Protein kinase C-dependent increase in reactive oxygen species (ROS) production in vascular tissues of diabetes: role of vascular NAD(P)H oxidase

Diabetic cardiomyopathy: mechanisms and new treatment strategies targeting antioxidant signaling pathways

Cardiovascular disease is the primary cause of morbidity and mortality among the diabetic population. Both experimental and clinical evidence suggest that diabetic subjects are predisposed to a distinct cardiomyopathy, independent of concomitant macro- and microvascular disorders. 'Diabetic cardiomyopathy' is characterized by early impairments in diastolic function, accompanied by the development of cardiomyocyte hypertrophy, myocardial fibrosis and cardiomyocyte apoptosis. The pathophysiology underlying diabetes-induced cardiac damage is complex and multifactorial, with elevated oxidative stress as a key contributor. We now review the current evidence of molecular disturbances present in the diabetic heart, and their role in the development of diabetes-induced impairments in myocardial function and structure. Our focus incorporates both the contribution of increased reactive oxygen species production and reduced antioxidant defenses to diabetic cardiomyopathy, together with modulation of protein signaling pathways and the emerging role of protein O-GlcNAcylation and miRNA dysregulation in the progression of diabetic heart disease. Lastly, we discuss both conventional and novel therapeutic approaches for the treatment of left ventricular dysfunction in diabetic patients, from inhibition of the renin-angiotensin-aldosterone-system, through recent evidence favoring supplementation of endogenous antioxidants for the treatment of diabetic cardiomyopathy. Novel therapeutic strategies, such as gene therapy targeting the phosphoinositide 3-kinase PI3K(p110α) signaling pathway, and miRNA dysregulation, are also reviewed. Targeting redox stress and protective protein signaling pathways may represent a future strategy for combating the ever-increasing incidence of heart failure in the diabetic population.

Reduction of advanced-glycation end products levels and inhibition of RAGE signaling decreases rat vascular calcification induced by diabetes

Advanced-glycation end products (AGEs) were recently implicated in vascular calcification, through a process mediated by RAGE (receptor for AGEs). Although a correlation between AGEs levels and vascular calcification was established, there is no evidence that reducing in vivo AGEs deposition or inhibiting AGEs-RAGE signaling pathways can decrease medial calcification. We evaluated the impact of inhibiting AGEs formation by pyridoxamine or elimination of AGEs by alagebrium on diabetic medial calcification. We also evaluated if the inhibition of AGEs-RAGE signaling pathways can prevent calcification. Rats were fed a high fat diet during 2 months before receiving a low dose of streptozotocin. Then, calcification was induced with warfarin. Pyridoxamine was administered at the beginning of warfarin treatment while alagebrium was administered 3 weeks after the beginning of warfarin treatment. Results demonstrate that AGEs inhibitors prevent the time-dependent accumulation of AGEs in femoral arteries of diabetic rats. This effect was accompanied by a reduced diabetes-accelerated calcification. Ex vivo experiments showed that N-methylpyridinium, an agonist of RAGE, induced calcification of diabetic femoral arteries, a process inhibited by antioxidants and different inhibitors of signaling pathways associated to RAGE activation. The physiological importance of oxidative stress was demonstrated by the reduction of femoral artery calcification in diabetic rats treated with apocynin, an inhibitor of reactive oxygen species production. We demonstrated that AGE inhibitors prevent or limit medial calcification. We also showed that diabetes-accelerated calcification is prevented by antioxidants. Thus, inhibiting the association of AGE-RAGE or the downstream signaling reduced medial calcification in diabetes.

Paternal high-fat diet consumption induces common changes in the transcriptomes of retroperitoneal adipose and pancreatic islet tissues in female rat offspring

We previously showed that paternal high-fat diet (HFD) consumption programs β-cell dysfunction in female rat offspring, together with transcriptome alterations in islets. Here we investigated the retroperitoneal white adipose tissue (RpWAT) transcriptome using gene and pathway enrichment and pathway analysis to determine whether commonly affected network topologies exist between these two metabolically related tissues. In RpWAT, 5108 genes were differentially expressed due to a paternal HFD; the top 5 significantly enriched networks identified by pathway analysis in offspring of HFD fathers compared with those of fathers fed control diet were: mitochondrial and cellular response to stress, telomerase signaling, cell death and survival, cell cycle, cellular growth and proliferation, and cancer. A total of 187 adipose olfactory receptor genes were down-regulated. Interrogation against the islet transcriptome identified specific gene networks and pathways, including olfactory receptor genes that were similarly affected in both tissues (411 common genes, P<0.05). In particular, we highlight a common molecular network, cell cycle and cancer, with the same hub gene, Myc, suggesting early onset developmental changes that persist, shared responses to programmed systemic factors, or crosstalk between tissues. Thus, paternal HFD consumption triggers unique gene signatures, consistent with premature aging and chronic degenerative disorders, in both RpWAT and pancreatic islets of daughters.

Low molecular weight fucoidan alleviates cardiac dysfunction in diabetic Goto-Kakizaki rats by reducing oxidative stress and cardiomyocyte apoptosis

Diabetic cardiomyopathy (DCM) is characterized by cardiac dysfunction and cardiomyocyte apoptosis. Oxidative stress is suggested to be the major contributor to the development of DCM. This study was intended to evaluate the protective effect of low molecular weight fucoidan (LMWF) against cardiac dysfunction in diabetic rats. Type 2 diabetic goto-kakizaki rats were untreated or treated with LMWF (50 and 100 mg/kg/day) for three months. The establishment of DCM model and the effects of LMWF on cardiac function were evaluated by echocardiography and isolated heart perfusion. Ventricle staining with H-E or Sirius Red was performed to investigate the structural changes in myocardium. Functional evaluation demonstrated that LMWF has a beneficial effect on DCM by enhancing myocardial contractility and mitigating cardiac fibrosis. Additionally, LMWF exerted significant inhibitory effects on the reactive oxygen species production and myocyte apoptosis in diabetic hearts. The depressed activity of superoxide dismutase in diabetic heart was also improved by intervention with LMWF. Moreover, LMWF robustly inhibited the enhanced expression of protein kinase C β, an important contributor to oxidative stress, in diabetic heart and high glucose-treated cardiomyocytes. In conclusion, LMWF possesses a protective effect against DCM through ameliorations of PKCβ-mediated oxidative stress and subsequent cardiomyocyte apoptosis in diabetes.

Histone lysine methylation in diabetic nephropathy

Diabetic nephropathy (DN) belongs to debilitating microvascular complications of diabetes and is the leading cause of end-stage renal diseases worldwide. Furthermore, outcomes from the DCCT/EDIC study showed that DN often persists and progresses despite intensive glucose control in many diabetes patients, possibly as a result of prior episode of hyperglycemia, which is called "metabolic memory." The underlying mechanisms responsible for the development and progression of DN remain poorly understood. Activation of multiple signaling pathways and key transcription factors can lead to aberrant expression of DN-related pathologic genes in target renal cells. Increasing evidence suggests that epigenetic mechanisms in chromatin such as DNA methylation, histone acetylation, and methylation can influence the pathophysiology of DN and metabolic memory. Exciting researches from cell culture and experimental animals have shown that key histone methylation patterns and the related histone methyltransferases and histone demethylases can play important roles in the regulation of inflammatory and profibrotic genes in renal cells under diabetic conditions. Because histone methylation is dynamic and potentially reversible, it can provide a window of opportunity for the development of much-needed novel therapeutic potential for DN in the future. In this minireview, we discuss recent advances in the field of histone methylation and its roles in the pathogenesis and progression of DN.

