Glucagon-like peptide-1 (GLP-1) was discovered as an incretin hormone, which is released from the intestine upon nutrient intake and stimulates insulin secretion from the pancreatic islet β-cells. Subsequently, its ability to suppress appetite was recognized. Ghrelin, discovered as the ligand for growth hormone secretagogue-receptor (GHS-R), is released from the stomach and produces appetite. Later, its ability to inhibit insulin secretion and elevate blood glucose was found. Thus, GLP-1 and ghrelin regulate insulin secretion and appetite toward opposite directions. The receptor agonists for GLP-1 and ghrelin have been developed and are now used to treat metabolic diseases, in which insulin plays a key role. However, underlying action mechanism and possible interplay of these hormones have remained elusive. Here, we describe that GLP-1 and ghrelin reciprocally regulate the insulin system. GLP-1 enhances and ghrelin suppresses insulin secretion in pancreatic β-cells. Moreover, GLP-1 cooperates with and ghrelin counteracts insulin action in the vagal afferent and hypothalamic arcuate nucleus (ARC) neurons, the interfaces between the peripheral metabolism and brain. Notably, ghrelin rises and works preprandially and GLP-1 rises and works postprandially. The interplay of ghrelin, GLP-1, and insulin leads to optimal circadian control of feeding, glycemia, and metabolism.

Physiological stress in non-neural tissues drives aversive learning for sensory cues associated with stress. However, the identities of signals derived from non-neural tissues and the mechanisms by which these signals mediate aversive learning remain elusive. Here, we show that intercellular sphingolipid signaling contributes to aversive learning under mitochondrial stress in C. elegans. We found that stress-induced aversive learning requires sphingosine kinase, SPHK-1, the enzyme that produces sphingosine-1-phosphate (S1P). Genetic and biochemical studies revealed an intercellular signaling pathway in which intestinal or hypodermal SPHK-1 signals through the neuronal G protein-coupled receptor, SPHR-1, and modulates responses of the octopaminergic RIC neuron to promote aversive learning. We further show that SPHK-1-mediated sphingolipid signaling is required for learned aversion of Chryseobacterium indologenes, a bacterial pathogen found in the natural habitats of C. elegans, which causes mitochondrial stress. Taken together, our work reveals a sphingolipid signaling pathway that communicates from intestinal or hypodermal tissues to neurons to promote aversive learning in response to mitochondrial stress and pathogen infection.

G protein-coupled receptors (GPCRs) are key pharmacological targets, yet many remain underutilized due to unknown activation mechanisms and ligands. Orphan GPCRs, lacking identified natural ligands, are a high priority for research, as identifying their ligands will aid in understanding their functions and potential as drug targets. Most GPCRs, including orphans, couple to Gi/o/z family members, however current assays to detect their activation are limited, hindering ligand identification efforts. We introduce GzESTY, a sensitive, cell-based assay developed in an easily deliverable format designed to study the pharmacology of Gi/o/z-coupled GPCRs and assist in deorphanization. We optimized assay conditions and developed an all-in-one vector employing cloning methods to ensure the correct expression ratio of GzESTY components. GzESTY successfully assessed activation of a library of ligand-activated GPCRs, detecting both full and partial agonism, and responses from endogenous GPCRs. Notably, with GzESTY we established the presence of endogenous ligands for GPR176 and GPR37 in brain extracts, validating its use in deorphanization efforts. This assay enhances the ability to find ligands for orphan GPCRs, expanding the toolkit for GPCR pharmacologists.

Pharmacological research has showed that multi-targeted drug therapies offer superior efficacy and reduced side effects compared to single-target drug therapies. In this study, we designed and characterized four novel chimeric peptides G (1-5)-EM2, EM2-G (1-5), G (1-9)-EM2 and EM2-G (1-9) which incorporate endomorphin-2 (EM-2) and the active fragments of ghrelin. Calcium mobilization assays revealed that these four chimeric peptides acted as weak mixed agonists for the μ-opioid receptor (MOR), κ-opioid receptor (KOR), and growth hormone secretagogue receptor 1α (GHS-R1α). The results of fluorescence imaging experiments indicated that G (1-5)-EM2 and G (1-9)-EM2 could penetrate the blood-brain barrier (BBB) following intravenous (i.v.) injection. All chimeric peptides induced almost equal antinociceptive effects compared with EM-2 or better antinociceptive effects than EM-2 after intracerebroventricular (i.c.v.) injection in the acute pain in mice. Among them, G (1-5)-EM2 could cross the BBB and enter the brain to induce antinociceptive effect through central opioid receptors after i. v. Injection. Our findings demonstrated that the chimeric peptides produced significant antinociception mainly via MOR, DOR and GHS-R1α without inducing antinociceptive tolerance, or with a lower tendency for antinociceptive tolerance after i. c.v. Injection in the acute pain in mice. Furthermore, the chimeric peptides mitigated or eliminated the digestive side effects associated with EM-2. The collective results highlight G (1-5)-EM2 as the most promising candidate among the chimeric peptides. The chimeric peptides represent a promising class of potential analgesics for clinical pain management. However, further optimization is necessary to maximize their therapeutic potential.

Cancer cachexia is characterized by weight loss, muscle mass loss, and reduced food intake. Anamorelin is a ghrelin receptor agonist approved for the treatment of cancer cachexia. In this study, we established and validated an assay for quantification of anamorelin in human plasma.

For quantification of anamorelin, samples were pretreated with solid-phase extraction and analyzed by ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). This analytical method was validated in accordance with the Food and Drug Administration (FDA) bioanalytical method validation guidance. We used the established assay to quantify plasma anamorelin concentrations in five patients with cancer cachexia treated with anamorelin.

