Stable expression of manganese superoxide dismutase (MnSOD) in insulinoma cells prevents IL-1beta- induced cytotoxicity and reduces nitric oxide production

Newer therapeutic approaches towards the management of diabetes mellitus: an update

Diabetes mellitus is a chronic metabolic condition characterized by an elevation of blood glucose levels, resulting from defects in insulin secretion, insulin action, or both. The prevalence of the disease has been rapidly rising all over the globe at an alarming rate. Despite advances in the management of diabetes mellitus, it remains a growing epidemic that has become a significant public health burden due to its high healthcare costs and its complications. There is no cure has yet been found for the disease, however, treatment modalities include insulin and antidiabetic agents along with lifestyle modifications are still the mainstay of therapy for diabetes mellitus. The treatment spectrum for the management of diabetes mellitus has rapidly developed in recent years, with new class of therapeutics and expanded indications. This article focused on the emerging therapeutic approaches other than the conventional pharmacological therapies, which include stem cell therapy, gene therapy, siRNA, nanotechnology and theranostics.

Novel Fusion Protein Targeting Mitochondrial DNA Improves Pancreatic Islet Functional Potency and Islet Transplantation Outcomes

Long-term graft survival is an ongoing challenge in the field of islet transplantation. With the growing demand for transplantable organs, therapies to improve organ quality and reduce the incidence of graft dysfunction are of paramount importance. We evaluated the protective role of a recombinant DNA repair protein targeted to mitochondria (Exscien I-III), as a therapeutic agent using a rodent model of pancreatic islet transplantation. We first investigated the effect of therapy on isolated rat islets cultured with pro-inflammatory cytokines (interleukin-1 β, interferon γ, and tumor necrosis factor α) for 48 h and documented a significant reduction in apoptosis by flow cytometry, improved viability by immunofluorescence, and conserved functional potency in vitro and in vivo in Exscien I-III-treated islets. We then tested the effect of therapy in systemic inflammation using a rat model of donor brain death (BD) sustained for a 6-h period. Donor rats were allocated to 4 groups: (non-BD + vehicle, non-BD + Exscien I-III, BD + vehicle, and BD + Exscien I-III) and treated with Exscien I-III (4 mg/kg) or vehicle 30 min after BD induction. Sham (non-BD)-operated animals receiving either Exscien I-III or vehicle served as controls. Islets purified from BD + Exscien I-III-treated donors showed a significant increase in glucose-stimulated insulin release in vitro when compared to islets from vehicle-treated counterparts. In addition, donor treatment with Exscien I-III attenuated the effects of BD and significantly improved the functional potency of transplanted islets in vivo. Our data indicate that mitochondrially targeted antioxidant therapy is a novel strategy to protect pancreas and islet quality from the deleterious effects of cytokines in culture and during the inflammatory response associated with donation after BD. The potential for rapid translation into clinical practice makes Exscien I-III an attractive therapeutic option for the management of brain-dead donors or as an additive to islets in culture after isolation setting.

Pro-inflammatory cytokines attenuate glucose-stimulated insulin secretion from INS-1E insulinoma cells by restricting mitochondrial pyruvate oxidation capacity - Novel mechanistic insight from real-time analysis of oxidative phosphorylation

Pro-inflammatory cytokines cause pancreatic beta cell failure during the development of type 2 diabetes. This beta cell failure associates with mitochondrial dysfunction, but the precise effects of cytokines on mitochondrial respiration remain unclear. To test the hypothesis that pro-inflammatory cytokines impair glucose-stimulated insulin secretion (GSIS) by inhibiting oxidative ATP synthesis, we probed insulin release and real-time mitochondrial respiration in rat INS-1E insulinoma cells that were exposed to a combination of 2 ng/mL interleukin-1-beta and 50 ng/mL interferon-gamma. We show that 24-h exposure to these cytokines dampens both glucose- and pyruvate-stimulated insulin secretion (P < 0.0001 and P < 0.05, respectively), but does not affect KCl-induced insulin release. Mirroring secretory defects, glucose- and pyruvate-stimulated mitochondrial respiration are lowered after cytokine exposure (P < 0.01). Further analysis confirms that cytokine-induced mitochondrial respiratory defects occur irrespective of whether fuel oxidation is coupled to, or uncoupled from, ATP synthesis. These observations demonstrate that pro-inflammatory cytokines attenuate GSIS by restricting mitochondrial pyruvate oxidation capacity. Interleukin-1-beta and interferon-gamma also increase mitochondrial superoxide levels (P < 0.05), which may reinforce the inhibition of pyruvate oxidation, and cause a modest (20%) but significant (P < 0.01) loss of INS-1E cells. Cytokine-induced INS-1E cell failure is insensitive to palmitoleate and linoleate, which is at odds with the cytoprotection offered by unsaturated fatty acids against harm caused by nutrient excess. Our data disclose a mitochondrial mechanism for cytokine-impaired GSIS in INS-1E cells, and suggest that inflammatory and nutrient-related beta cell failure emerge, at least partly, through distinct paths.

Comparison of Size, Viability, and Function of Fetal Pig Islet-Like Cell Clusters after Digestion Using Collagenase or Liberase

Liberase is a highly purified blend of collagenases that has been specifically developed to eliminate the numerous problems associated with the conventional use of crude collagenase when isolating islet-like cell clusters (ICCs) from pancreases of different species. The influence of Liberase on yield, size, viability, and function of ICCs has been documented when this enzyme was used to digest adult but not fetal pancreases. In this study, we compared the effects of collagenase and Liberase on fetal pig ICCs. A total of eight fetal pig pancreas digestions were analyzed. Fetuses were obtained from Large White Landrace pigs of gestational age 80 ± 2.1 days. The pancreases were digested with either 3 mg/ml collagenase P or 1.2 mg/ml Liberase HI. The time taken to digest the pancreas was shorter for collagenase when compared with Liberase (22 ± 2 vs. 31 ± 2 min). The size of ICCs was similar for both collagenase (83 ± 0.5 μm) and Liberase (79 ± 0.4 μm) as was the number of ICCs produced per pancreas (7653 ± 1297 vs. 8101 ± 1177). Viability, as assessed using fluorescent markers, was slightly greater for Liberase (79 ± 1% vs. 76 ± 1%, p < 0.05). Responsiveness to β-cell stimulus (20 mM KCl) was similar for both methods of isolation, as was the insulin content of the ICCs, both in vitro and at 1 month after transplantation of 1500 ICCs beneath the renal capsule of immunoincompetent mice. Despite the high content of endotoxins in collagenase, the above results show that this enzyme was equally as efficient as Liberase in isolating functional ICCs from fetal pig pancreas.

