Effects of the angiotensin II type 1 receptor antagonist valsartan on the expression of superoxide dismutase in hypertensive patients

The role of oxidative stress in the pathogenesis of vascular diseases such as hypertension has been well recognized. Angiotensin (Ang) II is regarded as a pro-oxidant because it can stimulate the production of reactive oxygen species. The purpose of this study was to evaluate whether treatment with the Ang II type 1 (AT(1)) receptor antagonist valsartan has an antioxidant effect in patients with mild to moderate hypertension. A randomized, double-blind, placebo-controlled study was conducted in 48 stage I and II hypertensive subjects. Patients were followed every 4 weeks for 12 weeks after randomization to valsartan titrated to 80 to 160 mg once or twice daily or matching placebo. The erythrocyte superoxide dismutase (SOD) activity and expression of SOD-mRNA in polymorphonuclear leukocytes were measured before and after treatment. Valsartan showed concentration-dependent inhibition of reactive oxygen species generation in polymorphonuclear leukocytes from hypertensive patients. The erythrocyte superoxide dismutase activity before treatment was more than 2 times higher in hypertensive subjects compared to normal controls. Superoxide dismutase activity decreased significantly after 12 weeks of treatment with valsartan but did not change with placebo. The amount of SOD-mRNA in the polymorphonuclear leukocytes decreased progressively over 3 months in the hypertensive subjects receiving valsartan treatment but did not change in the placebo group. The production of reactive oxygen species is increased in hypertension, and superoxide dismutase activity is increased, presumably as a compensatory mechanism. Treatment with valsartan but not placebo resulted in a progressive down-regulation of SOD-mRNA expression and a reduction in superoxide dismutase activity, suggesting antioxidant activity and a reduction of reactive oxygen species generation. These findings imply that AT(1) receptor antagonists may provide benefits to hypertensive patients beyond blood pressure reduction.     

Reactive oxygen species and glucocorticoid-induced hypertension

1. There is increasing evidence for a role of oxidative stress and nitric oxide deficiency in experimental glucocorticoid-induced hypertension, as evidenced by increased biomarkers of oxidative stress; the effectiveness of antioxidants or reduced NADPH oxidase antagonists in lowering blood pressure; and secondary upregulation of endogenous antioxidant enzymes in response to oxidative stress. 2. In the vasculature, the main sources of superoxide are NADPH oxidase, xanthine oxidase, uncoupled endothelial nitric oxide synthase (eNOS) and mitochondria. 3. NADPH oxidase plays a significant role in the pathogenesis of glucocorticoid-induced hypertension in the rats, but xanthine oxidase and uncoupled eNOS pathways are not important sources of reactive oxygen species in these models. The role of mitochondrial reactive oxygen species in glucocorticoid-induced hypertension remains to be clarified.     

Blockade of T-type voltage-dependent Ca2+ channels by benidipine, a dihydropyridine calcium channel blocker, inhibits aldosterone production in human adrenocortical cell line NCI-H295R

Benidipine, a long-lasting dihydropyridine calcium channel blocker, is used for treatment of hypertension and angina. Benidipine exerts pleiotropic pharmacological features, such as renoprotective and cardioprotective effects. In pathophysiological conditions, the antidiuretic hormone aldosterone causes development of renal and cardiovascular diseases. In adrenal glomerulosa cells, aldosterone is produced in response to extracellular potassium, which is mainly mediated by T-type voltage-dependent Ca2+ channels. More recently, it has been demonstrated that benidipine inhibits T-type Ca2+ channels in addition to L-type Ca2+ channels. Therefore, effect of calcium channel blockers, including benidipine, on aldosterone production and T-type Ca2+ channels using human adrenocortical cell line NCI-H295R was investigated. Benidipine efficiently inhibited KCl-induced aldosterone production at low concentration (3 and 10 nM), with inhibitory activity more potent than other calcium channel blockers. Patch clamp analysis indicated that benidipine concentration-dependently inhibited T-type Ca2+ currents at 10, 100 and 1000 nM. As for examined calcium channel blockers, inhibitory activity for T-type Ca2+ currents was well correlated with aldosterone production. L-type specific calcium channel blockers calciseptine and nifedipine showed no effect in both assays. These results indicate that inhibition of T-type Ca2+ channels is responsible for inhibition of aldosterone production in NCI-H295R cells. Benidipine efficiently inhibited KCl-induced upregulation of 11-beta-hydroxylase mRNA and aldosterone synthase mRNA as well as KCl-induced Ca2+ influx, indicating it as the most likely inhibition mechanism. Benidipine partially inhibited angiotensin II-induced aldosterone production, plus showed additive effects when used in combination with the angiotensin II type I receptor blocker valsartan. Benidipine also partially inhibited angiotensin II-induced upregulation of the above mRNAs and Ca2+ influx inhibitory activities of benidipine for aldosterone production. T-type Ca2+ channels may contribute to additional benefits of this drug for treating renal and cardiovascular diseases, beyond its primary anti-hypertensive effects from blocking L-type Ca2+ channels.     

