Angiotensin II and vascular injury

Vascular injury, characterized by endothelial dysfunction, structural remodelling, inflammation and fibrosis, plays an important role in cardiovascular diseases. Cellular processes underlying this include altered vascular smooth muscle cell (VSMC) growth/apoptosis, fibrosis, increased contractility and vascular calcification. Associated with these events is VSMC differentiation and phenotypic switching from a contractile to a proliferative/secretory phenotype. Inflammation, associated with macrophage infiltration and increased expression of redox-sensitive pro-inflammatory genes, also contributes to vascular remodelling. Among the many factors involved in vascular injury is Ang II. Ang II, previously thought to be the sole biologically active downstream peptide of the renin-angiotensin system (RAS), is converted to smaller peptides, [Ang III, Ang IV, Ang-(1-7)], that are functional and that modulate vascular tone and structure. The actions of Ang II are mediated via signalling pathways activated upon binding to AT1R and AT2R. AT1R activation induces effects through PLC-IP3-DAG, MAP kinases, tyrosine kinases, tyrosine phosphatases and RhoA/Rho kinase. Ang II elicits many of its (patho)physiological actions by stimulating reactive oxygen species (ROS) generation through activation of vascular NAD(P)H oxidase (Nox). ROS in turn influence redox-sensitive signalling molecules. Here we discuss the role of Ang II in vascular injury, focusing on molecular mechanisms and cellular processes. Implications in vascular remodelling, inflammation, calcification and atherosclerosis are highlighted.

Therapeutic strategies of diabetic nephropathy: recent progress and future perspectives

Diabetic nephropathy (DN) is one of the most common complications of diabetes with high mortality rates worldwide. The treatment of DN has posed a formidable challenge to the scientific community. Simple control of risk factors has been insufficient to cope with the progression of DN. During the process of anti-DN drug discovery, multiple pathogeneses such as oxidative stress, inflammation and fibrosis should all be considered. In this review, the pathogenesis of DN is summarized. The major context focuses on a few small molecules toward the pathogenesis available in animal models and clinical trials for the treatment of DN. The perspectives of novel anti-DN agents and the future directions for the prevention of DN are discussed.

Effects of folic acid on renal endothelial function in patients with diabetic nephropathy: results from a randomized trial

Endothelial dysfunction has been shown to promote podocyte injury and albuminuria in diabetes, highlighting the importance of the interaction between renal endothelial cells and podocytes. Folic acid (FA) improves nitric oxide synthase (NOS) function and reduces progression of diabetic nephropathy in animal models. We tested whether high-dose FA treatment improves renal endothelial function and albuminuria in human subjects with incipient diabetic nephropathy. Following a double-blind, randomized, cross-over design, 28 patients with Type 2 diabetes and albuminuria were allocated to 4 weeks' treatment with placebo and high-dose FA (5 mg/day). Renal nitric oxide (NO) production determined as the response of renal plasma flow (RPF) to NOS inhibition with NG-monomethyl-L-arginine (L-NMMA) (4.25 mg/kg intravenously), renal oxidant stress as response of RPF to vitamin C infusion (3 mg/kg) and albuminuria were determined after each treatment phase. Neither the reduction in RPF to L-NMMA nor the increase in RPF to vitamin C infusion differed between treatment phases (ΔRPF to

L-NMMA

-74±71 ml/min per m2 during placebo compared with -63±56 ml/min per m2 during FA, P=0.57; ΔRPF to vitamin C: +93±118 ml/min per m2 compared with +94±108 ml/min per m2; P=0.70). In line with the lack of effect on the renal endothelium, albuminuria was not affected by FA treatment (110±179 mg/day during placebo compared with 87±146 mg/day during FA; P=0.12). High-dose FA treatment does not improve renal endothelial function and fails to reduce albuminuria in human subjects with diabetic nephropathy. Novel treatment options for oxidant stress and endothelial dysfunction in patients with diabetes are urgently needed.

