Reduced circulating apelin in essential hypertension and its association with cardiac dysfunction

Decreased plasma ELABELA level as a novel screening indicator for heart failure: a cohort and observational study

The predictive power of B-type natriuretic peptide (BNP) and left ventricular ejection fraction (LVEF) is limited by its low specificity in patients with heart failure (HF). Discovery of more novel biomarkers for HF better diagnosis is necessary and urgent. ELABELA, an early endogenous ligand for the G protein-coupled receptor APJ (Apelin peptide jejunum, Apelin receptor), exhibits cardioprotective actions. However, the relationship between plasma ELABELA and cardiac function in HF patients is unclear. To evaluate plasma ELABELA level and its diagnostic value in HF patients, a total of 335 patients with or without HF were recruited for our monocentric observational study. Plasma ELABELA and Apelin levels were detected by immunoassay in all patients. Spearman correlation analysis was used to analyze the correlation between plasma ELABELA or Apelin levels and study variables. The receiver operating characteristic curves were used to access the predictive power of plasma ELABELA or Apelin levels. Plasma ELABELA levels were lower, while plasma Apelin levels were higher in HF patients than in non-HF patients. Plasma ELABELA levels were gradually decreased with increasing New York Heart Association grade or decreasing LVEF. Plasma ELABELA levels were negatively correlated with BNP, left atrial diameter, left ventricular end-diastolic diameter, left ventricular end-systolic diameter, and left ventricular posterior wall thickness and positively correlated with LVEF in HF patients. In contrast, the correlation between plasma Apelin levels and these parameters is utterly opposite to ELABELA. The diagnostic value of ELABELA, Apelin, and LVEF for all HF patients was 0.835, 0.673, and 0.612; the sensitivity was 62.52, 66.20, and 32.97%; and the specificity was 95.92, 67.23, and 87.49%, respectively. All these parameters in HF patients with preserved ejection fraction were comparable to those in total HF patients. Overall, plasma ELABELA levels were significantly reduced and negatively correlated with cardiac function in HF patients. Decreased plasma ELABELA levels may function as a novel screening biomarker for HF. A combined assessment of BNP and ELABELA may be a good choice to increase the accuracy of the diagnosis of HF.

Analyzing molecular signatures in preeclampsia and fetal growth restriction: Identifying key genes, pathways, and therapeutic targets for preterm birth

Background

Intrauterine growth restriction (IUGR) and preeclampsia (PE) are intricately linked with specific maternal health conditions, exhibit shared placental abnormalities, and play pivotal roles in precipitating preterm birth (PTB) incidences. However, the molecular mechanism underlying the association between PE and IUGR has not been determined. Therefore, we aimed to analyze the data of females with PE and those with PE + IUGR to identify the key gene(s), their molecular pathways, and potential therapeutic interactions.

Methods

In this study, a comprehensive relationship analysis of both PE and PE + IUGR was conducted using RNA sequence datasets. Using two datasets (GSE148241 and GSE114691), differential gene expression analysis via DESeq2 through R-programming was performed. Gene set enrichment analysis was performed using ClusterProfiler, protein‒protein interaction (PPI) networks were constructed, and cluster analyses were conducted using String and MCODE in Cytoscape. Functional enrichment analyses of the resulting subnetworks were performed using ClueGO software. The hub genes were identified under both conditions using the CytoHubba method. Finally, the most common hub protein was docked against a library of bioactive flavonoids and PTB drugs using the PyRx AutoDock tool, followed by molecular dynamic (MD) simulation analysis. Pharmacokinetic analysis was performed to determine the ADMET properties of the compounds using pkCSM.

Results

We identified eight hub genes highly expressed in the case of PE, namely, PTGS2, ENG, KIT, MME, CGA, GAPDH, GPX3, and P4HA1, and the network of the PE + IUGR gene set demonstrated that nine hub genes were overexpressed, namely, PTGS2, FGF7, FGF10, IL10, SPP1, MPO, THBS1, CYBB, and PF4. PTGS2 was the most common hub gene found under both conditions (PE and PEIUGR). Moreover, the greater (-9.1 kcal/mol) molecular binding of flavoxate to PTGS2 was found to have satisfactory pharmacokinetic properties compared with those of other compounds. The flavoxate-bound PTGS2 protein complex remained stable throughout the simulation; with a ligand fit to protein, i.e., a RMSD ranging from ∼2.0 to 4.0 Å and a RMSF ranging from ∼0.5 to 2.9 Å, was observed throughout the 100 ns analysis.

Conclusion

The findings of this study may be useful for treating PE and IUGR in the management of PTB.

Targeting the apelin system for the treatment of cardiovascular diseases

Cardiovascular disease is the leading cause of death worldwide. Its prevalence is rising due to ageing populations and the increasing incidence of diseases such as chronic kidney disease, obesity, and diabetes that are associated with elevated cardiovascular risk. Despite currently available treatments, there remains a huge burden of cardiovascular disease-associated morbidity for patients and healthcare systems, and newer treatments are needed. The apelin system, comprising the apelin receptor and its two endogenous ligands apelin and elabela, is a broad regulator of physiology that opposes the actions of the renin-angiotensin and vasopressin systems. Activation of the apelin receptor promotes endothelium-dependent vasodilatation and inotropy, lowers blood pressure, and promotes angiogenesis. The apelin system appears to protect against arrhythmias, inhibits thrombosis, and has broad anti-inflammatory and anti-fibrotic actions. It also promotes aqueous diuresis through direct and indirect (central) effects in the kidney. Thus, the apelin system offers therapeutic promise for a range of cardiovascular, kidney, and metabolic diseases. This review will discuss current cardiovascular disease targets of the apelin system and future clinical utility of apelin receptor agonism.

Canagliflozin Ameliorates Ventricular Remodeling through Apelin/Angiotensin-Converting Enzyme 2 Signaling in Heart Failure with Preserved Ejection Fraction Rats

INTRODUCTION

The aim of this study was to investigate the effect of canagliflozin (CANA) on ventricular remodeling in patients with preserved ejection fraction (HFpEF) heart failure and to further investigate its possible molecular mechanisms.

METHODS

A high-salt diet was used to induce the formation of HFpEF model in salt-sensitive rats. The rats were fed with CANA and irbesartan, respectively. The mice were divided into control group, model group, CANA group, irbesartan group, and combined drug group. After 12 weeks of feeding, the rats were evaluated by measuring the relevant indexes and echocardiography for cardiac function. Histological analysis was performed using Masson trichrome staining and immunohistochemical staining. RT-qPCR and Western blot were used to quantify the relevant genes and proteins.

RESULTS

In this study, CANA exhibited diuresis, decreased blood pressure, weight loss, and increased food and water intake. Following a high-salt diet, Dahl salt-sensitive rats developed hypertension followed by left ventricular diastolic dysfunction, myocardial fibrosis, and left ventricular remodeling. Myocardial hypertrophy and fibrosis were reduced, and left ventricular diastolic function and ventricular remodeling improved after CANA treatment. The combination of CANA and irbesartan was superior to monotherapy in reducing blood pressure and improving cardiac insufficiency and left ventricular diastolic dysfunction in rats. CANA improves myocardial fibrosis, left ventricular diastolic dysfunction, and ventricular remodeling by upregulating apelin, activating angiotensin-converting enzyme 2 (ACE2), and increasing ACE2/Ang (1-7)/MASR axis levels.

CONCLUSION

CANA improves myocardial fibrosis, left ventricular diastolic dysfunction, and ventricular remodeling in HFpEF rats through upregulation of apelin/ACE2 signaling.

