Ischemic postconditioning: from receptor to end-effector

Chaihu-Shugan-San inhibits neuroinflammation in the treatment of post-stroke depression through the JAK/STAT3-GSK3β/PTEN/Akt pathway

Post-stroke depression (PSD) is one of the most common neuropsychiatric consequence of stroke, affecting cognitive function, recovery of somatic function, and patient survival. The aim of this study was to evaluate whether Chaihu-Shugan-San, a traditional Chinese medicine formula used clinically to treat depression, could improve symptoms in a rat model for PSD, to investigate the potential mechanisms, and to validate the findings in an in vitro oxygen and glucose deprivation (OGD) model. Male rats were subjected to middle cerebral artery occlusion (MCAO) and to chronic unpredictable mild stress (CUMS). The rats were then allocated to experimental groups (n = 15) that were treated with Chaihu-Shugan-San, a JAK-STAT3 inhibitor, a GSK3β overexpressing virus, or an empty virus (control). The subjects allocated to each group, as well as those that received no treatment and rats that did not undergo MCAO/CUMS, were then subjected to forced swimming, tail suspension, and sugar water preference tests, and their neurological deficit score was determined. Inflammatory factor levels and the expression of proteins related to the JAK/STAT3-GSK3β/PTEN/Akt pathway were measured, and the synaptic ultrastructure was observed using transmission electron microscopy. Flow cytometry showed microglia polarization towards the M1 phenotype in an in vitro PSD model, which was reversed after treatment with a GSK3β overexpression virus, Chaihu-Shugan-San, or a JAK-STAT3 inhibitor. The results showed that Chaihu-Shugan-San has a therapeutic effect on an in vivo model for PSD and can regulate microglia polarization through the activation of the JAK/STAT3-GSK3β/PTEN/Akt pathway, suggesting that it exerts its effect via the inhibition of neuroinflammation.

Purinergic signaling in myocardial ischemia-reperfusion injury

Purines and their derivatives, extensively distributed in the body, act as a class of extracellular signaling molecules via a rich array of receptors, also known as purinoceptors (P1, P2X, and P2Y). They mediate multiple intracellular signal transduction pathways and participate in various physiological and pathological cell behaviors. Since the function in myocardial ischemia-reperfusion injury (MIRI), this review summarized the involvement of purinergic signal transduction in diversified pathological processes, including energy metabolism disorder, oxidative stress injury, calcium overload, inflammatory immune response, platelet aggregation, coronary vascular dysfunction, and cell necrosis and apoptosis. Moreover, increasing evidence suggests that purinergic signaling also mediates the prevention and treatment of MIRI, such as ischemic conditioning, pharmacological intervention, and some other therapies. In conclusion, this review exhibited that purinergic signaling mediates the complex processes of MIRI which shows its promising application and prospecting in the future.

The importance of natural chalcones in ischemic organ damage: Comprehensive and bioinformatic analysis review

Over the last few decades, extensive research has been conducted, yielding a detailed account of thousands of newly discovered compounds of natural origin and their biological activities, all of which have the potential to be used for a wide range of therapeutic purposes. There are multiple research papers denoting the central objective of chalcones, which have been shown to have therapeutic potential against various forms of ischemia. The various aspects of chalcones are discussed in this review regarding molecular mechanisms involved in the promising anti-ischemic potential of these chalcones. The main mechanisms involved in these protective effects are Nrf2/Akt activation and NF-κB/TLR4 suppression. Furthermore, in-silico studies were carried out to discover the probable binding of these chalcones to Keap-1 (an inhibitor of Nrf2), Akt, NF-κB, and TLR4 protein molecules. Besides, network pharmacology analysis was conducted to predict the interacting partners of these signals. The obtained results indicated that Nrf2, Akt, NF-κB, and TLR4 are involved in the beneficial anti-ischemic actions of chalcones. Conclusively, the present findings show that chalcones as anti-ischemic agents have a valid rationale. The discussed studies will provide a comprehensive viewpoint on chalcones and can help to optimize their effects in different ischemia. PRACTICAL APPLICATIONS: Ischemic organ damage is an unavoidable pathological condition with a high worldwide incidence. According to the current research progress, natural chalcones have been proved to treat and/or prevent various types of ischemic organ damage by alleviating oxidative stress, inflammation, and apoptosis by different molecular mechanisms. This article displays the comprehensive research progress and the molecular basis of ischemic organ damage pathophysiology and introduces natural chalcones' mechanism in the ischemic organ condition.

Molecular mechanism in trigeminal nerve and treatment methods related to orthodontic pain

BACKGROUND

Orthodontic treatment is the main treatment approach for malocclusion. Orthodontic pain is an inevitable undesirable adverse reaction during orthodontic treatment. It is reported orthodontic pain has become one of the most common reason that patients withdraw from orthodontic treatment. Therefore, understanding the underlying mechanism and finding treatment of orthodontic pain are in urgent need.

AIMS

This article aims to sort out the mechanisms and treatments of orthodontic pain, hoping to provide some ideas for future orthodontic pain relief.

MATERIALS

Tooth movement will cause local inflammation. Certain inflammatory factors and cytokines stimulating the trigeminal nerve and further generating pain perception, as well as drugs and molecular targeted therapy blocking nerve conduction pathways, will be reviewed in this article.

METHOD

We review and summaries current studies related to molecular mechanisms and treatment approaches in orthodontic pain control.

RESULTS

Orthodontics pain related influencing factors and molecular mechanisms has been introduced. Commonly used clinical methods in orthodontic pain control has been evaluated.

DISCUSSION

With the clarification of more molecular mechanisms, the direction of orthodontic pain treatment will shift to targeted drugs.

Cellular crosstalk in cardioprotection: Where and when do reactive oxygen species play a role?

A well-balanced intercellular communication between the different cells within the heart is vital for the maintenance of cardiac homeostasis and function. Despite remarkable advances on disease management and treatment, acute myocardial infarction remains the major cause of morbidity and mortality worldwide. Gold standard reperfusion strategies, namely primary percutaneous coronary intervention, are crucial to preserve heart function. However, reestablishment of blood flow and oxygen levels to the infarcted area are also associated with an accumulation of reactive oxygen species (ROS), leading to oxidative damage and cardiomyocyte death, a phenomenon termed myocardial reperfusion injury. In addition, ROS signaling has been demonstrated to regulate multiple biological pathways, including cell differentiation and intercellular communication. Given the importance of cell-cell crosstalk in the coordinated response after cell injury, in this review, we will discuss the impact of ROS in the different forms of inter- and intracellular communication, as well as the role of gap junctions, tunneling nanotubes and extracellular vesicles in the propagation of oxidative damage in cardiac diseases, particularly in the context of ischemia/reperfusion injury.

