*4.8. Evaluation of Caco-2 Monolayer Permeability*

Monolayers of Caco-2 differentiated cells were incubated for 24 h in the presence or absence of POE (15 μg GAE/mL). Resistance measurement was performed by TEER. Cells were incubated at 37 ◦C and 5% CO2 for the duration of the experiment. TEER was measured using an EVOM with a chopstick electrode (Millicell ERS-2, EMD Millipore, Billerica, MA, USA). The electrode was immersed at a 90◦ angle with one tip in the basolateral chamber and the other in the apical chamber. Care was taken to avoid electrode contact with the monolayer and triplicate measurements were recorded for each monolayer. An insert without cells was used as a blank and its mean resistance was subtracted from all samples. TEER measurements were registered hourly for 24 h. Results are reported as TEER % versus time [39].
