Biological, physiological, and pharmacological aspects of ghrelin

Ghrelin reduces myocardial injury following global ischemia and reperfusion via suppression of myocardial inflammatory response

Ghrelin is a small endogenous peptide principally produced and secreted by the gastric mucosa, with a major role in appetite and metabolism regulation. We hypothesized that anti-inflammatory therapy, as produced by exogenous administration of ghrelin, would decrease the myocardial inflammatory response to global hypothermia I/R, thereby affording myocardial protection. Heterotopic cervical heart transplantation that allows to subject donor hearts to global hypothermic ischemia and blood reperfusion, which very closely stimulates I/R conditions associated with cardiac surgical operations. Ghrelin administration prior to blood reperfusion significantly decreased serum concentrations of cTn-I versus animals subjected I/R alone, with a significantly attenuated VCAM-1 expression in I/R animals pre-treated with ghrelin. The tissue concentrations of pro-inflammatory cytokines (IL-6, IL-1β, and MCP-1) were ameliorated by the administration of ghrelin prior to reperfusion versus the concentrations observed in animals subjected to I/R alone. Significantly fewer monocytes in the tissue sections of I/R+ghrelin animals versus those subjected to I/R alone. Exogenous ghrelin administration prior to reperfusion of an ischemic heart resulted in a significant reduction in myocardial injury as measured by cTn-I. The reduced myocardial injury was accompanied by an attenuated tissue expression of several pro-inflammatory mediators, including VCAM-1, IL-6, IL-1β, and MCP-1.

Acylated ghrelin and leptin concentrations in patients with type 2 diabetes mellitus, people with prediabetes and first degree relatives of patients with diabetes, a comparative study

Background

Ghrelin is known as a new endocrine component supposed to have an influence in control of feeding behavior and energy balance. Recent studies have shown that ghrelin concentration in the subjects with diabetes mellitus type 2 (DM 2) is lower than normal. To clarify the relationship between ghrelin and insulin resistance and also DM 2, a cross-sectional study was designed.

Methods

In a cross-sectional study, 87 subjects were enrolled in three groups, 29 with DM2, 29 pre-diabetes state and 29 normoglycemic subjects of first-degree relatives of diabetic group. After clinical examination, blood samples were taken to measure fasting blood glucose, HbA1c, lipids, insulin, leptin and acylated ghrelin concentrations.

Results

Mean serum concentrations of acylated ghrelin in all groups (47.4 ± 27.9 pg/ml) were lower than normal values (150.3 ± 56.4 pg/ml) (P: 0.006) without significant difference within groups comparison(P: 0.1). A significant correlation was found between ghrelin concentration with body mass index (BMI) (r: -0.23, p <0.02) and abdominal circumference (AC) (r: -0.28, P < 0.008). Also inverse relationship between ghrelin level and insulin resistance (HOMA-IR) (r: -.032, p: 0.002) was seen in all subjects. Leptin level has a significant correlation with abdominal circumference (AC) and BMI (P < 0.0001) but not with ghrelin.

Conclusion

This study showed that obesity has a strong association with the reduced level of ghrelin concentration. It seems that the process of ghrelin reduction is initiated in earlier stages of insulin resistance prior to the onset of overt DM.

Different forms of ghrelin exhibit distinct biological roles in tilapia

Ghrelin has been identified in all vertebrate classes, including sharks. Each species possesses multiple forms of ghrelin that vary in peptide length and acyl modifications (e.g., n-hexanoic, n-non-anoic, n-octanoic, and n-decanoic acids) including des-acyl ghrelin. Octanoylated ghrelin has been shown to be a potent GH secretagogue, orexigenic factor, and plays a role in overall metabolism in vertebrates. In the tilapia model, octanoylated ghrelin (ghrelin-C8) and decanoylated ghrelin (ghrelin-C10) exhibit different biological actions. This mini review highlights the current knowledge of the differential actions of ghrelin-C8 and ghrelin-C10 from studies in the tilapia model. These findings suggest that the multiple forms of ghrelin may exhibit distinct yet complimentary actions directed toward maintaining overall energy balance in other vertebrates.

Leptin and ghrelin levels in colostrum, milk and blood plasma of sows and pig neonates during the first week of lactation

Radioimmunology was used to determine leptin and ghrelin levels in sow colostrum and milk in relation to those in sow and neonatal pig blood plasma and to the body weight of piglets during the first week of lactation. The highest concentration of leptin was found in colostrum on the second day of lactation (69.3 ± 6.3 ng/mL). Leptin concentrations in sow plasma were significantly lower than in colostrum/milk (2.19 ± 0.9 ng/mL, P = 0.7692) and were stable in the first 7 days of lactation. Total and active ghrelin concentrations in colostrum/milk were stable in the measured time points (6734 ± 261 pg/mL, P = 0.3397; 831 ± 242 pg/mL, P = 0.3988, respectively). Total ghrelin concentrations in sow plasma were lower than in colostrum/milk. These results indicate that pigs follow a unique species-specific pattern of leptin and ghrelin synthesis, release and existence, and that the mammary gland is an important source of leptin and ghrelin contained in colostrum/milk.

Perinatal programming of neuroendocrine mechanisms connecting feeding behavior and stress

Feeding behavior is closely regulated by neuroendocrine mechanisms that can be influenced by stressful life events. However, the feeding response to stress varies among individuals with some increasing and others decreasing food intake after stress. In addition to the impact of acute lifestyle and genetic backgrounds, the early life environment can have a life-long influence on neuroendocrine mechanisms connecting stress to feeding behavior and may partially explain these opposing feeding responses to stress. In this review I will discuss the perinatal programming of adult hypothalamic stress and feeding circuitry. Specifically I will address how early life (prenatal and postnatal) nutrition, early life stress, and the early life hormonal profile can program the hypothalamic-pituitary-adrenal (HPA) axis, the endocrine arm of the body's response to stress long-term and how these changes can, in turn, influence the hypothalamic circuitry responsible for regulating feeding behavior. Thus, over- or under-feeding and/or stressful events during critical windows of early development can alter glucocorticoid (GC) regulation of the HPA axis, leading to changes in the GC influence on energy storage and changes in GC negative feedback on HPA axis-derived satiety signals such as corticotropin-releasing-hormone. Furthermore, peripheral hormones controlling satiety, such as leptin and insulin are altered by early life events, and can be influenced, in early life and adulthood, by stress. Importantly, these neuroendocrine signals act as trophic factors during development to stimulate connectivity throughout the hypothalamus. The interplay between these neuroendocrine signals, the perinatal environment, and activation of the stress circuitry in adulthood thus strongly influences feeding behavior and may explain why individuals have unique feeding responses to similar stressors.

Growth hormone-releasing hormone stimulates GH release while inhibiting ghrelin- and sGnRH-induced LH release from goldfish pituitary cells

Goldfish GH-releasing hormone (gGHRH) has been recently identified and shown to stimulate GH release in goldfish. In goldfish, neuroendocrine regulation of GH release is multifactorial and known stimulators include goldfish ghrelin (gGRLN19) and salmon gonadotropin-releasing hormone (sGnRH), factors that also enhance LH secretion. To further understand the complex regulation of pituitary hormone release in goldfish, we examined the interactions between gGHRH, gGRLN19, and sGnRH on GH and LH release from primary cultures of goldfish pituitary cells in perifusion. Treatment with 100nM gGHRH for 55min stimulated GH release. A 5-min pulse of either 1nM gGRLN19 or 100nM sGnRH induced GH release in naïve cells, and these were just as effective in cells receiving gGHRH. Interestingly, gGHRH abolished both gGRLN19- and sGnRH-induced LH release and reduced basal LH secretion levels. These results suggest that gGHRH does not interfere with sGnRH or gGRLN19 actions in the goldfish somatotropes and further reveal, for the first time, that GHRH may act as an inhibitor of stimulated and basal LH release by actions at the level of pituitary cells.

