Effetti benefici in vitro di un estratto standardizzato da foglie di Cynara cardunculus L. sulla funzionalità della barriera e sull’infiammazione acuta in cellule epiteliali intestinali Caco-2

Intestinal epithelial cells act as a barrier by protecting the body against harmful substances from the external environment thanks to the presence of tight junctions (TJ), which connect cells to each other, regulate paracellular permeability, and are responsible for maintaining cell polarity. Variations in the organization of the TJ lead to alterations in the epithelial barrier function with a consequent increase in intestinal permeability. This condition, also known as "leaky gut syndrome", has been observed in some gastrointestinal diseases such as inflammatory bowel disease (IBD), which is characterized by chronic immune-mediated inflammation and impaired gastrointestinal function. Numerous studies support the beneficial effects of polyphenols on intestinal health thanks to their ability to improve the functionality of the intestinal barrier, preserve the integrity of the TJs, and reduce the release of cytokines involved in inflammatory processes. Therefore, the aim of the present work was to investigate in vitro the molecular mechanisms involved in the beneficial effects of a standardized and commercially available extract, rich in polyphenols, obtained from the leaves of Cynara cardunculus L. subsp. scolymus (CCLE), on the function and integrity of the intestinal barrier, as well as its protective effects in a model of acute intestinal inflammation induced by TNF-α on intestinal epithelial Caco-2 cells. Treatment with CCLE during the differentiation process improved the functionality and integrity of the intestinal epithelial barrier by increasing TEER values and reducing fluorescein permeability, stimulated epithelial differentiation and TJ expression by increasing alkaline phosphatase activity and inducing protein levels of occludin, claudin-1 and ZO-1, and induced a more rapid TJ assembly in the Ca2+ switch assay. The effects induced by CCLE on the modulation of TJ expression were attributed to the ability of the extract to activate the AMPK/SIRT1 pathway and this mechanism was confirmed by treatment with an irreversible AMPK inhibitor, Compound C. Furthermore, in the TNF-α-induced acute intestinal inflammation model, CCLE inhibited the TNF-α-induced NF-κB pathway activation and the overexpression of IL-8 and COX-2. CCLE reduced 2 TNF-α-induced oxidative stress and improved intracellular redox power even in the absence of TNF-α, and this effect was associated with the ability of CCLE to stimulate an adaptive cellular response by Nrf2 pathway activation. In conclusion, these data highlight the ability of CCLE to improve intestinal barrier function and counteract acute intestinal inflammation, and support the possible use of Cynara cardunculus L. subsp. scolymus, considered a waste product, for obtaining extracts rich in bioactive polyphenols potentially useful for intestinal function and for the prevention and/or treatment of inflammatory bowel diseases.