Improvement in behaviour after substrate deprivation therapy with rhodamine B in a mouse model of MPS IIIA

Substrate reduction using a glucosamine analogue in Drosophila melanogaster and mouse models of Sanfilippo syndrome

Mucopolysaccharidosis (MPS) types III A and C are inherited neurodegenerative disorders resulting from the lack of a specific enzyme involved in heparan sulfate (HS) catabolism, leading to the accumulation of partially-degraded HS fragments. At present, there are no approved treatments and death is commonly in the second decade of life. Several therapies have undergone pre-clinical evaluation for these conditions, including substrate reduction therapy, with the most studied compound of this class being the isoflavone genistein. However, findings from a Phase III clinical trial demonstrated that high dose oral genistein did not significantly improve neurodevelopmental outcomes in patients with MPS III (Sanfilippo syndrome). Here, we have tested an N-acetylglucosamine analogue, 4-deoxy-N-acetylglucosamine peracetate, as a novel substrate reduction therapy for HS-storing lysosomal storage disorders such as MPS III. Treatment with this compound significantly reduced HS levels in cultured MPS IIIA patient and mouse fibroblasts in a time- and dose-dependent manner. MPS IIIC Drosophila fed 4-deoxy-N-acetylglucosamine peracetate contained significantly less HS relative to those raised on control diets. Likewise, improvements in HS load within the MPS IIIA mouse brain suggests that the compound crossed the blood-brain barrier after oral administration. Although long-term studies are needed, these findings indicate that 4-deoxy-GlcNAc peracetate may be beneficial in slowing the accumulation of HS and may represent a novel substrate reduction therapeutic for MPS III and potentially other HS-storing disorders.

The diagnosis and management of mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II) is a rare X-linked recessive inherited lysosomal storage disease. With pathogenic variants of the IDS gene, the activity of iduronate-2-sulfatase (IDS) is reduced or lost, causing the inability to degrade glycosaminoglycans (GAGs) in cells and influencing cell function, eventually resulting in multisystemic manifestations, such as a coarse face, dysostosis multiplex, recurrent respiratory tract infections, and hernias. Diagnosing MPS II requires a combination of clinical manifestations, imaging examinations, urinary GAGs screening, enzyme activity, and genetic testing. Currently, symptomatic treatment is the main therapeutic approach. Owing to economic and drug availability issues, only a minority of patients opt for enzyme replacement therapy or hematopoietic stem cell transplantation. The limited awareness of the disease, the lack of widespread detection technology, and uneven economic development contribute to the high rates of misdiagnosis and missed diagnosis in China.

Neurocognitive testing in a murine model of mucopolysaccharidosis type IIIA

Mucopolysaccharidosis type IIIA (MPS IIIA) is an inherited metabolic disorder caused by a lysosomal enzyme deficiency resulting in heparan sulphate (HS) accumulation and manifests with a progressive neurodegenerative phenotype. A naturally occurring MPS IIIA mouse model is invaluable for preclinical evaluation of potential treatments but the ability to effectively assess neurological function has proved challenging. Here, the aim was to evaluate a set of behaviour tests for their reliability in assessing disease progression in the MPS IIIA mouse model. Compared to wild-type (WT) mice, MPS IIIA mice displayed memory and learning deficits in the water crossmaze from mid-stage disease and locomotor impairment in the hind-limb gait assessment at late-stage disease, supporting previous findings. Declined wellbeing was also observed in the MPS IIIA mice via burrowing and nest building evaluation at late-stage disease compared to WT mice, mirroring the progressive nature of neurological disease. Excessive HS accumulation observed in the MPS IIIA mouse brain from 1 month of age did not appear to manifest as abnormal behaviours until at least 6 months of age suggesting there may be a threshold of HS accumulation before measurable neurocognitive decline. Results obtained from the open field and three-chamber sociability test are inconsistent with previous studies and do not reflect MPS IIIA patient disease progression, suggesting these assessments are not reliable. In conclusion, water cross-maze, hind-limb gait, nest building and burrowing, are promising assessments in the MPS IIIA mouse model, which produce consistent results that mimic the human disease.

Differences in gene expression patterns, revealed by RNA-seq analysis, between various Sanfilippo and Morquio disease subtypes

Mucopolysaccharidoses (MPS) are genetic disorders that affect up to 1 in 25,000 births. They are caused by dysfunctions of lysosomal hydrolases that degrade glycosaminoglycans (GAGs) which accumulate in cells, damaging their proper functioning. There are 7 types of MPS, distinguished by the kind of accumulated GAG and the defective enzyme, which differ significantly in the course of the disease. Despite the storage of the same GAGs, two of them (MPS III and IV) are divided into subtypes. While the course of MPS IV A and B is similar, the variability between MPS III A, B, C and D is high. This suggests that there are additional aspects that could influence the course of the disease. Therefore, the aim of this study was to determine differences of patterns of gene expression between all MPS III and IV subtypes. Transcriptomic studies, carried out with dermal fibroblasts from patients with all MPS III and IV subtypes, showed a significant variation in the gene expression pattern between individual MPS III subtypes, in contrast to MPS IV. Detailed analysis of transcripts with altered expression levels between MPS III subtypes indicated that these transcripts are mainly involved in maintaining the proper structure of connective tissue (COL4A1, COL4A2, COMP) and the structure of ribosomes (RPL10, RPL23, RPLP2). The results presented in this study indicate a significant role of genetic factors in the diversified course of MPS III subtypes.

Novel therapies for mucopolysaccharidosis type III

Mucopolysaccharidosis type III (MPS III) or Sanfilippo disease is an orphan inherited lysosomal storage disease and one of the most common MPS subtypes. The classical presentation is an infantile-onset neurodegenerative disease characterised by intellectual regression, behavioural and sleep disturbances, loss of ambulation, and early death. Unlike other MPS, no disease-modifying therapy has yet been approved. Here, we review the numerous approaches of curative therapy developed for MPS III from historical ineffective haematopoietic stem cell transplantation and substrate reduction therapy to the promising ongoing clinical trials based on enzyme replacement therapy or adeno-associated or lentiviral vectors mediated gene therapy. Preclinical studies are presented alongside the most recent translational first-in-man trials. In addition, we present experimental research with preclinical mRNA and gene editing strategies. Lessons from animal studies and clinical trials have highlighted the importance of an early therapy before extensive neuronal loss. A disease-modifying therapy for MPS III will undoubtedly mandate development of new strategies for early diagnosis.

Failures of Endochondral Ossification in the Mucopolysaccharidoses

PURPOSE OF REVIEW

The mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage disorders characterized by abnormal accumulation of glycosaminoglycans (GAGs) in cells and tissues. MPS patients frequently exhibit failures of endochondral ossification during postnatal growth leading to skeletal deformity and short stature. In this review, we outline the current understanding of the cellular and molecular mechanisms underlying failures of endochondral ossification in MPS and discuss associated treatment challenges and opportunities.

