Cytotoxic effect of IFN-gamma plus TNF-alpha on human islet cells

DECORIN, a triceps-derived myokine, protects sorted β-cells and human islets against chronic inflammation associated with type 2 diabetes

AIM

Pancreatic β-cells are susceptible to inflammation, leading to decreased insulin production/secretion and cell death. Previously, we have identified a novel triceps-derived myokine, DECORIN, which plays a pivotal role in skeletal muscle-to-pancreas interorgan communication. However, whether DECORIN can directly impact β-cell function and susceptibility to inflammation remains unexplored.

METHODS

The effect of DECORIN was assessed in sorted human and rat β-cell and human islets from healthy and type 2 diabetes (T2D) donors. We assessed glucose-stimulated insulin secretion (GSIS) and cytokine-mediated cell death. We then challenged sorted β-cells and human islets with inflammatory cytokines commonly associated with diabetes, such as tumor necrosis factor-α (TNF-α) alone or in combination with interleukin1-β (IL1-β) and interferon-γ (cytomix).

RESULTS

DECORIN enhanced cell spreading and the localization of phosphorylated FAK at adhesions, promoting GSIS under basal conditions. It also increased insulin granule docking adhesion length and countered the inhibitory effects of TNF-α on adhesion and actin remodeling at the β-cell surface, resulting in preserved GSIS. DECORIN protected from cell death in sorted β-cells and islets challenged with TNF-α alone or TNF-α + cytomix. Interestingly, DECORIN increased both insulin content and secretion in human islets from T2D individuals. Additionally, DECORIN treatment reversed the impaired gene expression caused by T2D and enhanced the expression of genes essential for islet function and metabolism.

CONCLUSION

Collectively, we have shown that DECORIN had a beneficial effect on human islets, protecting them from inflammation-induced cell death. In T2D islets, DECORIN restores islet function and reverses the expression of T2D-associated genes. Based on our data, we propose that DECORIN is a promising therapeutic target for diabetes-associated inflammation and diabetes itself.

CD39 delineates chimeric antigen receptor regulatory T cell subsets with distinct cytotoxic & regulatory functions against human islets

Human regulatory T cells (Treg) suppress other immune cells. Their dysfunction contributes to the pathophysiology of autoimmune diseases, including type 1 diabetes (T1D). Infusion of Tregs is being clinically evaluated as a novel way to prevent or treat T1D. Genetic modification of Tregs, most notably through the introduction of a chimeric antigen receptor (CAR) targeting Tregs to pancreatic islets, may improve their efficacy. We evaluated CAR targeting of human Tregs to monocytes, a human β cell line and human islet β cells in vitro. Targeting of HLA-A2-CAR (A2-CAR) bulk Tregs to HLA-A2+ cells resulted in dichotomous cytotoxic killing of human monocytes and islet β cells. In exploring subsets and mechanisms that may explain this pattern, we found that CD39 expression segregated CAR Treg cytotoxicity. CAR Tregs from individuals with more CD39low/- Tregs and from individuals with genetic polymorphism associated with lower CD39 expression (rs10748643) had more cytotoxicity. Isolated CD39- CAR Tregs had elevated granzyme B expression and cytotoxicity compared to the CD39+ CAR Treg subset. Genetic overexpression of CD39 in CD39low CAR Tregs reduced their cytotoxicity. Importantly, β cells upregulated protein surface expression of PD-L1 and PD-L2 in response to A2-CAR Tregs. Blockade of PD-L1/PD-L2 increased β cell death in A2-CAR Treg co-cultures suggesting that the PD-1/PD-L1 pathway is important in protecting islet β cells in the setting of CAR immunotherapy. In summary, introduction of CAR can enhance biological differences in subsets of Tregs. CD39+ Tregs represent a safer choice for CAR Treg therapies targeting tissues for tolerance induction.

RIPK1 and RIPK3 regulate TNFα-induced β-cell death in concert with caspase activity

OBJECTIVE

Type 1 diabetes (T1D) is characterized by autoimmune-associated β-cell loss, insulin insufficiency, and hyperglycemia. Although TNFα signaling is associated with β-cell loss and hyperglycemia in non-obese diabetic mice and human T1D, the molecular mechanisms of β-cell TNF receptor signaling have not been fully characterized. Based on work in other cell types, we hypothesized that receptor interacting protein kinase 1 (RIPK1) and receptor interacting protein kinase 3 (RIPK3) regulate TNFα-induced β-cell death in concert with caspase activity.

METHODS

We evaluated TNFα-induced cell death, caspase activity, and TNF receptor pathway molecule expression in immortalized NIT-1 and INS-1 β-cell lines and primary mouse islet cells in vitro. Our studies utilized genetic and small molecule approaches to alter RIPK1 and RIPK3 expression and caspase activity to interrogate mechanisms of TNFα-induced β-cell death. We used the β-cell toxin streptozotocin (STZ) to determine the susceptibility of Ripk3+/+ and Ripk3-/- mice to hyperglycemia in vivo.

RESULTS

Expression of TNF receptor signaling molecules including RIPK1 and RIPK3 was identified in NIT-1 and INS-1 β cells and isolated mouse islets at the mRNA and protein levels. TNFα treatment increased NIT-1 and INS-1 cell death and caspase activity after 24-48 h, and BV6, a small molecule inhibitor of inhibitor of apoptosis proteins (IAPs) amplified this TNFα-induced cell death. RIPK1 deficient NIT-1 cells were protected from TNFα- and BV6-induced cell death and caspase activation. Interestingly, small molecule inhibition of caspases with zVAD-fmk (zVAD) did not prevent TNFα-induced cell death in either NIT-1 or INS-1 cells. This caspase-independent cell death was increased by BV6 treatment and decreased in RIPK1 deficient NIT-1 cells. RIPK3 deficient NIT-1 cells and RIPK3 kinase inhibitor treated INS-1 cells were protected from TNFα+zVAD-induced cell death, whereas RIPK3 overexpression increased INS-1 cell death and promoted RIPK3 and MLKL interaction under TNFα+zVAD treatment. In mouse islet cells, BV6 or zVAD treatment promoted TNFα-induced cell death, and TNFα+zVAD-induced cell death was blocked by RIPK3 inhibition and in Ripk3-/- islet cells in vitro. Ripk3-/- mice were also protected from STZ-induced hyperglycemia and glucose intolerance in vivo.

