Enzyme replacement and enhancement therapies: lessons from lysosomal disorders

Preclinical dose-finding study with a liver-tropic, recombinant AAV-2/8 vector in the mouse model of galactosialidosis

Galactosialidosis (GS) is a lysosomal storage disease linked to deficiency of the protective protein/cathepsin A (PPCA). Similarly to GS patients, Ppca-null mice develop a systemic disease of the reticuloendothelial system, affecting most visceral organs and the nervous system. Symptoms include severe nephropathy, visceromegaly, infertility, progressive ataxia, and shortened life span. Here, we have conducted a preclinical, dose-finding study on a large cohort of GS mice injected intravenously at 1 month of age with increasing doses of a GMP-grade rAAV2/8 vector, expressing PPCA under the control of a liver-specific promoter. Treated mice, monitored for 16 weeks post-treatment, had normal physical appearance and behavior without discernable side effects. Despite the restricted expression of the transgene in the liver, immunohistochemical and biochemical analyses of other systemic organs, serum, and urine showed a dose-dependent, widespread correction of the disease phenotype, suggestive of a protein-mediated mechanism of cross-correction. A notable finding was that rAAV-treated GS mice showed high expression of PPCA in the reproductive organs, which resulted in reversal of their infertility. Together these results support the use of this rAAV-PPCA vector as a viable and safe method of gene delivery for the treatment of systemic disease in non-neuropathic GS patients.

Neural stem cell transplantation as a therapeutic approach for treating lysosomal storage diseases

Treating the central nervous system manifestations of subjects with neuropathic lysosomal storage diseases remains a major technical challenge. This is because of the low efficiency by which lysosomal enzymes in systemic circulation are able to traverse the blood brain barrier into the central nervous system. Intracranial transplantation of neural stems cells genetically modified to overexpress the respective deficient enzymes represents a potential approach to addressing this group of diseases. The unique properties of neural stem cells and progenitor cells, such as their ability to migrate to distal sites, differentiate into various cell types and integrate within the host brain without disrupting normal function, making them particularly attractive therapeutic agents. In addition, neural stem cells are amenable to ex vivo propagation and modification by gene transfer vectors. In this regard, transplanted cells can serve not only as a source of lysosomal enzymes but also as a means to potentially repair the injured brain by replenishing the organ with healthy cells and effecting the release of neuroprotective factors. This review discusses some of the well-characterized neural stem cell types and their possible use in treating neuropathic lysosomal storage diseases such as the Niemann Pick A disease.

Cell-specific aptamers as emerging therapeutics

Aptamers are short nucleic acids that bind to defined targets with high affinity and specificity. The first aptamers have been selected about two decades ago by an in vitro process named SELEX (systematic evolution of ligands by exponential enrichment). Since then, numerous aptamers with specificities for a variety of targets from small molecules to proteins or even whole cells have been selected. Their applications range from biosensing and diagnostics to therapy and target-oriented drug delivery. More recently, selections using complex targets such as live cells have become feasible. This paper summarizes progress in cell-SELEX techniques and highlights recent developments, particularly in the field of medically relevant aptamers with a focus on therapeutic and drug-delivery applications.

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.

Enzyme replacement therapy for Fabry disease: some answers but more questions

Fabry disease (FD) is a multisystem, X-linked disorder of glycosphingolipid metabolism caused by enzyme deficiency of α-galactosidase A. Affected patients have symptoms including acroparesthesias, angiokeratomas, and hypohidrosis. More serious manifestations include debilitating pain and gastrointestinal symptoms, proteinuria and gradual deterioration of renal function leading to end-stage renal disease, hypertrophic cardiomyopathy, and stroke. Heterozygous females may have symptoms as severe as males with the classic phenotype. Before 2001, treatment of patients with FD was supportive. The successful development of enzyme replacement therapy (ERT) has been a great advancement in the treatment of patients with FD and can stabilize renal function and cardiac size, as well as improve pain and quality of life of patients with FD. In this review, we have provided a critical appraisal of the literature on the effects of ERT for FD. This analysis shows that data available on the treatment of FD are often derived from studies which are not controlled, rely on surrogate markers, and are of insufficient power to detect differences on hard clinical endpoints. Further studies of higher quality are needed to answer the questions that remain concerning the efficacy of ERT for FD.

Ca2+ homeostasis modulation enhances the amenability of L444P glucosylcerebrosidase to proteostasis regulation in patient-derived fibroblasts

Gaucher's disease is caused by deficiency of lysosomal glucocerebrosidase (GC) activity and accumulation of GC substrate, glucosylceramide. A number of point mutations in GC encoding gene have been reported to destabilize the enzyme native structure, resulting in protein misfolding and degradation. Particularly, the L444P GC variant, often associated with neuropathic manifestations of the disease, is severely destabilized and immediately degraded, resulting in complete loss of enzymatic activity. In addition, glucosylceramide accumulation causes Ca(2+) efflux from the endoplasmic reticulum (ER) through ryanodine receptors (RyRs) in the neurons of Gaucher's disease patients. We hypothesized that excessive [Ca(2+)](ER) efflux impairs ER folding and studied how modulation of [Ca(2+)](ER) affects folding of L444P GC in patient-derived fibroblasts. We report that RyRs blockers mediated [Ca(2+)] modulation, recreating a "wild type-like" folding environment in the ER, more amenable to rescuing the folding of mutated L444P GC through proteostasis regulation. Treating patient-derived fibroblasts with a RyRs blocker and a proteostasis modulator, MG-132, results in enhanced folding, trafficking, and activity of the severely destabilized L444P GC variant. Global gene expression profiling and mechanistic studies were conducted to investigate the folding quality control expression pattern conducive to native folding of mutated L444P GC and revealed that the ER-lumenal BiP/GRP78 plays a key role in the biogenesis of this GC variant.

Long-term amelioration of feline Mucopolysaccharidosis VI after AAV-mediated liver gene transfer

Mucopolysaccharidosis VI (MPS VI) is caused by deficient arylsulfatase B (ARSB) activity resulting in lysosomal storage of glycosaminoglycans (GAGs). MPS VI is characterized by dysostosis multiplex, organomegaly, corneal clouding, and heart valve thickening. Gene transfer to a factory organ like liver may provide a lifetime source of secreted ARSB. We show that intravascular administration of adeno-associated viral vectors (AAV) 2/8-TBG-felineARSB in MPS VI cats resulted in ARSB expression up to 1 year, the last time point of the study. In newborn cats, normal circulating ARSB activity was achieved following delivery of high vector doses (6 × 10(13) genome copies (gc)/kg) whereas delivery of AAV2/8 vector doses as low as 2 × 10(12) gc/kg resulted in higher than normal serum ARSB levels in juvenile MPS VI cats. In MPS VI cats showing high serum ARSB levels, independent of the age at treatment, we observed: (i) clearance of GAG storage, (ii) improvement of long bone length, (iii) reduction of heart valve thickness, and (iv) improvement in spontaneous mobility. Thus, AAV2/ 8-mediated liver gene transfer represents a promising therapeutic strategy for MPS VI patients.

