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Sudden myocardial ischaemia causes an acute coronary syndrome. In the case of ST-elevation myocardial infarction (STEMI), this is usually caused by the acute rupture of atherosclerotic plaque and obstruction of a coronary artery. Timely restoration of blood flow can reduce infarct size, but ischaemic regions of myocardium remain in up to two-thirds of patients due to microvascular obstruction (MVO). Experimentally, cardioprotective strategies can limit infarct size, but these are primarily intended to target reperfusion injury. Here, we address the question of whether it is possible to specifically prevent ischaemic injury, for example in models of chronic coronary artery occlusion. Two main types of intervention are identified: those that preserve ATP levels by reducing myocardial oxygen consumption, (e.g. hypothermia; cardiac unloading; a reduction in heart rate or contractility; or ischaemic preconditioning), and those that increase myocardial oxygen/blood supply (e.g. collateral vessel dilation). An important consideration in these studies is the method used to assess infarct size, which is not straightforward in the absence of reperfusion. After several hours, most of the ischaemic area is likely to become infarcted, unless it is supplied by pre-formed collateral vessels. Therefore, therapies that stimulate the formation of new collaterals can potentially limit injury during subsequent exposure to ischaemia. After a prolonged period of ischaemia, the heart undergoes a remodelling process. Interventions, such as those targeting inflammation, may prevent adverse remodelling. Finally, harnessing of the endogenous process of myocardial regeneration has the potential to restore cardiomyocytes lost during infarction.

The Hatter Cardiovascular Institute biennial workshop, originally scheduled for April 2020 but postponed for 2 years due to the Covid pandemic, was organised to debate and discuss the future of Remote Ischaemic Conditioning (RIC). This evolved from the large multicentre CONDI-2–ERIC–PPCI outcome study which demonstrated no additional benefit when using RIC in the setting of ST-elevation myocardial infarction (STEMI). The workshop discussed how conditioning has led to a significant and fundamental understanding of the mechanisms preventing cell death following ischaemia and reperfusion, and the key target cyto-protective pathways recruited by protective interventions, such as RIC. However, the obvious need to translate this protection to the clinical setting has not materialised largely due to the disconnect between preclinical and clinical studies. Discussion points included how to adapt preclinical animal studies to mirror the patient presenting with an acute myocardial infarction, as well as how to refine patient selection in clinical studies to account for co-morbidities and ongoing therapy. These latter scenarios can modify cytoprotective signalling and need to be taken into account to allow for a more robust outcome when powered appropriately. The workshop also discussed the potential for RIC in other disease settings including ischaemic stroke, cardio-oncology and COVID-19. The workshop, therefore, put forward specific classifications which could help identify so-called responders vs. non-responders in both the preclinical and clinical settings.

RationaleIntracellular Na elevation is a hallmark of the ischaemic and failing heart – pathologies in which both acute and chronic metabolic remodelling occur.ObjectiveTo assess whether acute (75 µM ouabain 100 nM blebbistatin) and chronic myocardial Nai load (PLM3SA mouse) are causally linked to metabolic remodelling and if the failing heart shares a common Na-mediated metabolic ‘fingerprint’.Methods23Na, 31P and 13C NMRS were performed in normal and hypertrophied (pressure overload) Langendorff perfused mouse hearts followed by 1 hour NMRS metabolomic profiling, mass spec and in silico modelling.ResultsNa overload (acute, chronic (PLM3SA), and hypertrophy 2, 1.3 and 1.4-fold respectively) resulted in common metabolic perturbations: substrate switch (palmitate 35% reduction, glucose 58% increase), flux (TCA cycle, OXPHOS, glycolysis) and metabolomic profile (TCA cycle, glycolysis, anaplerosis) without energetic impairment (PCr/ATP 1.5±0.1 vs control 1.3±0.1). Inhibition of mitochondrial Na/Ca exchanger by CGP37157 during both acute and chronic Na load ameliorated the metabolic changes.ConclusionElevated Na leads to complex metabolic alterations preceding any energetic and functional impairment. Early prevention of Na overload and inhibition of Na/Camito could ameliorate metabolic dysregulation in hypertrophy and failure.

