Abstract
Glucuronidation is often recognized as one of the rate-determining factors that limit the bioavailability of flavonols. Hence, design and synthesis of more bioavailable flavonols would benefit from the establishment of predictive models of glucuronidation using kinetic parameters [e.g., Km, Vmax, intrinsic clearance (CLint) = Vmax/Km] derived for flavonols. This article aims to construct position (3-OH)-specific comparative molecular field analysis (CoMFA) models to describe UDP-glucuronosyltransferase (UGT) 1A9-mediated glucuronidation of flavonols, which can be used to design poor UGT1A9 substrates. The kinetics of recombinant UGT1A9-mediated 3-O-glucuronidation of 30 flavonols was characterized, and kinetic parameters (Km, Vmax, CLint) were obtained. The observed Km, Vmax, and CLint values of 3-O-glucuronidation ranged from 0.04 to 0.68 μM, 0.04 to 12.95 nmol/mg/min, and 0.06 to 109.60 ml/mg/min, respectively. To model UGT1A9-mediated glucuronidation, 30 flavonols were split into the training (23 compounds) and test (7 compounds) sets. These flavonols were then aligned by mapping the flavonols to specific common feature pharmacophores, which were used to construct CoMFA models of Vmax and CLint, respectively. The derived CoMFA models possessed good internal and external consistency and showed statistical significance and substantive predictive abilities (Vmax model: q2 = 0.738, r2 = 0.976, rpred2 = 0.735; CLint model: q2 = 0.561, r2 = 0.938, rpred2 = 0.630). The contour maps derived from CoMFA modeling clearly indicate structural characteristics associated with rapid or slow 3-O-glucuronidation. In conclusion, the approach of coupling CoMFA analysis with a pharmacophore-based structural alignment is viable for constructing a predictive model for regiospecific glucuronidation rates of flavonols by UGT1A9.
Footnotes
This work was supported by the National Institutes of Health National Institute of General Medical Sciences [Grant GM070737] (to M.H.).
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.175356.
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The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- UGT
- UDP-glucuronosyltransferase
- CoMFA
- comparative molecular field analysis
- UPLC
- ultra performance liquid chromatography
- CLint
- intrinsic clearance
- 2D
- two-dimensional
- 3D
- three-dimensional
- QSAR
- quantitative structure-activity relationship
- HF
- hydroxyflavone
- DHF
- dihydroxyflavone
- THF
- trihydroxyflavone
- QHF
- tetrahydroxyflavone
- RMS
- root mean square.
- Received September 23, 2010.
- Accepted November 4, 2010.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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