The emerging role of the apelinergic system in kidney physiology and disease

The apelinergic system (AS) is a novel pleiotropic system with an essential role in renal and cardiovascular physiology and disease, including water homeostasis and blood pressure regulation. It consists of two highly conserved peptide ligands, apelin and apela, and a G-protein-coupled apelin receptor. The two ligands have many isoforms and a short half-life and exert both similar and divergent effects. Vasopressin, apelin and their receptors colocalize in hypothalamic regions essential for body fluid homeostasis and interact at the central and renal levels to regulate water homeostasis and diuresis in inverse directions. In addition, the AS and renin-angiotensin system interact both systemically and in the kidney, with implications for the cardiovascular system. A role for the AS in diverse pathological states, including disorders of sodium and water balance, hypertension, heart failure, pre-eclampsia, acute kidney injury, sepsis and diabetic nephropathy, has recently been reported. Furthermore, several metabolically stable apelin analogues have been developed, with potential applications in diverse diseases. We review here what is currently known about the physiological functions of the AS, focusing on renal, cardiovascular and metabolic homeostasis, and the role of the AS in associated diseases. We also describe several hurdles and research opportunities worthy of the attention of the nephrology community.

Significance and Determinants of Plasma Apelin in Patients With Obstructive Hypertrophic Cardiomyopathy

Background

Recent studies suggest apelin has multiple protective effects in some cardiovascular diseases. However, there are few data concerning apelin levels in patients with obstructive hypertrophic cardiomyopathy (OHCM) or the relationship between apelin levels and severity of OHCM.

Methods

We studied 88 patients with OHCM and 32 control subjects with matched age and sex distribution. Complete medical history was collected and related examinations were performed. Cardiac magnetic resonance (CMR) and echocardiography were employed to characterize cardiac morphology and function. Plasma apelin was measured by enzyme-linked immunosorbent assay (ELISA).

Results

Plasma apelin levels were significantly lower in patients with OHCM than those in control subjects (96.6 ± 34.3 vs. 169.4 ± 62.5 μg/L, p < 0.001). When patients with OHCM were divided into two groups according to the mean value of plasma apelin, patients with lower apelin levels (plasma apelin ≤ 96.6 μg/L) had greater septal wall thickness (SWT; 25.6 ± 5.5 vs. 23.2 ± 4.3 mm, p = 0.035) and less right ventricular end-diastolic diameter (RVEDD; 20.4 ± 3.3 vs. 23.0 ± 3.6 mm, p = 0.001). Consistently, plasma apelin levels were inversely correlated with SWT (r = −0.334, p = 0.002) and positively correlated with RVEDD (r = 0.368, p < 0.001). Besides, plasma apelin levels were inversely correlated with Ln (NT-proBNP) (r = −0.307, p = 0.008) and positively correlated with body mass index (BMI; r = 0.287, p = 0.008). On multivariate analysis, the SWT was independently associated with decreasing plasma apelin, while the RVEDD was independently associated with increasing plasma apelin.

Conclusion

Plasma apelin levels are reduced in patients with OHCM. The apelin levels are inversely related to SWT and positively related to RVEDD.

APELIN IN HEART FAILURE

Apelin is a biologically active protein encoded by the APLN gene. It was first isolated in 1998 as a ligand for the APJ receptor. It exists in several isoforms differing in polypeptide chain length and biological activity. It is secreted by white adipose tissue, and its expression has been identified in many body tissues, including the cardiovascular system, kidneys, lungs, CNS (especially the hypothalamus, suprachiasmatic and ventricular nuclei), skeletal muscle, mammary glands, adrenal glands, ovaries, stomach, liver cells, placenta, and breast milk. However, the highest concentrations were observed in the endocardium and endothelium of vascular smooth muscle cells. In myocardial tissue, apelin has a positive inotropic effect and exerts an opposing effect to the RAA (renin-angiotensin-aldosterone) system, lowering blood pressure. Therefore, its positive role in early stages of heart failure, in patients with hypertension and ischemic heart disease is emphasized. The synthesis and secretion of apelin by adipocytes makes it possible to classify this peptide as an adipokine. Therefore, its production in adipose tissue is enhanced in obesity. Furthermore, apelin has been shown to increase cellular sensitivity to insulin and improve glucose tolerance in the onset of type 2 diabetes, and therefore appears to play a significant role in the pathogenesis of metabolic disease. An accurate assessment of the importance of apelin in cardiovascular disease requires further studies, which may contribute to the use of apelin in the treatment of heart failure.

Targeting the elabela/apelin-apelin receptor axis as a novel therapeutic approach for hypertension

ABSTRACT

Hypertension is the leading risk factor for global mortality and morbidity and those with hypertension are more likely to develop severe symptoms in cardiovascular and cerebrovascular system, which is closely related to abnormal renin-angiotensin system and elabela/apelin-apelin receptor (APJ) axis. The elabela/apelin-APJ axis exerts essential roles in regulating blood pressure levels, vascular tone, and cardiovascular dysfunction in hypertension by counterbalancing the action of the angiotensin II/angiotensin II type 1 receptor axis and enhancing the endothelial nitric oxide (NO) synthase/NO signaling. Furthermore, the elabela/apelin-APJ axis demonstrates beneficial effects in cardiovascular physiology and pathophysiology, including angiogenesis, cellular proliferation, fibrosis, apoptosis, oxidative stress, and cardiovascular remodeling and dysfunction during hypertension. More importantly, effects of the elabela/apelin-APJ axis on vascular tone may depend upon blood vessel type or various pathological conditions. Intriguingly, the broad distribution of elabela/apelin and alternative isoforms implicated its distinct functions in diverse cardiac and vascular cells and tissue types. Finally, both loss-of-function and gain-of-function approaches have defined critical roles of the elabela/apelin-APJ axis in reducing the development and severity of hypertensive diseases. Thus, targeting the elabela/apelin-APJ axis has emerged as a pre-warning biomarker and a novel therapeutic approach against progression of hypertension, and an increased understanding of cardiovascular actions of the elabela/apelin-APJ axis will help to develop effective interventions for hypertension. In this review, we focus on the physiology and biochemistry, diverse actions, and underlying mechanisms of the elabela/apelin-APJ axis, highlighting its role in hypertension and hypertensive cardiovascular injury and dysfunction, with a view to provide a prospective strategy for hypertensive disease therapy.

The Elabela-APJ axis: a promising therapeutic target for heart failure

Heart failure (HF) is a growing epidemic with high morbidity and mortality at an international scale. The apelin-APJ receptor pathway has been implicated in HF, making it a promising therapeutic target. APJ has been shown to be activated by a novel endogenous peptide ligand known as Elabela (ELA, also called Toddler or Apela), with a critical role in cardiac development and function. Activation of the ELA-APJ receptor axis exerts a wide range of physiological effects, including depressor response, positive inotropic action, diuresis, anti-inflammatory, anti-fibrotic, and anti-remodeling, leading to its cardiovascular protection. The ELA-APJ axis is essential for diverse biological processes and has been shown to regulate fluid homeostasis, myocardial contractility, vasodilation, angiogenesis, cellular differentiation, apoptosis, oxidative stress, cardiorenal fibrosis, and dysfunction. The beneficial effects of the ELA-APJ receptor system are well-established by treating hypertension, myocardial infarction, and HF. Additionally, administration of ELA protects human embryonic stem cells against apoptosis and stress-induced cell death and promotes survival and self-renewal in an APJ-independent manner (X receptor) via the phosphatidylinositol 3-kinase/Akt pathway, which may provide a new therapeutic approach for HF. Thus, targeting the ELA-APJ axis has emerged as a pre-warning biomarker and a novel therapeutic approach against progression of HF. An increased understanding of cardiovascular actions of ELA will help to develop effective interventions. This article gives an overview of the characteristics of the ELA-apelin-APJ axis and summarizes the current knowledge on its cardioprotective roles, potential mechanisms, and prospective application for acute and chronic HF.

