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D Pipeleers

Publications and source records attributed to D Pipeleers.

At least 37 records · Page 2Linked to original sources
PubMed1999

Nicotinamide protects human beta cells against chemically-induced necrosis, but not against cytokine-induced apoptosis.

Nicotinamide intervention trials are presently undertaken to prevent Type I (insulin-dependent) diabetes in high risk subjects. They are based on studies in rodents reporting nicotinamide protection against beta-cell injury in vitro and in vivo. This study examines whether nicotinamide can protect human beta cells in vitro. At concentrations (2 and 5 mmol/l) to protect rat beta cells against necrosis by streptozotocin or hydrogen peroxide, nicotinamide prevents hydrogen peroxide-induced necrosis of human beta cells. As with rat beta cells, nicotinamide fails to protect human beta cells against apoptosis induced by a combination of the cytokines interleukin-1beta, interferon-gamma and tumour necrosis factor-alpha. In rat beta cells, nicotinamide (2 to 20 mmol/l) was also found to induce apoptosis, in particular during the days following its protection against necrosis; this cytotoxic effect was not observed with human beta cells. These data demonstrate that nicotinamide can protect human beta cells against radical-induced necrosis, but not against cytokine-induced apoptosis. This effect is not associated with a delayed apoptosis as in rat beta cells.

Animals↗
PubMed1999

Prolonged exposure of pancreatic beta cells to raised glucose concentrations results in increased cellular content of islet amyloid polypeptide precursors.

Most non-insulin dependent diabetic patients have amyloid deposits in their pancreatic islets. It is not known whether chronic hyperglycaemia contributes to the formation of amyloid fibrils from the islet amyloid polypeptide that is produced by the pancreatic beta cells. Since islet amyloid exhibits islet amyloid polypeptide precursors immunoreactivity, we examined whether sustained in vitro exposure to raised glucose increases the abundance of these precursors in human beta cells. After 6 days stimulation with 20 mmol/l glucose the cellular content of insulin but not islet amyloid polypeptide was decreased leading to an increase in the ratio of the latter over insulin (3.0 +/- 0.6 vs 1.8 +/- 0.3 after 6 mmol/l glucose culture, p < 0.05). Similar changes occurred in rat beta cells cultured for 3 days in the presence of 20 mmol/l glucose plus 3-isobutyl-1-methylxanthine. Western blot analysis of cellular islet amyloid polypeptide after prolonged exposure to high glucose indicated the presence of higher proportions of its precursor- and intermediate forms. In human beta cells cultured in 20 mmol/l glucose, the major form corresponds to an intermediate species which exhibits an immunoreactivity for the N-flanking peptide, as is also the case in islet amyloid. We concluded that prolonged in vitro exposure of beta cells to raised glucose concentrations increases the relative proportion of islet amyloid polypeptide over insulin, as well as of its precursors over the mature form of islet amyloid polypeptide.

1-Methyl-3-isobutylxanthine↗
PubMed1999

Regulation of tumor necrosis factor-induced, mitochondria- and reactive oxygen species-dependent cell death by the electron flux through the electron transport chain complex I.

Tumor necrosis factor (TNF) induces a caspase-independent but mitochondria-dependent cell death process in the mouse fibrosarcoma cell line L929. Mitochondria actively participate in this TNF-induced necrotic cell death by the generation of mitochondrial reactive oxygen species (ROS). The aim of this study was to identify the mitochondrial components involved in TNF-induced production of ROS and their regulation by bioenergetic pathways. Therefore, we analyzed the bioenergetic characteristics in two metabolic L929 variants that exhibit different sensitivities to TNF. L929gln cells use glutamine as respiratory substrate and are far more susceptible to TNF-induced ROS generation and cell death as L929glc cells that use glucose as respiratory substrate. We show that the higher levels of reducing NAD(P)H equivalents, detected in the desensitized L929glc cells, do not cause diminished ROS generation. To the contrary, TNF increases the levels of NAD(P)H, probably altering complex I activity. A multiparameter analysis of electron flux through the mitochondrial electron transport chain, TNF-induced ROS levels, and cell death convincingly demonstrates a dependence of TNF signaling on complex I activity. Also, the sensitizing effect of glutamine metabolism correlates with an enhanced contribution of complex I to the overall electron flux. This participation of complex I activity in TNF-induced cell death is regulated by substrate availability rather than by a direct modification of complex I proteins. From the results presented in this paper we conclude that TNF-induced ROS generation and cell death are strongly regulated by bioenergetic pathways that define electron flux through complex I of the electron transport chain.

