Abstract
It was hypothesized that cis-resveratrol glucuronidation contributes to a greater extent to in-vitro disposition of total resveratrol than previously assumed. To this end, the kinetic data for cis-resveratrol glucuronidation are reported.
Glucuronidation assays were conducted in human liver and intestinal microsomes and in uridine diphosphate-glucuronosyltransferases (UGTs) UGT1A1, UGT1A6, UGT1A9, and UGT1A10. Kinetic parameters were estimated for the major cis-resveratrol-3-O-glucuronide (cis-R3G). Substrate inhibition was observed with apparent Vmax, Km and Ki of 6.1 ± 0.3/27.2 ± 1.2 nmol min−1 mg−1, 415 ± 48.1/989.9 ± 92.8 and 789.6 ± 76.3/1012 ± 55.9 μM in human intestinal microsomes (HIMs) and UGT1A6, respectively (estimate ± standard error (SE)). Biphasic kinetics were observed in human liver microsomes (HLMs), while sigmoidal kinetics were seen in UGT1A9 (Vmax = 11.92 ± 0.2 nmol min−1 mg−1; Km = 360 μM; n = 1.27 ± 0.07). The 4′-O-glucuronide (cis-R4′G) exhibited atypical kinetics in HLM, HIM, UGT1A1, and UGT1A10. UGT1A9 catalysed cis-R4′G formation at high substrate concentrations (Vmax = 0.33 ± 0.015 nmol min−1 mg−1; Km = 537.8 ± 67.8 μM).
In conclusion, although the rates of formation of cis-R3G in HLM and UGT1A9 were higher than those for trans-R3G, the contribution to total resveratrol disposition could not be determined fully due to atypical kinetics observed.
Acknowledgements
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.