Antioxidant inhibition of protein kinase C-signaled increases in transforming growth factor-beta in mesangial cells

Fetal chronic hypoxia and oxidative stress in diabetic pregnancy. Could fetal erythropoietin improve offspring outcomes?

Oxidative stress is responsible for microvascular complications (hypertension, nephropathy, retinopathy, peripheral neuropathy) of diabetes, which during pregnancy increase both maternal and fetal complications. Chronic hypoxia and hyperglycemia result in increased oxidative stress and decreased antioxidant enzyme activity. However, oxidative stress induces also anti-oxidative reactions both in pregnant diabetes patients and in their fetuses. Not all type 1 diabetes patients with long-lasting disease develop microvascular complications, which suggests that some of these patients have protective mechanisms against these complications. Fetal erythropoietin (EPO) is the main regulator of red cell production in the mother and in the fetus, but it has also protective effects in various maternal and fetal tissues. This dual effect of EPO is based on EPO receptor (EPO-R) isoforms, which differ structurally and functionally from the hematopoietic EPO-R isoform. The tissue protective effects of EPO are based on its anti-apoptotic, anti-oxidative, anti-inflammatory, cell proliferative and angiogenic properties. Recent experimental and clinical studies have shown that EPO has also positive metabolic effects on hyperglycemia and diabetes, although these have not yet been fully delineated. Whether the tissue protective and metabolic effects of EPO could have clinical benefits, are important topics for future research in diabetic pregnancies.

Interleukin (IL)-13, Prostaglandin E2 (PGE2), and Prostacyclin 2 (PGI2) Activate Hepatic Stellate Cells via Protein kinase C (PKC) Pathway in Hepatic Fibrosis

BACKGROUND Protein kinase C (PKC), interleukin (IL)-13, prostaglandin E2 (PGE2), and prostacyclin 2 (PGI2) can all play crucial roles in pulmonary fibrosis. However, their functions remain unclear in hepatic fibrosis mediated by hepatic stellate cells (HSCs), which has been demonstrated to be related to transforming growth factor-β (TGF-β) and platelet-derived growth factor (PDGF). MATERIAL AND METHODS All the experiments were based on LX-2 Hepatic stellate cells. The expression of TGF-β1 and PDGF were assessed by ELISA, RT-PCR, and Western blotting in human HSCs treated by IL-13, PGE2, and PGI2, respectively. At the same time, bridge assay and CCK8 assay were used to detect the cell proliferation and activity, PKC activity assay was used to test the activity of PKC, and PKC agonist and antagonist were used to verify the results obtained previously. RESULTS We found that IL-13, PGE2, and PGI2 significantly enhanced the expression of TGF-β1 and PDGF in human HSCs, which also clearly improved the proliferation and cell activity of HSCs. Moreover, PKC activity was significantly increased following IL-13, PGE2, and PGI2 treatments. We also found that the expression of TGF-β1 and PDGF, as well as the proliferation and cell activity of HSCs, were significantly enhanced by the PKC agonist phorbol 12-myristate 13-acetate (PMA), but suppressed by the PKC antagonist calphostin C. CONCLUSIONS We found that IL-13, PGE2, and PGI2 stimulated HSCs proliferation and secretion of TGF-β1 and PDGF by activating PKC, which predicted their potential roles in hepatic fibrosis.

Flavonoids

Diabetes Mellitus is one of the major healthcare problems faced by the society today and has become alarmingly epidemic in many parts of the world. Despite enormous knowledge and technology advancement, available diabetes therapeutics only provide symptomatic relief by reducing blood glucose level, thereby, just slows down development and progression of diabetes and its associated complications. Thus, the need of the day is to develop alternate strategies that can not only prevent the progression but also reverse already “set-in” diabetic complications. Many flavonoids are reported, traditionally as well as experimentally, to be beneficial in averting diabetes and lowering risk of its accompanying complications. In the present chapter we have convened different flavonoids beneficial in diabetes and comorbid complications and discussed their mechanisms of action. Further, we conclude that coupling current therapeutics with flavonoids might provide exceptional advantage in the management of diabetes and its complications.

Antioxidant Supplementation Normalizes Elevated Protein Kinase C Activity in the Proximal Tubules of Old Rats

Aging is associated with increase in oxidative stress. Earlier, we have shown that higher basal protein kinase C (PKC) activity in the proximal tubules (PTs) of old rats contributes to the hyperphosphorylation of Na,K-ATPase and subsequent decrease in basal Na,K-ATPase activity, resulting in diminished natriuretic response to dopamine in these animals. We hypothesized that the increase in PKC activity in PTs of old rats is caused by increased oxidative stress and that antioxidants administration should reduce/normalize the elevated PKC activity in the renal PTs of old rats. We studied the effect of two antioxidants, namely, α-lipoic acid (LA) and tempol, on oxidants level and PKC activity in the PTs of adult (6-month) and old (24-month) Fischer 344 rats. We found that the accumulation of fluorescent dichlorofluorescein (DCF), an indicator of oxidant production, was higher in the PTs of old compared to adult rats. Dietary supplementation with LA for 2 weeks normalized the increased DCF level in old rats. Carboxymethylysine and malondialdehyde, markers of oxidative damage, were elevated in the PTs of old rats, which were normalized to the level of adult rats when tempol was provided in drinking water for 3 weeks. Both LA and tempol treatment also normalized the higher basal PKC activity in the PTs of old rats to the level seen in adult rats. These results suggest that increase in oxidative stress causes an increase in PKC activity, and that antioxidants, while reducing oxidative stress, also normalize PKC activity in the PTs of old rats.

Canonical Transient Receptor Potential 6 Channel: A New Target of Reactive Oxygen Species in Renal Physiology and Pathology

SIGNIFICANCE

Regulation of Ca2+ signaling cascade by reactive oxygen species (ROS) is becoming increasingly evident and this regulation represents a key mechanism for control of many fundamental cellular functions. Canonical transient receptor potential (TRPC) 6, a member of Ca2+-conductive channel in the TRPC family, is widely expressed in kidney cells, including glomerular mesangial cells, podocytes, tubular epithelial cells, and vascular myocytes in renal microvasculature. Both overproduction of ROS and dysfunction of TRPC6 channel are involved in renal injury in animal models and human subjects. Although regulation of TRPC channel function by ROS has been well described in other tissues and cell types, such as vascular smooth muscle, this important cell regulatory mechanism has not been fully reviewed in kidney cells. Recent Advances: Accumulating evidence has shown that TRPC6 is a redox-sensitive channel, and modulation of TRPC6 Ca2+ signaling by altering TRPC6 protein expression or TRPC6 channel activity in kidney cells is a downstream mechanism by which ROS induce renal damage.

CRITICAL ISSUES

This review highlights how recent studies analyzing function and expression of TRPC6 channels in the kidney and their response to ROS improve our mechanistic understanding of oxidative stress-related kidney diseases.

FUTURE DIRECTIONS

Although it is evident that ROS regulate TRPC6-mediated Ca2+ signaling in several types of kidney cells, further study is needed to identify the underlying molecular mechanism. We hope that the newly identified ROS/TRPC6 pathway will pave the way to new, promising therapeutic strategies to target kidney diseases such as diabetic nephropathy. Antioxid. Redox Signal. 25, 732-748.

Mitochondria: a new therapeutic target in chronic kidney disease

Cellular metabolic changes during chronic kidney disease (CKD) may induce higher production of oxygen radicals that play a significant role in the progression of renal damage and in the onset of important comorbidities. This condition seems to be in part related to dysfunctional mitochondria that cause an increased electron "leakage" from the respiratory chain during oxidative phosphorylation with a consequent generation of reactive oxygen species (ROS). ROS are highly active molecules that may oxidize proteins, lipids and nucleic acids with a consequent damage of cells and tissues. To mitigate this mitochondria-related functional impairment, a variety of agents (including endogenous and food derived antioxidants, natural plants extracts, mitochondria-targeted molecules) combined with conventional therapies could be employed. However, although the anti-oxidant properties of these substances are well known, their use in clinical practice has been only partially investigated. Additionally, for their correct utilization is extremely important to understand their effects, to identify the correct target of intervention and to minimize adverse effects. Therefore, in this manuscript, we reviewed the characteristics of the available mitochondria-targeted anti-oxidant compounds that could be employed routinely in our nephrology, internal medicine and renal transplant centers. Nevertheless, large clinical trials are needed to provide more definitive information about their use and to assess their overall efficacy or toxicity.

