Superoxide dismutase is a prophylactic against alloxan diabetes

Oral delivery of a highly stable superoxide dismutase as a skin aging inhibitor

As an effective antioxidant enzyme, superoxide dismutase (SOD) has been widely used as a food supplement, cosmetic additive, and therapeutic agent. However, oral delivery of SOD is challenging due to its relative instability, limited bioavailability, and low absorption efficiency in the gastrointestinal (GI) tract. We addressed these issues using a highly stable superoxide dismutase (hsSOD) generated from a hot spring microbial sample. This SOD exhibited a specific activity of 5000 IU/mg while retaining its enzymatic activity under low pH environments of an artificial GI system and in the presence of surfactants and various proteolytic enzymes. The inhibitory effects of hsSOD against skin-aging was evaluated under both in vitro and in vivo experiments using fibroblast cell and D-galactose induced aging-mouse models, respectively. Effective oral delivery of hsSOD promises wide applicability in pharmaceutical and food industries.

β-Cell Death in Diabetes: Past Discoveries, Present Understanding, and Potential Future Advances

β-cell death is regarded as a major event driving loss of insulin secretion and hyperglycemia in both type 1 and type 2 diabetes mellitus. In this review, we explore past, present, and potential future advances in our understanding of the mechanisms that promote β-cell death in diabetes, with a focus on the primary literature. We first review discoveries of insulin insufficiency, β-cell loss, and β-cell death in human diabetes. We discuss findings in humans and mouse models of diabetes related to autoimmune-associated β-cell loss and the roles of autoreactive T cells, B cells, and the β cell itself in this process. We review discoveries of the molecular mechanisms that underlie β-cell death-inducing stimuli, including proinflammatory cytokines, islet amyloid formation, ER stress, oxidative stress, glucotoxicity, and lipotoxicity. Finally, we explore recent perspectives on β-cell death in diabetes, including: (1) the role of the β cell in its own demise, (2) methods and terminology for identifying diverse mechanisms of β-cell death, and (3) whether non-canonical forms of β-cell death, such as regulated necrosis, contribute to islet inflammation and β-cell loss in diabetes. We believe new perspectives on the mechanisms of β-cell death in diabetes will provide a better understanding of this pathological process and may lead to new therapeutic strategies to protect β cells in the setting of diabetes.

Autocrine C-peptide protects INS1 β cells against palmitic acid-induced oxidative stress in peroxisomes by inducing catalase

AIMS

C-peptide, produced by pancreatic β cells and co-secreted in the bloodstream with insulin, has antioxidant properties in glucose- and hydrogen peroxide (H2O2)-exposed INS1 β cells. Palmitic acid, the most physiologically abundant long-chain free fatty acid in humans, is metabolized in peroxisomes of β cells accumulating H2O2 that can lead to oxidative stress. Here, we tested the hypothesis that C-peptide protects β cells from palmitic acid-induced stress by lowering peroxisomal H2O2.

MATERIALS AND METHODS

We exposed INS1 β cells to palmitic acid and C-peptide in the setting of increasing glucose concentration and tested for changes in parameters of stress and death. To study the ability of C-peptide to lower peroxisomal H2O2, we engineered an INS1 β cell line stably expressing the peroxisomal-targeted H2O2 sensor HyPer, whose fluorescence increases with cellular H2O2. An INS1 β cell line stably expressing a live-cell fluorescent catalase reporter was used to detect changes in catalase gene expression.

RESULTS

C-peptide protects INS1 β cells from the combined effect of palmitic acid and glucose by reducing peroxisomal H2O2 to baseline levels and increasing expression of catalase.

CONCLUSIONS

In conditions of glucolipotoxicity, C-peptide increases catalase expression and reduces peroxisomal oxidative stress and death of INS1 β cells. Maintenance of C-peptide secretion is a pro-survival requisite for β cells in adverse conditions. Loss of C-peptide secretion would render β cells more vulnerable to stress and death leading to secretory dysfunction and diabetes.

Protective role of (Bronco-T) against formaldehyde induced antioxidant, oxidative and histopathological changes in lung of male Wistar rats

The present study was sought to evaluate the oxidative, antioxidant status and histopathological changes by the acute chronic exposure of formaldehyde. Bronco-T a poly-herbal formulation treatment, changes the oxidative, antioxidant status and histopathology of rat lungs with antioxidant and regenerative property. In this experiment thirty adult male albino Wister rats were used for the study and subdivided in to five groups consist of 6 rats for each group. Group-I served as control and the other 4 groups such as II, III, IV and V are considered as experimental. The control and treatment rats are maintained for 21 days of experimental period. Experimental rats are exposed to 40 percent formaldehyde for 1 h treated with Bronco-T and salbutamol. In the present investigation, the formaldehyde exposed rats a series of free radical chain reactions were grimly provoked, the evaluation of antioxidant enzymes (SOD, CAT), other enzymes oxidative enzymes (G-6-PDH, SDH) and (ALT, ALAT and LDH) were measured. A clear assertive imbalance between oxidation and anti-oxidation status was critically observed, and oxidative stress was clearly exacerbated in lung tissue leading to altrations in architecture of lung histopathology. Oral gavage Bronco-T exhibits a beneficial action by bringing normal architecture in lung tissue of formaldehyde inhaled rats with antioxidant properties. Bronco-T treatment may be a suitable remedy for formalin occupational diseases.

Effect of hydroalcoholic Allium ampeloprasum extract on oxidative stress, diabetes mellitus and dyslipidemia in alloxan-induced diabetic rats

Allium ampeloprasum (AA) is a medicinal plant which is used in Iranian traditional medicine to treat or prevent different diseases. The aim of this study is to investigate the effect of AA extract on oxidative stress and dyslipidemia in diabetic rats induced by alloxan. In this experimental study, 60 male Wistar rats weighing 200-250gr were randomly divided to five groups of 12 each including healthy control (group I), diabetic control (group II), metformin-treated diabetic positive control (group III) and two groups treated with doses 400 (group IV) and 800 (groupV) mg/kg/BW of AA extracts. Diabetes mellitus was experimentally induced by injection of two doses of alloxan-120 and 65mg/kg-within two consecutive days. Alloxan-induced diabetes caused significant increase in serum glucose, triglyceride (TG), total cholesterol (TC), low density lipoprotein (LDL), very low density lipoprotein (VLDL) and high density lipoprotein (HDL) levels in group II (p<0.05). Furthermore, serum malondialdehyde (MDA) levels increased significantly and liver catalase activity decreased significantly in the 2nd group compared to 1st control; respectively p=0.0001 and p=0.009. In the group IV has seen a significant decrease in serum TG (p=0.01), TC (p=0.0001), VLDL (p=0.01), and MDA (p=0.0001) levels and significant increase in the liver and kidney catalase activities of the rats compared to the group II; respectively p=0.0001 and p=0.0001. In Conclusion our results highlight potentially relevant health beneficial effects of AA extract which exerts hypoglycemic, hypolipidemic, and anti-oxidative stress effects in rats with alloxan-induced diabetes. Therefore, it may be considered as useful dietary supplements in diabetic patients.

