Cartilage oligomeric matrix protein (COMP) levels in digital sheath synovial fluid and serum with tendon injury

Equine non-septic tenosynovitis: A systematic literature review of site-specific pathological lesions, outcomes and surgical complications

BACKGROUND

Non-septic tenosynovitis is a clinically relevant and often performance limiting musculoskeletal injury in the horse.

OBJECTIVES

To review the published literature to determine which tendon sheaths are commonly affected by non-septic tenosynovitis and to describe the most frequently reported pathological lesions, outcomes, and surgical complications in equine non-septic tenosynovitis.

STUDY DESIGN

Systematic review.

METHODS

Literature searches were conducted in July 2021 from the online search engines PubMed, Scopus, Web of Science Core, VetMed Resource and ProQuest Theses & Dissertations. The inclusion criteria followed a participants, interventions, comparisons, outcome and study design (PICOS) approach. For inclusion, studies had to include live equids with non-septic tenosynovitis of any tendon sheath. Studies were excluded if they only described non-equine species, if they included data only on non-tendon sheath structures, or if they included data exclusively on cases of septic or contaminated tendon sheaths. Determination of non-sepsis relied on the diagnosis of the original authors; however, if non-sepsis was not explicitly specified, then cases that had a history of contamination of the sheath, a wound near the sheath or a positive bacterial culture were excluded from analysis. Data analysed included the distribution of structures affected by non-septic tenosynovitis, the most common pathological lesions identified within each sheath, and the most frequently reported surgical complications of non-septic tenosynovitis. The quality of each study was assessed using a methodological quality analysis.

RESULTS

A total of 85 studies describing non-septic tenosynovitis in the horse were included. Across all 85 studies, there were a total of 2449 tendon sheaths in 2101 horses reported to be affected by non-septic tenosynovitis. The digital flexor sheath was the most reported structure to be diagnosed with non-septic tenosynovitis: 41/85 (48%) studies examined the digital flexor sheath exclusively, followed by the carpal flexor sheath, tarsal flexor sheath, carpal extensor sheaths, tarsal extensor sheaths, and one case of biceps brachii non-septic tenosynovitis. For most tendon sheaths, the most common pathological lesion was an intrathecal tear of a soft tissue structure, including tears of the deep digital flexor tendon and tears of the manica flexoria. Bilateral disease was most common in the carpal flexor sheath, where distal radial physeal exostoses were the most common pathological lesions. Less common causes of non-septic tenosynovitis included neoplasia, fracture of a bone adjacent to a tendon sheath, and mineralisation of an intrathecal tendon. The likelihood of return to previous level of athletic function following non-septic tenosynovitis of most structures was approximately 50%, and the most common complication was persistent effusion following tenoscopy. While iatrogenic infection following surgery was uncommon, it was most likely following tenoscopy of the digital flexor sheath.

CONCLUSION

Non-septic tenosynovitis is commonly reported in equine athletes, with intra-thecal tears of the deep digital flexor tendon, superficial digital flexor tendon and manica flexoria frequently reported. Directions for future research include more thorough assessment of and reporting of complications following non-septic tenosynovitis and correlation of characteristics of intrathecal pathological lesions with clinical outcomes.

The molecular mechanism study of COMP involved in the articular cartilage damage of Kashin-Beck disease

Aims

Kashin-Beck disease (KBD) is a kind of chronic osteochondropathy, thought to be caused by environmental risk factors such as T-2 toxin. However, the exact aetiology of KBD remains unclear. In this study, we explored the functional relevance and biological mechanism of cartilage oligosaccharide matrix protein (COMP) in the articular cartilage damage of KBD.

Methods

The articular cartilage specimens were collected from five KBD patients and five control subjects for cell culture. The messenger RNA (mRNA) and protein expression levels were detected by quantitative reverse transcription PCR (qRT-PCR) and western blot. The survival rate of C28/I2 chondrocyte cell line was detected by MTT assay after T-2 toxin intervention. The cell viability and mRNA expression levels of apoptosis related genes between COMP-overexpression groups and control groups were examined after cell transfection.

Results

The mRNA and protein expression levels of COMP were significantly lower in KBD chondrocytes than control chondrocytes. After the T-2 toxin intervention, the COMP mRNA expression of C28/I2 chondrocyte reduced and the protein level of COMP in three intervention groups was significantly lower than in the control group. MTT assay showed that the survival rate of COMP overexpression KBD chondrocytes were notably higher than in the blank control group. The mRNA expression levels of Survivin, SOX9, Caspase-3, and type II collagen were also significantly different among COMP overexpression, negative control, and blank control groups.

Conclusion

Our study results confirmed the functional relevance of COMP with KBD. COMP may play an important role in the excessive chondrocytes apoptosis of KBD patients.Cite this article: Bone Joint Res 2020;9(9):578-586.

