A Translational Model for Repeated Episodes of Joint Inflammation: Welfare, Clinical and Synovial Fluid Biomarker Assessment

SIMPLE SUMMARY: Repeated episodes of joint inflammation play a key role in the progression of joint diseases such as osteoarthritis. In order to better understand diseases and develop treatments, animal studies are needed. Most models of joint inflammation cause severe discomfort and irreversible damage to joints which is neither truly reflective of naturally occurring disease processes nor desirable for the welfare of the experimental animals. This study examines a potential model of recurrent lower levels of inflammation. Minute doses of lipopolysaccharide (LPS), a substance that causes inflammation, were injected into the joints of horses three times at two-week intervals, and the effect of these injections on the horses’ comfort and welfare and markers of inflammation within the joint fluid were closely monitored. We found that each of these injections produced reliable and comparable levels of inflammation within the joints, with minimal impact on the horses’ comfort and welfare. The joints also showed complete recovery when re-examined at a later timepoint. These results suggest that this model has potential as a refined translational model of repeated episodes of joint inflammation that is more representative of natural disease states and can be used to evaluate potential therapeutics over several weeks. ABSTRACT: This study investigates repeated low-dose lipopolysaccharide (LPS) injections in equine joints as a model for recurrent joint inflammation and its impact on animal welfare. Joint inflammation was induced in eight horses by injecting 0.25 ng of LPS three times at two-week intervals. Welfare scores and clinical parameters were recorded at baseline and over 168 h post-injection. Serial synoviocentesis was performed for the analysis of a panel of synovial fluid biomarkers of inflammation and cartilage turnover. Clinical parameters and a final synoviocentesis were also performed eight weeks after the last sampling point to assess the recovery of normal joint homeostasis. Statistical methods were used to compare the magnitude of response to each of the 3 LPS inductions and to compare the baseline and final measurements. Each LPS injection produced consistent clinical and biomarker responses, with minimal changes in welfare scores. General matrix metalloproteinase (MMP) activity and joint circumference showed greater response to the second LPS induction, but response to the third was comparable to the first. Gylcosaminoglycans (GAG) levels showed a significantly decreased response with each induction, while collagen-cleavage neoepitope of type II collagen (C2C) and carboxypropetide of type II collagen epitope (CPII) showed quicker responses to the second and third inductions. All parameters were comparable to baseline values at the final timepoint. In conclusion, a consistent, reliable intra-articular inflammatory response can be achieved with repeated injections of 0.25 ng LPS, with minimal impact on animal welfare, suggesting potential as a refined translational model of recurrent joint inflammation.