Targeting Mitochondria and Reactive Oxygen Species-Driven Pathogenesis in Diabetic Nephropathy

Diabetic kidney disease is one of the major microvascular complications of both type 1 and type 2 diabetes mellitus. Approximately 30% of patients with diabetes experience renal complications. Current clinical therapies can only mitigate the symptoms and delay the progression to end-stage renal disease, but not prevent or reverse it. Oxidative stress is an important player in the pathogenesis of diabetic nephropathy. The activity of reactive oxygen and nitrogen species (ROS/NS), which are by-products of the diabetic milieu, has been found to correlate with pathological changes observed in the diabetic kidney. However, many clinical studies have failed to establish that antioxidant therapy is renoprotective. The discovery that increased ROS/NS activity is linked to mitochondrial dysfunction, endoplasmic reticulum stress, inflammation, cellular senescence, and cell death calls for a refined approach to antioxidant therapy. It is becoming clear that mitochondria play a key role in the generation of ROS/NS and their consequences on the cellular pathways involved in apoptotic cell death in the diabetic kidney. Oxidative stress has also been associated with necrosis via induction of mitochondrial permeability transition. This review highlights the importance of mitochondria in regulating redox balance, modulating cellular responses to oxidative stress, and influencing cell death pathways in diabetic kidney disease. ROS/NS-mediated cellular dysfunction corresponds with progressive disease in the diabetic kidney, and consequently represents an important clinical target. Based on this consideration, this review also examines current therapeutic interventions to prevent ROS/NS-derived injury in the diabetic kidney. These interventions, mainly aimed at reducing or preventing mitochondrial-generated oxidative stress, improving mitochondrial antioxidant defense, and maintaining mitochondrial integrity, may deliver alternative approaches to halt or prevent diabetic kidney disease.

Role of dietary and endogenous antioxidants in diabetes

Diabetes affects different people of all ages, race, and sex. This is a condition characterized by a state of chronic hyperglycaemia that leads to an increase of intracellular oxidative stress linked to the overproduction of free radicals. In the present review, we focus our attention on the molecular mechanisms leading to oxidative stress-mediates complications with particular regard to central nervous system (CNS). Furthermore, the present review reports the effects of different kind of antioxidants with enzymatic and nonenzymatic action that may significantly decrease the intracellular free radicals' overproduction and prevents the hyperglycaemia-mediated complications.

Antioxidant and renoprotective effects of Spirogyra neglecta (Hassall) Kützing extract in experimental type 2 diabetic rats

Spirogyra neglecta extract (SNE) has shown antihyperglycemia and antihyperlipidemia in type 2 diabetic mellitus (T2DM) rats. This study investigated the antioxidant and renoprotective effects of SNE in T2DM rats induced by high-fat diet with low-single dose streptozotocin. T2DM rats were fed daily with SNE (0.25, 0.5, and 1 g/kg BW) for 12 weeks. Renal morphology, malondialdehyde levels, qPCR, and western blotting were analyzed. Renal cortical slices were used to determine renal transport of organic anions, which are estrone sulfate and para-aminohippurate, mediated through organic anion transporter 3-Oat3. Insulin and PKCζ were known to activate Oat3 function while it was inhibited by PKCα. Compared to T2DM, plasma glucose, triglyceride, insulin resistance, renal morphology, and malondialdehyde levels were significantly improved by SNE supplementation. Reduced glutathione peroxidase and nuclear factor κB expressions were related to antioxidant effect of SNE. Oat3 mRNA and protein were not different among groups, but insulin-stimulated rOat3 followed by anion uptakes was abolished in T2DM. This was restored in the slices from SNE treatment. The mechanism of SNE-improved Oat3 was associated with PKCα and PKCζ expressions and activities. These findings indicate that SNE has beneficial effects on renal transport through antioxidant enzymes and PKCs in T2DM rats.

Chronic Administration of Oil Palm (Elaeis guineensis) Leaves Extract Attenuates Hyperglycaemic-Induced Oxidative Stress and Improves Renal Histopathology and Function in Experimental Diabetes

Oil palm (Elaeis guineensis) leaves extract (OPLE) has antioxidant properties and because oxidative stress contributes to the pathogenesis of diabetic nephropathy (DN), we tested the hypothesis that OPLE prevents diabetes renal oxidative stress, attenuating injury. Sprague-Dawley rats received OPLE (200 and 500 mg kg(-1)) for 4 and 12 weeks after diabetes induction (streptozotocin 60 mg kg(-1)). Blood glucose level, body and kidney weights, urine flow rate (UFR), glomerular filtration rate (GFR), and proteinuria were assessed. Oxidative stress variables such as 8-hydroxy-2'-deoxyguanosine (8-OHdG), glutathione (GSH), and lipid peroxides (LPO) were quantified. Renal morphology was analysed, and plasma transforming growth factor-beta1 (TGF-β1) was measured. Diabetic rats demonstrated increase in blood glucose and decreased body and increased kidney weights. Renal dysfunction (proteinuria, elevations in UFR and GFR) was observed in association with increases in LPO, 8-OHdG, and TGF-β1 and a decrease in GSH. Histological evaluation of diabetic kidney demonstrated glomerulosclerosis and tubulointerstitial fibrosis. OPLE attenuated renal dysfunction, improved oxidative stress markers, and reduced renal pathology in diabetic animals. These results suggest OPLE improves renal dysfunction and pathology in diabetes by reducing oxidative stress; furthermore, the protective effect of OPLE against renal damage in diabetes depends on the dose of OPLE as well as progression of DN.

Long-term dietary antioxidant cocktail supplementation effectively reduces renal inflammation in diabetic mice

Diabetic nephropathy is a serious complication for diabetic patients, yet the precise mechanism that underlies the development of diabetic complications remains unknown. We hypothesised that dietary antioxidant supplementation with single N-acetylcysteine (NAC) or vitamin C combined with either vitamin E or vitamin E and NAC improves diabetic renal inflammation through the modulation of blood glucose levels, oxidative stress and inflammatory response. Experimental animals were treated with alloxan monohydrate to induce diabetes. Mice were divided into five groups and supplemented with single or a combination of antioxidants. Body weights and blood glucose levels were measured once a week. After 8 weeks of dietary antioxidant supplementation, mice were killed and blood urea N (BUN) and plasma creatinine levels were measured to evaluate renal function. NF-κB protein was indirectly demonstrated by the phosphorylated IκBα (pIκBα) level, and the expressions of oxidative stress- and inflammatory response-related proteins were also determined. We demonstrated that dietary antioxidant supplementation decreased lipid peroxidation levels demonstrated by thiobarbituric acid-reacting substances, BUN and plasma creatinine levels in diabetic kidneys. Moreover, dietary antioxidant cocktail supplementation improved blood glucose levels and selectively regulated the expressions of Cu-Zn superoxide dismutase, haeme oxygenase-1, pIκBα, inducible NO synthase, cyclo-oxygenase-2 and C-reactive protein in diabetic kidneys effectively. These findings demonstrated that diabetic renal failure was associated with inflammatory responses induced by hyperglycaemia. In addition, results in the study suggest that antioxidant cocktail supplementation may have beneficial effects on diabetic nephropathy through selective reduction of blood glucose levels and inflammatory response.

