Post-conditioning reduces infarct size in the isolated rat heart: role of coronary flow and pressure and the nitric oxide/cGMP pathway

Effects of sevoflurane and its metabolite hexafluoroisopropanol on hypoxia/reoxygenation-induced injury and mitochondrial bioenergetics in murine cardiomyocytes

Background

The volatile anaesthetic sevoflurane protects cardiac tissue from reoxygenation/reperfusion. Mitochondria play an essential role in conditioning. We aimed to investigate how sevoflurane and its primary metabolite hexafluoroisopropanol (HFIP) affect necrosis, apoptosis, and reactive oxygen species formation in cardiomyocytes upon hypoxia/reoxygenation injury. Moreover, we aimed to describe the similarities in the mode of action in a mitochondrial bioenergetics analysis.

Methods

Murine cardiomyocytes were exposed to hypoxia (0.2% O2 for 6 h), followed by reoxygenation (air with 5% CO2 for 2 h) in the presence or absence sevoflurane 2.2% or HFIP 4 mM. Lactate dehydrogenase (LDH) release (necrosis), caspase activation (apoptosis), reactive oxygen species, mitochondrial membrane potential, and mitochondrial function (Seahorse XF analyser) were measured.

Results

Hypoxia/reoxygenation increased cell death by 44% (+31 to +55%, P<0.001). Reoxygenation in the presence of sevoflurane 2.2% or HFIP 4 mM increased LDH release only by +18% (+6 to +30%) and 20% (+7 to +32%), respectively. Apoptosis and reactive oxygen species formation were attenuated by sevoflurane and HFIP. Mitochondrial bioenergetics analysis of the two substances was profoundly different. Sevoflurane did not influence oxygen consumption rate (OCR) or extracellular acidification rate (ECAR), whereas HFIP reduced OCR and increased ECAR, an effect similar to oligomycin, an adenosine triphosphate (ATP) synthase inhibitor. When blocking the metabolism of sevoflurane into HFIP, protective effects of sevoflurane - but not of HFIP - on LDH release and caspase were mitigated.

Conclusion

Together, our data suggest that sevoflurane metabolism into HFIP plays an essential role in cardiomyocyte postconditioning after hypoxia/reoxygenation injury.

Pathways for Cardioprotection in Perspective: Focus on Remote Conditioning and Extracellular Vesicles

Despite the development of cutting-edge treatments, coronary artery disease (CAD) morbidity and mortality rates remain present at high levels. Therefore, new cardioprotective approaches are crucial to improve the health of patients. To date, experimental investigations of acute ischemia-reperfusion injury (IRI) have generally demonstrated the efficacy of local ischemic preconditioning and postconditioning cardioprotection techniques as well as of remote conditioning. However, application in clinical settings is still highly controversial and debated. Currently, remote ischemic conditioning (RIC) seems to be the most promising method for heart repair. Protective factors are released into the bloodstream, and protection can be transferred within and across species. For a long time, the cross-function and cross-transmission mechanisms of cardioprotection were largely unknown. Recently, it has been shown that small, anuclear, bilayered lipid membrane particles, known as extracellular vesicles (EVs), are the drivers of signal transduction in cardiac IRI and RIC. EVs are related to the pathophysiological processes of cardiovascular diseases (CVDs), according to compelling evidence. In this review, we will first review the current state of knowledge on myocardial IRI and cardioprotective strategies explored over the past 37 years. Second, we will briefly discuss the role of EVs in CVD and the most recent improvements on EVs as prognostic biomarkers, diagnostic, and therapeutic agents. We will discuss how EVs can be used as a new drug delivery mechanism and how they can be employed in cardiac treatment, also from a perspective of overcoming the impasse that results from neglecting confounding factors.

Endless Journey of Adenosine Signaling in Cardioprotective Mechanism of Conditioning Techniques: Clinical Evidence

Myocardial ischemic injury is a primary cause of death among various cardiovascular disorders. The condition occurs due to an interrupted supply of blood and vital nutrients (necessary for normal cellular activities and viability) to the myocardium, eventually leading to damage. Restoration of blood supply to ischemic tissue is noted to cause even more lethal reperfusion injury. Various strategies, including some conditioning techniques, like preconditioning and postconditioning, have been developed to check the detrimental effects of reperfusion injury. Many endogenous substances have been proposed to act as initiators, mediators, and end effectors of these conditioning techniques. Substances, like adenosine, bradykinin, acetylcholine, angiotensin, norepinephrine, opioids, etc., have been reported to mediate cardioprotective activity. Among these agents, adenosine has been widely studied and suggested to have the most pronounced cardioprotective effects. The current review article highlights the role of adenosine signaling in the cardioprotective mechanism of conditioning techniques. The article also provides an insight into various clinical studies that substantiate the applicability of adenosine as a cardioprotective agent in myocardial reperfusion injury.

cGMP and mitochondrial K+ channels-Compartmentalized but closely connected in cardioprotection

The 3',5'-cGMP pathway triggers cytoprotective responses and improves cardiomyocyte survival during myocardial ischaemia and reperfusion (I/R) injury. These beneficial effects were attributed to NO-sensitive GC induced cGMP production leading to activation of cGMP-dependent protein kinase I (cGKI). cGKI in turn phosphorylates many substrates, which eventually facilitate opening of mitochondrial ATP-sensitive potassium channels (mitoK_ATP ) and Ca²⁺ -activated potassium channels of the BK type (mitoBK). Accordingly, agents activating mitoK_ATP or mitoBK provide protection against I/R-induced damages. Here, we provide an up-to-date summary of the infarct-limiting actions exhibited by the GC/cGMP axis and discuss how mitoK_ATP and mitoBK, which are present at the inner mitochondrial membrane, confer mito- and cytoprotective effects on cardiomyocytes exposed to I/R injury. In view of this, we believe that the functional connection between the cGMP cascade and mitoK⁺ channels should be exploited further as adjunct to reperfusion therapy in myocardial infarction.

