Metabolism of benzo[a]pyrene and other carcinogens in mouse epidermal keratinocytes in culture.

The metabolism of benzo[a]pyrene (BP) and other carcinogens was investigated in primary cultures of mouse epidermal keratinocytes isolated from the C3H/He inbred strain, a responsive strain in the Ah locus. The basal aryl hydrocarbon hydroxylase activity of these cells was 9.2 pmol equivalents of 3-hydroxy-BP per mg protein per hr. This enzyme was induced dose-dependently by benz[a]anthracene (BA) and a 7-fold increase was obtained by treatment with 13 microM BA for 24 hr. The metabolism of BP increased with the time of incubation. On thin layer chromatography, 60% of the added BP was separated as metabolites at 24 hr and 96% at 48 hr. High pressure liquid chromatography indicated that mouse epidermal cells produced almost the whole series of metabolites of BP; dihydrodiols at the 9,10-,4,5- and 7,8-positions, quinones, and phenols at the 3- and 9-positions. The metabolic activity of mouse epidermal cells was further demonstrated by a cell-mediated assay, in which V79 Chinese hamster cells were cultured on top of epidermal cells and treated with BP and other carcinogens. Mutation of V79 cells, detected as ouabain resistance, was induced in a dose-related fashion by BP, BP-7,8-dihydrodiol, methylcholanthrene, and 7,12-dimethylbenz[a]anthracene, but not by aflatoxin B1; of these compounds BP-7,8-dihydrodiol was the most potent.