Progression in attenuating myocardial reperfusion injury: An overview

New advances in the protective mechanisms of acidic pH after ischemia: Participation of NO

BACKGROUND

It has been previously demonstrated that the maintenance of ischemic acidic pH or the delay of intracellular pH recovery at the onset of reperfusion decreases ischemic-induced cardiomyocyte death.

OBJECTIVE

To examine the role played by nitric oxide synthase (NOS)/NO-dependent pathways in the effects of acidic reperfusion in a regional ischemia model.

METHODS

Isolated rat hearts perfused by Langendorff technique were submitted to 40 min of left coronary artery occlusion followed by 60 min of reperfusion (IC). A group of hearts received an acid solution (pH = 6.4) during the first 2 min of reperfusion (AR) in absence or in presence of l-NAME (NOS inhibitor). Infarct size (IS) and myocardial function were determined. In cardiac homogenates, the expression of P-Akt, P-endothelial and inducible isoforms of NOS (P-eNOS and iNOS) and the level of 3-nitrotyrosine were measured. In isolated cardiomyocytes, the intracellular NO production was assessed by confocal microscopy, under control and acidic conditions. Mitochondrial swelling after Ca2+ addition and mitochondrial membrane potential (Δψ) were also determined under control and acidosis.

RESULTS

AR decreased IS, improved postischemic myocardial function recovery, increased P-Akt and P-eNOS, and decreased iNOS and 3-nitrotyrosine. NO production increased while mitochondrial swelling and Δψ decreased in acidic conditions. l-NAME prevented the beneficial effects of AR.

CONCLUSIONS

Our data strongly supports that a brief acidic reperfusion protects the myocardium against the ischemia-reperfusion injury through eNOS/NO-dependent pathways.

The low expression of miR-155 promotes the expression of SHP2 by inhibiting the activation of the ERK1/2 pathway and improves cell pyroptosis induced by I/R in mice

This study aims to explore the specific mechanism by which miR-155 regulates SHP2 expression in mouse ischemia-reperfusion (I/R) induced necroptosis. Various methods including cardiac ultrasound, TTC staining, Masson staining, TUNEL staining, and Western blotting were used to examine changes in the morphology and function of the rat left ventricle, myocardial fibrosis, as well as the expression of proteins related to tissue and cardiomyocyte necroptosis pathways. In vivo results showed that knockdown (KD) of miR-155 significantly improved cardiac ultrasound parameters (EF, FS, LVAW;d, and LVAW;s), reduced the myocardial infarction area, myocardial fibrosis, and cell apoptosis in I/R mice, upregulated cardiac SHP2 protein expression, and other proteins including p-ERK1/2, NLRP3, GSDMD, caspase-3, caspase-4, and caspase-11 were also significantly decreased. In vitro experiments showed that compared with the SHP2 WT miR-155 KD group, SHP2 protein expression was significantly increased in the SHP2 WT miR-155 KD group, while the expression of other proteins was significantly reduced, consistent with in vivo results. MiR-155 can regulate ERK1/2 and NLRP3 through SHP2. After adding the ERK1/2 inhibitor U0126 to cardiomyocytes from SHP2 KO mice, it was found that the expression of proteins other than SHP2 significantly decreased compared to SHP2 KO cells without the inhibitor. In summary, low expression of miR-155 promoted the expression of SHP2 and improved mouse I/R-induced necroptosis by inhibiting the activation of the ERK1/2 pathway.

Trehalose Alleviates Myocardial Ischemia/Reperfusion Injury by Inhibiting NLRP3-Mediated Pyroptosis

Myocardial ischemia/reperfusion (I/R) injury is a pathological damage secondary to myocardial ischemia that can further aggravate tissue and organ injuries. Therefore, there is an urgent need to develop an effective approach for alleviating myocardial I/R injury. Trehalose (TRE) is a natural bioactive substance that has been shown to have extensive physiological effects in various animals and plants. However, TRE's protective effects against myocardial I/R injury remain unclear. This study aimed to evaluate the protective effect of TRE pre-treatment in mice with acute myocardial I/R injury and to explore the role of pyroptosis in this process. Mice were pre-treated with trehalose (1 mg/g) or an equivalent amount of saline solution for 7 days. The left anterior descending coronary artery was ligated in mice from the I/R and I/R + TRE groups, followed by 2-h or 24-h reperfusion after 30 min. Transthoracic echocardiography was performed to assess cardiac function in mice. Serum and cardiac tissue samples were obtained to examine the relevant indicators. We established an oxygen-glucose deprivation and re-oxygenation model in neonatal mouse ventricular cardiomyocytes and validated the mechanism by which trehalose affects myocardial necrosis via overexpression or silencing of NLRP3. TRE pre-treatment significantly improved cardiac dysfunction and reduced the infarct size in mice after I/R, accompanied by a decrease in the I/R-induced levels of CK-MB, cTnT, LDH, reactive oxygen species, pro-IL-1β, pro-IL-18, and TUNEL-positive cells. Furthermore, TRE intervention suppressed the expression of pyroptosis-related proteins following I/R. TRE attenuates myocardial I/R injury in mice by inhibiting NLRP3-mediated caspase-1-dependent pyroptosis in cardiomyocytes.