The Inflammatory Cytokine IL-3 Hampers Cardioprotection Mediated by Endothelial Cell-Derived Extracellular Vesicles Possibly via Their Protein Cargo

The biological relevance of extracellular vesicles (EV) released in an ischemia/reperfusion setting is still unclear. We hypothesized that the inflammatory microenvironment prevents cardioprotection mediated by endothelial cell (EC)-derived extracellular vesicles. The effects of naïve EC-derived EV (eEV) or eEV released in response to interleukin-3 (IL-3) (eEV-IL-3) were evaluated in cardiomyoblasts (H9c2) and rat hearts. In transwell assay, eEV protected the H9c2 exposed to hypoxia/reoxygenation (H/R) more efficiently than eEV-IL-3. Conversely, only eEV directly protected H9c2 cells to H/R-induced damage. Consistent with this latter observation, eEV, but not eEV-IL-3, exerted beneficial effects in the whole heart. Protein profiles of eEV and eEV-IL-3, established using label-free mass spectrometry, demonstrated that IL-3 drives changes in eEV-IL-3 protein cargo. Gene ontology analysis revealed that both eEV and eEV-IL-3 were equipped with full cardioprotective machinery, including the Nitric Oxide Signaling in the Cardiovascular System. eEV-IL-3 were also enriched in the endothelial-nitric oxide-synthase (eNOS)-antagonist caveolin-1 and proteins related to the inflammatory response. In vitro and ex vivo experiments demonstrated that a functional Mitogen-Activated Protein Kinase Kinase (MEK1/2)/eNOS/guanylyl-cyclase (GC) pathway is required for eEV-mediated cardioprotection. Consistently, eEV were found enriched in MEK1/2 and able to induce the expression of B-cell-lymphoma-2 (Bcl-2) and the phosphorylation of eNOS in vitro. We conclude that an inflammatory microenvironment containing IL-3 changes the eEV cargo and impairs eEV cardioprotective action.

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.

Possible role of mitochondrial K-ATP channel and nitric oxide in protection of the neonatal rat heart

Cardioprotective effect of ischemic preconditioning (IPC) and ischemic postconditioning (IPoC) in adult hearts is mediated by mitochondrial-K-ATP channels and nitric oxide (NO). During early developmental period, rat hearts exhibit higher resistance to ischemia–reperfusion (I/R) injury and their resistance cannot be further increased by IPC or IPoC. Therefore, we have speculated, whether mechanisms responsible for high resistance of neonatal heart may be similar to those of IPC and IPoC. To test this hypothesis, rat hearts isolated on days 1, 4, 7, and 10 of postnatal life were perfused according to Langendorff. Developed force (DF) of contraction was measured. Hearts were exposed to 40 min of global ischemia followed by reperfusion up to the maximum recovery of DF. IPoC was induced by 5 cycles of 10-s ischemia. Mito-K-ATP blocker (5-HD) was administered 5 min before ischemia and during first 20 min of reperfusion. Another group of hearts was isolated for biochemical analysis of 3-nitrotyrosine, and serum samples were taken to measure nitrate levels. Tolerance to ischemia did not change from day 1 to day 4 but decreased on days 7 and 10. 5-HD had no effect either on neonatal resistance to I/R injury or on cardioprotective effect of IPoC on day 10. Significant difference was found in serum nitrate levels between days 1 and 10 but not in tissue 3-nitrotyrosine content. It can be concluded that while there appears to be significant difference of NO production, mito-K-ATP and ROS probably do not play role in the high neonatal resistance to I/R injury.

Cyclic Nucleotide-Directed Protein Kinases in Cardiovascular Inflammation and Growth

Cardiovascular disease (CVD), including myocardial infarction (MI) and peripheral or coronary artery disease (PAD, CAD), remains the number one killer of individuals in the United States and worldwide, accounting for nearly 18 million (>30%) global deaths annually. Despite considerable basic science and clinical investigation aimed at identifying key etiologic components of and potential therapeutic targets for CVD, the number of individuals afflicted with these dreaded diseases continues to rise. Of the many biochemical, molecular, and cellular elements and processes characterized to date that have potential to control foundational facets of CVD, the multifaceted cyclic nucleotide pathways continue to be of primary basic science and clinical interest. Cyclic adenosine monophosphate (cyclic AMP) and cyclic guanosine monophosphate (cyclic GMP) and their plethora of downstream protein kinase effectors serve ubiquitous roles not only in cardiovascular homeostasis but also in the pathogenesis of CVD. Already a major target for clinical pharmacotherapy for CVD as well as other pathologies, novel and potentially clinically appealing actions of cyclic nucleotides and their downstream targets are still being discovered. With this in mind, this review article focuses on our current state of knowledge of the cyclic nucleotide-driven serine (Ser)/threonine (Thr) protein kinases in CVD with particular emphasis on cyclic AMP-dependent protein kinase (PKA) and cyclic GMP-dependent protein kinase (PKG). Attention is given to the regulatory interactions of these kinases with inflammatory components including interleukin 6 signals, with G protein-coupled receptor and growth factor signals, and with growth and synthetic transcriptional platforms underlying CVD pathogenesis. This article concludes with a brief discussion of potential future directions and highlights the importance for continued basic science and clinical study of cyclic nucleotide-directed protein kinases as emerging and crucial controllers of cardiac and vascular disease pathologies.

N-Methyl-D-Aspartate Receptor-Driven Calcium Influx Potentiates the Adverse Effects of Myocardial Ischemia-Reperfusion Injury Ex Vivo

BACKGROUND

Despite the adverse effects of N-methyl-D-aspartate receptor (NMDAR) activity in cardiomyocytes, no study has yet examined the effects of NMDAR activity under ex vivo ischemic-reperfusion (I/R) conditions. Therefore, our aim was to comprehensively evaluate the effects of NMDAR activity through an ex vivo myocardial I/R rat model.

METHODS

Isolated rat hearts were randomly segregated into 6 groups (n = 20 in each group): (1) an untreated control group; (2) a NMDA-treated control group; (3) an untreated I/R group; (4) an I/R+NMDA group treated with NMDA; (5) an I/R+NMDA+MK-801 group treated with NMDA and the NMDAR inhibitor MK-801; and (6) an I/R+NMDA+[Ca]-free group treated with NMDA and [Ca]-free buffer. The 4 I/R groups underwent 30 minutes of ischemia followed by 50 minutes of reperfusion. Left ventricular pressure signals were analyzed to assess cardiac performance. Myocardial intracellular calcium levels ([Ca]i) were assessed in isolated ventricular cardiomyocytes. Creatine kinase, creatine kinase isoenzyme MB, lactate dehydrogenase, cardiac troponin I, and cardiac troponin T were assayed from coronary effluents. TTC and TUNEL staining were used to measure generalized myocardial necrosis and apoptosis levels, respectively. Western blotting was applied to assess the phosphorylation of PKC-δ, PKC-ε, Akt, and extracellular signal-regulated kinase.

