p22phox mRNA expression and NADPH oxidase activity are increased in aortas from hypertensive rats

Losartan improves impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in type 1 diabetic rats

We examined whether activation of angiotensin-1 receptors (AT1R) could account for impaired responses of cerebral arterioles during type 1 diabetes (T1D). First, we measured responses of cerebral arterioles in nondiabetic rats to eNOS-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists before and during application of angiotensin II. Next, we examined whether losartan could improve impaired responses of cerebral arterioles during T1D. In addition, we harvested cerebral microvessels for Western blot analysis of AT1R protein and measured production of superoxide anion by brain tissue under basal conditions and in response to angiotensin II in the absence or presence of losartan. We found that angiotensin II specifically impaired eNOS-dependent reactivity of cerebral arterioles. In addition, while losartan did not alter responses in nondiabetics, losartan restored impaired eNOS-dependent vasodilatation in diabetics. Further, AT1R protein was higher in diabetics compared to nondiabetics. Finally, superoxide production was higher in brain tissue from diabetics compared to nondiabetics under basal conditions, angiotensin II increased superoxide production in nondiabetics and diabetics, and losartan decreased basal (diabetics) and angiotensin II-induced production of superoxide (nondiabetics and diabetics). We suggest that activation of AT1R during T1D plays a critical role in impaired eNOS-dependent dilatation of cerebral arterioles.

Cardiovascular disease in dialysis patients: do some antihypertensive drugs have specific antioxidant effects or is it just blood pressure reduction? Does antioxidant treatment reduce the risk for cardiovascular disease?

PURPOSE OF REVIEW

Patients with end-stage renal disease have an extremely high cardiovascular disease mortality. Oxidative stress is one of the 'nontraditional' risk factors for cardiovascular disease mortality in dialysis patients. This review discusses antioxidant activity of the commonly prescribed antihypertensive agents and the effects of antioxidant interventions on cardiovascular disease mortality in patients with end-stage renal disease.

RECENT FINDINGS

Several lines of evidence confirm antioxidant activity of the renin-angiotensin-aldosterone antagonists, some of the calcium channel blockers, carvedilol, and hydralazine. This appears to be independent of their antihypertensive activity. Clinical evidence of their superiority in improving cardiovascular disease endpoints in end-stage renal disease, however, is lacking. There are no randomized trials that have examined the effect of correcting oxidative stress on clinical endpoints. One randomized study in patients on hemodialysis reported a reduction in oxidative stress and the plasma methylarginines with valsartan and amlodipine but no clinical endpoints were examined.

SUMMARY

The effects of the antihypertensive agents with antioxidant activity on cardiovascular disease mortality in end-stage renal disease have not been examined in randomized clinical trials. These agents may offer specific clinical advantage in addition to lowering the blood pressure, but this remains to be proven. Two studies show a reduction in cardiovascular disease events with vitamin E and N-acetylcysteine in patients on hemodialysis without an effect on overall mortality.

NADPH oxidases, reactive oxygen species, and hypertension: clinical implications and therapeutic possibilities

Reactive oxygen species (ROS) influence many physiological processes including host defense, hormone biosynthesis, fertilization, and cellular signaling. Increased ROS production (termed "oxidative stress") has been implicated in various pathologies, including hypertension, atherosclerosis, diabetes, and chronic kidney disease. A major source for vascular and renal ROS is a family of nonphagocytic NAD(P)H oxidases, including the prototypic Nox2 homolog-based NAD(P)H oxidase, as well as other NAD(P)H oxidases, such as Nox1 and Nox4. Other possible sources include mitochondrial electron transport enzymes, xanthine oxidase, cyclooxygenase, lipoxygenase, and uncoupled nitric oxide synthase. NAD(P)H oxidase-derived ROS plays a physiological role in the regulation of endothelial function and vascular tone and a pathophysiological role in endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis, and rarefaction, important processes underlying cardiovascular and renal remodeling in hypertension and diabetes. These findings have evoked considerable interest because of the possibilities that therapies against nonphagocytic NAD(P)H oxidase to decrease ROS generation and/or strategies to increase nitric oxide (NO) availability and antioxidants may be useful in minimizing vascular injury and renal dysfunction and thereby prevent or regress target organ damage associated with hypertension and diabetes. Here we highlight current developments in the field of reactive oxygen species and cardiovascular disease, focusing specifically on the recently identified novel Nox family of NAD(P)H oxidases in hypertension. We also discuss the potential role of targeting ROS as a therapeutic possibility in the management of hypertension and cardiovascular disease.

Does increased oxidative stress cause hypertension?

Hypertension is associated with increased vascular oxidative stress; however, there is still a debate whether oxidative stress is a cause or a result of hypertension. Animal studies have generally supported the hypothesis that increased blood pressure is associated with increased oxidative stress; however, human studies have been inconsistent. Oxidative stress promotes vascular smooth muscle cell proliferation and hypertrophy and collagen deposition, leading to thickening of the vascular media and narrowing of the vascular lumen. In addition, increased oxidative stress may damage the endothelium and impair endothelium-dependent vascular relaxation and increases vascular contractile activity. All these effects on the vasculature may explain how increased oxidative stress can cause hypertension. Treatment with antioxidants has been suggested to lower oxidative stress and therefore blood pressure. However, to date, clinical studies investigating antioxidant supplements have failed to show any consistent benefit. It is noteworthy that lowering blood pressure with antihypertensive medications is associated with reduced oxidative stress. Therefore, it seems that oxygen stress is not the cause, but rather a consequence, of hypertension.

Pathophysiology, diagnosis and prognostic implications of endothelial dysfunction

Endothelial dysfunction (ED) in the setting of cardiovascular risk factors such as hypercholesterolemia, hypertension, diabetes mellitus, chronic smoking as well as in patients with heart failure has been shown to be at least in part dependent on the production of reactive oxygen species (ROS) such as superoxide and the subsequent decrease in vascular bioavailability of nitric oxide (NO). Methods to quantify endothelial dysfunction include forearm plethysmography, flow-dependent dilation of the brachial artery, finger-pulse plethysmography, pulse curve analysis, and quantitative coronary angiography after intracoronary administration of the endothelium-dependent vasodilator acetylcholine. Superoxide sources include the NADPH oxidase, xanthine oxidase, and mitochondria. Superoxide produced by the NADPH oxidase may react with NO released by the endothelial nitric oxide synthase (eNOS) thereby generating peroxynitrite (ONOO-), leading to eNOS uncoupling and therefore eNOS-mediated superoxide production. The present review will discuss current concepts of how to assess endothelial function, prognostic implications of ED, mechanisms underlying ED with focus on oxidative stress and circulating biomarkers, which have been proposed to indicate endothelial dysfunction and/or damage, respectively.

Endothelial superoxide production is altered in sheep programmed by early gestation dexamethasone exposure

BACKGROUND

Animal models have demonstrated that maternal undernutrition or early gestation glucocorticoid exposure induces endothelial dysfunction in the offspring.

OBJECTIVES

We sought to determine whether early gestation dexamethasone (DEX) exposure is further associated with increased vascular superoxide anion production.

METHODS

DEX (0.28 mg/kg/day i.v. for 48 h) was administered to pregnant ewes at 27-28 days' gestation (term 145 days). Tissues were harvested from DEX-exposed and control lambs at 125 days' gestation (n = 6 for each group) and 4 months following delivery (n = 9 and 12, respectively).

RESULTS

By lucigenin-enhanced chemiluminescence, coronary and mesenteric arteries from DEX-exposed fetuses exhibited diminished basal superoxide production (both p < 0.01). Similarly, DEX-exposed carotid arteries from 4-month-old lambs had decreased superoxide production (p < 0.01) that localized to the endothelium by endothelial cell culture and dihydroethidium fluorescence. In contrast, DEX-exposed coronary arteries from the 4-month-old sheep had increased superoxide production (p < 0.05). Although early gestation DEX exposure did not alter lipid peroxidation, DEX exposure was associated with significantly increased renal and cerebral cortex aconitase activity (consistent with decreased protein oxidation). These changes occurred in the absence of alterations in renal cortex superoxide dismutase activity.

