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

The role played by the ceramides in the interaction of a mixture of tetrade cylbetaine (C-14-Bet)/sodium dodecyl sulfate (mole fraction of the zwitteri onic surfactant, 0.6) with liposomes modeling the stratum corneum (SC) lipi d composition was studied. The surfactant/lipid molar ratios (Re) and the b ilayer/aqueous phase partition coefficients (K) were determined by monitori ng the changes in the fluorescence intensity of liposomes due to the 5(6)-c arboxyfluorescein released from the interior of vesicles. The presence in l iposomes 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 surf actant mixture on these structures, respectively, However, the surfactant m ixture partitioning into liposomes (or affinity with these bilayer structur es) increased as the proportion of ceramides type III (Cer) increased to ac hieve the highest value for a Cer proportion similar to that in the SC lipi ds (about 40%). Thus, at low Cer proportions, the ability of the surfactant mixture to alter the permeability of these bilayer structures was higher t han that for liposomes approximating the SC lipid composition, despite thei r reduced partitioning into liposomes. These findings are in agreement with the recently reported dependencies of the level of ceramides in skin lipid s and function barrier abnormalities, and could explain, in part, these dep endencies. The fact that the free surfactant concentration needed to achiev e the interaction levels investigated was lower than the surfactant mixture critical micellar concentration indicates that permeability alterations we re mainly ruled by the action of surfactant monomers, regardless of the lip osome lipid composition. (C) 1999 Elsevier Science B.V. All rights reserved .