Expression of synovial fluid and articular cartilage VIP in human osteoarthritic knee: a new indicator of disease severity?

OBJECTIVES: Vasoactive intestinal peptide (VIP) is a molecule shared by the neuroendocrine immune network and is considered to be a potential candidate for treatment of inflammatory and autoimmune diseases. Although some recent studies demonstrate that VIP has a protective role in animal RA models, its variant in different disease grade of OA remains uncertain. DESIGN AND METHODS: Fifty patients with primary knee OA and ten controls with severe trauma were enrolled. Synovial fluid and articular cartilage samples were collected from specimens of total knee arthroplasty (TKA) or knee above amputation. VIP levels in these samples were assessed by ELISA and immunohistochemistry. Kellgren-Lawrence criteria and Mankin score were taken to determine the disease severity.
RESULTS: Compared to the controls, OA patients have lower VIP concentration in synovial fluid (659.70±112.79, 95%CI 579.01-740.38 vs 470.83±156.40, 95%CI 426.38-515.28 pg/mL, P<0.001) and articular cartilage (0.26±0.02, 95%CI 0.24-0.28 vs 0.20±0.04, 95%CI 0.18-0.21, P<0.001). Subsequent analysis show that the VIP expression in synovial fluid is markedly correlated with its OD in articular cartilage (Pearson's r=0.580, P<0.001). Furthermore, the synovial fluid and articular cartilage levels of VIP both demonstrated to be negatively correlated with severity of disease (Spearman's ρ=0.838, P<0.001; Spearman's ρ=0.814, P<0.001).
CONCLUSIONS: VIP in synovial fluid and articular cartilage is negatively associated with progressive joint damage in OA and is a potential indictor of disease severity.