Solubilization of stratum corneum lipid liposomes by C14-betaine/sodium dodecyl sulfate mixtures. Influence of the level of ceramides in the solubilization process

The solubilization of liposomes modeling the stratum corneum (SC) lipids by tetradecylbetaine (C14-Bet)/sodium dodecyl sulfate (SDS) mixtures and the role played by the content of ceramide in this process were studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light scattering of the system during solubilization. The fact that the free surfactant concentration was always similar to its CMC indicates that the liposome solubilization was mainly ruled by the formation of mixed micelles. The mole fraction of the zwitterionic component (Xzwitter), 0.4, showed the lowest ability to saturate or solubilize liposomes, whereas that of Xzwitter=0.6 exhibited the highest degree of partitioning into liposomes. The presence in liposomes of higher and lower proportion of ceramides than that existing in the SC led to a fall and to a rise in both the activity and the partitioning of a specific surfactant mixture (Xzwitter=0.4) in these bilayer structures. This finding could be related to the recently reported dependencies of the level of ceramides in skin function and barrier abnormalities. Comparison of the present Re and K values with those reported for phosphatidylcholine (PC) liposomes shows that although SC liposomes were more resistant to the action of surfactant mixtures their degree of partitioning into SC bilayers was always higher than that reported for PC liposomes.