Regioselective metabolism of benzo[a]pyrene and 7-chlorobenz[a]anthracene by fish liver microsomes

Abstract

Many polycyclic aromatic hydrocarbons (PAHs) and chlorinated PAHs in the environment are potent mutagens and carcinogens. Using benzo[a]pyrene (BaP) and 7-chlorobenz[a]anthracene (7-Cl-BA) as representatives of PAHs and chlorinated PAHs, respectively, we studied the metabolism of these compounds in liver microsomes of Tilapia ( Oreochromis hybrid), one of the most common fish in south Asia. The regioselective metabolism of BaP and 7-Cl-BA by the fish liver microsomes resulted in the formation of hydroxylated and trans-dihydrodiol metabolites of both BaP and 7-Cl-BA. The metabolites were purified by HPLC and identified by both UV/VIS and mass spectroscopic methods. The fish liver microsomes metabolized BaP to form BaP-7,8-dihydrodiol (11%), 3-hydroxy-BaP (17%), and 9-hydroxy-BaP (22%) as the major products and metabolized 7-Cl-BA to form 7-Cl-BA trans-8,9-dihydrodiol as the major metabolite (40%). The Tilapia liver microsomal P-450 enzyme activities were inducible by pretreatment with 3-methylcholanthrene (3-MC), which increased microsomal aryl hydrocarbon hydroxylase and 7-ethoxyresorufin O-deethylase activities by 74- and 360-fold, respectively. The induction of these enzymes by 3-MC was greater in fish microsomes than in rat liver. This study is the first to demonstrate the regioselective metabolism of BaP and 7-Cl-BA by fish liver microsomes.