Intracellular thiol depletion causes mitochondrial permeability transition in ebselen-induced apoptosis.
Ebselen, a selenoorganic compound, has recently been shown to display a novel property of inducing apoptosis through rapid depletion of intracellular thiols in human hepatoma cells, HepG(2). The present study was thus designed to explore the mechanism of how ebselen triggers apoptosis upon depletion of intracellular thiols. The results demonstrated that ebselen treatment triggered mitochondrial permeability transition rather rapidly as revealed by redistribution of calcein green fluorescence from cytosol into mitochondria. Ebselen treatment also caused a dose- and time-dependent loss of mitochondrial membrane potential (MMP) and release of cytochrome c. Pretreatment with N-acetylcysteine, a precursor of intracellular reduced glutathione (GSH) synthesis, significantly attenuated the ebselen-induced MMP disruption and subsequently inhibited the apoptosis. In contrast, pretreatment with buthionine sulfoximine, a specific inhibitor of intracellular GSH synthesis, significantly augmented the ebselen-induced MMP alteration, and enhanced the apoptosis. Although ebselen treatment significantly increased the intracellular superoxide radical and calcium concentrations, superoxide dismutase, and BAPTA (a calcium chelator), however, failed to prevent ebselen-induced MMP loss and apoptosis. Neither caspase-9 nor caspase-3 activation was detected in ebselen-treated cells. Z-VAD-FMK, a general caspase inhibitor, also had no effect on ebselen-induced MMP decrease and apoptosis. The overall findings thus suggest that mitochondrial permeability transition resulted from intracellular thiol depletion is a critical event in ebselen-induced apoptosis.
Department of Community, Occupational and Family Medicine, Faculty of Medicine, MD3, National University of Singapore, 16 Medical Drive, 117597, Singapore.
C F
CF
Yang
H M
HM
Shen
C N
CN
Ong
D000111:Acetylcysteine / Q000494:pharmacology; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001393:Azoles / Q000494:pharmacology*; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D054833:Isoindoles; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism*; D016566:Organoselenium Compounds / Q000494:pharmacology*; D010539:Permeability / Q000187:drug effects; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000590:Amino Acid Chloromethyl Ketones; D001393:Azoles; D003574:Cytochrome c Group; D054833:Isoindoles; D016566:Organoselenium Compounds; D013438:Sulfhydryl Compounds; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D013481:Superoxides; C042986:ebselen; D019328:Buthionine Sulfoximine; D004533:Egtazic Acid; D016572:Cyclosporine; D013482:Superoxide Dismutase; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D000111:Acetylcysteine