Activation of EpRE-mediated gene transcription by quercetin glucuronides depends on their deconjugation.

Quercetin is a flavonoid reported to have health-promoting properties. Due to its extensive metabolism to glucuronides in vivo, questions were raised if studies conducted with quercetin aglycone, stating its health-promoting activity, are of actual relevance. Here we show that glucuronides of quercetin, and its methylated forms isorhamnetin and tamarixetin, can induce EpRE-mediated gene expression up to 5-fold. Furthermore, evidence is presented that EpRE-mediated gene induction by these glucuronides involves their deglucuronidation. This indicates that although quercetin-derived glucuronides are the major metabolites present in the systemic circulation, deglucuronidated derivatives are the active compounds responsible for their beneficial EpRE-mediated gene expression effects.