Altered expression of alkaline phosphatase (ALP) in the liver of primary biliary cirrhosis (PBC) patients

Serum alkaline phosphatase (ALP) is a representative marker of cholestasis, in diseases such as primary biliary cirrhosis (PBC). However, the hepatic localization of ALP in patients with cholestatic liver diseases has not been fully clarified. Accordingly, we studied the expression of ALP in the liver of PBC, chronic hepatitis C and controls. By immunohistochemistry, in the liver tissue of controls and chronic hepatitis C patients, ALP was found to be localized in the canalicular membrane of hepatocytes and the apical area of the cytoplasm of bile duct epithelial cells. In PBC, ALP was localized in both the canalicular and baso-lateral membranes of hepatocytes and in the whole cytoplasm of the remaining bile duct epithelial cells. The expression of ALP in liver tissues evaluated by Western blotting was increased to 3.6-fold in PBC compared with that in the controls and chronic hepatitis C patients, while the expression of mRNA of ALP evaluated by RT-PCR was increased to 7.0-fold in PBC compared with that in the controls and chronic hepatitis C patients. The present study is the first study to reveal altered localization and increased expression of ALP which may result in the elevation of serum ALP in PBC.