Functional effect of the p22phox -930A/G polymorphism on p22phox expression and NADPH oxidase activity in hypertension

Oxidative stress induced by superoxide is implicated in hypertension. NADPH oxidase is the main source of superoxide in phagocytic and vascular cells, and the p22phox subunit is involved in NADPH oxidase activation. Recently we reported an association of -930A/G polymorphism in the human p22phox gene promoter with hypertension. This study was designed to investigate the functional role of this polymorphism in hypertension. We thus investigated the relationships between the -930A/G polymorphism and p22phox expression and NADPH oxidase-mediated superoxide production in phagocytic cells from 70 patients with essential hypertension and 70 normotensive controls. Genotyping of the polymorphism was performed by restriction fragment length polymorphism. NADPH oxidase activity was determined by chemiluminescence assays, and p22phox mRNA and protein expression was measured by Northern and Western blotting, respectively. Compared with hypertensive subjects with the AA/AG genotype, hypertensive subjects with the GG genotype exhibited increased (P<0.05) phagocytic p22phox mRNA (1.26+/-0.06 arbitrary unit [AU] versus 0.99+/-0.03 AU) and protein levels (0.58+/-0.05 AU versus 0.34+/-0.04 AU) and enhanced NADPH oxidase activity (1998+/-181 counts/s versus 1322+/-112 counts/s). No differences in these parameters were observed among genotypes in normotensive cells. Transfection experiments on vascular smooth muscle cells showed that the A-to-G substitution of this polymorphism produced an increased reporter gene expression in hypertensive cells. Nitric oxide production, as assessed by measurement of serum nitric oxide metabolites, was lower in GG hypertensive subjects than in AA/AG hypertensive subjects. In conclusion, these results suggest that hypertensive subjects carrying the GG genotype of the p22phox -930A/G polymorphism are highly exposed to NADPH oxidase-mediated oxidative stress.     

RNA silencing in vivo reveals role of p22phox in rat angiotensin slow pressor response

The angiotensin II (Ang II) slow-pressor response entails an increase in mean arterial pressure and reactive oxygen species. We used double-stranded interfering RNAs (siRNAs) in Sprague Dawley rats in vivo to test the hypothesis that an increase in the p22phox component of NADPH oxidase is required for this response. Reactive oxygen species were assessed from excretion of 8-isoprostane prostaglandin F2alpha and blood pressure by telemetry. Two siRNA sequences to p22phox (sip22phox) reduced mRNA >85% in cultured vascular smooth muscle cells. Rats received rapid (10 second) IV injections (50 to 100 microg) of 1 of 2 different sip22phox, control siRNA, or vehicle (TransIt in saline) during 14 day SC infusions of Ang II (200 ng.kg(-1).min(-1)) or sham infusions. In both groups, sip22phox, relative to control siRNA, led to significant (P<0.001; approximately 50%) reductions in expression of p22phox mRNA and protein and of NADPH oxidase activity in the kidney cortex. In Ang II-infused rats, sip22phox decreased protein expression for Nox-1, -2, and -4 but increased p47phox. Three days after sip22phox, conscious rats infused with Ang II had a reduced excretion of 8-isoprostane (10+/-1 versus 19+/-2 pg.24 h(-1); P<0.01) and a reduced mean arterial pressure (142+/-5 versus 168+/-4 mm Hg; P<0.005). An increase in p22phox is required for increased renal NADPH oxidase activity, expression of Nox proteins and oxidative stress, and contributes < or =50% to hypertension during an Ang II slow-pressor response.     

Role of extracellular superoxide dismutase in the mouse angiotensin slow pressor response

