Hydrogen Protects Mitochondrial Function by Increasing the Expression of PGC-1α and Ameliorating Myocardial Ischaemia-Reperfusion Injury

To investigate the application of H2 to alleviate cardiac ischaemia-reperfusion (I/R) injury in a PGC-1α-dependent manner. A rat in vitro myocardial I/R injury model was used, Western blot was used to detect the expression levels of apoptosis markers (Bax, cleaved caspase-3, Bcl2), inflammatory factors (IL-1β, TNF-α), mitochondrial fission (DRP1, MFF) and mitochondrial fusion (MFN1, MFN2, OPA1). HE staining was used to observe the effect of H2 on the myocardial tissue structure injured by I/R. Transmission electron microscopy (TEM) was used to observe the changes in the mitochondrial structure of myocardial tissue after I/R injury. Real-time quantitative PCR (qPCR) was used to detect the expression of PGC-1α in the myocardial tissue of rats after I/R injury and H2 treatment. H2 increases the expression level of PGC-1α, while the deletion of PGC-1α inhibited the therapeutic effect of H2. H2 can improve the changes of the myocardial tissue and mitochondrial structure caused by I/R injury. H2 treatment effectively inhibited the inflammatory response, and the loss of PGC-1α could inhibit the therapeutic effect of H2. The application of H2 can alleviate myocardial I/R injury, and the loss of PGC-1α weakens the protective effect of H2 on the I/R heart.

Myocardial protection in cardiac surgery: a comprehensive review of current therapies and future cardioprotective strategies

Cardiac surgery with cardiopulmonary bypass results in global myocardial ischemia-reperfusion injury, leading to significant postoperative morbidity and mortality. Although cardioplegia is the cornerstone of intraoperative cardioprotection, a number of additional strategies have been identified. The concept of preconditioning and postconditioning, despite its limited direct clinical application, provided an essential contribution to the understanding of myocardial injury and organ protection. Therefore, physicians can use different tools to limit perioperative myocardial injury. These include the choice of anesthetic agents, remote ischemic preconditioning, tight glycemic control, optimization of respiratory parameters during the aortic unclamping phase to limit reperfusion injury, appropriate choice of monitoring to optimize hemodynamic parameters and limit perioperative use of catecholamines, and early reintroduction of cardioprotective agents in the postoperative period. Appropriate management before, during, and after cardiopulmonary bypass will help to decrease myocardial damage. This review aimed to highlight the current advancements in cardioprotection and their potential applications during cardiac surgery.

Postconditioning with Lactate-Enriched Blood for Reducing Lethal Reperfusion Injury in Humans

Ischemic myocardium cannot survive without reperfusion. However, reperfusion of the ischemic myocardium paradoxically induces myocyte death; this phenomenon is termed lethal reperfusion injury. To date, no effective approach has been demonstrated for ST-segment elevation myocardial infarction (STEMI) in clinical settings. Recently, we demonstrated a novel approach for cardioprotection, termed postconditioning with lactate-enriched blood (PCLeB). PCLeB comprises intermittent reperfusion and timely coronary injections of lactated Ringer's solution, which is implemented at the beginning of reperfusion. This approach is aimed at reducing lethal reperfusion injury via prolonging intracellular acidosis during the early period of reperfusion, compared with the original postconditioning protocol. Patients with STEMI treated using PCLeB have reported positive outcomes. This article represents an effort, with a perspective different from current insights, toward preventing lethal reperfusion injury, in light of the historical background of reperfusion injury research. PCLeB is considered the new approach for cardioprotection.

Metabolic Acidosis Results in Sexually Dimorphic Response in the Heart Tissue

Metabolic acidosis (MA) is a highly prevalent disorder in a significant proportion of the population, resulting from imbalance in blood pH homeostasis. The heart, being an organ with very low regenerative capacity and high metabolic activity, is vulnerable to chronic, although low-grade, MA. To systematically characterize the effect of low-grade MA on the heart, we treated male and female mice with NH4Cl supplementation for 2 weeks and analyzed their blood chemistry and transcriptomic signature of the heart tissue. The reduction of pH and plasma bicarbonate levels without an associated change in anion gap indicated a physiological manifestation of low-grade MA with minimal respiratory compensation. On transcriptomic analysis, we observed changes in cardiac-specific genes with significant gender-based differences due to MA. We found many genes contributing to dilated cardiomyopathy to be altered in males, more than in females, while cardiac contractility and Na/K/ATPase-Src signaling were affected in the opposite way. Our model presents a systems-level understanding of how the cardiovascular tissue is affected by MA. As low-grade MA is a common ailment with many dietary and pharmaceutical interventions, our work presents avenues to limit chronic cardiac damage and disease manifestation, as well as highlighting the sex differences in MA-induced cardiovascular damage.

Impairment of μ-calpain activation by rhTNFR:Fc reduces severe burn-induced membrane disruption in the heart

Stress cardiomyopathy is a major clinical complication after severe burn. Multiple upstream initiators have been identified; however, the downstream targets are not fully understood. This study assessed the role of the plasma membrane in this process and its relationship with the protease μ-calpain and tumor necrosis factor-alpha (TNF-α). Here, third-degree burn injury of approximately 40% of the total body surface area was established in rats. Plasma levels of LDH and cTnI and cardiac cell apoptosis increased at 0.5 h post burn, reached a peak at 6 h, and gradually declined at 24 h. This effect correlated well with not only the disruption of cytoskeletal proteins, including dystrophin and ankyrin-B, but also with the activation of μ-calpain, as indicated by the cleaved fragments of α-spectrin and membrane recruitment of the catalytic subunit CAPN1. More importantly, these alterations were diminished by blocking calpain activity with MDL28170. Burn injury markedly increased the cellular uptake of Evans blue, indicating membrane integrity disruption, and this effect was also reversed by MDL28170. Compared with those in the control group, cardiac cells in the burn plasma-treated group were more prone to damage, as indicated by a marked decrease in cell viability and increases in LDH release and apoptosis. Of note, these alterations were mitigated by CAPN1 siRNA. Moreover, after neutralizing TNF-α with rhTNFR:Fc, calpain activity was blocked, and heart function was improved. In conclusion, we identified μ-calpain as a trigger for severe burn-induced membrane disruption in the heart and provided evidence for the application of rhTNFR:Fc to inhibit calpain for cardioprotection.

pH-Responsive Charge-Conversion Progelator Peptides

A simple strategy for generating stimuli-responsive peptide-based hydrogels via charge-conversion of a self-assembling peptide (SAP) is described. These materials are formulated as soluble, polyanionic peptides, containing maleic acid, citraconic acid, or dimethylmaleic acid masking groups on each lysine residue, which do not form assemblies, but instead flow easily through high gauge needles and catheters. Acid-induced mask hydrolysis renews the zwitterionic nature of the peptides with concomitant and rapid self-assembly via β-sheet formation into rehealable hydrogels. The use of different masks enables one to tune pH responsiveness and assembly kinetics. In anticipation of their potential for in vivo hydrogel delivery and use, progelators exhibit hemocompatibility in whole human blood, and their peptide components are shown to be noncytotoxic. Finally, demonstration of stimuli-induced self-assembly for dye sequestration suggests a simple, non-covalent strategy for small molecule encapsulation in a degradable scaffold. In summary, this simple, scalable masking strategy allows for preparation of responsive, dynamic self-assembling biomaterials. This work sets the stage for implementing biodegradable therapeutic hydrogels that assemble in response to physiological, disease-relevant states of acidosis.

