Desacyl ghrelin inhibits the orexigenic effect of peripherally injected ghrelin in rats

The effects of exercise on food intake and hunger: relationship with acylated ghrelin and leptin

This study investigated the effects of a long bout of aerobic exercise on hunger and energy intake and circulating levels of leptin and acylated ghrelin. Ten healthy male subjects undertook two, 4 h trials in a randomized crossover design. In the exercise trial subjects ran for 105 min at 50% of maximal oxygen uptake and the last 15 min at 70% of maximal oxygen uptake followed by a 120 min rest period. In the control trial, subjects rested for 4 h. Subjects consumed a buffet test meal at 180 min during each trial. Hunger ratings, acylated ghrelin, leptin, glucose and insulin concentrations were measured at 0, 1, 2, 3 and 4 h. No differences were found at baseline values for hunger, acylated ghrelin, leptin, insulin and glucose for both trials (p > 0.05). The estimated energy expenditure of the exercise trial was 1550 ± 136 kcal. Exercise did not change subsequent absolute energy intake, but produced a significant decrease (p < 0.05) in relative energy intake. A two-way ANOVA revealed a significant (p < 0. 05) interaction effect for hunger and acylated ghrelin. In conclusion, this exercise regimen had a positive effect on reducing appetite which is related to reduced acylated ghrelin responses over time. This finding lends support for a role of exercise in weight management. Key pointsPhysical exercise is a strategy used to counteract obesity, since it lowers the energetic balance by increasing energy expenditure. However, because any energy expended in exercise elevates the intensity of hunger and drives food consumption, it is pertinent to ask how effective exercise could be in helping people to lose weight or to prevent weight gain.The effects of exercise on hunger sensations and food intake are fairly controversial and depend on the intensity and duration of exercise.120 min prolonged treadmill exercise with mix intensity, temporarily decreased hunger sensations, acylated ghrelin and relative energy intake.Variations in exercise intensity should theoretically be a useful means of weight loss.

Interaction between gastric and upper small intestinal hormones in the regulation of hunger and satiety: ghrelin and cholecystokinin take the central stage

Several peptides are produced and released from endocrine cells scattered within the gastric oxyntic and the small intestinal mucosa. These peptide hormones are crucially involved in the regulation of gastrointestinal functions and food intake by conveying their information to central regulatory sites located in the brainstem as well as in the forebrain, such as hypothalamic nuclei. So far, ghrelin is the only known hormone that is peripherally produced in gastric X/A-like cells and centrally acting to stimulate food intake, whereas the suppression of feeding seems to be much more redundantly controlled by a number of gut peptides. Cholecystokinin produced in the duodenum is a well established anorexigenic hormone that interacts with ghrelin to modulate food intake indicating a regulatory network located at the first site of contact with nutrients in the stomach and upper small intestine. In addition, a number of peptides including leptin, urocortin 2, amylin and glucagon-like peptide 1 interact synergistically with CCK to potentiate its satiety signaling effect. New developments have led to the identification of additional peptides in X/A-like cells either derived from the pro-ghrelin gene by alternative splicing and posttranslational processing (obestatin) or a distinct gene (nucleobindin2/nesfatin-1) which have been investigated for their influence on food intake.

The effects of ghrelin on energy balance and psychomotor activity in a goldfish model: an overview

The goldfish (Carassius auratus) has a number of merits as a laboratory animal, and we have extensively identified the mechanisms by which ghrelin regulates food intake in this species. For the first time, we have purified and characterized 11 molecular variants of ghrelin that are present in goldfish intestine and shown that 17-residue ghrelin, the predominant form with n-octanoyl modification, is biologically active and implicated in the regulation of food intake as an endogenous orexigenic factor. Ghrelin and its receptor system are present not only in peripheral tissues such as stomach and intestine, but also in the central nervous system. Recent studies have also revealed that a number of neuropeptides are widely distributed in the brain in key areas of emotional regulation, and their role as modulators of behavioral states is being increasingly recognized. Interestingly, administration of ghrelin induces an orexigenic effect and also modifies locomotor activity, suggesting the involvement of ghrelin in feeding control and regulation of energy balance. Information derived from studies of ghrelin has been increasing, and important results have been obtained from both fish and mammals. Here, we present an overview of the effects of ghrelin on energy balance and psychomotor activity in the goldfish as an animal model. The available data provide an insight into evolutionary background of ghrelin's multiple actions on energy homeostasis in vertebrates.