SIRT1 is a regulator of autophagy: Implications for the progression and treatment of myocardial ischemia-reperfusion

SIRT1 is a highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase. It is involved in the regulation of various pathophysiological processes, including cell proliferation, survival, differentiation, autophagy, and oxidative stress. Therapeutic activation of SIRT1 protects the heart and cardiomyocytes from pathology-related stress, particularly myocardial ischemia/reperfusion (I/R). Autophagy is an important metabolic pathway for cell survival during energy or nutrient deficiency, hypoxia, or oxidative stress. Autophagy is a double-edged sword in myocardial I/R injury. The activation of autophagy during the ischemic phase removes excess metabolic waste and helps ensure cardiomyocyte survival, whereas excessive autophagy during reperfusion depletes the cellular components and leads to autophagic cell death. Increasing research on I/R injury has indicated that SIRT1 is involved in the process of autophagy and regulates myocardial I/R. SIRT1 regulates autophagy through various pathways, such as the deacetylation of FOXOs, ATGs, and LC3. Recent studies have confirmed that SIRT1-mediated autophagy plays different roles at different stages of myocardial I/R injury. By targeting the mechanism of SIRT1-mediated autophagy at different stages of I/R injury, new small-molecule drugs, miRNA activators, or blockers can be developed. For example, resveratrol, sevoflurane, quercetin, and melatonin in the ischemic stage, coptisine, curcumin, berberine, and some miRNAs during reperfusion, were involved in regulating the SIRT1-autophagy axis, exerting a cardioprotective effect. Here, we summarize the possible mechanisms of autophagy regulation by SIRT1 in myocardial I/R injury and the related molecular drug applications to identify strategies for treating myocardial I/R injury.

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.

Recent advances in nanomedicines for imaging and therapy of myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion injury (IRI) is becoming a typical cardiovascular disease with increasing worldwide incidence. It is usually induced by the restoration of normal blood flow to the ischemic myocardium after a period of recanalization and directly leads to myocardial damage. Notably, the pathological mechanism of myocardial IRI is closely related to inflammation, oxidative stress, Ca²⁺ overload, and the opening of mitochondrial permeability transition pore channels. Therefore, monitoring of these changes and imaging lesions is a key to timely clinical diagnosis. Nanomedicines have shown great value in the diagnosis and treatment of myocardial IRI, with advantages including passive/active targeting, prolonged circulation, improved bioavailability, versatile carrier selection, and synergistic integration of different imaging and therapeutic agents in single particles with the same pharmaceutics. Because theranostic nanomedicines for myocardial IRI have advanced rapidly, we conduct an updated review on this topic. The special focus is on how to rationally design the nanomedicines to achieve optimal imaging and therapy. We hope this review would stimulate the interest of researchers with different backgrounds and expedite the development of nanomedicines for myocardial IRI.

Ethyl pyruvate: A newly discovered compound against ischemia-reperfusion injury in multiple organs

Ischemia-reperfusion injury (IRI) is a process whereby an initial ischemia injury and subsequent recovery of blood flow, which leads to the propagation of an innate immune response and the changes of structural and functional of multiple organs. Therefore, IRI is considered to be a great challenge in clinical treatment such as organ transplantation or coronary angioplasty. In recent years, ethyl pyruvate (EP), a derivative of pyruvate, has received great attention because of its stability and low toxicity. Previous studies have proved that EP has various pharmacological activities, including anti-inflammation, anti-oxidative stress, anti-apoptosis, and anti-fibrosis. Compelling evidence has indicated EP plays a beneficial role in a variety of acute injury models, such as brain IRI, myocardial IRI, renal IRI, and hepatic IRI. Moreover, EP can not only effectively inhibit multiple IRI-induced pathological processes, but also improve the structural and functional lesion of tissues and organs. In this study, we review the recent progress in the research on EP and discuss their implications for a better understanding of multiple organ IRI, and the prospects of targeting the EP for therapeutic intervention.

Inhibiting miR-205 Alleviates Cardiac Ischemia/Reperfusion Injury by Regulating Oxidative Stress, Mitochondrial Function, and Apoptosis

BACKGROUND

miR-205 is important for oxidative stress, mitochondrial dysfunction, and apoptosis. The roles of miR-205 in cardiac ischemia/reperfusion (I/R) injury remain unknown. The aim of this research is to reveal whether miR-205 could regulate cardiac I/R injury by focusing upon the oxidative stress, mitochondrial function, and apoptosis.

METHODS

Levels of miR-205 and Rnd3 were examined in the hearts with I/R injury. Myocardial infarct size, cardiac function, oxidative stress, mitochondria function, and cardiomyocyte apoptosis were detected in mice with myocardial ischemia/reperfusion (MI/R) injury. The primary neonatal cardiomyocytes underwent hypoxia/reoxygenation (H/R) to simulate MI/R injury.

RESULTS

miR-205 levels were significantly elevated in cardiac tissues from I/R in comparison with those from Sham. In comparison with controls, levels of Rnd3 were significantly decreased in the hearts from mice with MI/R injury. Furthermore, inhibiting miR-205 alleviated MI/R-induced apoptosis, reduced infarct size, prevented oxidative stress increase and mitochondrial fragmentation, and improved mitochondrial functional capacity and cardiac function. Consistently, overexpression of miR-205 increased infarct size and promoted apoptosis, oxidative stress, and mitochondrial dysfunction in mice with MI/R injury. In cultured mouse neonatal cardiomyocytes, downregulation of miR-205 reduced oxidative stress in H/R-treated cardiomyocytes. Finally, inhibiting Rnd3 ablated the cardioprotective effects of miR-205 inhibitor in MI/R injury.

CONCLUSIONS

We conclude that inhibiting miR-205 reduces infarct size, improves cardiac function, and suppresses oxidative stress, mitochondrial dysfunction, and apoptosis by promoting Rnd3 in MI/R injury. miR-205 inhibitor-induced Rnd3 activation is a valid target to treat MI/R injury.

