Reduction of GAG storage in MPS II mouse model following implantation of encapsulated recombinant myoblasts

Glycosaminoglycan signatures in body fluids of mucopolysaccharidosis type II mouse model under long-term enzyme replacement therapy

Abstract

Mucopolysaccharidosis type II (MPS II) is a neurometabolic disorder, due to the deficit of the lysosomal hydrolase iduronate 2-sulfatase (IDS). This leads to a severe clinical condition caused by a multi-organ accumulation of the glycosaminoglycans (GAGs/GAG) heparan- and dermatan-sulfate, whose elevated levels can be detected in body fluids. Since 2006, enzyme replacement therapy (ERT) has been clinically applied, showing efficacy in some peripheral districts. In addition to clinical monitoring, GAG dosage has been commonly used to evaluate ERT efficacy. However, a strict long-term monitoring of GAG content and composition in body fluids has been rarely performed. Here, we report the characterization of plasma and urine GAGs in Ids knock-out (Ids-ko) compared to wild-type (WT) mice, and their changes along a 24-week follow-up, with and without ERT. The concentration of heparan-sulfate (HS), chondroitin-sulfate (CS), and dermatan-sulfate (DS), and of the non-sulfated hyaluronic acid (HA), together with their differentially sulfated species, was quantified by capillary electrophoresis with laser-induced fluorescence. In untreated Ids-ko mice, HS and CS + DS were noticeably increased at all time points, while during ERT follow-up, a substantial decrease was evidenced for HS and, to a minor extent, for CS + DS. Moreover, several structural parameters were altered in untreated ko mice and reduced after ERT, however without reaching physiological values. Among these, disaccharide B and HS 2s disaccharide showed to be the most interesting candidates as biomarkers for MPS II. GAG chemical signature here defined provides potential biomarkers useful for an early diagnosis of MPS II, a more accurate follow-up of ERT, and efficacy evaluations of newly proposed therapies.

Key messages

Plasmatic and urinary GAGs are useful markers for MPS II early diagnosis and prognosis.

CE-LIF allows GAG structural analysis and the quantification of 17 different disaccharides.

Most GAG species increase and many structural features are altered in MPS II mouse model.

GAG alterations tend to restore to wild-type levels following ERT administration.

CS+DS/HS ratio, % 2,4dis CS+DS, and % HS 2s are potential markers for MPS II pathology and ERT efficacy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-022-02221-3.

Differences in MPS I and MPS II Disease Manifestations

Mucopolysaccharidosis (MPS) type I and II are two closely related lysosomal storage diseases associated with disrupted glycosaminoglycan catabolism. In MPS II, the first step of degradation of heparan sulfate (HS) and dermatan sulfate (DS) is blocked by a deficiency in the lysosomal enzyme iduronate 2-sulfatase (IDS), while, in MPS I, blockage of the second step is caused by a deficiency in iduronidase (IDUA). The subsequent accumulation of HS and DS causes lysosomal hypertrophy and an increase in the number of lysosomes in cells, and impacts cellular functions, like cell adhesion, endocytosis, intracellular trafficking of different molecules, intracellular ionic balance, and inflammation. Characteristic phenotypical manifestations of both MPS I and II include skeletal disease, reflected in short stature, inguinal and umbilical hernias, hydrocephalus, hearing loss, coarse facial features, protruded abdomen with hepatosplenomegaly, and neurological involvement with varying functional concerns. However, a few manifestations are disease-specific, including corneal clouding in MPS I, epidermal manifestations in MPS II, and differences in the severity and nature of behavioral concerns. These phenotypic differences appear to be related to different ratios between DS and HS, and their sulfation levels. MPS I is characterized by higher DS/HS levels and lower sulfation levels, while HS levels dominate over DS levels in MPS II and sulfation levels are higher. The high presence of DS in the cornea and its involvement in the arrangement of collagen fibrils potentially causes corneal clouding to be prevalent in MPS I, but not in MPS II. The differences in neurological involvement may be due to the increased HS levels in MPS II, because of the involvement of HS in neuronal development. Current treatment options for patients with MPS II are often restricted to enzyme replacement therapy (ERT). While ERT has beneficial effects on respiratory and cardiopulmonary function and extends the lifespan of the patients, it does not significantly affect CNS manifestations, probably because the enzyme cannot pass the blood-brain barrier at sufficient levels. Many experimental therapies, therefore, aim at delivery of IDS to the CNS in an attempt to prevent neurocognitive decline in the patients.

