Identification and quantification of daidzein-7-glucuronide-4′-sulfate, genistein-7-glucuronide-4′-sulfate and genistein-4′,7-diglucuronide as major metabolites in human plasma after administration of kinako

Abstract

Much attention has been paid to the metabolism and disposition of isoflavones daidzein (Dein) and genistein (Gein) with regard to the prevention of several hormone-dependent diseases. Recent studies have reported that several conjugates as well as aglycones may be biologically active or may be activated within target cells. However, the disposition of Dein and Gein in plasma is still uncertain. This paper describes the identification and quantification of the highly polar metabolites, daidzein-7-glucuronide-4′-sulfate (D-7G-4′S), genistein-7-glucuronide-4′-sulfate (G-7G-4′S), daidzein-4′,7-diglucuronide (D-4′,7-diG), and genistein-4′,7-diglucuronide (G-4′,7-diG) in human plasma after dietary administration of kinako (baked soybean powder) to two healthy volunteers. The structure identification of these conjugated metabolites in plasma was performed in comparison to the LC-ESI-MS and 600 MHz ¹H-NMR spectral data of the chemically synthesized compounds. Furthermore, 16 isoflavone metabolites including D-7G-4′S, G-7G-4′S, D-4′,7-diG, and G-4′,7-diG in plasma were simultaneously measured by a high-performance liquid chromatography–UV-diode-array detector method combined with solid-phase extraction using an Oasis HLB cartridge. D-7G-4′S, G-7G-4′S and G-4′,7-diG were found to be major metabolites of Dein and Gein in plasma, while intact aglycones were detected to be only ca. 2% in both subjects. The findings suggest that the conjugated metabolites could be the key compounds responsible for pharmacological and medicinal properties of isoflavones.