Corn protein hydrolysate with glutamine-rich peptides protects intestinal barrier in Caco-2 cells: Insights into structural characteristics of identified glutamine peptides

Intestinal barrier is an important basis for intestinal function, which can strictly control the exchange of substances between the host and the external environment. An intact intestianl barrier is also the guardian of human health. In this study, the protective effect of corn protein hydrolysate with glutamine-rich peptides (APH) on intestinal epithelial cell barrier was evaluated in Caco-2 cell inflammatory damage model induced by lipopolysaccharide (LPS). Then, the sequences of glutamine peptides in APH were identified by Nano LC-MS/MS, and the structural characteristics of the identified glutamine peptides were analyzed. The results showed that the hydrolysate effectively alleviated LPS-induced cell damage and decreased the inflammatory response by down-regulating the levels of pro-inflammatory cytokines (TNF-α, IL-8, and IL-1β) and up-regulating the levels of anti-inflammatory cytokine (IL-10). Moreover, the hydrolysate also up-regulated the gene expression of three tight junction proteins (ZO-1, Occludin, Claudin-1) to maintain the integrity of the intestinal epithelial barrier. More importantly, the hydrolysate protected the intestinal barrier function via down-regulating the key genes expression (TLR4, MyD88, NF-κB) in the NF-κB signaling pathway and inhibiting the overexpression of MLCK gene in the MLCK signaling pathway. Finally, 374 corn glutamine peptides were identified from APH, and their structural characteristics showed that corn glutamine peptides had high affinity with membrane proteins. Taken together, these results indicated that APH has excellent potential to protect intestinal barrier function and can be developed into a functional health food.