CONCLUSIONS

RIPK1 and RIPK3 regulate TNFα-induced β-cell death in concert with caspase activity in immortalized and primary islet β cells. TNF receptor signaling molecules such as RIPK1 and RIPK3 may represent novel therapeutic targets to promote β-cell survival and glucose homeostasis in T1D.

A nanofibrous encapsulation device for safe delivery of insulin-producing cells to treat type 1 diabetes

Transplantation of stem cell-derived β (SC-β) cells represents a promising therapy for type 1 diabetes (T1D). However, the delivery, maintenance, and retrieval of these cells remain a challenge. Here, we report the design of a safe and functional device composed of a highly porous, durable nanofibrous skin and an immunoprotective hydrogel core. The device consists of electrospun medical-grade thermoplastic silicone-polycarbonate-urethane and is soft but tough (~15 megapascal at a rupture strain of >2). Tuning the nanofiber size to less than ~500 nanometers prevented cell penetration while maintaining maximum mass transfer and decreased cellular overgrowth on blank (cell-free) devices to as low as a single-cell layer (~3 micrometers thick) when implanted in the peritoneal cavity of mice. We confirmed device safety, indicated as continuous containment of proliferative cells within the device for 5 months. Encapsulating syngeneic, allogeneic, or xenogeneic rodent islets within the device corrected chemically induced diabetes in mice and cells remained functional for up to 200 days. The function of human SC-β cells was supported by the device, and it reversed diabetes within 1 week of implantation in immunodeficient and immunocompetent mice, for up to 120 and 60 days, respectively. We demonstrated the scalability and retrievability of the device in dogs and observed viable human SC-β cells despite xenogeneic immune responses. The nanofibrous device design may therefore provide a translatable solution to the balance between safety and functionality in developing stem cell-based therapies for T1D.

Pancreatic stellate cell-potentiated insulin secretion from Min6 cells is independent of interleukin 6-mediated pathway

Pancreatic stellate cells (PSCs) secrete various factors, which can influence the β-cell function. The identification of stellate cell infiltration into the islets in pancreatic diseases suggests possible existence of cross-talk between these cells. To elucidate the influence of PSCs on β-cell function, mouse PSCs were cocultured with Min6 cells using the Transwell inserts. Glucose-stimulated insulin secretion from Min6 cells in response to PSCs was quantified by enzyme-linked immunosorbent assay and insulin gene expression was measured by quantitative polymerase chain reaction. Upon cytometric identification of IL6 in PSC culture supernatants, Min6 cells were cultured with IL6 to assess its influence on the insulin secretion and gene expression. PLC-IP3 pathway inhibitors were added in the cocultures, to determine the influence of PSC-secreted IL6 on Glucose-stimulated insulin secretion from Min6 cells. Increased insulin secretion with a concomitant decrease in total insulin content was noticed in PSC-cocultured Min6 cells. Although increased GSIS was noted from IL6-treated Min6 cells, no change in the total insulin content was noted. Coculture of Min6 cells with PSCs or their exposure to IL6 did not alter either the expression of β-cell-specific genes or that of miRNA-375. PSC-cocultured Min6 cells, in the presence of PLC-IP3 pathway inhibitors (U73122, Neomycin, and Xestospongin C), did not revoke the observed increase in GSIS. In conclusion, the obtained results indicate that augmented insulin secretion from Min6 cells in response to PSC secretions is independent of IL6-mediated PLC-IP3 pathway.

Sensitivity profile of the human EndoC-βH1 beta cell line to proinflammatory cytokines

AIMS/HYPOTHESIS

The aim of this study was to perform a detailed analysis of cytokine toxicity in the new human EndoC-βH1 beta cell line.

METHODS

The expression profile of the antioxidative enzymes in the new human EndoC-βH1 beta cells was characterised and compared with that of primary beta cells in the human pancreas. The effects of proinflammatory cytokines on reactive oxygen species formation, insulin secretory responsiveness and apoptosis of EndoC-βH1 beta cells were determined.

RESULTS

EndoC-βH1 beta cells were sensitive to the toxic action of proinflammatory cytokines. Glucose-dependent stimulation of insulin secretion and an increase in the ATP/ADP ratio was abolished by proinflammatory cytokines without induction of IL-1β expression. Cytokine-mediated caspase-3 activation was accompanied by reactive oxygen species formation and developed more slowly than in rodent beta cells. Cytokines transiently increased the expression of unfolded protein response genes, without inducing endoplasmic reticulum stress-marker genes. Cytokine-mediated NFκB activation was too weak to induce inducible nitric oxide synthase expression. The resultant lack of nitric oxide generation in EndoC-βH1 cells, in contrast to rodent beta cells, makes these cells dependent on exogenously generated nitric oxide, which is released from infiltrating immune cells in human type 1 diabetes, for full expression of proinflammatory cytokine toxicity.

CONCLUSIONS/INTERPRETATION

EndoC-βH1 beta cells are characterised by an imbalance between H2O2-generating and -inactivating enzymes, and react to cytokine exposure in a similar manner to primary human beta cells. They are a suitable beta cell surrogate for cytokine-toxicity studies.

