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Chronic kidney disease (CKD) increases myocardial infarct size by an unknown mechanism. Here we examined the hypothesis that impairment of protective PI3K-PDK1-Akt and/or mTORC-Akt signaling upon reperfusion contributes to CKD-induced enlargement of infarct size. CKD was induced in rats by 5/6 nephrectomy (SNx group) 4 weeks before myocardial infarction experiments, and sham-operated rats served as controls (Sham group). Infarct size as a percentage of area at risk after ischemia/reperfusion was significantly larger in the SNx group than in the Sham group (56.3 ± 4.6 vs. 41.4 ± 2.0%). In SNx group, myocardial p-Akt-Thr308 level at baseline was elevated, and reperfusion-induced phosphorylation of p-Akt-Ser473, p-p70s6K and p-GSK-3β was significantly suppressed. Inhibition of Akt-Ser473 phosphorylation upon reperfusion by Ku-0063794 significantly increased infarct size in the Sham group but not in the SNx group. There was no difference between the two groups in activities of mTORC2 and PDK1 and protein level of PTEN. However, the PP2A regulatory subunit B55α, which specifically targets Akt-Thr308, was reduced by 24% in the SNx group. Knockdown of B55α by siRNA increased baseline p-Akt-Thr308 and blunted Akt-Ser473 phosphorylation in response to insulin-like growth factor-1 (IGF-1) in H9c2 cells. A blunted response of Akt-Ser473 to IGF-1 was also observed in HEK293 cells transfected with a p-Thr308-mimetic Akt mutant (T308D). These results indicate that increased Akt-Thr308 phosphorylation by down-regulation of B55α inhibits Akt-Ser473 phosphorylation upon reperfusion in CKD and that the impaired Akt activation by insufficient Ser473 phosphorylation upon reperfusion contributes to infarct size enlargement by CKD.

To commemorate the auspicious occasion of the 30th anniversary of IPC, leading pioneers in the field of cardioprotection gathered in Barcelona in May 2016 to review and discuss the history of IPC, its evolution to IPost and RIC, myocardial reperfusion injury as a therapeutic target, and future targets and strategies for cardioprotection. This article provides an overview of the major topics discussed at this special meeting and underscores the huge importance and impact, the discovery of IPC has made in the field of cardiovascular research., Competing Interests: HEB is shareholder of CellAegis Inc. PF is a founder and CEO of Pharmahungary, a group of R&D companies. GH served as a consultant to Servier. MO was a consultant for Neurovive Pharmaceuticals. DGD served as consultant to Neurovive Pharmaceuticals. All other authors have no relevant disclosures.

In this meeting report, particularly addressing the topic of protection of the cardiovascular system from ischemia/reperfusion injury, highlights are presented that relate to conditioning strategies of the heart with respect to molecular mechanisms and outcome in patients' cohorts, the influence of co-morbidities and medications, as well as the contribution of innate immune reactions in cardioprotection. Moreover, developmental or systems biology approaches bear great potential in systematically uncovering unexpected components involved in ischemia-reperfusion injury or heart regeneration. Based on the characterization of particular platelet integrins, mitochondrial redox-linked proteins, or lipid-diol compounds in cardiovascular diseases, their targeting by newly developed theranostics and technologies opens new avenues for diagnosis and therapy of myocardial infarction to improve the patients' outcome., Competing Interests: HEB is a shareholder of CellAegis Inc.

Sirtuins are a highly conserved family of histone/protein deacetylases whose activity can prolong the lifespan of model organisms such as yeast, worms and flies. In mammalian cells, seven sirtuins (SIRT1-7) modulate distinct metabolic and stress-response pathways, SIRT1 and SIRT3 having been most extensively investigated in the cardiovascular system. SIRT1 and SIRT3 are mainly located in the nuclei and mitochondria, respectively. They participate in biological functions related to development of heart failure, including regulation of energy production, oxidative stress, intracellular signaling, angiogenesis, autophagy and cell death/survival. Emerging evidence indicates that the two sirtuins play protective roles in failing hearts. Here, we summarize current knowledge of sirtuin functions in the heart and discuss its translation into therapy for heart failure.

This review takes a critical look at the current effectiveness of reperfusion therapy for acute myocardial infarction and at the potential for cardioprotective agents to improve it. Reperfusion alone limits the median value of infarct size to approximately 50% of the ischemic region. However, the range of infarct sizes is very wide, and one-fourth of these patients have more than 75% of the ischemic zone infarcted despite successful coronary reperfusion. Available studies suggest that mortality and morbidity is increased when more than 20% of the left ventricle is infarcted. Therefore, to be effective infarct size-limiting therapy would have to reduce infarction to or below this 20% target. To achieve this goal in the quartile of patients with the biggest infarcts the cardioprotective agent would have to be potent enough to reduce infarct size from its current value of 75% of the ischemic zone to 40% or less. While ischemic preconditioning and some pretreatment drugs might be potent enough to achieve this goal, few of the agents given at the clinically relevant time of at or just before reperfusion have exhibited such potency. Several cardioprotective agents have recently been evaluated in clinical trials but their results have been disappointing. Some of the poor clinical trial performance may stem from study designs which fail to identify those patients falling within the upper quartile of infarct sizes, presumably the only group that would be expected to actually benefit from a reduction in infarct size. Other possible causes could be that co-morbidities or drugs patients are taking may block the pathways involved in the anti-infarct effect or that the drugs simply do not protect even in animal models. Few agents have been thoroughly tested in clinically relevant animal models prior to their testing in man.

