Liver-directed gene therapy corrects neurologic disease in a murine model of mucopolysaccharidosis type I-Hurler

Mucopolysaccharidosis type I-Hurler (MPS I-H) is a neurodegenerative lysosomal storage disorder (LSD) caused by inherited defects of the α-L-iduronidase (IDUA) gene. Current treatments are ineffective for treating central nervous system (CNS) manifestations because lysosomal enzymes do not effectively cross the blood-brain barrier (BBB). To enable BBB transport of the enzyme, we engineered a modified IDUA protein by adding a brain-targeting peptide from melanotransferrin. We demonstrated that fusion of melanotransferrin peptide (MTfp) at the N terminus of human IDUA (hIDUA) was enzymatically active and could efficiently cross the BBB in vitro. Then, liver-directed gene therapy using the adeno-associated virus 8 (AAV8) vector, which encoded the modified hIDUA cDNA driven by a liver-specific expression cassette was evaluated in an adult MPS I-H mouse model. The results showed that intravenous (i.v.) infusion of AAV8 resulted in sustained supraphysiological levels of IDUA activity and normalized glycosaminoglycan (GAG) accumulation in peripheral tissues. Addition of MTfp to the hIDUA N terminus allowed efficient BBB transcytosis and IDUA activity restoration in the brain, resulting in significant improvements in brain pathology and neurobehavioral deficits. Our results provide a novel strategy to develop minimally invasive therapies for treatment of MPS I-H and other neurodegenerative LSDs.

Clinical Development of Cell Therapies to Halt Lysosomal Storage Diseases: Results and Lessons Learned

Although cross-correction was discovered more than 50 years ago, and held the promise of drastically improving disease management, still no cure exists for lysosomal storage diseases (LSDs). Cell therapies hold the potential to halt disease progression: either a subset of autologous cells can be ex vivo/ in vivo transfected with the functional gene or allogenic wild type stem cells can be transplanted. However, majority of cell-based attempts have been ineffective, due to the difficulties in reversing neuronal symptomatology, in finding appropriate gene transfection approaches, in inducing immune tolerance, reducing the risk of graft versus host disease (GVHD) when allogenic cells are used and that of immune response when engineered viruses are administered, coupled with a limited secretion and uptake of some enzymes. In the last decade, due to advances in our understanding of lysosomal biology and mechanisms of cross-correction, coupled with progresses in gene therapy, ongoing pre-clinical and clinical investigations have remarkably increased. Even gene editing approaches are currently under clinical experimentation. This review proposes to critically discuss and compare trends and advances in cell-based and gene therapy for LSDs. Systemic gene delivery and transplantation of allogenic stem cells will be initially discussed, whereas proposed brain targeting methods will be then critically outlined.

Enzyme Replacement Therapy for Genetic Disorders Associated with Enzyme Deficiency

Mutations in human genes might lead to loss of functional proteins, causing diseases. Among these genetic disorders, a large class is associated with the deficiency in metabolic enzymes, resulting in both an increase in the concentration of substrates and a loss in the metabolites produced by the catalyzed reactions. The identification of therapeutic actions based on small molecules represents a challenge to medicinal chemists because the target is missing. Alternative approaches are biology-based, ranging from gene and stem cell therapy, CRISPR/Cas9 technology, distinct types of RNAs, and enzyme replacement therapy (ERT). This review will focus on the latter approach that since the 1990s has been successfully applied to cure many rare diseases, most of them being lysosomal storage diseases or metabolic diseases. So far, a dozen enzymes have been approved by FDA/EMA for lysosome storage disorders and only a few for metabolic diseases. Enzymes for replacement therapy are mainly produced in mammalian cells and some in plant cells and yeasts and are further processed to obtain active, highly bioavailable, less degradable products. Issues still under investigation for the increase in ERT efficacy are the optimization of enzymes interaction with cell membrane and internalization, the reduction in immunogenicity, and the overcoming of blood-brain barrier limitations when neuronal cells need to be targeted. Overall, ERT has demonstrated its efficacy and safety in the treatment of many genetic rare diseases, both saving newborn lives and improving patients' life quality, and represents a very successful example of targeted biologics.

Intravenous delivery for treatment of mucopolysaccharidosis type I: A comparison of AAV serotypes 9 and rh10

Mucopolysaccharidosis type I (MPS I) is an inherited metabolic disorder caused by deficiency of alpha-L-iduronidase (IDUA), resulting in accumulation of heparan and dermatan sulfate glycosaminoglycans (GAGs). Individuals with the most severe form of the disease (Hurler syndrome) suffer from neurodegeneration, intellectual disability, and death by age 10. Current treatments for this disease include allogeneic hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT). However, these treatments do not address CNS manifestations of the disease. In this study we compared the ability of intravenously administered AAV serotypes 9 and rh10 (AAV9 and AAVrh10) for delivery and expression of the IDUA gene in the CNS. Adult C57BL/6 MPS I mice were infused intravenously with either AAV9 or AAVrh10 vector encoding the human IDUA gene. Treated animals demonstrated supraphysiological levels and widespread restoration of IDUA enzyme activity in the plasma and all organs including the CNS. High levels of IDUA enzyme activity were observed in the plasma, brain and spinal cord ranging from 10 to 100-fold higher than heterozygote controls, while levels in peripheral organs were also high, ranging from 1000 to 10,000-fold higher than control animals. In general, levels of IDUA expression were slightly higher in peripheral organs for AAVrh10 administered animals although these differences were not significant except for the lung. Levels of IDUA expression between AAV 9 and rh10 were roughly equivalent in the brain. Urinary and tissue GAGs were significantly reduced starting at 3 weeks after vector infusion, with restoration of normal GAG levels by the end of the study in animals treated with either AAV9 or rh10. These results demonstrate that non-invasive intravenous AAV9 or AAVrh10-mediated IDUA gene therapy is a potentially effective treatment for both systemic and CNS manifestations of MPS I, with implications for the treatment of other metabolic and neurological diseases as well.

A Highly Efficacious PS Gene Editing System Corrects Metabolic and Neurological Complications of Mucopolysaccharidosis Type I

Our previous study delivered zinc finger nucleases to treat mice with mucopolysaccharidosis type I (MPS I), resulting in a phase I/II clinical trial (ClinicalTrials.gov: NCT02702115). However, in the clinical trial, the efficacy needs to be improved due to the low transgene expression level. To this end, we designed a proprietary system (PS) gene editing approach with CRISPR to insert a promoterless α-l-iduronidase (IDUA) cDNA sequence into the albumin locus of hepatocytes. In this study, adeno-associated virus 8 (AAV8) vectors delivering the PS gene editing system were injected into neonatal and adult MPS I mice. IDUA enzyme activity in the brain significantly increased, while storage levels were normalized. Neurobehavioral tests showed that treated mice had better memory and learning ability. Also, histological analysis showed efficacy reflected by the absence of foam cells in the liver and vacuolation in neuronal cells. No vector-associated toxicity or increased tumorigenesis risk was observed. Moreover, no off-target effects were detected through the unbiased genome-wide unbiased identification of double-stranded breaks enabled by sequencing (GUIDE-seq) analysis. In summary, these results showed the safety and efficacy of the PS in treating MPS I and paved the way for clinical studies. Additionally, as a therapeutic platform, the PS has the potential to treat other lysosomal diseases.

