The Effect of Intra-Articular Corticosteroids on the Systemic Messenger RNA Response in an Equine Experimental Inflammation Model

Intra-articular (IA) corticosteroids are regularly used in equine athletes for the control of joint inflammation. The goal of this study was to utilize an acute synovitis inflammation model to determine the residual effects of IA betamethasone and triamcinolone acetonide on various inflammatory parameters and lameness. Five mixed-breed, 2-year-old horses were randomly allocated to an IA treatment of the radiocarpal joint with 9 mg of either betamethasone or triamcinolone acetonide. Two weeks following treatment, horses were injected with 1μg of lipopolysaccharide (LPS) diluted in 1 mL of 0.9% sterile saline. Following LPS injection, horses were crossed-over and both sets of injections repeated. Lameness was subjectively scored and blood samples were collected for mRNA analysis, as well as serum amyloid A (SAA) and cortisol determination. Additional injections with saline-only or LPS-only were conducted as negative and positive controls, respectively. Two-way repeated measures analysis of variance was used to analyze all data. Corticosteroid-only treatments results in significant mRNA expression differences, as well as significant and prolonged serum cortisol suppression. Following LPS injection, there was a residual treatment effect with triamcinolone evidenced by a significant treatment effect on IL-6 and PTGS1 (cyclooxygenase-1) expression, lameness, SAA, and cortisol concentrations, while only IL-6 expression was affected by betamethasone. Current regulatory guidelines may be insufficient if the concern is residual anti-inflammatory effects. Additionally, intra-articular corticosteroid administration is not without risk, as evidenced by a significant and prolonged suppression of serum cortisol concentration, and, as such, the benefits of their administration should be weighed against those risks