Development of a Cartilage Oligomeric Matrix Protein Neo-Epitope Assay for the Detection of Intra-Thecal Tendon Disease

The diagnosis of tendon injury relies on clinical signs and diagnostic imaging but imaging is subjective and does not always correlate with clinical signs. A molecular marker would potentially offer a sensitive and specific diagnostic tool that could also provide objective assessment of healing for the comparison of different treatments. Cartilage Oligomeric Matrix Protein (COMP) has been used as a molecular marker for osteoarthritis in humans and horses but assays for the protein in tendon sheath synovial fluids have shown overlap between horses affected by tendinopathy and controls. We hypothesized that quantifying a COMP neoepitope would be more discriminatory of injury. COMP fragments were purified from synovial fluids of horses with intra-thecal tendon injuries and media from equine tendon explants, and mass spectrometry of a consistent and abundant fragment revealed a ~100 kDa COMP fragment with a new N-terminus at the 78th amino-acid (NH₂-TPRVSVRP) located just outside the junctional region of the protein. A competitive inhibition ELISA based on a polyclonal antibody raised to this sequence yielded more than a 10-fold rise in the mean neoepitope levels for tendinopathy cases compared to controls (5.3 ± 1.3 µg/mL (n = 7) versus 58.8 ± 64.3 µg/mL (n = 13); p = 0.002). However, there was some cross-reactivity of the neoepitope polyclonal antiserum with intact COMP, which could be blocked by a peptide spanning the neoepitope. The modified assay demonstrated a lower concentration but a significant > 500-fold average rise with tendon injury (2.5 ± 2.2 ng/mL (n = 6) versus 1029.8 ± 2188.8 ng/ml (n = 14); p = 0.013). This neo-epitope assay therefore offers a potentially useful marker for clinical use.

Effect of circadian rhythm, age, training and acute lameness on serum concentrations of cartilage oligomeric matrix protein (COMP) neo-epitope in horses

Background

Molecular serum markers that can identify early reversible osteoarthritis (OA) in horses are lacking.

Objectives

We studied serum concentrations of a novel cartilage oligomeric matrix protein (COMP) neo‐epitope in horses subjected to short‐term exercise and with acute lameness. The effects of circadian rhythm and age were also evaluated.

Study design

Longitudinal studies in healthy horses and cross‐sectional comparison of lame and non‐lame horses.

Methods

Sera were collected from five horses before and after short‐term interval exercise and during full‐day box rest. Sera from 32 acutely lame horses were used to evaluate age‐related effects. Independent samples from control horses (n = 41) and horses with acute lameness (n = 71) were included. COMP neo‐epitope concentrations were analysed using custom‐developed inhibition ELISAs validated for equine serum. The presence of COMP neo‐epitope was delineated in healthy and osteoarthritic articular cartilage with immunohistochemistry.

Results

COMP neo‐epitope concentrations decreased after speed training but returned to baseline levels post‐exercise. No correlations between age and serum COMP neo‐epitope concentrations were found (r = 0.0013). The mean (±s.d.) serum concentration of COMP neo‐epitope in independent samples from non‐lame horses was 0.84 ± 0.38 μg/mL, and for lame horses was 5.24 ± 1.83 μg/mL (P<0.001). Antibodies against COMP neo‐epitope did not stain normal articular cartilage, but intracytoplasmic staining was found in superficial chondrocytes of mild OA cartilage and in the extracellular matrix of moderately osteoarthritic cartilage.

Main limitations

ELISA was based on polyclonal antisera rather than a monoclonal antibody. There is a sex and breed bias within the groups of horses, also it could have been of value to include horses with septic arthritis and tendonitis and investigated joint differences.

Conclusions

This COMP neo‐epitope can be measured in sera, and results indicate that it could be a biomarker for pathologic fragmentation of cartilage in connection with acute joint lameness.

Cartilage oligomeric protein, matrix metalloproteinase-3, and Coll2-1 as serum biomarkers in knee osteoarthritis: a cross-sectional study