Effect of biosynthesized gold nanoparticles by Sargassum swartzii in alloxan induced diabetic rats

Biosynthesis of gold nanoparticles (AuNPs) using Sargassum swartzii and its anti-diabetic effect were studied using male wistar Albino rats. Formation of AuNPs were confirmed by UV-vis spectroscopy, Fourier transformed infrared (FTIR) spectroscopy, High-Resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). Fasting blood glucose levels, serum insulin, hemoglobin and glycosylated hemoglobin levels in diabetic treated rats with AuNPs were significantly decreased compared to the control group. The results of the blood glucose level and serum insulin levels indicated that AuNPs could significantly improve the insulin resistance and glucose level in diabetic rats. AuNPs also shows reduction in anti-inflammation, tumor necrosis factor-alpha, interleukin-6 and high-sensitive C-reactive protein in diabetic rats. The data showed that AuNPs synthesized using S. swartzii exerted antidiabetic effect, accordingly improve pancreas, liver and kidney damage caused by alloxan induced diabetic rats.

Does bilirubin protect against developing diabetes mellitus?

After 25 years of evaluating bilirubin as a possible protective agent in neonatal and cardiovascular disease, interest has moved on to a exploring a possible protective role in diabetes mellitus (DM). This review finds conflicting prospective data for a protective relationship though there are retrospective, case-controlled data, that can only show association, which is not causality. Only prospective studies can show causality. Also, it would appear that the underlying biochemical assumptions do not readily translate from the animal to the human setting. Given that many factors impact on circulating bilirubin levels, it is not surprising that a clear-cut answer is not available; the jury is still out. Any relationship between DM and bilirubin might relate to intermediates in bilirubin metabolism, including relationships involving the genes for the enzymes participating in those steps. Nevertheless, the pursuit of bilirubin in disease causation is opening new avenues for research and if it is established that serum bilirubin can predict risks, much will have been achieved. The answer may have to come from molecular genetic analyses.

A multidisciplinary guided practical on type I diabetes engaging students in inquiry-based learning

In the present article, we describe a 3-day experimental workshop on type I diabetes aimed at helping high school students to understand how fundamental research on glycemia regulation contributes to the development of scientific knowledge and therapeutic strategies. The workshop engaged students in open-ended investigations and guided experiments. Each class was divided into three or four groups, with each group working with a trained doctoral student or postdoctoral fellow. During an initial questioning phase, students observed slides depicting the glycemia of individuals in various situations. Students identified hyperglycemic individuals relative to the average glycemia of the displayed population. Students were asked to devise a treatment for these diabetics. They quickly realized that they couldn't experiment on patients and understood the need for laboratory models. Each group gave ideas of experiments to perform. We then explained, taking into account their propositions, the protocols students could execute to address one of the following questions: Which criteria must an animal model of diabetes fulfill? How do pancreatic cells maintain glycemia? Is there a way to produce an insulin protein similar to the one released by human pancreatic cells? We used two different evaluation metrics of the workshop: a questionnaire filled out by the students before and after the workshop and a poster produced by students at the end of the workshop. We found that this educational approach successfully improved student awareness and understanding of the scientific reasoning and research process.

Hands-on experiments on glycemia regulation and type 1 diabetes

In the present article, we describe a 3-day experimental workshop on glycemia regulation and type 1 diabetes that engages students in open-ended investigations and guided experiments leading to results that are not already known to them. After an initial questioning phase during which students observe PowerPoint slides depicting the glycemia (blood glucose levels) of individuals in various situations, students design, execute, and interpret experiments to address one of the following questions: 1) Which criteria must an animal model of diabetes fulfill? 2) How do pancreatic cells maintain glycemia constant? and 3) Is there a way to produce an insulin protein similar to the one released by human pancreatic cells? Students then 1) measure glycemia and glycosuria in control mice and in a mouse model of type 1 diabetes (Alloxan-treated mice), 2) measure the release of insulin by pancreatic β-cells (INS-1 cell line) in response to different concentrations of glucose in the extracellular medium, and 3) transfect Chinese hamster ovary cells with a plasmid coding for green fluorescent protein, observe green fluorescent protein fluorescence of some of the transfected Chinese hamster ovary cells under the microscope, and observe the characteristics of human insulin protein and its three-dimensional conformation using RASMOL software. At the end of the experimental session, students make posters and present their work to researchers. Back at school, they may also present their work to their colleagues.

The effect of Nrf2 pathway activation on human pancreatic islet cells

Background

Pancreatic islets are known to contain low level of antioxidants that renders them vulnerable to oxidative stress. Nrf2 is the master regulator of numerous genes, encoding antioxidant, detoxifying, and cytoprotective molecules. Activation of Nrf2 pathway induces up-regulation of numerous genes encoding antioxidant and phase II detoxifying enzymes and related proteins. However, little is known regarding the role of this pathway in human islet cells. The aim was to investigate the effect of Nrf2 activator (dh404, CDDO-9,11-dihydro-trifluoroethyl amide) on human islet cells.

Methods

Human islets were obtained from cadaveric donors. After dh404 treatment, Nrf2 translocation, mRNA expression, and protein abundance of its key target gene products were examined. The proportion of dh404-treated or non-treated viable islet beta cells was analyzed using flowcytemetry. The cytoprotective effects against oxidative stress and production of inflammatory mediators, and in vivo islet function after transplantation were determined.

Results

Nrf2 nuclear translocation was confirmed by con-focal microscope within 2 hours after treatment, which was associated with a dose-dependent increase in mRNA expression of anti-oxidants, including NQO1, HO-1, and GCLC. Enhanced HO-1 expression in dh404 treated islets was confirmed by Western Blot assay. Islet function after transplantation (2000 IEQ/mouse) to diabetic nude mice was not affected with or without dh404 treatment. After induction of oxidative stress with hydrogen peroxide (200 μM) the proportion of dh404-treated viable islet cells was significantly higher in the dh404-treated than untreated islets (74% vs.57%; P<0.05). Dh404 significantly decreased production of cytokines/chemokines including IL-1β, IL-6, IFN-γ and MCP-1.

Conclusion

Treatment of human pancreatic islets with the potent synthetic Nrf2 activator, dh404, significantly increased expression of the key anti-oxidants enzymes, decreased inflammatory mediators in islets and conferred protection against oxidative stress in beta cells.

