ToxSci Advance Access originally published online on April 21, 2004
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Toxicological Sciences 79, 178-188 (2004)
Toxicological Sciences vol. 79 no. 1 © Society of Toxicology; all rights reserved.
The Value of DNA Methylation Analysis in Basic, Initial Toxicity Assessments
* Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan 48824, and Pharmacia Corporation, Investigative Toxicology, Kalamazoo, Michigan 49048
Received December 5, 2003; accepted January 27, 2004
DNA methylation is an epigenetic mechanism regulating patterns of gene expression. Our goal was to see if the assessment of DNA methylation might be a useful tool, when used in conjunction with initial, basic in vitro tests, to provide a more informative preliminary appraisal of the toxic potential of chemicals to prioritize them for further evaluation. We sought to give better indications of a compound's toxic potential and its possible mechanism of action at an earlier time and, thereby, contribute to a rational approach of an overall reduction in testing by making improved early decisions. Global and GC-rich patterns of DNA methylation were evaluated along with more traditional cytolethality measurements, e.g., cytolethality and genotoxicity assessments, on rat hepatoma (H4IIE) cells. The relative toxic potential of model compounds camptothecin, 5-fluorouracil, rotenone, and staurosporine was estimated by employing DNA methylation assessments combined with our cytolethality data plus genotoxicity information gleaned from the literature. The overall contribution of the methylation assessment was threefold; it (1) strengthened a ranking based on genotoxicity; (2) provided an indication that a compound might be more potentially problematic than what cytolethality and genotoxicity assessments alone would indicate; and (3) suggested that compounds, particularly nongenotoxins, that are more potent regarding their ability to alter methylation, especially at noncytolethal concentrations, may be more potentially toxic. Altered methylation per se is not proof of toxicity; this needs to be viewed as a component of an evaluation.