Inhibition of nitric oxide generation affects the induction of diabetes by streptozocin in mice

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.

Transgenic Overexpression of Galectin-3 in Pancreatic β Cells Attenuates Hyperglycemia in Mice: Synergistic Antidiabetic Effect With Exogenous IL-33

Galectin-3 (Gal-3) has diverse roles in inflammatory and autoimmune diseases. There is evidence that Gal-3 plays a role in both type 1 and type 2 diabetes. While the role of Gal-3 expression in immune cells invading the pancreatic islets in the experimental model of type 1 diabetes mellitus has been already studied, the importance of the overexpression of Gal-3 in the target β cells is not defined. Therefore, we used multiple low doses of streptozotocin (MLD-STZ)-induced diabetes in C57Bl/6 mice to analyze the effect of transgenic (TG) overexpression of Gal-3 in β cells. Our results demonstrated that the overexpression of Gal-3 protected β cells from apoptosis and attenuated MLD-STZ-induced hyperglycemia, glycosuria, and ketonuria. The cellular analysis of pancreata and draining lymph nodes showed that Gal-3 overexpression significantly decreased the number of pro-inflammatory cells without affecting the presence of T-regulatory cells. As the application of exogenous interleukin 33 (IL-33) given from the beginning of MLD-STZ diabetes induction attenuates the development of disease, by increasing the presence of regulatory FoxP3+ ST2+ cells, we evaluated the potential synergistic effect of the exogenous IL-33 and TG overexpression of Gal-3 in β cells at the later stage of diabetogenesis. The addition of IL-33 potentiated the survival of β cells and attenuated diabetes even when administered later, after the onset of hyperglycemia (12-18 days), suggesting that protection from apoptosis and immunoregulation by IL-33 may attenuate type 1 diabetes.

Overexpression of Galectin 3 in Pancreatic β Cells Amplifies β-Cell Apoptosis and Islet Inflammation in Type-2 Diabetes in Mice

Aims/Hypothesis: Galectin 3 appears to play a proinflammatory role in several inflammatory and autoimmune diseases. Also, there is evidence that galectin 3 plays a role in both type-1 and type-2 diabetes. During obesity, hematopoietic cell-derived galectin 3 induces insulin resistance. While the role of galectin 3 expressed in islet-invading immune cells in both type-1 and type-2 diabetes has been studied, the importance of the expression of this molecule on the target pancreatic β cells has not been defined. Methods: To clarify the role of galectin 3 expression in β cells during obesity-induced diabetogenesis, we developed transgenic mice selectively overexpressing galectin 3 in β cells and tested their susceptibility to obesity-induced type-2 diabetes. Obesity was induced with a 16-week high-fat diet regime. Pancreatic β cells were tested for susceptibility to apoptosis induced by non-esterified fatty acids and cytokines as well as parameters of oxidative stress. Results: Our results demonstrated that overexpression of galectin 3 increases β-cell apoptosis in HFD conditions and increases the percentage of proinflammatory F4/80+ macrophages in islets that express galectin 3 and TLR4. In isolated islets, we have shown that galectin 3 overexpression increases cytokine and palmitate-triggered β-cell apoptosis and also increases NO2--induced oxidative stress of β cells. Also, in pancreatic lymph nodes, macrophages were shifted toward a proinflammatory TNF-α-producing phenotype. Conclusions/Interpretation: By complementary in vivo and in vitro approaches, we have shown that galectin 3-overexpression facilitates β-cell damage, enhances cytokine and palmitate-triggered β-cell apoptosis, and increases NO2--induced oxidative stress in β cells. Further, the results suggest that increased expression of galectin 3 in the pancreatic β cells affects the metabolism of glucose and glycoregulation in mice on a high-fat diet, affecting both fasting glycemic values and glycemia after glucose loading.

The protective effect of Satureja bachtiarica hydroalcoholic extract on streptozotocin-induced diabetes through modulating glucose transporter 2 and 4 expression and inhibiting oxidative stress

CONTEXT

Oxidative stress plays an important role in development of diabetes mellitus. Satureja bachtiarica Bunge (Lamiaceae) is a rich source of bioactive compounds with antioxidant properties.

OBJECTIVE

This study investigates the antidiabetic effect of hydroalcoholic extract of aerial parts of S. bachtiarica.

METHODS AND MATERIALS

Male Wistar rats were randomly divided into six groups (n = 8) including control (normal saline), diabetic [Streptozotocin (STZ)], intervention (STZ plus hydroalcoholic extract of S. bachtiarica at doses of 75, 150 and 250 mg/kg/d) and positive control (STZ plus captopril 50 mg/kg/d) groups. A single intraperitoneal (IP) injection of STZ (60 mg/kg) was used to induce diabetes and IP therapy with drugs was performed for four weeks.

RESULTS

In diabetic rats, serum total antioxidant capacity (TAC) decreased significantly, but glucose, alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyltransferase (GGT) and malondialdehyde (MDA) increased significantly as compared to the control (p < 0.05). Treatment with extract (250 mg/kg) caused a significant decline in serum glucose, GGT, ALT, AST and MDA as well as a significant increase in serum TAC (p < 0.05). During the intervention period, diabetic rats showed significant weight loss, but extract (250 mg/kg) treated rats did not show any weight loss. Extract (250 mg/kg) up-regulated GLUT2 expression and down-regulated GLUT4 expression in the liver (p < 0.05). S. bachtiarica extract at all dosage levels prevented STZ-induced histological damage of liver, kidney and pancreas.

DISCUSSION AND CONCLUSIONS

S. bachtiarica extract exhibits antidiabetic effects through modulation of oxidative stress and expression of GLUT2 and GLUT4.

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

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

Inhibitory effect and mechanism of mesenchymal stem cells on melanoma cells

PURPOSE

To explore the inhibitory effect and mechanism of MSCs on melanoma proliferation.

METHODS

The inhibitory effect of MSCs on melanoma A375 cells was detected by co-culture and conditioned medium (CM) experiments using MTT method. The cell cycle was analyzed by flow cytometry. Then, Western Blot experiment detected the expression of proteins related to NF-κB signaling in A375 cells. The expression of IL-1Ra in MSCs was proved by RT-PCR. The over-expression and silencing vector pcDNA3.1-EGFP-IL-1Ra and pGPH1-IL-1R were constructed and transfected into MSCs cells. After that, the changes of inhibitory effect and cell cycle from MSCs-S and MSCs-O CM on A375 cells were explored. The expression of proteins related to NF-κB signaling in A375 cells after MSCs-S or MSCs-O CM treatment was detected by Western Blot. MSCs, MSCs-S, or MSCs-O and A375 cells were co-injected into nude mice under the arms, the growth of tumor was observed, the frozen sections were made, and H&E staining of tumor tissue was performed.

