Beta Cell Toxicity Research Articles

Streptozotocin-resistant BRIN-BD11 cells possess wide spectrum of toxin tolerance and enhanced insulin-secretory capacity

Since streptozotocin (STZ) exhibits beta-cell toxicity, mediated through diverse mechanisms, multiple toxin resistance can be expected in insulin-secretory cells rendered STZ-resistant. RINm5F, but not all cell lines surviving STZ treatment, possess higher insulin content than native parental cells and additional tolerance against alloxan. To understand the impact of STZ tolerant cell selection on toxin resistance and insulin-secretory function, STZ-resistant BRIN-BD11 cells were generated by iterative acute exposure to 20 mM STZ. These cells, denoted BRINst cells, exhibited resistance to toxic challenges from STZ, H(2)O(2), and ninhydrin. Insulin content and both glucose and arginine-stimulated insulin secretion were significantly enhanced in BRINst cells. The toxin-resistance of BRINst cells was gradually lost during continuous cultivation without STZ challenge. However, enhanced insulin secretory capacity at high passage in BRINst cells persisted. Although total SOD activity was decreased, catalase activity was increased and appeared to be important for the ninhydrin and STZ resistance of BRINst cells. This was associated with reductions of both STZ- and ninhydrin-induced DNA damage, although DNA repair was abolished. Further characterization of cells exhibiting multiple toxin tolerance and an enhanced insulin secretory function could provide useful lessons for understanding of beta-cell survival.

Inhibition of histone deacetylases prevents cytokine-induced toxicity in beta cells

The immune-mediated elimination of pancreatic beta cells in type 1 diabetes involves release of cytotoxic cytokines such as IL-1beta and IFNgamma, which induce beta cell death in vitro by mechanisms that are both dependent and independent of nitric oxide (NO). Nuclear factor kappa B (NFkappaB) is a critical signalling molecule in inflammation and is required for expression of the gene encoding inducible NO synthase (iNOS) and of pro-apoptotic genes. NFkappaB has recently been shown to associate with chromatin-modifying enzymes histone acetyltransferases and histone deacetylases (HDAC), and positive effects of HDAC inhibition have been obtained in several inflammatory diseases. Thus, the aim of this study was to investigate whether HDAC inhibition protects beta cells against cytokine-induced toxicity. The beta cell line, INS-1, or intact rat islets were precultured with HDAC inhibitors suberoylanilide hydroxamic acid or trichostatin A in the absence or presence of IL-1beta and IFNgamma. Effects on insulin secretion and NO formation were measured by ELISA and Griess reagent, respectively. iNOS levels and NFkappaB activity were measured by immunoblotting and by immunoblotting combined with electrophoretic mobility shift assay, respectively. Viability was analysed by 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and apoptosis by terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay and histone-DNA complex ELISA. HDAC inhibition reduced cytokine-mediated decrease in insulin secretion and increase in iNOS levels, NO formation and apoptosis. IL-1beta induced a bi-phasic phosphorylation of inhibitor protein kappa Balpha (IkappaBalpha) with the 2nd peak being sensitive to HDAC inhibition. No effect was seen on IkappaBalpha degradation and NFkappaB DNA binding. HDAC inhibition prevents cytokine-induced beta cell apoptosis and impaired beta cell function associated with a downregulation of NFkappaB transactivating activity.

P35/Cyclin-dependent kinase 5 is required for protection against β-amyloid-induced cell death but not tau phosphorylation by ceramide

Ceramide is a bioactive sphingolipid that can prevent calpain activation and beta-amyloid (A beta) neurotoxicity in cortical neurons. Recent evidence supports A beta induction of a calpain-dependent cleavage of the cyclin-dependent kinase 5 (cdk5) regulatory protein p35 that contributes to tau hyperphosphorylation and neuronal death. Using cortical neurons isolated from wild-type and p35 knockout mice, we investigated whether ceramide required p35/cdk5 to protect against A beta-induced cell death and tau phosphorylation. Ceramide inhibited A beta-induced calpain activation and cdk5 activity in wild-type neurons and protected against neuronal death and tau hyperphosphorylation. Interestingly, A beta also increased cdk5 activity in p35-/- neurons, suggesting that the alternate cdk5 regulatory protein, p39, might mediate this effect. In p35 null neurons, ceramide blocked A beta-induced calpain activation but did not inhibit cdk5 activity or cell death. However, ceramide blocked tau hyperphosphorylation potentially via inhibition of glycogen synthase kinase-3beta. These data suggest that ceramide can regulate A beta cell toxicity in a p35/cdk5-dependent manner.

