Functionally active α2-macroglobulin and kinin release in synovial fluids of rheumatoid arthritis

Abstract

The function of a2M (a2-macroglobulin) as a proteinase inhibitor in synovial fluid of rheumatoid arthritis was investigated. Low esterase activity was found in the 19S sieve fraction of Sephadex G-200 gel filtered synovial fluid samples, comparable with that obtained with normal human plasma. The molar binding ratio of uzM isolated from the synovial fluid and trypsin was estimated according to earlier established methods. The formation of an equimolar complex indicated that the synovial u2M was functionally intact.Esterase activities were measured on uN-tosyI-Larginine [3H]methyl ester. Synovial fluid samples were all found to contain proteinase enzyme which did not bind to the synovlal ohM nor to the added functionally intact, immunologically pure a2M prepared from normal human plasma.Albumin, uL-acid glycoprotein, a2HS-glyeoprotein , u2M and kininogen in synoviai fluids were determined by single radial immunodiffuslon. Only the ct2M contents were clearly lower than in normal human serum per ml.The higher than 1 ratio between the immunoreactive kininogen determined with monospeeific anti-human kininogen serum and the pharmacologically active klninogen indicated that klnin release had occurred possibly in the synovial membrane. Protelnase enzymes present in the synovial fluids and unbound to ohM caused further depletion of the active klnin Segment in synovlal kininogen. A model of the regulation by u2M of the synovlal klninogen-klnin system is given.

Interaction of urokinase with α2-macroglobulin investigated by isoelectric focusing. Evidence for non-specific dissociable binding

“…The lack of subunit conversion with urokinase is in keeping with our previous findings with pancreatic and urinary kallikreins (Vahtera & Hamberg, 1976), suggesting that enzymes with limited proteolytic actions are unable to form the true inhibitor complex. In pathological states the disposal by complexformation with a2M of activated extravascular proteinases may be important, as was suggested in pur recent study of the kinin system in synovial fluid (Hamberg et al, 1978).…”