The Effectiveness of Various Salacca Vinegars as Therapeutic Agent for Management of Hyperglycemia and Dyslipidemia on Diabetic Rats

The aim of this study was to explore the potency of salacca vinegar made from various Indonesian salacca fruit extracts as therapeutic agent for hyperglycemia and dyslipidemia for STZ-induced diabetic rats. The rats were grouped into untreated rats, STZ-induced diabetic rats without treatment, and STZ-induced diabetic rats treated with Pondoh salacca vinegar, Swaru salacca vinegar, Gula Pasir salacca vinegar, Madu salacca vinegar, or Madura salacca vinegar. Parameter observed included blood glucose, total cholesterol (TC), high density lipoprotein (HDL), low density lipoprotein (LDL), triglyceride (TG), malondialdehyde (MDA), superoxide dismutase (SOD), and pancreas histopathology of the samples. The results demonstrated that all salacca vinegars were capable of reducing blood sugar (from 25.1 to 62%) and reducing LDL (from 9.5 to 14.8 mg/dL), TG (from 58.3 to 69.5 mg/dL), MDA (from 1.1 to 2.2 mg/dL), and TC (from 56.3 to 70.5 mg/dL) as well as increasing HDL blood sugar of STZ-induced diabetic Wistar rats (from 52.3 to 60 mg/dL). Various salacca vinegars were also capable of regenerating pancreatic cells. Nevertheless, the ability of Swaru salacca vinegar to manage hyperglycemia and dyslipidemia appeared to be superior to other salacca vinegars. Swaru salacca vinegar is a potential therapeutic agent to manage hyperglycemia and dyslipidemia of STZ-induced diabetic rats.

Tat-DJ-1 inhibits oxidative stress-mediated RINm5F cell death through suppression of NF-κB and MAPK activation

Oxidative stress is highly involved in the development of diabetes mellitus by destruction of pancreatic β-cells. DJ-1 is an antioxidant protein and DJ-1 expression levels are known to be reduced in diabetes mellitus. Thus, we examined the effects of DJ-1 protein against oxidative stress-induced pancreatic β-cell (RINm5F) death using cell permeable wild-type and mutant-type (C106A) Tat-DJ-1 proteins, which both efficiently transduced into RINm5F cells. Intracellular stability of wild-type Tat-DJ-1 persisted two times longer than C106A Tat-DJ-1. Wild-type Tat-DJ-1 protein markedly protected cells from hydrogen peroxide-induced toxicities such as cell death, reactive oxygen species generation, and DNA fragmentation. Further, wild-type Tat-DJ-1 protein significantly inhibited hydrogen peroxide-induced activation of mitogen-activated protein kinases and NF-κB signaling. On the other hand, C106A Tat-DJ-1 protein did not show the same protective effects. These results indicate that wild-type Tat-DJ-1 inhibits oxidative stress-induced cellular toxicity and activation of mitogen-activated protein kinases and NF-κB signals in RINm5F cells. These results suggest that wild-type Tat-DJ-1 protein may be a potential therapeutic agent against diabetes mellitus or toward the prevention of pancreatic β-cell destruction.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Alternative Medicine in Diabetes - Role of Angiogenesis, Oxidative Stress, and Chronic Inflammation

Diabetes is a chronic metabolic disorder that is characterized by hyperglycemia due to lack of or resistance to insulin. Patients with diabetes are frequently afflicted with ischemic vascular disease and impaired wound healing. Type 2 diabetes is known to accelerate atherosclerotic processes, endothelial cell dysfunction, glycosylation of extracellular matrix proteins, and vascular denervation. Herbal medicines and naturally occurring substances may positively affect diabetes management, and could thus be utilized as cost-effective means of supporting treatment in developing countries. Natural treatments have been used in these countries for a long time to treat diabetes. The present review analyses the features of aberrant angiogenesis, abnormalities in growth factors, oxidative stress, and metabolic derangements relevant to diabetes, and how herbal substances and their active chemical constituents may counteract these events. Evidence for possible biochemical effectiveness and limitations of herbal medicines are given, as well as details regarding the role of cytokines and nitric oxide.

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.

Manganese supplementation protects against diet-induced diabetes in wild type mice by enhancing insulin secretion

Mitochondrial dysfunction is both a contributing mechanism and complication of diabetes, and oxidative stress contributes to that dysfunction. Mitochondrial manganese-superoxide dismutase (MnSOD) is a metalloenzyme that provides antioxidant protection. We have previously shown in a mouse model of hereditary iron overload that cytosolic iron levels affected mitochondrial manganese availability, MnSOD activity, and insulin secretion. We therefore sought to determine the metallation status of MnSOD in wild-type mice and whether altering that status affected β-cell function. 129/SvEVTac mice given supplemental manganese exhibited a 73% increase in hepatic MnSOD activity and increased metallation of MnSOD. To determine whether manganese supplementation offered glucose homeostasis under a situation of β-cell stress, we challenged C57BL/6J mice, which are more susceptible to diet-induced diabetes, with a high-fat diet for 12 weeks. Manganese was supplemented or not for the final 8 weeks on that diet, after which we examined glucose tolerance and the function of isolated islets. Liver mitochondria from manganese-injected C57BL/6J mice had similar increases in MnSOD activity (81%) and metallation as were seen in 129/SvEVTac mice. The manganese-treated group fed high fat had improved glucose tolerance (24% decrease in fasting glucose and 41% decrease in area under the glucose curve), comparable with mice on normal chow and increased serum insulin levels. Isolated islets from the manganese-treated group exhibited improved insulin secretion, decreased lipid peroxidation, and improved mitochondrial function. In conclusion, MnSOD metallation and activity can be augmented with manganese supplementation in normal mice on normal chow, and manganese treatment can increase insulin secretion to improve glucose tolerance under conditions of dietary stress.

