Subsolubilizing Effects of Alkyl Sulfates on Liposomes Modeling the Stratum Corneum Lipid Composition

The subsolubilizing interactions of three alkyl sulfates (chain lengths C<INF>10</INF>, C<INF>12</INF>, and C<INF>14</INF>), with liposomes modeling the stratum corneum lipid composition, were investigated. Liposomes were formed from a lipid mixture containing by weight 40% ceramides, 25% cholesterol, 25% palmitic acid and 10% cholesteryl sulfate. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the increase in the fluorescence intensity of liposomes due to the 5(6)-carboxyfluorescein (CF) released from the interior of vesicles. The free surfactant concentration was always lower than the critical micelle concentration. At the two interaction levels studied (50% and 100% CF release) the tetradecyl sulfate showed the highest ability to release the CF trapped in the liposomes (lowest Re values) and the highest degree of partitioning into the bilayers (highest K values). Whereas stratum corneum liposomes were more resistant to the action of alkyl sulfates than were phosphatidylcholine (PC) liposomes, the degree of partitioning of these surfactants into stratum corneum bilayers was always greater than that reported for PC ones.