Study On Mechanism And Effect Of Triclosan Exposure On Ulcerative Colitis In Mice

Objective:To elucidate the mechanism and effect of triclosan on gut microbiota and DSS-induced ulcerative colitis in mice.Methods:Balb/c mice（age,4w）were maintained on AIN-93G diet containing 80ppm triclosan（TCS）dissolved in polyethylene as vehicle or vehicle alone for 1 week or 4 weeks.At the end of the 1^stweek and 4^thweek,the mice were sacrificed,blood samples and colon tissues were collected for analysis of inflammation as well as fecal samples were collected for 16S r RNA sequencing of gut microbiota.Then a mouse model of ulcerative colitis induced by DSS was established.Balb/c mice were maintained on the diet with or without TCS for 4 weeks,and at the beginning of the 4^thweek,all the mice were treated with 2%DSS in drinking water for 1week.At last,mice were sacrificed for analysis of colitis and 16S r RNA sequencing.Results:In common mice,16S r RNA sequencing showed 1-week treated-mice had higher enrichment of Eubacterium＿fissicatena and＿nodatum as well as lower Lachnospiraceae＿UCG＿006 and Anaerotruncus at phylum level,and less species Oscillibacter＿sp.＿1-3 in stool samples.1-week TCS-treated mice enhanced expression of p-NF-κb and Toll-like receptor 4（TLR4）as well as reduced expression of occludin in colon.And histological test showed TCS damaged the intestinal mucosa mildly.4-week TCS-treated mice had increasing phylum Proteobacteria.At genus level,Sulfate-reducing bacteria（SRB）increased,including Sva0081＿sediment＿group,SEEP-SRB1 and Desulfovirga,while butyrate-producing probiotic,Roseburia and Blautia,were reduced than control group.4-week exposure of TCS further reduced Occludin and enhanced the activation of TLR4 than 1-week exposure significantly.Histological test reported that4-week TCS exposure jeopardized intestinal mucosa,but the difference in duration of exposure did not work.In DSS-model mice,TCS increased abundance of SRB Desulfovibrio,Prevotella＿1 and Bacteroides but reduced Barnesiella,Bifidobacterium＿animalis and uncultured＿Alistipes＿sp.in gut microbiota.TCS exposure increased plasma concentration of IL-13,the expression of inflammatory cytokines（IL-10,IL-13,IL-17,TNF-α,IFN-γ,p-NF-κb）and reduced the expression of Occludin in colon tissue.Histology tests showed TCS exaggerated the degree of damage to intestinal mucosa and crypt,infiltration of inflammation cells and atypia of glandular cells.Conclusion:TCS induced and exaggerated ulcerative colitis by disturbance of gut microbiota.The possible proinflammatory mechanism as follows:triclosan decreased the diversity and changed the composition of gut microbiota.The alteration was characterized as the increase of harmful bacteria,such as sulfate-reducing bacteria and Bacteroides,and the reduction of protective probiotics,butyrate-producing bacteria.Meanwhile,TCS damaged intestinal mucosa barrier by the decrease of Occludin,one of the most crucial tight junction protein.Bacteria translocation activated TLR4-NF-κb inflammatory signal pathway and promote the release of Th1、Th2 and Th17 related inflammatory cytokines,which caused non-specific colitis.