Angiotensin II type 1 receptor blockers prevent tumor necrosis factor-α-mediated endothelial nitric oxide synthase reduction and superoxide production in human umbilical vein endothelial cells

Decrease in endothelial nitric oxide synthase (eNOS) expression is one of the adverse outcomes of endothelial dysfunction. Tumor necrosis factor-α (TNF-α) is known to decrease eNOS expression and is an important mediator of endothelial dysfunction. We hypothesized that an angiotensin II type 1 (AT1) receptor blocker would improve endothelial function via not only inhibition of the angiotensin II signaling but also inhibition of the TNF-α-mediated signaling. Therefore we investigated whether an AT1 receptor blocker would restore the TNF-α-induced decrease in eNOS expression in cultured human umbilical vein endothelial cells (HUVEC). Pretreatment of HUVEC with an antioxidant (superoxide dismutase, α-tocopherol) or AT1 receptor blockers (olmesartan or candesartan) restored the TNF-α-dependent reduction of eNOS. The AT1 receptor blocker decreased the TNF-α-dependent increase of 8-isoprostane. The superoxide dismutase activities in HUVEC were stable during AT1 receptor blocker treatment, and the AT1 receptor blocker did not scavenge superoxide directly. The AT1 receptor blocker also decreased TNF-α-induced phosphorylation of IκBα and cell death. These results suggest that AT1 receptor blockers are able to ameliorate TNF-α-dependent eNOS reduction or cell injury by inhibiting superoxide production or nuclear factor-κB activation.