Fluorescence analysis with diphenylhexatriene and its ionic derivatives of the fluidity of liposomes constituted from stratum corneum lipids: Contribution of each lipid component and effects of long-chain unsaturated fatty acids

Abstract

The fluidity of bilayer liposomes of stratum corneum lipids, consisting of ceramide, cholesterol, cholesteryl sulfate and palmitic acid, was examined by observing the fluorescence anisotropies of diphenylhexatriene (DPH) and its ionic derivatives as reporters of the fluidity of the two interfacial regions and the central region of the lipid bilayer. The effect of each lipid component was studied by comparing the fluorescence anisotropies of the probes in liposomes from which individual lipids were omitted with those in liposomes consisting of all four lipid components. The fluorescence anisotropies of DPH and its ionic derivatives at 37°C were decreased by omission of cholesterol, but not affected by omission of cholesteryl sulfate or palmitic acid. The phase transition temperature was also decreased significantly by omission of cholesterol. These results indicated the possibility that cholesterol is the main component causing solidity of the stratum corneum lipid bilayer. Addition of long-chain cis-unsaturated fatty acids, which are penetration enhancers, resulted in decreases in the fluorescence anisotropies of DPH and its ionic derivatives as well as decreases in the phase transition temperature. The results indicated that perturbation by these fatty acids of lamellar lipid domains in a wide range from the interfacial to deeper regions enhances penetration of drugs.