Endothelin-1 increases vascular superoxide via endothelin(A)-NADPH oxidase pathway in low-renin hypertension

Reactive oxygen species participate in acute renal vasoconstrictor responses induced by ETAand ETBreceptors

Reactive oxygen species (ROS) play important roles in renal vasoconstrictor responses to acute and chronic stimulation by angiotensin II and norepinephrine, as well as in long-term effects of endothelin-1 (ET-1). Little is known about participation of ROS in acute vasoconstriction produced by ET-1. We tested the influence of NAD(P)H oxidase inhibition by apocynin [4 mg·kg−1·min−1, infused into the renal artery (ira)] on ETAand ETBreceptor signaling in the renal microcirculation. Both receptors were stimulated by ET-1, ETAreceptors by ET-1 during ETBantagonist BQ-788, and ETBby ETBagonist sarafotoxin 6C. ET-1 (1.5 pmol injected ira) reduced renal blood flow (RBF) 17 ± 4%. Apocynin raised baseline RBF (+10 ± 1%, P < 0.001) and attenuated the ET-1 response to 10 ± 2%, i.e., 35 ± 9% inhibition ( P < 0.05). Apocynin reduced ETA-induced vasoconstriction by 42 ± 12% ( P < 0.05) and that of ETBstimulation by 50 ± 8% ( P < 0.001). During nitric oxide (NO) synthase inhibition ( Nω-nitro-l-arginine methyl ester), apocynin blunted ETA-mediated vasoconstriction by 60 ± 8% ( P < 0.01), whereas its effect on the ETBresponse (by 87 ± 8%, P < 0.001) was even larger without than with NO present ( P < 0.05). The cell-permeable superoxide dismutase mimetic tempol (5 mg·kg−1·min−1ira), which reduces O2−and may elevate H2O2, attenuated ET-1 responses similar to apocynin (by 38 ± 6%, P < 0.01). We conclude that ROS, O2−rather than H2O2, contribute substantially to acute renal vasoconstriction elicited by both ETAand ETBreceptors and to basal renal vasomotor tone in vivo. This physiological constrictor action of ROS does not depend on scavenging of NO. In contrast, scavenging of O2−by NO seems to be more important during ETBstimulation.

Quercetin inhibits vascular superoxide production induced by endothelin-1: Role of NADPH oxidase, uncoupled eNOS and PKC

Chronic administration of the most abundant dietary flavonoid quercetin exerts antihypertensive effects and improves endothelial function. We have investigated the effects of quercetin and its methylated metabolite isorhamnetin (1-10microM) on endothelial dysfunction and superoxide (O(2*)(-)) production induced by endothelin-1 (ET-1, 10nM). ET-1 increased the contractile response induced by phenylephrine and reduced the relaxant responses to acetylcholine in phenylephrine contracted intact aorta, and these effects were prevented by co-incubation with quercetin, isorhamnetin or chelerythrine (protein kinase C (PKC) inhibitor). This endothelial dysfunction was also improved by superoxide dismutase (SOD), apocynin (NADPH oxidase inhibitor) and sepiapterin (tetrahydrobiopterin synthesis substrate). Furthermore, ET-1 increased intracellular O(2*)(-) production in all layers of the vessel, protein expression of NADPH oxidase subunit p47(phox) without affecting p22(phox) expression and lucigenin-enhanced chemiluminescence signal stimulated by calcium ionophore A23187. All these changes were prevented by both quercetin and isorhamnetin. Moreover, apocynin, endothelium denudation and N(G)-nitro-l-arginine methylester (l-NAME, nitric oxide synthase inhibitor) suppressed the ET-1-induced increase in A23187-stimulated O(2*)(-) generation. Moreover, quercetin but not isorhamnetin, inhibited the increased PKC activity induced by ET-1. Taken together these results indicate that ET-1-induced NADPH oxidase up-regulation and eNOS uncoupling via PKC leading to endothelial dysfunction and these effects were prevented by quercetin and isorhamnetin.

Endothelium-specific GTP cyclohydrolase I overexpression attenuates blood pressure progression in salt-sensitive low-renin hypertension

BACKGROUND

Tetrahydrobiopterin (BH4) is an essential cofactor of endothelial nitric oxide synthase (eNOS). When BH4 levels are decreased, eNOS becomes uncoupled to produce superoxide anion (O2(-)) instead of NO, which contributes to endothelial dysfunction. Deoxycorticosterone acetate (DOCA)-salt hypertension is characterized by a suppressed plasma renin level due to sodium retention but manifests in eNOS uncoupling; however, how endogenous BH4 regulates blood pressure is unknown. GTP cyclohydrolase I (GTPCH I) is the rate-limiting enzyme for de novo BH4 synthesis. This study tested the hypothesis that endothelium-specific GTPCH I overexpression retards the progression of hypertension through preservation of the structure and function of resistance mesenteric arteries.

METHODS AND RESULTS

During 3 weeks of DOCA-salt treatment, arterial blood pressure was increased significantly in wild-type mice, as determined by radiotelemetry, but this increase was attenuated in transgenic mice with endothelium-specific GTPCH I overexpression (Tg-GCH). Arterial GTPCH I activity and BH4 levels were decreased significantly in wild-type DOCA-salt mice, but both were preserved in Tg-GCH mice despite DOCA-salt treatment. Significant remodeling of resistance mesenteric arteries (approximately 100-microm outside diameter) in wild-type DOCA-salt mice exists, evidenced by increased medial cross-sectional area, media thickness, and media-lumen ratio and overexpression of tenascin C, an extracellular matrix glycoprotein that contributes to hypertrophic remodeling; all of these effects were prevented in DOCA-salt-treated Tg-GCH mice. Furthermore, NO-mediated relaxation in mesenteric arteries was significantly improved in DOCA-salt-treated Tg-GCH mice, in parallel with reduced O2(-) levels. Finally, phosphorylation of eNOS at serine residue 1177 (eNOS-S1177), but not its dimer-monomer ratio, was decreased significantly in wild-type DOCA-salt mice compared with sham controls but was preserved in DOCA-salt-treated Tg-GCH mice.

CONCLUSIONS

These results demonstrate that endothelium-specific GTPCH I overexpression abrogates O2(-) production and preserves eNOS phosphorylation, which results in preserved structural and functional integrity of resistance mesenteric arteries and lowered blood pressure in low-renin hypertension.

Endothelins and NADPH oxidases in the cardiovascular system

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

Endothelin, sex and hypertension

The ETs (endothelins) comprise a family of three 21-amino-acid peptides (ET-1, ET-2 and ET-3) and 31-amino-acid ETs (ET-1(1-31), ET-2(1-31) and ET-3(1-31)). ET-1 is synthesized from a biologically inactive precursor, big ET-1, by ECEs (ET-converting enzymes). The actions of ET-1 are mediated through activation of the G-protein-coupled ET(A) and ET(B) receptors, which are found in a variety of cells in the cardiovascular and renal systems. ET-1 has potent vasoconstrictor, mitogenic, pro-inflammatory and antinatriuretic properties, which have been implicated in the pathophysiology of a number of cardiovascular diseases. Overexpression of ET-1 has been consistently described in salt-sensitive models of hypertension and in models of renal failure, and has been associated with disease progression. Sex differences are observed in many aspects of mammalian cardiovascular function and pathology. Hypertension, as well as other cardiovascular diseases, is more common in men than in women of similar age. In experimental models of hypertension, males develop an earlier and more severe form of hypertension than do females. Although the reasons for these differences are not well established, the effects of gonadal hormones on arterial, neural and renal mechanisms that control blood pressure are considered contributing factors. Sex differences in the ET-1 pathway, with males displaying higher ET-1 levels, greater ET-1-mediated vasoconstrictor and enhanced pressor responses in comparison with females, are addressed in the present review. Sex-associated differences in the number and function of ET(B) receptors appear to be particularly important in the specific characteristics of hypertension between females and males. Although the gonadal hormones modulate some of the differences in the ET pathway in the cardiovascular system, a better understanding of the exact mechanisms involved in sex-related differences in this peptidergic system is needed. With further insights into these differences, we may learn that men and women could require different antihypertensive regimens.