Ghrelin family of peptides and gut motility

Acyl ghrelin, des-acyl ghrelin, and obestatin are three peptides isolated from the gastrointestinal tract and encoded by the same preproghrelin gene. Three ghrelin gene products participate in modulating appetite, adipogenesis, glucose metabolism, cell proliferation, immune, sleep, memory, anxiety, cognition, and stress. We have investigated the effects of ghrelin family of peptides on fed and fasted motor activities in the stomach and duodenum of freely moving conscious rats by manometric method. Intracerebroventricular (ICV) and intravenous (IV) administration of acyl ghrelin induced fasted motor activity in the duodenum in fed rats. ICV and IV administration of des-acyl ghrelin disrupted fasted motor activity in the antrum. Changes in gastric motility induced by IV administration of des-acyl ghrelin were antagonized by ICV administration of a corticotropin-releasing factor (CRF) 2 receptor antagonist. IV administration of obestatin decreased the percentage motor index in the antrum and prolonged the time taken to return to fasted motility in the duodenum in fed rats. ICV administration of CRF 1 and 2 receptor antagonists prevented the effects of obestatin on gastroduodenal motility. Ghrelin gene products regulate feeding-associated gastroduodenal motility. Stomach may regulate various functions including gastrointestinal motility via acyl ghrelin, des-acyl ghrelin and obestatin as an endocrine organ. Increasing knowledge of the effects of ghrelin family of peptides on gastrointestinal motility could lead to innovative new therapies for functional gastrointestinal disorders.

Central injection of des-acyl chicken ghrelin does not affect food intake in chicks

In rodents and goldfish, ghrelin is well known as an orexigenic peptide, and des-acyl ghrelin, which is a ghrelin gene-derived peptide lacking Ser-3 acylation, affects feeding behavior when injected with or without ghrelin. Intracerebroventricular (i.c.v.) injection of ghrelin inhibits food intake in chicks (Gallus gallus), but has the opposite effect in rodents and goldfish. The aim of the present study was to investigate the effect of chicken des-acyl ghrelin on feeding in chicks. I.c.v. injection of des-acyl ghrelin alone at doses from 4 to 1000 pmol did not affect food intake in fed and 12-h fasted chicks. Co-injection of des-acyl ghrelin with ghrelin tended to attenuate ghrelin-induced anorexia. In an in vitro study, only the highest concentration (10(-6) M) of des-acyl ghrelin increased intracellular calcium ion concentration in chicken GHS-R1a-expressing cells. Des-acyl ghrelin (10(-6) M) slightly but significantly decreased intracellular calcium ion influx induced by 1 or 3 nM ghrelin. The present results demonstrate that des-acyl ghrelin is not positively involved in the central regulation of feeding in chicks. The feeding regulatory network between ghrelin and des-acyl ghrelin in chicks would be different from those in rodents and goldfish.

The importance of using the optimal plasticware and glassware in studies involving peptides

The unpredictable nature of peptide binding to surfaces requires optimization of experimental containers to be used. To demonstrate the variable recoveries of peptides from multiple surfaces commonly employed in peptide research, we tested the recovery of radiolabeled (125)I endocrine peptides under different conditions and provide guidelines for determining the surfaces to use for other peptides. (125)I-labeled peptides (ghrelin, sulfated cholecystokinin-8, corticotropin-releasing factor, glucagon-like peptide-1 [GLP-1], insulin, leptin, nesfatin-1, and peptide YY), representing a wide spectrum in net charge, size, end group, and modification, were incubated for 48 h in glass and plastic tubes untreated or coated with siliconizing fluid. Best surfaces were chosen and peptides were incubated with bovine serum albumin (BSA, 1%) with or without subsequent lyophilization. Recovery of (125)I-labeled peptides was determined by gamma counting. Important differences in (125)I-labeled peptide binding capacities to various types of surfaces exist. Siliconization decreased, whereas the addition of BSA improved recovery from surfaces tested. Lyophilizing solutions containing (125)I-labeled peptides and BSA in the tubes best suited for individual peptides rendered more than 89% recovery for all peptides. Ghrelin specifically displaced (125)I-ghrelin from borosilicate glass, whereas GLP-1 and Fmoc-arginine did not. Choosing the appropriate experimental container avoids unpredictable peptide loss that results in inaccurate measurements and false conclusions.

