Protein Kinase C Beta II Peptide Inhibitor Elicits Potent Cardioprotective Effects on Attenuating Ischemia/Reperfusion Injury

Ischemia-reperfusion (I/R) injury mediated by excessive reactive oxygen species (ROS) is a well-known mechanism of myocardial tissue damage following cardio-angioplasty in the treatment of heart attacks. Previous studies have shown that Protein Kinase C beta II (PKCβII) inhibition during reperfusion with peptide (N-myr-SLNPEWNET; PKCβII-) attenuated ROS release in rat hind-limb I/R and leukocyte infiltration in myocardial I/R models, in part, via NOX-2 inhibition. However, the effects of PKCβII activation during reperfusion have not been elucidated. In this study, we hypothesize that myristic acid (myr-) conjugated PKCβII- will attenuate cell death resulting in decreased infarct size and improved post-reperfused cardiac function compared to untreated controls, whereas PKCβII peptide activator (N-myr-SVEIWD; myr-PKCβII+) will show no improvement compared to controls. Global I(30 min)/R(50 min) was induced in isolated perfused male rat hearts, followed by infusion of myr-PKCβII+ (20μM; n=10), myr-PKCβII- (20μM; n=10) or plasma (control; n=10) during the first 5 min of reperfusion. Cardiac function was assessed using a pressure transducer placed in the left ventricle (LV). At the end of 50 min reperfusion, hearts were frozen (-20oC), sectioned, and stained using 1% triphenyltetrazolium chloride to assess infarct size by comparing dead tissue vs. total heart tissue weight. Data was evaluated using ANOVA with Fisher’s post-hoc analysis. The maximal rate of LV developed pressure (+dP/dtmax) at 50min postreperfusion was significantly improved in myr-PKCβII- hearts (1607±134 mmHg/s) compared to control (950 ±130 mmHg/s) and myr-PKCβII+ hearts (954± 138 mmHg/s). The difference in +dP/dtmax most likely is attributed to the significant difference in post-reperfused LV end diastolic pressure, which recovered to 37±5 mmHg compared to control (57±5 mmHg) and myr-PKCβII+ (60±4 mmHg; both p<0.01). Additionally, Myr-PKCβII- significantly reduced infarct size to 14±3% compared to control (26±5%; p<05); whereas myr-PKCβII+ (24±3%) showed no significant difference. The data suggests that myr-PKCβII+ does not exacerbate I/R injury, while myr-PKCβII- may be an effective therapeutic to reduce I/R injury following cardio-angioplasty.