Translocation of glomerular p47phox and p67phox by protein kinase C-beta activation is required for oxidative stress in diabetic nephropathy

Nox4 and diabetic nephropathy: with a friend like this, who needs enemies?

Oxidative stress has been linked to the pathogenesis of diabetic nephropathy, a complication of diabetes in the kidney. NADPH oxidases of the Nox family are a major source of reactive oxygen species in the diabetic kidney and are critical mediators of redox signaling in glomerular and tubulointerstitial cells exposed to the diabetic milieu. Here, we present an overview of the current understanding of the roles of Nox catalytic and regulatory subunits in the processes that control mesangial cell, podocyte, and tubulointerstitial cell injury induced by hyperglycemia and other predominant factors enhanced in the diabetic milieu, including the renin-angiotensin system and transforming growth factor-β. The role of the Nox isoform Nox4 in the redox processes that alter renal biology in diabetes is highlighted.

Melatonin regulates L-arginine transport and NADPH oxidase in young rats with bile duct ligation: role of protein kinase C

BACKGROUND

Bile duct ligation (BDL) is a commonly used cholestatic liver disease (CLD) model. We recently found that L-arginine levels were significantly raised by melatonin in young rats with BDL. We hypothesized that protein kinase C-α (PKC-α) is involved in the increases of L-arginine in melatonin-treated BDL rats. In addition, we tested whether melatonin prevents nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-induced reactive oxygen species (ROS) production, in rats with BDL, through PKC.

METHODS

Four groups of young male rats were studied: shams (n = 6), untreated BDL rats (n = 9), melatonin-treated shams (n = 6, M), and melatonin-treated BDL rats (n = 6, BDL + M). Melatonin-treated rats received daily melatonin 1 mg/kg/d via i.p. injection. All surviving rats were killed 14 d after surgery.

RESULTS

Melatonin prevented BDL-induced mortality and kidney injury. Melatonin additionally increased L-arginine concentrations in BDL liver, which is correlated with decreased PKC-α translocation. Next, melatonin increased L-arginine levels in BDL kidneys, which was correlated with decreased renal levels of arginase II. In the BDL kidney, melatonin decreased PKC-β translocation, reduced p47phox translocation, and diminished NADPH-dependent superoxide production.

CONCLUSION

Melatonin inhibits PKC-α to increase cationic amino acid transporter-1 (CAT-1)-mediated L-arginine uptake in BDL liver, whereas it inhibits PKC-β to reduce NADPH-dependent superoxide production.

Effects of telmisartan or amlodipine monotherapy versus telmisartan/amlodipine combination therapy on vascular dysfunction and oxidative stress in diabetic rats

Our previous studies identified potent antioxidant effects and improvement of vascular function by telmisartan therapy in experimental diabetes and nitrate tolerance. The present study compared the beneficial effects of single telmisartan or amlodipine versus telmisartan/amlodipine combination therapy (T+A) in streptozotocin (STZ)-induced type 1 diabetic rats. Male Wistar rats were injected once with STZ (60 mg/kg, i.v.) and 1 week later the drugs (telmisartan, amlodipine, or T+A) were administrated orally by a special diet (2.5-5 mg kg(-1) day(-1)) for another 7 weeks. We only observed a marginal beneficial on-top effect of T+A therapy over the single drug regimen that was most evident in the improvement of endothelial function (acetylcholine response) and less pronounced in the reduction of whole blood, vascular and cardiac oxidative stress (blood leukocyte oxidative burst, aortic dihydroethidine and 3-nitrotyrosine staining, as well as cardiac NADPH oxidase activity and uncoupling of endothelial nitric oxide synthase) in diabetic rats. These effects on oxidative stress parameters were paralleled by those on the expression pattern of NADPH oxidase and nitric oxide synthase isoforms. In addition, development of mild hypotension in the T+A-treated rats was observed. Reasons for this moderate synergistic effect of T+A therapy may be related to the potent beneficial effects of telmisartan alone and the fact that amlodipine and telmisartan share similar pathways to improve endothelial function. Moreover, hypotension in the T+A-treated rats could partially antagonize the beneficial additive effects by counter-regulatory mechanisms (e.g., activation of the renin-angiotensin-aldosterone system).

Thioredoxin-interacting protein mediates high glucose-induced reactive oxygen species generation by mitochondria and the NADPH oxidase, Nox4, in mesangial cells

Thioredoxin-interacting protein (TxNIP) is up-regulated by high glucose and is associated with oxidative stress. It has been implicated in hyperglycemia-induced β-cell dysfunction and apoptosis. As high glucose and oxidative stress mediate diabetic nephropathy (DN), the contribution of TxNIP was investigated in renal mesangial cell reactive oxygen species (ROS) generation and collagen synthesis. To determine the role of TxNIP, mouse mesangial cells (MC) cultured from wild-type C3H and TxNIP-deficient Hcb-19 mice were incubated in HG. Confocal microscopy was used to measure total and mitochondrial ROS production (DCF and MitoSOX) and collagen IV. Trx and NADPH oxidase activities were assayed and NADPH oxidase isoforms, Nox2 and Nox4, and antioxidant enzymes were determined by immunoblotting. C3H MC exposed to HG elicited a significant increase in cellular and mitochondrial ROS as well as Nox4 protein expression and NADPH oxidase activation, whereas Hcb-19 MC showed no response. Trx activity was attenuated by HG only in C3H MC. These defects in Hcb-19 MC were not due to increased antioxidant enzymes or scavenging of ROS, but associated with decreased ROS generation. Adenovirus-mediated overexpression of TxNIP in Hcb-19 MC and TxNIP knockdown with siRNA in C3H confirmed the specific role of TxNIP. Collagen IV accumulation in HG was markedly reduced in Hcb-19 cells. TxNIP is a critical component of the HG-ROS signaling pathway, required for the induction of mitochondrial and total cell ROS and the NADPH oxidase isoform, Nox4. TxNIP is a potential target to prevent DN.

Molecular mechanisms in the pathogenesis of diabetic nephropathy: an update

Diabetes mellitus is known to trigger retinopathy, neuropathy and nephropathy. Diabetic nephropathy, a long-term major microvascular complication of uncontrolled hyperglycemia, affects a large population worldwide. Recent findings suggest that numerous pathways are activated during the course of diabetes mellitus and that these pathways individually or collectively play a role in the induction and progression of diabetic nephropathy. However, clinical strategies targeting these pathways to manage diabetic nephropathy remain unsatisfactory, as the number of diabetic patients with nephropathy is increasing yearly. To develop ground-breaking therapeutic options to prevent the development and progression of diabetic nephropathy, a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of the disease is mandatory. Therefore, the purpose of this paper is to discuss the underlying mechanisms and downstream pathways involved in the pathogenesis of diabetic nephropathy.

Inflammation and oxidative stress in diabetic nephropathy: new insights on its inhibition as new therapeutic targets

Diabetes and insulin resistance can greatly increase microvascular complications of diabetes including diabetic nephropathy (DN). Hyperglycemic control in diabetes is key to preventing the development and progression of DN. However, it is clinically very difficult to achieve normal glucose control in individual diabetic patients. Many factors are known to contribute to the development of DN. These include diet, age, lifestyle, or obesity. Further, inflammatory- or oxidative-stress-induced basis for DN has been gaining interest. Although anti-inflammatory or antioxidant drugs can show benefits in rodent models of DN, negative evidence from large clinical studies indicates that more effective anti-inflammatory and antioxidant drugs need to be studied to clear this question. In addition, our recent report showed that potential endogenous protective factors could decrease inflammation and oxidative stress, showing great promise for the treatment of DN.