CONCLUSIONS

We conclude that in a DEX-exposure model of fetal programming, endothelial superoxide production and protein oxidation are decreased in the mesenteric and carotid circulation. This contrasts with the postnatal coronary artery-specific increase in superoxide production.

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.

Syndecans are differentially expressed during the course of aortic aneurysm formation

BACKGROUND

The syndecan family of cell surface proteoglycans can bind and modulate the activity of a diverse group of soluble and insoluble ligands, which have been shown to modulate events relevant to acute tissue repair and chronic injury responses. The expression of members of the syndecan family of heparan sulfate proteoglycans during the course of aortic aneurysm formation has not been previously investigated. In this investigation, the spatiotemporal expression of syndecan-1, -2, and -4 was characterized in a murine model of aneurysm formation.

METHODS

ApoE-deficient mice were maintained on an atherogenic diet for 8 weeks with concurrent infusion of angiotensin II (0.75 mg/kg/day SQ). The expression of syndecan-1, -2, and -4 at the site of aneurysm formation was characterized by immunohistochemical staining and colocalization determined by double fluorescent immunostaining. Correlative examination was performed on tissue specimens harvested from patients at the time of open aneurysm repair.

RESULTS

In the aortic wall of age-matched, untreated mice, syndecan-4 was localized to the smooth muscle cells of the media. However, neither syndecan-1 nor syndecan-2 could be detected. Within 1 week of initiating a high fat diet and infusion of angiotensin II, syndecan-1 was abundantly expressed in infiltrating macrophages, predominantly localized to the periadventitial aorta. The expression of macrophage-associated syndecan-1 was accentuated during the course of aneurysm formation. As the aneurysm matured, syndecan-2 was abundantly expressed within the aortic thrombus and heterogeneous syndecan-4 staining noted within the aortic media. Significantly, abundant syndecan-1 positive macrophages were observed in explanted human specimens.

CONCLUSIONS

Given the established functional properties of this family heparan sulfate proteoglycans, chronically accelerated macrophage syndecan-1 shedding could generate a sustained proinflammatory, proteolytic, growth-stimulating environment. As a component of a counterbalancing reparative process, cell surface syndecan-2 may assist in TGF-beta mediated responses to limit the growth of abdominal aortic aneurysms.

A novel CYBA variant, the -675A/T polymorphism, is associated with essential hypertension

OBJECTIVE

Oxidative stress is implicated in hypertension and the NADPH oxidase systems constitute the main source of superoxide in vascular wall. We searched for new polymorphisms within the CYBA promoter, the human gene that encodes the p22phox protein, and studied their potential association with essential hypertension.

DESIGN

A case-control study in a random sample of the general population.

METHODS

CYBA polymorphisms were determined by restriction fragment length polymorphism and allelic discrimination. NADPH oxidase activity was quantified in phagocytic cells by chemiluminescence.

RESULTS

We identified three novel polymorphisms, at positions -852, -675 and -536 from the ATG codon. Only the -675(A/T) polymorphism associated with essential hypertension. The prevalence of the TT genotype and the T allele frequency were significantly higher (P < 0.05) in hypertensives than in normotensives. Furthermore, TT hypertensives exhibited higher (P < 0.05) systolic blood pressure values than TA/AA hypertensives. Increased phagocytic NADPH oxidase activity was observed in TT subjects compared to TA and AA individuals (P < 0.05). Enhanced carotid intima-media thickness, a surrogate marker of atherosclerosis, was found in TT subjects compared to TA and AA individuals (P < 0.05). Finally, mutagenesis experiments demonstrated a functional role of this polymorphism on the CYBA promoter activity.

CONCLUSION

The -675 (A/T) CYBA polymorphism may be a novel genetic marker associated with essential hypertension. Furthermore, TT subjects exhibit features of NADPH oxidase-mediated oxidative stress and asymptomatic atherosclerosis.

Chronic alcohol-induced oxidative endothelial injury relates to angiotensin II levels in the rat

The link between chronic alcohol consumption and cardiovascular injury including hypertension is well known. However, molecular mediators implicated with alcohol-induced elevation in blood pressure (BP) remain elusive. The aim of this study was to investigate the relationship of chronic ethanol-induced endothelial injury and elevation in BP with angiotensin II levels in rats. Male Fisher rats were divided into two groups of seven animals each and treated as follows: (1) Control (5% sucrose, orally) daily for 12 weeks and (2) ethanol (4 g kg(-1), orally) daily for 12 weeks. The BP (systolic, diastolic, and mean) was recorded every week. The animals were anesthetized with pentobarbital after 12 weeks; blood and thoracic aorta were isolated and analyzed for aortic reactivity response, angiotensin II levels, and oxidative endothelial injury. The results show that the systolic, diastolic, and mean BP were significantly elevated 12 weeks after ethanol ingestion. The increased BP was related to elevated angiotensin II levels in the plasma and aorta of alcohol treated group compared to control. The aortic NADPH oxidase activity, ratio of oxidized to reduced glutathione (GSSG/GSH) and lipid peroxidation significantly increased, whereas nitric oxide (NO), endothelial NO synthase (eNOS), and vascular endothelial growth factor (VEGF) protein expressions were depressed in alcohol group compared to control. The phenylephrine-mediated vasoconstriction response was not altered, while acetylcholine-mediated vasorelaxation response was depressed in the aorta of ethanol treated rats compared to control. It is concluded that chronic ethanol ingestion induces hypertension which is correlated with elevated tissue angiotensin II levels, activation of NADPH oxidase activity causing endothelial injury, depletion of endothelial NO generating system, and impaired vascular relaxation in rats.

l-Carnitine attenuates oxidative stress in hypertensive rats

The present study aimed to investigate whether l-carnitine (LC) protects the vascular endothelium and tissues against oxidative damage in hypertension. Antioxidant enzyme activities, glutathione and lipid peroxidation were measured in the liver and heart of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Nitrite and nitrate levels and total antioxidant status (TAS) were evaluated in plasma, and the expression of endothelial nitric oxide synthase (eNOS) and p22phox subunit of NAD(P)H oxidase was determined in aorta. Glutathione peroxidase activity was lower in SHR than in WKY rats, and LC increased this activity in SHR up to values close to those observed in normotensive animals. Glutathione reductase and catalase activities, which were higher in SHR, tended to increase after LC treatment. No differences were found in the activity of superoxide dismutase among any animal group. The ratio between reduced and oxidized glutathione and the levels of lipid peroxidation were respectively decreased and increased in hypertensive rats, and both parameters were normalized after the treatment. Similarly, LC was able to reverse the reduced plasma nitrite and nitrate levels and TAS observed in SHR. We found no alterations in the expression of aortic eNOS among any group; however, p22phox mRNA levels showed an increase in SHR that was reversed by LC. In conclusion, chronic administration of LC leads to an increase in hepatic and cardiac antioxidant defense and a reduction in the systemic oxidative process in SHR. Therefore, LC might increase NO availability in SHR aorta by a reduction in superoxide anion production.