Age-dependent reduction of ghrelin- and motilin-induced contractile activity in the chicken gastrointestinal tract

Ghrelin is an endogenous ligand for growth hormone secretagogue-receptor 1a (GHS-R1a) and stimulates gastrointestinal (GI) motility in the chicken. Since ghrelin stimulates GH release, which regulates growth, it might be interesting to compare ghrelin-induced responses in GI tract of different-aged chickens. Motilin is a ghrelin-related gut peptide that induces strong contraction in the small intestine. Aim of this study was to clarify age-dependent changes in ghrelin- and motilin-induced contractions of the chicken GI tract and expression of their receptor mRNAs. Chicken ghrelin caused contraction of the crop and proventriculus. Ghrelin-induced contraction in the proventriculus decreased gradually up to 100 days after hatching, but the responses to ghrelin in the crop were the same during the growth period. GHS-R1a mRNA expression in the crop tended to increase, but that in the proventriculus decreased depending on the age. Chicken motilin caused contraction of the chicken GI tract. Atropine decreased the responses to motilin in the proventriculus but not in the ileum. Motilin-induced contraction in the proventriculus but not that in the ileum decreased depending on post-hatching days. On the other hand, motilin receptor mRNA expression in every region of the GI tract decreased with age, but the decrease was more marked in the proventriculus than in the ileum. In conclusion, ghrelin- and motilin-induced GI contractions selectively decreased in the chicken proventriculus depending on post-hatching days, probably due to the age-related decrease in respective receptors expression. The results suggest an age-related contribution of ghrelin and motilin to the regulation of chicken GI motility.

Plasma ghrelin is positively associated with body fat, liver fat and milk fat content but not with feed intake of dairy cows after parturition

Ghrelin is a gastrointestinal peptide hormone that is present in blood mostly in a non-posttranslationally modified form, with a minor proportion acylated at Ser(3). Both ghrelin forms were initially assigned a role in the control of food intake but there is accumulating evidence for their involvement in fat allocation and utilization. We investigated changes in the ghrelin system in dairy cows, exhibiting differences in body fat mobilization and fatty liver, from late pregnancy to early lactation. Sixteen dairy cows underwent liver biopsy and were retrospectively grouped based on high (H) or low (L) liver fat content post-partum. Both groups had a comparable feed intake in week -6 (before parturition) and week 2 (after parturition). Only before parturition was preprandial total ghrelin concentration higher in L than in H cows and only after parturition was the basal plasma concentration of non-esterified fatty acids higher in H than in L cows. Both before and after parturition, H cows had higher preprandial plasma concentrations of acyl ghrelin, a higher acyl:total ghrelin ratio, lower plasma triacylglyceride concentrations and a lower respiratory quotient compared with L cows. These group differences could not be attributed to an allelic variant of the acyl ghrelin receptor. Rather, the ratio of acyl:total ghrelin correlated with several aspects of fat metabolism and with respiratory quotient but not with feed intake. These results show that endogenous ghrelin forms are associated with fat allocation, fatty liver, and utilization of fat during the periparturient period.

Ghrelin receptors in non-Mammalian vertebrates

The growth hormone secretagogue-receptor (GHS-R) was discovered in humans and pigs in 1996. The endogenous ligand, ghrelin, was discovered 3 years later, in 1999, and our understanding of the physiological significance of the ghrelin system in vertebrates has grown steadily since then. Although the ghrelin system in non-mammalian vertebrates is a subject of great interest, protein sequence data for the receptor in non-mammalian vertebrates has been limited until recently, and related biological information has not been well organized. In this review, we summarize current information related to the ghrelin receptor in non-mammalian vertebrates.

Differential patterns in the periodicity and dynamics of clock gene expression in mouse liver and stomach

The rhythmic recurrence of biological processes is driven by the functioning of cellular circadian clocks, operated by a set of genes and proteins that generate self-sustaining transcriptional-translational feedback loops with a free-running period of about 24 h. In the gastrointestinal apparatus, the functioning of the biological clocks shows distinct patterns in the different organs. The aim of this study was to evaluate the time-related variation of clock gene expression in mouse liver and stomach, two components of the digestive system sharing vascular and autonomic supply, but performing completely different functions. The authors analyzed the periodicity by cosinor analysis and the dynamics of variation by computing the fractional variation to assess the rate of change in gene expression. Five-week-old male Balb/c mice were exposed to 2 wks of 12-h light/12-h dark cycles, then kept in complete darkness for 3 d as a continuation of the dark span of the last light-dark cycle. The authors evaluated the expression of Bmal1, Clock, Cry1, Cry2, Per1, Per2, Per3, Rev-erbα, Rev-erbβ, Npas2, Timeless, Dbp, Csnk1d, and Csnk1e by using real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in mouse liver and stomach. A significant 24-h rhythmic component was found for 10 genes in the liver (Bmal1, Clock, Cry1, Per1, Per2, Per3, Rev-erbα, Rev-erbβ, Npas2, and Dbp), and for 9 genes in the stomach (Bmal1, Cry1, Per1, Per2, Per3, Rev-erbα, Rev-erbβ, Npas2, and Dbp). In particular, Clock showed marked rhythm differences between liver and stomach, putatively due to some compensation by Npas2. The acrophase of the original values of Bmal1, Per2, Per3, Rev-erbα, Rev-erbβ, Npas2, and Dbp expression was delayed in the stomach, and the average delay expressed as mean ± SD was 14.30 ± 7.94 degrees (57.20 ± 31.78 minutes). A statistically significant difference was found in the acrophases of Bmal1 (p = .015) and Npas2 (p = .011). Fractional variations provided significant circadian rhythms for nine genes in the liver (Bmal1, Per1, Per2, Per3, Rev-erbα, Rev-erbβ, Npas2, Timeless, and Dbp), and for seven genes in the stomach (Bmal1, Clock, Per2, Rev-erbα, Npas2, Dbp, and Csnk1e). The acrophase of the fractional variations of Bmal1, Per2, Per3, Rev-erbα, Rev-erbβ, and Dbp expression was delayed in the stomach, and the average delay expressed as mean ± SD was 19.10 ± 9.39 degrees (76.40 ± 37.59 minutes). A significantly greater fractional variation was found in the liver for Clock at 06:00 h (p = .034), Per1 at 02:00 h (p = .037), and Per3 at 02:00 h (p = .029), whereas the fractional variation was greater in the stomach for Clock at 10:00 h (p = .016), and for Npas2 at 02:00 h (p = .029) and at 06:00 h (p = .044). In conclusion, liver and stomach show different phasing and dynamics of clock gene expression, which are probably related to prevailing control by different driving cues, and allow them to keep going the various metabolic pathways and diverse functional processes that they manage.