The role of adrenomedullin in the renal NADPH oxidase and (pro)renin in diabetic mice

Adrenomedullin has an antioxidative action and protects organs in various diseases. To clarify the role of adrenomedullin in diabetic nephropathy, we investigated the NADPH oxidase expression, renin-secreting granular cell (GC) hyperplasia, and glomerular matrix expansion in the streptozotocin (STZ)-induced diabetic adrenomedullin gene knockout (AMKO) mice compared with the STZ-diabetic wild mice at 10 weeks. The NADPH oxidase p47phox expression and lipid peroxidation products were enhanced in the glomeruli of the diabetic mice compared with that observed in the controls in both wild and AMKO mice. These changes were more obvious in the AMKO mice than in the wild mice. Glomerular mesangial matrix expansion was more severe in the diabetic AMKO mice than in the diabetic wild mice and exhibited a positive correlation with the degree of lipid peroxidation products in the glomeruli. Proteinuria was significantly higher in the diabetic AMKO mice than in the diabetic wild mice. The GC hyperplasia score and the renal prorenin expression were significantly increased in the diabetic AMKO mice than in the diabetic wild mice, and a positive correlation was observed with the NADPH oxidase expression in the macula densa. The endogenous adrenomedullin gene exhibits an antioxidant action via the inhibition of NADPH oxidase probably by suppressing the local renin-angiotensin system.

Ferulsinaic acid attenuation of diabetic nephropathy

BACKGROUND

Different factors are involved in the development of diabetic nephropathy (DN). Oxidative stress and inflammation play an important role in the pathogenesis of DN. Ferulsinaic Acid (FA) was isolated in 2007. In 2011, we found that FA prolonged the lifespan of C. elegans due to its antioxidative effect, and we hypothesized that FA restores the kidney function of diabetic rats via its antioxidant activity.

METHODS

Male Wistar rats were injected with STZ and divided into 5 groups of 10 each: control, diabetic untreated, diabetic treated with 500, 750 and 1000 ng/kg FA. FA treatment was continued for 21 weeks after induction of diabetes.

RESULTS

In the diabetic rats treated with FA, fasting blood sugar, HbA1C kidney/body weight ratio, creatinine, BUN, sodium and albuminurea were significantly decreased compared with untreated diabetic rats. Diabetic rats showed decreased activities of superoxide dismutase, glutathione peroxidase and catalase, increased concentrations of malondialdehyde and IL-6 in the kidney homogenate. In addition levels of 8-hydroxy-2'-deoxyguanosine in the urine and in the renal cortex DNA were increased. Moreover, severe destruction in glomerular and tubulointerstitial lesions such as glomerular sclerosis, atrophy, interstitial expansion and interstitial cellular infiltration was seen in the kidney of the diabetic untreated rats. Furthermore, the diabetic kidney was found to be positive for NF-κB p65 antigen in the immunohistochemistry examinations. Treatment with FA restored all the altered parameters in a dose-dependent manner. Furthermore, all the ultra-morphologic abnormalities and NF-κB activation in the kidney of diabetic rats were markedly ameliorated by FA treatment.

CONCLUSION

FA confers a considerable protection against kidney injuries of the diabetic rats by increasing activities of antioxidant enzymes, attenuating the formation of AGEs, attenuating the NF-κB activation, ameliorating the inflammatory markers and inhibiting the accumulation of oxidized DNA in the kidney, suggesting a potential drug for the prevention and therapy of DN.

Diphenyleneiodonium protects preoligodendrocytes against endotoxin-activated microglial NADPH oxidase-generated peroxynitrite in a neonatal rat model of periventricular leukomalacia

The contribution of microglial activation to preoligodendroglial (preOL) damage in the central nervous system (CNS) is considered to be one of the principal causes of periventricular leukomalacia (PVL) pathogenesis. The present study explores the effect of diphenyleneiodonium (DPI), a NADPH oxidase (NOX) inhibitor, on protection of preOLs from bacterial lipopolysaccharide (LPS)-induced microglial toxicity in vivo and in vitro. In vitro, preOLs co-cultured with microglia exhibited increased preOL apoptosis, accompanied by overproduction of superoxide anion (O(2)(-)) and the formation of peroxynitrite (ONOO(-)) after LPS exposure. LPS also significantly up-regulated accumulation of activated microglial NOX subunits p67-phox and gp91-phox in the plasma membrane. Diphenyleneiodonium (DPI) (10μm) was found to significantly attenuate up-regulation of this NOX activity. In vivo, DPI was administered (1mg/kg/day) by subcutaneous injection for 3 days to two-day-old neonatal Sprague-Dawley rats subjected to intracerebral injection of LPS. Treatment with DPI within 24h of LPS injection significantly ameliorated white matter injury, decreasing preOL loss, O(2)(-) generation, and ONOO(-) formation, and inhibiting p67-phox, gp91-phox synthesis and p67phox membrane translocation in microglia. These results indicated that LPS-induced preOL apoptosis may have been mediated by microglia-derived ONOO(-). DPI prevented this LPS-induced brain injury, most likely by inhibiting ONOO(-) formation via NOX, thereby preventing preOL loss and immature white matter injury.

Differential regulation of free radicals (reactive oxygen and nitrogen species) by contact allergens and irritants in human keratinocyte cell line

Immune responses to chemicals resulting in sensitization and the appearance of allergic responses following subsequent exposures are dependent upon activation of T lymphocytes. On the contrary, irritant responses are independent of immune response. The aim of this project was to identify the differential signaling cascade operated in allergic and irritant contact dermatitis. Recently, we have shown that keratinocyte cell line A431 can function as an antigen presenting cell (APC) and hence can be used as a model to differentiate between an allergen and irritant molecule. Allergen- and irritant-induced regulation of reactive oxygen species (ROS) and nitric oxide (NO) has been explored. Irritants induce release of ROS even at noncytotoxic concentration. ROS generation by allergens was not detected at nontoxic concentration but as the concentration was increased to a toxic dose there was a drastic increase in the ROS level compared to the untreated cells. Hence, the regulation of ROS is not significant in allergic responses but important in irritant responses. The major difference exists in the fact that the source of ROS for irritants is mitochondria, while that of allergens is mostly cytosolic. Antioxidant-induced protection from irritant-induced cell death has also been demonstrated. NO level was found to increase by allergens and irritants in a concentration-dependent manner. Hence, the regulation of ROS and NO can be used as important mediators in contact allergic and irritant dermatitis.

GLP-1 analog liraglutide protects against oxidative stress and albuminuria in streptozotocin-induced diabetic rats via protein kinase A-mediated inhibition of renal NAD(P)H oxidases

Accumulating evidence has implicated that GLP-1 may have a beneficial effect on cardiovascular and renal diseases but the mechanism is not fully understood. Here we show that GLP-1 analog, liraglutide, inhibits oxidative stress and albuminuria in streptozotocin (STZ)-induced type 1 diabetes mellitus rats, via a protein kinase A (PKA)-mediated inhibition of renal NAD(P)H oxidases. Diabetic rats were randomly treated with subcutaneous injections of liraglutide (0.3 mg/kg/12 h) for 4 weeks. Oxidative stress markers (urinary 8-hydroxy-2'-deoxyguanosine and renal dihydroethidium staining), expression of renal NAD(P)H oxidase components, transforming growth factor-β (TGF-β), fibronectin and urinary albumin excretion were measured. In vitro effect of liraglutide was evaluated using cultured renal mesangial cells. Administration of liraglutide did not affect plasma glucose levels or body weights in STZ diabetic rats, but normalized oxidative stress markers, expression of NAD(P)H oxidase components, TGF-β, fibronectin in renal tissues and urinary albumin excretion, all of which were significantly increased in diabetic rats. In addition, in cultured renal mesangial cells, incubation with liraglutide for 48 h inhibited NAD(P)H-dependent superoxide production evaluated by lucigenin chemiluminescence in a dose-dependent manner. This effect was reversed by both PKA inhibitor H89 and adenylate cyclase inhibitor SQ22536, but not by Epac2 inhibition via its small interfering RNA. Liraglutide may have a direct beneficial effect on oxidative stress and diabetic nephropathy via a PKA-mediated inhibition of renal NAD(P)H oxidase, independently of a glucose-lowering effect.

