Effect of esaxerenone on ischaemia and reperfusion injury in rat hearts

OBJECTIVES

In myocardial infarction, the addition of mineralocorticoid receptor blockers to standard therapies, such as angiotensin-converting enzyme inhibitors or beta-blockers, reportedly reduces mortality and cardiac events. We investigated whether the non-steroidal mineralocorticoid receptor blocker esaxerenone has cardioprotective effects and its protective mechanisms.

METHODS

Isolated rat hearts were Langendorff-perfused (constant pressure, 80 mmHg) with oxygenated Krebs-Henseleit bicarbonate buffer and reperfused for 60 min; afterwards, recovery of function (left ventricular pressure, measured with an intraventricular balloon) and myocardial injury were measured. In a preliminary study, we determined the optimal concentration of esaxerenone required for myocardial protection. Next, esaxerenone was administered in the pre- and post-ischaemic phases to determine the optimal timing of administration. In addition, we assessed coronary flow response to acetylcholine with and without esaxerenone. We examined whether esaxerenone-induced cardioprotection was prevented by targeting putative components in the preconditioning manner (the mitochondrial ATP-sensitive potassium [KATP] channel).

RESULTS

Myocardial protection by esaxerenone was observed when esaxerenone was administered before ischaemia but not after ischaemia. The coronary flow response to acetylcholine was significantly better in the esaxerenone group than in the control group. The cardioprotective effect of esaxerenone was eliminated by the mitochondrial KATP channel blocker, 5-hydroxy decanoate.

CONCLUSIONS

This study confirmed the myocardial protective effect of the pre-ischaemic administration of esaxerenone. Esaxerenone may contribute to coronary endothelial protection and exert pharmacological preconditioning via the mitochondrial KATP channel.

The RISK pathway leading to mitochondria and cardioprotection: how everything started

Ischaemic heart disease, which often manifests clinically as myocardial infarction (MI), remains a major cause of mortality worldwide. Despite the development of effective pre-clinical cardioprotective therapies, clinical translation has been disappointing. Nevertheless, the 'reperfusion injury salvage kinase' (RISK) pathway appears to be a promising target for cardioprotection. This pathway is crucial for the induction of cardioprotection by numerous pharmacological and non-pharmacological interventions, such as ischaemic conditioning. An important component of the cardioprotective effects of the RISK pathway involves the prevention of mitochondrial permeability transition pore (MPTP) opening and subsequent cardiac cell death. Here, we will review the historical perspective of the RISK pathway and focus on its interaction with mitochondria in the setting of cardioprotection.

New Drug Targets and Preclinical Modelling Recommendations for Treating Acute Myocardial Infarction

Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality worldwide and the primary underlying risk factor for heart failure. Despite decades of research and clinical trials, there are no drugs currently available to prevent organ damage from acute ischaemic injuries of the heart. In order to address the increasing global burden of heart failure, drug, gene, and cell-based regeneration technologies are advancing into clinical testing. In this review we highlight the burden of disease associated with AMI and the therapeutic landscape based on market analyses. New studies revealing the role of acid-sensitive cardiac ion channels and other proton-gated ion channels in cardiac ischaemia are providing renewed interest in pre- and post-conditioning agents with novel mechanisms of action that may also have implications for gene- and cell-based therapeutics. Furthermore, we present guidelines that couple new cell technologies and data resources with traditional animal modelling pipelines to help de-risk drug candidates aimed at treating AMI. We propose that improved preclinical pipelines and increased investment in drug target identification for AMI is critical to stem the increasing global health burden of heart failure.

The effects of ischaemic conditioning on lung ischaemia-reperfusion injury

Ischaemia-reperfusion injury (IRI) encompasses the deleterious effects on cellular function and survival that result from the restoration of organ perfusion. Despite their unique tolerance to ischaemia and hypoxia, afforded by their dual (pulmonary and bronchial) circulation as well as direct oxygen diffusion from the airways, lungs are particularly susceptible to IRI (LIRI). LIRI may be observed in a variety of clinical settings, including lung transplantation, lung resections, cardiopulmonary bypass during cardiac surgery, aortic cross-clamping for abdominal aortic aneurysm repair, as well as tourniquet application for orthopaedic operations. It is a diagnosis of exclusion, manifesting clinically as acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Ischaemic conditioning (IC) signifies the original paradigm of treating IRI. It entails the application of short, non-lethal ischemia and reperfusion manoeuvres to an organ, tissue, or arterial territory, which activates mechanisms that reduce IRI. Interestingly, there is accumulating experimental and preliminary clinical evidence that IC may ameliorate LIRI in various pathophysiological contexts. Considering the detrimental effects of LIRI, ranging from ALI following lung resections to primary graft dysfunction (PGD) after lung transplantation, the association of these entities with adverse outcomes, as well as the paucity of protective or therapeutic interventions, IC holds promise as a safe and effective strategy to protect the lung. This article aims to provide a narrative review of the existing experimental and clinical evidence regarding the effects of IC on LIRI and prompt further investigation to refine its clinical application.

