PERMEABILITY CHANGES CAUSED BY SURFACTANTS IN LIPOSOMES THAT MODEL THE STRATUM-CORNEUM LIPID-COMPOSITION

The alterations caused by different surfactants in the permeability of liposomes formed by a lipid mixture that models the stratum corneum ( SC) composition (40% ceramides, 25% cholesterol, 25% palmitic acid, an d 10% cholesteryl sulfate) were investigated. The surfactant/lipid mol ar ratios (Re) and the bilayer/aqueous phase surfactant partition coef ficients (K) were determined at two sublytic levels. The selected surf actants were sodium dodecyl sulfate (SDS); sodium dodecyl ether sulfat e (SDES) to assess the influence of the ethylene oxide groups on the a nionic surfactant's behavior; Triton X-100 (OP-10EO) and dodecyl betai ne (D-Bet) as representatives of nonionic and amphoteric surfactants. Permeability alterations were determined by monitoring the increase in the fluorescence intensity of liposomes due to the 5(6) carboxyfluore scein (CF) released from the interior of vesicles. The SC liposomes/su rfactant sublytic interactions were mainly ruled by the action of surf actant monomers. OP-10EO showed the highest ability to alter the perme ability of bilayers and the highest affinity with these structures, wh ereas D-Bet showed the lowest tendencies. Although SDS and SDES exhibi ted similar activity at 50% CF release (similar Re values), SDES appea red to be more active at 100% CF release, its affinity with bilayers b eing also increased. The different ability exhibited by SDS, SDES, and D-Bet (same alkyl chainlength) to alter the permeability of SC liposo mes emphasizes the role played by the polar part of these surfactants in this interaction. Different trends in the evolution of Re and K wer e observed when comparing the results with those reported for phosphat idylcholine (PC) liposomes. Thus, whereas SC liposomes appeared to be more resistant to the action of surfactants, the surfactant affinity w ith SC bilayers was always greater than that reported for PC bilayers.