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

The structural analogue of apelin-12 prevents energy disorders in the heart in experimental type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is the most severe form of diabetes, which is characterized by absolute insulin deficiency induced by the destruction of pancreatic beta cells. The aim of this study was to evaluate the effect of a structural analogue of apelin-12 ((NαMe)Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Pro-Phe-OH, metilin) on hyperglycemia, mitochondrial (MCh) respiration in permeabilized cardiac left ventricular (LV) fibers, the myocardial energy state, and cardiomyocyte membranes damage in a model of streptozotocin (STZ) diabetes in rats. Metilin was prepared by solid-phase synthesis using the Fmoc strategy and purified using HPLC. Four groups of animals were used: initial state (IS); control (C), diabetic control (D) and diabetic animals additionally treated with metilin (DM). The following parameters have been studied: blood glucose, MCh respiration in LV fibers, the content of cardiac ATP, ADP, AMP, phosphocreatine (PCr) and creatine (Cr), the activity of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) in blood plasma. Administration of metilin to STZ-treated rats decreased blood glucose, increased state 3 oxygen consumption, the respiratory control ratio in MCh of permeabilized LV fibers, and increased the functional coupling of mitochondrial CK (mt-CK) to oxidative phosphorylation compared with these parameters in group D. In STZ-treated animals metilin administration caused an increase in the PCr content and prevention of the loss of total creatine (ΣCr=PCr+Cr) in the diabetic hearts, as well as restoration of the PCr/ATP ratio in the myocardium and a decrease in the activity of CK-MB and LDH in plasma to initial values. Thus, metilin prevented energy disorders disturbances in cardiomyocytes of animals with experimental T1DM.

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.

Protective Role of Short-term Aerobic Exercise Against Zinc Oxide Nanoparticles-Induced Cardiac Oxidative Stress Via Possible Changes of Apelin, Angiotensin II/Angiotensin II Type I Signalling Pathway

This study examined the protective role of short-term aerobic exercise on ZnO NPs-induced cardiac oxidative stress and possible changes of apelin, angiotensin II (AngII) and angiotensin II type I receptor (AT1R) signalling pathway. Thirty-five male Wistar rats were randomized into five groups of seven rats, including control, saline, ZnO NPs, exercise and exercise + ZnO NPs groups. The animal in ZnO NPs and exercise + ZnO NPs groups received 1 mg/kg of ZnO NPs. Rats underwent the treadmill exercise program. Treatments lasted four weeks, 5 days/week. After 4 weeks of treatment, superoxide dismutase (SOD) activity, malondialdehyde (MDA), apelin, Ang II and AT1R concentration were measured in heart tissue.Cardiac MDA, Ang II and AT1R levels significantly increased while SOD activity and apelin levels significantly decreased following ZnO NPs administration. The aerobic exercise induced a significant increase in the SOD activity and apelin levels and a significant decrease in the enhanced MDA, Ang II and AT1R levels in the heart of ZnO NPs-exposed rats. These results suggest that the exercise-induced attenuation of the Ang II-AT1R signalling pathway is mediated by reduced lipid peroxidation, augmented antioxidant defence and enhanced apelin synthesis that may be a protective mechanism to prevent and/or treatment ZnO NPs-induced cardiac oxidative stress.

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.

Protective effect of Apelin-13 in a cyclophosphamide-induced cardiorenal toxicity model in rats

Cyclophosphamide is a chemotherapeutic drug that is widely used in the clinic and can cause multi-organ toxicity. Apelin-13 is an endogenous adipocytokine with antioxidant properties. Therefore, this study aimed to investigate the possibility of apelin-13 being a potential therapeutic agent on cardiac toxicity and nephrotoxicity caused by cyclophosphamide. In this study, a total of 4 groups were formed, including 8 rats in each group. Group 1: The control group was administered only saline (ip). Group 2: Cyclophosphamide, a single dose of 200 mg/kg (ip) on day 7. Group 3: Apelin-13 (15 μg/kg), for 7 days (ip). Group 4: Administering apelin-13 (15 μg/kg) (ip) for 7 days and a single dose of cyclophosphamide (200 mg/kg) (ip) on day 7, the rats were sacrificed on day 8. LDH, cTn1, cK-Mb, AST, ALT, ALP, MDA, creatinine, and BUN were found to be high in the cyclophosphamide group, however, these values were reduced with apelin-13 administration. Antioxidant enzymes such as SOD, GPx, CAT, and GSH decreased in the cyclophosphamide group, apelin-13 increased these enzyme activities. In addition, histopathological examinations also supported the results obtained. The findings of this study showed that apelin-13 has a protective effect against cardiorenal toxicity caused by cyclophosphamide.

