Measurement of cartilage oligomeric matrix protein (COMP) in normal and diseased equine synovial fluids

Objective: This study was designed to assay cartilage oligomeric matrix protein (COMP) in equine synovial fluids and to compare the concentration in synovial fluids from normal horses with joint diseased horses. The relationship between the COMP degradation and the matrix metalloproteinase activity in synovial fluids was also investigated. Design: Using COMP antigen prepared from equine articular cartilage and murine monoclonal antibody (12C4) raised against human COMP, an inhibition ELISA was developed. COMP in equine synovial fluids from normal and diseased joints was quantified. Metalloproteinase activities were evaluated in the same synovial fluids by a gelatin degradation ELISA. COMP fragments were evaluated qualitatively by Western blotting. Results: The COMP inhibition ELISA was reliable at concentrations of equine COMP between 62.5 and 2000 ng/ml. COMP values in joint fluids in both aseptic and septic joint disease (19.7+/-15.3 and 16.1+/-11.2 mug/ml, respectively) were significantly (P<0.001) lower than normal (53.2+/-29.0 <mu>g/ml). The molecular sizes of COMP on immunoblots were different between normal and diseased synovial fluids; more fragments were seen in diseased fluids. The aseptic (26.6 +/- 20.6%) and septic joint disease synovial fluids (36.1 +/- 37.5%) had significantly higher (P<0.02 and 0.002, respectively) gelatinolytic activities than normal (13.6+/-13.7%). There was a negative correlation (R=-0.31, P<0.002) between COMP level and gelatinase activity. Conclusions: We conclude that the fragment pattern and the absolute COMP concentration maybe useful for monitoring joint disease, and that COMP degradation in synovial fluids from progressed joint disease may be due to MMP gelatinolytic activity. (C) 2001 OsteoArthritis Research Society International.