Abstract
Ferulic acid (FA) is an abundant dietary antioxidant of the series of hydroxycinnamates which may offer beneficial effects against cancer, cardiovascular disease, diabetes, osteoarthritis and Alzheimer's disease. In this study, evidence for sulfation and glucuronidation of FA was investigated upon incubation with human liver microsomes and cytosol. Two main glucuronides, M1 (ether O-glucuronide) and M2 (ester acylglucuronide), were formed with a similar affinity (apparent Km 3.53 and 5.15 mM, respectively). A phenol sulfoconjugate was also formed with a higher affinity (Km 0.53 mM). Identification of UDP-glucuronosyltransferases (UGT) isoforms involved in FA glucuronidation was investigated with 12 human recombinant enzymes. FA was mainly glucuronidated by UGT1A isoforms and by UGT2B7. UGT1A4, 2B4, 2B15 and 2B17 failed to glucuronidate the substance. Kinetic constants examination revealed that FA was mainly glucuronidated by UGT1A1 on the two nucleophilic groups. UGT1A3 was able to glucuronidate the two positions with the same, but low efficiency. UGT1A6, 1A8 were strictly involved in the formation of the ether glucuronide, whereas UGT1A7, 1A10 and 2B7 preferentially glucuronidated on the carboxyl group. Moreover, octyl gallate, a marker substrate of UGT1A1 competitively inhibited FA glucuronidation mediated by this isoform. Altogether, the results suggest that FA glucuronidation is primarily mediated by UGT1A1.