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.

A novel gene editing system to treat both Tay-Sachs and Sandhoff diseases

The GM2-gangliosidoses are neurological diseases causing premature death, thus developing effective treatment protocols is urgent. GM2-gangliosidoses result from deficiency of a lysosomal enzyme β-hexosaminidase (Hex) and subsequent accumulation of GM2 gangliosides. Genetic changes in HEXA, encoding the Hex α subunit, or HEXB, encoding the Hex β subunit, causes Tay-Sachs disease and Sandhoff disease, respectively. Previous studies have showed that a modified human Hex μ subunit (HEXM) can treat both Tay-Sachs and Sandhoff diseases by forming a homodimer to degrade GM2 gangliosides. To this end, we applied this HEXM subunit in our PS813 gene editing system to treat neonatal Sandhoff mice. Through AAV delivery of the CRISPR system, a promoterless HEXM cDNA will be integrated into the albumin safe harbor locus, and lysosomal enzyme will be expressed and secreted from edited hepatocytes. Four months after the i.v. of AAV vectors, plasma MUGS and MUG activities reached up to 144- and 17-fold of wildtype levels (n=10, p<0.0001), respectively. More importantly, MUGS and MUG activities in the brain also increased significantly compared with untreated Sandhoff mice (p<0.001). Further, HPLC-MS/MS analysis showed that GM2 gangliosides in multiple tissues, except the brain, of treated mice were reduced to normal levels. Rotarod analysis showed that coordination and motor memory of treated mice were improved (p<0.05). Histological analysis of H&E stained tissues showed reduced cellular vacuolation in the brain and liver of treated Sandhoff mice. These results demonstrate the potential of developing a treatment of in vivo genome editing for Tay-Sachs and Sandhoff patients.

Enzyme replacement therapy with recombinant pro-CTSD (cathepsin D) corrects defective proteolysis and autophagy in neuronal ceroid lipofuscinosis

CTSD (cathepsin D) is one of the major lysosomal proteases indispensable for the maintenance of cellular proteostasis by turning over substrates of endocytosis, phagocytosis and autophagy. Consequently, CTSD deficiency leads to a strong impairment of the lysosomal-autophagy machinery. In mice and humans CTSD dysfunction underlies the congenital variant (CLN10) of neuronal ceroid lipofuscinosis (NCL). NCLs are distinct lysosomal storage disorders (LSDs) sharing various hallmarks, namely accumulation of protein aggregates and ceroid lipofuscin leading to neurodegeneration and blindness. The most established and clinically approved approach to treat LSDs is enzyme replacement therapy (ERT) aiming to replace the defective hydrolase with an exogenously applied recombinant protein. Here we reveal that recombinant human pro-CTSD produced in a mammalian expression system can be efficiently taken up by a variety of cell models, is correctly targeted to lysosomes and processed to the active mature form of the protease. In proof-of-principle experiments we provide evidence that recombinant human CTSD (rhCTSD) can improve the biochemical phenotype of CTSD-deficient hippocampal slice cultures in vitro and retinal cells in vivo. Furthermore, we demonstrate that dosing of rhCTSD in the murine CLN10 model leads to a correction of lysosomal hypertrophy, storage accumulation and impaired autophagic flux in the viscera and central nervous system (CNS). We establish that direct delivery of the recombinant protease to the CNS is required for improvement of neuropathology and lifespan extension. Together these data support the continuation of the pre-clinical studies for the application of rhCTSD in the treatment of NCL.Abbreviations: AIF1/IBA1: allograft inflammatory factor 1; BBB: blood brain barrier; CNS: central nervous system; CTSB: cathepsin B; CTSD: cathepsin D; CTSL: cathepsin L; ERT: enzyme replacement therapy; GFAP: glial fibrillary acidic protein; INL: inner nuclear layer; LAMP1: lysosomal-associated membrane protein 1; LAMP2: lysosomal-associated membrane protein 2; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; LDL: low-density lipoprotein; LRP1: low density lipoprotein receptor-related protein 1; LSD: lysosomal storage disorder; MEFs: mouse embryonic fibroblasts; M6P: mannose 6-phosphate; mCTSD: mature CTSD; NCL: neuronal ceroid lipofuscinosis; ONL: outer nuclear layer; PB: phosphate buffer; proCTSD: pro-cathepsin D; LRPAP1: low density lipoprotein receptor-related protein associated protein 1; rhCTSD: human recombinant CTSD; SAPC: saposin C; SAPD: saposin D; ATP5G1: ATP synthase, H+ transporting, mitochondrial F0 complex, subunit C1 (subunit 9); SQSTM1/p62: sequestosome 1; TPP1: tripeptidyl peptidase I.

Alpha-Mannosidosis: Therapeutic Strategies

Alpha-mannosidosis (α-mannosidosis) is a rare lysosomal storage disorder with an autosomal recessive inheritance caused by mutations in the gene encoding for the lysosomal α-d-mannosidase. So far, 155 variants from 191 patients have been identified and in part characterized at the biochemical level. Similarly to other lysosomal storage diseases, there is no relationship between genotype and phenotype in alpha-mannosidosis. Enzyme replacement therapy is at the moment the most effective therapy for lysosomal storage disease, including alpha-mannosidosis. In this review, the genetic of alpha-mannosidosis has been described together with the results so far obtained by two different therapeutic strategies: bone marrow transplantation and enzyme replacement therapy. The primary indication to offer hematopoietic stem cell transplantation in patients affected by alpha-mannosidosis is preservation of neurocognitive function and prevention of early death. The results obtained from a Phase I⁻II study and a Phase III study provide evidence of the positive clinical effect of the recombinant enzyme on patients with alpha-mannosidosis.

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.

Absence of RNase H2 triggers generation of immunogenic micronuclei removed by autophagy

Hypomorphic mutations in the DNA repair enzyme RNase H2 cause the neuroinflammatory autoimmune disorder Aicardi-Goutières syndrome (AGS). Endogenous nucleic acids are believed to accumulate in patient cells and instigate pathogenic type I interferon expression. However, the underlying nucleic acid species amassing in the absence of RNase H2 has not been established yet. Here, we report that murine RNase H2 knockout cells accumulated cytosolic DNA aggregates virtually indistinguishable from micronuclei. RNase H2-dependent micronuclei were surrounded by nuclear lamina and most of them contained damaged DNA. Importantly, they induced expression of interferon-stimulated genes (ISGs) and co-localized with the nucleic acid sensor cGAS. Moreover, micronuclei associated with RNase H2 deficiency were cleared by autophagy. Consequently, induction of autophagy by pharmacological mTOR inhibition resulted in a significant reduction of cytosolic DNA and the accompanied interferon signature. Autophagy induction might therefore represent a viable therapeutic option for RNase H2-dependent disease. Endogenous retroelements have previously been proposed as a source of self-nucleic acids triggering inappropriate activation of the immune system in AGS. We used human RNase H2-knockout cells generated by CRISPR/Cas9 to investigate the impact of RNase H2 on retroelement propagation. Surprisingly, replication of LINE-1 and Alu elements was blunted in cells lacking RNase H2, establishing RNase H2 as essential host factor for the mobilisation of endogenous retrotransposons.