Probucol inhibited Nox2 expression and attenuated podocyte injury in type 2 diabetic nephropathy of db/db mice

The present study was conducted to investigate the effects of probucol on the progression of diabetic nephropathy and the underlying mechanism in type 2 diabetic db/db mice. Eight weeks db/db mice were treated with regular diet or probucol-containing diet (1%) for 12 weeks. Non-diabetic db/m mice were used as controls. We examined body weight, blood glucose, and urinary albumin. At 20 weeks, experimental mice were sacrificed and their blood and kidneys were extracted for the analysis of blood chemistry, kidney histology, oxidative stress marker, and podocyte marker. As a result, 24 h urinary albumin excretions were reduced after probucol treatment. There were improvements of extracellular matrix accumulation and fibronectin and collagen IV deposition in glomeruli in the probucol-treated db/db mice. The reduction of nephrin and the loss of podocytes were effectively prevented by probucol in db/db mice. Furthermore, probucol significantly decreased the production of thiobarbituric acid-reactive substances (TBARS), an index of reactive oxygen species (ROS) generation and down-regulated the expression of Nox2. Taken together, our findings support that probucol may have the potential to protect against type 2 diabetic nephropathy via amelioration of podocyte injury and reduction of oxidative stress.

Advances and strategies in NADPH oxidase inhibitors and activators patents

The NADPH oxidase (NOX) enzymes were identified as a family of seven isoforms contributing to the production of reactive oxygen species. During the past 15 years, this class of enzymes has increasingly gained interest from the academic and pharmaceutical laboratories. Extensive research efforts focused on the decryption of their mechanism of action has shown that Nox enzymes are the most important source of reactive oxygen species and key contributors in the pathogenesis of several diseases. Recent publications and patents suggest that NOX modulators may provide major opportunities in many diseases as novel therapeutics. This review covers application patents and current state-of-the-art on Nox modulators from 2005 to December 2013 and examines the different approaches patented to modulate the activity of Nox enzymes.

Therapeutic approaches to diabetic nephropathy--beyond the RAS

Despite improvements in glycaemic and blood pressure control, and the efficacy of renin-angiotensin system (RAS) blockade for proteinuria reduction, diabetic nephropathy is the most frequent cause of end-stage renal disease in developed countries. This finding is consistent with the hypothesis that key pathogenetic mechanisms leading to progression of renal disease are not modified or inactivated by current therapeutic approaches. Although extensive research has elucidated molecular signalling mechanisms that are involved in progression of diabetic kidney disease, a number of high-profile clinical trials of potentially nephroprotective agents have failed, highlighting an insufficient understanding of pathogenic pathways. These include trials of paricalcitol in early diabetic kidney disease and bardoxolone methyl in advanced-stage disease. Various strategies based on encouraging data from preclinical studies that showed renoprotective effects of receptor antagonists, neutralizing antibodies, kinase inhibitors, small compounds and peptide-based technologies are currently been tested in randomized controlled trials. Phase II clinical trials are investigating approaches targeting inflammation, fibrosis and signalling pathways. However, only one trial that aims to provide evidence for marketing approval of a potentially renoprotective drug (atrasentan) is underway-further research into the potential nephroprotective effects of novel glucose-lowering agents is required.

Novel targets of antifibrotic and anti-inflammatory treatment in CKD

Chronic kidney disease (CKD) is becoming a worldwide epidemic, driven largely by the dramatic rise in the prevalence of diabetes and obesity. Novel targets and treatments for CKD are, therefore, desperately needed-to both mitigate the burden of this disease in the general population and reduce the necessity for renal replacement therapy in individual patients. This Review highlights new insights into the mechanisms that contribute to CKD, and approaches that might facilitate the development of disease-arresting therapies for CKD. Particular focus is given to therapeutic approaches using antifibrotic agents that target the transforming growth factor β superfamily. In addition, we discuss new insights regarding the roles of vascular calcification, the NADPH oxidase family, and inflammation in the pathogenesis of CKD. We also highlight a new understanding regarding kidney energy sensing pathways (AMPK, sirtuins, and mTOR) in a variety of kidney diseases and how they are linked to inflammation and fibrosis. Finally, exciting new insights have been made into the role of mitochondrial function and mitochondrial biogenesis in relation to progressive kidney disease. Prospective therapeutics based on these findings will hopefully renew hope for clinicians and patients in the near future.