The apelin/APJ system in the regulation of vascular tone: friend or foe?

The apelin (APJ) receptor was originally cloned as a gene encoding a putative G protein-coupled receptor related to angiotensin receptor type I. To date, two endogenous peptide ligands for APJ have been identified: apelin and elabela/Toddler. The apelin/APJ system regulates blood pressure and vascular tone. The endothelial and smooth muscle apelin/APJ systems exert opposite actions in the regulation of vascular tone. Binding of apelin to endothelial APJ promotes the release of vasodilators, such as nitric oxide and prostacyclin, leading to vasodilation. Alternatively, binding of apelin to smooth muscle APJ induces vasoconstriction, although the molecular mechanisms of the apelin-induced vasoconstriction are poorly understood. Recently, a critical role for interaction of APJ with α1-adrenergic receptor in the apelin-induced vasoconstriction was reported. The action of apelin on vascular tone may depend upon blood vessel type or pathological condition. Although the apelin/APJ system could serve as a potential therapeutic target for hypertension and cardiovascular disease, the role of this system in various cell types appears to be complicated.

The Impact of Transcatheter Aortic Valve Implantation (TAVI) on Serum Apelin Levels in Patients with Aortic Valvular Stenosis

INTRODUCTION

In this study, we aimed to investigate the impact of transcatheter aortic valve implantation (TAVI) on serum apelin levels in patients with severe symptomatic aortic valve stenosis (AS).

METHODS

Forty-six consecutive patients (76.9±7.4 years, n=27 women) who underwent TAVI and 45 age- and sex-matched control subjects were included in the study. Echocardiographic parameters, serum apelin, pro-brain natriuretic peptide (Pro-BNP), and troponin I levels were compared between the groups. In addition, the preprocedural and first-month follow-up echocardiographic parameters and serum apelin values of TAVI patients were compared.

RESULTS

Serum median troponin I and Pro-BNP levels were significantly higher and serum apelin levels were significantly lower in TAVI patients before TAVI procedure than in the control subjects (P<0.001, for all). Median troponin I and Pro-BNP levels were significantly decreased and apelin levels were significantly increased after TAVI procedure compared to the peri-procedural levels. There was a significant and moderate negative correlation between Pro-BNP and apelin levels measured before and after TAVI procedure. A statistically significant and strong negative correlation was found between aortic valve area and Pro-BNP level before TAVI procedure, while a statistically significant but weak positive correlation was found between valve area and apelin level.

CONCLUSION

In our study, apelin levels were significantly lower and Pro-BNP levels were higher in AS patients compared with the control group. Moreover, after TAVI procedure, a significant increase in apelin levels and a significant decrease in Pro-BNP levels were observed. There was also a negative and moderate correlation between apelin and Pro-BNP levels.

Interaction between the apelinergic system and ACE2 in the cardiovascular system: therapeutic implications

The apelinergic system is widely expressed and acts through autocrine and paracrine signaling to exert protective effects, including vasodilatory, metabolic, and inotropic effects on the cardiovascular (CV) system. The apelin pathway's dominant physiological role has delineated therapeutic implications for coronary artery disease, heart failure (HF), aortic aneurysm, pulmonary arterial hypertension (PAH), and transplant vasculopathy. Apelin peptides interact with the renin-angiotensin system (RAS) by promoting angiotensin converting enzyme 2 (ACE2) transcription leading to increased ACE2 protein and activity while also antagonizing the effects of angiotensin II (Ang II). Apelin modulation of the RAS by increasing ACE2 action is limited due to its rapid degradation by proteases, including ACE2, neprilysin (NEP), and kallikrein. Apelin peptides are hence tightly regulated in a negative feedback manner by ACE2. Plasma apelin levels are suppressed in pathological conditions, but its diagnostic and prognostic utility requires further clinical exploration. Enhancing the beneficial actions of apelin peptides and ACE2 axes while complementing existing pharmacological blockade of detrimental pathways is an exciting pathway for developing new therapies. In this review, we highlight the interaction between the apelin and ACE2 systems, discuss their pathophysiological roles and potential for treating a wide array of CV diseases (CVDs).

The interaction partners of (pro)renin receptor in the distal nephron

The (pro)renin receptor (PRR), a key regulator of intrarenal renin-angiotensin system (RAS), is predominantly presented in podocytes, proximal tubules, distal convoluted tubules, and the apical membrane of collecting duct A-type intercalated cells, and plays a crucial role in hypertension, cardiovascular disease, kidney disease, and fluid homeostasis. In addition to its well-known renin-regulatory function, increasing evidence suggests PRR can also act in a variety of intracellular signaling cascades independently of RAS in the renal medulla, including Wnt/β-catenin signaling, cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂ ) signaling, and the apelinergic system, and work as a component of the vacuolar H⁺ -ATPase. PRR and these pathways regulate the expression/activity of each other that controlling blood pressure and renal functions. In this review, we highlight recent findings regarding the antagonistic interaction between PRR and ELABELA/apelin, the mutually stimulatory relationship between PRR and COX-2/PGE₂ or Wnt/β-catenin signaling in the renal medulla, and their involvement in the regulation of intrarenal RAS thereby control blood pressure, renal injury, and urine concentrating ability in health and patho-physiological conditions. We also highlight the latest progress in the involvement of PRR for the vacuolar H⁺ -ATPase activity.

Apelin, Omentin-1, and Vaspin in patients with essential hypertension: association of adipokines with trace elements, inflammatory cytokines, and oxidative damage markers

BACKGROUND

Hypertension (HT) is a disease associated with endothelial dysfunction which is related to some adipokines and pro- and anti-inflammatory cytokines.

AIMS

Our aim was to investigate roles of apelin, omentin-1, and vaspin in essential HT and to evaluate their relationships with other pro- and anti-inflammatory cytokines, trace elements, and oxidative stress. We also investigated these parameters to determine asymptomatic target organ damage period and grading essential hypertension.

METHODS

One hundred fifty-three patients diagnosed with essential hypertension and 45 healthy controls were included in the study. Hypertension was defined as a systolic blood pressure > 140 mmHg and/or a diastolic blood pressure > 90 mm Hg or current use of an antihypertensive medication. The patients who had secondary HT, other chronic metabolic, cardiovascular, cerebrovascular diseases were excluded. History and physical exam including detailed cardiovascular examination were performed in all participants. Adipokines, cytokines, trace elements, lipid peroxidation, and ischemia-modified albumin levels were measured in blood samples by biochemical methods.

RESULTS

Vaspin, IL-4, IL-8, IL-10, selenium, and zinc levels were significantly lower in the HT group compared to healthy controls while omentin-1, TNF-α, copper, iron, MDA, SOD, and IMA-C levels were significantly higher in HT patients compared to controls. Multiple ordinal regression revealed that TNF-α, IL-10, and body mass index of patients were statistically significant independent predictors (P = 0.024, P = 0.019, and P = 0.032, respectively) for grading of HT. IL-4 and IL-10 were significantly higher in patients with asymptomatic target organ damage, compared to patients without asymptomatic target organ damage (P = 0.032 and P = 0.015, respectively). Our findings suggest that adipokines apelin, omentin, and vaspin may be involved in hypertension by a complex interaction with the anti- and pro-inflammatory cytokines, trace elements, and oxidative stress pathways.

