Induced pluripotent stem cell models of lysosomal storage disorders.

Induced pluripotent stem cells (iPSCs) have provided new opportunities to explore the cell biology and pathophysiology of human diseases, and the lysosomal storage disorder research community has been quick to adopt this technology. Patient-derived iPSC models have been generated for a number of lysosomal storage disorders, including Gaucher disease, Pompe disease, Fabry disease, metachromatic leukodystrophy, the neuronal ceroid lipofuscinoses, Niemann-Pick types A and C1, and several of the mucopolysaccharidoses. Here, we review the strategies employed for reprogramming and differentiation, as well as insights into disease etiology gleaned from the currently available models. Examples are provided to illustrate how iPSC-derived models can be employed to develop new therapeutic strategies for these disorders. We also discuss how models of these rare diseases could contribute to an enhanced understanding of more common neurodegenerative disorders such as Parkinson's disease, and discuss key challenges and opportunities in this area of research.

[Lysosomal Storage Diseases: Challenges in Multiprofessional Patient Care with Enzyme Replacement Therapy]. / Lysosomale Speichererkrankungen: Herausforderungen bei der sektorübergreifenden, multiprofessionellen Patientenversorgung mit Enzymersatztherapie.

Background Due to their rarity studies in (ultra-) rare diseases are difficult. Only for a minority of these diseases causal therapies are available. Development and production of enzyme replacement therapies (ERT) for example are challenging and expensive. The number of patients is low, costs per patient are high. We will focus on the challenges of providing long-term ERT to patients with lysosomal storage diseases (LSD) in an out- and inpatient setting based on a literature search in Pubmed and own experience. Many ERTs for LSDs have a positive cost-benefit ratio. Possible side-effects are severe allergic reactions. ERT is covered by the insurance companies when prescribed by a physician, however they are liable to recourse by the insurance company as the expenses for drugs of the prescribing physician will be above average. In most cases the recourse can be averted if diagnoses of individual patients are disclosed. Intravenous infusion of ERT is not well-regulated in Germany/Austria. Infusion on a ward is safe however often not covered by the insurance companies as patients do not stay overnight. Another option is infusion in a day-care setting, however the lump sum paid for infusion does not cover costs for ERT. On an individual basis, reimbursement for medication (ERT) has to be negotiated with the insurance companies before infusion takes place. Home infusions are feasible, however careful evaluations of the infusion-team and the risk for side-effects have to be performed on an individual basis, legal issues have to be considered. In- and outpatient ERT of patients with LSDs is challenging but feasible after individual evaluation of patient and infusion team.

Less Is More: Substrate Reduction Therapy for Lysosomal Storage Disorders.

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

Terapia génica en el tratamiento de los errores congénitos del metabolismo / Gene therapy for the treatment of inborn errors of metabolism

En la mayoría de los errores congénitos del metabolismo existe un defecto enzimático que produce el bloqueo de una ruta metabólica y el acúmulo de metabolitos tóxicos. Para su tratamiento actualmente disponemos de la restricción dietética, la potenciación de otras vías metabólicas alternativas y la sustitución de la enzima deficitaria mediante el trasplante de células, el trasplante hepático o la administración de la enzima purificada. La terapia génica, mediante la trasferencia en el organismo de una copia correcta del gen alterado mediante un vector, se perfila como el futuro en el tratamiento de este tipo de enfermedades. Sin embargo, la dificultad de los vectores actualmente empleados en atravesar la barrera hematoencefálica, su respuesta inmunitaria, su toxicidad celular, así como su potencial oncogénesis limitan enormemente su aplicación clínica en humanos (AU)

Due to the enzymatic defect in inborn errors of metabolism, there is a blockage in the metabolic pathways and an accumulation of toxic metabolites. Currently available therapies include dietary restriction, empowering of alternative metabolic pathways, and the replacement of the deficient enzyme by cell transplantation, liver transplantation or administration of the purified enzyme. Gene therapy, using the transfer in the body of the correct copy of the altered gene by a vector, is emerging as a promising treatment. However, the difficulty of vectors currently used to cross the blood brain barrier, the immune response, the cellular toxicity and potential oncogenesis are some limitations that could greatly limit its potential clinical application in human beings (AU)

[Current therapeutic strategies in lysosomal disorders]. / Stratégies thérapeutiques actuelles dans les maladies lysosomales.

