596 Complementary sun protection of two antioxidants (OTZ and DTG) in a sunscreen emulsion based on skin release

Abstract

Sunscreens have been shown to be extremely effective in preventing DNA lesions due to ultraviolet (UV) radiation. Indeed, recent studies indicate that the number of UV-induced lesions decreased up to 95% depending on sunfilter combination and sun protection factor (SPF). Thus, sunblockers protect the skin from the harmful effects of UV, but they do not provide 100% protection. As a result, sunscreens are now being developed with antioxidants to provide additional protection against oxidative stress-mediated cell damage especially reactive oxygen species (ROS). We investigated the bioavailability, release and antioxidative properties of a sunscreen formulation (emulsion) containing two antioxidants, oxothiazolidine (OTZ) and delta-tocopheryl glucoside (DTG) using reconstructed human epidermis (RHE) model. OTZ reacts directly with ROS to form taurine; while DTG is metabolized into α-tocopherol to achieve antioxidative activities. Their penetration and metabolism 0.5-24 h were measured after solar-simulated irradiation as well as their antioxidative responses on RHE models. Oxidative stress markers included malondialdehyde (MDA), superoxide dismutase (SOD) and catalase activities. The two antioxidants had different penetration profiles: OTZ was rapidly and extensively absorbed whereas DTG was slowly absorbed. The yield of protection increased over time, with maximal protection 2 h post-irradiation. DTG slowly penetrated in the RHE and was present in the epidermis at all post-irradiation timepoints, thus allowing a slow but constant supply of α-tocopherol over at least 24 h. By contrast, the OTZ antioxidative protection was immediate but short-lived due to its rapid penetration. These results indicate a complementary sunlight protective action of OTZ and DTG; with immediate bioavailability of OTZ, and a prolonged skin delivery of α-tocopherol from the slower bioavailability and metabolism of DTG.