Updates of reactive oxygen species in melanoma etiology and progression

Reactive oxygen species (ROS) play crucial roles in all aspects of melanoma development, however, the source of ROS is not well defined. In this review we summarize recent advancement in this rapidly developing field. The cellular ROS pool in melanocytes can be derived from mitochondria, melanosomes, NADPH oxidase (NOX) family enzymes, and uncoupling of nitric oxide synthase (NOS). Current evidence suggests that Nox1, Nox4 and Nox5 are expressed in melanocytic lineage. While there is no difference in Nox1 expression levels in primary and metastatic melanoma tissues, Nox4 expression is significantly higher in a subset of metastatic melanoma tumors as compared to the primary tumors; suggesting distinct and specific signals and effects for NOX family enzymes in melanoma. Targeting these NOX enzymes using specific NOX inhibitors may be effective for a subset of certain tumors. ROS also play important roles in BRAF inhibitor induced drug resistance; hence identification and blockade of the source of this ROS may be an effective way to enhance efficacy and overcome resistance. Furthermore, ROS from different sources may interact with each other and interact with reactive nitrogen species (RNS) and drive the melanomagenesis process at all stages of disease. Further understanding ROS and RNS in melanoma etiology and progression is necessary for developing new prevention and therapeutic approaches.

An inhibitor of NADPH oxidase-4 attenuates established pulmonary fibrosis in a rodent disease model

Idiopathic pulmonary fibrosis is a chronic progressive disease of increasing prevalence for which there is no effective therapy. Increased oxidative stress associated with an oxidant-antioxidant imbalance is thought to contribute to disease progression. NADPH oxidases (Nox) are a primary source of reactive oxygen species within the lung and cardiovascular system. We demonstrate that the Nox4 isoform is up-regulated in the lungs of patients with IPF and in a rodent model of bleomycin-induced pulmonary fibrosis and vascular remodeling. Nox4 is constitutively active, and therefore increased expression levels are likely to contribute to disease pathology. Using a small molecule Nox4/Nox1 inhibitor, we demonstrate that targeting Nox4 results in attenuation of an established fibrotic response, with reductions in gene transcripts for the extracellular matrix components collagen 1α1, collagen 3α1, and fibronectin and in principle pathway components associated with pulmonary fibrosis and hypoxia-mediated vascular remodeling: transforming growth factor (TGF)-β1, plasminogen activator inhibitor-1, hypoxia-inducible factor, and Nox4. TGF-β1 is a principle fibrotic mediator responsible for inducing up-regulation of profibrotic pathways associated with disease pathology. Using normal human lung-derived primary fibroblasts, we demonstrate that inhibition of Nox4 activity using a small molecule antagonist attenuates TGF-β1-mediated up-regulation in expression of profibrotic genes and inhibits the differentiation of fibroblast to myofibroblasts, that is associated with up-regulation in smooth muscle actin and acquisition of a contractile phenotype. These studies support the view that targeting Nox4 may provide a therapeutic approach for attenuating pulmonary fibrosis.

Valsartan slows the progression of diabetic nephropathy in db/db mice via a reduction in podocyte injury, and renal oxidative stress and inflammation

Higher doses of AngII (angiotensin II) blockers are intended to optimize albuminuria reduction rather than for blood pressure control in chronic kidney disease. However, the long-term renoprotection of high-dose AngII blockers has yet to be defined. The present study sought to determine whether doses of ARB (AngII receptor blocker) that maximally reduce proteinuria could slow the progression of glomerulosclerosis in the uninephrectomized db/db mouse, a model of Type 2 diabetes. Untreated uninephrectomized db/db mice had normal blood pressure, but developed progressive albuminuria and mesangial matrix expansion between 18 and 22 weeks of age, which was associated with increased renal expression of TGFβ1 (transforming growth factor β1), PAI-1 (plasminogen-activator inhibitor-1), type IV collagen and FN (fibronectin). Treatment with valsartan in the drinking water of db/db mice from 18 to 22 weeks of age, at a dose that was determined previously to maximally reduce proteinuria, prevented the increases in albuminuria and the markers of renal fibrosis seen in untreated db/db mice. In addition, WT-1 (Wilms tumour protein-1)-immunopositive podocyte numbers were found to be lower in the untreated glomeruli of mice with diabetes. The expression of podocin and nephrin were continually decreased in mice with diabetes between 18 and 22 weeks of age. These changes are indicative of podocyte injury and the administration of valsartan ameliorated them substantially. Renal expression of TNFα (tumour necrosis factor α), MCP-1 (monocyte chemoattractant protein-1), Nox2 (NADPH oxidase 2), p22phox and p47phox and urine TBARS (thiobarbituric acid-reacting substance) levels, the markers of renal inflammation and oxidative stress, were increased during disease progression in mice with diabetes. Valsartan treatment was shown to reduce these markers. Thus high doses of valsartan not only reduce albuminuria maximally, but also halt the progression of the glomerulosclerosis resulting from Type 2 diabetes via a reduction in podocyte injury and renal oxidative stress and inflammation.

