Remote postconditioning by humoral factors in effluent from ischemic preconditioned rat hearts is mediated via PI3K/Akt-dependent cell-survival signaling at reperfusion. Basic Res Cardiol. 2011;106:135-145. [PMID: 21103992 PMCID: PMC3012213 DOI: 10.1007/s00395-010-0133-0]

Remote Ischemic Preconditioning Before Drug-Coated Balloon Implantation can Improve the Long-Term Prognosis of Patients with CAD

Background

Drug-coated balloons (DCBs) have become increasingly vital to percutaneous coronary intervention, offering many advantages. However, a significant challenge is that many patients are intolerant to the myocardial ischemia caused by DCB dilation. Remote ischemic preconditioning (RIPC) is known to enhance heart's tolerance to ischemia and hypoxia. This study investigated whether preoperative RIPC could extend the tolerated DCB inflation time and improve the long-term prognosis of patients with coronary artery disease (CAD).

Methods

A total of 653 patients with CAD were recruited and randomized into a RIPC group (n = 323) and a control (n = 330) group. The RIPC group underwent RIPC on the left upper limb twice daily, starting three days before the DCB implantation. The patients were followed up for one year after the operation, and 197 patients returned for coronary angiography (CAG) examination where the quantitative flow ratio (QFR) of the target vessels was measured. The primary endpoint of the study was the incidence of target lesion failure (TLF), which included target lesion revascularization (TLR), target vessel myocardial infarction, and cardiac death. The secondary endpoint was the rate of QFR loss in the target vessels.

Results

The findings revealed a significantly lower incidence of TLR in the RIPC group compared to the control group. Additionally, at the one-year follow-up, the rate of QFR loss in target vessels was lower in the RIPC group than in the control group.

Conclusions

The preoperative application of RIPC effectively extended the duration patients could tolerate DCB inflation. Furthermore, this approach positively impacted the long-term prognosis of CAD patients undergoing DCB treatment.

Clinical Trial Registration Information

NCT04766749.

Mesenchymal stromal cells for improvement of cardiac function following acute myocardial infarction: a matter of timing

Acute myocardial infarction (AMI) is the leading cause of cardiovascular death and remains the most common cause of heart failure. Reopening of the occluded artery, i.e., reperfusion, is the only way to save the myocardium. However, the expected benefits of reducing infarct size are disappointing due to the reperfusion paradox, which also induces specific cell death. These ischemia-reperfusion (I/R) lesions can account for up to 50% of final infarct size, a major determinant for both mortality and the risk of heart failure (morbidity). In this review, we provide a detailed description of the cell death and inflammation mechanisms as features of I/R injury and cardioprotective strategies such as ischemic postconditioning as well as their underlying mechanisms. Due to their biological properties, the use of mesenchymal stromal/stem cells (MSCs) has been considered a potential therapeutic approach in AMI. Despite promising results and evidence of safety in preclinical studies using MSCs, the effects reported in clinical trials are not conclusive and even inconsistent. These discrepancies were attributed to many parameters such as donor age, in vitro culture, and storage time as well as injection time window after AMI, which alter MSC therapeutic properties. In the context of AMI, future directions will be to generate MSCs with enhanced properties to limit cell death in myocardial tissue and thereby reduce infarct size and improve the healing phase to increase postinfarct myocardial performance.

Reperfusion Injury: How Can We Reduce It by Pre-, Per-, and Postconditioning

While early coronary reperfusion via primary percutaneous coronary intervention (pPCI) is established as the most efficacious therapy for minimizing infarct size (IS) in acute ST-elevation myocardial infarction (STEMI), the restoration of blood flow also introduces myocardial ischemia-reperfusion injury (IRI), leading to cardiomyocyte death. Among diverse methods, ischemic conditioning (IC), achieved through repetitive cycles of ischemia and reperfusion, has emerged as the most promising method to mitigate IRI. IC can be performed by applying the protective stimulus directly to the affected myocardium or indirectly to non-affected tissue, which is known as remote ischemic conditioning (RIC). In clinical practice, RIC is often applied by serial inflations and deflations of a blood pressure cuff on a limb. Despite encouraging preclinical studies, as well as clinical studies demonstrating reductions in enzymatic IS and myocardial injury on imaging, the observed impact on clinical outcome has been disappointing so far. Nevertheless, previous studies indicate a potential benefit of IC in high-risk STEMI patients. Additional research is needed to evaluate the impact of IC in such high-risk cohorts. The objective of this review is to summarize the pathophysiological background and preclinical and clinical data of IRI reduction by IC.

The Signaling Mechanism of Remote Postconditioning of the Heart: Prospects of the Use of Remote Postconditioning for the Treatment of Acute Myocardial Infarction

Acute myocardial infarction (AMI) remains the leading cause of mortality in the world, highlighting an urgent need for the development of novel, more effective approaches for the treatment of AMI. Remote postconditioning (RPost) of the heart could be a useful approach. It was demonstrated that RPost triggers infarct size reduction, improves contractile function of the heart in reperfusion, mitigates apoptosis, and stimulates autophagy in animals with coronary artery occlusion and reperfusion. Endogenous opioid peptides and adenosine could be involved in RPost. It was found that kinases and NO-synthase participate in RPost. KATP channels, MPT pore, and STAT3 could be hypothetical end-effectors of RPost. Metabolic syndrome and old age abolish the cardioprotective effect of RPost in rats. The data on the efficacy of RPost in clinical practice are inconsistent. These data are discussed in the review.

Effect of Rho-Kinase and Autophagy on Remote Ischemic Conditioning-Induced Cardioprotection in Rat Myocardial Ischemia/Reperfusion Injury Model

Objective. Remote ischemic conditioning (RIC) is a cardioprotective method in ischemia/reperfusion (I/R) injury. This study investigated the mechanism of Rho-kinase-mediated autophagy in RIC. Methods. Sixty male Sprague–Dawley rats were randomly divided into six groups: sham, I/R, RIC, I/R+fasudil, RIC+wortmannin, and RIC+fasudil+wortmannin. Throughout the experiment, mean arterial pressure and heart rate were continuously monitored. Histopathology and ultrastructure and myocardial enzymes’ expression were evaluated to determine the degree of cardiac injury. The protein expression of the Rho-kinase substrates myosin light chain (MLC) and myosin phosphatase target subunit 1 (MYPT1), autophagy-related protein light chain 3-II (LC3-II) and Beclin 1, and protein kinase B (AKT) was measured in the myocardial tissue. Results. Compared with the sham group, the mean arterial pressure and heart rate were decreased, myocardial enzyme levels were increased, and myocardial damage was aggravated in the I/R group; however, RIC improved these alterations. The expression of phosphorylated MLC and MYPT1 was lower, while LC3-II, Beclin 1, and phospho-AKT expression levels were higher in the RIC group compared with the I/R group. Obviously, treatment of the I/R group rats with fasudil, a Rho-kinase inhibitor, significantly ameliorated the I/R effects, whereas treatment of the RIC group rats with wortmannin, a phosphatidylinositol-3 kinase (PI3K) inhibitor, inhibited the RIC protective effects. Moreover, the rats in the RIC+fasudil+wortmannin group showed similar changes to those in the RIC+wortmannin group. Conclusion. These results showed that RIC protected the myocardium from I/R injury by suppressing Rho-kinase and the underlying mechanism may be related to enhancing autophagy via the PI3K/AKT pathway.

Plasma Exosomes at the Late Phase of Remote Ischemic Pre-conditioning Attenuate Myocardial Ischemia-Reperfusion Injury Through Transferring miR-126a-3p

Background: Remote ischemic pre-conditioning (RIPC) alleviated the myocardial ischemia-reperfusion injury, yet the underlying mechanisms remain to be fully elucidated, especially at the late phase. Searching a key component as a transfer carrier may provide a novel insight into RIPC-mediated cardioprotection in the condition of myocardial ischemia-reperfusion.

Objective: To investigate the cardioprotective effect of plasma exosomes at the late phase of RIPC and its potential signaling pathways involved.

