Effect of enzyme replacement therapy on bone formation in a feline model of mucopolysaccharidosis type VI

Skeletal phenotype amelioration in mucopolysaccharidosis VI requires intervention at the earliest stages of postnatal development

Mucopolysaccharidosis VI (MPS VI) is a rare lysosomal disease arising from impaired function of the enzyme arylsulfatase B (ARSB). This impairment causes aberrant accumulation of dermatan sulfate, a glycosaminoglycan (GAG) abundant in cartilage. While clinical severity varies along with age at first symptom manifestation, MPS VI usually presents early and strongly affects the skeleton. Current enzyme replacement therapy (ERT) does not provide effective treatment for the skeletal manifestations of MPS VI. This lack of efficacy may be due to an inability of ERT to reach affected cells or to the irreversibility of the disease. To address the question of reversibility of skeletal phenotypes, we generated a conditional by inversion (COIN) mouse model of MPS VI, ArsbCOIN/COIN, wherein Arsb is initially null and can be restored to WT using Cre. We restored Arsb at different times during postnatal development, using a tamoxifen-dependent global Cre driver. By restoring Arsb at P7, P21, and P56-P70, we determined that skeletal phenotypes can be fully rescued if Arsb restoration occurs at P7, while only achieving partial rescue at P21 and no significant rescue at P56-P70. This work has highlighted the importance of early intervention in patients with MPS VI to maximize therapeutic impact.

Dose-dependent effects of enzyme replacement therapy on skeletal disease progression in mucopolysaccharidosis VII dogs

Mucopolysaccharidosis (MPS) VII is an inherited lysosomal storage disorder characterized by deficient activity of the enzyme β-glucuronidase. Skeletal abnormalities are common in patients and result in diminished quality of life. Enzyme replacement therapy (ERT) for MPS VII using recombinant human β-glucuronidase (vestronidase alfa) was recently approved for use in patients; however, to date there have been no studies evaluating therapeutic efficacy in a large animal model of MPS VII. The objective of this study was to establish the effects of intravenous ERT, administered at either the standard clinical dose (4 mg/kg) or a high dose (20 mg/kg), on skeletal disease progression in MPS VII using the naturally occurring canine model. Untreated MPS VII animals exhibited progressive synovial joint and vertebral bone disease and were no longer ambulatory by age 6 months. Standard-dose ERT-treated animals exhibited modest attenuation of joint disease, but by age 6 months were no longer ambulatory. High-dose ERT-treated animals exhibited marked attenuation of joint disease, and all were still ambulatory by age 6 months. Vertebral bone disease was recalcitrant to ERT irrespective of dose. Overall, our findings indicate that ERT administered at higher doses results in significantly improved skeletal disease outcomes in MPS VII dogs.

Mucopolysaccharidosis Type VI, an Updated Overview of the Disease

Mucopolysaccharidosis type VI, or Maroteaux-Lamy syndrome, is a rare, autosomal recessive genetic disease, mainly affecting the pediatric age group. The disease is due to pathogenic variants of the ARSB gene, coding for the lysosomal hydrolase N-acetylgalactosamine 4-sulfatase (arylsulfatase B, ASB). The enzyme deficit causes a pathological accumulation of the undegraded glycosaminoglycans dermatan-sulphate and chondroitin-sulphate, natural substrates of ASB activity. Intracellular and extracellular deposits progressively take to a pathological scenario, often severe, involving most organ-systems and generally starting from the osteoarticular apparatus. Neurocognitive and behavioral abilities, commonly described as maintained, have been actually investigated by few studies. The disease, first described in 1963, has a reported prevalence between 0.36 and 1.3 per 100,000 live births across the continents. With this paper, we wish to contribute an updated overview of the disease from the clinical, diagnostic, and therapeutic sides. The numerous in vitro and in vivo preclinical studies conducted in the last 10-15 years to dissect the disease pathogenesis, the efficacy of the available therapeutic treatment (enzyme replacement therapy), as well as new therapies under study are here described. This review also highlights the need to identify new disease biomarkers, potentially speeding up the diagnostic process and the monitoring of therapeutic efficacy.

Failures of Endochondral Ossification in the Mucopolysaccharidoses

PURPOSE OF REVIEW

The mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage disorders characterized by abnormal accumulation of glycosaminoglycans (GAGs) in cells and tissues. MPS patients frequently exhibit failures of endochondral ossification during postnatal growth leading to skeletal deformity and short stature. In this review, we outline the current understanding of the cellular and molecular mechanisms underlying failures of endochondral ossification in MPS and discuss associated treatment challenges and opportunities.

RECENT FINDINGS

Studies in MPS patients and animal models have demonstrated that skeletal cells and tissues exhibit significantly elevated GAG storage from early in postnatal life and that this is associated with impaired cartilage-to-bone conversion in primary and secondary ossification centers, and growth plate dysfunction. Recent studies have begun to elucidate the underlying cellular and molecular mechanisms, including impaired chondrocyte proliferation and hypertrophy, diminished growth factor signaling, disrupted cell cycle progression, impaired autophagy, and increased cell stress and apoptosis. Current treatments such as hematopoietic stem cell transplantation and enzyme replacement therapy fail to normalize endochondral ossification in MPS. Emerging treatments including gene therapy and small molecule-based approaches hold significant promise in this regard. Failures of endochondral ossification contribute to skeletal deformity and short stature in MPS patients, increasing mortality and reducing quality of life. Early intervention is crucial for effective treatment, and there is a critical need for new approaches that normalize endochondral ossification by directly targeting affected cells and signaling pathways.

Urinary glycosaminoglycans as a potential biomarker for evaluating treatment efficacy in subjects with mucopolysaccharidoses

Accumulations of glycosaminoglycans (GAGs) that result from deficiencies in lysosomal hydrolases are characteristic of mucopolysaccharidoses (MPS). Enzyme replacement therapies (ERTs) are now available for several MPS diseases (MPS I, MPS II, MPS IVA, MPS VI, and MPS VII), but assessment of the efficacy of treatment can be challenging because these are rare, progressive, and highly heterogeneous diseases; because some clinical manifestations may be irreversible if treatment initiation is delayed; and because determining the benefits of a treatment to prevent those manifestations may take prolonged periods of time. In addition to accumulation of GAGs in tissues, elevated urinary GAG (uGAG) levels are evident and are reduced rapidly after initiation of ERT. Studies in MPS animal models and clinical studies in subjects with MPS diseases have revealed correlations between reductions of uGAG levels and clinical effects of ERTs. In this article, we review the growing body of evidence to support the potential for the use of uGAG levels as predictive biomarkers of treatment efficacy.

Cell cycle progression is disrupted in murine MPS VII growth plate leading to reduced chondrocyte proliferation and transition to hypertrophy

Endochondral bone growth is abnormal in 6 of the 11 types of mucopolysaccharidoses (MPS) disorders; resulting in short stature, reduced size of the thoracic cavity and compromised manual dexterity. Current therapies for MPS have had a limited effect on bone growth and to improve these therapies or develop adjunct approaches requires an understanding of the underlying basis of abnormal bone growth in MPS. The MPS VII mouse model replicates the reduction in long bone and vertebral length observed in human MPS. Using this model we have shown that the growth plate is elongated but contains fewer chondrocytes in the proliferative and hypertrophic zones. Endochondral bone growth is in part regulated by entry and exit from the cell cycle by growth plate chondrocytes. More MPS VII chondrocytes were positive for Ki67, a marker for active phases of the cell cycle, suggesting that more MPS VII chondrocytes were in the cell cycle. The number of cells positive for phosphorylated histone H3 was significantly reduced in MPS VII chondrocytes, suggesting fewer MPS VII chondrocytes progressed to mitotic division. While MPS VII HZ chondrocytes continued to express cyclin D1 and more cells were positive for E2F1 and phos pRb than normal, fewer MPS VII HZ chondrocytes were positive for p57^kip2 a marker of terminal differentiation, suggesting fewer MPS VII chondrocytes were able to exit the cell cycle. In addition, multiple markers typical of PZ to HZ transition were not downregulated in MPS VII, in particular Sox9, Pthrpr and Wnt5a. These findings are consistent with MPS VII growth plates elongating at a slower rate than normal due to a delay in progression through the cell cycle, in particular the transition between G1 and S phases, leading to both reduced cell division and transition to the hypertrophic phenotype.

