Supranuclear melanin caps reduce ultraviolet induced DNA photoproducts in human epidermis

Melanin can form supranuclear caps in human epidermis, suggesting that intracellular melanin reduces ultraviolet transmission to underlying cell nuclei and inhibits the formation of ultraviolet induced DNA photoproducts. The purpose of this study was to determine the photoprotective effect of epidermal melanin. We irradiated normal human skin explants with ultraviolet B and determined the formation of cyclobutane pyrimidine dimers and (6-4)photoproducts in individual epidermal cells by indirect immunofluorescence and by laser cytometry using monoclonal antibodies specific for cyclobutane dimers or for (6-4)photoproducts. We found that epidermal cells with supranuclear melanin caps had significantly less DNA photoproducts (both types) than epidermal cells without supranuclear melanin caps. Moreover, the protection factor against both types of photolesions correlated with melanin concentration in epidermal cells. These results indicate that melanin reduces ultraviolet induced DNA photoproducts in human epidermis in a concentration dependent manner.