Plasma apelin levels, blood pressure and cardiovascular risk factors in a coastal Chinese population

Connection between the Plasma Level of Apelin and Diabetic Nephropathy in Type 2 Diabetic Patients. A Case Control Study

BACKGROUND

Apelin is an adipokine that may have an advantageous role in the prediction of early diabetic nephropathy. A few studies on apelin in diabetes have been performed and this research was performed to establish the connection between the apelinergic system and diabetic nephropathy.

MATERIALS AND METHODS

The research included 60 patients with type 2 diabetes mellitus (T2DM) who were equally divided into Group-I (diabetic nephropathy) and Group-II (non-diabetic nephropathy), and 30 healthy subjects in the control group (Group-III). Body mass index (BMI) and waist circumference were calculated. FBG, 2 h-PPG, HbA1c, fasting lipids, urea, creatinine, eGFR, urine analysis, A/C ratio, and apelin levels were assessed.

RESULTS

A statistically significant between-group difference in plasma apelin levels was found (P < 0.001). Apelin was the highest in Group-I than in Group-II relative to Group-III (325.79 ± 59.42 pg/mL, 162.83 ± 29.88 pg/mL, and 77.43 ± 8.44 pg/mL, respectively). Among diabetic patients, plasma apelin had a significantly positive correlation with disease duration (r = 0.612), SBP (r = 0.427), DBP (r = 0.466), weight (r = 0.372), and height (r = 0.372), FBG (r = 0.684), 2 h-PPG (r = 0.744), HbA1C (r = 0.890), total (T)-cholesterol (r = 0.316), low density lipoprotein (LDL)-C (r = 0.397), urea (r = 0.575), and creatinine (r = 0.591). A significantly negative correlation was observed between plasma apelin and HDL-C (r = -0.303), and eGFR (r = -0.566).

CONCLUSION

Apelin levels in diabetics were elevated in the case of nephropathy, impaired glucose tolerance, and dyslipidemia. This supports the relationship between the apelinergic system and diabetic nephropathy.

Circumventricular Organ Apelin Receptor Knockdown Decreases Blood Pressure and Sympathetic Drive Responses in the Spontaneously Hypertensive Rat

The central site(s) mediating the cardiovascular actions of the apelin-apelin receptor (APJ) system remains a major question. We hypothesized that the sensory circumventricular organs (CVOs), interfacing between the circulation and deeper brain structures, are sites where circulating apelin acts as a signal in the central nervous system to decrease blood pressure (BP). We show that APJ gene (aplnr) expression was elevated in the CVOs of spontaneously hypertensive rats (SHRs) compared to normotensive Wistar Kyoto (WKY) controls, and that there was a greater mean arterial BP (MABP) decrease following microinjection of [Pyr¹]apelin-13 to the CVOs of SHRs compared to WKY rats. Lentiviral APJ-specific-shRNA (LV-APJ-shRNA) was used to knockdown aplnr expression, both collectively in three CVOs and discretely in individual CVOs, of rats implanted with radiotelemeters to measure arterial pressure. LV-APJ-shRNA-injection decreased aplnr expression in the CVOs and abolished MABP responses to microinjection of [Pyr¹]apelin-13. Chronic knockdown of aplnr in any of the CVOs, collectively or individually, did not affect basal MABP in SHR or WKY rats. Moreover, knockdown of aplnr in any of the CVOs individually did not affect the depressor response to systemic [Pyr¹]apelin-13. By contrast, multiple knockdown of aplnr in the three CVOs reduced acute cardiovascular responses to peripheral [Pyr¹]apelin-13 administration in SHR but not WKY rats. These results suggest that endogenous APJ activity in the CVOs has no effect on basal BP but that functional APJ in the CVOs is required for an intact cardiovascular response to peripherally administered apelin in the SHR.

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.

Impact of Apelin-13 on the Development of Coronary Artery Ectasia

Background

Coronary artery ectasia (CAE) is the limitation or diffuse expansion of the epicardial coronary artery. In most cases, the pathological basis of CAE is considered to be coronary atherosclerosis. Previous studies have confirmed the association between Apelin and arterial atherosclerosis. Apelin-13 (AP-13) is the main serum Apelin subtype in healthy humans, however the effect of serum AP-13 on CAE has yet to be elucidated. In this research, we analysed the relationship between serum AP-13 levels and CAE.

