Melanin offers protection against induction of cyclobutane pyrimidine dimers and 6-4 photoproducts by UVB in cultured human melanocytes

The goal of this investigation was to correlate the melanin content in huma n pigmentary cells with the generation of UVB-induced photoproducts and to examine the relationship between the melanin content and the removal of the photoproducts. Cultured melanocytes from light-skinned individuals synthes ized less melanin and produced more cyclobutane pyrimidine dimers and 6-4 p hotoproducts upon UVB exposure than did melanocytes from black skin. Tyrosi ne-stimulated melanogenesis provided protection against DNA damage in both cell types. In another set of pigmented cell lines a ratio between eumelani n and pheomelanin was determined. The assessment of association between DNA damage induction and the quantity and quality of melanin revealed that eum elanin concentration correlated better with DNA protection than pheomelanin . Skin type-I and skin type-VI melanocytes, congenital nevus (CN)-derived c ells and skin type-II melanocytes from a multiple-melanoma patient were gro wn in media with low or high L-tyrosine concentration. The cells were irrad iated with 200 J/m(2) UVB, and the levels of the photoproducts were determi ned immediately and after 6 and 24 h. Once again the induction of the photo products was mitigated by increased melanogenesis, and it was inversely cor related with the skin type. No significant differences were found for the r emoval of photoproducts in the cultures of skin types I and VI and CN cells . No indications of a delay in the removal of photoproducts in the melanocy tes from the multiple-melanoma patient were found either.