Angiotensin-Converting Enzyme 2: SARS-CoV-2 Receptor and Regulator of the Renin-Angiotensin System: Celebrating the 20th Anniversary of the Discovery of ACE2

ACE2 (angiotensin-converting enzyme 2) has a multiplicity of physiological roles that revolve around its trivalent function: a negative regulator of the renin-angiotensin system, facilitator of amino acid transport, and the severe acute respiratory syndrome-coronavirus (SARS-CoV) and SARS-CoV-2 receptor. ACE2 is widely expressed, including, in the lungs, cardiovascular system, gut, kidneys, central nervous system, and adipose tissue. ACE2 has recently been identified as the SARS-CoV-2 receptor, the infective agent responsible for coronavirus disease 2019, providing a critical link between immunity, inflammation, ACE2, and cardiovascular disease. Although sharing a close evolutionary relationship with SARS-CoV, the receptor-binding domain of SARS-CoV-2 differs in several key amino acid residues, allowing for stronger binding affinity with the human ACE2 receptor, which may account for the greater pathogenicity of SARS-CoV-2. The loss of ACE2 function following binding by SARS-CoV-2 is driven by endocytosis and activation of proteolytic cleavage and processing. The ACE2 system is a critical protective pathway against heart failure with reduced and preserved ejection fraction including, myocardial infarction and hypertension, and against lung disease and diabetes mellitus. The control of gut dysbiosis and vascular permeability by ACE2 has emerged as an essential mechanism of pulmonary hypertension and diabetic cardiovascular complications. Recombinant ACE2, gene-delivery of Ace2, Ang 1-7 analogs, and Mas receptor agonists enhance ACE2 action and serve as potential therapies for disease conditions associated with an activated renin-angiotensin system. rhACE2 (recombinant human ACE2) has completed clinical trials and efficiently lowered or increased plasma angiotensin II and angiotensin 1-7 levels, respectively. Our review summarizes the progress over the past 20 years, highlighting the critical role of ACE2 as the novel SARS-CoV-2 receptor and as the negative regulator of the renin-angiotensin system, together with implications for the coronavirus disease 2019 pandemic and associated cardiovascular diseases.

The Association of Plasma Apelin Levels with Plaque Vulnerability

Objectives:

Apelin is a recently discovered peptide that is expressed in many tissues particularly in the cardiovascular system and exerts several actions, most of which are vasodilatory and positive inotropic effects. Based on this, an apelin deficiency is believed to play a significant role in the development of hypertension and heart failure. However, the association of apelin with the pathogenesis of atherosclerosis and especially plaque vulnerability remains unestablished. Thus, to contribute to the literature, in this study, we sought to determine the association of apelin concerning plaque vulnerability in the setting of the acute coronary syndrome.

Methods:

In this study, we prospectively enrolled a total of 80 patients; 40 with acute coronary syndrome and 40 patients with stable chronic ischemic heart disease. Plasma apelin levels were measured in all patients along with other routine biochemical parameters, and all patients underwent a transthoracic echocardiographic examination.

Results:

Plasma apelin levels were significantly lower in patients with the acute coronary syndrome (221.2±66.7 vs 254.3±77.9 p=0.04). However, there was no correlation between plasma apelin levels and serum inflammatory markers or coronary artery disease severity.

Conclusion:

Low plasma apelin levels may create a tendency towards vulnerable plaque and acute coronary syndrome.

The apelinergic system: a perspective on challenges and opportunities in cardiovascular and metabolic disorders

The apelinergic pathway has been generating increasing interest in the past few years for its potential as a therapeutic target in several conditions associated with the cardiovascular and metabolic systems. Indeed, preclinical and, more recently, clinical evidence both point to this G protein-coupled receptor as a target of interest in the treatment of not only cardiovascular disorders such as heart failure, pulmonary arterial hypertension, atherosclerosis, or septic shock, but also of additional conditions such as water retention/hyponatremic disorders, type 2 diabetes, and preeclampsia. While it is a peculiar system with its two classes of endogenous ligand, the apelins and Elabela, its intricacies are a matter of continuing investigation to finely pinpoint its potential and how it enables crosstalk between the vasculature and organ systems of interest. In this perspective article, we first review the current knowledge on the role of the apelinergic pathway in the above systems, as well as the associated therapeutic indications and existing pharmacological tools. We also offer a perspective on the challenges and potential ahead to advance the apelinergic system as a target for therapeutic intervention in several key areas.

Apelin-36-[L28A] and Apelin-36-[L28C(30kDa-PEG)] peptides that improve diet induced obesity are G protein biased ligands at the apelin receptor

BACKGROUND

Apelin signalling pathways have important cardiovascular and metabolic functions. Recently, apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)], were reported to function independent of the apelin receptor in vivo to produce beneficial metabolic effects without modulating blood pressure. We aimed to show that these peptides bound to the apelin receptor and to further characterise their pharmacology in vitro at the human apelin receptor.

METHODS

[Pyr¹]apelin-13 saturation binding experiments and competition binding experiments were performed in rat and human heart homogenates using [¹²⁵I]apelin-13 (0.1 nM), and/or increasing concentrations of apelin-36, apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)] (50pM-100μM). Apelin-36 and its analogues apelin-36-[F36A], apelin-36-[L28A], apelin-36-[L28C(30kDa-PEG)], apelin-36-[A28 A13] and [40kDa-PEG]-apelin-36 were tested in forskolin-induced cAMP inhibition and β-arrestin assays in CHO-K1 cells heterologously expressing the human apelin receptor. Bias signaling was quantified using the operational model for bias.

RESULTS

In both species, [Pyr¹]apelin-13 had comparable subnanomolar affinity and the apelin receptor density was similar. Apelin-36, apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)] competed for binding of [¹²⁵I]apelin-13 with nanomolar affinities. Apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)] inhibited forskolin-induced cAMP release, with nanomolar potencies but they were less potent compared to apelin-36 at recruiting β-arrestin. Bias analysis suggested that these peptides were G protein biased. Additionally, [40kDa-PEG]-apelin-36 and apelin-36-[F36A] retained nanomolar potencies in both cAMP and β-arrestin assays whilst apelin-36-[A13 A28] exhibited a similar profile to apelin-36-[L28C(30kDa-PEG)] in the β-arrestin assay but was more potent in the cAMP assay.

CONCLUSIONS

Apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)] are G protein biased ligands of the apelin receptor, suggesting that the apelin receptor is an important therapeutic target in metabolic diseases.

Dietary glycemic index and dietary glycemic load is associated with apelin gene expression in visceral and subcutaneous adipose tissues of adults

Background

Apelin, as an adipokine, plays an important role in the pathogenesis of insulin resistance and type 2 diabetes. This study aimed to determine whether the quality and quantity of dietary carbohydrates were associated with apelin gene expression in subcutaneous and visceral adipose tissues.

Methods

In this cross-sectional study, 102 adults who underwent minor abdominal surgery were selected. Approximately 100 mg of subcutaneous and visceral adipose tissues were collected during the surgery to measure apelin gene expression. Anthropometric measurment, blood samples, and dietary intakes were collected before surgery. The dietary carbohydrate intake, glycemic index (GI), and glycemic load (GL) were determined.

Results

The average apelin concentration was 269.6 ± 98.5(pg/mL), and 16.3% of participants were insulin resistant. There was a correlation between insulin (p-value = 0.043), Homeostatic Model Assessment for Insulin Resistance (HOMA-IR)(p-value = 0.045) and apelin gene expression in visceral adipose tissue. There was a positive association of apelin gene expression with dietary GI and GL after adjustment for age, sex, and waist circumference in visceral and subcutaneous adipose tissues(p < 0.05). Apelin gene expression in visceral(p = 0.002) and subcutaneous(p = 0.003) adipose tissues was directly associated with foods with a higher GI. There was no association between total carbohydrate intake and apelin gene expression in both visceral and subcutaneous adipose tissues.