Kidney-specific enhancement of ANG II stimulates endogenous intrarenal angiotensinogen in gene-targeted mice

This study was performed in transgenic mice to test the hypothesis that the selective intrarenal overproduction of ANG II increases intrarenal mouse (m) angiotensinogen (AGT) expression. We used the following three groups: 1) single transgenic mice (group A, n = 14) expressing human (h) AGT only in the kidney, 2) double-transgenic mice (group D, n = 13) expressing human renin systemically in addition to hAGT only in the kidney, and 3) wild-type (group W, n = 12) mice. Exogenous hAGT protein is inactive in group A because endogenous mouse renin cannot cleave hAGT to ANG I because of a high species specificity. All mice were monitored from 12 to 18 wk of age. Systolic blood pressure progressively increased from 116 +/- 5 mmHg (12 wk) to 140 +/- 7 (18 wk) in group D. This increase was not observed in groups A or W. Intrarenal hAGT levels were similar in groups A and D; however, hAGT was not detectable in kidneys of group W. Kidney ANG II levels were increased in group D (216 +/- 43 fmol/g) compared with groups A (117 +/- 16) and W (118 +/- 17). However, plasma ANG II concentrations were similar among the three groups. Endogenous renal mAGT mRNA was increased significantly in group D (1.46 +/- 0.19, ratio) compared with groups A (0.97 +/- 0.12) and W (1.00 +/- 0.08). Endogenous renal mAGT protein was also significantly increased in group D compared with groups A and W. Interstitial collagen-positive area, interstitial macrophage/monocyte infiltration, and afferent arteriolar wall thickness were increased significantly in group D compared with groups A and W. These data indicate for the first time that the selective stimulation of intrarenal production of ANG II from hAGT augments endogenous intrarenal mAGT mRNA and protein expression.

Fluvastatin reverses endothelial dysfunction and increased vascular oxidative stress in rat adjuvant-induced arthritis

OBJECTIVE

To investigate the effect of statins on vascular dysfunction in rat adjuvant-induced arthritis (AIA).

METHODS

Fluvastatin (5 mg/kg/day) was administered orally to rats with AIA, for 21 days after the onset of arthritis. The vasodilatory response to acetylcholine of aortic rings isolated from rats with AIA that were not treated or were treated with fluvastatin and from normal rats was determined. The amounts of 4-hydroxy-2-nonenal (HNE) and nitrotyrosine in aortas were measured by Western blotting. In vitro and in situ superoxide production in aortas was evaluated based on fluorogenic oxidation of dihydroethidium to ethidium. Expression of NAD(P)H components and endothelial nitric oxide synthase (eNOS) in aortas was examined by real-time reverse transcriptase-polymerase chain reaction and Western blotting. Serum levels of tetrahydrobiopterin, a critical eNOS cofactor, were determined by high-performance liquid chromatography.

RESULTS

Fluvastatin reversed endothelial dysfunction in AIA without affecting the clinical severity of arthritis or serum cholesterol concentration. Fluvastatin reduced the amounts of HNE and nitrotyrosine in the aorta, and the levels of superoxide expressed in endothelial cells and smooth muscle cells in the tissue, in rats with AIA. NADH- or L-arginine-induced superoxide production was not observed in the aortic samples from fluvastatin-treated rats with AIA. Fluvastatin decreased the levels of expression of messenger RNA for p22phox, a NAD(P)H oxidase component, in the aortas of rats with AIA, but did not affect the expression of eNOS. Serum levels of tetrahydrobiopterin were significantly reduced in rats with AIA, and were increased by administration of fluvastatin.

CONCLUSION

Our findings demonstrate that fluvastatin has potent vascular protective effects in AIA and provide additional scientific rationale for the use of statins to reduce cardiovascular mortality in patients with rheumatoid arthritis.

Intrarenal renin-angiotensin system and counteracting protective mechanisms in angiotensin II-dependent hypertension

It is now well accepted that alterations in kidney function, due either to primary renal disease or to inappropriate hormonal influences on the kidney, are a cardinal characteristic in all forms of hypertension, and lead to a reduced ability of the kidneys to excrete sodium and the consequent development of elevated arterial pressures. However, it is also apparent that many extrarenal factors are important contributors to altered kidney function and hypertension. Central to many hypertensinogenic processes is the inappropriate activation of the renin-angiotensin system (RAS) and its downstream consequences by various pathophysiologic mechanisms. There may also be derangements in arachidonic acid metabolites, endothelium derived factors such as nitric oxide and carbon monoxide, and various paracrine and neural systems that normally interact with or provide a counteracting balance to the actions of the RAS. Thus, when the capacity of the kidneys to maintain sodium balance and extracellular fluid volume within appropriate ranges is compromised, increases in arterial pressure become necessary to re-establish normal balance.

Reduced expression of SKCa and IKCa channel proteins in rat small mesenteric arteries during angiotensin II-induced hypertension

Ca2+-activated K+ channels (KCa), in particular, the small and intermediate KCa (SKCa and IKCa, respectively) channels, are key players in endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation in small arteries. Hypertension is characterized by an endothelial dysfunction, possibly via reduced EDHF release and/or function. We hypothesize that during angiotensin II (14 days)-induced hypertension (ANG II-14d), the contribution of SKCa and IKCa channels in ACh-induced relaxations is reduced due to decreased expression of SKCa and IKCa channel proteins in rat small mesenteric arteries (MAs). Nitric oxide- and prostacyclin-independent vasorelaxation to ACh was similar in small MAs of sham-operated and ANG II-14d rats. Catalase had no inhibitory effects on these relaxations. The highly selective SKCa channel blocker UCL-1684 almost completely blocked these responses in MAs of sham-operated rats but partially in MAs of ANG II-14d rats. These changes were pressure dependent since UCL-1684 caused a greater inhibition in MAs of 1-day ANG II-treated normotensive rats compared with ANG II-14d rats. Expression levels of both mRNA and protein SK3 were significantly reduced in MAs of ANG II-14d rats. The IKCa channel blocker 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34) resulted in comparable reductions in the relaxation responses to ACh in MAs of sham-operated and ANG II-14d rats. Relative mRNA expression levels of IK1 were significantly reduced in MAs of ANG II-14d rats, whereas protein levels of IK1 were not but tended to be lower in MAs of ANG II-14d rats. The findings demonstrate that EDHF-like responses are not compromised in a situation of reduced functional activity and expression of SK3 channels in small MAs of ANG II-induced hypertensive rats. The role of IK1 channels is less clear but might compensate for reduced SK3 activity.

Vascular inflammation in hypertension and diabetes: molecular mechanisms and therapeutic interventions

More than 80% of patients with type 2 diabetes mellitus develop hypertension, and approx. 20% of patients with hypertension develop diabetes. This combination of cardiovascular risk factors will account for a large proportion of cardiovascular morbidity and mortality. Lowering elevated blood pressure in diabetic hypertensive individuals decreases cardiovascular events. In patients with hypertension and diabetes, the pathophysiology of cardiovascular disease is multifactorial, but recent evidence points toward the presence of an important component dependent on a low-grade inflammatory process. Angiotensin II may be to a large degree responsible for triggering vascular inflammation by inducing oxidative stress, resulting in up-regulation of pro-inflammatory transcription factors such as NF-kappaB (nuclear factor kappaB). These, in turn, regulate the generation of inflammatory mediators that lead to endothelial dysfunction and vascular injury. Inflammatory markers (e.g. C-reactive protein, chemokines and adhesion molecules) are increased in patients with hypertension and metabolic disorders, and predict the development of cardiovascular disease. Lifestyle modification and pharmacological approaches (such as drugs that target the renin-angiotensin system) may reduce blood pressure and inflammation in patients with hypertension and metabolic disorders, which will reduce cardiovascular risk, development of diabetes and cardiovascular morbidity and mortality.

Effect of losartan, compared with atenolol, on endothelial function and oxidative stress in patients with type 2 diabetes and hypertension

OBJECTIVE

It has been shown that angiotensin-converting enzyme inhibition or angiotensin receptor blockade may improve endothelial dysfunction, an early manifestation of atherosclerosis, in patients with diabetes. Whether this protective effect is mediated through blood pressure-lowering effects or other specific mechanisms such as a reduction in oxidative stress is not clear. We investigated the influence of losartan, compared with atenolol, on endothelial function and oxidative stress in patients with type 2 diabetes and hypertension.

