SYNTHETIC GLYCOLIPIDS AS MEMBRANE-BOUND CRYOPROTECTANTS IN THE FREEZE-DRYING PROCESS OF LIPOSOMES

A number of different synthetic alkylglycosides were incorporated into soybean phosphatidylcholine (SPC) liposomes and tested for their acti vity as membrane-bound cryoprotectants in the freeze-drying process of large unilamellar vesicles (LUV). These glycosidic derivatives posses s the same hydrophobic proportions but different headgroup sugars (gal actose or cellobiose) and a number (0-3) of ethoxy spacer units betwee n the chain and headgroup as modifications in the hydrophilic moieties . Analysis of freeze dried liposomes were conducted by 6-carboxyfluore scein (6-CF) retention, fusion assay employed resonance energy transfe r (RET), particle size distribution and electron micrographs. Cooperat ion of all glycolipids (GLs) with a phosholipid (PL) matrix in dehydra ted and rehydrated state was demonstrated by calorimetric studies. All GLs were effective in preventing dehydration induced fusion of SPC-LU V related to their head group size, but fusion was unaffected from spa cer induced sugar location on membrane surface. Considering 6-CF reten tion, it could be shown that GLs are not able to stabilize vesicles co mpletely. Galactosides cause an increased 6-CF retention in the presen ce of free carbohydrates (glucose or sucrose) which could not be expla ined by a simple addition of cryoprotective effects of free and membra ne bound sugars. According to the aggregation results, the protective role of membrane bound carbohydrates is discussed, focusing on their a bility to form hydrogen bondings in vesicle bulk sugar area.