The novel peptide apelin lowers blood pressure via a nitric oxide-dependent mechanism

Investigation of serum apelin-13 and apelin-36 concentrations in pregnancies complicated by preeclampsia; a prospective case-control study

OBJECTIVE

We aimed to investigate the relationship between preeclampsia and maternal serum apelin-13 and apelin-36 concentrations.

METHODS

This cross-sectional study was carried out in the Gynecology and Obstetrics Clinic of Umraniye Training and Research Hospital. The preeclampsia group consisted of 40 pregnant women diagnosed with preeclampsia, and the control group consisted of 40 healthy pregnant women matched with the preeclampsia group in terms of age and body mass index. The two groups were compared in terms of maternal serum apelin-13 and apelin-36 concentrations.

RESULTS

Both groups were similar in terms of demographic characteristics and the gestational week at blood sampling. Maternal serum apelin-13 and apelin-36 concentrations were significantly lower in the preeclampsia group than in the control group (p = 0.005, p = 0.001, respectively). The optimal cutoff value for the prediction of preeclampsia in receiver operator curve analysis for apelin-13 was determined as 1781.67 pg/ml with 60% sensitivity and 60% specificity, and 885.5 pg/ml for apelin-36 with 67% sensitivity and 65% specificity. We divided the preeclampsia group into two groups mild and severe and compared the three groups in terms of maternal serum apelin-13 and apelin-36 concentrations. The lowest apelin-13 concentration was detected in the severe preeclampsia group, while the lowest apelin-36 concentration was detected in the mild preeclampsia group (p = 0.020, p = 0.003, respectively). Considering the onset of the disease, we divided the preeclampsia group into two groups early and late-onset, then compared the three groups in terms of maternal serum apelin-13 and apelin-36 concentrations. The lowest maternal serum apelin-13 and apelin-36 concentrations were detected in the early-onset preeclampsia group (p = 0.016, p = 0.001, respectively).

CONCLUSION

It was determined that serum apelin-13 and apelin-36 concentrations were significantly lower in preeclamptic pregnant women, this decrease was more significant in early-onset preeclampsia, and low maternal serum apelin-13 concentration was more associated with the severity of preeclampsia.

MMDB: Multimodal dual-branch model for multi-functional bioactive peptide prediction

Bioactive peptides can hinder oxidative processes and microbial spoilage in foodstuffs and play important roles in treating diverse diseases and disorders. While most of the methods focus on single-functional bioactive peptides and have obtained promising prediction performance, it is still a significant challenge to accurately detect complex and diverse functions simultaneously with the quick increase of multi-functional bioactive peptides. In contrast to previous research on multi-functional bioactive peptide prediction based solely on sequence, we propose a novel multimodal dual-branch (MMDB) lightweight deep learning model that designs two different branches to effectively capture the complementary information of peptide sequence and structural properties. Specifically, a multi-scale dilated convolution with Bi-LSTM branch is presented to effectively model the different scales sequence properties of peptides while a multi-layer convolution branch is proposed to capture structural information. To the best of our knowledge, this is the first effective extraction of peptide sequence features using multi-scale dilated convolution without parameter increase. Multimodal features from both branches are integrated via a fully connected layer for multi-label classification. Compared to state-of-the-art methods, our MMDB model exhibits competitive results across metrics, with a 9.1% Coverage increase and 5.3% and 3.5% improvements in Precision and Accuracy, respectively.

The possible mechanism and research progress of ACE2 involved in cardiovascular injury caused by COVID-19: a review

ACE2 is the earliest receptor discovered to mediate the entry of SARS-CoV-2. In addition to the receptor, it also participates in complex pathological and physiological processes, including regulating the RAS system, apelin, KKS system, and immune system. In addition to affecting the respiratory system, viral infections also interact with cardiovascular diseases. SARS-CoV-2 can directly invade the cardiovascular system through ACE2; Similarly, cardiovascular diseases such as hypertension and coronary heart disease can affect ACE2 levels and exacerbate the disease, and ACE2 dysregulation may also be a potential mechanism for long-term acute sequelae of COVID-19. Since the SARS CoV-2 epidemic, many large population studies have tried to clarify the current focus of debate, that is, whether we should give COVID-19 patients ACEI and ARB drug treatment, but there is still no conclusive conclusion. We also discussed potential disease treatment options for ACE2 at present. Finally, we discussed the researchers' latest findings on ACE2 and their prospects for future research.

Quercetin prevents kidney against diabetes mellitus (type 1) in rats by inhibiting TGF-β/apelin gene expression

BACKGROUND

One of the main causes of diabetic nephropathy is oxidative stress induced by hyperglycemia. Apelin inhibits insulin secretion. Besides, renal expression of TGF-β is increased in diabetes mellitus (DM). The preventive effect of quercetin (Q) against renal functional disorders and tissue damage developed by DM in rats was assessed.

METHODS

Forty male Wistar rats were grouped into normal control (NC), normal + quercetin (NQ: quercetin, 50 mg/kg/day by gavage), diabetic control (DC: streptozotocin, 65 mg/kg, i.p.), diabetic + quercetin pretreatment (D + Qpre), and diabetic + quercetin post-treatment (D + Qpost). All samples (24-hour urine, plasma, pancreatic, and renal tissues) were obtained at the terminal of the experiment.

RESULTS

Compared to NC and NQ groups, DM ended in elevated plasma and glucose levels, decreased plasma insulin level, kidney dysfunction, augmented levels of malondialdehyde, decreased level of reduced glutathione, reduced enzymatic activities of superoxide dismutase and catalase, elevated gene expression levels of apelin and TGF-β, also renal and pancreatic histological damages. Quercetin administration diminished entire the changes. However, the measure of improvement in the D + Qpre group was higher than that of the D + Qpost group.

CONCLUSION

Quercetin prevents renal dysfunction induced by DM, which might be related to the diminution of lipid peroxidation, strengthening of antioxidant systems, and prevention of the apelin/ TGF-β signaling pathway.

Apelin-13 modulates the endometrial transcriptome of the domestic pig during implantation

BACKGROUND

The peri-implantation period is a critical time during pregnancy that mostly defines the overall litter size. Most authors agree that the highest percentage of embryo mortality occurs during this time. Despite the brevity of the peri-implantation period, it is the most dynamic part of pregnancy in which the sequential and uninterrupted course of several processes is essential to the animal's reproductive success. Also then, the maternal uterine tissues undergo an intensive remodelling process, and their energy demand dramatically increases. It is believed that apelin, a member of the adipokine family, is involved in the control of female reproductive functions in response to the current metabolic state. The verified herein hypothesis assumed the modulatory effect of apelin on the endometrial tissue transcriptome on days 15 to 16 of gestation (beginning of implantation).

RESULTS

The analysis of data obtained during RNA-seq (Illumina HiSeq2500) of endometrial slices treated and untreated with apelin (n = 4 per group) revealed changes in the expression of 68 genes (39 up-regulated and 29 down-regulated in the presence of apelin), assigned to 240 gene ontology terms. We also revealed changes in the frequency of alternative splicing events (397 cases), as well as single nucleotide variants (1,818 cases) in the presence of the adipokine. The identified genes were associated, among others, with the composition of the extracellular matrix, apoptosis, and angiogenesis.

CONCLUSIONS

The obtained results indicate a potential role of apelin in the regulation of uterine tissue remodelling during the peri-implantation period.

The Neglected Sibling: NLRP2 Inflammasome in the Nervous System

While classical NOD-like receptor pyrin domain containing protein 1 (NLRP1) and NLRP3 inflammasomal proteins have been extensively investigated, the contribution of NLRP2 is still ill-defined in the nervous system. Given the putative significance of NLRP2 in orchestrating neuroinflammation, further inquiry is needed to gain a better understanding of its connectome, hence its specific targeting may hold a promising therapeutic implication. Therefore, bioinformatical approach for extracting information, specifically in the context of neuropathologies, is also undoubtedly preferred. To the best of our knowledge, there is no review study selectively targeting only NLRP2. Increasing, but still fragmentary evidence should encourage researchers to thoroughly investigate this inflammasome in various animal- and human models. Taken together, herein we aimed to review the current literature focusing on the role of NLRP2 inflammasome in the nervous system and more importantly, we provide an algorithm-based protein network of human NLRP2 for elucidating potentially valuable molecular partnerships that can be the beginning of a new discourse and future therapeutic considerations.

