Fate of Protein‐Containing Liposomes Injected into Rats

Abstract

[ 3 H]Amyloglucosidase and 131 I‐labelled albumin were entrapped into liposomes (lipid spherules) composed of phosphatidyl choline, cholesterol and dicetyl phosphate (7:2:1 molar ratio). 131 I‐labelled albumin was also entrapped in [ 3 H]cholesterol‐liposomes. Investigations on the fate in vivo following intravenous injection of such protein‐containing liposomes into rats, showed that the bulk of liposomal radioactivity is removed from the blood within minutes. There is no measurable leakage of entrapped 131 I‐labelled albumin while liposomes are in the circulation. Most of the removed liposomal radioactivity was recovered in the liver. Autoradiographic examination of the liver 3 min after injection of albumin‐containing [ 3 H]cholesterol‐liposomes suggests that hepatocytes and probably Kupffer cells are involved in the uptake of liposomes. It appears that liposomes enter this tissue intact but subsequently liposomal membranes and entrapped protein are catabolized. These catabolic processes are probably occurring in the liver lysosomes, as most of the liposomal radioactivity in this tissue was recovered in the mitochondrial‐lysosomal fraction. Liposomes appear to be promising as a vehicle for the administration of enzymes and possibly also drugs to patients with storage diseases.