In vivo measurement and mapping of skin redox stress induced by ultraviolet light exposure

Exposure of skin to UV light presents a potent oxidative stress and this could alter the skin redox state. In this context, we evaluated the ability of electron paramagnetic resonance (EPR) imaging to provide noninvasive in vivo mapping of the redox status of the skin of living rats. The redox status was measured using a topically applied nitroxyl spin probe, ¹⁵N-PDT. The nitroxyl intensity profile obtained across the skin layers showed that the concentration of the probe was higher in the epidermis and lower in the dermis and hypodermis. Skin permeability and reduction metabolism were evaluated in the skin exposed to UVB (312 nm) radiation. Exposure of skin to UVB decreased the overall reduction rate constant of the nitroxyl probe to 25 ± 6% of the value obtained in the untreated skin. EPR imaging data showed that after the UVB treatment, the reduction rate constant decreased to 41 ± 1% in epidermis, 28 ± 1% in dermis, and 21 ± 8% in hypodermis layers. The data suggested that UVB decreased the overall reducing capability of the skin with a larger decrease in the dermis and hypodermis. In summary, in vivo EPR imaging measurements showed significant alterations in the redox state of the skin exposed to UV light.