Equine Peripheral Gene Expression Changes in Response to Dose-Dependent Lipopolysaccharide-Induced Synovitis.

The research analyses the effects of using lipopolysaccharide to induce inflammation in horses, studying its impact on systemic mRNA expression, and how these effects change with different dosage levels.

Study Background and Objectives

• The study builds on previous research exploring the use of lipopolysaccharide to trigger local inflammation (acute synovitis) in horses, which in turn affects systemic mRNA expression. This method can be used to monitor gene expression changes resulting from the inflammatory response.
• The main goal of this investigation was to trigger a noticeable systemic mRNA response without causing severe lameness in the horses. This would allow for the evaluation of different anti-inflammatory treatments on mRNA expression.

Methodology

• Three mixed breed, four-year-old geldings were used in the study.
• A saline solution infused with 1,000 ng or less of E.coli O111:B4 lipopolysaccharide was injected into alternating radiocarpal joints after washout periods.
• Data was collected before each injection and at various times post-injection, including a complete blood cell count, serum amyloid A concentration, and mRNA expression analysis of 23 distinct genes using RT-qPCR.
• Lameness severity was monitored and recorded at each time point.
• For statistical analysis, two-way, repeated measures analysis of variance was employed.

Results and Interpretation

• The results echoed earlier findings, noting significant expression changes in multiple genes, including CD14, TLR4, IL-1β, IL1RN, MMP1, and MMP9 during the acute inflammatory period. Some genes exhibited dose-dependent changes.
• There were significant increases in complete blood cell count parameters and serum amyloid A concentrations. These are both markers of inflammation, indicating the effects of the lipopolysaccharide injections.
• Attempts to control the severity of lameness were less successful. Nonweight bearing lameness was identified at doses of 10ng or higher, while a dose of 1ng neither elicit detected lameness nor significant mRNA expression changes. This entry indicates that balancing the control of inflammation and prevention of severe lameness remains more complicated than anticipated.

Conclusions

• The study adds to the understanding of how lipopolysaccharide-induced inflammation impacts systemic gene expression in horses. It confirms that significant changes in gene expression and markers of inflammation can be produced, but that controlling the severity of lameness is challenging.
• This helps guide future investigations on optimizing dosage to observe the desired systemic response without excessive lameness and paves the way for more detailed studies on the effects of inflammation on gene expression in horses and potentially other large animal subjects.