Effects of phenobarbital, 3-methylcholanthrene and β-naphthoflavone pretreatment on mouse liver microsomal enzymes and on metabolite patterns of benzo[a]pyrene

Abstract

C57B1/6 (B6), C3H, and DBA/2 (D2) strains of mice were pretreated with either a single dose of 3-methylcholanthrene (3-MC), β-naphthoflavone (β-NF) or α-naphthoflavone (α-NF), or with daily injections of phenobarbital (PB) for 4 days; control mice were injected with corn oil or saline only. Comparisons were made of the patterns of hepatic microsomal-protein bands on acrylamide gel electropherograms as well as the patterns of individual metabolites of benzo[ a]pyrene (BP) extracted by ethyl acetate from incubation systems using these microsomes. Hepatic microsomes from control mice of all three strains produced similar protein bands and BP metabolite profiles, with B6 mice having slightly higher yields of the 9,10-diol and phenols of BP. α-NF had no apparent effect on the protein bands or the yields of BP metabolites. Sodium dodecylsulfate-polyacrylamide gel electrophoresis of hepatic microsomes revealed that PB pretreatment was followed by increases in the intensities of five protein bands with molecular weights between 43,000 and 68,000. The yields of BP metabolites were increased 1.5- to 3-fold for all three strains of mice after PB pretreatment. Pretreatment with 3-MC or β-NF had no apparent effect on the hepatic microsomal enzymes of D2 mice, either in terms of protein bands or metabolites of BP. For B6 and C3H mice, pretreatment with 3-MC or β-NF resulted in the appearance of a new protein band easily detectable in the range between molecular weights 53,000 and 58,000, as well as in increases of all BP metabolites. Pretreatment of B6 and C3H mice with 3-MC caused 10-fold increases in the microsomal yields of the 7,8-diol, and 5-fold increases in the yields of BP phenols. Pretreatment with β-NF caused a 7-fold increase of the 7,8-diol catalyzed by the hepatic microsomes of B6 mice and a 4-fold increase in the 7,8-diol in C3H mice; the yields of phenols were increased about 2.5-fold for both B6 and C3H mice. The results suggest that the induced microsomal proteins with molecular weights between 43,000 and 58,000 may contain induced forms of cytochromes(s) P-450 that activate different carbon atoms of the BP molecule and, therefore, lead to different metabolite profiles.