Ghrelin and obestatin levels in type 2 diabetic patients with and without delayed gastric emptying

Treatment with Obestatin-A Ghrelin Gene-Encoded Peptide-Reduces the Severity of Experimental Colitis Evoked by Trinitrobenzene Sulfonic Acid

Obestatin is a 23-amino acid peptide derived from proghrelin, a common prohormone for ghrelin and obestatin. Previous studies showed that obestatin exhibited some protective and therapeutic effects in the gut. The aim of our presented study was to examine the effect of treatment with obestatin on trinitrobenzene sulfonic acid (TNBS)-induced colitis. In rats anesthetized with ketamine, colitis was induced through intrarectal administration of 25 mg of 2,4,6-trinitrobenzene sulfonic acid (TNBS). Obestatin was administered intraperitoneally at doses of 4, 8, or 16 nmol/kg, twice per day for four consecutive days. The first dose of obestatin was given one day before the induction of colitis, and the last one was given two days after administration of TNBS. Fourteen days after the induction of colitis, rats were anesthetized again with ketamine, and the severity of colitis was determined. The administration of obestatin had no effect on the parameters tested in rats without the induction of colitis. In rats with colitis, administration of obestatin at doses of 8 or 16 nmol/kg reduced the area of colonic damage, and improved mucosal blood flow in the colon. These effects were accompanied by a reduction in the colitis-evoked increase in the level of blood leukocytes, and mucosal concentration of pro-inflammatory interleukin-1β. Moreover, obestatin administered at doses of 8 or 16 nmol/kg reduced histological signs of colonic damage. The administration of obestatin at a dose of 4 nmol/kg failed to significantly affect the parameters tested. Overall, treatment with obestatin reduced the severity of TNBS-induced colitis in rats. This effect was associated with an improvement in mucosal blood flow in the colon, and a decrease in local and systemic inflammatory processes.

Biochemical properties and biological actions of obestatin and its relevence in type 2 diabetes

Obestatin was initially discovered in rat stomach extract, and although it is principally produced in the gastric mucosa, it can be found throughout the gastrointestinal tract. This 23-amino acid C-terminally amidated peptide is derived from preproghrelin and has been ascribed a wide range of metabolic effects relevant to type 2 diabetes. Obestatin reportedly inhibits gastrointestinal motility, reduces food intake and lowers body weight and improves lipid metabolism. Furthermore, it appears to exert actions on the pancreatic β-cell, most notably increasing β-cell mass and upregulating genes associated with insulin production and β-cell regeneration, with relevance to type 2 diabetes. It is becoming evident that obestatin also exerts pleiotropic effects on the cardiovascular system, possibly modulating blood pressure, endothelial function and triggering cardioprotective mechanisms, which may be important in determining cardiovascular outcomes in type 2 diabetes. Furthermore, it seems that like other gut peptides obestatin has neuroprotective properties. This review examines the biochemical properties of the obestatin peptide (its structure, sequence, stability and distribution) and the candidate receptors through which it may act. It provides a balanced examination of the reported pancreatic and extrapancreatic actions of obestatin and evaluates its potential relevance with respect to diabetes therapy, together with discussion of direct evidence linking alterations in obestatin signalling with obesity/diabetes and other diseases.

Gastroparesis: Medical and Therapeutic Advances

Gastroparesis is a chronic, bothersome, and often disabling neuromuscular disorder of the upper gastrointestinal tract. The most frequently reported symptoms of gastroparesis include nausea, vomiting, epigastric pain, early satiety, and unintentional weight loss. Etiologies of gastroparesis include diabetes, connective tissue disorders, prior infection, mesenteric ischemia, and post-surgical complications. The largest category of gastroparesis patients is comprised of those in whom no definitive cause can be identified (idiopathic gastroparesis). The individual and societal burden of gastroparesis is substantial. It considerably reduces patients' quality of life accompanied by a significant negative impact to the healthcare system. The current treatments of gastroparesis are less than ideal. Dietary modification may improve symptoms in patients with mild disease. Metoclopramide is the only medication currently approved for the treatment of gastroparesis; however, it is associated with adverse effects in a sizable proportion of patients. Other medications are frequently employed to treat symptoms of nausea and vomiting, although technically all are used off-label since they are not FDA approved for the treatment of gastroparesis. These data highlight the need to identify novel, more effective treatment options for this disabling disease. This review will provide a brief synopsis on the epidemiology, etiology, and impact of gastroparesis, discussing new therapeutic advances.

Endoglin and obestatin levels, cardiometabolic risk factors and subclinical atherosclerosis in children aged 10-18 years

BACKGROUND

The aim of this study was to investigate the early signs of atherosclerosis and to evaluate serum endoglin and obestatin levels as predictors of subclinical atherosclerosis in obese children.

