Decreased circulating levels of active ghrelin are associated with increased oxidative stress in obese subjects

Pterostilbene alleviates cafeteria diet-induced obesity and underlying depression in adolescent male Swiss albino mice and affects insulin resistance, inflammation, HPA axis dysfunction and SIRT1 mediated leptin-ghrelin signaling

Cafeteria diet (CD) model for in-vivo studies mimics the western diet having imbalanced nutritional value, high caloric-density and palatability. Uncontrolled eating leads to the development of childhood obesity, poor self-esteem and depression due to its effects on brain development. Herbal supplements are novel inclusion in the management of obesity and mental well-being. Pterostilbene (PTE) found in blueberries and Pterocarpus marsupium heartwood, is known to prevent obesity in invivo models. Adolescent Swiss albino male mice were fed on CD for 70 days and the development of obesity was assessed by gain in body weight, abdominal circumference. Forced swim and tail suspension test confirmed depression in CD fed mice. Obesity induced depressed (OID) mice were treated with PTE (10, 20, 40 mg/kg), standard antiobesity drug cetilistat (10 mg/kg), antidepressant fluoxetine (10 mg/kg) for 28 days. Post treatment, PTE-treated mice showed reduction in BW and depression-like behavior analysed using paradigms such as sucrose preference, open field, marble burying, and resident intruder test in comparison to the CD group. Insulin resistance, lipid profile, antioxidant enzyme, inflammatory cytokines (NF-κB, IL-6, TNF α) and cortisol levels were mitigated by PTE. It also restored normal cellular architecture of the brain and adipose tissue and increased the Silent mating type information regulation 2 homolog1 (SIRT1), leptin and ghrelin receptors gene expression in the brain. Thus, it can be concluded that PTE might have inhibited OID like behavior in mice via inhibition of IR, modulating neuroinflammation and hypothalamic-pituitary-adrenal axis dysfunction and upregulating SIRT1 mediated leptin-ghrelin signaling.

Differences in gastrointestinal hormones and appetite ratings between individuals with and without obesity-A systematic review and meta-analysis

Determining if gastrointestinal (GI) hormone response to food intake differs between individuals with, and without, obesity may improve our understanding of obesity pathophysiology. A systematic review and meta-analysis of studies assessing the concentrations of GI hormones, as well as appetite ratings, following a test meal, in individuals with and without obesity was undertaken. Systematic searches were conducted in the databases MEDLINE, Embase, Cochrane Library, PsycINFO, Web of Science, and ClinicalTrials.gov. A total of 7514 unique articles were retrieved, 115 included in the systematic review, and 70 in the meta-analysis. The meta-analysis compared estimated standardized mean difference in GI hormones' concentration, as well as appetite ratings, between individuals with and without obesity. Basal and postprandial total ghrelin concentrations were lower in individuals with obesity compared with controls, and this was reflected by lower postprandial hunger ratings in the former. Individuals with obesity had a lower postprandial concentration of total peptide YY compared with controls, but no significant differences were found for glucagon-like peptide 1, cholecystokinin, or other appetite ratings. A large methodological and statistical heterogeneity among studies was found. More comprehensive studies are needed to understand if the differences observed are a cause or a consequence of obesity.

Circulating acyl and des-acyl ghrelin levels in obese adults: a systematic review and meta-analysis

Ghrelin is the only known orexigenic gut hormone, and its synthesis, secretion and degradation are affected by different metabolic statuses. This meta-analysis aimed to investigate the potential differences in plasma acyl ghrelin (AG) and des-acyl ghrelin (DAG) concentrations between normal weight and obese adults. Systematic literature searches of PubMed, Embase and Web of Science through October 2021 were conducted for articles reporting AG or DAG levels in obesity and normal weight, and 34 studies with 1863 participants who met the eligibility criteria were identified. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated to evaluate group differences in circulating AG and DAG levels. Pooled effect size showed significantly lower levels of baseline AG (SMD: - 0.85; 95% CI: - 1.13 to - 0.57; P_SMD < 0.001) and DAG (SMD: - 1.06; 95% CI: - 1.43 to - 0.69; P_SMD < 0.001) in obese groups compared with healthy controls, and similar results were observed when subgroup analyses were stratified by the assay technique or storage procedure. Postprandial AG levels in obese subjects were significantly lower than those in controls when stratified by different time points (SMD _30 min: - 0.85, 95% CI: - 1.18 to - 0.53, P_SMD < 0.001; SMD _60 min: - 1.00, 95% CI: - 1.37 to - 0.63, P_SMD < 0.001; SMD _120 min: - 1.21, 95% CI: - 1.59 to - 0.83, P_SMD < 0.001). In healthy subjects, a postprandial decline in AG was observed at 120 min (SMD: - 0.42; 95% CI: - 0.77 to - 0.06; P_SMD = 0.021) but not in obese subjects (SMD: - 0.28; 95% CI: - 0.60 to 0.03; P_SMD = 0.074). The mean change in AG concentration was similar in both the obese and lean health groups at each time point (ΔSMD_30min: 0.31, 95% CI: - 0.35 to 0.97, P_SMD = 0.359; ΔSMD_60min: 0.17, 95% CI: - 0.12 to 0.46, P_SMD = 0.246; ΔSMD_120min: 0.21, 95% CI: - 0.13 to 0.54, P_SMD = 0.224). This meta-analysis strengthens the clinical evidence supporting the following: lower baseline levels of circulating AG and DAG in obese individuals; declines in postprandial circulating AG levels, both for the healthy and obese individuals; a shorter duration of AG suppression in obese subjects after meal intake. These conclusions have significance for follow-up studies to elucidate the role of various ghrelin forms in energy homeostasis.

Beneficial Impact of Pork Dry-Cured Ham Consumption on Blood Pressure and Cardiometabolic Markers in Individuals with Cardiovascular Risk

Background: Evidence suggests that bioactive peptides reduce hypertension and affect certain metabolic pathways. Methods: Fifty-four volunteers with stage 1 prehypertension and/or hypercholesterolemia and/or basal glucose >100 mg/dL were recruited and randomized to pork dry-cured ham (n = 35) or cooked ham (placebo group; n = 19) for 28 days. After a wash-out period, meat products were changed for 28 additional days. Bioactive peptides composition and enzyme inhibitory activities of both products were characterized. Treatment comparisons for the main effects were made using a two (treatment) × two (times) repeated measures minus the effect of cooked ham (placebo). Results: 24 h mean systolic and diastolic pressures decreased up to 2.4 mmHg in the dry-cured ham period (treatment effect, p = 0.0382 y p = 0.0233, respectively) as well as the number of systolic pressure measures > 135 mmHg (treatment effect, p = 0.0070). Total cholesterol levels also decreased significantly after dry-cured ham intake (p = 0.049). No significant differences were observed between the two treatments for basal glucose, HOMA-IR index and insulin levels (p > 0.05). However, a significant rise of ghrelin levels was observed (treatment effect, p = 0.0350), while leptin plasma values slightly decreased (treatment effect, p = 0.0628). Conclusions: This study suggested the beneficial effects of regular dry-cured ham consumption on the improvement of systolic/diastolic blood pressures and facilitated the maintenance of metabolic pathways, which may be beneficial in the primary prevention of cardiovascular disease.