The validation results of this assay method met the acceptance criteria recommended by the FDA guidance. Within-batch and batch-to-batch precision at the lower limit of quantification and three quality control levels were within 6.20 % and 6.55 % coefficient of variation, respectively. Within-batch and batch-to-batch accuracies ranged from -2.58 to -1.33 % and -3.78 to -1.69 %, respectively. Recovery rates and matrix effects corrected by internal standard were 82.7-84.2 % and 102.7-104.6 %, respectively. Using the established assay with a calibration range of 0.1-2500 ng/mL, plasma anamorelin concentrations were successfully quantified in all 15 plasma samples from 5 patients with cancer cachexia.

We established and validated a method to measure plasma anamorelin concentrations using UHPLC/MS-MS combined with SPE, and successfully applied the novel method to measure plasma anamorelin concentrations in patients with cancer cachexia. By measuring plasma anamorelin concentrations in large scale studies, the established quantitative method is expected to contribute to the pharmacokinetic study of anamorelin.

Fat composition of milk replacer (MR) for calves differs from that of bovine milk fat, resulting in lower levels of butyric (C4:0) and caproic acid (C6:0). These fatty acids play a critical role in the gastrointestinal and metabolic development of calves by supporting rumen epithelial growth, enhancing energy metabolism, and promoting overall gut health. The objective of this study was to evaluate the effects of inclusion of a spray-dried fat concentrate containing tributyrin (TB) and tricaproin (TC) in a high-fat MR on growth, feed intake, and metabolic profiles of ad libitum-fed calves. Forty-eight newborn Holstein calves were blocked based on arrival sequence. Within each block of 2 calves, calves were randomly assigned to a control MR (CON, n = 24) including vegetable fats from palm, coconut, and linseed fats, or to an experimental MR including the same fat blend, to which TB and TC (TRI, n = 24) was added to the same levels found in milk fat. Both MR contained 23.7% crude protein, 27.7% fat, and 35.6% lactose (DM basis) and were fed at 13.5% solids. Calves were group housed and fed ad libitum MR with automated feeders. Weaning was gradual and induced between wk 7-10, after which calves were only fed solid feeds. Starter feed, chopped straw, and water were offered ad libitum throughout the whole study period. Calves were weighed and blood was collected once weekly at 1300h. Calves fed TRI showed a ∼50% reduction in therapeutic intervention days compared with CON. In addition, calves fed TRI consumed significantly more MR and starter feed, resulting in a greater growth. Serum NEFA and plasma total cholesterol were lower, whereas the enzymatic activity of serum ALP was higher in calves fed TRI than in CON. In addition, calves fed TRI had lower serum ghrelin and higher insulin-like growth factor-I concentrations. Incorporating TB and TC is a suitable strategy to increase solid feed intake upon weaning, resulting in better growth performance in ad libitum systems, and to improve health of dairy rearing calves.

Acute kidney injury (AKI) is a common fatal condition among hospitalized patients. AKI may be induced by a variety of complicating factors such as sepsis, ischemia-reperfusion injury, nephrotoxic substances, and rhabdomyolysis. At present, symptomatic treatment is mainly used, and there are no US Food and Drug Administration (FDA)-approved drugs for the prevention or treatment of AKI. Peptides have become a promising area of research in AKI treatment because of their high efficiency and low toxicity. In this paper, we systematically review the experimental advancements of peptide therapy for AKI, analyze the mechanism of peptide action in different pathological models, discuss the challenges facing peptide therapy, and provide a scientific basis for further clinical research.

Ghrelin, an acylated peptide hormone, acts through its sole known receptor, the growth hormone secretagogue receptor (GHSR).Previous research indicated that ghrelin may be involved in rheumatoid arthritis (RA), yet the specific mechanisms remain unclear. This study aimed to explore the mechanism of ghrelin in RA synovial inflammation. Serum and synovial tissue from RA patients were collected for ghrelin expression analysis. We conducted our study using a collagen-induced arthritis (CIA) mouse model and an in vitro model using fibroblast-like synoviocytes (FLSs) induced by tumor necrosis factor-alpha (TNF-α). RNA-sequencing was performed to identify the potential signaling pathways involved in RA. Ghsr shRNA interference was used to assess whether the ghrelin receptor was involved. Ghrelin expression was decreased in synovial tissue of RA patients, and was negatively associated with TNF-α in the synovial fluid. In vivo experiments, acyl-ghrelin effectively suppressed CIA development, and Ghsr-/- mice exhibited the significantly aggravated arthritis symptoms of CIA mice. RNA sequence analyses of synovial tissue in Ghsr-/- and wild type mice indicated that ghrelin/GHSRsystem may inhibit inflammation through the PI3K/AKT pathway. In RA-FLSs, we found that acyl-ghrelin significantly suppressed the TNF-α induced increase in p-PI3K, p-AKT, p-NF-κB p65, IL-6 and IL-1β in RA FLSs. The effects of acyl-ghrelin on inflammatory factors were attenuated by the PI3K/AKT agonists. Ghsr shRNA reversed the anti-inflammatory effects of acyl-ghrelin. These results indicated that ghrelin/GHSR system has an important role in RA and could be a suitable candidate for RA therapy.

Cancer cachexia is a complex metabolic syndrome that severely impacts patient mobility, treatment strategies, and quality of life. However, no treatments are available to mitigate the debilitating consequences of cancer cachexia. Unacylated ghrelin (UnAG), the main circulating form of ghrelin, enhances muscle growth and mitochondrial function in various diseases, but its effects in cancer cachexia remain to be tested.

Male C57Bl6/N mice were assigned to one of three treatment groups: non-tumor-bearing (NTB), tumor-bearing (TB), or tumor-bearing treated with unacylated ghrelin (TB+UnAG). Over four weeks, we monitored body weight, food intake, and tumor size. We assessed muscle mass, contractility, mitochondrial oxygen consumption rate (OCR), and reactive oxygen species (ROS) production. Proteomic analysis was performed to elucidate the downstream effects of UnAG. Cell culture assays were performed to measure the in vitro effects of cancer cell-secreted factors and UnAG on myoblasts.

