Abstract
Doxorubicin (DOX) is a widely prescribed anthracycline antineoplastic drug for treating human solid tumors and leukemias. However, DOX therapy is limited by a cumulative, dose-dependent, and irreversible cardiomyopathy that occurs with repeated administration. Presumably, a pivotal initiating event of DOX-induced cardiotoxicity is the production of reactive oxygen species (ROS) and oxidation of lipids, DNA, and proteins. We recently identified activation of the Keap1/Nrf2-antioxidant response system-a major cellular defense mechanism against such oxidative stress-as an important response to acute DOX exposure in vitro. In the present study, we address the hypothesis that dysregulation of this pathway in cardiac tissue is also manifested in vivo following chronic DOX administration. Male, Sprague-Dawley rats received 6 weekly injections of 2 mg/kg (s.c.) DOX or saline followed by a 5-week drug-free period prior to analysis of cardiac tissue transcripts and proteins. In contrast to in vitro findings, the Keap1/Nrf2-antioxidant response system was suppressed in hearts of DOX-treated animals and consistent with the observed decrease in protein abundance for Nrf2 and PGAM5, both of which are substrates for Keap1. Although this shift in Keap1/Nrf2 suppresses the antioxidant pathway, the concurrent loss of PGAM5 could function as a signal for disposal of damaged mitochondria from the cell, thus removing the source of ROS. These findings identify the Keap1/Nrf2 and Keap1/PGAM5 pathways as important responses to DOX-induced cardiac injury in vivo; disruption of this system for mitochondrial hormesis may be an important contributing factor to cardiotoxicity after chronic drug administration.