Modifications in rat plasma proteome after remote ischemic preconditioning (RIPC) stimulus: identification by a SELDI-TOF-MS approach

Vago-splenic signal transduction of cardioprotection in humans

BACKGROUND AND AIMS

The spleen serves as an important relay organ that releases cardioprotective factor(s) upon vagal activation during remote ischaemic conditioning (RIC) in rats and pigs. The translation of these findings to humans was attempted.

METHODS

Remote ischaemic conditioning or electrical auricular tragus stimulation (ATS) were performed in 10 healthy young volunteers, 10 volunteers with splenectomy, and 20 matched controls. Venous blood samples were taken before and after RIC/ATS or placebo, and a plasma dialysate was infused into isolated perfused rat hearts subjected to global ischaemia/reperfusion.

RESULTS

Neither left nor right RIC or ATS altered heart rate and heart rate variability in the study cohorts. With the plasma dialysate prepared before RIC or ATS, respectively, infarct size (% ventricular mass) in the recipient rat heart was 36 ± 6% (left RIC), 34 ± 3% (right RIC) or 31 ± 5% (left ATS), 35 ± 5% (right ATS), and decreased with the plasma dialysate from healthy volunteers after RIC or ATS to 20 ± 4% (left RIC), 23 ± 6% (right RIC) or to 19 ± 4% (left ATS), 26 ± 9% (right ATS); infarct size was still reduced with plasma dialysate 4 days after ATS and 9 days after RIC. In a subgroup of six healthy volunteers, such infarct size reduction was abrogated by intravenous atropine. Infarct size reduction by RIC or ATS was also abrogated in 10 volunteers with splenectomy, but not in their 20 matched controls.

CONCLUSIONS

In humans, vagal innervation and the spleen as a relay organ are decisive for the cardioprotective signal transduction of RIC and ATS.

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.

Remote ischemic conditioning-induced hyperacute and acute responses of plasma proteome in healthy young male adults: a quantitative proteomic analysis

BACKGROUND

Long-term remote ischemic conditioning (RIC) has been proven to be beneficial in multiple diseases, such as cerebral and cardiovascular diseases. However, the hyperacute and acute effects of a single RIC stimulus are still not clear. Quantitative proteomic analyses of plasma proteins following RIC application have been conducted in preclinical and clinical studies but exhibit high heterogeneity in results due to wide variations in experimental setups and sampling procedures. Hence, this study aimed to explore the immediate effects of RIC on plasma proteome in healthy young adults to exclude confounding factors of disease entity, such as medications and gender.

METHODS

Young healthy male participants were enrolled after a systematic physical examination and 6-month lifestyle observation. Individual RIC sessions included five cycles of alternative ischemia and reperfusion, each lasting for 5 min in bilateral forearms. Blood samples were collected at baseline, 5 min after RIC, and 2 h after RIC, and then samples were processed for proteomic analysis using liquid chromatography-tandem mass spectrometry method.

RESULTS

Proteins related to lipid metabolism (e.g., Apolipoprotein F), coagulation factors (hepatocyte growth factor activator preproprotein), members of complement cascades (mannan-binding lectin serine protease 1 isoform 2 precursor), and inflammatory responses (carboxypeptidase N catalytic chain precursor) were differentially altered at their serum levels following the RIC intervention. The most enriched pathways were protein glycosylation and complement/coagulation cascades.

CONCLUSIONS

One-time RIC stimulus may induce instant cellular responses like anti-inflammation, coagulation, and fibrinolysis balancing, and lipid metabolism regulation which are protective in different perspectives. Protective effects of single RIC in hyperacute and acute phases may be exploited in clinical emergency settings due to apparently beneficial alterations in plasma proteome profile. Furthermore, the beneficial effects of long-term (repeated) RIC interventions in preventing chronic cardiovascular diseases among general populations can also be expected based on our study findings.

Potential Anti-Inflammatory and Anti-Coagulation Effects of One-Time Application of Remote Ischemic Conditioning in Patients With Subacute/Chronic Cerebral Arteriostenosis and Venostenosis

BACKGROUND

Remote ischemic conditioning (RIC) is an extremely simple, non-invasive, and cost-effective method with a neuroprotective effect. This study aimed to evaluate the immediate effects of one-time application of RIC on inflammation and coagulation in patients with chronic cerebral vascular stenosis, and compare the different effects of RIC on cerebral arteriostenosis and cerebral venostenosis.

