Endogenous nature of estra-4,9-diene-3,17-dione in entire male horses.

Estra-4,9-diene-3,17-dione (dienedione) is an anabolic androgenic steroid (AAS) sold as a bodybuilding supplement. It is prohibited in both human and equine sports. With no report of 4,9-diene configuration in endogenous steroids, dienedione has long been considered a synthetic AAS. Nevertheless, the reoccurring detection of dienedione in colt (entire male horse) urine samples lead to the investigation of its possible endogenous nature in horses. This paper describes (i) the detection of naturally occurring dienedione in colts, (ii) the conjugation study of dienedione and (iii) the population study of free and glucuronide-conjugated dienedione in colt urine. Qualitative and quantitative analyses of dienedione content in colt urine were performed, employing liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Qualitative analyses showed that dienedione was endogenous in colt urine and mainly in the form of glucuronide conjugates. Glucuronidation of dienedione was believed to happen at 3-enol leading to dienedione-3-glucuronide. Upon the population study of free and glucuronide-conjugated dienedione in colt urine samples (n = 175), the mean ± SD was determined to be 2.5 ± 3.5 ng/ml. The population data fitted a normal distribution after a fifth root transformation with the exclusion of one outlier by Grubb's test. A possible in-house threshold was proposed at 30 ng/ml of free and glucuronide-conjugated dienedione in colt urine associated with a risk factor of 1 in 14,269 (with a degree of freedom of 173). This is the first report of endogenous dienedione in entire male horses and the approach for controlling its potential misuse by using a threshold is also presented.

Identification of erythropoietin mimetic peptide 1 linear form in a sealed vial and its administration study in horses for doping control purpose.

The erythropoietin mimetic peptide 1 linear form (EMP1-linear), GGTYSCHFGPLTWVCKPQGG-NH2 , was identified in an unknown preparation consisting of white crystalline powder contained in sealed glass vials using ultrahigh performance liquid chromatography-high-resolution mass spectrometry (UPLC-HRMS). The white crystalline powder, allegedly used for doping racehorses, was found to contain around 2% (w/w) of EMP1-linear. EMP1-linear can be cyclised in equine plasma at physiological temperature of 37°C by forming an intramolecular disulfide bond to give EMP1, which is a well-known erythropoiesis stimulating agent that can bind to and activate the receptor for cytokine erythropoietin (EPO). Thus, EMP1-linear is a prodrug of EMP1, which is a performance-enhancing doping agent that can be misused in equine sports. In order to identify potential target(s) for detecting the misuse of EMP1-linear in horses, an in vitro metabolic study using horse liver S9 fraction was performed. After incubation, EMP1-linear mainly existed in its cyclic form as EMP1, and four N-terminus truncated in vitro metabolites TYSCHFGPLTWVCKPQGG-NH2 (M1), SCHFGPLTWVCKPQGG-NH2 (M2), WVCKPQGG-NH2 (M3) and VCKPQGG-NH2 (M4) were identified. An intravenous administration study with the preparation of white crystalline powder containing EMP1-linear was also conducted using three retired thoroughbred geldings. EMP1 was detectable only in the postadministration plasma samples, whereas the four identified in vitro metabolites were detected in both postadministration plasma and urine samples. For controlling the misuse of EMP1-linear in horse, its metabolite M3 gave the longest detection time in both plasma and urine and could be detected for up to 4 and 27 h postadministration, respectively.

Screening and confirmation of recombinant human follistatin in equine plasma for doping control purposes.

