Effect of Oral Testosterone on Steroid Metabolome and Discovery of a Potential Serum Biomarker of UGT2B17 Interindividual Variability
Authors: Basit Abdul , Amory John K. , Prasad Bhagwat 
Published: June 2021

Background and objectives

UGT2B17 is a highly variable enzyme, which is responsible for metabolism of drugs and androgens (1–3). Because UGT2B17 variability could not be explained by genetic polymorphism alone, it is important to identify a circulating biomarker of UGT2B17 activity for stratification of patients receiving UGT2B17 substrates such as vorinostat, exemestane and testosterone (T) (1–3). The overarching objective of this study was to identify a potential serum biomarker of UGT2B17 by i) accomplishing metabolomics analysis after oral T dosing, ii) performing an in vitro mechanistic study to compare correlation of steroid glucuronides vs. UGT2B17 protein abundance in T‐treated human hepatocytes.

Methods

A targeted metabolomics study was performed on previously collected samples from an oral T pharmacokinetics (PK) study (800 mg) (4). T and its primary and secondary metabolites in serum were quantified and PK data of these steroids were analyzed using the non‐compartmental method. UGT2B reaction phenotyping was also performed to identify whether UGT2B7, UGT2B15 and/or UGT2B17 metabolize T, androsterone (A) and etiocholanolone (Etio) in recombinant UGT2Bs and human liver microsomes characterized for UGT2B abundance. Additionally, T‐metabolism study was also performed in human hepatocytes for 1 h. The media and cell pellets were collected for subsequent metabolomics and proteomics analyses, respectively. Effect of dutasteride treatment on androgen metabolome was also investigated, both in vivo and in vitro. Potential UGT2B17 biomarker was identified based on correlation of TG or TG/AG vs. UGT2B17 abundance in human hepatocytes and the approach was applied to predict in vivo UGT2B17 variability.

Results

With 800 mg dose, AUC0‐24h of T‐glucuronide (TG), androsterone glucuronide (AG), etiocholanolone glucuronide (EtioG) was 85, 389 and 87‐fold higher in human serum as compared to T AUC0‐24h (nmol.h/L). Similarly, TG and AG were also detected in hepatocyte media, albeit TG levels were 3.7‐fold lower than AG in the media. AG formation rate (i.e., AG/A) was constant in all the four hepatocyte donors, whereas TG/T ratio was highly variable, which strongly correlates with UGT2B17 protein abundance (r2 = 0.93) (Fig 1A). The correlation between TG and TG/AG remained strong when 5α‐reductase was inhibited by dutasteride (r2 = 0.90). Consistent to these findings, the superosomes and microsomes reaction phenotyping data also confirmed UGT2B17 as a selective T‐glucuronidation enzyme, with limited AG and EtioG formation activity. This approach when applied to the in vivo data, confirmed high variability in TG/AG ratio consistent with UGT2B17 in vivo expression, which was also reflected by strong correlation (r2= 0.84) between serum TG and TG/AG was also observed (Fig 1C).

Conclusion

TG/AG ratio could be used as a potential serum biomarker of UGT2B17 variability because TG and AG formation is mediated by different UGTs. The approach proposed here could be promising in precision therapy of vorinostat, exemestane and T. Further, the serum biomarker of UGT2B17 variability will be useful in T doping control.

Support or Funding Information

Department of Pharmaceutics, University of Washington, Seattle, WA 98195

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.