In vitro phase I metabolism of selective estrogen receptor modulators in horse using ultra-high performance liquid chromatography-high resolution mass spectrometry.

The research explores the in vitro phase I metabolism of selective estrogen receptor modulators (SERMs) in horses, to identify possible detection targets for doping control in equine sports. It utilizes ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) for this purpose.

About Selective Estrogen Receptor Modulators (SERMs)

• SERMs are chemicals exhibiting anti-oestrogenic activities.
• The World Anti-Doping Agency (WADA) in human sports and the International Federation of Horseracing Authorities (IFHA) in horseracing, have banned their use in and out of competition.
• They can be used as performance-enhancing drugs to increase androgen levels or to counteract the adverse effects resulting from extensive use of androgenic anabolic steroids (AASs).
• There’s a history of SERMs being misused in human sports, a threat which also looms over horseracing.

Results from Analytical Findings

• Several analytical findings, including 42 cases of tamoxifen and 2 cases of toremifene in 2014, have been reported by WADA-accredited laboratories, implicating the usage of SERMs.
• In this research, 13 and 11 in vitro metabolites have been identified for tamoxifen and toremifene, respectively, after incubation with homogenized horse liver, using UHPLC-HRMS.
• N-desmethylation, hydroxylation, and carboxylation have emerged as the more dominant in vitro biotransformation pathways.
• The research also reported, for the first time, some novel metabolites for tamoxifen and toremifene, with hydroxylation occurring at the N-methyl group.

Significance and Novelty of the Study

• This is the first study of in vitro phase I metabolism of tamoxifen and toremifene in horses using homogenized horse liver.
• The findings could serve as potential screening targets for equine sports doping control, thereby helping to better regulate the use of performance-enhancing substances in horseracing.