Low rates of angiotensin II (Ang II) infusion raise blood pressure, renal vascular resistance (RVR), NADPH oxidase activity, and superoxide. We tested the hypothesis that these effects are ameliorated by extracellular superoxide dismutase (EC-SOD). EC-SOD knockout (-/-) and wild type (+/+) mice were equipped with blood pressure telemeters and infused subcutaneously with Ang II (400 ng/kg per minute) or vehicle for 2 weeks. During vehicle infusion, EC-SOD -/- mice had significantly (P<0.05) higher MAP (+/+: 107+/-3 mm Hg versus -/-: 114+/-2 mm Hg; n=11 to 14), RVR, lipid peroxidation, renal cortical p22(phox) expression, and NADPH oxidase activity. Ang II infusion in EC-SOD +/+ mice significantly (P<0.05) increased MAP, RVR, p22(phox), NADPH oxidase activity, and lipid peroxidation. Ang II reduced SOD activity in plasma, aorta, and kidney accompanied by reduced renal EC-SOD expression. During Ang II infusion, both groups had similar values for MAP (+/+ Ang II: 125+/-3 versus -/- Ang II: 124+/-3 mmHg; P value not significant), RVR, NADPH oxidase activity, and lipid peroxidation. SOD activity in the kidneys of Ang II-infused mice was paradoxically higher in EC-SOD -/- mice (+/+: 8.8+/-1.2 U/mg protein(-1) versus -/-: 13.7+/-1.6 U/mg protein(-1); P<0.05) accompanied by a significant upregulation of mRNA and protein for Cu/Zn-SOD. In conclusion, EC-SOD protects normal mice against oxidative stress by attenuating renal p22(phox) expression, NADPH oxidase activation, and the accompanying renal vasoconstriction and hypertension. However, during an Ang II slow pressor response, renal EC-SOD expression is reduced and, in its absence, renal Cu/Zn-SOD is upregulated and may prevent excessive Ang II-induced renal oxidative stress, renal vasoconstriction, and hypertension.     

Angiotensin II and oxidative stress in Dahl Salt-sensitive rat with heart failure

Reactive oxygen species have an important pathogenic role in organ damage. We investigated the role of oxidative stress via nicotinamide adenine dinucleotide phosphate (NAD[P]H) oxidase in the kidney of the Dahl salt-sensitive (DS) rats with heart failure (DSHF). Eleven-week-old DS rats fed an 8%-NaCl diet received either vehicle or imidapril (1 mg/kg per day) for 7 weeks. The renal expression of the NAD(P)H oxidase p47phox and endothelial NO synthase were evaluated. In DSHF rats, associated with increased renal angiotensin II, mRNA and protein expression of NAD(P)H oxidase p47phox were enhanced with an increase in renal lipid peroxidation production (0.33+/-0.03 versus 0.22+/-0.01 nmol/mg protein, P<0.05) and urinary excretion of hydrogen peroxide (26.9+/-6.6 versus 9.5+/-2.1 U/mg creatinine, P<0.01) compared with levels in Dahl salt-resistant rats. The endothelial NO synthase expression was decreased in the kidney. Treatment with imidapril reduced renal angiotensin II and NAD(P)H oxidase expression and the oxidative products (kidney lipid peroxidation product: 0.16+/-0.02, P<0.001; urinary hydrogen peroxide: 3.1+/-0.2, P<0.01 versus DSHF rats). Imidapril significantly decreased albuminuria and reduced glomerulosclerosis without changes in the blood pressure. In conclusion, DSHF rats showed increased oxidative stress in the kidney via NAD(P)H oxidase. Blockade of local angiotensin II with subpressor dose of imidapril inhibited NAD(P)H oxidase and prevented renal damage.     

Hyperactivity and altered mRNA isoform expression of the Cl(-)/HCO(3)(-) anion-exchanger in the hypertrophied myocardium

OBJECTIVE: The aim was to examine the regulation of the cardiac Na(+)-independent Cl(-)/HCO(3)(-) exchanger (AE) mRNA isoform expression in association to the enhanced AE activity in the hypertrophied myocardium of spontaneously hypertensive rats (SHR). METHODS: AE activity was determined by the initial rates of the pH(i) recovery from imposed intracellular alkalinization (forward mode of exchange) and the pH(i) rise induced by Cl(-) removal (reverse mode). Net HCO(3)(-) (J(HCO(3)(-))) efflux and influx were respectively determined. AE mRNA isoforms were analyzed by Northern blot with specific probes to detect AE1, AE2 and AE3 mRNAs. RESULTS: Initial J(HCO(3)(-)) efflux after imposed alkaline load (pH(i) congruent with 7.5) was higher in SHR than in normotensive WKY rats (3.01+/-0.33, n=7, vs. 0.64+/-0.29 mM/min, n=5, P<0.05). J(HCO(3)(-)) influx induced by Cl(-) deprivation was also increased in SHR, 4.24+/-0.56 mM/min (n=10) versus 2.31+/-0.26 (n=10, P<0.05) in WKY. In arbitrary units, the 4.1-kb AE1 mRNA decreased in SHR (0.15+/-0.01, n=7) compared to WKY (0.29+/-0.06, n=7, P<0.05), whereas the 3.6-kb mRNA did not change. AE2 mRNAs were similarly expressed in WKY and SHR. Cardiac specific AE3 (cAE3) mRNA decreased in SHR, 1.10+/-0.16 arbitrary units (n=8) versus 1.79+/-0.24, (n=8, P<0.05) in WKY. Full length AE3 (flAE3) mRNA increased from 0.69+/-0.06 (WKY, n=8) to 1.25+/-0.19 arbitrary units in SHR (n=8, P<0.05). CONCLUSIONS: The increase in flAE3 mRNA expression in cardiac tissue from the SHR is an adaptive change of the hypertrophied myocardium that might be in connection with the increased activity of the AE.     

