Alleviating Effect Of Chitin Derivatives On Experimental Colitis In Mice And The Action Mechanism

Ulcerative colitis(UC)is a kind of intestinal disease,and cannot be cured completely due to its vague pathogenesis.Its onset is mainly located in the middle and distal ends of the colon.Clinical treatments for UC often include anti-inflammatory drugs,glucocorticoids and even surgery,which are prone to relapse and cause a great burden on the patient’s body and mind.Chitin,the second most abundant natural polymer compound in nature,can be degraded to a series of derivatives with different polymerization degrees,such as chitosan(CS),chitooligosaccharides(COS),and glucosamine(GLcN).Chitin derivatives(CDs)are safe and non-toxic,and has various activities such as anti-inflammatory,antioxidant,antibacterial and regulating intestinal homeostasis.However,there is a lack of systematic research on the effect of CDs on the symptoms of colitis and the action mechanism.Based on the previous researches of our lab,a UC mouse model was constructed by inducing with Dextran Sodium Sulfate(DSS)in this study.The anti-inflammatory activity of CDs and its mechanism in UC intervention were explored to provide a theoretical basis for subsequent research and development.The main results are as follows:1.After inducing the mouse UC model using 2.5% DSS,three kinds of CDs at different moleculer wight(CS,COS2500,COS1500,and GLcN)were administrated at the dosages of 50 mg/kg and 200 mg/kg,respectively.After the end of the 14 d experimental period,the treatment effects were evaluated based on the apparent data.The results showed that of CS,COS(50 mg/kg,200 mg/kg)and GLcN(200 mg/kg)can improve the symptoms of body weight loss,less food intake,higher disease activity index(DAI),shorten colon length,and increased spleen index in UC model mice.2.Colon tissue biochemical indicators,including colonic cytokine levels,oxidative stress kinase contents,expression of proteins involved in inflammatory signal pathway and related to intestinal barrier function,was analyzed.The results showed that CS,COS(50 mg/kg,200 mg/kg)and GLcN(200 mg/kg)significantly reduced the levels of IL-1β,IL-6 and other pro-inflammatory cytokines,and enhanced the content of anti-inflammatory factor IL-10.Moreover,CS,COS(50 mg/kg,200 mg/kg)and GLcN(200 mg/kg)up-regulated the expression of tight junction related proteins ZO-1,Occludin,and Claudin-1 either in protein translation level or m RNA transcription level,down-regulated protein expression in the TLR4/NF-κB inflammation signaling pathway,activated mitogen-activated protein kinase p38.In addition,the activities of inducible nitric oxide synthase(i NOS)and myeloperoxidase(MPO)was inhibited,leading to reducing the level of oxidative stress in colon tissue.3.After collecting mouse feces on days 1,7,11,and 14,and colon contents on day14,high-throughput sequencing analysis on intestinal microbes was performed.The results showed that CS,COS(50 mg/kg,200 mg/kg)and GLcN(200 mg/kg)alleviated the symptoms of UC.Compared to DSS group,CS,COS(50 mg/kg,200 mg/kg)and GLcN(200 mg/kg)significantly improved intestinal microbial diversity and decreased the abundance of pathogenic bacteria.The analysis of the intestinal contents on day 14 revealed that reduction in abundance of Bacteroidetes caused by UC was improved significantly in the CSL,COS2500,COS1500 L,and GLcNL groups,and the abundance of Proteobacteria was reduced by all kinds of CDs.Compared to DSS group,abund-ance of Ruminococcaceae＿UCG-014 significantly increased in CSL,COS2500 L,and GLcN groups,the abundance of Prevotellaceae＿UCG-001 significantly increased in CSL,COS2500,COS1500,and GLcNL groups,and the abundance of Escherichia-Shigella was significantly reduced by all CDs.Moreover,the abundance of harmful bacteria in Bacteroides was significantly reduced in CS,COS2500 H,COS1500,and GLcNH groups.In addition,CS,COS and GLcN can significantly improve the up-regulation of genes in related metabolic pathways such as intestinal microbial carbohydrate metabolism and infectious diseases caused by UC.In summary,CS,COS(at the dosages of 50 mg/kg and 200 mg/kg)and GLcN(at the dosage of 200 mg/kg)can effectively relieve the symptoms of UC by inhibiting excessive activation of inflammation,reducing the level of oxidative stress,repairing the barrier function of the colon,and maintaining the diversity of intestinal flora.Our results suggest that CDs have the potential to develope agents or products for application in food,pharmaceutical,and stockbreeding industries.