Ghrelin and insulin metabolism

Exploring the underlying mechanisms of obesity and diabetes and the potential of Traditional Chinese Medicine: an overview of the literature

Obesity and diabetes are closely related metabolic disorders that have become major public health concerns worldwide. Over the past few decades, numerous studies have explored the underlying mechanisms of these disorders and identified various risk factors, including genetics, lifestyle, and dietary habits. Traditional Chinese Medicine (TCM) has been increasingly recognized for its potential to manage obesity and diabetes. Weight loss is difficult to sustain, and several diabetic therapies, such as sulfonylureas, thiazolidinediones, and insulin, might make it harder to lose weight. While lifestyle changes should be the primary approach for people interested in lowering weight, drugs are also worth investigating. Since some of the newer glucose-lowering medications that cause weight loss, such as glucagon-like peptide-1 receptor agonists (GLP-1 RAs) and sodium-glucose cotransporter 2 inhibitors (SGLT2i), are additionally utilized or are under consideration for use as anti-obesity drugs, the frontier between glucose-lowering medication and weight loss drugs appears to be shifting. This review provides an overview of the literature on the underlying mechanisms of obesity and diabetes and the prospect of TCM in their management. We discuss the various TCM interventions, including acupuncture, herbal medicine, and dietary therapy, and their effects on metabolic health. We also highlight the potential of TCM in regulating gut microbiota, reducing inflammation, and improving insulin sensitivity. The findings suggest that TCM may provide a promising approach to preventing and managing obesity and diabetes. However, further well-designed studies are needed to confirm the efficacy and safety of TCM interventions and to elucidate their underlying mechanisms of action.

Is there any interaction of resistin and adiponectin levels with protein-energy wasting among patients with chronic kidney disease

The aim of this study was to evaluate the effects of adipocytokines including adiponectin, leptin, resistin, neuropeptide Y and ghrelin in chronic kidney disease (CKD) patients on appearance of protein-energy wasting (PEW). One hundred fifty patients with mean age of 45.4 ± 15.9 years, without active infections or chronic inflammatory conditions were recruited into the study. Study groups were control group (consisting of 30 healthy volunteers with normal kidney functions), hemodialysis group, predialysis group, peritoneal dialysis group and kidney transplant group. Fasting morning serum leptin, ghrelin, acylated ghrelin, neuropeptide Y, adiponectin, resistin levels of all of the groups were measured. Anthropometric and nutritional assessments of all patients were obtained. Diagnosis of PEW was made according to definition recommended by the International Society of Renal Nutrition and Metabolism. Presence of PEW in hemodialysis (23.3%) and peritoneal dialysis (26.7%) groups were significantly higher than those of predialysis (3.3%), and transplantation (0%) groups. Adiponectin and resistin levels in predialysis, peritoneal dialysis and hemodialysis patients were significantly higher than control group (p: 0.0001). This study had given significant positive correlations between presence of PEW and serum resistin (r: 0.267, p: 0.001), and serum adiponectin levels (r: 0.349, p: 0.0001). There were no relationship between presence of PEW and ghrelin, acylated-ghrelin, neuropeptide Y, and leptin levels of the groups. CKD patients except transplant patients had higher adiponectin and resistin levels than control group. PEW was found to be linearly correlated with resistin and adiponectin. High serum resistin and adiponectin levels might have a role in development of PEW among dialysis patients.

Effect of ghrelin on glucose regulation in mice

Improvement of glucose metabolism after bariatric surgery appears to be from the composite effect of the alterations in multiple circulating gut hormone concentrations. However, their individual effect on glucose metabolism during different conditions is not clear. The objective of this study was to determine whether ghrelin has an impact on glycogenolysis, gluconeogenesis, and insulin sensitivity (using a mice model). Rate of appearance of glucose, glycogenolysis, and gluconeogenesis were measured in wild-type (WT), ghrelin knockout (ghrelin(-/-)), and growth hormone secretagogue receptor knockout (Ghsr(-/-)) mice in the postabsorptive state. The physiological nature of the fasting condition was ascertained by a short-term fast commenced immediately at the end of the dark cycle. Concentrations of glucose and insulin were measured, and insulin resistance and hepatic insulin sensitivity were calculated. Glucose concentrations were not different among the groups during the food-deprived period. However, plasma insulin concentrations were lower in the ghrelin(-/-) and Ghsr(-/-) than WT mice. The rates of gluconeogenesis, glycogenolysis, and indexes of insulin sensitivity were higher in the ghrelin(-/-) and Ghsr(-/-) than WT mice during the postabsorptive state. Insulin receptor substrate 1 and glucose transporter 2 gene expressions in hepatic tissues of the ghrelin(-/-) and Ghsr(-/-) were higher compared with that in WT mice. This study demonstrates that gluconeogenesis and glycogenolysis are increased and insulin sensitivity is improved by the ablation of the ghrelin or growth hormone secretagogue receptor in mice.

Association of ghrelin Leu72Met polymorphism with type 2 diabetes mellitus in Chinese population

BACKGROUND

Ghrelin, a novel endogenous ligand for the growth hormone secretagogue receptor, is considered to implicate the development of the type 2 diabetes mellitus (T2DM). The Leu72Met (+408C>A) polymorphism of the preproghrelin, has been linked to obesity, insulin resistance and diabetes.

OBJECTIVE

To investigate the distribution of ghrelin gene Leu72Met polymorphism and its association with the type 2 diabetes mellitus in Chinese population.

METHODS

We conducted a case-control study on 877 patients with T2DM and 864 controls, which were genotyped by the polymerase chain reaction (PCR) technique, denaturing high performance liquid chromatography (DHPLC) and DNA sequence analysis. Laboratory analyses were carried out in the hospital laboratory.

RESULTS

No significant difference in the Leu72Met genotype distributions and allele frequency was observed between type 2 diabetes mellitus and controls (both P>0.05). The polymorphism was not associated with T2DM. However, among the T2DM group, the patients carrying Leu72Leu genotype had significantly increased levels of FPG and serum creatinine compared with variant genotypes (Leu72Met and Met72Met) (P<0.05). In the control group, the subjects with variant genotypes had significantly increased levels of FINS, HOMA-IR compared with Leu72Leu genotype (P<0.05).