Recombinant human follistatin (rhFST) is a potential performance-enhancing agent owing to its stimulating effect on muscle growth. Administration of rhFST to athletes is prohibited in human sports by the World Anti-Doping Agency (WADA) and in horseracing according to Article 6 of the International Agreement on Breeding, Racing and Wagering published by the International Federation of Horseracing Authorities (IFHA). For effective control of the potential misuse of rhFST in flat racing, methods for screening and confirmatory analysis are required. This paper describes the development and validation of a complete solution for detecting rhFST and confirming its presence in plasma samples collected from racehorses. A high-throughput analysis of rhFST with a commercially available enzyme-linked immunosorbent assay (ELISA) was evaluated for the screening of equine plasma samples. Any suspicious finding would then be subjected to a confirmatory analysis using immunocapture, followed by nano-liquid chromatography/high-resolution tandem mass spectrometry (nanoLC-MS/HRMS). The confirmation of rhFST by nanoLC-MS/HRMS was achieved by comparing the retention times and relative abundances of three characteristic product-ions with those from the reference standard in accordance with the industry criteria published by the Association of Official Racing Chemists. The two methods achieved comparable limit of detection (~2.5-5 ng/mL) and limit of confirmation (2.5 ng/mL or below), as well as adequate specificity, precision and reproducibility. To our knowledge, this is the first report of the screening and confirmation methods for rhFST in equine samples.

An enhanced label-free proteomics approach for deep-diving into equine plasma proteome, including the discovery of protein biomarkers for strenuous exercise.

Plasma proteins have been a valuable source of biomarkers for clinical uses and for monitoring of the illicit use of prohibited substances or practices in equine sports. We have previously reported the first use of label-free proteomics in profiling equine plasma proteome. This study aimed to refine the method by systematically evaluating various plasma fractionation methods and the use of narrower precursor mass ranges in data-independent acquisition (DIA) mass spectrometry (MS). Tandem fractionations of equine plasma with octanoic acid precipitation followed by solid-phase extraction (SPE) with C4 cartridges provided the largest increase in the number of new proteins identified. The use of two narrow precursor mass ranges of m/z 400-600 and 600-800 in DIA not only identified most proteins detectable by using a single mass range of m/z 350-1500 but also identified ~27% more proteins. The improved method was applied to analyse the plasma proteome of 'postrace' samples which, unlike other samples, had been collected from racehorses soon after racing. Multivariate data analysis has identified upregulation of 14 proteins and downregulation of six proteins in postrace plasma compared with the non-postrace plasma samples. Literature review of these proteins has provided evidence of exercise-induced haemolysis and changes in antioxidant enzyme activities, kinin system, insulin signalling and energy metabolism after strenuous exercise. The improved method has enabled a deeper profiling of the equine plasma proteome and identified the proteins associated with normal physiological changes after racing which are potential confounding factors in the development of a biomarker approach for doping control.

A multiplex qPCR assay for transgenes detection: A novel approach for gene doping control in horseracing using conventional laboratory setup.

Illicit administration of transgene into horses is a form of gene doping that has been a key concern in equine sports. The large number of potential performance-enhancing transgenes has demanded a cost-effective and reliable detection method. Multiplex qPCR is a relevant technique, but the cross-talking between fluorophores and high background noise limits the method sensitivity and specificity. This study reports a simpler multiplexing approach by using the same fluorophore for four hydrolysis probes each targeting one of the four transgenes: human growth hormone, insulin-like growth factor 1, equine erythropoietin and interleukin-10. Any positive findings from this multiplex qPCR assay can then be confirmed by individual qPCR assays to identify potential transgene(s). This has effectively eliminated the cross-talking issue and allowed an improved signal-to-noise than conventional multiplex qPCR assay. It has also removed the limitation imposed by the available choice of fluorophores and optical channels of qPCR instruments on the number of transgenes that can be analysed in a multiplex qPCR assay. This novel multiplex qPCR has been successfully validated. The estimated limits of detection were ~1500-2500 copies/mL of blood, thus demonstrating comparable sensitivity with the corresponding duplex qPCR assays. Concurring results were obtained by analysing hundreds of official blood samples provided by racehorses with this multiplex qPCR assay and the accredited individual duplex qPCR assays. This novel multiplex qPCR assay for detecting multiple transgenes is a cost-effective screening method using a conventional laboratory setup and has opened up the potential to include the testing of additional transgenes in a single assay.

