Detection of the growth hormone secretagogue MK-0677 in equine hair following oral administration

MK-0677 (ibutamoren) is an orally active non-peptide growth hormone secretagogue that binds to the ghrelin receptor stimulating the secretion of endogenous growth hormone. It is one of the most prevalent performance-enhancing compounds currently available online and is potentially subject to abuse both in human and equine sports. The aim of the current study was to investigate whether it could be detected in equine hair following oral administration of MK-0677 mesylate to a Thoroughbred racehorse. MK-0677 and its O-dealkylated metabolite were extracted using an existing method for prohibited substances in equine hair and analysed by liquid chromatography tandem mass spectrometry. This enabled the detection of MK-0677 in all hair samples collected, up to 209 days in mane and 358 days in tail. A follow-up methodology with an extensive wash procedure was carried out for selected hair samples, which unambiguously verified the presence of MK-0677. Wash criteria to differentiate between internal incorporation (via bloodstream) and external deposition (via sweat and sebum) was also assessed and indicated internal incorporation for the samples collected at later time points (≥52 days) and a combination of internal incorporation and external deposition for hair samples collected at the earlier time point (2 days).

Characterization of growth hormone secretagogue small molecule ibutamoren (MK-0677) and its possible metabolites in thoroughbred horses for doping control

RATIONALE

It is important to remember that performance-enhancing agents such as non-peptide growth hormone secretagogues present a significant risk of abuse. Ibutamoren (MK-0677) is a potent, long-acting, selective non-peptide growth hormone secretagogue that can be taken orally.

METHODS

This study examines ibutamoren and its metabolites in thoroughbred horses after oral administration. Liquid chromatography/high-resolution mass spectrometry was used to determine the probable structures of the detected metabolites.

RESULTS

In this study, 22 metabolites of ibutamoren were identified (17 phase I and 5 phase II). Oxidation of ibutamoren leads to hydroxylated metabolites (mono and di). The study also detected dissociated side chains (benzyl group and 2-amino-2-methylpropanamide) and hydrogenated metabolites. The glucuronic acid conjugated analogs of ibutamoren were detected during phase II of the study, but no sulfonic acid conjugated analogs were observed. The major metabolites can be detected up to 96 hours after a single dose, and ibutamoren can persist for up to 72 hours.

CONCLUSIONS

These findings will aid in the detection of ibutamoren and the detection of its illegal use in competitive sports.

Equine metabolism of the growth hormone secretagogue MK-0677 in vitro and in urine and plasma following oral administration

Ibutamoren mesylate, or MK-0677, is an orally active, non-peptide growth hormone secretagogue that has been developed to stimulate excretion of endogenous growth hormone. It has been evaluated for the treatment of a range of clinical conditions but is not available therapeutically. Nonetheless, MK-0677 is widely available to purchase online, sold as 'supplement' products. The mode of action and relative ease of purchase make MK-0677 a potential threat with regard to sports doping. The aim of this study was to investigate the metabolism of MK0677 in the horse following in vitro incubation and oral administration to two Thoroughbred racehorses, in order to identify the most appropriate analytical targets for doping control laboratories. Liquid chromatographyhigh resolution mass spectrometry was used for metabolite identification, and subsequently liquid chromatography-tandem mass spectrometry was used to generate full metabolite profiles for post-administration urine and plasma samples. Fourteen phase I metabolites were identified in vitro; thirteen of these were subsequently detected in urine and nine in plasma collected post-administration, alongside the parent compound in both matrices. In both urine and plasma, the longest duration of detection was observed for an O-dealkylated metabolite of MK-0677 and, therefore, this would be the best target for the detection of MK-0677 administration. MK-0677 and the O-dealkylated metabolite were found to be excreted largely unconjugated in urine and plasma.

Characterization of equine liver microsome-generated metabolites of growth hormone secretagogue small molecule ibutamoren

RATIONALE

Interest in growth hormone secretagogues has intensified during the past several years based on capable, ever-widening investigational applications of recombinant growth hormone in animals and humans. Ibutamoren is a potent, long-acting, selective and orally active non-peptide growth hormone secretagogue, which has a great potential for abuse as a performance-enhancing agent in sports.

METHODS

To support drug metabolism and pharmacokinetic studies of chiral pharmaceuticals, it is necessary to combine the resolving power of high-performance liquid chromatography with the sensitivity of mass spectrometric techniques. This paper describes the metabolic conversion of ibutamoren using equine liver microsomes and metabolite characterization using a QExactive high-resolution mass spectrometer.

RESULTS

A total of 32 metabolites for ibutamoren (20 phase I and 12 phase II) were detected. The important findings of the current research are as follows: (1) the growth hormone secretagogue ibutamoren was prone to oxidation, resulting in corresponding hydroxylated metabolites; (2) in ibutamoren, the dissociation of the phenyl ring and 2-amino-2-methylpropanamide side chain was also observed; (3) the glucuronic acid conjugates of mono-, di- and trihydroxylated analogues were detected; and (4) no sulfonic acid conjugated metabolites were observed in this study of ibutamoren.

CONCLUSIONS

The reported data help in the speedy detection of the growth hormone secretagogue ibutamoren and reveal its illegal use in competitive sports.

Development and validation of liquid chromatography-tandem mass spectrometry method for screening six selective androgen receptor modulators in dietary supplements

Selective androgen receptor modulators (SARMs) are compounds with specific androgenic properties that have been investigated for the treatment of conditions such as muscle wasting disease. The reported androgenic properties have resulted in their use by athletes, and consequently they have been on the World Anti-Doping Agency prohibited list for more than a decade. To minimise the chance of an unattended positive doping test and to avoid potential serious health problems, adequate screening methods for the detection of a wide range of SARMs in these supplements is necessary. In this study, a rapid and accurate liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated simultaneously to screen and quantify six SARMs in dietary supplements, with confirmation by liquid chromatography-quadrupole-time of flight mass spectrometry (LC-Q-TOF/MS). The validated method was applied to 60 dietary supplements obtained by on-line and direct purchase from international vendors in 2020. Various SARMs were detected at high concentrations in 20 products which were advertised as having androgenic properties. For example, andarine was present at 7.2% in one product, and GW501516 was found at 3.49% in the another product. Furthermore, MK-677 and YK-11, not disclosed on the label, were detected in some products. YK-11 is easily hydrolysed in just a few hours. Although YK-11 is particularly unstable, such that the protonated ion [M + H]⁺ at m/z 431 for YK-11 was not detected, mass fragmentation, and a [M+ Na]⁺ ion at m/z 453.3 confirmed the presence of YK-11. Additionally, hydrolysed YK-11 under acidic conditions was confirmed by NMR spectral data, and ¹H NMR and ¹³C NMR spectral data for YK-11 were in good agreement with literature data. This rapid and accurate LC-MS/MS method can therefore be successfully applied to screen and identify SARMs for the continuous control and supervision of dietary supplements.