Beneficial effect of the oligomerized polyphenol oligonol on high glucose-induced changes in eNOS phosphorylation and dephosphorylation in endothelial cells

BACKGROUND AND PURPOSE

Hyperglycaemia is known to reduce nitric oxide (NO) bioavailability by modulating endothelial NO synthase (eNOS) activity, and polyphenols are believed to have cardiovascular benefit. One possible mechanism could be through interaction with eNOS.

EXPERIMENTAL APPROACH

The effects of the oligomerized polyphenol oligonol on eNOS phosphorylation status and activity were examined in porcine aortic endothelial cells cultured in high glucose concentrations.

KEY RESULTS

Exposure to high glucose concentrations strongly inhibited eNOS phosphorylation at Ser-1177 and dephosphorylation at Thr-495 in bradykinin (BK)-stimulated cells. These inhibitory effects of high glucose were significantly prevented by treatment with oligonol. Akt and p38 mitogen-activated protein kinase (MAPK) were activated in BK-stimulated cells. High glucose inhibited Akt activation but enhanced p38 MAPK activation, both of which were reversed by oligonol treatment. The phosphatidylinositol 3-kinase inhibitor wortmannin blocked the reversal by oligonol of phosphorylation at Ser-1177, but not dephosphorylation at Thr-495, in BK-stimulated cells exposed to high glucose. The effect of oligonol on BK dephosphorylation under high glucose was mimicked by protein kinase C (PKC) epsilon-neutralizing peptides. These data suggest that the effects of oligonol on high glucose-induced attenuation of eNOS Ser-1177 phosphorylation and Thr-495 dephosphorylation may be regulated by Akt activation and PKCepsilon inhibition respectively. Oligonol also prevented high glucose-induced attenuation of BK-stimulated NO production.

CONCLUSIONS AND IMPLICATIONS

Oligonol prevented the impairment of eNOS activity induced by high glucose through reversing altered eNOS phosphorylation status. This mechanism may underlie the beneficial cardiovascular health effects of this oligomerized polyphenol.

PKC-dependent superoxide production by the renal medullary thick ascending limb from diabetic rats

Type 1 diabetes (T1D) is a state of oxidative stress accompanied by PKC activation in many tissues. The primary site of O2*- production by the normal rat kidney is the medullary thick ascending limb (mTAL). We hypothesized that T1D increases O2*- production by the mTAL through a PKC-dependent mechanism involving increased expression and translocation of one or more PKC isoforms. mTAL suspensions were prepared from rats with streptozotocin-induced T1D (STZ mTALs) and from normal or sham rats (normal/sham mTALs). O2*- production by STZ mTALs was fivefold higher than normal/sham mTALs (P < 0.05). PMA (30 min) mimicked the effect of T1D on O2*- production. Exposure to calphostin C or chelerythrine (PKC inhibitors), Gö6976 (PKCalpha/beta inhibitor), or rottlerin (PKCdelta inhibitor) decreased O2*- production to <20% of untreated baseline in both normal/sham and STZ mTALs. PKCbeta inhibitors had no effect. PKC activity was increased in STZ mTALs (P < 0.05 vs. normal/sham mTALs) and was unaltered by antioxidant exposure (tempol). PKCalpha protein levels were increased by 70% in STZ mTALs, with a approximately 30% increase in the fraction associated with the membrane (both P < 0.05 vs. sham). PKCbeta protein levels were elevated by 29% in STZ mTALs (P < 0.05 vs. sham) with no change in the membrane-bound fraction. Neither PKCdelta protein levels nor its membrane-bound fraction differed between groups. Thus STZ mTALs display PKC activation, upregulation of PKCalpha and PKCbeta protein levels, increased PKCalpha translocation to the membrane, and accelerated O2*- production that is eradicated by inhibition of PKCalpha or PKCdelta (but not PKCbeta). We conclude that increased PKCalpha expression and activity are primarily responsible for PKC-dependent O2*- production by the mTAL during T1D.

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.

Protective effect of salvianolic acid B on chronic pancreatitis induced by trinitrobenzene sulfonic acid solution in rats

OBJECTIVES

To investigate the effects of salvianolic acid B (Sal-B) on pancreatic damage in experimental chronic pancreatitis.

METHODS

Chronic pancreatitis was induced by infusion of trinitrobenzene sulfonic acid into the pancreatic duct in male Sprague-Dawley rats. From the beginning of 5 weeks, the rats in group 2 were treated with Sal-B by gavage for 8 weeks. Salvianolic acid B was given at a daily dose of 10 mg/kg body weight. At the end of 12 weeks, the levels of serum biochemical indexes were measured on an automatic biochemical analyzer; serum hyaluronic acid and laminin levels were determined by radioimmunoassay; pancreatic tissue malondialdehyde (MDA) was analyzed, and the degree of pancreatic damage was determined.

RESULTS

The level of serum biochemical indexes were similar in all groups (P > 0.05 for all). Salvianolic acid B treatment did not obviously reduce hyaluronic acid and laminin concentration in blood (P > 0.05). Salvianolic acid B treatment decreased MDA concentration in pancreatic tissue (P < 0.01). Salvianolic acid B clearly improved pancreatic histological findings and prevented the activation of pancreatic stellate cells.

CONCLUSIONS

Sal-B treatment decreased MDA concentration in pancreatic tissue, attenuated morphological pancreatic damage, and prevented the activation of pancreatic stellate cells in experimental chronic pancreatitis.

Neuroprotective effect of N-acetylcysteine in the development of diabetic encephalopathy in streptozotocin-induced diabetes

Diabetic encephalopathy is characterized by impaired cognitive functions that involve neuronal damage triggered by glucose driven oxidative stress. The objective of the present study was to determine whether N-acetylcysteine (NAC) supplementation ameliorates learning and memory deficits caused by hyperglycemia-induced oxidative stress in experimental diabetes. Male Wistar rats (200-250 g) were rendered diabetic by a single intraperitoneal injection of streptozotocin (50 mg/kg). Cognitive deficits were observed in diabetic animals assessed using elevated plus maze test after 8 weeks of induction of diabetes. Acetylcholinesterase activity, a marker of cholinergic function, was decreased by 15.6% in the cerebral cortex, 20.9% in cerebellum and 14.9% in brain stem of diabetic rats compared to control rats. There was an increase in lipid peroxidation in cerebral cortex (21.97%), cerebellum (20.4%) and brain stem (25.5%) of diabetic rats. This was accompanied by decrease in glutathione and total thiol content along with decrease in the activities of superoxide dismutase, catalase and glutathione reductase. However, glutathione peroxidase activity increased by 11.2%, 13.6% and 23.1% in cerebral cortex, cerebellum and brain stem respectively, while the activity of glutathione-s-transferase decreased only in cerebral cortex (21.7%). Supplementation with NAC (1.4 g/kg/day in drinking water) significantly attenuated cognitive deficits and oxidative stress in diabetic rats. Our results emphasize the involvement of increased oxidative stress in cognitive impairment in diabetic animals and point towards the potential beneficial role of NAC as an adjuvant therapy to conventional anti-hyperglycemic regimens for the prevention and treatment of diabetic encephalopathy.

Role of reactive oxygen species in the pathogenesis of diabetic nephropathy

There is an increasing evidence that reactive oxygen species (ROS) play a major role in the development of diabetic complications. Oxidative stress is increased in diabetes and the overproduction of ROS in diabetes is a direct consequence of hyperglycemia. Various types of vascular cells including renal cells are able to produce ROS under hyperglycemic condition. Both NADPH oxidase and mitochondrial electron gradient play roles in hyperglycemia-induced ROS generation. In addition to their ability to directly inflict macromolecular damage, ROS can function as signaling molecules. ROS mediate hyperglycemia-induced activation of signal transduction cascades and transcription factors leading to transcriptional activation of profibrotic genes in the kidney. Furthermore, ROS-activated signaling molecules generate and signal through ROS and thus ROS act as a signal amplifier. Intensive glycemic control and inhibition of angiotensin II delay the onset and progression of diabetic nephropathy, in part, through prevention of overproduction of ROS. Conventional and catalytic antioxidants have been shown to prevent or delay the onset of diabetic nephropathy. Combination of strategies to prevent overproduction of ROS and to increase the removal of preformed ROS may prove to be effective in preventing the development and progression of diabetic nephropathy.

