Endothelial apoptosis induced by oxidative stress through activation of NF-kappa B - Antiapoptotic effect of antioxidant agents on endothelial cells

Injury of endothelial cells has been assumed to be an initial trigger of th e development or atherosclerosis. In this study, we investigated the molecu lar mechanisms of endothelial cell death induced by hypoxia, which leads to oxidative stress. To study the relation between hypoxia-induced cell death and activation of nuclear factor-kappaB (NF-kappaB) in a hypoxic state, we evaluated the effect of 2 antioxidant drugs, probucol and pyrrolidine dith iocarbamate (PDTC), on human endothelial apoptosis. Although hypoxic treatm ent of human aortic endothelial cells resulted in a significant decrease in cell number and a significant increase in apoptotic cells compared with th at of cells under normoxia (P <0.01), treatment with probucol (50 mu mol/L) or PDTC (100 mu mol/L) significantly attenuated the decrease in cell numbe r (P <0.01) and was accompanied by inhibition of NF-kappaB activation. Furt hermore, downregulation of bcl-2 caused by hypoxia was inhibited by these d rugs. We further investigated the translocation of bax protein from the cyt oplasm to the mitochondrial heavy fraction membrane, as translocation of ba x protein is considered to be a determinant of apoptosis. Interestingly, we found that antioxidant treatment inhibited the translocation of bax protei n caused by hypoxia. Moreover, upregulation of p53, a proapoptotic molecule , was observed in hypoxia, whereas treatment with probucol attenuated the e xpression of p53 accompanied by suppression of NF-kappaB activation. These data suggest functional links between p53 and endothelial apoptosis through the activation of NF-kappaB. Overall, the current study demonstrated that oxidative stress induced apoptosis in human aortic endothelial cells throug h the downregulation of bcl-2, translocation of bax, and upregulation of p5 3, probably through NF-kappaB activation. Oxidative stress may play an impo rtant role in endothelial apoptosis mediated by hypoxia, through the activa tion of NF-kappaB.