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Abstract
Among all disorders of the musculoskeletal system, joint diseases are most frequently encountered and represent a major part of the caseload for equine clinicians.
Since many injuries or conditions causing lameness in equine athletes are associated with damage to the joint tissue as well as due to the economic impact of these musculoskeletal injuries that cause lameness, both the prevention and successful treatment of these injuries are important to the equine industry, the ultimate goal in horses with joint disease is to make an accurate and early diagnosis, institute appropriate treatment and prevent ongoing deterioration of joint tissue
This study is designated for establishment of a system enabling picking up horses which may be exposed to a joint disease during their career life through detection of cartilage oligomeric matrix protein (COMP) as a molecular biomarker derived mainly from cartilage.
The present study is divided into 2 main studies
I - Joint Diseases study.
To quantify the urinary concentration of (COMP), and to evaluate the relationship between urinary COMP concentration and the catabolic activity of synovial fluid in diseased horses.
COMP in horse urine was detected by immunoblotting with a monoclonal antibody (mAb; 14G4) raised against equine COMP from articular cartilage. Urine and serum samples were obtained from 83 Thoroughbred horses with aseptic joint diseases (AJD, 79 horses) or septic joint diseases (SJD, 4 horses) at the time of anesthesia induction, and samples of synovial fluid were obtained during surgery. Control samples of urine (n=111) were collected from normal horses free of any orthopaedic diseases after they had been racing. COMP concentration was determined in all samples using inhibition ELISA with mAb 14G4. SF samples were also used for the quantification of gelatinase activity.
Results:
Positive bands of COMP fragments were determined on the immunoblots with mAb 14G4. The urinary COMP concentrations in AJD and SJD horses (1.02±0.75 and 1.55±1.17 µg/100 mg creatinine, respectively) were significantly higher than normal (0.57±0.29 µg/100 mg creatinine). In 55 horses with fractures in the AJD group there was a logarithmic relationship between the urinary and SF COMP measurements, while the urinary COMP level was positively correlated with MMP-2 and -9 activitiy in synovial fluid.
Conclusions:
The urinary COMP assay with mAb 14G4 is useful for discriminating horses with osteoarthritis. The higher COMP levels in urine from such horses would be indicative of enhanced proteolytic activity, in addition to the increased COMP levels in the diseased joints.
II - Joint loading exercise study.
1- Interrupted workout exercise protocol 2- Daily workout exercise protocol
Objective:
To evaluate changes in the serum level of cartilage oligomeric matrix protein (COMP) in horses in response to exercise protocol as well as training and rest protocol. Serum samples were taken from 15 horses in experiment one and from 27 horses in experiment two.
Procedure:
In the first study, 15 thoroughbreds free of any orthopaedic diseases (20±1 months of age) were subjected to a standardized exercise protocol on a riding track. Running velocity and heart rate (HR) were calculated, and blood samples were taken immediately before (baseline) and 1, 5 and 24 h after exercise.
In the second study, 27 thoroughbreds (22±1 months of age) were subjected to nine stages of a training program. Each stage was followed by one day of rest. Blood samples were taken immediately before (baseline) the first and the final daily workouts for each stage. In both experiments, serum COMP values were measured by inhibition ELISA with a monoclonal antibody (14G4) against equine COMP.
Results:
In the first study, the serum level of COMP was increased significantly 1 and 5 h after exercise, and then returned to the baseline value 24 h later. The serum baseline level of COMP increased (being significantly higher during the 3rd and 4th exercise tests than during the 1st) as the velocity at maximum and 200beats/min of HR increased. In experiment 2, starting at stage 3, the COMP baseline value at the final workout was increased significantly in comparison with that at the first workout, while the higher baseline value decreased after one day of rest. As the workload of the horses increased, the decline in the COMP baseline value after rest became less marked.
Conclusion:
The present study has identified a significant change in serum COMP concentration associated with exercise in horses. Exercise may enhance the movement of COMP into the blood circulation as well as change the basal turnover of the COMP molecule in response to the daily workload. These findings indicate the usefulness of periodic measurements of serum COMP in trained racehorses.
Clinical relevance:
1- This joint disease study represents the first attempt to quantify the concentration of COMP in urine, and is the first to demonstrate increased urinary COMP levels in horses with AJD and SJD.
2- Assay of urinary COMP using mAb 14G4 is useful for discriminating horses with OA. The higher COMP levels in urine from horses with OA are indicative of augmented proteolytic activity, in addition to increased COMP levels in the diseased joints themselves.
3- the joint loading study demonstrated the usefulness of the periodic measurements of serum COMP in the detection of early joint diseases in the horses
4- pathological up-regulation of the serum COMP could be exaggerated by the effect of joint loading.
5- The daily workout should be considered during the analysis of serum COMP specially during the comparative studies for example between the normal and osteoarthritic horses.