Ghrelin does not affect gastrointestinal contractility in rainbow trout and goldfish in vitro

Ghrelin has been identified in rainbow trout and goldfish, and it has been shown to regulate growth hormone release and food intake in these species as seen in mammals. The aim of this study was to investigate the functional role of ghrelin in regulation of gastrointestinal contractility in both fishes. Neither rainbow trout ghrelin nor rat ghrelin affected the contractility of gastrointestinal strips of rainbow trout. Similarly, goldfish ghrelin-17 and rat ghrelin did not cause marked contraction in the goldfish intestinal bulb. Detail examinations using the goldfish intestine revealed that human neurotensin, substance-P, goldfish neuromedine-U and carbachol showed apparent contractile activities in the intestinal strips. Electrical field stimulation (EFS, 1-20 Hz) caused a frequency-dependent contraction of the intestinal bulb. Atropine partially inhibited and tetrodotoxin abolished the EFS-induced contraction. Pretreatments with goldfish ghrelin-17 and rat ghrelin did not modify the EFS-induced contraction. The mRNAs of two types of growth hormone secretagogue receptor (GHS-R), GHS-R1a-1 and GHS-R1a-2, were detected in the goldfish intestine, and the expression level of GHS-R1a-2 was 4-times higher than that of GHS-R1a-1. The expression levels of GHS-R1a-1 and GHS-R1a-2 in four regions of the goldfish intestine (intestinal bulb, intestine-1, intestine-2 and intestine-3) were almost the same. In conclusion, ghrelin does not affect gastrointestinal contractility of the rainbow trout and goldfish, although GHSR-like receptor/GHS-R1a is expressed entire intestine. These results suggest diversity of ghrelin function in vertebrates.

Ghrelin- and serotonin-producing gastric carcinoid

We report the case of a 57-year-old woman with gastric carcinoid. The tumor was surgically removed and immunohistochemical investigation demonstrated a rare combination: ghrelin and serotonin in the cytoplasm of the tumor cells. The functional significance of simultaneous production of ghrelin and serotonin is not clear. It may be that an autocrine/paracrine interaction exists between these two different hormones.

Food motivation circuitry hypoactivation related to hedonic and nonhedonic aspects of hunger and satiety in women with active anorexia nervosa and weight-restored women with anorexia nervosa

BACKGROUND

Previous studies have provided evidence of food motivation circuitry dysfunction in individuals with anorexia nervosa. However, methodological limitations present challenges to the development of a cohesive neurobiological model of anorexia nervosa. Our goal was to investigate the neural circuitry of appetite dysregulation across states of hunger and satiety in active and weight-restored phases of anorexia nervosa using robust methodology to advance our understanding of potential neural circuitry abnormalities related to hedonic and nonhedonic state and trait.

METHODS

We scanned women with active anorexia nervosa, weight-restored women with anorexia nervosa and healthy-weight controls on a 3-T Siemens magnetic resonance scanner while they viewed images of high- and low-calorie foods and objects before (premeal) and after (postmeal) eating a 400 kcal meal.

RESULTS

We enrolled 12 women with active disease, 10 weight-restored women with anorexia nervosa and 11 controls in our study. Compared with controls, both weight-restored women and those with active disease demonstrated hypoactivity premeal in the hypothalamus, amygdala and anterior insula in response to high-calorie foods (v. objects). Postmeal, hypoactivation in the anterior insula persisted in women with active disease. Percent signal change in the anterior insula was positively correlated with food stimuli ratings and hedonic and nonhedonic appetite ratings in controls, but not women with active disease.

LIMITATIONS

Our findings are limited by a relatively small sample size, which prevented the use of an analysis of variance model and exploration of interaction effects, although our substantial effect sizes of between-group differences suggest adequate power for our statistical analysis approach. Participants taking psychotropic medications were included.

CONCLUSION

Our data provide evidence of potential state and trait hypoactivations in food motivation regions involved in the assessment of food's reward value and integration of these with interoceptive signalling of one's internal state of well-being, with important relations between brain activity and homeostatic and hedonic aspects of appetite. Our findings give novel evidence of disruption in neurobiological circuits and stress the importance of examining both state and trait characteristics in the investigation of brain phenotypes in individuals with anorexia nervosa.

A role of ghrelin in cancerogenesis

Ghrelin is a 28 amino-acid multi-functional peptide hormone, which was identified as a natural ligand of the growth hormone secretagogue receptor (GHS-R). Pituitary growth hormone-releasing activity in both animals and humans has been well documented. It has various biological functions, including regulation of appetite and body weight, control of energy homeostasis, modulation of cardiovascular and gastrointestinal system and anti-inflammatory effect. However, both ghrelin and its receptor (GHS-R) are widely distributed in various tumors, which strongly implies their role in neoplastic cell growth trough autocrine/paracrine mechanism. Multiple studies have demonstrated the role of ghrelin in cancer cells proliferation, differentiation, invasiveness and apoptosis inhibition. The ghrelin axis is more complex than it was originally thought and consist of several compounds that might interact with each other and affect ghrelin activities. Here, we provide an overview of the ghrelin and its receptor role in tumor progression.

Obesity and appetite control

Obesity is one of the major challenges to human health worldwide; however, there are currently no effective pharmacological interventions for obesity. Recent studies have improved our understanding of energy homeostasis by identifying sophisticated neurohumoral networks which convey signals between the brain and gut in order to control food intake. The hypothalamus is a key region which possesses reciprocal connections between the higher cortical centres such as reward-related limbic pathways, and the brainstem. Furthermore, the hypothalamus integrates a number of peripheral signals which modulate food intake and energy expenditure. Gut hormones, such as peptide YY, pancreatic polypeptide, glucagon-like peptide-1, oxyntomodulin, and ghrelin, are modulated by acute food ingestion. In contrast, adiposity signals such as leptin and insulin are implicated in both short- and long-term energy homeostasis. In this paper, we focus on the role of gut hormones and their related neuronal networks (the gut-brain axis) in appetite control, and their potentials as novel therapies for obesity.

Obesity and appetite control

Obesity is one of the major challenges to human health worldwide; however, there are currently no effective pharmacological interventions for obesity. Recent studies have improved our understanding of energy homeostasis by identifying sophisticated neurohumoral networks which convey signals between the brain and gut in order to control food intake. The hypothalamus is a key region which possesses reciprocal connections between the higher cortical centres such as reward-related limbic pathways, and the brainstem. Furthermore, the hypothalamus integrates a number of peripheral signals which modulate food intake and energy expenditure. Gut hormones, such as peptide YY, pancreatic polypeptide, glucagon-like peptide-1, oxyntomodulin, and ghrelin, are modulated by acute food ingestion. In contrast, adiposity signals such as leptin and insulin are implicated in both short- and long-term energy homeostasis. In this paper, we focus on the role of gut hormones and their related neuronal networks (the gut-brain axis) in appetite control, and their potentials as novel therapies for obesity.

Mapping analysis of ghrelin producing cells in the human stomach associated with chronic gastritis and early cancers

OBJECTIVE

The majority of ghrelin producing cells (GPC) are present in the fundic gland of the stomach and recognized as X/A like cells. The detailed distribution of GPC in the stomach is still unknown in healthy and pathological subjects.

METHODS

We investigated the detailed distribution of GPC in the stomach, especially in relation with chronic gastritis, using surgical specimens from 12 patients with early gastric cancer. Either the anterior or posterior half of the whole stomach, which was a counterpart of the tumor bearing side, was subjected for immunohistochemistry of ghrelin, and the number of total GPC were semi quantitatively evaluated as GPC score. GPC score was compared with the degree of chronic gastritis, serum ghrelin concentration and body weight.

RESULTS

GPC was not observed in the pyloric gland, but heterogeneously distributed in the fundic gland mainly in upper body and the greater curvature. The GPC score showed about nine-fold difference, which correlated well with the degree of chronic gastritis by Sydney score (r = -0.84, P < 0.001). The serum ghrelin concentration was basically determined by the GPC score (r = 0.75, P = 0.0047); however, the obese patients showed low serum ghrelin concentration in spite of the presence of abundant GPCs. In the low GPC score patients, serum ghrelin was constantly low regardless of their body weight.

CONCLUSIONS

GPC was inversely correlated with progression of chronic gastritis. Its quantification using immunohistochemistry of the whole stomach was useful to comprehensively evaluate ghrelin profile.

