Immunochemical characterization of cytochrome P-450 isozymes responsible for benzene oxidation in the rat liver.

Abstract

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.