The electrogenic sodium bicarbonate cotransporter and its roles in the myocardial ischemia-reperfusion induced cardiac diseases

Cardiac tissue ischemia/hypoxia increases glycolysis and lactic acid accumulation in cardiomyocytes, leading to intracellular metabolic acidosis. Sodium bicarbonate cotransporters (NBCs) play a vital role in modulating intracellular pH and maintaining sodium ion concentrations in cardiomyocytes. Cardiomyocytes mainly express electrogenic sodium bicarbonate cotransporter (NBCe1), which has been demonstrated to participate in myocardial ischemia/reperfusion (I/R) injury. This review outlines the structural and functional properties of NBCe1, summarizes the signaling pathways and factors that may regulate the activity of NBCe1, and reviews the roles of NBCe1 in the pathogenesis of I/R-induced cardiac diseases. Further studies revealing the regulatory mechanisms of NBCe1 activity should provide novel therapeutic targets for preventing I/R-induced cardiac diseases.

Efficacy of Trimetazidine in Limiting Periprocedural Myocardial Injury in Patients Undergoing Percutaneous Coronary Intervention: A Systematic Review and Meta-Analysis

We systematically searched the literature to assess the efficacy of trimetazidine in reducing periprocedural myocardial injury and improving postoperative left ventricular ejection fraction (LVEF) in patients with coronary artery disease (CAD) undergoing percutaneous coronary intervention (PCI). An electronic search was conducted based on the PubMed, Ovid, Scopus, Springer, CENTRAL, and Google Scholar databases; 14 randomized controlled trials (RCTs) were included. Our meta-analysis showed a significant reduction in cardiac troponin I (cTnI) levels with trimetazidine compared with controls (P < .00001) but not in serum creatine kinase-myocardial band levels (P = .49). There were significantly reduced odds of ischemic ST-T segment changes with trimetazidine (P = .0.03) but lack of significant difference in the incidence of anginal attacks between the 2 groups (P = .10). Results also suggest significantly higher LVEF with trimetazidine compared with controls (P < .00001). Meta-regression analysis indicated no influence of duration of trimetazidine therapy on cTnI levels. The administration of preprocedure trimetazidine may have a role in reducing periprocedural myocardial injury in patients with CAD undergoing PCI. Evidence also suggests that postoperative trimetazidine may improve LVEF in the short term. Lack of high-quality trials and the heterogeneity of studies limit the ability of our analysis to draw strong conclusions. Further well-designed RCTs are required to supplement current evidence.

Mechanisms dissection of the combination GRS derived from ShengMai preparations for the treatment of myocardial ischemia/reperfusion injury

ETHNOPHARMACOLOGICAL RELEVANCE

Recently, a new drug combination GRS comprising ginsenoside Rb1 (G-Rb1), ruscogenin (R-Rus) and schisandrin (S-SA) was screened based on ShengMai preparations, which exhibited a prominent cardioprotective effects against myocardial ischemia/reperfusion (MI/R) injury.

AIM OF THE STUDY

To investigate their systemic and individual mechanism of each compound in combination GRS.

MATERIALS AND METHODS

The mice model of MI/R and hypoxia/reoxygenation (H/R)-induced cardiomyocytes injury were performed to explore the respective characteristics of each compound in GRS against myocardial injury.

RESULTS

Each component in the combination GRS attenuated MI/R injury as evidenced by decreased myocardial infarct size, ameliorated histological features, and improved biochemical indicators. Meanwhile, ingredient G, R and S in combination also individually performed a significant decrease of apoptotic index in MI/R mice and H/R-induced cardiomyocytes injury. Mechanistically, component G in GRS could markedly increase the ATP content in cardiomyocytes through activation of AMPKα phosphorylation. Interestingly, the anti-apoptotic actions of G were profoundly attenuated by knockdown of AMPKα, while no alteration was observed on composition R and S. Moreover, component R in GRS significantly reduced the IL-6 and TNF-α mRNA expression, as well as the content of IL-6 via the modulation of NF-κB signaling pathway. Further, component S exhibited the most powerful anti-oxidative capacity in GRS and remarkably decreased the production of MDA and ROS, and potential mechanisms might at least in part through activating the Akt-14-3-3 signaling pathway and inhibiting the phosphorylation of Bad and ERK1/2.

CONCLUSIONS

Our results indicated that the respective mechanism of each compound in combination GRS against MI/R injury might closely associated with energy metabolism modulation, suppression of inflammation and oxidative stress.

Protective effect of dimethyl fumarate on oxidative damage and signaling in cardiomyocytes

Myocardial ischemia/reperfusion (I/R) injury contributes to the pathogenesis of numerous diseases. Based on its antioxidant and anti‑inflammatory effects, dimethyl fumarate (DMF) has been reported to exert protective effects against I/R. However, to the best of our knowledge, its potential role as a myocardial protective agent in heart disease has received little attention. Previous studies have suggested that DMF may exert its protective effects by activating nuclear factor erythroid 2‑related factor 2 (Nrf2); however, the exact underlying mechanisms remain to be elucidated. The aim of the present study was to investigate the protective role of DMF in myocardial I/R injury, and to determine the role of Nrf2 in mediating the activity of DMF. H9c2 cells were incubated with DMF (20 µM) for 24 h before establishing the I/R model, and were then subjected to myocardial ischemia for 6 h, followed by reperfusion. Cell viability, lactate dehydrogenase levels, anti‑oxidant enzyme expression levels and anti‑apoptotic effects were evaluated, and AKT/Nrf2 pathway‑associated mechanisms were investigated. The results of the present study indicated that DMF may reduce myocardial I/R injury in a Nrf2‑dependent manner. DMF significantly improved cellular viability, suppressed the expression of apoptotic markers, decreased the production of reactive oxygen species and increased the expression of Nrf2‑regulated antioxidative genes. Notably, these beneficial DMF‑mediated effects were not observed in the control or I/R groups. In conclusion, the results of the present study suggested that DMF may exert protective effects against a myocardial I/R model, and further validated Nrf2 modulation as a primary mode of action. Thus suggesting that DMF may be a potential therapeutic agent for AKT/Nrf2 pathway activation in myocardial, and potentially systemic, diseases.