Reduced Plasma NT-proBNP Levels Months after Myocardial Infarction Postconditioned with Lactate-Enriched Blood

Background: We recently reported a new approach, namely postconditioning with lactate-enriched blood (PCLeB), for cardioprotection in patients with ST-segment elevation myocardial infarction (STEMI). Objectives: We examined the effects of PCLeB on plasma NT-proBNP levels months after myocardial infarction (MI). Methods: The study included consecutive patients (n = 31) undergoing percutaneous coronary intervention (PCI) for anterior STEMI within 12 h of symptom onset in our hospital between March 2014 and August 2018. We retrospectively compared plasma NT-proBNP levels several months after MI in these patients with those in historical control patients (n = 32). The control patients included consecutive patients who underwent successful PCI without PCLeB for anterior STEMI within 12 h of symptom onset in our hospital between March 2009 and February 2014. We compared the highest plasma NT-proBNP values 6–10 months after MI in the postconditioned patients with the lowest plasma NT-proBNP values 6–10 months after MI in the control patients. In the PCLeB protocol, the duration of each brief reperfusion was increased stepwise from 10 to 60 s. Lactated Ringer’s solution (30 mL) was injected directly in the culprit coronary artery at the end of each brief reperfusion. Each ischemic episode lasted 60 s. Results: Plasma NT-proBNP levels in the postconditioned patients months after MI (211 ± 207 pg/mL) were significantly lower than those in the control patients (516 ± 598 pg/mL; p < 0.0001). Conclusion: PCLeB was associated with reduced plasma NT-proBNP levels months after MI.

Postconditioning Protection Against Myocardiocyte Anoxia/Reoxygenation Injury From Penehyclidine Hydrochloride

BACKGROUND/AIMS

To investigate the postconditioning protective effect of penehyclidine hydrochloride (PHC) against anoxia/reoxygenation (A/R) injury in H9c2 cells along with the involved mechanism and timing effect.

METHODS

We divided H9c2 cells into 7 groups: control group, A/R group and PHC+A/R groups at 0 min, 5 mins, 10 mins, 20 mins, 30 mins, respectively (treated with 0.1 μm/L PHC at 0 min, 5 mins, 10 mins, 20 mins, 30 mins after the reoxygenation procedure began). Cell apoptosis, oxidative stress, intracellular Ca2+ concentration, mitochondrial membrane potential and mitochondrial permeability transition pore (MPTP) opening were explored. Bcl-2, Bax, Cyt C, caspase-3 and caspase-9 levels were measured.

RESULTS

A/R significantly increased both cell injury and cell apoptosis. PHC showed postconditioning protective effect by attenuating superoxide production, decreasing Ca2+ overload, restraining MPTP activities, restoring mitochondrial membrane potential, regulating cell apoptosis proteins and modulation of mitochondrial pathway. Earlier administration of PHC offered greater postconditioning protective effect.

CONCLUSION

H9c2 cells were protected by PHC from A/R injury regardless of timing of PHC administration (0 min, 5 mins, 10 mins, 20 mins, 30 mins). However, earlier administration of PHC resulted in better PHC postconditioning protection.

Degradation of GRK2 and AKT is an early and detrimental event in myocardial ischemia/reperfusion

BACKGROUND

Identification of signaling pathways altered at early stages after cardiac ischemia/reperfusion (I/R) is crucial to develop timely therapies aimed at reducing I/R injury. The expression of G protein-coupled receptor kinase 2 (GRK2), a key signaling hub, is up-regulated in the long-term in patients and in experimental models of heart failure. However, whether GRK2 levels change at early time points following myocardial I/R and its functional impact during this period remain to be established.

METHODS

We have investigated the temporal changes of GRK2 expression and their potential relationships with the cardioprotective AKT pathway in isolated rat hearts and porcine preclinical models of I/R.

FINDINGS

Contrary to the maladaptive up-regulation of GRK2 reported at later times after myocardial infarction, successive GRK2 phosphorylation at specific sites during ischemia and early reperfusion elicits GRK2 degradation by the proteasome and calpains, respectively, thus keeping GRK2 levels low during early I/R in rat hearts. Concurrently, I/R promotes decay of the prolyl-isomerase Pin1, a positive regulator of AKT stability, and a marked loss of total AKT protein, resulting in an overall decreased activity of this pro-survival pathway. A similar pattern of concomitant down-modulation of GRK2/AKT/Pin1 protein levels in early I/R was observed in pig hearts. Calpain and proteasome inhibition prevents GRK2/Pin1/AKT degradation, restores bulk AKT pathway activity and attenuates myocardial I/R injury in isolated rat hearts.

INTERPRETATION

Preventing transient degradation of GRK2 and AKT during early I/R might improve the potential of endogenous cardioprotection mechanisms and of conditioning strategies.

Multimodal cardioprotective strategy in cardiac surgery (the ProCCard trial): Study protocol for a multicenter randomized controlled trial

BACKGROUND

Myocardial damage in patients undergoing cardiac surgery increases both morbidity and mortality. Different protective strategies dealing with either preconditioning or postconditioning or assessing a single aspect of cardioprotection have shown conflicting results. We tested the hypothesis that a multimodal approach would improve cardioprotection and limit myocardial damage following cardiac surgery with cardiopulmonary bypass.

METHODS

This study is a pragmatic multicenter (six French institutions), prospective, randomized, single-blinded, controlled trial. The randomization is stratified by centers. In the study, 210 patients scheduled for aortic valve surgery with or without coronary artery bypass grafting will be assigned to a control or a treatment group (105 patients in each group). In the control group, patients receive total intravenous anesthesia with propofol and liberal intraoperative blood glucose management (initiation of insulin infusion when blood glucose, measured every 60 min, is greater than 180 mg/dl), as a standard of care. The treatment group receives a bundle of care combining five techniques of cardioprotection: (1) remote ischemic preconditioning applied before aortic cross-clamping; (2) maintenance of anesthesia with sevoflurane; (3) tight intraoperative blood glucose management (initiation of insulin infusion when blood glucose, measured every 30 min, is greater than 140 mg/dl); (4) moderate respiratory acidosis (pH 7.30) at the end of cardiopulmonary bypass; and (5) a gentle reperfusion protocol following aortic unclamping. The primary outcome is myocardial damage measured by postoperative 72-h area under the curve of high-sensitivity cardiac troponin I.

