Expression and activity profiling of selected cysteine cathepsins and matrix metalloproteinases in synovial fluids from patients with rheumatoid arthritis and osteoarthritis.

: Cysteine cathepsins and matrix metalloproteases are considered to play important roles in the development of arthritic diseases. Their accumulation in synovial fluid of primarily rheumatoid arthritis patients is also well documented. However, a detailed comparison between the protease levels and activities between rheumatoid arthritis samples and osteoarthritis samples has never been made. Here, we report that both cysteine cathepsins B and S and matrix metalloproteases-1, -3 and -13 are detected in patient synovial fluid samples with significantly higher levels detected in rheumatoid arthritis patients. Among the proteases, cathepsin S was found to be significantly elevated, consistent with its critical role in the immune response. These results suggest that cysteine cathepsins have a major role in inflammation at least in rheumatoid arthritis. In addition to proteases, interleukin-6 was detected at significant levels in most samples, suggesting that proinflammatory cytokines might be in-volved in the stimulation of expression of these proteases during inflammation.