Acylated ghrelin protects against doxorubicin-induced nephropathy by activating silent information regulator 1

This study investigated the nephroprotective role of acylated ghrelin (AG) against DOX-induced nephropathy and examined whether the protection involves silent information regulator 1 (SIRT1). Rats were divided into control, control + AG, DOX, DOX + AG, DOX + AG + [D-Lys3]-GHRP-6 (a ghrelin receptor antagonist), and DOX + AG + EX-527 (a sirt1 inhibitor). DOX was given over the first 2 weeks. AG (10 ng/kg) and both inhibitors were given as 3 doses/wk for 5 weeks. AG improved the structure and the function of the kidneys; down-regulated the renal expression of TGF-β1, collagen 1A1 and α-SMA; and inhibited the renal collagen deposition in the kidneys of DOX-treated rats. Concomitantly, it reduced the renal levels of ROS, MDA, TNF-α, and IL-6 and protein levels of cytochrome-c, TGF-β1, Smad3 and α-SMA in these rats. In both the control and DOX-treated rats, AG significantly increased the renal levels of SOD and GSH, decreased the expression of cleaved caspase-3 and Bax, increased the total levels and the nuclear activity of SIRT1 and reduced the deacetylation of p53, NF-κB and FOXO-31. All the effects were abolished by the concurrent administration of EX-527 and [D-Lys3]-GHRP-6. In conclusion, AG prevents DOX-induced nephropathy in SIRT1 and GSHRa1-dependent mechanism.

Circ_0010729 regulates hypoxia-induced cardiomyocyte injuries by activating TRAF5 via sponging miR-27a-3p

Ischemic cardiomyopathy is a severe cardiovascular disease with high mortality. Circular RNAs (circRNAs) are widely regulated in diverse human diseases, including Ischemic cardiomyopathy. This study aimed to investigate a novel functional mechanism of circRNA circ_0010729 in hypoxia-induced cardiomyocyte injuries. Human cardiomyocytes (AC16) were exposed to hypoxia to mimic ischemic cardiomyopathy in vitro. Cell viability, apoptosis/necrosis and glycolysis progress, were determined using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, flow cytometry assay and glycolysis stress test, respectively. Cell apoptosis was also assessed by the activity of cleaved caspase-3/7. The levels of glycolysis-related proteins and tumor necrosis factor receptor-associated factor 5 (TRAF5) were examined by western blot. The expression of circ_0010729 and miR-27a-3p was measured by real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The prediction about the targeted relationship was verified by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay. As a result, hypoxia treatment inhibited cell viability, induced cell apoptosis and blocked glycolysis, however, these injuries were alleviated by circ_0010729 knockdown. MiR-27a-3p was targeted by circ_0010729, and miR-27a-3p inhibition reversed the role of circ_0010729 knockdown, leading to the deterioration of cell injuries. Further, TRAF5 was a target of miR-27a-3p, and circ_0010729 upregulated the expression of TRAF5 by sponging miR-27a-3p. MiR-27a-3p restoration enhanced cell viability, depleted cell apoptosis and promoted glycolysis of hypoxia-induced AC16 cells, while these effects were abolished by TRAF5 overexpression. In conclusion, circ_0010729 knockdown alleviated hypoxia-induced AC16 cell injuries by mediating the miR-27a-3p/TRAF5 axis.

Ghrelin forms in the modulation of energy balance and metabolism

Ghrelin is a gastric hormone circulating in acylated (AG) and unacylated (UnAG) forms. This narrative review aims at presenting current emerging knowledge on the impact of ghrelin forms on energy balance and metabolism. AG represents ~ 10% of total plasma ghrelin, has an appetite-stimulating effect and is the only form for which a receptor has been identified. Moreover, other metabolic AG-induced effects have been reported, including the modulation of glucose homeostasis with stimulation of liver gluconeogenesis, the increase of fat mass and the improvement of skeletal muscle mitochondrial function. On the other hand, UnAG has no orexigenic effects, however recent reports have shown that it is directly involved in the modulation of skeletal muscle energy metabolism by improving a cluster of interlinked functions including mitochondrial redox activities, tissue inflammation and insulin signalling and action. These findings are in agreement with human studies which show that UnAG circulating levels are positively associated with insulin sensitivity both in metabolic syndrome patients and in a large cohort from the general population. Moreover, ghrelin acylation is regulated by a nutrient sensor mechanism, specifically set on fatty acids availability. These recent findings consistently point towards a novel independent role of UnAG as a regulator of muscle metabolic pathways maintaining energy status and tissue anabolism. While a specific receptor for UnAG still needs to be identified, recent evidence strongly supports the hypothesis that the modulation of ghrelin-related molecular pathways, including those involved in its acylation, may be a potential novel target in the treatment of metabolic derangements in disease states characterized by metabolic and nutritional complications.Level of evidence Level V, narrative review.

Acyl-ghrelin mediated lipid retention and inflammation in obesity-related Type 2 diabetes

Acyl-ghrelin has various peripheral effects including the potential role in mediating cellular lipid removal and macrophage polarization. Previous reports are contradictory as to how glycaemia and acyl-ghrelin mediates lipid retention and inflammation within individuals with Type 2 diabetes (T2D). Our aim was to explore acyl-ghrelin levels and ghrelin expression in relation to lipid and inflammatory markers within an ex vivo human model, biopsied visceral adipose tissue. Results indicated that acyl-ghrelin was associated with a decline in key lipid homeostasis genes ABCG1 and LXRβ expression. Within T2D there was also a down regulation of these genes which was independent of acyl-ghrelin levels. Circulatory pro-inflammatory markers (IL-6 and TNFα) had no association with ghrelin expression nor circulating acyl-ghrelin levels. Anti-inflammatory marker (IL-10) and total antioxidant status (TAOS%) were positively associated with ghrelin expression across samples from all groups combined (total sample cohort) and specifically within the obesity sample cohorts. Data supported the hypothesis that hyperglycaemia and acyl-ghrelin have a regulatory role in lipid retention. Furthermore, that both acyl- and desacyl-ghrelin is responsible for a protective inflammatory response; however this response is diminished in T2D.

Ghrelin protects the myocardium with hypoxia/reoxygenation treatment through upregulating the expression of growth hormone, growth hormone secretagogue receptor and insulin-like growth factor-1, and promoting the phosphorylation of protein kinase B

