Effects of ghrelin on food caching behaviour and body composition in black-capped chickadees (Poecile atricapillus)

Several metabolic hormones signal an organism's energy balance to the brain and modulate feeding behaviours accordingly. These metabolic signals may also regulate other behaviour related to energy balance, such as food caching or hoarding. Ghrelin is one such hormone, but it appears to exert different effects on appetite and fat levels in birds and mammals. Ghrelin treatment inhibits food intake and decreases fat stores in some bird species, but these effects may differ between acylated and unacylated (des-acyl) forms of ghrelin. The effect of ghrelin on food caching in birds has been examined in only one study, that found both leptin and unacylated ghrelin reduced food caching and mass gain in coal tits (Periparus ater). We expanded on this to test how both forms of ghrelin affect food caching and body composition in black-capped chickadees (Poecile atricapillus). We injected each bird with acylated ghrelin, unacylated ghrelin, and a saline control and then measured food caching every 20 min for two hours post-injection. We also measured body mass fat levels the day before, and after treatment using quantitative magnetic resonance (QMR). Contrary to prior work, we found no effects of either form of ghrelin on food caching, or body or fat mass. Future work is required to determine if the difference between our results and those of the prior study stems from species differences in response to ghrelin and/or in the motivation to cache food, or ghrelin effects being modulated by energy reserves.

Low- and high-load resistance training exercise to volitional fatigue generate exercise-induced appetite suppression

Research on exercise-induced appetite suppression often does not include resistance training (RT) exercise and only compared matched volumes.

PURPOSE

To compare the effects of low-load and high-load RT exercise completed to volitional fatigue on appetite-regulation.

METHODS

11 resistance-trained males (24 ± 2 y) completed 3 sessions in a crossover experimental design: 1) control (CTRL); 2) RT exercise at 30% 1-repetition maximum (RM); and 3) RT exercise at 90% 1-RM. RT sessions consisted of 3 sets of 5 exercises completed to volitional fatigue. Acylated ghrelin, active glucagon-like peptide-1 (GLP-1), active peptide tyrosine (PYY), lactate, and subjective appetite perceptions were measured pre-exercise, 0-, 60-, and 120-min post-exercise. Energy intake was recorded the day before, of, and after each session.

RESULTS

Lactate was elevated following both 30% (0-, 60-, 120-min post-exercise) and 90% (0-, 60-min post-exercise; P < 0.001, d > 3.92) versus CTRL, with 30% greater than 90% (0-min post-exercise; P = 0.011, d = 1.14). Acylated ghrelin was suppressed by 30% (P < 0.007, d > 1.22) and 90% (P < 0.028, d > 0.096) post-exercise versus CTRL, and 30% suppressed concentrations versus 90% (60-min post-exercise; P = 0.032, d = 0.95). There was no effect on PYY (P > 0.171, ηp2 <0.149) though GLP-1 was greater at 60-min post-exercise in 90% (P = 0.052, d = 0.86) versus CTRL. Overall appetite was suppressed 0-min post-exercise following 30% and 90% versus CTRL (P < 0.013, d > 1.10) with no other differences (P > 0.279, d < 0.56). There were no differences in energy intake (P > 0.101, ηp2 <0.319).

CONCLUSIONS

RT at low- and high-loads to volitional fatigue induced appetite suppression coinciding with changes in acylated ghrelin though limited effects on anorexigenic hormones or free-living energy intake were present.

Octanoic acid-rich enteral nutrition attenuated hypercatabolism through the acylated ghrelin-POMC pathway in endotoxemic rats

OBJECTIVES

Metabolic disorders and no response to intravenous nutrition because of sepsis have been urgent problems for clinical nutrition support. Enteral nutrition (EN) has been an important clinical therapeutic measure in septic patients; however, simple EN has not demonstrated good performance. This study aimed to investigate the effects of different concentrations of octanoic acid (OA)-rich EN on hypercatabolism in endotoxemic rats and test whether OA-rich EN could attenuate hypercatabolism through the acylated ghrelin-proopiomelanocortin (POMC) pathway.

METHODS

Rats were randomly divided into six groups: sham, lipopolysaccharide (LPS), LPS + EN and LPS + EN + OA (0.25, 0.5, and 1 g/kg, respectively) groups to investigate the effects of different concentrations of OA-rich EN on hypercatabolism in endotoxemic rats. The rats were then randomly divided into four groups: sham, LPS, LPS + OA, and LPS + OA + Go-CoA-Tat, to test whether OA-rich EN attenuated hypercatabolism through the acylated ghrelin-POMC pathway. Rats received nutrition support via a gastric tube for 3 d (100 kcal/kg daily). Insulin resistance, muscle protein synthesis and atrophy, inflammatory cytokines, ghrelin in circulation and hypothalamus, ghrelin O-acyltransferase (GOAT), and the adenosine 5'-monophosphate-activated protein kinase (AMPK)-autophagy-POMC pathway were measured.

RESULTS

Compared with simple EN, OA-rich EN promoted the acylation of ghrelin in a dose-dependent manner and attenuated POMC-mediated hypercatabolism in endotoxemic rats. Inhibition of GOAT activity decreased the level of acylated ghrelin and aggravated POMC-mediated hypercatabolism conferred by OA-rich EN.

CONCLUSIONS

OA-rich EN could increase the level of acylated ghrelin and attenuate hypercatabolism through the acylated ghrelin-POMC pathway compared with simple EN in endotoxemic rats.

Acylated ghrelin suppresses doxorubicin-induced testicular damage and improves sperm parameters in rats via activation of Nrf2 and mammalian target of rapamycin

Background

Exogenous administration of acylated ghrelin (AG) afforded reproductive protective effect in several animal models but not in those treated with doxorubicin (DOX). This study evaluated the protective effect of AG against DOX-induced testicular damage and impairment in sperm parameters in rats and examined the potential mechanisms of action.