Type 2 Gaucher disease: phenotypic variation and genotypic heterogeneity

Gaucher disease (GD), the most common lysosomal storage disease, results from a deficiency of the lysosomal enzyme glucocerebrosidase. GD has been classified into 3 types, of which type 2 (the acute neuronopathic form) is the most severe, presenting pre- or perinatally, or in the first few months of life. Traditionally, type 2 GD was considered to have the most uniform clinical phenotype when compared to other GD subtypes. However, case studies over time have demonstrated that type 2 GD, like types 1 and 3, manifests with a spectrum of phenotypes. This review includes case reports that illustrate the broad range of clinical presentations encountered in type 2 GD, as well as a discussion of associated manifestations, pathological findings, diagnostic techniques, and a review of current therapies. While type 2 GD is generally associated with severe mutations in the glucocerebrosidase gene, there is also significant genotypic heterogeneity.

Lysosomal alpha-galactosidase controls the generation of self lipid antigens for natural killer T cells

Natural Killer T (NKT) cells are lipid-reactive, CD1d-restricted T lymphocytes important in infection, cancer, and autoimmunity. In addition to foreign antigens, NKT cells react with endogenous self lipids. However, in the face of stimulating self antigen, it remains unclear how overstimulation of NKT cells is avoided. We hypothesized that constantly degraded endogenous antigen only accumulates upon inhibition of alpha-galactosidase A (alpha-Gal-A) in lysosomes. Here, we show that alpha-Gal-A deficiency caused vigorous activation of NKT cells. Moreover, microbes induced inhibition of alpha-Gal-A activity in antigen-presenting cells. This temporary enzyme block depended on Toll-like receptor (TLR) signaling and ultimately triggered lysosomal lipid accumulation. Thus, we present TLR-dependent negative regulation of alpha-Gal-A as a mechanistic link between pathogen recognition and self lipid antigen induction for NKT cells.

Different serum enzyme levels are required to rescue the various systemic features of the mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are lysosomal storage disorders characterized by progressive accumulation of glycosaminoglycans (GAGs) in various tissues. Enzyme replacement therapy (ERT) for several MPSs is available to date. However, the efficacy of ERT is limited, in particular in compartments such as bone, cartilage, the brain, and the eyes. We selected a rodent model of an MPS, with no central nervous system storage, to study the impact, on systemic features of the disease, of various stable levels of exogenous enzymes produced by adeno-associated viral vector (AAV)-mediated liver gene transfer. Low levels (6% of normal) of circulating enzyme were enough to reduce storage and inflammation in the visceral organs and to ameliorate skull abnormalities; intermediate levels (11% of normal) were required to reduce urinary GAG excretion; and high levels (>or=50% of normal) rescued abnormalities of the long bones and motor activity. These data will be instrumental to design appropriate clinical protocols based on either enzyme or gene replacement therapy for MPS and to predict their impact on the pathological features of MPS.

Feasibility of using cryopreserved lymphoblastoid cells to diagnose some lysosomal storage diseases

OBJECTIVE

The Epstein-Barr virus (EBV) is utilized as a tool in the study of cellular biology because of its capacity to transform B-lymphocytes. For this reason, EBV is used in conservation of human B-lymphocytes for long periods for subsequent evaluation of lysosomal hydrolase activity. Lymphoblastoid cell lines have several advantages for use over other cell types, such as prompt availability and possibility to develop, characterize and standardize cell banks, to test effects of promising pharmaceutical reagents. The study below presents biochemical data that demonstrate validity of lymphoblastoid cell lines for diagnosis of GM1-gangliosidosis, Gaucher, Fabry and Pompe diseases and mucopolysaccharidosis type I.

MATERIALS AND METHODS

Cultures were prepared from peripheral blood, collected from 25 normal subjects and 13 affected individuals. Enzyme activities and immunohistochemistry (IHC) were measured. Activities of enzymes beta-galactosidase, beta-glucosidase, alpha-iduronidase, alpha-galactosidase and alpha-glucosidase were measured before and after cryopreservation for 180 days. Enzymatic activity was measured when transformation was confirmed by IHC.

RESULTS

We observed some significant alterations in enzymatic activity of non-cultured cells when compared to others that had been cultured for 12 days and kept frozen for 180 days.

CONCLUSIONS

However, these alterations did not invalidate use of the technology of transformation of lymphoblastoid cell lines with EBV, to diagnose the diseases mentioned above, in view of the fact that the cultured cells, before and after freezing, demonstrated similar enzymatic activities.

Development of GlcNAc-inspired iminocyclitiols as potent and selective N-acetyl-beta-hexosaminidase inhibitors

Human N-acetyl-beta-hexosaminidase (Hex) isozymes are considered to be important targets for drug discovery. They are directly linked to osteoarthritis because Hex is the predominant glycosidase released by chondrocytes to degrade glycosaminoglycan. Hex is also associated with lysosomal storage disorders. We report the discovery of GlcNAc-type iminocyclitiols as potent and selective Hex inhibitors, likely contributed by the gain of extra electrostatic and hydrophobic interactions. The most potent inhibitor had a K(i) of 0.69 nM against human Hex B and was 2.5 x 10(5) times more selective for Hex B than for a similar human enzyme O-GlcNAcase. These glycosidase inhibitors were shown to modulate intracellular levels of glycolipids, including ganglioside-GM2 and asialoganglioside-GM2.