Antidiabetic effect of Sida cordata in alloxan induced diabetic rats

Medicinal plants are efficient ameliorator of oxidative stress associated with diabetes mellitus. In this study, ethyl acetate fraction (SCEE) of Sida cordata was investigated for scientific validation of its folk use in diabetes. Antidiabetic effect of SCEE was confirmed by antihyperglycemic activity in normal glucose loaded and diabetic glucose loaded animals as well as normal off feed animals. Confirmation of antidiabetic activity and toxicity ameliorative role of S. cordata was investigated in a chronic multiple dose treatment study of fifteen days. A single dose of alloxan (120 mg/kg) produced a decrease in insulin level, hyperglycemia, elevated total lipids, triglycerides, and cholesterol and decreased the high-density lipoproteins. Concurrent with these changes, there was an increase in the concentration of lipid peroxidation (TBARS), H₂O₂, and nitrite in pancreas, liver, and testis. This oxidative stress was related to a decrease in glutathione content (GSH) and antioxidant enzymes. Administration of SCEE for 15 days after diabetes induction ameliorated hyperglycemia, restored lipid profile, blunted the increase in TBARS, H₂O₂, and nitrite content, and stimulated the GSH production in the organs of alloxan-treated rats. We suggested that SCEE could be used as antidiabetic component in case of diabetes mellitus. This may be related to its antioxidative properties.

Padina arborescens extract protects high glucose-induced apoptosis in pancreatic β cells by reducing oxidative stress

BACKGROUND/OBJECTIVES

This study investigated whether Padina arborescens extract (PAE) protects INS-1 pancreatic β cells against glucotoxicity-induced apoptosis.

MATERIALS/METHODS

Assays, including cell viability, lipid peroxidation, generation of intracellular ROS, NO production, antioxidant enzyme activity and insulin secretion, were conducted. The expressions of Bax, Bcl-2, and caspase-3 proteins in INS-1 cells were evaluated by western blot analysis, and apoptosis/necrosis induced by high glucose was determined by analysis of FITC-Annexin V/PI staining.

RESULTS

Treatment with high concentrations of glucose induced INS-1 cell death, but PAE at concentrations of 25, 50 or 100 µg/ml significantly increased cell viability. The treatment with PAE dose dependently reduced the lipid peroxidation and increased the activities of antioxidant enzymes reduced by 30 mM glucose, while intracellular ROS levels increased under conditions of 30 mM glucose. PAE treatment improved the secretory responsiveness following stimulation with glucose. The results also demonstrated that glucotoxicity-induced apoptosis is associated with modulation of the Bax/Bcl-2 ratio. When INS-1 cells were stained with Annexin V/PI, we found that PAE reduced apoptosis by glucotoxicity.

CONCLUSIONS

In conclusion, the present study indicates that PAE protects against high glucose-induced apoptosis in pancreatic β cells by reducing oxidative stress.

Oxidative stress in the etiology of age-associated decline in glucose metabolism

One of the most common pathologies in aging humans is the development of glucose metabolism dysfunction. The high incidence of metabolic dysfunction, in particular type 2 diabetes mellitus, is a significant health and economic burden on the aging population. However, the mechanisms that regulate this age-related physiological decline, and thus potential preventative treatments, remain elusive. Even after accounting for age-related changes in adiposity, lean mass, blood lipids, etc., aging is an independent factor for reduced glucose tolerance and increased insulin resistance. Oxidative stress has been shown to have significant detrimental impacts on the regulation of glucose homeostasis in vitro and in vivo. Furthermore, oxidative stress has been shown to be modulated by age and diet in several model systems. This review provides an overview of these data and addresses whether increases in oxidative stress with aging may be a primary determinant of age-related metabolic dysfunction.

Counteraction by glutathione and selenium of the prooxidant effect of alloxan in erythrocytes in vitro

Alloxan produces reactive oxygen species which cause injury to the insulin-producing beta-cells of the pancreas. The action of alloxan in the production of free radicals was studied in vitro using rat erythrocytes. Alloxan increased lipid peroxidation (LPO) and decreased the activities of the antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase in the erythrocytes. Treatment with glutathione (GSH) and/or selenium along with alloxan was able to decrease LPO and increase the activities of the antioxidant enzymes in the erythrocytes. The results suggest that GSH and selenium both counteract the prooxidant effect of alloxan in rat erythrocytes.

Beta cell function: the role of macrophage migration inhibitory factor

During evolution, beta cells adapted to a sole aim: the production and stimulus-dependent secretion of insulin. This acquired specificity was accompanied by a loss of protection mechanisms predisposing beta cell to a high vulnerability. Among beta cell-damaging molecules, a new one has been identified recently: macrophage migration inhibitory factor (MIF). MIF was at first designated as a T-cell product that inhibits random movement of macrophages. Over the years, the number of functions attributed to this protein increased significantly, positioning MIF at the top of inflammatory cascade in the combat against infection and in immunoinflammatory and autoimmune diseases. This exceptionally versatile molecule regulates insulin secretion in physiological conditions, while in pathological states it alters beta cell function and induces their apoptosis or necrosis and affects beta cell neoplasia.

Oxidative stress and beta cell dysfunction

Autoimmune Type 1 A Diabetes (T1D) is characterized by dependence on exogenous insulin consequential to the autoimmune attack and destruction of insulin-producing islet beta cells. Pancreatic islet cell inflammation, or insulitis, precedes beta cell death and T1D onset. In the insulitic lesion, innate immune cells produce chemokines and cytokines that recruit and activate adaptive immune cells (Eizirik D et al., Nat Rev Endocrinol 5:219-226, 2009). Locally produced cytokines not only increase immune surveillance of beta cells (Hanafusa T and Imagawa A, Ann NY Acad Sci 1150:297-299, 2008), but also cause beta cell dysfunction and decreased insulin secretion due to the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) by the beta cells. This, coupled to the high levels of ROS and RNS secreted by activated macrophages and the low antioxidant capacities of beta cells (Huurman VA, PLoS One 3:e2435, 2008; Schatz D, Pediatr Diabetes 5:72-79, 2004; Verge CF, Diabetes 44:1176-1179, 1995), implicates free radicals as important effectors in T1D pathogenesis (Eizirik D et al., Nat Rev Endocrinol 5:219-226, 2009; Hanafusa T and Imagawa A, Ann NY Acad Sci 1150:297-299, 2008; Eisenbarth GS and Jeffrey J, Arq Bras Endocrinol Metabol 52:146-155, 2008; Pietropaolo M et al., Pediatr Diabetes 6:184-192, 2005).