Materials and Methods

Adult male rats were divided into five groups (n = 8/each) as control, control + AG (40 nmol/kg/day; subcutaneous), DOX (10 mg/kg/day 1; intraperitoneal [i.p.]), DOX + AG, and DOX + AG + brusatol (an Nrf2 inhibitor) (2 mg/kg/every 3 days; i.p.). The treatment regimen continued for 65 days.

Results

AG prevented testicular damage and apoptosis; increased sperm count, motility, and viability; and reduced the number of abnormal sperms. It also increased their circulatory levels of AG, des-acylated ghrelin (DAG), and AG/DAG ratio and the testicular mRNA levels of ghrelin and growth hormone secretagogue receptor 1a Concomitantly, AG increased serum and testicular testosterone levels, reduced serum levels of the follicle-stimulating hormone and luteinizing hormone, and upregulated the testicular protein levels of the steroidogenic acute regulatory protein and 3β-hydroxysteroid dehydrogenase in DOX-treated rats. In the testes of the control and DOX-treated rats, AG increased the phosphorylation of mammalian target of rapamycin and stimulated the levels of glutathione and superoxide dismutase, as well as the nuclear activation of Nrf2. All these effects were completely prevented by co-treatment with brusatol.

Conclusion

AG replacement therapy could be a novel strategy to prevent reproductive toxicity in cancer patients.

Acyl ghrelin improves cardiac function in heart failure and increases fractional shortening in cardiomyocytes without calcium mobilization

BACKGROUND AND AIMS

Ghrelin is an endogenous appetite-stimulating peptide hormone with potential cardiovascular benefits. Effects of acylated (activated) ghrelin were assessed in patients with heart failure and reduced ejection fraction (HFrEF) and in ex vivo mouse cardiomyocytes.

METHODS AND RESULTS

In a randomized placebo-controlled double-blind trial, 31 patients with chronic HFrEF were randomized to synthetic human acyl ghrelin (0.1 µg/kg/min) or placebo intravenously over 120 min. The primary outcome was change in cardiac output (CO). Isolated mouse cardiomyocytes were treated with acyl ghrelin and fractional shortening and calcium transients were assessed. Acyl ghrelin but not placebo increased cardiac output (acyl ghrelin: 4.08 ± 1.15 to 5.23 ± 1.98 L/min; placebo: 4.26 ± 1.23 to 4.11 ± 1.99 L/min, P < 0.001). Acyl ghrelin caused a significant increase in stroke volume and nominal increases in left ventricular ejection fraction and segmental longitudinal strain and tricuspid annular plane systolic excursion. There were no effects on blood pressure, arrhythmias, or ischaemia. Heart rate decreased nominally (acyl ghrelin: 71 ± 11 to 67 ± 11  b.p.m.; placebo 69 ± 8 to 68 ± 10  b.p.m.). In cardiomyocytes, acyl ghrelin increased fractional shortening, did not affect cellular Ca2+ transients, and reduced troponin I phosphorylation. The increase in fractional shortening and reduction in troponin I phosphorylation was blocked by the acyl ghrelin antagonist D-Lys 3.

CONCLUSION

In patients with HFrEF, acyl ghrelin increased cardiac output without causing hypotension, tachycardia, arrhythmia, or ischaemia. In isolated cardiomyocytes, acyl ghrelin increased contractility independently of preload and afterload and without Ca2+ mobilization, which may explain the lack of clinical side effects. Ghrelin treatment should be explored in additional randomized trials.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05277415.

Breaking up sitting with short frequent or long infrequent physical activity breaks does not lead to compensatory changes in appetite, appetite-regulating hormones or energy intake

The aim of this study was to determine the appetite-related responses to breaking up prolonged sitting with physical activity bouts differing in frequency and duration among adult females. Fourteen sedentary females aged 34 ± 13 years with a body mass index of 27.1 ± 6.3 kg/m2 (mean ± SD) took part in a randomised crossover trial with three, 7.5 h conditions: (1) uninterrupted sitting (SIT), (2) sitting with short frequent 2-min moderate-intensity walking breaks every 30 min (SHORT-BREAKS), and (3) sitting with longer duration, less frequent 10-min moderate-intensity walking breaks every 170-180 min (LONG-BREAKS). The intensity and total duration of physical activity was matched between the SHORT-BREAKS and LONG-BREAKS conditions. Linear mixed models were used to compare the outcomes between conditions with significance being accepted as p ≤ 0.05. There were no significant between-condition differences in hunger, satisfaction, prospective food consumption or overall appetite area under the curve (AUC) (all p ≥ 0.801). Absolute ad libitum energy intake and relative energy intake (REI) did not differ significantly between conditions (all p ≥ 0.420). Acylated ghrelin and total peptide YY incremental and total AUC did not differ significantly between conditions (all p ≥ 0.388). Yet, there was a medium effect size for the higher acylated ghrelin incremental AUC in SHORT-BREAKS versus SIT (d = 0.61); the reverse was seen for total AUC, which was lower in SHORT-BREAKS versus SIT (d = 0.69). These findings suggest that breaking up sitting does not lead to compensatory changes in appetite, appetite hormones or energy intake regardless of physical activity bout duration and frequency among adult females.

Does butyrylcholinesterase mediate exercise-induced and meal-induced suppression in acylated ghrelin?

Ample evidence supports the notion that an acute bout of aerobic exercise and meal consumption reduces acylated ghrelin concentration. However, the mechanisms by which this exercise- and meal-induced suppression of acylated ghrelin occurs in humans is unknown. This study aimed to examine the concentration of butyrylcholinesterase (BChE), an enzyme responsible for hydrolysing ghrelin and other appetite-related hormones in response to a single bout of running and a standardised meal in young, healthy men. Thirty-three men (aged 23 ± 2 years, mean ± standard deviation) underwent two (exercise and meal conditions) 2-h laboratory-based experiments. In the exercise condition, all participants ran for 30 min at 70% of the maximum oxygen uptake (0930-1000) and rested until 1130. In the meal condition, participants reported to the laboratory at 0930 and rested until 1000. Subsequently, they consumed a standardised meal (1000-1015) and rested until 1130. Blood samples were collected at baseline (0930), 1000, 1030, 1100 and 1130. BChE concentration was not altered in both the exercise and meal conditions (p > 0.05). However, acylated ghrelin was suppressed after exercise (p < 0.05) and meal consumption (p < 0.05). There was no association between the change in BChE concentration and the change in acylated ghrelin before and after exercise (p = 0.571). Although des-acylated ghrelin concentration did not change during exercise (p > 0.05), it decreased after meal consumption (p < 0.05). These findings suggest that BChE may not be involved in the suppression of acylated ghrelin after exercise and meal consumption.