LMP-420, a small molecular inhibitor of TNF-α, prolongs islet allograft survival by induction of suppressor of cytokine signaling-1: synergistic effect with cyclosporin-A

Inflammatory insults following islet transplantation (ITx) hinders engraftment and long-term function of the transplanted (Tx) islets. Using a murine model of ITx, we determined the role of LMP-420, a novel TNF-α inhibitor, both individually and in combination with the immunosuppressant cyclosporine A (CSA) in islet engraftment and survival. Diabetic C57BL/6 mice were Tx with 500 BALB/c islets under the kidney capsule. Four cohorts were used: LMP-420 only, CSA only, combination of LMP-420 and CSA (LMP+CSA), and control (n = 12 per cohort). Serial monitoring of blood glucose levels revealed that LMP+CSA (35 ± 5 days) prolonged stable blood insulin levels compared to control (6 ± 4 days). Immunohistology demonstrated that coadministration (LMP+CSA) results in a significant decrease in CD8(+) T-cell infiltration (LMP+CSA: 31 ± 18 vs. control: 224 ± 51 cells, p < 0.001). Serum cytokine analysis revealed that LMP-420 administration resulted in an increase in the anti-inflammatory cytokine IL-10 (2.5-fold), and a decrease in TNF-α (threefold) with no change in IL-2. However, coadministration resulted in a marked decrease in both IL-2 and TNF-α (threefold) along with increase in IL-10 (threefold). Coadministration also demonstrated increase of antiapoptotic SOCS-1 and Mn-SOD expression and significant reduction of donor-specific antibodies (p < 0.005). In conclusion, LMP-420 administration with CSA results in the upregulation of anti-inflammatory and antiapoptotic mechanisms which facilitate islet allograft engraftment and survival.

Protective Effect of Heme Oxygenase-1 on High Glucose-Induced Pancreatic β-Cell Injury

BACKGROUND

Glucose toxicity that is caused by chronic exposure to a high glucose concentration leads to islet dysfunction and induces apoptosis in pancreatic β-cells. Heme oxygenase-1 (HO-1) has been identified as an anti-apoptotic and cytoprotective gene. The purpose of this study is to investigate whether HO-1 up-regulation when using metalloprotophyrin (cobalt protoporphyrin, CoPP) could protect pancreatic β-cells from high glucose-induced apoptosis.

METHODS

Reverse transcription-polymerase chain reaction was performed to analyze the CoPP-induced mRNA expression of HO-1. Cell viability of INS-1 cells cultured in the presence of CoPP was examined by acridine orange/propidium iodide staining. The generation of intracellular reactive oxygen species (ROS) was measured using flow cytometry. Glucose stimulated insulin secretion (GSIS) was determined following incubation with CoPP in different glucose concentrations.

RESULTS

CoPP increased HO-1 mRNA expression in both a dose- and time-dependent manner. Overexpression of HO-1 inhibited caspase-3, and the number of dead cells in the presence of CoPP was significantly decreased when exposed to high glucose conditions (HG). CoPP also decreased the generation of intracellular ROS by 50% during 72 hours of culture with HG. However, decreased GSIS was not recovered even in the presence of CoPP.

CONCLUSION

Our data suggest that CoPP-induced HO-1 up-regulation results in protection from high glucose-induced apoptosis in INS-1 cells; however, glucose stimulated insulin secretion is not restored.

Advanced glycation end products are direct modulators of β-cell function

OBJECTIVE

Excess accumulation of advanced glycation end products (AGEs) contributes to aging and chronic diseases. We aimed to obtain evidence that exposure to AGEs plays a role in the development of type 1 diabetes (T1D).

RESEARCH DESIGN AND METHODS

The effect of AGEs was examined on insulin secretion by MIN6N8 cells and mouse islets and in vivo in three separate rodent models: AGE-injected or high AGE-fed Sprague-Dawley rats and nonobese diabetic (NODLt) mice. Rodents were also treated with the AGE-lowering agent alagebrium.

RESULTS

β-Cells exposed to AGEs displayed acute glucose-stimulated insulin secretory defects, mitochondrial abnormalities including excess superoxide generation, a decline in ATP content, loss of MnSOD activity, reduced calcium flux, and increased glucose uptake, all of which were improved with alagebrium treatment or with MnSOD adenoviral overexpression. Isolated mouse islets exposed to AGEs had decreased glucose-stimulated insulin secretion, increased mitochondrial superoxide production, and depletion of ATP content, which were improved with alagebrium or with MnTBAP, an SOD mimetic. In rats, transient or chronic exposure to AGEs caused progressive insulin secretory defects, superoxide generation, and β-cell death, ameliorated with alagebrium. NODLt mice had increased circulating AGEs in association with an increase in islet mitochondrial superoxide generation, which was prevented by alagebrium, which also reduced the incidence of autoimmune diabetes. Finally, at-risk children who progressed to T1D had higher AGE concentrations than matched nonprogressors.

CONCLUSIONS

These findings demonstrate that AGEs directly cause insulin secretory defects, most likely by impairing mitochondrial function, which may contribute to the development of T1D.

Canonical notch pathway protects hepatocytes from ischemia/reperfusion injury in mice by repressing reactive oxygen species production through JAK2/STAT3 signaling

Hepatic ischemia/reperfusion (I/R) injury is initiated by reactive oxygen species (ROS) accumulated during the early reperfusion phase after ischemia, but cellular mechanisms controlling ROS production and scavenging have not been fully understood. In this study, we show that blocking Notch signal by knockout of the transcription factor RBP-J or a pharmacological inhibitor led to aggravated hepatic I/R injury, as manifested by deteriorated liver function and increased apoptosis, necrosis, and inflammation, both in vitro and in vivo. Interruption of Notch signaling resulted in increased intracellular ROS in hepatocytes, and a ROS scavenger cured exacerbated hepatic I/R injury after Notch signaling blockade, suggesting that Notch signal deficiency aggravated I/R injury through increased ROS levels. Notch signal blockade resulted in down-regulation of Hes5, leading to reduced formation of the Hes5-STAT3 complex and hypophosphorylation of STAT3, which further attenuated manganese superoxide dismutase (MnSOD) expression and increased ROS and apoptosis. Indeed, overexpression of a constitutively active STAT3 rescued MnSOD expression and I/R injury-induced apoptosis in the absence of Notch signaling. Finally, forced Notch activation by ligand stimulation or Hes5 overexpression reduced intracellular ROS and protected hepatocytes from apoptosis after I/R injury through the activation of STAT3 and MnSOD expression.

CONCLUSION

Notch signal protects hepatocytes from I/R injury by Hes5-dependent activation of STAT3, which activates the expression of MnSOD, leading to the scavenging of ROS.

Pancreatic β-cell death in response to pro-inflammatory cytokines is distinct from genuine apoptosis

A reduction in functional β-cell mass leads to both major forms of diabetes; pro-inflammatory cytokines, such as interleukin-1beta (IL-1β) and gamma-interferon (γ-IFN), activate signaling pathways that direct pancreatic β-cell death and dysfunction. However, the molecular mechanism of β-cell death in this context is not well understood. In this report, we tested the hypothesis that individual cellular death pathways display characteristic phenotypes that allow them to be distinguished by the precise biochemical and metabolic responses that occur during stimulus-specific initiation. Using 832/13 and INS-1E rat insulinoma cells and isolated rat islets, we provide evidence that apoptosis is unlikely to be the primary pathway underlying β-cell death in response to IL-1β+γ-IFN. This conclusion was reached via the experimental results of several different interdisciplinary strategies, which included: 1) tandem mass spectrometry to delineate the metabolic differences between IL-1β+γ-IFN exposure versus apoptotic induction by camptothecin and 2) pharmacological and molecular interference with either NF-κB activity or apoptosome formation. These approaches provided clear distinctions in cell death pathways initiated by pro-inflammatory cytokines and bona fide inducers of apoptosis. Collectively, the results reported herein demonstrate that pancreatic β-cells undergo apoptosis in response to camptothecin or staurosporine, but not pro-inflammatory cytokines.