p47(phox) is required for afferent arteriolar contractile responses to angiotensin II and perfusion pressure in mice

Myogenic and angiotensin contractions of afferent arterioles generate reactive oxygen species. Resistance vessels express neutrophil oxidase-2 and -4. Angiotensin II activates p47(phox)/neutrophil oxidase-2, whereas it downregulates NOX-4. Therefore, we tested the hypothesis that p47(phox) enhances afferent arteriolar angiotensin contractions. Angiotensin II infusion in p47(phox) +/+ but not -/- mice increased renal cortical NADPH oxidase activity (7±1-12±1 [P<0.01] versus 5±1-7±1 10(3) · RLU · min(-1) · μg protein(-1) [P value not significant]), mean arterial pressure (77±2-91±2 [P<0.005] versus 74±2-77±1 mm Hg [P value not significant]), and renal vascular resistance (7.5±0.4-10.1±0.7 [P<0.01] versus 7.9±0.4-8.3±0.4 mm Hg/mL · min(-1) · gram kidney weight(-1) [P value not significant]). Afferent arterioles from p47(phox) -/- mice had a lesser myogenic response (3.1±0.4 versus 1.4±0.2 dynes · cm(-1) · mm Hg(-1); P<0.02) and a lesser (P<0.05) contraction to 10(-6) M angiotensin II (diameter change +/+: 9.3±0.2-3.4±0.6 μm versus -/-: 9.9±0.6-7.5±0.4 μm). Angiotensin and increased perfusion pressure generated significantly (P<0.05) more reactive oxygen species in p47(phox) +/+ than -/- arterioles. Angiotensin II infusion increased the maximum responsiveness of afferent arterioles from p47(phox) +/+ mice to 10(-6) M angiotensin II yet decreased the response in p47(phox) -/- mice. The angiotensin infusion increased the sensitivity to angiotensin II only in p47(phox) +/+ mice. We conclude that p47(phox) is required to enhance renal NADPH oxidase activity and basal afferent arteriolar myogenic and angiotensin II contractions and to switch afferent arteriolar tachyphylaxis to sensitization to angiotensin during a prolonged angiotensin infusion. These effects likely contribute to hypertension and renal vasoconstriction during infusion of angiotensin II.     

Increased myocardial NADPH oxidase activity in human heart failure

OBJECTIVES: This study was designed to investigate whether nicotinamide adenine dinucleotide 3-phosphate (reduced form) (NADPH) oxidase is expressed in the human heart and whether it contributes to reactive oxygen species (ROS) production in heart failure. BACKGROUND: A phagocyte-type NADPH oxidase complex is a major source of ROS in the vasculature and is implicated in the pathophysiology of hypertension and atherosclerosis. An increase in myocardial oxidative stress due to excessive production of ROS may be involved in the pathophysiology of congestive heart failure. Recent studies have suggested an important role for myocardial NADPH oxidase in experimental models of cardiac disease. However, it is unknown whether NADPH oxidase is expressed in the human myocardium or if it has any role in human heart failure. METHODS: Myocardium of explanted nonfailing (n = 9) and end-stage failing (n = 13) hearts was studied for the expression of NADPH oxidase subunits and oxidase activity. RESULTS: The NADPH oxidase subunits p22(phox), gp91(phox), p67(phox), and p47(phox) were all expressed at messenger ribonucleic acid and protein level in cardiomyocytes of both nonfailing and failing hearts. NADPH oxidase activity was significantly increased in end-stage failing versus nonfailing myocardium (5.86 +/- 0.41 vs. 3.72 +/- 0.39 arbitrary units; p < 0.01). The overall level of oxidase subunit expression was unaltered in failing compared with nonfailing hearts. However, there was increased translocation of the regulatory subunit, p47(phox), to myocyte membranes in failing myocardium. CONCLUSIONS: This is the first report of the presence of NADPH oxidase in human myocardium. The increase in NADPH oxidase activity in the failing heart may be important in the pathophysiology of cardiac dysfunction by contributing to increased oxidative stress.     