METHODS

Thirteen patients were included in this randomized, double-blind, crossover study; they received losartan 50 mg twice daily for 4 weeks followed by atenolol 50 mg twice daily or vice versa. Concomitant medication with renin-angiotensin blocking agents or beta-blockers was withdrawn, whereas other medication remained unchanged. At baseline and after each treatment period, flow-mediated dilation of the brachial artery and oxidative stress were measured in serum samples.

RESULTS

Flow-mediated dilation was increased significantly after 4 weeks' treatment with losartan (3.4 +/- 0.44%) compared with atenolol (2.58 +/- 0.42%; P = 0.01). 8-Isoprostanes, a marker of oxidative stress, were significantly reduced in the losartan group compared with baseline (0.039 +/- 0.007 versus 0.067 +/- 0.006 ng/ml; P = 0.01), but did not differ from baseline with atenolol. Glucose, hemoglobin A1c, highly sensitive C-reactive protein, lipids and systolic blood pressure remained unaltered, whereas diastolic blood pressure tended to be lower in the atenolol group.

CONCLUSIONS

This study demonstrates that losartan significantly improved endothelial function in type 2 diabetes patients with hypertension compared with atenolol. This must be independent of the blood pressure-lowering effect of losartan and is probably caused by an antioxidative effect of the angiotensin receptor blocker.

Possible role of exogenous cAMP to improve vascular endothelial dysfunction in hypertensive rats

The study has been designed to investigate the effect of 8-Br-cAMP, an activator of protein kinase A, in hypertension-induced vascular endothelial dysfunction. Rats were uninephroctomized and desoxycortisone acetate (DOCA) (40 mg/kg, s.c.) was administered to rats to produce hypertension (mean arterial blood pressure > 140 mmHg). Vascular endothelial dysfunction was assessed using isolated aortic ring preparation, electron microscopy of thoracic aorta and serum concentration of nitrite/nitrate. The expression of mRNA for p22phox and eNOS was assessed by using reverse transcriptase-polymerase chain reaction. Serum thiobarbituric acid reactive substances concentration and aortic superoxide anion concentration were estimated to assess oxidative stress. 8-Br-cAMP (5 mg/kg, i.p.) or atorvastatin (30 mg/kg, p.o.) prevented hypertension-induced attenuation of acetylcholine-induced endothelium-dependent relaxation, impairment of vascular endothelial lining, decrease in expression of mRNA for endothelial nitric oxide synthase (eNOS), serum nitrite/nitrate concentration and increase in expression of mRNA for p22phox, superoxide anion and serum TBARS. The ameliorative effect of 8-Br-cAMP was prevented by N-nitro-L-arginine methyl ester (25 mg/kg, i.p.) and glibenclamide (30 mg/kg, i.p.). It may be concluded that 8-Br-cAMP may stimulate expression and activity of eNOS and suppress expression of p22phox subunit of NADPH oxidase to reduce oxidative stress and subsequently improve vascular endothelial dysfunction.

Increased expression of gp91phox homologues of NAD(P)H oxidase in the aortic media during chronic hypertension: involvement of the renin-angiotensin system

Although vascular cells express multiple members of the Nox family of nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase, including gp91phox, Nox1, and Nox4, the reasons for the different expressions and specific roles of these members in vascular injury in chronic hypertension have remained unclear. Thus, we quantified the mRNA expressions of these NAD(P)H oxidase components by real-time polymerase chain reaction and evaluated superoxide production and morphological changes in the aortas of 32-week-old stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched Wistar Kyoto rats (WKY). The aortic media of SHRSP had an approximately 2.5-fold greater level of Nox4 mRNA and an approximately 10-fold greater level of Nox1 mRNA than WKY. The mRNA expressions of gp91phox and p22phox in SHRSP and WKY were comparable. SHRSP were treated from 24 weeks of age for 8 weeks with either high or low doses of candesartan (4 mg/kg/day or 0.2 mg/kg/day), or a combination of hydralazine (30 mg/kg/day) and hydrochlorothiazide (4.5 mg/kg/day). The high-dose candesartan or the hydralazine plus hydrochlorothiazide decreased the blood pressure of SHRSP to that of WKY, whereas the low-dose candesartan exerted no significant antihypertensive action. Media thickening and fibrosis, as well as the increased production of superoxide in SHRSP, were nearly normalized with high-dose candesartan and partially corrected with low-dose candesartan or hydralazine plus hydrochlorothiazide. These changes by antihypertensive treatment paralleled the decrease in mRNA expression of Nox4 and Nox1. These results suggest that blood pressure and angiotensin II type 1 receptor activation are involved in the up-regulation of Nox1 and Nox4 expression, which could contribute to vascular injury during chronic hypertension.

Interleukin-10 counteracts impaired endothelium-dependent relaxation induced by ANG II in murine aortic rings

ANG II stimulates the production of reactive oxygen species and activates proinflammatory cytokines leading to endothelial dysfunction. We hypothesized that the anti-inflammatory cytokine IL-10 counteracts the impairment in endothelium-dependent ACh relaxation caused by ANG II. Aortic rings of C57BL/6 mice were incubated in DMEM in the presence of vehicle (deionized H(2)O), ANG II (100 nmol/l), recombinant mouse IL-10 (300 ng/ml), or both ANG II and IL-10 for 22 h at 37 degrees C. After incubation, rings were mounted in a wire myograph to assess endothelium-dependent vasorelaxation to cumulative concentrations of ACh. Overnight exposure of aortic rings to ANG II resulted in blunted ACh-induced vasorelaxation compared with that shown in untreated rings (maximal response = 44 +/- 3% vs. 64 +/- 3%, respectively; P<0.05). IL-10 treatment significantly restored this impairment in relaxation (63 +/- 2%). In addition, the NADPH oxidase inhibitor apocynin restored the impairment in relaxation (maximal response = 76 +/- 3%). Western blotting showed increased gp91(phox) expression (a subunit of NADPH oxidase) in response to ANG II. Vessels treated with a combination of ANG II and IL-10 showed decreased expression of gp91(phox). Immunohistochemical analysis showed increased gp91(phox) expression in ANG II-treated vessels compared with those treated with combined ANG II and IL-10. We found that the anti-inflammatory cytokine IL-10 prevents impairment in endothelium-dependent vasorelaxation in response to long-term incubation with ANG II via decreasing NADPH oxidase expression.

ERK activation contributes to regulation of spontaneous contractile tone via superoxide anion in isolated rat aorta of angiotensin II-induced hypertension

Arteries from hypertensive animals and humans have increased spontaneous tone. Increased superoxide anion (superoxide) contributes to elevated blood pressure (BP) and spontaneous tone in hypertension. The association between the extracellular signaling-regulated kinase 1/2 (ERK1/2)-mitogen-activated protein kinase (MAPK) signaling pathway and generation of superoxide and spontaneous tone in isolated aorta was studied in angiotensin II (ANG II)-infused hypertensive (HT) rats. Systolic BP, phosphorylation of ERK, aortic superoxide formation, and aortic spontaneous tone were compared in sham normotensive and HT rats. Infusion of ANG II (0.5 mg x kg(-1) x day(-1) for 6 days) significantly elevated the systolic BP (P<0.01). The phosphorylation of ERK1/2 vs. total ERK1/2 in thoracic aorta was enhanced, and superoxide was increased in the HT vs. the sham group (P<0.01). Spontaneous tone developed in the HT group, but not in the normotensive group. MAPK/ERK1/2 (MEK1/2)-ERK1/2 signaling pathway inhibitors, PD-98059 (10 micromol/l), and U-0126 (10 micromol/l), significantly reduced the phosphorylation of ERK1/2, superoxide generation (P<0.01), and spontaneous tone (P<0.01) in HT. These findings suggest that ANG II infusion induces the production of superoxide and spontaneous tone and that both are dependent on ERK-MAPK activation. In endothelium-denuded aorta, however, MEK1/2 inhibitors did not inhibit the spontaneous tone, even though they significantly reduced superoxide generation similar to endothelium-intact aorta. These data suggest that inhibition of ERK1/2 signaling pathway, via PD-98059 or U-0126, may regulate spontaneous tone in an endothelium-dependent manner. In conclusion, these findings support the importance of the ERK1/2 signaling pathway in modulating vascular oxidative stress and subsequently mediating spontaneous tone in HT.