RESULTS

Enhanced NMDAR activity under control conditions had no significant effects on the foregoing variables. In contrast, enhanced NMDAR activity under I/R conditions produced significant increases in [Ca]i levels (∼1.2% increase), significant losses in left ventricular function (∼5.4% decrease), significant multi-fold increases in creatine kinase, creatine kinase isoenzyme MB, lactate dehydrogenase, cardiac troponin I, and cardiac troponin T, significant increases in generalized myocardial necrosis (∼36% increase) and apoptosis (∼150% increase), and significant multi-fold increases in PKC-δ, PKC-ε, Akt, and extracellular signal-regulated kinase phosphorylation (all P < 0.05). These adverse effects were rescued by the NMDAR inhibitor MK-801 or [Ca]-free buffer (all P < 0.05).

CONCLUSIONS

NMDAR-driven calcium influx potentiates the adverse effects of myocardial I/R injury ex vivo.

Obestatin regulates cardiovascular function and promotes cardioprotection through the nitric oxide pathway

Patients with ischaemic heart disease or chronic heart failure show altered levels of obestatin, suggesting a role for this peptide in human heart function. We have previously demonstrated that GH secretagogues and the ghrelin gene-derived peptides, including obestatin, exert cardiovascular effects by modulating cardiac inotropism and vascular tone, and reducing cell death and contractile dysfunction in hearts subjected to ischaemia/reperfusion (I/R), through the Akt/nitric oxide (NO) pathway. However, the mechanisms underlying the cardiac actions of obestatin remain largely unknown. Thus, we suggested that obestatin-induced activation of PI3K/Akt/NO and PKG signalling is implicated in protection of the myocardium when challenged by adrenergic, endothelinergic or I/R stress. We show that obestatin exerts an inhibitory tone on the performance of rat papillary muscle in both basal conditions and under β-adrenergic overstimulation, through endothelial-dependent NO/cGMP/PKG signalling. This pathway was also involved in the vasodilator effect of the peptide, used both alone and under stress induced by endothelin-1. Moreover, when infused during early reperfusion, obestatin reduced infarct size in isolated I/R rat hearts, through an NO/PKG pathway, comprising ROS/PKC signalling, and converging on mitochondrial ATP-sensitive potassium [mitoK(ATP)] channels. Overall, our results suggest that obestatin regulates cardiovascular function in stress conditions and induces cardioprotection by mechanisms dependent on activation of an NO/soluble guanylate cyclase (sGC)/PKG pathway. In fact, obestatin counteracts exaggerated β-adrenergic and endothelin-1 activity, relevant factors in heart failure, suggesting multiple positive effects of the peptide, including the lowering of cardiac afterload, thus representing a potential candidate in pharmacological post-conditioning.

Cardioprotective effects of calcitonin gene-related peptide in isolated rat heart and in H9c2 cells via redox signaling

The calcitonin-gene-related-peptide (CGRP) release is coupled to the signaling of Angeli's salt in determining vasodilator effects. However, it is unknown whether CGRP is involved in Angeli's salt cardioprotective effects and which are the mechanisms of protection. We aimed to determine whether CGRP is involved in myocardial protection induced by Angeli's salt. We also analyzed the intracellular signaling pathway activated by CGRP. Isolated rat hearts were pre-treated with Angeli's salt or Angeli's salt plus CGRP_8-37, a specific CGRP-receptor antagonist, and subjected to ischemia (30-min) and reperfusion (120-min). Moreover, we studied CGRP-induced protection during oxidative stress (H₂O₂) and hypoxia/reoxygenation protocols in H9c2 cardiomyocytes. Cell vitality and mitochondrial membrane potential (ΔYm, MMP) were measured using MTT and JC-1 dyes. Angeli's salt reduced infarct size and ameliorated post-ischemic cardiac function via a CGRP-receptor-dependent mechanism. Pre-treatment with CGRP increased H9c2 survival upon challenging with either H₂O₂ (redox stress) or hypoxia/reoxygenation (H/R stress). Under these stress conditions, reduction in MMP and cell death were partly prevented by CGRP. These CGRP beneficial effects were blocked by CGRP_8-37. During H/R stress, pre-treatment with either CGRP-receptor, protein kinase C (PKC) or mitochondrial K_ATP channel antagonists, and pre-treatment with an antioxidant (2-mercaptopropionylglycine) blocked the protection mediated by CGRP. In conclusion, CGRP is involved in the cardioprotective effects of Angeli's salt. In H9c2 cardiomyocytes, CGRP elicits PKC-dependent and mitochondrial-K_ATP-redox-dependent mechanisms. Hence, CGRP is an important factor in the redox-sensible cardioprotective effects of Angeli's salt.

Myocardial ischemia/reperfusion upregulates the transcription of the Neuregulin1 receptor ErbB3, but only postconditioning preserves protein translation: Role in oxidative stress

BACKGROUND

Neuregulin1 (Nrg1) and its receptors ErbB are crucial for heart development and for adult heart structural maintenance and function and Nrg1 has been proposed for heart failure treatment. Infarct size is the major determinant of heart failure and the mechanism of action and the role of each ErbB receptor remain obscure, especially in the post-ischemic myocardium. We hypothesized that Nrg1 and ErbB are affected at transcriptional level early after ischemia/reperfusion (I/R) injury, and that the protective postconditioning procedure (PostC, brief cycles of ischemia/reperfusion carried out after a sustained ischemia) can influence this pathway.

METHODS AND RESULTS

The Langendorff's heart was used as an ex-vivo model to mimic an I/R injury in the whole rat heart; after 30min of ischemia and 2h of reperfusion, with or without PostC, Nrg1 and ErbB expression were analysed by quantitative real-time PCR and Western blot. While no changes occur for ErbB2, ErbB4 and Nrg1, an increase of ErbB3 expression occurs after I/R injury, with and without PostC. However, I/R reduces ErbB3 protein, whereas PostC preserves it. An in vitro analysis with H9c2 cells exposed to redox-stress indicated that the transient over-expression of ErbB3 alone is able to increase cell survival (MTT assay), limiting mitochondrial dysfunction (JC-1 probe) and apoptotic signals (Bax/Bcl-2 ratio).

CONCLUSIONS

This study suggests ErbB3 as a protective factor against death pathways activated by redox stress and supports an involvement of this receptor in the pro-survival responses.

