Reactive oxygen species, PKC-beta1, and PKC-zeta mediate high-glucose-induced vascular endothelial growth factor expression in mesangial cells

SIRT6's function in controlling the metabolism of lipids and glucose in diabetic nephropathy

Diabetic nephropathy (DN) is a complication of diabetes mellitus (DM) and the main cause of excess mortality in patients with type 2 DM. The pathogenesis and progression of DN are closely associated with disorders of glucose and lipid metabolism. As a member of the sirtuin family, SIRT6 has deacetylation, defatty-acylation, and adenosine diphosphate-ribosylation enzyme activities as well as anti-aging and anticancer activities. SIRT6 plays an important role in glucose and lipid metabolism and signaling, especially in DN. SIRT6 improves glucose and lipid metabolism by controlling glycolysis and gluconeogenesis, affecting insulin secretion and transmission and regulating lipid decomposition, transport, and synthesis. Targeting SIRT6 may provide a new therapeutic strategy for DN by improving glucose and lipid metabolism. This review elaborates on the important role of SIRT6 in glucose and lipid metabolism, discusses the potential of SIRT6 as a therapeutic target to improve glucose and lipid metabolism and alleviate DN occurrence and progression of DN, and describes the prospects for future research.

The Role of Diacylglycerol Kinase in the Amelioration of Diabetic Nephropathy

The drastic increase in the number of patients with diabetes and its complications is a global issue. Diabetic nephropathy, the leading cause of chronic kidney disease, significantly affects patients’ quality of life and medical expenses. Furthermore, there are limited drugs for treating diabetic nephropathy patients. Impaired lipid signaling, especially abnormal protein kinase C (PKC) activation by de novo-synthesized diacylglycerol (DG) under high blood glucose, is one of the causes of diabetic nephropathy. DG kinase (DGK) is an enzyme that phosphorylates DG and generates phosphatidic acid, i.e., DGK can inhibit PKC activation under diabetic conditions. Indeed, it has been proven that DGK activation ameliorates diabetic nephropathy. In this review, we summarize the involvement of PKC and DGK in diabetic nephropathy as therapeutic targets, and its mechanisms, by referring to our recent study.

Polyol pathway and redox balance in diabetes

Diabetes is a major public health disease that is globally approaching epidemic proportions. One of the major causes of type 2 diabetes is either a defect in insulin secretion or insulin action which is usually caused by a combination of genetic and environmental factors. Not only these factors but others such as deregulation of various pathways, and oxidative stress are also known to trigger the redox imbalance in diabetics. Increasing evidences suggest that there are tight interactions between the development of diabetes and redox imbalance. An alternate pathway of glucose metabolism, the polyol pathway, becomes active in patients with diabetes that disturbs the balance between NADH and NAD+ . The occurrence of such redox imbalance supports other pathways that lead to oxidative damage to DNA, lipids, and proteins and consequently to oxidative stress which further ascend diabetes and its complications. However, the precise mechanism through which oxidative stress regulates diabetes progression remains to be elucidated. The understanding of how antioxidants and oxidants are controlled and impact the generation of oxidative stress and progression of diabetes is essential. The main focus of this review is to provide an overview of redox imbalance caused by oxidative stress through the polyol pathway. Understanding the pathological role of oxidative stress in diabetes will help to design potential therapeutic strategies against diabetes.

N-type calcium channel and renal injury

Accumulating evidences indicated that voltage-gated calcium channels (VDCC), including L-, T-, N-, and P/Q-type, are present in kidney and contribute to renal injury during various chronic diseases trough different mechanisms. As a voltage-gated calcium channel, N-type calcium channel was firstly been founded predominately distributed on nerve endings which control neurotransmitter releases. Since sympathetic nerve is distributed along renal afferent and efferent arterioles, N-type calcium channel blockade on sympathetic nerve terminals would bring renal dynamic improvement by dilating both arterioles and reducing glomerular pressure. In addition, large body of scientific research indicated that neurotransmitters, such as norepinephrine, releases by activating N-type calcium channel can trigger inflammatory and fibrotic signaling pathways in kidney. Interestingly, we recently demonstrated that N-type calcium channel is also expressed on podocytes and may directly contribute to podocyte injury in denervated animal models. In this paper, we will summarize our current knowledge regarding renal N-type calcium channels, and discuss how they might contribute to the river that terminates in renal injury.

Anti-Diabetic Effects of Isolated Lipids from Natural Sources through Modulation of Angiogenesis

BACKGROUND

Aberrant angiogenesis plays a fateful role in the development of diabetes and diabetic complications. Lipids, as a diverse group of biomacromolecules, are able to relieve diabetes through the modulation of angiogenesis.

OBJECTIVE

Owing to the present remarkable anti-diabetic effects with no or few side effects of lipids, the aim of this study was to assess the state-of-the-art research on anti-diabetic effects of lipids via the modulation of angiogenesis.

METHODS

To study the effects of lipids in diabetes via modulation of angiogenesis, we have searched the electronic databases including Scopus, PubMed, and Cochrane.

RESULTS

The promising anti-diabetic effects of lipids were reported in several studies. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil (FO) were reported to significantly induce neovasculogenesis in high glucose (HG)-mediated endothelial progenitor cells (EPCs) neovasculogenic dysfunction in type 2 diabetic mice. Linoleic acid, mono-epoxy-tocotrienol-α (MeT3α), and ginsenoside Rg1 facilitate wound closure and vessel formation. N-Palmitoylethanolamine (PEA), α-linolenic acid (ALA), omega-3 (ω3) lipids from flaxseed (FS) oil, ω-3 polyunsaturated fatty acids (PUFA), lipoic acid, taurine, and zeaxanthin (Zx) are effective in diabetic retinopathy via suppression of angiogenesis. Lysophosphatidic acid, alkyl-glycerophosphate, crocin, arjunolic acid, α-lipoic acid, and FS oil are involved in the management of diabetes and its cardiac complications. Furthermore, in two clinical trials, R-(+)-lipoic acid (RLA) in combination with hyperbaric oxygenation therapy (HBOT) for treatment of chronic wound healing in DM patients, as well as supplementation with DHA plus antioxidants along with intravitreal ranibizumab were investigated for its effects on diabetic macular edema.

CONCLUSION

Proof-of-concept studies presented here seem to well shed light on the anti-diabetic effects of lipids via modulation of angiogenesis.

