Early degradation of type IX and type II collagen with the onset of experimental inflammatory arthritis

Objective. To determine whether following the onset of intraarticular infla mmation, there is early damage to articular cartilage, specifically to type s If and IX collagen, and the proteoglycan (PG) aggrecan, and whether measu rement of the degradation products of these molecules in synovial fluid (SF ) and serum may permit the detection of cartilage damage. Methods. A. rabbit model of rheumatoid arthritis, antigen (ovalbumin)-induc ed arthritis, was studied. Articular cartilage samples were analyzed by imm unoassays for total type II collagen content, its denaturation and cleavage by collagenases, and for type IX collagen content. PG content was determin ed by colorimetric assay. In serum and SF, total PG content and collagenase -generated peptides of type II collagen were measured. Results. After 6 days, both the PG content and the NC4 domain of type IX co llagen were reduced in femoral and tibial cartilage, concomitant with the o nset of arthritis. In only the tibial cartilage did this reduction in PG pe rsist up to day 20, However, denatured type II. collagen was increased in a ll cartilage samples, but only on day 20. In SF, the PG content was signifi cantly reduced on day 20, and products of type II collagen cleavage by coll agenase were significantly increased on both day 6 and day 20. Conclusion, This study, which is the first of its kind examining changes in both types II and IX collagen and PG content, reveals early damage to both types of collagen as well as to PG in articular cartilage samples followin g induction of joint inflammation. SF analyses reveal this early damage and may be of value in the study and treatment of inflammatory arthritic disea ses such as rheumatoid arthritis.