Modulation of the in vitro cardiotoxicity of doxorubicin by flavonoids

Cancer therapy with the anthracycline doxorubicin (Dox) is limited by cardiomyopathy, which develops in animals and patients after cumulative dosing. Generation of free radicals by Dox may be involved in this cardiotoxicity. Dox binds strongly to metal ions, especially iron(III). This Dox-metal complex stimulates the generation of free radicals through self-reduction of the complex. We investigated the possibility of inhibiting Dox-induced cardiotoxicity by scavenging of free radicals and/or chelating metal ions. The effects of Dox, both alone and in combination with iron-chelating agents, were studied on inotropy of the isolated mouse left atrium, lipid peroxidation (LPO) in cardiac microsomal membranes, ferricytochrome c (cyt.c3+) reduction, and oxygen consumption. The flavonoids 7-monohydroxyethylrutoside (mono-HER) and 7,3',4'-trihydroxyethylrutoside (tri-HER) and the ethylenediaminetetraacetic acid (EDTA) analogue ICRF-198 and its precursor ICRF-187 were used as iron-chelating agents. The latter were used for comparison since ICRF-187 has been reported to inhibit the cardiotoxic effects of Dox both in vitro and in vivo. Only the flavonoids could inhibit the negative inotropic effect of Dox (35 microM) on the mouse left atrium; in the presence of tri-HER (500 microM) the beating force decreased by 18% instead of 50%, whereas mono-HER completely prevented the Dox-induced negative inotropic effect. ICRF-198 and both flavonoids (500 microM) completely inhibited Dox (35 microM)-induced LPO, whereas ICRF-187 provided 65% inhibition. The observation that both cyt.c3+ reduction and oxygen consumption induced by the Dox-iron(III) complex (50/16.6 microM Dox3Fe3+) could be inhibited by superoxide dismutase proved the involvement of superoxide anions (O2-.). The iron-chelating agents (50 microM) inhibited cyt.c3+ reduction by 91% (mono-HER), 43% (tri-HER), and 100% (ICRF-198). Only mono-HER and ICRF-198 (50 microM) were capable of inhibiting the oxygen consumption by 70% and 43%, respectively. It is concluded that flavonoids offer a good perspective for further studies on the prevention of Dox-induced cardiomyopathy.