Free radicals and the pathogenesis of type 1 diabetes: beta-cell cytokine-mediated free radical generation via cyclooxygenase-2

Nanobiotechnology-Modified Cellular and Molecular Therapy as a Novel Approach for Autoimmune Diabetes Management

Several cellular and molecular therapies such as stem cell therapy, cell replacement therapy, gene modification therapy, and tolerance induction therapy have been researched to procure a permanent cure for Type 1 Diabetes. However, due to the induction of undesirable side effects, their clinical utility is questionable. These anti-diabetic therapies can be modified with nanotechnological tools for reducing adverse effects by selectively targeting genes and/or receptors involved directly or indirectly in diabetes pathogenesis, such as the glucagon-like peptide 1 receptor, epidermal growth factor receptor, human leukocyte antigen (HLA) gene, miRNA gene and hepatocyte growth factor (HGF) gene. This paper will review the utilities of nanotechnology in stem cell therapy, cell replacement therapy, beta-cell proliferation strategies, immune tolerance induction strategies, and gene therapy for type 1 diabetes management.

Maternal diabetes negatively impacts fetal health

Diabetes is a chronic metabolic disease affecting an increasing number of people. Although diabetes has negative health outcomes for diagnosed individuals, a population at particular risk are pregnant women, as diabetes impacts not only a pregnant woman's health but that of her child. In this review, we cover the current knowledge and unanswered questions on diabetes affecting an expectant mother, focusing on maternal and fetal outcomes.

Human Islet Expression Levels of Prostaglandin E2 Synthetic Enzymes, But Not Prostaglandin EP3 Receptor, Are Positively Correlated with Markers of β-Cell Function and Mass in Nondiabetic Obesity

Elevated islet production of prostaglandin E₂ (PGE₂), an arachidonic acid metabolite, and expression of prostaglandin E₂ receptor subtype EP3 (EP3) are well-known contributors to the β-cell dysfunction of type 2 diabetes (T2D). Yet, many of the same pathophysiological conditions exist in obesity, and little is known about how the PGE₂ production and signaling pathway influences nondiabetic β-cell function. In this work, plasma arachidonic acid and PGE₂ metabolite levels were quantified in a cohort of nondiabetic and T2D human subjects to identify their relationship with glycemic control, obesity, and systemic inflammation. In order to link these findings to processes happening at the islet level, cadaveric human islets were subject to gene expression and functional assays. Interleukin-6 (IL-6) and cyclooxygenase-2 (COX-2) mRNA levels, but not those of EP3, positively correlated with donor body mass index (BMI). IL-6 expression also strongly correlated with the expression of COX-2 and other PGE₂ synthetic pathway genes. Insulin secretion assays using an EP3-specific antagonist confirmed functionally relevant upregulation of PGE₂ production. Yet, islets from obese donors were not dysfunctional, secreting just as much insulin in basal and stimulatory conditions as those from nonobese donors as a percent of content. Islet insulin content, on the other hand, was increased with both donor BMI and islet COX-2 expression, while EP3 expression was unaffected. We conclude that upregulated islet PGE₂ production may be part of the β-cell adaption response to obesity and insulin resistance that only becomes dysfunctional when both ligand and receptor are highly expressed in T2D.

Emerging Roles of Metallothioneins in Beta Cell Pathophysiology: Beyond and Above Metal Homeostasis and Antioxidant Response

Simple Summary

Defective insulin secretion by pancreatic beta cells is key for the development of type 2 diabetes but the precise mechanisms involved are poorly understood. Metallothioneins are metal binding proteins whose precise biological roles have not been fully characterized. Available evidence indicated that Metallothioneins are protective cellular effectors involved in heavy metal detoxification, metal ion homeostasis and antioxidant defense. This concept has however been challenged by emerging evidence in different medical research fields revealing novel negative roles of Metallothioneins, including in the context of diabetes. In this review, we gather and analyze the available knowledge regarding the complex roles of Metallothioneins in pancreatic beta cell biology and insulin secretion. We comprehensively analyze the evidence showing positive effects of Metallothioneins on beta cell function and survival as well as the emerging evidence revealing negative effects and discuss the possible underlying mechanisms. We expose in parallel findings from other medical research fields and underscore unsettled questions. Then, we propose some future research directions to improve knowledge in the field.

Abstract

Metallothioneins (MTs) are low molecular weight, cysteine-rich, metal-binding proteins whose precise biological roles have not been fully characterized. Existing evidence implicated MTs in heavy metal detoxification, metal ion homeostasis and antioxidant defense. MTs were thus categorized as protective effectors that contribute to cellular homeostasis and survival. This view has, however, been challenged by emerging evidence in different medical fields revealing novel pathophysiological roles of MTs, including inflammatory bowel disease, neurodegenerative disorders, carcinogenesis and diabetes. In the present focused review, we discuss the evidence for the role of MTs in pancreatic beta-cell biology and insulin secretion. We highlight the pattern of specific isoforms of MT gene expression in rodents and human beta-cells. We then discuss the mechanisms involved in the regulation of MTs in islets under physiological and pathological conditions, particularly type 2 diabetes, and analyze the evidence revealing adaptive and negative roles of MTs in beta-cells and the potential mechanisms involved. Finally, we underscore the unsettled questions in the field and propose some future research directions.

JUND regulates pancreatic β cell survival during metabolic stress

OBJECTIVE

In type 2 diabetes (T2D), oxidative stress contributes to the dysfunction and loss of pancreatic β cells. A highly conserved feature of the cellular response to stress is the regulation of mRNA translation; however, the genes regulated at the level of translation are often overlooked due to the convenience of RNA sequencing technologies. Our goal is to investigate translational regulation in β cells as a means to uncover novel factors and pathways pertinent to cellular adaptation and survival during T2D-associated conditions.

METHODS

Translating ribosome affinity purification (TRAP) followed by RNA-seq or RT-qPCR was used to identify changes in the ribosome occupancy of mRNAs in Min6 cells. Gene depletion studies used lentiviral delivery of shRNAs to primary mouse islets or CRISPR-Cas9 to Min6 cells. Oxidative stress and apoptosis were measured in primary islets using cell-permeable dyes with fluorescence readouts of oxidation and activated cleaved caspase-3 and-7, respectively. Gene expression was assessed by RNA-seq, RT-qPCR, and western blot. ChIP-qPCR was used to determine chromatin enrichment.