Methods

One hundred and forty subjects who underwent selective diagnostic coronary angiography were enrolled in this research. We identified and included 40 patients with CAE as the study subjects. Another 50 patients with coronary artery disease (CAD) were randomly selected as the CAD group, and 50 patients without CAD were selected as the normal control group. Serum AP-13 levels were collected for all subjects.

Results

There were no statistically significant differences in baseline data except for gender. After unconditional logistic regression analysis, AP-13 and HDL-c were independent risk factors for CAE (both p < 0.05). The serum AP-13 level was significantly lower in the CAE patients than in the CAD patients (1.86 ± 0.59 vs. 2.49 ± 1.19 ng/mL, p = 0.004). Serum AP-13 levels were slightly lower in the CAD patients than in the controls (2.49 ± 1.19 vs. 3.12 ± 1.64, p = 0.079).

Conclusions

Apelin-13 may have an effect on the development of CAE. Further studies should be performed to elucidate the possible pathogenic role of AP-13 in CAE.

Blockade of Rostral Ventrolateral Medulla Apelin Receptors Does Not Attenuate Arterial Pressure in SHR and L-NAME-Induced Hypertensive Rats

Dysfunction of the apelinergic system, comprised of the neuropeptide apelin mediating its effects via the G protein-coupled apelin receptor (APJ), may underlie the onset of cardiovascular disease such as hypertension. Apelin expression is increased in the rostral ventrolateral medulla (RVLM) in spontaneously hypertensive rats (SHRs) compared to Wistar-Kyoto (WKY) normotensive rats, however, evidence that the apelinergic system chronically influences mean arterial blood pressure (MABP) under pathophysiological conditions remains to be established. In this study we investigated, in conscious unrestrained rats, whether APJ contributes to MABP and sympathetic vasomotor tone in the progression of two models of hypertension - SHR and _L-NAME-treated rats - and whether APJ contributes to the development of hypertension in pre-hypertensive SHR. In SHR we showed that APJ gene (aplnr) expression was elevated in the RVLM, and there was a greater MABP increase following microinjection of [Pyr¹]apelin-13 to the RVLM of SHR compared to WKY rats. Bilateral microinjection of a lentiviral APJ-specific-shRNA construct into the RVLM of WKY, SHR, and _L-NAME-treated rats, chronically implanted with radiotelemeters to measure MABP, decreased aplnr expression in the RVLM and abolished acute [Pyr¹]apelin-13-induced increases in MABP. However, chronic knockdown of aplnr in the RVLM did not affect MABP in either SHR or _L-NAME-treated rats. Moreover, knockdown of aplnr in the RVLM of prehypertensive SHR did not protect against the development of hypertension. These results show that endogenous apelin, acting via APJ, is not involved in the genesis or maintenance of hypertension in either animal model used in this study.

Relations of Apelin with Cardiac Remodeling in Patients with Hypertension and Type 2 Diabetes

Background: The peptide apelin has antihypertensive and antidiabetic properties, but its role in the processes of cardiac remodeling in patients with hypertension and type 2 diabetes (T2D) is poorly understood.

Aim: The aim of the study was to investigate apelin levels in patients with hyper-tension and T2D and to determine its relations to heart structural parameters and types of cardiac remodeling.

Materials and methods: We examined 63 patients with hypertension and T2D. Investigation complex included physical examination, standard transthoracic echocardiography and determination of apelin serum levels by ELISA. Control group consisted of 16 volunteers.

Results: The apelin levels in patients were significantly lower than those in volunteers (0.882(0.788; 0.924) ng/ml versus 1.097(0.944; 1.171) ng/ml, p<0.001). Negative correlation relations of apelin with septal wall thickness (r=−0.50, p<0.001), posterior wall thickness (r=−0.46, p<0.001), left ventricle (LV) mass (r=−0.39, p<0.01), LV mass index (r=−0.42, p<0.001) and left atrium size (r=−0.45, p<0.001) were found. In patients with concentric remodeling of LV apelin levels were 0.918 (0.892; 0.984) ng/ml, with concentric LV hypertrophy – 0.855(0.722; 0.899) ng/ml, with eccentric LV hypertrophy – 0.884(0.856; 0.929) ng/ml (p<0.05, p<0.001, p<0.001 versus control, respectively). Patients with concentric LV hypertrophy had significantly lower apelin levels than patients with concentric remodeling of LV (p<0.05).

