Inducible nitric oxide synthase (iNOS) in pancreatic islets of nonobese diabetic mice: identification of iNOS- expressing cells and relationships to cytokines expressed in the islets

Redox regulation in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most devastating complications of diabetes mellitus, where currently there is no cure available. Several important mechanisms contribute to the pathogenesis of this complication, with oxidative stress being one of the key factors. The past decades have seen a large number of publications with various aspects of this topic; however, the specific details of redox regulation in DKD are still unclear. This is partly because redox biology is very complex, coupled with a complex and heterogeneous organ with numerous cell types. Furthermore, often times terms such as "oxidative stress" or reactive oxygen species are used as a general term to cover a wide and rich variety of reactive species and their differing reactions. However, no reactive species are the same, and not all of them are capable of biologically relevant reactions or "redox signaling." The goal of this review is to provide a biochemical background for an array of specific reactive oxygen species types with varying reactivity and specificity in the kidney as well as highlight some of the advances in redox biology that are paving the way to a better understanding of DKD development and risk.

Diabetes and zinc dyshomeostasis: Can zinc supplementation mitigate diabetic complications?

Zinc present in the islet cells of the pancreas is crucial for the synthesis, storage, and secretion of insulin. The excretion of large amounts of zinc from the body is reported in diabetic situations. Zinc depletion and increased oxidative stress have a major impact on the pathogenesis of diabetic complications. It would be most relevant to ascertain if intervention with supplemental zinc compensating for its depletion would beneficially mitigate hyperglycemia and the attendant metabolic abnormalities, and secondary complications in diabetes. An exhaustive literature search on this issue indicates: (1) Concurrent hypozincemia and decreased tissue zinc stores in diabetes as a result of its increased urinary excretion and/or decreased intestinal absorption, (2) Several recent experimental studies have documented that supplemental zinc has a potential hypoglycemic effect in the diabetic situation, and also beneficially modulate the attendant metabolic abnormalities and compromised antioxidant status, and (3) Supplemental zinc also alleviates renal lesions, cataract and the risk of cardiovascular disease accompanying diabetes mellitus, and help restore gastrointestinal health in experimental diabetes. These studies have also attempted to identify the precise mechanisms responsible for zinc-mediated beneficial effects in diabetic situation. The evidence discussed in this review highlights that supplemental zinc may significantly contribute to its clinical application in the management of diabetic hyperglycemia and related metabolic abnormalities, and in the alleviation of secondary complications resulting from diabetic oxidative stress.

Primary cilia control glucose homeostasis via islet paracrine interactions

Pancreatic islets regulate glucose homeostasis through coordinated actions of hormone-secreting cells. What underlies the function of the islet as a unit is the close approximation and communication among heterogeneous cell populations, but the structural mediators of islet cellular cross talk remain incompletely characterized. We generated mice specifically lacking β-cell primary cilia, a cellular organelle that has been implicated in regulating insulin secretion, and found that the β-cell cilia are required for glucose sensing, calcium influx, insulin secretion, and cross regulation of α- and δ-cells. Protein expression profiling in islets confirms perturbation in these cellular processes and reveals additional targets of cilia-dependent signaling. At the organism level, the deletion of β-cell cilia disrupts circulating hormone levels, impairs glucose homeostasis and fuel usage, and leads to the development of diabetes. Together, these findings demonstrate that primary cilia not only orchestrate β-cell-intrinsic activity but also mediate cross talk both within the islet and from islets to other metabolic tissues, thus providing a unique role of cilia in nutrient metabolism and insight into the pathophysiology of diabetes.

Survival of an Islet Allograft Deficient in iNOS after Implantation into Diabetic NOD Mice

Proinflammatory cytokines play a major role in rejection of pancreatic islet allografts and in type 1 diabetes (T1D). In rodent islets, exposure to IL-1β alone or combined with IFN-γ induces expression of inducible nitric oxide synthase (iNOS). Inhibition of iNOS or a deletion of the iNOS gene has been shown to be protective in animal models of T1D. In the present study we tested the hypothesis that transplantation of pancreatic islets deficient in iNOS (iNOS–/–) would permit increased graft survival. Pancreatic islets isolated from wild-type (wt) mice and iNOS–/– mice were allogeneically transplanted beneath the kidney capsule of spontaneously diabetic NOD mice. When blood glucose increased above 12.0 mM after preceding normalization of hyperglycemia, animals were sacrificed. Histological examinations of grafts were performed and graft gene expression was analyzed by real-time PCR. Transplantations of the two types of islets could reverse hyperglycemia and the grafts functioned for on average 1 week posttransplantation. Morphological examination of both types of islet grafts showed immune cell infiltration around and within the grafts. Remaining endocrine cells could be observed in wt and iNOS–/– islet grafts. In the removed grafts iNOS-/islet tissue contained higher mRNA levels of insulin, proinsulin convertases (PC-1 and PC-2), and IL-1β compared to transplanted wt islets. The assessments of insulin, PC-1 and PC-2 mRNAs of the grafts suggest that the iNOS–/– islets may be more resistant to destruction in the transplantation model used; however, this was not sufficient to prolong the period of normoglycemia posttransplantation.

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

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

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.

Pancreatic β-cell dysfunction, expression of iNOS and the effect of phosphodiesterase inhibitors in human pancreatic islets of type 2 diabetes

AIMS

Induction of inducible nitric oxide synthase (iNOS) in pancreatic islets leads to exaggerated nitric oxide (NO) production associated with dysfunctional β-cells. We examined insulin secretion, iNOS expression and its relationship to the cAMP system in islets from human type 2 diabetes.

METHODS

Insulin, glucagon and cAMP were analysed by RIA; iNOS or phosphodiesterase (PDE) expression by quantitative PCR (qPCR), Western blot and confocal microscopy; cell viability by MTS.

RESULTS

Diabetic islets displayed impaired insulin and glucagon responses to glucose, disturbed cAMP generation and high inducible nitric oxide synthase (iNOS) mRNA and protein expression. Confocal microscopy showed iNOS protein expression in diabetic islets being confined to insulin, glucagon and somatostatin cells. Culture of diabetic islets at 5.5 mmol/l glucose with dibutyryl-cAMP (Bt(2) -cAMP) for 24 h was accompanied by marked suppression of iNOS mRNA, reduced nitrite production and increased insulin secretion. Diabetic islets displayed marked increase in PDE3A and PDE3B mRNA expression. Short-time incubation of diabetic islets showed, among the PDE inhibitors tested, cilostazol being most favourable to increase insulin secretion. Diabetic islets were most susceptible to long-term (72 h) culture at high glucose (20 mmol/l) reacting with increased apoptosis. Bt(2) -cAMP and the PDE inhibitors cilostazol, milrinone and IBMX efficiently increased cell viability at high glucose during culture. Defective glucose-stimulated insulin release upon induction of iNOS was restored by iNOS inhibitor aminoguanidine.

CONCLUSION

Our results suggest that in islets from type 2 diabetes, stimulatory effects in certain cAMP-compartments induced by PDE inhibitors might play a central role in the suppression of iNOS, resulting in increased β-cell viability and improved secretory response to glucose.