Biochemical markers reflecting joint remodeling in osteoarthritis (OA) are a promising diagnostic tool. The aim of this study was to investigate serum levels of candidate biomarkers in subjects with and without knee OA and assess their correlation with clinical parameters and knee structural damage. 56 patients with primary knee OA and 31 healthy controls participated in this study. Patients were separated into two groups: isolated knee OA and generalized OA. Clinical parameters were obtained by validated self-reported questionnaires and a visual analogue scale. Serum levels of cartilage oligomeric protein (COMP), matrix metalloproteinase-3 (MMP-3), and Coll2-1 were quantified by enzyme-linked immunosorbent assay. Knee structural damage was determined by plain X-ray and 1.5 T magnetic resonance imaging (MRI), using Kellgren-Lawrence (KL) grading scale and Whole-Organ Magnetic Resonance Imaging Score (WORMS), respectively. Compared to controls, patients had significantly higher median serum COMP (985 vs. 625 ng/ml; p < 0.001) and MMP-3 (36.85 vs. 22.10 ng/ml; p = 0.003) levels. Patients with radiographic evidence of KLII/III knee OA had greater median COMP levels than KLI patients (1095 vs. 720 ng/ml; p = 0.001). In the generalized OA group, mean MMP-3 levels were higher than in the isolated knee OA group (30.40 vs. 55.13 ng/ml; p < 0.001). COMP correlated positively with WORMS (r _s = 0.454, p < 0.001) and MMP-3 (r _s = 0.337, p = 0.003). Cut-off values for serum COMP and MMP-3 were determined. We observed higher serum COMP and MMP-3 levels in knee OA patients compared to controls. COMP may reflect knee structural damage, while MMP-3-OA "generalization".

In silico target fishing and pharmacological profiling for the isoquinoline alkaloids of Macleaya cordata (Bo Luo Hui)

Background

Some isoquinoline alkaloids from Macleaya cordata (Willd). R. Br. (Bo Luo Hui) exhibited antibacterial, antiparasitic, antitumor, and analgesic effects. The targets of these isoquinoline alkaloids are undefined. This study aims to investigate the compound–target interaction network and potential pharmacological actions of isoquinoline alkaloids of M. cordata by reverse pharmacophore database screening.

Methods

The targets of 26 isoquinoline alkaloids identified from M. cordata were predicted by a pharmacophore-based target fishing approach. Discovery Studio 3.5 and two pharmacophore databases (PharmaDB and HypoDB) were employed for the target profiling. A compound–target interaction network of M. cordata was constructed and analyzed by Cytoscape 3.0.

Results

Thirteen of the 65 predicted targets identified by PharmaDB were confirmed as targets by HypoDB screening. The targets in the interaction network of M. cordata were involved in cancer (31 targets), microorganisms (12 targets), neurodegeneration (10 targets), inflammation and autoimmunity (8 targets), parasitosis (5 targets), injury (4 targets), and pain (3 targets). Dihydrochelerythrine (C6) was found to hit 23 fitting targets. Macrophage migration inhibitory factor (MIF) hits 15 alkaloids (C1–2, C11–16, C19–25) was the most promising target related to cancer.

Conclusion

Through in silico target fishing, the anticancer, anti-inflammatory, and analgesic effects of M. cordata were the most significant among many possible activities. The possible anticancer effects were mainly contributed by the isoquinoline alkaloids as active components.

Cartilage oligomeric matrix protein: a new promising biomarker of liver fibrosis in chronic hepatitis C

Cartilage oligomeric matrix protein (COMP) is a biomarker of fibrosis in lung and skin. In this exploratory study we investigated the biomarker potential of COMP in chronic hepatitis C (CHC). We included consecutive patients with CHC admitted to the Department of Infectious Diseases, Lund University Hospital. COMP was analysed in serum using ELISA. The correlations between COMP and liver fibrosis, determined by transient elastography (TE) (n = 47) and liver biopsy (n = 28) were assessed. We also studied COMP prospectively in relation to antiviral treatment (n = 10). COMP correlated with the degree of liver fibrosis as assessed by TE (r = 0.71, p < 0.001) and liver biopsy (rs = 0.65, p < 0.001). After successful treatment of CHC, COMP decreased from 18 to 13 U/l (p = 0.011). We suggest that COMP is associated with the stage of liver fibrosis in CHC. The biomarker potential of COMP in CHC warrants further investigation.

Targeting pro-inflammatory cytokines following joint injury: acute intra-articular inhibition of interleukin-1 following knee injury prevents post-traumatic arthritis

Introduction

Post-traumatic arthritis (PTA) is a progressive, degenerative response to joint injury, such as articular fracture. The pro-inflammatory cytokines, interleukin 1(IL-1) and tumor necrosis factor alpha (TNF-α), are acutely elevated following joint injury and remain elevated for prolonged periods post-injury. To investigate the role of local and systemic inflammation in the development of post-traumatic arthritis, we targeted both the initial acute local inflammatory response and a prolonged 4 week systemic inflammatory response by inhibiting IL-1 or TNF-α following articular fracture in the mouse knee.

Methods

Anti-cytokine agents, IL-1 receptor antagonist (IL-1Ra) or soluble TNF receptor II (sTNFRII), were administered either locally via an acute intra-articular injection or systemically for a prolonged 4 week period following articular fracture of the knee in C57BL/6 mice. The severity of arthritis was then assessed at 8 weeks post-injury in joint tissues via histology and micro computed tomography, and systemic and local biomarkers were assessed in serum and synovial fluid.

