Ghrelin and the Cardiovascular System

Ghrelin improves endothelial function and reduces blood pressure in Ang II-induced hypertensive mice: Role of AMPK

BACKGROUND

Endothelial dysfunction is a major pathophysiology observed in hypertension. Ghrelin, a key regulator of metabolism, has been shown to play protective roles in cardiovascular system. However, whether it has the effect of improving endothelial function and lowering blood pressure in Ang II-induced hypertensive mice remains unclear.

METHODS

In this study, hypertension was induced by continuous infusion of Ang II with a subcutaneous osmotic pumps and ghrelin (30 μg/kg/day) was intraperitoneal injection for 4 weeks. Acetylcholine-induced endothelium-dependent relaxation in aortae was measured on wire myograph and superoxide production in mouse aortae was assessed by fluorescence imaging.

RESULTS

We found that ghrelin had protective effects on Ang II-induced hypertension by inhibiting oxidative stress, increasing NO production, improving endothelial function, and lowering blood pressure. Furthermore, ghrelin activated AMPK signaling in Ang II-induced hypertension, leading to inhibition of oxidative stress. Compound C, a specific inhibitor of AMPK, reversed the protective effects of ghrelin on the reduction of oxidative stress, the improvement of endothelial function and the reduction of blood pressure.

CONCLUSIONS

our findings indicated that ghrelin protected against Ang II-induced hypertension by improving endothelial function and lowering blood pressure partly through activating AMPK signaling. Thus, ghrelin may be a valuable therapeutic strategy for hypertension.

Ghrelin hormone a new molecular modulator between obesity and glomerular damage

The incidence of glomerular diseases is increasing worldwide due to increased prevalence of obesity which is a major risk factor for type-2 diabetes mellitus and cardiovascular disorders.Ghrelin, an orexigenic peptide hormone, has been implicated in obesity, and its impact on the pathology and function of the kidneys was found to be significant. Ghrelin known to regulate energy homeostasis and growth hormone release, has been shown to modulate critical signaling pathways involved in the health and survival of podocytes. These derangements directly affect glomerular function and manifest as impaired glomerular filtration barrier and leakage of albumin into urine. Although the pathological features of the above-mentioned disorders are different, they interestingly lead to similar clinical features of glomerular damage. The pathological events are majorly initiated by endocrine imbalance leading to abnormal activation of downstream signaling pathways involved in the development of glomerulosclerosis. In fact, obesity increases the risk of developing chronic kidney disease by altering the secretion of pro-inflammatory cytokines and adipokines, activating the renin-angiotensin-aldosterone system (RAAS), promoting lipotoxicity, oxidative stress and fibrosis within the kidneys. Whilst these bioregulators are well described, their direct involvement in renal homeostasis is still mostly elusive. This review summarized previous and recent evidence on the endocrine properties of ghrelin and perivascular adipose tissue involved in modulating kidney physiology.

Cancer- and cardiac-induced cachexia: same fate through different inflammatory mediators?

BACKGROUND

Inflammation is widely recognized as the driving force of cachexia induced by chronic diseases; however, therapies targeting inflammation do not always reverse cachexia. Thus, whether inflammation per se plays an important role in the clinical course of cachectic patients is still a matter of debate.

AIMS

To give new insights into cachexia's pathogenesis and diagnosis, we performed a comprehensive literature search on the contribution of inflammatory markers to this syndrome, focusing on the noncommunicable diseases cancer and cardiovascular diseases.

METHODS

A systematic review was performed in PubMed using the keywords ("cancer" OR "cardiac" cachexia AND "human" OR "patient" AND "plasma" or "serum"). A total of 744 studies were retrieved and, from these, 206 were selected for full-text screening. In the end, 98 papers focusing on circulating biomarkers of cachexia were identified, which resulted in a list of 113 different mediators.

RESULTS

Data collected from the literature highlight the contribution of interleukin-6 (IL-6) and C-reactive protein (CRP) to cachexia, independently of the underlying condition. Despite not being specific, once the diagnosis of cachexia is established, CRP might help to monitor the effectiveness of anti-cachexia therapies. In cardiac diseases, B-type natriuretic peptide (BNP), renin, and obestatin might be putative markers of body wasting, whereas in cancer, growth differentiation factor (GDF) 15, transforming growth factor (TGF)-β1 and vascular endothelial growth factor (VEGF) C seem to be better markers of this syndrome. Independently of the circulating mediators, NF-κB and JAK/STAT signaling pathways play a key role in bridging inflammation with muscle wasting; however, therapies targeting these pathways were not proven effective for all cachectic patients.

CONCLUSION

The critical and integrative analysis performed herein will certainly feed future research focused on the better comprehension of cachexia pathogenesis toward the improvement of its diagnosis and the development of personalized therapies targeting specific cachexia phenotypes.

MRAP2 inhibits β-arrestin recruitment to the ghrelin receptor by preventing GHSR1a phosphorylation

The melanocortin receptor accessory protein 2 (MRAP2) is essential for several physiological functions of the ghrelin receptor growth hormone secretagogue receptor 1a (GHSR1a), including increasing appetite and suppressing insulin secretion. In the absence of MRAP2, GHSR1a displays high constitutive activity and a weak G-protein-mediated response to ghrelin and readily recruits β-arrestin. In the presence of MRAP2, however, G-protein-mediated signaling via GHSR1a is strongly dependent on ghrelin stimulation and the recruitment of β-arrestin is significantly diminished. To better understand how MRAP2 modifies GHSR1a signaling, here we investigated the role of several phosphorylation sites within the C-terminal tail and third intracellular loop of GHSR1a, as well as the mechanism behind MRAP2-mediated inhibition of β-arrestin recruitment. We show that Ser252 and Thr261 in the third intracellular loop of GHSR1a contribute to β-arrestin recruitment, whereas the C-terminal region is not essential for β-arrestin interaction. Additionally, we found that MRAP2 inhibits GHSR1a phosphorylation by blocking the interaction of GRK2 and PKC with the receptor. Taken together, these data suggest that MRAP2 alters GHSR1a signaling by directly impacting the phosphorylation state of the receptor and that the C-terminal tail of GHSR1a prevents rather than contribute to β-arrestin recruitment.