The Lysosomal Protein Arylsulfatase B Is a Key Enzyme Involved in Skeletal Turnover

Skeletal pathologies are frequently observed in lysosomal storage disorders, yet the relevance of specific lysosomal enzymes in bone remodeling cell types is poorly defined. Two lysosomal enzymes, ie, cathepsin K (Ctsk) and Acp5 (also known as tartrate-resistant acid phosphatase), have long been known as molecular marker proteins of differentiated osteoclasts. However, whereas the cysteine protease Ctsk is directly involved in the degradation of bone matrix proteins, the molecular function of Acp5 in osteoclasts is still unknown. Here we show that Acp5, in concert with Acp2 (lysosomal acid phosphatase), is required for dephosphorylation of the lysosomal mannose 6-phosphate targeting signal to promote the activity of specific lysosomal enzymes. Using an unbiased approach we identified the glycosaminoglycan-degrading enzyme arylsulfatase B (Arsb), mutated in mucopolysaccharidosis type VI (MPS-VI), as an osteoclast marker, whose activity depends on dephosphorylation by Acp2 and Acp5. Similar to Acp2/Acp5^-/- mice, Arsb-deficient mice display lysosomal storage accumulation in osteoclasts, impaired osteoclast activity, and high trabecular bone mass. Of note, the most prominent lysosomal storage accumulation was observed in osteocytes from Arsb-deficient mice, yet this pathology did not impair production of sclerostin (Sost) and Fgf23. Because the influence of enzyme replacement therapy (ERT) on bone remodeling in MPS-VI is still unknown, we additionally treated Arsb-deficient mice by weekly injection of recombinant human ARSB from 12 to 24 weeks of age. We found that the high bone mass phenotype of Arsb-deficient mice and the underlying bone cell deficits were fully corrected by ERT in the trabecular compartment. Taken together, our results do not only show that the function of Acp5 in osteoclasts is linked to dephosphorylation and activation of lysosomal enzymes, they also provide an important proof-of-principle for the feasibility of ERT to correct bone cell pathologies in lysosomal storage disorders. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Pathogenesis and treatment of spine disease in the mucopolysaccharidoses

The mucopolysaccharidoses (MPS) are a family of lysosomal storage disorders characterized by deficient activity of enzymes that degrade glycosaminoglycans (GAGs). Skeletal disease is common in MPS patients, with the severity varying both within and between subtypes. Within the spectrum of skeletal disease, spinal manifestations are particularly prevalent. Developmental and degenerative abnormalities affecting the substructures of the spine can result in compression of the spinal cord and associated neural elements. Resulting neurological complications, including pain and paralysis, significantly reduce patient quality of life and life expectancy. Systemic therapies for MPS, such as hematopoietic stem cell transplantation and enzyme replacement therapy, have shown limited efficacy for improving spinal manifestations in patients and animal models. Therefore, there is a pressing need for new therapeutic approaches that specifically target this debilitating aspect of the disease. In this review, we examine how pathological abnormalities affecting the key substructures of the spine - the discs, vertebrae, odontoid process and dura - contribute to the progression of spinal deformity and symptomatic compression of neural elements. Specifically, we review current understanding of the underlying pathophysiology of spine disease in MPS, how the tissues of the spine respond to current clinical and experimental treatments, and discuss future strategies for improving the efficacy of these treatments.

Pharmacodynamics, pharmacokinetics and biodistribution of recombinant human N-acetylgalactosamine 4-sulfatase after 6months of therapy in cats using different IV infusion durations

BACKGROUND

Mucopolysaccharidosis VI (MPS VI) is a lysosomal storage disease characterized by an absence or marked reduction of lysosomal N-acetylgalactosamine-4-sulfatase activity. Affected individuals have widespread accumulation of unmetabolized glycosaminoglycan substrates leading to detrimental effects. Recombinant human N-acetylgalactosamine 4-sulfatase (rhASB) is an approved enzyme replacement therapy for patients with MPS VI. Despite the known efficacy of weekly 4-h rhASB infusions, some clinicians wish to treat patients using reduced infusion times. This study compared the pharmacodynamics, pharmacokinetics, and tissue biodistribution of rhASB when administered as 2- and 4-h intravenous infusions using a feline model of MPS VI.

METHODS

Study animals were MPS VI-affected cats that demonstrate clinical signs and biochemical derangements similar to human MPS VI patients. Beginning at age 4weeks, animals received weekly 2-h (N=6) or 4-h (N=6) IV infusions of rhASB for 26weeks (Naglazyme® [galsulfase] Solution for Intravenous Infusion; BioMarin Pharmaceutical, Inc.). The control group consisted of untreated MPS VI-affected cats (N=6). The pharmacokinetic parameters of plasma rhASB and urinary glycosaminoglycan were determined at weeks 13 and 26. Animals were euthanized 48h after the last infusion and tissue concentration of ASB, GAG and β-glucuronidase were measured in the liver, spleen, aorta, and kidney. Skeletal and ophthalmological evaluations were performed within 2weeks of euthanasia.

RESULTS

At week 13, the mean AUC0-t in animals treated with 4-h infusions was similar to 2-h infusions while the Cmax of the 4-h infusion was 50% of the 2-h infusion. By week 26, the mean AUC0-t of the 4-h infusion was 1.3-fold higher than the 2-h infusion (p<0.05) while Cmax of the 4-h infusion was 70% of the 2-h infusion (p<0.05). Among animals treated with 2- and 4-h infusions, there was no difference in urinary GAG excretion, tissue GAG storage, tissue galsulfase activity, and β-glucuronidase but all were significantly different than control animals (for each, p<0.001). Radiographic skeletal abnormality scores for animals were also similar for both treatment groups and significantly higher than control animals (p<0.001). There was no significant difference in corneal clouding scores among treated and untreated animals.

CONCLUSIONS

There was no significant difference in clinical outcomes when rhASB was administered to MPS VI affected cats as 2- and 4-h infusions over 26weeks. Additional studies may determine if shorter infusion times are appropriate for MPS VI patients without significant infusion-associated reactions.

