title: Superoxide radical-initiated apoptotic signalling pathway in selenite-treated HepG(2) cells: mitochondria serve as the main target.
abstract: The exact role of superoxide radicals (O(2)(*)(-)) in apoptosis is still a matter of debate. The main objective of the present study is to evaluate the apoptotic signalling pathway initiated by O(2)(*)(-). The reductive reaction of sodium selenite with glutathione was used as the intracellular O(2)(*)(-)-generating system. When cells were exposed to 5 to 25 microM selenite, a temporal pattern of apoptotic events was observed following the elevation of O(2)(*)(-), in which cytochrome c release and mitochondrial depolarization preceded caspase-3 activation and DNA fragmentation. The simultaneous treatment with N-acetylcysteine and 4-hydroxy-2,2,6, 6-tetramethylpiperidine-N-oxyl markedly reduced O(2)(*)(-) level and suppressed the mitochondrial changes and the downstream apoptotic events. Moreover, pretreatment with cyclosporin A plus trifluoperazine, two mitochondrial permeability transition (MPT) inhibitors, was capable of attenuating O(2)(*)(-)-mediated cytochrome c release and mitochondrial depolarization, and subsequently inhibiting apoptosis. Thus, the present results provide convincing evidence that O(2)(*)(-) generated from the reductive reaction of selenite with GSH is capable of triggering a mitochondria-dependent apoptotic pathway. Such knowledge may not only help to obtain a better understanding of the apoptotic effect of selenite per se, but of the role of O(2)(*)(-) in initiation and execution of apoptosis.
authors.affiliation: Department of Community, Occupational, and Family Medicine, Faculty of Medicine, National University of Singapore, Singapore. cofshm@nus.edu.sg
authors.forename: H M
authors.initials: HM
authors.lastname: Shen
authors.forename: C F
authors.initials: CF
authors.lastname: Yang
authors.forename: W X
authors.initials: WX
authors.lastname: Ding
authors.forename: J
authors.initials: J
authors.lastname: Liu
authors.forename: C N
authors.initials: CN
authors.lastname: Ong
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D006528:Carcinoma, Hepatocellular; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D003497:Cyclic N-Oxides / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D007700:Kinetics; D008113:Liver Neoplasms; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction; D018038:Sodium Selenite / Q000378:metabolism / Q000494:pharmacology*; D013113:Spin Labels; D013481:Superoxides / Q000378:metabolism / Q000494:pharmacology*; D014268:Trifluoperazine / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D061945:Caspase Inhibitors; D003497:Cyclic N-Oxides; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D013113:Spin Labels; D013481:Superoxides; D014268:Trifluoperazine; D016572:Cyclosporine; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D005978:Glutathione; D018038:Sodium Selenite; C001803:tempol; D000111:Acetylcysteine