Tissue distribution of unentrapped or liposome-entrapped 131I-labeled beta-galactosidase injected into rats.

Either unentrapped (free) or liposome-entrapped 131I-labeled beta-galactosidase was injected into rats from tail veins. Tissue distribution and intracellular localization of the radioactivity of both sources were compared. The half-life of liposome-entrapped enzyme in the circulation was much longer than that of the free enzyme. The radioactivity removed from the circulation was recovered primarily in the liver, and to a lesser extent in almost all tissues studied. A small but significant uptake of liposome-entrapped enzyme by the brain was also observed. Uptake of liposome-entrapped enzyme was greater thant that of free enzyme in the spleen, heart, lungs and brain, excepting the liver and kidneys. Subcellular fractionation showed distribution of the radioactivity of liposome-entrapped enzyme favoring the mitochondrial-lysosomal fraction from these tissues except the heart. There was a difference in the pattern of intracellular distribution of the radioactivity in the brain of rats between the administration of free enzyme and that of liposome-entrapped enzyme. These findings suggest that when liposomes containing beta-galactosidase were injected into rats from the tail veins, they would penetrate the blood-brain barrier and would reach the lysosomes in the central nervous system tissue more effectively than the free enzyme itself. Beta-galactosidase; liposome; enzyme replacement therapy; rat tissues, 131I.