Idebenone: a new antioxidant – Part I. Relative assessment of oxidative stress protection capacity compared to commonly known antioxidants

Topical applications of skin care products containing antioxidants have become increasingly popular. Numerous studies have elucidated the biological effects of these substances. General antiaging effects, anti-inflammatory properties, photoprotective properties, and prevention of ultraviolet (UV) immunosuppression have been documented. However, a standardized method to characterize and compare the properties and oxidative stress protection capacity of antioxidants was lacking. A multistep in vitro process utilizing a variety of biochemical and cell biological methods combined with in vivo studies was designed to compare the oxidative stress protective capacity of commonly used antioxidants. Data were presented for L-ascorbic acid, dl-alpha-tocopherol, kinetin, dl-alpha lipoic acid, ubiquinone, and idebenone. Methods included using UV-induced radical trapping/scavenging capacity measured by photochemiluminescence, pro-oxidative systems (LDL-CuSO(4), microsome-NADPH/ADP/Fe(3+)) with measurement of primary and secondary oxidation products, UVB irradiation of human keratinocytes, and in vivo evaluation, using the human sunburn cell (SBC) assay. Correlation and trends between in vitro and in vivo results were established, and the standardized test protocol was used to quantify oxidative stress protection capacity of antioxidants. Summarizing and totaling the data equally weighted for each oxidative stress study, the overall oxidative protection capacity scores of 95, 80, 68, 55, 52, and 41 were obtained for idebenone, dl-alpha tocopherol, kinetin, ubiquinone, L-ascorbic acid, and dl-alpha lipoic acid, respectively. The higher the score, the more effective the overall oxidative stress protection capacity of the antioxidant became. This multistep protocol may serve as a standard in investigating and comparing new putative antioxidants for topical use as well as a valuable tool to assess the anti-inflammatory properties, photoprotective properties, and prevention of UV immunosuppression of topical antioxidants.