The lysosomal storage disorders (LSD) comprise a heterogeneous group of inborn errors of metabolism. The resulting enzymatic defect leads to accumulation of its substrate in the lysosome. Their clinical patterns reflect the site of substrate storage. Central nervous system involvement is often present in the younger patients affected by the most severe phenotypes. Substantial progress has been made in the pathophysiological knowledge, leading to new therapeutic options in LSD. Enzyme replacement therapy (ERT) is the dominant approach and is actually proposed in six LSD: Gaucher disease, Fabry disease, Pompe disease and mucopolysaccharidoisis (MPS) I (Hurler disease), II (Hunter disease) and VI (Maroteaux-Lamy disease). This treatment reduces lysosomal storage, and sometimes reduces, but most often limits the progression of visceral involvement and of its clinical consequences. However, ERT does not cross the blood-brain barrier and is ineffective on neurological symptoms. In the younger patients with MPS I (Hurler disease) and with selected cases of other LSD, haematopoietic stem cell transplantation remains the optimal option. Other strategies using small molecules are being explored in order to cross the blood-brain barrier. This includes substrate reduction or depletion therapies, which decrease the amount of substrate, and the use of pharmacological chaperones, which enhance the residual activity of the mutant enzyme. Miglustat is the proposed substrate reduction therapy in Niemann-Pick C disease and clinical trials are actually performed in several LSD using other substrate reduction or chaperone drugs.

Use of complementary and alternative medicine by patients with lysosomal storage diseases.

PURPOSE: To evaluate the extent of complementary and alternative medicine use and perceived effectiveness in patients with lysosomal storage diseases. METHODS: A 26-item survey was distributed to 495 patients with type 1 Gaucher, Fabry, and type B Niemann-Pick diseases who were seen at the Lysosomal Storage Disease Program at the Mount Sinai School of Medicine. Survey responses were entered into an access database and analyzed using descriptive statistics. RESULTS: Surveys were completed by 167 respondents with an overall response rate of 34%. Complementary and alternative medicines were used by 45% of patients with type 1 Gaucher disease, 41% of patients with Fabry disease, and 47% of patients with type B Niemann-Pick for symptoms related to their disease. Complementary and alternative medicines were used most frequently by adult females (55%), in patients who reported having one or more invasive procedures due to their disease, patients who use one or more conventional medical therapies, or those with depression and/or anxiety. Overall perceived effectiveness of complementary and alternative medicine supplements was low; however, complementary and alternative medicine therapies were perceived as effective. CONCLUSION: Complementary and alternative medicines are commonly used among patients with lysosomal storage diseases. Assessment of the effectiveness of these approaches in the lysosomal storage diseases is needed, and physicians should be aware of complementary and alternative medicine therapies used by patients to evaluate safety and possible drug interactions.

Substrate deprivation therapy: a new hope for patients suffering from neuronopathic forms of inherited lysosomal storage diseases.

Lysosomal storage diseases are a group of disorders caused by defects in enzymes responsible for degradation of particular compounds in lysosomes. In most cases, these diseases are fatal, and until recently no treatment was available. Introduction of enzyme replacement therapy was a breakthrough in the treatment of some of the diseases. However, while this therapy is effective in reduction of many somatic symptoms, its efficacy in the treatment of the central nervous system is negligible, if any, mainly because of problems with crossing the blood-brain-barrier by intravenously administered enzyme molecules. On the other hand, there are many lysosomal storage diseases in which the central nervous system is affected. Results of very recent studies indicate that in at least some cases, another type of therapy, called substrate deprivation therapy (or substrate reduction therapy) may be effective in the treatment of neuronopathic forms of lysosomal storage diseases. This therapy, based on inhibition of synthesis of the compounds that cannot be degraded in cells of the patients, has been shown to be effective in several animal models of various diseases, and recent reports demonstrate its efficacy in the treatment of patients suffering from Niemann-Pick C disease and Sanfilippo disease.

Use of nonviral promoters in adenovirus-mediated gene therapy: reduction of lysosomal storage in the aspartylglucosaminuria mouse.