Low-dose dextromethorphan, a NADPH oxidase inhibitor, reduces blood pressure and enhances vascular protection in experimental hypertension

Background

Vascular oxidative stress may be increased with age and aggravate endothelial dysfunction and vascular injury in hypertension. This study aimed to investigate the effects of dextromethorphan (DM), a NADPH oxidase inhibitor, either alone or in combination treatment, on blood pressure (BP) and vascular protection in aged spontaneous hypertensive rats (SHRs).

Methodology/Principal Findings

Eighteen-week-old WKY rats and SHRs were housed for 2 weeks. SHRs were randomly assigned to one of the 12 groups: untreated; DM monotherapy with 1, 5 or 25 mg/kg/day; amlodipine (AM, a calcium channel blocker) monotherapy with 1 or 5 mg/kg/day; and combination therapy of DM 1, 5 or 25 mg/kg/day with AM 1 or 5 mg/kg/day individually for 4 weeks. The in vitro effects of DM were also examined. In SHRs, AM monotherapy dose-dependently reduced arterial systolic BP. DM in various doses significantly and similarly reduced arterial systolic BP. Combination of DM with AM gave additive effects on BP reduction. DM, either alone or in combination with AM, improved aortic endothelial function indicated by ex vivo acetylcholine-induced relaxation. The combination of low-dose DM with AM gave most significant inhibition on aortic wall thickness in SHRs. Plasma total antioxidant status was significantly increased by all the therapies except for the combination of high-dose DM with high-dose AM. Serum nitrite and nitrate level was significantly reduced by AM but not by DM or the combination of DM with AM. Furthermore, in vitro treatment with DM reduced angiotensin II-induced reactive oxygen species and NADPH oxidase activation in human aortic endothelial cells.

Conclusions/Significance

Treatment of DM reduced BP and enhanced vascular protection probably by inhibiting vascular NADPH oxidase in aged hypertensive animals with or without AM treatment. It provides the potential rationale to a novel combination treatment with low-dose DM and AM in clinical hypertension.

Ferulsinaic Acid Modulates SOD, GSH, and Antioxidant Enzymes in Diabetic Kidney

The efficacy of Ferulsinaic acid (FA) to modulate the antioxidant enzymes and to reduce oxidative stress induced-diabetic nephropathy (DN) was studied. Rats were fed diets enriched with sucrose (50%, wt/wt), lard (30%, wt/wt), and cholesterol (2.5%, wt/wt) for 8 weeks to induce insulin resistance. After a DN model was induced by streptozotocin; 5, 50 and 500 mg/kg of FA were administrated by oral intragastric intubation for 12 weeks. In FA-treated diabetic rats, glucose, kidney/body weight ratio, creatinine, BUN, albuminurea, and creatinine clearance were significantly decreased compared with non treated diabetic rats. Diabetic rats showed decreased activities of SOD and GSH; increased concentrations of malondialdehyde and IL-6 in the serum and kidney, and increased levels of 8-hydroxy-2′-deoxyguanosine in urine and renal cortex. FA-treatment restored the altered parameters in a dose-dependent manner. The ultra morphologic abnormalities in the kidney of diabetic rats were markedly ameliorated by FA treatment. Furthermore, FA acid was found to attenuate chronic inflammation induced by both Carrageenan and dextran in rats. We conclude that FA confers protection against injuries in the kidneys of diabetic rats by increasing activities of antioxidant enzymes and inhibiting accumulation of oxidized DNA in the kidney, suggesting a potential drug for the prevention and therapy of DN.

Mutant p53R273H attenuates the expression of phase 2 detoxifying enzymes and promotes the survival of cells with high levels of reactive oxygen species

Uncontrolled accumulation of reactive oxygen species (ROS) causes oxidative stress and induces harmful effects. Both high ROS levels and p53 mutations are frequent in human cancer. Mutant p53 forms are known to actively promote malignant growth. However, no mechanistic details are known about the contribution of mutant p53 to excessive ROS accumulation in cancer cells. Herein, we examine the effect of p53(R273H), a commonly occurring mutated p53 form, on the expression of phase 2 ROS-detoxifying enzymes and on the ability of cells to readopt a reducing environment after exposure to oxidative stress. Our data suggest that p53(R273H) mutant interferes with the normal response of human cells to oxidative stress. We show here that, upon oxidative stress, mutant p53(R273H) attenuates the activation and function of NF-E2-related factor 2 (NRF2), a transcription factor that induces the antioxidant response. This effect of mutant p53 is manifested by decreased expression of phase 2 detoxifying enzymes NQO1 and HO-1 and high ROS levels. These findings were observed in several human cancer cell lines, highlighting the general nature of this phenomenon. The failure of p53(R273H) mutant-expressing cells to restore a reducing oxidative environment was accompanied by increased survival, a known consequence of mutant p53 expression. These activities are attributable to mutant p53(R273H) gain of function and might underlie its well-documented oncogenic nature in human cancer.

Fcγ receptor deficiency attenuates diabetic nephropathy

Among patients with diabetes, increased production of immunoglobulins against proteins modified by diabetes is associated with proteinuria and cardiovascular risk, suggesting that immune mechanisms may contribute to the development of diabetes complications, such as nephropathy. We investigated the contribution of IgG Fcγ receptors to diabetic renal injury in hyperglycemic, hypercholesterolemic mice. We used streptozotocin to induce diabetes in apolipoprotein E-deficient mice and in mice deficient in both apolipoprotein E and γ-chain, the common subunit of activating Fcγ receptors. After 15 weeks, the mice lacking Fcγ receptors had significantly less albuminuria and renal hypertrophy, despite similar degrees of hyperglycemia and hypercholesterolemia, immunoglobulin production, and glomerular immune deposits. Moreover, diabetic Fcγ receptor-deficient mice had less mesangial matrix expansion, inflammatory cell infiltration, and collagen and α-smooth muscle actin content in their kidneys. Accordingly, expression of genes involved in leukocyte infiltration, fibrosis, and oxidative stress was significantly reduced in diabetic kidneys and in mesangial cells cultured from Fcγ receptor-deficient mice. In summary, preventing the activation of Fcγ receptors alleviates renal hypertrophy, inflammation, and fibrosis in hypercholesterolemic mice with diabetes, suggesting that modulating Fcγ receptor signaling may be renoprotective in diabetic nephropathy.

The role of oxidative stress in the pathogenesis of diabetic vascular complications

Oxidative stress has been paid increasing attention to as an important causative factor for diabetic vascular complications. Among possible various sources, accumulating evidence has indicated that NAD(P)H oxidase may be the most important source for reactive oxygen species production in diabetic vascular tissues. The mechanisms underlying activation and up-regulation of NAD(P)H oxidase has been supposed to be mediated by high glucose-induced protein kinase C (PKC) activation. In this review article, activation of local renin-angiotensin II system induced by chymase activation is also shown to amplify such a PKC-dependent activation of NAD(P)H oxidase. Additionally, human evidence showing the beneficial effect of antioxidants on diabetic vascular complications. Bilirubin has been recognized as a strong endogenous antioxidant. Here markedly lower prevalence of vascular complications is shown in diabetic patients with Gilbert syndrome, a congenital hyperbilirubinemia, as well as reduced markers of oxidative stress and inflammation. Lastly, statin, angiotensin II receptor blocker, chymase inhibitor, bilirubin and biliverdin, PKC β isoform inhibitor, and glucagon-like peptide-1 analog, are shown to serve as antioxidants and have some beneficial effect on diabetic vascular complications, via inhibiting PKC-NAD(P)H oxidase activation, supporting the notion that this mechanism may be an effective therapeutic target for preventing diabetic vascular complications.

