Effect of chrysotile asbestos and silica on the microsomal metabolism of benzo(a)pyrene

The effects of chrysotile, water-leached chrysotile, and silica on microsomal metabolism of benzo(a)pyrene in vitro were studied. Examination of benzo(a)pyrene metabolites generated by 3-methylcholanthrene-pretreated rat liver microsomes, in the presence of chrysotile fibers, revealed a reduction in the overall metabolism of the hydrocarbon. Thus, chrysotile appeared to modify the activities of aryl hydrocarbon hydroxylase and epoxide hydrolase. Leaching chrysotile in deionized water for 24 hr elicited a similar response. Silica, in contrast to chrysotile, did not decrease the microsomal metabolism of benzo(a)pyrene. Chrysotile, as well as water-leached chrysotile, considerably diminished the microsomal production of water-soluble benzo(a)pyrene metabolites. Precoating the fibers with heparin or bovine serum albumin partially abolished this inhibition. The liver microsomal metabolism of benzo(a)pyrene in rats subjected to intraperitoneal administration of chrysotile was 58% of that in untreated rats.