A Randomized Trial of the Effect of a GnRH Analogue Injection on Ghrelin Levels in Girls

INTRODUCTION

Ghrelin concentrations decline during puberty by an unclear mechanism. Acylated ghrelin (AG) is unstable in sampling tubes, but no standardized sampling protocol exists. We hypothesized that ghrelin levels decrease as a consequence of increased gonadotropin-releasing hormone (GnRH) signalling and that the addition of a protease inhibitor to sampling tubes preserves the AG levels.

METHODS

In this randomized, placebo-controlled, cross-over study, 13 girls with suspected central precocious puberty were included. They performed an adjusted GnRH stimulation test twice and were given Relefact LHRH® (100 μg/m2) or saline in a randomized order. Blood was sampled repeatedly for 150 min for the analysis of hormone concentrations. Oestradiol levels were only measured at baseline. The protease inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF) was added to the sampling tubes. Specific ELISA kits were used for the analysis of AG and desacylated ghrelin (DAG) levels.

RESULTS

Neither AG nor DAG levels changed after GnRH analogue injection in comparison to saline. The addition of AEBSF preserved AG levels (650.1 ± 257.1 vs. 247.6 ± 123.4 pg/mL, p < 0.001) and decreased DAG levels (51.9 [12.5-115.7] vs. 143.5 [71.4-285.7] pg/mL, p < 0.001). Both AG and DAG levels were inversely associated with insulin levels (r = -0.73, p = 0.005, and r = -0.78, p = 0.002, respectively). AG levels were inversely associated with oestradiol levels (rho = -0.57, p = 0.041).

CONCLUSION

Ghrelin levels do not decrease following a pharmacological dose of a GnRH analogue in the short term in girls. Addition of a protease inhibitor to the sampling tubes decreases AG degradation, resulting in preserved AG and decreased DAG levels.

Decreased acylated and total ghrelin levels in bipolar disorder patients recovering from a manic episode

BACKGROUND

To date, only few studies have investigated ghrelin levels in bipolar disorders, and all have exclusively measured acylated ghrelin, with none investigating total ghrelin (acylated and des-acylated). We aimed to investigate peripheral levels of acylated and total ghrelin in subjects experiencing a manic episode of bipolar disorder.

METHODS

Peripheral levels of acylated and total ghrelin were measured in hospitalised medicated individuals recovering from a manic episode. Enzyme-linked immunosorbent assays (ELISA) were used to measure ghrelin levels in patients and compared with healthy controls. The relationship between ghrelin levels in bipolar disorder, self-reported hunger measures, demographic and clinical parameters was investigated with correlational analyses.

RESULTS

Twenty-four subjects (15 males, 9 females) recovering from mania and 27 matched healthy controls (13 males, 14 females) were recruited for the study. Mean values of both acylated (187 vs.520 pg/mL) and total ghrelin (396 vs. 648 pg/mL) were significantly reduced in bipolar disorder (p = 0.001). Ghrelin levels correlated positively with markers of illness severity and negatively with prescribed mood stabilizers, second-generation antipsychotics, weight and body mass index.

CONCLUSION

Peripheral measurements of acylated and total ghrelin were both reduced in bipolar disorder patients compared to healthy controls. Whilst illness severity promotes higher ghrelin levels, pharmacological treatment and weight gain exercise the opposite effect.

Is ghrelin a biomarker of early-onset scoliosis in children with Prader-Willi syndrome?

Background

Adolescents with idiopathic scoliosis display high ghrelin levels. As hyperghrelinemia is found in patients with PWS and early-onset scoliosis (EOS) is highly prevalent in these patients, our aims were to explore (1) whether ghrelin levels differ between those with and without EOS and correlate with scoliosis severity, and (2) whether ghrelin levels in the first year of life are associated with the later development of EOS.

Methods

We used a case control study design for the first question and a longitudinal design for the second. Patients with PWS having plasma ghrelin measurements recorded between 2013 and 2018 in our database were selected and 30 children < 10 years old with EOS and 30 age- and BMI-matched controls without EOS were included. The Cobb angle at diagnosis was recorded. In addition, 37 infants with a ghrelin measurement in the first year of life were followed until 4 years of age and assessed for EOS. Total ghrelin (TG), acylated (AG) and unacylated ghrelin (UAG), and the AG/UAG ratio were analyzed.

Results

EOS children had an AG/UAG ratio statistically significantly lower than controls. The Cobb angle was positively correlated with TG and UAG. TG and AG in the first year of life were higher in infants who later develop EOS without reaching a statistically significant difference.

Conclusions

Our results suggest that ghrelin may play a role in the pathophysiology of EOS in PWS. Higher ghrelinemia in the first year of life required careful follow-up for EOS.

Ghrelin uses the GHS-R1a/Gi/cAMP pathway and induces differentiation only in mature osteoblasts. This ghrelin pathway is impaired in AIS patients

We have examined the Acylated Ghrelin (AG)/Gi pathway in different human osteoblastic cell lines. We have found that: 1) AG induces differentiation/mineralization only in mature osteoblasts; 2) the expression of GHS-R1a increases up to the mature cell stage, 3) the action is mediated via the GHS-R/Gi/cAMP pathway only in mature osteoblasts, and 4) osteoblastic cells from adolescent idiopathic scoliosis (AIS) are resistant to the AG/Gi/cAMP pathway. Altogether, these results suggested that AG uses the GHS-R1a/Gi/cAMP pathway to induce differentiation in mature osteoblasts only. This pathway is impaired in AIS osteoblasts. Understanding AG-specific pathways involved in normal and pathological osteoblasts may be useful for developing new treatments for pathologies such as AIS or osteoporosis.

