Apelin-13 limits infarct size and improves cardiac postischemic mechanical recovery only if given after ischemia

Apelin C-Terminal Fragments: Biological Properties and Therapeutic Potential

Creation of bioactive molecules for treatment of cardiovascular diseases based on natural peptides is the focus of intensive experimental research. In the recent years, it has been established that C-terminal fragments of apelin, an endogenous ligand of the APJ receptor, reduce metabolic and functional disorders in experimental heart damage. The review presents literature data and generalized results of our own experiments on the effect of apelin-13, [Pyr]apelin-13, apelin-12, and their chemically modified analogues on the heart under normal and pathophysiological conditions in vitro and in vivo. It has been shown that the spectrum of action of apelin peptides on the damaged myocardium includes decrease in the death of cardiomyocytes from necrosis, reduction of damage to cardiomyocyte membranes, improvement in myocardial metabolic state, and decrease in formation of reactive oxygen species and lipid peroxidation products. The mechanisms of protective action of these peptides associated with activation of the APJ receptor and manifestation of antioxidant properties are discussed. The data presented in the review show promise of the molecular design of APJ receptor peptide agonists, which can serve as the basis for the development of cardioprotectors that affect the processes of free radical oxidation and metabolic adaptation.

Apelin receptor inhibition in ischemia-reperfused mouse hearts protected by endogenous n-3 polyunsaturated fatty acids

Background: While the protective effects of n-3 polyunsaturated fatty acids (PUFAs) on cardiac ischemia-reperfusion (IR) injury have been previously reported, limited data are available regarding how these fatty acids affect membrane receptors and their downstream signaling following IR injury. We aimed to identify potential receptors activated by n-3 PUFAs in IR hearts to understand the regulatory mechanisms of these receptors. Methods: We used fat-1 mice, which naturally have elevated levels of n-3 PUFAs, and C57BL/6J mice as a control group to create a myocardial IR injury model through Langendorff perfusion. We assessed the impact of endogenous n-3 PUFAs on left ventricular function, myocardial infarct size, myocardial apoptosis, and ATP production. RNA sequencing (RNA-seq) and bioinformatics analysis were conducted to identify molecular targets affected by n-3 PUFAs. Based on these analyses we then treated IR hearts of WT and fat-1 mice with an antagonist (ML221) or an agonist (apelin-13) for the predicted receptor to assess cardiac contractile function and intracellular signaling pathways. An in vitro hypoxia-reoxygenation (HR) model was also used to confirm the effects of n-3 PUFAs on the examined intracellular signaling pathways. Results: Endogenous n-3 PUFAs protected cardiac structure and function in post-IR hearts, and modulated phosphorylation patterns in the PI3K-AKT-mTOR signaling pathways. RNA-seq analysis revealed that n-3 PUFAs affected multiple biological processes as well as levels of the apelin receptor (APLNR). Consistent with a role for the PLNNR, ML221 synchronized the activation of the PI3K-AKT-mTOR signaling axis, suppressed the expression of PKCδ and phosphorylated p38α, upregulated PKCε expression, upregulated or restored the phosphorylation of myofilaments, and prevented myocardial injury and contractile dysfunction in WT IR hearts. By contrast, apelin-13 disrupted the PI3K-AKT-mTOR signaling axis in post-IR fat-1 hearts. The phosphorylation signaling targeted by APLNR inhibition in post-IR fat-1 hearts was also observed after treating HR cells with eicosatetraenoic acid (EPA). Conclusion: Endogenous n-3 PUFAs protect against post-IR injury and preserve cardiac contractile function possibly through APLNR inhibition. This inhibition synchronizes the PI3K-AKT-mTOR axis, suppresses detrimental phosphorylation signaling, and restores or increases myofilament phosphorylation in post-IR hearts. The beneficial effects observed in fat-1 transgenic mouse hearts can be attributed, at least in part, to elevated EPA levels. This study is the first to demonstrate that n-3 PUFAs protect hearts against IR injury through APLNR inhibition.

Design and preclinical evaluation of a novel apelin-based PET radiotracer targeting APJ receptor for molecular imaging of angiogenesis

APJ has been extensively described in the pathophysiology of angiogenesis and cell proliferation. The prognostic value of APJ overexpression in many diseases is now established. This study aimed to design a PET radiotracer that specifically binds to APJ. Apelin-F13A-NODAGA (AP747) was synthesized and radiolabeled with gallium-68 ([68Ga]Ga-AP747). Radiolabeling purity was excellent (> 95%) and stable up to 2 h. Affinity constant of [67Ga]Ga-AP747 was measured on APJ-overexpressing colon adenocarcinoma cells and was in nanomolar range. Specificity of [68Ga]Ga-AP747 for APJ was evaluated in vitro by autoradiography and in vivo by small animal PET/CT in both colon adenocarcinoma mouse model and Matrigel plug mouse model. Dynamic of [68Ga]Ga-AP747 PET/CT biodistributions was realized on healthy mice and pigs for two hours, and quantification of signal in organs showed a suitable pharmacokinetic profile for PET imaging, largely excreted by urinary route. Matrigel mice and hindlimb ischemic mice were submitted to a 21-day longitudinal follow-up with [68Ga]Ga-AP747 and [68Ga]Ga-RGD2 small animal PET/CT. [68Ga]Ga-AP747 PET signal in Matrigel was significantly more intense than that of [68Ga]Ga-RGD2. Revascularization of the ischemic hind limb was followed by LASER Doppler. In the hindlimb, [68Ga]Ga-AP747 PET signal was more than twice higher than that of [68Ga]Ga-RGD2 on day 7, and significantly superior over the 21-day follow-up. A significant, positive correlation was found between the [68Ga]Ga-AP747 PET signal on day 7 and late hindlimb perfusion on day 21. We developed a new PET radiotracer that specifically binds to APJ, [68Ga]Ga-AP747 that showed more efficient imaging properties than the most clinically advanced tracer of angiogenesis, [68Ga]Ga-RGD2.

APJ as Promising Therapeutic Target of Peptide Analogues in Myocardial Infarction- and Hypertension-Induced Heart Failure

The widely expressed G protein-coupled apelin receptor (APJ) is activated by two bioactive endogenous peptides, apelin and ELABELA (ELA). The apelin/ELA-APJ-related pathway has been found involved in the regulation of many physiological and pathological cardiovascular processes. Increasing studies are deepening the role of the APJ pathway in limiting hypertension and myocardial ischaemia, thus reducing cardiac fibrosis and adverse tissue remodelling, outlining APJ regulation as a potential therapeutic target for heart failure prevention. However, the low plasma half-life of native apelin and ELABELA isoforms lowered their potential for pharmacological applications. In recent years, many research groups focused their attention on studying how APJ ligand modifications could affect receptor structure and dynamics as well as its downstream signalling. This review summarises the novel insights regarding the role of APJ-related pathways in myocardial infarction and hypertension. Furthermore, recent progress in designing synthetic compounds or analogues of APJ ligands able to fully activate the apelinergic pathway is reported. Determining how to exogenously regulate the APJ activation could help to outline a promising therapy for cardiac diseases.

