Apple Polyphenols Improve Intestinal Antioxidant Capacity and Barrier Function by Activating the Nrf2/Keap1 Signaling Pathway in a Pig Model

In recent years, the function of plant polyphenols to improve the intestinal barrier has been fully demonstrated. However, the exact mechanisms linking plant polyphenols with the intestinal barrier function have not yet been established. Apple polyphenols (APs) are safe and healthy nutrients, which are extracted from apples and their byproducts. Using pig and IPEC-J2 cell models, this study investigated the effects of dietary AP supplementation on intestinal antioxidant capacity and barrier function. Then, we further explored the role of the Nrf2/Keap1 signaling pathway in maintaining intestinal antioxidant capacity and barrier function. Our study found that dietary AP supplementation improved the intestinal mechanical barrier by promoting the intestinal morphology and intestinal tight junction protein expression, improved the intestinal immune barrier by increasing intestinal secretory immunoglobulin A production, and improved the intestinal biological barrier by increasing probiotics and decreasing the Escherichia coli population. Further research found that dietary AP supplementation increased the intestinal antioxidant capacity and activated the Nrf2/Keap1 signaling pathway. Finally, after treatment with Nrf2-specific inhibitor ML-385, the upregulation effect of APs on antioxidant capacity and tight junction protein expression was reduced in IPEC-J2 cells. Our results suggested that APs promoted intestinal antioxidant capacity and barrier function via the Nrf2/Keap1 signaling pathway.