Perivascular Adipose Tissue Inflammation: The Anti-Inflammatory Role of Ghrelin in Atherosclerosis Progression

Perivascular adipose tissue (PVAT) and its adipokines engage in bidirectional crosstalk with the vascular wall. Atherosclerosis disrupts this interaction through inflammation, rupture-prone plaques, and subsequent thrombosis. The cardioprotective effects of ghrelin are in contradiction to its adipogenic properties. The concurrent research of anti-/pro-atherogenic mechanisms of ghrelin and PVAT-derived adipokines provides a better understanding of atherosclerosis progression in metabolic disorders. In-depth coverage of the characteristic features of PVAT concerning vascular dysfunction, with a survey of ghrelin-induced anti-inflammatory effects on adipose tissue macrophage infiltration and the inhibitory activity of ghrelin on the proinflammatory adipokine secretion, show that the impact of ghrelin on the endothelial function should be studied in relation to PVAT.

Relationship Between Sarcopenia and Cardiovascular Diseases in the Elderly: An Overview

With the advent of population aging, aging-related diseases have become a challenge for governments worldwide. Sarcopenia has defined as a clinical syndrome associated with age-related loss such as skeletal muscle mass, strength, function, and physical performance. It is commonly seen in elderly patients with chronic diseases. Changes in lean mass are common critical determinants in the pathophysiology and progression of cardiovascular diseases (CVDs). Sarcopenia may be one of the most important causes of poor physical function and decreased cardiopulmonary function in elderly patients with CVDs. Sarcopenia may induce CVDs through common pathogenic pathways such as malnutrition, physical inactivity, insulin resistance, inflammation; these mechanisms interact. In this study, we aimed to investigate the relationship between sarcopenia and CVDs in the elderly. Further research is urgently needed to understand better the relationship, pathophysiology, clinical presentation, diagnostic criteria, and mechanisms of sarcopenia and CVDs, which may shed light on potential interventions to improve clinical outcomes and provide greater insight into the disorders above.

The role of ghrelin and leptin in feeding behavior: Genetic and molecular evidence

Feeding behavior is integrated within a wide variety of eating behaviors, which depend on psychosocial, biological and environmental factors. These types of behavior can cause nutrition-related diseases such as obesity, which affects more than 650 million people worldwide. Ghrelin and leptin are key hormones that regulate appetite, food intake and energy metabolism. Research in genetics suggests that genetic variants of both hormones are associated with complex forms of eating behavior, such as a preference for palatable food, making individuals susceptible to the modern obesogenic environment. This review analyses the scientific evidence around polymorphisms in the ghrelin and leptin genes and their association with eating behavior. The understanding of these mechanisms is relevant since it could impact on the objectives of pharmacological or behavioral interventions for their treatment.

High-Fat Diet Induced Gut Microbiota Alterations Associating With Ghrelin/Jak2/Stat3 Up-Regulation to Promote Benign Prostatic Hyperplasia Development

The role of high-fat diet (HFD) induced gut microbiota alteration and Ghrelin as well as their correlation in benign prostatic hyperplasia (BPH) were explored in our study. The gut microbiota was analyzed by 16s rRNA sequencing. Ghrelin levels in serum, along with Ghrelin and Ghrelin receptor in prostate tissue of mice and patients with BPH were measured. The effect of Ghrelin on cell proliferation, apoptosis, and induction of BPH in mice was explored. Our results indicated that BPH mice have the highest ratio of Firmicutes and Bacteroidetes induced by HFD, as well as Ghrelin level in serum and prostate tissue was significantly increased compared with control. Elevated Ghrelin content in the serum and prostate tissue of BPH patients was also observed. Ghrelin promotes cell proliferation while inhibiting cell apoptosis of prostate cells. The effect of Ghrelin on enlargement of the prostate was found almost equivalent to that of testosterone propionate (TP) which may be attenuated by Ghrelin receptor antagonist YIL-781. Ghrelin could up-regulate Jak2/pJak2/Stat3/pStat3 expression in vitro and in vivo. Our results suggested that Gut microbiota may associate with Ghrelin which plays an important role in activation of Jak2/Stat3 in BPH development. Gut microbiota and Ghrelin might be pathogenic factors for BPH and could be used as a target for mediation.

