Ameliorating Effects Of Chitooligosaccharides On DSS-induced Colitis In Mice

Ulcerative colitis is a kind of inflammatory bowel disease with alternating phases of clinical relapse and remission,with unknown etiology remains.It is characterized by inflammatory infiltration of distal colon and rectum,with intestinal mucosal damage.And there has been a rise in the incidence of UC year by year.Current clinic therapies mainly depend on anti-inflammatory and immunity enhancing drugs,which might cause many adverse reactions,and drug resistance is easy to occur.Therefore,it is difficult for patients to persist for a long time.Chitooligosaccharides(COS),are natural,non-toxic oligosaccharides derived from chitin.They have many biological activities,such as anti-oxidation,antiinflammatory,promoting immunity,maintaining the homeostasis of intestinal flora,and play an important role in inflammation and intestinal tract.The study aimed to explore the protective effect and molecular mechanism of COS on symptoms of dextran sodium sulfate(DSS)-induced colitis in mice.The details were as follows:First of all,the mice model of ulcerative colitis was established to observe the protective effects of COS on UC and determine the optimal dose.Experimental ulcerative colitis was evoked by administration of 3% dextran sulphate sodium(DSS)for 7 days in C57BL/6 male mice.At the same time,35,70,140,280 mg/kg COS and 50 mg/kg SASP aqueous solution via intragastric catheter every day.The results showed that COS had the protective effect in UC mice,and there was a bell shaped relationship between the dose and the effect.70 and 140 mg/kg COS treatment significantly attenuated many of the clinical features of IBD,such as weight loss,disease activity index,colon length reduction and MPO activity.The pathological sections showed that 70 and 140 mg/kg COS reduced infiltration of colonic inflammatory cells,and loss of the lamina propria,epithelial cells.Meanwhile,COS significantly improved the phenomenon of anorexia and anemia.Secondly,the mechanism of COS was explored in DSS-induced colitis from intestinal barrier,inflammatory response,oxidative stress,neutrophil infiltration.The results showed that COS could up-regulate the expression of Muc-2 mRNA,intestinal tight junction proteins ZO-1 and Occludin,down-regulate the expression of Claudin-1 and 2,to remodeled intestinal barrier.COS treatment significantly reduced the level of inflammatory factors IL-6,IL-1β and TNF-α,the expression of COX-2,i NOS,TLR4 mRNA in colon,inhibited the activation of NF-κB inflammasome signal pathway.Moreover,COS treatment markedly attenuated DSSmediated colonic oxidative stress via decreasing the level of MDA and NO,increasing the activity of SOD and the expression of Nrf2 and HO-1.COS also alleviated the recruitment and infiltration of neutrophils by down regulating the level of chemokines MCP-1,CXCL-1,MMP-9 mRNA.Finally,the protective effect of COS on DSS induced colitis in mice was studied from the intestinal flora change and SCFAs content.The colonic flora of colitis mice was analyzad by high-throughput sequencing technologies.The results showed that DSS reduced the diversity of intestinal flora,and disorder the structure of fore.And COS could improve these changes.At genus level,it increased the abundance of prebiotics such as Akkermansia,inhibited harmful bacteria such as Allobaculum and Parabaracteroids,but had no significant effect on Bifidobacteria.Moreover,different doses of COS had different effects on the flora.70 mg/kg COS could increase the diversity of flora,while 140 mg/kg COS had the opposite trend.In addition,the function analysis of the flora showed that COS may play an important role in biosynthesis,and metabolism of the intestinal.Then the content of SCFAs in cecum was analyzed by GC-MS.It was found that 70 mg/kg COS could significantly increase the content of acetic acid,propionic acid and butyric acid,while 140 mg/kg COS only significantly increased the content of butyric acid.The results showed that 70 mg/kg COS had better effects in maintaining the homeostasis of intestinal microenvironment compared with 140 mg/kg COS.In conclusion,70 and 140 mg/kg COS had protective effects on ulcerative colitis induced by DSS,by protecting intestinal barrier,inhibiting inflammatory response,alleviating oxidative stress and neutrophil infiltration.In addition,70 mg/kg COS could increase intestinal SCFAs and maintain intestinal homeostasis.