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.

The inducible nitric-oxide synthase modulates endothelin-1-dependent release of prostacyclin and inhibition of platelet aggregation ex vivo in the mouse

Nitric oxide and other reactive oxygen species generated by nitric-oxide synthases (NOS) modulate, among several other cellular responses, the production of eicosanoids and platelet aggregation. The roles of specific NOS in these two phenomena remain to be determined. Thus, the present study assessed whether inducible NOS (iNOS) and endothelial NOS (eNOS) modulate in a similar manner the production of eicosanoids and platelet aggregation. Mice knocked out for eNOS (eNOS-/-) or iNOS (iNOS-/-) and their wild-type (WT) congeners were used to analyze agonist-induced increases in plasma levels of eicosanoids as well as inhibition of platelet aggregation ex vivo. Systemically administered endothelin-1 (ET-1) triggered an increase in plasma levels of 6-keto prostaglandin F(1alpha) (6-keto PGF(1alpha)) in WT and eNOS-/- but not in iNOS-/- mice. ET-1 (0.01-1 nmol/kg) also induced a dose-dependent inhibition of platelet aggregation in WT and eNOS-/- but not in iNOS-/- mice. Another agonist, bradykinin (10 nmol/kg), triggered the release of 6-keto PGF(1alpha) and inhibited platelet aggregation in all strains of mice studied. In addition, ADP-induced platelet aggregation in vitro was similarly reduced by iloprost (100 nM) in iNOS-/- mice and WT congeners. In another series of experiments, ET-1 (0.1 nmol/kg) significantly increased 8-isoprostane plasma levels in WT but not in iNOS-/- mice. Finally, a 3-week treatment with anti-oxidants inhibited the capacity of ET-1 to significantly increase plasma 6-keto PGF(1alpha) in WT mice. We show for the first time that iNOS is involved in the control of ET-1-induced prostacyclin release and related inhibition of platelet aggregation in the murine model.

Endothelin stimulates vascular hydroxyl radical formation: effect of obesity

Reactive oxygen species (ROS) and endothelin-1 (ET-1) contribute to vascular pathophysiology in obesity. In this context, whether ET-1 modulates hydroxyl radical (•OH) formation and the function of ROS/•OH in obesity is not known. In the present study, formation and function of ROS, including •OH, were investigated in the aorta of lean and leptin-deficient obese ob/ob mice. Hydroxyl radical formation was detected ex vivo using terephthalic acid in intact aortic rings and the involvement of ROS in ET-1-mediated vasoreactivity was analyzed using the antioxidant EPC-K1, a combination of α-tocopherol and ascorbic acid. Generation of either •OH, •O2−, and H2O2was strongly inhibited by EPC-K1 (all P < 0.05). In obese mice, basal vascular •OH formation and ROS activity were reduced by 3-fold and 5-fold, respectively ( P < 0.05 vs. lean). ET-1 markedly enhanced •OH formation in lean (6-fold, P < 0.05 vs. untreated) but not in obese mice. Obesity increased ET-1-induced contractions ( P < 0.05 vs. lean), and ROS scavenging further enhanced the response ( P < 0.05 vs. untreated). Exogenous ROS, including •OH caused stronger vasodilation in obese animals ( P < 0.05 vs. lean), whereas endothelium-dependent relaxation was similar between lean and obese animals. In conclusion, we present a sensitive method allowing ex vivo measurement of vascular •OH generation and provide evidence that ET-1 regulates vascular •OH formation. The data indicate that in obesity, vascular formation of ROS, including •OH is lower, whereas the sensitivity to ROS is increased, suggesting a novel and important role of ROS, including •OH in the regulation of vascular tone in disease status associated with increased body weight.

Differential Regulation of NADPH Oxidase in Sympathetic and Sensory Ganglia in Deoxycorticosterone Acetate–Salt Hypertension

We demonstrated recently that superoxide anion levels are elevated in prevertebral sympathetic ganglia of deoxycorticosterone acetate–salt hypertensive rats and that this superoxide anion is generated by reduced nicotinamide-adenine dinucleotide phosphate oxidase. In this study we compared the reduced nicotinamide-adenine dinucleotide phosphate oxidase enzyme system of dorsal root ganglion (DRG) and sympathetic celiac ganglion (CG) and its regulation in hypertension. The reduced nicotinamide-adenine dinucleotide phosphate oxidase activity of ganglion extracts was measured using fluorescence spectrometry of dihydroethidine; the activity in hypertensive dorsal root ganglion was 34% lower than in normotensive DRG. In contrast, activity was 79% higher in hypertensive CG than normotensive CG. mRNA for the oxidase subunits NOX1, NOX2, NOX4, p47 phox , and p22 phox were present in both CG and DRG; mRNA for NOX4 was significantly higher in CG than in DRG. The levels of mRNA and protein expression of the membrane-bound catalytic subunit p22 phox and of the regulatory subunits p47 phox and Rac-1 were measured in CG and DRG in normotensive and hypertensive rats. p22 phox mRNA and protein expression was greater in CG of hypertensive rats but not in DRG. Compared with normotensive controls, p47 phox mRNA and protein, as well as Rac-1 protein, were significantly decreased in hypertensive DRG but not in CG. Immunohistochemical staining of p47 phox showed translocation from cytoplasm to membrane in hypertensive CG but not in hypertensive DRG. This suggests that reduced nicotinamide-adenine dinucleotide phosphate oxidase activation in sympathetic neurons and sensory neurons is regulated in opposite directions in hypertension. This differential regulation may contribute to unbalanced vasomotor control and enhanced vasoconstriction in the splanchnic circulation.

Involvement of the endothelin ET(B) receptor in gender differences in deoxycorticosterone acetate-salt-induced hypertension

1. In the present study, we investigated the role of endothelin ET(B) receptors in gender differences in the development of deoxycorticosterone acetate (DOCA)-salt-induced hypertension by using the spotting-lethal (sl) rat, which carries a naturally occurring deletion in the ET(B) receptor gene. 2. In wild-type rats, the elevation of systolic blood pressure (SBP) by DOCA-salt treatment for 4 weeks was extremely lower in females than in males, but this gender difference was partially attenuated in ovariectomized (OVX) animals. These alterations of SBP corresponded with vascular superoxide () production. 3. In homozygous (sl/sl) group, the SBP of male, intact female and OVX rats was markedly elevated by DOCA-salt treatment to the same extent, indicating that the gender difference in DOCA-salt-induced hypertension was abolished by the genetic ET(B) receptor deficiency. There were similar increases in the vascular endothelin (ET)-1 content in the three DOCA-salt-treated animal groups, but vascular production in male and OVX rats was much higher than that in intact females. 4. Daily oral administration of ABT-627, an ET(A) receptor antagonist, to sl/sl rats for 2 weeks suppressed the DOCA-salt-induced hypertension more efficiently in intact female rats than in male animals. 5. Thus, vascular oxidative stress is related, at least in part, to differences in the development of DOCA-salt-induced hypertension between male and female rats, but this gender difference is abolished by the genetic ET(B) receptor deficiency, suggesting that ET(B) receptor-mediated vasoprotective actions contribute to the gender differences seen. In addition, in both sexes, vascular ET-1 overproduction and the ET(A) receptor-mediated action seem to be responsible for the enhanced susceptibility to DOCA-salt hypertension in genetic ET(B) receptor deficiency.