RESULTS

TRAP-seq in a PDX1-deficiency model of β cell dysfunction uncovered a cohort of genes regulated at the level of mRNA translation, including the transcription factor JUND. Using a panel of diabetes-associated stressors, JUND was found to be upregulated in mouse islets cultured with high concentrations of glucose and free fatty acid, but not after treatment with hydrogen peroxide or thapsigargin. This induction of JUND could be attributed to increased mRNA translation. JUND was also upregulated in islets from diabetic db/db mice and in human islets treated with high glucose and free fatty acid. Depletion of JUND in primary islets reduced oxidative stress and apoptosis in β cells during metabolic stress. Transcriptome assessment identified a cohort of genes, including pro-oxidant and pro-inflammatory genes, regulated by JUND that are commonly dysregulated in models of β cell dysfunction, consistent with a maladaptive role for JUND in islets.

CONCLUSIONS

A translation-centric approach uncovered JUND as a stress-responsive factor in β cells that contributes to redox imbalance and apoptosis during pathophysiologically relevant stress.

Spirulina Extract Enhanced a Protective Effect in Type 1 Diabetes by Anti-Apoptosis and Anti-ROS Production

Interest in the nutritional value and pharmacological activities of blue-green algae has gradually increased. Spirulina extracts show protective effects against apoptosis and inflammatory damage in various cell types. Here, we investigated the protective effects of extracts from Spirulina maxima in a cytokine-mediated type 1 diabetes model in vitro and in streptozotocin-induced diabetic Wistar rats in vivo. Interleukin-1β and interferon-gamma induced substantial cytotoxicity to RINm5F rat insulinoma cells, increasing nitric oxide (NO) production, nuclear factor-kappa B (NF-κB) activity, the expression of endoplasmic reticulum (ER) stress genes, and activation of mitogen-activated protein kinases and key genes related apoptosis. However, the cytotoxicity of cytokines was significantly attenuated by Spirulina extract, which effectively prevented NO production by inhibiting the synthesis of cytokine-activated NO synthase (iNOS), and apoptosis was suppressed. These results suggest that Spirulina extract might be effective to preserve the viability and function of pancreatic β-cells against cytotoxic conditions. Moreover, diabetic mice orally administered Spirulina extract showed decreased glucose levels, increased insulin, and improvement in liver enzyme markers. The antioxidant effect of Spirulina extract may be helpful in treating type 1 diabetes by enhancing the survival, and reducing or delaying cytokine-mediated β-cells destruction.

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

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

COX-2 inhibitor NS-398 suppresses doxorubicin-induced p53 accumulation through inhibition of ROS-mediated Jnk activation

Cyclooxygenase-2 (COX-2) is one of the isoforms of cyclooxygenase, a rate-limiting enzyme in the arachidonic acid cascade. COX-2 protein expression is highly induced by numerous factors and it has been reportedly overexpressed in various human malignancies. Although anti-tumorigenic effects of COX-2 inhibitors have been shown, several lines of evidence suggest that COX-2 inhibitors antagonize the cytotoxicity of chemotherapeutic agents. In this study, we investigated the effect of NS-398, a COX-2 inhibitor, on modulation of doxorubicin (DOX)-induced p53 accumulation. Non-selective and selective COX-2 inhibitors attenuated DOX-induced accumulation of wild type (WT) but not mutant p53. Nutlin-3α or MG132 abolished the suppressive effect of a COX-2 inhibitor on DOX-induced p53 increase. Moreover, the DOX-induced increase in p53 protein levels was reduced in COX-2 knockout (KO) mouse embryonic fibroblasts (MEFs) compared to those in WT or COX-1 KO MEFs. DOX-induced accumulation of p53 was attenuated by a specific inhibitor or knockdown of Jun-N-terminal kinase (Jnk). In addition, DOX-induced Jnk activation was decreased in COX-2 KO MEFs or by COX-2 inhibition, suggesting that Jnk stabilizes p53 by a mechanism that involves COX-2. Pre-treatment with a reactive oxygen species (ROS) scavenger, N-acetylcysteine, attenuated DOX-induced Jnk activation and subsequent p53 accumulation. Furthermore, the absence or inhibition of COX-2 resulted in suppression of DOX-induced increase in ROS levels. These results suggest that COX-2 activates Jnk through modulation of ROS levels, leading to accumulation of p53. Our study identifies a putative novel cross-talk between COX-2 and p53. © 2016 Wiley Periodicals, Inc.

N-(2-Bromo-4-fluorophenyl)-3-(3,4-dihydroxyphenyl)-acrylamide (CPAM), a small catecholic amide as an antioxidant, anti diabetic and antibacterial compound

The trans conformation ofN-(2-bromo-4-fluorophenyl)-3-(3,4-dihydroxyphenyl)-acrylamide (CPAM), a small catecholic amide with halogen moieties, may be used as an anti diabetic compound.

Exendin-4 protects rat islets against loss of viability and function induced by brain death

Islet quality loss after isolation from brain-dead donors still hinders the implementation of human islet transplantation for treatment of type 1 diabetes. In this scenario, systemic inflammation elicited by donor brain death (BD) is among the main factors influencing islet viability and functional impairment. Exendin-4 is largely recognized to promote anti-inflammatory and cytoprotective effects on β-cells. Therefore, we hypothesized that administration of exendin-4 to brain-dead donors might improve islet survival and insulin secretory capabilities. Here, using a rat model of BD, we demonstrate that exendin-4 administration to the brain-dead donors increases both islet viability and glucose-stimulated insulin secretion. In this model, exendin-4 treatment produced a significant decrease in interleukin-1β expression in the pancreas. Furthermore, exendin-4 treatment increased the expression of superoxide dismutase-2 and prevented BD-induced elevation in uncoupling protein-2 expression. Such observations were accompanied by a reduction in gene expression of two genes often associated with endoplasmic reticulum (ER) stress response in freshly isolated islets from treated animals, C/EBP homologous protein and immunoglobulin heavy-chain binding protein. As ER stress response has been shown to be triggered by and to participate in cytokine-induced β-cell death, we suggest that exendin-4 might exert its beneficial effects through alleviation of pancreatic inflammation and oxidative stress, which in turn could prevent islet ER stress and β-cell death. Our findings might unveil a novel strategy to preserve islet quality from brain-dead donors. After testing in the human pancreatic islet transplantation setting, this approach might sum to the ongoing effort to achieve consistent and successful single-donor islet transplantation.

Phoenix dactylifera seeds ameliorate early diabetic complications in streptozotocin-induced diabetic rats

CONTEXT

In Arabic folk medicine, the seeds of Phoenix dactylifera L. (Arecaceae) have been used to manage diabetes for many years. Few studies have reported the antidiabetic effect of P. dactylifera seeds; however, their effect on diabetic complications is still unexplored.

OBJECTIVE

The present study investigates the protective effect of P. dactylifera seeds against diabetic complications in rats.

MATERIAL AND METHODS

The aqueous suspension of P. dactylifera seeds (aqPDS) (1 g/kg/d) was orally administered to streptozotocin-induced diabetic rats for 4 weeks. The serum biochemical parameters were assessed spectrophotometrically. Furthermore, oxidative stress was examined in both liver and kidney tissues by assessment of thiobarbituric acid reactive substances (TBARS), nitric oxide (NO), reduced glutathione, superoxide dismutase (SOD), glutathione S-transferase, and catalase.