RECENT FINDINGS

Studies in MPS patients and animal models have demonstrated that skeletal cells and tissues exhibit significantly elevated GAG storage from early in postnatal life and that this is associated with impaired cartilage-to-bone conversion in primary and secondary ossification centers, and growth plate dysfunction. Recent studies have begun to elucidate the underlying cellular and molecular mechanisms, including impaired chondrocyte proliferation and hypertrophy, diminished growth factor signaling, disrupted cell cycle progression, impaired autophagy, and increased cell stress and apoptosis. Current treatments such as hematopoietic stem cell transplantation and enzyme replacement therapy fail to normalize endochondral ossification in MPS. Emerging treatments including gene therapy and small molecule-based approaches hold significant promise in this regard. Failures of endochondral ossification contribute to skeletal deformity and short stature in MPS patients, increasing mortality and reducing quality of life. Early intervention is crucial for effective treatment, and there is a critical need for new approaches that normalize endochondral ossification by directly targeting affected cells and signaling pathways.

Comparative analysis of brain pathology in heparan sulphate storing mucopolysaccharidoses

The cause of neurodegeneration in MPS mouse models is the focus of much debate and what the underlying cause of disease pathology in MPS mice is. The timing of development of pathology and when this can be reversed or impacted is the key to developing suitable therapies in MPS. This study is the first of its kind to correlate the biochemical changes with the functional outcome as assessed using non-invasive behaviour testing across multiple mucopolysaccharidosis (MPS) mouse models. In the MPS brain, the primary lysosomal enzyme dysfunction leads to accumulation of primary glycosaminoglycans (GAGs) with gangliosides (G_M2 and G_M3) being the major secondary storage products. With a focus on the neuropathology, a time course experiment was conducted in MPS I, MPS IIIA, MPS VII (severe and attenuated models) in order to understand the relative timing and level of GAG and ganglioside accumulation and how this correlates to behaviour deficits. Time course analysis from 1 to 6 months of age was conducted on brain samples to assess primary GAG (uronic acid), β-hexosaminidase enzyme activity and levels of G_M2 and G_M3 gangliosides. This was compared to a battery of non-invasive behaviour tests including open field, inverted grid, rotarod and water cross maze were assessed to determine effects on motor function, activity and learning ability. The results show that the GAG and ganglioside accumulation begins prior to the onset of detectable changes in learning ability and behaviour. Interestingly, the highest levels of GAG and ganglioside accumulation was observed in the MPS IIIA mouse despite having 3% residual enzyme activity. Deficits in motor function were clearly observed in the severe Gus^mps/mps_, which were significantly delayed in the attenuated Gus^tm(L175F)Sly model despite their minimal increase in detectable enzyme activity. This suggests that genotype and residual enzyme activity are not indicative of severity of disease pathology in MPS disease and there exists a window when there are considerable storage products without detectable functional deficits which may allow an alteration to occur with therapy.

Pre-clinical Mouse Models of Neurodegenerative Lysosomal Storage Diseases

There are over 50 lysosomal hydrolase deficiencies, many of which cause neurodegeneration, cognitive decline and death. In recent years, a number of broad innovative therapies have been proposed and investigated for lysosomal storage diseases (LSDs), such as enzyme replacement, substrate reduction, pharmacologic chaperones, stem cell transplantation, and various forms of gene therapy. Murine models that accurately reflect the phenotypes observed in human LSDs are critical for the development, assessment and implementation of novel translational therapies. The goal of this review is to summarize the neurodegenerative murine LSD models available that recapitulate human disease, and the pre-clinical studies previously conducted. We also describe some limitations and difficulties in working with mouse models of neurodegenerative LSDs.

Neuronal and Astrocytic Differentiation from Sanfilippo C Syndrome iPSCs for Disease Modeling and Drug Development

Sanfilippo syndrome type C (mucopolysaccharidosis IIIC) is an early-onset neurodegenerative lysosomal storage disorder, which is currently untreatable. The vast majority of studies focusing on disease mechanisms of Sanfilippo syndrome were performed on non-neural cells or mouse models, which present obvious limitations. Induced pluripotent stem cells (iPSCs) are an efficient way to model human diseases in vitro. Recently developed transcription factor-based differentiation protocols allow fast and efficient conversion of iPSCs into the cell type of interest. By applying these protocols, we have generated new neuronal and astrocytic models of Sanfilippo syndrome using our previously established disease iPSC lines. Moreover, our neuronal model exhibits disease-specific molecular phenotypes, such as increase in lysosomes and heparan sulfate. Lastly, we tested an experimental, siRNA-based treatment previously shown to be successful in patients' fibroblasts and demonstrated its lack of efficacy in neurons. Our findings highlight the need to use relevant human cellular models to test therapeutic interventions and shows the applicability of our neuronal and astrocytic models of Sanfilippo syndrome for future studies on disease mechanisms and drug development.

Molecular Bases of Neurodegeneration and Cognitive Decline, the Major Burden of Sanfilippo Disease

The mucopolysaccharidoses (MPS) are a group of diseases caused by the lysosomal accumulation of glycosaminoglycans, due to genetic deficiencies of enzymes involved in their degradation. MPS III or Sanfilippo disease, in particular, is characterized by early-onset severe, progressive neurodegeneration but mild somatic involvement, with patients losing milestones and previously acquired skills as the disease progresses. Despite being the focus of extensive research over the past years, the links between accumulation of the primary molecule, the glycosaminoglycan heparan sulfate, and the neurodegeneration seen in patients have yet to be fully elucidated. This review summarizes the current knowledge on the molecular bases of neurological decline in Sanfilippo disease. It emerges that this deterioration results from the dysregulation of multiple cellular pathways, leading to neuroinflammation, oxidative stress, impaired autophagy and defects in cellular signaling. However, many important questions about the neuropathological mechanisms of the disease remain unanswered, highlighting the need for further research in this area.

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.

Safety Study of Sodium Pentosan Polysulfate for Adult Patients with Mucopolysaccharidosis Type II

Current therapies for the mucopolysaccharidoses (MPS) do not effectively address skeletal and neurological manifestations. Pentosan polysulfate (PPS) is an alternative treatment strategy that has been shown to improve bone architecture, mobility, and neuroinflammation in MPS animals. The aims of this study were to a) primarily establish the safety of weekly PPS injections in attenuated MPS II, b) assess the efficacy of treatment on MPS pathology, and c) define appropriate clinical endpoints and biomarkers for future clinical trials. Subcutaneous injections were administered to three male Japanese patients for 12 weeks. Enzyme replacement therapy was continued in two of the patients while they received PPS and halted for two months in one patient before starting PPS. During treatment, one patient experienced an elevation of alanine transaminase, and another patient experienced convulsions; however, these incidences were non-cumulative and unrelated to PPS administration, respectively. Overall, the drug was well-tolerated in all patients, and no serious drug-related adverse events were noted. Generally, PPS treatment led to an increase in several parameters of shoulder range of motion and decrease of the inflammatory cytokines, MIF and TNF-α, which are potential clinical endpoints and biomarkers, respectively. Changes in urine and serum glycosaminoglycans were inconclusive. Overall, this study demonstrates the safety of using PPS in adults with MPS II and suggests the efficacy of PPS on MPS pathology with the identification of potential clinical endpoints and biomarkers.

