Ghrelin Impairs Prandial Glucose Tolerance and Insulin Secretion in Healthy Humans Despite Increasing GLP-1

Weight Loss Improved Hypothalamic GH Deficiency but not Hypogonadotropic Hypogonadism in a Man With Down Syndrome

Down syndrome (DS) is associated with several endocrine disorders, including diabetes, obesity, and primary hypogonadism. Here, we present a man with DS who manifested with atypical hypogonadotropic hypogonadism and in whom weight loss resulted in the improvement of hypothalamic GH deficiency. A 27-year-old man with DS and severe obesity was admitted for hypoxia resulting from obesity hypoventilation syndrome. Laboratory tests showed normal levels of LH and FSH despite low testosterone and free testosterone levels. Moreover, thyroid stimulating hormone and prolactin levels were slightly elevated, although a euthyroid function was observed, and GH and IGF-1 levels were low. Endocrinological stimulation tests revealed hypogonadotropic hypogonadism and hypothalamic GH deficiency. Reduction in body weight by 35.3% resulted in the improvement of the IGF-1, thyroid stimulating hormone, and prolactin levels to the reference range, whereas the LH and FSH levels remained low, despite slight elevation. Levels of leptin, which suppresses the hypothalamus-gonadotroph-gonadal axis and upregulates thyrotropin-releasing hormone expression, decreased with weight loss. Furthermore, ghrelin, whose levels increase with weight loss, stimulates GH secretion. Thus, leptin and ghrelin could have contributed to the observed changes in the pituitary hormone profile after weight loss.

Acyl ghrelin, desacyl ghrelin and their ratio affect hepatic steatosis via PPARγ signaling pathway

BACKGROUND AND STUDY AIMS

Ghrelin is an appetite hormone-containing 28-amino acid and has 4 different forms in the body. Ghrelin forms have different physiological functions in the body. This study aims to analyze the effect of acyl and desacyl ghrelin hormone on hepatic steatosis and biochemical findings in 36 male Wistar rats.

MATERIALS AND METHODS

Rats were split into 6 equal groups, consisting of control, acyl ghrelin, desacyl ghrelin, acyl/desacyl 3:1, acyl/desacyl 1:1, and acyl/desacyl 1:3 groups, and administered placebo or 200 ng/kg hormone subcutaneous twice a day for 14 days. Oral Glucose Tolerance Test (OGTT) was performed on Day 15, Insulin Tolerance Test (ITT) on Day 16, and scarification procedure on Day 17. Certain biochemical data and liver diacylglycerol (DAG), glycogen, protein kinase C and PPAR-γ levels were detected in the blood. Histological analyses were also conducted on the liver tissues.

RESULTS

The highest plasma total cholesterol and VLDL-K levels were found in the acyl/desacyl 1:3 group, and lower insulin, and HOMA-IR levels were found in groups where acyl and desacyl were administered together (p < 0.05). PPAR-γ gene expression level increased in acyl ghrelin and acyl/desacyl 1:3 groups compared to the control group. Protein kinase C gene expression was highest in the acyl/desacyl 1:3 group. The most severe degenerative findings compliant with steatosis in the liver were observed in the acyl ghrelin group (p < 0.05).

CONCLUSION

It was determined that administering rats acyl alone and acyl/desacyl by 1:3 caused the highest PPAR-γ gene expression, serum total cholesterol, HDL-K, and VLDL-K levels in the body. Besides, it is shown that desacyl ghrelin effectively regulates the blood glucose level when administered alone.

Ghrelin as a Biomarker of "Immunometabolic Depression" and Its Connection with Dysbiosis

Ghrelin, a gastrointestinal peptide, is an endogenous ligand of growth hormone secretagogue receptor 1a (GHSR1a), which is mainly produced by X/A-like cells in the intestinal mucosa. Beyond its initial description as a growth hormone (GH) secretagogue stimulator of appetite, ghrelin has been revealed to have a wide range of physiological effects, for example, the modulation of inflammation; the improvement of cardiac performance; the modulation of stress, anxiety, taste sensation, and reward-seeking behavior; and the regulation of glucose metabolism and thermogenesis. Ghrelin secretion is altered in depressive disorders and metabolic syndrome, which frequently co-occur, but it is still unknown how these modifications relate to the physiopathology of these disorders. This review highlights the increasing amount of research establishing the close relationship between ghrelin, nutrition, microbiota, and disorders such as depression and metabolic syndrome, and it evaluates the ghrelinergic system as a potential target for the development of effective pharmacotherapies.

Effects of ileal glucose infusion on enteropancreatic hormone secretion in humans: relationship to glucose absorption

BACKGROUNDS

The distal small intestine plays an important role in regulating the secretion of entero-pancreatic hormones that are critical to the control of glucose metabolism and appetite, but the quantitative contribution of a specific segment to these effects is unknown.

PURPOSES

To determine the effects of 30 cm of the ileum exposed to glucose on the secretion of ghrelin, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) insulin, C-peptide and glucagon, in relation to glucose absorption in non-diabetic subjects.

BASIC PROCEDURES

10 non-diabetic subjects with a loop ileostomy after early-stage rectal cancer resection were studied on 2 days in a double-blind, randomized and crossover fashion, when a catheter was inserted retrogradely 30 cm from the ileostomy for infusion of a glucose solution containing 30 g glucose and 3 g 3-O-methylglucose (as a marker of active glucose absorption), or 0.9% saline, over 60 min. Ghrelin, GIP, GLP-1, insulin, C-peptide, glucagon and ileal glucose absorption (from concentrations of 3-O-methylglucose in serum and glucose in ileostomy effluent) were measured over 180 min.

MAIN FINDINGS

12.0 ± 1.2 g glucose was absorbed over 180 min. Compared to saline, ileal glucose resulted in minimal increases in blood glucose and plasma insulin and C-peptide, but substantial increases in plasma GLP-1, without affecting ghrelin, GIP or glucagon. The magnitude of the GLP-1 response to glucose was strongly related to the increase in serum 3-O-methylglucose.

PRINCIPAL CONCLUSIONS

Stimulation of the terminal ileum by glucose, even over a short length (30 cm), induces substantial GLP-1 release, coupled primarily to active glucose absorption.

