Activation of aryl hydrocarbon receptor signaling by cotton balls used for environmental enrichment.

Dioxins are nearly ubiquitous environmental contaminants that are produced as byproducts during industrial processes, including the bleaching of paper and textiles. Contamination of animal bedding material with dioxins has been a concern for both laboratory and farm animals. The objective of this study was to determine whether the presence of cotton balls, provided to mice for enrichment, caused induction of the cytochrome P450 1A1 gene (Cyp1A1), which typically is stimulated through activation of the aryl hydrocarbon receptor (AhR) by dioxins and dioxin-like compounds. Cyp1A1 transcripts and protein in the liver were increased significantly by either exposure to cotton balls or treatment with a single dose of 2,3,7,8-tetrachlorodibenzo-para-dioxin. Unexposed controls displayed low levels of Cyp1A1 transcript and undetectable levels of CYP1A1 protein. These results suggest that cotton balls are potentially contaminated with dioxins and/or dioxin-like compounds that act as potent inducers of Cyp1a1 in laboratory animals if used as nesting material. This study underscores the necessity of considering dioxin content in products used for enrichment in animal facilities.