John J. Hopwood

Immune tolerance after long-term enzyme-replacement therapy among patients who have mucopolysaccharidosis I

BACKGROUNDnEnzyme-replacement therapy has been assessed as a treatment for patients who have mucopolysaccharidosis I (alpha-L-iduronidase deficiency). We aimed to investigate the humoral immune response to recombinant human alpha-L-iduronidase among these patients.nnnMETHODSnWe characterised the antibody titres and specific linear sequence epitope reactivity of serum antibodies to alpha-L-iduronidase for ten patients with mucopolysaccharidosis I, at the start of treatment and after 6, 12, 26, 52, and 104 weeks. We compared the values for patients samples with those for samples from normal human controls.nnnFINDINGSnBefore enzyme-replacement therapy, all patients had low serum antibody titres to recombinant human alpha-L-iduronidase that were within the control range. Five of the ten patients produced higher-than-normal titres of antibody to the replacement protein during the treatment course (serum antibody titres 130000-500000 and high-affinity epitope reactivity). However, by week 26, antibody reactivity was reduced, and by week 104 all patients had low antibody titres and only low-affinity epitope reactivity. Patients who had mucopolysaccharidosis I with antibody titres within the normal range at 6-12 weeks did not subsequently develop immune responses.nnnINTERPRETATIONnAfter 2 years of treatment, patients who initially had an immune reaction developed immune tolerance to alpha-L-iduronidase. This finding has positive implications for long-term enzyme-replacement therapy in patients who have mucopolysaccharidosis I.

Lysosomal storage disorders: emerging therapeutic options require early diagnosis

Lysosomal storage disorders have been recognised as one of the major groups of genetic disorders affecting children and adults. With over 40 different disorders and a combined prevalence of up to 1:5000 births, this group of disorders is a major public health problem and places an enormous burden on the individuals and families affected. Since the introduction of enzyme replacement therapy for Gaucher disease over 10 years ago there has been considerable progress in the development of enzyme based therapies for other disorders, in addition to alternate therapies including substrate deprivation and gene based therapies. Early diagnosis of these disorders before the onset of irreversible pathologies will lead to better outcomes for current and proposed therapies. In this review we describe the strategies and technology being used for the development of newborn screening for lysosomal storage disorders and discuss the future requirements for the early diagnosis and effective therapy of this group of disorders.

Effect of lysosomal storage on bis(monoacylglycero)phosphate

BMP [bis(monoacylglycero)phosphate] is an acidic phospholipid and a structural isomer of PG (phosphatidylglycerol), consisting of lysophosphatidylglycerol with an additional fatty acid esterified to the glycerol head group. It is thought to be synthesized from PG in the endosomal/lysosomal compartment and is found primarily in multivesicular bodies within the same compartment. In the present study, we investigated the effect of lysosomal storage on BMP in cultured fibroblasts from patients with eight different LSDs (lysosomal storage disorders) and plasma samples from patients with one of 20 LSDs. Using ESI-MS/MS (electrospray ionization tandem MS), we were able to demonstrate either elevations or alterations in the individual species of BMP, but not of PG, in cultured fibroblasts. All affected cell lines, with the exception of Fabry disease, showed a loss of polyunsaturated BMP species relative to mono-unsaturated species, and this correlated with the literature reports of lysosomal dysfunction leading to elevations of glycosphingolipids and cholesterol in affected cells, processes thought to be critical to the pathogenesis of LSDs. Plasma samples from patients with LSDs involving storage in macrophages and/or with hepatomegaly showed an elevation in the plasma concentration of the C(18:1)/C(18:1) species of BMP when compared with control plasmas, whereas disorders involving primarily the central nervous system pathology did not. These results suggest that the release of BMP is cell/tissue-specific and that it may be useful as a biomarker for a subset of LSDs.

Effect of high dose, repeated intra-cerebrospinal fluid injection of sulphamidase on neuropathology in mucopolysaccharidosis type IIIA mice.