Endoplasmic reticulum Ca2+ increases enhance mutant glucocerebrosidase proteostasis

Altering intracellular calcium levels is known to partially restore mutant enzyme homeostasis in several lysosomal storage diseases, but why? We hypothesize that endoplasmic reticulum (ER) calcium level increases enhance the folding, trafficking and function of these mutant misfolding/degradation-prone lysosomal enzymes by increasing chaperone function. Herein, we report that increasing ER calcium levels by reducing ER calcium efflux through the ryanodine receptor (antagonists or RNAi) or by promoting ER calcium influx by SERCA2b overexpression enhances mutant glucocerebrosidase (GC) homeostasis in Gaucher’s disease patient-derived cells. Post-translational regulation of the calnexin folding pathway by increasing the ER calcium concentration appears to enhance the capacity of this chaperone system to fold mutant misfolding-prone enzymes, increasing the folded mutant GC population that can engage the trafficking receptor at the expense of ER-associated degradation, increasing the lysosomal GC concentration.

Targeted Delivery of Protein Drugs by Nanocarriers

Recent advances in biotechnology demonstrate that peptides and proteins are the basis of a new generation of drugs. However, the transportation of protein drugs in the body is limited by their high molecular weight, which prevents the crossing of tissue barriers, and by their short lifetime due to immuno response and enzymatic degradation. Moreover, the ability to selectively deliver drugs to target organs, tissues or cells is a major challenge in the treatment of several human diseases, including cancer. Indeed, targeted delivery can be much more efficient than systemic application, while improving bioavailability and limiting undesirable side effects. This review describes how the use of targeted nanocarriers such as nanoparticles and liposomes can improve the pharmacokinetic properties of protein drugs, thus increasing their safety and maximizing the therapeutic effect.

New biotechnological and nanomedicine strategies for treatment of lysosomal storage disorders

This review discusses the multiple bio- and nanotechnological strategies developed in the last few decades for treatment of a group of fatal genetic diseases termed lysosomal storage disorders. Some basic foundation on the biomedical causes and social and clinical relevance of these diseases is provided. Several treatment modalities, from those currently available to novel therapeutic approaches under development, are also discussed; these include gene and cell therapies, substrate reduction therapy, chemical chaperones, enzyme replacement therapy, multifunctional chimeras, targeting strategies, and drug carrier approaches.

Catalytic mechanism of human alpha-galactosidase

The enzyme alpha-galactosidase (alpha-GAL, also known as alpha-GAL A; E.C. 3.2.1.22) is responsible for the breakdown of alpha-galactosides in the lysosome. Defects in human alpha-GAL lead to the development of Fabry disease, a lysosomal storage disorder characterized by the buildup of alpha-galactosylated substrates in the tissues. alpha-GAL is an active target of clinical research: there are currently two treatment options for Fabry disease, recombinant enzyme replacement therapy (approved in the United States in 2003) and pharmacological chaperone therapy (currently in clinical trials). Previously, we have reported the structure of human alpha-GAL, which revealed the overall structure of the enzyme and established the locations of hundreds of mutations that lead to the development of Fabry disease. Here, we describe the catalytic mechanism of the enzyme derived from x-ray crystal structures of each of the four stages of the double displacement reaction mechanism. Use of a difluoro-alpha-galactopyranoside allowed trapping of a covalent intermediate. The ensemble of structures reveals distortion of the ligand into a (1)S(3) skew (or twist) boat conformation in the middle of the reaction cycle. The high resolution structures of each step in the catalytic cycle will allow for improved drug design efforts on alpha-GAL and other glycoside hydrolase family 27 enzymes by developing ligands that specifically target different states of the catalytic cycle. Additionally, the structures revealed a second ligand-binding site suitable for targeting by novel pharmacological chaperones.

Deregulated sphingolipid metabolism and membrane organization in neurodegenerative disorders

Sphingolipids are polar membrane lipids present as minor components in eukaryotic cell membranes. Sphingolipids are highly enriched in nervous cells, where they exert important biological functions. They deeply affect the structural and geometrical properties and the lateral order of cellular membranes, modulate the function of several membrane-associated proteins, and give rise to important intra- and extracellular lipid mediators. Sphingolipid metabolism is regulated along the differentiation and development of the nervous system, and the expression of a peculiar spatially and temporarily regulated sphingolipid pattern is essential for the maintenance of the functional integrity of the nervous system: sphingolipids in the nervous system participate to several signaling pathways controlling neuronal survival, migration, and differentiation, responsiveness to trophic factors, synaptic stability and synaptic transmission, and neuron-glia interactions, including the formation and stability of central and peripheral myelin. In several neurodegenerative diseases, sphingolipid metabolism is deeply deregulated, leading to the expression of abnormal sphingolipid patterns and altered membrane organization that participate to several events related to the pathogenesis of these diseases. The most impressive consequence of this deregulation is represented by anomalous sphingolipid-protein interactions that are at least, in part, responsible for the misfolding events that cause the fibrillogenic and amyloidogenic processing of disease-specific protein isoforms, such as amyloid beta peptide in Alzheimer's disease, huntingtin in Huntington's disease, alpha-synuclein in Parkinson's disease, and prions in transmissible encephalopathies. Targeting sphingolipid metabolism represents today an underexploited but realistic opportunity to design novel therapeutic strategies for the intervention in these diseases.

Induced secretion of beta-hexosaminidase by human brain endothelial cells: a novel approach in Sandhoff disease?

Sandhoff disease is an autosomal recessive lysosomal disorder due to mutations in the beta-hexosaminidase beta-chain gene, resulting in beta-hexosaminidases A (alphabeta) and B (betabeta) deficiency and GM2 ganglioside accumulation in the brain. In this study, our aim was to demonstrate that transduction of cerebral endothelial cells cultured in two-chamber culture inserts with a lentiviral vector encoding the hexosaminidases alpha and beta chains could induce a vectorial secretion of hexosaminidases. Therefore, the human cerebral endothelial cell line hCMEC/D3 was infected with the bicistronic vector from the apical compartment, and beta-hexosaminidase activity was measured in transduced cells and in deficient fibroblasts co-cultured in the basal (i.e. brain) compartment. Induced beta-hexosaminidase secretion by transduced hCMEC/D3 cells was sufficient to allow for a 70-90% restoration of beta-hexosaminidase activity in deficient fibroblasts. On the basis of these in vitro data, we propose that brain endothelium be considered as a novel therapeutic target in Sandhoff disease.

