Phase-II metabolism of androgens and its relevance for doping control analysis

Phase-II metabolism has a major contribution to androgen metabolism, converting the highly non-polar compounds to a more easily excreted form prior to their excretion in urine. In the human body the main phase-II metabolic reactions are glucuronidation and sulphonation. These reactions are catalysed by enzymes, which are categorised into families and further subfamilies based on their function and similarities of their amino-acid sequences. Due to inter-individual variation of the metabolising enzymes and their activities, the metabolic patterns of prohibited substances should be estimated for efficient doping control. In addition to target analytes the phase-II reactions have an effect on the selection of sample preparation procedure, chromatographic technique and ionisation method of the analysis routine. For method development and identification purposes adequate reference material is required, and to replace the laborious in vivo excretion studies, in vitro methodologies have been implemented to produce intact phase-II metabolites of androgens.