Inducible nitric-oxide synthase and nitric oxide donor decrease insulin receptor substrate-2 protein expression by promoting proteasome-dependent degradation in pancreatic beta-cells: involvement of glycogen synthase kinase-3beta

Insulin receptor substrate-2 (IRS-2) plays a critical role in the survival and function of pancreatic β-cells. Gene disruption of IRS-2 results in failure of the β-cell compensatory mechanism and diabetes. Nonetheless, the regulation of IRS-2 protein expression in β-cells remains largely unknown. Inducible nitric-oxide synthase (iNOS), a major mediator of inflammation, has been implicated in β-cell damage in type 1 and type 2 diabetes. The effects of iNOS on IRS-2 expression have not yet been investigated in β-cells. Here, we show that iNOS and NO donor decreased IRS-2 protein expression in INS-1/832 insulinoma cells and mouse islets, whereas IRS-2 mRNA levels were not altered. Interleukin-1β (IL-1β), alone or in combination with interferon-γ (IFN-γ), reduced IRS-2 protein expression in an iNOS-dependent manner without altering IRS-2 mRNA levels. Proteasome inhibitors, MG132 and lactacystin, blocked the NO donor-induced reduction in IRS-2 protein expression. Treatment with NO donor led to activation of glycogen synthase kinase-3β (GSK-3β) and c-Jun N-terminal kinase (JNK/SAPK) in β-cells. Inhibition of GSK-3β by pharmacological inhibitors or siRNA-mediated knockdown significantly prevented NO donor-induced reduction in IRS-2 expression in β-cells. In contrast, a JNK inhibitor, SP600125, did not effectively block reduced IRS-2 expression in NO donor-treated β-cells. These data indicate that iNOS-derived NO reduces IRS-2 expression by promoting protein degradation, at least in part, through a GSK-3β-dependent mechanism. Our findings suggest that iNOS-mediated decreased IRS-2 expression may contribute to the progression and/or exacerbation of β-cell failure in diabetes.

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.

Efficacy of Setarud (IMOD™), a novel electromagnetically-treated multi-herbal compound, in mouse immunogenic type-1 diabetes

INTRODUCTION

The aim of this study was to evaluate the effects and mechanisms of Setarud (IMOD™) as a multi-herbal medicinal formula on a mouse model of type 1 diabetes. METERIAL AND METHODS: Autoimmune diabetes was induced by multiple low-dose intraperitoneal injection of 40 mg/kg of streptozotocin (STZ) for five consecutive days. IMOD™ was administered at an effective dose of 20 mg/kg/day for 21 days. After 21 days of treatment, the pancreases of the animals were separated and homogenized. In the pancreas tissue, the level of lipid peroxidation as thiobarbituric acid reactive substances (TBARS), total antioxidant power as ferric reducing ability of pancreas (FRAP), myeloperoxidase (MPO), and the concentrations of interleukin-1 (IL-1β) and tumour necrosis factor-α (TNF-α) were evaluated. Glucose changes were tested in the blood. Microscopic changes in the pancreas were followed by histological examinations.

RESULTS

No significant difference was found between IMOD™ and diabetic control groups in blood glucose pattern. STZ-exposed mice showed a significant increase in pancreatic TBARS, MPO, IL-1β, and TNF-α levels, along with a significant decrease in FRAP value. Co-administration of IMOD™ significantly improved all the mentioned parameters disrupted by STZ administration except for blood glucose and histological changes.

CONCLUSION

IMOD™ could ameliorate oxidative and immunological distresses of type-1 immunogenic diabetes but could not normalize blood glucose. Further studies are recommended to clarify the effects of IMOD™ on immunological factors to address whether this new agent could be applied in diabetes prevention or therapy.

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.

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.

In the Italian population sexual dimorphism affects pre-natal thyroid migration but not biochemical severity of gland ectopia and pre-natal bone maturation

The aim of the present study was to retrospectively re-evaluate a population of selected infants with congenital hypothyroidism (CH), in order to investigate whether sexual dimorphism affects: a) CH etiology; b) its biochemical severity at the time of screening and recall; c) patients' biochemical response to replacement treatment during the 1st yr of life; d) their bone maturation (BM) at birth; e) their psychomotor status at 1 yr. This retrospective study covers 192 infants (116 females) with persistent CH who were selected from a larger population of CH patients identified during a 10-yr period (1990-1999) by the screening programs of 5 northern, central, and southern regions of Italy. Thirty boys (39.5%) and 66 girls (56.9%) were found to have ectopia, whereas the remaining 46 boys and 50 girls exhibited the other causes of CH. When compared with the prevalence of the remaining causes that of ectopia was significantly higher in girls than in boys (66/116 vs 30/76; chi2=5.57, p<0.025), and sex ratio in ectopia was significantly different also compared with the orthotopic gland group only (66/84 vs 30/51; chi2=6.02, p<0.025). No differences between males and females were detected in the groups with either athyreosis or orthotopic gland. In no groups were there differences between sexes for gestational age, birth auxological data, percentage of newborns with bone retardation or developmental quotient at 1 yr. Thyroid tests at birth, age at TSH normalization and average thyroid tests under L-T4 treatment during the 1st yr did not differ between sexes in any of the groups.

CONCLUSIONS

a) in the Italian population sexual dimorphism affects pre-natal thyroid migration but neither biochemical severity of ectopia, nor pre-natal bone maturation and psychomotor development; b) girls with CH do not require higher doses of initial therapy in order to achieve TSH normalization; c) future developmental and molecular studies on ectopia etiology in CH need to take into account the effect of sexual dimorphism.

Suppressive effects of glucagon-like peptide-1 on interferon-gamma-induced nitric oxide production in insulin-producing cells is mediated by inhibition of tumor necrosis factor-alpha production

During the development of Type 1 diabetes, inflammatory cytokines are known to induce the expression of inducible nitric oxide synthase (iNOS) in pancreatic islets, and subsequent production of nitric oxide (NO) contributes to beta cell destruction. Glucagon-like peptide-1 (GLP-1) has been shown to reduce cytokine-induced apoptosis of beta cells. In this study, we investigated whether GLP-1 affects cytokine-induced NO production, resulting in the inhibition of beta-cell apoptosis. We treated MIN6N8a mouse beta cells with interferon (IFN)-gamma in the presence or absence of GLP-1 and found that IFN-gamma treatment induced iNOS mRNA expression and NO production, which was significantly inhibited by treatment with GLP-1. Blocking of GLP-1 receptor signaling via the cyclic AMP and phosphatidylinositol 3-kinase pathway did not directly affect the suppressive effect of GLP-1 on IFN- gamma-induced iNOS mRNA expression. Further studies revealed that IFN-gamma induced the expression of TNF-alpha mRNA and protein, which synergistically induced NO production, and GLP-1 treatment inhibited this induction of TNF-alpha. To examine whether the reduction of TNF-alpha by GLP-1 treatment plays a role in suppressing NO production, we treated MIN6N8a cells with IFN-gamma in the presence of anti-TNF-alpha neutralizing antibody and found that NO production was reduced. In addition, treatment of mouse islets with GLP-1 inhibited the expression of iNOS and TNFmRNA. These results suggest that GLP-1 inhibits IFN-gamma-induced NO production by suppression of TNF-alpha production.

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.

