Studies on microsomal cytochrome P-450, monooxygenases and epoxide hydrolase in cultured keratinocytes and intact epidermis from BALB/C mice.

Studies of drug and carcinogen metabolism in cultured keratinocytes and in intact epidermis from the skin of BALB/C mice were performed. The cultured cells were shown to retain 33 to 40% of corresponding intact epidermal aryl hydrocarbon hydroxylase (AHH), 7-ethoxycoumarin-O-de-ethylase (7-ED) and epoxide hydrolase activities. In vitro treatment of the cells or in vivo application to the skin of animals with the polycyclic aromatic hydrocarbons benz(a)anthracene (BA) or benzo(a)pyrene resulted in significant induction of AHH and 7-ED activities. The responsiveness of AHH was greater than that of 7-ED in both preparations. BA (4 x 10(-4) M) induced AHH and 7-ED at least 12- and 4-fold, respectively, in either the keratinocytes or intact epidermis, whereas epoxide hydrolase activity was not altered in either preparation. All of these enzyme activities were predominantly located in the microsomal fraction of the keratinocytes and the epidermis. Keratinocyte AHH had a pH optimum at 7.4. The apparent Km for benzo(a)pyrene as substrate in control and BA-induced cells was 10 and 6 microM, respectively, whereas Vmax was 15-fold greater in the carcinogen-treated cells. CO-difference spectra demonstrated the presence of the heme-protein cytochrome P-450 in microsomes prepared from keratinocytes and intact epidermis; absorption maximum was between 451 to 453 nm. The metabolic activity of keratinocytes was further demonstrated in the Ames mutagen assay. A supernatant (9000 x g) prepared from keratinocytes pretreated with BA enhanced the mutagenesis of 2-aminoanthracene in the TA98 strain of Salmonella typhimurium. These studies indicate that cultured keratinocytes provide a useful experimental model system for the study of epidermal drug and carcinogen metabolism.