Arginase in retinopathy

Ischemic retinopathies, such as diabetic retinopathy (DR), retinopathy of prematurity and retinal vein occlusion are a major cause of blindness in developed nations worldwide. Each of these conditions is associated with early neurovascular dysfunction. However, conventional therapies target clinically significant macula edema or neovascularization, which occur much later. Intra-ocular injections of anti-VEGF show promise in reducing retinal edema, but the effects are usually transient and the need for repeated injections increases the risk of intraocular infection. Laser photocoagulation can control pathological neovascularization, but may impair vision and in some patients the retinopathy continues to progress. Moreover, neither treatment targets early stage disease or promotes repair. This review examines the potential role of the ureahydrolase enzyme arginase as a therapeutic target for the treatment of ischemic retinopathy. Arginase metabolizes l-arginine to form proline, polyamines and glutamate. Excessive arginase activity reduces the l-arginine supply for nitric oxide synthase (NOS), causing it to become uncoupled and produce superoxide and less NO. Superoxide and NO react and form the toxic oxidant peroxynitrite. The catabolic products of polyamine oxidation and glutamate can induce more oxidative stress and DNA damage, both of which can cause cellular injury. Studies indicate that neurovascular injury during retinopathy is associated with increased arginase expression/activity, decreased NO, polyamine oxidation, formation of superoxide and peroxynitrite and dysfunction and injury of both vascular and neural cells. Furthermore, data indicate that the cytosolic isoform arginase I (AI) is involved in hyperglycemia-induced dysfunction and injury of vascular endothelial cells whereas the mitochondrial isoform arginase II (AII) is involved in neurovascular dysfunction and death following hyperoxia exposure. Thus, we postulate that activation of the arginase pathway causes neurovascular injury by uncoupling NOS and inducing polyamine oxidation and glutamate formation, thereby reducing NO and increasing oxidative stress, all of which contribute to the retinopathic process.

TRPV1-mediated UCP2 upregulation ameliorates hyperglycemia-induced endothelial dysfunction

Background

Diabetic cardiovascular complications are characterised by oxidative stress-induced endothelial dysfunction. Uncoupling protein 2 (UCP2) is a regulator of mitochondrial reactive oxygen species (ROS) generation and can antagonise oxidative stress, but approaches that enhance the activity of UCP2 to inhibit ROS are scarce. Our previous studies show that activation of transient receptor potential vanilloid 1 (TRPV1) by capsaicin can prevent cardiometabolic disorders. In this study, we conducted experiments in vitro and in vivo to investigate the effect of capsaicin treatment on endothelial UCP2 and oxidative stress. We hypothesised that TRPV1 activation by capsaicin attenuates hyperglycemia-induced endothelial dysfunction through a UCP2-mediated antioxidant effect.

Methods

TRPV1^-/-, UCP2 ^-/- and db/db mice, as well as matched wild type (WT) control mice, were included in this study. Some mice were subjected to dietary capsaicin for 14 weeks. Arteries isolated from mice and endothelial cells were cultured. Endothelial function was examined, and immunohistological and molecular analyses were performed.

Results

Under high-glucose conditions, TRPV1 expression and protein kinase A (PKA) phosphorylation were found to be decreased in the cultured endothelial cells, and the effects of high-glucose on these molecules were reversed by the administration of capsaicin. Furthermore, high-glucose exposure increased ROS production and reduced nitric oxide (NO) levels both in endothelial cells and in arteries that were evaluated respectively by dihydroethidium (DHE) and DAF-2 DA fluorescence. Capsaicin administration decreased the production of ROS, restored high-glucose-induced endothelial dysfunction through the activation of TRPV1 and acted in a UCP2-dependent manner in vivo. Administration of dietary capsaicin for 14 weeks increased the levels of PKA phosphorylation and UCP2 expression, ameliorated the vascular oxidative stress and increased NO levels observed in diabetic mice. Prolonged dietary administration of capsaicin promoted endothelium-dependent relaxation in diabetic mice. However, the beneficial effect of capsaicin on vasorelaxation was absent in the aortas of UCP2 ^-/- mice exposed to high-glucose levels.

Conclusion

TRPV1 activation by capsaicin might protect against hyperglycemia-induced endothelial dysfunction through a mechanism involving the PKA/UCP2 pathway.

Implications of treatment that target protective mechanisms against diabetic nephropathy

Diabetes results in vascular changes and dysfunction, and vascular complications are the leading cause of morbidity and mortality in diabetic patients. There has been a continual increase in the number of diabetic nephropathy patients and epidemic increases in the number of patients progressing to end-stage renal diseases. To identify targets for therapeutic intervention, most studies have focused on understanding how abnormal levels of glucose metabolites cause diabetic nephropathy, which is of paramount importance in devising strategies to combat the development and progression of diabetic nephropathy. However, less studied than the systemic toxic mechanisms, hyperglycemia and dyslipidemia might inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, and platelet-derived growth factor. In this review, we highlight the importance of enhancing endogenous protective factors to prevent or delay diabetic nephropathy.

Cellular defense mechanisms against lead toxicity in the vascular system

Lead is a toxic heavy metal that can cause a range of health problems. In this context, the vascular system is a particular target of the deleterious effects of lead. Lead exerts its toxicity through substitution of other divalent cations such as calcium and zinc, resulting in disruption of homeostasis. Based on the evidence that lead up-regulates endoplasmic reticulum (ER) chaperone glucose-regulated protein 78 (GRP78) and/or antioxidant proteins such as hemeoxygenase-1, it is believed that the heavy metal is able to induce ER and/or oxidative stress in cells. These events also suggest that the unfolded protein response (UPR) system and the antioxidant defense system Kelch-like ECH-associated protein 1-nuclear factor (NF)-E2-related factor 2 (Keap1-Nrf2) play a critical role in adaptive response to lead. In this review, we summarize recent progress in lead toxicity in terms of cellular defense systems, including stress proteins and transcription factors involved in the vascular system.

Recent advances in understanding the biochemical and molecular mechanism of diabetic nephropathy

Diabetic nephropathy (DN) is a chronic disease characterized by proteinuria, glomerular hypertrophy, decreased glomerular filtration and renal fibrosis with loss of renal function. DN is the leading cause of end-stage renal disease, accounting for millions of deaths worldwide. Hyperglycemia is the driving force for the development of diabetic nephropathy. The exact cause of diabetic nephropathy is unknown, but various postulated mechanisms are: hyperglycemia (causing hyperfiltration and renal injury), advanced glycosylation products, activation of cytokines. In this review article, we have discussed a number of diabetes-induced metabolites such as glucose, advanced glycation end products, protein kinase C and oxidative stress and other related factors that are implicated in the pathophysiology of the DN. An understanding of the biochemical and molecular changes especially early in the DN may lead to new and effective therapies towards prevention and amelioration of DN.

The renal endothelium in diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease. Diabetes mellitus is characterized by generalized endothelial dysfunction. However, recent data also emphasizes the role of local renal endothelium dysfunction in the pathogenesis of diabetic nephropathy. Hyperglycemia triggers a complex network of signal-transduction molecules, transcription factors, and mediators that culminate in endothelial dysfunction. In the glomerulus, vascular endothelial growth factor-A (VEGF)-induced neoangiogenesis may contribute to the initial hyperfiltration and microalbuminuria due to increased filtration area and immaturity of the neovessels, respectively. However, subsequent decrease in podocytes number decreases VEGF production resulting in capillary rarefaction and decreased glomerular filtration rate (GFR). Decreased nitric oxide availability also plays a significant role in the development of advanced lesions of diabetic nephropathy through disruption of glomerular autoregulation, uncontrolled VEGF action, release of prothrombotic substances by endothelial cells and angiotensin-II-independent aldosterone production. In addition, disturbances in endothelial glycocalyx contribute to decreased permselectivity and microalbuminuria; whereas there are recent evidences that reduced glomerular fenestral endothelium leads to decreased GFR levels. Endothelial repair mechanisms are also impaired in diabetes, since circulating endothelial progenitor cells number is decreased in diabetic patients with microalbuminuria. Finally, in the context of elevated profibrotic cytokine transforming growth factor-β levels, endothelial cells also confer to the deteriorating process of fibrosis in advanced diabetic nephropathy through endothelial to mesenchymal transition.