Conclusion: Patients with hypertension and T2D have significant reduction of apelin blood levels, which is accompanied by cardiac remodeling development primarily concentric LV hypertrophy and have negative correlation relations of apelin with heart structural parameters that characterize LV remodeling and left atrium size.

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.

Apelin/APJ system: A critical regulator of vascular smooth muscle cell

APJ, an orphan G protein-coupled receptor, is first identified through homology cloning in 1993. Apelin is endogenous ligand of APJ extracted from bovine stomach tissue in 1998. Apelin/APJ system is widely expressed in many kinds of cells such as endothelial cells, cardiomyocytes, especially vascular smooth muscle cell. Vascular smooth muscle cell (VSMC), an integral part of the vascular wall, takes part in many normal physiological processes. Our experiment firstly finds that apelin/APJ system enhances VSMC proliferation by ERK1/2-cyclin D1 signal pathway. Accumulating studies also show that apelin/APJ system plays a pivotal role in mediating the function of VSMC. In this paper, we review the exact role of apelin/APJ system in VSMC, including induction of proliferation and migration, enhance of contraction and relaxation, inhibition of calcification. Furthermore, we discuss the role of apelin/APJ system in vascular diseases, such as atherosclerosis, hypertension, and chronic kidney disease (CKD) from the point of VSMC. Above all, apelin/APJ system is a promising target for managing vascular disease.

Agonist-induced internalization and desensitization of the apelin receptor

Apelin acts via the G protein-coupled apelin receptor (APJ) to mediate effects on cardiovascular and fluid homeostasis. G protein-coupled receptor (GPCR) trafficking has an important role in the regulation of receptor signalling pathways and cellular functions, however in the case of APJ the mechanisms and proteins involved in apelin-induced trafficking are not well understood. We generated a stable HEK-293 cell line expressing N-terminus HA-tagged mouse (m) APJ, and used a semi-automated imaging protocol to quantitate APJ trafficking and ERK1/2 activation following stimulation with [Pyr¹]apelin-13. The mechanisms of [Pyr¹]apelin-13-induced internalization and desensitization were explored using dominant-negative mutant (DNM) cDNA constructs of G protein-coupled receptor kinase 2 (GRK2), β-arrestin1, EPS15 and dynamin. The di-phosphorylated ERK1/2 (ppERK1/2) response to [Pyr¹]apelin-13 desensitized during sustained stimulation, due to upstream APJ-specific adaptive changes. Furthermore, [Pyr¹]apelin-13 stimulation caused internalization of mAPJ via clathrin coated vesicles (CCVs) and also caused a rapid reduction in cell surface and whole cell HA-mAPJ. Our data suggest that upon continuous agonist exposure GRK2-mediated phosphorylation targets APJ to CCVs that are internalized from the cell surface in a β-arrestin1-independent, EPS15- and dynamin-dependent manner. Internalization does not appear to contribute to the desensitization of APJ-mediated ppERK1/2 activation in these cells.

Serum Apelin 13 Levels in Patients With Pulmonary Embolism

Introduction and Aim:

Expression and peptide immunoreactivity of apelin messenger RNA have been described in a variety of tissues, including gastrointestinal tract, adipose tissue, brain, kidney, liver, cardiovascular system, and lungs. This study aimed to investigate the possible involvement of the endogenous apelin in the pathophysiological events that occur in patients with pulmonary embolism (PE).

Materials and Methods:

In total, 53 patients with PE and 35 healthy volunteers were included the study. This cross-sectional study was conducted at a tertiary care university hospital and among patients diagnosed as having PE. The control group consisted of healthy volunteers who applied to hospital for a routine checkup examination. Serum apelin 13 levels were measured in both the groups and their results were compared.

Results:

The median ages were 57 and 53 years, and female–male ratios were 30/23 and 20/15, in the PE and control groups, respectively. The mean serum apelin 13 levels were found to be significantly higher in the PE group (76.94 ± 10.70 ng/mL) than in the control group (50.01 ± 7.13 ng/mL; P < .001).

Conclusion:

This study demonstrated that apelin 13 levels are elevated in patients with PE. These results suggest that apelin may be a novel biomarker and a potential therapeutic target in patients with acute PE in the future.