Mucopolysaccharidosis type II (Hunter syndrome): Clinical and biochemical aspects of the disease and approaches to its diagnosis and treatment

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is a rare X-linked lysosomal storage disease caused by mutations of the gene encoding the lysosomal enzyme iduronate-2-sulfatase (IDS), the role of which is to hydrolytically remove O-linked sulfates from the two glycosaminoglycans (GAGs) heparan sulfate (HS) and dermatan sulfate (DS). HS and DS are linear, heterogeneous polysaccharides composed of repeating disaccharide subunits of l-iduronic acid (IdoA) or d-glucuronic acid, (1→4)-linked to d-glucosamine (for HS), or (1→3)-linked to 2-acetamido-2-deoxy-d-galactose (N-acetyl-d-galactosamine) (for DS). In healthy cells, IDS cleaves the sulfo group found at the C-2 position of terminal non-reducing end IdoA residues in HS and DS. The loss of IDS enzyme activity leads to progressive lysosomal storage of HS and DS in tissues and organs such as the brain, liver, spleen, heart, bone, joints and airways. Consequently, this leads to the phenotypic features characteristic of the disease. This review provides an overview of the disease profile and clinical manifestation, with a particular focus on the biochemical basis of the disease and chemical approaches to the development of new diagnostics, as well as discussing current treatment options and emerging new therapies.

Therapeutic Options for Mucopolysaccharidoses: Current and Emerging Treatments

Mucopolysaccharidoses (MPS) are inborn errors of metabolism produced by a deficiency of one of the enzymes involved in the degradation of glycosaminoglycans (GAGs). Although taken separately, each type is rare. As a group, MPS are relatively frequent, with an overall estimated incidence of around 1 in 20,000-25,000 births. Development of therapeutic options for MPS, including hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT), has modified the natural history of many MPS types. In spite of the improvement in some tissues and organs, significant challenges remain unsolved, including blood-brain barrier (BBB) penetration and treatment of lesions in avascular cartilage, heart valves, and corneas. Newer approaches, such as intrathecal ERT, ERT with fusion proteins to cross the BBB, gene therapy, substrate reduction therapy (SRT), chaperone therapy, and some combination of these strategies may provide better outcomes for MPS patients in the near future. As early diagnosis and early treatment are imperative to improve therapeutic efficacy, the inclusion of MPS in newborn screening programs should enhance the potential impact of treatment in reducing the morbidity associated with MPS diseases. In this review, we evaluate available treatments, including ERT and HSCT, and future treatments, such as gene therapy, SRT, and chaperone therapy, and describe the advantages and disadvantages. We also assess the current clinical endpoints and biomarkers used in clinical trials.

Treatment of brain disease in the mucopolysaccharidoses

The mucopolysaccharidosis (MPS) disorders are a group of lysosomal storage diseases caused by lysosomal enzyme deficits that lead to glycosaminoglycan accumulation, affecting various tissues throughout the body based on the specific enzyme deficiency. These disorders are characterized by their progressive nature and a variety of somatic manifestations and neurological symptoms. There are established treatments for some MPS disorders, but these mostly alleviate somatic and non-neurological symptoms and do not cure the disease. Patients with MPS I, II, III, and VII can present with neurological manifestations such as neurocognitive decline and behavioral problems. Treatment of these neurological manifestations remains challenging due to the blood-brain barrier (BBB) that limits delivery of therapeutic agents to the central nervous system (CNS). New therapies that circumvent this barrier and target brain disease in MPS are currently under development. They primarily focus on facilitating penetration of drugs through the BBB, delivery of recombinant enzyme to the brain by gene therapy, or direct CNS administration. This review summarizes existing and potential future treatment approaches that target brain disease in MPS. The information in this review is based on current literature and presentations and discussions during a closed meeting by an international group of experts with extensive experience in managing and treating MPS.

Substrate Deprivation Therapy to Reduce Glycosaminoglycan Synthesis Improves Aspects of Neurological and Skeletal Pathology in MPS I Mice

Mucopolysaccharidosis type I (MPS I) is the most common form of the MPS group of genetic diseases. MPS I results from a deficiency in the lysosomal enzyme α-l-iduronidase, leading to accumulation of undegraded heparan and dermatan sulphate glycosaminoglycan (GAG) chains in patient cells. MPS children suffer from multiple organ failure and die in their teens to early twenties. In particular, MPS I children also suffer from profound mental retardation and skeletal disease that restricts growth and movement. Neither brain nor skeletal disease is adequately treated by current therapy approaches. To overcome these barriers to effective therapy we have developed and tested a treatment called substrate deprivation therapy (SDT). MPS I knockout mice were treated with weekly intravenous injections of 1 mg/kg rhodamine B for six months to assess the efficacy of SDT. Mice were assessed using biochemistry, micro-CT and a battery of behaviour tests to determine the outcome of treatment. A reduction in female bodyweight gain was observed with the treatment as well as a decrease in lung GAG. Behavioural studies showed slight improvements in inverted grid and significant improvements in learning ability for female MPS I mice treated with rhodamine B. Skeletal disease also improved with a reduction in bone mineral volume observed. Overall, rhodamine B is safe to administer to MPS I knockout mice where it had an effect on improving aspects of neurological and skeletal disease symptoms and may therefore provide a potential therapy or adjunct therapy for MPS I patients.

Less Is More: Substrate Reduction Therapy for Lysosomal Storage Disorders

Lysosomal storage diseases (LSDs) are a group of rare, life-threatening genetic disorders, usually caused by a dysfunction in one of the many enzymes responsible for intralysosomal digestion. Even though no cure is available for any LSD, a few treatment strategies do exist. Traditionally, efforts have been mainly targeting the functional loss of the enzyme, by injection of a recombinant formulation, in a process called enzyme replacement therapy (ERT), with no impact on neuropathology. This ineffectiveness, together with its high cost and lifelong dependence is amongst the main reasons why additional therapeutic approaches are being (and have to be) investigated: chaperone therapy; gene enhancement; gene therapy; and, alternatively, substrate reduction therapy (SRT), whose aim is to prevent storage not by correcting the original enzymatic defect but, instead, by decreasing the levels of biosynthesis of the accumulating substrate(s). Here we review the concept of substrate reduction, highlighting the major breakthroughs in the field and discussing the future of SRT, not only as a monotherapy but also, especially, as complementary approach for LSDs.