NAD(P)H oxidase isoforms as therapeutic targets for diabetic complications

The development of macro- and microvascular complications is accelerated in diabetic patients. While some therapeutic regimes have helped in delaying progression of complications, none have yet been able to halt the progression and prevent vascular disease, highlighting the need to identify new therapeutic targets. Increased oxidative stress derived from the NADPH oxidase (Nox) family has recently been identified to play an important role in the pathophysiology of vascular disease. In recent years, specific Nox isoforms have been implicated in contributing to the development of atherosclerosis of major vessels, as well as damage of the small vessels within the kidney and the eye. With the use of novel Nox inhibitors, it has been demonstrated that these complications can be attenuated, indicating that targeting Nox derived oxidative stress holds potential as a new therapeutic strategy.

Redox-mediated signal transduction by cardiovascular Nox NADPH oxidases

The only known function of the Nox family of NADPH oxidases is the production of reactive oxygen species (ROS). Some Nox enzymes show high tissue-specific expression and the ROS locally produced are required for synthesis of hormones or tissue components. In the cardiovascular system, Nox enzymes are low abundant and function as redox-modulators. By reacting with thiols, nitric oxide (NO) or trace metals, Nox-derived ROS elicit a plethora of cellular responses required for physiological growth factor signaling and the induction and adaptation to pathological processes. The interactions of Nox-derived ROS with signaling elements in the cardiovascular system are highly diverse and will be detailed in this article, which is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

Genetic targeting or pharmacologic inhibition of NADPH oxidase nox4 provides renoprotection in long-term diabetic nephropathy

Diabetic nephropathy may occur, in part, as a result of intrarenal oxidative stress. NADPH oxidases comprise the only known dedicated reactive oxygen species (ROS)-forming enzyme family. In the rodent kidney, three isoforms of the catalytic subunit of NADPH oxidase are expressed (Nox1, Nox2, and Nox4). Here we show that Nox4 is the main source of renal ROS in a mouse model of diabetic nephropathy induced by streptozotocin administration in ApoE(-/-) mice. Deletion of Nox4, but not of Nox1, resulted in renal protection from glomerular injury as evidenced by attenuated albuminuria, preserved structure, reduced glomerular accumulation of extracellular matrix proteins, attenuated glomerular macrophage infiltration, and reduced renal expression of monocyte chemoattractant protein-1 and NF-κB in streptozotocin-induced diabetic ApoE(-/-) mice. Importantly, administration of the most specific Nox1/4 inhibitor, GKT137831, replicated these renoprotective effects of Nox4 deletion. In human podocytes, silencing of the Nox4 gene resulted in reduced production of ROS and downregulation of proinflammatory and profibrotic markers that are implicated in diabetic nephropathy. Collectively, these results identify Nox4 as a key source of ROS responsible for kidney injury in diabetes and provide proof of principle for an innovative small molecule approach to treat and/or prevent chronic kidney failure.

Aggravation of diabetic nephropathy in BCL-2 interacting cell death suppressor (BIS)-haploinsufficient mice together with impaired induction of superoxide dismutase (SOD) activity

AIMS/HYPOTHESIS

B cell CLL/lymphoma 2 (BCL-2)-interacting cell death suppressor (BIS), known as an anti-stress and anti-apoptotic protein, has been reported to modulate susceptibility to oxidative stress. This study investigated the potential role of BIS as an antioxidant protein in diabetic nephropathy.

