title: Characterization of hepatic and intestinal glucuronidation of magnolol: application of the relative activity factor approach to decipher the contributions of multiple UDP-glucuronosyltransferase isoforms.
abstract: Magnolol is a food additive that is often found in mints and gums. Human exposure to this compound can reach a high dose; thus, characterization of magnolol disposition in humans is very important. Previous studies indicated that magnolol can undergo extensive glucuronidation in humans in vivo. In this study, in vitro assays were used to characterize the glucuronidation pathway in human liver and intestine. Assays with recombinant human UDP-glucuronosyltransferase enzymes (UGTs) revealed that multiple UGT isoforms were involved in magnolol glucuronidation, including UGT1A1, -1A3, -1A7, -1A8, -1A9, -1A10, and -2B7. Magnolol glucuronidation by human liver microsomes (HLM), human intestine microsomes (HIM), and most recombinant UGTs exhibited strong substrate inhibition kinetics. The degree of substrate inhibition was relatively low in the case of UGT1A10, whereas the reaction catalyzed by UGT1A9 followed biphasic kinetics. Chemical inhibition studies and the relative activity factor (RAF) approach were used to identify the individual UGTs that played important roles in magnolol glucuronidation in HLM and HIM. The results indicate that UGT2B7 is mainly responsible for the reaction in HLM, whereas UGT2B7 and UGT1A10 are significant contributors in HIM. In summary, the current study clarifies the glucuronidation pathway of magnolol and demonstrates that the RAF approach can be used as an efficient method for deciphering the roles of individual UGTs in a given glucuronidation pathway in the native tissue that is catalyzed by multiple isoforms with variable and atypical kinetics.
authors.affiliation: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Rd., Dalian, 116023 China.
authors.forename: Liangliang
authors.initials: L
authors.lastname: Zhu
authors.forename: Guangbo
authors.initials: G
authors.lastname: Ge
authors.forename: Hongbo
authors.initials: H
authors.lastname: Zhang
authors.forename: Huixin
authors.initials: H
authors.lastname: Liu
authors.forename: Guiyuan
authors.initials: G
authors.lastname: He
authors.forename: Sicheng
authors.initials: S
authors.lastname: Liang
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Zhongze
authors.initials: Z
authors.lastname: Fang
authors.forename: Peipei
authors.initials: P
authors.lastname: Dong
authors.forename: Moshe
authors.initials: M
authors.lastname: Finel
authors.forename: Ling
authors.initials: L
authors.lastname: Yang
mesh_terms: D001713:Biphenyl Compounds / Q000378:metabolism / Q000493:pharmacokinetics*; D020719:Glucuronides / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D017705:Lignans / Q000378:metabolism / Q000493:pharmacokinetics*; D008099:Liver / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism; D020033:Protein Isoforms; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D001713:Biphenyl Compounds; D020719:Glucuronides; D017705:Lignans; D020033:Protein Isoforms; D011994:Recombinant Proteins; C005498:magnolol; D014453:Glucuronosyltransferase