Levels of chemerin and interleukin 8 in the synovial fluid of patients with inflammatory arthritides and osteoarthritis

OBJECTIVES: Chemerin and interleukin (IL)-8 are pro-inflammatory mediators whose role in joint inflammation and cartilage degradation has been demonstrated in in-vitro findings. Studies on their presence in synovial fluid (SF) samples may offer further information on their pathogenic role. The aim of this study was to investigate SF chemerin and IL-8 levels in patients with different joint diseases. METHODS: 37 patients were enrolled: 18 with rheumatoid arthritis (RA), 8 with psoriatic arthritis (PsA) and 11 with osteoarthritis (OA). 41 SF samples were obtained by arthrocentesis in case of knee synovitis. Serum samples were obtained from 13 patients (4 with RA, 6 with PsA and 3 with OA) at the time of arthrocentesis. Chemerin, IL-8, TNF-α and IL-6 levels were measured using commercially available ELISA kits. Immunohistochemical analysis of synovial RA specimens was also performed. RESULTS: No difference in chemerin SF levels emerged between patients with immune-mediated inflammatory arthritides and those with OA (p=0.0656), while subjects with inflammatory arthritis displayed significantly higher levels of SF IL-8 compared to OA (p=0.0020). No significant difference emerged across the three conditions in the serum levels of both chemerin and IL-8. IL-8 strongly correlated with inflammatory markers as ESR, CRP, IL-6 and TNF-α. CONCLUSIONS: We observed similar chemerin SF and serum levels in the three conditions. Although flawed by some limitations, our findings support the emerging concept of OA as an inflammatory disorder. However the increased IL-8 levels we described in patients with inflammatory arthritis suggest a selective involvement of this pro-inflammatory and angiogenic cytokine in these conditions.