RESULTS

Oral administration of aqPDS significantly ameliorated the elevated levels of glucose (248 ± 42 versus 508 ± 60 mg/dl), urea (32 ± 3.3 versus 48.3 ± 5.6 mg/dl), creatinine (2.2 ± 0.35 versus 3.8 ± 0.37 mg/dl), ALT (29.6 ± 3.9 versus 46.4 ± 5.9 IU/l), and AST (73.3 ± 13 versus 127.8 ± 18.7 IU/l) compared with the untreated diabetic rats. In addition to significant augmentation in the activities of antioxidant enzymes, there was reduction in TBARS and NO levels and improvement of histopathological architecture of the liver and kidney of diabetic rats.

DISCUSSION AND CONCLUSION

The aqPDS showed potential protective effects against early diabetic complications of both liver and kidney. This effect may be explained by the antioxidant and free radical scavenging capabilities of P. dactylifera seeds.

Nigella sativa and thymoquinone suppress cyclooxygenase-2 and oxidative stress in pancreatic tissue of streptozotocin-induced diabetic rats

OBJECTIVE

The aim of this study was to investigate the effect of Nigella sativa and thymoquinone (TQ) on oxidative stress, cyclooxygenase-2 (COX-2), and intracellular adhesion molecule-1 mRNA expression in the pancreas of streptozotocin (STZ)-induced diabetic rats as a model of type 1 diabetes.

METHODS

Five experimental groups including control group, STZ-induced diabetic group, aqueous extract diabetic treated group, oil diabetic treated group, and TQ diabetic treated group were used to obtain the pancreatic tissue samples and serum for investigation.

RESULTS

A significant increase in COX-2 mRNA expression was detected in STZ-induced diabetic group after 10 days of diabetes induction indicating an important role of the enzyme COX-2 in the inflammation accompanying STZ diabetes in contrast to that detected for intracellular adhesion molecule-1. Treatment of STZ diabetic rats with N. sativa aqueous extract and TQ significantly suppressed the expression of COX-2 enzyme in the pancreatic tissue. Nigella sativa and TQ treatment also suppressed pancreatic tissue lipid peroxidation malondialdehyde levels and increased the level of superoxide dismutase antioxidant enzyme correlated with the decrease in COX-2 mRNA expression.

CONCLUSIONS

Results obtained in this study support a potential role for N. sativa and TQ in ameliorating inflammation during diabetes and preserving β cells.

PTGS-2-PTGER2/4 signaling pathway partially protects from diabetogenic toxicity of streptozotocin in mice

Prostanoids are suggested to participate in diabetes pathology, but their roles are controversially discussed. The purpose of the current study was to examine the role of cyclooxygenase (prostaglandin synthase [PTGS]) enzymes and prostaglandin (PG) E(2) signaling pathways in streptozotocin (STZ)-induced type 1 diabetes. Blood glucose, insulin, and survival rate were studied in mice with targeted disruption of the genes for PTGS and PGE receptors (PTGERs). PGE(2) was found as the main prostanoid formed by the pancreas. Contrarily to PTGS-1, deficiency of PTGS-2 activity significantly amplified STZ effect, causing dramatic loss of insulin production and rise in blood glucose and death rate. STZ metabolism was unaffected by PTGS deficiency. Diabetogenicity of STZ in PTGER1(-/-), PTGER2(-/-), PTGER3(-/-), and PTGER4(-/-) mice was comparable to control mice. In striking contrast, combined knockout of PTGER2 and PTGER4 by blocking PTGER4 in PTGER2(-/-) mice strongly enhanced STZ pathology. Treatment of PTGS-2(-/-) and wild-type mice with PTGER2/PTGER4 agonists partially protected against STZ-induced diabetes and restored β-cell function. Our data uncover a previously unrecognized protective role of PTGS-2-derived PGE(2) in STZ-induced diabetes mediated by the receptor types PTGER2 and PTGER4. These findings offer the possibility to intervene in early progression of type 1 diabetes by using PTGER-selective agonists.

Gene expression changes in human islets exposed to type 1 diabetic serum

A major obstacle to the success of islet cell transplantation as a standard treatment for labile type 1 diabetes mellitus is the immediate loss of up to 70% of the transplanted islet mass. Activation of the complement cascade and coagulation factors has been implicated in initiating the destruction of the islet graft. In this study, we analyzed the gene expression changes in islet cells following exposure to type 1 diabetes mellitus serum (T1DM). Isolated human pancreatic islet cells were cultured for 2 d to stabilize islet cell gene expression. Cultured islets were divided into three groups for treatment as follows: group 1 was treated with autologous donor serum, while groups two and three were treated with sera from ABO-matched allogeneic donors or autoantibody positive type 1 diabetic patient, respectively. Complement was detected using anti-C3 FITC and CH50 assay. Islet gene expression was analyzed using Illumina micro-array technology. Results were confirmed using real-time PCR. Immunofluorescent imaging demonstrated complement deposition only in the T1DM condition. Gene array and class prediction analysis generated a list of 50 genes that were able to predict the effect of T1DM serum on islets. Quantitative PCR corroborated microarray results. Both techniques demonstrated upregulation of MMP9 (243%), IL-1β (255%), IL-11 (220%), IL-12A (132%), RAD (343%) and a concomitant downregulation of IL-1RN (64%) in islets treated with T1DM serum. Islets treated with T1DM serum overexpressed genes associated with angiogenesis while decreasing transcription of genes that protect islets from inflammatory cytokines and reactive oxygen species.

Immunomodulatory role of Ocimum gratissimum and ascorbic acid against nicotine-induced murine peritoneal macrophages in vitro

The aim of this present study was to evaluate the immune functions and immune responses in nicotine-induced (10 mM) macrophages and concurrently establish the immunomodulatory role of aqueous extract of Ocimum gratissimum (Ae-Og) and ascorbic acid. In this study, nitrite generations and some phenotype functions by macrophages were studied. Beside that, release of Th1 cytokines (TNF-α, IL-12) and Th2 cytokines (IL-10, TGF-β) was measured by ELISA, and the expression of these cytokines at mRNA level was analyzed by real-time PCR. Ae-Og, at a dose of 10 μg/mL, significantly reduced the nicotine-induced NO generation and iNOSII expression. Similar kinds of response were observed with supplementation of ascorbic acid (0.01 mM). The administration of Ae-Og and ascorbic acid increased the decreased adherence, chemotaxis, phagocytosis, and intracellular killing of bacteria in nicotine-treated macrophages. Ae-Og and ascorbic acid were found to protect the murine peritoneal macrophages through downregulation of Th1 cytokines in nicotine-treated macrophages with concurrent activation of Th2 responses. These findings strongly enhanced our understanding of the molecular mechanism leading to nicotine-induced suppression of immune functions and provide additional rationale for application of anti-inflammatory therapeutic approaches by O. gratissimum and ascorbic acid for different inflammatory disease prevention and treatment during nicotine toxicity.

