An inhibitor of inducible nitric oxide synthase and scavenger of peroxynitrite prevents diabetes development in NOD mice

Ferroptosis Signaling in Pancreatic β-Cells: Novel Insights & Therapeutic Targeting

Metabolic stress impairs pancreatic β-cell survival and function in diabetes. Although the pathophysiology of metabolic stress is complex, aberrant tissue damage and β-cell death are brought on by an imbalance in redox equilibrium due to insufficient levels of endogenous antioxidant expression in β-cells. The vulnerability of β-cells to oxidative damage caused by iron accumulation has been linked to contributory β-cell ferroptotic-like malfunction under diabetogenic settings. Here, we take into account recent findings on how iron metabolism contributes to the deregulation of the redox response in diabetic conditions as well as the ferroptotic-like malfunction in the pancreatic β-cells, which may offer insights for deciphering the pathomechanisms and formulating plans for the treatment or prevention of metabolic stress brought on by β-cell failure.

Arginase: Biological and Therapeutic Implications in Diabetes Mellitus and Its Complications

Arginase is a ubiquitous enzyme in the urea cycle (UC) that hydrolyzes L-arginine to urea and L-ornithine. Two mammalian arginase isoforms, arginase1 (ARG1) and arginase2 (ARG2), play a vital role in the regulation of β-cell functions, insulin resistance (IR), and vascular complications via modulating L-arginine metabolism, nitric oxide (NO) production, and inflammatory responses as well as oxidative stress. Basic and clinical studies reveal that abnormal alterations of arginase expression and activity are strongly associated with the onset and development of diabetes mellitus (DM) and its complications. As a result, targeting arginase may be a novel and promising approach for DM treatment. An increasing number of arginase inhibitors, including chemical and natural inhibitors, have been developed and shown to protect against the development of DM and its complications. In this review, we discuss the fundamental features of arginase. Next, the regulatory roles and underlying mechanisms of arginase in the pathogenesis and progression of DM and its complications are explored. Furthermore, we review the development and discuss the challenges of arginase inhibitors in treating DM and its related pathologies.

Effect of Plantain Bulb's Extract-Beverage Blend on Blood Glucose Levels, Antioxidant Status, and Carbohydrate Hydrolysing Enzymes in Streptozotocin-Induced Diabetic Rats

The pharmacological properties of various parts of plantain trees have directed its use in folkloric management of diabetes and other human ailments. However, little is known about plantain bulb extract (PBE) and their mechanisms of action. This study evaluated the effect of PBE-beverage blends (including 1% and 2 % cocoa powder) sweetened with honey on blood glucose levels, antioxidant status, and carbohydrate hydrolysing enzyme activities in streptozotocin (STZ)-induced diabetic rats. Animals were selected at random and distributed into 7 groups (n=7), as follows: normal control (NC), untreated diabetic rats, diabetic rats treated with acarbose (STZ-ACA), diabetic rats administered PBE (STZ- PBE), diabetic rats administered honey and PBE (STZ-HPBE), diabetic rats administered 1% cocoa powder-with HPBE blend (STZ-CHPBE-1), and diabetic rats administered 2% cocoa powder with HPBE blend (STZ-CHPBE-2). Compared with the controls, untreated diabetic rats exhibited increased blood glucose levels and hydrolysing enzyme activities, and significant decreases in the activities of antioxidant (catalase, superoxide dismutase, glutathione-S-transferase, and glutathione peroxidase) enzyme and non-enzymatic (glutathione) antioxidants. However, changes in activities were comparatively reversed in all rats administered plantain bulb formulations. CHPBE-2 was slightly more effective than CHPBE-1. Overall, both blends could serve as nutraceutical and/or functional drinks in the management of diabetes.

Oxidative Stress in Cytokine-Induced Dysfunction of the Pancreatic Beta Cell: Known Knowns and Known Unknowns

Compelling evidence from earlier studies suggests that the pancreatic beta cell is inherently weak in its antioxidant defense mechanisms to face the burden of protecting itself against the increased intracellular oxidative stress following exposure to proinflammatory cytokines. Recent evidence implicates novel roles for nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Noxs) as contributors to the excessive intracellular oxidative stress and damage under metabolic stress conditions. This review highlights the existing evidence on the regulatory roles of at least three forms of Noxs, namely Nox1, Nox2, and Nox4, in the cascade of events leading to islet beta cell dysfunction, specifically under the duress of chronic exposure to cytokines. Potential crosstalk between key signaling pathways (e.g., inducible nitric oxide synthase [iNOS] and Noxs) in the generation and propagation of reactive molecules and metabolites leading to mitochondrial damage and cell apoptosis is discussed. Available data accrued in investigations involving small-molecule inhibitors and antioxidant protein expression methods as tools toward the prevention of cytokine-induced oxidative damage are reviewed. Lastly, current knowledge gaps in this field, and possible avenues for future research are highlighted.

Diol-ginsenosides from Korean Red Ginseng delay the development of type 1 diabetes in diabetes-prone biobreeding rats

Background

The effects of diol-ginsenoside fraction (Diol-GF) and triol-ginsenoside fraction (Triol-GF) from Korean Red Ginseng on the development of type 1 diabetes (T1D) were examined in diabetes-prone biobreeding (DP-BB) rats that spontaneously develop T1D through an autoimmune process.

Methods

DP-BB female rats were treated with Diol-GF or Triol-GF daily from the age of 3-4 weeks up to 11-12 weeks (1 mg/g body weight).

Results

Diol-GF delayed the onset, and reduced the incidence, of T1D. Islets of Diol-GF-treated DP-BB rats showed significantly lower insulitis and preserved higher plasma and pancreatic insulin levels. Diol-GF failed to change the proportion of lymphocyte subsets such as T cells, natural killer cells, and macrophages in the spleen and blood. Diol-GF had no effect on the ability of DP-BB rat splenocytes to induce diabetes in recipients. Diol-GF and diol-ginsenoside Rb1 significantly decreased tumor necrosis factor α production, whereas diol-ginsenosides Rb1 and Rd decreased interleukin 1β production in RAW264.7 cells. Furthermore, mixed cytokine- and chemical-induced β-cell cytotoxicity was greatly inhibited by Diol-GF and diol-ginsenosides Rc and Rd in RIN5mF cells. However, nitric oxide production in RAW264.7 cells was unaffected by diol-ginsenosides.

Conclusion

Diol-GF, but not Triol-GF, significantly delayed the development of insulitis and T1D in DP-BB rats. The antidiabetogenic action of Diol-GF may result from the decrease in cytokine production and increase in β-cell resistance to cytokine/free radical-induced cytotoxicity.

Reactive Oxygen Comes of Age: Mechanism-Based Therapy of Diabetic End-Organ Damage

Reactive oxygen species (ROS) have been mainly viewed as unwanted by-products of cellular metabolism, oxidative stress, a sign of a cellular redox imbalance, and potential disease mechanisms, such as in diabetes mellitus (DM). Antioxidant therapies, however, have failed to provide clinical benefit. This paradox can be explained by recent discoveries that ROS have mainly essential signaling and metabolic functions and evolutionally conserved physiological enzymatic sources. Disease can occur when ROS accumulate in nonphysiological concentrations, locations, or forms. By focusing on disease-relevant sources and targets of ROS, and leaving ROS physiology intact, precise therapeutic interventions are now possible and are entering clinical trials. Their outcomes are likely to profoundly change our concepts of ROS in DM and in medicine in general.

Is There a Role for Bioactive Lipids in the Pathobiology of Diabetes Mellitus?

