Chronic administration of genistein improves endothelial dysfunction in spontaneously hypertensive rats: involvement of eNOS, caveolin and calmodulin expression and NADPH oxidase activity

NAD(P)H oxidase-derived peroxide mediates elevated basal and impaired flow-induced NO production in SHR mesenteric arteries in vivo

Nitric oxide (NO) and reactive oxygen species (ROS) have fundamentally important roles in the regulation of vascular tone and remodeling. Although arterial disease and endothelial dysfunction alter NO and ROS levels to impact vasodilation and vascular structure, direct measurements of these reactive species under in vivo conditions with flow alterations are unavailable. In this study, in vivo measurements of NO and H2O2 were made on mesenteric arteries to determine whether antioxidant therapies could restore normal NO production in spontaneously hypertensive rats (SHR). Flow was altered from approximately 50-200% of control in anesthetized Wistar-Kyoto rats (WKY) and SHR by selective placement of microvascular clamps on adjacent arteries while NO and H2O2 were directly measured with microelectrodes. Relative to WKY, SHR had significantly increased baseline NO and H2O2 concentrations (2,572 +/- 241 vs. 1,059 +/- 160 nM, P < 0.01; and 26 +/- 7 vs. 7 +/- 1 microM, P < 0.05, respectively). With flow elevation, H2O2 but not NO increased in SHR; NO but not H2O2 was elevated in WKY. Apocynin and polyethylene-glycolated catalase decreased baseline SHR NO and H2O2 to WKY levels and restored flow-mediated NO production. Suppression of NAD(P)H oxidase with gp91ds-tat decreased SHR H2O2 to WKY levels. Addition of topical H2O2 to increase peroxide to the basal concentration measured in SHR elevated WKY NO to levels observed in SHR. The results support the hypothesis that increased vascular peroxide in SHR is primarily derived from NAD(P)H oxidase and increases NO concentration to levels that cannot be further elevated with increased flow. Short-term and even acute administration of antioxidants are able to restore normal flow-mediated NO signaling in young SHR.

Targeting reactive oxygen species in hypertension

Oxidative stress plays an important role in the pathogenesis of hypertension. A number of sources of reactive oxygen species have been identified including NADPH oxidase, endothelial NO synthase, and xanthine oxidase. Inhibitors of these systems reduce blood pressure in experimental models. Targeted overexpression of antioxidant systems and interference with expression of oxidant systems has also been successfully used in animal models of hypertension. It is expected that these strategies will eventually be translated to human disease, but currently, the specificity and toxicity of such measures are not yet fulfilling quality criteria for treatment of humans. In the meantime, presumably nontoxic measures, such as administration of antioxidant vitamins, are the only available treatments for oxidative stress in humans. In this review, we discuss strategies to target oxidative stress both in experimental models and in humans. We also discuss how patients could be selected who particularly benefit from antioxidant treatment. In clinical practice, diagnostic procedures beyond measurement of blood pressure will be necessary to predict the response to antioxidants; these procedures will include measurement of antioxidant status and detailed assessment of vascular structure and function.

Intracoronary genistein acutely increases coronary blood flow in anesthetized pigs through beta-adrenergic mediated nitric oxide release and estrogenic receptors

Various studies have suggested that the phytoestrogen genistein has beneficial cardioprotective and vascular effects. However, there has been scarce information regarding the primary effect of genistein on coronary blood flow and its mechanisms including estrogen receptors, autonomic nervous system, and nitric oxide (NO). The present study was planned to determine the primary effect of genistein on coronary blood flow and the mechanisms involved. In anesthetized pigs, changes in left anterior descending coronary artery caused by intracoronary infusion of genistein at constant heart rate and arterial pressure were assessed using ultrasound flowmeters. In 25 pigs, genistein infused at 0.075 mg/min increased coronary blood flow by about 16.3%. This response was graded in a further five pigs by increasing the infused dose of the genistein between 0.007 and 0.147 mg/min. In the 25 pigs, blockade of cholinergic receptors (iv atropine; five pigs) and alpha-adrenergic receptors (iv phentolamine; five pigs) did not abolish the coronary response to genistein, whose effects were prevented by blockade of beta(2)-adrenergic receptors (iv butoxamine; five pigs), nitric oxide synthase (intracoronary N(omega)-nitro-L-arginine methyl ester; five pigs) and estrogenic receptors (ERs; ERalpha/ERbeta; intracoronary fulvestrant; five pigs). In porcine aortic endothelial cells, genistein induced the phosphorylation of endothelial nitric oxide synthase and NO production through ERK 1/2, Akt, and p38 MAPK pathways, which was prevented by the concomitant treatment by butoxamine and fulvestrant. In conclusion, genistein primarily caused coronary vasodilation the mechanism of which involved ERalpha/ERbeta and the release of NO through vasodilatory beta(2)-adrenoreceptor effects.

Genistein, a soy phytoestrogen, upregulates the expression of human endothelial nitric oxide synthase and lowers blood pressure in spontaneously hypertensive rats

Genistein, a soy phytoestrogen, may improve vascular function, but the mechanism of this effect is unclear. Endothelial-derived nitric oxide (NO) is a key regulator of vascular tone and atherogenesis. Previous studies have established that estrogen can act directly on vascular endothelial cells (EC) to enhance NO synthesis through genomic stimulation of endothelial NO synthase (eNOS) expression. However, it is unknown whether genistein has a similar effect. We therefore investigated whether genistein directly regulates NO synthesis in primary human aortic EC (HAEC) and human umbilical vein EC (HUVEC). Genistein, at physiologically achievable concentrations in individuals consuming soy products, enhanced the expression of eNOS and subsequently elevated NO synthesis in both HAEC and HUVEC, with 1-10 micromol/L genistein inducing the maximal effects. However, the effects of genistein on eNOS and NO were not mediated by activation of estrogen signaling or inhibition of tyrosine kinases, 2 known biological actions of genistein. Genistein (1-10 micromol/L) increased eNOS gene expression (1.8- to 2.6-fold of control) and significantly increased eNOS promoter activity of the human eNOS gene in HAEC and HUVEC, suggesting that genistein activates eNOS transcription. Dietary supplementation of genistein to spontaneously hypertensive rats restored aortic eNOS levels, improved aortic wall thickness, and alleviated hypertension, confirming the biological relevance of the in vitro findings. Our data suggest that genistein has direct genomic effects on the vascular wall that are unrelated to its known actions, leading to increased eNOS expression and NO synthesis, thereby improving hypertension.