Perfil favorable de glucohemoglobina y lípidos plasmáticos en niños trasplantados renales tratados con basiliximab, tacrolimus, ácido micofenólico y esteroides en dosis decrecientes

Introduction The use of tacrolimus in pediatric kidney transplantation carries a risk of pancreatic beta cell toxicity. Close monitoring of tacrolimus levels in blood, glycosylated hemoglobin levels and lipid metabolism may increase safety. Objetive The aim of the present study was to report our experience of pancreatic toxicity and lipid metabolism over a 2-year period. Patients and methods Thirty one pediatric kidney transplant recipients treated with basiliximab, tacrolimus, mycophenolate and steroids at tapered doses. They were 18 boys and 13 girls (mean age, 9 ± 8 years), who underwent cadaveric kidney transplantation (mean age, 11 ± 9 years). Results Basiliximab was administered on post-transplant days 0 and 4, and tacrolimus was administered orally with- in the first 24 hours of transplantation (0,15 mg/kg/day) to achieve levels of between 6 and 10 μg/ml. When higher levels were achieved, the dose was reduced. Steroid dose was progressively tapered and the drug was discontinued within the first year. Glycosylated hemoglobin, cholesterol and triglyceride levels were maintained at normal values throughout the study. Conclusions Our experience suggests that the use of tacrolimus in pediatric kidney transplant recipients is safe from the point of view of pancreatic toxicity and cardiovascular morbidity if glycosylated hemoglobin levels and lipid metabolism are monitored. Palabras clave : Trasplante renal ; Terapia ; Glucohemoglobina ; Lípidos ; Inmunosupresión

HLA Class I Epitope Discovery in Type 1 Diabetes

Islet autoreactive CD8 T cells are plausible candidates for direct beta cell toxicity in type 1 diabetes (T1DM). In 2005, cellular studies in the pathogenesis of this disease have reached a new milestone. Autoreactive CD8 T cells have been defined and several target islet epitopes of these have been discovered and validated simultaneously in three independent studies. The insulin B10-B18 peptide that displays exceptional binding affinity for HLA-A2 has been reported in all three studies, and its recognition shows an association with autoimmune beta cell destruction and T1DM. These studies imply that CD8 T cell-based HLA tetramers and ELISPOT analyses can be useful to monitor T1DM as well as islet transplantation, and may provide useful tools to assess immunological efficacy of immune intervention trials.

Interleukin-17 stimulates inducible nitric oxide synthase-dependent toxicity in mouse beta cells.

The influence of the proinflammatory cytokine interleukin (IL)-17 on inducible nitric oxide (NO) synthase (iNOS)-mediated NO release was investigated in the mouse insulinoma cell line MIN6 and mouse pancreatic islets. IL-17 markedly augmented iNOS mRNA/protein expression and subsequent NO production induced in MIN6 cells or pancreatic islets by different combinations of interferon-gamma, tumor necrosis factor-alpha, and IL-1beta. The induction of iNOS by IL-17 was preceded by phosphorylation of p38 mitogen-activated protein kinase (MAPK), and inhibition of p38 MAPK activation completely abolished IL-17-stimulated NO release. IL-17 enhanced the NO-dependent toxicity of proinflammatory cytokines toward MIN6 cells, while IL-17-specific neutralizing antibody partially reduced the NO production and rescued insulinoma cells and pancreatic islets from NO-dependent damage induced by activated T cells. Finally, a significant increase in blood IL-17 levels was observed in a multiple low-dose streptozotocin model of diabetes, suggesting that T cell-derived IL-17 might be involved in NO-dependent damage of beta cells in this disease.

