title: Reactive oxygen species mediate caspase activation and apoptosis induced by lipoic acid in human lung epithelial cancer cells through Bcl-2 down-regulation.
abstract: 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.
authors.affiliation: West Virginia University, Department of Pharmaceutical Sciences, Morgantown, WV 26506, USA.
authors.forename: Jirapan
authors.initials: J
authors.lastname: Moungjaroen
authors.forename: Ubonthip
authors.initials: U
authors.lastname: Nimmannit
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Callery
authors.forename: Liying
authors.initials: L
authors.lastname: Wang
authors.forename: Neelam
authors.initials: N
authors.lastname: Azad
authors.forename: Vimolmas
authors.initials: V
authors.lastname: Lipipun
authors.forename: Pithi
authors.initials: P
authors.lastname: Chanvorachote
authors.forename: Yon
authors.initials: Y
authors.lastname: Rojanasakul
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004847:Epithelial Cells / Q000187:drug effects*; D019254:Genes, bcl-2 / Q000187:drug effects / Q000502:physiology*; D005979:Glutathione Peroxidase / Q000235:genetics / Q000502:physiology; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D008175:Lung Neoplasms / Q000188:drug therapy*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D016877:Oxidants / Q000494:pharmacology; D010957:Plasmids / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000235:genetics / Q000502:physiology; D000072105:Superoxide Dismutase-1; D008063:Thioctic Acid / Q000494:pharmacology*; D014162:Transfection
chemical_list: D016877:Oxidants; D017382:Reactive Oxygen Species; C000606290:SOD1 protein, human; D008063:Thioctic Acid; D006861:Hydrogen Peroxide; D005979:Glutathione Peroxidase; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D020169:Caspases