Results

Intra-articular inhibition of IL-1 significantly reduced cartilage degeneration, synovial inflammation, and did not alter bone morphology following articular fracture. However, systemic inhibition of IL-1, and local or systemic inhibition of TNF provided no benefit or conversely led to increased arthritic changes in the joint tissues.

Conclusion

These results show that intra-articular IL-1, rather than TNF-α, plays a critical role in the acute inflammatory phase of joint injury and can be inhibited locally to reduce post-traumatic arthritis following a closed articular fracture. Targeted local inhibition of IL-1 following joint injury may represent a novel treatment option for PTA.

Resolving an inflammatory concept: the importance of inflammation and resolution in tendinopathy

Injuries to the superficial digital flexor tendon (SDFT) are an important cause of morbidity and mortality in equine athletes, but the healing response is poorly understood. One important drive for the healing of connective tissues is the inflammatory cascade, but the role of inflammation in tendinopathy has been contentious in the literature. This article reviews the processes involved in the healing of tendon injuries in natural disease and experimental models. The importance of inflammatory processes known to be active in tendon disease is discussed with particular focus on recent findings related specifically to the horse.

Whilst inflammation is necessary for debridement after injury, persistent inflammation is thought to drive fibrosis, a perceived adverse consequence of tendon healing. Therefore the ability to resolve inflammation by the resident cell populations in tendons at an appropriate time would be crucial for successful outcome. This review summarises new evidence for the importance of resolution of inflammation after tendon injury. Given that many anti-inflammatory drugs suppress both inflammatory and resolving components of the inflammatory response, prolonged use of these drugs may be contraindicated as a therapeutic approach. We propose that these findings have profound implications not only for current treatment strategies but also for the possibility of developing novel therapeutic approaches involving modulation of the inflammatory process.

Proteomic analysis of tendon extracellular matrix reveals disease stage-specific fragmentation and differential cleavage of COMP (cartilage oligomeric matrix protein)

During inflammatory processes the extracellular matrix (ECM) is extensively remodeled, and many of the constituent components are released as proteolytically cleaved fragments. These degradative processes are better documented for inflammatory joint diseases than tendinopathy even though the pathogenesis has many similarities. The aims of this study were to investigate the proteomic composition of injured tendons during early and late disease stages to identify disease-specific cleavage patterns of the ECM protein cartilage oligomeric matrix protein (COMP). In addition to characterizing fragments released in naturally occurring disease, we hypothesized that stimulation of tendon explants with proinflammatory mediators in vitro would induce fragments of COMP analogous to natural disease. Therefore, normal tendon explants were stimulated with IL-1β and prostaglandin E₂, and their effects on the release of COMP and its cleavage patterns were characterized. Analyses of injured tendons identified an altered proteomic composition of the ECM at all stages post injury, showing protein fragments that were specific to disease stage. IL-1β enhanced the proteolytic cleavage and release of COMP from tendon explants, whereas PGE₂ had no catabolic effect. Of the cleavage fragments identified in early stage tendon disease, two fragments were generated by an IL-1-mediated mechanism. These fragments provide a platform for the development of neo-epitope assays specific to injury stage for tendon disease.

Matrix metalloproteinase-dependent turnover of cartilage, synovial membrane, and connective tissue is elevated in rats with collagen induced arthritis

BACKGROUND

Rheumatoid arthritis is a disease affecting the extracellular matrix of especially synovial joints. The thickness of the synovial membrane increases and surrounding tissue degrades, leading to altered collagen balance in the tissues. In this study, we investigated the altered tissue balance of cartilage, synovial membrane, and connective tissue in collagen induced arthritis (CIA) in rats.

METHODS

Six newly developed ELISAs quantifying MMP-derived collagen degradation (C1M, C2M, and C3M) and formation (P1NP, P2NP, and P3NP) was used to detect cartilage turnover in rats with CIA. Moreover, CTX-II was used to detect alternative type II collagen degradation and as control of the model. 10 Lewis rats were injected with porcrine type II collagen twice with a 7 day interval and 10 rats was injected with 0.05 M acetic acid as control. The experiment ran for 26 days.

RESULTS

A significant increase in the degradation of type I, II, and III collagen (C1M, C2M, and C3M, respectively) was detected on day 22 (P = 0.0068, P = 0.0068, P < 0.0001, respectively), whereas no significant difference in formation (P1NP, P2NP, and P3NP) was detected at any time point (P=0.22, P=0.53, P=0.53, respectively). The CTX-II level increased strongly from disease onset and onwards.

CONCLUSION

A nearly total separation between diseased and control animals was detected with C3M, making it a good diagnostic marker. The balance of type I, II, and III collagen was significantly altered with CIA in rats, with favour of degradation of the investigated collagens. This indicates unbalanced turnover of the surrounding tissues of the synovial joints, leading to increased pain and degeneration of the synovial joints.

