Primary cell cultures derived from human skin epithelium metabolized benzo(a)pyrene to three classes of compounds: phenols, quinones, and dihydrodiols. The relative proportions of metabolites varied according to the skin donor but differed from the pattern of metabolites in rat liver microsome preparations. While appreciable amounts of 7,8- and 9,10-dihydrodiol; 1,6-, 3,6-, and 6,12-quinone; and 3- and 9-hydroxy derivatives were found in the medium, no 4,5 (K-region)-dihydrodiol or epoxide was detected. Reduced amounts of quinones were produced when the cultures were pretreated with hydrocortisone before exposure to the hydrocarbon. The cultures did not require a period of enzyme induction for efficient metabolism of the hydrocarbon. Cultures of fibroblasts derived from the same skin samples as the epithelial cells metabolized the hydrocarbon but to a much different extent. Preexposure of the epithelial cell cultures to mixtures of polycyclic hydrocarbons resulted in a decrease in the amounts of carcinogen metabolized to phenols and dihydrodiols.

These findings suggest that the prevalence of carcinomatous disease in humans is due to the differential capacity of the epithelial cells to metabolize potential carcinogens to active forms, a capacity reduced in fibroblasts or other nonepithelial cells. This suggestion is supported by the observations that supposedly normal prostate cells also efficiently metabolize polycyclic hydrocarbons in a manner similar to that of epidermal cells. No evidence of neoplastic transformation was seen in cytological preparations of cells exfoliated into the medium.

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