Doxorubicin paradoxically protects cardiomyocytes against iron-mediated toxicity - Role of reactive oxygen species and ferritin

The cardiotoxicity induced by the anticancer anthracycline doxorubicin (DOX) is attributed to reactions between iron and reactive oxygen species (ROS) that lead to oxidative damage. We found that DOX forms ROS in H9c2 cardiomyocytes, as shown by dichlorodihydrofluorescein oxidation and the expression of stress-responsive genes such as catalase or aldose reductase. DOX also increased ferritin levels in these cells, particularly the H subunit. A considerable increase in ferritin mRNA levels showed that DOX acted at transcriptional level, but an additional potential mechanism was identified as the down-regulation of iron regulatory protein-2, post-transcriptional inhibitor of ferritin synthesis. Pretreatment with DOX protected H9c2 cells against the damage induced by subsequent exposure to ferric ammonium citrate, and experiments with Fe-55 revealed that the protection was due to the deposition of iron in ferritin. Cytoprotection was also observed when DOX was replaced by glucose/glucose oxidase, a source of H2O2, thus suggesting that DOX increases ferritin synthesis through the action of ROS. This concept was supported by three more lines of evidence. (i) DOX-induced ferritin synthesis was blocked by N-acetylcysteine, a scavenger of ROS. (ii) Mitoxantrone, a ROS-forming analogue, similarly induced ferritin expression and protected the cells against iron toxicity. (iii) 5-Iminodaunorubicin, an analogue lacking ROS-forming activity, did not induce ferritin synthesis or protect the cells against iron toxicity. These results characterize a paradoxically beneficial link between anthracycline-derived ROS, increased ferritin synthesis, and resistance to iron-mediated damage. The role of iron and ROS in anthracycline-induced cardiotoxicity may, therefore, be more complex than previously believed.