RESULTS

The proliferation of A375 cells was inhibited and the cell cycle of A375 was arrested by MSCs. The expressions of cytokines related to NF-κB signaling were down-regulated. Over-expression and silence of Interleukin 1 receptor antagonist (IL-1Ra), specifically blocking activation of NF-κB signaling, indicated that inhibitory effect from MSCs was enhanced or weakened respectively, which suggested that IL-1Ra was involved in the inhibitory effect. In vivo, tumor initiation and growth were significantly inhibited when A375 cells were co-injected with MSCs into nude mice, which were related to the expression level of IL-1Ra.

CONCLUSION

MSCs could inhibit the proliferation and tumor initiation of melanoma A375 cells through NF-κB signaling. MSCs could secret IL-1Ra and inhibit expressions of NF-κB signaling-related factors of tumor cells, and cause cell cycle arrest in G1 phase.

Cytokines and Pancreatic β-Cell Apoptosis

The discovery 30 years ago that inflammatory cytokines cause a concentration, activity, and time-dependent bimodal response in pancreatic β-cell function and viability has been a game-changer in the fields of research directed at understanding inflammatory regulation of β-cell function and survival and the causes of β-cell failure and destruction in diabetes. Having until then been confined to the use of pathophysiologically irrelevant β-cell toxic chemicals as a model of β-cell death, researchers could now mimic endocrine and paracrine effects of the cytokine response in vitro by titrating concentrations in the low to the high picomolar-femtomolar range and vary exposure time for up to 14-16h to reproduce the acute regulatory effects of systemic inflammation on β-cell secretory responses, with a shift to inhibition at high picomolar concentrations or more than 16h of exposure to illustrate adverse effects of local, chronic islet inflammation. Since then, numerous studies have clarified how these bimodal responses depend on discrete signaling pathways. Most interest has been devoted to the proapoptotic response dependent upon mainly nuclear factor κ B and mitogen-activated protein kinase activation, leading to gene expressional changes, endoplasmic reticulum stress, and triggering of mitochondrial dysfunction. Preclinical studies have shown preventive effects of cytokine antagonism in animal models of diabetes, and clinical trials demonstrating proof of concept are emerging. The full clinical potential of anticytokine therapies has yet to be shown by testing the incremental effects of appropriate dosing, timing, and combinations of treatments. Due to the considerable translational importance of enhancing the precision, specificity, and safety of antiinflammatory treatments of diabetes, we review here the cellular, preclinical, and clinical evidence of which of the death pathways recently proposed in the Nomenclature Committee on Cell Death 2012 Recommendations are activated by inflammatory cytokines in the pancreatic β-cell to guide the identification of antidiabetic targets. Although there are still scarce human data, the cellular and preclinical studies point to the caspase-dependent intrinsic apoptosis pathway as the prime effector of inflammatory β-cell apoptosis.

Effect of Nitric Oxide Synthesis Blockade on the Morphology of Langerhans Islets in August and Wistar Rats with Acute Alloxan Diabetes

Alloxan diabetes was modeled in August rats with high activity of the NO system and in Wistar rats, and the effects of NO system blockade (by a course treatment with L-NNA) on Langerhans islet β cells were studied in 15 days. The toxic effects of diabetes on the rat β cells and islets were similar: the content of active β cells in the islets decreased to 15-20%, the number of islets to 24-29% of control. A course of L-NNA reduced the β cell and islet death, in August cells greater than in Wistar: the number of islets in August rats was restored to 81%, in Wistar rats to 60% of initial level; the activity of β cells remained at the control level in the former and 2-fold lower than in the control in the latter. It seems that a less pronounced protective effect of L-NNA in Wistar rats was explained by excessive reduction of NO level essential for β cell regeneration.

Nitric oxide-induced regulatory T cells inhibit Th17 but not Th1 cell differentiation and function

NO is a free radical with pleiotropic functions. We have shown earlier that NO induces a population of CD4(+)CD25(+)Foxp3(-) regulatory T cells (NO-Tregs) that suppress the functions of CD4(+)CD25(-) effector T cells in vitro and in vivo. We report in this study an unexpected finding that NO-Tregs suppressed Th17 but not Th1 cell differentiation and function. In contrast, natural Tregs (nTregs), which suppressed Th1 cells, failed to suppress Th17 cells. Consistent with this observation, NO-Tregs inhibited the expression of retinoic acid-related orphan receptor γt but not T-bet, whereas nTregs suppressed T-bet but not retinoic acid-related orphan receptor γt expression. The NO-Treg-mediated suppression of Th17 was partially cell contact-dependent and was associated with IL-10. In vivo, adoptively transferred NO-Tregs potently attenuated experimental autoimmune encephalomyelitis. The disease suppression was accompanied by a reduction of Th17, but not Th1 cells in the draining lymph nodes, and a decrease in the production of IL-17, but an increase in IL-10 synthesis. Our results therefore demonstrate the differential suppressive function between NO-Tregs and nTregs and indicate specialization of the regulatory mechanism of the immune system.

The good and bad effects of cysteine S-nitrosylation and tyrosine nitration upon insulin exocytosis: a balancing act

As understanding of the mechanisms driving and regulating insulin secretion from pancreatic beta cells grows, there is increasing and compelling evidence that nitric oxide (•NO) and other closely-related reactive nitrogen species (RNS) play important roles in this exocytic process. •NO and associated RNS, in particular peroxynitrite, possess the capability to effect signals across both intracellular and extracellular compartments in rapid fashion, affording extraordinary signaling potential. It is well established that nitric oxide signals through activation of guanylate cyclase-mediated production of cyclic GMP. The intricate intracellular redox environment, however, lends credence to the possibility that •NO and peroxynitrite could interact with a wider variety of biological targets, with two leading mechanisms involving 1) Snitrosylation of cysteine, and 2) nitration of tyrosine residues comprised within a variety of proteins. Efforts aimed at delineating the specific roles of •NO and peroxynitrite in regulated insulin secretion indicate that a highly-complex and nuanced system exists, with evidence that •NO and peroxynitrite can contribute in both positive and negative regulatory ways in beta cells. Furthermore, the ultimate biochemical outcome within beta cells, whether to compensate and recover from a given stress, or not, is likely a summation of contributory signals and redox status. Such seeming regulatory dichotomy provides ample opportunity for these mechanisms to serve both physiological and pathophysiologic roles in onset and progression of diabetes. This review focuses attention upon recent accumulating evidence pointing to roles for nitric oxide induced post-translational modifications in the normal regulation as well as the dysfunction of beta cell insulin exocytosis.

