UBC Theses and Dissertations

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UBC Theses and Dissertations

The role of beta-glucuronidase in enterohepatic recycling and prostate cancer progression Haefling, Brandon Robert


Phase II metabolism regulates endo- and xenobiotic levels through compound inactivation and elimination. The major phase II drug metabolizing enzyme family, UDP-glucuronosyltransferases (UGTs), conjugate a broad variety of substrates through glucuronidation. Historically, drug metabolism research focused extensively on UGT activity and compound elimination, with minimal comparative data investigating beta-glucuronidase (βG) catalyzing the reverse recycling reaction. Despite this, available research shows βG activity is upregulated in a variety of clinically relevant conditions including human immunodeficiency virus (HIV) and cancer. The purpose of this thesis is to characterize βG expression and activity in health and disease, providing novel insights into the role of recycling in chemical homeostasis in the body. In Chapter 2, the first comprehensive profile showing differential βG expression and activity across 14 distinct human tissues was developed. Greatest enzyme activity was observed in prostate, caecum, liver and adrenal, with intestinal tissues showing closest UGT:βG activity at pH 7.4 suggesting further investigation into the recycling role in the gut. Measuring E. coli and human βG at each respective optimal pH revealed that bacterial strains showed enzyme activity comparable or greater to that in human. However, human βG activity increased 13-fold from pH 7.4 to pH 5.4 (native lysosomal pH), suggesting that more acidic environments favour the human enzyme. These findings demonstrate that enterohepatic recycling is likely due to a combination of both bacterial and human βG. In Chapter 3, the role of βG in prostate cancer was assessed. Upregulated βG activity was related to disease progression, with greatest activity reported in PC3 cells and adenocarcinoma tissue. In androgen-sensitive models, elevated enzyme activity suggests a role for βG in locally recycling androgens whereas the recycling of other endobiotics may stimulate cancer growth in androgen-insensitive models. Total UGT activity was greatest in PNT1A cells and adenocarcinoma tissue, with UGT2B17 more commonly expressed in prostate cell lines and UGT2B15 in prostate tissues. Overall, βG is upregulated in androgen-sensitive and androgen-insensitive models and may represent a novel prostate cancer biomarker and/or therapeutic target.

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