Therapeutic Options for Mucopolysaccharidosis II (Hunter Disease)

BACKGROUND

Mucopolysaccharidosis type II (Hunter syndrome, or MPS II) is an X-linked lysosomal disorder caused by the deficiency of iduronate-2-sulfatase, which leads to the accumulation of glycosaminoglycans (GAGs) in a variety of tissues, resulting in a multisystemic disease that can also impair the central nervous system (CNS).

OBJECTIVE

This review focuses on providing the latest information and expert opinion about the therapies available and under development for MPS II.

METHODS

We have comprehensively revised the latest studies about hematopoietic stem cell transplantation (HSCT), enzyme replacement therapy (ERT - intravenous, intrathecal, intracerebroventricular, and intravenous with fusion proteins), small molecules, gene therapy/genome editing, and supportive management.

RESULTS AND DISCUSSION

Intravenous ERT is a well-established specific therapy, which ameliorates the somatic features but not the CNS manifestations. Intrathecal or intracerebroventricular ERT and intravenous ERT with fusion proteins, presently under development, seem to be able to reduce the levels of GAGs in the CNS and have the potential of reducing the impact of the neurological burden of the disease. Gene therapy and/or genome editing have shown promising results in preclinical studies, bringing hope for a "one-time therapy" soon. Results with HSCT in MPS II are controversial, and small molecules could potentially address some disease manifestations. In addition to the specific therapeutic options, supportive care plays a major role in the management of these patients.

CONCLUSION

At this time, the treatment of individuals with MPS II is mainly based on intravenous ERT, whereas HSCT can be a potential alternative in specific cases. In the coming years, several new therapy options that target the neurological phenotype of MPS II should be available.

Mucopolysaccharidosis Type II: One Hundred Years of Research, Diagnosis, and Treatment

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) was first described by Dr. Charles Hunter in 1917. Since then, about one hundred years have passed and Hunter syndrome, although at first neglected for a few decades and afterwards mistaken for a long time for the similar disorder Hurler syndrome, has been clearly distinguished as a specific disease since 1978, when the distinct genetic causes of the two disorders were finally identified. MPS II is a rare genetic disorder, recently described as presenting an incidence rate ranging from 0.38 to 1.09 per 100,000 live male births, and it is the only X-linked-inherited mucopolysaccharidosis. The complex disease is due to a deficit of the lysosomal hydrolase iduronate 2-sulphatase, which is a crucial enzyme in the stepwise degradation of heparan and dermatan sulphate. This contributes to a heavy clinical phenotype involving most organ-systems, including the brain, in at least two-thirds of cases. In this review, we will summarize the history of the disease during this century through clinical and laboratory evaluations that allowed its definition, its correct diagnosis, a partial comprehension of its pathogenesis, and the proposition of therapeutic protocols. We will also highlight the main open issues related to the possible inclusion of MPS II in newborn screenings, the comprehension of brain pathogenesis, and treatment of the neurological compartment.

Current and Emerging Therapies for Mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are caused by deficiencies of specific lysosomal enzymes that affect the degradation of mucopolysaccharides or glycosaminoglycans (GAGs). Enzyme replacement therapies are available for an increasing number of MPSs since more than 15 years. Together with hematopoietic stem cell transplantation, these enzyme therapies are currently the gold standard of causal treatment in MPS. Both treatments can improve symptoms and prognosis, but they do not cure these severe conditions. The limitations of intravenous enzyme replacement and cell therapy can be summarized as the development of immune reactions against the therapeutic molecules/cells and failure to restore enduring and sufficient drug exposures in all relevant tissues. Thus innovative approaches include small molecules and encapsulated cells that do not induce immune reactions, gene therapy approaches that aim for sustained enzyme expression, and new enzymes that are able to penetrate barriers to drug distribution like the blood-brain barrier. This chapter provides an update on the state of development of these new therapies and highlights current challenges.