CONCLUSION

The Leu72Met polymorphism of the preproghrelin gene was not associated with T2DM in Chinese population. However, it may have some roles in the etiology of insulin resistance.

[Endocrine function in obesity]

Obesity is associated to significant disturbances in endocrine function. Hyper insulinemia and insulin resistance are the best known changes in obesity, but their mechanisms and clinical significance are not clearly established. Adipose tissue is considered to be a hormone-secreting endocrine organ; and increased leptin secretion from the adipocyte, a satiety signal, is a well-established endocrine change in obesity. In obesity there is a decreased GH secretion. Impairment of somatotropic function in obesity is functional and may be reversed in certain circumstances. The pathophysiological mechanism responsible for low GH secretion in obesity is probably multifactorial. There are many data suggesting that a chronic state of somatostatin hypersecretion results in inhibition of GH release. Increased FFA levels, as well as a deficient ghrelin secretion, probably contribute to the impaired GH secretion. In women, abdominal obesity is associated to hyperandrogenism and low sex hormone-binding globulin levels. Obese men, particularly those with morbid obesity, have decreased testosterone and gonadotropin levels. Obesity is associated to an increased cortisol production rate, which is compensated for by a higher cortisol clearance, resulting in plasma free cortisol levels that do not change when body weight increases. Ghrelin is the only known circulating orexigenic factor, and has been found to be decreased in obese people. In obesity there is also a trend to increased TSH and free T3 levels.

Total and acylated ghrelin in liver cirrhosis: correlation with clinical and nutritional status

OBJECTIVES

The pathogenesis of anorexia in cirrhotic patients is complex and the appetite-modulating hormone ghrelin could be involved. Acylated ghrelin is the biologically active form that modifies insulin sensitivity and body composition. The aim of the present study was to compare acylated and total ghrelin concentration in patients with liver cirrhosis and to investigate the possible relationship between ghrelin and clinical and nutritional parameters.

DESIGN AND METHODS

Sixty patients with viral liver cirrhosis who did not have hepatocellular carcinoma or acute infections were studied. Twenty healthy volunteers were recruited after matching for age, gender, and body mass index with the patients and served as controls. Fasting levels of total, acylated ghrelin, leptin, TNF-alpha and insulin were measured in all subjects, in addition, clinical and nutrition parameters were assessed.

RESULTS

In cirrhotic patients, plasma levels of both acylated and total ghrelin were significantly higher than those in the controls. The mean plasma acylated ghrelin levels were significantly higher in Child C cirrhosis compared to Child A and B. Ghrelin (total and acylated) were negatively correlated with leptin in cirrhotic patients confirming the fact that leptin acts as a physiological counterpart of ghrelin.

CONCLUSIONS

Nutritional and metabolic abnormalities in cirrhotic patients may be dependent on the changes in the ghrelin/leptin systems, mainly the acylated form of ghrelin.

Fasting and postprandial plasma ghrelin levels are decreased in patients with liver failure previous to liver transplantation

Anorexia is a problem of paramount importance in patients with advanced liver failure. Ghrelin has important actions on feeding and weight homeostasis. Concentrations of ghrelin are controversial in liver cirrhosis. Our aim was to study fasting ghrelin and their response to an oral glucose tolerance test (OGTT) in liver failure patients and normal subjects.

METHODS

We included 16 patients with severe liver failure prior to liver transplantation. As a control group we included 10 age- and BMI-matched healthy subjects. After an overnight fast, 75 g of oral glucose were administered; glucose, insulin, and ghrelin were obtained at baseline and at times 30, 60, 90, and 120 min, respectively.

RESULTS

Fasting ghrelin (median and range) were statistically significantly lower for patients compared to the controls, 527 (377-971) pg/ml vs. 643 (523-2163) pg/ml, P = 0.045, for patients and controls, respectively. The area under the curve for total ghrelin post-OGTT were lower in end-stage liver failure patients than in the control group, 58815 (44730-87420) pg/ml min vs. 76560 (56160-206385) pg/ml min, for patients and controls, respectively, P = 0.027.

CONCLUSIONS

Ghrelin levels are significantly decreased both fasting and post-OGTT in patients with liver failure candidates for transplantation. Decreased ghrelin levels could contribute to anorexia in patients with cirrhosis.

Recent Developments in Ghrelin Receptor Ligands

The 28-amino acid peptide ghrelin is a neuroendocrine hormone synthesized primarily in the stomach. It stimulates growth hormone secretion and appetite, thus promoting food intake and body-weight gain. The pharmacological properties of this peptide are mediated by the growth hormone secretagogue receptor type 1a (GHS-R1a). Given its wide spectrum of biological activities, it is evident that the discovery of ghrelin and its receptor has opened up many perspectives in the fields of neuroendocrine and metabolic research and has had an influence on such fields of internal medicine as gastroenterology, oncology, and cardiology. It is therefore increasingly likely that synthetic, peptidyl, and nonpeptidyl GHS-R1a ligands, acting as agonists, partial agonists, antagonists, or inverse agonists, could have both clinical and therapeutic potential. This review summarizes the various types of GHS-R1a ligands that have been described in the literature and discusses the recent progress made in this research area.

Effects of Homologous Ghrelins on the Growth Hormone/Insulin-like Growth Factor-I Axis in the Tilapia, Oreochromis mossambicus

Ghrelin is a gut-brain peptide synthesized mainly in the oxyntic mucosal cells of the stomach, and has potent growth hormone (GH)-releasing and orexigenic activities. Recently, two forms of ghrelin, ghrelin-C8 and -C10, were identified in the Mozambique tilapia (Oreochromis mossambicus). The present study describes in vitro and in vivo effects of these endogenous ghrelins on the GH/insulin-like growth factor-I (IGF-I) axis. Ghrelin-C8 (100 nM) stimulated GH release from primary cultures of pituitary cells after 4 and 8 h of incubation, whereas no effect was seen on prolactin (PRL) release. Stimulatory effects of ghrelin-C8 and -C10 (100 nM) on GH release during 6 h of incubation were blocked by pre-incubation with GHS receptor antagonist, [D-Lys(3)]-GHRP-6 (10 microM). Intraperitoneal injection of ghrelin-C8 (1 ng/g body weight) and -C10 (0.1 and 1 ng/g body weight) significantly increased plasma GH levels after 5 h. Significant increases were observed also in hepatic expression of IGF-I and GH receptor (GHR) mRNA following injections of both forms of ghrelin (0.1 and 1 ng/g body weight), although there was no effect on plasma levels of IGF-I. In the next experiment, both forms of ghrelin (1 ng/g body weight) significantly increased plasma IGF-I levels 10 h after the injection. No significant effect of either ghrelin was observed on plasma PRL levels. Both forms of GHS receptor (GHSR-1a and -1b) were found in the pituitary, clearly indicating that tilapia ghrelins stimulate primarily GH release through the GHS receptor. Stimulation of hepatic expression of IGF-I and GHR suggests metabolic roles of ghrelin in tilapia.

