RESUMO
PURPOSE: The aim of our study was to evaluate the photoprotective potential of melanin and ß-carotene against protoporphyrine IX-induced phototoxicity via photo hen's egg test. METHODS: In three independent test groups, the yolk sac blood vessel system of hen's eggs was exposed to protoporphyrine IX and irradiated with ultraviolet A (UVA). One of the test groups also received melanin to investigate its photoprotective capacity; another test group received ß-carotene for the same purpose. Morphological changes and embryo lethality were recorded in these three test groups for a period of 24 h. The same parameters were obtained in five different control groups. RESULTS: The control groups exhibited only minimal morphological changes and no fatalities. In contrast, severe phototoxic damage and a high lethality rate (75%) were observed in the test group exposed to protoporphyrine IX and UVA. Lethality was somewhat lower in the ß-carotene test group (58%) and was considerably lower in the melanin test group (17%). CONCLUSIONS: The photoprotective potential against protoporphyrine IX-induced phototoxic damage was moderate for ß-carotene and was remarkable for melanin. Given that synthetic melanocyte stimulating hormone (MSH) analogues induce a de novo synthesis of melanin without any previous ultraviolet irradiation in human skin, the application of MSH analogues might be conceived of as 'light hardening' without light. Synthetic MSH analogues thus may represent a new promising therapeutic option for photodermatoses especially for erythropoietic protoporphyria.