Delayed hypertrophic differentiation of epiphyseal chondrocytes contributes to failed secondary ossification in mucopolysaccharidosis VII dogs

Mucopolysaccharidosis (MPS) VII is a lysosomal storage disorder characterized by deficient β-glucuronidase activity, which leads to the accumulation of incompletely degraded glycosaminoglycans (GAGs). MPS VII patients present with severe skeletal abnormalities, which are particularly prevalent in the spine. Incomplete cartilage-to-bone conversion in MPS VII vertebrae during postnatal development is associated with progressive spinal deformity and spinal cord compression. The objectives of this study were to determine the earliest postnatal developmental stage at which vertebral bone disease manifests in MPS VII and to identify the underlying cellular basis of impaired cartilage-to-bone conversion, using the naturally-occurring canine model. Control and MPS VII dogs were euthanized at 9 and 14 days-of-age, and vertebral secondary ossification centers analyzed using micro-computed tomography, histology, qPCR, and protein immunoblotting. Imaging studies and mRNA analysis of bone formation markers established that secondary ossification commences between 9 and 14 days in control animals, but not in MPS VII animals. mRNA analysis of differentiation markers revealed that MPS VII epiphyseal chondrocytes are unable to successfully transition from proliferation to hypertrophy during this critical developmental window. Immunoblotting demonstrated abnormal persistence of Sox9 protein in MPS VII cells between 9 and 14 days-of-age, and biochemical assays revealed abnormally high intra and extracellular GAG content in MPS VII epiphyseal cartilage at as early as 9 days-of-age. In contrast, assessment of vertebral growth plates and primary ossification centers revealed no significant abnormalities at either age. The results of this study establish that failed vertebral bone formation in MPS VII can be traced to the failure of epiphyseal chondrocytes to undergo hypertrophic differentiation at the appropriate developmental stage, and suggest that aberrant processing of Sox9 protein may contribute to this cellular dysfunction. These results also highlight the importance of early diagnosis and therapeutic intervention to prevent the progression of debilitating skeletal disease in MPS patients.

Effects of neonatal enzyme replacement therapy and simvastatin treatment on cervical spine disease in mucopolysaccharidosis I dogs

Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease characterized by deficient α-L-iduronidase activity, leading to the accumulation of poorly degraded glycosaminoglycans (GAGs). Children with MPS I exhibit high incidence of spine disease, including accelerated disc degeneration and vertebral dysplasia, which in turn lead to spinal cord compression and kyphoscoliosis. In this study we investigated the efficacy of neonatal enzyme replacement therapy (ERT), alone or in combination with oral simvastatin (ERT + SIM) for attenuating cervical spine disease progression in MPS I, using a canine model. Four groups were studied: normal controls; MPS I untreated; MPS I ERT-treated; and MPS I ERT + SIM-treated. Animals were euthanized at age 1 year. Intervertebral disc condition and spinal cord compression were evaluated from magnetic resonance imaging (MRI) images and plain radiographs, vertebral bone condition and odontoid hypoplasia were evaluated using micro-computed tomography (µCT), and epiphyseal cartilage to bone conversion was evaluated histologically. Untreated MPS I animals exhibited more advanced disc degeneration and more severe spinal cord compression than normal animals. Both treatment groups resulted in partial preservation of disc condition and cord compression, with ERT + SIM not significantly better than ERT alone. Untreated MPS I animals had significantly lower vertebral trabecular bone volume and mineral density, whereas ERT treatment resulted in partial preservation of these properties. ERT + SIM treatment demonstrated similar, but not greater, efficacy. Both treatment groups partially normalized endochondral ossification in the vertebral epiphyses (as indicated by absence of persistent growth plate cartilage), and odontoid process size and morphology. These results indicate that ERT begun from a very early age attenuates the severity of cervical spine disease in MPS I, particularly for the vertebral bone and odontoid process, and that additional treatment with simvastatin does not provide a significant additional benefit over ERT alone.

Galsulfase (Naglazyme®) therapy in infants with mucopolysaccharidosis VI

OBJECTIVE

To evaluate the efficacy and safety of two dose levels of galsulfase (Naglazyme®) in infants with MPS VI.

STUDY DESIGN

This was a phase 4, multicenter, multinational, open-label, two-dose level study. Subjects were randomized 1:1 to receive weekly infusions of 1.0 or 2.0 mg/kg of galsulfase for a minimum of 52 weeks. Progression of skeletal dysplasia was determined by monitoring physical appearance, radiographic changes, and growth. Urinary glycosaminoglycan (GAG) levels, gross and fine motor function, cardiac function, vision, hearing, and health resource utilization were evaluated. Safety assessments were performed.

RESULTS

Four infants (aged 3.3-12.7 months) participated in the study. Galsulfase was well tolerated at 1.0 and 2.0 mg/kg/week dose levels with no drug-related serious adverse events. Two subjects experienced a total of four possible treatment-related adverse events which were all considered mild. Length and weight remained within age-expected norms. Skeletal abnormalities continued to progress in all subjects. High baseline urinary GAG levels (mean: 870 μg/mg creatinine) decreased by approximately 70%; these reduced levels were maintained (mean: 220 μg/mg creatinine at week 52) despite the development of anti-galsulfase antibodies. Hearing, cardiac function, hepatosplenomegaly, and facial dysmorphism stabilized or improved, but corneal clouding progressed. There was no clear difference in safety or efficacy between the two doses.

CONCLUSIONS

Galsulfase at two dose levels was safe and well tolerated in infants. Normal growth was maintained but skeletal abnormalities continued to progress. Urinary GAG levels decreased with treatment. Early initiation of galsulfase may prevent or slow progression of some disease manifestations.

Osteoimmunology in mucopolysaccharidoses type I, II, VI and VII. Immunological regulation of the osteoarticular system in the course of metabolic inflammation

BACKGROUND

Mucopolysaccharidoses (MPSs) are rare genetic diseases caused by a deficient activity of one of the lysosomal enzymes involved in the glycosaminoglycan (GAG) breakdown pathway. These metabolic blocks lead to the accumulation of GAGs in various organs and tissues, resulting in a multisystemic clinical picture. The pathological GAG accumulation begins a cascade of interrelated responses: metabolic, inflammatory and immunological with systemic effects. Metabolic inflammation, secondary to GAG storage, is a significant cause of osteoarticular symptoms in MPS disorders.

OBJECTIVE AND METHOD

The aim of this review is to present recent progress in the understanding of the role of inflammatory and immune processes in the pathophysiology of osteoarticular symptoms in MPS disorders and potential therapeutic interventions based on published reports in MPS patients and studies in animal models.

RESULTS AND CONCLUSIONS

The immune and skeletal systems have a number of shared regulatory molecules and many relationships between bone disorders and aberrant immune responses in MPS can be explained by osteoimmunology. The treatment options currently available are not sufficiently effective in the prevention, inhibition and treatment of osteoarticular symptoms in MPS disease. A lot can be learnt from interactions between skeletal and immune systems in autoimmune diseases such as rheumatoid arthritis (RA) and similarities between RA and MPS point to the possibility of using the experience with RA in the treatment of MPS in the future. The use of different anti-inflammatory drugs requires further study, but it seems to be an important direction for new therapeutic options for MPS patients.

Skeletal response to lentiviral mediated gene therapy in a mouse model of MPS VII

Mucopolysaccharidosis VII (MPS VII) is an autosomal recessive, lysosomal storage disorder caused by β-glucuronidase (GUSB) deficiency, resulting in the accumulation of glycosaminoglycans (GAGs), in a variety of cell types. Severe, progressive skeletal pathology, termed dysostosis multiplex, is a prominent clinical feature of MPS VII. We have evaluated a gene therapy protocol for its efficacy in preventing the development and progression of bone pathology in MPS VII mice treated with a lentiviral vector at birth or at 7 weeks. Two weeks after injections, high levels of vector expression were observed in liver, spleen and bone marrow and to a lesser extent in kidney, lung and heart. Widespread clearance of GAG storage was observed in somatic tissues of both groups and some clearance of neuronal storage was observed in mice treated from birth. Micro-CT analysis demonstrated a significant decrease in vertebral and femoral bone mineral volume, trabecular number, bone surface density and cortical bone thickness in both treatment groups. Lumbar and femoral bone lengths were significantly decreased in untreated MPS VII mice, while growth plate heights were increased and these parameters did not change upon treatment. Small improvements in performance in the open field and rotarod behaviour tests were noted. Overall, systemic lentiviral-mediated gene therapy results in a measurable improvement in parameters of bone mass and architecture as well as biochemical and enzymatic correction. Conversely, growth plate chondrocytes were not responsive to treatment, as evidenced by the lack of improvement in vertebral and femoral bone length and growth plate height.

