Moungjaroen Jirapan, Nimmannit Ubonthip, Callery Patrick S, Wang Liying, Azad Neelam, Lipipun Vimolmas, Chanvorachote Pithi, Rojanasakul Yon
West Virginia University, Department of Pharmaceutical Sciences, Morgantown, WV 26506, USA.
J Pharmacol Exp Ther. 2006 Dec;319(3):1062-9. doi: 10.1124/jpet.106.110965. Epub 2006 Sep 21.
The antioxidant alpha-lipoic acid (LA) is a naturally occurring compound that has been shown to possess promising anticancer activity because of its ability to preferentially induce apoptosis and inhibit proliferation of cancer cells relative to normal cells. However, the molecular mechanisms underlying the apoptotic effect of LA are not well understood. We report here that LA induced reactive oxygen species (ROS) generation and a concomitant increase in apoptosis of human lung epithelial cancer H460 cells. Inhibition of ROS generation by ROS scavengers or by overexpression of antioxidant enzymes glutathione peroxidase and superoxide dismutase effectively inhibited LA-induced apoptosis, indicating the role of ROS, especially hydroperoxide and superoxide anion, in the apoptotic process. Apoptosis induced by LA was found to be mediated through the mitochondrial death pathway, which requires caspase-9 activation. Inhibition of caspase activity by the pan-caspase inhibitor (z-VAD-FMK) or caspase-9-specific inhibitor (z-LEHD-FMK) completely inhibited the apoptotic effect of LA. Likewise, the mitochondrial respiratory chain inhibitor rotenone potently inhibited the apoptotic and ROS-inducing effects of LA, supporting the role of mitochondrial ROS in LA-induced cell death. LA induced down-regulation of mitochondrial Bcl-2 protein through peroxide-dependent proteasomal degradation, and overexpression of the Bcl-2 protein prevented the apoptotic effect of LA. Together, our findings indicate a novel pro-oxidant role of LA in apoptosis induction and its regulation by Bcl-2, which may be exploited for the treatment of cancer and related apoptosis disorders.
抗氧化剂α-硫辛酸（LA）是一种天然存在的化合物，因其能够优先诱导癌细胞凋亡并抑制其相对于正常细胞的增殖，已显示出具有良好的抗癌活性。然而，LA凋亡效应背后的分子机制尚不清楚。我们在此报告，LA诱导人肺上皮癌H460细胞产生活性氧（ROS）并伴随凋亡增加。ROS清除剂或抗氧化酶谷胱甘肽过氧化物酶和超氧化物歧化酶的过表达抑制ROS生成，有效抑制了LA诱导的凋亡，表明ROS，特别是氢过氧化物和超氧阴离子在凋亡过程中的作用。发现LA诱导的凋亡是通过线粒体死亡途径介导的，这需要半胱天冬酶-9激活。泛半胱天冬酶抑制剂（z-VAD-FMK）或半胱天冬酶-9特异性抑制剂（z-LEHD-FMK）抑制半胱天冬酶活性，完全抑制了LA的凋亡效应。同样，线粒体呼吸链抑制剂鱼藤酮有效抑制了LA的凋亡和ROS诱导效应，支持线粒体ROS在LA诱导的细胞死亡中的作用。LA通过过氧化物依赖性蛋白酶体降解诱导线粒体Bcl-2蛋白下调，Bcl-2蛋白的过表达阻止了LA的凋亡效应。总之，我们的研究结果表明LA在凋亡诱导中具有新的促氧化作用及其受Bcl-2调节，这可能被用于治疗癌症和相关的凋亡紊乱。