Ghrelin is an endogenous ligand of growth hormone (GH) secretagogue receptor (GHSR) and has a number of biological effects, including heart protection. The present study aimed to reveal the positive effect of ghrelin on myocardium with hypoxia/reoxygenation (H/R) treatment and the involved molecular mechanisms. Successful construction of lentiviral expression vector (ghrelin-pLVX-Puro) was confirmed by colony polymerase chain reaction (PCR) verification. Primary rat cardiac myocytes were isolated and identified by immunofluorescence staining. Existence of red fluorescence of α-sarcomeric actinin indicated the successful isolation. Following ghrelin transfection and H/R treatment, primary cells were divided into four groups: Control, H/R, empty (empty pLVX-Puro + H/R) and ghrelin (ghrelin-pLVX-Puro + H/R). Cell viability and apoptosis were evaluated by Cell Counting Kit-8 (CCK-8) and Hoechst staining, respectively. The cell viability in the ghrelin group was significantly higher than that in the empty control group (P<0.05). The apoptosis rate in the ghrelin group was significantly lower than that in the empty control group (P<0.05). An ex vivo rat cardiac perfusion model was established. Following ghrelin incubation and H/R treatment, ex vivo myocardium was divided into four groups: Control, sham, H/R and ghrelin (ghrelin + H/R). Immunohistochemical analysis demonstrated that ghrelin increased the integrity of cardiac myocytes, and decreased shrinkage and apoptosis. mRNA and protein expression levels of GH, GHSR, insulin-like growth factor-1 (IGF-1), protein kinase B (Akt), phosphorylated Akt (p-Akt) were determined by reverse transcription (RT)-PCR, western blot analysis and immunohistochemical analysis. Ghrelin upregulated the mRNA and protein expression levels of GH, GHSR and IGF-1, and increased the ratio of p-Akt to Akt protein level (p-Akt/Akt) in cardiac myocytes and myocardial tissues with H/R treatment. In conclusion, ghrelin protected the myocardium with H/R treatment through upregulating the expression of GH, GHSR and IGF-1, and promoting the phosphorylation of Akt. This would provide promising insights into the treatment of hypoxic myocardial injury by ghrelin.

The Role of Adipokines in the Establishment and Progression of Head and Neck Neoplasms

Adipokines constitute a family of protein factors secreted by white adipose tissue (WAT), that regulate the functions of WAT and other sites. Leptin, adiponectin and resistin, are the main adipokines present in serum and saliva, targeting several tissues and organs, including vessels, muscles, liver and pancreas. Besides body mass regulation, adipokines affect glucose homeostasis, inflammation, angiogenesis, cell proliferation and apoptosis, and other crucial cell procedures. Their involvement in tumor formation and growth is well established and deregulation of adipokine and adipokine receptors' expression is observed in several malignancies including those located in the head and neck region. Intracellular effects of adipokines are mediated by a plethora of receptors that activate several signaling cascades including Janus kinase/ Signal transducer and activator of transcription (JAK/ STAT pathway), Phospatidylinositol kinase (PI3/ Akt/ mTOR) and Peroxisome proliferator-activated receptor (PPAR). The present review summarizes the current knowledge on the role of adipokines family members in carcinogenesis of the head and neck region. The diagnostic and prognostic significance of adipokines and their potential role as serum and saliva biomarkers are also discussed.

Ghrelin expression and significance in 92 patients with atrial fibrillation

OBJECTIVE

Ghrelin is a polypeptide that is closely associated with many cardiovascular diseases, such as hypertension, atherosclerosis, and heart failure. This article aims to understand the expression of ghrelin in patients with atrial fibrillation (AF).

METHODS

A total of 182 patients with non-valvular heart diseases were recruited, among whom 92 had AF and 90 had sinus arrhythmia (SA). The serum ghrelin amount was tested by the ELASA method. Moreover, blood sugar, lipids, liver function, and renal function were tested. All recruited patients underwent echocardiographic examination following admission. Three cardiac cycles were observed under continuous exhalation. The left atrial diameter (LAD) and the left ventricular ejection fraction (LVEF) were measured and averaged. Patients with AF received conventional treatment, and the aforementioned parameters were re-measured after 8 weeks. The results were statistically analyzed.

RESULTS

The serum ghrelin level in the patients in the AF group (199.55±79.59 pg/mL) was lower than that in the patients in the SA group (313.89±71.13 pg/mL, p<0.01), whereas the serum ghrelin level in those in the paroxysmal AF group (224.44±72.33 pg/mL) was higher than that in those in the persistent AF group (176.00±79.88 pg/mL, p<0.01). There was a positive correlation between the serum ghrelin level and LVEF in the patients in the AF group (r=0.704, p=0.046). After treatment, the serum ghrelin level and LVEF in the patients in the AF group significantly increased, whereas LAD decreased.

CONCLUSION

The serum ghrelin level in patients with AF was reduced, and after treatment, it significantly increased. There was a positive correlation between the serum ghrelin level and LVEF in the patients in the AF group.

Plasma levels of leptin and ghrelin and their correlation with BMI, and circulating lipids and glucose in obese Tunisian women

Background

A National Survey on the Effect of Nutrition conducted in 1996−1997 showed a 14% overall prevalence of obesity in Tunisia with a female predominance. Leptin and ghrelin play crucial roles in regulating body weight and energy balance. Leptin, an anorectic hormone, and ghrelin, an orexigenic hormone, appear to interact with glucose and lipid metabolism.

Objectives

To determine the circulating levels of ghrelin and leptin in obese Tunisian women and to investigate the correlations of these hormones with body mass index (BMI), and circulating lipids and glucose.

Methods

Forty obese women were recruited from patients in the “C” Unit of the National Institute of Nutrition and Food Technology. Twenty normal women were recruited as controls. Plasma levels of the studied variables were measured in patients from both groups and findings were analyzed.

Results

Circulating levels of leptin were significantly higher, while high-density lipoprotein (HDL)-cholesterol and ghrelin levels were significantly lower in the obese women. In the obese women, significant positive correlations were found between circulating levels of leptin and low-density lipoprotein (LDL)-cholesterol, BMI, and glucose; and ghrelin and HDL-cholesterol. Significant negative correlations were found between circulating levels of leptin and HDL-cholesterol and ghrelin; and ghrelin and leptin, LDL-cholesterol, BMI, and glucose. Multivariate analysis revealed that ghrelin was significantly associated with HDL-cholesterol, LDL-cholesterol, and blood glucose.

Conclusions

The significant negative correlation between leptin and ghrelin suggests that these two hormones may be antagonistic. Increased levels of ghrelin are correlated with decreased circulating levels of HDL-cholesterol and increased levels of LDL-cholesterol.

An Evaluation of Acylated Ghrelin and Obestatin Levels in Childhood Obesity and Their Association with Insulin Resistance, Metabolic Syndrome, and Oxidative Stress

Background: Ghrelin is a 28-amino acid peptide with an orexigenic property, which is predominantly produced by the stomach. Acylated ghrelin is the active form of this hormone. Obestatin is a 23-amino acid peptide which is produced by post-translational modification of a protein precursor that also produces ghrelin. Obestatin has the opposite effect of ghrelin on food intake. The aim of this study was to evaluate acylated ghrelin and obestatin levels and their ratio in obese and normal-weight children and adolescents, and their association with metabolic syndrome (MetS) parameters. Methods: Serum acyl-ghrelin, obestatin, leptin, insulin, fasting plasma glucose (FPG), lipid profile, and malondialdehyde (MDA) were evaluated in 73 children and adolescents (42 obese and 31 control). Insulin resistance was calculated by a homeostasis model assessment of insulin resistance (HOMA-IR). MetS was determined according to IDF criteria. Results: Acyl-ghrelin levels were significantly lower in obese subjects compared to the control group and lower in obese children with MetS compared to obese subjects without MetS. Obestatin was significantly higher in obese subjects compared to that of the control, but it did not differ significantly among those with or without MetS. Acyl-ghrelin to obestatin ratio was significantly lower in obese subjects compared to that in normal subjects. Acyl-ghrelin showed significant negative and obestatin showed significant positive correlations with body mass index (BMI), BMI Z-score, leptin, insulin, and HOMA-IR. Acyl-ghrelin had a significant negative correlation with MDA as an index of oxidative stress. Conclusion: Ghrelin is decreased and obestatin is elevated in obesity. Both of these hormones are associated with insulin resistance, and ghrelin is associated with oxidative stress. The balance between ghrelin and obestatin seems to be disturbed in obesity.

