Effect of sterols on liposomes: Membrane characteristics and physicochemical changes during storage

The differences in sterol chemical structures influenced the membrane characteristics of liposomes, especially the physicochemical changes during storage. Therefore, the effects of sterols (cholesterol, β-sitosterol, and stigmasterol) on membrane characteristics were investigated and compared with liposomes without sterols. The incorporation of sterols increased the particle size of liposomes. Transmission electron microscopy images showed that sterols improved the rigidity and decreased the deformability of membranes. Cholesterol produced a more condensing effect on membranes, whereas stigmasterol reduced the effectiveness of lipid packing as shown by Raman spectroscopy. The addition of sterols provided good vesicle size stability during storage. Fluorescence probe analysis demonstrated decreased membrane hydrophobicity and micropolarity with prolonged storage. Phospholipid hydrolysis and oxidation played a major role in regulating membrane characteristics. Among the three sterols, β-sitosterol was the most effective for the inhibition of hydrolysis and oxidation.