Lessons learned from the development of enzyme therapy for Gaucher disease

Advancements in Viral Gene Therapy for Gaucher Disease

Gaucher disease, an autosomal recessively inherited lysosomal storage disorder, results from biallelic mutations in the GBA1 gene resulting in deficient activity of the enzyme glucocerebrosidase. In Gaucher disease, the reduced levels and activity of glucocerebrosidase lead to a disparity in the rates of formation and breakdown of glucocerebroside and glucosylsphingosine, resulting in the accumulation of these lipid substrates in the lysosome. This gives rise to the development of Gaucher cells, engorged macrophages with a characteristic wrinkled tissue paper appearance. There are both non-neuronopathic (type 1) and neuronopathic (types 2 and 3) forms of Gaucher disease, associated with varying degrees of severity. The visceral and hematologic manifestations of Gaucher disease respond well to both enzyme replacement therapy and substrate reduction therapy. However, these therapies do not improve the neuronopathic manifestations, as they cannot cross the blood-brain barrier. There is now an established precedent for treating lysosomal storage disorders with gene therapy strategies, as many have the potential to cross into the brain. The range of the gene therapies being employed is broad, but this review aimed to discuss the progress, advances, and challenges in developing viral gene therapy as a treatment for Gaucher disease.

Gene therapy for lysosomal storage disorders: recent advances for metachromatic leukodystrophy and mucopolysaccaridosis I

Lysosomal storage diseases (LSDs) are rare inherited metabolic disorders characterized by a dysfunction in lysosomes, leading to waste material accumulation and severe organ damage. Enzyme replacement therapy (ERT) and haematopoietic stem cell transplant (HSCT) have been exploited as potential treatments for LSDs but pre-clinical and clinical studies have shown in some cases limited efficacy. Intravenous ERT is able to control the damage of visceral organs but cannot prevent nervous impairment. Depending on the disease type, HSCT has important limitations when performed for early variants, unless treatment occurs before disease onset. In the attempt to overcome these issues, gene therapy has been proposed as a valuable therapeutic option, either ex vivo, with target cells genetically modified in vitro, or in vivo, by inserting the genetic material with systemic or intra-parenchymal, in situ administration. In particular, the use of autologous haematopoietic stem cells (HSC) transduced with a viral vector containing a healthy copy of the mutated gene would allow supra-normal production of the defective enzyme and cross correction of target cells in multiple tissues, including the central nervous system. This review will provide an overview of the most recent scientific advances in HSC-based gene therapy approaches for the treatment of LSDs with particular focus on metachromatic leukodystrophy (MLD) and mucopolysaccharidosis type I (MPS-I).

Gaucher disease in Syrian children: common mutations identification, and clinical futures

BACKGROUND AND OBJECTIVES

Gaucher disease (GD) is caused by the deficiency of glucosidase beta acid (GBA). Three clinical forms of GD are available. Some mutations in the GBA gene have a high frequency in spe.cific populations. The aim of this study was to analyze the characteristics of phenotypes and genotypes of GD in Syrian pediatric patients and assess whether a genotype-phenotype relationship could be helpful in treatment decision-making.

DESIGN AND SETTINGS

A cross-sectional clinical genetic study of 19 Syrian children admitted to Children's Hospital, Damascus University.

PATIENTS AND METHODS

Nineteen Syrian children with GD were enrolled in the study; DNA was extracted from peripheral blood leukocytes. The GBA gene was amplified by polymerase chain reaction, and the 9 most common mutations were studied using a Gaucher Disease Strip Assay (ViennaLab Diagnostics GmbH, Vienna, Austria).

RESULTS

The majority of children had an early age of onset. A total of17 patients presented severe hematological and skeletal complications. Neurological involvement was encountered in 2 patients. Twelve patients (63, 2%) were homozygous for the L444P mutation, 1 patient (5.3%) was homozygous for the N370S mutation, and 1 patient (5.3%) was heterozygous for the N370S mutation. Five patients (26.3%) had unknown mutations.

CONCLUSION

L444P/L444P was the most common genotype in the studied patients. GD3 with severe visceral presentation in childhood was the dominant phenotype; N370S was found in the heterozygote state in 1 case and in the homozygote state in 1 case. This phenotype and genotype pattern is encountered in the Middle East. There was no genotype-phenotype correlation.