Exercise in the metabolic syndrome

The metabolic syndrome is a clustering of obesity, diabetes, hyperlipidemia, and hypertension that is occurring in increasing frequency across the global population. Although there is some controversy about its diagnostic criteria, oxidative stress, which is defined as imbalance between the production and inactivation of reactive oxygen species, has a major pathophysiological role in all the components of this disease. Oxidative stress and consequent inflammation induce insulin resistance, which likely links the various components of this disease. We briefly review the role of oxidative stress as a major component of the metabolic syndrome and then discuss the impact of exercise on these pathophysiological pathways. Included in this paper is the effect of exercise in reducing fat-induced inflammation, blood pressure, and improving muscular metabolism.

Role of oxidative stress in diabetes-mediated vascular dysfunction: unifying hypothesis of diabetes revisited

Oxidative stress is recognized as a key participant in the development of diabetic complications in the vasculature. One of the seminal studies advancing the role of oxidative stress in vascular endothelial cells proposed that oxidative stress-mediated diversion of glycolytic intermediates into pathological pathways was a key underlying element in the development of diabetic complications. It is widely recognized that flux through glycolysis slows during diabetes. However, several bottlenecks develop in the glycolytic pathway, including glucose transport, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and pyruvate kinase. Of these limiting steps in glycolysis, glyceraldehyde-3-phosphate dehydrogenase is most sensitive to oxidative stress, leading to the hypothesis that glyceraldehyde-3-phosphate inactivation by ribosylation underlies the diversion of glycolytic intermediates into pathological pathways. However, recent studies question the mechanism underlying the effect of reactive oxygen species on key enzymes of the glycolytic pathway. The present review critiques the major premises of the hypothesis and concludes that further study of the role of oxidative stress in the development of diabetes-mediated vasculature dysfunction is warranted.

Differential activations of PKC/PKA related to microvasculopathy in diabetic GK rats

Microvasculopathy is the most serious and predictable threat to the health of diabetic patients, which often results in end-stage renal disease, blindness, and limb amputations. Up to the present, the underlying mechanisms have remained elusive. Here, it was found that the differential activations of PKC/PKA were involved in diabetic microvasculopathy in diabetic GK rats. By real-time PCR, Western blot, immunohistochemistry, and enzyme activity assay, upregulation of PKC was prominent in kidney but was not significant in liver and brain. The expression and activity of PKA were lowered in kidney but comparable in brain and liver during diabetic nephropathy. Furthermore, the generation of reactive oxygen species, production of nitric oxide, and expression of inducible nitric oxide synthase induced by advanced glycation end products were inhibited by PKCβ inhibitor LY-333531 or a PKA agonist in rat glomerular microvascular endothelial cells. Finally, albuminuria was significantly lowered by a PKA agonist and boosted by a PKA antagonist. It suggested that the differential activations of PKC/PKA related to microvasculopathy in diabetes and that activation of PKA may protect the diabetic microvasculature.

Trigonella foenum graecum seed extract protects kidney function and morphology in diabetic rats via its antioxidant activity

Oxidative stress is involved in the development and progression of diabetic nephropathy (DN). Because Trigonella foenum graecum has been reported to have antidiabetic and antioxidative effects, we hypothesized that T foenum graecum seed aqueous extract (TE) restores the kidney function of diabetic rats via its antioxidant activity. Rats were fed diets enriched with sucrose (50%, wt/wt), lard (30%, wt/wt), and cholesterol (2.5%, wt/wt) for 8 weeks to induce insulin resistance. After a DN model was induced by streptozotocin, the rats were administered a low (440 mg/kg), medium (870 mg/kg), or high (1740 mg/kg) dose of TE by oral intragastric intubation for 6 weeks. In TE-treated DN rats, blood glucose, kidney/body weight ratio, serum creatinine, blood urea nitrogen, 24-hour content of urinary protein, and creatinine clearance were significantly decreased compared with nontreated DN rats. Diabetic rats showed decreased activities of superoxide dismutase and catalase, increased concentrations of malondialdehyde in the serum and kidney, and increased levels of 8-hydroxy-2'-deoxyguanosine in urine and renal cortex DNA. Treatment with TE restored the altered parameters in a dose-dependent manner. Furthermore, all of the ultramorphologic abnormalities in the kidney of diabetic rats, including the uneven thickening of the glomerular base membrane, were markedly ameliorated by TE treatment. We conclude that TE confers protection against functional and morphologic injuries in the kidneys of diabetic rats by increasing activities of antioxidants and inhibiting accumulation of oxidized DNA in the kidney, suggesting a potential drug for the prevention and therapy of DN.

PKCβ inhibition with ruboxistaurin reduces oxidative stress and attenuates left ventricular hypertrophy and dysfunction in rats with streptozotocin-induced diabetes

Oxidative stress plays critical roles in the development of diabetic cardiovascular complications, including myocardial hypertrophy. The β isoform of PKC (protein kinase C) is preferentially overexpressed in the myocardium of diabetic subjects accompanied with increased activation of the pro-oxidant enzyme NADPH oxidase, which may exacerbate oxidative stress. We hypothesized that myocardial PKCβ is a major upstream mediator of oxidative stress in diabetes and that PKCβ inhibition can attenuate myocardial hypertrophy and dysfunction. Control or streptozotocin-induced diabetic rats were treated with the selective PKCβ inhibitor RBX (ruboxistaurin; 1 mg/kg of body weight per day) or the antioxidant NAC (N-acetylcysteine) for 4 weeks. LV (left ventricular) dimensions and functions were detected by echocardiography. 15-F2t-isoprostane (a specific index of oxidative stress) and myocardial activities of superoxide dismutase as well as protein levels of NADPH oxidase were assessed by immunoassay or Western blotting. Echocardiography revealed that the LV mass/body weight ratio was significantly increased in diabetic rats (P<0.01 compared with the control group) in parallel with the impaired LV relaxation. A significant increase in cardiomyocyte cross-sectional area was observed in diabetic rats accompanied by an increased production of O2- (superoxide anion) and 15-F2t-isoprostane (all P<0.05 compared with the control group). RBX normalized these changes with concomitant inhibition of PKCβ2 activation and prevention of NADPH oxidase subunit p67phox membrane translocation and p22phox overexpression. The effects of RBX were comparable with that of NAC, except that NAC was inferior to RBX in attenuating cardiac dysfunction. It is concluded that RBX can ameliorate myocardial hypertrophy and dysfunction in diabetes, which may represent a novel therapy in the prevention of diabetic cardiovascular complications.

Apocynin attenuates oxidative stress and hypertension in young spontaneously hypertensive rats independent of ADMA/NO pathway

Both NADPH oxidase-derived reactive oxygen species (ROS) and asymmetric dimethylarginine (ADMA) are increased in hypertension. Apocynin, an NADPH oxidase inhibitor, could inhibit ROS, thus we tested whether apocynin can block NADPH oxidase and prevent increases of ADMA and blood pressure (BP) in spontaneously hypertensive rats (SHRs). SHRs and Wistar Kyoto (WKY) rats, aged 4 weeks, were assigned to four groups: untreated SHRs and WKY rats, SHRs and WKY rats that received 2.5 mM apocynin for 8 weeks. BP was significantly higher in SHRs compared to WKY rats, which was attenuated by apocynin. Apocynin prevented p47phox translocation in SHR kidneys, but not the increase of superoxide and H(2)O(2). Additionally, apocynin did not protect SHRs against increased ADMA. Apocynin blocks NADPH oxidase to attenuate hypertension, but has little effect on the ADMA/nitric oxide (NO) pathway in young SHRs. The reduction of ROS and the preservation of NO simultaneously might be a better approach to restoring ROS-NO balance to prevent hypertension.

