THE FORMATION OF LIPOSOMES IN-VITRO BY MIXTURES OF LIPIDS MODELING THE COMPOSITION OF THE STRATUM-CORNEUM

The influence of different synthetic lipid mixtures approximating the composition of stratum corneum on the formation and physicochemical pr operties of liposomes was investigated with the aim of characterizing these structures. To this end, a lipid mixture containing ceramide (40 %), cholesterol (25%), palmitic acid (25%) and cholesteryl sulfate (10 %) was chosen as a central composition of the optimizing Box and Behnk en experimental model for three variables. From these compositions, th e optimizing lipid percentage range was varied for each lipid +/-15%, except for the cholesteryl sulfate in which case the variation was ext ended to +/-100%. Liposomes were prepared by sonication at 63 degrees C in a buffered medium (100 mM NaCl, 5 mM TRIS) at pH 7.5 and suppleme nted in some cases with 10 mM of 5(6)-carboxyfluorescein. The vesicle size distribution of liposome suspensions (nm) was determined by photo n correlation spectrometry, whereas the internal volume (ml per mmol l ipid) was determined by spectrofluorometry. Transmission electron micr oscopy (TEM) reveals the presence of unilamellar liposomes in al the l ipid mixtures investigated. With regard to the physicochemical propert ies of the systems, increasing concentrations of ceramide, palmitic ac id and cholesterol (or low cholesteryl sulfate concentrations) result in a decrease in both the size of the vesicles and the internal volume of these structures, This direct correlation confirms the formation o f similar bilayer structures in all cases.