Animal models of early osteoarthritis: their use for the evaluation of potential chondroprotective agents

Survey of the therapeutic approach and efficacy of pentosan polysulfate for the prevention and treatment of equine osteoarthritis in veterinary practice in Australia

OBJECTIVE

To survey veterinary practitioners in Australia on how they administer pentosan polysulfate (PPS) to horses and their perceptions of the efficacy of PPS for: the prevention and treatment of osteoarthritis (OA), the treatment of OA when PPS is combined with other drugs, and the efficacy of PPS compared with other disease-modifying osteoarthritic drugs.

DESIGN

Practitioners were contacted by email, which contained a link to an online survey.

RESULTS

A total of 76 responses (34.5%) to the survey were received. Respondents most commonly used PPS as prophylactic therapy prior to competition (80.3%). As a prophylactic agent, PPS was considered by 48.2% of respondents to have high efficacy. The most common dose regimen for prevention and treatment of OA was 3 mg/kg, intramuscularly, once weekly for 4 weeks followed by monthly injections. Most respondents (78%) combined PPS with other drugs for treatment of OA. Intra-articular corticosteroids and hyaluronate (HA) was the most common drug combination used with PPS. PPS was preferred as a prophylactic agent when compared with HA (88.7% vs 11.3%). For treating OA, 83% of respondents considered a combination of PPS, HA and glucosamine to be more efficacious than PPS alone. However, the most common reason not to use this combination was cost (79.1%).

CONCLUSION

All respondents used PPS for prophylaxis and/or treatment of OA despite limited published scientific evidence proving its efficacy in horses. Further research is necessary to provide evidence of the clinical efficacy of PPS for the prevention and treatment of OA in horses.

Treatment of experimentally induced osteoarthritis in horses using an intravenous combination of sodium pentosan polysulfate, N-acetyl glucosamine, and sodium hyaluronan

OBJECTIVE

To assess the effects of sodium pentosan polysulfate (PPS), N-acetyl glucosamine (NAG), and sodium hyaluronan (HA) in horses with induced osteoarthritis (OA).

STUDY DESIGN

Experimental.

ANIMALS

Adult Standard bred horses (n = 16).

METHODS

OA was induced arthroscopically in 1 intercarpal joint; 8 horses were administered 3 mg/kg PPS, 4.8 mg/kg NAG, and 0.12 mg/kg HA (PGH), intravenously (IV), weekly and 8 horses were administered an equivalent volume of saline IV until study completion (day 70). Horses underwent a standardized treadmill exercise program. Clinical and radiographic findings and synovial fluid analysis were evaluated throughout the study. Macroscopic, histologic, histochemical, and biochemical findings were evaluated after necropsy. Comparisons of interest included OA and non-OA joints of saline treated horses and OA joints of PGH treated horses and OA joints of saline treated horses. Results were statistically analyzed with significance set at P < .05.

RESULTS

OA caused increases in clinical assessment scores, synovial fluid variables, radiographic, macroscopic, and histologic cartilage scores, synovial fluid and cartilage chondroitin sulfate 846-epitope and glycosaminoglycan concentration. Total radiographic scores, total macroscopic joint pathology and macroscopic cartilage pathology scores were significantly reduced in horses treated with PGH compared with saline treated horses. Synovial fluid total protein concentration and white blood cell count were higher in OA joints of PGH treated horses compared with saline treated horses. There were no other significant differences between treatment groups.

CONCLUSIONS

Improvements in macroscopic variables were not supported by other outcomes. Further evidence is needed before PGH can be recommended as a therapeutic option for osteoarthritis in horses.

Significant synovial pathology in a meniscectomy model of osteoarthritis: modification by intra-articular hyaluronan therapy

Objective. IA therapy with hyaluronan (HA) is reported to provide symptomatic relief and disease modification in OA. This study assessed the pathological changes in the synovium of an ovine model of OA and evaluated the effects of two HA preparations on this pathology.