Long-term enzyme replacement therapy improves neurocognitive functioning and hippocampal synaptic plasticity in immune-tolerant alpha-mannosidosis mice

Alpha-mannosidosis is a glycoproteinosis caused by deficiency of lysosomal acid alpha-mannosidase (LAMAN), which markedly affects neurons of the central nervous system (CNS), and causes pathognomonic intellectual dysfunction in the clinical condition. Cognitive improvement consequently remains a major therapeutic objective in research on this devastating genetic error. Immune-tolerant LAMAN knockout mice were developed to evaluate the effects of enzyme replacement therapy (ERT) by prolonged administration of recombinant human enzyme. Biochemical evidence suggested that hippocampus may be one of the brain structures that benefits most from long-term ERT. In the present functional study, ERT was initiated in 2-month-old immune-tolerant alpha-mannosidosis mice and continued for 9months. During the course of treatment, mice were trained in the Morris water maze task to assess spatial-cognitive performance, which was related to synaptic plasticity recordings and hippocampal histopathology. Long-term ERT reduced primary substrate storage and neuroinflammation in hippocampus, and improved spatial learning after mid-term (10weeks+) and long-term (30weeks+) treatment. Long-term treatment substantially improved the spatial-cognitive abilities of alpha-mannosidosis mice, whereas the effects of mid-term treatment were more modest. Detailed analyses of spatial memory and spatial-cognitive performance indicated that even prolonged ERT did not restore higher cognitive abilities to the level of healthy mice. However, it did demonstrate marked therapeutic effects that coincided with increased synaptic connectivity, reflected by improvements in hippocampal CA3-CA1 long-term potentiation (LTP), expression of postsynaptic marker PSD-95 as well as postsynaptic density morphology. These experiments indicate that long-term ERT may hold promise, not only for the somatic defects of alpha-mannosidosis, but also to alleviate cognitive impairments of the disorder.

Enzyme replacement therapy and beyond-in memoriam Roscoe O. Brady, M.D. (1923-2016)

Lysosomal storage disorders are strong candidates for the development of specific innovative therapies. The discovery of enzyme deficiencies is an important milestone in understanding the underlying cause of disease. Being able to replace the first missing enzyme in a lysosomal storage required three decades of dedicated research. Successful drug development for lysosomal storage disorders was fostered by the U.S. Orphan Drug Act. Various optimization strategies have the potential to overcome the current limitations of enzyme replacement therapies. In addition, substrate reduction therapies are an alternative approach to treat lysosomal storage disorders, chemical chaperones enhance residual enzyme activity, and small molecules can facilitate substrate transport through subcellular compartments. Bone-marrow derived multipotent stem cells and gene therapies have received FDA orphan drug designation status. The science of small clinical trials played an essential role: non-neurological endpoints, biomarker, and regulatory alignment are key factors in successful drug development for lysosomal storage disorders. Being able to treat brain disease is the next frontier. This review is dedicated to the memory of Roscoe O. Brady, an early pioneer in the research of lysosomal storage diseases.

Origin of α-mannosidase activity in CSF

The α-mannosidase activity in human frontal gyrus, cerebrospinal fluid and plasma has been analyzed by DEAE-cellulose chromatography to investigate the origin of the α-mannosidase activity in cerebrospinal fluid (CSF). The profile of α-mannosidase isoenzymes obtained in CSF was similar to that in the frontal gyrus but different from that in human plasma. In particular the two characteristic peaks of lysosomal α-mannosidase, A and B, which have a pH-optimum of 4.5 and are found in human tissues, were present in both the frontal gyrus and CSF. In contrast the majority of α-mannosidase activity in human plasma was due to the so called intermediate form, which has a pH-optimum of 5.5. The results suggest that the intermediate form of α-mannosidase in plasma does not cross the blood-brain barrier and that the α-mannosidase activity present in the cerebrospinal fluid is of lysosomal type and of brain origin. Thus the α-mannosidase activity in cerebrospinal fluid might mirror the brain pathological changes linked to neurodegenerative disorders such as Parkinson's disease.

Pharmacologic manipulation of lysosomal enzyme transport across the blood-brain barrier

The adult blood-brain barrier, unlike the neonatal blood-brain barrier, does not transport lysosomal enzymes into brain, making enzyme replacement therapy ineffective in treating the central nervous system symptoms of lysosomal storage diseases. However, enzyme transport can be re-induced with alpha-adrenergics. Here, we examined agents that are known to alter the blood-brain barrier transport of large molecules or to induce lysosomal enzyme transport across the blood-brain barrier ((±)epinephrine, insulin, retinoic acid, and lipopolysaccharide) in 2-week-old and adult mice. In 2-week-old adolescent mice, all these pharmacologic agents increased brain and heart uptake of phosphorylated human β-glucuronidase. In 8-week-old adult mice, manipulations with (±)epinephrine, insulin, and retinoic acid were significantly effective on uptake by brain and heart. The increased uptake of phosphorylated human β-glucuronidase was inhibited by mannose 6-phosphate for the agents (±)epinephrine and retinoic acid and by L-NG-nitroarginine methyl ester for the agent lipopolysaccharide in neonatal and adult mice. An in situ brain perfusion study revealed that retinoic acid directly modulated the transport of phosphorylated human β-glucuronidase across the blood-brain barrier. The present study indicates that there are multiple opportunities to at least transiently induce phosphorylated human β-glucuronidase transport at the adult blood-brain barrier.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.

Effect of systemic high dose enzyme replacement therapy on the improvement of CNS defects in a mouse model of mucopolysaccharidosis type II

Background

Mucopolysaccharidosis type II (MPS II, Hunter syndrome), is caused by a deficiency of iduronate-2-sulfatase (IDS). Despite the therapeutic effect of intravenous enzyme replacement therapy (ERT), the central nervous system (CNS) defects persist because the enzyme cannot cross the blood-brain barrier (BBB). There have been several trials of direct infusion to the cerebrospinal space showing promising results; however, this approach may have limitations in clinical situations such as CNS infection. The objective of this study was to improve the CNS defect with systemic high-dose ERT.

Methods

Systemic ERT was performed using three doses (1, 5, and 10 mg/kg weekly) of IDS for three different durations (1, 3, and 6 months) in IDS knock out (KO) mice of two age groups (2 months, 8 months). GAG measurement in tissues, brain pathology, and behavioral assessment were analyzed.

Results

Brain IDS activities increased in parallel with the concentrations of IDS injected. The glycosaminoglycan (GAG) level and histopathology in the brains of the young mice improved in a dose- and duration-dependent manner; however, those were not improved in the old mice, even at higher doses of IDS. The spontaneous alternation behavior was recovered in young KO mice treated with ≥ 5 mg/kg IDS; however, no significant improvement was observed in old KO mice.

Conclusions

These results suggest that high-dose ERT given to mice of earlier ages may play a role in preventing GAG accumulation and preventing CNS damage in IDS KO mice. Therefore, ERT above the present standard dose, starting in early childhood, could be a promising treatment regimen for reducing neurological impairment in Hunter syndrome.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-015-0356-0) contains supplementary material, which is available to authorized users.