Diabetes and alpha lipoic Acid

Diabetes mellitus is a multi-faceted metabolic disorder where there is increased oxidative stress that contributes to the pathogenesis of this debilitating disease. This has prompted several investigations into the use of antioxidants as a complementary therapeutic approach. Alpha lipoic acid, a naturally occurring dithiol compound which plays an essential role in mitochondrial bioenergetic reactions, has gained considerable attention as an antioxidant for use in managing diabetic complications. Lipoic acid quenches reactive oxygen species, chelates metal ions, and reduces the oxidized forms of other antioxidants such as vitamin C, vitamin E, and glutathione. It also boosts antioxidant defense system through Nrf-2-mediated antioxidant gene expression and by modulation of peroxisome proliferator activated receptors-regulated genes. ALA inhibits nuclear factor kappa B and activates AMPK in skeletal muscles, which in turn have a plethora of metabolic consequences. These diverse actions suggest that lipoic acid acts by multiple mechanisms, many of which have only been uncovered recently. In this review we briefly summarize the known biochemical properties of lipoic acid and then discussed the oxidative mechanisms implicated in diabetic complications and the mechanisms by which lipoic acid may ameliorate these reactions. The findings of some of the clinical trials in which lipoic acid administration has been tested in diabetic patients during the last 10 years are summarized. It appears that the clearest benefit of lipoic acid supplementation is in patients with diabetic neuropathy.

Modulation of renal superoxide dismutase by telmisartan therapy in C57BL/6-Ins2(Akita) diabetic mice

Renal superoxide excess, which is induced by an imbalance of the superoxide-producing enzyme NAD(P)H oxidase and the superoxide-scavenging enzyme superoxide dismutase (SOD) under hyperglycemia, increases oxidative stress and contributes to the development of diabetic nephropathy. In this study, we treated non-obese and hypoinsulinemic C57BL/6-Ins2^Akita (C57BL/6-Akita) diabetic mice with telmisartan (5 mg kg⁻¹ per day), an angiotensin II type 1 receptor blocker, or amlodipine (5 mg kg⁻¹ per day), a calcium channel blocker, for 4 weeks and compared the effects of these two anti-hypertensive drugs on renal NAD(P)H oxidase, SOD and transcription factor Nrf2 (NF-E2-related factor 2), which is known to upregulate several antioxidant enzymes including SOD. Vehicle-treated C57BL/6-Akita mice exhibited higher renal NAD(P)H oxidase and lower renal SOD activity with increased levels of renal superoxide than the C57BL/6-wild-type non-diabetic mice. Interestingly, telmisartan treatment not only reduced NAD(P)H oxidase activity but also enhanced SOD activity in C57BL/6-Akita mouse kidneys, leading to a reduction of renal superoxide levels. Furthermore, telmisartan-treated C57BL/6-Akita mice increased the renal protein expression of SOD and Nrf2. In parallel with the reduction of renal superoxide levels, a reduction of urinary albumin levels and a normalization of elevated glomerular filtration rate were observed in telmisartan-treated C57BL/6-Akita mice. In contrast, treatment with amlodipine failed to modulate renal NAD(P)H oxidase, SOD and Nrf2. Finally, treatment of C57BL/6-Akita mice with apocynin, an NAD(P)H oxidase inhibitor, also increased the renal protein expression of SOD and Nrf2. Collectively, our data suggest that NAD(P)H oxidase negatively regulates renal SOD, possibly by downregulation of Nrf2, and that telmisartan could upregulate renal SOD by the suppression of NAD(P)H oxidase and subsequent upregulation of Nrf2, leading to the amelioration of renal oxidative stress and diabetic renal changes.

Angiotensin II type II receptor deficiency accelerates the development of nephropathy in type I diabetes via oxidative stress and ACE2

Since the functional role(s) of angiotensin II (Ang II) type II receptor (AT₂R) in type I diabetes is unknown, we hypothesized that AT₂R is involved in decreasing the effects of type I diabetes on the kidneys. We induced diabetes with low-dose streptozotocin (STZ) in both AT₂R knockout (AT₂RKO) and wild-type (WT) male mice aged 12 weeks and followed them for 4 weeks. Three subgroups nondiabetic, diabetic, and insulin-treated diabetic (Rx insulin implant) were studied. Systolic blood pressure (SBP), physiological parameters, glomerular filtration rate (GFR), renal morphology, gene expression, and apoptosis were assessed. After 4 weeks of diabetes, compared to WT controls, AT₂RKO mice clearly developed features of early diabetic nephropathy (DN), such as renal hypertrophy, tubular apoptosis, and progressive extracellular matrix (ECM) protein accumulation as well as increased GFR. AT₂RKO mice presented hypertension unaffected by diabetes. Renal oxidative stress (measured as heme oxygenase 1 (HO-1) gene expression and reactive oxygen species (ROS) generation) and intrarenal renin angiotensin system components, such as angiotensinogen (Agt), AT₁R, and angiotensin-converting enzyme (ACE) gene expression, were augmented whereas angiotensin-converting enzyme2 (ACE2) gene expression was decreased in renal proximal tubules (RPTs) of AT₂RKO mice. The renal changes noted above were significantly enhanced in diabetic AT₂RKO mice but partially attenuated in insulin-treated diabetic WT and AT₂RKO mice. In conclusion, AT₂R deficiency accelerates the development of DN, which appears to be mediated, at least in part, via heightened oxidative stress and ACE/ACE2 ratio in RPTs.

High glucose-induced RhoA activation requires caveolae and PKCβ1-mediated ROS generation

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. We previously showed that RhoA activation by high glucose in mesangial cells (MC) leads to matrix upregulation (Peng F, Wu D, Gao B, Ingram AJ, Zhang B, Chorneyko K, McKenzie R, Krepinsky JC. Diabetes 57: 1683-1692, 2008). Here, we study the mechanism whereby RhoA is activated. In primary rat MC, RhoA activation required glucose entry and metabolism. Broad PKC inhibitors (PMA, bisindolylmaleimide, Gö6976), as well as specific PKCβ blockade with an inhibitor and small interfering RNA (siRNA), prevented RhoA activation by glucose. PKCβ inhibition also abrogated reactive oxygen species (ROS) generation by glucose. The ROS scavenger N-acetylcysteine (NAC) or NADPH oxidase inhibitors apocynin and DPI prevented glucose-induced RhoA activation. RhoA and some PKC isoforms localize to caveolae. Chemical disruption of these microdomains prevented RhoA and PKCβ1 activation by glucose. In caveolin-1 knockout cells, glucose did not induce RhoA and PKCβ1 activation; these responses were rescued by caveolin-1 reexpression. Furthermore, glucose-induced ROS generation was significantly attenuated by chemical disruption of caveolae and in knockout cells. Downstream of RhoA signaling, activator protein-1 (AP-1) activation was also inhibited by disrupting caveolae, was absent in caveolin-1 knockout MC and rescued by caveolin-1 reexpression. Finally, transforming growth factor (TGF)-β1 upregulation, mediated by AP-1, was prevented by RhoA signaling inhibition and by disruption or absence of caveolae. In conclusion, RhoA activation by glucose is dependent on PKCβ1-induced ROS generation, most likely through NADPH oxidase. The activation of PKCβ1 and its downstream effects, including upregulation of TGF-β1, requires caveolae. These microdomains are thus important mediators of the profibrogenic process associated with diabetic nephropathy.

Effects of training and nitric oxide on diabetic nephropathy progression in type I diabetic rats

The aim of the paper is to assess nitric oxide (NO) production during aerobic training and its role on the progression of diabetic nephropathy in rats. Induction of diabetes mellitus (DM) was achieved in adult male Wistar rats with streptozotocin. Half of the animals underwent training on a treadmill and the others (sedentary) stayed on a turned-off treadmill for the same period according to the following groups: sedentary control (CTL + SE); training control (CTL + EX); sedentary diabetic (DM + SE); and training diabetic (DM + EX) (n = 9 for all groups). The training on treadmill was carried out at a work rate of 16 m/min, 60 min/d, 5 d/week for eight weeks. Before and after the exercises, rats were placed in individual metabolic cages with standard chow and water ad libitum, for 24-h urine collection, followed by three hours' fasting blood sample withdrawal from the retro-orbital plexus, under anesthesia. Diabetic animals showed reduction of body weight, creatinine and urea depurations and NO excretion, increased blood glucose concentrations, albuminuria and thiobarbituric acid reactive substance (TBARS) excretion, when compared with the respective controls. All these alterations induced by DM were attenuated in the DM + EX versus DM + SE group. Analysis of insulin concentrations at the end of the protocol showed no significant change between the DM + SE and DM + EX groups. In conclusion, our data show that a routine physical exercise resulted in a better control of glycemia with an increased NO bioavailability and oxidative stress control, associated with an amelioration of renal function. We suggest aerobic training and the control of oxidative and nitrosative stress as useful non-pharmacological tools to delay the progression of diabetic nephropathy.