The Rationale of Neprilysin Inhibition in Prevention of Myocardial Ischemia-Reperfusion Injury during ST-Elevation Myocardial Infarction

During the last three decades, timely myocardial reperfusion using either thrombolytic therapy or primary percutaneous intervention (pPCI) has allowed amazing improvements in outcomes with a more than halving in 1-year ST-elevation myocardial infarction (STEMI) mortality. However, mortality and left ventricle (LV) remodeling remain substantial in these patients. As such, novel therapeutic interventions are required to reduce myocardial infarction size, preserve LV systolic function, and improve survival in reperfused-STEMI patients. Myocardial ischemia-reperfusion injury (MIRI) prevention represents the main goal to reach in order to reduce STEMI mortality. There is currently no effective therapy for MIRI prevention in STEMI patients. A significant reason for the weak and inconsistent results obtained in this field may be the presence of multiple, partially redundant, mechanisms of cell death during ischemia-reperfusion, whose relative importance may depend on the conditions. Therefore, it is always more recognized that it is important to consider a "multi-targeted cardioprotective therapy", defined as an additive or synergistic cardioprotective agents or interventions directed to distinct targets with different timing of application (before, during, or after pPCI). Given that some neprilysin (NEP) substrates (natriuretic peptides, angiotensin II, bradykinin, apelins, substance P, and adrenomedullin) exert a cardioprotective effect against ischemia-reperfusion injury, it is conceivable that antagonism of proteolytic activity by this enzyme may be considered in a multi-targeted strategy for MIRI prevention. In this review, by starting from main pathophysiological mechanisms promoting MIRI, we discuss cardioprotective effects of NEP substrates and the potential benefit of NEP pharmacological inhibition in MIRI prevention.

[MeArg1, NLe10]-apelin-12: Optimization of solid-phase synthesis and evaluation of biological properties in vitro and in vivo

Chemically modified peptide apelin-12 ([MeArg¹, NLe¹⁰]-apelin12, peptide M) is able to reduce reactive oxygen species (ROS) formation, cell death, and metabolic and ionic homeostasis disorders in experimental myocardial ischemia-reperfusion injury. These beneficial effects indicate the therapeutic potential of this compound in cardiovascular diseases. The goals of this work were to optimize the synthesis of peptide M, and to study its proteolytic stability and effect on the heart function of rabbits with doxorubicin (Dox) cardiomyopathy. We have developed a rational method of solid-phase synthesis of peptide M using the Fmoc methodology in combination with the temporary protection of the guanidine function of arginine residues by protonation (salt formation) during the formation of the amide bond. It avoids the formation of by-products, and simplifies the post-synthetic procedures, providing an increase in the yield of the final product of higher purity. Comparative evaluation of the proteolytic stability of peptide M and apelin-12 in human blood plasma was carried out using ¹H NMR spectroscopy. It was shown that the half-life of peptide M in plasma is approximately three times longer than that of apelin-12. Intravenous infusion of increasing doses of peptide M caused a gradual increase in left ventricular (LV) fractional shortening and ejection fraction in rabbits after 8 weeks of Dox administration (2 mg/kg weekly). The effect of the modified peptide on LV systolic dysfunction was significantly more pronounced than the effect of apelin-12, which suggests the promise of using this pharmacological agonist of the APJ receptor in patients with heart failure.

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.

miR-503/Apelin-12 mediates high glucose-induced microvascular endothelial cells injury via JNK and p38MAPK signaling pathway

Introduction

Diabetic patients are often accompanied by complications of diabetic vascular disease, which could lead to heart failure or stroke. In this work, we explored the role of miR-503/Apelin-12 in diabetic angiopathy (DA) in vitro.

Methods

ELISA and qPCR were applied to assess the expression of miR-503 and Apelin-12 in high glucose (HG)-treated microvascular endothelial cells (HMEC-1). The effects of miR-503 on apoptosis, inflammation and oxidative stress were assessed by flow cytometry, western blotting, qPCR, and ELISA. The interaction between miR-503 and Apelin-12 was evaluated by dual-luciferase reporter assay, qPCR and ELISA, respectively. Western blotting was performed to examine the function of miR-503/Apelin-12 on JNK and p38MAPK activation.

Results

MiR-503 was markedly increased and Apelin-12 was decreased in HG-treated HMEC-1 cells. MiR-503 inhibitor significantly assuaged apoptosis, inflammation and oxidative stress in HMEC-1 cells. MiR-503 could specifically bind to the 3′UTR of Apelin and inversely downregulate Apelin-12 expression. Furthermore, Apelin-12 suppressed apoptosis, inflammation and oxidative stress. Inhibition of Apelin-12 could partially reverse the decrease of p-JNK and p-p38 expression levels induced by miR-503 suppression.

Conclusion

In HG-induced microvascular cells injury, miR-503/Apelin-12 enhances inflammation and oxidative stress by regulating JNK and p38MAPK pathway, suggesting a potential therapeutic target for DA.

