Quantitative proteomic study identified cathepsin B associated with doxorubicin-induced damage in H9c2 cardiomyocytes

Doxorubicin is one of the most effective chemotherapeutic agents, and is indicated for many cancers including breast cancers, lung cancers, and ovary cancers. However, the optimal clinical use of this agent is limited by its major adverse effect of cardiomyopathy which leads to congestive heart failure, which would cause a mortality of approximately 50% (1,2). Extensive research has suggested several possible mechanisms for its cardiomyopathy including apoptosis, oxidative stress, inactivated cardiomyocyte specific genes, and altered molecular signaling (for example, MAPKs) (3). However, unfortunately, no effective treatment for established doxorubicin cardiomyopathy is available. Therefore, there is a great need to identify novel targets to protect the heart from doxorubicin damage. Recent developments in proteomic technology provide an opportunity for the discovery of novel molecular pathways and biomarkers of drug-induced toxicity. Especially, in a recent proteomic study using the common two-dimensional electrophoresis (2-DE) and mass spectrometry technologies, Kumar et al. (4) identified several oxidative stress response-related proteins differently regulated in rat cardiomyocytes and heart tissues exposed to doxorubicin. Compared with the traditional proteomic methods such as 2-DE Summary The study was performed to analyze the proteomic profiling of doxorubicin-treated H9c2 cardiomyocytes in order to identify novel protein biomarkers associated with doxorubicininduced cardiomyopathy. The protein profiling of H9c2 cells in response to doxorubicin at an apoptosis-induced concentration of 0.5 μM were compared using iTRAQ analysis. Western-blot analysis was used to confirm differentially expressed proteins identified in the proteomic study. A total of 22 differently expressed proteins were identified in doxorubicin-treated H9c2 cells including 15 up-regulated and 7 down-regulated proteins. Gene Ontology (GO) analysis revealed that 10 altered proteins were enriched in the process of apoptosis. We further validated the expression of cathepsin B and its possible regulator nuclear factor kappa B (NF-κB) in H9c2 cells were increased during doxorubicin treatment using Western-blots. Differentially expressed proteins might provide clues to clarify novel mechanisms underlying doxorubicin-induced cardiomyopathy. Our results also suggest that increased cathepsin B expression might be associated with NF-κB upregulation, and the exact mechanisms need to be clarified.