Bile Acids

Bile acids (BAs), which are produced in liver from cholesterol, are important signaling molecules for intermediary metabolism within the gut-liver axis and in extrahepatic organs, such as brown adipose tissue and muscle. The primary BAs are secreted across the canalicular membrane of hepatocytes via the bile salt export pump (Bsep) into bile. In the intestine, gut microbiota convert primary BAs to secondary BAs via dehydroxylation, deconjugation, and epimerization. The intestinal microbiota contains enzymes that metabolize BAs such as bile salt hydrolases (Bshs), which removes glycine or taurine from conjugated BAs. Ninety-five percent of BAs undergoes reabsorption from the intestinal lumen via active transport and recirculates to liver by the portal blood. Upon reaching the liver BAs are taken up across the sinusoidal membrane of hepatocytes via sodium taurocholate cotransporting polypeptide (Ntcp/Slc10a1) and organic anion transporting polypeptide 1b2 (Oatp1b2/Slco1b2) transporters.

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