Methods. Eighteen sheep had bilateral lateral meniscectomy to induce OA. Four months post-surgery animals received IA saline or HA (Hyalgan®) weekly for 5 weeks or three injections of an amide derivative of HA (HYADD®4-G) every 2 weeks (n = 6 per group). Six months after meniscectomy, sheep were killed, knee joint synovium processed, scored for pathological change and compared with synovium from non-operated animals. Sections of synovium from normal and treated joints were also immunostained for TNF-α, HSP-47, TGF-β, CD44, connective tissue growth factor (CTGF) or iNOS. HA synthesis by synovial fibroblasts isolated from each OA joint was quantified.

Results. Aggregate scores of pathological change were higher in OA joint synovia compared with controls, with individual measures of subintimal fibrosis and vascularity predominantly affected. Depth of intimal fibrosis was also significantly higher in meniscectomized joints. IA treatment with Hyalgan® decreased aggregate score, vascularity and depth of fibrosis. HYADD®4-G treatment decreased vascularity, intimal hyperplasia and increased high-molecular weight HA synthesis by synovial fibroblasts. CD44, CTGF or iNOS expression was increased in the synovial lining of OA joints compared with normal, but there was no significant modulation of this increase by either HA preparation.

Conclusion. Increased fibrosis and vascularity are hallmarks of pathological change in synovium in this meniscectomy model of OA. Both the IA HA and an amide derivative of HA reduced aspects of this pathology thus providing a potential mechanism for improving joint mobility and function in OA.

Modification of articular cartilage and subchondral bone pathology in an ovine meniscectomy model of osteoarthritis by avocado and soya unsaponifiables (ASU)

OBJECTIVE

To examine the effect of an oral preparation of avocado and soya unsaponifiables (ASU) on the development of joint pathology in an ovine model of osteoarthritis (OA), using computer-assisted histomorphometric methods.

DESIGN

OA was induced in ovine knee joints by bilateral lateral meniscectomy (N=32). ASU (900 mg/weekday) was given orally to half the group (MenX+ASU), the remainder receiving placebo (MenX). Sixteen animals were used as non-operated controls (NOC). At 3 and 6 months post-meniscectomy, histological sections from the medial and lateral femoral condyles (MFC, LFC), tibial plateaux (MTP, LTP) and trochlear groove (TG) were prepared from all joints. Sections were scored using traditional histopathological scales, and computerized image analysis, measuring total cartilage area, uncalcified cartilage (UCC) and subchondral bone plate (SCP) thickness, and intensity of articular cartilage toluidine blue staining (mean greyscale intensity, black=255) as an index of proteoglycan (PG) content.

RESULTS

Computerized image analysis showed significant histological differences not detectable by traditional scoring methods. ASU-treated animals at 6 months showed reduced loss of toluidine blue stain in the MTP (P=0.015) and LTP (P=0.001), and significantly greater staining in the TG than either placebo or NOC groups (P=0.011). UCC thickness increased after meniscectomy, but tended to be highest in ASU-treated animals, significantly so in the middle zone of the LFC (MenX+ASU: 1.03+/-0.21mm vs MenX: 0.79+/-0.14 mm, P=0.018; NOC: 0.77+/-0.17 mm). Lateral compartment SCP thickness increased post-meniscectomy but was increased significantly less in the inner zone of the LTP in ASU-treated sheep (MenX+ASU: 1.37+/-0. 23 mm vs MenX: 1.68+/-0.28 mm, P=0.033; NOC=1.22+/-0.33 mm).

CONCLUSIONS

In this model ASU treatment following meniscectomy appeared to confer a subtle but statistically significant protective effect on articular cartilage. Although the drug failed to prevent focal cartilage lesions, characteristic of this model, histomorphometric analysis demonstrated greater PG content and UCC thickness in adjacent joint regions of ASU-treated animals. In addition, a statistically significant reduction of subchondral bone sclerosis was noted in the LTP region of the drug-treated group. An anabolic effect on chondrocytes, resulting in the stimulation of matrix production in regions distant to the insult, was also suggested by the data. These findings support other studies which have proposed that ASU may exhibit disease-modifying anti-OA activity.

