Liposome Mediated Modulation of Macrophage Functions

Abstract

Liposomes are artificially prepared spheres, consisting of concentric phospholipid bilayers separated by aqueous compartments. They form, when phospholipids e.g. phosphatidylcholine molecules, are dispersed in water. The phospholipid molecules will find a conformation in which their hydrophobic fatty acid chains are prevented from contact with water. For that reason, phospholipid bilayers are formed in which the relatively hydrophilic head groups are making up both of the outer parts of each bilayer, whereas the hydrophobic fatty acid groups are located directly opposed to each other in the inner side of the bilayer. Part of the aqueous solution together with hydrophilic molecules, solved in it, will be encapsulated during the formation of the liposomes. Lipophilic molecules will be associated with the phospholipid bilayers themselves. The hydrophobic parts of amphipathic molecules will be inserted in the bilayers, whereas their hydrophilic parts are extending in the aqueous compartments or are exposed on the outer surfaces of the liposomes (figure 1). Numbers of concentric phospholipid bilayers (unilamellar and multilamellar liposomes), phospholipid composition and charge of the liposomes can be varied. Targeting of the liposomes may be achieved by the insertion of target molecules (e.g. monoclonal antibodies or sugar residues) in their outer (surface) bilayer (Gregoriadis, I988).