Alkyl sulfate surfactants as solubilizing agents of liposomes modeling thecomposition of the stratum corneum lipids

The interaction of a series of alkyl sulfates (alkyl chain lengths C-10 (C- 10-SO4), C-12 (C-12-SO4) and C-14 (C-14-SO4)) with liposomes modeling the s tratum corneum (SC) lipid composition (40% ceramides, 25% cholesterol, 25% palmitic acid and 10% cholesteryl sulfate) was investigated. The surfactant /lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficien ts (K) were determined by monitoring the changes in the static light scatte ring of the system during solubilization. The fact that the free concentrat ion for each surfactant tested was always similar to its critical micelle c oncentration (in the experimental working medium) indicates that the liposo me solubilization was mainly ruled by the formation of mixed micelles. The K parameter progressively rose as the surfactant CMC decreased or its alkyl chain length increased, whereas the Re showed a minimum for C-12-SO4. Thus , although the maximum ability to saturate or solubilize SC liposomes corre sponded to the C-12-SO4, the C-14-SO4 showed the highest degree of partitio ning into liposomes or affinity with these bilayer structures. The overall balance of these two tendencies shows that the C-14-SO4 and the C-12-SO4 ha d, respectively the highest power to saturate and solubilize SC liposomes i n terms of total surfactant amount needed to produce these effects. Differe nt trends in the interaction of these surfactants with SC liposomes were ob served when comparing the Re and K parameters with those reported for PC on es. Whereas SC liposomes were more resistant to the surfactant action, the affinity of these surfactants with these bilayer structures was higher in a ll cases. (C) 1999 Elsevier Science B.V. All rights reserved.