The stabilities of immunoliposomes incorporated with variable amounts of ganglioside $G_{M1}$, were investigated as a function of time and temperature, by observing absorbance of vacant liposomes and calcein release from entrapped liposomes.
The bilayer of unsaturated PE(dioleoylphosphatidylethanolamine:DOPE), an hexagonal phase forming lipid, which dose not form stable liposomes at physiological temperature and pH, were formed when palmitoyl-immunoglobulin G(IgG) (2.5*$10^{-4}$ mol/DOPE mol) added, but destabilized within several hours. The incorporation of ganglioside $G_{M1}$ into immunolisome, enhanced the stabilities of bilayers, but aggregation and fusion between liposomes may be also promoted without any leaking of calcein. Such rapid aggregation and fusion would be because of the interaction between ganglioside $G_{M1}$ and protein(IgG).
The turbidity of immunoliposomes coated with ganglioside $G_{M1}$ increased up to 20mol% $G_{M1}$/DOPE mol, but decreased above the maximum. Such phenomena may be attributed to the disturbance of the bilayer characteristics, i.e. surface charge, layer transition or reorientation of interaction sites, when the concentration of ganglioside $G_{M1}$ increased.
The immunoliposomes coated with ganglioside $G_{M1}$ at 5℃ showed the higher stability than samples tested at elevated temperatures. After on week of storage, the precipitants at all temperatures were redispersed by mild sonication, and the redispersed liposomal solutions at lower temperatures maintained the original elution patterns in chromatography but broader distribution at elvated temperatures. Such observations suggested that during storage, the aggregation of liposomes kept at 5℃ is more dominant mechanism, but that the fusion is at elevated temperatures.
