Surface Coating of Liposomes with Hydrophobized Polysaccharides

Coating the outermost surface of a liposomal membrane with several different hydrophobized polysaccharides was investigated by fluorescence depolarization, gel chromatography, and dynamic light scattering methods. The binding of cholesterol-bearing pullulan to the liposomal surface was biphasic. The first process was finished within minutes while the subsequent slow stages took over several hours. The binding isotherms followed Langmuir-type adsorption. The binding constant (K) increased with increases in the substitution degree of the cholesteryl moiety and the molecular weight of the pullulan derivatives used, while the maximum amount of the polysaccharide coating (qs) was almost the same. The apparent liposome size increased by 20-30 nm upon coating. Chemical structure of the parent polysaccharide had only a slight effect on the binding constant, while the structures of the hydrophobic moiety had a significant effect on the coating behavior of the liposomes. In the case of dodecyl diglyceryl group-bearing pullulan, both K and qs were smaller than those of other cholesterol-bearing polysaccharides. The addition of hexadecyl-bearing pullulan to the liposome induced aggregation of the liposomes. The cholesteryl moiety is an excellent hydrophobic anchor for polysaccharide coating liposomal surfaces compared with simple monoalkyl or dialkyl chains.

Enhanced Growth of Cultured Fibroblasts by a Synthetic Polyanionic Polymer

A synthetic polyanionic polymer, poly(maleic acid-alt-7,12-dioxaspiro[5,6]dodec-9-ene), exhibits mitogen-like behavior for cultured fibro-blasts. Cultures of L929 and STO fibroblasts in the presence of this polymer resulted in enhanced growth by both fibroblast cell lines. After three days, at optimum polymer concentrations, the cell numbers increased 3.7-fold for the STO cells and 1.9-fold for the L929 cells compared to the cells cultured in the same environment without the polymer. The polymer promoted this growth without any other external growth factors. This result suggests that the polymer has a direct effect on the growth of both of these fibroblast cells.

Partition of polysaccharide-coated liposomes in aqueous two-phase systems

Hydrophobized polysaccharides such as cholesterol-bearing pullulan (CHP), dextran (CHD) and mannan (CHM) effectively coat the liposomal surface. Partition of the hydrophobized polysaccharide-coated liposomes in an aqueous two-phase system (PEO (top)/pullulan (bottom) or PEO (top)/dextran (bottom)) was investigated (PEO = poly(ethylene oxide)). Conventional liposomes without a polysaccharide coat mostly locate at the interface between the two polymer phases. The polysaccharide-coated liposomes, on the other hand, were partly partitioned to the bottom polysaccharide phase depending on the structure of the hydrophobized polysaccharide on the liposomal surface. The affinity between the polysaccharide on the liposomal surface and that in the bulk bottom phase controls the efficiency of partition. The sequence of interaction strength between the two carbohydrates was the following: for the PEO/dextran two-phase system, dextran(liposome)-dextran(bulk) > mannan(liposome)- dextran(bulk) > pullulan(liposome)-dextran(bulk); while for the PEO/pullulan system, the sequence of interaction strength was pullulan(liposome)- pullulan(bulk) > dextran(liposome)-pullulan(bulk) approximately mannan(liposome)-pullulan(bulk).