METHODS

Diabetes was induced in BIS-heterozygote (BIS-HT) mice via streptozotocin injections and the resulting phenotypes were compared with those of BIS-wild-type (BIS-WT) mice over the 20 weeks following diabetes induction.

RESULTS

Renal injuries, represented by increased plasma creatinine levels and increased albuminuria, were greater in diabetic BIS-HT mice than in diabetic BIS-WT mice, and were accompanied by a significant increase in reactive oxygen species (ROS) and oxidative stress markers. Moreover, renal pathological changes and the apoptotic process were accelerated in diabetic BIS-HT mice compared with diabetic BIS-WT mice with the same degree of hyperglycaemia; all were restored by 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) treatment. The levels of NADPH oxidase and related proteins were not significantly higher in diabetic BIS-HT mice compared with diabetic BIS-WT mice. However, levels of superoxide dismutase (SOD)1 and SOD2 increased on the induction of diabetes in BIS-WT mice but not in BIS-HT mice, correlating with the total SOD activity. An in vitro study showed that knockdown of BIS production also resulted in impaired induction of SOD activity as well as SOD levels in HK-2 and NMS cells, concomitant with significant ROS accumulation.

CONCLUSION/INTERPRETATION

Our results suggest that the decreased antioxidant capacity of BIS aggravates diabetic nephropathy in diabetic BIS-HT mice, possibly as a result of the disruption in the regulation of SOD protein quality under oxidative stress.

Reactive oxygen species, vascular Noxs, and hypertension: focus on translational and clinical research

SIGNIFICANCE

Reactive oxygen species (ROS) are signaling molecules that are important in physiological processes, including host defense, aging, and cellular homeostasis. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in the onset and/or progression of chronic diseases, including hypertension.

RECENT ADVANCES

Although oxidative stress may not be the only cause of hypertension, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors, such as salt loading, activation of the renin-angiotensin-aldosterone system, and sympathetic hyperactivity, at least in experimental models. A major source for ROS in the cardiovascular-renal system is a family of nicotinamide adenine dinucleotide phosphate oxidases (Noxs), including the prototypic Nox2-based Nox, and Nox family members: Nox1, Nox4, and Nox5.

CRITICAL ISSUES

Although extensive experimental data support a role for increased ROS levels and altered redox signaling in the pathogenesis of hypertension, the role in clinical hypertension is unclear, as a direct causative role of ROS in blood pressure elevation has yet to be demonstrated in humans. Nevertheless, what is becoming increasingly evident is that abnormal ROS regulation and aberrant signaling through redox-sensitive pathways are important in the pathophysiological processes which is associated with vascular injury and target-organ damage in hypertension.

FUTURE DIRECTIONS

There is a paucity of clinical information related to the mechanisms of oxidative stress and blood pressure elevation, and a few assays accurately measure ROS directly in patients. Such further ROS research is needed in humans and in the development of adequately validated analytical methods to accurately assess oxidative stress in the clinic.

New insight into the molecular drug target of diabetic nephropathy

Diabetic nephropathy (DN) lowered quality of life and shortened life expectancy amongst those affected. Evidence indicates interaction between advanced glycation end products (AGEs), activated protein kinase C (PKC) and angiotensin II exacerbate the progression of DN. Inhibitors of angiotensin-converting enzyme (ACEIs), renin angiotensin aldosterone system (RAAS), AGEs, and PKC have been tested for slowing down the progression of DN. The exact molecular drug targets that lead to the amelioration of renal injury in DN are not well understood. This review summarizes the potential therapeutic targets, based on putative mechanism in the progression of the disease.

Calcineurin Aβ regulates NADPH oxidase (Nox) expression and activity via nuclear factor of activated T cells (NFAT) in response to high glucose