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.

Repeated intrathecal injections of recombinant human 4-sulphatase remove dural storage in mature mucopolysaccharidosis VI cats primed with a short-course tolerisation regimen

All MPS-VI cats treated thus far with weekly intravenous enzyme replacement therapy (IV ERT) with recombinant human N-acetylgalactosamine-4-sulphatase (rhASB) from 3 months of age onwards developed circulating anti-rhASB antibodies. In view of this, the possibility of inducing immune tolerance by using a short-course tolerisation regimen was tested. Starting at 4 months of age, MPS-VI (n=5) and unaffected cats (n=2) received cyclosporine and azathioprine over a 22-day period plus weekly IV ERT with 0.1mg/kg rhASB. After a 4-week resting period, these cats were administered weekly IV ERT with 1mg/kg rhASB until 11 or 17 months of age. Four unaffected cats (n=4) received weekly IV ERT only. Health, growth and seroconversion were regularly monitored. Four out of five MPS-VI cats tolerated rhASB well, as indicated by negligible or low antibody titres and absence of hypersensitivity reactions. One MPS-VI cat exhibited elevated antibody titres and hypersensitivity reactions during some IV treatments. The two unaffected cats that received the tolerisation regimen remained seronegative, however, only half of the unaffected cats not submitted to this regimen seroconverted. Only minor side-effects were attributed to the short-course of cyclosporine and azathioprine. Two MPS-VI cats also well-tolerated four weekly intrathecal injections of rhASB and consequently exhibited less oligosaccharide fragments in cerebrospinal fluid and less vacuolation within their dura mater. These data indicate that a relatively high rate of immunotolerance towards rhASB can be achieved in MPS-VI cats with a short-course tolerisation regimen ultimately permitting removal of lysosomal storage within the dura mater with the use of intrathecal therapy.

Enzyme replacement therapy for mucopolysaccharidosis VI: Growth and pubertal development in patients treated with recombinant human N-acetylgalactosamine 4-sulfatase

BACKGROUND AND METHODS: Growth failure is characteristic of untreated mucopolysaccharidosis type VI (MPS VI: Maroteaux-Lamy syndrome). Growth was studied in fifty-six MPS VI patients (5 to 29 years old) prior to and for up to 240 weeks of weekly infusions of recombinant human arylsulfatase B (rhASB) at 1 mg/kg during Phase 1/2, Phase 2, Phase 3 or Phase 3 Extension clinical trials. Height, weight, and Tanner stage data were collected. Pooled data were analyzed to determine mean height increase by treatment week, growth impacts of pubertal status, baseline urinary GAG, and age at treatment initiation. Growth rate for approximately 2 years prior to and following treatment initiation was analyzed using longitudinal modeling. RESULTS: Mean height increased by 2.9 cm after 48 weeks and 4.3 cm after 96 weeks on enzyme replacement therapy (ERT). Growth on ERT was not correlated with baseline urinary GAG. Patients under 16 years of age showed greatest increases in height on treatment. Model results based on pooled data showed significant improvement in growth rate during 96 weeks of ERT when compared to the equivalent pretreatment time period. Delayed pubertal onset or progression was noted in 10 patients entering the clinical trials; all of whom showed progression of at least one Tanner stage during 2 years on ERT, and 6 of whom (60%) completed puberty. CONCLUSION: Analysis of mean height by treatment week and longitudinal modeling demonstrate significant increase in height and growth rate in MPS VI patients receiving long-term ERT. This impact was greatest in patients aged below 16 years. Height increase may result from bone growth and/or reduction in joint contractures. Bone growth and resolution of delayed puberty may be related to improvements in general health, bone cell health, nutrition, endocrine gland function and reduced inflammation.

Growth patterns and the use of growth hormone in the mucopolysaccharidoses

Short stature is characteristic of patients with mucopolysaccharidosis (MPS) diseases. For children with skeletal dysplasias, such as MPS, it is important to know the natural history of growth. An understanding of the natural growth pattern in each MPS disease provides a measurement to which treatments can be compared, as well as data which can help families and providers make individualized decisions about growth promoting treatments. Multiple advancements have been made in the treatment of MPS with both hematopoietic cell transplantation (HCT) and enzyme replacement therapy (ERT). The long term benefit of these treatments on growth is unknown. This article will review the published data on growth in children with MPS, and describe preliminary data on the use of human growth hormone (hGH) in children with MPS.

Potential role of cathepsin K in the pathophysiology of mucopolysaccharidoses

Cathepsin K, a papain-like cysteine protease, is highly expressed in osteoclasts and plays a critical role in bone resorption. Dysfunction of the enzyme leads to various skeletal abnormalities. The recent knowledge that the collagenolytic activity of cathepsin K depends on interactions with bone and cartilage-resident glycosaminoglycans (GAGs) may shed some light on diseases such as mucopolysaccharidoses (MPSs). MPSs are a group of lysosomal storage diseases characterized by the accumulation of GAGs in tissues including bone. Typical pathological features of these diseases include skeletal abnormalities such as dysostosis multiplex, short stature, and multiple irregularities in bone development. We describe how further investigation of the cathepsin K/GAG complexes could provide valuable insights into the bone pathology associated with MPS diseases. In this review, we discuss the inhibition of osteoclast function through altered activity of cathepsin K by GAGs and offer insight into a mechanism for the bone pathology seen in MPS patients.

Enzyme replacement therapy for mucopolysaccharidosis VI from 8 weeks of age--a sibling control study

Mucopolysaccharidosis type VI (MPS VI) is a progressive, multisystem disorder caused by a deficiency of the lysosomal enzyme N-acetylgalactosamine-4-sulphatase (ASB). Enzyme replacement therapy (ERT) has been shown to clinically benefit affected individuals greater than 6 years of age. This case control study of affected siblings assessed the safety, efficacy and benefits of ERT in children less than 5 years of age. Siblings, aged 8 weeks and 3.6 years, were treated weekly with 1 mg/kg recombinant human N-acetylgalactosamine-4-sulphatase (rhASB) with an end-point of 3.6 years. Clinical and biochemical parameters were monitored to assess the benefits of ERT. The treatment was well tolerated by both siblings. In the younger sibling, ERT was associated with the absence of the development of scoliosis and preserved joint movement, cardiac valves and facial morphology. The older sibling had a marked improvement in joint mobility and cardiac valve pathology and scoliosis slowed or stabilized. Corneal clouding and progressive skeletal changes were observed despite treatment. This study demonstrated a clear benefit of early initiation of ERT to slow or prevent the development of significant pathological changes of MPS VI. These results indicate that the earlier ERT is started, the greater the response.