Differential effects of ET(A) and ET(B) receptor antagonism on oxidative stress in type 2 diabetes

Endothelin (ET-1) is chronically elevated in diabetes. However, role of ET-1 in increased oxidative stress in type 2 diabetes is less clear. This study tested the hypotheses that: 1) oxidative stress markers are increased and total antioxidant capacity is decreased in diabetes, and 2) activation of ET(A) receptors mediates oxidative stress whereas ET(B) receptors display opposing effects. Plasma total antioxidant status (TAS) and 8-isoprostane (8-iso PGF(2alpha)) as well as total nitrotyrosine levels in mesenteric resistance vessels were measured in control Wistar and diabetic Goto-Kakizaki (GK) rats (n=5-10) treated with vehicle, ET(A) antagonist (atrasentan, 5 mg/kg/day), or ET(B) receptor antagonist (A-192621, 15 or 30 mg/kg/day, low and high dose, respectively) for 4 weeks. 8-iso PGF(2alpha) (pg/ml) levels were significantly higher in low dose A-192621 treatment groups of control and diabetic rats than in atrasentan or high-dose A-192621 treated groups. Protein nitration was increased in diabetes and ET(A) receptor antagonism prevented this increase. TAS levels were similar in all experimental groups. Thus, ET-1 contributes to oxidative stress in type 2 diabetes and ET receptor antagonism with atrasentan or A-192612 displays differential effects depending on dose and receptor subtype.

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.

Mechanisms underlying the chronic pioglitazone treatment-induced improvement in the impaired endothelium-dependent relaxation seen in aortas from diabetic rats

The objectives of this study were to determine the effects of chronic treatment with pioglitazone, a peroxisome proliferator-activated receptor gamma agonist, on the impaired endothelium-dependent relaxation seen in aortas from established streptozotocin (STZ)-induced diabetic rats, and to identify some of the molecular mechanisms involved. Starting at 8 weeks of diabetes, pioglitazone (10 mg/kg) was administered to STZ-induced diabetic rats for 4 weeks. In untreated STZ rats (vs age-matched control rats): (1) ACh-induced relaxation, cGMP accumulation, phosphorylation of the cGMP-dependent protein kinase substrate vasodilator-stimulated phosphoprotein at Ser-239 [an established biochemical end-point of nitric oxide (NO)/cGMP signaling], and Cu/Zn-superoxide dismutase (SOD) expression and SOD activity were all reduced; (2) aortic superoxide generation, nitrotyrosine expression, and NAD(P)H oxidase activity were increased; (3) plasma endothelin-1 (ET-1) and aortic c-Jun (AP-1 component) protein expressions were increased. Pioglitazone treatment markedly corrected the above abnormalities. Collectively, these results suggest that pioglitazone treatment improves endothelium-dependent relaxation by reducing oxidative stress via increased SOD activity, decreased NAD(P)H oxidase activity, and a decreased ET-1 level, and that this decreased ET-1 level may be attributable to an inhibition of the AP-1 signaling pathway.

Activation of insulin-like growth factor type-1 receptor is required for H2O2-induced PKB phosphorylation in vascular smooth muscle cells

Evidence accumulated in recent years has revealed a potential role for reactive oxygen species (ROS) in the pathophysiology of cardiovascular diseases. However, the precise mechanisms by which ROS contribute to the development of these diseases are not fully established. Previous work from our laboratory has indicated that exogenous hydrogen peroxide (H2O2) activates several signaling protein kinases, such as extracellular signal-regulated kinase 1 and 2 (ERK1/2) and protein kinase B (PKB) in A10 vascular smooth muscle cells (VSMC). However, the upstream elements responsible for this activation remain unclear. Although a role for epidermal growth factor receptor (EGFR) protein tyrosine kinase (PTK) in H2O2-induced ERK1/2 signaling has been suggested, the contribution of this PTK or other receptor or nonreceptor PTKs to PKB activation is not well defined in VSMC. In this study, we used pharmacological inhibitors to investigate the role of receptor and Src-family-PTKs in H2O2-induced PKB phosphorylation. AG1478, a specific inhibitor of EGFR, failed to attenuate the H2O2-induced increase in PKB Ser473 phosphorylation, whereas AG1024, an inhibitor of insulin-like growth factor type1 receptor (IGF-1R)-PTK, almost completely blocked this response. H2O2 treatment also enhanced tyrosine phosphorylation of the IGF-1Rbeta subunit, which was significantly inhibited by AG1024 pretreatment of cells. Furthermore, pharmacological inhibition of Src by PP2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazole(3,4-d) pyrimidine) decreased PKB phosphorylation. Moreover, H2O2-induced PKB phosphorylation was associated with increased tyrosine phosphorylation of c-Src and Pyk2 in an AG1024- and PP2-inhibitable manner. In conclusion, these data provide evidence of the contribution of IGF-1R-PTK in initiating H2O2-evoked PKB phosphorylation in A10 VSMC, with an intermediary role for c-Src and Pyk2 in this process.

An analysis of the DOCA-salt model of hypertension in HO-1-/- mice and the Gunn rat

Heme oxygenase-1 (HO-1) is induced in the vasculature in the DOCA-salt model of hypertension in rats. Whereas the HO system and its products may exert vasodilator effects, recent studies have suggested that the HO system may predispose to hypertension. The present study examined the effects of selected components of the HO system, specifically, the HO-1 isozyme and the product bilirubin in the DOCA-salt model of systemic hypertension; the experimental approach employed mutant rodent models, namely, the HO-1(-/-) mouse and the hyperbilirubinemic Gunn rat. DOCA-salt induced HO-1 protein in the aorta in HO-1(+/+) mice and provoked a significant rise in systolic arterial pressure in HO-1(-/-) mice but not in HO-1(+/+) mice; this effect could not be ascribed to impaired urinary sodium excretion or impaired glomerular filtration rate in the DOCA-salt-treated HO-1(-/-) mice. The administration of DOCA salt to uninephrectomized rats significantly increased systolic arterial pressure in wild-type rats, an effect that was attenuated in the mutant Gunn rat; this reduction in systemic hypertension in the DOCA-salt-treated Gunn rat was not due to a greater induction of HO-1 in the vasculature or to a more avid urinary sodium excretion. DOCA-salt impaired endothelium-dependent and endothelium-independent vasorelaxation in wild-type rats but not in Gunn rats; prior exposure to bilirubin repaired the defect in endothelium-dependent vasorelaxation in aortic rings in DOCA-salt-treated rats. DOCA salt stimulated vascular production of superoxide anion in wild-type but not in Gunn rats. We suggest that HO-1 and the product bilirubin may exert a countervailing effect in the DOCA-salt model of systemic hypertension.

Inactivation of Extracellular Superoxide Dismutase Contributes to the Development of High-Volume Hypertension

Objectives— Extracellular superoxide dismutase (ecSOD) lowers superoxide anions and maintains vascular nitric oxide level. We studied the function of ecSOD in high-volume hypertension induced by the 1-kidney-1-clip model in wild-type, ecSOD −/− mice, and endothelial nitric oxide synthase (eNOS) −/− mice.

Methods and Results— The 1-kidney–1-clip model resulted in impaired endothelium-dependent relaxation and hypertension and vascular oxidative stress in wild-type and ecSOD −/− mice. Recombinant ecSOD lowered the blood pressure and improved aortic nitric oxide bioavailability in wild-type and ecSOD −/− but not eNOS −/− mice. ecSOD had no effect on blood pressure in eNOS −/− or wild-type mice treated with a nitric oxide synthase inhibitor. The 1-kidney–1-clip model markedly induced ecSOD protein expression, whereas activity was increased by only 25%, suggesting a partial inactivation of ecSOD in high-volume hypertension. Incubation of aortic segments with peroxynitrite or hydrogen peroxide attenuated ecSOD activity, but peroxynitrite did not induce tyrosine nitration of ecSOD, suggesting oxidative inactivation of the enzyme. Administration of polyethyleneglycol-catalase for 3 days selectively lowered the blood pressure in ecSOD +/+ but not ecSOD −/− mice and improved nitric oxide bioavailability. In contrast, acute application of catalase had no effect.