Gastrocnemius and quadriceps muscle masses were reduced by 20-30% in TB mice compared to NTB controls; however, UnAG treatment prevented approximately 50% of this loss. Beyond muscle mass, UnAG enhanced the isometric maximum specific force of the extensor digitorum longus by 70% in TB mice. This improvement in muscle quality was associated with preferential upregulation of myosin heavy chain expression in TB+UnAG mice. UnAG also increased mitochondrial OCR while reducing ROS production. Mitochondrial DNA (mtDNA) copy number, which was reduced in TB mice, was restored by UnAG, while the reduced mtDNA mutation frequency in TB mice was maintained with treatment, indicating improved mtDNA integrity. Consistent with enhanced mitochondrial function, treadmill running time was significantly increased in TB+UnAG mice. Proteomic analysis revealed that UnAG downregulated proteins associated with proteolysis, while normalizing antioxidant enzyme thioredoxin and proteins involved in calcium handling. Cancer cell-conditioned medium reduced myotube width in vitro, but UnAG treatment preserved myotube structure..

UnAG protects against cancer cachexia by targeting multiple risk factors, including myosin heavy chain expression, mitochondrial bioenergetics, and modulation of protein degradation pathways.

Loss of appetite following gastric cancer surgery, particularly total gastrectomy, significantly impacts patient quality of life due to the removal of the ghrelin-secreting region. We developed appetite-preserving gastrectomy (APG), a modified total gastrectomy that preserves this region.

Ten consecutive patients with esophagogastric junction cancer who were indicated for total gastrectomy and underwent APG between April 2023 and April 2024 were evaluated for early surgical outcomes, appetite, and changes in weight and body composition.

There were no postoperative complications of grade II or higher (Clavien-Dindo classification). Appetite, assessed using the Simplified Nutritional Appetite Questionnaire, showed no significant impairment at 3 months (14.5 points, P = 0.82) and 6 months (15 points, P = 0.44) postoperatively compared with preoperative values. Oral calorie intake was maintained at 3 months (1675 kcal, P = 0.97) and 6 months (1675 kcal, P = 0.22) postoperatively compared with preoperative levels. The patients' body weight decreased by 9.2% at 6 months postoperatively compared with preoperative values, but their lean body mass remained stable. Although a significant decrease in the blood Ghrelin levels was observed postoperatively, 53% and 60.4% of the preoperative levels was maintained at one month and 6 months, respectively.

APG is a safe procedure that preserves the residual stomach as an endocrine organ, maintains ghrelin secretion and appetite, and prevents muscle loss. However, further trials are required to compare the efficacy of APG with total gastrectomy in preventing postoperative appetite loss.

In major depressive disorder (MDD), alterations in ghrelin levels and cognitive impairment coexist, yet their association has remained largely elusive. This study aimed to investigate the association between ghrelin levels and cognition in both MDD patients and healthy controls (HCs) while also exploring sex-specific differences in this correlation. A total of 155 Chinese Han subjects, including 90 first-episode drug-naive MDD patients and 65 HCs, were enrolled. Ghrelin levels were measured using ELISA kits, and neurocognitive assessments were conducted using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). MDD patients exhibited significantly higher ghrelin levels and lower cognitive scores of RBANS compared to HCs. However, there was no significant correlation between ghrelin levels and cognitive function in both MDD patients and HCs. Exploratory analyses revealed sex-specific associations between ghrelin and cognitive function, particularly in MDD patients. Females with MDD showed distinct patterns of association between ghrelin levels and cognitive domains such as attention and language, which were not observed in healthy controls or male MDD patients. The relationship between ghrelin and cognition only existed in MDD patients, not in the HCs, and there was a sex-specific difference in this association. Further research on the mechanism of ghrelin in the cognitive function of MDD should focus on sex differences.

Ghrelin is a signal involved in the initiation of meals in rodents and humans. Circulating ghrelin levels are elevated before mealwes and reduced after food intake. Several factors have been identified as effective modulators of ghrelin levels. Vagal activation reduced ghrelin in rats, as well as oral carbohydrate and lipid administration in rats and humans. Some hormones, such as incretins, also reduce ghrelin: GLP-1 reduced ghrelin in humans, and Ex4, a GLP-1 receptor agonist, potently inhibited ghrelin in rodents. On the other hand, fasting promotes increases in ghrelin that anticipate the start of meals. We report that beta-adrenergic activation with isoproterenol promotes large acute elevations of circulating ghrelin levels, both in anesthetized and conscious freely-moving rats, either on "ad libitum" feeding or on a fasting regimen.These effects are dose-dependent, caused by intravenous, intraperitoneal, and oral administration, and independent of variations in glucose levels. Pharmacological modulation of β1 and β2 adrenergic receptors with specific agonists and antagonists showed that ghrelin increases are stimulated by β1-adrenergic activation, but also partially by β2-adrenergic activation, suggesting that activation of both is necessary to elicit complete ghrelin elevations. Meanwhile, glucose increases dependent on adrenergic activation appear to be mediated only by β2-adrenergic receptors. In addition, the effects of isoproterenol on increasing ghrelin levels are potent enough to overcome the marked inhibition exerted by exendin-4 that we have previously demonstrated. We also found that administration of isoproterenol in drinking water increases basal ghrelin levels and simultaneous food intake in animals eating ad libitum. Beta-adrenergic activation promotes increases in ghrelin levels in vivo prior to food intake, both in rats eating ad libitum and in fasting rats that already have elevated ghrelin levels, in a time- and dose-dependent manner. In addition, the effects of isoproterenol on increasing ghrelin levels are potent enough to overcome the marked inhibition exerted by exendin-4 that we have previously demonstrated. We also found that administration of isoproterenol in drinking water increases basal ghrelin levels and simultaneous food intake in animals eating ad libitum. Beta-adrenergic activation promotes increases in ghrelin levels in vivo prior to food intake, both in eating ad libitum and in fasting rats that already have elevated ghrelin levels, in a time- and dose-dependent manner.

