title: Bile acids and the gut microbiome.
abstract: OBJECTIVE
  We examine the latest research on the emerging bile acid-gut microbiome axis and its role in health and disease. Our focus revolves around two key microbial pathways for degrading bile salts, and the impact of bile acid composition in the gut on the gut microbiome and host physiology.
  
  
  RESULTS
  Bile acid pool size has recently been shown to be a function of microbial metabolism of bile acids in the intestines. Recent studies have shown potential mechanisms explaining how perturbations in the microbiome affect bile acid pool size and composition. Bile acids are emerging as regulators of the gut microbiome at the highest taxonomic levels. The role of bile acids as hormones and potentiators of liver cancer is also emerging.
  
  
  CONCLUSIONS
  The host and microbiome appear to regulate bile acid pool size. The host produces a large, conjugated hydrophilic bile acid pool, maintained through positive-feedback antagonism of farnesoid X receptor (FXR) in intestine and liver. Members of the microbiome utilize bile acids and their conjugates resulting in agonism of FXR in intestine and liver resulting in a smaller, unconjugated hydrophobic bile acid pool. Hydrophilicity of the bile acid pool is associated with disease states. Reduced bile acid levels in the gut are associated with bacterial overgrowth and inflammation. Diet, antibiotic therapy, and disease states affect the balance of the microbiome-bile acid pool.
authors.affiliation: aDepartment of Microbiology and Immunology, Virginia Commonwealth University bMcGuire VA Medical Center cDivision of Gastroenterology, Hepatology and Nutrition, Virginia Commonwealth University, Richmond, Virginia, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Ridlon
authors.forename: Dae J
authors.initials: DJ
authors.lastname: Kang
authors.forename: Phillip B
authors.initials: PB
authors.lastname: Hylemon
authors.forename: Jasmohan S
authors.initials: JS
authors.lastname: Bajaj
mesh_terms: D001647:Bile Acids and Salts / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D002790:Cholesterol 7-alpha-Hydroxylase / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000382:microbiology*; D008113:Liver Neoplasms / Q000378:metabolism / Q000382:microbiology; D064307:Microbiota / Q000502:physiology*
chemical_list: D001647:Bile Acids and Salts; D002790:Cholesterol 7-alpha-Hydroxylase