Photoprotection by Total Melanin Content and Pigment Phenotype (Eumelanin, Pheomelanin) in Human Melanoma Cell Lines

Abstract

Melanin pigments are likely to represent the most important light protecting factor of human skin. Two subtypes of melanins have been identified, occurring in various amounts in skin and hair. The black to brown eumelanin is found predominantly in dark hair and eyes as well as in the skin of dark-haired subjects. The yellow-reddish pheomelanin mainly occurs in the hair and skin of blond- and redhaired individuals. Distinguished amounts of pheomelanin were detected in melanocytic especially dysplastic lesions, and the highest degrees of pheomelanin were found in melanoma cells [1,2]. Melanins do absorb ultraviolet radiation (UVR) and visible light as a filter, thus protecting cellular structures in the lower layers of the skin [3]. In addition, melanins can act as scavengers of UV-induced free radicals [1]. On the other hand, melanins are very photoreactive and thus, capable themselves to cause generation of reactive oxygen species [4]. The role of the 2 subtypes eu- and pheomelanin during the interaction with UVR is not clear. Eumelanin appears to be a most photoprotective factor of human skin, whereas, pheomelanin is also associated with phototoxic effects [5,6]. Individuals of Celtic origin, e.g. pheomelanic skin types, show higher frequency of light-induced skin damages [6–10]. Patients with numerous dysplastic nevi also show a reduced tolerance of UV light [11,12]. Upon UV-irradiation pheomelanin exhibits higher prooxidative effects [13], whereas eumelanin is assumed to possess no phototoxic potential [14].