Comparison of bioavailability of quercetin and its structural analogs in mice.

Flavonoids are thought to provide beneficial effects on health. However, there are still uncertainties regarding their bioavailability. In this study, we investigated the bioavailability of 6 flavonoids, galangin, kaempferol, quercetin, myricetin, fisetin, and luteolin, by oral administration to mice. Analysis of plasma concentrations of free flavonoids after deconjugation by LC-MS/MS revealed that all flavonoids were rapidly absorbed after administration. Among 6 flavonoids, kaempferol and fisetin showed high absorbed amounts in blood plasma. With the LogP value of the two flavonoids as the maximum value, the amount absorbed decreased for both lower and higher LogP values. The results of the tissue distribution of galangin, kaempferol, and quercetin suggested that the order of fastest movement from the stomach to the small intestine was kaempferol > quercetin > galangin. In addition, the amount of kaempferol and quercetin distributed in the liver was greater than that of galangin. These results suggest that the bioavailability of flavonoids varies with the slight structural differences, possibly due to differences in their rapid accessibility to the small intestine that is the primary site of absorption and metabolism within the body.