Effects of sulfatide on peripheral nerves in metachromatic leukodystrophy.

OBJECTIVE: To evaluate the longitudinal correlations between sulfatide/lysosulfatide levels and central and peripheral nervous system function in children with metachromatic leukodystrophy (MLD) and to explore the impact of intravenous recombinant human arylsulfatase A (rhASA) treatment on myelin turnover. METHODS: A Phase 1/2 study of intravenous rhASA investigated cerebrospinal fluid (CSF) and sural nerve sulfatide levels, 88-item Gross Motor Function Measure (GMFM-88) total score, sensory and motor nerve conduction, brain N-acetylaspartate (NAA) levels, and sural nerve histology in 13 children with MLD. Myelinated and unmyelinated nerves from an untreated MLD mouse model were also analyzed. RESULTS: CSF sulfatide levels correlated with neither Z-scores for GMFM-88 nor brain NAA levels; however, CSF sulfatide levels correlated negatively with Z-scores of nerve conduction parameters, number of large (≥7 µm) myelinated fibers, and myelin/fiber diameter slope, and positively with nerve g-ratios and cortical latencies of somatosensory-evoked potentials. Quantity of endoneural litter positively correlated with sural nerve sulfatide/lysosulfatide levels. CSF sulfatide levels decreased with continuous high-dose treatment; this change correlated with improved nerve conduction. At 26 weeks after treatment, nerve g-ratio decreased by 2%, and inclusion bodies per Schwann cell unit increased by 55%. In mice, abnormal sulfatide storage was observed in non-myelinating Schwann cells in Remak bundles of sciatic nerves but not in unmyelinated urethral nerves. INTERPRETATION: Lower sulfatide levels in the CSF and peripheral nerves correlate with better peripheral nerve function in children with MLD; intravenous rhASA treatment may reduce CSF sulfatide levels and enhance sulfatide/lysosulfatide processing and remyelination in peripheral nerves.

Engineered arylsulfatase A with increased activity, stability and brain delivery for therapy of metachromatic leukodystrophy.

A deficiency of human arylsulfatase A (hASA) causes metachromatic leukodystrophy (MLD), a lysosomal storage disease characterized by sulfatide accumulation and central nervous system (CNS) demyelination. Efficacy of enzyme replacement therapy (ERT) is increased by genetic engineering of hASA to elevate its activity and transfer across the blood-brain barrier (BBB), respectively. To further improve the enzyme's bioavailability in the CNS, we mutated a cathepsin cleavage hot spot and obtained hASAs with substantially increased half-lives. We then combined the superstabilizing exchange E424A with the activity-promoting triple substitution M202V/T286L/R291N and the ApoEII-tag for BBB transfer in a trimodal modified neoenzyme called SuPerTurbo-ASA. Compared with wild-type hASA, half-life, activity, and M6P-independent uptake were increased more than 7-fold, about 3-fold, and more than 100-fold, respectively. ERT of an MLD-mouse model with immune tolerance to wild-type hASA did not induce antibody formation, indicating absence of novel epitopes. Compared with wild-type hASA, SuPerTurbo-ASA was 8- and 12-fold more efficient in diminishing sulfatide storage of brain and spinal cord. In both tissues, storage was reduced by ∼60%, roughly doubling clearance achieved with a 65-fold higher cumulative dose of wild-type hASA previously. Due to its enhanced therapeutic potential, SuPerTurbo-ASA might be a decisive advancement for ERT and gene therapy of MLD.

Substrate reduction therapy for Krabbe disease and metachromatic leukodystrophy using a novel ceramide galactosyltransferase inhibitor.

Krabbe disease (KD) and metachromatic leukodystrophy (MLD) are caused by accumulation of the glycolipids galactosylceramide (GalCer) and sulfatide and their toxic metabolites psychosine and lysosulfatide, respectively. We discovered a potent and selective small molecule inhibitor (S202) of ceramide galactosyltransferase (CGT), the key enzyme for GalCer biosynthesis, and characterized its use as substrate reduction therapy (SRT). Treating a KD mouse model with S202 dose-dependently reduced GalCer and psychosine in the central (CNS) and peripheral (PNS) nervous systems and significantly increased lifespan. Similarly, treating an MLD mouse model decreased sulfatides and lysosulfatide levels. Interestingly, lower doses of S202 partially inhibited CGT and selectively reduced synthesis of non-hydroxylated forms of GalCer and sulfatide, which appear to be the primary source of psychosine and lysosulfatide. Higher doses of S202 more completely inhibited CGT and reduced the levels of both non-hydroxylated and hydroxylated forms of GalCer and sulfatide. Despite the significant benefits observed in murine models of KD and MLD, chronic CGT inhibition negatively impacted both the CNS and PNS of wild-type mice. Therefore, further studies are necessary to elucidate the full therapeutic potential of CGT inhibition.

