Acute inflammation causes endothelial dysfunction, which is partly mediated by oxidant stress and inactivation of nitric oxide. The contribution of depletion of tetrahydrobiopterin (BH4), the cofactor required for nitric oxide generation, is unclear. In this randomized, double-blind, three-way crossover study, forearm blood flow (FBF) responses to ACh and glyceryltrinitrate (GTN) were measured before and 3.5 h after infusion of Escherichia coli endotoxin (LPS, 20 IU/kg iv) in eight healthy men. The effect of intra-arterial BH4(500 μg/min), placebo, or vitamin C (24 mg/min) was studied on separate days 3.5 h after LPS infusion. In addition, human umbilical vein endothelial cells were incubated for 24 h with vitamin C and LPS. ACh and GTN caused dose-dependent forearm vasodilation. The FBF response to ACh, which was decreased by 23 ± 17% ( P < 0.05) by LPS infusion, was restored to baseline reactivity by BH4and vitamin C. FBF responses to GTN were not affected by BH4or vitamin C. LPS increased leukocyte count, high-sensitivity C-reactive protein, IL-6, IL-1β, IFN-γ, monocyte chemoattractant protein-1, pulse rate, and body temperature and decreased platelet count and vitamin C concentration. Vitamin C increased forearm plasma concentration of BH4by 32% ( P < 0.02). Incubation with LPS and vitamin C, but not LPS alone, increased intracellular BH4concentration in human umbilical vein endothelial cells. Impaired endothelial function during acute inflammation can be restored by BH4or vitamin C. Vitamin C may exert some of its salutary effects by increasing BH4concentration.
A role for heterotrimeric GTP-binding proteins and ERK1/2 in insulin-mediated, nitric-oxide-dependent, cyclic GMP production in human umbilical vein endothelial cells