Proinsulin Disulfide Maturation and Misfolding in the Endoplasmic Reticulum

Upon nonreducing Tris-Tricine-urea-SDS-PAGE, newly synthesized proinsulin from pancreatic islets of normal rodents forms a band fast mobility representing the native disulfide isomer, which is efficiently secreted. In addition at least two slower migrating "isomer 1 and 2" bands are recovered, not discernible under reducing conditions, which represent minor species that exhibit less efficient secretion. Although rats and mice have two proinsulin genes, three distinct migrating species are also produced upon proinsulin expression from a single wild-type human proinsulin cDNA. The "Akita-type" proinsulin mutation, which causes dominant-negative diabetes mellitus due to point mutation C(A7)Y that leaves B7-cysteine without its disulfide pairing partner, is recovered as a form that near quantitatively co-migrates with the aberrant isomer 1 band of proinsulin. Anomalous migration is also demonstrated for several other mutants lacking a single cysteine. In islets from PERK-/- mice, which exhibit premature loss of pancreatic beta cells, hypersynthesis of proinsulin increases the amount of nonnative proinsulin isomers. Such findings appear consistent with an hypothesis that supranormal production of nonnative proinsulin may predispose to pancreatic beta cell toxicity.

Oxidative Stress-mediated, Post-translational Loss of MafA Protein as a Contributing Mechanism to Loss of Insulin Gene Expression in Glucotoxic Beta Cells

Glucose toxicity in pancreatic islet beta cells causes loss of insulin gene expression, content, and secretion due to loss of binding of transcription factors, most notably PDX-1 and RIPE-3b1 activator, to the promoter region of the insulin gene. Recently, RIPE-3b1 activator was cloned and identified as the mammalian homologue of avian MafA/Maf-L (MafA). This enabled us to carry out more extensive studies of the role of MafA in glucotoxicity than were hitherto possible. Northern analysis of glucotoxic HIT-T15 cells revealed normal amounts of MafA mRNA, but Western analysis demonstrated a 97 +/- 1% reduction in MafA protein (p < 0.0001). The proteasome is a likely site for MafA degradation as lactacystin, an irreversible proteasome inhibitor, caused an accumulation of MafA protein. Antioxidants have previously been shown to prevent the adverse effects of glucose toxicity on beta cell function both in vivo and in vitro. In the current study, chronic culturing of HIT-T15 cells with the antioxidant N-acetylcysteine (NAC) prevented loss of MafA protein (late passage = 18.9 +/- 10.4% of early passage, p < 0.001; late passage with NAC = 68.7 +/- 19.7% of early passage, p = not significant) and loss of DNA binding (late passage = 63.7 +/- 9% of early passage, p < 0.02; late passage with NAC = 116 +/- 10% of early passage, p = not significant). Additionally, transient transfection of PDX-1 or MafA cDNA into glucotoxic cells increased PDX-1 and MafA protein levels and individually increased insulin promoter activity (untreated = 34%, PDX-1 = 70%, MafA = 78%; percentage of activity of early passage cells), whereas the combined transfection of MafA and PDX-1 completely restored insulin promoter activity. This recovery of promoter activity following transient transfection had no effect on endogenous insulin mRNA. However, adenoviral infection of MafA and PDX-1 significantly increased endogenous insulin mRNA levels by 93% (121 +/- 9 versus 233 +/- 18 density light units; n = 5, p < 0.001). We conclude that the absence of MafA protein from beta cells via chronic oxidative stress contributes importantly to the loss of endogenous insulin gene expression as glucose toxicity develops.

Activation of 12-lipoxygenase in proinflammatory cytokine-mediated beta cell toxicity

