Cytochrome P450 peroxidase/peroxygenase mediated xenobiotic metabolic activation and cytotoxicity in isolated hepatocytes.
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.
Anari
M R
MR
Faculty of Pharmacy, University of Toronto, Ontario, Canada.
Khan
S
S
Liu
Z C
ZC
O'Brien
P J
PJ
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
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