Rap1a Overlaps the AGE/RAGE Signaling Cascade to Alter Expression of α-SMA, p-NF-κB, and p-PKC-ζ in Cardiac Fibroblasts Isolated from Type 2 Diabetic Mice

Cardiovascular disease, specifically heart failure, is a common complication for individuals with type 2 diabetes mellitus. Heart failure can arise with stiffening of the left ventricle, which can be caused by “active” cardiac fibroblasts (i.e., myofibroblasts) remodeling the extracellular matrix (ECM). Differentiation of fibroblasts to myofibroblasts has been demonstrated to be an outcome of AGE/RAGE signaling. Hyperglycemia causes advanced glycated end products (AGEs) to accumulate within the body, and this process is greatly accelerated under chronic diabetic conditions. AGEs can bind and activate their receptor (RAGE) to trigger multiple downstream outcomes, such as altering ECM remodeling, inflammation, and oxidative stress. Previously, our lab has identified a small GTPase, Rap1a, that possibly overlaps the AGE/RAGE signaling cascade to affect the downstream outcomes. Rap1a acts as a molecular switch connecting extracellular signals to intracellular responses. Therefore, we hypothesized that Rap1a crosses the AGE/RAGE cascade to alter the expression of AGE/RAGE associated signaling proteins in cardiac fibroblasts in type 2 diabetic mice. To delineate this cascade, we used genetically different cardiac fibroblasts from non-diabetic, diabetic, non-diabetic RAGE knockout, diabetic RAGE knockout, and Rap1a knockout mice and treated them with pharmacological modifiers (exogenous AGEs, EPAC, Rap1a siRNA, and pseudosubstrate PKC-ζ). We examined changes in expression of proteins implicated as markers for myofibroblasts (α-SMA) and inflammation/oxidative stress (NF-κB and SOD-1). In addition, oxidative stress was also assessed by measuring hydrogen peroxide concentration. Our results indicated that Rap1a connects to the AGE/RAGE cascade to promote and maintain α-SMA expression in cardiac fibroblasts. Moreover, Rap1a, in conjunction with activation of the AGE/RAGE cascade, increased NF-κB expression as well as hydrogen peroxide concentration, indicating a possible oxidative stress response. Additionally, knocking down Rap1a expression resulted in an increase in SOD-1 expression suggesting that Rap1a can affect oxidative stress markers independently of the AGE/RAGE signaling cascade. These results demonstrated that Rap1a contributes to the myofibroblast population within the heart via AGE/RAGE signaling as well as promotes possible oxidative stress. This study offers a new potential therapeutic target that could possibly reduce the risk for developing diabetic cardiovascular complications attributed to AGE/RAGE signaling.

Cinnamaldehyde mitigates placental vascular dysfunction of gestational diabetes and protects from the associated fetal hypoxia by modulating placental angiogenesis, metabolic activity and oxidative stress

Gestational diabetes mellitus (GDM) is a major pregnancy-related disorder with an increasing prevalence worldwide. GDM is associated with altered placental vascular functions and has severe consequences for fetal growth. There is no commonly accepted medication for GDM due to safety considerations. Actions of the currently limited therapeutic options focus exclusively on lowering the blood glucose level without paying attention to the altered placental vascular reactivity and remodelling. We used the fat-sucrose diet/streptozotocin (FSD/STZ) rat model of GDM to explore the efficacy of cinnamaldehyde (Ci; 20 mg/kg/day), a promising antidiabetic agent for GDM, and glyburide/metformin-HCl (Gly/Met; 0.6 + 100 mg/kg/day), as a reference drug for treatment of GDM, on the placenta structure and function at term pregnancy after their oral intake one week before mating onward. Through genome-wide transcriptome, biochemical, metabolome, metal analysis and histopathology we obtained an integrated understanding of their effects. GDM resulted in maternal and fetal hyperglycemia, fetal hyperinsulinemia and placental dysfunction with subsequent fetal anemia, hepatic iron deficiency and high serum erythropoietin level, reflecting fetal hypoxia. Differentially-regulated genes were overrepresented for pathways of angiogenesis, metabolic transporters and oxidative stress. Despite Ci and Gly/Met effectively alleviated the maternal and fetal glycemia, only Ci offered substantial protection from GDM-associated placental vasculopathy and prevented the fetal hypoxia. This was explained by Ci's impact on the molecular regulation of placental angiogenesis, metabolic activity and redox signaling. In conclusion, Ci provides a dual impact for the treatment of GDM at both maternal and fetal levels through its antidiabetic effect and the direct placental vasoprotective action. Lack of Gly/Met effectiveness to restore it's impaired functionality demonstrates the vital role of the placenta in developing efficient medications for GDM.

Redox imbalance stress in diabetes mellitus: Role of the polyol pathway

In diabetes mellitus, the polyol pathway is highly active and consumes approximately 30% glucose in the body. This pathway contains 2 reactions catalyzed by aldose reductase (AR) and sorbitol dehydrogenase, respectively. AR reduces glucose to sorbitol at the expense of NADPH, while sorbitol dehydrogenase converts sorbitol to fructose at the expense of NAD⁺, leading to NADH production. Consumption of NADPH, accumulation of sorbitol, and generation of fructose and NADH have all been implicated in the pathogenesis of diabetes and its complications. In this review, the roles of this pathway in NADH/NAD⁺ redox imbalance stress and oxidative stress in diabetes are highlighted. A potential intervention using nicotinamide riboside to restore redox balance as an approach to fighting diabetes is also discussed.

Diabetic macular edema-like ocular lesions in male spontaneously diabetic torii fatty rats

Diabetic macular edema (DME) is a major factor contributing to visual disabilities in diabetic patients, and the number of patients is increasing. Animal models play a key role in the development of novel therapies. In this study, pathophysiological analyses of ocular lesions in Spontaneously Diabetic Torii (SDT) fatty rats were performed. First, vascular endothelial growth factor (VEGF) concentrations in vitreous humor, retinal vascular permeability and retinal thickness were measured in SDT fatty rats (Experiment 1). Furthermore, the pharmacological effects of two anti-diabetic drugs, phlorizin and pioglitazone, on retinal lesions were evaluated (Experiment 2). As results, the SDT fatty rats exhibited VEGF increase in vitreous humor at 8 and 16 weeks of age, and both retinal vascular hyperpermeability and retinal thickening at 16 weeks of age. In particular, the layers between the retinal internal limiting membrane and the outer nuclear layer were thickened. Phlorizin treatment from 4 to 16 weeks of age improved hyperglycemia and normalized retinal thickness; however, the effect of pioglitazone on retinal thickness was not strong despite the normalization of hyperglycemia. These data demonstrate that the male SDT fatty rat is a useful model for developing new therapeutic approaches in DME.