Rosiglitazone protects diabetic rats from liver destruction

AIMS

To investigate whether rosiglitazone (ROS) protects diabetic rats from destructive changes in the liver.

METHODS

Twenty-four Sprague Dawley rats were randomly divided into 3 groups: control (NC) group (no.=8), streptozocin (STZ)-treated diabetic (DM) group (no.=8), and STZ+ROStreated diabetic (RSG) group (no.=8). After 8 weeks, the liver structure was observed by light microscopy and transmission electron microscopy. Apoptosis was detected by TUNEL, and apoptosis index was calculated. The Fas ligand (FasL) mRNA expression of apoptosis-promoting gene and cyclooxygenase- 2 (COX-2) mRNA in the liver were detected by RTPCR. COX-2 protein in the liver was tested via immunohistochemical staining.

RESULTS

Compared to NC group, DM group showed a visible fatty degeneration and inflammatory cell infiltration in the liver under microscopy. Obvious hepatocyte swelling with atrophic mitochondria was observed, and the central zone of cholangiole was severely outstretched. Meanwhile, in RSG group, the hepatocyte steatosis and inflammatory cell infiltration decreased, and the hepatic ultra-structure was markedly improved. Hepatocyte apoptosis (p<0.05) and the expression levels for hepatic COX-2 mRNA (p<0.05), FasL mRNA (p<0.01), and COX-2 protein (p<0.05) were higher in DM group compared to the NC group, while the expression level of hepatic COX-2 mRNA (p<0.05), FasL mRNA (p<0.01), COX-2 protein (p<0.05), and hepatocyte apoptosis (p<0.05) in RSG group were decreased compared to DM group.

CONCLUSION

Diabetes causes severe liver injury and ROS can protect diabetic rats from liver destruction, which may be related to inhibition of the expression of COX-2 and the hepatocyte apoptosis induced by FasL gene over expression.

Comparative study of the binding characteristics to and inhibitory potencies towards PARP and in vivo antidiabetogenic potencies of taurine, 3-aminobenzamide and nicotinamide

BACKGROUND

Poly(ADP-ribose) is a NAD+-requiring, DNA-repairing, enzyme playing a central role in pancreatic beta-cell death and in the development of endothelial dysfunction in humans and experimental animals. PARP activation is also relevant to the development of complications of diabetes. Hence, agents capable of inhibiting PARP may be useful in preventing the development of diabetes and in slowing down complications of diabetes.

METHODS

PARP inhibition was assessed with a colorimetric assay kit. Molecular docking studies on the active site of PARP were conducted using the crystalline structure of the enzyme available as Protein Data Bank Identification No. 1UK1. Type 2 diabetes was induced in male Sprague-Dawley rats with streptozotocin (STZ, 60 mg/kg, i.p.). The test compounds (3-aminobenzamide = 3-AB, nicotinamide = NIC, taurine = TAU) were given by the i.p. route 45 min before STZ at 2.4 mM/kg (all three compounds) or 1.2 and 3.6 mM/kg (only NIC and TAU). Blood samples were collected at 24 hr after STZ and processed for their plasma. The plasma samples were used to measure glucose, insulin, cholesterol, triglycerides, malondialdehyde, nitric oxide, and glutathione levels using reported methods.

RESULTS

3-AB, NIC and TAU were able to inhibit PARP, with the inhibitory potency order being 3-AB>NIC> or =TAU. Molecular docking studies at the active site of PARP showed 3-AB and NIC to interact with the binding site for the nicotinamide moiety of NAD+ and TAU to interact with the binding site for the adenine moiety of NAD+. While STZ-induced diabetes elevated all the experimental parameters examined and lowered the insulin output, a pretreatment with 3-AB, NIC or TAU reversed these trends to a significant extent. At a dose of 2.4 mm/kg, the protective effect decreased in the approximate order 3-AB>NIC> or =TAU. The attenuating actions of both NIC and TAU were dose-related except for the plasma lipids since NIC was without a significant effect at all doses tested.

CONCLUSIONS

At equal molar doses, 3-AB was generally more potent than either TAU or NIC as an antidiabetogenic agent, but the differences were not as dramatic as would have been predicted from their differences in PARP inhibitory potencies. NIC and TAU demonstrated dose-related effects, which in the case of TAU were only evident at doses > or =2.4 mM/kg. The present results also suggest that in the case of NIC and TAU an increase in dose will enhance the magnitude of their attenuating actions on diabetes-related biochemical alterations to that achieved with a stronger PARP inhibitor such as 3-AB. Hence, dosing will play a critical role in clinical studies assessing the merits of NIC and TAU as diabetes-preventing agents.

Contribution of type 1 diabetes to rat liver dysfunction and cellular damage via activation of NOS, PARP, IkappaBalpha/NF-kappaB, MAPKs, and mitochondria-dependent pathways: Prophylactic role of arjunolic acid

Diabetic mellitus, a chronic metabolic disorder, is one of the most important health problems in the world, especially in developing countries. Our earlier investigations reported the beneficial action of arjunolic acid (AA) against streptozotocin-mediated type 1 hyperglycemia. We have demonstrated that AA possesses protective roles against drug- and chemical- (environmental toxins) induced hepatotoxicity. Liver is the main organ of detoxification. The purpose of this study was to explore whether AA plays any protective role against hyperglycemic hepatic dysfunctions and, if so, what molecular pathways it utilizes for the mechanism of its protective action. In experimental rats, type 1 hyperglycemia was induced by streptozotocin. AA was administered orally at a dose of 20mg/kg body wt both before and after diabetic induction. An insulin-treated group was included in the study as a positive control for type 1 diabetes. Hyperglycemia caused a loss in body weight, reduction in serum insulin level, and increased formation of HbA(1C) as well as advanced glycation end products (AGEs). Elevated levels of serum ALT and ALP, increased production of ROS and RNS, increased lipid peroxidation, increased 8-OHdG/2-dG ratio, and decreased GSH content and cellular antioxidant defense established the hyperglycemic liver dysfunction. Activation of iNOS, IkappaBalpha/NF-kappaB, and MAPK pathways as well as signals from mitochondria were found to be involved in initiating apoptotic cell death. Hyperglycemia caused overexpression of PARP, reduction in intracellular NAD as well as ATP level, and increased DNA fragmentation in the liver tissue of the diabetic animals. Results of immunofluorescence (using anti-caspase-3 and anti-Apaf-1 antibodies), DAPI/PI staining, and DNA ladder formation and information obtained from FACS analysis confirmed the apoptotic cell death in diabetic liver tissue. Histological studies also support the experimental findings. AA treatment prevented or ameliorated the diabetic liver complications and apoptotic cell death. The effectiveness of AA in preventing the formation of ROS, RNS, HbA(1C), AGEs, and oxidative stress signaling cascades and protecting against PARP-mediated DNA fragmentation can speak about its potential uses for diabetic patients.

