Long-term enzyme correction and lipid reduction in multiple organs of primary and secondary transplanted Fabry mice receiving transduced bone marrow cells

Fabry disease is a compelling target for gene therapy as a treatment strategy. A deficiency in the lysosomal hydrolase alpha-galactosidase A (alpha-gal A; EC ) leads to impaired catabolism of alpha-galactosyl-terminal lipids such as globotriaosylceramide (Gb3). Patients develop vascular occlusions that cause cardiovascular, cerebrovascular, and renal disease. Unlike for some lysosomal storage disorders, there is limited primary nervous system involvement in Fabry disease. The enzyme defect can be corrected by gene transfer. Overexpression of alpha-gal A by transduced cells results in secretion of this enzyme. Secreted enzyme is available for uptake by nontransduced cells presumably by receptor-mediated endocytosis. Correction of bystander cells may occur locally or systemically after circulation of the enzyme in the blood. In this paper we report studies on long-term genetic correction in an alpha-gal A-deficient mouse model of Fabry disease. alpha-gal A-deficient bone marrow mononuclear cells (BMMCs) were transduced with a retrovirus encoding alpha-gal A and transplanted into sublethally and lethally irradiated alpha-gal A-deficient mice. alpha-gal A activity and Gb3 levels were analyzed in plasma, peripheral blood mononuclear cells, BMMCs, liver, spleen, heart, lung, kidney, and brain. Primary recipient animals were followed for up to 26 weeks. BMMCs were then transplanted into secondary recipients. Increased alpha-gal A activity and decreased Gb3 storage were observed in all recipient groups in all organs and tissues except the brain. These effects occurred even with a low percentage of transduced cells. The findings indicate that genetic correction of bone marrow cells derived from patients with Fabry disease may have utility for phenotypic correction of patients with this disorder.

Infusion of alpha-galactosidase A reduces tissue globotriaosylceramide storage in patients with Fabry disease

Fabry disease is a lysosomal storage disorder caused by a deficiency of the lysosomal enzyme alpha-galactosidase A (alpha-gal A). This enzymatic defect results in the accumulation of the glycosphingolipid globotriaosylceramide (Gb(3); also referred to as ceramidetrihexoside) throughout the body. To investigate the effects of purified alpha-gal A, 10 patients with Fabry disease received a single i.v. infusion of one of five escalating dose levels of the enzyme. The objectives of this study were: (i) to evaluate the safety of administered alpha-gal A, (ii) to assess the pharmacokinetics of i.v.-administered alpha-gal A in plasma and liver, and (iii) to determine the effect of this replacement enzyme on hepatic, urine sediment and plasma concentrations of Gb(3). alpha-Gal A infusions were well tolerated in all patients. Immunohistochemical staining of liver tissue approximately 2 days after enzyme infusion identified alpha-gal A in several cell types, including sinusoidal endothelial cells, Kupffer cells, and hepatocytes, suggesting diffuse uptake via the mannose 6-phosphate receptor. The tissue half-life in the liver was greater than 24 hr. After the single dose of alpha-gal A, nine of the 10 patients had significantly reduced Gb(3) levels both in the liver and shed renal tubular epithelial cells in the urine sediment. These data demonstrate that single infusions of alpha-gal A prepared from transfected human fibroblasts are both safe and biochemically active in patients with Fabry disease. The degree of substrate reduction seen in the study is potentially clinically significant in view of the fact that Gb(3) burden in Fabry patients increases gradually over decades. Taken together, these results suggest that enzyme replacement is likely to be an effective therapy for patients with this metabolic disorder.

Aging accentuates and bone marrow transplantation ameliorates metabolic defects in Fabry disease mice

Fabry disease is an X-linked metabolic disorder caused by a deficiency of alpha-galactosidase A (alpha-Gal A). The enzyme defect leads to the systemic accumulation of glycosphingolipids with alpha-galactosyl moieties consisting predominantly of globotriaosylceramide (Gb3). In patients with this disorder, glycolipid deposition in endothelial cells leads to renal failure and cardiac and cerebrovascular disease. Recently, we generated alpha-Gal A gene knockout mouse lines and described the phenotype of 10-week-old mice. In the present study, we characterize the progression of the disease with aging and explore the effects of bone marrow transplantation (BMT) on the phenotype. Histopathological analysis of alpha-Gal A -/0 mice revealed subclinical lesions in the Kupffer cells in the liver and macrophages in the skin with no gross lesions in the endothelial cells. Gb3 accumulation and pathological lesions in the affected organs increased with age. Treatment with BMT from the wild-type mice resulted in the clearance of accumulated Gb3 in the liver, spleen, and heart with concomitant elevation of alpha-Gal A activity. These findings suggest that BMT may have a potential role in the management of patients with Fabry disease.