Inflammation, decreased levels of circulating endothelial nitric oxide (eNO) and brain-derived neurotrophic factor (BDNF), altered activity of hypothalamic neurotransmitters (including serotonin and vagal tone) and gut hormones, increased concentrations of free radicals, and imbalance in the levels of bioactive lipids and their pro- and anti-inflammatory metabolites have been suggested to play a role in diabetes mellitus (DM). Type 1 diabetes mellitus (type 1 DM) is due to autoimmune destruction of pancreatic β cells because of enhanced production of IL-6 and tumor necrosis factor-α (TNF-α) and other pro-inflammatory cytokines released by immunocytes infiltrating the pancreas in response to unknown exogenous and endogenous toxin(s). On the other hand, type 2 DM is due to increased peripheral insulin resistance secondary to enhanced production of IL-6 and TNF-α in response to high-fat and/or calorie-rich diet (rich in saturated and trans fats). Type 2 DM is also associated with significant alterations in the production and action of hypothalamic neurotransmitters, eNO, BDNF, free radicals, gut hormones, and vagus nerve activity. Thus, type 1 DM is because of excess production of pro-inflammatory cytokines close to β cells, whereas type 2 DM is due to excess of pro-inflammatory cytokines in the systemic circulation. Hence, methods designed to suppress excess production of pro-inflammatory cytokines may form a new approach to prevent both type 1 and type 2 DM. Roux-en-Y gastric bypass and similar surgeries ameliorate type 2 DM, partly by restoring to normal: gut hormones, hypothalamic neurotransmitters, eNO, vagal activity, gut microbiota, bioactive lipids, BDNF production in the gut and hypothalamus, concentrations of cytokines and free radicals that results in resetting glucose-stimulated insulin production by pancreatic β cells. Our recent studies suggested that bioactive lipids, such as arachidonic acid, eicosapentaneoic acid, and docosahexaenoic acid (which are unsaturated fatty acids) and their anti-inflammatory metabolites: lipoxin A4, resolvins, protectins, and maresins, may have antidiabetic actions. These bioactive lipids have anti-inflammatory actions, enhance eNO, BDNF production, restore hypothalamic dysfunction, enhance vagal tone, modulate production and action of ghrelin, leptin and adiponectin, and influence gut microbiota that may explain their antidiabetic action. These pieces of evidence suggest that methods designed to selectively deliver bioactive lipids to pancreatic β cells, gut, liver, and muscle may prevent type 1 and type 2 DM.

Tetrabromobisphenol A induces cellular damages in pancreatic β-cells in vitro

Tetrabromobisphenol A (TBBPA) is a well-known organobrominated flame retardant. TBBPA has been detected in the environment. The roles played by environmental pollutants in increasing the prevalence of metabolic syndrome are attracting increasing concern. In the present work, we investigated the effects of TBBPA on rat pancreatic β-cells (the RIN-m5F cell line). RIN-m5F cells were incubated with different concentrations of TBBPA for 48 h, and cell viability and the extent of apoptosis were determined. We also measured the levels of inflammatory cytokines, reactive oxygen species (ROS), mitochondrial adenosine triphosphate (ATP), and cardiolipin, as well as the extent of cytochrome c release from mitochondria. TBBPA reduced the ATP level, induced cardiolipin peroxidation and cytochrome c release, and triggered apoptotic cell death. Moreover, TBBPA increased the levels of inflammatory cytokines (TNF-α and IL-1β), nitric oxide, intracellular ROS, and mitochondrial superoxide. Together, our results indicate that TBBPA damages pancreatic β-cells by triggering mitochondrial dysfunction and inducing apoptosis.

Cross-talk between lipid and protein carbonylation in a dynamic cardiomyocyte model of mild nitroxidative stress

Reactive oxygen and nitrogen species (ROS/RNS) play an important role in the regulation of cardiac function. Increase in ROS/RNS concentration results in lipid and protein oxidation and is often associated with onset and/or progression of many cardiovascular disorders. However, interplay between lipid and protein modifications has not been simultaneously studied in detail so far. Biomolecule carbonylation is one of the most common biomarkers of oxidative stress. Using a dynamic model of nitroxidative stress we demonstrated rapid changes in biomolecule carbonylation in rat cardiomyocytes. Levels of carbonylated species increased as early as 15min upon treatment with the peroxynitrite donor, 3-morpholinosydnonimine (SIN-1), and decreased to values close to control after 16h. Total (lipids+proteins) vs. protein-specific carbonylation showed different dynamics, with a significant increase in protein-bound carbonyls at later time points. Treatment with SIN-1 in combination with inhibitors of proteasomal and autophagy/lysosomal degradation pathways allowed confirmation of a significant role of the proteasome in the degradation of carbonylated proteins, whereas lipid carbonylation increased in the presence of autophagy/lysosomal inhibitors. Electrophilic aldehydes and ketones formed by lipid peroxidation were identified and relatively quantified using LC-MS/MS. Molecular identity of reactive species was used for data-driven analysis of their protein targets. Combination of different enrichment strategies with LC-MS/MS analysis allowed identification of more than 167 unique proteins with 332 sites modified by electrophilic lipid peroxidation products. Gene ontology analysis of modified proteins demonstrated enrichment of several functional categories including proteins involved in cytoskeleton, extracellular matrix, ion channels and their regulation. Using calcium mobilization assays, the effect of nitroxidative stress on the activity of several ion channels was further confirmed.

Rpl13a small nucleolar RNAs regulate systemic glucose metabolism

Small nucleolar RNAs (snoRNAs) are non-coding RNAs that form ribonucleoproteins to guide covalent modifications of ribosomal and small nuclear RNAs in the nucleus. Recent studies have also uncovered additional non-canonical roles for snoRNAs. However, the physiological contributions of these small RNAs are largely unknown. Here, we selectively deleted four snoRNAs encoded within the introns of the ribosomal protein L13a (Rpl13a) locus in a mouse model. Loss of Rpl13a snoRNAs altered mitochondrial metabolism and lowered reactive oxygen species tone, leading to increased glucose-stimulated insulin secretion from pancreatic islets and enhanced systemic glucose tolerance. Islets from mice lacking Rpl13a snoRNAs demonstrated blunted oxidative stress responses. Furthermore, these mice were protected against diabetogenic stimuli that cause oxidative stress damage to islets. Our study illuminates a previously unrecognized role for snoRNAs in metabolic regulation.

The Role of Type I Interferon Subtypes and Interferon-Gamma in Type I Interferon Diabetes Inhibitory Activity in the NOD Mouse

As in bacterial infections and endotoxin shock, type I interferons (IFNs) also have complex and often opposing effects in various models of autoimmune disease. We have shown that type I IFN paradoxically inhibits autoimmune diabetes in the nonobese diabetic mouse (NOD) and biobreeding (BB) rat. We hypothesize that type I IFN activity differs by IFN subtype and interaction with IFN-gamma. We examined the structure-function relationship of the type I IFN molecule and the mechanism of its diabetes-sparing activity in the NOD mouse. While both recombinant human IFN-alpha A/D (bgl 11) (rHuIFN-alphaA/D) and ovine IFN-tauImod (ovIFN-tau) potently inhibited the development of diabetes (P < 0.01), neither recombinant human IFN-alpha B/D (rHuIFN-alphaB/D) nor recombinant human IFN-alpha consensus (CIFN) were efficacious. The activity of IFN subtypes correlate with their NH3-terminal amino acid sequences. All type I IFN save CIFN, which has no diabetes-sparing activity, inhibited the accessory cell function. IFN-tau administration decreased the expression of Fas and ICAM on total cells, class II MHC expression on B cells, and CD40L expression on T cells by 39%, 45%, 45%, and 60%, respectively. In addition, IFN-tau inhibited the development of diabetes in the NOD.IL4(null) but not the NOD.IFN-gamma(null) mice, suggesting a coordinated interaction between type I and type II IFNs to suppress diabetes development. Thus, the amino terminal portion of the type I IFN molecule influences its ability to inhibit the development of autoimmune diabetes in NOD mice. These data also support the contention that IFN-gamma may have a role in mediating the diabetes-sparing effect of high-dose type I IFNs by the inhibition of the IFN-gamma-inducible immune modulators, class II MHC, Fas, ICAM, and CD40L.