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.

Streptozotocin induced activation of oxidative stress responsive splenic cell signaling pathways: protective role of arjunolic acid

Present study investigates the beneficial role of arjunolic acid (AA) against the alteration in the cytokine levels and simultaneous activation of oxidative stress responsive signaling pathways in spleen under hyperglycemic condition. Diabetes was induced by injection of streptozotocin (STZ) (at a dose of 70 mg/kg body weight, injected in the tail vain). STZ administration elevated the levels of IL-2 as well as IFN-gamma and attenuated the level of TNF-alpha in the sera of diabetic animals. In addition, hyperglycemia is also associated with the increased production of intracellular reactive intermediates resulting with the elevation in lipid peroxidation, protein carbonylation and reduction in intracellular antioxidant defense. Investigating the oxidative stress responsive cell signaling pathways, increased expressions (immunoreactive concentrations) of phosphorylated p65 as well as its inhibitor protein phospho IkappaBalpha and phosphorylated mitogen activated protein kinases (MAPKs) have been observed in diabetic spleen tissue. Studies on isolated splenocytes revealed that hyperglycemia caused disruption of mitochondrial membrane potential, elevation in the concentration of cytosolic cytochrome c as well as activation of caspase 3 leading to apoptotic cell death. Histological examination revealed that diabetic induction depleted the white pulp scoring which is in agreement with the reduced immunological response. Treatment with AA prevented the hyperglycemia and its associated pathogenesis in spleen tissue. Results suggest that AA might act as an anti-diabetic and immunomodulatory agent against hyperglycemia.

Diabetic GK/Par rat beta-cells are spontaneously protected against H2O2-triggered apoptosis. A cAMP-dependent adaptive response

The alteration of the beta-cell population in the Goto-Kakizaki rat (GK/Par line), a model of spontaneous type 2 diabetes, has been ascribed to significantly decreased beta-cell replication and neogenesis, while beta-cell apoptosis is surprisingly not enhanced and remains in the normal range. To gain insight into the mechanisms by which those beta-cells are protected from death, we studied ex vivo the apoptotic activity and the expression of a large set of pro/antiapoptotic and pro/antioxidant genes in GK/Par islet cells. This was done in vitro in freshly isolated islets as well as in response to culture conditions and calibrated reactive oxygen species (ROS) exposure (i.e., H2O2). We also investigated the intracellular mechanisms of the diabetic beta-cell response to ROS, the role if any of the intracellular cAMP metabolism, and finally the kinetic of ROS response, taking advantage of the GK/Par rat normoglycemia until weaning. Our results show that the peculiar GK/Par beta-cell phenotype was correlated with an increased expression of a large panel of antioxidant genes as well as pro/antiapoptotic genes. We demonstrate that such combination confers resistance to cytotoxic H2O2 exposure in vitro, raising the possibility that at least some of the activated stress/defense genes have protective effects against H2O2-triggered beta-cell death. We also present some evidence that the GK/Par beta-cell resistance to H2O2 is at least partly cAMP dependent. Finally, we show that such a phenotype is not innate but is spontaneously acquired after diabetes onset as the result of an adaptive response to the diabetic environment.

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

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

Upregulation of endogenous glutathione system by 3H-1,2-dithiole-3-thione in pancreatic RINm5F beta-cells as a novel strategy for protecting against oxidative beta-cell injury

This study was undertaken to investigate the inducibility of glutathione (GSH), glutathione reductase (GR) and glutathione peroxidase (GPx) by 3H-1,2-dithiole-3-thione (D3T) in beta-cells, and the resultant cytoprotection against oxidant injury. Incubation of the insulin-secreting RINm5F cells with D3T led to significant induction of GSH, GR and GPx. D3T-mediated induction of GSH was abolished by buthionine sulfoximine (BSO), suggesting a critical involvement of gamma-glutamylcysteine ligase (gammaGCL). Consistently, incubation of RINm5F cells with D3T resulted in increased expression of gammaGCL protein and mRNA. Pretreatment of RINm5F cells with D3T provided remarkable protection against oxidant-elicited cytotoxicity. On the other hand, depletion of cellular GSH by BSO sensitized RINm5F cells to oxidant injury. Furthermore, cotreatment of RINm5F cells with BSO to reverse D3T-mediated GSH induction abolished the cytoprotective effects of D3T on oxidant injury. Taken together, this study demonstrates that upregulation of glutathione system by D3T is effective for protecting against oxidative beta-cell injury.

Early low protein diet aggravates unbalance between antioxidant enzymes leading to islet dysfunction

BACKGROUND

Islets from adult rat possess weak antioxidant defense leading to unbalance between superoxide dismutase (SOD) and hydrogen peroxide-inactivating enzymatic activities, catalase (CAT) and glutathione peroxidase (GPX) rending them susceptible to oxidative stress. We have shown that this vulnerability is influenced by maternal diet during gestation and lactation.

METHODOLOGY/PRINCIPAL FINDINGS

The present study investigated if low antioxidant activity in islets is already observed at birth and if maternal protein restriction influences the development of islet antioxidant defenses. Rats were fed a control diet (C group) or a low protein diet during gestation (LP) or until weaning (LPT), after which offspring received the control diet. We found that antioxidant enzymatic activities varied with age. At birth and after weaning, normal islets possessed an efficient GPX activity. However, the antioxidant capacity decreased thereafter increasing the potential vulnerability to oxidative stress. Maternal protein malnutrition changed the antioxidant enzymatic activities in islets of the progeny. At 3 months, SOD activity was increased in LP and LPT islets with no concomitant activation of CAT and GPX. This unbalance could lead to higher hydrogen peroxide production, which may concur to oxidative stress causing defective insulin gene expression due to modification of critical factors that modulate the insulin promoter. We found indeed that insulin mRNA level was reduced in both groups of malnourished offspring compared to controls. Analyzing the expression of such critical factors, we found that c-Myc expression was strongly increased in islets from both protein-restricted groups compared to controls.

CONCLUSION AND SIGNIFICANCE

Modification in antioxidant activity by maternal low protein diet could predispose to pancreatic islet dysfunction later in life and provide new insights to define a molecular mechanism responsible for intrauterine programming of endocrine pancreas.