Conclusions

Dietary GI and GL, not total carbohydrate intake, were positively associated with apelin gene expression in both visceral and subcutaneous adipose tissues. Future studies are warranted to illustrate the chronic and acute effect of carbohydrate quality on apelin homeostasis.

Electronic supplementary material

The online version of this article (10.1186/s12986-019-0389-9) contains supplementary material, which is available to authorized users.

The impact of apelin and relaxin plasma levels in masked hypertension and white coat hypertension

Masked hypertension (HTN) and white coat hypertension represent two reverse forms of clinical HTN with questionable prognostic significance. Recent evidence supports that low apelin and relaxin plasma levels contribute to vascular damage accelerating atherogenesis and predisposing to HTN and cardiovascular (CV) events. The aim of this study was to compare apelin and relaxin plasma levels between patients with masked hypertension (MH) and those with white coat HTN (WCH). Overall, 130 patients not receiving antihypertensive therapy were studied. All patients underwent 24-hour ambulatory BP monitoring (ABPM) and office BP measurements. Plasma apelin and relaxin levels were measured by ELISA method. According to BP recordings, 24 subjects had MH (group A) and 32 had WCH (group B). Apelin (200 ± 111 pg/mL vs 305 ± 127 pg/mL, P < 0.01) and relaxin (35.2 ± 6.7 pg/mL vs 46.8 ± 23.6 pg/mL, P < 0.01) plasma levels were significantly lower in patients with MH compared to those with WCH, respectively. In conclusion, our findings showed that patients with MH had significantly lower apelin and relaxin levels compared to those with WCH. This observation implies an additional prognostic role for adipokines supporting the concept that MH is closer to essential HTN whereas WCH is a more benign condition.

Downregulation of the Apelinergic Axis Accelerates Aging, whereas Its Systemic Restoration Improves the Mammalian Healthspan

Aging drives the occurrence of numerous diseases, including cardiovascular disease (CVD). Recent studies indicate that blood from young mice reduces age-associated pathologies. However, the "anti-aging" factors in juvenile circulation remain poorly identified. Here, we characterize the role of the apelinergic axis in mammalian aging and identify apelin as an anti-aging factor. The expression of apelin (apln) and its receptor (aplnr) exhibits an age-dependent decline in multiple organs. Reduced apln signaling perturbs organismal homeostasis; mice harboring genetic deficiency of aplnr or apln exhibit enhanced cardiovascular, renal, and reproductive aging. Genetic or pharmacological abrogation of apln signaling also induces cellular senescence mediated, in part, by the activation of senescence-promoting transcription factors. Conversely, restoration of apln in 15-month-old wild-type mice reduces cardiac hypertrophy and exercise-induced hypertensive response. Additionally, apln-restored mice exhibit enhanced vigor and rejuvenated behavioral and circadian phenotypes. Hence, a declining apelinergic axis promotes aging, whereas its restoration extends the murine healthspan.

Apelin/APJ expression in the heart and kidneys of hypertensive rats

Hypertension is an important health problem that is manifested by systemic arterial blood pressure being permanently elevated and leading to serious complications. Hypertension is the basis for coronary heart diseases, heart failure, kidney damage, cerebrovascular diseases. Due to ethical concerns, there is no detailed study of the mechanism, side effects and treatment of hypertension in humans. For this reason, specific studies related to the organ of hypertension are performed in experimental animals. The heart and kidney tissue, which are the most important organs that hypertension has damaged, have formed specific organs of our work. In our experimental study, a total of 35 (hypertensive group: 20, control group: 15) Rattus Norvegicus Wistar albino rats were used. In order to obtain our hypertension model, our experimental animals were given L-NAME together with drinking water for six weeks. After six weeks, the experimental procedures were terminated. Heart and kidney tissues of the hypertensive and control group were obtained. Expression of apelin and apelin receptor (APJ) was demonstrated by immunohistochemical and Western Blot protocols. Hypertrophic cardiac atrium of the hearts of the large cavities, interventricular septum and myocardium to the disintegration, as well as an increase in the diameter of the coronary artery has been observed. In general, kidney tissues of the hypertensive group showed narrowing in cortical renal structures and enlargement in structures in the renal medulla. As a result, in hypertensive cases, there was an increase in expression of Apelin and APJ receptor in heart tissue, and a decrease in expression of Apelin and APJ receptor in kidney tissue. We think that our findings may contribute to experimental or clinical studies related to hypertension and apelin.

Apelin and Atrial Fibrillation: The Role in the Arrhythmia Recurrence Prognosis

Apelin is a novel peptide of wide expression and multiple biological functions including the crucial role in cardiovascular homeostasis. The apelin role in the pathophysiology of heart rhythm disorders is considered, although the reports are scarce so far. The purpose of this study is to investigate the potential utility of apelin as a marker of arrhythmia recurrence after direct-current cardioversion (DC). The prospective, observational study included 60 patients (aged 41–86; 30% female) with nonvalvular, persistent atrial fibrillation from the group of 204 consecutive patients scheduled for DC during the 12-month period (from May 2010 to May 2011) in the Cardiology Clinic Medical University of Lodz, Poland. The study group was divided into SCD (successful DC), 45 (75%) patients, and NDC (nonsuccessful DC), 15 (25%) patients. Within the SCD group, the subgroups were distinguished depending on the time sinus rhythm maintenance after DC: up to 7 days (SDC-7), 11 patients; 7 to 30 days (SDC-30), 12 patients; over 90 days (SDC-90), 22 patients. Patients were evaluated during the hospitalization and within the 3-month follow-up period. The apelin level was determined within the plasma samples collected at the admission, using the commercially available enzyme-linked immunosorbent assay (ELISA) Kit for apelin-36. It was found that the median value of initial apelin in the subset of patients from groups NDC + SDC-7 + SDC-30 is significantly higher than from group SDC-90 (p = 0.0463); there was no relationship between NDC and SCD overall. Neither of the compared subgroup pairs revealed statistically significant correlation between the proBNP concentration and the DC effectiveness in our population. In conclusion, in our study, proBNP was not a marker of arrhythmia recurrence whereas higher apelin concentration at the admission indicated patients in whom DC was not effective or they had an arrhythmia recurrence within a month-period observation.

A promoter polymorphism in APJ gene is significantly associated with blood pressure changes and hypertension risk in Chinese women

The aim of this study was to interrogate the gender-specific association of 5 well-defined polymorphisms in apelin/APJ system with both blood pressure changes and hypertension risk in a northeastern Chinese population. This is a population-based case-control study, including 650 hypertensive patients and 645 normotensive controls. Data were analyzed by STATA and Haplo.Stats. The genotype distributions of 5 study polymorphisms were in Hardy-Weinberg equilibrium in both genders. The rs7119375 and rs10501367 were completely linked. The genotypes (P = 0.001) and alleles (P < 0.001) of rs7119375 differed significantly between patients and controls in women. Carriers of rs7119375-AA genotype had significant higher systolic blood pressure (SBP) than carriers of rs7119375-GG genotype in both patients and controls of female gender (P < 0.01). Moreover, carriers of rs7119375-A allele were 1.80 times more likely to develop hypertension relative to carriers of rs7119375-GG genotype after adjusting for age, body mass index and glucose (odds ratio: 1.80; 95% confidence interval: 1.03–3.16; P = 0.040). Further allele combination analysis supported the leading contribution of rs7119375 to hypertension risk. Our findings demonstrated that the mutation of promoter polymorphism rs7119375 in APJ gene was significantly associated with elevated SBP and increased hypertension risk in Chinese women.