METHOD

A total of 47 patients with defined cerebral arteriostenosis (n=21) or venostenosis (n=26) were prospectively enrolled. RIC intervention was given once with 5 cycles of inflating and deflating for 5 minutes alternately. Blood was sampled 5 minutes before and after RIC for inflammatory and thrombophilia biomarkers. Differences in inflammatory and thrombotic variables at differing time points in the group were assessed using paired t tests or Wilcoxon matched-pairs signed-rank test.

RESULTS

Patients with cerebral arteriostenosis had a higher level of pre-RIC neutrophil-to-lymphocyte ratio ( P =0.034), high-sensitivity C-reactive protein ( P =0.037), and fibrinogen ( P =0.002) than that with cerebral venostenosis. In the arterial group, levels of fibrinogen ( P =0.023) decreased, and interleukin-6 levels were elevated ( P =0.019) after a single RIC. Age was negatively related to interleukin-6, C-reactive protein, and fibrinogen.

CONCLUSION

One-time RIC interventions may show seemingly coexisted proinflammatory and anti-coagulation effects of a single bout on patients with cerebral arteriostenosis. Older age was a negative predictor for multiple biomarkers in the cerebral arteriostensosis group. The protective effect of RIC on cerebral venostenosis patients needs to be further studied in a larger sample size.

Remote but not Distant: a Review on Experimental Models and Clinical Trials in Remote Ischemic Conditioning as Potential Therapy in Ischemic Stroke

Stroke is one of the main causes of neurological disability worldwide and the second cause of death in people over 65 years old, resulting in great economic and social burden. Ischemic stroke accounts for 85% of total cases, and the approved therapies are based on re-establishment of blood flow, and do not directly target brain parenchyma. Thus, novel therapies are urgently needed. In this review, limb remote ischemic conditioning (RIC) is revised and discussed as a potential therapy against ischemic stroke. The review targets both (i) fundamental research based on experimental models and (ii) clinical research based on clinical trials and human interventional studies with healthy volunteers. Moreover, it also presents two approaches concerning RIC mechanisms in stroke: (i) description of the underlying cerebral cellular and molecular mechanisms triggered by limb RIC that promote neuroprotection against stroke induced damage and (ii) the identification of signaling factors involved in inter-organ communication following RIC procedure. Limb to brain remote signaling can occur via circulating biochemical factors, immune cells, and/or stimulation of autonomic nervous system. In this review, these three hypotheses are explored in both humans and experimental models. Finally, the challenges involved in translating experimentally generated scientific knowledge to a clinical setting are also discussed.

Quantitative Proteomic Analysis of Plasma after Remote Ischemic Conditioning in a Rhesus Monkey Ischemic Stroke Model

Background: Animal and clinical studies have shown that remote ischemic conditioning (RIC) has protective effects for cerebral vascular diseases, with induced humoral factor changes in the peripheral blood. However, many findings are heterogeneous, perhaps due to differences in the RIC intervention schemes, enrolled populations, and sample times. This study aimed to examine the RIC-induced changes in the plasma proteome using rhesus monkey models of strokes. Methods: Two adult rhesus monkeys with autologous blood clot-induced middle cerebral artery (MCA) occlusion underwent RIC interventions twice a week for five consecutive weeks. Each RIC treatment included five cycles of five minutes of ischemia alternating with five minutes of reperfusion of the forearm. The blood samples were taken from the median cubital vein of the monkeys at baseline and immediately after each week’s RIC stimulus. The plasma samples were isolated for a proteomic analysis using mass spectrometry (MS). Results: Several proteins related to lipid metabolism (Apolipoprotein A-II and Apolipoprotein C-II), coagulation (Fibrinogen alpha chain and serpin), immunoinflammatory responses (complement C3 and C1), and endovascular hemostasis (basement membrane-specific heparan sulfate proteoglycan) were significantly modulated after the RIC intervention. Many of these induced changes, such as in the lipid metabolism regulation and anticoagulation responses, starting as early as two weeks following the RIC intervention. The complementary activation and protection of the endovascular cells occurred more than three weeks postintervention. Conclusions: Multiple protective effects were induced by RIC and involved lipid metabolism regulation (anti-atherogenesis), anticoagulation (antithrombosis), complement activation, and endovascular homeostasis (anti-inflammation). In conclusion, this study indicates that RIC results in significant modulations of the plasma proteome. It also provides ideas for future research and screening targets.

