INFLUENCE OF THE LEVEL OF CERAMIDES IN THE PERMEABILITY OF STRATUM-CORNEUM LIPID LIPOSOMES CAUSED BY SODIUM DODECYL-SULFATE

The role played by the ceramides in the sublytic interactions of sodiu m dodecyl sulfate (SDS) with liposomes modeling the stratum corneum (S C) lipid composition was studied. The surfactant/lipid molar ratios (R e) and the bilayer/aqueous phase partition coefficients (K) were deter mined by monitoring the changes in the fluorescence intensity of lipos omes due to the 5(6) carboxyfluorescein (CF) released from the interio r 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 SDS on these structures. However, th e SDS partitioning into liposomes (or affinity with these bilayer stru ctures) increased as the proportion of Cer increased up to achieve alm ost a constant value for a Cer proportion similar to that in the SC li pids (about 40%). Thus, at low Cer proportions the ability of SDS mole cules to alter these bilayer structures was higher than that for lipos omes approximating the SC lipid composition despite their reduced part itioning into liposomes. These findings are in agreement with the rece ntly reported dependencies of the level of ceramides in skin lipids an d function barrier abnormalities and could explain in part these depen dencies. The fact that the free surfactant concentration needed to ach ieve the two interaction levels investigated was lower than the surfac tant critical micellar concentration (CMC) indicates that permeability alterations were mainly ruled by the action of surfactant monomers, r egardless of the liposome lipid composition. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.