Biomarkers for the Eradication of Infection in Equine Septic Arthritis
Date
2024-11-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-1009-7814
Type
Thesis
Degree Level
Doctoral
Abstract
Septic arthritis is a life-threatening condition in horses, and identifying eradication of infection can be challenging. Currently used laboratory methods for diagnosis of septic arthritis, such as bacterial culture and cytologic evaluation of synovial fluid, often lack sensitivity. In many cases of equine septic arthritis, synovial fluid culture is negative. Synovial fluid parameters can be variable, and depend on the health status of the animal and type of joint injury. Serum amyloid A (SAA) measured in synovial fluid has been investigated as a potentially more sensitive marker of equine septic arthritis. However, our research group has shown that synovial fluid SAA remains elevated for a prolonged period after the eradication of infection, and is increased in non-affected joints in horses with experimental septic arthritis, suggesting it is not an ideal marker of eradication of joint infection. Since all these methods of detecting septic arthritis are suboptimal for the detection of eradication of infection, antibiotic therapy is usually aggressive and prolonged, which increases the risk of adverse effects in the animal and development of antibiotic resistance. Therefore, better biomarkers that indicate the eradication of joint infection in horses are needed. Thus, the objective of this research project was to investigate potential biomarkers of eradication of infection in an experimental model of equine septic arthritis.
First, we have successfully established a model of eradication of joint infection in horses using standard diagnostic techniques. We found that synovial fluid bacterial culture and total nucleated cell count were the most useful parameters to establish the eradication of infection, while total protein and percentage neutrophils were not useful. Next, we detected a putative SAA isoform produced locally within the equine joint based on the peptide sequence difference detected by mass spectrometry. We found this putative isoform in synovial fluid both from horses with septic arthritis and from horses with systemic inflammation without joint pathology. This suggested that locally produced isoforms of SAA should be interpreted with caution and may not be ideal markers of eradication of infection. We also confirmed that SAA increases significantly in synovial fluid from non-affected joints of horses with septic arthritis and systemic inflammation, which should be taken into account when interpreting synovial fluid SAA measurements. Based on our experimental model we found that the previously reported synovial fluid SAA cut-off values for the detection of septic arthritis may be too low, and may need to be revised higher based on the acuteness of the lesion. We then performed discovery proteomics analysis of synovial fluid based on our experimental model and identified 26 putative biomarkers of eradication of infection. These proteins were differentially abundant in synovial fluid from horses with septic arthritis before and after the eradication of infection, and they were also differentially abundant between horses with septic arthritis and non-septic synovitis. Finally, we performed transcriptomics analysis of synovial fluid from experimental horses, and identified 8 potential mRNA-based biomarkers of eradication of equine joint infection. The results provide valuable data for future research to better characterize joint-specific SAA isoforms, as well as to verify and validate protein and mRNA-based putative biomarkers that could be used to indicate eradication of joint infection in horses.
Description
Keywords
Horse, equine, joint, septic arthritis, biomarker
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Veterinary Pathology
Program
Veterinary Pathology