DISCUSSION

The ProCCard study will be the first multicenter randomized controlled trial aiming to assess the role of a bundle of care combining several cardioprotective strategies to reduce myocardial damage in patients undergoing cardiac surgery with cardiopulmonary bypass.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03230136 . Registered on July 26, 2017. Last updated on April 17, 2019.

Protection of Myocardial Ischemia-Reperfusion by Therapeutic Hypercapnia: a Mechanism Involving Improvements in Mitochondrial Biogenesis and Function

Previous studies proposed that acidic reperfusion may be a protective strategy for myocardial ischemia-reperfusion therapy with potential of clinical transformation. In this study, we investigated whether therapeutic hypercapnia could mimic acidosis postconditioning in isolated hearts with a 30-min left coronary artery ligation-reperfusion model in rats. Therapeutic hypercapnia (inhalation 20% CO₂ for 10 min) is cardioprotective with a strict therapeutic time window and acidity: it reduced the infarct ratio and serum myocardial enzyme and increased the myocardial ATP content. Furthermore, mitochondrial morphology damage, the loss of mitochondrial membrane potential, and the formation of mitochondrial permeability transition pore were effectively inhibited, indicating the improvements in mitochondrial function. The expression of the mitochondrial biogenesis regulators was upregulated simultaneously. These findings indicated therapeutic hypercapnia in animals can mimic ex vivo acidosis postconditioning to alleviate myocardial ischemia-reperfusion injury. The effect is related to improvement in mitochondrial function and regulation of the mitochondrial biogenesis pathway.

Metabolomics and Heart Diseases: From Basic to Clinical Approach

BACKGROUND

The field of metabolomics has been steadily increasing in size for the last 15 years. Advances in analytical and statistical methods have allowed metabolomics to flourish in various areas of medicine. Cardiovascular diseases are some of the main research targets in metabolomics, due to their social and medical relevance, and also to the important role metabolic alterations play in their pathogenesis and evolution. Metabolomics has been applied to the full spectrum of cardiovascular diseases: from patient risk stratification to myocardial infarction and heart failure. However - despite the many proof-ofconcept studies describing the applicability of metabolomics in the diagnosis, prognosis and treatment evaluation in cardiovascular diseases - it is not yet used in routine clinical practice. Recently, large phenome centers have been established in clinical environments, and it is expected that they will provide definitive proof of the applicability of metabolomics in clinical practice. But there is also room for small and medium size centers to work on uncommon pathologies or to resolve specific but relevant clinical questions.

OBJECTIVES

In this review, we will introduce metabolomics, cover the metabolomic work done so far in the area of cardiovascular diseases.

CONCLUSION

The cardiovascular field has been at the forefront of metabolomics application and it should lead the transfer to the clinic in the not so distant future.

Protective role of soluble adenylyl cyclase against reperfusion-induced injury of cardiac cells

AIMS

Disturbance of mitochondrial function significantly contributes to the myocardial injury that occurs during reperfusion. Increasing evidence suggests a role of intra-mitochondrial cyclic AMP (cAMP) signaling in promoting respiration and ATP synthesis. Mitochondrial levels of cAMP are controlled by type 10 soluble adenylyl cyclase (sAC) and phosphodiesterase 2 (PDE2), however their role in the reperfusion-induced injury remains unknown. Here we aimed to examine whether sAC may support cardiomyocyte survival during reperfusion.

METHODS AND RESULTS

Adult rat cardiomyocytes or rat cardiac H9C2 cells were subjected to metabolic inhibition and recovery as a model of simulated ischemia and reperfusion. Cytosolic Ca²⁺, pH, mitochondrial cAMP (live-cell imaging), and cell viability were analyzed during a 15-min period of reperfusion. Suppression of sAC activity in cardiomyocytes and H9C2 cells, either by sAC knockdown, by pharmacological inhibition or by withdrawal of bicarbonate, a natural sAC activator, compromised cell viability and recovery of cytosolic Ca²⁺ homeostasis during reperfusion. Contrariwise, overexpression of mitochondria-targeted sAC in H9C2 cells suppressed reperfusion-induced cell death. Analyzing cAMP concentration in mitochondrial matrix we found that inhibition of PDE2, a predominant mitochondria-localized PDE isoform in mammals, during reperfusion significantly increased cAMP level in mitochondrial matrix, but not in cytosol. Accordingly, PDE2 inhibition attenuated reperfusion-induced cardiomyocyte death and improved recovery of the cytosolic Ca²⁺ homeostasis.

CONCLUSION

sAC plays an essential role in supporting cardiomyocytes viability during reperfusion. Elevation of mitochondrial cAMP pool either by sAC overexpression or by PDE2 inhibition beneficially affects cardiomyocyte survival during reperfusion.

Neuroprotective effects of inhibitors of Acid-Sensing ion channels (ASICs) in optic nerve crush model in rodents

PURPOSE

The purpose of the current study was to assess the potential involvement of acid-sensing ion channel 1 (ASIC1) in retinal ganglion cell (RGC) death and investigate the neuroprotective effects of inhibitors of ASICs in promoting RGC survival following optic nerve crush (ONC).

RESULTS

ASIC1 protein was significantly increased in optic nerve extracts at day 7 following ONC in rats. Activated calpain-1 increased at 2 and 7 days following ONC as evidenced by increased degradation of α-fodrin, known substrate of calpain. Glial fibrillary acidic protein levels increased significantly at 2 and 7 days post-injury. By contrast, glutamine synthetase increased at 2 days while decreased at 7 days. The inhibition of ASICs with amiloride and psalmotoxin-1 significantly increased RGC survival in rats following ONC (p < 0.05, one-way ANOVA). The mean number of surviving RGCs in rats (n = 6) treated with amiloride (100 µM) following ONC was 1477 ± 98 cells/mm² compared with ONC (1126 ± 101 cells/mm²), where psalmotoxin-1 (1 μM) treated rats (n = 6) and subjected to ONC had 1441 ± 63 RGCs/mm² compared with ONC (1065 ± 76 RGCs/mm²). Average number of RGCs in control rats (n = 12) was 2092 ± 46 cells/mm². Blocking of ASICs also significantly increased RGC survival from ischemic-like insult from 473 ± 80 to 842 ± 49 RGCs/mm² (for psalmotoxin-1) and from 628 ± 53 RGCs/mm² to 890 ± 55 RGCs/mm² (for amiloride) with p ≤ 0.05, using one-way ANOVA. Acidification (a known activator of ASIC1) increased intracellular Ca²⁺ ([Ca²⁺]_i) in rat primary RGCs, which was statistically blocked by pretreatment with 100 nM psalmotoxin-1.