The role of novel biomarkers in predicting diabetic nephropathy: a review

Diabetic nephropathy (DN) is one of the microvascular complications of the kidney arising commonly from type 1 diabetes mellitus (T1DM), and occasionally from type 2 diabetes mellitus (T2DM). Microalbuminuria serves as an early indicator of DN risk and a predictor of its progression as well as cardiovascular disease risk in both T1DM and T2DM. Although microalbuminuria remains the gold standard for early detection of DN, it is not a sufficiently accurate predictor of DN risk due to some limitations. Thus, there is a paradigm shift to novel biomarkers which would help to predict DN risk early enough and possibly prevent the occurrence of end-stage kidney disease. These new biomarkers have been broadly classified into glomerular biomarkers, tubular biomarkers, biomarkers of inflammation, biomarkers of oxidative stress, and miscellaneous biomarkers which also include podocyte biomarkers, some of which are also considered as tubular and glomerular biomarkers. Although they are potentially useful for the evaluation of DN, current data still preclude the routine clinical use of majority of them. However, their validation using high-quality and large longitudinal studies is of paramount importance, as well as the subsequent development of a biomarker panel which can reliably predict and evaluate this renal microvascular disease. This paper aims to review the predictive role of these biomarkers in the evaluation of DN.

Tempol effects on diabetic nephropathy in male rats

INTRODUCTION

Diabetic nephropathy (DN) is the most common cause of the chronic kidney disease in the world. Oxidative stress on the other hand has a major and well known role in its pathophysiology.

OBJECTIVES

The aim of the study is to figure out if tempol, a synthetic antioxidant agent, modifies DN and to determine its relevance to changes of serum oxidative biomarkers.

MATERIALS AND METHODS

Twenty-seven male rats were equally divided in to 4 groups (7 rats for each group). Group I (control or C), group II (diabetic or D), groups III (Tempol) which were given tempol (100 mg/kg/day) by gavages for 28 days and group IV (D&T) which includes diabetic rats that also received same dose of tempol. After treatment, blood samples were isolated. Enzymatic scavengers including catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities, lipid peroxidation (LPO), total antioxidant capacity (TAC) and total thiol molecules (TTM) were measured. Blood urea nitrogen (BUN), creatinine (Cr) an albumin/Cr ratio were evaluated as well. Statistical differences were assessed with one-way analysis of variance (ANOVA) by SPSS followed by Tukey t test.

RESULTS

Oxidative stress biomarkers modified and Alb/Cr ratio increased in diabetic group (II), however, they were altered to normal in group IV (D&T) compared with diabetic group (D).

CONCLUSION

Tempol can modify oxidative stress biomarkers and presumably nephropathy in diabetic rats.

Protein Modifications as Manifestations of Hyperglycemic Glucotoxicity in Diabetes and Its Complications

Diabetes and its complications are hyperglycemic toxicity diseases. Many metabolic pathways in this array of diseases become aberrant, which is accompanied with a variety of posttranslational protein modifications that in turn reflect diabetic glucotoxicity. In this review, we summarize some of the most widely studied protein modifications in diabetes and its complications. These modifications include glycation, carbonylation, nitration, cysteine S-nitrosylation, acetylation, sumoylation, ADP-ribosylation, O-GlcNAcylation, and succination. All these posttranslational modifications can be significantly attributed to oxidative stress and/or carbon stress induced by diabetic redox imbalance that is driven by activation of pathways, such as the polyol pathway and the ADP-ribosylation pathway. Exploring the nature of these modifications should facilitate our understanding of the pathological mechanisms of diabetes and its associated complications.

Hyperglycemic Stress and Carbon Stress in Diabetic Glucotoxicity

Diabetes and its complications are caused by chronic glucotoxicity driven by persistent hyperglycemia. In this article, we review the mechanisms of diabetic glucotoxicity by focusing mainly on hyperglycemic stress and carbon stress. Mechanisms of hyperglycemic stress include reductive stress or pseudohypoxic stress caused by redox imbalance between NADH and NAD(+) driven by activation of both the polyol pathway and poly ADP ribose polymerase; the hexosamine pathway; the advanced glycation end products pathway; the protein kinase C activation pathway; and the enediol formation pathway. Mechanisms of carbon stress include excess production of acetyl-CoA that can over-acetylate a proteome and excess production of fumarate that can over-succinate a proteome; both of which can increase glucotoxicity in diabetes. For hyperglycemia stress, we also discuss the possible role of mitochondrial complex I in diabetes as this complex, in charge of NAD(+) regeneration, can make more reactive oxygen species (ROS) in the presence of excess NADH. For carbon stress, we also discuss the role of sirtuins in diabetes as they are deacetylases that can reverse protein acetylation thereby attenuating diabetic glucotoxicity and improving glucose metabolism. It is our belief that targeting some of the stress pathways discussed in this article may provide new therapeutic strategies for treatment of diabetes and its complications.

Fluorofenidone offers improved renoprotection at early interventions during the course of diabetic nephropathy in db/db mice via multiple pathways

Diabetic nephropathy (DN) remains the leading cause of end-stage renal disease (ESRD), a situation that is in part attributable to the lack of effective treatments. Fluorofenidone is a newly developed reagent with anti-fibrotic activity. While fluorofenidone was previously demonstrated to possess renoprotection from DN pathogenesis in db/db mice, the protective process and its underlying mechanisms have not been well studied. To characterize fluorofenidone-derived renoprotection, we treated 5, 8, or 12-week old db/db mice with daily doses of placebo, fluorofenidone, or losartan until 24 weeks of age; the time at which diabetes and DN were fully developed in placebo-treated animals. In comparison to db/db mice receiving fluorofenidone at 12-weeks old, those treated at 5-weeks had less glomerular expansion and better preservation of renal functions, judged by serum creatinine levels, albumin to creatinine ratio, and urinary albumin excretion (mg/24 hours). These benefits of early treatment were associated with significant reductions of multiple DN-promoting events, such as decreased expression of TGF-β1 and the p22^phox subunit of NADPH oxidase as well as downregulated activation of protein kinase C-zeta (ζ), ERK and AKT. This improvement in renoprotection following early interventions is not a unique property of DN pathogenesis, as losartan does not apparently offer the same benefits and is not more renoprotective than fluorofenidone. Additionally, the enhanced renoprotection provided by fluorofenidone did not affect the diabetic process, as it did not alter serum levels of glycated serum proteins, glucose, triglyceride or cholesterol. Collectively, we provide evidence that fluorofenidone offers improved renoprotection at early stages of DN pathogenesis.

