Cartilage oligomeric matrix protein (COMP): The role of a non-collagenous cartilage matrix protein as a marker of disease activity and joint destruction in RA-and OA-patients

Today, we can assess criteria to predict the tissue destruction and progres sion of Rheumatoid Arthritis (RA) and Osteoarthritis (OA) only in a late st age of the disease. It would be an advantage to have biochemical markers of disease activity and joint destruction to optimize therapy. Patients and Methods: In this cross-sectional study with 37 RA and 20 OA pa tients (disease duration 119 +/- 130 months for RA and 41 +/- 73 months for GA), ESR, CRP, disease activity score (DAS), the functional status of RA ( American College of Rheumatology), and the radiological scoring systems of Larsen and Kellgren/Lawrence, respectively, were used as parameters for dis ease activity and joint destruction. Cartilage oligomeric matrix protein (C OMP) was measured with an enzyme-linked immunosorbent assay (ELISA) in seru m and synovial fluid, COMP fragments with immunoblot in the synovial fluid. Results: The mean COMP value in synovial fluid was 38 ug/l (RA) and 46 ug/l (OA); 6.5 ug/ml (RA) and 3.4 ug/ml (OA) in serum. RA patients had a higher amount of small COMP fragments in synovial fluid than OA patients. In RA p atients, there was a significant positive correlation between disease activ ity (DAS) and COMP in synovial fluid and serum, a negative correlation betw een functional status of RA and serum COMP and between radiologic joint des truction of the knee and serum COMP. In OA patients, there was a significan t correlation of joint space width and synovial fluid COMP. Discussion: A high clinical disease activity (DAS) correlated with high COM P values in serum and synovial fluid and with increasing proteolytic activi ty (higher amount of small COMP fragments especially in RA). An increased t urnover of cartilage matrix in joint inflammation might explain this correl ation. The correlation of decreased COMP with decreased functional status i n RA and increased joint destruction is compatible with a loss of cartilage and less turnover. The correlation between joint space width and increased COMP in OA patients with short disease duration might be explained with a higher turnover of the cartilage matrix in the early stage of the disease.