CLINICAL REGISTRATION

NCT05030376 (ClinicalTrials.gov).

Peptides in the regulation of glucagon secretion

Glucose homeostasis is maintained by the glucoregulatory hormones, glucagon, insulin and somatostatin, secreted from the islets of Langerhans. Glucagon is the body's most important anti-hypoglycemic hormone, mobilizing glucose from glycogen stores in the liver in response to fasting, thus maintaining plasma glucose levels within healthy limits. Glucagon secretion is regulated by both circulating nutrients, hormones and neuronal inputs. Hormones that may regulate glucagon secretion include locally produced insulin and somatostatin, but also urocortin-3, amylin and pancreatic polypeptide, and from outside the pancreas glucagon-like peptide-1 and 2, peptide tyrosine tyrosine and oxyntomodulin, glucose-dependent insulinotropic polypeptide, neurotensin and ghrelin, as well as the hypothalamic hormones arginine-vasopressin and oxytocin, and calcitonin from the thyroid. Each of these hormones have distinct effects, ranging from regulating blood glucose, to regulating appetite, stomach emptying rate and intestinal motility, which makes them interesting targets for treating metabolic diseases. Awareness regarding the potential effects of the hormones on glucagon secretion is important since secretory abnormalities could manifest as hyperglycemia or even lethal hypoglycemia. Here, we review the effects of each individual hormone on glucagon secretion, their interplay, and how treatments aimed at modulating the plasma levels of these hormones may also influence glucagon secretion and glycemic control.

Gastrointestinal Hormones and β-Cell Function After Gastric Bypass and Sleeve Gastrectomy: A Randomized Controlled Trial (Oseberg)

CONTEXT

Whether Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) differentially affect postprandial gastrointestinal hormones and β-cell function in type 2 diabetes remains unclear.

OBJECTIVE

We aimed to compare gastrointestinal hormones and β-cell function, assessed by an oral glucose tolerance test (OGTT) 5 weeks and 1 year after surgery, hypothesizing higher glucagon-like peptide-1 (GLP-1) levels and greater β-cell response to glucose after RYGB than after SG.

METHODS

This study was a randomized, triple-blind, single-center trial at a tertiary care center in Norway. The primary outcomes were diabetes remission and IVGTT-derived β-cell function. Participants with obesity and type 2 diabetes were allocated (1:1) to RYGB or SG. We measured gastrointestinal hormone profiles and insulin secretion as β-cell glucose sensitivity (β-GS) derived from 180-minute OGTTs.

RESULTS

Participants were 106 patients (67% women), mean (SD) age 48 (10) years. Diabetes remission rates at 1 year were higher after RYGB than after SG (77% vs 48%; P = 0.002). Incremental area under the curve (iAUC0-180) GLP-1 and β-GS increased more after RYGB than after SG, with 1-year between-group difference 1173 pmol/L*min (95% CI, 569-1776; P = 0.0010) and 0.45 pmol/kg/min/mmol (95% CI, 0.15-0.75; P = 0.0032), respectively. After surgery, fasting and postprandial ghrelin levels were higher and decremental AUC0-180 ghrelin, iAUC0-180 glucose-dependent insulinotropic polypeptide, and iAUC0-60 glucagon were greater after RYGB than after SG. Diabetes remission at 1 year was associated with higher β-GS and higher GLP-1 secretion.

CONCLUSION

RYGB was associated with greater improvement in β-cell function and higher postprandial GLP-1 levels than SG.

High Coexpression of the Ghrelin and LEAP2 Receptor GHSR With Pancreatic Polypeptide in Mouse and Human Islets

Islets represent an important site of direct action of the hormone ghrelin, with expression of the ghrelin receptor (growth hormone secretagogue receptor; GHSR) having been localized variably to alpha cells, beta cells, and/or somatostatin (SST)-secreting delta cells. To our knowledge, GHSR expression by pancreatic polypeptide (PP)-expressing gamma cells has not been specifically investigated. Here, histochemical analyses of Ghsr-IRES-Cre × Cre-dependent ROSA26-yellow fluorescent protein (YFP) reporter mice showed 85% of GHSR-expressing islet cells coexpress PP, 50% coexpress SST, and 47% coexpress PP + SST. Analysis of single-cell transcriptomic data from mouse pancreas revealed 95% of Ghsr-expressing cells coexpress Ppy, 100% coexpress Sst, and 95% coexpress Ppy + Sst. This expression was restricted to gamma-cell and delta-cell clusters. Analysis of several single-cell human pancreatic transcriptome data sets revealed 59% of GHSR-expressing cells coexpress PPY, 95% coexpress SST, and 57% coexpress PPY + SST. This expression was prominent in delta-cell and beta-cell clusters, also occurring in other clusters including gamma cells and alpha cells. GHSR expression levels were upregulated by type 2 diabetes mellitus in beta cells. In mice, plasma PP positively correlated with fat mass and with plasma levels of the endogenous GHSR antagonist/inverse agonist LEAP2. Plasma PP also elevated on LEAP2 and synthetic GHSR antagonist administration. These data suggest that in addition to delta cells, beta cells, and alpha cells, PP-expressing pancreatic cells likely represent important direct targets for LEAP2 and/or ghrelin both in mice and humans.

The incessant increase curve during oral glucose tolerance tests in Chinese adults with type 2 diabetes and its association with gut hormone levels