Glycosaminoglycan-mediated loss of cathepsin K collagenolytic activity in MPS I contributes to osteoclast and growth plate abnormalities

Mucopolysaccharidoses are a group of lysosomal storage diseases characterized by the build-up of glycosaminoglycans (GAGs) and severe skeletal abnormalities. As GAGs can regulate the collagenolytic activity of the major osteoclastic protease cathepsin K, we investigated the presence and activity of cathepsin K and its co-localization with GAGs in mucopolysaccharidosis (MPS) type I bone. The most dramatic difference between MPS I and wild-type mice was an increase in the amount of cartilage in the growth plates in MPS I bones. Though the number of cathepsin K-expressing osteoclasts was increased in MPS I mice, these mice revealed a significant reduction in cathepsin K-mediated cartilage degradation. As excess heparan and dermatan sulfates inhibit type II collagen degradation by cathepsin K and the spatial overlap between cathepsin K and heparan sulfate strongly increased in MPS I mice, the build up of subepiphyseal cartilage is speculated to be a direct consequence of cathepsin K inhibition by MPS I-associated GAGs. Moreover, isolated MPS I and Ctsk(-/-) osteoclasts displayed fewer actin rings and formed fewer resorption pits on dentine disks, as compared with wild-type cells. These results suggest that the accumulation of GAGs in murine MPS I bone has an inhibitory effect on cathepsin K activity, resulting in impaired osteoclast activity and decreased cartilage resorption, which may contribute to the bone pathology seen in MPS diseases.

Mucopolysaccharidosis VI: the Italian experience

The current paper describes the natural history and management of mucopolysaccharidosis VI (MPS VI) in all patients currently diagnosed with the disease in Italy. Nine patients (5.5-14.4 years) were included in the data review in March 2008. Gestational and perinatal data were normal for all patients. Median age at diagnosis was 1.9 years. During the course of the disease, all patients developed coarsened facial features, short stature, heart valve disease, eye problems, musculoskeletal problems, hepatosplenomegaly and neurological abnormalities. All patients received rhASB enzyme replacement therapy (ERT) and showed improvement or stabilisation in clinical manifestations after onset of therapy. The most frequently reported improvements were increased joint mobility and reduced hepatosplenomegaly. No relevant safety issues of ERT were reported. In conclusion, patients in Italy with MPS VI are diagnosed early in life. All patients have access to ERT and appear to benefit from this therapy.

Gene therapy for lysosomal storage diseases (LSDs) in large animal models

Lysosomal storage diseases (LSDs) are inherited metabolic disorders caused by deficient activity of a single lysosomal enzyme or other defects resulting in deficient catabolism of large substrates in lysosomes. There are more than 40 forms of inherited LSDs known to occur in humans, with an aggregate incidence estimated at 1 in 7,000 live births. Clinical signs result from the inability of lysosomes to degrade large substrates; because most lysosomal enzymes are ubiquitously expressed, a deficiency in a single enzyme can affect multiple organ systems. Thus LSDs are associated with high morbidity and mortality and represent a significant burden on patients, their families, the health care system, and society. Because lysosomal enzymes are trafficked by a mannose 6-phosphate receptor mechanism, normal enzyme provided to deficient cells can be localized to the lysosome to reduce and prevent storage. However, many LSDs remain untreatable, and gene therapy holds the promise for effective therapy. Other therapies for some LSDs do exist, or are under evaluation, including heterologous bone marrow or cord blood transplantation (BMT), enzyme replacement therapy (ERT), and substrate reduction therapy (SRT), but these treatments are associated with significant concerns, including high morbidity and mortality (BMT), limited positive outcomes (BMT), incomplete response to therapy (BMT, ERT, and SRT), life-long therapy (ERT, SRT), and cost (BMT, ERT, SRT). Gene therapy represents a potential alternative, albeit with its own attendant concerns, including levels and persistence of expression and insertional mutagenesis resulting in neoplasia. Naturally occurring animal homologues of LSDs have been described in all common domestic animals (and in some that are less common) and these animal models play a critical role in evaluating the efficacy and safety of therapy.

Lentiviral-mediated correction of MPS VI cells and gene transfer to joint tissues

Joint disease in mucopolysaccharidosis type VI (MPS VI) remains difficult to treat despite the success of enzyme replacement therapy in treating other symptoms. In this study, the efficacy of a lentiviral vector to transduce joint tissues and express N-acetylgalactosamine-4-sulphatase (4S), the enzyme deficient in MPS VI, was evaluated in vitro and the expression of beta-galactosidase was used to evaluate transduction in vivo. High viral copy number was achieved in MPS VI fibroblasts and 4-sulphatase activity reached 12 times the normal level. Storage of accumulated glycosaminoglycan was reduced in a dose dependent manner in both MPS VI skin fibroblasts and chondrocytes. Enzyme expression was maintained in skin fibroblasts for up to 41 days. Comparison of two promoters; the murine phosphoglycerate kinase gene promoter (pgk) and the myeloproliferative sarcoma virus long terminal repeat promoter (mpsv), demonstrated a higher level of marker gene expression driven by the mpsv promoter in both chondrocytes and synoviocytes in vitro. When injected into the rat knee, the expression of beta-galactosidase from the mpsv promoter was widespread across the synovial membrane and the fascia covering the cruciate ligaments and meniscus. No transduction of chondrocytes or ligament cells was observed. Transduction was maintained for at least 8 weeks after injection. These results indicate that the lentiviral vector can be used to deliver 4S to a range of joint tissues in vitro and efficiently transduce synovial cells and express beta-galactosidase in vivo.

Long-term intra-articular administration of recombinant human N-acetylgalactosamine-4-sulfatase in feline mucopolysaccharidosis VI

Degenerative joint disease (DJD) is one aspect of mucopolysaccharidosis VI (MPS VI) pathology that has proven resistant to systemic enzyme replacement therapy (ERT). In this study the effect of repeated intra-articular injections (IA INJ) of recombinant human acetylgalactosamine-4-sulfatase (rh4S) on DJD was examined. Four MPS VI cats received i.v. ERT weekly from birth plus IA INJ (0 or 500 microg of rh4S per joint; monthly or every three months) while three MPS VI cats received IA INJ only. After 10 months, shoulders, elbows and knees were compared. Taken individually, an improvement in joint appearance was observed between the joints that received rh4S monthly or every three months compared with the contralateral joints treated with buffer or at lower frequency. Within articular cartilage of joints treated more frequently, the depth of clearance of lysosomal storage tended to be greater and uronic acid content was reduced reflecting the removal of glycosaminoglycans. Synovium in treated joints also showed less storage. No abnormal clinical signs were observed after the IA INJ and negligible antibody titres were measured throughout the study. No clear benefit was observed by combining IA INJ with weekly ERT and the most significant improvement in joint appearance resulted from increased IA INJ frequency. These data support the view that intra-articular therapy may be a good option for preventing the development of the severe articular pathology in MPS VI.

Animal models for mucopolysaccharidosis disorders and their clinical relevance

Progress in understanding how a particular genotype produces the phenotype of an inborn error of metabolism, such as a mucopolysaccharidosis, in human patients has been facilitated by the study of animals with mutations in the orthologous genes. These are not just animal models, but true orthologues of the human genetic disease, with defects involving the same evolutionarily conserved genes and the same molecular, biochemical, and anatomic lesions as in human patients. These animals are often domestic species because of the individual medical attention paid to them, particularly dogs and cats. In addition, naturally occurring mouse models have also been found in breeding colonies. Within the last several decades, advances in molecular biology have allowed the production of knockout mouse models of human genetic disease, including the lysosomal storage diseases. The ability to use both inbred strains of a small, prolific species together with larger out-bred animals found because of their disease phenotype provides a powerful combination with which to investigate pathogenesis, develop approaches to therapy, and define biomarkers to evaluate therapeutic success. This has been true for the inborn errors of metabolism and, in particular, the mucopolysaccharidoses.

CONCLUSION

Animal models of human genetic disease continue to play an important role in understanding the molecular and physiological consequences of lysosomal storage diseases and to provide an opportunity to evaluate the efficacy and safety of therapeutic interventions.