Choline inadequacy impairs trophoblast function and vascularization in cultured human placental trophoblasts

Maternal choline intake during gestation may influence placental function and fetal health outcomes. Specifically, we previously showed that supplemental choline reduced placental and maternal circulating concentrations of the anti-angiogenic factor, fms-like tyrosine kinase-1 (sFLT1), in pregnant women as well as sFLT1 production in cultured human trophoblasts. The current study aimed to quantify the effect of choline on a wider array of biomarkers related to trophoblast function and to elucidate possible mechanisms. Immortalized HTR-8/SVneo trophoblasts were cultured in different choline concentrations (8, 13, and 28 µM [control]) for 96-h and markers of angiogenesis, inflammation, apoptosis, and blood vessel formation were examined. Choline insufficiency altered the angiogenic profile, impaired in vitro angiogenesis, increased inflammation, induced apoptosis, increased oxidative stress, and yielded greater levels of protein kinase C (PKC) isoforms δ and ϵ possibly through increases in the PKC activators 1-stearoyl-2-arachidonoyl-sn-glycerol and 1-stearoyl-2-docosahexaenoyl-sn-glycerol. Notably, the addition of a PKC inhibitor normalized angiogenesis and apoptosis, and partially rescued the aberrant gene expression profile. Together these results suggest that choline inadequacy may contribute to placental dysfunction and the development of disorders related to placental insufficiency by activating PKC.

Bioactive lipids in pathological retinopathy

Diabetic retinopathy is a common condition that occurs in patients with diabetes with long-standing hyperglycemia that is characterized by inappropriate angiogenesis. This pathological angiogenesis could be a sort of physiological proliferative response to injury by the endothelium. Recent studies suggested that reactive oxygen species (ROS) play a significant role in this angiogenesis. Vascular endothelial growth factor (VEGF) is a potent angiogenic growth factor that plays a significant role in diabetic retinopathy. The interaction between VEGF and ROS, and theirs in turn with pro- and anti-inflammatory cytokines and anti-inflammatory bioactive lipid molecules such as lipoxins, resolvins, protectins, and maresins is particularly relevant to understand the pathophysiology of diabetic retinopathy and develop future therapeutic interventions.

Impaired insulin signaling affects renal organic anion transporter 3 (Oat3) function in streptozotocin-induced diabetic rats

Organic anion transporter 3 (Oat3) is a major renal Oats expressed in the basolateral membrane of renal proximal tubule cells. We have recently reported decreases in renal Oat3 function and expression in diabetic rats and these changes were recovered after insulin treatment for four weeks. However, the mechanisms by which insulin restored these changes have not been elucidated. In this study, we hypothesized that insulin signaling mediators might play a crucial role in the regulation of renal Oat3 function. Experimental diabetic rats were induced by a single intraperitoneal injection of streptozotocin (65 mg/kg). One week after injection, animals showing blood glucose above 250 mg/dL were considered to be diabetic and used for the experiment in which insulin-treated diabetic rats were subcutaneously injected daily with insulin for four weeks. Estrone sulfate (ES) uptake into renal cortical slices was examined to reflect the renal Oat3 function. The results showed that pre-incubation with insulin for 30 min (short term) stimulated [3H]ES uptake into the renal cortical slices of normal control rats. In the untreated diabetic rats, pre-incubation with insulin for 30 min failed to stimulate renal Oat3 activity. The unresponsiveness of renal Oat3 activity to insulin in the untreated diabetic rats suggests the impairment of insulin signaling. Indeed, pre-incubation with phosphoinositide 3-kinase (PI3K) and protein kinase C zeta (PKCζ) inhibitors inhibited insulin-stimulated renal Oat3 activity. In addition, the expressions of PI3K, Akt and PKCζ in the renal cortex of diabetic rats were markedly decreased. Prolonged insulin treatment in diabetic rats restored these alterations toward normal levels. Our data suggest that the decreases in both function and expression of renal Oat3 in diabetes are associated with an impairment of renal insulin-induced Akt/PKB activation through PI3K/PKCζ/Akt/PKB signaling pathway.

Pathogenesis of chronic hyperglycemia: from reductive stress to oxidative stress

Chronic overnutrition creates chronic hyperglycemia that can gradually induce insulin resistance and insulin secretion impairment. These disorders, if not intervened, will eventually be followed by appearance of frank diabetes. The mechanisms of this chronic pathogenic process are complex but have been suggested to involve production of reactive oxygen species (ROS) and oxidative stress. In this review, I highlight evidence that reductive stress imposed by overflux of NADH through the mitochondrial electron transport chain is the source of oxidative stress, which is based on establishments that more NADH recycling by mitochondrial complex I leads to more electron leakage and thus more ROS production. The elevated levels of both NADH and ROS can inhibit and inactivate glyceraldehyde 3-phosphate dehydrogenase (GAPDH), respectively, resulting in blockage of the glycolytic pathway and accumulation of glycerol 3-phospate and its prior metabolites along the pathway. This accumulation then initiates all those alternative glucose metabolic pathways such as the polyol pathway and the advanced glycation pathways that otherwise are minor and insignificant under euglycemic conditions. Importantly, all these alternative pathways lead to ROS production, thus aggravating cellular oxidative stress. Therefore, reductive stress followed by oxidative stress comprises a major mechanism of hyperglycemia-induced metabolic syndrome.

Effect of α-linolenic acid on streptozotocin-induced diabetic retinopathy indices in vivo

BACKGROUND AND AIMS

Both oxidative stress and inflammation play a significant role in the pathobiology of diabetic retinopathy. Increased consumption of polyunsaturated fatty acids (PUFAs) may prevent or postpone the occurrence of diabetic retinopathy. Hence, the effect of α-linolenic acid (ALA), an essential fatty acid, on oxidative stress, inflammatory indices and production of vascular endothelial growth factor (VEGF) in streptozotocin-induced diabetic retinopathy indices in vivo was studied.