Beta cell inflammation and cytokine-induced toxicity are central to autoimmune diabetes development. Lipid mediators generated upon lipoxygenase (LO) activation can participate in inflammatory pathways. 12LO-deficient mice are resistant to streptozotocin-induced diabetes. This study sought to characterise the cellular processes involving 12LO-activation lipid inflammatory mediator production in cytokine-treated pancreatic beta cells. Islets and beta cell lines were treated with a combination of IL-1beta, IFN-gamma and TNF-alpha, or the 12LO product 12(S)-hydroxyeicosatetraenoic acid (HETE). Insulin secretion was measured using an enzyme immunoassay, and cell viability was evaluated using an in situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling assay. 12LO activity was evaluated and 12LO protein levels were determined using immunoblotting with a selective leucocyte type 12LO antibody. Cellular localisation of 12LO was evaluated using immunocytochemistry. Basal expression of leucocyte type 12LO protein was found in human and mouse islets and in several rodent beta cell lines. In mouse beta-TC3 cells, and in human islets, cytokines induced release of 12-HETE within 30 min. Cytokine addition also induced a rapid translocation of 12LO protein from the cytosol to the nucleus of beta-TC3 cells as shown by subcellular fractionation and immunostaining. Cytokine-induced cell death and inhibition of insulin secretion were partially reversed by baicalein, a 12LO inhibitor. 12(S)-HETE inhibited beta-TC3 cell insulin release in a time- and concentration-dependent manner. Incubating beta-TC3 cells with 100 nmol/l of 12(S)-HETE resulted in a 57% reduction in basal insulin release (6 h), and a 17% increase in cell death (18 h) as compared with untreated cells. 12(S)-HETE activated the stress-activated protein kinase c-Jun N-terminal kinase and p38 within 15 min, as judged by increased kinase protein phosphorylation. The data suggest that inflammatory cytokines rapidly activate 12LO and show for the first time that cytokines induce 12LO translocation. The effects of 12-HETE on insulin secretion, cytotoxicity and kinase activation were similar to the effects seen with cytokines. The results provide mechanistic information of cytokine-induced toxic effects on pancreatic beta cells and support the hypothesis that blocking 12LO activation could provide a new therapeutic way to protect pancreatic beta cells from autoimmune injury.

Adenoviral Overexpression of the Glutamylcysteine Ligase Catalytic Subunit Protects Pancreatic Islets against Oxidative Stress

The catalytic subunit of glutamylcysteine ligase (GCLC) primarily regulates de novo synthesis of glutathione (GSH) in mammalian cells and is central to the antioxidant capacity of the cell. However, GCLC expression in pancreatic islets has not been previously examined. We designed experiments to ascertain whether GCLC is normally expressed in islets and whether it is up-regulated by interleukin-1 beta (IL-1 beta). GCLC expression levels were intermediate compared with other metabolic tissues (kidney, liver, muscle, fat, and lung). IL-1 beta up-regulated GCLC expression (10 ng/ml IL-1 beta, 3.76 +/- 0.86; 100 ng/ml IL-1 beta, 4.22 +/- 0.68-fold control) via the p38 form of mitogen-activated protein kinase and NF kappa B and also increased reactive oxygen species levels (10 ng/ml IL-1 beta, 5.41 +/- 1.8-fold control). This was accompanied by an increase in intraislet GSH/GSSG ratio (control, 7.1 +/- 0.1; 10 ng/ml IL-1 beta, 8.0 +/- 0.5; 100 ng/ml IL-1 beta, 8.2 +/- 0.5-fold control; p < 0.05). To determine whether overexpression of GCLC increases the antioxidant capacity of the islet and prevents the adverse effects of IL-1 beta on glucose-induced insulin secretion, islets were infected with an adenovirus encoding GCLC. IL-1 beta significantly decreased glucose-stimulated insulin secretion (control, 123.8 +/- 17.7; IL-1 beta, 40.2 +/- 3.9 microunits/ml insulin/islet). GCLC overexpression increased intraislet GSH levels and partially prevented the decrease in glucose-stimulated insulin secretion caused by IL-1 beta. These data provide the first report of GCLC expression in the islet and demonstrate that adenoviral overexpression of GCLC increases intracellular GSH levels and protects the beta cell from the adverse effects of IL-1 beta.

Chronic Oxidative Stress as a Central Mechanism for Glucose Toxicity in Pancreatic Islet Beta Cells in Diabetes

Chronic Oxidative Stress as a Central Mechanism for Glucose Toxicity in Pancreatic Islet Beta Cells in Diabetes

D-Glyceraldehyde Causes Production of Intracellular Peroxide in Pancreatic Islets, Oxidative Stress, and Defective Beta Cell Function via Non-mitochondrial Pathways