The ghrelin O-acyltransferase-ghrelin system: a novel regulator of glucose metabolism

PURPOSE OF REVIEW

Ghrelin, an orexigenic hormone secreted from the stomach, exists in the circulation in two isoforms: des-acyl and acyl ghrelin. Acylation by the enzyme ghrelin O-acyl-transferase (GOAT) enables ghrelin to activate the ghrelin receptor. This review discusses recent findings illustrating the role of acyl ghrelin, des-acyl ghrelin and GOAT in regulating glucose homeostasis.

RECENT FINDINGS

Recent publications support a role of ghrelin in modulating glucose homeostasis. Novel cellular mechanisms have been proposed to explain these effects. Controversy on this topic continues to exist owing to inconsistent observations made in both rodents and humans. Many recent studies are uncovering a role of des-acyl ghrelin in glucose metabolism specifically in modulating insulin sensitivity and glucose uptake into adipocytes. A novel role of ghrelin acylation by the enzyme GOAT in regulating glucose metabolism during caloric deprivation has newly been discovered.

SUMMARY

Ghrelin plays a role in regulating glucose homeostasis through the modulation of insulin secretion and insulin sensitivity. Acyl ghrelin and des-acyl ghrelin appear to have opposing glucoregulatory effects and regulation of acylation by the enzyme GOAT appears to play a role in mediating glucose metabolism. Modulation of GOAT or ghrelin signaling may be a clinically relevant strategy to treat metabolic diseases such as type II diabetes.

Relationship between total ghrelin and inflammation in hemodialysis patients

In hemodialysis (HD) patients studies have shown that plasma ghrelin is increased and it has been speculated that ghrelin levels might be related to systemic inflammation. The present study attempted to correlate the serum levels of total ghrelin with serum TNF-α and IL-6, and with nutritional status and body composition in HD patients. Forty-seven HD patients from a single dialysis unit (18 women, mean age 55.3±12.2 yr; BMI 24.4±4.2kg/m(2); % body fat 29.4±7.4%) were studied and compared to 21 healthy subjects (12 women, 50.7±15.7 yr and BMI 25.6±4.0kg/m(2); % body fat 30.0±5.7%). Biochemical data, serum total ghrelin, TNF-α and IL-6 levels were measured. The body composition was evaluated by dual energy X-ray absortiometry (DEXA) and energy and protein intake were evaluated. Patients showed elevated plasma ghrelin levels when compared to healthy subjects (1.14±1.0ng/mL vs 0.58±0.4; p<0.001). There was a positive correlation between ghrelin levels and TNF-α (r=0.25; p<0.04), IL-6 (r=0.42; p<0.02), and a negative correlation between TNF-α and protein intake (r=-0.28; p<0.03), and energy intake (r=-0.34; p<0.01). No correlation was observed with any aspect of body composition. Plasma ghrelin levels are elevated in HD patients and associated with the state of systemic inflammation. We suggest that the inflammatory state may affect ghrelin bioactivity and metabolism in hemodialysis patients.

GSK1614343, a novel ghrelin receptor antagonist, produces an unexpected increase of food intake and body weight in rodents and dogs

Ghrelin is a 28-amino-acid polypeptide expressed in the stomach and hypothalamus that stimulates GH secretion, increases food intake (FI) and promotes body weight (BW) gain most likely via activation of the growth hormone secretagogue receptor type 1a (GHSR1a). GSK1614343 is a novel selective and potent GHSR antagonist with no partial agonist properties, recently characterized as GH secretion inhibitor by Sabbatini et al. [Chem Med Chem 2010;5:1450-1455]. In the present study, GSK1614343 (10 mg/kg) was not able to antagonize ghrelin-induced food consumption in rat, but unexpectedly stimulated FI and BW gain in both rats and dogs, a profile associated with decreased ghrelin plasma level. Interestingly, GSK1614343 selectively reduced the pro-opiomelanocortin mRNA levels in rat hypothalami chronically treated with the compound. To better understand the observed effects, we administered GSK1614343 (30 mg/kg) to Ghsr null mice and measured body mass components (fat, lean and free fluid) by using a NMR spectrometer. The increases of FI and BW were abolished in Ghsr null mice, while fat and lean masses increased in wild-type mice. Taken together, these results indicate that the orexigenic effect of GSK1614343 is mediated by GHSR1a and that the weight gain could be attributed to the increase of both adiposity and muscle mass, but not to fluid retention. The observed dissociation between effects on GH secretion and effects on FI/BW is inconsistent with a simple hormone-receptor model, suggesting unknown underlying regulations of the ghrelin system whose understanding require further investigation.

