Toluene effects on gene expression in the hippocampus of young adult, middle-age, and senescent Brown Norway Rats

Abstract

Differential susceptibility to environmental exposures across life stages is an area of toxicology about which little is known. We examined the effects of toluene on transcriptomic changes and oxidative stress (OS) parameters (e.g., NQO1 and GPX) in the rat brain at different life stages to elucidate key molecular pathways responsible for toluene-induced neurotoxicity, as well as possible age-related interactions. Changes in assessed end points following acute oral toluene (0, 0.65, and 1.0 g/kg) were examined 4 h after exposure in hippocampi of Brown Norway Rats at 4, 12, and 24 months of age. Genomic data were analyzed by two-way ANOVA to identify the effects of age, toluene, and interactions between the two factors. Analysis by one-way ANOVA identified 183 genes whose expression changed ≥ 1.25-fold with age. The majority of the genes were upregulated between life stages (> 79%). Similar analysis for toluene-related genes found only two sequences to vary significantly with dose. Fifty-six genes were identified to have expression changes due to an age-toluene interaction. Expression of genes with roles in immune response, cytoskeleton, protein, and energy metabolism was changed with advancing life stage, indicating changes in basic cellular homeostasis. Toluene affected similar cell functions, enhancing the effects of aging. OS parameters also indicated age-related changes in response mechanisms, evidence of toluene damage, and supported an age-toluene interaction. The data indicate that life stage can alter the toxicity of acute toluene exposure in various and complex ways, highlighting the need for further investigation into the role of aging in susceptibility.