SR-135, a peroxynitrite decomposing catalyst, enhances β-cell function and survival in B6D2F1 mice fed a high fat diet

Peroxynitrite has been implicated in β-cell dysfunction and insulin resistance in obesity. Chemical catalysts that destroy peroxynitrite, therefore, may have therapeutic value for treating type 2 diabetes. To this end, we have recently demonstrated that Mn(III) bis(hydroxyphenyl)-dipyrromethene complexes, SR-135 and its analogs, can effectively catalyze the decomposition of peroxynitrite in vitro and in vivo through a 2-electron mechanism (Rausaria et al., 2011). To study the effects of SR-135 on glucose homeostasis in obesity, B6D2F1 mice were fed with a high fat-diet (HFD) for 12 weeks and treated with vehicle, SR-135 (5mg/kg), or a control drug SRB for 2 weeks. SR-135 significantly reduced fasting blood glucose and insulin levels, and enhanced glucose tolerance as compared to HFD control, vehicle or SRB. SR-135 also enhanced glucose-stimulated insulin secretion based on ex vivo studies. Moreover, SR-135 increased insulin content, restored islet architecture, decreased islet size, and reduced tyrosine nitration and apoptosis. These results suggest that a peroxynitrite decomposing catalyst enhances β-cell function and survival under nutrient overload.

Forced IDO1 expression in dendritic cells restores immunoregulatory signalling in autoimmune diabetes

Indoleamine 2,3-dioxygenase (IDO1), a tryptophan catabolizing enzyme, is recognized as an authentic regulator of immunity in several physiopathologic conditions. We have recently demonstrated that IDO1 does not merely degrade tryptophan and produce immunoregulatory kynurenines, but it also acts as a signal-transducing molecule, independently of its enzymic function. IDO1 signalling activity is triggered in plasmacytoid dendritic cells (pDCs) by transforming growth factor-β (TGF-β), an event that requires the non-canonical NF-κB pathway and induces long-lasting IDO1 expression and autocrine TGF-β production in a positive feedback loop, thus sustaining a stably regulatory phenotype in pDCs. IDO1 expression and catalytic function are defective in pDCs from non-obese diabetic (NOD) mice, a prototypic model of autoimmune diabetes. In the present study, we found that TGF-β failed to activate IDO1 signalling function as well as up-regulate IDO1 expression in NOD pDCs. Moreover, TGF-β-treated pDCs failed to exert immunosuppressive properties in vivo. Nevertheless, transfection of NOD pDCs with Ido1 prior to TGF-β treatment resulted in activation of the Ido1 promoter and induction of non-canonical NF-κB and TGF-β, as well as decreased production of the pro-inflammatory cytokines, interleukin 6 (IL-6) and tumour necrosis factor-α (TNF-α). Overexpression of IDO1 in TGF-β-treated NOD pDCs also resulted in pDC ability to suppress the in vivo presentation of a pancreatic β-cell auto-antigen. Thus, our data suggest that a correction of IDO1 expression may restore its dual function and thus represent a proper therapeutic manoeuvre in this autoimmune setting.

Protective Effect of Padina arborescens Extract against High Glucose-induced Oxidative Damage in Human Umbilical Vein Endothelial Cells

Dysfunction of endothelial cells is considered a major cause of vascular complications in diabetes. In the present study, we investigated the protective effect of Padina arborescens extract against high glucose-induced oxidative damage in human umbilical vein endothelial cells (HUVECs). High-concentration of glucose (30 mM) treatment induced cytotoxicity whereas Padina arborescens extract protected the cells from high glucose-induced damage and significantly restored cell viability. In addition, lipid peroxidation, intracellular reactive oxygen species (ROS), and nitric oxide (NO) levels induced by high glucose treatment were effectively inhibited by treatment of Padina arborescens extract in a dose-dependent manner. High glucose treatment also induced the overexpressions of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and NF-κB proteins in HUVECs, but Padina arborescens extract treatment reduced the over-expressions of these proteins. These findings indicate the potential benefits of Padina arborescens extract as a valuable source in reducing the oxidative damage induced by high glucose.

Regulation of iNOS gene transcription by IL-1β and IFN-γ requires a coactivator exchange mechanism

The proinflammatory cytokines IL-1β and IFN-γ decrease functional islet β-cell mass in part through the increased expression of specific genes, such as inducible nitric oxide synthase (iNOS). Dysregulated iNOS protein accumulation leads to overproduction of nitric oxide, which induces DNA damage, impairs β-cell function, and ultimately diminishes cellular viability. However, the transcriptional mechanisms underlying cytokine-mediated expression of the iNOS gene are not completely understood. Herein, we demonstrated that individual mutations within the proximal and distal nuclear factor-κB sites impaired cytokine-mediated transcriptional activation. Surprisingly, mutating IFN-γ-activated site (GAS) elements in the iNOS gene promoter, which are classically responsive to IFN-γ, modulated transcriptional sensitivity to IL-1β. Transcriptional sensitivity to IL-1β was increased by generation of a consensus GAS element and decreased correspondingly with 1 or 2 nucleotide divergences from the consensus sequence. The nuclear factor-κB subunits p65 and p50 bound to the κB response elements in an IL-1β-dependent manner. IL-1β also promoted binding of serine-phosphorylated signal transducer and activator of transcription-1 (STAT1) (Ser727) but not tyrosine-phosphorylated STAT1 (Tyr701) to GAS elements. However, phosphorylation at Tyr701 was required for IFN-γ to potentiate the IL-1β response. Furthermore, coactivator p300 and coactivator arginine methyltransferase were recruited to the iNOS gene promoter with concomitant displacement of the coactivator CREB-binding protein in cells exposed to IL-1β. Moreover, these coordinated changes in factor recruitment were associated with alterations in acetylation, methylation, and phosphorylation of histone proteins. We conclude that p65 and STAT1 cooperate to control iNOS gene transcription in response to proinflammatory cytokines by a coactivator exchange mechanism. This increase in transcription is also associated with signal-specific chromatin remodeling that leads to RNA polymerase II recruitment and phosphorylation.

Oxidative stress in diabetes

Oxidative stress and diabetes, both Type 1 and Type 2 as well as their related conditions have been extensively studied. As diabetes, obesity and metabolic syndrome have reached at epidemic levels, there is a huge need and effort to understand the detailed molecular mechanisms of the possible redox imbalance, underlying the cause of pathology and progression of the disease. These studies provide new insights at cellular and subcellular levels to design effective clinical interventions. This chapter is intended to emphasize the latest knowledge and current evidence on the role of oxidative stress in diabetes as well as to discuss some key questions that are currently under discussion.

Modulation of myocardial contraction by peroxynitrite

Peroxynitrite is a potent oxidant that is quickly emerging as a crucial modulator of myocardial function. This review will focus on the regulation of myocardial contraction by peroxynitrite during health and disease, with a specific emphasis on cardiomyocyte Ca²⁺ handling, proposed signaling pathways, and protein end-targets.

