EPR Detection of Free Radicals in UV‐lrradiated Skin: Mouse Versus Human

Abstract

Ultraviolet radiation produces free radicals in Skh-1 mouse skin, contributing to photoaging and carcinogenesis. If a mouse model is a general indicator of free radical processes in human skin photobiology, then radical production observed in mouse and human skin should be directly comparative. In this work we show that UV radiation (A > 300 nm, 14 pW/cmZ W B ; 3.5 mW/cmz UVA) increases the ascorbate free radical (Ax'-) electron paramagnetic resonance (EPR) signal in both Skh-1 mouse skin (45%) and human facial skin biopsies (340%). Visible light (A > 400 nm; 0.23 mW/cm* UVA) also increased the Ax*-signal in human skin samples (45%) but did not increase baseline mouse Asc*-, indicating that human skin is more susceptible to free radical formation and that a chromophore for visible light may be present. Using EPR spin-trapping techniques, UV radiation produced spin adducts consistent with trapping lipid alkyl radicals in mouse skin (a-[4-pyridyl l-oxidel-N-terf-butyl nitrondalkyl radical adduct; aN = 15.56 G and a" = 2.70 G) and lipid akoxyl radicals in human skin (53-dimethylpyrroline-l-oxiddalkoxyl radical adduct; aN = 14.54 G and aH = 16.0 G). Topical application of the iron chelator Desferal' to human skin significantly decreases these radicals (-SO%), indicating a role for iron in lipid peroxidation; Desferal has previously been shown to decrease radical production in mouse skin. This work supports the use of the Skh-1 mouse as a predictive tool for free radical formation in human skin. These results provide the first direct evidence for W radiationinduced free radical formation at near physiological temperatures in human skin and suggest that iron chelators may be useful as photoprotective agents.

Sunscreen enhancement of UV-induced reactive oxygen species in the skin

“…All images are displayed using the same intensity scale, in which regions of bright red and yellow indicate high fluorescence signal. R-123 fluorescence was predominately detected from the cytoplasm of the keratinocytes of each epidermal layer, which is consistent with data collected previously on Epiderm and ex vivo tissues and is attributed to ROS generation from intrinsic chromophores (i.e., NADH, riboflavin, mitochondria) [19,20,[29][30][31]. Regions of dark blue in the nuclei and extracellular spaces indicate low fluorescence signal equivalent to typical autofluorescence levels as displayed in Figs.…”

Electron paramagnetic resonance and mass spectrometry: Useful tools to detect ultraviolet light induced skin lesions on a molecular basis – A short review

“…Increase of signal intensity, measured as height of signal amplitude of cw EPR measurements, indicates that during irradiation free radical oxidative stress occurs [35,36]. However, Haywood et al showed that a significant increase of ascorbate radical concentration is detectable during irradiation only.…”

“…The use of spin traps is the most frequently applied method for this purpose [18,36,38]. It involves the reaction of a free radical with a diamagnetic trapping compound resulting in a longer living, EPR detectable species.…”

An Analysis of the Toxicity of Dihydroxyacetone in Spray Tanners when Exposed to Ultraviolet Radiation

“…Due to the range of reactions DHA must undergo to become melanoidin, it could form free radical intermediates that could prove toxic to the skin (Wiseman & Halliwell, 1996;Thorpe & Baynes, 2003). If spray tan users are consistently exposed to sunlight without the protection of sunscreen, then free radicals could form with the help of DHA as UV light has been documented to produce free radicals in direct exposure to skin (Jurkiewicz & Buettnerf, 1996). This paper aims to determine whether dihydroxyacetone is capable of presenting any significant risk of toxicity in humans when exposed to ultraviolet radiation by investigating current toxicological studies and data performed on DHA activity.…”