caa a22 4500 445313528 CHVBK 20180317142638.0 cr unu---uuuuu 170323e20110801xx s 000 0 eng 10.1007/s11095-011-0418-5 doi (NATIONALLICENCE)springer-10.1007/s11095-011-0418-5 Regioselective Glucuronidation of Flavonols by Six Human UGT1A Isoforms [Elektronische Daten] [Baojian Wu, Beibei Xu, Ming Hu] ABSTRACT: Purpose: Glucuronidation is a major barrier to flavonoid bioavailability; understanding its regiospecificity and reaction kinetics would greatly enhance our ability to model and predict flavonoid disposition. We aimed to determine the regioselective glucuronidation of four model flavonols using six expressed human UGT1A isoforms (UGT1A1, 1A3, 1A7, 1A8, 1A9, 1A10). Methods: In vitro reaction kinetic profiles of six UGT1A-mediated metabolism of four flavonols (all with 7-OH group) were characterized; kinetic parameters (Km, Vmax and CLint = Vmax/Km) were determined. Results: UGT1A1 and 1A3 regioselectively metabolized the 7-OH group, whereas UGT1A7, 1A8, 1A9 and 1A10 preferred to glucuronidate the 3-OH group. UGT1A1 and 1A9 were the most efficient conjugating enzymes with Km values of ≤1μM and relative catalytic efficiency ratios of ≥5.5. Glucuronidation by UGT1As displayed surprisingly strong substrate inhibition. In particular, Ksi values (substrate inhibition constant) were less than 5.4μM for UGT1A1-mediated metabolism. Conclusion: UGT1A isoforms displayed distinct positional preferences between 3-OH and 7-OH of flavonols. Differentiated kinetic properties between 3-O- and 7-O- glucuronidation suggested that (at least) two distinct binding modes within the catalytic domain were possible. The existence of multiple binding modes should provide better "expert” knowledge to model and predict UGT1A-mediated glucuronidation. Springer Science+Business Media, LLC, 2011 flavonols nationallicence glucuronidation nationallicence regioselectivity nationallicence substrate inhibition nationallicence UGTs nationallicence DHF : dihydroxyflavone nationallicence MS : mass spectroscopy nationallicence NMR : nuclear magnetic resonance nationallicence QHF : tetrahydroxyflavone nationallicence QSAR : quantitative structure activity relationship nationallicence SN2 : bimolecular nucleophilic substitution nationallicence THF : trihydroxyflavone nationallicence UDPGA : uridine diphosphoglucuronic acid nationallicence UGTs : UDP-glucuronosyltransferases nationallicence UPLC : ultra performance liquid chromatography nationallicence Wu Baojian Department of Pharmacological and Pharmaceutical Sciences College of Pharmacy, University of Houston, 1441 Moursund Street, 77030, Houston, Texas, USA aut Xu Beibei Department of Pharmacological and Pharmaceutical Sciences College of Pharmacy, University of Houston, 1441 Moursund Street, 77030, Houston, Texas, USA aut Hu Ming Department of Pharmacological and Pharmaceutical Sciences College of Pharmacy, University of Houston, 1441 Moursund Street, 77030, Houston, Texas, USA aut Pharmaceutical Research Springer US; http://www.springer-ny.com 28/8(2011-08-01), 1905-1918 0724-8741 28:8<1905 2011 28 11095 https://doi.org/10.1007/s11095-011-0418-5 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11095-011-0418-5 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Wu Baojian Department of Pharmacological and Pharmaceutical Sciences College of Pharmacy, University of Houston, 1441 Moursund Street, 77030, Houston, Texas, USA aut NATIONALLICENCE 700 1- Xu Beibei Department of Pharmacological and Pharmaceutical Sciences College of Pharmacy, University of Houston, 1441 Moursund Street, 77030, Houston, Texas, USA aut NATIONALLICENCE 700 1- Hu Ming Department of Pharmacological and Pharmaceutical Sciences College of Pharmacy, University of Houston, 1441 Moursund Street, 77030, Houston, Texas, USA aut NATIONALLICENCE 773 0- Pharmaceutical Research Springer US; http://www.springer-ny.com 28/8(2011-08-01), 1905-1918 0724-8741 28:8<1905 2011 28 11095 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer