Primary bile acid synthesis

Primary bile acid synthesis is a complex metabolic pathway exclusively located in the liver that converts cholesterol into the primary bile acids, cholic acid (CA) and chenodeoxycholic acid (CDCA). This pathway involves approximately 17 enzymes, with cholesterol 7-alpha-monooxygenase (CYP7A1) serving as the key rate-limiting step. It represents the primary route for cholesterol elimination from the body and produces molecules essential for the emulsification and absorption of dietary lipids and fat-soluble vitamins. Beyond digestion, bile acids act as signaling molecules via receptors like the farnesoid X receptor (FXR) and TGR5 to regulate lipid, glucose, and energy homeostasis. Dysregulation of this synthesis pathway is a hallmark of several cholestatic and metabolic liver diseases, including primary biliary cholangitis and nonalcoholic steatohepatitis. Pharmacological interventions targeting the pathway, such as FXR agonists that inhibit synthesis or sequestrants that stimulate it, are critical therapeutic strategies for managing bile acid-related pathologies and systemic metabolic disorders.

Other names

Classic pathway of bile acid synthesisNeutral pathway of bile acid synthesisBile acid biosynthesisCholesterol catabolic pathway

Drugs targeting this pathway primarily act through farnesoid X receptor (FXR) activation to transcriptionally repress the rate-limiting enzyme CYP7A1, activation of the FGF19/FGFR4 signaling axis to suppress synthesis, or interruption of the enterohepatic circulation via bile acid sequestration or IBAT inhibition to stimulate compensatory synthesis from cholesterol.