A glimpse of various pathogenetic mechanisms of diabetic nephropathy

Diabetic nephropathy is a well-known complication of diabetes and is a leading cause of chronic renal failure in the Western world. It is characterized by the accumulation of extracellular matrix in the glomerular and tubulointerstitial compartments and by the thickening and hyalinization of intrarenal vasculature. The various cellular events and signaling pathways activated during diabetic nephropathy may be similar in different cell types. Such cellular events include excessive channeling of glucose intermediaries into various metabolic pathways with generation of advanced glycation products, activation of protein kinase C, increased expression of transforming growth factor β and GTP-binding proteins, and generation of reactive oxygen species. In addition to these metabolic and biochemical derangements, changes in the intraglomerular hemodynamics, modulated in part by local activation of the renin-angiotensin system, compound the hyperglycemia-induced injury. Events involving various intersecting pathways occur in most cell types of the kidney.

Oxidative stress and beta-cell dysfunction

Diabetes mellitus type 1 and 2 (T1DM and T2DM) are complex multifactorial diseases. Loss of beta-cell function caused by reduced secretory capacity and enhanced apoptosis is a key event in the pathogenesis of both diabetes types. Oxidative stress induced by reactive oxygen and nitrogen species is critically involved in the impairment of beta-cell function during the development of diabetes. Because of their low antioxidant capacity, beta-cells are extremely sensitive towards oxidative stress. In beta-cells, important targets for an oxidant insult are cell metabolism and K(ATP) channels. The oxidant-evoked alterations of K(ATP) channel activity seem to be critical for oxidant-induced dysfunction because genetic ablation of K(ATP) channels attenuates the effects of oxidative stress on beta-cell function. Besides the effects on metabolism, interference of oxidants with mitochondria induces key events in apoptosis. Consequently, increasing antioxidant defence is a promising strategy to delay beta cell failure in (pre)-diabetic patients or during islet transplantation. Knock-out of K(ATP) channels has beneficial effects on oxidant-induced inhibition of insulin secretion and cell death. Interestingly, these effects can be mimicked by sulfonylureas that have been used in the treatment of T2DM for many years. Loss of functional K(ATP) channels leads to up-regulation of antioxidant enzymes, a process that depends on cytosolic Ca(2+). These observations are of great importance for clinical intervention because they show a possibility to protect beta-cells at an early stage before dramatic changes of the secretory capacity and loss of cell mass become manifest and lead to glucose intolerance or even overt diabetes.

Reactive oxygen intermediate-induced pathomechanisms contribute to immunosenescence, chronic inflammation and autoimmunity

Deregulation of reactive oxygen intermediates (ROI) resulting in either too high or too low concentrations are commonly recognized to be at least in part responsible for many changes associated with aging. This article reviews ROI-dependent mechanisms critically contributing to the decline of immune function during physiologic - or premature - aging. While ROI serve important effector functions in cellular metabolism, signalling and host defence, their fine-tuned generation declines over time, and ROI-mediated damage to several cellular components and/or signalling deviations become increasingly prevalent. Although distinct ROI-associated pathomechanisms contribute to immunosenescence of the innate and adaptive immune system, mutual amplification of dysfunctions may often result in hyporesponsiveness and immunodeficiency, or in chronic inflammation with hyperresponsiveness/deregulation, or both. In this context, we point out how imbalanced ROI contribute ambiguously to driving immunosenescence, chronic inflammation and autoimmunity. Although ROI may offer a distinct potential for therapeutic targeting along with the charming opportunity to rescue from deleterious processes of aging and chronic inflammatory diseases, such modifications, owing to the complexity of metabolic interactions, may carry a marked risk of unforeseen side effects.

Serum albumin protects from cytokine-induced pancreatic beta cell death by a phosphoinositide 3-kinase-dependent mechanism

The present study was undertaken to investigate the biological activity of serum albumin when pancreatic beta cells were challenged by cytokines and pro-apoptotic reactive oxygen species like H(2)O(2). Culture of mouse islets or INS-1E beta cells for 24 h in the presence of H(2)O(2) (25 micromol/l) increased cell death. This demise was prevented by serum albumin, dependent on its free sulfhydryl group, emphasizing that albumin may scavenge H(2)O(2) due to its antioxidant properties. Culture for 48 h with a cytokine mixture of IL-1beta (160 pg/ml), IFN-gamma (200 ng/ml), and TNF-alpha (2 ng/ml) revealed that albumin, also protected against cytokine-induced death of both mouse islets and INS-1E beta cells. This protective effect against cytokine-induced beta cell death was, however, not dependent on albumins free sulfhydryl group, but was inhibited by the phosphoinositide 3-kinase (PI3K) inhibitors LY294002 (25 micromol/l) and wortmannin (1 micromol/l), suggesting that albumin may rescue beta cells from cytokine-induced cell death by activation of PI3K. In accordance, albumin stimulated phosphorylation of Akt, a down-stream target for PI3K. In conclusion, it is suggested that albumin may be a survival factor for pancreatic beta cells through scavenging of reactive oxygen species and by PI3K-dependent activation of Akt.

Glucolipotoxicity: fuel excess and beta-cell dysfunction

Glucotoxicity, lipotoxicity, and glucolipotoxicity are secondary phenomena that are proposed to play a role in all forms of type 2 diabetes. The underlying concept is that once the primary pathogenesis of diabetes is established, probably involving both genetic and environmental forces, hyperglycemia and very commonly hyperlipidemia ensue and thereafter exert additional damaging or toxic effects on the beta-cell. In addition to their contribution to the deterioration of beta-cell function after the onset of the disease, elevations of plasma fatty acid levels that often accompany insulin resistance may, as glucose levels begin to rise outside of the normal range, also play a pathogenic role in the early stages of the disease. Because hyperglycemia is a prerequisite for lipotoxicity to occur, the term glucolipotoxicity, rather than lipotoxicity, is more appropriate to describe deleterious effects of lipids on beta-cell function. In vitro and in vivo evidence supporting the concept of glucotoxicity is presented first, as well as a description of the underlying mechanisms with an emphasis on the role of oxidative stress. Second, we discuss the functional manifestations of glucolipotoxicity on insulin secretion, insulin gene expression, and beta-cell death, and the role of glucose in the mechanisms of glucolipotoxicity. Finally, we attempt to define the role of these phenomena in the natural history of beta-cell compensation, decompensation, and failure during the course of type 2 diabetes.

