Additive Protection of the Ischemic Heart Ex Vivo by Combined Treatment With δ-Protein Kinase C Inhibitor and ε-Protein Kinase C Activator

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Abstract
Background— Protein kinase C (PKC) plays a major role in cardioprotection from ischemia/reperfusion injury. Using an HIV-1 Tat protein–derived peptide to mediate rapid and efficient transmembrane delivery of peptide regulators of PKC translocation and function, we examined the cardioprotective effect of selective δ-PKC inhibitor (δV1-1) and ε-PKC activator (ψεRACK) peptides for ischemia/reperfusion damage in isolated perfused rat hearts. Furthermore, we examined the protective effects of these PKC isozymes in isolated perfused hearts subjected to ischemia/reperfusion damage using transgenic mice expressing these peptides specifically in their cardiomyocytes. Methods and Results— In isolated perfused rat hearts, administration of δV1-1 but not ψεRACK during reperfusion improved cardiac function and decreased creatine phosphokinase release. In contrast, pretreatment with ψεRACK but not δV1-1, followed by a 10-minute washout before ischemia/reperfusion, also improved cardiac function and decreased creatine phosphokinase release. Furthermore, administration of ψεRACK before ischemia followed by δV1-1 during reperfusion only conferred greater cardioprotective effects than that obtained by each peptide treatment alone. Both the δ-PKC inhibitor and ε-PKC activator conferred cardioprotection against ischemia/reperfusion injury in transgenic mice expressing these peptides in the heart, and coexpression of both peptides conferred greater cardioprotective effects than that obtained by the expression of each peptide alone. Conclusions— δ-PKC inhibitor prevents reperfusion injury, and ε-PKC activator mimics ischemic preconditioning. Furthermore, treatment with both peptides confers additive cardioprotective effects. Therefore, these peptides mediate cardioprotection by regulating ischemia/reperfusion damage at distinct time points.