Berberine Protests the Heart from Ischemic Reperfusion Injury via Interference with Oxidative and Inflammatory Pathways

BACKGROUND

Ischemia and reperfusion (I/R) is a pathological condition characterized by an initial restriction of blood supply to an organ followed by the subsequent restoration of perfusion and concomitant reoxygenation.

OBJECTIVE

The aim of the study is to assess the possible cardioprotective potential effect of berberine in myocardial ischemia reperfusion injury induced by ligation of coronary artery in a male rat model.

METHODS

Total amount of 28 adult male albino rats were randomized into 4 equal groups: 1) Sham group, rats underwent the same anesthetic and surgical procedure as the control group except for LAD ligation; 2), Active control group, rats subjected to regional ischemia for 30 min by ligation of LAD coronary artery and reperfusion for 2 hours, 3), Control vehicle group, rats received dimethyl sulphoxide (DMSO) (vehicle of berberine) via IP route and subjected to ischemia for 30 minutes before ligation of LAD coronary artery & reperfusion for 2 hr; 4), Berberine treated group, rats pretreated with berberine10 mg/kg via IP injection 30minutes before ligation of LAD coronary artery & then subjected to reperfusion for 2 hr.

RESULTS

In the control group, as compared with sham, tissue TNF-α, IL-6, IL-10, caspase-3 and BAX, plasma cTn-T and serum MDA significantly increased (P<0.05), while serum GSH significantly decreased (P<0.05). The histopathological control group showed a significant cardiac injury (P<0.05) compared with the sham group. Berberine significantly counteracted (P<0.05) the increase of TNF-α, IL-6, caspase-3 and BAX and counteracted the increase in plasma cTn-T and serum MDA. Berberine produces a significant elevation (P<0.05) in cardiac IL-10 and serum GSH with a significant reduction in (P<0.05) cardiac injury.

CONCLUSION

Berberine attenuates myocardial I/R injury in male rats via interfering with inflammatory reactions and apoptosis which were induced by I/R injury.

Effect of hyperglycaemia and diabetes on acute myocardial ischaemia-reperfusion injury and cardioprotection by ischaemic conditioning protocols

Diabetic patients are at increased risk of developing coronary artery disease and experience worse clinical outcomes following acute myocardial infarction. Novel therapeutic strategies are required to protect the myocardium against the effects of acute ischaemia-reperfusion injury (IRI). These include one or more brief cycles of non-lethal ischaemia and reperfusion prior to the ischaemic event (ischaemic preconditioning [IPC]) or at the onset of reperfusion (ischaemic postconditioning [IPost]) either to the heart or to extracardiac organs (remote ischaemic conditioning [RIC]). Studies suggest that the diabetic heart is resistant to cardioprotective strategies, although clinical evidence is lacking. We overview the available animal models of diabetes, investigating acute myocardial IRI and cardioprotection, experiments investigating the effects of hyperglycaemia on susceptibility to acute myocardial IRI, the response of the diabetic heart to cardioprotective strategies e.g. IPC, IPost and RIC. Finally we highlight the effects of anti-hyperglycaemic agents on susceptibility to acute myocardial IRI and cardioprotection. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc.

Mechanisms Involved in Cardioprotection Induced by Physical Exercise

Significance: Regular exercise training can reduce myocardial damage caused by acute ischemia/reperfusion (I/R). Exercise can reproduce the phenomenon of ischemic preconditioning, due to the capacity of brief periods of ischemia to reduce myocardial damage caused by acute I/R. In addition, exercise may also activate the multiple kinase cascade responsible for cardioprotection even in the absence of ischemia. Recent Advances: Animal and human studies highlighted the fact that, besides to reduce risk factors related to cardiovascular disease, the beneficial effects of exercise are also due to its ability to induce conditioning of the heart. Exercise behaves as a physiological stress that triggers beneficial adaptive cellular responses, inducing a protective phenotype in the heart. The factors contributing to the exercise-induced heart preconditioning include stimulation of the anti-radical defense system and nitric oxide production, opioids, myokines, and adenosine-5'-triphosphate (ATP) dependent potassium channels. They appear to be also involved in the protective effect exerted by exercise against cardiotoxicity related to chemotherapy. Critical Issues and Future Directions: Although several experimental evidences on the protective effect of exercise have been obtained, the mechanisms underlying this phenomenon have not yet been fully clarified. Further studies are warranted to define precise exercise prescriptions in patients at risk of myocardial infarction or undergoing chemotherapy.

Loss of methionine sulfoxide reductases increases resistance to oxidative stress

Oxidation of methionine residues to methionine sulfoxide scavenges reactive species, thus protecting against oxidative stress. Reduction of the sulfoxide back to methionine by methionine sulfoxide reductases creates a cycle with catalytic efficiency. Protection by the methionine sulfoxide reductases is well documented in cultured cells, from microorganisms to mammals. However, knocking out one or two of the 4 mammalian reductases had little effect in mice that were not stressed. We hypothesized that the minimal effect is due to redundancy provided by the 4 reductases. We tested the hypothesis by creating a transgenic mouse line lacking all 4 reductases and predicted that this mouse would be exceptionally sensitive to oxidative stress. The mutant mice were phenotypically normal at birth, exhibited normal post-natal growth, and were fertile. Surprisingly, rather than being more sensitive to oxidative stress, they were more resistant to both cardiac ischemia-reperfusion injury and to parenteral paraquat, a redox-cycling agent. Resistance was not a result of hormetic induction of the antioxidant transcription factor Nrf2 nor activation of Akt. The mechanism of protection may be novel.