High-intensity interval training lowers blood pressure and improves apelin and NOx plasma levels in older treated hypertensive individuals

Hypertension is the major risk factor for cardiovascular diseases and is one of the primary causes of morbidity and mortality worldwide. Apelin levels and NO bioavailability are impaired in older hypertensive patients. Exercise is an effective intervention for treating hypertension. Our purpose was to evaluate the effect of high-intensity interval training on blood pressure, apelin, and NOx plasma levels in older treated hypertensive individuals. Thirty treated hypertensive subjects (61.70 ± 5.78 years, 17 males, 13 females) were randomly divided into 6 weeks of high-intensity interval training (n = 15) and control (n = 15). The exercise training was conducted for three 35-min sessions a week (1.5-min interval at 85-90% of heart rate reserve [HRR] and 2 min active phase at 50-55% of HRR). Assessment of plasma apelin, nitrite/nitrate (NOx), and endothelin-1 (ET-1) was performed before and after the intervention. At the end of the study, apelin, and NOx plasma levels increased significantly in the high-intensity interval training (HIIT) group (P = 0.021, P = 0.003, respectively). Conversely, ET-1 plasma levels significantly decreased in the training group after the intervention (P = 0.015). Moreover, there was a positive correlation between the change of plasma apelin and change of plasma NOx (r = 0. 771, P = 0.0008). In addition, there was a negative correlation between the change of plasma ET-1, change of plasma apelin (r = - 0.595, P = 0.019), and variation of NOx (r = - 0.572, P = 0.025). This study indicates that, by increasing of apelin and NOx plasma levels, HIIT may be effective in reducing blood pressure.

Treatment-associated change in apelin concentration in patients with hypertension and its relationship with left ventricular diastolic function

OBJECTIVE

We examined the change in apelin concentration and its relationship with left ventricular diastolic function in patients treated for hypertension.

METHODS

Ninety treatment-naive patients with newly diagnosed hypertension and 33 age- and sex-matched control subjects were prospectively enrolled. Patients with hypertension were randomized to treatment either with telmisartan 80 mg or amlodipine 10 mg. Apelin concentration was measured and echocardiography was performed at baseline and after 1 month of treatment.

RESULTS

The data of 77 patients and 33 controls were analyzed. Mean age, gender, baseline blood pressure, apelin levels, and echocardiographic measurements were similar between the treatment groups (p>0.05 for all). Apelin concentration was significantly lower in patients with hypertension than in controls. There was a significant increase in apelin level after 1 month of treatment in both groups (0.32±0.17 vs. 0.38±0.17 ng/dL in telmisartan group, p=0.009, and 0.27±0.13 vs. 0.34±0.18 ng/dL in amlodipine group, p=0.013). Diastolic function improved significantly in both groups (p<0.05) but was not significantly associated with change in apelin concentration.

CONCLUSION

Apelin concentration increased significantly after 1 month of effective treatment with telmisartan or amlodipine to a similar extent. Change in apelin concentration was not associated with improvement in diastolic function.

Biochemical and genetic role of apelin in essential hypertension and acute coronary syndrome

BACKGROUND

Apelin-APJ pathway has emerged as a potent regulator of blood pressure (BP) and blood flow in vasculature and heart. Variants in apelin gene may affect the vascular tone in peripheral circulation or heart, thereby predisposing to cardiovascular diseases. The aim of our study was to investigate the association of two apelin gene polymorphisms rs3761581 and rs2235312, and apelin levels in patients with essential hypertension (EH) and acute coronary syndrome (ACS).

METHODS

The study comprised of three groups namely, (1) 118 healthy control subjects, (2) 92 EH patients, and (3) 60 ACS patients. DNA was extracted from peripheral blood leukocytes and genotyping was performed by SNaPshot method. Plasma apelin 13 levels were estimated using ELISA.

RESULTS

EH and ACS patients had a significantly lower level of apelin 13, regardless of gender (p=0.003, p=0.017, respectively). Interestingly, the female EH and ACS patients had lower levels of apelin 13 than their male counterparts. The G allele of rs3761581 was more apparent in patients especially in ACS than the controls.

CONCLUSION

Reduced apelin levels may enhance vasoconstriction to influence high BP and heart's workload in EH and ACS. Genetic involvement of apelin needs to be established in well-defined larger sample size.

Associations of Apelin, Visfatin, and Urinary 8-Isoprostane With Severe Hypertension in African Americans: The MH-GRID Study

BACKGROUND

Apelin is an adipokine directly associated with adiposity, insulin resistance, and decreased blood pressure. Urinary 8-isoprostane is a marker of chronic oxidative endothelial stress. Visfatin, an adipokine that acts by binding and activating the insulin receptor, has been associated with hypertension. As severe hypertension (SH) is highly prevalent among African Americans (AA), we aimed to assess the association of these biomarkers with SH status.

METHODS

A sample of 250 AA participants (134 normotensive controls and 116 with SH (including 98 treatment controlled, SCH: severe controlled hypertension, and 18 treatment resistant, SRH: severe resistant hypertension)) from the Minority Health Genomics and Translational Research Bio-Repository Database (MH-GRID) in metro Atlanta had blood analyzed for apelin and visfatin and urine for 8-isoprostane. T-tests, sex-specific age-adjusted correlation coefficients, and multivariable logistic regression models were used to assess the association of biomarkers with hypertensive status.

RESULTS

Levels of apelin and 8-isoprostane were not statistically different between controls and SCH or SRH. Statistically significant differences were present in levels of visfatin between controls (1.03±0.84 pg/ml), SCH (1.34±1.14 pg/ml), and SRH (1.59±0.85 pg/ml). After multivariable adjustment, categorization in the middle 2 quartiles of urinary 8-isoprostane were associated with SH. In similar models, categorization into the highest quartile of visfatin was associated with SH (odds ratio = 2.80; 95% confidence interval: 1.02-7.02). A continuous association of visfatin with SH was present.

CONCLUSION

In our community sample of AA, there were increased odds of SH with increased levels of urinary 8-isoprostane and visfatin, but not with apelin.

Microvascular endothelial cells from preeclamptic women exhibit altered expression of angiogenic and vasopressor factors

Preeclampsia (PE) is a severe complication of pregnancy associated with maternal and fetal morbidity and mortality. The underlying pathophysiology involves maternal systemic vascular and endothelial dysfunction associated with circulating antiangiogenic factors, although the specific etiology of the disease remains elusive. Our aim was to investigate the maternal endothelium in PE by exploring the expression of genes involved with endothelial function in a novel platform of maternal primary endothelial cells. Adipose tissue was sampled at the time of caesarean section from both normal and preeclamptic patients. Maternal microvascular endothelial cells were isolated by tissue digestion and CD31 magnetic Dynabeads. Cell purity was confirmed by immunofluorescence microscopy and flow cytometry. Western analyses revealed VEGF activation of VEGF receptor 2 (VEGFR2) and ERK in primary cells. Quantitative PCR analyses revealed significantly altered mRNA levels of various genes involved with angiogenesis and blood pressure control in preeclamptic cells, including soluble fms-like tyrosine kinase-1, endoglin, VEGFR2, angiotensin receptor 1, and endothelin compared with cells isolated from normal pregnancies. Overall, maternal endothelial cells from preeclamptic patients exhibit extensive alteration of expression of factors associated with antiangiogenic and vasoconstrictive phenotypes, shedding light on the underlying mechanisms associated with the vascular dysfunction characteristic of PE.