Introduction: Based on data that outcome in patients with acute myocardial infarction is predicted by final infarct size (IS), reducing IS is of paramount importance. Recent experimental studies have demonstrated a strong infarct-sparing effect of SGLT2 inhibitors – a class of drugs which have proved to be safe and beneficial in patients with heart failure. Repurposing SGLT2 inhibitors for the benefit of patients presenting with acute myocardial infarction should be preceded by investigation of the underlying mechanisms of this infarct limitation. Experimental and clinical data indicate a potential role for autonomic modulation in these mechanisms, specifically sympatho-inhibition. The aim of this study was to investigate the role of the parasympathetic mechanism in the infarct-limiting effect of SGLT2 inhibition. Methods: Fortyeight Sprague Dawley male rats were fed with a standard diet containing either the SGLT2 inhibitor ertugliflozin or vehicle, for 5-7 days. Myocardial ischaemia/reperfusion injury was initiated by a 40-min occlusion of the left anterior descending coronary artery followed by a 2hr period of reperfusion under isoflurane anaesthesia. Bilateral cervical vagotomy was performed 10min prior to myocardial ischaemia. Alternatively, muscarinic receptors were blocked systemically with the non-selective blocker atropine sulphate (2 mg/kg bolus, then 1 mg/kg/h) or the M3-selective blocker 4-DAMP (2 mg/kg bolus). Results: Pre-treatment with ertugliflozin reduced IS in comparison with the vehicle-treated controls (p<0.001). Bilateral vagotomy, atropine sulphate and 4-DAMP all abolished this infarct-limiting effect (IS 35±10%, 44±8%, and 35±4% respectively; P<0.01 vs. Ertu for vagotomy, P<0.001 vs. Ertu for both atropine sulphate and 4-DAMP). Conclusion: These results suggest that the Infarct-limiting effect of the SGLT2 inhibitor ertugliflozin, may be mediated via activation of the vagus nerve and M3-cholinoreceptors. Competing Interest Statement The authors have declared no competing interest.

PurposeA substantial number of ischaemic stroke patients who receive reperfusion therapy in the acute phase do not ever fully recover. This reveals the urgent need to develop new adjunctive neuroprotective treatment strategies alongside reperfusion therapy. Previous experimental studies demonstrated the potential of glucagon-like peptide-1 (GLP-1) to reduce acute ischaemic damage in the brain. Here, we examined the neuroprotective effects of two GLP-1 analogues, liraglutide and semaglutide.MethodsA non-diabetic rat model of acute ischaemic stroke involved 90, 120 or 180 min of middle cerebral artery occlusion (MCAO). Liraglutide or semaglutide was administered either i.v. at the onset of reperfusion or s.c. 5 min before the onset of reperfusion. Infarct size and functional status were evaluated after 24 h or 72 h of reperfusion.ResultsLiraglutide, administered as a bolus at the onset of reperfusion, reduced infarct size by up to 90% and improved neuroscore at 24 h in a dose-dependent manner, following 90-min, but not 120-min or 180-min ischaemia. Semaglutide and liraglutide administered s.c. reduced infarct size by 63% and 48%, respectively, and improved neuroscore at 72 h following 90-min MCAO. Neuroprotection by semaglutide was abolished by GLP1-R antagonist exendin(9-39).ConclusionInfarct-limiting and functional neuroprotective effects of liraglutide are dose-dependent. Neuroprotection by semaglutide is at least as strong as by liraglutide and is mediated by GLP-1Rs.

Remote ischaemic conditioning (RIC) is a promising method of cardioprotection, with numerous clinical studies having demonstrated its ability to reduce myocardial infarct size and improve prognosis. On the other hand, there are several clinical trials, in particular those conducted in the setting of elective cardiac surgery, that have failed to show any benefit of RIC. These contradictory data indicate that there is insufficient understanding of the mechanisms underlying RIC. RIC is now known to signal indiscriminately, protecting not only the heart, but also other organs. In particular, experimental studies have demonstrated that it is able to reduce infarct size in an acute ischaemic stroke model. However, the mechanisms underlying RIC-induced neuroprotection are even less well understood than for cardioprotection. The existence of bidirectional feedback interactions between the heart and the brain suggests that the mechanisms of RIC-induced neuroprotection and cardioprotection should be studied as a whole. This review, therefore, addresses the topic of the neural component of the RIC mechanism.

Due to its poor capacity for regeneration, the heart is particularly sensitive to the loss of contractile cardiomyocytes. The onslaught of damage caused by ischaemia and reperfusion, occurring during an acute myocardial infarction and the subsequent reperfusion therapy, can wipe out upwards of a billion cardiomyocytes. A similar program of cell death can cause the irreversible loss of neurons in ischaemic stroke. Similar pathways of lethal cell injury can contribute to other pathologies such as left ventricular dysfunction and heart failure caused by cancer therapy. Consequently, strategies designed to protect the heart from lethal cell injury have the potential to be applicable across all three pathologies. The investigators meeting at the 10th Hatter Cardiovascular Institute workshop examined the parallels between ST-segment elevation myocardial infarction (STEMI), ischaemic stroke, and other pathologies that cause the loss of cardiomyocytes including cancer therapeutic cardiotoxicity. They examined the prospects for protection by remote ischaemic conditioning (RIC) in each scenario, and evaluated impasses and novel opportunities for cellular protection, with the future landscape for RIC in the clinical setting to be determined by the outcome of the large ERIC-PPCI/CONDI2 study. It was agreed that the way forward must include measures to improve experimental methodologies, such that they better reflect the clinical scenario and to judiciously select combinations of therapies targeting specific pathways of cellular death and injury.