N-butyldeoxynojirimycin treatment restores the innate fear response and improves learning in mucopolysaccharidosis IIIA mice

Mucopolysaccharidosis IIIA is a heritable neurodegenerative disorder resulting from the dysfunction of the lysosomal hydrolase sulphamidase. This leads to the primary accumulation of the complex carbohydrate heparan sulphate in a wide range of tissues and the secondary neuronal storage of gangliosides GM2 and GM3 in the brain. GM2 storage is associated with CNS deterioration in the GM2 gangliosidosis group of lysosomal storage disorders and may also contribute to MPS CNS disease. N-butyldeoxynojirimycin, an inhibitor of ceramide glucosyltransferase activity and therefore of ganglioside synthesis, was administered to MPS IIIA mice both prior to maximal GM2 and GM3 accumulation (early treatment) and after the maximum level of ganglioside had accumulated in the brain (late treatment) to determine if behaviour was altered by ganglioside level. Ceramide glucosyltransferase activity was decreased in both treatment groups; however, brain ganglioside levels were only decreased in the late treatment group. Learning in the water cross maze was improved in both groups and the innate fear response was also restored in both groups. A reduction in the expression of inflammatory gene Ccl3 was observed in the early treatment group, while IL1β expression was reduced in both treatment groups. Thus, it appears that NB-DNJ elicits a transient decrease in brain ganglioside levels, some modulation of inflammatory cytokines and a functional improvement in behaviour that can be elicited both before and after overt neurological changes manifest.

SYNOPSIS

NB-DNJ improves learning and restores the innate fear response in MPS IIIA mice by decreasing ceramide glucosyltransferase activity and transiently reducing ganglioside storage and/or modulating inflammatory signals.

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.

Sanfilippo syndrome: causes, consequences, and treatments

Sanfilippo syndrome, or mucopolysaccharidosis (MPS) type III, refers to one of five autosomal recessive, neurodegenerative lysosomal storage disorders (MPS IIIA to MPS IIIE) whose symptoms are caused by the deficiency of enzymes involved exclusively in heparan sulfate degradation. The primary characteristic of MPS III is the degeneration of the central nervous system, resulting in mental retardation and hyperactivity, typically commencing during childhood. The significance of the order of events leading from heparan sulfate accumulation through to downstream changes in the levels of biomolecules within the cell and ultimately the (predominantly neuropathological) clinical symptoms is not well understood. The genes whose deficiencies cause the MPS III subtypes have been identified, and their gene products, as well as a selection of disease-causing mutations, have been characterized to varying degrees with respect to both frequency and direct biochemical consequences. A number of genetic and biochemical diagnostic methods have been developed and adopted by diagnostic laboratories. However, there is no effective therapy available for any form of MPS III, with treatment currently limited to clinical management of neurological symptoms. The availability of animal models for all forms of MPS III, whether spontaneous or generated via gene targeting, has contributed to improved understanding of the MPS III subtypes, and has provided and will deliver invaluable tools to appraise emerging therapies. Indeed, clinical trials to evaluate intrathecally-delivered enzyme replacement therapy in MPS IIIA patients, and gene therapy for MPS IIIA and MPS IIIB patients are planned or underway.

Delivery of therapeutic protein for prevention of neurodegenerative changes: comparison of different CSF-delivery methods

Injection of lysosomal enzyme into cisternal or ventricular cerebrospinal fluid (CSF) has been carried out in 11 lysosomal storage disorder models, with each study demonstrating reductions in primary substrate and secondary neuropathological changes, and several reports of improved neurological function. Whilst acute studies in mucopolysaccharidosis (MPS) type II mice revealed that intrathecally-delivered enzyme (into thoraco-lumbar CSF) accesses the brain, the impact of longer-term treatment of affected subjects via this route is unknown. This approach is presently being utilized to treat children with MPS types I, II and III. Our aim was to determine the efficacy of repeated intrathecal injection of recombinant human sulfamidase (rhSGSH) on pathological changes in the MPS IIIA dog brain. The outcomes were compared with those in dogs treated via intra-cisternal or ventricular routes. Control dogs received buffer or no treatment. Significant reductions in primary/secondary substrate levels in brain were observed in dogs treated via all routes, although the extent of the reduction differed regionally. Treatment via all CSF access points resulted in large reductions in microgliosis in superficial cerebral cortex, but only ventricular injection enabled amelioration in deep cerebral cortex. Formation of glutamic acid decarboxylase-positive axonal spheroids in deep cerebellar nuclei was prevented by treatment delivered via any route. Anti-rhSGSH antibodies in the sera of some dogs did not reduce therapeutic efficacy. Our data indicates the capacity of intra-spinal CSF-injected rhSGSH to circulate within CSF-filled spaces, penetrate into brain and mediate a significant reduction in substrate accumulation and secondary pathology in the MPS IIIA dog brain.

Factors and processes modulating phenotypes in neuronopathic lysosomal storage diseases

Lysosomal storage diseases are inherited metabolic disorders caused by genetic defects causing deficiency of various lysosomal proteins, and resultant accumulation of non-degraded compounds. They are multisystemic diseases, and in most of them (>70%) severe brain dysfunctions are evident. However, expression of various phenotypes in particular diseases is extremely variable, from non-neuronopathic to severely neurodegenerative in the deficiency of the same enzyme. Although all lysosomal storage diseases are monogenic, clear genotype-phenotype correlations occur only in some cases. In this article, we present an overview on various factors and processes, both general and specific for certain disorders, that can significantly modulate expression of phenotypes in these diseases. On the basis of recent reports describing studies on both animal models and clinical data, we propose a hypothesis that efficiency of production of compounds that cannot be degraded due to enzyme deficiency might be especially important in modulation of phenotypes of patients suffering from lysosomal storage diseases.

Current and potential therapeutic strategies for mucopolysaccharidoses

WHAT IS KNOWN AND OBJECTIVE

Mucopolysaccharidoses (MPSs) are a group of rare inherited metabolic diseases caused by genetic defects in the production of lysosomal enzymes. MPSs are clinically heterogeneous and are characterized by progressive deterioration in visceral, skeletal and neurological functions. This article aims to review the classification and pathophysiology of MPSs and discuss current therapies and new targeted agents under development.

METHODS

A Medline search through PubMed was performed for relevant articles and treatment guidelines on MPSs published in English for years 1970 to September of 2013 inclusive. The references listed in the identified articles, prescribing information of the drugs approved for the treatment of MPSs, as well as recent clinical trial information posted on Clinicaltrials.gov website, were reviewed.

RESULTS AND DISCUSSION

Until recently, supportive care was the only option available for the management of MPSs. In the early 2000s, enzyme replacement therapy (ERT) was approved by the United States Food and Drug Administration (FDA) for the treatment of MPS I, II and VI. Clinical trials of ERT showed substantial improvements in patients' somatic symptoms; however, no benefit was found in the neurological symptoms because the enzymes do not readily cross the blood-brain barrier (BBB). Haematopoietic stem cell transplantation (HSCT), another potentially curative treatment, is not routinely advocated in clinical practice due to its high risk profile and lack of evidence for efficacy, except in preserving cognition and prolonging survival in young patients with severe MPS I. In recent years, substrate reduction therapy (SRT) and gene therapy have been rapidly gaining greater recognition as potential therapeutic avenues.

WHAT IS NEW AND CONCLUSION

Enzyme replacement therapy (ERT) is effective for the treatment of many somatic symptoms, particularly walking ability and respiratory function, and remains the mainstay of MPS treatment. The usefulness of HSCT has not been established adequately for most MPSs. Although still under investigation, SRT and gene therapy are promising MPS treatments that may prevent the neurodegeneration not affected by ERT.