Janus-faced role of endothelial NO synthase in vascular disease: uncoupling of oxygen reduction from NO synthesis and its pharmacological reversal

Endothelial NO synthase (eNOS) is the predominant enzyme responsible for vascular NO synthesis. A functional eNOS transfers electrons from NADPH to its heme center, where L-arginine is oxidized to L-citrulline and NO. Common conditions predisposing to atherosclerosis, such as hypertension, hypercholesterolemia, diabetes mellitus and smoking, are associated with enhanced production of reactive oxygen species (ROS) and reduced amounts of bioactive NO in the vessel wall. NADPH oxidases represent major sources of ROS in cardiovascular pathophysiology. NADPH oxidase-derived superoxide avidly interacts with eNOS-derived NO to form peroxynitrite (ONOO(-)), which oxidizes the essential NOS cofactor (6R-)5,6,7,8-tetrahydrobiopterin (BH(4)). As a consequence, oxygen reduction uncouples from NO synthesis, thereby rendering NOS to a superoxide-producing pro-atherosclerotic enzyme. Supplementation with BH(4) corrects eNOS dysfunction in several animal models and in patients. Administration of high local doses of the antioxidant L-ascorbic acid (vitamin C) improves endothelial function, whereas large-scale clinical trials do not support a strong role for oral vitamin C and/or E in reducing cardiovascular disease. Statins, angiotensin-converting enzyme inhibitors and AT1 receptor blockers have the potential of reducing vascular oxidative stress. Finally, novel approaches are being tested to block pathways leading to oxidative stress (e.g. protein kinase C) or to upregulate antioxidant enzymes.

Effect of demethylasterriquinone b1 in hypertension associated vascular endothelial dysfunction

BACKGROUND

Activation of Akt stimulates phosphorylation of eNOS, production of nitric oxide and reduces oxidative stress. The study has been designed to investigate the effect of DAQ B1, an activator of Akt, in hypertension associated vascular endothelial dysfunction.

METHODS

Rats were uninephroctomized and DOCA (40 mg kg(-1), s.c.) was administered to rats to produce hypertension (MABP>140 mm Hg). Vascular endothelial dysfunction was assessed using isolated aortic ring preparation, electron microscopy of thoracic aorta and serum concentration of nitrite/nitrate. The expression of messenger RNA for p22phox and eNOS was assessed by reverse transcription-polymerase chain reaction. Serum TBARS and aortic superoxide anion were estimated to assess oxidative stress.

RESULTS

DAQ B1 (5 mg kg(-1), p.o.) or atorvastatin (30 mg kg(-1), p.o.) markedly improved acetylcholine induced endothelium dependent relaxation, vascular endothelial lining, expression of mRNA for eNOS and p22phox, serum nitrite/nitrate concentration and serum TBARS in hypertensive rats. However, this ameliorative effect of DAQ B1 has been prevented by L-NAME (25 mg kg(-1), i.p.), an inhibitor of eNOS.

CONCLUSION

Therefore, it may be concluded that DAQ B1 induced activation of Akt may activate eNOS and consequently reduce oxidative stress to improve hypertension associated vascular endothelial dysfunction.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Characterizing intramural stress and inflammation in hypertensive arterial bifurcations

A histology-based methodology was developed and used to determine whether intramural stress and combined monocyte/macrophage density positively correlate within hypertensive bifurcations. Hypertension was induced in Sprague-Dawley rats using Angiotensin II pumps. Analysis focused on mesenteric bifurcations harvested 7 days (n = 4) post implant, but also included normotensive (n = 2) and 21-day hypertensive (n = 1) samples. Mesentery was processed in a manner that preserves morphology, corrects for histology-related distortions and results in reconstructions suitable for finite element analysis. Peaks in intramural stress and monocyte/macrophage density occurred near bifurcations after the onset of hypertension. Cell density peaks occurred in regions where surface curvature is complex and tends to heighten intramural stress. Also, a strong positive correlation between mean stress and mean cell density suggests that they are related phenomena. A point-by-point comparison of stress and cell density throughout each bifurcation did not exhibit a consistent pattern. We offer reasons why this most stringent test did not corroborate our other findings that high intramural stress is correlated with increased inflammation near the center of the bifurcation.

Elevated pressure selectively blunts flow-evoked vasodilatation in rat mesenteric small arteries

BACKGROUND AND PURPOSE

The present study investigated mechanisms underlying impaired endothelium-dependent vasodilatation elicited by elevating the intraluminal pressure in rat mesenteric small arteries.

EXPERIMENTAL APPROACH

Arterial segments (internal diameter 316+/-2 microm, n=86) were mounted in a pressure myograph. The effect of elevating pressure from 50 to 120 mmHg for 1 h before resetting it to 50 mmHg was studied on endothelium-dependent vasodilatation.

KEY RESULTS

In arteries constricted with U46619 in the presence of indomethacin, shear stress generated by flow, evoked vasodilatation that was abolished by an inhibitor of nitric oxide (NO) synthase, asymmetric dimethylarginine (1 mM), whereas acetylcholine-induced vasodilatation was unchanged. After elevation of intraluminal pressure for 1 h and then resetting it to 50 mmHg, vasodilatation induced by shear stress and the NO donor, S-nitrosopenicillamine was inhibited, while vasodilatation induced by a guanylyl cyclase activator, BAY 412272, and acetylcholine was unaltered. Superoxide levels sensitive to polyethylene glycol superoxide dismutase were increased in segments exposed to elevated pressure. A superoxide scavenger, tempol (300 microM), a general endothelin receptor antagonist, SB 217242 and the selective ET(A) receptor antagonist, BQ 123 preserved shear stress-evoked vasodilatation.

CONCLUSIONS AND IMPLICATIONS

The present study shows that transient exposure to an elevated intraluminal pressure selectively inhibits flow-evoked NO-mediated vasodilatation, probably through activation of endothelin receptors and increased formation of superoxide. In contrast, elevation of pressure did not affect the acetylcholine-evoked endothelium-derived hyperpolarizing factor type vasodilatation in mesenteric small arteries.

Inhibition of NAD(P)H oxidase alleviates impaired NOS-dependent responses of pial arterioles in type 1 diabetes mellitus

OBJECTIVE

The goal was to identify the role of NAD(P)H oxidase in cerebrovascular dysfunction in type 1 diabetes mellitus (T1D).

METHODS

In a first series of studies, rats were assigned to nondiabetic, diabetic (streptozotocin; 50 mg/kg IP), nondiabetic-apocynin (40 mg/kg/day in drinking water)-treated and diabetic-apocynin-treated groups. Two to three months later, the authors examined in vivo responses of pial arterioles to nitric oxide synthase (NOS)-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists. Next, they used Western blot analysis to examine protein levels for subunits of NAD(P)H oxidase in cerebral microvessels and parietal cortex tissue of nondiabetic and diabetic rats. Finally, they measured superoxide production by parietal cortex tissue in nondiabetic and diabetic rats.

RESULTS

Acetylcholine- and ADP-induced dilatation of pial arterioles was impaired in diabetic compared to nondiabetic rats. In addition, while apocynin did not alter responses in nondiabetic rats, apocynin alleviated T1D-induced impairment of NOS-dependent vasodilatation. In addition, p47phox and gp91phox proteins were elevated in cerebral microvessels and parietal cortex tissue, respectively, of diabetic compared to nondiabetic rats. Further, basal production of superoxide was increased in diabetic compared to nondiabetic rats and apocynin decreased this basal production.

CONCLUSIONS

The findings suggest that T1D impairs NOS-dependent reactivity of cerebral arterioles by a mechanism related to the formation of superoxide via activation of NAD(P)H oxidase.