Exploring exercise-driven exerkines: unraveling the regulation of metabolism and inflammation

Exercise has many beneficial effects that provide health and metabolic benefits. Signaling molecules are released from organs and tissues in response to exercise stimuli and are widely termed exerkines, which exert influence on a multitude of intricate multi-tissue processes, such as muscle, adipose tissue, pancreas, liver, cardiovascular tissue, kidney, and bone. For the metabolic effect, exerkines regulate the metabolic homeostasis of organisms by increasing glucose uptake and improving fat synthesis. For the anti-inflammatory effect, exerkines positively influence various chronic inflammation-related diseases, such as type 2 diabetes and atherosclerosis. This review highlights the prospective contribution of exerkines in regulating metabolism, augmenting the anti-inflammatory effects, and providing additional advantages associated with exercise. Moreover, a comprehensive overview and analysis of recent advancements are provided in this review, in addition to predicting future applications used as a potential biomarker or therapeutic target to benefit patients with chronic diseases.

The vascular footprint in cardiac homeostasis and hypertensive heart disease-A link between apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase

Recent studies have suggested a connection between disturbances of the apelin system and various cardiac pathologies, including hypertension, heart failure, and atherosclerosis. Vascular endothelial growth factor is crucial for cardiac homeostasis as a critical molecule in cardiac angiogenesis. Neuronal nitric oxide synthase is an essential enzyme producing nitric oxide, a key regulator of vascular tone. The present study aims to shed light upon the complex interactions between these three vital signaling molecules and examine their changes with the progression of hypertensive heart disease. We used two groups of spontaneously hypertensive rats and age-matched Wistar rats as controls. The expression of the apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase were assessed immunohistochemically. We used capillary density and cross-sectional area of the cardiomyocytes as quantitative parameters of cardiac hypertrophy. Immunoreactivity of the molecules was more potent in both ventricles of spontaneously hypertensive rats compared with age-matched controls. However, capillary density was lower in both ventricles of the two age groups of spontaneously hypertensive rats compared with controls, and the difference was statistically significant. In addition, the cross-sectional area of the cardiomyocytes was higher in both ventricles of the two age groups of spontaneously hypertensive rats compared with controls, and the difference was statistically significant. Our study suggests a potential link between the apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase in cardiac homeostasis and the hypertensive myocardium. Nevertheless, further research is required to better comprehend these interactions and their potential therapeutic implications.

The Role of Adipokines in the Control of Pituitary Functions

The pituitary gland is a key endocrine gland in all classes of vertebrates, including mammals. The pituitary gland is an important component of hypothalamus-pituitary-target organ hormonal regulatory axes and forms a functional link between the nervous system and the endocrine system. In response to hypothalamic stimuli, the pituitary gland secretes a number of hormones involved in the regulation of metabolism, stress reactions and environmental adaptation, growth and development, as well as reproductive processes and lactation. In turn, hormones secreted by target organs at the lowest levels of the hormonal regulatory axes regulate the functions of the pituitary gland in the process of hormonal feedback. The pituitary also responds to other peripheral signals, including adipose-tissue-derived factors. These substances are a broad group of peptides known as adipocytokines or adipokines that act as endocrine hormones mainly involved in energy homeostasis. Adipokines, including adiponectin, resistin, apelin, chemerin, visfatin, and irisin, are also expressed in the pituitary gland, and they influence the secretory functions of this gland. This review is an overview of the existing knowledge of the relationship between chosen adipose-derived factors and endocrine functions of the pituitary gland, with an emphasis on the pituitary control of reproductive processes.

Adipo-oncology: adipocyte-derived factors govern engraftment, survival, and progression of metastatic cancers

Conventional therapies for metastatic cancers have limited efficacy. Recently, cancer therapies targeting noncancerous cells in tumor microenvironments have shown improved clinical outcomes in patients. However, further advances in our understanding of the metastatic tumor microenvironment are required to improve treatment outcomes. Adipocytes are distributed throughout the body, and as a part of the metastatic tumor microenvironment, they interact with cancer cells in almost all organs. Adipocytes secrete various factors that are reported to exert clinical effects on cancer progression, including engraftment, survival, and expansion at the metastatic sites. However, only a few studies have comprehensively examined their impact on cancer cells. In this review, we examined the impact of adipocytes on cancer by describing the adipocyte-secreted factors that are involved in controlling metastatic cancer, focusing on adipokines, such as adiponectin, leptin, visfatin, chemerin, resistin, apelin, and omentin. Adipocyte-secreted factors promote cancer metastasis and contribute to various biological functions of cancer cells, including migration, invasion, proliferation, immune evasion, and drug resistance at the metastatic sites. We propose the establishment and expansion of "adipo-oncology" as a research field to enhance the comprehensive understanding of the role of adipocytes in metastatic cancers and the development of more robust metastatic cancer treatments.

Participation of the nitric oxide pathway in lordosis induced by apelin-13 in female rats

The present study investigated the participation of the nitric oxide pathway in facilitating lordosis behavior induced by intrahypothalamic administration of apelin-13 in ovariectomized rats primed with estradiol benzoate (EB). The experiments involved the administration of a nitric oxide synthase inhibitor (L-NAME) or a nitric oxide-dependent, soluble guanylyl cyclase inhibitor (ODQ), and an inhibitor of protein kinase G (KT5823) to the ventromedial hypothalamus (VMH) of EB-primed rats 30 min before infusion of apelin-13 (0.75 μg/μl). This dose of apelin-13 consistently induces lordosis behavior at 30 min, 120 min, and 240 min following infusion. Results showed that injections of either L-NAME or KT5823 significantly reduced the lordosis induced by apelin at 120 and 240 min. However, VMH infusion of ODQ 30 min before apelin-13 infusion reduced but did not significantly inhibit, the lordosis elicited by this peptide at the same time points. We conclude that the nitric oxide pathway in the VMH plays an important role in lordosis induced by apelin-13 in EB-primed rats.

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.

Signaling mechanisms underlying lymphatic vessel dysfunction in skin aging and possible anti-aging strategies

Aging-related skin diseases are gradually increasing due to the imbalance of cutaneous homeostasis in the aging population. Skin aging-induced inflammation promotes systemic inflammation and may lead to whole-body aging. Lymphatic vessels play an important role in maintaining fluid and homeostasis balance. In intrinsically aged skin, the number of lymphatic vessels decrease and their functions decline, which is related to the reduced adhesion junctions between lymphatic endothelial cells, particularly VE-cadherin. VEGFC/VEGFR-3 signal pathway plays an important role in remodeling and expansion of lymphatic vessels; the downregulation of this pathway contributes to the dysfunction of lymphatic vessels. Meanwhile, we proposed some additional mechanisms. Decline of the pumping activity of lymphatic vessels might be related to age-related changes in extracellular matrix, ROS increase, and eNOS/iNOS disturbances. In extrinsically aged skin, the hyperpermeability of lymphatic vessels results from a decrease in endothelial-specific tight junction molecules, upregulation of VEGF-A, and downregulation of the VEGFC/VEGFR-3 signaling pathway. Furthermore, some of the Phyto therapeutics could attenuate skin aging by modulating the lymphatic vessels. This review summarized the lymphatic vessel dysfunction in skin aging and anti-aging strategies based on lymphatic vessel modulation.

