Synovial fluid concentrations of cold-inducible RNA-binding protein are associated with severity in knee osteoarthritis.

Background: Cold-inducible RNA-binding protein (CIRP) is a pro-inflammatory cytokine. We determined whether serum or synovial fluid concentrations are associated with severity in osteoarthritis (OA).

Methods: CIRP concentrations in serum and synovial fluid from 156 knee OA patients and serum from 156 controls were determined. The Kellgren and Lawrence (KL) grade, Lequesne index and Western Ontario McMaster University Osteoarthritis Index (WOMAC) pain score were used to assess radiographic, clinical severity and pain severity respectively. Their scores were dichotomized based on their median values.

Results: OA patients had similar serum CIRP concentrations compared to controls. In OA patients, CIRP concentrations in synovial fluid were dramatically higher compared to, but not correlated with paired serum samples. CIRP concentrations in synovial fluid were significantly correlated with synovial fluid or serum C-reactive protein, tumor necrosis factor- alpha and interleukin-6 concentrations, KL grade, Lequesne index and WOMAC pain score. Synovial fluid CIRP concentrations were independently related to the KL grade>2, Lequesne index >13 and WOMAC pain score>12. Under receiver operating characteristic curves, Synovial fluid CIRP concentrations significantly predicted them.

Conclusions: Increased synovial fluid CIRP concentrations were closely associated with the severity, substantializing CIRP as a potential marker for synovial inflammation of OA.