Inhibition of the nitric oxide/cyclic guanosine monophosphate pathway limited the cardioprotective effect of post-conditioning in hearts with apical myocardial infarction

Reperfusion damage involves opening of the mitochondrial permeability transition pore (mPTP) and loss of ATP synthesis. Several cardioprotective pathways are activated by ischemic or pharmacological post-conditioning (PC). The mechanisms that are activated by PC in no co-morbidity murine models include: activation of rescue kinases, oxidative stress reduction, glycolytic flux regulation and preservation of ATP synthesis. However, relatively scarce efforts have been made to define whether the efficacy of PC signaling is blunted by risk factors or systemic diseases associated with ischemic heart pathology. Experimental evidence has shown that the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling is a main mechanism activated by PC in hearts without pathological history. In this work we evaluated the participation of the NO pathway, through downstream kinase activation and inhibition of mPTP in hearts with previous infarct. Myocardial infarction was induced with a single dose of isoproterenol (85 mg/kg i.p.) to male Wistar rats. After 24 h, the hearts were mounted into the Langendorff system and subjected to 30 min of ischemia and 60 min of reperfusion. PC consisted of 5 cycles of 30 s of reperfusion/30 s of ischemia, then the hearts were reperfused with or without inhibitors of the NO/cGMP pathway. PC activates the NO/cGMP pathway, as increased cGMP and NO levels were detected in isoproterenol-treated hearts. The cardioprotective effect of PC was abolished with both L-NAME (inhibitor of constitutive NO synthase) and ODQ (inhibitor of soluble guanylate cyclase), whereas the NO donor (DETA-NO) restored cardioprotection even in the presence of L-NAME or ODQ. We also found that mitochondrial structure and function was preserved in PC hearts. We conclude that PC exerts cardioprotection in hearts with previous infarct by maintaining mitochondrial structure and function through NO-dependent pathway.

Chromofungin, CgA47-66-derived peptide, produces basal cardiac effects and postconditioning cardioprotective action during ischemia/reperfusion injury

Endogenous chromogranin A (CgA)-derived peptides are secreted by nervous, endocrine and immune cells. Chromofungin (Chr: CgA47-66) is one of these peptides that display antimicrobial activities and activate neutrophils, with important implications in inflammation and innate immunity. The aim of the present study is to examine the effects of Chr on isolated and Langendorff perfused rat hearts. The study was performed by using the isolated and Langendorff perfused rat hearts, Elisa assay and real-time PCR. We found that, under basal conditions, increasing doses (11-165nM) of Chr induced negative inotropic effects without changing coronary pressure. This action was mediated by the AKT/eNOS/cGMP/PKG pathway. We also found that Chr acted as a postconditioning (PostC) agent against ischemia/reperfusion (I/R) damages, reducing infarct size and LDH level. Cardioprotection involved PI3K, RISK pathway, MitoKATP and miRNA-21. We suggest that Chr directly affects heart performance, protects against I/R myocardial injuries through the activation of prosurvival kinases. Results may propose Chr as a new physiological neuroendocrine modulator able to prevent heart dysfunctions, also encouraging the clarification of its clinical potential.

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.

Rapid ventricular pacing-induced postconditioning attenuates reperfusion injury: effects on peroxynitrite, RISK and SAFE pathways

BACKGROUND AND PURPOSE

Rapid ventricular pacing (RVP) applied before an index ischaemia has anti-ischaemic effects. Here, we investigated whether RVP applied after index ischaemia attenuates reperfusion injury and whether peroxynitrite, reperfusion injury salvage kinase (RISK) and survival activating factor enhancement (SAFE) pathways as well as haem oxygenase 1 (HO1) are involved in the mechanism of RVP-induced postconditioning.

EXPERIMENTAL APPROACH

Langendorff perfused rat hearts were subjected to 30 min regional ischaemia and 120 min reperfusion with or without ischaemic postconditioning (6 × 10/10 s reperfusion/ischaemia; IPost) or RVP (6 × 10/10 s non-pacing/rapid pacing at 600 bpm) applied at the onset of reperfusion.

KEY RESULTS

Meta-analysis of our previous studies revealed an association between longer reperfusion-induced ventricular tachycardia/fibrillation with decreased infarct size. In the present experiments, we tested whether RVP is cardioprotective and found that both IPost and RVP significantly decreased infarct size; however, only RVP attenuated the incidence of reperfusion-induced ventricular tachycardia. Both postconditioning methods increased the formation of cardiac 3-nitrotyrosine and superoxide, and non-significantly enhanced Akt phosphorylation at the beginning of reperfusion without affecting ERK1/2 and STAT3, while IPost alone induced HO1. Application of brief ischaemia/reperfusion cycles or RVP without preceding index ischaemia also facilitated peroxynitrite formation; nevertheless, only brief RVP increased STAT3 phosphorylation.

CONCLUSIONS AND IMPLICATIONS

Short periods of RVP at the onset of reperfusion are cardioprotective and increase peroxynitrite formation similarly to IPost and thus may serve as an alternative postconditioning method. However, downstream mechanisms of the protection elicited by IPost and RVP seem to be partially different.

LINKED ARTICLES

This article is part of a themed section on Conditioning the Heart - Pathways to Translation. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-8.

Cardiac and hepatic role of r-AtHSP70: basal effects and protection against ischemic and sepsis conditions

Heat shock proteins (HSPs), highly conserved in all organisms, act as molecular chaperones activated by several stresses. The HSP70 class of stress-induced proteins is the most studied subtype in cardiovascular and inflammatory disease. Because of the high similarity between plant and mammalian HSP70, the aim of this work was to evaluate whether recombinant HSP70 of plant origin (r-AtHSP70) was able to protect rat cardiac and hepatic function under ischemic and sepsis conditions. We demonstrated for the first time that, in ex vivo isolated and perfused rat heart, exogenous r-AtHSP70 exerted direct negative inotropic and lusitropic effects via Akt/endothelial nitric oxide synthase pathway, induced post-conditioning cardioprotection via Reperfusion Injury Salvage Kinase and Survivor Activating Factor Enhancement pathways, and did not cause hepatic damage. In vivo administration of r-AtHSP70 protected both heart and liver against lipopolysaccharide-dependent sepsis, as revealed by the reduced plasma levels of interleukin-1β, tumour necrosis factor alpha, aspartate aminotransferase and alanine aminotransferase. These results suggest exogenous r-AtHSP70 as a molecular modulator able to protect myocardial function and to prevent cardiac and liver dysfunctions during inflammatory conditions.

