Plasma steroid profiles before and after ACTH stimulation test in healthy horses

Identification of Potential miRNA Biomarkers to Detect Hydrocortisone Administration in Horses

Circulating microRNAs (miRNAs) are stable in bodily fluids and are potential biomarkers of various diseases and physiological states. Although several studies have been conducted on humans to detect drug doping by miRNAs, research on drugs and miRNAs in horses is limited. In this study, circulating miRNAs in horses after hydrocortisone administration were profiled and variations in miRNAs affected by hydrocortisone administration during endogenous hydrocortisone elevation were examined. The miRNAs were extracted from thoroughbred horse plasma before and after hydrocortisone administration and subjected to small RNA sequencing and reverse transcription quantitative PCR (RT-qPCR). RT-qPCR validation was performed for the 20 miRNAs that were most affected by hydrocortisone administration. The effects of elevated endogenous hydrocortisone levels due to exercise and adrenocorticotropic hormone administration were also confirmed. The validation results showed that approximately half of the miRNAs showed the same significant differences as those obtained using small RNA sequencing. Among the twenty miRNAs, two novel miRNAs and miR-133a were found to vary differently between exogenous hydrocortisone administration and endogenous hydrocortisone elevation. This study provides basic knowledge regarding the circulating miRNA profile of horses after hydrocortisone administration and identifies three miRNAs that could potentially be used as biomarkers to detect hydrocortisone administration.

Salivary cortisol measurement in horses: immunoassay or LC-MS/MS?

The aim of the present study was to measure salivary cortisol concentrations of horses before and after hypothalamic-pituitary-adrenal (HPA) axis stimulation by means of liquid chromatography-tandem-mass spectrometry (LC-MS/MS) and an immunoassay (cELISA) for method comparison. Nine clinically healthy horses participated in the study. An ACTH stimulation test was performed. Saliva samples were collected before (T0) and 60 (T60) min after intravenous injection of 1 μg/kg BW synthetic ACTH1-24. LC-MS/MS was assessed for the determination of equine salivary cortisol. The results of these measurements were then compared to the results obtained by a cELISA, which has previously been validated for use in horses. The Pearson correlation coefficient was calculated and showed no correlation at T0 (r = -0.2452; P = 0.5249) and significantly correlated results at T60 (r = 0.8334; P = 0.0053). Bland-Altman-Plots of T60 revealed that immunoassay measurements led to higher outcome values than LC-MS/MS. On average, immunoassay results were 2.3 times higher. Poor agreement between both methods at T0 is potentially a consequence of inaccuracy in the very low measuring range of the immunoassay, and to a smaller extent, structurally similar cross-reacting agents and matrix effects, which might bias the results. Overestimation of immunoassay results at T60 might be due to different standardization of both methods, non-avoidable matrix effects on the antigen-antibody interaction in the ELISA, and possibly cross-reactions of other steroids. While immunoassay measurements of equine salivary cortisol yielded higher but reasonably correlated results for elevated cortisol concentrations after stimulation of the HPA axis, LC-MS/MS provided more accurate results, particularly for baseline cortisol concentrations close to the limit of detection of the ELISA.