Considerations for Defining Cytokine Dose, Duration, and Milieu That Are Appropriate for Modeling Chronic Low-Grade Inflammation in Type 2 Diabetes

Proinflammatory cytokines have been implicated in the pathophysiology of both type 1 diabetes (T1D) and type 2 diabetes (T2D). T1D is an autoimmune disease involving the adaptive immune system responding to pancreatic beta-cells as antigen-presenting cells. This attracts immune cells that surround pancreatic islets (insulitis) and secrete cytokines, such as IL-1beta, IFN-gamma, and TNF-alpha, in close proximity to pancreatic beta-cells. In contrast, there is little evidence for such a focused autoimmune response in T2D. Instead, the innate immune system, which responds to cellular damage and pathogens, appears to play a key role. There are three major sources of proinflammatory cytokines that may impact islet/beta-cell function in T2D: (1) from islet cells, (2) from increased numbers of intraislet macrophages/immune cells, and (3) from increased circulating levels of proinflammatory cytokines due to obesity, presumably coming from inflamed adipose tissue. These differences between T1D and T2D are reflected by significant differences in the cytokine concentration, duration, and milieu. This review focuses on chronic versus acute cytokine action, cytokine concentrations, and cytokine milieu from the perspective of the pancreatic islet in T2D. We conclude that new cytokine models may be needed to reflect the pathophysiology of T2D more effectively than what are currently employed.

Benzimidazole derivatives protect against cytokine-induced apoptosis in pancreatic β-Cells

Apoptotic cell death is the cause of the loss of insulin-producing β-cells in all forms of diabetes mellitus. The identification of small molecules capable of protecting cytokine-induced apoptosis could form the basis of useful therapeutic interventions. Here in, we present the discovery and synthesis of new benzimidazole derivatives, capable of rescuing pancreatic β-cells from cytokine-induced apoptosis. Three hydrazone derivatives of benzimidazole significantly increased the cellular ATP levels, reduced caspase-3 activity, reduced nitrite production and increased glucose-stimulated insulin secretion in the presence of proinflammatory cytokines. These findings suggest that these compounds may protect β-cells from the harmful effects of cytokines and may serve as candidates for therapeutic intervention for diabetes.

Islet neogenesis-associated protein-related pentadecapeptide improves the function of allograft after islets transplantation

OBJECTIVE

To investigate the protective effects of a pentadecapeptide of islet neogenesis-associated protein (INGAP-PP) on transplanted islets function.

METHODS

Islets were cultured in RPMI 1640 with or without INGAP-PP (10 μg/mL). After 24 h, the viability of the islets and glucose-stimulated insulin secretion (GSIS) were measured. The expression of genes B cell lymphoma/lewkmia2 (Bcl2) and protein kinase B (Akt) were detected by RT-PCR assay. Healthy rats transplanted with islets under the renal capsule were injected with INGAP-PP or saline in in the abdominal cavity. One week later, the expression of insulin nestin pancreatic (nestin) and duodenal homeobox 1 (Pdx1) and proliferating cell nuclear antigen (PCNA) in the transplanted islets were observed by immunohistochemistry. After that they were transplanted to the renal capsule of diabetic rats.

RESULTS

1. The amount of insulin released was increased in co-cultured group in concentration of 16.7 mmol/L glucose, which was (185.00±20.01 μU/mL) vs. (58.67±17.03 μU/mL). Gene expression of Bcl2 (0.61±0.22 vs. 0.50±0.21) and Akt (1.12±0.19 vs. 0.94±0.16) in the co-cultured group were increased compared with that of the control group. Islets viability in the co-cultured group (683.9±7.08) was higher than that of control group (547.9±8.02). The stimulating index (SI) of the co-cultured group was also higher than that of the control group. 2. The group of islets under the renal capsule which were co-cultured and injected with INGAP-PP had the more nestin expression in the islets.

CONCLUSIONS

The function of islet can be protected by the INGAP-PP, which will promote the viability, differentiation and regeneration of islet before transplantation. And it will be beneficial for the function of allograft after islets transplantation.

Inflammatory response in islet transplantation

Islet cell transplantation is a promising beta cell replacement therapy for patients with brittle type 1 diabetes as well as refractory chronic pancreatitis. Despite the vast advancements made in this field, challenges still remain in achieving high frequency and long-term successful transplant outcomes. Here we review recent advances in understanding the role of inflammation in islet transplantation and development of strategies to prevent damage to islets from inflammation. The inflammatory response associated with islets has been recognized as the primary cause of early damage to islets and graft loss after transplantation. Details on cell signaling pathways in islets triggered by cytokines and harmful inflammatory events during pancreas procurement, pancreas preservation, islet isolation, and islet infusion are presented. Robust control of pre- and peritransplant islet inflammation could improve posttransplant islet survival and in turn enhance the benefits of islet cell transplantation for patients who are insulin dependent. We discuss several potent anti-inflammatory strategies that show promise for improving islet engraftment. Further understanding of molecular mechanisms involved in the inflammatory response will provide the basis for developing potent therapeutic strategies for enhancing the quality and success of islet transplantation.

Inhibition of histone deacetylase 3 protects beta cells from cytokine-induced apoptosis

Cytokine-induced beta-cell apoptosis is important to the etiology of type-1 diabetes. Although previous reports have shown that general inhibitors of histone deacetylase (HDAC) activity, such as suberoylanilide hydroxamic acid and trichostatin A, can partially prevent beta-cell death, they do not fully restore beta-cell function. To understand HDAC isoform selectivity in beta cells, we measured the cellular effects of 11 structurally diverse HDAC inhibitors on cytokine-induced apoptosis in the rat INS-1E cell line. All 11 compounds restored ATP levels and reduced nitrite secretion. However, caspase-3 activity was reduced only by MS-275 and CI-994, both of which target HDAC1, 2, and 3. Importantly, both MS-275 and genetic knockdown of Hdac3 alone were sufficient to restore glucose-stimulated insulin secretion in the presence of cytokines. These results suggest that HDAC3-selective inhibitors may be effective in preventing cytokine-induced beta-cell apoptosis.

