Immunochemical characterization of cytochrome P-450 isozymes responsible for benzene oxidation in the rat liver.
The contribution of cytochrome P-450 isozymes to benzene metabolism in liver microsomes from fed, fasted, pyrazole-, phenobarbital (PB)- and ethanol-treated rats and in respective isocaloric controls was investigated using monoclonal antibodies (mAbs). Clone 1-7-1 mAb did not inhibit benzene metabolism, whereas clone 2-66-3 inhibited only in PB-induced microsomes at a high concentration of benzene (6.26 mM), and clone 1-91-3 mAb inhibited benzene metabolism in all cases. The degree of inhibition was as follows: fed congruent to isocaloric control congruent to PB less than fasted less than pyrazole congruent to ethanol. The pattern of inhibition was similar with clone 1-91-3 for low (0.23 mM) and high concentrations of benzene, except in PB-induced microsomes. Western blot analysis showed that clone 1-7-1 mAb did not bind any liver microsomal protein in the region of cytochrome P-450s, whereas with clone 2-66-3 a clear-cut band was seen only in liver microsomes from PB-treated rats, with clone 1-98-1, a band was detected in microsomes from all treated groups, in the following order: PB = isocaloric control less than fed less than fasted less than pyrazole less than ethanol. These results indicate that (i) cytochromes P-450b,e and P-450j contribute to benzene metabolism in rat liver; (ii) the former has a low affinity to benzene and is induced by PB; and (iii) P-450j has a high affinity to benzene and is induced by 1-day fasting, pyrazole and ethanol, but decreased by PB treatment.
Department of Industrial Hygiene and Toxicology, Institute of Occupational Health, Helsinki, Finland.
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Nakajima
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Elovaara
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Park
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Gelboin
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Hietanen
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Vainio
D000818:Animals; D001554:Benzene / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000431:Ethanol / Q000494:pharmacology; D005215:Fasting; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010084:Oxidation-Reduction; D010634:Phenobarbital / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
D007527:Isoenzymes; D011720:Pyrazoles; D000431:Ethanol; C031280:pyrazole; D003577:Cytochrome P-450 Enzyme System; D001554:Benzene; D010634:Phenobarbital