Methods and Results: Exosomes were isolated from the plasma of rats 48 h after the RIPC or control protocol. Although the total plasma exosomes level had no significant change at the late phase of RIPC (RIPC-exosome) compared with the control exosomes (Control-exosome), the RIPC-exosome afforded remarkable protection against myocardial ischemia-reperfusion (MI/R) injury in rats and hypoxia-reoxygenation (H/R) injury in cells. The miRNA array revealed significant enrichment of miR-126a-3p in RIPC-exosome. Importantly, both miR-126a-3p inhibitor and antagonist significantly blunted the cardioprotection of RIPC-exosome in H/R cells and MI/R rats, respectively, while miR-126a-3p mimic and agomir showed significant cardioprotection against H/R injury in cells and MI/R injury in rats. Mechanistically, RIPC-exosome, especially exosomal miR-126a-3p, activated the reperfusion injury salvage kinase (RISK) pathway by enhancing the phosphorylation of Akt and Erk1/2, and simultaneously inhibited Caspase-3 mediated apoptotic signaling.

Conclusions: Our findings reveal a novel myocardial protective mechanism that plasma exosomes at the late phase of RIPC attenuate myocardial ischemia-reperfusion injury via exosomal miR-126a-3p.

Plasma obtained following murine hindlimb ischemic conditioning protects against oxidative stress in zebrafish models through activation of nrf2a and downregulation of duox

Ischemia/reperfusion of organ systems in trauma patients with resuscitated hemorrhagic shock (HSR) contributes to tissue injury and organ dysfunction. Previous studies using a murine model of HSR showed that remote ischemic preconditioning (RIC) protected against organ injury and that the plasma was able to prevent neutrophil migration in a zebrafish tailfin-cut inflammation model. In this study, we hypothesized that RIC plasma inhibits neutrophil function through a decrease in reactive oxygen species (ROS) production via the upregulation of the transcription factor Nrf2 and downstream antioxidative genes. Plasma from mice subjected to RIC (4 cycles of 5-min hindlimb ischemia/reperfusion) was microinjected into zebrafish. The results show that RIC plasma caused a reduction of ROS generation in response to tail injury. In addition, RIC plasma protected the fish larvae in the survival studies when exposed to either H2O2 or LPS. Oxidative stress PCR Array showed that RIC plasma treatment led to upregulation of antioxidative related genes including hsp70, hmox1a, nqo1 as well as downregulation of duox, the producer of H2O2. To explore the role of nrf2 in RIC, RIC plasma from Nrf2 KO mice were injected to the zebrafish and showed no inhibitory effect on neutrophil migration. Moreover, knockdown of nrf2a attenuated the anti-inflammatory and protective effect of RIC plasma. The downregulation of duox and upregulation of hmox1a were confirmed to require the activation of nrf2a. Therefore, we show that the protective effect of RIC may be related to the elaboration of humoral factors which counter injury-induced ROS generation in a nrf2-dependent fashion.

Extracellular vesicles from patients with Acute Coronary Syndrome impact on ischemia-reperfusion injury

The relevance of extracellular vesicles (EV) as mediators of cardiac damage or recovery upon Ischemia Reperfusion Injury (IRI) and Remote Ischemic PreConditioning (RIPC) is controversial. This study aimed to investigate whether serum-derived EV, recovered from patients with Acute Coronary Syndrome (ACS) and subjected to the RIPC or sham procedures, may be a suitable therapeutic approach to prevent IRI during Percutaneous-Coronary-Intervention (PCI). A double-blind, randomized, sham-controlled study (NCT02195726) has been extended, and EV were recovered from 30 patients who were randomly assigned (1:1) to undergo the RIPC- (EV-RIPC) or sham-procedures (EV-naive) before PCI. Patient-derived EV were analyzed by TEM, FACS and western blot. We found that troponin (TnT) was enriched in EV, compared to healthy subjects, regardless of diagnosis. EV-naive induced protection against IRI, both in-vitro and in the rat heart, unlike EV-RIPC. We noticed that EV-naive led to STAT-3 phosphorylation, while EV-RIPC to Erk-1/2 activation in the rat heart. Pre-treatment of the rat heart with specific STAT-3 and Erk-1/2 inhibitors led us to demonstrate that STAT-3 is crucial for EV-naive-mediated protection. In the same model, Erk-1/2 inhibition rescued STAT-3 activation and protection upon EV-RIPC treatment. 84 Human Cardiovascular Disease mRNAs were screened and DUSP6 mRNA was found enriched in patient-derived EV-naive. Indeed, DUSP6 silencing in EV-naive prevented STAT-3 phosphorylation and cardio-protection in the rat heart. This analysis of ACS-patients' EV proved: (i) EV-naive cardio-protective activity and mechanism of action; (ii) the lack of EV-RIPC-mediated cardio-protection; (iii) the properness of the in-vitro assay to predict EV effectiveness in-vivo.

Citric Acid Cycle Metabolites Predict Infarct Size in Pigs Submitted to Transient Coronary Artery Occlusion and Treated with Succinate Dehydrogenase Inhibitors or Remote Ischemic Perconditioning

Succinate dehydrogenase (SDH) inhibition with malonate during reperfusion reduced myocardial infarction in animals, whereas its endogenous substrate, succinate, is detected in plasma from STEMI patients. We investigated whether protection by SDH inhibition is additive to that of remote ischemic perconditioning (RIC) in pigs submitted to transient coronary artery occlusion, and whether protective maneuvers influence plasma levels of citric acid cycle metabolites. Forty pigs were submitted to 40 min coronary occlusion and reperfusion, and allocated to four groups (controls, sodium malonate 10 mmol/L, RIC, and malonate + RIC). Plasma was obtained from femoral and great cardiac veins and analyzed by LC-MS/MS. Malonate, RIC, and malonate + RIC reduced infarct size (24.67 ± 5.98, 25.29 ± 3.92 and 29.83 ± 4.62% vs. 46.47 ± 4.49% in controls, p < 0.05), but no additive effects were detected. Enhanced concentrations of succinate, fumarate, malate and citrate were observed in controls during initial reperfusion in the great cardiac vein, and most were reduced by cardioprotective maneuvers. Concentrations of succinate, fumarate, and malate significantly correlated with infarct size. In conclusion, despite the combination of SDH inhibition during reperfusion and RIC did not result in additive protection, plasma concentrations of selected citric acid cycle metabolites are attenuated by protective maneuvers, correlate with irreversible injury, and might become a prognosis tool in STEMI patients.

Cardioprotection by remote ischemic conditioning is transferable by plasma and mediated by extracellular vesicles

BACKGROUND

Remote ischemic conditioning (RIC) by brief periods of limb ischemia and reperfusion protects against ischemia-reperfusion injury. We studied the cardioprotective role of extracellular vesicles (EV)s released into the circulation after RIC and EV accumulation in injured myocardium.

METHODS

We used plasma from healthy human volunteers before and after RIC (pre-PLA and post-PLA) to evaluate the transferability of RIC. Pre- and post-RIC plasma samples were separated into an EV enriched fraction (pre-EV + and post-EV +) and an EV poor fraction (pre-EV- and post-EV-) by size exclusion chromatography. Small non-coding RNAs from pre-EV + and post-EV + were purified and profiled by NanoString Technology. Infarct size was compared in Sprague-Dawley rat hearts perfused with isolated plasma and fractions in a Langendorff model. In addition, fluorescently labeled EVs were used to assess homing in an in vivo rat model. (ClinicalTrials.gov, number: NCT03380663) RESULTS: Post-PLA reduced infarct size by 15% points compared with Pre-PLA (55 ± 4% (n = 7) vs 70 ± 6% (n = 8), p = 0.03). Post-EV + reduced infarct size by 16% points compared with pre-EV + (53 ± 15% (n = 13) vs 68 ± 12% (n = 14), p = 0.03). Post-EV- did not affect infarct size compared to pre-EV- (64 ± 3% (n = 15) and 68 ± 10% (n = 16), p > 0.99). Three miRNAs (miR-16-5p, miR-144-3p and miR-451a) that target the mTOR pathway were significantly up-regulated in the post-EV + group. Labelled EVs accumulated more intensely in the infarct area than in sham hearts.

