Endocrine Abstracts

The ratio of the glucuronidated epitestosterone (E) and testosterone (T), used in doping tests, is currently under question. The key enzyme involved in E metabolism is UGT2B7 in contrast to T which is mainly metabolised by UGT2B17. Previous results demonstrated that at very high concentrations E acts as a competitive inhibitor to UGT2B17. Similarly, the literature reports competitive inhibition of UGTs by NSAIDS and phenolics that are not substrates of UGT2B17. The aim of this study was to investigate if either T or E glucuronidation is affected by food components (red wine and teas) or by varying ratios of the epimer.

Glucuronidation of T and E was assessed using a novel assay with UGT2B17 supersomes and microsomes pooled separately from males and females. HPLC-UV and LC-MS/MS methods were used to monitor E and T glucuronidation at μg/ml and ng/ml levels. Red wine and tea samples were subjected to HPLC analyses to determine their principal active components (catechins and flavonols) which were assessed for inhibitory activity against UGT2B17 and UGT2B7. The effects of E on T glucuronidation were monitored over the concentration range of 0–200 ng/ml E.

The results show that in supersomes the tea samples and red wine along with their component catechins and flavonols exhibit considerable competitive inhibitory activity against UGT2B17 (e.g. IC₅₀ of 64 μM for epigallocatechin gallate). For both microsome and supersome based studies, at 50 ng/ml T, an increase in E resulted in an inhibition of T glucuronidation by up 30% (at T:E 0.5). The use of microsomes also showed variation of testosterone metabolism between males and females as well as varying inhibition levels of T glucuronidation by E. These results highlight the effect of common foods, their components and epitestosterone on testosterone metabolism at physiological concentrations. These results warrant further studies including in vivo investigations.