Phytogenic Substances in a Model for Intestinal Barrier Function after Tight Junction Disruption

For humans and animals alike, gut integrity is crucial for gut health and performance. Amongst others, the intestinal barrier is composed of epithelial cells and intercellular tight junctions. Phytogenic substances are plant-derived feed additives commonly used in animal nutrition for health and productivity. The objective of this experiment was to explore the influence of selected phytogenic substances on the recovery of the barrier function after disturbance.

Intestinal porcine epithelial cells (IPEC-J2) were cultivated in 12-well Transwell® plates. After removal of the cell culture medium and a washing step, 2 mM EGTA was added as a chelator. This caused a disruption of the tight junctions between the cells. After washing, the cells were further incubated for 24 hours with either cell culture medium alone (negative control), an additional MAP-kinase inhibitor (positive control) or additional phytogenic extracts. The trans-epithelial electrical resistance (TEER) was measured after 0, 6, and 24 hours.

After EGTA addition, the TEER of all cultures dropped below 0.2 kΩ/cm², indicating a complete loss of barrier function. After 6 hours, the cell control TEER increased to 3.29 ± 0.83, while it was significantly enhanced (p < 0.001) by a liquorice extract at 1000 µg/ml (5.35 ± 0.96). After 24 hours, the cell control showed a TEER of 7.55 ± 0.71 and it was significantly enhanced (p < 0.05) by the liquorice extract at 1000 µg/ml (9.93 ± 0.65), a herbal mixture at 80 µg/ml (8.66 ± 0.27), and one of its constituents, angelica root at 80 µg/ml (8.74 ± 0.31).

Glycyrrhizic acid, the sweet tasting principle of liquorice, and its metabolite glycyrrhetinic acid, did not influence the recovery of epithelial integrity when tested in corresponding concentrations as found in the liquorice extract.

Additional experiments on tight junction proteins are ongoing, in order to further elucidate the mode of action of phytogenic substances in this intestinal barrier model.