Apelin Is a Prototype of Novel Drugs for the Treatment of Acute Myocardial Infarction and Adverse Myocardial Remodeling

In-hospital mortality in patients with ST-segment elevation myocardial infarction (STEMI) is 5-6%. Consequently, it is necessary to develop fundamentally novel drugs capable of reducing mortality in patients with acute myocardial infarction. Apelins could be the prototype for such drugs. Chronic administration of apelins mitigates adverse myocardial remodeling in animals with myocardial infarction or pressure overload. The cardioprotective effect of apelins is accompanied by blockage of the MPT pore, GSK-3β, and the activation of PI3-kinase, Akt, ERK1/2, NO-synthase, superoxide dismutase, glutathione peroxidase, matrix metalloproteinase, the epidermal growth factor receptor, Src kinase, the mitoK_ATP channel, guanylyl cyclase, phospholipase C, protein kinase C, the Na⁺/H⁺ exchanger, and the Na⁺/Ca²⁺ exchanger. The cardioprotective effect of apelins is associated with the inhibition of apoptosis and ferroptosis. Apelins stimulate the autophagy of cardiomyocytes. Synthetic apelin analogues are prospective compounds for the development of novel cardioprotective drugs.

Apelin pathway in cardiovascular, kidney, and metabolic diseases: Therapeutic role of apelin analogs and apelin receptor agonists

The apelin/apelin receptor (ApelinR) signal transduction pathway exerts essential biological roles, particularly in the cardiovascular system. Disturbances in the apelin/ApelinR axis are linked to vascular, heart, kidney, and metabolic disorders. Therefore, the apelinergic system has surfaced as a critical therapeutic strategy for cardiovascular diseases (including pulmonary arterial hypertension), kidney disease, insulin resistance, hyponatremia, preeclampsia, and erectile dysfunction. However, apelin peptides are susceptible to rapid degradation through endogenous peptidases, limiting their use as therapeutic tools and translational potential. These proteases include angiotensin converting enzyme 2, neutral endopeptidase, and kallikrein thereby linking the apelin pathway with other peptide systems. In this context, apelin analogs with enhanced proteolytic stability and synthetic ApelinR agonists emerged as promising pharmacological alternatives. In this review, we focus on discussing the putative roles of the apelin pathway in various physiological systems from function to dysfunction, and emphasizing the therapeutic potential of newly generated metabolically stable apelin analogs and non-peptide ApelinR agonists.

Angiotensin-converting enzyme 2: a key enzyme in key organs

2020 marked the 20th anniversary of the discovery of the angiotensin-converting enzyme 2 (ACE2). This major event that changed the way we see the renin-angiotensin system today could have passed quietly. Instead, the discovery that ACE2 is a major player in the severe acute respiratory syndrome coronavirus 2 pandemic has blown up the literature regarding this enzyme. ACE2 connects the classical arm renin-angiotensin system, consisting mainly of angiotensin II peptide and its AT1 receptor, with a protective arm, consisting mainly of the angiotensin 1-7 peptide and its Mas receptor. In this brief article, we have reviewed the literature to describe how ACE2 is a key protective arm enzyme in the function of many organs, particularly in the context of brain and cardiovascular function, as well as in renal, pulmonary and digestive homeostasis. We also very briefly review and refer to recent literature to present an insight into the role of ACE2 in determining the course of coronavirus diseases 2019.

Plasma apelin level in acute myocardial infarction and its relation with prognosis: A prospective study

Objective

Apelin is a novel adipocytokine with a significant role in ischemia/reperfusion injury that is synthesized and secreted in myocardial cells and coronary endothelium. There is debate on its value for the diagnosis and prognosis of myocardial infarction. We aimed to investigate plasma apelin level in patients with acute ST segment elevation (STEMI) and non-ST segment elevation (NSTEMI) myocardial infarction and its relationship with left ventricular function and prognostic parameters.

Methods

Forty-one patients with STEMI, 21 patients with NSTEMI and 10 patients as control group with normal coronary angiograms were included. Plasma apelin level at presentation was investigated regarding its relationship with other diagnostic and prognostic parameters.

Results

Apelin level was significantly higher in acute myocardial infarction (0.31 ± 0.56 ng/mL) compared to control group (0.08 ± 0.05 ng/mL) (p < 0.01). Likewise, it was found to be significantly higher in STEMI group (0.45 ± 0.73 ng/mL) compared to control group (0.08 ± 0.05 ng/mL) (p < 0.01). Although apelin was higher in NSTEMI group (0.13 ± 0.10 ng/mL) compared to control group (0.08 ± 0.05 ng/mL), this difference was not statistically significant (p > 0.05). No correlation was found between apelin and NT-proBNP, hsCRP, troponin, ejection fraction (EF) and Killip score (p > 0.05). A positive correlation was found between apelin and TIMI, GRACE and Gensini scores (p < 0.05). Only GRACE score was found to be correlated with apelin in MI groups.

Conclusion

Apelin level was found to be high in acute myocardial infarction. With its inotropic and vasodilator effects, apelin was thought to have a protective role against severe ischemia.

Inflammation Triggered by SARS-CoV-2 and ACE2 Augment Drives Multiple Organ Failure of Severe COVID-19: Molecular Mechanisms and Implications

The widespread occurrence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to a pandemic of coronavirus disease 2019 (COVID-19). The S spike protein of SARS-CoV-2 binds with angiotensin-converting enzyme 2 (ACE2) as a functional "receptor" and then enters into host cells to replicate and damage host cells and organs. ACE2 plays a pivotal role in the inflammation, and its downregulation may aggravate COVID-19 via the renin-angiotensin system, including by promoting pathological changes in lung injury and involving inflammatory responses. Severe patients of COVID-19 often develop acute respiratory distress syndrome and multiple organ dysfunction/failure with high mortality that may be closely related to the hyper-proinflammatory status called the "cytokine storm." Massive cytokines including interleukin-6, nuclear factor kappa B (NFκB), and tumor necrosis factor alpha (TNFα) released from SARS-CoV-2-infected macrophages and monocytes lead inflammation-derived injurious cascades causing multi-organ injury/failure. This review summarizes the current evidence and understanding of the underlying mechanisms of SARS-CoV-2, ACE2 and inflammation co-mediated multi-organ injury or failure in COVID-19 patients.