Correlations of circulating peptide YY and ghrelin with body weight, rate of weight gain, and time required to achieve the recommended daily intake in preterm infants

The objective was to elucidate the relationships between serum concentrations of the gut hormone peptide YY (PYY) and ghrelin and growth development in infants for potential application to the clinical observation index. Serum concentrations of PYY and ghrelin were measured using radioimmunoassay from samples collected at the clinic. For each patient, gestational age, birth weight, time required to return to birth weight, rate of weight gain, time required to achieve recommended daily intake (RDI) standards, time required for full-gastric feeding, duration of hospitalization, and time of administration of total parenteral nutrition were recorded. Serum PYY and ghrelin concentrations were significantly higher in the preterm group (N = 20) than in the full-term group (N = 20; P < 0.01). Within the preterm infant group, the serum concentrations of PYY and ghrelin on postnatal day (PND) 7 (ghrelin = 1485.38 ± 409.24; PYY = 812.37 ± 153.77 ng/L) were significantly higher than on PND 1 (ghrelin = 956.85 ± 223.09; PYY = 545.27 ± 204.51 ng/L) or PND 3 (ghrelin = 1108.44 ± 351.36; PYY = 628.96 ± 235.63 ng/L; P < 0.01). Both serum PYY and ghrelin concentrations were negatively correlated with body weight, and the degree of correlation varied with age. Serum ghrelin concentration correlated negatively with birth weight and positively with the time required to achieve RDI (P < 0.05). In conclusion, serum PYY and ghrelin concentrations reflect a negative energy balance, predict postnatal growth, and enable compensation. Further studies are required to elucidate the precise concentration and roles of PYY and ghrelin in newborns and to determine the usefulness of measuring these hormones in clinical practice.

Ghrelin expression in esophageal adenocarcinoma and Barrett's esophagus

AIM: To investigate the expression of Ghrelin in the esophageal mucosa of patients with esophageal adenocarcinoma and those with Barrett's esophagus (BE).

METHODS: Thirty patients with esophageal adenocarcinoma, 35 patients with BE, and 35 normal controls were enrolled in the study. The expression of Ghrelin in specimens taken from the above subjects was detected by immunohistochemistry.

RESULTS: The expression of Ghrelin in esophageal adenocarcinoma was lower than that in normal controls and patients with BE. The expression of Ghrelin in the BE group was higher than that in the control group (1.34 ± 0.51 vs 4.86 ± 0.82 vs 3.54 ± 0.79, F = 27.21, P < 0.05). In the esophageal adenocarcinoma group, the expression of Ghrelin in moderately and well differentiated specimens were higher than that in poorly differentiated specimens (Z = 4.60, P < 0.05).

CONCLUSION: The expression of Ghrelin in the esophageal adenocarcinoma is different from that in BE. The level of Ghrelin changes during the evolution of esophageal cancer. Disruption of the esophageal Ghrelin-producing mechanism may occur during esophageal carcinogenesis. There is an association between the degree of esophageal carcinoma differentiation and Ghrelin production.

Peptides and their potential role in the treatment of diabetes and obesity

It is estimated that 347 million people worldwide have diabetes and that over 1.5 billion adults worldwide are overweight. Predictions suggest these rates are increasing. Diabetes is a common complication in overweight and obese subjects, and in 2004, an estimated 3.4 million people died from consequences of high blood sugar. Thus, there is great interest in revealing the physiological systems that regulate body weight and blood sugar. Several peptidergic systems within the central nervous system and the periphery regulate energy homeostasis. A number of these systems have been investigated as potential treatments for obesity and the metabolic syndrome. However, manipulation of peptidergic systems poses many problems. This review discusses the peptidergic systems currently attracting research interest for their clinical potential to treat obesity. We consider first neuropeptides in the brain, including the orexigenic neuropeptide Y and melanin-concentrating hormone, and anorectic factors such as the melanocortins, ciliary neurotrophic factor, and neuromedin U. We subsequently discuss the utility of targeting peripheral gut peptides, including pancreatic polypeptide, peptide YY, amylin, and the gastric hormone ghrelin. Also, we analyze the evidence that these factors or drugs based on them may be therapeutically useful, while considering the disadvantages of using such peptides in a clinical context.

Importance of reward and prefrontal circuitry in hunger and satiety: Prader-Willi syndrome vs simple obesity

Background

The majority of research on obesity has focused primarily on clinical features (eating behavior, adiposity measures), or peripheral appetite-regulatory peptides (leptin, ghrelin). However, recent functional neuroimaging studies have demonstrated that some reward circuitry regions which are associated with appetite-regulatory hormones are also involved in the development and maintenance of obesity. Prader-Willi syndrome (PWS), characterized by hyperphagia and hyperghrelinemia reflecting multi-system dysfunction in inhibitory and satiety mechanisms, serves as an extreme model of genetic obesity. Simple (non-PWS) obesity (OB) represents an obesity control state.

Objective

This study investigated subcortical food motivation circuitry and prefrontal inhibitory circuitry functioning in response to food stimuli before and after eating in individuals with PWS compared with OB. We hypothesized that groups would differ in limbic regions (i.e., hypothalamus, amygdala) and prefrontal regions associated with cognitive control [i.e., dorsolateral prefrontal cortex (DLPFC), orbitofrontal cortex (OFC)] after eating.

Design and Participants

Fourteen individuals with PWS, 14 BMI- and age-matched individuals with OB, and 15 age-matched healthy-weight controls (HWC) viewed food and non-food images while undergoing functional MRI before (pre-meal) and after (post-meal) eating. Using SPM8, group contrasts were tested for hypothesized regions: hypothalamus, nucleus accumbens (NAc), amygdala, hippocampus, OFC, medial PFC, and DLPFC.

Results

Compared with OB and HWC, PWS demonstrated higher activity in reward/limbic regions (NAc, amygdala) and lower activity in hypothalamus and hippocampus, in response to food (vs. non-food) images pre-meal. Post-meal, PWS exhibited higher subcortical activation (hypothalamus, amygdala, hippocampus) compared to OB and HWC. OB showed significantly higher activity versus PWS and HWC in cortical regions (DLPFC, OFC) associated with inhibitory control.

Conclusion

In PWS compared with obesity per se, results suggest hyperactivations in subcortical reward circuitry and hypoactivations in cortical inhibitory regions after eating, which provides evidence of neural substrates associated with variable abnormal food motivation phenotypes in PWS and simple obesity.

Breastmilk ghrelin, leptin, and fat levels changing foremilk to hindmilk: is that important for self-control of feeding?

The aim of this study was to evaluate the changes in the ghrelin, leptin, and fat levels in the foremilk and hindmilk and the possible relationship between these levels with the age and growth of term healthy infants. Sixty-two babies were subdivided (according to their nutrition) into breastfed (BF), formula-fed (FF), and BF plus FF (BF + FF) groups. The total and active ghrelin and tryglyceride levels and the total cholesterol levels in the foremilk and hindmilk were studied at the first and second visits (mean of the second and fifth months, respectively). At both visits, the total and active ghrelin and the total cholesterol levels were lower in the hindmilk than in the foremilk. However, the triglyceride levels were higher in the hindmilk than in the foremilk (p < 0.001). The leptin levels were also higher in the hindmilk, but this difference was not statistically significant. At the second visit, the mean total foremilk ghrelin (p < 0.01), leptin (p < 0.05), tryglyceride (p < 0.001), and cholesterol (p < 0.01) levels in the BF group were decreased compared with the levels at the first visit, whereas the active ghrelin levels increased (p < 0.001). At the second visit, we observed a 3.5% increase in the body mass index in BF infants, a 14.6% increase in FF infants, and an 11.8% increase in BF + FF infants (p < 0.01). The foremilk leptin levels were lower in the BF + FF group than in the BF group at both visits. In conclusion, at the first and second visits, the decreased ghrelin and increased tryglyceride and leptin levels in the hindmilk might be associated with the important role of self-control when feeding BF infants. The stable content of formulas might be associated with a lack of self-control during feeding and increased nutrition. Changing the breast milk ghrelin, leptin, and fat levels between the foremilk and hindmilk and between the first and second visits might explain the differences in the weight gain patterns of BF and FF infants.