Optimization and implementation of four duplex quantitative polymerase chain reaction assays for gene doping control in horseracing.

The concern about gene doping has remained high in horseracing and other equestrian competitions. Our laboratory has previously developed a duplex quantitative polymerase chain reaction (qPCR) assay capable of detecting in equine blood the human erythropoietin (hEPO) transgene and equine tubulin α 4a (TUBA4A) gene as an internal control the latter providing quality control over DNA extraction and qPCR. This study aimed to optimize the method for routine testing of regulatory samples. The use of an automated DNA extraction system has increased the sample throughput, consistency of DNA extraction, and recovery of reference materials. The use of reduced concentration of primers and hydrolysis probe for internal control minimized their competition with transgene amplification and improved the assay sensitivity. Spike-in of an exogenous internal control at low concentration for plasma analysis has also been validated. Using the new workflow, four duplex qPCR assays have been developed for the detection of transgenes, namely, hEPO, human growth hormone (hGH), insulin-like growth factor 1 (hIGF-1), and equine EPO (eEPO). The estimated limits of detection (LODs) of each transgene were 2000 copies/mL of blood and 200 copies/mL of plasma. This method could detect the presence of transgene in blood and plasma collected from a horse administered intramuscularly (IM) with recombinant adeno-associated virus (rAAV) carrying the hEPO transgene. A longer detection time was observed in blood than in plasma. The methods have been applied to the screening of over a thousand official racehorse samples since June 2020 for the presence of these transgenes.

Long-term monitoring of IOX4 in horse hair and its longitudinal distribution with segmental analysis using liquid chromatography/electrospray ionization Q Exactive high-resolution mass spectrometry for the purpose of doping control.

IOX4, a hypoxia-inducible factor stabilizer, is classified as a banned substance for horses in both horse racing and equestrian sports. We recently reported the pharmacokinetic profiles of IOX4 in horse plasma and urine and also identified potential monitoring targets for the doping control purpose. In this study, a long-term longitudinal analysis of IOX4 in horse hair after a nasoesophageal administration of IOX4 (500 mg/day for 3 days) to three thoroughbred mares is presented for the first time for controlling the abuse/misuse of IOX4. Six bunches of mane hair were collected at 0 (pre), 1, 2, 3, and 6 month(s) postadministration. Our results showed that the presence of IOX4 was identified in all postadministration horse hair samples, but no metabolite could be detected. The detection window for IOX4 could achieve up to 6-month postadministration (last sampling point) by monitoring IOX4 in hair. In order to evaluate the longitudinal distribution of IOX4 over 6 months, a validated quantification method of IOX4 in hair was developed for the analysis of the postadministration samples. Segmental analysis of 2-cm cut hair across the entire length of postadministration hair showed that IOX4 could be quantified up to the level of 1.84 pg/mg. In addition, it was found that the movement of the incorporated IOX4 band in the hair shaft over 6 months varied among the three horses due to individual variation and a significant diffusion of IOX4 band up to 10 cm width was also observed in the 6-month postadministration hair samples.

Comprehensive metabolic study of IOX4 in equine urine and plasma using liquid chromatography/electrospray ionization Q Exactive high-resolution mass spectrometer for the purpose of doping control.