Hyperactivation of protein phosphatase 2A in models of glucolipotoxicity and diabetes: potential mechanisms and functional consequences

The protein phosphatase 2A [PP2A] family of enzymes has been implicated in the regulation of a variety of cellular functions including hormone secretion, growth, survival and apoptosis. PP2A accounts for ~1% of total cellular protein and ∼ 80% of total serine/threonine phosphatases, thus representing a major class of protein phosphatases in mammalian cells. Despite significant advances in our current understanding of regulation of cellular function by PP2A under physiological conditions, little is understood with regard to its regulation under various pathological conditions, such as diabetes. Emerging evidence suggests hyperactivation of PP2A in liver, muscle, retina and the pancreatic islet under the duress of glucolipotoxicity and diabetes. Interestingly, pharmacological inhibition of PP2A or siRNA-mediated depletion of the catalytic subunit of PP2A [PP2Ac] levels largely restored PP2A activity to near normal levels under these conditions. Herein, we provide an overview of PP2A subunit expression and activity in in vitro and in vivo models of glucolipotoxicity and diabetes, and revisit the existing data, which are suggestive of alterations in post-translational methylation, phosphorylation and nitration of PP2Ac under these conditions. Potential significance of hyperactive PP2A in the context of cell function, survival and apoptosis is also highlighted. It is hoped that this commentary will provide a basis for future studies to explore the potential for PP2Ac as a therapeutic target for the treatment of diabetes and other metabolic disorders.

Nitric oxide, a janus-faced therapeutic target for diabetic microangiopathy-Friend or foe?

Accelerated atherosclerosis and microvascular complications are the leading causes of coronary heart disease, end-stage renal failure, acquired blindness and a variety of neuropathy, which could account for disabilities and high mortality rates in patients with diabetes. As the prevalence of diabetes has risen to epidemic proportions worldwide, diabetic vascular complications have now become one of the most challenging health problems. Nitric oxide (NO) is a pleiotropic molecule critical to a number of physiological and pathological processes in humans. NO not only inhibits the inflammatory-proliferative reactions in vascular wall cells, but also exerts anti-thrombogenic and endothelial cell protective properties, all of which could potentially be exploited as a therapeutic option for the treatment of vascular complications in diabetes. However, high amounts of NO produced by inducible NO synthase (iNOS) and/or peroxynitrite (ONOO(-)), a reactive intermediate of NO with superoxide anion are involved in pro-inflammatory reactions and tissue damage as well. This implies that NO is a janus-faced molecule and acts as a double-edged sword in vascular complications in diabetes. Further, NO is synthesized from l-arginine via the action of NO synthase (NOS), while NOS is blocked by endogenous l-arginine analogues such as asymmetric dimethylarginine (ADMA), a naturally occurring amino acid which is found in the plasma and various tissues. These findings suggest that amounts of NO locally produced, oxidative stress conditions and level of ADMA could determine the beneficial and detrimental effects of NO on vascular complications in diabetes. In this paper, we review the janus-faced aspects of NO in diabetic microangiopathy.

Peroxynitrite-driven mechanisms in diabetes and insulin resistance - the latest advances

Since its discovery, peroxynitrite has been known as a potent oxidant in biological systems, and a rapidly growing body of literature has characterized its biochemistry and role in the pathophysiology of various conditions. Either directly or by inducing free radical pathways, peroxynitrite damages vital biomolecules such as DNA, proteins including enzymes with important functions, and lipids. It also initiates diverse reactions leading eventually to disrupted cell signaling, cell death, and apoptosis. The potential role and contribution of this deleterious species has been the subject of investigation in several important diseases, including but not limited to, cancer, neurodegeneration, stroke, inflammatory conditions, cardiovascular problems, and diabetes mellitus. Diabetes, obesity, insulin resistance, and diabetes-related complications represent a major health problem at epidemic levels. Therefore, tremendous efforts have been put into investigation of the molecular basics of peroxynitrite-related mechanisms in diabetes. Studies constantly seek new therapeutical approaches in order to eliminate or decrease the level of peroxynitrite, or to interfere with its downstream mechanisms. This review is intended to emphasize the latest findings about peroxynitrite and diabetes, and, in addition, to discuss recent and novel advances that are likely to contribute to a better understanding of peroxynitrite-mediated damage in this disease.

Cytokine toxicity in insulin-producing cells is mediated by nitro-oxidative stress-induced hydroxyl radical formation in mitochondria

Although nitric oxide (NO) and oxidative stress both contribute to proinflammatory cytokine toxicity in pancreatic β-cells during type 1 diabetes mellitus (T1DM) development, the interactions between NO and reactive oxygen species (ROS) in cytokine-mediated β-cell death have not been clarified. Exposure of insulin-producing RINm5F cells to IL-1β generated NO, while exposure to a combination of IL-1β, TNF-α, and IFN-γ, which simulates T1DM conditions, generated both NO and ROS. In theory, two reactions between NO and ROS are possible, one with the superoxide radical yielding peroxynitrite, and the other with hydrogen peroxide (H(2)O(2)) yielding hydroxyl radicals. Results of the present work exclude peroxynitrite involvement in cytokine toxicity to β-cells because its generation did not correlate with the toxic action of cytokines. On the other hand, we show that H(2)O(2), produced upon exposure of insulin-producing cell clones and primary rat islet cells to cytokines almost exclusively in the mitochondria, reacted in the presence of trace metal (Fe(++)) with NO forming highly toxic hydroxyl radicals, thus explaining the severe toxicity that causes apoptotic β-cell death. Expression of the H(2)O(2)-inactivating enzyme catalase in mitochondria protected against cytokine toxicity by preventing hydroxyl radical formation. We therefore conclude that proinflammatory cytokine-mediated β-cell death is due to nitro-oxidative stress-mediated hydroxyl radical formation in the mitochondria.

Transgenic expression of haem oxygenase-1 in pancreatic beta cells protects non-obese mice used as a model of diabetes from autoimmune destruction and prolongs graft survival following islet transplantation

AIMS/HYPOTHESIS

Haem oxygenase 1 (HO-1) has strong anti-apoptotic, anti-inflammatory and antioxidative effects that help protect cells against various forms of immune attack. We investigated whether transgenic expression of Ho-1 (also known as Hmox1) in pancreatic beta cells would protect NOD mice from autoimmune damage and prolong graft survival following islet transplantation.

METHODS

To evaluate the protective effect of beta cell-specific HO-1 in autoimmune diabetes, we used an insulin promoter-driven murine Ho-1 construct (pIns-mHo-1) to generate a transgenic NOD mouse. Transgene expression, insulitis and the incidence of diabetes in mice were characterised. Lymphocyte composition, the development of T helper (Th)1, Th2 and T regulatory (Treg) cells, T cell proliferation and lymphocyte-mediated disease transfer were analysed. The potential effects of transgenic islets and islet transplantation on apoptosis, inflammation and the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) were evaluated.

RESULTS

Transgenic mice showed less severe insulitis and a lower incidence of diabetes than non-transgenic control littermates. Lymphocyte composition and functions were not affected. Islets from transgenic mice expressed lower levels of proinflammatory cytokines/chemokines, proapoptotic gene expression and amounts of ROS/RNS, and were more resistant to TNF-α- and IFN-γ-induced apoptosis. Islet grafts from transgenic mice also survived longer in diabetic recipients than control islets.

CONCLUSIONS/INTERPRETATION

Transgenic overexpression of Ho-1 in beta cells protected NOD mice from diabetes and delayed the autoimmune destruction of islet grafts, providing valuable insight into the development of better strategies for clinical islet transplantation in patients with type 1 diabetes.

