive Feedback, mRna expression levels, Microarray Analysis, Major histocompatibility complex, High Density Concrete, Full Length Movies, islets of Langerhans, Gene expression profiling, Interferon gamma, High density, and Paediatrics and reproductive medicine
... Please use this identifier to cite or link to this item: Record Details. Record ID, 415290. Record Type, conference. Author, Joanne Rasschaert; Zeynep Dogusan; Monica García; Daisy Flamez [801000753526] - Ghent University... more
... Please use this identifier to cite or link to this item: Record Details. Record ID, 415290. Record Type, conference. Author, Joanne Rasschaert; Zeynep Dogusan; Monica García; Daisy Flamez [801000753526] - Ghent University Daisy.Flamez@UGent.be; Lena Alexopoulou; ...
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OBJECTIVE— Viral infections contribute to the pathogenesis of type 1 diabetes. Viruses, or viral products such as double-stranded RNA (dsRNA), affect pancreatic β-cell survival and trigger autoimmunity by unknown mechanisms. We presently... more
OBJECTIVE— Viral infections contribute to the pathogenesis of type 1 diabetes. Viruses, or viral products such as double-stranded RNA (dsRNA), affect pancreatic β-cell survival and trigger autoimmunity by unknown mechanisms. We presently investigated the mediators and downstream effectors of dsRNA-induced β-cell death. RESEARCH DESIGN AND METHODS— Primary rat β-cells and islet cells from wild-type, toll-like receptor (TLR) 3, type I interferon receptor (IFNAR1), or interferon regulatory factor (IRF)-3 knockout mice were exposed to external dsRNA (external polyinosinic-polycytidylic acid [PICex]) or were transfected with dsRNA ([PICin]). RESULTS— TLR3 signaling mediated PICex-induced nuclear factor-κB (NF-κB) and IRF-3 activation and β-cell apoptosis. PICin activated NF-κB and IRF-3 in a TLR3-independent manner, induced eukaryotic initiation factor 2α phosphorylation, and triggered a massive production of interferon (IFN)-β. This contributed to β-cell death, as islet cells from IFNAR...
Research Interests: Research Design, Diabetes, Biology, Type 2 Diabetes, Medicine, and 15 moreToll like receptor signaling, Mice, Animals, Male, Cell Death, Rats, Viral Infection, Wistar Rats, Type 2 Diabetes Mellitus, Cell Survival, Knockout Mice, double-stranded RNA, reverse transcriptase polymerase chain reaction, Interferon Regulatory FACTOR-1, and Medical and Health Sciences
In several animal models of non-insulin-dependent diabetes, a decreased activity of FAD-linked glycerophosphate dehydrogenase was recently documented in pancreatic islet, but not liver, homogenates. The present study reveals that, on the... more
In several animal models of non-insulin-dependent diabetes, a decreased activity of FAD-linked glycerophosphate dehydrogenase was recently documented in pancreatic islet, but not liver, homogenates. The present study reveals that, on the contrary, the activity of the same mitochondrial enzyme is increased in islet, but not liver or spleen, homogenates of BB, as compared to BW, rats examined before the onset of severe hyperglycemia in this animal model of autoimmune insulin-dependent diabetes.
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Human bone marrow-derived mesenchymal stem cells (hBMSC) are able to differentiate into cells of connective tissue lineages, including bone and cartilage. They are therefore considered as a promising tool for the treatment of bone... more
Human bone marrow-derived mesenchymal stem cells (hBMSC) are able to differentiate into cells of connective tissue lineages, including bone and cartilage. They are therefore considered as a promising tool for the treatment of bone degenerative diseases. One of the major issues in regenerative cell therapy is the biosafety of fetal bovine serum used for cell culture. Therefore, the development of a culture medium devoid of serum but preserving hBMSC viability will be of clinical value. The glucose-dependent insulinotropic peptide (GIP) has an anti-apoptotic action in insulin-producing cells. Interestingly, GIP also exerts beneficial effects on bone turnover by acting on osteoblasts and osteoclasts. We therefore evaluated the ability of GIP to prevent cell death in osteoblastic cells cultured in serum-free conditions. In hBMSC and SaOS-2 cells, activation of the GIP receptor increased intracellular cAMP levels. Serum deprivation induced apoptosis in SaOS-2 and hBMSC that was reduced by 30 and 50 %, respectively, in the presence of GIP. The protective effect of GIP involves activation of the adenylate cyclase pathway and inhibition of caspases 3/7 activation. These findings demonstrate that GIP exerts a protective action against apoptosis in hBMSC and suggest a novel approach to preserve viability of hBMSC cultured in the absence of serum.