Beneficial impact of L-carnitine in liver: a study in a rat model of syndrome X

The present study was designed to explore whether L-carnitine (CA) regulates insulin signaling and modulates the changes in liver in a well-characterized insulin resistant rat model. Adult male Wistar rats were divided into 4 groups. Groups I and IV animals received starch-based control diet, while groups II and III rats were fed a high fructose-diet (60 g/100 g). Groups III and IV animals additionally received CA (300 mg/kg/day i.p). After a period of 60 days hepatic tyrosine phosphorylation status was determined by assaying protein tyrosine phosphatase (PTP) and protein tyrosine kinase (PTK) activities. Oxidative damage was monitored by immunohistochemical localization of 4-hydroxynonenal (4-HNE), 3-nitrotyrosine (3-NT) and dinitrophenol (DNP)-protein adducts. In addition protein kinase C beta II (PKC beta II) expression, propidium iodide staining of isolated hepatocytes and histology of liver tissue were determined to examine liver integrity. Fructose-fed rats displayed reduced insulin action, increased expression of PKC beta II, altered histology, fragmentation of hepatocyte nuclear DNA, and accumulation of oxidatively modified proteins. Simultaneous treatment with CA alleviated the abnormalities associated with fructose feeding. In summary the data suggest that elevated oxidative damage and PKC expression could in part induce insulin resistance and CA has beneficial impact on liver during insulin resistance with modulatory effects at the post-receptor level.

Radical approach to diabetic nephropathy

There is increasing evidence that reactive oxygen species (ROS) play a major role in the development of diabetic complications. Oxidative stress is increased in diabetes and in chronic kidney disease (CKD). High glucose upregulates transforming growth factor-beta1 (TGF-beta1) and angiotensin II (Ang II) in renal cells and high glucose, TGF-beta1, and Ang II all generate and signal through ROS. ROS mediate high glucose-induced activation of protein kinase C and nuclear factor-kappaB in renal cells. Intensive glycemic control and inhibition of Ang II delay the onset and progression of diabetic nephropathy, in part, through antioxidant activity. Conventional and catalytic antioxidants were shown to prevent or delay the onset of diabetic nephropathy. Transketolase activators and poly (ADP-ribose) polymerase inhibitors were shown to block major biochemical pathways of hyperglycemic damage. Combination of strategies to prevent overproduction of ROS, to increase the removal of preformed ROS, and to block ROS-induced activation of biochemical pathways leading to cellular damage may prove to the effective in preventing the development and progression of CKD in diabetes.

Activation of sphingosine kinase-1 mediates inhibition of vascular smooth muscle cell apoptosis by hyperglycemia

Vascular smooth muscle cell (VSMC) apoptosis plays an essential role in vascular development and atherosclerosis. Hyperglycemia inhibits VSMC apoptosis, which may contribute to the development of diabetic vasculopathy. In the present study, we analyzed the mechanism of high-glucose-induced anti-apoptotic effect in cultured human aortic smooth muscle cells (HASMCs). Compared with normoglycemia, exposure of HASMCs to hyperglycemia but not mannitol significantly increased sphingosine kinase 1 (SK1) activity but not SK2 activity. This increase was inhibited by protein kinase C (PKC) inhibitor GF109203X, the antioxidant N-acetylcysteine, and the reduced form of glutathione. The mechanism of SK1 activation by high glucose involves plasma membrane translocation. In addition, hyperglycemia markedly inhibited serum withdrawal-induced apoptosis in HASMCs. Importantly, inhibition of SK1 by either a competitive inhibitor N',N'-dimethylsphingosine or expression of dominant-negative mutant of SK1(G82D) or specific small interference RNA knockdown substantially attenuated hyperglycemia-induced anti-apoptotic effect and anti-apoptotic protein Bcl-2 expression in HASMCs. Moreover, SK1-mediated anti-apoptotic effect requires the intracellular effects of sphingosine-1-phosphate. We conclude that hyperglycemia stimulates SK1 activity via PKC- and oxidative stress-dependent pathways, leading to decreased apoptosis in HASMCs. Taken together, these observations have important implications for understanding the roles of the SK1 signaling pathway in the pathogenesis of diabetic vasculopathy.

Oxidants in chronic kidney disease

Chronic kidney disease is a worldwide public health problem that affects approximately 10% of the US adult population and is associated with a high prevalence of cardiovascular disease and high economic cost. Chronic renal insufficiency, once established, tends to progress to end-stage kidney disease, suggesting some common mechanisms for ultimately causing scarring and further nephron loss. This review defines the term reactive oxygen metabolites (ROM), or oxidants, and presents the available experimental evidence in support of the role of oxidants in diabetic and nondiabetic glomerular disease and their role in tubulointerstitial damage that accompanies progression. It concludes by reviewing the limited human data that provide some proof of concept that the observations in experimental models may be relevant to human disease.

The influence of rutin on the extracellular matrix in streptozotocin-induced diabetic rat kidney

We previously reported that rutin administration to streptozotocin (STZ)-induced diabetic rats decreased plasma glucose and increased plasma insulin levels. In this study, we have examined the role of rutin on matrix remodelling in the kidney of STZ-induced diabetic rats. STZ was administered intraperitoneally (50 mg kg(-1)) to male albino Wistar rats to induce experimental diabetes. Rutin (100 mg kg(-1)) was orally administered to normal and STZ-induced diabetic rats for a period of 45 days and its influence on the content of hydroxyproline and collagen and on the activity of matrix metalloproteinases (MMPs) were studied. We have also studied the levels of tissue inhibitors of metalloproteinases (TIMPs) in the kidney. STZ-induced diabetic control rats showed increased content of hydroxyproline and collagen, decreased activity of MMPs and increased levels of TIMPs in the kidney. These changes were positively modulated by rutin treatment in STZ-induced diabetic rats, thereby protecting the kidney. In normal rats treated with rutin, none of the parameters studied were significantly altered. From the results obtained, we could conclude that rutin influences MMPs and effectively protects kidney against STZ-induced damage in rats. The effects observed are due to the reduction of plasma glucose levels by rutin.

Renoprotective Effect of Breviscapine through Suppression of Renal Macrophage Recruitment in Streptozotocin-Induced Diabetic Rats

BACKGROUND/AIMS

Experimental and clinical evidence has consistently demonstrated that renal macrophage infiltration is one of the most important events for the progression of diabetic nephropathy. Breviscapine is a flavonoid extracted from the Chinese herb Erigeron breviscapus. Previously, it was shown that treatment with breviscapine attenuated renal injury in the diabetic rats. The purpose of this study is to investigate whether the renoprotective effect of breviscapine is through suppression of renal macrophage recruitment in diabetic rats.

METHODS

Diabetes was induced bystreptozotocin injection, and breviscapine was administered orally at a dose of 20 mg/kg/day for 8 weeks. Control rats received vehicle or breviscapine with the same schedule.

RESULTS

Breviscapine treatment markedly inhibited both an increase of albuminuria and glomeruli hypertrophy and tubulointerstitial injury without modifying mean arterial blood pressure and creatinine clearance. Levels of malondialdehyde and protein kinase C activities were markedly higher and antioxidant enzyme activities such as superoxide dismutase, catalase as well as glutathione peroxidase were significantly lower in the kidneys of diabetic rats than of the control group, breviscapine administration markedly remitted these changes. ED-1-positive cells and expression of intercellular adhesion molecule-1 (ICAM-1) and monocyte chemoattractant protein-1 (MCP-1) in glomeruli and tubulointerstitium were all markedly elevated but were significantly reduced by breviscapine. Western blot analysis noted that the expression of transforming growth factor beta1 protein was increased 1.8-fold in the kidney in diabetic rats, breviscapine treatment could reduce increased expression of TGF-beta1 protein by 47%.