Animals↗
PubMed1999

Prolonged exposure of human beta-cells to high glucose increases their release of proinsulin during acute stimulation with glucose or arginine.

The disproportionate hyperproinsulinemia in type 2 diabetes has been attributed to either a primary beta-cell defect or a secondary dysregulation of beta cells under sustained hyperglycemia. This study examines the effect of a 10- to 13-day exposure to 20 mmol/L glucose on subsequent proinsulin and insulin release by human islets isolated from nondiabetic donors. Compared to control preparations kept at 6 mmol/L glucose, the high glucose cultured beta-cells released more proinsulin and less insulin during perifusion at 5, 10, or 20 mmol/L glucose. The lower amounts of secreted insulin resulted from a marked reduction in cellular insulin content (5-fold lower than in controls). The higher amount of secreted proinsulin is attributed to the sustained state of cellular activation that is known to occur after prolonged exposure to high glucose levels. This activated state of the beta-cell population is also held responsible for its higher secretory responsiveness to 5 mmol/L arginine at a submaximal (5 mmol/L) glucose concentration (8-fold higher proinsulin levels than in the control population). It results, together with the reduction in cellular insulin content, in 7- to 10-fold higher proinsulin over insulin ratios in the medium; at 5 mmol/L glucose, this extracellular ratio is similar to that in the cells. These data add direct support to the view that a disproportionate hyperproinsulinemia can result from a sustained activation of human beta-cells after prolonged exposure to elevated glucose levels.

Arginine↗
PubMed1999

Contribution of ductal cells to cytokine responses by human pancreatic islets.

In type 1 diabetes, autoimmune destruction of pancreatic beta-cells has been attributed to cytokines released from infiltrating immunocytes. Exposure of isolated islets to cytokines leads to nitric oxide (NO) production, which can damage beta-cells. Because ductal cells are closely associated with human beta-cells, we examined whether they can contribute to this process. Isolated human ductal cells were cultured for 48 h with various cytokines. The combination of interleukin-1beta (IL-1beta) plus interferon-gamma (IFN-gamma) increased nitric oxide production 12-fold while stimulating mRNA expression of inducible nitric oxide synthase (iNOS). In this condition, 10-20% of cells positive for the cytokeratin-19 duct marker also stained positive for iNOS protein, whereas no positive cells were found in control preparations. Comparison of the magnitude of iNOS mRNA expression and nitric oxide production in these cells with that in isolated human islets suggests that >50% of total islet nitric oxide production might originate from associated ductal cells. It is concluded that ductal cells are a potential source of nitric oxide production in human islets infiltrated by cytokine-releasing immunocytes.

Adolescent↗
PubMed1999

Auto- and alloimmune reactivity to human islet allografts transplanted into type 1 diabetic patients.

