NF-kappaB activation plays a role in superoxide-mediated cerebral endothelial dysfunction after hypoxia/reoxygenation.

Abstract

Cerebral vascular injury occurs in response to hypoxia/reoxygenation (H/R). However, the cellular signaling pathways that regulate this event remain unclear. The present study was designed to determine whether reactive oxygen species (ROS) mediate endothelial dysfunction after H/R in cerebral resistance arteries and, if so, the relative contribution of ROS, NADPH oxidase, and a nuclear factor-kappaB (NF-kappaB) pathway. Arterial diameter and intraluminal pressure were simultaneously measured on rat posterior cerebral arteries (PCA). Superoxide was measured by 5-micromol/L lucigenin-enhanced chemiluminescence. Hypoxia/reoxygenation selectively inhibited cerebral vasodilation to the endothelium-dependent agonist acetylcholine (Ach) (0.01 to 10 micromol/L) by approximately 50%. Impaired vasodilation after H/R was reversed by 2,2,6,6-tetramethylpiperidine-N-oxyl (Tempo) (100 micromol/L), a cell-permeable superoxide dismutase mimetic, and partially by ebselen (10 micromol/L), a peroxynitrite scavenger. H/R-impaired vasodilation to Ach was also preserved by apocynin (1 mmol/L), a specific inhibitor for NADPH oxidase. Correspondingly, H/R significantly increased lucigenin-detectable superoxide, which was reduced by either Tempo or apocynin, but not by allopurinol (10 micromol/L), an inhibitor of xanthine oxidase. Finally, the NF-kappaB inhibitors helenalin (10 micromol/L) and MG-132 (1 micromol/L) independently antagonized H/R-impaired Ach-induced vasodilation without affecting dilator response to sodium nitroprusside, an endothelium-independent vasodilator. These results indicate that superoxide mediates cerebral endothelial dysfunction after hypoxia/reoxygenation largely via activation of NADPH oxidase and possibly activation of NF-kappaB pathway.