Apelin and Visfatin Plasma Levels in Healthy Individuals With High Normal Blood Pressure

BACKGROUND

High normal blood pressure (BP; 130-139/85-89 mm Hg) is related with increased cardiovascular (CV) risk compared to normal BP (120-129/80-84 mm Hg) or/and optimal BP (<120/80 mm Hg). Low apelin plasma levels have been associated with arterial hypertension and atherosclerosis, while high visfatin plasma levels may promote vascular inflammation and atherosclerotic plaque destabilization and have been evaluated as a marker for identifying stages of essential hypertension. We sought to compare the apelin and visfatin plasma levels between subjects with high normal BP and subjects with normal or optimal BP matched for age, gender, smoking, and body mass index (BMI).

METHODS

Twenty-five subjects with high normal BP (office BP 136±3/88±2 mm Hg, age 57±4 years, 76% males, 32% smokers, BMI 24.0±1.7 kg/m2) and 35 subjects with normal or optimal BP (office BP 118±2/78±2 mm Hg, age 55±7 years, 63% males, 29% smokers, BMI 23.2±1.4 kg/m2) were studied. The apelin and visfatin plasma levels were determined with the enzyme-linked immunosorbent assay.

RESULTS

Compared to normal or optimal BP subjects, apelin levels were significantly lower (205±108 vs. 325±152 pg/ml, P < 0.001) and visfatin levels significantly higher (11.0±2.0 vs. 7.2±0.9 ng/ml, P = 0.002) in high normal BP subjects. No significant differences were found between the 2 groups (P = NS) regarding the basic clinical characteristics, the glycemic/lipid profile, and the renal function parameters.

CONCLUSIONS

The emerging, from the present study, data raise the hypothesis that lower apelin and higher visfatin plasma levels in high normal BP subjects compared to normal or optimal BP individuals could partially explain the higher CV risk of the high normal BP group.

Serum apelin is associated with left ventricular hypertrophy in untreated hypertension patients

BACKGROUND

Apelin is an endogenous ligand for the G protein-coupled receptor APJ. The association between apelin and cardiac modeling has been reported. However, if serum apelin affect the left ventricular hypertrophy (LVH) prevalence in hypertensive patients remains unknown.

METHODS

We enrolled 344 untreated hypertensive patients. The presence of LVH was determined by echocardiography. The blood was drawn from these patients and serum apelin level was detected. To study the direct effect of apelin on cardiac hypertrophy, cardiomyocytes were cultured and were transfected with apelin gene. Morphometric analysis and measurement of protein contain per cell were then performed.

RESULTS

We observed a significantly lower serum apelin level in hypertensive patients with LVH compared with those without LVH. Receiver operating characteristic analyses shows that serum apelin level is robust in discriminating patients with LVH from those without. Our in vitro study showed that cellular protein content and cellular size was increased by Ang II treatment, which can be markedly inhibited by the apelin over-expression in cultured cardiomyocytes.

CONCLUSION

Our clinical date established a link between apelin and LVH, suggesting serum apelin may be used as a predicator for LVH prevalence in hypertensive patients. The direct evidence in vitro suggest apelin pathway is involved in the cardiomyocyte adaption to hypertrophic stimuli.

The Emerging Potential of the Apelin-APJ System in Heart Failure

The apelin-APJ system is a novel neurohormonal pathway, with studies to date suggesting that it may be of pathophysiologic relevance in heart failure and may indeed be a viable therapeutic target in this syndrome. This interest is driven primarily by the demonstration of its vasodilator, inotropic, and aquaretic actions as well as its apparent antagonistic relationship with the renin-angiotensin system. However, its promise is heightened further by the observation that, unlike other and more established cardioprotective pathways, it appears to be down-regulated in heart failure, suggesting that augmentation of this axis may have a powerful effect on the heart failure syndrome. We review the literature regarding the apelin-APJ system in heart failure and suggest areas requiring further research.

The association between apelin-12 levels and paroxysmal supraventricular tachycardia

AIMS

Our aim was to investigate the apelin-12 levels in patients with atrioventricular tachyarrhythmias and compare with those in patients with lone atrial fibrillation.

METHODS

Forty four patients with supraventricular tachycardia as atrial fibrillation, 44 patients with paroxysmal supraventricular tachycardia (P-SVT) as atrioventricular tachyarrhythmias, including atrioventricular nodal reentrant tachycardia or atrioventricular reentrant tachycardia, and 30 age- and sex-matched healthy individuals were included in the study.

RESULTS

The apelin-12 levels were significantly lower in both atrial fibrillation and P-SVT groups than control group. In post-hoc analysis, there was no significant difference in apelin-12 levels between atrial fibrillation and P-SVT groups (P = 0.9). Patients in atrial fibrillation group and patients in P-SVT group had significantly lower apelin-12 levels than control group, separately (P < 0.001 and P < 0.001, respectively). The sensitivity and specificity values of the apelin-12 levels for predicting SVT, including both atrial fibrillation and atrioventricular reentrant tachycardia or atrioventricular nodal reentrant tachycardia were 64.77 and 90%, respectively (cut-off value was 0.87). The area under the receiver operator characteristic curve was 0.834 for the apelin-12 levels (P = 0.0001).

CONCLUSION

Apelin-12 levels are lower in patients with atrial fibrillation and P-SVT than control groups. Lower apelin levels in patients with atrial fibrillation and P-SVT would be expected to result in a decrease in the conduction velocity.

The ACE2/Apelin Signaling, MicroRNAs, and Hypertension

The renin-angiotensin aldosterone system (RAAS) plays a pivotal role in the development of hypertension. Angiotensin converting enzyme 2 (ACE2), which primarily metabolises angiotensin (Ang) II to generate the beneficial heptapeptide Ang-(1-7), serves as a negative regulator of the RAAS. Apelin is a second catalytic substrate for ACE2 and functions as an inotropic and cardiovascular protective peptide. The physiological effects of Apelin are exerted through binding to its receptor APJ, a seven-transmembrane G protein-coupled receptor that shares significant homology with the Ang II type 1 receptor (AT1R). The deregulation of microRNAs, a class of short and small noncoding RNAs, has been shown to involve cardiovascular remodeling and pathogenesis of hypertension via the activation of the Ang II/AT1R pathway. MicroRNAs are linked with modulation of the ACE2/Apelin signaling, which exhibits beneficial effects in the cardiovascular system and hypertension. The ACE2-coupled crosstalk among the RAAS, the Apelin system, and microRNAs provides an important mechanistic insight into hypertension. This paper focuses on what is known about the ACE2/Apelin signaling and its biological roles, paying particular attention to interactions and crosstalk among the ACE2/Apelin signaling, microRNAs, and hypertension, aiming to facilitate the exploitation of new therapeutic medicine to control hypertension.

