Doxorubicin-dependent reduction of ferrylmyoglobin and inhibition of lipid peroxidation: implications for cardiotoxicity of anticancer anthracyclines

Lipid peroxidation has been proposed to mediate cardiotoxicity induced by doxorubicin (DOX) and other anticancer anthracyclines; however, there have been reports showing that DOX can also inhibit lipid peroxidation. Here we characterized the effects of DOX on the oxo-ferryl moiety Fe(IV)=O, Mb(IV)] of H(2)O(2)-activated myoglobin, a lipid oxidant likely formed in the heart during treatment with DOX. Mb(IV) was formed in vitro by reacting 100 microM H(2)O(2) with 50 microM horse heart metmyoglobin (Mb(III)). Spectral studies showed that DOX reduced Mb(IV) to Mb(III), half-maximal regeneration of Mb(III) occurring at approximately 18 microM DOX. Comparisons between DOX, its aglycone doxorubicinone, and other approved or investigational anthracyclines or model compounds (daunorubicin, idarubicin, aclarubicin, and naphthazarin), showed that DOX reduced Mb(IV) through the hydroquinone moiety of its tetracyclic ring. DOX inhibited Mb(IV)-dependent peroxidation of arachidonic acid, suppressing the formation of thiobarbituric acid-reactive substances with an IC(50) of approximately 18 microM. Lipid peroxidation was inhibited also by the hydroquinone-containing daunorubicin and idarubicin but not by the hydroquinone-deficient aclarubicin; moreover, neither simple hydroquinone nor other known Mb(IV) reductants (ascorbate, glutathione, and ergothioneine) reached measurable IC(50)s in a micromolar range. DOX-dependent inhibition of lipid peroxidation correlated with its ability to reduce Mb(IV) to Mb(III) in competition with arachidonic acid (r = 0.83, P = 0.029); it did not correlate with its ability to scavenge other free radical species like e.g., peroxyl radicals generated through the thermal decomposition of 2,2'-azo-bis(2-amidinopropane)]. DOX reduced Mb(IV) and inhibited lipid peroxidation also when H(2)O(2), Mb(III) and arachidonic acid were reacted in cytosol of human myocardial biopsies, a model developed to predict the cardiotoxic mode of action of DOX in patients. These results illustrate "antioxidant" properties of DOX, mediated by reduction of Mb(IV) to Mb(III), and cast doubts on lipid peroxidation as a causative mechanism of anthracycline-induced cardiotoxicity.