Upregulation of PTEN by peroxynitrite contributes to cytokine-induced apoptosis in pancreatic beta-cells

Phosphatase and tensin homolog (PTEN), a tumor suppressor gene, by negatively regulating the PI3K-Akt signaling pathway, participates in multiple biological processes such as cell proliferation, apoptosis, differentiation, and migration. Recent studies show that selective deletion of PTEN in pancreatic beta-cells leads to resistance to streptozotocin (STZ)-induced diabetes, but the mechanism is unclear. One major mechanism underlying STZ toxicity is cytokine-mediated beta-cell destruction in which oxidative stress plays a key role. The present study investigated the role of PTEN in cytokine-induced beta-cell apoptosis, and further explored whether oxidative stress, particularly peroxynitrite formation, could regulate PTEN-Akt pathway. Incubation of betaTC-6 cells with cytokine mixture (IL-1beta, TNF-alpha, and IFN-gamma) or exogenous peroxynitrite significantly increased apoptotic cell percentage, elevated PTEN and p-PTEN levels, and inhibited Akt activation. Transfection with PTEN-specific siRNA protected betaTC-6 cells from cytokine or peroxynitrite-mediated cell apoptosis and partially reversed Akt inhibition. Furthermore, nitrotyrosine formation, an indicator of peroxynitrite production, was significantly elevated after cytokine treatment. Preventing peroxynitrite formation by administrating NAC/L: -NMMA, or scavenging peroxynitrite directly by UA, attenuated cytokine-induced PTEN upregulation, Akt inhibition, and beta-cell apoptosis. These findings suggest that peroxynitrite-mediated PTEN upregulation plays an important role in cytokine-induced pancreatic beta-cell apoptosis.

New insights into the role of VIP on the ratio of T-cell subsets during the development of autoimmune diabetes

Type I diabetes is an autoimmune T-cell-mediated disease associated with overexpression of inflammatory mediators and the disturbance of different T-cell subsets. Vasoactive intestinal peptide (VIP) is a potent anti-inflammatory agent with regulatory effects on activated T cells. As the equilibrium between different T-cell subsets is involved in the final outcome, leading to tolerance or autoimmunity, we studied the evolution of markers for T cells in nonobese diabetic (NOD) mice. The study of different transcription factors, cytokines or cytokine receptors, shows that VIP interferes with functional phase of T helper 17 (Th17) cells and prevents the increase in the proportion of Th1 to Th17 cells. On the other hand, VIP-treated NOD mice show an increase in the proportion of CD4(+)CD25(+) cells in the spleen. Thus, VIP switches the Tregs/Th17 ratio leading to tolerance in NOD mice. Similarly, VIP reverses the ratio of Th1-/Th2-cell subsets associated with autoimmune pathology. All these effects on the ratio of T-cell subsets and the anti-inflammatory effect of VIP in decreasing proinflammatory mediators result in a reduction of β-cell destruction in pancreas. Taken together, these results show that VIP provides significant protection against spontaneous diabetes by modulating T-cell subsets and counterbalancing tolerance and immunity.

Protective effects of dieckol isolated from Ecklonia cava against high glucose-induced oxidative stress in human umbilical vein endothelial cells

The effect of dieckol, one of phlorotannin polyphenol compound purified from Ecklonia cava (E. cava) against high glucose-induced oxidative stress was investigated using human umbilical vein endothelial cells (HUVECs), which is susceptible to oxidative stress. High glucose (30mM) treatment induced HUVECs cell death, but dieckol, at concentration 10 or 50microg/ml, significantly inhibited the high glucose-induced cytotoxicity. Furthermore, treatment with dieckol dose-dependently decreased thiobarbituric acid reactive substances (TBARS), intracellular reactive oxygen species (ROS) generation and nitric oxide level increased by high glucose. In addition, high glucose levels induced the overexpressions of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and nuclear factor-kappa B (NF-kB) proteins in HUVECs, but dieckol treatment reduced the overexpressions of these proteins. These findings indicate that dieckol is a potential therapeutic agent that will reduce the damage caused by hyperglycemia-induced oxidative stress associated with diabetes.

Protection against cytokine toxicity through endoplasmic reticulum and mitochondrial stress prevention by prostacyclin synthase overexpression in insulin-producing cells

Proinflammatory cytokines play a crucial role in the pathogenesis of type 1 diabetes mellitus. One of the cytokine-regulated pathways mediating inflammation in this autoimmune disease is the arachidonic acid metabolism pathway, comprising both the induction of cyclooxygenases and the production of different prostaglandins. Cytokine toxicity is mediated in many cell types, including pancreatic beta cells through this pathway. Interestingly, some cell types have been shown to be insensitive to such toxicity, and this correlated with a high expression of prostacyclin synthase (PGIS). Using insulin-producing RINm5F cells as a model for pancreatic beta cells, PGIS was overexpressed and exhibited a large protective effect against cytokine toxicity. This protective effect of PGIS against cytokine toxicity correlated with a decreased activation of the transcription factor NFkappaB and the inducible NO synthase promoter as well as a reduced inducible NO synthase protein expression and nitrite production. A reduction in the cytokine-stimulated endoplasmic reticulum and mitochondrial stress was also found in the PGIS-overexpressing cells. Moreover, cytokine-induced caspase-3 activation and reduction of glucose oxidation and cell proliferation were suppressed. Thus, PGIS overexpression apparently protects insulin-producing cells against cytokine toxicity via suppression of endoplasmic reticulum and mitochondrial stress-mediated cell death pathways.

Protective effects of enzymatic digest from Ecklonia cava against high glucose-induced oxidative stress in human umbilical vein endothelial cells

BACKGROUND

Antioxidants can prevent pathological damage caused by hyperglycaemia-induced oxidative stress associated with diabetes. In the present study, we investigated whether the brown alga Ecklonia cava has protective effects against high glucose-induced oxidative stress in Human umbilical vein endothelial cells (HUVECs). For that purpose, we prepared an enzymatic digest from E. cava (ECC) by using the carbohydrate, Celluclast.

RESULTS

High glucose treatment induced HUVECs cell death, but ECC, at a concentration of 10 or 100 microg mL(-1), significantly inhibited the high glucose-induced cytotoxicity. Furthermore, treatment with ECC dose-dependently decreased thiobarbituric acid reactive substances (TBARS), intracellular generation of reactive oxygen species, and the nitric oxide level increased by high glucose. In addition, ECC treatment increased activities of antioxidant enzymes including catalase, superoxide dismutase and glutathione peroxidase in high-glucose pretreated HUVECs. High glucose levels induced the overexpression of inducible nitric oxide synthase, cyclooxygenase-2 and nuclear factor-kappa B proteins in HUVECs, but ECC treatment reduced the overexpression of these proteins.

CONCLUSION

These results suggest that ECC is a potential therapeutic agent that will reduce the damage caused by hyperglycaemia-induced oxidative stress associated with diabetes.

Nitric Oxide Synthase Inhibitors as Antidepressants

Affective and anxiety disorders are widely distributed disorders with severe social and economic effects. Evidence is emphatic that effective treatment helps to restore function and quality of life. Due to the action of most modern antidepressant drugs, serotonergic mechanisms have traditionally been suggested to play major roles in the pathophysiology of mood and stress-related disorders. However, a few clinical and several pre-clinical studies, strongly suggest involvement of the nitric oxide (NO) signaling pathway in these disorders. Moreover, several of the conventional neurotransmitters, including serotonin, glutamate and GABA, are intimately regulated by NO, and distinct classes of antidepressants have been found to modulate the hippocampal NO level in vivo. The NO system is therefore a potential target for antidepressant and anxiolytic drug action in acute therapy as well as in prophylaxis. This paper reviews the effect of drugs modulating NO synthesis in anxiety and depression.

