Effect Of Cathelicidin-associated Antimicrobial Peptides (CRAMP) On DSS Induced Inflammatory Bowel Disease In Mice

Antibacterial peptides(Cathelicidin)are a class of active peptides that exist in mammals.Its member antibacterial peptide LL-37/Cathelicidin Related Antibacterial Peptide(LL-37/CRAMP)is an antibacterial peptide shared by human and mice.Human source is called LL-37,and mice source is called CRAMP.Its mechanism is complex and involved in the regulation of diseases such as inflammation,autoimmune diseases and tumors.Inflammatory Bowel Disease(IBD)is an intestinal inflammatory disease that can involve the ileum,rectum and colon and has complex pathogenesis.The imbalance of intestinal homeostasis will lead to chronic inflammation,and continuous tissue inflammation will lead to tissue repair disorder and thus lead to the occurrence of Colorectal Cancer(CRC).Moreover,colorectal cancer caused by IBD is called Colitis Associated Cancer(CAC).In recent years,studies have pointed out that CRAMP has different or even opposite effects in different disease models.In the oxazolone-induced inflammatory bowel disease model,CRAMP has two different effects of anti-inflammation and pro-inflammation through different administration routes.In recent years,studies have pointed out that CRAMP has different or even opposite effects in different disease models.In the oxazolone-induced inflammatory bowel disease model,CRAMP has two different effects of anti-inflammation and pro-inflammation through different administration routes.Therefore,this study will establish acute,chronic inflammatory bowel disease and CAC animal models to explore the role of CRAMP in the development of inflammatory bowel disease and CAC.In this study,we first analyzed the research frontiers and hotspots of CRAMP and inflammatory bowel disease through literature analysis,and explored the role of CRAMP through acute,chronic IBD and CAC animal models:(1)Construction of acute inflammatory bowel disease mouse model: acute IBD mouse model was induced by drinking water containing 3%Dextran sulfate sodium(DSS)for 7days.The intervention group was given recombinant CRAMP protein(4 mg/kg/day)by intraperitoneal injection on 4-7days.During the experiment,the body weight and diarrhea of mice were observed and recorded every day.At the end of the experiment,the length and weight of the intestine were recorded,and the pathological changes of intestinal tissue were observed.The contents of Interleukin-6(IL-6),Monocyte Chemoattractant Protein(MCP-1)and Tumor Necrosis Factor-α(TNF-α)in peripheral blood and colon tissue,and the m RNA in colon tissue were detected.(2)Construction of a mouse model of chronic inflammatory bowel disease: 5days after drinking 3% DSS and 14 days after drinking normal water,as a cycle,a total of three cycles were repeated to establish a mouse model of chronic IBD.The intervention group was given 3mg/kg CRAMP recombinant protein by intraperitoneal injection at the third cycle.During the experiment,body weight and diarrhea were observed and recorded.At the end of the experiment,the length and weight of the intestine were recorded,the pathological changes of the intestine were observed,and the contents of IL-6,MCP-1 and TNF-α in peripheral blood and colon tissue and the m RNA level in colon tissue were detected.(3)Colitis-associated colon cancer model in mice induced by AOM/DSS: One day after intraperitoneal injection of AOM,the treatment method was the same as that of chronic IBD mouse model.During the experiment,the weight and diarrhea were observed and recorded.At the end of the experiment,the colon tumor and intestinal histopathological changes were observed.This study found that:(1)Through literature analysis,we found that the domestic researchers’ attention to CRAMP has increased year by year in the past 20 years,but there was no active research team.Inflammatory bowel disease researchers were concentrated in a small range,and the research contents were mostly colonoscopy,fecal bacteria transplantation and other diagnostic or therapeutic methods.(2)In acute IBD model,CRAMP significantly attenuated DSSinduced weight loss and shortened colon length;after CRAMP intervention,the inflammatory index of colon tissue was significantly decreased,the degree of inflammation,inflammatory cell infiltration and histological damage were significantly decreased,and the villus length and crypt depth were significantly prolonged;after CRAMP intervention,the content of IL-6 in peripheral blood was significantly decreased,the contents of IL-6,MCP-1 and TNF-α in the supernatant of colon tissue in vitro were significantly decreased,and the m RNA levels of IL-6,MCP-1 and TNF-α in colon tissue were significantly decreased.(3)In the chronic IBD model,although the induced weight was significantly reduced after CRAMP intervention,the length of the small intestine was significantly increased;after CRAMP intervention,the ileal inflammatory index was significantly reduced,and the inflammatory degree,inflammatory cell infiltration and histological damage of colon and ileal tissues were significantly reduced;after CRAMP intervention,the contents of IL-6,MCP-1 and TNF-α in peripheral blood were significantly decreased,the contents of IL-6 and TNF-α in colon tissue supernatant in vitro were significantly decreased,and the m RNA levels of IL-6,MCP-1 and TNF-α in colon tissue were significantly decreased.(4)There was no significant change in body weight and cancer pathological score between CAC intervention group and intestinal cancer group.Therefore,we found that CRAMP had a significant protective effect in acute and chronic inflammatory bowel disease mice,but in colitis-associated colon cancer mice,CRAMP had no significant effect on the occurrence and development of tumors.This will provide important guidance for clinical rational application of CRAMP.