Plasma ghrelin response to an oral glucose load in growth hormone-deficient adults treated with growth hormone

BACKGROUND

Little is known about the pathophysiology of ghrelin secretion in growth hormone-deficient adults treated with growth hormone, and the relationship between plasma ghrelin and hyperinsulinemia induced by an oral glucose load has not been investigated in these patients.

OBJECTIVE

In the present study we examined the relationship between plasma ghrelin, insulin, C-peptide and leptin after an oral glucose load in growth hormone-deficient adults receiving treatment with growth hormone.

METHODS

Plasma ghrelin, leptin, insulin, C-peptide and blood glucose were measured before and then at 30, 60, 90 and 120 min after the ingestion of glucose (75 g orally) in 20 growth hormone-deficient adults (12 women and 8 men), who had been treated with growth hormone for 7.2 +/- 1.3 years (mean +/- SE). Plasma ghrelin was also determined before and after the glucose load in 10 age-and weight-matched healthy persons (5 women and 5 men).

RESULTS

The oral glucose load induced a similar percent suppression of plasma ghrelin in the growth hormone-deficient patients and in the healthy persons. In both groups plasma ghrelin decreased significantly 30 min after the glucose load and remained suppressed throughout the test period. In the patients plasma insulin (baseline, 15.9 +/- 3.9 microIU/ml) and C-peptide (baseline, 2.5 +/- 0.3 ng/ml) showed opposite changes with peak responses at 30 min (insulin, 109.5 +/- 15.6 microIU/ml) or 60 min (C-peptide, 10.3 +/- 1.1 ng/ml). In these patients, post-glucose, but not baseline plasma ghrelin levels correlated negatively with plasma insulin, C-peptide and blood glucose levels, whereas baseline plasma ghrelin correlated inversely with baseline plasma leptin.

CONCLUSIONS

The similar suppression of plasma ghrelin in growth hormone-deficient patients treated with growth hormone and in healthy persons after an oral glucose load argues against disturbed regulation of ghrelin secretion in these patients. The correlations between post-glucose plasma ghrelin, insulin and blood glucose support the existence of a previously proposed link between hyperinsulinemia (or increased blood glucose) and suppression of ghrelin levels.

Effect of ghrelin in dry matter intake and energy metabolism in prepartum sheep: A preliminary study

The objective of this study was to determine the effect of ghrelin on dry matter intake and energy metabolites in ewes during the last 10d of gestation. Ewes were randomly assigned to either a treatment (n=6) or a control group (n=6). One hour after feeding (08:00 and 16:00), ewes in the treated group were given ovine ghrelin (3 microg/kg, i.m.) and the control group received an equivalent volume of saline. Treatments were continued until lambing. Daily blood samples were taken starting at assignment. The principal findings were that: (1) ewes treated with ghrelin had a higher dry matter intake only on the first day of treatment; (2) treated ewes had lower serum concentrations of non-esterified fatty acids and insulin but higher serum concentrations of growth hormone; (3) serum concentrations of beta-hydroxy butyrate and cortisol were not different between treated and non-treated ewes. In conclusion, treatment with ghrelin affected dry matter intake and energy metabolites of pre-partum ewes during the last 10 d of pregnancy.

Oral glucose load inhibits circulating ghrelin levels to the same extent in normal and obese children

OBJECTIVE

The presence of both the GH secretagogue (GHS) receptor and ghrelin in the pancreas indicates an involvement of this hormone in glucose metabolism. Ghrelin secretion is increased by fasting and energy restriction, decreased by food intake, glucose load, insulin and somatostatin in normal adults; however, food intake is not able to inhibit circulating ghrelin levels in children, suggesting that the profile of ghrelin secretion in children is different from that in adults. Moreover, how ghrelin secretion is regulated in childhood as a function of fat mass is still unclear.

DESIGN AND SUBJECTS

We studied the effect of oral glucose load (75 g solution orally) on circulating total ghrelin levels in 14 obese children (group A, four boys and 10 girls, aged 9.3 +/- 2.3 years) and 10 lean children (group B, five boys and five girls, aged 9.7 +/- 3.8 years).

MEASUREMENTS

In all the sessions, blood samples were collected every 30 min from 0 up to +120 min. GH, insulin and glucose levels were assayed at each time point.

RESULTS

Glucose peaks following an oral glucose tolerance test (OGTT) in groups A and B were similar; however, both basal and OGTT-stimulated insulin levels in group A were higher than in group B (P < 0.05). Basal total ghrelin levels in group A (281.3 +/- 29.5 pg/ml) were lower (P < 0.0005) than in group B (563.4 +/- 81.5 pg/ml). In both groups A and B, the OGTT inhibited total ghrelin levels (P < 0.005). In terms of absolute values, total ghrelin levels in group A were lower (P < 0.0005) than those in group B at each time point after glucose load. The percentage nadir in total ghrelin levels recorded in group A (-25% at 90 min) was similar to that recorded in group B (-31% at 120 min). Total ghrelin levels were negatively associated with BMI (r = 0.5, P < 0.005) but not with glucose or insulin levels.

CONCLUSION

Ghrelin secretion is reduced in obese children. It is, however, equally sensitive in both obese and lean children to the inhibitory effect of oral glucose load.