NADPH oxidase inhibitors: new antihypertensive agents?

NADPH oxidases have recently been shown to contribute to the pathogenesis of hypertension. The development of specific inhibitors of these enzymes has focused attention on their potential therapeutic use in hypertensive disease. Two of the most specific inhibitors, gp91ds-tat and apocynin, have been shown to decrease blood pressure in animal models of hypertension. Other inhibitors, including diphenylene iodonium, aminoethyl benzenesulfono fluoride, S17834, PR39, protein kinase C inhibitors, and VAS2870, have shown promise in vitro, but their in vivo specificity, pharmacokinetics, and effectiveness in hypertension remains to be determined. Of importance, the currently available antihypertensive agents angiotensin-converting enzyme inhibitors and angiotensin receptor blockers also effectively inhibit NADPH oxidase activation. Similarly, the cholesterol-lowering agents, statins, have been shown to attenuate NADPH oxidase activation. Although, antioxidants act to scavenge the reactive oxygen species produced by these enzymes, their effectiveness is limited. Targeting NADPH homologues may have a distinct advantage over current therapies because it would specifically prevent the pathophysiological formation of reactive oxygen species that contributes to hypertension.     

Allopurinol modulates reactive oxygen species generation and Ca2+ overload in ischemia-reperfused heart and hypoxia-reoxygenated cardiomyocytes

Myocardial oxidative stress and Ca2+ overload induced by ischemia-reperfusion may be involved in the development and progression of myocardial dysfunction in heart failure. Xanthine oxidase, which is capable of producing reactive oxygen species, is considered as a culprit regarding ischemia-reperfusion injury of cardiomyocytes. Even though inhibition of xanthine oxidase by allopurinol in failing hearts improves cardiac performance, the regulatory mechanisms are not known in detail. We therefore hypothesized that allopurinol may prevent the xanthine oxidase-induced reactive oxygen species production and Ca2+ overload, leading to decreased calcium-responsive signaling in myocardial dysfunction. Allopurinol reversed the increased xanthine oxidase activity in ischemia-reperfusion injury of neonatal rat hearts. Hypoxia-reoxygenation injury, which simulates ischemia-reperfusion injury, of neonatal rat cardiomyocytes resulted in activation of xanthine oxidase relative to that of the control, indicating that intracellular xanthine oxidase exists in neonatal rat cardiomyocytes and that hypoxia-reoxygenation induces xanthine oxidase activity. Allopurinol (10 microM) treatment suppressed xanthine oxidase activity induced by hypoxia-reoxygenation injury and the production of reactive oxygen species. Allopurinol also decreased the concentration of intracellular Ca2+ increased by enhanced xanthine oxidase activity. Enhanced xanthine oxidase activity resulted in decreased expression of protein kinase C and sarcoendoplasmic reticulum calcium ATPase and increased the phosphorylation of extracellular signal-regulated protein kinase and p38 kinase. Xanthine oxidase activity was increased in both ischemia-reperfusion-injured rat hearts and hypoxia-reoxygenation-injured cardiomyocytes, leading to reactive oxygen species production and intracellular Ca2+ overload through mechanisms involving p38 kinase and extracellular signal-regulated protein kinase (ERK) via sarcoendoplasmic reticulum calcium ATPase (SERCA) and protein kinase C (PKC). Xanthine oxidase inhibition with allopurinol modulates reactive oxygen species production and intracellular Ca2+ overload in hypoxia-reoxygenation-injured neonatal rat cardiomyocytes.     