Interleukin-1 receptor antagonist (IL-1Ra) and IL-1Ra producing mesenchymal stem cells as modulators of diabetogenesis

The increase of pro-inflammatory cytokines and oxidative stress leads to beta-cell damage and promotes beta-cells apoptosis, in types I and II of diabetes mellitus. Therefore, blocking of pro-inflammatory cytokines should be an effective way for the treatment of diabetes mellitus. When IL-1 occupies its receptor, various pro-inflammatory events are initiated including the synthesis and releases of chemokines and these chemokines attract neutrophils, macrophages, and lymphocytes that cause tissue inflammation. IL-1Ra is a naturally occurring cytokine and is the inhibitor of IL-1. When IL-1Ra binds to the IL-1 receptor, binding of IL-1 is blocked by IL-1Ra and pro-inflammatory signal from IL-1 receptor is stopped. There are mounting evidences to suggest that anti-inflammatory IL-1Ra reduces the inflammatory effects of IL-1 and preserves cell function in both types of diabetes. Therefore, IL-1Ra maybe a new therapeutic agent for diabetes mellitus types I and II. Mesenchymal stem cells (MSCs) are self-renewable multipotent stromal cells that have immunomodulatory capacity. Recently, well characterized subpopulations of MSCs which express IL-1Ra have been described. IL-1Ra expressed by these MSCs effectively binds to IL-1 receptor and protects tissues from inflammation-induced injuries. It has been previously shown that bone marrow-derived MSC therapy could be considered for the treatment of diabetes mellitus type 1 and complications of diabetes mellitus. This review presents understanding of potential use of IL-1Ra and MSCs as modulators of diabetogenesis.

Macrophage migration inhibitory factor (MIF) is necessary for progression of autoimmune diabetes mellitus

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine of the innate immune system that plays a major role in the induction of immunoinflammatory responses. To examine the role of endogenous MIF in the pathogenesis of type 1 diabetes (TID) we evaluated the effects of administration of neutralizing anti-MIF antibodies to NOD mice with accelerated forms of diabetes induced by injection of cyclophosphamide or by transfer of diabetogenic spleen cells. Both accelerated forms of diabetes were markedly reduced by anti-MIF antibody. Furthermore, MIF-deficient (MIF(-/-)) mice were less susceptible to the induction of immunoinflammatory diabetes, insulitis and apoptosis within the endocrine pancreas by multiple low doses of streptozotocin (MLD-STZ) than genetically matched wild type (WT) mice. MIF deficiency resulted in lower proliferation and lymphocyte adhesion, as well as reduced production from the spleens and peritoneal cells of a variety of inflammatory mediators typically associated with development of the disease including IL-12, IL-23, TNF-alpha, and IL-1beta. Furthermore, MIF deletion affected the production of IL-18, TNF-alpha, IL-1beta, and iNOS in the islets of Langerhans. These data, along with the higher expression of IL-4 and TGF-beta observed in the periphery and in the pancreas of MLD-STZ-challenged MIF(-/-) mice as compared to WT controls suggest that MIF deficiency has induced an immune deviation towards protective type 2/3 response. These results suggest that MIF participates in T1D by controlling the functional activity of monocytes/macrophages and T cells and modulating their secretory capacity of pro- and anti-inflammatory molecules.

The radical scavenger edaravone counteracts diabetes in multiple low-dose streptozotocin-treated mice

Edaravone is a potent scavenger of hydroxyl radicals and attenuates oxidative damage-related neurodegenerative diseases. Previous studies suggest that oxidative stress plays a key role in the pathogenesis of diabetes. The present study examined the effect of edaravone on diabetes in multiple low-dose streptozotocin-treated mice. Mice treated with low-doses of streptozotocin for five consecutive days showed progressive hyperglycemia and an increased incidence of diabetes. Daily treatment with edaravone during the streptozotocin injections counteracted the multiple low-dose streptozotocin-induced hyperglycemia in a dose-dependent manner. Edaravone protected against the multiple low-dose streptozotocin-induced reduction in pancreatic insulin. The suppressive effects of edaravone were also observed when it was administered after the last injection of streptozotocin. Histochemical examination showed that multiple low-dose streptozotocin treatment caused mononuclear cell infiltration in pancreatic islets, followed by hyperglycemia, and that edaravone significantly inhibited the multiple low-dose streptozotocin-induced insulitis. Multiple low-dose streptozotocin treatment also increased the lipid peroxidation product thiobarbituric acid reactive substance in pancreatic tissues of mice, and this effect was completely inhibited by edaravone. These findings suggest that edaravone, even after streptozotocin treatment, counteracts the development of multiple low-dose streptozotocin-induced diabetes by scavenging free radicals, which are possible mediators of the immune destruction of islet beta cells.

Functional capacity of macrophages determines the induction of type 1 diabetes

Macrophages are potent immune regulators and are critical in the development and pathogenesis of autoimmune diabetes. They are said to be the first cell type to infiltrate the pancreatic islet, serve as antigen-presenting cells, and are important as effector cells during diabetogenesis. The article examines the role of macrophages in autoimmune diabetes with particular emphasis on the role of galectin-3, a beta-galactoside-binding lectin, and T1/ST2, an IL-1 receptor-like protein, both of which play significant roles in the immunomodulatory functions of macrophages. Multiple low-dose streptozotocin (MLD-STZ) induces infiltration of mononuclear cells in the islets of susceptible strains leading to insulitis. Deletion of the galectin-3 gene from C57BL/6 mice significantly attenuates this effect as evaluated by quantitative histology of mononuclear cells and loss of insulin-producing beta cells. In contrast, deletion of the ST2 gene enhanced insulitis after MLD-STZ treatment when compared with relatively resistant wild-type BALB/c mice. Thus, it appears that functional capacity of macrophages influences their participation in T helper (Th) 1-mediated autoimmunity and the development of autoimmune diabetogenesis.

Protein tyrosine nitration and poly(ADP-ribose) polymerase activation in N-methyl-N-nitro-N-nitrosoguanidine-treated thymocytes: implication for cytotoxicity

1-Methyl-3-nitro-1-nitrosoguanidine (MNNG) is a DNA alkylating agent. DNA alkylation by MNNG is known to trigger accelerated poly(ADP-ribose) metabolism. Various nitroso compounds release nitric oxide (NO). Therefore, we set out to investigate whether MNNG functions as NO donor and whether MNNG-derived NO or secondary NO metabolites such as peroxynitrite contribute to MNNG-induced cytotoxicity. MNNG in aqueous solutions resulted in time- and concentration-dependent NO release and nitrite/nitrate formation. Moreover, various proteins in MNNG-treated thymocytes were found to be nitrated, indicating that MNNG-derived NO may combine with cellular superoxide to form peroxynitrite, a nitrating agent. MNNG also caused DNA breakage and increased poly(ADP-ribose) polymerase activity and cytotoxicity in thymocytes. MNNG-induced DNA damage (measured by the comet assay) and thymocyte death (measured by propidium iodide uptake) was prevented by the PARP inhibitor PJ-34 and by glutathione (GSH) or N-acetylcysteine (NAC). The cytoprotection provided by PJ-34 against necrotic parameters was paralleled by increased outputs in apoptotic parameters (caspase activity, DNA laddering) indicating that PARP activation diverts apoptotic death toward necrosis. As MNNG-induced cytotoxicity showed many similarities to peroxynitrite-induced cell death, we tested whether peroxynitrite was responsible for at least part of the cytotoxicity induced by MNNG. Cell-permeable enzymic antioxidants (superoxide dismutase and catalase), the NO scavenger cPTIO or the peroxynitrite decomposition catalyst FP15 failed to inhibit MNNG-induced DNA breakage and cytotoxicity. In conclusion, MNNG induces tyrosine nitration in thymocytes. Furthermore, MNNG damages DNA by a radical mechanism that does not involve NO or peroxynitrite.