Subclinical effects of remote ischaemic conditioning in human kidney transplants revealed by quantitative proteomics

Background

Remote ischaemic conditioning (RIC) is currently being explored as a non-invasive method to attenuate ischaemia/reperfusion injuries in organs. A randomised clinical study (CONTEXT) evaluated the effects of RIC compared to non-RIC controls in human kidney transplants.

Methods

RIC was induced prior to kidney reperfusion by episodes of obstruction to arterial flow in the leg opposite the transplant using a tourniquet (4 × 5 min). Although RIC did not lead to clinical improvement of transplant outcomes, we explored whether RIC induced molecular changes through precision analysis of CONTEXT recipient plasma and kidney tissue samples by high-resolution tandem mass spectrometry (MS/MS).

Results

We observed an accumulation of muscle derived proteins and altered amino acid metabolism in kidney tissue proteomes, likely provoked by RIC, which was not reflected in plasma. In addition, MS/MS analysis demonstrated transient upregulation of several acute phase response proteins (SAA1, SAA2, CRP) in plasma, 1 and 5 days post-transplant in RIC and non-RIC conditions with a variable effect on the magnitude of acute inflammation.

Conclusions

Together, our results indicate sub-clinical systemic and organ-localised effects of RIC.

Nuclear Factor (Erythroid-Derived 2)-Like 2 Regulates the Hepatoprotective Effects of Remote Ischemic Conditioning in Hemorrhagic Shock

AIMS

Remote ischemic conditioning (RIC) protects against organ ischemia/reperfusion injury in experimental and clinical settings. We have demonstrated that RIC prevents liver and lung inflammation/injury after hemorrhagic shock/resuscitation (S/R). In this study, we used a murine model of S/R to investigate the role of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in mediating hepatoprotection.

RESULTS

The combination of RIC with S/R caused a synergistic rise in Nrf2 and its translocation to the nucleus in the liver. Increased activation of Nrf2 by RIC augmented heme oxygenase-1 (HO-1) and autophagy and exerted hepatoprotection, concurrent with reductions in S/R-induced TNF-α (tumor necrosis factor alpha) and IL-6 (interleukin-6). In Nrf2 knockout (KO) animals, RIC did not exert hepatoprotection, and it failed to upregulate HO-1 and autophagy. Further, resuscitating wildtype (WT) animals with blood from donor WT animals undergoing RIC was hepatoprotective, but not in Nrf2 KO recipient animals. Interestingly, RIC blood from Nrf2 KO donor animals was also not protective when used to resuscitate WT animals, suggesting a role for Nrf2 both in the afferent arm of RIC where protective factors are generated and also in the efferent arm where organ protection is exerted. Finally, RIC plasma prevented oxidant-induced zebrafish mortality, but not in Nrf2a morpholino knockdown fish.

INNOVATION

Activation of Nrf2 is an essential mechanism underlying the hepatoprotective effects of RIC. Nrf2 appears to play a role in the afferent limb of RIC protection, as its absence precludes the generation of the protective humoral factors induced by RIC.

CONCLUSION

Our studies demonstrate the critical role of Nrf2 in the ability of RIC to prevent organ injury after S/R.

The role of adenosine in up-regulation of p38 MAPK and ERK during limb ischemic preconditioning-induced brain ischemic tolerance

Our previous studies have demonstrated that limb ischemic preconditioning (LIP) induced brain ischemic tolerance and up-regulated the expression of p38 MAPK and ERK in the hippocampal CA1 region in rats. The present study was undertaken to investigate the role of adenosine in brain protection and up-regulation of p38 MAPK and ERK induced by LIP. It was found that adenosine A1 receptor antagonist DPCPX dose-dependently inhibited the protective effect of LIP. The up-regulation of p38 MAPK and ERK induced by LIP could be blocked by DPCPX. Furthermore, we observed the effect of adenosine on the brain ischemia. The results showed that pre-administration of adenosine could partly mimic the neuroprotective effect on the brain, up-regulate the expression of p38 MAPK and ERK. Based on the above results, it can be concluded that adenosine participated in brain protection and up-regulation of the expression of p38 MAPK and ERK during the induction of brain ischemic tolerance after LIP.