METHODS

Serum and retina concentrations of vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF), interleukin-6 (IL-6), plasma and retina concentrations of lipid peroxides and antioxidant enzymes were estimated in streptozotocin (STZ)-induced diabetic animals.

RESULTS

STZ-induced diabetic rats had significantly higher levels of VEGF in the serum and retina and IL-6 in the serum, whereas BDNF was lower in the serum, all of which reverted to near normal in ALA-treated diabetic animals. STZ treatment decreased serum glutathione peroxidase levels, which was restored to normal by both pre- and post-ALA treatment groups.

CONCLUSIONS

STZ-induced changes in serum glutathione peroxidase, BDNF, VEGF and IL-6 that reverted to near control by ALA treatment, especially in ALA + STZ group, lending support to the concept that both oxidative stress and inflammation participate in DR and ALA treatment is of benefit in its prevention.

A potential role for caveolin-1 in VEGF-induced fibronectin upregulation in mesangial cells: involvement of VEGFR2 and Src

VEGF is known to be an endothelial cell mitogen that stimulates angiogenesis by promoting endothelial cell survival, proliferation, migration, and differentiation. Recent studies have suggested that VEGF may play a pivotal role in glomerular sclerosis through extracellular matrix protein (ECM) accumulation, although the signaling mechanism is still unclear. The GTPase RhoA has been implicated in VEGF-induced type IV collagen accumulation in some settings. Here we study the role of different VEGF receptors and membrane microdomain caveolae in VEGF-induced RhoA activation and fibronectin upregulation in mesangial cells (MCs). In primary rat MC, VEGF time and dose dependently increased fibronectin production. Rho pathway inhibition blocked VEGF-induced fibronectin upregulation. VEGF-induced RhoA activation was prevented by disrupting caveolae with cholesterol depletion and rescued by cholesterol repletion. VEGF stimulation led to a markedly increased VEGFR2/caveolin-1 but failed to increase VEGFR1/caveolin-1 association. VEGF also increased caveolin-1/Src association and activated Src, and Src inhibitor blocked RhoA activation and fibronectin upregulation. Src-mediated phosphorylation of caveolin-1 on Y14 has also been implicated in signaling responses. Overexpression of nonphosphorylatable caveolin-1 Y14A prevented VEGF-induced RhoA activation and fibronectin upregulation. In vivo, although VEGFR1 and VEGFR2 protein levels were both increased in the kidney cortices of diabetic rats, VEGFR2/caveolin-1 association but not VEGFR1/caveolin-1 association was significantly increased. In conclusion, VEGF-induced RhoA activation and fibronectin upregulation require caveolae and caveolin-1 interaction with VEGFR2 and Src. Interference with caveolin/-ae signaling may provide new avenues for the treatment of fibrotic renal disease.

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.

Prevention of VEGF-induced growth and tube formation in human retinal endothelial cells by aldose reductase inhibition

OBJECTIVE

Since diabetes-induced vascular endothelial growth factor (VEGF) is implicated in retinal angiogenesis, we aimed to examine the role of aldose reductase (AR) in VEGF-induced human retinal endothelial cells (HREC) growth and tube formation.

MATERIALS AND METHODS

HRECs were stimulated with VEGF and cell-growth was determined by MTT assay. AR inhibitor, fidarestat, to block the enzyme activity and AR siRNA to ablate AR gene expression in HREC were used to investigate the role of AR in neovascularization using cell-migration and tube formation assays. Various signaling intermediates and angiogenesis markers were assessed by Western blot analysis. Immuno-histochemical analysis of diabetic rat eyes was performed to examine VEGF expression in the retinal layer.

RESULTS

Stimulation of primary HREC with VEGF caused increased cell growth and migration, and AR inhibition with fidarestat or ablation with siRNA significantly prevented it. VEGF-induced tube formation in HREC was also significantly prevented by fidarestat. Treatment of HREC with VEGF also increased the expression of VCAM, AR, and phosphorylation and activation of Akt and p38-MAP kinase, which were prevented by fidarestat. VEGF-induced expression of VEGFRII in HREC was also prevented by AR inhibition or ablation.

CONCLUSIONS

Our results indicate that inhibition of AR in HREC prevents tube formation by inhibiting the VEGF-induced activation of the Akt and p38-MAPK pathway and suggest a mediatory role of AR in ocular neovascularization generally implicated in retinopathy and AMD.

Effects of high glucose on vascular endothelial growth factor synthesis and secretion in aortic vascular smooth muscle cells from obese and lean Zucker rats

Type 1 diabetes is characterized by insulin deficiency, type 2 by both insulin deficiency and insulin resistance: in both conditions, hyperglycaemia is accompanied by an increased cardiovascular risk, due to increased atherosclerotic plaque formation/instabilization and impaired collateral vessel formation. An important factor in these phenomena is the Vascular Endothelial Growth Factor (VEGF), a molecule produced also by Vascular Smooth Muscle Cells (VSMC). We aimed at evaluating the role of high glucose on VEGF-A₁₆₄ synthesis and secretion in VSMC from lean insulin-sensitive and obese insulin-resistant Zucker rats (LZR and OZR). In cultured aortic VSMC from LZR and OZR incubated for 24 h with d-glucose (5.5, 15 and 25 mM) or with the osmotic controls l-glucose and mannitol, we measured VEGF-A₁₆₄ synthesis (western, blotting) and secretion (western blotting and ELISA). We observed that: (i) d-glucose dose-dependently increases VEGF-A₁₆₄ synthesis and secretion in VSMC from LZR and OZR (n = 6, ANOVA p = 0.002–0.0001); (ii) all the effects of 15 and 25 mM d-glucose are attenuated in VSMC from OZR vs. LZR (p = 0.0001); (iii) l-glucose and mannitol reproduce the VEGF-A₁₆₄ modulation induced by d-glucose in VSMC from both LZR and OZR. Thus, glucose increases via an osmotic mechanism VEGF synthesis and secretion in VSMC, an effect attenuated in the presence of insulin resistance.