Reduction of SIRT1 blunts the protective effects of ischemic post-conditioning in diabetic mice by impairing the Akt signaling pathway

Ischemic post-conditioning (IPO) activates Akt signaling to confer cardioprotection. The responsiveness of diabetic hearts to IPO is impaired. We hypothesized that decreased cardiac SIRT1, a positive regulator of Akt, may be responsible for the impaired responsiveness of diabetic hearts to IPO-mediated cardioprotection. High-fat diet and streptozotocin-induced diabetic mice were subjected to myocardial ischemia/reperfusion (MI/R, 30 min ischemia and 180 min reperfusion) or IPO (three cycles of 10 s of reperfusion and ischemia at the onset of reperfusion). Adenoviral vectors encoding GFP or SIRT1 (Ad-SIRT1) were administered by direct injection into the left ventricular. Our results showed that IPO activated the Akt signaling pathway and reduced MI/R injury in non-diabetic hearts but not in diabetic hearts, in which reduced expression of SIRT1 and increased Akt acetylation were observed. Delivery of Ad-SIRT1 into the diabetic hearts reduced Akt acetylation and restored the cardioprotective effects of IPO by modulating Akt signaling pathway. In contrast, cardiac-specific SIRT1 knockout increased Akt acetylation and blunted the cardioprotective effects of IPO. In in vitro study, transfection with wild-type SIRT1 but not inactive mutant SIRT1 reduced the expression of Akt acetylation and restored the protective effects of hypoxic post-conditioning in high glucose-incubated cardiomyocytes. Moreover, the cardiomyocytes transfected with constitutive Akt acetylation showed repressed Akt phosphorylation and blunted protective effects against hypoxia/reoxygenation injury. These findings demonstrate that the reduction of SIRT1 blunts the protective effects of IPO by impairing Akt signaling pathway and that SIRT1 up-regulation restores IPO-mediated cardioprotection in diabetic mice via deacetylation-dependent activation of Akt signaling pathway.

Effect of Platelet GPIIb/IIIa Receptor Blockade With MK383 on Infarct Size and Myocardial Blood Flow in a Canine Reocclusion Model

Platelet activation and aggregation during ischemia influence reperfusion-related myocyte necrosis, myocardial perfusion at the microvascular level, and thereby eventual recovery of cardiac performance. Inhibition of platelet activity therefore represents a worthwhile target to reduce cellular injury. The current study examined the effects of MK383 (tirofiban), a potent inhibitor of platelet aggregation, on infarct size and myocardial perfusion in canine subjects to either reocclusion (ie, 120-minute + 60-minute ischemia with intervening reperfusion) or prolonged occlusion (ie, 3 hours) followed by reperfusion (180 minutes). Platelet aggregation, infarct size (tetrazolium staining), coronary blood flow (flow probe), coronary vascular reserve, and myocardial perfusion (microspheres) were evaluated. MK383, administered at the time of reperfusion, produced a modest reduction of tissue necrosis (compared to saline-treated controls) in the reocclusion and prolonged occlusion studies. Blood flow in the infarct-related artery after coronary occlusion was comparable between treatment groups, as was myocardial perfusion in the deeper layers of the ischemic region; coronary vascular reserve decreased progressively during reperfusion. Of note, compensatory changes in blood flow within the adjacent nonischemic myocardium were not observed. In conclusion, we report that that limiting platelet aggregation during reperfusion impacted infarct development. Continued investigation into the mechanisms by which inhibition of platelet activity protects myocardium against ischemia-reperfusion injury and improves clinical outcomes is necessary.

Pharmacological preconditioning with inhaled nitric oxide (NO): Organ-specific differences in the lifetime of blood and tissue NO metabolites

BACKGROUND

Endogenous nitric oxide (NO) may contribute to ischemic and anesthetic preconditioning while exogenous NO protects against ischemia-reperfusion (I/R) injury in the heart and other organs. Why those beneficial effects observed in animal models do not always translate into clinical effectiveness remains unclear. To mitigate reperfusion damage a source of NO is required. NO inhalation is known to increase tissue NO metabolites, but little information exists about the lifetime of these species. We therefore sought to investigate the fate of major NO metabolite classes following NO inhalation in mice in vivo.

METHODS

C57BL/6J mice were exposed to 80 ppm NO for 1 h. NO metabolites were measured in blood (plasma and erythrocytes) and tissues (heart, liver, lung, kidney and brain) immediately after NO exposure and up to 48 h thereafter. Concentrations of S-nitrosothiols, N-nitrosamines and NO-heme products as well as nitrite and nitrate were quantified by gas-phase chemiluminescence and ion chromatography. In separate experiments, mice breathed 80 ppm NO for 1 h prior to cardiac I/R injury (induced by coronary arterial ligation for 1 h, followed by recovery). After sacrifice, the size of the myocardial infarction (MI) and the area at risk (AAR) were measured.

RESULTS

After NO inhalation, elevated nitroso/nitrosyl levels returned to baseline over the next 24 h, with distinct multi-phasic decay profiles in each compartment. S/N-nitroso compounds and NO-hemoglobin in blood decreased exponentially, but remained above baseline for up to 30min, whereas nitrate was elevated for up to 3hrs after discontinuing NO breathing. Hepatic S/N-nitroso species concentrations remained steady for 30min before dropping exponentially. Nitrate only rose in blood, liver and kidney; nitrite tended to be lower in all organs immediately after NO inhalation but fluctuated considerably in concentration thereafter. NO inhalation before myocardial ischemia decreased the ratio of MI/AAR by 30% vs controls (p = 0.002); only cardiac S-nitrosothiols and NO-hemes were elevated at time of reperfusion onset.

CONCLUSIONS

Metabolites in blood do not reflect NO metabolite status of any organ. Although NO is rapidly inactivated by hemoglobin-mediated oxidation in the circulation, long-lived tissue metabolites may account for the myocardial preconditioning effects of inhaled NO. NO inhalation may afford similar protection in other organs.

Mitochondrial protein sulfenation during aging in the rat brain

There is accumulating evidence that cysteine sulfenation (cys-SOH) in proteins plays an important role in cellular response to oxidative stress. The purpose of the present study was to identify mitochondrial proteins that undergo changes in cys-SOH during aging. Studies were conducted in rats when they were 5 or 30 months of age. Following blocking of free protein thiols with N-ethylmaleimide, protein sulfenic acids were reduced by arsenite to free thiol groups that were subsequently labeled with biotin-maleimide. Samples were then comparatively analyzed by two-dimensional Western blots, and proteins showing changes in sulfenation were selectively identified by mass spectrometry peptide sequencing. As a result, five proteins were identified. Proteins showing an age-related decrease in sulfenation include pyruvate carboxylase and pyruvate dehydrogenase; while those showing an age-related increase in sulfenation include aconitase, mitofilin, and tubulin (α-1). Results of the present study provide a general picture of mitochondrial protein sulfenation in brain oxidative stress and implicate the involvement of protein sulfenation in overall decline of mitochondrial function during brain aging.

