Gary J. Murray

Replacement therapy for inherited enzyme deficiency--macrophage-targeted glucocerebrosidase for Gaucher's disease.

BACKGROUND AND METHODS Gauchers disease, the most prevalent of the sphingolipid storage disorders, is caused by a deficiency of the enzyme glucocerebrosidase (glucosylceramidase). Enzyme replacement was proposed as a therapeutic strategy for this disorder in 1966. To assess the clinical effectiveness of this approach, we infused macrophage-targeted human placental glucocerebrosidase (60 IU per kilogram of body weight every 2 weeks for 9 to 12 months) into 12 patients with type 1 Gauchers disease who had intact spleens. The frequency of infusions was increased to once a week in two patients (children) during part of the trial because they had clinically aggressive disease. RESULTS The hemoglobin concentration increased in all 12 patients, and the platelet count in 7. Serum acid phosphatase activity decreased in 10 patients during the trial, and the plasma glucocerebroside level in 9. Splenic volume decreased in all patients after six months of treatment, and hepatic volume in five. Early signs of skeletal improvements were seen in three patients. The enzyme infusions were well tolerated, and no antibody to the exogenous enzyme developed. CONCLUSIONS Intravenous administration of macrophage-targeted glucocerebrosidase produces objective clinical improvement in patients with type 1 Gauchers disease. The hematologic and visceral responses to enzyme replacement develop more rapidly than the skeletal response.

Pediatric Fabry Disease

Background. Fabry disease is an underdiagnosed, treatable, X-linked, multisystem disorder. Objectives. To test the hypothesis that quality of life and sweating are decreased among pediatric patients with Fabry disease, compared with control subjects, and to provide quantitative natural history data and novel clinical end points for therapeutic trials. Design. Prospective, cross-sectional, observational study. Setting. Referral to the National Institutes of Health. Participants. Twenty-five male children with Fabry disease (mean age: 12.3 ± 3.5 years) and 21 age-matched control subjects. Main Outcome Measures. Quality of life (measured with the Child Health Questionnaire) and sweating (assessed with the quantitative sudomotor axon reflex test). Results. Quality of life scores for pediatric patients <10 years of age with Fabry disease, compared with published normative values, were 55 ± 17 vs 83 ± 19 for bodily pain and 62 ± 19 vs 80 ± 13 for mental health. Bodily pain scores for patients ≥10 years of age were 54 ± 22 vs 74 ± 23. Sweat volume in the Fabry disease group was 0.41 ± 0.46 μL/mm2, compared with 0.65 ± 0.44 μL/mm2 in the control group. Renal function, urinary protein excretion, and cardiac function and structure were normal for the majority of patients. The 3 patients with residual α-galactosidase A activity ≥1.5% of normal values were free of cornea verticillata and had normal serum and urinary globotriaosylceramide levels. All other children had glycolipid levels comparable to those of adult patients with Fabry disease. Acroparesthesia and cardiac abnormalities were generally present before anhidrosis and proteinuria. Mapping of the missense mutations on the crystallographic structure of α-galactosidase A revealed that the mutations were partially surface-exposed and distal to the active site among individuals with residual enzyme activity. Mutations associated with left ventricular hypertrophy (defined as left ventricular mass index of >51 g/m2.7) were localized near the catalytic site of the enzyme. Conclusions. Despite the absence of major organ dysfunction, Fabry disease demonstrates significant morbidity already in childhood. We have identified important, potentially correctable or preventable, outcome measures for future therapeutic trials. Prevention of complications involving major organs should be the goal for long-term specific therapy.

