Abstract

The dietary polyphenol trans-resveratrol (3,5,4′-trihydroxy-trans-stilbene) is glucuronidated at the 3 and 4′ positions to yield two major glucuronide conjugates, resveratrol-3-O-glucuronide (R3G) and resveratrol-4′-O-glucuronide (R4′G). The major enzymes catalyzing this conjugation reaction are members of the UDP-glucuronosyl transferase (UGT) 1A family and include UGT1A1 and UGT1A9, with minor contributions by UGT1A10. The kinetics of resveratrol glucuronidation in these three UGT1A isoforms as well as in human liver and intestinal microsomes were characterized across a wide concentration range. Atypical kinetics were observed for resveratrol glucuronidation in all the protein sources studied. The V_max estimate per total protein for both glucuronides was higher in human intestinal microsomes compared with human liver microsomes (12.2 ± 0.34 versus 7.4 ± 0.25 nmol/min/mg for R3G and 8.9 ± 0.14 versus 0.45 ± 0.01 nmol/min/mg for R4′G). The kinetic profile for formation of R3G in both human liver and intestinal microsomes fits a substrate inhibition model, whereas that for R4′G exhibited a biphasic kinetic profile in human liver microsomes and substrate inhibition in human intestinal microsomes. In recombinant human UGT supersomes, for both glucuronides, UGT1A9 exhibited higher activity than UGT1A1, whereas the lowest activity was observed with UGT1A10. The kinetic profile for R3G exhibited substrate inhibition for all three isoforms, whereas that for R4′G differed, exhibiting substrate inhibition for UGT1A1 and UGT1A10 and Hill kinetics for UGT1A9. These results suggest that in vitro kinetics of resveratrol glucuronidation at high concentrations cannot be ignored in predicting in vivo clearance upon high-dose consumption of resveratrol.