Protection of liposomes during dehydration or freezing.

When liposomes are subjected to dehydration or freeze-thawing, vesicle fusion and/or leakage of vesicle contents can occur. The disaccharide, trehalose and the cryoprotectant, glycerol, are known to protect vesicle integrity during dehydration and freezing respectively. Here we examine their protective abilities as a function of vesicle size and lipid composition. It is shown that fatty acyl composition, cholesterol content and, with the exception of phosphatidylglycerol, acidic lipid content do not significantly alter the retention of aqueous contents by vesicles dehydrated and rehydrated in the presence of trehalose. The susceptibility to leakage induced by both dehydration and freezing is, however, critically dependent upon vesicle size with the smallest systems (70-100 nm diameter) being most stable. The mechanism whereby trehalose protects against vesicle fusion and leakage is also discussed.