Enzyme replacement therapy in newborn mucopolysaccharidosis IVA mice: early treatment rescues bone lesions?

We treated mucopolysaccharidosis IVA (MPS IVA) mice to assess the effects of long-term enzyme replacement therapy (ERT) initiated at birth, since adult mice treated by ERT showed little improvement in bone pathology [1]. To conduct ERT in newborn mice, we used recombinant human N-acetylgalactosamine-6-sulfate sulfatase (GALNS) produced in a CHO cell line. First, to observe the tissue distribution pattern, a dose of 250units/g body weight was administered intravenously in MPS IVA mice at day 2 or 3. The infused enzyme was primarily recovered in the liver and spleen, with detectable activity in the bone and brain. Second, newborn ERT was conducted after a tissue distribution study. The first injection of newborn ERT was performed intravenously, the second to fourth weekly injections were intraperitoneal, and the remaining injections from 5th to 14th weeks were intravenous into the tail vein. MPS IVA mice treated with GALNS showed clearance of lysosomal storage in the liver and spleen, and sinus lining cells in bone marrow. The column structure of the growth plate was organized better than that in adult mice treated with ERT; however, hyaline and fibrous cartilage cells in the femur, spine, ligaments, discs, synovium, and periosteum still had storage materials to some extent. Heart valves were refractory to the treatment. Levels of serum keratan sulfate were kept normal in newborn ERT mice. In conclusion, the enzyme, which enters the cartilage before the cartilage cell layer becomes mature, prevents disorganization of column structure. Early treatment from birth leads to partial remission of bone pathology in MPS IVA mice.

The role of microglia in human disease: therapeutic tool or target?

Microglia have long been the focus of much attention due to their strong proliferative response (microgliosis) to essentially any kind of damage to the CNS. More recently, we reached the realization that these cells play specific roles in determining progression and outcomes of essentially all CNS disease. Thus, microglia has ceased to be viewed as an accessory to underlying pathologies and has now taken center stage as a therapeutic target. Here, we review how our understanding of microglia's involvement in promoting or limiting the pathogenesis of diseases such as amyotrophic lateral sclerosis, Alzheimer's disease, Huntington's disease, multiple sclerosis, X-linked adrenoleukodystrophy (X-ALD) and lysosomal storage diseases (LSD) has changed over time. While strategies to suppress the deleterious and promote the virtuous functions of microglia will undoubtedly be forthcoming, replacement of these cells has already proven its usefulness in a clinical setting. Over the past few years, we have reached the realization that microglia have a developmental origin that is distinct from that of bone marrow-derived myelomonocytic cells. Nevertheless, microglia can be replaced, in specific situations, by the progeny of hematopoietic stem cells (HSCs), pointing to a strategy to engineer the CNS environment through the transplantation of modified HSCs. Thus, microglia replacement has been successfully exploited to deliver therapeutics to the CNS in human diseases such as X-ALD and LSD. With this outlook in mind, we will discuss the evidence existing so far for microglial involvement in the pathogenesis and the therapy of specific CNS disease.

Generation of polyclonal antibodies against recombinant human glucocerebrosidase produced in Escherichia coli

Deficiency of the lysosomal glucocerebrosidase (GCR) enzyme results in Gaucher's disease, the most common inherited storage disorder. Treatment consists of enzyme replacement therapy by the administration of recombinant GCR produced in Chinese hamster ovary cells. The production of anti-GCR antibodies has already been described with placenta-derived human GCR that requires successive chromatographic procedures. Here, we report a practical and efficient method to obtain anti-GCR polyclonal antibodies against recombinant GCR produced in Escherichia coli and further purified by a single step through nickel affinity chromatography. The purified GCR was used to immunize BALB/c mice and the induction of anti-GCR antibodies was evaluated by enzyme-linked immunosorbent assay. The specificity of the antiserum was also evaluated by western blot analysis against recombinant GCR produced by COS-7 cells or against endogenous GCR of human cell lines. GCR was strongly recognized by the produced antibodies, either as cell-associated or as secreted forms. The detected molecular masses of 59-66 kDa are in accordance to the expected size for glycosylated GCR. The GCR produced in E. coli would facilitate the production of polyclonal (shown here) and monoclonal antibodies and their use in the characterization of new biosimilar recombinant GCRs coming in the near future.

