Non-genotoxic hepatocarcinogenesis in vitro: the FaO hepatoma line responds to peroxisome proliferators and retains the ability to undergo apoptosis

Abstract

A range of hepatoma cell lines (RH1, HTC, FaO, 7800C1 and MH1C1), has been studied with the aim of establishing an in vitro model to investigate the molecular mechanisms of hepatocarcinogenicity induced by the peroxisome proliferator class of non-genotoxic carcinogens. In view of speculation that peroxisome proliferators suppress hepatocyte apoptosis in vivo, we have placed particular emphasis on evaluating whether hepatoma cell lines retain the ability to undergo apoptotic cell death. Expression of the liver-specific differentiation marker albumin and the peroxisome proliferator-activated receptor (PPAR) was highest in the Reuber hepatoma cell line, FaO. This cell line also demonstrated the most marked response to the peroxisome proliferator nafenopin with a 2.2-fold induction of the microsomal enzyme cytochrome p450IVA1. This response was found to display intercellular heterogeneity by immunocytochemistry. Thus, the FaO cell line maintained characteristics of hepatocytes, both in vivo and in vitro, in terms of expression of constitutive and inducible markers. However, none of the cell lines tested mirrored the hyperplastic response of hepatocytes to nafenopin, since no increase in cell growth kinetics was observed on addition of nafenopin to the growth medium. The mode of cell death in confluent FaO cultures was characterised as apoptosis, by fluorescence microscopy and agarose gel electrophoresis of extracted DNA. Cells detaching from confluent FaO cultures exhibited chromatin condensation and DNA fragmentation patterns characteristic of cels undergoing apoptotic death.Interestingly, no apoptosis was seen in monolayer cells, suggesting that apoptosis in vitro is associated with cell shrinkage and detachment similar to that documented for the liver in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)