Immunohistochemical Demonstration of Nitrotyrosine, a Biomarker of Oxidative Stress, in Islet Cells of the NOD Mouse

Reactive oxygen species and nitric oxide generated within the beta cell or by intraislet immune cells may be major mediators of beta cell death during insulin-dependent diabetes mellitus. Here, the intraislet expression of nitrotyrosine, a biomarker of oxidative damage, and its cellular sources were examined in the islets of NOD mice at various stages of spontaneous and cyclophosphamide-accelerated diabetes. At day 30, nitrotyrosine-positive cells were undetectable; they were rare at day 40, being expressed in only a few beta cells and in macrophages located in the periphery of some islets. At day 90 and at onset of diabetes, an increasing number of macrophages and beta cells were nitrotyrosine positive. In the cyclophosphamide group at day 4, the number of beta cells and macrophages with positive immunolabeling declined slightly from day 0 (day of cyclophosphamide injection = day 90). This pattern of immunolabeling increased gradually by day 7 but increased markedly by days 11 and 14 after cyclophosphamide administration. In the spontaneous and cyclophosphamide groups, macrophages were the predominant source of nitrotyrosine and were present within the intraislet and periislet regions. Nitrotyrosine labeling was observed in a significant number of beta cells but less than in immunolabeled macrophages. We conclude that protein nitration in beta cells and macrophages is an important feature of the diabetogenic process in the NOD mouse. Whether this deleterious process also occurs during the very early stages of the disease and preceding insulitis is unclear.

Experimental autoimmune thyroiditis in nonobese diabetic mice lacking interferon regulatory factor-1

Interferon regulatory factor-1 (IRF-1) is pivotal in the regulation of interferon (IFN)-mediated immune reactions, and studies suggest that IRF-1 is involved in the development of autoimmune diseases. IRF-1+/+, +/-, and -/- nonobese diabetic (NOD) mice were immunized with mouse thyroglobulin (mTg) to determine whether IRF-1 is required in experimental autoimmune thyroiditis (EAT), a murine model for Hashimoto's thyroiditis (HT). IRF-1-deficient mice developed EAT and anti-mTg antibodies comparable to IRF-1+/+ and +/- mice. Whereas both CD4+ and CD8+ T cells were found in thyroids of IRF-1+/+ mice, the latter was not in IRF-1-/- mice. Major histocompatibility complex class II antigen was comparably expressed in thyroids of IRF-1+/+ and -/- mice. Lack of IRF-1 resulted in decreased CD8+ T cell number in the spleen and reduced IFNgamma production by splenocytes. Our results suggest that IRF-1 is not pivotal in EAT in NOD mice.

Immunoregulatory role of nitric oxide in Kilham rat virus-induced autoimmune diabetes in DR-BB rats

Macrophages play a critical role in the pathogenesis of Kilham rat virus (KRV)-induced autoimmune diabetes in diabetes-resistant BioBreeding (DR-BB) rats. This investigation was initiated to determine the role of macrophage-derived soluble mediators, particularly NO, in the pathogenesis of KRV-induced diabetes in DR-BB rats. We found that the expression of inducible NO synthase (iNOS), an enzyme responsible for NO production, was significantly increased during the early phase of KRV infection. Inhibition of iNOS by aminoguanidine (AG) treatment resulted in the prevention of diabetes in KRV-infected animals. The expression of IL-1beta, TNF-alpha, and IL-12 was significantly decreased in the spleen of AG-treated, KRV-infected DR-BB rats compared with PBS-treated, KRV-infected control rats. Subsequent experiments revealed that AG treatment exerted its preventive effect in KRV-infected rats by maintaining the finely tuned immune balance normally disrupted by KRV, evidenced by a significant decrease in the expression of IFN-gamma, but not IL-4, and a decrease in Th1-type chemokine receptors CCR5, CXCR3, and CXCR4. We also found that iNOS inhibition by AG decreased the KRV-induced expression of MHC class II molecules and IL-2R alpha-chain, resulting in the suppression of T cell activation, evidenced by the decreased cytolytic activity of CD8(+) T cells. We conclude that NO plays a critical immunoregulatory role by up-regulating macrophage-derived proinflammatory cytokines, up-regulating the Th1 immune response, and activating T cells, leading to type 1 diabetes after KRV infection, whereas suppression of NO production by AG treatment prevents KRV-induced autoimmune diabetes in DR-BB rats.

Role for activating transcription factor 3 in stress-induced beta-cell apoptosis

Activating transcription factor 3 (ATF3) is a stress-inducible gene and encodes a member of the ATF/CREB family of transcription factors. However, the physiological significance of ATF3 induction by stress signals is not clear. In this report, we describe several lines of evidence supporting a role of ATF3 in stress-induced beta-cell apoptosis. First, ATF3 is induced in beta cells by signals relevant to beta-cell destruction: proinflammatory cytokines, nitric oxide, and high concentrations of glucose and palmitate. Second, induction of ATF3 is mediated in part by the NF-kappaB and Jun N-terminal kinase/stress-activated protein kinase signaling pathways, two stress-induced pathways implicated in both type 1 and type 2 diabetes. Third, transgenic mice expressing ATF3 in beta cells develop abnormal islets and defects secondary to beta-cell deficiency. Fourth, ATF3 knockout islets are partially protected from cytokine- or nitric oxide-induced apoptosis. Fifth, ATF3 is expressed in the islets of patients with type 1 or type 2 diabetes, and in the islets of nonobese diabetic mice that have developed insulitis or diabetes. Taken together, our results suggest ATF3 to be a novel regulator of stress-induced beta-cell apoptosis.

IL-1 receptor deficiency slows progression to diabetes in the NOD mouse

Proinflammatory cytokines are believed to be important in pancreatic beta-cell destruction in the development of type 1 diabetes. They act by upregulation of genes including Fas and inducible nitric oxide synthase (iNOS), which have both been shown to lead to beta-cell death in vitro. We used mice deficient in the interleukin (IL)-1 receptor (IL-1R) to assess the contribution of IL-1 to different models of diabetes. IL-1R-deficient islets were protected from the damaging effects of tumor necrosis factor (TNF) and interferon (IFN)-gamma in vitro, and beta-cell expression of iNOS was reduced, suggesting that IL-1 mediates the induction of iNOS by TNF and IFN-gamma. IL-1 action was not required for induction of class I major histocompatibility complex or Fas by TNF and IFN-gamma. IL-1R-deficient nonobese diabetic (NOD) mice developed diabetes significantly slower than wild-type mice. IL-1R deficiency did not affect diabetes in 8.3 TCR transgenic NOD mice but prolonged the time to diabetes in BDC2.5 TCR transgenic NOD mice. We conclude that IL-1R deficiency slows progression to diabetes in NOD mice but on its own does not prevent diabetes.

Aminoguanidine downregulates expression of cytokine-induced Fas and inducible nitric oxide synthase but not cytokine-enhanced surface antigens of rat islet cells

Autoimmune beta-cell destruction occurs directly by cell-mediated cytotoxicity or indirectly by cytokines released from infiltrating lymphocytes. Cytokines (IL-1beta/IFN-gamma) modify or induce expression of MHC antigens and ICAM-1 on beta-cells which can lead to an improved binding of T-lymphocytes to beta-cells and finally to an enhanced cell-mediated cytotoxicity. Cytokines also induce Fas-expression and inducible nitric oxide synthase (iNOS) causing generation of nitric oxide (NO) which is toxic for beta-cells. The iNOS inhibitor aminoguanidine (AG) delays diabetes onset, but does not reduce diabetes incidence. We wanted to know whether AG inhibits cytokine-induced expression of Fas, MHC antigens and ICAM-1 on beta-cells of LEW.1W and BB/OK rat islets after culture with IL-1beta/IFN-gamma. NO was completely inhibited by 5.0 mmol/L AG while 0.5 mmol/L had no inhibitory effect. AG downregulated Fas-expression on the surface of beta-cells. Cytokine-induced/enhanced expression of MHC class-II and ICAM-1 was not affected by any AG concentration. AG syngergistically increased cytokine-induced enhancement of MHC class-I antigen density. AG possibly blocks the indirect pathway of beta-cell damage in vivo due to inhibition of Fas and iNOS and improves direct cell-mediated cytotoxicity due to drastic increased MHC class-I expression. Inhibition of only one pathway of beta-cell destruction is not sufficient to prevent diabetes.