Novel in vivo and in vitro mechanisms of positive inotropic effect of atractylodin

This study was to investigate the inotropic effect of atractylodin and its underlying mechanism. The cardiac pressure-volume loop (P-V loop), Langendroff-perfused isolated rat heart, patch-clamp, Ca2+ transient and western blot techniques were used. The results demonstrated that atractylodin (3 mg/kg, ip) remarkably increased the left ventricular stroke work, cardiac output, stroke volume, heart rate, ejection fraction, end-systolic pressure, peak rates of rise and fall of left ventricular pressures (+dP/dtmax , -dP/dtmax ), the slopes of end-systolic pressure-volume relationship (also named as end-systolic elastance, Ees) and reducing end-systolic volume and end-diastolic volume in the in vivo rat study. Also, atractylodin (3 mg/kg, ip) significantly decreased diastolic blood pressure and the arterial elastance (Ea) without significant systolic blood pressure change. In addition, atractylodin (0.1, 1, 10 µmol/L) also increased the isolated rat heart left ventricular developed pressure which is the difference between the systolic and diastolic pressure in non-pacing and pacing modes. Furthermore, JMV-2959 (1 μmol/L), a ghrelin receptor unbiased antagonist, blocked the increased left ventricular developed pressure of atractylodin in isolated rat hearts. Finally, atractylodin (5 µmol/L) increased the amplitude of Ca2+ transient by enhancing SERCA2a activity, the sarcoplasmic reticulum Ca2+ content and the phosphorylation of phospholamban at 16-serine. These results demonstrated that atractylodin had a positive inotropic effect by enhancing SERCA2a activity which might be mediated by acting ghrelin receptor in myocardium. In conclusion, atractylodin which had the positive inotropic effect and decreased diastolic blood pressure might serve as an agent for the treatment of heart failure in clinical settings.

The role of ghrelin and leptin in feeding behavior: Genetic and molecular evidence

Feeding behavior is integrated within a wide variety of eating behaviors, which depend on psychosocial, biological and environmental factors. These types of behavior can cause nutrition-related diseases such as obesity, which affects more than 650 million people worldwide. Ghrelin and leptin are key hormones that regulate appetite, food intake and energy metabolism. Research in genetics suggests that genetic variants of both hormones are associated with complex forms of eating behavior, such as a preference for palatable food, making individuals susceptible to the modern obesogenic environment. This review analyses the scientific evidence around polymorphisms in the ghrelin and leptin genes and their association with eating behavior. The understanding of these mechanisms is relevant since it could impact on the objectives of pharmacological or behavioral interventions for their treatment.

Ghrelin inhibited pressure overload-induced cardiac hypertrophy by promoting autophagy via CaMKK/AMPK signaling pathway

Ghrelin, a novel gut hormone, has been shown to exert protective effects on cardiac dysfunction and remodeling. However, the underlying mechanisms of its protective effects remain unclear. Here, we investigated the effects of ghrelin on cardiac hypertrophy and explored the mechanisms involved. Ghrelin (30 μg.kg^-1. day^-1) was systemically administered to rats with cardiac hypertrophy induced by abdominal aortic constriction (AAC) by a mini-osmotic pump the next day after surgery continuously for 4 weeks. The AAC treated rats without ghrelin infusion showed decreased ghrelin content and expression of its receptors in the hearts. Exogenous ghrelin greatly attenuated cardiac hypertrophy as shown by heart weight to tibial length (HW/TL), hemodynamics, echocardiography, histological analyses, and expression of hypertrophic markers induced by AAC. This corresponded with decreased cardiac fibrosis and inflammation in the hearts of AAC rats treated with ghrelin. Moreover, ghrelin significantly increased the myocardial expression of autophagy markers, which was further confirmed in cultured cardiomyocytes. Concurrently, cardiomyocyte apoptosis in vivo and in vitro was ameliorated by ghrelin, which was reversed by inhibition of autophagy. The enhancement of autophagy and inhibition of apoptosis by ghrelin were eliminated on pretreatment with compound C, an AMP-activated protein kinase (AMPK) inhibitor. Furthermore, inhibition of Ca²⁺/Calmodulin-dependent protein kinase kinase (CaMKK), an upstream kinase of AMPK, made ghrelin fail to activate AMPK and simultaneously reversed ghrelin's promotion of autophagy. In conclusion, ghrelin could exert its cardioprotective effects on cardiac hypertrophy by promoting autophagy, possibly via CaMKK/AMPK signaling pathway.

Research progress of ghrelin on cardiovascular disease

Ghrelin, a 28-aminoacid peptide, was isolated from the human and rat stomach and identified in 1999 as an endogenous ligand for the growth hormone secretagogue-receptor (GHS-R). In addition to stimulating appetite and regulating energy balance, ghrelin and its receptor GHS-R1a have a direct effect on the cardiovascular system. In recent years, it has been shown that ghrelin exerts cardioprotective effects, including the modulation of sympathetic activity and hypertension, enhancement of the vascular activity and angiogenesis, inhibition of arrhythmias, reduction in heart failure and inhibition of cardiac remodeling after myocardial infarction (MI). The cardiovascular protective effect of ghrelin may be associated with anti-inflammation, anti-apoptosis, inhibited sympathetic nerve activation, regulated autophagy, and endothelial dysfunction. However, the molecular mechanisms underlying the effects of ghrelin on the cardiovascular system have not been fully elucidated, and no specific therapeutic agent has been established. It is important to further explore the pharmacological potential of ghrelin pathway modulation for the treatment of cardiovascular diseases.