Conclusions— Nitric oxide mediates the vascular effects of ecSOD. Vascular dysfunction in 1-kidney–1-clip model hypertension is partially a consequence of inactivation of ecSOD by reactive oxygen species.

INHIBITION OF NAD(P)H OXIDASE REDUCES FIBRONECTIN EXPRESSION IN STROKE-PRONE RENOVASCULAR HYPERTENSIVE RAT BRAIN

1. The aim of the present study was to test the hypothesis that in vivo chronic inhibition of NAD(P)H oxidase reduces cerebrovascular fibronectin expression in stroke-prone renovascular hypertensive rats (RHRSP). 2. The RHRSP model was induced by two clips and NAD(P)H oxidase was inhibited with apocynin. The mRNA and protein expression of NAD(P)H oxidase subunit p22(phox) in brains of RHRSP and Sprague-Dawley (control) rats was determined using real-time reverse transcription-polymerase chain reaction, western blot and immunohistochemistry. The expression of fibronectin protein was localized immunohistochemically in cerebral vessels and then quantified by western blot. 3. Cerebrovascular fibronectin levels in RHRSP (n = 6) were significantly higher than control (n = 5) levels 8 weeks after operation (1.29 +/- 0.04 vs 1.15 +/- 0.02, respectively; P = 0.007). The p22(phox) immunopositive reactivity was localized in the cerebral vasculature of control rats and RHRSP. Furthermore, chronic treatment of RHRSP with apocynin, a selective NAD(P)H oxidase inhibitor, in the drinking water for 4 weeks (1.5 mmol/L, 5 weeks after operation) resulted in a significant decrease in the expression of p22(phox) protein (0.85 +/- 0.01 vs 0.93 +/- 0.01 in non-treated RHRSP; n = 5; P = 0.002), with a concomitant reduction of fibronectin levels in the cerebral vasculature (1.31 +/- 0.03 vs 1.56 +/- 0.05 in non-treated RHRSP; n = 5; P = 0.002). No significant differences were detected in the expression of p22(phox) mRNA and protein between RHRSP (4 and 8 weeks after renal artery constriction) and the control group. 4. These findings suggest that the chronic inhibition of NAD(P)H oxidase in vivo by apocynin reduces cerebrovascular fibronectin levels, which may lessen hypertensive cerebrovascular fibrosis.

Preconditioning protects endothelium by preventing ET-1-induced activation of NADPH oxidase and xanthine oxidase in post-ischemic heart

The hypothesis was tested that endothelin-1 (ET-1)-induced superoxide (O(2)(-)) generation mediates post-ischemic coronary endothelial injury, that ischemic preconditioning (IPC) affords endothelial protection by preventing post-ischemic ET-1, and thus O(2)(-), generation, and that opening of the mitochondrial ATP-dependent potassium channel (mK(ATP)) triggers the mechanism of IPC. Furthermore, the study was aimed at identifying the source of O(2)(-) mediating the endothelial injury. Langendorff-perfused guinea-pig hearts were subjected either to 30 min ischemia/35 min reperfusion (IR) or were preconditioned prior to IR with three cycles of either 5 min ischemia/5 min reperfusion or 5 min infusion/5 min washout of mK(ATP) opener diazoxide (0.5 mM). Coronary flow responses to acetylcholine (ACh) served as a measure of endothelium-dependent vascular function. Myocardial outflow of ET-1 and O(2)(-) and functional recoveries were followed during reperfusion. NADPH oxidase and xanthine oxidase (XO) activities were measured in cardiac homogenates. IR augmented ET-1 and O(2)(-) outflow and impaired ACh response. All these effects were attenuated or prevented by IPC and diazoxide, and 5-hydroxydecanoate (a selective mK(ATP) blocker) abolished the effects of IPC and diazoxide. Superoxide dismutase and tezosentan (a mixed ET-1-receptor antagonist) mimicked the effects of IPC, although they had no effect on the ET-1 generation. IR augmented also the activity of NADPH oxidase and XO. Apocynin treatment, that resulted in NADPH oxidase inhibition, prevented XO activation and O(2)(-) generation in IR hearts. The inhibition of XO, either by allopurinol or feeding the animals with tungsten-enriched chow, prevented post-ischemic O(2)(-) generation, although these interventions had no effect on the NADPH activity. In addition, the post-ischemic activation of NADPH oxidase and XO, and O(2)(-) generation were prevented by IPC, tezosentan, thenoyltrifluoroacetone (mitochondrial complex II inhibitor), and tempol (cell-membrane permeable O(2)(-) scavenger). In guinea-pig heart: (i) ET-1-induced O(2)(-) generation mediates post-ischemic endothelial dysfunction; (ii) IPC and diazoxide afford endothelial protection by attenuating the ET-1, and thus O(2)(-) generation, and the mK(ATP) opening triggers the protection; (iii) the NADPH oxidase maintains the activity of XO, and the XO-derived O(2)(-) mediates the endothelial injury, and (iv) ET-1 and O(2)(-) (probably of mitochondrial origin) are upstream activators of the NADPH oxidase-XO cascade, and IPC prevents the cascade activation and the endothelial dysfunction by preventing the ET-1 generation.

Increased vascular contractility in isolated vessels from cigarette smoking rats is mediated by basal endothelin release

The effect of chronic cigarette smoking on endothelin modulation of vascular contraction, and CYP enzyme levels was studied in 20 male Sprague-Dawley rats. The animals were divided equally into smoking and non-smoking groups. The smoking group was exposed to 6 research cigarettes per rat per day 5 days a week for 16 weeks. The control group was sham smoked. Functional contractile studies were performed in aortas and carotid arteries to determine the regulation of vascular tone by basal release of endothelin. Liver samples were analyzed for CYP1A1 and CYP1A2 gene expression by RT-PCR. Plasma samples were assessed for endothelin-1 (ET-1) level by enzyme immuno assay (EIA). Treatment of aortas and carotid arteries with bosentan, the dual endothelin receptor antagonist, caused a significant reduction in constrictor responses of smoking rats, indicating, increase greater regulation of tone by endothelin in smoker rats compared to controls. There was a greater expression of the cytochrome P450-liver enzymes (CYP1A1 and CYP1A2) in smoker rats. Body weight gain was also significantly decreased in smoker rats. We conclude that increased endothelin release in smoker rats significantly contributes to increased arterial tone and so contribute to the cardiovascular pathophysiology associated with cigarette smoking, such as increased vascular muscularization, increased contraction, decreased dilation and possibly vasospasm.

Endothelin A receptor blockade reduces diabetic renal injury via an anti-inflammatory mechanism

Endothelin (ET) receptor blockade delays the progression of diabetic nephropathy; however, the mechanism of this protection is unknown. Therefore, the aim of this study was to test the hypothesis that ET(A) receptor blockade attenuates superoxide production and inflammation in the kidney of diabetic rats. Diabetes was induced by streptozotocin (diabetic rats with partial insulin replacement to maintain modest hyperglycemia [HG]), and sham rats received vehicle treatments. Some rats also received the ETA antagonist ABT-627 (sham+ABT and HG+ABT; 5 mg/kg per d; n = 8 to 10/group). During the 10-wk study, urinary microalbumin was increased in HG rats, and this effect was prevented by ET(A) receptor blockade. Indices of oxidative stress, urinary excretion of thiobarbituric acid reactive substances, 8-hydroxy--deoxyguanosine, and H2O2 and plasma thiobarbituric acid reactive substances were significantly greater in HG rats than in sham rats. These effects were not prevented by ABT-627. In addition, renal cortical expression of 8-hydroxy--deoxyguanosine and NADPH oxidase subunits was not different between HG and HG+ABT rats. ETA receptor blockade attenuated increases in macrophage infiltration and urinary excretion of TGF-beta and prostaglandin E2 metabolites in HG rats. Although ABT-627 did not alleviate oxidative stress in HG rats, inflammation and production of inflammatory mediators were reduced in association with prevention of microalbuminuria. These observations indicate that ETA receptor activation mediates renal inflammation and TGF-beta production in diabetes and are consistent with the postulate that ETA blockade slows progression of diabetic nephropathy via an anti-inflammatory mechanism.