Oxidative stress and myocardial injury in the diabetic heart

Reactive oxygen or nitrogen species play an integral role in both myocardial injury and repair. This dichotomy is differentiated at the level of species type, amount and duration of free radical generated. Homeostatic mechanisms designed to prevent free radical generation in the first instance, scavenge, or enzymatically convert them to less toxic forms and water, playing crucial roles in the maintenance of cellular structure and function. The outcome between functional recovery and dysfunction is dependent upon the inherent ability of these homeostatic antioxidant defences to withstand acute free radical generation, in the order of seconds to minutes. Alternatively, pre-existent antioxidant capacity (from intracellular and extracellular sources) may regulate the degree of free radical generation. This converts reactive oxygen and nitrogen species to the role of second messenger involved in cell signalling. The adaptive capacity of the cell is altered by the balance between death or survival signal converging at the level of the mitochondria, with distinct pathophysiological consequences that extends the period of injury from hours to days and weeks. Hyperglycaemia, hyperlipidaemia and insulin resistance enhance oxidative stress in the diabetic myocardium that cannot adapt to ischaemia-reperfusion. Altered glucose flux, mitochondrial derangements and nitric oxide synthase uncoupling in the presence of decreased antioxidant defence and impaired prosurvival cell signalling may render the diabetic myocardium more vulnerable to injury, remodelling and heart failure.

Role of Nox2 in diabetic kidney disease

NADPH oxidase (Nox) isoforms have been implicated in contributing to diabetic microvascular complications, but the functional role of individual isoforms in diabetic kidney are unclear. Nox2, in particular, is highly expressed in phagocytes and may play a key inflammatory role in diabetic kidney disease. To determine the role of Nox2, we evaluated kidney function and pathology in wild-type (WT; C57BL/6) and Nox2 knockout (KO) mice with type 1 diabetes. Diabetes was induced in male Nox2 KO and WT mice with a multiple low-dose streptozotocin protocol. Groups were studied for kidney disease after 8 and 20 wk of diabetes. Hyperglycemia and body weights were similar in WT and Nox2 KO diabetic mice. All functional and structural features of early and later stage diabetic kidney disease (albuminuria, mesangial matrix, tubulointerstitial disease, and gene expression of matrix and transforming growth factor-β) were similar in both diabetic groups compared with their respective nondiabetic groups, except for reduction of macrophage infiltration and monocyte chemoattractant protein-1 in the diabetic Nox2 KO mice. Systolic blood pressure by telemetry was surprisingly increased in Nox2 KO mice; however, the systolic blood pressure was reduced in the diabetic WT and Nox2 KO mice by tail-cuff. Interestingly, diabetic Nox2 KO mice had marked upregulation of renal Nox4 at both the glomerular and cortical levels. The present results demonstrate that lack of Nox2 does not protect against diabetic kidney disease in type 1 diabetes, despite a reduction in macrophage infiltration. The lack of renoprotection may be due to upregulation of renal Nox4.

Oxidative stress as an underlying contributor in the development of chronic complications in diabetes mellitus

The high prevalence of diabetes mellitus and its increasing incidence worldwide, coupled with several complications observed in its carriers, have become a public health issue of great relevance. Chronic hyperglycemia is the main feature of such a disease, being considered the responsible for the establishment of micro and macrovascular complications observed in diabetes. Several efforts have been directed in order to better comprehend the pathophysiological mechanisms involved in the course of this endocrine disease. Recently, numerous authors have suggested that excess generation of highly reactive oxygen and nitrogen species is a key component in the development of complications invoked by hyperglycemia. Overproduction and/or insufficient removal of these reactive species result in vascular dysfunction, damage to cellular proteins, membrane lipids and nucleic acids, leading different research groups to search for biomarkers which would be capable of a proper and accurate measurement of the oxidative stress (OS) in diabetic patients, especially in the presence of chronic complications. In the face of this scenario, the present review briefly addresses the role of hyperglycemia in OS, considering basic mechanisms and their effects in diabetes mellitus, describes some of the more commonly used biomarkers of oxidative/nitrosative damage and includes selected examples of studies which evaluated OS biomarkers in patients with diabetes, pointing to the relevance of such biological components in general oxidative stress status of diabetes mellitus carriers.

EGCG attenuates high glucose-induced endothelial cell inflammation by suppression of PKC and NF-κB signaling in human umbilical vein endothelial cells

AIMS

Vascular inflammation is a key factor in the pathogenesis of diabetes-related vascular complications. Our previous study showed that (-)-epigallocatechin-3-gallate (EGCG) inhibits high glucose-induced vascular smooth muscle cell proliferation, thus it may have beneficial effects in diabetes and its complications. However, the effect of EGCG on inflammation in diabetes is not known. In the present study, we investigated whether EGCG suppresses the vascular inflammation induced by high glucose in human umbilical vein endothelial cells (HUVECs).

MAIN METHODS

The inhibitory effect of EGCG on high glucose-induced up-regulation of the expression of vascular cell adhesion molecule 1 (VCAM-1) was measured using enzyme-linked immunosorbent, RT-PCR, immunoblotting and cell adhesion assays. The effect of EGCG on high glucose-induced nuclear factor-kappa B (NF-κB) activation was investigated by immunoblotting, immunofluorescence and electrophoretic mobility shift assays.

KEY FINDINGS

High glucose increased VCAM-1 expression and enhanced the adhesion of monocytes to HUVECs. Pretreatment with EGCG in a concentration-dependent manner (1.0-50 μM) significantly attenuated these effects. High glucose (25 mM)-mediated vascular inflammation was blocked by PKC pseudosubstrate (PKC inhibitor 19-31) or the NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC). Stimulation with high glucose increased the NF-κB translocation from the cytoplasm to the nucleus, and increased IκB-α phosphorylation, decreased its expression, and in the presence of EGCG, the effect of high glucose on NF-κB and IκB-α were blocked.

SIGNIFICANCE

EGCG suppresses high glucose-induced vascular inflammatory process via the inhibition of PKC and NF-κB activation in HUVECs, suggesting that EGCG may be a potential candidate for the treatment and prevention of diabetic vascular complications.