Hypertrophy is an adaptive response that enables organs to appropriately meet increased functional demands. Previously, we reported that calcineurin (Cn) is required for glomerular and whole kidney hypertrophy in diabetic rodents (Gooch, J. L., Barnes, J. L., Garcia, S., and Abboud, H. E. (2003). Calcineurin is activated in diabetes and is required for glomerular hypertrophy and ECM accumulation. Am. J. Physiol. Renal Physiol. 284, F144-F154; Reddy, R. N., Knotts, T. L., Roberts, B. R., Molkentin, J. D., Price, S. R., and Gooch, J. L. (2011). Calcineurin Aβ is required for hypertrophy but not matrix expansion in the diabetic kidney. J. Cell Mol. Med. 15, 414-422). Because studies have also implicated the reactive oxygen species-generating enzymes NADPH oxidases (Nox) in diabetic kidney responses, we tested the hypothesis that Nox and Cn cooperate in a common signaling pathway. First, we examined the role of the two main isoforms of Cn in hypertrophic signaling. Using primary kidney cells lacking a catalytic subunit of Cn (CnAα(-/-) or CnAβ(-/-)), we found that high glucose selectively activates CnAβ, whereas CnAα is constitutively active. Furthermore, CnAβ but not CnAα mediates hypertrophy. Next, we found that chronic reactive oxygen species generation in response to high glucose is attenuated in CnAβ(-/-) cells, suggesting that Cn is upstream of Nox. Consistent with this, loss of CnAβ reduces basal expression and blocks high glucose induction of Nox2 and Nox4. Inhibition of nuclear factor of activated T cells (NFAT), a CnAβ-regulated transcription factor, decreases Nox2 and Nox4 expression, whereas NFAT overexpression increases Nox2 and Nox4, indicating that the CnAβ/NFAT pathway modulates Nox. These data reveal that the CnAβ/NFAT pathway regulates Nox and plays an important role in high glucose-mediated hypertrophic responses in the kidney.

Metabolic syndrome-induced tubulointerstitial injury: role of oxidative stress and preventive effects of acetaminophen

The prevalence of metabolic syndrome persistently increases and affects over 30% of U.S. adults. To study how metabolic syndrome may induce tubulointerstitial injury and whether acetaminophen has renal-protective properties, 4-week-old obese Zucker rats were randomly assigned into three groups, control (OC), vehicle dimethyl sulfoxide (OV), and acetaminophen treatment (30 mg/kg/day for 26 weeks), and lean Zucker rats served as healthy controls. Significant tubulointerstitial injuries were observed in both OC and OV animals, evidenced by increased tubular cell death, tubular atrophy/dilation, inflammatory cell infiltration, and fibrosis. These tubulointerstitial alterations were significantly reduced by treatment with a chronic but low dose of acetaminophen, which acted to diminish NADPH oxidase isoforms Nox2 and Nox4 and decrease tubulointerstitial oxidative stress (reduced tissue superoxide and macromolecular oxidation). Decreased oxidative stress by acetaminophen was paralleled by the reduction of tubular proapoptotic signaling (diminished Bax/Bcl-2 ratio and caspase 3 activation) and the alleviation of tubular epithelial-to-mesenchymal transition (decreased transforming growth factor β, connective tissue growth factor, α-smooth muscle actin, and laminin). These data suggest that increased oxidative stress plays a critical role in mediating metabolic syndrome-induced tubulointerstitial injury and provide the first evidence suggesting that acetaminophen may be of therapeutic benefit for the prevention of tubulointerstitial injury.

Nephropathy and elevated BP in mice with podocyte-specific NADPH oxidase 5 expression

NADPH oxidase (Nox) enzymes are a significant source of reactive oxygen species, which contribute to glomerular podocyte dysfunction. Although studies have implicated Nox1, -2, and -4 in several glomerulopathies, including diabetic nephropathy, little is known regarding the role of Nox5 in this context. We examined Nox5 expression and regulation in kidney biopsies from diabetic patients, cultured human podocytes, and a novel mouse model. Nox5 expression increased in human diabetic glomeruli compared with nondiabetic glomeruli. Stimulation with angiotensin II upregulated Nox5 expression in human podocyte cultures and increased reactive oxygen species generation. siRNA-mediated Nox5 knockdown inhibited angiotensin II-stimulated production of reactive oxygen species and altered podocyte cytoskeletal dynamics, resulting in an Rac-mediated motile phenotype. Because the Nox5 gene is absent in rodents, we generated transgenic mice expressing human Nox5 in a podocyte-specific manner (Nox5(pod+)). Nox5(pod+) mice exhibited early onset albuminuria, podocyte foot process effacement, and elevated systolic BP. Subjecting Nox5(pod+) mice to streptozotocin-induced diabetes further exacerbated these changes. Our data show that renal Nox5 is upregulated in human diabetic nephropathy and may alter filtration barrier function and systolic BP through the production of reactive oxygen species. These findings provide the first evidence that podocyte Nox5 has an important role in impaired renal function and hypertension.

