Dietary Anthocyanins Modulate Redox Signalling in Colonic Cells A Protective Mechanism for Gut Health

Intestinal epithelium represents a protective physical barrier and actively contributes to the mucosal immune system. Chronic intestinal inflammatory disorders, such as Inflammatory Bowel Diseases (IBDs), are characterized by excessive release of pro-inflammatory mediators, intestinal barrier dysfunction, and excessive activation of NF-kB cascade. Polarized basolateral intestinal secretion of inflammatory mediators, followed by activation of NF-kB signaling and inflammatory pathways in endothelial cells, efficiently trigger extravasation of neutrophils from the vasculature, thus contributing to the development and maintenance of intestinal inflammation. Proper regulation of NF-κB activation at the epithelial interface is crucial for the maintenance of physiological tissue homeostasis. Many papers reported that anthocyanins, a group of compounds belonging to flavonoids, possess anti-inflammatory effects and modulate NF-kB activity. An in vitro model of acute intestinal inflammation using intestinal Caco-2 cells exposed to TNF-α (a proinflammatory cytokine playing a central role in intestinal inflammation of IBDs) was employed to investigate the activity of the dietary anthocyanin cyanidin-3-O-glucoside (C3G). Caco-2 cells exposure to TNF-α induced the activation of the NF-kB pathway, as well as the subsequent increased expression of IL6, TNF-α, IL8, and COX-2 in Caco-2. C3G (20-40 µM) pretreatment for 24h dose-dependently prevented TNF-α-induced changes, and improved intracellular redox status. Furthermore, by using a co-culture in vitro system, the effects of TNF-α-activated intestinal cells on endothelial cells dysfunction, as well as the protective effects of C3G, were evaluated. TNF-α-activated Caco-2 cells induced endothelial dysfunction with increased E-selectin and VCAM-1 mRNA, leukocyte adhesion, and NF-kB levels in HUVECs, effects all inhibited by C3G pretreatment of Caco-2. Moreover, C3G, also without any kind of stimulus, increased the translocation of the transcription factor Nrf2 into the nucleus, thus activating antioxidant and detoxifying genes. Finally, this model demonstrated that selective inhibition of the NF-kB pathway in epithelial cells represents the main mechanism by which C3G exerts these protective effects. In conclusion, C3G anti-inflammatory activity on colonic cells are very likely mediated by NF-kB pathway inhibition, and the beneficial effects appear to be due to its ability to activate cellular protective responses modulated by Nrf2. These data suggest that anthocyanins could contribute, as complementary or preventive approaches, to the management of chronic gut inflammatory diseases.