Investigating the role of the aryl hydrocarbon receptor in benzene-initiated toxicity in vitro.

Chronic occupational exposure to benzene has been correlated with aplastic aneamia and acute myelogenous leukemia, however mechanisms behind benzene toxicity remain unknown. Interestingly, benzene-initiated hematotoxicity is absent in mice lacking the aryl hydrocarbon receptor (AhR) suggesting an imperative role for this receptor in benzene toxicities. This study investigated two potential roles for the AhR in benzene toxicity using hepa 1c1c7 wild type and AhR deficient cells. Considering that many toxic effects of AhR ligands are dependent on AhR activation, our first objective was to determine if benzene, hydroquinone (HQ) or benzoquinone (BQ) could activate the AhR. Secondly, because the AhR regulates a number of enzymes involved in oxidative stress pathways, we sought to determine if the AhR had a role in HQ and BQ induced production of reactive oxygen species (ROS). Dual luciferase assays measuring dioxin response element (DRE) activation showed no significant change in DRE activity after exposure to benzene, HQ or BQ for 24h. Immunofluorescence staining showed cytosolic localization of the AhR after 2h incubations with benzene, HQ or BQ. Western blot analysis of cells exposed to benzene, HQ or BQ for 1, 12 and 24h did not demonstrate induction of CYP1A1 protein expression. Dichlorodihydrofluorescein staining of cells exposed to benzene, HQ or BQ revealed that the presence of the AhR did not affect BQ and HQ induced ROS production. These results indicate that the involvement of the AhR in benzene toxicity does not seem to be through classical activation of this receptor or through interference of oxidative stress pathways.