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.

Experimental Study on the Role of Apelin-13 in Alleviating Spinal Cord Ischemia Reperfusion Injury Through Suppressing Autophagy

Background

This study aimed to explore the effect of Apelin-13 in protecting rats against spinal cord ischemia reperfusion injury (SCIR), as well as the related molecular mechanisms.

Methods

One week prior to the experiment, experimental Sprague–Dawley rats were injected with Apelin-13 and the autophagy activator rapamycin through the tail vein once a day for 7 consecutive days. The SCIR rat model was prepared through the abdominal aorta clamping method. At 72 h after injury, the spinal cord tissue water content, infarct volume, and normal neuron count were determined to evaluate the degree of spinal cord tissue injury in the rats. The Basso–Beattie–Bresnahan scoring standard was adopted for functional scoring of the rat hind leg, to reflect the post-injury motor function. At 72 h after injury, changes in mitochondrial membrane potential, reactive oxygen species content, and mitochondrial ATP were detected. ELISA was carried out to detect the malonaldehyde content, as well as catalase, superoxide dismutase, and glutathione catalase activities in spinal cord tissues at 72 h after injury. Quantitative chemistry was conducted to examine the contents of nitric oxide (NO) and endothelial nitric oxide synthase (eNOS) in spinal cord tissues. Finally, the expression of autophagy-related proteins, Beclin1, ATG5, and LC3, in spinal cord tissues was detected through the Western blotting assay.

Results

Apelin-13 pretreatment alleviated SCIR, promoted motor function recovery, suppressed mitochondrial dysfunction, resisted oxidative stress, and inhibited autophagy in spinal cord tissues following ischemia reperfusion injury.

Conclusion

Apelin-3 exerts protection against SCIR by suppressing autophagy.

Distinct hemodynamic responses to (pyr)apelin-13 in large animal models

This study tested the hypothesis that (pyr)apelin-13 dose-dependently augments myocardial contractility and coronary blood flow, irrespective of changes in systemic hemodynamics. Acute effects of intravenous (pyr)apelin-13 administration (10 to 1,000 nM) on blood pressure, heart rate, left ventricular pressure and volume, and coronary parameters were measured in dogs and pigs. Administration of (pyr)apelin-13 did not influence blood pressure (P = 0.59), dP/dt_max (P = 0.26), or dP/dt_min (P = 0.85) in dogs. However, heart rate dose-dependently increased > 70% (P < 0.01), which was accompanied by a significant increase in coronary blood flow (P < 0.05) and reductions in left ventricular end-diastolic volume and stroke volume (P < 0.001). In contrast, (pyr)apelin-13 did not significantly affect hemodynamics, coronary blood flow, or indexes of contractile function in pigs. Furthermore, swine studies found no effect of intracoronary (pyr)apelin-13 administration on coronary blood flow (P = 0.83) or vasorelaxation in isolated, endothelium-intact (P = 0.89) or denuded (P = 0.38) coronary artery rings. Examination of all data across (pyr)apelin-13 concentrations revealed an exponential increase in cardiac output as peripheral resistance decreased across pigs and dogs (P < 0.001; R² = 0.78). Assessment of the Frank-Starling relationship demonstrated a significant linear relationship between left ventricular end-diastolic volume and stroke volume across species (P < 0.001; R² = 0.70). Taken together, these findings demonstrate that (pyr)apelin-13 does not directly influence myocardial contractility or coronary blood flow in either dogs or pigs.NEW & NOTEWORTHY Our findings provide much needed insight regarding the pharmacological cardiac and coronary effects of (pyr)apelin-13 in larger animal preparations. In particular, data highlight distinct hemodynamic responses of apelin across species, which are independent of any direct effect on myocardial contractility or perfusion.

Chronic treatment with apelin, losartan and their combination reduces myocardial infarct size and improves cardiac mechanical function

The renin-angiotensin system (RAS) has a deleterious and apelin/APJ system has protective effect on the ischaemic heart. The collaboration between these systems in the pathophysiology of myocardial infarction is not clear. We determined the effect of chronic pretreatment with apelin, losartan and their combination on ischaemia-reperfusion (IR) injury in the isolated perfused rat heart and on the expression of apelin-13 receptor (APJ) and angiotensin type 1 receptor (AT1R) in the myocardium. During 5 days before the induction of IR, saline (vehicle), apelin-13 (Apl), F13A (apelin antagonist), losartan (Los, AT1R antagonist) and the combination of Apl and Los were administered intraperitoneally in rats. Ischaemia was induced by left anterior descending (LAD) artery occlusion for 30 minutes followed by reperfusion for 55 minutes in the Langendorff isolated heart perfusion system. Pretreatment with Apl, Los and the combination of Apl + Los significantly reduced infarct size by about 30, 33 and 48 percent respectively; and significantly improved the left ventricular function indices such as left ventricular developed pressure (LVDP), left ventricular end-diastolic pressure (LVEDP) and rate pressure product (RPP). IR increased AT1R protein level but it did not change APJ significantly. AT1R expression was reduced in groups treated with Apl, Los and Apl + Los. Findings showed that chronic pretreatment with apelin along with AT1R antagonist had more protective effects against IR injury. Combination therapy may diminish the risk of IR-induced heart damage, by reducing AT1R expression, in the heart of patients with coronary artery disease that are at the risk of MI and reperfusion injury.

Apelin shorten QT interval by inhibiting Kir2.1/IK1 via a PI3K way in acute myocardial infarction

QT interval prolongation and depolarization of resting membrane potential (RMP) were found in acute myocardial infarction (MI) which is involved in the arrhythmogenic mechanism and raising the risk to initiate torsade de pointes. However, clinical anti-arrhythmic agents that primarily act on QT interval and RMP are not currently available. Our objective was to determine whether Apelin, an endogenous peptide ligand of receptor APJ, affects QT interval and RMP and underlying mechanisms. To test this viewpoint, mice were subjected to MI by ligating the left main coronary artery and Apelin was applied through tail vein at 5 min prior coronary occlusion in tested group. Compared to MI group, pretreatment of Apelin (15 μg/kg) shortened QTc and QT interval induced by MI, significantly elevated RMP and shortened action potential duration (APD) by increased I_K1 currents recorded using whole-cell patch technique from cardiomyocytes underwent MI. In cultured neonatal mouse cardiomyocytes, Apelin (1 μmol/L) restored hypoxia-induced Kir2.1 down-regulation, which was abolished by IP3K inhibitor LY-294002. Additionally, Apelin elicited a time-dependent increase in phosphorylation of Akt leading to increase in PI3-kinase activity. These results showed that Apelin enhanced I_K1/Kir2.1 currents via IP3K pathway as by rescue ischemia- and hypoxia-induced RMP depolarization and prolongation of QT interval, which may prevent or cure acute ischemic-mediated arrhythmias. This study brings new information to anti-arrhythmic theories and provides a potential target for the clinical management of acute ischemia-related arrhythmias.