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.

Fasting ghrelin levels after gastric bypass and vertical sleeve gastrectomy: An analytic cohort study

BACKGROUND AND OBJECTIVE

Neuronal populations involved in the regulation of food intake, particularly the orexigenic (appetite-stimulating) hormone ghrelin, are found in the hypothalamus. Changes in plasma ghrelin levels have been observed following different bariatric surgery procedures, but the results from different studies are contradictory. Much remains unknown regarding the role of ghrelin in the weight loss process following bariatric surgery. Our objective was to describe the behaviour of fasting ghrelin levels, comparing the changes occurring between 2 different surgical techniques (gastric bypass versus vertical sleeve gastrectomy) and their correlation with weight loss.

PATIENTS AND METHOD

A prospective, observational, analytic cohort study of 54 patients (27 for each surgical technique) with a 12-month follow-up period. We analysed demographic data, anthropometric data, comorbidities, weight loss and evolution of fasting ghrelin.

RESULTS

The behaviour of acylated ghrelin was similar with the 2 surgical techniques, with no significant differences between gastric bypass and vertical sleeve gastrectomy. With both procedures, there was an increase in acylated ghrelin on day 5 and a subsequent decrease, and levels then gradually increased to reach values at 12 months that were higher than those reported preoperatively. This increase in ghrelin levels did not affect weight loss, since one year post-surgery, 30% weight loss was achieved with both types of surgery.

CONCLUSIONS

We observed an increase in fasting acylated ghrelin levels at one year of follow-up with both surgical techniques, with 30% weight loss.

The effects of exercise and ambient temperature on dietary intake, appetite sensation, and appetite regulating hormone concentrations

BACKGROUND

It is not clear whether the frequently reported phenomenon of exercise-induced anorexia is exacerbated or blunted in warm or cold environments. Therefore, this study investigated the effects of exercise in three different environmental temperatures vs. rest, on perceptions of appetite, appetite regulating hormones, and food intake.

METHODS

In a randomized repeated-measures design, 18 Canadian Armed Forces members (14 male, 4 female) completed four 8-h trials in a thermally-controlled chamber: one 8-h resting trial at 21 °C (Sedentary); and three trials where participants completed two 2-h circuits of standardized military tasks interspersed with two 2-h rest periods, once at 30 °C (Hot), once at 21 °C (Temperate), and once at - 10 °C (Cold). Participants consumed military field rations ad libitum and had their appetite assessed with visual analogue scales. Plasma concentrations of GLP-1, PYY, acylated ghrelin, and leptin were also determined.

RESULTS

Appetite was perceived as being suppressed in the heat compared to the cold (p < 0.05). While neither exercise nor environmental temperature altered circulating GLP-1 levels, exercise in all environments increased blood concentrations of PYY (p < 0.05). Leptin concentrations were elevated in the heat and diminished in the cold (p < 0.05), and acylated ghrelin concentrations were affected by both exercise and ambient temperature resulting in Sedentary = Cold>Temperate = Hot (p < 0.05). Contrary to the changes in appetite perceptions and hormonal concentrations, dietary intake was not different between conditions (p > 0.05). Relative energy intake (total 24 h energy intake minus 24 h energy expenditure) on the other hand, was significantly higher during the Sedentary condition than it was during any of the active conditions (p < 0.05). Most (83%) of the participants were in a positive energy balance during the Sedentary condition, whereas during most (80%) of the active conditions (Hot, Temperate, Cold) participants were in a negative energy balance.

CONCLUSIONS

In this study where food was freely available, variations in ambient temperature, exercise vs. rest, appetite-regulating hormone concentrations, and subjective appetite sensation were not associated with any changes in dietary intake within 24-h of acute, prolonged exercise.

Total and acylated ghrelin plasma levels as potential long-term response markers in alcohol-dependent patients receiving high-dose of the GABA-B receptor agonist baclofen

The orexigenic hormone ghrelin is involved in the regulation of food intake and energy balance. Previous findings suggest its involvement in the modulation of mesolimbic reward pathways, thus potentially being relevant in the pathophysiology of substance use disorders such as alcohol dependence. In the present study, we assessed plasma levels of total and acylated ghrelin within the BACLAD trial, where alcohol-dependent patients received individually titrated high-dose baclofen (30-270 mg/d) within a randomized, placebo-controlled design. Plasma levels of total ghrelin and acylated ghrelin were measured at baseline, during treatment with individually titrated high-dose baclofen and after termination of the study medication within a timeframe of up to 20 weeks. Multivariate longitudinal non-parametric analysis revealed that plasma levels of total ghrelin significantly decreased in the group of abstinent patients receiving high-dose baclofen. In addition, plasma levels of total ghrelin correlated negatively with days of abstinence during treatment with high-dose baclofen. Plasma levels of acylated ghrelin increased during the study in the group of relapsed patients under baclofen and placebo treatment. These findings suggest that the long-term response to baclofen treatment in alcohol use disorder (AUD) might be monitored by assessing total and acylated ghrelin plasma levels.

Increased Serum Acylated Ghrelin Levels in Patients with Mild Cognitive Impairment

Ghrelin is a stomach-derived circulating hormone. In addition to its function as an orexigenic stimulant, the role of ghrelin in the consolidation of learning and memory has been implicated in recent years. However, the status of circulating acylated ghrelin (AG, that is, the functional form of ghrelin) in the symptomatic predementia stage of Alzheimer's disease (AD) has rarely been investigated. In the current study, we examined the serum levels of acylated and total ghrelin in 22 patients with mild cognitive impairment (MCI) and 30 cognitively normal controls. We have found that patients with MCI had significantly increased serum AG levels, which were inversely associated with defected short- and long-term memory as well as language skills. Of note, the levels of total circulating ghrelin were similar between the two groups. Intriguingly, serum AG but not total ghrelin was associated with AD risk factors including the age, hypertension, and hyperlipidemia. Therefore, circulating AG may serve as a potential early systemic biomarker for AD-related cognitive impairments. Nevertheless, the simplest interpretation of the results is that the levels of circulating AG are associated with cognitive impairments in patients with MCI, thereby forming the groundwork for our future studies on the systemic mechanisms of AD pertaining to the ghrelin system.