Stroke remains one of the most common causes of death and disability worldwide. Several preclinical studies demonstrated that the brain can be effectively protected against ischaemic stroke by two seemingly distinct treatments: remote ischaemic conditioning (RIC), involving cycles of ischaemia/reperfusion applied to a peripheral organ or tissue, or by systemic administration of glucagon-like-peptide-1 (GLP-1) receptor (GLP-1R) agonists. The mechanisms underlying RIC- and GLP-1-induced neuroprotection are not completely understood. In this study, we tested the hypothesis that GLP-1 mediates neuroprotection induced by RIC and investigated the effect of GLP-1R activation on cerebral blood vessels, as a potential mechanism of GLP-1-induced protection against ischaemic stroke. A rat model of ischaemic stroke (90 min of middle cerebral artery occlusion followed by 24-h reperfusion) was used. RIC was induced by 4 cycles of 5 min left hind limb ischaemia interleaved with 5-min reperfusion periods. RIC markedly (by ~ 80%) reduced the cerebral infarct size and improved the neurological score. The neuroprotection established by RIC was abolished by systemic blockade of GLP-1R with a specific antagonist Exendin(9–39). In the cerebral cortex of GLP-1R reporter mice, ~ 70% of cortical arterioles displayed GLP-1R expression. In acute brain slices of the rat cerebral cortex, activation of GLP-1R with an agonist Exendin-4 had a strong dilatory effect on cortical arterioles and effectively reversed arteriolar constrictions induced by metabolite lactate or oxygen and glucose deprivation, as an ex vivo model of ischaemic stroke. In anaesthetised rats, Exendin-4 induced lasting increases in brain tissue PO2, indicative of increased cerebral blood flow. These results demonstrate that neuroprotection against ischaemic stroke established by remote ischaemic conditioning is mediated by a mechanism involving GLP-1R signalling. Potent dilatory effect of GLP-1R activation on cortical arterioles suggests that the neuroprotection in this model is mediated via modulation of cerebral blood flow and improved brain perfusion.

[...]despite a successful recanalization being achieved in more than 70% of patients treated with mechanical thrombectomy +/– intravenous tissue recombinant plasminogen activator, functional independence (modified Rankin score 0–2 at 3 months after ischemic stroke) is obtained only in ~45% of cases. No reflow can occur within 5–10 minutes of ischemia in the brain, and may, therefore, contribute to neuronal death, whereas in the heart it only occurs after 30+ minutes and its contribution to cell death is less clear. [...]the time window for neuroprotection at reperfusion is presumably wider than that for cardioprotection. GLP-1 is known to be a growth factor with its classical inherent effects, i.e. activation of the expression of genes responsible for cell growth, repair and replacement, increase of cell metabolism, and inhibition of apoptosis and inflammatory responses (Hölscher, 2014). Regarding the rationale of using the same pharmacological approach based on GLP-1 analogues for neuroprotection as for cardioprotection, there are important data from in vitro studies, which indicate that the GLP-1R agonists possess a neurotrophic property, reduce oxidative stress, and protect cortical neurons from hypoxia-triggered cell death (Salcedo et al., 2012).

Reperfusion is the only existing strategy for patients with acute ischemic stroke, however it causes further brain damage itself. A feasible therapy targeting reperfusion injury is remote ischemic conditioning (RIC). This was a two-centre, randomized, blinded international study, using translational imaging endpoints, aimed to examine the neuroprotective effects of RIC in ischemic stroke model. 80 male rats underwent 90-min middle cerebral artery occlusion. RIC consisted of 4 × 5 min cycles of left hind limb ischemia. The primary endpoint was infarct size measured on T2-weighted MRI at 24 h, expressed as percentage of the area-at-risk. Secondary endpoints were: hemispheric space-modifying edema, infarct growth between per-occlusion and 24 h MRI, neurofunctional outcome measured by neuroscores. 47 rats were included in the analysis after applying pre-defined inclusion criteria. RIC significantly reduced infarct size (median, interquartile range: 19% [8%; 32%] vs control: 40% [17%; 59%], p = 0.028). This effect was still significant after adjustment for apparent diffusion coefficient lesion size in multivariate analysis. RIC also improved neuroscores (6 [3; 8] vs control: 9 [7; 11], p = 0.032). Other secondary endpoints were not statistically different between groups. We conclude that RIC in the setting of acute ischemic stroke in rats is safe, reduces infarct size and improves functional recovery.