The 1.9 a structure of human alpha-N-acetylgalactosaminidase: The molecular basis of Schindler and Kanzaki diseases

alpha-N-acetylgalactosaminidase (alpha-NAGAL; E.C. 3.2.1.49) is a lysosomal exoglycosidase that cleaves terminal alpha-N-acetylgalactosamine residues from glycopeptides and glycolipids. In humans, a deficiency of alpha-NAGAL activity results in the lysosomal storage disorders Schindler disease and Kanzaki disease. To better understand the molecular defects in the diseases, we determined the crystal structure of human alpha-NAGAL after expressing wild-type and glycosylation-deficient glycoproteins in recombinant insect cell expression systems. We measured the enzymatic parameters of our purified wild-type and mutant enzymes, establishing their enzymatic equivalence. To investigate the binding specificity and catalytic mechanism of the human alpha-NAGAL enzyme, we determined three crystallographic complexes with different catalytic products bound in the active site of the enzyme. To better understand how individual defects in the alpha-NAGAL glycoprotein lead to Schindler disease, we analyzed the effect of disease-causing mutations on the three-dimensional structure.

Inherited metabolic disorders involving the eye: a clinico-biochemical perspective

The diagnosis of inborn errors of metabolism is challenging for most physicians. Improvements in medical technology and greater knowledge of the human genome are resulting in significant changes in the diagnosis, classification, and treatment of inherited metabolic disorders (IMDs). Many known inborn errors of metabolism will be recognised earlier or treated differently because of these changes. It is important that physicians recognise the clinical signs of IMDs and know when to propose advanced laboratory testing or referral to a higher centre for better patient management. Ocular manifestations occur in various metabolic disorders. Although there is an extensive understanding of many inborn errors of metabolism at the biochemical, molecular, and metabolic levels, little is known about their pathogenesis. In particular, how systemic metabolic disease contributes to ocular defects remains to be elucidated in IMDs. The occurrence of eye abnormalities could be due to direct toxic mechanisms of abnormal metabolic products or accumulation of normal metabolites by errors of synthetic pathways or by deficient energy metabolism. A detailed ophthalmological assessment is essential. Definitive diagnosis and management of patients with IMDs is ideally carried out by a combination of specialists, including an ophthalmologist, paediatrician, biochemist, and medical geneticist. Recent advances in the diagnosis and treatment of IMDs have substantially improved the prognosis for many of these conditions.

Doença de Fabry

A doença de Fabry é enfermidade de armazenamento lisossômico rara, ligada ao cromossomo-X, causada pela deficiência parcial ou completa da enzima alfagalactosidase A. O defeito resulta no acúmulo de globotriaosilceramida no endotélio vascular e tecidos viscerais, sendo a pele, o coração, os rins e o sistema nervoso central os mais afetados. As autoras realizam revisão da literatura relacionada a essa afecção e ressaltam que o reconhecimento precoce dos angioqueratomas e da hipoidrose constitui sinal-chave no diagnóstico dessa doença grave. Destacam também a necessidade de esses doentes serem avaliados por equipe multidisciplinar.

Design, synthesis, and biological evaluation of enantiomeric beta-N-acetylhexosaminidase inhibitors LABNAc and DABNAc as potential agents against Tay-Sachs and Sandhoff disease

N-Acetylhexosaminidases are of considerable importance in mammals and are involved in various significant biological processes. In humans, deficiencies of these enzymes in the lysosome, resulting from inherited genetic defects, cause the glycolipid storage disorders Tay-Sachs and Sandhoff diseases. One promising therapy for these diseases involves the use of beta-N-acetylhexosaminidase inhibitors as chemical chaperones to enhance the enzyme activity above sub-critical levels. Herein we describe the synthesis and biological evaluation of a potent inhibitor, 2-acetamido-1,4-imino-1,2,4-trideoxy-L-arabinitol (LABNAc), in a high-yielding 11-step procedure from D-lyxonolactone. The N-benzyl and N-butyl analogues were also prepared and found to be potent inhibitors. The enantiomers DABNAc and NBn-DABNAc were synthesised from L-lyxonolactone, and were also evaluated. The L-iminosugar LABNAc and its derivatives were found to be potent noncompetitive inhibitors of some beta-N-acetylhexosaminidases, while the D-iminosugar DABNAc and its derivatives were found to be weaker competitive inhibitors. These results support previous work postulating that D-iminosugar mimics inhibit D-glycohydrolases competitively, and that their corresponding L-enantiomers show noncompetitive inhibition of these enzymes. Molecular modelling studies confirm that the spatial organisation in enantiomeric inhibitors leads to a different overlay with the monosaccharide substrate. Initial cell-based studies suggest that NBn-LABNAc can act as a chemical chaperone to enhance the deficient enzyme's activity to levels that may cause a positive pharmacological effect. LABNAc, NBn-LABNAc, and NBu-LABNAc are potent and selective inhibitors of beta-N-acetylhexosaminidase and may be useful as therapeutic agents for treating adult Tay-Sachs and Sandhoff diseases.

Abnormal autophagy, ubiquitination, inflammation and apoptosis are dependent upon lysosomal storage and are useful biomarkers of mucopolysaccharidosis VI

Background

Lysosomal storage diseases are characterized by intracellular accumulation of metabolites within lysosomes. Recent evidence suggests that lysosomal storage impairs autophagy resulting in accumulation of polyubiquitinated proteins and dysfunctional mitochondria, ultimately leading to apoptosis. We studied the relationship between lysosome storage and impairment of different intracellular pathways and organelle function in mucopolysaccharidosis VI, which is characterized by accumulation of dermatan sulfate and signs of visceral and skeletal but not cerebral involvement.

Results

We show lysosomal storage, impaired autophagy, accumulation of polyubiquitinated proteins, and mitochondrial dysfunction in fibroblasts from mucopolysaccharidosis VI patients. We observe similar anomalies, along with inflammation and cell death, in association with dermatan sulfate storage in the visceral organs of mucopolysaccharidosis VI rats, but not in their central nervous system where dermatan sulfate storage is absent. Importantly, we show that prevention of dermatan sulfate storage in the mucopolysaccharidosis VI rat visceral organs by gene transfer results in correction of abnormal autophagy, inflammation, and apoptosis, suggesting that dermatan sulfate accumulation impairs lysosomal ability to receive and degrade molecules and organelles from the autophagic pathway, thus leading to cell toxicity.

Conclusion

These results indicate that the non-lysosomal degradation pathways we found activated in mucopolysaccharidosis VI can be both targets of new experimental therapies and biomarkers for follow-up of existing treatments.