CONCLUSION

This study describes a novel mechanism by which breviscapine confers a renoprotective effect.

Acute effect of high glucose on long-term cell growth: a role for transient glucose increase in proximal tubule cell injury

Although chronic exposure of renal cells to high glucose has been shown to cause cell injury, the effect of acute exposure has not been elucidated. In this study, we demonstrate that acute (10 min) exposure of human proximal tubule epithelial cells (hPTEC) to high glucose (25 mM) induces a time-dependent dual effect consisting of an early proliferation and a late apoptosis. Acute exposure of hPTEC to high glucose induced a twofold increase in DNA synthesis and cell number at 12 h. However, after 36 h, a significant decrease in cell growth is observed, followed by apoptosis. On glucose treatment, both p42/p44 mitogen-activated protein (MAP) kinases and the downstream signaling intermediate NF-κB were phosphorylated and translocated to the nucleus. Pretreatment of cells with MAP kinase and NF-κB-specific inhibitors abolished glucose-induced proliferation. However, these inhibitors were ineffective in preventing glucose-induced apoptosis. Interestingly, conditioned medium from cells exposed to high-glucose concentrations inhibited proliferation and concomitantly induced apoptosis in normal cells, suggesting that the inhibitory effect of glucose occurs through secretion of a secondary factor(s). In parallel to apoptosis, we observed an increased production of reactive oxygen species (ROS). Pretreatment of cells with the antioxidant N-acetyl cysteine reversed glucose-mediated ROS production and apoptosis, suggesting that ROS is involved in apoptosis. Our study demonstrates for the first time that a single high-glucose exposure for 10 min alone is sufficient to elicit proliferation and apoptosis in hPTEC and suggests that episodes of transient increase in glucose may contribute to cell damage leading to epithelial cell dysfunction.

Isoflavones made simple - genistein's agonist activity for the beta-type estrogen receptor mediates their health benefits

Soy isoflavones, the focus of much research and controversy, are often referred to as "weak estrogens". In fact, genistein is a relatively potent agonist for the recently characterized beta isoform of the estrogen receptor (ERbeta). The low nanomolar serum concentrations of unconjugated free genistein achieved with high-nutritional intakes of soy isoflavones are near the binding affinity of genistein for this receptor, but are about an order of magnitude lower than genistein's affinity for the "classical" alpha isoform of the estrogen receptor (ERalpha). Moreover, these concentrations are far too low to inhibit tyrosine kinases or topoisomerase II, in vitro activities of genistein often cited as potential mediators of its physiological effects. The thesis that these physiological effects are in fact mediated by ERbeta activation provides a satisfying rationale for genistein's clinical activities. Hepatocytes do not express ERbeta; this explains why soy isoflavones, unlike oral estrogen, neither modify serum lipids nor provoke the prothrombotic effects associated with increased risk for thromboembolic disorders. The lack of uterotrophic activity of soy isoflavones reflects the fact that ERalpha is the exclusive mediator of estrogen's impact in this regard. Vascular endothelium expresses both ERalpha and ERbeta, each of which has the potential to induce and activate nitric oxide synthase; this may account for the favorable influence of soy isoflavones on endothelial function in postmenopausal women and ovariectomized rats. The ERbeta expressed in osteoblasts may mediate the reported beneficial impact of soy isoflavones on bone metabolism. Suggestive evidence that soy-rich diets decrease prostate cancer risk, accords well with the observation that ERbeta appears to play an antiproliferative role in healthy prostate. In the breast, ERalpha promotes epithelial proliferation, whereas ERbeta has a restraining influence in this regard - consistent with the emerging view that soy isoflavones do not increase breast cancer risk, and possibly may diminish it. Premenopausal women enjoy a relative protection from kidney failure; since ERbeta is an antagonist of TGF-beta signaling in mesangial cells, soy isoflavones may have nephroprotective potential. Estrogen also appears to protect women from left ventricular hypertrophy, and recent evidence suggests that this effect is mediated by ERbeta. In conjunction with reports that isoflavones may have a modestly beneficial impact on menopausal symptoms - perhaps reflecting the presence of ERbeta in the hypothalamus - these considerations suggest that soy isoflavone regimens of sufficient potency may represent a safe and moderately effective alternative to HRT in postmenopausal women. Further clinical research is required to characterize the impact of optimal genistein intakes on endothelial and bone function in men. Studies with ERbeta-knockout mice could be helpful for clarifying whether ERbeta does indeed mediate the chief physiological effects of low nanomolar genistein. S-equol, a bacterial metabolite of daidzein, has an affinity for ERbeta nearly as high as that of genistein; whether this compound contributes meaningfully to the physiological efficacy of soy isoflavones in some individuals is still unclear.

Mesangial cell NADPH oxidase upregulation in high glucose is protein kinase C dependent and required for collagen IV expression

Excess collagen IV expression by mesangial cells contributes to diabetic glomerulosclerosis. We hypothesized that in high glucose reactive oxygen species (ROS) generation by NADPH oxidase is PKC dependent and required for collagen IV expression by mesangial cells. In rat mesangial cells cultured in 5 mM (NG) or 25 mM d-glucose (HG), RT-PCR and Western immunoblotting detected p22phoxand p47phoxmRNA and protein, respectively. Quantitative real-time RT-PCR analyzed collagen IV mRNA. With the use of confocal microscopy, ROS were detected with dichlorofluorescein and intracellular collagen IV by immunofluorescence. In HG, ROS were generated within 1 h, sustained up to 48 h, and prevented by a NADPH oxidase inhibitor, diphenylenechloride iodonium (DPI), or a conventional PKC isozyme inhibitor, Gö6976. In NG, phorbol myristate acetate stimulated ROS generation that was inhibited with DPI. In HG, expression of p22phoxand p47phoxwas increased within 3 to 6 h and inhibited by Gö6976. In HG, Gö6976 or transfection with antisense against p22phoxreversed the 1.8-fold increase in collagen IV mRNA. In HG, the antioxidants Tempol or Tiron, or transfection with antisense against p22phoxor p47phox, prevented ROS generation and the 2.3-fold increase in collagen IV protein. Increased mitochondrial redox potential in HG was unaffected by transfection with antisense against p22phox. We conclude that in HG, mesangial cell ROS generation by upregulated NADPH oxidase is dependent on conventional PKC isozymes and also required for collagen IV expression.

The pathogenesis of myocardial fibrosis in the setting of diabetic cardiomyopathy

Diabetes has emerged as a major threat to worldwide health. The increasing incidence of diabetes in young individuals is particularly worrisome given that the disease is likely to evolve over a period of years. In 1972, the existence of a diabetic cardiomyopathy was proposed based on the experience with four adult diabetic patients who suffered from congestive heart failure in the absence of discernible coronary artery disease, valvular or congenital heart disease, hypertension, or alcoholism. The exact mechanisms underlying the disease are unknown; however, an important component of the pathological alterations observed in these hearts includes the accumulation of extracellular matrix (ECM) proteins, in particular collagens. The excess deposition of ECM in the heart mirrors what occurs in other organs such as the kidney and peritoneum of diabetics. Mechanisms responsible for these alterations may include the excess production, reduced degradation, and/or chemical modification of ECM proteins. These effects may be the result of direct or indirect actions of high glucose concentrations. This article reviews our state of knowledge on the effects that diabetes-like conditions exert on the cells responsible for ECM production as well as relevant experimental and clinical data.