The effect of ghrelin O-acyltransferase inhibitor on gastric H+-K+-ATPase activity and GOAT/ghrelin system in gastric mucosal cells in vitro

Ghrelin is implicated in the regulation of gastric functional development. The octanoylation of ghrelin is critical for its physiological functions which dependent upon ghrelin O-acyltransferase (GOAT) catalyzation. To investigate the effect of GOAT on gastric acid secretion and expression of ghrelin in vitro. Primary cultures of gastric mucosal cells were challenged with 1.5 × 10^-5, 1.5 × 10^-4 and 1.5 × 10^-3 mol/mL GO-CoA-Tat (The GOAT inhibitor), respectively, for 24 h in order to further clarify the effect of GOAT on H⁺-K⁺-ATPase activity. In vitro, GO-CoA-Tat significantly increased ghrelin and GOAT mRNA expression at 1.5 × 10^-5, 1.5 × 10^-4 and 1.5 × 10^-3 mol/mL, and augmented cell total ghrelin secretion at 1.5 × 10^-3 mol/mL. But cell acylated ghrelin secretion was reduced at 1.5 × 10^-3 mol/mL GO-CoA-Tat (P < 0.05). And cell acylated ghrelin synthesis was reduced at 1.5 × 10^-4 and 1.5 × 10^-3 mol/mL GO-CoA-Tat (P < 0.05). In accordance with acylated ghrelin level, H⁺-K⁺-ATPase activity were decreased with 1.5 × 10^-4 and 1.5 × 10^-3 mol/mL GO-CoA-Tat (P < 0.05). These results indicated that GOAT inhibitor decreases the acylated ghrelin level and H⁺-K⁺-ATPase activity in vitro.

Evaluating the Levels of Nesfatin-1 and Ghrelin Hormones in Patients with Moderate and Severe Major Depressive Disorders

OBJECTIVE

The goal of this study was to evaluate the importance of nesfatin-1, acylated and des-acylated ghrelin, which are known as energy regulatory hormones, in patients with moderate and severe major depression disorders (MDD).

METHODS

Thirty patients with a moderate degree of MDD and, 30 with a severe degree of MDD were used as participants in this study. Thirty subjects without depression were enrolled as a control group. The Hamilton Depression Rating Scale was used to classify the patients with MDD. Blood samples were taken after overnight fasting. The plasma nesfatin-1, acylated ghrelin and des-acylated ghrelin levels were measured using a commercially available enzyme-linked immunosorbent assay kit.

RESULTS

The nesfatin-1, the acylated ghrelin and the des-acylated ghrelin levels were found to be significantly higher in severe MDD (3.92±0.4 ng/mL; 88.56±4.1 pg/mL; 962.76±67 pg/mL) as compared to moderate MDD (2.91±0.5 ng/mL; 77.63±4.19 pg/mL; 631.16±35 pg/mL), or the control (1.01±0.3 ng/mL; 58.60±9.00 pg/mL; 543.13±62 pg/mL), respectively.

CONCLUSION

Although nesfatin-1 and ghrelin are known as adversely affecting the hormones involving the regulation of appetite and food intake, they all increase in depressive patients and are even associated with the severity of the disease. In clinical medicine, the evaluation of the role of nesfatin-1 and ghrelin in endocrine and neu-roendocrine regulation of major metabolic functions is an important key mechanism in solving numerous diseases associated with endocrine and neuroendocrine disturbance. Increased levels of nesfatin-1 and ghrelin may also be important criteria in describing the prognoses of the patients and the effectiveness of the treatments.

The Relationship between Ghrelin and Copeptin Levels, and Anxiety and Depression Levels in Suicide Attempts

Objective

It was aimed to detect acylated ghrelin (AG), unacylated ghrelin (UG) and copeptin levels in patients with suicide attempts and to determine if these biomarkers are risk factors for suicide attempts.

Methods

Serum copeptin, AG and GU levels were screened in 128 patients who were admitted to emergency department with suicide attempts and 59 healthy controls. Beck Anxiety Inventory (BAI) and Beck Depression Inventory (BDI) were applied simultaneously, and the data were compared statistically.

Results

AG, UG and copeptin levels were higher in the patient group compared with the healthy control group. BAI scores of patients were found to be positively correlated with BDI scores. While there was a significant difference (p=0.0064) between psychiatric and non-psychiatric patients with suicide attempts in terms of BAI scores, there were no differences in BDI scores and levels of biomarkers. We found significantly increased BDI and BAI scores and increased levels of AG, UG and copeptin in psychiatric and non-psychiatric patients compared with healthy individuals. The specificities yielded by receiver operating characteristic curve analysis in patients with suicide attempts were as follows: 91.53% for AG, 72.88% for UG and 94.92% for copeptin.

Conclusion

Serum levels of AG, UG and copeptin increase with increasing anxiety and depression in patients with suicide attempts. Increased levels of AG, UG and copeptin could be considered a risk factor for suicide attempts.

