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 piceatannol 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 microm and 3.8 +/- 1.3 microl/mg protein per min, respectively, for M1 and 233 +/- 61.4 microm and 19.8 +/- 9.5 microl/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 microm 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 in the human liver, which must be taken into account in humans after dietary intake of piceatannol.