Immunohistochemical demonstration of β-naphthoflavone-inducible cytochrome P450 1A1/1A2 in rat intrahepatic biliary epithelial cells

Although intrahepatic biliary epithelial cells are targets for certain hepatotoxic chemicals, including some procarcinogens, their ability to monooxygenate, and thereby bioactivate and inactivate xenobiotics, remains to be established. Thus, the present study was undertaken to immunohistochemically determine if cytochrome P450 (CYP) 1A1/1A2 is present and can be induced within these non- parenchymal liver cells. Immunoperoxidase and immunofluorescent staining for CYP1A1/1A2 was detected within intrahepatic biliary epithelial cells as well as hepatocytes of control rats and was markedly enhanced in both cell types by β-naphthoflavone (BNF). Color confocal laser microscopic analyses of dual immunofluorescent staining for CYP1A1/1A2 and cytokeratins 6 and 9 (56 and 64 kd, respectively) provided unequivocal evidence for the presence and induction of CYP1A1/1A2 within intrahepatic bile duct epithelia. Moreover, microdensitometric analyses of immunoperoxidase staining intensities for CYP1A1/1A2 revealed that intrahepatic biliary epithelial cells of control rats contain 44%, 56%, and 58% as much CYP1A1/1A2 as do centrilobular, midzonal, and periportal hepatocytes, respectively. These analyses further revealed that BNF increased the content of CYP1A1/1A2 in biliary epithelial cells by approximately 120%, while CYP1A1/1A2 levels in centrilobular, midzonal, and periportal hepatocytes were increased by 82%, 159%, and 160%, respectively. The results of this study represent the first in situ demonstration that mammalian intrahepatic biliary epithelial cells contain a CYP isoform, and further that CYP1A1/1A2 can be induced in these cells by BNF. These findings therefore indicate that intrahepatic biliary epithelial cells can oxidatively metabolize xenobiotics in situ and that their ability to bioactivate and inactivate xenobiotics can be significantly enhanced by CYP1A1/1A2 induction.