The effect of moderate versus severe simulated altitude on appetite, gut hormones, energy intake and substrate oxidation in men

Acute exposure to high altitude (>3500 m) is associated with marked changes in appetite regulation and substrate oxidation but the effects of lower altitudes are unclear. This study examined appetite, gut hormone, energy intake and substrate oxidation responses to breakfast ingestion and exercise at simulated moderate and severe altitudes compared with sea-level. Twelve healthy males (mean ± SD; age 30 ± 9years, body mass index 24.4 ± 2.7 kg·m^-2) completed in a randomised crossover order three, 305 min experimental trials at a simulated altitude of 0 m, 2150 m (∼15.8% O₂) and 4300 m (∼11.7% O₂) in a normobaric chamber. Participants entered the chamber at 8am following a 12 h fast. A standardised breakfast was consumed inside the chamber at 1 h. One hour after breakfast, participants performed a 60 min treadmill walk at 50% of relative V˙O_2max. An ad-libitum buffet meal was consumed 1.5 h after exercise. Blood samples were collected prior to altitude exposure and at 60, 135, 195, 240 and 285 min. No trial based differences were observed in any appetite related measure before exercise. Post-exercise area under the curve values for acylated ghrelin, pancreatic polypeptide and composite appetite score were lower (all P < 0.05) at 4300 m compared with sea-level and 2150 m. There were no differences in glucagon-like peptide-1 between conditions (P = 0.895). Mean energy intake was lower at 4300 m (3728 ± 3179 kJ) compared with sea-level (7358 ± 1789 kJ; P = 0.007) and 2150 m (7390 ± 1226 kJ; P = 0.004). Proportional reliance on carbohydrate as a fuel was higher (P = 0.01) before breakfast but lower during (P = 0.02) and after exercise (P = 0.01) at 4300 m compared with sea-level. This study suggests that altitude-induced anorexia and a subsequent reduction in energy intake occurs after exercise during exposure to severe but not moderate simulated altitude. Acylated ghrelin concentrations may contribute to this effect.

RNAi-mediated Ghrelin affects gastric H(+)-K(+)-ATPase activity and expression of GOAT-Ghrelin system in vitro

Ghrelin has been implicated in the regulation of gastric functional development, and its physiological functions are mediated by Ghrelin-O-acyltransferase (GOAT) which is capable of generating the active form of this polypeptide hormone. However, whether and how ghrelin gene silencing may modify gastric acid secretion and GOAT-Ghrelin system is yet to be explored. The study was performed in gastric mucosal cells from weanling piglets in vitro. We evaluated the effect of ghrelin on gastric acid secretion, gene expression of GOAT and ghrelin as well as ghrelin levels by RNA interference assay. shGhrelin triggered the down-regulation of ghrelin mRNA expression (P<0.05) via an RNAi mechanism, as observed by real-time RT-PCR. In addition, shGhrelin showed reduced total ghrelin production and secretion (P<0.05) using ELISA in vitro. We also detected that GOAT mRNA expression was reduced in shGhrelin group (P<0.05), compared with control groups. In accordance with the GOAT expression, acylated ghrelin production and secretion were reduced in gastric mucosal cells and culture medium (P<0.05). Silencing of ghrelin gene achieved by RNAi-mediation inhibited the activity of H(+)-K(+)-ATPase and pepsin (P<0.05) in gastric mucosal cells. These results indicated that RNAi of Ghrelin gene inhibited the gastric acid secretion with decreased GOAT mRNA and acylated Ghrelin in gastric mucosal cells.

Elevated ratio of acylated to unacylated ghrelin in children and young adults with Prader-Willi syndrome

Prader-Willi syndrome (PWS) is characterized by a switch from failure to thrive to excessive weight gain and hyperphagia in early childhood. Hyperghrelinemia may be involved in the underlying mechanisms of the switch. The purpose of this study is to evaluate acylated ghrelin (AG) and unacylated ghrelin (UAG) levels in PWS and investigate their associations with hyperphagia. This is a cross-sectional clinical study conducted in three PWS expert centers in the Netherlands and France. Levels of AG and UAG and the AG/UAG ratio were determined in 138 patients with PWS (0.2-29.4 years) and compared with 50 age-matched obese subjects (4.3-16.9 years) and 39 healthy controls (0.8-28.6 years). AEBSF was used to inhibit deacylation of AG. As a group, PWS patients had higher AG but similar UAG levels as healthy controls (AG 129.1 vs 82.4 pg/ml, p = 0.016; UAG 135.3 vs 157.3 pg/ml, resp.), resulting in a significantly higher AG/UAG ratio (1.00 vs 0.61, p = 0.001, resp.). Obese subjects had significantly lower AG and UAG levels than PWS and controls (40.3 and 35.3 pg/ml, resp.), but also a high AG/UAG ratio (1.16). The reason for the higher AG/UAG ratio in PWS and obese was, however, completely different, as PWS had a high AG and obese a very low UAG. PWS patients without weight gain or hyperphagia had a similar AG/UAG ratio as age-matched controls, in contrast to those with weight gain and/or hyperphagia who had an elevated AG/UAG ratio. The switch to excessive weight gain in PWS seems to coincide with an increase in the AG/UAG ratio, even prior to the start of hyperphagia.

Acylated ghrelin as provocative test for the diagnosis of ACTH deficiency in patients with hypothalamus-pituitary disease

The insulin tolerance test (ITT) is the gold standard to evaluate adrenocorticotropic hormone (ACTH) insufficiency. However, alternative tests have been proposed such as metyrapone, glucagon, and ACTH stimulation test. We determined the diagnostic reliability of testing with ghrelin, the natural GH secretagogue that is a potent stimulus exploring the integrity of hypothalamic-pituitary-adrenal axis. We studied the ACTH and cortisol response to acylated ghrelin in 49 patients with history of pituitary disease. The best cortisol and ACTH cut offs to ghrelin test, defined as those with the best sensitivity (SE) and specificity (SP), were identified using the ROC analysis. We also compared accuracy of ghrelin test with that of a simple and cheap test like basal cortisol and ACTH levels. The best cortisol and ACTH cut offs to ghrelin test were ≤11.6 µg/dl (SE 86.4%, SP 77.8%) and ≤32.5 pg/ml (SE 72.7%, SP 51.9%), respectively; the best basal cortisol and ACTH cut offs were ≤10.7 µg/dl (SE 90.9%, SP 70.4%) and ≤25.0 pg/ml (SE 85%, SP 37%), respectively. The diagnostic accuracy was 81.6, 60.9, 79.6, and 57.4%, respectively. A comparison between ROC AUC showed a great diagnostic power for cortisol, both stimulated and basal, versus ACTH, both stimulated and basal, but no difference between stimulated and basal cortisol evaluation. Our data show that testing with acylated ghrelin is not a useful diagnostic tool for the diagnosis of central hypocortisolism; particularly ghrelin test adds no more information that basal cortisol evaluation in the diagnosis of ACTH deficiency in patients with hypothalamus-pituitary disease.