Chronic enzyme replacement therapy ameliorates neuropathology in alpha-mannosidosis mice

OBJECTIVE

The lysosomal storage disease alpha-mannosidosis is caused by the deficiency of the lysosomal acid hydrolase alpha-mannosidase (LAMAN) leading to lysosomal accumulation of neutral mannose-linked oligosaccharides throughout the body, including the brain. Clinical findings in alpha-mannosidosis include skeletal malformations, intellectual disabilities and hearing impairment. To date, no curative treatment is available. We previously developed a beneficial enzyme replacement therapy (ERT) regimen for alpha-mannosidase knockout mice, a valid mouse model for the human disease. However, humoral immune responses against the injected recombinant human alpha-mannosidase (rhLAMAN) precluded long-term studies and chronic treatment.

METHODS

Here, we describe the generation of an immune-tolerant alpha-mannosidosis mouse model that allowed chronic injection of rhLAMAN by transgenic expression of a catalytically inactive variant of human LAMAN in the knockout background.

RESULTS

Chronic ERT of rhLAMAN revealed pronounced effects on primary substrate storage throughout the brain, normalization of lysosomal enzyme activities and morphology as well as a decrease in microglia activation. The positive effect of long-term ERT on neuronal lysosomal function was reflected by an improvement of cognitive deficits and exploratory activity. in vivo and in vitro uptake measurements indicate rapid clearance of rhLAMAN from circulation and a broad uptake into different cell types of the nervous system.

INTERPRETATION

Our data contribute to the understanding of neurological disorders treatment by demonstrating that lysosomal enzymes such as rhLAMAN can penetrate into the brain and is able to ameliorate neuropathology.

Delivering drugs to the central nervous system: an overview

Developing therapies for the brain is perhaps the greatest challenge facing modern medicine today. While a great many potential therapies show promise in animal models, precious few make it to approval or are even studied in human patients. The particular challenges to the translation of neurotherapeutics to the clinic are many, but a major barrier is difficulty in delivering therapeutics into the brain. The goal of this workshop was to present ways to deliver therapeutics to the brain, including the limitations of each method, and describe ways to track their delivery, safety, and efficacy. Solving the problem of delivery will aid translation of therapeutics for patients suffering from neurodegeneration and other disorders of the brain.

Lysosomal storage disease: gene therapy on both sides of the blood-brain barrier

Most lysosomal storage disorders affect the nervous system as well as other tissues and organs of the body. Previously, the complexities of these diseases, particularly in treating neurologic abnormalities, were too great to surmount. However, based on recent developments there are realistic expectations that effective therapies are coming soon. Gene therapy offers the possibility of affordable, comprehensive treatment associated with these diseases currently not provided by standards of care. With a focus on correction of neurologic disease by systemic gene therapy of mucopolysaccharidoses types I and IIIA, we review some of the major recent advances in viral and non-viral vectors, methods of their delivery and strategies leading to correction of both the nervous and somatic tissues as well as evaluation of functional correction of neurologic manifestations in animal models. We discuss two questions: what systemic gene therapy strategies work best for correction of both somatic and neurologic abnormalities in a lysosomal storage disorder and is there evidence that targeting peripheral tissues (e.g., in the liver) has a future for ameliorating neurologic disease in patients?

LAMP-2 deficiency leads to hippocampal dysfunction but normal clearance of neuronal substrates of chaperone-mediated autophagy in a mouse model for Danon disease

The Lysosomal Associated Membrane Protein type-2 (LAMP-2) is an abundant lysosomal membrane protein with an important role in immunity, macroautophagy (MA) and chaperone-mediated autophagy (CMA). Mutations within the Lamp2 gene cause Danon disease, an X-linked lysosomal storage disorder characterized by (cardio)myopathy and intellectual dysfunction. The pathological hallmark of this disease is an accumulation of glycogen and autophagic vacuoles in cardiac and skeletal muscle that, along with the myopathy, is also present in LAMP-2-deficient mice. Intellectual dysfunction observed in the human disease suggests a pivotal role of LAMP-2 within brain. LAMP-2A, one specific LAMP-2 isoform, was proposed to be important for the lysosomal degradation of selective proteins involved in neurodegenerative diseases such as Huntington’s and Parkinson’s disease.

To elucidate the neuronal function of LAMP-2 we analyzed knockout mice for neuropathological changes, MA and steady-state levels of CMA substrates. The absence of LAMP-2 in murine brain led to inflammation and abnormal behavior, including motor deficits and impaired learning. The latter abnormality points to hippocampal dysfunction caused by altered lysosomal activity, distinct accumulation of p62-positive aggregates, autophagic vacuoles and lipid storage within hippocampal neurons and their presynaptic terminals. The absence of LAMP-2 did not apparently affect MA or steady-state levels of selected CMA substrates in brain or neuroblastoma cells under physiological and prolonged starvation conditions.

Our data contribute to the understanding of intellectual dysfunction observed in Danon disease patients and highlight the role of LAMP-2 within the central nervous system, particularly the hippocampus.

LIMP-2 expression is critical for β-glucocerebrosidase activity and α-synuclein clearance

Mutations within the lysosomal enzyme β-glucocerebrosidase (GC) result in Gaucher disease and represent a major risk factor for developing Parkinson disease (PD). Loss of GC activity leads to accumulation of its substrate glucosylceramide and α-synuclein. Since lysosomal activity of GC is tightly linked to expression of its trafficking receptor, the lysosomal integral membrane protein type-2 (LIMP-2), we studied α-synuclein metabolism in LIMP-2-deficient mice. These mice showed an α-synuclein dosage-dependent phenotype, including severe neurological impairments and premature death. In LIMP-2-deficient brains a significant reduction in GC activity led to lipid storage, disturbed autophagic/lysosomal function, and α-synuclein accumulation mediating neurotoxicity of dopaminergic (DA) neurons, apoptotic cell death, and inflammation. Heterologous expression of LIMP-2 accelerated clearance of overexpressed α-synuclein, possibly through increasing lysosomal GC activity. In surviving DA neurons of human PD midbrain, LIMP-2 levels were increased, probably to compensate for lysosomal GC deficiency. Therefore, we suggest that manipulating LIMP-2 expression to increase lysosomal GC activity is a promising strategy for the treatment of synucleinopathies.

Gene therapy for the neurological manifestations in lysosomal storage disorders

Over the past several years, considerable progress has been made in the development of gene therapy as a therapeutic strategy for a variety of inherited metabolic diseases, including neuropathic lysosomal storage disorders (LSDs). The premise of gene therapy for this group of diseases is borne of findings that genetic modification of a subset of cells can provide a more global benefit by virtue of the ability of the secreted lysosomal enzymes to effect cross-correction of adjacent and distal cells. Preclinical studies in small and large animal models of these disorders support the application of either a direct in vivo approach using recombinant adeno-associated viral vectors or an ex vivo strategy using lentiviral vector-modified hematopoietic stem cells to correct the neurological component of these diseases. Early clinical studies utilizing both approaches have begun or are in late-stage planning for a small number of neuropathic LSDs. Although initial indications from these studies are encouraging, it is evident that second-generation vectors that exhibit a greater safety profile and transduction activity may be required before this optimism can be fully realized. Here, I review recent progress and the remaining challenges to treat the neurological aspects of various LSDs using this therapeutic paradigm.

Fast urinary screening of oligosaccharidoses by MALDI-TOF/TOF mass spectrometry

Background

Oligosaccharidoses, which belong to the lysosomal storage diseases, are inherited metabolic disorders due to the absence or the loss of function of one of the enzymes involved in the catabolic pathway of glycoproteins and indirectly of glycosphingolipids. This enzymatic deficiency typically results in the abnormal accumulation of uncompletely degraded oligosaccharides in the urine. Since the clinical features of many of these disorders are not specific for a single enzyme deficiency, unambiguous screening is critical to limit the number of costly enzyme assays which otherwise must be performed.

