All the intestinal condition characterized by an inflammatory process are generally matched to an altered intestinal permeability. With this concept it is indicated the phenomenon for which toxins, bacteria and macromolecules of partially digested food can cross the intestinal epithelial barrier, reaching the blood circle. This unwanted passage further sustains the inflammatory process and activates the immunity response. The causes are multiple and include the wrong expression of the tight junction proteins, structures deputed to keep tight the intestinal cells, or dysbiosis conditions which have a negative influence on these structures having natural molecules able to modulate the intestinal permeability is of great interest in the context of the treatment of all the intestinal conditions characterized also by altered intestinal permeability. Berberine and quercetin are supported by numerous literature studies for their ability to contribute and maintain the structural integrity of the intestinal barrier.
In this first study we can observe that, in an induced colitis model, berberine is able to stimulate the expression of three tight junction proteins, zonula-occludens 1, E-cadherin and occluding. In the inflammatory model their expression significantly decreases compared to the healthy control but the berberine treatment restores the condition similarly to the healthy control (Zhang et al., 2017).
Interestingly, berberine maintains the proper distribution of the tight junction proteins. In these immunohistochemistry images it is shown that the induced colitis determines the redistribution of the tight junction protein zonula-occludens 1 from apical tight junctional complexes to the cytoplasmic compartment of colon epithelial cells; the berberine treatment prevents this translocation (Yan et al., 2011).
Also quercetin is able to counteract the altered intestinal permeability, as shown in the following study where, as permeability parameter, FITC fluorescence in the serum was monitored. In this kind of experiments, animals are fed with a solution containing dextran-FITC, a fluorescence molecule, and then the serum fluorescence is monitored. Higher degrees of intestinal permeability correspond to higher serum fluorescence (Dong et al., 2020).
In conclusion, berberine and quercetin are two natural molecules useful for maintaining and restore the proper intestinal permeability.