Extracellular Vesicles Released by Cardiomyocytes in a Doxorubicin-induced Cardiac Injury Mouse Model Contain Protein Biomarkers of Early Cardiac Injury

Significant advances in the efficacy of cancer therapy have been accompanied by an escalation in side effects that result from therapy-induced injury to normal tissues. Cardiac injury is a major cause of death in cancer survivors, but biomarkers for it are detectable only after tissue injury has occurred. Extracellular vesicles (EVs) sort out oxidized proteins from tissues into the circulation as a compensatory mechanism for preventing cellular proteotoxicity. Thus, the protein contents of EVs released during the pre-degeneration stage reflects oxidative stress phenomenon that is occurring in the early damaged tissue. Here, we evaluate the potential of using circulating EVs as early diagnostic markers for long-term cardiac injury. Using a mouse model of doxorubicin (DOX)-induced cardiac injury, we found a significant increase in circulating EVs (DOX_EVs) compared to saline-treated controls. DOX_EVs exhibited a higher level of 4-hydroxynonenal adducted proteins, a lipid peroxidation product linked to DOX-induced cardiotoxicity. Proteomic profiling of DOX_EVs revealed the distinctive presence of brain/heart, muscle, and liver isoforms of glycogen phosphorylase (GP), and their origins were verified to be heart, skeletal muscle, and liver, respectively. The presence of brain/heart GP (PYGB) in DOX_EVs correlated with a reduction of PYGB in heart, but not brain tissues. Manganese superoxide dismutase (MnSOD) overexpression as well as pretreatment with FDA- approved cardioprotective agents and MnSOD mimetics resulted in a reduction of EV-associated PYGB in mice treated with DOX. Kinetic studies indicated that EVs containing PYGB are released prior to the rise of cardiac troponin (the current standard-of-care marker of cardiac injury) in the blood after DOX treatment, suggesting that PYGB is an earlier indicator of cardiac injury than conventional serum biomarkers. Thus, EVs containing PYGB serve as a liquid biopsy that is clinically attractive diagnostic biomarker for therapeutic interventions.