Therapeutic potential of apelin and Elabela in cardiovascular disease

Apelin and Elabela (Ela) are peptides encoded by APLN and APELA, respectively, which act on their receptor APJ and play crucial roles in the body. Recent research has shown that they not only have important effects on the endocrine system, but also promote vascular development and maintain the homeostasis of myocardial cells. From a molecular biology perspective, we explored the roles of Ela and apelin in the cardiovascular system and summarized the mechanisms of apelin-APJ signaling in the progression of myocardial infarction, ischemia-reperfusion injury, atherosclerosis, pulmonary arterial hypertension, preeclampsia, and congenital heart disease. Evidences indicated that apelin and Ela play important roles in cardiovascular diseases, and there are many studies focused on developing apelin, Ela, and their analogues for clinical treatments. However, the literature on the therapeutic potential of apelin, Ela and their analogues and other APJ agonists in the cardiovascular system is still limited. This review summarized the regulatory pathways of apelin/ELA-APJ axis in cardiovascular function and cardiovascular-related diseases, and the therapeutic effects of their analogues in cardiovascular diseases were also included.

Hypophagia induced by intracerebroventricular injection of apelin-13 is mediated via CRF1/CRF2 and MC3/MC4 receptors in neonatal broiler chicken

Previous studies have shown the role of apelin and its receptors in the regulation of food intake. In the present study, we investigate the mediating role of melanocortin, corticotropin, and neuropeptide Y systems in apelin-13- induced food intake in broilers. Eight trials were run in the current investigation to ascertain the relationships between the aforementioned systems and apelin-13 on food intake and behavioral changes after apelin-13 administration. In experiment 1, hens were given an intracerebroventricular administration of a solution for control in addition to apelin-13 (0.25, 0.5, and 1 µg). Astressin-B (a CRF1/CRF2 receptor antagonist, 30 µg), apelin-13 (1 µg), and administration of astressin-B and apelin-13 concurrently, were all injected into the birds in experiment 2. Experiments 3 through 8 were quite similar to experiment 2, with the exception of astressin2-B (CRF2 receptor antagonist, 30 µg), SHU9119 (MC3/MC4 receptor antagonist, 0.5 nmol), MCL0020 (MC4 receptor antagonist, 0.5 nmol), BIBP-3226 (NPY1 receptor antagonist, 1.25 nmol), BIIE 0246 (NPY2 receptor antagonist, 1.25 nmol), and CGP71683A (NPY5 receptor antagonist, 1.25 nmol) were injected instead of astressin-B. After then, total food consumption was monitored for 6 h. Apelin-13 injections of 0.5 and 1 µg decreased feeding (P < 0.05). The hypophagic effects of apelin were attenuated following the simultaneous administration of Astressin-B and Astressin2-B with apelin-13 (P > 0.05). Co-infusion of SHU9119 and apelin-13 reduced the appetite-decreasing effects of apelin-13 (P > 0.05). When MCL0020 and apelin-13 were injected at the same time, the hypophagia that apelin-13 induced was eliminated (P > 0.05). BIBP-3226, BIIE 0246, and CGP71683A had no effect on the hypophagia brought on by apelin-13 (P > 0.05). Also, apelin-13 significantly increased number of steps, jumps, exploratory food, pecks and standing time while decreased siting time (P < 0.05). These findings suggest that apelin-13-induced hypophagia in hens may involve the CRF1/CRF2 and MC3/MC4 receptors.

A First-in-Human Study of AMG 986, a Novel Apelin Receptor Agonist, in Healthy Subjects and Heart Failure Patients

PURPOSE

AMG 986 is a novel apelin receptor (APJ) agonist that improves cardiac contractility in animal models without adversely impacting hemodynamics. This phase 1b study evaluated the safety/tolerability, pharmacokinetics, and pharmacodynamics of AMG 986 in healthy subjects and patients with heart failure (HF).

METHODS

Healthy adults (Parts A/B) and HF patients (Part C) aged 18-85 years were randomized 3:1 to single-dose oral/IV AMG 986 or placebo (Part A); multiple-dose oral/IV AMG 986 or placebo (Part B); or escalating-dose oral AMG 986 or placebo (Part C).

PRIMARY ENDPOINT

treatment-emergent adverse events, laboratory values/vital signs/ECGs; others included AMG 986 pharmacokinetics, left ventricular (LV) function.

RESULTS

Overall, 182 subjects were randomized (AMG 986/healthy: n = 116, placebo, n = 38; AMG 986/HF: n = 20, placebo, n = 8). AMG 986 had acceptable safety profile; no clinically significant dose-related impact on safety parameters up to 650 mg/day was observed. AMG 986 exposures increased nonlinearly with increasing doses; minimal accumulation was observed. In HF with reduced ejection fraction patients, there were numerical increases in percent changes from baseline in LV ejection fraction and stroke volume by volumetric assessment with AMG 986 vs placebo (stroke volume increase not recapitulated by Doppler).

CONCLUSIONS

In healthy subjects and HF patients, short-term AMG 986 treatment was well tolerated. Consistent with this observation, clinically meaningful pharmacodynamic effects in HF patients were not observed. Changes in ejection fraction and stroke volume in HF patients suggest additional studies may be needed to better define the clinical utility and optimal dosing for this molecule.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT03276728.

DATE OF REGISTRATION

September 8, 2017.

The role of apelinergic system in metabolism and reproductive system in normal and pathological conditions: an overview

Lifestyle changes have made metabolic disorders as one of the major threats to life. Growing evidence demonstrates that obesity and diabetes disrupt the reproductive system by affecting the gonads and the hypothalamus-pituitary-gonadal (HPG) axis. Apelin, an adipocytokine, and its receptor (APJ) are broadly expressed in the hypothalamus nuclei, such as paraventricular and supraoptic, where gonadotropin-releasing hormone (GnRH) is released, and all three lobes of the pituitary, indicating that apelin is involved in the control of reproductive function. Moreover, apelin affects food intake, insulin sensitivity, fluid homeostasis, and glucose and lipid metabolisms. This review outlined the physiological effects of the apelinergic system, the relationship between apelin and metabolic disorders such as diabetes and obesity, as well as the effect of apelin on the reproductive system in both gender. The apelin-APJ system can be considered a potential therapeutic target in the management of obesity-associated metabolic dysfunction and reproductive disorders.

The Apelin-Apela Receptor APJ is Necessary for Formation and Healing of Ischemia Reperfusion-Induced Gastric Ulcer in Rats

The apelinergic system, widely expressed and regulates hormone-enzyme secretion, motility, and protective mechanisms of the stomach. This system consists of the apelin receptor (APJ) and two peptides known as apela and apelin. The IR-induced experimental gastric ulcer model, is a well-known and commonly used one that induces hypoxia and causes the release of proinflammatory cytokines. Expressions of apelin and its receptor APJ are induced by hypoxia and inflammation in the gastrointestinal tract. Apelin has been shown to affect angiogenesis positively, considered the most critical component of the healing process. Although it is known that apelin and AJP expressions are induced by inflammatory stimuli and hypoxia, stimulate endothelial cell proliferation and have a role in regenerative angiogenesis, no information or has been found in the literature regarding the role of APJ in the formation and healing of gastric mucosal lesions induced by I/R. So, we conducted a study to clarify the role of APJ in formation and healing mechanisms of IR-induced gastric lesions. Male Wistar rats were divided into five groups; control, sham-operated, IR, APJ antagonist treated-IR group (F13A+IR), and the healing groups. F13A was intravenously given to the animals. Gastric lesion index, mucosal blood flow, PGE₂, NOx, 4-HNE-MDA, HO activity, and protein expressions of VEGF and HO-1 were measured. F13A application before the IR increased the mucosal injury, F13A application following the ischemia delayed the mucosal healing during the reperfusion period. Consequently, blocking apelin receptors may worsen gastric injury due to the IR and delay mucosal healing.