Molecular basis of cardioprotection: signal transduction in ischemic pre-, post-, and remote conditioning

Reperfusion is mandatory to salvage ischemic myocardium from infarction, but reperfusion per se contributes to injury and ultimate infarct size. Therefore, cardioprotection beyond that by timely reperfusion is needed to reduce infarct size and improve the prognosis of patients with acute myocardial infarction. The conditioning phenomena provide such cardioprotection, insofar as brief episodes of coronary occlusion/reperfusion preceding (ischemic preconditioning) or following (ischemic postconditioning) sustained myocardial ischemia with reperfusion reduce infarct size. Even ischemia/reperfusion in organs remote from the heart provides cardioprotection (remote ischemic conditioning). The present review characterizes the signal transduction underlying the conditioning phenomena, including their physical and chemical triggers, intracellular signal transduction, and effector mechanisms, notably in the mitochondria. Cardioprotective signal transduction appears as a highly concerted spatiotemporal program. Although the translation of ischemic postconditioning and remote ischemic conditioning protocols to patients with acute myocardial infarction has been fairly successful, the pharmacological recruitment of cardioprotective signaling has been largely disappointing to date.

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.

Postconditioning signalling in the heart: mechanisms and translatability

The protective effect of ischaemic postconditioning (short cycles of reperfusion and reocclusion of a previously occluded vessel) was identified over a decade ago commanding intense interest as an approach for modifying reperfusion injury which contributes to infarct size in acute myocardial infarction. Elucidation of the major mechanisms of postconditioning has identified potential pharmacological targets for limitation of reperfusion injury. These include ligands for membrane-associated receptors, activators of phosphokinase survival signalling pathways and inhibitors of the mitochondrial permeability transition pore. In experimental models, numerous agents that target these mechanisms have shown promise as postconditioning mimetics. Nevertheless, clinical studies of ischaemic postconditioning and pharmacological postconditioning mimetics are equivocal. The majority of experimental research is conducted in animal models which do not fully portray the complexity of risk factors and comorbidities with which patients present and which we now know modify the signalling pathways recruited in postconditioning. Cohort size and power, patient selection, and deficiencies in clinical infarct size estimation may all represent major obstacles to assessing the therapeutic efficacy of postconditioning. Furthermore, chronic treatment of these patients with drugs like ACE inhibitors, statins and nitrates may modify signalling, inhibiting the protective effect of postconditioning mimetics, or conversely induce a maximally protected state wherein no further benefit can be demonstrated. Arguably, successful translation of postconditioning cannot occur until all of these issues are addressed, that is, experimental investigation requires more complex models that better reflect the clinical setting, while clinical investigation requires bigger trials with appropriate patient selection and standardization of clinical infarct size measurements.

Post-conditioning with gradually increased reperfusion provides better cardioprotection in rats

BACKGROUND

Rapid and complete reperfusion has been widely adopted in the treatment of patients with acute myocardial infarction (AMI), but this process sometimes can cause severe reperfusion injury. This study aimed to investigate different patterns of post-conditioning in acute myocardial ischemia-reperfusion injury, and to detect the role of mitogen activated protein kinase (MAPK) during the injury.

METHODS

RATS WERE RANDOMLY DIVIDED INTO FIVE GROUPS: sham group, reperfusion injury (R/ I) group, gradually decreased reperfusion group (GDR group, 30/10-25/15-15/25-10/30 seconds of reperfusion/ischemia), equal reperfusion group (ER group, 20/20 seconds reperfusion/ischemia, 4 cycles), and gradually increased reperfusion group (GIR group, 10/30-15/25-25/15-30/10 seconds of reperfusion/ischemia). Acute myocardial infarction and ischemic post-conditioning models were established in the rats. Six hours after reperfusion, 3 rats from each group were sacrificed and myocardial tissues were taken to measure the expressions of phosphorylation of extracellular signal-regulated protein kinase (P-ERK), phosphorylated c-Jun N-terminal kinase (P-JNK), mitogen-activated protein kinase p38 (p38 MAPK), tumor necrosis factor-α (TNF-α), caspases-8 in the myocardial tissue, and cytochrome c in the cytosol using Western blot. Hemodynamics was measured at 24 hours after reperfusion, the blood was drawn for the determination of cardiac enzymes, and the heart tissue was collected for the measurement of apoptosis using TUNEL. One-way analysis of variance and the Q test were employed to determine differences in individual variables between the 5 groups.

RESULTS

Three post-conditioning patterns were found to provide cardioprotection (P<0.05) compared with R/I without postconditioning. GIR provided the best cardioprotection effect, followed by ER and then GDR. Apoptotic index and serum marker levels were reduced more significantly in GIR than in ER (P<0.05). The enhanced cardioprotection provided by GIR was accompanied with significantly increased levels of P-ERK 1/2 (1.82±0.22 vs. 1.54±0.32, P<0.05), and lower levels of p-JNK, p38 MAPK, TNF-α, caspase-8, caspase-9 and cytochrome in the cytoplasm (P<0.05), compared with ER. The infarct size was smaller in the GIR group than in the ER group, but this difference was not significant (16.30%±5.22% vs. 20.57%±6.32%, P<0.05). All the measured variables were improved more significantly in the GIR group than in the GDR group (P<0.05).

CONCLUSION

Gradually increased reperfusion in post-conditioning could attenuate reperfusion injury more significantly than routine method, thereby the MAPK pathway plays an important role in this process.

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.

Effects of acute and chronic atorvastatin on cardioprotection of ischemic postconditioning in isolated rat hearts

BACKGROUND

Myocardial reperfusion therapy remains the most effective strategy to limit infarct size and improve clinical outcome. However, reperfusion injury is still inevitable, and a number of strategies have been developed to ameliorate its lethal outcome. The beneficial roles of ischemic postconditioning (Ipost) have regained more interest in targeting myocardial reperfusion phase to improve cardioprotection.

AIMS

This study was to determine whether acute or chronic treatment with atorvastatin affects cardioprotection when it was combined with Ipost.

RESULTS

Acute or chronic atorvastatin treatment significantly reduced infarct size and recovered contractile dysfunction during reperfusion. When Ipost was combined with atorvastatin treatment, chronic, but not acute, atorvastatin therapy attenuated the cardioprotective effects of Ipost. Chronic, but not acute, atorvastatin treatment also abolished Ipost-induced phosphorylation level of Akt and endothelial nitric oxide synthase (eNOS).

CONCLUSIONS

Chronic atorvastatin treatment could interfere with cardioprotective effects of Ipost on limiting infarct size and contractile dysfunction, possibly via inhibition of Akt and eNOS activity. This study suggests that Ipost should be used carefully when atorvastatin is taken by patients with AMI.