The pathobiology of osteoarthritis and the rationale for the use of pentosan polysulfate for its treatment

OBJECTIVES

Structure-modifying osteoarthritis (OA) drugs (SMOADs) may be defined as agents that reverse, retard, or stabilize the underlying pathology of OA, thereby providing symptomatic relief in the long-term. The objective of this review was to evaluate the literature on sodium pentosan polysulfate (NaPPS) and calcium pentosan polysulfate (CaPPS), with respect to the pathobiology of OA to ascertain whether these agents should be classified as SMOADs.

METHODS

Published studies on NaPPS and CaPPS were selected on the basis of their relevance to the known pathobiology of OA, which also was reviewed.

RESULTS

Both NaPPS and CaPPS exhibit a wide range of pharmacological activities. Of significance was the ability of these agents to support chondrocyte anabolic activities and attenuate catabolic events responsible for loss of components of the cartilage extracellular matrix in OA joints. Although some of the anti-catabolic activities may be mediated through direct enzyme inhibition, NaPPS and CaPPS also have been shown to enter chondrocytes and bind to promoter proteins and alter gene expression of matrix metalloproteinases and possibly other mediators. In rat models of arthritis, NaPPS and CaPPS reduced joint swelling and inflammatory mediator levels in pouch fluids. Moreover, synoviocyte biosynthesis of high-molecular-weight hyaluronan, which is diminished in OA, was normalized when these cells were incubated with NaPPS and CaPPS or after intraarticular injection of NaPPS into arthritic joints. In rabbit, canine, and ovine models of OA, NaPPS and CaPPS preserved cartilage integrity, proteoglycan synthesis, and reduced matrix metalloproteinase activity. NaPPS and CaPPS stimulated the release of tissue plasminogen activator (t-PA), superoxide dismutase, and lipases from vascular endothelium while concomitantly decreasing plasma levels of the endogenous plasminogen activator inhibitor PAI-1. The net thrombolytic and lipolytic effects exhibited by NaPPS and CaPPS may serve to improve blood flow through subchondral capillaries of OA joints and improve bone cell nutrition. In geriatric OA dogs, NaPPS and CaPPS reduced symptoms, as well as normalized their thrombolytic status, threshold for platelet activation, and plasma triglyceride levels. These hematologic parameters were shown to be abnormal in OA animals before drug treatment. Similar outcomes were observed in OA patients when CaPPS or NaPPS were given orally or parenterally in both open and double-blind trials.

CONCLUSIONS

The data presented in this review support the contention that NaPPS and CaPPS should be classified as SMOADs. However, additional long-term clinical studies employing methods of assessing joint structural changes will be needed to confirm this view.

The surgical anatomy of the stifle joint in sheep

OBJECTIVE

To provide a detailed description of the surgical anatomy of the stifle joint in sheep.

STUDY DESIGN

The results from analysis of cadaveric dissections (14 stifle joints) and stifle radiographs (8 sets of mediolateral and craniocaudal radiographs) are presented.

ANIMALS

Skeletally mature ewes of mixed breeds.

CONCLUSIONS

Although the anatomy of the ovine stifle joint is similar to that of the human knee joint, a number of unique features were identified. These included the presence of the tendon of the m. extensor digitorum longus on the craniolateral aspect of the stifle joint, the absence of a cranial meniscofemoral ligament (ligament of Humphrey) in the caudal joint space, and attachment of the patellar tendon to the cranial pole of the patella (rather than to the distal pole, as in humans). The implications of these differences are discussed with reference to the suitability of the ovine stifle as a surgical model for the human knee joint.

Animal models for osteoarthritis: processes, problems and prospects

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