Glucose curve shapes during oral glucose tolerance tests (OGTTs) are mainly classified as incessant increase, monophasic and biphasic. Youth with an incessant increase curve have worse β-cell function. The aim of this paper was to investigate the incessant increase curve in Chinese adults with type 2 diabetes (T2DM), and its association with β-cell function and gut hormone levels. Eighty-nine Chinese patients (59 males and 30 females) were included in this study with a mean age of 50.56 ± 16.00 years. They were all recently diagnosed with T2DM and underwent 180-min OGTTs. Data on demographics, β-cell function, and insulin sensitivity were also collected. Gut hormones, including glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and ghrelin, were also detected during the OGTT. A total of 39.3 % of subjects had an incessant increase in the glucose response curve, while 59.6 % had a monophasic curve. Because only one curve was classified as biphasic, patients with a biphasic curve were omitted from further research. Lower plasma C-peptide, HOMA2-β, area under the curve (AUC) of C-peptide, and ratio of AUC of insulin to AUC of glucose were found in patients with incessant increase curves compared to those with monophasic curves (P < 0.05). Higher glycated hemoglobin (HbA_1c) was found in subjects with an incessant increase curve (P < 0.05). Importantly, fasting plasma ghrelin was lower and incremental ghrelin at 120 min was higher in the incessant increase group (P < 0.05), irrespective of age, sex, body mass index (BMI), fasting glucose, and fasting insulin. Time to peak is also a parameter of the OGTT curve shape. In the late-peak group, GLP-1 at 120 min and the AUC of GLP-1 were elevated compared with those in the early-peak group (P < 0.05). In Chinese adults with T2DM, the incessant increase in OGTT shape indicated impaired insulin secretion. Lower fasting ghrelin and absence of ghrelin drops after glucose load may be associated with the incessant increase OGTT shape. In addition, compensatory elevated GLP-1 dose not prevent peak delay in the OGTT curve. Gut hormones may have an effect on OGTT shapes in T2DM adults.

Secondary analysis of gut hormone data from children with and without in utero exposure to gestational diabetes: Differences in the associations among ghrelin, GLP-1, and insulin secretion

BACKGROUND

Intrauterine exposure to gestational diabetes mellitus (GDM) increases risk for type 2 diabetes (T2D). Ghrelin and GLP-1 have opposite functions in nutritional homeostasis and are associated with insulin secretion, but it is not known if individuals exposed to GDM exhibit dysregulation in these associations.

OBJECTIVE

Test the hypothesis that children exposed to GDM in utero will exhibit dysregulation among ghrelin, GLP-1, and C-peptide (reflecting insulin secretion).

METHODS

Data from N = 43 children aged 5 to 10 years were included in this secondary analysis of ghrelin, GLP-1, and C-peptide response to a liquid meal test. Repeated measures mixed model analyses were used to measure associations among hormones.

RESULTS

The association of ghrelin and GLP-1 was moderated by GDM group (P < .01), such that ghrelin was inversely associated with GLP-1 in children without GDM exposure, but not for those exposed to GDM. GLP-1 was positively associated with C-peptide in both groups, but the association was stronger in those exposed to GDM (estimate = 1.06 vs 1.01).

CONCLUSIONS

Differences in the associations among ghrelin, GLP-1, and C-peptide displayed here suggest novel lines of research about whether the regulation of gut hormones and insulin secretion contribute to obesity and risk for T2D in children exposed to GDM.

The Links of Ghrelin to Incretins, Insulin, Glucagon, and Leptin After Bariatric Surgery

Type 2 diabetes mellitus (T2DM) is one of the most prominent and socially significant problems. The present study aimed to identify the mechanisms of interaction of critical regulators of carbohydrate metabolism using bioinformatics and experimental methods and to assess their influence on the development of T2DM. We conducted an in silico search for the relationship of hormones and adipokines and performed functional annotation of the receptors for ghrelin and incretins. Hormones and adipokines were assessed in the plasma of obese patients with and without T2DM as well as after laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (RYGB) surgeries. Incretin- and ghrelin-associated functions and metabolic processes were discovered. Low ghrelin levels were observed in obese patients without T2DM compared with healthy volunteers and the other groups. The highest ghrelin levels were observed in obese patients with T2DM. This defense mechanism against insulin resistance could be realized through the receptors G-protein-coupled receptor (GPCR), growth hormone secretagogue receptor (GHSR), and growth hormone-releasing hormone receptor (GHRHR). These receptors are associated with proliferative, inflammatory, and neurohumoral signaling pathways and regulate responses to nutrient intake. Signaling through the GPCR class unites ghrelin, glucagon, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide (GLP)-1. Ghrelin impairs carbohydrate and lipid metabolism in obese patients. Ghrelin is associated with elevated plasma levels of insulin, glucagon, and leptin. Specific activation of receptors and modulation by posttranslational modifications of ghrelin can control IR’s development in obesity, which is a promising area for research.

Do Gut Hormones Contribute to Weight Loss and Glycaemic Outcomes after Bariatric Surgery?

Bariatric surgery is an effective intervention for management of obesity through treating dysregulated appetite and achieving long-term weight loss maintenance. Moreover, significant changes in glucose homeostasis are observed after bariatric surgery including, in some cases, type 2 diabetes remission from the early postoperative period and postprandial hypoglycaemia. Levels of a number of gut hormones are dramatically increased from the early period after Roux-en-Y gastric bypass and sleeve gastrectomy—the two most commonly performed bariatric procedures—and they have been suggested as important mediators of the observed changes in eating behaviour and glucose homeostasis postoperatively. In this review, we summarise the current evidence from human studies on the alterations of gut hormones after bariatric surgery and their impact on clinical outcomes postoperatively. Studies which assess the role of gut hormones after bariatric surgery on food intake, hunger, satiety and glucose homeostasis through octreotide use (a non-specific inhibitor of gut hormone secretion) as well as with exendin 9–39 (a specific glucagon-like peptide-1 receptor antagonist) are reviewed. The potential use of gut hormones as biomarkers of successful outcomes of bariatric surgery is also evaluated.

Neuroendocrine Response to Exogenous Ghrelin Administration, Combined With Alcohol, in Heavy-Drinking Individuals: Findings From a Randomized, Double-Blind, Placebo-Controlled Human Laboratory Study

BACKGROUND

Accumulating evidence has established a role for the orexigenic hormone ghrelin in alcohol-seeking behaviors. Accordingly, the ghrelin system may represent a potential pharmacotherapeutic target for alcohol use disorder. Ghrelin modulates several neuroendocrine pathways, such as appetitive, metabolic, and stress-related hormones, which are particularly relevant in the context of alcohol use. The goal of the present study was to provide a comprehensive assessment of neuroendocrine response to exogenous ghrelin administration, combined with alcohol, in heavy-drinking individuals.