Targeting Brain Disease in MPSII: Preclinical Evaluation of IDS-Loaded PLGA Nanoparticles

Mucopolysaccharidosis type II (MPSII) is a lysosomal storage disorder due to the deficit of the enzyme iduronate 2-sulfatase (IDS), which leads to the accumulation of glycosaminoglycans in most organ-systems, including the brain, and resulting in neurological involvement in about two-thirds of the patients. The main treatment is represented by a weekly infusion of the functional enzyme, which cannot cross the blood-brain barrier and reach the central nervous system. In this study, a tailored nanomedicine approach based on brain-targeted polymeric nanoparticles (g7-NPs), loaded with the therapeutic enzyme, was exploited. Fibroblasts from MPSII patients were treated for 7 days with NPs loaded with the IDS enzyme; an induced IDS activity like the one detected in healthy cells was measured, together with a reduction of GAG content to non-pathological levels. An in vivo short-term study in MPSII mice was performed by weekly administration of g7-NPs-IDS. Biochemical, histological, and immunohistochemical evaluations of liver and brain were performed. The 6-weeks treatment produced a significant reduction of GAG deposits in liver and brain tissues, as well as a reduction of some neurological and inflammatory markers (i.e., LAMP2, CD68, GFAP), highlighting a general improvement of the brain pathology. The g7-NPs-IDS approach allowed a brain-targeted enzyme replacement therapy. Based on these positive results, the future aim will be to optimize NP formulation further to gain a higher efficacy of the proposed approach.

Dose-Dependent Prevention of Metabolic and Neurologic Disease in Murine MPS II by ZFN-Mediated In Vivo Genome Editing

Mucopolysaccharidosis type II (MPS II) is an X-linked recessive lysosomal disorder caused by deficiency of iduronate 2-sulfatase (IDS), leading to accumulation of glycosaminoglycans (GAGs) in tissues of affected individuals, progressive disease, and shortened lifespan. Currently available enzyme replacement therapy (ERT) requires lifelong infusions and does not provide neurologic benefit. We utilized a zinc finger nuclease (ZFN)-targeting system to mediate genome editing for insertion of the human IDS (hIDS) coding sequence into a "safe harbor" site, intron 1 of the albumin locus in hepatocytes of an MPS II mouse model. Three dose levels of recombinant AAV2/8 vectors encoding a pair of ZFNs and a hIDS cDNA donor were administered systemically in MPS II mice. Supraphysiological, vector dose-dependent levels of IDS enzyme were observed in the circulation and peripheral organs of ZFN+donor-treated mice. GAG contents were markedly reduced in tissues from all ZFN+donor-treated groups. Surprisingly, we also demonstrate that ZFN-mediated genome editing prevented the development of neurocognitive deficit in young MPS II mice (6-9 weeks old) treated at high vector dose levels. We conclude that this ZFN-based platform for expression of therapeutic proteins from the albumin locus is a promising approach for treatment of MPS II and other lysosomal diseases.

Subcutaneous implantation of microencapsulated cells overexpressing α-L-iduronidase for mucopolysaccharidosis type I treatment

Mucopolysaccharidosis type I (MPS I) is caused by a deficiency of α-L-iduronidase (IDUA), resulting in accumulation of glycosaminoglycans (GAG) in lysosomes. Microencapsulation of recombinant cells is a promising gene/cell therapy approach that could overcome the limitations of the current available treatments. In the present study we produced alginate-poly-L-lysine-alginate (APA) microcapsules containing recombinant cells overexpressing IDUA, which were implanted in the subcutaneous space of MPS I mice in order to evaluate their potential effect as a treatment for this disease. APA microcapsules enclosing genetically modified Baby Hamster Kidney cells overexpressing IDUA were produced and implanted in the subcutaneous space of 4-month-old MPS I mice (Idua ^-/-). Treatment was performed using two cell concentrations: 8.3 × 10⁷ and 8.3 × 10⁶ cells/mL. Untreated MPS I and normal mice were used as controls. Microcapsules were retrieved and analyzed after treatment. Increased IDUA in the liver, kidney and heart was detected 24 h postimplantation. After 120 days, higher IDUA activity was detected in the liver, kidney and heart, in both groups, whereas GAG accumulation was reduced only in the high cell concentration group. Microcapsules analysis showed blood vessels around them, as well as inflammatory cells and a fibrotic layer. Microencapsulated cells were able to ameliorate some aspects of the disease, indicating their potential as a treatment. To achieve better performance of the microcapsules, improvements such as the modulation of inflammatory response are suggested.