Adeno-associated viral vector-mediated gene transfer results in long-term enzymatic and functional correction in multiple organs of Fabry mice

Fabry disease is a lysosomal storage disorder caused by a deficiency of the lysosomal enzyme α-galactosidase A (α-gal A). This enzyme deficiency leads to impaired catabolism of α-galactosyl-terminal lipids such as globotriaosylceramide (Gb3). Patients develop painful neuropathy and vascular occlusions that progressively lead to cardiovascular, cerebrovascular, and renal dysfunction and early death. Although enzyme replacement therapy and bone marrow transplantation have shown promise in the murine analog of Fabry disease, gene therapy holds a strong potential for treating this disease in humans. Delivery of the normal α-gal A gene (cDNA) into a depot organ such as liver may be sufficient to elicit corrective circulating levels of the deficient enzyme. To investigate this possibility, a recombinant adeno-associated viral vector encoding human α-gal A (rAAV-AGA) was constructed and injected into the hepatic portal vein of Fabry mice. Two weeks postinjection, α-gal A activity in the livers of rAAV-AGA-injected Fabry mice was 20–35% of that of the normal mice. The transduced animals continued to show higher α-gal A levels in liver and other tissues compared with the untouched Fabry controls as long as 6 months after treatment. In parallel to the elevated enzyme levels, we see significant reductions in Gb3 levels to near normal at 2 and 5 weeks posttreatment. The lower Gb3 levels continued in liver, spleen, and heart, up to 25 weeks with no significant immune response to the virus or α-gal A. Also, no signs of liver toxicity occurred after the rAAV-AGA administration. These findings suggest that an AAV-mediated gene transfer may be useful for the treatment of Fabry disease and possibly other metabolic disorders.

Studies on the galactose-binding site of ricin and the hybrid toxin man6P-ricin

N-acetylimidazole (NAI) was used to O-acetylate the plant seed toxin ricin. O-acetylation of one to two tyrosine residues per molecule of ricin inhibited ricin binding to Sepharose 4B and decreased toxicity by 90% in a protein synthesis inhibition assay in HeLa cells. Lactose, known to block the binding site on the ricin B subunit, protected ricin from NAI modification of binding or toxicity. Thus NAI, under these conditions, can be a lactose site-specific inhibitor. The lactose site-specific modification of the hybrid toxin, Man6P-ricin, performed under the same conditions, exhibited the same 90% inhibition of Man6P receptor-mediated toxicity as the galactose-containing receptor-mediated toxicity of either Man6P-ricin or ricin. Thus the ricin B chain lactose-binding site appears to be essential for the high potency of Man6P-ricin via the new cell type-specific Man6P receptor. Treatment of fibroblasts with neuraminidase exposes galactose residues, thus increasing the sensitivity to ricin eight fold. The Man6P receptor-mediated toxicity of Man6P-ricin is not affected by this treatment, although the galactose-inhibited route is potentiated eight fold. The Man6P-ricin hybrid appears to require the ricin B chain galactose-binding site to enter the cytosol after initially binding to the Man6P receptor. These data provide some insights into the proper design of hybrid toxins. We discuss a number of possible models for hybrid toxin entry.

Long-term correction of globotriaosylceramide storage in Fabry mice by recombinant adeno-associated virus-mediated gene transfer

Fabry disease is an X-linked recessive inborn metabolic disorder characterized by systemic and vascular accumulation of globotriaosylceramide (Gb3) caused by a deficiency of the lysosomal enzyme α-galactosidase A (α-gal A). The condition is associated with an increased morbidity and mortality due to renal failure, cardiac disease, and early onset of stroke. Hemizygous males are primarily affected clinically with variable expression in heterozygous females. Gene-therapy trials have been initiated recently in α-gal A knockout mouse models of Fabry disease by using a variety of viral vectors. In the present investigation we administered single i.v. injections of 1 × 1010 genomes of recombinant adeno-associated virus (rAAV) encoding the human α-gal A gene driven by a modified chicken β-actin (CAG) promoter to α-gal A knockout (Fabry) mice. Transgenic mice were analyzed for expression of α-gal A activity and Gb3 levels in liver, kidney, heart, spleen, small intestine, lung, and brain. Administration of the rAAV-CAG-hAGA vector resulted in stable expression of α-gal A in organs of the Fabry mice for >6 months. α-Gal A activity in the organs became equal to or higher than that of wild-type mice. Accumulated Gb3 in the liver, heart, and spleen was reduced to that of wild-type mice with lesser but significant reductions in kidney, lung, and small intestine. Injection of the rAAV-CAG-hAGA construct into skeletal muscle did not result in expression of α-gal A in it or in other tissues. This study provides a basis for a simple and efficient gene-therapy approach for patients with Fabry disease and is indicative of its potential for the treatment of other lysosomal storage disorders.

