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Biochemical and Molecular Actions of Nutrients

Increased Heme Oxygenase-1 Expression during Copper Deficiency in Rats Results from Increased Mitochondrial Generation of Hydrogen Peroxide^1–,4

U.S. Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND 58202-9034

⁵To whom correspondence should be addressed. E-mail: tjohnson{at}gfhnrc.ars.usda.gov.

The activity of hepatic heme oxygenase (HO) in rats is elevated in response to copper deficiency. However, the mechanism responsible for the increase in HO activity is poorly understood. Oxidative stress is a common denominator for many of the signals that induce HO-1, the inducible isoform of HO. The present study evaluated the role of H₂O₂ and the mitochondrial electron transport chain as a potential mechanism for the induction of HO-1 during copper deficiency. Mitochondria isolated from the livers of young male rats fed a copper-deficient diet for 5 wk had significantly (P < 0.05) reduced levels of NADH:cytochrome c reductase (31% reduction), succinate:cytrochrome c reductase (42% reduction), and cytochrome c oxidase (70% reduction) activities and significantly increased production of H₂O₂ (48% increase) when glutamate was used as a substrate. Hepatic levels of HO-1 protein and mRNA were also significantly elevated (48 and 20%, respectively) in copper-deficient rats, indicating that copper deficiency stimulated the expression of the HO-1 gene. Furthermore, hepatic HO-1 protein content was best described by a regression model that included mitochondrial NADH:cytochrome c reductase and succinate:cytochrome c reductase activities, but not cytochrome c oxidase activity (R² = 0.54, P < 0.02). Hydrogen peroxide is a known inducer of HO-1, and our results suggest that increased mitochondrial H₂O₂ production resulting from inhibition of respiratory complex activities contributes to the induction of HO-1 during copper deficiency. The levels of HO-1 protein and mRNA were also elevated (85 and 95%, respectively) in hearts from copper-deficient rats, indicating that the effects of copper deficiency on HO-1 gene expression are not limited to hepatic tissue.

KEY WORDS: • heme oxygenase • mitochondria • hydrogen peroxide • respiratory complexes • copper deficiency

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