Doxorubicin (DOX) is one of the most effective chemotherapeutic agents, but
cardiotoxicity limits DOX
therapy. Although the mechanisms are not entirely understood,
reactive oxygen species (ROS) appear to be involved in DOX
cardiotoxicity. Ca/
calmodulin dependent protein kinase II (
CaMKII) can be activated by ROS through oxidation and is known to contribute to myocardial dysfunction through Ca leakage from the sarcoplasmic reticulum (SR). We hypothesized that
CaMKII contributes to DOX-induced defects in intracellular Ca ([Ca](i)) handling. Cardiac myocytes were isolated from wild-type (WT) adult rat hearts and from mouse hearts lacking the predominant myocardial
CaMKII isoform (CaMKIIδ(-/-), KO) vs. WT. Isolated cardiomyocytes were investigated 30 min after DOX (10 μmol/L) superfusion, using epifluorescence and confocal microscopy. Intracellular ROS-generation ([ROS](i)) and [Ca](i) handling properties were assessed. In a subset of experiments,
KN-93 or AIP (each 1 μmol/L) were used to inhibit
CaMKII.
Melatonin (Mel, 100 μmol/L) served as ROS-scavenger. Western blots were performed to determine the amount of
CaMKII phosphorylation and oxidation. DOX increased [ROS](i) and led to significant diastolic [Ca](i) overload in rat myocytes. This was associated with reduced [Ca](i) transients, a 5.8-fold increased diastolic SR Ca leak and diminished SR Ca content. ROS-scavenging partially rescued Ca handling. Western blots revealed increased
CaMKII phosphorylation, but not
CaMKII oxidation after DOX. Pharmacological
CaMKII inhibition attenuated diastolic [Ca](i) overload after DOX superfusion and led to partially restored [Ca](i) transients and SR Ca content, presumably due to reduced Ca spark frequency. In line with this concept,
isoform-specific CaMKIIδ-KO attenuated diastolic [Ca](i) overload and Ca spark frequency. DOX exposure induces
CaMKII-dependent SR Ca leakage, which partially contributes to impaired cellular [Ca](i) homeostasis. Pharmacological and genetic
CaMKII inhibition attenuated but did not completely abolish the effects of DOX on [Ca](i). In light of the clinical relevance of DOX, further investigations seem appropriate to determine if
CaMKII inhibition could reduce DOX-induced
cardiotoxicity.