Methods

Here we provide evidence for the advantages of using a MALDI-TOF/TOF (matrix-assisted laser desorption ionization time-of-flight) mass spectrometric (MS) method for screening oligosaccharidoses. Urine samples from previously diagnosed patients or from unaffected subjects were randomly divided into a training set and a blind testing set. Samples were directly analyzed without prior treatment.

Results

The characteristic MS and MS/MS molecular profiles obtained allowed us to identify fucosidosis, aspartylglucosaminuria, GM1 gangliosidosis, Sandhoff disease, α-mannosidosis, sialidosis and mucolipidoses type II and III.

Conclusions

This method, which is easily run in less than 30 minutes, is performed in a single step, and is sensitive and specific. Invaluable for clinical chemistry purposes this MALDI-TOF/TOF mass spectrometry procedure is semi-automatizable and suitable for the urinary screening of oligosacharidoses.

Lysosomal enzymes may cross the blood-brain-barrier by pinocytosis: implications for enzyme replacement therapy

Here we hypothesized that the water-soluble lysosomal enzymes may cross the blood-brain-barrier and reach the brain using the mechanism of unspecific fluid-phase endocytosis. We also highlight studies that show that, at higher serum concentrations, a fraction of these proteins can reach the brain after intravenous injection, and we suggest some experiments to study this hypothesis. Finally we discuss the implications of this for treatments such as enzyme replacement of lysosomal storage disorders.

High-dose enzyme replacement therapy in murine Hurler syndrome

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disease that is systemic, including progressive neurodegeneration, mental retardation and death before the age of 10 years. MPS I results from deficiency of α-L-iduronidase (IDUA) in lysosomes and subsequent accumulation of glycosaminoglycans (GAG). Clinical enzyme replacement therapy (ERT) with intravenous laronidase reverses some aspects of MPS I disease (e.g., hepatomegaly, splenomegaly, glycosaminoglycanuria) and ameliorates others (e.g., pulmonary function, cardiac disease, arthropathy, exercise tolerance). However, neurologic benefits are thought to be negligible because the blood-brain barrier (BBB) blocks enzyme from reaching the central nervous system (CNS). We considered the possibility that a very high dose of intravenous laronidase might be able to traverse the BBB in small quantities, and provide some metabolic correction in the brain. To address this question, high-dose laronidase was administered (11.6 mg/kg, once per week, 4 weeks) to adult MPS I mice. IDUA enzyme activity in the cortex of treated mice increased to 97% of that in wild type mice (p<0.01). GAG levels in cortex were reduced by 63% of that from untreated MPS I mice (p<0.05). Further, immunohistochemical analysis showed that treatment reduced secondary GM3-ganglioside accumulation in treated MPS I mice. Water T-maze tests showed that the learning abnormality in MPS I mice was reduced (p<0.0001). In summary, repeated, high-dose ERT facilitated laronidase transit across the BBB, reduced GAG accumulation within the CNS, and rescued cognitive impairment.

Enzyme replacement therapy for alpha-mannosidosis: 12 months follow-up of a single centre, randomised, multiple dose study

BACKGROUND

Alpha-mannosidosis (OMIM 248500) is a rare lysosomal storage disease (LSD) caused by alpha-mannosidase deficiency. Manifestations include intellectual disabilities, facial characteristics and hearing impairment. A recombinant human alpha-mannosidase (rhLAMAN) has been developed for weekly intravenous enzyme replacement therapy (ERT). We present the preliminary data after 12 months of treatment.

METHODS

This is a phase I-II study to evaluate safety and efficacy of rhLAMAN. Ten patients (7-17 y) were treated. We investigated efficacy by testing motor function (6-minutes-Walk-Test (6-MWT), 3-min-Stair-Climb-Test (3-MSCT), The Bruininks-Oseretsky Test of Motor Proficiency (BOT2), cognitive function (Leiter-R), oligosaccharides in serum, urine and CSF and Tau- and GFA-protein in CSF.

RESULTS

Oligosaccharides: S-, U- and CSF-oligosaccharides decreased 88.6% (CI -92.0 -85.2, p < 0.001), 54.1% (CI -69.5- -38.7, p < 0,001), and 25.7% (CI -44.3- -7.1, p < 0.05), respectively. Biomarkers: CSF-Tau- and GFA-protein decreased 15%, p < 0.009) and 32.5, p < 0.001 respectively. Motor function: Improvements in 3MSCT (31 steps (CI 6.8-40.5, p < 0.01) and in 6MWT (60.4 m (CI -8.9 -51.1, NS) were achieved. Cognitive function: Improvement in the total Equivalence Age of 4 months (0.34) was achieved in the Leiter R test (CI -0.2-0.8, NS).

CONCLUSIONS

These data suggest that rhLAMAN may be an encouraging new treatment for patients with alpha-mannosidosis.The study is designed to continue for a total of 18 months. Longer-term follow-up of patients in this study and the future placebo-controlled phase 3 trial are needed to provide greater support for the findings in this study.

Distribution and Severity of Neuropathology in β-Mannosidase-Deficient Mice is Strain Dependent

Neurological dysfunction is common in humans and animals with lysosomal storage diseases. β-Mannosidosis, an autosomal recessive inherited disorder of glycoprotein catabolism caused by deficiency of the lysosomal enzyme β-mannosidase, is characterized by intracellular accumulation of small oligosaccharides in selected cell types. In ruminants, clinical manifestation is severe, and neuropathology includes extensive intracellular vacuolation and dysmyelination. In human cases of β-mannosidosis, the clinical symptoms, including intellectual disability, are variable and can be relatively mild. A β-mannosidosis knockout mouse was previously characterized and showed normal growth, appearance, and lifespan. Neuropathology between 1 and 9 months of age included selective, variable neuronal vacuolation with no hypomyelination. This study characterized distribution of brain pathology in older mutant mice, investigating the effects of two strain backgrounds. Morphological analysis indicated a severe consistent pattern of neuronal vacuolation and disintegrative degeneration in all five 129X1/SvJ mice. However, the mice with a mixed genetic background showed substantial variability in the severity of pathology. In the severely affected animals, neuronal vacuolation was prominent in specific layers of piriform area, retrosplenial area, anterior cingulate area, selected regions of isocortex, and in hippocampus CA3. Silver degeneration reaction product was prominent in regions including specific cortical layers and cerebellar molecular layer. The very consistent pattern of neuropathology suggests metabolic differences among neuronal populations that are not yet understood and will serve as a basis for future comparison with human neuropathological analysis. The variation in severity of pathology in different mouse strains implicates genetic modifiers in the variable phenotypic expression in humans.

Natural history of alpha mannosidosis a longitudinal study

Background

Alpha-Mannosidosis is a rare lysosomal storage disorder, caused by the deficiency of the enzyme alpha-Mannosidase. Clinically it is characterized by hearing impairment, skeletal and neurological abnormalities and mental retardation. In order to characterize the clinical features and disease progression of patients affected by alpha-Mannosidosis, a survey study was conducted. 43 patients from 4 European countries participated in this longitudinal study. Age range of the participants was 3 to 42 years. For each patient a medical history, complete physical and neurological examination, joint range of motion and assessment of physical endurance and of lung function were completed. In addition, serum and urinary oligosaccharide levels were analysed.

