Effect of soybean-derived sterol and its glucoside mixtures on the stability of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylcholine/cholesterol liposomes

The stability of liposomes is important when using them as a reservoir for drugs. A soybean-derived sterol mixture (S) and a sterol glucoside mixture (SG) were used to stabilize liposomes prepared from dipalmitoylphosphatidyl-choline (DPPC) and cholesterol (Ch). Four kinds of liposomes were prepared: liposomes consisting only of DPPC (DPPC-liposomes); DPPC-liposomes containing Ch (DPPC/Ch-liposomes); and DPPC-liposomes or DPPC/Chliposomes containing S or SG, respectively. In the present study, the effect of S and SG on the stability of liposomes entrapping calcein was investigated by measuring the leakage of calcein, by differential scanning calorimetry (DSC) and fluorescence anisotropy. The stable liposomes on heating showed that the initial leakage temperatures of calcein and the transition temperatures were high, the heats large, and the fluidity of the liposomal layer low. The results indicated that the stability of the liposomes depended on the concentration of S and SG in the DPPC- and DPPC/Ch-liposomes. The effect of S and SG on the stability of DPPC- and DPPC/Ch-liposomes in the gel state was greater in the following order: S > Ch > SG above about 10 mol% S or SG in the DPPC-liposomes and 5 mol% in the DPPC/Ch-liposomes.