Polymerizable superoxide dismutase mimetic protects cells encapsulated in poly(ethylene glycol) hydrogels from reactive oxygen species-mediated damage

A polymerizable superoxide dismutase mimetic (SODm) was incorporated into poly(ethylene glycol) (PEG) hydrogels to protect encapsulated cells from superoxide-mediated damage. Superoxide and other small reactive oxygen species (ROS) can cause oxidative damage to donor tissue encapsulated within size exclusion barrier materials. To enzymatically breakdown ROS within biomaterial cell encapsulation systems, Mn(III) Tetrakis[1-(3-acryloxy-propyl)-4-pyridyl] porphyrin (MnTTPyP-acryl), a polymerizable manganese metalloporphyrin SOD mimetic, was photopolymerized with PEG diacrylate (PEGDA) to create functional gels. In unmodified PEG hydrogels, a significant reduction in metabolic activity was observed when encapsulated Min6 β-cells were challenged with chemically generated superoxide. Cells encapsulated within MnTPPyP-co-PEG hydrogels, however, demonstrated greatly improved metabolic activity following various superoxide challenges. Further, cells were encapsulated and cultured for 10 days within MnTPPyP-co-PEG hydrogels and challenged with superoxide on days 4, 6, and 8. At the conclusion of this study, cells in blank PEG hydrogels had no observable metabolic activity but when encapsulated in MnTPPyP-functionalized hydrogels, cells retained 60 ± 5% of the metabolic activity compared to untreated controls.

α-Lipoic acid protects diabetic apolipoprotein E-deficient mice from nephropathy

AIM

Both hyperglycemia and hyperlipidemia increase oxidative stress and contribute to the development of diabetic nephropathy (DN). We investigated the effects of α-lipoic acid, a natural antioxidant and a cofactor in the multienzyme complexes, on the development of DN in diabetic apolipoprotein E-deficient mice.

METHODS

Twelve-week-old male apoE-/- mice on C57BL/6J genetic background were made diabetic with injections of streptozotocin (STZ). STZ-treated diabetic apoE-/- mice and non-diabetic control were fed with a synthetic high-fat (HF) diet with or without lipoic acid (LA) supplementation. Multiple parameters including plasma glucose, cholesterol, oxidative stress markers, cytokines, and kidney cortex gene expression, and glomerular morphology were evaluated.

RESULTS

LA supplementation markedly protected the β cells, reduced cholesterol levels, and attenuated albuminuria and glomerular mesangial expansion in the diabetic mice. Renoprotection by LA was equally effective regardless of whether the dietary supplementation was started 4 weeks before, simultaneously with, or 4 weeks after the induction of diabetes by STZ. LA supplementation significantly improved DN and oxidative stress in the diabetic mice. Severity of albuminuria was positively correlated with level of thiobarbituric acid reactive substances (TBARs) in the kidney (r(2)=0.62, P<.05). Diabetes significantly changed the kidney expression of Rage, Sod2, Tgfb1 and Ctgf, Pdp2, nephrin, and Lias. LA supplementation corrected these changes except that it further suppressed the expression of the Lias gene coding for lipoic acid synthase.

CONCLUSIONS

Our data indicate that LA supplementation effectively attenuates the development and progression of DN through its antioxidant effect as well as enhances glucose oxidation.

Sensitization to alloxan-induced diabetes and pancreatic cell apoptosis in acatalasemic mice

Human acatalasemia may be a risk factor for the development of diabetes mellitus. However, the mechanism by which diabetes is induced is still poorly understood. The impact of catalase deficiency on the onset of diabetes has been studied in homozygous acatalasemic mutant mice or control wild-type mice by intraperitoneal injection of diabetogenic alloxan. The incidence of diabetes was higher in acatalasemic mice treated with a high dose (180 mg/kg body weight) of alloxan. A higher dose of alloxan accelerated severe atrophy of pancreatic islets and induced pancreatic beta cell apoptosis in acatalasemic mice in comparison to wild-type mice. Catalase activity remained low in the acatalasemic pancreas without the significant compensatory up-regulation of glutathione peroxidase or superoxide dismutase. Furthermore, daily intraperitoneal injection of angiotensin II type 1 (AT1) receptor antagonist telmisartan (0.1 mg/kg body weight) prevented the development of alloxan-induced hyperglycemia in acatalasemic mice. This study suggests that catalase plays a crucial role in the defense against oxidative-stress-mediated pancreatic beta cell death in an alloxan-induced diabetes mouse model. Treatment with telmisartan may prevent the onset of alloxan-induced diabetes even under acatalasemic conditions.

Suppression of KATP channel activity protects murine pancreatic beta cells against oxidative stress

The enhanced oxidative stress associated with type 2 diabetes mellitus contributes to disease pathogenesis. We previously identified plasma membrane-associated ATP-sensitive K+ (KATP) channels of pancreatic beta cells as targets for oxidants. Here, we examined the effects of genetic and pharmacologic ablation of KATP channels on loss of mouse beta cell function and viability following oxidative stress. Using mice lacking the sulfonylurea receptor type 1 (Sur1) subunit of KATP channels, we found that, compared with insulin secretion by WT islets, insulin secretion by Sur1-/- islets was less susceptible to oxidative stress induced by the oxidant H2O2. This was likely, at least in part, a result of the reduced ability of H2O2 to hyperpolarize plasma membrane potential and reduce cytosolic free Ca2+ concentration ([Ca2+]c) in the Sur1-/- beta cells. Remarkably, Sur1-/- beta cells were less prone to apoptosis induced by H2O2 or an NO donor than WT beta cells, despite an enhanced basal rate of apoptosis. This protective effect was attributed to upregulation of the antioxidant enzymes SOD, glutathione peroxidase, and catalase. Upregulation of antioxidant enzymes and reduced sensitivity of Sur1-/- cells to H2O2-induced apoptosis were mimicked by treatment with the sulfonylureas tolbutamide and gliclazide. Enzyme upregulation and protection against oxidant-induced apoptosis were abrogated by agents lowering [Ca2+]c. Sur1-/- mice were less susceptible than WT mice to streptozotocin-induced beta cell destruction and subsequent hyperglycemia and death, which suggests that loss of KATP channel activity may protect against streptozotocin-induced diabetes in vivo.

