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

Abstract

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 nonparenchymal 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 ␤-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.

Phase I and Phase II drug-metabolizing enzymes are expressed and heterogeneously distributed in the biliary epithelium

“…37 In addition, immunostaining for CYP1A1/1A2 has been detected within intrahepatic BEC as well as hepatocytes, and markedly enhanced in both cell types by ␤-naphtoflavone in rainbow trout 38 and in rat. 39 In the latter study, a proteolytic treatment of liver sections was an obligatory requirement for unmasking CYP1A1/1A2 epitopes in BEC, adding to the view that CYP1A antigen determinants are not easily accessible to antibodies on tissue sections.…”

Cytochromes 1A1/1B1- and Catechol-O-Methyltransferase-Derived Metabolites Mediate Estradiol-Induced Antimitogenesis in Human Cardiac Fibroblast

“…In contrast, our finding that the growth inhibitory effect of estradiol is attenuated by ellipticine and pyrene, selective inhibitors of CYP1A1 and CYP1B1, respectively (28,35), provides strong evidence that the inhibitory effect of estradiol is mediated primarily by CYP1A1 and CYP1B1. This conclusion is strengthened by the observations that the inhibitory effect of estradiol is increased by exposure of CFs to ␤-naphthoflavone, a selective inducer of CYP1A1 (32), and that CFs express both CYP1A1 and CYP1B1.…”