Roles of reactive oxygen and nitrogen species in pain

Peroxynitrite (PN; ONOO⁻) and its reactive oxygen precursor superoxide (SO; O₂•⁻) are critically important in the development of pain of several etiologies including pain associated with chronic use of opiates such as morphine (also known as opiate-induced hyperalgesia and antinociceptive tolerance). This is now an emerging field in which considerable progress has been made in terms of understanding the relative contributions of SO, PN, and nitroxidative stress in pain signaling at the molecular and biochemical levels. Aggressive research in this area is poised to provide the pharmacological basis for development of novel nonnarcotic analgesics that are based upon the unique ability to selectively eliminate SO and/or PN. As we have a better understanding of the roles of SO and PN in pathophysiological settings, targeting PN may be a better therapeutic strategy than targeting SO. This is because, unlike PN, which has no currently known beneficial role, SO may play a significant role in learning and memory. Thus, the best approach may be to spare SO while directly targeting its downstream product, PN. Over the past 15 years, our team has spearheaded research concerning the roles of SO and PN in pain and these results are currently leading to the development of solid therapeutic strategies in this important area.

Curcumin attenuates diabetic nephropathy by inhibiting PKC-α and PKC-β1 activity in streptozotocin-induced type I diabetic rats

SCOPE

We hypothesized that curcumin, a potent anti-oxidant, might be beneficial in ameliorating the development of diabetic nephropathy through inhibition of PKC-α and PKC-β1 activity-ERK1/2 pathway.

METHODS AND RESULTS

Diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ) (55 mg/kg) in rats. Three weeks after STZ injection, rats were divided into three groups, namely, normal, diabetic and diabetic treated with curcumin at 100 mg/kg/day, p.o., for 8 wk. At 11 wk after STZ injection, diabetic rats exhibited renal dysfunction, as evidenced by reduced creatinine clearance, increased blood urea nitrogen (BUN) and proteinuria, marked increases in lipid peroxidation, NOX4 and p67phox and decrease in anti-oxidant enzyme. All of these abnormalities were significantly reversed by curcumin. Furthermore, the high-glucose-induced PKC-α and PKC-β1 activities and phosphorylated ERK1/2 was significantly diminished by curcumin. Curcumin also attenuated the expression of TGF-β1, CTGF, osteopontin, p300 and ECM proteins such as fibronectin and type IV collagen. The high-glucose-induced expression of VEGF and its receptor VEGF receptor II (flk-1) was also ameliorated by curcumin.

CONCLUSION

These results prove that curcumin produces dual blockade of both PKC-α and PKC-β1 activities, which suggests that curcumin is a potential adjuvant therapy for the prevention and treatment of diabetic nephropathy.

Protein kinase CbetaII-mediated phosphorylation of endothelial nitric oxide synthase threonine 495 mediates the endothelial dysfunction induced by FK506 (tacrolimus)

FK506 [tacrolimus; hexadecahydro-5,19-dihydroxy-3-[2-(4-hydroxy-3-methoxycyclohexyl)-1-methylethenyl]-14,16-dimethoxy-4,10,12,18-tetramethyl-8-(2-propenyl)-15,19-epoxy-3H-pyrido[2,1-c][1,4]oxa-azacyclotricosine-1,7,20,21(4H,23H)-tetrone] is used clinically to reduce the incidence of allograft rejection; however, chronic administration leads to endothelial dysfunction and hypertension. We have previously shown that FK506 activates Ca(2+)/diacylglycerol-dependent conventional protein kinase C (cPKC), which phosphorylates endothelial nitric oxide synthase (eNOS) at one of its inhibitory sites, Thr495. However, which cPKC isoform is responsible for phosphorylating eNOS Thr495 is unknown. The aim of the current study was to determine the cPKC isoform that is activated by FK506, leading to decreased endothelial function. FK506 reduced endothelium-dependent relaxation responses, yet had no effect on endothelium-independent relaxation responses in aortas from control mice. Of the various cPKC isoforms, only the administration of a PKCβ(II) isoform-specific peptide inhibitor restored aortic relaxation responses to that of controls. In aortic endothelial cells, FK506 significantly increased PKCβ(II) activation compared with vehicle-treated controls, and this was prevented by a PKCβ(II) isoform-specific peptide inhibitor. In addition, a PKCβ(II) isoform-specific peptide inhibitor prevented the increase in eNOS Thr495 phosphorylation induced by FK506. Taken together, our results indicate that β(II) is the cPKC isoform responsible for phosphorylating eNOS at the inhibitory site Thr495 in response to FK506. PKCβ(II) inhibition could prove beneficial in ameliorating the endothelial dysfunction and hypertension in patients treated with FK506.

Augmented NADPH oxidase activity and p22phox expression in monocytes underlie oxidative stress of patients with type 2 diabetes mellitus

BACKGROUND

This study was to test the hypothesis that enhanced oxidative stress is induced in monocytes with over-activated NADPH oxidase during the development of type 2 diabetes mellitus.

METHODS

Levels of glucose and lipids were analyzed in 73 diabetic patients and 36 controls. Superoxide dismutase (SOD), malondialdehyde (MDA), reactive oxygen species (ROS) and protein carbonylation were tested. Expression of NADPH oxidase was examined and p47phox translocation was assessed.

RESULTS

With the abnormality of glucose and lipid metabolism, diabetic patients showed a higher oxidative stress state indicated by decreased SOD activity but elevated MDA and protein carbonylation level. Monocytes in diabetes also showed elevated ROS generation and protein carbonylation level. Furthermore, NADPH oxidase was highly activated in monocytes represented by p22phox up-regulation and p47phox translocation. Significant positive bivariate correlation was found between glucose and MDA level as well as p22phox expression. In vitro experiments also indicated that glucose could stimulate ROS generation in a NADPH oxidase dependent manner. Moreover, we carried out same measurement in 40 diabetic patients with anti-diabetic intervention and obtained the reinforced results.

CONCLUSIONS

Hyperglycemia is the main factor which induces oxidative stress mainly by activation of NADPH oxidase in monocytes of diabetic patients.

Myofibroblast differentiation during fibrosis: role of NAD(P)H oxidases

Progression of fibrosis involves interstitial hypercellularity, matrix accumulation, and atrophy of epithelial structures, resulting in loss of normal function and ultimately organ failure. There is common agreement that the fibroblast/myofibroblast is the cell type most responsible for interstitial matrix accumulation and consequent structural deformations associated with fibrosis. During wound healing and progressive fibrotic events, fibroblasts transform into myofibroblasts acquiring smooth muscle features, most notably the expression of alpha-smooth muscle actin and synthesis of mesenchymal cell-related matrix proteins. In renal disease, glomerular mesangial cells also acquire a myofibroblast phenotype and synthesize the same matrix proteins. The origin of interstitial myofibroblasts during fibrosis is a matter of debate, where the cells are proposed to derive from resident fibroblasts, pericytes, perivascular adventitial, epithelial, and/or endothelial sources. Regardless of the origin of the cells, transforming growth factor-beta1 (TGF-β1) is the principal growth factor responsible for myofibroblast differentiation to a profibrotic phenotype and exerts its effects via Smad signaling pathways involving mitogen-activated protein kinase and Akt/protein kinase B. Additionally, reactive oxygen species (ROS) have important roles in progression of fibrosis. ROS are derived from a variety of enzyme sources, of which the nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase family has been identified as a major source of superoxide and hydrogen peroxide generation in the cardiovasculature and kidney during health and disease. Recent evidence indicates that the NAD(P)H oxidase homolog Nox4 is most accountable for ROS-induced fibroblast and mesangial cell activation, where it has an essential role in TGF-β1 signaling of fibroblast activation and differentiation into a profibrotic myofibroblast phenotype and matrix production. Information on the role of ROS in mesangial cell and fibroblast signaling is incomplete, and further research on myofibroblast differentiation during fibrosis is warranted.