Comparison of equine tendon- and bone marrow-derived cells cultured on tendon matrix with or without insulin-like growth factor-I supplementation

OBJECTIVE

To compare in vitro expansion, explant colonization, and matrix synthesis of equine tendon- and bone marrow-derived cells in response to insulin-like growth factor-I (IGF-I) supplementation.

SAMPLE

Cells isolated from 7 young adult horses.

PROCEDURES

Tendon- and bone marrow-derived progenitor cells were isolated, evaluated for yield, and cultured on autogenous cell-free tendon matrix for 7 days. Samples were analyzed for cell viability and expression of collagen type I, collagen type III, and cartilage oligomeric matrix protein mRNAs. Collagen and glycosaminoglycan syntheses were quantified over a 24-hour period.

RESULTS

Tendon- and bone marrow-derived cells required 17 to 19 days of monolayer culture to reach 2 passages. Mean ± SE number of monolayer cells isolated was higher for tendon-derived cells (7.9 ± 0.9 × 10(6)) than for bone marrow-derived cells (1.2 ± 0.1 × 10(6)). Cell numbers after culture for 7 days on acellular tendon matrix were 1.6- to 2.8-fold higher for tendon-derived cells than for bone marrow-derived cells and 0.8- to 1.7-fold higher for IGF-I supplementation than for untreated cells. New collagen and glycosaminoglycan syntheses were significantly greater in tendon-derived cell groups and in IGF-I-supplemented groups. The mRNA concentrations of collagen type I, collagen type III, and cartilage oligomeric matrix protein were not significantly different between tendon- and bone marrow-derived groups.

CONCLUSIONS AND CLINICAL RELEVANCE

In vitro results of this study suggested that tendon-derived cells supplemented with IGF-I may offer a useful resource for cell-based strategies in tendon healing.

Biochemical and anisotropical properties of tendons

Tendons are formed by dense connective tissue composed of an abundant extracellular matrix (ECM) that is constituted mainly of collagen molecules, which are organized into fibrils, fibers, fiber bundles and fascicles helicoidally arranged along the largest axis of the tendon. The biomechanical properties of tendons are directly related to the organization of the collagen molecules that aggregate to become a super-twisted cord. In addition to collagen, the ECM of tendons is composed of non-fibrillar components, such as proteoglycans and non-collagenous glycoproteins. The capacity of tendons to resist mechanical stress is directly related to the structural organization of the ECM. Collagen is a biopolymer and presents optical anisotropies, such as birefringence and linear dichroism, that are important optical properties in the characterization of the supramolecular organization of the fibers. The objective of this study was to present a review of the composition and organization of the ECM of tendons and to highlight the importance of the anisotropic optical properties in the study of alterations in the ECM.

Biomarkers of cartilage turnover. Part 2: Non-collagenous markers

Osteoarthritis (OA) results in the destruction and breakdown of articular cartilage matrix. Breakdown of the cartilage proteoglycan component results in the generation of constituent fragments that can be detected in the blood, synovial fluid or urine. Non-collagenous, non-proteoglycan components of cartilage can also be detected following their release as a result of turnover and disease. OA also alters the circulating profile of metabolites in the body. Metabolomic strategies have been used to distinguish populations with OA from normal populations by the creation of a metabolomic 'fingerprint' attributable to the disease. This paper is the second part of a two-part review and describes some of the techniques used to measure the concentrations of some of these 'non-collagenous' biomarkers, and how the application of these measurements assists the study of joint disease. Collagen-based biomarkers were discussed in part one.

Ultrasonographic assessment of the superficial digital flexor tendons of National Hunt racehorses in training over two racing seasons

REASONS FOR PERFORMING STUDY

It is important to ascertain the prevalence of superficial digital flexor tendon (SDFT) injuries and to improve methods of predicting injury in National Hunt (NH) racehorses.

OBJECTIVES

To establish: 1) the prevalence of SDFT tendinopathy in NH horses; 2) whether routine ultrasonography can be used to predict SDFT injuries; 3) whether previous tendinopathy predisposes to reinjury; 4) a normal range for the SDFT cross-sectional area (CSA); and 5) the effects of gender, age, background (ex-flat or ex-store), limb, training and rest periods on SDFT CSA.

METHODS

Routine ultrasound assessment of the palmar metacarpal soft tissues of 263 NH racehorses was performed on up to 6 occasions over 2 NH racing seasons.

