Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake

Hormones of the gut-brain axis as targets for the treatment of upper gastrointestinal disorders

The concept of the gut forming the centre of an integrated gut-brain-energy axis - modulating appetite, metabolism and digestion - opens up new paradigms for drugs that can tackle multiple symptoms in complex upper gastrointestinal disorders. These include eating disorders, nausea and vomiting, gastroesophageal reflux disease, gastroparesis, dyspepsia and irritable bowel syndrome. The hormones that modulate gastric motility represent targets for gastric prokinetic drugs, and peptides that modify eating behaviours may be targeted to develop drugs that reduce nausea, a currently poorly treated condition. The gut-brain axis may therefore provide a range of therapeutic opportunities that deliver a more holistic treatment of upper gastrointestinal disorders.

Obestatin induction of early-response gene expression in gastrointestinal and adipose tissues and the mediatory role of G protein-coupled receptor, GPR39

Obestatin was identified as a brain/gut peptide hormone encoded by the ghrelin gene and found to interact with the G protein-coupled receptor, GPR39. We investigated target cells for obestatin based on induction of an early-response gene c-fos in different tissues. After ip injection of obestatin, c-fos staining was found in the nuclei of gastric mucosa, intestinal villi, white adipose tissues, hepatic cords, and kidney tubules. Immunohistochemical analyses using GPR39 antibodies further revealed cytoplasmic staining in these tissues. In cultured 3T3-L1 cells, treatment with obestatin, but not motilin, induced c-fos expression. In these preadipocytes, treatment with obestatin also stimulated ERK1/2 phosphorylation. Because phenotypes of GPR39 null mice are partially consistent with a role of GPR39 in mediating obestatin actions, we hypothesized that inconsistencies on the binding of iodinated obestatin to GPR39 are due to variations in the bioactivity of iodinated obestatin. We obtained monoiodoobestatin after HPLC purification and demonstrated its binding to jejunum, stomach, ileum, pituitary, and white adipose tissue. Furthermore, human embryonic kidney 293T cells transfected with plasmids encoding human or mouse GPR39 or a human GPR39 isoform, but not the ghrelin receptor, exhibited high-affinity binding to monoiodoobestatin. Binding studies using jejunum homogenates and recombinant GPR39 revealed obestatin-specific displacement curves. Furthermore, treatment with obestatin induced c-fos expression in gastric mucosa of wild-type, but not GPR39 null, mice, underscoring a mediating role of this receptor in obestatin actions. The present findings indicate that obestatin is a metabolic hormone capable of binding to GPR39 to regulate the functions of diverse gastrointestinal and adipose tissues.

Ghrelin is a physiological regulator of insulin release in pancreatic islets and glucose homeostasis

Ghrelin, an acylated 28-amino acid peptide, was isolated from the stomach as the endogenous ligand for the growth hormone (GH) secretagogue receptor (GHS-R). Circulating ghrelin is produced predominantly in the oxyntic mucosa of stomach. Ghrelin potently stimulates GH release and feeding, and exhibits positive cardiovascular effects, suggesting a possible clinical application. Low plasma ghrelin levels are associated with elevated fasting insulin levels and insulin resistance, suggesting both physiological and pathophysiological roles for ghrelin in glucose metabolism. Here, we review the physiological role of ghrelin in the regulation of insulin release and glucose metabolism, and a potential therapeutic avenue to treat type 2 diabetes by manipulating ghrelin and/or its signaling. Ghrelin inhibits insulin release in mice, rats and humans. The signal transduction mechanisms of ghrelin in islet beta-cells are distinct from those utilized in GH-releasing and/or GHS-R-expressing cells. Ghrelin is expressed in pancreatic islets and released into pancreatic microcirculations. Pharmacological and genetic blockades of islet-derived ghrelin markedly augment glucose-induced insulin release in vitro. In high-fat diet-induced mildly obese mice, ghrelin-deficiency enhances insulin release and prevents impaired glucose tolerance. Thus, manipulation of insulinostatic function of ghrelin--GHS-R system, particularly that in islets, could optimize the amount of insulin release to meet the systemic demand, providing a potential therapeutic application to prevent type 2 diabetes.

Gastric motor effects of ghrelin and growth hormone releasing peptide 6 in diabetic mice with gastroparesis

AIM: To investigate the potential therapeutic significance of ghrelin and growth hormone releasing peptide 6 (GHRP-6) in diabetic mice with gastric motility disorders.

METHODS: A diabetic mouse model was established by intraperitoneal (ip) injection of alloxan. Diabetic mice were injected ip with ghrelin or GHRP-6 (20-200 &mgr;g/kg), and the effects on gastric emptying were measured after intragastric application of phenol red. The effect of atropine, N^G-nitro-L-arginine methyl ester hydrochloride (L-NAME) or D-Lys³-GHRP-6 (a growth hormone secretagogue receptor (GHS-R) antagonist) on the gastroprokinetic effect of ghrelin or GHRP-6 (100 &mgr;g/kg) was also investigated. The effects of ghrelin or GHRP-6 (0.01-10 &mgr;mol/L) on spontaneous or carbachol-induced contractile amplitude were also investigated in vitro, in gastric fundic circular strips taken from diabetic mice. The presence of growth hormone secretagogue receptor 1a transcripts in the fundic strips of diabetic mice was detected by reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS: We established a diabetic mouse model with delayed gastric emptying. Ghrelin and GHRP-6 accelerated gastric emptying in diabetic mice with gastroparesis. In the presence of atropine or L-NAME, which delayed gastric emptying, ghrelin and GHRP-6 (100 &mgr;g/kg) failed to accelerate gastric emptying. D-Lys³-GHRP-6 also delayed gastric emptying induced by the GHS-R agonist. Ghrelin and GHRP-6 increased the carbachol-induced contractile amplitude in gastric fundic strips taken from diabetic mice. RT-PCR confirmed the presence of GHS-R mRNA in the strip preparations.

CONCLUSION: Ghrelin and GHRP-6 increase gastric emptying in diabetic mice with gastroparesis, perhaps by activating peripheral cholinergic pathways in the enteric nervous system.

Identification of the acyltransferase that octanoylates ghrelin, an appetite-stimulating peptide hormone

Ghrelin is a 28 amino acid, appetite-stimulating peptide hormone secreted by the food-deprived stomach. Serine-3 of ghrelin is acylated with an eight-carbon fatty acid, octanoate, which is required for its endocrine actions. Here, we identify GOAT (Ghrelin O-Acyltransferase), a polytopic membrane-bound enzyme that attaches octanoate to serine-3 of ghrelin. Analysis of the mouse genome revealed that GOAT belongs to a family of 16 hydrophobic membrane-bound acyltransferases that includes Porcupine, which attaches long-chain fatty acids to Wnt proteins. GOAT is the only member of this family that octanoylates ghrelin when coexpressed in cultured endocrine cell lines with prepro-ghrelin. GOAT activity requires catalytic asparagine and histidine residues that are conserved in this family. Consistent with its function, GOAT mRNA is largely restricted to stomach and intestine, the major ghrelin-secreting tissues. Identification of GOAT will facilitate the search for inhibitors that reduce appetite and diminish obesity in humans.