Intravenous administration of apeling-13 induces a depressor response by releasing an unidentified substance

Apelin and APJ receptor play an important role in the regulating cardiovascular function; however, conflicting results have been reported regarding the effect of apelin on cardiovascular regulation. In this study, blood pressure and heart rate were measured by femoral arterial catheterization; and cardiac contractility was recorded by left ventricular catheterization through the right carotid artery in rats before and after intravenous administration of [pyr1]-apelin-13. The results show that intravenous administration of apelin-13 caused a dramatic reduction in BP but did not significantly alter heart rate and contractility. To study the mechanism of the apelin-induced depressor response, isometric tension was measured in isolated mesenteric arteries using a myograph approach. Surprisingly, treatment of the arteries with [pyr1]-apelin-13 did not cause relaxation of mesenteric arteries preconstricted with norepinephrine; however, treatment with plasma collected from rats that received intravenous administration of [pyr1]-apelin-13 caused pronounced relaxation of isolated arteries. Incubation with the guanylyl cyclase inhibitor, ODQ, blocked NO-induced relaxation, but did not significantly alter the relaxation response to the plasma from apelin-treated rats. Taken together, these findings demonstrate that intravenous injection of apelin causes a significant depressor response that is mediated by a NO-independent mechanism involving an unidentified substance released into the bloodstream leading to vasodilation.

The Apelinergic System in Pregnancy

The apelinergic system is a highly conserved pleiotropic system. It comprises the apelin receptor apelin peptide jejunum (APJ) and its two peptide ligands, Elabela/Toddler (ELA) and apelin, which have different spatiotemporal localizations. This system has been implicated in the regulation of the adipoinsular axis, in cardiovascular and central nervous systems, in carcinogenesis, and in pregnancy in humans. During pregnancy, the apelinergic system is essential for embryo cardiogenesis and vasculogenesis and for placental development and function. It may also play a role in the initiation of labor. The apelinergic system seems to be involved in the development of placenta-related pregnancy complications, such as preeclampsia (PE) and intrauterine growth restriction, but an improvement in PE-like symptoms and birth weight has been described in murine models after the exogenous administration of apelin or ELA. Although the expression of ELA, apelin, and APJ is altered in human PE placenta, data related to their circulating levels are inconsistent. This article reviews current knowledge about the roles of the apelinergic system in pregnancy and its pathophysiological roles in placenta-related complications in pregnancy. We also discuss the challenges in translating the actors of the apelinergic system into a marker or target for therapeutic interventions in obstetrics.

Signaling pathways in vascular function and hypertension: molecular mechanisms and therapeutic interventions

Hypertension is a global public health issue and the leading cause of premature death in humans. Despite more than a century of research, hypertension remains difficult to cure due to its complex mechanisms involving multiple interactive factors and our limited understanding of it. Hypertension is a condition that is named after its clinical features. Vascular function is a factor that affects blood pressure directly, and it is a main strategy for clinically controlling BP to regulate constriction/relaxation function of blood vessels. Vascular elasticity, caliber, and reactivity are all characteristic indicators reflecting vascular function. Blood vessels are composed of three distinct layers, out of which the endothelial cells in intima and the smooth muscle cells in media are the main performers of vascular function. The alterations in signaling pathways in these cells are the key molecular mechanisms underlying vascular dysfunction and hypertension development. In this manuscript, we will comprehensively review the signaling pathways involved in vascular function regulation and hypertension progression, including calcium pathway, NO-NOsGC-cGMP pathway, various vascular remodeling pathways and some important upstream pathways such as renin-angiotensin-aldosterone system, oxidative stress-related signaling pathway, immunity/inflammation pathway, etc. Meanwhile, we will also summarize the treatment methods of hypertension that targets vascular function regulation and discuss the possibility of these signaling pathways being applied to clinical work.

Variations in protein levels of the apelinergic system in adipose tissue of hypertensive individuals with class 3 obesity

The aim of this study was to investigate the expression of apelin (APLN) and its receptor (APLNR) in visceral adipose tissue (VAT), and its effect on the downstream expression of endothelial nitric oxide synthase (eNOS) in individuals with class 3 obesity, with or without hypertension. Seventy-five unrelated individuals presenting obesity class 3 with or without hypertension were included. Gene expression of APLN, and APLNR were analyzed in VAT, by reverse transcription quantitative polymerase chain reaction. The APLN, APLNR and eNOS (total and phosphorylated) levels in VAT were evaluated by Western blot. Analysis of differences between groups of APLN, APLNR and eNOS were performed by a logistic regression adjusting by confounding factors. Forty-five individuals with hypertension formed the case group, and 30 individuals constituted the control group. The APLN mRNA and protein levels were higher in the group of individuals with hypertension versus individuals without hypertension (p = 0.027 and p = 0.036, respectively). Meanwhile, APLNR mRNA and protein levels in subjects with hypertension were lower versus the group of subjects without hypertension (p = 0.001 and p = 0.008, respectively). Further, the group with hypertension presented a lower level of phosphorylation of eNOS Ser1177, compared to the control group (p = 0.002). In conclusion, individuals with class 3 obesity and hypertension present a modified APLN/APLNR expression in visceral adipose tissue, which could be secondary to reduced eNOS phosphorylation.

Is the anti-aging effect of ACE2 due to its role in the renin-angiotensin system?-Findings from a comparison of the aging phenotypes of ACE2-deficient, Tsukuba hypertensive, and Mas-deficient mice

Angiotensin converting enzyme 2 (ACE2) functions as an enzyme that produces angiotensin 1-7 (A1-7) from angiotensin II (AII) in the renin-angiotensin system (RAS). We evaluated aging phenotypes, especially skeletal muscle aging, in ACE2 systemically deficient (ACE2 KO) mice and found that ACE2 has an antiaging function. The characteristic aging phenotype observed in ACE2 KO mice was not reproduced in mice deficient in the A1-7 receptor Mas or in Tsukuba hypertensive mice, a model of chronic AII overproduction, suggesting that ACE2 has a RAS-independent antiaging function. In this review, the results we have obtained and related studies on the aging regulatory mechanism mediated by RAS components will be presented and summarized. We evaluated the aging phenotype of ACE2 systemically deficient (ACE2 KO) mice, particularly skeletal muscle aging, and found that ACE2 has an antiaging function. The characteristic aging phenotype observed in ACE2 KO mice was not reproduced in Mas KO mice, angiotensin 1-7 receptor-deficient mice or in Tsukuba hypertensive mice, a model of chronic angiotensin II overproduction, suggesting that the antiaging functions of ACE2 are independent of the renin-angiotensin system (RAS).

Signaling Modulation via Minimal C-Terminal Modifications of Apelin-13

Apelin is an endogenous peptide that is involved in many diseases such as cardiovascular diseases, obesity, and cancer, which has made it an attractive target for drug discovery. Herein, we explore the penultimate and final sequence positions of [Pyr1]-apelin-13 (Ape13) via C-terminal N α-alkylated amide bonds and the introduction of positive charges, potentially targeting the allosteric sodium pocket, by assessing the binding affinity and signaling profiles at the apelin receptor (APJ). Synthetic analogues modified within this segment of Ape13 showed high affinity (K i 0.12-0.17 nM vs Ape13 K i 0.7 nM), potent Gαi1 activation (EC50 Gαi1 0.4-0.9 nM vs Ape13 EC50 1.1 nM), partial agonist behavior disfavoring β-arrestin 2 recruitment for positively charged ligands (e.g., 49 (SBL-AP-058), EC50 β-arr2 275 nM, E max 54%) and high plasma stability for N-alkyl ligands (t 1/2 > 7 h vs Ape13 t 1/2 0.5 h). Combining the benefits of the N α-alkylated amide bond with the guanidino substitution in a constrained ligand led to 63 (SBL-AP-049), which displayed increased plasma stability (t 1/2 5.3 h) and strong reduction of β-arrestin 2 signaling with partial maximal efficacy (EC50 β-arr 864 nM, E max 48%), significantly reducing the hypotensive effect in vivo.

