A standardized extract from Cynara cardunculus L. leaves as a promoter of intestinal epithelial differentiation and barrier function in Caco-2 cells.

Background Intestinal epithelial cells play a fundamental role in the transport of essential nutrients and in protecting against harmful agents from the external environment. They form a physical barrier thanks to the presence of tight junctions (TJ) strictly connecting the cells each other and responsible for maintaining their polarity. Destruction of TJ proteins is called “leaky gut syndrome” and has been observed in some gastrointestinal diseases, such as inflammatory bowel disease. Polyphenols are important nutrients derived from plant-based foods that have been shown to improve intestinal health preserving TJ integrity and improving intestinal barrier function. In particular, AMPK/SIRT1 pathway, recently associated to TJ assembly in intestinal epithelial cells, seems to be involved in the protective effects. The objective of this study was to investigate the beneficial effects of a standardized extract obtained from the leaves of Cynara cardunculus L. (CCLE), rich in chlorogenic acid and luteolin derivates, on intestinal mucosal paracellular permeability and the intracellular mechanisms involved. Methods Caco-2 cells were treated with CCLE (5 to 15 μg/mL) during intestinal epithelial cells differentiation for 18 days. For the in vitro evaluation of the barrier function Transepithelial electrical resistance (TEER), monitored during differentiation, and fluorescein permeability were determined. Western blot analysis was used to evaluate TJ expression (ZO-1 and claudin-1). In addition, AMPK/SIRT1 pathway was evaluated by western blot and qPCR techniques. Furthermore, the involvement of AMPK in the observed effects, was evaluated exposing Caco-2 cells to an AMPK pharmacological inhibitor (compound C). Results Treatment with CCLE improved intestinal epithelial barrier function as demonstrated by dose-dependent increase of TEER values during Caco-2 differentiation period and the decrease in fluorescein permeability. These functional improvements can be correlated with a corresponding increase in TJ, since CCLE induced ZO-1 and claudin-1 protein levels. Furthermore, Ca2+ switch assay confirmed TJ assembly. Interestingly, CCLE was able to activate AMPK/SIRT1 pathway supposed to be involved in TJ assembly during intestinal epithelial differentiation. Molecular mechanism involved in the observed effects was confirmed by compound C treatment. Conclusions In conclusion, for the first time, these data evidence the beneficial effects of CCLE on intestinal barrier function and support the hypothesis that this action is due to the activation of the AMPK/SIRT1 signaling pathway. Finally, these data support the possibility of using Cynara cardunculus L. leaves, considered waste products, to obtain extracts rich in polyphenols potentially useful for improving intestinal barrier function. References Li et al., 2021 doi:10.1186/s12876-021-01934-y Ben Salem et al., 2015 doi:10.1007/s11130-015-0503-8 Suzuki, 2020 doi:10.1111/asj.13357