title: Cytochrome P450 peroxidase/peroxygenase mediated xenobiotic metabolic activation and cytotoxicity in isolated hepatocytes.
abstract: Cytochrome P450 (P450) can utilize organic hydroperoxides and peracids to support hydroxylation and dealkylation of various P450 substrates. However, the biological significance of this P450 peroxygenase/peroxidase activity in the bioactivation of xenobiotics in intact cells has not been demonstrated. We have shown that tert-butyl hydroperoxide (tBHP) markedly enhances 3-20-fold the cytotoxicity of various aromatic hydrocarbons and their phenolic metabolites. The tBHP-enhanced hepatocyte cytotoxicity of 4-nitroanisole (4-NA) and 4-hydroxyanisole (4-HA) was also accompanied by an increase in the hepatocyte O-demethylation of 4-NA and 4-HA up to 7.5- and 21-fold, respectively. Hepatocyte GSH conjugation by 4-HA was also markedly increased by tBHP. An LC/MS analysis of the GSH conjugates identified hydroquinone-GSH and 4-methoxy-catechol:GSH conjugates as the predominant adducts. Pretreatment of hepatocytes with P450 inhibitors, e.g., phenylimidazole, prevented tBHP-enhanced 4-HA metabolism, GSH depletion, and cytotoxicity. In conclusion, hydroperoxides can therefore be used by intact cells to support the bioactivation of xenobiotics through the P450 peroxidase/peroxygenase system.
authors.affiliation: Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: M R
authors.initials: MR
authors.lastname: Anari
authors.forename: S
authors.initials: S
authors.lastname: Khan
authors.forename: Z C
authors.initials: ZC
authors.lastname: Liu
authors.forename: P J
authors.initials: PJ
authors.lastname: O'Brien
mesh_terms: D000818:Animals; D000840:Anisoles / Q000378:metabolism; D001711:Biotransformation; D002470:Cell Survival / Q000187:drug effects; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D005978:Glutathione / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D006899:Mixed Function Oxygenases / Q000502:physiology*; D010544:Peroxidases / Q000502:physiology*; D010545:Peroxides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015262:Xenobiotics / Q000378:metabolism* / Q000633:toxicity; D020122:tert-Butylhydroperoxide
chemical_list: D000840:Anisoles; D010545:Peroxides; D015262:Xenobiotics; C009760:mequinol; D003577:Cytochrome P-450 Enzyme System; D020122:tert-Butylhydroperoxide; D006899:Mixed Function Oxygenases; D010544:Peroxidases; C022333:peroxygenase; D005978:Glutathione