Genetic differences in metabolism of benzo(a)pyrene in cultured epidermal and dermal cells of responsive and nonresponsive mice.

Genetic differences in metabolism of benzo(a)pyrene (BP) were investigated using cultured epidermal keratinocytes and dermal fibroblasts isolated from four inbred strains of mice: C3H/HeJms and C57BL/6J that are responsive; and DBA/2 and AKR/Jms that are nonresponsive in terms of inducibility of aryl hydrocarbon hydroxylase (AHH) activity. Primary cultures of epidermal and dermal cells isolated from newborn mice were treated with benz(a)anthracene for 24 hr. In both types of cells, AHH activity was induced in all four strains of mice, irrespective of their responsiveness in vivo. In the epidermal cells, basal AHH activity varied within a relatively small range of 4.6 to 8.8 pmol per mg protein per hr, and the activity was increased 4.4 to 8.7 times by benz(a)anthracene treatment. There was no difference in the extent of the induction in different strains of mice. In dermal cells, the basal level of AHH activity was in the range of 3.6 to 9.1 pmol per mg protein per hr, and benz(a)anthracene treatment induced AHH, but to various degrees depending on the responsiveness in vivo. Epidermal cells of the responsive mice metabolized more than 90% of the added BP in 48 hr, while those of nonresponsive mice metabolized only 60 to 70%. Dermal cells also metabolized BP, but to a lesser extent than did epidermal cells, and there was no strain difference in its metabolism. Time-course studies revealed that epidermal cells of responsive mice metabolized BP more rapidly than did those of nonresponsive mice. The activities of epidermal and dermal cells to metabolize BP were further demonstrated by a cell-mediated mutation assay. Consistent with the results of time-course analysis of the metabolites, shorter treatments with BP (less than 24 hr) showed a clear difference in BP metabolism associated with responsiveness.