CONCLUSIONS

ASIC1 up-regulation-induced influx of extracellular calcium may be responsible for activation of calcium-sensitive calpain-1 in the retina. Calpain-1 induced degradation of α-fodrin and leads to morphological changes and eventually neuronal death. Therefore, blockers of ASIC1 can be used as potential therapeutics in the treatment of optic nerve degeneration.

ABBREVIATIONS

4-(2-Aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF); acid-sensing ion channels (ASICs); analysis of variance (ANOVA); bicinchoninic acid (BCA); brain-derived neurotrophic factor (BDNF); central nervous system (CNS); ciliary neurotrophic factor (CNTF); dimethyl sulfoxide (DMSO); endoplasmic reticulum (ER); ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA); ethylenediaminetetraacetic acid (EDTA); Food and Drug Administration (FDA); glial fibrillary acidic protein (GFAP); glutamine synthetase (GS); intraocular pressure (IOP); kilodalton (kDa); Krebs-Ringer Buffer (KRB); optic nerve crush (ONC); phosphate-buffered saline (PBS); plasma membrane (PM); polymerase chain reaction (PCR); retinal ganglion cell (RGC); RNA Binding Protein With Multiple Splicing (RBPMS); room temperature (RT); standard error of the mean (SEM).

microRNA-183 Mediates Protective Postconditioning of the Liver by Repressing Apaf-1

AIMS

Ischemic postconditioning (iPoC) is known to mitigate ischemia-reperfusion (IR) injury of the liver, the mechanisms of which remain to be elucidated. This study explored the role of microRNA-183 (miR-183) in the protective mechanism of iPoC.

RESULTS

Microarray analysis showed miR-183 was robustly expressed in rats' livers with iPoC. miR-183 repressed the mRNA expression of Apaf-1, which is an apoptosis promoting factor. Using an oxygen-glucose deprivation (OGD) injury model in Clone 9 cells, hypoxic postconditioning (HPoC) and an miR-183 mimetic significantly decreased cell death after OGD, but miR-183 inhibitors eliminated the protection of HPoC. The increased expression of Apaf-1 and the downstream activation of capsase-3/9 after OGD were mitigated by HPoC or the addition of miR-183 mimetics, whereas miR-183 inhibitor diminished the effect of HPoC on Apaf-1-caspase signaling. In the in vivo experiment, iPoC and agomiR-183 decreased the expression of serum ALT after liver IR in the mice, but antagomiR-183 mitigated the effect of iPoC. The results of hematoxylin and eosin and TUNEL staining were compatible with the biochemical assay. Moreover, iPoC and agomiR-183 decreased the expression of Apaf-1 and 4-HNE after IR injury in mouse livers, whereas the antagomiR-mediated prevention of miR-183 expression led to increased protein expression of Apaf-1 and 4-HNE in the postischemic livers.

INNOVATION

Our experiment showed the first time that miR-183 was induced in protective postconditioning and reduced reperfusion injury of the livers via the targeting of apoptotic signaling.

CONCLUSION

miR-183 mediated the tolerance induced by iPoC in livers via Apaf-1 repressing. Antioxid. Redox Signal. 26, 583-597.

Mechanisms Underlying the Emergence of Post-acidosis Arrhythmia at the Tissue Level: A Theoretical Study

Acidosis has complex electrophysiological effects, which are associated with a high recurrence of ventricular arrhythmias. Through multi-scale cardiac computer modeling, this study investigated the mechanisms underlying the emergence of post-acidosis arrhythmia at the tissue level. In simulations, ten Tusscher-Panfilov ventricular model was modified to incorporate various data on acidosis-induced alterations of cellular electrophysiology and intercellular electrical coupling. The single cell models were incorporated into multicellular one-dimensional (1D) fiber and 2D sheet tissue models. Electrophysiological effects were quantified as changes of action potential profile, sink-source interactions of fiber tissue, and the vulnerability of tissue to the genesis of unidirectional conduction that led to initiation of re-entry. It was shown that acidosis-induced sarcoplasmic reticulum (SR) calcium load contributed to delayed afterdepolarizations (DADs) in single cells. These DADs may be synchronized to overcome the source-sink mismatch arising from intercellular electrotonic coupling, and produce a premature ventricular complex (PVC) at the tissue level. The PVC conduction can be unidirectionally blocked in the transmural ventricular wall with altered electrical heterogeneity, resulting in the genesis of re-entry. In conclusion, altered source-sink interactions and electrical heterogeneity due to acidosis-induced cellular electrophysiological alterations may increase susceptibility to post-acidosis ventricular arrhythmias.

Cardioprotection with halogenated gases: how does it occur?

Numerous studies have studied the effect of halogenated agents on the myocardium, highlighting the beneficial cardiac effect of the pharmacological mechanism (preconditioning and postconditioning) when employed before and after ischemia in patients with ischemic heart disease. Anesthetic preconditioning is related to the dose-dependent signal, while the degree of protection is related to the concentration of the administered drug and the duration of the administration itself. Triggers for postconditioning and preconditioning might have numerous pathways in common; mitochondrial protection and a decrease in inflammatory mediators could be the major biochemical elements. Several pathways have been identified, including attenuation of NFκB activation and reduced expression of TNFα, IL-1, intracellular adhesion molecules, eNOS, the hypercontraction reduction that follows reperfusion, and antiapoptotic activating kinases (Akt, ERK1/2). It appears that the preconditioning and postconditioning triggers have numerous similar paths. The key biochemical elements are protection of the mitochondria and reduction in inflammatory mediators, both of which are developed in various ways. We have studied this issue, and have published several articles on cardioprotection with halogenated gases. Our results confirm greater cardioprotection through myocardial preconditioning in patients anesthetized with sevoflurane compared with propofol, with decreasing levels of troponin and N-terminal brain natriuretic peptide prohormone. The difference between our studies and previous studies lies in the use of sedation with sevoflurane in the postoperative period. The results could be related to a prolonged effect, in addition to preconditioning and postconditioning, which could enhance the cardioprotective effect of sevoflurane in the postoperative period. With this review, we aim to clarify the importance of various mechanisms involved in preconditioning and postconditioning with halogenated gases, as supported by our studies.

Mitochondrial Ca2+ and regulation of the permeability transition pore

The mitochondrial permeability transition pore was originally described in the 1970's as a Ca2+ activated pore and has since been attributed to the pathogenesis of many diseases. Here we evaluate how each of the current models of the pore complex fit to what is known about how Ca2+ regulates the pore, and any insight that provides into the molecular identity of the pore complex. We also discuss the central role of Ca2+ in modulating the pore's open probability by directly regulating processes, such as ATP/ADP balance through the tricarboxylic acid cycle, electron transport chain, and mitochondrial membrane potential. We review how Ca2+ influences second messengers such as reactive oxygen/nitrogen species production and polyphosphate formation. We discuss the evidence for how Ca2+ regulates post-translational modification of cyclophilin D including phosphorylation by glycogen synthase kinase 3 beta, deacetylation by sirtuins, and oxidation/ nitrosylation of key residues. Lastly we introduce a novel view into how Ca2+ activated proteolysis through calpains in the mitochondria may be a driver of sustained pore opening during pathologies such as ischemia reperfusion injury.

