CHARACTERIZATION AND PHOTOPROTECTION STUDIES OF A MODEL GAMMA-CYCLODEXTRIN-INCLUDED PHOTOLABILE DRUG ENTRAPPED IN LIPOSOMES INCORPORATING LIGHT ABSORBERS

Riboflavin (R), a photosensitive model drug, was included into gamma-cyclodextrin (gamma CD) and the complex formed (R gamma CD) characterized by nuclear magnetic resonance and differential scanning calorimetry: R or R gamma CD was entrapped into the aqueous phase of liposomes by the dehydration-rehydration procedure (DRV liposomes) or the classical method (MLV liposomes) both of which produce multilamellar vesicles. Liposomes, composed of egg phosphatidylcholine and equimolar cholesterol, were made to contain in a number of formulations one or more of the lipid-soluble light absorbers oil red O, oxybenzone, and dioxybenzone and, in some cases, the antioxidant beta-carotene, all incorporated into the bilayer structure. Exposure of R-containing liposomal formulations to UV light revealed various degrees of photoprotection depending on the type of liposomes used, whether or not the vitamin was included in gamma CD, the identity of light absorbers as well as the presence of beta-carotene. optimal photoprotection (267-fold stabilization compared to free R in solution) under the conditions described, was obtained when the R gamma CD complex was entrapped in DRV liposomes incorporating all lipid-soluble absorbers and beta-carotene.