Transport of wheat gluten exorphins A5 and C5 through an in vitro model of intestinal epithelium

The gluten exorphins (GEs) A5 and C5 are peptides with a potential opioid-like activity derived from enzymatic degradation of wheat gluten. In this study, a 70% Caco2/30% HT-29 co-culture layer was used as an in vitro model of human small intestine to investigate the transport of the two GEs and their resistance to brush border peptidases. Thirty, 150 or 600 μg of the peptides, GE A5 and GE C5, were added to the apical chamber of the transwells. We previously demonstrated these amounts to be released during in vitro digestion of wheat-derived bread and pasta samples. The solutions in apical and basolateral chambers were analyzed for intact GEs or related fragments by UPLC/HRMS. The two peptides behaved differently since after 120 min higher amount of intact GE A5 (0.55–24.60%) compared to GE C5 (0.20–1.00%) was recovered in the basolateral chamber, depending on the initial dose that was added to the transwell apical compartment. The GE C5 was strongly hydrolyzed by cellular peptidases. The fluxes of two GEs through the in vitro intestinal epithelium were concentration- and time-dependent. The transport inhibitors Wortmannin and Glycyl-sarcosine did not significantly affect the apical-to-basolateral fluxes of the two GEs. Differently, Cytochalasin D slightly increased the transepithelial transport of both GEs, and decreased the TEER values of the co-culture cells. These results suggest the paracellular route as a possible transport mechanism of both GEs. Overall, this study indicates the possibility that food-derived GEs can cross the human intestinal epithelium as intact peptides, and improves the knowledge for exploiting the opioid-like activity potentially associated with the ingestion of wheat-derived foods.