Ghrelin receptors are expressed by distal tubules of the mouse kidney

Ghrelin, a peptide hormone from the stomach, has been recently discovered to reduce sodium excretion from the kidney. Although the effects on the kidney suggest actions in the distal nephron, the sites of expression of ghrelin receptors have not been localised. In the present work we have used a mouse that expresses green fluorescent protein under the control of the ghrelin receptor promoter to locate sites of receptor expression in the kidney. Receptor expression was confined to the straight parts of the distal tubules and the thin limbs of the loops of Henle. No expression was detected in other structures, including the glomeruli, proximal tubules and collecting ducts. Ghrelin receptors were not found in extra-renal or intra-renal arteries, despite observations that ghrelin is a vasodilator. The distribution revealed by in situ hybridisation histochemistry was the same as that revealed by the reporter. In conclusion, ghrelin receptors have a restricted distribution in the kidney. The location in the straight parts of the distal tubules accords with observations that ghrelin promotes sodium retention.

Ghrelin postsynaptically depolarizes dorsal raphe neurons in rats in vitro

Ghrelin promotes growth hormone (GH) secretion and feeding. Recent studies further showed that ghrelin displayed a defending effect against the depressive-like symptoms and affected sleep in animals and humans. Serotonergic system is considered to be implicated in feeding, depression and other mood disorders, and sleep. The dorsal raphe nucleus (DRN) utilizes serotonin (5-HT) as its major neurotransmitter and expresses GH secretagogue receptors (GHS-Rs). Therefore, the present study was carried out to examine the electrophysiological effect of ghrelin on rat DRN neurons in vitro and determine the ionic mechanism involved. Whole-cell recording revealed that ghrelin depolarized DRN neurons dose-dependently in tetrodotoxin-containing artificial cerebrospinal fluid (TTX ACSF). Pretreatment with [D-Lys(3)]-GHRP-6, a selective antagonist for GHS-Rs, antagonized the ghrelin-induced depolarization. The depolarization was significantly reduced in a low-Na(+) TTX ACSF and in a high-K(+) TTX ACSF and was abolished in the combination of both ACSFs, suggesting that the ghrelin-induced depolarization is mediated by a dual ionic mechanism including an increase in nonselective cationic conductance and a decrease in K(+) conductance. The experiments on the reversal potential also supported an involvement of the dual ionic mechanism in the ghrelin-induced depolarization. On the basis of their electrophysiological and pharmacological properties, approximately 80% of DRN neurons were classified as putative 5-HT-containing neurons and ghrelin depolarized 75% of them. These results suggest that DRN neurons, especially 5-HT-containing neurons, might be involved in the neural mechanisms through which ghrelin participates in the development and/or regulation of feeding behavior, sleep-wake states and depressive-like symptoms.

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.

Impact of food restriction and cocaine on locomotion in ghrelin- and ghrelin-receptor knockout mice

Food restriction (FR) augments the behavioral and reinforcing effects of psychomotor stimulants such as cocaine or amphetamine; effects that may be related to the capacity of FR to increase plasma levels of ghrelin (GHR), a 28-amino acid orexigenenic peptide linked to activation of brain dopamine systems. The present study used wild-type (WT) mice or mutant mice sustaining knockout of either GHR [GHR((-/-)) ] or of the growth hormone secretagogue receptor [GHS-R((-/-)) ] and subjected to FR or not to evaluate the role of GHR and GHS-R in cocaine-stimulated locomotion. WT, GHR((-/-)) , and GHS-R((-/-)) mice were either restricted to 60% of baseline caloric intake or allowed to free-feed (FF). Mice were treated with 0, 1.25, 2.5 and 5.0 mg/kg cocaine on separate test days (in random dose order) and forward locomotion was recorded on each drug day for 45 minutes after drug dosing. Food (and water) was available immediately after (but not during) each activity test. For FF mice, there was no interaction between cocaine and GHR status on locomotion. FR-WT mice treated with saline exhibited significant increases in anticipatory locomotion (relative to FF-WT mice), whereas FR-GHS-R((-/-)) mice did not. Cocaine significantly increased locomotion in FR-GHR((-/-)) and FR-GHS-R((-/-)) mice to the levels noted in FR-WT mice. These results suggest that GHS-R activity, but not GHR activity, is required for FR to augment food-associated anticipatory locomotion, but do not support the contention that GHR pathways are required for the capacity of FR to augment the acute effect of cocaine on locomotion.

The glucocorticoid contribution to obesity

Obesity is fast becoming the scourge of our time. It is one of the biggest causes of death and disease in the industrialized world, and affects as many as 32% of adults and 17% of children in the USA, considered one of the world's fattest nations. It can also cost countries billions of dollars per annum in direct and indirect care, latest estimates putting the USA bill for obesity-related costs at $147 billion in 2008. It is becoming clear that the pathophysiology of obesity is vastly more complicated than the simple equation of energy in minus energy out. A combination of genetics, sex, perinatal environment and life-style factors can influence diet and energy metabolism. In this regard, psychological stress can have significant long-term impact upon the propensity to gain and maintain weight. In this review, we will discuss the ability of psychological stress and ultimately glucocorticoids (GCs) to alter appetite regulation and metabolism. We will specifically focus on (i) GC regulation of appetite and adiposity, (ii) the apparent sexual dimorphism in stress effects on obesity and (iii) the ability of early life stress to programme obesity in the long term.

Assay of ghrelin concentration in infant formulas and breast milk

AIM: To test if total ghrelin is present in infant formulas.

METHODS: Using a radioimmunoassay, we measured total ghrelin concentrations in 19 samples of commercial infant formulas and in 20 samples of human milk. We also determined ghrelin concentration in the serum of infants and lactating mothers.

RESULTS: Ghrelin concentrations were significantly higher in artificial milk (2007.1 ± 1725.36 pg/mL) than in human milk (828.17 ± 323.32 pg/mL) (P = 0.005). The mean ghrelin concentration in infant serum (n = 56) was 1115.86 ± 42.89 pg/mL, and was significantly higher (P = 0.023) in formula-fed infants (1247.93 ± 328.07 pg/mL) than in breast-fed infants (1045.7 ± 263.38 pg/mL). The mean serum ghrelin concentration (mean ± SD) in lactating mothers (n = 20) was 1319.18 ± 140.18 pg/mL.

CONCLUSION: This study provides evidence that total ghrelin is present in infant formulas. This finding raises diverse questions regarding the uptake, absorption and metabolic effects of this hormone.

Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy: understanding weight loss and improvements in type 2 diabetes after bariatric surgery

Obesity increases the likelihood of diseases like type 2 diabetes (T2D), heart disease, and cancer, and is one of the most serious public health problems of this century. In contrast to ineffectual prevention strategies, lifestyle modifications, and pharmacological therapies, bariatric surgery is a very effective treatment for morbid obesity and also markedly improves associated comorbidities like T2D. However, weight loss and resolution of T2D after bariatric surgery is heterogeneous and specific to type of bariatric procedure performed. Conventional mechanisms like intestinal malabsorption and gastric restriction do not fully explain this, and potent changes in appetite and the enteroinsular axis, as a result of anatomical reorganization and altered hormonal, neuronal, and nutrient signaling, are the portended cause. Uniquely these signaling changes appear to override vigorous homeostatic defenses of stable body weight and compelling self-gratifying motivations to eat and to reverse defects in beta-cell function and insulin sensitivity. Here we review mechanisms of weight loss and T2D resolution after Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy bariatric surgery, two markedly different procedures with robust clinical outcomes.

