Chronic
iron overload has slow and insidious effects on heart, liver, and other organs. Because
iron-driven oxidation of most biologic materials (such as
lipids and
proteins) is readily repaired, this slow progression of organ damage implies some kind of biological "memory." We hypothesized that cumulative
iron-catalyzed
oxidant damage to
mtDNA might occur in
iron overload, perhaps explaining the often lethal cardiac dysfunction. Real time PCR was used to examine the "intactness" of mttDNA in cultured H9c2 rat cardiac myocytes. After 3-5 days exposure to high
iron, these cells exhibited damage to
mtDNA reflected by diminished amounts of near full-length 15.9-kb PCR product with no change in the amounts of a 16.1-kb product from a nuclear gene. With the loss of intact
mtDNA, cellular respiration declined and mRNAs for three electron transport chain subunits and 16 S rRNA encoded by
mtDNA decreased, whereas no decrements were found in four subunits encoded by nuclear
DNA. To examine the importance of the interactions of
iron with metabolically generated
reactive oxygen species, we compared the toxic effects of
iron in wild-type and rho(o) cells. In wild-type cells, elevated
iron caused increased production of
reactive oxygen species, cytostasis, and cell death, whereas the rho(o) cells were unaffected. We conclude that long-term damage to cells and organs in
iron-overload disorders involves interactions between
iron and mitochondrial
reactive oxygen species resulting in cumulative damage to
mtDNA, impaired synthesis of respiratory chain subunits, and respiratory dysfunction.