The Effect of Zinc supplementation on Ghrelin-Immunoreactive Cells and Lipid Parameters in Gastrointestinal Tissue of Streptozotocin-Induced Female Diabetic Rats

Zinc is an essential nutrient with a wide range of functions and closely involved in a variety of enzymatic processes of importance in glucose, protein and lipid metabolism. Ghrelin is the endogenous ligand of the G protein coupled growth hormone secretagogue receptor. The regulatory mechanism that explain the biosynthesis and secretion of ghrelin in the gastrointestinal tract has not been clarified. This study was undertaken to examine the effect of zinc supplementation on the streptozotocin (STZ)-induced diabetic rats, which exhibits ghrelin production and secretion, and lipid metabolism on the gastrointestinal tract. The animals were divided into four groups. Group I: Non-diabetic untreated animals. Group II: Zinc-treated non-diabetic rats. Group III: STZ-induced diabetic untreated animals. Group IV: Zinc-treated diabetic animals. Zinc sulfate was given to some of the experimental animals by gavage at a dose of 100 mg/kg body weight every day for 60 days. In the zinc-treated diabetic group, the blood glucose levels decreased and body weight increased as compared to the diabetic untreated group. Zinc supplementation to STZ-diabetic rats revealed the protective effect of zinc on lipids parameters such as total lipid, cholesterol, HDL-cholesterol and atherogenic index. There is no statistically change in ghrelin-immunoreactive cells in gastrointestinal tissue. But, it has found that zinc supplementation caused a significant reduction in densities of ghrelin-producing cells of fundic mucosa of zinc-treated diabetic animals as compared to untreated, non-diabetic controls. Zinc supplementation may contribute to prevent some complications of diabetic rats, biochemically.

Serum ghrelin concentrations in patients with chronic renal failure undergoing dialysis

BACKGROUND

Ghrelin is a recently discovered protein hormone mainly synthesized in the gastric endocrine cells. This hormone not only is a potent growth hormone secretagogue but also is involved in the regulation of food ingestion and energy metabolism. Derangements in ghrelin secretion in patients with chronic renal failure (CRF) have not been fully evaluated.

OBJECTIVE

Our aim has been to quantify serum concentrations of total ghrelin in a group of patients with CRF on chronic therapy with both haemodialysis (HD) and peritoneal dialysis (PD) in comparison with a group of patients on conservative management (predialysis).

PATIENTS AND MEASUREMENTS

We studied 68 CRF patients treated by HD (n = 30, 16 men, age 61.2 +/- 1.8 years) and PD groups (n = 38, 21 men, age 54.4 +/- 1.7 years). A group of 19 uraemic patients on conservative management served as the control. Serum concentrations of ghrelin, leptin, insulin, IGF I and GH were measured in all subjects.

RESULTS

Patients undergoing HD showed similar concentrations of ghrelin in comparison with the control group (9491 +/- 787 vs 9280 +/- 918 pg/ml, NS). However, PD patients exhibited baseline ghrelin concentrations significantly lower than those found in patients on conservative management (3230 +/- 216 pg/ml, P < 0.0001). Men and women showed similar serum ghrelin levels in both HD (9845.9 +/- 1071 vs 9085 +/- 1194 pg/ml) and PD patients (3214 +/- 297 vs 3250 +/- 324 pg/ml). Hypertension and diabetes mellitus did not influence ghrelin levels. Serum GH levels were positively correlated with serum ghrelin concentrations in both HD (r = 0.46, P < 0.05) and PD (r = 0.53, P < 0.001) patients; however, no relationships between ghrelin, leptin, insulin and IGF I were found.

CONCLUSIONS

These results suggest that PD is accompanied by a striking decrement in baseline ghrelin concentrations in comparison with values found both in HD and control patients. Further studies are necessary to determine mechanisms involved in ghrelin regulation in uraemic patients.

Low plasma ghrelin concentration is an indicator of the metabolic syndrome

BACKGROUND

Low ghrelin concentration has been associated with several features of metabolic syndrome (MS), but the relationship between ghrelin concentration and MS as a cluster of metabolic aberrations has not yet been studied.

AIMS OF THE STUDY

To analyse whether ghrelin concentration is associated with MS.

RESEARCH DESIGN AND METHODS

Fasting plasma ghrelin concentrations of the population-based cohort of 1037 middle-aged men and women were analysed using a commercial radioimmunoassay kit (Phoenix Peptide). MS was determined using the new International Diabetes Federation criteria.

RESULTS

The prevalence of MS was 37.2%. The ghrelin concentrations were decreased in subjects with MS (635 pg/mL) compared to those without MS (687 pg/mL) (P=0.001). Ghrelin levels decreased with an increase in the number of metabolic abnormalities. Low ghrelin was a statistically significant predictor of MS in logistic regression analysis (P=0.005) so that the subjects in the 1st ghrelin quartile were at higher risk of having MS compared to the subjects in the 4th quartile (OR=1.82, 95% CI: 1.27-2.60, P=0.001). This association remained statistically significant after adjustment for age and sex (OR=1.76, 95% CI: 1.24-2.55, P=0.002).

CONCLUSIONS

Metabolic syndrome is associated with low ghrelin levels suggesting a relationship of ghrelin in the metabolic disturbances of MS.

Ghrelin and the metabolic balance

Several studies have provided evidence that ghrelin is involved in the regulation of metabolic balance. Recent data provide evidence that when studying the effects of ghrelin on energy balance, differential influences of the acylated and non-acylated forms of the peptide must be considered. Although the correlation between the two forms is good, they may be different hormones with opposite actions with non-acylated ghrelin being able to antagonize some of the effects of the acylated form. Future studies will reveal which of the two forms of ghrelin, the acylated or non-acylated forms, dominates and determines the net influence on energy balance.

Glucagon inhibits ghrelin secretion in humans

OBJECTIVE

It is well known that i.m. glucagon administration stimulates GH and cortisol release in humans, although the mechanisms are unclear. These effects are similar to those described for ghrelin on somatotroph and corticotroph function. The aim of the present study was to investigate the role of ghrelin in mediating the stimulatory effects of glucagon and to evaluate the effect of glucagon on ghrelin secretion.

DESIGN AND METHODS

We studied the endocrine and metabolic response to i.m. glucagon administration in 24 subjects (14 men, 10 women; age 19-65 years; body mass index, 25.3 +/- 1 kg/m(2)), who were shown to have an intact anterior pituitary function as evaluated before enclosure.