Allogeneic islet transplantation can restore an insulin-independent state in C-peptide-negative type 1 diabetic patients. We recently reported three cases of surviving islet allografts that were implanted in type 1 diabetic patients under maintenance immune suppression for a previous kidney graft. The present study compares islet graft-specific cellular auto- and alloreactivity in peripheral blood from those three recipients and from four patients with failing islet allografts measured over a period of 6 months after portal islet implantation. The three cases that remained C-peptide-positive for >1 year exhibited no signs of alloreactivity, and their autoreactivity to islet autoantigens was only marginally increased. In contrast, rapid failure (<3 weeks) in three other cases was accompanied by increases in precursor frequencies of graft-specific alloreactive T-cells; in one of them, the alloreactivity was preceded by a sharply increased autoreactivity to several islet autoantigens. One recipient had a delayed loss of islet graft function (33 weeks); he did not exhibit signs of graft-specific alloimmunity, but developed a delayed increase in autoreactivity. The parallel between metabolic outcome of human beta-cell allografts and cellular auto- and alloreactivity in peripheral blood suggests a causal relationship. The present study therefore demonstrates that T-cell reactivities in peripheral blood can be used to monitor immune mechanisms, which influence survival of beta-cell allografts in diabetic patients.

Adult↗
PubMed1998

The changes in adenine nucleotides measured in glucose-stimulated rodent islets occur in beta cells but not in alpha cells and are also observed in human islets.

Glucose metabolism by pancreatic beta and alpha cells is essential for stimulation of insulin secretion and inhibition of glucagon secretion. Studies using rodent islets have suggested that the ATP/ADP ratio serves as second messenger in beta cells. This study compared the effects of glucose on glucose oxidation ([U-14C]glucose) and adenine nucleotides (luminometric method) in purified rat alpha and beta cells. The rate of glucose oxidation at 1 mM glucose was higher in beta than alpha cells (4.5-fold, i.e. approximately 2-fold after normalization for cell size). It was more strongly stimulated by 10 mM glucose in beta cells (9-fold) than in alpha cells (5-fold). At 1 mM glucose, ATP levels were similar in both cell types, which corresponds to an approximately 2-fold higher concentration in alpha cells ( approximately 6.5 mM) than in beta cells ( approximately 3 mM). In beta cells, glucose dose-dependently increased ATP and decreased ADP levels, causing a rise in the ATP/ADP ratio from 2.4 to 11.6 at 1 and 10 mM, respectively. In alpha cells, glucose did not affect ATP and ADP levels, and the ATP/ADP ratio remained stable around 7.5. In human islets, the ATP/ADP ratio progressively increased between 1 and 10 mM glucose. In duct cells, which often contaminate human islet preparations, an increase in the ATP/ADP ratio sometimes occurred between 1 and 3 mM glucose. In conclusion, the present observations establish that the regulation of glucagon secretion by glucose does not involve changes in alpha cell adenine nucleotides and further support the role of the ATP/ADP ratio in the control of insulin secretion.

Adenosine Diphosphate↗
PubMed1998

Differential expression of rat insulin I and II messenger ribonucleic acid after prolonged exposure of islet beta-cells to elevated glucose levels.

Prolonged exposure of rat islet beta-cells to 10 mmol/liter glucose has been previously shown to activate more cells into a glucose-responsive state (>90%) than has exposure to 6 mmol/liter glucose (50%). The present study demonstrates that this recruitment of more activated cells results in 4- to 6-fold higher levels of proinsulin I and proinsulin II messenger RNA (mRNA). However, only the rate of proinsulin I synthesis is increased. Failure to increase the rate of proinsulin II synthesis in the glucose-activated cells results in cellular depletion of the insulin II isoform, which can be responsible for degranulation of beta-cells cultured at 10 mmol/liter glucose. Higher glucose levels (20 mmol/liter) during culture did not correct this dissociation between the stimulated insulin I formation and the nonstimulated insulin II formation. On the contrary, the rise from 10 to 20 mmol/liter glucose resulted in a 2-fold reduction in the levels of proinsulin II mRNA, but not of proinsulin I mRNA; this process further increased the ratio of insulin I over insulin II to 5-fold higher values than those in freshly isolated beta-cells. The present data suggest that an elevated insulin I over insulin II ratio in pancreatic tissue is a marker for a prolonged exposure to elevated glucose levels. The increased ratio in this condition results from a transcriptional and/or a posttranscriptional failure in elevating insulin II formation while insulin I production is stimulated in the glucose-activated beta-cells.

