Characterization of dipalmitoylphosphatidylcholine liposomes containing a soybean-derived sterylglucoside mixture by differential scanning calorimetry, Fourier transform infrared spectroscopy, and enzymatic assay.

Previously, we reported that dipalmitoylphosphatidylcholine liposomes (DPPC-liposomes) containing soybean-derived steryl glucoside mixtures (SG) (DPPC/SG-liposomes) accumulated in the liver, especially in parenchymal cells. DPPC/SG-liposomes and a mixture of DPPC and SG (DPPC/SG mixture) were compared by means of differential scanning calorimetry, Fourier transform infrared (FT-IR), and enzymatic assays. The results suggested that the maximum molar mixing ratios of DPPC and SG in a powder was DPPC:SG = 7:2.2. Enzymatic assays indicated that the glucose group of SG projected outward from the liposomal surface and that the amount of SG on the liposomal surface was limited, the maximum mole fraction of SG in DPPC/SG-liposomes being 0.27 (DPPC: SG = 7:2.6). FT-IR spectra indicated that the glucose group of SG interacts with the phosphate group of DPPC on the surface of liposomes, since the phosphate symmetric and asymmetric stretching bands of DPPC/ SG-liposomes were shifted to lower frequencies with increasing SG. These results suggested that the glucose group of SG projecting outward from the liposomal membrane contributes to the hepatic cellular distribution of DPPC/SG-liposomes.