METHODS

This was a randomized, crossover, double-blind, placebo-controlled human laboratory study, which included 2 experimental alcohol administration paradigms: i.v. alcohol self-administration and i.v. alcohol clamp. Each paradigm consisted of 2 counterbalanced sessions of i.v. ghrelin or placebo administration. Repeated blood samples were collected during each session, and peripheral concentrations of the following hormones were measured: leptin, glucagon-like peptide-1, pancreatic polypeptide, gastric inhibitory peptide, insulin, insulin-like growth factor-1, cortisol, prolactin, and aldosterone.

RESULTS

Despite some statistical differences, findings were consistent across the 2 alcohol administration paradigms: i.v. ghrelin, compared to placebo, increased blood concentrations of glucagon-like peptide-1, pancreatic polypeptide, cortisol, and prolactin, both acutely and during the whole session. Lower levels of leptin and higher levels of aldosterone were also found during the ghrelin vs placebo session.

CONCLUSION

These findings, gathered from a clinically relevant sample of heavy-drinking individuals with alcohol use disorder, provide a deeper insight into the complex interplay between ghrelin and appetitive, metabolic, and stress-related neuroendocrine pathways in the context of alcohol use.

"A LEAP 2 conclusions? Targeting the ghrelin system to treat obesity and diabetes"

BACKGROUND

The hormone ghrelin stimulates food intake, promotes adiposity, increases body weight, and elevates blood glucose. Consequently, alterations in plasma ghrelin levels and the functioning of other components of the broader ghrelin system have been proposed as potential contributors to obesity and diabetes. Furthermore, targeting the ghrelin system has been proposed as a novel therapeutic strategy for obesity and diabetes.

SCOPE OF REVIEW

The current review focuses on the potential for targeting ghrelin and other proteins comprising the ghrelin system as a treatment for obesity and diabetes. The main components of the ghrelin system are introduced. Data supporting a role for the endogenous ghrelin system in the development of obesity and diabetes along with data that seemingly refute such a role are outlined. An argument for further research into the development of ghrelin system-targeted therapeutic agents is delineated. Also, an evidence-based discussion of potential factors and contexts that might influence the efficacy of this class of therapeutics is provided.

MAJOR CONCLUSIONS

It would not be a "leap to" conclusions to suggest that agents which target the ghrelin system - including those that lower acyl-ghrelin levels, raise LEAP2 levels, block GHSR activity, and/or raise desacyl-ghrelin signaling - could represent efficacious novel treatments for obesity and diabetes.

Type 2 diabetes progression: A regulatory network approach

In order to elucidate central elements underlying type 2 diabetes, we constructed a regulatory network model involving 37 components (molecules, receptors, processes, etc.) associated to signaling pathways of pancreatic beta-cells. In a first approximation, the network topology was described by Boolean rules whose interacting dynamics predicted stationary patterns broadly classified as health, metabolic syndrome, and diabetes stages. A subsequent approximation based on a continuous logic analysis allowed us to characterize the progression of the disease as transitions between these states associated to alterations of cell homeostasis due to exhaustion or exacerbation of specific regulatory signals. The method allowed the identification of key transcription factors involved in metabolic stress as essential for the progression of the disease. Integration of the present analysis with existent mathematical models designed to yield accurate account of experimental data in human or animal essays leads to reliable predictions for beta-cell mass, insulinemia, glycemia, and glycosylated hemoglobin in diabetic fatty rats.

Decreased Consumption of Added Fructose Reduces Waist Circumference and Blood Glucose Concentration in Patients with Overweight and Obesity. The DISFRUTE Study: A Randomised Trial in Primary Care

The relationship between fructose intake and insulin resistance remains controversial. Our purpose was to determine whether a reduction in dietary fructose is effective in decreasing insulin resistance (HOMA2-IR). This field trial was conducted on 438 adults with overweight and obese status, without diabetes. A total of 121 patients in a low fructose diet (LFD) group and 118 in a standard diet (SD) group completed the 24-week study. Both diets were prescribed with 30–40% of energy intake restriction. There were no between-group differences in HOMA2-IR. However, larger decreases were seen in the LFD group in waist circumference (−7.0 vs. −4.8 = −2.2 cms, 95% CI: −3.7, −0.7) and fasting blood glucose −0.25 vs. −0.11 = −0.14 mmol/L, 95% CI: −0.028, −0.02). The percentage of reduction in calorie intake was similar. Only were differences observed in the % energy intake for some nutrients: total fructose (−2 vs. −0.6 = −1.4, 95% CI: −2.6, −0.3), MUFA (−1.7 vs. −0.4 = −1.3, 95% CI: −2.4, −0.2), protein (5.1 vs. 3.6 = 1.4, 95% CI: 0.1, 2.7). The decrease in fructose consumption originated mainly from the reduction in added fructose (−2.8 vs. −1.9 = −0.9, 95% CI: −1.6, −0.03). These results were corroborated after multivariate adjustments. The low fructose diet did not reduce insulin resistance. However, it reduced waist circumference and fasting blood glucose concentration, which suggests a decrease in hepatic insulin resistance.

Ghrelin Does Not Directly Stimulate Secretion of Glucagon-like Peptide-1

CONTEXT

The gastrointestinal hormone ghrelin stimulates growth hormone secretion and appetite, but recent studies indicate that ghrelin also stimulates the secretion of the appetite-inhibiting and insulinotropic hormone glucagon-like peptide-1 (GLP-1).

OBJECTIVE

To investigate the putative effect of ghrelin on GLP-1 secretion in vivo and in vitro.

SUBJECTS AND METHODS

A randomized placebo-controlled crossover study was performed in eight hypopituitary subjects. Ghrelin or saline was infused intravenously (1 pmol/min × kg) after collection of baseline sample (0 min), and blood was subsequently collected at time 30, 60, 90, and 120 minutes. Mouse small intestine was perfused (n = 6) and GLP-1 output from perfused mouse small intestine was investigated in response to vascular ghrelin administration in the presence and absence of a simultaneous luminal glucose stimulus. Ghrelin receptor expression was quantified in human (n = 11) and mouse L-cells (n = 3) by RNA sequencing and RT-qPCR, respectively.