Critical role of the NAD(P)H oxidase subunit p47phox for left ventricular remodeling/dysfunction and survival after myocardial infarction

Accumulating evidence suggests a critical role of increased reactive oxygen species production for left ventricular (LV) remodeling and dysfunction after myocardial infarction (MI). An increased myocardial activity of the NAD(P)H oxidase, a major oxidant enzyme system, has been observed in human heart failure; however, the role of the NAD(P)H oxidase for LV remodeling and dysfunction after MI remains to be determined. MI was induced in wild-type (WT) mice (n=46) and mice lacking the cytosolic NAD(P)H oxidase component p47(phox) (p47(phox)-/- mice) (n=32). Infarct size was similar among the groups. NAD(P)H oxidase activity was markedly increased in remote LV myocardium of WT mice after MI as compared with sham-operated mice (83+/-8 versus 16.7+/-3.5 nmol of O(2)(-) x microg(-1) x min(-1); P<0.01) but not in p47(phox)-/- mice after MI (13.5+/-3.6 versus 15.5+/-3.5 nmol of O(2)(-) x microg(-1) x min(-1)), as assessed by electron-spin resonance spectroscopy using the spin probe CP-H. Furthermore, increased myocardial xanthine oxidase activity was observed in WT, but not in p47(phox)-/- mice after MI, suggesting NAD(P)H oxidase-dependent xanthine oxidase activation. Myocardial reactive oxygen species production was increased in WT mice, but not in p47(phox)-/- mice, after MI. LV cavity dilatation and dysfunction 4 weeks after MI were markedly attenuated in p47(phox)-/- mice as compared with WT mice, as assessed by echocardiography (LV end-diastolic diameter: 4.5+/-0.2 versus 6.3+/-0.3 mm, P<0.01; LV ejection fraction, 35.8+/-2.5 versus 22.6+/-4.4%, P<0.05). Furthermore, cardiomyocyte hypertrophy, apoptosis, and interstitial fibrosis were substantially reduced in p47(phox)-/- mice as compared with WT mice. Importantly, the survival rate was markedly higher in p47(phox)-/- mice as compared with WT mice after MI (72% versus 48%; P<0.05). These results suggest a pivotal role of NAD(P)H oxidase activation and its subunit p47(phox) for LV remodeling/dysfunction and survival after MI. The NAD(P)H oxidase system represents therefore a potential novel therapeutic target to prevent cardiac failure after MI.     

Interaction of angiotensin II type 1 and D5 dopamine receptors in renal proximal tubule cells

Angiotensin II type 1 (AT1) receptor and D1 and D3 dopamine receptors directly interact in renal proximal tubule (RPT) cells from normotensive Wistar-Kyoto rats (WKY). There is indirect evidence for a D5 and AT1 receptor interaction in WKY and spontaneously hypertensive rats (SHR). Therefore, we sought direct evidence of an interaction between AT1 and D5 receptors in RPT cells. D5 and AT1 receptors colocalized in WKY cells. Angiotensin II decreased D5 receptors in WKY cells in a time- and concentration-dependent manner (EC50=2.7x10(-9) M; t(1/2)=4.9 hours), effects that were blocked by an AT1 receptor antagonist (losartan). In SHR, angiotensin II (10(-8) M/24 hours) also decreased D5 receptors (0.96+/-0.08 versus 0.72+/-0.08; n=12) and to the same degree as in WKY cells (1.44+/-0.07 versus 0.92+/-0.08). However, basal D5 receptors were decreased in SHR RPT cells (SHR 0.96+/-0.08; WKY 1.44+/-0.07; n=12 per strain; P<0.05) and renal brush border membranes of SHR compared with WKY (SHR 0.54+/-0.16 versus WKY 1.46+/-0.10; n=5 per strain; P<0.05). Angiotensin II decreased AT1 receptor expression in WKY (1.00+/-0.04 versus 0.72+/-0.08; n=8; P<0.05) but increased it in SHR (0.96+/-0.04 versus 1.32+/-0.08; n=8; P<0.05). AT(1) and D5 receptors also interacted in vivo; renal D5 receptor protein was higher in mice lacking the AT1A receptor (AT1A-/-; 1.61+/-0.31; n=6) than in wild-type littermates used as controls (AT1A+/+; 0.81+/-0.08; n=6; P<0.05), and renal cortical AT1 receptor protein was higher in D5 receptor null mice than in wild-type littermates (1.18+/-0.08 versus 0.84+/-0.07; n=4; P<0.05). We conclude that D5 and AT1 receptors interact with each other. Altered interactions between AT1 and dopamine receptors may play a role in the pathogenesis of hypertension.     