Immune-mediated β-cell death in type 1 diabetes: lessons from human β-cell lines

Type 1 diabetes (T1D) is a chronic, multifactorial disorder that results from a contretemps of genetic and environmental factors. Autoimmune attack and functional inhibition of the insulin-producing β cells in the pancreas lead to the inability of β cells to metabolize glucose, and thus results the hallmark clinical symptom of diabetes: abnormally high blood glucose levels. Treatment and protection from T1D require a detailed knowledge of the molecular effectors and the mechanism(s) of cell death leading to β-cell demise. Primary islets and surrogate β cells have been utilized in vitro to investigate in isolation-specific mechanisms associated with progression to T1D in vivo. This review focuses on the data obtained from these experiments. Studies using transformed β cells of human sources are described.

Role of the mitochondria in immune-mediated apoptotic death of the human pancreatic β cell line βLox5

Mitochondria are indispensable in the life and death of many types of eukaryotic cells. In pancreatic beta cells, mitochondria play an essential role in the secretion of insulin, a hormone that regulates blood glucose levels. Unregulated blood glucose is a hallmark symptom of diabetes. The onset of Type 1 diabetes is preceded by autoimmune-mediated destruction of beta cells. However, the exact role of mitochondria has not been assessed in beta cell death. In this study, we examine the role of mitochondria in both Fas- and proinflammatory cytokine-mediated destruction of the human beta cell line, βLox5. IFNγ primed βLox5 cells for apoptosis by elevating cell surface Fas. Consequently, βLox5 cells were killed by caspase-dependent apoptosis by agonistic activation of Fas, but only after priming with IFNγ. This beta cell line undergoes both apoptotic and necrotic cell death after incubation with the combination of the proinflammatory cytokines IFNγ and TNFα. Additionally, both caspase-dependent and -independent mechanisms that require proper mitochondrial function are involved. Mitochondrial contributions to βLox5 cell death were analyzed using mitochondrial DNA (mtDNA) depleted βLox5 cells, or βLox5 ρ⁰ cells. βLox5 ρ⁰ cells are not sensitive to IFNγ and TNFα killing, indicating a direct role for the mitochondria in cytokine-induced cell death of the parental cell line. However, βLox5 ρ⁰ cells are susceptible to Fas killing, implicating caspase-dependent extrinsic apoptotic death is the mechanism by which these human beta cells die after Fas ligation. These data support the hypothesis that immune mediators kill βLox5 cells by both mitochondrial-dependent intrinsic and caspase-dependent extrinsic pathways.

Small-Molecule Suppressors of Cytokine-Induced beta-Cell Apoptosis

Pancreatic beta-cell apoptosis is a critical event during the development of type-1 diabetes. The identification of small molecules capable of preventing cytokine-induced apoptosis could lead to avenues for therapeutic intervention. We developed a set of phenotypic cell-based assays designed to identify such small-molecule suppressors. Rat INS-1E cells were simultaneously treated with a cocktail of inflammatory cytokines and a collection of 2,240 diverse small molecules and screened using an assay for cellular ATP levels. Forty-nine top-scoring compounds included glucocorticoids, several pyrazole derivatives, and known inhibitors of glycogen synthase kinase-3beta. Two compounds were able to increase cellular ATP levels, reduce caspase-3 activity and nitrite production, and increase glucose-stimulated insulin secretion in the presence of cytokines. These results indicate that small molecules identified by this screening approach may protect beta cells from autoimmune attack and may be good candidates for therapeutic intervention in early stages of type-1 diabetes.

Evidence for Induced Expression of HLA Class II on Human Islets: Possible Mechanism for HLA Sensitization in Transplant Recipients

Recent reports have shown that islet transplant recipients develop antibodies against donor human leukocyte antigen (HLA) class I and II. Because human islets do not express HLA class II under normal conditions, mechanisms underlying induction of the anti-class II response are unclear. We hypothesized that under inflammatory conditions, islets will have induced expression of HLA class II leading to sensitization. Isolated human islets were divided into two groups. Group 1 was cultured at 37 degrees C as control; group 2 was cultured similarly in presence of tumor necrosis factor alpha and interferon gamma. After treatment, islets were analyzed for expression of HLA class II using real-time polymerase chain reaction, immunofluorescence and flow cytometry. Furthermore, serum from an islet transplant recipient who developed anti-class II antibody was tested by flow cytometry for immunoglobulin (Ig) binding to cytokine-stimulated islets. Real-time polymerase chain reaction analysis for gene transcripts of class II transactivator, HLA-DRagr;, and HLA-DRbeta1 showed maximum 9.38-, 18.95-, and 46.5-fold increase, respectively in group 2 when compared with control at 24 hr. Cytokine treatment increased HLA class II expression markedly on both alpha and beta cells in islets as evidenced by fluorescent imaging and flow cytometric analysis. When patient serum was analyzed by flow cytometry, both IgM and IgG binding was observed in cytokine-treated, HLA class II matched islet cells alone. We conclude that inflammation leads to induced expression of HLA class II on transplanted islet cells potentially causing antidonor sensitization and adversely impacting islet transplant outcomes.

Interferon alpha--a potential link in the pathogenesis of viral-induced type 1 diabetes and autoimmunity

The incidence of type 1 diabetes has been rapidly rising. Environmental factors such as viruses have been implicated as a possible agent accounting for this rise. Enteroviruses have recently been the focus in many research studies as a potential agent in the pathogenesis of type 1 diabetes. The mechanism of viral infection leading to beta cell destruction not only involves multiple pathways but also the cytokine-interferon alpha (IFN-alpha). Our hypothesis is that activation of toll receptors by double-stranded RNA or poly-IC (viral mimic) through induction of IFN-alpha may activate or accelerate immune-mediated beta cell destruction. Numerous clinical case reports have implicated that IFN-alpha therapy is associated with autoimmune diseases and that elevated serum IFN-alpha levels have been associated with type 1 diabetes. In multiple animal models, given specific genetic susceptibility, poly-IC can induce insulitis or diabetes. Therapeutic agents targeting IFN-alpha may potentially be beneficial in the prevention of type 1 diabetes and autoimmunity.

