Co‐occurrence of gut microbiota dysbiosis and bile acid metabolism alteration is associated with psychological disorders in Crohn's disease

Abstract This study aims to elucidate the relationships between gut microbiota, bile acid metabolism, and psychological comorbidity in Crohn's disease (CD). We profiled the fecal microbiota composition and quantified the bile acid pool of 39 CD patients and 14 healthy controls using 16S rRNA gene sequencing and liquid chromatography–tandem mass spectrometry, respectively. Significant reductions in the secondary bile acids, LCA and DCA, were found in both the feces and serum samples of CD patients, while the concentration of 7‐DHCA was particularly higher in the serum of CD patients with psychological disorders. The fecal levels of HDCA and 12‐DHCA of the CD patients were inversely correlated with their Self‐Rated Depression Scale (SDS) scores, whereas the serum level of 7‐DHCA was positively correlated with the SDS scores. In addition, the fecal levels of TDCA, TLCA, and TβMCA showed a positive correlation with the Self‐Rated Anxiety Scale (SAS) scores. The fecal microbiota biodiversity was particularly declined in CD patients with psychological disorders. An enrichment of Ruminococcus gnavus in CD patients may cause psychological disorders by affecting the microbiota–gut–brain axis via its ability to degrade the gut barrier, regulate the tryptophan–kynurenine metabolism, and modulate bile acid metabolism. In addition, the overabundant Enterobacteriaceae and Lachnospiraceae in CD patients may contribute to psychological comorbidity via dysregulating their bile acids metabolism. Taken together, changes in the gut microbiota composition may cooperate with alterations in the bile acid metabolism that are involved in the development of psychological disorders in CD.