Current therapies for Morquio A syndrome and their clinical outcomes

INTRODUCTION

Morquio A syndrome is characterized by a unique skeletal dysplasia, leading to short neck and trunk, pectus carinatum, laxity of joints, kyphoscoliosis, and tracheal obstruction. Cervical spinal cord compression/inability, a restrictive and obstructive airway, and/or bone deformity and imbalance of growth, are life-threatening to Morquio A patients, leading to a high morbidity and mortality. It is critical to review the current therapeutic approaches with respect to their efficacy and limitations.

AREAS COVERED

Patients with progressive skeletal dysplasia often need to undergo orthopedic surgical interventions in the first two decades of life. Recently, we have treated four patients with a new surgery to correct progressive tracheal obstruction. Enzyme replacement therapy (ERT) has been approved clinically. Cell-based therapies such as hematopoietic stem cell therapy (HSCT) and gene therapy are typically one-time, permanent treatments for enzyme deficiencies. We report here on four Morquio A patients treated with HSCT approved in Japan and followed for at least ten years after treatment. Gene therapy is under investigation on mouse models but not yet available as a therapeutic option.

EXPERT OPINION

ERT and HSCT in combination with surgical intervention(s) are a therapeutic option for Morquio A; however, the approach for bone and cartilage lesion remains an unmet challenge.

Targeted Polymeric Nanoparticles for Brain Delivery of High Molecular Weight Molecules in Lysosomal Storage Disorders

Lysosomal Storage Disorders (LSDs) are a group of metabolic syndromes, each one due to the deficit of one lysosomal enzyme. Many LSDs affect most of the organ systems and overall about 75% of the patients present neurological impairment. Enzyme Replacement Therapy, although determining some systemic clinical improvements, is ineffective on the CNS disease, due to enzymes' inability to cross the blood-brain barrier (BBB). With the aim to deliver the therapeutic enzymes across the BBB, we here assayed biodegradable and biocompatible PLGA-nanoparticles (NPs) in two murine models for LSDs, Mucopolysaccharidosis type I and II (MPS I and MPS II). PLGA-NPs were modified with a 7-aminoacid glycopeptide (g7), yet demonstrated to be able to deliver low molecular weight (MW) molecules across the BBB in rodents. We specifically investigated, for the first time, the g7-NPs ability to transfer a model drug (FITC-albumin) with a high MW, comparable to the enzymes to be delivered for LSDs brain therapy. In vivo experiments, conducted on wild-type mice and knockout mouse models for MPS I and II, also included a whole series of control injections to obtain a broad preliminary view of the procedure efficiency. Results clearly showed efficient BBB crossing of albumin in all injected mice, underlying the ability of NPs to deliver high MW molecules to the brain. These results encourage successful experiments with enzyme-loaded g7-NPs to deliver sufficient amounts of the drug to the brain district on LSDs, where exerting a corrective effect on the pathological phenotype.

Emerging drugs for the treatment of mucopolysaccharidoses

INTRODUCTION

Despite being reported for the first time almost one century ago, only in the last few decades effective have treatments become available for the mucopolysaccharidoses (MPSs), a group of 11 inherited metabolic diseases that affect lysosomal function. These diseases are progressive, usually severe, and, in a significant number of cases, involve cognitive impairment.

AREAS COVERED

This review will not cover established treatments such as bone marrow/hematopoietic stem cell transplantation and classic intravenous enzyme replacement therapy (ERT), whose long-term outcomes have already been published (MPS I, MPS II, and MPS VI), but it instead focuses on emerging therapies for MPSs. That includes intravenous ERT for MPS IVA and VII, intrathecal ERT, ERT with fusion proteins, substrate reduction therapy, gene therapy, and other novel approaches.

EXPERT OPINION

The available treatments have resulted in improvements for several disease manifestations, but they still do not represent a cure for these diseases; thus, it is important to develop alternative methods to approach the unmet needs (i.e. bone disease, heart valve disease, corneal opacity, and central nervous system (CNS) involvement). The work in progress with novel approaches makes us confident that in 2017, when MPS will commemorate 100 years of its first report, we will be much closer to an effective cure for these challenging conditions.

Intraperitoneal implant of recombinant encapsulated cells overexpressing alpha-L-iduronidase partially corrects visceral pathology in mucopolysaccharidosis type I mice

BACKGROUND AIMS

Mucopolysaccharidosis type I (MPS I) is characterized by deficiency of the enzyme alpha-L-iduronidase (IDUA) and storage of glycosaminoglycans (GAG) in several tissues. Current available treatments present limitations, thus the search for new therapies. Encapsulation of recombinant cells within polymeric structures combines gene and cell therapy and is a promising approach for treating MPS I.