A state-of-the-art review of the current role of cardioprotective techniques in cardiac transplantation

OBJECTIVES

The use of 'extended criteria' donor hearts and reconditioned hearts from donation after circulatory death has corresponded with an increase in primary graft dysfunction, with ischaemia-reperfusion injury being a major contributing factor in its pathogenesis. Limiting ischaemia-reperfusion injury through optimising donor heart preservation may significantly improve outcomes. We sought to review the literature to evaluate the evidence for this.

METHODS

A review of the published literature was performed to assess the potential impact of organ preservation optimisation on cardiac transplantation outcomes.

RESULTS

Ischaemia-reperfusion injury is a major factor in myocardial injury during transplantation with multiple potential therapeutic targets. Innate survival pathways have been identified, which can be mimicked with pharmacological conditioning. Although incompletely understood, discoveries in this domain have yielded extremely encouraging results with one of the most exciting prospects being the synergistic effect of selected agents. Ex situ heart perfusion is an additional promising adjunct.

CONCLUSIONS

Cardiac transplantation presents a unique opportunity to perfuse the whole heart before, or immediately after, the onset of ischaemia, thus maximising the potential for global cardioprotection while limiting possible systemic side effects. While clinical translation in the setting of myocardial infarction has often been disappointing, cardiac transplantation may afford the opportunity for cardioprotection to finally deliver on its preclinical promise.

Sodium-glucose cotransporter 2 inhibitors reduce myocardial infarct size in preclinical animal models of myocardial ischaemia-reperfusion injury: a meta-analysis

AIMS/HYPOTHESIS

Large cardiovascular outcome trials demonstrated that the cardioprotective effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors might reach beyond glucose-lowering action. In this meta-analysis, we sought to evaluate the potential infarct size-modulating effect of SGLT2 inhibitors in preclinical studies.

METHODS

In this preregistered meta-analysis (PROSPERO: CRD42020189124), we included placebo-controlled, interventional studies of small and large animal models of myocardial ischaemia-reperfusion injury, testing the effect of SGLT2 inhibitor treatment on myocardial infarct size (percentage of area at risk or total area). Standardised mean differences (SMDs) were calculated and pooled using random-effects method. We evaluated heterogeneity by computing Τ² and I² values. Meta-regression was performed to explore prespecified subgroup differences according to experimental protocols and their contribution to heterogeneity was assessed (pseudo-R² values).

RESULTS

We identified ten eligible publications, reporting 16 independent controlled comparisons on a total of 224 animals. Treatment with SGLT2 inhibitor significantly reduced myocardial infarct size compared with placebo (SMD = -1.30 [95% CI -1.79, -0.81], p < 0.00001), referring to a 33% [95% CI 20%, 47%] difference. Heterogeneity was moderate (Τ² = 0.58, I² = 60%). SGLT2 inhibitors were only effective when administered to the intact organ system, but not to isolated hearts (p interaction <0.001, adjusted pseudo-R² = 47%). While acute administration significantly reduced infarct size, chronic treatment was superior (p interaction <0.001, adjusted pseudo-R² = 85%). The medications significantly reduced infarct size in both diabetic and non-diabetic animals, favouring the former (p interaction = 0.030, adjusted pseudo-R² = 12%). Treatment was equally effective in rats and mice, as well as in a porcine model. Individual study quality scores were not related to effect estimates (p = 0.33). The overall effect estimate remained large even after adjusting for severe forms of publication bias.

CONCLUSIONS/INTERPRETATION

The glucose-lowering SGLT2 inhibitors reduce myocardial infarct size in animal models independent of diabetes. Future in vivo studies should focus on clinical translation by exploring whether SGLT2 inhibitors limit infarct size in animals with relevant comorbidities, on top of loading doses of antiplatelet agents. Mechanistic studies should elucidate the potential relationship between the infarct size-lowering effect of SGLT2 inhibitors and the intact organ system.

Novel device-based therapies to improve outcome in ST-segment elevation myocardial infarction

Primary percutaneous coronary intervention (PPCI) has dramatically changed the outcome of patients with ST-elevation myocardial infarction (STEMI). However, despite improvements in interventional technology, registry data show little recent change in the prognosis of patients who survive STEMI, with a significant incidence of cardiogenic shock, heart failure, and cardiac death. Despite a technically successful PPCI procedure, a variable proportion of patients experience suboptimal myocardial reperfusion. Large infarct size and coronary microvascular injury, as the consequence of ischaemia-reperfusion injury and distal embolization of atherothrombotic debris, account for suboptimal long-term prognosis of STEMI patients. In order to address this unmet therapeutic need, a broad-range of device-based treatments has been developed. These device-based therapies can be categorized according to the pathophysiological pathways they target: (i) techniques to prevent distal atherothrombotic embolization, (ii) techniques to prevent or mitigate ischaemia/reperfusion injury, and (iii) techniques to enhance coronary microvascular function/integrity. This review is an overview of these novel technologies with a focus on their pathophysiological background, procedural details, available evidence, and with a critical perspective about their potential future implementation in the clinical care of STEMI patients.