A Novel Chinese Medicine, Xinfeng Capsule, Modulates Proinflammatory Cytokines via Regulating the Toll-Like Receptor 4 (TLR4)/Mitogen-Activated Protein Kinase (MAPK)/Nuclear Kappa B (NF-κB) Signaling Pathway in an Adjuvant Arthritis Rat Model

Background

Rheumatoid arthritis (RA) is a chronic autoimmune disease targeting joints. This research aimed to explore the effects of Xinfeng capsules (XFC) on cardiac injury in adjuvant arthritis (AA) model rats and assessed the associated mechanism.

Material/Methods

An adjuvant arthritis (AA) rat model was established by intracutaneously injection with Freund’s complete adjuvant (FCA). Model rats were divided into 4 groups: an AA model group, an astragalus polysaccharides (APS) group, a methotrexate (MTX) group, and an XFC and triptolide (TPT) group. Hematoxylin-eosin (HE) staining was used to observe histopathologic changes. TUNEL assay was utilized to evaluate the apoptosis of cardiomyocytes. ELISA was utilized to evaluate levels of tumor necrosis factor α (TNF-α), interleukin 17 (IL-17), and interleukin 6 (IL-6) in myocardial tissues. Quantitative RT-PCR (qRT-PCR) was used to detect microRNA-21 (miRNA21) levels. Mitogen-activated protein kinase (MAPK)/p38, Toll-like receptor 4 (TLR4), and nuclear kappa B (NF-κB)/p65 levels were evaluated using Western blot.

Results

XFC significantly improved proinflammatory response compared to the AA model group (p<0.05). XFC treatment significantly decreased the number of cells staining TUNEL-positive compared with the model group (p<0.05). XFC treatment significantly reduced TNF-α, IL-17, and IL-6 levels in myocardial tissues compared to the model group (p<0.05). Levels of miRNA21 were significantly lower in the XFC group compared to the AA model group (p<0.05). TLR4, MAPK/p38, and NF-κB/p65 expression levels were significantly lower in the XFC group than in the model group (p<0.05).

Conclusions

Xinfeng capsule, a traditional Chinese medicine preparation, protects against cardiac injury in AA rats by modulating proinflammatory cytokines expression via the TLR4/MAPK/NF-κB signaling pathway.

Plasma Apelin Concentration in Exercised Horses: Preliminary Study

Physical effort is one of the key aspects of keeping horses in good condition. The condition of the animal is reflected by multiple blood parameters. The newly discovered cytokine-apelin can pose one of them, however, so far, has not been studied in the horse population. Apelin is produced by adipocytes and myocytes and plays an important role in the energy metabolism of the body through the influence, for example, on the process of adipogenesis and lipolysis. The aim of this study was to investigate if physical effort of various intensity affects the plasma concentration of apelin in horses. The study involved 20 purebred Arabian horses divided into two groups. The first group included 10 race horses, aged 3 years, and second group included 10 horses aged from 6 to 12 years, used in endurance rides. Blood samples were collected from each horse at rest and after exercise. The concentrations of apelin, lactic acid, cortisol, uric acid (UA), triacylglycerols, total plasma protein, and glucose were determined in plasma samples. Race training sessions induced significant decreases in plasma apelin concentrations (P < .05). In endurance horses, significant correlations were found only between exercise-induced changes of apelin and cortisol (r = 0.55) and apelin and UA (r = 0.67) concentrations. In conclusion, the concentration of apelin in equine plasma decreases in response to short-time exercise unlike endurance exercise. Blood plasma apelin concentration determined at rest is lower in long-time regularly trained horses than in the ones at the beginning of their training process.

Inhibition of CLU4A exhibits a cardioprotective role in hypoxia/reoxygenation-induced injury by an ERK-dependent pathway

CLU4A is identified as a proto-oncogene in various human cancers. CLU4A was reported to be up-regulated in myocardial ischemia/reperfusion injury, but the precise role of CLU4A played in myocardial ischemia/reperfusion injury remains unknown; and the underlying mechanism of CLU4A in myocardial ischemia/reperfusion injury needs to be investigated. CLU4A expression was measured after myocardial ischemia/reperfusion in mice and in H9C2 cells with hypoxia/reoxygenation treatment by q-PCR and western blotting. The cardioprotective effect of CLU4A inhibition was detected by monitoring the cell viability, cell apoptosis, and LDH activity in vitro and in vivo, and examining the infarct size and cardiac function in vivo. The molecular mechanism was further determined by examining the effects of PD98059, a specific inhibitor of the ERK signaling pathways in H9C2 cells with hypoxia/reoxygenation treatment. CLU4A expression was up-regulated after myocardial ischemia/reperfusion in mice and in H9C2 cells with hypoxia/reoxygenation treatment. Inhibition of CLU4A improved the cell viability, restrained the cell apoptosis, and suppressed LDH activity in vitro. Consistently, knockdown of CLU4A reduced the myocardial infarct size and improved cardiac function in vivo. si-CLU4A treatment increased phosphorylated ERK (p-ERK) in vitro, but the protection role of si-CLU4A was abolished by the ERK inhibitor, PD98059. In conclusion, CLU4A expression was up-regulated in myocardial ischemia/reperfusion. Inhibition of CLU4A exhibited a cardioprotective role by an ERK-dependent pathway.