MiRNA-30d and miR-770-5p as potential clinical risk predictors of Vasoplegic Syndrome in Patients undergoing on-pump coronary artery bypass grafting

The aims of this study were to perform pre-surgery miRNA profiling of patients who develop Vasoplegic syndrome (VS) after coronary artery bypass grafting (CABG) and identify those miRNAs that could be used as VS prognostic tools and biomarkers. The levels of 754 microRNAs (miRNAs) were measured in whole blood samples from a cohort of patients collected right before the coronary artery bypass grafting (CABG) surgery. We compared the miRNA levels of those who developed VS (VASO group) with those who did not (NONVASO group) after surgery. Six miRNAs (hsa-miR-548c-3p, -199b-5p, -383-5p -571 -183-3p, -30d-5p) were increased and two (hsa-1236-3p, and hsa-miR770-5p) were decreased in blood of VASO compared to NONVASO groups. Receiver Operating Characteristic (ROC) curve analysis revealed that a combination of the miRNAs, hsa-miR-30d-5p and hsa-miR-770-5p can be used as VS predictors (AUC = 0.9615, p < 0.0001). The computational and functional analyses were performed to gain insights into the potential role of these dysregulated miRNAs in VS and have identified the "Apelin Liver Signaling Pathway" as the canonical pathway containing the most target genes regulated by these miRNAs. The expression of the combined miRNAs hsa-miR-30d and hsa-miR-770-5p allowed the ability to distinguish between patients who could and could not develop VS, representing a potential predictive biomarker of VS.

The G protein-coupled receptor ligand apelin-13 ameliorates skeletal muscle atrophy induced by chronic kidney disease

BACKGROUND

Targeting of the apelin-apelin receptor (Apj) system may serve as a useful therapeutic intervention for the management of chronic kidney disease (CKD)-induced skeletal muscle atrophy. We investigated the roles and efficacy of the apelin-Apj system in CKD-induced skeletal muscle atrophy.

METHODS

The 5/6-nephrectomized mice were used as CKD models. AST-120, a charcoal adsorbent of uraemic toxins (8 w/w% in diet), or apelin (1 μmol/kg) was administered to CKD mice to investigate the mechanism and therapeutic potential of apelin on CKD-induced skeletal muscle atrophy. The effect of indoxyl sulfate, a uraemic toxin, or apelin on skeletal muscle atrophy was evaluated using mouse myoblast cells (C2C12 cells) in vitro.

RESULTS

Skeletal muscle atrophy developed over time following nephrectomy at 12 weeks, as confirmed by a significant increase of atrogin-1 and myostatin mRNA expression in the gastrocnemius (GA) muscle and a decrease of lower limb skeletal muscle weight (P < 0.05, 0.01 and 0.05, respectively). Apelin expression in GA muscle was significantly decreased (P < 0.05) and elabela, another Apj endogenous ligand, tended to show a non-significant decrease at 12 weeks after nephrectomy. Administration of AST-120 inhibited the decline of muscle weight and increase of atrogin-1 and myostatin expression. Apelin and elabela expression was slightly improved by AST-120 administration but Apj expression was not, suggesting the involvement of uraemic toxins in endogenous Apj ligand expression. The administration of apelin at 1.0 μmol/kg for 4 weeks to CKD mice suppressed the increase of atrogin-1 and myostatin, increased apelin and Apj mRNA expression at 30 min after apelin administration and significantly ameliorated weight loss and a decrease of the cross-sectional area of hindlimb skeletal muscle.

CONCLUSIONS

This study demonstrated for the first time the association of the Apj endogenous ligand-uraemic toxin axis with skeletal muscle atrophy in CKD and the utility of therapeutic targeting of the apelin-Apj system.

Structure-function relationship and physiological role of apelin and its G protein coupled receptor

Apelin receptor (APJR) is a class A peptide (apelin) binding G protein-coupled receptor (GPCR) that plays a significant role in regulating blood pressure, cardiac output, and maintenance of fluid homeostasis. It is activated by a wide range of endogenous peptide isoforms of apelin and elabela. The apelin peptide isoforms contain distinct structural features that aid in ligand recognition and activation of the receptor. Site-directed mutagenesis and structure-based studies have revealed the involvement of extracellular and transmembrane regions of the receptor in binding to the peptide isoforms. The structural features of APJR activation of the receptor as well as mediating G-protein and β-arrestin-mediated signaling are delineated by multiple mutagenesis studies. There is increasing evidence that the structural requirements of APJR to activate G-proteins and β-arrestins are different, leading to biased signaling. APJR also responds to mechanical stimuli in a ligand-independent manner. A multitude of studies has focused on developing both peptide and non-peptide agonists and antagonists specific to APJR. Apelin/elabela-activated APJR orchestrates major signaling pathways such as extracellular signal-regulated kinase (ERKs), protein kinase B (PKB/Akt), and p70S. This review focuses on the structural and functional characteristics of apelin, elabela, APJR, and their interactions involved in the binding and activation of the downstream signaling cascade. We also focus on the diverse signaling profile of APJR and its ligands and their involvement in various physiological systems.

Epidemiological, mechanistic, and practical bases for assessment of cardiorespiratory fitness and muscle status in adults in healthcare settings

Given their importance in predicting clinical outcomes, cardiorespiratory fitness (CRF) and muscle status can be considered new vital signs. However, they are not routinely evaluated in healthcare settings. Here, we present a comprehensive review of the epidemiological, mechanistic, and practical bases of the evaluation of CRF and muscle status in adults in primary healthcare settings. We highlight the importance of CRF and muscle status as predictors of morbidity and mortality, focusing on their association with cardiovascular and metabolic outcomes. Notably, adults in the best quartile of CRF and muscle status have as low as one-fourth the risk of developing some of the most common chronic metabolic and cardiovascular diseases than those in the poorest quartile. The physiological mechanisms that underlie these epidemiological associations are addressed. These mechanisms include the fact that both CRF and muscle status reflect an integrative response to the body function. Indeed, muscle plays an active role in the development of many diseases by regulating the body's metabolic rate and releasing myokines, which modulate metabolic and cardiovascular functions. We also go over the most relevant techniques for assessing peak oxygen uptake as a surrogate of CRF and muscle strength, mass, and quality as surrogates of muscle status in adults. Finally, a clinical case of a middle-aged adult is discussed to integrate and summarize the practical aspects of the information presented throughout. Their clinical importance, the ease with which we can assess CRF and muscle status using affordable techniques, and the availability of reference values, justify their routine evaluation in adults across primary healthcare settings.

Expanding the apelin receptor pharmacological toolbox using novel fluorescent ligands

INTRODUCTION

The apelin receptor binds two distinct endogenous peptides, apelin and ELA, which act in an autocrine/paracrine manner to regulate the human cardiovascular system. As a class A GPCR, targeting the apelin receptor is an attractive therapeutic strategy. With improvements in imaging techniques, and the stability and brightness of dyes, fluorescent ligands are becoming increasingly useful in studying protein targets. Here, we describe the design and validation of four novel fluorescent ligands; two based on [Pyr1]apelin-13 (apelin488 and apelin647), and two based on ELA-14 (ELA488 and ELA647).

METHODS

Fluorescent ligands were pharmacologically assessed using radioligand and functional in vitro assays. Apelin647 was validated in high content imaging and internalisation studies, and in a clinically relevant human embryonic stem cell-derived cardiomyocyte model. Apelin488 and ELA488 were used to visualise apelin receptor binding in human renal tissue.

RESULTS

All four fluorescent ligands retained the ability to bind and activate the apelin receptor and, crucially, triggered receptor internalisation. In high content imaging studies, apelin647 bound specifically to CHO-K1 cells stably expressing apelin receptor, providing proof-of-principle for a platform that could screen novel hits targeting this GPCR. The ligand also bound specifically to endogenous apelin receptor in stem cell-derived cardiomyocytes. Apelin488 and ELA488 bound specifically to apelin receptor, localising to blood vessels and tubules of the renal cortex.

DISCUSSION

Our data indicate that the described novel fluorescent ligands expand the pharmacological toolbox for studying the apelin receptor across multiple platforms to facilitate drug discovery.