Intravenous arylsulfatase A in metachromatic leukodystrophy: a phase 1/2 study.

OBJECTIVE: Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by deficient activity of arylsulfatase A (ASA), resulting in severe motor and cognitive dysfunction. This phase 1/2 study evaluated the safety and efficacy of intravenous (IV) recombinant human ASA (rhASA; HGT-1111, previously known as Metazym) in children with MLD. METHODS: Thirteen children with MLD (symptom onset < 4 years of age) were enrolled in an open-label, nonrandomized, dose-escalation trial and received IV rhASA at 50, 100, or 200 U/kg body weight every 14 (± 4) days for 52 weeks (NCT00418561; NCT00633139). Eleven children continued to receive rhASA at 100 or 200 U/kg during a 24-month extension period (NCT00681811). Outcome measures included safety observations, changes in motor and cognitive function, and changes in nerve conduction and morphometry. RESULTS: There were no serious adverse events considered related to IV rhASA. Motor function and developmental testing scores declined during the study in all dose groups; no significant differences were observed between groups. Nerve conduction studies and morphometric analysis indicated that peripheral nerve pathology did not worsen during the study in any dose group. INTERPRETATION: IV rhASA was generally well tolerated. There was no evidence of efficacy in preventing motor and cognitive deterioration, suggesting that IV rhASA may not cross the blood-brain barrier in therapeutic quantities. The relative stability of peripheral nerve function during the study indicates that rhASA may be beneficial if delivered to the appropriate target site and supports the development of rhASA for intrathecal administration in MLD.

Safety of intrathecal delivery of recombinant human arylsulfatase A in children with metachromatic leukodystrophy: Results from a phase 1/2 clinical trial.

BACKGROUND: Metachromatic leukodystrophy (MLD) is an autosomal recessive disorder caused by deficient arylsulfatase A (ASA) activity and characterized by neurological involvement that results in severe disability and premature death. We examined the safety and tolerability of intrathecally delivered recombinant human ASA (rhASA; SHP611, now TAK-611) in children with MLD (NCT01510028). Secondary endpoints included change in cerebrospinal fluid (CSF) sulfatide and lysosulfatide levels, and motor function (assessed by Gross Motor Function Measure-88 total score). METHODS: Twenty-four children with MLD who experienced symptom onset aged ≤ 30 months were enrolled. Patients received rhASA every other week (EOW) for 38 weeks at 10, 30, or 100 mg (cohorts 1-3; n = 6 per cohort), or 100 mg manufactured using a revised process (cohort 4; n = 6). RESULTS: No rhASA-related serious adverse events (SAEs) were observed; 25% of patients experienced an SAE related to the intrathecal device or drug delivery method. Mean CSF sulfatide and lysosulfatide levels fell to within normal ranges in both 100 mg cohorts following treatment. Although there was a general decline in motor function over time, there was a tendency towards a less pronounced decline in patients receiving 100 mg. CONCLUSION: Intrathecal rhASA was generally well tolerated at doses up to 100 mg EOW. These preliminary data support further development of rhASA as a therapy for patients with MLD.

Synthesis and structure-activity relationships of cerebroside analogues as substrates of cerebroside sulphotransferase and discovery of a competitive inhibitor.

Metachromatic leukodystrophy (MLD) is a rare genetic disease characterised by a dysfunction of the enzyme arylsulphatase A leading to the lysosomal accumulation of cerebroside sulphate (sulphatide) causing subsequent demyelination in patients. The enzyme galactosylceramide (cerebroside) sulphotransferase (CST) catalyses the transfer of a sulphate group from 3'-phosphoadenosine-5'-phosphosulphate (PAPS) to cerebrosides producing sulphatides. Substrate reduction therapy for arylsulphatase A by inhibition of CST was proposed as a promising therapeutic approach. To identify competitive CST inhibitors, we synthesised and investigated analogues of the substrate galactosylceramide with variations at the anomeric position, the acyl substituent and the carbohydrate moiety, and investigated their structure-activity relationships. While most of the compounds behaved as substrates, α-galactosylceramide 16 was identified as the first competitive CST inhibitor. Compound 16 can serve as a new lead structure for the development of drugs for the treatment of this devastating disease, MLD, for which small molecule therapeutics are currently not available.