Oxidative Stress in Type 1 Diabetes

We have been investigating the effects of preventing oxidative stress on pathogenesis and complications of type 1 diabetes in the NOD mouse model. Our studies have shown that damage caused by oxidative stress is higher in islets and vascular tissue of NOD mice than in nonautoimmune controls or a diabetes-resistant NOD mouse. In addition, phagocytic function and cytokine production by macrophages are aberrant in the NOD. We have demonstrated that treatment of prediabetic NOD mice for 2 weeks with a metalloporphyrin superoxide dismutase (SOD) mimetic results in marked reduction of oxidative stress in islets and vascular tissue and a reversal of macrophage defects.

Kinetics of TNF-alpha and IFN-gamma mRNA expression in islets and spleen of NOD mice

Insulin-dependent diabetes mellitus is caused by autoimmune destruction of pancreatic beta cells. Non-obese diabetic (NOD) mice spontaneously develop diabetes similar to the human disease. Cytokines produced by islet-infiltrating mononuclear cells may be directly cytotoxic and can be involved in islet destruction coordinated by CD4+ and CD8+ cells. We utilized a semiquantitative RT-PCR assay to analyze in vitro the mRNA expression of TNF-alpha and IFN-gamma cytokine genes in isolated islets (N = 100) and spleen cells (5 x 10(5) cells) from female NOD mice during the development of diabetes and from female CBA-j mice as a related control strain that does not develop diabetes. Cytokine mRNAs were measured at 2, 4, 8, 14 and 28 weeks of age from the onset of insulitis to the development of overt diabetes. An increase in IFN-gamma expression in islets was observed for females aged 28 weeks (149 +/- 29 arbitrary units (AU), P<0.05, Student t-test) with advanced destructive insulitis when compared with CBA-j mice, while TNF-alpha was expressed in both NOD and CBA-j female islets at the same level at all ages studied. In contrast, TNF-alpha in spleen was expressed at higher levels in NOD females at 14 weeks (99 +/- 8 AU, P<0.05) and 28 weeks (144 +/- 17 AU, P<0.05) of age when compared to CBA-j mice. The data suggest that IFN-gamma and TNF-alpha expression in pancreatic islets of female NOD mice is associated with beta cell destruction and overt diabetes.

A metalloporphyrin-based superoxide dismutase mimic inhibits adoptive transfer of autoimmune diabetes by a diabetogenic T-cell clone

We present here the first report of a metalloporphyrin-based antioxidant that can prevent or delay the onset of autoimmune diabetes. Type 1 diabetes is an autoimmune process whereby T-cells recognize pancreatic beta-cell antigens and initiate a leukocyte infiltrate that produces proinflammatory cytokines and reactive oxygen species (ROS), ultimately leading to beta-cell destruction. Because islet beta-cells have a reduced capacity to scavenge free radicals, they are very sensitive to ROS action. Metalloporphyrin-based superoxide dismutase (SOD) mimics scavenge ROS and protect cells from oxidative stress and apoptosis. To investigate the effect of SOD mimics and the role of oxidative stress in the development of autoimmune diabetes in vivo, we used a diabetogenic T-cell clone, BDC-2.5, to induce rapid onset of diabetes in young nonobese diabetic-severe combined immunodeficient mice (NOD.scid). Disease was significantly delayed or prevented altogether by treatment of recipient mice with an SOD mimic, AEOL-10113, before transfer of the BDC-2.5 clone. To investigate the mechanisms of protection, in vitro assays for T-cell proliferation and gamma-interferon (IFN-gamma) production were carried out using the T-cell clone BDC-2.5. We found that the SOD mimic significantly inhibited antigen-presenting cell-dependent T-cell proliferation and IFN-gamma production in vitro. In addition, pretreatment of lipopolysaccharide (LPS)-stimulated peritoneal macrophages with SOD mimic inhibited the LPS-dependent increase in TNF-alpha as well as the NADPH oxidase-dependent release of superoxide. Finally, this compound protected NIT-1 insulinoma cells from interleukin-1beta and alloxan cytotoxicity in vitro.

Specific expression of Bax-omega in pancreatic beta-cells is down-regulated by cytokines before the onset of apoptosis

Cytokines have been implicated in the process of pancreatic beta-cell destruction that leads to type 1 diabetes. This study investigates the beta-cell expression of pro- and antiapoptotic proteins from the Bcl-2 family and their variation during cytokine-mediated apoptosis. Exposure of rat beta-cells to the combination of IL-1beta plus interferon-gamma causes a time-dependent increase in apoptotic cells starting after 3 d (<10% on d 3 and 28 +/- 2% on d 7). This effect was preceded by a marked down-regulation of two antiapoptotic proteins, Bcl-2 and Bax-omega (respectively reduced by 60% and 80% after 3 d), whereas no changes occurred in the expression of Bcl-x(L) and the proapoptotic protein Bax-alpha. No apoptosis or down-regulation of Bcl-2 and Bax-omega proteins was observed with individual cytokines or in the presence of N-methyl-L-arginine, an inhibitor of nitric oxide synthase. The lowered Bcl-2 protein content was associated with a decrease in Bcl-2 mRNA, which was initiated after 24 h of exposure. In MIN6 cells, the cytokine-induced suppression of Bcl-2- and Bax-omega, and apoptosis, occurred within 24 h. Primary rat beta-cells exhibited a higher expression of Bax-omega than MIN6 cells or than other rat cell types. These data suggest that suppression of the antiapoptotic proteins Bcl-2 and Bax-omega mediates cytokine-induced apoptosis of beta-cells. The beta-cell-specific expression of Bax-omega makes this protein a possible effector in the protection of this cell type against apoptosis.

Heme oxygenase-1 protects pancreatic beta cells from apoptosis caused by various stimuli

BACKGROUND

Several problems can occur after allogeneic islet transplantation: primary nonfunction, rejection, and the recurrence of autoimmune disease, which involve attack by the recipient's cytokines, T cells, natural killer cells, and monocytes on the donor's beta cells, which leads to beta-cell destruction. Recent studies have revealed that loss of transplanted islets is caused mainly by apoptosis. Heme oxygenase-1 (HO-1) is one of the antiapoptotic genes up-regulated under stress conditions. The aim of this work was to investigate any mechanisms of HO-1-mediated protection of beta cells from apoptosis.

METHODS

Apoptosis was assessed by comparison of viable transfected cells with and without apoptotic stimuli, and with and without HO-1 overexpression. Activation and function of p38 mitogen-activated protein kinase were determined using the specific inhibitor SB203580.