RESULTS

The prevalence of SDFT pathology detected using ultrasonography was 24% (n = 148), with a nonsignificant variation between yards of 10-40%. No changes in SDFT CSA or ultrasonographic appearance were detected prior to injury. Older horses had a significantly higher prevalence of SDFT pathology compared to younger horses, and horses with tendinopathy were more likely to suffer an acute injury compared to horses with no evidence of pathology. A reference range for normal CSA measurements was established as 77-139 mm2 at level 4, from 142 horses with no ultrasonographic evidence of SDFT pathology. The CSA of normal horses did not vary significantly with age, limb or over 2 racing seasons, but did with sex and background.

CONCLUSIONS

The study confirms that SDFT tendinopathy is common in NH horses, with substantial variation between training yards. Ultrasonography at 3 month intervals did not seem to predict acute SDFT injuries.

POTENTIAL RELEVANCE

Variation in the prevalence of tendinopathy between yards suggests that training methods may influence injury rate. It was not possible to predict injury using routine ultrasonography and therefore other methods must be identified. A normal reference range for SDFT CSA is provided.

Comparison of equine tendon-, muscle-, and bone marrow-derived cells cultured on tendon matrix

OBJECTIVE

To compare viability and biosynthetic capacities of cells isolated from equine tendon, muscle, and bone marrow grown on autogenous tendon matrix.

SAMPLE POPULATION

Cells from 4 young adult horses.

PROCEDURES

Cells were isolated, expanded, and cultured on autogenous cell-free tendon matrix for 7 days. Samples were analyzed for cell viability, proteoglycan synthesis, collagen synthesis, and mRNA expression of collagen type I, collagen type III, and cartilage oligomeric matrix protein (COMP).

RESULTS

Tendon- and muscle-derived cells required less time to reach confluence (approx 2 weeks) than did bone marrow-derived cells (approx 3 to 4 weeks); there were fewer bone marrow-derived cells at confluence than the other 2 cell types. More tendon- and muscle-derived cells were attached to matrices after 7 days than were bone marrow-derived cells. Collagen and proteoglycan synthesis by tendon- and muscle-derived cells was significantly greater than synthesis by bone marrow-derived cells. On a per-cell basis, tendon-derived cells had more collagen synthesis, although this was not significant. Collagen type I mRNA expression was similar among groups. Tendon-derived cells expressed the highest amounts of collagen type III and COMP mRNAs, although the difference for COMP was not significant.

CONCLUSIONS AND CLINICAL RELEVANCE

Tendon- and muscle-derived cells yielded greater cell culture numbers in shorter time and, on a per-cell basis, had comparable biosynthetic assays to bone marrow-derived cells. More in vitro experiments with higher numbers may determine whether tendon-derived cells are a useful resource for tendon healing.

Ultrastructural immunolocalization of cartilage oligomeric matrix protein, thrombospondin-4, and collagen fibril size in rodent achilles tendon in relation to exercise

Fourteen 3-week-old Sprague-Dawley rats were housed in pairs in standard cages (5 controls) and in individual cages with a running wheel. Four of these rats had run 27-36 km/week (low training - LT) and 5 had run 56-92 km/week (high training - HT). After 4 weeks, the rats were euthanized and Achilles tendons were fixed for electron microscopy. The ultrastructural distribution of cartilage oligomeric matrix protein (COMP) and thrombospondin (TSP)-4 and collagen fibril thickness in two different extracellular compartments were studied. The immunolabeling of COMP decreased with longer running distance and was significantly lower in both the pericellular (p = 0.009) and interterritorial (p = 0.03) compartments of the HT rats compared with the controls. TSP-4 immunolabeling was higher in the pericellular compared with the interterritorial compartments in all rats (p = 0.013) but was not correlated with COMP immunolabeling. No alterations in collagen fibril size were found in relation to running; however, the gold markers representing COMP and TSP-4 were mostly found at the dark bands, representing the gap region of the fibril.

Analysis of cartilage oligomeric matrix protein (COMP) degradation and synthesis in equine joint disease

REASONS FOR PERFORMING STUDY

Cartilage oligomeric matrix protein (COMP) is abundant within cartilage; its turnover and/or degradation have been investigated in various equine joint diseases and it has been suggested that COMP fragmentation might be useful for monitoring such conditions.

OBJECTIVES

To determine whether COMP metabolism is compromised in equine osteoarthritis (OA) and whether COMP degradation is a useful joint marker representing cartilage destruction.

HYPOTHESIS

A monoclonal antibody (mAb) with a higher affinity for degraded COMP allows discrimination of diseased joints by quantifying COMP levels and fragmentation.

METHODS

A mAb (clone14G4) was generated against equine cartilage COMP. The NH2-terminal sequence of enzyme-cut COMP fragments recognised by 14G4 was determined, as was the efficiency of binding to COMP (using a generated COMP peptide). COMP concentration and fragmentation were analysed in synovial fluid (SF) from normal horses and those with OA.