RESULTS

Ghrelin did not affect GLP-1 secretion in humans (area under the curve [AUC; 0-120 min]: ghrelin infusion = 1.37 ± 0.05 min × nmol vs. saline infusion = 1.40 ± 0.06 min × nmol [P = 0.63]), but induced peripheral insulin resistance. Likewise, ghrelin did not stimulate GLP-1 secretion from the perfused mouse small intestine model (mean outputs during baseline/ghrelin infusion = 19.3 ± 1.6/25.5 ± 2.0 fmol/min, n = 6, P = 0.16), whereas glucose-dependent insulinotropic polypeptide administration, used as a positive control, doubled GLP-1 secretion (P < 0.001). Intraluminal glucose increased GLP-1 secretion by 4-fold (P < 0.001), which was not potentiated by ghrelin. Finally, gene expression of the ghrelin receptor was undetectable in mouse L-cells and marginal in human L-cells.

CONCLUSIONS

Ghrelin does not interact directly with the L-cell and does not directly affect GLP-1 secretion.

Effects of Bariatric Surgeries on the Size of Myocardial Infarction and Ghrelin Level in Rats with Experimental Decompensated Type 2 Diabetes Mellitus

The effects of bariatric surgeries (sleeve gastrectomy and ileal transposition) on the dynamics of changes in ghrelin level were studied in rats with severe decompensated type 2 diabetes mellitus under conditions of glucose challenge as well as on the size of myocardial infarction in these animals. Diabetes was modelled by high fat diet and a single administration of streptozotocin (25 mg/kg, intraperitoneally). Both bariatric surgeries significantly decreased glucose-induced ghrelin level in the blood of rats with type 2 diabetes mellitus, which attested to an increase in the tissue sensitivity to ghrelin. Sleeve gastrectomy resulted in a decrease in the size of myocardial infarction in diabetic rats, which was calculated as the ratio of the necrosis zone to the zone of the risk of myocardial infarction. Ileal transposition had no effect on this parameter. Our data can be used as the basis for optimization of treatment approaches when using bariatric surgery in the treatment of patients with severe forms of type 2 diabetes mellitus with a high risk of cardiovascular diseases.

Acute effect of a cod protein hydrolysate on postprandial acylated ghrelin concentration and sensations associated with appetite in healthy subjects: a double-blind crossover trial

Background

Fish protein hydrolysates are suggested to contain bioactive sequences capable of affecting metabolic pathways involved in the regulation of glucose metabolism and body weight when consumed in low doses. Modulation of the appetite-regulating hormone ghrelin may explain suppression of insulin secretion and weight loss observed in previous studies with fish protein hydrolysates.

Objective

This study aimed to assess the effect of a single, low dose of cod protein hydrolysate (CPH) before a breakfast meal on postprandial acylated ghrelin concentration and sensations associated with appetite in healthy subjects.

Design

In this explorative trial with a crossover design, 41 healthy individuals (15 males and 26 females, age 51 ± 6 years) completed 2 study days separated by 4–7 days of washout. On both study days, a test drink containing 20 mg CPH or casein (control) per kg body weight was given immediately before a standardized breakfast meal. Acylated ghrelin concentrations were measured before test drink/breakfast (baseline) and at time 0, 20, 40, 80, and 180 min postprandially. Sensations associated with appetite were measured by a Visual Analog Scale (100 mm) at baseline and 0, 20, 40, and 180 min postprandially.

Results

Statistically, no difference was observed between CPH and control for postprandial acylated ghrelin concentrations (mean difference geometric mean: 1.05 pg/mL, 95% confidence interval [CI]: 0.97–1.13, P = 0.266), or between the total area under the curve (tAUC) for acylated ghrelin after CPH (tAUC = 17518 pg/mL × min, 95% CI: 0–47941) and control (tAUC = 17272 pg/mL × min, 95% CI: 0–48048, P = 0.991). No differences were found between CPH and control for sensation of appetite, according to tAUC of postprandial scores for satiety (P = 0.794) and the feeling of fullness (P = 0.996).

Conclusion

We did not find an effect of a single dose of CPH on postprandial concentrations of acylated ghrelin or sensations related to feeling of hunger, compared to control. Further studies should aim to evaluate the effect of a supplement with CPH given daily over a period of time.

[Ghrelin deficiency in patients with type 2 diabetes: the relationships with obesity, adipose tissue dysfunction and glucose variability]

AIM

Ghrelin, a peptide hormone mostly produced by stomach, plays an important role in regulation of feeding behavior, energy balance and glucose homeostasis.

THE AIM

to determine the relationships between fasting serum levels of ghrelin, body composition, adipose tissue endocrine function and glucose variability (GV) in type 2 diabetic subjects with and without obesity.

MATERIALS AND METHODS

We observed 124 individuals with type 2 diabetes, including 42 non - obese subjects and 82 patients with obesity. Thirty non - obese healthy subjects were acted as control. The concentrations of ghrelin, leptin, resistin, and visfatin in the fasting serum were determined by Multiplex analysis. Body composition was assessed with DEXA. The 24-hour and nocturnal GV parameters were derived from continuous glucose monitoring.

RESULTS AND DISCUSSION

Ghrelin levels in patients with diabetes were decreased significantly as compared to control (p.

Intraislet Ghrelin Signaling Does Not Regulate Insulin Secretion From Adult Mice

Exogenous ghrelin reduces glucose-stimulated insulin secretion and endogenous ghrelin protects against hypoglycemia during starvation. Islet ε-cells produce ghrelin and δ-cells express growth hormone secretagogue receptor (GHSR), suggesting the possibility of a paracrine mechanism for islet ghrelin to reach high local concentrations and affect insulin secretion. GHSR has high constitutive activity and may act independently of ghrelin. The objective in this study was to determine whether an intraislet ghrelin-GHSR axis modulates insulin secretion and glucose metabolism using mouse models lacking ghrelin (Ghrl-/- ) or GHSR (Ghsr-/- ). Ghsr-/- and Ghsr+/+ mice had comparable islet ghrelin concentrations. Exogenous ghrelin decreased insulin secretion in perifused isolated islets in a GHSR-dependent manner. Islets isolated from Ghrl-/- or Ghsr-/- mice did not differ from controls in glucose-, alanine-, or GLP-1-stimulated insulin secretion during perifusion. Consistent with this finding, Ghrl-/- and Ghsr-/- male mice studied after either 6 or 16 h of fasting had blood glucose concentrations comparable with those of controls following intraperitoneal glucose, or insulin tolerance tests, or after mixed nutrient meals. Collectively, our data provide strong evidence against a paracrine ghrelin-GHSR axis mediating insulin secretion or glucose tolerance in lean, chow-fed adult mice.