Cardioprotective apelin effects and the cardiac-renal axis: review of existing science and potential therapeutic applications of synthetic and native regulated apelin

First described in 1998, apelin is one of the endogenous ligands of the apelinergic receptor. Since its discovery, its possible role in human physiology and disease has been intensively studied. Apelin is a native cardioprotective agent that the body synthesizes to create atheroprotective, antihypertensive, and regenerative effects in the body. By antagonizing the RAA system, apelin could play an important role in heart failure and hypertension. It is also involved in myocardial protection against ischemia/reperfusion injury, post-ischemic remodeling, and myocardial fibrosis. A small number of studies even suggest that serum apelin levels may be involved the development of life-threatening arrhythmias. All this information generated excitement about potential therapeutic effects in patients with heart failure and myocardial infarction. The therapeutic index of apelin is unknown but is anticipated to be favorable based on the small number of studies. In this review, we summarize the mechanisms by which apelin exerts its cardioprotective effects and its connection with the cardiorenal axis. Also, we report the potential therapeutic applications of synthetic and native regulated apelin. If larger studies can be performed, it is possible that apelin-mediated drug treatment may play a major role for a large number of patients worldwide in the future.

EFFECTS OF EXERCISE COMBINED WITH APELIN-13 ON CARDIAC FUNCTION IN THE ISOLATED RAT HEART

ABSTRACT Exercise and apelin have been shown to increase cardiac function and elicit tolerance to ischemia/reperfusion (IR) injuries. This study aimed at determining whether the combination of exercise training and apelin pretreatment could integrate the protective effects of each of them in the heart against IR injury. Male rats were divided into four experimental groups: 1: Rats with ischemia/reperfusion (IR), 2: subjected to exercise training for 8 weeks (EX+IR), 3: apelin-13 (10 nmol/kg/day) for 7 days (Apel+IR) in the last week of training, and 4: exercise training plus apelin-13 (EX+Apel+IR). Isolated hearts were perfused using the Langendorff method and subjected to 30 min of regional ischemia followed by 60 min of reperfusion. Treadmill exercise training was conducted for 8 weeks. Hemodynamic parameters were recorded throughout the experiment. Ischemia-induced arrhythmias, myocardial infarct size (IS), creatine kinase-MB (CK-MB) isoenzyme and plasma lactate dehydrogenase (LDH) activity was measured in all animals. Administration of apelin-13 plus exercise increased left ventricular developed pressure (LVDP) at the end of ischemia and reperfusion compared with other groups. After 30 min of ischemia, dP/dtmax was higher in EX+Apel+IR than in Apel+IR and EX+IR groups. During 30 min ischemia, exercise training, apelin-13 and combined treatment produced a significant reduction in the numbers of premature ventricular complexes. A combination of exercise and apelin-13 also reduced infarct size, CK-MB, LDH and severity of arrhythmia. These results suggest that combined therapies with apelin-13 and exercise training may integrate the beneficial effects of each of them alone on cardiac contractility, arrhythmia and limiting of infarct size. Level of evidence I; Therapeutic Studies - Investigating the Results of Treatment.

The Role of Apelin in Cardiovascular Diseases, Obesity and Cancer

Apelin is an endogenous peptide identified as a ligand of the G protein-coupled receptor APJ. Apelin belongs to the family of adipokines, which are bioactive mediators released by adipose tissue. Extensive tissue distribution of apelin and its receptor suggests, that it could be involved in many physiological processes including regulation of blood pressure, body fluid homeostasis, endocrine stress response, cardiac contractility, angiogenesis, and energy metabolism. Additionally, this peptide participates in pathological processes, such as heart failure, obesity, diabetes, and cancer. In this article, we review current knowledge about the role of apelin in organ and tissue pathologies. We also summarize the mechanisms by which apelin and its receptor mediate the regulation of physiological and pathological processes. Moreover, we put forward an indication of apelin as a biomarker predicting cardiac diseases and various types of cancer. A better understanding of the function of apelin and its receptor in pathologies might lead to the development of new medical compounds.

Protective effects of a modified apelin-12 and dinitrosyl iron complexes in experimental cardioplegic ischemia and reperfusion

The maintenance of nitric oxide (NO) bioavailability has been recognized as an important component of myocardial protection during cardiac surgery. This study was designed to evaluate the efficacy of using two NO-donating compounds in cardioplegia and reperfusion: (i) a modified peptide apelin-12 (MA12) that activates endothelial NO synthase (eNOS) and (ii) dinitrosyl iron complexes with reduced glutathione (DNIC-GS), a natural NO vehicle. Isolated perfused working rat hearts were subjected to normothermic global ischemia and reperfusion. St. Thomas' Hospital cardioplegic solution (STH) containing 140 μM MA12 or 100 μM DNIC-GS was used. In separate series, 140 μM MA12 or 100 μM DNIC-GS was administered at early reperfusion. Metabolic state of the hearts was evaluated by myocardial content of high-energy phosphates and lactate. Lactate dehydrogenase (LDH) activity in myocardial effluent was used as an index of cell membrane damage. Cardioplegia with MA12 or DNIC-GS improved recovery of coronary flow and cardiac function, and reduced LDH leakage in perfusate compared with STH without additives. Cardioplegic arrest with MA12 significantly enhanced preservation of high-energy phosphates and decreased accumulation of lactate in reperfused hearts. The overall protective effect of cardioplegia with MA12 was significantly greater than with DNIC-GS. The administration of MA12 or DNIC-GS at early reperfusion also increased metabolic and functional recovery of reperfused hearts. In this case, recovery of cardiac contractile and pump function indices was significantly higher if reperfusion was performed with DNIC-GS. The results show that MA12 and DNIC-GS are promising adjunct agents for protection of the heart during cardioplegic arrest and reperfusion.