Simultaneous deletion of ghrelin and its receptor increases motor activity and energy expenditure

Administration of chemically synthesized ghrelin (Ghr) peptide has been shown to increase food intake and body adiposity in most species. However, the biological role of endogenous Ghr in the molecular control of energy metabolism is far less understood. Mice deficient for either Ghr or its receptor (the growth hormone secretagogue receptor, GHS-R1a) seem to exhibit enhanced protection against high-fat diet-induced obesity but do not show a substantial metabolic phenotype on a standard diet. Here we present the first mouse mutant lacking both Ghr and the Ghr receptor. We demonstrate that simultaneous genetic disruption of both genes of the Ghr system leads to an enhanced energy metabolism phenotype. Ghr/Ghr receptor double knockout (dKO) mice exhibit decreased body weight, increased energy expenditure, and increased motor activity on a standard diet without exposure to a high caloric environment. Mice on the same genetic background lacking either the Ghr or the Ghr receptor gene did not exhibit such a phenotype on standard chow, thereby confirming earlier reports. No differences in food intake, meal pattern, or lean mass were observed between dKO, Ghr-deficient, Ghr receptor-deficient, and wild-type (WT) control mice. Only dKO showed a slight decrease in body length. In summary, simultaneous deletion of Ghr and its receptor enhances the metabolic phenotype of single gene-deficient mice compared with WT mice, possibly suggesting the existence of additional, as of yet unknown, molecular components of the endogenous Ghr system.

Impact of atypical antipsychotic therapy on leptin, ghrelin, and adiponectin

BACKGROUND

Many adverse effects of atypical antipsychotic treatment are associated with antagonism of monoamine receptors; however, data indicate that important metabolic effects, such as hypertriglyceridemia and impairment in glucose/insulin homeostasis, may not be related to these mechanisms, leading investigators to explore alternative hypotheses. Promising candidates include a possible impact of antipsychotics on peptide hormonal regulators of metabolic control such as leptin, ghrelin, and adiponectin. The purpose of this review is to summarize recent data on changes in these hormones during atypical antipsychotic treatment.

METHODS

A Medline search was performed for papers published from January 1999 to January 2007 using key words antipsychotic, atypical antipsychotic, and individual atypical antipsychotic drug names cross-referenced with leptin, ghrelin, and adiponectin.

RESULTS

The bulk of the published work focused on changes in body weight and serum leptin, with far less data on ghrelin, and adiponectin, and nonweight metabolic changes. Leptin changes were directly related to a medication's weight gain liability, with no added antipsychotic effects on leptin signaling. Conflicting results emerged for the other markers, but all three long-term studies on ghrelin showed increased levels in patients on atypical antipsychotics with weight gain liabilities.

CONCLUSIONS

Leptin increases during antipsychotic treatment are a result of weight gain rather than a direct impact of atypical antipsychotics on leptin physiology. Preliminary long-term data show increased ghrelin levels, but this finding must be replicated. The association with antipsychotic effects on glucose and lipid metabolism and these hormones remains virtually unstudied. Future research should indicate whether ghrelin and other peptide hormones may be useful predictors of weight gain or metabolic changes in patients on antipsychotics.

Anticipatory physiological regulation in feeding biology: cephalic phase responses

Anticipatory physiological regulation is an adaptive strategy that enables animals to respond faster to physiologic and metabolic challenges. The cephalic phase responses are anticipatory responses that prepare animals to digest, absorb, and metabolize nutrients. They enable the sensory aspects of the food to interact with the metabolic state of the animal to influence feeding behavior. The anticipatory digestive secretions and metabolic adjustments in response to food cues are key adaptations that affect digestive and metabolic efficiency and aid in controlling the resulting elevation of metabolic fuels in the blood. Cephalic phase responses enable digestion, metabolism, and appetite to be regulated in a coordinated fashion. These responses have significant effects on meal size. For example, if the cephalic phase insulin response is blocked the result is poor glucose control and smaller meals. Cephalic phase responses also are linked to motivation to feed, and may play a more direct role in regulating meal size beyond the permissive one of ameliorating negative consequences of feeding. For example, the orexigenic peptide ghrelin appears to display a cephalic phase response, rising before expected meal times. This anticipatory ghrelin response increases appetite; interestingly it also enhances fat absorption, linking appetite with digestion and metabolism.

A single circuit-resistance exercise has no effect on plasma obestatin levels in female college students

Obestatin is a 23 amino acid peptide recently isolated from rat stomach that is encoded by the same gene as ghrelin. Obestatin has opposite action to ghrelin on food intake and plays a role in energy balance. The purpose of the present study was to investigate the effect of a circuit-resistance exercise (9 exercises, 25s per exercise, at 40, 60, 80% of 1RM) at different intensities on plasma obestatin and growth hormone (GH). Twenty volunteer females were randomly divided into four; 40, 60, 80%, combined (40+80+80%) loads groups (COL). Blood samples were collected before and immediately following the exercise protocol. Changes in plasma obestatin levels were not significant within and between groups. Plasma GH concentrations were significantly higher in high and COL groups, respectively. The data indicate that although circuit-resistance exercise resulted in a significant change in GH levels, it had no effect on plasma obestatin levels.

Motilin, ghrelin and related neuropeptides as targets for the treatment of GI diseases

Motilin and ghrelin are released from the upper gut during fasting, to stimulate gastric motility. Additional actions of ghrelin (e.g. changes in appetite, nausea or endocrine functions) improve the possibility of using ghrelin receptor agonists to treat complex disorders such as functional dyspepsia. However, changes in endocrine functions increase the risk of unacceptable side effects. By comparison, the more restricted prokinetic activity of motilin limits the therapeutic possibilities but improves the risk:benefit ratio. Compounds targeting both receptors are in development. Recently, additional peptides have been identified from preproghrelin (obestatin) and prepromotilin. These exert biological activity but their pathophysiological significance is unknown.

