Doping control analysis of GW1516 in equine plasma using liquid chromatography/electrospray ionization Q‐Exactive high‐resolution mass spectrometry

Rationale GW1516 is a peroxisome proliferator‐activated receptor‐δ agonist in the class of hormones and metabolic modulators. The use of GW1516 is banned in both horseracing and equestrian competitions. To the best of our knowledge, this is the first metabolic study of GW1516 in horses. Methods After protein precipitation of pre‐ and post‐administration plasma GW1516 samples, the supernatants were analyzed using liquid chromatography/electrospray ionization Q‐Exactive high‐resolution mass spectrometry to detect GW1516 and its metabolites. Monoisotopic ions of GW1516 and its metabolites were monitored from the full‐scan mass spectral data of pre‐ and post‐administration samples. Quantification methods were developed and validated to establish the elimination profiles of GW1516, its sulfoxide, and its sulfone in equine plasma. Results GW1516 and its four metabolites GW1516 sulfoxide, GW1516 sulfone, 5‐(hydroxymethyl)‐4‐methyl‐2‐(4‐trifluoromethylphenyl)thiazole (HMTT), and M1 were detected in post‐administration plasma samples. GW1516 sulfoxide, GW1516 sulfone, and HMTT were identified by comparison with their respective reference standards whereas M1 was tentatively identified as 4‐methyl‐2‐[4‐(trifluoromethyl)phenyl]‐1,3‐thiazole‐5‐carboxylic acid by mass spectral interpretation. GW1516 had the longest detection time in post‐administration plasma. The elimination profiles of GW1516, its sulfoxide, and its sulfone in plasma were established. Conclusions For the purpose of doping control, GW1516 is recommended as the target analyte to be monitored in equine plasma due to its long detection time (around 1 week) and the ready availability of its reference material.