The vascular endothelium in hypertension

The vascular endothelium plays a fundamental role in the basal and dynamic regulation of the circulation. Thus, it has a crucial role in the pathogenesis of hypertension. A spectrum of vasoactive substances is synthesised in the endothelium; of these, nitric oxide (NO), prostacyclin (PGI2) and endothelin (ET)-1 are the most important. There is a continuous basal release of NO determining the tone of peripheral blood vessels. Systemic inhibition of NO synthesis or scavenging of NO through oxidative stress causes an increase in arterial blood pressure. Also, the renin-angiotensin-aldosterone system has a major role in hypertension as it has a direct vasoconstrictor effect and important interactions with oxygen free radicals and NO. Prostacyclin, in contrast to NO, does not contribute to the maintenance of basal vascular tone of conduit arteries, but its effect on platelets is most important. ET acts as the natural counterpart to endothelium-derived NO and has an arterial blood pressure-raising effect in man. Anti-hypertensive therapy lowers blood pressure and may influence these different mediators, thus influencing endothelial function. In summary, due to its position between the blood pressure and smooth muscle cells responsible for peripheral resistance, the endothelium is thought to be both victim and offender in arterial hypertension. The delicate balance of endothelium-derived factors is disturbed in hypertension. Specific anti-hypertensive and anti-oxidant treatment is able to restore this balance.

Diabetes-induced cerebrovascular dysfunction: role of poly(ADP-ribose) polymerase

Our goal was to identify the role of poly(ADP-ribose) polymerase (PARP) in cerebrovascular dysfunction in Type 1 diabetes mellitus (T1D). In a first series of studies, rats were assigned to nondiabetic and diabetic (streptozotocin; 50 mg/kg IP) groups. Two to three months after injection of streptozotocin, we examine in vivo responses of pial arterioles to nitric oxide synthase (NOS)-dependent (adenosine diphosphate (ADP), acetylcholine and histamine) and -independent (nitroglycerin) agonists. After the initial examination of reactivity to the agonists, we treated pial arterioles acutely with an inhibitor of PARP (PJ-34; 1 microM), and then we again examined responses to the agonists. In a second series of studies, we examine superoxide production (lucigenin chemiluminescence) by parietal cortex tissue in nondiabetic and diabetic rats. We found that dilation of pial arterioles in response to ADP, acetylcholine and histamine, but not to nitroglycerin, was impaired in diabetic compared to nondiabetic rats. In addition, although PJ-34 did not alter responses in nondiabetic rats, PJ-34 alleviated T1D-induced impairment of NOS-dependent vasodilation. We also found that basal production of superoxide was increased in diabetic compared to nondiabetic rats and that PJ-34 decreased this basal production of superoxide. Our findings suggest that T1D impairs NOS-dependent reactivity of cerebral arterioles by a mechanism that appears to be related to the formation of superoxide via activation of PARP.

Mechanoregulation of monocyte chemoattractant protein-1 expression in rat vascular smooth muscle cells

The authors have previously shown that arterial wall strain mediates the development of vessel wall inflammation in experimental hypertension. The current studies explore the mechanoregulation of monocyte chemoattractant protein-1 (MCP-1), a potent pro-inflammatory chemokine, by mitogen-activated protein kinases (MAPK) and oxidative stress. Rat aortic smooth muscle (RASM) cells were subjected to cyclic strain on a uniform biaxial strain device. Strain rapidly activated both ERK1/2(MAPK) and p38(MAPK), with peak activation at 5 min. Strain induced a twofold increase in MCP-1 mRNA, which was attenuated by PD 98059, a specific ERK1/2(MAPK) inhibitor, and SB 203580, a specific p38(MAPK) inhibitor. Cyclic strain also increased production of superoxide anion via an NADPH oxidase-dependent mechanism. To assess the potential role of reactive oxygen species in MAPK activation, cells were stretched in the presence of N-acetylcysteine, which had no effect on p38(MAPK) activation, but significantly inhibited ERK1/2(MAPK) activation and MCP-1 expression. In conclusion, redox-sensitive activation of ERK1/2(MAPK) and redox-insensitive activation of p38(MAPK) regulate straininduced MCP-1 expression in RASM cells. These findings define a role for MAPK signal transduction in establishing a pro-inflammatory state in the arterial wall, and thus implicate a potential molecular link between arterial wall strain and atherosclerosis.

Effect of fasudil on macrovascular disorder-induced endothelial dysfunction

The present study has been designed to investigate the effect of fasudil (Rho-kinase inhibitor) in hypercholesterolemia- and hypertension-induced endothelial dysfunction. High fat diet (8 weeks) and desoxycortisone acetate (DOCA) (40 mg·kg–1) were administered (s.c.) to rats to produce hypercholesterolemia and hypertension (mean arterial blood pressure > 120 mmHg), respectively. Endothelial dysfunction was assessed using isolated aortic ring, electron microscopy of thoracic aorta, and serum concentration of nitrite/nitrate. The expression of mRNA for p22phox and eNOS was assessed by using RT-PCR. Serum thiobarbituric acid reactive substances concentration and aortic superoxide anion concentration were estimated to assess oxidative stress. Fasudil (30 mg·kg–1, p.o.) and atorvastatin (30 mg·kg–1, p.o.) treatments markedly prevented hypercholesterolemia- and hypertension-evoked attenuation of acetylcholine-induced endothelium-dependent relaxation, impairment of vascular endothelial lining, decrease in expression of mRNA for eNOS and serum nitrite/nitrate concentration, and an increase in expression of mRNA for p22phox, superoxide anion, and serum thiobarbituric acid reactive substances. The ameliorative effect of fasudil was prevented by L-NAME. In conclusion, fasudil-induced inhibition of Rho-kinase may improve hypercholesterolemia- and hypertension-induced endothelial dysfunction.

NADPH oxidases in the kidney

NADPH oxidases have a distinct cellular localization in the kidney. Reactive oxygen species (ROS) are produced in the kidney by fibroblasts, endothelial cells (EC), vascular smooth muscle cells (VSMC), mesangial cells (MCs), tubular cells, and podocyte cells. All components of the phagocytic NADPH oxidase, as well as the Nox-1 and -4, are expressed in the kidney, with a prominent expression in renal vessels, glomeruli, and podocytes, and cells of the thick ascending limb of the loop of Henle (TAL), macula densa, distal tubules, collecting ducts, and cortical interstitial fibroblasts. NADPH oxidase activity is upregulated by prolonged infusion of angiotensin II (Ang II) or a high salt diet. Since these are major factors underlying the development of hypertension, renal NADPH oxidase may have an important pathophysiological role. Indeed, recent studies with small interference RNAs (siRNAs) targeted to p22( phox ) implicate p22( phox ) in Ang II-induced activation of renal NADPH oxidase and the development of oxidative stress and hypertension, while studies with apocynin implicate activation of p47( phox ) in the development of nephropathy in a rat model of type 1 diabetes mellitus (DM). Experimental studies of the distribution, signaling, and function of NADPH oxidases in the kidney are described.

Synergistic effect of mechanical stretch and angiotensin II on superoxide production via NADPH oxidase in vascular smooth muscle cells

OBJECTIVE

Mechanical forces and angiotensin II influence the structure and function of vascular cells, and play an important role in reactive oxygen species production. In this study, we examined the effects of mechanical stretch and angiotensin II on the expression of p22-phox and Nox-1, essential membrane components of NADPH oxidase, and superoxide production in rat vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Neither a stretch force nor angiotensin II alone altered p22-phox and Nox-1 expression in VSMCs. Combined stimulation markedly increased p22-phox and Nox-1 mRNA, however, which was associated with increased NADPH oxidase activity, superoxide production and total 8-iso-prostaglandin F2alpha concentration. The increases in p22-phox mRNA levels induced by a stretch force in combination with angiotensin II were prevented by treatment with an angiotensin type I (AT1) receptor antagonist, RNH-6270 (100 nmol/l). Protein expression of the AT1 receptor was upregulated by a stretch force.