Role of increased ROS dissipation in prevention of T1D

Protection of pancreatic beta cells is an approach to prevent autoimmune type 1 diabetes (T1D) and to protect transplanted islets. Reactive oxygen species (ROS) are important mediators of beta cell death during the development of T1D. We have examined the role of elevated ROS dissipation in the prevention of T1D using the ALR mouse strain. The selection of ALR, for resistance against alloxan-induced free radical-mediated diabetes, led to a strain of mice with an elevated systemic as well as pancreatic ROS dissipation. Independent genetic mapping studies have identified ALR-derived diabetes protective loci. Conplastic and congenic mouse as well as cell line studies have confirmed the genetic mapping and demonstrated that the elevated ROS dissipation protects ALR beta cells from autoimmune destruction. Our data support the hypothesis that elevated ROS dissipation protects beta cells against autoimmune destruction and prevents T1D development.

NO-mediated cytotoxicity contributes to multiple low-dose streptozotocin-induced diabetes but not to NOD diabetes

Type 1 diabetes (T1D) is caused mostly by autoimmune destruction of pancreatic beta-cells, the precise mechanism of which remains unclear. Two major effector mechanisms have been proposed: direct cell-mediated and indirect cytokine-mediated cytotoxicity. Cytokine-mediated beta-cell destruction is presumed mainly caused by NO production. To evaluate the role of iNOS expression in T1D, this study used a novel iNOS inhibitor ONO-1714. ONO-1714 significantly reduced cytokine-mediated cytotoxicity and NO production in both MIN6N9a cells and C57BL/6 islets in the presence of IL-1beta, TNF-alpha, and IFN-gamma. To evaluate whether NO contributes to diabetes progression in vivo, ONO-1714 was administered to four different mouse models of autoimmune diabetes: multiple low-dose STZ (MLDS)-induced C57BL/6, CY-induced, adoptive transfer and spontaneous NOD diabetes. Exposure to STZ in vitro induced NO production in MIN6N9a cells and C57BL/6 islets, and in vivo injection of ONO-1714 to MLDS-treated mice significantly reduced hyperglycemia and interestingly, led to complete suppression of cellular infiltration of pancreatic islets. In contrast, when ONO-1714 was injected into spontaneous NOD mice and CY-induced and adoptive transfer models of NOD diabetes, overt diabetes could not be inhibited in these models. These findings suggest that NO-mediated cytotoxicity significantly contributes to MLDS-induced diabetes but not to NOD diabetes.

Commonalities of genetic resistance to spontaneous autoimmune and free radical--mediated diabetes

ALR/Lt, a NOD-related mouse strain, was selected for resistance to alloxan free radical-mediated diabetes (ALD). Despite extensive genomic identity with NOD (>70%), ALR mice display strong resistance to autoimmune type 1 diabetes (T1D) due to both an unusual elevation in systemic antioxidant defenses and a reduction in cellular ROS production that extends to the beta cell level. Reciprocal backcross to NOD previously linked the ALR-derived T1D resistance to Chr. 3, 8, and 17 as well as to the ALR mt-Nd2(a) allele encoded by the mitochondrial genome (mtDNA). To determine whether any of the ALR-derived loci protecting against T1D also protected against ALD, 296 six-week-old F2 mice from reciprocal outcrosses were alloxan-treated and assessed for diabetes onset, and a genome-wide scan (GWS) was conducted. GWS linked mt-Nd2 as well as three nuclear loci with alloxan-induced diabetes. A dominant ALR-derived ALD resistance locus on Chr. 8 colocalized with the ALR-derived T1D resistance locus identified in the previous backcross analysis. In contrast, whereas ALR contributed a novel T1D resistance locus on Chr. 3 marked by Susp, a more proximal ALR-derived region marked by Il-2 contributed ALD susceptibility, not resistance. In addition, a locus was mapped on Chr. 2, where heterozygosity provided heightened susceptibility. Tests for alloxan sensitivity in ALR conplastic mice encoding the NOD mt-Nd2(c) allele and NOD mice congenic for the protective Chr. 8 locus supported our mapping results. Alloxan sensitivity was increased in ALR.mt(NOD) mice, whereas it was decreased by congenic introduction of ALR genome on Chr. 8 into NOD. These data demonstrate both similarities and differences in the genetic control of T1D versus ROS-induced diabetes.

The novel inosine analogue, INO-2002, protects against diabetes development in multiple low-dose streptozotocin and non-obese diabetic mouse models of type I diabetes

Endogenous purines including inosine have been shown to exert immunomodulatory and anti-inflammatory effects in a variety of disease models. The dosage of inosine required for protection is very high because of the rapid metabolism of inosine in vivo. The aim of this study was to determine whether a metabolic-resistant purine analogue, INO-2002, exerts anti-inflammatory effects in two animal models of type I diabetes. Type I diabetes was induced chemically with streptozotocin or genetically using the non-obese diabetic (NOD) female mouse model. Mice were treated with INO-2002 or inosine as required at 30, 100, or 200 mg/kg per day, while blood glucose and diabetes incidence were monitored. The effect of INO-2002 on the pancreatic cytokine profile was also determined. INO-2002 reduced both the hyperglycaemia and incidence of diabetes in both streptozotocin-induced and spontaneous diabetes in NOD mice. INO-2002 proved to be more effective in protecting against diabetes than the naturally occurring purine, inosine, when administered at the same dose. INO-2002 treatment decreased pancreatic levels of interleukin (IL)-12 and tumour necrosis factor-alpha, while increasing levels of IL-4 and IL-10. INO-2002 also reduced pancreatic levels of the chemokine MIP-1 alpha. The inosine analogue, INO-2002, was protected more effectively than the naturally occurring purine, inosine, against development of diabetes in two separate animal models. INO-2002 exerts protective effects by changing the pancreatic cytokine expression from a destructive Th1 to a protective Th2 profile. The use of analogues of inosine such as INO-2002 should be considered as a potential preventative therapy in individuals susceptible to developing type I diabetes.

In vitro and in vivo suppression of cellular activity by guanidinoethyl disulfide released from hydrogel microspheres composed of partially oxidized hyaluronan and gelatin

This paper describes the preparation of oxidized hyaluronan crosslinked gelatin microspheres for drug delivery. Microspheres were prepared by a modified water-in-oil-emulsion crosslinking method, where three-dimensional crosslinked hydrogel microspheres formed in the absence of any extraneous crosslinker. SEM analyses of the microspheres showed rough surfaces in their dried state with an average diameter of 90 microm. Lyophilization of fully swollen microspheres revealed a highly porous structure. Guanidinoethyl disulfide (GED) was used as a model drug for incorporation into the microspheres; encapsulation of GED was confirmed by HPLC. There was an inverse correlation between the diameters of the microspheres with their GED loading. Macrophage was used as a model cell to evaluate the in vitro efficacy of GED release from the microspheres. The in vivo efficacy of the microspheres was further validated in a mouse full-thickness transcutaneous dermal wound model through suppression of cell infiltration.

Role of NF-κB in β-cell death

Apoptotic β-cell death appears to be central to the pathogenesis of Type 1 diabetes mellitus and in islet graft rejection. The β-cell destruction is partially mediated by cytokines, such as IL-1β (interleukin 1β), TNFα (tumour necrosis factor α) and IFN-γ (interferon γ). IL-1β and TNFα mediate activation of the transcription factor NF-κB (nuclear factor κB) pathway. Use of a degradation-resistant NF-κB protein inhibitor (ΔNIκBα), specifically expressed in β-cells, significantly reduced IL-1β+IFN-γ-induced apoptosis. Moreover, in vivo, it protected against multiple low-dose streptozocin-induced diabetes, with reduced intra-islet lymphocytic infiltration. Thus β-cell-specific activation of NF-κB is a key event in the progressive loss of β-cells in diabetes. Inhibition of this process could be a potential effective strategy for β-cell protection.