Factors associated with plasma ghrelin level in Japanese general population

OBJECTIVE

Ghrelin is a novel gastric peptide identified in 1999 as a 'hunger hormone'. Plasma ghrelin level is decreased in human obesity. Factors associated with ghrelin have been mainly investigated in western countries where the prevalence of obesity is high. The aim of this study is to examine factors associated with plasma ghrelin in a Japanese general population where obesity is not so common.

METHODS

Fasting ghrelin levels were measured by ELISA in 638 subjects in 2005-2007. We measured body mass index (BMI), waist circumference and blood pressure. Blood was drawn in the morning after a 12-h fast for determinations of ghrelin, lipid, glucose (FPG), insulin, estimated glomerular filtration rate (eGFR) and uric acid levels. Univariate and multiple stepwise regression analyses were performed to find out factors associated with ghrelin.

RESULTS

In our population, the mean BMI was 23·8 kg/m(2) , indicating a nonobese population. Results of univariate analysis showed that age (P<0·001), BMI (P<0·001), waist (P<0·001), triglycerides (P<0·01), FPG (P<0·01), insulin (P<0·001) and uric acid (P<0·05) were inversely associated with ghrelin. High-density lipoprotein (HDL) cholesterol (P<0·001) and eGFR (P<0·05) were positively associated with ghrelin. Men had lower ghrelin levels than women (P<0·001). Results of the multiple stepwise regression analysis revealed that age (P<0·001; inversely), female gender (P<0·001), insulin (P<0·001; inversely), HDL cholesterol (P=0·005), BMI (P=0·01; inversely) and uric acid (P=0·045; inversely) were significantly and independently associated with ghrelin.

CONCLUSIONS

The present study demonstrated that age and gender affected plasma ghrelin levels more than BMI. This may well be because of the low prevalence of overweight in our population.

Vitamins B status and antioxidative defense in patients with chronic hepatitis B or hepatitis C virus infection

BACKGROUND & AIMS

The impact of hepatitis B virus (HBV) or hepatitis C virus (HCV) infection upon B vitamins status and antioxidative defense in infected patients was examined.

METHODS

Dietary record and blood levels of B vitamins and oxidative stress-associated biomarkers were determined for 195 healthy controls, 132 HBV, and 114 HCV patients.

RESULTS

HBV-infected patients had significantly higher levels of total cholesterol, free fatty acids (FFA), and lower ghrelin level (p < 0.05); and HCV-infected patients had significantly higher Ishak inflammation score and lactate dehydrogenase activity (p < 0.05). HBV patients had significantly lower red blood cell (RBC) vitamins B(2) and B(6) levels, and HCV infection significantly decreased vitamins B(2,) B(6) and folate levels in RBC and/or plasma (p < 0.05). Correlation coefficients of RBC vitamin B(2) versus serum FFA in HBV patients, RBC vitamins B(2) and B(6) versus HCV RNA and Ishak inflammation score, and plasma vitamin B(6) vs Ishak inflammation score in HCV patients were <-0.5. HBV-infected patients had significantly higher oxidized glutathione level and lower glutathione peroxidase activity (p < 0.05), but HCV patients had significantly lower superoxide dismutase and catalase activities (p < 0.05).

CONCLUSION

HBV or HCV infection enhanced oxidative stress and lowered B vitamins in circulation. In order to avoid other healthy risk, nutrition status should be monitored and limitation or supplementation of certain nutrients might be helpful for HBV- or HCV-infected patients.

Current and potential roles of ghrelin in clinical practice

Ghrelin is a novel GH-releasing peptide, which has been identified as an endogenous ligand for GH-secretagogue receptor. Ghrelin is mainly secreted by the stomach and plays a critical role in a variety of physiological processes including endocrine, metabolic, cardiovascular, immunological, and other actions. Ghrelin stimulates food intake via hypothalamic neurons and causes a positive energy balance and body weight gain by decreasing fat utilization and promoting adiposity. Given the multiple effects of ghrelin, its potential clinical applications have been evaluated in various conditions. Preliminary trials have shown that it may prove valuable in the management of disease-induced cachexia. Ghrelin may improve the wasting syndrome through GH-dependent or GH-independent effects. Moreover, ghrelin may play a role in the management of disorders of gut motility and obesity. Finally, other potential clinical applications of ghrelin include the treatment of patients with diabetes mellitus, infections, rheumatological diseases or GH deficiency and the diagnosis of this hormonal disorder.

Identification and characterization of acyl-protein thioesterase 1/lysophospholipase I as a ghrelin deacylation/lysophospholipid hydrolyzing enzyme in fetal bovine serum and conditioned medium

Ghrelin contains an octanoic acid at the third residue serine, and the presence of octanoic acid on ghrelin is critical to its physiological functions. The precise mechanism for the deacylation of ghrelin in circulation remains to be clarified, although the level of deacylated ghrelin (des-acyl ghrelin) is higher than that of acylated ghrelin in serum. In this study, rapid identification of ghrelin deacylation activity was achieved by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and a ghrelin deacylation enzyme was purified 1515-fold from fetal bovine serum. Chromatographic separation showed a 24-kDa band on SDS-PAGE corresponding to ghrelin deacylation activity, and the protein band was identified as acyl-protein thioesterase 1 (APT1)/lysophospholipase I. A ghrelin deacylation enzyme in medium from HepG2 cells was also purified and identified as APT1. Although it lacks a secretion signal sequence, APT1 may be released by cells expressing APT1, mainly from liver in vivo. APT1 was originally purified as a cytosolic lysophospholipid hydrolyzing enzyme (lysophospholipase I), and recombinant APT1 exhibited deacylation activity as well as lysophospholipase activity in vitro. APT1 is released at high levels from RAW264.7 macrophage-like cells into the culture medium after stimulation with lipopolysaccharide (LPS), and LPS suppresses APT1 mRNA and protein expressions in these cells. More potent ghrelin deacylase activities were detected in sera from LPS-treated rats than in control sera. These results suggested that the serum activity of APT1 may play an important role in determination of the concentration of des-acyl ghrelin in circulation, especially under septic inflammation.

Molecular mechanistic associations of human diseases

Background

The study of relationships between human diseases provides new possibilities for biomedical research. Recent achievements on human genetic diseases have stimulated interest to derive methods to identify disease associations in order to gain further insight into the network of human diseases and to predict disease genes.

Results

Using about 10000 manually collected causal disease/gene associations, we developed a statistical approach to infer meaningful associations between human morbidities. The derived method clustered cardiometabolic and endocrine disorders, immune system-related diseases, solid tissue neoplasms and neurodegenerative pathologies into prominent disease groups. Analysis of biological functions confirmed characteristic features of corresponding disease clusters. Inference of disease associations was further employed as a starting point for prediction of disease genes. Efforts were made to underpin the validity of results by relevant literature evidence. Interestingly, many inferred disease relationships correspond to known clinical associations and comorbidities, and several predicted disease genes were subjects of therapeutic target research.

Conclusions

Causal molecular mechanisms present a unifying principle to derive methods for disease classification, analysis of clinical disorder associations, and prediction of disease genes. According to the definition of causal disease genes applied in this study, these results are not restricted to genetic disease/gene relationships. This may be particularly useful for the study of long-term or chronic illnesses, where pathological derangement due to environmental or as part of sequel conditions is of importance and may not be fully explained by genetic background.