Does Glucagon-like Peptide-1 Ameliorate Oxidative Stress in Diabetes? Evidence Based on Experimental and Clinical Studies

Glucagon-like peptide-1 (GLP-1) has shown to influence the oxidative stress status in a number of in vitro, in vivo and clinical studies. Well-known effects of GLP-1 including better glycemic control, decreased food intake, increased insulin release and increased insulin sensitivity may indirectly contribute to this phenomenon, but glucose-independent effects on ROS level, production and antioxidant capacity have been suggested to also play a role. The potential 'antioxidant' activity of GLP-1 along with other proposed glucose-independent modes of action related to ameliorating redox imbalance remains a controversial topic but could hold a therapeutic potential against micro- and macrovascular diabetic complications. This review discusses the presently available knowledge from experimental and clinical studies on the effects of GLP-1 on oxidative stress in diabetes and diabetes-related complications.

Pure human butyrylcholinesterase hydrolyzes octanoyl ghrelin to desacyl ghrelin

The ghrelin hormone is a 28 amino acid peptide esterified on serine 3 with octanoic acid. Ghrelin is inactivated by hydrolysis of the ester bond. Previous studies have relied on inhibitors to identify human butyrylcholinesterase (BChE) as the hydrolase in human plasma that converts ghrelin to desacyl ghrelin. The reaction of BChE with ghrelin is unusual because the rate of hydrolysis is very slow and the substrate is ten times larger than standard BChE substrates. These unusual features prompted us to re-examine the reaction, using human BChE preparations that were more than 98% pure. Conversion of ghrelin to desacyl ghrelin was monitored by MALDI TOF mass spectrometry. It was found that 5 different preparations of pure human BChE all hydrolyzed ghrelin, including BChE purified from human plasma, from Cohn fraction IV-4, BChE immunopurified by binding to monoclonals mAb2 and B2 18-5, and recombinant human BChE purified from culture medium. We reasoned that it was unlikely that a common contaminant that could be responsible for ghrelin hydrolysis would appear in all of these preparations. km was <1 μM, and kcat was ~1.4 min(-1). A Michaelis-Menten analysis employing these kinetic values together with serum concentrations of ghrelin and BChE demonstrated that BChE could hydrolyze all of the ghrelin in serum in ~1 h. It was concluded that BChE is physiologically relevant for the hydrolysis of ghrelin.

Insights into the molecular mechanisms of diabetes-induced endothelial dysfunction: focus on oxidative stress and endothelial progenitor cells

Diabetes mellitus is a heterogeneous, multifactorial, chronic disease characterized by hyperglycemia owing to insulin insufficiency and insulin resistance (IR). Recent epidemiological studies showed that the diabetes epidemic affects 382 million people worldwide in 2013, and this figure is expected to be 600 million people by 2035. Diabetes is associated with microvascular and macrovascular complications resulting in accelerated endothelial dysfunction (ED), atherosclerosis, and cardiovascular disease (CVD). Unfortunately, the complex pathophysiology of diabetic cardiovascular damage is not fully understood. Therefore, there is a clear need to better understand the molecular pathophysiology of ED in diabetes, and consequently, better treatment options and novel efficacious therapies could be identified. In the light of recent extensive research, we re-investigate the association between diabetes-associated metabolic disturbances (IR, subclinical inflammation, dyslipidemia, hyperglycemia, dysregulated production of adipokines, defective incretin and gut hormones production/action, and oxidative stress) and ED, focusing on oxidative stress and endothelial progenitor cells (EPCs). In addition, we re-emphasize that oxidative stress is the final common pathway that transduces signals from other conditions-either directly or indirectly-leading to ED and CVD.

Increased acyl ghrelin but decreased total ghrelin and unacyl ghrelin in Chinese Han people with impaired fasting glucose combined with impaired glucose tolerance

We assessed the plasma acyl ghrelin (AG), unacyl ghrelin (UAG), and total ghrelin (TGhr) levels in Chinese adults with pre-diabetes and newly diagnosed diabetes mellitus (NDDM) after an oral glucose tolerance test (OGTT), and abdominal subcutaneous fat area and visceral fat area (VFA) were measured. Fasting AG level was increased in the impaired fasting glucose (IFG) combined with impaired glucose tolerance (IFG+IGT) and NDDM groups. AG, UAG, and TGhr levels were significantly decreased post-OGTT, and the decrements of 30-min AG, UAG, and TGhr post-OGTT were not significantly different among groups. UAG and TGhr levels did not differ significantly among the normal glucose tolerance (NGT), IFG and NDDM groups, but they decreased obviously in the IFG+IGT and impaired glucose tolerance (IGT) groups. The NDDM group had larger VFA than the NGT, IGT, and IFG+IGT groups, even after adjustment for height, it was still larger than the NGT group. The factors such as dyslipidemia and obesity which are prone to develop insulin resistance (IR) and decrease insulin sensitivity (IS) were negatively correlated with UAG and TGhr, positively with AG/UAG, while no correlations with AG. In terms of evaluating IS and IR, AG/UAG ratio may be superior in AG concentration. Our findings suggest that relative sufficiency of AG, the deficiency of TGhr and UAG are already present in IFG+IGT patients. We speculate that there is UAG resistance in severe hyperglycemia (diabetic state), which could produce elevated TGhr and UAG compared to IFG+IGT group. In the development of T2D, increase of VFA could be the initiating factor, leading elevated AG, reduced UAG, IR, decreased IS, and finally hyperglycemia.

Effects of ghrelin on protein expression of antioxidative enzymes and iNOS in the rat liver

INTRODUCTION

We investigated the effects of ghrelin on protein expression of the liver antioxidant enzymes superoxide dismutases (SODs), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR), nuclear factor κB (NFκB) and inducible nitric oxide synthase (iNOS). Furthermore, we aimed to investigate whether extracellular regulated protein kinase (ERK1/2) and protein kinase B (Akt) are involved in ghrelin-regulated liver antioxidant enzymes and iNOS protein expression.

MATERIAL AND METHODS

Male Wistar rats were treated with ghrelin (0.3 nmol/5 µl) injected into the lateral cerebral ventricle every 24 h for 5 days, and 2 h after the last treatment the animals were sacrificed and the liver excised. The Western blot method was used to determine expression of antioxidant enzymes, iNOS, phosphorylation of Akt, ERK1/2 and nuclear factor κB (NFκB) subunits 50 and 65.

RESULTS

There was significantly higher protein expression of CuZnSOD (p < 0.001), MnSOD (p < 0.001), CAT (p < 0.001), GPx, (p < 0.001), and GR (p < 0.01) in the liver isolated from ghrelin-treated animals compared with control animals. In contrast, ghrelin significantly (p < 0.01) reduced protein expression of iNOS. In addition, phosphorylation of NFκB subunits p65 and p50 was significantly (p < 0.001 for p65; p < 0.05 for p50) reduced by ghrelin when compared with controls. Phosphorylation of ERK1/2 and of Akt was significantly higher in ghrelin-treated than in control animals (p < 0.05 for ERK1/2; p < 0.01 for Akt).