RESULTS

The mAb 14G4 had a higher affinity for the smaller fragments of equine COMP, compared with a mAb (clone 12C4) generated against human COMP. The 14G4 epitope was identified as between C134 and F147. The COMP values in OA (mean +/- s.d. 205.8 +/- 90.9 microg/ml) were significantly higher than in the normal (133.1 +/- 31.5 microg/ml) SF. On the immunoblots of OA sample, the proportions of intact COMP were significantly lower, while smaller fragments ranging from 75 to 290 kDa were higher compared with the normal SF.

CONCLUSIONS AND POTENTIAL RELEVANCE

The mAb 14G4 reliably detects COMP degradation as well as synthesis, and fragmentation analysis combined with quantification in SF could be useful to study equine OA.

Role of extracellular matrix in adaptation of tendon and skeletal muscle to mechanical loading

The extracellular matrix (ECM), and especially the connective tissue with its collagen, links tissues of the body together and plays an important role in the force transmission and tissue structure maintenance especially in tendons, ligaments, bone, and muscle. The ECM turnover is influenced by physical activity, and both collagen synthesis and degrading metalloprotease enzymes increase with mechanical loading. Both transcription and posttranslational modifications, as well as local and systemic release of growth factors, are enhanced following exercise. For tendons, metabolic activity, circulatory responses, and collagen turnover are demonstrated to be more pronounced in humans than hitherto thought. Conversely, inactivity markedly decreases collagen turnover in both tendon and muscle. Chronic loading in the form of physical training leads both to increased collagen turnover as well as, dependent on the type of collagen in question, some degree of net collagen synthesis. These changes will modify the mechanical properties and the viscoelastic characteristics of the tissue, decrease its stress, and likely make it more load resistant. Cross-linking in connective tissue involves an intimate, enzymatical interplay between collagen synthesis and ECM proteoglycan components during growth and maturation and influences the collagen-derived functional properties of the tissue. With aging, glycation contributes to additional cross-linking which modifies tissue stiffness. Physiological signaling pathways from mechanical loading to changes in ECM most likely involve feedback signaling that results in rapid alterations in the mechanical properties of the ECM. In developing skeletal muscle, an important interplay between muscle cells and the ECM is present, and some evidence from adult human muscle suggests common signaling pathways to stimulate contractile and ECM components. Unaccostumed overloading responses suggest an important role of ECM in the adaptation of myofibrillar structures in adult muscle. Development of overuse injury in tendons involve morphological and biochemical changes including altered collagen typing and fibril size, hypervascularization zones, accumulation of nociceptive substances, and impaired collagen degradation activity. Counteracting these phenomena requires adjusted loading rather than absence of loading in the form of immobilization. Full understanding of these physiological processes will provide the physiological basis for understanding of tissue overloading and injury seen in both tendons and muscle with repetitive work and leisure time physical activity.

Animal models of inflammatory spinal and sacroiliac joint diseases

Many cartilage matrix proteins or domains such as collagen types II, IX, and XI, GP39, AG1, VG1, and LP are potential antigens that might induce polyarthritis in susceptible animals (Table 1). Ordinarily, spondylitis is not a feature of polyarthritis induced with collagen types II, IX, and XI, GP39, cartilage matrix protein (matrilin-1) and cartilage LP. It seems that only the proteoglycans aggrecan and versican are capable of inducing sacroiliitis and spondylitis. Both molecules are structural proteins in intervertebral discs. Moreover, the arthritogenic or spondylitogenic epitopes of both molecules have been localized to the homologous N-terminal G1 globular domains. This region of versican and aggrecan is highly conserved, with 52% identity of amino acids. The homology is seen exclusively in the G1 domain and is concentrated between residues 115 and 332 (AG1 numbering) near the natural cleavage DIPEN site of aggrecan [84, 85]. Extra-articular pathology is often seen in rheumatic diseases, especially in AS. Other tissues, such as the sclera of the eye [86] and the media of the arteries [86, 87], also contain type II collagen, AG1, VG1, and LP, and versican is present in the central and peripheral nervous systems. Thus, there is the potential for an immune response against cartilage G1 and LP to be directed against related structures in extra-articular tissues. The presence of versican in the tendon and trochlea of the human superior oblique muscle might account for the occurrence of transient attacks of acquired Brown syndrome in patients with juvenile and adult forms of chronic RA [88]. Thus, it will be interesting to determine whether or not extra-articular expression of these cartilage proteins is closely related to extra-articular pathogenic expression in rheumatic diseases. Uveitis develops in VG1-immunized BALB/c mice, which is not seen in AG1-, and LP-treated animals. There is evidence that aggrecan and LP are also localized at these sites in the eye, but only immunity to versican can induce uveitis. In sacroiliitis and enthesitis of AS patients, the inflammation is associated with chondrometaplasia. In versican-induced sacroiliitis, replacement of cartilage by bone is seen with relatively little inflammation, somewhat resembling the situation in AS (Fig. 2). Versican can also stimulate chondrocyte proliferation [43]. Three conserved domains of human cartilage matrix molecules, namely VG1, AG1, and LP, show considerable homology [77, 79, 80, 89], and each is capable of inducing a unique inflammatory arthritis in BALB/c mice, with VG1 inducing only spondylitis [65], LP inducing peripheral arthritis with no spondylitis [90], and AG1 inducing axial and peripheral arthritis [66, 91]. It remains a mystery why such similar molecules cause different pathology in different target tissues. The exact immunopathogenic mechanisms deserve further study.