An update on ocular involvement in mucopolysaccharidoses

PURPOSE OF REVIEW

The purpose of this review is to provide an update on ocular manifestations of mucopolysaccharidoses (MPS), to highlight diagnostic pitfalls in the evaluation of affected patients, and to briefly review etiopathogenesis, systemic manifestations, and therapeutic interventions in MPS.

RECENT FINDINGS

Advances in hematopoietic stem cell transplantation and enzyme replacement therapy for MPS have led to decreased morbidity and increased life-span of patients. Besides other causes, visual impairment because of corneal opacification, retinal degeneration, and optic atrophy remains a common cause of disability in MPS. The application of a standard ophthalmic evaluation protocol may serve as an important diagnostic and disease monitoring tool in patients.

SUMMARY

Diagnostic delays are not uncommon in patients with MPS. Given the early ocular involvement in MPS, ophthalmologists play a crucial role in early detection and follow-up of patients with MPS. Ophthalmic evaluation can be impeded by corneal opacification and patient cooperation. Altered corneal biomechanics confound intraocular pressure measurements. Recently developed therapies have made early detection increasingly important. Accurate diagnosis of specific MPS subtypes is of paramount importance for initiating appropriate therapy. Combined with advances in supportive care of ocular and systemic manifestations, the prognosis for patients with MPS has vastly improved.

Putative biological mechanisms of efficiency of substrate reduction therapies for mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are inherited metabolic diseases caused by mutations in genes coding for lysosomal enzymes involved in the degradation of glycosaminoglycans (GAGs). Dysfunction of any of these enzymes results in the accumulation of GAGs, which leads to severe clinical symptoms and significantly shortened life span. Several kinds of therapies have been proposed to treat MPS, including bone marrow or stem cell transplantation, enzyme replacement therapy, and gene therapy. Another option is substrate reduction therapy (SRT), in which synthesis of GAGs is inhibited. Recent studies employing in vitro and animal models suggested that this therapy may be efficient in decreasing levels of GAGs in MPS cells, including those bearing two null alleles of the affected gene. Results of behavioral tests in animals as well as some preliminary clinical observations with pediatric patients corroborated the suggestions about possible efficacy of SRT in MPS treatment, including brain functions. Efficient reduction of GAG levels in MPS cells homozygous for null mutations may be intriguing in the commonly accepted scheme of SRT mode of action. In this paper, we propose an explanation of this phenomenon, based on already known facts. Thus, we suggest that SRT may lead to reduction of GAG levels in MPS cells due to inhibition of efficiency of GAG synthesis combined with (a) any readthrough of the stop codon, (b) dilution of already accumulated GAGs due to cell growth followed by cell divisions, and (c) action of endoglycosidases degrading GAGs, e.g., heparanase, in combination with functional GAG-specific hydrolases.

Synthetic genistein derivatives as modulators of glycosaminoglycan storage

Background

Mucopolysaccharidoses (MPS) are severe metabolic disorders caused by accumulation of undegraded glycosaminoglycans (GAGs) in lysosomes due to defects in certain lysosomal hydrolases. Substrate reduction therapy (SRT) has been proposed as one of potential treatment procedures of MPS. Importantly, small molecules used in such a therapy might potentially cross the blood–brain barrier (BBB) and improve neurological status of patients, as reported for a natural isoflavone, 5, 7-dihydroxy-3- (4-hydroxyphenyl)-4 H-1-benzopyran-4-one, also known as genistein. Although genistein is able to cross BBB to some extent, its delivery to the central nervous system is still relatively poor (below 10% efficiency). Thus, we aimed to develop a set of synthetically modified genistein molecules and characterize physicochemical as well as biological properties of these compounds.

Methods

Following parameters were determined for the tested synthetic derivatives of genistein: cytotoxicity, effects on cell proliferation, kinetics of GAG synthesis, effects on epidermal growth factor (EGF) receptor’s tyrosine kinase activity, effects on lysosomal storage, potential ability to cross BBB.

Results

We observed that some synthetic derivatives inhibited GAG synthesis similarly to, or more efficiently than, genistein and were able to reduce lysosomal storage in MPS III fibroblasts. The tested compounds were generally of low cytotoxicity and had minor effects on cell proliferation. Moreover, synthetic derivatives of genistein revealed higher lipophilicity (assessed in silico) than the natural isoflavone.

Conclusion

Some compounds tested in this study might be promising candidates for further studies on therapeutic agents in MPS types with neurological symptoms.

Skeletal response to lentiviral mediated gene therapy in a mouse model of MPS VII

Mucopolysaccharidosis VII (MPS VII) is an autosomal recessive, lysosomal storage disorder caused by β-glucuronidase (GUSB) deficiency, resulting in the accumulation of glycosaminoglycans (GAGs), in a variety of cell types. Severe, progressive skeletal pathology, termed dysostosis multiplex, is a prominent clinical feature of MPS VII. We have evaluated a gene therapy protocol for its efficacy in preventing the development and progression of bone pathology in MPS VII mice treated with a lentiviral vector at birth or at 7 weeks. Two weeks after injections, high levels of vector expression were observed in liver, spleen and bone marrow and to a lesser extent in kidney, lung and heart. Widespread clearance of GAG storage was observed in somatic tissues of both groups and some clearance of neuronal storage was observed in mice treated from birth. Micro-CT analysis demonstrated a significant decrease in vertebral and femoral bone mineral volume, trabecular number, bone surface density and cortical bone thickness in both treatment groups. Lumbar and femoral bone lengths were significantly decreased in untreated MPS VII mice, while growth plate heights were increased and these parameters did not change upon treatment. Small improvements in performance in the open field and rotarod behaviour tests were noted. Overall, systemic lentiviral-mediated gene therapy results in a measurable improvement in parameters of bone mass and architecture as well as biochemical and enzymatic correction. Conversely, growth plate chondrocytes were not responsive to treatment, as evidenced by the lack of improvement in vertebral and femoral bone length and growth plate height.

Rhodamine B and 2-acetamido-1,3,6-tri-O-acetyl-4-deoxy-4-fluoro-D-glucopyranose (F-GlcNAc) inhibit chondroitin/dermatan and keratan sulphate synthesis by different mechanisms in bovine chondrocytes

MPS disorders result from a deficiency or absence of glycosaminoglycan (GAG) degrading enzymes leading to an imbalance between the synthesis and degradation of GAGs and their subsequent accumulation in a range of cells. The inhibition of GAG synthesis using small chemical inhibitors has been proposed as a novel therapeutic approach to treatment. Several inhibitors have been shown to decrease heparan sulphate GAG synthesis and in this study we evaluated a novel fluorinated analog of N-acetylglucosamine (2-acetamido-1,3,6-tri-O-acetyl-4-deoxy-4-fluoro-D-glucopyranose (F-GlcNAc)) and rhodamine B for their ability to also inhibit the synthesis of chondroitin/dermatan and keratan sulphate GAGs present in bovine cartilage. Both inhibitors decreased GAG synthesis in chondrocyte monolayer culture and in cartilage chip explant culture in a dose dependent manner. Both inhibitors decreased the size of newly synthesised proteoglycans and in the case of F-GlcNAc this was due to a decrease in newly synthesised GAG chain size. Rhodamine B, however, did not affect GAG chain size, while both inhibitors decreased the amount of chondroitin/dermatan and keratan sulphate GAG equally. The expression of genes responsible for the initiation and elongation of chondroitin/dermatan sulphate and keratan sulphate GAGs were downregulated in the presence of rhodamine B but not in the presence of F-GlcNAc. Thus the 2 inhibitors appear to have differing effects on GAG synthesis, with F-GlcNAc inhibiting the epimerisation of UDP-GlcNAc to UDP-GalNAc thus decreasing the availability of monosaccharides for addition to the growing GAG chain, whereas rhodamine B is more likely to reduce the number of GAG chains. Together with previous data these 2 inhibitors are capable of non-specific inhibition of GAG synthesis, reducing the production of chondroitin/dermatan sulphate, keratan sulphate and heparan sulphate GAGs. As such they would be applicable to therapy in a range of MPS disorders.

