Establishment of safely and effectively consumption methods of soy isoflavone

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Excessive ingestion of isoflavones may result in endocrine disruption, hence a maximum intake level needs to be established. Soy isoflavones contain isoflavone aglycones, such as genistein, daidzein, and glycitein, and their glygosides, which are considered to have the same intestinal permeability. In this study, we aimed to evaluate in detail the absorption mechanisms of these isoflavones, and examine by comparing the characteristics of absorption. We performed in vitro studies using Caco-2 cells and an artificial membrane permeation assay(PAMPA) with different pH gradients and iso-pH conditions. The permeability coefficients of some isoflavone aglycones were greater in the presence of a proton gradient than its absence. Furthermore, passive and active transports were observed in Caco-2 cells. Evaluation of passive transport by PAMPA suggested that isoflavone aglycones were transported efficiently by passive diffusion. These aglycones have been suggested to have high permeability in the human intestine. Therefore, care should be taken when consuming these compounds. Furthermore, we evaluated the absorption of other flavonoid aglycones in the same manner. A comparison of the permeability characteristics among flavanones using Caco-2 cells and PAMPA as well as consideration of their physicochemical properties, suggested that the flavanones were transported efficiently via passive diffusion according to the pH-partition hypothesis.