Time course of cardiomyopathy induced by doxorubicin in rats

Abstract

Doxorubicin (DOX)-related cardiotoxicity may expose cancer survivors to increased risk of cardiovascular morbidity and mortality. Here, we characterized the time course of DOX-induced cardiomyopathy in rats. Sprague-Dawley male rats (12 wk old) received doxorubicin hydrochloride (1 mg/kg/d, ip) during 10 consecutive days and they were euthanized one (DOX1), two (DOX2) or four (DOX4) weeks after the last drug injection. Control group received NaCl 0.9% (ip). Hearts were mounted on a Langendorff perfusion system, left ventricle fragments were processed for microscopy and oxidative stress-related assays, and blood was collected for cardiac troponin I assay. All DOX-treated groups showed swollen and vacuolated cardiomyocytes with myofilaments disarray and mitochondrial damage. These changes were already evident after one week and became more pronounced after four weeks. Cardiac troponin I plasma levels were significantly increased in DOX1 and further increased in DOX4 compared to control group. Increased oxidative damage to lipids was observed in DOX1, and to proteins in DOX4. Glutathione peroxidase activity increased in DOX4. The morphological changes resulted in cardiac remodeling, including interstitial fibrosis, apoptosis and significant impairment of both contractile and relaxation function in DOX 4 compared to control group. Hearts from all animals displayed an early reduction in the responsiveness to norepinephrine. These findings support the view that DOX cardiotoxicity occurs in a "continuum", and as the hypothesis of an irreversible cardiac injury is being challenged, understanding the progression of morphological and functional changes caused by DOX may allow proper timing of initiation of prophylactic treatment.