Modification of Ca(2+)-handling in cardiomyocytes by redox sensitive mechanisms in response to ouabain

We examined the role of redox-sensitive signal transduction mechanisms in modifying the changes in [Ca(2+)](i) produced by ouabain upon incubating adult rat cardiomyocytes with antioxidants or inhibitors of different protein kinases and monitoring alterations in fura-2 fluorescence. Ouabain increased basal [Ca(2+)](i), augmented the KCl-induced increase in [Ca(2+)](i), and promoted oxyradical production in cardiomyocytes. These actions of ouabain were attenuated by an oxyradical scavenging mixture (superoxide dismutase plus catalase), and the antioxidants (N-acetyl-L-cysteine and N-(2-mercaptoproprionyl)glycine). An inhibitor of MAP kinase (PD98059) depressed the ouabain-induced increase in [Ca(2+)], whereas inhibitors of tyrosine kinase (tyrphostin and genistein) and PI3 kinase (Wortmannin and LV294002) enhanced the ouabain-induced increase in [Ca(2+)](i). Inhibitors of protein kinase C (calphostin and bisindolylmalaimide) augmented the ouabain-induced increase in [Ca(2+)](i), whereas stimulation of protein kinase C by a phorbol ester (phorbol 12-myristate 13-acetate) depressed the action of ouabain. These results suggest that ouabain-induced inhibition of Na (+)-K(+) ATPase may alter the redox status of cardiomyocytes through the production of oxyradicals, and increase the activities of various protein kinases. Thus, these redox-sensitive signal transduction mechanisms involving different protein kinases may modify Ca(2+)-handling sites in cardiomyocytes and determine the magnitude of net increase in [Ca(2+)](i) in response to ouabain.

ATP stimulates PGE(2)/cyclin D1-dependent VSMCs proliferation via STAT3 activation: role of PKCs-dependent NADPH oxidase/ROS generation

Vascular smooth muscle cells (VSMCs) that function as synthetic units play important roles in cardiovascular diseases. Extracellular nucleotides, such as ATP, have been shown to act via activation of P2 purinoceptors implicated in various inflammatory diseases, we hypothesized that extracellular nucleotides contribute to vascular diseases via up-regulation of inflammatory proteins, including cyclooxygenase-2 (COX-2) and cytosolic phospholipase A2 (cPLA2) in VSMCs. However, the mechanisms of ATP-induced cPLA2 and COX-2 expression and PGE2 synthesis remain largely unclear. We showed that pretreatment with the inhibitors of STAT3 (CBE), NADPH oxidase [diphenyleneiodonium chloride (DPI) or apocynin (APO)], ROS [N-acetyl-l-cysteine (NAC)], and PKC (Ro-318220, Gö6983, or Rottlerin) or transfection with siRNAs of STAT3 and p47(phox) markedly inhibited ATPγS-induced cPLA2 and COX-2 mRNA/protein expression and promoter activity and PGE2 secretion. ATPγS further stimulated PKC, p47(phox), and STAT3 translocation. Moreover, ATPγS-induced STAT3 phosphorylation and translocation was inhibited by pretreatment with the inhibitors of PKC, NADPH oxidase, and ROS. ATPγS enhanced NADPH oxidase activity and ROS generation in VSMCs, which were reduced by pretreatment with Ro-318220, Gö6983, or Rottlerin. Finally, we found that ATPγS significantly induced cyclin D1 expression and VSMCs proliferation, which were inhibited by pretreatment with NAC, APO, DPI, Ro-318220, Gö6983, Rottlerin, or CBE or transfection with siRNAs of COX-2 and cyclin D1. We also demonstrated that ATPγS induced cyclin D1 expression via a PGE2-dependent pathway. These results suggested that ATPγS-induced cPLA2/COX-2 expression and PGE2 secretion is mediated through a PKC/NADPH oxidase/ROS/STAT3-dependent pathway in VSMCs.

ATP mediates NADPH oxidase/ROS generation and COX-2/PGE2 expression in A549 cells: role of P2 receptor-dependent STAT3 activation

BACKGROUND

Up-regulation of cyclooxygenase (COX)-2 and its metabolite prostaglandin E(2) (PGE(2)) are frequently implicated in lung inflammation. Extracellular nucleotides, such as ATP have been shown to act via activation of P2 purinoceptors, leading to COX-2 expression in various inflammatory diseases, such as lung inflammation. However, the mechanisms underlying ATP-induced COX-2 expression and PGE(2) release remain unclear.

PRINCIPAL FINDINGS

Here, we showed that ATPγS induced COX-2 expression in A549 cells revealed by western blot and real-time PCR. Pretreatment with the inhibitors of P2 receptor (PPADS and suramin), PKC (Gö6983, Gö6976, Ro318220, and Rottlerin), ROS (Edaravone), NADPH oxidase [diphenyleneiodonium chloride (DPI) and apocynin], Jak2 (AG490), and STAT3 [cucurbitacin E (CBE)] and transfection with siRNAs of PKCα, PKCι, PKCμ, p47(phox), Jak2, STAT3, and cPLA(2) markedly reduced ATPγS-induced COX-2 expression and PGE(2) production. In addition, pretreatment with the inhibitors of P2 receptor attenuated PKCs translocation from the cytosol to the membrane in response to ATPγS. Moreover, ATPγS-induced ROS generation and p47(phox) translocation was also reduced by pretreatment with the inhibitors of P2 receptor, PKC, and NADPH oxidase. On the other hand, ATPγS stimulated Jak2 and STAT3 activation which were inhibited by pretreatment with PPADS, suramin, Gö6983, Gö6976, Ro318220, GF109203X, Rottlerin, Edaravone, DPI, and apocynin in A549 cells.

SIGNIFICANCE

Taken together, these results showed that ATPγS induced COX-2 expression and PGE(2) production via a P2 receptor/PKC/NADPH oxidase/ROS/Jak2/STAT3/cPLA(2) signaling pathway in A549 cells. Increased understanding of signal transduction mechanisms underlying COX-2 gene regulation will create opportunities for the development of anti-inflammation therapeutic strategies.

Exendin-4 attenuates high glucose-induced cardiomyocyte apoptosis via inhibition of endoplasmic reticulum stress and activation of SERCA2a

Hyperglycemia-induced cardiomyocyte apoptosis contributes to diabetic cardiomyopathy. Glucagon-like peptide-1 (Glp1) receptor (Glp1r) agonists improve cardiac function and survival in response to ischemia-reperfusion and myocardial infarction. The present studies assessed whether Glp1r activation exerts direct cardioprotective effects in response to hyperglycemia. Treatment with the Glp1r agonist Exendin-4 attenuated apoptosis in neonatal rat ventricular cardiomyocytes cultured in high (33 mM) glucose. This protective effect was mimicked by the cAMP inducer forskolin. The Exendin-4 protective effect was blocked by the Glp1r antagonist Exendin(9-39) or the PKA antagonist H-89. Exendin-4 also protected cardiomyocytes from hydrogen peroxide (H2O2)-induced cell death. Cardiomyocyte protection by Exendin-4 was not due to reduced reactive oxygen species levels. Instead, Exendin-4 treatment reduced endoplasmic reticulum (ER) stress, demonstrated by decreased expression of glucose-regulated protein-78 (GRP78) and CCAT/enhancer-binding homologous protein (CHOP). Reduced ER stress was not due to activation of the unfolded protein response, indicating that Exendin-4 directly prevents ER stress. Exendin-4 treatment selectively protected cardiomyocytes from thapsigargin- but not tunicamycin-induced death. This suggests that Exendin-4 attenuates thapsigargin-mediated inhibition of the sarco/endoplasmic reticulum Ca(2+) ATPase-2a (SERCA2a). High glucose attenuates SERCA2a function by reducing SERCA2a mRNA and protein levels, but Exendin-4 treatment prevented this reduction. Exendin-4 treatment also enhanced phosphorylation of the SERCA2a regulator phospholamban (PLN), which would be expected to stimulate SERCA2a activity. In sum, Glp1r activation attenuates high glucose-induced cardiomyocyte apoptosis in association with decreased ER stress and markers of enhanced SERCA2a activity. These findings identify a novel mechanism whereby Glp1-based therapies could be used as treatments for diabetic cardiomyopathy.

