Identification and characterization of human UDP-glucuronosyltransferases responsible for the in vitro glucuronidation of ursolic acid

• Published in: Drug metabolism and pharmacokinetics Vol. 31; no. 4; pp. 261 - 268
• Main Authors: Gao, Rui, Liu, Mingyi, Chen, Yu, Xia, Chunhua, Zhang, Hong, Xiong, Yuqing, Huang, Shibo
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.08.2016
• Subjects: Glucuronic Acid - metabolism; Glucuronosyltransferase - genetics; Glucuronosyltransferase - metabolism; Humans; Intestines - enzymology; Metabolism characterization; Metabolism pathway; Microsomes - enzymology; Microsomes, Liver - enzymology; Recombinant Proteins - metabolism; Triterpenes - chemistry; Triterpenes - metabolism; UDP-glucuronosyltransferases; Ursolic Acid; Metabolism pathway; Km; Clint; HIMs; Vmax; DDI; RILD; HLMs; UA; UDP-glucuronosyltransferases; LC-MS/MS; SD; LC-MS; NMR; Metabolism characterization; UGTs; UDPGA; SIM; m/z; Ursolic acid; ESI
• ISSN: 1347-4367; 1880-0920
• DOI: 10.1016/j.dmpk.2015.11.010

This study aims to characterize the glucuronidation kinetics of ursolic acid (UA) in human liver microsomes (HLMs) and intestinal microsomes (HIMs) and identify the main UDP-glucuronosyltransferases (UGTs) involved. In our present study, only one type of UA glucuronide was observed after incubation with HLMs and HIMs respectively and was identified as a UA hydroxyl O-glucuronide. The glucuronidation of UA can be shown in HLMs and HIMs with Km values of 3.29 ± 0.16 and 3.74 ± 0.22 μM and Vmax values of 0.33 ± 0.03 and 0.42 ± 0.03 nmol/min/(mg protein). Among the 12 recombinant UGT enzymes investigated, UGT1A3 and UGT1A4 were identified as the major enzymes catalyzing the glucuronidation of UA [Km values of 2.58 ± 0.12 and 4.66 ± 0.60 μM, Vmax values of 0.72 ± 0.01 and 1.00 ± 0.06 nmol/min/(mg protein)]. The chemical inhibition study showed that the IC50 for hecogenin inhibition of UA glucuronidation was 51.79 ± 4.32 μM in HLMs. And chenodeoxycholic acid inhibited UA glucuronidation in HLMs with an IC50 of 28.26 ± 2.91 μM. In addition, UA glucuronidation in a panel of eight HLM was significantly correlated with telmisartan glucuronidation (r2 = 0.7660, p < 0.01) and trifluoperazine glucuronidation (r2 = 0.5866, p < 0.01) respectively. These findings collectively indicate that UGT1A3 and UGT1A4 were the main enzymes responsible for the glucuronidation of UA in human.