Animals↗
PubMed1998

Effect of glucose on production and release of proinsulin conversion products by cultured human islets.

Isolated human islets were examined for the rates of conversion and release of newly formed (pro)insulin-like peptides. The rate of proinsulin (PI) conversion was 2-fold slower in human beta-cells (t(1/2) = 50 min) than in rat beta-cells (t(1/2) = 25 min). During the first hour following labeling of newly synthesized proteins, PI represented the main newly formed hormonal peptide in the medium; its release was stimulated 2-fold over the basal level by 20 mmol/L glucose. During the second hour, newly synthesized hormone was mainly released as insulin, with 10- to 20-fold higher rates at 20 mmol/L glucose. Prolonged preculture of the islets at 20 mmol/L glucose did not delay PI conversion, but markedly increased the release of newly formed PI, des(31,32)-PI, and insulin at both low and high glucose levels. Our data demonstrate that 1) the release of PI provides an extracellular index for the hormone biosynthetic activity of human beta-cells; 2) an acute rise in glucose exerts a stronger amplification of the release of converted hormone than in that of nonconverted hormone; and 3) prolonged exposure to high glucose levels results in an elevated basal release of converted and nonconverted PI; this elevation is not associated with a delay in PI conversion, but is attributed to the hyperactivated state of the human beta-cell population, which was recently found to be responsible for an elevation in basal rates of hormone synthesis. These in vitro observations on human beta-cells provide a possible explanation for the altered circulating (pro)insulin levels measured in nondiabetic and noninsulin-dependent diabetic subjects.

Animals↗
PubMed1998

Dual glucagon recognition by pancreatic beta-cells via glucagon and glucagon-like peptide 1 receptors.

cAMP is required for normal glucose-induced insulin release by pancreatic beta-cells. In a previous study, we showed that cAMP production in beta-cells depends on the expression of receptors for glucagon, glucagon-like peptide 1(7-36) amide [GLP-1(7-36) amide], and glucose-dependent insulinotropic polypeptide. Although the latter two peptides are thought to amplify meal-induced insulin release (incretin effect), the role of glucagon in the regulation of insulin release remains elusive. In the present study, we analyzed the interaction of glucagon with its own receptor and with the glucagon-like peptide 1 (GLP-1) receptor using purified rat beta-cells. Glucagon binding was partially displaced by 1 micromol/l des-His1-[Glu9]glucagon-amide, a glucagon receptor antagonist, and by 1 micromol/l GLP-1. Conversely, GLP-1 binding was competitively inhibited by high glucagon concentrations (Ki = 0.3 micromol/l). Glucagon-induced cAMP production in beta-cells was inhibited both by 1 micromol/l des-His1-[Glu9]glucagon-amide and exendin-(9-39)-amide, a specific GLP-1 receptor antagonist, whereas GLP-1-induced cAMP formation was suppressed only by exendin-(9-39)-amide. Finally, addition of 1 micromol/l exendin-(9-39)-amide to 20 mmol/l glucose-stimulated beta-cells did not antagonize the potentiating effect of 1 nmol/l glucagon, although it prevented 45% of glucagon potentiation when the peptide was administered at 10 nmol/l. Our data suggest that glucagon recognition via two distinct receptors allows pancreatic beta-cells to detect this peptide both when diluted in the systemic circulation and when concentrated as local signal in the islet interstitium.

Animals↗
PubMed1998

Mouse pancreatic beta-cells exhibit preserved glucose competence after disruption of the glucagon-like peptide-1 receptor gene.