Urocortin trafficking in cerebral microvessel endothelial cells

Urocortin, a potent peptide inhibitor of feeding behavior, can enter the brain from blood by leptin-facilitated permeation across the blood-brain barrier. Here, we show in cultured RBE4 cerebral microvessel endothelial cells that urocortin endocytosis is increased by leptin in a time- and dose-dependent manner. Fluorescently labeled urocortin (Alexa488-urocortin) shows vesicular trafficking localized in early endosomes at 1 min and the Golgi complex at 20 min. The endocytosis at 20 min was increased by 10 microg/mL, but not 2 microg/mL, of leptin. The facilitating effect of leptin at the dose of 10 microg/mL was seen at 20 and 30 min but not at 10 min. This increase could be abolished by excess unlabeled urocortin in radio-tracer uptake studies, indicating selective rather than nonsaturable entry. The specificity of the effect was further supported by the lack of changes in gamma-glutamyl transpeptidase activity and endothelial nitric oxide synthase upon stimulation by high doses of leptin and urocortin. Leptin did not affect the level of expression of the urocortin corticotropin-releasing hormone receptor (CRHR) after 30 min of treatment but appeared to slow the turnover of CRHRs induced by urocortin. In MDCK cells overexpressing CRHR2, leptin facilitated urocortin uptake, whereas ObRa coexpression did not exert an additional effect. Thus, urocortin endocytosis is a saturable process leading to vesicular intracellular transport that can be enhanced by cell-surface leptin.

Obestatin and ghrelin levels in obese children and adolescents before and after reduction of overweight

OBJECTIVES

Obestatin and ghrelin, which are derived from the same gene, are observed to have opposite effects on weight status. The aims of this study were to compare obestatin concentrations in obese and normal-weight children and to analyse the effect of weight loss on obestatin and ghrelin levels.

METHODS

We examined anthropometrical markers and fasting serum obestatin, ghrelin, leptin, glucose and insulin concentrations in 44 obese children (mean age 11.2 years) before and after participating in a 1-year outpatient obesity intervention programme based on a high-carbohydrate, fat-reduced diet and increased physical activity. Additionally, total ghrelin, obestatin and leptin levels were determined in 22 normal-weight healthy children of similar age, gender and pubertal stage.

RESULTS

Obestatin and leptin concentrations were significantly (P < 0.001) higher and ghrelin concentrations were significantly (P < 0.001) lower in obese children compared to nonobese children. In contrast to the 13 children without weight loss, substantial weight loss in 31 children led to a significant (P = 0.007) increase in obestatin and to a significant (P < 0.05) decrease in leptin and insulin concentrations, while ghrelin concentrations did not change significantly. Children with substantial weight loss demonstrated significantly (P = 0.009) lower obestatin and a tendency (P = 0.064) to higher ghrelin concentrations at baseline. Changes in insulin were not related to changes in ghrelin or obestatin.

CONCLUSION

The increase in obestatin and the decrease in ghrelin in obese children point towards an adaptation process of weight status. Weight reduction due to a long-term lifestyle intervention resulted in an increase in obestatin levels.

Ghrelin and reproduction: ghrelin as novel regulator of the gonadotropic axis

Identification of ghrelin in late 1999, as the endogenous ligand of the growth hormone secretagogue receptor (GHSR), opened up a new era in our understanding of the regulatory mechanisms of several neuroendocrine systems, including growth and energy homeostasis. Based on similarities with other endocrine integrators and its proposed role as signal for energy insufficiency, it appeared tempting to hypothesize that ghrelin might also operate as regulator of reproductive function. Yet, contrary to other of its biological actions the reproductive "dimension" of ghrelin has remained largely unexplored. Nonetheless, experimental evidence, coming mostly from animal studies, have been gathered during the last years suggesting that ghrelin may actually function as a metabolic modulator of the gonadotropic axis, with predominant inhibitory effects in line with its role as signal of energy deficit. These effects likely include inhibition of luteinizing hormone (LH) secretion (which has been reported in different species and developmental stages), as well as partial suppression of normal puberty onset. In addition, expression and/or direct gonadal actions of ghrelin have been reported in the human, rat, and chicken. Altogether, those findings document a novel reproductive facet of ghrelin, which may cooperate with other neuroendocrine integrators, as leptin, in the joint control of energy balance and reproduction.

Influence of short- and long-term treadmill exercises on levels of ghrelin, obestatin and NPY in plasma and brain extraction of obese rats

This study aims to clarify the effects of exercise on levels of appetite regulatory hormones in plasma and hypothalamus of obese rats. Diet-induced obese rats undergo short- (40 min) and long-term (40 min, 5 days/week for 8 weeks) exercises. The rats ran at a speed of 20 m/min on a 5 degrees slope treadmill. Rats undergoing short-term exercise were divided into C, E0, E1, E3, E12, and E24. Rats undergoing long-term exercise (LE) were compared to long-term control (LC). Concentrations of ghrelin, obestatin, and neuropeptide Y (NPY) were measured using radio immuno-assay. Expression of ghrelin receptor (GHSR-1a), putative obestatin receptor (GPR-39), and NPY in the hypothalamus was measured by quantitative RT-PCR. After short-term exercise, the plasma concentrations of ghrelin and obestatin were not changed, but NPY decreased. Ghrelin and obestatin in the hypothalamus decreased, and recovered 12 until 24 h. NPY increased and recovered after 24 h. Expression of GHSR-1a and NPY was not changed and GPR-39 was not observed. In LE, these changes are different in plasma and hypothalamus. It would be concluded appetite and body weight of obese rats are decreased by exercise through reduced level of ghrelin in the hypothalamus. Obestatin seems to have no effect in exercise-induced change in appetite.

Obesity: the hormonal milieu

PURPOSE OF REVIEW

Obesity has reached epidemic proportions throughout the world and poses significant health and economic burdens to both developed and developing societies. Most recent data from the NHANES study (2003-2004) report that 17.1% of US children are overweight and 32.2% of adults are obese, a significant increase compared with data obtained only 6 years earlier.

RECENT FINDINGS

The neurohormonal control of appetite, body composition, and glucose homeostasis is mediated by hormones secreted from adipose tissue, endocrine glands, and enteroendocrine cells, which converge at the vagus nerve, brainstem and hypothalamus to modulate complex interactions of neurotransmitters and central appetite-regulating peptides. These hormonal signals are tightly regulated to maintain body weight/adiposity within a narrow, individually defined range that may be further impacted by variables such as ingested calories, meal composition, and lifestyle.

SUMMARY

Clinical manifestations of obesity, the metabolic syndrome and impaired glucose tolerance reflect biochemical alterations in a complex hormonal milieu. Elucidation of these hormonal perturbations in obese patients has already provided novel pharmacologic treatments to improve weight management and address the metabolic sequelae of obesity. The remarkable redundancy of these hormones, however, and their interactions make a monopharmaceutical approach unlikely to be successful.