METHODS

We produced alginate microcapsules containing baby hamster kidney (BHK) cells overexpressing IDUA and implanted these capsules in the peritoneum of MPS I mice.

RESULTS

An increase in serum and tissue IDUA activity was observed at early time-points, as well as a reduction in GAG storage; however, correction in the long term was only partially achieved, with a drop in the IDUA activity being observed a few weeks after the implant. Analysis of the capsules obtained from the peritoneum revealed inflammation and a pericapsular fibrotic process, which could be responsible for the reduction in IDUA levels observed in the long term. In addition, treated mice developed antibodies against the enzyme.

CONCLUSIONS

The results suggest that the encapsulation process is effective in the short term but improvements must be achieved in order to reduce the immune response and reach a stable correction.

Cell microencapsulation: a potential tool for the treatment of neuronopathic lysosomal storage diseases

Lysosomal storage disorders (LSD) are monogenic diseases caused by the deficiency of different lysosomal enzymes that degrade complex substrates such as glycosaminoglycans, sphingolipids, and others. As a consequence there is multisystemic storage of these substrates. Most treatments for these disorders are based in the fact that most of these enzymes are soluble and can be internalized by adjacent cells via mannose-6-phosphate receptor. In that sense, these disorders are good candidates to be treated by somatic gene therapy based on cell microencapsulation. Here, we review the existing data about this approach focused on the LSD treatments, the advantages and limitations faced by these studies.

Early clinical markers of central nervous system involvement in mucopolysaccharidosis type II

OBJECTIVE

To identify early clinical markers of neurologic involvement in mucopolysaccharidosis type II.

STUDY DESIGN

A retrospective review of neurobehavioral standardized assessments of patients with mucopolysaccharidosis type II evaluated at the Program for Neurodevelopmental Function in Rare Disorders was completed. Patients were grouped based on the presence or absence of central nervous system (CNS) involvement at the most recent evaluation. Differences in early signs and symptoms between resulting cohorts were tested for significance, and an index severity score was developed.

RESULTS

Between December 2002 and November 2010, clinical evaluations of 49 patients and 151 patient encounters were reviewed. Thirty-seven patients exhibited neurologic deterioration. Of the 25 signs evaluated, 7 early clinical markers were strongly correlated with subsequent cognitive dysfunction: sleep disturbance, increased activity, behavior difficulties, seizure-like behavior, perseverative chewing behavior, and inability to achieve bowel training and bladder training. A new severity score index was developed, with a score ≥3 indicating a high likelihood of developing CNS disease.

CONCLUSION

Seven early clinical markers and a severity score index of CNS involvement can be used for initial screening of children who might benefit from CNS-directed therapies.

Natural progression of neurological disease in mucopolysaccharidosis type II

OBJECTIVE

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder characterized by insufficiency of the iduronate-2-sulfatase enzyme, which results in excess heparan and dermatan sulfates within the lysosomes of various tissues and organs, including the central nervous system. The purpose of this study was to investigate the natural progression of neurologic disease in a large cohort of patients evaluated with standardized testing at a single institution.

METHODS

During the period of December 2002 to October 2010, patients with MPS II were referred to the Program for Neurodevelopmental Function in Rare Disorders. A retrospective review of patient data was performed, which included the use of detailed questionnaires that addressed medical history, notes from previous health care providers, and the results of a multidisciplinary evaluation that lasted 4 to 6 hours and was performed by a team of neurodevelopmental pediatricians, speech pathologists, psychologists, audiologists, psychometricians, and occupational and physical therapists. Patients were evaluated annually for management of disease progression.

RESULTS

A total of 50 male patients with MPS II were evaluated over 152 encounters. Two distinct subgroups of children were identified. One subset of patients had normal cognitive, speech and language, and adaptive functions whereas the other showed a dramatic decline in these areas. All patients developed fine and gross motor deficits.

CONCLUSION

The natural progression of MPS II manifests as 2 divergent and distinct neurologic phenotypes with similar somatic disease. Patients may have primary neural parenchymal disease with cognitive involvement or may maintain normal cognitive abilities.