Previous work suggested that glucagon-like peptide 1 (GLP-1) can acutely regulate insulin secretion in two ways, 1) by acting as an incretin, causing amplification of glucose-induced insulin release when glucose is given orally as opposed to intravenous glucose injection; and 2) by keeping the beta-cell population in a glucose-competent state. The observation that mice with homozygous disruption of the GLP-1 receptor gene are diabetic with a diminished incretin response to glucose underlines the first function in vivo. Isolated islets of Langerhans from GLP-1 receptor -/- mice were studied to assess the second function in vitro. Absence of pancreatic GLP-1 receptor function was observed in GLP-1 receptor -/- mice, as exemplified by loss of [125I]GLP-1 binding to pancreatic islets in situ and by the lack of GLP-1 potentiation of glucose-induced insulin secretion from perifused islets. Acute glucose competence of the beta-cells, assessed by perifusing islets with stepwise increases of the medium glucose concentration, was well preserved in GLP-1 receptor -/- islets in terms of insulin secretion. Furthermore, neither islet nor total pancreatic insulin content was significantly changed in the GLP-1 receptor -/- mice when compared with age-and sex-matched controls. In conclusion, mouse islets exhibit preserved insulin storage capacity and glucose-dependent insulin secretion despite the loss of functional GLP-1 receptors. The results demonstrate that the glucose responsiveness of islet beta-cells is well preserved in the absence of GLP-1 receptor signaling.

Animals↗
PubMed1997

Metabolic fate of glucose in purified islet cells. Glucose-regulated anaplerosis in beta cells.

Previous studies in rat islets have suggested that anaplerosis plays an important role in the regulation of pancreatic beta cell function and growth. However, the relative contribution of islet beta cells versus non-beta cells to glucose-regulated anaplerosis is not known. Furthermore, the fate of glucose carbon entering the Krebs cycle of islet cells remains to be determined. The present study has examined the anaplerosis of glucose carbon in purified rat beta cells using specific 14C-labeled glucose tracers. Between 5 and 20 mM glucose, the oxidative production of CO2 from [3,4-14C]glucose represented close to 100% of the total glucose utilization by the cells. Anaplerosis, quantified as the difference between 14CO2 production from [3,4-14C]glucose and [6-14C]glucose, was strongly influenced by glucose, particularly between 5 and 10 mM. The dose dependence of glucose-induced insulin secretion correlated with the accumulation of citrate and malate in beta(INS-1) cells. All glucose carbon that was not oxidized to CO2 was recovered from the cells after extraction in trichloroacetic acid. This indirectly indicates that lactate output is minimal in beta cells. From the effect of cycloheximide upon the incorporation of 14C-glucose into the acid-precipitable fraction, it could be calculated that 25% of glucose carbon entering the Krebs cycle via anaplerosis is channeled into protein synthesis. In contrast, non-beta cells (approximately 80% glucagon-producing alpha cells) exhibited rates of glucose oxidation that were (1)/(3) to (1)/(6) those of the total glucose utilization and no detectable anaplerosis from glucose carbon. This difference between the two cell types was associated with a 7-fold higher expression of the anaplerotic enzyme pyruvate carboxylase in beta cells, as well as a 4-fold lower ratio of lactate dehydrogenase to FAD-linked glycerol phosphate dehydrogenase in beta cells versus alpha cells. Finally, glucose caused a dose-dependent suppression of the activity of the pentose phosphate pathway in beta cells. In conclusion, rat beta cells metabolize glucose essentially via aerobic glycolysis, whereas glycolysis in alpha cells is largely anaerobic. The results support the view that anaplerosis is an essential pathway implicated in beta cell activation by glucose.

Animals↗
PubMed1997

Length of metabolic normalization after rat islet cell transplantation depends on endocrine cell composition of graft and on donor age.