Protein homeostasis (proteostasis) is preserved by an orchestrated network of molecular mechanisms that regulate protein synthesis, folding, and degradation, ensuring cellular integrity and function. Proteostasis declines with age and is related to pathologies such as neurodegenerative diseases and cardiac disorders, which are accompanied by the accumulation of toxic protein aggregates. In this context, therapeutic strategies enhancing the two primary degradative systems involved in the cellular clearance of those abnormal proteins, namely ubiquitin-proteasome system and autophagy-lysosomal pathway, represent a promising approach to counteract the collapse of proteostasis in such pathological conditions. In this work, we explored the processing of ghrelin, a pleiotropic peptide hormone linked to energy metabolism and higher brain functions, which is reported to modulate the protein degradative mechanisms. According to our data, ghrelin is processed by serine hydrolases secreted into the conditioned medium of SH-SY5Y neuroblastoma cell line, commonly used in neurotoxicology and neuroscience research. Ghrelin processing leads to the formation of a shorter peptide (ghrelin(1-11)) that stimulates both the cell proteasome system and autophagy-lysosomal pathway, encompassing the selective autophagy of mitochondria. Our findings suggest that ghrelin processing may contribute to the maintenance of neuronal proteostasis.

The neural substrates of anxiety are poorly understood, which hinders treatment of anxiety disorders. Here we found, αCaMKII+ neurons in the ventral medial hypothalamic nucleus (VMH) responded to stressors with increased activity in male mice, both under physiological conditions and after repeated restraint stress. Activation of VMH αCaMKII+ neurons were necessary and sufficient to ameliorate stress-induced anxiety. The peripheral metabolic hormone ghrelin and receptor GHS-R1a play a complex role in emotion regulation; however, the mechanism is uncertain. A delayed increase in GHS-R1a expression in VMH αCaMKII+ neurons coincided with the development of stress-induced enhancement of anxiety-related behavior. GHS-R1a expression in VMH αCaMKII+ neurons promoted anxiety-related behavior, whereas GHS-R1a knockdown had the opposite effect. GHS-R1a upregulation inhibited the excitability of VMH αCaMKII+ neurons. We conclude that GHSR1a signaling drives stress-induced anxiety by shaping the activity of VMH αCaMKII+ neurons. GHS-R1a may be a therapeutic target for treating anxiety disorders such as post-traumatic stress disorder.

The growth hormone (GH) secretagogue receptor, encoded by GHSR, is expressed on somatotrophs of the pituitary gland. Stimulation with its ligand ghrelin, as well as its constitutive activity, enhances GH secretion. Studies in knockout mice suggest that heterozygous loss-of-function of GHSR is associated with decreased GH response to fasting, but patient observations in small case reports have been equivocal.

This work aims to establish the phenotype of GHSR haploinsufficiency and its growth response to GH treatment.

This case series includes 26 patients with short stature and heterozygous GHSR variants. Pathogenicity was studied in vitro using total protein levels, cell surface expression, and receptor activity in basal, stimulated, and inhibited states.

Ten different variants were identified, of which 6 were novel. Variants showed either partial or complete loss of function, primarily through loss of constitutive activity. Patients (aged 4.0-15.1 years) had proportionate short stature (height -2.8 ± 0.5 SDS), failure to thrive with low appetite (n = 4), a mean serum insulin-like growth factor-I (IGF-I) of -1.6 ± 0.7 SDS, and a normal stimulated GH response. Nine patients received GH treatment, showing a height gain of 0.9 ± 0.4 SDS after 1 year and 1.5 ± 0.4 SDS after 2 years (n = 5).

This study combines phenotypical and functional data in a uniquely large group of children with short stature carrying GHSR variants, and shows their good response to GH treatment. The results strengthen the hypothesis of GHSR's role in GH secretion.

Bulimia nervosa (BN) involves recurrent episodes of uncontrolled eating followed by compensatory behaviors. Stress is implicated in BN, affecting the hypothalamic-pituitary-adrenal (HPA) axis and ghrelin, a key appetite-regulating hormone. Studies report conflicting HPA axis findings in BN, necessitating further investigation.

To examine the impact of acute stress on cortisol and serum ghrelin and eating disorder symptoms in women with BN and healthy controls (HC).

Participants underwent a socially evaluated cold pressor test (CPT) and control condition (quiet rest) before consuming a sweet-fat liquid meal (530 Kcal milkshake). Hormonal responses and subjective measures of stress, interoception, and appetite were assessed.

In BN but not HC, desire to binge remained consistently high in both conditions and correlated with perceived hunger. There were no group differences in total ghrelin levels and levels were not influenced by the CPT. Baseline cortisol levels were similar for HC and BN groups, however BN subjects did not demonstrate a CPT-induced elevation in cortisol as observed in HC.

Results confirm HPA axis dysregulation in BN in response to a passive stressor and liquid meal challenge. Meal-related total ghrelin however does not appear to be involved in the stress response in women with or without BN. Desire to binge is persistent in BN, irrespective of the presence or absence of an acute stressor with a sweet-fat liquid meal and may be associated with heightened emotional states in general.

Bioactive peptides consist of multiple linked amino acids that are secreted from cells and act on specific receptors in order to transmit information from one cell to another. Through signal transduction, bioactive peptides regulate various physiological functions in the body, and the discovery of new bioactive peptides is therefore likely to lead to the development of various diagnostic and therapeutic agents. In this article, we have focused on the bioactive peptides that are known as feeding regulatory peptides. They are among the bioactive peptides discovered as ligands for G protein-coupled receptors (GPCRs), and we have reviewed their diverse functions. In addition, the status of structural analysis of GPCRs, which is necessary in the drug discovery process, and research on orphan GPCRs, for which new ligands are expected to be discovered in the future, is introduced to systematize modern peptide research and discuss future developments in bioactive peptide research.

