Studies on epidermis reconstructed with and without melanocytes: melanocytes prevent sunburn cell formation but not appearance of DNA damaged cells in fair-skinned caucasians

To assess the photoprotective role of melanocytes in the epidermis, we studied the effects of ultraviolet B on an epidermis reconstructed with and without melanocytes. To address more specifically the role of melanin in fair-skinned individuals, experiments were done with cells obtained from human skin of low phototypes (II-III). To study the effect of constitutive melanin and possibly that of newly synthesized melanin precursors, a single dose of ultraviolet B (0.10 or 0.15 J per cm2, corresponding to a 4-5 minimal erythema dose in vivo) was administered to reconstructs and the effects were monitored over the first 24 h. When reconstructs with and without melanocytes were compared, no difference was found for DNA damage/repair assessed with antibodies to cyclobutane pyrimidine dimers and 6-4 photoproducts. More necrotic/apoptotic cells, however, were noted 24 h following ultraviolet B irradiation in reconstructs lacking melanocytes. Twenty-four hours following ultraviolet B irradiation the number of necrotic/apoptotic cells and the number of cyclobutane pyrimidine dimer positive cells was coarsely concentration-dependent. The number of cyclobutane pyrimidine dimer positive cells, however, was independent of the type of reconstruct used (with/without melanocytes). In conclusion, low phototype melanocytes seem to protect epidermal basal cells against ultraviolet B-induced apoptosis/necrosis and may preserve the overall integrity of the epidermis after ultraviolet B irradiation. On the contrary, such melanocytes do not seem to have a protective role against DNA damage and may not prevent cancer.