Melatonin enhances antioxidative enzyme gene expression (CAT,GPx, SOD), prevents their UVR‐induced depletion,and protects against the formation of DNA damage (8‐hydroxy‐2'‐deoxyguanosine) in ex vivo human skin

UV radiation (UVR) induces serious structural and functional alterations in human skin leading to skin aging and carcinogenesis. Reactive oxygen species are key players in UVR‐mediated photodamage and induce the DNA‐base‐oxidized, intermediate 8‐hydroxy‐2'‐deoxyguanosine (8‐OHdG). Herein, we report the protective action of melatonin against UVR‐induced 8‐OHdG formation and depletion of antioxidative enzymes using ex vivo human full‐thickness skin exposed to UVR in a dose (0, 100, 300 mJ/cm²)‐ and time‐dependent manner (0, 24, 48 hr post‐UVR). Dynamics of depletion of antioxidative enzymes including catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD), or 8‐OHdG formation were studied by real‐time PCR and immunofluorescence/immunohistochemical staining. UVR‐treated skin revealed significant and immediate (0 hr 300 mJ/cm²) reduction of gene expression, and this effect intensified within 24 hr post‐UVR. Simultaneous increase in 8‐OHdG‐positive keratinocytes occurred already after 0 hr post‐UVR reaching 71% and 99% up‐regulation at 100 and 300 mJ/cm², respectively (P < 0.001). Preincubation with melatonin (10^?3 m ) led to 32% and 29% significant reductions in 8‐OHdG‐positive cells and the prevention of antioxidative enzyme gene and protein suppression. Thus, melatonin was shown to play a crucial role as a potent antioxidant and DNA protectant against UVR‐induced oxidative damage in human skin.