D-Glyceraldehyde (D-GLYC) is usually considered to be a stimulator of insulin secretion but theoretically can also form reactive oxygen species (ROS), which can inhibit beta cell function. We examined the time- and concentration-dependent effects of D-GLYC on insulin secretion, insulin content, and formation of ROS. We observed that a 2-h exposure to 0.05-2 mM D-GLYC potentiated glucose-stimulated insulin secretion (GSIS) in isolated Wistar rat islets but that higher concentrations inhibited GSIS. A 24-h exposure to 2 mm D-GLYC inhibited GSIS, decreased insulin content, and increased intracellular peroxide levels (2.14 +/- 0.31-fold increase, n = 4, p < 0.05). N-Acetylcysteine (10 mM) prevented the increase in intracellular peroxides and the adverse effects of d-GLYC on GSIS. In the presence of 11.1 but not 3.0 mm glucose, koningic acid (10 microM), a specific glyceraldehyde-3-phosphate dehydrogenase inhibitor, increased intracellular peroxide levels (1.88 +/- 0.30-fold increase, n = 9, p < 0.01) and inhibited GSIS (control GSIS = p < 0.001; koningic acid GSIS, not significant). To determine whether oxidative phosphorylation was the source of ROS formation, we cultured rat islets with mitochondrial inhibitors. Neither rotenone or myxothiazol prevented D-GLYC-induced increases in islet ROS. Adenoviral overexpression of manganese superoxide dismutase also failed to prevent the effect of D-GLYC to increase ROS levels. These observations indicate that exposure to excess D-GLYC increases reactive oxygen species in the islet via non-mitochondrial pathways and suggest the hypothesis that the oxidative stress associated with elevated D-GLYC levels could be a mechanism for glucose toxicity in beta cells exposed chronically to high glucose concentrations.

Interleukin (IL)-1beta toxicity to islet beta cells: Efaroxan exerts a complete protection.

Interleukin (IL)-1beta-treated rat islets of Langerhans were exposed in vitro either to the imidazoline compound, Efaroxan, or to the selective inducible nitric oxide synthase (iNOS) inhibitor, 1400W, in a medium containing a high concentration of glucose (16.7 mmol/L). Our data have evidenced the following: (i) addition of Efaroxan to islet cultures inhibited IL-1beta activation of ICE (cysteine protease IL-1beta converting enzyme) while addition of 1400W did not; (ii) Efaroxan completely inhibited IL-1beta-induced suppression of insulin secretion and induction of iNOS mRNA transcripts, and, in addition, counteracted islet beta-cell protein profile alterations, Bax-cytochrome c translocation, caspase activation, and apoptosis; (iii) 1400W inhibited IL-1beta induction of iNOS, but failed to completely counteract the other cytotoxic effects; (iv) the two compounds, moreover, exerted different effects on manganese superoxide dismutase (MnSOD), in fact, while Efaroxan inhibited the early stimulatory effect of IL-1beta on MnSOD, 1400W did not. Thus, Efaroxan completely protected islet beta cells from damage caused by IL-1beta-induced toxicity, while compound 1400W only inhibited NO radical production without altering the cytokine's cytotoxicity. Our observations have evidenced that suppression of ICE activation is required to counteract IL-1beta-mediated islet beta cell toxicity, and that IL-1beta-induced apoptosis is NO-independent and involves the cytochrome c-mitochondrial pathway.

Glucosamine-induced alterations of mitochondrial function in pancreatic beta-cells: possible role of protein glycosylation.

Chronic exposure of rat pancreatic islets and INS-1 insulinoma cells to glucosamine (GlcN) produced a reduction of glucose-induced (22.2 mM) insulin release that was associated with a reduction of ATP levels and ATP/ADP ratio compared with control groups. To further evaluate mitochondrial function and ATP metabolism, we then studied uncoupling protein-2 (UCP2), F1-F0-ATP-synthase, and mitochondrial membrane potential, a marker of F1-F0-ATP-synthase activity. UCP2 protein levels were unchanged after chronic exposure to GlcN on both pancreatic islets and INS-1 beta-cells. Due to the high number of cells required to measure mitochondrial F1-F0-ATP-synthase protein levels and mitochondrial membrane potential, we used INS-1 cells, and we found that chronic culture with GlcN increased F1-F0-ATP-synthase protein levels but decreased glucose-stimulated changes of mitochondrial membrane potential. Moreover, F1-F0-ATP-synthase was highly glycosylated, as demonstrated by experiments with N-glycosidase F and glycoprotein staining. Tunicamycin (an inhibitor of protein N-glycosylation), when added with GlcN in the culture medium, was able to partially prevent all these negative effects on insulin secretion, adenine nucleotide content, mitochondrial membrane potential, and protein glycosylation. Thus we suggest that GlcN-induced pancreatic beta-cell toxicity might be mediated by reduced cell energy production. An excessive protein N-glycosylation of mitochondrial F1-F0-ATP-synthase might lead to cell damage and secretory alterations in pancreatic beta-cells.