Neuroendocrine control of food intake

Appetite is regulated by a complex system of central and peripheral signals which interact in order to modulate the individual response to nutrient ingestion. Peripheral regulation includes satiety signals and adiposity signals, while central control is accomplished by several effectors, including the neuropeptidergic, monoaminergic and endocannabinoid systems. Satiety signals, including cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), originate from the gastrointestinal (GI) tract during a meal and, through the vagus nerve, reach the nucleus tractus solitarius (NTS) in the caudal brainstem. From NTS afferents fibers project to the arcuate nucleus (ARC), where satiety signals are integrated with adiposity signals, namely leptin and insulin, and with several hypothalamic and supra-hypothalamic inputs, thus creating a complex network of neural circuits which finally elaborate the individual response to a meal. As for the neuropeptidergic system, ARC neurons secrete orexigenic substances, such as neuropeptide Y (NPY) and agouti-related peptide (AGRP), and anorexigenic peptides such as pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART). Other brain areas involved in the control of food intake are located downstream the ARC: among these, the paraventricular nucleus (PVN), which produces anorexigenic peptides such as thyrotropin releasing hormone (TRH), corticotrophin releasing hormone (CRH) and oxytocin, the lateral hypothalamus (LHA) and perifornical area (PFA), secreting the orexigenic substances orexin-A (OXA) and melanin concentrating hormone (MCH). A great interest in endocannabinoids, important players in the regulation of food intake, has recently developed. In conclusion, the present work reviews the most recent insights into the complex and redundant molecular mechanisms regulating food intake, focusing on the most encouraging perspectives for the treatment of obesity.

Gastrointestinal peptides controlling body weight homeostasis

Obesity has become an international public health problem. Unfortunately, effective treatment options are limited. In the last 20 years, research in obesity and associated pathologies has derived in a significant increase in the knowledge of the physiological and molecular mechanism regulating body mass, such as gastrointestinal-neuroendocrine communications. Gut-brain peptides may provide attractive therapeutic targets against this disease. This review summarizes research into energy balance through gastrointestinal tract peptides. Understanding these molecular mechanisms will provide new pharmacological targets for the treatment of obesity and appetite disorders.

Effect of peripheral obestatin on food intake and gastric emptying in ghrelin-knockout mice

BACKGROUND AND PURPOSE

The finding that obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's stimulatory effect on food intake and gastric emptying has been questioned. The effect of obestatin has been mostly investigated in fasted rodents, a condition associated with high blood levels of ghrelin which may mask the effect of obestatin. We therefore investigated the effect of obestatin on food intake, gastric emptying and gastric contractility in ghrelin knockout mice.

EXPERIMENTAL APPROACH

The effect of obestatin on 6-h cumulative food intake was studied in fasted wildtype (ghrelin+/+) and ghrelin knockout (ghrelin-/-) mice. In both genotypes, the effect of obestatin and/or ghrelin was studied in vivo on gastric emptying measured with the (14)C-octanoic acid breath test and in vitro on neural responses elicited by electrical field stimulation (EFS) of fundic smooth muscle strips.

KEY RESULTS

Administration of obestatin did not influence fasting-induced hyperphagia or gastric emptying in both genotypes. Injection of ghrelin accelerated gastric emptying in ghrelin+/+ and ghrelin-/- mice but the effect was not reversed by co-injection with obestatin. In fundic strips from ghrelin+/+ and ghrelin-/- mice, ghrelin increased EFS-induced contractions, but obestatin was without effect. However, co-administration with obestatin tended to reduce the excitatory effect of ghrelin in both genotypes.

CONCLUSIONS AND IMPLICATIONS

In ghrelin-/- mice, obestatin failed to affect food intake and gastric motility. These results suggest that endogenous ghrelin does not mask the effect of obestatin and confirm that obestatin administered peripherally is not a major regulator of satiety signalling or gut motility.

Pathophysiology of obesity: why surgery remains the most effective treatment

Obesity is a rapidly increasing, worldwide epidemic. Despite recent scientific advances, no currently recommended dietary program or medication results in long-term weight loss of more than 10% of body weight for the vast majority of people who attempt these interventions. Hence, surgical intervention is recommended for patients with a BMI > or =40 kg/m2. Although surgery is an effective, sustainable treatment of obesity, it can be associated with potentially significant perioperative risks and long-term complications. Current research is focused on developing a medical therapy, which produces more effective and sustainable weight loss, yet avoids the risks inherent in major surgery. With a reduced risk profile, such therapy could also be appropriately offered to those who are less obese and, in theory, help those who have BMIs as low as 27 kg/m2. Toward that end, numerous scientists are working to both unravel the pathophysiology of obesity and to determine why surgical intervention is so effective. This review briefly examines the current status of obesity pathophysiology and management, the reasons for failure of conventional medical treatments, and the success of surgical intervention. Finally, future areas of research are discussed.

Sea bass ghrelin: molecular cloning and mRNA quantification during fasting and refeeding

Ghrelin is a novel appetite-inducing peptide hormone secreted by the stomach. The purpose of this study was first to identify the cDNA encoding sequence for ghrelin in sea bass (Dicentrarchus labrax). Using molecular cloning techniques we sequenced the cDNA corresponding to sea bass ghrelin mRNA. A total of 798 bases including a 5'-untranslated region (89 bp), an open reading frame (ORF) (324 bp), and a 3'-untranslated region (385 bp) were detected. Nucleotide sequence (ORF) encoded a 108 amino acid prepropeptide that demonstrated complete conservation of the N-terminal "biological active core" (GSSF) of the predicted mature ghrelin peptide. We also analyzed fasting-induced changes in the expression of ghrelin mRNA, using a one-tube two-temperature real-time RT-PCR with which the gene expression can be absolutely quantified using the standard curve method. Our results revealed that ghrelin was highly expressed in the stomach with much lower levels of expression in the proximal intestine and brain. Levels of ghrelin mRNA in the stomach were upregulated under conditions of negative energy balance, such as starvation, and downregulated during positive energy balance, such as refeeding. These findings offer new information about the sea bass ghrelin gene and support a role of this orexigenic hormone in the regulation of food intake in sea bass.

Obestatin, acyl ghrelin, and des-acyl ghrelin responses to an oral glucose tolerance test in the restricting type of anorexia nervosa

BACKGROUND

Obestatin is a recently identified peptide encoded by the same ghrelin gene. It has been reported that obestatin has anorexigenic and antigastroprokinetic activities as opposed to ghrelin. We investigated simultaneously obestatin, acyl ghrelin, and des-acyl ghrelin in the restricting type of anorexia nervosa (AN-R) patients.

METHODS

Three hormonal responses to the oral glucose tolerance test (OGTT) were measured in 10 AN-R patients and 10 healthy women.

RESULTS

Plasma obestatin, acyl ghrelin, and des-acyl ghrelin levels were significantly higher in AN-R patients than in control subjects throughout the OGTT. All of the three hormones decreased after the OGTT in both groups.

CONCLUSIONS

We found that AN-R patients exhibited increased plasma levels of obestatin, acyl ghrelin, and des-acyl ghrelin throughout the OGTT compared with control subjects. The hormonal differences between groups are statistically most significant in obestatin, suggesting obestatin may serve as a marker reflecting both acute and chronic changes of the nutritional state in AN-R patients.