Unacylated ghrelin analog prevents myocardial reperfusion injury independently of permeability transition pore

Reperfusion injury is responsible for an important part of myocardial infarct establishment due notably to triggering cardiomyocytes death at the first minutes of reperfusion. AZP-531 is an optimized analog of unacylated ghrelin currently in clinical development in several metabolic diseases. We investigated a potential cardioprotective effect of AZP-531 in ischemia/reperfusion (IR) and the molecular underlying mechanism(s) involved in this protection. In vivo postconditioning with AZP-531 in C57BL6 mouse IR model decreased infarct size. Western blot analysis on areas at risk from the different mouse groups showed that AZP-531 activates Akt, ERK1-2 as well as S6 and 4EBP1, mTORC1 effectors. We also showed an inhibition of caspase 3 cleavage and Bax translocation to the mitochondria. AZP-531 also stimulated the expression of antioxidants and was capable of decreasing mitochondrial H₂O₂ production, contributing to the reduction of ROS accumulation. AZP-531 exhibits cardioprotective effect when administrated for postconditioning in C57BL6 mouse IR model. Treatment with AZP-531 rescued the myocardium from cell death at early reperfusion by stimulating protein synthesis, inhibiting Bax/caspase 3-induced apoptosis as well as ROS accumulation and oxidative stress-induced necrosis. AZP-531 may prove useful in the treatment of IR injury.

Ionic homeostasis in brain conditioning

Most of the current focus on developing neuroprotective therapies is aimed at preventing neuronal death. However, these approaches have not been successful despite many years of clinical trials mainly because the numerous side effects observed in humans and absent in animals used at preclinical level. Recently, the research in this field aims to overcome this problem by developing strategies which induce, mimic, or boost endogenous protective responses and thus do not interfere with physiological neurotransmission. Preconditioning is a protective strategy in which a subliminal stimulus is applied before a subsequent harmful stimulus, thus inducing a state of tolerance in which the injury inflicted by the challenge is mitigated. Tolerance may be observed in ischemia, seizure, and infection. Since it requires protein synthesis, it confers delayed and temporary neuroprotection, taking hours to develop, with a pick at 1–3 days. A new promising approach for neuroprotection derives from post-conditioning, in which neuroprotection is achieved by a modified reperfusion subsequent to a prolonged ischemic episode. Many pathways have been proposed as plausible mechanisms to explain the neuroprotection offered by preconditioning and post-conditioning. Although the mechanisms through which these two endogenous protective strategies exert their effects are not yet fully understood, recent evidence highlights that the maintenance of ionic homeostasis plays a key role in propagating these neuroprotective phenomena. The present article will review the role of protein transporters and ionic channels involved in the control of ionic homeostasis in the neuroprotective effect of ischemic preconditioning and post-conditioning in adult brain, with particular regards to the Na⁺/Ca2⁺ exchangers (NCX), the plasma membrane Ca2⁺-ATPase (PMCA), the Na⁺/H⁺ exchange (NHE), the Na⁺/K⁺/2Cl⁻ cotransport (NKCC) and the acid-sensing cation channels (ASIC). Ischemic stroke is the third leading cause of death and disability. Up until now, all clinical trials testing potential stroke neuroprotectants failed. For this reason attention of researchers has been focusing on the identification of brain endogenous neuroprotective mechanisms activated after cerebral ischemia. In this context, ischemic preconditioning and ischemic post-conditioning represent two neuroprotecive strategies to investigate in order to identify new molecular target to reduce the ischemic damage.

Heart mitochondria and calpain 1: Location, function, and targets

Calpain 1 is an ubiquitous Ca(2+)-dependent cysteine protease. Although calpain 1 has been found in cardiac mitochondria, the exact location within mitochondrial compartments and its function remain unclear. The aim of the current review is to discuss the localization of calpain 1 in different mitochondrial compartments in relationship to its function, especially in pathophysiological conditions. Briefly, mitochondrial calpain 1 (mit-CPN1) is located within the intermembrane space and mitochondrial matrix. Activation of the mit-CPN1 within intermembrane space cleaves apoptosis inducing factor (AIF), whereas the activated mit-CPN1 within matrix cleaves complex I subunits and metabolic enzymes. Inhibition of the mit-CPN1 could be a potential strategy to decrease cardiac injury during ischemia-reperfusion.

Treatment of Myocardial Ischemia/Reperfusion Injury by Ischemic and Pharmacological Postconditioning

Timely reperfusion is the only way to salvage ischemic myocardium from impending infarction. However, reperfusion also adds a further component to myocardial injury such that the ultimate infarct size is the result of both ischemia- and reperfusion-induced injury. Modification of reperfusion can attenuate reperfusion injury and thus reduce infarct size. Ischemic postconditioning is a maneuver of repeated brief interruption of reperfusion by short-lasting coronary occlusions which results in reduced infarct size. Cardioprotection by ischemic postconditioning is mediated through delayed reversal of acidosis and the activation of a complex signal transduction cascade, including triggers such as adenosine, bradykinin, and opioids, mediators such as protein kinases and, notably, mitochondrial function as effector. Inhibition of the mitochondrial permeability transition pore appears to be a final signaling step of ischemic postconditioning. Several drugs which recruit in part such signaling steps of ischemic postconditioning can induce cardioprotection, even when the drug is only administered at reperfusion, that is, there is also pharmacological postconditioning. Ischemic and pharmacological postconditioning have been translated to patients with acute myocardial infarction in proof-of-concept studies, but further mechanistic insight is needed to optimize the conditions and algorithms of cardioprotection by postconditioning.

The cGMP/PKG pathway as a common mediator of cardioprotection: translatability and mechanism

Cardiomyocyte cell death occurring during myocardial reperfusion (reperfusion injury) contributes to final infarct size after transient coronary occlusion. Different interrelated mechanisms of reperfusion injury have been identified, including alterations in cytosolic Ca(2+) handling, sarcoplasmic reticulum-mediated Ca(2+) oscillations and hypercontracture, proteolysis secondary to calpain activation and mitochondrial permeability transition. All these mechanisms occur during the initial minutes of reperfusion and are inhibited by intracellular acidosis. The cGMP/PKG pathway modulates the rate of recovery of intracellular pH, but has also direct effect on Ca(2+) oscillations and mitochondrial permeability transition. The cGMP/PKG pathway is depressed in cardiomyocytes by ischaemia/reperfusion and preserved by ischaemic postconditioning, which importantly contributes to postconditioning protection. The present article reviews the mechanisms and consequences of the effect of ischaemic postconditioning on the cGMP/PKG pathway, the different pharmacological strategies aimed to stimulate it during myocardial reperfusion and the evidence, limitations and promise of translation of these strategies to the clinical practice. Overall, the preclinical and clinical evidence suggests that modulation of the cGMP/PKG pathway may be a therapeutic target in the context of myocardial infarction.