Therapeutic effects of interleukin-37 and induced cardiosphere on treating myocardial ischemia-reperfusion injury

BACKGROUNDS

Myocardial ischemia-reperfusion injury (MI-RI) has many adverse complications with high mortality rate. In the current study, we investigated the therapeutic advantages of delivering Interleukin-37 (IL-37) by induced cardiospheres (iCS), generated from adult skin fibroblasts via somatic reprogramming, in treating the mice model MI-RI.

METHODS

The mouse model of MI-RI was established and the iCS cells with IL-37 overexpression (iCS-IL37) were transplanted into the mice via tail-vein injection. Left ventricular (LV) dimensions and LV pressure-volume measurements were assessed by parasternal long-axis echocardiography and hemodynamic assessment. The infarct size was determined by histology analysis. And the inflammatory responses were analyzed by using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The LV function was significantly improved after the iCS-IL37 transplantation when compared to the vehicle control group and iCS group, including the end-systolic pressure and dP/dtMax. Furthermore, the infarct size was significantly decreased after the iCS-IL37 transplantation. The protein levels of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), were down-regulated by the iCS-IL37 transplantation.

CONCLUSION

The present study indicated that the iCS with IL-37 overexpression had therapeutic effects on the mice model of MI-RI.

Protective effects of induced cardiosphere on myocardial ischemia-reperfusion injury through secreting interleukin 10

BACKGROUNDS

Myocardial ischemia-reperfusion injury (MI-RI) has many adverse complications with high mortality rate. It has been demonstrated that the induced cardiospheres (iCS), generated from adult skin fibroblasts via somatic reprogramming, represents a novel source for cell therapy in myocardial infarction. However, whether the iCS could also be applied to treat MI-RI remains unclear. Thus, we investigated the therapeutic application of iCS in the mice model MI-RI.

METHODS

The mice model of MI-RI was established and the iCS cells were transplanted to the mice via tail-vein injection. Left ventricular (LV) dimensions and LV pressure-volume measurements were assessed by parasternal long-axis echocardiography. The infarct size was determined by histology analysis. And the inflammatory responses were analyzed by using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The LV function was significantly improved after the iCS transplantation when compared to the vehicle control group, including the end-systolic pressure and dP/dtMax. Furthermore, the infarct size was significantly decreased after the iCS transplantation. The protein levels of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), were down-regulated by the iCS transplantation while the IL-10 was up-regulated. The anti-inflammatory factor IL-10 was found to be expressed and secreted by the iCS cells and knocking down the IL-10 in iCS would significantly impair the therapeutic effects of iCS in the mice model of MI-RI.

CONCLUSION

The present study indicated that the iCS had therapeutic effects on the mice model of MI-RI through secreting the IL-10.

Effects of Trimetazidine Pretreatment on Endothelial Dysfunction and Myocardial Injury in Unstable Angina Patients Undergoing Percutaneous Coronary Intervention

Objectives

Trimetazidine is an anti-ischemic medication licensed for the treatment of angina pectoris. However, the molecular mechanisms underlying its action remain incompletely elucidated. In this study, therefore, we examined the potential beneficial effects of trimetazidine on myocardial injury and endothelial dysfunction in patients with unstable angina in the perioperative period of percutaneous coronary intervention (PCI).

Methods

A total of 97 patients with unstable angina were randomly divided into trimetazidine (n = 48) and control (n = 49) groups. All subjects received standard medical therapy. The trimetazidine group additionally received 20 mg trimetazidine three times daily 24 hours before and after PCI. Serum levels of creatine kinase-muscle/brain (CK-MB), cardiac troponin I (cTnI), heart-type fatty acid-binding protein (h-FABP), von Willebrand factor (vWF), and nitric oxide (NO) were measured before and the morning following PCI.

Results

In the control group, levels of CK-MB, cTnI, and vWF were significantly elevated (P < 0.05) and NO level was decreased after PCI (P < 0.05). By contrast, no significant changes in the levels of these proteins were observed in the trimetazidine group after PCI (P > 0.05). Moreover, h-FABP levels were not significantly altered after PCI whether in the control or in the trimetazidine group (P > 0.05). Finally, a time-dependent increase in the levels of h-FABP from 0 to 6 hours after PCI, followed by a progressive decline, was observed (P < 0.05).

Conclusions

PCI induces endothelial dysfunction and myocardial damage in patients with unstable angina. Trimetazidine therapy in the perioperative period can reduce this damage.

Cortical bone-derived stem cell therapy reduces apoptosis after myocardial infarction

Ischemic heart diseases such as myocardial infarction (MI) are the largest contributors to cardiovascular disease worldwide. The resulting cardiac cell death impairs function of the heart and can lead to heart failure and death. Reperfusion of the ischemic tissue is necessary but causes damage to the surrounding tissue by reperfusion injury. Cortical bone stem cells (CBSCs) have been shown to increase pump function and decrease scar size in a large animal swine model of MI. To investigate the potential mechanism for these changes, we hypothesized that CBSCs were altering cardiac cell death after reperfusion. To test this, we performed TUNEL staining for apoptosis and antibody-based immunohistochemistry on tissue from Göttingen miniswine that underwent 90 min of lateral anterior descending coronary artery ischemia followed by 3 or 7 days of reperfusion to assess changes in cardiomyocyte and noncardiomyocyte cell death. Our findings indicate that although myocyte apoptosis is present 3 days after ischemia and is lower in CBSC-treated animals, myocyte apoptosis accounts for <2% of all apoptosis in the reperfused heart. In addition, nonmyocyte apoptosis trends toward decreased in CBSC-treated hearts, and although CBSCs increase macrophage and T-cell populations in the infarct region, the occurrence of apoptosis in CD45⁺ cells in the myocardium is not different between groups. From these data, we conclude that CBSCs may be influencing cardiomyocyte and noncardiomyocyte cell death and immune cell recruitment dynamics in the heart after MI, and these changes may account for some of the beneficial effects conferred by CBSC treatment.NEW & NOTEWORTHY The following research explores aspects of cell death and inflammation that have not been previously studied in a large animal model. In addition, apoptosis and cell death have not been studied in the context of cell therapy and myocardial infarction. In this article, we describe interactions between cell therapy and inflammation and the potential implications for cardiac wound healing.