The good Samaritan glutathione-S-transferase P1: An evolving relationship in nitric oxide metabolism mediated by the direct interactions between multiple effector molecules

Glutathione-S-transferases (GSTs) are phase II detoxification isozymes that conjugate glutathione (GSH) to xenobiotics and also suppress redox stress. It was suggested that GSTs have evolved not to enhance their GSH affinity, but to better interact with and metabolize cytotoxic nitric oxide (NO). The interactions between NO and GSTs involve their ability to bind and store NO as dinitrosyl-dithiol iron complexes (DNICs) within cells. Additionally, the association of GSTP1 with inducible nitric oxide synthase (iNOS) results in its inhibition. The function of NO in vasodilation together with studies associating GSTM1 or GSTT1 null genotypes with preeclampsia, additionally suggests an intriguing connection between NO and GSTs. Furthermore, suppression of c-Jun N-terminal kinase (JNK) activity occurs upon increased levels of GSTP1 or NO that decreases transcription of JNK target genes such as c-Jun and c-Fos, which inhibit apoptosis. This latter effect is mediated by the direct association of GSTs with MAPK proteins. GSTP1 can also inhibit nuclear factor kappa B (NF-κB) signaling through its interactions with IKKβ and Iκα, resulting in decreased iNOS expression and the stimulation of apoptosis. It can be suggested that the inhibitory activity of GSTP1 within the JNK and NF-κB pathways may be involved in crosstalk between survival and apoptosis pathways and modulating NO-mediated ROS generation. These studies highlight an innovative role of GSTs in NO metabolism through their interaction with multiple effector proteins, with GSTP1 functioning as a "good Samaritan" within each pathway to promote favorable cellular conditions and NO levels.

Apelin-Induced Relaxation of Coronary Arteries Is Impaired in a Model of Second-Hand Cigarette Smoke Exposure

ABSTRACT

Apelin, an endogenous ligand for APJ receptors, causes nitric oxide (NO)-dependent relaxation of coronary arteries. Little is known about the effects of apelin/APJ receptor signaling in the coronary circulation under pathological conditions. Here, we tested the hypothesis that the vasorelaxing effect of apelin is impaired by cigarette smoke extract (CSE), an established model for second-hand smoke exposure. Isolated rat coronary arteries were treated with 2% CSE for 4 hours. Apelin-induced relaxation of coronary arteries was abolished by CSE exposure, while relaxations to acetylcholine (ACh) (endothelium-dependent relaxation) and to diethyl amine NONOate (NO donor) were similar in control and CSE-treated arteries. Immunoblot analysis demonstrated that apelin increased eNOS ser1177 phosphorylation under control conditions but had no effect after exposure to CSE. Moreover, GRK2 expression was increased in CSE-exposed coronary endothelial cells. Pretreatment with CMPD101, a GRK2 inhibitor, improved the relaxation response to apelin in CSE-exposed coronary arteries. CSE treatment failed to inhibit relaxations evoked by CMF-019, an APJ receptor biased agonist that has little effect on GRK2. In arteries exposed to CSE, apelin impaired the response to ACh but not to diethyl amine NONOate. ACh-induced relaxation was unaffected by CMF-019 in either control or CSE-treated coronary arteries. The results suggest that APJ receptor signaling using the GRK2 pathway contributes to both loss of relaxation to apelin itself and the ability of apelin to inhibit endothelium-dependent relaxation to ACh in CSE-exposed coronary arteries, likely because of impaired production of NO from endothelial cells. These changes in apelin/APJ receptor signaling under pathological conditions (eg, exposure to second-hand smoke) could create an environment that favors increased vasomotor tone in coronary arteries.

Presence and localization of apelin and its cognate receptor in canine testes using immunohistochemical and RT-PCR techniques

Apelin, a member of the adipokine family, is a novel endogenous peptide which regulates the male reproductive system of mammals by interacting with a specific receptor. Recent studies have highlighted that apelin may play a role in the regulation of reproduction by reducing testosterone production and inhibiting LH secretion. To the best of our knowledge, there is no available data on the presence of the apelin and its receptor in canine testes. Therefore, the aim of this study was to reveal the presence of apelin and evaluate its distribution in the canine testes using immunohistochemical and RT-PCR techniques. For this purpose, five fertile and healthy male dogs were subjected to elective orchiectomy. The immunohistochemical reaction revealed the presence of apelin and its receptor in the canine testes. Apelin was localized in spermatids and spermatozoa with a positive signal in the "acrosomal bodies". As regards the apelin receptor, a positive immunoreaction was detected in the cytoplasm of the cells localized near to the basal membrane of the seminiferous tubules and in the cytoplasm of Leydig cells. The RT-PCR analysis showed the presence of transcripts for apelin and apelin receptor in all of the samples under study. A 35kDa band confirmed apelin receptor protein expression in all of the samples analysed. In conclusion, the paracrine and endocrine role of apelin and its cognate receptor on male reproduction reported in humans and laboratory animals could also be hypothesized in dogs.

Endocrine disruptor chemicals, adipokines and reproductive functions

The prevalence of adult obesity has risen markedly in recent decades. The endocrine system precisely regulates energy balance, fat abundance and fat deposition. Interestingly, white adipose tissue is an endocrine gland producing adipokines, which regulate whole-body physiology, including energy balance and reproduction. Endocrine disruptor chemicals (EDCs) include natural substances or chemicals that affect the endocrine system by multiple mechanisms and increase the risk of adverse health outcomes. Numerous studies have associated exposure to EDCs with obesity, classifying them as obesogens by their ability to activate different mechanisms, including the differentiation of adipocytes, increasing the storage of triglycerides, or elevating the number of adipocytes. Moreover, in recent years, not only industrial deception and obesity have intensified but also the problem of human infertility. Reproductive functions depend on hormone interactions, the balance of which may be disrupted by various EDCs or obesity. This review gives a brief summary of common EDCs linked with obesity, the mechanisms of their action, and the effect on adipokine levels, reproduction and connected disorders, such as polycystic ovarian syndrome, decrease in sperm motility, preeclampsia, intrauterine growth restriction in females and decrease of sperm motility in males.

How does apelin affect LH levels? An investigation at the level of GnRH and KNDy neurons

Hypothalamic control of reproduction relies on GnRH and kisspeptin (KP) secretions. KP neurons are sensitive to sex steroids and metabolic status and their distribution overlaps with neurons producing apelin, a metabolic hormone known to decrease LH secretion in rats. Here, we observed neuroanatomical contacts between apelin fibers and both KP and GnRH neurons in the hypothalamus of male rodents. Intracerebroventricular apelin infusion for 2 weeks in male mice did not decrease LH levels nor did it affect gene expression for KP, neurokinin B and dynorphin. Finally, increasing apelin concentrations did not modulate Ca²⁺ levels of cultured GnRH neurons, while 10 μM apelin infusion on forskolin pretreated GnRH neurons revoked a rhythmic activity in 18% of GnRH neurons. These results suggest that acute apelin effect on LH secretion does not involve modulation of gene expression in KP neurons but may affect the secretory activity of GnRH neurons.

Empagliflozin prevents neointima formation by impairing smooth muscle cell proliferation and accelerating endothelial regeneration

Background

Empagliflozin, an inhibitor of the sodium glucose co-transporter 2 (SGLT2) and developed as an anti-diabetic agent exerts additional beneficial effects on heart failure outcomes. However, the effect of empagliflozin on vascular cell function and vascular remodeling processes remains largely elusive.

Methods/Results

Immunocytochemistry and immunoblotting revealed SGLT2 to be expressed in human smooth muscle (SMC) and endothelial cells (EC) as well as in murine femoral arteries. In vitro, empagliflozin reduced serum-induced proliferation and migration of human diabetic and non-diabetic SMCs in a dose-dependent manner. In contrast, empagliflozin significantly increased the cell count and migration capacity of human diabetic ECs, but not of human non-diabetic ECs. In vivo, application of empagliflozin resulted in a reduced number of proliferating neointimal cells in response to femoral artery wire-injury in C57BL/6J mice and prevented neointima formation. Comparable effects were observed in a streptozocin-induced diabetic model of apolipoprotein E–/– mice. Conclusive to the in vitro-results, re-endothelialization was not significantly affected in C57BL/6 mice, but improved in diabetic mice after treatment with empagliflozin assessed by Evan’s Blue staining 3 days after electric denudation of the carotid artery. Ribonucleic acid (RNA) sequencing (RNA-seq) of human SMCs identified the vasoactive peptide apelin to be decisively regulated in response to empagliflozin treatment. Recombinant apelin mimicked the in vitro-effects of empagliflozin in ECs and SMCs.