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The metabolism of ketone bodies was investigated in rat pancreatic islets incubated in the absence or presence of D-glucose. The generation of 14CO2 from 3-14C-labeled ketone bodies, the interconversion of D-(-)-beta-hydroxybutyrate and... more
The metabolism of ketone bodies was investigated in rat pancreatic islets incubated in the absence or presence of D-glucose. The generation of 14CO2 from 3-14C-labeled ketone bodies, the interconversion of D-(-)-beta-hydroxybutyrate and acetoacetate (AcAc), the reciprocal effects of ketone bodies and D-glucose on their respective catabolism, and the influence of these exogenous nutrients on the output of 14CO2 from islets preincubated with either L-[U-14C]glutamine or [U-14C]palmitate provided an estimation of the nutrient-induced changes in O2 uptake that was in fair agreement with the observed modifications of islet respiration. There was a close correlation between such changes and the corresponding values for insulin output. Because the stimulation of insulin release by ketone bodies also coincided with a decrease in 86Rb outflow from prelabeled islets, these findings suggest that the insulinotropic action of ketone bodies is causally linked to their catabolism through an increa...
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Page 1. NUTRIENT REGULATION OF INSULIN SECRETION 107 17. Flatt, PR, DeSilva, M., Swanston-Flatt, S. K., Powell, C. J. & Marks, V. ( 1987) J. Endocrinol. 118,429-437 18. Lenzen, S., Brand, F.-H. &... more
Page 1. NUTRIENT REGULATION OF INSULIN SECRETION 107 17. Flatt, PR, DeSilva, M., Swanston-Flatt, S. K., Powell, C. J. & Marks, V. ( 1987) J. Endocrinol. 118,429-437 18. Lenzen, S., Brand, F.-H. & Panten, U. ( 1988) Br. J. I'hurmucol. 9585 1-859 19. ...
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The aim of the present study is to compare normal and tumoral pancreatic islet cells in terms of both the activity of selected cytosolic and mitochondrial enzymes participating to nutrient catabolism and the intrinsic properties of... more
The aim of the present study is to compare normal and tumoral pancreatic islet cells in terms of both the activity of selected cytosolic and mitochondrial enzymes participating to nutrient catabolism and the intrinsic properties of FAD-glycerophosphate dehydrogenase. The activity of the glycolytic enzymes hexokinase and lactate dehydrogenase was higher in tumoral (RINm5F) than normal islet cells. The opposite was seen for glutamate decarboxylase, glutamate-oxaloacetate transaminase, glutamate-pyruvate transaminase, glutamate dehydrogenase, 2-ketoglutarate dehydrogenase and FAD-glycerophosphate dehydrogenase (m-GDH). These findings are consistent with the high rates of glycolysis and protein synthesis seen in tumoral islet cells compared with normal islet cells, which favour mitochondrial oxidative events associated with the catabolism of D-glucose and amino acids. The intrinsic catalytic properties of m-GDH were comparable, albeit not identical, in normal and tumoral islet cells. Si...
Research Interests: Kinetics, Biology, Calcium, Mitochondria, Medicine, and 15 moreCell line, Glutamate, Gene Cloning, Animals, Glycolysis, Insulinoma, Amino Acids, Oxidative phosphorylation, Lactate dehydrogenase, Glutamate Dehydrogenase, Glutamate decarboxylase, Biochemistry and cell biology, islets of Langerhans, Pancreatic islets, and hexokinase
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The respective contribution of exogenous and intramitochondrially formed ATP to D-glucose phosphorylation by mitochondria-bound hexokinase was examined in both rat liver and pancreatic islet mitochondria by comparing the generation of... more
The respective contribution of exogenous and intramitochondrially formed ATP to D-glucose phosphorylation by mitochondria-bound hexokinase was examined in both rat liver and pancreatic islet mitochondria by comparing the generation of D-glucose 6-[32P]phosphate from exogenous [gamma-32P]ATP to the total rate of D-[U-14C]glucose phosphorylation. In liver mitochondria, the fractional contribution of exogenous ATP to D-glucose phosphorylation ranged from 4 to 74%, depending on the availability of endogenous ATP formed by either oxidative phosphorylation or in the reaction catalyzed by adenylate kinase. Likewise, in islet mitochondria exposed to exogenous ATP but deprived of exogenous nutrient, about 60% of D-glucose phosphorylation was supported by mitochondrial ATP. Such a fractional contribution was further increased in the presence of ADP and succinate, and suppressed by mitochondrial poisons. It is concluded that, in islet like in liver mitochondria, mitochondrial ATP is used preferentially to exogenous ATP as a substrate for D-glucose phosphorylation by mitochondria-bound hexokinase. This may favour the maintenance of a high cytosolic ATP concentration in glucose-stimulated islet cells.