Multiple sclerosis (MS) is an inflammatory central nervous system disease characterized by demyelination and axonal loss and is the main cause of non-traumatic neurological disability in young adults. Although there are several treatment approaches to manage the disease, there is no definitive cure for multiple sclerosis. Inflammation and oxidative stress are known to play important roles in the pathophysiology of MS. Ghrelin, a peptide secreted by the stomach, is reported to have neuroprotective properties through several pathways, including attenuating oxidative stress and inflammation. In the present study cuprizone (CPZ)-induced model of MS was used in Wistar albino rats to study the possible anti-inflammatory, antioxidant and neuroprotective effects of ghrelin. Rats were randomly divided into six groups: Control groups (Control35 and Control-S42), demyelination group, remyelination group, remyelination + ghrelin (20 µg/kg) group and remyelination + ghrelin (40 µg/kg) group. Y maze test was performed on the rats on their last day of the experiment. Oxidative stress and inflammatory parameters were investigated in brain using commercial kits by enzyme-linked immunosorbent assay (ELISA). Luxol fast blue (LFB) and hematoxylen&eosin (H&E) staining were performed in brain tissues. CPZ leads to a significant decrease in glutathione peroxidase (GSH-Px) levels and myelin content and a significant increase in malondialdehyde (MDA), tumor necrosis factor-alpha (TNF-ɑ), interleukin- 6 (IL- 6) levels, the number of lymphatic cells and inflammatory cells. A significant increase in the antioxidant parameter levels and a significant decrease in MDA levels were found in the ghrelin treated groups (p < 0.05). CPZ leads to irregular, fragmented, demyelinating nerve fibers. A more significant remyelination was observed in the ghrelin treated groups compared to the other groups (p < 0.05). In conclusion, ghrelin treatment showed neuroprotective and antioxidant properties and reduced demyelination in the CPZ-induced rat model of multiple sclerosis.

Ghrelin, discovered in 1999 as an endogenous ligand of the growth hormone secretagogue receptor (now known as the ghrelin receptor), is a peptide hormone with diverse physiological activities, such as stimulation of growth hormone release, increased appetite, fat accumulation, thermoregulation, and cardioprotection. As a distinctive feature, ghrelin needs to undergo octanoylation, a specific acyl modification, to exert its biological activities. Although the ghrelin receptor specifically recognizes this modification, the underlying molecular mechanism had remained unclear for decades. Recent advancements in structural biology have facilitated the elucidation of this recognition mechanism 25 years after ghrelin's discovery. This review highlights the structural basis of ghrelin octanoylation, particularly emphasizing the mechanism by which the ghrelin receptor recognizes this acyl-modified hormone.

Ghrelin circulates in acylated (AG) and deacylated (DAG) isoforms and both may impact endothelial function (EF). Although acute exercise has been shown to modulate ghrelin levels and EF, data on the impact of exercise intensity on these parameters are scarce. To investigate the effect of exercise intensity and sex on EF and ghrelin levels, nine males (age: 43.8 ± 10.3 y; BMI: 22.5 ± 1.8 kg/m2) and eight females (age: 33.75 ± 10.2 y; BMI: 22.4 ± 1.6 kg/m2) completed a maximal cycle ergometer lactate threshold (LT)/VO2peak test. This test determined the exercise intensity for three visits: (a) CON, no exercise; (b) MOD, the power output (PO) at LT; (c) HIGH, the PO associated with 75% of the difference between LT and VO2peak. Ghrelin levels and EF [flow-mediated dilation (FMD), shear rate (SR)] were measured at baseline and then 30-120 min post-exercise. HIGH and MOD increased FMD (p < 0.0001). Each ghrelin isoform was suppressed by HIGH; only females exhibited reduced DAG levels in HIGH compared to MOD and CON (p < 0.0001-0.004). FMD was associated with ghrelin levels in females (r = -0.26-0.47). High-intensity exercise is key for ghrelin suppression and appears to only be weakly/moderately related to EF.

Depression is a widespread disease affecting over 300 million individuals of various ethnicities and socioeconomic backgrounds globally. It frequently strikes early in life and becomes a chronic or recurring lifelong illness. Out of the various hypotheses for the pathophysiology of depression, the gut-brain axis and stress hypothesis are the ones that need to be researched, as psychological stress impairs one or more pathways of the brain-gut axis and is likely to cause brain-gut axis dysfunction and depression. A dysfunctional reciprocal gut-brain relationship may contribute to many diseases, including inflammatory disorders, abnormal stress responses, impaired behavior, and metabolic changes. The hormone ghrelin is a topic of interest concerning the gut-brain axis as it interacts with the gut-brain axis indirectly via the central nervous system or via crossing the blood-brain barrier. Ghrelin release is also affected by the gut microbes, which has also been discussed in the review. This review elaborates on Ghrelin's role in depression and its effect on various aspects like neurogenesis, HPA axis, and neuroinflammation. Furthermore, this review focuses on ghrelin as a potential target for alleviation of depressive symptoms.

Ghrelin produced in the stomach promotes food intake and GH secretion, and acts as an anabolic peptide during starvation. Ghrelin binds to the growth hormone secretagogue receptor, a G protein-coupled receptor (GPCR), whose high-resolution complex structures have been determined in the apo state and when bound to an antagonist. Anamorelin, a low-molecular-weight ghrelin agonist, has been launched in Japan for the treatment of cancer cachexia, and its therapeutic potential has attracted attention due to the various biological activities of ghrelin. In 2019, liver-expressed antimicrobial peptide (LEAP2), initially discovered as an antimicrobial peptide produced in the liver, was identified to be upregulated in the stomach of diet-induced obese mice after vertical sleeve gastrectomy. LEAP2 binds to the GHSR and antagonizes ghrelin's activities. The serum concentrations of human LEAP2 are positively correlated with body mass index, body fat accumulation, and fasting serum concentrations of glucose and triglyceride. Serum LEAP2 elevated and ghrelin reduced in obesity. Ghrelin and LEAP2 regulate body weight, food intake, and GH and blood glucose concentrations, and other physiological phenomena through their interactions with the same receptor, GHSR.

