IMMUNOHISTOCHEMICAL DEMONSTRATION OF BETA-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 t o monooxygenate, and thereby bioactivate and inactivate xenobiotics, r emains to be established. Thus, the present study was undertaken to im munohistochemically determine if cytochrome P450 (CYP) 1A1/1A2 is pres ent and can be induced within these nonparenchymal liver cells. Immuno peroxidase 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 beta-nap hthoflavone (BNF), Color confocal laser microscopic analyses of dual i mmunofluorescent staining for CYP1A1/1A2 and cytokeratins 6 and 9 (56 and 64 kd, respectively) provided unequivocal evidence for the presenc e and induction of CYP1A1/1A2 within intrahepatic bile duct epithelia. Moreover, microdensitometric analyses of immunoperoxidase staining in tensities 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 CYP 1A1/1A2 in biliary epithelial cells by approximately 120%, while CYP1A 1/1A2 levels in centrilobular, midzonal, and periportal hepatocytes we re increased by 82%, 159%, and 160%, respectively. The results of this study represent the first in situ demonstration that mammalian intrah epatic biliary epithelial cells contain a CYP isoform, and Further tha t CYP1A1/1A2 can be induced in these cells by BNE These findings there fore indicate that intrahepatic biliary epithelial cells can oxidative ly metabolize xenobiotics in situ and that their ability to bioactivat e and inactivate xenobiotics can be significantly enhanced by CYP1A1/1 A2 induction.