Exposure to benzene was reported to lower the cytochrome P450 (CYP; EC 1.14.14.1) content in phenobarbital-pretreated (PB) rats in vivo (Gut I, Zbl Pharm 122: 1139-1161, 1983). In this paper we followed the ability of benzene and its metabolites, phenol, catechol, hydroquinone and benzoquinone to destroy CYP in liver microsomes from PB rats in vitro. The spectrophotometric determinations of the total CYP content, 7-pentoxyresorufin O-depentylase and aniline hydroxylase activities, electrophoresis and western blot analysis after incubation of PB-microsomes with benzene or its metabolites revealed that: (1) benzene is metabolically activated to intermediates causing CYP destruction; phenol is not responsible for this effect. (2) Quinonic metabolites of benzene cause CYP destruction with different potency (30% CYP was destroyed by 3 mM catechol, 0.3 mM hydroquinone and 0.03 mM benzoquinone). (3) Low concentrations of quinones are capable of protecting CYP against reactive oxygen species produced in the CYP futile cycle. (4) Ascorbate effectively protects CYP against quinones, apparently by maintaining them in the reduced state. (5) Quinones attack both heme and protein of CYP. (6) CYP activities differ in the sensitivity to quinone-mediated destruction. In conclusion, we suggest that quinones may be responsible for CYP destruction by benzene in vivo.

National Institute of Public Health Center of Industrial Hygiene and Occupational Diseases Praha Czech Republic

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Cytochromes P450 in benzene metabolism and involvement of their metabolites and reactive oxygen species in toxicity