Gene expression-targeted isoflavone therapy

Lysosomal storage diseases (LSD) form a group of inherited metabolic disorders caused by dysfunction of one of the lysosomal proteins, resulting in the accumulation of certain compounds. Although these disorders are among first genetic diseases for which specific treatments were proposed, there are still serious unsolved problems that require development of novel therapeutic procedures. An example is neuronopathy, which develops in most of LSD and cannot be treated efficiently by currently approved therapies. Recently, a new potential therapy, called gene expression-targeted isoflavone therapy (GET IT), has been proposed for a group of LSD named mucopolysaccharidoses (MPS), in which storage of incompletely degraded glycosaminoglycans (GAGs) results in severe symptoms of virtually all tissues and organs, including central nervous system. The idea of this therapy is to inhibit synthesis of GAGs by modulating expression of genes coding for enzymes involved in synthesis of these compounds. Such a modulation is possible by using isoflavones, particularly genistein, which interfere with a signal transduction process necessary for stimulation of expression of certain genes. Results of in vitro experiments and studies on animal models indicated a high efficiency of GET IT, including correction of behavior of affected mice. However, clinical trials, performed with soy isoflavone extracts, revealed only limited efficacy. This caused a controversy about GET IT as a potential, effective treatment of patients suffering from MPS, especially neuronopathic forms of these diseases. It this critical review, I present possible molecular mechanisms of therapeutic action of isoflavones (particularly genistein) and suggest that efficacy of GET IT might be sufficiently high when using relatively high doses of synthetic genistein (which was employed in experiments on cell cultures and mouse models) rather than low doses of soy isoflavone extracts (which were used in clinical trials). This proposal can be tested in double-blinded, placebo-controlled clinical trials.

Female mucopolysaccharidosis IIIA mice exhibit hyperactivity and a reduced sense of danger in the open field test

Reliable behavioural tests in animal models of neurodegenerative diseases allow us to study the natural history of disease and evaluate the efficacy of novel therapies. Mucopolysaccharidosis IIIA (MPS IIIA or Sanfilippo A), is a severe, neurodegenerative lysosomal storage disorder caused by a deficiency in the heparan sulphate catabolising enzyme, sulfamidase. Undegraded heparan sulphate accumulates, resulting in lysosomal enlargement and cellular dysfunction. Patients suffer a progressive loss of motor and cognitive function with severe behavioural manifestations and premature death. There is currently no treatment. A spontaneously occurring mouse model of the disease has been described, that has approximately 3% of normal enzyme activity levels. Behavioural phenotyping of the MPS IIIA mouse has been previously reported, but the results are conflicting and variable, even after full backcrossing to the C57BL/6 background. Therefore we have independently backcrossed the MPS IIIA model onto the C57BL/6J background and evaluated the behaviour of male and female MPS IIIA mice at 4, 6 and 8 months of age using the open field test, elevated plus maze, inverted screen and horizontal bar crossing at the same circadian time point. Using a 60 minute open field, we have demonstrated that female MPS IIIA mice are hyperactive, have a longer path length, display rapid exploratory behaviour and spend less time immobile than WT mice. Female MPS IIIA mice also display a reduced sense of danger and spend more time in the centre of the open field. There were no significant differences found between male WT and MPS IIIA mice and no differences in neuromuscular strength were seen with either sex. The altered natural history of behaviour that we observe in the MPS IIIA mouse will allow more accurate evaluation of novel therapeutics for MPS IIIA and potentially other neurodegenerative disorders.

Glycosaminoglycan storage disorders: a review

Impaired degradation of glycosaminoglycans (GAGs) with consequent intralysosomal accumulation of undegraded products causes a group of lysosomal storage disorders known as mucopolysaccharidoses (MPSs). Characteristically, MPSs are recognized by increased excretion in urine of partially degraded GAGs which ultimately result in progressive cell, tissue, and organ dysfunction. There are eleven different enzymes involved in the stepwise degradation of GAGs. Deficiencies in each of those enzymes result in seven different MPSs, all sharing a series of clinical features, though in variable degrees. Usually MPS are characterized by a chronic and progressive course, with different degrees of severity. Typical symptoms include organomegaly, dysostosis multiplex, and coarse facies. Central nervous system, hearing, vision, and cardiovascular function may also be affected. Here, we provide an overview of the molecular basis, enzymatic defects, clinical manifestations, and diagnosis of each MPS, focusing also on the available animal models and describing potential perspectives of therapy for each one.

Two-year follow-up of Sanfilippo Disease patients treated with a genistein-rich isoflavone extract: assessment of effects on cognitive functions and general status of patients

Background

Mucopolysaccharidoses (MPS) are inherited metabolic disorders caused by deficiencies in enzymes involved in degradation of glycosaminoglycans. MPS type III (Sanfilippo disease) is clinically characterized mainly by progressive and severe behavioral disturbances and cognitive dysfunction. Recent 1-year experimental treatment of 10 patients with a genistein (4′, 5, 7-trihydroxyisoflavone)-rich extract resulted in improvement of tested parameters, including cognitive and behavioral functions.

Material/Methods

Eight pediatric patients with Sanfilippo disease were enrolled into the study. The modified version of the Brief Assessment Examination was used to assess cognitive functions. Moreover, 18 different parameters concerning changes in conditions of patients were assessed by their parents.

Results

During the first year of the treatment, an improvement of cognitive functions in 7 patients and stabilization in 1 patient were assessed, while after the third year (2-year follow-up) further improvement was observed in 2 patients, stabilization in 3 patients and some deterioration in 3 patients. Monitoring of general and behavioral symptoms revealed improvement in all patients after the first year of the treatment, further improvement in 5 patients, and deterioration in 3 patients during the next 2 years.

Conclusions

We conclude that the treatment of Sanfilippo patients with a genistein-rich soy isoflavone extract (called gene expression-targeted isoflavone therapy [GET IT]) may be effective in either inhibition (in some patients) or slowing down (in other patients) of behavioral and cognitive problems over a longer period. An increased dose of genistein may improve the efficacy of the treatment.

