Quantitative characterization of UDP-glucuronosyltransferase 2B17 in human liver and intestine and its role in testosterone first-pass metabolism

Abstract

<p class="first" id="P2">Protein abundance and activity of UGT2B17, a highly variable drug- and androgen-metabolizing enzyme, was quantified in microsomes, S9, and primary cells isolated from human liver and intestine by a validated LC-MS/MS methods. UGT2B17 protein abundance showed &gt;160-fold variation (mean ± SD, 1.7 ± 2.7 pmol/mg microsomal protein) in adult human liver microsomes (n=26) and significant correlation (r ²= 0.77, <i>p</i>&lt;0.001) with TG formation. Primary role of UGT2B17 in TG formation compared to UGT2B15 was confirmed by performing the activity assay in UGT2B17 gene deletion samples and with a selective UGT2B17 inhibitor, imatinib. Human intestinal microsomes isolated from small intestine (n=6) showed on average significantly higher protein abundance (7.4 ± 6.6 pmol/mg microsomal protein, <i>p</i>=0.016) compared to liver microsomes, with an increasing trend towards distal segments of gastrointestinal (GI) tract. Commercially available pooled microsomes and S9 fractions confirmed greater abundance and activity of UGT2B17 in intestinal fractions compared to liver fractions. To further investigate the quantitative role of UGT2B17 in testosterone metabolism in whole cell system, a targeted metabolomics study was performed in hepatocytes (n=5), and enterocytes (n=16). TG was the second most abundant metabolite after androstenedione in both cell systems. Reasonable correlation between UGT2B17 abundance and activity were observed enterocytes (r ²=0.69, <i>p</i>=0.003), but not in hepatocytes. These observational and mechanistic data will be useful in developing a physiologically-based pharmacokinetic (PBPK) model for predicting highly-variable first-pass metabolism of testosterone and other UGT2B17 substrates. </p><p id="P3"> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/d0690dd6-54ad-44d8-8eef-7ff5cd910c98/PubMedCentral/image/nihms1503452u1.jpg"/> </div> </p>