Attenuation of cardiovascular remodeling in DOCA-salt rats by the vasopeptidase inhibitor, omapatrilat

Omapatrilat, a vasopeptidase inhibitor, inhibits both neutral endopeptidase and angiotensin-converting enzyme with similar potency. The aim of this study was to investigate whether omapatrilat prevents or reverses cardiovascular remodeling and hypertension in deoxycorticosterone acetate (DOCA)-salt rats. Male Wistar rats (313 +/- 2 g, n = 114) were uninephrectomized (UNX) with or without further treatment with DOCA and 1% NaCl in the drinking water. Compared with UNX control rats, DOCA-salt rats developed hypertension, cardiovascular hypertrophy, perivascular and interstitial cardiac fibrosis and inflammation, endothelial dysfunction, and the prolongation of ventricular action potential duration within four weeks. The administration of omapatrilat (40 mg/kg/day po) for two weeks commencing two weeks after surgery attenuated the development of cardiovascular hypertrophy, inflammation, fibrosis, and ventricular action potential prolongation. In contrast, omapatrilat treatment did not lower systolic blood pressure nor improve endothelial dysfunction. This study concludes that the renin-angiotensin-aldosterone, natriuretic peptide, and bradykinin systems are directly involved in the pathogenesis of cardiovascular remodeling in the DOCA-salt model of hypertension in rats, which may be independent of their effects on blood pressure.

Role of Reactive Oxygen Species in Kv Channel Inhibition and Vasoconstriction Induced by TP Receptor Activation in Rat Pulmonary Arteries

Voltage-gated potassium channels (Kv) and thromboxane A(2) (TXA(2)) have been involved in several forms of human and experimental pulmonary hypertension. We have reported that the TXA(2) analog U46619, via activation of TP receptors and PKCzeta, inhibited Kv currents in rat pulmonary artery smooth muscle cells (PASMC), increased cytosolic calcium, and induced a contractile response in isolated rat and piglet pulmonary arteries (PA). Herein, we have analyzed the role of reactive oxygen species (ROS) in this signaling pathway. In rat PA, U46619 increased dichlorofluorescein fluorescence, an indicator of intracellular hydrogen peroxide, and this effect was prevented by the NADPH oxidase inhibitor apocynin and by polyethyleneglycol-catalase (PEG-catalase, a membrane-permeable form of catalase). U46619 inhibited Kv currents in native PASMC and these effects were strongly inhibited by apocynin. The contractile responses to U46619 in isolated PA were inhibited by PEG-catalase and the NADPH oxidase inhibitors diphenylene iodonium (DPI) and apocynin. A membrane permeable of hydrogen peroxide, t-butyl hydroperoxide, also inhibited Kv currents and induced a contractile response. Activation of NADPH oxidase and the subsequent production of hydrogen peroxide are involved in the Kv channel inhibition and the contractile response induced by TP receptor activation in rat PA.

Iron Chelation Inhibits NF-κB–Mediated Adhesion Molecule Expression by Inhibiting p22 phox Protein Expression and NADPH Oxidase Activity

Objective— Excess iron may increase oxidative stress and play a role in vascular inflammation and atherosclerosis. Here we determined whether the iron chelator, desferrioxamine (DFO), ameliorates oxidative stress and cellular adhesion molecule expression in a murine model of local inflammation.

Methods and Results— Dorsal air pouches were created in C57BL/6J mice by subcutaneous injection of air. DFO (100 mg/kg body weight) was injected into the air pouch once a day for two days followed immediately on the second day by lipopolysaccharide (LPS; 2.5 mg/kg body weight). The animals were euthanized 24 hours later for analysis of oxidative stress markers and adhesion molecules in air pouch tissue. LPS treatment enhanced protein levels of p22 phox , a catalytic subunit of NADPH oxidase, and increased NADPH oxidase activity and levels of superoxide radicals and hydrogen peroxide. Furthermore, LPS activated NF-κB and increased expression of adhesion molecules. All of these inflammatory responses were strongly suppressed by DFO, but not iron-loaded DFO.

Conclusions— Our data show that DFO inhibits LPS-induced, NADPH oxidase–mediated oxidative stress and, hence, NF-κB activation and adhesion molecule expression in a murine model of local inflammation. Iron chelation may be helpful in treating atherosclerotic vascular diseases by ameliorating oxidative stress and inflammation.

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.

Femoral artery constriction by norepinephrine is enhanced by methylprednisolone in a rat model

BACKGROUND

Corticosteroids are associated with femoral head osteonecrosis and arterial hypertension. The patho-mechanism of femoral head osteonecrosis is often attributed to ischemia. The aim of this study was to investigate if corticosteroids directly constrict the femoral artery or if they have a permissive effect on norepinephrine and endothelin-1-induced vasoconstriction.

METHODS

Femoral artery segments were harvested from twenty Wistar rats and mounted as ring preparations on a small-vessel myograph for the purpose of making isometric force measurements. For the norepinephrine study, twenty femoral artery segments from ten rats were stimulated cumulatively with norepinephrine before and after incubation with methylprednisolone (5 mug/mL). For the endothelin-1 study, forty femoral artery segments from ten rats were used. The four artery segments from each animal were randomized by pairs to either a corticosteroid treatment group (5 mug/mL methylprednisolone incubation, n = 20) or a control group (placebo incubation, n = 18, as two of the twenty control-group vessels did not meet protocol requirements). Isometric wall tension was plotted and quantified by the EC(50) (the plasma concentration of endothelin-1 required for obtaining 50% of maximal constriction in vivo).

RESULTS

In the norepinephrine-stimulated group, incubation with methylprednisolone did not directly induce any vasoconstriction but did enhance norepinephrine-elicited vasoconstriction. The norepinephrine dose-response curve displayed a shift to the left after incubation with methylprednisolone. This shift was reflected by a significantly lower mean EC50 of 9.5 x 10(-7) M +/- 5.1 x 10(-7) M after methylprednisolone incubation compared with a mean of 2.5 x 10(-6) M +/- 1.1 x 10(-6) M before incubation (p < 0.005). In the endothelin-1-stimulated group, the endothelin-1 dose-response curve displayed a tendency toward stronger contraction in the vessels that were incubated with methylprednisolone, but this tendency did not reach significance.

CONCLUSIONS

Incubation with methylprednisolone enhances norepinephrine-mediated contraction of the femoral artery in a rat model.

CLINICAL RELEVANCE

Vasoconstriction of the vascular bed supplying the femoral head can diminish femoral head blood flow, and this may be a factor in the early pathogenesis of corticosteroid-associated femoral head osteonecrosis.

Reactive oxygen species and erectile dysfunction: possible role of NADPH oxidase

Erectile dysfunction (ED) is a widespread condition, the incidence of which is increasing globally. ED is also indicative of underlying vasculopathy and represents a predictor of more serious cardiovascular disorders. Understanding the aetiology of ED may therefore provide invaluable pointers to the pathobiology of other cardiovascular diseases (CVDs) and syndromes. It follows, too, that therapeutic interventions that are successful in treating ED may, ipso facto, be effective in treating the early stages of conditions that include atherosclerosis, angina, plaque rupture and diabetic angiopathy. One common pathological denominator in both CVD and ED is oxidative stress, that is, the overproduction of reactive oxygen species (ROS), in particular, superoxide (O(2)(*-)) and hydrogen peroxide (H(2)O(2)). In this review, therefore, we consider the aetiology and pathobiology of O(2)(*-) in promoting ED and focus on NADPH oxidase as an inducible source of O(2)(*-) and H(2)O(2). Therapeutic strategies aimed at reducing oxidative stress to improve erectile function are also discussed.

Is there a role for reactive oxygen species in arterial medial elastocalcinosis?

