INFLUENCE OF LIPOSOME BILAYER FLUIDITY ON THE TRANSPORT OF ENCAPSULATED SUBSTANCE INTO THE SKIN AS EVALUATED BY EPR

Purpose. The influence of liposome composition on the bilayer fluidity and on the transport of encapsulated substance into the skin was inve stigated. Methods. Multilamellar vesicles (MLV) from dipalmitoylphosph atidylcholine (DPPC) or dimyristoylphosphatidylcholine (DMPC) with var ious amounts of cholesterol were prepared by the film method and chara cterised by photon correlation spectroscopy and electron paramagnetic resonance (EPR) methods. The transport of the hydrophilic spin probe e ncapsulated in MLV into pig ear skin was investigated by EPR imaging m ethods. The bilayer domain structure was studied by fitting the linesh ape of the experimental EPR spectra with the spectra calculated by the model, which takes into account the heterogeneous structure of the bi layer with several coexisting domains. Results. Cholesterol strongly i nfluences the entrapped volume of liposomes, the domain structure of t he lipid bilayer, and the transport of hydrophilic spin probe into the skin. Transport was not observed for liposomes composed of phospholip id:cholesterol 1:0 or 9:1 (mol:mol), not even above the phase transiti on temperature from the gel to the liquid crystalline phase of DMPC. A significant delivery of hydrophilic spin probe was observed only if t here was 30 or 50 mol% of cholesterol in the liposome bilayer. Conclus ions, It can be concluded that the domain structure of the liposome bi layer is more important for the delivery of encapsulated substance int o the skin than the liquid crystalline phase of the pure phospholipids bilayer.