Gene therapy for lysosomal storage diseases

Systemic correction of storage disease in MPS I NOD/SCID mice using the sleeping beauty transposon system

The Sleeping Beauty (SB) transposon system is a nonviral vector that directs transgene integration into vertebrate genomes. We hydrodynamically delivered SB transposon plasmids encoding human alpha-L-iduronidase (hIDUA) at two DNA doses, with and without an SB transposase gene, to NOD.129(B6)-Prkdc(scid) IDUA(tm1Clk)/J mice. In transposon-treated, nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice with mucopolysaccharidosis type I (MPS I), plasma IDUA persisted for 18 weeks at levels up to several hundred-fold wild-type (WT) activity, depending on DNA dose and gender. IDUA activity was present in all examined somatic organs, as well as in the brain, and correlated with both glycosaminoglycan (GAG) reduction in these organs and level of expression in the liver, the target of transposon delivery. IDUA activity was higher in the treated males than in females. In females, omission of transposase source resulted in significantly lower IDUA levels and incomplete GAG reduction in some organs, confirming the positive effect of transposition on long-term IDUA expression and correction of the disease. The SB transposon system proved efficacious in correcting several clinical manifestations of MPS I in mice, including thickening of the zygomatic arch, hepatomegaly, and accumulation of foamy macrophages in bone marrow and synovium, implying potential effectiveness of this approach in treatment of human MPS I.

Widespread biochemical correction of murine mucopolysaccharidosis type VII pathology by liver hydrodynamic plasmid delivery

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by a deficiency of the acid hydrolase beta-glucuronidase. MPS VII mice develop progressive lysosomal accumulation of glycosaminoglycans (GAGs) within multiple organs, including the brain. Using this animal model, we compared two plasmid gene administration techniques: muscle electrotransfer and liver-directed transfer using hydrodynamic injection. We have evaluated both the expression kinetics and the biodistribution of beta-glucuronidase activity after gene transfer, as well as the correction of biochemical abnormalities in various organs. This study shows that MPS VII mice treated with a plasmid-bearing mouse beta-glucuronidase cDNA, acquire the ability to produce the beta-glucuronidase enzyme for an extended period of time. The liver seemed to be more appropriate than the muscle as a target organ to enable enzyme secretion into the systemic circulation. A beneficial effect on the MPS VII pathology was also observed, as liver-directed gene transfer led to the correction of secondary enzymatic elevations and to the reduction of GAGs storage in peripheral tissues and brain, as well as to histological correction in many tissues. This work is one of the first examples showing that non-viral plasmid DNA delivery can lead to improvements in both peripheral and brain manifestations of MPS VII disease. It confirms the potential of non-viral systemic gene transfer strategy in neurological lysosomal disorders.

Lysosomal storage disorders in the newborn

Lysosomal storage disorders are rare inborn errors of metabolism, with a combined incidence of 1 in 1500 to 7000 live births. These relatively rare disorders are seldom considered when evaluating a sick newborn. A significant number of the >50 different lysosomal storage disorders, however, do manifest in the neonatal period and should be part of the differential diagnosis of several perinatal phenotypes. We review the earliest clinical features, diagnostic tests, and treatment options for lysosomal storage disorders that can present in the newborn. Although many of the lysosomal storage disorders are characterized by a range in phenotypes, the focus of this review is on the specific symptoms and clinical findings that present in the perinatal period, including neurologic, respiratory, endocrine, and cardiovascular manifestations, dysmorphic features, hepatosplenomegaly, skin or ocular involvement, and hydrops fetalis/congenital ascites. A greater awareness of these features may help to reduce misdiagnosis and promote the early detection of lysosomal storage disorders. Implementing therapy at the earliest stage possible is crucial for several of the lysosomal storage disorders; hence, an early appreciation of these disorders by physicians who treat newborns is essential.

