No abstract

Reactive oxygen species (ROS) play a major role in cardiac dysfunction during myocardial ischemia. ROS production has been linked to oxidative stress injury and mitochondrial perturbations including permeability transition pore opening (mPTP), loss of mitochondrial membrane potential ([[Unable to Display Character: ∆]]Ψm) and necrotic cell death. Previously we identified the inducible Bcl-2 protein, Bnip3 as critical regulator of mitochondrial function and cell death of ventricular myocytes. Polyphenolic compounds including ellagic acid from pomegranate, have strong anti-oxidant properties. The effects of ellagic acid on oxidative stress injury in the heart has not been explored. In this report, we provide new compelling evidence that ellagic acid suppressed mitochondrial ROS production, loss of [[Unable to Display Character: ∆]]Ψm and necrotic cell death of cardiac myocytes induced by doxorubicin (DOX) or hypoxia. We further show mechanistically that the cytoprotective effects of ellagic acid were related to the transcriptional repression of Bnip3. In contrast to vehicle treated cells, cells treated with DOX or hypoxia displayed a marked increase in Bnip3 expression and mitochondrial association, concordant with increased ROS, mPTP, and loss of [[Unable to Display Character: ∆]]Ψm. Consistent with these mitochondrial defects there was a marked increase in mitophagy as confirmed by the dual emission Mitokeima probe that detects autophagic degradation by labelling mitochondria containing autophagosomes fused with lysosome. Mitophagy was accompanied by a marked increase in LDH release, loss of nuclear HMGB1 immunostaining and cell death. Interestingly, cells treated with ellagic acid were resistant to mitochondrial and the cytotoxic effects of DOX displaying reduced ROS production, mitophagy and were indistinguishable from vehicle treated control cells with respect to cell viability. Notably, Dox-induced Bnip3 expression was dramatically reduced in cells treated with ellagic acid. Hence, the findings of the present study demonstrate that ellagic acid suppresses mitochondrial perturbations and cell death of cardiac myocytes by mechanism that links to the repression of mitochondrial Bnip3.