Coronary effluent from postconditioned hearts promotes survival of mesenchymal stem cells under hypoxia

OBJECTIVES

Mesenchymal stem cells are sensitive to hypoxia under myocardial micro-environment of ischemia and reperfusion. Ischemic postconditioning, which is cardioprotective against ischemia-reperfusion injury, enhances in-vivo survival and therapeutic effects of transplanted stem cells. In this study, we investigated the effects of coronary effluent from postconditioned rat hearts on proliferation and survival of mesenchymal stem cells in vitro under hypoxia.

DESIGN

Isolated perfused rat hearts were divided into three groups (n = 6): the Sham group--receiving a 90 min perfusion; the Control group--receiving a 30 min global ischemia followed by a 60 min reperfusion; the ischemic postconditioning group--before sustained reperfusion, 3 cycles of 30 s reperfusion and 30 s ischemia were performed. Inflammation-related factors in coronary effluent were assessed by ELISA. Mesenchymal stem cells from bone marrow of Sprague-Dawley rats were cultured with coronary effluent under hypoxia (95% nitrogen, 5% carbon dioxide, and < 1% oxygen) for 6- or 18 h. Cell proliferation was determined by methyl thiazolyl tetrazolium. Survival rate was measured by Annexin V/PI.

RESULTS

Compared with ischemia-reperfusion treatment alone, postconditioning treatment increased the level of interleukin-10 and decreased the level of tumor necrosis factor-α and interleukin-1β in coronary effluent (P < 0.01). Stem cells cultured with postconditioned effluent, compared with those with ischemia-reperfusion effluent, had a higher proliferation (optical density value), more surviving cells, and less necrosis (P < 0.01).

CONCLUSIONS

Coronary effluent from postconditioned hearts may promote the proliferation and survival of mesenchymal stem cells under hypoxia, and the suppression of inflammation may be involved in this process.

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.

Frequent biomarker analysis in the isolated perfused heart reveals two distinct phases of reperfusion injury

BACKGROUND

Reperfusion injury and its modulation are incompletely characterized. The purpose of the present study was to characterize the dynamics of reperfusion injury by portraying the temporal release of lactate dehydrogenase (LDH) during ischemia-reperfusion injury in an isolated heart model.

METHODS

We studied infarct size and LDH release in the following groups: I) Effect of reperfusion length was evaluated in 79 rats subjected to 40 minute ischemia and 60, 90, 120 or 180 minute reperfusion and a) ischemic preconditioning (IPC) or b) No IPC (control). II) LDH release kinetics was studied in 6 rats subjected to calcium-paradox to verify the applicability of LDH as a dynamic marker of cellular injury. III) Ischemia-reperfusion injury modification was studied in 36 rats subjected to: a) ischemic postconditioning, b) prolonged ischemia, c) Reperfusion Injury Salvage Kinase (RISK) pathway inhibition with wortmannin in IPC hearts, d) RISK activation with insulin or e) mitochondrial permeability transition pore (mPTP) inhibition with cyclosporine A.

RESULTS

Infarct size increased from 60 to 180 minute reperfusion in control hearts. LDH was released in two separate peaks from 2 to 20 and 30 to 120 min of reperfusion. IPC attenuated both peaks. Postconditioning and agents known to modify reperfusion injury attenuated the second peak.

CONCLUSIONS

Frequent measurement of myocardial ischemia markers for 120 min of reperfusion allows identification of two phases of reperfusion injury that are affected by cardioprotective stimuli. The second phase contributes significantly to final infarct size, which is modifiable and a potential target for cardioprotective interventions.

An improved postconditioning algorithm: gradually increased reperfusion provides improved cardioprotection in rats

The aim of the present study was to investigate whether a gradually increasing reperfusion algorithm, in which the brief reperfusion was lengthened as the duration of each reperfusion/reocclusion cycle remained fixed, enhances cardioprotection. Rats were randomized into 5 groups: the sham, reperfusion injury (R/I), gradually decreased reperfusion (GDR; 30/10‑25/15‑15/25‑10/30 sec of reperfusion/reocclusion), equal reperfusion (ER; 4 20/20‑sec reperfusion/reocclusion cycles) and gradually increased reperfusion (GIR; 10/30‑15/25‑25/15‑30/10 sec of reperfusion/reocclusion). The rats were sacrificed to measure serum markers, apoptotic indices and infarct size. Western blot analyses were used to analyze the expression of molecules involved in important signaling pathways. All the three postconditioning patterns were found to provide cardioprotection (P<0.05 compared with the R/I group). GIR provided optimum cardioprotection, followed by ER and then GDR. Apoptotic index and serum marker levels were significantly reduced in the GIR compared with the ER group (P<0.05). The enhanced cardioprotection provided by GIR was accompanied by significantly increased levels of extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and Bcl‑2, as well as lower levels of p38/c‑Jun N‑terminal kinase (JNK) phosphorylation, tumor necrosis factor α (TNFα), caspase‑8, Bax, caspase‑9 and cytochrome c (Cyt‑c) in the cytoplasm of rats (P<0.05, all compared with ER). The infarct size in the rats of the GIR group was also smaller compared with that in the rats of the ER group, but this difference was not significant (16.30±5.22 vs. 20.57±6.32%, P>0.05). All the variables measured in the present study were significantly improved in the GIR group compared with the GDR group (P<0.05). In conclusion, the association between brief reperfusion and reocclusion is an important factor in postconditioning algorithms. Additionally, GIR results in improved cardioprotection compared with that achieved by the remaining algorithms examined.

High plasma concentrations of asymmetric dimethylarginine inhibit ischemic cardioprotection in hypercholesterolemic rats

A low concentration of nitric oxide associated with a high concentration of asymmetric dimethylarginine (ADMA) can explain the lack of ischemic cardioprotection observed in the presence of hypercholesterolemia. The objective of the present study was to evaluate the effect of hypercholesterolemia on ischemic pre- and postconditioning and its correlation with plasma concentrations of ADMA. Male Wistar rats (6-8 weeks old) fed a 2% cholesterol diet (n = 21) for 8 weeks were compared to controls (n = 25) and were subjected to experimental myocardial infarction and reperfusion, with ischemic pre- and postconditioning. Total cholesterol and ADMA were measured in plasma before the experimental infarct and the infarct area was quantified. Weight, total cholesterol and plasma ADMA (means ± SE; 1.20 ± 0.06, 1.27 ± 0.08 and 1.20 ± 0.08 vs 0.97 ± 0.04, 0.93 ± 0.05 and 0.97 ± 0.04 µM) were higher in animals on the hypercholesterolemic diet than in controls, respectively. Cardioprotection did not reduce infarct size in the hypercholesterolemic animals (pre: 13.55% and post: 8% compared to 7.95% observed in the group subjected only to ischemia and reperfusion), whereas infarct size was reduced in the animals on a normocholesterolemic diet (pre: 8.25% and post: 6.10% compared to 12.31%). Hypercholesterolemia elevated ADMA and eliminated the cardioprotective effects of ischemic pre- and postconditioning in rats.