Involvement of inducible nitric oxide synthase in hydroxyl radical-mediated lipid peroxidation in streptozotocin-induced diabetes

Free radical production is implicated in the pathogenesis of diabetes mellitus, where several pathways and different mechanisms were suggested in the pathophysiology of the complications. In this study, we used electron paramagnetic resonance (EPR) spectroscopy combined with in vivo spin-trapping techniques to investigate the sources and mechanisms of free radical formation in streptozotocin-induced diabetic rats. Free radical production was directly detected in the diabetic bile, which correlated with lipid peroxidation in the liver and kidney. EPR spectra showed the trapping of a lipid-derived radical. Such radicals were demonstrated to be induced by hydroxyl radical through isotope-labeling experiments. Multiple enzymes and metabolic pathways were examined as the potential source of the hydroxyl radicals using specific inhibitors. No xanthine oxidase, cytochrome P450s, the Fenton reaction, or macrophage activation were required for the production of radical adducts. Interestingly, inducible nitric oxide synthase (iNOS) (apparently uncoupled) was identified as the major source of radical generation. The specific iNOS inhibitor 1400W as well as L-arginine pretreatment reduced the EPR signals to baseline levels, implicating peroxynitrite as the source of hydroxyl radical production. Applying immunological techniques, we localized iNOS overexpression in the liver and kidney of diabetic animals, which was closely correlated with the lipid radical generation and 4-hydroxynonenal-adducted protein formation, indicating lipid peroxidation. In addition, protein tyrosine nitration occurred in the diabetic target organs. Taken together, our studies support inducible nitric oxide synthase as a significant source of EPR-detectable reactive intermediates, which leads to lipid peroxidation and may contribute to disease progression as well.

N-acetylcysteine derivative inhibits CD40-dependent proinflammatory properties of human pancreatic duct cells

OBJECTIVES

We recently observed that duct cells constitutively express CD40, a membrane molecule whose engagement results in duct cell activation and proinflammatory cytokine secretion. This observation suggests a potential role of this pathway in the pathogenesis of type 1 diabetes, islet graft rejection, or acute pancreatitis. In this article, we investigated whether a salt derivative of N-acetyl-L-cysteine, Nacystelyn, could modulate CD40 expression on duct cells and the response of activated duct cells to CD40 engagement.

METHODS

We assessed the effects of Nacystelyn on CD40 expression and function in human caucasian pancreatic adenocarcinoma, ATCC n degrees THB-80 (CAPAN-2) cells, a human pancreatic duct cell line. CD40 expression was analyzed by flow cytometry. To assess CAPAN-2 cell responses to CD40 engagement, we looked at nuclear factor-kappaB transcription factor activation using enzyme-linked immunosorbent assay and electrophoretic mobility shift assay and cytokine mRNA levels by quantitative real-time reverse transcriptase polymerase chain reaction.

RESULTS

We observed that Nacystelyn dose-dependently inhibited CD40 expression on CAPAN-2 cells as well as CD40-induced nuclear factor kappaB activation and proinflammatory cytokines up-regulation.

CONCLUSIONS

Our data suggest that Nacystelyn could be considered as a useful tool to prevent immune and inflammatory responses in pancreatic disorders by interfering with the CD40 pathway in pancreatic duct cells.

Reactive oxygen species-mediated pancreatic beta-cell death is regulated by interactions between stress-activated protein kinases, p38 and c-Jun N-terminal kinase, and mitogen-activated protein kinase phosphatases

Pancreatic beta-cells are susceptible to reactive oxygen species (ROS), which are known to be generated by high or low glucose (LG), hypoxic, or cytokine-producing conditions. When we cultured mouse beta-cell-derived MIN6 cells in a LG condition, we detected a significant generation of ROS, including hydrogen peroxide, which was comparable to the ROS production in hypoxic or cytokine-treated conditions. ROS accumulation induced by the LG culture led to cell death, which was prevented by the ROS scavengers N-acetylcysteine and manganese(III)tetrakis(4-benzoic acid) porphyrin. We next investigated the mechanism of stress-activated protein kinases (SAPKs), c-jun N-terminal kinase (JNK) and p38, in ROS-induced MIN6 cell death. Activation of p38 occurred immediately after the LG culture, whereas JNK activation increased slowly 8 h later. Adenoviral p38 expression decreased MIN6 cell death, whereas the JNK expression increased it. Consistently, blocking p38 activation by inhibitors increased beta-cell death, whereas JNK inhibitors decreased it. We then examined the role of MAPK phosphatases (MKPs) specific for stress-activated protein kinases in beta-cell death. We found that MKP-1 presented an increase in its oxidized product after the LG culture. ROS scavengers prevented the appearance of this oxidized product and JNK activation. Thus, ROS-induced MKP inactivation causes sustained activation of JNK, which contributes to beta-cell death. Adenoviral overexpression of MKP-1 and MKP-7 prevented the phosphorylation of JNK at 36 h after the LG culture, and decreased MIN6 beta-cell death. We suggest that beta-cell death is regulated by interactions between JNK and its specific MKPs.

Effects of flavonoids on the expression of the pro-inflammatory response in human monocytes induced by ligation of the receptor for AGEs

Increasing evidence has shown advanced glycation end products (AGEs) receptor ligation (RAGE) to be an important part of complex interactions of the oxidative stress and pro-inflammatory responses. In this study, flavonoids were used to monitor the protective effects against the oxidative damage and inflammation mediated by AGEs in human monocytes. S100B (RAGE ligand) treatment in human THP-1 monocytic cells (THP-1) significantly increased gene expression of the pro-inflammatory cytokines TNF-alpha and IL-1beta; chemokines MCP-1 and IP-10; adhesion factors platelet endothelial cell adhesion molecule (PECAM-1) and beta2-integrin; and pro-inflammatory cyclooxygenase-2 (COX-2). S100B treatment with quercetin and catechin in THP-1 cells had inhibitory effects on the expression of pro-inflammatory genes and protein levels. Quercetin and catechin could regulate S100B-activated oxidant stress-sensitive pathways through blocking p47phox protein expression. Treatment with quercetin and catechin could eliminate reactive oxygen species (ROS) to reduce oxidative stress stimulated by S100B in THP-1 cells. Quercetin and catechin also showed different regulatory abilities on mitogen-activated protein kinase (MAPK) signaling pathways by inhibiting protein expression in S100B-stimulated inflammatory responses in THP-1 cells. This study suggests that quercetin and catechin may be of benefit for diabetic vascular complications due to its antioxidant abilities against AGE-mediated oxidative stress through oxidative stress-sensitive and oxidative stress-responsive signaling pathways, which lead to inflammation in human monocytes.