Conclusion

Empagliflozin significantly reduces serum-induced proliferation and migration of SMCs in vitro and prevents neointima formation in vivo, while augmenting EC proliferation in vitro and re-endothelialization in vivo after vascular injury. These data document the functional impact of empagliflozin on vascular human SMCs and ECs and vascular remodeling in mice for the first time.

Modulation of Vasomotor Function by Perivascular Adipose Tissue of Renal Artery Depends on Severity of Arterial Dysfunction to Nitric Oxide and Severity of Metabolic Parameters

Perivascular adipose tissue (PVAT) enhances vascular relaxation of mesenteric arteries in SHRSP.Z-Leprfa/IzmDmcr rats (SPZF), a metabolic syndrome model. We investigated and compared the effects of PVAT on the renal artery in SPZF with those on SHR/NDmcr-cp rats (CP). Renal arteries with and without PVAT were isolated from 23-week-old SPZF and CP. The effects of PVAT on acetylcholine- and nitroprusside-induced relaxation were examined using bioassays with phenylephrine-contracted arterial rings. Acetylcholine-induced relaxations without PVAT in SPZF and CP were 0.7- and 0.5-times lower in females than in males, respectively. In the presence of PVAT, acetylcholine-induced relaxations increased 1.4- and 2-times in male and female CP, respectively, but did not differ in SPZF. Nitroprusside-induced relaxation with and without PVAT was 0.7-times lower in female than in male SPZF but did not differ in CP. Angiotensin-II type-1 receptor (AT1R)/AT1R-associated protein mRNA ratios were lower in CP than in the SPZF and negatively correlated with the difference in arterial relaxation with and without PVAT. The effects of renal artery PVAT differed between the SPZF and CP groups. Higher levels of enhanced AT1R activity in SPZF PVAT may drive these differences by impairing the vascular smooth muscle responses to nitric oxide.

AMPK and the Challenge of Treating Hypoxic Pulmonary Hypertension

Hypoxic pulmonary hypertension (HPH) is characterized by sustained elevation of pulmonary artery pressure produced by vasoconstriction and hyperproliferative remodeling of the pulmonary artery and subsequent right ventricular hypertrophy (RVH). The search for therapeutic targets for cardiovascular pathophysiology has extended in many directions. However, studies focused on mitigating high-altitude pulmonary hypertension (HAPH) have been rare. Because AMP-activated protein kinase (AMPK) is involved in cardiovascular and metabolic pathology, AMPK is often studied as a potential therapeutic target. AMPK is best characterized as a sensor of cellular energy that can also restore cellular metabolic homeostasis. However, AMPK has been implicated in other pathways with vasculoprotective effects. Notably, cellular metabolic stress increases the intracellular ADP/ATP or AMP/ATP ratio, and AMPK activation restores ATP levels by activating energy-producing catabolic pathways and inhibiting energy-consuming anabolic pathways, such as cell growth and proliferation pathways, promoting cardiovascular protection. Thus, AMPK activation plays an important role in antiproliferative, antihypertrophic and antioxidant pathways in the pulmonary artery in HPH. However, AMPK plays contradictory roles in promoting HPH development. This review describes the main findings related to AMPK participation in HPH and its potential as a therapeutic target. It also extrapolates known AMPK functions to discuss the less-studied HAPH context.

Sports activities at a young age decrease hypertension risk-The J-Fit+ study

This study aimed to assess (1) blood pressure between young, current athletes, and non-athletes early in life; (2) hypertension prevalence between former athletes and the general population later in life; and (3) understand the mechanisms between exercise training and hypertension risks in the form of DNA methylation. Study 1: A total of 354 young male participants, including current athletes, underwent blood pressure assessment. Study 2: The prevalence of hypertension in 1269 male former athletes was compared with that in the Japanese general population. Current and former athletes were divided into three groups: endurance-, mixed-, and sprint/power-group. Study 3: We analyzed the effect of aerobic- or resistance-training on DNA methylation patterns using publicly available datasets to explore the possible underlying mechanisms. In young, current athletes, the mixed- and sprint/power-group exhibited higher systolic blood pressure, and all groups exhibited higher pulse pressure than non-athletes. In contrast, the prevalence of hypertension in former athletes was significantly lower in all groups than in the general population. Compared to endurance-group (reference), adjusted-hazard ratios for the incidence of hypertension among mixed- and sprint/power-group were 1.24 (0.87-1.84) and 1.50 (1.04-2.23), respectively. Moreover, aerobic- and resistance-training commonly modified over 3000 DNA methylation sites in skeletal muscle, and these were suggested to be associated with cardiovascular function-related pathways. These findings suggest that the high blood pressure induced by exercise training at a young age does not influence the development of future hypertension. Furthermore, previous exercise training experiences at a young age could decrease the risk of future hypertension.

Potassium Channels Contributes to Apelin-induced Vasodilation in Rat Thoracic Aorta

Background:

Apelin is a newly discovered peptide hormone and originally discovered endogenous apelin receptor ligand.

Objective:

In this study, we aimed to investigate the possible roles of potassium channel subtypes in the vasorelaxant effect mechanisms of apelin.

Methods:

The vascular rings obtained from the thoracic aortas of the male Wistar Albino rats were placed into the isolated tissue bath system. The resting tension was set to 2 g. After the equilibration period, the aortic rings were precontracted with 10-5 M phenylephrine (PHE) or 45 mM KCl. Pyroglutamyl-apelin-13 ([Pyr1]apelin-13), which is the dominant apelin isoform in the human cardiovascular tissues and human plasma, was applied cumulatively (10-10-10-6 M) to the aortic rings in the plateau phase. The experimental protocol was repeated in the presence of specific K+ channel subtype blockers to determine the role of K+ channels in the vasorelaxant effect mechanisms of apelin.

Results:

[Pyr1]apelin-13 induced a concentration-dependent vasorelaxation (p < 0.001). The maximum relaxation level was approximately 52%, according to PHE-induced contraction. Tetraethylammonium, iberiotoxin, 4-Aminopyridine, glyburide, anandamide, and BaCl2 statistically significantly decreased the vasorelaxant effect level of [Pyr1]apelin-13 (p < 0.001). However, apamin didn’t statistically significantly change the vasorelaxant effect level of [Pyr1]apelin-13.

Conclusion:

In conclusion, our findings suggest that BKCa, IKCa, Kv, KATP, Kir, and K2P channels are involved in the vasorelaxant effect mechanisms of apelin in the rat thoracic aorta.

Serum Chemerin and Apelin Levels in Obese Children: Relation to Endothelial Function and Inflammation from a Cross-sectional Case–Control Study

BACKGROUND: Childhood obesity is a global threat with subsequent health problems among which and most important is cardiovascular problems. It is now claimed that adipokines secreted by adipose tissue are responsible for such consequences. Newly discovered adipokines chemerin and apelin are under investigation for their link with obesity related co-morbidites. AIM: The aim of the present study was to assess the serum levels of chemerin and apelin in obese children and to explore the correlation between these two biomarkers and the inflammatory as well as the endothelial cell activation markers PATIENTS AND METHODS: This study was a cross-sectional case control study that comprised 45 pre-pubertal obese children aged (6– < 12) years old of both sexes (22 males and 23 females), in addition to 45 matched age and sex lean children serving as controls (21 males and 24 females). Serum levels of chemerin, apelin, ICAM-1, E-selectin and hs-CRP were measured for obese and controls. RESULTS: Obese children showed higher levels of chemerin, apelin, ICAM-1 and E-selectin than controls. Chemerin and apelin showed significant correlations with all parameters except for age. Anthropometric parameters with hs-CRP revealed significant correlation even after adjustment for age and sex while apelin only showed a significant correlation with age. Multiple regression analyses with hs -CR , E-selectin and ICAM-1 as dependent variables and BMI Z score ,age, sex, chemerin and apelin as independent variables showed the effect of chemerin and apelin on  the increased  levels of hs -CR , E-selectin and ICAM-1 . CONCLUSION: Elevated levels of chemerin and apelin may serve as indices of ongoing obesity-related disorders in obese children.