CONCLUSION

Cardioprotection by RIC can be mediated by circulating EVs that accumulate in injured myocardium. The underlying mechanism involves modulation of EV miRNA that may promote cell survival during reperfusion.

MicroRNA-144 promotes remote limb ischemic preconditioning-mediated neuroprotection against ischemic stroke via PTEN/Akt pathway

Ischemic stroke is a refractory disease generally caused by cerebral ischemic injury. Remote ischemic preconditioning (RIPC) caused by transient ischemia and reperfusion of the femoral artery exerts a protective effect on ischemic stroke-induced brain injury. This study was designed to investigate the potential molecular mechanism of RIPC-mediated neuroprotection, namely, the biological effects of microRNA-144 on RIPC in mice with ischemic stroke and its effects on PTEN and Akt signaling pathways. Healthy adult C57BL6 mice were selected for the establishment of middle cerebral artery occlusion (MCAO). One hour before the start, remote ischemic preconditioning of limbs was performed in mice. Brain edema and infarct volume were measured. The expressions of microRNA-144, PTEN, and Akt were measured. The results showed that, compared with MCAO group, the RIPC group protected mice from cerebral ischemia-reperfusion injury, systemic accumulation of inflammatory cytokines, and accelerated apoptosis of parenchymal cells. In RIPC group, PTEN expression decreased, and mir-144 and Akt expression increased. The level of phosphorylated PTEN in the transfected microRNA-144 inhibitor group increased and the level of phosphorylated Akt reduced significantly. In conclusion, our results suggest that microRNA-144 may play a protective role in remote ischemic pretreatment by downregulating PTEN and upregulating Akt, suggesting that microRNA-144 via PTEN/Akt pathway may be of therapeutic significance in ischemic stroke.

Grape Seed Proanthocyanidin Extract Ameliorates Cardiac Remodelling After Myocardial Infarction Through PI3K/AKT Pathway in Mice

Myocardial infarction is one of the most serious fatal diseases in the world, which is due to acute occlusion of coronary arteries. Grape seed proanthocyanidin extract (GSPE) is an active compound extracted from grape seeds that has anti-oxidative, anti-inflammatory and anti-tumor pharmacological effects. Natural products are cheap, easy to obtain, widely used and effective. It has been used to treat numerous diseases, such as cancer, brain injury and diabetes complications. However, there are limited studies on its role and associated mechanisms in myocardial infarction in mice. This study showed that GSPE treatment in mice significantly reduced cardiac dysfunction and improved the pathological changes due to MI injury. In vitro, GSPE inhibited the apoptosis of H9C2 cells after hypoxia culture, resulting in the expression of Bax decreased and the expression of Bcl-2 increased. The high expression of p-PI3K and p-AKT was detected in MI model in vivo and in vitro. The use of the specific PI3K/AKT pathway inhibitor LY294002 regressed the cardio-protection of GSPE. Our results showed that GSPE could improve the cardiac dysfunction and remodeling induced by MI and inhibit cardiomyocytes apoptosis in hypoxic conditions through the PI3K/AKT signaling pathway.

Effluent from ischemic preconditioned hearts confers cardioprotection independent of the number of preconditioning cycles

Coronary effluent collected from ischemic preconditioning (IPC) treated hearts induces myocardial protection in non-ischemic-preconditioned hearts. So far, little is known about the number of IPC cycles required for the release of cardioprotective factors into the coronary effluent to successfully induce cardioprotection. This study investigated the cardioprotective potency of effluent obtained after various IPC cycles in the rat heart. Experiments were performed on isolated hearts of male Wistar rats, mounted onto a Langendorff system and perfused with Krebs-Henseleit buffer. In a first part, effluent was taken before (Con) and after each IPC cycle (Eff 1, Eff 2, Eff 3). IPC was induced by 3 cycles of 5 min of global myocardial ischemia followed by 5 minutes of reperfusion. In a second part, hearts of male Wistar rats were randomized to four groups (each group n = 4–5) and underwent 33 min of global ischemia followed by 60 min of reperfusion. The previously obtained coronary effluent was administered for 10 minutes before ischemia as a preconditioning stimulus. Infarct size was determined at the end of reperfusion by triphenyltetrazoliumchloride (TTC) staining. Infarct size with control effluent was 54±12%. Effluent obtained after IPC confers a strong infarct size reduction independent of the number of IPC cycles (Eff 1: 27±5%; Eff 2: 35±7%; Eff 3: 35±8%, each P<0.05 vs. Con). Effluent extracted after one cycle IPC is comparably protective as after two or three cycles IPC.

Pre- and Post-Conditioning of the Heart: An Overview of Cardioprotective Signaling Pathways

Since the discovery of ischemic pre- and post-conditioning, more than 30 years ago, the knowledge about the mechanisms and signaling pathways involved in these processes has significantly increased. In clinical practice, on the other hand, such advancement has yet to be seen. This article provides an overview of ischemic pre-, post-, remote, and pharmacological conditioning related to the heart. In addition, we reviewed the cardioprotective signaling pathways and therapeutic agents involved in the above-mentioned processes, aiming to provide a comprehensive evaluation of the advancements in the field. The advancements made over the last decades cannot be ignored and with the exponential growth in techniques and applications. The future of pre- and post-conditioning is promising.

Low density lipoprotein receptor related protein 6 (LRP6) protects heart against oxidative stress by the crosstalk of HSF1 and GSK3β

Low density lipoprotein receptor-related protein 6 (LRP6), a Wnt co-receptor, induces multiple functions in various organs. We recently reported cardiac specific LRP6 deficiency caused cardiac dysfunction in mice. Whether cardiomyocyte-expressed LRP6 protects hearts against ischemic stress is largely unknown. Here, we investigated the effects of cardiac LRP6 in response to ischemic reperfusion (I/R) injury. Tamoxifen inducible cardiac specific LRP6 overexpression mice were generated to build I/R model by occlusion of the left anterior descending (LAD) coronary artery for 40 min and subsequent release of specific time. Cardiac specific LRP6 overexpression significantly ameliorated myocardial I/R injury as characterized by the improved cardiac function, strain pattern and infarct area at 24 h after reperfusion. I/R induced-apoptosis and endoplasmic reticulum (ER) stress were greatly inhibited by LRP6 overexpression in cardiomyocytes. LRP6 overexpression enhanced the expression of heat shock transcription factor-1(HSF1) and heat shock proteins (HSPs), the level of p-glycogen synthase kinase 3β(GSK3β)(S9) and p-AMPK under I/R. HSF1 inhibitor deteriorated the apoptosis and decreased p-GSK3β(S9) level in LRP6 overexpressed -cardiomyocytes treated with H2O2. Si-HSF1 or overexpression of active GSK3β significantly attenuated the increased expression of HSF1 and p-AMPK, and the inhibition of apoptosis and ER stress induced by LRP6 overexpression in H2O2-treated cardiomyocytes. AMPK inhibitor suppressed the increase in p-GSK3β (S9) level but didn't alter HSF1 nucleus expression in LRP6 overexpressed-cardiomyocytes treated with H2O2. Active GSK3β, but not AMPK inhibitor, attenuated the inhibition of ubiquitination of HSF1 induced by LRP6-overexpressed-cardiomyocytes treated with H2O2. LRP6 overexpression increased interaction of HSF1 and GSK3β which may be involved in the reciprocal regulation under oxidative stress. In conclusion, cardiac LRP6 overexpression significantly inhibits cardiomyocyte apoptosis and ameliorates myocardial I/R injury by the crosstalk of HSF1 and GSK3β signaling.