Genistein reduces glycosaminoglycan levels in a mouse model of mucopolysaccharidosis type II

BACKGROUND AND PURPOSE

Mucopolysaccharidoses (MPS) are lysosomal storage disorders resulting from a deficit of specific lysosomal enzymes catalysing glycosaminoglycan (GAG) degradation. The typical pathology involves most of the organ systems, including the brain, in its severe forms. The soy isoflavone genistein has recently attracted considerable attention as it can reduce GAG synthesis in vitro. Furthermore, genistein is able to cross the blood-brain barrier in the rat. The present study was undertaken to assess the ability of genistein to reduce urinary and tissue GAG levels in vivo.

EXPERIMENTAL APPROACH

We used mice with genetic deletion of iduronate-2-sulphatase (one of the GAG catabolizing enzymes) which provide a model of MPS type II. Two doses of genistein, 5 or 25 mg.kg(-1).day(-1), were given, in the diet for 10 or 20 weeks. Urinary and tissue GAG content was evaluated by biochemical and histochemical procedures.

KEY RESULTS

Urinary GAG levels were reduced after 10 weeks' treatment with genistein at either 5 or 25 mg.kg(-1).day(-1). In tissue samples from liver, spleen, kidney and heart, a reduction in GAG content was observed with both dosages, after 10 weeks' treatment. Decreased GAG deposits in brain were observed after genistein treatment in some animals.

CONCLUSIONS AND IMPLICATIONS

There was decreased GAG storage in the MPSII mouse model following genistein administration. Our results would support the use of this plant-derived isoflavone in a combined therapeutic protocol for treatment of MPS.

In vitro correction of ARSA deficiency in human skin fibroblasts from metachromatic leukodystrophy patients after treatment with microencapsulated recombinant cells

Metachromatic leukodystrophy (MLD) is an autosomal recessive disorder due to arylsulfatase A (ARSA) deficiency that affects primarily the central nervous system. Ongoing treatments include enzyme replacement therapy and bone marrow transplantation, both limited in their effects due to the blood-brain barrier. An alternative approach would be the in situ implantation of encapsulated cells over expressing ARSA. Based on that, we tested the ability of encapsulated BHK cells over expressing ARSA to correct the enzyme deficiency in MLD patients' fibroblasts. Three groups were analyzed: fibroblasts treated with ARSA-over expressing BHK cells (rBHK) trapped in alginate capsules (capsules group), fibroblasts treated with supernatant of non-encapsulated rBHK (uptake control) and fibroblasts treated with empty capsules (empty group). Untreated and normal fibroblasts were used as controls. rBHK obtained by clone selection after non-viral transfection with pTARSA-CMV2. ARSA activity was measured after 1, 2, 3 and 4 weeks of treatment and beta-gal was used as reference enzyme. Statistical analysis was performed using ANOVA and Tukey's test. Normal fibroblasts showed ARSA activity of 23.9 + /- 2.01 nmol/h/mg of protein, whereas untreated MLD fibroblasts had the low ARSA activity (2.22 + /- 0.17). In the empty group, ARSA activity was equal to that of untreated fibroblasts (2.71 + /- 0.34). Capsules and uptake control groups showed higher enzymatic activity levels, compared to MLD untreated, 23.42 + /- 6.39 and 42.35 + /- 5.20, respectively (p < 0.01 for all groups). Encapsulated rBHK clones show potential as a new therapeutic strategy for the treatment of MLD, reaching normal enzyme levels in human MLD fibroblasts.

Gene therapy of Hunter syndrome: evaluation of the efficiency of muscle electro gene transfer for the production and release of recombinant iduronate-2-sulfatase (IDS)

Mucopolysaccharidosis type II (MPSII) is an inherited disorder due to a deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS). The disease is characterized by a considerable deposition of heparan- and dermatan-sulfate, causing a general impairment of physiological functions. Most of the therapeutic protocols proposed so far are mainly based upon enzyme replacement therapy which is very expensive. There is a requirement for an alternative approach, and to this aim, we evaluated the feasibility of muscle electro gene transfer (EGT) performed in the IDS-knockout (IDS-ko) mouse model. EGT is a highly efficient method of delivering exogenous molecules into different tissues. More recently, pre-treatment with bovine hyaluronidase has shown to further improve transfection efficiency of muscle EGT. We here show that, by applying such procedure, IDS was very efficiently produced inside the muscle. However, no induced IDS activity was measured in the IDS-ko mice plasma, in contrast to matched healthy controls. In the same samples, an anticipated and rapidly increasing immune response against the recombinant protein was observed in the IDS-ko vs control mice, although reaching the same levels at 5 weeks post-injection. Additional experiments performed on healthy mice showed a significant contribution of hyaluronidase pre-treatment in increasing the immune response.