Research Interests: Metabolism, Statistical Analysis, Mitochondria, Comparative Study, Biological Sciences, and 15 moreGlucose, Animals, Physical sciences, CAT, Phosphorylation, Ion Exchange Chromatography, Rats, Rat, Biochemistry and cell biology, islets of Langerhans, Adenosine Triphosphate, Pancreatic islets, Mitochondrion, hexokinase, and In Vitro Techniques
ABSTRACT
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Osteoporosis is a metabolic bone disease associated with unequilibrated bone remodeling resulting from decreased bone formation and/or increased bone resorption, leading to progressive bone loss. In osteoporotic patients, low bone mass is... more
Osteoporosis is a metabolic bone disease associated with unequilibrated bone remodeling resulting from decreased bone formation and/or increased bone resorption, leading to progressive bone loss. In osteoporotic patients, low bone mass is associated with an increase of bone marrow fat resulting from accumulation of adipocytes within the bone marrow. Marrow adipocytes are active secretory cells, releasing cytokines, adipokines and free fatty acids (FA) that influence the bone marrow microenvironment and alter the biology of neighboring cells. Therefore, we examined the effect of palmitate (Palm) and oleate (Ole), 2 highly prevalent FA in human organism and diet, on the function and survival of human mesenchymal stem cells (MSC) and MSC-derived osteoblastic cells. The saturated FA Palm exerted a cytotoxic action via initiation of endoplasmic reticulum stress and activation of the nuclear factor κB (NF-κB) and ERK pathways. In addition, Palm induced a proinflammatory response, as deter...
Research Interests: Endocrinology, Endoplasmic Reticulum Stress, Adolescent, Gene expression, Western blotting, and 15 moreSignal Transduction, Biological Sciences, Humans, NF-kappa B, Young Adult, Middle Aged, Adult, Oleic Acid, Osteoblasts, Cell Survival, Mesenchymal Stromal Cells, Bone Marrow Cells, Interleukin, reverse transcriptase polymerase chain reaction, and Medical and Health Sciences
The metabolism of ketone bodies was investigated in rat pancreatic islets incubated in the absence or presence of D-glucose. The generation of ¹â´COâ from 3-¹â´C-labeled ketone bodies, the interconversion of D-(-)-beta-hydroxybutyrate... more
The metabolism of ketone bodies was investigated in rat pancreatic islets incubated in the absence or presence of D-glucose. The generation of ¹â´COâ from 3-¹â´C-labeled ketone bodies, the interconversion of D-(-)-beta-hydroxybutyrate and acetoacetate (AcAc), the reciprocal effects of ketone bodies and D-glucose on their respective catabolism, and the influence of these exogenous nutrients on the output of ¹â´COâ from islets
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D-mannoheptulose was recently proposed as a possible tool to label preferentially insulin-producing cells in the pancreatic gland. In the present study, D-[3H]-mannoheptulose uptake by rat pancreatic islets or dispersed islet cells was... more
D-mannoheptulose was recently proposed as a possible tool to label preferentially insulin-producing cells in the pancreatic gland. In the present study, D-[3H]-mannoheptulose uptake by rat pancreatic islets or dispersed islet cells was found to represent a time-related and temperature-sensitive process inhibited by cytochalasin B. This mould metabolite also inhibited the efflux of D-[3H]-mannoheptulose from prelabelled islets. After 60 min incubation at 37 degrees C, the apparent intracellular distribution space of the tritiated heptose was close to or somewhat higher than that of D-[5-3H]glucose and close to 50% of the intracellular 3HOH space. It was further enhanced by D-glucose and a high concentration of 10 mM of D-mannoheptulose. The uptake of D-[3H]mannoheptulose was much lower however than that of D-[3H]mannoheptulose hexaacetate. As judged from the fate of D-mannoheptulose hexa[2-14C]acetate, the latter ester was efficiently hydrolyzed in the islet cells. The internalization of D-[3H]mannoheptulose (or its ester) coincided with the generation of tritiated acidic metabolites, reflecting phosphorylation of the heptose. The situation found in normal islet cells sharply differed from that found in tumoral islet cells of either the RINm5F or INS-1 line, in which the apparent distribution space of D-[3H]mannoheptulose represented only about 3 and 9%, respectively, of the intracellular 3HOH space. These results indicate that the entry of D-mannoheptulose into islet cells represents a carrier-mediated process, possibly mediated at the intervention of GLUT2 and, hence, provide further support to the possible use of a suitable D-mannoheptulose analog as a tool for the preferential labelling of insulin-producing cells in the pancreatic gland.
