Down-regulation of the expression of alcohol dehydrogenase 4 and CYP2E1 by the combination of α-endosulfan and dioxin in HepaRG human cells

Pesticides and other persistent organic pollutants are considered as risk factors for liver diseases. We treated the human hepatic cell line HepaRG with both 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) and the organochlorine pesticide, alpha-endosulfan, to evaluate their combined impact on the expression of hepatic genes involved in alcohol metabolism. We show that the combination of the two pollutants (25 nM TCDD and 10 mu M alpha-endosulfan) led to marked decreases in the amounts of both the mRNA (up to 90%) and protein (up to 60%) of ADH4 and CYP2E1. Similar results were obtained following 24 h or 8 days of treatment with lower concentrations of these pollutants. Experiments with siRNA and AHR agonists and antagonist demonstrated that the genomic AHR/ARNT pathway is necessary for the dioxin effect. The PXR, CAR and estrogen receptor alpha transcription factors were not modulators of the effects of alpha-endosulfan, as assessed by siRNA transfection. In another human hepatic cell line, HepG2, TCDD decreased the expression of ADH4 and CYP2E1 mRNAs whereas alpha-endosulfan had no effect on these genes. Our results demonstrate that exposure to a mixture of pollutants may deregulate hepatic metabolism.