Heal the heart through gut (hormone) ghrelin: a potential player to combat heart failure

Ghrelin, a small peptide hormone (28 aa), secreted mainly by X/A-like cells of gastric mucosa, is also locally produced in cardiomyocytes. Being an orexigenic factor (appetite stimulant), it promotes release of growth hormone (GH) and exerts diverse physiological functions, viz. regulation of energy balance, glucose, and/or fat metabolism for body weight maintenance. Interestingly, administration of exogenous ghrelin significantly improves cardiac functions in CVD patients as well as experimental animal models of heart failure. Ghrelin ameliorates pathophysiological condition of the heart in myocardial infarction, cardiac hypertrophy, fibrosis, cachexia, and ischemia reperfusion injury. This peptide also exerts significant impact at the level of vasculature leading to lowering high blood pressure and reversal of endothelial dysfunction and atherosclerosis. However, the molecular mechanism of actions elucidating the healing effects of ghrelin on the cardiovascular system is still a matter of conjecture. Some experimental data indicate its beneficial effects via complex cellular cross talks between autonomic nervous system and cardiovascular cells, some other suggest more direct receptor-mediated molecular actions via autophagy or ionotropic regulation and interfering with apoptotic and inflammatory pathways of cardiomyocytes and vascular endothelial cells. Here, in this review, we summarise available recent data to encourage more research to find the missing links of unknown ghrelin receptor-mediated pathways as we see ghrelin as a future novel therapy in cardiovascular protection.

The Additional Prognostic Value of Ghrelin for Mortality and Readmission in Elderly Patients with Acute Heart Failure

Purpose

To evaluate the prognostic value of ghrelin, a growth hormone-releasing peptide, for mortality and readmission in elderly patients with acute heart failure (AHF).

Patients and Methods

We measured plasma ghrelin and pro B-type natriuretic peptide (NT-proBNP) levels upon emergency admission in 241 prospectively recruited elderly AHF patients (61.0% men). The outcomes were all-cause mortality and/or readmission due to heart failure (HF). Multivariate Cox proportional hazards regression analyses were used to evaluate the prognostic value of ghrelin. Discrimination, calibration, and reclassification indices were compared between models, with or without ghrelin.

Results

During 1.2 years of follow-up, we observed 90 events (57 deaths and 33 readmissions due to HF). Plasma ghrelin levels were significantly elevated in elderly AHF patients, when compared to healthy control subjects (P < 0.001). Patients with events had significantly higher baseline ghrelin levels, when compared to those without (P < 0.001). Ghrelin levels were positively correlated with NT-proBNP levels and HF severity, whereas they were negatively correlated with nutritional status (all P < 0.05). Log transformed ghrelin levels were independently associated with AHF events (hazard ratio = 2.64, 95% confidence interval = 1.11–6.25, P = 0.028). The incorporation of ghrelin into the reference model, or reference with the NT-proBNP model, both improved C-statistics (from 0.742–0.780 and 0.836–0.857; P = 0.074 and 0.044, respectively), resulting in an improvement in net reclassification index (14.42% and 10.45%, P = 0.020 and 0.025, respectively), and integrated discrimination index (5.64% and 3.60%, both P < 0.001). Patients who displayed the above NT-proBNP and ghrelin median levels had a markedly higher risk of AHF adverse events (P < 0.001).

Conclusion

Plasma ghrelin is an independent predictor of adverse events in elderly AHF patients. Ghrelin may provide additional value to clinical parameters or NT-proBNP for prognostic risk stratification in AHF.

Dysregulation of ghrelin in diabetes impairs the vascular reparative response to hindlimb ischemia in a mouse model; clinical relevance to peripheral artery disease

Type 2 diabetes is a prominent risk factor for peripheral artery disease (PAD). Yet, the mechanistic link between diabetes and PAD remains unclear. This study proposes that dysregulation of the endogenous hormone ghrelin, a potent modulator of vascular function, underpins the causal link between diabetes and PAD. Moreover, this study aimed to demonstrate the therapeutic potential of exogenous ghrelin in a diabetic mouse model of PAD. Standard ELISA analysis was used to quantify and compare circulating levels of ghrelin between (i) human diabetic patients with or without PAD (clinic) and (ii) db/db diabetic and non-diabetic mice (lab). Db/db mice underwent unilateral hindlimb ischaemia (HLI) for 14 days and treated with or without exogenous ghrelin (150 µg/kg/day.) Subsequently vascular reparation, angiogenesis, hindlimb perfusion, structure and function were assessed using laser Doppler imaging, micro-CT, microangiography, and protein and micro-RNA (miRNA) analysis. We further examined hindlimb perfusion recovery of ghrelin KO mice to determine whether an impaired vascular response to HLI is linked to ghrelin dysregulation in diabetes. Patients with PAD, with or without diabetes, had significantly lower circulating levels of endogenous ghrelin, compared to healthy individuals. Diabetic db/db mice had ghrelin levels that were only 7% of non-diabetic mice. The vascular reparative capacity of diabetic db/db mice in response to HLI was impaired compared to non-diabetic mice and, importantly, comparable to ghrelin KO mice. Daily therapeutic treatment of db/db mice with ghrelin for 14 days post HLI, stimulated angiogenesis, and improved skeletal muscle architecture and cell survival, which was associated with an increase in pro-angiogenic miRNAs-126 and -132. These findings unmask an important role for endogenous ghrelin in vascular repair following limb ischemia, which appears to be downregulated in diabetic patients. Moreover, these results implicate exogenous ghrelin as a potential novel therapy to enhance perfusion in patients with lower limb PAD, especially in diabetics.

