Increased heme oxygenase-1 expression during copper deficiency in rats results from increased mitochondrial generation of hydrogen peroxide1-4

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 (R-2 = 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.