Apelin counteracts vasopressin-induced water reabsorption via cross talk between apelin and vasopressin receptor signaling pathways in the rat collecting duct

Apelin receptors (ApelinRs) are expressed along an increasing cortico-medullary gradient in collecting ducts (CDs). We showed here that iv injection of apelin 17 (K17F) in lactating rats characterized by increases in both synthesis and release of arginine vasopressin (AVP) increased diuresis concomitantly with a significant decrease in urine osmolality and no change in Na(+) and K(+) excretion. Under these conditions, we also observed a significant decrease in apical aquaporin-2 immunolabeling in CD, with a cortico-medullary gradient, suggesting that K17F-induced diuresis could be linked to a direct action of apelin on CD. We then examined the potential cross talk between V1a AVP receptor (V1a-R), V2 AVP receptor (V2-R) and ApelinR signaling pathways in outer medullary CD (OMCD) and inner medullary CD microdissected rat CD. In OMCD, expressing the 3 receptors, K17F inhibited cAMP production and Ca(2+) influx induced by 1-desamino-8-D-arginine vasopressin a V2-R agonist. Similar effects were observed in inner medullary CD expressing only V2-R and ApelinR. In contrast, in OMCD, K17F increased by 51% the Ca(2+) influx induced by the stimulation of V1a-R by AVP in the presence of the V2-R antagonist SR121463B, possibly enhancing the physiological antagonist effect of V1a-R on V2-R. Thus, the diuretic effect of apelin is not only due to a central effect by inhibiting AVP release in the blood circulation as previously shown but also to a direct action of apelin on CD, by counteracting the antidiuretic effect of AVP occurring via V2-R.

Regulation of apelin and its receptor expression in adipose tissues of obesity rats with hypertension and cultured 3T3-L1 adipocytes

The apelin/APJ system has been implicated in obesity-related hypertension. We investigated the mechanism responsible for the pathogenesis of obesity-related hypertension with a special focus on the crosstalk between AngII/its type 1 receptor (AT1R) signaling and apelin/APJ expression. Sprague-Dawley rats fed a high-fat (obesity-related hypertension, OH) or normal-fat diet (NF) for 15 weeks were randomly assigned to one of two groups and administered vehicle or perindopril for 4 weeks. Compared to the NF rats, the OH rats showed lower levels of plasma apelin and apelin/APJ mRNAs of perirenal adipose tissues, and these changes were restored by perindopril. Administration of the AT1R antagonist olmesartan resulted in the restoration of the reduction of apelin and APJ expressions induced by AngII for 48 h in 3T3-L1 adipocytes. Among several inhibitors for extracellular signal-regulated kinases 1/2 (ERK1/2) PD98059, p38 mitogen-activated protein kinase (p38MAPK) SB203580 and phosphatidylinositol 3-kinase (PI3K) LY294002, the latter showed an additive effect on AngII-mediated inhibitory effects. In addition, the levels of p-Akt, p-ERK and p38MAPK proteins were decreased by long-term treatment with AngII (120 min), and these changes were restored by Olmesartan. Apelin/APJ appears to be impaired in obesity-related hypertension. The AngII inhibition-mediated beneficial effects are likely attributable, at least in part, to restoration of p38/ERK-dependent apelin/APJ expression in diet-induced obesity-related hypertension.

Effect of apelin on the cardiac hemodynamics in hypertensive rats with heart failure

It is known that apelin has definite protective effects on various cardiovascular diseases; however, the mechanism through which hypertension with heart failure (H-HF) is affected by pyroglutamylated apelin-13 (Pyr-AP13) remain unclear. Thus, in the present study, we investigated the effects of apelin on the cardiac hemodynamics in rats with hypertension and heart failure. In our study, cardiac function, dimensions and histological determination of the fibrosis of rats with two-kidney, one-clip induced hypertension and sham-operated rats were assessed using an echocardiography system and Masson’s trichrome. The infusion of either 5% glucose injection (GS) alone or 5% GS containing Pyr-AP13 as a dose, time-matched design on the cardiac hemodynamics in H-HF rats and sham-operated rats was recorded. For the determination of the effects of potential related proteins on cardiac hemodynamics in the H-HF rats, the animals were divided into 5 groups: i) the sham-operated group (n=8); ii) H-HF (n=8); iii) H-HF with infusion of 0.1 μg dose of Pyr-AP13 (n=8) or 5% glucose (GS) (n=8); iv) H-HF with infusion of 1 μg dose of Pyr-AP13 (n=8) or 5% GS (n=8); and v) H-HF with infusion of 10 μg dose of Pyr-AP13 (n=8) or 5% GS (n=8). The concentration of cyclic adenosine 3′,5′-monophosphate (cAMP) was determined by ELISA. The expression of membrane and cytosolic proteins was evaluated by western blot analysis. Significant cardiac and perivascular fibrosis was observed in the H-HF rats. Following the infusion of Pyr-AP13, the systolic and diastolic function was significantly improved in the cardiac hemodynamic parameters in the H-HF rats treated with Pyr-AP13. The apelin receptor (APJ), which was activated by the exogenous infusion of Pyr-AP13, was partially recycled from the cytoplasm back to the plasma membrane; however, membrane APJ was eventually downregulated in the H-HF rats treated with Pyr-AP13 compared with the sham-operated group rats. Our findings suggested that a complex was formed after Pyr-AP13 combined with cellular membrane APJ receptor. However, the endogenous downregulation of the APJ receptor results in benefits from the exogenous administration of apelin.

Reduction of arterial stiffness by exercise training is associated with increasing plasma apelin level in middle-aged and older adults

Aging-induced deterioration of arterial stiffness is decreased by regular exercise, and increased nitric oxide (NO) production participates in this effect. Apelin regulates endothelial NO synthase in endothelial cells, promoting NO production. However, the effect of aerobic exercise training on circulating apelin levels in healthy middle-aged and older adults remains unknown. Accordingly, this study aimed to clarify the effects of regular aerobic exercise on apelin concentrations in middle-aged and older adults. Thirty-four healthy middle-aged and older subjects (67.0 ± 1.3 years) were randomly divided into two groups: exercise intervention and sedentary controls. Subjects in the training group completed 8-week of aerobic exercise training (60–70% peak oxygen uptake [VO_2peak] for 45 min, 3 days/week). Before and after the intervention, we evaluated plasma apelin and nitrite/nitrate (NOx) concentrations, VO_2peak, and arterial stiffness index. In the training group, VO_2peak was significantly increased, and carotid β-stiffness was significantly decreased, after the intervention (P<0.05). Moreover, plasma apelin and NOx levels were significantly increased in the training group after the intervention (P<0.05). Additionally, there was a correlation between the training effects of plasma apelin levels and carotidβ-stiffness (r = −0.508, P = 0.032) and plasma NOx levels (r = 0.494, P = 0.037). By contrast, none of these parameters changed significantly in the control group. These results suggest that the increased in plasma apelin levels may be associated with exercise training-induced alternation of arterial stiffness in middle-aged and older adults.

Apelin and relaxin plasma levels in young healthy offspring of patients with essential hypertension

Epidemiologic studies have shown that healthy offspring of hypertensive patients exhibit many features of the metabolic syndrome, such as hyperinsulinemia, insulin resistance, and lipid disorders, while hypoapelinemia and hyporelaxinemia may contribute to vascular damage that accelerates atherogenesis. The aim of this study was to determine apelin and relaxin plasma levels in the healthy offspring of hypertensive patients and to compare the findings with those of healthy offspring of healthy parents, matched for age, sex, and body mass index (BMI). Forty-six (24 men and 22 women) healthy offspring of hypertensive patients, mean age 18±3 years and BMI 22.4±1.4 kg/m(2) (group A), and 50 healthy offspring of healthy parents (28 men and 22 women), mean age 18±3.2 years and BMI 22.6±1.7 kg/m(2) (group B), were studied. The apelin and relaxin plasma levels (enzyme-linked immunosorbent assay method) were determined in the study population. The two groups were matched for age, sex, and BMI. Plasma apelin levels (6±3 vs 105 pg/mL, P<.001) and relaxin plasma levels (20±7 vs 29±8 pg/mL, P<.001) were significantly lower in group A compared with group B, respectively. Our findings suggest that healthy offspring of healthy parents have significantly lower plasma apelin and relaxin levels. This group of individuals needs closer follow-up and further examination.