Trigonelline ameliorates oxidative stress in type 2 diabetic Goto-Kakizaki rats

Previously, we showed that trigonelline (TRG) exerts antidiabetic effects in type 2 diabetic Goto-Kakizaki (GK) rats and also lowers blood and liver thiobarbituric acid reactive substances and urinary 8-hydroxydeoxyguanosine when compared with those levels in GK control rats without TRG. These results suggested that TRG also mitigates oxidative stress, which accelerates diabetes. In this study, the mechanisms of TRG prevention of oxidative stress were determined by measuring erythrocyte and liver antioxidant enzyme activities, and expressions of genes associated with reactive oxygen species production, and carbohydrate and lipid metabolisms by DNA microarray. Erythrocyte and liver glutathione peroxidase, and liver catalase activities in the GK rats fed with TRG were significantly lower than those of the GK control rats. TRG downregulated the gene expressions involved with NADPH oxidase and mitochondrial electron transfer system when compared with those of the GK control group. These results suggested that mitigation of diabetes by TRG is mediated by its ameliorating effects on oxidative stress.

Protein kinase Cα is involved in impaired perinatal hypothyroid rat brain development

Protein kinase Cα (PKCα) has been implicated in the regulation of a variety of cellular functions, such as proliferation, differentiation, and apoptosis, in response to a diverse range of stimuli. Activated PKCα mediates oxidative stress, apoptosis, and inflammatory reaction. Thyroid hormone (TH) is essential for the proper development of the mammalian central nervous system. TH deficiency during critical periods of brain development results in permanent cognitive and neurological impairments. In the present study, we attempted to explore whether PKCα is involved in impaired brain function in developing hypothyroid rat brain. Severe perinatal hypothyroidism was obtained by administration of 30 mg/day propylthiouracil to dams. Brain PKC activity in hypothyroid pups was increased significantly in cytosol and membrane fractions. The change of membrane PKC activity was more marked than that of cytosol, and hypothyroidism led to a higher ratio of membrane PKC activity to that in cytosol, which means abnormal activation of PKC in developing hypothyroid rat brain. Thyroxine replacement partially corrected these changes. After being treated with bisindolmaleimide XI, a mainly selective inhibitor for PKCα, the hypothyroid pups showed improved place navigation test results, and further Western blot analysis showed that PKCα expression in cytosol fractions was increased in hypothyroid rat brain with or without bisindolmaleimide XI treatment, but, after treatment with bisindolmaleimide XI, PKCα content in membrane fractions decreased almost to normal. Therefore, we conclude that PKCα appears to be involved in the impaired brain development observed in perinatal hypothyroid rat brain.

Phycocyanin and phycocyanobilin from Spirulina platensis protect against diabetic nephropathy by inhibiting oxidative stress

We and other investigators have reported that bilirubin and its precursor biliverdin may have beneficial effects on diabetic vascular complications, including nephropathy, via its antioxidant effects. Here, we investigated whether phycocyanin derived from Spirulina platensis, a blue-green algae, and its chromophore phycocyanobilin, which has a chemical structure similar to that of biliverdin, protect against oxidative stress and renal dysfunction in db/db mice, a rodent model for Type 2 diabetes. Oral administration of phycocyanin (300 mg/kg) for 10 wk protected against albuminuria and renal mesangial expansion in db/db mice, and normalized tumor growth factor-β and fibronectin expression. Phycocyanin also normalized urinary and renal oxidative stress markers and the expression of NAD(P)H oxidase components. Similar antioxidant effects were observed following oral administration of phycocyanobilin (15 mg/kg) for 2 wk. Phycocyanobilin, bilirubin, and biliverdin also inhibited NADPH dependent superoxide production in cultured renal mesangial cells. In conclusion, oral administration of phycocyanin and phycocyanobilin may offer a novel and feasible therapeutic approach for preventing diabetic nephropathy.

Angiotensin-II-dependent NHE1 activation in human monocytes

Angiotensin II, a potent vasoconstrictor, has been demonstrated to be involved in the pathogenesis of atherosclerosis, and its complications. Na(+)/H(+) exchanger isoform-1 (NHE1) is related to hypertension activation and can augment atherosclerosis-related functions in human monocytes. The purpose of this study is to investigate in monocytes the signal transduction pathway induced by angiotensin II, in which the Na(+)/H(+) exchanger (NHE1) takes part. Monocytes were isolated, and intracellular pH (pHi) was measured by the use of Bis-(carboxyethyl)-5(6)-carboxy-fluorescein acetoxymethylester. Superoxide anions were measured by nitroblue tetrazolium. Monocyte binding to laminin-1 was quantified using the myeloperoxidase assay. Angiotensin II caused a significant increase in pHi of monocytes, which indicates NHE activation. Cariporide, an NHE1 inhibitor, GF109203X, and Gö6976, inhibitors of isoforms of protein kinase C (PKC), diphenyleneiodonium chloride, the inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and N(omega)-Nitro-L-arginine methyl ester hydrochloride, the inhibitor of nitric oxide (NO) synthase, reversed this effect. Moreover, it was shown that angiotensin II caused an increase in superoxide ion (O(2)(-.)) levels as well as an increase in monocytes' adhesion to laminin-1, in relation to controls. The use of cariporide inhibited these effects. Furthermore, angiotensin II caused an increase in pHi, which was reversed by cariporide in monocytes derived from hypertensive patients. Consequently, in human monocytes angiotensin II caused NHE1 activation through pathways involving isoforms of PKC with the participation of O(2)(-.) and NO. In addition, a link between angiotensin II and the atherogenic properties of monocytes was shown, where NHE1 plays a central role.

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

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

Recent advances in understanding the biochemical and molecular mechanism of diabetic cardiomyopathy

Cardiovascular complications account for significant morbidity and mortality in the diabetic population. Diabetic cardiomyopathy (DCM), a prominent cardiovascular complication, has been recognized as a microvascular disease that may lead to heart failure. During the past few decades, research progress has been made in investigating the pathophysiology of the disease; however, the exact molecular mechanism has not been elucidated, making therapeutic a difficult task. In this review article, we have discussed a number of diabetes-induced metabolites such as glucose, advanced glycation end products, protein kinase C, free fatty acid and oxidative stress and other related factors that are implicated in the pathophysiology of the DCM. An understanding of the biochemical and molecular changes especially early in the DCM may lead to new and effective therapies toward prevention and amelioration of DCM, which is important for the millions of individuals who already have or are likely to develop the disease before a cure becomes available.

The influence of reactive oxygen species on cell cycle progression in mammalian cells

Cell cycle regulation is performed by cyclins and cyclin dependent kinases (CDKs). Recently, it has become clear that reactive oxygen species (ROS) influence the presence and activity of these enzymes and thereby control cell cycle progression. In this review, we first describe the discovery of enzymes specialized in ROS production: the NADPH oxidase (NOX) complexes. This discovery led to the recognition of ROS as essential players in many cellular processes, including cell cycle progression. ROS influence cell cycle progression in a context-dependent manner via phosphorylation and ubiquitination of CDKs and cell cycle regulatory molecules. We show that ROS often regulate ubiquitination via intermediate phosphorylation and that phosphorylation is thus the major regulatory mechanism influenced by ROS. In addition, ROS have recently been shown to be able to activate growth factor receptors. We will illustrate the diverse roles of ROS as mediators in cell cycle regulation by incorporating phosphorylation, ubiquitination and receptor activation in a model of cell cycle regulation involving EGF-receptor activation. We conclude that ROS can no longer be ignored when studying cell cycle progression.