Isolated systolic hypertension results from a gradual stiffening of large arteries, to which medial elastocalcinosis (calcification of elastic lamellae) contributes. There is compelling evidence that reactive oxygen species (ROS) are associated with several disease processes affecting the cardiovascular system, including hypertension. The present study was designed to investigate whether the inhibition of ROS production by alpha-lipoic acid can prevent vascular calcification. Sprague-Dawley rats were treated with warfarin (20 mg/kg/day) and vitamin K (15 mg/kg/day) (WVK) for 4 weeks to induce large artery calcification. Subgroups received either a normal diet or a diet supplemented with lipoic acid (1000 mg/kg/day). The WVK treatment produced a small elevation of aortic superoxide levels that did not reach statistical significance. Alpha-lipoic acid reduced the elevation below baseline levels. In rats treated with alpha-lipoic acid, the WVK-induced elevation of pulse wave velocity (an index of arterial stiffness), left ventricular hypertrophy, and aortic, femoral and carotid elastocalcinosis were not prevented. Although a contribution of oxidative stress has been suggested in the aging cardiovascular system, this alteration does not appear to contribute to the calcification process and the subsequent stiffening of large arteries in the animal model tested.

The effect of xanthine oxidase inhibition upon ejection fraction in heart failure patients: La Plata Study

BACKGROUND

Reactive oxygen species (ROS) have been linked to hypertrophy, remodeling and abnormal excitation-contraction coupling. Previous data demonstrated that an increase in oxidative stress is associated to the pathogenesis of congestive heart failure (CHF). We examined whether inhibition of the superoxide anion (*O2(-))-generating enzyme xanthine oxidase (XO) with oxypurinol may improve cardiac function in patients with CHF.

METHODS AND RESULTS

A randomized, placebo-controlled, double-blind study on 60 patients (30/group) with New York Heart Association class II-III CHF, comparing 600-mg/day oxypurinol during 1 month with placebo, added to standard therapy. Effects on left ventricular ejection fraction (LVEF), serum uric acid (SUA) level, and 6-minute walking test were analyzed. SUA decreased by 16.0 +/- 2.8 mg/L from baseline to Week 4 in the oxypurinol group relative to placebo (P < .01, n = 30 per group). LVEF showed an increase of 4.7 +/- 2.6% from baseline to Week 4 in the oxypurinol group relative to placebo that did not reach statistical significance (P < .08). When patients with LVEF > 40% at baseline were excluded, a statistically significant increase of 6.8 +/- 2.8% from baseline to Week 4 was seen in the oxypurinol group relative to placebo (P < .02, n = 26 placebo, n = 21 oxypurinol). No treatment-related adverse effects or increase in walking capacity were detected.

CONCLUSION

Inhibition of XO by oxypurinol in patients with CHF decreases SUA and improves LVEF in patients with LVEF < or = 40% after 1 month of treatment.

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.

Preventing oxidative stress in rats with aldosteronism by calcitriol and dietary calcium and magnesium supplements

BACKGROUND

Prominent features of the clinical syndrome of congestive heart failure (CHF) include aldosteronism and the presence of oxidative stress. Secondary hyperparathyroidism (SHPT) accompanies aldosteronism due to increased urinary and fecal excretion of Ca. SHPT accounts for intracellular Ca overloading of diverse cells, including peripheral blood mononuclear cells (PBMC), and the appearance of oxidative stress. Parathyroidectomy or a Ca channel blocker each prevent these responses. Herein, we hypothesized calcitriol, or 1,25(OH)2D3, plus a diet supplemented with Ca and Mg (CMD) would prevent SHPT and Ca overloading of PBMC and thereby oxidative stress in these cells in rats receiving aldosterone/salt treatment (ALDOST).

METHODS AND RESULTS

In rats with ALDOST for 4 weeks, without or with CMD, we monitored plasma-ionized [Ca]o and parathyroid hormone (PTH), and PBMC cytosolic-free [Ca]i and H2O2 production. Untreated, age- and gender-matched rats served as controls. Compared to controls, ALDOST led to an expected fall in plasma [Ca]o level with accompanying rise in plasma PTH level and intracellular Ca overloading of PBMC and their increased production of H2O2. CMD prevented SHPT and abrogated intracellular Ca overloading of PBMC and their increased H2O2 production.

CONCLUSIONS

The appearance of SHPT in aldosteronism, induced by fallen plasma [Ca]o, leads to PTH-mediated Ca overloading of PBMC and their increased production of H2O2. SHPT in rats with aldosteronism can be prevented by calcitriol and a diet supplemented with Ca and Mg. These findings raise the prospect that the SHPT found in CHF could be managed with macro- and micronutrients.

NADPH-oxidase activity is elevated in penumbral and non-ischemic cerebral arteries following stroke

Reactive oxygen species play a role in neuronal damage following cerebral ischemia-reperfusion. We tested whether activity of the superoxide-generating enzyme, NADPH-oxidase, is enhanced in cerebral arteries within, adjacent and distant from the ischemic core. The right middle cerebral artery (MCA) of conscious rats was temporarily occluded by perivascular injection of endothelin-1 to induce stroke (ET-1; n=19). Control rats were injected with saline (n=9). At 24 h or 72 h post-administration of ET-1, the MCA and its branches within the ipsilateral penumbra and infarcted core, corresponding arteries in the contralateral hemisphere, and basilar artery were excised. Anatomically similar arteries were excised from saline-injected rats. At 24 h after stroke, NADPH-stimulated superoxide production by arteries from the infarcted core did not differ from levels generated by arteries from control rats, whereas levels were significantly lower 72 h after stroke. However, at both time points after stroke, superoxide production by arteries from the ischemic penumbra was 8-fold greater than levels generated by arteries from control rats. Surprisingly, even in the non-ischemic arteries from the contralateral hemisphere and in the basilar artery, superoxide production was increased approximately 4- to 6-fold at 24 h, but had returned to normal 72 h after stroke. The NADPH-oxidase inhibitor, diphenyleneiodonium, virtually abolished superoxide production by all arteries. Thus, the activity of NADPH-oxidase is enhanced in cerebral arteries from the ischemic penumbra at 24 h and 72 h following cerebral ischemia. Additionally, NADPH-oxidase activity is temporarily enhanced after cerebral ischemia within arteries from non-ischemic parts of the brain.

Novel isoforms of NADPH-oxidase in cerebral vascular control

Reactive oxygen species (ROS) are thought to play an important role in the initiation and progression of a variety of vascular diseases. Furthermore, accumulating evidence indicates that ROS may also serve as important cell signalling molecules for the regulation of normal vascular function. Recently, a novel family of proteins (Nox1, 2 and 4) that act as the catalytic subunit of the superoxide (O2-) producing enzyme NADPH-oxidase has been discovered in vascular cells. There is now preliminary evidence suggesting that NADPH-oxidase-derived ROS may serve as a physiological vasodilator mechanism in the cerebral circulation. Moreover, the activity of NADPH-oxidase is profoundly greater in cerebral versus systemic arteries. Studies have shown that Nox1, Nox2 (also known as gp91phox) and Nox4 are all expressed in cerebral arteries, suggesting that multiple isoforms of NADPH-oxidase may be important for ROS production by cerebral arteries. Enhanced NADPH-oxidase activity is associated with several vascular-related diseases, including hypertension, stroke, subarachnoid haemorrhage and Alzheimer's dementia; however, the consequences of this for cerebral vascular function are controversial. For example, there is some evidence suggesting that NADPH-oxidase-derived O2- may play a role in endothelial dysfunction of cerebral arteries and a subsequent rise in cerebral vascular tone, associated with hypertension. However, activation of NADPH-oxidase elicits cerebral vasodilatation in vivo, and this mechanism is enhanced in chronic hypertension. While further supportive evidence is needed, it is an intriguing possibility that NADPH-oxidase-derived ROS may play a protective role in regulating cerebral vascular tone during disease.

