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Testosterone and epitestosterone differentially regulate UDP-glucuronosyltransferases (UGT) activity
Ling Xiao1, Juan Qi2, Yuanyuan Zhang2
1School of Resources and Environment, Anqing Normal University, Anqing 246311, China.
None:
Despite being constantly exposed to endogenous substrates, the effects of these substrates on UDP-glucuronosyltransferase (UGT) activity remain poorly understood. This study investigated the effects of testosterone (T) and its 17-epimer epitestosterone (epiT) on UGTs using in vitro and in silico approaches. T competitively inhibited UGT2B7 with Ki values ranging from 11.4 to 30.2 μM, while displaying mixed-type inhibition towards UGT2B15 with a Ki of 7.74 μM. In contrast, epiT showed substantially stronger competitive inhibition against both UGT2B7 and -2B15, with Ki values of 1.06-2.12 μM and 2.75 μM, respectively. Both T and epiT activated UGT2B17 via a two-site kinetic model, with activator binding constants of 8.30 μM (T) and 9.52 μM (epiT). Androgen binding similarly enhanced substrate affinity, but epiT increased the turnover number more (β = 4.01) than T (β = 2.34). Molecular docking revealed that epiT binds more tightly to UGT2B7 and -2B15 (binding energies: -9.1 and -7.51 kcal/mol) than T (-8.4 and -6.98 kcal/mol), owing to additional hydrogen bonds formed by its 17α-hydroxyl group. In summary, this study reveals that a single stereochemical inversion dramatically enhances UGT modulation, positioning epiT as an important endogenous modulator of glucuronidation in androgen-rich tissues.
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