Protective effect of Amomi semen extract on alloxan-induced pancreatic beta-cell damage

The protective effect of Amomi semen extract (ASE) on alloxan-induced pancreatic beta-cell damage was investigated in HIT T-15 cells, a Syrian hamster pancreatic beta-cell line. Alloxan caused pancreatic beta-cell damage through the generation of reactive oxygen species (ROS), the elevation of cytosolic free Ca2+, DNA fragmentation and the decrease of cellular NAD+ and ATP levels. All these effects of alloxan were significantly prevented by pretreatment with a water-soluble extract of Amomi semen. Pretreatment with ASE in pancreatic islets isolated from mice, also significantly abolished the inhibition of glucose-stimulated insulin secretion by alloxan. The results of this study provide evidence that ASE may have a protective activity on alloxan-induced beta-cell damage, and that the protective effect is primarily due to the inhibition of ROS generation by alloxan.

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.

Further studies on antioxidant potential and protection of pancreatic beta-cells by Embelia ribes in experimental diabetes

This study was designed to examine the antioxidant defense by ethanolic extract of Embelia ribes on streptozotocin-(40 mg/kg, intravenously, single-injection) induced diabetes in Wistar rats. Forty days of oral feeding the extract (100 mg/kg and 200 mg/kg) to diabetic rats resulted in significant (P < .01) decrease in blood glucose, blood glycosylated haemoglobin, serum lactate dehydrogenase, creatine kinase, and increase in blood glutathione levels as compared to pathogenic diabetic rats. Further, the extract also significantly (P < .01) decreased the pancreatic thiobarbituric acid-reactive substances (TBARS) levels and significantly (P < .01) increased the superoxide dismutase, catalase, and glutathione levels as compared to above levels in pancreatic tissue of pathogenic diabetic rats. The islets were shrunken in diabetic rats in comparison to normal rats. In the drug-treated diabetic rats, there was expansion of islets. The results of test drug were comparable to gliclazide (25 mg/kg, daily), a standard antihyperglycemic agent. The study concludes that Embelia ribes enhances the antioxidant defense against reactive oxygen species produced under hyperglycemic condition and this protects β-cells against loss, and exhibit antidiabetic property.

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.

Succinic acid monoethyl ester prevents oxidative stress in streptozotocin-nicotinamide-induced type2 diabetic rats

Succinic acid mono ethyl ester (EMS) was recently proposed as an insulinotropic tool in the treatment of non-insulin dependent diabetes mellitus. The aim of this study was to investigate the effect of EMS on oxidative stress in a streptozotocin (STZ)-nicotinamide induced type 2 diabetic model. The EMS was injected intraperitoneally at 8 micro mol/g body weight for 30 days. Plasma glucose, plasma insulin, thiobarbituricacid reactive substances (TBARS), hydroperoxides, superoxide dismutase (SOD), catalase (CAT), glutathione peroxide (Gpx), reduced glutathione (GSH), glutathione-S-transferase (GST), and vitamins C and E were assayed in liver and kidney. Treatment with EMS and metformin to diabetic rats resulted in a significant reduction in plasma glucose, TBARS, and hydroperoxides. In addition, the treated groups also showed a significant increase in the activities of plasma insulin, SOD, CAT, GPx, GST, GSH, vitamin C, and vitamin E in liver and kidney of STZ-nicotinamide-induced diabetic rats. Our result suggest that non glucidic nutrient, such as EMS as a potent antidiabetic, may optimalize antiperoxidative and antioxidants status by restoring the biochemical alterations found in STZ-nicotinamide-induced type 2 diabetes.

Induction of squamous cell carcinoma of forestomach in diabetic rats by single alloxan treatment

Male rats of WBN/Kob strain are one of the diabetic model animals and develop long-lasting diabetic symptoms and some complications from about 40 weeks of age without any treatment. A single intravenous dose of alloxan, a non-genotoxic diabetogenic chemical, frequently induced proliferative lesions of squamous epithelium in tongue, esophagus and forestomach of male and female WBN/Kob rats, and hastened the onset and acceleration of diabetic conditions. Histopathologically, proliferative changes of squamous cell of forestomach varied with the severity of hyperplasia in alloxan-treated rats (100% of 31 males and 94.1% of 17 females) and progressed to SCC in approximately 20% of all rats. Metastasis to regional lymph nodes was also observed in two cases. Proliferative changes were most severe in the forestomach and were constantly accompanied with chronic suppurative inflammation of the mucosal epithelium with infection of filamentous fungi and/or bacterial colonies. In contrast, forestomach of the spontaneously diabetic male rats showed only slight hyperplasia of the mucosal epithelium confined to the limiting ridge in approximately 30% of the cases. All non-diabetic female rats showed neither proliferative changes nor the inflammatory process in the mucosa. Immunohistochemically, COX-2 and iNOS were positive in these chronic suppurative inflammatory lesions accompanied by proliferative squamous epithelium. From these results, it is suggested that chronic inflammatory processes play an important role in the pathogenesis of alloxan-induced SCC. An experimental system of alloxan-induced SCC might serve as a suitable model for the study of the inflammation-related promotion of carcinogenesis.

Action of Hygrophila auriculata against streptozotocin-induced oxidative stress

Hygrophila auriculata (K. Schum.) Heine (Family: Acanthaceae) is a wild herb widely used in 'Ayurveda' as 'Rasayana' drug for treatment of various disorders. Treatment of diabetic rats with aerial parts of Hygrophila auriculata extract (HAEt, 100 and 250 mg/kg body weight) for 3 weeks showed significant reduction in blood glucose, thiobarbituric acid reactive substances (TBARS) and hydroperoxide in both liver and kidney. The treatment with HAEt significantly increased the glutathione (GSH), glutathione peroxidase (GPx), glutathione S-transferase (GST) and catalase (CAT) in the drug-treated group, which is comparable to the control group. HAEt and glibenclamide-treated rats also showed decreased lipid peroxidation that is associated with increased activity of superoxide dismutase (SOD) and catalase. The ability of HAEt on tissue lipid peroxidation and antioxidant status in diabetic animals has not been studied before. The result of this study thus shows that HAEt possesses significant antidiabetic activity along with potent antioxidant potential in diabetic conditions.

Membrane Switch Hypothesis. 2. Domain Structure of Phagocytes in Horses with Recurrent Airway Obstruction

The mechanism of recurrent airway obstruction (RAO) in horses was investigated by measuring the membrane domain structure and oxy-redoxy activity in phagocytes isolated from bronchoalveolar lavage fluid (BAL) and from the blood of healthy and RAO horses by electron paramagnetic resonance (EPR). Differences in the activity of intracellular antioxidant enzymes CAT, GPx, and SOD measured in phagocytes of RAO horses in comparison to healthy horses showed that the phagocytes were affected by oxidative stress. In comparison with polymorphonuclear leukocytes (phagocytes) from the blood of healthy horses the reduction mechanisms in BAL were faster and coincided with the merging of disordered membrane domains, while in horses with RAO the reduction and membrane domain structure remained unchanged. We assume that the merging of lipid domains observed in phagocytes from BAL of healthy horses could promote cluster formation of membrane proteins or ligands, which could trigger the activation process in phagocytes of healthy horses and consequently the physiological response that probably did not happen in phagocytes of RAO horses.