Possible involvement of alpha B-crystallin in the cardioprotective effect of n-butanol extract of Potentilla anserina L. on myocardial ischemia/reperfusion injury in rat

BACKGROUND

It has been reported that n-butanol extract of Potentilla anserina L (NP) had protective effect against acute myocardial ischemia/reperfusion (I/R) injury in mice. Because of limited phytochemical study on NP, its bioactive compounds and underlying protective mechanisms are largely unclear.

PURPOSE

The purpose of this study was to investigate the major bioactive compounds and possible mechanism for the cardioprotective effect of NP on rat with I/R injury.

METHODS

We analyzed the phytochemical isolation of NP and identified the structure of compounds, which was elucidated by a combination of spectroscopic analyses. An I/R model was established by I-30 min/R-2 h in Sprage-Dawley rats. The rats were given intragastric administration of NP (49.3, 98.6, and 197.2 mg•kg^-1) continuously for 10 days before I/R operation. The morphological changes and apoptosis of cardiomyocytes were observed by H&E staining, Transmission electron microscope and TUNEL staining respectively. The activities or contents of catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA) and glutathione (GSH) in plasma were detected. Apoptosis related factors were also measured by RT-PCR and western blot. In order to discover the underlying mechanism of NP on I/R, we performed proteomic analysis using two-dimensional gel electrophoresis (2D-DIGE) and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF/MS) to describe differential proteins expression. Potential target protein resulted from 2D-DIGE coupled to MALDI-TOF/MS analysis were further confirmed by immunohistochemical staining, RT-PCR, and western blot.

RESULTS

We isolated and identified 14 compounds, of which 7 compounds belong to triterpenes. Rats pretreated with NP showed a significant increase on the activities of GSH, SOD and CAT, and remarkable decrease on the content of MDA. NP significantly inhibited the apoptosis of cardiomyocyte and decreased the expression of Cyt C and cleaved-caspase-3. Proteomic analysis revealed that alpha B-crystallin (CryAB) might participate in the NP protective effect against I/R. NP enhanced the level of pCryAB Ser59, whereas the expression of CryAB was decreased.

CONCLUSION

NP was showed to alleviate I/R injury and inhibit myocardial apoptosis, which might be associated with reduction on oxidative stress and apoptosis. CryAB as a possible target involved in the NP protective effect. This study supplied valuable information to develop novel cardioprotective agents from NP extract.

Protective efficacy of dinitrosyl iron complexes with reduced glutathione in cardioplegia and reperfusion

Disturbed homeostasis of nitric oxide (NO) is one of the causes of myocardial ischemia/reperfusion (I/R) injury during open-heart surgery. This study was designed to explore mechanisms of action of dinitrosyl iron complexes with reduced glutathione ({(GS^-)₂Fe⁺(NO⁺)₂}⁺, DNIC-GS) added to crystalloid cardioplegia or reperfusion solution in isolated working rat hearts. Hearts of male Wistar rats were subjected to cardioplegic arrest by St. Thomas' Hospital cardioplegic solution (STH) and normothermic global ischemia followed by reperfusion. DNIC-GS were used with STH or during early reperfusion. Lactate dehydrogenase (LDH) activity in the coronary effluent and myocardial contents of adenine nucleotides, phosphocreatine, and lactate were determined spectrophotometrically. Reactive oxygen species (ROS) formation in the coronary effluent and myocardial DNIC content was assessed by EPR technique. Cardioplegia or reperfusion with DNIC-GS significantly improved recovery of coronary flow and cardiac function compared with control. Carboxy-[2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidozoline-1-oxy-3-oxide] (C-PTIO), a selective NO scavenger, reduced/abolished protective action of DNIC-GS. Enhanced recovery of cardiac function with DNIC-GS reduced LDH release in the coronary effluent, augmented recovery of myocardial energy state, and decreased formation of ROS-generating systems at reperfusion. Beneficial effects of DNIC-GS were related to the transfer of [Fe(NO)₂] cores to thiol groups of myocardial proteins to form intracellular DNIC pools. The study concluded that DNIC-GS is a promising adjunct agent for metabolic and antioxidant protection of the heart during cardioplegic arrest and reperfusion.