CONCLUSIONS

These data indicate that mechanical stretch and angiotensin II synergistically increase NADPH oxidase expression in VSMCs, and suggest that part of this mechanism is mediated through an upregulation of the AT1 receptor induced by mechanical stretch. The combined effects of mechanical strain and angiotensin II might promote vascular damage through the production of superoxide in a hypertensive state.

Inhibition of the renin angiotensin system: implications for the endothelium

The endothelium is critically involved in modulating vascular tone through the release of vasodilator (mainly nitric oxide; NO) and vasoconstrictor agents. Under normal conditions the endothelium induces NO-mediated vasodilation, and opposes cell adhesion and thrombosis. Angiotensin II-induced generation of reactive oxygen species plays a key role in the pathophysiology of endothelial dysfunction by reducing NO bioavailability. Endothelial dysfunction is associated with several pathologic conditions, including hypertension and diabetes, and is characterized by altered vascular tone, inflammation, and thrombosis in the vascular wall. Inhibition of the renin-angiotensin-aldosterone system has induced beneficial effects on endothelial function in animals and humans. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and mineralocorticoid receptor antagonists have improved endothelial function in hypertension and diabetes, slowed the progression of atherosclerosis, and reduced the risk associated with cardiovascular disease.

Interferon-gamma enhances superoxide production in human mesangial cells via the JAK-STAT pathway

Immune reactive cytokines, such as interferon (IFN)-gamma, have multiple effects in glomerulonephritis. Superoxide anions (O(2)(-)), which are associated with the progression of glomerulonephritis, are mainly generated by nicotinamide adenine dinucleotide phosphate (reduced form) NAD(P)H oxidases. We determined the effects of IFN-gamma on O(2)(-) production, phosphorylation of signal transducer and activator of transcription (STAT)-1alpha, and the mRNA and protein expressions of p22phox and Nox1, components of NAD(P)H oxidases, in human mesangial cells (HMCs). Significant increases in O(2)(-) production with IFN-gamma were completely abolished by the flavin-containing enzyme inhibitor, diphenyleneiodonium (10 micromol/l), and the Janus-activated kinase (JAK)2 inhibitor, AG490 (100 micromol/l). Phosphorylated STAT-1alpha was detected after 5 min of IFN-gamma stimulation using Western blot analysis, and binding to the gamma-activating site was observed from 30 min to 4 h, thereafter by electrophoretic mobility shift assay (EMSA). Super-shift analysis in EMSA revealed that the main transcription factor was STAT-1alpha. IFN-gamma significantly increased the expression of p22phox mRNA and protein, although expression was inhibited by AG490. These data suggest that IFN-gamma stimulates O(2)(-) production in HMCs via the JAK-STAT pathway and NAD(P)H oxidase.

Mechanosensitive production of reactive oxygen species in endothelial and smooth muscle cells: role in microvascular remodeling?

Changes in the hemodynamic environment (e.g., hypertension, increased blood flow/shear stress) are known to lead to vascular remodeling; however, the underlying mechanisms by which hemodynamic forces control gene expression in vascular cells are not yet completely understood. This review considers how mechanosensitive generation of reactive oxygen species (ROS) by NAD(P)H oxidases and other sources interacts with downstream signaling systems [including activation of nuclear factor kappa B (NF-kappaB) and AP-1] that modulate the phenotype of endothelial and smooth muscle cells, leading to vascular remodeling. We propose a model for an interaction between direct mechanosensitive ROS signaling and pathways activated by pressure-induced upregulation of prooxidant paracrine signaling mechanisms [local renin-angiotensin system, TNF-alpha- converting enzyme (TACE)/tumor necrosis factor alpha (TNF-alpha) system, and endothelin signaling].

Oxidative stress and post-transplant hypertension in pediatric kidney-transplanted patients

OBJECTIVE

To test the hypothesis that oxidative stress signaling contributes to post-transplant endothelial dysfunction and hypertension in pediatric post-transplant hypertension.

STUDY DESIGN

This study evaluated in 16 pediatric renal transplant patients, divided in two groups based on the presence of post-transplant hypertension, the oxidative stress status measuring the gene expression (reverse transcription-polymerase chain reaction) of two major oxidative stress-related proteins, p22(phox) and heme oxygenase-1 (HO-1). Total plasma antioxidant power (ELISA) was also evaluated.

RESULTS

Mononuclear cell p22(phox) gene expression was higher in hypertensive patients compared with the normotensive group (0.91 +/- 0.06 vs 0.79 +/- 0.08 densitometric units, P < .02), whereas HO-1 RNA production and total plasma antioxidant power were higher in the normotensive group (0.38 +/- 0.04 vs 0.20 +/- 0.11 d.u., P < .006, and 1189.35 +/- 145.75 vs 772.71 +/- 196.03 micromol/L, P < .01, respectively).

CONCLUSIONS

Oxidative stress is associated with post-transplant hypertension in hypertensive pediatric kidney-transplant patients, who therefore are at risk of oxidative stress-induced organ damage. They might benefit from treatments addressing not only hypertension but also oxidant-related complications.

The C242T CYBA polymorphism of NADPH oxidase is associated with essential hypertension

OBJECTIVE

Oxidative stress is implicated in hypertension. The reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidases are the main source of superoxide in phagocytic and vascular cells. The C242T polymorphism of CYBA, the human gene that encodes p22phox, has been found to be functionally associated with vascular NADPH oxidase activity in atherosclerotic patients. We investigated the association of the C242T polymorphism with hypertension and its potential impact on NADPH oxidase activity. We also analysed the interaction of C242T polymorphism with the -930A/G CYBA variant.

DESIGN

Case-control study in a random sample of 623 subjects (326 hypertensive patients and 297 normotensive controls) from the general population.

METHODS

CYBA polymorphisms were determined by restriction fragment length polymorphism (RFLP) or allelic discrimination. NADPH oxidase activity and p22phox expression were quantified in phagocytic cells by chemiluminescence and by northern and western blots, respectively.

RESULTS

The prevalence of the CC genotype and the C allele frequency were significantly higher (P < 0.05) in hypertensives than in normotensives. CC genotype remained associated with hypertension after adjusting for potential confounders in a logistic regression analysis. Increased phagocytic NADPH oxidase activity was observed in CC hypertensives compared with CT and TT hypertensives (P < 0.05). Enhanced plasma levels of von Willebrand factor were found in CC hypertensives compared with TT hypertensives (P < 0.05). The C242T polymorphism was not in linkage disequilibrium with the -930A/G CYBA promoter variation, which also associates with hypertension.

CONCLUSION

The C242T CYBA polymorphism is associated with essential hypertension. Furthermore, hypertensives carrying the CC genotype of this polymorphism exhibit features of NADPH oxidase-mediated oxidative stress and endothelial damage.

Vascular NADPH oxidases as drug targets for novel antioxidant strategies

Reactive oxygen species (ROS) play important roles in the pathogenesis of cardiovascular disease. Surprisingly, large clinical trials have shown that ROS scavenging by antioxidant vitamins is ineffective or harmful. Therefore, prevention of ROS formation, by targeting specific sources of superoxide anion and other ROS, might prove beneficial. Potential targets include the NADPH oxidases (Nox enzymes), xanthine oxidase, endothelial nitric oxide synthase and mitochondrial oxidases. Nox enzymes play a central role because they can regulate other enzymatic sources of ROS. Statins, angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists block upstream signaling of Nox activation, which contributes to their clinical effectiveness. Here, we discuss novel possibilities where drugs that directly inhibit Nox activation could successfully inhibit oxidative stress.