Benidipine, a dihydropyridine-calcium channel blocker, inhibits lysophosphatidylcholine-induced endothelial injury via stimulation of nitric oxide release.

Benidipine hydrochloride (benidipine), which is a long-lasting dihydropyridine calcium channel blocker, exerts antihypertensive action via inhibition of Ca(2+) influx through L-type voltage-dependent calcium channels. In addition, benidipine is shown to restore endothelial function. However, the mechanisms whereby benidipine has protective effects on endothelium are poorly defined. Nitric oxide (NO), which is produced by endothelial NO synthase (eNOS), plays important roles in endothelial function. In this study, we examined effects of benidipine on NO production from human umbilical vein endothelial cells. Benidipine (0.3-10 microM) augmented eNOS expression and total eNOS enzymatic activities. Benidipine also promoted the production of NO and the accumulation of cGMP, a second messenger of NO. Lysophosphatidylcholine (lysoPC), a component of oxidized low-density lipoproteins, induced caspase-3 activation followed by apoptosis of endothelial cells. Benidipine (0.3-10 microM) prevented lysoPC-induced caspase-3 activation, which was canceled by Nomega-nitro-L-arginine-methyl ester (L-NAME) (250-2500 microM), an inhibitor of NOS. Moreover, diethylenetetraamine NONOate (30-100 microM), a NO donor, inhibited the caspase-3 activation. These results suggested that the increase in NO production by benidipine might be involved in the inhibition of caspase induction. The direct enhancement of endothelial NO release by benidipine may be in part responsible for amelioration of endothelial dysfunction.     

Pharmacological, pharmacokinetic, and clinical properties of benidipine hydrochloride, a novel, long-acting calcium channel blocker

Benidipine is a dihydropyridine-derived calcium channel blocker developed in Japan, with several unique mechanisms of action, that is, triple calcium channels (L, N, and T) blocking action with a membrane approach. Benidipine has relatively high vascular selectivity and is expected to show protective effects on vascular endothelial cells. Renal protective effects of benidipine also have been shown in several basic and clinical studies. Moreover, anti-oxidative action and enhancing nitric oxide production have been noted with this drug, following its cardio-protective effects in patients with ischemic heart diseases. In fact, benidipine exerted a better prognostic effect than other calcium channel blockers in the therapy for patients with vasospastic angina. In addition, benidipine showed reliable antihypertensive, renoprotective effects if used in combination with angiotensin II type 1 receptor blockers (ARBs) when adequate anti-hypertensive effects are not achieved by ARBs alone, indicating that benidipine is an useful calcium channel blocker in combination therapy for hypertension. Benidipine was launched on the Japanese market 14 years ago, but few severe side effects have been reported, suggesting that this is a drug with established safety and long-acting pharmacological effects.     

Endothelin and oxidative stress in the vascular system

Both endothelin(ET)-1 and oxidative stress have been the subjects of intense investigation within the cardiovascular field over the past decade and a half, yet little is known about the precise relationship between these important modulators of vascular function. There is a firm evidence that ET-1 can stimulate the production of superoxide via NADPH oxidase activation, and at the same time, reactive oxygen species appear to stimulate ET-1 production. What is less clear is how these changes participate in the pathogenesis of vascular dysfunction. There is mixed evidence on whether oxidative stress plays a role in ET-dependent hypertension, however, a specific influence of ET-induced oxidative stress to reduce vascular reactivity is more convincing. The current review summarizes recent investigations into the relationship between ET-1 and oxidative stress and highlights several areas that require further investigation.     

Effects of benidipine hydrochloride (Coniel®), a new calcium antagonist,on the cardiac output,regional blood flow and vascular resistance in conscious,spontaneously hypertensive rats

Benidipine hydrochloride is a calcium antagonist with a 1,4-dihydropyridine derivative structure, and exhibits long-lasting antihypertensive effects by inhibiting the voltagedependent Ca²⁺ channels. This study was undertaken to examine the effect of benidipine on central haemodynamics and regional blood flow (RBF) after intravenous administration of benidipine in conscious, spontaneously hypertensive rats. The microsphere method was used to measure cardiac output and RBF before and after the drug administration, using microspheres labelled with ⁵⁷Co and ⁵¹Cr. Thirty minutes after the intravenous administration of benidipine (3 μg kg^?1), the mean arterial pressure fell by 15% without significantly increasing the heart rate. The cardiac output increased by 41% and the systemic resistance decreased by 39%. Benidipine significantly increased RBF by 37,35, and 22% in kidney, heart, and small intestine, respectively, and decreased vascular resistance by 38, 38, and 32%, respectively. We concluded that benidipine reduced blood pressure by increasing RBF in the kidney and heart, while keeping RBF in other organs at a normal level. These results will provide a fundamental basis in support of the clinical benefits of benidipine for hypertensive patients, particularly those with renal failure.     