The constitutively active orphan G-protein-coupled receptor GPR39 protects from cell death by increasing secretion of pigment epithelium-derived growth factor

GPR39 is a constitutively active orphan G-protein-coupled receptor capable of increasing serum response element-mediated transcription. We found GPR39 to be up-regulated in a hippocampal cell line resistant against diverse stimulators of cell death and show that its overexpression protects against oxidative and endoplasmic reticulum stress, as well as against direct activation of the caspase cascade by Bax overexpression. In contrast, silencing GPR39 rendered cells more susceptible to cell death. An array analysis of transcripts induced by GPR39 revealed up-regulation of RGS16 (inhibitor of G-protein signaling 16), which suggested coupling to Galpha(13) and induction of serum response element-mediated transcription by the small GTPase RhoA. In line with this, co-expression of GPR39 with RGS16, dominant-negative RhoA, or serum response factor abolished cell protection, whereas overexpression of the serum response factor protected from cell death. Further downstream the signaling cascade, GPR39 overexpression leads to increased secretion of the cytoprotective pigment epithelium-derived growth factor (PEDF). Medium conditioned by cells overexpressing GPR39 contained 4-fold more PEDF, and when stripped off it lost most but not all of its protective properties. We conclude that GPR39 is a novel inhibitor of cell death, which might represent a therapeutic target with implications for processes involving apoptosis and endoplasmic reticulum stress like cancer, ischemia/reperfusion injury, and neurodegenerative disease.

Identification of genes for the ghrelin and motilin receptors and a novel related gene in fish, and stimulation of intestinal motility in zebrafish (Danio rerio) by ghrelin and motilin

In mammals ghrelin has a diverse range of effects including stimulation of gut motility but although present in teleost fish its effects on motility have not been investigated. The present study used bioinformatics to search for fish paralogues of the ghrelin receptor and the closely related motilin receptor, and investigated the effects of ghrelin and motilin on gut motility in zebrafish, Danio rerio. Fish paralogues of the human ghrelin and motilin receptor genes were identified, including those from the zebrafish. In addition, a third gene was identified in three species of pufferfish (the only fish genome completely sequenced), which is distinct from the ghrelin and motilin receptors but more closely aligned to these receptors relative to other G-protein coupled receptors. Immunohistochemistry demonstrated strong ghrelin receptor-like reactivity in the muscle of the zebrafish intestine. In isolated intestinal bulb and mid/distal intestine preparations, ghrelin, motilin, and the motilin receptor agonist erythromycin all evoked contraction; these responses ranged between 9% and 51% of the contractions evoked by carbachol (10(-6) M). There were some variations in the concentrations found to be active in the different tissues, e.g., whereas motilin and rat ghrelin caused contraction of the intestinal bulb circular muscle at concentrations as low as 10(-8) M, human ghrelin (10(-8) to 10(-6) M) was without activity. Neither ghrelin (10(-7) M) nor erythromycin (10(-5) M) affected the contractions evoked by electrical field stimulation. The results suggest that both ghrelin and motilin can regulate intestinal motility in zebrafish and most likely other teleosts, and are discussed in relation to the evolution of these regulatory peptides.

Ecdysteroids, juvenile hormone and insect neuropeptides: Recent successes and remaining major challenges

In the recent decade, tremendous progress has been realized in insect endocrinology as the result of the application of a variety of advanced methods in neuropeptidome- and receptor research. Hormones of which the existence had been shown by bioassays four decades ago, e.g. bursicon (a member of the glycoprotein hormone family) and pupariation factor (Neb-pyrokinin 2, a myotropin), could be identified, along with their respective receptors. In control of diurnal rhythms, clock genes got company from the neuropeptide Pigment Dispersing Factor (PDF), of which the receptor could also be identified. The discovery of Inka cells and their function in metamorphosis was a true hallmark. Analysis of the genomes of Caenorhabditis elegans, Drosophila melanogaster and Apis mellifera yielded about 75, 100 and 200 genes coding for putative signaling peptides, respectively, corresponding to approximately 57, 100 and 100 peptides of which the expression could already be proven by means of mass spectrometry. The comparative approach invertebrates-vertebrates recently yielded indications for the existence of counterparts in insects for prolactin, atrial natriuretic hormone and Growth Hormone Releasing Hormone (GRH). Substantial progress has been realized in identifying the Halloween genes, a membrane receptor(s) for ecdysteroids, a nuclear receptor for methylfarnesoate, and dozens of GPCRs for insect neuropeptides. The major remaining challenges concern the making match numerous orphan GPCRs with orphan peptidic ligands, and elucidating their functions. Furthermore, the endocrine control of growth, feeding-digestion, and of sexual differentiation, in particular of males, is still poorly understood. The finding that the prothoracic glands produce an autocrine factor with growth factor-like properties and secrete proteins necessitates a reevaluation of their role in development.

Primary structure and tissue distribution of GPR39 messenger ribonucleic acid in Japanese quail, Coturnix japonica

It has been found that GPR39 is an orphan receptor that belongs to the family of G protein-coupled receptors. In mammals, GPR39 has been shown to be involved in the regulation of gastrointestinal and metabolic function. In this study, we performed cDNA cloning for GPR39 in Japanese quail and characterized the tissue expression profiles of its mRNA. The cDNA encoded 462 amino acids, showing very high sequence homology to chicken GPR39 (95.5%) and moderate homology to mouse (64.7%), rat (63.7%), and human (59.9%) GPR39. Real-time PCR analysis revealed that GPR39 mRNA is expressed at high levels in the digestive tissues such as stomach, duodenum, jejunum, ileum, cecum, and colon and rectum and at moderate levels in the oviduct including infundibulum, magnum, isthmus, and uterus. These findings suggest that GPR39 may be involved in gastrointestinal and oviductal functions in Japanese quail.

Characterization of obestatin- and ghrelin-producing cells in the gastrointestinal tract and pancreas of rats: an immunohistochemical and electron-microscopic study

Both ghrelin and obestatin are derived from preproghrelin by post-translational processing. We have morphologically characterized the cells that produce obestatin and ghrelin in new-born and adult Sprague-Dawley rats that were freely fed, fasted, or subjected to gastric bypass surgery or reserpine treatment. Tissue samples collected from the gastrointestinal tract and pancreas were examined by double-immunofluorescence staining, immunoelectron microscopy, and conventional electron microscopy. Obestatin was present in the stomach, duodenum, jejunum, colon, and pancreas. In the stomach, differences were noted in the development of obestatin- and preproghrelin-immunreactive (IR) cells on the one hand and ghrelin-IR cells on the other, particularly 2 weeks after birth. Preproghrelin- and obestatin-IR cells were more numerous than ghrelin-IR cells in the stomach, suggesting the lack of ghrelin in some A-like cells. Most obestatin-producing cells in the stomach were distributed in the basal part of the oxyntic mucosa; these cells co-localized with chromogranin A (pancreastatin) and vesicle monoamine transporters type 1 and 2, but not with serotonin or histidine decarboxylase. Immunoelectron microscopy revealed the obestatin- and ghrelin-producing cells to be A-like cells, characterized by numerous highly electron-dense granules containing ghrelin and obestatin. Some granules exhibited an even electron density with thin electron-lucent halos, suggestive of monoamines. Feeding status, gastric bypass surgery, and reserpine treatment had no obvious effect on the A-like cells. In the pancreas, obestatin was present in the peripheral part of the islets, with a distribution distinct from that of glucagon-producing A cells, insulin-producing beta cells, and cells producing pancreatic polypeptide Y. Thus, obestatin and ghrelin co-localize with an anticipated monoamine in A-like cells in the stomach, and obestatin is found in pancreatic islets.

