Investigation into the potential chemical mechanism of the pro-oxidant activity of carotenoids with liposomes under UV-irradiation

This study focuses on the behavior of beta-carotene and lutein inside multilamellar liposomes under continuous UV-irradiation. The liposomes were obtained by the thin film method and carotenoids (Crts) were incorporated by mixing at various concentrations (0.005, 0.0075, 0.02, 0.07 and 0.5 mol %). Liposomes formation and the presence of Crts inside them were confirmed by SEM microscopy and FT-IR spectroscopy, respectively. The antioxidant/pro- oxidant activity of Crts inside liposomes was determined by the thiobarbituric acid-malondialdehyde (TBA-MDA) test. The investigated Crts acted more or less unexpected (as pro-oxidants) inside the lipid bilayers, interacting with the UV-produced lipid radicals and simultaneously suffering under the UV-irradiation. Their pro-oxidant activity with liposomes and under UV-irradiation could be explained by the formation of unstable adducts in the reaction with peroxyl radicals, or by Crts-cation radicals formation via the electron transfer mechanism. Such tentatively unexpected behavior of carotenoids should be taken into consideration in further carotenoids-based UV-filters projections in cosmetic formulations for skin protection.