Analysis of redox and apoptotic effects of anthracyclines to delineate a cardioprotective strategy.

PURPOSE: Cardiotoxic side effects of anthracyclines limit their use as effective chemotherapeutics. One mechanistic model of anthracycline-induced cardiotoxicity is attributed to the generation of intracellular reactive oxygen species (ROS). However, this theory has been questioned because several cardioprotective strategies have included the use of antioxidants without significant clinical benefit. We sought to determine whether measurement of intracellular reactive oxygen species after anthracycline exposure in vivo and in vitro could provide a means for designing more effective antioxidant-based cardioprotective schemes.
METHODS: Intracellular levels of ROS were assessed in peripheral blood mononuclear cells from leukemia bearing mice exposed to anthracyclines and in patients receiving anthracyclines. Comparison of cell death induction and ROS levels were also conducted in vitro in cardiomyocyte and leukemia lines. ROS blockade using antioxidants was conducted, and effects on cell death were assessed.
RESULTS: Elevated ROS in blood of mice and representative patient samples correlated with cardiomyocyte necrosis and decreased ejection fraction. In vitro, comparison of the cytotoxic effects of anthracyclines in acute leukemia cells and in cardiomyocytes revealed distinct kinetics of cell death induction and dependence upon oxidative stress. Although apoptotic cell death was observed in both acute leukemia cells and cardiomyocytes, the antioxidant N-acetylcysteine protected cardiomyocytes but not acute leukemia cells from anthracycline cytotoxicity.
CONCLUSIONS: Our findings point toward revisiting the use of NAC as a cardioprotective agent since it does not appear to interfere with the cytotoxic action of anthracyclines. NAC has been evaluated clinically for cardioprotective activity but future trials must ensure that adequate dose, scheduling and incorporation of markers of oxidative stress are included.