Antioxidant efficacy on human skin in vivo investigated by UVA-induced chemiluminescence decay analysis via induced chemiluminescence of human skin.

BACKGROUND/AIMS: Exogenous factors (e.g. physical: UV irradiation; or chemical: hydrogen peroxide) and endogenous metabolic processes (e.g. cellular respiration, oxidative burst, etc.) generate oxidative stress in living tissues which are in balance with enzymatic antioxidative systems and ingested antioxidants under normal conditions. These complex biological reactions are accompanied by chemiluminescence (ultraweak photon emission). However, knowledge about the chemiluminescence decay characteristics of human skin and the modulatory influence of topically applied antioxidants is still scarce. METHODS: Using ICL-S (induced chemiluminescence of human skin), a highly sensitive in vivo method, the decay characteristics of UVA-induced photon emission caused by different UVA doses were investigated in detail. In addition, modulatory properties of topical antioxidant pretreatment were examined for 2 weeks. RESULTS: UVA-induced chemiluminescence signals were generally characterized by two distinct decay phases: an initial burst (0-5 s), contributing approximately 80% of the complete signal with an inverse dose-response relationship (UVA dose vs. chemiluminescence intensity), followed by a second decay phase (delayed chemiluminescence, 5-200 s) showing a direct correlation. Antioxidant pretreatment caused a reduction in signal intensity of approximately 50%, which was calculated by signal integration and confirmed using the modulation of the intersection point of decay curves resulting from irradiation with different UVA doses at constant intensity with and without treatment. CONCLUSION: In addition to the established UVA filter testing (independent from UVB filter content) on human skin in vivo, ICL-S is also a valuable tool for the efficacy testing of topically applied antioxidants under in vivo conditions in humans. The first rapid, but short, decay phase not only provides approximately 80% of the complete chemiluminescence signal, but is also essential for the investigation of antioxidant-mediated effects. Chemiluminescence signal modulations induced by UVA intensity reduction (e.g. UV filters in daily care products) can be clearly distinguished from antioxidant-mediated signal modulations. The probe head dimensions permit comprehensive in vivo testing in humans on practically every skin area (e.g. arms, legs, back, abdomen and face).