Increased serum levels of cartilage oligomeric matrix protein in chronic erosive arthritis in rats

OBJECTIVE: To investigate the utility of serum cartilage oligomeric matrix protein (COMP) for disease monitoring in rats with chronic pristane-induced arthritis, and to examine the influence of age, sex, and genes on COMP concentrations in rat serum. METHODS: Serum COMP levels were quantified by immunoassay. Sera were obtained from DA, E3, and (E3 x DA)F1 rats each week between the ages of 4 and 30 weeks. The (E3 x DA)F2 (second generation after intercrossing) rats were injected intradermally with the synthetic oil pristane. Arthritis was monitored by a macroscopic scoring system, and serum levels of COMP were measured on days 6, 35, and 49 after immunization. RESULTS: Serum levels of COMP decreased during growth, and reached a plateau after the age of 12 weeks. The DA rats had higher COMP levels than the E3 rats, and the (E3 x DA)F1 rats had intermediate levels. No differences were observed in these levels when the rats were grouped by sex. Arthritic (E3 x DA)F2 rats had increased serum concentrations of COMP on days 35 and 49 after pristane injection (P < 0.0001 versus the nonarthritic animals). COMP levels correlated with the severity of macroscopically detectable arthritis at both time points (r > 0.9). Rats with a chronic disease course were distinguished by higher serum concentrations of COMP during the acute stage than animals with similar clinical scores but with resolving arthritis (P < 0.01). CONCLUSION: Serum analyses of COMP offer promise for monitoring tissue involvement in experimental arthritis. Such analyses should be useful for monitoring therapeutic interventions aimed at retarding tissue destruction as well as for studies of the genetically determined regulation of COMP turnover and susceptibility to arthritis. The application of molecular marker measurements to experimental arthritis offers a new possibility for verifying the utility of such measurements in human arthritis.