Alterations of peripheral gene expression in response to lipopolysaccharide-induced synovitis as a model for inflammation in horses.

The research analyses the effect of lipopolysaccharide-induced inflammation on peripheral gene expression in horses. The study found significant variation in gene expression related to inflammation following repeated intra-articular LPS injections in different joints and in horses of varying ages.

Study Design and Methodology

• This study employed six mixed breed horses divided into two distinct age groups – an older group comprising three horses aged between 10 and 17 years, and a younger group comprising three horses all aged 3 years.
• Each horse received aseptic injections of lipopolysaccharide (LPS) derived from Escherichia coli O111:B4 in either the radiocarpal (wrist) or fetlock (ankle) joint. These injections were given a total of four times to each horse, with a minimum interval of two weeks between injections, and a change of joint each time.
• The researchers collected blood samples from the horses before and after each injection to analyze the expression of 20 different genes. Serum was also taken for protein concentration analysis.

Results and Findings

• All horses manifested signs of minimal to non-weight-bearing lameness between 4 – 6 hours post-injection. These symptoms largely subsided within 24 hours and disappeared by 48 hours.
• The study revealed significant differential expression in multiple genes, including CD14, TLR4, MMP1, MMP9, IL-1β, IL1RN, IL-10, ALOX5AP, IL-8, TNFα, CCL8, IGF1, and PTGS2, when compared to both pre-injection and sham injection time points.
• It was also found that multiple genes showed increased expression in horses where the radiocarpal joint was injected when compared to the fetlock joint. Similarly, increased gene expression was seen in younger horses compared to older horses.
• Serum amyloid A (SAA) levels were negative before injection but showed an increase 9 hours post-injection, often lasting up to 144 hours.

Conclusion

• Through the study, it was demonstrated that mRNA expression of pro- and anti-inflammatory genes can provide important information about the response to acute, localized inflammation.
• However, the researchers highlighted that caution should be used when selecting target joints or age groups of horses for such a study, as the transcriptional response can vary based on these factors. Attempts to measure in vivo serum cytokine levels using a multiplex assay were not successful, likely due to the low detection limits of the assays.