CONCLUSIONS

The results show that activation of Akt and ERK1/2 is involved in ghrelin-mediated regulation of protein expression of antioxidant enzymes and iNOS in the rat liver.

Ghrelin and cardiovascular diseases

Ghrelin, a newly discovered bioactive peptide, is a natural endogenous ligand of the growth hormone (GH) secretagogue receptor and initially identified as a strong stimulant for the release of GH. Subsequent research has shown that ghrelin and its various receptors are ubiquitous in many other organs and tissues. Moreover, they participate in the regulation of appetite, energy, bodyweight, metabolism of glucose and fat, as well as modulation of gastrointestinal, cardiovascular, pulmonary, immune functions and cell proliferation/apoptosis. Increasing evidence has demonstrated that ghrelin has a close relationship with cardiovascular system. Ghrelin and its receptors are widely distributed in cardiovascular tissues, and there is no doubt that the effects of ghrelin in the cardiovascular system are mediated not only via its growth-hormone-releasing effect but also by its direct effects on the heart. Exogenous administration of ghrelin can dilate peripheral blood vessels, constrict coronary artery, improve endothelial function, as well as inhibit myocardial cell apoptosis. So, ghrelin may have cardiovascular protective effect, including lowering of blood pressure, regulation of atherosclerosis, and protection from ischemia/reperfusion injury as well as improving the prognosis of myocardial infarction and heart failure. Some of these new functions of ghrelin may provide new potential therapeutic opportunities for ghrelin in cardiovascular medicine. In this paper, we will review the existing evidence for cardiovascular effects of ghrelin, including the cardiovascular function, the variations in ghrelin plasma levels in pathophysiologicalogical conditions, the possible protective mechanisms of ghrelin, as well as its future potential therapeutic roles.

Ghrelin and oxidative stress in gastrointestinal tract

Oxidative stress is a major cause of the gastrointestinal damage under physical or psychological stress. Ghrelin exhibits gastroprotective effects and they are supposed to be derived from antioxidant effects. In gastroduodenal mucosal injury, the plasma ghrelin levels increase in response to the demand for gastroduodenal cytoprotection. However, in the condition of Helicobacter pylori-induced gastric mucosal severe atrophy, the plasma ghrelin concentration shifted to lower levels. In diabetic gastroparesis, the regulation of ghrelin secretion is impaired with vagal nerve dysfunction. Selective ghrelin agonist is expected to represent a new class of prokinetic agent. In addition, the plasma ghrelin levels are also enhanced by systemic oxidative stress, and ghrelin exhibits antioxidant effects in many organs, such as heart, pancreas, and lung. This suggests that ghrelin would be an important player as a sensor of systemic oxidative stress.

Small intestinal clustered contractions and bacterial overgrowth: a frequent finding in obese patients

BACKGROUND

Small intestinal bacterial overgrowth (SIBO) has been observed in several disorders of the gastrointestinal tract. Studies have shown abnormalities of motor function in obese patients, and there is indirect evidence suggesting that SIBO is present in them.

AIMS

To study small intestinal motility and the prevalence of SIBO in obese patients and to determine whether there was any relationship between both parameters.

METHODS

Thirty-nine patients scheduled for bariatric surgery were subjected to hydrogen breath test with lactulose and to a stationary small intestinal motility study with perfused catheters.

RESULTS

SIBO was observed in 41% of obese patients and was not related to body mass index. Small intestinal manometry showed a marked increase of clustered contractions in obese patients with SIBO compared to obese subjects without SIBO, whereas all the other parameters of fasting cyclic activity were not different.

CONCLUSIONS

SIBO was a frequent finding in obese patients and was associated with an increased pattern of clustered contractions, which was not observed in absence of SIBO.

Ghrelin Receptor Deficiency does not Affect Diet-Induced Atherosclerosis in Low-Density Lipoprotein Receptor-Null Mice

OBJECTIVE

Ghrelin, a stomach-derived, secreted peptide, and its receptor (growth hormone secretagogue receptor, GHSR) are known to modulate food intake and energy homeostasis. The ghrelin system is also expressed broadly in cardiovascular tissues. Since ghrelin has been associated with anti-inflammatory and anti-atherogenic properties, but is also well known to promote obesity and impair glucose metabolism, we investigated whether ghrelin has any impact on the development of atherosclerosis. The hypothesis that endogenous ghrelin signaling may be involved in atherosclerosis has not been tested previously.

METHODS AND RESULTS

We crossed ghrelin receptor knockout mice (GHSr(-/-)) into a low-density lipoprotein receptor-null (Ldlr(-/-)) mouse line. In this model, atherosclerotic lesions were promoted by feeding a high-fat, high-cholesterol Western-type diet for 13 months, following a standard protocol. Body composition and glucose homeostasis were similar between Ldlr(-/-) and Ldlr/GHSR(-/-)ko mice throughout the study. Absence or presence of GHSr did not alter the apolipoprotein profile changes in response to diet exposure on an LDLRko background. Atherosclerotic plaque volume in the aortic arch and thoracic aorta were also not affected differentially in mice without ghrelin signaling due to GHSR gene disruption as compared to control LDLRko littermates. In light of the associations reported for ghrelin with cardiovascular disease in humans, the lack of a phenotype in these loss-of-function studies in mice suggests no direct role for endogenous ghrelin in either the inhibition or the promotion of diet-induced atherosclerosis.

CONCLUSION

These data indicate that, surprisingly, the complex and multifaceted actions of endogenous ghrelin receptor mediated signaling on the cardiovascular system have minimal direct impact on atherosclerotic plaque progression as based on a loss-of-function mouse model of the disease.

Adipocytokines in atherothrombosis: focus on platelets and vascular smooth muscle cells

Visceral obesity is a relevant pathological condition closely associated with high risk of atherosclerotic vascular disease including myocardial infarction and stroke. The increased vascular risk is related also to peculiar dysfunction in the endocrine activity of adipose tissue responsible of vascular impairment (including endothelial dysfunction), prothrombotic tendency, and low-grade chronic inflammation. In particular, increased synthesis and release of different cytokines, including interleukins and tumor necrosis factor-α (TNF-α), and adipokines—such as leptin—have been reported as associated with future cardiovascular events. Since vascular cell dysfunction plays a major role in the atherothrombotic complications in central obesity, this paper aims at focusing, in particular, on the relationship between platelets and vascular smooth muscle cells, and the impaired secretory pattern of adipose tissue.

Plasma ghrelin levels and polymorphisms of ghrelin gene in Chinese obese children and adolescents

AIM

To evaluate the role of fasting plasma ghrelin levels [ln(ghrelin)] and polymorphisms of ghrelin gene in Chinese obese children.

METHODS

Genotyping for ghrelin polymorphism was performed in 230 obese and 100 normal weight children. Among them, plasma ghrelin levels were measured in 91 obese and 23 health subjects.

RESULTS

(1) Bivariate correlation analysis showed the ln(ghrelin) was inversely correlated with abnormality of glucose metabolism (r = -0.240, P = 0.023). Stepwise multiple regression analysis showed that abnormality of glucose metabolism was an independent determinant of plasma ghrelin levels (P = 0.023). (2) There was no difference in frequency of Leu72Met polymorphisms between obese and control groups (36.09 vs. 41.00%).