Glucocerebroside: an evolutionary advantage for patients with Gaucher disease and a new immunomodulatory agent

Gaucher disease (GD) is caused by the reduced activity of a lysosomal enzyme, glucocerebrosidase, leading to the accumulation of glucocerebroside (GC). The relatively high prevalence of this disease within an ethnic group is believed to reflect a selective advantage. Treatment with enzyme replacement therapy (ERT) is safe and effective in ameliorating the primary symptoms of the disease, yet there have been reports that some patients on ERT have developed type 2 diabetes or metabolic syndrome, malignancies and central nervous system disorders. A series of animal studies suggest that these complications may be related to the reduction of GC levels by the enzyme administered. GC has been shown to have an immunomodulatory effect through the promotion of dendritic cells, natural killer T cells, and regulatory T cells. The break down of GC to ceramide can underline part of these findings. Clinical trials suggested a beneficial effect of GC in type 2 diabetes or nonalcoholic steatohepatitis. This review of the data from animal models and humans proposes that the increased level of GC may provide an evolutionary advantage for patients with GD. Indirectly, these data support treating symptomatic patients with mild/moderate GD with low-dose ERT and re-evaluating the use of ERT in asymptomatic patients.

Eight-year clinical outcomes of long-term enzyme replacement therapy for 884 children with Gaucher disease type 1

OBJECTIVE

The goal was to analyze the clinical responses to enzyme replacement therapy with alglucerase or imiglucerase in a large international cohort of children with Gaucher disease type 1.

METHODS

Anonymized data from 884 children in the International Collaborative Gaucher Group Gaucher Registry were analyzed to determine the effects of long-term enzyme replacement therapy with alglucerase or imiglucerase on hematologic and visceral manifestations, linear growth, and skeletal disease. The parameters measured were hemoglobin levels, platelet counts, spleen and liver volumes, z scores for height and bone mineral density, and reports of bone pain and bone crises.

RESULTS

The median height z score for the study population was -1.4 at baseline. After 8 years of treatment, the median height approximated the median value for the normal population. Anemia, although not severe, was present in >50% of patients at baseline and resolved for all patients after 8 years of treatment. More than 50% of patients had platelet counts of <100000 platelets per mm3 at baseline, but >95% had platelet counts above this level after 8 years of treatment. Liver and spleen volumes decreased over 8 years of treatment. The mean bone mineral density z score was -0.34 at baseline, and values normalized within 6.6 years of treatment. Seventeen percent of patients reported a bone crisis before treatment and in the first 2 years of treatment, but no bone crises were reported after 2 years of enzyme replacement therapy. Few patients (2.5%) without bone crises before enzyme replacement therapy had a crisis after the start of treatment.

CONCLUSIONS

These longitudinal data quantitate the benefits of continuous enzyme replacement therapy with alglucerase/imiglucerase for children with Gaucher disease type 1. Within 8 years of enzyme replacement therapy, most clinical parameters studied became normal or nearly normal.

Acidic amino acid tag enhances response to enzyme replacement in mucopolysaccharidosis type VII mice

We have tested an acidic oligopeptide-based targeting system for delivery of enzymes to tissues, especially bone and brain, in a murine mucopolysaccharidosis type VII (MPS VII) model. This strategy is based upon tagging a short peptide consisting of acidic amino acids (AAA) to N terminus of human beta-glucuronidase (GUS). The pharmacokinetics, biodistribution, and the pathological effect on MPS VII mouse after 12 weekly infusions were determined for recombinant human untagged and tagged GUS. The tagged GUS was taken up by MPS VII fibroblasts in a mannose 6-phosphate receptor-dependent manner. Intravenously injected AAA-tagged enzyme had five times more prolonged blood clearance compared with the untagged enzyme. The tagged enzyme was delivered effectively to bone, bone marrow, and brain in MPS VII mice and was effective in reversing the storage pathology. The storage in osteoblasts was cleared similarly with both enzyme types. However, cartilage showed a little response to any of the enzymes. The tagged enzyme reduced storage in cortical neurons, hippocampus, and glia cells. A highly sensitive method of tandem mass spectrometry on serum indicated that the concentration of serum dermatan sulfate and heparan sulfate in mice treated with the tagged enzyme decreased more than the untagged enzyme. These preclinical studies suggest that this AAA-based targeting system may enhance enzyme-replacement therapy.