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D-[3H]mannoheptulose was recently reported to be poorly taken up by tumoral pancreatic islet cells of the RINm5F and INS-1 lines. We have now investigated the effects of D-mannoheptulose upon D-glucose metabolism in these two cell lines.... more
D-[3H]mannoheptulose was recently reported to be poorly taken up by tumoral pancreatic islet cells of the RINm5F and INS-1 lines. We have now investigated the effects of D-mannoheptulose upon D-glucose metabolism in these two cell lines. D-mannoheptulose (1.0-10.0 mM) only caused a minor decrease of D-glucose metabolism in RINm5F cells, whether at low (1.1 mM) or higher (8.3 mM) D-glucose concentration. A comparable situation was found in INS-1 cells examined after more than 20 passages. In both cases, however, the hexaacetate ester of D-mannoheptulose (5.0 mM) efficiently inhibited D-glucose metabolism. In the INS-1 cells, the relative extent of the inhibitory action of D-mannoheptulose upon D-glucose metabolism increased from 12.4 +/- 2.6 to 38.3 +/- 3.8% as the number of passages was decreased from more than 20 to 13-15 passages, the latter percentage remaining lower, however, than that recorded in INS-I cells also examined after 13-15 passages but exposed to D-mannoheptulose hex...
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Tumoral pancreatic islet cells of either the RINm5F or INS-1 cell lines, when cultured in the presence of 30.0 mM D-glucose, accumulate about 50 times more glycogen than tumoral pancreatic acinar cells of the AR42J line cultured under the... more
Tumoral pancreatic islet cells of either the RINm5F or INS-1 cell lines, when cultured in the presence of 30.0 mM D-glucose, accumulate about 50 times more glycogen than tumoral pancreatic acinar cells of the AR42J line cultured under the same experimental conditions. Expressed per nl of intracellular water, the glycogen content of the RINm5F or INS-1 cells is even higher than that found in rat pancreatic islets also cultured under the same experimental conditions. Moreover, at variance with normal islet cells, tumoral islet cells do not require to be exposed to a high concentration of D-glucose to accumulate large amounts of glycogen. Based on these findings, it is proposed that the labelling of the glycogen pool, e.g. by 11C-labelled D-glucose or 2-deoxy-2-[18F]fluoro-D-glucose, may allow identification and localization of insulinomas in the pancreatic gland by a non-invasive imaging procedure.
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A novel insulin-secreting cell line, BRIN-BD11, was recently established following electrofusion of RINm5F cells with NEDH rat pancreatic islet cells. In the present study, D-glucose metabolism was compared in BRIN-BD11 and RINm5F cells.... more
A novel insulin-secreting cell line, BRIN-BD11, was recently established following electrofusion of RINm5F cells with NEDH rat pancreatic islet cells. In the present study, D-glucose metabolism was compared in BRIN-BD11 and RINm5F cells. The concentration dependency of D[5-3H]glucose utilization displayed a comparable pattern in the two cell lines, but the absolute values were lower in BRIN-BD11 than RINm5F cells. Except in the case of D-[1-14C]glucose, the ratio between 14C labeled D-glucose oxidation and D-[5-3H]glucose utilization was higher, however, in BRIN-BD11 than RINm5F cells. Moreover, BRIN-BD11 cells were less affected than RINm5F cells by a rise in D-glucose concentration, in terms of the inhibitory action of the hexose upon oxidative variables, such as oxidative glycolysis, pyruvate decarboxylation, and oxidation of glucose-derived acetyl residues in the Krebs cycle. The total energy yield from D-glucose catabolism appeared similar, however, in BRIN-BD11 and RINm5F cell...
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The adenosine analogue formycin A was recently introduced as a potent insulin secretagogue in normal pancreatic islet cells. In the present study, formycin A was found to inhibit insulin release and to exert a cytotoxic effect in tumor... more
The adenosine analogue formycin A was recently introduced as a potent insulin secretagogue in normal pancreatic islet cells. In the present study, formycin A was found to inhibit insulin release and to exert a cytotoxic effect in tumor islet cells of the RINm5F line. The latter effect was concentration-related in the 10-100 microM range of formycin A concentrations, not rapidly reversed, and not reproduced by adenosine. This study thus reveals that formycin A may display cytotoxic potential in the same range of concentrations in which it causes a progressive increase of glucose-stimulated insulin secretion in normal pancreatic islets.