Protection through postconditioning or a mitochondria-targeted S-nitrosothiol is unaffected by cardiomyocyte-selective ablation of protein kinase G

Protein kinase G type I (PKGI) plays a critical role in survival signaling of pre- and postconditioning downstream of cardiac cGMP. However, it is unclear whether PKGI exerts its protective effects in the cardiomyocyte or if other cardiac cell types are involved, and whether nitric oxide (NO) metabolism can target cardiomyocyte mitochondria independently of cGMP/PKGI. We tested whether protection against reperfusion injury by ischemic postconditioning (IPost), soluble guanylyl cyclase (sGC) activation and inhibition, adenosine A(2B) receptor (A(2B)AR) agonist, phosphodiesterase type-5 (PDE-5) inhibitor, or mitochondria-targeted S-nitrosothiol (MitoSNO) was affected by a cardiomyocyte-specific ablation of the PKGI gene in the mouse (CMG-KO). In situ hearts underwent 30 min of regional ischemia followed by 2 h of reperfusion. As expected, in CMG-CTRs all interventions at early reperfusion lead to profound infarct size reduction: IPost (six cycles of 10-s reperfusion and 10-s coronary occlusion) with or without treatment with the sGC inhibitor ODQ, treatment with the specific sGC activator BAY58-2667 (BAY58), the selective A(2B)AR agonist BAY60-6583 (BAY60), PDE-5 inhibitor sildenafil, and MitoSNO. MitoSNO accumulates within mitochondria, driven by the membrane potential, where it generates NO· and S-nitrosates thiol proteins. In contrast, the hearts of CMG-KO animals were not protected by BAY58 and sildenafil, whereas the protective effects of IPost, IPost with ODQ, BAY60, and MitoSNO were unaffected by the lack of PKGI. Taken together, PKGI is important for the protection against ischemia reperfusion injury afforded by sGC activation or PDE-5 inhibition. However, the beneficial effects of IPost, activation of the A(2B)AR, as well as the direct effects via mitochondrial S-nitrosation do not depend on PKGI in cardiomyocytes.

Mitochondrial pathways, permeability transition pore, and redox signaling in cardioprotection: therapeutic implications

Reperfusion therapy is the indispensable treatment of acute myocardial infarction (AMI) and must be applied as soon as possible to attenuate the ischemic insult. However, reperfusion is responsible for additional myocardial damage likely involving opening of the mitochondrial permeability transition pore (mPTP). A great part of reperfusion injury occurs during the first minute of reperfusion. The prolonged opening of mPTP is considered one of the endpoints of the cascade to myocardial damage, causing loss of cardiomyocyte function and viability. Opening of mPTP and the consequent oxidative stress due to reactive oxygen and nitrogen species (ROS/RNS) are considered among the major mechanisms of mitochondrial and myocardial dysfunction. Kinases and mitochondrial components constitute an intricate network of signaling molecules and mitochondrial proteins, which interact in response to stressors. Cardioprotective pathways are activated by stimuli such as preconditioning and postconditioning (PostC), obtained with brief intermittent ischemia or with pharmacological agents, which drastically reduce the lethal ischemia/reperfusion injury. The protective pathways converging on mitochondria may preserve their function. Protection involves kinases, adenosine triphosphate-dependent potassium channels, ROS signaling, and the mPTP modulation. Some clinical studies using ischemic PostC during angioplasty support its protective effects, and an interesting alternative is pharmacological PostC. In fact, the mPTP desensitizer, cyclosporine A, has been shown to induce appreciable protections in AMI patients. Several factors and comorbidities that might interfere with cardioprotective signaling are considered. Hence, treatments adapted to the characteristics of the patient (i.e., phenotype oriented) might be feasible in the future.

Pharmacologically active microcarriers influence VEGF-A effects on mesenchymal stem cell survival

Resistance of transplanted mesenchymal stem cells (MSCs) in post-ischemic heart is limited by their poor vitality. Vascular-endothelial-growth-factor-A (VEGF-A) as such or slowly released by fibronectin-coated pharmacologically-active-microcarriers (FN-PAM-VEGF) could differently affect survival kinases and anti-apoptotic mediator (e.g. Bcl-2). Therefore VEGF-A or FN-PAM-VEGF could differently enhance cell proliferation, and/or resistance to hypoxia/reoxygenation (H/R) of MSCs. To test these hypotheses MSCs were incubated for 6-days with VEGF-A alone or with FN-PAM-VEGF. In addition, MSCs pre-treated for 24-hrs with VEGF-A or FN-PAM-VEGF were subsequently exposed to H/R (72-hrs 3% O₂ and 3-hrs of reoxygenation). Cell-proliferation and post-hypoxic vitality were determined. Kinases were studied at 30-min., 1- and 3-days of treatment. Cell-proliferation increased about twofold (P < 0.01) 6-days after VEGF-A treatment, but by a lesser extent (55% increase) with FN-PAM-VEGF (P < 0.05). While MSC pre-treatment with VEGF-A confirmed cell-proliferation, pre-treatment with FN-PAM-VEGF protected MSCs against H/R. In the early phase of treatments, VEGF-A increased phospho-Akt, phospho-ERK-1/2 and phospho-PKCε compared to the untreated cells or FN-PAM-VEGF. Afterword, kinase phosphorylations were higher with VGEF, except for ERK-1/2, which was similarly increased by both treatments at 3 days. Only FN-PAM-VEGF significantly increased Bcl-2 levels. After H/R, lactate dehydrogenase release and cleaved Caspase-3 levels were mainly reduced by FN-PAM-VEGF. While VEGF-A enhances MSC proliferation in normoxia, FN-PAM-VEGF mainly hampers post-hypoxic MSC death. These different effects underscore the necessity of approaches suited to the various conditions. The use of FN-PAM-VEGF could be considered as a novel approach for enhancing MSC survival and regeneration in hostile environment of post-ischemic tissues.

