Anthracycline Cardiotoxicity Induces Progressive Changes in Myocardial Metabolism and Mitochondrial Quality Control: Novel Therapeutic Target.

Background: Anthracycline-induced cardiotoxicity (AIC) debilitates quality of life in cancer survivors. Serial characterizations are lacking of the molecular processes occurring with AIC.

Objectives: The aim of this study was to characterize AIC progression in a mouse model from early (subclinical) to advanced heart failure stages, with an emphasis on cardiac metabolism and mitochondrial structure and function.

Methods: CD1 mice received 5 weekly intraperitoneal doxorubicin injections (5 mg/kg) and were followed by serial echocardiography for 15 weeks. At 1, 9, and 15 weeks after the doxorubicin injections, mice underwent fluorodeoxyglucose positron emission tomography, and hearts were extracted for microscopy and molecular analysis.

Results: Cardiac atrophy was evident at 1 week post-doxorubicin (left ventricular [LV] mass 117 ± 26 mg vs 97 ± 25 mg at baseline and 1 week, respectively;  < 0.001). Cardiac mass nadir was observed at week 3 post-doxorubicin (79 ± 16 mg;  = 0.002 vs baseline), remaining unchanged thereafter. Histology confirmed significantly reduced cardiomyocyte area (167 ± 19 μm in doxorubicin-treated mice vs 211 ± 26 μm in controls;  = 0.004). LV ejection fraction declined from week 6 post-doxorubicin (49% ± 9% vs 61% ± 9% at baseline;  < 0.001) until the end of follow-up at 15 weeks (43% ± 8%;  < 0.001 vs baseline). At 1 week post-doxorubicin, when LV ejection fraction remained normal, reduced cardiac metabolism was evident from down-regulated markers of fatty acid oxidation and glycolysis. Metabolic impairment continued to the end of follow-up in parallel with reduced mitochondrial adenosine triphosphate production. A transient early up-regulation of nutrient-sensing and mitophagy markers were observed, which was associated with mitochondrial enlargement. Later stages, when mitophagy was exhausted, were characterized by overt mitochondrial fragmentation.

Conclusions: Cardiac atrophy, global hypometabolism, early transient-enhanced mitophagy, biogenesis, and nutrient sensing constitute candidate targets for AIC prevention.