Mucopolysaccharidosis type IIIA (MPS IIIA) is an inherited neurodegenerative lysosomal storage disorder characterized by progressive loss of learned skills, sleep disturbance and behavioural problems. Reduced activity of sulphamidase (N‐sulphoglucosamine sulphohydrolase; SGSH; EC 3.10.1.1) results in intracellular accumulation of heparan sulphate (HS), with the brain as the primary site of pathology. We have used a naturally occurring MPS IIIA mouse model to determine the effectiveness of SGSH replacement through the cerebrospinal fluid (CSF) to decrease neuropathology. This is a potential therapeutic option for patients with this disorder. Mice received intra‐CSF injections of recombinant human SGSH (30, 50 or 70u2003μg) fortnightly from 6 to 18u2003weeks of age, and the cumulative effect on neuropathology was examined and quantified. Anti‐SGSH antibodies detected in plasma at euthanasia did not appear to impact upon the health of the mice or the experimental outcome, with significant but region‐dependent and dose‐dependent reductions in an HS‐derived oligosaccharide observed in the brain and spinal cord using tandem mass spectrometry. SGSH infusion reduced the number of storage inclusions observed in the brain when visualized using electron microscopy, and this correlated with a significant decrease in the immunohistochemical staining of a lysosomal membrane marker. Reduced numbers of activated isolectin B4‐positive microglia and glial fibrillary acidic protein‐positive astrocytes were seen in many, but not all, brain regions. Significant reductions in the number of ubiquitin‐positive intracellular inclusions were also observed. These outcomes show the effectiveness of this method of enzyme delivery in reducing the spectrum of neuropathological changes in murine MPS IIIA brain.

Laronidase treatment of mucopolysaccharidosis I.

The lysosomal storage disorder (LSD) mucopolysaccharidosis type I (MPS I, McKusick 25280, Hurler syndrome, Hurler-Scheie syndrome, Scheie syndrome) is caused by a deficiency in the lysosomal enzyme, α-L-iduronidase (EC 3.2.1.76). MPS I patients can present within a diverse clinical spectrum, ranging from classical Hurler syndrome to attenuated Scheie syndrome. Laronidase (Aldurazyme®) enzyme replacement therapy has been developed as a treatment strategy for MPS I patients and has been approved for clinical practice. Here we review the pre-clinical studies and clinical trials that have been used to demonstrate that intravenous laronidase therapy is well tolerated and effective for treating MPS I patients who do not have neuronal pathology. Current challenges for a viable treatment strategy for all MPS I patients include development of an early screening protocol that identifies patients before the onset of irreversible pathology, methods to predict disease severity, appropriate treatment for neuropathology, and an effective patient monitoring regimen.

Open field locomotor activity and anxiety-related behaviors in mucopolysaccharidosis type IIIA mice.

Mucopolysaccharidosis (MPS) IIIA, or Sanfilippo syndrome, is a lysosomal storage disorder characterized by severe and progressive neuropathology. Following an asymptomatic period, patients may present with sleep disturbances, cognitive decline, aggressive tendencies and hyperactivity. A naturally-occurring mouse model of MPS IIIA also exhibits many of these behavioral features and has been recently back-crossed onto a C57BL/6 genetic background. To more thoroughly characterize the behavioral phenotype of congenic MPS IIIA mice, we assessed exploratory activity and unconditioned anxiety-related behavior in the elevated plus maze (EPM) and open field locomotor activity. Although MPS IIIA male mice were less active in the EPM at 18 and 20 weeks of age, they were more likely to explore the open arms than their normal counter-parts suggesting reduced anxiety. Repeated EPM testing reduced exploration of the open arms in MPS IIIA mice. In the open field test, significant reductions in activity were evident in naïve-tested male MPS IIIA mice from 10 weeks of age. Female normal and MPS IIIA mice displayed similar exploratory activity in the open field test. These differences in anxiety and locomotor activity will allow us to evaluate the efficacy of therapeutic regimes for MPS IIIA as a forerunner to developing safe and effective therapies for Sanfilippo patients.

Diagnosis of lysosomal storage disorders: current techniques and future directions

Lysosomal storage disorders represent a group of over 45 distinct genetic diseases. The broad spectrum of clinical presentation of this group of disorders has led to the development of diagnostic protocols to facilitate their rapid and accurate diagnosis. However, with the development of new therapies, testing for many of these disorders now extends beyond diagnosis of affected individuals. The efficacy of many current and proposed therapies will rely heavily upon early detection and treatment prior to the onset of irreversible pathology. Newborn screening holds the promise of early detection. However, presymptomatic diagnosis raises a number of issues relating to patient management and treatment. Methods for prognoses and monitoring therapy in asymptomatic individuals will be required.

Immunolocation analysis of glycosaminoglycans in the human growth plate.

