α2-Macraglobulin from rheumatoid arthritis synovial fluid:: Functional analysis defines a role for oxidation in inflammation

A hallmark of inflammation is the release of oxidants, proteinases, and cytokines, all important mediators of the inflammatory cascade, alpha (2)-Macroglobulin (alpha M-2) is a high-affinity, broad-specificity proteinase inhibitor that also binds and regulates the biological activities of a number of cytokines, We demonstrated recently that hypochlorite-oxidized alpha M-2 has decreased ability to inhibit proteinases and regulate cytokines in vitro, The role of oxidation in regulating alpha M-2 functions in vivo is largely unknown. To determine the extent and biological consequence of in vivo alpha M-2 oxidation, we measured the degree of oxidative alpha M-2 modification from rheumatoid arthritis (RA) synovial fluid and compared this with osteoarthritis (OA) as noninflammatory controls. We found that RA synovial fluid alpha M-2 is significantly more oxidized than that from Ok RA synovial fluid also contains a twofold higher median alpha M-2 level than OA, while having only half the alpha M-2-proteinase inhibitory activity. Detailed biochemical analysis demonstrates proteolytically degraded alpha M-2 in RA greater than in OA synovial fluid, Additionally, the hypochlorite-mediated oxidation product, chlorotyrosine, is present in RA more than in OA or plasma alpha M-2 samples. Taken together, these findings confirm a role for oxidative regulation of inflammation by altering the functions of extracellular mediators such as alpha M-2. (C) 2001 Academic Press.