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Dioxin increases reactive oxygen production in mouse liver mitochondria
Albert P Senft1, Timothy P Dalton, Daniel W Nebert
1Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati Medical Center, Cincinnati, Ohio 45267-0056, USA.
Abstract:
Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) causes an oxidative stress response in liver and several extrahepatic tissues. The subcellular sources and underlying mechanisms of dioxin-induced reactive oxygen, however, are not well understood. In this study, we examined whether mitochondria, organelles that consume the majority of cellular oxygen, might be a source of dioxin-induced reactive oxygen. Female C57BL/6 mice were treated with dioxin (15 microg/kg body wt ip) on 3 consecutive days, and liver mitochondria were examined at 1, 4, and 8 weeks after the first treatment. Mitochondrial aconitase activity, an enzyme inactivated by superoxide, was decreased by 44% at 1 week, 22% at 4 weeks, and returned to control levels at 8 weeks. Dioxin elevated succinate-stimulated mitochondrial H2O2 production twofold at 1 and 4 weeks; H2O2 production remained significantly elevated at 8 weeks. The enhanced H2O2 production was due to neither increased Mn-superoxide dismutase activity nor decreased mitochondrial glutathione peroxidase activity. Dioxin treatment augmented mitochondrial glutathione, but not glutathione disulfide levels, a result that might be explained by increased mitochondrial glutathione reductase activity. Liver ATP levels were significantly lowered at 1 and 4 weeks, the peak times of mitochondrial reactive oxygen production. Increased dioxin-stimulated reactive oxygen at 1 and 4 weeks did not appear to be related to the observed decrease in cytochrome oxidase activity, since State 3 and State 4 respiration were not diminished. To our knowledge, this is the first report to show that dioxin increases mitochondrial respiration-dependent reactive oxygen production, which may play an important role in dioxin-induced toxicity and disease.
Insights
Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) exposure increases reactive oxygen production in liver mitochondria. This mitochondrial oxidative stress may contribute to dioxin
Area of Science:
- Biochemistry
- Toxicology
- Cell Biology
Background:
- Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) exposure triggers oxidative stress in the liver and other tissues.
- The specific cellular origins and mechanisms of dioxin-induced reactive oxygen species (ROS) remain unclear.
Purpose of the Study:
- To investigate if mitochondria, major cellular oxygen consumers, are a source of dioxin-induced ROS.
- To elucidate the role of mitochondrial dysfunction in dioxin toxicity.
Main Methods:
- Female C57BL/6 mice were administered dioxin (15 microg/kg) for three consecutive days.
- Liver mitochondria were isolated and analyzed at 1, 4, and 8 weeks post-treatment.
- Mitochondrial function markers including aconitase activity, H2O2 production, enzyme activities (Mn-SOD, glutathione peroxidase, glutathione reductase), ATP levels, and respiration were assessed.
Main Results:
- Dioxin significantly decreased mitochondrial aconitase activity and elevated H2O2 production at 1 and 4 weeks, with elevated H2O2 persisting at 8 weeks.
- Enhanced ROS production was not linked to altered Mn-superoxide dismutase or glutathione peroxidase activity but may involve increased mitochondrial glutathione reductase.
- Liver ATP levels were reduced at 1 and 4 weeks, coinciding with peak mitochondrial ROS production, but cytochrome oxidase activity remained unaffected.
Conclusions:
- This study provides the first evidence that dioxin exposure enhances mitochondrial respiration-dependent ROS production.
- Mitochondrial oxidative stress is a key mechanism contributing to dioxin-induced liver toxicity and potential disease development.