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.

Deletion of Endothelial Cell Endothelin B Receptors Does Not Affect Blood Pressure or Sensitivity to Salt

Endothelin B receptors in different tissues regulate diverse physiological responses including vasoconstriction, vasodilatation, clearance of endothelin-1, and renal tubular sodium reabsorption. To examine the role of endothelial cell endothelin B receptors in these processes, we generated endothelial cell-specific endothelin B receptor knockout mice using a Cre- loxP approach. We have demonstrated loss of endothelial cell endothelin B receptor expression and function and preservation of nonendothelial endothelin B receptor-mediated responses through binding and functional assays. Ablation of endothelin B receptors exclusively from endothelial cells produces endothelial dysfunction in the absence of hypertension, with evidence of decreased endogenous release of NO and increased plasma endothelin-1. In contrast to models of total endothelin B receptor ablation, the blood pressure response to a high-salt diet is unchanged in endothelial cell–specific endothelin B receptor knockouts compared with control floxed mice. These findings suggest that the endothelial cell endothelin B receptor mediates a tonic vasodilator effect and that nonendothelial cell endothelin B receptors are important for the regulation of blood pressure.

Impact of androgen-induced oxidative stress on hypertension in male SHR

Men have higher blood pressure than women, and androgens and oxidative stress have been implicated as playing roles in this sexual dimorphism. The spontaneously hypertensive rat (SHR) is an animal model of both androgen- and oxidative stress-mediated hypertension. Therefore, the present studies were performed to test the hypothesis that androgens cause hypertension in SHR in part by stimulating superoxide production via NADPH oxidase. Castration of male SHR reduced blood pressure by 15% and attenuated both basal and NADPH-stimulated superoxide production in kidney cortical homogenates. Expression of p47(phox) and gp91(phox) but not p22(phox) subunits of NADPH oxidase were significantly lower in kidney cortex from castrated males compared with intact males. Moreover, inhibition of NADPH oxidase with apocynin caused approximately 15 mmHg reduction in blood pressure and reduced basal and NADPH-stimulated superoxide production in intact male SHR, but had no effect on blood pressure or superoxide production in castrated males. These data support the hypothesis that androgens cause oxidative stress and thereby increase blood pressure in male SHR via an NADPH oxidase-dependent mechanism.

Enhanced endothelium-dependent vasodilatation by dual endothelin receptor blockade in individuals with insulin resistance

Insulin resistance is associated with endothelial dysfunction and increased production of the pro-inflammatory vasoconstrictor peptide endothelin-1 (ET-1). The aim of this study was to test the hypothesis that blockade of ET receptors results in enhanced endothelium-dependent vasodilatation (EDV) in individuals with insulin resistance. Twelve individuals with insulin resistance without any history of diabetes or cardiovascular disease and 8 age-matched controls with high insulin sensitivity, as determined by hyperinsulinemic-euglycemic clamp, were investigated on 2 separate occasions using forearm venous occlusion plethysmography. Endothelium-dependent and endothelium-independent vasodilatation was determined before and after selective ET(A) and dual ET(A)/ET(B) receptor blockade. A 60 minute intraarterial infusion of the ET(A) receptor antagonist BQ123 (10 nmol/min) combined with the ET(B) receptor antagonist BQ788 (5 nmol/min) evoked a significant increase in acetylcholine-mediated EDV (P < 0.01) in individuals with insulin resistance. The endothelium-independent vasodilator response to nitroprusside was not changed by dual ET(A)/ET(B) receptor blockade. Dual ET(A)/ET(B) receptor blockade did not affect the response to acetylcholine or nitroprusside in the insulin-sensitive group. Selective ET(A) receptor blockade did not evoke any changes in endothelium-dependent or endothelium-independent vasodilatation in either group. This study demonstrates that dual ET(A)/ET(B) receptor blockade, but not selective ET(A) blockade, enhances EDV in subjects with insulin resistance, suggesting that ET-1 is involved in the regulation of endothelial function in individuals with insulin resistance.

Endothelin-1-induced oxidative stress in DOCA-salt hypertension involves NADPH-oxidase-independent mechanisms

We have demonstrated recently [Callera, Touyz, Teixeira, Muscara, Carvalho, Fortes, Schiffrin and Tostes (2003) Hypertension 42, 811-817] that increased vascular oxidative stress in DOCA (deoxycorticosterone acetate)-salt rats is associated with activation of the ET (endothelin) system via ETA receptors. The exact source of ET-1-mediated oxidative stress remains unclear. The aim of the present study was to investigate whether ET-1 increases generation of ROS (reactive oxygen species) in DOCA-salt hypertension through NADPH-oxidase-dependent mechanisms. Xanthine oxidase, eNOS (endothelial nitric oxide synthase) and COX-2 (cyclo-oxygenase-2) were also examined as potential ET-1 sources of ROS as well as mitochondrial respiration. DOCA-salt and control UniNX (uninephrectomized) rats were treated with the ETA antagonist BMS182874 (40 mg.day(-1).kg(-1) of body weight) or vehicle. Plasma TBARS (thiobarbituric acid-reacting substances) were increased in DOCA-salt compared with UniNX rats. Activity of NADPH and xanthine oxidases in aorta, mesenteric arteries and heart was increased in DOCA-salt rats. BMS182874 decreased plasma TBARS levels without influencing NADPH and xanthine oxidase activities in DOCA-salt rats. Increased p22(phox) protein expression and increased p47(phox) membrane translocation in arteries from DOCA-salt by rats were not affected by BMS182874 treatment. Increased eNOS and COX-2 expression, also observed in aortas from DOCA-salt rats, was unaltered by BMS182874. Increased mitochondrial generation of ROS in DOCA-salt rats was normalized by BMS182874. ETA antagonism also increased the expression of mitochondrial MnSOD (manganese superoxide dismutase) in DOCA-salt rats. In conclusion, activation of NADPH oxidase does not seem to be the major source of oxidative stress induced by ET-1/ETA in DOCA-salt hypertension, which also appears to be independent of increased activation of xanthine oxidase or eNOS/COX-2 overexpression. Mitochondria may play a role in ET-1-driven oxidative stress, as evidenced by increased mitochondrial-derived ROS in this model of hypertension.

How does endothelin induce vascular oxidative stress in mineralocorticoid hypertension?

Endothelin and reactive oxygen species have been identified as important mediators in the pathogenesis of hypertension and associated end-organ damage. In the present issue of Clinical Science, Callera and co-workers have provided new evidence that endothelin stimulates mitochondria to generate reactive oxygen species in the vascular wall during mineralocorticoid-induced hypertension in the rat. These studies open a new line of investigation that could be important for the development of therapeutic strategies; however, there still remains a great deal of uncertainty about the mechanisms that define the relationship between endothelin and oxidative stress in hypertension.

NADPH oxidase-derived reactive oxygen species in cardiac pathophysiology

Chronic heart failure, secondary to left ventricular hypertrophy or myocardial infarction, is a condition with increasing morbidity and mortality. Although the mechanisms underlying the development and progression of this condition remain a subject of intense interest, there is now growing evidence that redox-sensitive pathways play an important role. This article focuses on the involvement of reactive oxygen species derived from a family of superoxide-generating enzymes, termed NADPH oxidases (NOXs), in the pathophysiology of ventricular hypertrophy, the accompanying interstitial fibrosis and subsequent heart failure. In particular, the apparent ability of the different NADPH oxidase isoforms to define the response of a cell to a range of physiological and pathophysiological stimuli is reviewed. If confirmed, these data would suggest that independently targeting different members of the NOX family may hold the potential for therapeutic intervention in the treatment of cardiac disease.

