Angiotensin II-induced superoxide anion generation in human vascular endothelial cells Role of membrane-bound NADH-/NADPH-oxidases

Abstract

Angiotensin II (ANG II) mediated hypertension accelerates atherosclerosis (AS) and thereby increases the incidence of myocardial infarction (MI). On the other hand, superoxide anion (O2-) is involved in the modification of low density lipoproteins, inhibition of prostacyclin (PGI2) formation and breakdown of nitric oxide. These events finally lead to rapid progression of AS and MI. In the present study, we investigate whether ANG II can induce O2- release from human vascular endothelial cells (HVECs) and the possible mechanisms involved. The expression of ANG receptors subtype-1 (AT-1) and subtype-2 (AT-2) were identified by using reverse transcription polymerase chain reaction and sequence analysis. The O2- production was dose-dependently increased in HVECs treated with ANG II (10(-7)-10(-9) M) and with a maximum rate after 1 h of incubation. This event was significantly inhibited by pretreatment of cells with the specific AT-1 blocker losartan (10(-7) M) and to a lesser extent by the specific AT-2 receptor blocker PD123319 (10(-7) M). The combined incubation of both receptor blockers was even more effective. In addition, our lucigenin-enhanced chemiluminescence assay showed that the activity of plasma membrane-bound NADH-/NADPH-oxidases derived from ANG II-treated cells was also significantly increased, this effect was reduced in cells pretreated with losartan or to lesser extent by PD123319. However, the activity of xanthine oxidase remained unchanged in response to ANG II. Furthermore, the basal O2- release from HVECs was inhibited in cells treated with angiotensin-converting enzyme (ACE) inhibitor, Lisinopril (10(-6) M), and this event could be reversed by ANG II. ANG II induces O2- release in HVECs via activation of membrane-bound NADH-/NADPH-oxidase, an effect, that is mediated by both AT-1 and AT-2 receptors. This suggests that acceleration of AS and MI in ANG II-mediated hypertension may at least be due to ANG II-induced O2- generation from vascular endothelial cells. In this case, the ACE inhibitors and the ANG receptor antagonists may act as causative "antioxidants".