Galanin/GalR1-3 system: A promising therapeutic target for myocardial ischemia/reperfusion injury

N-terminal fragments of galanin (2-11) and (2-15) are critical for binding to GalR1-3 receptors, members of the G-protein-coupled receptor superfamily, and are involved in myocardial protection against ischemia/reperfusion (I/R) injury. This study was designed to synthesize novel GalR1-3 agonists with improved properties and evaluate their efficiency as cardioprotective agents. Peptide agonists were synthesized by the automatic solid phase method using Fmoc technology and purified by preparative HPLC. Their chemical structure was identified by ¹H-NMR spectroscopy and MALDI-TOF mass spectrometry. Novel ligands of galanin receptors have greater solubility in water than natural galanin fragments. Cardiac function indices, myocardial infarct size and plasma activity of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) were measured to assess the peptide bioactivity. Infusion of optimal concentrations of the peptides (210-240 μM) after global ischemia enhanced functional recovery of isolated rat heart during reperfusion. Intravenous administration of the peptides in a dose range of 1-2 mg/kg at the onset of reperfusion significantly reduced infarct size and plasma levels of CK-MB and LDH in rats in vivo. The chimeric ligand [βAla14, His15]-galanin (2-15) exhibited the most beneficial effect on both models of I/R injury. The results suggest that pharmacological agonists of GalR1-3 receptors can be a rational basis for drug developments in the field of cardiovascular diseases.

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.

Apelin, a promising target for Alzheimer disease prevention and treatment

Alzheimer's disease (AD) is a progressive neurodegenerative disease with high outbreak rates. It is estimated that about 35 million individuals around the world suffered from dementia in 2010. AD is expected to increase twofold every 20 years and, by 2030, approximately 65 million people could suffer from this illness. AD is determined clinically by a cognitive impairment and pathologically by the production of amyloid beta (Aβ), neurofibrillary tangles, toxic free radicals and inflammatory mediators in the brain. There is still no treatment to cure or even alter the progressive course of this disease; however, many new therapies are being investigated and are at various stages of clinical trials. Neuropeptides are signaling molecules used by neurons to communicate with each other. One of the important neuropeptides is apelin, which can be isolated from bovine stomach. Apelin and its receptor APJ have been shown to broadly disseminate in the neurons and oligodendrocytes of the central nervous system. Apelin-13 is known to be the predominant neuropeptide in neuroprotection. It is involved in the processes of memory and learning as well as the prevention of neuronal damage. Studies have shown that apelin can directly or indirectly prevent the production of Aβ and reduce its amounts by increasing its degradation. Phosphorylation and accumulation of tau protein may also be inhibited by apelin. Apelin is considered as an anti-inflammatory agent by preventing the production of inflammatory mediators such as interleukin-1β and tumor necrosis factor alpha. It has been shown that in vivo and in vitro anti-apoptotic effects of apelin have prevented the death of neurons. In this review, we describe the various functions of apelin associated with AD and present an integrated overview of recent findings that, in general, recommend apelin as a promising therapeutic agent in the treatment of this ailment.

Contribution of Apelin-17 to Collateral Circulation Following Cerebral Ischemic Stroke

Apelin, an essential mediator of homeostasis, is crucially involved in cardiovascular diseases, including ischemic stroke. However, the functional roles of apelin-17 in cerebral collateral circulation and ischemic stroke protection are unknown. Here, we investigated the association between plasma apelin-17 levels and collateral circulation in patients with ischemic stroke and examined the mechanism undergirding the effects of apelin-17 on cerebral artery contraction and ischemic stroke protection in an animal model. Plasma nitric oxide (NO), apelin-17, and apelin-36 levels were assessed by enzyme-linked immunosorbent assays in ischemic stroke patients with good or poor collateral circulation and in healthy participants. Additionally, the effects of apelin-17 on rat basilar artery contractions (in vitro) and cerebral ischemia (in vivo) were determined using vessel tension measurements and nuclear magnetic resonance, respectively. Patients with good collateral circulation had significantly higher plasma apelin-17 and apelin-36 levels than both patients with poor collateral circulation and healthy participants and plasma NO levels significantly higher than those in healthy participants. In vitro, apelin-17 pretreatment markedly attenuated U46619-induced rat basilar artery contractions in an endothelium-dependent manner. Additionally, NO production or guanylyl cyclase inhibitors abolished the apelin-17 effect on U46619-induced vascular contraction. Intravenous pretreatment of rats with apelin-17 markedly reduced cerebral infarct volume at 24 h after middle cerebral artery occlusion. Plasma apelin-17 levels in ischemic stroke patients were positively associated with enhanced collateral circulation, which our animal study data suggested may have resulted from an apelin-17-induced cerebral artery dilation mediated through the NO-cGMP pathway.

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.

