Metabolic study of GW1516 in equine urine using liquid chromatography/electrospray ionization Q-Exactive high-resolution mass spectrometry for doping control.

Rationale: The use of GW1516, a peroxisome proliferator-activated receptor δ (PPAR δ) agonist, is strictly prohibited in both horseracing and equestrian competitions. However, little is known about its metabolic fate in horses. To the best of our knowledge, this is the first reported metabolic study of GW1516 in equine urine.

Methods: Urine samples obtained from a thoroughbred after nasoesophageal administration with GW1516 were protein-precipitated and the supernatants were subsequently analyzed by liquid chromatography/electrospray ionization high-resolution mass spectrometry (LC/ESI-HRMS) with a Q-Exactive mass spectrometer. Monoisotopic ions of GW1516 and its metabolites were monitored from the full-scan mass spectral data of pre- and post-administration samples. A quantification method was developed and validated to establish the excretion profiles of GW1516, its sulfoxide, and its sulfone in equine urine.

Results: GW1516 and its nine metabolites [including GW1516 sulfoxide, GW1516 sulfone, 5-(hydroxymethyl)-4-methyl-2-(4-trifluoromethylphenyl)thiazole (HMTT), methyl 4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazole-5-carboxylate (MMTC), 4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazole-5-carboxylic acid (MTTC), and M1 to M4] were detected in post-administration urine samples. GW1516 sulfoxide and GW1516 sulfone showed the longest detection times in post-administration urine samples and were therefore recommended as potential screening targets for doping control purposes. Quantitative analysis was also conducted to establish the excretion profiles of GW1516 sulfoxide and GW1516 sulfone in urine.

Conclusions: For the purposes of doping control of GW1516, the GW1516 sulfoxide and GW1516 sulfone metabolites are recommended as the target analytes to be monitored in equine urine due to their high specificities, long detection times (1 and 4 weeks, respectively), and the ready availability of their reference materials.