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In several animal models of non-insulin-dependent diabetes, a decreased activity of FAD-linked glycerophosphate dehydrogenase was recently documented in pancreatic islet, but not liver, homogenates. The present study reveals that, on the... more
In several animal models of non-insulin-dependent diabetes, a decreased activity of FAD-linked glycerophosphate dehydrogenase was recently documented in pancreatic islet, but not liver, homogenates. The present study reveals that, on the contrary, the activity of the same mitochondrial enzyme is increased in islet, but not liver or spleen, homogenates of BB, as compared to BW, rats examined before the onset of severe hyperglycemia in this animal model of autoimmune insulin-dependent diabetes.
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The methyl esters of succinic acid were introduced a few years ago as new potent insulin secretagogues. In the present study, they were found to increase O2 uptake by rat islets incubated in the absence or presence of D-glucose; to... more
The methyl esters of succinic acid were introduced a few years ago as new potent insulin secretagogues. In the present study, they were found to increase O2 uptake by rat islets incubated in the absence or presence of D-glucose; to decrease 86Rb outflow from prelabeled islets; to stimulate biosynthetic activity in the islets, with a preferential effect on the synthesis of proinsulin; to inhibit 45Ca efflux from prelabeled islets perifused in the absence of extracellular Ca2+ but to augment 45Ca net uptake and to cause a biphasic stimulation of 45Ca outflow in islets incubated or perifused in the presence of extracellular Ca2+; and to evoke a biphasic stimulation of insulin release. The insulinotropic action of these methyl esters coincided with a shift to the left of the sigmoidal relationship between insulin output and D-glucose concentration, was concentration related in the 2-10 mM range, failed to be duplicated by succinic acid, displayed both Ca2+ dependency and resistance to a...
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Palmitate and oleate (0.5 to 1.0 mM) caused a time- and concentration-related augmentation of insulin release evoked by D-glucose (6.0 to 16.7 mM) in rat isolated pancreatic islets. This contrasted with an inhibitory action of the fatty... more
Palmitate and oleate (0.5 to 1.0 mM) caused a time- and concentration-related augmentation of insulin release evoked by D-glucose (6.0 to 16.7 mM) in rat isolated pancreatic islets. This contrasted with an inhibitory action of the fatty acids upon L-[4-3H]phenylalanine incorporation into TCA-precipitable material, but coincided with an increased biosynthesis of proinsulin relative to that of other islet peptides. The failure of palmitate to cause an immediate increase in insulin output at a low glucose concentration (6.0 mM) coincided with an unchanged rate of O2 uptake over a 10- to 15-min exposure to this fatty acid. Over prolonged incubation (90 min), however, both palmitate and oleate (1.0 mM) stimulated 45Ca net uptake by islets exposed to 6.0 mM D-glucose. Like their insulinotropic effect, the time course for the oxidation of [U-14C]palmitate and [U-14C]oleate was characterized by a progressive buildup in 14CO2 production rate. Moreover, palmitate and oleate decreased D-[5-3H]...
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Glutamic acid dimethyl ester (GME; 3.0-10.0 mM) enhanced insulin release evoked by 6.0-8.3 mM D-glucose, 1.0-10.0 mM L-leucine, or 5.0-10.0 mM 2-amino-bicyclo(2,2,1)heptane-2-carboxylic acid, causing a shift to the left of the sigmoidal... more
Glutamic acid dimethyl ester (GME; 3.0-10.0 mM) enhanced insulin release evoked by 6.0-8.3 mM D-glucose, 1.0-10.0 mM L-leucine, or 5.0-10.0 mM 2-amino-bicyclo(2,2,1)heptane-2-carboxylic acid, causing a shift to the left of the sigmoidal relationship between insulin output and D-glucose concentration. In the absence of D-glucose, GME also unmasked the insulinotropic potential of glibenclamide. In islets exposed to L-leucine, the insulinotropic action of GME coincided with an early fall and later increase in 86Rb outflow and augmentation of 45Ca outflow from prelabeled islets. The measurement of O2 uptake, NH4+ output, production of 14CO2 from islets prelabeled with [U-14C]palmitate, generation of 14C-labeled amino acids and 14CO2 from the dimethyl ester of either L-[1-14C]glutamic acid or L-[U-14C]glutamic acid, and D-[2-14C]glucose as well as D-[6-14C]glucose oxidation in the presence or absence of GME indicated that the latter ester was efficiently converted to L-glutamate and its ...
