The xanthine derivative KMUP-1 inhibits models of pulmonary artery hypertension via increased NO and cGMP-dependent inhibition of RhoA/Rho kinase

Abstract

Background and purpose: KMUP-1 is known to increase cGMP, enhance endothelial nitric oxide synthase (eNOS) and suppress Rho kinase (ROCK) expression in smooth muscle. Here, we investigated the mechanism of action of KMUP-1 on acute and chronic pulmonary artery hypertension (PAH) in rats. Experimental approach: We measured pulmonary vascular contractility, wall thickening, eNOS immunostaining, expressions of ROCK II, RhoA activation, myosin phosphatase target subunit 1 (MYPT1) phosphorylation, eNOS, soluble guanylyl cyclase (sGC), protein kinase G (PKG) and phosphodiesterase 5A (PDE-5A), blood oxygenation and cGMP/cAMP, and right ventricular hypertrophy (RVH) in rats. Key results: In rings of intact pulmonary artery (PA), KMUP-1 relaxed the vasoconstriction induced by phenylephrine (10 μM) or the thromboxane A 2-mimetic U46619 (0.5 μM). In endothelium-denuded PA rings, this relaxation was reduced. In acute PAH induced by U46619 (2.5 μg·kg -1·min-1, 30 min), KMUP-1 relaxed vasoconstriction by enhancing levels of eNOS, sGC and PKG, suppressing those of PDE-5A, RhoA/ROCK II activation and MYPT1 phosphorylation, and restoring oxygenation in blood and cGMP/cAMP in plasma. Incubating smooth muscle cells from PA (PASMCs) with KMUP-1 inhibited thapsigargin-induced Ca2+ efflux and angiotensin II-induced Ca2+ influx. In chronic PAH model induced by monocrotaline, KMUP-1 increased eNOS and reduced RhoA/ROCK II activation/expression, PA wall thickening, eNOS immunostaining and RVH. KMUP-1 and sildenafil did not inhibit monocrotaline-induced PDE-5A expression. Conclusion and implications: KMUP-1 decreased PAH by enhancing NO synthesis by eNOS, with consequent cGMP-dependent inhibition of RhoA/ROCK II and Ca 2+ desensitization in PASMCs. KMUP-1 has the potential to reduce vascular resistance, remodelling and RVH in PAH. © 2010 The British Pharmacological Society.