Brain transcriptome profile after CRISPR-induced ghrelin mutations in zebrafish

Ghrelin (GRL) is a gut-brain hormone with a role in a wide variety of physiological functions in mammals and fish, which points out the ghrelinergic system as a key element for the appropriate biological functioning of the organism. However, many aspects of the multifunctional nature of GRL remain to be better explored, especially in fish. In this study, we used the CRISPR/Cas9 genome editing technique to generate F0 zebrafish in which the expression of grl is compromised. Then, we employed high-throughput mRNA sequencing (RNA-seq) to explore changes in the brain transcriptome landscape associated with the silencing of grl. The CRISPR/Cas9 technique successfully edited the genome of F0 zebrafish resulting in individuals with considerably lower levels of GRL mRNAs and protein and ghrelin O-acyl transferase (goat) mRNAs in the brain, intestine, and liver compared to wild-type (WT) zebrafish. Analysis of brain transcriptome revealed a total of 1360 differentially expressed genes (DEGs) between the grl knockdown (KD) and WT zebrafish, with 664 up- and 696 downregulated DEGs in the KD group. Functional enrichment analysis revealed that DEGs are highly enriched for terms related to morphogenesis, metabolism (especially of lipids), entrainment of circadian clocks, oxygen transport, apoptosis, and response to stimulus. The present study offers valuable information on the central genes and pathways implicated in functions of GRL, and points out the possible involvement of this peptide in some novel functions in fish, such as apoptosis and oxygen transport.

Physiological Effect of Ghrelin on Body Systems

Ghrelin is a relatively novel multifaceted hormone that has been found to exert a plethora of physiological effects. In this review, we found/confirmed that ghrelin has effect on all body systems. It induces appetite; promotes the use of carbohydrates as a source of fuel while sparing fat; inhibits lipid oxidation and promotes lipogenesis; stimulates the gastric acid secretion and motility; improves cardiac performance; decreases blood pressure; and protects the kidneys, heart, and brain. Ghrelin is important for learning, memory, cognition, reward, sleep, taste sensation, olfaction, and sniffing. It has sympatholytic, analgesic, antimicrobial, antifibrotic, and osteogenic effects. Moreover, ghrelin makes the skeletal muscle more excitable and stimulates its regeneration following injury; delays puberty; promotes fetal lung development; decreases thyroid hormone and testosterone; stimulates release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin; inhibits insulin release; and promotes wound healing. Ghrelin protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. Having a clear understanding of the ghrelin effect in each system has therapeutic implications. Future studies are necessary to elucidate the molecular mechanisms of ghrelin actions as well as its application as a GHSR agonist to treat most common diseases in each system without any paradoxical outcomes on the other systems.

Chronic peripheral ghrelin injection exerts antifibrotic effects by increasing growth differentiation factor 15 in rat hearts with myocardial fibrosis induced by isoproterenol

This study aimed to investigate the anti-fibrotic effects of ghrelin in isoproterenol (ISO)-induced myocardial fibrosis and the underlying mechanism. Sprague-Dawley rats were randomized to control, ISO, and ISO + ghrelin groups. ISO (2 mg/kg per day, subcutaneous) or vehicle was administered once daily for 7 days, then ghrelin (100 microg/kg per day, subcutaneous) was administered once daily for the next 3 weeks. Ghrelin treatment greatly improved the cardiac function of ISO-treated rats. Ghrelin also decreased plasma brain natriuretic peptide level and ratios of heart weight to body weight and left ventricular weight to body weight. Ghrelin significantly reduced myocardial collagen area and hydroxyproline content, accompanied by decreased mRNA levels of collagen type I and III. Furthermore, ghrelin increased plasma level of growth differentiation factor 15 (GDF15) and GDF15 mRNA and protein levels in heart tissues, which were significantly decreased with ISO alone. The phosphorylation of Akt at Ser473 and GSK-3beta at Ser9 was decreased with ISO, and ghrelin significantly reversed the downregulation of p-Akt and p-GSK-3beta. Mediated by GDF15, ghrelin could attenuate ISO-induced myocardial fibrosis via Akt-GSK-3beta signaling.

Pretreatment of ghrelin protects H9c2 cells against hypoxia/reoxygenation-induced cell death via PI3K/AKT and AMPK pathways

Ghrelin has been widely recognized as a key peptide in the cardiovascular system. This study detected the potential of ghrelin in MI management and tried to decode one of the possible underlying mechanisms. H9c2 cells were pretreated with ghrelin and were subjected to hypoxia/reoxygenation (H/R). CCK-8, flow cytometry, Western blot and LDH analysis were conducted to assess the changes in cell survival. LY294002 and Compound C were used to treat H9c2 cells for blocking PI3K/AKT and AMPK pathways, respectively. Ghrelin expression in H9c2 cells was suppressed by siRNA-mediated silencing to see the effects of endogenous ghrelin. We found that, following H/R, H9c2 cells viability was decreased, CyclinD1 and CDK4 were down-regulated, apoptosis was induced, the release of LDH was enhanced, and the expression levels of Cox-2 and iNOS were up-regulated. Ghrelin protected H9c2 cells against H/R induced these alterations. Besides, ghrelin activated PI3K/AKT and AMPK pathways even in H/R-stimulated cells. The protective effects of ghrelin against H/R-induced cell damage were all attenuated by the addition of LY294002 or Compound C. Moreover, endogenous inhibition of ghrelin significantly induced cell death of H9c2 cells. In conclusion, this study demonstrated that ghrelin pretreatment protected H9c2 cells against H/R-induced cell damage, possibly via PI3K/AKT and AMPK pathways.

[Ghrelin Physiology and Pathophysiology: Focus on the Cardiovascular System]

Ghrelin is a multifunctional peptide hormone, mainly synthesized by P / D1 cells of the stomach fundus mucosa. Its basic effect, which is realized via GHS-R1 α receptor in the arcuate and the ventromedial nucleuses of hypothalamus, is stimulation of the synthesis of pituitary hormones. Ghrelin is involved in control of appetite and energy balance, regulation of carbohydrate and lipid metabolism, cell proliferation and apoptosis, as well as modulation of functioning of gastrointestinal, cardiovascular, pulmonary and immune systems. It was found that cardiomyocytes are able to synthesize ghrelin. High concentrations of GHS-R1α in the heart and major blood vessels evidence for its possible participation in functioning of cardiovascular system. Ghrelin inhibits apoptosis of cardiomyocytes and endothelial cells, and improves the functioning of the left ventricle (LV) after injury of ischemia-reperfusion mechanism. In rats with heart failure (HF) ghrelin improves LV function and attenuates development of cardiac cachexia. In addition, ghrelin exerts vasodilatory effects in humans, improves cardiac function and reduces peripheral vascular resistance in patients with chronic HF. The review contains of the predictive value of ghrelin in the development and prevention of cardiovascular disease.