SUMO4 and its role in type 1 diabetes pathogenesis

Susceptibility to type 1 diabetes (T1D) is determined by interactions of multiple genes with unknown environmental factors. Despite the characterization of over 20 susceptibility regions for T1D, identification of specific genes in these regions is still a formidable challenge. In 2004, we first reported the cloning of a novel, small ubiquitin-like modifier (SUMO) gene, SUMO4, in the IDDM5 interval on chromosome 6q25, and presented strong genetic and functional evidence suggesting that SUMO4 is a T1D susceptibility gene. Subsequent studies have consistently confirmed this association in multiple Asian populations despite controversial observations in Caucasians. In this review, we will update the genetic evidence supporting SUMO4 as a T1D susceptibility gene and discuss the possible explanations for the discrepant associations observed in Caucasians. We will then discuss the mechanisms through which SUMO4 contributes to the pathogenesis of T1D.

Chronic oxidative stress as a mechanism for glucose toxicity of the beta cell in type 2 diabetes

Type 2 diabetes is characterized by a relentless decline in pancreatic islet beta cell function and worsening hyperglycemia despite optimal medical treatment. Our central hypothesis is that residual hyperglycemia, especially after meals, generates reactive oxygen species (ROS), which in turn causes chronic oxidative stress on the beta cell. This hypothesis is supported by several observations. Exposure of isolated islets to high glucose concentrations induces increases in intracellular peroxide levels. The beta cell has very low intrinsic levels of antioxidant proteins and activities and thus is very vulnerable to ROS. Treatment with antioxidants protects animal models of type 2 diabetes against complete development of phenotypic hyperglycemia. The molecular mechanisms responsible for the glucose toxic effect on beta cell function involves disappearance of two important regulators of insulin promoter activity, PDX-1 and MafA. Antioxidant treatment in vitro prevents disappearance of these two transcription factors and normalizes insulin gene expression. These observations suggest that the ancillary treatment with antioxidants may improve outcomes of standard therapy of type 2 diabetes in humans.

Leptin induces inflammation-related genes in RINm5F insulinoma cells

BACKGROUND

Leptin acts not only on hypothalamic centers to control food intake but has additional functions in peripheral tissues, e.g. inhibition of insulin secretion from pancreatic islets. The leptin receptor (LEPRb) is a class I cytokine receptor that mediates activation of STAT transcription factors. In this study, we characterise the regulation of inflammation-related genes by leptin in insulinoma cells and compare the effect of transcriptional regulation by leptin with that of other cytokines.

RESULTS

We have used RINm5F insulinoma cells as a model system for a peripheral target cell of leptin. Six transcripts encoding inflammation-related proteins were found to be upregulated by activation of LEPRb, namely lipocalin-2, pancreatitis-associated protein, preprotachykinin-1, fibrinogen-beta, tissue-type plasminogen activator (tPA) and manganese-dependent superoxide dismutase (MnSOD). Four of these transcripts (fibrinogen-beta, lipocalin-2, tPA, MnSOD) were also induced by the proinflammatory cytokine interleukin-1beta (IL-1beta). Interferon-gamma alone had no effect on the leptin-induced transcripts but enhanced the upregulation by IL-1beta of lipocalin-2, tPA and MnSOD mRNA levels. Experiments with LEPRb point mutants revealed that the upregulation of the inflammation-related genes depended on the presence of tyrosine-1138 which mediates the activation of the transcription factors STAT1 and STAT3. Reporter gene assays showed that leptin induced the expression of preprotachykinin-1 and lipocalin-2 on the level of promoter regulation. Finally, leptin treatment increased caspase 3-like proteolytic activity in RINm5F cells.

CONCLUSION

The present data show that leptin induces a cytokine-like transcriptional response in RINm5F cells, consistent with the proposed function of leptin as a modulator of immune and inflammatory responses.

Diets rich in polyphenols and vitamin A inhibit the development of type I autoimmune diabetes in nonobese diabetic mice

Type I juvenile diabetes mellitus is characterized by the infiltration of activated T lymphocytes and monocytes into the islets of Langerhans of the pancreas, resulting in inflammation and progressive destruction of the insulin-producing beta cells. We hypothesized that feeding nonobese diabetic (NOD) mice diets rich in polyphenols or vitamin A, both known modulators of immune function, would decrease the autoimmune inflammatory process associated with type I diabetes. NOD mice were fed a control diet (C) and diets containing either 1% freeze-dried grape powder (GP) or 250 IU vitamin A/g (VA; 0.262 micromol retinyl acetate/g) of food. Mice were considered diabetic and killed when blood glucose reached 13.9 mmol/L or greater. By approximately 7 mo of age, 71% of C mice progressed to diabetes. Incidence of diabetes was reduced to 33% (P < 0.05) and 25% (P < 0.05) in mice receiving 1% dietary grape powder and VA, respectively. Splenocytes from mice receiving both GP and VA had lower TNF-alpha production after LPS stimulation than C mice (P < 0.05). Histological analysis of pancreatic tissue showed a significant reduction in the severity of insulitis in the mice receiving GP and VA compared with C mice. These data suggest that diets rich in polyphenols or vitamin A have protective effects against autoimmune inflammatory attack of the islet beta cells and have the potential to reduce the onset and pathogenesis of autoimmune diabetes.

Involvement of oxidative stress in the pathogenesis of diabetes

Pancreatic beta-cell failure is the common characteristic of type 1 and type 2 diabetes. Type 1 diabetes is induced by pancreatic beta-cell destruction, which is mediated by an autoimmune mechanism and consequent inflammatory process. Various inflammatory cytokines and oxidative stress produced by islet-infiltrating immune cells have been proposed to play an important role in mediating the destruction of beta cells. The JNK pathway is also activated by such cytokines and oxidative stress and is involved in beta-cell destruction. Type 2 diabetes is the most prevalent and serious metabolic disease affecting people all over the world. Pancreatic beta-cell dysfunction and insulin resistance are the hallmark of type 2 diabetes. Once hyperglycemia becomes apparent, beta-cell function gradually deteriorates, and insulin resistance is aggravated. This process is called "glucose toxicity." Under such conditions, oxidative stress is provoked, and the JNK pathway is activated, which is likely involved in pancreatic beta-cell dysfunction and insulin resistance. In addition, oxidative stress and activation of the JNK pathway are involved in the progression of atherosclerosis, which is often observed under diabetic conditions. Taken together, it is likely that oxidative stress and subsequent activation of the JNK pathway are involved in the pathogenesis of type 1 and type 2 diabetes.

