Mitochondrial dynamics and myocardial metabolism alterations during anthracycline-cardiotoxicity

Abstract Background Despite the increased effectiveness of chemotherapeutic agents, cancer represents a lethal illness worldwide and anticancer strategies still present severe adverse effects. Cardiac dysfunction is a dose-dependent common affliction of anthracyclines treatment. Anthracycline-induced cardiotoxicity (AIC) and consequent heart failure has recently been suggested to be mediated by mitochondrial dysfunction; however, the molecular mechanisms driving this connection are incompletely understood. Purpose To study the early molecular changes (before onset of overt heart failure phenotype) related to mitochondrial biology and cardiac metabolism in a mouse model of AIC. Methods CD1 mice underwent 5 weekly i.p. injections (5 mg/kg) of doxorubicin. Cardiac anatomic and functional changes were evaluated by echocardiography at 1, 9 and 15 weeks-after last doxorubicin injection. At each time-point, some animals were sacrificed and hearts were collected for characterisation of mitochondrial dynamics and metabolic substrate utilization by western blot, PCR, immunocytochemistry, high-resolution respirometry, transmission electron microscopy and PET/CT. Results Doxorubicin administration resulted in an early reduction in left ventricle (LV) mass which was the result of marked cardiomyocyte atrophy as early as 1 week after doxorubicin completion. Cardiac atrophy preceded functional abnormalities, which were apparent in the form of reduction in LV ejection fraction at 9 weeks. Mitochondrial dynamics (fusion/fission) and membranes were altered as early as 1 week after doxorubicin completion (i.e. long before changes in LV function). Moreover, mitochondrial respiratory rate was decreased in these animals, together with a decrease in mitochondrial DNA content and biogenesis at early timepoints. Early (1 week) mitochondrial molecular changes were accompanied by altered cardiac metabolism (i.e. switch in substrate utilization to glucose). Conclusions Here we have characterized the dynamics of molecular, anatomical and functional changes during AIC. LV systolic dysfunction is a late phenomenon happening long after molecular and metabolic changes in the heart. Cardiomyocyte atrophy, altered mitochondrial dynamics and respiration, and metabolic switching occur long before overt heart failure phenotype. These early changes appear as promising therapeutic targets to prevent overt AIC and heart failure.