Orphan GPCR research

Orphan G protein-coupled receptors (GPCRs) are receptors lacking endogenous ligands. Found by molecular biological analyses, they became the roots of reverse pharmacology, in which receptors are attempted to be matched to potential transmitters. Later, when high-throughput screening technology was applied to reverse pharmacology, dozens of orphan GPCRs became deorphanized. Furthermore, novel neuropeptides were discovered. This review retraces the history of the orphan GPCRs and of the discoveries of their endogenous ligands, it also discusses the difficulties that the search for new ligands is presently encountering.

Potential therapies based on antidiabetic peptides

Since adipose tissue was shown to be more than a storage organ, the many cytokines it produces have been identified, along with their roles in energy homeostasis, appetite, and insulin resistance. Concurrently, numerous gut hormones with a diversity of effects have been discovered. They include, amongst many others, peptide YY, ghrelin and oxyntomodulin. As these peptides have been investigated, the potential for their use as novel anti-obesity and antidiabetic therapies has been realized. In this chapter we describe the actions of four of the peptides that have been proposed as the basis for promising new therapies for diabetes: leptin, adiponectin, obestatin and peptide YY. They each have an effect on appetite and, directly or indirectly, on glucose metabolism. We synthesize available data for these peptides and consider the therapeutic potential of each.

Central dysregulations in the control of energy homeostasis and endocrine alterations in anorexia and bulimia nervosa

In the last decades we have come to understand that the hypothalamus is a key region in controlling energy homeostasis. A number of control models have been proposed to explain the regulation of feeding behavior in physiological and pathological conditions, but all those based on imbalances of single factors fail to explain the disrupted regulation of energy supply in eating disorders such as anorexia nervosa and bulimia nervosa, as well as other psychiatric disorders. A growing amount of evidence demonstrates that many signaling molecules originated within the brain or coming from the adipose tissue or the gastro-enteric tract are involved in the highly complex process controlling food intake and energy expenditure. The recent discovery of leptin, ghrelin, and other factors have made it possible to penetrate in the still undefined pathophysiology of eating disorders with the hope of finding effective treatments for such diseases.

Central neural and endocrine mechanisms of non-exercise activity thermogenesis and their potential impact on obesity

The rise in obesity is associated with a decline in the amount of physical activity in which people engage. The energy expended through everyday non-exercise activity, called non-exercise activity thermogenesis (NEAT), has a considerable potential impact on energy balance and weight gain. Comparatively little attention has been paid to the central mechanisms of energy expenditure and how decreases in NEAT might contribute to obesity. In this review, we first examine the sensory and endocrine mechanisms through which energy availability and energy balance are detected that may influence NEAT. Second, we describe the neural pathways that integrate these signals. Lastly, we consider the effector mechanisms that modulate NEAT through the alteration of activity levels as well as through changes in the energy efficiency of movement. Systems that regulate NEAT according to energy balance may be linked to neural circuits that modulate sleep, addiction and the stress response. The neural and endocrine systems that control NEAT are potential targets for the treatment of obesity.

Stimulation of extracellular signal-regulated kinases and proliferation in the human gastric cancer cells KATO-III by obestatin

Obestatin, the ghrelin-associated peptide, activates cell proliferation in the gastric cancer cell line KATO-III. The results showed that this peptide induced cell proliferation by mitogen-activated kinase kinase/extracellular signal-regulated kinases1/2 (ERK1/2) phosphorylation. A sequential analysis of the obestatin transmembrane signalling pathway indicated that the ERK1/2 activity is partially blocked after preincubation of the cells with pertussis toxin, as well as by wortmannin (an inhibitor of phosphoinositide 3-kinase (PI3K)), staurosporine (an inhibitor of protein kinase C (PKC)) and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2, which inhibits the non receptor tyrosine kinase Src). Upon administration of obestatin, the intracellular levels of phospho-PKCepsilon- and theta-isoenzymes rise with similar time-courses, from which PKCepsilon appears to be the responsible for ERK1/2 response. Based on the experimental data, a signalling pathway involving the consecutive activation of G(i), PI3K, novel PKCepsilon and Src for ERK1/2 activation is proposed. These results point to a functionally active peptide that regulates proliferation of the gastric cancer cells KATO-III.

Insulin and ghrelin: peripheral hormones modulating memory and hippocampal function

Peptide hormones, initially identified in the periphery and best known for regulation of food intake and appetite, have increasingly been shown to regulate brain functions not only within the hypothalamus but elsewhere. The hippocampus, in particular, expresses receptors for many hormones. Both insulin and ghrelin are now known to enhance hippocampal memory processes; in addition, insulin acts to increase local hippocampal metabolism and regulate synaptic plasticity, while administration of ghrelin has been shown to promote dendritic spine synaptic formation and to increase anxiety. While insulin's effects appear to be specifically within the hippocampus, ghrelin may act at a range of sites within the limbic system.

Isolation of Zn2+ as an endogenous agonist of GPR39 from fetal bovine serum

We attempted to determine natural agonists of GPR39 in fetal bovine serum (FBS). FBS was conditioned to extract peptides and fractionated by two types of HPLC. The activity of each fraction was monitored by intracellular calcium mobilization. Then the purified active ingredient was analyzed by inductively coupled plasma mass spectrometry. In this fashion, Zn2+ ion was identified as an agonist of GPR39, though no peptidergic molecules were found. The calcium-mobilizing activity of Zn2+ was not abolished by pertussis toxin but was by a phospholipase C (PLC) inhibitor, U73122, indicating that the activity of GPR39 is mediated through the Gqalpha -PLC pathway. In addition, Zn2+ also activated mouse and rat GPR39, showing that the function of GPR39 as a Zn2+ receptor is conserved across species. This study is the first exploration of GPR39 agonists in FBS and indicates that GPR39 functions as a Gq-coupled Zn2+-sensing receptor.

