Preclinical evaluation of infrared A radiation and visible light on melanogenesis process using an in vitro and ex vivo model of skin culture
Author: Samara Eberlin
Published at: September 21, 2015
23rd IFSCC Conference (International Federation of Societies of Cosmetic Chemists), Zurich, 21-23 September, 2015.
Eberlin S, Clerici SP, Eberlin S, Pinheiro ALTA, Pinheiro AS.
Skin pigmentation is dependent on both the increased number of melanocytes and the increase in 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 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 an ex vivo model of skin culture. All radiation types (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 the 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 the non-irradiated control. Despite IR-A showing 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 had a higher melanin density in comparison with control fragments. An increasing number of papers have been published describing the harmful effects of exposure to mainly or exclusively short-wavelength IR (IR-A) radiation in cultures of human skin cells and in human skin biopsies. Similarly, visible light has been identified as not inert radiation, and studies have demonstrated that it increases cutaneous pigmentation, even more than UV radiation. Our results corroborate previous data from the literature and indicate the need for specific photoprotection strategies that are not addressed by conventional sunscreens available.