Danno alla Barriera Intestinale nella Patogenesi delle Malattie Infiammatorie Gastrointestinali

Inflammatory Bowel Disease (IBD) is a term used to describe a collection of disorders defined by chronic intestinal inflammation occurring in specific gastrointestinal sites. The two most representative conditions of this disease are Crohn’s Disease and Ulcerative Colitis. The intestinal epithelial barrier provides an essential function in the intestinal tract as it modulates the passage of substances and antigens from the lumen to the internal tissues. Impairment of the intestinal mucosa is associated with gut disorders, where altered inflammatory responses occur, such as in IBD. TNF-α has been demonstrated over the years to be a highly produced cytokine in IBD patients; it is a target for therapies aimed to reduce inflammation. Other cytokines such as IL-8 and MCP-1 are essential for phagocyte recruitment in the inflammatory environment. Thanks to the availability of a serum bank from the Gastroenterology division of Città della Salute e della Scienza - Molinette Hospital, we analyzed cytokine levels in the serum of IBD patients and compared them with those present in Irritable Bowel Syndrome (IBS) patients that presumably do not show a strong inflammation. TNF-α was exceptionally high in those IBD patients with an active phase of the disease. In order to in-vitro mimic the mucosal inflammatory environment, we used a monolayer of intestinal differentiated CaCo-2 cells, exposed to a conditioned medium with IBD and IBS patient sera. As a positive control of inflammation, cells were treated with increasing concentrations of TNF-α. Tight junction Claudin-1 and Occludin, and the adherens junction E-cadherin were used to analyze the cell monolayer integrity. They were decreased in cells conditioned with either IBD or IBS sera; in particular, E-cadherin was significantly deranged. These findings interestingly suggest that intestinal permeability is a mechanism of damage found not only in IBD but also in IBS. Matrix metalloproteinases (MMP), MMP-2, and MMP-9 were also evaluated because of their essential role in barrier destabilization: both MMP-2 and MMP-9 appeared to be activated in IBD-conditioned cells. Short-chain fatty acids (SCFAs) are bacterial metabolites, fermentation products, which may regulate intestinal inflammation as they directly interact with intestinal epithelial cells. Among these metabolites, butyrate could contribute to the intestinal barrier maintenance integrity and gut homeostasis in general. SCFAs have a potential therapeutic effect in suppressing inflammation. However, some studies suggest that the intestinal response to butyrate is not intrinsically altered in IBD patients. Cell exposure to the serum of IBD/IBS patients in our experimental model could better mimic the in-vivo response in patients. Therefore, in the second group of experiments, we found that butyrate CaCo-2 cell pre-treatment restored tight junction protein levels and decreased cytokine production due to patients’ serum exposure. These studies suggest specific tight junctions as intestinal permeability markers for inflammation-associated gut diseases. In addition, we observed a beneficial effect of butyrate in lowering intestinal damage, suggesting this molecule to be used in association with routine anti-inflammatory drugs. However, because of the small number of sera analyzed and the high variability in the disease activity of IBD and IBS patients, further studies are required to confirm our observations.