Cardioprotection with esmolol-based cardioplegia for non-infarcted and infarcted rat hearts

OBJECTIVES

Esmolol-based cardioplegic arrest offers better cardioprotection than crystalloid cardioplegia but has been compared experimentally with blood cardioplegia only once. We investigated the influence of esmolol crystalloid cardioplegia (ECCP), esmolol blood cardioplegia (EBCP) and Calafiore blood cardioplegia (Cala) on cardiac function, metabolism and infarct size in non-infarcted and infarcted isolated rat hearts.

METHODS

Two studies were performed: (i) the hearts were subjected to a 90-min cardioplegic arrest with ECCP, EBCP or Cala and (ii) a regional myocardial infarction was created 30 min before a 90-min cardioplegic arrest. Left ventricular peak developed pressure (LVpdP), velocity of contractility (dLVP/dtmax), velocity of relaxation over time (dLVP/dtmin), heart rate and coronary flow were recorded. In addition, the metabolic parameters were analysed. The infarct size was determined by planimetry, and the myocardial damage was determined by electron microscopy.

RESULTS

In non-infarcted hearts, cardiac function was better preserved with ECCP than with EBCP or Cala relative to baseline values (LVpdP: 100 ± 28% vs 86 ± 11% vs 57 ± 7%; P = 0.002). Infarcted hearts showed similar haemodynamic recovery for ECCP, EBCP and Cala (LVpdP: 85 ± 46% vs 89 ± 55% vs 56 ± 26%; P = 0.30). The lactate production with EBCP was lower than with ECCP (0.6 ± 0.7 vs 1.4 ± 0.5 μmol/min; P = 0.017). The myocardial infarct size and (ECCP vs EBCP vs Cala: 16 ± 7% vs 15 ± 9% vs 24 ± 13%; P = 0.21) the ultrastructural preservation was similar in all groups.

CONCLUSIONS

In non-infarcted rat hearts, esmolol-based cardioplegia, particularly ECCP, offers better myocardial protection than Calafiore. After an acute myocardial infarction, cardioprotection with esmolol-based cardioplegia is similar to that with Calafiore.

Myocardial MMP-2 contributes to SERCA2a proteolysis during cardiac ischaemia-reperfusion injury

AIMS

Matrix metalloproteinase-2 (MMP-2) is a zinc-dependent protease which contributes to cardiac contractile dysfunction when activated during myocardial ischaemia-reperfusion (IR) injury. MMP-2 is localized to several subcellular sites inside cardiac myocytes; however, its role in the sarcoplasmic reticulum (SR) is unknown. The Ca2+ ATPase SERCA2a, which pumps cytosolic Ca2+ into the SR to facilitate muscle relaxation, is degraded in cardiac IR injury; however, the protease responsible for this is unclear. We hypothesized that MMP-2 contributes to cardiac contractile dysfunction by proteolyzing SERCA2a, thereby impairing its activity in IR injury.

METHODS AND RESULTS

Isolated rat hearts were subjected to IR injury in the presence or absence of the selective MMP inhibitor ARP-100, or perfused aerobically as a control. Inhibition of MMP activity with ARP-100 significantly improved the recovery of cardiac mechanical function and prevented the increase of a 70 kDa SERCA2a degradation fragment following IR injury, although 110 kDa SERCA2a and phospholamban levels appeared unchanged. Electrophoresis of IR heart samples followed by LC-MS/MS confirmed the presence of a SERCA2a fragment of ∼70 kDa. MMP-2 activity co-purified with SR-enriched microsomes prepared from the isolated rat hearts. Endogenous SERCA2a in SR-enriched microsomes was proteolyzed to ∼70 kDa products when incubated in vitro with exogenous MMP-2. MMP-2 also cleaved purified porcine SERCA2a in vitro. SERCA activity in SR-enriched microsomes was decreased by IR injury; however, this was not prevented with ARP-100.

CONCLUSION

This study shows that MMP-2 activity is found in SR-enriched microsomes from heart muscle and that SERCA2a is proteolyzed by MMP-2. The cardioprotective actions of MMP inhibition in myocardial IR injury may include the prevention of SERCA2a degradation.

Imaging the injured beating heart intravitally and the vasculoprotection afforded by haematopoietic stem cells

Aims

Adequate microcirculatory perfusion, and not just opening of occluded arteries, is critical to salvage heart tissue following myocardial infarction. However, the degree of microvascular perfusion taking place is not known, limited primarily by an inability to directly image coronary microcirculation in a beating heart in vivo. Haematopoietic stem/progenitor cells (HSPCs) offer a potential therapy but little is known about their homing dynamics at a cellular level and whether they protect coronary microvessels. This study used intravital microscopy to image the anaesthetized mouse beating heart microcirculation following stabilization.