Differential distribution of heparan sulfate glycoforms and elevated expression of heparan sulfate biosynthetic enzyme genes in the brain of mucopolysaccharidosis IIIB mice

The primary pathology in mucopolysaccharidosis (MPS) IIIB is lysosomal storage of heparan sulfate (HS) glycosaminoglycans, leading to complex neuropathology and dysfunction, for which the detailed mechanisms remain unclear. Using antibodies that recognize specific HS glycoforms, we demonstrate differential cell-specific and domain-specific lysosomal HS-GAG distribution in MPS IIIB mouse brain. We also describe a novel neuron-specific brain HS epitope with broad, non-specific increase in the expression in all neurons in MPS IIIB mouse brain, including cerebellar granule neurons, which do not exhibit lysosomal storage pathology. This suggests that biosynthesis of certain HS glycoforms is enhanced throughout the CNS of MPS IIIB mice. Such a conclusion is further supported by demonstration of increased expression of multiple genes encoding enzymes essential in HS biosynthesis, including HS sulfotransferases and epimerases, as well as FGFs, for which HS serves as a co-receptor, in MPS IIIB brain. These data suggest that lysosomal storage of HS may lead to the increase in HS biosyntheses, which may contribute to the neuropathology of MPS IIIB by exacerbating the lysosomal HS storage.

Effects of flavonoids on glycosaminoglycan synthesis: implications for substrate reduction therapy in Sanfilippo disease and other mucopolysaccharidoses

Sanfilippo disease (mucopolysaccharidosis type III, MPS III) is a severe metabolic disorder caused by accumulation of heparan sulfate (HS), one of glycosaminoglycans (GAGs), due to a genetic defect resulting in a deficiency of GAG hydrolysis. This disorder is characterized as the most severe neurological form of MPS, revealing rapid deterioration of brain functions. Among therapeutic approaches for MPS III, one of the most promising appears to be the substrate reduction therapy (SRT). Genistein (5, 7-dihydroxy-3- (4-hydroxyphenyl)-4H-1-benzopyran-4-one) is an isoflavone that has been used in SRT for MPS III. In this report, we tested effects of other flavonoids (apigenin, daidzein, kaempferol and naringenin) on GAG synthesis. Their cytotoxicity and anti-proliferation features were also tested. We found that daidzein and kaempferol inhibited GAG synthesis significantly. Moreover, these compounds were able to reduce lysosomal storage in MPS IIIA fibroblasts. Interestingly, although genistein is believed to inhibit GAG synthesis by blocking the tyrosine kinase activity of the epidermal growth factor receptor, we found that effects of other flavonoids were not due to this mechanism. In fact, combinations of various flavonoids resulted in significantly more effective inhibition of GAG synthesis than the use of any of these compounds alone. These results, together with results published recently by others, suggest that combination of flavonoids can be considered as a method for improvement of efficiency of SRT for MPS III.

Mouse mutagenesis and disease models for neuropsychiatric disorders

In this chapter, mutant mouse resources which have been developed by classical genetics as well as by modern large-scale mutagenesis projects are summarized. Various spontaneous and induced mouse mutations have been archived since the rediscovery of Mendel's genetics in 1900. Moreover, genome-wide, large-scale mutagenesis efforts have recently been expanding the available mutant mouse resources. Forward genetics projects using ENU mutagenesis in the mouse were started in the mid-1990s. The widespread adoption of reverse genetics, using knockouts and conditional mutagenesis based on gene-targeting technology, followed. ENU mutagenesis has now evolved to provide a further resource for reverse genetics, with multiple point mutations in a single gene and this new approach is described. Researchers now have various options to obtain mutant mice: point mutations, transgenic mouse strains, and constitutional or conditional knockout mice. The established mutant strains have already contributed to modeling human diseases by elucidating the underlying molecular mechanisms as well as by providing preclinical applications. Examples of mutant mice, focusing on neurological and behavioral models for human diseases, are reviewed. Human diseases caused by a single gene or a small number of major genes have been well modeled by corresponding mutant mice. Current evidence suggests that quantitative traits based on polygenes are likely to be associated with a range of psychiatric diseases, and these are now coming within the range of modeling by mouse mutagenesis.

Correction of mucopolysaccharidosis type IIIA somatic and central nervous system pathology by lentiviral-mediated gene transfer

BACKGROUND

The hallmark of lysosomal storage disorders (LSDs) is microscopically demonstrable lysosomal distension. In mucopolysaccharidosis type IIIA (MPS IIIA), this occurs as a result of an inherited deficiency of the lysosomal hydrolase sulphamidase. Consequently, heparan sulphate, a highly sulphated glycosaminoglycan, accumulates primarily within the cells of the reticulo-endothelial and monocyte-macrophage systems and, most importantly, neurones. Children affected by MPS IIIA experience a severe, progressive neuropathology that ultimately leads to death at around 15 years of age.

METHODS

MPS IIIA pathology was addressed in a mouse model using two separate methods of therapeutic gene delivery. A lentiviral vector expressing murine sulphamidase was delivered to 6-week-old MPS IIIA affected mice either by intravenous injection, or by intraventricular infusion. Therapeutic outcomes were assessed 7 months after gene transfer.

RESULTS

After intravenous gene delivery, liver sulphamidase was restored to approximately 30% of wild-type levels. The resultant widespread delivery of enzyme secreted from transduced cells to somatic tissues via the peripheral circulation corrected most somatic pathology. However, unlike an earlier study, central nervous system (CNS) pathology remained unchanged. Conversely, intraventricular gene delivery resulted in widespread sulphamidase gene delivery in (and reduced lysosomal storage throughout) the brain. Improvements in behaviour were observed in these mice, and interestingly, pathological urinary retention was prevented.

CONCLUSIONS

The CNS remains the last major barrier to effective therapy for children affected by LSDs. The blood-brain barrier (BBB) limits the uptake of lysosomal enzymes from the peripheral circulation into the CNS, making direct gene delivery to the brain a reasonable, albeit more challenging, therapeutic option. Future work will further assess the relative advantages of directly targeting the brain with somatic gene delivery with sulphamidase modified to increase the efficiency of transport across the BBB.

Trans-generational exposure to low levels of rhodamine B does not adversely affect litter size or liver function in murine mucopolysaccharidosis type IIIA

MPS IIIA is a lysosomal storage disorder caused by mutations in the sulphamidase gene, resulting in the accumulation of heparan sulphate glycosaminoglycans (HS GAGs). Symptoms predominantly manifest in the CNS and there is no current therapy that effectively addresses neuropathology in MPS IIIA patients. Recent studies in MPS IIIA mice have shown that rhodamine B substrate deprivation therapy (SDT) (also termed substrate reduction therapy/SRT) inhibits GAG biosynthesis and, improves both somatic and CNS disease pathology. Acute overexposure to high doses of rhodamine B results in liver toxicity and is detrimental to reproductive ability. However, the long-term effects of decreasing GAG synthesis, at the low dose sufficient to alter neurological function are unknown. A trans-generational study was therefore initiated to evaluate the continuous exposure of rhodamine B treatment in MPS IIIA mice over 4 generations, including treatment during pregnancy. No alterations in litter size, liver histology or liver function were observed. Overall, there are no long-term issues with the administration of rhodamine B at the low dose tested and no adverse effects were noted during pregnancy in mice.

