Study Of The Effects And Mechanisms Of Bifidobacteria On Constipation Alleviation

Constipation is a common functional gut disease and an evoke factor to many diseases with high lethal rate.The clinical symptoms of constipation including: reduced frequency of defecation,dry stool,increased length of gastrointestinal drainage.In the recent years,the incidence of the constipation increased in China.The reasons might be the aging of the society,accelerated pace of modern life,improved living standards,changes in the diets and other social and psychological factors.Nowadays,osmotic or secretory laxatives are used to treat constipation.However,all those mentioned drugs have defeats,such as,high price,toxicity and easy to produce drug dependence.Moreover,the universality of all these drugs are low among individuals.Clinical studies showed that the gut microbiota of constipation patients is normally in dysbiosis.The features of the imbalanced gut microbiota composition including the decrease in the relative abundances of Bifidobacterium and Lactobacillus and the significant increase in the relative abundances of pathogens and conditional pathogens.Many animal studies have given the proof that gut microbiota are involved in the developing of constipation.Thus,the constipation might be cured by rebuilding the balance of in-site microbiota in the gut.In which,exogenous probiotics introducing is one of the leading ideas in this filed.In this study,we used 14 strains of Bifidobacterium and 3 oligosaccharides that can be utilized by these strains to understand the effects of how Bifidobacterium effect the constipation in mouse model and the mechanism behind it.At first,a mouse constipation model was developed.Then,each 14 strains of Bifidobacterium were gavaged to the constipation mice.By testing the indexes of constipation,including water content of the stool,small intestine transit rate and the time to the first black stool defecation,it was found that the differences in relieving constipation is species-dependent.Among the tested strains,Bifidobacterium bifidum,Bifidobacterium longum and Bifidobacterium infantis strains showed the best results considering all indexes followed by some strains of Bifidobacterium adolescentis and Bifidobacterium breve.With the analysis of Short Chain Fatty Acids(SCFAs)content in the stool,gut microbiota,gastrointestinal regulation peptide involved in constipation and characterization of the strains,we found that the bfidobacterium strains which possess the ability of adhesion can increase the amount of acetic acid in the stool and the ratio of Firmicute/Bacteroidetes.At the genus level,the relative abundance of Lactobacillus was increased and those of Alistipes,Odoribacter and Clostridium were decreased.Moreover,the bifidobacterium gavaged mice tend to have similar levels of excitatory neurotransmitters(MTL,Gas and SP)and inhibitory neurotransmitters(ET-1,SS and VIP)with the normal in the serum.After the discovery that the adhesion of Bifidobacterium might be related to its ability in relieving constipation,all 14 Bifidobacterium strains were grouped based on their adhesion ability,one group composed of all strains with adhesion ability(MB1)and the other composed of all strains deficit in adhesion(MB2).According to the animal tests by gavaging these two groups of mix strains to the constipation mice,MB1 clearly increased the water content in the stool and the small intestine transit rate and shortened the time to the first black stool defecation.Besides,the contents of acetic acid,propionic acid and butyric acid in feces were higher in the MB1 gavaged mice.By comparing the gut microbiota of MB1 and MB2 gavaved constipation mice,it showed that the adhesion strains can increase the relative abundance of Bifidobacterium and Lactobacillus and decrease the relative abundance of Coprococcus and Odoribacter.Moreover,in the serum of the MB1 gavaged mice,the secretions of excitatory neurotransmitters(MTL,Gas and SP)were promoted and inhibitory neurotransmitters(ET-1,SS and VIP)were demoted.Because of the strict incubation conditions of Bifidobacterium and the sensitivity of them to gastric liquid and bile acid,the number of living Bifidobacterium that reach to the gut is in limitation.With this restriction,a shift to prebiotic that could promote the growth of Bifidobacterium in the gut seems reasonable.Therefore,we tested the 3 oligosaccharides that can be used by the Bifidobacterium strains on their effects on the gut microbiota and fecal SCFAs levels of constipation mice.It turns out that the effect of galacto-oligosaccharides(GOS)on relieving constipation was the best,which significantly increased the content of acetic acid and butyric acid in feces.GOS also increased the relative abundance of Lactobacillus and Bifidobacterium and reduced the relative abundance of Odoribacter,Alistipes and Bacteroides.The incidence of constipation normally results from reduced intestinal motility,changes in immune system,dysbiosis in gut microbiota and the intestinal nervous system(mainly neurotransmitter imbalance)et al.Our study demonstrated that SCFAs can relieve constipation.We then explored the effects of SCFAs on intestinal nervous system(especially on 5-HT),gut microbiota,Treg cells and related cytokines.The results showed that the mechanism of Bifidobacteria in relieving constipation by adhering to the intestinal mucosa,affecting the level of SCFAs in gut.On the one hand,SCFAs relieved constipation by improving the phenomenon of intestinal flora imbalance caused by constipation.On the other hand,it can relieve constipation by regulating the imbalance of Th17 / Treg.