Sublytic Interactions of Octylphenol Surfactants with Liposomes Modeling the Stratum Corneum Lipid Composition
The subsolubilizing interactions of a series of octylphenol polyethoxylated surfactants (average ethylene oxide units (EO) between 8.5 and 20) with liposomes modeling the stratum corneum lipid composition was investigated. Liposomes were formed from a lipid mixture containing 40% ceramides, 25% cholesterol, 25% palmitic acid, and 10% cholesteryl sulfate. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined at two sublytic levels (50% and 100% CF release) by monitoring the increase in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein (CF) released from the interior of vesicles. Given that the free surfactant concentrations were always lower than the critical micelle concentrations, we may assume that the SC liposomes/surfactant sublytic interactions were mainly ruled by the action of surfactant monomers. At the two interaction levels studied the octylphenol with 8.5 EO units showed the highest ability to alter the release of the CF trapped into bilayers (lowest Re values), whereas that with 9.5 EO showed the highest degree of partitioning into liposomes or affinity with these structures (highest K values). The octylphenol with 20.0 EO units showed the lowest tendencies. Different trends in the interaction of these surfactants with SC and phosphatidylcholine (PC) liposomes were observed when comparing the present Re and K parameters with those reported for PC liposomes. Thus, although SC liposomes were more resistant to the action of octylphenols, the degree of partitioning of these surfactants into SC bilayers was always greater than that reported for PC liposomes.
Maza
ADL
Centro de Investigacion y Desarrollo, Consejo Superior de Investigaciones Cientificas, Madrid, 28006, Spain
Baucells
J
Ensenat
PG
Parra
JL