Methods

In this multicenter longitudinal study clinical data of 43 alpha-Mannosidosis patients were collected. In addition to objective clinical measurements biochemical assays were performed.

Results

Data analysis revealed a wide spectrum of clinical presentation regarding the severity and disease progression. Most clinical abnormalities were observed in the musculoskeletal and neurological system. All patients showed mental retardation and hearing loss from early childhood. An impairment in physical endurance was revealed by the 6-minute walk and 3-minute stair stair climb tests. There was only slight progression of a few clinical findings: Psychiatric troubles in both groups essentially, and respiratory dysfunction under 18 years. The serum and urinary oligosaccharide levels were increased in all affected individuals and correlated well with the 6-minute walk and 3-minute stair climb test results.

Conclusions

This study confirms that alpha-Mannosidosis is a very heterogeneous disorder regarding both, disease severity and progression. As it has been shown that Mannosidosis patients are able to perform lung function tests and the 6MWT and stair-climb test, these clinical parameters apparently can be used as clinical endpoints for clinical trials. Oligosaccharide levels appeared correlated with functional testing and may serve as biomarkers of disease severity, progression and response to treatment.

Trial registration

ClinicalTrials.gov Identifier = NCT00498420 and EuropeanCommission FP VI contract LHSM-CT-2006-018692.

Cerebral Magnetic Resonance Spectroscopy Demonstrates Long-Term Effect of Bone Marrow Transplantation in α-Mannosidosis

α-Mannosidosis, OMIM #248500, is an autosomal recessive lysosomal storage disease caused by acidic α-mannosidase deficiency. Treatment options include bone marrow transplantation (BMT) and, possibly in the future, enzyme replacement therapy. Brain magnetic resonance spectroscopy (MRS) enables non-invasive monitoring of cerebral treatment effect. Accumulated cerebral mannose-containing oligosaccharides were demonstrated by MRS in a patient who at age 2 years and 11 months received a BMT from a haploidentical non-carrier sibling. The cerebral mannose-containing oligosaccharides had disappeared as early as 9½ months after BMT. MRS furthermore demonstrated the persistent treatment effect at regular intervals up to 5½ years after BMT. MRS is a non-invasive tool that can demonstrate the effect of BMT treatment. Likewise, MRS may be used to demonstrate the cerebral effect of other potential treatments such as enzyme replacement therapy.

A highly secreted sulphamidase engineered to cross the blood-brain barrier corrects brain lesions of mice with mucopolysaccharidoses type IIIA

Mucopolysaccharidoses type IIIA (MPS-IIIA) is a neurodegenerative lysosomal storage disorder (LSD) caused by inherited defects of the sulphamidase gene. Here, we used a systemic gene transfer approach to demonstrate the therapeutic efficacy of a chimeric sulphamidase, which was engineered by adding the signal peptide (sp) from the highly secreted iduronate-2-sulphatase (IDS) and the blood-brain barrier (BBB)-binding domain (BD) from the Apolipoprotein B (ApoB-BD). A single intravascular administration of AAV2/8 carrying the modified sulphamidase was performed in adult MPS-IIIA mice in order to target the liver and convert it to a factory organ for sustained systemic release of the modified sulphamidase. We showed that while the IDS sp replacement results in increased enzyme secretion, the addition of the ApoB-BD allows efficient BBB transcytosis and restoration of sulphamidase activity in the brain of treated mice. This, in turn, resulted in an overall improvement of brain pathology and recovery of a normal behavioural phenotype. Our results provide a novel feasible strategy to develop minimally invasive therapies for the treatment of brain pathology in MPS-IIIA and other neurodegenerative LSDs.

Lysosomal dysfunction causes neurodegeneration in mucolipidosis II 'knock-in' mice

Mucolipidosis II is a neurometabolic lysosomal trafficking disorder of infancy caused by loss of mannose 6-phosphate targeting signals on lysosomal proteins, leading to lysosomal dysfunction and accumulation of non-degraded material. However, the identity of storage material and mechanisms of neurodegeneration in mucolipidosis II are unknown. We have generated 'knock-in' mice with a common mucolipidosis II patient mutation that show growth retardation, progressive brain atrophy, skeletal abnormalities, elevated lysosomal enzyme activities in serum, lysosomal storage in fibroblasts and brain and premature death, closely mimicking the mucolipidosis II disease in humans. The examination of affected mouse brains at different ages by immunohistochemistry, ultrastructural analysis, immunoblotting and mass spectrometric analyses of glycans and anionic lipids revealed that the expression and proteolytic processing of distinct lysosomal proteins such as α-l-fucosidase, β-hexosaminidase, α-mannosidase or Niemann-Pick C2 protein are more significantly impacted by the loss of mannose 6-phosphate residues than enzymes reaching lysosomes independently of this targeting mechanism. As a consequence, fucosylated N-glycans, GM2 and GM3 gangliosides, cholesterol and bis(monoacylglycero)phosphate accumulate progressively in the brain of mucolipidosis II mice. Prominent astrogliosis and the accumulation of organelles and storage material in focally swollen axons were observed in the cerebellum and were accompanied by a loss of Purkinje cells. Moreover, an increased neuronal level of the microtubule-associated protein 1 light chain 3 and the formation of p62-positive neuronal aggregates indicate an impairment of constitutive autophagy in the mucolipidosis II brain. Our findings demonstrate the essential role of mannose 6-phosphate for selected lysosomal proteins to maintain the capability for degradation of sequestered components in lysosomes and autophagolysosomes and prevent neurodegeneration. These lysosomal proteins might be a potential target for a valid therapeutic approach for mucolipidosis II disease.

Systemic administration of tripeptidyl peptidase I in a mouse model of late infantile neuronal ceroid lipofuscinosis: effect of glycan modification

Late-infantile neuronal ceroid lipofuscinosis (LINCL) is a recessive genetic disease of childhood caused by deficiencies in the lysosomal protease tripeptidyl peptidase I (TPP1). Disease is characterized by progressive and extensive neuronal death. One hurdle towards development of enzyme replacement therapy is delivery of TPP1 to the brain. In this study, we evaluated the effect of modifying N-linked glycans on recombinant human TPP1 on its pharmacokinetic properties after administration via tail vein injection to a mouse model of LINCL. Unmodified TPP1 exhibited a dose-dependent serum half-life of 12 min (0.12 mg) to 45 min (2 mg). Deglycosylation or modification using sodium metaperiodate oxidation and reduction with sodium borohydride increased the circulatory half-life but did not improve targeting to the brain compared to unmodified TPP1. Analysis of liver, brain, spleen, kidney and lung demonstrated that for all preparations, >95% of the recovered activity was in the liver. Interestingly, administration of a single 2 mg dose (80 mg/kg) of unmodified TPP1 resulted in ∼10% of wild-type activity in brain. This suggests that systemic administration of unmodified recombinant enzyme merits further exploration as a potential therapy for LINCL.