Intra-articular enzyme administration for joint disease in feline mucopolysaccharidosis VI: enzyme dose and interval

Degenerative joint changes have been reported in human mucopolysaccharidosis VI (MPS VI) and are a prominent feature of feline MPS VI. Joint disease has proven refractory to intravenous enzyme replacement therapy (ERT) in the MPS VI cat because enzyme is unable to reach cells in cartilage. In this study, enzyme was infused directly into the intraarticular space to determine whether joint tissues are able to respond to replacement enzyme. Clearance of glycosaminoglycans from chondrocytes was observed at a dose of 10 microg recombinant human N-acetylgalactosamine-4-sulfatase (rh4S), but greater clearance was observed with higher doses. The chondrocytes at the articular surface were cleared preferentially. Lysosomal vacuolation in cruciate ligament and synovial cells also decreased upon addition of rh4S. One month after injection of rh4S, a slight reaccumulation of storage was observed at the surface of the joint, but extensive reaccumulation was observed 2 mo after injection. These results indicate that by bypassing the synovium using intraarticular ERT, significant reduction in storage material in joint tissues can be achieved. Localized ERT in the joint space provides a mechanism for delivering enzyme directly to the articular cartilage and a potential therapy for joint pathology in MPS VI.

Direct comparison of measures of endurance, mobility, and joint function during enzyme-replacement therapy of mucopolysaccharidosis VI (Maroteaux-Lamy syndrome): results after 48 weeks in a phase 2 open-label clinical study of recombinant human N-acetylgalactosamine 4-sulfatase

OBJECTIVE

Mucopolysaccharidosis VI (MPS VI; Maroteaux-Lamy syndrome) is a lysosomal storage disease caused by a deficiency of the enzyme N-acetylgalactosamine 4-sulfatase (ASB). This enzyme deficiency leads to a progressive disorder with multiple tissue and organ involvement. The disease is rare and is heterogeneous in its clinical presentation and progression. A potential treatment for this disease exists in the form of enzyme-replacement therapy (ERT) with recombinant human ASB (rhASB), and a phase 1/2 randomized, double-blind, 2-dose (0.2 and 1 mg/kg) study in 6 patients showed the treatment at 48 weeks to be well tolerated. Greater biochemical efficacy based on a urine glycosaminoglycan occurred in the high-dose (1 mg/kg) group, and functional improvement seemed greater in patients in the high-dose group with rapidly advancing disease. On the basis of the phase 1/2 results, a phase 2, open-label study in patients with rapidly advancing disease was initiated primarily to evaluate efficacy variables that measure endurance, mobility, and joint function in a larger group of patients.

METHODS

This was an open-label, multinational study of 10 MPS VI patients who received 48 weekly intravenous treatments with 1.0 mg/kg rhASB and had assessments of biochemical and clinical responses at regular intervals.

RESULTS

After 24 weeks of treatment, each patient on average experienced a 155-m (98%) improvement in the 12-minute walk, a 64-m (62%) improvement at the 6-minute time point of the 12-minute walk, and a 48-stair (110%) gain in the 3-minute stair climb versus the baseline mean values. Additional improvements after 48 weeks of treatment were observed, including mean values of 211 m (138%) in the 12-minute walk, 75 m (80%) at the 6-minute time point of the 12-minute walk, and 61-stair (147%) gain in the 3-minute stair climb versus the baseline mean values. Joint Pain and Stiffness Questionnaire scores improved by at least 50% by week 24 and were maintained at week 48, whereas there were only small improvements in active shoulder range of motion (<10 degrees ) and in the time taken to stand, walk, and turn starting from a seated position (Expanded Timed Get-Up and Go test). Improvement in pulmonary function based on forced vital capacity and forced expiratory volume at 1 minute in the absence of growth was observed in 3 of 6 patients, and the observed gains occurred in the 24- to 48-week treatment interval. A mean decrease of 76% in urinary excretion of glycosaminoglycans indicated that a satisfactory biochemical response was achieved and the ERT was well tolerated.

CONCLUSIONS

The results suggest that a 12-minute walk extends the dynamic range of the conventional 6-minute walk and, along with the 3-minute stair climb, provide a robust approach to documenting the improvement in endurance in MPS VI patients who undergo ERT with rhASB.

Development of an assay for the detection of mucopolysaccharidosis type VI patients using dried blood-spots

BACKGROUND

Mucopolysaccharidosis type VI (MPS VI) is a lysosomal storage disorder (LSD), which is caused by a deficiency in the enzyme N-acetylgalactosamine 4-sulfatase (4-sulfatase). MPS VI is characterized by severe skeletal abnormalities, somatic tissue pathology and early death. Treatment possibilities include bone marrow transplantation (BMT) and enzyme replacement therapy (ERT; currently in phase III clinical trial). Early diagnosis of MPS VI will allow treatment before the onset of irreversible pathology.

METHODS

Sensitive immune assays have been developed to detect 4-sulfatase protein and activity in normal control and MPS VI blood-spots.

RESULTS

Dried blood-spots from MPS VI patients contained no detectable 4-sulfatase protein and activity, compared to 3.5-21 microg/L of 4-sulfatase protein and 291-1298 nmol/min/L of activity for normal human controls. In this evaluation study, the assay was sensitive and 100% specific, allowing reliable detection of individuals with MPS VI.

CONCLUSIONS

The assays reported here have the potential to detect MPS VI patients using dried blood-spots.

Monitoring dose response of enzyme replacement therapy in feline mucopolysaccharidosis type VI by tandem mass spectrometry

Mucopolysaccharidosis type VI is an inherited disorder of glycosaminoglycan metabolism characterized by organomegaly, corneal clouding, and skeletal dysplasia. Recent developments in the use of tandem mass spectrometry to measure sulfated mono- and disaccharides have enabled us to perform noninvasive, biochemical monitoring during therapy regimes in mucopolysaccharidosis type VI cats in addition to established methods of disease evaluation. In this study, mucopolysaccharidosis type VI animals were given high-dose (20 mg/kg) enzyme replacement therapy for the first month after birth followed by low doses (1 mg/kg) for a further 2 mo and were compared with animals maintained on 1 mg/kg enzyme replacement therapy for 3 mo. A sulfated monosaccharide (N-acetylhexosamine) and a sulfated disaccharide (N-acetylhexosamine-uronic acid) were elevated in MPS VI cat urine and blood. These markers showed a clear discrimination between the treatment groups during the first 4 wk of therapy: values in the high-dose group were close to normal whereas those in the low-dose group were only slightly lower than the untreated mucopolysaccharidosis type VI cats. However, within 2 mo of cessation of the high-dose therapy there was minimal difference in the oligosaccharide levels, with both groups lying between the untreated and unaffected cats. At the completion of the trial, subjective minor improvement was noted in overall physical disease features and also in lysosomal vacuolation in tissues from animals on the initial high-dose enzyme replacement therapy compared to the low-dose therapy animals. Initial high-dose therapy reduced storage load in the animals but had no lasting clinical benefit over continuous low-dose therapy.

Comparative Effects of Recombinant Acid Sphingomyelinase Administration by Different Routes in Niemann-Pick Disease Mice

An inherited deficiency of acid sphingomyelinase (ASM) activity results in the Type A and B forms of Niemann-Pick disease (NPD). The aim of this study was to evaluate the effects of recombinant human ASM (rhASM) replacement therapy on the mouse model, by comparing different routes of administration. Eight NPD mice received rhASM via an intravenous injection (IV) administered at a dose of 1 mg/kg and another group of 8 NPD mice received the same dose by subcutaneous injection (SC). The plasma levels of ASM activity in intravenously administered mice were significantly elevated immediately after injection. In contrast, in the subcutaneously injected mice, the level of ASM activity was maximal 6 h after injection. The levels of ASM activity in both groups had declined substantially by 2 days after injection. It was concluded that rhASM administered by subcutaneous injection is completely absorbed, and offers a similar efficacy to intravenously administered recombinant enzyme.

