Improving the predictivity of human maximum plasma concentrations for soybean isoflavones and glucosides using an improved culture method of human induced pluripotent stem cell–derived small intestinal epithelial cells

Accurately predicting human exposure to food-related compounds is crucial for evaluating their health effects without conducting animal testing. We previously reported an in vitro method using human induced pluripotent stem cell-derived small intestinal epithelial cells (hiSIECs) for predicting human maximum plasma concentrations (C max ) of food-related compounds. However, the C max predictivity of flavonoids and their glycosides is relatively low, potentially due to complex gastrointestinal absorption processes. This study aimed to assess whether hiSIECs cultured using with a modified culture method (mod-hiSIECs) can mimic human intestinal absorption and enhance C max predictivity. Consistent with observations in the human intestine, the mod-hiSIECs formed a column-like morphology. The expression levels of key saccharide-related genes, such as sucrase-isomaltase, lactase, and cytosolic β-glucosidase, and disaccharidase and glycosidase activities similar to those of human primary enterocytes were obtained using mod-hiSIECs when compared with hiSIECs cultured using the conventional culture method (conv-hiSIECs) and Caco-2 cells. In addition, the mod-hiSIECs accurately mimicked the intestinal glucosidase, glucuronidase, and sulfatase activities against daidzein, genistein, and their corresponding glucosides. The C max predictability for flavonoid aglycones and their glucosides was significantly improved with mod-hiSIECs compared to conv-hiSIECs, reducing the fold-difference from 2.3–9.0 to 0.46–5.5. The mod-hiSIECs could be a useful tool for predicting gastrointestinal absorption of flavonoids in humans.