Therapy for lysosomal storage disorders

In the last years, much progress has been achieved in the field of lysosomal storage disorders. In the past, no specific treatment was available for the affected patients; management mainly consisted of supportive care and treatment of complications. As orphan drug regulations, however, encouraged development of drugs for these disorders by granting marketing exclusivity for 10 years and other commercial benefits, enzyme replacement therapy became available for lysosomal storage disorders, such as Gaucher disease, Fabry disease, mucopolysaccharidoses type I, II, and VI, and Pompe disease. This review will summarize the efficacy and clinical status of hematopoietic stem cell transplantation, enzyme replacement, and substrate deprivation therapy, and describe new therapeutic perspectives currently under preclinical investigations such as chaperone-mediated therapy, stop-codon read-through therapy, and gene therapy.

Genistein: a natural isoflavone with a potential for treatment of genetic diseases

Genistein [4′,5,7-trihydroxyisoflavone or 5,7-dihydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one] is a natural isoflavone occurring in many plants known to possess various biological activities, ranging from phyto-oestrogenic to antioxidative actions. Recent studies indicated that this isoflavone can also be considered as a drug for as yet untreatable genetic diseases. In the present review, we discuss a plausible use of genistein in treatment of two genetic disorders: CF (cystic fibrosis) and MPS (mucopolysaccharidosis). Although various biological actions of genistein are employed in these two cases, in vitro studies, tests on animal models and pilot clinical trials suggest that this plant-derived compound might be a real hope for patients suffering from severe inherited disorders with relatively complicated pathomechanisms, including those affecting the central nervous system.

Treating lysosomal storage diseases with pharmacological chaperones: from concept to clinics

Lysosomal storage diseases (LSDs) are a group of genetic disorders due to defects in any aspect of lysosomal biology. During the past two decades, different approaches have been introduced for the treatment of these conditions. Among them, enzyme replacement therapy (ERT) represented a major advance and is used successfully in the treatment of some of these disorders. However, ERT has limitations such as insufficient biodistribution of recombinant enzymes and high costs. An emerging strategy for the treatment of LSDs is pharmacological chaperone therapy (PCT), based on the use of chaperone molecules that assist the folding of mutated enzymes and improve their stability and lysosomal trafficking. After proof-of-concept studies, PCT is now being translated into clinical applications for Fabry, Gaucher and Pompe disease. This approach, however, can only be applied to patients carrying chaperone-responsive mutations. The recent demonstration of a synergistic effect of chaperones and ERT expands the applications of PCT and prompts a re-evaluation of their therapeutic use and potential. This review discusses the strengths and drawbacks of the potential therapies available for LSDs and proposes that future research should be directed towards the development of treatment protocols based on the combination of different therapies to improve the clinical outcome of LSD patients.

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.

Impairment of glycosaminoglycan synthesis in mucopolysaccharidosis type IIIA cells by using siRNA: a potential therapeutic approach for Sanfilippo disease

Mucopolysaccharidoses (MPS) are severe inherited metabolic disorders from the group of lysosomal storage diseases. They are caused by deficiency in the activity of enzymes involved in the degradation of glycosaminoglycans (GAGs) and resultant accumulation of these compounds in the cells of patients. Although enzyme replacement therapy has become available for some MPS types (MPS I, MPS II and MPS VI), this treatment is not efficient when neurological symptoms occur, especially in MPS III (Sanfilippo disease). Recent studies indicated that substrate reduction therapy (SRT) may be an effective option for the treatment of neurodegenerative lysosomal storage diseases, including MPS III. However, previous attempts to SRT for MPS III focused on the use of non-specific inhibitors of GAG synthesis. Thus, we aimed to use the small interfering RNA (siRNA) procedure to control expression of particular genes, whose products are involved in GAG synthesis. In this report we show that, in MPS IIIA fibroblasts, we were able to reduce mRNA levels of four genes, XYLT1, XYLT2, GALTI and GALTII, whose products are involved in GAG synthesis. This decrease in levels of transcripts corresponded to a decrease in levels of proteins encoded by them. Moreover, efficiency of GAG production in these fibroblasts was considerably reduced after treatment of the cells with siRNA. These results indicate that efficient reduction of GAG synthesis may be achieved by the use of siRNA.

Gene silencing of EXTL2 and EXTL3 as a substrate deprivation therapy for heparan sulphate storing mucopolysaccharidoses

Neurological pathology is characteristic of the mucopolysaccharidoses (MPSs) that store heparan sulphate (HS) glycosaminoglycan (gag) and has been proven to be refractory to systemic therapies. Substrate deprivation therapy (SDT) using general inhibitors of gag synthesis improves neurological function in mouse models of MPS, but is not specific to an MPS type. We have investigated RNA interference (RNAi) as a method of targeting SDT to the HS synthesising enzymes, EXTL2 and EXTL3. Multiple shRNA molecules specific to EXTL2 or EXTL3 were designed and validated in a reporter gene assay, with four out of six shRNA constructs reducing expression by over 90%. The three EXTL2-specific shRNA constructs reduced endogenous target gene expression by 68, 32 and 65%, and decreased gag synthesis by 46, 50 and 27%. One EXTL3-specific shRNA construct reduced endogenous target gene expression by 14% and gag synthesis by 39%. Lysosomal gag levels in MPS IIIA and MPS I fibroblasts were also reduced by EXTL2 and EXTL3-specific shRNA. Incorporation of shRNAs into a lentiviral expression system reduced gene expression, and one EXTL2-specific shRNA reduced gag synthesis. These results indicate that deprivation therapy through shRNA-mediated RNAi has potential as a therapy for HS-storing MPSs.

Gastrointestinal pathology in a mouse model of mucopolysaccharidosis type IIIA

Mucopolysaccharidosis type IIIA (MPS IIIA) is a lysosomal storage disorder caused by a deficiency in sulphamidase (NS), a lysosomal enzyme required for the degradation of heparan sulphate glycosaminoglycans (gags). The MPS IIIA mouse is a naturally occurring model that accurately reflects the human pathology and disease course. It displays primarily central nervous system pathology accompanied by widespread accumulation of gag in somatic tissues. MPS IIIA mice exhibit greater bodyweight gain than normal littermates and attain a higher mature bodyweight. In this study, gastrointestinal morphology and function was characterised in the IIIA mouse. Stomach and duodenum weight increased in MPS IIIA mice and duodenum length also increased. An increased submucosal thickness was observed in MPS IIIA intestine compared to normal mice and lysosomal storage of gag was observed in this region. Storage was also observed in the lamina propria of the villus tip. All other morphometric measurements including villus height and crypt depth fell within the normal range. The gastric emptying half-life of solid and liquid meals decreased with age in normal mice whereas the T(1/2) of solid meals did not alter with age in MPS IIA mice such that they were elevated above normal by 38 weeks of age. Sucrase activity was higher than normal in MPS IIIA at all ages tested. These abnormalities in GI structure and function observed in MPS IIIA may contribute to weight gain in this disorder.