Methods and results

A 3D-printed stabilizer was attached to the ischaemia–reperfusion injured (IRI) beating heart. The kinetics of neutrophil, platelet and HSPC recruitment, as well as functional capillary density (FCD), was imaged post-reperfusion. Laser speckle contrast imaging (LSCI) was used for the first time to monitor ventricular blood flow in beating hearts. Sustained hyperaemic responses were measured throughout reperfusion, initially indicating adequate flow resumption. Intravital microscopy confirmed large vessel perfusion but demonstrated poor transmission of flow to downstream coronary microvessels. Significant neutrophil adhesion and microthrombus formation occurred within capillaries with the latter occluding them, resulting in patchy perfusion and reduced FCD. Interestingly, ‘patrolling’ neutrophils were also observed in capillaries. Haematopoietic stem/progenitor cells readily trafficked through the heart but local retention was poor. Despite this, remarkable anti-thromboinflammatory effects were observed, consequently improving microvascular perfusion.

Conclusion

We present a novel approach for imaging multiple microcirculatory perturbations in the beating heart with LSCI assessment of blood flow. Despite deceptive hyperaemic responses, increased microcirculatory flow heterogeneity was seen, with non-perfused areas interspersed with perfused areas. Microthrombi, rather than neutrophils, appeared to be the major causative factor. We further applied this technique to demonstrate local stem cell presence is not a pre-requisite to confer vasculoprotection. This is the first detailed in vivo characterization of coronary microcirculatory responses post-reperfusion injury.

Small extracellular vesicles secreted from human amniotic fluid mesenchymal stromal cells possess cardioprotective and promigratory potential

Mesenchymal stromal cells (MSCs) exhibit antiapoptotic and proangiogenic functions in models of myocardial infarction which may be mediated by secreted small extracellular vesicles (sEVs). However, MSCs have frequently been harvested from aged or diseased patients, while the isolated sEVs often contain high levels of impurities. Here, we studied the cardioprotective and proangiogenic activities of size-exclusion chromatography-purified sEVs secreted from human foetal amniotic fluid stem cells (SS-hAFSCs), possessing superior functional potential to that of adult MSCs. We demonstrated for the first time that highly pure (up to 1.7 × 1010 particles/µg protein) and thoroughly characterised SS-hAFSC sEVs protect rat hearts from ischaemia-reperfusion injury in vivo when administered intravenously prior to reperfusion (38 ± 9% infarct size reduction, p < 0.05). SS-hAFSC sEVs did not protect isolated primary cardiomyocytes in models of simulated ischaemia-reperfusion injury in vitro, indicative of indirect cardioprotective effects. SS-hAFSC sEVs were not proangiogenic in vitro, although they markedly stimulated endothelial cell migration. Additionally, sEVs were entirely responsible for the promigratory effects of the medium conditioned by SS-hAFSC. Mechanistically, sEV-induced chemotaxis involved phosphatidylinositol 3-kinase (PI3K) signalling, as its pharmacological inhibition in treated endothelial cells reduced migration by 54 ± 7% (p < 0.001). Together, these data indicate that SS-hAFSC sEVs have multifactorial beneficial effects in a myocardial infarction setting.

Glycogen synthase kinase 3β promotes liver innate immune activation by restraining AMP-activated protein kinase activation

BACKGROUND & AIMS

Glycogen synthase kinase 3β (Gsk3β [Gsk3b]) is a ubiquitously expressed kinase with distinctive functions in different types of cells. Although its roles in regulating innate immune activation and ischaemia and reperfusion injuries (IRIs) have been well documented, the underlying mechanisms remain ambiguous, in part because of the lack of cell-specific tools in vivo.

METHODS

We created a myeloid-specific Gsk3b knockout (KO) strain to study the function of Gsk3β in macrophages in a murine liver partial warm ischaemia model.

RESULTS

Compared with controls, myeloid Gsk3b KO mice were protected from IRI, with diminished proinflammatory but enhanced anti-inflammatory immune responses in livers. In bone marrow-derived macrophages, Gsk3β deficiency resulted in an early reduction of Tnf gene transcription but sustained increase of Il10 gene transcription on Toll-like receptor 4 stimulation in vitro. These effects were associated with enhanced AMP-activated protein kinase (AMPK) activation, which led to an accelerated and higher level of induction of the novel innate immune negative regulator small heterodimer partner (SHP [Nr0b2]). The regulatory function of Gsk3β on AMPK activation and SHP induction was confirmed in wild-type bone marrow-derived macrophages with a Gsk3 inhibitor. Furthermore, we found that this immune regulatory mechanism was independent of Gsk3β Ser9 phosphorylation and the phosphoinositide 3-kinase-Akt signalling pathway. In vivo, myeloid Gsk3β deficiency facilitated SHP upregulation by ischaemia-reperfusion in liver macrophages. Treatment of Gsk3b KO mice with either AMPK inhibitor or SHP small interfering RNA before the onset of liver ischaemia restored liver proinflammatory immune activation and IRI in these otherwise protected hosts. Additionally, pharmacological activation of AMPK protected wild-type mice from liver IRI, with reduced proinflammatory immune activation. Inhibition of the AMPK-SHP pathway by liver ischaemia was demonstrated in tumour resection patients.