Nox4 as a potential therapeutic target for treatment of uremic toxicity associated to chronic kidney disease

Watanabe et al. report that Nox4 NADPH oxidase catalytic moiety and the subunit p22^phox mediate the increase in oxidative stress and human tubular epithelial cell injury induced by p-cresyl sulfate, a protein-bound uremic toxin. These findings could be instrumental for the design of novel therapeutic intervention utilizing small molecule inhibitors specifically targeting Nox oxidases to prevent or slow down the progression of chronic kidney disease and the associated disorders due to uremic toxicity.

Role of NADPH oxidase isoforms NOX1, NOX2 and NOX4 in myocardial ischemia/reperfusion injury

Myocardial reperfusion injury is mediated by several processes including increase of reactive oxygen species (ROS). The aim of the study is to identify potential sources of ROS contributing to myocardial ischemia-reperfusion injury. For this purpose, we investigated myocardial ischemia/reperfusion pathology in mice deficient in various NADPH oxidase isoforms (Nox1, Nox2, Nox4, as well as Nox1/2 double knockout). Following 30min of ischemia and 24h of reperfusion, a significant decrease in the size of myocardial infarct was observed in Nox1-, Nox2- and Nox1/Nox2-, but not in Nox4-deficient mice. However, no protection was observed in a model of chronic ischemia, suggesting that NOX1 and NOX2-mediated oxidative damage occurs during reperfusion. Cardioprotective effect of Nox1 and Nox2 deficiencies was associated with decrease of neutrophil invasion, but, on the other hand an improved reperfusion injury was also observed in isolated perfused hearts (Langendorff model) suggesting that inflammatory cells were not the major source of oxidative damage. A decrease in global post-reperfusion oxidative stress was clearly detected in Nox2-, but not in Nox1-deficient hearts. Analysis of key signaling pathways during reperfusion suggests distinct cardioprotective patterns: increased phosphorylation was seen for Akt and Erk in Nox1-deficient mice and for Stat3 and Erk in Nox2-deficient mice. Consequently, NOX1 and NOX2 represent interesting drug targets for controlling reperfusion damage associated with revascularization in coronary disease.

NADPH oxidases, reactive oxygen species, and the kidney: friend and foe

Reactive oxygen species (ROS) play an important role in normal cellular physiology. They regulate different biologic processes such as cell defense, hormone synthesis and signaling, activation of G protein-coupled receptors, and ion channels and kinases/phosphatases. ROS are also important regulators of transcription factors and gene expression. On the other hand, in pathologic conditions, a surplus of ROS in tissue results in oxidative stress with various injurious consequences such as inflammation and fibrosis. NADPH oxidases are one of the many sources of ROS in biologic systems, and there are seven isoforms (Nox1-5, Duox1, Duox2). Nox4 is the predominant form in the kidney, although Nox2 is also expressed. Nox4 has been implicated in the basal production of ROS in the kidney and in pathologic conditions such as diabetic nephropathy and CKD; upregulation of Nox4 may be important in renal oxidative stress and kidney injury. Although there is growing evidence indicating the involvement of NADPH oxidase in renal pathology, there is a paucity of information on the role of NADPH oxidase in the regulation of normal renal function. Here we provide an update on the role of NADPH oxidases and ROS in renal physiology and pathology.

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

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

Nox as a target for diabetic complications

Oxidative stress has been linked to the pathogenesis of the major complications of diabetes in the kidney, the heart, the eye or the vasculature. NADPH oxidases of the Nox family are a major source of ROS (reactive oxygen species) and are critical mediators of redox signalling in cells from different organs afflicted by the diabetic milieu. In the present review, we provide an overview of the current knowledge related to the understanding of the role of Nox in the processes that control cell injury induced by hyperglycaemia and other predominant factors enhanced in diabetes, including the renin–angiotensin system, TGF-β (transforming growth factor-β) and AGEs (advanced glycation end-products). These observations support a critical role for Nox homologues in diabetic complications and indicate that NADPH oxidases are an important therapeutic target. Therefore the design and development of small-molecule inhibitors that selectively block Nox oxidases appears to be a reasonable approach to prevent or retard the complications of diabetes in target organs. The bioefficacy of these agents in experimental animal models is also discussed in the present review.