Bilirubin and biliverdin protect rodents against diabetic nephropathy by downregulating NAD(P)H oxidase

We recently found a markedly lower prevalence of vascular complications, including kidney disease, in diabetic patients with Gilbert syndrome, a congenital form of hyperbilirubinemia, suggesting a beneficial effect of bilirubin (BIL) on diabetic nephropathy. To directly examine this, we determined whether hereditary hyperbilirubinemic Gunn j/j rats and biliverdin (BVD)-treated diabetic db/db mice were resistant to the development of renal disease. Both rodent models had less albuminuria and complete protection against the progression of mesangial expansion accompanied by normalization of transforming growth factor-β1 and fibronectin expression. Simultaneously, there was normalization of urinary and renal oxidative stress markers, and the expression of nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase subunits in the kidney. In cultured vascular endothelial and mesangial cells, BIL and BVD significantly inhibited NADPH-dependent superoxide production, and both high glucose- and angiotensin II-induced production of reactive oxygen species. Collectively, our findings suggest that BIL and BVD may protect against diabetic nephropathy and may lead to novel antioxidant therapies for diabetic nephropathy.

Melatonin prevents increased asymmetric dimethylarginine in young rats with bile duct ligation

Identifying and treating kidney injury in cirrhosis is important. Bile duct ligation (BDL) is a commonly used cholestatic liver disease model. We hypothesized that asymmetric dimethylarginine (ADMA) is involved in BDL-induced oxidative stress and kidney injury, which can be prevented by melatonin. We also intended to elucidate whether increased ADMA is due to increased protein arginine methyltransferase-1 (PRMT1, ADMA-synthesizing enzyme) and/or decreased dimethylarginine dimethylaminohydrolase (DDAH, ADMA-metabolizing enzyme). Three groups of young rats were studied, sham (N = 7), untreated BDL rats (N = 9), and melatonin-treated BDL rats (N = 6, BDL + M). Melatonin-treated BDL rats received daily melatonin 1 mg/kg/day via intraperitoneal injection. One-third of the young BDL rats died compared with none in the BDL + M group. All surviving rats were killed 14 days after surgery. BDL rats had higher plasma aspartate aminotransferase, alanine aminotransferase, direct and total bilirubin, and ammonia levels than shams. They also had kidney injury characterized by increased tubulointerstitial injury scores and plasma creatinine and symmetric dimethylarginine levels, which melatonin prevented. Plasma ADMA levels were elevated in BDL rats, combined with increased hepatic PRMT1 and decreased renal DDAH activity. In addition, melatonin increased hepatic DDAH2 expression, increased DDAH activity and concomitantly decreased ADMA contents in both the liver and kidney. In conclusion, melatonin therapy decreased mortality and prevented kidney injury induced by BDL via reduction of ADMA (by increasing DDAH activity) and oxidative stress.

Oxidative stress mediates nephropathy in type Ia glycogen storage disease

Glycogen storage disease type Ia (GSD-Ia) patients, deficient in glucose-6-phosphatase-alpha, manifest disturbed glucose homeostasis with long-term renal disease. We have previously shown that renal fibrosis in GSD-Ia is mediated by the angiotensin/transforming growth factor-beta1 (TGF-beta1) pathway, which also elicits renal damage through oxidative stress. In this study, we further elucidate the mechanism of renal disease by showing that renal expression of Nox-2, p22(phox), and p47(phox), components of NADPH oxidase, are upregulated in GSD-Ia mice compared with controls. Akt/protein kinase B, a downstream mediator of angiotensin II and TGF-beta1, is also activated, leading to phosphorylation and inactivation of the Forkhead box O family of transcription factors. This in turn triggers downregulation of superoxide dismutase and catalase (CAT) activities that have essential roles in oxidative detoxification in mammals. Renal oxidative stress in GSD-Ia mice is shown by increased oxidation of dihydroethidium and by oxidative damage of DNA. Importantly, renal dysfunction, reflected by elevated serum levels of blood urea nitrogen, reduced renal CAT activity, and increased renal fibrosis, is improved in GSD-Ia mice treated with the antioxidant drug tempol. These data provide the first evidence that oxidative stress is one mechanism that underlies GSD-Ia nephropathy.

Effects of an oral adsorbent on oxidative stress and fibronectin expression in experimental diabetic nephropathy

BACKGROUND

Previous studies have demonstrated that AST-120 (Kremezin((R))), a well-known oral adsorbent, inhibits the progression of diabetic (DM) and non-DM chronic kidney disease along with a decrease in oxidative stress. This study was undertaken to investigate whether AST-120 could reduce oxidative stress and ameliorate the development of nephropathy in experimental DM rats with normal renal function.

METHODS

Rats were injected with diluent (C, n = 16) or 65 mg/kg streptozotocin intraperitoneally (DM, n = 16), and eight rats from each group were treated with chow containing 5% AST-120. After 3 months, plasma advanced oxidation protein products (AOPP) and total malondialdehyde (MDA) levels, 24-h urinary albumin excretion, and urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) excretion were determined by ELISA. Glomerular endothelial nitric oxide synthase (eNOS), subunits of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (gp91phox, p47phox and p22phox), and fibronectin (FN) mRNA and protein expressions were determined by real-time PCR and western blot, respectively. In addition, dichlorodihydrofluorescein diacetate (DCF-DA) staining was performed to detect glomerular reactive oxygen species (ROS) production.

RESULTS

Compared to the C group, 24-h urinary albumin excretion was significantly higher in the DM group (P < 0.01), and AST-120 treatment significantly reduced albuminuria in DM rats (P < 0.05). Glomerular eNOS, gp91phox, p47phox and FN expression were significantly increased in DM rats compared to C rats, and these increases in DM glomeruli were significantly abrogated by AST-120 treatment (P < 0.05). The increases in plasma AOPP and MDA levels as well as renal oxidative stress in DM rats, assessed by DCF-DA staining and urinary 8-OHdG excretion rates, were also significantly attenuated by AST-120 treatment (P < 0.05).

CONCLUSION

In conclusion, the renoprotective effects of AST-120 in DM nephropathy seem to be associated with the amelioration of enhanced oxidative stress and FN expression under diabetic conditions.

Metformin induces suppression of NAD(P)H oxidase activity in podocytes

Hyperglycemia increases the production of reactive oxygen species (ROS). NAD(P)H oxidase, producing superoxide anion, is the main source of ROS in diabetic podocytes and their production contributes to the development of diabetic nephropathy. We have investigated the effect of an antidiabetic drug, metformin on the production of superoxide anion in cultured podocytes and attempted to elucidate underlying mechanisms. The experiments were performed in normal (NG, 5.6mM) and high (HG, 30mM) glucose concentration. Overall ROS production was measured by fluorescence of a DCF probe. Activity of NAD(P)H oxidase was measured by chemiluminescence method. The AMP-dependent kinase (AMPK) activity was determined by immunobloting, measuring the ratio of phosphorylated AMPK to total AMPK. Glucose accumulation was measured using 2-deoxy-[1,2-(3)H]-glucose. ROS production increased by about 27% (187+/-8 vs. 238+/-9 arbitrary units AU, P<0.01) in HG. Metformin (2mM, 2h) markedly reduced ROS production by 45% in NG and 60% in HG. Metformin decreased NAD(P)H oxidase activity in NG (36%) and HG (86%). AMPK activity was increased by metformin in NG and HG (from 0.58+/-0.07 to. 0.99+/-0.06, and from 0.53+/-0.03 to 0.64+/-0.03; P<0.05). The effects of metformin on the activities of NAD(P)H oxidase and AMPK were abolished in the presence of AMPK inhibitor, compound C. We have shown that metformin decreases production of ROS through reduction of NAD(P)H oxidase activity. We also have demonstrated relationship between activity of NAD(P)H oxidase and AMPK.