IOX4 is a hypoxia-inducible factor prolyl hydroxylase (HIF-PHD) inhibitor, which was developed for the treatment of anemia by exerting hematopoietic effects. The administration of HIF-PHD inhibitors such as IOX4 to horses is strictly prohibited by the International Federation of Horseracing Authorities and the Fédération Équestre Internationale. To the best of our knowledge, this is the first comprehensive metabolic study of IOX4 in horse plasma and urine after a nasoesophageal administration of IOX4 (500 mg/day, 3 days). A total of four metabolites (three mono-hydroxylated IOX4 and one IOX4 glucuronide) were detected from the in vitro study using homogenized horse liver. As for the in vivo study, post-administration plasma and urine samples were comprehensively analyzed with liquid chromatography/electrospray ionization high-resolution mass spectrometry to identify potential metabolites and determine their corresponding detection times. A total of 10 metabolites (including IOX4 glucuronide, IOX4 glucoside, O-desbutyl IOX4, O-desbutyl IOX4 glucuronide, four mono-hydroxylated IOX4, N-oxidized IOX4, and N-oxidized IOX4 glucoside) were found in urine and three metabolites (glucuronide, glucoside, and O-desbutyl) in plasma. Thus, the respective quantification methods for the detection of free and conjugated IOX4 metabolites in urine and plasma with a biphase enzymatic hydrolysis were developed and applied to post-administration samples for the establishment of elimination profiles of IOX4. The detection times of total IOX4 in urine and plasma could be successfully prolonged to at least 312 h.

Metabolic studies of selective androgen receptor modulators RAD140 and S-23 in horses.

This paper describes the studies of the in vitro biotransformation of two selective androgen receptor modulators (SARMs), namely, RAD140 and S-23, and the in vivo metabolism of RAD140 in horses using ultra-high performance liquid chromatography-high resolution mass spectrometry. in vitro metabolic studies of RAD140 and S-23 were performed using homogenised horse liver. The more prominent in vitro biotransformation pathways for RAD140 included hydrolysis, hydroxylation, glucuronidation and sulfation. Metabolic pathways for S-23 were similar to those for other arylpropionamide-based SARMs. The administration study of RAD140 was carried out using three retired thoroughbred geldings. RAD140 and the majority of the identified in vitro metabolites were detected in post-administration urine samples. For controlling the misuse of RAD140 in horses, RAD140 and its metabolite in sulfate form gave the longest detection time in hydrolysed urine and could be detected for up to 6 days post-administration. In plasma, RAD140 itself gave the longest detection time of up to 13 days. Apart from RAD140 glucuronide, the metabolites of RAD140 described herein have never been reported before.

Label-free proteomics for discovering biomarker candidates of RAD140 administration to castrated horses.

Selective androgen receptor (AR) modulators (SARMs) are potent anabolic agents with a high potential of misuse in horseracing and equestrian sports. In this study, we applied label-free proteomics to discover plasma protein biomarkers in geldings (castrated horses) after administration with a popular SARM named RAD140. Tryptic peptides were prepared from plasma samples and analyzed by nano-flow ultrahigh-performance liquid chromatography-high-resolution tandem mass spectrometry (nano-UHPLC-HRMS/MS) using data-independent acquisition (DIA) method. Orthogonal projection on latent structure-discriminant analysis (OPLS-DA) has led to the development of a predictive model that could discriminate RAD140-administered samples from control samples and could also correctly classify 18 out of 19 in-training horses as control samples. The model comprises 75 proteins with variable importance in projection (VIP) score above 1. Gene Ontology (GO) enrichment analysis and literature review have identified upregulation of AR-regulated clusterin, and proteins associated with inflammation (haptoglobin, cluster of differentiation 14 [CD14], and inter-alpha-trypsin inhibitor heavy chain 4 [ITIH4]) and erythropoiesis (glycosylphosphatidylinositol-specific phospholipase D1 [GPLD1]) after RAD140 administration. Their changes were confirmed by selected reaction monitoring (SRM) experiments. Similar effects have been reported by the use of androgens and other SARMs. This is the first reported study that describes the use of a proteomic biomarker approach to detect horses that have been administered with RAD140 by applying label-free proteomic profiling of plasma samples. These results support the concept of a biomarker-driven approach to enhance the doping control of RAD140 and potentially other SARMs in the future.

Tiludronic acid can be detected in blood and urine samples from Thoroughbred racehorses over 3 years after last administration.