Nanovehicular intracellular delivery systems

This article provides an overview of principles and barriers relevant to intracellular drug and gene transport, accumulation and retention (collectively called as drug delivery) by means of nanovehicles (NV). The aim is to deliver a cargo to a particular intracellular site, if possible, to exert a local action. Some of the principles discussed in this article apply to noncolloidal drugs that are not permeable to the plasma membrane or to the blood-brain barrier. NV are defined as a wide range of nanosized particles leading to colloidal objects which are capable of entering cells and tissues and delivering a cargo intracelullarly. Different localization and targeting means are discussed. Limited discussion on pharmacokinetics and pharmacodynamics is also presented. NVs are contrasted to micro-delivery and current nanotechnologies which are already in commercial use. Newer developments in NV technologies are outlined and future applications are stressed. We also briefly review the existing modeling tools and approaches to quantitatively describe the behavior of targeted NV within the vascular and tumor compartments, an area of particular importance. While we list "elementary" phenomena related to different level of complexity of delivery to cancer, we also stress importance of multi-scale modeling and bottom-up systems biology approach.

Co-expression of MGMT(P140K) and alpha-L-iduronidase in primary hepatocytes from mucopolysaccharidosis type I mice enables efficient selection with metabolic correction

BACKGROUND

Systemic in vivo gene therapy has resulted in widespread correction in animal models when treated at birth. However, limited improvement was observed in postnatally treated animals with mainly targeting to the liver and bone marrow. It has been shown that an O(6)-methylguanine-DNA-methyltransferase variant (MGMT(P140K)) mediated in vivo selection of transduced hematopoietic stem cells (HSC) in animals.

METHODS

We investigated the feasibility of MGMT(P140K)-mediated selection in primary hepatocytes from a mouse model of mucopolysaccharidosis type I (MPS I) in vitro using lentiviral vectors.

RESULTS

We found that multiple cycles of O(6)-benzylguanine (BG)/1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) treatment at a dosage effective for ex vivo HSC selection led to a two-fold increase of MGMT-expressing primary hepatocytes under culture conditions with minimum cell expansion. This enrichment level was comparable to that obtained after selection at a hepatic maximal tolerated dose of BCNU. Similar levels of increase were observed regardless of initial transduction frequency, or the position of MGMT (upstream or downstream of internal ribosome entry site) in the vector constructs. In addition, we found that elongation factor 1alpha promoter was superior to the long-terminal repeat promoter from spleen focus-forming virus with regard to transgene expression in primary hepatocytes. Moreover, the levels of therapeutic transgene expression in transduced, enzyme-deficient hepatocytes directly correlated with the doses of BCNU, leading to metabolic correction in transduced hepatocytes and metabolic cross-correction in neighbouring non-transduced MPS I cells.

CONCLUSIONS

These results demonstrate that MGMT(P140K) expression confers successful protection/selection in primary hepatocytes, and provide 'proof of concept' to the prospect of MGMT(P140K)-mediated co-selection for hepatocytes and HSC using BG/BCNU treatment.

Development of gene therapy for blood disorders

The concept of introducing genes into human cells for therapeutic purposes developed nearly 50 years ago as diseases due to defects in specific genes were recognized. Development of recombinant DNA techniques in the 1970s and their application to the study of mouse tumor viruses facilitated the assembly of the first gene transfer vectors. Vectors of several different types have now been developed for specific applications and over the past decade, efficacy has been demonstrated in many animal models. Clinical trials began in 1989 and by 2002 there was unequivocal evidence that children with severe combined immunodeficiency could be cured by gene transfer into primitive hematopoietic cells. Emerging from these successful trials was the realization that proto-oncogene activation by retroviral integration could contribute to leukemia. Much current effort is focused on development of safer vectors. Successful gene therapy applications have also been developed for control of graft-versus-host disease and treatment of various viral infections, leukemias, and lymphomas. The hemophilias seem amenable to gene therapy intervention and informative clinical trials have been conducted. The hemoglobin disorders, an early target for gene therapy, have proved particularly challenging although ongoing research is yielding new information that may ultimately lead to successful clinical trials.