CONCLUSIONS

Gsk3β promotes innate proinflammatory immune activation by restraining AMPK activation.

LAY SUMMARY

Glycogen synthase kinase 3β promotes macrophage inflammatory activation by inhibiting the immune regulatory signalling of AMP-activated protein kinase and the induction of small heterodimer partner. Therefore, therapeutic targeting of glycogen synthase kinase 3β enhances innate immune regulation and protects liver from ischaemia and reperfusion injury.

Pathogenetic role of endothelial nitric oxide synthase uncoupling during lung ischaemia-reperfusion injury

OBJECTIVES

Ischaemia-reperfusion injury is a necessary part of organ transplantation and a key determinant of both acute and chronic graft failure. We have assessed the contribution of endothelial nitric oxide synthase (eNOS) and eNOS uncoupling to oxidative and nitrosative stress formation during lung ischaemia-reperfusion injury dependent on ischaemia time.

METHODS

Forty eNOS wild-type mice (eNOS +/+ ) and 40 eNOS knock-out mice (eNOS -/- ) received either a sham thoracotomy or 60 or 90 min of ischaemia, followed by 0, 1 or 24 h of reperfusion. Lung tissue was analysed with electron spin resonance for NO production and reactive oxygen species content. Protein nitrosation, eNOS and eNOS uncoupling were determined using western blotting. In peripheral blood, arterial blood gases were taken and reactive oxygen species content was determined.

RESULTS

eNOS +/+ mice had lower reactive oxygen species production in their peripheral circulation but worse blood gas values after 1 h of reperfusion. Lung tissue of eNOS -/- mice showed lower reactive oxygen species and NO production and lower protein nitrosation compared with wild-type mice. Longer ischaemia times result in more elaborate oxidative and nitrosative stress dependent on eNOS genotype. Structural eNOS uncoupling was present after 60 min of ischaemia but diminished after 90 min of ischaemia.

CONCLUSIONS

eNOS uncoupling may contribute to lung ischaemia-reperfusion injury and inflammation. This ultimately leads to worse clinical outcome. Stabilizing eNOS may therefore be a new approach to extend pulmonary graft survival.

Lung Ischaemia-Reperfusion Injury: The Role of Reactive Oxygen Species

Lung ischaemia-reperfusion injury (LIRI) occurs in many lung diseases and during surgical procedures such as lung transplantation. The re-establishment of blood flow and oxygen delivery into the previously ischaemic lung exacerbates the ischaemic injury and leads to increased microvascular permeability and pulmonary vascular resistance as well as to vigorous activation of the immune response. These events initiate the irreversible damage of the lung with subsequent oedema formation that can result in systemic hypoxaemia and multi-organ failure. Alterations in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been suggested as crucial mediators of such responses during ischaemia-reperfusion in the lung. Among numerous potential sources of ROS/RNS within cells, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, nitric oxide synthases and mitochondria have been investigated during LIRI. Against this background, we aim to review here the extensive literature about the ROS-mediated cellular signalling during LIRI, as well as the effectiveness of antioxidants as treatment option for LIRI.

Chemokine Involvement in Lung Injury Secondary to Ischaemia/Reperfusion

INTRODUCTION

During transplant surgeries, the lung experiences an ischaemia-reperfusion (I/R)-induced damage identified as a significant cause of morbidity and mortality. However, the mechanisms by which I/R induces leucocyte accumulation and subsequent tissue damage in lung surgeries remain unknown. Therefore, the present study aims to assess the role of monocyte chemotactic protein 1 (MCP-1) and macrophage inflammatory protein 2 (MIP-2) in leucocyte chemotaxis related to lung injury secondary to I/R.

METHODS

Six pigs were subjected to an orthotopic left caudal lobe lung transplantation with a subsequent 60-min graft reperfusion (Transplant group). In addition, six animals underwent to sham surgery (Sham Group). Plasma samples and lung biopsies were collected before the beginning of pneumonectomy, before starting the reperfusion, and 30 min and 60 min after the beginning of the reperfusion. Plasma levels of intercellular adhesion molecule 1 (ICAM-1) and lung expressions of MCP-1, MIP-2, myeloperoxidase (MPO), and lung oedema were measured.