Immune system irregularities in lysosomal storage disorders

Lysosomal storage disorders (LSDs) are genetically inherited diseases characterized by the accumulation of disease-specific biological materials such as proteolipids or metabolic intermediates within the lysosome. The lysosomal compartment's central importance to normal cellular function can be appreciated by examining the various pathologies that arise in LSDs. These disorders are invariably fatal, and many display profound neurological impairment that begins in childhood. However, recent studies have revealed that several LSDs also have irregularities in the function of the immune system. Gaucher disease, mucopolysaccharidosis VII, and alpha-mannosidosis are examples of a subset of LSD patients that are predisposed towards immune suppression. In contrast, GM2 gangliosidosis, globoid cell leukodystrophy, Niemann-Pick disease type C1 and juvenile neuronal ceroid lipofuscinosis are LSDs that are predisposed towards immune system hyperactivity. Antigen presentation and processing by dedicated antigen presenting cells (APCs), secretion of pore-forming perforins by cytotoxic-T lymphocytes, and release of pro-inflammatory mediators by mast cells are among the many crucial immune system functions in which the lysosome plays a central role. Although the relationship between the modification of the lysosomal compartment in LSDs and modulation of the immune system remains unknown, there is emerging evidence for early neuroimmune responses in a variety of LSDs. In this review we bridge biochemical studies on the lysosomal compartment's role in the immune system with clinical data on immune system irregularities in a subset of LSDs.

Novel candidate disease for gene therapy: metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare, fatal, inherited, autosomal recessive, lysosomal storage disorder, characterized by severe and progressive demyelination affecting the central and peripheral nervous systems. Despite some initial expectations in hematopoietic stem cell transplantation, and despite the ameliorated supportive therapy, MLD remains a life-threatening disease, with an extremely poor quality of life and a severe prognosis for all affected patients. Prospectively, in children affected by MLD, who have no other therapeutic option and an extremely poor prognosis, the potential risks associated with the use of a novel technology, such as gene therapy, might be well balanced by the potential benefit of a positive outcome. Thus, MLD might be considered an optimal candidate disease for testing innovative and potentially efficacious therapeutic approaches. Some of the gene therapy approaches discussed here, such as hematopoietic stem cells gene therapy, are likely to enter clinical testing in the near future.

Characterization and pharmacokinetic study of recombinant human N-acetylgalactosamine-6-sulfate sulfatase

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disorder caused by a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). The aims of this study were to establish Chinese hamster ovary (CHO) cells overexpressing recombinant human GALNS (rhGALNS) and to assess pharmacokinetics and tissue distribution of purified enzymes by using MPS IVA knock-out mouse (Galns(-/-)). The CHO-cell derived rhGALNS was purified from the media by a two-step affinity chromatography procedure. The rhGALNS was administered intravenously to 3-month-old Galns(-/-) mice at a single dose of 250U/g of body weight. The treated mice were examined by assaying the GALNS activity at baseline and up to 240min to assess clearance of the enzyme from blood circulation. The mice were sacrificed 4h after infusion of the enzyme to study the enzyme distribution in tissues. The rhGALNS was purified 1317-fold with 71% yield. The enzyme was taken up by Galns(-/-) chondrocytes (150U/mg/15h). The uptake was inhibited by mannose-6-phosphate. The enzyme activity disappeared from circulation with a half-life of 2.9min. After enzyme infusion, the enzyme was taken up and detected in multiple tissues (40.7% of total infused enzymes in liver). Twenty-four hours after a single infusion of the fluorescence-labeled enzymes into MPS IVA mice, biodistribution pattern showed the amount of tagged enzyme retained in bone, bone marrow, liver, spleen, kidney, and heart. In conclusion, we have shown that the phosphorylated rhGALNS is delivered to multiple tissues, including bone, and that it functions bioactively in Galns(-/-) chondrocytes implying a potential enzyme replacement treatment.

