Ursodiol (ursodeoxycholic acid; UDCA; URSO; Actigall) is a bile acid originally identified in black bears; the name ursodiol derives from the Latin name of the bear family, Ursidae (Hagey et al., 1993). It was first used in Western medicine for the dissolution of gallstones in gall bladder disease patients.

Both primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) cause accumulation of toxic bile acids (such as deoxycholic acid (DCA)) in the liver, leading to liver cell death. UDCA therapy therefore is often associated with an improvement of liver biochemistry, including a reduction in serum alanine aminotransferase and aspartate aminotransferase activity. Serum alkaline phosphatase activity may also be reduced. The beneficial effects of ursodiol in PBC and PSC patients are in part attributable to a protective effect of this bile acid against toxic bile acids in liver cells (Paumgartner and Beuers, 2002). In addition, ursodiol increases bile transport activity, stimulating hepatobiliary secretion by preserving activity of the bile-salt export pump (BSEP), a key component of the bile transport system in the liver (Paoloni et al., 2002).

UDCA also seems to have anti-inflammatory properties. It binds to the glucocorticoid receptor and suppresses a key inflammatory component, nuclear factor-kappa B (NFkB) (Miura et al., 2001).

Anticholestatic effects of ursodiol have also been reported in other liver diseases, including progressive familial intrahepatic cholestasis, intrahepatic cholestasis of pregnancy, and liver disease associated with cystic fibrosis (Colombo et al., 1992; Angulo, 2002; Paumgartner and Beuers, 2002).