Correction to: Neuroimmune Response in Ischemic Preconditioning

Ischemic preconditioning (IPC) is a robust neuroprotective phenomenon in which a brief period of cerebral ischemia confers transient tolerance to subsequent ischemic challenge. Research on IPC has implicated cellular, molecular, and systemic elements of the immune response in this phenomenon. Potent molecular mediators of IPC include innate immune signaling pathways such as Toll-like receptors and type 1 interferons. Brain ischemia results in release of pro- and anti-inflammatory cytokines and chemokines that orchestrate the neuroinflammatory response, resolution of inflammation, and transition to neurological recovery and regeneration. Cellular mediators of IPC include microglia, the resident central nervous system immune cells, astrocytes, and neurons. All of these cell types engage in cross-talk with each other using a multitude of signaling pathways that modulate activation/suppression of each of the other cell types in response to ischemia. As the postischemic neuroimmune response evolves over time there is a shift in function toward provision of trophic support and neuroprotection. Peripheral immune cells infiltrate the central nervous system en masse after stroke and are largely detrimental, with a few subtypes having beneficial, protective effects, though the role of these immune cells in IPC is largely unknown. The role of neural progenitor cells in IPC-mediated neuroprotection is another active area of investigation as is the role of microglial proliferation in this setting. A mechanistic understanding of these molecular and cellular mediators of IPC may not only facilitate more effective direct application of IPC to specific clinical scenarios, but also, more broadly, reveal novel targets for therapeutic intervention in stroke.

Remote ischemic preconditioning fails to reduce infarct size in the Zucker fatty rat model of type-2 diabetes: role of defective humoral communication

Remote ischemic preconditioning (RIPC), the phenomenon whereby brief ischemic episodes in distant tissues or organs render the heart resistant to infarction, has been exhaustively demonstrated in preclinical models. Moreover, emerging evidence suggests that exosomes play a requisite role in conveying the cardioprotective signal from remote tissue to the myocardium. However, in cohorts displaying clinically common comorbidities-in particular, type-2 diabetes-the infarct-sparing effect of RIPC may be confounded for as-yet unknown reasons. To investigate this issue, we used an integrated in vivo and in vitro approach to establish whether: (1) the efficacy of RIPC is maintained in the Zucker fatty rat model of type-2 diabetes, (2) the humoral transfer of cardioprotective triggers initiated by RIPC are transported via exosomes, and (3) diabetes is associated with alterations in exosome-mediated communication. We report that a standard RIPC stimulus (four 5-min episodes of hindlimb ischemia) reduced infarct size in normoglycemic Zucker lean rats, but failed to confer protection in diabetic Zucker fatty animals. Moreover, we provide novel evidence, via transfer of serum and serum fractions obtained following RIPC and applied to HL-1 cardiomyocytes subjected to hypoxia-reoxygenation, that diabetes was accompanied by impaired humoral communication of cardioprotective signals. Specifically, our data revealed that serum and exosome-rich serum fractions collected from normoglycemic rats attenuated hypoxia-reoxygenation-induced HL-1 cell death, while, in contrast, exosome-rich samples from Zucker fatty rats did not evoke protection in the HL-1 cell model. Finally, and unexpectedly, we found that exosome-depleted serum from Zucker fatty rats was cytotoxic and exacerbated hypoxia-reoxygenation-induced cardiomyocyte death.

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.

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.

Glucagon-like peptide-1 (GLP-1) mediates cardioprotection by remote ischaemic conditioning

Aims

Although the nature of the humoral factor which mediates cardioprotection established by remote ischaemic conditioning (RIc) remains unknown, parasympathetic (vagal) mechanisms appear to play a critical role. As the production and release of many gut hormones is modulated by the vagus nerve, here we tested the hypothesis that RIc cardioprotection is mediated by the actions of glucagon-like peptide-1 (GLP-1).

