Cryoprotective effects of cycloinulohexaose on freezing and freeze-drying of liposomes.

Cycloinulohexaose (CF-6) maintained the membrane structure of the liposomes during freeze-thawing, and thus CF-6 was very effective in inhibiting both drug leakage from liposomes and the size change of liposomes during freezing and freeze-drying. As the ratio of CF-6 to lipid increased from 1 to 5, calcein retention in the liposomes increased from 70% up to 85% and a maximum retention was obtained at a ratio of more than 2. The addition of glycerol enhanced the above cryoprotective effect of CF-6 and improved calcein retention up to 90%. Neither detectable leakage of calcein nor particle size change was observed after the storage of liposomes freeze-dried with CF-6 for 6 months at 4 and 25 degrees C.