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

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

Analysis of human DNA-arginine photoadduct modified with peroxynitrite

The aim of the study is the biochemical characterization of human DNA modified with arginine and peroxynitrite. In the present study, DNA was isolated from human blood cells and its adduct was formed with one of the amino acid, arginine. The DNA-arginine adduct was then modified with peroxynitrite, a reactive nitrogen species. The modified DNA adduct was characterized by ultraviolet (UV) absorption spectroscopy, thermal melting profile, and electrophoresis studies. UV spectroscopic analysis of the photoadduct showed hyperchromicity, indicating the formation of single-strand breaks and photomodification. Thermal denaturation studies of DNA-arginine adduct and peroxynitrite-modified adduct showed a decrease in the temperature (T(m)) value by 4.5°C and an increase in the T(m) of 8°C, respectively. Peroxynitrite modification is evident by an increase in the T(m) value and a change in the migration pattern of native and modified photoadducts on agarose gel electrophoresis. The DNA-arginine and peroxynitrite-modified photoadducts could have important implications in various pathophysiological and immunopathological conditions.

Mechanisms of angiotensin II-enhanced connecting tubule glomerular feedback

Increasing Na delivery to the connecting tubule (CNT) causes afferent arteriole (Af-Art) dilation, a process we call CNT glomerular feedback (CTGF). Angiotensin II (ANG II) in the CNT lumen enhances CTGF via PKC. We hypothesized that luminal ANG II stimulates CTGF via activation of protein kinase C (PKC), NADPH oxidase 2 (NOX2), and enhanced production of superoxide (O(2)(-)). Rabbit Af-Arts and adherent CNTs were microdissected and microperfused in vitro. Dilation of the Af-Art was induced by increasing luminal CNT NaCl from 0 to 5, 10, 30, 45, and 80 mM, and the concentration of NaCl that elicited a half-maximal response (EC(50)) was calculated. Compared with vehicle, adding ANG II (10(-9) M) to the CNT lumen reduced EC(50) from 37 ± 3 to 14 ± 1 mM (P < 0.001), indicating ANG II potentiates CTGF. In the presence of ANG II, the O(2)(-) scavenger tempol (10(-4) M) increased EC(50) from 20 ± 4 to 41 ± 3 mM (P < 0.01), the NOX inhibitor apocynin (10(-5) M) increased EC(50) from 17 ± 2 to 39 ± 4 mM (P < 0.01), and the specific NOX2 inhibitor gp91ds-tat (10(-5) M) increased EC(50) from 19 ± 2 to 34 ± 2 mM (P < 0.01). However, tempol, apocynin, and gp91ds-tat had no effect on CTGF in the absence of ANG II. Compared with vehicle, the PKC activator PMA (2 × 10(-7) M) decreased EC(50) from 35 ± 2 to 14 ± 1 (P < 0.001). In the presence of PMA, tempol increased EC(50) from 14 ± 2 to 35 ± 2 mM (P < 0.01). We conclude the PKC/NOX2/O(2)(-) pathway mediates the enhancement of CTGF by luminal ANG II but it does not participate in CTGF in the absence of ANG II.

Puerarin inhibits the retinal pericyte apoptosis induced by advanced glycation end products in vitro and in vivo by inhibiting NADPH oxidase-related oxidative stress

Retinal pericyte loss is one of the histopathological hallmarks of early diabetic retinopathy. Puerarin (4'-7-dihydroxy-8-beta-d-glucosylisoflavone), which is an isoflavone-C-glucoside, causes various pharmacological effects that include antihyperglycemic and anti-inflammatory activities. In the present study, we determined the efficacy and possible mechanism of puerarin on the advanced glycation end product (AGE)-modified bovine serum albumin (BSA)-induced apoptosis of cultured bovine retinal pericytes and rat retinal pericytes in intravitreally AGE-modified rat serum albumin (RSA)-injected eyes. Puerarin significantly inhibited pericyte apoptosis, the generation of reactive oxygen species (ROS), and NADPH oxidase activity by inhibiting the phosphorylation of p47phox and Rac1 which were induced by the AGE-BSA treatment. The puerarin treatment markedly suppressed the activation of nuclear factor-kappaB (NF-κB). In addition, the in vivo apoptosis of the retinal pericyte of rats that was stimulated by the intravitreal injection of AGE-RSA was evidently attenuated by the puerarin treatment. These results demonstrate that puerarin may exert inhibitory effects on AGE-induced pericyte apoptosis by interfering with the NADPH oxidase-related ROS pathways and blocking NF-κB activation, thereby ameliorating retinal microvascular dysfunction.

Protein kinase Cα protects against multidrug resistance in human colon cancer cells

Multidrug resistance is the phenomenon by which, after exposure to a single chemotherapeutic agent, cancer cells evade the agent's cytotoxic effects as well as become resistant to several classes of diverse drugs. ATP-binding cassette (ABC) transporters are a family of transporter proteins that contribute to drug resistance via a n ATP - dependent drug efflux pump. P-glycoprotein (P-gp) is a prominent ABC superfamily protein encoded by the mdr gene which has the ability to mediate the cellular extrusion of xenobiotics and anticancer drugs from tumor cells. Exclusively expressed P-gp cells from the human colon cancer HCT15/DOX line showed resistance to doxorubicin while parental HCT15 cells treated with doxorubicin displayed typical signs of apoptosis. In order to verify the hypothesis that expression of MDR is controlled in part, by protein kinase C (PKC), expression patterns of different PKC isoforms were examined in both cell lines. Of the PKC isoforms evaluated, the membrane translocation and expression levels of PKCα were strikingly increased in HCT15/DOX cells. PKCα reversed doxorubicin-induced apoptosis through the scavenging of ROS as well as inhibition of PARP cleavage. In addition, inhibition of PKCα with Go6976, a specific inhibitor of classical PKC, led to reduced MDR expression and increased doxorubicin-induced apoptosis. Knockdown of PKCα by siRNA diminished the protective effects of PKCα for doxorubicin-induced apoptosis. These results suggested that over-expression and activity of PKCα is closely associated with the regulation of the MDR phenotype in human colon cancer HCT15 cells and provided insight into a new strategy for inhibiting doxorubicin resistance in human cancers.

Adipocyte expression of PU.1 transcription factor causes insulin resistance through upregulation of inflammatory cytokine gene expression and ROS production

We have reported previously that ETS family transcription factor PU.1 is expressed in mature adipocytes of white adipose tissue. PU.1 expression is increased greatly in mouse models of genetic or diet-induced obesity. Here, we show that PU.1 expression is increased only in visceral but not subcutaneous adipose tissues of obese mice, and the adipocytes are responsible for this increase in PU.1 expression. To further address PU.1's physiological function in mature adipocytes, PU.1 was knocked down in 3T3-L1 cells using retroviral-mediated expression of PU.1-targeting shRNA. Consistent with previous findings that PU.1 regulates its target genes, such as NADPH oxidase subunits and proinflammatory cytokines in myeloid cells, the mRNA levels of proinflammatory cytokines (TNFα, IL-1β, and IL-6) and cytosolic components of NADPH oxidase (p47phox and p40phox) were downregulated significantly in PU.1-silenced adipocytes. NADPH oxidase is a main source for reactive oxygen species (ROS) generation. Indeed, silencing PU.1 suppressed NADPH oxidase activity and attenuated ROS in basal or hydrogen peroxide-treated adipocytes. Silencing PU.1 in adipocytes suppressed JNK1 activation and IRS-1 phosphorylation at Ser(307). Consequently, PU.1 knockdown improved insulin signaling and increased glucose uptake in basal and insulin-stimulated conditions. Furthermore, knocking down PU.1 suppressed basal lipolysis but activated stimulated lipolysis. Collectively, these findings indicate that obesity induces PU.1 expression in adipocytes to upregulate the production of ROS and proinflammatory cytokines, both of which lead to JNK1 activation, insulin resistance, and dysregulation of lipolysis. Therefore, PU.1 might be a mediator for obesity-induced adipose inflammation and insulin resistance.