Mucopolysaccharidosis type II (Hunter syndrome): a clinical review and recommendations for treatment in the era of enzyme replacement therapy

Mucopolysaccharidosis type II (MPS II; Hunter syndrome) is a rare X-linked recessive disease caused by deficiency of the lysosomal enzyme iduronate-2-sulphatase, leading to progressive accumulation of glycosaminoglycans in nearly all cell types, tissues and organs. Clinical manifestations include severe airway obstruction, skeletal deformities, cardiomyopathy and, in most patients, neurological decline. Death usually occurs in the second decade of life, although some patients with less severe disease have survived into their fifth or sixth decade. Until recently, there has been no effective therapy for MPS II, and care has been palliative. Enzyme replacement therapy (ERT) with recombinant human iduronate-2-sulphatase (idursulfase), however, has now been introduced. Weekly intravenous infusions of idursulfase have been shown to improve many of the signs and symptoms and overall wellbeing in patients with MPS II. This paper provides an overview of the clinical manifestations, diagnosis and symptomatic management of patients with MPS II and provides recommendations for the use of ERT. The issue of treating very young patients and those with CNS involvement is also discussed. ERT with idursulfase has the potential to benefit many patients with MPS II, especially if started early in the course of the disease.

Recognition and diagnosis of mucopolysaccharidosis II (Hunter syndrome)

Mucopolysaccharidosis II, also known as Hunter syndrome, is a rare, X-linked disorder caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase, which catalyzes a step in the catabolism of glycosaminoglycans. In patients with mucopolysaccharidosis II, glycosaminoglycans accumulate within tissues and organs, contributing to the signs and symptoms of the disease. Mucopolysaccharidosis II affects multiple organs and physiologic systems and has a variable age of onset and variable rate of progression. Common presenting features include excess urinary glycosaminoglycan excretion, facial dysmorphism, organomegaly, joint stiffness and contractures, pulmonary dysfunction, myocardial enlargement and valvular dysfunction, and neurologic involvement. In patients with neurologic involvement, intelligence is impaired, and death usually occurs in the second decade of life, whereas those patients with minimal or no neurologic involvement may survive into adulthood with normal intellectual development. Enzyme replacement therapy has emerged as a new treatment for mucopolysaccharidosis disorders, including Hunter syndrome. The purpose of this report is to provide a concise review of mucopolysaccharidosis II for practitioners with the hope that such information will help identify affected boys earlier in the course of their disease.

The characterization of a murine model of mucopolysaccharidosis II (Hunter syndrome)

Mucopolysaccharidosis II (MPS II, Hunter syndrome in humans) is an X-linked inherited lysosomal storage disease caused by a deficiency in the lysosomal enzyme iduronate-2-sulfatase (I2S). I2S catalyses a step in the catabolism of glycosaminoglycans (GAGs) dermatan sulfate and heparan sulfate, and when it is deficient or absent GAGs accumulate in tissues and organs. Male knockout mice (IdS-KO), which lack the gene coding for I2S, exhibit many of the characteristics seen in the human disease. Compared to wild-type control mice, urine GAG excretion was elevated at 4 weeks of age and remained high throughout the lifespan, and tissue GAG levels were elevated as early as 7 weeks of age. Liver, spleen and other organs were significantly larger in the IdS-KO mice than in the wild-type. Radiographic examination revealed sclerosis and enlargement of the skull at 4 weeks of age and appendicular bone enlargement at 10-13 weeks of age. Micro CT scans showed severe periosteal bone formation at the lateral aspect of the distal tibia and calcification of the calcaneus tendon. This model was used in the development of idursulfase for treatment of MPS II and may continue to be useful in the evaluation of treatment strategies of this chronic and progressive disorder.

Gene therapy for mucopolysaccharidosis

Mucopolysaccharidoses (MPS) are due to deficiencies in activities of lysosomal enzymes that degrade glycosaminoglycans. Some attempts at gene therapy for MPS in animal models have involved intravenous injection of vectors derived from an adeno-associated virus (AAV), adenovirus, retrovirus or a plasmid, which primarily results in expression in liver and secretion of the relevant enzyme into blood. Most vectors can correct disease in liver and spleen, although correction in other organs including the brain requires high enzyme activity in the blood. Alternative approaches are to transduce hematopoietic stem cells, or to inject a vector locally into difficult-to-reach sites such as the brain. Gene therapy holds great promise for providing a long-lasting therapeutic effect for MPS if safety issues can be resolved.

