Superoxide anions modulate the effects of alarin in the paraventricular nucleus on sympathetic activity and blood pressure in spontaneously hypertensive rats

Serum levels of galanin-like peptide and alarin are highly correlated with polycystic ovary syndrome

To compare the levels of galanin-like peptide (GALP) and alarin between patients with polycystic ovary syndrome (PCOS) and a control group, and to explore the correlations between GALP/alarin and PCOS. We selected a total of 103 PCOS patients and 89 non-PCOS control patients who visited the hospital during the same period. The PCOS patients and the controls were assigned by body mass index (BMI) into PCOS subgroup 1 and control subgroup 1 (18.5 < BMI < 24 kg/m2) and into PCOS subgroup 2 and control subgroup 2 (BMI ≥ 24 kg/m2). The general indices (weight, height, waist circumference, and hip circumference), serum sex hormone concentrations, biochemical indices, and GALP and alarin levels were measured for all subjects, and the differences in each index were compared between the two groups. (1) The BMI, waist-to-hip ratio (WHR), lipid accumulation product (LAP), total testosterone (total T), luteinizing hormone (LH) levels, fasting insulin (FINS), triglycerides (TG), alanine transaminase (ALT), HOMA-IR, and GALP and alarin concentrations were significantly higher and the AST/ALT ratio was significantly lower in the PCOS patients than in the controls. (2) Correlation analysis showed that serum GALP levels were positively correlated with BMI, WHR, LAP, total T, LH, FINS, TG, HOMA-IR, and alarin, and negatively correlated with AST/ALT. Serum alarin levels were correlated positively with BMI, WHR, LAP, total T, LH, FINS, TG, HOMA-IR, and GALP, and negatively with FSH and AST/ALT. Serum LAP, FINS, LH, and alarin were independent factors that influenced serum GALP levels, and serum FINS, LAP, LH, and GALP were independent factors that influenced serum alarin concentrations. The areas under the receiver operating characteristic curves (95% confidence intervals) for serum GALP and alarin levels in predicting PCOS were 0.78 (0.713, 0.847) and 0.828 (0.766, 0.889), respectively, and the cutoff values were 0.895 and 0.355, respectively. GALP and alarin were highly expressed in PCOS patients and closely associated with factors such as IR, HA, and obesity, and they showed favorable predictive values for PCOS.

Can Galanin Be Used as a Marker of Microvascular Dysfunction in Prehypertensives?

Objectives

Coronary microvascular dysfunction is present in large percentage of the population, and it has been shown to have a pathological and prognostic role in many conditions. Therefore, early detection of microvascular dysfunction is important, especially in selected populations. The aim of this study was to investigate the association of galanin with coronary flow reserve (CFR) in prehypertensive individuals to determine whether it can be used as a marker to detect microvascular dysfunction.

Methods

A total of 100 participants, 50 prehypertensive and 50 normotensive were included in this prospective study. Serum galanin levels were measured and CFR was calculated by detailed transthoracic echocardiography.

Results

CFR was significantly lower in the prehypertensive group (p<0.001). Also, galanin values were numerically lower in the prehypertensive group, but the difference between the groups did not reach statistical significance (p=0.062). There was no significant correlation between CFR and galanin (r=-0.161, p=0.11).

Conclusion

Lower CFR values in prehypertensives suggest that microvascular dysfunction starts above normotensive values even if hypertension does not develop. The reason why low galanin levels were not statistically significant in prehypertensives and no correlation was found between galanin and CFR may be due to the small study population. Relationship between galanin, prehypertension and microvascular dysfunction will become clearer if large-scale population studies are carried out.

GLP-1 in the Hypothalamic Paraventricular Nucleus Promotes Sympathetic Activation and Hypertension