Oxidative Stress and Cardiovascular Disease: Antioxidants and Unresolved Issues

Experimental and clinical studies suggest that oxidative stress contributes to the development and progression of cardiovascular disease. However, clinical trials with classic vitamin antioxidants failed to demonstrate any benefit in cardiovascular outcomes. Recent advances in our understanding of mechanisms involved in free radical generation reinstate that a more comprehensive approach targeting the prevention of reactive oxygen species (ROS) formation early in the disease process may prove beneficial. Experimental studies and reviews in oxidative stress were selected to provide a better understanding of the roles of the reactive species in the initiation and progression of cardiovascular disease (CVD). Clinical studies that evaluated the efficacy of several classes of antioxidants in CVD were included in the second part of this review to discuss future therapeutic guidelines based on currently available evidence. In conclusion, before a potential role for antioxidants in the treatment of CVD is eliminated, more carefully designed studies with classic as well as new antioxidants in well-defined patient populations are warranted to provide a definitive answer.

Aldosterone mediates angiotensin II-induced interstitial cardiac fibrosis via a Nox2-containing NADPH oxidase

Angiotensin (ANG) II (AngII) and aldosterone contribute to the development of interstitial cardiac fibrosis. We investigated the potential role of a Nox2-containing NADPH oxidase in aldosterone-induced fibrosis and the involvement of this mechanism in AngII-induced effects. Nox2-/- mice were compared with matched wild-type controls (WT). In WT mice, subcutaneous (s.c.) AngII (1.1 mg/kg/day for 2 wk) significantly increased NADPH oxidase activity, interstitial fibrosis (11.5+/-1.0% vs. 7.2+/-0.7%; P<0.05), expression of fibronectin, procollagen I, and connective tissue growth factor mRNA, MMP-2 activity, and NF-kB activation. These effects were all inhibited in Nox2-/- hearts. The mineralocorticoid receptor antagonist spironolactone inhibited AngII-induced increases in NADPH oxidase activity and the increase in interstitial fibrosis. In a model of mineralocorticoid-dependent hypertension involving chronic aldosterone infusion (0.2 mg/kg/day) and a 1% Na Cl diet ("ALDO"), WT animals exhibited increased NADPH oxidase activity, pro-fibrotic gene expression, MMP-2 activity, NF-kB activation, and significant interstitial cardiac fibrosis (12.0+/-1.7% with ALDO vs. 6.3+/-0.3% without; P<0.05). These effects were inhibited in Nox2-/- ALDO mice (e.g., fibrosis 6.8+/-0.8% with ALDO vs. 5.8+/-1.0% without ALDO; P=NS). These results suggest that aldosterone-dependent activation of a Nox2-containing NADPH oxidase contributes to the profibrotic effect of AngII in the heart as well as the fibrosis seen in mineralocorticoid-dependent hypertension.

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.

Increased expression of cyclooxygenase-2 mediates enhanced contraction to endothelin ETA receptor stimulation in endothelial nitric oxide synthase knockout mice

The aim of this study was to determine whether prolonged loss of NO activity, in endothelial NO synthase knockout (eNOS(-/-)) mice, influences endothelin (ET) ETA receptor-mediated smooth muscle contraction and, if so, to define the underlying mechanism(s). In isolated endothelium-denuded abdominal aortas, contractions to the selective ETA receptor agonist ET-1(1-31) were significantly increased in aortas from eNOS(-/-) compared with wild-type (WT) mice. In contrast, contractions to the alpha1-adrenergic agonist phenylephrine or the thromboxane (TX) A2 analog U-46619 were similar between eNOS(-/-) and WT mice. Immunofluorescent and Western blot analysis demonstrated that the aortic expression of ETA receptors was decreased in eNOS(-/-) compared with WT mice. Contractions evoked by ET-1(1-31), but not phenylephrine, were reduced by inhibition of cyclooxygenase-2 (COX-2) (indomethacin or celecoxib) or of TXA2/prostaglandin H2 receptors (SQ-29548). After COX inhibition, contractions to ET-1(1-31) were no longer increased and were actually decreased in eNOS(-/-) compared with WT aortas. Western blot analysis revealed that endothelium-denuded abdominal aortas express COX-2, but not COX-1, and that expression of COX-2 was significantly increased in eNOS(-/-) compared with WT mice. Contractions to the COX substrate arachidonic acid were also increased in eNOS(-/-) aortas. Furthermore, ET-1(1-31) but not phenylephrine stimulated production of the TXA2 metabolite TXB2, which was increased in eNOS(-/-) compared with WT aortas. Therefore, COX-2 plays a crucial and selective role in ETA-mediated smooth muscle contraction. Furthermore, COX-2 expression is increased in eNOS(-/-) mice, which overcomes a reduced expression of ETA receptors and enables a selective increase in contraction to ETA receptor stimulation.

Chronic treatment with vascular endothelial growth factor preserves agonist-evoked vascular responses in the streptozotocin-induced diabetic rat

AIMS/HYPOTHESIS

Vascular dysfunction is a hallmark of diabetes mellitus and endothelial dysfunction is considered to be a key early component of vascular dysfunction. Attenuated agonist-evoked responses are considered to be a barometer of endothelial/vascular dysfunction. We sought to determine whether vascular endothelial growth factor (VEGF) could prevent dysfunction from developing in the streptozotocin (STZ)-induced rat model of type 1 diabetes.

MATERIALS AND METHODS

One week after induction of diabetes, STZ rats began a 4-week treatment protocol of twice-weekly i.v. injections of 2 microg VEGF or inactivated VEGF. Corresponding non-diabetic rats served as controls. Agonist-evoked vascular responses were recorded 1 day after the last treatment in anaesthetised rats.

RESULTS

Acetylcholine (0.1-12.5 microg/kg) evoked increases in superior mesenteric arterial conductance and decreases in mean blood pressure, while methoxamine (12.5-100 microg/kg) and endothelin-1 (100-1,200 pmol/kg) evoked decreases in superior mesenteric arterial conductance and increases in mean blood pressure. These responses to all three agonists were attenuated in STZ rats, and chronic treatment with VEGF improved these responses dramatically. Both the reduction in plasma nitrate and nitrite and the elevation in aortic superoxide associated with STZ diabetes were normalised with VEGF treatment. VEGF also prevented the apparent paradoxical increased endothelial nitric oxide synthase expression seen in untreated STZ rats.

CONCLUSIONS/INTERPRETATION

Chronic treatment with VEGF early in diabetes is able to prevent the attenuated agonist-evoked vascular responses in STZ rats and normalise the oxidative environment associated with the disease.

Vitamin C blocks vascular dysfunction and release of interleukin-6 induced by endothelin-1 in humans in vivo

OBJECTIVE

Inflammation of the vessel wall is of importance in atherosclerosis. Endothelin-1 (ET-1) exerts pro-inflammatory effects and contributes to endothelial dysfunction. The objective was to test whether ET-1 impairs vascular function by increasing oxidative stress and release of pro-inflammatory cytokines in humans.

METHODS

Forearm blood flow (FBF) was determined in 12 young healthy males with venous occlusion plethysmography.

RESULTS

Intra-brachial infusion of ET-1 (20 pmol/min) decreased both endothelium-dependent and -independent vasodilatation (P<0.001). ET-1 also increased venous IL-6 levels (0.96+/-0.14-1.40+/-0.15 ng/ml; P<0.001). Administration of Vitamin C (24 mg/min) following the ET-1 infusion did not restore vascular function. However, pre-treatment with Vitamin C before ET-1 prevented the decrease in endothelium-dependent and -independent vasodilatation as well as the increase in IL-6 levels (1.20+/-0.28 versus 1.29+/-0.27 ng/ml; P=0.57). Infusion of a control vasoconstrictor substance, noradrenaline (80 ng/min) for 30 min did not affect IL-6 levels.

CONCLUSIONS

ET-1 impairs endothelium-dependent and -independent vasodilatation and stimulates release of IL-6 in humans in vivo. These effects are inhibited by pre-treatment with the antioxidant Vitamin C. This suggests that the mechanism by which ET-1 impairs vascular function and stimulates release of IL-6 involves increased oxidative stress.