Prolongation of islet allograft survival following ex vivo transduction with adenovirus encoding a soluble type 1 TNF receptor–Ig fusion decoy

Islet transplantation is a viable long-term therapeutic alternative to daily insulin replacement for type I diabetes. The allogeneic nature of the transplants poses immunological challenges for routine clinical utility. Gene transfer of immunoregulatory molecules and those that improve insulin release kinetics provides rational approaches to facilitate allogeneic islet transplantation as a potential therapy. We have examined the efficacy of a soluble type 1 tumor necrosis factor receptor (TNFR) immunoglobulin-Fc fusion transgene (TNFR-Ig) to protect human islets from cytokine-induced apoptosis in culture, as well as in facilitating allogeneic islet transplants in diabetic mice. Cultured human islets were transduced with an adenoviral vector encoding human TNFR-Ig (Ad-TNFR-Ig). TNFR-Ig protein was secreted by cultured islets, as well as by transduced mouse islet transplants recovered from mouse recipients. Glucose-induced insulin release kinetics were comparable among untransduced, Ad-TNFR-Ig-infected human islets and vector-transduced islets exposed to cytokines. In parallel, Ad-TNFR-Ig-infected islets were protected from cytokine-induced apoptosis activation. Finally, diabetic mice transplanted with allogeneic islets expressing TNFR-Ig returned to and maintained normoglycemia significantly longer than untransduced islet recipients. These data support the potential utility of TNFR-Ig gene transfer to islets as a means of facilitating allogeneic islet transplantation.

Viruses and diabetes

Insulin-dependent diabetes mellitus (IDDM) is a multifactorial disease. Besides a genetic predisposition environmental factors have been implicated in the pathogenesis of beta cell destruction. Among these environmental factors viruses have been the focus of many studies. Some viruses are diabetogenic in animals, and others have been implicated as triggers in human IDDM by temporal and geographical association between IDDM and viral infections, serological evidence of infection in recently diagnosed diabetic patients, and the isolation of viruses from the pancreas of affected individuals. We discuss possible pathomechanisms of viral infections in beta cell destruction and review the studies on involvement of enteroviruses, retroviruses, rubella viruses, cytomegaloviruses, and Epstein-Barr viruses in human IDDM. We also report on studies of diabetogenic viruses in animal models as well as on viral infections protecting from IDDM. Some of the difficulties in linking viral infections to IDDM will be illustrated with data from a transgenic mouse model in which IDDM can be precipitated by infections with certain strains of lymphocytic choriomeningitis virus (LCMV). Emerging treatment concepts that do not rely on defining the initiating autoantigens but involve self-reactive regulatory lymphocytes such as oral antigen administration, as well as DNA vaccines, will be discussed briefly.

Peroxynitrite is a mediator of cytokine-induced destruction of human pancreatic islet beta cells

The proinflammatory cytokines, interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNFalpha), and interferon gamma (IFNgamma), are cytotoxic to pancreatic islet beta cells, possibly by inducing nitric oxide and/or oxygen radical production in the beta cells. Peroxynitrite, the reaction product of nitric oxide and the superoxide radical, is a strong oxidant and cytotoxic mediator; therefore, we hypothesized that peroxynitrite might be a mediator of cytokine-induced islet beta-cell destruction. To test this hypothesis we incubated islets isolated from human pancreata with the cytokine combination of IL-1beta, TNFalpha, and IFNgamma. We found that these cytokines induced significant increases in nitrotyrosine, a marker of peroxynitrite, in islet beta cells, and the increase in nitrotyrosine preceded islet-cell destruction. Peroxynitrite mimicked the effects of cytokines on nitrotyrosine formation and islet beta-cell destruction. L-N(G)-monomethyl arginine, an inhibitor of nitric oxide synthase, prevented cytokine-induced nitric oxide production but not hydrogen peroxide production, nitrotyrosine formation, or islet beta-cell destruction. In contrast, guanidinoethyldisulphide, an inhibitor of inducible nitric oxide synthase and scavenger of peroxynitrite, prevented cytokine-induced nitric oxide and hydrogen peroxide production, nitrotyrosine formation, and islet beta-cell destruction. These results suggest that cytokine-induced peroxynitrite formation is dependent upon increased generation of superoxide (measured as hydrogen peroxide) and that peroxynitrite is a mediator of cytokine-induced destruction of human pancreatic islet beta cells.

Beta cell destruction in the development of autoimmune diabetes in the non-obese diabetic (NOD) mouse

In the non-obese diabetic (NOD) mouse model of Type 1 (insulin-dependent) diabetes, evidence suggests that pancreatic beta cells are destroyed in part by apoptotic mechanisms. The precise mechanisms of beta cell destruction leading to diabetes remain unclear. The NOD mouse has been studied to gain insight into the cellular and molecular mediators of beta cell death, which are discussed in this review. Perforin, secreted by CD8(+) T cells, remains one of the only molecules confirmed to be implicated in beta cell death in the NOD mouse. There are many other molecules, including Fas ligand and cytokines such as interferon-gamma, interleukin-1 and tumor necrosis factor-alpha, which may lead to beta cell destruction either directly or indirectly via regulation of toxic molecules such as nitric oxide. As beta cell death can occur in the absence of perforin, these other factors, in addition to other as yet unidentified factors, may be important in the development of diabetes. Effective protection of NOD mice from beta cell destruction may therefore require inhibition of multiple effector mechanisms.

