The Role Of Bile Acids In The Pathogenesis Of Irritable Bowel Syndrome With Predominant Diarrhea

Part ? Exploration of the associations between clinical and pathophysiological features and fecal bile acid pool in IBS-D patientsBackground:Bile acids(BAs)are a group of endogenous metabolites that can modulate intestinal motility and secretion as well as participate in visceral hypersensitivity.Recently,BAs has attracted attention in the researches on irritable bowel syndrome with predominant diarrhea(IBS-D),whereas the studies exploring BAs metabolism in Chinese IBS-D patients are still sparse.Primary BAs are synthesized in the liver and converted into secondary BAs in the gut.Fibroblast growth factor 19(FGF19)is synthesized in the ileal enterocytes and can negatively regulate the synthesis of BAs in the liver.Aim:To investigate the fecal bile acid profile of IBS-D patients and healthy controls(HCs),explore the associations between clinical and pathophysiological features and fecal BAs in IBS-D patients,and indirectly assess the synthesis of BAs by fasting serum FGF19 level.Methods:Clinical manifestations,psychological status,and quality of life were assessed with standardized questionnaires.Visceral sensitivity was evaluated via the rectal distension test.Colonic motility was evaluated via the 24h gastrointestinal transit test.Fecal BAs were measured using UPLC-MS/MS.Serum FGF19 was measured using ELISA.Results:Sixty-nine IBS-D patients diagnosed according to the Rome ? criteria and 34 HCs were enrolled in this study.The maximum tolerable threshold in the rectal distension test was significantly lower in the patients compared to that in HCs,and the defecating sensation threshold tended to decrease in the patients.In the 24h gastrointestinal transit test,the residual rate of barium bars above the sigmoid and the discharge rate of barium bars of IBS-D patients were significantly lower and higher compared with HCs.respectively.Fecal BAs were measured in 55 IBS-D patients and 28 HCs.We observed a significantly higher level of cholic acid(C A),chenodeoxycholic acid(CDCA),and their conjugated BAs in IBS-D patients,as well as a significantly lower level of lithocholic acid(LCA)and a moderately lower level of deoxycholic acid(DCA)in IBS-D patients.The total BAs in feces was significantly higher in IBS-D patients.Defecation frequency was positively associated with CA and CDCA as well as negatively associated with DCA and LCA in IBS-D patients.The residual rate of barium bars above the sigmoid of IBS-D patients in the 24h gastrointestinal transit was negatively associated with fecal CA and CDCA.In the IBS-D group,there was a negative association between the first sensation threshold and CDCA,and the defecating sensation threshold also tended to be negatively associated with CDCA.The level of fasting serum FGF19 of IBS-D patients and HCs exhibited no significant difference,while serum FGF19 was negatively correlated with fecal total BAs in IBS-D patients.Conclusion:The fecal bile acid profile was featured with increased primary BAs,decreased secondary BAs,and increased total BAs in IBS-D patients.The increase of total BAs might be related to the decrease of FGF19 and the impairment of negative feedback regulation of BAs synthesis.BAs might participate in the pathogenesis of IBS-D by modulating intestinal motility and visceral sensitivity.Part ? Exploration of the association between fecal bile acid pool and gut microbiota in IBS-D patientsBackground:The metabolism of BAs in the intestine depends on the gut microbiota.The bacteria capable of converting conjugated BAs into unconjugated BAs are abundant in the gut,while those capable of converting primary BAs into secondary BAs are limited to only a small number of species,with an overwhelming majority belonging to Ruminococcaceae.Aim:To compare the fecal microbiota of IBS-D patients and HCs,and explore the correlation between the components of fecal BA pool and the fecal microbiota.Methods:Fecal microbiota was analyzed using 16S rRNA gene sequencing.Fecal BAs were examined by UPLC-MS/MS.A food frequency questionnaire was used to assess the dietary habits of participants in the preceding year.Results:This study recruited 55 IBS-D patients and 28 HCs.The relative abundances of the class Clostridia,the order Clostridiales,and the family Ruminococcaceae were significantly reduced in the feces of IBS-D patients compared with HCs.Among all the participants,the relative abundance of Ruminococcaceae showed negative correlations with the level of fecal CA and CDCA and a positive correlation with the level of fecal LCA,as well as a trend of positive correlation with the level of fecal DCA.The intake frequencies of vegetables,fruits,potatoes,and legumes were significantly lower in IBS-D patients,whereas the intake frequencies of processed meat,deep-fried food,and barbecued food were significantly higher in IBS-D patients compared with HCs.Conclusion:The disbalance between primary BAs and secondary BAs in the gut might be associated with the reduction of Ruminococcaceae in IBS-D patients.Dietary factors might be involved in the dysbiosis of gut microbiota in IBS-D patients.Part ? Comparison of the expression of bile acid receptors in the colonic mucosa of IBS-D patients and healthy controlsBackground:Bile acid receptors participate in the modulation of intestinal functions by BAs.Bile acid receptors TGR5(Takeda G protein-coupled receptor 5)and VDR(Vitamin D receptor)are widely expressed in the colon.Different bile acid species have different degrees of potency in activating bile acid receptors.For TGR5,LCA>DCA>CDCA>CA.For VDR,LCA is the most effective ligand among the natural BAs,while CA,CDCA,and DCA can not activate it.Aim:To compare the expression of TGR5 and VDR in the colonic mucosa of IBS-D patients and HCs,and explore their associations with clinical characteristics and fecal BAs.Methods:Clinical manifestations,psychological status,and quality of life were assessed with standardized questionnaires.Fecal BAs were examined by UPLC-MS/MS.Rectosigmoid biopsies were taken for the analyses of TGR5 and VDR expression using immunohistochemistry.Results:This study enrolled 52 IBS-D patients and 32 HCs.TGR5 and VDR immunoreactivity in the colonic mucosa were both mainly distributed in the epithelium and crypts.The level of TGR5 immunoreactivity in mucosal biopsies was significantly higher in IBS-D patients than in HCs,while the VDR immunoreactivity displayed no significant difference between the two groups.The patients with relevant or severe abdominal pain had significantly higher TGR5 immunoreactivity than the patients with mild abdominal pain,and the patients with abdominal pain?4 days per week had borderline significantly higher TGR5 immunoreactivity than the patients with abdominal pain<4 days per week.Thirty-eight IBS-D patients and 20 HCs provided both the feces and colonic mucosa specimens.Among all the participants,the expression level of TGR5 was positively associated with fecal CA and CDCA,and negatively associated with fecal DCA and LCA.Conclusion:The TGR5 protein expression level in the colonic mucosa of IBS-D patients was significantly higher than that of HCs.TGR5 might be implicated in the abdominal pain of IBS-D patients.The TGR5 level in the colonic mucosa might be affected by the abnormality of intestinal BAs metabolism in IBS-D patients.