Glucuronidation of piceatannol by human liver microsomes: major role of UGT1A1, UGT1A8 and UGT1A10

Objectives Piceatannol, a dietary polyphenol present in grapes and wine, is known for its promising anticancer and anti-inflammatory activity. The aim of this study was to analyse the concentration-dependent glucuronidation of piceatamol in vitro. Methods To determine the glucuronidation of piceatannol, experiments were conducted with human liver microsomes as well as using a panel of 12 recombinant UDP-glucuronosyltransferase isoforms. Furthermore, the chemical structures of novel glucuronides were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Key findings Along with piceatannol it was possible to identify three metabolites whose structures were identified by LC-MS/MS as piceatannol monoglucuronides (M1-M3). Formation of M1 and M3 exhibited a pattern of substrate inhibition, with apparent K-i and V-max/K-m values of 103 +/- 26.6 mu M and 3.8 +/- 1.3 mu l/mg protein per min, respectively, for M1 and 233 +/- 61.4 mu M and 19.8 +/- 9.5 mu l/mg protein per min, respectively, for M3. In contrast, formation of metabolite M2 followed classical Michaelis-Menten kinetics, with a K-m of 18.9 +/- 8.1 mu M and a V-max of 0.21 +/- 0.02 nmol/mg protein per min. Incubation in the presence of human recombinant UDP-glucuronosyltransferases (UGTs) demonstrated that M1 was formed nearly equally by UGT1A1 and UGT1A8. M2 was preferentially catalysed by UGT1A10 and to a lesser extent by UGT1A1 and UGT1A8. The formation of M3, however, was mainly catalysed by UGT1A1 and UGT1A8. Conclusions Our results elucidate the importance of piceatannol glucuronidation ill the human liver, which must be taken into account in humans after dietary intake of piceatannol.