Metabolic studies of HIF stabilizers IOX2, IOX3, and IOX4 (in vitro) for doping control.

Abstract

The transcriptional activator HIF (hypoxia-inducible factor) is a vital arbitrator in the performance of cellular responses lacking oxygen supply in aerobic organisms. Since these compounds are capable of enhancing the organism s capacity for molecular oxygen transport, they possess great potential for abuse as a performance-enhancing agent in sports. A comprehensive study of the metabolic conversion of the most popular HIF stabilizers such as IOX2, IOX3, and IOX4 using equine liver microsomes (in vitro) is reported. The parents and their metabolites were identified and characterised by liquid chromatography-mass spectrometry in negative ionisation mode using a QExactive high-resolution mass spectrometer. Under the current experimental condition, a total of ten metabolites for IOX2 (three phase I and seven phase II), nine metabolites for IOX3 (four phase I and five phase II), and five metabolites for IOX4 (three phase I and two phase II) were detected. The outcome of the present study is as follows: (1) All the three IOX candidates are prone to oxidation, results in subsequent monohydroxylated, and some dihydroxylated metabolites. (2) Besides oxidation, there is a possibility of hydrolysis and de-alkylation, which results in corresponding carboxylic acid, and amide respectively. (3) The glucuronide and sulfate conjugate of the parent drugs as well as the monohydroxylated analogues were observed in this study. The characterised in vitro metabolites can potentially serve as target analytes for doping control analysis.