Effect of L-Carnitine Supplementation on Apelin and Apelin Receptor (Apj) Expression in Cardiac Muscle of Obese Diabetic Rats

Objective

L-carnitine (LC) has been shown to protect cardiac metabolism in diabetes patients with cardiovascular diseases (CVDs). Apelin, a newly discovered adipocytokines, is an important regulator of cardiac muscle function; however, the role of the level of expression of Apelin axis in improvement of cardiac function by LC in diabetic patients, is not clear. In the present study, obese insulin-resistant rats were used to determine the effect of LC, when given orally with a high-calorie diet, on Apelin and Apelin receptor (Apj) expression in cardiac muscle.

Materials and Methods

In this experimental study, rats were fed with high-fat/high-carbohydrate diet for five weeks and subsequently were injected with streptozotocin 30 mg/kg for induction of obesity and insulin resistance. After confirming the induction of diabetes (serum glucose above 7.5 mmol/L), the animals received LC 300 mg/kg in drinking water for 28 days. On days 0, 14 and 28 after treatment, cardiac Apelin and Apj gene expression was evaluated by real time polymerase chain reaction (PCR) analysis. Serum levels of insulin, Apelin, glucose, tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and the homeostasis model assessment of insulin resistance (HOMA-IR) were also measured using commercial kits.

Results

Cardiac Apelin and Apj expression and serum Apelin were increased in obese rats, while LC supplementation decreased the serum levels of Apelin and down-regulated Apelin and Apj expression in cardiac muscle. These changes were associated with reduced insulin resistance markers and serum inflammatory factors and improved lipid profile.

Conclusion

We concluded that LC supplementation could attenuate the over-expression of Apelin axis in heart of diabetic rats, a novel mechanism by which LC improves cardiovascular complications in diabetic patients.

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.

Myocardial protection from ischemia/reperfusion injury by exogenous galanin fragment

Background and purpose

Galanin is a multifunctional neuropeptide with pleiotropic roles. The present study was designed to evaluate the potential effects of galanin (2-11) (G1) on functional and metabolic abnormalities in response to myocardial ischemia-reperfusion (I/R) injury.

Experimental approach

Peptide G1 was synthesized by the 9-fluorenylmethoxycarbonyl (Fmoc)-based solid-phase method. The chemical structure was identified by ¹H-NMR spectroscopy and mass spectrometry. Experiments were conducted using a rat model of I/R injury in vivo, isolated perfused rat hearts ex vivo and cultured rat cardiomyoblast H9C2 cells in vitro. Cardiac function, infarct size, myocardial energy metabolism, hemodynamic parameters, plasma levels of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) were measured in order to evaluate the effects of G1 on myocardial I/R injury.

Key results

Treatment with G1 increased cell viability in a dose-dependent manner, inhibited cell apoptosis and excessive mitochondrial reactive oxygen species (ROS) production in response to oxidative stress in H9C2 cells. Pre- or postischemic infusion of G1 enhanced functional and metabolic recovery during reperfusion of the ischemic isolated rat heart. Administration of G1 at the onset of reperfusion significantly reduced infarct size and plasma levels of CK-MB and LDH in rats subjected to myocardial I/R injury.

Conclusions and implications

These data provide the first evidence for cardioprotective activity of galanin G1 against myocardial I/R injury. Therefore, peptide G1 may represent a promising treatment strategy for ischemic heart disease.

Cardioprotective properties of N-terminal galanin fragment (2-15) in experimental ischemia/reperfusion injury

Background and purpose

Galanin is an endogenous peptide involved in diverse physiological functions in the central nervous system including central cardiovascular regulation. The present study was designed to evaluate the potential effects of the short N-terminal galanin fragment 2-15 (G) on cardiac ischemia/reperfusion (I/R) injury.

Experimental Approach

Peptide G was synthesized by the automatic solid phase method and identified by 1H-NMR spectroscopy and mass spectrometry. Experiments were performed on cultured rat cardiomyoblast (H9C2) cells, isolated perfused working rat hearts and anaesthetized open-chest rats.

Key Results

Cell viability increased significantly after treatment with 10 and 50 nM of G peptide. In hypoxia and reoxygenation conditions, exposure of H9C2 cells to G peptide decreased cell apoptosis and mitochondrial reactive oxygen species (ROS) production. Postischemic infusion of G peptide reduced cell membrane damage and improved functional recovery in isolated hearts during reperfusion. These effects were accompanied by enhanced restoration of myocardial metabolic state. Treatment with G peptide at the onset of reperfusion induced minor changes in hemodynamic variables but significantly reduced infarct size and plasma levels of necrosis markers.

Conclusion and implications

These findings suggest that G peptide is effective in mitigating cardiac I/R injury, thereby providing a rationale for promising tool for the treatment of cardiovascular diseases.