[Physiological role of the apelin receptor: implication in body fluid homeostasis and hyponatremia]

Apelin, a vasoactive neuropeptide, its receptor and arginine-vasopressin (AVP, antidiuretic hormone) are co-localized in magnocellular vasopressinergic neurons. In the kidney, the apelin receptor is present in glomerular arterioles and the collecting duct (CD) where the AVP type 2 (V2-R) receptors are located. Apelin exerts an aquaretic action both by its inhibitory effect on the phasic electrical activity of vasopressinergic neurons and the secretion of AVP into the bloodstream and by its direct actions at the kidney level resulting in an increase in the renal microcirculation and the inhibition of the antidiuretic effect of AVP mediated by V2-R in the CD. Plasma apelin and AVP are conversely regulated by osmotic stimuli in both humans and rodents, showing that apelin is involved with AVP in maintaining body fluid homeostasis. Clinically, in patients with inappropriate antidiuresis syndrome (SIAD), the apelin/AVP balance is altered, which contributes to water metabolism defect. Activation of the apelin receptor by the metabolically stable apelin-17 analog, that increases aqueous diuresis and moderately water intake and gradually corrects hyponatremia, may constitute a new approach for the treatment of SIAD.

Apelin-13 facilitates lordosis behavior following infusions to the ventromedial hypothalamus or preoptic area in ovariectomized, estrogen-primed rats

In normal hormonal conditions, increased neuronal activity in the ventromedial hypothalamus (VMH) induces lordosis whereas activation of the preoptic area (POA) exerts an opposite effect. In the present work, we explored the effect of bilateral infusion of different doses of the apelin-13 (0.37, 0.75, 1.5, and 15 μg) in both brain areas on the expression of lordosis behavior. Lordosis quotient and lordosis reflex score were performed at 30, 120, and 240 min. Weak lordosis was observed following the 0.37 μg dose of apelin-13 at 30 min in the VMH of EB-primed rats; however, the rest of the doses induced significant lordosis relative to the control group. At 120 min, all doses induced lordosis behavior, while at 240 min, the highest dose of 15 μg did not induce significant differences. Interestingly, only the 0.75 μg infusion of apelin in the POA induced significant lordosis at 120 and 240 min. These results indicate that apelin-13 acts preferably in HVM and slightly in POA to initiate lordosis behavior in estrogen-primed rats.

The relationship between apelin and carotid intima media thickness, and the presence of plaque in dialysis patients

BACKGROUND

Apelin is a peptide that has important effects on the cardiovascular system due to its anti-atherogenic properties and regulating blood pressure. There is not enough research evaluating the effects of apelin levels on the cardiovascular system in hemodialysis (HD) and peritoneal dialysis (PD) patients concurrently. The aim of this study was to determine apelin levels in dialysis, and control groups and to investigate the relationship between apelin and carotid intima media thickness (CIMT).

MATERIALS AND METHODS

Thirty three HD patients, 35 PD patients, and 15 healthy individuals were included in the study. All laboratory data, N-terminal pro-B-type natriuretic peptide (NT-proBNP), IL-6, and apelin-13 levels were analyzed. To prevent interobserver errors in CIMT measurement, the analyses were performed by a single radiologist.

RESULT

CIMT, presence of plaque, apelin, NT-proBNP, IL-6, and C-reactive protein (CRP) levels were higher in dialysis patients. There was a relationship between apelin and CIMT, and between apelin and high-density lipoprotein (HDL) in PD patients. Age, apelin, HDL, parathormone (PTH), glucose, and smoking were found to affect the presence of plaque in dialysis patients.

CONCLUSION

Apelin levels were high in dialysis patients. Especially in PD patients, there was a negative correlation between apelin and CIMT, and between apelin and HDL. Therefore, apelin may play a role in the pathogenesis of cardiovascular diseases in PD patients.

The Role of Apelin-APJ System in Diabetes and Obesity

Nowadays, diabetes and obesity are two main health-threatening metabolic disorders in the world, which increase the risk for many chronic diseases. Apelin, a peptide hormone, exerts its effect by binding with angiotensin II protein J receptor (APJ) and is considered to be linked with diabetes and obesity. Apelin and its receptor are widely present in the body and are involved in many physiological processes, such as glucose and lipid metabolism, homeostasis, endocrine response to stress, and angiogenesis. In this review, we summarize the literatures on the role of the Apelin-APJ system in diabetes and obesity for a better understanding of the mechanism and function of apelin and its receptor in the pathophysiology of diseases that may contribute to the development of new therapies.

Serum miRNA Profile in Diabetic Patients With Ischemic Heart Disease as a Promising Non-Invasive Biomarker

The increasing morbidity and mortality of type 2 diabetic mellitus (T2DM) patients with ischemic heart disease (IHD) highlight an urgent need to identify early biomarkers, which would help to predict individual risk of development of IHD. Here, we postulate that circulating serum-derived micro RNAs (miRNAs) may serve as potential biomarkers for early IHD diagnosis and support the identification of diabetic individuals with a predisposition to undergo IHD. We obtained serum samples from T2DM patients either with IHD or IHD-free and analysed the expression levels of 798 miRNAs using the NanoString nCounter technology platform. The prediction of the putative miRNAs targets was performed using the Ingenuity Pathway Analysis (IPA) software. Gene Ontology (GO) analysis was used to identify the biological function and signalling pathways associated with miRNA target genes. Hub genes of protein-protein interaction (PPI) network were identified by STRING database and Cytotoscape tool. Receiver operating characteristic (ROC) analysis was used to assess the diagnostic value of identified miRNAs. Real-time quantitative polymerase chain reaction (qRT-PCR) was used for nCounter platform data validation. Our data showed that six miRNAs (miR-615-3p, miR-3147, miR-1224-5p, miR-5196-3p, miR-6732-3p, and miR-548b-3p) were significantly upregulated in T2DM IHD patients compared to T2DM patients without IHD. Further analysis indicated that 489 putative target genes mainly affected the endothelin-1 signalling pathway, glucocorticoid biosynthesis, and apelin cardiomyocyte signalling pathway. All tested miRNAs showed high diagnostic value (AUC = 0.779 - 0.877). Taken together, our research suggests that circulating miRNAs might have a crucial role in the development of IHD in diabetic patients and may be used as a potential biomarker for early diagnosis.

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

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

The therapeutic potential of apelin in kidney disease

Chronic kidney disease (CKD) is a leading cause of global morbidity and mortality and is independently associated with cardiovascular disease. The mainstay of treatment for CKD is blockade of the renin-angiotensin-aldosterone system (RAAS), which reduces blood pressure and proteinuria and slows kidney function decline. Despite this treatment, many patients progress to kidney failure, which requires dialysis or kidney transplantation, and/or die as a result of cardiovascular disease. The apelin system is an endogenous physiological regulator that is emerging as a potential therapeutic target for many diseases. This system comprises the apelin receptor and its two families of endogenous ligands, apelin and elabela/toddler. Preclinical and clinical studies show that apelin receptor ligands are endothelium-dependent vasodilators and potent inotropes, and the apelin system has a reciprocal relationship with the RAAS. In preclinical studies, apelin regulates glomerular haemodynamics and acts on the tubule to promote aquaresis. In addition, apelin is protective in several kidney injury models. Although the apelin system has not yet been studied in patients with CKD, the available data suggest that apelin is a promising potential therapeutic target for kidney disease.

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.