RESULTS

Serum ghrelin concentrations fell significantly at 30, 60, 120 and 180 min after glucagon administration (means +/- s.e.m.; baseline, 377.9 +/- 34.5 pg/ml; nadir, 294.6 +/- 28.3 pg/ml (60 min); P < 0.01). Conversely, i.m. glucagon elicited an increase in GH (baseline, 1.5 +/- 0.4 microg/l; peak, 14.2 +/- 2.7 microg/l (180 min); P < 0.01) and cortisol concentrations (baseline, 452.6 +/- 35.2 nmol/l; peak, 622.1 +/- 44 nmol/l (180 min); P < 0.01). The changes in ghrelin concentration at both 120 and 180 min were still significant after correction for glucose and insulin (P < 0.05).

CONCLUSIONS

We show that i.m. glucagon decreases ghrelin significantly. Therefore, the already known stimulatory effects of i.m. glucagon on cortisol and GH are not mediated by a change in ghrelin concentrations. The mechanisms underlying the ghrelin suppression after i.m. glucagon are unlikely to include glucose or insulin variations and need to be further elucidated.

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

OBJECTIVE

To investigate the relationship between active ghrelin and oxidative stress in obese subjects.

DESIGN

We measured the plasma levels of free 8-epi-prostaglandin F(2alpha) (8-epi-PGF(2alpha), a reliable and systemic marker of oxidative stress) and the active form of ghrelin in 17 obese and 17 normal subjects. The biologically active forms of ghrelin were measured using a commercially available radio-immunoassay kit and free 8-epi-PGF(2alpha) was measured using an enzyme immunoassay kit.

RESULTS

The circulating level of active ghrelin was significantly decreased (20.4 +/- 2.6 vs 40.9 +/- 3.9 fmol/ml, P < 0.01) while that of 8-epi-PGF(2alpha) was significantly increased (61.5 +/- 9.6 vs 17.3 +/- 3.4 pg/ml, P < 0.01) in obese subjects compared with normal subjects. The plasma levels of active ghrelin and 8-epi-PGF(2alpha) were significantly correlated in obese (r = -0.507, P < 0.05) and in all (r = -0.577, P < 0.01) subjects. Multivariate analysis showed that the plasma levels of active ghrelin and 8-epi-PGF(2alpha) were significantly and independently correlated in all subjects (F = 7.888, P < 0.01).

CONCLUSIONS

There is an inverse correlation between circulating levels of active ghrelin and oxidative stress in obesity. Low circulating levels of active ghrelin may enhance oxidative stress and the process of atherosclerosis in obese subjects.

Circulating acylated and total ghrelin and galanin in children with insulin-treated type 1 diabetes: relationship to insulin therapy, metabolic control and pubertal development

OBJECTIVE

To study the circulating levels of two gut-derived peptides in children with type 1 (insulin-dependent) diabetes mellitus (IDDM).

RESEARCH DESIGN AND METHODS

Plasma levels of ghrelin, both total ghrelin (TG) and the acylated form (AG), and galanin and their relationships with insulin dosage, metabolic control, IGFBP-1, body mass and pubertal development were evaluated in 91 children, aged 11.1 +/- 2.7 years, affected by IDDM and treated with insulin. Ninety-one healthy children were selected as controls.

RESULTS

Body mass index (BMI)-adjusted levels of both forms of ghrelin were reduced in IDDM compared with healthy subjects, with greater values in prepubertal than pubertal IDDM subjects. A negative association was found between AG and fasting insulin serum levels and insulin resistance [measured by using the homeostasis model assessment of insulin resistance (HOMA IR)] among the healthy children. IDDM children showed a negative association of their plasma ghrelin (both acylated and total) with daily insulin dosage, and the three adiposity indices (BMI, skinfold thickness and percentage fat mass). IGFBP-1 levels were higher among the IDDM children without any association with ghrelin serum values. BMI-adjusted plasma levels of galanin were higher among IDDM compared to healthy subjects, irrespective of sex or pubertal development. Greater values for galanin were found among pubertal than prepubertal subjects in both groups without any significant differences between the genders. A positive association was found between galanin and BMI in both groups and between galanin and haemoglobin A1c (HbA1c) among the IDDM children. No relationship existed between either galanin and fasting serum insulin among the healthy subjects or galanin and both insulin dosage or duration of treatment among the IDDM subjects.

CONCLUSIONS

The associations found between both ghrelin and galanin with adiposity indices could be considered as an indirect signal of involvement of the two peptides in the development of the nutritional status of the IDDM adolescents. The reduction in both forms of ghrelin could be involved in the development of the body mass increase of IDDM subjects with opposite effects, either influencing insulin sensitivity or exerting a compensatory restraint of feeding.

The negative association between plasma ghrelin and IGF-I is modified by obesity, insulin resistance and type 2 diabetes

AIMS/HYPOTHESIS

Ghrelin is a natural growth hormone-releasing peptide thought to be involved in the regulation of energy metabolism. The recent studies concerning the association between ghrelin and insulin-like growth factor-I (IGF-I) concentrations have shown either negative correlation or no correlation at all. The aims of this study were to clarify the association between ghrelin and IGF-I concentrations in a large cohort and to characterize whether obesity, insulin resistance and type 2 diabetes affect this association.

METHODS

We analysed fasting plasma ghrelin and IGF-I concentrations of 1,004 middle-aged subjects of the population-based OPERA study. Insulin resistance was estimated using QUICKI.

RESULTS

IGF-I concentrations were negatively associated with ghrelin concentrations in the analysis of all subjects before (beta=-0.32, p<0.001) and after adjustments for BMI, insulin levels, sex and age (beta=-0.40, p<0.001). The association was particularly strong in males and in the higher BMI tertiles. The degree of association varied in relation to the glycaemic status: no insulin resistance: r(2)=6.5% (p<0.001), insulin resistance without type 2 diabetes: r(2)=21.0% (p<0.001), type 2 diabetes: r(2)=25.4 (p<0.001). IGF-I levels explained larger proportion (r(2)=9.8%) of the variation in ghrelin concentrations compared to fasting insulin concentration (r(2)=3.0%) and BMI (r(2)=1.5%).

CONCLUSIONS/INTERPRETATION

There is a negative and independent association between ghrelin and IGF-I concentrations in middle-aged subjects. The interaction between IGF-I and ghrelin is modified by obesity, IR and type 2 diabetes. Further studies are warranted to elucidate the role of ghrelin in the development of these states.