Residual levels of tripeptidyl-peptidase I activity dramatically ameliorate disease in late-infantile neuronal ceroid lipofuscinosis

Classical late-infantile neuronal ceroid lipofuscinosis (LINCL) is a hereditary neurodegenerative disease of childhood that is caused by mutations in the gene (CLN2) encoding the lysosomal protease tripeptidyl-peptidase I (TPPI). LINCL is fatal and there is no treatment of demonstrated efficacy in affected children but preclinical studies with AAV-mediated gene therapy have demonstrated promise in a mouse model. Here, we have generated mouse CLN2-mutants that express different amounts of TPPI activity to benchmark levels required for therapeutic benefits. Approximately 3% of normal TPPI activity in brain delayed disease onset and doubled lifespan to a median of approximately 9 months compared to mice expressing approximately 0.2% of normal levels. Expression of 6% of normal TPPI activity dramatically attenuated disease, with a median lifespan of approximately 20 months which approaches that of unaffected mice. While the lifespan of this hypomorph is shortened, disease is late-onset, less severe and progresses slowly compared to mice expressing lower TPPI levels. For gene therapy and other approaches that restore enzyme activity, these results suggest that 6% of normal TPPI activity throughout the CNS of affected individuals will provide a significant therapeutic benefit but higher levels will be required to cure this disease.

Home therapy for lysosomal storage disorders

Lysosomal storage disorders (LSDs) are a group of rare inherited metabolic disorders each resulting from the deficiency of a specific lysosomal enzyme and leading to the pathological accumulation of undegraded substrate. There are now several possible modalities of therapy for LSDs including intravenous enzyme replacement therapy (ERT). ERT is administered by intravenous infusion every week or 2 weeks. Therapy is lifelong and therefore a serious undertaking for patients and healthcare providers. Most patients will travel some distance to their specialist LSD centre and may therefore find frequent visits stressful, time-consuming and disruptive. The facility to administer enzyme replacement therapy in the home limits time spent at the hospital, restores independence and control of the disease to the patient, and reduces utilization of hospital resources and is associated with improved quality of life. A recent questionnaire survey indicates high levels of compliance with infusions in the home setting. Home therapy requires a well organized and regulated community infrastructure, individual assessments of patient suitability and protocols for management of possible infusion associated reactions.

Complete correction of enzymatic deficiency and neurochemistry in the GM1-gangliosidosis mouse brain by neonatal adeno-associated virus-mediated gene delivery

GM1-gangliosidosis is a glycosphingolipid (GSL) lysosomal storage disease caused by autosomal recessive deficiency of lysosomal acid beta-galactosidase (betagal), and characterized by accumulation of GM1-ganglioside and GA1 in the brain. Here we examined the effect of neonatal intracerebroventricular (i.c.v.) injection of an adeno-associated virus (AAV) vector encoding mouse betagal on enzyme activity and brain GSL content in GM1-gangliosidosis (betagal(-/-)) mice. Histological analysis of betagal distribution in 3-month-old AAV-treated betagal(-/-) mice showed that enzyme was present at high levels throughout the brain. Biochemical quantification showed that betagal activity in AAV-treated brains was 7- to 65-fold higher than in wild-type controls and that brain GSL levels were normalized. Cerebrosides and sulfatides, which were reduced in untreated betagal(-/-) mice, were restored to normal levels by AAV treatment. In untreated betagal(-/-) brains, cholesterol was present at normal levels but showed abnormal cellular distribution consistent with endosomal/lysosomal localization. This feature was also corrected in AAV-treated mice. The biochemical and histological parameters analyzed in this study showed that normal brain neurochemistry was achieved in AAV-treated betagal(-/-) mice. Therefore we show for the first time that neonatal AAV-mediated gene delivery of lysosomal betagal to the brain may be an effective approach for treatment of GM1-gangliosidosis.

