Protein Kinase C Beta II Inhibitor combined with Conjugated Myristic Acid and Trans-Activator of Transcription achieves cardiovascular protection in porcine myocardial ischemia/reperfusion model

Philadelphia, PA

Introduction

While timely reperfusion is critical during resuscitation of ischemic myocardium, oxidative stress still leads to ischemia/reperfusion (I/R) injury and ultimately, cardiomyocyte death. The major targets for mitigating oxidative stress are NADPH oxidase (NOX-2) and mitochondria, which are both activated by Protein Kinase C Beta II (PKCβII). In previous studies with an ex-vivo rat heart I/R model, Myristic Acid (Myr) and Trans-Activator Transcription (Tat) conjugated PKCβII inhibitor (Myr-Tat-PKCβII-; N-Myr-Tat-CC-SLNPEWNET) showed cardioprotective effects and a decrease in infarct area. In this study, we investigated the cardioprotective effects of Myr-Tat-PKCβII- in comparison with a scrambled peptide control.

Methods

Regional I(1 hour)/R(3 hours) was induced in Male Yorkshire pigs (38-50kg) using balloon-assisted occlusion of the second diagonal branch of the Left Anterior Descending Artery (LAD) which is responsible for supplying 40% of the anterior myocardium. At the end of ischemia, the balloon was deflated to allow for reperfusion and the LAD was treated immediately with a bolus of either Myr-Tat-PKCβII- or scrambled peptide. Cardiac function was measured by monitoring changes in ejection fraction (EF). Cardiac injury was assessed through routine measurements of serum creatine phosphokinase (CPK), troponin I, and myoglobin. After I/R, the hearts were stained with Evans Blue dye to identify the area at risk (AR) and 1% triphenyltetrazolium chloride to determine the area of necrosis (AN). Infarct size was then quantified (AN/AR) and was analyzed via Student’s t-test, along with EF and cardiac marker measurements.

Results

Analysis showed that Myr-Tat-PKCβII- significantly restored EF to within 1.40.7% of baseline compared to controls which only restored EF to within 6.42.1% (p<0.05) of baseline. Myr-Tat-PKCβII- showed a significant decrease in serum myoglobin levels at 1 hr of reperfusion (135132 ng/mL, n=4) compared to scrambled control (1022346 ng/mL, n=3 p<0.05). Myr-Tat-PKCβII- reduced infarct size to 10.0±2.8%; n=4; compared to scrambled control hearts (28.5±8.3%; n=6; *p<0.05). CPK and Troponin I levels were comparable in both groups. These results suggest that Myr-Tat-PKCβII- can help prevent cardiac injury when given immediately after an ischemic event.

Discussion

Data from ex-vivo rat heart I/R model, coupled with data from this in-vivo porcine I/R model indicate the efficacy of Myr-Tat-PKCβII- in preventing oxidative stress-induced cardiac injury. These findings suggest that Myr-Tat-PKCβII- could be useful in the clinical setting when administered immediately after cardiac resuscitation following an ischemic event. Future studies include the treatment of human umbilical vein endothelial cells with Myr-Tat-PKCβII- prior to hypoxia and at the beginning of reperfusion conditions, followed by cell viability assays in comparison with the untreated control. This additional data can help determine the optimal dose to use in an 8 week survival study using the same porcine myocardial I/R protocol for Myr-Tat-PKCβII-.