Metabolic correction in oligodendrocytes derived from metachromatic leukodystrophy mouse model by using encapsulated recombinant myoblasts

In an effort to develop an encapsulated cell-based system to deliver arylsulfatase A (ARSA) to the central nervous system of metachromatic leukodystrophy (MLD) patients, we engineered C2C12 mouse myoblasts with a retroviral vector containing a full-length human ARSA cDNA and evaluated the efficacy of the recombinant secreted enzyme to revert the MLD phenotype in oligodendrocytes (OL) of the As2-/- mouse model. After transduction, C2C12 cells showed a fifteen-fold increase in intracellular ARSA activity and five-fold increase in ARSA secretion. The secreted hARSA collected from transduced cells encapsulated in polyether-sulfone polymer, was taken up by enzyme-deficient OL derived from MLD mice and normally sorted to the lysosomal compartment, where transferred enzyme reached 80% of physiological levels, restoring the metabolism of sulfatide. To evaluate whether secreted enzyme could restore metabolic function in the brain, encapsulated cells and secreted ARSA were shown to be stable in CSF in vitro. Further, to test cell viability and enzyme release in vivo, encapsulated cells were implanted subcutaneously on the dorsal flank of DBA/2J mice. One month later, all retrieved implants released hARSA at rates similar to unencapsulated cells and contained well preserved myoblasts, demonstrating that encapsulation maintains differentiation of C2C12 cells, stable transgene expression and long-term cell viability in vivo. Thus, these results show the promising potential of developing an ARSA delivery system to the CNS based on the use of a polymer-encapsulated transduced xenogenic cell line for gene therapy of MLD.

Reliability of 1,9-dimethylmethylene blue tests in comparison to agarose gel electrophoresis for quantification of urinary glycosaminoglycans

BACKGROUND

The relevance of glycosaminoglycan determination in biological fluids is gradually gaining importance in the literature. Nevertheless, the results obtained by different methods vary widely. We evaluated 1,9-dimethylmethylene blue (DMB) dye-binding assays for quantification of urinary glycosaminoglycans, in comparison to densitometry after agarose gel electrophoresis.

METHODS

Urinary glycosaminoglycans from different mammalian species were quantified by 3 different DMB dye-binding assays. The results were compared to those obtained by densitometry after agarose gel electrophoresis of glycosaminoglycans isolated from urine samples by ion exchange chromatography.

RESULTS

Densitometry after agarose gel electrophoresis showed glycosaminoglycan urinary concentrations of 1-20 mg/l, and glycosaminoglycan/creatinine ratios of 2-25x10(-3), for all the mammalian species here studied. A decrease with age was observed for humans, cats and horses. In comparison, DMB assays gave much higher results - up to 200 mg/l and 500x10(-3) glycosaminoglycan/creatinine ratios. These values were greatly reduced after 4-h dialysis, suggesting that low molecular weight compounds do interfere. Furthermore, urinary anions such as sulfate, phosphate and citrate, react with metachromatic dyes, such as Toluidine Blue and DMB.

CONCLUSION

DMB assays, although rapid and simple, are not appropriate to quantify urinary glycosaminoglycans in normal mammalians, since other urinary components interfere with the reactions.

Idursulfase: enzyme replacement therapy for mucopolysaccharidosis Type II (Hunter syndrome)

Mucopolysaccharidosis type II (Hunter syndrome) is a lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase leading to tissue accumulation of glycosaminoglycans. It manifests with short stature, joint stiffness, coarse facial features, hepatosplenomegaly, and progressive mental retardation. Most children die in the first or second decade from pulmonary or cardiac involvement. Until recently, no specific treatment was available. A Phase II/III trial of idursulfase, a recombinant enzyme replacement therapy for this disorder, demonstrated significant improvement in a 6-min walk test and in pulmonary function tests, and a decrease in liver and spleen size among those receiving active therapy once weekly. Major side effects include allergic reactions, which generally are easily managed and do not require discontinuing therapy. Idursulfase is now approved in the US, and should provide significant improvement in quality of life for these individuals. This article reviews the disease and treatment, with comments on future therapeutic directions.