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

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

IL-23 leads to diabetes induction after subdiabetogenic treatment with multiple low doses of streptozotocin

IL-23, a proximal regulator of IL-17, may be a major driving force in the induction of autoimmune inflammation. We have used a model of subdiabetogenic treatment with multiple low doses of streptozotocin (MLD-STZ; 4 x 40 mg/kg body weight) in male C57BL/6 mice to study the effect of IL-23 on immune-mediated beta cell damage and the development of diabetes, as evaluated by blood glucose, quantitative histology, immunohistochemistry and expression of relevant cytokines in the islets. Ten daily injections of 400 ng IL-23, starting on the first day of MLD-STZ administration led to significant and sustained hyperglycemia along with weight loss compared with controls (no IL-23), and a significant increase in the number of infiltrating cells, a lower insulin content, enhanced apoptosis, expression of IFN-gamma and IL-17 (not seen in the controls) and a significant increase in the expression of TNF-alpha and IL-18 in the pancreatic islets. IL-23 treatment started 5 days prior to MLD-STZ administration had no effect on diabetogenesis or cytokines expression in the pancreatic islets. We provide the first evidence in an animal model that IL-23 is involved in the development of type-1 diabetes, by inducing IL-17 and possibly IFN-gamma production in the target tissue.

Effects of single high-dose and multiple low-dose streptozotocin on contraction and intracellular Ca2+ in ventricular myocytes from diabetes resistant and susceptible rats

Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a diabetic cardiomyopathy. Albino Oxford (AO) and Dark Agouti (DA) inbred strains of rats are susceptible to developing diabetes when administered a SHD of STZ but differ in susceptibility to multiple low-dose (MLD) STZ. We have investigated the effects of SHD and MLD-STZ on contraction and intracellular Ca2+, measured with fura-2, in ventricular myocytes from AO and DA rats at 18-20 weeks after treatment. Time to peak shortening was significantly prolonged in myocytes from DA rats after SHD-STZ but was not altered in DA rats after MLD-STZ or in AO rats by either MLD or SHZ-STZ treatment. Time to peak shortening in myocytes from DA control and DA rats after SHD-STZ were 88+/-2 ms and 107+/-4 ms, respectively. Time to half relaxation and the amplitude of myocyte shortening were not altered in AO or DA rats by either MLD or SHD-STZ treatment. Amplitude, time to peak fura-2 transient and time to half relaxation of the fura-2 transient were not significantly altered in AO or DA rats by either MLD or SHD-STZ treatment. Contractile defects reported in myocytes from SHD-STZ treated DA rats may be a consequence of altered myofilament sensitivity to Ca2+. The hyperglycaemic effects of MLD-STZ and SHD-STZ induced diabetes was much greater in DA compared to AO rats and the effects of the hyperglycaemia on the time-course of ventricular myocyte contraction was most profound in DA rats after SHD-STZ.

Successful abrogation by thymoquinone against induction of diabetes mellitus with streptozotocin via nitric oxide inhibitory mechanism

Nitric oxide (NO) is involved in the destruction of beta-cells during the development of type I diabetes mellitus (DM). We demonstrated the possibility of rescuing beta-cells by intervention with thymoquinone (TQ) using streptozotocin (STZ) rat diabetic model. The hyperglycemic and hypoinsulinemic responses to STZ were significantly abrogated in rats cotreated with TQ, and this abrogating effect has persisted for 1 month after stopping of TQ treatment. Unlike observations recorded after diabetic chronicity of 1month, where there was a significant reduction of both serum and pancreatic nitrites, a significant increase in both nitrites was observed within the first 3 days in STZ rats, with or without lipopolysaccharide (LPS) stimulation, compared with controls and the TQ-cotreated. In vitro production of nitrite was significantly higher by 3-day-diabetic macrophages with or without stimulation compared to control or TQ-treated ones. However, 1-month-diabetic macrophages showed insignificant decrease of nitrite which turned significant upon stimulation. TQ has no effect on either IkB degradation or NF-kB activation; however, it significantly inhibited both p44/42 and p38 mitogen-activated protein kinases (MAPKs) which contribute to the transcriptional machinery of inducible nitric oxide synthase and NO production. These data emphasize the protective value of TQ against development of type I DM via NO inhibitory pathway.

Oxytalan elastic and collagen fibers during the repair process in experimental nitric oxide inhibition

PURPOSE

To evaluate the repair process in rats with experimentally induced arterial hypertension. This study aimed to evaluate lesions in the ventricular myocardium and the repair process during experimental hypertension induced by systemic blockage of nitric oxide using N-omega-nitro-L-arginine methyl ester hydrochloride (L-NAME). Nitric oxide is an endothelial vasorelaxing factor and is necessary for the maintenance of normal arterial pressure, and L-NAME is an analog and antagonist of L-arginine, the substrate of the nitric oxide synthase.

MATERIALS AND METHODS

We used 26 normotensive young male Wistar rats belonging to several litters. Animals were treated with oral administration of L-NAME dissolved in water (75 mg/100 mL) for 43 days. Hearts were weighed and processed by routine methods. Special stains utilized were Gomori's trichrome (aniline blue), picrosirius red polarization to identify fibrillar collagen, alcian blue technique (pH 0.5 and pH 2.5) to identify glycosaminoglycans, periodic acid-Schiff technique (with and without amylases) to identify proteoglycans, and Weigert's resorcinol fuchsin solution (with and without oxone) to identify elastic fibers.

RESULTS

The results showed significant elevation of the arterial pressure (P <0.01) and significant increase of cardiac weight (P <.0001) in the L-NAME (hypertensive) treated group, as compared to an untreated control group. The histological analysis demonstrated wide infarcted myocardial areas in animals with nitric oxide blockade; several vascular changes such as thickening of the muscular tunica with fibrosis; thickening in the wall of small arteries and arterioles; and fibrinoid necrosis in the wall to nearly complete luminal obliteration. Reparative fibrosis involved mainly oxytalan elastic and collagen fibers.

CONCLUSION

Oxytalan elastic and collagen fibers are of great importance for the postinfarct repair process occurring during experimental nitric oxide inhibition.

