Neutral proteases in human osteoarthritic synovium.

The activities of neutral collagenolytic enzymes (CE) and neutral proteoglycan-degrading enzymes (PE) in the synovial membranes of osteoarthritis (OA) patients were determined. The total neutral metallo-CE activity showed a significantly higher level of activity when the membranes of OA patients were compared with those of controls. The severely and moderately inflamed synovia had significantly more enzyme activity than did either mildly inflamed or control synovia. Steroids reduced the total metallo-CE activity. In specimens with severe inflammation, the active form of the neutral metallo-CE was significantly elevated over that found in controls. The serine-CE activity was also significantly elevated in OA synovia with severe inflammation and synovial hypertrophy. The total and active neutral metallo-PE was significantly elevated in synovial membranes of OA patients with severe inflammation. Moreover, the serine-PE showed much more activity in OA patients than in controls. The enzyme activity remained at a significantly high level in the OA synovium, regardless of the presence or absence of macroscopic synovial hypertrophy or the histologic grading of the synovium (mild, moderate, severe). Our data indicate that, in OA, an increased level of neutral proteases in the synovia could be involved in the local tissue destruction of the periarticular structures. Because of the very high level of serine proteases, their diffusion may render plausible a degradative action on the cartilage surface.