全反式维甲酸对高血压大鼠心脏氧化应激水平的影响

目的:探讨全反式维甲酸(atRA)对高血压心脏还原型辅酶I氧化酶P22亚单位(p22phox)表达以及氧化应激水平的影响。方法:采用12周龄雄性自发性高血压大鼠(SHR)及其同源对照WKY大鼠,经腹腔注射at-RA,为期1月。分别采用免疫印迹、硫代巴比妥酸比色以及透射电镜技术测定atRA治疗后SHR心脏p22phox的表达、丙二醛(MDA)含量以及心肌超微结构情况。结果:与WKY对照组相比,SHR心脏组织中p22phox蛋白表达与MDA含量明显升高(P均<0.01)。而atRA治疗后SHR(低、高剂量atRA组)大鼠心脏组织中p22phox蛋白表达与MDA水平出现下调(P均<0.05),同时伴有心肌损伤减轻。结论:长期atRA治疗可降低SHR大鼠心脏组织中p22phox表达与MDA水平,提示atRA在高血压病中具有一定的抗氧化效应。     

Differential gene expression of NADPH oxidase (p22phox) and hemoxygenase-1 in patients with Type 2 diabetes and microangiopathy.

AIMS: While the downstream effects of increased reactive oxygen species (ROS) in the pathogenesis of diabetes were well studied, only a few studies have explored the cellular sources of ROS. We examined whether protection against oxidative stress is altered in patients with diabetes and microangiopathy by examining changes in NADPH oxidase (p22(phox)) and hemoxygenase-1 (HO-1) levels. METHODS: NADPH oxidase (p22(phox)) and HO-1 gene expression were probed by RT-PCR using leucocytes from patients with Type 2 diabetes without (n = 19) and with microangiopathy (n = 20) and non-diabetic subjects (n = 17). Levels of lipid peroxidation as measured by thiobarbituric reactive substances (TBARS) and protein carbonyl content (PCO) were determined by fluorimetric and spectrophotometric methods, respectively. RESULTS: p22(phox) gene expression (mean +/- SE) was significantly (P < 0.05) higher in diabetic patients with (0.99 +/- 0.04) and without microangiopathy (0.86 +/- 0.05) compared with control subjects (0.66 +/- 0.05). Consistent with the mRNA data, the p22(phox) protein expression and NADPH oxidase activity was also increased in cells from diabetic patients compared with control subjects. However, HO-1 gene expression was significantly (P < 0.05) lower in patients with (0.73 +/- 0.03) and without microangiopathy (0.85 +/- 0.02) compared with control subjects (1.06 +/- 0.03). The mean (+/- SE) levels of TBARS were significantly (P < 0.05) higher in diabetic patients with (14.36 +/- 1.3 nM/ml) and without microangiopathy (12.20 +/- 1.3 nM/ml) compared with control subjects (8.58 +/- 0.7 nM/ml). The protein carbonyl content was also significantly (P < 0.05) higher in diabetic patients with (1.02 +/- 0.04 nmol/mg protein) and without microangiopathy (0.84 +/- 0.06 nmol/mg protein) compared with control subjects (0.48 +/- 0.02 nmol/mg protein). In diabetic subjects, increased p22(phox) gene expression was negatively correlated with HO-1 and positively correlated with TBARS, PCO, HbA(1c) and diabetes duration. In contrast, HO-1 gene expression was correlated negatively with p22phox, TBARS, PCO, HbA(1c) and diabetes duration. CONCLUSION: Our results indicate that increased oxidative damage is seen in Asian Indians with Type 2 diabetes and microangiopathy and is associated with increased NADPH oxidase (p22(phox)) and decreased HO-1 gene expression.     

