Gene induction/repression response profiling of hepatotoxic agents using cDNA microarrays

DNA microarray technology is a powerful technique that allows for the simultaneous expression analysis of thousands of genes. In the field of toxicology, microarray analysis can be used to identify individual genes or families of genes regulated during adverse drug reactions. Such information provides us with a more detailed understanding of the molecular mechanisms underlying toxic effects. Additionally, microarray technology can be used to identify gene expression profiles for new therapeutic compounds, thus providing an early screening method for potential toxic effects. An important step in using microarray analysis in toxicity screening is to construct a library of genes that are regulated positively or negatively during hepatotoxicity, as these genes may not be represented in libraries prepared from normal tissue. In order to facilitate this, we have treated rats with hepatotoxins representing diverse structural and therapeutic classes. These compounds induce a variety of hepatotoxic responses including peroxisomal proliferation, hepatic necrosis and apoptosis, cholestasis, DNA damage, protein synthesis inhibition, oxidative stress, mitochondrial damage, P-450 induction and phospholipidosis. The livers were harvested from the treated rats and mRNA was isolated. The mRNA was pooled and gene expression analysis of treated versus untreated rats was assayed using microarray analysis. The data gathered from microarray and sequence analysis allows us to identify signature sets of genes regulated during toxicity. These gene responses are then used to identify mechanisms of toxicity. Knowledge of specific toxicologic pathways can help determine potential human liabilities, and the identification of signature gene sets can be used to evaluate drug candidates for potential adverse effects. In a follow-up case study, using microarrays, we evaluated changes in gene expression in rat liver associated with hypertrophy, hyperplasia and single cell necrosis (apoptosis) following administration of a drug candidate.