Endothelial regulation of vasomotion in ApoE-deficient mice - Implicationsfor interactions between peroxynitrite and tetrahydrobiopterin

Background-Altered endothelial cell nitric oxide (NO.) production in athero sclerosis may be due to a reduction of intracellular tetrahydrobiopterin, w hich is a critical cofactor for NO synthase (NOS). In addition, previous li terature suggests that inactivation of NO. by increased vascular production superoxide (O-2(.-)) also reduces NO. bioactivity in several disease state s. We sought to determine whether these 2 seemingly disparate mechanisms we re related. Methods and Results-Endothelium-dependent vasodilation was abnormal in aort as of apoE-deficient (apoE(-/-)) mice, whereas vascular superoxide producti on (assessed by 5 mu mol/L lucigenin) was markedly increased. Treatment wit h either liposome-entrapped superoxide dismutase or sepiapterin, a precurso r to tetrahydrobiopterin, improved endothelium-dependent vasodilation in ao rtas from apoE(-/-) mice. Hydrogen peroxide had no effect on the decay of t etrahydrobiopterin, as monitored spectrophotometrically. In contrast, super oxide modestly and peroxynitrite strikingly increased the decay of tetrahyd robiopterin over 500 seconds. Luminol chemiluminescence, inhibitable by the peroxynitrite scavengers ebselen and uric acid, was markedly increased in apoE(-/-) aortic rings. In vessels from apoE(-/-) mice, uric acid improved endothelium-dependent relaxation while having no effect in vessels from con trol mice. Treatment of normal aortas with exogenous peroxynitrite dramatic ally increased vascular O-2(.-) production, seemingly from eNOS, because th is effect was absent in vessels lacking endothelium, was blocked by NOS inh ibition, and did not occur in vessels from mice lacking eNOS. Conclusions-Reactive oxygen species may alter endothelium-dependent vascula r relaxation not only by the interaction of O-2(.-) with NO. but also throu gh interactions between peroxynitrite and tetrahydrobiopterin. Peroxynitrit e oxidation of tetrahydrobiopterin may represent a pathogenic cause of "unc oupling" of NO synthase.