EMULSION AND VESICLE FORMATION OF RETINOL AND RETINYL PALMITATE WITH EGG YOLK PHOSPHATIDYLCHOLINE

摘要

Spreading pressure measurements showed that retinyl palmitate (retinol palmitate, ReO-Pal) and egg yolk phosphatidylcholine (PC) were practically immiscible and separated into PC bilayers and ReO-Pal liquid. On the contrary, substantial amounts of retinol (ReOH) were incorporated into PC bilayers. The molar ratios of PC in the outer surface and the inside of sonicated particles of these lipid mixtures were determined on the basis of H-1-NMR measurements in the presence of a paramagnetic cation Pr3+. The higher ratio for the PC/ReO-Pal particles than 1.4 (the maximum value for vesicle structure) showed that part of the PC in the inner leaflet of vesicle bilayers was moved to the outer leaflet by addition of the neutral lipid, indicating formation of emulsion particles. Production of emulsion particles in the sonicated dispersion of PC/ReO-Pal mixtures was cofirmed by electron microscopy (EM). Small angle X-ray scattering (SAXS) and EM measurements on (vortexed) hydrated lipid mixtures of PC/ReO-Pal demonstrated that excess PC, coexisting with emulsion particles, was organized into regular bilayer lamellas with a repeating distance of 64.8 nm. On the other hand, vesicles with irregularly stacked lamellar structures were observed in EM pictures on hydrated PC/ReOH mixtures. The irregular structures caused broad SAXS spectra with a repeating distance of about 70 nm and a sharp isotropic peak in P-31-NMR spectra. Thus, esterification and hydrolysis of retinoids lead to remarkable changes in the structure organization With phospholipids. (C) 1995 Academic Press, Inc. [References: 31]