Antioxidant Activity of Inulin and Its Ability to Prevent Human Colonic Muscle Cell Impairment Induced by Lipopolysaccharide Mucosal Exposure

Background: Fructans, such as Inulin, are dietary fibers with pro-healthy properties which stimulate gastro-intestinal (GI) function acting as prebiotics. Lipopolysaccharide (LPS) is known to impair GI motility, following production of reactive oxygen species and other inflammatory mediators. The antioxidant activity of various fructans has been tested here and the protective effect of inulin on colonic muscle cell impairment, induced by exposure of human mucosa to LPS, was assessed in an ex vivo experimental model. Methods: The antioxidant capacity of fructans (inulins, agavins, and levans) was measured using the TEAC (Trolox Equivalent Antioxidant Capability) method. Cooking and digestion were simulated in an vitro system to test modifications in the antioxidant activity of inulin possibly caused by these processes. Human colonic mucosa and submucosa, obtained from disease-free margins of resected segments for cancer, were sealed between two chambers, with the mucosal side facing upwards and covered with 5 mL of Krebs solution with or without purified LPS from a pathogenic strain of Escherichia coli (O111:B4) and Inulin (Frutafit IQ®), and the submucosal side facing downwards into 25 mL of Krebs solution. The solution on the submucosal side was collected after 30 min of mucosal exposure to Krebs in the absence (N-undernatant) or presence of LPS (LPS-undernatant) and in the presence of LPS and Inulin (LPS+INU undernatant). Undernatants were tested for the antioxidant activity and their effects on isolated smooth muscle cells (SMCs). The inulin protective effect on the mucosa and submucosa were assessed measuring the protein oxidation level in all the experimental conditions analysed, as well as its ability to revert the LPS-induced impairment of SMC contraction. Results: Antioxidant activity of inulin was significantly higher compared to their constituent simple sugars and remained unaltered despite the cooking and digestive processes, simulated in vitro. Inulin treatment protected mucosa and submucosa against protein oxidation. Following thirty-minute exposure to LPS-undernatant a significant decrease in maximal Ach-induced contraction was observed when compared to the contraction induced in cells incubated with the N-undernatant (148.4±5.2 vs 98.1±9.0μm, p<0.05) and this effect was partially prevented by pre-incubation of LPS with Inulin (81.3±7.9μm of cell length following Ach exposure, p<0.005). Conclusions: Inulin, with an antioxidant activity resistant to cooking and digestion, protects the human colon mucosa from damage induced by LPS and this effect appears to be related to the scavenging activity of inulin during LPS-induced oxidative stress