Analysis Of The Alleviation Effects On Constipation By Bifidobacterium And Its Mechanisms

With the changes in diet,lifestyle and work rhythm,the incidence of constipation is increasing year by year.At present,the commonly used constipation relief medicines show the disadvantages such as obvious side effects,strong medicine dependence and high price.Therefore,it is urgent to seek medicine substitutes.Clinical studies indicated that in patients with constipation,the homeostasis of the gut microbiota was imbalanced and the intestinal environment was destroyed.Regulating the gut microbiota by treating the body a certain amount of active probiotics has become an important method for constipation treatment.Previous studies in our laboratory have discovered that Bifidobacterium may have certain interspecific differences in the capacity of constipation alleviation,but the reasons for the interspecific differences and the specific mechanisms of Bifidobacterium in alleviating constipation were still unknown.In this study,constipation animal model was used to screen out strains with different effects on constipation alleviation.Combined with the physiological characteristics of strains,the possible mechanisms of Bifidobacterium in alleviating constipation and the reasons for interspecific different constipation alleviating capacity were explored from the repair effects of Bifidobacterium on chemical barrier,immune barrier,mechanical barrier and biological barrier.Firstly,loperamide was used to induce constipation in mice.Bifidobacterium longum,B.infantis,B.adolescentis and B.breve were used to treat constipation.The strains were screened with the indexes of fecal water content,small intestinal proptosis rate and time to first black stools.5 strains of B.longum,3 strains of B.adolescentis,2 strains of B.infantis and a strain of B.breve were screened out to have the effect of relieving constipation.Meanwhile,the physiological characteristics of 24 strains were evaluated.The results showed that the strains with fast growth speed and strong acid-tolerant abilities were more conducive to play the probiotic function.Specifically,B.longum with higher growth speed and stronger acid resistance had the most significant effect on constipation,which were followed by B.adolescentis,B.infantis and B.breve.Secondly,the possible mechanisms of Bifidobacterium alleviating constipation were analyzed from chemical barrier,immune barrier,mechanical barrier and biological barrier.a)For chemical barrier,Bifidobacterium could inhibit the expression of aquaporins,improve the secretion of gastrointestinal active peptides,up-regulate the transcription level of c-kit gene,promote the production of short-chain fatty acids and regulate the 5-hydroxytryptamine signaling pathway.b)For immune barrier,Bifidobacterium could increase intestinal mucosal thickness and decrease the release of interleukin-1?or tumor necrosis factor-?.c)For mechanical barrier,Bifidobacterium could restore the expression of tight junction protein.d)For biological barriers,Bifidobacterium could increase the?-diversity of gut microbiota and regulate the abundance changes at the level of phylum and genus.In conclusion,Bifidobacterium can regulate intestinal fluid secretion or smooth muscle contraction,alleviate intestinal inflammation,reduce intestinal permeability and restore gut microbiota homeostasis.Therefore,it can repair chemical barrier,immune barrier,mechanical barrier and biological barrier to achieve the goal of relieving constipation.Among them,B.longum had advantages in repairing intestinal barrier,which was particularly reflected in its influence on aquaporins,SCFAs,inflammatory factors and the diversity of gut microbiota.Finally,principal component analysis was carried out on gastrointestinal indexes.Combining with the changes of gut microbiota,the role of different Bifidobacterium in alleviating constipation were further speculated.The results showed that B.longum had the most prominent effect on the expression of c-kit gene in the colon.B.adolescentis mainly affected the content of butyric acid,while B.infantis and B.breve showed a unique effect on the intestinal 5-HT signaling pathway.In addition,Bifidobacterium could change the gut microbiota to varying degrees.Therefore,after the intervention of different Bifidobacterium,the microbes with significant different abundance in the intestine were analyzed.The results showed that B.longum and B.adolescentis had significant effects on the abundance of Lachnoclostridium and Lactobacillus,respectively.B.infantis and B.breve could significantly regulate the relative abundance of Alistipes,Lachnospiraceae NK4A136 group and Lactobacillus.These changes in gut microbiota were significantly correlated with the concentration of butyrate and the transcription levels of c-kit,Tph1,5-HT₄R genes.Therefore,it is speculated that the reasons for the diversity in the pathways of different Bifidobacterium in alleviating constipation may be due to the different changes in the abundance of these significantly related microorganisms caused by different Bifidobacterium,thereby changing the short-chain fatty acids produced by the metabolism of the gut microbes or activating relevant signal pathways to repair the intestinal barrier and improve the symptoms of constipation.