This is the first study that demonstrates an association between ADMA and important measures of vascular function, such as vascular O2- production and NO bioavailability directly in human vessels. Although serum ADMA has no effect on NADPH-stimulated superoxide in intact vessels, it is associated with greater eNOS uncoupling in the human vascular endothelium of patients with coronary artery disease.

Background-Tetrahydrobiopterin (BH 4 ) is a key regulator of endothelial nitric oxide synthase (eNOS) activity and coupling. However, the extent to which vascular and/or systemic BH 4 levels are altered in human atherosclerosis and the importance of BH 4 bioavailability in determining endothelial function and oxidative stress remain unclear. We sought to define the relationships between plasma and vascular biopterin levels in patients with coronary artery disease and to determine how BH 4 levels affect endothelial function, eNOS coupling, and vascular superoxide production. Methods and Results-Samples of saphenous veins and internal mammary arteries were collected from 219 patients with coronary artery disease undergoing coronary artery bypass grafting. We determined plasma and vascular levels of biopterins, vasomotor responses to acetylcholine, and vascular superoxide production in the presence and absence of the eNOS inhibitor N G -nitro-L-arginine methyl ester. High vascular BH 4 was associated with greater vasorelaxations to acetylcholine (PϽ0.05), whereas high plasma BH 4 was associated with lower vasorelaxations in response to acetylcholine (PϽ0.05). Furthermore, an inverse association was observed between plasma and vascular biopterins (PϽ0.05 for both saphenous veins and internal mammary arteries). High vascular (but not plasma) BH 4 was associated with reduced total and N G -nitro-L-arginine methyl ester-inhibitable superoxide, suggesting improved eNOS coupling. Finally, plasma but not vascular biopterin levels were correlated with plasma C-reactive protein levels (PϽ0.001). Conclusions-An inverse association exists between plasma and vascular biopterins in patients with coronary artery disease. Vascular but not plasma BH 4 is an important determinant of eNOS coupling, endothelium-dependent vasodilation, and superoxide production in human vessels, whereas plasma biopterins are a marker of systemic inflammation.

Background-The endothelial nitric oxide synthase cofactor tetrahydrobiopterin (BH4) plays a pivotal role in maintaining endothelial function in experimental vascular disease models and in humans. Augmentation of endogenous BH4 levels by oral BH4 treatment has been proposed as a potential therapeutic strategy in vascular disease states. We sought to determine the mechanisms relating exogenous BH4 to human vascular function and to determine oral BH4 pharmacokinetics in both plasma and vascular tissue in patients with coronary artery disease. Methods and Results-Forty-nine patients with coronary artery disease were randomized to receive low-dose (400 mg/d) or high-dose (700 mg/d) BH4 or placebo for 2 to 6 weeks before coronary artery bypass surgery. Vascular function was quantified by magnetic resonance imaging before and after treatment, along with plasma BH4 levels. Vascular superoxide, endothelial function, and BH4 levels were determined in segments of saphenous vein and internal mammary artery. Oral BH4 treatment significantly augmented BH4 levels in plasma and in saphenous vein (but not internal mammary artery) but also increased levels of the oxidation product dihydrobiopterin (BH2), which lacks endothelial nitric oxide synthase cofactor activity. There was no effect of BH4 treatment on vascular function or superoxide production. Supplementation of human vessels and blood with BH4 ex vivo revealed rapid oxidation of BH4 to BH2 with predominant BH2 uptake by vascular tissue. Conclusions-Oral BH4 treatment augments total biopterin levels in patients with established coronary artery disease but has no net effect on vascular redox state or endothelial function owing to systemic and vascular oxidation of BH4. Alternative strategies are required to target BH4-dependent endothelial function in established vascular disease states. Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT00423280.