Electron Microscopic Cytochemical Localization of Intravenously Injected Liposome-Encapsulated Horseradish Peroxidase in Rat Liver Cells

Abstract

Liposomes have been studied extensively during the last few years because of interest in their ability to act as a vehicle for various substances. Their structure, consisting of concentric lipid membranes enclosing aqueous compartments (2), enables them to carry both lipid and water soluble components. After intravenous (i.v.) injection, the liposomal membranes can prevent undesirable interaction between the entrapped substance and the blood or tissues, and vice versa (5–8). The entrapment permitted demonstration of the reduced toxicity of actinomycin D (11) and nitroblue tetrazolium (14); serum sickness and Arthus type of reactions could be avoided by encapsulation of the antigens concerned (1,5,6). Among the substances enclosed in liposomes, the anti-tumor drugs (11) and enzymes (5,7,8,10,13,16) seem to give promising results, the latter being introduced into cells for enzyme replacement therapy in lysosomal storage diseases (5,13). By varying the lipid composition, the surface charge of the liposomes can be varied at will and as a result, the i.v. clearance rate can be influenced (5,9). In addition, the coating of liposomes with (de)sialylated glycoproteins or antibodies against certain types of cells together with the variation in diameter seem to offer ways to control their clearance rates, organ distribution and direction to a certain tissue or cell type (5).