Ca2+ enhances the activity of prodelphinidin B digallate in lowering postprandial hyperglycemia via regulating the mucus layer

Introduction Phenolic compounds are regarded as promising α-glucosidase inhibitors for regulating postprandial blood glucose, but their α-glucosidase inhibitory activity in vivo is much lower than that in vitro . The small intestinal mucus layer serves as a barrier that impedes the binding of phenolic compounds to α-glucosidase, thereby attenuating their activity in vivo , yet the solution to this bottleneck remains unclear. Objectives Selecting prodelphinidin B digallate (proDB DG) as a representative phenolic compound, this study aimed to enhance its in vivo α-glucosidase inhibitory activity by screening the compound that can pre-regulate the barrier properties of the mucus layer. Methods The Caco-2/HT29-MTX-E12 co-culture model was used to screen the compound that can enhance the α-glucosidase inhibitory activity of proDB DG in vivo . This enhanced mechanism was analyzed using ultraviolet–visible light spectroscopy, zeta potential, rheological behavior, transmission electron microscopy, molecular dynamics simulation and Transwell mucus diffusion model. The improved α-glucosidase inhibitory activity and its biosafety were further confirmed by animal experiments. Moreover, the screened compound and proDB DG based tablets were developed. Results Ca 2+ improved the activity of proDB DG in lowering postprandial hyperglycemia in vivo . This enhancement of activity is attributed to its pre-regulation on the barrier properties of the mucus layer. Specifically, Ca 2+ -derived mucin aggregation increased the porosity and diffusivity of the mucus layer, thereby improving the permeability of proDB DG and facilitating its binding to α‑glucosidase. Ca 2+ also competitively bound with the mucus layer, and weakened the interaction between proDB DG and mucins. Furthermore, Ca 2+ –proDB DG based tablets possessed significant hypoglycemic effect and biosafety in vivo . Conclusion Ca 2+ regulates the barrier properties of the mucus layer, thereby promoting proDB DG to reach the mucosa quickly and then interact with α-glucosidase effectively, which may break the application limitations of proDB DG and even phenolic compounds as α-glucosidase inhibitors clinically.