NF-κB Activation Plays a Role in Superoxide-Mediated Cerebral Endothelial Dysfunction After Hypoxia/Reoxygenation

Abstract

Background and Purpose— 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-κB (NF-κB) pathway. Methods— Arterial diameter and intraluminal pressure were simultaneously measured on rat posterior cerebral arteries (PCA). Superoxide was measured by 5-μmol/L lucigenin-enhanced chemiluminescence. Results— Hypoxia/reoxygenation selectively inhibited cerebral vasodilation to the endothelium-dependent agonist acetylcholine (Ach) (0.01 to 10 μmol/L) by ≈50%. Impaired vasodilation after H/R was reversed by 2,2,6,6-tetramethylpiperidine- N -oxyl (Tempo) (100 μmol/L), a cell-permeable superoxide dismutase mimetic, and partially by ebselen (10 μmol/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 μmol/L), an inhibitor of xanthine oxidase. Finally, the NF-κB inhibitors helenalin (10 μmol/L) and MG-132 (1 μmol/L) independently antagonized H/R-impaired Ach-induced vasodilation without affecting dilator response to sodium nitroprusside, an endothelium-independent vasodilator. Conclusions— These results indicate that superoxide mediates cerebral endothelial dysfunction after hypoxia/reoxygenation largely via activation of NADPH oxidase and possibly activation of NF-κB pathway.