Systems pharmacology and genome medicine: a future perspective

Genome medicine uses genomic information in the diagnosis of disease and in prescribing treatment. This transdisciplinary field brings together knowledge on the relationships between genetics, pathophysiology and pharmacology. Systems pharmacology aims to understand the actions and adverse effects of drugs by considering targets in the context of the biological networks in which they exist. Genome medicine forms the base on which systems pharmacology can develop. Experimental and computational approaches enable systems pharmacology to obtain holistic, mechanistic information on disease networks and drug responses, and to identify new drug targets and specific drug combinations. Network analyses of interactions involved in pathophysiology and drug response across various scales of organization, from molecular to organismal, will allow the integration of the systems-level understanding of drug action with genome medicine. The interface of the two fields will enable drug discovery for personalized medicine. Here we provide a perspective on the questions and approaches that drive the development of these new interrelated fields.

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

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

Aptamer-based endocytosis of a lysosomal enzyme

Enzyme replacement therapy for lysosomal storage diseases is currently based on endocytosis of lysosomal enzymes via the mannose or mannose 6-phosphate receptors. We are developing a technology for endocytosis of lysosomal enzymes that depends on generic, chemically conjugated reagents. These reagents are aptamers (single-stranded nucleic acid molecules) selected to bind to the extracellular domain of the mouse transferrin receptor. After selection, an RNA aptamer and a DNA aptamer were modified with biotin and linked to dye-labeled streptavidin for detection by confocal microscopy. Aptamer-streptavidin conjugates showed saturable uptake into mouse fibroblasts (Ltk(-) cells), which could be inhibited by an excess of free aptamer but not by tRNA, calf thymus DNA, or transferrin. The RNA aptamer-streptavidin conjugate was mouse-specific, as human cells (293T) did not take it up unless first transfected with the mouse transferrin receptor. Some streptavidin separated from the recycling pathway of transferrin and colocalized with lysosomes. After characterization in the model system, the DNA aptamer was conjugated to a lysosomal enzyme, alpha-l-iduronidase, from which mannose 6-phosphate had been removed. The aptamer had been modified by attachment of terminal glycerol for oxidation by periodate and reaction of the resulting aldehyde with amino groups on the protein. Dephospho-alpha-L-iduronidase-aptamer conjugate was taken up in saturable manner by alpha-L-iduronidase-deficient mouse fibroblasts, with half-maximal uptake estimated as 1.6 nM. Endocytosed enzyme-aptamer conjugate corrected glycosaminoglycan accumulation, indicating that it reached lysosomes and was functional in those organelles. Both uptake and correction were inhibited by unconjugated aptamer, confirming the role of the aptamer in receptor-mediated endocytosis.

Umbilical cord-blood transplantations from unrelated donors in patients with inherited metabolic diseases: Single-institute experience

We evaluated the feasibility of UCBT from unrelated donors and a myeloablative preparative regimen that did not involve anti-thymocyte globulin in five children with lysosomal and peroxisomal diseases. Patients with MPS II (n = 1), adrenoleukodystrophy (n = 1), metachromatic leukodystrophy (n = 2), and Krabbe disease (n = 1) received UCBT between December 2001 and September 2005. All patients received oral Bu (600 mg/m2), CY (200 mg/kg IV), and fludarabine (180 mg/m2 IV). Prophylaxis for GVHD consisted of a combination of tacrolimus and a short methotrexate course. Neutrophil engraftment occurred a median of 24 days (range, 21-25) after transplantation. None had graft rejection. One patient developed grade III acute GVHD and the other four patients had grade I acute GVHD; none had extensive chronic GVHD. One patient developed hemorrhagic cystitis. There were no treatment-related deaths. Although one child with MPS II died of PTLD 10 months after the UCBT, four of the five children are alive 14, 20, 31, and 55 months after transplantation with complete donor chimerism. These results suggest the feasibility of the UCBT with Bu, fludarabine, and CY-preparative regimen for patients with inherited metabolic diseases.

Partial restoration of mutant enzyme homeostasis in three distinct lysosomal storage disease cell lines by altering calcium homeostasis

A lysosomal storage disease (LSD) results from deficient lysosomal enzyme activity, thus the substrate of the mutant enzyme accumulates in the lysosome, leading to pathology. In many but not all LSDs, the clinically most important mutations compromise the cellular folding of the enzyme, subjecting it to endoplasmic reticulum–associated degradation instead of proper folding and lysosomal trafficking. A small molecule that restores partial mutant enzyme folding, trafficking, and activity would be highly desirable, particularly if one molecule could ameliorate multiple distinct LSDs by virtue of its mechanism of action. Inhibition of L-type Ca²⁺ channels, using either diltiazem or verapamil—both US Food and Drug Administration–approved hypertension drugs—partially restores N370S and L444P glucocerebrosidase homeostasis in Gaucher patient–derived fibroblasts; the latter mutation is associated with refractory neuropathic disease. Diltiazem structure-activity studies suggest that it is its Ca²⁺ channel blocker activity that enhances the capacity of the endoplasmic reticulum to fold misfolding-prone proteins, likely by modest up-regulation of a subset of molecular chaperones, including BiP and Hsp40. Importantly, diltiazem and verapamil also partially restore mutant enzyme homeostasis in two other distinct LSDs involving enzymes essential for glycoprotein and heparan sulfate degradation, namely α-mannosidosis and type IIIA mucopolysaccharidosis, respectively. Manipulation of calcium homeostasis may represent a general strategy to restore protein homeostasis in multiple LSDs. However, further efforts are required to demonstrate clinical utility and safety.

Lysosomes are organelles that contain more than 50 hydrolytic enzymes that break down macromolecules in a cell. A lysosomal storage disease results from deficient activity of one or more of these enzymes, leading to the accumulation of corresponding substrate(s). Currently, lysosomal storage diseases are treated by enzyme replacement therapy, which can be challenging because the enzyme has to enter the cell and the lysosome to function; in neuropathic diseases, enzyme replacement is not useful because recombinant enzymes do not enter the brain. We have shown that diltiazem and verapamil, potent US Food and Drug Administration–approved L-type Ca²⁺ channel blocker drugs, increased the endoplasmic reticulum (ER) folding capacity, trafficking, and activity of mutant lysosomal enzymes associated with three distinct lysosomal storage diseases. These compounds appear to function through a Ca²⁺ ion–mediated up-regulation of a subset of cytoplasmic and ER lumenal chaperones, possibly by activating signaling pathways that mitigate cellular stress. We have shown that increasing ER calcium levels appears to be a relatively selective strategy to partially restore mutant lysosomal enzyme homeostasis in diseases caused by the misfolding and degradation of nonhomologous mutant enzymes. Because diltiazem crosses the blood–brain barrier, it may be useful for the treatment of neuropathic lysosomal storage diseases, and possibly other loss-of-function diseases, although efficacy needs to be demonstrated.

