Detection and Identification of Free Radicals Generated by UV and Visible Light in Ex Vivo Human Skin

Abstract

Citation: IFSCC Magazine, 11 (2008) (3) 207–215Contrary to the skin biological end points used for determination of the sun protection factor and UVA protection factor, generation of excess free radicals in skin – mainly reactive oxygen species – is potentially the source of much skin damage and so represents a more general biophysical answer to the effects of sun exposure of different wavelengths. By applying electron spin resonance spectroscopy to human skin biopsies, we determined in previous work a free radical action spectrum covering the ultraviolet and visible light range. Convolution of the action spectrum with sunlight spectral irradiance (280–700nm) showed the importance of visible light in free radical generation. This unexpected finding led us to perform further investigations. Firstly, an existing sun simulator was modified so that its output truly mimics the sun's full spectrum, including visible light. Human skin biopsies were irradiated either by this device or a conventional UV source, confirming our previous calculations: half of the free radicals are generated in the 400–700nm visible wavelength range. Secondly, the visible spectrum of the modified sun simulator was divided into narrow‐band lights using different pairs of short‐ and long‐pass filters. Human skin biopsies impregnated with specific spin traps were exposed to the different narrow‐band lights to identify different types of free radicals. Generation of dangerous radical species like •O2‐, •OH and •CH‐R was observed in different parts of the visible range, confirming the relevance of the free radical action spectrum and its ability to predict skin protection.Keywords: UV + VIS solar simulator, ex vivo human skin, free radicals, action spectrum, Electron Spin Resonance