Hypertension, hypertrophy, and reperfusion injury

The heart of patients with hypertension and cardiac hypertrophy is more vulnerable to ischemia-reperfusion injury (IRI). Here we discuss the main mechanisms of IRI and possible targets for cardioprotection. In particular, we consider the viewpoint that hypertension and cardiac hypertrophy may act synergistically in increasing the predisposition to cardiovascular accidents and in worsening IRI. There is no doubt that hypertrophic hearts may be redirected to be less vulnerable to IRI. Some experimental evidences suggest that antihypertensive drugs may have beneficial effects, some of which are not directly related to hypertension-lowering effect. However, more thorough experimental and clinical studies are necessary to understand the mechanisms and to maximize the beneficial effects of reperfusion after a heart attack in the presence of comorbidities, such as hypertension and cardiac hypertrophy.

Mitochondrial Cx43, an important component of cardiac preconditioning

Connexin 43 (Cx43) forms gap junction channels that are essential for the propagation of electrical depolarization in cardiomyocytes, but also with important roles in the pathophysiology of reperfusion injury. However, more recent studies have shown that Cx43 has also important functions independent from intercellular communication between adjacent cardiomyocytes. Some of these actions have been related to the presence of Cx43 in the mitochondria of these cells (mitoCx43). The functions of mitoCx43 have not been completely elucidated, but there is strong evidence indicating that mitoCx43 modulates mitochondrial respiration at respiratory complex I, production of radical oxygen species and ATP synthesis. These functions of mitoCx43 modulate mitochondrial and cellular tolerance to reperfusion after prolonged ischemia and are necessary for the cardioprotective effect of ischemic preconditioning. In the present review article we discuss available knowledge on these functions of mitoCx43 in relation to reperfusion injury, the molecular mechanisms involved and explore the possibility that mitoCx43 may constitute a new pharmacological target in patients with ST-segment elevation myocardial infarction (STEMI). This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Understanding pacing postconditioning-mediated cardiac protection: a role of oxidative stress and a synergistic effect of adenosine

We and others have demonstrated a protective role for pacing postconditioning (PPC) against ischemia/reperfusion (I/R) injury in the heart; however, the underlying mechanisms behind these protective effects are not completely understood. In this study, we wanted to further characterize PPC-mediated cardiac protection, specifically identify optimal pacing sites; examine the role of oxidative stress; and test the existence of a potential synergistic effect between PPC and adenosine. Isolated rat hearts were subjected to coronary occlusion followed by reperfusion. PPC involved three, 30 s, episodes of alternating left ventricular (LV) and right atrial (RA) pacing. Multiple pacing protocols with different pacing electrode locations were used. To test the involvement of oxidative stress, target-specific agonists or antagonists were infused at the beginning of reperfusion. Hemodynamic data were digitally recorded, and cardiac enzymes, oxidant, and antioxidant status were chemically measured. Pacing at the LV or RV but not at the heart apex or base significantly (P < 0.001) protected against ischemia-reperfusion injury. PPC-mediated protection was completely abrogated in the presence of reactive oxygen species (ROS) scavenger, ebselen; peroxynitrite (ONOO^-) scavenger, uric acid; and nitric oxide synthase inhibitor, L-NAME. Nitric oxide (NO) donor, snap, however significantly (P < 0.05) protected the heart against I/R injury in the absence of PPC. The protective effects of PPC were significantly improved by adenosine. PPC-stimulated protection can be achieved by alternating LV and RA pacing applied at the beginning of reperfusion. NO, ROS, and the product of their interaction ONOO^- play a significant role in PPC-induced cardiac protection. Finally, the protective effects of PPC can be synergized with adenosine.

Ischaemic conditioning and targeting reperfusion injury: a 30 year voyage of discovery

To commemorate the auspicious occasion of the 30th anniversary of IPC, leading pioneers in the field of cardioprotection gathered in Barcelona in May 2016 to review and discuss the history of IPC, its evolution to IPost and RIC, myocardial reperfusion injury as a therapeutic target, and future targets and strategies for cardioprotection. This article provides an overview of the major topics discussed at this special meeting and underscores the huge importance and impact, the discovery of IPC has made in the field of cardiovascular research.

Cardioprotection by H2S Donors: Nitric Oxide-Dependent and ‑Independent Mechanisms

Hydrogen sulfide (H2S) is a signaling molecule with protective effects in the cardiovascular system. To harness the therapeutic potential of H2S, a number of donors have been developed. The present study compares the cardioprotective actions of representative H2S donors from different classes and studies their mechanisms of action in myocardial injury in vitro and in vivo. Exposure of cardiomyocytes to H2O2 led to significant cytotoxicity, which was inhibited by sodium sulfide (Na2S), thiovaline (TV), GYY4137 [morpholin-4-ium 4 methoxyphenyl(morpholino) phosphinodithioate], and AP39 [(10-oxo-10-(4-(3-thioxo-3H-1,2-dithiol5yl)phenoxy)decyl) triphenylphospho-nium bromide]. Inhibition of nitric oxide (NO) synthesis prevented the cytoprotective effects of Na2S and TV, but not GYY4137 and AP39, against H2O2-induced cardiomyocyte injury. Mice subjected to left anterior descending coronary ligation were protected from ischemia-reperfusion injury by the H2S donors tested. Inhibition of nitric oxide synthase (NOS) in vivo blocked only the beneficial effect of Na2S. Moreover, Na2S, but not AP39, administration enhanced the phosphorylation of endothelial NOS and vasodilator-associated phosphoprotein. Both Na2S and AP39 reduced infarct size in mice lacking cyclophilin-D (CypD), a modulator of the mitochondrial permeability transition pore (PTP). Nevertheless, only AP39 displayed a direct effect on mitochondria by increasing the mitochondrial Ca(2+) retention capacity, which is evidence of decreased propensity to undergo permeability transition. We conclude that although all the H2S donors we tested limited infarct size, the pathways involved were not conserved. Na2S had no direct effects on PTP opening, and its action was nitric oxide dependent. In contrast, the cardioprotection exhibited by AP39 could result from a direct inhibitory effect on PTP acting at a site different than CypD.