Oxidative Stress Is a Mediator of Glucose Toxicity in Insulin-secreting Pancreatic Islet Cell Lines

Pancreatic beta cells secrete insulin in response to changes in the extracellular glucose. However, prolonged exposure to elevated glucose exerts toxic effects on beta cells and results in beta cell dysfunction and ultimately beta cell death (glucose toxicity). To investigate the mechanism of how increased extracellular glucose is toxic to beta cells, we used two model systems where glucose metabolism was increased in beta cell lines by enhancing glucokinase (GK) activity and exposing cells to physiologically relevant increases in extracellular glucose (3.3-20 mm). Exposure of cells with enhanced GK activity to 20 mm glucose accelerated glycolysis, but reduced cellular NAD(P)H and ATP, caused accumulation of intracellular reactive oxygen species (ROS) and oxidative damage to mitochondria and DNA, and promoted apoptotic cell death. These changes required both enhanced GK activity and exposure to elevated extracellular glucose. A ROS scavenger partially prevented the toxic effects of increased glucose metabolism. These results indicate that increased glucose metabolism in beta cells generates oxidative stress and impairs cell function and survival; this may be a mechanism of glucose toxicity in beta cells. The level of beta cell GK may also be critical in this process.

Hepatocyte growth factor gene therapy for pancreatic islets in diabetes: reducing the minimal islet transplant mass required in a glucocorticoid-free rat model of allogeneic portal vein islet transplantation.

Islet transplantation for diabetes is limited by the availability of human islet donors. Hepatocyte growth factor (HGF) is a potent beta-cell mitogen and survival factor and improves islet transplant outcomes in a murine model. However, the murine model employs renal subcapsular transplant and immunodeficient mice, features not representative of human islet transplantation protocols. Therefore, we have developed a more rigorous, marginal-mass rat islet transplant model that more closely resembles human islet transplantation protocols: islet donors are allogeneic Lewis islets; recipients are normal Sprague Dawley rats; islets are delivered intraportally; and immunosuppression is accomplished using the same immunosuppressants employed by the Edmonton group. We demonstrate that 1) surprisingly, the Edmonton immunosuppression regimen induces marked insulin resistance and beta-cell toxicity in rats, 2) adenovirus does not adversely affect islet transplant outcomes, 3) the Edmonton immunosuppressants may delay or block rejection of adenovirally transduced islets, and more importantly, 4) pretransplant islet adenoviral gene therapy with HGF markedly improves islet transplant outcomes, 5) this enhanced function persists for months, and 6) HGF enhances islet function and survival even in the setting of immunosuppressant-induced insulin resistance and beta-cell toxicity. This approach may enhance islet transplantation outcomes in humans.

Adenoviral-Induced Islet Cell Cytotoxicity Is Not Counteracted by Bcl-2 Overexpression

The ability to transfer immunoregulatory, cytoprotective, or anti-apoptotic genes into pancreatic islet cells may allow enhanced resistance against the autoimmune destruction of these cells in type 1 diabetes. We describe here an inducible transduction system for expression of the anti-apoptotic bcl-2 gene in insulin-producing cells as a potential tool for protecting against beta-cell death. Isolated pancreatic rat islet cells or rat insulinoma (RINm5F) cells were transduced using a progesterone antagonist (RU 486) inducible adenoviral vector system, expressing the bcl-2 gene. Bcl-2 overexpression was measured by Western blot assays and flow cytometry analysis. Following exposure to cytokines or to the mitochondrial uncoupler FCCP, cell survival was determined using fluorescence and electron microscopy, and a colorimetric assay (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]- 2H-tetrazolium-5-carboxanilide [XTT]-based) for cell viability. The mitochondrial membrane potential ((m)) was assessed using the lipophilic cationic membrane potential-sensitive dye JC-1. The adenoviral gene transfer system induced Bcl-2 expression in more than 70% of beta-cells and the protein expression levels were successfully regulated in response to varying concentrations of progesterone antagonist RU 486. Exposure of islet cells to proinflammatory cytokines IL-1beta, TNF-alpha, and IFN-gamma, or to the mitochondrial uncoupler FCCP resulted in disruption of the mitochondrial membrane potential ((m)) and beta-cell death. Bcl-2 overexpression stabilized (m) and prevented cell death in RINm5F cells but not in islet cells. In addition, prolonged in vitro culture revealed adenoviral-induced islet cell necrosis. The RU 486-regulated adenoviral system can achieve an efficient control of gene transfer at relatively low doses of the adenoviral vector. However, Bcl-2 overexpression in islet cells did not prevent adenoviral- or cytokine-induced toxicity, suggesting that the specific death pathway involved in adenoviral toxicity in beta-cells may bypass the mitochondrial permeability transition event.

