Hyperhomocysteinemia impairs endothelium-derived hyperpolarizing factor–mediated vasorelaxation in transgenic cystathionine beta synthase–deficient mice

Abstract

AbstractHyperhomocysteinemia (HHcy) is associated with endothelial dysfunction (ED), but the mechanism is largely unknown. In this study, we investigated the role and mechanism of HHcy-induced ED in microvasculature in our newly established mouse model of severe HHcy (plasma total homocysteine, 169.5μM). We found that severe HHcy impaired nitric oxide (NO)– and endothelium-derived hyperpolarizing factor (EDHF)–mediated, endothelium-dependent relaxations of small mesenteric arteries (SMAs). Endothelium-independent and prostacyclin-mediated endothelium-dependent relaxations were not changed. A nonselective Ca2+-activated potassium channel (KCa) inhibitor completely blocked EDHF-mediated relaxation. Selective blockers for small-conductance KCa (SK) or intermediate-conductance KCa (IK) failed to inhibit EDHF-mediated relaxation in HHcy mice. HHcy increased the levels of SK3 and IK1 protein, superoxide (O2−), and 3-nitrotyrosine in the endothelium of SMAs. Preincubation with antioxidants and peroxynitrite (ONOO−) inhibitors improved endothelium-dependent and EDHF-mediated relaxations and decreased O2− production in SMAs from HHcy mice. Further, EDHF-mediated relaxation was inhibited by ONOO− and prevented by catalase in the control mice. Finally, L-homocysteine stimulated O2− production, which was reversed by antioxidants, and increased SK/IK protein levels and tyrosine nitration in cultured human cardiac microvascular endothelial cells. Our results suggest that HHcy impairs EDHF relaxation in SMAs by inhibiting SK/IK activities via oxidation- and tyrosine nitration–related mechanisms.