SOX9 protein induces a chondrogenic phenotype of mesangial cells and contributes to advanced diabetic nephropathy

Diabetic nephropathy (DN) is the most important chronic kidney disease. We previously reported that Smad1 transcriptionally regulates the expression of extracellular matrix in DN. Phenotypic change in mesangial cells (MCs) is a key pathologic event in the progression of DN. The aim of this study is to investigate a novel mechanism underlying chondrogenic phenotypic change in MCs that results in the development of DN. MCs showed chondrogenic potential in a micromass culture, and BMP4 induced the expression of chondrocyte markers (SRY-related HMG Box 9 (SOX9) and type II collagen (COL2)). Advanced glycation end products induced the expression of chondrocyte marker proteins downstream from the BMP4-Smad1 signaling pathway in MCs. In addition, hypoxia also induced the expression of BMP4, hypoxia-inducible factor-1α (HIF-1α), and chondrocyte markers. Overexpression of SOX9 caused ectopic expression of proteoglycans and COL2 in MCs. Furthermore, forced expression of Smad1 induced chondrocyte markers as well. Dorsomorphin inhibited these inductions. Glomerular expressions of HIF-1α, BMP4, and chondrocyte markers were observed in diabetic nephropathy mice. These positive stainings were observed in mesangial sclerotic lesions. SOX9 was partially colocalized with HIF-1α and BMP4 in diabetic glomeruli. BMP4 knock-in transgenic mice showed not only similar pathological lesions to DN, but also the induction of chondrocyte markers in the sclerotic lesions. Here we demonstrate that HIF-1α and BMP4 induce SOX9 expression and subsequent chondrogenic phenotype change in DN. The results suggested that the transdifferentiation of MCs into chondrocyte-like cells in chronic hypoxic stress may result in irreversible structural change in DN.

Isolation and identification of compounds responsible for antioxidant capacity of Euryale ferox seeds

Euryale ferox seed is consumed medicinally or for food in China. The present study revealed it to contain significant antioxidant activity, which may be associated with its medical applications as a proteinuria inhibitor of diabetic nephropathy. This study resulted in the identification of 3 new sesquineolignans, named euryalins A-C (1-3), and 16 known compounds, which were all first isolated from this plant apart from 5,7,4-trihydroxy-flavanone. The antioxidant potential of the partial isolates was evaluated using the DPPH radical scavenging assay and mesangial cellular assay. Compounds 2, rel-(2α,3β)-7-O-methylcedrusin (4), syringylglycerol-8-O-4-(sinapyl alcohol) ether (5), and (+)-syringaresinol (7) were found to be most active on DPPH assay, whereas compounds 2, 4, 7, (1R,2R,5R,6S)-2-(3,4-dimethoxyphenyl)-6-(3,4-dihydroxyphenyl)-3,7-dioxabicyclo[3.3.0]octane, and buddlenol E could significantly inhibit high glucose-stimulated reactive oxygen species production in mesangial cells. The results suggested that E. ferox seed could be considered as an excellent source of natural antioxidants and is useful in the prevention of diabetic nephropathy.

Signaling of reactive oxygen and nitrogen species in Diabetes mellitus

Disorder of physiological signaling functions of reactive oxygen species (ROS) superoxide and hydrogen peroxide and reactive nitrogen species (RNS) nitric oxide and peroxynitrite is an important feature of diabetes mellitus type 1 and type 2. It is now known that hyperglycemic conditions of cells are associated with the enhanced levels of ROS mainly generated by mitochondria and NADPH oxidase. It has been established that ROS stimulate many enzymatic cascades under normal physiological conditions, but hyperglycemia causes ROS overproduction and the deregulation of ROS signaling pathways initiating the development of diabetes mellitus. On the other hand the deregulation of RNS signaling leads basically to a decrease in NO formation with subsequent damaging disorders. In the present work we will consider the pathological changes of ROS and RNS signaling in enzyme/gene regulated processes catalyzed by protein kinases C and B (Akt/B), phosphatidylinositol 3'-kinase (PI3-kinase), extracellular signal-regulated kinase 1/2 (ERK1/2), and some others. Furthermore we will discuss a particularly important role of several ROS-regulated genes and adapter proteins such as the p66shc, FOXO3a, and Sirt2. The effects of low and high ROS levels in diabetes will be also considered. Thus the regulation of damaging ROS levels in diabetes by antioxidants and free radical scavengers must be one of promising treatment of this disease, however, because of the inability of traditional antioxidative vitamin E and C to interact with superoxide and hydrogen peroxide, new free radical scavengers such as flavonoids, quinones and synthetic mimetics of superoxide dismutase (SOD) should be intensively studied.

Vascular dysfunction in the diabetic placenta: causes and consequences

The development and functioning of the human fetoplacental vascular system are vulnerable to the maternal diabetic milieu. These vessels are in direct continuum with the fetal vascular system and are therefore also vulnerable to fetal endocrine derangements. Increased angiogenesis, altered junctional maturity and molecular occupancy, together with increased leakiness, constitute a well-described phenotype of vessels in the Type 1 diabetic human placenta and can be related to increased levels of placental vascular endothelial growth factor. The causes of these observed changes, whether maternal hyperglycaemia or fetal hyperinsulinaemia, still remain to be shown in the human placenta. Mechanistic studies using different vascular systems have shown high glucose and insulin to have profound vascular effects, with elevations in vascular endothelial growth factor, nitric oxide and protein kinase C being behind alterations in junctional adhesion molecules such as occludin and vascular endothelial-cadherin and vascular leakage of albumin. The role of advanced glycation products and oxidative stress in this vascular pathology is also discussed. The altered molecular mechanisms underlying the vascular changes in the diabetic human placenta may reflect similar consequences of high glucose and hyperinsulinaemia.

Inflammatory cytokines as predictive markers for early detection and progression of diabetic nephropathy

Diabetic nephropathy is a major complication of diabetes mellitus and the leading cause of end-stage renal disease. Both hyperglycemia and hypertension (systemic and/or intraglomerular) are established causal factors for diabetic nephropathy. Nonetheless, there is growing evidence that activated innate immunity and inflammation are also contributing factors to the pathogenesis of diabetic nephropathy. This notion is based on increasing evidence indicating that both cytokines-chemokines and pro-fibrotic growth factors are important players in the progression of diabetic nephropathy, effectively accelerating and exacerbating inflammatory and fibrotic processes leading to end-stage renal disease. In this review, we focus on several predominant cytokines-chemokines as potential predictive markers for diabetic nephropathy. These cytokines-chemokines may also be helpful as biomarkers to monitor the progression of the disease and the impact of interventional modalities aimed at halting eventual manifestation of end-stage renal disease in diabetic patients.