Glucagon-like peptide-1 (GLP-1) and its analogs are widely used for diabetes treatment. The paraventricular nucleus (PVN) is crucial for regulating cardiovascular activity. This study aims to determine the roles of GLP-1 and its receptors (GLP-1R) in the PVN in regulating sympathetic outflow and blood pressure. Experiments were carried out in male normotensive rats and spontaneously hypertensive rats (SHR). Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded. GLP-1 and GLP-1R expressions were present in the PVN. PVN microinjection of GLP-1R agonist recombinant human GLP-1 (rhGLP-1) or EX-4 increased RSNA and MAP, which were prevented by GLP-1R antagonist exendin 9-39 (EX9-39) or GLP-1R antagonist 1, superoxide scavenger tempol, antioxidant N-acetylcysteine, NADPH oxidase (NOX) inhibitor apocynin, adenylyl cyclase (AC) inhibitor SQ22536 or protein kinase A (PKA) inhibitor H89. PVN microinjection of rhGLP-1 increased superoxide production, NADPH oxidase activity, cAMP level, AC, and PKA activity, which were prevented by SQ22536 or H89. GLP-1 and GLP-1R were upregulated in the PVN of SHR. PVN microinjection of GLP-1 agonist increased RSNA and MAP in both WKY and SHR, but GLP-1 antagonists caused greater effects in reducing RSNA and MAP in SHR than in WKY. The increased superoxide production and NADPH oxidase activity in the PVN of SHR were augmented by GLP-1R agonists but attenuated by GLP-1R antagonists. These results indicate that activation of GLP-1R in the PVN increased sympathetic outflow and blood pressure via cAMP-PKA-mediated NADPH oxidase activation and subsequent superoxide production. GLP-1 and GLP-1R upregulation in the PVN partially contributes to sympathetic overactivity and hypertension.

The evolving roles of alarin in physiological and disease conditions, and its future potential clinical implications

Alarin is a member of the galanin family of neuropeptides that is widely expressed in the central nervous system and peripheral tissues in humans and rodents. It was initially isolated fifteen years ago in ganglionic cells of human neuroblastoma. Subsequently, it was demonstrated to be broadly distributed in the blood vessels, skin, eyes, peripheral and central nervous systems, thymus, gastrointestinal tract, and endocrine organs of different species. Alarin is a 25 amino acid neuropeptide derived from the alternative splicing of the GALP gene, missing exon 3. It is found to be involved in several physiological functions that include feeding behavior, energy homeostasis, glucose homeostasis, body temperature, and reproduction. It has also vasoactive, anti-inflammatory, anti-edema, and antimicrobial activities. However, the physiological effects of alarin have not been fully elucidated and the receptors that mediate these effects are not currently known. Unearthing the novel biological effects of alarin and its unidentified receptors will therefore be a task in future biomedical research. In addition, alarin is involved in various disease conditions, such as metabolic syndrome, obesity, insulin resistance, type 2 diabetes, diabetic retinopathy, hypertension, cardiac fibrosis, polycystic ovarian syndrome, and depression. Thus, alarin may serve as a promising tool for future pharmacological treatment and diagnosis. But further research is awaited to confirm whether alarin has a protective or pathological role in these diseases. This article provides a comprehensive review on the evolving implications of alarin in a variety of physiological and disease conditions, and its future perspectives.

Regulatory effects and potential therapeutic implications of alarin in depression, and arguments on its receptor

Alarin is a pleiotropic peptide involved in a multitude of putative biological activities, notably, it has a regulatory effect on depression-like behaviors. Although further elucidating research is needed, animal-based cumulative evidence has shown the antidepressant-like effects of alarin. In light of its regulatory role in depression, alarin could be used as a promising antidepressant in future treatment for depression. Nevertheless, the available information is still insufficient and the therapeutic relevance of alarin in depression is still of concern. Moreover, a plethora of studies have reported that the actions of alarin, including antidepressant activities, are mediated by a separate yet unidentified receptor, highlighting the need for more extensive research. This review focuses on the current understanding of the regulatory effects and future therapeutic relevance of alarin on depression, and the arguments on its receptors.

Alarin moderated myocardial hypertrophy via inhibiting cyclic adenosine monophosphate/protein kinase A signaling pathway to attenuate autophagy