Lack of the mediators of innate immunity attenuate the development of autoimmune diabetes in mice

Interleukin 15 (IL-15) and Interleukin 18 (IL-18) are key cytokines produced by macrophages during innate immune response. These cytokines can profoundly affect subsequent adaptive immune responses including autoimmunity. We have investigated the role of IL-15 and IL-18 in the development of autoimmune diabetes in mice induced by multiple low dose streptozotocin (MLD-STZ). To analyze the role of IL-15, we tested the effects of a soluble murine IL-15 receptor alpha-chain (smIL-15Ralpha), on the development of MLD-STZ in C57BL/6 mice. Animals were treated with 10 daily injections of 32 microg of smIL-15Ralpha starting on the first day of diabetes induction. This treatment significantly attenuated the development of diabetes as evaluated by significantly lower glycemia compared with control mice treated with an inactive mutant form of sIL-15Ra. To directly address the role of IL-18 in MLD-STZ we used IL-18 knockout (KO) mice on DBA/1 background. IL-18 deficient mice were significantly more resistant to the induction of diabetes compared with the wild-type controls and did not develop the typical mononuclear cell infiltrates in the islets. Taken together our data suggest that the innate mediators, IL-15 and IL-18, are essential for the development of diabetes and may be important targets in prevention and early treatment of autoimmune diabetes.

Cytokine-induced PGE(2) formation is reduced from iNOS deficient murine islets

Cytokines may be involved in islet destruction during Type 1 diabetes. Exposure to interleukin-1beta (IL-1beta) or IL-1beta plus interferon-gamma (IFN-gamma) of rodent islets induces expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Subsequent formation of nitric oxide (NO) and prostaglandin E(2) (PGE(2)) may impair beta-cell function. Using iNOS deficient (iNOS -/-) islets, we have further investigated the relation between NO formation and PGE(2) induction. We found that iNOS -/- islets responded with a reduced PGE(2) formation following IL-1beta or (IL-1beta + IFN-gamma) treatment compared to wild-type (wt) islets, while COX-2 mRNA or protein content were unchanged. By the addition of an NO donor together with IL-1beta, PGE(2) formation could be stimulated from iNOS -/- islets. We conclude that the lowered capacity of PGE(2) formation observed from cytokine exposed iNOS -/- islets is due to a decreased stimulation of PGE(2) formation by the COX-2 enzyme in the absence of NO, rather then differences in expressed COX-2 protein.

The novel anti-inflammatory compound, lisofylline, prevents diabetes in multiple low-dose streptozotocin-treated mice

INTRODUCTION

Proinflammatory cytokines play an important role in the development of type 1 diabetes. Lisofylline (LSF) is a novel anti-inflammatory compound that specifically inhibits proinflammatory cytokine production and action.

AIM

To investigate the effect of LSF on diabetes prevention.

METHODOLOGY

A mouse with diabetes induced by multiple low doses of streptozotocin (STZ) can be used as an animal model for type 1 diabetes. In this study, we used this method to induce diabetes in C57BL/6J mice. The daily LSF treatment started 5 days before STZ injections and lasted for 2 weeks. The incidence of diabetes was monitored. Insulin secretion was assessed in pancreatic islets isolated from experimental mice. Cytokine production was measured in mouse sera. Islet apoptosis was assessed quantitatively.

RESULTS

In LSF-treated mice, there was a significant reduction of diabetes incidence (25% vs. 91.6%). This protection was associated with suppression of systemic levels of IFN-gamma and TNF-alpha, inhibition of macrophage infiltration in islets, restoration of islet insulin secretion, and reduction of beta-cell apoptosis.

CONCLUSIONS

This study suggests that treatment with LSF suppresses proinflammatory cytokines and protects beta-cells from inflammation. LSF may be useful for prevention of type 1 diabetes and other disorders associated with excessive proinflammatory cytokines.

Presentation of nitric oxide regulates monocyte survival through effects on caspase-9 and caspase-3 activation

In the absence of survival factors, blood monocytes undergo spontaneous apoptosis, which involves the activation of caspase-3. Although nitric oxide can block caspase-3 activation and promote cell survival, it can also induce apoptosis. We hypothesized that nitrosothiols that promote protein S-nitrosylation would reduce caspase-3 activation and cell survival, whereas nitric oxide donors (such as 1-propamine 3-(2-hydroxy-2-nitroso-1-propylhydrazine (PAPA) NONOate and diethylamine (DEA) NONOate) that do not target thiol residues would not. Using human monocytes as a model, we observed that nitrosothiol donors S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine suppressed caspase-9 and caspase-3 activity and DNA fragmentation. In contrast, PAPA or DEA NONOate did not promote monocyte survival events and appeared to inhibit monocyte survival induced by macrophage colony-stimulating factor. The caspase-3-selective inhibitor DEVD-fluoromethyl ketone reversed DNA fragmentation events, and the caspase-9 inhibitor LEHD-fluoromethyl ketone reversed caspase-3 activity in monocytes treated with PAPA or DEA NONOate in the presence of macrophage colony-stimulating factor. These results were not caused by differences in glutathione levels or the kinetics of nitric oxide release. Moreover, S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine directly blocked the activity of recombinant caspase-3, which was reversed by the reducing agent dithiothreitol, whereas PAPA or DEA NONOate did not block the enzymatic activity of caspase-3. These data support the hypothesis that nitrosylation of protein thiol residues by nitric oxide is critical for promoting the survival of human monocytes.

Down-regulation of multiple low dose streptozotocin-induced diabetes by mycophenolate mofetil

The new immunosuppressive agent mycophenolate mofetil (MMF) has been shown recently to exert a protective effects in certain animal models of autoimmunity, including diabetes in diabetes-prone bio-breeding (BB) rats. In the present study, the immunomodulatory potential of MMF was investigated in autoimmune diabetes induced by multiple low doses of streptozotocin (MLD-STZ) in genetically susceptible DA rats 20 mg STZ/kg body weight (b.w.) for 5 days] and CBA/H mice (40 mg STZ/kg b.w. for 5 days). In both species, short time treatment of animals with MMF (25 mg/kg) during the early development of the disease, as well as continuous MMF treatment, prevented the appearance of hyperglycaemia and inflammatory infiltrates in the pancreatic tissue. Moreover, clinical manifestations of diabetes were suppressed by application of the drug after the onset of clinical symptoms. Treatment with guanosine (1 mg/kg) in parallel with MMF completely reversed MMF activity in vivo, indicating that inhibition of inosine monophosphate dehydrogenase (IMPDH) was responsible for the observed suppressive effects. MMF-mediated protection from diabetes correlated with reduced ex vivo spontaneous spleen mononuclear cell (MNC) proliferation and defective adhesive cell interactions. MMF-treated animals also had lower local production of IFN-gamma, as well as IL-12 and nitric oxide (NO) production by peripheral tissues (spleen and peritoneal cells), compared to that in control diabetic groups, while IL-10 level was elevated. Together, these data demonstrate that MMF interferes with autoimmune process in streptozotocin-induced diabetes at multiple levels, including lymphocyte proliferation and adhesion, as well as pro/anti-inflammatory cytokine balance.

Aqueous humor nitric oxide levels in patients with Behçet disease

PURPOSE

The purpose of this study was to quantify aqueous humor nitric oxide levels in patients with Behçet uveitis and age-matched controls to assess how nitric oxide is involved in this ocular condition.