Enhancement of drug delivery to bone: characterization of human tissue-nonspecific alkaline phosphatase tagged with an acidic oligopeptide

Hypophosphatasia is caused by deficiency of activity of the tissue-nonspecific alkaline phosphatase (TNSALP), resulting in a defect of bone mineralization. Enzyme replacement therapy (ERT) with partially purified plasma enzyme was attempted but with little clinical improvement. Attaining clinical effectiveness with ERT for hypophosphatasia may require delivering functional TNSALP enzyme to bone. We tagged the C-terminal-anchorless TNSALP enzyme with an acidic oligopeptide (a six or eight residue stretch of L-Asp), and compared the biochemical properties of the purified tagged and untagged enzymes derived from Chinese hamster ovary cell lines. The specific activities of the purified enzymes tagged with the acidic oligopeptide were the same as the untagged enzyme. In vitro affinity experiments showed the tagged enzymes had 30-fold higher affinity for hydroxyapatite than the untagged enzyme. Lectin affinity chromatography for carbohydrate structure showed little difference among the three enzymes. Biodistribution pattern from single infusion of the fluorescence-labeled enzymes into mice showed delayed clearance from the plasma up to 18 h post infusion and the amount of tagged enzyme retained in bone was 4-fold greater than that of the untagged enzyme. In vitro mineralization assays with the bone marrow from a hypophosphatasia patient using each of the three enzymes in the presence of high concentrations of pyrophosphate provided evidence of bone mineralization. These results show the anchorless enzymes tagged with an acidic oligopeptide are delivered efficiently to bone and function bioactively in bone mineralization, at least in vitro. They suggest potential advantages for use of these tagged enzymes in ERT for hypophosphatasia, which should be explored.

Substrate reduction therapy of glycosphingolipid storage disorders

In the last 15 years enormous progress has been made regarding therapy of type I Gaucher disease, a severely disabling disorder characterized by intralysosomal storage of glucosylceramide in tissue macrophages. Effective enzyme replacement therapy of type I Gaucher disease, based on chronic intravenous administration of mannose-terminated recombinant human glucocerebrosidase, has been available since 1990 and has been applied in several thousand patients without serious adverse effects. An alternative therapeutic approach, so-called substrate reduction therapy, is based on partial reduction of the synthesis of glucosylceramide and hence of subsequent metabolites. Oral administration of an inhibitor of glucosylceramide synthesis (N-butyldeoxynojirimycin, registered in Europe since 2002 as miglustat (Zavesca)), is effective in reversing clinical symptoms in type I Gaucher patients with mild to moderate disease manifestations. The growing long-term experience with substrate reduction therapy indicates that this treatment is also without major adverse effects. Substrate reduction therapy, in conjunction with enzyme replacement therapy, may play an important role in the future clinical management of patients suffering from type I Gaucher disease. Clinical trials are under way that should reveal the value of substrate reduction for maintenance therapy of type I Gaucher disease and for treatment of neuronopathic variants of Gaucher disease, Niemann-Pick disease type C, late-onset Tay-Sachs disease and Sandhoff disease.

Recombinant glucocerebrosidase uptake by Gaucher disease human osteoblast culture model

Bone lesions are a major cause of morbidity in Gaucher disease (GD) type I. Enzyme replacement therapy (ERT) has been successful in treating many symptoms of type I GD but skeletal response lags behind. Local exogenous glucocerebrosidase supplementation in bone lesions via a drug delivery system may overcome this limitation. Although local enzyme supplementation aims to target lipid-engorged macrophages (Gaucher Cells) in bone compartment, enzyme uptake by osteoblasts is not excluded. To investigate the ability of human osteoblasts to internalize recombinant glucocerebrosidase (rGCR), we have used an artificial GD human osteoblasts cell culture system. MG63 human osteoblasts were treated with conduritol B epoxide (CBE) to induce complete and prolonged inhibition of endogenous glucocerebrosidase activity of cells. rGCR uptake by glucocerebrosidase-inactivated osteoblasts was examined using (125)I-radiolabelling, Western blot analysis and measurement of glucocerebrosidase activity. Analysis of radiolabeled enzyme uptake by CBE treated osteoblasts showed 67.9% of internalized protein in cell extract. Enzyme internalization was also observed by Western blot analysis where the amount of mature form of glucocerebrosidase protein recognized by the glucocerebrosidase antibody was increased following the administrations of rGCR. Moreover, enzymatic activity measurement showed 23.9% of glucocerebrosidase activity of control cells. The rGCR internalization by MG63 osteoblast seems to be partially mediated by mannose receptors. These data provide evidence that MG63 human osteoblasts are able to internalize rGCR.