Endothelins and NADPH oxidases in the cardiovascular system

1. The endothelin (ET) system and NADPH oxidase play important roles in the regulation of cardiovascular function, as well as in the pathogenesis of hypertension and other cardiovascular diseases. 2. Endothelins activate NADPH oxidases and thereby increase superoxide production, resulting in oxidative stress and cardiovascular dysfunction. Thus, NADPH oxidases may mediate the role of endothelins in some cardiovascular diseases. However, the role of reactive oxygen species (ROS) in mediating ET-induced vasoconstriction and cardiovascular disease remains under debate, as evidenced by conflicting reports from different research teams. Conversely, activation of NADPH oxidase can stimulate ET secretion via ROS generation, which further enhances the cardiovascular effects of NADPH oxidase. However, little is known about how ROS activate the endothelin system. It seems that the relationship between ET-1 and ROS may vary with cardiovascular disorders. 3. Endothelins activate NADPH oxidase via the ET receptor-proline-rich tyrosine kinase-2 (Pyk2)-Rac1 pathway. Rac1 is an important regulator of NADPH oxidase. There is ample evidence supporting direct stimulation by Rac1 of NADPH oxidase activity. In addition, Rac1-induced cardiomyocyte hypertrophy is mediated by the generation of ROS.     

Suppressing renal NADPH oxidase to treat diabetic nephropathy

Renal nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase is an important source of oxidative stress and its expression is enhanced in the glomerulus and distal tubules of diabetic nephropathy. High glucose-induced protein kinase C signalling or renal angiotensin II signalling increases the membrane translocation of cytosolic component p47phox. NADPH oxidase-derived reactive oxygen species (ROS) in the podocytes damage the glomerular basement membrane and the slit diaphragm causing proteinuria, and mesangial and glomerular endothelial NADPH oxidase increase TGF-β and cause collagen and fibronectin accumulation. Tubular NADPH oxidase stimulated by angiotensin II or aldosterone contributes to sodium retention and to tubulointerstitial damage. Thus, inhibition of the renal renin–angiotensin II–aldosterone system with angiotensin-converting enzyme inhibitor, angiotensin II type 1 receptor blocker or selective aldosterone inhibitor indirectly suppresses NADPH oxidase reducing renal ROS, proteinuria and glomerulosclerosis. Statins are also effective in blocking the membrane translocation of Rac, especially in diabetes with hypercholesterolemia where ROS is produced by the intrinsic NADPH oxidase and by the activated macrophages. A medical herb, picrorhiza, inhibits the membrane translocation of p47phox, is a specific inhibitor of NADPH oxidase and, more so than superoxide dismutase mimetics, may be a promising strategy for the treatment of diabetic nephropathy.     

Suppressing renal NADPH oxidase to treat diabetic nephropathy

Renal nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase is an important source of oxidative stress and its expression is enhanced in the glomerulus and distal tubules of diabetic nephropathy. High glucose-induced protein kinase C signalling or renal angiotensin II signalling increases the membrane translocation of cytosolic component p47phox. NADPH oxidase-derived reactive oxygen species (ROS) in the podocytes damage the glomerular basement membrane and the slit diaphragm causing proteinuria, and mesangial and glomerular endothelial NADPH oxidase increase TGF-beta and cause collagen and fibronectin accumulation. Tubular NADPH oxidase stimulated by angiotensin II or aldosterone contributes to sodium retention and to tubulointerstitial damage. Thus, inhibition of the renal renin-angiotensin II-aldosterone system with angiotensin-converting enzyme inhibitor, angiotensin II type 1 receptor blocker or selective aldosterone inhibitor indirectly suppresses NADPH oxidase reducing renal ROS, proteinuria and glomerulosclerosis. Statins are also effective in blocking the membrane translocation of Rac, especially in diabetes with hypercholesterolemia where ROS is produced by the intrinsic NADPH oxidase and by the activated macrophages. A medical herb, picrorhiza, inhibits the membrane translocation of p47phox, is a specific inhibitor of NADPH oxidase and, more so than superoxide dismutase mimetics, may be a promising strategy for the treatment of diabetic nephropathy.     