The aim of this study was to examine possible interactions of ERK and calcineurin in cardioprotection afforded by delta-opioid receptor stimulation. Infarction was induced in rat hearts by 20-min coronary occlusion and reperfusion. Tissue ERK level and calcienurin activity were determined by immunoblotting and an assay using a phosphopeptide substrate, respectively. Administration of a delta-opioid receptor agonist, D-Ala2-D-Leu5-enkephalin (DADLE, 1 mg/kg), before ischemia increased the phospho-ERK levels during ischemia and reduced infarct size (as percentage of risk area, %IS/AR) from 47.7 +/- 2.3% to 23.2 +/- 2.5%. This protection was abolished by 10 mg/kg of natrindole hydrochloride (NTI), a delta-opioid receptor antagonist. PD98059, a MEK1/2 inhibitor, abolished both ERK1/2 activation and infarct size limitation by DADLE. Calcineurin inhibitors, cyclosporine-A (5 mg/kg) and FK506 (3.5 mg/kg), reduced %IS/AR (27.4 +/- 4.4% and 29.9 +/- 3.4%, respectively). The protective effects of these calcineurin inhibitors were inhibited by PD98059, and the combination of DADLE with cyclosporine-A or FK506 did not afford further cardioprotection. DADLE significantly suppressed myocardial calcineurin activity, and this effect was inhibited by NTI. Suppression of calcineurin activity by FK506 was associated with modest activation of ERK1/2. These results suggest that suppression of calcineurin and activation of ERK1/2 are interacting mechanisms involved in cardioprotection by delta-opioid receptor activation.

To obtain insight into the role of the mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel in ischemic preconditioning (PC), we aimed to clarify the mitoK(ATP) channel-dependent phase of PC in two PC protocols with different intervals between PC ischemia and an index ischemia. The possible contribution of mitoK(ATP) channel opening to protein kinase C activation in PC was also examined by Western blotting. Myocardial infarction was induced by 30-min coronary occlusion/2-h reperfusion in rat hearts in situ, and infarct size was expressed as a percentage of the area at risk (% IS/AR). PC was performed with 2 episodes of 5-min ischemia, and each heart was subjected to 30-min ischemia either 5 min or 20 min after PC. At 5 min after PC, both PKC-delta and -epsilon were translocated and the myocardium was protected against infarction (% IS/AR = 28.3 +/- 2.7 % vs. 72.7 +/- 2.2 in controls p < 0.05). Pretreatment with a selective mitoK(ATP) channel blocker, 5-hydroxydecanoate (5-HD, 10 mg/kg), abolished the cardioprotection but not PKC translocation by PC. At 20 min after PC, PKC translocation remained at the same level as that 5 min after PC, but the anti-infarct tolerance was attenuated (%IS/AR = 43.5 +/- 4.7 %). Injection of 5-HD after PC did not affect anti-infarct tolerance at 5 min after PC but abolished the protection at 20 min after PC without any effects on PKC. These results suggest that the mitoK(ATP) channel plays a role in triggering of PC in a PKC-independent manner and that the role of the mitoK(ATP) channel as a mediator of protection is detectable after, but not before, the PC effect starts to decay without a change in the level of PKC translocation in the rat heart.

Objective: The present study was designed to assess the relationship between the timing of a mitoK(ATP) channel opener, diazoxide, and its infarct size-limiting effect., Methods: In isolated rabbit hearts, infarction was induced by 30 min of global ischemia and 2 h of reperfusion, and infarct size was determined by tetrazolium staining and expressed as a percentage of the left ventricle (%IS/LV). Diazoxide, a mitoK(ATP) channel selective opener, and/or 5-hydroxydecanoate (5-HD), a mitoK(ATP) channel blocker, were infused before or after the onset of ischemia. When these agents were infused during the ischemic period, they were dissolved in a hypoxic buffer at concentrations 10-fold higher than those in the pre-ischemic period, and the infusion rate was set at 2% of the pre-ischemic coronary flow., Results: In untreated controls, %IS/LV was 53.2+/-4.1 (SE). Pretreatment with diazoxide (100 microM) with a 10-min washout period reduced %IS/LV to 7.8+/-2.4 and this protection was abolished by co-infusion of 5-HD (50 microM). Pre-ischemic infusion of diazoxide without a washout period reduced %IS/LV to 7.3+/-1.4, and infusion of diazoxide from 10 min after the onset of ischemia also limited %IS/LV to 14.9+/-4.6. However, diazoxide infusion from 25 min after the onset of ischemia failed to reduce infarct size (%IS/LV = 54.5+/-7.2). Furthermore, pretreatment with 5-HD (50 microM) also completely abolished the protection afforded by early post-ischemic diazoxide infusion (%IS/LV = 48.3+/-6.5). Neither infusion of 5-HD nor the anoxic vehicle alone during ischemia modified %IS/LV., Conclusion: These findings suggest that opening of mitoK(ATP) channels before ischemia and during early ischemia, but not that upon reperfusion, is important for enhancement of myocardial tolerance against infarction.