Protein Kinase C β Inhibitor LY333531 Attenuates Intercellular Adhesion Molecule-1 and Monocyte Chemotactic Protein-1 Expression in the Kidney in Diabetic Rats

In vitro studies have shown that activation of protein kinase C (PKC) is a key mediator of intercellular adhesion molecule-1 (ICAM-1) and monocyte chemoattractant protein-1 (MCP-1) in a range of cell types and in response to high glucose, however, its role in the in vivo setting has not been clearly delineated. Streptozotocin-induced diabetic rats were treated with the PKC-beta isoform inhibitor LY333531 for 8 weeks. LY333531 treatment significantly attenuated increased urinary albumin excretion rate and glomerular volume and tubulointerstitial injury index as well as elevated PKC activity and PKC-beta protein expression in the kidney. Level of malondialdehyde was markedly higher and antioxidant enzyme activity such as superoxide diamutase and catalase as well as glutathione peroxidase were significantly lower in the kidney from diabetic rats than that of the control group. LY333531 administration could remit these changes. Increased macrophages recruitment as well as ICAM-1 and MCP-1 protein expression in the kidney were significantly inhibited by LY333531 in diabetic rats. It is concluded that mechanism of renoprotection of LY333531 may be correlated, at least partly, with suppression of increased macrophages recruitment and overexpression of ICAM-1 and MCP-1 in diabetic rats.

Adjuvant strategies for prevention of glomerulosclerosis

The glomerulosclerosis which frequently complicates diabetes and severe hypertension is mediated primarily by increased mesangial production and activation of transforming growth factor-beta (TGF-beta), which acts on mesangial cells to boost their production of matrix proteins while suppressing extracellular proteolytic activity. Hyperglycemia and glomerular hypertension work in various complementary ways to stimulate superoxide production via NADPH oxidase in mesangial cells; the resulting oxidant stress results in the induction and activation of TFG-beta. Nitric oxide, generated by glomerular capillaries and by mesangial cells themselves, functions physiologically to oppose mesangial TGF-beta overproduction; however, NO bioactivity is compromised by oxidant stress. In addition to low-protein diets and drugs that suppress angiotensin II activity, a variety of other agents and measures may have potential for impeding the process of glomerulosclerosis. These include vitamin E, which blunts the rise in mesangial diacylglycerol levels induced by hyperglycemia; statins and (possibly) policosanol, which down-regulate NADPH oxidase activity by diminishing isoprenylation of Rac1; lipoic acid, whose potent antioxidant activity antagonizes the impact of oxidant stress on TGF-beta expression; pyridoxamine, which inhibits production of advanced glycation endproducts; arginine, high-dose folate, vitamin C, and salt restriction, which may support glomerular production of nitric oxide; and estrogen and soy isoflavones, which may induce nitric oxide synthase in glomerular capillaries while also interfering with TGF-beta signaling. Further research along these lines may enable the development of complex nutraceuticals which have important clinical utility for controlling and preventing glomerulosclerosis and renal failure. Most of these measures may likewise reduce risk for left ventricular hypertrophy in hypertensives, inasmuch as the signaling mechanisms which mediate this disorder appear similar to those involved in glomerulosclerosis.

Reactive oxygen species amplify glucose signalling in renal cells cultured under high glucose and in diabetic kidney

Diabetic nephropathy is characterized by excessive accumulation of extracellular matrix (ECM) in the kidney. Reactive oxygen species (ROS) play a central role in the ECM synthesis and degradation in the glomeruli and tubulointerstitium leading to renal fibrosis. High glucose (HG) induces cellular ROS through protein kinase C (PKC)-dependent activation of NADPH oxidase and through mitochondrial metabolism. ROS thus generated activate signal transduction cascade (PKC, mitogen-activated protein kinases, and janus kinase/signal transducers and activators of transcription) and transcription factors (nuclear factor-kappaB, activated protein-1, and specificity protein-1), up-regulate transforming growth factor-beta1 (TGF-beta1), angiotensin II (Ang II), monocyte chemoattractant protein-1 (MCP-1), and plasminogen activator inhibitor-1 (PAI-1) gene and protein expression, and promote formation of advanced glycation end-products (AGE). PKC, TGF-beta1, Ang II, and AGE also induce cellular ROS and signal through ROS leading to enhanced ECM synthesis. NF-kappaB-MCP-1 pathway is activated by ROS and promotes monocyte recruitment and profibrotic process in the kidney. HG- and TGF-beta1-induced PAI-1 up-regulation is mediated by ROS and contribute to ECM accumulation via suppression of plasmin ativity. TGF-beta1-induced myofibroblast transformation of renal tubular epithelial cells (epithelial-mesenchymal transition) is also mediated by ROS and contribute to tubulointerstitial fibrosis. In summary, ROS transduce and amplify glucose signalling in renal cells under high glucose environment and play a critical role in excessive ECM deposition in the diabetic kidney. A better understanding of ROS production and removal will allow more effective therapeutic strategies in diabetic renal and other vascular complications.

Inhibition of NF-kappa B and oxidative pathways in human dendritic cells by antioxidative vitamins generates regulatory T cells

Dendritic cells (DCs) are central to T cell immunity, and many strategies have been used to manipulate DCs to modify immune responses. We investigated the effects of antioxidants ascorbate (vitamin C) and alpha-tocopherol (vitamin E) on DC phenotype and function. Vitamins C and E are both antioxidants, and concurrent use results in a nonadditive activity. We have demonstrated that DC treated with these antioxidants are resistant to phenotypic and functional changes following stimulation with proinflammatory cytokines. Following treatment, the levels of intracellular oxygen radical species were reduced, and the protein kinase RNA-regulated, eukaryotic translation initiation factor 2alpha, NF-kappaB, protein kinase C, and p38 MAPK pathways could not be activated following inflammatory agent stimulation. We went on to show that allogeneic T cells (including CD4(+)CD45RO, CD4(+)CD45RA, and CD4(+)CD25(-) subsets) were anergized following exposure to vitamin-treated DCs, and secreted higher levels of Th2 cytokines and IL-10 than cells incubated with control DCs. These anergic T cells act as regulatory T cells in a contact-dependent manner that is not dependent on IL-4, IL-5, IL-10, IL-13, and TGF-beta. These data indicate that vitamin C- and E-treated DC might be useful for the induction of tolerance to allo- or autoantigens.

Rho-kinase mediates hyperglycemia-induced plasminogen activator inhibitor-1 expression in vascular endothelial cells

BACKGROUND

Elevated levels of plasminogen activator inhibitor-1 (PAI-1) are associated with myocardial infarction and stroke, especially in patients with diabetes. The induction of PAI-1 expression by hyperglycemia involves oxidative stress and protein kinase C (PKC). However, the mechanism by which hyperglycemia increases PAI-1 expression is unknown.

METHODS AND RESULTS

Compared with normoglycemia, exposure of human endothelial cells to hyperglycemia, but not mannitol, increased Rho-kinase activity in a time- and concentration-dependent manner. This increase was inhibited by a PKC inhibitor, GF109203X, and antioxidants N-acetylcysteine (NAC) and reduced form of glutathione (GSH). This correlated with inhibition of hyperglycemia-induced PAI-1 expression by GF109203X, NAC, and GSH. Hyperglycemia-increased PAI-1 mRNA and protein levels were inhibited by Rho-kinase inhibitors hydroxyfasudil and Y27632 and by a dominant-negative mutant of Rho-kinase. The mechanism for this inhibition occurs at the level of gene transcription because Rho-kinase inhibitors repress hyperglycemia-stimulated PAI-1 promoter activity without affecting mRNA stability. Hyperglycemia failed to stimulate Rho-kinase activity and PAI-1 expression in heterozygous ROCK I-knockout murine endothelial cells.

CONCLUSIONS

Hyperglycemia stimulates Rho-kinase activity via PKC- and oxidative stress-dependent pathways, leading to increased PAI-1 gene transcription. These results suggest that inhibition of ROCK I may be a novel therapeutic target for preventing thromboembolic complications of diabetes and cardiovascular disease.