Lymphocytic subsets play distinct roles in heart diseases

Heart diseases are one of the leading causes of death for humans in the world. Increasing evidence has shown that myocardial injury induced innate and adaptive immune responses upon early cellular damage but also during chronic phases post-injury. The immune cells can not only aggravate the injury but also play an essential role in the induction of wound healing responses, which means they play a complex role throughout the acute inflammatory response and reparative response after cardiac injury. This review will summarize the current experimental and clinical evidence of lymphocytes, one of the major types of immune cells, participate in heart diseases and try to explain the possible role of these immune cells following cardiac injury.

Post-Genomic Methodologies and Preclinical Animal Models: Chances for the Translation of Cardioprotection to the Clinic

Although many cardioprotective strategies have demonstrated benefits in animal models of myocardial infarction, they have failed to demonstrate cardioprotection in the clinical setting highlighting that new therapeutic target and treatment strategies aimed at reducing infarct size are urgently needed. Completion of the Human Genome Project in 2001 fostered the post-genomic research era with the consequent development of high-throughput “omics” platforms including transcriptomics, proteomics, and metabolomics. Implementation of these holistic approaches within the field of cardioprotection has enlarged our understanding of ischemia/reperfusion injury with each approach capturing a different angle of the global picture of the disease. It has also contributed to identify potential prognostic/diagnostic biomarkers and discover novel molecular therapeutic targets. In this latter regard, “omic” data analysis in the setting of ischemic conditioning has allowed depicting potential therapeutic candidates, including non-coding RNAs and molecular chaperones, amenable to pharmacological development. Such discoveries must be tested and validated in a relevant and reliable myocardial infarction animal model before moving towards the clinical setting. Moreover, efforts should also focus on integrating all “omic” datasets rather than working exclusively on a single “omic” approach. In the following manuscript, we will discuss the power of implementing “omic” approaches in preclinical animal models to identify novel molecular targets for cardioprotection of interest for drug development.

KRT1 gene silencing ameliorates myocardial ischemia-reperfusion injury via the activation of the Notch signaling pathway in mouse models

Myocardial ischemia and reperfusion injury (MIRI) includes major drawbacks, such as excessive formation of free radicals and also overload of calcium, which lead to cell death, tissue scarring, and remodeling. The current study aims to explore whether KRT1 silencing may ameliorate MIRI via the Notch signaling pathway in mouse models. Myocardial tissues were used for the determination of the positive rate of KRT1 protein expression, apoptosis of myocardial cells, creatine kinase (CK) and lactate dehydrogenase (LDH) expression, expression of related biomarkers as well as myocardial infarction area. The transfected myocardial cells were treated with KRT1-siRNA, Jagged1, and DAPT (inhibitor of Notch-1 signaling pathway). The expression of KRT1, NICD, Hes1, Bcl-2, and Bax protein was detected. The MTT assay was applied for cell proliferation and flow cytometry was used for cell apoptosis. Mice with MIRI had a higher positive rate of KRT1 protein expression, apoptosis of myocardial cells, CK and LDH expression, myocardial infarction area, increased expression of MDA, NO, SDH, IL-1, IL-6, TNF-α, CRP, KRT1, Bax protein, CK, and LDH, and decreased expression of SOD, NICD, Hes1, and Bcl-2. The downregulation of KRT1 led to decreased expression of KRT1 and Bax protein, increased expression of NICD, Hes1, and Bcl-2, decreased cell apoptosis, and improved cell proliferation. The inhibition of the Notch signaling pathway leads to reduced expression of Bax, increased expression of NICD, Hes1, and Bcl 2, and also decreased cell apoptosis and increased cell proliferation. Our data conclude that KRT1 silencing is able to make MIRI better by activating the Notch signaling pathway in mice.

Current Modalities and Mechanisms Underlying Cardioprotection by Ischemic Conditioning

Ischemic preconditioning is a process which serves to mitigate reperfusion injury. Preconditioning of the heart can be achieved through natural, pharmacological, and mechanical means. Mechanical preconditioning appears to have the greatest chance of good outcomes while methods employing pharmacologic preconditioning have been largely unsuccessful. Remote ischemic preconditioning achieves a cardioprotective effect by applying cycles of ischemia and reperfusion in a distal limb, stimulating the release of a neurohumoral cardioprotective factor incited by stimulation of afferent neurons. The cardioprotective factor stimulates the reperfusion injury salvage kinase (RISK) and survivor activator factor enhancement (SAFE) signaling cascades in cardiomyocytes which promote cell survival by the expression of anti-apoptotic genes and inhibition of the opening of mitochondrial permeability transition pores. Clinical application of ischemic preconditioning involving targets in the RISK and SAFE signaling appears promising in the treatment of acute myocardial infarction; however, clinical trials have yet to demonstrate additional benefit to current therapy.

Cellular and molecular approaches to enhance myocardial recovery after myocardial infarction

Reperfusion therapy has resulted in significant improvement in post-myocardial infarction morbidity and mortality in over the last 4 decades. Nonetheless, it is well recognized that simply restoring patency of the epicardial artery may not stop or reverse damage at microvascular level, and myocardial salvage is often suboptimal. Numerous efforts have been undertaken to elucidate the mechanisms underlying extensive myonecrosis to facilitate the discovery of therapies to provide additional and incremental benefits over current therapeutic pathways. To date, conclusively effective strategies to promote myocardial recovery have not yet been established. Novel approaches are investigating the foundational cellular and molecular bases of myocardial ischemia and irreversible injury. Herein, we review the emerging concepts and proposed therapies that may improve myocardial protection and reduce infarct size. We examine the preclinical and clinical evidence for reduced infarct size with these strategies, including anti-inflammatory agents, intracellular ion channel modulators, agents affecting the reperfusion injury salvage kinase (RISK) and nitric oxide signaling pathways, modulators of mitochondrial function, anti-apoptotic agents, and stem cell and gene therapy. We review the potential reasons of failures to date and the potential for new strategies to further promote myocardial recovery and improve prognosis.

