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-c yclodextrin (gamma CD) and the complex formed (R gamma CD) characteriz ed 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 classica l method (MLV liposomes) both of which produce multilamellar vesicles. Liposomes, composed of egg phosphatidylcholine and equimolar choleste rol, were made to contain in a number of formulations one or more of t he lipid-soluble light absorbers oil red O, oxybenzone, and dioxybenzo ne and, in some cases, the antioxidant beta-carotene, all incorporated into the bilayer structure. Exposure of R-containing liposomal formul ations to UV light revealed various degrees of photoprotection dependi ng on the type of liposomes used, whether or not the vitamin was inclu ded in gamma CD, the identity of light absorbers as well as the presen ce of beta-carotene. optimal photoprotection (267-fold stabilization c ompared to free R in solution) under the conditions described, was obt ained when the R gamma CD complex was entrapped in DRV liposomes incor porating all lipid-soluble absorbers and beta-carotene.