Abstract 648: Nebivolol and Valsartan Increase Nitric Oxide Release from Human Endothelial Cells in a Synergistic Fashion

Abstract

Introduction: Nebivolol is a β1-adrenergic receptor antagonist that stimulates endothelial nitric oxide (NO) release through β3-adrenergic receptor activation, ATP-mediated stimulation of purinergic P2Y receptors, and inhibition of membrane lipid oxidation. Valsartan is an angiotensin II receptor blocker (ARB) that selectively inhibits angiotensin II type 1 (AT1) receptors, thereby exerting no direct effect at type 2 (AT2) receptors, which have been shown to stimulate NO synthase activity through a bradykinin-mediated pathway. As NO is a key regulator of blood pressure and these two antihypertensive agents promote NO release through distinct mechanisms, we compared their individual and combined effects on NO release from human endothelial cells. Methods: Human umbilical vein endothelial cells (HUVECs) were incubated for 1 hr with vehicle, nebivolol or valsartan alone (each at 1.0 μM), or nebivolol (1.0 μM) and valsartan (0.5-5.0 μM) combined. The comparative effects of these agents on maximal NO release were measured in individual cells using porphyrinic nanosensors following stimulation with calcium ionophore (1.0 μM). Results: Nebivolol treatment increased HUVEC NO release by 49% (509 ± 18 nM, mean ± SD) as compared to vehicle treatment alone (342 ± 26 nM; p<0.001). Valsartan had a more modest effect, increasing NO release by 13% (385 ± 19 nM) as compared to vehicle-treated controls (p<0.01). Treatment with both agents at 1.0 μM increased HUVEC NO release by 91% (655 ± 19 nM) as compared to vehicle alone (p<0.001) and was 29% (p<0.001) and 70% (p<0.001) greater than the separate effects observed for nebivolol and valsartan, respectively. The additive effect of valsartan was dose-dependent and was also observed at 0.5 and 5.0 μM in combination with nebivolol. Conclusions: These data suggest that nebivolol and valsartan, when applied in combination, increase the ability of endothelial cells to release NO in a synergistic manner. The exact mechanism of this process remains unclear but, considering the importance of NO in regulating blood pressure, merits further study.