Continuous infusion of enzyme replacement therapy is inferior to weekly infusions in MPS I dogs.

Intravenous enzyme replacement therapy with recombinant human α-L-iduronidase (rhIDU) is used weekly to treat mucopolysaccharidosis (MPS) I. We tested continuous administration of rhIDU at two dosing levels (0.58 mg/kg per week and 2 mg/kg per week) in MPS I dogs, and compared the efficacy of continuous infusion with the clinically used 0.58 mg/kg weekly three-hour infusion. Peak plasma concentrations of rhIDU were much higher in weekly-treated dogs (mean 256 units/ml) than steady-state concentrations in dogs treated with continuous infusion (mean 1.97 units/ml at 0.58 mg/kg per week; 8.44 units/ml at 2 mg/kg per week). Dogs receiving continuous IV rhIDU, even at a higher (2 mg/kg per week) dose, had consistently lower iduronidase levels in tissues than dogs receiving a weekly (0.58 mg/kg per week) dose. GAG storage was also less improved by continuous intravenous infusion. Adverse events were similar in all dosing groups. We found that continuous administration of 2 mg/kg per week rhIDU to MPS I dogs was insufficient to achieve GAG storage reduction comparable to 0.58 mg/kg weekly dosing.

Penetration, diffusion, and uptake of recombinant human alpha-L-iduronidase after intraventricular injection into the rat brain.

Central nervous system disease can have devastating consequences in the severe or Hurler form of mucopolysaccharisosis I (MPS I). Intravenously administered recombinant human alpha-L-iduronidase (rhIDU) is not expected to reach and treat the brain disease due to the blood-brain barrier. To determine whether administration of rhIDU into the cerebrospinal fluid could successfully treat the brain, we studied intraventricular administration of rhIDU in rats. RhIDU was stereotactically administered directly to the lateral ventricle of the intact rat brain and the brain tissues assessed by enzyme assays, immunofluorescence and confocal microscopy 30 min, 24 h, or 7 days later. Quantitation of activity revealed that rhIDU was widely distributed throughout the brain following injection into the lateral ventricle, with activities increased by a factor of 3.3 higher than control in most samples 30 min-24 h after injection and highest levels on the side of injection. The enzyme crossed the ependymal lining of the ventricle and entered neurons into lysosomal-like vesicles. The enzyme was able to diffuse through brain tissue as demonstrated by a decreasing signal gradient from 0.2 to 4.8 mm from the ventricle surface. The largest amount of rhIDU, as detected by immunostaining, was observed 24 h after injection and decreased approximately 50% during the first 7 days. Although the immunostaining decreased with time, specific vesicular staining was still detectable 28 days after injection. The data suggest that rhIDU given into the ventricle can diffuse, penetrate at least several millimeters of brain tissue and be taken up into neurons and glial cells.

Identification and molecular characterization of alpha-L-iduronidase mutations present in mucopolysaccharidosis type I patients undergoing enzyme replacement therapy.

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disorder caused by a deficiency of alpha-L-iduronidase (IDUA). Mutations in the gene are responsible for the enzyme deficiency, which leads to the intralysosomal storage of the partially degraded glycosaminoglycans dermatan sulfate and heparan sulfate. Molecular characterization of MPS I patients has resulted in the identification of over 70 distinct mutations in the IDUA gene. The high degree of molecular heterogeneity reflects the wide clinical variability observed in MPS I patients. Six novel mutations, c.1087C>T (p.R363C), c.1804T>A (p.F602I), c.793G>C, c.712T>A (p.L238Q), c.1727+2T>A, and c.1269C>G (p.S423R), in a total of 14 different mutations, and 13 different polymorphic changes, including the novel c.246C>G (p.H82Q), were identified in a cohort of 10 MPS I patients enrolled in a clinical trial of enzyme-replacement therapy. Five novel amino acid substitutions and c.236C>T (p.A79V) were engineered into the wild-type IDUA cDNA and expressed. A p.G265R read-through mutation, arising from the c.793G>C splice mutation, was also expressed. Each mutation reduced IDUA protein and activity levels to varying degrees with the processing of many of the mutant forms also affected by IDUA. The varied properties of the expressed mutant forms of IDUA reflect the broad range of biochemical and clinical phenotypes of the 10 patients in this study. IDUA kinetic data derived from each patient's cultured fibroblasts, in combination with genotype data, was used to predict disease severity. Finally, residual IDUA protein concentration in cultured fibroblasts showed a weak correlation to the degree of immune response to enzyme-replacement therapy in each patient.

Enzyme replacement therapy in feline mucopolysaccharidosis I.