CONCLUSION

Ghrelin is associated with obesity in childhood, especially associated with the glucose homeostasis. Lower ghrelin levels might be a result of obesity, but not a cause of obesity. The Leu72Met polymorphism of ghrelin gene is not associated with obesity and metabolic syndrome in Chinese children.

Positive and negative regulation of insulin signaling by reactive oxygen and nitrogen species

Regulated production of reactive oxygen species (ROS)/reactive nitrogen species (RNS) adequately balanced by antioxidant systems is a prerequisite for the participation of these active substances in physiological processes, including insulin action. Yet, increasing evidence implicates ROS and RNS as negative regulators of insulin signaling, rendering them putative mediators in the development of insulin resistance, a common endocrine abnormality that accompanies obesity and is a risk factor of type 2 diabetes. This review deals with this dual, seemingly contradictory, function of ROS and RNS in regulating insulin action: the major processes for ROS and RNS generation and detoxification are presented, and a critical review of the evidence that they participate in the positive and negative regulation of insulin action is provided. The cellular and molecular mechanisms by which ROS and RNS are thought to participate in normal insulin action and in the induction of insulin resistance are then described. Finally, we explore the potential usefulness and the challenges in modulating the oxidant-antioxidant balance as a potentially promising, but currently disappointing, means of improving insulin action in insulin resistance-associated conditions, leading causes of human morbidity and mortality of our era.

The change in ghrelin and obestatin levels in obese children after weight reduction

AIM

To investigate the role of ghrelin and obestatin in obesity mechanisms.

METHODS

A total of 88 obese children and 25 normal children were enrolled. Moreover, 46 obese children took part in a summer camp for weight reduction. Fasting ghrelin, obestatin and other biochemical parameters were measured in all subjects and re-measured in 45 obese children finishing the camp.

RESULTS

The ghrelin levels in the control and obese groups were 67.26 +/- 23.41 pmol/L and 56.53 +/- 15.97 pmol/L with a significant difference (p = 0.039), while the obestatin levels (89.41 +/- 23.63 vs. 83.13 +/- 17.21 pmol/L) were not significantly different (p = 0.083). The ghrelin/obestatin ratio in the controls was significantly higher than that in the obese group (p = 0.014). In the latter, fasting insulin and alanine aminotransferase were independent factors for ghrelin; fasting insulin, weight and gender were independent factors for obestatin and alanine aminotransferase was an independent factor for ghrelin/obestatin. Moreover, ghrelin, obestatin and ghrelin/obestatin increased after weight reduction (p < 0.05, respectively), and the increment in ghrelin and obestatin was associated with a decrement in insulin resistance.

CONCLUSION

These data suggest that ghrelin, obestatin and/or the ghrelin/obestatin ratio are associated with obesity in childhood.

Plasma obestatin concentrations are negatively correlated with body mass index, insulin resistance index, and plasma leptin concentrations in obesity and anorexia nervosa

BACKGROUND

Obestatin is a recently identified ghrelin gene product that was reported to inhibit appetite and gastric motility in contrast to ghrelin. We investigated fasting obestatin and ghrelin levels in patients with obesity and anorexia nervosa.

METHODS

Fasting plasma obestatin, acyl-ghrelin, desacyl-ghrelin, leptin, glucose serum adiponectin, and insulin were measured in 10 obese subjects, 11 restricting-type anorexics, and 11 control subjects.

RESULTS

Obese group had significantly lower levels of obestatin (p < .01), while anorexic group had significantly higher levels (p < .01). Obestatin was negatively correlated with body mass index (BMI) (r = -.74), glucose (r = -.56), insulin (r = -.55), leptin (r = -.66), and also with the homeostasis model assessment of insulin resistance (HOMA-R) (r = -.49) and was positively correlated with acyl-ghrelin (r = .65) and desacyl-ghrelin (r = .60). No correlation was seen between obestatin and adiponectin, but the latter was negatively correlated with both acyl-ghrelin and desacyl-ghrelin. Desacyl-ghrelin to acyl-ghrelin ratio was significantly different between anorexic and control groups (p < .05), while no difference was seen between obese and control groups.

CONCLUSIONS

Both obestatin and ghrelin are increased in anorexic and decreased in obesity. We suggest that obestatin is a nutritional marker reflecting body adiposity and insulin resistance.

Effect of adiponectin and ghrelin on apoptosis of Barrett adenocarcinoma cell line

BACKGROUND

Obesity is an important risk factor for Barrett adenocarcinoma. However, the role of adiponectin (anti-inflammatory adipokine from adipose tissue) and ghrelin (orexigenic peptide gastric origin) on the progression of Barrett's carcinogenesis has not been investigated so far. The aim of the present study was: (1) to compare the expression of adiponectin and ghrelin receptors in Barrett's esophagus and in normal squamous epithelium; (2) to assess the effect of adiponectin and ghrelin on apoptosis in Barrett's adenocarcinoma cells in vitro; and (3) to investigate the effect of ghrelin on IL-1beta and COX-2 expression in OE-19 cells incubated with TNFalpha.

METHODS

The expression of ghrelin and adiponectin receptors (GHS-R1a, Adipo-R1, Adipo R-2) in biopsies from Barrett's esophagus and in Barrett's adenocarcinoma cell line OE-19 was assessed by quantitative RT-PCR (qRT-PCR). The OE-19 cells were also incubated with adiponectin (5-10 microg/ml), and the apoptosis and proliferation were assessed by FACS and MTT assays. Additionally, effects of adiponectin on the mRNA and protein expression of proapoptotic Bax and antiapoptotic Bcl-2 were assessed by RT-PCR and Western blot, respectively. In two different in vitro models of esophagitis the OE-19 cells were incubated with ghrelin alone or in the presence of TNFalpha or bile acids in the normal or pulse acidified medium, and the expression of IL-1beta and COX-2 as markers for inflammation were assessed by FACS and qRT-PCR, respectively.

RESULTS

Adiponectin caused a significant increase in apoptosis, and this affect was accompanied by increased Bax and decreased Bcl-2 expression. In contrast, ghrelin had no effect on apoptosis of OE-19 cells incubated in neutral or acidified medium with or without addition of deoxycholic acid. At the mRNA level, the expression of adiponectin receptors (Adipo-R1, Adipo-R2) was decreased, and the expression of ghrelin receptor (GHS-R1a) was increased in Barrett's mucosa. Ghrelin caused a decrease in TNFalpha-induced COX-2 and IL-1beta expression in OE-19 cells.

CONCLUSION

Adiponectin and ghrelin have an inhibitory effect on Barrett's carcinogenesis by two different mechanisms: (1) by an increase in apoptosis by adiponectin, and (2) by anti-inflammatory actions of ghrelin. The decrease in levels of these two peptides in obesity may explain the progression of Barrett's carcinoma in obese individuals.

Factors associated with fasting plasma ghrelin levels in children and adolescents

AIM: To measure plasma ghrelin levels in children and adolescents, analyze the associated factors, and investigate the role of ghrelin in obesity, insulin resistance and reproductive physiology.

