Influence of the level of ceramides on the permeability of stratum corneum lipid liposomes caused by a C 14-alkyl betaine/sodium dodecyl sulfate mixture

Abstract

The role played by the ceramides in the interaction of a mixture of tetradecylbetaine (C 14-Bet)/sodium dodecyl sulfate (mole fraction of the zwitterionic surfactant, 0.6) with liposomes modeling the stratum corneum (SC) lipid composition was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients ( K) were determined by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6)-carboxyfluorescein released from the interior of vesicles. The presence in liposomes of higher and lower ceramide proportions than that existing in the SC lipids led to a fall and to a rise in the sublytic activity of the surfactant mixture on these structures, respectively. However, the surfactant mixture partitioning into liposomes (or affinity with these bilayer structures) increased as the proportion of ceramides type III (Cer) increased to achieve the highest value for a Cer proportion similar to that in the SC lipids (about 40%). Thus, at low Cer proportions, the ability of the surfactant mixture to alter the permeability of these bilayer structures was higher than that for liposomes approximating the SC lipid composition, despite their reduced partitioning into liposomes. These findings are in agreement with the recently reported dependencies of the level of ceramides in skin lipids and function barrier abnormalities, and could explain, in part, these dependencies. The fact that the free surfactant concentration needed to achieve the interaction levels investigated was lower than the surfactant mixture critical micellar concentration indicates that permeability alterations were mainly ruled by the action of surfactant monomers, regardless of the liposome lipid composition.