Hyperhomocysteinemia potentiates diabetes-impaired EDHF-induced vascular relaxation: Role of insufficient hydrogen sulfide

Insufficient hydrogen sulfide (H(2)S) has been implicated in Type 2 diabetic mellitus (T2DM) and hyperhomocysteinemia (HHcy)-related cardiovascular complications. We investigated the role of H(2)S in T2DM and HHcy-induced endothelial dysfunction in small mesenteric artery (SMA) of db/db mice fed a high methionine (HM) diet. HM diet (8 weeks) induced HHcy in both T2DM db/db mice and non-diabetic db/+ mice (total plasma Hcy: 48.4 and 31.3 µM, respectively), and aggravated the impaired endothelium-derived hyperpolarization factor (EDHF)-induced endothelium-dependent relaxation to acetylcholine (ACh), determined by the presence of eNOS inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME) and prostacyclin (PGI(2)) inhibitor indomethacin (INDO), in SMA from db/db mice but not that from db/+ mice. A non-selective Ca(2+)-active potassium channel (K(Ca)) opener NS309 rescued T2DM/HHcy-impaired EDHF-mediated vascular relaxation to ACh. EDHF-induced relaxation to ACh was inhibited by a non-selective K(Ca) blocker TEA and intermediate-conductance K(Ca) blocker (IK(Ca)) Tram-34, but not by small-conductance K(Ca) (SK(Ca)) blocker Apamin. HHcy potentiated the reduction of free sulfide, H(2)S and cystathionine γ-lyase protein, which converts L-cysteine to H(2)S, in SMA of db/db mice. Importantly, a stable H(2)S donor DATS diminished the enhanced O(2)(-) production in SMAs and lung endothelial cells of T2DM/HHcy mice. Antioxidant PEG-SOD and DATS improved T2DM/HHcy impaired relaxation to ACh. Moreover, HHcy increased hyperglycemia-induced IK(Ca) tyrosine nitration in human micro-vascular endothelial cells. EDHF-induced vascular relaxation to L-cysteine was not altered, whereas such relaxation to NaHS was potentiated by HHcy in SMA of db/db mice which was abolished by ATP-sensitive potassium channel blocker Glycolamide but not by K(Ca) blockers. CONCLUSIONS: Intermediate HHcy potentiated H(2)S reduction via CSE-downregulation in microvasculature of T2DM mice. H(2)S is justified as an EDHF. Insufficient H(2)S impaired EDHF-induced vascular relaxation via oxidative stress and IK(Ca) inactivation in T2DM/HHcy mice. H(2)S therapy may be beneficial for prevention and treatment of micro-vascular complications in patients with T2DM and HHcy.