Alarin could alleviate myocardial infarction-induced heart failure. The present study was to explore whether alarin could alleviate myocardial hypertrophy via inhibiting cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) signaling pathway to attenuate autophagy. Myocardial hypertrophy was induced by angiotensin (Ang) II infusion in vivo in mice and by Ang II treatment of neonatal rat cardiomyocytes (NRCMs) in vitro. The Ang II-induced hypertrophy and fibrosis of the heart were alleviated after alarin administration in mice. The increased atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and beta-myosin heavy chain (β-MHC), and the decreased alpha-myosin heavy chain (α-MHC) induced by Ang II were reversed by alarin treatment in NRCMs. Alarin inhibited the increases of cAMP and PKA in NRCMs. Treatment with cAMP or overexpression of PKA blocked the attenuating effects of alarin on Ang II-induced hypertrophy in NRCMs. Alarin reduced the Ang II-induced increases of LC3, Beclin 1, autophagy-related gene (Atg)3 and Atg5 in NRCMs. The overexpression of cAMP and PKA reversed the alleviating effects of alarin on the increased autophagy induced by Ang II in NRCMs. These results indicated that alarin could moderate cardiac remodeling. Alarin improved myocardial hypertrophy via inhibiting the cAMP/PKA signaling pathway to attenuate autophagy.

Relaxin increased blood pressure and sympathetic activity in paraventricular nucleus of hypertensive rats via enhancing oxidative stress

Relaxin, an ovarian polypeptide hormone, is found in the hypothalamic paraventricular nucleus (PVN) which is an important central integrative site for the control of blood pressure and sympathetic outflow. The aim of this study was to determine if superoxide anions modulate the effects of relaxin in the PVN. Experiments were performed in normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). Relaxin mRNA and protein, and its receptor, relaxin family peptide receptor 1 (RXFP1) levels in PVN were 3.24, 3.17, and 3.64 times higher in SHRs than in WKY rats, respectively. Microinjection of relaxin-2 into the PVN dose-dependently increased mean arterial pressure (MAP), renal sympathetic nerve activity (RSNA) and heart rate (HR) in both WKY rats and SHRs, although the effects on MAP (16.87 ± 1.99 vs. 8.97 ± 1.48 mm Hg in 100 nmol), RSNA (22.60 ± 2.15 vs. 11.77 ± 1.43 % in 100 nmol) and HR (22.85 ± 3.13 vs. 12.62 ± 2.83 beats/min in 100 nmol) were greater in SHRs. Oxidative stress level was enhanced after relaxin-2 microinjection into the PVN. Pretreatment with superoxide anion scavengers or NADPH oxidase inhibitor blocked, and superoxide dismutase inhibitor potentiated the effects of relaxin-2 on MAP, RSNA and HR. RXFP1 knockdown significantly attenuated the blood pressure of SHRs, and inhibited the increases of atrial natriuretic peptide, brain natriuretic peptide, collagen I, collagen III and fibronectin in the heart of SHRs. These results demonstrated that relaxin is expressed in the PVN, and contributes to hypertension and sympathetic overdrive via oxidative stress. Down-regulation of RXFP1 in the PVN could attenuate hypertension and cardiac remodeling.

Alarin alleviated cardiac fibrosis via attenuating oxidative stress in heart failure rats

The present study was to explore whether alarin could alleviate heart failure (HF) and attenuate cardia fibrosis via inhibiting oxidative stress. The fibrosis of cardiac fibroblasts (CFs) was induced by angiotensin (Ang) II. HF models were induced by ligation of the left anterior descending artery to cause ischemia myocardial infarction (MI) in Sprague–Dawley rats. Alarin (1.0 nM/kg/d) was administrated by intraperitoneal injection for 28 days. The decreases of left ventricular (LV) ejection fraction (EF), fractional shortening (FS), the maximum of the first differentiation of LV pressure (LV ± dp/dt_max) and LV systolic pressure (LVSP), and the increases of LV volume in systole (LVVS), LV volume in diastole (LVVD), LV end-systolic diameter (LVESD) and LV end-diastolic diameter (LVEDD) in MI rats were improved by alarin treatment. The increases in the expression levels of collagen I, collagen III, and transforming growth factor (TGF)-β were inhibited by alarin treatment in CFs and in the hearts of MI rats. The levels of NADPH oxidase (Nox) activity, superoxide anions and malondialdehyde (MDA) levels were increased, and the level of superoxide dismutase (SOD) activity was reduced in Ang II-treated CFs, which were reversed by alarin. Nox1 overexpression reversed the effects of alarin on attenuating the increases of collagen I, collagen III and TGF-β expression levels induced by Ang II in CFs. These results indicated that alarin improved HF and cardiac fibrosis via inhibiting oxidative stress in HF rats. Nox1 played important roles in the regulation of alarin effects on attenuating CFs fibrosis induced by Ang II.