Antioxidant approach to disease management and the role of 'Rasayana' herbs of Ayurveda

The disease preventive and health promotive approach of 'Ayurveda', which takes into consideration the whole body, mind and spirit while dealing with the maintenance of health, promotion of health and treating ailments is holistic and finds increasing acceptability in many regions of the world. Ancient Ayurvedic physicians had developed certain dietary and therapeutic measures to arrest/delay ageing and rejuvenating whole functional dynamics of the body system. This revitalization and rejuvenation is known as the 'Rasayan chikitsa' (rejuvenation therapy). Traditionally, Rasayana drugs are used against a plethora of seemingly diverse disorders with no pathophysiological connections according to modern medicine. Though, this group of plants generally possesses strong antioxidant activity, only a few have been investigated in detail. Over about 100 disorders like rheumatoid arthritis, hemorrhagic shock, CVS disorders, cystic fibrosis, metabolic disorders, neurodegenerative diseases, gastrointestinal ulcerogenesis and AIDS have been reported as reactive oxygen species mediated. In this review, the role of free radicals in these diseases has been briefly reviewed. 'Rasayana' plants with potent antioxidant activity have been reviewed for their traditional uses, and mechanism of antioxidant action. Fifteen such plants have been dealt with in detail and some more plants with less work have also been reviewed briefly.

Reduction of diabetes-induced oxidative stress by phosphodiesterase inhibitors in rats

Increased oxidative stress has been suggested to be involved in the pathogenesis and progression of diabetic tissue damage. The aim of this study was to investigate the effect of different phosphodiesterase inhibitors on lipid peroxidation and total antioxidant capacity (TAC) of plasma in streptozotocin-induced diabetic rats (Rattus norvegicus). Rats became diabetic by a single administration of streptozotocin (STZ, 45 mg/kg). The effects of 15-days treatment by milrinone, sildenafil, and theophylline as cyclic-AMP and -GMP phosphodiesterase inhibitors (PDEIs) on diabetes-induced oxidative stress were studied. The levels of glucose, malonedialdehyde (MDA) the by product of lipid peroxides, and TAC (FRAP test) were estimated in plasma of control and experimental groups of rats. A significant increase in the levels of plasma glucose, and MDA and a concomitant decrease in the levels of TAC were observed in diabetic rats. These alterations were reverted back to near normal level after the treatment with PDEIs. Treatment of diabetic rats by PDEIs reduced MDA levels and increased TAC in the order of milrinone>sildenafil>theophylline. In conclusion, the present investigation show that PDIS possesses antioxidant activities, which may be attributed to their enhancing effect on cellular cyclic nucleotides contributing to the protection against oxidative stress in streptozotocin-induced diabetes. Exact mechanism of protective actions of cAMP- and cGMP-phosphodiesterase remains to be elucidated by further studies. This finding may suggest a place for PDEIs in maintaining health in diabetes.

A salen-manganese catalytic free radical scavenger inhibits type 1 diabetes and islet allograft rejection

Reactive oxygen species, such as superoxide, and nitrogen oxides, such as peroxynitrite, are thought to contribute to beta-cell destruction during the disease process that leads to type 1 diabetes. EUK-8 is a member of a new class of synthetic salen-manganese compounds with low toxicity that possess catalytic superoxide dismutase, peroxidase, and catalase activity that can inactivate superoxide and nitrogen oxides (e.g., peroxynitrite and nitrogen dioxide). We observed that EUK-8 administration inhibited the adoptive transfer of type 1 diabetes to NOD mice. In addition, administration of EUK-8 to NOD mice with established autoimmunity completely prevented the development of type 1 diabetes for up to 1 year in age, even though the treatment was discontinued after 35 weeks of age. EUK-8 treatment also prolonged the survival of islet allografts in newly diabetic NOD mice. Thus, reactive oxygen and nitrogen species contribute to the pathoetiology of both spontaneous type 1 diabetes and allograft rejection. In cultures of NIT-1 cells, EUK-8 inhibited cytotoxicity caused by superoxide as well as nitric oxide. Collectively, our findings implicate a greater role for nitrogen oxides (other than peroxynitrite) in beta-cell damage. Antioxidants designed to prevent the formation of both cytotoxic reactive oxygen and nitrogen species may effectively protect beta-cells from spontaneous autoimmunity and alloresponses.

Association study of human MTH1 gene polymorphisms with type 1 diabetes mellitus

Reactive oxygen species are considered to play a role in the development of diabetes mellitus and its complications. Human MTH1 (mutT homologue 1) has 8-oxo-7,8-dihydrodeoxyguanosine triphosphatase activity, which repairs oxidized forms of dGTP. This enzyme is known to have a thermolabile Met83 variant. We examined whether Val83Met polymorphism of human MTH1 gene is associated with type 1 diabetes mellitus. We recruited 156 type 1 diabetic patients (59 males and 97 females). The polymorphism was analyzed by restriction fragment length polymorphism analysis with Nsi I. The Met/Met genotype at codon 83 was very rare in both control and patient groups. Val/Met genotype tended to be more frequent in the whole type 1 diabetic patients than in controls. When subjects were divided into subgroups according to gender, there were no differences in the genotype and allele frequencies between patients and controls in males. On the other hand, in female type 1 diabetic patients, the Val/Met genotype was more frequent than in female controls (corrected P = 0.102). The Met allele was significantly more frequent in female type 1 diabetic patients than in female controls (corrected P = 0.022). Our results suggested that the Met allele at codon 83 of MTH1 gene might be involved in the development of type 1 diabetes mellitus in the Japanese female population.

Modulatory effects of gymnema montanum leaf extract on alloxan-induced oxidative stress in wistar rats

OBJECTIVES

In light of evidence that some complications of diabetes mellitus may be caused or exacerbated by oxidative damage, we investigated the effect of Gymnema montanum leaf extract (GLEt) on tissue antioxidant defense systems in alloxan-induced diabetes in rats.

METHODS

GLEt was administered orally at a doses of 50, 100, and 200 mg/kg of body weight for 30 d, after which liver and kidney tissues were assayed for the degree of lipid peroxidation by means of markers, reduced glutathione content and activities of catalase, superoxide dismutase, glutathione peroxidase, and glutathione-S-transferase.

RESULTS

Treatment of diabetic rats with GLEt increased the antioxidant levels. Liver and kidney from diabetic animals exhibited disturbances in antioxidant defense when compared with normal rats. GLEt at a dose of 200 mg/kg of body weight exhibited a significant effect as compared with 50 and 100 mg/kg of body weight. These effects were compared with glibenclamide, a reference drug.

