Metabolism and covalent binding of [3H]benzo(a)pyrene by isolated perfused lungs and short-term tracheal organ culture of cigarette smoke-exposed rats.

Abstract

The metabolism and covalent binding of the environmental carcinogen benzo( a )pyrene, a constituent of cigarette smoke, has been determined in isolated perfused lungs of sham- and cigarette smoke-exposed and 3-methylcholanthrene-pretreated male Wistar rats. Rats were exposed to cigarette smoke for 1 hr daily for either 1 or 10 days. Benzo( a )pyrene (2 nmoles) was instilled intratracheally, and metabolites in lungs and a nonrecirculating perfusate were determined. Benzo( a )pyrene was metabolized by isolated perfused lungs of sham-, cigarette smoke-exposed, and 3-methylcholanthrene-treated animals to ethyl acetate-soluble metabolites, which cochromatographed with 9,10-dihydro-9,10-dihydroxybenzo( a )pyrene, 7,8-dihydro-7,8-dihydroxybenzo( a )pyrene, 4,5-dihydro-4,5-dihydroxybenzo( a )-pyrene, and 3-hydroxybenzo( a )pyrene. An unidentified metabolite (Y) migrating between 4,5-dihydro-4,5-dihydroxybenzo( a )pyrene and 3-hydroxybenzo( a )pyrene was observed in perfusates from lungs of animals that had been exposed either to cigarette smoke or 3-methylcholanthrene. Metabolite production was significantly increased by exposure to either cigarette smoke or 3-methylcholanthrene. Tracheas of sham and smoke-exposed animals also converted benzo( a )pyrene to metabolites that cochromatographed with reference dihydrodiols and 3-hydroxybenzo( a )pyrene; however, no increase in metabolite production was observed in the smoke-exposed animals. Dihydrodiols were the major ethyl acetate-soluble metabolites formed by the trachea, whereas 3-hydroxybenzo( a )pyrene was the major metabolite formed in lung perfusions. After intratracheal instillation of [3H]benzo( a )pyrene, the amount of covalently bound radioactivity was significantly increased in the lungs of animals exposed to cigarette smoke compared to the corresponding sham-exposed animals.