BACKGROUND: Administration of bisphosphonates, including tiludronic acid, to Thoroughbred racehorses below 3 and a half years of age is prohibited in most racing jurisdictions. OBJECTIVES: To determine if evidence of administration of tiludronic acid could be obtained from analysis of blood and urine samples beyond 40 days after administration. STUDY DESIGN: Retrospective cohort. METHODS: Horses maintained in a highly controlled environment and treated with Tildren®a were selected from clinical records. Twenty-four horses were identified, 21 of which were still in race training. Blood and urine samples were collected and analysed for the presence of tiludronic acid using ultra-high-performance liquid chromatography-high-resolution mass spectrometry. RESULTS: Tiludronic acid was detected in samples from every horse, including two that had been given a therapeutic dose of the drug 3 years prior to sample collection. The estimated concentrations of tiludronic acid in the blood collected at least 2 years post-administration were consistently very low (less than 0.3 ng/mL). The estimated concentrations in urine were less consistent and were generally lower than those in blood, although higher levels were inconsistently detected in individual horses (up to about 16 ng/mL almost 1 year post-administration in 1 horse and about 3.7 ng/mL at almost 3 years post-administration in another). MAIN LIMITATIONS: The study was performed in horses that are older than the primary target group. A single sample was obtained from most horses and so we cannot comment on elimination profiles. CONCLUSIONS: Evidence that a therapeutic dose of tiludronic acid has been administered to a horse can be obtained from detection of the drug in blood and urine samples over 3 years after it was administered.

Unravelling androgens in sport: Altrenogest shows strong activation of the androgen receptor in a mammalian cell bioassay.

Altrenogest is a commonly used progestogen for the suppression of oestrus and associated distracting behaviours that interfere with training and performance of female racehorses. The steroid is derived from 19-nor testosterone and is structurally similar to the anabolic androgenic steroid, trenbolone. In this study, the relative androgen potency of altrenogest was determined by a kidney (HEK293) cell androgen bioassay. The HEK293 bioassay shows that in its pure form, altrenogest has a high relative potency compared with testosterone but is not as strong as ß-trenbolone. Our results also show that altrenogest is able to activate the androgen receptor at the concentrations relevant to the administration regime of racehorses and retains its activity ex vivo. Thus, we show unequivocally that altrenogest, a progestogen used widely in female racehorses, acts as a strong androgen in a mammalian cell bioassay.

Application of a non-target variable data independent workflow (vDIA) for the screening of prohibited substances in doping control testing.

A non-target variable Data Independent Acquisition (vDIA) workflow based on accurate mass measurements using a Q Exactive OrbiTrap is presented for the first time for equine doping control testing. The vDIA workflow uses a combination of MS1 events (1 to 2) and multiple vDIA events to cover the analytes of interest. The workflow basically captures a digital image of a sample allowing all relevant MS1 and MS2 data to be recorded. In theory, the workflow can accommodate an unlimited number of analytes as long as they are amenable to the sample extraction protocol and fall within the mass limits of the workflow. Additional targets fulfilling the above requirements can be added without changing any settings. The performance of the vDIA workflow was illustrated by applying it to two screening methods in horse urine, with one workflow covering 331 basic drugs and the other covering 45 quaternary ammonium drugs (QADs). Both screening methods have good detection sensitivity with 84% of the basic drugs having Limits of Detection (LoDs) of ≤ 1 ng/mL and 84% of the QADs having LoDs of ≤ 0.4 ng/mL. Other method characteristics including retention reproducibility, method precision and false hit rate will also be presented.

A duplex qPCR assay for human erythropoietin (EPO) transgene to control gene doping in horses.