Antioxidants in kidney diseases: the impact of bardoxolone methyl

Drugs targeting the renin-angiotensin-aldosterone system (RAAS) are the mainstay of therapy to retard the progression of proteinuric chronic kidney disease (CKD) such as diabetic nephropathy. However, diabetic nephropathy is still the first cause of end-stage renal disease. New drugs targeted to the pathogenesis and mechanisms of progression of these diseases beyond RAAS inhibition are needed. There is solid experimental evidence of a key role of oxidative stress and its interrelation with inflammation on renal damage. However, randomized and well-powered trials on these agents in CKD are scarce. We now review the biological bases of oxidative stress and its role in kidney diseases, with focus on diabetic nephropathy, as well as the role of the Keap1-Nrf2 pathway and recent clinical trials targeting this pathway with bardoxolone methyl.

Redox balance dynamically regulates vascular growth and remodeling

Vascular growth and remodeling responses entail several complex biochemical, molecular, and cellular responses centered primarily on endothelial cell activation and function. Recent studies reveal that changes in endothelial cell redox status critically influence numerous cellular events that are important for vascular growth under different conditions. It has been known for some time that oxidative stress actively participates in many aspects of angiogenesis and vascular remodeling. Initial studies in this field were largely exploratory with minimal insight into specific molecular mechanisms and how these responses could be regulated. However, it is now clear that intracellular redox mechanisms involving hypoxia, NADPH oxidases (NOX), xanthine oxidase (XO), nitric oxide and its synthases, and intracellular antioxidant defense pathways collectively orchestrate a redox balance system whereby reactive oxygen and nitrogen species integrate cues controlling vascular growth and remodeling. In this review, we discuss key redox regulation pathways that are centrally important for vascular growth in tissue health and disease. Important unresolved questions and issues are also addressed that requires future investigation.

Nicotine exposure and the progression of chronic kidney disease: role of the α7-nicotinic acetylcholine receptor

Clinical studies have established the role of cigarette smoking as a risk factor in the progression of chronic kidney disease (CKD). We have shown that nicotine promotes mesangial cell proliferation and hypertrophy via nonneuronal nicotinic acetylcholine receptors (nAChRs). The α7-nAChR is one of the most important subunits of the nAChRs. These studies were designed to test the hypothesis that nicotine worsens renal injury in rats with 5/6 nephrectomy (5/6Nx) and that the α7-nAChR subunit is required for these effects. We studied five different groups: Sham, 5/6Nx, 5/6Nx + nicotine (Nic; 100 μg/ml dry wt), 5/6Nx + Nic + α7-nAChR blocker methyllicaconitine (MLA; 3 mg·kg(-1)·day(-1) sq), and Sham + Nic. Blood pressure was measured by the tail-cuff method, and urine was collected for proteinuria. After 12 wk, the rats were euthanized and kidneys were collected. We observed expression of the α7-nAChR in the proximal and distal tubules. The administration of nicotine induced a small increase in blood pressure and resulted in cotinine levels similar to those found in the plasma of smokers. In 5/6Nx rats, the administration of nicotine significantly increased urinary protein excretion (onefold), worsened the glomerular injury score and increased fibronectin (∼ 50%), NADPH oxidase 4 (NOX4; ∼100%), and transforming growth factor-β expression (∼200%). The administration of nicotine to sham rats increased total proteinuria but not albuminuria, suggesting direct effects on tubular protein reabsorption. These effects were prevented by MLA, demonstrating a critical role for the α7-nAChR as a mediator of the effects of nicotine in the progression of CKD.

Angiotensin-(1-7) administration reduces oxidative stress in diabetic bone marrow

Diabetics have an increased risk of developing cardiovascular disease, in part due to oxidative stress, resulting in endothelial nitric oxide synthase (eNOS) dysfunction. Studies have demonstrated that angiotensin-(1-7) [Ang-(1-7)] can activate eNOS activity. Because the bone marrow is a primary source of a number of progenitors important in physiological homeostasis and healing, the goal of this study was to evaluate the in vivo effects of Ang-(1-7) treatment on oxidative stress and the ensuing nitrative stress in diabetic bone marrow and its potential pathways. BKS.Cg-Dock7(m) +/+ Lepr(db)/J mice and their heterozygous controls were administered Ang-(1-7) alone or combined with A-779, losartan, PD123,319, nitro-l-arginine methyl ester, or icatibant sc for 14 d. The bone marrow was then collected to measure nitric oxide levels, eNOS phosphorylation, and expression of nitric oxide synthase, superoxide dismutase, and p22-phox. Nitric oxide levels in the bone marrow were significantly decreased in diabetic mice, and Ang-(1-7) treatment was able to significantly increase these measures (P < 0.01). This effect was blocked by the coadministration of PD123,319, A-779, nitro-l-arginine methyl ester, and icatibant. In addition, Ang-(1-7) treatment reversed the paradoxical increase in eNOS and neuronal nitric oxide synthase expression and decreased the phosphorylation of eNOS at Thr495 seen in diabetic mice. Ang-(1-7) also reversed diabetes-induced production of reactive oxygen species by decreasing p22-phox expression and increasing superoxide dismutase 3 expression, leading to a significant reduction in 3-nitrotyrosine formation in diabetic bone marrow (P < 0.05). Our findings demonstrate that Ang-(1-7) administration decreases diabetes-induced oxidative stress in the bone marrow and modifies pathways involved in eNOS dysfunction.

Inhibition of protein kinase C β(2) prevents tumor necrosis factor-α-induced apoptosis and oxidative stress in endothelial cells: the role of NADPH oxidase subunits

We investigate the cell signal transduction pathway protein kinase C (PKC) and the role of NADPH subunits in the process of TNF-α-induced endothelial apoptosis. Human umbilical vein endothelial cells (HUVEC) were treated with one of these: 1 mM PKC β(2) inhibitor CGP53353, 10 mM PKC δ inhibitor rottlerin, combination CGP53353 with rottlerin, 3 ×10(-4)M NADPH oxidase inhibitor apocynin, 5 × 10(-6)M NADPH oxidase peptide inhibitor gp91ds-tat. The apoptosis process was assessed by Hoechst 33342 stain, flow cytometry and Western blot analysis, while intracellular reactive oxygen species (ROS) production was detected by 2,7'-dichlorodihydrofluorescein diacetate (DCFH-DA). The NADPH oxidase subunit gene and protein expression were assessed by quantitative real-time PCR and Western blot analysis, respectively. TNF-α significantly induced HUVEC apoptosis and ROS production, accompanying with dramatic upregulation of NADPH oxidase subunits: NOX2/gp91(phox), NOX4, p47(phox) and p67(phox), whereas these enhancements were abolished by the treatment with PKC inhibitors. High TNF-α level exposure induces HUVEC apoptosis, as well as a ROS generation increase via the PKC β(2)-dependent activation of NADPH oxidase. Although the PKC δ pathway may enhance TNF-α-induced HUVEC apoptosis, it does not involve the ROS pathway. Upregulation of expression of NADPH subunits is important in this process, which leads to a new target in antioxidative therapy for vascular disease prevention.