Exercise preconditioning of myocardial infarct size in dogs is triggered by calcium

We showed that exercise induces early and late myocardial preconditioning in dogs and that these effects are mediated through nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase activation. As the intracoronary administration of calcium induces preconditioning and exercise enhances the calcium inflow to the cell, we studied if this effect of exercise triggers exercise preconditioning independently of its hemodynamic effects. We analyzed in 81 dogs the effect of blocking sarcolemmal L-type Ca channels with a low dose of verapamil on early and late preconditioning by exercise, and in other 50 dogs, we studied the effect of verapamil on NADPH oxidase activation in early exercise preconditioning. Exercise reduced myocardial infarct size by 76% and 52% (early and late windows respectively; P < 0.001 both), and these effects were abolished by a single low dose of verapamil given before exercise. This dose of verapamil did not modify the effect of exercise on metabolic and hemodynamic parameters. In addition, verapamil blocked the activation of NADPH oxidase during early preconditioning. The protective effect of exercise preconditioning on myocardial infarct size is triggered, at least in part, by calcium inflow increase to the cell during exercise and, during the early window, is mediated by NADPH oxidase activation.

Pathobiology of Ischemic Heart Disease: Past, Present and Future

This review provides a perspective on knowledge of ischemic heart disease (IHD) obtained from the contemporary era of research which began in the 1960s and has continued to the present day. Important discoveries have been made by basic and translational scientists and clinicians. Pathologists have contributed significantly to insights obtained from experimental studies and clinicopathological studies in humans. The review also provides a perspective for future directions in research in IHD aimed at increasing basic knowledge and developing additional therapeutic options for patients with IHD.

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

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

Enhanced intestinal epithelial cell proliferation in diabetic rats correlates with β-catenin accumulation

The Wnt/β-catenin signaling cascade is implicated in the control of stem cell activity, cell proliferation, and cell survival of the gastrointestinal epithelium. Recent evidence indicates that the Wnt/β-catenin pathway is activated under diabetic conditions. The purpose of this study was to evaluate the role of Wnt/β-catenin signaling during diabetes-induced enteropathy in a rat model. Male rats were divided into three groups: control rats received injections of vehicle; diabetic rats received injections of one dose of streptozotocin (STZ); and diabetic-insulin rats received injections of STZ and were treated with insulin given subcutaneously at a dose of 1 U/kg twice daily. Rats were killed on day 7. Wnt/β-catenin-related genes and expression of proteins was determined using real-time PCR, western blotting, and immunohistochemistry. Among 13 genes identified by real-time PCR, seven genes were upregulated in diabetic rats compared with control animals including the target genes c-Myc and Tcf4. Diabetic rats also showed a significant increase in β-catenin protein compared with control animals. Treatment of diabetic rats attenuated the stimulating effect of diabetes on intestinal cell proliferation and Wnt/β-catenin signaling. In conclusion, enhanced intestinal epithelial cell proliferation in diabetic rats correlates with β-catenin accumulation.

Delayed low pressure at reperfusion: A new approach for cardioprotection

OBJECTIVES

The aims of this study were to evaluate whether the delayed application of low-pressure reperfusion could reduce lethal reperfusion injury and whether the inhibition of the opening of the mitochondrial permeability transition pore is involved in this protection.

METHODS

Isolated rat hearts (n = 120) underwent 40 minutes of global ischemia followed by 60 minutes of reperfusion. Hearts were randomly assigned to the following groups: control, postconditioning (comprising 2 episodes of 30 seconds of ischemia and 30 seconds of reperfusion), and low-pressure reperfusion (using a reduction of perfusion pressure at 70 cm H2O for 10 minutes). In additional groups, postconditioning and low-pressure reperfusion were applied after a delay of 3, 10, and 20 minutes after the initial 40-minute ischemic insult.

RESULTS

As expected, infarct size (triphenyltetrazolium chloride staining) and lactate dehydrogenase release were significantly reduced in low-pressure reperfusion and postconditioning versus controls (P < .01), whereas functional parameters (coronary flow, rate pressure product) were improved (P < .01). Although delaying postconditioning by more than 3 minutes resulted in a loss of protection, low-pressure reperfusion still significantly reduced infarct size when applied as late as 20 minutes after reperfusion. This delayed low-pressure reperfusion protection was associated with an improved mitochondrial respiration, lower reactive oxygen species production, and enhanced calcium retention capacity, related to inhibition of permeability transition pore opening.

CONCLUSIONS

We demonstrated for the first time that low-pressure reperfusion can reduce lethal myocardial reperfusion injury even when performed 10 to 20 minutes after the initiation of reperfusion.

Near infrared spectroscopy (NIRS) to assess the effects of local ischemic preconditioning in the muscle of healthy volunteers and critically ill patients

Near-infrared spectroscopy (NIRS) permits non-invasive evaluation of tissue oxygen saturation (StO2). A vascular occlusion test (VOT) produces transient controlled ischemia similar to that used in ischemic preconditioning. We hypothesized that we could evaluate local responses to ischemic preconditioning by performing repeated VOTs and observing the changes in different NIRS VOT-derived variables. In healthy volunteers (n=20), four VOTs were performed at 30-min intervals on one day and, in a second group (n=21), two VOTs with time intervals of 5, 15 or 30min were performed on 3 separate days. Two cohorts of patients, one with circulatory shock (n=23) and a hemodynamically stable group (n=20), were also studied, repeating the VOT twice with a 5-min interval. In the 1-day volunteers, there was a median decrease of 15 (6-21)% in the Desc slope (StO2 decrease during VOT) after the second VOT, but no significant change in the Asc slope (StO2 increase after VOT). In the 3-day volunteers, the Desc slope also decreased, regardless of the time interval between VOTs. There was no overall decrease in the Desc slope in either patient cohort with repeated VOTs but there was marked individual patient variability. Patients in whom the Desc slope decreased had less organ dysfunction at admission, required less norepinephrine (0.00 vs 0.08mcg/kg/min, p=0.02), less frequently had sepsis (12 vs 50%, p=0.02) and had a lower mortality (6 vs 39%, p=0.03) compared to those in whom it did not decrease. Repeated NIRS VOT can non-invasively assess the local effects of ischemic preconditioning in the muscle.

