Effect of asbestos fibers on aryl hydrocarbon hydroxylase and aminopyrine N-demethylase activities of rat liver microsomes.

Chrysotile asbestos fibers impair the activities of rat liver microsomal aryl hydrocarbon hydroxylase (AHH), aminopyrine (AP) N-demethylase and dimethylnitrosamine (DMN) demethylase in vitro. This inhibition is concentration-dependent. Preincubation of 3-methylcholanthrene (3-MC)-pretreated rat liver microsomes with chrysotile depresses the overall metabolism of [G-3H]benzo[a]pyrene (BaP). Various forms of asbestos employed inhibit AHH activity to the same extent. However, other types of asbestos are not as effective as chrysotile in diminishing AP demethylase activity. Chrysotile and crocidolite fibers are not found to significantly change the apparent Km of AHH activity, from 3-MC-pretreated rat liver microsomes, for BaP. Increasing the microsomal protein concentration partially abolishes the inhibition of AHH activity caused by chrysotile fibers. Inhibition of AP demethylase and AHH activities is attenuated by bovine serum albumin (BSA) or ferritin. Depression of AHH activity by crocidolite is significantly reversed by ferritin. Since polymers such as ferritin override enzyme inhibition by chrysotile as well as crocidolite, surface chemical groups of the fibers may be involved in enzyme modification.