Animal models for mucopolysaccharidoses and their clinical relevance

The mucopolysaccharidoses (MPS) are characterized by the accumulation of glycosaminoglycans (GAG) and result from the impaired function of one of 11 enzymes required for normal GAG degradation. MPS II was the first MPS to be defined clinically in humans and is caused by deficient activity of the enzyme iduronate-2-sulphatase. MPS VI was the first MPS recognized in an animal; since then, all but MPS IIIC and IX have been described as naturally occurring in animals or made by knock-out technology. As in humans, all are inherited as autosomal recessive traits, except for MPS II, which is X-linked. Most animal colonies have been established from single related heterozygous animals, making the affected offspring homozygous for the same mutant allele. Importantly, these models have disease pathology that is similar to that seen in humans, making the animals extremely valuable for the investigation of disease pathogenesis and the testing of therapies. Large animal homologues are similar to humans in natural genetic diversity, approaches to therapy and care, and the possibility of evaluating long-term effects of treatment. Therapeutic strategies for MPS include enzyme replacement therapy, heterologous bone marrow transplantation, and somatic cell gene transfer, all of which have been tested in animals with some success.

New prospects for the treatment of lysosomal storage diseases

Although individually rare, lysosomal storage disorders constitute a significant burden on society. To date, enzyme replacement therapy (ERT) has been the most successful therapeutic approach for lysosomal storage disorders. ERT reverses systemic manifestations of Gaucher disease but does not effectively treat the neurological complications. Recently, ERT produced a reduction of severe neuropathic pain, stabilisation of renal disease, and improved vascular function and structure in short-term, placebo-controlled trials in patients with Fabry's disease. Long-term studies are necessary to evaluate the full potential of ERT in this disease. In patients with Pompe disease, a fatal cardiac and skeletal muscle disorder, ERT improved cardiac function and structure, and increased overall muscle strength. It has already increased survival in a small number of affected infants. ERT also decreased liver and spleen size, joint mobility and quality of life in patients with mucopolysaccharidosis type I, but when the therapeutic protein is administered intravenously, it is unlikely to modify the neurological outcome in this or in other similar disorders. Bone marrow transplantation continues to be effective in Gaucher disease, in some forms of mucopolysaccharidosis and in mild forms of Krabbé disease, but it has high morbidity and mortality that limits its use in lysosomal storage disorders. Drugs that slow the rate of formation of accumulating glycolipids are being developed and one of them, OGT-918 (N-butyldeoxynojirimycin), is showing promise in patients with Gaucher disease. Gene therapy for lysosomal storage disorders holds promise as a replacement for the other therapies described here but requires much more development before clinical efficacy trials.

Enzyme replacement therapy for the mucopolysaccharide storage disorders

The mucopolysaccharide storage disorders are a group of lysosomal storage disorders associated with deficiencies of lysosomal enzymes required for the normal sequential degradation of glycosaminoglycans, formerly known as mucopolysaccharides. The accumulation of glycosaminoglycans in a wide variety of tissues results in a complex and progressive disease leading to death in the first or second decade in most patients. Studies of enzyme replacement in animal models of mucopolysaccharide disorders have demonstrated the potential of parenterally administered enzyme to reduce glycosaminoglycan storage and microscopic pathology. Clinical studies of enzyme replacement therapy are currently underway for mucopolysaccharidosis I, mucopolysaccharidosis VI and mucopolysaccharidosis II. The complexity and heterogeneity of the mucopolysaccharide disorders provide significant challenges for clinical study design and evaluation. Innovative clinical development strategies may be needed to lower the development cost and time for complex rare disease therapies to assure that such patients receive therapies they deserve.

Enzyme replacement therapy in a feline model of MPS VI: modification of enzyme structure and dose frequency

Enzyme replacement therapy (ERT) in the MPS VI cat is effective at reducing or eliminating pathology in most connective tissues. One exception is that cartilage and chondrocytes remained distended with extensive lysosomal vacuolation after long-term, high-dose ERT. In this study, we demonstrate that recombinant human N-acetylgalactosamine-4-sulphatase (4S) is taken up by chondrocytes via a mannose-6-phosphate-dependent mechanism and is effective at removing MPS storage. In vitro, the penetration of 4S into articular cartilage is low (partitioning coefficient = 0.06) and i.v. administered enzyme does not distribute significantly into articular cartilage in vivo. To alter the tissue distribution of 4S, the enzyme was coupled to ethylene diamine or poly-L-lysine, increasing its overall charge and diffusion into cartilage, and the dosing frequency of unmodified 4S was increased. Modification resulted in active 4S that maintained its ability to correct MPS storage and increased the partitioning coefficient of 4S into cartilage by 77% and 50% for ethylene diamine and poly-L-lysine, respectively. However, in vivo ERT studies demonstrated that response to therapy was not significantly improved by either the enzyme modifications or change to the dosing regimen, when compared with ERT with unmodified enzyme. Distribution experiments indicated the majority of enzyme is taken up by the liver irrespective of modification. To optimize therapy and improve the amount of enzyme reaching cartilage and other tissues demonstrating poor uptake, it may be necessary to bypass the liver or prolong plasma half-life so that proportionately more enzyme is delivered to other tissues.

Recombinant canine alpha-l-fucosidase: expression, purification, and characterization

Canine fucosidosis has proven to be an excellent large animal model both for the equivalent human disorder and, in more general terms, for the central nervous system pathology found in many of the lysosomal storage disorders. Most importantly studies in this animal model were among the first to convincingly show that bone marrow transplantation could successfully modify the course of clinical central nervous system disease and to define some of the important parameters for successful treatment. In order to evaluate other, more generally applicable routes to treatment of central nervous system disease in the lysosomal storage disorders we have expressed recombinant canine alpha-l-fucosidase (rcFUC) in Chinese hamster ovary and Madin-Darby canine kidney cells to levels of between 2 and 13 mg/liter of culture medium and purified the enzyme to apparent homogeneity by affinity chromatography on fucosylamine-linked agarose. rcFUC is composed of subunits of M(r) 50 kDa and the native enzyme is a homotrimer of M(r) 156 kDa. Kinetic properties of rcFUC were similar to those of FUC isolated from both human and dog liver. rcFUC was shown to be effective in correcting the storage phenotype of human fucosidosis cells after endocytosis via the mannose-6-phosphate-receptor-mediated pathway. It was also shown to degrade fucosylated storage products isolated from affected dog brain. The availability of large amounts of rcFUC will allow us to explore ways of extending the proven efficacy of enzyme replacement therapy to the treatment of central nervous system pathology using the fucosidosis dog as a model system.

Advantages of using same species enzyme for replacement therapy in a feline model of mucopolysaccharidosis type VI

In a feline model of mucopolysaccharidosis type VI (MPS VI), recombinant feline N-acetylgalactosamine-4-sulfatase (rf4S) administered at a dose of 1 mg/kg of body weight, altered the clinical course of the disease in two affected cats treated from birth. After 170 days of therapy, both cats were physically indistinguishable from normal cats with the exception of mild corneal clouding. Feline N-acetylgalactosamine-4-sulfatase was effective in reducing urinary glycosaminoglycan levels and lysosomal storage in all cell types examined except for corneal keratocytes and cartilage chondrocytes. In addition, skeletal pathology was nearly normalized as assessed by radiographic evidence and bone morphometric analysis. Comparison of results with a previous study in which recombinant human 4S (rh4S) was used at an equivalent dose and one 5 times higher indicated that rf4S had a more pronounced effect on reducing pathology than the same dose of rh4S, and in some instances such as bone pathology and lysosomal storage in aorta smooth muscle cells, it was as good as, or better than, the higher dose of rh4S. We conclude that in the feline MPS VI model the use of native or same species enzyme for enzyme replacement therapy has significant benefits.

