Functional consequences of endothelial nitric oxide synthase uncoupling in congestive cardiac failure

Background-Impaired endothelium-mediated vasodilatation (EMVD) in congestive cardiac failure (CCF) has been linked to decreased nitric oxide (NO) bioavailability because of its interaction with vascular superoxide (O-2(.-)), derived predominantly from NAD(P)H-dependent oxidases. When uncoupled from essential cofactors, endothelial nitric oxide synthase ( eNOS) produces O-2(.-). We studied the functional consequences of eNOS uncoupling in relation to EMVD in patients with CCF. Methods and Results-We employed the platelet as a compartmentalized ex-vivo model to examine O-2(.-) and NO production. When eNOS is functioning normally, incorporation of N-omega-Nitro-L-Arginine methyl ester (L-NAME, 1 mmol/L), results in increased O-2(.-) detection, as inhibition of NO production prevents NO scavenging of O-2(.-). This was observed in controls and 9 of the CCF patients, in whom O-2(.-) detection increased by 63% and 101%, respectively. In the remaining 9 CCF patients, incorporation of L-NAME reduced O-2(.-) production by 39%, indicating O-2(.-) production by eNOS uncoupling. Detection of platelet-derived NO was significantly greater in eNOS-coupled platelets compared with the uncoupled group (2.8+/-1.4 versus 0.9+/-0.4 pmol/10(8) platelets, P=0.04). Endothelium-dependent and-independent vasodilator responses to acetylcholine and sodium nitroprusside recorded using venous occlusion plethysmography were significantly impaired in patients exhibiting eNOS uncoupling. Conclusions-This study provides first evidence that platelet eNOS can become uncoupled in human CCF. Impaired endothelium-dependent and -independent vasodilator responses and diminished platelet-derived NO production occurred in association with enzyme uncoupling.