METHODS: A total of 283 subjects aged 4.8-15.8 year were enrolled. Fasting blood samples were collected and plasma ghrelin levels were measured by radioimmunoassay. Fasting glucose (FG), fasting insulin (FI), baseline testosterone (T), estradiol (E2), prolactin (PRL), luteinizing hormone (LH), follicle-stimulating hormone (FSH), serum total cholesterol (TC), triglyceride (TG), alanine aminotransferase (ALT) and uric acid (UA) were measured. Body mass index (BMI), insulin resistance by homeostasis model (HOMA-IR) and beta cell function by homeostasis model (HOMA-β) were calculated.

RESULTS: The median ghrelin level was 290 ng/L (15.0-1325.0 ng/L). Bivariate correlation analysis showed that ghrelin levels were inversely correlated with BMI, ALT, TG, UA, LH, FI and HOMA-IR (all P < 0.05). No other significant correlation was found between ghrelin levels and age, gender, TC, E2, FSH, PRL, FG and HOMA-β. Stepwise multiple regression analysis showed that only BMI and FI were independent determinants of plasma ghrelin levels in these children and adolescents (P = 0.018 and P = 0.046, respectively), which explained 25.4% of the variance.

CONCLUSION: These data suggest that the lower ghrelin levels in obese subjects may be the result of obesity and hyperinsulinemia, which is very common in obese subjects. Moreover, ghrelin may regulate human reproductive physiology indirectly.

Oxidative stress and potential interventions to reduce oxidative stress in overweight and obesity

PURPOSE

Obesity may be a state of chronic oxidative stress. Oxidative stress may be the mechanism underlying the development of co-morbidities in obesity. This review provides a summary of the available evidence regarding systemic oxidative stress in young, older and clinical obese populations.

METHODS

Medline was searched for all available articles published between 1975 and 2006 that evaluated oxidative stress biomarkers in resting conditions or following various interventions in overweight and obese humans.

RESULTS

Obesity elevates oxidative stress in young, old and clinical populations as shown by elevations in lipid peroxidation (malondialdehyde, hydroperoxides, 4-hydroxynonenal, isoprostanes, conjugated dienes) or protein oxidation (8-hydroxy-deoxyguanosine). Lipid peroxidation is associated with several indices of adiposity and a low systemic antioxidant defence (i.e. antioxidant enzymes, tissue dietary antioxidants, glutathione). Oxidative stress may be exacerbated with acute exercise, advancing age or co-existing clinical conditions and may be corrected by improving antioxidant defences through fat volume reduction via surgery, pharmacological agents, exercise and/or dietary modification.

CONCLUSION

Oxidative stress is related to chronic disease in obesity, but is reversible with one or more interventions described above.

The relationship between metabolic status and levels of adiponectin and ghrelin in lean women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is commonly associated with insulin resistance, obesity, dyslipidemia and hypertension. Adiponectin, an adipocyte-specific protein with important roles in glucose and lipid homeostasis, possesses antidiabetic and insulin-sensitizing properties. Ghrelin, a protein ligand for the growth hormone secretagog receptor, has been shown to stimulate food intake and to influence energy balance, insulin signaling and glucose metabolism. We aimed to evaluate the relationships between metabolic alterations and adiponectin and ghrelin levels in lean PCOS women, compared with lean and obese women. The study was carried out on 20 non-obese PCOS women aged 20 - 48 years and age-matched groups of 45 healthy lean and 37 obese women. Hormonal and biochemical parameters, adiponectin and ghrelin concentrations and anthropometric data were determined. In PCOS subjects, we found increased homeostasis model assessment - insulin resistance index (HOMA-IR) with non-significant differences in adiponectin and ghrelin concentrations compared with healthy women, although the PCOS group showed a tendency to lower adiponectin levels. However, ghrelin levels in PCOS women were significantly higher than in obese women. Moreover, we observed a negative correlation between adiponectin and testosterone, cholesterol, triglycerides, glucose and diastolic blood pressure in PCOS. In conclusion, it can be suggested that higher values of HOMA-IR with lower adiponectin levels may indicate future development of metabolic syndrome or other metabolic disturbances in lean PCOS women.

Serum ghrelin levels and risk of subsequent adenocarcinoma of the esophagus

OBJECTIVE

Several large studies have shown a negative association between Helicobacter pylori (H. pylori) infection and esophageal adenocarcinoma. Diminution of gastric ghrelin secretion by H. pylori could protect against esophageal malignancy by decreasing appetite, food intake, and acid production, thereby decreasing weight and gastroesophageal reflux.

METHODS

We evaluated the association of ghrelin with esophageal adenocarcinoma using a population from a previous nested case-control study. Among 128,992 enrolled in a multiphasic health checkup (MHC) between 1964 and 1969, 52 patients developed esophageal adenocarcinoma by the year 2000. Three random controls from the MHC cohort were matched to each case by age, sex, race, and the date and site of their MHC. Serum samples collected at the MHC had been previously tested for IgG antibodies against H. pylori and the CagA protein. Serum ghrelin concentrations were determined by a commercial EIA on 52% of the initial subjects (31 cases and 79 controls).

RESULTS

A concentration of ghrelin greater than 3,200 pg/mL at MHC (fourth quartile) was associated with a lower risk of esophageal cancer (H. pylori and body mass index [BMI] adjusted OR=0.18 [CI 0.04-0.78]). This inverse association was seen only in overweight subjects (BMI>or=25, P value for interaction=0.09). The effects of H. pylori and ghrelin were independent.

CONCLUSION

Contrary to the original hypothesis, high rather than low serum ghrelin was associated with protection against esophageal adenocarcinoma but only among overweight subjects.

Ghrelin interacts with human plasma lipoproteins

Ghrelin, a peptide hormone produced predominantly by the stomach, stimulates food intake and GH secretion. The Ser(3) residue of ghrelin is mainly modified by a n-octanoic acid. In the human bloodstream, ghrelin circulates in two forms: octanoylated and desacylated. We previously demonstrated that ghrelin is desoctanoylated in human serum by butyrylcholinesterase (EC 3.1.1.8) and other esterase(s), whereas in rat serum, only carboxylesterase (EC 3.1.1.1) is involved. The aims of this study were to determine the role of lipoprotein-associated enzymes in ghrelin desoctanoylation and the role of lipoproteins in the transport of circulating ghrelin. Our results show that ghrelin desoctanoylation mostly occurred in contact with low-density lipoproteins (LDLs) and lipoprotein-poor plasma subfractions. Butyrylcholinesterase and platelet-activating factor acetylhydrolase (EC 3.1.1.47) were responsible for the ghrelin hydrolytic activity of the lipoprotein-poor plasma and LDL subfractions, respectively. Moreover, we observed that ghrelin is associated with triglyceride-rich lipoproteins (TRLs), high-density lipoproteins (HDLs), very high-density lipoproteins (VHDLs), and to some extent LDLs. In conclusion, we report that the presence of the acyl group is necessary for ghrelin interaction with TRLs and LDLs but not HDLs and VHDLs. Ghrelin interacts via its N- and C-terminal parts with HDLs and VHDLs. This suggests that, whereas TRLs mostly transport acylated ghrelin, HDLs and VHDLs transport both ghrelin and des-acyl ghrelin.

