Title:Metabolic Pathway of Osilodrostat in Equine Urine Established through High-resolution Mass Spectrometric Characterization for Doping Control
Volume: 25
Issue: 7
Author(s): Hideaki Ishii*, Ryo Shigematsu, Shunsuke Takemoto, Yuhiro Ishikawa, Fumiaki Mizobe, Motoi Nomura, Daisuke Arima, Hirokazu Kunii, Reiko Yuasa, Takashi Yamanaka, Sohei Tanabe, Shun-ichi Nagata, Masayuki Yamada and Gary Ngai-Wa Leung
Affiliation:
- Drug Analysis Department, Laboratory of Racing Chemistry, 1731-2 Tsuruta-machi, Utsunomiya, Tochigi, 320-0851, Japan
- Department of Pharmaceutical Sciences, Tohoku University Hospital, 1-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi, 980-8574, Japan
Keywords:
Osilodrostat, anabolic, doping control, equine, metabolism study, cushing's disease, metabolic pathway.
Abstract:
Objective: Osilodrostat, used to treat Cushing's disease, exhibits an anabolic effect, leading to its
classification as a prohibited substance in horseracing and equestrian sports. This study reports the characterization
of osilodrostat metabolites in horse urine and elucidates its metabolic pathways for the first time for
doping control purposes.
Methods: Osilodrostat was administered nasoesophageally to four thoroughbreds (one gelding and three
mares) at a dose of 50 mg each. Potential metabolites were extensively screened via our developed generic
approach employing differential analysis to identify metabolites. Specifically, high-resolution mass spectral
data were compared between pre- and post-administration samples on the basis of criteria of fold-changes of
peak areas and their P values. Potential metabolite candidates were further identified through mass spectral
interpretations using product ion scan data.
Results: A total of 37 metabolites were identified after comprehensive analysis. Osilodrostat was predominantly
metabolized into a mono-hydroxylated form M1c (~40%) alongside osilodrostat glucuronide M2
(~17%). Given their longest detection time (2 weeks after administration) and the identification of several
conjugates of osilodrostat and M1c, including a novel conjugate of riburonic acid, we recommend monitoring
both osilodrostat and M1c after hydrolysis during the screening stage. However, only osilodrostat can be used
for confirmation because of the availability of a reference material.
Conclusion: It is advisable to screen for both osilodrostat and its mono-hydroxylated metabolite M1c to effectively
monitor horse urine for the potential misuse or abuse of osilodrostat. For suspicious samples, confirmation
of osilodrostat using its reference material is required.
