Elastase activity in cartilage extracts and synovial fluids from subjects with osteoarthritis or rheumatoid arthritis: The prominent role of metalloproteinases

Objective: Polymorphonuclear leukocyte (PMN) elastase is able to degrade the extra-cellular matrix components of cartilage. However, in vitro several proteinases can degrade elastin. The purpose of this study was to evaluate the role of the serine proteinases and metalloproteinases in the elastase activity measured in cartilage extracts from patients with osteoarthritis (OA), as well as in synovial fluid (SF) from patients with rheumatoid arthritis (RA) and OA. Methods: Elastase activity was determined using synthetic low molecular weight substrates and radiolabelled insoluble elastin. Aminophenyl mercuric acetate was used to activate the prometalloproteinases. Results: Elastase activity, measured using synthetic substrates, was higher in RASF (0.76 + 0.03 mu U/ml, n = 12) than in OASF (0.14 + 0.04 mu U/ml, n = 12) (p < 0.001). This activity was inhibited by metal chelating agents: 86% inhibition in OA and 75% inhibition in RA. However, in RASF the inhibitor of serine proteinase (PMSF) also induced a 40% inhibition. Elastase activity, measured using radiolabelled elastin, in OASF and RASF samples and in OA cartilage extract was very low, but increased following activation by mercurial agents. Again this activity was inhibited by metal chelating agents. Conclusions: Taken together these results indicate that elastase activity (measured by standard methods) in OA and RASF is mainly due to metalloenzymes.