Granulocyte elastase as a new biochemical marker in the diagnosis of chronic joint diseases

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Abstract
Human granulocyte elastase (EC 3.4.21.37) is released from granulocytes in large amounts in chronic inflammatory joint diseases and is therefore of special pathogenic and diagnostic importance. In order to examine the diagnostic significance of this enzyme as a clinico-chemical parameter, we determined the concentration of granulocyte elastase in complex with α1-proteinase inhibitor by an enzyme immunoassay in synovial fluids and plasma of patients with chronic joint diseases. In inflammatory synovial fluids the concentration of complexed elastase correlates well with the granulocyte number and may increase to an extremely high level. In 90% of patients with manifest rheumatoid arthritis increased elastase levels are also observed in the plasma, probably due to the large gradient between the synovial fluid and plasma concentration, whereas in osteoarthrosis normal plasma concentrations were observed. Thus, these results indicate that normal plasma concentrations in patients with chronic joint diseases exclude the diagnosis of rheumatoid arthritis with high probability. The simultaneous determination of complexed elastase in plasma and synovial fluid improves the nosological differentiation of chronic joint diseases. Elastase activity on a specific chromogenic substrate, which was found in many inflammatory synovial fluids, is mainly attributed to elastase α2-macroglobulin complexes. In some purulent synovial fluids, however, we were able to detect free elastase, which has been shown to play an important role in the destruction of articular cartilage.