Changes of metabolic profiles in urine after oral administration of quercetin in rats

Quercetin has been studied extensively. However, its actions in vivo are not well understood. We investigated the overall metabolic changes in urine after oral quercetin administration in rats and try to provide useful information on the actions of quercetin in vivo. Rats were orally administered a single dose of quercetin aglycon (40 mg/kg body weight). Urine samples were collected and subjected to 1H nuclear magnetic resonance (NMR)-based metabolomic analysis and high performance liquid chromatography–mass spectrometry (HPLC–MS). Significant changes of metabolic profiles were observed in urine after quercetin administration. Relative increase in the concentrations of choline, creatinine, dimethylglycine, hippurate, taurine, trimethylamine N-oxide and reduction in acetate, alanine, lactate were observed. The concentrations of citrate, 2-oxoglutarate and succinate increased in the 0–24 h period after treatment and decreased thereafter. Some peaks assignable to quercetin metabolites were found in the aromatic regions of 1H NMR spectra. HPLC–MS analysis identified quercetin, methyl quercetin, quercetin sulfate, quercetin monoglucuronide, and methyl quercetin monoglucuronide in urine after administration of quercetin. Our current findings indicate that quercetin behaves not only as an antioxidant, but also a modulator for some metabolic processes in vivo. The active forms of quercetin present in the biofluids must be investigated further.