Chasing cardiac physiology and pathology down the CaMKII cascade

Calcium dynamics is central in cardiac physiology, as the key event leading to the excitation-contraction coupling (ECC) and relaxation processes. The primary function of Ca(2+) in the heart is the control of mechanical activity developed by the myofibril contractile apparatus. This key role of Ca(2+) signaling explains the subtle and critical control of important events of ECC and relaxation, such as Ca(2+) influx and SR Ca(2+) release and uptake. The multifunctional Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is a signaling molecule that regulates a diverse array of proteins involved not only in ECC and relaxation but also in cell death, transcriptional activation of hypertrophy, inflammation, and arrhythmias. CaMKII activity is triggered by an increase in intracellular Ca(2+) levels. This activity can be sustained, creating molecular memory after the decline in Ca(2+) concentration, by autophosphorylation of the enzyme, as well as by oxidation, glycosylation, and nitrosylation at different sites of the regulatory domain of the kinase. CaMKII activity is enhanced in several cardiac diseases, altering the signaling pathways by which CaMKII regulates the different fundamental proteins involved in functional and transcriptional cardiac processes. Dysregulation of these pathways constitutes a central mechanism of various cardiac disease phenomena, like apoptosis and necrosis during ischemia/reperfusion injury, digitalis exposure, post-acidosis and heart failure arrhythmias, or cardiac hypertrophy. Here we summarize significant aspects of the molecular physiology of CaMKII and provide a conceptual framework for understanding the role of the CaMKII cascade on Ca(2+) regulation and dysregulation in cardiac health and disease.

Ca2+ Sparks and Ca2+ waves are the subcellular events underlying Ca2+ overload during ischemia and reperfusion in perfused intact hearts

Abnormal intracellular Ca(2+) cycling plays a key role in cardiac dysfunction, particularly during the setting of ischemia/reperfusion (I/R). During ischemia, there is an increase in cytosolic and sarcoplasmic reticulum (SR) Ca(2+). At the onset of reperfusion, there is a transient and abrupt increase in cytosolic Ca(2++), which occurs timely associated with reperfusion arrhythmias. However, little is known about the subcellular dynamics of Ca(2+) increase during I/R, and a possible role of the SR as a mechanism underlying this increase has been previously overlooked. The aim of the present work is to test two main hypotheses: (1) An increase diastolic Ca(2+) sparks frequency (cspf) constitutes a mayor substrate for the ischemia-induced diastolic Ca(2+) increase; (2) an increase in cytosolic Ca(2+) pro-arrhythmogenic events (Ca(2+) waves), mediates the abrupt diastolic Ca(2+) rise at the onset of reperfusion. We used confocal microscopy on mouse intact hearts loaded with Fluo-4. Hearts were submitted to global I/R (12/30 min) to assess epicardial Ca(2+) sparks in the whole heart. Intact heart sparks were faster than in isolated myocytes whereas cspf was not different. During ischemia, cspf significantly increased relative to preischemia (2.07±0.33 vs. 1.13±0.20 sp/s/100 μm, n=29/34, 7 hearts). Reperfusion significantly changed Ca(2+) sparks kinetics, by prolonging Ca(2+) sparks rise time and decreased cspf. However, it significantly increased Ca(2+) wave frequency relative to ischemia (0.71±0.14 vs. 0.38±0.06 w/s/100 μm, n=32/33, 7 hearts). The results show for the first time the assessment of intact perfused heart Ca(2+) sparks and provides direct evidence of increased Ca(2+) sparks in ischemia that transform into Ca(2+) waves during reperfusion. These waves may constitute a main trigger for reperfusion arrhythmias.

RNase1 prevents the damaging interplay between extracellular RNA and tumour necrosis factor-α in cardiac ischaemia/reperfusion injury

Despite optimal therapy, the morbidity and mortality of patients presenting with an acute myocardial infarction (MI) remain significant, and the initial mechanistic trigger of myocardial "ischaemia/reperfusion (I/R) injury" remains greatly unexplained. Here we show that factors released from the damaged cardiac tissue itself, in particular extracellular RNA (eRNA) and tumour-necrosis-factor α (TNF-α), may dictate I/R injury. In an experimental in vivo mouse model of myocardial I/R as well as in the isolated I/R Langendorff-perfused rat heart, cardiomyocyte death was induced by eRNA and TNF-α. Moreover, TNF-α promoted further eRNA release especially under hypoxia, feeding a vicious cell damaging cycle during I/R with the massive production of oxygen radicals, mitochondrial obstruction, decrease in antioxidant enzymes and decline of cardiomyocyte functions. The administration of RNase1 significantly decreased myocardial infarction in both experimental models. This regimen allowed the reduction in cytokine release, normalisation of antioxidant enzymes as well as preservation of cardiac tissue. Thus, RNase1 administration provides a novel therapeutic regimen to interfere with the adverse eRNA-TNF-α interplay and significantly reduces or prevents the pathological outcome of ischaemic heart disease.

Potential role of cardiac chloride channels and transporters as novel therapeutic targets

The heart and blood vessels express a range of anion currents (e.g. ICl.PKA) and symporter/antiporters (e.g. Cl(-)/HCO3(-) exchanger) that translocate chloride (Cl(-)). They have been proposed to contribute to a variety of physiological processes including cellular excitability, cell volume homeostasis and apoptosis. Additionally there is evidence that Cl(-) currents or transporters may play a role in cardiac pathophysiology. Arrhythmogenesis, the process of cardiac ischaemic preconditioning, and the adaptive remodelling process in myocardial hypertrophy and heart failure have all been linked to such channels or transporters. We have explored the possibility that selective targeting of one or more of these may provide benefit in cardiovascular disease. Existing evidence points to an emerging role of cardiac cell anion channels as potential therapeutic targets, the 'disease-specificity' of which may represent a substantial improvement on current targets. However, the limitations of current techniques hitherto applied (such as developmental compensation in gene-modified animals) and pharmacological agents (which do not at present possess sufficient selectivity for the adequate probing of function) have thus far hindered translation to the introduction of new therapy.