METHODS

Samples of aqueous humor were collected from 11 patients with Behçet uveitis who were undergoing cataract surgery. Sampling was done by paracentesis at the beginning of the operation. Similar samples were collected from 20 age-matched normal patients (controls). For each sample, we used the spectrophotometric method based on the Griess reaction to determine the amount of nitrite, which is the stable metabolite of nitric oxide.

RESULTS

The amount of nitrite in aqueous humor samples from patients with Behçet disease was above the detection limit in 8 of 11 cases; the mean level +/- SEM was 2.13 +/- 0.621 micromol/L. Levels in the control group were below the detection limit in all cases (<0.08 micromol/L). There was a statistically significant difference between the aqueous humor nitrite levels in patients with Behçet disease and those in controls (P = 0.00002).

CONCLUSIONS

Aqueous humor nitric oxide levels are elevated in patients with a history of Behçet disease.

Generation of hydroxyl radicals mediated by streptozotocin in pancreatic islets of mice in vitro

Type I diabetes is considered a multifactorial autoimmune process initiated by an environmental factor. There is evidence that reactive oxygen species are involved in destructing insulin-producing beta-cells. In mice, reactive oxygen species and nitric monoxide contribute to beta-cell damage in the non-obese diabetic strain developing spontaneously diabetes and in diabetes induced with multiple low doses of streptozotocin. Previously, we found that zinc sulfate induced metallothionein in pancreatic islets, protected beta-cells against streptozotocin toxicity in vitro, and prevented diabetes induced with multiple low doses of streptozotocin. Since metallothionein is known to scavenge hydroxyl radicals in cell-free systems, we hypothesize that the protective effect of zinc sulfate results from metallothionein induction scavenging hydroxyl radicals generated by multiple low doses of streptozotocin. Therefore, we studied whether levels of hydroxyl radicals are increased by streptozotocin in isolated islets in vitro. Here, we demonstrate basal and streptozotocin-stimulated hydroxyl radicals by electron spin resonance spectroscopy in combination with hydroxyl radical-specific spin trapping in islet homogenates. Furthermore, in islet cultures, streptozotocin augmented generation of reactive oxygen species as determined by fluorescence. Of the group of reactive oxygen species, the streptozotocin-augmented generation of hydrogen peroxide was also specifically determined. We conclude that streptozotocin-mediated hydroxyl radicals and generation of reactive oxygen species may be crucial effectors in beta-cell damage.

Downregulation of apoptosis in the target tissue prevents low-dose streptozotocin-induced autoimmune diabetes

3,7-dimethyl-1-(5-oxohexyl) xanthine, pentoxifylline (PTX) is shown to affect cytokine-induced apoptosis in several experimental models and clinical conditions. It had been also shown to prevent insulitis and hyperglycemia in non-obese diabetic (NOD) mice, and mice and rats susceptible to diabetes induction with multiple low-doses of streptozotocin (MLD-STZ). We therefore analysed the development of diabetes and apoptosis of pancreatic beta islet cells in CBA/mice after diabetes induction with MLD-STZ. We have evaluated the effect of PTX on the level of apoptosis in the islet at different time intervals after diabetes induction. Complementary histological and immunohistochemical studies and analyses of the expression of cytokines and nitric oxide have also been done. It was concluded that PTX significantly attenuated apoptosis of the beta-cells in the islet and suppressed the induction of diabetes. Our data are compatible with the notion that interferon-gamma (IFN-gamma)/tumor necrosis factor (TNF)/nitric oxide (NO)-induced apoptosis of beta-cells in experimental diabetes is attenuated by PTX.

Involvement of inducible isoforms of COX and NOS in streptozotocin-pancreatic damage in the rat: interactions between nitridergic and prostanoid pathway

Streptozotocin-induced pancreatic damage involves nitric oxide (NO) and prostaglandins (PGs) overproduction. In this work we aim to evaluate a putative relationship between the elevated NO levels and the altered prostanoid production in pancreatic tissue from streptozotocin-diabetic rats. Total NOS activity and nitrate/nitrite pancreatic levels in tissues from diabetic rats are decreased when the cyclooxygenase (COX) inhibitor indomethacin (INDO) is added to the incubating medium, while the addition of PGE(2)increases nitrate/nitrite production and NOS levels. INDO and PGE(2)selectively affect Ca(2+)-dependent NOS (iNOS) activity in diabetic tissues, and they have not been able to modify nitrate/nitrite levels, iNOS or Ca(2+)-dependent (cNOS) in control tissues. When the NOS inhibitor L-NMMA was present in the incubating medium, control pancreatic [(14)C]-Arachidonic Acid ([(14)C]-AA) conversion to 6-keto PGF(1 alpha)and to TXB(2)was lower, and PGF(2 alpha), PGE(2)and TXB(2)production from diabetic tissues diminished. The NO donors, spermine nonoate (SN) and SIN-1, enhanced TXB(2)levels in control tissues, while PGF(2 alpha), PGE(2)and TXB(2)levels from diabetic tissues were increased. PGE(2)production from control and diabetic tissues was assessed in the presence of the NO donor SN plus INDO or NS398, a specific PG synthase 2 inhibitor. When SN combined with INDO or NS398 was added, the increment of PGE(2)production was abolished by both inhibitors in equal amounts, indicating that the activating effect of nitric oxide is exerted on the inducible isoform of cyclooxygenase. In the diabetic rat, prostaglandins and NO seem to stimulate the generation of each other, suggesting a lack of regulatory mechanisms that control the levels of vasoactive substances in acute phase of beta-cell destruction.

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.

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.

Effect of nitric oxide on proliferation of human retina pigment epithelial cells

PURPOSE

To investigate the effects of exogenous and endogenous nitric oxide (NO) on the proliferation of human retina pigment epithelial (RPE) cells.

METHODS

We stimulated cultured human RPE cells with 3-morphosydnonimine (SIN-1) to analyse the effect of exogenous NO. Incubation with a cytokine cocktail (interleukin 1-beta + interferon gamma + tumour necrosis factor alpha) plus lipopolysaccharide (LPS) induced cells to synthesise NO endogenously. The cultures were then incubated for 48 h, after which the cells were stained with crystal violet and absorbance at 550 nm was measured spectrophotometrically.

RESULTS

SIN-1 inhibited human RPE cell proliferation, while haemoglobin, an NO inhibitor, almost completely blocked the inhibitory effect. On the other hand, treatment with the cytokine cocktail plus LPS did not inhibit RPE cell proliferation.

CONCLUSION

These findings confirm that exogenous NO inhibits human RPE cell proliferation, while endogenous NO has no such blocking effect.

