LIPID-COMPOSITION INFLUENCE ON THE SURFACTANT-INDUCED RELEASE OF THE CONTENTS IN LIPOSOMES FORMED BY LIPIDS MODELING THE STRATUM-CORNEUM

The influence of the lipid composition on the surfactant-induced relea se from liposomes formed by synthetic lipid mixtures modelling the str atum corneum lipids was investigated. To this end, a mixture containin g ceramide (40%), cholesterol (25%), palmitic acid (25%) and cholester yl sulfate (10%) was chosen as a central composition of the optimizing Box and Behnken experimental model for three variables. From these co mpositions, the lipid percentage range was varied for each lipid by +/ -15% except for the cholesteryl sulfate where the variation was extend ed 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 con stant concentration of the non-ionic surfactant Triton X-100 were dete rmined by monitoring the increase in the fluorescence intensity of the liposome suspensions due to the CF released from the interior of vesi cles to the bulk aqueous phase. The presence of increasing concentrati ons of ceramide, palmitic acid and cholesterol resulted in a decrease in the percentage of CF released. However, increasing cholesteryl sulf ate concentrations also led to the fall in the release of this dye, es pecially for higher levels of the other components. At a high ceramide concentration, the proportion of palmitic acid played an important ro le in the variation of surfactant-induced CF release regardless of the cholesterol concentration present in the bilayers.