Discovery proteomics for the detection of putative markers for eradication of infection in an experimental model of equine septic arthritis using LC-MS/MS

Septic arthritis (SA) is a life-threatening condition in horses, and identifying eradication of infection in equine SA is challenging. This study explored the discovery of putative biomarkers for the eradication of joint infection in horses. We performed proteomics analysis of synovial fluid (SF) and plasma from horses with experimental SA, non-septic lipopolysaccharide-induced arthritis, and controls. The point of eradication of infection in horses with SA was determined previously. We compared spectral intensities between groups as well as before and after the eradication of infection. Twenty-six differentially abundant proteins were identified, which were upregulated in SF of horses with SA compared to the other groups, as well as compared to the same horses post-eradication of infection. In plasma, we did not identify differentially abundant proteins. Differentially abundant proteins in SF were of cellular origin and their biological functions included ubiquitination, signal transduction, apoptosis etc. The difference in their relative abundance between experimental groups was ≥10-fold compared to the abundance expected based on the difference in cell count alone (2-fold). Since most of cells in joints with bacterial infection are neutrophils, we suggest that the variable abundance of neutrophil- and cell-associated proteins represent potential biomarkers of eradication of infection in equine SA.