Doxorubicin-associated late developing cardiomyopathy may be related to the depletion of cardiac primitive cells pool in the adult human heart.

The cumulative dose-dependent toxicity of doxorubicin, with the late development of the chronic heart failure that does not respond to digitalis, imposes serious limits on cancer treatment and often leads to heart transplantation in relatively young patients. Known studies of the mechanisms of doxorubicin toxicity focused on cardiomyocytes damage. According to the new notion of cardiac tissue biology, cardiac primitive cells are considered to provide the adult heart with a substantial growth reserve determining the function of the heart throughout life. Hence, numerous factors that can influence the subtle balance between cardiac primitive cells death and survival, can be implicated in the development and progression of cardiomyopathy and heart failure. The scope of the study was to examine the effects of doxorubicin on human adult CD117-positive cardiac primitive cells in vitro. Moreover, the role of dexrazoxane, a chelating agent with cardioprotective action, was revisited with respect to the reduction of doxorubicin toxicity on cardiac primitive cells. CD117-positive cells were incubated with increasing concentrations of doxorubicin hydrochloride (0,1; 0,5 and 1,0μM), followed by the evaluation of proliferation and apoptosis after 12, 24 and 48 hours. Proliferation was evaluated by BrdU incorporation and it decreased at all time-points, with the most significant effects after 24 hours, when its rate dropped from 12,84±1,83% (n=4) to 2,41±0,27% (n=4, p<0,05) at the 1,0μM. Apoptosis was evidentiated by the detection of mitochondrial potential disruption and caspase activation, implicating the generation of free radicals of oxygen in the mechanisms of doxorubicin-induced damage. The quantification of apoptotic cells in TUNEL assay revealed the maximum increase of apoptosis rate from 3,26±0,48% (n=5) to 21,85±3,26% (n=5, p<0,001) after 12 hours of incubation with 0,5μM doxorubicin. Pre-treatment of cells with dexrazoxane hydrochloride diminished apoptosis; however, its rates did not reach the baseline. Moreover, its statistically significant effects were visible only for up to 24 hours. These results indicate a profound influence of doxorubicin on human cardiac primitive cells proliferation and survival, suggesting the new mechanism for the doxorubicin-associated late developing cardiomyopathy, related to the depletion of cardiac primitive cells pool in the adult human heart. Revealed mechanism of cardiomyopathy should stimulate the studies of the rescue therapy with cardiac primitive cells transplantation in the patients after doxorubicin treatment.