Creation of a genetic system for analysis of the phagocyte respiratory burst: high-level reconstitution of the NADPH oxidase in a nonhematopoietic system

The phagocyte nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase was functionally reconstituted in monkey kidney COS-7 cells by transfection of essential subunits, gp91(phox), p22(phox), p47(phox), and p67(phox). COS-7 cells express the essential small guanosine 5'-triphosphatase, Rac1. Transgenic COS-phox cells were capable of arachidonic acid-induced NADPH oxidase activity up to 80% of that of human neutrophils, and of phorbol myristate acetate (PMA)-induced activity up to 20% of that of neutrophils. Expression of all 4 phox components was required for enzyme activity, and enzyme activation was associated with membrane translocation of p47(phox), p67(phox), and Rac1. Expression of p47(phox) Ser303Ala/Ser304Ala or Ser379Ala phosphorylation-deficient mutants resulted in significantly impaired NAPDH oxidase activity, compared with expression of wild-type p47(phox) or the p47(phox) Ser303Glu/Ser304Glu phosphorylation mimic, suggesting that p47(phox) phosphorylation contributes to enzyme activity in the COS system, as is the case in neutrophils. Hence, COS-phox cells should be useful as a new whole-cell model that is both capable of high-level superoxide production and readily amenable to genetic manipulation for investigation of NADPH oxidase function. PMA-elicited superoxide production in COS-phox cells was regulated by activation of protein kinase C (PKC) and Rac. Although COS-7 cells differ from human neutrophils in PKC isoform expression, transient expression of major neutrophil isoforms in COS-phox cells did not increase PMA-induced superoxide production, suggesting that endogenous isoforms were not rate limiting. Val204 in p67(phox), previously shown to be required for NADPH oxidase activity under cell-free conditions, was found to be essential for superoxide production by intact COS-phox cells, on the basis of transfection studies using a p67(phox) (Val204Ala) mutant.     

p47phox-dependent NADPH oxidase regulates flow-induced vascular remodeling

Chronic alterations in blood flow elicit an adaptive response that tends to normalize shear stress, involving nitric oxide (NO) and matrix metalloproteinases (MMPs). To evaluate the role of NADPH oxidase in this process, we developed a new model of mouse arteriovenous fistula (AVF) connecting the right common carotid artery (RCCA) with the jugular vein, which does not affect blood pressure. Mice deficient for gp91phox and p47phox subunits of NADPH and wild-type controls were used. AVF greatly increased RCCA blood flow (0.78+/-0.12 to 4.71+/-0.78 mL/min; P<0.01), producing an abrupt rise in shear stress (35+/-1 to 261+/-17 dynes/cm2; P<0.01) within 24 hours. RCCA diameter (460+/-14 microm) gradually enlarged 1 and 3 weeks after AVF (534+/-14 microm and 627+/-19 microm; P<0.01), reducing shear stress (173+/-13 and 106+/-10 dynes/cm2, respectively). In gp91phox(-/-) mice, changes in RCCA caliber and shear stress matched controls. However, p47phox(-/-) mouse RCCAs enlarged only marginally, such that shear stress remained high (199+/-8 dynes/cm2 at 3 weeks). Likewise, remodeling was minimal in endothelial NO synthase (eNOS)(-/-) mice. In both control and gp91phox(-/-) animals, reactive oxygen species (ROS) production and MMP induction was enhanced by AVF, whereas in p47phox(-/-) and eNOS(-/-) mice such response was negligible. Similarly, nitrotyrosine staining, indicating peroxynitrite formation, was more pronounced in control and gp91phox(-/-) mice than in p47phox(-/-) and eNOS(-/-) mice. Hence, shear stress induces vascular NADPH oxidase comprising p47phox but not gp91phox. Generated ROS interact with NO to produce peroxynitrite, which in turn activates MMPs, facilitating vessel remodeling. Our study provides the first evidence that ROS play a fundamental role in flow-induced vascular enlargement.     