Protective effect of boldine on oxidative mitochondrial damage in streptozotocin-induced diabetic rats

Increased oxidative stress has been suggested to be involved in the pathogenesis and progression of diabetic tissue damage. Several antioxidants have been described as beneficial for oxidative stress-associated diseases. Boldine ([s]-2,9-dihydroxy-1, 10-dimethoxyaporphine) is a major alkaloid found in the leaves and bark of boldo (Peumus boldus Molina), and has been shown to possess antioxidant activity and anti-inflammatory effects. From this point of view, the possible anti-diabetic effect of boldine and its mechanism were evaluated. The experiments were performed on male rats divided into four groups: control, boldine (100 mg kg(-1), daily in drinking water), diabetic [single dose of 80 mg kg(-1)of streptozotocin (STZ), i.p.] and diabetic simultaneously fed with boldine for 8 weeks. Diabetic status was evaluated periodically with changes of plasma glucose levels and body weight in rats. The effect of boldine on the STZ-induced diabetic rats was examined with the formation of malondialdehydes and carbonyls and the activities of endogenous antioxidant enzymes (superoxide dismutase and glutathione peroxidase) in mitochondria of the pancreas, kidney and liver. The scavenging action of boldine on oxygen free radicals and the effect on mitochondrial free-radical production were also investigated. The treatment of boldine attenuated the development of hyperglycemia and weight loss induced by STZ injection in rats. The levels of malondialdehyde (MDA) and carbonyls in liver, kidney and pancreas mitochondria were significantly increased in STZ-treated rats and decreased after boldine administration. The activities of mitochondrial manganese superoxide dismutase (MnSOD) in the liver, pancreas and kidney were significantly elevated in STZ-treated rats. Boldine administration decreased STZ-induced elevation of MnSOD activity in kidney and pancreas mitochondria, but not in liver mitochondria. In the STZ-treated group, glutathione peroxidase activities decreased in liver mitochondria, and were elevated in pancreas and kidney mitochondria. The boldine treatment restored the altered enzyme activities in the liver and pancreas, but not the kidney. Boldine attenuated both STZ- and iron plus ascorbate-induced MDA and carbonyl formation and thiol oxidation in the pancreas homogenates. Boldine decomposed superoxide anions, hydrogen peroxides and hydroxyl radicals in a dose-dependent manner. The alkaloid significantly attenuated the production of superoxide anions, hydrogen peroxide and nitric oxide caused by liver mitochondria. The results indicate that boldine may exert an inhibitory effect on STZ-induced oxidative tissue damage and altered antioxidant enzyme activity by the decomposition of reactive oxygen species and inhibition of nitric oxide production and by the reduction of the peroxidation-induced product formation. Boldine may attenuate the development of STZ-induced diabetes in rats and interfere with the role of oxidative stress, one of the pathogeneses of diabetes mellitus.

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.

Involvement of nitric oxide in nickel-induced hyperglycemia in rats

Nitric oxide is an important bioactive signaling molecule that mediates a variety of normal physiological functions which, if altered, could contribute to the genesis of many pathological conditions, including diabetes. In the present study we have shown the involvement of NO in nickel-induced hyperglycemia in male albino rats. Administration of nickel chloride (25 to 100 micromol/kg; ip) to overnight-fasted rats resulted in significant dose and time-dependent increase in plasma glucose, attaining maximum level at 1 h posttreatment and thereafter decreasing to normal levels by 4 h. The involvement of NO in nickel-induced hyperglycemia was evident by the observation that pretreatment of rats with NG-monomethyl-l-arginine (10 to 50 micromol/kg; ip), an inhibitor of nitric oxide synthase (NOS), significantly attenuated the nickel-mediated increase in the plasma glucose levels in a dose-dependent fashion. The activity of Ca(2+)-dependent NOS (constitutive form, c-NOS) was found to be significantly elevated in adrenals (5.5-fold) and brain (1.4-fold) at 1 and 2 h posttreatment, attaining normal levels by 4 h. In contrast, the activity of c-NOS in pancreas was significantly decreased (2.8-fold) with a concomitant increase (11.6-fold) in inducible NOS (i-NOS) at the same time interval. As observed by immunoblot analysis, a significant increase in i-NOS protein expression in the pancreas was observed at 1 and 2 h posttreatment. This was associated with a significant elevation in cGMP levels in adrenals, brain, and pancreas, possibly via the stimulation of cytosolic guanylate cyclase. This elevation in cGMP was abolished by low concentration of hemoglobin. These effects were associated with the accumulation of nickel in the target tissues. Taken together, our data suggest that nickel causes a significant increase in the levels of (i) cGMP and c-NOS in adrenals and brain and (ii) i-NOS in pancreas. These events may be responsible for modulating the release of insulin from pancreas finally leading to hyperglycemic condition in rats.

Inhibition of the cytokine-mediated inducible nitric oxide synthase expression in rat insulinoma cells by phenyl N-tert-butylnitrone

Cytokines and nitric oxide (NO) have been implicated in the pathogenesis of insulin-dependent diabetes mellitus (IDDM). We have shown that the spin-trapping agent phenyl N-tert-butylnitrone (PBN) protects against streptozotocin (STZ)-induced IDDM in mice. In order to gain more insights into the mechanism(s) of the protective action of PBN against IDDM, we have investigated the effect of this compound on the cytokine-induced NO generation (measured as nitrite) in rat insulinoma RIN-5F cells. Our results demonstrate that PBN cotreatment prevents the generation of nitrite by RIN-5F cells induced by treatment with tumor necrosis factor-alpha, interleukin 1beta, and interferon-gamma in a dose-dependent fashion. The generation of NO as a result of cytokine treatment and the inhibitory effect of PBN were further confirmed by electron paramagnetic resonance spectroscopy. Aminoguanidine, a selective inhibitor of inducible nitric oxide synthase (iNOS), abolished the cytokine-induced nitrite generation whereas N-nitro-l-arginine, an inhibitor more selective for other NOS isoforms, was significantly less effective. Western and Northern analyses demonstrated that PBN inhibits the cytokine-mediated expression of iNOS at the transcriptional level. Cytokine-induced nitrite formation was also inhibited by the two antioxidant agents alpha-lipoic acid and N-acetylcysteine. These results indicate that PBN protects against IDDM at least in part by prevention of cytokine-induced NO generation by pancreatic beta-cells.

Cell-specific inhibition of inducible nitric oxide synthase activation by leflunomide

The influence of a novel immunomodulating drug, leflunomide, on iNOS-dependent nitric oxide (NO) production in rodent macrophages and fibroblasts was investigated. Leflunomide's active metabolite A77 1726 caused a dose-dependent decrease of NO production in IFN-gamma-treated L929 fibroblasts. The observed effect was cell-specific, as well as stimulus-specific, since A77 1726 did not affect NO production in IFN-gamma-stimulated murine peritoneal macrophages or db-cAMP-treated L929 cells. A77 1726 reduced expression of IFN-gamma-induced iNOS and IRF-1 mRNA in L929 cells, while iNOS enzymatic activity remained unchanged. Specific inhibitor of MAP kinase kinase (MEK), PD98059, but not unselective protein kinase inhibitor genistein, completely mimicked cell-type-specific and stimulus-specific NO-inhibitory action of leflunomide. Therefore, the recently described inhibition of MEK/MAP pathway by leflunomide could present a possible mechanism for its suppression of iNOS activation in L929 fibroblasts. Finally, a similar inhibitory effect of A77 1726 on both NO production and iNOS mRNA expression was observed also in IFN-gamma + LPS-activated murine and rat primary fibroblasts.