RESULTS

Lung I/R caused substantial damage observed as pulmonary oedema. The oedema was evident after the ischemic insult and increased after reperfusion. After reperfusion, increased levels of MPO were observed which suggests an activation and infiltration of neutrophils into the lung tissue. After 30 min of reperfusion, MCP-1, MIP-2, and ICAM-1 levels were significantly increased compared to prepneumonectomy levels (p < 0.05) and a further increase was observed after 60 min of reperfusion (p < 0.05).

CONCLUSION

The present study demonstrates that activated neutrophils, as well as MCP-1, MIP-2, and ICAM-1, are involved in inflammatory response induced by ischaemia-reperfusion-induced lung injury.

Lack of MG53 in human heart precludes utility as a biomarker of myocardial injury or endogenous cardioprotective factor

AIMS

Mitsugumin-53 (MG53/TRIM72) is an E3-ubiquitin ligase that rapidly accumulates at sites of membrane injury and plays an important role in membrane repair of skeletal and cardiac muscle. MG53 has been implicated in cardiac ischaemia-reperfusion injury, and serum MG53 provides a biomarker of skeletal muscle injury in the mdx mouse model of Duchenne muscular dystrophy. We evaluated the clinical utility of MG53 as a biomarker of myocardial injury.

METHODS AND RESULTS

We performed Langendorff ischaemia-reperfusion injury on wild-type and dysferlin-null murine hearts, using dysferlin deficiency to effectively model more severe outcomes from cardiac ischaemia-reperfusion injury. MG53 released into the coronary effluent correlated strongly and significantly (r = 0.79-0.85, P < 0.0001) with functional impairment after ischaemic injury. We initiated a clinical trial in paediatric patients undergoing corrective heart surgery, the first study of MG53 release with myocardial injury in humans. Unexpectedly, we reveal although MG53 is robustly expressed in rat and mouse hearts, MG53 is scant to absent in human, ovine, or porcine hearts. Absence of MG53 in 11 human heart specimens was confirmed using three separate antibodies to MG53, each subject to epitope mapping and confirmed immunospecificity using MG53-deficient muscle cells.

CONCLUSION

MG53 is an effective biomarker of myocardial injury and dysfunction in murine hearts. However, MG53 is not expressed in human heart and therefore does not hold utility as a clinical biomarker of myocardial injury. Although cardioprotective roles for endogenous myocardial MG53 cannot be extrapolated from rodents to humans, potential therapeutic application of recombinant MG53 for myocardial membrane injury prevails.

Sphingosine-1-phosphate reduces ischaemia-reperfusion injury by phosphorylating the gap junction protein Connexin43

AIM

Increasing evidence points to lipoprotein composition rather than reverse cholesterol transport in the cardioprotective properties of high-density lipoproteins (HDLs). HDL binding to receptors at the surface of cardiomyocytes activates signalling pathways promoting survival, but downstream targets are largely unknown. Here, we investigate the pathways by which the sphingosine-1-phosphate (S1P) constituent of HDL limits cell death induced by cardiac ischaemia-reperfusion (I/R).

METHODS AND RESULTS

Apolipoprotein M (ApoM) transgenic (Apom-Tg) mice, in which plasma S1P is increased by 296%, and wild-type (WT) mice were subjected to in vivo I/R. Infarct size, neutrophil infiltration into the infarcted area, and serum Troponin I were less pronounced in Apom-Tg mice. In vitro experiments suggest that this cardioprotection depends on direct effects of S1P on cardiomyocytes, whereas leucocyte recruitment seems only indirectly affected. Importantly, short-term S1P treatment at the onset of reperfusion was sufficient to reduce I/R injury in isolated perfused hearts. Mechanistic in vitro and ex vivo studies revealed that 5 min of S1P treatment induced phosphorylation of the gap junction protein Connexin43 (Cx43) on Serine368 (S368), which was mediated by S1P2 and S1P3, but not by S1P1, receptors in cardiomyocytes. Finally, S1P-induced reduction of infarct size after ex vivo I/R was lost in hearts of mice with a truncated C-terminus of Cx43 (Cx43(K258/KO)) or in which the S368 is mutated to a non-phosphorylatable alanine (Cx43(S368A/S368A)).

CONCLUSION

Our study reveals an important molecular pathway by which modulating the apoM/S1P axis has a therapeutic potential in the fight against I/R injury in the heart.