Ghrelin attenuates myocardial fibrosis after acute myocardial infarction via inhibiting endothelial-to mesenchymal transition in rat model

Ghrelin, a peptide hormone produced in the gastrointestinal tract, has recently been found to be associated with the onset of myocardial fibrosis (MF). The exact mechanism, however, remains elusive. This study sought to identify the function and mechanism of ghrelin on MF after acute myocardial infarction (AMI). AMI was established in Spraque-Dawley rats by ligation of the left anterior descending (LAD). Ghrelin or saline was intraperitoneally injected two times per day for 8 weeks after ligation. The weight of heart (mg) and the weight ratio of heart to body (mg/g) as well as the fibrotic area were increased, while serum level of ghrelin was decreased after AMI. Ghrelin significantly ameliorated MF and decreased deposition of collagens in perivascular fibrosis area. In addition, ghrelin inhibited Endothelial-to-mesenchymal transition (EndMT), a crucial process for MF, in perivascular fibrosis area and TGF-β1-induced human coronary artery endothelial cells (HCAECs). Mechanistically, ghrelin persistently decreased the phosphorylation of Smad2/3 and enhanced the expression of Smad7 and p-AMPK in vivo and in vitro. After the abolition of Smad7, GHSR-1a and AMPK pathway, the effect of ghrelin on EndMT was significantly inhibited. In conclusion, these results presented a novel finding that ghrelin attenuated MF after AMI via regulation EndMT in a GHSR-1a/AMPK/Smad7- dependent manner.

Baseline levels of serum high sensitivity C reactive protein and lipids in predicting the residual risk of cardiovascular events in Chinese population with stable coronary artery disease: a prospective cohort study

BACKGROUND

The contributions of inflammation, triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) to the residual risk of cardiovascular events have not been determined in a large cohort of Chinese population before. This study was aimed to investigate the association of serum levels of high sensitive C reactive protein (hs-CRP), TG and HDL-C with the residual risk of cardiovascular events in patients with stable coronary artery disease (CAD).

METHODS

We enrolled 4090 patients with stable CAD from 13 hospitals in China. All participants received optimal medical treatment (OMT) for stable CAD suggested by guidelines and were followed. The endpoint measures were the first occurrence of a major adverse cardiovascular event (MACE), defined as cardiovascular death, non-fatal myocardial infarction, non-fatal stroke or unplanned coronary revascularization. Cox proportional regression analysis was conducted to identify independent predictors of MACE.

RESULTS

We found that hs-CRP and HDL-C levels were associated with coronary lesion severity at baseline (both p < 0.001). After 3 months OMT, 91.2% (3730/4090) patients achieved the therapeutic goal for low density lipoprotein cholesterol (LDL-C) (< 1.8 mmoL/L). During a mean follow-up period of 39.5 months, 11.5% (471/4090) patients suffered MACE. In multivariate Cox proportional regression analysis, the hazard ratio for MACE was 1.17 (95% confidence interval: 1.07-1.28, p < 0.001) per standardized deviation in the log-transformed hs-CRP levels after adjustment for other traditional cardiovascular risk factors. However, baseline TG and HDL-C levels were not associated with MACE in this study.

CONCLUSIONS

Baseline hs-CRP level was an independent predictor of residual risk of cardiovascular events in Chinese population with stable CAD. However, TG and HDL-C levels were not associated with MACE.

Neuroimmunophysiology of the gut: advances and emerging concepts focusing on the epithelium

The epithelial lining of the gastrointestinal tract serves as the interface for digestion and absorption of nutrients and water and as a defensive barrier. The defensive functions of the intestinal epithelium are remarkable considering that the gut lumen is home to trillions of resident bacteria, fungi and protozoa (collectively, the intestinal microbiota) that must be prevented from translocation across the epithelial barrier. Imbalances in the relationship between the intestinal microbiota and the host lead to the manifestation of diseases that range from disorders of motility and sensation (IBS) and intestinal inflammation (IBD) to behavioural and metabolic disorders, including autism and obesity. The latest discoveries shed light on the sophisticated intracellular, intercellular and interkingdom signalling mechanisms of host defence that involve epithelial and enteroendocrine cells, the enteric nervous system and the immune system. Together, they maintain homeostasis by integrating luminal signals, including those derived from the microbiota, to regulate the physiology of the gastrointestinal tract in health and disease. Therapeutic strategies are being developed that target these signalling systems to improve the resilience of the gut and treat the symptoms of gastrointestinal disease.

Pharmacological manipulation of the ghrelin system and alcohol hangover symptoms in heavy drinking individuals: Is there a link?