N-Acetylcysteine Decreases Angiotensin II Receptor Binding in Vascular Smooth Muscle Cells

Antioxidants seem to inhibit angiotensin II (Ang II) actions by consuming stimulated reactive oxygen species. An alternative hypothesis was investigated: Antioxidants that are also strong reducers of disulfide bonds inhibit the binding of Ang II to its surface receptors with consequent attenuation of signal transduction and cell action. Incubation of cultured vascular smooth muscle cells, which possess Ang II type 1a receptors, with the reducing agent n-acetylcysteine (NAC) for 1 h at 37 degrees C resulted in decreased Ang II radioligand binding in a concentration-dependent pattern. NAC removal restored Ang II binding within 30 min. Incubation with n-acetylserine, a nonreducing analogue of NAC, did not lower Ang II binding, and oxidized NAC was less effective than reduced NAC in lowering Ang II binding. NAC did not decrease Ang II type 1a receptor protein content. Other antioxidants regulated Ang II receptors differently: alpha-Lipoic acid lowered Ang II binding after 24 h, and vitamin E did not lower Ang II binding at all. NAC inhibited Ang II binding in cell membranes at 21 or 37 but not 4 degrees C. Dihydrolipoic acid (the reduced form of alpha-lipoic acid), which contains free sulfhydryl groups as NAC does, decreased Ang II receptor binding in cell membranes, whereas alpha-lipoic acid, which does not contain free sulfhydryl groups, did not. Ang II-stimulated inositol phosphate formation was decreased by preincubation with NAC (1 h) or alpha-lipoic acid (24 h) but not vitamin E. In conclusion, certain antioxidants that are reducing agents lower Ang II receptor binding, and Ang II-stimulated signal transduction is decreased in proportion to decreased receptor binding.

Role of oxidative stress in diabetic nephropathy

Accumulating research suggests that oxidative stress is a significant contributor to the pathogenesis of diabetic nephropathy. The normal kidney generates a substantial amount of oxidative stress because of its high metabolic activity that is balanced by an extensive antioxidant system. However, in pathologic states such as hyperglycemia, nitroso-oxidant balance shifts toward a pro-oxidant state that accelerates tissue and vascular injury. This oxidative damage progresses concomitant with worsening glucose metabolism, vascular dysfunction, and kidney disease. Accordingly, strategies to reduce oxidative stress in diabetes mellitus may exert favorable effects on the progression of diabetic nephropathy.

Role of Reactive Oxygen Species in TGF-β1-Induced Mitogen-Activated Protein Kinase Activation and Epithelial-Mesenchymal Transition in Renal Tubular Epithelial Cells

Epithelial-mesenchymal transition (EMT) plays an important role in renal tubulointerstitial fibrosis and TGF-beta1 is the key inducer of EMT. Phosphorylation of Smad proteins and/or mitogen-activated protein kinases (MAPK) is required for TGF-beta1-induced EMT. Because reactive oxygen species (ROS) are involved in TGF-beta1 signaling and are upstream signaling molecules to MAPK, this study examined the role of ROS in TGF-beta1-induced MAPK activation and EMT in rat proximal tubular epithelial cells. Growth-arrested and synchronized NRK-52E cells were stimulated with TGF-beta1 (0.2 to 20 ng/ml) or H(2)O(2) (1 to 500 microM) in the presence or absence of antioxidants (N-acetylcysteine or catalase), inhibitors of NADPH oxidase (diphenyleneiodonium and apocynin), mitochondrial electron transfer chain subunit I (rotenone), and MAPK (PD 98059, an MEK [MAP kinase/ERK kinase] inhibitor, or p38 MAPK inhibitor) for up to 96 h. TGF-beta1 increased dichlorofluorescein-sensitive cellular ROS, phosphorylated Smad 2, p38 MAPK, extracellular signal-regulated kinases (ERK)1/2, alpha-smooth muscle actin (alpha-SMA) expression, and fibronectin secretion and decreased E-cadherin expression. Antioxidants effectively inhibited TGF-beta1-induced cellular ROS, phosphorylation of Smad 2, p38 MAPK, and ERK, and EMT. H(2)O(2) reproduced all of the effects of TGF-beta1 with the exception of Smad 2 phosphorylation. Chemical inhibition of ERK but not p38 MAPK inhibited TGF-beta1-induced Smad 2 phosphorylation, and both MAPK inhibitors inhibited TGF-beta1- and H(2)O(2)-induced EMT. Diphenyleneiodonium, apocynin, and rotenone also significantly inhibited TGF-beta1-induced ROS. Thus, this data suggest that ROS play an important role in TGF-beta1-induced EMT primarily through activation of MAPK and subsequently through ERK-directed activation of Smad pathway in proximal tubular epithelial cells.

HNE-dependent molecular damage in diabetic nephropathy and its possible prevention by N-acetyl-cysteine and oxerutin

Accumulation of Advanced Lipoxidation End-products (ALE), such as MDA- and HNE-protein adducts, and Advanced Glycation End-products, such as carboxymethyl-lysine (CML), are probably involved in the development of diabetic nephropathy. In this study the effect of some antioxidant treatments (oxerutin, N-acetylcysteine, taurine and N-acetylcysteine+taurine) on kidney lipoxidative damage has been evaluated by immunohistochemistry in streptozotocined rats. Diabetic rats showed marked glomerular positivity for ALE, while the samples from Control rats were negative. All treatments except taurine were able to protect the glomeruli from ALE accumulation; the failure of taurine may be due to residual oxidative properties of its derivatives. These data are consistent with those of our previous study, which showed that all the antioxidants used except taurine protected the glomeruli from diabetes-induced enlargement, increased apoptotic rate, decreased cell density and CML accumulation. These data attest to a role of glycoxidative and lipoxidative damage in diabetes-dependent damage of the kidney, and indicate that specific antioxidants can prevent or attenuate diabetic nephropathy.

Oxidative Stress and Antioxidant Treatment in Diabetes

The many studies on oxidative stress, antioxidant treatment, and diabetic complications have shown that oxidative stress is increased and may accelerate the development of complications through the metabolism of excessive glucose and free fatty acids in diabetic and insulin-resistant states. However, the contribution of oxidative stress to diabetic complications may be tissue-specific, especially for microvascular disease that occurs only in diabetic patients but not in individuals with insulin resistance without diabetes, even though both groups suffer from oxidative stress. Although antioxidant treatments can show benefits in animal models of diabetes, negative evidence from large clinical trials suggests that new and more powerful antioxidants need to be studied to demonstrate whether antioxidants can be effective in treating complications. Furthermore, it appears that oxidative stress is only one factor contributing to diabetic complications; thus, antioxidant treatment would most likely be more effective if it were coupled with other treatments for diabetic complications.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Reactive oxygen species amplify protein kinase C signaling in high glucose-induced fibronectin expression by human peritoneal mesothelial cells

BACKGROUND

We previously demonstrated that high glucose up-regulates fibronectin mRNA and protein expression by human peritoneal mesothelial cells (HPMC) through activation of protein kinase C (PKC). PKC is known to induce cellular reactive oxygen species (ROS) and PKC-dependent activation of the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase has recently been shown to be responsible, in part, for increased oxidative stress in diabetes. On the other hand, high glucose-induced mitochondrial overproduction of superoxide anion was found to activate PKC. We, therefore, hypothesized that high glucose-induced activation of PKC in HPMC may increase cellular ROS and ROS, in turn, may activate PKC and thus provide signal amplification in high glucose-induced fibronectin up-regulation in HPMC.

METHODS

The role of ROS in high glucose- and PKC-induced fibronectin expression was examined by quantification of cellular ROS after stimulation with high glucose and phorbol 12-myristate 13-acetate (PMA), by the effect of hydrogen peroxide (H(2)O(2)) and PMA on fibronectin expression, and finally by inhibition of ROS and PKC. The source of cellular ROS was further examined by inhibition of NADPH oxidase and mitochondrial metabolism.

