Abstract
Isoneochamaejasmin A (INCA), a biflavonoid, is one of main active ingredients in the dried root of Stellera chamaejasme L., a widely used traditional Chinese medicine. In the present study, we identified the glucuronidation metabolite of INCA and characterized the UDP glucuronosyltransferases (UGTs) responsible for INCA glucuronidation. 7-O-glucuronide (M1) and 4′-O-glucuronide (M2) were identified by incubation of INCA with human liver microsomes (HLMs) in the presence of UDP glucuronic acid, and their structures were confirmed by high-resolution mass spectrometry and nuclear magnetic resonance analyses. Although INCA is a single enantiomer molecule, its M1 metabolite showed two equal-size peaks on a πNAP stationary phase but only one peak on a C18 stationary phase, indicating that the 7-/7′′- and 4′-/4′′′-hydroxyl groups of INCA were in different spatial configurations relative to each other. Among the recombinant human UGT isoform test and correlation analysis, UGT1A1, UGT1A3, and UGT1A9 were found to mediate M1 formation, whereas only UGT1A3 mediated M2 formation. Kinetic studies showed obvious species differences between human, mouse, rat, dog, and pig liver microsomes. UGT1A1, HLMs, and human intestinal microsomes, but not human kidney microsomes, exhibited substrate inhibition for the formation of M1. UGT1A1-mediated formation of M1 showed a 6- and 11-fold higher Vmax than did UGT1A3- and UGT1A9-mediated formation of M1, respectively. The results of the relative activity factor assay showed that UGT1A1 contributed approximately 75% in the formation of M1. These findings collectively indicate that UGT1A1 is the major enzyme in the formation of M1, whereas UGT1A3 is the major enzyme in the formation of M2.
Footnotes
- Received November 14, 2013.
- Accepted January 22, 2014.
L.Y. and J.P. contributed equally to this work.
This research was supported by the Natural Science Foundation of China [Grants 81230080, 81102500, and 81172983]; National Major Projects of China [Grants 2011CB710800 and 2012ZX09506001-004]; and the Zhejiang Natural Science Foundation [LH12H31007].
- Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|