RESULTS

We have shown that HO-1 mediates antiapoptotic effects in beta cells. The percentage of apoptotic cells after stimulation with tumor necrosis factor a decreased from 75% without HO-1 to 5% when HO-1 was overexpressed. Our data indicate that HO-1 acts as a signal terminator of tumor necrosis factor alpha-induced apoptosis by modulation of the p38 mitogen-activated protein kinase pathway.

CONCLUSIONS

Profound cell stress that occurs in islets after transplantation, as well as at the onset of diabetes, results in beta-cell loss through apoptosis. Protection of beta cells by HO-1 improves their survival in vitro after various proapoptotic stimuli, suggesting that HO-1 suppresses one or several signaling pathways leading to apoptosis. We hypothesize that our in vitro findings can be extrapolated to the in vivo situation, and we propose that expression of HO-1 in islets may illuminate a valuable new approach to improving diabetes treatment.

Increase of CD5(+) B cells during adolescence in female mice

We examined physiological changes in CD5(+) B lymphocytes in mice associated with aging (from 1 or 5 to 50 weeks of age). The most predominant populations of lymphocytes among these mice were mainly CD5(-) B cells in the spleen and peritoneal cavity, and T cells in the thymus. However, in the spleen, CD5(+) B cells increased from 1 to 15 weeks, and then decreased with aging. In the thymus, CD5(+) B cells increased from 3 to 9 weeks of age, and subsequently became more predominant than CD5(-) B cells. In the peritoneal cavity, CD5(+) B cells increased from 5 to 9 weeks of age, became the most predominant population in lymphocytes at 7 to 9 weeks of age, and decreased with aging. The proportion of CD5(+) B cells in total B cells increased from 5 to 7 or 9 weeks of age, and then decreased with aging, with the highest proportion at 9 weeks of age in the spleen (15%), thymus (94%), and peritoneal cavity (54%). These findings indicate that CD5(+) B cells increase physiologically during mouse adolescence, and subsequently decrease with aging.

Complete suppression of insulitis and diabetes in NOD mice lacking interferon regulatory factor-1

Interferon regulatory factor-1 (IRF-1), a transcriptional factor, regulates type I interferon and interferon-induced genes. It was reported that IRF-1 regulates important molecules required for inflammation and immune reactions. To investigate the role of IRF-1 in the development of autoimmune diabetes, we established IRF-1 deficient (IRF-1(-/-)) non-obese diabetic (NOD) mice. IRF-1-deficient C57BL/6J mice were out-crossed to NOD mice, and F1 were backcrossed to NOD mice. At the N8 generation, the heterozygote for IRF-1 mutation was intercrossed and N8F1 was obtained. Out of three NOD genotypes, IRF-1(+/+) and IRF-1(+/-) developed spontaneous diabetes with an incidence of 47% (9/19) and 50% (10/20) by 30 weeks of age, respectively; whereas IRF-1(-/-) did not develop diabetes (0/18, P< 0.01 vs. (+/+) and (+/-)). Histologically, IRF-1(+/+) and IRF-1(+/-) had various degrees of insulitis, but IRF-1(-/-) had no insulitis. In comparison with IRF-1(+/+), the percentage of CD4(+) and Mac-1(+) splenic cells significantly increased, whereas CD3(+), CD8(+) and B220(+) cells decreased in IRF-1(-/-). Furthermore, spleen cell proliferation in response to Con A or murine GAD65 peptide, a major autoantigen of the pancreatic beta-cell, significantly increased, and the IFN-gamma/IL-10 ratio in the culture supernatant significantly decreased in IRF-1(-/-), suggesting Th2 deviation in cytokine balance. These results indicate that IRF-1 plays a key role in developing insulitis and diabetes in NOD mice.

Cytokine induction of Fas gene expression in insulin-producing cells requires the transcription factors NF-kappaB and C/EBP

Fas-mediated cell death may play a role in the autoimmune destruction of pancreatic beta-cells in type 1 diabetes. beta-Cells do not express Fas under physiological conditions, but Fas mRNA and protein are induced in cytokine-exposed mouse and human islets, rendering the beta-cells susceptible to Fas ligand-induced apoptosis. The aim of the present study was to investigate the molecular regulation of Fas by cytokines in rat beta-cells and in insulin-producing RINm5F cells. Fas mRNA expression was increased 15-fold in fluorescence-activated cell sorting-purified rat beta-cells exposed to interleukin (IL)-1beta, whereas gamma-interferon had no effect. Transfection experiments of rat Fas promoter-luciferase reporter constructs into purified rat beta-cells and RINm5F insulinoma cells identified an IL-1beta-responsive region between nucleotides -223 and -54. Inactivation of two adjacent NF-kappaB and C/EBP sites in this region abolished IL-1beta-induced Fas promoter activity in RINm5F cells. Binding of NF-kappaB and C/EBP factors to their respective sites was confirmed by gel shift assays. In cotransfection experiments, NF-kappaB p65 transactivated the Fas promoter. NF-kappaB p50 and C/EBPbeta overexpression had no effect by themselves on the Fas promoter activity, but when cotransfected with p65, each factor inhibited transactivation by p65. These results suggest a critical role for NF-kappaB and C/EBP factors in cytokine-regulation of Fas expression in insulin-producing cells.

Inhibition of poly (ADP-ribose) synthetase by gene disruption or inhibition with 5-iodo-6-amino-1,2-benzopyrone protects mice from multiple-low-dose-streptozotocin-induced diabetes

Activation of poly(ADP-ribose) synthetase (PARS, also termed polyADP-ribose polymerase or PARP) has been proposed as a major mechanism contributing to beta-cell destruction in type I diabetes. In the present study, we have investigated the role of PARS in mediating the induction of diabetes and beta-cell death in the multiple-low-dose-streptozotocin (MLDS) model of type I diabetes. Mice genetically deficient in PARS were found to be less sensitive to MLDS than wild type mice, with a lower incidence of diabetes and reduced hyperglycemia. A potent inhibitor of PARS, 5-iodo-6-amino-1,2-benzopyrone (INH(2)BP), was also found to protect mice from MLDS and prevent beta-cell loss, in a dose-dependent manner. Paradoxically, in the PARS deficient mice, the compound increased the onset of diabetes. In vitro the cytokine combination; interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma inhibited glucose-stimulated insulin secretion from isolated rat islets of Langerhans and decreased RIN-5F cell viability. The PARS inhibitor, INH(2)BP, protected both the rat islets and the beta-cell line, RIN-5F, from these cytokine-mediated effects. These protective effects were not mediated by inhibition of cytokine-induced nitric oxide formation. Inhibition of PARS by INH(2)BP was unable to protect rat islet cells from cytokine-mediated apoptosis. Cytokines, peroxynitrite and streptozotocin were all shown to induce PARS activation in RIN-5F cells, an effect suppressed by INH(2)BP. The present study provides evidence for in vivo PARS activation contributing to beta-cell damage and death in the MLDS model of diabetes, and indicates a role for PARS activation in cytokine-mediated depression of insulin secretion and cell viability in vitro.