Simvastatin reverses podocyte injury but not mesangial expansion in early stage type 2 diabetes mellitus

Statins may confer renal protection in a variety of glomerular diseases, including diabetic nephropathy (DN). However, various glomerular lesions have different etiologies and may have different responses to statins. This study was performed to determine the differential effects of simvastatin (SMV) on glomerular pathology including mesangial expansion and podocyte injury in a mouse model of early stage type 2 diabetes mellitus (DM). Type 2 DM was induced in male C57BL/6 mice by feeding a high fat diet (HF; 45 kcal% fat). After 22 weeks, one group of HF mice was treated with SMV (HF-SMV; 7 mug/day/g BW) and another group was treated with vehicle (HF-vehicle) for 4 weeks via osmotic mini-pump. A third group served as age-matched normal diet vehicle controls (ND-vehicle; 10 kcal% fat). At the end of treatment, glomerular morphology was evaluated in a blind manner to determine the progression of DN. Body weight, blood glucose, insulin, HDL-cholesterol and triglycerides, but not LDL-cholesterol, were increased in HF mice. Over the course of treatment, the 24-hour urinary albumin excretion (UAE) was unchanged in ND-vehicle. HF mice exhibited elevated UAE, which decreased with SMV, but was unchanged with vehicle. The absolute mesangial volume and the relative mesangial volume per glomerular volume increased in HF-vehicle and remained elevated with SMV treatment. The immuno-staining of nephrin, a protein marker of the integrity of podocyte slit diaphragms, was decreased in HF-vehicle; however, the nephrin quantity of the HF-SMV group was not different from ND-vehicle. It is concluded that SMV reverses podocyte damage, but does not affect mesangial expansion in the kidneys of early stage proteinuria of type 2 DM.

Rosiglitazone prevents high glucose-induced vascular endothelial growth factor and collagen IV expression in cultured mesangial cells

Peroxisome proliferator-activated receptor (PPARγ), a ligand-dependent transcription factor, negatively modulates high glucose effects. We postulated that rosiglitazone (RSG), an activator of PPARγ prevents the upregulation of vascular endothelial growth factor (VEGF) and collagen IV by mesangial cells exposed to high glucose. Primary cultured rat mesangial cells were growth-arrested in 5.6 mM (NG) or 25 mM D-glucose (HG) for up to 48 hours. In HG, PPARγ mRNA and protein were reduced within 3 h, and enhanced ROS generation, expression of p22^phox, VEGF and collagen IV, and PKC-ζ membrane association were prevented by RSG. In NG, inhibition of PPARγ caused ROS generation and VEGF expression that were unchanged by RSG. Reduced AMP-activated protein kinase (AMPK) phosphorylation in HG was unchanged with RSG, and VEGF expression was unaffected by AMPK inhibition. Hence, PPARγ is a negative modulator of HG-induced signaling that acts through PKC-ζ but not AMPK and regulates VEGF and collagen IV expression by mesangial cells.

Role of protein kinase C in the expression of endothelin converting enzyme-1

Increased expression of endothelin converting enzyme-1 (ECE-1) is associated with diabetic nephropathy. The molecular mechanisms underlying this association, as yet unknown, possibly involve protein kinase C (PKC) pathways. In the present study, we examined the effects of high glucose and PKC activation on ECE-1 expression in primary human umbilical vein endothelial cells (HUVECs) and in HUVEC line (EA.hy926). Increasing glucose concentration, but not mannitol, from 5.5-22.2 mmol/liter for 3 d, enhanced prepro endothelin-1 (ET-1) mRNA expression, ET-1 levels, ECE-1 protein, and mRNA expressions by 7, 4, 20, and 2.6-fold, respectively. High glucose increased ECE-1 protein expression dose and time dependently. By Western blot analysis, PKC-beta1, -beta2, and -delta isoform levels were significantly increased relative to other isoforms when glucose level was increased. Treatment with Rottlerin, a PKC-delta isoform inhibitor, reduced significantly the glucose-induced ET-1 secretion, and ECE-1 protein expression, but (S)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16,21-dimetheno 1H,1(3)H-dibenzo[e,k]pyrrolo[3,4-h] (1, 4, 3) oxadiaza-cyclohexadecene-1,3(2H)-dione or Gö6976, specific PKC-beta and -alpha inhibitors, respectively, did not. Overexpression of PKC-delta but not PKC-alpha or -beta1 isoforms by adenovirus vector containing the respective cDNA in HUVECs incubated with 5.5 mmol/liter glucose, increased in parallel PKC proteins, and glucose-induced endothein-1 and ECE-1 protein expression by 4- to 6-fold. These results show that enhanced ECE-1 expression induced by hyperglycemia is partly due to activation of the PKC-delta isoform. Thus, inhibition of this PKC isoform may prevent diabetes-related increase in ET-1.

Effects of NADPH oxidase inhibitor on diabetic nephropathy in OLETF rats: the role of reducing oxidative stress in its protective property

Diabetic nephropathy is the most serious complication in diabetes mellitus. Oxidative stress via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and vascular endothelial growth factor (VEGF) pathway play critical roles in the development of diabetic nephropathy. We evaluated the effects of apocynin, NADPH oxidase inhibitor on diabetic nephropathy in a type 2 diabetic rat model. Sixteen Otsuka Long Evans Tokushima Fatty (OLETF) rats and 9 Long Evans Tokushima Otsuka (LETO) were divided into the following three groups: LETO rats (n=9), control OLETF rats (n=7) and apocynin-treated OLETF rats (n=9). We examined body weights, plasma glucose levels, urinary albumin-creatinine ratio (ACR) and protein-creatinine ratio (PCR). At 50 weeks, experimental rats were sacrificed and their kidneys were extracted for hematoxylin eosin stain, immunohistochemical VEGF stain and VEGF mRNA real-time RT-PCR. To examine oxidative stress, we checked 24h urinary 8-OHdG (8-hydroxy-2'-deoxyguanosine) and MDA (malondialdehyde). Urinary protein and albumin excretions were reduced after apocynin treatment, though apocynin could not significantly decrease serum glucose levels. There were improvements of glomerular and mesangial expansion in the apocynin-treated OLETF rats. Apocynin significantly decreased optical density of glomerular VEGF expression in immunohistochemical stain and reduced the concentration of 24h urinary 8-OHdG and MDA. From these results, it was suggested that apocynin may have the potential to protect against diabetic nephropathy via amelioration of oxidative stress.