Apelin Ameliorates High Glucose-Induced Downregulation of Connexin 43 via AMPK-Dependent Pathway in Neonatal Rat Cardiomyocytes

Diabetes Mellitus is a common disorder, with increasing risk of cardiac arrhythmias. Studies have shown that altered connexin expression and gap junction remodeling under hyperglycemia contribute to the high prevalence of cardiac arrhythmias and even sudden death. Connexin 43 (Cx43), a major protein that assembles to form cardiac gap junctions, has been found to be downregulated under high glucose conditions, along with inhibition of gap junctional intercellular communication (GJIC). While, apelin, a beneficial adipokine, increases Cx43 protein expression in mouse and human embryonic stem cells during cardiac differentiation. However, it remains unknown whether apelin influences GJIC capacity in cardiomyocytes. Here, using Western blotting and dye transfer assays, we found that Cx43 protein expression was reduced and GJIC was impaired after treatment with high glucose, which, however, could be abrogated after apelin treatment for 48 h. We also found that apelin increased Cx43 expression under normal glucose. Real-time PCR showed that the Cx43 mRNA was not significantly affected under high glucose conditions in the presence of apelin or high glucose and apelin. High glucose decreased the phosphorylation of AMPKα; however, apelin activated AMPKα. Interestingly, we found that Cx43 expression was increased after treatment with AICAR, an activator of AMPK signaling. AMPKα inhibition mediated with transfection of siRNA-AMPKα1 and siRNA-AMPKα2 abolished the protective effect of apelin on Cx43 expression. Our data suggest that apelin attenuates high glucose-induced Cx43 downregulation and improves the loss of functional gap junctions partly through the AMPK pathway.

Apelin-induced cardioprotection against ischaemia/reperfusion injury: roles of epidermal growth factor and Src

AIM

Apelin, the ligand of the G-protein-coupled receptor (GPCR) APJ, exerts a post-conditioning-like protection against ischaemia/reperfusion injury through activation of PI3K-Akt-NO signalling. The pathway connecting APJ to PI3K is still unknown. As other GPCR ligands act through transactivation of epidermal growth factor receptor (EGFR) via a matrix metalloproteinase (MMP) or Src kinase, we investigated whether EGFR transactivation is involved in the following three features of apelin-induced cardioprotection: limitation of infarct size, suppression of contracture and improvement of post-ischaemic contractile recovery.

METHOD

Isolated rat hearts underwent 30 min of global ischaemia and 2 h of reperfusion. Apelin (0.5 μm) was infused during the first 20 min of reperfusion. EGFR, MMP or Src was inhibited to study the pathway connecting APJ to PI3K. Key components of RISK pathway, namely PI3K, guanylyl cyclase or mitochondrial K⁺ -ATP channels, were also inhibited. Apelin-induced EGFR and phosphatase and tensing homolog (PTEN) phosphorylation were assessed. Left ventricular pressure and infarct size were measured.

RESULTS

Apelin-induced reductions in infarct size and myocardial contracture were prevented by the inhibition of EGFR, Src, MMP or RISK pathway. The involvement of EGFR was confirmed by its phosphorylation. However, neither direct EGFR nor MMP inhibition affected apelin-induced improvement of early post-ischaemic contractile recovery, which was suppressed by Src and RISK inhibitors only. Apelin also increased PTEN phosphorylation, which was removed by Src inhibition.

CONCLUSION

While EGFR and MMP limit infarct size and contracture, Src or RISK pathway inhibition suppresses the three features of cardioprotection. Src does not only transactivate EGFR, but also inhibits PTEN by phosphorylation thus playing a crucial role in apelin-induced cardioprotection.

Apelinergic System Structure and Function

Apelin and apela (ELABELA/ELA/Toddler) are two peptide ligands for a class A G-protein-coupled receptor named the apelin receptor (AR/APJ/APLNR). Ligand-AR interactions have been implicated in regulation of the adipoinsular axis, cardiovascular system, and central nervous system alongside pathological processes. Each ligand may be processed into a variety of bioactive isoforms endogenously, with apelin ranging from 13 to 55 amino acids and apela from 11 to 32, typically being cleaved C-terminal to dibasic proprotein convertase cleavage sites. The C-terminal region of the respective precursor protein is retained and is responsible for receptor binding and subsequent activation. Interestingly, both apelin and apela exhibit isoform-dependent variability in potency and efficacy under various physiological and pathological conditions, but most studies focus on a single isoform. Biophysical behavior and structural properties of apelin and apela isoforms show strong correlations with functional studies, with key motifs now well determined for apelin. Unlike its ligands, the AR has been relatively difficult to characterize by biophysical techniques, with most characterization to date being focused on effects of mutagenesis. This situation may improve following a recently reported AR crystal structure, but there are still barriers to overcome in terms of comprehensive biophysical study. In this review, we summarize the three components of the apelinergic system in terms of structure-function correlation, with a particular focus on isoform-dependent properties, underlining the potential for regulation of the system through multiple endogenous ligands and isoforms, isoform-dependent pharmacological properties, and biological membrane-mediated receptor interaction. © 2018 American Physiological Society. Compr Physiol 8:407-450, 2018.

Apelin protects against myocardial ischemic injury by inhibiting dynamin-related protein 1

It is known that dynamin-related protein 1 (Drp1)-mediated mitochondrial fission plays an important role in ischemic injury of myocardial infarction (MI). Apelin, an endogenous ligand for Apelin receptor, acts as a key modulator of cardiovascular diseases. Here, we examined the effects of Apelin on MI injury and underlying mechanisms. Adult male C57BL/6J mice were treated with Apelin for 4 weeks and then subjected coronary artery ligation (LAD) to induce MI and the protective effects of Apelin on MI injury were evaluated at 6 h post LAD. Mitochondrial fission was significantly increased in MI as evidenced by enhanced expression of phosphorylated Drp1 (p-Drp1^{ser 616}) without affecting total Drp-1 level and degenerative transformation of mitochondria into short rods as typical fission. Apelin markedly inhibited p-Drp1^{ser 616} and preserved mitochondrial morphology in MI. Similar effects of Apelin were consistently observed in primary cultured cardiomyocytes under hypoxia. Apelin decreased hypoxia-induced cardiomyocyte apoptosis as evidenced by decreased TUNEL-positive cells and preserved mitochondrial membrane potential (MMP). Apelin decreased Bax/Bcl-2 ratio and limited the release of cytochrome C and activation of caspase-9 and caspase-3 both in vivo and in vitro. Finally, Apelin diminished the infarct size and normalized the impaired cardiac function as indicated by rescuing of the decreased ejection faction and fractional shortening in MI mice. In conclusion, Apelin prevented mitochondrial fission by inhibiting p-Drp1^Ser616, which prevents loss of MMP and inhibits the mitochondria-mediated apoptosis. These results indicate that the inhibition of Drp-1 activation by Apelin is a novel mechanism of cardioprotection against MI injury.