Proteases in cardiometabolic diseases: Pathophysiology, molecular mechanisms and clinical applications

Cardiovascular disease is the leading cause of death in the U.S. and other developed countries. Metabolic syndrome, including obesity, diabetes/insulin resistance, hypertension and dyslipidemia is a major threat for public health in the modern society. It is well established that metabolic syndrome contributes to the development of cardiovascular disease collective called as cardiometabolic disease. Despite documented studies in the research field of cardiometabolic disease, the underlying mechanisms are far from clear. Proteases are enzymes that break down proteins, many of which have been implicated in various diseases including cardiac disease. Matrix metalloproteinase (MMP), calpain, cathepsin and caspase are among the major proteases involved in cardiac remodeling. Recent studies have also implicated proteases in the pathogenesis of cardiometabolic disease. Elevated expression and activities of proteases in atherosclerosis, coronary heart disease, obesity/insulin-associated heart disease as well as hypertensive heart disease have been documented. Furthermore, transgenic animals that are deficient in or over-express proteases allow scientists to understand the causal relationship between proteases and cardiometabolic disease. Mechanistically, MMPs and cathepsins exert their effect on cardiometabolic diseases mainly through modifying the extracellular matrix. However, MMP and cathepsin are also reported to affect intracellular proteins, by which they contribute to the development of cardiometabolic diseases. On the other hand, activation of calpain and caspases has been shown to influence intracellular signaling cascade including the NF-κB and apoptosis pathways. Clinically, proteases are reported to function as biomarkers of cardiometabolic diseases. More importantly, the inhibitors of proteases are credited with beneficial cardiometabolic profile, although the exact molecular mechanisms underlying these salutary effects are still under investigation. A better understanding of the role of MMPs, cathepsins, calpains and caspases in cardiometabolic diseases process may yield novel therapeutic targets for treating or controlling these diseases. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Blood pressure-targeted stepwise resuscitation for hemorrhagic shock in rats

BACKGROUND

Generation of reactive oxygen species (ROS) is an important mechanism of ischemia-reperfusion injury. Abrupt reoxygenation compared with slow reoxygenation has been known to increase ROS generation. Thus, slow and stepwise reperfusion can reduce ROS generation and subsequent ischemia-reperfusion injury. This study investigated the effect of slow reperfusion by blood pressure-targeted stepwise resuscitation (PSR) in hemorrhagic shock.

METHODS

Pressure-controlled hemorrhagic shock was induced in male Sprague-Dawley rats for 1 hour. Rats were then allocated to one of three groups (no-resuscitation group, n = 14; PSR group, n = 15; rapid normalization of blood pressure (RR) group, n = 15). Survival time and hemodynamic changes were recorded and compared. Blood samples and liver tissue were harvested after 6 hours of resuscitation in surviving rats.

RESULTS

All of the rats in the no-resuscitation group were expired before the end of the 6-hour observation period. Survival times were significantly longer in the PSR group than in the RR group (survival rates, 11 of 15 vs. 5 of 15, log rank p = 0.032). Plasma amino alanine transferase, histologic liver injury, and ROS generation in the liver tissue were significantly lower in the PSR group than in the RR group (all findings significant, p < 0.05). In addition, PSR significantly decreased plasma nitric oxide, liver interleukin 1β, and liver interleukin 6 compared with rapid resuscitation in addition to augmenting Akt survival pathways (all p < 0.05).

CONCLUSION

Slow reperfusion by PSR decreased mortality, ROS generation, and liver injury in rats undergoing hemorrhagic shock. Stepwise resuscitation also decreased inflammatory cytokine production and augmented Akt survival pathways.

Atrial Calpains: Mediators of Atrialmyopathies in Atrial Fibrillation

Atrial fibrillation (AF) is associated with substantial structural changes at cell and tissue level. Cellular hypertrophy, disintegration of sarcomeres, mitochondrial swelling and apoptosis have been described as typical histo-morphologic alterations in AF. Main initiators for cellular alterations in fibrillating atrial myocytes are cytosolic calcium overload and oxidative stress. Calpains are intracellular Ca2+- activated proteases and important mediators of calcium overload. Activation of calpains and down-regulation of the calpain inhibitor, calpastatin, contribute to myocardial damage in fibrillating atria. Thus, deregulations of the expression, activity, or subcellular localization of calpain within atrial myocytes have been established as important mediators of atrial myopathy during AF.

Transient complex I inhibition at the onset of reperfusion by extracellular acidification decreases cardiac injury

A reversible inhibition of mitochondrial respiration by complex I inhibition at the onset of reperfusion decreases injury in buffer-perfused hearts. Administration of acidic reperfusate for a brief period at reperfusion decreases cardiac injury. We asked if acidification treatment decreased cardiac injury during reperfusion by inhibiting complex I. Exposure of isolated mouse heart mitochondria to acidic buffer decreased the complex I substrate-stimulated respiration, whereas respiration with complex II substrates was unaltered. Evidence of the rapid and reversible inhibition of complex I by an acidic environment was obtained at the level of isolated complex, intact mitochondria and in situ mitochondria in digitonin-permeabilized cardiac myocytes. Moreover, ischemia-damaged complex I was also reversibly inhibited by an acidic environment. In the buffer-perfused mouse heart, reperfusion with pH 6.6 buffer for the initial 5 min decreased infarction. Compared with untreated hearts, acidification treatment markedly decreased the mitochondrial generation of reactive oxygen species and improved mitochondrial calcium retention capacity and inner mitochondrial membrane integrity. The decrease in infarct size achieved by acidic reperfusion approximates the reduction obtained by a reversible, partial blockade of complex I at reperfusion. Extracellular acidification decreases cardiac injury during reperfusion in part via the transient and reversible inhibition of complex I, leading to a reduction of oxyradical generation accompanied by a decreased susceptibility to mitochondrial permeability transition during early reperfusion.

Protection against myocardial ischemia-reperfusion injury in clinical practice

Even when reperfusion therapy is applied as early as possible, survival and quality of life are compromised in a considerable number of patients with ST-segment elevation acute myocardial infarction. Some cell death following transient coronary occlusion occurs during reperfusion, due to poor handling of calcium in the sarcoplasmic reticulum-mitochondria system, calpain activation, oxidative stress, and mitochondrial failure, all promoted by rapid normalization of intracellular pH. Various clinical trials have shown that infarct size can be limited by nonpharmacological strategies--such as ischemic postconditioning and remote ischemic conditioning--or by drugs--such as cyclosporine, insulin, glucagon-like peptide-1 agonists, beta-blockers, or stimulation of cyclic guanosine monophosphate synthesis. However, some clinical studies have yielded negative results, largely due to a lack of consistent preclinical data or a poor design, especially delayed administration. Large-scale clinical trials are therefore necessary, particularly those with primary clinical variables and combined therapies that consider age, sex, and comorbidities, to convert protection against reperfusion injury into a standard treatment for patients with ST-segment elevation acute myocardial infarction.

Contribution of calpain to myoglobin efflux from cardiomyocytes during ischaemia and after reperfusion in anaesthetized rats

AIM

Calpain activation has a putative role in ischaemia-reperfusion injury of cardiomyocytes. This study clarified the in vivo contribution of calpain to disruption of cardiomyocyte sarcolemma during ischaemia and after reperfusion in anaesthetized rats.

