Lipid composition influence on the surfactant-induced release of the contents in liposomes formed by lipids modelling the stratum corneum

The influence of the lipid composition on the surfactant-induced release from liposomes formed by synthetic lipid mixtures modelling the stratum corneum lipids was investigated. To this end, a mixture containing ceramide (40%), cholesterol (25%), palmitic acid (25%) and cholesteryl sulfate (10%) was chosen as a central composition of the optimizing Box and Behnken experimental model for three variables. From these compositions, the lipid percentage range was varied for each lipid by +/-15% except for the cholesteryl sulfate where the variation was extended to +/-100%. The liposomes were prepared by sonication at 63 degrees C in a buffered medium containing 10 mM 5-(6)carboxyfluorescein (CF). Surfactant-induced release variations caused by the presence of a constant concentration of the non-ionic surfactant Triton X-100 were determined by monitoring the increase in the fluorescence intensity of the liposome suspensions due to the CF released from the interior of vesicles to the bulk aqueous phase. The presence of increasing concentrations of ceramide, palmitic acid and cholesterol resulted in a decrease in the percentage of CF released. However, increasing cholesteryl sulfate concentrations also led to the fall in the release of this dye, especially for higher levels of the other components. At a high ceramide concentration, the proportion of palmitic acid played an important role in the variation of surfactant-induced CF release regardless of the cholesterol concentration present in the bilayers.