Basic and clinical aspects of bile acids

Abstract

Bile acids play an important role on bile formation as well as the solubilization of cholesterol in the bile. Bile acids are biosynthesized from cholesterol, excreted into bile. Bile acids play enterohepatic circulation, in which the effective transport systems in the terminal ileum and liver play important roles. The excretion of cholesterol and phospholipids from the bile canaliculus to the liver is mediated by ABCG5/G7 and MDR2, respectively. These molecules make unilamellar vesicles, which in turn change to micelles by the participation of bile acids excreted by BSEP. FXR, a nuclear receptor with bile acids as ligands, decreases intrahepatic bile acids by the down-regulation of CYP7A1 and NTCP and the up-regulation of BSEP. TGR5, a membrane receptor of bile acids, is considered to regulate the excretion of ductular bile flow.