Strategies to increase nitric oxide signalling in cardiovascular disease

Nitric oxide (NO) is a key signalling molecule in the cardiovascular, immune and central nervous systems, and crucial steps in the regulation of NO bioavailability in health and disease are well characterized. Although early approaches to therapeutically modulate NO bioavailability failed in clinical trials, an enhanced understanding of fundamental subcellular signalling has enabled a range of novel therapeutic approaches to be identified. These include the identification of: new pathways for enhancing NO synthase activity; ways to amplify the nitrate-nitrite-NO pathway; novel classes of NO-donating drugs; drugs that limit NO metabolism through effects on reactive oxygen species; and ways to modulate downstream phosphodiesterases and soluble guanylyl cyclases. In this Review, we discuss these latest developments, with a focus on cardiovascular disease.

Protein S-nitrosylation in preconditioning and postconditioning

The coronary artery disease is a leading cause of death and morbidity worldwide. This disease has a complex pathophysiology that includes multiple mechanisms. Among these is the oxidative/nitrosative stress. Paradoxically, oxidative/nitrosative signaling plays a major role in cardioprotection against ischemia/reperfusion injury. In this context, the gas transmitter nitric oxide may act through several mechanisms, such as guanylyl cyclase activation and via S-nitrosylation of proteins. The latter is a covalent modification of a protein cysteine thiol by a nitric oxide-group that generates an S-nitrosothiol. Here, we report data showing that nitric oxide and S-nitrosylation of proteins play a pivotal role not only in preconditioning but also in postconditioning cardioprotection.

Cardioprotection by H2S engages a cGMP-dependent protein kinase G/phospholamban pathway

AIMS

H2S is known to confer cardioprotection; however, the pathways mediating its effects in vivo remain incompletely understood. The purpose of the present study is to evaluate the contribution of cGMP-regulated pathways in the infarct-limiting effect of H2S in vivo.

METHODS AND RESULTS

Anaesthetized rabbits were subjected to myocardial ischaemia (I)/reperfusion (R), and infarct size was determined in control or H2S-exposed groups. The H2S donor sodium hydrosulfide (NaHS, an agent that generates H2S) increased cardiac cGMP and reduced the infarct size. The cGMP-dependent protein kinase (PKG)-I inhibitor DT2 abrogated the protective effect of NaHS, whereas the control peptide TAT or l-nitroarginine methyl ester (l-NAME) did not alter the effect of NaHS. Moreover, the KATP channel inhibitor, glibenclamide, partially reversed the effects of NaHS, whereas inhibition of mitochondrial KATP did not modify the NaHS response. NaHS enhanced phosphorylation of phospholamban (PLN), in a PKG-dependent manner. To further investigate the role of PLN in H2S-mediated cardioprotection, wild-type and PLN KO mice underwent I/R. NaHS did not exert cardioprotection in PLN KO mice. Unlike what was observed in rabbits, genetic or pharmacological inhibition of eNOS abolished the infarct-limiting effect of NaHS in mice.

CONCLUSIONS

Our findings demonstrate (i) that administration of NaHS induces cardioprotection via a cGMP/PKG/PLN pathway and (ii) contribution of nitric oxide to the H2S response is species-specific.

HDAC inhibition prevents white matter injury by modulating microglia/macrophage polarization through the GSK3β/PTEN/Akt axis

Severe traumatic brain injury (TBI) elicits destruction of both gray and white matter, which is exacerbated by secondary proinflammatory responses. Although white matter injury (WMI) is strongly correlated with poor neurological status, the maintenance of white matter integrity is poorly understood, and no current therapies protect both gray and white matter. One candidate approach that may fulfill this role is inhibition of class I/II histone deacetylases (HDACs). Here we demonstrate that the HDAC inhibitor Scriptaid protects white matter up to 35 d after TBI, as shown by reductions in abnormally dephosphorylated neurofilament protein, increases in myelin basic protein, anatomic preservation of myelinated axons, and improved nerve conduction. Furthermore, Scriptaid shifted microglia/macrophage polarization toward the protective M2 phenotype and mitigated inflammation. In primary cocultures of microglia and oligodendrocytes, Scriptaid increased expression of microglial glycogen synthase kinase 3 beta (GSK3β), which phosphorylated and inactivated phosphatase and tensin homologue (PTEN), thereby enhancing phosphatidylinositide 3-kinases (PI3K)/Akt signaling and polarizing microglia toward M2. The increase in GSK3β in microglia and their phenotypic switch to M2 was associated with increased preservation of neighboring oligodendrocytes. These findings are consistent with recent findings that microglial phenotypic switching modulates white matter repair and axonal remyelination and highlight a previously unexplored role for HDAC activity in this process. Furthermore, the functions of GSK3β may be more subtle than previously thought, in that GSK3β can modulate microglial functions via the PTEN/PI3K/Akt signaling pathway and preserve white matter homeostasis. Thus, inhibition of HDACs in microglia is a potential future therapy in TBI and other neurological conditions with white matter destruction.

Redox signalling and cardioprotection: translatability and mechanism

The morbidity and mortality from coronary artery disease (CAD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of culprit coronary arteries. Although it is mandatory to reperfuse the ischaemic territory as soon as possible, paradoxically this leads to additional myocardial injury, namely ischaemia/reperfusion (I/R) injury, in which redox stress plays a pivotal role and for which no effective therapy is currently available. In this review, we report evidence that the redox environment plays a pivotal role not only in I/R injury but also in cardioprotection. In fact, cardioprotective strategies, such as pre- and post-conditioning, result in a robust reduction in infarct size in animals and the role of redox signalling is of paramount importance in these conditioning strategies. Nitrosative signalling and cysteine redox modifications, such as S-nitrosation/S-nitrosylation, are also emerging as very important mechanisms in conditioning cardioprotection. The reasons for the switch from protective oxidative/nitrosative signalling to deleterious oxidative/nitrosative/nitrative stress are not fully understood. The complex regulation of this switch is, at least in part, responsible for the diminished or lack of cardioprotection induced by conditioning protocols observed in ageing animals and with co-morbidities as well as in humans. Therefore, it is important to understand at a mechanistic level the reasons for these differences before proposing a safe and useful transition of ischaemic or pharmacological conditioning. Indeed, more mechanistic novel therapeutic strategies are required to protect the heart from I/R injury and to improve clinical outcomes in patients with CAD.