In vitro studies have demonstrated that beta-cell functions are negatively influenced by age and positively by the presence of glucagon producing alpha cells. This study examines whether the function of beta-cell grafts varies with the age of the donor and with the presence of other endocrine islet cells. Islet beta and endocrine non-beta-cells were purified from 10- to 30-week-old Lewis rats, and reaggregated into pure beta and mixed endocrine cell aggregates. Grafts consisted of 1.2 to 1.7 million beta cells with or without 0.6-0.7 million alpha cells. Their intraportal transplantation in 10-week-old streptozotocin-diabetic rats corrected hyperglycaemia in all experimental groups, with normal glucose tolerance curves at post-transplantation week (PT wk) 4. Recipients of mixed endocrine cell grafts from 10-week-old donors maintained a glucose tolerant state until PT wk 20, but turned glucose intolerant thereafter; only 1 of 12 animals was overtly diabetic at PT wk 64. Recipients of pure beta-cell grafts from 10-week-old donors became glucose-intolerant from PT wk 4 on, with 5 of 11 cases developing overt diabetes before PT wk 64. When grafts were prepared from 30-week-old donors, metabolic deterioration started earlier, again with a more rapid loss for pure beta-cell grafts; at PT wk 64, virtually all recipients were overtly diabetic. It is concluded that delayed graft failure can be the consequence of an insufficient number of islet endocrine non-beta-cells as well as of a higher donor age. This observation can explain late failures in animal and human islet transplantation using marginally low beta-cell numbers. The interpretation of long-term studies on islet cell transplantation can benefit from the use of standardized grafts with well defined cellular composition.

Age Factors↗
PubMed1997

Nutrient regulation of gamma-aminobutyric acid release from islet beta cells.

Glutamate decarboxylase (GAD) of pancreatic beta cells seems to be involved in the development of autoimmune reactivities which occur in insulin-dependent diabetes mellitus. Little is known about the regulation and role of the GAD activity in normal beta cells. In the betaTC6 line, the enzymatic product, gamma-aminobutyric acid (GABA) was reported to be released under glucose stimulation, thus supporting the concept that GABA transmits a suppressive action of glucose-stimulated beta cells on neighbouring alpha cells. In this study GABA was found to be released from normal rat beta cells. Over 24-h culture periods, the released amounts represented a constant fraction (25% per h) of the cellular GABA content. Cellular GABA content and release were dose-dependently increased by the glutamine concentration in the medium; both values decreased following a sustained (24 h) glucose activation (culture at 10 or 20 mmol/l glucose instead of 3 mmol/l). The variations in the medium GABA content did not parallel the changes in insulin release, indicating that both beta-cell secretory products follow different routes of storage and release. We suggest that beta cells can discharge GABA via exocytosis of microvesicles storing GABA as well as via direct transport from the cytoplasmic pool of newly formed product. Variations in GABA production result in parallel changes in extracellular GABA concentration; the high fractional release of GABA makes it also a likely parameter of the cellular GAD activity. Since chronically elevated glucose levels result in a reduced GABA discharge from the beta cells, it is conceivable that the subsequent decrease in GABA-mediated suppression of the alpha cells is responsible for a higher glucagon release, as observed in diabetes.

Acetylcholine↗
PubMed1997

Proinsulin and its conversion intermediates in human pancreas and isolated islet tissue: kinetics and steady-state analysis.