Pharmacological Inhibition of PTEN Restores Remote Ischemic Postconditioning Cardioprotection in Hypercholesterolemic Mice: Potential Role of PTEN/AKT/GSK3β SIGNALS

Although remote ischemic postconditioning (RIPC) was shown to confer cardioprotection against myocardial ischemia/reperfusion (I/R) injury in normal animals, whether RIPC-induced cardioprotection is altered in the presence of hypercholesterolemia, a comorbidity with acute myocardial infarction (AMI) patients has yet to be determined. Normal or 2% cholesterol chow was fed to male C57BL/6J mice for 12 weeks to induce hypercholesterolemia, then normal or hypercholesterolemic murine hearts were exposed to AMI by coronary artery ligation. RIPC was induced by four episodes of 5 min femoral artery occlusion followed by 5 min reperfusion immediately after myocardial reperfusion in mice. Following I/R, RIPC significantly attenuated postischemic infarct size, hindered cardiomyocyte apoptosis, improved cardiac systolic function, decreased phosphatase and tensin homolog deleted on chromosome ten (PTEN) expression, and further increased Akt and GSK-3β phosphorylation in non-hypercholesterolemic, but not in hypercholesterolemic mice. Application of the PTEN inhibitor bisperoxovanadium (BpV) (1.0 mg/kg) reduced postischemic infarct size, attenuated cardiomyocyte apoptosis, and improved cardiac dysfunction in normal, but not in hypercholesterolemic mice. Further, increased dose of BpV (2 mg/kg or 10 mg/kg) failed to rescue the detrimental effects of hypercholesterolemia on I/R in mice following I/R. Especially important, we demonstrated that the combination BpV and RIPC exerted marked cardioprotective effects both in normal and hypercholesterolemic mice with I/R, indicating that PTEN inhibition restores RIPC-elicited myocardial protection in the presence of hypercholesterolemia. Our results demonstrated that hypercholesterolemia attenuated RIPC-induced cardioprotection against I/R injury by alteration of PTEN/Akt/GSK3β signals, and inhibition of PTEN rescued RIPC-induced cardioprotection in the presence of hypercholesterolemia.

Egr-1 functions as a master switch regulator of remote ischemic preconditioning-induced cardioprotection

Despite improved treatment options myocardial infarction (MI) is still a leading cause of mortality and morbidity worldwide. Remote ischemic preconditioning (RIPC) is a mechanistic process that reduces myocardial infarction size and protects against ischemia reperfusion (I/R) injury. The zinc finger transcription factor early growth response-1 (Egr-1) is integral to the biological response to I/R, as its upregulation mediates the increased expression of inflammatory and prothrombotic processes. We aimed to determine the association and/or role of Egr-1 expression with the molecular mechanisms controlling the cardioprotective effects of RIPC. This study used H9C2 cells in vitro and a rat model of cardiac ischemia reperfusion (I/R) injury. We silenced Egr-1 with DNAzyme (ED5) in vitro and in vivo, before three cycles of RIPC consisting of alternating 5 min hypoxia and normoxia in cells or hind-limb ligation and release in the rat, followed by hypoxic challenge in vitro and I/R injury in vivo. Post-procedure, ED5 administration led to a significant increase in infarct size compared to controls (65.90 ± 2.38% vs. 41.00 ± 2.83%, p < 0.0001) following administration prior to RIPC in vivo, concurrent with decreased plasma IL-6 levels (118.30 ± 4.30 pg/ml vs. 130.50 ± 1.29 pg/ml, p < 0.05), downregulation of the cardioprotective JAK-STAT pathway, and elevated myocardial endothelial dysfunction. In vitro, ED5 administration abrogated IL-6 mRNA expression in H9C2 cells subjected to RIPC (0.95 ± 0.20 vs. 6.08 ± 1.40-fold relative to the control group, p < 0.05), resulting in increase in apoptosis (4.76 ± 0.70% vs. 2.23 ± 0.34%, p < 0.05) and loss of mitochondrial membrane potential (0.57 ± 0.11% vs. 1.0 ± 0.14%-fold relative to control, p < 0.05) in recipient cells receiving preconditioned media from the DNAzyme treated donor cells. This study suggests that Egr-1 functions as a master regulator of remote preconditioning inducing a protective effect against myocardial I/R injury through IL-6-dependent JAK-STAT signaling.

Trigger, Signaling Mechanism and End Effector of Cardioprotective Effect of Remote Postconditioning of Heart

The hypothetical trigger of remote postconditioning (RPost) of the heart is the high-molecular weight hydrophobic peptide(s). Nitric oxide and adenosine serve as intermediaries between the peptide and intracellular structures. The role of the autonomic nervous system in RPost requires further study. In signaling mechanism RPost, kinases are involved: protein kinase C, PI3, Akt, JAK. The hypothetical end effector of RPost is aldehyde dehydrogenase-2, the transcription factors STAT, Nrf2, and also the BKCa channel.

Circulating mediators of remote ischemic preconditioning: search for the missing link between non-lethal ischemia and cardioprotection

Acute myocardial infarction (AMI) is one of the leading causes of mortality and morbidity worldwide. There has been an extensive search for cardioprotective therapies to reduce myocardial ischemia-reperfusion (I/R) injury. Remote ischemic preconditioning (RIPC) is a phenomenon that relies on the body's endogenous protective modalities against I/R injury. In RIPC, non-lethal brief I/R of one organ or tissue confers protection against subsequent lethal I/R injury in an organ remote to the briefly ischemic organ or tissue. Initially it was believed to be limited to direct myocardial protection, however it soon became apparent that RIPC applied to other organs such as kidney, liver, intestine, skeletal muscle can reduce myocardial infarct size. Intriguing discoveries have been made in extending the concept of RIPC to other organs than the heart. Over the years, the underlying mechanisms of RIPC have been widely sought and discussed. The involvement of blood-borne factors as mediators of RIPC has been suggested by a number of research groups. The main purpose of this review article is to summarize the possible circulating mediators of RIPC, and recent studies to establish the clinical efficacy of these mediators in cardioprotection from lethal I/R injury.

Exercise and Cardioprotection: A Natural Defense Against Lethal Myocardial Ischemia-Reperfusion Injury and Potential Guide to Cardiovascular Prophylaxis

Similar to ischemic preconditioning, high-intensity exercise has been shown to decrease infarct size following myocardial infarction. In this article, we review the literature on beneficial effects of exercise, exercise requirements for cardioprotection, common methods utilized in laboratories to study this phenomenon, and discuss possible mechanisms for exercise-mediated cardioprotection.

Piceatannol pretreatment alleviates acute cardiac injury via regulating PI3K-Akt-eNOS signaling in H9c2 cells

Piceatannol (3,3',4,5'-trans-trihydroxystilbene) is a natural polyphenols compound that occurs hydroxylated analogue of resveratrol showing widely biological activities. Previous studies have demonstrated its functions on anti-cancer, neuroprotection and cardioprotection. However, few studies have clarified the benefits of piceatannol on cardiomyocytes except its anti-oxidative effect based on the original property of polyphenols. Here we apply H9c2 cardiomyocytes to study the cardioprotective mechanisms of piceatannol in vitro. We firstly verify its anti-peroxidation effect by using H₂O₂-induced in vitro model. Then, flow cytometry results show piceatannol reduce cellular apoptosis by enhancing Bcl-2 expressions in immunoblot analysis. Meantime, piceatannol decreases H₂O₂-induced excessive ROS and calcium overloading, and prevents mitochondrial depolarization. Most importantly, piceatannol pretreatment can regulate PI3K-Akt-eNOS signaling pathway to alleviate peroxidative injury. Immunoblot analysis of PI3K, Akt, p-Akt and eNOS shows H₂O₂ significantly reduces expressions of these proteins. Pretreatment of piceatannol evidently increases their expressions and decreases iNOS expression, implying piceatannol can upregulate PI3K-Akt-eNOS signaling to protect cardiomyocytes from peroxidative injury.

Protecting the heart from ischemia/reperfusion injury: an update on remote ischemic preconditioning and postconditioning

PURPOSE OF REVIEW

The most effective strategy for reducing acute myocardial ischemic injury is timely and effective reperfusion. However, myocardial reperfusion can induce further cardiomyocyte death (reperfusion injury). Interventions that protect the heart from ischemia/reperfusion injury, reducing infarct size, can involve remote ischemic preconditioning and postconditioning. These interventions have a promising potential clinical application, and have been the focus of recent research. In this review, we provide an update of remote ischemic preconditioning and postconditioning mechanisms.

