Characterization of Human UDP-Glucuronosyltransferases responsible for the in vitro Glucuronidation of Armillarisin A

Armillarisin A, a new coumarin derivative isolated from the fungus Armillariella tabescens (Scop. ex Fr.) Singer, has been used for treatment of acute cholecystitis, infection of biliary system and pancreatitis in China for several years, but its metabolic pathway remains unknown. In the current study, the UDP-glucuronosyltransferase (UGT) conjugation pathway of Armillarisin A was investigated by using human liver microsomes (HLMs) and 12 commercially available recombinant human UGTs. One mono-glucuronide Armillarisin A was identified by liquid chromatography/mass spectrometry (LC/MS), when Armillarisin A was incubated with human liver microsomes in the presence of UDPGA. Assays with the recombinant human UGT isoform(s) revealed that human UGT1A1, UGT1A9, UGT1A7 and UGT2B15 involved in the glucuronidation of Armillarisin A. The Km values of HLM, rUGT1A9, rUGT1A1, rUGT1A7 and rUGT2B15 for the glucuronidation of Armillarisin A were 799.8 ± 51.5, 134.0 ± 17.2, 124.3 ± 4.8, 399.4 ± 37.8 and 420.2 ± 41.5 μM respectively. The intrinsic clearance of rUGT1A9 (48 ul/min/mg protein) is significantly larger than that of other recombinant UGT isoforms. Furthermore, the glucuronidation of Armillarisin A in HLMs (n=11) had the strong correlation (r=0.93, p