title: Enhancement of DMNQ-induced hepatocyte toxicity by cytochrome P450 inhibition.
abstract: Two mechanisms have been proposed to explain quinone cytotoxicity: oxidative stress via the redox cycle and the arylation of intracellular nucleophiles. As the redox cycle is catalyzed by NADPH cytochrome P450 reductase, cytochrome P450 systems are expected to be related to the cytotoxicity induced by redox-cycling quinones. Thus, we investigated the relationship between cytochrome P450 systems and quinone toxicity for rat primary hepatocytes using an arylator, 1,4-benzoquinone (BQ), and a redox cycler, 2,3-dimethoxy-1,4-naphthoquinone (DMNQ). The hepatocyte toxicity of both BQ and DMNQ increased in a time- and dose-dependent manner. Pretreatment with cytochrome P450 inhibitors, such as SKF-525A (SKF), ketoconazole and 2-methy-1,2-di-3-pyridyl-1-propanone, enhanced the hepatocyte toxicity induced by DMNQ but did not affect BQ-induced hepatocyte toxicity. The production of superoxide anion and the levels of glutathione disulfide and thiobarbituric-acid-reactive substances were increased by treatment with DMNQ, and SKF pretreatment further enhanced their increases. In addition, NADPH oxidation in microsomes was increased by treatment with DMNQ and further augmented by pretreatment with SKF, and a NADPH cytochrome P450 reductase inhibitor, diphenyleneiodonium chloride completely suppressed NADPH oxidations increased by treatment with either DMNQ- or DMNQ + SKF. Pretreatment with antioxidants, such as alpha-tocopherol, reduced glutathione, N-acetyl cysteine or an iron ion chelator deferoxamine, totally suppressed DMNQ- and DMNQ + SKF-induced hepatocyte toxicity. These results indicate that the hepatocyte toxicity of redox-cycling quinones is enhanced under cytochrome P450 inhibition, and that this enhancement is caused by the potentiation of oxidative stress.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka University, Osaka 532-8686, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Ishihara
authors.forename: Dai
authors.initials: D
authors.lastname: Shiba
authors.forename: Norio
authors.initials: N
authors.lastname: Shimamoto
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D016227:Benzoquinones / Q000737:chemistry / Q000633:toxicity; D002395:Catecholamines / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D065607:Cytochrome P-450 Enzyme Inhibitors; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D019803:Glutathione Disulfide / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D048288:Imidazolines / Q000494:pharmacology; D007502:Iron Chelating Agents / Q000494:pharmacology; D007654:Ketoconazole / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D008797:Metyrapone / Q000494:pharmacology; D015394:Molecular Structure; D009249:NADP / Q000378:metabolism; D009285:Naphthoquinones / Q000737:chemistry / Q000633:toxicity*; D018384:Oxidative Stress / Q000187:drug effects; D011335:Proadifen / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013481:Superoxides / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism
chemical_list: D000975:Antioxidants; D016227:Benzoquinones; D002395:Catecholamines; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D048288:Imidazolines; D007502:Iron Chelating Agents; D009285:Naphthoquinones; D017392:Thiobarbituric Acid Reactive Substances; D013481:Superoxides; C004532:quinone; D009249:NADP; C063002:2,3-dimethoxy-1,4-naphthoquinone; D011335:Proadifen; C011775:(3,4-dihydroxyphenylamino)-2-imidazoline; D007770:L-Lactate Dehydrogenase; D007654:Ketoconazole; D019803:Glutathione Disulfide; D008797:Metyrapone