Relationship of intracellular calcium and oxygen radicals to Cisplatin-related renal cell injury

We investigated the involvement of reactive oxygen species (ROS) and intracellular calcium in nephrotoxicity related to an antitumor agent, cisplatin. In this study, we employed cultured renal epithelial cells (LLC-PK1). Cisplatin at 500 microM significantly increased the production of ROS 5 h and caused cell injury. This agent significantly increased the intracellular calcium level ([Ca2+]i) in a dose-dependent manner 1 h or more after exposure. DPPD (N,N'-diphenyl-p-phenylenediamine), an antioxidant, inhibited a cisplatin-related increase in active oxygen production and cell injury but did not inhibit an early increase in the [Ca2+]i level. An intracellular calcium-chelating compound BAPTA-AM (1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester) inhibited an increase in ROS production and cell injury induced by cisplatin. Furthermore, BAPTA-AM suppressed the rise of [Ca2+]i level in 1 h after exposure; however, an extracellular calcium chelator EGTA and a calcium antagonist nicardipine did not inhibit the rise in [Ca2+]i level in the early phase. An NADPH oxidase inhibitor inhibited a cisplatin-related increase in ROS production and cell disorder. These results suggest that cisplatin-related calcium release from the site of intracellular calcium storage in the early phase causes oxidative stress in renal tubular epithelial cells. Cisplatin may increase the intracellular production of ROS via NADPH oxidase.     

The role of the methoxyphenol apocynin, a vascular NADPH oxidase inhibitor, as a chemopreventative agent in the potential treatment of cardiovascular diseases

Oxidative stress has been linked to the origin and progression of cardiovascular diseases. Nicotinamide adenine dinucleotide phosphate, reduced form (NADPH) oxidase is a multi-component, NADPH-dependent enzyme that generates superoxide anion in the presence of molecular oxygen. The enzyme has been identified and characterized in all 3 vascular wall cell types and represents the major source of reactive oxygen species (ROS) production in the vascular wall. Inhibition of NADPH oxidase activation appears to suppress the sequence of cellular events that leads to a variety of cardiovascular diseases, including atherosclerosis. The naturally occurring methoxyphenol apocynin has been found to inhibit NADPH oxidase upon activation by peroxidases (e.g. soybean peroxidase, myeloperoxidase) or ROS under mild reaction conditions. Upon peroxidase-catalyzed activation, the apocynin oxidation products act to block the assembly and activation of NADPH oxidase. Although the mechanism of inhibition of NADPH oxidase remains largely unknown, apocynin's high effectiveness and low toxicity makes it a promising lead compound in the development of new therapeutic agents for cardiovascular diseases.     

A commercial mixture of the brominated flame retardant pentabrominated diphenyl ether (DE-71) induces respiratory burst in human neutrophil granulocytes in vitro.

Polybrominated diphenyl ethers (PBDEs) are widely used brominated flame retardants (BFRs), which have become ubiquitous in the environment. This study investigates the effects of the pentabrominated diphenyl ether mixture, DE-71, on human neutrophil granulocytes in vitro. DE-71 enhanced production of reactive oxygen species (ROS) in a concentration-dependent manner measured as lucigenin-amplified chemiluminescence. Octabrominated diphenyl ether (OBDE), decabrominated diphenyl ether (DBDE), and the non-brominated diphenyl ether did not induce ROS formation at the concentrations tested. DPI (4 microM), an inhibitor of the NADPH oxidase completely inhibited DE-71 induced ROS formation, highlighting a role for NADPH oxidase activation. The protein kinase C inhibitor BIM (0.25 microM) and the selective chelator of intracellular calcium, BAPTA-AM (5 microM), also inhibited NADPH oxidase activation, indicating a calcium-dependent activation of PKC. ROS formation was also inhibited by the tyrosine kinase inhibitor tyrphostin (1 microM), the phospholipase C inhibitor ET-18-OCH3 (5 microM), and the phosphatidylinositol-3 kinase inhibitor LY294002 (25 microM). Alterations in intracellular calcium were measured using fura-2/AM, and a significant increase was measured after exposure to DE-71 both with and without extracellular calcium. The tetra brominated compound BDE-47 also enhanced ROS formation in a concentration dependent manner. The combination of DE-71 with the bacteria-derived N-formyl peptide fMLP and PCB153 induced an additive effect in the lucigenin assay. We suggest that tyrosine kinase mediated activation of PI3K could result in enhanced activation of calcium-dependent PKC by enhanced PLC activity, followed by intracellular calcium release leading to ROS formation in neutrophil granulocytes.     

