The use of genomics technology to investigate gene expression changes in cultured human liver cells

The field of genomics has great potential in toxicology; however, the techn ology is still in its infancy and there are many questions that need to be addressed. In this study we focus on the use of toxicogenomics for the dete rmination of gene expression changes associated with hepatotoxicity. The hu man hepatoma cell line HepG2 was used to assess the toxic effects of two we ll-studied hepatotoxins, carbon tetrachloride (CCl4) and ethanol (EtOH). Re plicate dishes of HepG2 cells were exposed to two concentrations of CCl4 an d EtOH - doses which caused 20% and 50% cell death (as determined by the MT T assay) were chosen [0.18% and 0.4% (v/v) CCl4; 2.5% and 5% (v/v) EtOH] an d the cells exposed for periods of 2 and 24 h. mRNA was extracted and used to probe Atlas(TM) Human Toxicology II arrays (Clontech). Preliminary data revealed that following a 2-h exposure at the low doses of both compounds, few changes in gene expression were detected. However, after 24-h exposure of the cells to the same low concentration of both compounds, multiple chan ges in gene expression were observed, many of which were specific to the in dividual hepatotoxins, presumably reflecting their different mechanisms of action. CCl4 treatment of HepG2 cells gave rise to treatment specific up-re gulation of genes involved in extracellular transport and cell signalling, whereas EtOH treatment gave rise predominantly to down-regulation of genes involved in stress response and metabolism. In addition, changes in regulat ion of certain genes (involved in stress response and cell cycle) were comm on to both treatments. Exposure of HepG2 cells to higher doses of the hepat otoxins gave rise to more changes in gene expression at lower exposure time s. These results strongly suggest that different mechanisms of hepatotoxici ty may be associated with specific patterns of gene expression, while some genes associated with common cellular responses may be useful as early mark ers of toxicity. (C) 2001 Elsevier Science Ltd. All rights reserved.