Overexpression of the muscle-specific protein, melusin, protects from cardiac ischemia/reperfusion injury

Melusin is a muscle-specific protein which interacts with β1 integrin cytoplasmic domain and acts as chaperone protein. Its overexpression induces improved resistance to cardiac overload delaying left ventricle dilation and reducing the occurrence of heart failure. Here, we investigated possible protective effect of melusin overexpression against acute ischemia/reperfusion (I/R) injury with or without Postconditioning cardioprotective maneuvers. Melusin transgenic (Mel-TG) mice hearts were subjected to 30-min global ischemia followed by 60-min reperfusion. Interestingly, infarct size was reduced in Mel-TG mice hearts compared to wild-type (WT) hearts (40.3 ± 3.5 % Mel-TG vs. 59.5 ± 3.8 % WT hearts; n = 11 animals/group; P < 0.05). The melusin protective effect was also demonstrated by measuring LDH release, which was 50 % lower in Mel-TG compared to WT. Mel-TG hearts had a higher baseline level of AKT, ERK1/2 and GSK3β phosphorylation, and displayed increased phospho-kinases level after I/R compared to WT mice. Post-ischemic Mel-TG hearts displayed also increased levels of the anti-apoptotic factor phospho-BAD. Importantly, pharmacological inhibition of PI3K/AKT (Wortmannin) and ERK1/2 (U0126) pathways abrogated the melusin protective effect. Notably, HSP90, a chaperone known to protect heart from I/R injury, showed high levels of expression in the heart of Mel-TG mice suggesting a possible collaboration of this molecule with AKT/ERK/GSK3β pathways in the melusin-induced protection. Postconditioning, known to activate AKT/ERK/GSK3β pathways, significantly reduced IS and LDH release in WT hearts, but had no additive protective effects in Mel-TG hearts. These findings implicate melusin as an enhancer of AKT and ERK pathways and as a novel player in cardioprotection from I/R injury.

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.

Postconditioning leads to an increase in protein S-nitrosylation

Previous studies have shown a role for nitric oxide and S-nitrosylation (SNO) in postconditioning (PostC), but specific SNO proteins and sites have not been identified in the myocardium after PostC. In this study, we examined SNO signaling in PostC using a Langendorff-perfused mouse heart model. After 20 min of equilibrium perfusion and 25 min of global ischemia, PostC was applied at the beginning of reperfusion with six cycles of 10 s of reperfusion and 10 s of ischemia. The total period of reperfusion was 90 min. Compared with the ischemia-reperfusion (I/R) control, PostC significantly reduced postischemic contractile dysfunction and infarct size. PostC-induced protection was blocked by treatment with N(G)-nitro-l-arginine methyl ester (l-NAME) (10 μmol/l; a constitutive NO synthase inhibitor), but not by either ODQ (10 μmol/l, a highly selective soluble guanylyl cyclase inhibitor) or KT5823 (1 μmol/l, a specific protein kinase G inhibitor). Two biotin switch based methods, two dimensional CyDye-maleimide difference gel electrophoresis (2D CyDye-maleimide DIGE) and SNO-resin-assisted capture (SNO-RAC), were utilized to identify SNO-modified proteins and sites. Using 2D CyDye-maleimide DIGE analysis, PostC was found to cause a 25% or greater increase in SNO of a number of proteins, which was blocked by treatment with l-NAME in parallel with the loss of protection. Using SNO-RAC, we identified 77 unique proteins with SNO sites after PostC. These results suggest that NO-mediated SNO signaling is involved in PostC-induced cardioprotection and these data provide the first set of candidate SNO proteins in PostC hearts.

Combined cardioprotectant and antithrombotic actions of platelet P2Y12 receptor antagonists in acute coronary syndrome: just what the doctor ordered

Since the P2Y12 receptor antagonists were first introduced, they have been extensively tested in patients with acute coronary syndrome and are now standard of care. These antiplatelet drugs are very effective in reducing subsequent cardiovascular events, stent thromboses, and mortality in patients with acute myocardial infarction undergoing reperfusion therapy. Although the prevailing view is that their benefit derives from their antithrombotic properties, other unrelated pleiotropic effects appear to be equally beneficial. Accumulating clinical and animal evidence indicates that, if present at the time of reperfusion, these drugs have a direct anti-infarct effect similar to that of ischemic postconditioning. Four oral antagonists have been developed in rapid succession: ticlopidine, clopidogrel, prasugrel, and ticagrelor. Each agent had a more consistent and rapid onset of action than the previous one, and this has correlated with improved clinical outcomes when given early in treatment. Unfortunately, gut absorption causes an appreciable delay in the onset of effect, especially when morphine is used, and the constant push to minimize the door-to-balloon time has made it difficult to achieve adequate platelet inhibition at the time of percutaneous coronary intervention with an oral agent. An intravenous P2Y12 antagonist such as cangrelor may optimize treatment because it produces nearly maximal inhibition of platelet aggregation within minutes. If antiplatelet agents do protect through postconditioning's mechanism, then they would render any other intervention that protects through that mechanism redundant. Indeed, animals treated with cangrelor cannot be further protected by pre- or postconditioning. However, interventions that use a different mechanism such as mild hypothermia or cariporide, a Na(+)-H(+) exchange blocker, do add to cangrelor's protection. Future research should be directed toward identifying interventions that can augment the protection from antiplatelet therapy and finding a way to optimize P2Y12 inhibition at reperfusion in all patients.

LIF and the heart: just another brick in the wall?

Multiple studies have shown that the cytokine leukemia inhibitory factor (LIF) is protective of the myocardium in the acute stress of ischemia-reperfusion. All three major intracellular signaling pathways that are activated by LIF in cardiac myocytes have been linked to actions that protect against oxidative stress and cell death, either at the level of the mitochondrion or via nuclear transcription. In addition, LIF has been shown to contribute to post-myocardial infarction cardiac repair and regeneration, by stimulating the homing of bone marrow-derived cardiac progenitors to the injured myocardium, the differentiation of resident cardiac stem cells into endothelial cells, and neovascularization. Whether LIF offers protection to the heart under chronic stress such as hypertension-induced cardiac remodeling and heart failure is not known. However, mice with cardiac myocyte restricted knockout of STAT3, a principal transcription factor activated by LIF, develop heart failure with age, and cardiac STAT3 levels are reported to be decreased in heart failure patients. In addition, endogenously produced LIF has been implicated in the cholinergic transdiffrentiation that may serve to attenuate sympathetic overdrive in heart failure and in the peri-infarct region of the heart after myocardial infarction. Surprisingly, therapeutic strategies to exploit the beneficial actions of LIF on the injured myocardium have received scant attention. Nor is it established whether the purported so-called adverse effects of LIF observed in isolated cardiac myocytes have physiological relevance in vivo. Here we present an overview of the actions of LIF in the heart with the goal of stimulating further research into the translational potential of this pleiotropic cytokine.