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The possible relevance of D-glucose phosphorylation by mitochondria-bound hexokinase to the control of respiration was examined in mitochondria prepared from either tumoral pancreatic islet cells (RINm5F line) or normal rat liver. In both... more
The possible relevance of D-glucose phosphorylation by mitochondria-bound hexokinase to the control of respiration was examined in mitochondria prepared from either tumoral pancreatic islet cells (RINm5F line) or normal rat liver. In both systems, ATP generated by mitochondria exposed to ADP and succinate could serve as a substrate for the phosphorylation of D-glucose. However, after exposure to exogenous ADP in the presence of succinate, only mitochondria isolated from RINm5F cells displayed a sizeable increase in O2 consumption in response to a subsequent administration of D-glucose. In this respect, the discrepancy between mitochondria from islet cells and liver, respectively, was found to be attributable to the much lower hexokinase activity, relative to respiratory rate, in liver than in RINm5F cell mitochondria. It is speculated that the coupling between hexose phosphorylation and respiration in islet cells may prime the mitochondria to generate ATP during the early metabolic ...
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Glucose-6-phosphatase activity was measured in rat liver or pancreatic islet crude homogenates and microsomes. The data recorded in the liver were comparable to those reported in prior studies. However, in the islets, the hydrolysis of... more
Glucose-6-phosphatase activity was measured in rat liver or pancreatic islet crude homogenates and microsomes. The data recorded in the liver were comparable to those reported in prior studies. However, in the islets, the hydrolysis of D-glucose 6-phosphate by disrupted microsomes represented, when expressed relative to the protein content, less than 2% of the value recorded in liver microsomes. Moreover, no phosphotransferase activity was detected in the islets. These findings impose reservation on both the presence of glucose-6-phosphatase in rat islets and its participation to stimulus-secretion coupling.
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Research Interests: Obesity, Mitochondria, Insulin Resistance, Blood Glucose, Diabetes mellitus, and 15 moreFemale, Animals, Male, Animal Model, Enzyme, Rats, Specific Activity, Type 2 Diabetes Mellitus, Experimental Diabetes Mellitus Type 1 and 2, Aspartate Aminotransferases, Glutamate Dehydrogenase, Biochemistry and cell biology, islets of Langerhans, Alanine Transaminase, and Pancreatic islets
Purified rat pancreatic insulin-producing B-cells, which display a 12-fold higher activity of FAD-linked glycerophosphate dehydrogenase than other islet endocrine cells, were exposed for 30 min to 2 mM streptozotocin and subsequently... more
Purified rat pancreatic insulin-producing B-cells, which display a 12-fold higher activity of FAD-linked glycerophosphate dehydrogenase than other islet endocrine cells, were exposed for 30 min to 2 mM streptozotocin and subsequently cultured for 2 days in the absence or presence of 2 mM nicotinamide. Streptozotocin decreased by 54% the number of B-cells and, in surviving cells, lowered by 75% the activity of FAD-linked glycerophosphate dehydrogenase, whilst failing to affect that of glutamate dehydrogenase. This coincided with a 42-51% reduction of insulin secretion, when expressed relative to either the DNA or hormonal content of surviving cells. After exposure to streptozotocin, the presence of nicotinamide in the culture medium reduced cell death by 44% and also reduced the deleterious effects of streptozotocin upon both the enzymic and secretory activities of surviving cells. These findings indicate that the decreased activity of FAD-linked glycerophosphate dehydrogenase previously documented in pancreatic islets from streptozotocin-injected rats, as well as the protective effect of nicotinamide thereupon, are not attributable solely to changes in the number of B-cells but also to an altered enzymic activity in surviving B-cells. The latter anomaly may account, in part at least, for an impaired B-cell secretory response to D-glucose.
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This study aimed to compare the metabolic and secretory responses of pancreatic islets from animals with non-insulin-dependent diabetes to d-glucose with the effects of the methyl esters of succinic acid (SME) and glutamic acid (GME). The... more
This study aimed to compare the metabolic and secretory responses of pancreatic islets from animals with non-insulin-dependent diabetes to d-glucose with the effects of the methyl esters of succinic acid (SME) and glutamic acid (GME). The insulin secretory response to d-glucose was impaired in islets from rats with diabetes which was either inherited (Goto—Kakizaki (GK) rats) or acquired (streptozotocin-treated (STZ) rats). This coincided with a preferential alteration of oxidative relative to total glycolysis in intact islets and a selective defect of FAD-linked mitochondrial glycerophosphate dehydrogenase (m-GDH) in islet homogenates. This enzymatic defect was also found in purified B cells from STZ rats. It contrasted both with unaltered activities of glutamate dehydrogenase and succinate dehydrogenase in the islets of diabetic animals and with a normal or even increased activity of m-GDH in the livers of GK and STZ rats. The oxidation of [1,4-14C]SME and [U-14C]GME appeared decr...