Methods and results

A rat model of myocardial infarction (coronary artery occlusion followed by reperfusion) was used. Remote ischaemic pre- (RIPre) or perconditioning (RIPer) was induced by 15 min occlusion of femoral arteries applied prior to or during the myocardial ischaemia. The degree of RIPre and RIPer cardioprotection was determined in conditions of cervical or subdiaphragmatic vagotomy, or following blockade of GLP-1 receptors (GLP-1R) using specific antagonist Exendin(9–39). Phosphorylation of PI3K/AKT and STAT3 was assessed. RIPre and RIPer reduced infarct size by ∼50%. In conditions of bilateral cervical or subdiaphragmatic vagotomy RIPer failed to establish cardioprotection. GLP-1R blockade abolished cardioprotection induced by either RIPre or RIPer. Exendin(9–39) also prevented RIPre-induced AKT phosphorylation. Cardioprotection induced by GLP-1R agonist Exendin-4 was preserved following cervical vagotomy, but was abolished in conditions of M3 muscarinic receptor blockade.

Conclusions

These data strongly suggest that GLP-1 functions as a humoral factor of remote ischaemic conditioning cardioprotection. This phenomenon requires intact vagal innervation of the visceral organs and recruitment of GLP-1R-mediated signalling. Cardioprotection induced by GLP-1R activation is mediated by a mechanism involving M3 muscarinic receptors.

Neuroimmune Response in Ischemic Preconditioning

Ischemic preconditioning (IPC) is a robust neuroprotective phenomenon in which a brief period of cerebral ischemia confers transient tolerance to subsequent ischemic challenge. Research on IPC has implicated cellular, molecular, and systemic elements of the immune response in this phenomenon. Potent molecular mediators of IPC include innate immune signaling pathways such as Toll-like receptors and type 1 interferons. Brain ischemia results in release of pro- and anti-inflammatory cytokines and chemokines that orchestrate the neuroinflammtory response, resolution of inflammation, and transition to neurological recovery and regeneration. Cellular mediators of IPC include microglia, the resident central nervous system immune cells, astrocytes, and neurons. All of these cell types engage in cross-talk with each other using a multitude of signaling pathways that modulate activation/suppression of each of the other cell types in response to ischemia. As the postischemic neuroimmune response evolves over time there is a shift in function toward provision of trophic support and neuroprotection. Peripheral immune cells infiltrate the central nervous system en masse after stroke and are largely detrimental, with a few subtypes having beneficial, protective effects, though the role of these immune cells in IPC is largely unknown. The role of neural progenitor cells in IPC-mediated neuroprotection is another active area of investigation as is the role of microglial proliferation in this setting. A mechanistic understanding of these molecular and cellular mediators of IPC may not only facilitate more effective direct application of IPC to specific clinical scenarios, but also, more broadly, reveal novel targets for therapeutic intervention in stroke.

Transthyretin provides trophic support via megalin by promoting neurite outgrowth and neuroprotection in cerebral ischemia

Transthyretin (TTR) is a protein whose function has been associated to binding and distribution of thyroid hormones in the body and brain. However, little is known regarding the downstream signaling pathways triggered by wild-type TTR in the CNS either in neuroprotection of cerebral ischemia or in physiological conditions. In this study, we investigated how TTR affects hippocampal neurons in physiologic/pathologic conditions. Recombinant TTR significantly boosted neurite outgrowth in mice hippocampal neurons, both in number and length, independently of its ligands. This TTR neuritogenic activity is mediated by the megalin receptor and is lost in megalin-deficient neurons. We also found that TTR activates the mitogen-activated protein kinase (MAPK) pathways (ERK1/2) and Akt through Src, leading to the phosphorylation of transcription factor CREB. In addition, TTR promoted a transient rise in intracellular calcium through NMDA receptors, in a Src/megalin-dependent manner. Moreover, under excitotoxic conditions, TTR stimulation rescued cell death and neurite loss in TTR KO hippocampal neurons, which are more sensitive to excitotoxic degeneration than WT neurons, in a megalin-dependent manner. CREB was also activated by TTR under excitotoxic conditions, contributing to changes in the balance between Bcl2 protein family members, toward anti-apoptotic proteins (Bcl2/BclXL versus Bax). Finally, we clarify that TTR KO mice subjected to pMCAO have larger infarcts than WT mice, because of TTR and megalin neuronal downregulation. Our results indicate that TTR might be regarded as a neurotrophic factor, because it stimulates neurite outgrowth under physiological conditions, and promotes neuroprotection in ischemic conditions.