Influence of apelin-12 on troponin levels and the rate of MACE in STEMI patients

BACKGROUND

During acute myocardial infarction, phosphorylated TnI levels, Ca²⁺ sensitivity and ATPase activity are decreased in the myocardium, and the subsequent elevation in Ca²⁺ levels activates protease I (caplain I), leading to the proteolytic degradation of troponins. Concurrently, the levels of apelin and APJ expression are increased by limiting myocardial injury.

METHODS

In this prospective observational study, 100 consecutive patients with ST-elevation acute myocardial infarction were included. Patients meeting the following criteria were included in our study: (1) continuous chest pain lasting for >30 min, (2) observation of ST-segment elevation of more than 2 mm in two adjacent leads by electrocardiography (ECG), (3) increased cardiac troponin I levels, and (4) patients who underwent reperfusion therapy. We evaluated the levels of apelin-12 and troponin I on the first and seventh days after reperfusion therapy in all patients.

RESULTS

Apelin-12 was inversely correlated with troponin I levels (Spearman's correlation = -0.40) with a p value <0.001. There was variability in the apelin values on the seventh day (Kruskal-Wallis test) based on major adverse cardiac events (MACE) (p = 0.012). Using ROC curve analyses, a cut-off value of >2.2 for the association of apelin with MACE was determined, and the AUC was 0.71 (95% CI, 0.58-0.84). Survival analysis using the Kaplan-Meier method showed a lower rate of MACE among patients with apelin levels >2.2 (p = 0.002), and the ROC curve analysis showed a statistically significant difference in the area under the curve (p = 0.004).

CONCLUSION

The influence of apelin levels on troponin levels in the acute phase of STEMI is inversely correlated, whereas in the non-acute phase, low apelin values were associated with a high rate of MACE.

Apelin-13 protects against myocardial infarction-induced myocardial fibrosis

Myocardial infarction is a serious health threat. Apelin is an endogenous ligand of angiotensin II receptor-like 1 (APJ) and the apelin/APJ system is associated with various types of heart disease. However, whether apelin protects against myocardial infarction‑induced myocardial fibrosis remains unclear. The present study aimed to investigate the function of apelin‑13 during myocardial infarction‑induced myocardial fibrosis, and to determine the mechanism underlying the effects of apelin‑13. Apelin‑13 was demonstrated to improve left ventricular function and results of hematoxylin and eosin staining, Masson's trichrome staining and western blotting showed that apelin‑13 attenuated myocardial fibrosis. Further mechanistic investigation was performed by enzyme‑linked immunosorbent assay, western blotting and electrophoretic mobility shift assay. The results demonstrated that apelin‑13 inhibited the activation of nuclear factor (NF)‑κB signaling in vitro and in vivo. To the best of our knowledge, the present study was the first to demonstrate that apelin‑13 may attenuate myocardial infarction‑induced myocardial fibrosis, and that this protective function may be mediated by inhibition of NF‑κB signaling. The present study suggests a theoretical basis for the effects of apelin‑13 and provides insight into the potential clinical application of apelin-13.

Signaling pathways of a structural analogue of apelin-12 involved in myocardial protection against ischemia/reperfusion injury

Exogenously administered chemically modified apelin-12 (MA) has been shown to exhibit protective effects in myocardial ischemia/reperfusion (I/R) injury. They include reduction of ROS formation, cell death and cardiometabolic abnormalities. The aim of the present study was to explore the role of the underlying signaling mechanisms involved in cardioprotection afforded by MA. Isolated perfused working rat hearts subjected to global ischemia and anaesthetized rats in vivo exposed to LAD coronary artery occlusion were used. Myocardial infarct size, cell membrane damage, cardiac dysfunction and metabolic state of the heart were used as indices of I/R injury at the end of reperfusion. Administration of specific inhibitors of MEK1/2, PI3K, NO synthase (NOS) or the mitochondrial ATP-sensitive K(+) (mito KATP) channels (UO126, LY294002, L-NAME or 5-hydroxydecanoate, respectively) reduced protective efficacy of MA in both models of I/R injury. This was evidenced by abrogation of infarct size limitation, deterioration of cardiac function recovery, and attenuation of metabolic restoration and sarcolemmal integrity. An enhancement of functional and metabolic recovery in isolated reperfused hearts treated with MA was suppressed by U-73122, chelerythrine, amiloride or KB-R7943 (inhibitors of phospholipase С (PLC), protein kinase C (PKC), Na(+)/H(+) or Na(+)/Ca(2+) exchange, respectively). Additionally, co-infusion of MA with amiloride or L-NAME reduced the integrity of cell membranes at early reperfusion compared with the effect of peptide alone. In conclusion, cardioprotection with MA is mediated by signaling via PLC and survival kinases, PKC, PI3K, and MEK1/2, with activation of downstream targets, NOS and mito KATP channels, and the sarcolemmal Na(+)/H(+) and Na(+)/Ca(2+) exchangers.

Apelin-13 protects the heart against ischemia-reperfusion injury through the RISK-GSK-3β-mPTP pathway

INTRODUCTION

Apelin plays an important role in the protection against myocardial ischemia-reperfusion (I/R) injury, while the mechanism still remains unclear. In the current study, we aimed to evaluate the protective effect of apelin-13, and the main mechanism.

MATERIAL AND METHODS

The in vivo I/R injury model (Sprague-Dawley rat) was established, then infarct size, expression levels of phospho-protein kinase B (p-Akt), phospho-extracellular signal-regulated kinase (p-ERK) and phospho-glycogen synthase kinase-3β (p-GSK-3β) were measured. The fluorescence intensity of tetramethylrhodamine ethyl ester perchlorate (TMRE) of the isolated myocardial cells was determined to evaluate the opening of the mitochondrial permeability transition pore (mPTP) caused by oxidant stress and hypoxia/reoxygenation.

RESULTS

For the established I/R injury model, apelin-13 and SB216763 (GSK-3β inhibitor) significantly reduced the infarct size (p < 0.05), which could be abolished by LY294002 (PI3K inhibitor), PD98059 (MEK inhibitor) and atractyloside (mPTP accelerator). The enhanced expression levels of p-Akt, p-ERK and p-GSK-3β caused by apelin-13 (p < 0.05) could be counteracted by LY294002 and PD98059. The reduced fluorescence intensity of TMRE in the H2O2/apelin-13 and H2O2/SB216763 treated groups was significantly lower (p < 0.05), indicating that apelin-13 and SB216763 could reduce the decline in mitochondrial membrane potential caused by oxidant stress, and the fluorescence intensity in the hypoxia/reoxygenation + apelin-13 group was significantly lower (p < 0.05), which suggested that apelin-13 could inhibit the mitochondrial membrane potential changes induced by hypoxia/reoxygenation.