In non-insulin-dependent diabetes, circulating insulin-related immunoreactivity (IRI) is often composed of a higher fraction of the incompletely converted forms proinsulin and des-31,32 proinsulin. The present study describes an immunoadsorption method for measuring the proportions of proinsulin, its two split products, and insulin in human pancreatic tissue and for determining their rates of formation in human isolated islets. The method uses two junction-specific monoclonal proinsulin antibodies in a protein G fractionation; it is validated by > or = 90% specificity and recovery. The peptide contents measured in tissue extracts were comparable to those determined in a previously developed immunoradiometric assay. In the nine tissue extracts from nondiabetic donor organs, 97% of IRI corresponded to insulin, 1% to proinsulin, 2% to the des-31,32 proinsulin conversion product, and 0.1% to des-64,65 proinsulin. Two samples from non-insulin-dependent diabetics under sulfonylurea treatment contained a fourfold lower content of IRI but the peptide distribution was comparable except for a low percentage (0.3) of proinsulin in one case. In pulse-chase experiments on three-preparations of human islets isolated from nondiabetic donors, proinsulin represented the major (> 90%) IRI that was synthesized at the end of the 30-min pulse; a subsequent 90-min chase at either 2.5 or 10 mM glucose resulted in conversion of 75% of proinsulin to des-31,32 (20%) and des-64,65 (2%) intermediates and to insulin (50%); after a 180-min chase, 88% of proinsulin was converted to insulin, but 10% remained present as proinsulin. In a pulse-chase experiment on islets isolated from tissue with a high proportion of des-31,32 intermediate (5% instead of 2%), the conversion process was slower (45% after 90 min and 70% after 180 min) and resulted in a higher fraction of des-31,32 intermediate, suggesting that the elevated tissue content in this intermediate is caused by a reduced PC2 converting activity. These data confirm that des-31,32 proinsulin represents the major conversion intermediate in normal human islets and indicate the existence of slow converters, possibly as a result of decreased enzymatic processing of the prohormone's AC junction.

Adolescent↗
PubMed1997

Effect of interferon-gamma and glucose on major histocompatibility complex class I and class II expression by pancreatic beta- and non-beta-cells.

Surface major histocompatibility complex (MHC) class I and class II expression by pancreatic islet cells is considered a local initiator or regulator of immune processes that can lead to diabetes. Locally released cytokines, in particular interferon-gamma, are known to stimulate MHC antigen expression by islet cells. The present study quantifies MHC expression in cultured pancreatic beta- and non-beta-cells from both rat and human organs. Interferon-gamma increased MHC class I expression in endocrine beta- and non-beta-cells as well as in pancreatic ductal cells. The cytokine induced a 6-fold increase in the MHC class I messenger ribonucleic acid levels in pancreatic beta-cells; this effect was 2-fold amplified in the presence of elevated glucose levels (20 mmol/L instead of 6 mmol/L). No MHC class II expression was observed in endocrine beta- or non-beta-cells; human, but not rat, ductal cells exhibited MHC class II expression that increased in the presence of interferon-gamma. These data indicate that the increase in beta-cell MHC class I expression described in the pancreata of diabetic patients may result from stimulated transcription after exposure to locally released interferon-gamma and/or to a hyperglycemic state. The association of human islets with ductal cells in which MHC class II expression is stimulated by interferon-gamma makes these cells potential participants in the autoimmune process in diabetes.

Adolescent↗
PubMed1996

Damaged rat beta cells discharge glutamate decarboxylase in the extracellular medium.

In type I (insulin-dependent) diabetes, destruction of pancreatic beta cells has been associated with the presence of circulating antibodies against glutamate decarboxylase (GAD), a GABA (gamma-aminobutyric acid) synthesizing enzyme which is located in the beta cells. We examined whether destruction of islet beta cells can lead to discharge of GAD in the extracellular medium, making it a potential autoantigen. Rat islet beta cells were first exposed for 1 hour to streptozotocin and then cultured for 4 to 24 hours before cellular and medium GAD activities were measured. After 24 hours culture, 70 percent of streptozotocin-treated beta cells were disintegrated whereas the number of control cells remained unchanged. Control cells exhibited a stable cellular GAD activity over the 24 hour period with no enzyme activity detectable in their culture medium. The cells recovered 24 hours after streptozotocin treatment exhibited 10-fold lower levels of GAD-activity and of GABA; their culture medium contained GAD, its enzymatic activity reaching peak values after 10 hours. The beta-cell enzymes glutamate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase were not detectable in the medium of control or streptozotocin-treated cells. Similar observations were made when beta cells had been exposed to cytotoxic concentrations of alloxan. It is concluded that damage to rat islet beta cells results in transient discharge of GAD in the extracellular medium making this enzyme a candidate extracellular marker for beta cell toxic processes and a potential autoantigen for immune reactivity.

Animals↗