Ghrelin: more than a natural GH secretagogue and/or an orexigenic factor

Ghrelin, an acylated peptide produced predominantly by the stomach, has been discovered to be a natural ligand of the growth hormone secretagogue receptor type 1a (GHS-R1a). Ghrelin has recently attracted considerable interest as a new orexigenic factor. However, ghrelin exerts several other neuroendocrine, metabolic and also nonendocrine actions that are explained by the widespread distribution of ghrelin and GHS-R expression. The likely existence of GHS-R subtypes and evidence that the neuroendocrine actions, but not all the other actions, of ghrelin depend on its acylation in serine-3 revealed a system whose complexity had not been completely explored by studying synthetic GHS. Ghrelin secretion is mainly regulated by metabolic signals and, in turn, the modulatory action of ghrelin on the control of food intake and energy metabolism seems to be among its most important biological actions. However, according to a recent study, ghrelin-null mice are neither anorectics nor dwarfs and this evidence clearly depicts a remarkable difference from leptin null mice. Nevertheless, the original and fascinating story of ghrelin, as well as its potential pathophysiological implications in endocrinology and internal medicine, is not definitively cancelled by these data as GHS-R1a null aged mice show significant alterations in body composition and growth, in glucose metabolism, cardiac function and contextual memory. Besides potential clinical implications for natural or synthetic ghrelin analogues acting as agonists or antagonists, there are several open questions awaiting an answer. How many ghrelin receptor subtypes exist? Is ghrelin 'the' or just 'a' GHS-R ligand? That is, are there other natural GHS-R ligands? Is there a functional balance between acylated and unacylated ghrelin forms, potentially with different actions? Within the next few years suitable answers to these questions will probably be found, making it possible to gain a better knowledge of ghrelin's potential clinical perspectives.

Ghrelin secretion is inhibited by glucose load and insulin-induced hypoglycaemia but unaffected by glucagon and arginine in humans

OBJECTIVE

Circulating ghrelin levels are increased by fasting and decreased by feeding, glucose load, insulin and somatostatin. Whether hyperglycaemia and insulin directly inhibit ghrelin secretion still remains matter of debate. The aim of the present study was therefore to investigate further the regulatory effects of glucose and insulin on ghrelin secretion.

DESIGN AND SUBJECTS

We studied the effects of glucose [oral glucose tolerance test (OGTT) 100 g orally], insulin-induced hypoglycaemia [ITT, 0.1 IU/kg insulin intravenously (i.v.)], glucagon (1 mg i.v.), arginine (0.5 mg/kg i.v.) and saline on ghrelin, GH, insulin, glucose and glucagon levels in six normal subjects.

MEASUREMENTS

In all the sessions, blood samples were collected every 15 min from 0 up to + 120 min. Ghrelin, GH, insulin, glucagon and glucose levels were assayed at each time point.

RESULTS

OGTT increased (P < 0.01) glucose and insulin while decreasing (P < 0.01) GH and ghrelin levels. ITT increased (P < 0.01) GH but decreased (P < 0.01) ghrelin levels. Glucagon increased (P < 0.01) glucose and insulin without modifying GH and ghrelin. Arginine increased (P < 0.01) GH, insulin, glucagon and glucose (P < 0.05) but did not affect ghrelin secretion.

CONCLUSIONS

Ghrelin secretion in humans is inhibited by OGTT-induced hyperglycaemia and ITT but not by glucagon and arginine, two substances able to increase insulin and glucose levels. These findings question the assumption that glucose and insulin directly regulate ghrelin secretion. On the other hand, ghrelin secretion is not associated with the GH response to ITT or arginine, indicating that the somatotroph response to these stimuli is unlikely to be mediated by ghrelin.

Impact of laparoscopic adjustable gastric banding on plasma ghrelin, eating behaviour and body weight

BACKGROUND

Plasma ghrelin, an orexigenic peptide derived from the stomach and duodenum, increases following weight loss and might contribute to weight regain. The aim of the present study was to evaluate the effect of laparoscopic adjustable gastric banding (LAGB) on body weight and body composition as well as plasma ghrelin in relation to eating behaviour in morbidly obese patients.

MATERIALS AND METHODS

This study was performed in 23 morbidly obese subjects who underwent standardized LAGB. Fasting plasma ghrelin was measured before and 6 months after surgery and was correlated with body weight, body composition, and eating behaviour.

RESULTS

Six months after LAGB, body weight decreased significantly by -15.7 +/- 1.4 kg (mean +/- SEM, P = 0.0001) which was accompanied by an increased cognitive restraint of eating (P = 0.001), and by a decreased disinhibition of eating and susceptibility to hunger (P = 0.0001). Plasma ghrelin increased (P = 0.016) by 27.2% from 100.39 +/- 12.90 to 127.22 +/- 13.15 fmol mL(-1). The change in plasma ghrelin correlated with changes in body weight (r = -0.49, P = 0.02), BMI (r = -0.42, P = 0.048) and fat mass (r = -0.519, P = 0.013), but not with changes of fat-free mass and of the three dimensions of eating behaviour.

CONCLUSION

Weight loss following LAGB leads to an increase in fasting plasma ghrelin and is accompanied by a decrease in hunger, disinhibition of eating and an increase in cognitive restraint. Thus, changes in eating behaviour, which promote reduction of food intake and not fasting ghrelin, determines weight loss achieved by LAGB.

Plasma ghrelin in obesity before and after weight loss after laparoscopical adjustable gastric banding

Weight reduction after gastric bypass surgery has been attributed to a decrease of the orexigenic peptide ghrelin, which may be regulated by insulin and leptin. This study examined effects of long-term weight loss after laparoscopical adjustable gastric banding on plasma ghrelin and leptin concentrations and their relationship with insulin action. Severely obese patients (15 women, three men, 36 +/- 12 yr) underwent clinical examinations every 3 months and modified oral glucose tolerance tests to assess parameters of insulin sensitivity and secretion every 6 months. After surgery, body mass index fell from 45.3 +/- 5.3 to 37.2 +/- 5.3 and 33.6 +/- 5.5 kg/m(2) at 6 and 12 months, respectively (P < 0.0001). This was associated with lower (P < 0.0001) plasma glucose, insulin, insulin resistance, waist circumference, and blood pressure. Plasma leptin decreased from 27.6 +/- 9.5 to 17.7 +/- 9.8 (P = 0.0005) and 12.7 +/- 5.1 ng/ml (P < 0.0001). Plasma ghrelin was comparable before and at 6 months (234 +/- 53; 232 +/- 53 pmol/liter) but increased at 12 months (261 +/- 72 pmol/liter; P = 0.05 vs. 6 months). At 6 and 12 months, ghrelin levels correlated negatively with fasting plasma insulin levels and hepatic insulin extraction but not with body mass or insulin action. In conclusion, prolonged weight loss results in a rise of fasting ghrelin concentrations that correlates with fasting insulin concentrations but not improvement of insulin sensitivity.