Adipokines in breast milk and preterm infants

Studies have shown that the early life environment affects feeding behaviour, food intake and energy balance in later life, suggesting there is a link between foetal and infant growth and the risk of metabolic disorders in adulthood. Although there is an evident epidemiological association between low birth weight and adult-onset diseases, the incidence of metabolic diseases in adulthood among people who were born prematurely is still unknown. Considerable advances have been made during the last years in the scientific knowledge of the benefits of early nutrition, such as breastfeeding, on health and well-being later in life. Nutritional researchers have focussed their attention on the biological characteristics of human breast milk, which represents the main source of nutrients in the first months of life for breastfed infants. Recently, leptin and ghrelin have been detected in the breast milk of mothers of term and preterm infants. Adiponectin and resistin, present in term human milk, have not been investigated in the breast milk of mothers of preterm infants. These hormones are involved in the regulation of energy balance and may have a role in the regulation of growth and development in the neonatal period and infancy, as well as long-term effects on metabolic programming. Leptin, adiponectin and resistin have been found at lower levels in pre-term infants compared with term newborns, whereas there seems to be no difference in ghrelin levels. Future research is necessary to clarify the role of hormones present in breast milk for identifying potential short- and long-term effects of breastfeeding on the health of children born prematurely.

Altered metabolic and neurochemical responses to chronic unpredictable stressors in ghrelin receptor-deficient mice

Ghrelin, a hormone produced by the stomach, is generally associated with feeding responses and the regulation of food intake. Recent evidence, however, suggests that ghrelin is also a stress hormone, given that it is released following acute and chronic stressors. The present study examined the role of ghrelin in producing normal metabolic and neurochemical responses to chronic stress. This was achieved by examining these responses in mice with targeted deletions of the ghrelin receptor gene (GHSR KO mice), and comparing them with the same responses in their wild-type (WT) littermates. As expected, WT stressed mice decreased their caloric intake, body weight gain and caloric efficiency while maintaining adiposity. GHSR KO mice, however, did not show these alterations despite having normal glucocorticoid responses to stress. In parallel with these changes, chronic unpredictable stress caused changes in norepinephrine, dopamine and serotonin in a number of brain regions. Of these, norepinephrine neurotransmission in the arcuate nucleus and prefrontal cortex was differentially altered in GHSR KO mice. Within the nucleus acumbens, dopamine utilization was increased in WT mice but not in GHSR KO mice. Finally, there were strain differences in serotonin neurotransmission that may explain interstrain body weight and adiposity differences. These results suggest that the metabolic changes necessary to deal with the energetic challenge presented by repeated exposure to stressors do not occur in GHSR KO mice, and they are discussed within the context of the potential vulnerability to stress-induced pathology.

Involvement of endothelin B receptors in the endothelin-3-induced increase of ghrelin and growth hormone in Holstein steers

The present study was designed to determine the dose-dependent effects of endothelin-3 (ET-3) on the secretion of ghrelin and growth hormone (GH) and characterize the receptors involved in these effects. Eight Holstein steers were randomly assigned to receive intravenous bolus injections of vehicle (0.1% bovine serum albumin in saline), bovine ET-3 (0.1, 0.4, 0.7 and 1.0microg/kg), IRL1620 (selective ET(B) receptor agonist, 2.0microg/kg), [d-Lys(3)]-GHRP-6 (GH secretagogue receptor type 1a [GHS-R1a] antagonist, 20.0microg/kg) and bovine ET-3 (1.0microg/kg) combined with [d-Lys(3)]-GHRP-6 (20.0microg/kg), respectively. Blood samples were collected at -30, -15, 0, 5, 10, 15, 20, 25, 30, 35, 40, 50 and 60min relative to injection time. Concentrations of acyl ghrelin, total ghrelin (acyl and des-acyl ghrelin) and GH in plasma were analyzed by a double antibody radioimmunoassay system. Concentrations of acyl and total ghrelin were significantly increased by ET-3 in a dose-dependent manner. Concentrations of GH were markedly elevated by administration of 0.4, 0.7 and 1.0microg/kg of ET-3, and the effect of 0.7microg/kg was greater than that of 1.0microg/kg. The minimum effective dose of ET-3 in the secretion of ghrelin and GH was 0.4microg/kg. IRL 1620 mimicked the effects of ET-3 on the secretion of ghrelin and GH in plasma. ET-3-induced elevation of plasma GH was blocked by [d-Lys(3)]-GHRP-6. These results indicate that ET-3 dose-dependently stimulates ghrelin release, and ET(B) receptors involve in these processes. Moreover, this study shows that endogenous ghrelin response to ET-3 increases GH secretion through GHS-R1a.

Ghrelin: a potential therapeutic target for cancer

Ghrelin is a recently identified 28-amino-acid peptide, capable of stimulating pituitary growth hormone release in humans and other mammals. It is mainly secreted from the gastric mucosa, but it is also widely expressed in a variety of tissues, in both normal and malignant conditions. Ghrelin has a multiplicity of physiological functions in gastrointestinal, cardiovascular, pulmonary and immune system, and also exerts a variety of roles, from increasing food intake (orexigenic effect) to affecting cell proliferation. The actions of ghrelin are mediated by the ghrelin receptor, also known as the growth hormone secretagogue receptor (GHS-R). The purpose of this review is to provide an overview of the expression and putative role of ghrelin and its receptor in cancer. Ghrelin and its receptor are detected in tumor tissues, and evidence is emerging that ghrelin plays an autocrine/paracrine role in cancer and could serve as a diagnostic or prognostic tool or as therapeutic target.

The ghrelin-positive cells number is increased in duodenum in children with celiac disease

Ghrelin is predominately produced in the stomach, but new findings indicate that the intestinal wall is an important source of the hormone. In patients with shortbowel syndrome, reduction in the intestinal tissue resulted in a decrease in the circulating ghrelin levels. Since in celiac disease (CD) intestinal mucosa atrophy is the main finding, alterations in duodenal ghrelin-positive cell population can be expected. The aim of the study was to evaluate the density of ghrelin-positive cells in the duodenum of CD children and its relationship with body mass index (BMI) and clinical presentation. The study included 31 consecutive patients with newly diagnosed CD [BMI SD scores (BMISDS) -0.926+/-1.496]. The control group consisted of 21 children (BMISDS -0.517+/-1.186], diagnosed with growth retardation, anemia or abdominal pain. All the patients underwent endoscopy with biopsy samples taken from distal duodenum. Immunohistochemistry was performed using rabbit anti- ghrelin (human) antiserum. The number of ghrelin-positive cells in the duodenum was significantly higher in children with CD than in controls (14.82+/-11.12 vs 5.69+/-5.02, p<0.0013). The density of ghrelin-positive cells in the duodenum did not correlate with age, pubertal status, BMISDS or clinical presentation. In the duodenum of CD children, the number of ghrelin-positive cells is increased compared with the control patients. The population of ghrelin-positive cells in the duodenum does not simply reflect an altered mucosal morphology or failure to thrive but is under the influence of other conditions.

Ghrelin stimulation of growth hormone-releasing hormone neurons is direct in the arcuate nucleus

Background

Ghrelin targets the arcuate nucleus, from where growth hormone releasing hormone (GHRH) neurones trigger GH secretion. This hypothalamic nucleus also contains neuropeptide Y (NPY) neurons which play a master role in the effect of ghrelin on feeding. Interestingly, connections between NPY and GHRH neurons have been reported, leading to the hypothesis that the GH axis and the feeding circuits might be co-regulated by ghrelin.