The mucopolysaccharidoses: a success of molecular medicine

The mucopolysaccharidoses represent a devastating group of lysosomal storage diseases affecting approximately 1 in 25 000 individuals. Advances in biochemistry and genetics over the past 25 years have resulted in the identification of the key hydrolases underlying the mucopolysaccharidoses, with subsequent isolation and characterisation of the genes involved. Ultimately these advances have led to the recent development of specific treatment regimens for some of the mucopolysaccharidoses, in the form of direct enzyme replacement. Direct replacement of the defective gene product has been attempted for very few genetic disorders, and thus the experience gained in the lysosomal storage diseases by the development, evaluation and integration of treatment regimens into healthcare is instructive for other rare genetic disorders. This review focuses on the pathophysiology of the mucopolysaccharidoses and highlights the complex biochemical and physiological perturbations that underlie the disease phenotype.

Progress and prospects: gene therapy clinical trials (part 1)

Over the last two decades gene therapy has moved from preclinical to clinical studies for many diseases ranging from single gene disorders such as cystic fibrosis and Duchenne muscular dystrophy, to more complex diseases such as cancer and cardiovascular disorders. Gene therapy for severe combined immunodeficiency (SCID) is the most significant success story to date, but progress in many other areas has been significant. We asked 20 leaders in the field succinctly to summarize and comment on clinical gene therapy research in their respective areas of expertise and these are published in two parts in the Progress and Prospect series.

Gene therapy for mucopolysaccharidosis

Mucopolysaccharidoses (MPS) are due to deficiencies in activities of lysosomal enzymes that degrade glycosaminoglycans. Some attempts at gene therapy for MPS in animal models have involved intravenous injection of vectors derived from an adeno-associated virus (AAV), adenovirus, retrovirus or a plasmid, which primarily results in expression in liver and secretion of the relevant enzyme into blood. Most vectors can correct disease in liver and spleen, although correction in other organs including the brain requires high enzyme activity in the blood. Alternative approaches are to transduce hematopoietic stem cells, or to inject a vector locally into difficult-to-reach sites such as the brain. Gene therapy holds great promise for providing a long-lasting therapeutic effect for MPS if safety issues can be resolved.

Prolonged expression of a lysosomal enzyme in mouse liver after Sleeping Beauty transposon-mediated gene delivery: implications for non-viral gene therapy of mucopolysaccharidoses

BACKGROUND

The Sleeping Beauty (SB) transposon system is a non-viral vector system that can integrate precise sequences into chromosomes. We evaluated the SB transposon system as a tool for gene therapy of mucopolysaccharidosis (MPS) types I and VII.

METHODS

We constructed SB transposon plasmids for high-level expression of human beta-glucuronidase (hGUSB) or alpha-L-iduronidase (hIDUA). Plasmids were delivered with and without SB transposase to mouse liver by rapid, high-volume tail-vein injection. We studied the duration of expressed therapeutic enzyme activity, transgene presence by PCR, lysosomal pathology by toluidine blue staining and cell-mediated immune response histologically and by immunohistochemical staining.

RESULTS

Transgene frequency, distribution of transgene and enzyme expression in liver and the level of transgenic enzyme required for amelioration of lysosomal pathology were estimated in MPS I and VII mice. Without immunomodulation, initial GUSB and IDUA activities in plasma reached > 100-fold of wild-type (WT) levels but fell to background within 4 weeks post-injection. In immunomodulated transposon-treated MPS I mice plasma IDUA persisted for over 3 months at up to 100-fold WT activity in one-third of MPS I mice, which was sufficient to reverse lysosomal pathology in the liver and, partially, in distant organs. Histological and immunohistochemical examination of liver sections in IDUA transposon-treated WT mice revealed inflammation 10 days post-injection consisting predominantly of mononuclear cells, some of which were CD4- or CD8-positive.

