Liposomal membranes: VI. polysaccharide-induced aggregation of multilamellar liposomes of egg lecithin

Induced aggregation of multilamellar liposomes of egg lecithin with several polysaccharides, such as pullulan, dextran, hydroxyethylstarch, and amylopectin, has been investigated in conjunction with structural characteristics of polysaccharides, incubation temperature, ionic strength, and surface charge of liposomes. Aggregation of liposomes as a function of time was followed by monitoring turbidity of the liposome suspension at 600 nm. The inverse relationship between the minimal concentration and molecular weight of polysaccharides for the induced aggregation of liposomes was observed for all the polysaccharides employed. Polysaccharides having larger excluded volume more easily bind to liposomes, leading to the acceleration of the aggregation of liposomes. Hence, the order of efficiency of polysac charides for the promotion of liposome aggregation was pullulan>dextran>hydroxyethyl starch≃amylopectin Increasing the surface charge of liposomes brought about a decrease in aggregation irrespective of the sign. Even when negatively charged liposomes were incu-, bated with the cationic DEAE-dextran, the liposome aggregation was depressed. These results including salt effect and temperature dependency of the induced aggregation of lipo somes supported a plausible mechanism for the reaction, the polysaccharide-bridging mech anism, which has been provided for the polysaccharide-promoted agglutination of human erythrocytes.