Synovial fluid levels of tumor necrosis factor α and oncostatin M correlate with levels of markers of the degradation of crosslinked collagen and cartilage aggrecan in rheumatoid arthritis but not in osteoarthritis

To compare synovial fluid (SF) levels of oncostatin M (OSM), tumor necrosis factor α (TNFα), and interleukin-6 (IL-6) in patients with rheumatoid arthritis (RA) and osteoarthritis (OA) and to determine which correlate best with SF levels of antigenic keratan sulfate (Ag KS), a marker of aggrecan catabolism, and pyridinium crosslinks, markers of the degradation of mature collagen molecules. SF was drawn from the knee joints of patients with RA (n = 31) or OA (n = 31). Levels of Ag KS, D-pyridinoline (D-Pyr), pyridinoline (Pyr), OSM, TNFα, and IL-6 were measured by enzyme-linked immunosorbent assay. RA patients had higher median SF levels of OSM, TNFα, IL-6, and Pyr, but a lower median level of D-Pyr, than OA patients. In both groups, IL-6 levels correlated positively with those of OSM and TNFα. However, the correlation between levels of OSM and TNFα was only significant in the RA group. Ag KS and Pyr levels correlated positively in RA but not in OA. The correlation between TNFα and Ag KS was positive in RA and negative in OA. Further, in RA, OSM and IL-6 levels correlated strongly with Pyr and Ag KS levels but not with D-Pyr levels, while there were no strong correlations in OA for OSM or IL-6 levels with Pyr, Ag Ks, or D-Pyr levels. This in vivo study suggests that TNFα and other proinflammatory cytokines are involved in the up-regulation of the coordinated degradation of cartilage aggrecan and collagen in RA. Further, OSM may act synergistically with other proinflammatory cytokines in up-regulating the production of me- talloproteinases by chondrocytes in rheumatoid joints.