Rat liver epithelial cells express functional cytochrome P450 2E1.

Abstract

Rat liver epithelial cells (RLECs) isolated by trypsinization of the livers of normal 10 day old rats are largely used in co-culture with primary hepatocytes. The aim of the present study was to investigate the expression of biotransformation enzyme-encoding genes in three preparations of RLEC lines. Although no expression of cytochrome P450 1A1/2 (CYP1A1/2), CYP2B1/2, CYP2C6 or CYP3A mRNAs could be detected, we found that all of the different preparations of RLECs expressed a high level of CYP2E1 mRNA. We demonstrated the presence of the CYP2E1 apoprotein in microsomes of RLECs by immunoblot analyses, together with chlorzoxazone 6-hydroxylation, an activity known to be mainly catalyzed by CYP2E1. In addition, acetone treatment of these cells resulted in an increase in both CYP2E1 apoprotein and chlorzoxazone 6-hydroxylation activity levels. Finally, we showed the susceptibility of RLECs to N-methyl formamide- and diethylnitrosamine-induced toxicity, suggesting metabolic activation by CYP2E1. Thus, RLECs may cooperate with hepatocytes to CYP2E1-mediated metabolism in the co-culture model. In addition, transfection experiments with a CYP2E1 promoter construct, in which the proximal 539 bp containing the binding site for HNF1alpha were inserted upstream of the chloramphenicol acetyl transferase gene, demonstrated a strong induction upon co-transfection with an HNF1alpha expression plasmid. Thus, RLECs provide a useful tool for studying metabolism and cytotoxicity of CYP2E1 substrates in the absence of other expressed CYPs, and for analyzing CYP2E1 promoter function.