Involvement of oxidative stress in the pathogenesis of diabetes

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

Diabetes-altered gene expression in rat skeletal muscle corrected by oral administration of vanadyl sulfate

Treatment with vanadium, a representative of a class of antidiabetic compounds, alleviates diabetic hyperglycemia and hyperlipidemia. Oral administration of vanadium compounds in animal models and humans does not cause clinical symptoms of hypoglycemia, a common problem for diabetic patients with insulin treatment. Gene expression, using Affymetrix arrays, was examined in muscle from streptozotocin-induced diabetic and normal rats in the presence or absence of oral vanadyl sulfate treatment. This treatment affected normal rats differently from diabetic rats, as demonstrated by two-way ANOVA of the full array data. Diabetes altered the expression of 133 genes, and the expression of 30% of these genes dysregulated in diabetes was normalized by vanadyl sulfate treatment. For those genes, the ratio of expression in normal animals to the expression in diabetic animals showed a strong negative correlation with the ratio of expression in diabetic animals to the expression in diabetic animals treated with vanadyl sulfate ( P = −0.85). The genes identified belong to six major metabolic functional groups: lipid metabolism, oxidative stress, muscle structure, protein breakdown and biosynthesis, the complement system, and signal transduction. The identification of oxidative stress genes, coupled with the known oxidative chemistry of vanadium, implicates reactive oxygen species in the action of this class of compounds. These results imply that early transition metals or compounds formed from their chemical interactions with other metabolites may act as general transcription modulators, a role not usually associated with this class of compounds.

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

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

Increased oxidative stress and oxidative damage associated with chronic bacterial prostatitis

AIM

To investigate whether chronic bacterial prostatitis might increase oxidative stress and oxidative damage in chronic bacterial prostatitis patients (CBPP), and to explore its possible mechanism.

METHODS

Enrolled in a case-control study were 70 randomly sampled CBPP and 70 randomly sampled healthy adult volunteers (HAV), on whom plasma nitric oxide (NO), vitamin C (VC), vitamin E (VE) and beta-carotene (beta-CAR) level, erythrocyte malondialdehyde (MDA) level, as well as erythrocyte superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) activities were determined by spectrophotometry.

RESULTS

Compared with the HAV group, values of plasma NO and erythrocyte MDA in the CBPP group were significantly increased (P < 0.001); those of plasma VC, VE and beta-CAR as well as erythrocyte SOD, CAT and GPX activities in the CBPP group were significantly decreased (P < 0.001). Findings from partial correlation for the 70 CBPP showed that with prolonged course of disease, values of NO and MDA were gradually increased (P < 0.001), and those of VC, VE, beta-CAR, SOD, CAT and GPX were gradually decreased (P < 0.05-0.001). The findings from stepwise regression for the 70 CBPP suggested that the model was Y = -13.2077 + 0.1894MDA + 0.0415NO - 0.1999GPX, F = 18.2047, P < 0.001, r = 0.6729, P < 0.001.

CONCLUSION

The findings suggest that there exist increased oxidative stress and oxidative damage induced by chronic bacterial prostatitis in the patients, and such phenomenon was closely related to the course of disease.

Impact of plastic adhesion in vitro on analysis of Th1 and Th2 cytokines and immune cell distribution from mice with multiple low-dose streptozotocin-induced diabetes

Cytokines produced by Th1 or Th2 cells have been postulated to be important in the development of type 1 diabetes in humans and animal models, such as murine multiple low-dose streptozotocin (MLDSTZ)-induced diabetes. The aim of this study was to investigate cytokine production with or without in vitro depletion of plastic adherent cells from spleens isolated after MLDSTZ treatment. Spleen cells were prepared on day 14 from MLDSTZ- and saline-treated mice and divided into two fractions. One cell fraction was depleted of adherent cells by plastic adherence and the other was not. Both cell fractions were analysed by FACS for the distribution of immune cells. In other experiments, the cells were cultured for 48 h with concanavalin A stimulation. Supernatant samples were analysed by ELISA for TNFalpha, IFNgamma and IL-10 production. Either before or after the 48-h culture cytokine mRNA expression was determined by RT-PCR. Plastic adhesion decreased the macrophage numbers by approximately 30% and CD4(+)CD25(+) cells by about 60%. This was accompanied by increased medium levels of TNFalpha, IFNgamma and IL-10, which suggest that either CD4(+)CD25(+) cells, macrophages, or both, down-regulate production of both Th1 and certain Th2 cytokines. Depletion of adherent cells also decreased IL-4 mRNA amounts. MLDSTZ treatment increased the production of Th1 cytokines mainly at the protein level, and IL-10 mainly at the mRNA level. This indicates a sustained increase in Th1 production after MLDSTZ treatment and an increase in IL-10 that might reflect an attempt to counteract the MLDSTZ-induced immune damage. Plastic adhesion during cell preparation may affect the relative distribution of certain immune cells.

Mechanisms underlying resistance of pancreatic islets from ALR/Lt mice to cytokine-induced destruction

Nuclear and mitochondrial genomes combine in ALR/Lt mice to produce systemically elevated defenses against free radical damage, rendering these mice resistant to immune-mediated pancreatic islet destruction. We analyzed the mechanism whereby isolated islets from ALR mice resisted proinflammatory stress mediated by combined cytokines (IL-1beta, TNF-alpha, and IFN-gamma) in vitro. Such damage entails both superoxide and NO radical generation, as well as peroxynitrite, resulting from their combination. In contrast to islets from other mouse strains, ALR islets expressed constitutively higher glutathione reductase, glutathione peroxidase, and higher ratios of reduced to oxidized glutathione. Following incubation with combined cytokines, islets from control strains produced significantly higher levels of hydrogen peroxide and NO than islets from ALR mice. Nitrotyrosine was generated in NOD and C3H/HeJ islets but not by ALR islets. Western blot analysis showed that combined cytokines up-regulated the NF-kappaB inducible NO synthase in NOD-Rag and C3H/HeJ islets but not in ALR islets. This inability of cytokine-treated ALR islets to up-regulate inducible NO synthase and produce NO correlated both with reduced kinetics of IkappaB degradation and with markedly suppressed NF-kappaB p65 nuclear translocation. Hence, ALR/Lt islets resist cytokine-induced diabetogenic stress through enhanced dissipation and/or suppressed formation of reactive oxygen and nitrogen species, impaired IkappaB degradation, and blunted NF-kappaB activation. Nitrotyrosylation of beta cell proteins may generate neoantigens; therefore, resistance of ALR islets to nitrotyrosine formation may, in part, explain why ALR mice are resistant to type 1 diabetes when reconstituted with a NOD immune system.