Ruboxistaurin: PKC-beta inhibition for complications of diabetes

Diabetes mellitus is the most common cause of blindness among working-age adults, with a prevalence of 7 - 8% of adults in the USA, and is one of the most common causes of renal failure requiring kidney transplant and the most common cause of non-traumatic lower limb amputation in developed nations [1] . The role of the intracellular signaling enzyme protein kinase C (PKC) in the development of diabetic complications has become a field of intense research interest. An inhibitor of the PKC-beta isoform ruboxistaurin (RBX) has in vitro and in vivo benefits in ameliorating disturbances of cell regulation and blood flow related to hyperglycemia. The benefit of RBX for peripheral neuropathy has not been successfully demonstrated in Phase III trials. Although there was a beneficial effect of RBX on nephropathy in a pilot study, there has been no further clinical development for this indication. The major cause of visual disability - diabetic macular edema - seems to respond to RBX treatment with both anatomic and functional benefits. The manufacturer, Eli Lilly Co., has received an approvable letter from the FDA for the prevention of vision loss in patients with diabetic retinopathy with RBX, pending results of additional clinical trials for this indication.

Preventive effects of syngeneic bone marrow transplantation on diabetic nephropathy in mice

Treatment with autologous bone marrow transplantation (ABMT) can change the natural history of diabetes in patients with new-onset Type 1 diabetes (T1D). Effects of syngeneic bone marrow transplantation (syn-BMT) on diabetic nephropathy were studied in streptozotocin-induced diabetic mice. Diabetic mice received sibling's bone marrow on days 3, 10, 20, or 40 after T1D onset, respectively. Renal pathology, levels of oxidative stress, and the expressions of angiotensinogen (AGT), monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor beta 1 (Tgf-beta1) mRNA were investigated. Treatment with syn-BMT when disease was early-onset reduced mesangial area expansion and kidney enlargement; besides, if it is given on day 10, syn-BMT attenuated glomerular hypertrophy. Oxidative stress factors such as catalase (CAT) and superoxide radical anion O(2-) (O(2-)) were markedly maintained by syn-BMT compared to mice without treatment. In diabetic mice without treatment, renal AGT and MCP-1 mRNA were increased, while they were effectively suppressed by syn-BMT. But it showed no changes or even increment in Tgf-beta1 mRNA after syn-BMT. Syn-BMT, if applied when disease was early-onset, ameliorated diabetic renal injury. These preventive effects could be partly via maintaining oxidative stress and expression of AGT and MCP-1 in kidney in streptozotocin-diabetic mice.

Protein kinase C-dependent NAD(P)H oxidase activation induced by type 1 diabetes in renal medullary thick ascending limb

Type 1 diabetes provokes a protein kinase C (PKC)-dependent accumulation of superoxide anion in the renal medullary thick ascending limb (mTAL). We hypothesized that this phenomenon involves PKC-dependent NAD(P)H oxidase activation. The validity of this hypothesis was explored using mTAL suspensions prepared from rats with streptozotocin-induced diabetes and from sham (vehicle-treated) rats. Superoxide production was 5-fold higher in mTAL suspensions from diabetic rats compared with suspensions from sham rats. The NAD(P)H oxidase inhibitor apocynin caused an 80% decrease in superoxide production by mTAL from diabetic rats (P<0.05 vs untreated) without altering superoxide production by sham mTAL. NAD(P)H oxidase activity was >2-fold higher in mTAL from diabetic rats than in sham mTAL (P<0.05). Pretreatment with calphostin C (broad-spectrum PKC inhibitor) or rottlerin (PKCdelta inhibitor) reduced NAD(P)H oxidase activity by approximately 80% in both groups; however, PKCalpha/beta or PKCbeta inhibition did not alter NAD(P)H oxidase activity in either group. Protein levels of Nox2, Nox4, and p47phox were significantly higher in diabetic mTAL than in mTAL from sham rats. In summary, elevated superoxide production by mTAL from diabetic rats was normalized by NAD(P)H oxidase inhibition. PKC-dependent, PKCdelta-dependent, and total NAD(P)H oxidase activity was greater in mTAL from diabetic rats compared with sham. Protein levels of Nox2, Nox4, and p47phox were increased in mTAL from diabetic rats. We conclude that increased superoxide production by the mTAL during diabetes involves a PKCdelta-dependent increase in NAD(P)H oxidase activity in concert with increased protein levels of catalytic and regulatory subunits of the enzyme.

[Oxidative stress: a review on metabolic signaling in type 1 diabetes]

Diabetic complications appear to be multifactorial process. The biochemical and pathological mechanisms are associated with chronic hyperglycemia of diabetes and the increased oxidative stress which has been postulated to play a central role in these disorders. Accumulating evidence suggests that oxidative cell injury caused by free radicals contributes to the development of type 1 diabetes (DM1) complications and decreased efficiency of antioxidant defenses (both enzymatic and nonenzymatic) seems to correlate with the severity of pathological tissue changes in DM1. In this review, we report as oxidative stress may exert deleterious effects in diabetes, as well as address current strategies in study to down-regulating vascular injury.

NAD(P)H oxidase mediates TGF-beta1-induced activation of kidney myofibroblasts

TGF-beta1 expression closely associates with activation and conversion of fibroblasts to a myofibroblast phenotype and synthesis of an alternatively spliced cellular fibronectin variant, Fn-ED-A. Reactive oxygen species (ROS), such as superoxide, which is a product of NAD(P)H oxidase, also promote the transition of fibroblasts to myofibroblasts, but whether these two pathways are interrelated is unknown. Here, we examined a role for NAD(P)H oxidase-derived ROS in TGF-beta1-induced activation of rat kidney fibroblasts and expression of alpha-smooth muscle actin (alpha-SMA) and Fn-ED-A. In vitro, TGF-beta1 stimulated formation of abundant stress fibers and increased expression of both alpha-SMA and Fn-ED-A. In addition, TGF-beta1 increased both the activity of NADPH oxidase and expression of Nox2 and Nox4, homologs of the NAD(P)H oxidase family, indicating that this growth factor induces production of ROS. Small interfering RNA targeted against Nox4 markedly inhibited TGF-beta1-induced stimulation of NADPH oxidase activity and reduced alpha-SMA and Fn-ED-A expression. Inhibition of TGF-beta1 receptor 1 blocked Smad3 phosphorylation; reduced TGF-beta1-enhanced NADPH oxidase activity; and decreased expression of Nox4, alpha-SMA, and Fn-ED-A. Diphenyleneiodonium, an inhibitor of flavin-containing enzymes such as the Nox oxidases, had no effect on TGF-beta1-induced Smad3 but reduced both alpha-SMA and Fn-ED-A protein expression. The Smad3 inhibitor SIS3 reduced NADPH oxidase activity, Nox4 expression, and blocked alpha-SMA and Fn-ED-A, indicating that stimulation of myofibroblast activation by ROS is downstream of Smad3. In addition, TGF-beta1 stimulated phosphorylation of extracellular signal-regulated kinase (ERK1/2), and this was inhibited by blocking TGF-beta1 receptor 1, Smad3, or the Nox oxidases; ERK1/2 activation increased alpha-SMA and Fn-ED-A. Taken together, these results suggest that TGF-beta1-induced conversion of fibroblasts to a myofibroblast phenotype involves a signaling cascade through Smad3, NAD(P)H oxidase, and ERK1/2.