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.

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.

Across-Species Transfer of Protection by Remote Ischemic Preconditioning With Species-Specific Myocardial Signal Transduction by Reperfusion Injury Salvage Kinase and Survival Activating Factor Enhancement Pathways

RATIONALE

Reduction of myocardial infarct size by remote ischemic preconditioning (RIPC), that is, cycles of ischemia/reperfusion in an organ remote from the heart before sustained myocardial ischemia/reperfusion, was confirmed in all species so far, including humans.

OBJECTIVE

To identify myocardial signal transduction of cardioprotection by RIPC.

METHODS AND RESULTS

Anesthetized pigs were subjected to RIPC (4×5/5 minutes hindlimb ischemia/reperfusion) or placebo (PLA) before 60/180 minutes coronary occlusion/reperfusion. Phosphorylation of protein kinase B, extracellular signal-regulated kinase 1/2 (reperfusion injury salvage kinase [RISK] pathway), and signal transducer and activator of transcription 3 (survival activating factor enhancement [SAFE] pathway) in the area at risk was determined by Western blot. Wortmannin/U0126 or AG490 was used for pharmacological RISK or SAFE blockade, respectively. Plasma sampled after RIPC or PLA, respectively, was transferred to isolated bioassay rat hearts subjected to 30/120 minutes global ischemia/reperfusion. RIPC reduced infarct size in pigs to 16±11% versus 43±11% in PLA (% area at risk; mean±SD; P<0.05). RIPC increased the phosphorylation of signal transducer and activator of transcription 3 at early reperfusion, and AG490 abolished the protection, whereas RISK blockade did not. Signal transducer and activator of transcription 5 phosphorylation was decreased at early reperfusion in both RIPC and PLA. In isolated rat hearts, pig plasma taken after RIPC reduced infarct size (25±5% of ventricular mass versus 38±5% in PLA; P<0.05) and activated both RISK and SAFE. RISK or SAFE blockade abrogated this protection.

CONCLUSIONS

Cardioprotection by RIPC in pigs causally involves activation of signal transducer and activator of transcription 3 but not of RISK. Protection can be transferred with plasma from pigs to isolated rat hearts where activation of both RISK and SAFE is causally involved. The myocardial signal transduction of RIPC is the same as that of ischemic postconditioning.

A critical review of mechanisms regulating remote preconditioning-induced brain protection

Remote preconditioning (rPC) is the phenomenon whereby brief organ ischemia evokes an endogenous response such that a different (remote) organ is protected against subsequent, normally injurious ischemia. Experiments show rPC to be effective at evoking cardioprotection against ischemic heart injury and, more recently, neuroprotection against brain ischemia. Such is the enthusiasm for rPC that human studies have been initiated. Clinical trials suggest rPC to be safe (phase II trial) and effective in reducing stroke incidence in a population with high stroke risk. However, despite the therapeutic potential of rPC, there is a large gap in knowledge regarding the effector mechanisms of rPC and how it might be orchestrated to improve outcome after stroke. Here we provide a critical review of mechanisms that are directly attributable to rPC-induced neuroprotection in preclinical trials of rPC.

Remote ischemic preconditioning (RIPC) modifies the plasma proteome in children undergoing repair of tetralogy of fallot: a randomized controlled trial

BACKGROUND

Remote ischemic preconditioning (RIPC) has been applied in paediatric cardiac surgery. We have demonstrated that RIPC induces a proteomic response in plasma of healthy volunteers. We tested the hypothesis that RIPC modifies the proteomic response in children undergoing Tetralogy of Fallot (TOF) repair.

