Study On The Relationship Between Constipation Alleviation And Bile Acid Metabolism Regulation By Bifidobacteria

Constipation is a common clinical disease,mainly manifested by low frequency of defecation and dry stool,whose incidence is increasing year by year.Some of the medicines currently clinically used to treat constipation have strong side effects.So it is urgent search for an alternative to these drugs.People who use these medicines are prone to medicine dependence.With the global research on probiotics and human health is increasingly concerned,supplementing probiotics to regulate gut microbiota,has gradually become an important means to treat constipation.Previous research in our lab indicated that constipation is accompanied by low levels of inflammation,Bifidobacterium could relieve constipation as well as low levels of inflammation.However,the specific mechanism of relieving constipation is still unclear.Based on this,we designed the following experiment.Firstly,the animal model of constipation was established by treating mice with loperamide hydrochloride for 3 weeks.4 species(14 strains)of Bifidobacterium(Bifidobacterium longum subsp.longum,B.bifidum,B.breves and B.adolescentis)were used to intervene mice for 4weeks.By comparing the effects of different Bifidobacterium on 3 apparent evaluation indexes of constipation(fecal water content,first black stool time,and intestinal propulsion rate),3strains of Bifidobacterium with a significant effect of constipation relief were screened,including 1 strain of B.longum(S3)and 2 strains of B.bifidum(M203F02M632 and CCFM1167).Then,aiming at the 3 strains of Bifidobacterium with the effect of alleviating constipation,this study explored the possible mechanism of Bifidobacterium in alleviating constipation from the aspects of AQPs,the number of ICC,gastrointestinal motility,inflammation,gut microbiota and its metabolites.a)Bifidobacterium could down-regulate the transcription levels of Aqp genes(Aqp4 and Aqp8)related to intestinal water reabsorption but did not affect the number of ICC.b)Constipation is accompanied by low-level inflammation,which is mainly manifested in the imbalance of Treg / Th17 balance.Bifidobacterium up-regulated the number of Treg cells and down-regulate the level of IL-17,to restore the imbalance of Treg / Th17 balance caused by constipation.c)Bifidobacterium caused changes in gut microbiota.At the phylum level,Bifidobacterium reduced the ratio of Bacteroidetes/Firmicutes and increased the relative abundance of Actinomycetes.At the genus level,Bifidobacterium decreased the relative abundance of Clostridium,Akkermansia,and Roseburia,and increased the relative abundance of Ruminococcus.Meanwhile,Bifidobacterium which can relieve constipation increase the levels of secondary bile acids(LCA and DCA)and decreased the content of primary bile acid(T-β-MCA)in the colon.Finally,the correlation analyses of various indexes showed that B.longum subsp.longum down-regulated the relative abundance of Clostridium,Akkermansia and Roseburia,upregulated the relative abundance of Ruminococcus,which was significantly related to the increase of levels of secondary bile acids(LCA and DCA),and to the decrease of the content of T-β-MCA.Combined with the evidence of previous studies and the correlation analysis of this study,it is speculated that the intervention of Bifidobacterium could affect the content of some bile acids in the intestine,up-regulate the transcription levels of bile acid receptors Fxr and Vdr genes,and increase the content of TGR5,thereby promoting the colon and restore Treg/ Th17 immune balance.Bifidobacterium could down-regulate the transcription levels of Aqp4 and Aqp8 genes by increasing IL10 and reducing IL-17 content.Then reabsorption of intestinal water can be inhibited,resulting in increasing the fecal water content.Combined with the regulatory effects of the above-mentioned various factors,Bifidobacterium can relieve constipation by affecting bile acid metabolism.