Ghrelin is known to be a multifunctional peptide hormone that stimulates not only growth hormone secretion and feeding but also gastrointestinal (GI) functions, including motility, secretion and mucosa proliferation. The aim of this review is to provide a comprehensive overview on the physiological roles of ghrelin in the regulation of GI motility from a comparative perspective. The effects of ghrelin on GI motility differ depending on the species, and ghrelin is a possible regulator of gastric migrating motor complexes (MMCs) in rodents, dogs and house musk shrew (suncus). However, the role of ghrelin has not been clarified in detail in other mammals, including humans and rabbits. Ghrelin is also effective to cause contraction in the GI tract of some non-mammals, but its physiological role is also not clarified at present. Distribution of the growth hormone secretagogue receptor (GHSR, ghrelin receptor) in the GI tract might be connected with the regulatory role of ghrelin in vertebrates. Comparative studies of ghrelin among animals and identification of knowledge gaps must lead us to the functional transition and importance of ghrelin in the GI tract.

Because appetite-regulating hormones are implicated in neuronal survival, growth, and differentiation, they have been suggested to play a role in anxiety disorders. To date, few studies have focused on the association between these hormones and anxiety disorders in children. This study investigated the potential differences in leptin, ghrelin, and nesfatin-1 serum levels in drug-naïve children with anxiety disorders, including social anxiety disorder, separation anxiety disorder, and generalized anxiety disorder, and in healthy controls.

This study included 45 children (14 boys and 31 girls) with anxiety disorders and 35 healthy controls (13 boys and 22 girls) aged 8-18 years. The severity of anxiety disorders and additional symptoms were evaluated using the Revised Child Anxiety and Depression Scales-Child Version. Enzyme-linked immunosorbent assay (ELISA) was used to evaluate leptin, ghrelin, and nesfatin-1 serum levels.

Leptin levels were significantly higher in children with anxiety disorders than in the control group, and ghrelin and nesfatin-1 levels were significantly lower in children with anxiety disorders than in the control group for girls and for the entire sample. However, only low nesfatin-1 levels were significantly associated with anxiety disorders in boys. In the entire sample, potential confounders such as age, sex, body mass index, and the severity of depressive symptoms were controlled for, and the results were the same for ghrelin and nesfatin-1 levels. However, the difference in leptin levels between groups was not significant.

These findings suggest that dysregulation of ghrelin and nesfatin-1 concentrations may be related to the etiopathogenesis of childhood anxiety disorders.

Leptin and ghrelin are two key hormones that play opposing roles in the regulation of appetite and energy balance. Ghrelin stimulates appetite and food intake following binding to receptors and the subsequent activation of orexigenic neurons in the arcuate nucleus. Leptin, conversely, has been demonstrated to suppress appetite and reduce food intake. This occurs through the inhibition of ghrelin-activated neurons, while simultaneously activating those that promote satiety and increase energy expenditure. A lack of biological response despite elevated leptin levels, which is known as leptin resistance, is observed in individuals with excess body weight and represents a significant challenge. As the dysregulation of ghrelin and leptin signalling has been linked to the development of obesity and other metabolic disorders, an in-depth understanding of the genetic determinants affecting these two hormones may facilitate a more comprehensive grasp of the intricate interactions that underpin the pathogenesis of obesity.

In this study, the anti-inflammatory, antioxidative, and protective effects of ghrelin were investigated in a fat-fed streptozotocin (STZ) rat model and compared with metformin, diabetes and the healthy control groups. Histopathological evaluations were performed on H&E-stained pancreas and brain sections. Biochemical parameters were investigated by enzyme-linked immunosorbent assay. Blood glucose levels were significantly decreased with ghrelin or metformin treatments than the diabetes group. STZ administration increased brain, renal and pancreatic IL-1β, TNF-α and MDA while decreasing GPX, CAT, SOD, and NGF levels. Ghrelin increased renal GPX, CAT, NGF pancreatic GPX, SOD, CAT, NGF and brain SOD, NGF while it decreased renal, pancreatic and brain IL-1β, TNF-α and MDA levels. Ghrelin reduced neuronal loss and degeneration in the cerebral cortex and hippocampus and greatly ameliorated diabetes-related damage in pancreas. In conclusion, the data suggested that ghrelin is an effective candidate as a protectant for reducing the adverse effects of diabetes.

Obesity is a global health crisis, with increasing evidence linking environmental factors such as exposure to endocrine-disrupting chemicals (EDCs) to its development. This study examines the transgenerational effects of exposure to the model obesogen, tributyltin (TBT), on obesity and metabolic health, specifically focusing on how these effects interact with a diet modeling the 50th percentile of US dietary consumption [the Total Western Diet (TWD)]. Pregnant F0 dams were exposed to TBT, and their offspring were subjected at adulthood to different diets, including a high-fat diet and TWD, across multiple subsequent generations (F1-F3). We found that TBT exposure predisposed male offspring to increased fat accumulation, insulin resistance, and metabolic dysfunction, effects that were exacerbated by the TWD. Notably, male offspring displayed elevated leptin levels, hepatic fibrosis, and inflammatory responses under TWD exposure, suggesting an additive or synergistic relationship between obesogen exposure and dietary fat intake. These transgenerational effects were largely absent in female offspring, underscoring sex-specific vulnerabilities to environmental and dietary factors. Our results demonstrated that the combination of prenatal TBT exposure and TWD amplifies metabolic disturbances across generations, highlighting the need to consider both environmental chemicals and dietary patterns in addressing the obesity pandemic. This study underscores the critical role of early-life EDC exposures and dietary factors in shaping long-term metabolic health and the potential for transgenerational programming of susceptibility to obesity and metabolic disorders.