METHODS

Using a microdialysis technique in the hearts of anaesthetized rats, we investigated the effects of the calpain inhibitors on myocardial interstitial myoglobin level in the ischaemic region during coronary occlusion and after reperfusion. The calpain inhibitors were administered locally via a dialysis probe. Two durations of coronary occlusion were tested.

RESULTS

Thirty-minute coronary occlusion: dialysate myoglobin concentration increased markedly from 385 ± 46 ng mL(-1) at baseline to 3701 ± 527 ng mL(-1) at 20-30 min of occlusion. After reperfusion, dialysate myoglobin concentration further increased, reaching a peak (12 296 ± 1564 ng mL(-1) ) at 10-20 min post-reperfusion and then declined gradually. The calpain inhibitors, MDL-28170 and SNJ-1945 did not change dialysate myoglobin concentration during occlusion but attenuated the increase after reperfusion to 6826 ± 1227 and 8130 ± 938 ng mL(-1) at 10-20 min post-reperfusion (P < 0.05), respectively. Ninety-minute coronary occlusion: dialysate myoglobin concentration increased from 516 ± 33 ng mL(-1) at baseline to 5463 ± 387 ng mL(-1) at 80-90 min after occlusion. After reperfusion, there was no significant increase in dialysate myoglobin concentration. MDL-28170 did not affect dialysate myoglobin concentration during occlusion or after reperfusion.

CONCLUSION

Calpain contributes to sarcolemmal disruption immediately after reperfusion following 30-min coronary occlusion, but has little effects during ischaemia and after reperfusion in 90-min coronary occlusion.

A novel neuroprotective strategy for ischemic stroke: transient mild acidosis treatment by CO2 inhalation at reperfusion

Acidosis is one of the key components in cerebral ischemic postconditioning that has emerged recently as an endogenous strategy for neuroprotection. We set out to test whether acidosis treatment at reperfusion can protect against cerebral ischemia/reperfusion injury. Adult male C57BL/6 J mice were subjected to 60-minute middle cerebral arterial occlusion followed by 24-hour reperfusion. Acidosis treatment by inhaling 10%, 20%, or 30% CO2 for 5 or 10 minutes at 5, 50, or 100 minutes after reperfusion was applied. Our results showed that inhaling 20% CO2 for 5 minutes at 5 minutes after reperfusion-induced optimal neuroprotection, as revealed by reduced infarct volume. Attenuating brain acidosis with NaHCO3 significantly compromised the acidosis or ischemic postconditioning-induced neuroprotection. Consistently, both acidosis-treated primary cultured cortical neurons and acute corticostriatal slices were more resistant to oxygen-glucose deprivation/reperfusion insult. In addition, acidosis inhibited ischemia/reperfusion-induced apoptosis, caspase-3 expression, cytochrome c release to cytoplasm, and mitochondrial permeability transition pore (mPTP) opening. The neuroprotection of acidosis was inhibited by the mPTP opener atractyloside both in vivo and in vitro. Taken together, these findings indicate that transient mild acidosis treatment at reperfusion protects against cerebral ischemia/reperfusion injury. This neuroprotection is likely achieved, at least partly, by inhibiting mPTP opening and mitochondria-dependent apoptosis.

Cardioprotection by modulation of mitochondrial respiration during ischemia-reperfusion: role of apoptosis-inducing factor

The transient, reversible blockade of electron transport (BET) during ischemia or at the onset of reperfusion protects mitochondria and decreases cardiac injury. Apoptosis inducing factor (AIF) is located within the mitochondrial intermembrane space. A release of AIF from mitochondria into cytosol and nucleus triggers caspase-independent cell death. We asked if BET prevents the loss of AIF from mitochondria as a mechanism of protection in the buffer perfused heart. BET during ischemia with amobarbital, a rapidly reversible inhibitor of mitochondrial complex I, attenuated a release of AIF from mitochondria into cytosol, in turn decreasing the formation of cleaved and activated PARP-1. These results suggest that BET-mediated protection may occur through prevention of the loss of AIF from mitochondria during ischemia-reperfusion. In order to further clarify the role of mitochondrial AIF in BET-mediated protection, Harlequin (Hq) mice, a genetic model with mitochondrial AIF deficiency, were used to test whether BET could still decrease cell injury in Hq mouse hearts during reperfusion. BET during ischemia protected Hq mouse hearts against ischemia-reperfusion injury and improved mitochondrial function in these hearts during reperfusion. Thus, cardiac injury can still be decreased in the presence of down-regulated mitochondrial AIF content. Taken together, BET during ischemia protects both hearts with normal mitochondrial AIF content and hearts with mitochondrial AIF deficiency. Although preservation of mitochondrial AIF content plays a key role in reducing cell injury during reperfusion, the protection derived from the BET is not fully dependent on AIF-driven mechanisms.

Activation of cGMP/protein kinase G pathway in postconditioned myocardium depends on reduced oxidative stress and preserved endothelial nitric oxide synthase coupling

BACKGROUND

The cGMP/protein kinase G (PKG) pathway is involved in the cardioprotective effects of postconditioning (PoCo). Although PKG signaling in PoCo has been proposed to depend on the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt cascade, recent data bring into question a causal role of reperfusion injury signaling kinase (RISK) in PoCo protection. We hypothesized that PoCo increases PKG activity by reducing oxidative stress-induced endothelial nitric oxide synthase (NOS) uncoupling at the onset of reperfusion.

METHODS AND RESULTS

Isolated rat hearts were submitted to 40 minutes of ischemia and reperfusion with and without a PoCo protocol. PoCo reduced infarct size by 48% and cGMP depletion. Blockade of cGMP synthesis (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) and inhibition of PKG (KT5823) or NOS (l-NAME) abolished protection, but inhibition of PI3K/Akt cascade (LY294002) did not (n=5 to 7 per group). Phosphorylation of the RISK pathway was higher in PoCo hearts. However, this difference is due to increased cell death in control hearts because in hearts reperfused with the contractile inhibitor blebbistatin, a drug effective in preventing cell death at the onset of reperfusion, RISK phosphorylation increased during reperfusion without differences between control and PoCo groups. In these hearts, PoCo reduced the production of superoxide (O2(-)) and protein nitrotyrosylation and increased nitrate/nitrite levels in parallel with a significant decrease in the oxidation of tetrahydrobiopterin (BH4) and in the monomeric form of endothelial NOS.

CONCLUSIONS

These results demonstrate that PoCo activates the cGMP/PKG pathway via a mechanism independent of the PI3K/Akt cascade and dependent on the reduction of O2(-) production at the onset of reperfusion, resulting in attenuated oxidation of BH4 and reduced NOS uncoupling.