Reduced NO production improves early canine islet xenograft function: a role for nitric oxide in islet xenograft primary nonfunction

Isolated canine islets transplanted to hyperglycemic rats fail to restore euglycemia in almost all cases, although the grafted islet tissue appears to be morphologically intact for up to 48 h following transplantation. Cytokines typically produced in the xenograft environment (e.g., IL-1 and TNF) inhibit insulin biosynthesis and secretion from isolated pancreatic islets, and are associated with the production of nitric oxide (NO). To further define the relationship between NO production and islet xenotransplantation, the inhibition of NO in a splenocyte/islet coculture system, and the in vivo effect of this inhibition on canine islet xenotransplantation, was investigated. Splenocytes (SPLC) from Lewis rats were cocultured with canine islets (freshly isolated or cultured 7 days), supernatant removed, and NO concentration (NO2) determined by optical density (Griess reaction, 550 nm, expressed as nmol nitrite/10(6) cells/18 h). Lipopolysaccharide (LPS) was used as a positive control of SPLC production of NO. Stimulation by LPS resulted in maximal NO production (2.20 +/- 0.16 nmol/10(6) cells/18 h, p < 0.001 compared to baseline values of 0.73 +/- 0.04 nmol/10(6) cells/18 h). In the presence of NO inhibitors (NMA, polymyxin B, hydrocortisone, aminoguanidine, DMSO), nitrite levels did not significantly rise above unstimulated values. Freshly isolated canine islets did stimulate NO production (1.26 +/- 0.12 nmol/10(6) cells/18 h, p < 0.001). In contrast, cultured canine islets did not stimulate NO production (0.84 +/- 0.09 nmol/10(6) cells/18 h). Transplantation of freshly isolated canine islets to STZ-diabetic recipient Lewis rats resulted in amelioration of hyperglycemia in only 50% (n = 6) of recipients 12 h posttransplant, with a return to hyperglycemia at all subsequent time points. Transplantation of 7-day cultured canine islets resulted in amelioration of hyperglycemia in 88% of recipients 12 h posttransplant and 63% of recipients 24 h posttransplant [p = 0.028, mean survival time (MST) = 1.0 days, n = 8]. Transplantation of canine islet xenografts with aminoguanidine therapy (BID, n = 11) resulted in amelioration of hyperglycemia in 100% of recipients at 12 h posttransplant, decreasing to 82% by 24 h following transplantation (p = 0.002, MST = 0.9 days). These results demonstrate that freshly isolated canine islets are potent stimulators of NO production by rat SPLC in vitro, and that culture of canine islets, or addition of NO inhibitors, abrogates stimulated NO production. These results also demonstrate a statistically significant improvement (p < 0.001) in early function of canine islet xenografts following 7 days of islet culture prior to transplant, and following recipient treatment with aminoguanidine. These studies suggest that the production of NO in the microenvironment of the graft site may adversely affect engraftment and function of canine islets, and suggest that the abrogation of islet-stimulated NO production may improve engraftment following islet xenotransplantation.

Cytokines induce both necrosis and apoptosis via a common Bcl-2-inhibitable pathway in rat insulin-producing cells

The presence of activated macrophages within pancreatic islets in insulin-dependent diabetes mellitus suggests an involvement of beta-cell death by necrosis. The aim of this study was to investigate the frequencies and mechanisms of cytokine-induced beta-cell apoptosis and necrosis and the possible protection mediated by the antiapoptotic gene bcl-2. A combination of interleukin-1beta, interferon-gamma, and tumor necrosis factor-alpha increased both necrosis (17% of cells) and apoptosis (5% of cells) in isolated whole rat islets, as determined by vital staining and fluorescence microscopy. Hyperexpression of Bcl-2, achieved by stable transfection using a multicopy viral vector containing a bcl-2 complementary DNA in rat insulin-producing RINm5F cells, counteracted both apoptosis and necrosis. Cytokine-induced cleavage of the caspase-3 substrate poly(ADP-ribose) polymerase (which, in other cell types, may occur downstream or independently of a Bcl-2-preventable mitochondrial permeability transition) was observed in control- but neither in bcl-2-transfected cells nor in the presence of the iNOS inhibitor N(G)-methyl-L-arginine. Tumor necrosis factor-alpha alone did not clearly induce cell death or poly(ADP-ribose) polymerase-cleavage. These findings suggest that cytokines induce both necrosis and apoptosis in insulin-producing cells via a common Bcl-2-preventable nitric oxide-dependent pathway, which may involve mitochondrial permeability transition. The necrosis:apoptosis ratio might be increased by a relative lack of caspase activity.

Insulin secretion, DNA damage, and apoptosis in human and rat islets of Langerhans following exposure to nitric oxide, peroxynitrite, and cytokines

Cytokine-induced damage may contribute to destruction of insulin-secreting beta-cells in islets of Langerhans during autoimmune diabetes. There is considerable controversy (i) whether human and rat islets respond differently to cytokines, (ii) the extent to which cytokine damage is mediated by induction of nitric oxide formation, and (iii) whether the effects of nitric oxide on islets can be distinguished from those of reactive oxygen species or peroxynitrite. We have analyzed rat and human islet responses in parallel, 48 h after exposure to the nitric oxide donor S-nitrosoglutathione, the mixed donor 3-morpholinosydnonimine, hypoxanthine/xanthine oxidase, peroxynitrite, and combined cytokines (interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma). Insulin secretory response to glucose, insulin content, DNA strand breakage, and early-to-late stage apoptosis were recorded in each experiment. Rat islet insulin secretion was reduced by S-nitrosoglutathione or combined cytokines, but unexpectedly increased by peroxynitrite or hypoxanthine/xanthine oxidase. Effects on human islet insulin secretion were small; cytokines and S-nitrosoglutathione decreased insulin content. Both rat and human islets showed significant and similar levels of DNA damage following all treatments. Apoptosis in neonatal rat islets was increased by every treatment, but was at a low rate in adult rat or human islets and only achieved significance with cytokine treatment of human islets. All cytokine responses were blocked by an arginine analogue. We conclude: (i) Reactive oxygen species increased and nitric oxide decreased insulin secretory responsiveness in rat islets. (ii) Species differences lie mainly in responses to cytokines, applied at a lower dose and shorter time than in most studies of human islets. (iii) Cytokine effects were nitric oxide driven; neither reactive oxygen species nor peroxynitrite reproduced cytokine effects. (iv) Rat and human islets showed equal susceptibility to DNA damage. (v) Apoptosis was not the preferred death pathway in adult islets. (vi) We have found no evidence of human donor variation in the pattern of response to these treatments.

