Abstract: Objective: To investigate the effect of soluble dietary fiber from defatted rice bran (DRB-SDF) prepared by Trichoderma viride fermentation on glucose absorption and transport in the small intestine and to ascertain its mechanism of action. Methods: Using Caco-2 cells in vitro, glucose absorption and transport in small intestine were simulated and evaluated in the presence of different concentrations of DRB-SDF (2, 4 and 8 mg/mL). Acarbose (25 μg/mL) was served as a positive control and cells without any treatment were used as a normal control. The effect of DRB-SDF on the proliferation and viability of Caco-2 cells was detected by CCK-8 assay. Glucose concentration in the absorption and transport models was determined using a glucose test kit. Alpha-glucosidase activity was determined using an enzyme assay kit. The mRNA expression of α-glucosidase, SGLT-1, GLUT-2 and Na+-K+-ATPase was examined by reverse transcription real-time quantitative polymerase chain reaction (qPCR). Results: The proliferation of Caco-2 cells was not significantly affected when the concentration of DRB-SDF was less than 8 mg/mL. Compared with the normal control, the level of glucose absorption and transport in the DRB-SDF-treated groups was inhibited in a concentration-dependent way. The activity of α-glucosidase in Caco-2 cells was significantly inhibited after treatment with DRB-SDF, and the expression levels of α-glucosidase, SGLT-1, GLUT-2 and Na+-K+-ATPase mRNA were significantly decreased. Conclusion: DRB-SDF can delay the absorption and transport of glucose in the small intestine possibly by inhibiting α-glucosidase activity, decreasing the expression of glucose transporter proteins such as SGLT-1, GLUT-2 and Na+-K+-ATPase in intestinal epithelial cells, inhibiting carbohydrate hydrolysis, and occupying glucose absorption sites, and ultimately reducing postprandial hyperglycemia.

Key words: defatted rice bran, microbial fermentation, soluble dietary fiber, reverse transcription real-time quantitative polymerase chain reaction, Caco-2 cells, glucose absorption and transport