High-energy visible light at ambient doses and intensities induces oxidative stress of skin-Protective effects of the antioxidant and Nrf2 inducer Licochalcone A in vitro and in vivo

Background Solar radiation causes skin damage through the generation of reactive oxygen species (ROS). While UV filters effectively reduce UV-induced ROS, they cannot prevent VIS-induced (400-760 nm) oxidative stress. Therefore, potent antioxidants are needed as additives to sunscreen products. Methods We investigated VIS-induced ROS formation and the photoprotective effects of the Nrf2 inducer Licochalcone A (LicA). Results Visible spectrum of 400-500 nm dose-dependently induced ROS in cultured human fibroblasts at doses equivalent to 1 hour of sunshine on a sunny summer day (150 J/cm(2)). A pretreatment for 24 hours with 1 mu mol/L LicA reduced ROS formation to the level of unirradiated cells while UV filters alone were ineffective, even at SPF50+. In vivo, topical treatment with a LicA-containing SPF50 + formulation significantly prevented the depletion of intradermal carotenoids by VIS irradiation while SPF50 + control did not protect. Conclusion LicA may be a useful additive antioxidant for sunscreens.