The misuse of genetic manipulation technology to enhance athletic performance is termed gene doping which is prohibited in human sports, horseracing, and equestrian sports. Although many qPCR assays have been developed, most assays employ genomic DNA (gDNA) from humans, non-human primates, and mice as a background and they may not be applicable for testing horse samples. This study aimed to develop a qPCR assay for the detection of human erythropoietin (hEPO) transgene in horse blood cells where the viral vectors used in gene therapy can reside for months. For the detection of hEPO transgene, the performance of three sets of primers and a hydrolysis probe for hEPO were compared. One set showed adequate specificity, sensitivity, amplification efficiency, and a dynamic range of detection in the presence of horse gDNA. The assay was duplexed with the detection of horse tubulin α 4A (TUBA4A) gene as an endogenous internal control in order to prevent false-negative results due to poor recovery and storage of extracted DNA and/or qPCR experimental variation. For the extraction of hEPO-plasmid, the QIAGEN Gentra Puregene blood kit was shown to recover the majority (62%) of hEPO-plasmid from spiked horse blood cells. The specificity and limit of detection (LOD) of the duplex qPCR assay were determined in accordance with MIQE guidelines. These findings supported the application of this duplex qPCR assay to the detection of hEPO transgene in horse blood cells.

Doping control analysis of total arsenic in equine plasma.

Arsenic can be easily found in our surrounding environment. Because of its ubiquitous nature, horse urine and blood invariably contain low levels of arsenic. Nevertheless, inorganic arsenic, despite its general use as a tonic for horses, is an effective doping agent having a deleterious effect because of its ability to induce gastroenteritis. The misuse of arsenic in horseracing has been controlled by an international urinary threshold of total arsenic at 0.3 µg/mL. However, an equivalent threshold for total arsenic in plasma is yet to be established. In this study, an inductively coupled plasma-mass spectrometry method has been developed for quantifying total arsenic in equine plasma. Statistical analysis determined that the data from a population study of 1,552 post-race and out-of-competition plasma samples fits a Gaussian mixture model with two Gaussian components. A rounded-up provisional threshold for plasma total arsenic at 2.5 ng/mL was subsequently established. Results from administration trials with a sodium arsanilate-containing supplement showed that both urinary and plasma arsenic was significantly elevated after administration. The maximum urinary detection time was around 22 h based on the international threshold. However, the maximum plasma detection time would be longer than 73 h if the provisional threshold of 2.5 ng/mL was adopted. In view of the high discrepancy between the urine and plasma detection times, a revised plasma threshold of 15 ng/mL is proposed to afford a comparable detection time in both matrices. The risk of a normal sample exceeding the proposed plasma total arsenic threshold is practically zero.

Detection of bioactive peptides including gonadotrophin-releasing factors (GnRHs) in horse urine using ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC/HRMS).

The use of bioactive peptides as a doping agent in both human and animal sports has become increasingly popular in recent years. As such, methods to control the misuse of bioactive peptides in equine sports have received attention. This paper describes a sensitive accurate mass method for the detection of 40 bioactive peptides and two non-peptide growth hormone secretagogues (< 2 kDa) at low pg/mL levels in horse urine using ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC/HRMS). A simple mixed-mode cation exchange solid-phase extraction (SPE) cartridge was employed for the extraction of 42 targets and/or their in vitro metabolites from horse urine. The final extract was analyzed using UHPLC/HRMS in positive electrospray ionization (ESI) mode under both full scan and data independent acquisition (DIA, for MS2 ). The estimated limits of detection (LoD) for most of the targets could reach down to 10 pg/mL in horse urine. This method was validated for qualitative detection purposes. The validation data, including method specificity, method sensitivity, extraction recovery, method precision, and matrix effect were reported. A thorough in vitro study was also performed on four gonadotrophin-releasing factors (GnRHs), namely leuprorelin, buserelin, goserelin, and nafarelin, using the S9 fraction isolated from horse liver. The identified in vitro metabolites have been incorporated into the method for controlling the misuse of GnRHs. The applicability of this method was demonstrated by the identification of leuprorelin and one of its metabolites, Leu M4, in urine obtained after intramuscular administration of leuprorelin to a thoroughbred gelding (castrated horse).

Doping control analysis of antipsychotics and other prohibited substances in equine plasma by liquid chromatography/tandem mass spectrometry.

