In vitro and in vivo metabolism of the soy isoflavone glycitein.

Glycitein (GLY) is a major isoflavone of soy germ which is used as a functional ingredient to enrich foods with isoflavones as well as a component of soy supplements. Since data on the metabolism of GLY are incomplete, the in vitro phase I metabolism of GLY using rat liver microsomes, human liver microsomes (HLM), as well as human fecal flora was investigated. Furthermore, the in vivo metabolism has been studied after administration of GLY to Sprague-Dawley rats. The identification of the formed metabolites has been elucidated using HPLC/DAD, HPLC/API-ES MS, GC/MS, as well as reference compounds. With respect to the phase I metabolism, GLY has been converted to ten metabolites by liver microsomes of Aroclor-induced Wistar rats with 8-hydroxy(OH)-GLY as the main metabolite. HLM converted GLY to six metabolites with 8-OH-GLY and 6-OH-daidzein (DAI) being the major products. No sex-related differences were observed in each system. Intestinal metabolism of GLY led to four metabolites with 6-OH-DAI as the main product. The in vivo metabolism in rat urine after single-dose administration of GLY resulted in the identification of three oxidative and two bacterial metabolites as well as the demethylation product 6-OH-DAI as the main metabolite.