Synovial Fluid Cytokine Concentrations Are Influenced by Disease Etiology

Introduction: Establishing patient specific outcomes in dogs to document severity of joint inflammation and pain at one or several times remains challenging. Cytokines responsible for inflammation and pain are present in synovial fluid and are available as biomarkers for OA. The objective of this study was to evaluate synovial fluid cytokine concentrations (substance P, bradykinin, MMP’s (1, 2 and 3) and TIMP’s (1, 2, 3 and 4), interleukins 1, 6 and 8, TNF-α) in dogs with different etiology of OA (CHD, FMCP, OCD, acute CCLD and chronic CCLD).

Materials and Methods: Dogs with OA were enrolled if they had a history of lameness, abnormal physical examination, radiographic evidence of OA and had surgery to confirm etiology of disease. Synovial fluid cytokines were measured using previously validated methods. Groups were compared by establishing effect size (Cohen’s d).

Results: Fifty dogs (n = 10/group) were enrolled. Effect sizes > 0.6 were found in nearly 40% of comparisons between etiology groups. For example, CHD and OCD differed from each other and other etiologies for multiple cytokines. In contrast, acute and chronic CCLD were more similar than different, with a large Cohen’s d for only IL-6.

Discussion/Conclusion: We reject the null hypothesis that etiology of OA would not influence synovial fluid cytokine concentrations. Synovial fluid remains as an important tool for clinical research and may evolve into an outcome measure that can help document modulation of pain, inflammation or OA. Understanding that disease etiology contributes to variation in synovial fluid cytokine concentrations will assist in study design.

Acknowledgement: None.

No conflict of interest has been declared by the author(s).