METHODS

A total of 95 children (60 obese and 35 controls) aged 10-18 years were included in the study. Their endoglin and obestatin levels and biochemical parameters were measured. The carotid intima media thickness (cIMT) and brachial artery flow-mediated dilatation (FMD) responses were evaluated.

RESULTS

The cIMT values were higher (p < 0.001) and FMD responses were lower (p = 0.003) in the obese group than in the control group. A logistic regression multivariate analysis revealed that cIMT was independently associated with the body mass index (BMI) Z-score (β = 0.323, p = 0.003) and low density lipoprotein (LDL) (β = 0.29, p = 0.008), while FMD % was independently associated with waist circumference (β = -0.36, p = 0.002). The obese and control groups were similar in endoglin (p = 0.67) and obestatin levels (p = 0.70). The endoglin level was inversely correlated with the cholesterol and LDL levels (r = -0.23, p = 0.032; rho = -0.25, p = 0.019).

CONCLUSIONS

The cIMT and brachial artery FMD response in obese children are significantly different compared to healthy controls. Circulating endoglin and obestatin levels are not predictive markers for subclinical atherosclerosis in obese children aged 10-18 years old.

Obestatin as a key regulator of metabolism and cardiovascular function with emerging therapeutic potential for diabetes

Obestatin is a 23-amino acid C-terminally amidated gastrointestinal peptide derived from preproghrelin and which forms an α helix. Although obestatin has a short biological half-life and is rapidly degraded, it is proposed to exert wide-ranging pathophysiological actions. Whilst the precise nature of many of its effects is unclear, accumulating evidence supports positive actions on both metabolism and cardiovascular function. For example, obestatin has been reported to inhibit food and water intake, body weight gain and gastrointestinal motility and also to mediate promotion of cell survival and prevention of apoptosis. Obestatin-induced increases in beta cell mass, enhanced adipogenesis and improved lipid metabolism have been noted along with up-regulation of genes associated with beta cell regeneration, insulin production and adipogenesis. Furthermore, human circulating obestatin levels generally demonstrate an inverse association with obesity and diabetes, whilst the peptide has been shown to confer protective metabolic effects in experimental diabetes, suggesting that it may hold therapeutic potential in this setting. Obestatin also appears to be involved in blood pressure regulation and to exert beneficial effects on endothelial function, with experimental studies indicating that it may also promote cardioprotective actions against, for example, ischaemia-reperfusion injury. This review will present a critical appraisal of the expanding obestatin research area and discuss the emerging therapeutic potential of this peptide for both metabolic and cardiovascular complications of diabetes.

Role of ghrelin in the pathophysiology of gastrointestinal disease

Ghrelin is a 28-amino-acid peptide that plays multiple roles in humans and other mammals. The functions of ghrelin include food intake regulation, gastrointestinal (GI) motility, and acid secretion by the GI tract. Many GI disorders involving infection, inflammation, and malignancy are also correlated with altered ghrelin production and secretion. Although suppressed ghrelin responses have already been observed in various GI disorders, such as chronic gastritis, Helicobacter pylori infection, irritable bowel syndrome, functional dyspepsia, and cachexia, elevated ghrelin responses have also been reported in celiac disease and inflammatory bowel disease. Moreover, we recently reported that decreased fasting and postprandial ghrelin levels were observed in female patients with functional dyspepsia compared with healthy subjects. These alterations of ghrelin responses were significantly correlated with meal-related symptoms (bloating and early satiation) in female functional dyspepsia patients. We therefore support the notion that abnormal ghrelin responses may play important roles in various GI disorders. Furthermore, human clinical trials and animal studies involving the administration of ghrelin or its receptor agonists have shown promising improvements in gastroparesis, anorexia, and cancer. This review summarizes the impact of ghrelin, its family of peptides, and its receptors on GI diseases and proposes ghrelin modulation as a potential therapy.

Gastroparesis: concepts, controversies, and challenges

Patients with gastroparesis often present a challenge to the treating physician. Postprandial symptoms with nausea and vomiting may not only lead to nutritional and metabolic consequences, but also cause significant disruptions to social activities that often center around food. While the definition of gastroparesis focuses on impaired gastric emptying, treatment options that affect gastric function are limited and often disappointing. The female predominance, the mostly idiopathic nature of the illness with a common history of abuse, and coexisting anxiety or depression show parallels with other functional disorders of the gastrointestinal tract. These parallels provided the rationale for some initial studies investigating alternative therapies that target the brain rather than the stomach. This emerging shift in medical therapy comes at a time when clinical studies suggest that gastric electrical stimulation may exert its effects by modulating visceral sensory processing rather than altering gastric motility. Physiologic and detailed anatomic investigations also support a more complex picture with different disease mechanisms, ranging from impaired accommodation to apparent visceral hypersensitivity or decreased interstitial cells of Cajal to inflammatory infiltration of myenteric ganglia. Delayed gastric emptying remains the endophenotype defining gastroparesis. However, our treatment options go beyond prokinetics and may allow us to improve the quality of life of affected individuals.

