Time course effects of a latent carcinogen in mice

Early-life environmental factors can increase later-life susceptibility to cancer. Short-term exposure to dichloroacetic acid (DCA), a trace drinking water contaminant with distinctive metabolic effects, increased liver cancer in mice 84 weeks after exposure was stopped. Here we evaluated time course dynamics for key events related to this latent effect. This study followed a stop-exposure design in which 28-day-old male B6C3F1 mice were given the following treatments in drinking water for up to 93 weeks: deionized water (dH20, control); 3.5 g/l DCA continuously; or 3.5 g/l DCA for 4, 10, 26, or 52 weeks followed by dH20. Effects were evaluated at eight interim time points. A short-term biomarker study was used to evaluate DCA effects at 6, 15, and 30 days. Liver tumor incidence was higher in all DCA treatment groups, including carcinomas in 82% of mice previously treated with DCA for only 4 weeks. Direct effects of DCA in the short-term study included decreased liver cell proliferation and marked mRNA changes related to mitochrondrial dysfunction and altered cell metabolism. All observed short-term effects of DCA were reversible. Prior DCA treatment did not alter liver cell proliferation, apoptosis, necrosis, or DNA sequence variants with age. Key intermediate events resulting from early-life DCA exposure do not fit classical cytotoxic, mitogenic, or genotoxic modes of action for carcinogenesis, suggesting a novel epigenetic mechanism related to metabolic disruption. Overall design: Compare liver trancriptomic profiles from male mice following six day exposure to 0, 1.0, 2.0, and 3.5 g/L DCA (n=6 per dose group) using Illumina Hi-seq.