By adapting the protein homeostasis network, altering calcium homeostasis can restore the cell's ability to fold and traffic proteins prone to misfolding, offering a new strategy to ameliorate loss-of-function diseases.

Acidic amino acid tag enhances response to enzyme replacement in mucopolysaccharidosis type VII mice

We have tested an acidic oligopeptide-based targeting system for delivery of enzymes to tissues, especially bone and brain, in a murine mucopolysaccharidosis type VII (MPS VII) model. This strategy is based upon tagging a short peptide consisting of acidic amino acids (AAA) to N terminus of human beta-glucuronidase (GUS). The pharmacokinetics, biodistribution, and the pathological effect on MPS VII mouse after 12 weekly infusions were determined for recombinant human untagged and tagged GUS. The tagged GUS was taken up by MPS VII fibroblasts in a mannose 6-phosphate receptor-dependent manner. Intravenously injected AAA-tagged enzyme had five times more prolonged blood clearance compared with the untagged enzyme. The tagged enzyme was delivered effectively to bone, bone marrow, and brain in MPS VII mice and was effective in reversing the storage pathology. The storage in osteoblasts was cleared similarly with both enzyme types. However, cartilage showed a little response to any of the enzymes. The tagged enzyme reduced storage in cortical neurons, hippocampus, and glia cells. A highly sensitive method of tandem mass spectrometry on serum indicated that the concentration of serum dermatan sulfate and heparan sulfate in mice treated with the tagged enzyme decreased more than the untagged enzyme. These preclinical studies suggest that this AAA-based targeting system may enhance enzyme-replacement therapy.

Central nervous system therapy for lysosomal storage disorders

✓ Most lysosomal storage disorders are characterized by progressive central nervous system impairment, with or without systemic involvement. Affected individuals have an array of symptoms related to brain dysfunction, the most devastating of which is neurodegeneration following a period of normal development. The blood–brain barrier has represented a significant impediment to developing therapeutic approaches to treat brain disease, but novel approaches—including enzyme replacement, small-molecule, gene, and cell-based therapies—have given children afflicted by these conditions and those who care for them hope for the future.

Delivery of acid sphingomyelinase in normal and niemann-pick disease mice using intercellular adhesion molecule-1-targeted polymer nanocarriers

Type B Niemann-Pick disease (NPD) is a multiorgan system disorder caused by a genetic deficiency of acid sphingomyelinase (ASM), for which lung is an important and challenging therapeutic target. In this study, we designed and evaluated new delivery vehicles for enzyme replacement therapy of type B NPD, consisting of polystyrene and poly(lactic-coglycolic) acid polymer nanocarriers targeted to intercellular adhesion molecule (ICAM)-1, an endothelial surface protein up-regulated in many pathologies, including type B NPD. Real-time vascular imaging using intravital microscopy and postmortem imaging of mouse organs showed rapid, uniform, and efficient binding of fluorescently labeled ICAM-1-targeted ASM nanocarriers (anti-ICAM/ASM nanocarriers) to endothelium after i.v. injection in mice. Fluorescence microscopy of lung alveoli actin, tissue histology, and 125I-albumin blood-to-lung transport showed that anti-ICAM nanocarriers cause neither detectable lung injury, nor abnormal vascular permeability in animals. Radioisotope tracing showed rapid disappearance from the circulation and enhanced accumulation of anti-ICAM/125I-ASM nanocarriers over the nontargeted naked enzyme in kidney, heart, liver, spleen, and primarily lung, both in wild-type and ASM knockout mice. These data demonstrate that ICAM-1-targeted nanocarriers may enhance enzyme replacement therapy for type B NPD and perhaps other lysosomal storage disorders.

Lending a helping hand, screening chemical libraries for compounds that enhance beta-hexosaminidase A activity in GM2 gangliosidosis cells

Enzyme enhancement therapy is an emerging therapeutic approach that has the potential to treat many genetic diseases. Candidate diseases are those associated with a mutant protein that has difficulty folding and/or assembling into active oligomers in the endoplasmic reticulum. Many lysosomal storage diseases are candidates for enzyme enhancement therapy and have the additional advantage of requiring only 5-10% of normal enzyme levels to reduce and/or prevent substrate accumulation. Our long experience in working with the beta-hexosaminidase (EC 3.2.1.52) isozymes system and its associated deficiencies (Tay-Sachs and Sandhoff disease) lead us to search for possible enzyme enhancement therapy-agents that could treat the chronic forms of these diseases which express 2-5% residual activity. Pharmacological chaperones are enzyme enhancement therapy-agents that are competitive inhibitors of the target enzyme. Each of the known beta-hexosaminidase inhibitors (low microm IC50) increased mutant enzyme levels to >or= 10% in chronic Tay-Sachs fibroblasts and also attenuated the thermo-denaturation of beta-hexosaminidase. To expand the repertoire of pharmacological chaperones to more 'drug-like' compounds, we screened the Maybridge library of 50,000 compounds using a real-time assay for noncarbohydrate-based beta-hexosaminidase inhibitors and identified several that functioned as pharmacological chaperones in patient cells. Two of these inhibitors had derivatives that had been tested in humans for other purposes. These observations lead us to screen the NINDS library of 1040 Food and Drug Administration approved compounds for pharmacological chaperones. Pyrimethamine, an antimalarial drug with well documented pharmacokinetics, was confirmed as a beta-hexosaminidase pharmacological chaperone and compared favorably with our best carbohydrate-based pharmacological chaperone in patient cells with various mutant genotypes.

Cellular uptake and lysosomal delivery of galactocerebrosidase tagged with the HIV Tat protein transduction domain

A number of studies have shown that a short peptide, the protein transduction domain (PTD) derived from the HIV-1 Tat protein (Tat-PTD) improved cellular uptake in vitro and distribution in vivo of recombinant proteins bearing such PTDs when administered systemically. To investigate the effects of Tat-PTD addition on the subcellular localization of the lysosomal enzyme galactocerebrosidase (GALC, EC 3.2.2.46) and with a view towards designing improved therapeutic strategies for Krabbe disease (globoid cell leukodystrophy), mouse GALC was tagged C-terminally with the Tat-PTD. Compared with unmodified GALC, GALC bearing a Tat-PTD, a myc epitope and 6 consecutive His residues [GALC-TMH (Tat-PTD, a myc epitope and 6 consecutive His residues)] was found to be secreted more efficiently. Also, GALC-TMH was found to be taken up by cells both via mannose-6-phosphate receptor (M6PR)-mediated endocytosis as well as by M6PR-independent mechanisms. GALC-TMH displayed increased M6PR-independent uptake in fibroblasts derived from twitcher mice (a murine model of globoid cell leukodystrophy) and in neurons derived from the mouse brain cortex compared with GALC lacking a Tat-PTD. Immunocytochemical analyses revealed that Tat-modified GALC protein co-localized in part with the lysosome-associated membrane protein-1. Complete correction of galactosylceramide accumulation was achieved in twitcher mouse fibroblasts lacking GALC activity following addition of GALC-TMH. Therefore, GALC-TMH not only maintained the features of the native GALC protein including enzymatic function, intracellular transport and location, but also displayed more efficient cellular uptake.

