The metabolism of benzo(a)pyrene (BP) in epidermal keratinocytes and dermal fibroblasts of humans and mice was investigated with emphasis on variation among species, individuals, and cell types. Human epidermal and dermal cells were isolated from the skin of normal subjects by trypsinization at 4° overnight, followed by separation of the epidermis from the dermis with forceps. In confirmation of previous studies, metabolic activity of human epidermal cells on BP was consistently demonstrated by cell-mediated assay, in which V79 Chinese hamster cells were plated on top of sheets of epidermal cells and treated with BP for 48 hr. Mutation of the V79 cells, measured as ouabain resistance, was induced in a dose-related fashion, although the extent of induced mutation varied from 5 to 22 ouabain-resistant colonies per 105 survivors/10 µm BP in cultures derived from different individuals. The most striking observation was that human dermal fibroblasts did not activate BP to a form that was mutagenic to cocultured V79 cells. This was observed without exception in all nine cultures of dermal fibroblasts and the one culture of embryo fibroblasts (IMR-90) tested. Analysis by high-pressure liquid chromatography indicated that human epidermal and dermal cells both metabolized BP, producing almost the whole series of known metabolites of BP. The amount of BP 7, 8-dihydrodiol, a proximate metabolite of BP, produced by human dermal cells varied from 0.2 to 2.7% of the total BP added and seemed to be enough to induce mutation. Furthermore, human dermal cells not necessarily activated exogenously added BP 7,8-dihydrodiol to a form being mutagenic to V79 cells. These observations suggest that further metabolism of BP 7,8-dihydrodiol is partially or entirely blocked in human fibroblasts.

In contrast to human fibroblasts, mouse fibroblasts isolated from the dermis of embryos did activate BP and induced mutation in cocultured V79 cells to a higher extent than did mouse epidermal cells, indicating interspecies variation in metabolic activation of BP between human and mouse fibroblasts.

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This work was supported in part by a grant for cancer research from the Ministry of Education, Science, and Culture of Japan and by a grant from the Princess Takamatsu Foundation for Cancer Research.

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