Intra-articular enzyme replacement therapy with rhIDUA is safe, well-tolerated, and reduces articular GAG storage in the canine model of mucopolysaccharidosis type I

Abstract

Background: Treatment with intravenous enzyme replacement therapy and hematopoietic stem cell transplantation for mucopolysaccharidosis (MPS) type I does not address joint disease, resulting in persistent orthopedic complications and impaired quality of life. A proof-of-concept study was conducted to determine the safety, tolerability, and efficacy of intra-articular recombinant human iduronidase (IA-rhIDUA) enzyme replacement therapy in the canine MPS I model.

Methods: Four MPS I dogs underwent monthly rhIDUA injections (0.58 mg/joint) into the right elbow and knee for 6 months. Contralateral elbows and knees concurrently received normal saline. No intravenous rhIDUA therapy was administered. Monthly blood counts, chemistries, anti-rhIDUA antibody titers, and synovial fluid cell counts were measured. Lysosomal storage of synoviocytes and chondrocytes, synovial macrophages and plasma cells were scored at baseline and 1 month following the final injection.

Results: All injections were well-tolerated without adverse reactions. One animal required prednisone for spinal cord compression. There were no clinically significant abnormalities in blood counts or chemistries. Circulating anti-rhIDUA antibody titers gradually increased in all dogs except the prednisone-treated dog; plasma cells, which were absent in all baseline synovial specimens, were predominantly found in synovium of rhIDUA-treated joints at study-end. Lysosomal storage in synoviocytes and chondrocytes following 6 months of IA-rhIDUA demonstrated significant reduction compared to tissues at baseline, and saline-treated tissues at study-end. Mean joint synovial GAG levels in IA-rhIDUA joints were 8.62 ± 5.86 μg/mg dry weight and 21.6 ± 10.4 μg/mg dry weight in control joints (60% reduction). Cartilage heparan sulfate was also reduced in the IA-rhIDUA joints (113 ± 39.5 ng/g wet weight) compared to saline-treated joints (142 ± 56.4 ng/g wet weight). Synovial macrophage infiltration, which was present in all joints at baseline, was abolished in rhIDUA-treated joints only.

Conclusions: Intra-articular rhIDUA is well-tolerated and safe in the canine MPS I animal model. Qualitative and quantitative assessments indicate that IA-rhIDUA successfully reduces tissue and cellular GAG storage in synovium and articular cartilage, including cartilage deep to the articular surface, and eliminates inflammatory macrophages from synovial tissue.

Clinical relevance: The MPS I canine IA-rhIDUA results suggest that clinical studies should be performed to determine if IA-rhIDUA is a viable approach to ameliorating refractory orthopedic disease in human MPS I.

Keywords: Canine; Lysosomal storage disorder; Model; Mucopolysaccharidosis; Orthopedic; Therapy.

Figure 1

Circulating anti-rhIDUA antibody levels were absent at baseline but began to increase steadily beginning at the third IA-rhIDUA injection. Anti-rhIDUA levels in the prednisone-treated animal (sph, light blue) remained at low levels throughout the study.

Figure 2

A: Knee synovium, baseline: Synoviocytes are foamy-appearing and swollen with storage material. B: Knee synovium, IA-rhIDUA treated: Synoviocytes (*) no longer demonstrate storage and have adopted a normal, flattened morphology. Arrows: intra-synovial lymphocytic and plasma cell infiltrate.

Figure 3

A: Plasma cell infiltrate within the synovium was absent at baseline and developed only in rhIDUA-treated joints. B: At baseline, synoviocyte GAG storage was equivalent in all joints. Significant study-end reduction of storage was observed only in rhIDUA-treated joints, not in saline-treated joints. C: Similarly, chondrocyte GAG storage was equivalent in all joints at baseline, and was significantly reduced only in rhIDUA-treated joints, not in saline-treated joints. D: Inflammatory macrophages were prominently observed at baseline in all joints. Significant reduction in macrophages was observed only in rhIDUA-treated joints, not in saline-treated joints. E: Synovial fluid acid sphingomyelinase remained elevated in both saline and rhIDUA-treated joints throughout the study compared to levels measured in normal dogs (n = 7). Dashed lines: range of acid sphingomyelinase levels measured in normal dogs. Dotted line: mean enzyme level measured in normal dogs. F: Synovial fluid acid ceramidase levels were significantly reduced to near-normal levels in IA-rhIDUA treated joints, but remained significantly higher in saline-treated joint fluid throughout the study. Dashed lines: range of synovial fluid acid ceramidase levels measured in normal dogs (n = 7). Dotted line: mean enzyme level measured in normal dogs.

Figure 4

Cartilage heparan sulfate levels, quantified via tandem mass spectroscopy of Non-Reducing End (NRE) disaccharides, were reduced in rhIDUA-treated elbows (A) and knees (B). Cartilage heparan sulfate from normal dogs was 2.44 ng/g wet weight.

Figure 5

A: Full-thickness view of knee cartilage, treated with saline for six months (Storage score: 3). The sample is oriented with articular surface to the upper left, and the deep zone to the lower right. Higher-power views of the articular surface and deep zone demonstrate chondrocytes filled with foamy storage material. B: Full-thickness view of knee cartilage, treated with rhIDUA for six months (Storage score: 1). The sample is oriented like A, with higher-power views of articular surface and deep zone. Chondrocytes both at the surface and deep zone demonstrate more cytoplasm and much less storage than saline-treated chondrocytes. C: Knee cartilage from a similarly aged, wild-type dog for reference.

Figure 6

Transmission electron micrographs of chondrocytes taken from cartilage at baseline (A) and following treatment with IA-rhIDUA (B). Notice the large amount of lysosomal storage vacuoles in the untreated chondrocyte. The treated chondrocyte demonstrates a small number of residual lysosomal storage vacuoles but has normal-appearing cytoplasm and morphology.