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

Peroxynitrite (ONOO(-)) is a highly reactive oxidant produced by the interaction of the free radicals superoxide (O*-2) and nitric oxide (NO(*)). In a previous study, we found that peroxynitrite is formed in islet beta-cells of nonobese diabetic (NOD) mice. Here, we report that guanidinoethyldisulphide (GED), a selective inhibitor of inducible nitric oxide synthase (iNOS) and scavenger of peroxynitrite prevents diabetes in NOD mice. GED treatment of female NOD mice, starting at age 5 weeks, delayed diabetes onset (from age 12 to 22 weeks) and significantly decreased diabetes incidence at 30 weeks (from 80% to 17%). GED did not prevent pancreatic islet infiltration by leukocytes; however, beta-cells that stained positive for nitrotyrosine (a marker of peroxynitrite) were significantly decreased in islets of GED-treated mice (1+/-1%) compared with vehicle-treated mice (30+/-9%). In addition, GED significantly inhibited nitric oxide and nitrotyrosine formation and decreased destruction of beta-cells in NOD mouse islets incubated in vitro with the combination of proinflammatory cytokines interleukin 1-beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). These findings indicate that both superoxide and nitric oxide radicals contribute to islet beta-cell destruction in autoimmune diabetes via peroxynitrite formation in the beta-cells.

Islet protein expression changes during diabetes development in islet syngrafts in BB-DP rats and during rejection of BB-DP islet allografts

Interleukin 1beta (IL-1) is cytotoxic to rat pancreatic beta-cells in vitro, and increased expression of IL-1 mRNA is found in the islets of Langerhans during development of diabetes in BB/Wor/Mol-BB2 (BB-DP) rats and NOD mice. It has been proposed that IL-1 induces a race between protective and deleterious proteins in the beta-cells during development of diabetes, and that heat shock proteins 70 and 90, and manganese superoxide dismutase, all inducible by IL-1 are potentially protective proteins. We have established a database of approximately 2000 neonatal rat-islet proteins by two-dimensional gel (2-D gel) electrophoresis of [35S]-methionine labelled neonatal Wistar Furth rat islets. In these IL-1 was shown to up- or down-regulate the islet-expression level of 99, and to induce de novo synthesis of 6 proteins. The identity of most of the IL-1 induced proteins is unknown and under study. In this study we wished to investigate if changes in protein expression induced in vitro by IL-1 stimulation of islets are also seen in vivo during spontaneous development of diabetes in BB-DP rats, and during islet allograft rejection. Two-hundred neonatal BB-DP rat islets were grafted under the kidney capsule of either 30-day-old BB-DP rats killed at onset of diabetes or of 30-day-old Wistar Kyoto (WK) rats, killed 12 days after grafting. Proteins in excised islet-grafts and in vitro IL-1 exposed isolated neonatal BB-DP rat islets were labelled with [35S]-methionine, and processed for 2-D gel electrophoresis. Fluorographs of the gels were analysed by computer. A total of 1815 proteins were found in 3 of 3 12.5% polyacrylamide gels. Interleukin-1 was found to change expression level of 82 of these proteins (22 up- and 60 down-regulated) in neonatal BB-DP rat islets in vitro. Of these 82 proteins 33 (4 up- and 29 down-regulated) also changed level of expression during disease occurrence in syngeneic islet grafts from diabetic BB-DP rats, and 29 (4 up- and 25 down-regulated) during rejection of BB-DP islets grafted to WK rats. Changes in the expression level of 14 (3 up- and 11 down-regulated) of the 82 proteins altered by IL-1 in vitro were only found in syngeneic islet grafts in diabetic BB-DP rats, and changes in the expression level of 8 (2 up- and 6 down-regulated) of these 82 proteins expression were only found in BB-DP islet allografts in WK recipients. Identification of these proteins may be important in understanding the mechanisms of islet destruction during development of insulin-dependent diabetes mellitus and during islet allograft rejection.

Cytokine-induced inhibition of insulin release from mouse pancreatic beta-cells deficient in inducible nitric oxide synthase

Cytokines may participate in islet destruction during the development of type 1 diabetes. Expression of inducible nitric oxide synthase (iNOS) and subsequent NO formation induced by IL-1 beta or (IL-1 beta + IFN-gamma) may impair islet function in rodent islets. Inhibition of iNOS or a deletion of the iNOS gene (iNOS -/- mice) protects against cytokine-induced beta-cell suppression, although cytokines might also induce NO-independent impairment. Presently, we exposed wild-type (wt, C57BL/6 x 129SvEv) and iNOS -/- islets to IL-1 beta (25 U/ml) and (IL-1 beta (25 U/ml) + IFN-gamma (1000 U/ml)) for 48 h. IL-1 beta and (IL-1 beta + IFN-gamma) induced a significant increase in NO formation in wt but not in iNOS -/- islets. Both IL-1 beta and (IL-1 beta + IFN-gamma) impaired glucose-stimulated insulin release and reduced the insulin content of wt islets, while (IL-1 beta + IFN-gamma) reduced glucose oxidation rates and cell viability. IL-1 beta exposure to iNOS -/- islets impaired glucose-stimulated insulin release, increased insulin accumulation and reduced the insulin content, without any increase in cell death. Exposure to (IL-1 beta + IFN-gamma) had no effect on iNOS -/- islets except reducing the insulin content. Our data suggest that IL-1 beta may inhibit glucose-stimulated insulin release by pathways that are not NO-dependent and not related to glucose metabolism or cell death.

Antidiabetogenic effect of pentoxifylline is associated with systemic and target tissue modulation of cytokines and nitric oxide production

We have shown recently that xanthine derivative pentoxifylline (PTX) downregulates an inflammatory autoimmune process triggered in genetically susceptible Dark Agouti rats by multiple low doses of streptozotocin (MLD-SZ, 20 mg/kg/day ip for 5 days). We studied the cellular and molecular consequences of PTX treatment during MLD-SZ-induced diabetes with special emphasis on local vs. systemic production of inflammatory mediators. Administration of PTX (200 mg/kg/day for 10 days) during induction of the disease reduced clinical signs of diabetes and protected rats from development of destructive intrainsulitis. Pentoxifylline did not affect diabetogenic effect of single high dose of SZ (100 mg/kg SZ). Ex vivo analysis of the islets of Langerhans performed in early disease development revealed that PTX downregulates production of proinflammatory cytokines IFN-gamma and TNF, as well as inducible nitric oxide synthase (iNOS) expression and NO production. In addition, PTX treatment suppressed splenocyte autoreactivity, as well as the frequency of cells expressing IL-2R and MHC class II antigens. There was no evidence of any changes in proportion of ICAM-1 and LFA-1 expressing splenocytes in comparison to control MLD-SZ-treated animals. In contrast to suppressed intraislet production, high peripheral expression of both iNOS mRNA and NO was found in MLD-SZ rats treated with PTX. Taken together, the data indicate that the effect on both systemic and intra-islet production of NO, suppression of autoreactive cell activation and of local type 1 cytokine release may contribute to the therapeutic benefit achieved by PTX in the rat.