Emerging roles of proteases in tumour suppression

Proteases have long been associated with cancer progression because of their ability to degrade extracellular matrices, which facilitates invasion and metastasis. However, recent studies have shown that these enzymes target a diversity of substrates and favour all steps of tumour evolution. Unexpectedly, the post-trial studies have also revealed proteases with tumour-suppressive effects. These effects are associated with more than 30 different enzymes that belong to three distinct protease classes. What are the clinical implications of these findings?

Late endosomal cholesterol accumulation leads to impaired intra-endosomal trafficking

Background

Pathological accumulation of cholesterol in late endosomes is observed in lysosomal storage diseases such as Niemann-Pick type C. We here analyzed the effects of cholesterol accumulation in NPC cells, or as phenocopied by the drug U18666A, on late endosomes membrane organization and dynamics.

Methodology/Principal Findings

Cholesterol accumulation did not lead to an increase in the raft to non-raft membrane ratio as anticipated. Strikingly, we observed a 2–3 fold increase in the size of the compartment. Most importantly, properties and dynamics of late endosomal intralumenal vesicles were altered as revealed by reduced late endosomal vacuolation induced by the mutant pore-forming toxin ASSP, reduced intoxication by the anthrax lethal toxin and inhibition of infection by the Vesicular Stomatitis Virus.

Conclusions/Significance

These results suggest that back fusion of intralumenal vesicles with the limiting membrane of late endosomes is dramatically perturbed upon cholesterol accumulation.

A macrophage-nanozyme delivery system for Parkinson's disease

Selective delivery of antioxidants to the substantia nigra pars compacta (SNpc) during Parkinson's disease (PD) can potentially attenuate oxidative stress and as such increase survival of dopaminergic neurons. To this end, we developed a bone-marrow-derived macrophage (BMM) system to deliver catalase to PD-affected brain regions in an animal model of human disease. To preclude BMM-mediated enzyme degradation, catalase was packaged into a block ionomer complex with a cationic block copolymer, polyethyleneimine-poly(ethylene glycol) (PEI-PEG). The self-assembled catalase/PEI-PEG complexes, "nanozymes", were ca. 60 to 100 nm in size, stable in pH and ionic strength, and retained antioxidant activities. Cytotoxicity was negligible over a range of physiologic nanozyme concentrations. Nanozyme particles were rapidly, 40-60 min, taken up by BMM, retained catalytic activity, and released in active form for greater than 24 h. In contrast, "naked" catalase was rapidly degraded. The released enzyme decomposed microglial hydrogen peroxide following nitrated alpha-synuclein or tumor necrosis factor alpha activation. Following adoptive transfer of nanozyme-loaded BMM to 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine-intoxicated mice, ca. 0.6% of the injected dose were found in brain. We conclude that cell-mediated delivery of nanozymes can reduce oxidative stress in laboratory and animal models of PD.

Molecular pathogenesis of alpha-1-antitrypsin deficiency-associated liver disease: a meeting review

In recent years, we have witnessed several important paradigm shifts in understanding the molecular basis of liver disease in alpha-1-antitrypsin (AT) deficiency. These shifts have become possible as a result of a number of advances in research on the cell biology of aggregation-prone mutant proteins and in research on the pathobiological mechanisms of liver disease in general. Late-breaking research in these areas was the subject of an AASLD/Alpha-1 Foundation Single Topic Conference in Atlanta, Georgia, on January 26 to 28, 2006. The conference was titled "Alpha-1-Antitrypsin Deficiency and Other Liver Diseases Caused by Aggregated Proteins." Investigators from all over the world, representing a broad array of scientific disciplines and perspectives, discussed the pathobiology of AT deficiency, mechanisms of cell injury in diseases associated with aggregation-prone proteins, pathways by which cells respond to protein aggregation and mislocalization, and mechanisms of liver injury in general and in diseases related to AT deficiency. A session of the meeting was devoted to novel therapeutic strategies being developed for AT deficiency as well as to strategies either in development or already being applied to the class of diseases associated with mutant proteins.

Enzyme enhancement activity of N-octyl-β-valienamine on β-glucosidase mutants associated with Gaucher disease

Gaucher disease (GD), caused by a defect of beta-glucosidase (beta-Glu), is the most common form of sphingolipidosis. We have previously shown that a carbohydrate mimic N-octyl-beta-valienamine (NOV), an inhibitor of beta-Glu, could increase the protein level and enzyme activity of F213I mutant beta-Glu in cultured GD fibroblasts, suggesting that NOV acted as a pharmacological chaperone to accelerate transport and maturation of this mutant enzyme. In the current study, NOV effects were evaluated in GD fibroblasts with various beta-Glu mutations and in COS cells transiently expressing recombinant mutant proteins. In addition to F213I, NOV was effective on N188S, G202R and N370S mutant forms of beta-Glu, whereas it was ineffective on G193W, D409H and L444P mutants. When expressed in COS cells, the mutant proteins as well as the wild-type protein were localized predominantly in the endoplasmic reticulum and were sensitive to Endo-H treatment. NOV did not alter this localization or Endo-H sensitivity, suggesting that it acted in the endoplasmic reticulum. Profiling of N-alkyl-beta-valienamines with various lengths of the acyl chain showed that N-dodecyl-beta-valienamine was as effective as NOV. These results suggest a potential therapeutic value of NOV and related compounds for GD with a broad range of beta-Glu mutations.

