Dihydroxy-carotenoid liposomes inhibit phototoxicity in Paramecium caudatum

The phototoxic effects of hematoporphyrin derivative, using Paramecium caudatum as a model system, are significantly reduced in the presence of carotenoid-containing liposomes. Multilammelar large or small unilammelar vesicles, containing specific carotenoids, were effective in protecting the organism, whether administered exogenously in the bathing solution, or via incubation of paramecia in starved culture media containing carotenoid liposomes. The effectiveness of the carotenoids as inhibitors of phototoxic effects was found to depend on the mode of administration, with small unilammelar being more effective than multilammelar large vesicles for all carotenoids tested. Small unilammelar vesicles containing the dihydroxy-carotenoids zeaxanthin or astaxanthin afforded the greatest protection in both exogenous and endogenous studies. The results of this study suggest that carotenoid efficacy may be determined, in part, by the environment of the carotenoid molecules.