Pharmacokinetic Modeling of Intrathecally Administered Recombinant Human Arylsulfatase A (TAK-611) in Children With Metachromatic Leukodystrophy.

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by deficient arylsulfatase A (ASA) activity, which leads to neuronal sulfatide accumulation and motor and cognitive deterioration. Intrathecal delivery of a recombinant human ASA (TAK-611, formerly SHP611) is under development as a potential therapy for MLD. We used serum and cerebrospinal fluid (CSF) TAK-611 concentrations measured during the phase I/II trial of intrathecal TAK-611 to develop a pharmacokinetic (PK) model describing drug disposition. CSF data were well characterized by a two-compartment model in the central nervous system (CNS); a single central compartment described the serum data. Estimated parameters suggested rapid distribution of TAK-611 from CSF into the putative brain tissue compartment, with persistence in the brain between doses (median distributive and terminal half-lives in the CNS: 1.02 and 477 hours, respectively). This model provides a valuable basis for understanding the PK distribution of TAK-611 and for PK/pharmacodynamic analyses of functional outcomes.

Intrathecal baclofen in metachromatic leukodystrophy.

Metachromatic leukodystrophy (MLD) is a rare progressive neurological disorder, often accompanied by motor impairments that are challenging to treat. In this case series, we report the course of treatment with intrathecal baclofen (ITB), aimed at improving daily care and comfort in children and young adults with MLD. All patients with MLD in our centre on ITB treatment for a minimum of 6 months were included (n=10; 4 males, 6 females; mean age 10y 8mo [range 6-24y]). Eight patients had MLD with a predominant spastic movement disorder (sMLD) and two were mainly dyskinetic. Patients with sMLD were compared with matched patients with spastic cerebral palsy (CP). Complication rates related to ITB treatment were similar in both groups. ITB treatment course in the first 6 months after pump implantation appears to show more dose increase in most patients MLD, compared to patients with spastic CP. This may be due to the progressive disease in MLD. ITB is a feasible therapy to improve daily care and comfort in patients with MLD and should therefore be considered early. WHAT THIS PAPER ADDS: Intrathecal baclofen (ITB) is a feasible therapy to improve comfort and daily care in children and young people with metachromatic leukodystrophy (MLD). In the first 6 months of ITB treatment, MLD seems to show more dose increase compared to spastic cerebral palsy.

Potential of surfactant-coated nanoparticles to improve brain delivery of arylsulfatase A.

The lysosomal storage disorder (LSD) metachromatic leukodystrophy (MLD) is caused by a deficiency of the soluble, lysosomal hydrolase arylsulfatase A (ASA). The disease is characterized by accumulation of 3-O-sulfogalactosylceramide (sulfatide), progressive demyelination of the nervous system and premature death. Enzyme replacement therapy (ERT), based on regular intravenous injections of recombinant functional enzyme, is in clinical use for several LSDs. For MLD and other LSDs with central nervous system (CNS) involvement, however, ERT is limited by the blood-brain barrier (BBB) restricting transport of therapeutic enzymes from the blood to the brain. In the present study, the potential of different types of surfactant-coated biodegradable nanoparticles to increase brain delivery of ASA was evaluated. Three different strategies to bind ASA to nanoparticle surfaces were compared: (1) adsorption, (2) high-affinity binding via the streptavidin-biotin system, and (3) covalent binding. Adsorption allowed binding of high amounts of active ASA. However, in presence of phosphate-buffered saline or serum rapid and complete desorption occurred, rendering this strategy ineffective for in vivo applications. In contrast, stable immobilization with negligible dissociation was achieved by high-affinity and covalent binding. Consequently, we analyzed the brain targeting of two stably nanoparticle-bound ASA formulations in ASA-/- mice, an animal model of MLD. Compared to free ASA, injected as a control, the biodistribution of nanoparticle-bound ASA was altered in peripheral organs, but no increase of brain levels was detectable. The failure to improve brain delivery suggests that the ASA glycoprotein interferes with processes required to target surfactant-coated nanoparticles to brain capillary endothelial cells.