Orphan G-protein-coupled receptors : strategies for identifying ligands and potential for use in eating disorders

G-protein-coupled receptors (GPCRs) are key regulators of intercellular interactions, participating in almost every physiological response. They exert their effects by being activated by a variety of endogenous ligands. Traditionally, these ligands were identified first, providing tools to characterise the receptors. However, since the late 1980s, homology screening approaches have allowed the GPCRs to be found first, and in turn used as orphan targets to identify their ligands. Over the last decade this method has led to the identification of 12 novel neuropeptide families. Interestingly, four of these deorphanised GPCR systems, melanin-concentrating hormone, ghrelin, orexin and neuropeptide B/neuropeptide W, have been found to play a role in the control of energy balance. This article reviews the role of these GPCR systems in the control of food intake and energy expenditure, and discusses their potential use in therapies directed at eating disorders. As obesity has reached epidemic proportions across the developed world, pharmacotherapy has focused on this condition. However, difficulties in weight control also characterise disorders of binge eating such as bulimia and binge-eating disorder. Consequently, hypophagic treatments may be of potential benefit in normal, overweight or obese individuals displaying aberrant (out of control) eating behaviour.

Plasma obestatin is lower at fasting and not suppressed by insulin in insulin-resistant humans

Obestatin, a recently discovered 23-amino acid peptide, is involved in the regulation of appetite and body weight in antagonistic fashion to ghrelin, both deriving from a common precursor peptide. Ghrelin was shown to be associated with insulin resistance, which may also affect obestatin. We investigated the association between insulin resistance and plasma concentrations of obestatin and ghrelin in nondiabetic individuals with high (IS; n = 18, 13 females and 5 males, age 47 +/- 2 yr, BMI = 25.5 +/- 0.9 kg/m(2)) and low (IR; n = 18, 12 females and 6 males, age 45 +/- 2 yr, P = 0.49, BMI = 27.5 +/- 1.1 kg/m(2), P = 0.17) insulin-stimulated glucose disposal (M), measured by 2-h hyperinsulinemic (40 mU.min(-1).m(-2)) isoglycemic clamp tests. M(100-120 min) was higher in IS (10.7 +/- 0.7) than in IR (4.4 +/- 0.2 mg.min(-1).kg(-1), P < 10(-9)), whereas insulin-dependent suppression of free fatty acids (FFA) in plasma was reduced in IR (71 +/- 6% vs. IS: 82 +/- 5%, P < 0.02). In both groups, plasma ghrelin concentrations were comparable at fasting and similarly reduced by 24-28% during insulin infusion. IR had lower fasting plasma obestatin levels (383 +/- 26 pg/ml vs. IS: 469 +/- 23 pg/ml, P < 0.02). Clamp insulin infusion reduced plasma obestatin to approximately 81% of basal values in IS (P < 0.00002), but not in IR. Fasting plasma obestatin was correlated positively with M (r = 0.34, P = 0.04), HDL cholesterol (r = 0.45, P = 0.01), and plasma ghrelin concentrations (r = 0.80, P < 0.000001) and negatively with measures of adiposity, plasma FFA during clamp (r = -0.42, P < 0.01), and systolic blood pressure (r = -0.33, P < 0.05). In conclusion, fasting plasma concentrations of obestatin, but not of ghrelin, are reduced in insulin resistance and are positively associated with whole body insulin sensitivity in nondiabetic humans. Furthermore, plasma obestatin is reduced by insulin in insulin-sensitive but not in insulin-resistant persons.

Obestatin conformational features: A strategy to unveil obestatin’s biological role?

Obestatin and its derivative Ob(11-23) are recently discovered peptides produced in the rat stomach. They have proven to be involved in the regulation of energy balance, inhibiting feeding, causing reductions in food intake, body weight and jejunal contraction in rodents. The G-protein coupled receptor, GPR39, was originally proposed as being an obestatin target receptor, but this remains controversial. As such, the molecular mechanism for obestatin's effects in vivo is still uncertain. Here we report the CD and NMR conformational analysis of obestatin and Ob(11-23). Both peptides assume a regular secondary structure in the C-terminal region of the molecule. In this region, structural elements similar to other GPCR binding neuropeptides support the identity of obestatin as a new and functionally autonomous GPCR ligand. Conversely sequence and conformational specificity point to a new farmacoforic structure, on which innovative derivatives with a potential role in the treatment of obesity can be designed and synthetized.

Small-molecule ghrelin receptor antagonists improve glucose tolerance, suppress appetite, and promote weight loss

Ghrelin, through action on its receptor, GH secretagogue receptor type 1a (GHS-R1a), exerts a variety of metabolic functions including stimulation of appetite and weight gain and suppression of insulin secretion. In the present study, we examined the effects of novel small-molecule GHS-R1a antagonists on insulin secretion, glucose tolerance, and weight loss. Ghrelin dose-dependently suppressed insulin secretion from dispersed rat islets. This effect was fully blocked by a GHS-R1a antagonist. Consistent with this observation, a single oral dose of a GHS-R1a antagonist improved glucose homeostasis in an ip glucose tolerance test in rat. Improvement in glucose tolerance was attributed to increased insulin secretion. Daily oral administration of a GHS-R1a antagonist to diet-induced obese mice led to reduced food intake and weight loss (up to 15%) due to selective loss of fat mass. Pair-feeding experiments indicated that weight loss was largely a consequence of reduced food intake. The impact of a GHS-R1a antagonist on gastric emptying was also examined. Although the GHS-R1a antagonist modestly delayed gastric emptying at the highest dose tested (10 mg/kg), delayed gastric emptying does not appear to be a requirement for weight loss because lower doses produced weight loss without an effect on gastric emptying. Consistent with the hypothesis that ghrelin regulates feeding centrally, the anorexigenic effects of potent GHS-R1a antagonists in mice appeared to correspond with their brain exposure. These observations demonstrate that GHS-R1a antagonists have the potential to improve the diabetic condition by promoting glucose-dependent insulin secretion and promoting weight loss.

Genetically engineered mice: a new paradigm to study gastric physiology

PURPOSE OF REVIEW

To summarize key aspects from recent research as well as review articles on the topic of genetic mouse models, particularly in knockout mice, that have considerably contributed to understanding the pathways and mechanisms underlying gastric physiology.

RECENT FINDINGS

A series of knockout mouse models has proven to be invaluable in elucidating the mechanism and validating the current model of acid secretion. The interaction between the gastrin-histamine and cholecystokinin-somatostatin pathways was identified using the genetic approach as being critical in regulating acid secretion. Curiously, neither ghrelin nor ghrelin receptor knockout mice displayed the expected lean phenotype. Importantly, the study of obestatin in GPR39 knockout mice could be misleading, as zinc rather than obestatin is the endogenous ligand for GPR39. The physiological roles of ghrelin and obestatin have yet to be confirmed using knockout mouse models.

SUMMARY

The knockout mouse continues to serve as an excellent model to dissect the complexity of the mechanism of gastric acid secretion and to study the physiological importance of gastric ghrelin.

