PARTITION OF ALKYLBETAINE SURFACTANTS IN LIPOSOMES MODELING THE STRATUM-CORNEUM LIPID-COMPOSITION

The partitioning of a series of amphoteric alkylbetaine surfactants (a lkyl chain lengths C-10, C-12 and C-14) between the aqueous phase and the lipid bilayers of liposomes that model the stratum corneum lipid c ompositions was investigated. Liposomes were formed from a lipid mixtu re containing 40% ceramides, 25% cholesterol, 25% palmitic acid and 10 % of cholesteryl sulfate. The surfactant/lipid molar ratios (Re) and t he bilayer/aqueous phase partition coefficients (K) were determined at two sublytic levels by monitoring the increase in the fluorescence in tensity of liposomes due to 5(6)-carboxyfluorescein (CF) release from the interior of the vesicles. Given that the free surfactant concentra tions were always lower than their critical micelle concentrations, we may assume that the stratum corneum (SC) liposomes-surfactant sublyti c interactions were mainly determined by the action of surfactant mono mers. At the two interaction levels studied (50% and 100% of CF releas e) tetradecylbetaine showed the highest ability to alter the release o f the CF trapped into bilayers (lowest Re values) and the highest degr ee of partitioning into liposomes or affinity with these structures (h ighest K values), whereas decylbetaine showed the opposite tendencies. Different trends in the evolution of Re and K were observed when comp aring the results obtained with those reported for the interaction of the same surfactants with phosphatidylcholine (PC) liposomes. Thus, wh ereas SC liposomes appeared to be more resistant to the action of alky lbetaines, the degree of partitioning of these surfactants into the SC bilayers was always greater than that reported for PC bilayers. (C) 1 997 Elsevier Science B.V.