BACKGROUND: Aspartylglucosaminuria (AGU) is a lysosomal storage disease with severe neurodegenerative clinical features resulting from the deficiency of lysosomal aspartylglucosaminidase (AGA). The AGU knockout mouse is a good model to test different therapy strategies, as it mimics well the human pathogenesis of the disease exhibiting storage vacuoles in all tissues. In this study we investigated the efficiency of nonviral promoters in adenovirus-mediated gene therapy. METHODS: The deficient corrective enzyme, AGA, was expressed using two tissue-specific promoters, neuron-specific enolase (NSE), astrocyte-specific (GFAP) and the endogenous AGA promoter. An intrastriatal injection site was chosen due to its wide connections in the central nervous system (CNS). The expression of AGA was analyzed 1 week, 2 weeks, 4 weeks, 2 months and 4 months after the virus injection by lysosomal AGA-specific immunostaining. A correction of the lysosomal storage in the brain of treated mice was also studied using toluidine blue stained thin sections. RESULTS: The overexpressed AGA enzyme was detected in addition to the injection site, also in the ipsilateral parietal cortex indicating migration of AGA in the brain tissue. Duration of AGA expression was markedly longer with all the viruses used compared to the green fluorescent protein (GFP) expression driven by the viral cytomegalovirus (CMV) promoter. In most animals the storage was decreased by at least 50% as compared to untreated AGU mouse brains. Remarkably, >90% correction of storage at the ipsilateral cortex was found with the NSE promoter at 4 weeks and 2 months after injection. Additionally, partial clearance of storage was demonstrated also in the contralateral side of the brain. CONCLUSIONS: These data implicate that tissue-specific promoters are especially useful in virus-mediated gene therapy aiming at long-term gene expression.

Substrate reduction therapy for lysosomal storage diseases.

UNLABELLED: The treatment of disordered lipoprotein metabolism with the statin class of drugs is one of the most striking successes in the field of applied medical science: here the use of selective inhibitors of the first committed step of cholesterol biosynthesis, in a complex and highly regulated pathway, leads to improved outcome from a common lipid storage disease that is a blight on whole populations--atherosclerosis. By the same token, substrate reduction is an emerging therapeutic strategy for the arcane field of the lysosomal storage diseases (LSDs). Reduced biosynthesis of glucosylceramide is postulated to allow correction of the imbalance between formation and breakdown of glycosphingolipids; the therapeutic effect of substrate reduction depends upon the presence of residual hydrolytic activity towards those accumulated glycosphingolipid substrates derived from glucosylceramide. First pioneered in the laboratory by Norman Radin, this approach has now been introduced into the clinic: based on the ability to inhibit uridine diphosphate glucosylceramide transferase, the semi-selective iminosugar, N-butyldeoxynojirimycin, is licensed for the treatment of type 1 Gaucher disease. CONCLUSION: Inhibition of substrate formation has wide application in the treatment of LSDs. Decreased glucosylceramide biosynthesis has therapeutic potential in glycosphingolipidoses other than Gaucher disease, and offers promise in several neurodegenerative storage disorders that are currently beyond the reach of other procedures. The results of ongoing clinical trials of miglustat in type 3 Gaucher disease, Niemann-Pick disease type C and GM2 gangliosidosis are eagerly awaited.

Glycosphingolipid lysosomal storage diseases: therapy and pathogenesis.

Paediatric neurodegenerative diseases are frequently caused by inborn errors in glycosphingolipid (GSL) catabolism and are collectively termed the glycosphingolipidoses. GSL catabolism occurs in the lysosome and a defect in an enzyme involved in GSL degradation leads to the lysosomal storage of its substrate(s). GSLs are abundantly expressed in the central nervous system (CNS) and the disorders frequently have a progressive neurodegenerative course. Our understanding of pathogenesis in these diseases is incomplete and currently few options exist for therapy. In this review we discuss how mouse models of these disorders are providing insights into pathogenesis and also leading to progress in evaluating experimental therapies.

The molecular basis of lysosomal storage diseases and their treatment.

The lysosomal system is the main intracellular mechanism for the catabolism of naturally occurring endogenous and exogenous macromolecules and the subsequent recycling of their constituent monomeric components. It also plays an important part in processing essential metabolites. A genetic defect in a protein responsible for maintaining the lysosomal system results in the accumulation within lysosomes of partially degraded molecules, the initial step in the process leading to a lysosomal storage disease. The defective protein can be a luminal lysosomal enzyme or protein cofactor, a lysosomal membrane protein or a protein involved in the post-translational modification or transport of lysosomal proteins. Over 40 lysosomal storage diseases are known and they have a collective incidence of approximately 1 in 7000-8000 live births. Most of the genes for the lysosomal proteins have been cloned, permitting mutation analysis in individual cases. This information can be used for genotype/phenotype correlation, genetic counselling and the selection of patients for novel forms of therapy, such as substrate deprivation or dispersal, enzyme replacement, bone-marrow transplantation and gene transfer.