Evidence for a link between sphingolipid metabolism and expression of CD1d and MHC-class II: monocytes from Gaucher disease patients as a model

Gaucher disease (GD) is an autosomal recessive inherited defect of the lysosomal enzyme glucocerebrosidase (GluCerase) that leads to glucosylceramide (GluCer) accumulation. We previously demonstrated the existence of imbalances in certain lymphocyte populations in GD patients. We now show that GluCerase-deficient monocytes from GD patients or monocytes from healthy subjects treated with conduritol-B-epoxide (CBE), an irreversible inhibitor of GluCerase activity, display high levels of surface expression of the lipid-binding molecule CD1d. GluCerase-deficient monocytes from GD patients also showed increased surface expression of major histocompatibility complex (MHC)-class II, but not of other lysosomal trafficking molecules, such as CD63 and MHC-class I. However, CD1d and MHC-class II mRNA levels were not increased. GluCerase-deficient monocytes from GD patients undergoing enzyme replacement therapy also exhibited increased levels of CD1d and MHC-class II and imbalances in the percentage of CD4+, CD8+, and Valpha24+ T cells. Interestingly, follow-up studies revealed that enzyme replacement therapy induced a decrease in MHC-class II expression and partial correction of the CD4+ T cell imbalances. These results reveal a new link between sphingolipid accumulation in monocytes and the expression of certain MHC molecules that may result in imbalances of regulatory T cell subsets. These immunological anomalies may contribute to the clinical heterogeneity in GD patients.

Identification and use of biomarkers in Gaucher disease and other lysosomal storage diseases

The value of biomarkers in the clinical management of lysosomal storage diseases is best illustrated by the present use of plasma chitotriosidase levels in the diagnosis and monitoring of Gaucher disease. The enzyme chitotriosidase is specifically produced and secreted by the pathological storage macrophages (Gaucher cells). Plasma chitotriosidase levels are elevated on average 1000-fold in symptomatic patients with Gaucher disease and reflect the body burden on storage cells. Changes in plasma chitotriosidase reflect changes in clinical symptoms. Monitoring of plasma chitotriosidase levels is nowadays commonly used in decision making regarding initiation and optimization of costly therapeutic interventions (enzyme replacement therapy or substrate reduction therapy). A novel substrate has been developed that further facilitates the measurement of chitotriosidase in plasma samples. Moreover, an alternative Gaucher-cell marker, CCL18, has been very recently identified and can also be employed to monitor the disease, particularly in those patients lacking chitotriosidase due to a genetic mutation. There is a need for comparable surrogate markers for other lysosomal storage diseases and the search for such molecules is an area of intense investigation.

CONCLUSION

The use of biomarkers can provide valuable insight into the molecular pathogenesis of LSDs, such as Gaucher disease and Fabry disease.

Gaucher disease type 1: Revised recommendations on evaluations and monitoring for adult patients

For patients with type 1 Gaucher disease, challenges to patient care posed by clinical heterogeneity, variable progression rates, and potential permanent disability that can result from untreated or suboptimally treated hematologic, skeletal, and visceral organ involvement dictate a need for comprehensive, serial monitoring. An updated consensus on minimum recommendations for effective monitoring of all adult patients with type 1 Gaucher disease has been developed by the International Collaborative Gaucher Group (ICGG) Registry coordinators. These recommendations provide a schedule for comprehensive and reproducible evaluation and monitoring of all clinically relevant aspects of this disease. The initial assessment should include confirmation of deficiency of beta-glucocerebrosidase, genotyping, and a complete family medical history. Other assessments to be performed initially and at regular intervals include a complete physical examination, patient-reported quality of life using the SF-36 survey, and assessment of hematologic (hemoglobin and platelet count), visceral, and skeletal involvement, and biomarkers. Specific radiologic imaging techniques are recommended for evaluating visceral and skeletal pathology. All patients should undergo comprehensive regular assessment, the frequency of which depends on treatment status and whether therapeutic goals have been achieved. Additionally, reassessment should be performed whenever enzyme therapy dose is altered, or in case of significant clinical complication.