Serum level of cartilage oligomeric matrix protein (COMP) in equine osteoarthritis

This study was designed to assay and compare cartilage oligomeric matrix protein (COMP) in horse sera, in samples from normal and joint diseased horses, and to investigate the relationships between COMP in sera and synovial fluids (SF) with keratan sulphate (KS) data. Sera from 38 horses free of any joint pathology (controls) and from horses with aseptic joint disease (AJD horses, n = 40) were assayed for COMP and KS concentrations. Of the 78 horses in the study, 53 were also assayed for COMP and KS concentrations in SF. COMP and KS were measured by inhibition ELISA, using monoclonal antibodies 12C4 and 5D4, respectively. The COMP concentration in sera from AJD horses (mean +/- s.d. 10.7 +/- 7.4 microg/ml) was significantly (P<0.02) lower than in control sera (14.8 +/- 7.8 microg/ml). The joint disease sera also had significantly lower (P<0.01) KS levels (180.5 +/- 61.8 ng/ml) than controls (237.1 +/- 116.1 ng/ml). A significant correlation (r = 0.52, n = 53, P<0.001) was seen between serum and SF in COMP levels; no such relationship was seen in KS levels. It is possible that serum COMP concentration could be a more specific marker of equine joint disease than any other described to date.

Concentrations of cartilage oligomeric matrix protein in dogs with naturally developing and experimentally induced arthropathy

OBJECTIVE

To assay concentrations of cartilage oligomeric matrix protein (COMP) in canine sera and synovial fluid (SF), to compare COMP concentrations in clinically normal dogs and dogs with joint disease, and to analyze changes in COMP concentrations in dogs with experimentally induced acute synovitis.

ANIMALS

69 control dogs without joint disease, 23 dogs with naturally occurring aseptic arthropathy, and 6 dogs with experimentally induced synovitis.

PROCEDURE

Serum (n = 69) and SF (36) were obtained from control dogs. Samples of serum (n = 23) and SF (13) were obtained from dogs with naturally occurring aseptic arthropathy with or without radiographic features of osteoarthritis (OA). Serum and SF were obtained before and 1, 2, 3, and 7 days after induction of synovitis. The COMP concentrations were determined by use of an inhibition ELISA that had canine cartilage COMP and monoclonal antibody against human COMP.

RESULTS

Concentrations of COMP in serum and SF of control dogs were 31.3+/-15.3 and 298.7+/-124.7 microg/ml, respectively. In naturally occurring OA, COMP concentrations in serum (44.9+/-177 microg/ml) and SF (401.7+/-74.3 microg/ml) were significantly higher than corresponding concentrations in control dogs. The COMP concentration in SF peaked 24 and 48 hours after induction of synovitis, whereas concentration in serum peaked on day 3.

CONCLUSIONS AND CLINICAL RELEVANCE

These results supported the hypothesis that COMP concentration in serum and SF of dogs may be altered after cartilage degradation or synovitis. Measurement of COMP concentrations can be useful when differentiating arthropathies in dogs.

Superficial digital flexor tendonitis in the horse

The superficial digital flexor tendon (SDFT) is an elastic structure that during maximal exercise appears to operate close to its functional limits. The biomechanical and biochemical responses to exercise, injury, and healing are still poorly understood but ongoing research is providing valuable new information which is addressed in this review. It appears that the SDFT matures early, after which time it has limited ability to adapt to stress and undergoes progressive degeneration. Focal hypocellularity, collagen fibril degeneration, selective fibril loading and alterations in the noncollagenous matrix occur primarily within the central core region of the midmetacarpal segment. Current treatment strategies have had equivocal results in returning animals to optimal athletic activity. To date it would seem that progressive rehabilitation programmes coupled with regular ultrasonographic evaluations are a cost-effective and comparable strategy when compared to surgical treatment methods. Recent interest in pharmacological modulation of intrinsic healing of collagenous structures has led to the investigation of various growth factors as potential therapeutic aids in the healing of tendon injuries. However, one of the major goals in tendon research, and one which holds the most optimism for success in the immediate future, is the prevention of tendon injuries.