Plasma Levels of Acylated Ghrelin in Children with Pulmonary Hypertension Associated with Congenital Heart Disease

This study aims to estimate plasma levels of acylated ghrelin in children with pulmonary hypertension (PH) associated with congenital heart disease (CHD) and to correlate the levels of acylated ghrelin with endothelin-1 (ET-1), nitric oxide (NO), and clinical hemodynamic parameters. We investigated the plasma concentration of acylated ghrelin, ET-1, NO, and the hemodynamic parameters in 20 children with CHD, 20 children with PH-CHD, and 20 normal children. Plasma-acylated ghrelin and NO levels were significantly higher in CHD group than in control subjects (P < 0.001). Moreover, plasma-acylated ghrelin, ET-1, and NO levels were significantly elevated in PH-CHD group compared with the CHD group (P < 0.05). In PH-CHD children, plasma-acylated ghrelin levels correlated positively with pulmonary artery systolic pressure (PASP; r = 0.740, P < 0.001), pulmonary artery diastolic pressure (PADP; r = 0.613, P = 0.004), right ventricular systolic pressure (RVSP; r = 0.642, P = 0.002), mean pulmonary arterial hypertension (mPAP; r = 0.685, P = 0.001), right ventricle diameter (RVD; r = 0.473, P = 0.035), pulmonary artery trunk diameter (PAD; r = 0.613, P = 0.004), NO (r = 0.463, P = 0.04), and ET-1 (r = 0.524, P = 0.018). Plasma-acylated ghrelin levels were elevated both in CHD and in PH-CHD. Increased acylated ghrelin levels correlated positively with ET-1, NO, PASP, PADP, RVSP, mPAP, RVD, and PAD. Acylated ghrelin may be a new biomarker of PH-CHD.

Acylated ghrelin is not required for the surge in pituitary growth hormone observed in pregnant mice

OBJECTIVE

Ghrelin is produced by the stomach, hypothalamus and pituitary. It circulates as acylated ghrelin (AG, which stimulates growth hormone (GH) secretion) and unacylated ghrelin (UAG). Acylation is mediated by the enzyme ghrelin O-acyltransferase (GOAT). In mice, pregnancy is associated with a marked increase in circulating pituitary GH. We investigated the role of AG and UAG in the surge of plasma GH concentrations in pregnant mice at the end of pregnancy.

DESIGN

Using a mouse model generated on a C57BL/6 background (wild type, WT) in which the GOAT gene has been deleted (KO), we measured plasma AG, UAG and GH concentrations and tissue (stomach, pituitary and hypothalamus) preproghrelin and GOAT mRNA in non-pregnant (NP) and pregnant (P), WT and KO mice.

RESULTS

GOAT deletion was associated with undetectable concentrations of AG. UAG concentrations were similar in all groups. In both WT and KO animals, mean GH concentrations increased 30 to 50 times during pregnancy. There was a tendency toward lower median GH concentrations in KO (301 ng/mL) compared to WT (428 ng/mL) mice (p=0.059). Preproghrelin expression was not affected by GOAT deletion or by pregnancy in the stomach. In contrast, pituitary and hypothalamic ghrelin gene expression were lower in KO-NP and KO-P mice compared to their WT counterparts.

CONCLUSION

The complete absence of ghrelin acylation, which is associated with undetectable AG concentrations, does not prevent the marked increase in pituitary GH concentrations observed in pregnant mice, suggesting that AG is not the major mediator of GH secretion during pregnancy.

Appetite and gut hormone responses to moderate-intensity continuous exercise versus high-intensity interval exercise, in normoxic and hypoxic conditions

This study investigated the effects of continuous moderate-intensity exercise (MIE) and high-intensity interval exercise (HIIE) in combination with short exposure to hypoxia on appetite and plasma concentrations of acylated ghrelin, peptide YY (PYY), and glucagon-like peptide-1 (GLP-1). Twelve healthy males completed four, 2.6 h trials in a random order: (1) MIE-normoxia, (2) MIE-hypoxia, (3) HIIE-normoxia, and (4) HIIE-hypoxia. Exercise took place in an environmental chamber. During MIE, participants ran for 50 min at 70% of altitude-specific maximal oxygen uptake (V˙O2max) and during HIIE performed 6 × 3 min running at 90% V˙O2max interspersed with 6 × 3 min active recovery at 50% V˙O2max with a 7 min warm-up and cool-down at 70% V˙O2max (50 min total). In hypoxic trials, exercise was performed at a simulated altitude of 2980 m (14.5% O2). Exercise was completed after a standardised breakfast. A second meal standardised to 30% of participants' daily energy requirements was provided 45 min after exercise. Appetite was suppressed more in hypoxia than normoxia during exercise, post-exercise, and for the full 2.6 h trial period (linear mixed modelling, p <0.05). Plasma acylated ghrelin concentrations were lower in hypoxia than normoxia post-exercise and for the full 2.6 h trial period (p <0.05). PYY concentrations were higher in HIIE than MIE under hypoxic conditions during exercise (p = 0.042). No differences in GLP-1 were observed between conditions (p > 0.05). These findings demonstrate that short exposure to hypoxia causes suppressions in appetite and plasma acylated ghrelin concentrations. Furthermore, appetite responses to exercise do not appear to be influenced by exercise modality.