alpha-Galactosidase A deficient mice: a model of Fabry disease

Fabry disease is an X-linked inherited metabolic disorder that is caused by a deficiency of alpha-galactosidase A (alpha-Gal A). Progressive deposition of neutral glycosphingolipids that have terminal a-linked galactosyl moieties in vascular endothelial cells causes renal failure along with premature myocardial infarctions and strokes in patients with this condition. No specific treatment is available for patients with this disorder at this time. An animal model of this condition would be valuable for exploring therapeutic strategies for patients with Fabry disease. We report here the generation of alpha-Gal A deficient mice by gene targeting and an analysis of the resulting phenotype. The knockout mice display a complete lack of alpha-Gal A activity. The mice, however, appeared clinically normal at 10 weeks of age. Ultrastructural analysis revealed concentric lamellar inclusions in the kidneys, and confocal microscopy using a fluorescent-labeled lectin specific for alpha-D-galactosyl residues showed accumulation of substrate in the kidneys as well as in cultured fibroblasts. Lipid analysis revealed a marked accumulation of ceramidetrihexoside in the liver and the kidneys. These findings indicate the similarity of the pathophysiological process in the mutant mice and in patients with Fabry disease. The deficiency of alpha-Gal A activity and the accumulation of material containing terminal alpha-galactosyl residues in cultured embryonic fibroblasts derived from alpha-Gal A(-/0) mice were corrected by transducing these cells with bicistronic multidrug resistance retroviruses containing human alpha-Gal A cDNA.

Correction in trans for Fabry disease: expression, secretion and uptake of alpha-galactosidase A in patient-derived cells driven by a high-titer recombinant retroviral vector

Fabry disease is an X-linked metabolic disorder due to a deficiency of alpha-galactosidase A (alpha-gal A; EC 3.2.1.22). Patients accumulate glycosphingolipids with terminal alpha-galactosyl residues that come from intracellular synthesis, circulating metabolites, or from the biodegradation Of senescent cells. Patients eventually succumb to renal, cardio-, or cerebrovascular disease. No specific therapy exists. One possible approach to ameliorating this disorder is to target corrective gene transfer therapy to circulating hematopoietic cells. Toward this end, an amphotropic virus-producer cell line has been developed that produces a high titer (>10(6) i.p. per ml) recombinant retrovirus constructed to transduce and correct target cells. Virus-producer cells also demonstrate expression of large amounts of both intracellular and secreted alpha-gal A. To examine the utility of this therapeutic vector, skin fibroblasts from Fabry patients were corrected for the metabolic defect by infection with this recombinant virus and secreted enzyme was observed. Furthermore, the secreted enzyme was found to be taken up by uncorrected cells in a mannose-6-phosphate receptor-dependent manner. In related experiments, immortalized B cell lines from Fabry patients, created as a hematologic delivery test system, were transduced. As with the fibroblasts, transduced patient B cell lines demonstrated both endogenous enzyme correction and a small amount of secretion together with uptake by uncorrected cells. These studies demonstrate that endogenous metabolic correction in transduced cells, combined with secretion, may provide a continuous source of corrective material in trans to unmodified patient bystander cells (metabolic cooperativity).

Structural organization and expression of the mouse gene encoding alpha-galactosidase A

alpha-Galactosidase A (alpha-D-galactoside galactohydrolase, EC 3.2.1.22; alpha GalA) is a lysosomal enzyme that hydrolyses the alpha-D-galactosyl residues from glycosphingolipids. Fabry disease, an inhibited X-linked recessive human metabolic disorder, results from a mutation in the alpha GalA gene at Xq22. As a prerequisite for generating a mouse model of Fabry disease by gene targeting, we have isolated and characterized the mouse alpha GalA gene and cDNA. A cloned mouse alpha GalA cDNA encoded a putative precursor protein of 419 amino acids (aa), including a 31-aa signal peptide (SP). The deduced aa sequence showed high homology (79%) with the human alpha GalA protein. Nucleotide sequence analysis of genomic clones revealed that the overall structure and organization of the gene was very similar to that of human alpha GalA. All exon-intron splice junctions conformed to the GT/AG consensus sequence. Comparison of genomic and cDNA sequences revealed the occurrence of two putative polyadenylation signals whose alternative use results in the two mouse alpha GalA transcripts of 1.4 and 3.6 kb. The 5'-flanking region of mouse alpha GalA had no typical TATA box. Several putative promoter-associated elements including Sp1, AP1 and a potential cAMP-responsive element (CRE) were identified. Northern blot analysis revealed the widespread tissue distribution of mouse alpha GalA transcripts. Lower expression levels, however, were observed in some tissues, implying tissue-specific differences in alpha GalA promoter function.

