Keratinocyte damage produced by 12-O-tetradecanoylphorbol-13-acetate in rodent epidermis

Cell damage produced by 12-O-tetradecanoylphorbol-13-acetate (TPA) was evaluated in keratinocyte suspensions obtained from TPA treated mouse epidermis using a dye-exclusion technique, and in tissue sections studied by light microscopy and quantitative enzyme histochemistry. TPA induced a maximum of approximately 25% of trypan blue stained basal keratinocytes using topical doses of 2, 20 and 200 micrograms. With the first two doses this effect was detectable at 12-24 h and disappeared 48-96 h after TPA treatment, whereas with 200 micrograms TPA the cell damage persisted for a longer time. Oxidative enzyme changes were moderate, and no changes in acid phosphatase levels could be detected. The facts that no signs of cell necrosis could be seen in tissue sections from epidermis treated with 2 and 20 micrograms TPA; that only a moderate change in oxidative enzyme pattern, without statistically significant variations in succinic dehydrogenase and cytochrome oxidase, could be detected, and that no shift of the damaged basal keratinocytes into the suprabasal compartment was evident, are indicative of moderate, probably sublethal damage induced by TPA. Although eventually committed to terminal differentiation, the epidermal cells do not show the cytologic and metabolic features of lethally damaged cells, suggesting that the membrane damage detected by the dye exclusion technique may be sublethal. Thus, it is possible that TPA can induce a reactive or regenerative type of epidermal hyperplasia without the prerequisite of extensive keratinocyte necrosis.