Serum cartilage oligomeric matrix protein (COMP) in rheumatoid arthritis and knee osteoarthritis

The cartilage oligometrix matrix protein (COMP) is a noncollagenous protein, a glycoprotein, the function of which is to bind to type II collagen fibres and stabilise the collagen fibre network in the articular cartilage. In the serum of the normal population the COMP level is 5 mug/ml. An increased level of COMP in the synovial fluid was described in the early stage of rheumatoid arthritis (RA), whereas in advanced stages of RA, the level of COMP decreased. In this study we assessed the serum COMP level in patients with RA and knee osteoarthritis (OA) and found a correlation between the serum COMP level and other markers as well as bone mass density (BMD) changes, activity of disease, disease duration and the age of the patients. The blood was collected from 30 RA patients and 30 OA patients who constituted the control group. The serum COMP level was determined using an inhibition enzyme-linked immunosorbent assay (ELISA). The average value of the serum COMP level in RA patients was 10.4+/-3.6 U/l. There was a correlation between the serum COMP level and the age of RA patients (p<0.005) and disease activity score (DAS) value (p<0.01). According to correlation coefficients, the serum COMP level was independent of stage of disease, number of painful and swollen joints, duration of morning stiffness, disease duration and titre of the Waaler-Rose test. The influence of rheumatoid nodule presence on the serum COMP level was shown (p<0.05). In RA patients with erythrocyte sedimentation rate (ESR) values below 20 mm/h compared with patients with ESR values over 60 mm/h, the serum COMP level was observed to be significantly lower (p<0.05). The average value of COMP in OA patients was 10.4+/-2.7 U/l. No correlation was found between the serum COMP level and patients' age and disease duration. There was a correlation between the serum COMP level and Western Ontario and McMaster Universities (WOMAC) index pain scale for the lower limbs (p<0.005) and T-score value of densitometry examinations (p<0.036) in OA patients. No statistical differences were found between the average serum COMP level in RA and OA patients.