A further insight into methyltestosterone metabolism: New evidences fromin vitroandin vivoexperiments

Rationale Although the metabolism of methyltestosterone (MT) has been extensively studied since the 1950s using different techniques, the aim of this study was to investigate the hydroxylation in positions C2, C4 and C6 afterin vitroexperiments andin vivoexcretion studies using gas chromatography time-of-flight (GC/TOF) and gas chromatography/tandem mass spectrometry (GC/MS/MS). The results could be influenced by the mass spectrometric analyser used. Methods Incubations were carried out with human liver microsomes and six enzymes belonging to the cytochrome P450 family using MT as a substrate. The trimethylsilyl derivatives of the samples were analysed using GC/TOF and GC/MS/MS once the correct MS/MS transitions had been selected, mainly for 6-hydroxymethyltestosterone (6-OH-MT) to avoid artefact interferences. A urinary excretion study was then performed after the administration of a 10 mg single oral dose of MT to a volunteer. Results The formation of hydroxylated metabolites of MT in the C6, C4 and C2 positions after bothin vitroandin vivoexperiments was observed. Sample evaluation using GC/TOF showed an interference for 6-OH-MT that could only be resolved in GC/MS/MS by monitoring specific transitions. The transitory detection of these hydroxylated metabolites in urine agrees with previous investigations that had described this metabolic route as being of little significance. Conclusions In doping analysis, the formation of 4-hydroxymethyltestosterone (oxymesterone) from MT cannot be underestimated. Although it is only detected as a minor and short-term excretion metabolite, it cannot be overlooked as it was found in bothin vitroandin vivoexperiments. The use of a combination of different mass spectrometric instruments allowed reliable conclusions to be reached, and it was shown that special attention must be given to artefact formation.