title: Intracellular acidification triggered by mitochondrial-derived hydrogen peroxide is an effector mechanism for drug-induced apoptosis in tumor cells.
abstract: We recently showed that two photoproducts of merocyanine 540, C2 and C5, triggered cytochrome C release; however, C5 was inefficient in inducing caspase activity and apoptosis in leukemia cells, unlike C2. Here we show that HL60 cells acidified upon exposure to C2 but not C5. The intracellular drop in pH and caspase activation were dependent upon hydrogen peroxide production, and were inhibited by scavengers of hydrogen peroxide. On the contrary, caspase inhibitors did not block hydrogen peroxide production. In turn, increased intracellular hydrogen peroxide concentration was downstream of superoxide anion produced within 2 h of exposure to C2. Inhibitor of NADPH oxidase diphenyleneiodonium neither inhibited superoxide production nor caspase activation triggered by C2. However, exposure of purified mitochondria to C2 resulted in significantly increased superoxide production. Furthermore, cytochrome C release from isolated mitochondria induced by C2 was completely inhibited in the presence of scavengers of hydrogen peroxide. Contrarily, scavenging hydrogen peroxide had no effect on the cyclosporin A-sensitive mitochondrial permeability transition induced by C5. Our data suggest a scenario where drug-induced hydrogen peroxide production induces intracellular acidification and release of cytochrome C, independent of the inner membrane pore, thereby creating an intracellular environment permissive for caspase activation.
authors.affiliation: Department of Physiology, National University of Singapore, Singapore 119260.
authors.forename: J L
authors.initials: JL
authors.lastname: Hirpara
authors.forename: M V
authors.initials: MV
authors.lastname: Clément
authors.forename: S
authors.initials: S
authors.lastname: Pervaiz
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005434:Flow Cytometry; D016166:Free Radical Scavengers / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels; D008027:Light; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D011744:Pyrimidinones / Q000378:metabolism* / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism
chemical_list: D061945:Caspase Inhibitors; D003574:Cytochrome c Group; D016166:Free Radical Scavengers; D007473:Ion Channels; D008565:Membrane Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D011744:Pyrimidinones; D017382:Reactive Oxygen Species; D013481:Superoxides; C003954:merocyanine dye; D016572:Cyclosporine; D006861:Hydrogen Peroxide; D019255:NADPH Oxidases; D020169:Caspases