A general model for genetic regulation of turnover of glycosaminoglycans suggests a possible procedure for prediction of severity and clinical progress of mucopolysaccharidoses

Mucopolysaccharidoses are rare genetic diseases from the group of lysosomal storage disorders caused by deficiency of enzymes involved in degradation of mucopolysaccharides (glycosaminoglycans, GAGs). Within each mucopolysaccharidosis, there is a continuous spectrum of clinical features from the very severe to the more mildly affected individuals. Surprisingly, in most cases, it is not possible to predict severity and clinical progress (i.e., the natural history) of the disease on the basis of detection of particular mutations or residual activity of the deficient enzyme. In this article, the reasons for such an unexpected difficulty are discussed. A model for the correlation between residual activity of a lysosomal enzyme and the turnover rate of its substrate(s) has been proposed previously by others, however, in that model it was assumed that substrate concentration in the lysosome is not regulated, thus the residual activity of a hydrolase would be the only determinant of the rate of substrate accumulation. On the other hand, both a general model for genetic regulation of turnover of GAGs and results of very recent studies strongly suggest that expression of genes coding for enzymes involved in GAG synthesis is precisely regulated and may vary between individuals. Therefore, we propose that apart from measurement of residual activity of the enzyme involved in degradation of GAGs, the efficiency of synthesis of these compounds should also be estimated. If the hypothesis presented in this article is true, the ratio of the synthesis of glycosaminoglycans to the residual activity of the deficient enzyme should be of considerable prognostic value.

Systemic FIV vector administration: transduction of CNS immune cells and Purkinje neurons

The systemic effects of gene therapy have been previously described in a variety of peripheral organs following intravenous administration or intraperitoneal inoculation of viral vectors, as well as in the brain following intracranial administration. However, limited information is available on the ability of viral vectors to cross the blood-brain barrier and infect cells located within the central nervous system (CNS). We employed a VSV-G pseudotyped FIV(lacZ) vector capable of transducing dividing, growth-arrested, as well as post-mitotic cells with the reporter gene lacZ. Adult mice were injected intraperitoneally with FIV(lacZ), and the expression of beta-galactosidase was studied 5 weeks following treatment in the brain, liver, spleen and kidney by X-gal histochemistry and immunocytochemistry. Interestingly, relatively low doses of FIV(lacZ) administered intraperitoneally lead to beta-galactosidase detection in the brain and cerebellum. The identity of these cells was confirmed by double immunofluorescence, and included CD31-, CD3- and CD11b-positive cells. Fluorescent microspheres co-injected with FIV(lacZ) virus were identified within mononuclear cells in the brain parenchyma, suggesting infiltration of peripheral immune cells in the CNS. Cerebellar Purkinje neurons were also transduced in all adult-injected mice. Our observations indicate that relatively low doses of FIV(lacZ) administered intraperitoneally resulted in the transduction of immune cells in the brain, as well as a specific subset of cerebellar neurons.

Biochemistry of glycosphingolipid storage disorders: implications for therapeutic intervention

The physiological importance of the degradative processes in lysosomes is revealed by the existence of at least 40 distinct inherited diseases, the so-called lysosomal storage disorders. Most of these diseases are caused by a deficiency in a single lysosomal enzyme, or essential cofactor, and result in the lysosomal accumulation of one, or sometimes several, natural compounds. The most prevalent subgroup of the lysosomal storage disorders is formed by the sphingolipidoses, inherited disorders that are characterized by excessive accumulation of one or multiple (glyco)sphingolipids. The biology of glycosphingolipids has been extensively discussed in other contributions during this symposium. This review will therefore focus in depth on (type 1) Gaucher disease, a prototypical glycosphingolipidosis. The elucidation of the primary genetic defect, being a deficiency in the lysosomal glucocerebrosidase, is described. Characterization of glucocerebrosidase at protein and gene level has subsequently opened avenues for therapeutic intervention. The development of successful enzyme replacement therapy for type 1 Gaucher disease is discussed. Attention is also paid to the alternative approach of substrate modulation using orally administered inhibitors of glucosylceramide synthesis. Novel developments about the monitoring of age of onset, progression and correction of disease are described. The remaining challenges about pathophysiology of glycosphingolipidoses are discussed in view of further improvements in therapy for these debilitating disorders.

Enzyme replacement therapy in mucopolysaccharidosis type II (Hunter syndrome): a preliminary report

Mucopolysaccharidosis type II (MPS II; Hunter syndrome) is an X-linked disease caused by a deficiency of the enzyme iduronate-2-sulphatase (IDS), which results in the lysosomal accumulation of glycosaminoglycans (GAG). This paper describes a knockout mouse model of MPS II which has been used to assess the effect of enzyme replacement therapy. Therapy with IDS results in a marked decrease in urinary GAGs, as well as reduced GAG accumulation in several tissues. These studies have been used to support the first clinical trial of recombinant IDS in patients with Hunter syndrome.