CONCLUSIONS

The protective mechanism of apelin-13 might be that inactivation of GSK-3β could inhibit the opening of mPTP by activating PI3K/Akt and ERK1/2 involved in the reperfusion injury salvage kinase (RISK) pathway.

Structural apelin analogues: mitochondrial ROS inhibition and cardiometabolic protection in myocardial ischaemia reperfusion injury

BACKGROUND AND PURPOSE

Mitochondria-derived oxidative stress is believed to be crucially involved in cardiac ischaemia reperfusion (I/R) injury, although currently no therapies exist that specifically target mitochondrial reactive oxygen species (ROS) production. The present study was designed to evaluate the potential effects of the structural analogues of apelin-12, an adipocyte-derived peptide, on mitochondrial ROS generation, cardiomyocyte apoptosis, and metabolic and functional recovery to myocardial I/R injury.

EXPERIMENTAL APPROACH

In cultured H9C2 cardiomyoblasts and adult cardiomyocytes, oxidative stress was induced by hypoxia reoxygenation. Isolated rat hearts were subjected to 35 min of global ischaemia and 30 min of reperfusion. Apelin-12, apelin-13 and structural apelin-12 analogues, AI and AII, were infused during 5 min prior to ischaemia.

KEY RESULTS

In cardiac cells, mitochondrial ROS production was inhibited by the structural analogues of apelin, AI and AII, in comparison with the natural peptides, apelin-12 and apelin-13. Treatment of cardiomyocytes with AI and AII decreased cell apoptosis concentration-dependently. In a rat model of I/R injury, pre-ischaemic infusion of AI and AII markedly reduced ROS formation in the myocardial effluent and attenuated cell membrane damage. Prevention of oxidative damage by AI and AII was associated with the improvement of functional and metabolic recovery after I/R in the heart.

CONCLUSIONS AND IMPLICATIONS

These data provide the evidence for the potential of the structural apelin analogues in selective reduction of mitochondrial ROS generation and myocardial apoptosis and form the basis for a promising therapeutic strategy in the treatment of oxidative stress-related heart disease.

Alpha-linolenic acid protects against cardiac injury and remodelling induced by beta-adrenergic overstimulation

α-Linolenic acid (ALA)-enriched diet prevented isoproterenol (ISO)-induced fibrosis in the ventricular myocardium.

The protective effect of apelin on ischemia/reperfusion injury

Apelin is the endogenous ligand for the APJ, a member of the G protein coupled receptors family. Apelin/APJ system is widely distributed in central nervous system and peripheral tissues, especially in heart, lung and kidney. Apelin plays important physiological and pathological roles in cardiovascular system, immune system, neuroprotection, etc. This article outlines the protective effect of apelin on ischemia/reperfusion (I/R) injury. Apelin could activate multiple protective mechanisms to prevent heart, brain, liver and kidney I/R injury. Apelin/APJ system may be a promising therapeutic target for ischemic and other related diseases.

The role of gasotransmitters NO, H2S and CO in myocardial ischaemia/reperfusion injury and cardioprotection by preconditioning, postconditioning and remote conditioning

Ischaemic heart disease is one of the leading causes of morbidity and mortality worldwide. The development of cardioprotective therapeutic agents remains a partly unmet need and a challenge for both medicine and industry, with significant financial and social implications. Protection of the myocardium can be achieved by mechanical vascular occlusions such as preconditioning (PC), when brief episodes of ischaemia/reperfusion (I/R) are experienced prior to ischaemia; postconditioning (PostC), when the brief episodes are experienced at the immediate onset of reperfusion; and remote conditioning (RC), when the brief episodes are experienced in another vascular territory. The elucidation of the signalling pathways, which underlie the protective effects of PC, PostC and RC, would be expected to reveal novel molecular targets for cardioprotection that could be modulated by pharmacological agents to prevent reperfusion injury. Gasotransmitters including NO, hydrogen sulphide (H2S) and carbon monoxide (CO) are a growing family of regulatory molecules that affect physiological and pathological functions. NO, H2S and CO share several common properties; they are beneficial at low concentrations but hazardous in higher amounts; they relax smooth muscle cells, inhibit apoptosis and exert anti-inflammatory effects. In the cardiovascular system, NO, H2S and CO induce vasorelaxation and promote cardioprotection. In this review article, we summarize current knowledge on the role of the gasotransmitters NO, H2S and CO in myocardial I/R injury and cardioprotection provided by conditioning strategies and highlight future perspectives in cardioprotection by NO, H2S, CO, as well as their donor molecules.

Apelin-12 and its structural analog enhance antioxidant defense in experimental myocardial ischemia and reperfusion

This study investigated the effects of peptide apelin-12 (H-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe-OH, A12) and its novel structural analog (H-(N(α)Me)Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Pro-Phe-OH, AI) on myocardial antioxidant enzyme activities, lipid peroxidation, and reactive oxygen species formation in ex vivo and in vivo models of myocardial ischemia/reperfusion (I/R) injury. Isolated working rat hearts were subjected to global ischemia and reperfusion. Infusion of 140 μM A12 or AI before global ischemia improved cardiac function recovery; increased the activity of Cu,Zn superoxide dismutase (Cu,Zn SOD), catalase (CAT), and glutathione peroxidase (GSH-Px); decreased malondialdehyde (MDA) content in reperfused heart; and reduced the formation of hydroxyl radical adduct of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide in the myocardial effluent during early reperfusion compared with these indices in control. Anesthetized open-chest rats were subjected to the left anterior descending coronary artery occlusion and coronary reperfusion. Peptide A12 or its analog AI was injected intravenously at the onset of reperfusion at a dose of 0.35 μmol/kg. Treatment with A12 or AI significantly limited infarct size and reduced the activity of lactate dehydrogenase and creatine kinase MB isoenzyme in blood plasma at the end of reperfusion compared with control. These effects were accompanied by complete recovery of Cu,Zn SOD, CAT, and GSH-Px activities; and decrease in MDA content in the area at risk by the end of reperfusion. The study concluded that C-terminal fragment of native peptide apelin-12 and its synthesized analog is involved in the upregulation of cardiac antioxidant defense systems and attenuation of lipid peroxidation in myocardial I/R injury.