CONCLUSIONS

Our results demonstrate the feasibility of achieving prolonged expression of lysosomal enzymes in the liver and reversing MPS disease in adult mice with a single dose of therapeutic SB transposons.

Timing of therapeutic intervention determines functional and survival outcomes in a mouse model of late infantile batten disease

Classical late infantile neuronal ceroid lipofuscinosis (cLINCL) is a monogenic disorder caused by the loss of tripeptidyl peptidase 1 (TPP1) activity as a result of mutations in CLN2. Absence of TPP1 results in lysosomal storage with an accompanying axonal degeneration throughout the central nervous system (CNS), which leads to progressive neurodegeneration and early death. In this study, we compared the efficacies of pre- and post-symptomatic injections of recombinant adeno-associated virus (AAV) for treating the cellular and functional abnormalities of CLN2 mutant mice. Intracranial injection of AAV1-hCLN2 resulted in widespread human TPP1 (hTPP1) activity in the brain that was 10-100-fold above wild-type levels. Injections before disease onset prevented storage and spared neurons from axonal degeneration, reflected by the preservation of motor function. Furthermore, the majority of CLN2 mutant mice treated pre-symptomatically lived for at least 330 days, compared with a median survival of 151 days in untreated CLN2 mutant controls. In contrast, although injection after disease onset ameliorated lysosomal storage, there was evidence of axonal degeneration, motor function showed limited recovery, and the animals had a median lifespan of 216 days. These data illustrate the importance of early intervention for enhanced therapeutic benefit, which may provide guidance in designing novel treatment strategies for cLINCL patients.

Intraperitoneal inoculation of Sandhoff mouse neonates with an HIV-1 based lentiviral vector exacerbates the attendant neuroinflammation and disease phenotype

We aimed to evaluate the efficacy of VSV-G pseudotyped, defective HIV-1 based lentiviral vectors for the neonatal transfer of therapeutic genes following systemic administration in Sandhoff mouse pups. Despite transgene expression in mouse brains, these animals presented with significant exacerbation and acceleration of the disease neurological phenotype. We observed an increase and acceleration in the presence of MHC-II and CD45+ cells in their brains, along with neuroinflammation, but not in control heterozygous or wild type littermates that also received the same treatment.

Combination brain and systemic injections of AAV provide maximal functional and survival benefits in the Niemann-Pick mouse

Niemann-Pick disease (NPD) is caused by the loss of acid sphingomyelinase (ASM) activity, which results in widespread accumulation of undegraded lipids in cells of the viscera and CNS. In this study, we tested the effect of combination brain and systemic injections of recombinant adeno-associated viral vectors encoding human ASM (hASM) in a mouse model of NPD. Animals treated by combination therapy exhibited high levels of hASM in the viscera and brain, which resulted in near-complete correction of storage throughout the body. This global reversal of pathology translated to normal weight gain and superior recovery of motor and cognitive functions compared to animals treated by either brain or systemic injection alone. Furthermore, animals in the combination group did not generate antibodies to hASM, demonstrating the first application of systemic-mediated tolerization to improve the efficacy of brain injections. All of the animals treated by combination therapy survived in good health to an investigator-selected 54 weeks, whereas the median lifespans of the systemic-alone, brain-alone, or untreated ASM knockout groups were 47, 48, and 34 weeks, respectively. These data demonstrate that combination therapy is a promising therapeutic modality for treating NPD and suggest a potential strategy for treating disease indications that cause both visceral and CNS pathologies.