Importance of the GLUT2 glucose transporter for pancreatic beta cell toxicity of alloxan.

We investigated the importance of the low affinity GLUT2 glucose transporter in the diabetogenic action of alloxan in bioengineered RINm5F insulin-producing cells with different expressions of the transporter. GLUT2 glucose transporter expressing RINm5F cells were generated through stable transfection of the rat GLUT2 cDNA under the control of the cytomegalovirus promoter in the pcDNA3 vector. Viability of the cells was determined using a microtitre plate-based 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. Cells expressing the GLUT2 transporter were susceptible to alloxan toxicity due to the uptake of alloxan by this specific glucose transporter isoform. The extent of the toxicity of alloxan was dependent upon the GLUT2 protein expression in the cells. The lipophilic alloxan derivative, butylalloxan, was toxic also to non-transfected control cells. Expression of the GLUT2 glucose transporter caused only a marginal increase in the toxicity of this substance. Butylalloxan, unlike alloxan itself, is not diabetogenic in vivo although, like the latter substance, it is beta-cell toxic in vitro through its ability to generate free radicals during redox cycling with glutathione. Our results are consistent with the central importance of selective uptake of alloxan through the low affinity GLUT2 glucose transporter for the pancreatic beta-cell toxicity and diabetogenicity of this substance. Redox cycling and the subsequent generation of oxygen free radicals leads to necrosis of pancreatic beta cells and thus to a state of insulin-dependent diabetes mellitus, well-known as alloxan diabetes in experimental diabetes research.

Affinity-based inhibition of beta-amyloid toxicity.

Strategies for interfering with protein aggregation are important for elucidating and controlling the pathologies of amyloid diseases. We have previously identified compounds that block the cellular toxicity of the beta-amyloid peptide, but the relationship between their ability to inhibit toxicity and their affinity for A beta is unknown. To elucidate this relationship, we have developed an assay capable of measuring the affinities of small molecules for beta-amyloid peptide. Our approach employs immobilized beta-amyloid peptide at low density to minimize the problems that arise from variability in the beta-amyloid aggregation state. We found that low-molecular weight (MW of 700-1700) ligands for beta-amyloid can be identified readily by using surface plasmon resonance. The best of these bound effectively (K(d) approximately 40 microM) to beta-amyloid. The affinities measured for peptides in the SPR assay correspond to results from A beta cell toxicity assays. The most potent ligands for immobilized beta-amyloid are the most potent inhibitors of the neuronal cell toxicity of beta-amyloid. Compounds with dissociation constants above approximately 100 microM did not show significant activity in the cell toxicity assays. Our data support the hypothesis that ligands exhibiting greater affinity for the beta-amyloid peptide are effective at altering its aggregation and inhibiting cell toxicity.

Combined genome and proteome approach to identify new susceptibility genes.

Type 1 diabetes mellitus (T1DM) is a multifactorial disorder characterized by a specific destruction of the insulin-producing beta cells in the islets of Langerhans. Cells from the immune system infiltrate the islet during the pathogenesis, releasing a mixture of cytokines demonstrated to be specifically toxic to the beta cells within the islets. The goal is to understand the molecular mechanisms responsible for this specific beta-cell toxicity, which will allow the design of novel intervention strategies for T1DM. The proteome approach provides a detailed picture of the beta-cell proteins changing expression pattern during cytokine-mediated beta-cell destruction. Combining the information from this proteome approach with genetic studies makes us believe that it is possible to reach this goal.