Plasma nesfatin-1 concentrations in restricting-type anorexia nervosa

Restricting-type anorexia nervosa (AN-R) is characterized by chronic food restriction and severe emaciation due to various cognitive biases such as a distorted self-image. In spite of several treatments, AN-R continues to be a refractory disease because of its unknown pathogenesis. Although previous studies have shown that changes in feeding regulatory peptides such as ghrelin are involved in anorexia, few reports have described the relationship between AN-R and nesfatin-1, a recently identified satiety peptide. Therefore, we examined the plasma nesfatin-1 levels in AN-R patients to determine its role in AN-R. A total of 15 women participated in the study; 7 patients with AN-R and 8 age-matched healthy controls (average BMI, 13.02 ± 0.30 vs. 21.57 ± 0.48, respectively). Our results showed that plasma nesfatin-1 levels were significantly lower in AN-R group than in control group (6.23 ± 0.70 ng/ml vs. 8.91 ± 0.85 ng/ml, respectively, P<0.05). Plasma acyl ghrelin and des-acyl ghrelin levels were significantly higher in AN-R group than in control group (acyl ghrelin: 62.4 ± 10.15 fmol/ml vs. 27.20 ± 5.60 fmol/ml, P<0.01 and des-acyl ghrelin: 300.17 ± 55.95 fmol/ml vs. 107.34 ± 40.63 fmol/ml, P<0.05). Although AN-R is associated with emaciation for a prolonged period, our result suggested that nesfatin-1 levels may be regulated by nutrition status and response to starvation.

Hormonal regulation of energy-protein homeostasis in hemodialysis patients: an anorexigenic profile that may predispose to adverse cardiovascular outcomes

To assess whether endocrine dysfunction may cause derangement in energy homeostasis in patients undergoing hemodialysis (HD), we profiled hormones, during a 3-day period, from the adipose tissue and the gut and the nervous system around the circadian clock in 10 otherwise healthy HD patients and 8 normal controls. The protocol included a 40-h fast. We also measured energy-protein intake and output and assessed appetite and body composition. We found many hormonal abnormalities in HD patients: 1) leptin levels were elevated, due, in part, to increased production, and nocturnal surge in response to daytime feeding, exaggerated. 2) Peptide YY (PYY), an anorexigenic gut hormone, was markedly elevated and displayed an augmented response to feeding. 3) Acylated ghrelin, an orexigenic gut hormone, was lower and did not exhibit the premeal spike as observed in the controls. 4) neuropeptide Y (NPY), a potent orexigenic peptide, was markedly elevated and did not display any circadian variation. 5) Norepinephrine, marginally elevated, did not exhibit the normal nocturnal dip. By contrast, α-melanocyte-stimulating hormone and glucagon-like peptide-1 were not different between the two groups. Despite these hormonal abnormalities, HD patients maintained a good appetite and had normal body lean and fat mass, and there was no evidence of increased energy expenditure or protein catabolism. We explain the hormonal abnormalities as well as the absence of anorexia on suppression of parasympathetic activity (vagus nerve dysfunction), a phenomenon well documented in dialysis patients. Unexpectedly, we noted that the combination of high leptin, PYY, and NPY with suppressed ghrelin may increase arterial blood pressure, impair vasodilatation, and induce cardiac hypertrophy, and thus could predispose to adverse cardiovascular events that are the major causes of morbidity and mortality in the HD population. This is the first report attempting to link hormonal abnormalities associated with energy homeostasis to adverse cardiovascular outcome in the HD patients.

