Identification and characterization of human UDP-glucuronosyltransferases responsible for xanthotoxol glucuronidation

Abstract1. Xanthotoxol is a furanocoumarin that possesses many pharmacological activities and in this study its in vitro glucuronidation was studied.2. Xanthotoxol can be rapidly metabolized to a mono-glucuronide in both human intestine microsomes (HIM) and human liver microsomes (HLM); the structure of the metabolite was confirmed by NMR spectroscopy.3. Reaction phenotyping with 12 commercial recombinant human UGTs, as well as with the Helsinki laboratory UGT1A10 that carry a C-terminal His-tag (UGT1A10-H), revealed that UGT1A10-H catalyzes xanthotoxol glucuronidation at the highest rate, followed by UGT1A8. The other enzymes, namely UGT1A3, UGT1A1, UGT1A6, UGT1A10 (commercial), and UGT2B7 displayed moderate-to-low reaction rates.4. In kinetic analyses, HIM exhibited much higher affinity for xanthotoxol, along with high Vmax and mild substrate inhibition, whereas the kinetics in HLM was biphasic. UGT1A1 (high Km value), UGT1A10-H (low Km value), and UGT1A8 exhibited mild substrate inhibition.5. Consideri...