Enzyme replacement therapy (ERT) has long been considered an approach to treating lysosomal storage disorders caused by deficiency of lysosomal enzymes. ERT is currently used to treat Gaucher disease and is being developed for several lysosomal storage disorders now that recombinant sources of the enzymes have become available. We have continued development of ERT for mucopolysaccharidosis I (MPS I) using the feline model. Recombinant alpha-L-iduronidase was administered intravenously at low dose (approximately 0.1 mg/kg or 25,000 units/kg) to four cats and high dose (0.5 mg/kg or 125,000 units/kg) to two cats on a weekly basis for 3- or 6-month terms. Clinical examinations showed distinct clearing of corneal clouding in one cat although clinical effects in the others were not evident. Biochemical studies of the cats showed that the enzyme was distributed to a variety of tissues although the liver and spleen contained the highest enzyme activities. Glycosaminoglycan storage was decreased in liver and spleen, and the histologic appearance improved in liver, spleen, and renal cortex. Enzyme was not consistently detected in cerebral cortex, brainstem, or cerebellum and the histologic appearance and ganglioside profiles did not improve. A variety of other tissues showed low variable uptake of enzyme and no distinct improvement. IgG antibodies to alpha-L-iduronidase were observed in five cats with higher titers noted when higher doses were administered. Mild complement activation occurred in three cats. Enzyme replacement therapy was effective in reversing storage in some tissues at the biochemical and histologic level in MPS I cats but an improved tissue distribution and prevention of a significant immune response could make the therapy more effective.

Enzyme-replacement therapy in mucopolysaccharidosis I.

BACKGROUND: Mucopolysaccharidosis I is a lysosomal storage disease caused by a deficiency of the enzyme alpha-L-iduronidase. We evaluated the effect of enzyme-replacement therapy with recombinant human alpha-L-iduronidase in patients with this disorder. METHODS: We treated 10 patients with mucopolysaccharidosis I (age, 5 to 22 years) with recombinant human alpha-L-iduronidase at a dose of 125,000 U per kilogram of body weight given intravenously once weekly for 52 weeks. The patients were evaluated at base line and at 6, 12, 26, and 52 weeks by detailed clinical examinations, magnetic resonance imaging of the abdomen and brain, echocardiography, range-of-motion measurements, polysomnography, clinical laboratory evaluations, measurements of leukocyte alpha-L-iduronidase activity, and urinary glycosaminoglycan excretion. RESULTS: Hepatosplenomegaly decreased significantly in all patients, and the size of the liver was normal for body weight and age in eight patients by 26 weeks. The rate of growth in height and weight increased by a mean of 85 and 131 percent, respectively, in the six prepubertal patients. The mean maximal range of motion of shoulder flexion and elbow extension increased significantly. The number of episodes of apnea and hypopnea during sleep decreased 61 percent. New York Heart Association functional class improved by one or two classes in all patients. Urinary glycosaminoglycan excretion decreased after 3 to 4 weeks of treatment; the mean reduction was 63 percent of base-line values. Five patients had transient urticaria during infusions. Serum antibodies to alpha-L-iduronidase were detected in four patients. CONCLUSIONS: In patients with mucopolysaccharidosis I, treatment with recombinant human alpha-L-iduronidase reduces lysosomal storage in the liver and ameliorates some clinical manifestations of the disease.

Carbohydrate structures of recombinant human alpha-L-iduronidase secreted by Chinese hamster ovary cells.

alpha-L-Iduronidase is a lysosomal hydrolase that is deficient in Hurler syndrome and clinically milder variants. Recombinant human alpha-L-iduronidase, isolated from secretions of an overexpressing Chinese hamster ovary cell line, is potentially useful for replacement therapy of these disorders. Because of the importance of carbohydrate residues for endocytosis and lysosomal targeting, we examined the oligosaccharides of recombinant alpha-L-iduronidase at each of its six N-glycosylation sites. Biosynthetic radiolabeling showed that three or four of the six oligosaccharides of the secreted enzyme were cleaved by endo-beta-N-acetylglucosaminidase H, with phosphate present on the sensitive oligosaccharides and L-fucose on the resistant ones. For structural analysis, tryptic and chymotryptic glycopeptides were isolated by lectin binding and reverse phase high pressure liquid chromatography; their molecular mass was determined by matrix-assisted laser desorption-time of flight mass spectrometry before and after treatment with endo- or exoglycosidases or with alkaline phosphatase. Identification of the peptides was assisted by amino- or carboxyl-terminal sequence analysis. The major oligosaccharide structures found at each site were as follows: Asn-110, complex; Asn-190, complex; Asn-336, bisphosphorylated (P2Man7GlcNAc2); Asn-372, high mannose (mainly Man9GlcNAc2, some of which was monoglucosylated); Asn-415, mixed high mannose and complex; Asn-451, bisphosphorylated (P2Man7GlcNAc2). The Asn-451 glycopeptide was unexpectedly resistant to digestion by N-glycanase unless first dephosphorylated, but it was sensitive to endo-beta-N-acetylglucosaminidase H and to glycopeptidase A. The heterogeneity of carbohydrate structures must represent the accessibility of the glycosylation sites as well as the processing capability of the overexpressing Chinese hamster ovary cells.

Long-term and high-dose trials of enzyme replacement therapy in the canine model of mucopolysaccharidosis I.

