Conflicting roles for protein kinase C (PKC) isozymes in cardiac disease have been reported. Here, ␦PKC-selective activator and inhibitor peptides were designed rationally, based on molecular modeling and structural homology analyses. Together with previously identified activator and inhibitor peptides of PKC, ␦PKC peptides were used to identify cardiac functions of these isozymes. In isolated cardiomyocytes, perfused hearts, and transgenic mice, ␦PKC and PKC had opposing actions on protection from ischemiainduced damage. Specifically, activation of PKC caused cardioprotection whereas activation of ␦PKC increased damage induced by ischemia in vitro and in vivo. In contrast, ␦PKC and PKC caused identical nonpathological cardiac hypertrophy; activation of either isozyme caused nonpathological hypertrophy of the heart. These results demonstrate that two related PKC isozymes have both parallel and opposing effects in the heart, indicating the danger in the use of therapeutics with nonselective isozyme inhibitors and activators. Moreover, reduction in cardiac damage caused by ischemia by perfusion of selective regulator peptides of PKC through the coronary arteries constitutes a major step toward developing a therapeutic agent for acute cardiac ischemia.

Background-Current treatment for acute myocardial infarction (AMI) focuses on reestablishing blood flow (reperfusion).Paradoxically, reperfusion itself may cause additional injury to the heart. We previously found that ␦-protein kinase C (␦PKC) inhibition during simulated ischemia/reperfusion in isolated rat hearts is cardioprotective. We focus here on the role for ␦PKC during reperfusion only, using an in vivo porcine model of AMI. Methods and Results-An intracoronary application of a selective ␦PKC inhibitor to the heart at the time of reperfusion reduced infarct size, improved cardiac function, inhibited troponin T release, and reduced apoptosis. Using 31 P NMR in isolated perfused mouse hearts, we found a faster recovery of ATP levels in hearts treated with the ␦PKC inhibitor during reperfusion only. Conclusions-Reperfusion injury after cardiac ischemia is mediated, at least in part, by ␦PKC activation. This study suggests that including a ␦PKC inhibitor at reperfusion may improve the outcome for patients with AMI. (Circulation. 2003;108:2304-2307.)Key Words: reperfusion Ⅲ cardioprotection Ⅲ kinases C urrent treatment for acute myocardial infarction (AMI) is aimed at limiting the duration of the ischemic period by disrupting the occlusion in the coronary artery. However, no therapeutic treatment is available to prevent reperfusion injury, which occurs after these interventions. 1,2 We previously developed several isozyme-selective inhibitor and activator peptides of protein kinase C (PKC). 3 Recently, we found that treatment with a ␦PKC-selective inhibitor during ischemia/reperfusion reduced cardiac damage in isolated perfused rat hearts. 3,4 Here, we show that the ␦PKC inhibitor prevented reperfusion injury in an in vivo porcine model of AMI. Methods Peptide SynthesisThe ␦PKC inhibitor peptide ␦V1-1 was synthesized and conjugated to Tat-derived peptide 5 via a cysteine S-S bond as described. 3 In Vivo Local Occlusion, Peptide Delivery, and Pathological AssessmentWe applied a balloon catheter into the mid left anterior descending coronary artery of female juvenile Yorkshire pigs (35 to 40 kg) under anesthesia (1% isoflurane) and inflated the balloon to produce a total occlusion for 30 minutes. The guide wire was removed, and Tat alone (Tat) or Tat-␦V1-1 conjugate (␦V1-1) was infused via the lumen of the balloon catheter only for the last 1 minute of ischemia (250 ng/kg, 1 mL/min). Left ventriculograms were performed to determine cardiac function. Hearts were harvested 4 hours or 5 days after ischemia. Double staining with Evans blue dye and TTC marked areas at risk for ischemia and infarcted areas, respectively, as described previously. 6 Troponin T levels in blood, as an indicator of cardiac cytolysis, were also determined after 24 hours of reperfusion.Wedge biopsies of liver, spleen, lung and kidney were fixed in 10% buffered neutral formalin and embedded in paraffin, and 8-m-thick sections were stained with hematoxylin and eosin for pathological examination. Biochemical Analysis of Porcine Cardiac TissueH...