Mitochondrial reactive oxygen production is dependent on the aromatic hydrocarbon receptor

2,3,7,8-Tetrachlorodibenzo-p-dioxin (dioxin; TCDD) is a pervasive environmental contaminant that induces hepatic and extrahepatic oxidative stress. We have previously shown that dioxin increases mitochondrial respiration-dependent reactive oxygen production. In the present study we examined the dependence of mitochondrial reactive oxygen production on the aromatic hydrocarbon receptor (AHR), cytochrome P450 1A1 (CYP1A1), and cytochrome P450 1A2 (CYP1A2), proteins believed to be important in dioxin-induced liver toxicity. Congenic Ahr(−/−), Cyp1a1(−/−) and Cyp1a2(−/−) knockout mice, and C57BL/6J inbred mice as their Ahr/Cyp1a1/Cyp1a2(+/+) wild-type (wt) counterparts, were injected intraperitoneally with dioxin (15 μg/kg body weight) or corn-oil vehicle on 3 consecutive days. Liver mitochondria were examined 1 week following the first treatment. The level of mitochondrial H2O2 production in vehicle-treated Ahr(−/−) mice was one fifth that found in vehicle-treated wt mice. Whereas dioxin caused a rise in succinate-stimulated mitochondrial H2O2 production in the wt, Cyp1a1(−/−), and Cyp1a2(−/−) mice, this increase did not occur with the Ahr(−/−) knockout. The lack of H2O2 production in Ahr(−/−) mice was not due to low levels of Mn2+-superoxide dismutase (SOD2) as shown by Western immunoblot analysis, nor was it due to high levels of mitochondrial glutathione peroxidase (GPX1) activity. Dioxin decreased mitochondrial aconitase (an enzyme inactivated by superoxide) by 44% in wt mice, by 26% in Cyp1a2(−/−) mice, and by 24% in Cyp1a1(−/−) mice; no change was observed in Ahr(−/−) mice. Dioxin treatment increased mitochondrial glutathione levels in the wt, Cyp1a1(−/−), and Cyp1a2(−/−) mice, but not in Ahr(−/−) mice. These results suggest that both constitutive and dioxin-induced mitochondrial reactive oxygen production is associated with a function of the AHR, and these effects are independent of either CYP1A1 or CYP1A2.