Treatment of brain disease with recombinant proteins is difficult due to the blood-brain barrier. As an alternative to direct injections into the brain, we studied whether application of high concentrations of therapeutic enzymes via intrathecal (IT) injections could successfully drive uptake across the ependyma to treat brain disease. We studied IT enzyme replacement therapy with recombinant human iduronidase (rhIDU) in canine mucopolysaccharidosis I (MPS I, Hurler syndrome), a lysosomal storage disorder with brain and meningeal involvement. Monthly or quarterly IT treatment regimens with rhIDU achieved supranormal iduronidase enzyme levels in the brain, spinal cord, and spinal meninges. All regimens normalized total brain glycosaminoglycan (GAG) storage and reduced spinal meningeal GAG storage by 58-70%. The improvement in GAG storage levels persisted three months after the final IT dose. The successful use of enzyme therapy via the CSF represents a potentially useful approach for lysosomal storage disorders.

Recombinant mouse el-glucuronidase administered intravenously to newborn mice with mucopolysaccharidosis type VII (MPS VII) is rapidly cleared from the circulation and localized in many tissues. Here we determine the tissue distribution of injected enzyme and describe its effects on the histopathology in 6-wk-old MPS VII mice that received either one injection of 28,000 U recombinant 5-glucuronidase at 5 wk of age or received six injections of 28,000 U given at weekly intervals beginning at birth. These mice were compared with untreated 6-wk-old MPS VII mice. The single injection decreased lysosomal distention in the fixed tissue macrophage system. MPS VII mice that received multiple injections had 27.8, 3.5, and 3.3% of normal levels of f-glucuronidase in liver, spleen, and kidney, respectively. Brain had detectable f-glucuronidase, ranging from 2.0-12.1% of normal. Secondary elevations of agalactosidase and fl-hexosaminidase in brain, spleen, liver, and kidney were decreased compared with untreated MPS VII mice. Although no improvement was observed in chondrocytes, glia, and some neurons, the skeleton had less clinical and pathological evidence of disease and the brain had reduced lysosomal storage in meninges and selected neuronal groups. These data show that recombinant f-glucuronidase treatment begun in newborn MPS VII mice provides enzyme to most tissues and significantly reduces or prevents the accumulation of lysosomal storage during the first 6 wk of life. Whether therapy begun later in life can achieve this level of correction remains to be established.

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Enzyme replacement therapy (ERT) effectively reverses storage in several lysosomal storage diseases. However, improvement in brain is limited by the blood-brain barrier except in the newborn period. In this study, we asked whether this barrier could be overcome by higher doses of enzyme than are used in conventional trials. We measured the distribution of recombinant human ␤-glucuronidase (hGUS) and reduction in storage by weekly doses of 0.3-40 mg͞kg administered i.v. over 1-13 weeks to mucopolysaccharidosis type VII mice immunotolerant to recombinant hGUS. Mice given up to 5 mg͞kg enzyme weekly over 3 weeks had moderate reduction in meningeal storage but no change in neocortical neurons. Mice given 20 -40 mg͞kg three times over 1 week showed no reduction in storage in any area of the CNS except the meninges. In contrast, mice receiving 4 mg͞kg per week for 13 weeks showed clearance not only in meninges but also in parietal neocortical and hippocampal neurons and glia. Mice given 20 mg͞kg once weekly for 4 weeks also had decreased neuronal, glial, and meningeal storage and averaged 2.5% of wild-type hGUS activity in brain. These results indicate that therapeutic enzyme can be delivered across the blood-brain barrier in the adult mucopolysaccharidosis type VII mouse if administered at higher doses than are used in conventional ERT trials and if the larger dose of enzyme is administered over a sufficient period. These results may have important implications for ERT for lysosomal storage diseases with CNS involvement.␤-glucuronidase deficiency ͉ immune tolerance ͉ lysosomal storage disease ͉ mannose-6-phosphate receptor T he mucopolysaccharidoses (MPSs) are a group of lysosomal storage diseases (LSD) caused by the deficiency of enzymes needed for the stepwise degradation of glycosaminoglycans (GAGs). The widespread lysosomal accumulation of undegraded GAGs leads to progressive cellular and organ dysfunction (1). Current treatments for patients with MPSs include hematopoietic stem cell transplantation and enzyme replacement therapy (ERT) (2, 3). MPS type VII (also known as Sly disease) results from deficiency of ␤-D-glucuronoside glucuronosohydrolase (GUS; EC 3.2.1.31) and is inherited as an autosomal recessive trait. Affected patients share many clinical features with patients with other MPSs, including shortened life span, mental retardation, organomegaly, and bone and joint abnormalities, that are collectively referred to as dysostosis multiplex (4). The murine model of MPS VII has proven valuable for the evaluation of novel therapies for LSDs, including bone marrow transplantation, neural progenitor cell transplantation, somatic cell gene replacement therapy, and ERT (5).Previous studies have shown that i.v. injection of a fixed-dose of recombinant murine ␤-glucuronidase (mGUS) initiated at birth reduced pathological evidence of disease and prevented some of the learning, memory, and hearing deficits in the MPS VII mouse (6). However, recombinant mGUS reduced lysosomal storage in the neurons of the brain only i...