C-reactive protein levels determine systemic nitric oxide bioavailability in patients with coronary artery disease

Elevated C-reactive protein (CRP) levels are associated with impaired endothelial vasoreactivity in patients with coronary artery disease (CAD). Because inflammatory cytokines experimentally reduce basal and stimulated endothelial nitric oxide (NO) release, we hypothesised that patients with elevated CRP-levels are characterised by a systemic impairment in NO bioavailability.

Forearm blood flow (FBF) responses were measured by venous occlusion plethysmography in 75 male patients with documented CAD. Inhibition of NO synthesis by infusion of L-NMMA significantly reduced baseline FBF (2.2 +/- 0.5 vs. 1.9 +/- 0.5 mL/min/100 mL of forearm tissue, P < 0.001) and acetylcholine-stimulated FBF responses (AUC: 35.0 +/- 16.0 vs. 25.9 +/- 11.9; P < 0.001). CRP serum levels were inversely correlated with L-NMMA-induced decreases in baseline as well as acetylcholine-stimulated FBF responses. Co-infusion of the oxygen-derived free radical scavenger vitamin C significantly increased baseline FBF from 2.0 +/- 0.5 to 2.5 +/- 0.7 (mL/min/100 mL forearm tissue (P < 0.001)) and acetylcholine-stimulated FBF responses in patients with elevated CRP, but not in patients with low CRP serum levels. Vitamin C-induced increases in baseline FBF and in acetylcholine-stimulated FBF responses were significantly correlated with CRP serum levels. By multivariable analysis, CRP serum levels remained the only statistically significant independent predictor of NO bioavailability in the systemic circulation of patients with CAD.

In patients with CAD, low grade systemic inflammation is associated with increased in vivo oxidative stress leading to impaired systemic bioavailability of NO, which might significantly contribute to the transition from stable coronary artery disease to acute coronary syndromes.