Background: We recently reported that arterial superoxide (O2-) is augmented by increased endothelin-1 (ET-1) in deoxycorticosterone acetate (DOCA)-salt hypertension, a model of low renin hypertension. Tetrahydrobiopterin (BH4), a potent reducing molecule with antioxidant properties and an essential cofactor for endothelial nitric oxide synthase, protects against O2--induced vascular dysfunction. However, the interaction between O2- and BH4 on endothelial function and the underlying mechanisms are unknown.
Methods and results: The present study tested the hypothesis that BH4 deficiency due to ET-1-induced O2- leads to impaired endothelium-dependent relaxation and that gene transfer of human guanosine 5'-triphosphate (GTP) cyclohydrolase I (GTPCH I), the first and rate-limiting enzyme for BH4 biosynthesis, reverses such deficiency and endothelial dysfunction in carotid arteries of DOCA-salt rats. There were significantly increased arterial O2- levels and decreased GTPCH I activity and BH4 levels in DOCA-salt compared with sham rats. Treatment of arteries of DOCA-salt rats with the selective ETA receptor antagonist ABT-627, NADPH oxidase inhibitor apocynin, or superoxide dismutase (SOD) mimetic tempol abolished O2- and restored BH4 levels. Basal arterial NO release and endothelium-dependent relaxations were impaired in DOCA-salt rats, conditions that were improved by apocynin or tempol treatment. Gene transfer of GTPCH I restored arterial GTPCH I activity and BH4 levels, resulting in reduced O2- and improved endothelium-dependent relaxation and basal NO release in DOCA-salt rats.
Conclusions: These results indicate that a BH4 deficiency resulting from ET-1-induced O2- via an ETA/NADPH oxidase pathway leads to endothelial dysfunction, and gene transfer of GTPCH I reverses the BH4 deficiency and endothelial dysfunction by reducing O2- in low renin mineralocorticoid hypertension.