Bile acids are synthesized in the liver and stored in the gallbladder. After eating, bile acids are released from the gallbladder into the small intestine. The majority of bile acids are transported back to the liver, but some may then escape enterohepatic circulation to enter systemic circulation. The bile acids, deoxycholic acid (DCA) and chenodeoxy cholic acid (CDCA), may interact with gap junction proteins to cross the blood-brain barrier. Bile acids are endogenous ligands for farnesoid X receptor (FXR) and G-protein coupled BA receptor 1 (TGR5) and once they have crossed the blood brain barrier, the bile acids may interact with these receptors. FXR is a regulator of secretion and transport of bile acids. TGR5 receptor activation increases cAMP synthesis and activates the mitogen-activated protein kinase (MAPK) pathway. TGR5 regulates the use of energy and is a target of interest for metabolic disorders.

Bile Acid Direct Signalling Pathway (1) References