Glucocerebrosidase, a lysosomal enzyme that does not undergo oligosaccharide phosphorylation

Labelling of cultured human skin fibroblasts from either control subjects or patients with mucolipidosis II (I-cell disease) with [32P]phosphate resulted in tight association of phosphate with immunoprecipitated glucocerebrosidase, a membrane-associated lysosomal enzyme. Endoglycosidase F digestion of the immunoprecipitated glucocerebrosidase did not release labelled phosphate, suggesting that the phosphate was not associated with the oligosaccharide moiety of this glycoprotein. Purification of the enzyme from cells labelled with [32P]phosphate and [35S]methionine by an immunoaffinity chromatography procedure, which included a washing step with detergent, resulted in complete separation of the phosphate label from the peak of glucocerebrosidase activity and methionine labelling. We conclude that oligosaccharide phosphorylation, which is essential for transport of soluble lysosomal enzymes to the lysosomes in fibroblasts, does not occur in glucocerebrosidase.

Dose-dependent responses to macrophage-targeted glucocerebrosidase in a child with Gaucher disease

Long-term studies of a child with Gaucher disease indicated that the response to treatment with macrophage-targeted glucocerebrosidase (glucosylceramidase) is dose dependent, and that the hematologic response precedes the skeletal response.

Isolation of cDNA clones for human β-glucocerebrosidase using the λgtll expression system

Two cDNA clones (λGC-1 and λGC-2) for human β-glucocerebrosidase [EC 3.2.1.45] have been isolated from a human hepatoma library in λgtll by immunological screening using monospecific polyclonal antibody for β-glucocerebrosidase. Restriction endonuclease mapping indicates that these clones are probably identical in size, each with a 1900 bp insert. The 50 kDa size of the insert-encoded polypeptide produced by these clones in fusion with β-galactosidase of λgtll in E.coli BNN103 is consistent with the size of the nascent form of β-glucocerebrosidase. These fusion proteins are shown by Western blotting to react with antibody to β-glucocerebrosidase. Amino acid sequence deduced from the nucleotide sequence of the insert ir pGC-1 is identical to known amino acid sequence of β-glucocerebrosidase, and thus, confirms that the clones are specific for β-glucocerebrosidase.

Lectin-specific targeting of β-glucocerebrosidase to different liver cells via glycosylated liposomes

Galactosylated and mannosylated liposomes were more efficient in transporting liposome-entrapped beta-glucocerebrosidase to liver compared to nonglycosylated liposomes. The enzyme entrapped to glycoside-bearing liposomes was found to be cleared at a much faster rate than that entrapped in liposomes having no sugar on their surface. Asialoorosomucoid and hydrolyzed mannan were found to inhibit both the clearance and the uptake of galactosylated and mannosylated liposomes, respectively, supporting involvement of lectin-sugar interaction. Further studies on the uptake of glucocerebrosidase by isolated liver cells revealed that the enzyme entrapped in mannosylated liposomes has much higher affinity for nonparenchymal cells whereas the assimilation of the entrapped enzyme into hepatocytes is clearly favored for liposomes having galactose on their surface.

Isofagomine increases lysosomal delivery of exogenous glucocerebrosidase.

Intravenous enzyme replacement therapy (ERT) with purified glucocerebrosidase (GLA) leads to significant improvement of the clinical manifestations in patients with Type 1 Gaucher disease. However, the high doses required, slow response and inability to recover most of the infused enzyme in the target tissues may be attributed to losses occurring during transit en route to the lysosome. Preincubation of GLA with isofagomine (IFG), a slow-binding inhibitor, significantly increased stability of the enzyme to heat, neutral pH and denaturing agents in vitro. Preincubation of GLA with isofagomine prior to uptake by cultured cells results in increased intracellular enzyme activity accompanied by an increase in enzyme protein suggesting that reduced denaturation of GLA in the presence of isofagomine leads to a decrease in the degradation of the enzyme after internalization. Preincubation of GLA with slow-binding inhibitors before infusion may improve the effectiveness of ERT for Gaucher disease.