Levels of serum and synovial fluid pyridinium crosslinks in patients with rheumatoid arthritis

Objective, To elucidate the major source of pyridinium crosslinks in rheuma toid arthritis (RA). Methods. Serum samples were collected from 75 patients with RA and 41 healt hy controls, and synovial fluid (SF) samples were collected from 20 patient s with RA and 13 with osteoarthritis (OA). Paired samples of serum and SF w ere collected at the same time from 26 patients with RA. Levels of pyridini um crosslinks were determined by a recently developed high sensitivity assa y method using high pressure liquid chromatography. Results. The levels of serum pyridinoline (PYD) and serum deoxypyridinoline (DPD) were significantly higher in patients with RA than in healthy contro ls, and significantly correlated with laboratory variables indicating disea se activity and severity. The levels of SF DPD, but not SF PYD, were signif icantly higher in patients with RA than in patients with OA. The levels of SF PYD and SF DPD both showed a significantly positive correlation with tho se of either SF interleukin 1 beta or SF interleukin 6 in patients with RA, Finally, the levels of PYD, but nor DPD, were higher in SF than in serum i n all paired RA samples collected at the same time, with significant correl ation between the members of each pair. Conclusion. These observations suggest than an increase of PYD in RA serum may originate mostly from affected joints and that an increase of DPD in RA serum may be influenced more by systemic bone resorption.