Reperfusion injury in ST-segment elevation myocardial infarction: the final frontier

ST-segment elevation myocardial infarction is a major cause of morbidity and mortality worldwide. Reperfusion injury (RI) following the opening of an occluded coronary artery mitigates the effect of reperfusion by further accentuating ischemic damage and increasing infarct size. Experimental studies have shown that nearly 50% of final infarct size is attributable to RI, an elusive phenomenon that remains resistant to treatment. This review proposes a hypothesis to explain the failure of strategies that have been used in an attempt to prevent RI. This hypothesis suggests that, after a certain duration of myocardial ischemia in the affected myocardium, three phases of myocardial damage occur: reversible ischemia, irreversible ischemia, and necrosis. In the reversible ischemia phase, cellular adaptive responses remain functional, and cellular repair and thus recovery of cellular functions is possible, whereas in the irreversible ischemia phase protective maneuvers fail to confer cytoprotection. Preventive therapies for RI fail because they cannot prevent cell death once cells have entered the irreversible ischemia phase, although they may succeed in postponing cell death. Failure to salvage myocardium with irreversible ischemia in addition to postponement and change in the mode of cell death (mainly from necrosis to apoptosis) by various RI preventive strategies may be the key to understanding the failure of these strategies in the clinical setting, despite their success in the reduction of infarct size in the experimental setting. Early reperfusion before large amounts of myocardium at risk reach the stage of irreversible ischemia is the best strategy for reduction of RI-related myocardial damage.

Regulation of VDAC1 contributes to the cardioprotective effects of penehyclidine hydrochloride during myocardial ischemia/reperfusion

Penehyclidine hydrochloride (PHC) preconditioning can alleviate myocardial ischemia/reperfusion (I/R) injury and inhibits the upregulation of voltage-dependent anion channel 1 (VDAC1) during I/R. To validate that VDAC1 is a bona fide target of PHC for the protection against myocardial I/R injury, VDAC1 expression construct was delivered by lentiviruses into rat left ventricular myocardium before PHC preconditioning and myocardial I/R. Overexpression of VDAC1 exacerbated cardiac dysfunction and myocardial injury following I/R, and abolished the cardioprotective effect of PHC during I/R injury. Moreover, VDAC1 overexpression with myocardial I/R further increased cytochrome c release from mitochondria to cytoplasm, elevated the levels of cleaved caspase-3 and Bax, and decreased the level of Bcl-2 as compared with I/R alone, and PHC-mediated inhibition of mitochondria-dependent apoptosis during myocardial I/R was abolished by VDAC1 overexpression. In addition, VDAC1 was overexpressed in H9c2 cardiomyocytes undergoing anoxia/reoxygenation (A/R) with or without PHC pretreatment. The in vitro results showed that overexpression of VDAC1 further reduced mitochondrial membrane potential, increased mitochondrial membrane permeability and enhanced mitochondria-dependent apoptosis in H9c2 cells after A/R, and VDAC1 overexpression abrogated the protective effect of PHC on the mitochondrial function and integrity during A/R. In conclusion, exogenous overexpression of VDAC1 during myocardial I/R inhibits the cardioprotective effects of PHC. These effects may be associated with the suppression of VDAC1 expression.

shRNA interference of NLRP3 inflammasome alleviate ischemia reperfusion-induced myocardial damage through autophagy activation

Myocardial ischemia-reperfusion (I/R) injury always occur during the recovery of myocardial blood supply with high morbidity and mortality. Although, various therapeutic schedules were applied in clinic, there are real problems that have to be resolved on curative effect. Nod-like receptor protein 3 (NLRP3) inflammasome has moderation effects on cellular damage and inflammatory reaction after I/R injury. Our research aims to investigate a more effective approach to restrain the activation of NLRP3 inflammasome in treating myocardial I/R injury. Results indicated that cell viability, Bax/Bcl-2 expression were affected hardly by sh-NLRP3 transfection in normal cells. However, the decreased cell viability and increased Bax/Bcl-2 expression level caused by I/R were remarkably suppressed through sh-NLRP3 transfection. Besides that, the reduced levels of pro-autophagy proteins (Beclin1, Agt7, LC3II/LC3I) while enhanced level of anti-autophagy protein (p62) and apoptosis-related proteins (Bax/Bcl-2) were significantly repressed via sh-NLRP3 transfection. Nevertheless, the autophagy inhibitor 3 MA could reverse the results. Moreover, in vivo experiment suggested that NLRP3 was up-regulated in wild type (WT) rats with I/R injury. The expansion of infarct size induced by ischemia was tremendously constricted in NLRP3 knockout (KO) rats. NLRP3 silence had nearly no impact on myocardial enzymes (AST, LDH and CK) expressions, inflammatory factors (TNF-α and IL-1β) expressions and cell apoptosis in rats without I/R injury. Nonetheless, the elevated levels of myocardial enzymes, inflammatory factors and cell apoptosis caused by I/R injury were vastly inhibited in NLRP3 KO rats. Furthermore, NLRP3 KO itself would lead to higher level of pro-autophagy proteins (Beclin1, Agt7, LC3II/LC3I) while lower level of anti-autophagy protein (p62) in vivo. The decreased expressions of pro-autophagy proteins while increased expressions of anti-autophagy protein induced by I/R injury were remarkably suppressed by NLRP3 KO. Taken together, our study indicated that shRNA interference of NLRP3 inflammasome attenuated myocardial I/R injury via autophagy activation. These findings demonstrated that NLRP3 KO may a promising therapy in myocardial I/R injury.