MnSOD and catalase transgenes demonstrate that protection of islets from oxidative stress does not alter cytokine toxicity

Reactive oxygen species (ROS) and nitric oxide (NO) are proposed mediators of cytokine-induced beta-cell destruction in type 1 diabetes. We produced transgenic mice with increased beta-cell expression of manganese superoxide dismutase (MnSOD) and catalase. Expression of these antioxidants increased beta-cell ROS scavenging and improved beta-cell survival after treatment with different sources of ROS. MnSOD or catalase conferred protection against streptozotocin (STZ)-induced beta-cell injury. Coexpression of MnSOD and catalase provided synergistic protection against peroxynitrite and STZ. To determine the potential effect of these antioxidants on cytokine-induced toxicity, we exposed isolated islets to a cytokine mixture, including interleukin-1beta and interferon-gamma. Cytokine toxicity was measured as reduced metabolic activity after 6 days and reduced insulin secretion after 1 day. Cytokines increased ROS production, and both antioxidants were effective in reducing cytokine-induced ROS. However, MnSOD and/or catalase provided no protection against cytokine-induced injury. To understand this, the nuclear factor-kappaB (NF-kappaB) signaling cascade was investigated. Antioxidants reduced NF-kappaB activation by ROS, but none of the antioxidants altered activation by cytokines, as measured by inhibitor of kappaB phosphorylation, NF-kappaB translocation, inducible NO synthase activation, and NO production. Our data agree with previous reports that antioxidants benefit beta-cell survival against ROS damage, but they are not consistent with reports that antioxidants reduce cytokine toxicity. ROS appear to have no role in cytokine toxicity in primary beta-cells.

A biphasic role of nuclear transcription factor (NF)-κB in the islet β-cell apoptosis induced by interleukin (IL)-1β

IL-1beta is an important mediator in the pathogenesis of type 1 diabetes both in vivo and in vitro and it has been shown to induce islet beta-cell apoptosis. Most of the IL-1beta effects seem to be mediated by NF-kappaB transcription factor activation, but its role in the induction of islet beta-cell apoptosis has not yet been clarified. Taking advantage of the protease inhibitor TPCK (N-tosyl-L-phenylalanine chloromethyl ketone), which specifically inhibits the nuclear transcription factor NF-kappaB activation, we studied the role of NF-kappaB in the rIL-1beta treated rat pancreatic islets. Our results show that TPCK blocked rIL-1beta-mediated early increase of MnSOD activity and beta-cell defence/repair protein expression, suggesting a protective role for NF-kappaB at the beginning of IL-1beta treatment; but, in a second phase, NF-kappaB induces a sustained decrease of specific beta-cell proteins like insulin, GLUT-2 and PDX-1 with a concomitant increase of aspecific proteins and iNOS transcription. The appearance of iNOS expression correlates with increased levels of nitrite + nitrate levels and appearance of mitochondrial damage detected either at morphological and biochemical level. After 36 h of IL-1beta treatment islet beta-cells begin to undergo apoptosis. Since IL-1beta induction of apoptosis is completely prevented by TCPK treatment, this finding underscores the central role of NF-kappaB in this process. Thus, our results clearly indicate that NF-kappaB regulates MnSOD genes expression and MnSOD activity, which protects islet beta-cells by IL-1beta damage. Furthermore, when the IL-1beta stress impairs islet beta-cell function, NF-kappaB activation regulates the entrance of islet beta-cell into the cell death program.

Inhibitory effects of epicatechin on interleukin-1beta-induced inducible nitric oxide synthase expression in RINm5F cells and rat pancreatic islets by down-regulation of NF-kappaB activation

Cytokines that are released by infiltrating inflammatory cells around the pancreatic islets are involved in the pathogenesis of type 1 diabetes mellitus. Specifically, interleukin-1beta (IL-1beta) stimulates inducible nitric oxide synthase (iNOS) expression and nitric oxide overproduction, leading to the beta-cell damage. In activating this pathway, nuclear factor-kappaB (NF-kappaB) plays a crucial role, and many of the IL-1beta-sensitive genes contain NF-kappaB binding sites in their promoter regions. We have recently shown that epicatechin, which is a flavonoid, had a protective effect on pancreatic beta-cells in both streptozotocin-treated rats and islets. In the present study, the effects of epicatechin on IL-1beta-induced beta-cell damage were examined. RINm5F cells and islets were pretreated with epicatechin and next incubated with IL-1beta. The released nitrite, iNOS protein and mRNA expression levels were then measured. IkappaBalpha protein, nuclear translocation of NF-kappaB, and NF-kappaB DNA binding activity were also determined. Following the transient transfection of an iNOS promoter into the cells, the iNOS promoter activity was measured. ATP- or D-glucose-induced insulin release was measured in RINm5F cells and islets, respectively. Epicatechin significantly reduced IL-1beta-induced nitrite production, iNOS protein and mRNA expressions, and it also inhibited IL-1beta-induced IkappaBalpha protein degradation, NF-kappaB activation, and iNOS promoter activity. Epicatechin partly restored the IL-1beta-induced inhibition of insulin release. These results suggest that epicatechin inhibits the IL-1beta-induced iNOS expression by down-regulating NF-kappaB activation, and protecting beta-cells from IL-1beta.

CD40 expression on human pancreatic duct cells: role in nuclear factor-kappa B activation and production of pro-inflammatory cytokines

AIMS/HYPOTHESIS

Human pancreatic duct cells are closely associated with islet beta cells, and contaminate islet suspensions transplanted in Type 1 diabetes mellitus patients. Activated duct cells produce cytotoxic mediators and possibly contribute to the pathogenesis of Type 1 diabetes mellitus or islet graft rejection. As CD40 transduces activation signals involved in inflammatory and immune disorders, we investigated CD40 expression on duct cells and their response to CD40 engagement.

METHODS

CD40 expression on human pancreatic duct cells was analysed by flow cytometry and immunohistochemical analyses. To assess the function of CD40 expression on duct cells, activation of the transcription factor nuclear factor-kappa B was determined using electrophoretic mobility shift assay and ELISA. Cytokine mRNA levels were quantified by real-time RT-PCR, and protein levels by Luminex technology.

RESULTS

Isolated human pancreatic duct cells and Capan-2 cell lines were found to express constitutively CD40. The expression of CD40 on duct cells was confirmed in vivo on human normal and pathological pancreatic specimens. CD40 ligation on Capan-2 cells induced rapid nuclear factor-kappa B activation, and supershift assays demonstrated that p50/p65 heterodimers and p50/p50 homodimers were present in the activated complexes in the nucleus. This activation was accompanied by tumour necrosis factor-a and interleukin-1beta mRNA accumulation. Tumour necrosis factor-alpha protein secretion was confirmed in CD40-activated Capan-2 cells and in isolated human pancreatic duct cells.

CONCLUSIONS/INTERPRETATION

Interaction between activated T lymphocytes expressing CD40 ligand and duct cells expressing CD40 may contribute to the immune responses involved in Type 1 diabetes mellitus and islet graft rejection. Interfering with CD40-mediated duct cell activation could alleviate beta cell damage of immune origin.