Effect of clodronate on gene expression in the peripheral blood of horses.

The research explores the impact of administering the drug clodronate on gene expression levels in horses over time, with potential implications for drug detection methods in racehorses.

Introduction and Hypothesised Effects of Bisphosphonates

• Clodronate and tiludronate are two bisphosphonate products approved by the FDA for use in horses. However, there has been speculation on the actual impact of these drugs, with suggestions that they could produce analgesic effects and even interfere with bone healing.
• Because of these potential adverse effects, the use of bisphosphonates is banned in racehorses. Detecting their usage has proven challenging, however, as they rapidly sequestrate in the skeleton, leaving a short detection window in the blood; this hinders the reliability of most current drug tests.

Experimental Procedure and Findings

• The study involved the administration of clodronate to seven thoroughbred horses, and a saline solution to four others as a control. Sequencing and analysis of RNA from peripheral blood mononuclear cells (PBMCs) determined any differentially expressed transcripts over a series of days following clodronate or saline administration.
• The findings indicated that no single transcripts showed differential expression. However, pathway analysis revealed upregulation of p38 MAPK and Ras pathways, and downregulation of the cadherin signalling pathway on the first day after administration.
• Additionally, the researchers also looked at the biomarkers cathepsin K (CTSK) and type 5 acid phosphatase (ACP5) through a targeted gene approach using RT-qPCR. No significant difference was observed.

Conclusions and Suggestions for Future Research

• Beyond the primary findings, a significant effect of time on gene expression levels was also noted for ACP5 and CTSK. While these particular biomarkers did not show a significant initial change following clodronate administration, their expression levels appeared to fluctuate over time.
• The researchers note that these genes may therefore warrant further investigation. This could create more reliable methods of detecting clodronate use over an extended time period, even after the drug has sequestrated in the skeleton and become undetectable in the blood.