Group C Niemann-Pick disease: faulty regulation of low-density lipoprotein uptake and cholesterol storage in cultured fibroblasts

Incubation of mutant Niemann-Pick C fibroblasts with low-density lipoprotein (LDL) resulted in excessive internalization of lipoprotein and extensive cellular over-accumulation of unesterified cholesterol. The uptake of LDL by the mutant cells appeared to occur through the classic LDL receptor pathway and internalized lipoprotein was processed in lysosomes. Lipoprotein uptake into mutant cells was associated with delays in the initiation of established cellular cholesterol homeostatic responses. Subcellular fractionation of mutant Niemann-Pick C fibroblasts accumulating LDL-cholesterol showed excess unesterified sterol to be localized in the light lysosome-light membrane region of a Percoll gradient, and revealed that cholesterol storage was associated with a specific alteration in the normal profiles of lysosomal marker enzymes.

Niemann-pick variant disorders: comparison of errors of cellular cholesterol homeostasis in group D and group C fibroblasts

Fluorescence microscopic examination of filipin-stained cultured skin fibroblasts derived from two brothers with group D Niemann-Pick disease revealed abnormal storage of low density lipoprotein (LDL)-derived cholesterol. LDL stimulation of intracellular cholesteryl ester synthesis was severely compromised in the Niemann-Pick D fibroblasts, as it also was in fibroblasts obtained from Niemann-Pick C patients. Cholesteryl ester synthesis was intermediately deficient in cells derived from an obligate group-D heterozygous carrier. Activity of acyl-CoA:cholesterol acyltransferase was within the normal range in cell-free extracts of both LDL-depleted and LDL-supplemented cultures of Niemann-Pick C and D fibroblasts. Incubation of Niemann-Pick D fibroblasts with LDL did not lead to as high a level of intracellular cholesterol accumulation as the excessive storage observed with Niemann-Pick C fibroblasts. These findings suggest that the Niemann-Pick variant disorders may represent a family of specific and possibly individual mutations that disrupt cellular cholesterol homeostasis.

Animal and cellular models of sphingolipid storage disorders of humans

The synthesis of L-galactosylceramide is described. Data are presented indicating that this enantiomorph of D-galactocerebroside is not cleaved by galactocerebroside-beta-galactosidase obtained from mammalian tissues. The synthesis of L-glucosylceramide and beta-D-glucothiocerebroside are outlined. These compounds are also refractory to catabolism by glycosidases in mammalian tissues that catalyze the hydrolysis of naturally occurring cerebrosides. L-Hexosyl- and thioanalogs of cerebrosides and perhaps psychosines as well may be helpful for investigating the pathogenesis of Krabbe's disease and Gaucher's disease.

Animal and cellular models of Gaucher's disease. I. Refractoriness of thio analogs of glucocerebroside to enzymatic hydrolysis

In order to develop a nonmetabolizable analog of glucocerebroside to investigate the distribution and accumulation of this lipid in model systems, thiohemiacetal derivatives were synthesized and their susceptibility to enzymatic hydrolysis by purified human placental glucocerebrosidase was examined. Sulfur analogs were found to be completely refractory to the activity of this enzyme, indicating their potential use in animal and isolated cell models and possibly for the preparation of affinity chromatography columns for the isolation of glucocerebrosidase.

Delivery of active hexosaminidase across the blood-brain barrier in rats

The ability to deliver enzymatically active human hexosaminidase A across the blood-brain barrier and into brain cells of the normal rat was examined. Following osmotic blood-brain barrier modification in the rat, intraarterially administered human hexosaminidase A and B were shown to cross the barrier and enter brain cells. Subcellular fractionation studies demonstrated that most of the human enzyme delivered across the barrier was functionally active and appeared to be inside a subcellular organelle. These studies provide evidence that blood-brain barrier modification permits delivery of functionally active hexosaminidase A into subcellular organelles consistent with that known to be the appropriate site of physiologic activity.

Computer assisted small-scale Tay-Sachs carrier screening

Fluorescence data from serum beta-hexosaminidase assays for Tay-Sachs heterozygote screening is processed by a program in BASIC for a Wang 2200 desk-top computer. An estimation of overall error in the results gives a measure of reliability. A preliminary classification is made on the clinical status of the unknown samples as a normal, heterozygous, homozygous, or inconclusive carrier/normal condition. This program allows a small-scale screening center convenient and rapid data processing and analysis.