Ectopic expression of a conifer Abscisic Acid Insensitive3 transcription factor induces high-level synthesis of recombinant human alpha-L-iduronidase in transgenic tobacco leaves

We are examining various plant-based systems to produce enzymes for the treatment of human lysosomal storage disorders. Constitutive expression of the gene encoding the human lysosomal enzyme, alpha-L-iduronidase (IDUA; EC 3.2.1.76) in leaves of transgenic tobacco plants resulted in low-enzyme activity, and the protein appeared to be subject to proteolysis. Toward enhancing production of this recombinant enzyme in vegetative tissues, transgenic tobacco plants were generated to co-express a CaMV35S:Chamaecyparis nootkatensis Abscisic Acid Insensitive3 (CnABI3) gene construct, along with the human gene construct. The latter contained regulatory sequences of the Phaseolus vulgaris arcelin 5-I gene (5'-flanking, signal-peptide-encoding, and 3'-flanking regions). Ectopic synthesis of the CnABI3 protein led to the transactivation of the arcelin promoter and accordingly high activity (e.g., 25,000 pmol/min/mg total soluble protein) and levels of recombinant IDUA mRNA and protein were induced in leaves of transgenic tobacco, particularly in the presence of 150-200 microM S-(+)-ABA. Synthesis of human IDUA containing a carboxy-terminal ER retention (SEKDEL) sequence was also inducible by ABA in leaves co-transformed with the CnABI3 gene. As compared to the natural S-(+)-ABA, two persistent ABA analogues, (+)-8' acetylene ABA and (+)-8'methylene ABA, led to greater levels of beta-glucuronidase (GUS) reporter activities in leaves co-expressing the CnABI3 gene and a vicilin:GUS chimeric gene. In contrast, (+)-8' acetylene ABA and natural ABA appeared to be equally effective in stimulating the CnABI3-induced expression of an arcelin:GUS gene, and of the human IDUA gene, the latter also driven by arcelin-gene-regulatory sequences. Various stress-related treatments, particularly high concentrations of NaCl, had an even greater effect than ABA in promoting accumulation of human IDUA in co-transformed tobacco leaves. This strategy provides the means of enhancing the yields of recombinant proteins in transgenic plant vegetative tissues and potentially in cultured plant cells. The human recombinant protein can be readily induced in the presence of chemicals such as NaCl that can be added to cell cultures or even whole plants without a significant increase in production costs.

Enzyme, cell and gene-based therapies for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a demyelinating storage disease caused by deficiency of the lysosomal enzyme arylsulfatase A (ARSA). Lack of ARSA activity leads to the accumulation of galactosylceramide-3-O-sulfate (sulfatide) in the central and peripheral nervous systems. Based on the age at onset, the disease is usually classified into three forms: the late-infantile form, which manifests in the second year of life; the juvenile variants (onset between 4 and 12 years), which are subdivided into early-juvenile (EJ, onset before 6 years) and late-juvenile (LJ, onset after 6 years); and the adult form (onset after 12 years of age). Currently, there is no efficient therapy for the late-infantile form of MLD (50% of the patients), death occurring within a few years after onset of neurological symptoms. Allogeneic haematopoietic cell transplantation (HCT), when performed at a very early stage of the disease, may improve selected patients with juvenile or adult forms of MLD. As with other lysosomal storage diseases, the physiopathology of MLD is poorly understood. Demyelination is the main pathological finding, but substantial storage of sulfatides in neurons also occurs, and may contribute to the clinical phenotype. The physiopathological process leading to neuronal and glial cell degeneration and apoptosis involves accumulation of undegraded sulfatides but also secondary abnormalities (storage/mislocalization of unrelated lipids, inflammatory processes). This review summarizes the recent advances in the understanding of the physiopathology of MLD and the new therapeutic perspectives currently under preclinical investigation, including enzyme replacement therapy, gene therapy and cell therapy.

Pyrimethamine as a potential pharmacological chaperone for late-onset forms of GM2 gangliosidosis

Late-onset GM2 gangliosidosis is composed of two related, autosomal recessive, neurodegenerative diseases, both resulting from deficiency of lysosomal, heterodimeric beta-hexosaminidase A (Hex A, alphabeta). Pharmacological chaperones (PC) are small molecules that can stabilize the conformation of a mutant protein, allowing it to pass the quality control system of the endoplasmic reticulum. To date all successful PCs have also been competitive inhibitors. Screening for Hex A inhibitors in a library of 1040 Food Drug Administration-approved compounds identified pyrimethamine (PYR (2,4-diamino 5-(4-chlorophenyl)-6-ethylpyrimidine)) as the most potent inhibitor. Cell lines from 10 late-onset Tay-Sachs (11 alpha-mutations, 2 novel) and 7 Sandhoff (9 beta-mutations, 4 novel) disease patients, were cultured with PYR at concentrations corresponding to therapeutic doses. Cells carrying the most common late-onset mutation, alphaG269S, showed significant increases in residual Hex A activity, as did all 7 of the beta-mutants tested. Cells responding to PC treatment included those carrying mutants resulting in reduced Hex heat stability and partial splice junction mutations of the inherently less stable alpha-subunit. PYR, which binds to the active site in domain II, was able to function as PC even to domain I beta-mutants. We concluded that PYR functions as a mutation-specific PC, variably enhancing residual lysosomal Hex A levels in late-onset GM2 gangliosidosis patient cells.

Pharmacological Enhancement of Mutated α-Glucosidase Activity in Fibroblasts from Patients with Pompe Disease

We investigated the use of pharmacological chaperones for the therapy of Pompe disease, a metabolic myopathy due to mutations of the gene encoding the lysosomal hydrolase alpha-glucosidase (GAA) and characterized by generalized glycogen storage in cardiac and skeletal muscle. We studied the effects of two imino sugars, deoxynojirimycin (DNJ) and N-butyldeoxynojirimycin (NB-DNJ), on residual GAA activity in fibroblasts from eight patients with different forms of Pompe disease (two classic infantile, two non-classic infantile onset, four late-onset forms), and with different mutations of the GAA gene. We demonstrated a significant increase of GAA activity (1.3-7.5-fold) after imino sugar treatment in fibroblasts from patients carrying the mutations L552P (three patients) and G549R (one patient). GAA enhancement was confirmed in HEK293T cells where the same mutations were overexpressed. No increase of GAA activity was observed for the other mutations. Western blot analysis showed that imino sugars increase the amount of mature GAA molecular forms. Immunofluorescence studies in HEK293T cells overexpressing the L552P mutation showed an improved trafficking of the mutant enzyme to lysosomes after imino sugar treatment. These results provide a rationale for an alternative treatment, other than enzyme replacement, to Pompe disease.