Enzyme Therapy. V. In Vivo Fate of Erythrocyte-entrapped β-Glucuronidase in β-Glucuronidase-deficient mice

Extract: The use of erythrocyte entrapment as a strategy to deliver and protect exogenously administered enzymes for replacement therapy in selected genetic diseases has been evaluated in a mammalian model system. The uptake, tissue distribution, intracellular localization, and in vivo lifetime of erythrocyte-entrapped bovine β-glucuronidase were determined by a selective thermal inactivation assay after intravenous administration into β-glucuronidase-deficient mice. The exogenous activity was cleared from the circulation with a half-life of about 20 min and was no longer detectable at 2 hr. A concomitant uptake of the injected enzyme was observed in murine tissues, primarily the liver; approximately 30% of the bovine activity was recovered at 30 min and maximal hepatic uptake, 71% of dose, was detected at 2 hr. Hepatic recovery of the bovine activity was observed to decrease in a biphasic pattern to nondetectable levels by 5 days. The recovery of the entrapped activity was characterized by a latency of detection in hepatic tissue up to 13 hr postinjection. At each time point more than 80% (84-100%) of the recovered bovine activity was detected in the lyso-somally enriched hepatic subcellular fraction. Maximal recoveries of 10 % and 15% of administered dose were observed in splenic and renal tissues, respectively, soon after enzyme administration. In comparison to results obtained after intravenous administration of unentrapped bovine β-glucuronidase, erythrocyte-entrapped activity was retained fourfold longer in the circulation, fivefold longer in hepatic tissue, and was more efficiently delivered to a variety of tissues.Speculation: Entrapment in autologous erythrocytes may provide an effective means to optimize the delivery and protection of exogenous enzymes for the treatment of selected lysosomal storage diseases, such as Fabry and type 1 Gaucher diseases, by enzyme replacement therapy. Furthermore, efficient delivery to specific target sites of pathology may be accomplished by the entrapment of other therapeutic agents within these biodegradable vesicles.