Ghrelin regulation of glucose metabolism

Ghrelin and its receptor, the growth hormone secretagogue receptor 1a (GHSR1a), are implicated in the regulation of glucose metabolism via direct actions in the pancreatic islet, as well as peripheral insulin-sensitive tissues and the brain. Although many studies have explored the role of ghrelin in glucose tolerance and insulin secretion, a complete mechanistic understanding remains to be clarified. This review highlights the local expression and function of ghrelin and GHSR1a in pancreatic islets and how this axis may modulate insulin secretion from pancreatic β-cells. Additionally, we discuss the effect of ghrelin on in vivo glucose metabolism in rodents and humans, as well as the metabolic circumstances under which the action of ghrelin may predominate.

Enteroendocrine Connections in Congenital Isolated GH Deficiency Due to a GHRH Receptor Gene Mutation

CONTEXT

GH and IGF-1 are crucial for attainment of normal body size and regulation of food intake, nutrient storage, and insulin sensitivity. Enteroendocrine connections exist between the GH-IGF-1 axis and insulin, ghrelin, and glucagon-like peptide 1 (GLP-1). The status of these connections in GH deficiency (GHD) is unknown.

OBJECTIVE

To study the enteroendocrine connections before and after a standard meal test in a homogeneous population of adults with congenital untreated isolated GHD (IGHD) due to a mutation in the GHRH receptor gene.

DESIGN

In a cross-sectional study of 20 individuals with IGHD and 20 control subjects, we measured glucose, insulin, ghrelin, and GLP-1 before and 30, 60, 120, and 180 minutes after a standardized test meal. Homeostasis model assessment index of insulin resistance (HOMA-IR) and homeostasis model assessment (HOMA)-β were calculated. Participants scored feelings of hunger, fullness, and prospective food consumption on a visual analog scale.

MAIN OUTCOME MEASURES

Area under the curve (AUC) values of glucose, insulin, ghrelin, GLP-1, hunger, fullness, and prospective food consumption.

RESULTS

Fasting HOMA-IR and HOMA-β were lower in individuals with IGHD than in control subjects (P = 0.002 and P = 0.023, respectively). AUC was higher for hunger (P < 0.0001), glucose (P = 0.0157), ghrelin (P < 0.0001), and GLP-1 (P < 0.0001) and smaller for fullness (P < 0.0001) in individuals with IGHD compared with control subjects. There was no difference in AUC for prospective food consumption or insulin.

CONCLUSIONS

Untreated IGHD is associated with increased GLP-1 secretion and reduced postprandial ghrelin and hunger attenuation in response to a mixed meal. These enteroendocrine connections can result in a favorable outcome in terms of environmental adaptation and guaranteeing appropriate food intake and can confer metabolic benefits.

Ghrelin's Relationship to Blood Glucose

Much effort has been directed at studying the orexigenic actions of administered ghrelin and the potential effects of the endogenous ghrelin system on food intake, food reward, body weight, adiposity, and energy expenditure. Although endogenous ghrelin's actions on some of these processes remain ambiguous, its glucoregulatory actions have emerged as well-recognized features during extreme metabolic conditions. The blood glucose-raising actions of ghrelin are beneficial during starvation-like conditions, defending against life-threatening falls in blood glucose, but they are seemingly detrimental in obese states and in certain monogenic forms of diabetes, contributing to hyperglycemia. Also of interest, blood glucose negatively regulates ghrelin secretion. This article reviews the literature suggesting the existence of a blood glucose-ghrelin axis and highlights the factors that mediate the glucoregulatory actions of ghrelin, especially during metabolic extremes such as starvation and diabetes.

Incretin dysfunction and hyperglycemia in cystic fibrosis: Role of acyl-ghrelin

BACKGROUND

Insulin secretion is insufficient in cystic fibrosis (CF), even before diabetes is present, though the mechanisms involved remain unclear. Acyl-ghrelin (AG) can diminish insulin secretion and is elevated in humans with CF.

METHODS

We tested the hypothesis that elevated AG contributes to reduced insulin secretion and hyperglycemia in CF ferrets.

RESULTS

Fasting AG was elevated in CF versus non-CF ferrets. Similar to its effects in other species, AG administration in non-CF ferrets acutely reduced insulin, increased growth hormone, and induced hyperglycemia. During oral glucose tolerance testing, non-CF ferrets had responsive insulin, glucagon like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) levels and maintained normal glucose levels, whereas CF ferrets had insufficient responses and became hyperglycemic. Interestingly in wild-type ferrets, the acyl-ghrelin receptor antagonist [D-Lys3]-GHRP-6 impaired glucose tolerance, and abolished insulin, GLP-1, and GIP responses during glucose tolerance testing. By contrast, in CF ferrets [D-Lys3]-GHRP-6 improved glucose tolerance, enhanced the insulin-to-glucose ratio, but did not impact the already low GLP-1 and GIP levels.

CONCLUSIONS

These results suggest a mechanism by which elevated AG contributes to CF hyperglycemia through inhibition of insulin secretion, an effect magnified by low GLP-1 and GIP. Interventions that lower ghrelin, ghrelin action, and/or raise GLP-1 or GIP might improve glycemia in CF.

Gut ghrelin regulates hepatic glucose production and insulin signaling via a gut-brain-liver pathway

BACKGROUND

Ghrelin modulates many physiological processes. However, the effects of intestinal ghrelin on hepatic glucose production (HGP) are still unclear. The current study was to explore the roles of intestinal ghrelin on glucose homeostasis and insulin signaling in the liver.

METHODS

The system of intraduodenal infusion and intracerebral microinfusion into the nucleus of the solitary tract (NTS) in the normal chow-diet rats and pancreatic-euglycemic clamp procedure (PEC) combined with [3-³H] glucose as a tracer were used to analyze the effect of intestinal ghrelin. Intraduodenal co-infusion of ghrelin, tetracaine and Activated Protein Kinase (AMPK) activator (AICAR), or pharmacologic and molecular inhibitor of N-methyl-D-aspartate receptors within the dorsal vagal complex, or hepatic vagotomy in rats were used to explore the possible mechanism of the effect of intestinal ghrelin on HGP.