CONCLUSIONS

It may be concluded that, in diabetes, liver and kidney tissues are more vulnerable to oxidative stress and show increased lipid peroxidation. The antioxidant responsiveness mediated by G. montanum may be anticipated to have biological significance in eliminating reactive free radicals that may otherwise affect normal cell functioning and provide a scientific rationale for the use of G. montanum as an antidiabetic plant.

Oxidative stress in streptozotocin-induced diabetic rats: effects of garlic oil and melatonin

In the present study, oxidative stress in diabetic model and the effect of garlic oil or melatonin treatment were examined. Streptozotocin (60 mg/kg body weight, i.p.)-induced diabetic rats, showed a significant increase of plasma glucose, total lipids, triglyceride, cholesterol, lipid peroxides, nitric oxide and uric acid. Concomitantly, significant decreases in the levels of antioxidants ceruloplasmin, albumin and total thiols were found in the plasma of diabetic rats. Lipid peroxide levels were significantly increased in erythrocyte lysate and in homogenates of liver and kidney, while superoxide dismutase (SOD) activities were decreased in tissue homogenates of liver and kidney. Treatment of diabetic rats with garlic oil (10 mg/kg i.p.) or melatonin (200 microg/kg i.p.) for 15 days significantly increased plasma levels of total thiol, ceruloplasmin activities, albumin. Lipid peroxides, uric acid, blood glucose, total lipid, triglyceride and cholesterol were decreased significantly after treatment with garlic oil or melatonin. Nitric oxide levels were decreased significantly in rats treated with melatonin only. In erythrocytes lysate, glutathione S-transferase (GST) activities were increased significantly in rats treated with garlic oil or melatonin, while lipid peroxides decreased significantly and total thiol increased significantly in melatonin or garlic oil treatment, respectively. In liver homogenates of rats treated with garlic or melatonin, lipid peroxides were decreased significantly, and GST activities increased significantly, while SOD activities were increased significantly in liver and kidney after garlic or melatonin treatment. The results suggest that garlic oil or melatonin may effectively normalize the impaired antioxidants status in streptozotocin induced-diabetes. The effects of these antioxidants of both agents may be useful in delaying the complicated effects of diabetes as retinopathy, nephropathy and neuropathy due to imbalance between free radicals and antioxidant systems. Moreover, melatonin may be more powerful free radical scavenger than garlic oil.

Glucose toxicity in beta-cells: type 2 diabetes, good radicals gone bad, and the glutathione connection

Chronic exposure to hyperglycemia can lead to cellular dysfunction that may become irreversible over time, a process that is termed glucose toxicity. Our perspective about glucose toxicity as it pertains to the pancreatic beta-cell is that the characteristic decreases in insulin synthesis and secretion are caused by decreased insulin gene expression. The responsible metabolic lesion appears to involve a posttranscriptional defect in pancreas duodenum homeobox-1 (PDX-1) mRNA maturation. PDX-1 is a critically important transcription factor for the insulin promoter, is absent in glucotoxic islets, and, when transfected into glucotoxic beta-cells, improves insulin promoter activity. Because reactive oxygen species are produced via oxidative phosphorylation during anaerobic glycolysis, via the Schiff reaction during glycation, via glucose autoxidation, and via hexosamine metabolism under supraphysiological glucose concentrations, we hypothesize that chronic oxidative stress is an important mechanism for glucose toxicity. Support for this hypothesis is found in the observations that high glucose concentrations increase intraislet peroxide levels, that islets contain very low levels of antioxidant enzyme activities, and that adenoviral overexpression of antioxidant enzymes in vitro in islets, as well as exogenous treatment with antioxidants in vivo in animals, protect the islet from the toxic effects of excessive glucose levels. Clinically, consideration of antioxidants as adjunct therapy in type 2 diabetes is warranted because of the many reports of elevated markers of oxidative stress in patients with this disease, which is characterized by imperfect management of glycemia, consequent chronic hyperglycemia, and relentless deterioration of beta-cell function.

[Alloxan radical-induced generation of reactive oxygen species in the reaction system of alloxan with ascorbate]

The diabetogenic action of alloxan is thought to be initiated by generation of reactive oxygen species (ROS). Ascorbate can be an antioxidant in a predominantly aqueous environment, such as plasma and extracellular fluids. We have investigated the generation of ROS in the interaction of alloxan with ascorbate. Rapid oxygen consumption was observed in the reactin system of alloxan with ascorbate. The oxygen consumption was suppressed by superoxide dismutase and catalase, suggesting that superoxide and hydrogen peroxide could be generated in the reaction system. In addition, the generation of alloxan radical, an electron reductance of alloxan, and ascorbate free radical (AFR), an electron oxidant of ascorbate, was observed using electron spin resonance (ESR). Under anaerobic conditions, the ESR signal intensity of alloxan radical was significantly increased in comparison with that under aerobic conditions, whereas the intensity of AFR was significantly decreased. These results suggest that alloxan radical and AFR were generated in the reaction system of alloxan with ascorbate, and that the alloxan radical but not AFR reacted with molecular oxygen, resulting in the generation of ROS.

Overexpression of extracellular-SOD in islets of nonobese diabetic mice and development of diabetes

Mice of the nonobese diabetic strain develop a progressive insulitis resulting in beta-cell destruction and diabetes. Superoxide radicals are abundantly formed by leukocytes and other mechanisms in inflammatory reactions. We here aimed to determine whether superoxide radicals contribute to the beta cell destruction in the mouse model. Transgenic nonobese diabetic mice secreting extracellular-superoxide dismutase under control of the insulin promoter were generated and the development of glucosuria monitored. The overexpression of extracellular-superoxide dismutase resulted in a 6-fold increase in the total superoxide dismutase activity of the islets. The incidence of diabetes of the transgenic mice was, however, not modified. The results suggest that superoxide radicals secreted to the extracellular space do not contribute to the beta cell destruction in the nonobese diabetic mouse model.