1. Chicken ghrelin (GH) plays an important role in regulating growth hormone secretion, immunity and gastrointestinal motility. This study utilised haematoxylin-eosin staining, quantitative reverse transcription PCR and western blotting to examine the effects of high-level ghrelin on the proliferation of small intestinal epithelial cells, intestinal nutrient transport and the mucosal immune barrier in chicks.2. Eighty, 17-d-old layer type chicks were randomly divided into two groups: control (C treated with sterile phosphate buffer) and the ghrelin-treated group (GH; intraperitoneally injected with 0.5 nM GH per 100 g body weight). At 1, 3 and 5 d post-injection, six chicks from each group were randomly selected for sampling of the duodenum and ileum.3. Administering GH reduced the expression of proliferating cell nuclear antigen protein in the duodenum and leucine-rich repeat-containing G protein-coupled receptor 5 mRNA in both the duodenum and ileum. In addition, GH affected villus height and ratio of villus height to crypt (H/C) depth in these sections and fatty acid binding protein 6 expression in the ileum. The relative mRNA levels of oligopeptide transporter 1, solute carrier family 3 member 1, solute carrier family 1 member 1 and solute carrier family 5 member 1 were decreased by GH.4. Birds treated with GH had a decrease in duodenal intraepithelial lymphocytes, Paneth cells and ileal goblet cells. There was a reduction in mucin 2 mRNA in goblet cells and lysozyme C and phospholipaseA2 mRNA in Paneth cells. Additionally, the relative mRNA levels of avian β-defensin 1 (AvBD1), AvBD6 and AvBD7 in the duodenum and ileum decreased with GH administration.5. The GH inhibited proliferation of chicken duodenal epithelial cells and decreased surface area available for intestinal villus absorption. This affected the transport of intestinal amino acids, glucose and bile acids and impaired the function of the mucosal immune barrier in both the duodenum and ileum.

Liver-expressed antimicrobial peptide 2 (LEAP2) is an endogenous antagonist and inverse agonist of the ghrelin receptor, countering ghrelin's effects on cell signaling and feeding. However, despite an emerging interest in LEAP2's physiology and pharmacology, its endocrine regulation remains unclear. Here, we report that plasma LEAP2 levels decrease significantly upon glucagon infusions during somatostatin clamps in humans. This effect is preserved in patients with obesity and type 2 diabetes while diminished following a hypercaloric diet and a sedentary lifestyle for 2 weeks. Additionally, insulin receptor antagonism offsets the upregulation of LEAP2 during the postprandial state in mice. Finally, insulin and glucagon receptor-expressing hepatocytes are the primary source of hepatic LEAP2 expression, coinciding with a putative enhancer-like signature bound by insulin- and glucagon-regulated transcription factors at the LEAP2 locus. Collectively, our findings implicate insulin and glucagon in regulating LEAP2 and warrant further investigations into the exact mechanisms orchestrating this endocrine axis.

Risky drinking rates are rising, particularly in women, yet sex as a biological variable has only recently gained traction. The centrally projecting Edinger-Westphal (EWcp) nucleus has emerged as a key regulator of alcohol consumption. Here we found that EWcppeptidergic cells reduce binge drinking specifically in female mice. We show this effect is mediated by the ghrelin receptor (GHSR), with EWcppeptidergic inhibition blocking ghrelin-induced drinking and Ghsr knockdown in EWcppeptidergic, but not EWcpglutamatergic or ventral tegmental area cells, reducing binge drinking in females, independent of circulating sex hormones. Female mice showed higher EWcp Ghsr expression, and EWcppeptidergic neurons were more sensitive to ghrelin. Moreover, intra-EWcp delivery of GHSR inverse agonist and antagonist reduced binge drinking, suggesting direct actions of ghrelin. These findings highlight the EWcp as a critical mediator of excessive alcohol consumption via GHSR in female mice, offering insights into the ghrelin system's role in alcohol consumption.

Cystic echinococcosis (CE) is a parasitic disease caused by the larval stage of Echinococcus granulosus, and the immunosuppressive microenvironment exacerbates disease progression. Ghrelin, a peptide hormone, plays a role in modulating immune inflammation and may influence the progression of E. granulosus infection through its receptor, GHSR (growth hormone secretagogue receptor). However, whether GHSR downregulation can inhibit E. granulosus infection remains unclear. In this study, we extracted liver tissues from E. granulosus-infected mice and those treated with the GHSR antagonist [D-Lys3]-GHRP-6. Proteomic analysis revealed 341 differentially expressed proteins, of which 185 were upregulated and 156 were downregulated. Metabolomic sequencing revealed 101 differentially expressed metabolites, including 62 upregulated and 39 downregulated metabolites. KEGG pathway enrichment analysis of both proteomic and metabolomic data revealed seven key signalling pathways, 11 key proteins, and 26 key metabolites that interact through metabolic and organic system networks. Next, we examined the disease progression of E. granulosus infection in GHSR-knockout mice. Compared with the E. granulosus (Eg) group, the GHSR-KO group presented a significant reduction in the number of liver infection foci. The serum and liver ghrelin levels were significantly greater in the E. granulosus group than in the control group, along with increased secretion of proinflammatory cytokines (IL-2 and IFN-γ) and decreased secretion of anti-inflammatory cytokines (IL-4 and IL-10). In contrast, the GHSR-KO group presented significantly lower ghrelin levels in both the serum and liver, with reduced proinflammatory cytokine secretion and increased anti-inflammatory cytokine secretion, similar to those of the control group. Furthermore, ghrelin and inflammation-related factors, including MyD88, NF-κB p65, iNOS, and Arg-1, exhibited coordinated expression changes in liver lesions and surrounding areas. These findings suggest that GHSR gene knockout can ameliorate the progression of liver E. granulosus infection and associated liver inflammation.