Quantification of Constitutive Endothelial and Inducible Nitric Oxide Synthase mRNA by Competitive Reverse Transcription-polymerase Chain Reaction

Nitric oxide (NO) participates in the general homeostatic control of the vasculature, and it is involved in the process of vascular remodelling. NO in particular inhibits the proliferation of vascular smooth muscle cells and has been shown to possess antiatherogenic properties. Two important molecules control NO synthesis, namely constitutive endothelial (ecNOS) and inducible (iNOS) nitric oxide synthase. To investigate the regulation of the ecNOS and iNOS mRNA expression in various tissues, we describe the design and validation of a reliable and efficient competitive RT-PCR approach for quantification of ecNOS and iNOS mRNA in rat tissue. Prior to reverse transcription, the total RNA was supplemented with internal standard RNA-competitors, which were constructed by a modified site-directed mutagenesis followed by in vitro transcription using T7-polymerase. This technique allows the easy and fast (within a single day) construction of an internal, recombinant RNA-fragment without the use of cloning techniques. Only two additional "linker" primers containing the sequence of T7-promoter, the primers used for the wild type of ecNOS and iNOS mRNA and the primers of a spacer gene are needed. In addition, all steps of the procedure can be streamlined by convenient commercially available kits. We conclude that the described technique is a valid and reliable method for the absolute quantification of small amounts of specific mRNA. </hea

Sodium fusidate ameliorates the course of diabetes induced in mice by multiple low doses of streptozotocin

We studied the effects of the immunosuppressant sodium fusidate (fusidin) on murine immunoinflammatory diabetes mellitus (DM) induced by multiple low doses of streptozotocin (SZ). Fusidin was given by gavage to three strains of mice (C57KsJ, C57BL/6, CD1) at doses 10 or 100 mg/kg body weight every other day. The drug was administered as an early or late prophylactic regime starting either 1 day prior to the first or after the fifth and last injection of SZ. In both situations the largest dose of fusidin successfully reduced the clinical, chemical and histological signs of DM, the treated mice having significantly lower glycaemic values and milder (often absent) insulitis compared with sham-treated animals or controls given SZ alone. The antidiabetogenic effect was long-lasting as it was maintained up to 1 month after cessation of therapy. In contrast, fusidin prophylaxis failed to prevent development of hyperglycaemia acutely induced by one single and high (160 mg/kg) dose of SZ, which is a model of DM primarily due to the toxic action of SZ on the beta cells and does not involve immunopathogenetic mechanisms. On day 14 after SZ, fusidin markedly altered the circulating cytokine profile induced in vivo by ConA, reducing the levels of IFN-gamma, IL-2 and TNF-alpha and augmenting the level of IL-6. However, only the inhibitory effect of the drug on the synthesis/release of IFN-gamma seemed to be causally related to its capacity to counteract the SZ-induced DM. In fact, the disease was prevented by a neutralizing monoclonal antibody (mAb) against IFN-gamma, but not by anti-IL-2 receptor mAb, a soluble form of TNF-receptor type 1 or recombinant human IL-6. The prevention of disease by fusidin was also partly reversed by exogenously administered recombinant mouse IFN-gamma. The data provide further in-vivo evidence for the anti-diabetogenic and immunomodulatory properties of fusidin and indicate that this drug could have a role in prevention and treatment of human type 1 DM.

Age-related alterations in IL-1beta, TNF-alpha, and IL-6 concentrations in parotid acinar cells from BALB/c and non-obese diabetic mice

IL-1beta, TNF-alpha, and IL-6 have been implicated in the destruction of parotid gland acinar cells (but not duct cells) in autoimmune sialoadenitis. Here we report the temporal alterations of these cytokines in parotid acinar cells that may lead to this specificity in cell death in the non-obese diabetic (NOD) mouse model for Sjögren's syndrome. Immunohistochemistry on paraffin sections of parotid gland from 5- and 10-week-old BALB/c and NOD mice confirmed the presence of many peri-acinar lymphoid nodules but few T-cells and macrophages between acinar cells. RT-PCR on enzymatically dispersed mouse parotid acinar cells (MPACs) showed no bands for CD3varepsilon, CD20, or F4/80 regardless of mouse strain or age. By ELISA, MPACs from 10-week-old NODs showed a small but highly significant (p<0.003) increase in IL-1beta and a large significant decrease (p<0.008) in IL-6 compared to 5-week-old NODs. Norepinephrine-stimulated amylase release from MPACs was not different regardless of mouse strain or age. These data show that alterations in acinar cell production of IL-1beta and IL-6 in aging NODs precede periductal lymphoid aggregates and acinar cell secretory dysfunction. (J Histochem Cytochem 48:1033-1041,2000)

COX-2 inhibition prevents insulin-dependent diabetes in low-dose streptozotocin-treated mice

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease believed to be caused by an inflammatory process in the pancreas leading to selective destruction of the beta cells. Inducible cyclooxygenase (COX-2) is expressed under inflammatory conditions and its product prostaglandin E(2) (PGE(2)) is an important inflammation mediator. We report here that administration of the selective COX-2 inhibitor NS-398 prevents the onset of diabetes in mice brought on by multiple low-doses of streptozotocin (STZ). Histological observations indicated that STZ-mediated destruction of beta cells was prevented by NS-398 treatment. Delayed (day 3) administration of NS-398 was also protective in this model. No protective effect was observed when NS-398 was administered prior to a high, toxic dose of STZ. These results demonstrate the critical importance of COX-2 activity in autoimmune destruction of beta cells, and point to the fact that COX-2 inhibition can potentially develop into a preventive therapy against IDDM.

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

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

Novel experimental strategies to prevent the development of type 1 diabetes mellitus

Type 1 diabetes is an autoimmune disease leading to extensive destruction of the pancreatic beta-cells. Our research focusses on the role of beta-cells during the course of the disease, aiming at finding novel strategies to enhance beta-cell resistance against the cytotoxic damage inflicted by the immune system. Special attention has been paid to the possibility that cytokines released by the immune cells infiltrating the pancreatic islets can directly suppress and kill beta-cells. Certain cytokines (interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma) either alone or in combination, are able to activate signal transduction pathways in beta-cells leading to transcription factor activation and de novo gene expression. In this context, it has been found that induction of inducible nitric oxide synthase mediates an elevated production of nitric oxide, which impairs mitochondrial function and causes DNA damage eventually leading to apoptosis and necrosis. However, other induced proteins SUCH AS heat shock protein 70 and superoxide dismutase may reflect a defense reaction elicited in the beta-cells by the cytokines. Our strategy is to further seek for proteins involved in both destruction and protection of beta-cells. Based on this knowledge, we plan to apply gene therapeutic approaches to increase expression of protective genes in beta-cells. If this is feasible we will then evaluate the function and survival of such modified beta-cells in animal models of type 1 diabetes such as the NOD mouse. The long-term goal for this research line is to find novel approaches to influence beta-cell resistance in humans at risk of developing type 1 diabetes.

A20 inhibits cytokine-induced apoptosis and nuclear factor kappaB-dependent gene activation in islets

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease resulting from apoptotic destruction of beta cells in the islets of Langerhans. Low expression of antioxidants and a predilection to produce nitric oxide (NO) have been shown to underscore beta cell apoptosis. With this perspective in mind, we questioned whether beta cells could mount an induced protective response to inflammation. Here we show that human and rat islets can be induced to rapidly express the antiapoptotic gene A20 after interleukin (IL)-1beta activation. Overexpression of A20 by means of adenovirus-mediated gene transfer protects islets from IL-1beta and interferon gamma-induced apoptosis. The cytoprotective effect of A20 against apoptosis correlates with and is dependent on the abrogation of cytokine-induced NO production. The inhibitory effect of A20 on cytokine-stimulated NO production is due to transcriptional blockade of inducible NO synthase (iNOS) induction; A20 inhibits the activation of the transcription factor nuclear factor kappaB at a level upstream of IkappaBalpha degradation. These data demonstrate a dual antiapoptotic and antiinflammatory function for A20 in beta cells. This qualifies A20 as part of the physiological cytoprotective response of islets. We propose that A20 may have therapeutic potential as a gene therapy candidate to achieve successful islet transplantation and the cure of IDDM.