Plasma levels of acylated and total ghrelin in pediatric patients with chronic kidney disease

This cross-sectional study set out to compare total and acyl ghrelin levels in children with mild chronic kidney disease (CKD) undergoing conservative treatment (n = 19) with children with end-stage renal disease (ESRD) undergoing hemodialysis (n = 24), and with healthy controls (n = 20). The relationship between ghrelin levels and parameters of renal function, nutritional status, and selective hormones were investigated. ESRD patients had higher total ghrelin levels than those with mild CKD or control individuals. However, acyl ghrelin did not differ between groups, indicating that the excess circulating ghrelin was desacylated. Since desacyl ghrelin has been shown to inhibit appetite, increased levels might contribute to protein-energy wasting in pediatric renal patients. When all 43 renal patients were combined, multiple regression analysis found age and glomerular filtration rate (GFR) to be significant negative predictors of total ghrelin. Acyl ghrelin was influenced negatively by age and positively by energy intake. Acyl to total ghrelin ratio related positively to GFR and energy intake. The results indicate that total but not acyl ghrelin is influenced by low GFR in children with CKD and suggests that ghrelin activation may be impaired in these patients. Since energy intake is a positive predictor of acyl ghrelin, the physiological control of ghrelin secretion appears to be altered in pediatric renal patients.

Contrasting effects of ghrelin and des-acyl ghrelin on the lumbo-sacral defecation center and regulation of colorectal motility in rats

BACKGROUND

We have previously demonstrated that a centrally penetrant ghrelin receptor agonist enhances colorectal motility, through activation of the lumbo-sacral defecation center (L6-S1 region of the spinal cord) in rats. In the present study, we examined the effects of the native peptide and its non-acylated counterpart in eliciting this stimulatory effect on colorectal motility.

METHODS

Rats were anesthetised with α-chloralose and ketamine, and colorectal intraluminal pressure and propelled intraluminal liquid volume were recorded in vivo.

KEY RESULTS

Intrathecal application of acylated ghrelin to the L6-S1 region of the spinal cord, but not intravenous application, elicited groups of phasic increases in colorectal intraluminal pressure that were associated with increased fluid output through the anal cannula. The effect was dose-dependent. The colokinetic effects of ghrelin were prevented if the pelvic nerves were severed. Reverse transcription polymerase chain reaction revealed the expression of the ghrelin and ghrelin receptor genes in the lumbo-sacral spinal cord. In contrast to acylated ghrelin, des-acyl ghrelin failed to cause changes in colorectal motility. However, when des-acyl ghrelin and ghrelin were applied simultaneously at the L6-S1 region, the ghrelin-induced enhancement of colorectal motility was significantly attenuated.

CONCLUSION & INFERENCES

It is concluded that acylation of the ghrelin peptide is essential to promote propulsive contractions of the colorectum and that des-acyl ghrelin opposes this effect. At most other sites of ghrelin action, des-acyl ghrelin either has no effect or it mimics ghrelin. This is the first evidence that non-acylated ghrelin opposes the action of the acylated peptide in the spinal cord.

Identification and characterization of acyl-protein thioesterase 1/lysophospholipase I as a ghrelin deacylation/lysophospholipid hydrolyzing enzyme in fetal bovine serum and conditioned medium

Ghrelin contains an octanoic acid at the third residue serine, and the presence of octanoic acid on ghrelin is critical to its physiological functions. The precise mechanism for the deacylation of ghrelin in circulation remains to be clarified, although the level of deacylated ghrelin (des-acyl ghrelin) is higher than that of acylated ghrelin in serum. In this study, rapid identification of ghrelin deacylation activity was achieved by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and a ghrelin deacylation enzyme was purified 1515-fold from fetal bovine serum. Chromatographic separation showed a 24-kDa band on SDS-PAGE corresponding to ghrelin deacylation activity, and the protein band was identified as acyl-protein thioesterase 1 (APT1)/lysophospholipase I. A ghrelin deacylation enzyme in medium from HepG2 cells was also purified and identified as APT1. Although it lacks a secretion signal sequence, APT1 may be released by cells expressing APT1, mainly from liver in vivo. APT1 was originally purified as a cytosolic lysophospholipid hydrolyzing enzyme (lysophospholipase I), and recombinant APT1 exhibited deacylation activity as well as lysophospholipase activity in vitro. APT1 is released at high levels from RAW264.7 macrophage-like cells into the culture medium after stimulation with lipopolysaccharide (LPS), and LPS suppresses APT1 mRNA and protein expressions in these cells. More potent ghrelin deacylase activities were detected in sera from LPS-treated rats than in control sera. These results suggested that the serum activity of APT1 may play an important role in determination of the concentration of des-acyl ghrelin in circulation, especially under septic inflammation.