Transcriptional profiling of type 1 diabetes genes on chromosome 21 in a rat beta-cell line and human pancreatic islets

We recently finemapped a type 1 diabetes (T1D)-linked region on chromosome 21, indicating that one or more T1D-linked genes exist in this region with 33 annotated genes. In the current study, we have taken a novel approach using transcriptional profiling in predicting and prioritizing the most likely candidate genes influencing beta-cell function in this region. Two array-based approaches were used, a rat insulinoma cell line (INS-1alphabeta) overexpressing pancreatic duodenum homeobox 1 (pdx-1) and treated with interleukin 1beta (IL-1beta) as well as human pancreatic islets stimulated with a mixture of cytokines. Several candidate genes with likely functional significance in T1D were identified. Genes showing differential expression in the two approaches were highly similar, supporting the role of these specific gene products in cytokine-induced beta-cell damage. These were genes involved in cytokine signaling, oxidative phosphorylation, defense responses and apoptosis. The analyses, furthermore, revealed several transcription factor binding sites shared by the differentially expressed genes and by genes demonstrating highly similar expression profiles with these genes. Comparable findings in the rat beta-cell line and human islets support the validity of the methods used and support this as a valuable approach for gene mapping and identification of genes with potential functional significance in T1D, within a region of linkage.

Pancreatic B-cell function is altered by oxidative stress induced by acute hyperglycaemia

AIMS

Type 2 diabetes is preceded by a symptom-free period of impaired glucose tolerance (IGT). Pancreatic B-cell function decreases as glucose intolerance develops. In many patients with IGT, fasting blood glucose is within normal limits and hyperglycaemia occurs only postprandially. We examined whether pancreatic B-cell function changes during acute hyperglycaemia induced by oral glucose loading.

METHODS

We calculated the insulinogenic index (I.I.) as an indicator of pancreatic B-cell function and measured serum levels of thioredoxin, a marker of cellular redox state, and 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative stress, during a 75-g oral glucose tolerance test (OGTT) in 45 subjects [24 patients with normal glucose tolerance (NGT), 14 with IGT and seven with Type 2 diabetes].

RESULTS

Thioredoxin levels decreased after glucose loading [66.1 +/- 23.7, *59.3 +/- 22.4, *49.3 +/- 21.2 and *37.7 +/- 18.0 ng/ml, fasting (0 min) and at 30, 60 and 120 min, respectively; *P < 0.001 vs. fasting]. In contrast, concentrations of 8-OHdG peaked at 30 min and then gradually decreased (0.402 +/- 0.123, *0.440 +/- 0.120, 0.362 +/- 0.119 and 0.355 +/- 0.131 ng/ml, *P < 0.05 vs. fasting, P < 0.01 vs. 30 min). The insulinogenic index correlated with the change in thioredoxin levels (r = 0.34, P < 0.05). However, there was no relationship with the change in 8-OHdG levels from 0 to 30 min.

CONCLUSIONS

Hyperglycaemia in response to oral glucose impairs pancreatic B-cell function with decreasing thioredoxin levels. The augmented oxidative stress induced by hyperglycaemia may affect the cellular redox state. These findings strongly suggest that repeated postprandial hyperglycaemia may play an important role in the development and progression of diabetes mellitus.

Lung Injury and Recovery After Exposure to Blast Overpressure

BACKGROUND

A critical immediate determinant of survival after exposure to blast overpressure (BOP) is pulmonary damage, but mechanisms of injury and the course of recovery are not well understood. The objective of this study was to characterize the progression of oxidative and inflammatory responses in lungs as well as the activation of consequent protective mechanisms after exposure to medium intensity BOP.

METHODS

Rats were exposed to a moderate (approximately 120 kPa) level of BOP in a pneumatically driven shock tube. At different times (2-192 hours) after exposure, lungs were examined for pathologic signs of injury, markers of inflammatory responses, and indicators of oxidative and nitrative damage.

RESULTS

The results showed a postblast activation of inflammatory response (increase of myeloperoxidase activity, CINC-1, ICAM-1, and iNOS), increase in protein oxidation and nitration, and development of gross diffused hemorrhage in lungs. The initial phase of lung damage that peaked at 24 to 48 hours after exposure to BOP was followed by gradual dissolution of inflammation and oxidation that were complete by 192 hours. Resolution of morphologic damage and inflammation in lungs concurred with activation of expression of antioxidant enzymes heme oxygenase-1 (HO-1) and manganese superoxide dismutase (MnSOD). Plasma level of gelsolin, a marker of acute lung damage was decreased at 24 hours postblast and later returned to the control level.

CONCLUSIONS

The study shows the role of adaptive anti-oxidant and anti- inflammatory mechanisms in lung recovery after injury caused by exposure to BOP.

Protective effects of polysaccharide from Euphorbia kansui (Euphorbiaceae) on the swimming exercise-induced oxidative stress in mice

The present study examined the effects of derivatives of galactosides and glucosides in a polysaccharide extract from Euphorbia kansui (Euphorbiaceae) on exercise-induced oxidative stress in mice. Exhaustive swimming exercise significantly increases the degree of lipid peroxidation in terms of malondialdehyde content and reduces the antioxidant activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx). Our findings revealed that chronic oral treatment with the extract elevates enzymatic activities of SOD and GPx accompanied by a corresponding decrease in malondialdehyde. The antioxidative activities of these compounds against exercise-induced oxidative stress are correlated with various activities such as reducing the production of superoxide and hydroxyl radicals, inhibiting lipid peroxidation, enhancing antioxidative defenses, and increasing the production of SOD and GPx activity and expression in different tissues. These compounds may be involved in glycogen metabolism to meet the requirement of working skeletal muscles and act as antioxidants by terminating the chain reaction of lipid peroxidation to maintain the morphological stability of mitochondria in spinal motor neurons. These observations suggest that E. kansui has antioxidative and antifatigue properties and can be given as prophylactic and (or) therapeutic supplements for increasing antioxidant enzyme activities and preventing lipid peroxidation during strenuous exercise.

