Active MMPs captured by alpha 2 macroglobulin as a marker of disease activity in rheumatoid arthritis.

OBJECTIVE: The aim of the present study was to analyze alpha 2 Macroglobulin/MMP (alpha 2M/MMP) complex formation and to investigate whether MMP activity in alpha 2M/MMP complexes in serum can be used as a disease marker in rheumatoid arthritis (RA).
METHODS: High and low molecular weight (H/LMW) substrates and inhibitors and size exclusion were used to analyze alpha 2M/MMP complex formation. LMW fluorogenic substrates were used to quantify the level of MMPs in alpha 2M/MMP complexes in the serum of RA patients and healthy controls.
RESULTS: Active MMPs were fully inhibited by LMW inhibitor BB94 in the presence of alpha 2M, whereas no inhibition was achieved by HMW inhibitor TIMP-1. Size exclusion analysis showed alpha 2M/MMP complex formation in buffer and in normal plasma spiked with activated MMPs, which indicated alpha 2M/MMP complex formation in the systemic circulation. MMP activity in alpha 2M/MMP complexes in the serum of RA patients was significantly higher than in the serum of healthy controls (P < 0.001). MMP activity levels in the serum of RA patients were correlated with ESR (r = 0.72, P < 0.001).
CONCLUSION: In the systemic circulation of RA patients, active MMPs form complexes with alpha 2M and can be detected using LMW fluorogenic substrates. MMP activity measurements in serum allow discrimination between RA patients and healthy controls and provide a new tool for the assessment of the disease process in RA.