Role of saccharides for the freeze-thawing and freeze drying of liposome

For the preservation of liposomes, freeze-thawing and freeze-drying have been studied by various workers with saccharides (SA) and a freeze-dried liposome preparation is now commercially available. However, the mechanism of stabilizing action of SA in these processes, especially freeze-drying, is not yet fully understood. The interaction of egg yolk phosphatidylcholine (EPC: liquid crystaline state) and DPPC (gel state) liposomes with various glucose oligomers has been studied to elucidate the role of SA in these processes. The stability and property of freeze-dried products were determined by leakage of inner maker, liposomes size and thermal behavior. In the freeze-thawing process of EPC liposome, glucose and maltose are effectively cryoprotective, the large oligomers are not. In the freeze-drying of EPC liposome, glucose is ineffective and maltose is effective, however, oligomers with more than four glucose units are ineffective. As for the DPPC liposome, glucose is less effective and maltose is effective at every SA/PC molar ratio. The large oligomers with more than three glucose units are effective at low SA/PC molar ratio, however, become less effective at high SA/PC molar ratio. As for the DSC thermograms of freeze-dried products of DPPC and DMPC, the phase transition temperatures (T-c) at first scanning seem to be related residual water contents of dried product. At second scanning, T-c values move to certain low temperature almost independent of the kind of SA. The hydrogen bonding must be formed between SA molecule and PC molecule at first scanning. Based on these results, the role of SA will be discussed focusing on the hydrophilic and hydrophobic character of SA.