Simvastatin Ameliorates Angiotensin II-Induced Endothelial Dysfunction Through Restoration of Rho-BH4-eNOS-NO Pathway

Abstract

Endothelial dysfunction contributes to the initiation and development of hypertension. We previously found that simvastatin moderately decreases blood pressure in 2-kidney-2-clip (2k2c) renal hypertension, but the precise mechanisms are still unclear. The present study was designed to examine the protective actions of simvastatin in 2k2c-evoked endothelial dysfunction and also delineate the underlying mechanisms. Here we show that 2k2c-induced elevation in plasma angiotensin II impaired acetylcholine-induced endothelium-dependent vascular relaxation, suppressed endothelial NO synthase (eNOS) activity and reduced nitric oxide (NO) production. Additionally, the levels of tetrahydrobiopterin (BH4), an essential cofactor of eNOS, as well as the activity of GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme for BH4 synthesis, were markedly reduced. Administration of simvastatin significantly improved acetylcholine-induced endothelium-dependent carotid arteries relaxation at 9 weeks in reno-hypertensive rats. Notably, GTPCH I activity, BH4 production, p-eNOS expression and NO levels in the vascular endothelium were elevated as a result of simvastatin administration. In cultured rat arterial endothelial cells, simvastatin restored BH4, GTPCH I activity and NO release impaired by angiotensin II, and pretreatment with mevalonate (MVA) or geranylgeranyl pyrophosphate (GGPP) abolished the beneficial effects exerted by simvastatin. Moreover, RhoA inhibitor C3 exoenzyme, Rho kinase inhibitor Y-27632 and dominant negative mutant of RhoA prevented BH4 and NO loss due to Ang II treatment. Taken together, normalization of BH4-eNOS-NO pathway at least in part accounts for the beneficial actions of simvastatin on vascular endothelium during 2k2c hypertension, and RhoA-Rho kinase pathway is involved in regulation of BH4 production.

Obesity Alters the Peripheral Circadian Clock in the Aorta and Microcirculation

“…GTPCH1 is the rate-limited enzyme for the production of BH4 in which an essential cofactor for nitric oxide synthase to generate NO in endothelial cells [6]. Suppression of GTPCH1 expression causes a reduced BH4 bioavailability [6,37]. While minor variations in GTPCH1 are observed, these did not achieve significance and likely contribute little to the observed defects.…”

Differential Modulation of Nitric Oxide Synthases in Aging: Therapeutic Opportunities

“…Whereas streptozotocin (STZ) increases vascular oxidative stress and impairs NO-mediated endothelium-dependent vasodilatation in control mice, STZ-treated transgenic GTPCH-1 mice exhibit less superoxide production and normal NO-mediated vasodilatation (Alp et al, 2003). Similarly, treatment of hypertensive rats with simvastatin restored GTPCH-1 activity and the BH 4 /eNOS/NO pathway reversing the hypertension-associated endothelial dysfunction (Zhang et al, 2012). In vitro , statins rapidly increase BH 4 bioavailability and up-regulate GTPCH-1, leading to eNOS recoupling and NO generation in endothelial cells (Hattori et al, 2003; Aoki et al, 2012; Zhang et al, 2012).…”

Thirty Years of Saying NO

“…29,110,111 A similar endothelial dysfunction is observed when the circulating BH 4 levels are low or if the bioavailability of the cofactor is reduced by exaggerated oxidation to BH 2 , as can be the case in postmenopausal females, in diabetes mellitus, on prolonged exposure to aldosterone or cortisol, in hypertension (in particular, if caused by angiotensin II, which promotes ROS production) and during inflammation (accompanied by induction of iNOS); under those circumstances, supplementation with exogenous BH 4 improves endothelial function, as does the administration of erythropoietin, 112 which increases BH 4 levels by increasing the expressions of endogenous antioxidant enzymes (superoxide dismutases [SOD], catalase, and HO-1) and reducing that of NOX (see Reduced NO Bioavailability section of this article). 25,29,33,[110][111][112][113] Major causes of dysregulation in the BH 4 -balance include glucocorticoid receptor activation (decreasing GTP-cyclohydrolase I mRNA expression), 114 mineralocorticoid receptor activation (upregulating the expression of NOX) or increased oxidative stress (accelerating the degradation of BH 4 to BH 2 ), stimulation of the Rho-kinase pathway 113 (reducing the reconversion of BH 2 to BH 4 by dihydrofolate reductase or the synthesis of BH 4 by GTP-cyclohydrolase I), and impairment of eNOS function (see Reduced Protein Activity section of this article; reducing the amount of NO available for S-nitrosylation of dihydrofolate reductase that protects the latter from degradation; hence, reducing S-nitrosylation slows down the reconversion of BH 2 to BH 4 ; Figure 4). 25,29,33,[110][111][112][113][114] …”

“…25,29,33,[110][111][112][113] Major causes of dysregulation in the BH 4 -balance include glucocorticoid receptor activation (decreasing GTP-cyclohydrolase I mRNA expression), 114 mineralocorticoid receptor activation (upregulating the expression of NOX) or increased oxidative stress (accelerating the degradation of BH 4 to BH 2 ), stimulation of the Rho-kinase pathway 113 (reducing the reconversion of BH 2 to BH 4 by dihydrofolate reductase or the synthesis of BH 4 by GTP-cyclohydrolase I), and impairment of eNOS function (see Reduced Protein Activity section of this article; reducing the amount of NO available for S-nitrosylation of dihydrofolate reductase that protects the latter from degradation; hence, reducing S-nitrosylation slows down the reconversion of BH 2 to BH 4 ; Figure 4). 25,29,33,[110][111][112][113][114] …”