Natural endogenously occurring peptides exhibit desirable medicinal properties, but are often limited in application by rapid proteolysis and inadequate membrane permeability. However, editing naturally occurring peptide sequences to develop peptidomimetic analogs created a promising class of therapeutics that can augment or inhibit molecular interactions. Here, we discuss a variety of chemical modifications, including L to D isomerization, cyclization, and unnatural amino acid substitution, as well as design strategies, such as attachment to cell-penetrating peptides, which are used to develop peptidomimetics. We also provide examples of approved peptidomimetics and discuss several compounds in clinical trials.

BackgroundThe transient receptor potential vanilloid 1 (TRPV1) mediates cellular responses to pain, heat, or noxious stimuli by calcium influx; however, the cellular localization and function of TRPV1 in the cardiomyocyte is largely unknown. We studied whether myocardial injury is regulated by TRPV1 and whether we could mitigate reperfusion injury by limiting the calcineurin interaction with TRPV1.Methods and ResultsIn primary cardiomyocytes, confocal and electron microscopy demonstrates that TRPV1 is localized to the mitochondria. Capsaicin, the specific TRPV1 agonist, dose‐dependently reduced mitochondrial membrane potential and was blocked by the TRPV1 antagonist capsazepine or the calcineurin inhibitor cyclosporine. Using in silico analysis, we discovered an interaction site for TRPV1 with calcineurin. We synthesized a peptide, V1‐cal, to inhibit the interaction between TRPV1 and calcineurin. In an in vivo rat myocardial infarction model, V1‐cal given just prior to reperfusion substantially mitigated myocardial infarct size compared with vehicle, capsaicin, or cyclosporine (24±3% versus 61±2%, 45±1%, and 49±2%, respectively; n=6 per group; P<0.01 versus all groups). Infarct size reduction by V1‐cal was also not seen in TRPV1 knockout rats.Conclusions TRPV1 is localized at the mitochondria in cardiomyocytes and regulates mitochondrial membrane potential through an interaction with calcineurin. We developed a novel therapeutic, V1‐cal, that substantially reduces reperfusion injury by inhibiting the interaction of calcineurin with TRPV1. These data suggest that TRPV1 is an end‐effector of cardioprotection and that modulating the TRPV1 protein interaction with calcineurin limits reperfusion injury.

Deciphering the remote conditioning molecular mechanism may provide targets to develop therapeutics that can broaden the clinical application. To further investigate this, we tested whether two protein kinase C isozymes, the ubiquitously expressed epsilon PKC (εPKC) and the neuronal specific gamma PKC (γPKC), mediate nociceptive-induced remote myocardial conditioning. Male Sprague-Dawley rats were used for both in vivo and ex vivo myocardial ischemia-reperfusion protocols. For the in vivo studies, using a surgical abdominal incision for comparison, applying only to the abdomen either bradykinin or the εPKC activator (ψεRACK) reduced myocardial infarct size (45±1%, 44±2%, respectively, versus incision: 43±2%, and control: 63±2%, P < 0.001). Western blot showed only εPKC, and not γPKC, is highly expressed in the myocardium. However, applying a selective γPKC inhibitor (γV5-3) to the abdominal skin blocked remote protection by any of these strategies. Using an ex vivo isolated heart model without an intact nervous system, only selective εPKC activation, unlike a selective classical PKC isozyme activator (activating α, β, βII and γ), reduced myocardial injury. Importantly, the classical PKC isozyme activator given to the abdomen in vivo (with an intact nervous system including γPKC) during myocardial ischemia reduced infarct size as effectively as an abdominal incision or ψεRACK (45±1% versus 45±2% and 47±1%, respectively). The classical PKC activator-induced protection was also blocked by spinal cord surgical transection. These findings identified potential remote conditioning mimetics, with these strategies effective even during myocardial ischemia. A novel mechanism of nociceptive-induced remote conditioning, involving γPKC, was also identified.

Introduction: The transient receptor potential 1 channel (TRPV1) mediates signals from pain, heat, and/or noxious stimuli. TRPV1 sensitization can occur via a protein kinase C (PKC)-dependent mechanism in neurons. Therefore, we tested whether TRPV1 is a mediator of cardioprotection in models of ischemia-reperfusion and whether the molecular mechanism of cardioprotection occurs via PKC-induced TRPV1 channel sensitization. Methods: Male Sprague Dawley rats and H9C2 left ventricle-derived cells were used for whole animal and cellular ischemia-reperfusion studies to test this hypothesis. Statistical analysis regarding infarct size, calculated as percentage of area at risk per left ventricle, was performed by a one way ANOVA (*P<0.01). Results: Remote preconditioning-induced infarct size reduction via an abdominal surgical incision was blocked by prior administration of a selective TRPV1 peptide inhibitor, V1-B (3.0mg/kg), given over the incision site (Incision: 44±2*% V1-B+Incision: 65±2% versus Control: 64±1% n=6/group). Capsaicin (0.3mg/kg) given intravenously through the internal jugular vein reduced infarct size in vivo , which was blocked by prior capsazepine (TRPV1 inhibitor, 3.0mg/kg) administration (Capsaicin: 43±2* Capsaicin+ capsazepine: 64±4 versus Control: 62±3, n=7/group). Further in an ex vivo isolated heart model, infarct size reduction afforded by the selective epsilon PKC activator (pseudo epsilon RACK, 1uM) was partially blocked with prior treatment of V1-B (1uM), the TRPV1 peptide blocker (pseudo epsilon RACK: 20±2*%, pseudo epsilon RACK+V1-B: 42±4% versus control: 47±4%, n=7/group). TRPV1 expression was found in both whole heart homogenate and in the H9C2 cell line. Using a model of ischemia-reoxygenation in H9C2 cells, capsaicin treatment before and during ischemia-reoxygenation reduced cellular damage as assessed by MTT and LDH assays. Greater damage occurred with TRPV1 inhibition by capsazepine compared to control. Conclusions: Our studies suggest TRPV1 contributes an essential role for both remote and direct cardioprotection. Further studies are ongoing to determine the post-translational sites on TRPV1 and how a TRPV1-epsilon PKC protein-protein interaction induces cardioprotection.