Osteosarcoma (OS) is the most common primary bone malignancy because of its extra high tendency of metastasis. In-depth research is needed to uncover the pathogenesis of patients with OS cells. We collected 74 tissue samples from patients with OS cells and measured the expression levels of ghrelin by immunohistochemistry. Ghrelin was added into OS cell lines in CCK8 assays, JC-1 staining and Western blot analysis were performed to explore its effect on the aggressiveness of OS cells and drug resistance. To determine its function, ghrelin was overexpressed or knocked down in OS cells and then detect cell proliferation in the xenograft mouse model and orthotopic model. Western blot analysis was performed to explore ghrelin-regulated signal pathways. In this work, we identified the relation between the level of ghrelin expression and poor prognosis of OS patients. As well as promoting proliferation, migration, and invation, ghrelin promotes the survival of OS in vitro as well as in vivo, and reduces the apoptosis of OS cells. What's more, ghrelin increases the resistance of cis-platinum by changing mitochondrial function and decreases the expression of MDR-1. Above all, these results demonstrated ghrelin exerts tumorigenic and metastatic effects and may be a potential therapeutic target.

The Spontaneously Running Tokushima Shikoku (SPORTS) rat is characterized by hyperactive behavior but is also a potential model for studies of the role of the gut-pancreas axis in the regulation of insulin secretion. We here explored the role of ghrelin, a hormone associated with appetite regulation, in insulin dynamics within the context of streptozotocin (STZ) resistance in SPORTS rats. Comprehensive analyses-including histological examinations, gene expression profiling, and assessment of metabolic parameters-revealed that SPORTS rats are resistant to STZ-induced pancreatic injury and that, in addition to low circulating ghrelin levels, they manifest increased circulating levels of active glucagon-like peptide-1 (GLP-1) and upregulated expression of Pdx1 in the pancreas. Ghrelin administration attenuated the STZ resistance of these rats, with suppression of GLP-1 and downregulation of Pdx1 expression being implicated in this effect. Our results highlight the complex interplay among ghrelin, GLP-1, and insulin dynamics, and they suggest potential new therapeutic targets for diabetes.

Imbalance between gastrointestinal peptides has been implicated as a cause of chemotherapy-induced nausea and vomiting (CINV) and anorexia in cancer patients. This study comprehensively evaluated the changes in blood levels of five gastrointestinal peptide: substance P, neuropeptide (NPY), motilin, ghrelin and leptin, following chemotherapy, and the relationship between these peptides and CINV or anorexia.

This single-center, prospective, observational study recruited 20 patients with esophageal cancer, urothelial cancer, or testiculoma undergoing cisplatin-based chemotherapy. Plasma levels of five gastrointestinal peptides were measured on days 1 (baseline; before administering chemotherapy), 3, 5 and 8 of the chemotherapy session. Anorexia and CINV were defined as visual analog scale scores 25 mm or higher at least once during the observation period.

Plasma NPY and leptin were significantly elevated in the early phase (day 3) of the chemotherapy session, while plasma motilin and substance P were significantly elevated in the late phase (days 5 and 8). Plasma motilin showed significant elevation on days 5 and 8 compared to baseline in CINV group but no significant increase in non-CINV group, and the levels were significantly higher in CINV than in non-CINV group. Plasma leptin peaked significantly on day 3 in both anorexia and non-anorexia groups, and remained significantly higher on day 5 compared to baseline in anorexia group but not in non-anorexia group.

CINV is associated with excessive secretion of motilin and anorexia is related to sustained elevation of leptin, suggesting the potential of these peptides as quantitative indicators of CINV and anorexia.

Drugs targeting the ghrelin receptor hold therapeutic potential in anorexia, obesity and diabetes. However, developing effective drugs is challenging. To tackle this common issue across a broad drug target, this study aims to understand how anamorelin, the only approved drug targeting the ghrelin receptor, operates compared to other synthetic drugs. Our research elucidated the receptor's structure with anamorelin and miniGq, unveiling anamorelin's superagonistic activity. We demonstrated that ligands with distinct chemical structures uniquely bind to the receptor, resulting in diverse conformations and biasing signal transduction. Moreover, our study showcased the utility of structural information in effectively identifying natural genetic variations altering drug action and causing severe functional deficiencies, offering a basis for selecting the right medication on the basis of the individual's genomic sequence. Thus, by building on structural analysis, this study enhances the foundational framework for selecting therapeutic agents targeting the ghrelin receptor, by effectively leveraging signaling bias and genetic variations.

In general, ghrelin is known as one of the orexigenic (increasing appetite or food intake) hormones in mammals. However, it has also been shown that ghrelin inhibits water intake, which appears to be inconsistent with its role in the feeding response. In this study, the effect of ghrelin on water intake was comprehensively addressed using conscious seawater-acclimated eels as an experimental model for water drinking behaviour. When injected intra-arterially, ghrelin inhibited copious drinking in a dose-dependent manner without affecting arterial pressure. This effect contrasted with the inhibitory effect of atrial natriuretic peptide (ANP) on drinking, which is synchronized with a vasodepressor effect. Similarly, intra-cerebroventricular injection of ghrelin also decreased the drinking rate without affecting arterial pressure. Continuous infusion of ghrelin from the ventral aorta also decreased the drinking rate, concomitant with an increase in plasma ghrelin concentration. The inhibitory effects of ghrelin on drinking were as potent and efficacious as those of ANP. The inhibitory action was not blocked by pre-treatment with a ghrelin receptor antagonist ([D-Lys3] GHRP-6); consistently, the agonist form (GHRP-6) injected intra-arterially did not show any inhibitory effect of ghrelin when injected peripherally. These results demonstrate that ghrelin is a potent anti-dipsogen in eels without baroreflex and ANP secretion, and it is possible that ghrelin's effect might be mediated through another type of ghrelin receptor that [D-Lys3] GHRP-6 or GHRP-6 do not bind.