When intracellular logistics fails--genetic defects in membrane trafficking

The number of human genetic disorders shown to be due to defects in membrane trafficking has greatly increased during the past five years. Defects have been identified in components involved in sorting of cargo into transport carriers, vesicle budding and scission, movement of vesicles along cytoskeletal tracks, as well as in vesicle tethering, docking and fusion at the target membrane. The nervous system is extremely sensitive to such disturbances of the membrane trafficking machinery, and the majority of these disorders display neurological defects--particularly diseases affecting the motility of transport carriers along cytoskeletal tracks. In several disorders, defects in a component that represents a fundamental part of the trafficking machinery fail to cause global transport defects but result in symptoms limited to specific cell types and transport events; this apparently reflects the redundancy of the transport apparatus. In groups of closely related diseases such as Hermansky-Pudlak and Griscelli syndromes, identification of the underlying gene defects has revealed groups of genes in which mutations lead to similar phenotypic consequences. New functionally linked trafficking components and regulatory mechanisms have thus been discovered. Studies of the gene defects in trafficking disorders therefore not only open avenues for new therapeutic approaches but also significantly contribute to our knowledge of the fundamental mechanisms of intracellular membrane transport.

Prevention of lysosomal storage disorders in Israel

Prevention programs for the detection of heterozygotes of relatively prevalent autosomal recessive diseases in various ethnic groups are available in recent years in Israel. Several lysosomal storage disorders (LSD) are included in this program. The goal of the program is the ascertainment of high risk couples before the birth of affected offspring. This is performed by a population screening program that addresses the specific needs and requirements of various population groups in Israel. The programs are supervised and designed by medical/clinical geneticists and are accompanied by genetic counseling prior to and after testing. Three types of population screening programs are in operation. The first type is offered to the general population and is directed to premarital and married couples. High risk families mostly opt for prenatal diagnosis. The second type is performed for diseases with a frequency of about 1:1000. This occurrence is common in Israel only in various Arab communities due to the high rate of consanguinity. The third type is a premarital screening performed by the Orthodox Jewish community and is operated by a nonprofit organization--"Dor Yeshorim". Two heterozygotes for a particular disease are advised not to proceed with the marriage and thus avoid the dilemma of prenatal diagnosis. Founder mutations of the relevant genes for each ethnic group are tested and the testing is tailored for each individual according to his/her ethnic background. Genetic counseling presents family planning options to high risk couples. These programs have resulted in a significant reduction in the birth of affected patients of the tested LSD a well as other recessive diseases in recent years.

Clinical response to persistent, low-level beta-glucuronidase expression in the murine model of mucopolysaccharidosis type VII

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by beta-glucuronidase (GUSB) deficiency. This disease exhibits a broad spectrum of clinical signs including skeletal dysplasia, retinal degeneration, cognitive deficits and hearing impairment. Sustained, high-level expression of GUSB significantly improves the clinical course of the disease in the murine model of MPS VII. Low levels of enzyme expression (1-5% of normal) can significantly reduce the biochemical and histopathological manifestations of MPS VII. However, it has not been clear from previous studies whether persistent, low levels of circulating GUSB lead to significant improvements in the clinical presentation of this disease. We generated a rAAV2 vector that mediates persistent, low-level GUSB expression in the liver. Liver and serum levels of GUSB were maintained at approximately 5% and approximately 2.5% of normal, respectively, while other tissue ranged from background levels to 0.9%. This level of activity significantly reduced the secondary elevations of alpha-galactosidase and the levels of glycosaminoglycans in multiple tissues. Interestingly, this level of GUSB was also sufficient to reduce lysosomal storage in neurons in the brain. Although there were small but statistically significant improvements in retinal function, auditory function, skeletal dysplasia, and reproduction in rAAV-treated MPS VII mice, the clinical deficits were still profound and there was no improvement in lifespan. These data suggest that circulating levels of GUSB greater than 2.5% will be required to achieve substantial clinical improvements in MPS VII.