New targets for treatment of diabetic nephropathy: what we have learned from animal models

PURPOSE OF REVIEW

There has been an advance in our understanding of the mechanisms of diabetic nephropathy over the past few years and much of that has occurred because of studies in animal models of diabetic nephropathy.

RECENT FINDINGS

Studies in animal models of diabetic nephropathy, especially in mice, have underlined the multifactorial nature of the pathogenesis of the disease process and the recognition that these models only partly replicate the changes found in human disease. Despite these limitations, recent animal model studies have identified a number of new, specific molecular abnormalities that point to pathways and specific molecules as potential targets for preventive or therapeutic intervention. These specific targets include the diabetic nephropathy related decreases in endothelial nitric oxide synthase activity and renal dopamine production and the increases in Nrf-2, JAK/STAT, and mammalian target of rapamycin complex 1 signaling. These and other altered signaling pathways are described in this review. We emphasize the use of a unique investigative resource, Nephromine, to utilize a library of mRNA expression data obtained from the kidney biopsies of humans with diabetic nephropathy, to compare and validate findings in mouse models with human disease.

SUMMARY

Several new pathways have been implicated in the progression of diabetic nephropathy through studies of animal models. Some of these appear to be altered in human diabetic nephropathy and may be targets for therapy.

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.

Emerging drugs for managing kidney disease in patients with diabetes

INTRODUCTION

The need for new approaches to manage the increasing numbers of patients with diabetes and their burden of complications is urgent. Of these, chronic kidney disease imposes some of the highest costs, both in dollars and in terms of human suffering. In individuals with diabetes, the presence and severity of kidney disease adversely affects their well-being, contributes to disease morbidity and increases their risk of a premature death.

AREAS COVERED

To collect information for the strategies previously or currently under investigation for managing kidney disease in patients with diabetes, a literature search was performed through the search engines PubMed and ClinicalTrials.gov.

EXPERT OPINION

Despite advancing knowledge on the pathogenesis of diabetic kidney disease, and promising effects in experimental models, at present there are no new drugs that come close to providing the solutions we desire for our patients. Even when used in combination with standard care, renal complications are at best only modestly reduced, at the considerable expense of additional pill burden and exposure to serious off-target effects. Some of the most exciting advances over the last decade, including thiazolidinediones, direct renin inhibitors, endothelin antagonists and most recently bardoxolone methyl have all fallen at this last hurdle. Better targeted ('smarter') drugs appear to be the best hope for renoprotective therapy.

NOXious signaling in pain processing

Chronic pain affects millions of people and often causes major health problems. Accumulating evidence indicates that the production of reactive oxygen species (ROS), such as superoxide anion or hydrogen peroxide, is increased in the nociceptive system during chronic inflammatory and neuropathic pain, and that ROS can act as specific signaling molecules in pain processing. Reduction of ROS levels by administration of scavengers or antioxidant compounds attenuated the nociceptive behavior in various animal models of chronic pain. However, the sources of increased ROS production during chronic pain and the role of ROS in pain processing are poorly understood. Current work revealed pain-relevant functions of the Nox family of NADPH oxidases, a group of electron-transporting transmembrane enzymes whose sole function seems to be the generation of ROS. In particular, significant expression of the Nox family members Nox1, Nox2, and Nox4 in various cells of the nociceptive system has been discovered. Studies using knockout mice suggest that these Nox enzymes specifically contribute to distinct signaling pathways in chronic inflammatory and/or neuropathic pain states. Accordingly, targeting Nox1, Nox2, and Nox4 could be a novel strategy for the treatment of chronic pain. Currently selective inhibitors of Nox enzymes are being developed. Here, we introduce the distinct roles of Nox enzymes in pain processing, we summarize recent findings in the understanding of ROS-dependent signaling pathways in the nociceptive system, and we discuss potential analgesic properties of currently available Nox inhibitors.