RESULTS

Our results demonstrated that gut infusion of ghrelin inhibited duodenal AMP-dependent protein kinase (AMPK) signal pathways, increased HGP and expression of gluconeogenic enzymes, and decreased insulin signaling in the liver of the rat. Intraduodenal co-infusion of ghrelin receptor antagonist [D-Lys³]-GHRP-6 and AMPK agonist with ghrelin diminished gut ghrelin-induced increase in HGP and decrease in glucose infusion rate (GIR) and hepatic insulin signaling. The effects of gut ghrelin were also negated by co-infusion with tetracaine, or MK801, an N-methyl-D-aspartate (NMDA) receptor inhibitor, and adenovirus expressing the shRNA of NR1 subunit of NMDA receptors (Ad-shNR1) within the dorsal vagal complex, and hepatic vagotomy in rats. When ghrelin and lipids were co-infused into the duodenum, the roles of gut lipids in increasing the rate of glucose infusion (GIR) and lowering HGP were reversed.

CONCLUSIONS

The current study provided evidence that intestinal ghrelin has an effect on HGP and identified a neural glucoregulatory function of gut ghrelin signaling.

Interaction of GLP-1 and Ghrelin on Glucose Tolerance in Healthy Humans

Emerging evidence supports the importance of ghrelin to defend against starvation-induced hypoglycemia. This effect may be mediated by inhibition of glucose-stimulated insulin secretion as well as reduced insulin sensitivity. However, administration of ghrelin during meal consumption also stimulates the release of glucagon-like peptide 1 (GLP-1), an incretin important in nutrient disposition. The objective of this study was to evaluate the interaction between ghrelin and GLP-1 on parameters of glucose tolerance following a mixed-nutrient meal. Fifteen healthy men and women completed the study. Each consumed a standard meal on four separate occasions with a superimposed infusion of 1) saline, 2) ghrelin, 3) the GLP-1 receptor antagonist exendin(9-39) (Ex9), or 4) combined ghrelin and Ex9. Similar to previous studies, infusion of ghrelin caused glucose intolerance, whereas Ex9 had a minimal effect. However, combined ghrelin and Ex9 resulted in greater postprandial glycemia than either alone, and this effect was associated with impaired β-cell function and decreased glucose clearance. These findings suggest that in the fed state, stimulation of GLP-1 mitigates some of the effect of ghrelin on glucose tolerance. This novel interaction between gastrointestinal hormones suggests a system that balances insulin secretion and glucose disposal in the fed and fasting states.

Efficacy and Safety of Relamorelin in Diabetics With Symptoms of Gastroparesis: A Randomized, Placebo-Controlled Study

BACKGROUND & AIMS

Gastroparesis is a complication of diabetes with few treatment options. Relamorelin (also referred to as RM-131) is a selective, prokinetic agonist of ghrelin. We aimed to evaluate the efficacy of relamorelin on symptoms and gastric emptying (GE) in a 12-week, phase 2B study of diabetic patients with moderate to severe gastroparesis symptoms (DG).

METHODS

We performed a study of 393 patients with DG (37.7% male; 9.9% with type 1 diabetes; median age, 58.2 years [range 20-76]; median body mass index, 31.4 kg/m2 [range, 18.2-60.1]; HbA1c level, 7.6%, [range, 5.2-11.0]). All participants had 13C-spirulina GE breath test T1/2 values of 79 minutes or more (with 89.8% delayed relative to 90th %ile of normal, 85.75 minutes), recent vomiting, and gastroparesis cardinal symptom index-daily diary scores of 2.6 or more. Patients were randomly assigned to groups given placebo (n=104) or relamorelin (10 μg [n=98], 30 μg [n=109], or 100 μg [n=82] twice daily) for 12 weeks, following a 2-week, single-blind, placebo run-in period. Patient-reported outcomes were determined from DG Symptom Severity daily e-diaries, in which patients recorded vomiting frequency and symptom scores (nausea, abdominal pain, postprandial fullness, and bloating) on a 0-10 scale. Endpoints were change from baseline in vomiting frequency, composite DG Symptom Severity score, GE, and safety. We performed longitudinal, mixed-effects model analysis using repeated measures, with baseline and baseline-by-week interaction values as covariates.

RESULTS

Patients given relamorelin had a 75% reduction in vomiting frequency compared with baseline, but this difference was not significant compared with the placebo group. All 4 symptoms of DG (composite or individual symptoms) were significantly reduced over the 12-week study period in all 3 relamorelin dose groups compared with the placebo group (all P < .05, based on longitudinal analysis over 12 weeks). Relamorelin significantly accelerated GE from baseline compared with placebo (by 12%, P < .05 for the 10 μg and 30 μg groups; P = .051 for the 100 μg group). Dose-related worsening of glycemic control was noted in 14.5% of patients who received relamorelin; some required insulin or other diabetes drug dosage adjustments.

CONCLUSIONS

In a phase 2B randomized trial of patients with moderate to severe DG, relamorelin significantly reduced core symptoms of DG and overall composite score compared with placebo, accelerated GE, and was generally safe and well tolerated. ClinicalTrials.gov Identifier: NCT02357420.

Metabolic responses to exogenous ghrelin in obesity and early after Roux-en-Y gastric bypass in humans

AIMS

Ghrelin is a gastric-derived hormone that stimulates growth hormone (GH) secretion and has a multi-faceted role in the regulation of energy homeostasis, including glucose metabolism. Circulating ghrelin concentrations are modulated in response to nutritional status, but responses to ghrelin in altered metabolic states are poorly understood. We investigated the metabolic effects of ghrelin in obesity and early after Roux-en-Y gastric bypass (RYGB).