Protective effect of persimmon peel polyphenol against high glucose-induced oxidative stress in LLC-PK1 cells

The effect of persimmon peel polyphenol (PPP) on high glucose-induced oxidative stress was investigated using LLC-PK(1) cells, which is susceptible to oxidative stress. High-concentration glucose (30 mM) treatment induced LLC-PK(1) cell death, but high molecular-PPP (HMPPP) and low molecular-PPP (LMPPP), at concentrations of 5 or 10 microg/ml, significantly inhibited the high glucose-induced cytotoxicity. Furthermore, treatment with HMPPP or LMPPP dose-dependently reduced the intracellular reactive oxygen species level increased by 30 mM glucose. In addition, nitric oxide, superoxide and peroxynitrite levels were increased by 30 mM glucose treatment, but they were concentration-dependently inhibited by HMPPP or LMPPP treatment. High glucose levels induced the overexpressions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) proteins, but HMPPP or LMPPP treatment reduced the overexpressions of these proteins. HMPPP or LMPPP also inhibited the nuclear translocation of nuclear factor-kappa B (NF-kappaB) induced by 30 mM glucose in LLC-PK(1) cells. In particular, LMPPP exhibited stronger inhibitory activities on high glucose induced oxidative stress than HMPPP. These findings indicate the potential benefits of persimmon peel as a valuable source of antioxidants in the diabetic condition which will reduce the oxidative stress induced by hyperglycemia.

Peroxynitrite: biochemistry, pathophysiology and development of therapeutics

Peroxynitrite--the product of the diffusion-controlled reaction of nitric oxide with superoxide radical--is a short-lived oxidant species that is a potent inducer of cell death. Conditions in which the reaction products of peroxynitrite have been detected and in which pharmacological inhibition of its formation or its decomposition have been shown to be of benefit include vascular diseases, ischaemia-reperfusion injury, circulatory shock, inflammation, pain and neurodegeneration. In this Review, we first discuss the biochemistry and pathophysiology of peroxynitrite and then focus on pharmacological strategies to attenuate the toxic effects of peroxynitrite. These include its catalytic reduction to nitrite and its isomerization to nitrate by metalloporphyrins, which have led to potential candidates for drug development for cardiovascular, inflammatory and neurodegenerative diseases.

Beta cell cytoprotection using lentiviral vector-based iNOS-specific shRNA delivery

Cytokine-induced beta cell pathophysiology is characterised by the induction of iNOS expression. Inhibition of iNOS expression protects beta cells from cytokine-mediated destruction. The development of vector-based shRNA strategies capable of stably suppressing iNOS expression may provide a novel platform to protect beta cells from cytokine toxicity. In this report the utility of lentiviral shRNA vectors to silence iNOS expression was evaluated with respect to insulinoma cell viability, the induction of iNOS expression and the accumulation of nitrite in a cytokine-induced beta cell toxicity model. Here, we report for the first time on the use of lentiviral vector-based shRNA delivery to efficiently suppress the IL-1beta-mediated induction of iNOS expression, the accumulation of nitrite and provide significant protection against the cytotoxic effects of IL-1beta exposure. Moreover, non-specific knockdown of endogenous beta cell nNOS did not occur.

Impaired vascular function in normoglycemic mice prone to autoimmune diabetes: Role of nitric oxide

Type 1 diabetes is an immuno-inflammatory condition which increases the risk of cardiovascular disease, particularly in young adults. This study investigated whether vascular function is altered in mice prone to autoimmune diabetes and whether the nitric oxide (NO)-cyclic GMP axis is involved. Aortic rings suspended in organ chambers and precontracted with phenylephrine were exposed to cumulative concentrations of acetylcholine. To investigate the role of NO, some experiments were performed in the presence of either 1400W (N-(3-aminomethyl)benzyl-acetamidine hydrochloride), a selective inhibitor of the iNOS-isoform, L-NAME (N(G)-nitro-L-arginine methyl ester hydrochloride), an inhibitor of all three NOS-isoforms, or ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), a selective inhibitor of guanylate cyclase. Moreover, contractility to phenylephrine, big endothelin-1, and endothelin-1 was assessed and histological analysis and iNOS immunohistochemistry were performed. Endothelium-dependent relaxation was reduced in prediabetic NOD mice (78+/-4 vs. 88+/-2%, respectively, P<0.05 vs. control) despite normal plasma glucose levels (n.s. vs. control). Preincubation with 1400W further attenuated responses in prediabetic (P<0.05 vs. untreated) but not in diabetic or in control mice. In contrast, basal NO bioactivity remained unaffected until the onset of diabetes in NOD mice. Contractile responses to big endothelin-1 and endothelin-1 were reduced in prediabetic animals (P<0.05 vs. control), whereas in diabetic mice only responses to big endothelin-1 were decreased (P<0.05 vs. control). These data demonstrate that endothelium-dependent and -independent vascular function in NOD mice is abnormal already in prediabetes in the absence of structural injury. Early proinflammatory activation due to iNOS in diabetes-prone NOD mice appears to be one of the mechanisms contributing to impaired vasoreactivity.

Nuclear and Mitochondrial Interaction Involving mt-Nd2 Leads to Increased Mitochondrial Reactive Oxygen Species Production

NADH dehydrogenase subunit 2, encoded by the mtDNA, has been associated with resistance to autoimmune type I diabetes (T1D) in a case control study. Recently, we confirmed a role for the mouse ortholog of the protective allele (mt-Nd2(a)) in resistance to T1D using genetic analysis of outcrosses between T1D-resistant ALR and T1D-susceptible NOD mice. We sought to determine the mechanism of disease protection by elucidating whether mt-Nd2(a) affects basal mitochondrial function or mitochondrial function in the presence of oxidative stress. Two lines of reciprocal conplastic mouse strains were generated: one with ALR nuclear DNA and NOD mtDNA (ALR.mt(NOD)) and the reciprocal with NOD nuclear DNA and ALR mtDNA (NOD.mt(ALR)). Basal mitochondrial respiration, transmembrane potential, and electron transport system enzymatic activities showed no difference among the strains. However, ALR.mt(NOD) mitochondria supported by either complex I or complex II substrates produced significantly more reactive oxygen species when compared with both parental strains, NOD.mt(ALR) or C57BL/6 controls. Nitric oxide inhibited respiration to a similar extent for mitochondria from the five strains due to competitive antagonism with molecular oxygen at complex IV. Superoxide and hydrogen peroxide generated by xanthine oxidase did not significantly decrease complex I function. The protein nitrating agents peroxynitrite or nitrogen dioxide radicals significantly decreased complex I function but with no significant difference among the five strains. In summary, mt-Nd2(a) does not confer elevated resistance to oxidative stress; however, it plays a critical role in the control of the mitochondrial reactive oxygen species production.

In CD4+ T-cell-induced diabetes, macrophages are the final effector cells that mediate islet beta-cell killing: studies from an acute model

To understand better how diabetogenic CD4+ T cells induce islet beta-cell death and cause diabetes, a transfer model of acute diabetes using the diabetogenic CD4+ BDC2.5 T-cell clone was established. Transfer of activated BDC T cells into NOD.scid mice resulted in diabetes within a week, characterized by strong inflammatory reaction. Electron micrographs of pancreas depicted macrophages in close contact with beta cells that exhibited signs of apoptosis. Transfer into irradiated recipients inhibited inflammation and the development of diabetes, demonstrating an obligatory role for leukocytes. Selective depletion of neutrophils or natural killer cells had no effect on diabetes induced by BDC2.5 T cells. In contrast, in vivo depletion of phagocytic cells by injection of liposomes containing clodronate abolished diabetes, although inflammation remained present and was characterized mainly by neutrophil infiltration. Treatment with clodronate-liposomes did not affect the antigen-presenting cells within the pancreas. Last, activated macrophages isolated from infiltrated pancreas exhibited cytolytic activity toward primary islet beta cells. Taken together, these results demonstrate that activated macrophages are the key cells mediating islet beta-cell death induced by activated CD4+ T cells.

