Monoclonal antibody-directed analysis of benzo[a]pyrene metabolism in rat liver and extrahepatic tissues: effect of propyl and octyl gallate.

Monoclonal antibody (MAb) 1-7-1 against 3-methylcholanthrene (MC)-induced forms of cytochrome P-450 (CYP) was used to characterize benzo[a]pyrene (B[a]P) metabolism in rat liver and extrahepatic tissues and its modulation by phenolic antioxidants, propyl and octyl gallates. Male Wistar rats were treated with these food additives (50 mg/kg body wt i.p.) twice weekly for 14 days alone or in combination with MC. Immunochemical inhibition of aryl hydrocarbon hydroxylase (AHH) and [14C]B[a]P metabolism (analyzed by high-performance liquid chromatography) were measured in liver, kidney, and lung microsomes. Organ-specific changes in levels of MAb-mediated inhibition of microsomal metabolism of B[a]P were observed. In liver microsomes from untreated rats, AHH was not affected by MAb, but in kidney and lung, there was 70% and 50% inhibition, respectively. In MC-treated rats, MAb reduced AHH activity by 43% in liver. Kidney and lung AHH was inhibited up to 80% by this MAb. Formation of B[a]P metabolites in MC-induced microsomes from liver and kidney was affected by MAb in a similar way. In lung, the total metabolism was inhibited by 50% by MAb treatment, but significant differences in inhibition of individual metabolites were observed. Treatment with propyl or octyl gallate alone had no effect on MAb inhibition of AHH activity in liver and lung but decreased the level of inhibition in kidney. Combined treatment with MC and propyl or octyl gallate slightly reduced the effect of MAb on AHH activity in liver and significantly reduced the level of inhibition in kidney but did not affect AHH activity in lung. The same treatment regimen dramatically reduced MAb inhibition of B[a]P metabolism in kidney but had no effect on B[a]P metabolite formation in liver. Inhibition by MAb of renal 3-hydroxy-B[a]P, 7,8-B[a]P-dihydrodiol, and 1,6-quinone-B[a]P was the most affected. In lung, treatment with gallates affected only formation of 7,8-B[a]P-dihydrodiol. These results suggest that treatment with gallates affects the CYP 1A and may change the CYP isozyme composition and, thus, alter the tissues' susceptibility to tumor induction by B[a]P.