Bile acids are synthesized in the liver and tightly regulated through the enterohepatic circulation. Recent studies reveal that bile acids serve as hormone-like signaling molecules to activate nuclear receptors, notably farnesoid X receptor (FXR), regulating metabolic homeostasis of bile acids, cholesterol, lipids, and glucose. A connection between bile acids and nonalcoholic fatty liver disease (NAFLD) has long been recognized. Although inconsistent or even contradictory results are reported, a large body of evidence from clinical as well as preclinical studies demonstrates that bile acid homeostasis is disrupted in patients with NAFLD. The bile acid dysregulation gets worsening as NAFLD progresses from early stage simple steatosis to late stage nonalcoholic steatohepatitis (NASH) and NASH with fibrosis. As the risk factors for NAFLD, obesity and insulin resistance, which are often associated with NAFLD, contribute to the dysregulation of bile acids in patients with NAFLD. Total serum and fecal bile acid concentrations are mostly elevated in patients with NAFLD as a result of increased bile acid synthesis, elevated hepatic bile acids, and upregulation of bile acid transporters. The two negative feedback regulatory pathways for bile acid synthesis, FXR/SHP (small heterodimer partner) and fibroblast growth factor-19 (FGF19)/FGF receptor-4 (FGFR4), are impaired in patients with NAFLD.
Part of the book: Nonalcoholic Fatty Liver Disease