Gastrointestinal hormonal dysfunction in gastroparesis and functional dyspepsia

BACKGROUND

Numerous hormones secreted by the gut, during both the fasted state and in response to a meal, influence gastrointestinal motor and/or sensory function, and appear to contribute to the pathogenesis of delayed gastric emptying associated with gastroparesis, functional dyspepsia (FD) and feed intolerance in critical illness. Gut hormones are, accordingly, potential targets for the management of these patients.

PURPOSE

This article will discuss the hypersensitivity to enteral fat and endogenous (nutrient-stimulated) and exogenous cholecystokinin (CCK) in patients with FD, and the elevation in both fasting and postprandial CCK levels evident in this group. It will review the use of pharmacological agonists of motilin and ghrelin, which accelerate gastric emptying, in the management of gastroparesis and FD. The frequent finding of markedly delayed gastric emptying in the critically ill will be examined; this is associated with elevated plasma CCK and peptide YY in both the fasted and postprandial states, which may account for the increase in small intestinal nutrient inhibitory feedback on gastric motility in this group. The concepts that the rate of gastric emptying is a major determinant of postprandial glycemic excursions in diabetes, and that modulation of gastric emptying may improve glycemic control, will be addressed; in type 1 and insulin-treated type 2 diabetic patients, co-ordination of insulin administration with nutrient delivery and absorption should be optimized, while type 2 patients who are not on insulin are likely to respond to dietary and/or pharmacological interventions which slow gastric emptying.

Modulation of ingestive behavior and gastrointestinal motility by ghrelin in diabetic animals and humans

Acyl ghrelin, a 28-amino acid peptide hormone, is the endogenous cognate ligand for the growth hormone secretagogue receptor. Ghrelin is involved in stimulating growth hormone release, eliciting feeding behavior, inducing adiposity and stimulating gastrointestinal motility. Ghrelin is unique for its post-translational modification of O-n-octanoylation at serine 3 through ghrelin O-acyltransferase, and is the only peripheral signal to enhance food intake. Plasma ghrelin levels manifest "biphasic changes" in diabetes mellitus (DM). In the early stage of DM, the stomach significantly increases the secretion of ghrelin into the plasma, and elevated plasma ghrelin levels are correlated with diabetic hyperphagic feeding and accelerated gastrointestinal motility. In the late stage of DM, plasma ghrelin levels may be lower, which might be linked with anorexia/muscle wasting, delayed gastrointestinal transit, and even gastroparesis. Therefore, the unique ghrelin system may be the most important player compared to the other hindgut hormones participating in the "entero-insular axis". Further studies using either knockdown or knockout of ghrelin gene products and ghrelin O-acyltransferase may unravel the pathogenesis of DM, and show benefits in combating this disease and metabolic syndrome.

Integrating GHS into the Ghrelin System

Oligopeptide derivatives of metenkephalin were found to stimulate growth-hormone (GH) release directly by pituitary somatotrope cells in vitro in 1977. Members of this class of peptides and nonpeptidyl mimetics are referred to as GH secretagogues (GHSs). A specific guanosine triphosphatate-binding protein-associated heptahelical transmembrane receptor for GHS was cloned in 1996. An endogenous ligand for the GHS receptor, acylghrelin, was identified in 1999. Expression of ghrelin and homonymous receptor occurs in the brain, pituitary gland, stomach, endothelium/vascular smooth muscle, pancreas, placenta, intestine, heart, bone, and other tissues. Principal actions of this peptidergic system include stimulation of GH release via combined hypothalamopituitary mechanisms, orexigenesis (appetitive enhancement), insulinostasis (inhibition of insulin secretion), cardiovascular effects (decreased mean arterial pressure and vasodilation), stimulation of gastric motility and acid secretion, adipogenesis with repression of fat oxidation, and antiapoptosis (antagonism of endothelial, neuronal, and cardiomyocyte death). The array of known and proposed interactions of ghrelin with key metabolic signals makes ghrelin and its receptor prime targets for drug development.

Gastroparesis and functional dyspepsia: excerpts from the AGA/ANMS meeting

BACKGROUND

Despite the relatively high prevalence of gastroparesis and functional dyspepsia, the aetiology and pathophysiology of these disorders remain incompletely understood. Similarly, the diagnostic and treatment options for these two disorders are relatively limited despite recent advances in our understanding of both disorders.

PURPOSE

This manuscript reviews the advances in the understanding of the epidemiology, pathophysiology, diagnosis, and treatment of gastroparesis and functional dyspepsia as discussed at a recent conference sponsored by the American Gastroenterological Association (AGA) and the American Neurogastroenterology and Motility Society (ANMS). Particular focus is placed on discussing unmet needs and areas for future research.