The Human UDP-Glucuronosyltransferase UGT2A1 and UGT2A2 Enzymes Are Highly Active in Bile Acid Glucuronidation

Abstract

Bile acids (BA) are essential modulators of lipid, glucose, and cholesterol homeostasis, but they exert cytotoxic effects in the cholestatic liver. Glucuronidation, catalyzed by the UDP-glucuronosyltransferase (UGT) enzymes is a pharmacologically relevant BA detoxification process. The present study characterized the BA-conjugating activity of the little-studied human UGTs of subfamily 2A: UGT2A1, 2A2, and 2A3. Recombinant UGT2As, expressed in baculovirus-infected insect cells, were assayed for the glucuronidation of six major bile acids: chenodeoxycholic acid (CDCA), cholic acid (CA), lithocholic acid (LCA), deoxycholic acid (DCA), hyocholic acid (HCA) and hyodeoxycholic acid (HDCA). UGT2A3 exhibited detectable but very low activity with all the tested BA substrates. UGT2A1 was highly efficient in forming LCA-3 and LCA-24G, CDCA-24, DCA-24, HCA-24, and HDCA-24G, whereas UGT2A2 was the most active enzyme for CA-24G and CDCA-24G formation and also was able to generate HDCA-6G, HDCA-24G, LCA-24G, and HCA-24G. The K m values of UGT2A1 varied between 102.2 6 14.3 mM and 2.4 6 1.2 mM. With the exception of CA-24G, a low affinity substrate for UGT2A2, all the K m values for UGT2A2 were in the 100 to 400 mM range. We demonstrate the high reactivity of the human UGT2A1 and UGT2A2 for bile acid glucuronidation. The physiologic importance of these reactions to BA disposition remains, however, to be clarified in vivo.

Nicotine regulates the expression of UDP-glucuronosyltransferase (UGT) in humanized UGT1 mouse brain

“…CDCA glucuronide was quantified using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) [14–16]. The sample of enzyme assay was moved to a vial and 10 μL was separated on a 50 mm × 2.1 mm Acquity 1.6 μ m C18 column (Waters Corp, MA, USA) using an Acquity UPLC H-Class system (Waters).…”

Expression of hepatic cytochrome P450s and UDP-glucuronosyltransferases in PXR and CAR double humanized mice treated with rifampicin

“…Four UGT assays were performed using b-estradiol, serotonin, mefenamic acid, and chenodeoxycholic acid as probe substrates for the UGT1a1, UGT1a6, UGT1a9, and UGT2a3 isoforms, respectively (Zhu et al, 1996;Krishnaswamy et al, 2003;Perreault et al, 2013).…”

Upregulation of UGT2B4 Expression by 3′-Phosphoadenosine-5′-Phosphosulfate Synthase Knockdown: Implications for Coordinated Control of Bile Acid Conjugation

“…In this regard, several genes involved in BA conjugation were significantly regulated by PAPSS knockdown (Supplemental Table 2). For example, UGT2A1, which also catalyzes BA conjugation (Perreault et al, 2013), was upregulated 6.95-fold by PAPSS knockdown. Also, CYP3A5 and CYP3A7 were upregulated (;3-fold).…”