Diabetes Impairs Wall Shear Stress Mediated Dilation in Human Coronary Resistance Arteries

Peroxynitrite (ONOO(-)) contributes to coronary microvascular dysfunction in diabetes mellitus (DM). We hypothesized that in DM, ONOO(-) interferes with the function of coronary endothelial caveolae, which play an important role in nitric oxide (NO)-dependent vasomotor regulation. Flow-mediated dilation (FMD) of coronary arterioles was investigated in DM and non-DM patients undergoing heart surgery. NO-mediated coronary FMD was significantly reduced in DM patients, but was restored by the ONOO(-) scavenger, iron-(III)-tetrakis(N-methyl-4'pyridyl)porphyrin-pentachloride, or uric acid. Exogenous ONOO(-) reduced FMD in non-DM subjects. Immunoelectron microscopy demonstrated increased 3-nitrotyrosine formation (ONOO(-)-specific protein nitration) in endothelial plasma membranes in DM, which colocalized with caveolin-1 (Cav-1), the key structural protein of caveolae. The membrane-localized Cav-1 was significantly reduced in DM. We also found that DM patients exhibited a decreased number of endothelial caveolae, whereas exogenous ONOO(-) reduced caveolae number. Correspondingly, pharmacological (methyl-â-cyclodextrin) or genetic disruption of caveolae (Cav-1 knockout mice) abolished coronary FMD, which was rescued by sepiapterin, the stable precursor of the NO synthase (NOS) cofactor, tetrahydrobiopterin. Sepiapterin also restored coronary FMD in DM patients. Thus, we propose that ONOO(-) selectively targets and disrupts endothelial caveolae, which contributes to NOS uncoupling, and, hence, reduced NO-mediated coronary vasodilation in DM patients.