RECENT FINDINGS

Remote ischemic preconditioning cardioprotection can occur via a humoral pathway and/or a neural pathway. These two pathways have been described as mechanistically different, but it has been suggested that they could be interdependent. However, remote ischemic postconditioning mainly involves the humoral pathway. In this review, we will discuss the different pathways and mechanisms involved in remote ischemic preconditioning and postconditioning.

SUMMARY

Remote ischemic preconditioning and postconditioning is possible to perform in a clinical setting by intermittent ischemia of an upper or lower limb. Furthermore, clinical trials using this procedure in the context of predictable ischemia-reperfusion have produced promising results, and other studies to define the potential clinical use of these strategies are ongoing.

Signaling mediators modulated by cardioprotective interventions in healthy and diabetic myocardium with ischaemia-reperfusion injury

Ischaemic heart diseases are one of the major causes of death in the world. In most patients, ischaemic heart disease is coincident with other risk factors such as diabetes. Patients with diabetes are more prone to cardiac ischaemic dysfunctions including ischaemia-reperfusion injury. Ischaemic preconditioning, postconditioning and remote conditionings are reliable interventions to protect the myocardium against ischaemia-reperfusion injuries through activating various signaling pathways and intracellular mediators. Diabetes can disrupt the intracellular signaling cascades involved in these myocardial protections, and studies have revealed that cardioprotective effects of the conditioning interventions are diminished in the diabetic condition. The complex pathophysiology and poor prognosis of ischaemic heart disease among people with diabetes necessitate the investigation of the interaction of diabetes with ischaemia-reperfusion injury and cardioprotective mechanisms. Reducing the outcomes of ischaemia-reperfusion injury using targeted strategies would be particularly helpful in this population. In this study, we review the protective interventional signaling pathways and mediators which are activated by ischaemic conditioning strategies in healthy and diabetic myocardium with ischaemia-reperfusion injury.

Limb Remote Ischemic Conditioning: Mechanisms, Anesthetics, and the Potential for Expanding Therapeutic Options

Novel and innovative approaches are essential in developing new treatments and improving clinical outcomes in patients with ischemic stroke. Remote ischemic conditioning (RIC) is a series of mechanical interruptions in blood flow of a distal organ, following end organ reperfusion, shown to significantly reduce infarct size through inhibition of oxidation and inflammation. Ischemia/reperfusion (I/R) is what ultimately leads to the irreversible brain damage and clinical picture seen in stroke patients. There have been several reports and reviews about the potential of RIC in acute ischemic stroke; however, the focus here is a comprehensive look at the differences in the three types of RIC (remote pre-, per-, and postconditioning). There are some limited uses of preconditioning in acute ischemic stroke due to the unpredictability of the ischemic event; however, it does provide the identification of biomarkers for clinical studies. Remote limb per- and postconditioning offer a more promising treatment during patient care as they can be harnessed during or after the initial ischemic insult. Though further research is needed, it is imperative to discuss the importance of preclinical data in understanding the methods and mechanisms involved in RIC. This understanding will facilitate translation to a clinically feasible paradigm for use in the hospital setting.

Time Window Is Important for Adenosine Preventing Cold-induced Injury to the Endothelium

Cold cardioplegia is used to induce heart arrest during cardiac surgery. However, endothelial function may be compromised after this procedure. Accordingly, interventions such as adenosine, that mimic the effects of preconditioning, may minimize endothelial injury. Herein, we investigated whether adenosine prevents cold-induced injury to the endothelium. Cultured human cardiac microvascular endothelial cells were treated with adenosine for different durations. Phosphorylation and expression of endothelial nitric oxide synthase (eNOS), p38MAPK, ERK1/2, and p70S6K6 were measured along with nitric oxide (NO) production using diaminofluorescein-2 diacetate (DAF-2DA) probe. Cold-induced injury by hypothermia to 4°C for 45 minutes to mimic conditions of cold cardioplegia during open heart surgery was induced in human cardiac microvascular endothelial cells. Under basal conditions, adenosine stimulated NO production, eNOS phosphorylation at serine 1177 from 5 minutes to 4 hours and inhibited eNOS phosphorylation at threonine 495 from 5 minutes to 6 hours, but increased phosphorylation of ERK1/2, p38MAPK, and p70S6K only after exposure for 5 minutes. Cold-induced injury inhibited NO production and the phosphorylation of the different enzymes. Importantly, adenosine prevented these effects of hypothermic injury. Our data demonstrated that adenosine prevents hypothermic injury to the endothelium by activating ERK1/2, eNOS, p70S6K, and p38MAPK signaling pathways at early time points. These findings also indicated that 5 minutes after administration of adenosine or release of adenosine is an important time window for cardioprotection during cardiac surgery.

Preconditioning boosts regenerative programmes in the adult zebrafish heart

During preconditioning, exposure to a non-lethal harmful stimulus triggers a body-wide increase of survival and pro-regenerative programmes that enable the organism to better withstand the deleterious effects of subsequent injuries. This phenomenon has first been described in the mammalian heart, where it leads to a reduction of infarct size and limits the dysfunction of the injured organ. Despite its important clinical outcome, the actual mechanisms underlying preconditioning-induced cardioprotection remain unclear. Here, we describe two independent models of cardiac preconditioning in the adult zebrafish. As noxious stimuli, we used either a thoracotomy procedure or an induction of sterile inflammation by intraperitoneal injection of immunogenic particles. Similar to mammalian preconditioning, the zebrafish heart displayed increased expression of cardioprotective genes in response to these stimuli. As zebrafish cardiomyocytes have an endogenous proliferative capacity, preconditioning further elevated the re-entry into the cell cycle in the intact heart. This enhanced cycling activity led to a long-term modification of the myocardium architecture. Importantly, the protected phenotype brought beneficial effects for heart regeneration within one week after cryoinjury, such as a more effective cell-cycle reentry, enhanced reactivation of embryonic gene expression at the injury border, and improved cell survival shortly after injury. This study reveals that exposure to antecedent stimuli induces adaptive responses that render the fish more efficient in the activation of the regenerative programmes following heart damage. Our results open a new field of research by providing the adult zebrafish as a model system to study remote cardiac preconditioning.

Distinct effects of inflammation on preconditioning and regeneration of the adult zebrafish heart

The adult heart is able to activate cardioprotective programmes and modifies its architecture in response to physiological or pathological changes. While mammalian cardiac remodelling often involves hypertrophic expansion, the adult zebrafish heart exploits hyperplastic growth. This capacity depends on the responsiveness of zebrafish cardiomyocytes to mitogenic signals throughout their entire life. Here, we have examined the role of inflammation on the stimulation of cell cycle activity in the context of heart preconditioning and regeneration. We used thoracotomy as a cardiac preconditioning model and cryoinjury as a model of cardiac infarction in the adult zebrafish. First, we performed a spatio-temporal characterization of leucocytes and cycling cardiac cells after thoracotomy. This analysis revealed a concomitance between the infiltration of inflammatory cells and the stimulation of the mitotic activity. However, decreasing the immune response using clodronate liposome injection, PLX3397 treatment or anti-inflammatory drugs surprisingly had no effect on the re-entry of cardiac cells into the cell cycle. In contrast, reducing inflammation using the same strategies after cryoinjury strongly impaired cardiac cell mitotic activity and the regenerative process. Taken together, our results show that, while the immune response is not necessary to induce cell-cycle activity in intact preconditioned hearts, inflammation is required for the regeneration of injured hearts in zebrafish.

Remote ischemic conditioning provides humoural cross-species cardioprotection through glycine receptor activation

AIMS

Remote ischaemic conditioning (RIC) releases a humoural factor able to exert cross-species cardioprotection when plasma dialysate is applied to isolated hearts. However, the exact chemical nature of this factor is currently unknown.