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.

Role of nitric oxide in renal function in rats with short and prolonged periods of streptozotocin-induced diabetes

OBJECTIVE

Nitric oxide (NO) has been proposed to play a significant role in renal function. In addition, NO production has been found to increase in diabetes mellitus. The present study aimed to clarify the mechanism responsible for NO action in renal function in rats with short (10 days) or prolonged periods (8 weeks) of diabetic induction.

METHODS

Male Wistar rats were induced to develop diabetes mellitus by intraperitoneal injection of streptozotocin (STZ) (65 mg/kg b.w.), whereas the age-matched control rats were given normal saline. After diabetic induction for 10 days or 8 weeks, the experiment was begun. Three consecutive periods of 30 min each, were designed consisting of one control period, the first and the second period of L-arginine or L-NAME or insulin infusion. Mean arterial pressure (MAP) was determined every 15 min. Arterial blood and urine samples were collected to determine the plasma glucose level (PG), glomerular filtration rate (GFR), effective renal plasma flow (ERPF), urine flow rate (V), urinary protein excretion (Upro), fractional excretion of glucose (FEG) and fractional excretion of sodium (FENa) in each period.

RESULTS

No significant differences of MAP were apparent between control rats and rats with diabetic induction. L-arginine infusion had no effect whereas L-NAME markedly increased MAP in normal rats and rats after the short period of diabetes induction. Pressor response to L-NAME in rats exposed to the prolonged period of diabetes induction was lower than that of age-matched control rats. During L-NAME infusion, the PG level significantly declined from 394.9+/-13.1 - 338.0+/-14.1 mg/dl and from 399.9+/-7.9 - 354.3+/-18.8 mg/dl in rats after short and prolonged periods of diabetic induction, respectively. GFR significantly increased whereas ERPF slightly increased in diabetic rats. The elevation of GFR could be reversed by L-NAME or insulin infusion but it increased again after simultaneous infusion of insulin and glucose. Increases in V, the Upro and FEG without changes of FENa, were apparent in diabetic rats. Either L-arginine or L-NAME infusion could not reverse elevations of V, Upro and FEG. The rise of both V and Upro was reversed along with the attenuation of high FEG during insulin infusion, and it rose again close to the diabetic level during simultaneous infusion of insulin and glucose. Elevation of GFR, V and Upro appeared along with a rise of the PG level by approximately 300-350 mg/dl in diabetic rats.

CONCLUSIONS

Both NO and hyperglycaemia are involved in modulating renal hyperfiltration in diabetic rats. The elevations of urine flow rate and urinary excretion of both protein and glucose would be expected to represent the reduction of renal tubular reabsorption rather than renal hyperfiltration in diabetic rats. NO does not participate in the change of renal tubular function in diabetic rats. There was a parallel change of urine flow rate and urinary excretion of protein in diabetic rats. The rise of the PG level itself would account for the increases of GFR, V, Upro and FEG in diabetic rats. Glomerular hyperfiltration, diuresis and proteinuria in diabetic rats are not exhibited until the PG level rises to = 300-350 mg/dl.

Nitric oxide mediates IL-1beta stimulation of heat shock protein but not IL-1beta inhibition of glutamic acid decarboxylase

Interleukin-1beta (IL-1beta) has been implicated to play an important role in the autoimmune beta cell lesion of insulin-dependent diabetes mellitus (IDDM) because of its inhibition of insulin secretion, direct islet cytotoxicity and alteration of islet cell antigen expression. We have previously demonstrated that IL-1beta inhibits glutamic acid decarboxylase-65 (GAD-65) and increases heat shock protein-70 (HSP-70) expression in islet cells. IL-1beta stimulates the inducible form of nitric oxide (NO) synthase and the resultant increased NO mediates many of IL-1beta's effects. In this study we investigated the role of the NO pathway in mediating the effects of IL-1beta on GAD-65 and HSP-70 expression and on insulin secretion. Islets isolated from Sprague-Dawley rats were cultured with IL-1beta and aminoguanidine (AG), an inhibitor of inducible NO synthase, individually and in combination for 24 h. Accumulated nitrite production, insulin release and islet expression of GAD-65 and HSP-70 were measured. We found that (1) IL-1beta at 10 U/ml increased nitrite production, inhibited insulin release, increased HSP-70 expression and decreased GAD-65 expression. (2) AG alone at 1 mM/ml had no effect on nitrite production, insulin release, GAD-65 and HSP-70 expression. (3) In combination, AG completely blocked IL-1beta increased nitrite production, reversed IL-1beta inhibited insulin release by approximately 50%, completely reversed IL-1beta increased HSP-70 expression, but did not reverse IL-1beta inhibited GAD-65 expression. Our findings indicate that the effect of IL-1beta on HSP-70 expression is mediated by NO production, whereas a NO-independent pathway is involved in the effect of IL-1beta on GAD-65 expression and insulin secretion.

Leflunomide protects mice from multiple low dose streptozotocin (MLD-SZ)-induced insulitis and diabetes

In certain animal models of autoimmunity the isoxasol derivative leflunomide has been reported to exert a protective effect against autodestruction. In the present study, the immunomodulatory potential of the main metabolite of leflunomide, A77 1726, in experimentally induced autoimmune diabetes was investigated. The disease was induced in genetically susceptible CBA/H mice by multiple low doses of streptozotocin (MLD-SZ, 40 mg/kg per day, given intraperitoneally for 5 consecutive days). Effects of leflunomide were evaluated by two treatment protocols: mice treated with MLD-SZ were injected intraperitoneally with A77 1726 for 10 consecutive days, either during the first 10 days of the disease (early treatment), or starting from day 10 after disease induction (late treatment). Disease manifestations defined by hyperglycaemia, mononuclear infiltration into pancreas, expression of interferon-gamma (IFN-gamma) and inducible nitric oxide synthase (iNOS) and destruction of the islets of Langerhans were reduced in a dose-dependent fashion after early treatment with A77 1726 (dose range of 5-35 mg/kg per day). Moreover, late treatment with the high dose of the drug (25 mg/kg per day), started when the autoimmune disease was already apparent, arrested progression of ongoing inflammatory response. Analysis of the effects of A77 1726 on the adhesive interactions of spleen-derived or peripheral blood-derived mononuclear cells from MLD-SZ-treated and normal mice demonstrated that the drug inhibits both ex vivo and in vitro spontaneous mononuclear cell aggregation, thus suggesting that an important component of leflunomide's immunomodulatory action is suppression of adhesive interactions. These results demonstrate both preventive and therapeutic effects of leflunomide in a model of MLD-SZ-induced diabetes and suggest that the drug may be considered a potent therapeutic tool for autoimmune inflammatory disorders, including diabetes.