The effect of a brominated flame retardant, tetrabromobisphenol-A, on free radical formation in human neutrophil granulocytes: the involvement of the MAP kinase pathway and protein kinase C.

This study investigates the effects of one of the most frequently used brominated flame-retardants (BFR), tetrabromobisphenol-A (TBBPA), on formation of reactive oxygen species (ROS) and calcium levels in human neutrophil granulocytes. TBBPA enhanced ROS production in a concentration-depended manner (1-12 microM), measured as 2,7-dichlorofluorescein diacetate amplified (DCF) fluorescence. The results on ROS production by TBBPA was confirmed by lucigenin-amplified chemiluminescence. The TBBPA induced formation of ROS was due to activation of respiratory burst, as shown by the NADPH oxidase inhibitor DPI (10 microM). TBBPA induced activation of respiratory burst was also inhibited by the MEK 1/2 inhibitor U0126 (10 microM), the PKC inhibitor BIM (0.25 microM), and the tyrosine kinase inhibitor erbstatin-A (25 microM). We also found a small reduction in ROS formation in the absence of extracellular calcium and when verapamil was added. The phosphorylation of ERK 1/2 was confirmed by Western blotting. TBBPA also induced a concentration dependent increase in intracellular free calcium measured with Fura-2/AM. We suggest that exposure of human neutrophil granulocytes to the brominated flame retardant TBBPA leads to an activation of the NADPH oxidase primarily by an ERK 1/2 stimulated pathway. The data also show that PKC, calcium, and tyrosine kinases may be involved in the activation.     

Prevention of macrophage adhesion molecule-1 (Mac-1)-dependent neutrophil firm adhesion by taxifolin through impairment of protein kinase-dependent NADPH oxidase activation and antagonism of G protein-mediated calcium influx

Taxifolin has been reported to down-regulate the expression of intercellular adhesion molecule-1 (ICAM-1), a receptor-mediating firm adhesion with beta2 integrin (e.g., Mac-1) expressed on leukocytes. To evaluate whether taxifolin could modulate Mac-1-dependent firm adhesion by neutrophils, and the possible mechanism(s) underlying its anti-inflammatory action, its effects on N-formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol-12-myristate-13-acetate (PMA)-activated peripheral human neutrophils were studied. Pretreatment with taxifolin (1-100 microM) concentration-dependently diminished fMLP- or (PMA)-induced Mac-1-dependent firm adhesion and upexpression of surface Mac-1. Mobilisation of intracellular calcium and production of reactive oxygen species (ROS) signal the upexpression of Mac-1 and firm adhesion by neutrophils. Taxifolin impeded the calcium influx induced by fMLP (a receptor-mediated activator) or AlF(4)(-) (a G protein-mediated activator). Taxifolin also effectively inhibited the fMLP- or PMA-induced ROS production with 50% inhibitory concentration (IC(50)) less than 10microM, possibly through impairing the activation of NADPH oxidase, a major ROS-generating enzyme in neutrophils, by restricting the activation of p38 mitogen-activated protein kinase (p38 MAPK) and protein kinase C (PKC). In conclusion, we propose that impairment of ROS production by NADPH oxidase through interfering with p38 MAPK- and/or PKC-dependent signals, and antagonism of G protein-mediated calcium influx may account for the inhibition of Mac-1-dependent neutrophil firm adhesion that confers taxifolin the anti-inflammatory activity.     