β2 Agonists enhance the efficacy of simultaneous enzyme replacement therapy in murine Pompe disease

Enzyme replacement therapy (ERT) with recombinant human acid α-glucosidase (rhGAA) has improved clinical outcomes in patients with Pompe disease; however, the response of skeletal muscle and the central nervous system to ERT has been attenuated. The poor response of skeletal muscle to ERT has been attributed to the low abundance of the cation-independent mannose-6-phosphate receptor (CI-MPR), which mediates receptor-mediated uptake of rhGAA. Hence the ability of adjunctive therapy with β2-agonists to increase CI-MPR expression in skeletal muscle was evaluated during ERT in murine Pompe disease with regard to reversal of neuromuscular involvement. Mice with Pompe disease were treated with weekly rhGAA injections (20 mg/kg) and a selective β2-agonist, either albuterol (30 mg/l in drinking water) or low-dose clenbuterol (6 mg/l in drinking water). Biochemical correction was enhanced by β2-agonist treatment in both muscle and the cerebellum, indicating that adjunctive therapy could enhance efficacy from ERT in Pompe disease with regard to neuromuscular involvement. Intriguingly, clenbuterol slightly reduced muscle glycogen content independent of CI-MPR expression, as demonstrated in CI-MPR knockout/GAA knockout mice that were otherwise resistant to ERT. Thus, adjunctive therapy with β2 agonists might improve the efficacy of ERT in Pompe disease and possibly other lysosomal storage disorders through enhancing receptor-mediated uptake of recombinant lysosomal enzymes.

Developing treatment options for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) represents a devastating lysosomal storage disease characterized by intralysosomal accumulation of the sphingolipid sulfatide in various tissues. Three types of the disease are currently distinguished: the late-infantile, which is the most commonly observed, the juvenile and the adult type. Demyelination represents the main histopathological feature of the disorder, leading to neurological impairment with no curative treatment currently available. Nevertheless, the increased scientific interest on the disease has led to the experimental use of innovative therapeutic approaches in animal models, aiming to provide an effective therapeutic regimen for human patients, as well. This paper provides an overview of developing treatment options among patients with MLD. Apart from hematopoietic stem cell transplantation, already in use for decades, other recent data discussed includes umbilical cord blood and stem cell transplantation, enzyme replacement therapy, gene therapy and autologous hematopoietic transplantation of genetically modified stem cells. Gene therapy with oligodedroglial, neural progenitor, embryonic and microencapsulated recombinant cells represents add-on treatment options still on experimental level.

Emerging therapies for neurodegenerative lysosomal storage disorders - from concept to reality

Lysosomal storage disorders are inherited metabolic diseases in which a mutation in a gene encoding a lysosomal enzyme or lysosome-related protein results in the intra-cellular accumulation of substrate and reduced cell/tissue function. Few patients with neurodegenerative lysosomal storage disorders have access to safe and effective treatments although many therapeutic strategies have been or are presently being studied in vivo thanks to the availability of a large number of animal models. This review will describe the comparative advancement of a variety of therapeutic strategies through the 'research pipeline'. Our goal is to provide information for clinicians, researchers and patients/families alike on the leading therapeutic candidates at this point in time, and also to provide information on emerging approaches that may provide a safe and effective treatment in the future. The length of the pipeline represents the significant and sustained effort required to move a novel concept from the laboratory into the clinic.

Impact of high-dose, chemically modified sulfamidase on pathology in a murine model of MPS IIIA

Mucopolysaccharidosis type IIIA (MPS IIIA) is a neurodegenerative lysosomal storage disorder that results from a deficiency of sulfamidase (N-sulfoglucosamine sulfohydrolase), with consequential accumulation of its substrate, partially degraded heparan sulfate. Conventional doses (e.g. 1mg/kg) of intravenously delivered recombinant human sulfamidase (rhSGSH) do not improve neuropathology in MPS IIIA mice due to an inability to traverse the blood-brain barrier; however high-dose treatment or administration of enzyme that has been chemically modified to remove mannose-6-phosphate glycans has been shown to reduce neuropathology in related animal models. We have combined these approaches to evaluate the ability of 1, 5, 10 or 20mg/kg of similarly chemically modified or unmodified rhSGSH to reduce neuropathology following repeated intravenous delivery to adult MPS IIIA mice. rhSGSH was detected in brain homogenates from mice treated with all doses of modified rhSGSH and those receiving the two higher doses of unmodified rhSGSH, albeit at significantly lower levels. Immunohistochemically, rhSGSH visualized in the brain was localized to the endothelium, meninges and choroid plexus, with no convincing punctate intra-neuronal staining seen. This presumably underlies the failure of the treatment to reduce the relative level of a heparan sulfate-derived oligosaccharide (GlcNS-UA), or secondarily stored substrates that accumulate in MPS IIIA brain cells. However, modification of rhSGSH significantly increased its effectiveness in degrading GlcNS-UA in non-CNS tissues, potentially as a result of its reduced plasma clearance. If this observation is generally applicable, chemical modification may permit the use of significantly lower doses of lysosomal enzymes in patients currently receiving intravenous enzyme replacement therapy.

Transport of arylsulfatase A across the blood-brain barrier in vitro

Enzyme replacement therapy is an option to treat lysosomal storage diseases caused by functional deficiencies of lysosomal hydrolases as intravenous injection of therapeutic enzymes can correct the catabolic defect within many organ systems. However, beneficial effects on central nervous system manifestations are very limited because the blood-brain barrier (BBB) prevents the transfer of enzyme from the circulation to the brain parenchyma. Preclinical studies in mouse models of metachromatic leukodystrophy, however, showed that arylsulfatase A (ASA) is able to cross the BBB to some extent, thus reducing lysosomal storage in brain microglial cells. The present study aims to investigate the routing of ASA across the BBB and to improve the transfer in vitro using a well established cell culture model consisting of primary porcine brain capillary endothelial cells cultured on Transwell filter inserts. Passive apical-to-basolateral ASA transfer was observed, which was not saturable up to high ASA concentrations. No active transport could be determined. The passive transendothelial transfer was, however, charge-dependent as reduced concentrations of negatively charged monosaccharides in the N-glycans of ASA or the addition of polycations increased basolateral ASA levels. Adsorptive transcytosis is therefore considered to be the major transport pathway. Partial inhibition of the transcellular ASA transfer by mannose 6-phosphate indicated a second route depending on the insulin-like growth factor II/mannose 6-phosphate receptor, MPR300. We conclude that cationization of ASA and an increase of the mannose 6-phosphate content of the enzyme may promote blood-to-brain transfer of ASA, thus leading to an improved therapeutic efficacy of enzyme replacement therapy behind the BBB.

Cerebellar alterations and gait defects as therapeutic outcome measures for enzyme replacement therapy in α-mannosidosis

α-Mannosidosis is a rare lysosomal storage disease with accumulation of undegraded mannosyl-linked oligosaccharides in cells throughout the body, most notably in the CNS. This leads to a broad spectrum of neurological manifestations, including progressive intellectual impairment, disturbed motor functions, and cerebellar atrophy. To develop therapeutic outcome measures for enzyme replacement therapy that could be used for human patients, a gene knockout model of α-mannosidosis in mice was analyzed for CNS pathology and motor deficits. In the cerebellar molecular layer, α-mannosidosis mice display clusters of activated Bergman glia, infiltration of phagocytic macrophages, and accumulation of free cholesterol and gangliosides (GM1), notably in regions lacking Purkinje cells. α-Mannosidosis brain lysates also displayed increased expression of Lamp1 and hyperglycosylation of the cholesterol binding protein NPC2. Detailed assessment of motor function revealed age-dependent gait defects in the mice that resemble the disturbed motor function in human patients. Short-term enzyme replacement therapy partially reversed the observed cerebellar pathology with fewer activated macrophages and astrocytes but unchanged levels of hyperglycosylated NPC2, gangliosides, and cholesterol. The present study demonstrates cerebellar alterations in α-mannosidosis mice that relate to the motor deficits and pathological changes seen in human patients and can be used as therapeutic outcome measures.

