Single injection of intra-articular autologous protein solution in horses with acute interleukin-1B-induced synovitis decreases joint pathology scores.

BACKGROUND: Autologous protein solution (APS) has been shown to decrease lameness in horses with osteoarthritis (OA). Synovitis is an early driver of OA, providing an opportunity to intervene in the progression of disease via intra-articular (IA) therapeutics. OBJECTIVES: The objective of this study was to investigate the effects of a single IA APS injection in horses with interleukin-1β (IL-1β)-induced synovitis. We hypothesised that APS would decrease joint swelling and lameness, improve synovial fluid parameters and improve joint pathology scores in horses compared with untreated controls. STUDY DESIGN: Randomised controlled in vivo experiment. METHODS: Synovitis was induced with IL-1β (65 ng) in one randomly selected tarsocrural joint. Twenty-four hours later, joints were treated with APS (Pro-Stride®) (n = 12) or left as untreated controls (n = 6). Lameness examinations and joint circumference measurements were performed on Days 0 (prior to IL-1β), 1 (prior to APS), 2, 4, 7 and 14. Synovial fluid, obtained on the same days, was analysed for protein concentration, nucleated cell count, and cytokine (IL-1β, TNF-α, IFN-γ, IL-6, IL-10) and prostaglandin E2 (PGE2) concentrations. Gross pathology and synovial membrane histopathology scoring was performed on APS-treated (n = 5), untreated control (n = 4) and normal (n = 9) tarsocrural joints. RESULTS: APS did not decrease lameness or joint circumference compared with untreated controls. Synovial fluid parameters were not different between treatment groups. APS treatment did significantly decrease gross and histopathology scores. MAIN LIMITATIONS: Main limitations included the use of an induced model of the synovitis, inter-horse variability in the response to IL-1β and likely variability in the constituents of APS from individual horses. CONCLUSIONS: APS treatment of tarsocrural joints with synovitis did not significantly improve lameness or alter synovial fluid parameters. APS did lead to significant improvement in gross joint appearance and synovial membrane histology suggesting that APS may have disease-modifying effects.