Abstract 272: Hyperhomocysteinemia Potentiated the Impairment of Hydrogen Sulfide-induced Endothelium-derived Hyperpolarization-mediated Vascular Relaxation in Diabetic Db/db Mice

Abstract

Background: Cumulative evidence indicates that plasma homocysteine (Hcy) level is positively correlated with cardiovascular mortality in Type 2 diabetic patients. Aims: To explore the effects and mechanisms of elevated plasma Hcy level[[Unable to Display Character: ―]] hyperhomocysteinemia (HHcy) on endothelial function in db/db mice. Methods and Results: HHcy was induced in diabetic db/db and non-diabetic db/+ mice fed with a high methionine diet (HM, 2% methionine) for 8 weeks (plasma tHcy=54.31±5.4 and 34.21±4.15 μM). Endothelial function was examined in small mesenteric arteries (SMA) using myographs. In non-diabetic mice, HHcy did not change vascular relaxation to acetylcholine (Ach); whereas, nitric oxide (NO)- and prostacyclin (PGI2)-mediated relaxation to Ach were impaired. Interestingly, endothelium-derived hyperpolarization factor (EDHF)-mediated relaxation to Ach was improved. In diabetic mice, HHcy potentiated the impairment of NO-, PGI2- and EDHF-mediated relaxation to Ach. Moreover, sodium hydrogen sulfide (NaHS), a donor of hydrogen sulfide (H2S), induced EDHF-mediated relaxation which was impaired in diabetic mice and potentiated by HHcy. NS309, a non-specific calcium-activated potassium channel (Kca) activator, significantly improved H2S- and Ach-induced EDHF-mediated relaxation in diabetic mice with HHcy. Tram-34, an intermediate conductance Kca (IK) blocker, but not small conductance Kca blocker apamin, diminished HHcy-induced impairment of EDHF-mediated relaxation in diabetic mice, suggesting that IK inactivation plays a major role. Free sulfide was decreased in plasma and SMA of diabetic mice which was potentiated with HHcy. Superoxide generation was increased and potentiated by HHcy in lung ECs from diabetic mice. Moreover, PEG-SOD improved vascular relaxation in diabetic mice with HHcy. Finally, tyrosine nitration of IK was increased in human cardiac microvascular endothelial cells (ECs) treated with either D-glucose (25 mM) or DL-Hcy (500 μM) for 48h, which was potentiated by a combination of D-glucose and DL-Hcy. Conclusions: H2S is a major EDHF in resistant arteries in mouse. H2S-contributed EDHF-mediated vascular relaxation was impaired in diabetes and was potentiated by HHcy via oxidative stress and IK inactivation.