Anti-inflammatory Therapy With Simvastatin Improves Neuroinflammation and CNS Function in a Mouse Model of Metachromatic Leukodystrophy.

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by a functional deficiency of the lysosomal enzyme arylsulfatase A. The prevailing late-infantile variant of MLD is characterized by widespread and progressive demyelination of the central nervous system (CNS) causing death during childhood. In order to gain insight into the pathomechanism of the disease and to identify novel therapeutic targets, we analyzed neuroinflammation in two mouse models reproducing a mild, nondemyelinating, and a more severe, demyelinating, variant of MLD, respectively. Microgliosis and upregulation of cytokine/chemokine levels were clearly more pronounced in the demyelinating model. The analysis of the temporal cytokine/chemokine profiles revealed that the onset of demyelination is preceded by a sustained elevation of the macrophage inflammatory protein (MIP)-1α followed by an upregulation of MIP-1ß, monocyte chemotactic protein (MCP)-1, and several interleukins. The tumor necrosis factor (TNF)-α remains unchanged. Treatment of the demyelinating mouse model with the nonsteroidal anti-inflammatory drug simvastatin reduced neuroinflammation, improved the swimming performance and ataxic gait, and retarded demyelination of the spinal cord. Our data suggest that neuroinflammation is causative for demyelination in MLD mice and that anti-inflammatory treatment might be a novel therapeutic option to improve the CNS function of MLD patients.

Comparison of five peptide vectors for improved brain delivery of the lysosomal enzyme arylsulfatase A.

Enzyme replacement therapy (ERT) is a treatment option for lysosomal storage disorders (LSDs) caused by deficiencies of soluble lysosomal enzymes. ERT depends on receptor-mediated transport of intravenously injected recombinant enzyme to lysosomes of patient cells. The blood-brain barrier (BBB) prevents efficient transfer of therapeutic polypeptides from the blood to the brain parenchyma and thus hinders effective treatment of LSDs with CNS involvement. We compared the potential of five brain-targeting peptides to promote brain delivery of the lysosomal enzyme arylsulfatase A (ASA). Fusion proteins between ASA and the protein transduction domain of the human immunodeficiency virus TAT protein (Tat), an Angiopep peptide (Ang-2), and the receptor-binding domains of human apolipoprotein B (ApoB) and ApoE (two versions, ApoE-I and ApoE-II) were generated. All ASA fusion proteins were enzymatically active and targeted to lysosomes when added to cultured cells. In contrast to wild-type ASA, which is taken up by mannose-6-phosphate receptors, all chimeric proteins were additionally endocytosed via mannose-6-phosphate-independent routes. For ASA-Ang-2, ASA-ApoE-I, and ASA-ApoE-II, uptake was partially due to the low-density lipoprotein receptor-related protein 1. Transendothelial transfer in a BBB cell culture model was elevated for ASA-ApoB, ASA-ApoE-I, and ASA-ApoE-II. Brain delivery was, however, increased only for ASA-ApoE-II. ApoE-II was also superior to wild-type ASA in reducing lysosomal storage in the CNS of ASA-knock-out mice treated by ERT. Therefore, the ApoE-derived peptide appears useful to treat metachromatic leukodystrophy and possibly other neurological disorders more efficiently.

The natural course of gross motor deterioration in metachromatic leukodystrophy.

AIM: Motor deterioration is a key feature in metachromatic leukodystrophy (MLD). The lack of data about its natural course impedes evaluation of therapeutic interventions. This study aimed to provide data about motor decline in MLD. METHOD: Fifty-nine patients (27 males, 32 females) with MLD (21 with late-infantile MLD and 38 with juvenile MLD) were recruited within a nationwide survey (the German LEUKONET). Median (range) age at onset was 17 months (9-27) for the group with late-infantile MLD and 6 years 2 months (2y 11mo-14y) for the group with juvenile MLD. Gross motor function was assessed using the Gross Motor Function Classification for MLD. RESULTS: In late-infantile MLD, all patients showed loss of all gross motor function until 3 years 4 months of age. Patients with juvenile MLD showed a more variable and significantly longer motor decline (p<0.001). For a patient with the juvenile form showing first gait disturbances, the probability of remaining stable for more than 1 year was 84%, and 51% for more than 2 years. Having lost independent walking, subsequent motor decline was as steep as in the late-infantile form (median 5 mo, interquartile range 3-22). INTERPRETATION: The course of motor disease was more variable in juvenile MLD with respect to onset and dynamics. However, the motor decline after the loss of independent walking was similarly steep in both forms. These data can serve as a reference for clinical studies that are topics of current research and allow definition of inclusion/exclusion criteria.

