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Simple Summary: Joint infection, or septic arthritis, is an important disease in horses and requires aggressive treatment to eradicate the infection. Using current diagnostic methods, it is difficult to determine when the infection has been eliminated following treatment, leading to often prolonged antimicrobial therapy, which may be unnecessary and is associated with side effects and antimicrobial resistance. Thus, better markers of eradication of joint infection are needed. In this study, a class of molecules called messenger ribonucleic acid (mRNA) in synovial fluid was investigated for potential biomarkers of the eradication of infection in an experimental model of equine septic arthritis using transcriptomics methods. Transcriptomics data were also compared to our previously published data on putative protein biomarkers of the eradication of joint infection and to an mRNA biomarker panel used to differentiate septic from non-septic shock in humans. Eight mRNAs were identified that were at least three times increased in horses with active septic arthritis compared to horses post-eradication of infection after treatment and horses with non-septic synovitis. The presence of mRNAs corresponding to our previously reported protein markers of eradication of joint infection and to the validated mRNA biomarker panel detecting sepsis in humans was also confirmed. Further investigation of mRNAs as a source of potential markers of the eradication of joint infection in horses is needed. Septic arthritis (SA) in horses has long-term health implications. The success of its resolution hinges on the implementation of early, aggressive treatment, which is often sustained over a prolonged period. Common diagnostic methods do not allow for the reliable detection of the eradication of joint infection. A potential alternative is the discovery and characterization of mRNA biomarkers. The purpose of this study was to identify potential mRNA biomarkers for the eradication of joint infection in equine SA and to compare their expression with our previously published proteomics data. In addition, the transcriptomics data were compared to the mRNA biomarker panel, SeptiCyte Lab, used to distinguish sepsis from non-septic shock in humans. A comparative transcriptomics analysis of synovial fluid from the SA joints of five horses with active infection and subsequent post-treatment eradicated infection in the same joints and five horses with non-septic synovitis was performed. Eight novel mRNA transcripts were identified that were significantly upregulated (>3-fold) in horses with active SA compared to horses post-eradication of infection after treatment and horses with non-septic synovitis. Two proteins in our proteomics data corresponded to these mRNA transcripts, but were not statistically different. The transcripts used in the SeptiCyte test were not differentially expressed in our study. Our results suggest that mRNA may be a useful source of biomarkers for the eradication of joint infection in horses and warrants further investigation. [ABSTRACT FROM AUTHOR]

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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. Septic arthritis is an important condition in horses, which can be life-threatening. At present, identifying eradication of infection in cases of equine septic arthritis is challenging. In this study, we performed a global proteomics analysis of synovial fluid and plasma in horses with experimental septic arthritis and identified 26 differentially abundant proteins compared to non-septic arthritis and post eradication of infection. The results of this study provide the basis for further characterization of the differentially abundant proteins and identification of clinically relevant biomarkers of septic arthritis in horses. [Display omitted] • Equine synovial fluid (SF) and plasma proteomes were analyzed. • Septic arthritis was compared to non-septic synovitis and post eradication of infection. • In SF, 26 proteins were found to be upregulated in septic arthritis compared to other conditions. • The majority of the upregulated proteins were cellular, possibly from the neutrophilic infiltrate. [ABSTRACT FROM AUTHOR]