Delivery of hexosaminidase A to the cerebrum after osmotic modification of the blood--brain barrier

The present studies were undertaken to evaluate the possibility that hexosaminidase A, the enzyme deficient in Tay--Sachs disease, could be effectively delivered to brain. Previous studies from our laboratory have shown that hypertonic mannitol can be used to osmotically produce reversible disruption of the blood--brain barrier in animals (rat and dog) and man without significant neurotoxicity and that such barrier modification significantly increases the delivery of cytoreductive chemotherapy agents to selected areas of brain. By using the rat model of blood--brain barrier modification and radiolabeled enzyme, increased hexosaminidase A delivery to brain has been demonstrated in more than 85 animals. The time of injection of hexosaminidase A after blood--brain barrier disruption is critical for maximum delivery. Rapid (over 30 sec) intra-arterial administration of hexosaminidase A immediately after blood--brain barrier disruption resulted in a marked increase in enzyme delivery to the brain when compared with controls without prior barrier disruption. When the enzyme was administered 15-20 min after barrier disruption, approximately 50% less hexosaminidase A was delivered; when given 60-120 min after barrier modification, the amount delivered was the same as in control animals. This critical time course is very different than that seen in trials of low molecular weight chemotherapeutic agents (methotrexate and adriamycin). These preliminary studies suggest that hexosaminidase A can be delivered to the brain by blood--brain barrier modification and may be indicative of the potential for enzyme replacement in patients who hae Tay--Sachs disease.

A lysosomal storage disorder in mice characterized by a dual deficiency of sphingomyelinase and glucocerebrosidase

Lipid and lysosomal enzyme levels in the tissues of a strain of mice afflicted with an autosomal rescessive neuroviscereal storage disorder were examined. Sphingomyelinase and glucocerebrosidase activities were consistently diminished in a wide variety of tissues obtained from the affected mice. The activities of these enzymes were clearly attenuated in new-born mice, which at this age, were otherwise indistinguishable from littermates and age-matched controls. The deficiency of sphingomyelinase was more pronounced than glucocerebrosidase. There was progressive accumulation of sphingomyelin, glucocerebroside, lactosylceramide and unesterified cholesterol in the tissues of these mice in the postnatal period. Gangliosides GM2 and GM3 accumulated in the brain of the animals, and GM3 and asialo-GM2 were stored in the liver. Furthermore, there was a large increase in the quantity of hepatic bis(monoacylglycero)phosphate. The accumulation of lipids was parallelled by a progressive elevation in the activity of several lysosomal hydrolases in various tissues. Heterozygous mice were biochemically indistinguishable from normal controls. The phenotypic manifestations in these metabolically mutated animals are compared with those in Niemann-Pick disease and Gaucher's disease in humans.

Specific binding of 125I-labeled beta-hexosaminidase A to rat brain synaptosomes

Purified human beta-hexosaminidase A (beta-N-acetylgulcosaminidase; 2-acetamido-2-deoxy-beta-D-glucoside acetamidodeoxyglucohydrolase, EC 3.2.1.30) has been labeled with 125I to high specific activity with the retention of 80% of its enzyme activity. The binding of this enzyme to sonicated synaptosomes from rat brain was shown to be a saturable and specific process. Glycoproteins containing a sialic acid-terminal oligosaccharide or a galactose-terminal oligosaccharide (i.e., alpha 1-acid glycoprotein and fetuin and their asialo derivatives) were strong inhibitors of the binding. In contrast, ovalbumin, which contains a mannose-rich oligosaccharide, and mannans were poor inhibitors of the binding. Of the monosaccharides tested, sialic acid, galactosamine, mannose, galactose, and lactose were inhibitory in decreasing potency of inhibition. Optimal binding occurred at pH 7.0 in the presence of 3 mM calcium ions. The binding was a linear function of synaptosomal protein concentration between 25 and 200 microgram of protein per assay and was directly proportional to time up to 3 hr, beyond which there was no further increase in specific binding. The data suggest a unique but complex mode of interaction of glycoproteins with receptors on synaptic membranes.

Preparation of radioactive Tay-Sachs ganglioside labeled in the sialic acid moiety

A procedure is described for the preparation of Tay-Sachs ganglioside specifically labeled in the sialic acid portion of the molecule. Rat brain gangliosides were labeled biosynthetically by the intracranial injection of N-acetyl-(3)H-D-mannosamine. Radioactive gangliosides were isolated and selectively degraded with bacterial neuraminidase and rat liver beta-galactosidase to Tay-Sachs ganglioside-(3)H. Radioactivity in the labeled product was confined to the N-acetyl-neuraminic acid portion of the molecule.