Acidic infusion in early reperfusion affects the activity of antioxidant enzymes in postischemic isolated rat heart

BACKGROUND

Acidic perfusion (AP) performed at the onset of reperfusion (i.e., acid postconditioning) is cardioprotective. We investigated the effect of AP on postischemic cardiac function and on the activity of endogenous superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase. The role of exogenous CAT or SOD on AP cardioprotection was also investigated. Phosphorylation of redox-sensitive survival kinases (protein kinase C [PKC] ε and extracellular signal-regulated kinase [ERK] 1/2) was also checked.

MATERIALS AND METHODS

Isolated rat hearts underwent ischemia and reperfusion (I/R) for 30 and 120 min, respectively. AP was obtained by lowering [HCO3(-)] in the perfusion buffer. Infarct size and left ventricular pressure were measured. Protocols include I/R only, I/R plus acidic perfusion in early reperfusion (I/R + AP), and I/R plus AP and CAT (I/R + AP + CAT) or SOD (I/R + AP + SOD). I/R + SOD and I/R + CAT additional hearts served as controls. AP and/or antioxidants were given in the initial 3 min of reperfusion. Enzyme activities were studied in postischemic phase (seventh minute of reperfusion) in I/R or I/R + AP and Sham (buffer-perfused) hearts.

RESULTS

AP with (I/R + AP + CAT or I/R + AP + SOD) or without (I/R + AP) antioxidant enzymes resulted in a larger reduction of infarct size compared with I/R, I/R + SOD, or I/R + CAT. Compared with I/R, the postischemic systolic and diastolic recoveries of the cardiac function were markedly improved by the addition of AP and a lesser extent by AP + SOD or AP + CAT. AP increased the postischemic activity of CAT and lowered that of SOD and glutathione peroxidase compared with I/R only. Also, the phosphorylation and activity of ERK1/2 and PKCε were increased by AP.

CONCLUSIONS

Acid postconditioning affects the activity of endogenous antioxidant enzymes, activates ERK1/2-PKCε pathways, and protects against myocardial I/R injury. The combination of AP and exogenous SOD or CAT still provides cardioprotection. It is likely that intracellular (not extracellular) redox condition plays a pivotal role in acidic protection.

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.

Essential role of nitric oxide in acute ischemic preconditioning: S-nitros(yl)ation versus sGC/cGMP/PKG signaling?

Nitric oxide (NO) plays an important role in acute ischemic preconditioning (IPC). In addition to activating soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) signaling pathways, NO-mediated protein S-nitros(yl)ation (SNO) has been recently shown to play an essential role in cardioprotection against ischemia-reperfusion (I/R) injury. In our previous studies, we have shown that IPC-induced cardioprotection could be blocked by treatment with either N-nitro-L-arginine methyl ester (L-NAME, a constitutive NO synthase inhibitor) or ascorbate (a reducing agent to decompose SNO). To clarify NO-mediated sGC/cGMP/PKG-dependent or -independent (i.e., SNO) signaling involved in IPC-induced cardioprotection, mouse hearts were Langendorff-perfused in the dark to prevent SNO decomposition by light exposure. Treatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, a highly selective inhibitor of sGC) or KT5823 (a potent and selective inhibitor of PKG) did not abolish IPC-induced acute protection, suggesting that the sGC/cGMP/PKG signaling pathway does not play an important role in NO-mediated cardioprotective signaling during acute IPC. In addition, treatment with ODQ in IPC hearts provided an additional protective effect on functional recovery, in parallel with a higher SNO level in these ODQ+IPC hearts. In conclusion, these results suggest that the protective effect of NO is not related primarily to activation of the sGC/cGMP/PKG signaling pathway, but rather through SNO signaling in IPC-induced acute cardioprotection.

Mitochondria: A mirror into cellular dysfunction in heart disease

Cardiovascular (CV) disease is the single most significant cause of morbidity and mortality worldwide. The emerging global impact of CV disease means that the goals of early diagnosis and a wider range of treatment options are now increasingly pertinent. As such, there is a greater need to understand the molecular mechanisms involved and potential targets for intervention. Mitochondrial function is important for physiological maintenance of the cell, and when this function is altered, the cell can begin to suffer. Given the broad range and significant impacts of the cellular processes regulated by the mitochondria, it becomes important to understand the roles of the proteins associated with this organelle. Proteomic investigations of the mitochondria are hampered by the intrinsic properties of the organelle, including hydrophobic mitochondrial membranes; high proportion of basic proteins (pI greater than 8.0); and the relative dynamic range issues of the mitochondria. For these reasons, many proteomic studies investigate the mitochondria as a discrete subproteome. Once this has been achieved, the alterations that result in functional changes with CV disease can be observed. Those alterations that lead to changes in mitochondrial function, signaling and morphology, which have significant implications for the cardiomyocyte in the development of CV disease, are discussed.

Mitochondrial K+ channels are involved in ischemic postconditioning in rat hearts

The mitochondrial calcium-activated potassium channel (mitoK(Ca)) and the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) are both involved in cardiac preconditioning. Here, we examined whether these two channels are also involved in ischemic or pharmacological postconditioning. Using Langendorff perfusion, rat hearts were made hypoxic for 45 min and then reoxygenated for 30 min. Ischemic postconditioning (IPT) was achieved through application of 3 cycles of 10 s of reperfusion and 10 s of ischemia before reoxygenation, with and without paxilline (Pax; a mitoK(Ca) blocker) or 5-hydroxydecanoate (5-HD; a mitoK(ATP) blocker). Pharmacological postconditioning was carried out for 5 min at the onset of reoxygenation using NS1619 (a mitoK(Ca) opener) or diazoxide (Dia; a mitoK(ATP) opener). Pax and 5-HD abolished IPT-induced cardioprotection from reoxygenation injury, whereas administration of NS1619 or Dia significantly improved cardiac contractile activity and reduced aspartate aminotransferase (an index of myocyte injury) release following reoxygenation. In addition, isolated rat myocytes were loaded with tetramethylrhodamine methyl ester (TMRE; fluorescent mitochondrial membrane potential indicator) and 2',7'-dichlorofluorescein [DCFH; fluorescent reactive oxygen species (ROS) indicator] or Fluo-4-acetoxymethyl ester (Fluo-4-AM; fluorescent calcium indicator). When TMRE-loaded myocytes were laser illuminated, the DCFH and Fluo-4 fluorescence increased, and TMRE fluorescence decreased. These effects were significantly inhibited by NS1619 and Dia. We therefore conclude that IPT may protect the heart through activation of mitoK(ATP) and mitoK(Ca) channels, and that opening of these channels at the onset of reoxygenation protects the heart from reoxygenation injury, most likely by reducing excess generation of ROS and the resultant Ca(2+) overload.