Eberlin S, Clerici SP, Eberlin S, Pinheiro ALTA, Pinheiro AS.
Skin pigmentation is dependent on both the increased number of melanocytes as the increase on melanogenic enzymes. After exposure of the skin to sunlight, the melanogenesis process begins with the oxidation of the amino acid tyrosine by the enzyme tyrosinase, producing DOPA, which is metabolized to produce melanin. Melanin plays an important role in protecting the skin from the harmful effects of solar radiation, but excessive accumulation of this pigment can become an aesthetic problem. Exposure to sunlight, artificial tanning, pharmaceuticals and other chemicals, as well as chronic inflammatory processes and hormonal influences, can increase the production of factors such as melanocyte stimulating hormone and endothelin-1, which trigger the melanization of the skin. In addition to ultraviolet light, studies also show that the infrared radiation and visible light promote changes in skin pigmentation. In this work we evaluated the consequences of ultraviolet A and B (UVA/UVB), infrared-A (IR-A) and visible light (VL) irradiation on melanin and endothelin-1 synthesis, using an in vitro model of melanocyte and keratinocyte cultures, and ex vivo model of skin culture. All radiation (UV, IR-A, VL and Association) produced a significant increase of 8.22, 5.32, 5.97 and 10.56 %, respectively, in melanin production when compared to non-irradiated control (p<0.001), contributing to the process of cutaneous pigmentation. The association of radiation produced a further increase of 4.97 and 4.32 %, respectively, in melanin synthesis compared to IR-A and VL radiations applied alone. UV radiation, VL and the association of all radiation, produced a significant increase of 53.27, 63.81 and 57.81 %, respectively, in the production of endothelin-1 when compared to non-irradiated control. Despite IR-A have shown a trend in increased synthesis of endothelin-1, it did not produce a statistically significant result. Consistent with these results, skin fragments subjected to radiation have a higher melanin density in comparison with control fragments. An increasing number of papers has been published describing the harmful effects of exposures to mainly or exclusively short-wavelength IR (IR-A) radiation in cultures of human skin cells and in human skin biopsies. In the same way, visible light has been identified as not inert radiation and studies have demonstrated that it increases cutaneous pigmentation, even higher than the UV radiation. Our results corroborate previous data from literature and indicated the need for specific photoprotection strategies which are not addressed by conventional sunscreens available.