Metallothionein and catalase sensitize to diabetes in nonobese diabetic mice: reactive oxygen species may have a protective role in pancreatic beta-cells

It is widely proposed that reactive oxygen species (ROS) contribute to beta-cell death in type 1 diabetes. We tested this in nonobese diabetic (NOD) mice using beta-cell-specific overexpression of three antioxidant proteins: metallothionein (MT), catalase (Cat), or manganese superoxide dismutase (MnSOD). Unexpectedly, the cytoplasmic antioxidants, MT and catalase, greatly accelerated diabetes after cyclophosphamide and accelerated spontaneous diabetes in male NOD mice. This occurred despite the fact that they reduced cytokine-induced ROS production and MT reduced streptozotocin diabetes in NOD mice. Accelerated diabetes onset coincided with increased beta-cell death but not with increased immune attack. Islets from MTNOD mice were more sensitive to cytokine injury. In vivo and in vitro studies indicated reduced activation of the Akt/pancreatic duodenal homeobox-1 survival pathway in MTNOD and CatNOD islets. Our study indicates that cytoplasmic ROS may have an important role for protecting the beta-cell from autoimmune destruction.

A protective role for heme oxygenase-1 in INS-1 cells and rat islets that are exposed to high glucose conditions

Heme oxygenase-1 (HO-1) has been described as an inducible protein that is capable of cytoprotection via radical scavenging and the prevention of apoptosis. Chronic exposure to hyperglycemia can lead to cellular dysfunction that may become irreversible over time, and this process has been termed glucose toxicity. Yet little is known about the relation between glucose toxicity and HO-1 in the islets. The purposes of the present study were to determine whether prolonged exposure of pancreatic islets to a supraphysiologic glucose concentration disrupts the intracellular balance between reactive oxygen species (ROS) and HO-1, and so this causes defective insulin secretion; we also wanted to evaluate a protective role for HO-1 in pancreatic islets against high glucose levels. The intracellular peroxide levels of the pancreatic islets (INS-1 cell, rat islet) were increased in the high glucose media (30 mM glucose or 50 mM ribose). The HO-1 expression was induced in the INS-1 cells by the high glucose levels. Both the HO-1 expression and glucose stimulated insulin secretion (GSIS) was decreased simultaneously in the islets by treatment of the HO-1 antisense. The HO-1 was upregulated in the INS-1 cells by hemin, an inducer of HO-1. And, HO-1 upregulation induced by hemin reversed the GSIS in the islets at a high glucose condition. These results suggest HO-1 seems to mediate the protective response of pancreatic islets against the oxidative stress that is due to high glucose conditions.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.

Pro- and antiapoptotic proteins regulate apoptosis but do not protect against cytokine-mediated cytotoxicity in rat islets and beta-cell lines

Type 1 diabetes results from islet beta-cell death and dysfunction induced by an autoimmune mechanism. Proinflammatory cytokines such as interleukin-1beta and gamma-interferon are mediators of this beta-cell cytotoxicity, but the mechanism by which damage occurs is not well understood. In the current study, we present multiple lines of evidence supporting the conclusion that cytokine-induced killing of rat beta-cells occurs predominantly by a nonapoptotic mechanism, including the following: 1) A rat beta-cell line selected for resistance to cytokine-induced cytotoxicity (833/15) is equally sensitive to killing by the apoptosis-inducing agents camptothecin and etoposide as a cytokine-sensitive cell line (832/13). 2) Overexpression of a constitutively active form of the antiapoptotic protein kinase Akt1 in 832/13 cells provides significant protection against cell killing induced by camptothecin and etoposide but no protection against cytokine-mediated damage. 3) Small interfering RNA-mediated suppression of the proapoptotic protein Bax enhances viability of 832/13 cells upon exposure to the known apoptosis-inducing drugs but not the inflammatory cytokines. 4) Exposure of primary rat islets or 832/13 cells to the inflammatory cytokines causes cell death as evidenced by the release of adenylate kinase activity into the cell medium, with no attendant increase in caspase 3 activation or annexin V staining. In contrast, camptothecin- and etoposide-induced killing is associated with robust increases in caspase 3 activation and annexin V staining. 5) Camptothecin increases cellular ATP levels, whereas inflammatory cytokines lower ATP levels in both beta-cell lines and primary islets. We conclude that proinflammatory cytokines cause beta-cell cytotoxicity primarily through a nonapoptotic mechanism linked to a decline in ATP levels.

Cytoprotection of beta cells: rational gene transfer strategies

Gene transfer to pancreatic islets may prove useful in preventing islet cell destruction and prolonging islet graft survival after transplantation in patients with type 1 diabetes mellitus (T1DM). Potentially, a host of therapeutically relevant transgenes may be incorporated into an appropriate gene delivery vehicle and used for islet modification. An increasing understanding of the molecular pathogenesis of immune-mediated beta cell death has served to highlight molecules which have become suitable candidates for promoting islet cell survival in the face of oxidative stress. This review aims to give an overview of some conventional gene transfer strategies aimed at promoting islet cell survival in the face of cytokine onslaught. These strategies target three aspects of islet cell physiology: redox status and antioxidant defence, anti-apoptotic gene expression and mediators of cytokine signal transduction pathways.

Growth arrest- and DNA-damage-inducible 45beta gene inhibits c-Jun N-terminal kinase and extracellular signal-regulated kinase and decreases IL-1beta-induced apoptosis in insulin-producing INS-1E cells

AIMS/HYPOTHESIS

IL-1beta is a candidate mediator of apoptotic beta cell destruction, a process that leads to type 1 diabetes and progression of type 2 diabetes. IL-1beta activates beta cell c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and p38, all of which are members of the mitogen-activated protein kinase (MAPK) family. Inhibition of JNK prevents IL-1beta-mediated beta cell destruction. In mouse embryo fibroblasts and 3DO T cells, overexpression of the gene encoding growth arrest and DNA-damage-inducible 45beta (Gadd45b) downregulates pro-apoptotic JNK signalling. The aim of this study was to investigate if Gadd45b prevents IL-1beta-induced beta cell MAPK signalling and apoptosis.

MATERIALS

Rat insulinoma INS-1E cells and mouse beta-TC3 cells stably expressing Gadd45b were generated. The effects of Gadd45b expression on signalling by JNK, ERK and p38 were assessed by Western blotting and kinase assays. Apoptosis rate was measured by terminal deoxynucleotidyl-mediated dUTP-biotin nick end-labelling (TUNEL) and an ELISA designed to detect apoptotic nucleosomes. Expression of endogenous Gadd45b mRNA was measured by RT-PCR.

RESULTS

In INS-1E and beta-TC3 cells, expression of Gadd45b inhibited IL-1beta-induced activation of JNK and ERK, but augmented IL-1beta-mediated p38 activity. IL-1beta-induced nitric oxide production and decreases in insulin content and secretion were reduced by GADD45beta. IL-1beta-induced apoptosis was reduced by GADD45beta by up to 77%. Although IL-1beta stimulated the time-dependent induction of endogenous Gadd45b in INS-1E cells and rat islets, expression levels were lower in these cells than in IL-1beta-exposed NIH-3T3 and 3DO T cells.