Improvements in mucopolysaccharidosis I mice after adult retroviral vector-mediated gene therapy with immunomodulation

Mucopolysaccharidosis I (MPS I) is caused by deficient alpha-L-iduronidase (IDUA) activity and results in the accumulation of glycosaminoglycans and multisystemic disease. Gene therapy could program cells to secrete mannose 6-phosphate-modified IDUA, and enzyme in blood could be taken up by other cells. Neonatal retroviral vector (RV)-mediated gene therapy has been shown to reduce the manifestations of murine MPS I; however, intravenous injection of RV into adults was ineffective owing to a cytotoxic T lymphocyte (CTL) response against transduced cells. In this study, prolonged inhibition of CD28 signaling with CTLA4-Ig, or transient administration of CTLA4-Ig with an anti-CD40 ligand antibody or with an anti-CD4 antibody, resulted in stable expression in most mice that received RV as adults. Mice with stable expression had 81 +/- 41U/ml IDUA activity in serum. This resulted in reductions in bone disease, improvements in hearing and vision, and reductions in biochemical and pathological evidence of lysosomal storage in most organs. Improvements in brain were likely due to diffusion of enzyme from blood. However, aortic disease was refractory to treatment. This demonstrates that most manifestations of MPS I can be prevented using adult gene therapy if an immune response is blocked.

Pharmacotherapeutic strategies using small molecules for the treatment of glycolipid lysosomal storage disorders

The glycolipid lysosomal storage diseases are a collection of rare, inherited disorders of metabolism associated with heterogeneous pathologies and reduced life expectancy. Reduction of the substrate that accumulates due to catabolic enzyme deficiency can be mediated by an increasing number of therapeutic approaches, including enzyme replacement, pharmacological intervention to reduce substrate synthesis or enhance residual enzyme activity, and cell or gene therapy. The success of one agent, the imino sugar miglustat, has provided the impetus for using similar molecules for enzyme enhancement, or chaperone-mediated therapy for exiting medical conditions and for conditions where no disease-specific therapy is available. The advantages of using small molecules as therapy for the family of lysosomal storage disorders are discussed with reference to existing enzyme replacement therapies.

AAV1 Mediated Co-expression of Formylglycine-Generating Enzyme and Arylsulfatase A Efficiently Corrects Sulfatide Storage in a Mouse Model of Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by a deficiency of arylsulfatase A (ASA) and is characterized by deposition of sulfatide in all organs, particularly the nervous system. Recently, formylglycine-generating enzyme (FGE) was found to be essential for activation of sulfatases. This study examined the utility of FGE co-expression in AAV type 1 vector (AAV1)-mediated gene therapy of ASA knockout (MLD) mice. AAV1-ASA alone or AAV1-ASA and AAV1-FGE were co-injected into a single site of the hippocampus. Enzyme assay and immunohistochemical analysis showed that ASA was detected not only in the injected hemisphere but also in the non-injected hemisphere by 7 months after injection. Level of ASA activity and extent of ASA distribution were significantly enhanced by co-introduction of AAV1-FGE. Marked reductions in sulfatide levels were observed throughout the entire brain. The unexpectedly widespread distribution of ASA may be due to a combination of diffusion in extracellular spaces, transport through axons, and circulation in cerebrospinal fluid. The rotarod test revealed improvement of neurological functions. These results demonstrate that direct injection of AAV1 vectors expressing ASA and FGE represents a highly promising approach with significant implications for the development of clinical protocols for MLD gene therapy.

Partial cure of established disease in an animal model of metachromatic leukodystrophy after intracerebral adeno-associated virus-mediated gene transfer

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by genetic deficiency of arylsulfatase A (ARSA) enzyme. Failure in catalyzing the degradation of its major substrate, sulfatide (Sulf), in oligodendrocytes and Schwann cells leads to severe demyelination in the peripheral (PNS) and central nervous system (CNS), and early death of MLD patients. The ARSA knockout mice develop a disease that resembles MLD but is milder, without significant demyelination in the PNS and CNS. We showed that adeno-associated virus serotype 5-mediated gene transfer in the brain of ARSA knockout mice reverses Sulf storage and prevents neuropathological abnormalities and neuromotor disabilities when vector injections are performed at a pre-symptomatic stage of disease. Direct injection of viral particles into the brain of ARSA knockout mice at a symptomatic stage results in sustained expression of ARSA, prevention of Sulf storage and neuropathological abnormalities. Despite these significant corrections, the treated mice continue to develop neuromotor disability. We show that more subtle biochemical abnormalities involving gangliosides and galactocerebroside are in fact not corrected.