Jagged-1/Notch3 signaling transduction pathway is involved in apelin-13-induced vascular smooth muscle cells proliferation

The apelin/apelin receptor (APJ, apelin-angiotensin receptor-like 1) system is a newly deorphanized G protein-coupled receptor system. Both apelin and APJ that are important regulatory factors are expressed in the cardiovascular system. Our previous studies demonstrated that apelin-13 significantly stimulated vascular smooth muscle cell (VSMC) proliferation. In this paper, our data suggested that the Jagged-1/Notch3 signaling transduction pathway is involved in apelin-13-induced VSMC proliferation by promoting the expression of Cyclin D1. Results indicated that apelin-13 stimulates the proliferation of VSMC and the expression of Jagged-1 and Notch3 in concentration- and time-dependent manners. The increased expression of Jagged-1 and Notch3 induced by apelin-13 could be abolished by extracellular signal-regulated protein kinase (ERK) blockade. PD98059 (ERK inhibitor) can inhibit the activation of Jagged-1/Notch3 induced by apelin-13. Down-regulation of Notch3 using small interfering RNA inhibits the expression of Cyclin D1 and prevents apelin-13-induced VSMC proliferation. In conclusion, Jagged-1/Notch3 signaling transduction pathway is involved in VSMC proliferation induced by apelin-13.

The protective effects of 17beta-estradiol against ischemia-reperfusion injury and its effect on pacing postconditioning protection to the heart

The role of pacing postconditioning (PPC) in the heart protection against ischemia-reperfusion injury is not completely understood. The aim of this study was to investigated if 17-β-estradiol (estrogen, E2), endogenous atrial natriuretic peptide (ANP), endogenous brain natriuretic peptide (BNP), and tumor necrosis factor-alpha (TNF-α) are involved in PPC-mediated protection. Langendorff perfused female Wistar rat hearts were used for this study. Hearts challenged with regional ischemia for 30 min subjected to no further treatment served as a control. The PPC protocol was 3 cycles of 30 s pacing alternated between the right atrium and left ventricle (LV). Protection was assessed by recovery of LV contractility and coronary vascular-hemodynamics. Ischemia induced a significant (P < 0.05) deterioration in the heart function compared with baseline data. PPC alone or in combination with short-term E2 treatment (E2 infusion at the beginning of reperfusion) significantly (P < 0.05) improved the heart functions. Short-term E2 treatment post-ischemically afforded protection similar to that of PPC. However, long-term E2 substitution for 6 weeks completely attenuated the protective effects of PPC. Although no changes were noted in endogenous ANP levels, PPC significantly increased BNP expression level and decreased TNF-α in the cardiomyocyte lysate and coronary effluent compared to ischemia and controls. Our data suggested a protective role for short-term E2 treatment similar to that of PPC mediated by a pathway recruiting BNP and downregulating TNF-α. Our study further suggested a bad influence for long-term E2 substitution on the heart as it completely abrogated the protective effects of PPC.

Myocardial injection of apelin-overexpressing bone marrow cells improves cardiac repair via upregulation of Sirt3 after myocardial infarction

Our previous study shows that treatment with apelin increases bone marrow cells (BMCs) recruitment and promotes cardiac repair after myocardial infarction (MI). The objective of this study was to investigate whether overexpression of apelin in BMCs improved cell therapy and accelerated cardiac repair and functional recovery in post-MI mice. Mouse myocardial infarction was achieved by coronary artery ligation and BMCs overexpressing apelin (apelin-BMCs) or GFP (GFP-BMCs) were injected into ischemic area immediately after surgery. In vitro, exposure of cultured BMCs to apelin led to a gradual increase in SDF-1á and CXCR4 expression. Intramyocardial delivery of apelin-BMCs in post-MI mice resulted in a significant increase number of APJ⁺/c-kit⁺/Sca1⁺ cells in the injected area compared to GFP-BMCs treated post-MI mice. Treatment with apelin-BMCs increased expression of VEGF, Ang-1 and Tie-2 in post-MI mice. Apelin-BMCs treatment also significantly increased angiogenesis and attenuated cardiac fibrosis formation in post-MI mice. Most importantly, treatment with apelin-BMCs significantly improved left ventricular (LV) systolic function in post-MI mice. Mechanistically, Apelin-BMCs treatment led to a significant increase in Sirtuin3 (Sirt3) expression and reduction of reactive oxygen species (ROS) formation. Treatment of cultured BMCs with apelin also increased Notch3 expression and Akt phosphorylation. Apelin treatment further attenuated stress-induced apoptosis whereas knockout of Sirt3 abolished anti-apoptotic effect of apelin in cultured BMCs. Moreover, knockout of Sirt3 significantly attenuated apelin-BMCs-induced VEGF expression and angiogenesis in post-MI mice. Knockout of Sirt3 further blunted apelin-BMCs-mediated improvement of cardiac repair and systolic functional recovery in post-MI mice. These data suggest that apelin improves BMCs therapy on cardiac repair and systolic function in post-MI mice. Upregulation of Sirt3 may contribute to the protective effect of apelin-BMCs therapy.

Effects of structural analogues of apelin-12 in acute myocardial infarction in rats

Objective:

To examine cardioprotective effects of Ρ-terminal fragment of adipokine apelin-12 (A12), its novel structural analogue [MeArg¹, NLe¹⁰]-A12 (I), and [d-Ala¹²]-A12 (II), a putative antagonist of APJ receptor, employing in vivo model of ischemia/reperfusion (I/R) injury.

Materials and Methods:

Peptides were synthesized by the automatic solid phase method using Fmoc technology. Anesthetized open-chest male Wistar rats were subjected to left anterior descending (LAD) coronary artery occlusion and coronary reperfusion. Hemodynamic variables and electrocardiogram (ECG) were monitored throughout the experiment. Myocardial injury was assessed by infarct size (IS), activity of necrosis markers in plasma, and metabolic state of the area at risk (AAR).

Results:

Intravenous injection of A12, I, or II at the onset of reperfusion led to a transient reduction of the mean arterial pressure. A12 or I administration decreased the percent ratio of IS/AAR by 40% and 30%, respectively, compared with control animals which received saline. Both peptides improved preservation of high-energy phosphates, reduced lactate accumulation in the AAR, and lowered CK-MB and LDH activities in plasma at the end of reperfusion compared with these indices in control. Treatment with II did not significantly affect either the IS/AAR, % ratio, or activities of both markers of necrosis compared with control. The overall metabolic protection of the AAR in the treated groups increased in the following rank: II < A12 < I.

Conclusions:

The structural analogue of apelin-12 [MeArg¹, NLe¹⁰]-A12 may be a promising basis to create a new drug for the treatment of acute coronary syndrome.