Monoclonal antibodies were used in this study to immunolocate glycosaminoglycans throughout the human growth plate. Chondroitin-4-sulfate, chondroitin-6-sulfate, and keratan sulfate were observed in the extracellular matrix of all zones of the growth plate and persisted into the cartilage trabeculae of newly formed metaphyseal bone. Also present in the extracellular matrix was an oversulfated chondroitin/dermatan sulfate glycosaminoglycan which appeared to be specific to the proliferative and hypertrophic zones of the growth plate. As with the other extracellular matrix molecules, this epitope persisted into the cartilage trabeculae of the metaphyseal bone. Zonal differences between the extracellular and pericellular or lacunae matrix were also observed. The hypertrophic chondrocytes appeared to synthesize chondroitin sulfate chains containing a non-reducing terminal 6-sulfated disaccharide, which were located in areas immediately adjacent to the cells. This epitope was not found to any significant extent in the other zones. The pericellular region around hypertrophic chondrocytes also contained a keratan sulfate epitope which was also observed in the resting zone but not in the proliferative zone. These cell-associated glycosaminoglycans were not found in the cartilage trabeculae of metaphyseal bone, indicating their removal as the terminal hypertrophic chondrocytes and their lacunae are removed by invading blood vessels. These changes in matrix glycosaminoglycan content, both in the different zones and within zones, indicate constant subtle alterations in chondrocyte metabolic products as they proceed through their life cycle of proliferation, maturation, and hypertrophy.

The implantation of cartilaginous and periosteal tissue into growth plate defects

SummaryThis experimental study reports the results of implantation of cartilaginous and periosteal tissues into growth plate defects in the tibiae of sheep. When no material was used, the defect rapidly filled with marrow-like tissue. When cartilage from the margin of the secondary centre of ossification was implanted, endochondral ossification continued and no shortening or deformity resulted. Implantation of periosteum with or without reconstructed peripheral tissues resulted in the formation of a bony bridge which led to a 32% inhibition of longitudinal growth and a 12° varus deformity in the absence of peripheral connective tissues. After reconstruction with these tissues, the inhibition of longitudinal growth was 47% with a 28° varus deformity. The chondroprogenitor cells in the implanted tissues cannot change phenotypic expression. Periosteum has a strong potential for bone formation after it has been implanted.RésuméLexcision dune plaque de croissance partiellement fusionnée et son remplacement par interposition de différents tissus na permis de montrer ni re-formation ni réparation de la structure anatomique de cette zone. Dans cette étude expérimentale nous présentons les résultats de limplantation de cartilage ou de périoste dans la perte de substance créée au niveau de la partie interne de la plaque de croissance tibiale sur un modèle animal ovin. Sans interposition la cavité est rapidement remplie par un tissu ayant quelques ressemblances avec la moëlle osseuse. Le cartilage, à la limite du centre secondaire dossification, continue le processus dossification enchondrale avec formation dos nouveau; plus lentement cependant que dans la zone de croissance normale adjacente. Sans comblement, de même quaprès implantation de cartilage, il ne se produit ni raccourcissement, ni angulation du membre opéré. Limplantation de périoste, avec ou sans reconstruction des structures périphériques entraîne la formation dun pont osseux notable. Il y a une inhibition de la croissance en longueur de 32% et une angulation en varus de 12° en labsence de reconstruction des tissus périphériques. Il y a une inhibition de la croissance de 47% et une angulation de 28° dans léventualité inverse. Nous en concluons que les cellules chondroprogéniques du tissu implanté ne peuvent pas changer leur expression phénotypique. Le périoste a un potentiel remarquable pour induire la formation dos nouveau après transposition.

Intrathecal recombinant human 4-sulfatase reduces accumulation of glycosaminoglycans in dura of mucopolysaccharidosis VI cats

Introduction:Mucopolysaccharidosis VI (MPS-VI) is caused by a deficiency in N-acetylgalactosamine-4-sulfatase activity, resulting in lysosomal accumulation of partially degraded glycosaminoglycans (GAGs). Compressive myelopathy in early-onset MPS-VI patients has been partly attributed to thickening of the dura mater following engorgement with GAG. In this study, we therefore tested whether the dural abnormalities could be prevented in a feline model of the disorder.Results:All intrathecal injections (IT-INJs) were well tolerated. MPS-VI cats treated with IT-INJ of recombinant human N-acetylgalactosamine-4-sulfatase (rhASB) exhibited reduced vacuolation in the dural fibroblasts, diminished levels of sulfated-N-acetylhexosamine (HNAc(+S)) in the cerebrospinal fluid (CSF) and no hind-limb paresis. Serum anti-rhASB antibodies remained low in MPS-VI cats treated with intravenous enzyme replacement therapy (IV-ERT) and increased slightly in normal cats treated with IT-INJ of rhASB alone. Anti-rhASB antibodies in CSF remained undetectable.Discussion:These data indicate that repeated IT-INJ of rhASB can safely prevent GAG storage in MPS-VI dura.Methods:Cats were assigned to three groups: (i) receiving weekly IV-ERT of rhASB from birth plus six monthly IT-INJs of rhASB from age 2 months; (ii) receiving six monthly IT-INJs of vehicle; or (iii) untreated. Additional normal cats received five fortnightly IT-INJs of rhASB or vehicle alone.