Peripheral α2-β1 adrenergic interactions mediate the ghrelin response to brain urocortin 1 in rats

The autonomic nervous system (ANS) conveys neuronal input from the brain to the stomach. We investigated mechanisms through which urocortin 1 (UCN1) injected intracerebroventricularly (ICV, 300 pmol/rat) inhibits circulating ghrelin in rats. This was achieved by assessing (1) the induction of c-fos gene expression as a marker of neuronal activation in specific hypothalamic and caudal brainstem regulating ANS; (2) the influence of vagotomy and pharmacological blockade of central and peripheral α- and β-adrenergic receptor (AR) on ICV UCN1-induced reduction of plasma ghrelin levels (determined by ELISA); and (3) the relevance of this pathway in the feeding response to a fast in rats. UCN1 increased c-fos mRNA expression in key brain sites influencing sympathetic activity namely the hypothalamic paraventricular and ventromedial nuclei, locus coeruleus, nucleus of the solitary tract, and rostral ventrolateral medulla, by 16-, 29-, 6-, 37-, and 13-fold, respectively. In contrast, the dorsal motor nucleus of the vagus had little c-fos mRNA expression and ICV UCN1 induced a similar reduction in acylated ghrelin in the sham-operated (31%) and vagotomized (41%) rats. An intraperitoneal (IP) injection of either a non-selective α- or selective α2-AR antagonist reduced, while a selective α2-AR agonist enhanced ICV UCN1-induced suppression of plasma acylated ghrelin levels. In addition, IP injection of a non-selective β- or selective β1-AR agonist blocked, and selective β1-AR antagonist augmented, the ghrelin response to ICV UCN1. The IP injections of a selective α1- or non-selective β or β2-AR antagonists, or any of the pretreatments given ICV had no effect. ICV UCN1 reduced the 2-h food intake in response to a fast by 80%, and this effect was partially prevented by a selective α2-AR antagonist. These data suggest that ICV UCN1 reduces plasma ghrelin mainly through the brain sympathetic component of the ANS and peripheral AR specifically α2-AR activation and inactivation of β1-AR. The α2-AR pathway contributes to the associated reduction in food intake.

Interrelationships between ghrelin, insulin and glucose homeostasis: Physiological relevance

Ghrelin is a 28 amino acid peptide mainly derived from the oxyntic gland of the stomach. Both acylated (AG) and unacylated (UAG) forms of ghrelin are found in the circulation. Initially, AG was considered as the only bioactive form of ghrelin. However, recent advances indicate that both AG and UAG exert distinct and common effects in organisms. Soon after its discovery, ghrelin was shown to promote appetite and adiposity in animal and human models. In response to these anabolic effects, an impressive number of elements have suggested the influence of ghrelin on the regulation of metabolic functions and the development of obesity-related disorders. However, due to the complexity of its biochemical nature and the physiological processes it governs, some of the effects of ghrelin are still debated in the literature. Evidence suggests that ghrelin influences glucose homeostasis through the modulation of insulin secretion and insulin receptor signaling. On the other hand, insulin was also shown to influence circulating levels of ghrelin. Here, we review the relationship between ghrelin and insulin and we describe the impact of this interaction on the modulation of glucose homeostasis.

Appetite and gut peptide responses to exercise and calorie restriction. The effect of modest energy deficits

Weight loss is the result of a sustained negative energy balance, which is typically achieved by decreasing food intake and/or increasing physical activity. Current evidence suggests that acute energy deficits of ~4820 kJ elicit contrasting homeostatic responses when induced by exercise and food restriction but the response to government-recommended energy deficits is unknown. Twelve healthy men (mean(SD): age 24(5) years, body mass index 23.8(2.7) kg⋅m(-2), maximum oxygen uptake 55.4(9.1) mL⋅kg(-1)⋅min(-1)) completed three 8 h trials (control (Con), exercise-induced energy deficit (Ex-Def) and food restriction (Food-Def)) separated by 1 week. Thirty minutes of cycling at 64.5(3.2)% of maximum oxygen uptake was performed in Ex-Def from 0 to 0.5 h, which induced an energy deficit of 1469(256) kJ. An equivalent energy deficit was induced in Food-Def (1478(275) kJ) by reducing the energy content of standardised test meals at 1 h and 4 h. Appetite ratings, acylated ghrelin and peptide YY3-36 concentrations were measured throughout each trial. An ad libitum meal was provided at 7 h. Appetite was higher in Food-Def than Ex-Def from 4 to 8 h (P = 0.033) and tended to be higher across the entire 8 h trial (P = 0.059). However, energy intake at the ad libitum meal did not differ between trials (P = 0.634; Con 4376 (1634); Food-Def 4481 (1846); Ex-Def 4217 (1850) kJ). Acylated ghrelin was not related to changes in appetite but plasma PYY3-36 concentrations were higher in Ex-Def than Food-Def (P < 0.05) and negatively correlated with changes in appetite across the entire 8 h trial (P = 0.037). An energy deficit of ~1475 kJ stimulated compensatory increases in appetite when induced via calorie restriction but not when achieved by an acute bout of exercise. Appetite responses were associated with changes in plasma PYY3-36 but not acylated ghrelin concentrations and did not influence subsequent energy intake.

Plasma levels of acylated ghrelin in patients with functional dyspepsia

AIM: To investigate the relationship between plasma acylated ghrelin levels and the pathophysiology of functional dyspepsia.

METHODS: Twenty-two female patients with functional dyspepsia and twelve healthy volunteers were recruited for the study. The functional dyspepsia patients were each diagnosed based on the Rome III criteria. Eligible patients completed a questionnaire concerning the severity of 10 symptoms. Plasma acylated ghrelin levels before and after a meal were determined in the study participants using a commercial human acylated enzyme immunoassay kit; electrogastrograms were performed for 50 min before and after a standardized 10-min meal containing 265 kcal.

RESULTS: There were no significant differences in plasma acylated ghrelin levels between healthy volunteers and patients with functional dyspepsia. However, in patients with functional dyspepsia, there was a negative correlation between fasting plasma acylated ghrelin levels and the sum score of epigastric pain (r = -0.427, P = 0.047) and a positive correlation between the postprandial/fasting plasma acylated ghrelin ratio and the sum score of early satiety (r = 0.428, P =0.047). Additionally, there was a negative correlation between fasting acylated ghrelin plasma levels and fasting normogastria (%) (r = -0.522, P = 0.013). Interestingly, two functional dyspepsia patients showed paradoxically elevated plasma acylated ghrelin levels after the meal.

CONCLUSION: Abnormal plasma acylated ghrelin levels before or after a meal may be related to several of the dyspeptic symptoms seen in patients with functional dyspepsia.