Exercise prevents cardiac electrical remodeling in doxorubicin-treated female mice but does not provide cardioprotection in males
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Background
Doxorubicin (DOX) causes sex-specific cardiotoxicity. Metabolic impairment is a well-established cardiotoxic effect of DOX treatment that can contribute to other detrimental effects such as increased reactive oxygen species, reduced ATP, inflammation etc. We hypothesized that preserving cardiac metabolism by exercise can attenuate DOX cardiotoxicity.
Methods
Male and female C57BL/6J mice at 15 weeks of age were randomly assigned to one of four groups, 1) Control (sedentary), 2) EX (exercised, treadmill running), 3) DOX (doxorubicin at 5 mg/kg/week for 6 weeks), and 4) EXDOX (exercise + doxorubicin). Echocardiography was performed every other week during the 6-week protocol to measure cardiac mechanical function. At the end of the protocol, optical mapping and seahorse analysis were performed to measure electrophysiology and metabolism, respectively. RNA sequencing, cytokine array assay and transmission electron microscopy were also performed to determine sex-specific mechanisms of DOX cardiotoxicity.
Results
DOX reduced stroke volume and left ventricular diameter in males only and exercise did not prevent these effects of DOX. In female mice, DOX prolonged action potential duration (APD) and slowed conduction velocity (CV), and importantly, exercise prevented DOX-induced CV slowing. Exercise-induced cardioprotection against DOX in female mice was associated with preservation of aerobic metabolism and attenuation of inflammation which modulated ion channel gene expression. Specifically, Cacna1c was increased in both DOX and EXDOX females, but not in males and correlated with APD prolongation. Interestingly, despite CV slowing, Gja1 and Scn5a were increased. However, increased Kcnj8 along with metabolic impairment could cause membrane hyperpolarization and underlie CV slowing.
Conclusions
DOX cardiotoxicity is sex specific. Mechanical dysfunction is more prevalent in DOX-treated males while arrhythmogenic electrical remodeling is more prevalent in DOX-treated females. Exercise therapy during DOX did not prevent DOX induced mechanical dysfunction in male hearts but attenuated electrical remodeling in females by preserving metabolism and attenuating inflammation.