New therapeutic options for lysosomal storage disorders: enzyme replacement, small molecules and gene therapy

During the last few years, much progress has been made in the treatment of lysosomal storage disorders. In the past, no specific therapy was available for the affected patients, and management consisted solely of supportive care and treatment of complications. Since enzyme replacement therapy has been successfully introduced for patients with Gaucher disease, this principle of treatment has been taken into consideration for other lysosomal storage disorders as well. Clinical trials could demonstrate the clinical benefit of this therapeutic principle in Fabry disease, mucopolysaccharidoses type I, II and VI and in Pompe disease. However, the usefulness of enzyme replacement therapy is limited due to the fact that a given enzyme preparation does not have beneficial effects on all aspects of a disorder in the same degree. Additionally, clinical studies have shown that many symptoms of a lysosomal storage disorder even after long-term treatment are no more reversible. A further novel therapeutic option for lysosomal storage disorders consists of the application of small molecules that either inhibit a key enzyme which is responsible for substrate synthesis (substrate deprivation) or act as a chaperone to increase the residual activity of the lysosomal enzyme (enzyme enhancing therapy). Various gene therapeutic techniques (in vivo and ex vivo technique) have been developed in order to administer the gene that is defective in a patient to the bloodstream or directly to the brain in order to overcome the blood-brain barrier. This review will give an insight into these newly developed therapeutic strategies and will discuss their advantages and limitations.

Genetic diseases of sphingolipid metabolism: pathological mechanisms and therapeutic options

Although diseases in the pathway of sphingolipid degradation have been known for decades, the first disease in the biosynthetic pathway was only reported in 2004, when a form of infantile-onset symptomatic epilepsy was described as a genetic defect in GM3 synthase. Presumably other diseases in the sphingolipid biosynthetic pathway will yet be discovered, although many may remain undetected due to their putative lethal phenotypes. In contrast, diseases are known for essentially every step in the pathway of SL degradation, caused by the defective activity of one or other of the lysosomal hydrolases in this pathway. Despite the fact that some of these storage disorders were first discovered in the 19th century, the cellular and biochemical events that cause pathology are still poorly delineated. In this review, we focus on recent advances in our understanding of how defects in the pathways of sphingolipid metabolism may lead to pathology. In addition, we discuss currently-available and emerging therapeutic options.

Modest phenotypic improvements in ASA-deficient mice with only one UDP-galactose:ceramide-galactosyltransferase gene

Background

Arylsulfatase A (ASA)-deficient mice are a model for the lysosomal storage disorder metachromatic leukodystrophy. This lipidosis is characterised by the lysosomal accumulation of the sphingolipid sulfatide. Storage of this lipid is associated with progressive demyelination. We have mated ASA-deficient mice with mice heterozygous for a non-functional allele of UDP-galactose:ceramide-galactosyltransferase (CGT). This deficiency is known to lead to a decreased synthesis of galactosylceramide and sulfatide, which should reduce sulfatide storage and improve pathology in ASA-deficient mice.

Results

ASA-/- CGT+/- mice, however, showed no detectable decrease in sulfatide storage. Neuronal degeneration of cells in the spiral ganglion of the inner ear, however, was decreased. Behavioural tests showed small but clear improvements of the phenotype in ASA-/- CGT+/- mice.

Conclusion

Thus the reduction of galactosylceramide and sulfatide biosynthesis by genetic means overall causes modest improvements of pathology.