Targeting the delivery of systemically administered haematopoietic stem/progenitor cells to the inflamed colon using hydrogen peroxide and platelet microparticle pre-treatment strategies

Haematopoietic stem and progenitor cell (HSC) therapy may be promising for the treatment of inflammatory bowel disorders (IBDs). However, clinical success remains poor, partly explained by limited HSC recruitment following systemic delivery. The mechanisms governing HSC adhesion within inflamed colon, and whether this event can be enhanced, are not known. An immortalised HSC-like line (HPC7) was pre-treated with hydrogen peroxide (H2O2), activated platelet releasate enriched supernatant (PES) or platelet microparticles (PMPs). Subsequent adhesion was monitored using adhesion assays or in vivo ischaemia-reperfusion (IR) and colitis injured mouse colon intravitally. Integrin clustering was determined confocally and cell morphology using scanning electron microscopy. Both injuries resulted in increased HPC7 adhesion within colonic mucosal microcirculation. H2O2 and PES significantly enhanced adhesion in vitro and in the colitis, but not IR injured, colon. PMPs had no effect on adhesion. PES and PMPs induced clustering of integrins on the HPC7 surface, but did not alter their expression. Adhesion to the colon is modulated by injury but only in colitis injury can this recruitment be enhanced. The enhanced adhesion induced by PES is likely through integrin distribution changes on the HPC7 surface. Improving local HSC presence in injured colon may result in better therapeutic efficacy for treatment of IBD.

Distinct mPTP activation mechanisms in ischaemia-reperfusion: contributions of Ca2+, ROS, pH, and inorganic polyphosphate

AIMS

The mitochondrial permeability transition pore (mPTP) plays a central role for tissue damage and cell death during ischaemia-reperfusion (I/R). We investigated the contribution of mitochondrial inorganic polyphosphate (polyP), a potent activator of Ca(2+)-induced mPTP opening, towards mPTP activation and cardiac cell death in I/R.

METHODS AND RESULTS

A significant increase in mitochondrial free calcium concentration ([Ca(2+)]m), reactive oxygen species (ROS) generation, mitochondrial membrane potential depolarization (ΔΨm), and mPTP activity, but no cell death, was observed after 20 min of ischaemia. The [Ca(2+)]m increase during ischaemia was partially prevented by the mitochondrial Ca(2+) uniporter (MCU) inhibitor Ru360 and completely abolished by the combination of Ru360 and the ryanodine receptor type 1 blocker dantrolene, suggesting two complimentary Ca(2+) uptake mechanisms. In the absence of Ru360 and dantrolene, mPTP closing by polyP depletion or CSA decreased mitochondrial Ca(2+) uptake, suggesting that during ischaemia Ca(2+) can enter mitochondria through mPTP. During reperfusion, a burst of endogenous polyP production coincided with a decrease in [Ca(2+)]m, a decline in superoxide generation, and an acceleration of hydrogen peroxide (H2O2) production. An increase in H2O2 correlated with restoration of mitochondrial pHm and an increase in cell death. mPTP opening and cell death on reperfusion were prevented by antioxidants Trolox and MnTBAP [Mn (III) tetrakis (4-benzoic acid) porphyrin chloride]. Enzymatic polyP depletion did not affect mPTP opening during reperfusion, but increased ROS generation and cell death, suggesting that polyP plays a protective role in cellular stress response.

CONCLUSIONS

Transient Ca(2+)/polyP-mediated mPTP opening during ischaemia may serve to protect cells against cytosolic Ca(2+) overload, whereas ROS/pH-mediated sustained mPTP opening on reperfusion induces cell death.

Longitudinal quantification of radical bursts during pulmonary ischaemia and reperfusion

OBJECTIVES

Pulmonary ischaemia-reperfusion injury (IRI) is associated with several life-threatening pulmonary disorders, and may severely compromise the outcome of lung transplantation. Highly reactive molecules such as superoxide, nitric oxide (NO) and peroxynitrite (ONOO(-)) are presumed to contribute to IRI pathogenesis, but this assumption is based on indirect measurements. We use electron spin resonance (ESR) to directly quantify free radical formation after pulmonary ischaemia and reperfusion.

METHODS

Five groups of 10 Swiss mice were subjected to left pulmonary hilum clamping for 1 h of ischaemia followed by 0, 1, 4 and 24 h of reperfusion or to sham thoracotomy alone as control procedure. In five mice per group, ESR was used to measure iron-diethyldithio-carbamate trihydrate-trapped NO in the lung. In the other group of 5, reactive oxygen species generation in the lung and in blood was quantified with ESR by detection of ascorbyl radical and CMH spin probe, respectively. Pulmonary ONOO(-) was monitored with nitrotyrosine Western blotting.

RESULTS

After 1 h of reperfusion, a pulmonary NO peak (14.69 ± 0.91 × 10(4) Arbitrary Units (A.U.). vs 1.84 ± 0.75 × 10(4) A.U. in sham; P < 0.001) coincided with a significant increase in nitrosated proteins (0.105 ± 0.015 A.U.) compared with sham (0.047 ± 0.006 A.U.); P < 0.005). Peripheral blood showed a significant free radical burst after 1 h of ischaemia (11 774 ± 728 A.U. vs 6660 ± 833 A.U. in sham; P < 0.001).

CONCLUSIONS

Longitudinal quantification of free radicals during IRI reveals the occurrence of two major radical bursts. The radical peak in peripheral blood after ischaemia may be related to systemic hypoxia. After 1 h of reperfusion, the lung tissue shows a significant increase of superoxide, NO and their reaction products, which are probably involved in IRI pathogenesis.

