Enzyme therapy IV: A method for determining the In Vivo fate of bovine β-glucuronidase in β-glucuronidase deficient mice

A mammalian model system was developed to determine the in vivo fate of intravenously administered bovine β-glucuronidase in β-glucuronidase deficient mice. Sensitive and reliable discrimination of bovine liver β-glucuronidase activity from residual murine tissue activities was achieved by selective heat inactivation of the bovine activity, providing the ability to monitor the fate of administered enzyme. Following injection, the bovine activity was rapidly cleared from the circulation and recovered almost exclusively in the liver. Subcellular fractionation of hepatic tissue obtained 2 hours post injection localized 72% of recovered activity in the lysosomally-enriched fraction. This mammalian system provides an in vivo model to serially evaluate and maximize methods for the protection and delivery of an exogenous enzyme, prior to trials of enzyme replacement in patients with inherited enzymatic deficiency diseases.