Oxidative stress at the vascular wall. Mechanistic and pharmacological aspects

During the process of energy production in aerobic respiration, vascular cells produce reactive oxygen species (ROS). A growing body of evidence indicates that oxidative stress refers to a condition in which cells are subjected to excessive levels of ROS. Overall vascular function is dependent upon a fine balance of oxidant and antioxidant mechanisms, which determine endothelial functions. Considerable experimental and clinical data indicate that intracellular oxidant milieu is also involved in several redox-sensitive cellular signaling pathways such as ion transport systems, protein phosphorylation, and gene expression and thus also plays important roles as modulator of vascular cell functions such as cell growth, apoptosis, migration, angiogenesis and cell adhesion. Overproduction of ROS under pathophysiologic conditions is integral in the development of cardiovascular diseases. This fact has raised an intensive search of new pharmacological approaches to improve vascular hemostasis and particularly those intended to decrease oxidative stress or augment the antioxidant defense mechanisms.

NADPH oxidases in cardiovascular health and disease

Increased oxidative stress plays an important role in the pathophysiology of cardiovascular diseases such as hypertension, atherosclerosis, diabetes, cardiac hypertrophy, heart failure, and ischemia-reperfusion. Although several sources of reactive oxygen species (ROS) may be involved, a family of NADPH oxidases appears to be especially important for redox signaling and may be amenable to specific therapeutic targeting. These include the prototypic Nox2 isoform-based NADPH oxidase, which was first characterized in neutrophils, as well as other NADPH oxidases such as Nox1 and Nox4. These Nox isoforms are expressed in a cell- and tissue-specific fashion, are subject to independent activation and regulation, and may subserve distinct functions. This article reviews the potential roles of NADPH oxidases in both cardiovascular physiological processes (such as the regulation of vascular tone and oxygen sensing) and pathophysiological processes such as endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, angiogenesis, and vascular and cardiac remodeling. The complexity of regulation of NADPH oxidases in these conditions may provide the possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the disease process.

Targeting reactive oxygen species in hypertension

PURPOSE OF REVIEW

Hypertension is a major risk factor for vascular diseases such as stroke, myocardial infarction, and renal microvascular disease. The mechanism by which vascular disease develops is complex, and growing evidence suggests that an increase in reactive oxygen species during hypertension is a major contributing factor. NADPH oxidase, the primary source of reactive oxygen species in the cardiovascular system, is a strong candidate for the development of therapeutic agents to ameliorate hypertension and end-organ damage.

RECENT FINDINGS

Various scavengers and inhibitors of reactive oxygen species have been proposed for use in animal as well as human studies. While many of these agents are effective at lowering tissue reactive oxygen species levels, their specificity is a serious concern. Our laboratory has developed cell-permeant peptidic inhibitors targeting key interactions among the different NAD(P)H oxidase homologues. One of these inhibitors targeting nox2 and p47-phox interaction has proven useful in attenuating target neoplasia and hypertrophy.

SUMMARY

Strategies aimed at specifically inhibiting NAD(P)H oxidase have proven effective in attenuating cardiovascular oxidative stress. The development of new inhibitors targeting novel oxidase homologues appears to hold significant promise for clarifying the physiologic role of these homologues as well as for the development of new antioxidant therapies.

Oxidative stress produced with cell migration increases synthetic phenotype of vascular smooth muscle cells

Phenotypic modulation of vascular smooth muscle cells (VSMC) and reactive oxygen species (ROS) is important in vascular pathogenesis. Understanding how these factors relate to cell migration can improve design of therapeutic interventions to control vascular disease. We compared the proliferation, protein content and migration of cultured aortic VSMC from wild type (WT) versus transgenic mice (Tgp22phox), in which overexpression of p22phox was targeted to VSMC. Also, we compared H2O2 generation and expression of specific phenotypic markers of non-migrating with migrating WT versus Tgp22phox VSMC in an in vitro wound scratch model. Enhanced H2O2 production in Tgp22phox versus WT VSMC (p < 0.005) significantly correlated with increased protein content, proliferation, and migration. VSMC migrating across the wound edge produced more H2O2 than non-migrating VSMC (p < 0.05). The expression of synthetic phenotypic markers, tropomyosin 4 and myosin heavy chain embryonic (SMemb), was enhanced significantly, while the expression of contractile marker, smooth muscle alpha-actin, was reduced significantly in migrating versus non-migrating cells, and also in Tgp22phox versus WT (p < 0.005) VSMC. These results are consistent with increased production of ROS accelerating the switch from the contractile to the synthetic phenotype, characterized by increases in proliferation, migration, and expression of TM4 and SMemb and decreased alpha-actin.

Women and Ischemic Heart Disease

The current review highlights gender-specific issues in ischemic heart disease (IHD) presentation, evaluation, and outcomes with a special focus on the results derived from the National Institutes of Health-National Heart, Lung, and Blood Institute-sponsored Women's Ischemia Syndrome Evaluation (WISE) study. New evidence on gender-based differences in vascular wall, atherosclerotic plaque deposition, pathophysiology, and innovative cardiovascular imaging techniques are reviewed. Critical areas of further inquiry needed to advance new gender-specific IHD understanding are detailed.

Effect of the anti-anginal agent, perhexiline, on neutrophil, valvular and vascular superoxide formation

The prophylactic anti-anginal agent, perhexiline, may also be effective in acute coronary syndromes and advanced aortic valvular stenosis, conditions associated with enhanced inflammation. Its potential effects on superoxide formation via NADPH oxidase were measured by lucigenin-mediated chemiluminescence. Perhexiline inhibited superoxide formation in intact neutrophils stimulated with formyl Met Leu Phe (fMLP) 4 muM or with phorbol myristate acetate (PMA) 162 nM - IC50 2.3 microM (1.5-3.6), n=4. Sub-unit assembly of NADPH oxidase by PMA was unaffected by pretreatment with perhexiline 2 microM, a concentration which reduced superoxide formation by 44+/-5% (n=4) in intact neutrophils. Perhexiline inhibited preassembled neutrophil NADPH oxidase and that in membranes of pig valve interstitial cells, human umbilical vein endothelial cells (HUVECs) and cardiac fibroblasts, but not that in rat aorta (rings or membrane preparations). These data imply that perhexiline inhibits the phagocytic NADPH oxidase directly, and that pig aortic valvular interstitial cells possess a similar enzyme, a conclusion supported by immunohistochemical localisation of the gp91phox subunit in these cells. However further study is required to clarify the effect of perhexiline on different NADPH oxidase isoforms particularly in the vasculature.

NADPH oxidase is involved in angiotensin II-induced apoptosis in H9C2 cardiac muscle cells: effects of apocynin

Angiotensin II stimulates NADPH oxidase activity in vascular cells. However, it is not fully understood whether angiotensin II, which plays an important role in heart failure, stimulates NADPH oxidase activation and expression in cardiac myocytes. Previous studies have shown that angiotensin II induces myocyte apoptosis, but whether the change is mediated via NADPH oxidase remains to be elucidated. In this study we proposed to determine whether angiotensin II stimulated NADPH oxidase activation and NADPH oxidase subunit p47-phox expression in H9C2 cardiac muscle cells. If so, we would determine whether the NADPH oxidase inhibitor apocynin prevented angiotensin II-induced apoptosis. The results showed that angiotensin II increased NADPH oxidase activity, p47-phox protein and mRNA expression, intracellular reactive oxygen species, and apoptosis in H9C2 cells. Angiotensin II elevated p38 mitogen-activated protein kinase (MAPK) activity, decreased Bcl-2 protein, and increased Bax protein and caspase-3 activity. Apocynin treatment inhibited angiotensin II-induced NADPH oxidase activation and increases in p47-phox expression, intracellular reactive oxygen species, and apoptosis. The effect of apocynin on apoptosis was associated with reduced p38 MAPK activity, increased Bcl-2 protein, and decreased Bax protein and caspase-3 activity. These results suggest that angiotensin II-induced apoptosis is mediated via NADPH oxidase activation probably through p38 MAPK activation, a decrease in Bcl-2 protein, and caspase activation.