Research Interests: Molecular endocrinology, Glucose, Insulin, Liver, Animals, and 15 moreMale, Proteins, Clinical Sciences, Amino Acids, Rats, Wistar Rats, Veterinary Sciences, Type 2 Diabetes Mellitus, Experimental Diabetes Mellitus Type 1 and 2, Succinate Dehydrogenase, Glutamate Dehydrogenase, islets of Langerhans, Pancreatic islets, Paediatrics and reproductive medicine, and In Vitro Techniques
A preferential impairment of the pancreatic B cell secretory response to D-glucose occurs in adult rats injected with streptozotocin during the neonatal period. Three possible explanations for such a preferential defect were investigated... more
A preferential impairment of the pancreatic B cell secretory response to D-glucose occurs in adult rats injected with streptozotocin during the neonatal period. Three possible explanations for such a preferential defect were investigated in the present study. First, the time course for 3-O-methyl-D-glucose uptake by islets suggested that the anomaly in hexose transport was mainly attributable to a decrease in the space accessible to the D-glucose analog commensurate with the decrease in B cell mass, rather than to a delayed equilibration of hexose concentration across the B cell plasma membrane. Second, the activity of glucose-6-phosphatase was found to be equally low in islets from diabetic and control rats, ruling out the futile cycling between D-glucose and D-glucose 6-phosphate as a cause for the preferential alteration of the secretory response to the hexose. Third, the activity of flavine adenine dinucleotide-linked glycerophosphate dehydrogenase was found to be decreased to a greater relative extent than the B cell mass. This coincided with an impaired generation of 3HOH from L-[2-3H] glycerol in intact islets. It is proposed, therefore, that an altered circulation in the glycerol phosphate shuttle may play a major role in the impaired process of glucose-stimulated insulin release in this model of noninsulin-dependent diabetes.
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When cultured mouse pancreatic islets were exposed for 30 min to streptozotocin (STZ; 1.8 mM) and then maintained for 7 days in tissue culture, they displayed a decreased secretory response to D-glucose and an impairment of both... more
When cultured mouse pancreatic islets were exposed for 30 min to streptozotocin (STZ; 1.8 mM) and then maintained for 7 days in tissue culture, they displayed a decreased secretory response to D-glucose and an impairment of both FAD-linked glycerophosphate dehydrogenase and NAD-dependent 2-ketoglutarate dehydrogenase specific activities, with little change in either NAD-linked glycerophosphate dehydrogenase or glutamate dehydrogenase activity. The enzymatic defect was not reproduced by prolonged exposure of either rat islets to interleukin-1 (10 U/ml) or mouse islets to a high concentration of D-glucose (28 mM). In the former, but not latter, situation, the secretory response to D-glucose was again impaired. These findings reveal that STZ, but not all beta-cytotoxic agents, lowers the activity of selected islet mitochondrial dehydrogenases. Such enzymatic defects, especially the suppression of FAD-linked glycerophosphate dehydrogenase, may explain the preferential alteration of the B-cell metabolic and secretory responses to D-glucose, as previously observed in islets of adult rats injected with STZ during the neonatal period.
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In rats that received a low protein isocaloric diet (protein content of the diet: 8 instead of 20%) during fetal life and thereafter up to the time of sacrifice at 12-13 weeks of age, a low plasma insulin concentration, a decreased... more
In rats that received a low protein isocaloric diet (protein content of the diet: 8 instead of 20%) during fetal life and thereafter up to the time of sacrifice at 12-13 weeks of age, a low plasma insulin concentration, a decreased insulin content of isolated pancreatic islets, and an impaired secretory response of the islets to either D-glucose or the association of L-leucine and L-glutamine coincided, in islet homogenates, with a low activity of the mitochondrial glycerophosphate dehydrogenase and an abnormally high ratio between glutamate-alanine and glutamate-aspartate transaminase activities. Opposite enzymatic changes were found in liver extracts of the same rats. No obvious change in these hormonal, secretory, and enzymatic variables were observed when the period of protein deficiency was restricted to fetal life. These findings support the view that, in protein malnutrition, an impaired activity of pancreatic B-cell mitochondrial glycerophosphate dehydrogenase contributes, possibly in association with other enzymatic anomalies, to the perturbation of islet function.