Enzyme replacement is a potential therapy for mucopolysaccharidosis I (MPS I), a lysosomal storage disorder caused by alpha-L-iduronidase deficiency. Previous work showed improvement in the tissues of MPS I dogs treated intravenously for 3 months with recombinant human alpha-L-iduronidase (25,000 units or approximately 0.1 mg/kg/week). We have now treated an MPS I-affected dog for 13 months to assess the clinical effects of enzyme replacement. The treated dog gained more weight, was more active, and had less joint stiffness than the untreated littermate. Biochemical and histologic studies demonstrated uptake of alpha-L-iduronidase and decreased lysosomal storage in the liver, kidney, spleen, lymph nodes, synovium, adrenals, and lungs. The brain had detectable enzyme activity and decreased glycosaminoglycan storage although histologic improvement was not evident. Cartilage and heart valve did not show any detectable improvement. A fivefold higher dose (approximately 0.5 mg/kg) administered five times over 10 days to two other dogs resulted in higher tissue enzyme activity and similarly decreased glycosaminoglycan storage and excretion. Antibodies to human alpha-L-iduronidase were induced in all treated dogs and may be associated with immune complex deposition and proteinuria. Recombinant canine alpha-L-iduronidase also induced antibody formation to a similar degree. The results support the conclusion that enzyme replacement is a promising therapy for MPS I though immunologic complications may occur.

Enzyme replacement in a canine model of Hurler syndrome.

The Hurler syndrome (alpha-L-iduronidase deficiency disease) is a severe lysosomal storage disorder that is potentially amenable to enzyme-replacement therapy. Availability of a canine model of the disease and a sufficient supply of corrective enzyme have permitted a therapeutic trial lasting 3 mo. Recombinant human alpha-L-iduronidase, purified to apparent homogeneity from secretions of a stably transfected Chinese hamster ovary cell line, was administered i.v. to homozygous affected animals in doses of approximately 1 mg. The enzyme rapidly disappeared from the circulation in a biphasic manner, with t1/2 of 0.9 and 19 min, respectively, and was taken up primarily by the liver. Biopsy of the liver before and after a very short trial (seven doses administered over 12 days) showed remarkable resolution of lysosomal storage in both hepatocytes and Kupffer cells. After weekly administration of enzyme to three affected animals over a period of 3 mo, the level of enzyme was about normal in liver and spleen, lower but significant in kidney and lung, and barely detectable (0-5% of normal) in brain, heart valves, myocardium, cartilage, and cornea. Light and electron microscopic examination of numerous tissues showed normalization of lysosomal storage in liver, spleen, and kidney glomeruli, but there was no improvement in brain, heart valves, or cornea. Even though the treated dogs developed complement-activating antibodies against alpha-L-iduronidase, clinical symptoms could be prevented by slow infusion of enzyme and premedication.

Overexpression of the human lysosomal enzyme alpha-L-iduronidase in Chinese hamster ovary cells.

We developed a Chinese hamster ovary (CHO) cell line that produces and secretes large quantities of recombinant human alpha-L-iduronidase, the lysosomal hydrolase deficient in mucopolysaccharidosis I (Hurler, Hurler-Scheie, and Scheie syndromes). The alpha-L-iduronidase cDNA was introduced into a vector containing the cytomegalovirus immediate early gene promoter/enhancer, a murine immunoglobulin C alpha region intron, and the bovine growth hormone polyadenylation signal. Following cotransfection with a plasmid containing the neomycin resistance gene, stably transfected lines were selected with G-418. The highest expressing CHO cell line contained 1400-6000 units of alpha-L-iduronidase per milligram of protein, or 0.6-2.4% of total cell protein. Secreted alpha-L-iduronidase was 3000- to 7000 fold increased, with about 5000 units accumulating in 24 h per 10(7) cells. The activity and distribution of five other lysosomal glycosidases were not significantly affected. Metabolic labeling showed that half of the newly synthesized alpha-L-iduronidase was secreted, but generally less was recovered due to its instability in the medium. It was post-translationally processed as previously shown for alpha-L-iduronidase of human fibroblasts. Recombinant alpha-L-iduronidase was efficiently endocytosed by Hurler fibroblasts utilizing a mannose 6-phosphate-dependent mechanism (half maximal uptake at 0.7 nM) and was "corrective" for abnormal glycosaminoglycan accumulation (half-maximal correction at 0.7 pM). The half-life of the recombinant enzyme was 5 days following uptake into Hurler fibroblasts. Production in a 5-liter microcarrier culture system permitted the collection of 15 mg or more per day.(ABSTRACT TRUNCATED AT 250 WORDS)

DOOR syndrome (deafness, onycho-osteodystrophy, and mental retardation): a new patient and delineation of neurologic variability among recessive cases.

We report the seventeenth case of the recessive form of the DOOR syndrome. The parents were Guatemalan and not known to be consanguineous. The patient had developmental delay, severe sensorineural deafness, and abnormal nails and phalanges in the hands and feet. Urinary 2-oxoglutarate excretion was normal. The patient was among a subset of DOOR syndrome patients without seizures in infancy. This observation may be useful in discussing the prognosis for newly identified cases.