Stability and plasma apolipoprotein binding of lipid emulsions

The stability of lipid emulsions was studied during the ultracentrifugation flotation and freeze–thawing processes. The relationship between the droplets’ coalescence and the average spontaneous curvature of surface phospholipid monolayers was discussed on the basis of the coalescence transition state theory recently developed by Kabalnov et al. In addition, the effects of maltose on the emulsion coalescence in the frozen state were briefly discussed. The maximum binding amounts of apolipoprotein C-2 (apoC-2) and apolipoprotein E (apoE) to egg-phosphatidylcholine/triglyceride-emulsions were about 10 times larger than those to egg-phosphatidylcholine-vesicles (liposomes) in plasma. Accordingly, plasma-clearance of emulsions through apoE receptors was more rapid than vesicles in rat. The maximum binding amount of the isolated apolipoprotein A-1 (apoA-1) was also much larger for emulsions than vesicles. The different binding capacities between emulsions and vesicles were explained by the interaction of surface phosphatidylcholine and core triglyceride. Although binding of apolipoproteins to surface monolayers led to the packing stress (positive curvature), the interaction between core triglyceride and the surface egg PC monolayers releases the stress and increases the maximum binding amount (binding capacity).