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.

Intracerebroventricular enzyme infusion corrects central nervous system pathology and dysfunction in a mouse model of metachromatic leukodystrophy.

Arylsulfatase A (ASA) catalyzes the desulfation of sulfatide, a major lipid component of myelin. Inherited functional deficiencies of ASA cause the lysosomal storage disease (LSD) metachromatic leukodystrophy (MLD), which is characterized by intralysosomal accumulation of sulfatide, progressive neurological symptoms and early death. Enzyme replacement therapy (ERT) using intravenous injection of active enzyme is a treatment option for many LSDs as exogenous lysosomal enzymes are delivered to lysosomes of patient's cells via receptor-mediated endocytosis. Efficient treatment of MLD and other LSDs with central nervous system (CNS) involvement is, however, hampered by the blood-brain barrier (BBB), which limits transfer of therapeutic enzymes from the circulation to the brain parenchyma. To bypass the BBB, we infused recombinant human ASA (rhASA) by implanted miniature pumps into the cerebrospinal fluid (CSF) of a conventional and a novel, genetically aggravated ASA knockout mouse model of MLD. rhASA continuously delivered to the lateral ventricle for 4 weeks penetrated the brain parenchyma and was targeted to the lysosomes of brain cells. Histological analysis revealed complete reversal of lysosomal storage in the infused hemisphere. rhASA concentrations and sulfatide clearance declined with increasing distance from the infusion site. Correction of the ataxic gait indicated reversal of central nervous system dysfunctions. The profound histopathological and functional improvements, the requirement of low enzyme doses and the absence of immunological side effects suggest intracerebroventricular ERT to be a promising treatment option for MLD and other LSDs with prevailing CNS disease.

[Metachromatic leucodystrophy. Clinical, biological, and therapeutic aspects]. / La leucodystrophie métachromatique Aspects clinique, biologique et thérapeutique.

Scholz's disease or metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by a deficiency in arylsulfatase A (ARSA: EC 3.1.6.8). This enzyme is responsible for the degradation of sulfatides commonly called cerebroside-3-sulfate or 3-O-sulfogalactosylcéramide in galactocérébroside and sulfate. The success of hydrolysis of these sphingolipids by ARSA necessarily depends on the presence of saposine B forms a complex with the substrate. The pathological accumulation of sulfatides in the nervous system (myelin, neurons and glial cells) results most often neurological, mental retardation, nervous disorders, blindness. The metachromatic granules accumulated in the central nervous system and peripheral compounds are highly toxic. These are at high levels in the urine of patients affected by the MLD. Arylsulfatase A activity is collapsed in these patients. Unfortunately, the value of enzyme activity is not a predictor of clinical severity of the neuropathology. In contrast, the study of the gene that codes for the ARSA is seen as a way to diagnose the simplest and most reliable of the disease to avoid misdiagnosis due to the presence of pseudodeficit. The conventional therapeutic approaches are essentially symptomatic. They were made in order to restore the enzyme activity of arylsulfatase A and prevent the progression of the pathological accumulation of sulfatides and consequently reduce morbidity associated with MLD.

Clinical and biochemical study of 29 Brazilian patients with metachromatic leukodystrophy.

Metachromatic leukodystrophy (MLD) is a lysosomal disorder caused by arylsulfatase A (ARSA) deficiency. It is classified into three forms according to the age of onset of symptoms (late infantile, juvenile, and adult). We carried out a cross-sectional and retrospective study, which aimed to determine the epidemiological, clinical, and biochemical profile of MLD patients from a national reference center for Inborn Errors of Metabolism in Brazil. Twenty-nine patients (male, 17) agreed to participate in the study (late infantile form: 22; juvenile form: 4; adult form: 1; asymptomatic: 2). Mean ages at onset of symptoms and at biochemical diagnosis were, respectively, 19 and 39 months for late infantile form and 84.7 and 161.2 months for juvenile form. The most frequently reported first clinical symptom/sign of the disease was gait disturbance and other motor abnormalities (72.7%) for late infantile form and behavioral and cognitive alterations (50%) for juvenile form. Leukocyte ARSA activity level did not present significant correlation with the age of onset of symptoms (r = -0.09, p = 0.67). Occipital white matter and basal nuclei abnormalities were not found in patients with the late infantile MLD. Our results suggest that there is a considerable delay between the age of onset of signs and symptoms and the diagnosis of MLD in Brazil. Correlation between ARSA activity and MLD clinical form was not found. Further studies on the epidemiology and natural history of this disease with larger samples are needed, especially now when specific treatments should be available in the near future.