Comparing the Relative Role of Perforin/Granzyme Versus Fas/Fas Ligand Cytotoxic Pathways in CD8+ T Cell-Mediated Insulin-Dependent Diabetes Mellitus

CD8+ cytotoxic T cells play a critical role in initiating insulin-dependent diabetes mellitus. The relative contribution of each of the major cytotoxic pathways, perforin/granzyme and Fas/Fas ligand (FasL), in the induction of autoimmune diabetes remains controversial. To evaluate the role of each lytic pathway in β cell lysis and induction of diabetes, we have used a transgenic mouse model in which β cells expressing the influenza virus hemagglutinin (HA) are destroyed by HA-specific CD8+ T cells from clone-4 TCR-transgenic mice. Upon adoptive transfer of CD8+ T cells from perforin-deficient clone-4 TCR mice, there was a 30-fold increase in the number of T cells required to induce diabetes. In contrast, elimination of the Fas/FasL pathway of cytotoxicity had little consequence. When both pathways of cytolysis were eliminated, mice did not become diabetic. Using a model of spontaneous diabetes, which occurs in double transgenic neonates that express both clone-4 TCR and Ins-HA transgenes, mice deficient in either the perforin or FasL/Fas lytic pathway become diabetic soon after birth. This indicates that, in the neonate, large numbers of autoreactive CD8+ T cells can lead to destruction of islet β cells by either pathway.

Prolonged STAT1 activation is associated with interferon-gamma priming for interleukin-1-induced inducible nitric-oxide synthase expression by islets of Langerhans

In this study, the ability of interferon-gamma (IFN-gamma) to prime rat and nonobese diabetic (NOD) mouse islets for interleukin-1 (IL-1)-stimulated expression of inducible nitric-oxide synthase (iNOS) has been examined. IL-1-induced iNOS expression by rat islets is concentration-dependent with maximal expression occurring in response to 1.0 unit/ml. Individually, neither 0.1 unit/ml IL-1 nor 150 units/ml IFN-gamma stimulates iNOS expression or nitrite production by rat islets. However, a 30-60-min pulse of rat islets with IFN-gamma, followed by washing to remove the cytokine and continued culture with 0.1 unit/ml IL-1 for 40 h, results in iNOS expression and nitrite production to levels similar in magnitude to the individual effects of 1.0 unit/ml IL-1. A 1-h pulse with IFN-gamma primes for IL-1-induced islet degeneration that is mediated by the expression of iNOS and increased production of nitric oxide. IFN-gamma also primes for IL-1-induced iNOS expression and nitrite formation by NOD mouse islets. The priming actions of IFN-gamma appear to be selective for beta-cells, as IFN-gamma primes for IL-1-induced nitrite formation by primary beta-cells and RINm5F insulinoma cells, but not primary alpha-cells. The priming actions of IFN-gamma for IL-1-induced iNOS expression do not require de novo protein synthesis as preincubation of RINm5F cells with cycloheximide does not inhibit iNOS mRNA accumulation under priming conditions. The priming actions of IFN-gamma on IL-1-induced iNOS expression persists for extended periods of up to 7 days and are associated with persistent signal transducers and activators of transcription (STAT)-1 activation. A 30-min pulse of rat islets with IFN-gamma stimulates STAT1 phosphorylation, and STAT1 remains phosphorylated for up to 7 days following IFN-gamma removal. In addition, STAT1 remains nuclear for up to 7 days after IFN-gamma removal. These results indicate that IFN-gamma primes for IL-1-induced islet degeneration via a nitric oxide-dependent mechanism. These findings also provide evidence that the priming actions of IFN-gamma for IL-1-induced iNOS expression by islets are associated with the prolonged phosphorylation and activation of STAT1.

An immunohistochemical study of macrophage influx and the co-localization of inducible nitric oxide synthase in the pancreas of non-obese diabetic (NOD) mice during disease acceleration with cyclophosphamide

Cyclophosphamide has been used to accelerate and synchronize diabetes in non-obese diabetic (NOD) mice. It was injected to 70-day-old female NOD mice and its effect on the progression of insulitis studied at days 0, 4, 7, 11 and at onset of diabetes. Pancreatic sections were also examined for the influx of CD4 and CD8 T cells and macrophages following immunofluorescence staining. The kinetics of macrophage immunoreactive cells in the exocrine and intra-islet areas were also investigated. Light and confocal microscopy were-employed to examine the expression and co-localization of inducible nitric oxide synthase following dual- and triple-label immunofluorescence histochemistry. After cyclophosphamide administration, the severity of insulitis remained similar from days 0 to 4 but began to rise at day 7 and markedly by day 11 and at onset of diabetes. At these two later stages, the insulitis scores were close to 100% while in age-matched control groups the insulitis scores were considerably lower. Immunohistochemical staining showed increasing numbers of CD4 and CD8 T cell subsets and macrophages within the islets and in exocrine, sinusoidal and peri-vascular regions. At onset of diabetes, several islets contained prominent clusters of macrophage immunoreactive cells. Macrophage influx into the islets increased sharply from day 7 (mean number per islet: 119 +/- 54 SEM), peaked at day 11 (mean number per islet: 228 +/- 42), and then declined at onset of diabetes (mean number per islet: 148 +/- 49). Several cells with immunolabelling for inducible nitric oxide synthase were detectable from day 7 onwards until the onset of diabetes. Dual- and triple-label immunohistochemistry showed that a significant proportion of macrophages and only a few beta cells contained the enzyme. Macrophages positive for the enzyme were located as clusters or occasionally contiguously, in the peri-islet and intra-islet areas but rarely in the exocrine region. Islets with minimal distribution of macrophages in the peri-islet areas were not positive for inducible nitric oxide synthase. Beta cells positive for the enzyme were observed in islets with significant macrophage infiltration in locations close to macrophages. The present results show that cyclophosphamide administration to female NOD mice results in a rapid influx of CD4 and CD8 cells and macrophages. The marked up-regulation of inducible nitric oxide synthase in a selective proportion of macrophages, within the islets, immediately preceding and during the onset of diabetes suggests that nitric oxide released by islet macrophages may be an important molecular mediator of beta cell destruction in this accelerated model of insulin-dependent diabetes mellitus.

Pancreatic beta cell-specific expression of thioredoxin, an antioxidative and antiapoptotic protein, prevents autoimmune and streptozotocin-induced diabetes

The cytotoxicity of reactive oxygen intermediates (ROIs) has been implicated in the destruction of pancreatic beta cells in insulin-dependent diabetes mellitus (IDDM). Thioredoxin (TRX), a redox (reduction/oxidation)-active protein, has recently been shown to protect cells from oxidative stress and apoptosis. To elucidate the roles of oxidative stress in the development of autoimmune diabetes in vivo, we produced nonobese diabetic transgenic mice that overexpress TRX in their pancreatic beta cells. In these transgenic mice, the incidence of diabetes was markedly reduced, whereas the development of insulitis was not prevented. Moreover, induction of diabetes by streptozotocin, an ROI-generating agent, was also attenuated by TRX overexpression in beta cells. This is the first direct demonstration that an antioxidative and antiapoptotic protein protects beta cells in vivo against both autoimmune and drug-induced diabetes. Our results strongly suggest that oxidative stress plays an essential role in the destruction of beta cells by infiltrating inflammatory cells in IDDM.