Chronic Intermittent Hypobaric Hypoxia Improves Cardiac Function through Inhibition of Endoplasmic Reticulum Stress

We investigated the role of endoplasmic reticulum stress (ERS) in chronic intermittent hypobaric hypoxia (CIHH)-induced cardiac protection. Adult male Sprague-Dawley rats were exposed to CIHH treatment simulating 5000 m altitude for 28 days, 6 hours per day. The heart was isolated and perfused with Langendorff apparatus and subjected to 30-min ischemia followed by 60-min reperfusion. Cardiac function, infarct size, and lactate dehydrogenase (LDH) activity were assessed. Expression of ERS molecular chaperones (GRP78, CHOP and caspase-12) was assayed by western blot analysis. CIHH treatment improved the recovery of left ventricular function and decreased cardiac infarct size and activity of LDH after I/R compared to control rats. Furthermore, CIHH treatment inhibited over-expression of ERS-related factors including GRP78, CHOP and caspase-12. CIHH-induced cardioprotection and inhibition of ERS were eliminated by application of dithiothreitol, an ERS inducer, and chelerythrine, a protein kinase C (PKC) inhibitor. In conclusion CIHH treatment exerts cardiac protection against I/R injury through inhibition of ERS via PKC signaling pathway.

Activation of complement factor B contributes to murine and human myocardial ischemia/reperfusion injury

The pathophysiology of myocardial injury that results from cardiac ischemia and reperfusion (I/R) is incompletely understood. Experimental evidence from murine models indicates that innate immune mechanisms including complement activation via the classical and lectin pathways are crucial. Whether factor B (fB), a component of the alternative complement pathway required for amplification of complement cascade activation, participates in the pathophysiology of myocardial I/R injury has not been addressed. We induced regional myocardial I/R injury by transient coronary ligation in WT C57BL/6 mice, a manipulation that resulted in marked myocardial necrosis associated with activation of fB protein and myocardial deposition of C3 activation products. In contrast, in fB-/- mice, the same procedure resulted in significantly reduced myocardial necrosis (% ventricular tissue necrotic; fB-/- mice, 20 ± 4%; WT mice, 45 ± 3%; P < 0.05) and diminished deposition of C3 activation products in the myocardial tissue (fB-/- mice, 0 ± 0%; WT mice, 31 ± 6%; P<0.05). Reconstitution of fB-/- mice with WT serum followed by cardiac I/R restored the myocardial necrosis and activated C3 deposition in the myocardium. In translational human studies we measured levels of activated fB (Bb) in intracoronary blood samples obtained during cardio-pulmonary bypass surgery before and after aortic cross clamping (AXCL), during which global heart ischemia was induced. Intracoronary Bb increased immediately after AXCL, and the levels were directly correlated with peripheral blood levels of cardiac troponin I, an established biomarker of myocardial necrosis (Spearman coefficient = 0.465, P < 0.01). Taken together, our results support the conclusion that circulating fB is a crucial pathophysiological amplifier of I/R-induced, complement-dependent myocardial necrosis and identify fB as a potential therapeutic target for prevention of human myocardial I/R injury.

Late sodium current and intracellular ionic homeostasis in acute ischemia

Blockade of the late Na⁺ current (I _NaL) protects from ischemia/reperfusion damage; nevertheless, information on changes in I _NaL during acute ischemia and their effect on intracellular milieu is missing. I _NaL, cytosolic Na⁺ and Ca²⁺ activities (Na_cyt, Ca_cyt) were measured in isolated rat ventricular myocytes during 7 min of simulated ischemia (ISC); in all the conditions tested, effects consistently exerted by ranolazine (RAN) and tetrodotoxin (TTX) were interpreted as due to I _NaL blockade. The results indicate that I _NaL was enhanced during ISC in spite of changes in action potential (AP) contour; I _NaL significantly contributed to Na_cyt rise, but only marginally to Ca_cyt rise. The impact of I _NaL on Ca_cyt was markedly enhanced by blockade of the sarcolemmal(s) Na⁺/Ca²⁺ exchanger (NCX) and was due to the presence of (Na⁺-sensitive) Ca²⁺ efflux through mitochondrial NCX (mNCX). sNCX blockade increased Ca_cyt and decreased Na_cyt, thus indicating that, throughout ISC, sNCX operated in the forward mode, in spite of the substantial Na_cyt increment. Thus, a robust Ca²⁺ source, other than sNCX and including mitochondria, contributed to Ca_cyt during ISC. Most, but not all, of RAN effects were shared by TTX. (1) The paradigm that attributes Ca_cyt accumulation during acute ischemia to decrease/reversal of sNCX transport may not be of general applicability; (2) I _NaL is enhanced during ISC, when the effect of Na_cyt on mitochondrial Ca²⁺ transport may substantially contribute to I _NaL impact on Ca_cyt; (3) RAN may act mostly, but not exclusively, through I _NaL blockade during ISC.