Principal Findings

Here, we show that ghrelin stimulates the firing rate of identified GHRH neurons, in transgenic GHRH-GFP mice. This stimulation is prevented by growth hormone secretagogue receptor-1 antagonism as well as by U-73122, a phospholipase C inhibitor and by calcium channels blockers. The effect of ghrelin does not require synaptic transmission, as it is not antagonized by γ-aminobutyric acid, glutamate and NPY receptor antagonists. In addition, this hypothalamic effect of ghrelin is independent of somatostatin, the inhibitor of the GH axis, since it is also found in somatostatin knockout mice. Indeed, ghrelin does not modify synaptic currents of GHRH neurons. However, ghrelin exerts a strong and direct depolarizing effect on GHRH neurons, which supports their increased firing rate.

Conclusion

Thus, GHRH neurons are a specific target for ghrelin within the brain, and not activated secondary to altered activity in feeding circuits. These results support the view that ghrelin related therapeutic approaches could be directed separately towards GH deficiency or feeding disorders.

Endogenous ghrelin released in response to endothelin stimulates growth hormone secretion in cattle

The purpose of this study was to evaluate whether circulating ghrelin and growth hormone (GH) concentrations in cattle are regulated by endothelin-1 (ET-1), endothelin-3 (ET-3), and secretin. Six Holstein steers (242+/-1 d old, 280.5+/-4.4 kg body weight [BW]; mean+/-SEM) were allocated randomly in an incomplete Latin square design to receive each of 4 treatment compounds (vehicle, ET-1, ET-3, and secretin) with 1-d intervals between successive treatments. The treatment compounds were injected intravenously via a catheter inserted into the external jugular vein of each steer. Blood was sampled from the indwelling catheter at -30, -15, 0, 5, 10, 15, 20, 30, 45, 60, 90, 120, 150, and 180 min. Plasma ghrelin and GH responses to the treatment compounds were measured by a double-antibody radioimmunoassay system. Data were analyzed by using a MIXED procedure of SAS, version 9.1. Plasma acyl ghrelin, total ghrelin, and GH concentrations were increased by both ET-1 and ET-3 injection (ET-1 injection: 311+/-15 pg/mL vs 245+/-15 pg/mL, 2.4+/-0.2 ng/mL vs 1.61+/-0.05 ng/mL, 4.73+/-0.92 ng/mL vs 1.17+/-0.09 ng/mL for acyl ghrelin, total ghrelin, and GH, respectively; ET-3 injection: 337+/-27 pg/mL vs 245+/-15 pg/mL, 2.6+/-0.1 ng/mL vs 1.61+/-0.05 ng/mL, 5.56+/-0.97 ng/mL vs 1.17+/-0.09 ng/mL for acyl ghrelin, total ghrelin, and GH, respectively; P<0.01). Ghrelin and GH concentrations were not changed by secretin injection throughout the experimental periods. These results indicate that ET-1 and ET-3 stimulate ghrelin and GH secretion in cattle and demonstrate for the first time that endogenous ghrelin released in response to endothelin injection stimulates GH secretion in vivo in cattle.

Ghrelin-like peptide with fatty acid modification and O-glycosylation in the red stingray, Dasyatis akajei

Background

Ghrelin (GRLN) is now known to be an appetite-stimulating and growth hormone (GH)-releasing peptide that is predominantly synthesized and secreted from the stomachs of various vertebrate species from fish to mammals. Here, we report a GRLN-like peptide (GRLN-LP) in a cartilaginous fish, the red stingray, Dasyatis akajei.

Results

The purified peptide contains 16 amino acids (GVSFHPQPRS¹⁰TSKPSA), and the serine residue at position 3 is modified by n-octanoic acid. The modification is the characteristic of GRLN. The six N-terminal amino acid residues (GVSFHP) were identical to another elasmobranch shark GRLN-LP that was recently identified although it had low identity with other GRLN peptides. Therefore, we designated this peptide stingray GRLN-LP. Uniquely, stingray GRLN-LP was O-glycosylated with mucin-type glycan chains [N-acetyl hexosamine (HexNAc)₃ hexose(Hex)₂] at threonine at position 11 (Thr-11) or both serine at position 10 (Ser-10) and Thr-11. Removal of the glycan structure by O-glycanase made the in vitro activity of stingray GRLN-LP decreased when it was evaluated by the increase in intracellular Ca²⁺ concentrations using a rat GHS-R1a-expressing cell line, suggesting that the glycan structure plays an important role for maintaining the activity of stingray GRLN-LP.

Conclusions

This study reveals the structural diversity of GRLN and GRLN-LP in vertebrates.

Electrophysiological effects of ghrelin on laterodorsal tegmental neurons in rats: an in vitro study

Ghrelin, a gut and brain peptide, is a potent stimulant for growth hormone (GH) secretion and feeding. Recent studies further show a critical role of ghrelin in the regulation of sleep-wakefulness. Laterodorsal tegmental nucleus (LDT), that regulates waking and rapid eye movement (REM) sleep, expresses GH secretagogue receptors (GHS-Rs). Thus, the present study was carried out to examine electrophysiological effects of ghrelin on LDT neurons using rat brainstem slices, and to determine the ionic mechanism involved. Whole cell recording revealed that ghrelin depolarizes LDT neurons dose-dependently in normal artificial cerebrospinal fluid (ACSF). The depolarization persisted in tetrodotoxin-containing ACSF (TTX ACSF), and is partially blocked by the application of [D-Lys3]-GHRP-6, a selective antagonist for GHS-Rs. Membrane resistance during the ghrelin-induced depolarization increased by about 18% than that before the depolarization. In addition, the ghrelin-induced depolarization was drastically reduced in high-K+ TTX ACSF with a K+ concentration of 13.25 mM. Reversal potentials obtained from I-V curves before and during the depolarization were about -83 mV, close to the equilibrium potential of the K+ channel. Most of the LDT neurons recorded were characterized by an A-current or both the A-current and a low threshold Ca2+ spike, and they were predominantly cholinergic. These results indicate that ghrelin depolarizes LDT neurons postsynaptically and dose-dependently via GHS-Rs, and that the ionic mechanisms underlying the ghrelin-induced depolarization include a decrease of K+ conductance. The results also suggest that LDT neurons are implicated in the cellular processes through which ghrelin participates in the regulation of sleep-wakefulness.

Cognitive enhancing effects of ghrelin receptor agonists

RATIONALE

Ghrelin, the endogenous ligand for the growth hormone secretagogue receptor, has been shown to play a role in multiple physiological processes including appetite regulation, metabolism and, more recently, dendritic spine architecture, long-term potentiation and cognition.

OBJECTIVE

The objective of this study was to determine the effects of two structurally non-peptide ghrelin receptor agonists (GSK894490A and CP-464709-18) on rodent cognition.

METHODS

All experiments were performed in male Lister hooded rats. Effects of the test compounds on rat cognitive performance was determined using the novel object recognition test, a modified water maze paradigm and a scopolamine-induced deficit in cued fear conditioning. These tests were chosen as they each probe a relatively independent cognitive domain and therefore potentially have differing underlying neural substrates.

RESULTS

Both compounds significantly improved performance in the novel object recognition and modified water maze tests but were unable to attenuate a scopolamine deficit in cued fear conditioning.

CONCLUSIONS

These results demonstrate that the small-molecule ghrelin receptor agonists profiled here readily cross the blood/brain barrier and elicit pro-cognitive effects in recognition and spatial learning and memory tests. Based on these observations, the central ghrelin receptor would appear to be a chemically tractable receptor and perhaps should be considered as a new drug target for therapeutic approaches to treat diseases affecting cognition.