Activation of protein kinase C and nicotinamide adenine dinucleotide phosphate oxidase in leukocytes of spontaneously hypertensive rats.

The involvement of oxidative stress in polymorphonuclear leukocytes (PMN) in the pathogenesis of hypertension remains to be elucidated. We analyzed the generation of reactive oxygen species (ROS) by the circulating and peritoneally infiltrating PMN from spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Flow cytometric analysis revealed that ROS generation by PMN from SHR was higher than that from WKY before (at 6 weeks of age) and after (at 16 weeks of age) the onset of hypertension. In vivo, ROS generation by PMN from SHR, but not that by PMN from WKY, was significantly suppressed by 10-week treatment with 50 mg/kg/day carvedilol, and this treatment did not affect blood pressure. Western blotting analysis revealed that protein kinase C alpha (PKCalpha), but not PKCbetaI or betaII, was activated more strongly in PMN from SHR than in PMN from WKY. Furthermore, expression of p47phox of nicotinamide adenine dinucleotide phosphate oxidase, but not of p67phox, in PMN from SHR was higher than that in PMN from WKY. These results suggest that ROS generation by PMN is principally enhanced in SHR through activation of PKCalpha and p47phox.     

Diminished expression of constitutive nitric oxide synthases in the kidney of spontaneously hypertensive rat

In kidney, nitric oxide (NO) synthesized by nitric oxide synthase (NOS) regulates sodium and water excretion, and renal medullary blood flow. The expression of constitutive NOS, endothelial NOS (eNOS) and neuronal NOS (nNOS), were assessed in kidney of the spontaneously hypertensive rat (SHR) and the normotensive Wistar Kyoto (WKY) rat by Western blot analysis and immunocytochemistry. Neuronal NOS expression was observed in the cortex and eNOS was detected only in theinner medulla of both WKY and SHR. In SHR, expression of eNOS was attenuated to 35.1 +/- 10.8%, while expression of nNOS was only 57.5 +/- 5.7% of the levels seen in WKY rat. Immunocytochemical studies revealed decreased staining of nNOS in the macula densa, collecting ducts and in the glomerulus of SHR compared to WKY rat. Endothelial NOS immunoreactivity was restricted to vascular structures of the inner intima cells and smooth muscle cells, and was markedly reduced in the vasculature of SHR. The decreased renal blood flow observed in SHR may be linked to a diminished expression of eNOS and nNOS, underscoring the importance of these enzymes in the pathophysiology and maintenance of genetic hypertension.     

p21-activated kinase (Pak) regulates NADPH oxidase activation in human neutrophils

The phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase plays an instrumental role in host defense and contributes to microbicial killing by releasing highly reactive oxygen species. This multicomponent enzyme is composed of membrane and cytosolic components that assemble in the plasma membrane or phagolysosome. While the guanosine S'-triphosphatase (GTPase) Rac2 has been shown to be a critical regulator of NADPH oxidase activity and assembly, the role of its effector, p21-activated kinase (Pak), in oxidase function has not been well defined. Using HIV-1 Tat-mediated protein transduction of Pak inhibitory domain, we show here that Pak activity is indeed required for efficient superoxide generation in intact neutrophils. Furthermore, we show that Pak translocates to the plasma membrane upon N-formyl-methionyl-leucyl-phenylalanine (fMLF) stimulation and colocalizes with translocated p47(phox) and with p22phox, a subunit of flavocytochrome b558. Although activated Pak phosphorylated several essential serine residues in the C-terminus of p47phox, direct binding to p47phox was not observed. In contrast, active Pak bound directly to p22phox, suggesting flavocytochrome b was the oxidase-associated membrane target of this kinase and this association may facilitate further phosphorylation of p47phox in the assembling NADPH oxidase complex.     