METHODS AND RESULTS

RIC (4 × 5min femoral occlusion/5min reperfusion) was applied to 10 male pigs, and blood was taken before and after the manoeuvre. Discriminant analysis of ¹H-NMR spectra (n = 10-12) obtained from plasma dialysates (12-14 kDa cut-off) allowed to demonstrate a different metabolic profile between control and postRIC samples, with lactate (2.671 ± 0.294 vs. 3.666 ± 0.291 μmol/mL, P = 0.020), succinate (0.062 ± 0.005 vs. 0.082 ± 0.008 μmol/mL, P = 0.035) and glycine (0.055 ± 0.009 vs. 0.471 ± 0.151 μmol/mL, P = 0.015) being the main responsible for such differences. Plasma dialysates were then given to isolated mice hearts submitted to global ischaemia (35 min) and reperfusion (60 min), for 30 min before ischaemia or during the first 15 min of reflow. Infarct size was significantly reduced when postRIC dialysate was applied before ischaemia as compared with hearts pretreated with control dialysate (44.81 ± 3.22 vs. 55.55 ± 2.53%, P = 0.012, n = 12). Blockade of glycine receptors with strychnine 10 μM inhibited the protective effect caused by pretreatment with postRIC dialysate (52.76 ± 6.94 vs. 51.92 ± 5.78%, P-NS, n = 5), whereas pretreatment with glycine 3 mmol/L, but not succinate 100 μmol/L, mimicked RIC protection (41.90 ± 4.50% in glycine-treated vs. 61.51 ± 5.16 and 64.73 ± 4.47% in succinate-treated and control hearts, respectively, P < 0.05, n = 4-7).

CONCLUSIONS

RIC releases glycine and exerts cross-species cardioprotection against infarction through glycine receptor activation.

Downregulation of Na+/Ca2+ Exchanger Isoform 1 Protects Isolated Hearts by Sevoflurane Postconditioning but Not by Delayed Remote Ischemic Preconditioning in Rats

Background:

Calcium regulatory proteins-L-type Ca²⁺ channels (LTCCs), ryanodine receptor 2 (RyR2), and Na⁺/Ca²⁺ exchanger isoform 1 (NCX1) have been recognized as important protective mechanisms during myocardial ischemia-reperfusion injury (I/RI). Both sevoflurane postconditioning (SevoPoC) and delayed remote ischemic preconditioning (DRIPC) have been shown to protect the heart against I/RI. In this study, we aimed to compare the effects of SevoPoC and DRIPC on the expression of the three calcium regulatory proteins in an isolated rat heart model.

Methods:

After 30-min balanced perfusion, isolated hearts from rats were subjected to 30-min ischemia followed by 60-min reperfusion. Totally 40 isolated hearts were randomly assigned to four groups (n = 10/group): time control group, I/RI group, SevoPoC group, and DRIPC group. The effect of SevoPoC (3% v/v) and DRIPC were observed. Myocardial infarct size (IS), cardiac troponin I level, and heart function were measured. The protein and messenger RNA levels of LTCCs, RyR2, and NCX1 were determined.

Results:

Both SevoPoC and DRIPC improved the recovery of myocardial function, and reduced cardiac troponin I release after I/RI. The decrease in IS was more significant in the SevoPoC group than that in the DRIPC group (16.50% ± 4.54% in the SevoPoC group [P = 0.0006], and 22.34% ± 4.02% in the DRIPC group [P = 0.0007] vs. 35.00% ± 5.24% in the I/RI group, respectively). SevoPoC, but not DRIPC significantly inhibited the activity of NCX1 (0.59 ± 0.09 in the I/RI group vs. 0.32 ± 0.16 in the SevoPoC group, P = 0.006; vs. 0.57 ± 0.14 in the DRIPC group, P = 0.072). No statistical significant differences were observed in the expression of LTCCs and RyR2 between SevoPoC and DRIPC. In addition, subsequent correlation analysis showed a significantly positive relationship between the cardiac troponin I level and the protein expression of NCX1 (r = 0.505, P = 0.023).

Conclusion:

SevoPoC may be more effective in the cardioprotection than DRIPC partly due to the deactivation of NCX1.

Remote Ischemic Conditioning by Effluent Collected from a Novel Isolated Hindlimb Model Reduces Infarct Size in an Isolated Heart Model

Background and Objectives

Experimental protocols for remote ischemic conditioning (RIC) utilize models in which a tourniquet is placed around the hindlimb or effluent is collected from an isolated heart. In analyzing the humoral factors that act as signal transducers in these models, sampled blood can be influenced by systemic responses, while the effluent from an isolated heart might differ from that of the hindlimb. Thus, we designed a new isolated hindlimb model for RIC and tested whether the effluent from this model could affect ischemia/reperfusion (IR) injury and if the reperfusion injury salvage kinase (RISK) and survivor activating factor enhancement (SAFE) pathways are involved in RIC.

Materials and Methods

After positioning needles into the right iliac artery and vein of rats, Krebs-Henseleit buffer was perfused using a Langendorff apparatus, and effluent was collected. The RIC protocol consisted of 3 cycles of IR for 5 minutes. In the RIC effluent group, collected effluent was perfused in an isolated heart for 10 minutes before initiating IR injury.

Results

Compared with the control group, the infarct area in the RIC effluent group was significantly smaller (31.2%±3.8% vs. 20.6%±1.8%, p<0.050), while phosphorylation of signal transducer and activation of transcription-3 (STAT-3) was significantly increased. However, there was a trend of increased phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 in this group.

Conclusion

This is the first study to investigate the effect of effluent from a new isolated hindlimb model after RIC on IR injury in an isolated heart model. The RIC effluent was effective in reducing the IR injury, and the cardioprotective effect was associated with activation of the SAFE pathway.

Cardioprotective Effects of Transfusion of Late-Phase Preconditioned Plasma May Be Induced by Activating the Reperfusion Injury Salvage Kinase Pathway but Not the Survivor Activating Factor Enhancement Pathway in Rats

A previous study in our laboratory demonstrated that transfusion of plasma collected at the late phase of remote ischemic preconditioning (RIPC) could reduce myocardial infarct size. Here, we tested whether the reperfusion injury salvage kinase (RISK) and survivor activating factor enhancement (SAFE) pathways are involved in transferring protection. In a two-part study, donor rats (n = 3) donated plasma 48 hours after RIPC (preconditioned plasma) or control (nonpreconditioned plasma). Normal (part 1) or ischemic (part 2) myocardia were collected from recipients (n = 6) 24 hours after receiving normal saline, nonpreconditioned plasma, and preconditioned plasma or after further suffering ischemia reperfusion. Western blot was performed to analyze STAT3, Akt, and Erk1/2 phosphorylation in normal and ischemic myocardium (central area and border area). In normal myocardia, preconditioned plasma increased Akt and Erk1/2 phosphorylation significantly compared to nonpreconditioned plasma and normal saline; no STAT3 phosphorylation was detected. In ischemic myocardia, preconditioned plasma increased Akt and Erk1/2 phosphorylation significantly in both central and border areas compared to other fluids; no significant difference in STAT3 phosphorylation occurred among groups. Transfusion of preconditioned plasma collected at the late phase of RIPC could activate the RISK but not SAFE pathway, suggesting that RISK pathway may be involved in transferring protection.