Trimetazidine protects against cardiac ischemia/reperfusion injury via effects on cardiac miRNA‑21 expression, Akt and the Bcl‑2/Bax pathway

Trimetazidine is a piperazine-derived metabolic agent, which exerts cell protective effects and has been reported to be efficient in the treatment of chronic stable angina pectoris. In addition, it has been shown to exert protection against acute myocardial infarction. The present study aimed to investigate whether trimetazidine protects against cardiac ischemia/reperfusion (I/R) injury, and to determine whether its curative effects are associated with microRNA (miRNA)-21 expression, Akt, and the B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein (Bax) pathway. Cardiac I/R injury was induced by ligating the left anterior descending coronary artery in adult rats. Subsequently, cardiac function was evaluated, and the expression levels of miRNA-21, Bcl-2, Bax and phosphorylated-Akt were detected using quantitative polymerase chain reaction and western blotting. The results indicated that trimetazidine was able to significantly protect cardiac function and reduce infarct size in rats following cardiac I/R injury. Furthermore, trimetazidine significantly promoted miRNA-21 expression and phosphorylated-Akt protein expression, and reduced the Bcl-2/Bax ratio in rats following cardiac I/R injury. Knockdown of miRNA-21 using anti-miR-21 plasmids was able to reverse the protective effects of trimetazidine against cardiac I/R injury. These results indicated that miRNA-21 serves a protective role in cardiac I/R injury via Akt and the Bcl-2/Bax pathway. In addition, trimetazidine exerts protective effects against cardiac I/R injury through cardiac miRNA-21 expression, Akt, and the Bcl-2/Bax pathway. Therefore, the present study provided evidence regarding the protective effects of miRNA-21 on cardiac I/R injury following treatment with trimetazidine in vivo.

Potential beneficial effect of some adipokines positively correlated with the adipose tissue content on the cardiovascular system

Obesity is a risk factor of cardiovascular diseases. However, in the case of heart failure, obese and overweight patients have a more favourable prognosis compared to patients who have a normal body weight. This phenomenon is referred to as the "obesity paradox," and it is explained by, among others, a positive effect of adipokines produced by adipose tissue, particularly by the tissue located in the direct vicinity of the heart and blood vessels. The favourable effect on the cardiovascular system is mostly associated with adiponectin and omentin, but the levels of these substances are reduced in obese patients. Among the adipokines which levels are positively correlated with the adipose tissue content, favourable activity is demonstrated by apelin, progranulin, chemerin, TNF-α (tumour necrosis factor-)α, CTRP-3 (C1q/tumour necrosis factor (TNF) related protein), leptin, visfatin and vaspin. This activity is associated with the promotion of regeneration processes in the damaged myocardium, formation of new blood vessels, reduction of the afterload, improvement of metabolic processes in cardiomyocytes and myocardial contractile function, inhibition of apoptosis and fibrosis of the myocardium, as well as anti-inflammatory and anti-atheromatous effects. The potential use of these properties in the treatment of heart failure and ischaemic heart disease, as well as in pulmonary hypertension, arterial hypertension and the limitation of the loss of cardiomyocytes during cardioplegia-requiring cardiosurgical procedures, is studied. The most advanced studies focus on analogues of apelin and progranulin.

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.

Regulation of the Apelinergic System and Its Potential in Cardiovascular Disease: Peptides and Small Molecules as Tools for Discovery

Apelin peptides and the apelin receptor represent a relatively new therapeutic axis for the potential treatment of cardiovascular disease. Several reports suggest apelin receptor activation with apelin peptides results in cardioprotection as noted through positive ionotropy, angiogenesis, reduction of mean arterial blood pressure, and apoptosis. Considering the potential therapeutic benefit attainable through modulation of the apelinergic system, research is expanding to develop novel therapies that limit the inherent rapid degradation of endogenous apelin peptides and produce metabolically stable small molecule agonists and antagonists to more rigorously interrogate the apelin receptor system. This review details the structure-activity relationships for chemically modified apelin peptides and recent disclosures of small molecule agonists and antagonists and summarizes the peer reviewed and patented literature. Development of metabolically stable ligands of apelin receptor and their effects in various models over the coming years will hopefully lead to establishment of this receptor as a validated target for cardiovascular indications.

TIMP3 interplays with apelin to regulate cardiovascular metabolism in hypercholesterolemic mice

OBJECTIVE

Tissue inhibitor of metalloproteinase 3 (TIMP3) is an extracellular matrix (ECM) bound protein, which has been shown to be downregulated in human subjects and experimental models with cardiometabolic disorders, including type 2 diabetes mellitus, hypertension and atherosclerosis. The aim of this study was to investigate the effects of TIMP3 on cardiac energy homeostasis during increased metabolic stress conditions.

