Free radicals in human skin before and after exposure to light

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Abstract

Human skin exhibited a stable electron spin resonance (ESR) signal before irradiation, only if the samples were pigmented. The single almost symmetrical absorption peak with g = 2.003 and a line width of 5–6 gauss at 77 °K is associated with melanin. It was also observed in pigmented human and guinea pig hair, melanosomes, and melanin granules obtained from B-16 mouse melanoma and DOPA-melanin. Irradiation with wavelengths greater than 320 mμ, including ruby laser (λ = 694 mμ) and incoherent 600–700 mμ light, at 77 °K enhanced the melanin signals in pigmented samples only. “White” skin gave no intrinsic melanin free-radical signal, and irradiation with similar wavelengths produced no detectable free radicals. Ultraviolet radiation (λ < 320 mμ) enhanced the melanin signal in pigmented samples and also produced other radicals with a line width of approximately 24 gauss in both “white” and pigmented skin. Radiation-induced free radicals were only detected at 77 °K and were unstable at 300°K. The photo-enhanced melanin free-radical signal was also unstable, but the intrinsic melanin signal was not destroyed by warming. Radical yields measured in “white” and pigmented skin as a function of ultraviolet exposure dose showed that fewer radicals were generated in pigmented skin. The significance of this observation in relation to the photoprotective function of melanin is discussed.

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    This work was supported by the National Cancer Institute, United Slates Public Health Service (grant 5 R01 CA 05003), and the American Cancer Society, Inc. (grant T-82).

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