Perillaldehyde attenuates cerebral ischemia-reperfusion injury-triggered overexpression of inflammatory cytokines via modulating Akt/JNK pathway in the rat brain cortex

Perillaldehyde (PAH), one of the major oil components in Perilla frutescens, has anti-inflammatory effects. Few studies have examined the neuroprotective effect of PAH on stroke. So the aim of our study is to investigate the effect of PAH on ischemia-reperfusion-induced injury in the rat brain cortex. Middle cerebral artery occlusion (MCAO) model was selected to make cerebral ischemia-reperfusion injury. Rats were assigned randomly to groups of sham, MCAO, and two treatment groups by PAH at 36.0, 72.0mg/kg. Disease model was set up after intragastrically (i.g.) administering for 7 consecutive days. The neurological deficit, the cerebral infarct size, biochemical parameters and the relative mRNA and protein levels were examined. The results showed that the NO level, the iNOS activity, the neurological deficit scores, the cerebral infarct size and the expression of inflammatory cytokines including interleukin (IL)-1β, interleukin (IL)-6 and tumor necrosis factor (TNF)-α were significantly decreased by PAH treatment. PAH also increased the Phospho-Akt level and decrease the Phospho-JNK level by Western blot analysis. Meanwhile, the PAH groups exhibited a dramatically decrease of apoptosis-related mRNA expression such as Bax and caspase-3. Our findings shown that PAH attenuates cerebral ischemia/reperfusion injury in the rat brain cortex, and suggest its neuroprotective effect is relate to regulating the inflammatory response through Akt /JNK pathway. The activation of this signalling pathway eventually inhibits apoptotic cell death induced by cerebral ischemia-reperfusion.

Nucleolin protects the heart from ischaemia-reperfusion injury by up-regulating heat shock protein 32

AIMS

Nucleolin plays important roles in a variety of cellular processes. In this study, we aimed to investigate the role of nucleolin in cardiac ischaemia-reperfusion (I-R) injury.

METHODS AND RESULTS

We investigated the expression pattern of nucleolin in hearts subjected to I-R, or neonatal rat cardiomyocytes subjected to hypoxia-re-oxygenation. We found that nucleolin expression was significantly down-regulated and the cleaved protein was present, both in vivo and in vitro. Gene transfection and RNA interference approaches were employed in cardiomyocytes to investigate the function of nucleolin. Over-expression of nucleolin was cytoprotective, whereas nucleolin ablation enhanced both hypoxia- and H₂O₂-induced cardiomyocyte death. Furthermore, transgenic mice with cardiac-specific over-expression of nucleolin were resistant to I-R injury as indicated by decreased cellular necrosis and decreased infarct size. The cardio-protective roles of nucleolin in cardiomyocytes, are attributable to the interaction of nucleolin with the mRNA of heat shock protein 32 (Hsp32), resulting in an increase of Hsp32 mRNA stability, and subsequent up-regulation of Hsp32 expression. The selective Hsp32 inhibitor, zinc protoporphyrin-IX, abrograted the cardiac protection mediated by nucleolin.

CONCLUSION

This study has demonstrated that nucleolin is involved in the regulation of I-R-induced cardiac injury and dysfunction via the regulation of Hsp32, and may be a novel therapeutic target for ischaemic heart diseases.

Protective effects of dexmedetomidine in pneumoperitoneum-related ischaemia-reperfusion injury in rat ovarian tissue

OBJECTIVES

To determine the effects of dexmedetomidine on pneuomoperitoneum-related ischaemia-reperfusion (I/R) injury in rat ovarian tissue.

STUDY DESIGN

Animals were randomized into three groups: Group S (n=8), no pneumoperitoneum; Group C (n=8), pneumoperitoneum; and Group D (n=8), 100μg intraperitoneal dexmedetomidine 30min before pneumoperitoneum. Ovarian tissue was collected from all rats 30min after desufflation, and fresh frozen for histological and biochemical evaluation.

RESULTS

Body weight was similar in all three groups (202.62±28.86, 211.00±14.45 and 212.87±15.71g in Groups S, D and C, respectively). The mean malondialdehyde level was higher in Group C than the other groups (p<0.03). When the histological samples of ovarian tissue were compared, vascular congestion, haemorrhage, follicular cell degeneration and infiltrative cell infiltration scores were higher in Group C compared with the other groups (p<0.05). Significantly lower scores for the histological parameters were found in Group D compared with Group C (p<0.05). Similar scores for follicular cell degeneration and inflammatory cell infiltration were found in Group D and Group S (p>0.05). Although vascular congestion and haemorrhage scores were significantly lower compared with Group C, higher scores were found for Group D compared with Group S (p<0.05).

CONCLUSION

Pneumoperitoneum caused oxidative injury in rat ovarian tissue. Dexmedetomidine reduced oxidative stress and histological injury related to I/R.