MATERIALS AND METHODS

We assessed central and peripheral metabolic responses to acyl ghrelin infusion (1 pmol kg-1  min-1 ) in healthy, lean subjects (n = 9) and non-diabetic, obese subjects (n = 9) before and 2 weeks after RYGB. Central responses were assessed by GH and pancreatic polypeptide (surrogate for vagal activity) secretion. Peripheral responses were assessed by hepatic and skeletal muscle insulin sensitivity during a hyperinsulinaemic-euglycaemic clamp.

RESULTS

Ghrelin-stimulated GH secretion was attenuated in obese subjects, but was restored by RYGB to a response similar to that of lean subjects. The heightened pancreatic polypeptide response to ghrelin infusion in the obese was attenuated after RYGB. Hepatic glucose production and hepatic insulin sensitivity were not altered by ghrelin infusion in RYGB subjects. Skeletal muscle insulin sensitivity was impaired to a similar degree in lean, obese and post-RYGB individuals in response to ghrelin infusion.

CONCLUSIONS

These data suggest that obesity is characterized by abnormal central, but not peripheral, responsiveness to ghrelin that can be restored early after RYGB before significant weight loss. Further work is necessary to fully elucidate the role of ghrelin in the metabolic changes that occur in obesity and following RYGB.

Relamorelin for the treatment of gastrointestinal motility disorders

INTRODUCTION

Current treatments for gastroparesis are limited. Chronic idiopathic constipation (CIC) has more treatment options, but none are efficacious for severe cases. Areas covered: Molecular targets to accelerate GI motility are being identified, and relamorelin, a synthetic ghrelin analog, has been promising. In humans, relamorelin increases growth hormone levels and accelerates gastric emptying. Relamorelin was superior to placebo for symptom relief in phase IIA studies for diabetic gastroparesis (DG) and CIC. In phase IIB studies in DG, relamorelin did not significantly reduce vomiting frequency when compared to placebo, but it reduced four symptoms of DG (nausea, fullness, bloating and abdominal pain) and accelerated gastric emptying. To date, relamorelin has been well tolerated and safe in humans without cardiac or neurologic adverse effects. It is still in clinical trial stages and not yet approved by the Food and Drug Administration. Phase III studies are underway. Expert opinion: Relamorelin shows promise in treating DG, with a reduction in core symptoms. Relative to available treatments, it appears to be efficacious and well tolerated. The absence of neurological or cardiovascular adverse effects places it at an advantage over other available therapies. Once approved, it will likely become the drug of first choice for DG.

Acyl Ghrelin Induces Insulin Resistance Independently of GH, Cortisol, and Free Fatty Acids

Ghrelin produced in the gut stimulates GH and ACTH secretion from the pituitary and also stimulates appetite and gastric emptying. We have shown that ghrelin also induces insulin resistance via GH-independent mechanisms, but it is unknown if this effect depends on ambient fatty acid (FFA) levels. We investigated the impact of ghrelin and pharmacological antilipolysis (acipimox) on insulin sensitivity and substrate metabolism in 8 adult hypopituitary patients on stable replacement with GH and hydrocortisone using a 2 × 2 factorial design: Ghrelin infusion, saline infusion, ghrelin plus short-term acipimox, and acipimox alone. Peripheral and hepatic insulin sensitivity was determined with a hyperinsulinemic euglycemic clamp in combination with a glucose tracer infusion. Insulin signaling was assayed in muscle biopsies. Peripheral insulin sensitivity was reduced by ghrelin independently of ambient FFA concentrations and was increased by acipimox independently of ghrelin. Hepatic insulin sensitivity was increased by acipimox. Insulin signaling pathways in skeletal muscle were not consistently regulated by ghrelin. Our data demonstrate that ghrelin induces peripheral insulin resistance independently of GH, cortisol, and FFA. The molecular mechanisms remain elusive, but we speculate that ghrelin is a hitherto unrecognized direct regulator of substrate metabolism. We also suggest that acipimox per se improves hepatic insulin sensitivity.

Acute administration of acyl, but not desacyl ghrelin, decreases blood pressure in healthy humans

OBJECTIVE

To compare the effects of acyl ghrelin (AG) and desacyl ghrelin (DAG) on blood pressure (BP), heart rate (HR) and other autonomic parameters in healthy humans and to elucidate the hormonal mechanisms through which AG could exert its cardiovascular effects.

DESIGN

Seventeen healthy participants underwent frequent monitoring of systolic (sBP) and diastolic blood pressure (dBP), HR, respiratory rate (RR) and body surface temperature (Temp) during continuous infusion of AG, DAG, combined AG + DAG or saline control before and during an IV glucose tolerance test on 4 separate days. Plasma catecholamines, renin and aldosterone levels were also measured. Differences in outcome measures between treatment groups were assessed using mixed-model analysis.

RESULTS

Compared to the saline control, AG and combined AG + DAG infusions decreased sBP, dBP, mean arterial blood pressure (MAP), HR and Temp. In contrast, DAG infusion did not alter BP, RR or Temp, but did decrease HR. The AG and AG + DAG infusions also raised plasma aldosterone levels compared to saline (P < 0.001) without affecting renin or catecholamine levels.

CONCLUSIONS

The decrease in BP, HR, RR and Temp with AG infusion suggests mediation through the autonomic nervous system. The lack of response to DAG suggests that these autonomic effects require activation of the ghrelin receptor.

Ghrelin Is a Regulator of Glucagon-Like Peptide 1 Secretion and Transcription in Mice

The gut hormones ghrelin, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic peptide (GIP) have been intensively studied for their role in metabolism. It is, however, not well known whether the hormones interplay and regulate the secretion of each other. In this study, we studied the effect of ghrelin on GLP-1, GIP, and insulin secretion during an oral glucose tolerance test (OGTT) in mice. Intravenous administration of ghrelin caused increased GLP-1 secretion during the OGTT. On the other hand, ghrelin had no effect on circulating levels of glucose, insulin, and GIP. Furthermore, ghrelin treatment reduced proglucagon mRNA expression in GLUTag cells. The effect of ghrelin on GLP-1 secretion and proglucagon transcription was reinforced by the presence of GHS-R1a in human and mouse ileal L-cells, as well as in GLUTag cells. In summary, ghrelin is a regulator of GLP-1 secretion and transcription, and interfering with GHS-R1a signaling may be a way forward to enhance endogenous GLP-1 secretion in subjects with type 2 diabetes.