During myocardial ischemia/reperfusion (I/R), the generation of reactive oxygen species (ROS) contributes to post‐reperfusion cardiac injury and contractile dysfunction. Activation of protein kinase C epsilon (PKC ɛ) during I/R has been shown to increase ROS release, in part, by its stimulation of increased uncoupled endothelial nitric oxide synthase activity. We hypothesize that using a cell permeable PKC ɛ peptide inhibitor (PKC ɛ‐) (N‐myr‐EAVSLKPT, MW=1054 g/mol, 10μM or 20μM) will improve post‐reperfused cardiac function and attenuate infarct size compared to untreated controls in isolated perfused rat hearts subjected to I(30 min)/R(90 min). Male Sprague‐Dawley rats (275–325 g) were anesthetized with sodium pentobarbital (60 mg/kg) and anticoagulated with heparin 1000 units IP. PKC ɛ‐was dissolved in Krebs' buffer and infused during the first 10 min of reperfusion. PKC ɛ‐treated hearts exhibited significant improvement in post‐reperfused cardiac function at 90 min in the maximal rate of left ventricular developed pressure (+dP/dtmax): 56±5%; n=6 (10μM) and 46±3%; n=4 (20μM) compared to untreated controls (n=6) which only recovered to 32±5% of baseline values for +dP/dtmax respectively (p<0.05). Furthermore, PKC ɛ‐treated hearts showed significant reduction in infarct size of 27±2% (10μM) and 28 ±2% (20μM) compared to untreated control I/R hearts, 40±3% (p<0.05). The results suggest that PKC ɛ‐is effective in improving cardiac function and reducing infarct size and is a putative treatment that could aid in clinical myocardial infarction/organ transplantation patient recovery.Support or Funding InformationThis study was supported by the Center for Chronic Disorders of Aging, the Division of Research and the Department of Bio‐Medical Sciences at Philadelphia College of Osteopathic Medicine.
MI/R results in cardiac contractile dysfunction and increased cell death. MI/R is initiated in part by uncoupling of the electron transport chain in mitochondria, which generates reactive oxygen species (ROS). Increased ROS lead to the loss of mitochondrial membrane potential, which augments mitochondrial fission in MI/R. Mitochondrial fission is in turn associated with shortening of mitochondria, decreased ATP production, and is thought to promote cardiac contractile dysfunction and post‐reperfused cardiomyocyte loss, leading to increased infarct size. Therefore, inhibiting mitochondrial fission may be an effective new strategy to salvage injured cardiac myocytes during MI/R. Mdivi‐1 (MW= 353 g/mol), a mitochondrial fission inhibitor, that acts by selectively inhibiting dynamin related protein 1, a GTPase that promotes mitochondrial fission via interaction with outer mitochondrial membrane proteins, was used to test this strategy. Isolated perfused rat hearts subjected to I (30 min)/R (90 min) were infused with Mdivi‐1 (25 µM) given for 5 min at the beginning of reperfusion. Mdivi‐1 treated hearts (n=6) significantly reduced infarct size to 25% ± 2%, as compared to control I/R hearts (n=9) 44% ± 4% (p< 0.01). However, Mdivi‐1 only transiently improved post‐reperfused cardiac function at this dose, compared to control I/R hearts. These preliminary results suggest that inhibition of mitochondrial fission salvages cardiac tissue in MI/R. Future studies will test whether other Mdivi‐1 treatment regimens will prove to be more effective.
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