Clinical islet cell transplantation. Are we there yet?

Diabetes mellitus is perhaps the most devastating chronic disease of all time. A brief history of the evolution of treatment modalities is provided, culminating in the rationale for the physiologic replacement of a functioning beta-cell mass by transplantation. Vascularized pancreas transplantation is discussed briefly as an introduction to the transplantation of the isolated islet. A detailed review of the current state of human islet transplantation for the cure of diabetes is then described. Finally, areas for future development are highlighted.

An ataxia telangiectasia model: inefficient cell differentiation and possible reversal by serine protease inhibitors, tumor necrosis factor inhibitors, dexamethasone, and glutathione enhancers

Ataxia telangiectasia (AT) is a rare genetic disorder. Symptoms of the disease include cerebellar ataxia, depressed immunoresponsiveness, increased sensitivity to radiation, and leukemias. Various kinds of AT cells show reduced efficiency of differentiation. The ataxia telangiectasia gene (ATM) may reduce differentiation by suppressing cell responsivity to insulin. Insulin sensitivity seems lower in AT. Tumor necrosis factor may overactivate NF-kappa B in AT, and this increases the radiosensitivity of AT cells. Intracellular reduced glutathione may also become depleted. The reduced levels of glutathione may further alter differentiation of AT cells. Serine protease inhibitors may counteract the effects of tumor necrosis factor. Glutathione enhancers may also prove valuable as therapy.

Th1-like cytokine production profile and individual specific alterations in TCRBV-gene usage of T cells from newly diagnosed type 1 diabetes patients after stimulation with beta-cell antigens

In order to study cytokine production profile (IFN-gamma, IL-4 and TNF-alpha) and TCRBV-gene usage of peripheral autoreactive T cells from IDDM patients, we have generated antigen-specific T cell lines with either tetanus toxoid, insulinoma membranes or a single beta-cell protein, recombinant ICA69, which has been shown to be a target of both autoantibodies and T cells in IDDM. By semi-quantitative polymerase chain reaction (PCR) analysis, we have determined the composition of the T cell receptor repertoire of these T cell lines and compared this with the general peripheral repertoire. T cell responses against beta-cell antigens and tetanus toxoid (TT) were shown to be associated with IFN-gamma and TNF-alpha production, suggestive of a Th1-like phenotype of the T-cell lines. The production of IFN-gamma was significantly higher in T-cell lines generated with ISG compared to those generated with TT. The cytokine production profiles of the T-cell lines generated with ICA69 did not provide an obvious explanation for the inverse relation between cellular and humoral responses to this protein observed earlier. Upon stimulation with beta-cell antigens, outgrowth of T cells using a restricted set of TCRBV elements was observed in newly diagnosed IDDM patients. However, this skewing in TCRBV-gene expression was patient-specific rather than antigen-associated, since the T-cell repertoire that is used for the recognition of these antigens was, overall, heterogeneous.

Cytokines induce deoxyribonucleic acid strand breaks and apoptosis in human pancreatic islet cells

We have previously observed that a 6-day exposure of human pancreatic islets to a combination of cytokines (interleukin-1beta 50 U/ml + tumour necrosis factor-alpha 1000 U/ml + interferon-gamma 1000 U/ml) severely impairs beta-cell functions. In the present study, we examined whether this condition affects DNA integrity and viability of human islet cells. Cells were studied after 3, 6, and 9 days of cytokine treatment by both single cell gel electrophoresis (the "comet assay," a sensitive method for detection of DNA strand breaks) and by a cytotoxicity assay using the DNA binding dyes Hoechst 33342 and propidium iodide as indices for the number of viable, necrotic, and apoptotic cells. Cytokine treatment for 6 and 9 days resulted in a 50% increase in comet length (P < 0.01 vs. controls), indicating DNA strand breaks, as well as in a significant increase in the number of apoptotic cells (P < 0.02 vs. controls), but not in the number of necrotic cells. The arginine analogs N(G)-nitro-L-arginine and N(G)-monomethyl-L-arginine prevented nitric oxide formation by the cytokines but did not interfere with cytokine-induced DNA strand breaks and apoptosis. The present data suggest that prolonged (6-9 days) exposure of human pancreatic islets to a mixture of cytokines induces DNA strand breaks and cell death by apoptosis. These deleterious effects of cytokines appear to be independent of nitric oxide generation.

Elevated serum levels of macrophage-derived cytokines precede and accompany the onset of IDDM

To determine whether cytokines could have a role in the development of insulin-dependent diabetes mellitus (IDDM), we measured serum levels of cytokines derived from T helper 1 (interleukin-2 and interferon-gamma), T helper 2 (interleukin-4 and interleukin-10) lymphocytes and macrophages (tumour necrosis factor-alpha, interleukin-1 alpha and interleukin-1 beta) in patients before and after the onset of IDDM. Recently diagnosed IDDM patients had significantly higher levels of interleukin-2, interferon-gamma, tumour necrosis factor-alpha and interleukin-1 alpha than patients with either long-standing IDDM, non-insulin-dependent diabetes (NIDDM), Graves' disease, or control subjects (p < 0.05 for all). Compared with control subjects, patients with long-standing IDDM and those with NIDDM had higher interleukin-2 and tumour necrosis factor-alpha levels (p < 0.01 for all). Interleukin-4 and interleukin-10 were detectable in sera of patients with Graves' disease only, while interleukin-1 beta was not detectable in the serum of any control or test subject. To investigate whether high cytokine levels precede the onset of IDDM, we studied 28 non-diabetic identical co-twins of patients with IDDM, followed-up prospectively for up to 6 years after the diagnosis of the index. Levels of tumour necrosis factor-alpha and interleukin-1 alpha were elevated above the normal range more frequently in the eight twins who developed diabetes than in those 20 who did not (p < 0.005). Analysis of T helper 1 and T helper 2 profiles of the twin groups did not reveal a clear difference between prediabetic twins and twins remaining non-diabetic. These results support the notion that T helper 1 lymphocytes may play a role in the development of IDDM. This is associated with release of macrophage-derived cytokines, which is also a feature of the prediabetic period. The lack of evidence of a dominant T helper 1 profile of cytokine release before diabetes onset suggests that additional events, activating this arm of the cellular immune response, are required in the immediate prediabetic period.

