Enzyme therapy. V. In vivo fate of erythrocyte-entrapped beta-glucuronidase in beta-glucuronidase-deficient mice.

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 beta-glucuronidase were determined by a selective thermal inactivation assay after intravenous administration into beta-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 lysosomally 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 beta-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.