Zymographic analysis of latent and activated forms of matrix metalloproteinase-2 and -9 in synovial fluid: correlation to polymorphonuclear leukocyte infiltration and in response to infection

Abstract

Background: Matrix metalloproteinase-2 and-9 (MMP-2, MMP-9), and gelatinase A and B participate in the degradation of the extracellular matrix proteins in a variety of inflammatory connective tissue diseases including arthritis. Methods: Synovial fluid was collected by aseptic aspiration from patients with rheumatoid arthritis (RA), osteoarthritis (OA), gout, infected joint, septic arthritis, and systemic lupus erythematosus (SLE). Synovial fluid was subjected to cell count with polymorphonuclear leukocyte (PMN) differential, Gram staining and culture as necessary. MMP-2 and -9 were characterized by substrate gel electrophoresis (gelatin zymography) to resolve latent and activated ‘partially proteolyzed’ forms. Results: Gelatin zymography revealed that MMP-9 (92, 130, 225 kDa) in synovial fluid was associated with extent of white blood cell infiltration specifically PMNs. In contrast, fibroblast MMP-2 (72 kDa) was present in all synovial fluids irrespective of PMN count. No MMP-9 was detected in the osteoarthritic specimen with low PMN count. Higher PMN count was associated with the presence of activated MMPs, especially in specimens that were confirmed culture positive. Activated synovial fluid MMPs persisted despite resolution of infection. Discussion: Latent and activated MMP-2 and MMP-9 in synovial fluids fluctuate in proportion to PMN infiltration and specifically in response to infection. The presence of activated MMPs post-therapy would suggest that use of specific MMP inhibitors be indicated to eliminate activated MMPs that apparently persist post-infection.