Molecular mechanism underlying activation of superoxide-producing NADPH oxidases: roles for their regulatory proteins

The phagocyte NADPH oxidase is dormant in resting cells but becomes activated during phagocytosis to produce superoxide, a precursor of microbicidal oxidants, thereby playing a crucial role in host defence. The catalytic core of this enzyme comprises the two membranous subunits gp91phox/Nox2 and p22phox. The oxidase activation requires the small GTPase Rac and the SH3 domain-containing proteins p47phox and p67phox; they normally exist in the cytoplasm and translocate upon cell stimulation to the membrane. The translocation depends on a stimulus-induced conformational change of p47phox, which leads to the SH3 domain-mediated interaction with p22phox, a binding required for the gp91phox/Nox2-dependent superoxide production. Activation of Nox1, an oxidase that is likely involved in host defence at the colon, requires novel proteins homologous to p47phox and p67phox, designated Noxo1 and Noxa1, respectively. Noxo1 and Noxa1, both expressed abundantly in the colon, are capable of constitutively activating Nox1. The constitutive activation may be due to the property of Noxo1: in contrast with p47phox, Noxo1 seems to normally associate with p22phox, which is required for the Nox1 activation. We will also describe the mechanism underlying regulation of the third oxidase Nox3, which exits in fetal kidney and inner ears.     

Activation of the Na(+)-H+ exchanger modulates angiotensin II-stimulated Na(+)-dependent Mg2+ transport in vascular smooth muscle cells in genetic hypertension.

This study investigated the role of the Na(+)-H+ exchanger (NHE) on angiotensin II (Ang II)-induced activation of Na(+)-dependent Mg2+ transport in vascular smooth muscle cells (VSMCs) from Wistar-Kyoto rats (WKY; n=20) and spontaneously hypertensive rats (SHR; n=20). Intracellular free concentrations of Mg2+ ([Mg2+]i) and Na+ ([Na+]i) and intracellular pH (pHi) were measured with the specific fluorescent probes mag-fura 2-AM, SBFI-AM, and BCECF-AM, respectively. Na+ dependency of Mg2+ transport was assessed in Na(+)-free buffer, and the role of the NHE was determined with the highly selective NHE blocker 5-(N-methyl-N-isobutyl) amiloride (MIA). Basal [Mg2+]i was lower in SHR than WKY (0.59+/-0.01 versus 0.71+/-0.01 mmol/L, P<0.05). Basal pHi and [Na+]i were not different between the 2 groups. Ang II dose dependently increased [Na+]i and pHi and decreased [Mg2+]i. Responses were significantly greater (P<0.05) in SHR versus WKY ([Na+]i E(max)=37.5+/-1.1 versus 33.7+/-1.9 mmol/L; pHi E(max)=7.35+/-0.04 versus 7.20+/-0.01; [Mg2+]i E(min)=0. 28+/-0.09 versus 0.53+/-0.02 mmol/L, SHR versus WKY). In Na(+)-free buffer, Ang II-elicited [Mg2+]i responses were inhibited. MIA (1 micromol/L) inhibited Ang II-stimulated responses in WKY and normalized responses in SHR ([Mg2+]i E(min)=0.49+/-0.02). Ang II-stimulated activation of NHE was significantly increased (P<0.05) in SHR (0.07+/-0.002 DeltapH(i)/s) compared with WKY (0.05+/-0.004 DeltapH(i)/s). These data demonstrate that in VSMCs [Mg2+]i regulation is Na+ dependent, that activation of NHE modulates Na(+)-Mg2+ transport, and that increased activity of NHE may play a role in altered Na(+)-dependent regulation of [Mg2+]i in SHR.     

Phagocytosis-Coupled Activation of the Superoxide-Producing Phagocyte Oxidase, a Member of the NADPH Oxidase (Nox) Family

The phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase plays a crucial role in host defense by neutrophils and macrophages. When cells ingest invading microbes, this enzyme becomes activated to reduce molecular oxygen to superoxide, a precursor of microbicidal oxidants, in the phagosome. The catalytic core of the oxidase is membrane-bound cytochrome b558, which comprises gp91phox and p22phox. gp91phox belongs to the NADPH oxidase (Nox) family, which contains the entire electron-transporting apparatus from NADPH to molecular oxygen. In resting neutrophils, cytochrome b558 is mainly present in the membrane of the specific granule, an intracellular component, and is targeted to the phagosomal membrane during phagocytosis. Activation of gp91phox involves the integrated function of cytoplasmic proteins such as p47phox, p67phox, p40phox, and the small guanosine triphosphatase Rac; these proteins translocate to the phagosomal membrane to interact with cytochrome b558, leading to superoxide production. Here we describe a current molecular model for phagocytosis-coupled activation of the NADPH oxidase.