The role of A221 in improving the barrier-enhancing property of kale water extract. (a) The intestinal barrier-enhancing property was assessed for each test sample as described in the Methods section using a Caco-2 in vitro model. The Caco-2 cell monolayer was differentiated and treated with test samples on the apical side, and TEER values were recorded at the indicated time intervals. (b) KP and KP3S were administered to Caco-2 cells, and the TEER values were recorded as in the previous experiment. *P < 0.05 vs. Vehicle. **P < 0.01 vs. Vehicle.