Induction of tolerance to human arylsulfatase A in a mouse model of metachromatic leukodystrophy.

A deficiency of arylsulfatase A (ASA) causes metachromatic leukodystrophy (MLD), a lysosomal storage disorder characterized by accumulation of sulfatide, a severe neurological phenotype and early death. The efficacy of enzyme replacement therapy (ERT) has previously been determined in ASA knockout (ASA-/-) mice representing the only available animal model for MLD. Repeated intravenous injection of human ASA (hASA) improved the nervous system pathology and function, but also elicited a progressive humoral immune response leading to treatment resistance, anaphylactic reactions, and high mortality. In contrast to ASA-/- mice, most MLD patients express mutant hASA which may entail immunological tolerance to substituted wildtype hASA and thus protect from immunological complications. To test this notion, a cysteine-to-serine substitution was introduced into the active site of the hASA and the resulting inactive hASA-C69S variant was constitutively expressed in ASA-/- mice. Mice with sub-to supranormal levels of mutant hASA expression were analyzed. All mice, including those showing transgene expression below the limit of detection, were immunologically unresponsive to injected hASA. More than 100-fold overexpression did not induce an overt new phenotype except occasional intralysosomal deposition of minor amounts of glycogen in hepatocytes. Furthermore, long-term, low-dose ERT reduced sulfatide storage in peripheral tissues and the central nervous system indicating that high levels of extracellular mutant hASA do not prevent cellular uptake and lysosomal targeting of substituted wildtype hASA. Due to the tolerance to hASA and maintenance of the MLD-like phenotype, the novel transgenic strain may be particularly advantageous to assess the benefit and risk of long-term ERT.

[Promoting myelin repair in disorders such as multiple sclerosis and some types of leukodystrophy: current studies]. / Approche expérimentale des stratégies réparatrices des maladies demyélinisantes du système nerveux central.

Several ways of promoting myelin repair in myelin disorders such as multiple sclerosis and certain types of leukodystrophies are currently being investigated. Numerous studies suggest that it is possible to repair the central nervous system (CNS) by cell transplantation or by enhancing endogenous remyelination. Investigations in animal models indicate that cell therapy results in robust anatomical and functional recovery of acute myelin lesions. These models are also used to explore and validate the role of candidate molecules to stimulate endogenous remyelination by activating the myelin competent population or providing neuroprotection. However, in view of the heterogeneity of the lesion environment in MS, it seems more likely that cell therapy alone will not be able to contribute efficiently to the repair of the lesion. Further developments should indicate whether combining multiple approaches will be more powerful to achieve global myelin repair in the CNS than applying these strategies alone.

Enzyme replacement improves nervous system pathology and function in a mouse model for metachromatic leukodystrophy.

A deficiency of arylsulfatase A (ASA) causes the lysosomal storage disease metachromatic leukodystrophy, which is characterized by accumulation of the sphingolipid 3-O-sulfogalactosylceramide (sulfatide). Sphingolipid storage results in progressive demyelination and severe neurologic symptoms. The disease is lethal, and curative therapy is not available. To assess the therapeutic potential of enzyme replacement therapy (ERT), ASA knockout mice were treated by intravenous injection of recombinant human ASA. Plasma levels of ASA declined with a half-time of approximately 40 min, and enzyme was detectable in tissues within minutes after injection. The uptake of injected enzyme was high into liver, moderate into peripheral nervous system (PNS) and kidney and very low into brain. The apparent half-life of endocytosed enzyme was approximately 4 days. A single injection led to a time- and dose-dependent decline of the excess sulfatide in PNS and kidney by up to 70%, but no reduction was seen in brain. Four weekly injections with 20 mg/kg body weight not only reduced storage in peripheral tissues progressively, but also were surprisingly effective in reducing sulfatide storage in brain and spinal cord. The histopathology of kidney and central nervous system was ameliorated. Improved neuromotor coordination capabilities and normalized peripheral compound motor action potential demonstrate the benefits of ERT on the nervous system function. Enzyme replacement may therefore be a promising therapeutic option in this devastating disease.