Ghrelin, an orexigenic peptide synthesized in the stomach, is a key player in the gut-brain axis. In addition to its role in regulating food intake and energy homeostasis, ghrelin has been shown to modulate alcohol-related behaviors. Alcohol consumption frequently results in hangover, an underexplored phenomenon with considerable medical, psychological, and socioeconomic consequences. While the pathophysiology of hangover is not clear, contributions of mechanisms such as alcohol-induced metabolic/endocrine changes, inflammatory/immune response, oxidative stress, and gut dysbiosis have been reported. Interestingly, these mechanisms considerably overlap with ghrelin's physiological functions. Here, we investigated whether pharmacological manipulation of the ghrelin system may affect alcohol hangover symptoms. Data were obtained from two placebo-controlled laboratory studies. The first study tested the effects of intravenous (IV) ghrelin and consisted of two experiments: a progressive-ratio IV alcohol self-administration (IV-ASA) and a fixed-dose IV alcohol clamp. The second study tested the effects of an oral ghrelin receptor inverse agonist (PF-5190457) and included a fixed-dose oral alcohol administration experiment. Alcohol hangover data were collected the morning after each alcohol administration experiment using the Acute Hangover Scale (AHS). IV ghrelin, compared to placebo, significantly reduced alcohol hangover after IV-ASA (p = 0.04) and alcohol clamp (p = 0.04); PF-5190457 had no significant effect on AHS scores. Females reported significantly higher hangover symptoms than males following the IV-ASA experiment (p = 0.04), but no gender × drug condition (ghrelin vs. placebo) effect was found. AHS total scores were positively correlated with peak subjective responses, including 'stimulation' (p = 0.08), 'sedation' (p = 0.009), 'feel high' (p = 0.05), and 'feel intoxicated' (p = 0.03) during the IV-ASA. IV ghrelin blunted the positive association between alcohol sedation and hangover as shown by trend-level drug × sedation effect (p = 0.08). This is the first study showing that exogenous ghrelin administration, but not ghrelin receptor inverse agonism, affects hangover symptoms. Future research should investigate the potential mechanism(s) underlying this effect.

Ghrelin suppresses cardiac fibrosis of post-myocardial infarction heart failure rats by adjusting the activin A-follistatin imbalance

Ghrelin, a growth hormone-releasing peptide, potentially improves cardiac function, but the mechanisms remain unclear. In the study, the rat heart failure (HF) model was established by ligating the left anterior descending coronary artery (LAD) and treated with ghrelin (100μg/kg, subcutaneous injection, bid); neonatal rat cardiomyocytes were cultured and stimulated with Ang II (0.1μM) and ghrelin(0.1μM) to explore the underlying mechanism of ghrelin in myocardial remodeling. Hemodynamic changes and serum brain natriuretic peptide (BNP) concentrations were measured to assess cardiac function. Left ventricular mass index (LVMI), hematoxylin and eosin (H&E) staining, and Masson's trichrome staining were performed to evaluate myocardial fibrosis. Interestingly, ghrelin significantly improved cardiac function by inhibiting fibrous tissue proliferation. To further explore the mechanisms by which ghrelin interferes with myocardial fibrosis, the levels of activin A (Act A) and its blocker-follistatin (FS) were examined by immunohistochemistry; Act A levels were significantly increased in the myocardial infarction (MI), and ghrelin administeration downregulated Act A expression. In contrast, FS expression showed no significant change in all experimental groups. Furthermore, ghrelin decreased Ang II-induced Act A expression with no effect on FS expression in primary rat cardiomyocytes in vitro (real-time quantitative PCR and ELISA). Thus, ghrelin corrected the Act A/FS imbalance. Finally, Act A treated cultured primary rat cardiac fibroblasts (CFs) showed increased proliferation [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay] and enhanced expressions of type I and type III collagen (Col I and Col III) (real-time quantitative PCR). These data suggest that ghrelin inhibits myocardial fibrosis, attenuates left ventricular remodeling, and eventually improves cardiac function by adjusting Act A/FS imbalance.

Structural determination, distribution, and physiological actions of ghrelin in the guinea pig

We identified guinea pig ghrelin (gp-ghrelin), and examined its distribution and physiological actions in the guinea-pig. Gp-ghrelin is a 28-amino acid peptide (GASFR SPEHH SAQQR KESRK LPAKI QPR); seven amino acids are different from that of rat ghrelin at positions 2, 5, 10, 11, 19, 21, and 25, which include the conserved region known in mammals. The third serine residue is mainly modified by n-decanoyl acid. Both gp-ghrelin and rat ghrelin increased intracellular Ca²⁺ concentration of HEK293 cells expressing guinea pig growth hormone secretagogue receptor 1a (GHS-R1a), and the affinity of gp-ghrelin was slightly higher than that of rat ghrelin. In addition, gp-ghrelin was also effective in CHO cells expressing rat GHS-R1a with similar affinity to that of rat ghrelin. Gp-ghrelin mRNA was predominantly expressed in the stomach, whereas the expression levels in other organs was low. High levels of GHS-R1a mRNA expression were observed in the pituitary, medulla oblongata, and kidney, while medium levels were noted in the thalamus, pons, olfactory bulb, and heart. Immunohistochemistry identified gp-ghrelin-immunopositive cells in the gastric mucosa and pancreas. Intraperitoneal injection of gp-ghrelin increased food intake in the guinea pig. Gp-ghrelin did not cause any mechanical responses in isolated gastrointestinal smooth muscles in vitro, similar to rat ghrelin. In conclusion, the N-terminal structures that are conserved in mammals were different in gp-ghrelin. Moreover, the functional characteristics of gp-ghrelin, other than its distribution, were dissimilar from those in other Rodentia.