METHODS

ApoE(-/-)TIMP3(-/-) and ApoE(-/-) mice on a C57BL/6 background were subjected to telemetric ECG analysis and experimental myocardial infarction as models of cardiac stress induction. We used Western blot, qRT-PCR, histology, metabolomics, RNA-sequencing and in vivo phenotypical analysis to investigate the molecular mechanisms of altered cardiac energy metabolism.

RESULTS

ApoE(-/-)TIMP3(-/-) revealed decreased lifespan. Telemetric ECG analysis showed increased arrhythmic episodes, and experimental myocardial infarction by left anterior descending artery (LAD) ligation resulted in increased peri-operative mortality together with increased scar formation, ventricular dilatation and a reduction of cardiac function after 4 weeks in the few survivors. Hearts of ApoE(-/-)TIMP3(-/-) exhibited accumulation of neutral lipids when fed a chow diet, which was exacerbated by a high fat, high cholesterol diet. Metabolomics analysis revealed an increase in circulating markers of oxidative stress with a reduction in long chain fatty acids. Using whole heart mRNA sequencing, we identified apelin as a putative modulator of these metabolic defects. Apelin is a regulator of fatty acid oxidation, and we found a reduction in the levels of enzymes involved in fatty acid oxidation in the left ventricle of ApoE(-/-)TIMP3(-/-) mice. Injection of apelin restored the hitherto identified metabolic defects of lipid oxidation.

CONCLUSION

TIMP3 regulates lipid metabolism as well as oxidative stress response via apelin. These findings therefore suggest that TIMP3 maintains metabolic flexibility in the heart, particularly during episodes of increased cardiac stress.

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.

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.

Picroside Ⅱ inhibits hypoxia/reoxygenation-induced cardiomyocyte apoptosis by ameliorating mitochondrial function through a mechanism involving a decrease in reactive oxygen species production

Reactive oxygen species (ROS)‑induced mitochondrial dysfunction plays an important role in cardiomyocyte apoptosis during myocardial ischemia/reperfusion (I/R) injury. Picroside Ⅱ, isolated from Picrorhiza scrophulariiflora Pennell (Scrophulariaceae), has been reported to protect cardiomyocytes from hypoxia/reoxygenation (H/R)‑induced apoptosis, but the exact mechanism is not fully clear. The aim of the present study was to explore the protective effects of picroside Ⅱ on H/R‑induced cardiomyocyte apoptosis and the underlying mechanism. In the H9c2 rat cardiomyocyte cell line, picroside Ⅱ (100 µg/ml) was added for 48 h prior to H/R. The results showed that picroside Ⅱ markedly inhibited H/R‑induced cardiomyocyte apoptosis. In addition, picroside Ⅱ was also able to decrease the opening degree of mitochondrial permeability transition pore (mPTP), increase the mitochondrial membrane potential, inhibit cytochrome c release from mitochondria to cytosol and downregulate caspase‑3 expression and activity concomitantly with the decreased ROS production. These results suggested that picroside Ⅱ inhibited H/R‑induced cardiomyocyte apoptosis by ameliorating mitochondrial function through a mechanism involving a decrease in ROS production.

Enhancement of crystalloid cardioplegic protection by structural analogs of apelin-12

BACKGROUND

C-terminal fragments of adipokine apelin are able to attenuate myocardial ischemia-reperfusion (I/R) injury, but whether their effects are manifested during cardioplegic arrest remain obscure. This study was designed to evaluate the efficacy of natural apelin-12 (H-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe-OH, A12) and its novel structural analogs (H-(N(α)Me)Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Pro-Phe-OH, AI, and N(G)-Arg(N(G)NO2)-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Pro-Phe-NH2, AII) as additives to crystalloid cardioplegia and explore benefits of early reperfusion with these peptides.

METHODS

Isolated working rat hearts subjected to normothermic global ischemia and further reperfusion were used. St. Thomas' Hospital cardioplegic solution No.2 (STH2) containing 140 μM A12, AI, or AII was infused for 5 min at 25 °C before ischemia. In separate series, peptide administration was used for 5 min after ischemia. Metabolic state of the hearts was evaluated by myocardial content of high energy phosphates and lactate. Lactate dehydrogenase (LDH) leakage was assessed in myocardial effluent on early reperfusion.

RESULTS

Addition of the peptides to STH2 enhanced functional and metabolic recovery of reperfused hearts compared with those of control (STH2 without additives). Cardioplegia with analog AII was the most effective and accompanied by a reduction of postischemic LDH leakage. Infusion of A12, AI, or AII after ischemia improved the majority indices of cardiac function and metabolic state of the heart by the end of reperfusion. However, the overall protective effect of the peptides was less than when they were added to STH2.

CONCLUSIONS

Enhancement of apelin bioavailability may minimize myocardial I/R damage during cardiac surgery. Structural analogs of A12 are promising components of clinical cardioplegic solutions.