Combating oxidative stress in vascular disease: NADPH oxidases as therapeutic targets

NADPH oxidases are a family of enzymes that generate reactive oxygen species (ROS). The NOX1 (NADPH oxidase 1) and NOX2 oxidases are the major sources of ROS in the artery wall in conditions such as hypertension, hypercholesterolaemia, diabetes and ageing, and so they are important contributors to the oxidative stress, endothelial dysfunction and vascular inflammation that underlies arterial remodelling and atherogenesis. In this Review, we advance the concept that compared to the use of conventional antioxidants, inhibiting NOX1 and NOX2 oxidases is a superior approach for combating oxidative stress. We briefly describe some common and emerging putative NADPH oxidase inhibitors. In addition, we highlight the crucial role of the NADPH oxidase regulatory subunit, p47phox, in the activity of vascular NOX1 and NOX2 oxidases, and suggest how a better understanding of its specific molecular interactions may enable the development of novel isoform-selective drugs to prevent or treat cardiovascular diseases.     

Effect of gender and sex hormones on vascular oxidative stress

1. It is well documented that the incidence and severity of several vascular diseases, such as hypertension, atherosclerosis and stroke, are lower in premenopausal women than men of similar age and post-menopausal women. The mechanisms responsible for gender differences in the incidence and severity of vascular disease are not well understood. However, emerging evidence suggests that sex hormone-dependent differences in vascular oxidative stress may play an important role. The aim of the present brief review is to provide an insight into the effect of gender and sex hormones on vascular oxidative stress. 2. When production of reactive oxygen species (ROS) is enhanced and/or their metabolism by anti-oxidant enzymes is impaired, a condition known as 'oxidative stress' can develop. Oxidative stress is believed to play an important role in both the initiation and progression of a variety of vascular diseases, including hypertension and atherosclerosis. NADPH oxidases are believed to be the major source of vascular ROS. Moreover, excessive production of ROS by NADPH oxidases has been linked to the development of vascular oxidative stress. 3. Increasing evidence suggests that levels of vascular ROS may be lower in women than men during health and disease. Indeed, the activity and expression of vascular NADPH oxidase is lower in female versus male animals under healthy, hypertensive and atherosclerotic conditions. 4. Gonadal sex hormones may play an important role in the regulation of vascular oxidative stress. For example, oestrogens, which are present in highest levels in premenopausal women, have been reported to lower vascular oxidative stress by modulating the expression and function of NADPH oxidases, as well as anti-oxidant enzymes. 5. Further studies are needed to clarify whether lower vascular oxidative stress in women in fact protects against the initiation and development of vascular disease and to further define the roles of gonadal sex hormones in such an effect. Knowledge gained from these studies may potentially lead to advances in the clinical diagnosis and treatment of vascular disease in both genders.     

Prevention of hypertension and renal dysfunction in Dahl rats by alpha-tocopherol

Although hypertension is a risk factor for the development of end-stage renal disease, not all hypertensive patients progress to develop renal dysfunction. The mechanisms underlying hypertensive nephropathy are poorly understood. The authors have recently shown that the development of hypertension and renal dysfunction is accompanied by an accumulation of partially reduced oxygen and its derivatives, known collectively as reactive oxygen species. In the present study, the effect of a lipid-soluble antioxidant on the development of salt-dependent hypertensive nephropathy was evaluated in the Dahl rat. It was found that a high-salt diet (8% NaCl) led to the development of hypertension, increased renal oxidative stress (superoxide production and 8-epi-prostaglandin F2alpha), and decreased glomerular filtration rate and renal plasma flow in the Dahl salt-sensitive (DSS) rat, and that these adverse effects of salt were prevented by supplementing the high-salt diet with 1000 U/kg chow of alpha-tocopherol. It is well known that urinary cyclic guanosine monophosphate (cGMP) levels are lower in hypertensive DSS rats than in Dahl salt-resistant (DSR) rats on a high-salt diet. Most surprisingly, when supplemented with alpha-tocopherol, DSS rats on an 8% NaCl diet were able to excrete as much cGMP as DSR rats. Taken together, these findings suggest that, in the DSS rat, salt-dependent hypertensive nephropathy and decreased nitric oxide bioavailability are associated with increased oxidative stress, and that antioxidants can preclude these adverse effects of salt feeding, and consequently, prevent salt-dependent hypertension and nephropathy.