Enzyme therapy. VI: Comparative in vivo fates and effects on lysosomal integrity of enzyme entrapped in negatively and positively charged liposomes.

Entrapment of enzyme in liposomes, biodegradable lipid vesicles, offers an intriguing strategy for the intracellular delivery of these macromolecules to the lysosomal apparatus for enzyme replacement endeavors in selected lysosomal storage diseases. Therefore, the in vivo tissue and subcellular fate and effect on the subcellular distribution of endogenous lysosomal hydrolases was determined following intravenous administration of beta-glucuronidase entrapped in positively and negatively charged liposomes into C3H/HeJ beta-glucuronidase-deficient mice. Enzyme entrapped in negatively charged liposomes was rapidly cleared from the circulation (t1/2 approximately 4 min); maximal tissue recovery, 75% of dose, was detedtec in the liver at 1 h, was maintained fro 48 h and then gradually declined to non-detectable levels by 8 days. A similar circulatory clearance and reciprocal hepatic uptake was observed fro positively charged liposomes; however, the beta-glucuronidase was retained in murine liver for 11 days. Significant activity, 15% of dose, was found in the kidneys up to 1 and 4 days post-injection of positively and negatively charged liposomes, respectively. No activity was recovered in neural or other visceral tissues except in spleen and lungs (less than 5% of the dose). Exogenous beta-glucuronidase activity administered in negatively charged liposomes was primarily localized in the lysosomally-enriched hepatic subcellular fraction, compared to the predominantly soluble localization of exogenous activity entrapped in positively charged liposomes. Administration of negatively charged liposomes caused no detectable change in the subcellular localization of several endogenous lysosomal hydrolase activities compared to their distribution in untreated mice. In contrast, a marked but temporary translocation of these hydrolase activities into the soluble fraction was observed following the administration of positively charged liposomes, identifying possible deleterious effects on cellular physiology.