2-Ethylhexyl Diphenyl Phosphate (EHDPP) Induces Hepatic Expression of Cytochrome P450s, Liver Damage, and Genotoxicity in Mice

As a commonly present organophosphorus flame retardant and persistent organic pollutant, 2-ethylhexyl diphenyl phosphate (EHDPP) has been observed to be genotoxic in cultured human hepatoma (HepG2) cells which depends on CYP activities. Yet, its impacts on hepatic Cyp expression, hepatotoxicity and genotoxicity in intact mammalians remain unidentified. In this study, adult male C57BL/6J mice received EHDPP by gastric gavage at doses of 50, 100, and 150 mg/kg (b.w.)/d for 7 d, then the hepatic expression of several Cyp proteins, aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR) was analyzed by Western blotting; hepatoxicity was determined by serum ALT/AST activities and hepatic histological examination, while genotoxicity by comet assay, phosphorylated histone (γ-H2AX) protein, micronucleus test, and Pig-a assay. A micronucleus test in mouse hepatoma (Hepa1-6) cells in vitro was employed to observe the modulating effect of PCB 126 (100 nM)/BAY-218 (700 nM) (Ahr-Cyp1a1 activator/inhibitor). The results indicated that EHDPP induced hepatic Cyp1a1, 2e1, AhR, Cyp1a2, Cyp3a4 and PXR proteins and histologic liver damage at 50 mg/kg/d and/or higher doses, while at the highest dose (150 mg/kg/d) with hepatic DNA damage and micronucleus formation in bone marrow polychromatic erythrocytes. The result of Pig-a assay (at 14 and 28 d) was negative. In Hepa1-6 cells EHDPP induced micronucleus marginally; however, this effect was enhanced by PCB 126, while abolished by BAY-218. This study suggests that EHDPP may enhance protein expression of hepatic Cyp1a1, Cyp2e1, AhR and PXR and induce liver damage and DNA/chromosome damage in mice; Cyp1a1 might be a major activating enzyme.