Impact of metabolic activity of beta cells on cytokine-induced damage and recovery of rat pancreatic islets

The influence of beta cell activity on cytokine-induced functional and structural impairments as well as the ability of those damaged cells to recover were investigated. Rat islets cultured for 4 days in the presence of 5, 10, and 30 mmol/l glucose were exposed to interferon-gamma (IFN, 500 U/ml) and tumor necrosis factor-alpha (TNF, 250 U/ml) for the last 24 h. After cytokine removal islets were allowed to recover spontaneously in culture medium containing 10 mmol/l glucose for a further 7 days. Cytokines significantly inhibited insulin release into culture medium, insulin storage, glucose-stimulated insulin secretion, protein, and DNA synthesis. In the presence of cytokines there was a six- to eightfold increase in nitrite production by the islets. The functional impairments were more pronounced in metabolically stimulated beta cells. In addition, cytokines caused membrane alterations as indicated by increased spontaneous chromium-51 release. The cytokines specifically induced the synthesis of two proteins (72 and 88 kDa, respectively). By immunoblotting, the 72-kDa protein was identified as heat shock protein. After a 1-week recovery period, insulin storage and stimulated insulin secretion of cytokine-treated islets were still significantly diminished. However, protein and DNA synthesis of cytokine-exposed islets returned to pre-exposure levels. In conclusion, high beta cell activity increases islet susceptibility to TNF+IFN. Cytokine-induced, long-lasting, inhibitory effects are primarily directed to beta-cell-specific functions, while general vital cell functions clearly recover after cytokine removal. The induction of certain proteins and the increased protein synthesis and replication rate after cytokine removal might reflect activated repair processes.

Effects of prolonged exposure in vitro to interferon-gamma and tumour necrosis factor-alpha on nitric oxide and insulin production of rat pancreatic islets

It has been postulated that cytokines may mediate the beta-cell destructive process causing insulin-dependent diabetes mellitus. The aim of this investigation was to study cytokine effects on pancreatic islet functions in vitro. For this purpose 5-7 days precultured (medium RPMI 1640 +/- 10% fetal calf serum) rat pancreatic islets were exposed for another 48 h to either culture medium alone or with addition of rat interferon-gamma (IFN-gamma; 1000 U/ml), or human tumor necrosis factor-alpha (TNF-alpha; 1000 U/ml) or a combination of the cytokines. After the culture period the islets were subjected to short-term experiments in the absence of cytokines. Neither the DNA nor the insulin content of the islets were affected by the cytokines alone or by the combination. The combination IFN-gamma + TNF-alpha caused a 5-fold increase in the medium nitrite accumulation, indicating induction of nitric oxide formation. It was found that IFN-gamma reduced medium insulin accumulation and basal insulin secretion at 1.7 mM glucose, without affecting the medium nitrite level. On the other hand, the islet glucose oxidation rate at 16.7 mM glucose and the insulin secretory response to 16.7 mM glucose was normal or even increased when examined after 48 h. TNF-alpha alone had no significant effects. In conclusion, a combination of the cytokines can induce nitric oxide formation and inhibition of insulin production in rat pancreatic islets. However, this effect appears not to be sustained. Moreover, IFN-gamma alone seems to induce changes not related to nitric oxide.

Cytokines suppress human islet function irrespective of their effects on nitric oxide generation

Cytokines have been proposed as inducers of beta-cell damage in human insulin-dependent diabetes mellitus via the generation of nitric oxide (NO). This concept is mostly based on data obtained in rodent pancreatic islets using heterologous cytokine preparations. The present study examined whether exposure of human pancreatic islets to different cytokines induces NO and impairs beta-cell function. Islets from 30 human pancreata were exposed for 6-144 h to the following human recombinant cytokines, alone or in combination: IFN-gamma (1,000 U/ml), TNF-alpha (1,000 U/ml), IL-6 (25 U/ml), and IL-1 beta (50 U/ml). After 48 h, none of the cytokines alone increased islet nitrite production, but IFN-gamma induced a 20% decrease in glucose-induced insulin release. Combinations of cytokines, notably IL-1 beta plus IFN-gamma plus TNF-alpha, induced increased expression of inducible NO synthase mRNA after 6 h and resulted in a fivefold increase in medium nitrite accumulation after 48 h. These cytokines did not impair glucose metabolism or insulin release in response to 16.7 mM glucose, but there was an 80% decrease in islet insulin content. An exposure of 144 h to IL-1 beta plus IFN-gamma plus TNF-alpha increased NO production and decreased both glucose-induced insulin release and insulin content. Inhibitors of NO generation, aminoguanidine or NG-nitro-L-arginine, blocked this cytokine-induced NO generation, but did not prevent the suppressive effect of IL-1 beta plus IFN-gamma plus TNF-alpha on insulin release and content. In conclusion, isolated human islets are more resistant to the suppressive effects of cytokines and NO than isolated rodent islets. Moreover, the present study suggests that NO is not the major mediator of cytokine effects on human islets.