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Islets were isolated by automatic digestion from non-diabetic cadaveric organ donors and from Type 2 (non-insulin-dependent) diabetic subjects. The activity of FAD-glycerophosphate dehydrogenase, but not that of either glutamate... more
Islets were isolated by automatic digestion from non-diabetic cadaveric organ donors and from Type 2 (non-insulin-dependent) diabetic subjects. The activity of FAD-glycerophosphate dehydrogenase, but not that of either glutamate dehydrogenase, glutamate-oxalacetate transaminase or glutamate-pyruvate transaminase, was lower in Type 2 diabetic patients than control subjects. Hexokinase, glucokinase and glutamate decarboxylase activities were also measured in islets from control subjects. The utilization of D-[5-3H]glucose, oxidation of D-[6-14C]glucose and release of insulin evoked by D-glucose were all lower in Type 2 diabetic patients than control subjects. The secretory response to the combination of L-leucine and L-glutamine appeared less severely affected. Islets from Type 2 diabetic patients may thus display enzymatic, metabolic and secretory anomalies similar to those often observed in animal models of Type 2 diabetes, including a deficiency of beta-cell FAD-linked glycerophosphate dehydrogenase, the key enzyme of the glycerol phosphate shuttle.
Research Interests: Adolescent, Humans, Glucose, Insulin, Insulin Secretion, and 15 moreGlucose Metabolism, Glucokinase, Female, Animal Model, Glycolysis, Enzyme, Clinical Sciences, Aged, Adult, Aspartate Aminotransferases, Glutamate Dehydrogenase, Glutamate decarboxylase, islets of Langerhans, Alanine Transaminase, and hexokinase
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In islets from adult rats injected with streptozocin during the neonatal period, the oxidative and secretory responses to D-glucose are more severely affected than those evoked by L-leucine. A possible explanation for such a preferential... more
In islets from adult rats injected with streptozocin during the neonatal period, the oxidative and secretory responses to D-glucose are more severely affected than those evoked by L-leucine. A possible explanation for such a preferential defect was sought by comparing the rate of aerobic glycolysis, taken as the sum of D-[3,4-14C]glucose conversion to labeled CO2, pyruvate, and amino acid, with the total glycolytic flux, as judged from the conversion of D-[5-3H]glucose to 3H2O. A preferential impairment of aerobic relative to total glycolysis was found in islets from diabetic rats incubated at either low or high D-glucose concentration. This coincided in islet mitochondria of diabetic rats with a severe decrease in both the basal (no-Ca2+) generation of 3H2O from L-[2-3H]glycerol-3-phosphate and the Ca2(+)-induced increment in [3H]glycerophosphate detritiation. The mitochondria of diabetic rats were also less efficient than those of control animals in generating 14CO2 from [1-14C]-2-ketoglutarate. The diabetes-induced alteration of 2-ketoglutarate dehydrogenase in islet mitochondria was less marked, however, than that of the FAD-linked glycerophosphate dehydrogenase and was not associated with any change in responsiveness to Ca2+. Sonicated islet mitochondria of diabetic rats displayed normal to slightly elevated glutamate dehydrogenase activity. We propose, therefore, that the preferential impairment of the oxidative and secretory responses of islet cells to D-glucose in this experimental model of diabetes may be at least partly attributable to an altered transfer of reducing equivalents into the mitochondria as mediated by the glycerol phosphate shuttle.
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Research Interests: Adipose tissue, Humans, Insulin, Liver, Animals, and 15 moreMuscles, Proteins, Adiponectin, Rats, Lipoproteins, Wistar Rats, Species Specificity, Free Fatty Acid, Type 2 Diabetes Mellitus, Biochemistry and cell biology, islets of Langerhans, Interleukin, Pancreatic islets, Lipoprotein Lipase, and Medical biochemistry and metabolomics
In rat liver slices incubated in the absence of exogenous D-glucose, both the basal and glucagon-stimulated output of D-glucose resulted in the production of a greater relative amount of alpha-D-glucose than that found at anomeric... more
In rat liver slices incubated in the absence of exogenous D-glucose, both the basal and glucagon-stimulated output of D-glucose resulted in the production of a greater relative amount of alpha-D-glucose than that found at anomeric equilibrium. Comparable results were obtained in isolated hepatocytes. In these experiments, the rate of glycogenolysis largely exceeded that of glycogen synthesis. These findings indicate that liver glycogenolysis represents an alpha-stereospecific process.