Heterogeneity of ghrelin/growth hormone secretagogue receptors. Toward the understanding of the molecular identity of novel ghrelin/GHS receptors

Ghrelin is a gastric polypeptide displaying strong GH-releasing activity by activation of the type 1a GH secretagogue receptor (GHS-R1a) located in the hypothalamus-pituitary axis. GHS-R1a is a G-protein-coupled receptor that, upon the binding of ghrelin or synthetic peptidyl and non-peptidyl ghrelin-mimetic agents known as GHS, preferentially couples to G(q), ultimately leading to increased intracellular calcium content. Beside the potent GH-releasing action, ghrelin and GHS influence food intake, gut motility, sleep, memory and behavior, glucose and lipid metabolism, cardiovascular performances, cell proliferation, immunological responses and reproduction. A growing body of evidence suggests that the cloned GHS-R1a alone cannot be the responsible for all these effects. The cloned GHS-R1b splice variant is apparently non-ghrelin/GHS-responsive, despite demonstration of expression in neoplastic tissues responsive to ghrelin not expressing GHS-R1a; GHS-R1a homologues sensitive to ghrelin are capable of interaction with GHS-R1b, forming heterodimeric species. Furthermore, GHS-R1a-deficient mice do not show evident abnormalities in growth and diet-induced obesity, suggesting the involvement of another receptor. Additional evidence of the existence of another receptor is that ghrelin and GHS do not always share the same biological activities and activate a variety of intracellular signalling systems besides G(q). The biological actions on the heart, adipose tissue, pancreas, cancer cells and brain shared by ghrelin and the non-acylated form of ghrelin (des-octanoyl ghrelin), which does not bind GHS-R1a, represent the best evidence for the existence of a still unknown, functionally active binding site for this family of molecules. Finally, located in the heart and blood vessels is the scavenger receptor CD36, involved in the endocytosis of the pro-atherogenic oxidized low-density lipoproteins, which is a pharmacologically and structurally distinct receptor for peptidyl GHS and not for ghrelin. This review highlights the most recently discovered features of GHS-R1a and the emerging evidence for a novel group of receptors that are not of the GHS1a type; these appear involved in the transduction of the multiple levels of information provided by GHS and ghrelin.

Serum ghrelin and carotid atherosclerosis in older Japanese people with metabolic syndrome

Ghrelin may play a role in the development of atherosclerosis. However, the effect of serum ghrelin on carotid intima-media thickness (cIMT) (well-established as a surrogate marker to atherosclerosis) in metabolic syndrome (MS), particularly among relatively older subjects, has still not been thoroughly investigated. A total of 101 subjects >60 years of age (mean age, 72.3 years) with MS were enrolled in the study to investigate the relationship between serum total ghrelin and B-mode ultrasonographic cIMT levels. There were significantly positive correlations between cIMT and both age and systolic BP, but cIMT was significantly inversely correlated to ghrelin levels. In the multiple regression analysis for cIMT adjusted by other measured parameters, ghrelin was a significant and independent factor along with age and systolic BP. These findings suggest that decreased ghrelin levels may be related to carotid atherosclerosis among older subjects with MS.

Apocynin normalizes hyperreactivity to phenylephrine in mesenteric arteries from cholesterol-fed mice by improving endothelium-derived hyperpolarizing factor response

We studied the relationship among endothelial function, oxidative stress, and phenylephrine (PE; alpha(1)-adrenoceptor agonist)-induced contraction in mesenteric arteries from high-cholesterol (HC)-diet-fed mice. In HC mice (vs age-matched normal-diet-fed mice): (1) PE-induced contraction in endothelium-intact rings was enhanced (endothelial denudation increased contraction in "normal-diet" rings, but did not enhance it further in "HC" rings); (2) the enhanced PE-induced contraction was further enhanced in the presence of N(G)-nitro-L-arginine (L-NNA; nitric oxide synthase inhibitor) or L-NNA plus indomethacin (cyclooxygenase inhibitor) [to preserve endothelium-derived hyperpolarizing factor (EDHF)], but unchanged in the presence of charybdotoxin plus apamin (to block EDHF); (3) ACh-induced EDHF-type relaxation was reduced; and (4) oxidative stress [indicated by the plasma 8-isoprostane level (reliable systemic marker) and aortic superoxide production] was greater. In HC mice, PE-induced contraction was normalized by apocynin [NAD(P)H oxidase inhibitor] or tempol (superoxide dismutase mimetic), but enhanced by NADH [NAD(P)H oxidase substrate]. Oral dietary supplementation with apocynin (30 mg/kg/day for 4 weeks) corrected the above abnormalities. Hence: (1) PE-induced contraction is modulated by the endothelium, and the enhanced contractility in HC mice results from defective EDHF signaling and elevated oxidative stress, and (2) apocynin normalizes PE-induced contraction in HC mice by improving EDHF signaling.

Expression of Ghrelin in nervous system and its cytoprotective action in rats

AIM: To investigate the expression of Ghrelin in brain, intestinal myenteric plexus and plasma and study its possible cytoprotective effect and mechanism on gastric mucosa against stress-induced ulcers.

METHODS: Seventy-six healthy male Wistar rats were divided into 6 groups randomly: cold-water restraint group (n = 10); intracerebroventricular (icv) injection of Ghrelin group (n = 24); icv injection of Ghrelin after subcutaneous injection of Nω-Nitro-L-arginine methylester (L-NAME) group (n = 8) and three matched control groups. The expression of Ghrelin in rat brain, intestinal myenteric plexus and plasma were detected by radio-immunoassay (RIA) and double staining of immunofluorescence and immunohistochemistry. The effect and mechanism of Ghrelin on gastric mucosa against stress-induced ulcer were analyzed using neurophysiologic methods.

RESULTS: Ghrelin-positive immunoreaction (IR) was observed in the small intestinal myenteric plexus and primarily cultured myenteric plexus neurons. Ghrelin-IR co-localized with choline acetyl transferase (ChAT), but not with nitric oxide synthase (NOS) or Calbindin (Calb) in the same myenteric plexus neurons. In comparison with that in its matched control group, the content of Ghrelin-IR in plasma was significantly decreased (198.3 ± 29.6 ng/L vs 141.7 ± 26.5 ng/L, P < 0.05), but increased in hypothalamus, medulla oblongata, pituitary and intestinal myenteric plexus (96.2 ± 18.1 pg/mg vs 153.2 ± 11.6 pg/mg, P = 0.006; 89.8 ± 16.5 pg/mg vs 144.4 ± 13.9 pg/mg, P = 0.007; 108.3 ± 11.9 pg/mg vs 198.2 ± 23.3 pg/mg, P = 0.002; 48.8 ± 12.8 pg/mg vs 86.2 ± 21.5 pg/mg, P = 0.02; respectively). The formation of stress ulcers was markedly inhibited by microinjection of Ghrelin into the ventricle with a dose-dependent manner (ulcer index: normal saline 86.7 ± 6.2; 50 ng Ghrelin 79.3 ± 10.7, P = 2.18; 500 ng Ghrelin: 61.3 ± 11.7, P = 0.04; 5 000 ng Ghrelin: 35.6 ± 10.8, P = 0.005). However, after a subcutaneous injection of L-NAME, the cytoprotective effect of Ghrelin disappeared.

CONCLUSION: Ghrelin co-localizes with ChAT in intestinal myenteric plexus neurons. The expression of Ghrelin changes in the central nerves system (CNS) and plasma while stress ulcer happens. Ghrelin in the CNS can protect gastric mucosa with a dose-dependent manner, which is probably related to the synthesis of nitric oxide.