Ghrelin does not mediate the somatotroph and corticotroph responses to the stimulatory effect of glucagon or insulin-induced hypoglycaemia in humans

OBJECTIVE

Acylated ghrelin, a gastric peptide, possesses a potent GH- but also significant ACTH/cortisol-releasing activity mediated by the activation of GH secretagogue receptors (GHS-R) at the hypothalamus-pituitary level. The physiological role of ghrelin in the control of somatotroph and corticotroph function is, however, largely unclear. Glucagon is known to induce a clear increase of GH, ACTH and cortisol levels in humans, at least after intramuscular administration. In fact, glucagon is considered to be a classical alternative to insulin-induced hypoglycaemia (ITT) for the combined evaluation of the function of GH and the hypothalamus-pituitary-adrenal (HPA) axis. We aimed to clarify whether ghrelin mediate the GH and corticotroph responses to intramuscular glucagon or ITT, which has recently been reported able to induce a surprising ghrelin decrease.

SUBJECTS

To this aim we enrolled six normal young male subjects [age (mean +/- SD): 29.0 +/- 8.0 years, body mass index (BMI) 21.9 +/- 2.5 kg/m(2)].

DESIGN AND MEASUREMENTS

In all the subjects we studied ghrelin, GH, ACTH, cortisol and glucose levels after glucagon (GLU; 0.017 mg/kg intramuscularly), ITT (0.1 IU/kg insulin intravenously) or saline administration.

RESULTS

Saline infusion was not followed by any significant variation in ghrelin, GH and glucose levels while ACTH and cortisol showed the expected spontaneous morning trend toward a decrease. GLU administration increased (P < 0.01) circulating GH, ACTH and cortisol as well as insulin and glucose levels. ITT induced an obvious increase (P < 0.01) of GH, ACTH and cortisol levels. The ITT-induced increases in GH and ACTH, but not cortisol, levels were higher (P < 0.01) than those after GLU. Circulating ghrelin levels were not modified by GLU. On the other hand, ghrelin levels underwent a transient reduction (P < 0.01) after insulin-induced hypoglycaemia.

CONCLUSIONS

Ghrelin does not mediate the GH and ACTH responses to glucagon or to the ITT. In fact, ghrelin levels are not modified at all by glucagon and transiently decrease during the ITT. These findings support the assumption that ghrelin does not play a major role in the physiological control of somatotroph and corticotroph function.

The endocrine response to acute ghrelin administration is blunted in patients with anorexia nervosa, a ghrelin hypersecretory state

OBJECTIVE

Ghrelin, a gastric-derived natural ligand of the GH secretagogue (GHS)-receptor (GHS-R), strongly stimulates GH secretion but also possesses other neuroendocrine actions, stimulates food intake and modulates the endocrine pancreas and energy homeostasis. Ghrelin secretion is negatively modulated by food intake. Similarly, glucose and also insulin probably exert an inhibitory effect on ghrelin secretion. Fasting ghrelin levels are reduced in obesity, elevated in anorexia nervosa and restored by weight recovery. The chronic elevation of circulating ghrelin levels in anorexia suggested the hypothesis of an alteration of the sensitivity to the orexigenic action of ghrelin in this condition. The aim of this study was to define the endocrine actions of ghrelin in patients with anorexia nervosa.

DESIGN

We enrolled nine women with anorexia nervosa of restricter type [AN; age (mean +/- SEM) 24.2 +/- 1.8 years; body mass index (BMI) 14.7 +/- 0.4 kg/m2] and seven normal young women in their early follicular phase as control group (NW; age 30.6 +/- 3.1 years; BMI 20.3 +/- 0.5 kg/m2).

MEASUREMENTS

In all the subjects we studied the GH, PRL, ACTH, cortisol, insulin and glucose responses to acute ghrelin administration (1.0 microg/kg as i.v. bolus). The GH response to GHRH (1.0 microg/kg as i.v. bolus) and basal ghrelin and IGF-I levels were also evaluated in all the subjects.

RESULTS

Basal morning ghrelin and GH levels in AN (643.6 +/- 21.3 ng/l and 10.4 +/- 0.5 microg/l, respectively) were higher (P < 0.05) than in NW (233.5 +/- 14.2 ng/l and 0.7 +/- 0.7 microg/l, respectively). However, IGF-I levels in AN (145.3 +/- 10.9 microg/l) were lower (P < 0.05) than in NW (325.4 +/- 12.6 microg/l). The GH response to GHRH in AN was higher (P < 0.05) than that in NW, but in AN the GH response to ghrelin was lower (P < 0.05) than that in NW. In AN and NW ghrelin also induced similar increases (P < 0.05) in PRL, ACTH and cortisol levels. Ghrelin administration was followed by significant increase in glucose levels in NW (P < 0.05) but not in AN.

CONCLUSIONS

This study demonstrates that anorexia nervosa, a clinical condition of ghrelin hypersecretion, shows a specific reduction in the GH response to ghrelin, despite the hyper-responsiveness to GHRH administration. The impaired GH response to ghrelin in anorexia nervosa agrees with previous evidence of blunted GH response to synthetic GH secretagogues and could reflect desensitization of the GHS receptor induced by the chronic elevation of ghrelin levels in this pathological state.

Circulating ghrelin levels in the newborn are positively associated with gestational age

OBJECTIVE

Ghrelin exerts potent GH-releasing activity and stimulates food intake. Circulating ghrelin levels are increased in anorexia and cachexia, reduced in obesity and restored by weight recovery. Newborns are characterized by GH hypersecretion associated with low IGF-I levels reflecting peripheral GH resistance.

STUDY DESIGN

The aim of our study was to measure cord ghrelin levels in 117 newborns appropriate for gestational age, born either at term or preterm.

