Expression of the hepatocyte canalicular multidrug resistance protein (MRP2) in primary biliary cirrhosis

The canalicular multidrug resistance protein 2 (MRP2; gene symbol: ABCC2) mediates ATP-dependent biliary excretion of organic anions such as bilirubin diglucuronide, glutathione conjugates and sulfated and glucuronidated bile salts. In chronic cholestatic liver diseases, the biliary excretion of cholephilic organic anions is impaired. While the underlying transport defects have been studied in rat models of cholestasis, little is known about the molecular basis of impaired organic anion excretion in human cholestatic liver disease. Our aim, therefore, was to analyze expression of MRP2 in patients with primary biliary cirrhosis (PBC), a chronic cholestatic liver disease characterized by progressive destruction of small intrahepatic bile ducts. Four patients with PBC stages III (n=1) and IV (n=3) were compared with three non-cholestatic patients with alcoholic liver disease, idiopathic liver cirrhosis and cirrhosis from chronic hepatitis C. Immunohistochemistry was performed on paraffin-embedded tissue slides using a monoclonal antibody to MRP2. MRP2 was detected at the canalicular hepatocyte membrane of all patients. In two PBC patients (stages III and IV, respectively), the degree of immunostaining was comparable with controls, whereas in two other PBC patients with stage IV disease immunostaining was decreased. We conclude that MRP2 expression decreases with progressive cholestasis in PBC.