Ursodeoxycholic acid (UDCA)

Ursodeoxycholic acid (UDCA, ursodiol) is a naturally occurring secondary bile acid produced in trace amounts in humans and some other species via bacterial metabolism of primary bile acids[1][5][9]. As a therapeutically administered small molecule, UDCA is not a classical drug target (receptor, enzyme, or transporter); instead, it exerts multiple beneficial effects on the liver and biliary tract by replacing toxic, hydrophobic bile acids, thereby protecting hepatocytes and cholangiocytes, reducing cholesterol absorption and secretion, and promoting more hydrophilic bile flow[1][3][4][5]. UDCA is FDA-approved as the first-line therapy for primary biliary cholangitis and is also used for the prevention and dissolution of cholesterol gallstones, among other off-label uses[1][3][4]. Its mechanisms include altering bile acid composition, choleresis, immunomodulation, and acting as a partial agonist at the farnesoid X receptor (FXR)[1][10]. While UDCA is essential in liver therapeutics, it is not itself a molecular target but a modulator, and thus the query appears to misidentify the molecule as a target rather than a drug. Note: Ursodeoxycholic acid is a drug/substrate, not a receptor, enzyme, transporter, or typical therapeutic target. If requesting information for a true target (e.g., farnesoid X receptor), a different query would be appropriate. The present entry is best described as a drug used for its multiple effects in hepatobiliary diseases.

Other names

Ursodiol3α,7β-dihydroxy-5β-cholan-24-oic acid

Replaces hydrophobic, toxic bile acids in the bile acid pool Inhibits intestinal cholesterol absorption and hepatic secretion of cholesterol into bile Promotes hydrophilic bile acid pool, protecting hepatocytes/cholangiocytes from injury Upregulates biliary transport proteins (e.g., AE2 chloride-bicarbonate exchanger) Indirect, partial agonist/antagonist at the farnesoid X receptor (FXR)[1][3][10] Immunomodulation by decreasing MHC class I antigen expression in hepatocytes