Immune response to enzyme replacement therapy: 4-sulfatase epitope reactivity of plasma antibodies from MPS VI cats

The mucopolysaccharidoses (MPS) are a group of multiple pathology disorders which are part of a larger group of genetic diseases known as lysosomal storage disorders. Enzyme replacement therapy (ERT) has been developed as a therapy for MPS patients. However, immune responses to ERT have been reported in MPS animal models and in human Gaucher patients. Antibodies can have adverse effects during ERT, which include hypersensitivity/anaphylactic reactions, enzyme inactivation, and enzyme degradation. This study aimed to characterize the immune response to ERT in a feline model of MPS VI, by defining the epitope reactivity of cat plasma antibody against human recombinant N-acetylgalactosamine 4-sulfatase (4-sulfatase) replacement protein. For MPS VI cat plasma, antibody reactivity was observed prior to ERT, with distinct regions of 4-sulfatase linear sequence displaying low affinity antibody reactivity. There was an increase in antibody titer to 4-sulfatase for MPS VI cats post-ERT, with the majority of the immune response detected to linear sequence epitopes. One cat displayed a high titer and high affinity epitope reactivity following prolonged exposure (>/=9 months) to the replacement protein. MPS VI cats on shorter term ERT (3 months) showed high titers to 4-sulfatase and similar patterns of epitope reactivity, but lower affinity antibody reactivity, when compared to the latter cat. This study reports the linear amino acid sequence reactivity and nature of the immune response produced to 4-sulfatase before and after ERT. The monitoring of antibody production during replacement therapy is an important consideration for patient management, as high titer antibodies can affect the efficacy of therapy.

A genetic linkage map of microsatellites in the domestic cat (Felis catus)

Of the nonprimate mammalian species with developing comparative gene maps, the feline gene map (Felis catus, Order Carnivora, 2N = 38) displays the highest level of syntenic conservation with humans, with as few as 10 translocation exchanges discriminating the human and feline genome organization. To extend this model, a genetic linkage map of microsatellite loci in the feline genome has been constructed including 246 autosomal and 7 X-linked loci. Two hundred thirty-five dinucleotide (dC. dA)n. (dG. dT)n and 18 tetranucleotide repeat loci were identified and genotyped in a two-family, 108-member multigeneration interspecies backcross pedigree between the domestic cat (F. catus) and the Asian leopard cat (Prionailurus bengalensis). Two hundred twenty-nine loci were linked to at least one other marker with a lod score >/=3.0, identifying 34 linkage groups. Representative markers from each linkage group were assigned to specific cat chromosomes by somatic cell hybrid analysis, resulting in chromosomal assignments to 16 of the 19 feline chromosomes. Genome coverage spans approximately 2900 cM, and we estimate a genetic length for the sex-averaged map as 3300 cM. The map has an average intragroup intermarker spacing of 11 cM and provides a valuable resource for mapping phenotypic variation in the species and relating it to gene maps of other mammals, including human.

Evaluation of fibroblast-mediated gene therapy in a feline model of mucopolysaccharidosis type VI

Fibroblast-mediated ex vivo gene therapy was evaluated in the N-acetylgalactosamine 4-sulfatase (4S) deficient mucopolysaccharidosis type VI (MPS VI) cat. Skin biopsies were obtained at birth from severely affected MPS VI kittens and used to initiate fibroblast outgrowths for retroviral transduction with the 4S cDNA. 4S gene expression in transduced cells was under the transcriptional control of the MoMLV long terminal repeat promoter or the cytomegalovirus (CMV) immediate-early promoter. Characterisation of gene-transduced fibroblasts demonstrated the cells to be over-expressing 4S activity. Twenty-four to forty million autologous, gene-corrected fibroblasts were implanted under the renal capsule of three MPS VI kittens at 8-16 weeks of age. Transient, low levels of 4S activity were detected in peripheral blood leukocytes shortly after implantation but were not detectable within 3-8 weeks' post-implantation. Long-term biochemical and clinical evaluation of these cats demonstrated identical disease progression to that previously described in untreated, clinically severe MPS VI cats.

Mild feline mucopolysaccharidosis type VI. Identification of an N-acetylgalactosamine-4-sulfatase mutation causing instability and increased specific activity

The missense mutation, L476P, in the N-acetylgalactosamine 4-sulfatase (4S) gene, has previously been shown to be associated with a severe feline mucopolysaccharidosis type VI (MPS VI) phenotype. The present study describes a second mutation, D520N, in the same MPS VI cat colony, which is inherited independently of L476P and is associated with a clinically mild MPS VI phenotype in D520N/L476P compound heterozygous cats. Biochemical and clinical assessment of L476P homozygous, D520N/L476P compound heterozygous, and D520N homozygous cats demonstrated that the entire range of clinical phenotypes, from severe MPS VI, to mild MPS VI, to normal are clustered within a narrow range of residual 4S activity from 0. 5% to 4.6% of normal levels. When overexpressed in CHO-KI cells, the secreted form of D520N 4S was inactivated in neutral pH conditions. In addition, intracellular D520N 4S protein was rapidly degraded and corresponded to 37%, 14.5%, and 0.67% of normal 4S protein levels in the microsomal, endosomal, and lysosomal compartments, respectively. However, the specific activity of lysosomal D520N 4S was elevated 22. 5-fold when compared with wild-type 4S. These results suggest that the D520N mutation causes a rapid degradation of 4S protein. The effect of this is partially ameliorated as a result of a significant elevation in the specific activity of mutant D520N 4S reaching the lysosomal compartment.

Two mutations within a feline mucopolysaccharidosis type VI colony cause three different clinical phenotypes

Mucopolysaccharidosis type VI (MPS VI) is a lysosomal storage disease caused by a deficiency of N-acetylgalactosamine-4-sulfatase (4S). A feline MPS VI model used to demonstrate efficacy of enzyme replacement therapy is due to the homozygous presence of an L476P mutation in 4-sulfatase. An additional mutation, D520N, inherited independently from L476P and recently identified in the same family of cats, has resulted in three clinical phenotypes. L476P homozygotes exhibit dwarfism and facial dysmorphia due to epiphyseal dysplasia, abnormally low leukocyte 4S/betahexosaminidase ratios, dermatan sulfaturia, lysosomal inclusions in most tissues including chondrocytes, corneal clouding, degenerative joint disease, and abnormal leukocyte inclusions. Similarly, D520N/D520N and L476P/D520N cats have abnormally low leukocyte 4S/betahexosaminidase ratios, mild dermatan sulfaturia, lysosomal inclusions in some chondrocytes, and abnormal leukocyte inclusions. However, both have normal growth and appearance. In addition, L476P/D520N cats have a high incidence of degenerative joint disease. We conclude that L476P/D520N cats have a very mild MPS VI phenotype not previously described in MPS VI humans. The study of L476P/D520N and D520N/ D520N genotypes will improve understanding of genotype to phenotype correlations and the pathogenesis of skeletal dysplasia and joint disease in MPS VI, and will assist in development of therapies to prevent lysosomal storage in chondrocytes.