Protein kinase C-beta inhibition attenuates the progression of nephropathy in non-diabetic kidney disease

BACKGROUND

Activation of protein kinase C (PKC) has been implicated in the pathogenesis of diabetic nephropathy where therapy targeting the beta isoform of this enzyme is in advanced clinical development. However, PKC-beta is also increased in various forms of human glomerulonephritis with several potentially nephrotoxic factors, other than high glucose, resulting in PKC-beta activation. Accordingly, we sought to examine the effects of PKC-beta inhibition in a non-diabetic model of progressive kidney disease.

METHODS

Subtotally nephrectomized (STNx) rats were randomly assigned to receive either the selective PKC-beta inhibitor, ruboxistaurin or vehicle. In addition to functional and structural parameters, gene expression of the podocyte slit-pore diaphragm protein, nephrin, was also assessed.

RESULTS

STNx animals developed hypertension, proteinuria and reduced glomerular filtration rate (GFR) in association with marked glomerulosclerosis and tubulointerstitial fibrosis. Glomerular nephrin expression was also reduced. Without affecting blood pressure, ruboxistaurin treatment attenuated the impairment in GFR and reduced the extent of both glomerulosclerosis and tubulointerstitial fibrosis in STNx rats. In contrast, neither proteinuria nor the reduction in nephrin expression was improved by ruboxistaurin.

CONCLUSIONS

These findings indicate firstly that PKC-beta inhibition may provide a new therapeutic strategy in non-diabetic kidney disease and secondly that improvement in GFR is not inextricably linked to reduction in proteinuria.

Redox control of renal function and hypertension

Loss of redox homeostasis and formation of excessive free radicals play an important role in the pathogenesis of kidney disease and hypertension. Free radicals such as reactive oxygen species (ROS) are necessary in physiologic processes. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney, which in turn lead to reduced vascular compliance and proteinuria. The kidney is susceptible to the influence of various extracellular and intracellular cues, including the renin-angiotensin-aldosterone system (RAAS), hyperglycemia, lipid peroxidation, inflammatory cytokines, and growth factors. Redox control of kidney function is a dynamic process with reversible pro- and anti-free radical processes. The imbalance of redox homeostasis within the kidney is integral in hypertension and the progression of kidney disease. An emerging paradigm exists for renal redox contribution to hypertension.

High glucose-induced Nox1-derived superoxides downregulate PKC-betaII, which subsequently decreases ACE2 expression and ANG(1-7) formation in rat VSMCs

In rat diabetic animal models, ANG(1-7) treatment prevents the development of cardiovascular complications. Angiotensin-converting enzyme (ACE)2 is a major ANG(1-7)-generating enzyme in vascular smooth muscle cells (VSMCs), and its expression is decreased by a prolonged exposure to high glucose (HG), which is reflected by lower ANG(1-7) levels. However, the underlying mechanism of its downregulation is unknown and was the subject of this study. Rat aortic VSMCs were maintained in normal glucose (NG) or HG ( approximately 4.1 and approximately 23.1 mmol/l, respectively) for up to 72 h. Several PKC and NADPH oxidase inhibitors and short interfering (si)RNAs were used to determine the mechanism of HG-induced ACE2 downregulation. Cell lysates were subjected to Western blot analysis, real-time quantitative PCR, and ANG(1-7) radioimmunodetection. At 72 h of HG exposure, ACE2 mRNA, protein, and ANG(1-7) levels were decreased (0.17 +/- 0.01-, 0.47 +/- 0.03-, and 0.16 +/- 0.01-fold, respectively), and the expression of NADPH oxidase subunit Nox1 was increased (1.70 +/- 0.2-fold). The HG-induced ACE2 decrease was reversed by antioxidants and Nox1 siRNA as well as by inhibitors of glycotoxin formation. ACE2 expression was PKC-betaII dependent, and PKC-betaII protein levels were reduced in the presence of HG (0.32 +/- 0.03-fold); however, the PKC-betaII inhibitor CG-53353 prevented the HG-induced ACE2 loss and Nox1 induction, suggesting a nonspecific effect of the inhibitor. Our data suggest that glycotoxin-induced Nox1 expression is regulated by conventional PKCs. ACE2 expression is PKC-betaII dependent. Nox1-derived superoxides reduce PKC-betaII expression, which lowers ACE2 mRNA and protein levels and consequently decreases ANG(1-7) formation.

High glucose activates PKC-zeta and NADPH oxidase through autocrine TGF-beta1 signaling in mesangial cells

Conversion of normally quiescent mesangial cells into extracellular matrix-overproducing myofibroblasts in response to high ambient glucose and transforming growth factor (TGF)-beta(1) is central to the pathogenesis of diabetic nephropathy. Previously, we reported that mesangial cells respond to high glucose by generating reactive oxygen species (ROS) from NADPH oxidase dependent on protein kinase C (PKC) -zeta activation. We investigated the role of TGF-beta(1) in this action of high glucose on primary rat mesangial cells within 1-48 h. Both high glucose and exogenous TGF-beta(1) stimulated PKC-zeta kinase activity, as measured by an immune complex kinase assay and immunofluorescence confocal cellular imaging. In high glucose, Akt Ser473 phosphorylation appeared within 1 h and Smad2/3 nuclear translocation was prevented with neutralizing TGF-beta(1) antibodies. Neutralizing TGF-beta(1) antibodies, or a TGF-beta receptor kinase inhibitor (LY364947), or a phosphatidylinositol 3,4,5-trisphosphate (PI3) kinase inhibitor (wortmannin), prevented PKC-zeta activation by high glucose. TGF-beta(1) also stimulated cellular membrane translocation of PKC-alpha, -beta(1), -delta, and -epsilon, similar to high glucose. High glucose and TGF-beta(1) enhanced ROS generation by mesangial cell NADPH oxidase, as detected by 2,7-dichlorofluorescein immunofluorescence. This response was abrogated by neutralizing TGF-beta(1) antibodies, LY364947, or a specific PKC-zeta pseudosubstrate peptide inhibitor. Expression of constitutively active PKC-zeta in normal glucose caused upregulation of p22(phox), a likely mechanism of NADPH oxidase activation. We conclude that very early responses of mesangial cells to high glucose include autocrine TGF-beta(1) stimulation of PKC isozymes including PI3 kinase activation of PKC-zeta and consequent generation of ROS by NADPH oxidase.