CONCLUSIONS/INTERPRETATION

Inadequate induction of Gadd45b, which encodes a novel beta cell JNK and ERK inhibitor, may in part explain the pro-apoptotic response of beta cells to IL-1beta.

Gene therapy for type 1 diabetes

The most intensively studied autoimmune disorder, type 1 diabetes mellitus (DM1), has attracted perhaps the greatest interest for gene-based therapeutic and prophylactic interventions. The final clinical manifestation of this immunologically and genetically complex disease, the absence of insulin, is the major starting point for almost all the gene therapy modalities attempted to date. Insulin replacement by transplantation of islets of Langerhans or surrogate beta cells is the obvious choice, but the allogeneic nature of the transplants activates potent antidonor immunoreactivity necessitating gene and cell-based immunosuppressive strategies as an alternative to the toxic pharmacologic immunosuppressives indicated for classic solid organ transplants. Accumulating knowledge of the cellular mechanisms involved in onset, however, have yielded promising tolerance induction prophylactic approaches using genes and cells. Despite the early successes in a number of animal models, the true test of efficacy in humans remains to be demonstrated.

Targeted expression of the anti-apoptotic gene CrmA to NOD pancreatic islets protects from autoimmune diabetes

The activation of apoptosis is a critical mechanism by which pancreatic beta cells are destroyed in type 1 diabetes (T1DM). Strategies aimed at interfering with the apoptotic pathways could therefore be of potential therapeutic value. To this end, we generated NOD transgenic mice with targeted expression of the anti-apoptotic gene Cytokine response modifier A (CrmA) to pancreatic beta cells using the rat insulin promoter and the reverse tetracycline transactivator to express CrmA in a temporally controlled manner. Two lines of transgenic mice were studied whose expression of CrmA occurred only after feeding doxycycline food. Islet expression of CrmA partially protected pancreatic beta cells from the cytokine-mediated cytotoxicity in vitro and reduced modestly the spontaneous development of diabetes in NOD mice in vivo. In addition, beta cells from NOD CrmA mice were significantly protected from the destruction by diabetogenic T cells after adoptive transfer. More strikingly, NODCrmA mice were significantly resistant to the diabetogenic activity of a potent insulin-specific CD8 T-cell clone. Since these adoptive transfer models mainly represent the effector phase rather than the initiation phase of autoimmune diabetes, our data suggest that the latter is more sensitive to CrmA protection. We conclude that anti-apoptotic genes such as CrmA might be potential candidates to enhance islet graft survival in T1DM.

Selenium, the thyroid, and the endocrine system

Recent identification of new selenocysteine-containing proteins has revealed relationships between the two trace elements selenium (Se) and iodine and the hormone network. Several selenoproteins participate in the protection of thyrocytes from damage by H(2)O(2) produced for thyroid hormone biosynthesis. Iodothyronine deiodinases are selenoproteins contributing to systemic or local thyroid hormone homeostasis. The Se content in endocrine tissues (thyroid, adrenals, pituitary, testes, ovary) is higher than in many other organs. Nutritional Se depletion results in retention, whereas Se repletion is followed by a rapid accumulation of Se in endocrine tissues, reproductive organs, and the brain. Selenoproteins such as thioredoxin reductases constitute the link between the Se metabolism and the regulation of transcription by redox sensitive ligand-modulated nuclear hormone receptors. Hormones and growth factors regulate the expression of selenoproteins and, conversely, Se supply modulates hormone actions. Selenoproteins are involved in bone metabolism as well as functions of the endocrine pancreas and adrenal glands. Furthermore, spermatogenesis depends on adequate Se supply, whereas Se excess may impair ovarian function. Comparative analysis of the genomes of several life forms reveals that higher mammals contain a limited number of identical genes encoding newly detected selenocysteine-containing proteins.

Glucagon-like peptide-1 protects beta cells from cytokine-induced apoptosis and necrosis: role of protein kinase B

AIMS/HYPOTHESIS

The gut hormone glucagon-like peptide-1 (GLP-1) decreases beta cell apoptosis in a protein kinase B (PKB)-dependent fashion, and increases islet cell mass and function in vivo. In contrast, cytokines induce beta cell apoptosis, leading to decreased islet mass and type 1 diabetes. In the present study we used rat INS-1E beta cells and primary rat islet cells to examine the potential role of PKB as a mediator of the effect of GLP-1 on cytokine-induced apoptosis.

METHODS

Cell viability was determined by MTT assay, and apoptosis and necrosis by Hoechst 33342-propidium iodide staining. Immunoblot analysis was used to detect changes in protein expression, including active (phosphorylated) and total PKB, phosphorylated and total glycogen synthase kinase-3beta, activated caspase-3 and inducible nitric oxide synthase. Reactive oxygen species were determined by 1,7-dichlorofluorescein (DCF) analysis, and mutant forms of PKB were introduced into cells using adenoviral vectors.

RESULTS

Incubation of INS-1E cells with cytokines (IL-1beta, TNF-alpha and interferon-gamma; 10-50 ng/ml) for 18 h significantly decreased cell viability (by 44%, p<0.001), cell proliferation (by 80%, p<0.001), and activation of PKB (by 67%, p<0.001). Pre-treatment with exendin-4 (10(-7) mol/l), a long-acting GLP-1 receptor agonist, partially protected the cells against cytokine-induced toxicity (p<0.01) in association with a reduction in cytokine-induced inhibition of PKB phosphorylation (p<0.05). Exendin-4 pre-treatment did not change cell proliferation. Cytokine treatment increased apoptosis (by 156%, p<0.05) and necrosis (from undetectable to 2.6% of cells). These increases were both reduced by pre-treatment with exendin-4 (p<0.05-0.01). Furthermore, cytokine-induced apoptosis and necrosis were significantly increased in cells infected with kinase-dead PKB (p<0.05), and the protective effect of exendin-4 on both parameters was fully abolished in these cells. Similar changes were observed in primary islet cells. In parallel with these changes, exendin-4 decreased the cytokine-induced activation of caspase-3 (by 46%, p<0.05), and decreased levels of inducible nitric oxide synthase (by 71%, p<0.05) and reactive oxygen species (by 27%, p<0.05).

CONCLUSIONS/INTERPRETATION

The results of our study indicate that GLP-1 plays a protective role against cytokine-induced apoptosis and necrosis in beta cells through a PKB-dependent signalling pathway.