Ghrelin, MicroRNAs, and Critical Limb Ischemia: Hungering for a Novel Treatment Option

Critical limb ischemia (CLI) is the most severe manifestation of peripheral artery disease. It is characterized by chronic pain at rest, skin ulcerations, and gangrene tissue loss. CLI is a highly morbid condition, resulting in a severely diminished quality of life and a significant risk of mortality. The primary goal of therapy for CLI is to restore blood flow to the affected limb, which is only possible by surgery, but is inadvisable in up to 50% of patients. This subset of patients who are not candidates for revascularisation are referred to as "no-option" patients and are the focus of investigation for novel therapeutic strategies. Angiogenesis, arteriogenesis and vasculogenesis are the processes whereby new blood vessel networks form from the pre-existing vasculature and primordial cells, respectively. In therapeutic angiogenesis, exogenous stimulants are administered to promote angiogenesis and augment limb perfusion, offering a potential treatment option for "no option" patients. However, to date, very few clinical trials of therapeutic angiogenesis in patients with CLI have reported clinically significant results, and it remains a major challenge. Ghrelin, a 28-amino acid peptide, is emerging as a potential novel therapeutic for CLI. In pre-clinical models, exogenous ghrelin has been shown to induce therapeutic angiogenesis, promote muscle regeneration, and reduce oxidative stress via the modulation of microRNAs (miRs). miRs are endogenous, small, non-coding ribonucleic acids of ~20-22 nucleotides which regulate gene expression at the post-transcriptional level by either translational inhibition or by messenger ribonucleic acid cleavage. This review focuses on the mounting evidence for the use of ghrelin as a novel therapeutic for CLI, and highlights the miRs which orchestrate these physiological events.

Bariatric Surgery and Hypertension

Obesity continues to increase in prevalence worldwide. Hypertension has long been associated with obesity, and weight loss continues to be a first-line therapy in the treatment of hypertension. Lifestyle modification and pharmacologic therapy, however, often meet with treatment failure. Bariatric surgery continues to be the most successful approach to sustained weight loss. This review focuses on the underlying physiologic mechanisms of obesity-hypertension, and the impact of bariatric surgery on the treatment of hypertension. Current available literature on the physiologic mechanisms of obesity-hypertension, and the major trials, meta-analyses and systematic reviews of the impact of bariatric surgery procedures on hypertension are reviewed. Evidence suggests significant improvement in obesity-hypertension in patients who undergo surgical weight-reduction procedures. Malabsorptive techniques such as the Roux-en-Y gastric bypass or surgical resection techniques such as laparoscopic sleeve gastrectomy appear to offer superior results in regards to hypertension control over restrictive techniques such as Gastric Banding. Though long-term control of hypertension following surgery remains a concern, available follow-up post-operative data of up to 10 years suggests a sustained, if lessened, effect on hypertension control over time.

Relaxin-2 in Cardiometabolic Diseases: Mechanisms of Action and Future Perspectives

Despite the great effort of the medical community during the last decades, cardiovascular diseases remain the leading cause of death worldwide, increasing their prevalence every year mainly due to our new way of life. In the last years, the study of new hormones implicated in the regulation of energy metabolism and inflammation has raised a great interest among the scientific community regarding their implications in the development of cardiometabolic diseases. In this review, we will summarize the main actions of relaxin, a pleiotropic hormone that was previously suggested to improve acute heart failure and that participates in both metabolism and inflammation regulation at cardiovascular level, and will discuss its potential as future therapeutic target to prevent/reduce cardiovascular diseases.

Obestatin regulates cardiovascular function and promotes cardioprotection through the nitric oxide pathway

Patients with ischaemic heart disease or chronic heart failure show altered levels of obestatin, suggesting a role for this peptide in human heart function. We have previously demonstrated that GH secretagogues and the ghrelin gene-derived peptides, including obestatin, exert cardiovascular effects by modulating cardiac inotropism and vascular tone, and reducing cell death and contractile dysfunction in hearts subjected to ischaemia/reperfusion (I/R), through the Akt/nitric oxide (NO) pathway. However, the mechanisms underlying the cardiac actions of obestatin remain largely unknown. Thus, we suggested that obestatin-induced activation of PI3K/Akt/NO and PKG signalling is implicated in protection of the myocardium when challenged by adrenergic, endothelinergic or I/R stress. We show that obestatin exerts an inhibitory tone on the performance of rat papillary muscle in both basal conditions and under β-adrenergic overstimulation, through endothelial-dependent NO/cGMP/PKG signalling. This pathway was also involved in the vasodilator effect of the peptide, used both alone and under stress induced by endothelin-1. Moreover, when infused during early reperfusion, obestatin reduced infarct size in isolated I/R rat hearts, through an NO/PKG pathway, comprising ROS/PKC signalling, and converging on mitochondrial ATP-sensitive potassium [mitoK(ATP)] channels. Overall, our results suggest that obestatin regulates cardiovascular function in stress conditions and induces cardioprotection by mechanisms dependent on activation of an NO/soluble guanylate cyclase (sGC)/PKG pathway. In fact, obestatin counteracts exaggerated β-adrenergic and endothelin-1 activity, relevant factors in heart failure, suggesting multiple positive effects of the peptide, including the lowering of cardiac afterload, thus representing a potential candidate in pharmacological post-conditioning.

Parathyroid Hormone-Related Peptide: A Novel Endocrine Cardioprotective "Conditioning Mimetic"

An as-yet limited body of evidence suggests that calcium-regulating endocrine hormones-in particular, parathyroid hormone-related peptide (PTHrP)-may have unappreciated cardioprotective effects. The current review focuses on the concept that PTHrP may, via modulation of classic cardioprotective signaling pathways, provide a novel strategy to attenuate myocardial ischemia-reperfusion injury.