Antipsychotics are banned substances and considered by the Fédération Equestrian Internationale (FEI) to have no legitimate use in equine medicine and/or have a high potential for abuse. These substances are also prohibited in horseracing according to Article 6 of the International Agreement on Breeding, Racing and Wagering (published by the International Federation of Horseracing Authorities). Over the years, antipsychotics have been abused or misused in equestrian sports and horseracing. A recent review of literature shows that there is yet a comprehensive screening method for antipsychotics in equine samples. This paper describes an efficient liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the simultaneous detection of over 80 antipsychotics and other prohibited substances at sub-parts-per-billion (ppb) to low-ppb levels in equine plasma after solid-phase extraction (SPE).

A high-throughput and broad-spectrum screening method for analysing over 120 drugs in horse urine using liquid chromatography-high-resolution mass spectrometry.

A high-throughput method has been developed for the doping control analysis of 124 drug targets, processing up to 154 horse urine samples in as short as 4.5 h, from the time the samples arrive at the laboratory to the reporting deadline of 30 min before the first race, including sample receipt and registration, preparation and instrument analysis and data vetting time. Sample preparation involves a brief enzyme hydrolysis step (30 min) to detect both free and glucuronide-conjugated drug targets. This is followed by extraction using solid-supported liquid extraction (SLE) and analysis using liquid chromatography-high-resolution mass spectrometry (LC-HRMS). The entire set-up comprised of four sets of Biotage Extrahera automation systems for conducting SLE and five to six sets of Orbitrap for instrumental screening using LC-HRMS. Suspicious samples flagged were subject to confirmatory analyses using liquid chromatography-triple quadrupole mass spectrometry. The method comprises 124 drug targets from a spectrum of 41 drug classes covering acidic, basic and neutral drugs. More than 85% of the targets had limits of detection at or below 5 ng/mL in horse urine, with the lowest at 0.02 ng/mL. The method was validated for qualitative identification, including specificity, sensitivity, extraction recovery and precision. Method applicability was demonstrated by the successful detection of different drugs, namely (a) butorphanol, (b) dexamethasone, (c) diclofenac, (d) flunixin and (e) phenylbutazone, in post-race or out-of-competition urine samples collected from racehorses. This method was developed for pre-race urine testing in Hong Kong; however, it is also suitable for testing post-race or out-of-competition urine samples, especially when a quick total analysis time is desired.

Label-free Proteomics for Discovering Biomarker Candidates for Controlling Krypton Misuse in Castrated Horses (Geldings).

Recent advances in label-free quantitative proteomics may support its application in identifying and monitoring biomarkers for the purpose of doping control in equine sports. In this study, we developed a workflow of label-free quantitative proteomics to propose plasma protein biomarkers in horses after administration with krypton (Kr), a potential erythropoiesis-stimulating agent. Plasma proteomes were profiled by using nanoliquid chromatography-high-resolution mass spectrometry. An in-house mass spectral library consisting of 1121 proteins was compiled using samples collected from geldings (castrated horses) in the administration trial and geldings in training. A data-independent acquisition method was used to quantify an array of plasma proteins across plasma samples from the administration trial. Statistical analyses proposed a profile of 83 biomarker candidates that successfully differentiated Kr-administered samples from control samples, with the ability to detect Kr exposure for up to 13 days (the last sample collected in the administration trial). The model also correctly classified 32 in-training geldings as untreated controls. This is significantly longer than the 1 h detection time of plasma Kr using headspace gas chromatography-tandem mass spectrometry. Bioinformatic analyses enriched biomarker candidates relevant to complement activation and iron metabolism. The upregulation of transferrin receptor protein 1, one of the candidates related to iron metabolism, in plasma after Kr administration was validated by selected reaction monitoring of corresponding peptides. These results have demonstrated label-free quantitative proteomics as a promising approach to propose plasma protein biomarkers to enhance doping control. Data are available via ProteomeXchange with identifier PXD017262.