Cardioprotection by the transfer of coronary effluent from ischaemic preconditioned rat hearts: identification of cardioprotective humoral factors

Ischaemic preconditioning (IPC) provides myocardial resistance to ischaemia/reperfusion (I/R) injuries. The protection afforded by IPC is not limited to the target tissue but extends to remote tissues, suggesting a mechanism mediated by humoral factors. The aim of the present study was to identify the humoral factors that are responsible for the cardioprotection induced by the coronary effluent transferred from IPC to naïve hearts. Isolated rat hearts were submitted to IPC (three cycles of 5 min I/R) before 30-min global ischaemia and 60-min reperfusion. The coronary effluent (Efl_IPC) collected during IPC was fractionated by ultrafiltration in different molecular weight ranges (<3, 3-5, 5-10, 10-30, 30-50, and >50 kDa) and evaluated for cardioprotective effects by perfusion before I/R in naïve hearts. Only the <3, 5-10 and <10 kDa fractions of hydrophobic eluate reduced I/R injuries. The cardioprotective effect of the 5-10 fraction was blocked by K_ATP channel blockers and a PKC inhibitor. An Efl_IPC proteomic analysis revealed 14 cytoprotection-related proteins in 4-12 kDa peptides. HSP10 perfusion protected the heart against I/R injuries. These data provide insights into the mechanisms of cardioprotection in humoral factors released by IPC. Cardioprotection is afforded by hydrophobic peptides in the 4-12 kDa size range, which activate pathways that are dependent on PKC and K_ATP. Fourteen 4-12 kDa peptides were identified, suggesting a potential therapeutic role for these molecules in ischaemic diseases. One of these, HSP10, identified by mass spectrometry, reduced I/R injuries and may be a potential candidate as a therapeutic target.

Exploring effects of remote ischemic preconditioning in a pig model of hypothermic circulatory arrest

OBJECTIVES

During aortic and cardiac surgery, risks for mortality and morbidity are inevitable. Surgical setups involving deep hypothermic circulatory arrest (DHCA) are effective to achieve organ protection against ischemic injury. The aim of this study was to identify humoural factors mediating additive protective effects of remote ischemic preconditioning (RIPC) in a porcine model of DHCA.

DESIGN

Twenty-two pigs were randomized into the RIPC group (n = 11) and the control group (n = 11). The RIPC group underwent four 5-minute hind limb ischemia-reperfusion cycles prior to cardiopulmonary bypass and DHCA. All animals underwent identical surgical procedures including 60 min DHCA at 18 °C. Blood samples were collected from vena cava and sagittal sinus at several time points. After the 8-hour follow-up period, the brain, heart, and kidney tissue samples were collected for tissue analyses.

RESULTS

Serum levels of brain damage marker S100B recovered faster in the RIPC group, after 4 hours of the arrest, (p < .05). Systemic lactate levels were lower and cardiac index was higher in the RIPC group postoperatively. Immunohistochemical cerebellum regional scores of antioxidant response regulator Nrf2 were better in the RIPC group (mean: 1.1, IQR: 0.0-2.5) compared with the control group (mean: 0.0, IQR: 0.0-0.0), reaching borderline statistical significance (p = .064). RIPC induced detectable modulations of plasma proteome and metabolites.

CONCLUSIONS

The faster recovery of S100B, lower systemic lactate levels and favourable regional antioxidant response suggest possible neuronal cellular and mitochondrial protection by RIPC, whereas better cardiac index underlines functional effects of RIPC. The exact humoural factor remains unclear.

Insulin and GSK3β-inhibition abrogates the infarct sparing-effect of ischemic postconditioning in ex vivo rat hearts

OBJECTIVES

Pharmacological treatment of reperfusion injury using insulin and GSK3β inhibition has been shown to be cardioprotective, however, their interaction with the endogenous cardioprotective strategy, ischemic postconditioning, is not known.

DESIGN

Langendorff perfused ex vivo rat hearts were subjected to 30 min of regional ischemia and 120 min of reperfusion. For the first 15 min of reperfusion hearts received either vehicle (Ctr), insulin (Ins) or a GSK3β inhibitor (SB415286; SB41), with or without interruption of ischemic postconditioning (IPost; 3 × 30 s of global ischemia). In addition, the combination of insulin and SB41 for 15 min was assessed.

RESULTS

Insulin, SB41 or IPost significantly reduced infarct size versus vehicle treated controls (IPost 33.5 ± 3.3%, Ins 33.5 ± 3.4%, SB41 30.5 ± 3.0% vs. Ctr 54.7 ± 6.8%, p < 0.01). Combining insulin and SB415286 did not confer additional cardioprotection compared to the treatments given alone (SB41+ Ins 26.7 ± 3.5%, ns). Conversely, combining either of the pharmacological reperfusion treatments with IPost completely abrogated the cardioprotection afforded by the treatments separately (Ins + IPost 59.5 ± 3.4% vs. Ins 33.5 ± 3.4% and SB41 + IPost 50.2 ± 6.6% vs. SB41 30.5 ± 3.0%, both p < 0.01), and was associated with blunted Akt, GSK3β and STAT3 phosphorylation.

CONCLUSION

Pharmacological reperfusion treatment with insulin and SB41 interferes with the cardioprotection afforded by ischemic postconditioning.

Intrinsic cardiac ganglia and acetylcholine are important in the mechanism of ischaemic preconditioning

This study aimed to investigate the role of the intrinsic cardiac nervous system in the mechanism of classical myocardial ischaemic preconditioning (IPC). Isolated perfused rat hearts were subjected to 35-min regional ischaemia and 60-min reperfusion. IPC was induced as three cycles of 5-min global ischaemia–reperfusion, and provided significant reduction in infarct size (IS/AAR = 14 ± 2% vs control IS/AAR = 48 ± 3%, p < 0.05). Treatment with the ganglionic antagonist, hexamethonium (50 μM), blocked IPC protection (IS/AAR = 37 ± 7%, p < 0.05 vs IPC). Moreover, the muscarinic antagonist, atropine (100 nM), also abrogated IPC-mediated protection (IS/AAR = 40 ± 3%, p < 0.05 vs IPC). This indicates that intrinsic cardiac ganglia remain intact in the Langendorff preparation and are important in the mechanism of IPC. In a second group of experiments, coronary effluent collected following IPC, from ex vivo perfused rat hearts, provided significant cardioprotection when perfused through a naïve isolated rat heart prior to induction of regional ischaemia–reperfusion injury (IRI) (IS/ARR = 19 ± 2, p < 0.05 vs control effluent). This protection was also abrogated by treating the naïve heart with hexamethonium, indicating the humoral trigger of IPC induces protection via an intrinsic neuronal mechanism (IS/AAR = 46 ± 5%, p < 0.05 vs IPC effluent). In addition, a large release in ACh was observed in coronary effluent was observed following IPC (IPC_eff = 0.36 ± 0.03 μM vs C_eff = 0.04 ± 0.04 μM, n = 4, p < 0.001). Interestingly, however, IPC effluent was not able to significantly protect isolated cardiomyocytes from simulated ischaemia–reperfusion injury (cell death = 45 ± 6%, p = 0.09 vs control effluent). In conclusion, IPC involves activation of the intrinsic cardiac nervous system, leading to release of ACh in the ventricles and induction of protection via activation of muscarinic receptors.

Untargeted metabolomics reveals a mild impact of remote ischemic conditioning on the plasma metabolome and α-hydroxybutyrate as a possible cardioprotective factor and biomarker of tissue ischemia

INTRODUCTION

Remote ischemic conditioning (RIC) is a maneuver by which short non-lethal ischemic events are applied on distant organs or limbs to reduce ischemia and reperfusion injuries caused by e.g. myocardial infarct. Although intensively investigated, the specific mechanism of this protective phenomenon remains incompletely understood and in particular, knowledge on the role of small metabolites is scarce.

OBJECTIVES

In this study, we aimed to study perturbations in the plasma metabolome following RIC and gain insight into metabolic changes by the intervention as well as to identify potential novel cardio-protective metabolites.

METHODS

Blood plasma samples from ten healthy males were collected prior to and after RIC and tested for bioactivity in a HL-1 based cellular model of ischemia-reperfusion damage. Following this, the plasma was analyzed using untargeted LC-qTOF-MS and regulated metabolites were identified using univariate and multivariate statistical analysis. Results were finally verified in a second plasma study from the same group of volunteers and by testing a metabolite ester in the HL-1 cell model.

RESULTS

The analysis revealed a moderate impact on the plasma metabolome following RIC. One metabolite, α-hydroxybutyrate (AHB) however, stood out as highly significantly upregulated after RIC. AHB might be a novel and more sensitive plasma-biomarker of transient tissue ischemia than lactate. Importantly, it was also found that a cell permeable AHB precursor protects cardiomyocytes from ischemia-reperfusion damage.

