The secondary alcohol metabolite of doxorubicin irreversibly inactivates aconitase/iron regulatory protein‐1 in cytosolic fractions from human myocardium

Abstract

Anticancer therapy with doxorubicin (DOX) is limited by severe cardiotoxicity, presumably reflecting the intramyocardial formation of drug metabolites that alter cell constituents and functions. In a previous study, we showed that NADPH-supplemented cytosolic fractions from human myocardial samples can enzymatically reduce a carbonyl group in the side chain of DOX, yielding a secondary alcohol metabolite called doxorubicinol (DOXol). Here we demonstrate that DOXol delocalizes low molecular weight Fe(II) from the [4Fe-4S] cluster of cytoplasmic aconitase. Iron delocalization proceeds through the reoxidation of DOXol to DOX and liberates DOX-Fe(II) complexes as ultimate by-products. Under physiologic conditions, cluster disassembly abolishes aconitase activity and forms an apoprotein that binds to mRNAs, coordinately increasing the synthesis of transferrin receptor but decreasing that of ferritin. Aconitase is thus converted into an iron regulatory protein-1 (IRP-1) that causes iron uptake to prevail over sequestration, forming a pool of free iron that is used for metabolic functions. Conversely, cluster reassembly converts IRP-1 back to aconitase, providing a regulatory mechanism to decrease free iron when it exceeds metabolic requirements. In contrast to these physiologic mechanisms, DOXol-dependent iron release and cluster disassembly not only abolish aconitase activity, but also affect irreversibly the ability of the apoprotein to function as IRP-1 or to reincorporate iron within new Fe-S motifs. This damage is mediated by DOX-Fe(II) complexes and reflects oxidative modifications of -SH residues having the dual role to coordinate cluster assembly and facilitate interactions of IRP-1 with mRNAs. Collectively, these findings describe a novel mechanism of cardiotoxicity, suggesting that intramyocardial formation of DOXol may perturb the homeostatic processes associated with cluster assembly or disassembly and the reversible switch between aconitase and IRP-1. These results may also provide a guideline to design new drugs that mitigate the cardiotoxicity of DOX.

Doxorubicin increases the susceptibility of brain mitochondria to Ca2+-induced permeability transition and oxidative damage

“…Moreover, O 2 − -mediated mitochondrial aconitase inactivation leads to hydroxyl radical formation [53]. Minotti and collaborators [54] reported that doxorubicinol, the secondary alcohol metabolite of doxorubicin, irreversibly inactivates aconitase, contributing to DOX-induced cardiotoxicity. We also observed that DOX treatment induces a significant decrease in brain mitochondrial aconitase activity (Fig.…”

Regulation of ferritin genes and protein

“…Oxidants, including ROS 86,146,150 and nitric oxide, 151 may release iron from ferritin, IRP1, or hemoglobin, 152 either directly or through heme oxygenase (in the case of heme-containing proteins). 39 This can lead to ferritin induction through IRP inhibition (above), and perhaps through direct iron-mediated transcriptional regulation of ferritin.…”

Ameliorative effect of naringin against doxorubicin-induced acute cardiac toxicity in rats

“…There is evidence suggesting that the Dox treatment can induce apoptosis by multiple different mechanisms (Mukhopadhyay et al, 2009). Moreover, Dox causes iron dysregulation by the formation of Fe 3+ -Dox complex leading to inactivation of cytochrome c oxidase (Hasinoff & Davey, 1988), and changes in iron homeostatic processes associated with aconitase-iron regulatory protein-1 (ACO1) (Minotti et al, 1998).…”