The glucagon-like peptide 1 analog liraglutide reduces TNF-α-induced oxidative stress and inflammation in endothelial cells

OBJECTIVE

Glucagon-like peptide 1 (GLP-1), one of the incretin hormones, has been reported to increase positive inotropic activity in cardiac myocytes and protect against myocardial injury. However, the effects upon endothelial cells and the mechanisms involved are not fully understood. We assessed the hypothesis that GLP-1 has protective effects against inflammation and oxidative stress on human endothelial cells.

METHODS AND RESULTS

The effects of the GLP-1 analog liraglutide upon TNF-α-induced injury of the human umbilical vein endothelial cells (HUVECs) were evaluated. First, ROS induced by TNF-α was measured by staining with CM-H(2)DCFDA. Intracellular ROS production of HUVECs was significantly decreased in a dose-dependent manner until 30 nM while liraglutide inhibited the induction of gp91(phox) and p22(phox), subunit of NADPH oxidase, by TNF-α. In addition, protein levels of SOD-2, catalase and GPx were significantly increased by liraglutide. Second, rapid translocation of PKC-α into the membrane following TNF-α was evident. Liraglutide significantly inhibited this very rapid TNF-α-induced translocation of PKC-α into membrane at 2.5 min. Third, liraglutide significantly inhibited NF-κB activation and upregulated I-κB family while phosphorylation of IKK-α/β, which is upstream of NF-κB signaling, was also downregulated after 15 min of TNF-α treatment. Finally, liraglutide inhibited apoptosis of HUVEC and expression of Pentraxin-3 induced by TNF-α.

CONCLUSION

Liraglutide exerts marked anti-oxidative and anti-inflammatory effects on endothelial cells with inhibition of PKC-α, NADPH oxidase, NF-κB signaling and upregulation of protective anti-oxidative enzymes.

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

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

Role of NYGGF4 in insulin resistance

Insulin resistance is a clinical condition that is characterized by reducing glucose uptake in response to insulin. A major factor in the development of insulin resistance syndrome is obesity. NYGGF4 is a novel gene that is abundantly expressed in the adipose tissue of obese subjects. NYGGF4 induced the secretion of FFAs and TNF-α and caused mitochondrial dysfunction, which may cause insulin resistance. This review will summarize the effect of NYGGF4 on the adipogenesis, glucose uptake and mitochondrial dysfunction in vitro, and the possible mechanism and signal pathway of NYGGF4 for insulin resistance.

Ethyl pyruvate ameliorates albuminuria and glomerular injury in the animal model of diabetic nephropathy

Pyruvate is an endogenous antioxidant and anti-inflammatory substance. The present study was implemented to investigate the protective effect of ethyl pyruvate (EP) against the development and progression of diabetic nephropathy in an in vivo and in vitro model. Diabetic rats were prepared by injecting streptozotocin (65 mg/kg). Those that developed diabetes after 72 h were treated with EP (40 mg/kg) intraperitoneally. Diabetic rats without pyruvate treatment and nondiabetic rats were used for control. As an in vitro experiment, rat mesangial cells cultured primarily from Sprague-Dawley rats were treated in high-glucose (HG; 50 mM) or normal-glucose (NG; 5 mM) conditions and with or without pyruvate. Pyruvate-treated diabetic rats exhibited decreased albuminuria and attenuated NADPH-dependent reactive oxygen species generation. Immunohistochemistry showed reduced laminin, type IV collagen, and fibronectin deposition in the glomeruli compared with nontreated diabetic rats. Parallel changes were shown in tissue mRNA and protein expression levels of monocyte chemoattractant protein-1, transforming growth factor-β1, laminin, fibronectin, and type IV collagen in the kidney. Concordantly, protective effects were also exhibited in the mesangial cell culture system. These findings suggest that pyruvate protects against kidney injury via NADPH oxidase inhibition. The present study established that activation of NADPH oxidase plays a crucial role in diabetes-induced oxidative stress, glomerular hypertrophy, and ECM molecule expression. Pyruvate exhibited a renoprotective effect in the progression of experimental diabetic nephropathy. Future research is warranted to investigate the protective mechanism of pyruvate more specifically in relation to NADPH oxidase in diabetic nephropathy.

Role of differential signaling pathways and oxidative stress in diabetic cardiomyopathy

Diabetes mellitus increases the risk of heart failure independently of underlying coronary artery disease, and many believe that diabetes leads to cardiomyopathy. The underlying pathogenesis is partially understood. Several factors may contribute to the development of cardiac dysfunction in the absence of coronary artery disease in diabetes mellitus. There is growing evidence that excess generation of highly reactive free radicals, largely due to hyperglycemia, causes oxidative stress, which further exacerbates the development and progression of diabetes and its complications. Hyperglycemia-induced oxidative stress is a major risk factor for the development of micro-vascular pathogenesis in the diabetic myocardium, which results in myocardial cell death, hypertrophy, fibrosis, abnormalities of calcium homeostasis and endothelial dysfunction. Diabetes-mediated biochemical changes show cross-interaction and complex interplay culminating in the activation of several intracellular signaling molecules. Diabetic cardiomyopathy is characterized by morphologic and structural changes in the myocardium and coronary vasculature mediated by the activation of various signaling pathways. This review focuses on the oxidative stress and signaling pathways in the pathogenesis of the cardiovascular complications of diabetes, which underlie the development and progression of diabetic cardiomyopathy.

Inflammation and diabetic retinal microvascular complications

Diabetic retinopathy (DR) is one of the most common complications of diabetes and is a leading cause of blindness in people of the working age in Western countries. A major pathology of DR is microvascular complications such as non-perfused vessels, microaneurysms, dot/blot hemorrhages, cotton-wool spots, venous beading, vascular loops, vascular leakage and neovascularization. Multiple mechanisms are involved in these alternations. This review will focus on the role of inflammation in diabetic retinal microvascular complications and discuss the potential therapies by targeting inflammation.

Metabolic correction in the management of diabetic peripheral neuropathy: improving clinical results beyond symptom control

Current Clinical Management Guidelines of Diabetic Peripheral Neuropathy (DPN) are based on adequate glucose control and symptomatic pain relief. However, meticulous glycemic control could delay the onset or slow the progression of diabetic neuropathy in patients with DM type 2, but it does not completely prevent the progression of the disease. Complications of DPN as it continues its natural course, produce increasing pain and discomfort, loss of sensation, ulcers, infections, amputations and even death. In addition to the increased suffering, disability and loss of productivity, there is a very significant economic impact related to the treatment of DPN and its complications. In USA alone, it has been estimated that there are more than 5,000,000 patients suffering from DPN and the total annual cost of treating the disease and its complications is over $10,000 million dollars. In order to be able to reduce complications of DPN, it is crucial to improve or correct the metabolic conditions that lead to the pathology present in this condition. Pathophysiologic mechanisms implicated in diabetic neuropathy include: increased polyol pathway with accumulation of sorbitol and reduced Na+/K+-ATPase activity, microvascular damage and hypoxia due to nitric oxide deficit and increased oxygen free radical activity. Moreover, there is a decrease in glutathione and increase in homocysteine. Clinical trials in the last two decades have demonstrated that the use of specific nutrients can correct some of these metabolic derangements, improving symptom control and providing further benefits such as improved sensorium, blood flow and nerve regeneration. We will discuss the evidence on lipoic acid, acetyl-L-carnitine, benfotiamine and the combination of active B vitamins L-methylfolate, methylcobalamin and piridoxal-6-phosphate. In addition, we discuss the role of metformin, an important drug in the management of diabetes, and the presence of specific polymorphic genes, in the risk of developing DPN and how metabolic correction can reduce these risks.