Comparative Effects Of EPA And DHA On Ulcerative Colitis In Mice

Objective: To compare the effects of EPA and DHA on ulcerative colitis(UC),C57BL/6J mice were pretreated with different doses of EPA and DHA for a month.UC was established by drinking water containing dextran sulphate sodium(DSS).The mucosal barrier,activation of inflammatory pathways and proliferation of intestinal epithelium were evaluated to clarify the mechanism by which EPA and DHA influence UC in mice,and to provide scientific evidence for revealing the potential application of EPA and DHA in prevention and treatment of UC.Methods: Eight-week-old male mice were randomly divided into seven groups according to body weight: normal group,model group,positive drug group,low or high dose of EPA group,low or high dose of DHA group.At first,EPA and DHA groups were intervened by gavage with 100 mg/kg or 400 mg/kg of corresponding fatty acids respectively for one month.Other groups were administrated with solvent(10% arabic gum).Then,all groups were assigned to two cycles of 2% DSS exposure except normal control group.During the first cycle,mice were exposed to 2% DSS for 6 days followed by 15 days of drinking normal water.During the second cycle,mice were exposed to 2% DSS for 6 days followed by 8 days of drinking normal water.During the period of DSS exposure,EPA and DHA groups were kept on their fatty acids intervention;while positive drug group access to salicylazosulfapyridine(SASP)of 500 mg/kg.Body weight,stool consistency and gross bleeding were recorded daily to evaluate disease activity index(DAI)to dynamically assess the severity of DSS-induced UC in mice.At 36 th day of DSS exposure,the mice were anaesthetized using diethyl ether and sacrificed.Distal colon was excised,and the length of the colon as well as the degree of edema were observed and recorded.The inflammation degree and mucus production of goblet cells were evaluated using H&E and alicin blue staining.Gas chromatography was used to quantify the fatty acids content of colon.In order to explore the possible mechanisms,intestinal mucosal barrier related proteins,inflammatory pathways and proliferation related proteins were determined using western blot.Results: The treatment of EPA and DHA increased their concentration in intestinal epithelium of mice.EPA significantly blocked weight loss in mice,and decreased the DAI score compared with model group,whereas DHA did not.The infiltration of inflammatory cells and edema in colon of EPA group were markedly reduced relative to model group.Results of western blot showed that EPA acted to significantly strengthen integrity of the intestinal mucosal barrier by reducing the activity of Akt and ERK,upregulating the levels of Hedgehog pathway proteins(SHH and SMO)and tight junctions proteins(Claudin-1 and Occludin),triggering expression of c-myc and downstream E-cadherin.It was found that the mucous barrier of the intestinal epithelium was maintained in EPA group based on the increase of the expression of TFF3,and mucus production of goblet cells.The levels of chemokine(MCP-1)and inflammatory cytokines(IL-1?,IL-6,TNF-?)as well as the marker of neutrophil and macrophage infiltration(MPO and F4/80)were significantly reduced in EPA group compared with model group.In addition,inflammatory pathways including NLRP3/IL-1?,IL-6/Stat3,TLR4/NF-?B,TNF-?/NF-?B were down-regulated in EPA group.Moreover,EPA also promoted the expression of proliferation-related Wnt/?-catenin pathway(DVL2,?-catenin,c-myc,Cyclin-D1,PCNA)and apoptosis proteins(p53 and Caspase-3).Conclusion: 1.EPA significantly blocked DSS-induced UC in mice,suggesting a promising application in prevention and treatment of UC.2.The mechanism by which EPA inhibited UC involved maintaining the integrity of intestinal epithelium barrier mediated by inactivation of Akt and ERK,upregulation of Hedgehog pathway and c-myc mediated E-cadherin expression as well as increase of mucus secretion.3.EPA suppressed UC by inhibiting infiltration of inflammatory cells and inflammatory pathways such as NLRP3/IL-1?,IL-6/Stat3,TLR4/NF-?B,and TNF-?/NF-?B.4.EPA facilitated the balance of proliferation and apoptosis by upregulating Wnt/?-catenin pathway and promoting expression of apoptosis related proteins.