RESULTS

Ghrelin levels in cord blood (median; 25th-75th centile: 327.6; 206.0-413.0 pg/ml) were higher (P < 0.0001) than those in maternal blood at delivery (133.0; 89.0-173.7 pg/ml), without gender differences. A positive correlation between ghrelin levels in mothers and newborns (r = 0.26, P < 0.01) was observed. Ghrelin levels in newborns born at term (399.0; 229.0-438.0 pg/ml) were remarkably higher (P < 0.0001) than those in born preterm (208.0; 144.5-278.9 pg/ml). A clear positive association was present between ghrelin levels and gestational age. No association between ghrelin and GH, IGF-I, insulin, glucose and leptin levels were found.

CONCLUSIONS

Cord ghrelin levels show clear gestational age-related dependency. The lack of any direct relationship between ghrelin and anthropometric or biochemical parameters in adequate for gestational age newborns does not support the hypothesis that ghrelin has major role in foetal GH secretion and growth.

Normal regulation of elevated plasma ghrelin concentrations in dialysis patients

BACKGROUND

Chronic renal failure is often associated with malnutrition, and malnourished patients are subject to increased morbidity and mortality. Therefore plasma concentrations of the stomach-derived peptide hormone ghrelin, which has been shown to exert potent GH-releasing and appetite-stimulating effects, were determined and correlated with nutritional parameters.

METHODS

Twenty-four patients (15 male, 9 female) undergoing hemodialysis (HD) were studied. In addition, six patients were studied before and one hour after ingestion of a meal and five were studied immediately before and at the end of the dialysis session.

RESULTS

Chronic renal insufficiency was associated with significantly elevated ghrelin levels (320.1 +/- 57 fmol/mL vs. 75.6 +/- 12.4 fmol/mL in controls; p < 0.007). Plasma ghrelin concentrations were also significantly higher in the 16 normal-weight patients than in the eight overweight or obese patients (399.6 +/- 76.3 fmol/mL vs. 161.1 +/- 41.3 fmol/mL; p < 0.03). Ingestion of food induced a decrease in five out of six patients tested (mean 242.3 +/- 66.5 fmol/mL vs. 186 +/- 30.7 fmol/mL; n.s.). HD also resulted in a significant decrease of elevated ghrelin concentrations: ghrelin was in the normal range at the end of HD in four of the five patients tested. Plasma ghrelin concentrations did not correlate with nutritional parameters except for cholinesterase which was negatively correlated to ghrelin.

CONCLUSION

Plasma ghrelin concentrations are elevated in HD. The fact that ghrelin concentrations are higher in normal-weight than in overweight or obese HD patients and suppressed after ingestion of a meal suggests that the regulation of ghrelin release is retained in HD patients, albeit shifted to a higher level.

Ghrelin levels from fetal life through early adulthood: relationship with endocrine and metabolic and anthropometric measures

OBJECTIVE

To establish mean plasma ghrelin levels during fetal life and childhood. Study design Cord blood was obtained at birth from premature (n=29) and full-term newborns (n=124). Fasting blood samples were taken from 224 normal subjects divided according to Tanner stage and sex. Ponderal index or body mass index was determined. Ghrelin; insulin-like growth factor (IGF)-I; IGF-II; IGF binding proteins 1, 2, and 3; insulin; glucose; and leptin levels were measured.

RESULTS

Ghrelin levels did not differ between preterm and full-term newborns. Ghrelin increased significantly after birth, peaking during the first 2 years of life, then decreasing until the end of puberty. Ghrelin levels correlated negatively with anthropometric variables in full-term newborns and postnatally, but not in preterm newborns. A positive correlation between ghrelin and IGF binding protein 1 was found.

CONCLUSIONS

Ghrelin changes significantly throughout development, correlating with anthropometric and metabolic parameters during extrauterine life. The highest levels of ghrelin are found during early postnatal life, when growth hormone begins to exert its effects on growth and important changes in food intake occur, suggesting that this hormone may participate in these processes.

Preproghrelin Leu72Met polymorphism in patients with type 2 diabetes mellitus

OBJECTIVES

The association between the Leu72Met polymorphism of the preproghrelin gene and diabetic complications was examined in patients with type 2 diabetes mellitus.

SUBJECTS AND METHODS

A total of 258 patients with type 2 diabetes mellitus and 522 control subjects were screened. Genotypes were determined by polymerase chain reaction technique. The diagnosis of coronary heart disease was based on clinical and ECG criteria. Laboratory analyses were carried out in the hospital laboratory.

RESULTS

No differences in the genotype distributions and allele frequencies of the preproghrelin Leu72Met polymorphism were found between type 2 diabetes mellitus patients and controls. The polymorphism was not associated with macro- or micro-angiopathy or hypertension. However, Leu72Met polymorphism was associated with serum creatinine (P = 0.006) and lipoprotein(a) [Lp(a)] levels (P = 0.006) with Leu72Leu subjects showing the highest values. This association was observed only amongst diabetic group.

CONCLUSIONS

The Leu72Met polymorphism of the preproghrelin gene was not related to cardiovascular disease in type 2 diabetes mellitus patients. Leu72Met polymorphism was, however, associated with serum creatinine and Lp(a) levels in diabetic patients. The mechanism might be associated with a possible change in ghrelin product and its somatotropic effect.

Presence of cortistatin in the human pancreas

Cortistatin (CST), a 17-amino acid peptide partially homologous to somatostatin (SRIF), has been originally isolated from the cerebral cortex and recently found in monocytes and macrophages of the immune system. CST binds all 5 SRIF receptors, as well the GH secretagogue (GHS)/ghrelin receptors. CST exerts sleep promoting activities, acts on animal motility and behavior and inhibits GH and insulin secretion. To investigate the possible occurrence and activities in peripheral tissues, expression of CST at the mRNA and peptide level was analyzed in the human pancreas by means of RT-PCR, in situ hybridization and immunohistochemistry. The specific CST mRNA was found in 3 of 4 pancreatic RNA extracts and in the control cerebral cortex. By in situ hybridization, CST mRNA was localized in the pancreatic islets, but not in the exocrine pancreas. This finding was confirmed by immunostaining with a specific antibody to CST-17 which detected CST in single islet cells. These cells also expressed SRIF receptors types 2, 3 and 5, ghrelin and GHS receptors. Thus, our findings show the presence of CST in the human endocrine pancreas. Local autocrine or paracrine circuits, only in part overlapped with those of SRIF, may be active to modulate insulin and/or glucagon levels.