The effects of early and late bone marrow transplantation in siblings with alpha-mannosidosis. Is early haematopoietic cell transplantation the preferred treatment option?

This article documents both the neurological and physical outcomes of the first published set of siblings undergoing transplantation at differing ages for α-mannosidosis. The older brother, the index case, was diagnosed at the age of 3 years and underwent transplantation at 13 years for the treatment of increasing somatic problems and recurrent infections. The younger brother had undergone transplantation pre-symptomatically at 6 months of age. Their clinical, radiological and developmental outcomes are documented and compared with the previous published cases, with the case for early transplantation being weighted against other potential therapies.

Early initiation of enzyme replacement therapy improves metabolic correction in the brain tissue of aspartylglycosaminuria mice

Aspartylglycosaminuria (AGU) is a lysosomal storage disease caused by deficient activity of glycosylasparaginase (AGA), and characterized by motor and mental retardation. Enzyme replacement therapy (ERT) in adult AGU mice with AGA removes the accumulating substance aspartylglucosamine from and reverses pathology in many somatic tissues, but has only limited efficacy in the brain tissue of the animals. In the current work, ERT of AGU mice was initiated at the age of 1 week with three different dosage schedules of recombinant glycosylasparaginase. The animals received either 3.4 U of AGA/kg every second day for 2 weeks (Group 1), 1.7 U/kg every second day for 9 days followed by an enzyme injection once a week for 4 weeks (Group 2) or 17 U/kg at the age of 7 and 9 days (Group 3). In the Group 1 and Group 3 mice, ERT reduced the amount of aspartylglucosamine by 34 and 41% in the brain tissue, respectively. No therapeutic effect was observed in the brain tissue of Group 2 mice. As in the case of adult AGU mice, the AGA therapy was much more effective in the somatic tissues than in the brain tissue of the newborn AGU mice. The combined evidence demonstrates that a high dose ERT with AGA in newborn AGU mice is up to twofold more effective in reducing the amount of the accumulated storage material from the brain tissue than ERT in adult AGU animals, indicating the importance of early detection and treatment of the disease.

Correction of CNS defects in the MPSII mouse model via systemic enzyme replacement therapy

Mucopolysaccharidosis type II (MPSII), or Hunter syndrome, is a devastating disorder associated with a shortened life expectancy. Patients affected by MPSII have a variety of symptoms that affect all organs of the body and may include progressive cognitive impairment. MPSII is due to inactivity of the enzyme iduronate-2-sulfatase (IDS), which results in the accumulation of storage material in the lysosomes, such as dermatan and heparan sulfates, with consequent cell degeneration in all tissues including, in the severe phenotype, neurodegeneration in the central nervous system (CNS). To date, the only treatment available is systemic infusion of IDS, which ameliorates exclusively certain visceral defects. Therefore, it is important to simultaneously treat the visceral and CNS defects of the MPSII patients. Here, we have developed enzyme replacement therapy (ERT) protocols in a mouse model that allow the IDS to reach the brain, with the substantial correction of the CNS phenotype and of the neurobehavioral features. Treatments were beneficial even in adult and old MPSII mice, using relatively low doses of infused IDS over long intervals. This study demonstrates that CNS defects of MPSII mice can be treated by systemic ERT, providing the potential for development of an effective treatment for MPSII patients.

Pathology and current treatment of neurodegenerative sphingolipidoses

Sphingolipidoses constitute a large subgroup of lysosomal storage disorders (LSDs). Many of them are associated with a progressive neurodegeneration. As is the case for LSDs in general, most sphingolipidoses are caused by deficiencies in lysosomal hydrolases. However, accumulation of sphingolipids can also result from deficiencies in proteins involved in the transport or posttranslational modification of lysosomal enzymes, transport of lipids, or lysosomal membrane proteins required for transport of lysosomal degradation end products. The accumulation of sphingolipids in the lysosome together with secondary changes in the concentration and localization of other lipids may cause trafficking defects of membrane lipids and proteins, affect calcium homeostasis, induce the unfolded protein response, activate apoptotic cascades, and affect various signal transduction pathways. To what extent, however, these changes contribute to the pathogenesis of the diseases is not fully understood. Currently, there is no cure for sphingolipidoses. Therapies like enzyme replacement, pharmacological chaperone, and substrate reduction therapy, which have been shown to be efficient in non-neuronopathic LSDs, are currently evaluated in clinical trials of neuronopathic sphingolipidoses. In the future, neural stem cell therapy and gene therapy may become an option for these disorders.

Therapeutic approaches for neuronopathic lysosomal storage disorders

Therapy of the central nervous system (CNS) manifestations of lysosomal storage diseases (LSDs) has remained a major challenge because of its inability to deliver therapeutic agents efficiently across the intact blood-brain barrier. Non-specific therapies such as hematopoietic stem cell transplantation have been useful in globoid cell leukodystrophy (Krabbe disease) and in some mucopolysaccharidoses. Anti-inflammatory agents also show promise as adjuvant therapy. High doses of replacement therapy with native or modified enzyme show renewed promise for correction of CNS cells. Alternatively, small molecules can enter the brain relatively easily and promote reduction of accumulated substrate or function as pharmacological chaperones to enhance the level of the deficient enzyme. Gene therapy is still being developed and tested in patients. It is therefore likely that, thanks to a better understanding of disease mechanism, a variety of therapeutic approaches, used alone or in combination, will be useful to treat the devastating neurological complications of LSDs.

Human recombinant palmitoyl-protein thioesterase-1 (PPT1) for preclinical evaluation of enzyme replacement therapy for infantile neuronal ceroid lipofuscinosis

Infantile neuronal ceroid lipofuscinosis (INCL, also known as Haltia-Santavuori disease) is a lysosomal storage disorder of infants and children characterized by blindness, seizures and a progressive neurodegenerative course. Recent clinical trials have involved neural stem cells and gene therapy directed to the central nervous system; however, enzyme replacement therapy has never been addressed. In the current paper, we describe the production of human recombinant PPT1 (the defective enzyme in INCL) by standard methods in Chinese Hamster Ovary (CHO) cells. The enzyme is largely mannose 6-phosphorylated as assessed by mannose 6-phosphate receptor binding (80% bound) and taken up rapidly by immortalized patient lymphoblasts, where clearance of PPT substrates was demonstrated (EC(50) of 0.25 nM after overnight incubation). When injected intravenously into PPT1-deficient mice, the clearance of recombinant human PPT1 from plasma was rapid, with a half-life of 10 min. Most of the injected dose was distributed to the kidney and liver and potentially corrective levels were also observed in heart, lung and spleen. Brain uptake was minimal, as expected based on experience with other intravenously administered lysosomal enzymes. The enzyme may be useful as an adjunct to central nervous system-directed therapies and could be used as a starting point for modifications designed to improve brain delivery.