METHODS AND RESULTS

Children (n=40) were randomized to RIPC and control groups. Blood was sampled at baseline, after cardiopulmonary bypass (CPB) and 6, 12 and 24h post-CPB. Plasma was analysed by liquid chromatography mass spectrometry (LC-MS) in an untargeted approach. Peptides demonstrating differential expression (p<0.01) were subjected to tandem LC-MS/MS and protein identification. Corresponding proteins were identified using the NCBI protein database. There was no difference in age (7.3±3.5vs6.8±3.6 months)(p=0.89), weight (7.7±1.8vs7.5±1.9 kg)(p=0.71), CPB time (104±7vs94±7 min)(p=0.98) or aortic cross-clamp time (83±22vs75±20 min)(p=0.36). No peptides were differentially expressed at baseline or immediately after CPB. There were 48 peptides with higher expression in the RIPC group 6h post-CPB. This was no longer evident at 12 or 24h, with one peptide down-regulated in the RIPC group. The proteins identified were: inter-alpha globulin inhibitor (42.0±11.8 vs 820.8±181.1, p=0.006), fibrinogen preproprotein (59.3±11.2 vs 1192.6±278.3, p=0.007), complement-C3 precursor (391.2±160.9 vs 5385.1±689.4, p=0.0005), complement C4B (151.5±17.8 vs 4587.8±799.2, p=0.003), apolipoprotein B100 (53.4±8.3 vs 1364.5±278.2, p=0.005) and urinary proteinase inhibitor (358.6±74.9 vs 5758.1±1343.1, p=0.009). These proteins are involved in metabolism, haemostasis, immunity and inflammation.

CONCLUSIONS

We provided the first comprehensive analysis of RIPC-induced proteomic changes in children undergoing surgery. The proteomic changes peak 6h post-CPB and return to baseline within 24h of surgery.

TRIAL REGISTRATION

ACTR.org.au ACTRN12610000496011.

Remote ischaemic conditioning: cardiac protection from afar

For patients with ischaemic heart disease, remote ischaemic conditioning may offer an innovative, non‐invasive and virtually cost‐free therapy for protecting the myocardium against the detrimental effects of acute ischaemia‐reperfusion injury, preserving cardiac function and improving clinical outcomes. The intriguing phenomenon of remote ischaemic conditioning was first discovered over 20 years ago, when it was shown that the heart could be rendered resistant to acute ischaemia‐reperfusion injury by applying one or more cycles of brief ischaemia and reperfusion to an organ or tissue away from the heart – initially termed ‘cardioprotection at a distance’. Subsequent pre‐clinical and then clinical studies made the important discovery that remote ischaemic conditioning could be elicited non‐invasively, by inducing brief ischaemia and reperfusion to the upper or lower limb using a cuff. The actual mechanism underlying remote ischaemic conditioning cardioprotection remains unclear, although a neuro‐hormonal pathway has been implicated. Since its initial discovery in 1993, the first proof‐of‐concept clinical studies of remote ischaemic conditioning followed in 2006, and now multicentre clinical outcome studies are underway. In this review article, we explore the potential mechanisms underlying this academic curiosity, and assess the success of its application in the clinical setting.

Exploring the human plasma proteome for humoral mediators of remote ischemic preconditioning--a word of caution

Despite major advances in early revascularization techniques, cardiovascular diseases are still the leading cause of death worldwide, and myocardial infarctions contribute heavily to this. Over the past decades, it has become apparent that reperfusion of blood to a previously ischemic area of the heart causes damage in and of itself, and that this ischemia reperfusion induced injury can be reduced by up to 50% by mechanical manipulation of the blood flow to the heart. The recent discovery of remote ischemic preconditioning (RIPC) provides a non-invasive approach of inducing this cardioprotection at a distance. Finding its endogenous mediators and their operative mode is an important step toward increasing the ischemic tolerance. The release of humoral factor(s) upon RIPC was recently demonstrated and several candidate proteins were published as possible mediators of the cardioprotection. Before clinical applicability, these potential biomarkers and their efficiency must be validated, a task made challenging by the large heterogeneity in reported data and results. Here, in an attempt to reproduce and provide more experimental data on these mediators, we conducted an unbiased in-depth analysis of the human plasma proteome before and after RIPC. From the 68 protein markers reported in the literature, only 28 could be mapped to manually reviewed (Swiss-Prot) protein sequences. 23 of them were monitored in our untargeted experiment. However, their significant regulation could not be reproducibly estimated. In fact, among the 394 plasma proteins we accurately quantified, no significant regulation could be confidently and reproducibly assessed. This indicates that it is difficult to both monitor and reproduce published data from experiments exploring for RIPC induced plasma proteomic regulations, and suggests that further work should be directed towards small humoral factors. To simplify this task, we made our proteomic dataset available via ProteomeXchange, where scientists can mine for novel potential targets.