Overexpression of metallothionein in pancreatic beta-cells reduces streptozotocin-induced DNA damage and diabetes

The release of reactive oxygen species (ROS) has been proposed as a cause of streptozotocin (STZ)-induced beta-cell damage. This initiates a destructive cascade, consisting of DNA damage, excess activation of the DNA repair enzyme poly(ADP-ribose) polymerase, and depletion of cellular NAD+. Metallothionein (MT) is an inducible antioxidant protein that has been shown to protect DNA from chemical damage in several cell types. Therefore, we examined whether overexpression of MT could protect beta-cell DNA and thereby prevent STZ-induced diabetes. Two lines of transgenic mice were produced with up to a 30-fold elevation in beta-cell MT. Cultured islets from control mice and MT transgenic mice were exposed to STZ. MT was found to decrease STZ-induced islet disruption, DNA breakage, and depletion of NAD+. To assess in vivo protection, transgenic and control mice were injected with STZ. Transgenic mice had significantly reduced hyperglycemia. Ultrastructural examination of islets from STZ-treated mice showed that MT prevented degranulation and cell death. These results demonstrate that MT can reduce diabetes and confirm the DNA damage mechanism of STZ-induced beta-cell death.

Apoptosis and mitochondrial damage in INS-1 cells treated with alloxan

To evaluate the participation of mitochondrial damage, oxygen radicals and cell death in diabetes mellitus, we designed a way to investigate INS-1 cells, rat pancreatic beta-cell line, to die by treatment with alloxan which generate reactive oxygen species (ROS). Incubation of INS-1 cells with alloxan for 24 h resulted in a decrease in viability of cells as well as inhibition of glucose-stimulated insulin release; this could be prevented by antioxidants, vitamin E and butylated hydroxyanisol (BHA). The formation of a DNA ladder and the distribution of phosphatidylserine at the external surface of plasma membrane were observed as indicators of apoptosis in the cells treated with alloxan at concentrations below 0.5 mM. The formation of DNA ladder was prevented by vitamin E, BHA and catalase, suggesting that the ROS is involved in the process of apoptosis in INS-1 cells treated with alloxan. Lower levels of intracellular ATP, collapse of mitochondrial membrane potential and release of cytochrome c from mitochondria were also observed in INS-1 cells treated with alloxan, suggesting that alloxan caused the damage of mitochondria in cells and was related to the process of apoptosis. In contrast, rat liver RLC-18 cells treated with alloxan were not observed in the decrease of viability. It follows from the present study that mitochondrial damages by ROS generated from alloxan is linked to apoptosis in INS-1 cells.

Species differences in susceptibility of transplanted and cultured pancreatic islets to the beta-cell toxin alloxan

The beta-cell toxin alloxan, which produces oxygen radicals, is a model substance in studies of type 1 diabetes. Recently, human beta-cells have been found to be relatively resistant to this toxin. To clarify species differences in alloxan diabetogenicity, and oxygen radical toxicity, mouse, rat, rabbit, dog, pig, human and guinea pig islets have been studied after alloxan exposure. Using a standardized in vivo model, where islets were transplanted to nude mice, the different islets were compared. The results demonstrated that mouse and rat islet grafts were morphologically disturbed by alloxan and ROS. Rabbit and dog islet graft morphology was reasonably intact; and human, porcine, and guinea pig islet grafts were all well preserved. Furthermore, ultrastructural signs of apoptosis and necrosis, disturbances in the insulin secretory pattern during and after an alloxan perifusion, and islet lysosomal enzyme activities were studied in vitro in islets from some species. Guinea pig beta-cells were affected by alloxan, but a regeneration process compensated for the observed apoptotic and necrotic cell death. Human islets did not show any signs of alloxan-induced damage in the different models studied. Finally, no correlation between high alloxan sensitivity and high lysosomal enzyme activity was found. Thus, the beta-cell lysosomes are hardly specific targets for alloxan.

Radicals and oxidative stress in diabetes

Recent evidence is reviewed indicating increased oxidative damage in Type 1 and Type 2 diabetes mellitus as well as deficits in antioxidant defence enzymes and vitamins. Mechanisms are considered whereby hyperglycaemia can increase oxidative stress, and change the redox potential of glutathione and whereby reactive oxygen species can cause hyperglycaemia. It is argued that oxygen, antioxidant defences, and cellular redox status should now be regarded as central players in diabetes and the metabolic syndrome.

Alpha-phenyl-tert-butylnitrone (PBN) inhibits NFkappaB activation offering protection against chemically induced diabetes

Alpha-phenyl-tert-butylnitrone (PBN) is an effective spin trapping agent by reacting with and stabilizing free radical species. Reactive oxygen species (ROS) have been implicated in pancreatic beta cell death and the development of insulin-dependent diabetes mellitus (IDDM). We speculate that treatment with the PBN, will protect against diabetes development in two distinct chemically induced models for IDDM. Pretreatment with PBN (150 mg/kg ip) significantly reduced the severity of hyperglycemia in both alloxan- and streptozotocin (STZ) induced diabetes. To determine the mechanism by which PBN prevents hyperglycemia, we examined the ability of PBN to inhibit NFkappaB activation and to stabilize alloxan- and STZ-induced radicals. Both alloxan and STZ induced NFkappaB activation in the pancreas 30 min after their injection (50 mg/kg iv). PBN pretreatment inhibited both alloxan- and STZ-induced activation of NFkappaB and nitric oxide production. EPR studies showed that PBN could effectively trap alloxan-induced free radicals. It is clear that PBN can inhibit NFkappaB activation in the pancreas and reduce hyperglycemia in two distinct diabetogenic compounds. This research indicates that NFkappaB activation may be a key signal leading to beta cell death and IDDM. Understanding the cellular pathways leading to beta cell death may help in developing effective preventive or therapeutic targets for IDDM.

Human islets in mixed islet grafts protect mouse pancreatic beta-cells from alloxan toxicity

We have previously shown that human beta-cells are resistant to the toxic effects of alloxan. In order to further clarify this characteristic of human islets, we investigated whether these cells might transfer their alloxan resistance to alloxan-sensitive rat or mouse islets. Islets from two species (human-mouse or rat-mouse) were mixed into one graft, which was implanted into the subcapsular kidney space of nude mice. Alloxan or saline was injected intravenously two weeks after implantation and one week thereafter the mice were killed. The number of grafted and endogenous beta-cells were evaluated by a semi-quantitative method after immunohistochemistry. Human islet production of the scavenging enzymes extracellular superoxide dismutase and plasma glutathione peroxidase were analyzed with ELISA-techniques, and mouse and human islet hydrogen peroxide breakdown activity were monitored with a horseradish peroxidase-dependent assay. Mouse beta-cells transplanted together with human islets were protected against alloxan cytotoxicity. Rat islets did not protect mouse beta-cells against alloxan, suggesting that the mixing procedure as such did not impose the protection. Production of extracellular superoxide dismutase and plasma glutathione peroxidase by human islets was very low. Moreover, H2O2 breakdown in vitro, did not differ between human and mouse islets. Alloxan-insensitive human islets protect mouse beta-cells against alloxan-induced lesions, suggesting that yet to be identified extracellular factors are involved in human islet resistance to alloxan toxicity.