RESULTS

D-glucose increased dichlorofluorescein (DCF)-sensitive cellular ROS in HPMC in a dose-dependent manner. l-glucose did not induce ROS generation and cytochalasin B completely blocked high glucose-induced ROS generation, suggesting that glucose uptake, but not media hyperosmolality, is required in ROS generation in HPMC. PMA increased cellular ROS and fibronectin secretion. A single dose of H(2)O(2) or H(2)O(2) continuously generated by glucose oxidase up-regulated fibronectin expression [corrected]. Antioxidants trolox and catalase inhibited high glucose- and PMA-induced fibronectin mRNA and protein expression. Inhibition of PKC inhibited high glucose-and H(2)O(2)-induced fibronectin secretion. NADPH oxidase inhibitors (diphenyleneiodinium and apocynin) and an inhibitor of mitochondrial electron transport chain subunit I (rotenone) all effectively inhibited high glucose-induced cellular ROS generation and fibronectin secretion.

CONCLUSION

The present data demonstrate that high glucose increases cellular ROS in HPMC through activation of PKC, NADPH oxidase, and mitochondrial metabolism and that ROS, thus generated, up-regulate fibronectin expression by HPMC. ROS are not only downstream but also upstream signaling molecules to PKC and provide signal amplification in high glucose-induced fibronectin expression by HPMC. The present data imply that cellular ROS may be potential therapeutic targets in progressive accumulation of extracellular matrix in the peritoneal tissue of long-term peritoneal dialysis patients using high glucose-containing peritoneal dialysis solutions.

Taurine prevents streptozotocin impairment of hormone-stimulated glucose uptake in rat adipocytes

Streptozotocin-treated rats were used as models of type 1 diabetes to study the effects of dietary taurine on insulin- and adrenergic-stimulated 2-deoxyglucose uptake by isolated adipocytes. In addition to the well-established impairment of basal and insulin-stimulated 2-deoxyglucose uptakes in adipocytes prepared from streptozotocin-diabetic rats, the alpha-(phenylephrine) and beta-(isoproterenol) adrenergic stimulations of glucose uptake were also abolished. The insulin stimulation of glucose uptake in adipocytes was selectively abolished by the phosphatidylinositol 3-kinase inhibitor wortmannin, whereas that by the adrenergic agonists, phenylephrine and isoproterenol, was inhibited by prazosin and propranolol, respectively. Dietary taurine, 4 weeks before and 4 weeks after streptozotocin administration, prevented the loss of both insulin and adrenergic agonist stimulations of 2-deoxyglucose uptake, without affecting hyperglycaemia. Because insulin and adrenergic activations of glucose transport by adipocytes are coupled to different signalling pathways, it is unlikely that these effects of taurine are related to these disparate postreceptor mechanisms.

Vitamin E attenuates biochemical and morphological features associated with development of chronic pancreatitis

The objective was to investigate the effects of vitamin E on collagen deposition induced by Cyclosporin A (CsA) administration in rats with caerulein (Cr) pancreatitis. CsA transforms the fully regenerative, self-limited form of Cr pancreatitis into a chroniclike disease in conjunction with increased transforming growth factor (TGF)-beta and myofibroblast proliferation. Vitamin E inhibits TGF-beta release in mesangial cells and reduces CsA cytotoxicity. Wistar rats received CsA daily (20 mg/kg), and CR pancreatitis was induced on days 1 and 8 (Cr + CsA group). In a separate group, vitamin E (600 mg.kg(-1).day(-1)) was administered starting 4 days before CsA. Three other groups received either vehicle, CsA, or Cr alone. Thiobarbituric acid-reactive substance (TBARS), 8-isoprostanes, and hyaluronic acid were measured in plasma obtained on the day the animals were killed (day 15). Pancreases were weighed and processed for light microscopy to assess connective tissue and myofibroblast number. Pancreatic homogenates were also assayed for collagen (hydroxyproline) and TBARS content. TBARS, 8-isoprostane, and TGF-beta were elevated in CsA and Cr + CsA rats. Vitamin E treatment greatly decreased these parameters. Vitamin E also decreased the fall in pancreatic weight observed in Cr + CsA pancreas. Pancreatic hydroxyproline and plasma hyaluronic acid were increased in Cr + CsA rats but were effectively reduced by vitamin E. Morphology showed improvement in fibrosis score and a decreased number of myofibroblasts in vitamin E-treated rats. Vitamin E reduces oxidative stress and collagen deposition during the development of experimental chronic pancreatitis. Adjuvant antioxidants may be of value in the treatment of chronic pancreatitis.

Smad3 and PKCdelta mediate TGF-beta1-induced collagen I expression in human mesangial cells

Transforming growth factor (TGF)-beta has been associated with fibrogenesis in clinical studies and animal models. We previously showed that Smad3 promotes COL1A2 gene activation by TGF-beta1 in human mesangial cells. In addition to the Smad pathway, it has been suggested that TGF-beta1 could also activate more classical growth factor signaling. Here, we report that protein kinase C (PKC)delta plays a role in TGF-beta1-stimulated collagen I production. In an in vitro kinase assay, TGF-beta1 treatment specifically increased mesangial cell PKCdelta activity in a time-dependent manner. Translocation to the membrane was detected by immunocytochemistry and immunoblot, suggesting activation of PKCdelta by TGF-beta1. Inhibition of PKCdelta by rottlerin decreased basal and TGF-beta1-stimulated collagen I production, mRNA expression, and COL1A2 promoter activity, whereas blockade of conventional PKCs by Gö 6976 had little or no effect. In a Gal4-LUC assay system, inhibition of PKCdelta abolished TGF-beta1-induced transcriptional activity of Gal4-Smad3 and Gal4-Smad4(266-552). Overexpression of Smad3 or Smad3D, in which the three COOH-terminal serine phosphoacceptor residues have been mutated, increased activity of the SBE-LUC construct, containing four DNA binding sites for Smad3 and Smad4. This induction was blocked by PKCdelta inhibition, suggesting that rottlerin decreased Smad3 transcriptional activity independently of COOH-terminal serine phosphorylation. Blockade of PKCdelta abolished ligand-independent and ligand-dependent stimulation of COL1A2 promoter activity by Smad3. These data indicate that PKCdelta is activated by TGF-beta1 in human mesangial cells. TGF-beta1-stimulated PKCdelta activity positively regulates Smad transcriptional activity and is required for COL1A2 gene transcription. Thus cross talk among multiple signaling pathways likely contributes to the pathogenesis of glomerular matrix accumulation.

Reactive oxygen species-regulated signaling pathways in diabetic nephropathy

Diabetic nephropathy is characterized by excessive deposition of extracellular matrix (ECM) in the kidney. TGF-beta1 has been identified as the key mediator of ECM accumulation in diabetic kidney. High glucose induces TGF-beta1 in glomerular mesangial and tubular epithelial cells and in diabetic kidney. Antioxidants inhibit high glucose-induced TGF-beta1 and ECM expression in glomerular mesangial and tubular epithelial cells and ameliorate features of diabetic nephropathy, suggesting that oxidative stress plays an important role in diabetic renal injury. High glucose induces intracellular reactive oxygen species (ROS) in mesangial and tubular epithelial cells. High glucose-induced ROS in mesangial cells can be effectively blocked by inhibition of protein kinase C (PKC), NADPH oxidase, and mitochondrial electron transfer chain complex I, suggesting that PKC, NADPH oxidase, and mitochondrial metabolism all play a role in high glucose-induced ROS generation. Advanced glycation end products, TGF-beta1, and angiotensin II can also induce ROS generation and may amplify high glucose-activated signaling in diabetic kidney. Both high glucose and ROS activate signal transduction cascade (PKC, mitogen-activated protein kinases, and janus kinase/signal transducers and activators of transcription) and transcription factors (nuclear factor-kappaB, activated protein-1, and specificity protein 1) and upregulate TGF-beta1 and ECM genes and proteins. These observations suggest that ROS act as intracellular messengers and integral glucose signaling molecules in diabetic kidney. Future studies elucidating various other target molecules activated by ROS in renal cells cultured under high glucose or in diabetic kidney will allow a better understanding of the final cellular responses to high glucose.