Protective effect of the Chinese prescription Kangen-karyu against high glucose-induced oxidative stress in LLC-PK1 cells

We investigated the effects of Chinese prescription Kangen-karyu on high glucose-induced oxidative stress using LLC-PK(1) cells, renal tubular cells, which are the most vulnerable renal tissue to oxidative stress. High-concentration glucose (30mM) treatment induced LLC-PK(1) cell death, but Kangen-karyu, at a concentration of 5, 10 or 50 microg/ml, significantly inhibited high glucose-induced cytotoxicity. In addition, the intracellular reactive oxygen species level was increased by 30mM glucose treatment, but it was concentration-dependently inhibited by Kangen-karyu treatment. Moreover, 30mM glucose treatment induced high levels of superoxide anion, nitric oxide and peroxynitrite. However, Kangen-karyu treatment significantly reduced the radical overproduction induced by high glucose, suggesting Kangen-karyu has radical-scavenging activity that would protect against oxidative stress induced by high glucose. Kangen-karyu also reduced the overexpression of inducible nitric oxide synthase and cyclooxygenase-2 proteins induced by high glucose. Furthermore, treatment with Kangen-karyu, at a concentration of 50mug/ml, inhibited the nuclear translocation of nuclear factor-kappa B induced by 30mM glucose in LLC-PK(1) cells. These findings indicate that Kangen-karyu is a potential therapeutic agent that will reduce the damage caused by hyperglycemia-induced oxidative stress associated with diabetes.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

A potent immunomodulatory compound, (S,R)-3-Phenyl-4,5-dihydro-5-isoxazole acetic acid, prevents spontaneous and accelerated forms of autoimmune diabetes in NOD mice and inhibits the immunoinflammatory diabetes induced by multiple low doses of streptozotocin in CBA/H mice

(S,R)-3-Phenyl-4,5-dihydro-5-isoxasole acetic acid (VGX-1027) is an isoxazole compound that exhibits various immunomodulatory properties. The capacity of VGX-1027 to prevent interleukin (IL)-1beta plus interferon-gamma-induced pancreatic islet death in vitro prompted us to evaluate its effects on the development of autoimmune diabetes in preclinical models of human type 1 diabetes mellitus (T1D). Administration of VGX-1027 to NOD mice with spontaneous or accelerated forms of diabetes induced either by injection of cyclophosphamide or by transfer of spleen cells from acutely diabetic syngeneic donors markedly reduced the cumulative incidence of diabetes and insulitis. In addition, VGX-1027 given either i.p. or p.o. to CBA/H mice made diabetic with multiple low doses of streptozotocin successfully counteracted the development of destructive insulitis and hyperglycemia. The animals receiving VGX-1027 exhibited reduced production of the proinflammatory mediators tumor necrosis factor-alpha, IL-1beta, macrophage migration inhibitory factor, and inducible nitric-oxide synthase-mediated nitric oxide generation in both pancreatic islets and peripheral compartments. These results indicate that VGX-1027 probably exerts its antidiabetogenic effects by limiting cytokine-mediated immunoinflammatory events, leading to inflammation and destruction of pancreatic islets. VGX-1027 seems worthy of being considered as a candidate drug in the development of new therapeutic strategies for the prevention and early treatment of T1D.

Drugs modulating the biological effects of peroxynitrite and related nitrogen species

The term "reactive nitrogen species" includes nitrogen monoxide, commonly called nitric oxide, and some other remarkable chemical entities (peroxynitrite, nitrosoperoxycarbonate, etc.) formed mostly from nitrogen monoxide itself in biological environments. Regardless of the specific mechanisms implicated in their effects, however, it is clear that an integrated pharmacological approach to peroxynitrite and related species is only just beginning to take shape. The array of affected chemical and pathological processes is extremely broad. One of the most conspicuous mechanisms observed thus far has been the scavenging of the peroxynitrite anion by molecules endowed with antioxidant activity. This discovery has in turn lent great significance to several naturally occurring and synthetic antioxidants, which usually protect not only against oxidative reactions, but also from nitrating ones, both in vitro and in vivo. This has proven to be beneficial in different tissues, especially within the central nervous system. Taking these results and those of other biochemical investigations into account, many research lines are currently in progress to establish the true potential of reactive nitrogen species deactivators in the therapy of neurological diseases, ischemia-reperfusion damage, renal failure, and lung injury, among others.

beta cell cytoprotective strategies: establishing the relative roles for iNOS and ROS

Cytokine-induced beta cell destruction may be mediated by the generation of nitric oxide and/or reactive oxygen species. The relative importance of NO and ROS in cytokine-induced beta cell pathophysiology remains unclear. This investigation evaluates and contrasts the cytoprotective potential of antioxidant gene transfer, versus NF-kappaB inhibition, using a degradation-resistant mutant of IkappaBalpha. NF-kappaB inhibition conferred significant protection against cytokine-induced damage whereas antioxidant overexpression failed to provide protection. Conferred cytoprotection was associated with a suppression of iNOS activation and nitrite accumulation. Our data implicates iNOS, as opposed to ROS, as the pivotal player in cytokine-induced beta cell damage. From a therapeutic standpoint, strategies aimed at targeting the activation of iNOS may harbor therapeutic potential in preserving beta cell survival in the face of proinflammatory cytokine exposure.

Roles of poly(ADP-ribose) polymerase activation in the pathogenesis of diabetes mellitus and its complications

Activation of poly(ADP-ribose) polymerase (PARP) plays a role in the pathogenesis of beta-cell necrosis that occurs in response to autoimmune disease associated with Type I diabetes. In addition, PARP activation also plays a role in the pathogenesis of endothelial injury that underlies the ethiology of various diabetic complications (vasculopathy, cardiomyopathy, retinopathy, neuropathy), which develop on the basis of chronically elevated circulating glucose levels in diabetes. Both during the pathogenesis of diabetes and during the pathogenesis of diabetic complications, free radical and oxidant production leads to DNA strand-breakage which activates the nuclear enzyme PARP and initiates an energy consuming, inefficient cellular metabolic cycle with transfer of the ADP-ribosyl moiety of NAD+ to protein acceptors. These processes lead to the functional impairment of the affected cells (beta-cells or vascular endothelial cells, respectively). PARP also promotes the activation of various pro-inflammatory signal transduction pathways. During the last two decades, a growing number of experimental studies demonstrated the beneficial effects PARP inhibition in various models of diabetes and diabetic complications. The current review provides an overview of the experimental evidence implicating PARP as a causative factor in the pathogenesis of diabetes and diabetic complications in vitro and in vivo.

Effect of insulin nitration by peroxynitrite on its biological activity

Insulin may be a potential target of ONOO- during conditions involving accelerated rates of oxygen radical and nitric oxide generation in pancreatic islet beta-cells. To evaluate the effect of protein tyrosine nitration on insulin function, the porcine insulin was nitrated by ONOO-. Insulin nitration was confirmed by spectral changes, Native-PAGE, and mass spectrometry. The bioassay results show that mono-nitro-insulin affected its receptor binding and hypoglycemic capacities to a certain extent, but still hold high biological activities.