EPR DETECTION OF FREE-RADICALS IN UV-IRRADIATED SKIN - MOUSE VERSUS HUMAN

Ultraviolet radiation produces free radicals in Skh-1 mouse skin, cont ributing to photoaging and carcinogenesis. If a mouse model is a gener al indicator of free radical processes in human skin photobiology, the n radical production observed in mouse and human skin should be direct ly comparative, In this work we show that UV radiation (lambda > 300 n m, 14 mu W/cm(2) UVB; 3.5 mW/cm(2) WA) increases the ascorbate free ra dical (Asc(.-)) electron paramagnetic resonance (EPR) signal in both S kh-1 mouse skin (45%) and human facial skin biopsies (340%). Visible l ight (lambda > 400 mm; 0.23 mW/cm(2) UVA) also increased the Asc(.-) s ignal in human skin samples (45%) but did not increase baseline mouse Asc(.-), indicating that human skin is more susceptible to free radica l formation and that a chromophore for visible light may be present. U sing EPR spin-trapping techniques, UV radiation produced spin adducts consistent with trapping lipid alkyl radicals in mouse skin (alpha-[4- pyridyl 1-oxide]-N-tert-butyl nitrone/alkyl radical adduct; a(N) = 15. 56 G and a(H) = 2.70 G) and lipid alkoxyl radicals in human shin (5,5- dimethylpyrroline-1-oxide/alkoxy radical adduct; a(N) = 14.54 G and a( H) = 16.0 G), Topical application of the iron chelator Desferal(3) to human skin significantly decreases these radicals (approximate to 50%) , indicating a role for iron in lipid peroxidation; Desferal has previ ously been shown to decrease radical production in mouse skin, This wo rk supports the use of the Skh-1 mouse as a predictive tool for free r adical formation in human skin, These results provide the first direct evidence for UV radiation-induced free radical formation at near phys iological temperatures in human skin and suggest that iron chelators m ay be useful as photoprotective agents.