SOLUBILIZATION OF LIPOSOMES MODELING THE STRATUM-CORNEUM LIPID-COMPOSITION BY BETAINE-TYPE ZWITTERIONIC SURFACTANTS

The interaction of a series of alkylbetaines (alkyl chain lengths C-10 (C-10-Bet), C-12 (C-12-Bet) and C-14 (C-14-Bet)) with liposomes model ling the stratum corneum (SC) lipid composition (40% ceramides, 25% ch olesterol, 25% palmitic acid and 10% cholesteryl sulphate) was investi gated. The surfactant/lipid molar ratios Re and the bilayer/aqueous ph ase partition coefficients K were determined by monitoring the changes in the static light scattering of the system during solubilization. T he fact that the free concentration for solubilization by each surfact ant tested was always similar to its critical micelle concentration (C MC) indicates that the liposome solubilization was mainly ruled by the formation of mixed micelles. The K parameter rose as the surfactant a lkyl chain length increased or its CMC decreased, whereas the Re param eter showed a minimum for C-12-Bet. Thus, although the highest ability to saturate or solubilize SC liposomes corresponded to the C-12-Bet, the highest degree of partitioning into liposomes (or affinity with th ese bilayer structures) was reached for C-14-Bet. The overall balance of these two tendencies shows that C-12-Bet had the highest activity a t the two interaction levels investigated in terms of the total surfac tant amount needed to produce these effects. Different trends in the i nteraction of these surfactants with SC liposomes were observed when c omparing the Re and K parameters with those reported for phosphatidylc holine. Thus, whereas SC liposomes were more resistant to the surfacta nt action (especially for C-10-Bet), the affinity of these surfactants with these bilayer structures was higher in all cases. (C) 1998 Elsev ier Science B.V.