Sonoreperfusion Therapy Kinetics in Whole Blood Using Ultrasound, Microbubbles and Tissue Plasminogen Activator

Coronary intervention for myocardial infarction often results in microvascular embolization of thrombus. Sonoreperfusion therapy (SRP) using ultrasound and microbubbles restored perfusion in our in vitro flow model of microvascular obstruction. In this study, we assessed SRP efficacy using whole blood as the perfusate with and without tissue plasminogen activator (tPA). In a phantom vessel bearing a 40-μm-pore mesh to simulate the microvasculature, microthrombi were injected to cause microvascular obstruction and were treated using SRP. Without tPA, the lytic rate increased from 2.6 ± 1.5 mmHg/min with 1000-cycle pulses to 7.3 ± 3.2 mmHg/min with 5000-cycle ultrasound pulses (p < 0.01). The lytic index was similar for tPA-only ([2.0 ± 0.5] × 10^-3 mmHg^-1 min^-1) and 5000 cycles without tPA ([2.3 ± 0.5] × 10^-3 mmHg^-1 min^-1) (p = 0.5) but increased ([3.6 ± 0.8] × 10^-3 mmHg^-1 min^-1) with tPA in conjunction with 5000-cycles ultrasound (p < 0.01). In conclusion, SRP restored microvascular perfusion in whole blood, SRP lytic rate in experiments without tPA increased with ultrasound pulse length and efficacy increased with the addition of tPA.

Cardioprotection by combination of three compounds from ShengMai preparations in mice with myocardial ischemia/reperfusion injury through AMPK activation-mediated mitochondrial fission

GRS is a drug combination of three active components including ginsenoside Rb1, ruscogenin and schisandrin. It derived from the well-known TCM formula ShengMai preparations, a widely used traditional Chinese medicine for the treatment of cardiovascular diseases in clinic. The present study explores the cardioprotective effects of GRS on myocardial ischemia/reperfusion (MI/R) injury compared with ShengMai preparations and investigates the underlying mechanisms. GRS treatment significantly attenuated MI/R injury and exhibited similar efficacy as Shengmai preparations, as evidenced by decreased myocardium infarct size, ameliorated histological features, the decrease of LDH production and improved cardiac function, and also produced a significant decrease of apoptotic index. Mechanistically, GRS alleviated myocardial apoptosis by inhibiting the mitochondrial mediated apoptosis pathway as reflected by inhibition of caspase-3 activity, normalization of Bcl-2/Bax levels and improved mitochondrial function. Moreover, GRS prevented cardiomyocytes mitochondrial fission and upregulated AMPKα phosphorylation. Interestingly, AMPK activation prevented hypoxia and reoxygenation induced mitochondrial fission in cardiomyocytes and GRS actions were significantly attenuated by knockdown of AMPKα. Collectively, these data show that GRS is effective in mitigating MI/R injury by suppressing mitochondrial mediated apoptosis and modulating AMPK activation-mediated mitochondrial fission, thereby providing a rationale for future clinical applications and potential therapeutic strategy for MI/R injury.

No benefit of additional treatment with exenatide in patients with an acute myocardial infarction

OBJECTIVES

This double blinded, placebo controlled randomized clinical trial studies the effect of exenatide on myocardial infarct size. The glucagon-like peptide-1 receptor agonist exenatide has possible cardioprotective properties during reperfusion after primary percutaneous coronary intervention for ST-segment elevation myocardial infarction.

METHODS

191 patients were randomly assigned to intravenous exenatide or placebo initiated prior to percutaneous coronary intervention using 10μg/h for 30min followed by 0.84μg/h for 72h. Patients with a previous myocardial infarction, Trombolysis in Myocardial Infarction flow 2 or 3, multi-vessel disease, or diabetes were excluded. Magnetic resonance imaging (MRI) was performed to determine infarct size, area at risk (AAR) (using T2-weighted hyperintensity (T2W) and late enhancement endocardial surface area (ESA)). The primary endpoint was of 4-month final infarct size, corrected for the AAR measured in the acute phase using MRI.

RESULTS

After exclusion, 91 patients (age 57.4±10.1years, 76% male) completed the protocol. There were no baseline differences between groups. No difference was found in infarct size corrected for the AAR in the exenatide group compared to the placebo group (37.1±18.8 vs. 39.3±20.1%, p=0.662). There was also no difference in infarct size (18.8±13.2 vs. 18.8±11.3% of left ventricular mass, p=0.965). No major adverse cardiac events occurred during the in-hospital phase.

CONCLUSION

Exenatide did not reduce myocardial infarct size expressed as a percentage of AAR in ST elevated myocardial infarction patients successfully treated with percutaneous coronary intervention.

Leucocyte expression of complement C5a receptors exacerbates infarct size after myocardial reperfusion injury

AIMS

Early reperfusion is mandatory for the treatment of acute myocardial infarction. This process, however, also induces additional loss of viable myocardium, called ischaemia-reperfusion (IR) injury. Complement activation plays an important role in IR injury, partly through binding of C5a to its major receptor (C5aR). We investigated the role of C5aR on infarct size and cardiac function in a model for myocardial IR injury.

METHODS AND RESULTS

BALB/c (WT) mice and C5aR(-/-) mice underwent coronary occlusion for 30 min, followed by reperfusion. Infarct size, determined 24 h after IR, was reduced in C5aR(-/-) mice compared with WT mice (28.5 ± 2.1 vs. 35.7 ± 2.5%, P = 0.017). Bone marrow (BM) chimaera experiments showed that this effect was due to the absence of C5aR on circulating leucocytes, since a similar reduction in infarct size was observed in WT mice with C5aR-deficient BM cells (25.3 ± 2.2 vs. 34.6 ± 2.8%, P < 0.05), but not in C5aR(-/-) mice with WT BM cells. Reduced infarct size was associated with fewer neutrophils, T cells, and macrophages in the infarcted area 24 h after IR in C5aR(-/-) mice, and also with lower levels of Caspase-3/7 indicating less inflammation and apoptosis. Echocardiography 4 weeks after IR showed an improved ejection fraction in C5aR(-/-) mice (25.8 ± 5.5 vs. 19.2 ± 5.4%, P < 0.001).

CONCLUSION

The absence of C5aR on circulating leucocytes reduces infarct size, is associated with reduced leucocyte infiltration and with less apoptosis in the infarcted myocardium, and improves cardiac function in a mouse model of myocardial IR injury. Selective blocking of C5aR might be a promising strategy to prevent myocardial IR injury.