CONCLUSION

Untargeted metabolomics analysis of plasma following RIC has led to insight into metabolism during RIC and revealed a possible novel metabolite of relevance to ischemic-reperfusion damage.

Methylophiopogonanone A suppresses ischemia/reperfusion-induced myocardial apoptosis in mice via activating PI3K/Akt/eNOS signaling pathway

AIM

The dried tuber root of Ophiopogon japonicus has been used in the traditional Chinese medicine for treatment of myocardial ischemia and thrombosis. In this study we investigated the effects of methylophiopogonanone A (MO-A), a major homoisoflavonoid in Ophiopogon japonicus, on myocardial ischemia/reperfusion (I/R) injury.

METHODS

Mice were pretreated with MO-A (10 mg·kg(-1)·d(-1), po) for 2 weeks and then subjected to transient occlusion of the left anterior descending coronary artery. Cardiac function was evaluated, and the infarct size and apoptosis index were assessed. The mechanisms underlying the cardio-protection of MO-A were analyzed in H9C2 rat cardiomyocytes subjected to hypoxia/reoxygenation (H/R). The cell viability and apoptosis were evaluated; apoptotic and relevant signaling proteins were analyzed. NO levels in the culture medium were assessed.

RESULTS

In I/R mice, pretreatment with MO-A significantly reduced the infarct size (by 60.7%) and myocardial apoptosis (by 56.8%), and improved cardiac function. In H9C2 cells subjected to H/R, pretreatment with MO-A (10 μmol/L) significantly decreased apoptosis and cleaved caspase-3 expression, elevated the Bcl-2/Bax ratio and restored NO production. Furthermore, pretreatment with MO-A markedly increased the activation of PI3K/Akt/eNOS pathway in H9C2 cells subjected to H/R, and the protective effects of MO-A were abolished in the presence of the PI3K inhibitor wortmannin (100 nmol/L).

CONCLUSION

MO-A attenuates I/R-induced myocardial apoptosis in mice via activating the PI3K/Akt/eNOS signaling pathway.

Remote ischaemic conditioning and remodelling following myocardial infarction: current evidence and future perspectives

Remote ischaemic conditioning (rIC) has demonstrated its effectiveness as a powerful cardioprotective tool in number of preclinical and limited clinical settings. More recently, ischaemic postconditioning given after an ischaemic event such as a myocardial infarction (MI) has shown not only to reduce infarct size but also to have beneficial effects on acute remodelling post-MI and to reduce the burden of heart failure and other detrimental outcomes. Building on this platform, repeated rIC over a number of days has the potential to augment the protective process even further. This review considers the current evidence base from which the concept of rIC in the setting of post-MI remodelling has grown. It also discusses the ongoing and planned clinical trials which are attempting to elucidate whether the protection imparted by rIC in the preclinical setting can be translated to the clinic and become a realistic weapon in the clinician’s armoury to tackle acute remodelling and heart failure post-MI.

Myocardial triggers involved in activation of remote ischaemic preconditioning

NEW FINDINGS

What is the central question of this study? Ischaemia-reperfusion of peripheral tissues protects the heart from subsequent myocardial ischaemia-reperfusion injury, a phenomenon referred to as remote ischaemic preconditioning (rIPC). This study evaluated the possible myocardial triggers of rIPC. What is the main finding and its importance? Remote ischaemic preconditioning reduces infarct size through a vagal pathway and a mechanism involving phosphorylation of Akt and endothelial nitric oxide synthase, opening of mitochondrial ATP-dependent K(+) channels and an increase in mitochondrial H2 O2 production. All these phenomena occur before the myocardial ischaemia; hence, they could act as 'triggers' of rIPC. It has been proposed that remote ischaemic preconditioning (rIPC) activates a parasympathetic neural pathway. However, the myocardial intracellular mechanism of rIPC remains unclear. Here, we characterized some of the intracellular signals participating as rIPC triggers. Isolated rat hearts were subjected to 30 min of global ischaemia and 120 min of reperfusion (Non-rIPC group). In a second group, before the isolation of the heart, an rIPC protocol (three cycles of hindlimb ischaemia-reperfusion) was performed. The infarct size was measured with tetrazolium staining. Expression/phosphorylation of Akt and endothelial nitric oxide synthase (eNOS) and mitochondrial H2 O2 production were evaluated at the end of the rIPC protocol, before myocardial ischaemia-reperfusion. The rIPC significantly decreased the infarct size and induced Akt and eNOS phosphorylation. The protective effect on infarct size was abolished by cervical vagal section, l-NAME (an NO synthesis inhibitor) and 5-hydroxydecanoate (a mitochondrial ATP-dependent K(+) channel blocker). Mitochondrial production of H2 O2 was increased by rIPC, whereas it was abolished by cervical vagal section, l-NAME and 5-hydroxydecanoate. We conclude that rIPC activates a parasympathetic vagal pathway and a mechanism involving the phosphorylation of Akt and eNOS, the opening of mitochondrial ATP-dependent K(+) channels and the release of H2 O2 by the mitochondria. All these phenomena occur before myocardial ischaemia and could act as triggers of rIPC.

Combination of remote ischemic perconditioning and remote ischemic postconditioning fails to increase protection against myocardial ischemia/reperfusion injury, compared with either alone

Remote ischemic perconditioning (RIPerC) and remote ischemic postconditioning (RIPostC) have been previously demonstrated to protect the myocardium against ischemia/reperfusion (IR) injury. However, their combined effects remain to be fully elucidated. In order to investigate this, the present study used an in vivo rat model to assess whether synergistic effects are produced when RIPerC is combined with RIPostC. The rats were randomly assigned to the following groups: Sham, IR, RIPerC, RIPostC and RIPerC + RIPostC groups. The IR model was established by performing 40 min of left coronary artery occlusion, followed by 2 h of reperfusion. RIPerC and RIPostC were induced via four cycles of 5 min occlusion and 5 min reperfusion of the hindlimbs, either during or subsequent to myocardial ischemia. On measurement of infarct sizes, compared with the IR group (49.45±6.59%), the infarct sizes were significantly reduced in the RIPerC (34.36±5.87%) and RIPostC (36.04±6.16%) groups (P<0.05). However, no further reduction in infarct size was observed in the RIPerC + RIPostC group (31.43±5.43%; P>0.05), compared with the groups treated with either RIPerC or RIPostC alone. Activation of the reperfusion injury salvage kinase (RISK) Akt, extracellular signal-regulated kinase 1/2 and glycogen synthase kinase-3β, and survivor activating factor enhancement (SAFE) signal transducer and activator of transcription-3 pathways were enhanced in the RIPerC, RIPostC and the RIPerC + RIPostC groups, compared with the IR group, with no difference among the three groups. Therefore, whereas RIPerC and RIPostC were equally effective in providing protection against myocardial IR injury, the combination of RIPerC and RIPostC failed to provide further protection than treatment with either alone. The cardioprotective effects were found to be associated with increased activation of the RISK and SAFE pathways.

Cardioprotection by remote ischemic conditioning: Mechanisms and clinical evidences

In remote ischemic conditioning (RIC), several cycles of ischemia and reperfusion render distant organ and tissues more resistant to the ischemia-reperfusion injury. The intermittent ischemia can be applied before the ischemic insult in the target site (remote ischemic preconditioning), during the ischemic insult (remote ischemic perconditioning) or at the onset of reperfusion (remote ischemic postconditioning). The mechanisms of RIC have not been completely defined yet; however, these mechanisms must be represented by the release of humoral mediators and/or the activation of a neural reflex. RIC has been discovered in the heart, and has been arising great enthusiasm in the cardiovascular field. Its efficacy has been evaluated in many clinical trials, which provided controversial results. Our incomplete comprehension of the mechanisms underlying the RIC could be impairing the design of clinical trials and the interpretation of their results. In the present review we summarize current knowledge about RIC pathophysiology and the data about its cardioprotective efficacy.