Transient acidosis during early reperfusion attenuates myocardium ischemia reperfusion injury via PI3k-Akt-eNOS signaling pathway

In this paper, we concluded that transient acidosis reperfusion conferred cardioprotection against myocardial ischemia reperfusion injury in isolated rat hearts through activating PI3K-Akt-eNOS pathway.

Differential STAT3 signaling in the heart: Impact of concurrent signals and oxidative stress

Multiple lines of evidence suggest that the transcription factor STAT3 is linked to a protective and reparative response in the heart. Thus, increasing duration or intensity of STAT3 activation ought to minimize damage and improve heart function under conditions of stress. Two recent studies using genetic mouse models, however, report findings that appear to refute this proposition. Unfortunately, studies often approach the question of the role of STAT3 in the heart from the perspective that all STAT3 signaling is equivalent, particularly when it comes to signaling by IL-6 type cytokines, which share the gp130 signaling protein. Moreover, STAT3 activation is typically equated with phosphorylation of a critical tyrosine residue. Yet, STAT3 transcriptional behavior is subject to modulation by serine phosphorylation, acetylation, and redox status of the cell. Unphosphorylated STAT3 is implicated in gene induction as well. Thus, how STAT3 is activated and also what other signaling events are occurring at the same time is likely to impact on the outcome ultimately linked to STAT3. Notably STAT3 may serve as a scaffold protein allowing it to interact with other singling pathways. In this context, canonical gp130 cytokine signaling may function to integrate STAT3 signaling with a protective PI3K/AKT signaling network via mutual involvement of JAK tyrosine kinases. Differences in the extent of integration may occur between those cytokines that signal through gp130 homodimers and those through heterodimers of gp130 with a receptor α chain. Signal integration may have importance not only for deciding the particular gene profile linked to STAT3, but for the newly described mitochondrial stabilization role of STAT3 as well. In addition, disruption of integrated gp130-related STAT3 signaling may occur under conditions of oxidative stress, which negatively impacts on JAK catalytic activity. For these reasons, understanding the importance of STAT3 signaling to heart function requires a greater appreciation of the plasticity of this transcription factor in the context in which it is investigated.

Peroxynitrite is a key mediator of the cardioprotection afforded by ischemic postconditioning in vivo

Myocardial ischemic postconditioning (PosC) describes an acquired resistance to lethal ischemia-reperfusion (I/R) injury afforded by brief episodes of I/R applied immediately after the ischemic insult. Cardioprotection is conveyed by parallel signaling pathways converging to prevent mitochondria permeability transition. Recent observations indicated that PostC is associated with free radicals generation, including nitric oxide (NO^.) and superoxide (O₂^.-), and that cardioprotection is abrogated by antioxidants. Since NO. And O₂^{. -} react to form peroxynitrite, we hypothesized that postC might trigger the formation of peroxyntrite to promote cardioprotection in vivo. Rats were exposed to 45 min of myocardial ischemia followed by 3h reperfusion. PostC (3 cycles of 30 seconds ischemia/30 seconds reperfusion) was applied at the end of index ischemia. In a subgroup of rats, the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulphonatophenyl) porphyrinato iron (FeTPPS) was given intravenously (10 mg/kg^-1) 5 minutes before PostC. Myocardial nitrotyrosine was determined as an index of peroxynitrite formation. Infarct size (colorimetric technique and plasma creatine kinase-CK-levels) and left ventricle (LV) function (micro-tip pressure transducer), were determined. A significant generation of 3-nitrotyrosine was detected just after the PostC manoeuvre. PostC resulted in a marked reduction of infarct size, CK release and LV systolic dysfunction. Treatment with FeTPPS before PostC abrogated the beneficial effects of PostC on myocardial infarct size and LV function. Thus, peroxynitrite formed in the myocardium during PostC induces cardioprotective mechanisms improving both structural and functional integrity of the left ventricle exposed to ischemia and reperfusion in vivo.

Network interactions within the canine intrinsic cardiac nervous system: implications for reflex control of regional cardiac function

  The aims of the study were to determine how aggregates of intrinsic cardiac (IC) neurons transduce the cardiovascular milieu versus responding to changes in central neuronal drive and to determine IC network interactions subsequent to induced neural imbalances in the genesis of atrial fibrillation (AF). Activity from multiple IC neurons in the right atrial ganglionated plexus was recorded in eight anaesthetized canines using a 16-channel linear microelectrode array. Induced changes in IC neuronal activity were evaluated in response to: (1) focal cardiac mechanical distortion; (2) electrical activation of cervical vagi or stellate ganglia; (3) occlusion of the inferior vena cava or thoracic aorta; (4) transient ventricular ischaemia, and (5) neurally induced AF. Low level activity (ranging from 0 to 2.7 Hz) generated by 92 neurons was identified in basal states, activities that displayed functional interconnectivity. The majority (56%) of IC neurons so identified received indirect central inputs (vagus alone: 25%; stellate ganglion alone: 27%; both: 48%). Fifty per cent transduced the cardiac milieu responding to multimodal stressors applied to the great vessels or heart. Fifty per cent of IC neurons exhibited cardiac cycle periodicity, with activity occurring primarily in late diastole into isovolumetric contraction. Cardiac-related activity in IC neurons was primarily related to direct cardiac mechano-sensory inputs and indirect autonomic efferent inputs. In response to mediastinal nerve stimulation, most IC neurons became excessively activated; such network behaviour preceded and persisted throughout AF. It was concluded that stochastic interactions occur among IC local circuit neuronal populations in the control of regional cardiac function. Modulation of IC local circuit neuronal recruitment may represent a novel approach for the treatment of cardiac disease, including atrial arrhythmias.