The role of the vgf gene and VGF-derived peptides in nutrition and metabolism

Energy homeostasis is a complex physiological function coordinated at multiple levels. The issue of genetic regulation of nutrition and metabolism is attracting increasing interest and new energy homeostasis-regulatory genes are continuously identified. Among these genes, vgf is gaining increasing interest following two observations: (1) VGF-/- mice have a lean and hypermetabolic phenotype; (2) the first VGF-derived peptide involved in energy homeostasis, named TLQP-21, has been identified. The aim of this review will be to discuss the role of the vgf gene and VGF derived peptides in metabolic and nutritional functions. In particular we will: (1) provide a brief overview on the central systems regulating energy homeostasis and nutrition particularly focusing on the melanocortin system; (2) introduce the structure and molecular characteristic of vgf; (3) describe the phenotype of VGF deficient mice; (4) present recent data on the metabolic role of VGF-derived peptides, particularly focusing on one peptide named TLQP-21.

Incomplete restoration of the secretion of ghrelin and PYY compared to insulin after food ingestion following weight gain in anorexia nervosa

BACKGROUND

In humans, ghrelin has been found to stimulate appetite while PYY3-36 to reduce it; these orexigenic and anorexigenic peptides play significant roles in appetite control. We investigated pre- and postprandial responses of ghrelin and PYY in anorexia nervosa (AN) and the influence of weight gain.

METHODS

Plasma ghrelin, PYY3-36, glucose and insulin responses after ingestion of a 400 kcal standard meal were measured in 14 patients with restricting type of AN and 12 controls. The AN patients were evaluated before therapy and after inpatient therapy. Psychometry was performed by the use of Eating Disorders Inventory.

RESULTS

Ghrelin was suppressed during the meal test, while PYY3-36 was increased in all of the groups. Before therapy, AN patients had significantly increased levels of ghrelin and PYY3-36 compared to the control (P<0.01). After therapeutic intervention, as the nutritional status of AN patients improved, the secretion of these hormones were increased (P<0.05), but not normalized as in psychological testing. In contrast, insulin and glucose responses were normalized after inpatient therapy.

CONCLUSIONS

We found that both ghrelin and PYY3-36 increased in AN patients and these changes were not normalized in contrast to insulin after treatment. The increase in both orexigenic ghrelin and anorexigenic PYY3-36 may have a role in pathological eating behavior in AN.

Preproghrelin-derived peptide, obestatin, fails to influence food intake in lean or obese rodents

OBJECTIVES

Obestatin has been initially characterized as a new peptide derived from the ghrelin precursor, which suppresses food intake and inhibits the orexigenic and prokinetic actions of ghrelin when injected peripherally or centrally in lean mice. However, reproducing these data remains controversial. Reasons for the disparity may be the use of different doses, routes, and animal models. We aimed to investigate the effects of peripheral and intracisternal (IC) injection of obestatin on feeding, gastric motility, and blood glucose in rats as well as in diet-induced obese (DIO) mice.

RESEARCH METHODS AND PROCEDURES

Food intake and gastric emptying of a semi-liquid caloric meal were measured after intraperitoneal (IP) injection of obestatin in rats and DIO mice. Gastric phasic motility and blood glucose were monitored in urethane-anesthetized rats after IC or intravenous (IV) injection of obestatin.

RESULTS

Obestatin injected intraperitoneally at doses ranging from 0.1 to 3 mg/kg influenced neither acute food intake nor gastric emptying in rats. Obestatin injected intravenously at 0.3 or 3 mg/kg and IC at 7.5 or 30 microg/rat modified neither fasted gastric phasic motility nor blood glucose levels, while ghrelin (30 microg/kg, IV) increased and vagotomy suppressed gastric motility, and an oligosomatostatin analog (3 microg/rat, IC) decreased blood glucose. Obestatin, injected intraperitoneally (0.3 mg/kg) in DIO mice, did not alter feeding response to a fast, while urocortin 1 (10 microg/kg, IP) induced a 73.3% inhibition at 2 hours.

DISCUSSION

Our data demonstrate that peripheral administration of obestatin did not modify food intake in rats or obese mice or gastric motor function in rats.

LC-UV/MS characterization and DOE optimization of the iodinated peptide obestatin

The aim of this study was to investigate the direct iodination of the recently discovered peptide obestatin by LC-UV/ESI ion trap MS analysis. The influence of selected reaction parameters on obestatin iodination by chloramine-T, Iodo-Gen((R)) and lactoperoxidase was investigated by experimental design. Different responses, i.e. species percentage and yield, peptide recovery and iodination yield were evaluated. Mono-up till tetra-iodinated species are possible depending on the reaction conditions with electrophilic substitutions occurring at Tyr(16) and His(19) as confirmed by LC/MS/MS. The two possible mono-iodinated obestatin isomers, i.e. [I(1)-Tyr(16)]-obestatin and [I(1)-His(19)]-obestatin, could be chromatographically separated. Several significant main and quadratic effects, and interaction of factors were observed from which optimum conditions for a specific response could be derived. The highest impact on the response surface diagrams was overall attributed to the amount of iodide added. Synthesis methods were compared relative to the different response factors: lactoperoxidase was found to be the overall most robust iodination technique, and also gave the highest mono-iodinated species yield. The applicability of our research was demonstrated by non-carrier-added (125)I-radioiodination. To our knowledge, this is the first time an LC separation of mono-iodinated peptide isomers has been reported.

Molecular dissection of G protein preference using Gsalpha chimeras reveals novel ligand signaling of GPCRs

Although only 16 genes have been identified in mammals, several Galpha subunits can be simultaneously activated by G protein-coupled receptors (GPCRs) to modulate their complicated functions. Current GPCR assays are limited in the evaluation of selective Galpha activation, thus not allowing a comprehensive pathway screening. Because adenylyl cyclases are directly activated by G(s)alpha and the carboxyl termini of the various Galpha proteins determine their receptor coupling specificity, we proposed a set of chimeric G(s)alpha where the COOH-terminal five amino acids are replaced by those of other Galpha proteins and used these to dissect the potential Galpha linked to a given GPCR. Unlike G(q)alpha, G(12)alpha, and G(i)alpha outputs, compounding the signals from several Galpha members, the chimeric G(s)alpha proteins provide a superior molecular approach that reflects the previously uncharacterized pathways of GPCRs under the same cAMP platform. This is, to our knowledge, the first time allowing verification of the whole spectrum of Galpha coupling preference of adenosine A1 receptor, reported to couple to multiple G proteins and modulate many physiological processes. Furthermore, we were able to distinguish the uncharacterized pathways between the two neuromedin U receptors (NMURs), which distribute differently but are stimulated by a common agonist. In contrast to the G(q) signals mainly conducted by NMUR1, NMUR2 routed preferentially to the G(i) pathways. Dissecting the potential Galpha coupling to these GPCRs will promote an understanding of their physiological roles and benefit the pharmaceutical development of agonists/antagonists by exploiting the selective affinity toward a certain Galpha subclass.