Subcellular basis of vitamin C protection against doxorubicin-induced changes in cardiomyocytes and Sca-1 positive cells

• Main Author: Ludke, Ana
• Other Authors: Singal, Pawan (Physiology)
• Published: Springer/Kluwer Academic Publishers 2012
• Subjects: heart failure; apoptosis; stem cell; chemotherapy; oxidative stress
• Online Access: http://hdl.handle.net/1993/9677

Understanding the molecular basis of doxorubicin (Dox)-induced oxidative stress leading to cardiomyopathy is crucial to finding cardioprotective strategies to manage this important clinical problem. Improving the antioxidant defenses of cardiac cells could be one strategy for cardioprotection. The role of oxidative stress in Dox-induced cardiotoxicity as well as testing the efficacy of antioxidant Vitamin C (Vit C) in offering protection to cardiomyocytes was investigated. As stem cells have been suggested to play a role in this cardiotoxicity, Dox-mediated oxidative stress effects, with and without Vit C, on the stem cell antigen-1 (Sca) positive cells from heart as well as bone marrow were also examined. Our time-course studies of the effects of Dox on the isolated cardiomyocytes showed that the phosphorylation of mitogen-activated protein kinases and p53 followed the rise in reactive oxygen species (ROS) production. Dox also downregulated the Sodium-dependent Vit C Transporter-2 (SVCT-2) and this may have enhanced Dox-induced increase in oxidative stress. Pro-apoptotic markers Bax/Bcl-xL ratio and caspase 3 cleavage were higher after the activation of stress-induced pathways and viability of cells was decreased. Dox-induced increase in apoptosis and decrease in cell viability depended in part on the activation of p38/JNK and p53 proteins, but not on the ERK protein. Exposure to Dox, increased membrane leakage, autophagy and lipid peroxidation. On the other hand, Dox decreased overall antioxidant capacity as well as expression of the endogenous antioxidant enzymes glutathione peroxidase, Cu/Zn superoxide dismutase and catalase. Dox affected Sca-1 positive cells in a prominent manner which was marked by a dose-dependent increase in cell loss, cell leakage and ROS levels as well as decrease in cellular ATP levels. Vit C pre-treatment prior to the addition of Dox delayed and reduced Dox-induced injury to cardiomyocytes, preserving viability. Vit C was able to blunt the decrease in SVCT-2 as well as Dox-induced oxidative stress. Vit C also offered protection to Sca-1 positive cells by partially preventing Dox-induced changes to these cells. The data presented in this thesis improves our knowledge of the molecular mechanisms leading to Dox-induced cardiotoxicity as well as suggest cardioprotection by Vit C.