Viral-mediated delivery of the late-infantile neuronal ceroid lipofuscinosis gene, TPP-I to the mouse central nervous system

Classical late-infantile neuronal ceroid lipofuscinosis (LINCL) is caused by mutations in tripeptidyl peptidase I (TPP-I), a pepstatin-insensitive lysosomal protease, resulting in neurodegeneration, acute seizures, visual and motor dysfunction. In vitro studies suggest that TPP-I is secreted from cells and subsequently taken up by neighboring cells, similar to other lysosomal enzymes. As such, TPP-I is an attractive candidate for enzyme replacement or gene therapy. In the present studies, we examined the feasibility of gene transfer into mouse brain using recombinant adenovirus (Ad), feline immunodeficiency virus (FIV) and adeno-associated virus (AAV) vectors expressing TPP-I, after single injections into the striatum or cerebellum. A dual TPP-I- and beta-galactosidase-expressing adenovirus vector (AdTTP-I/nlsbetagal) was used to distinguish transduced (beta-galactosidase positive) cells from cells that endocytosed secreted TTP-I. Ten days after striatal injection of AdTTP-I/nlsbetagal, beta-galactosidase-positive cells were concentrated around the injection site, corpus callosum, ependyma and choroid plexus. In cerebellar injections, beta-galactosidase expression was confined to the region of injection and in isolated neurons of the brainstem. Immunohistochemistry for TPP-I expression showed that TPP-I extended beyond areas of beta-galactosidase activity. Immunohistochemistry for TTP-I after FIVTTP-I and AAV5TTP-I injections demonstrated TPP-I in neurons of the striatum, hippocampus and Purkinje cells. For all three vectors, TPP-I activity in brain homogenates was 3-7-fold higher than endogenous levels in the injected hemispheres. Our results indicate the feasibility of vector-mediated gene transfer of TPP-I to the CNS as a potential therapy for LINCL.

Pulmonary hypertension in type 1 Gaucher's disease: genetic and epigenetic determinants of phenotype and response to therapy

Type 1 Gaucher's disease (GD) is recognized for striking but unexplained phenotypic diversity. Rarely, severe pulmonary hypertension (PH) may occur in GD but its clinical spectrum, determinants or its response to enzyme replacement therapy (ERT)+/-vasodilators is not known. One hundred and thirty-four consecutive patients with Type 1 GD were screened to estimate right ventricular systolic pressure (RVSP) by Doppler echocardiography. Ninety-four patients were on ERT and 40 were untreated. Eight additional GD patients were studied that represented consecutive tertiary referrals with severe PH. Angiotensin converting enzyme (ACE) gene polymorphisms and acid beta-glucosidase gene (GBA) mutations were determined by DNA analysis. Mild, asymptomatic PH (RVSP>35<50 mmHg) was prevalent in Type 1 GD: 30% in untreated patients and 7.4% among patients receiving ERT (P<0.001). Splenectomy was strongly associated with severe, life-threatening PH: all patients with severe PH (RVSP 50-130 mmHg) were asplenic compared to only 31% of patients with RVSP<50 mmHg (Odds ratio [OR] 28.8, 95% CI 1.6-531.6, P<0.001). Other characteristics of patients presenting with severe PH were poor compliance to ERT (4/9 patients) or no ERT (5/9 patients), a family history of a sib with GD and PH (2/2 patients), an excess of ACE I allele (OR 2.3, 95% CI 1.1-4.9, P=0.034) and an excess of non-N370S GBA mutation (OR 6.0, 95% CI 1.1-33, P=0.003). Severe PH was ameliorated by ERT+/-vasodilators during 4.6+/-4.0 yr (range 1-12 yr) follow-up; three patients were initially considered for lung transplantation but improved such that they are no longer active transplant candidates. Our study reveals a remarkable predisposition for PH in type 1 GD. Progression to severe, life-threatening PH occurs in the presence of additional genetic factors (non-N370S GBA mutation, positive family history, and ACE I gene polymorphism) and epigenetic modifiers (i.e., asplenia and female sex). Splenectomy should be avoided and in high-risk patients, ERT+/-vasodilators/coumadin should be initiated.