Lipopolysaccharide differentially decreases plasma acyl and desacyl ghrelin levels in rats: potential role of the circulating ghrelin-acylating enzyme GOAT

Bacterial lipopolysaccharide (LPS) in rodents is an established model for studying innate immune responses to gram-negative bacteria and mimicking symptoms of infections including reduced food intake associated with decreased circulating total ghrelin levels. The ghrelin-acylating enzyme, ghrelin-O-acyltransferase (GOAT) involved in the formation of acyl ghrelin (AG) was recently identified. We investigated changes in circulating AG, desacyl ghrelin (DG) and GOAT induced by intraperitoneal LPS (100 microg/kg) and associated changes in food intake. Plasma AG and total ghrelin were assessed by radioimmunoassay, GOAT protein by Western blot and mRNA by RT-qPCR. DG was derived from total minus AG. Plasma AG and DG were decreased at 2, 5 and 7 h (p<0.01) post-injection compared to vehicle and recovered at 24 h. At 2 h there was a significantly greater decrease of AG (-53%) than DG (-28%) resulting in a decreased AG/DG ratio (1:5, p<0.01), which thereafter returned to pre-injection values (1:3). This altered ratio was associated with a 38% decrease in plasma GOAT protein compared to vehicle (p<0.001), whereas gastric GOAT protein was slightly increased by 10% (p<0.05). GOAT mRNA expression was unchanged. Food intake was reduced by 58% measured during the 1.5-2 h period post-LPS injection. Decreased plasma AG and DG preceded the rise in rectal temperature and blood glucose that peaked at 7 h. These data indicate that LPS induces a long-lasting reduction of AG and DG levels that may have a bearing with the decrease in food intake. The faster drop in AG than DG within 2 h is associated with reduced circulating GOAT.

Unacylated ghrelin rapidly modulates lipogenic and insulin signaling pathway gene expression in metabolically active tissues of GHSR deleted mice

Background

There is increasing evidence that unacylated ghrelin (UAG) improves insulin sensitivity and glucose homeostasis; however, the mechanism for this activity is not fully understood since a UAG receptor has not been discovered.

Methodology/Principal Findings

To assess potential mechanisms of UAG action in vivo, we examined rapid effects of UAG on genome-wide expression patterns in fat, muscle and liver of growth hormone secretagogue receptor (GHSR)-ablated mice using microarrays. Expression data were analyzed using Ingenuity Pathways Analysis and Gene Set Enrichment Analysis. Regulation of subsets of these genes was verified by quantitative PCR in an independent experiment. UAG acutely regulated clusters of genes involved in glucose and lipid metabolism in all three tissues, consistent with enhancement of insulin sensitivity.

Conclusions/Significance

Fat, muscle and liver are central to the control of lipid and glucose homeostasis. UAG rapidly modulates the expression of metabolically important genes in these tissues in GHSR-deleted mice indicating a direct, GHSR-independent, action of UAG to improve insulin sensitivity and metabolic profile.

Des-acyl ghrelin has specific binding sites and different metabolic effects from ghrelin in cardiomyocytes

The current study aimed to compare the effects of the peptide hormone ghrelin and des-G, its unacylated isoform, on glucose and fatty acid uptake and to identify des-G-specific binding sites in cardiomyocytes. In the murine HL-1 adult cardiomyocyte line, ghrelin and des-G had opposing metabolic effects: des-G increased medium-chain fatty acid uptake (BODIPY fluorescence intensity), whereas neither ghrelin alone nor in combination with des-G did so. Ghrelin inhibited the increase in glucose uptake normally induced by insulin (rate of 2-[(3)H]deoxy-d-glucose incorporation), but des-G did not; des-G was also able to partially reverse the inhibitory effect of ghrelin. In HL-1 cells and primary cultures of neonatal rat cardiomyocytes, des-G but not ghrelin increased insulin-induced translocation of glucose transporter-4 from nuclear to cytoplasmic compartments (immunohistochemistry and quantitative confocal analysis). AKT was phosphorylated by insulin but not affected by ghrelin or des-G, whereas neither AMP-activated protein kinase nor phosphatase and tensin homolog deleted from chromosome 10 was phosphorylated by any treatments. HL-1 and primary-cultured mouse and rat cardiomyocytes each possessed two independent specific binding sites for des-G not recognized by ghrelin (radioreceptor assays). Neither ghrelin nor des-G affected viability (dimethylthiazol diphenyltetrazolium bromide assays), whereas both isoforms were equally protective against apoptosis. Therefore, in cardiomyocytes, des-G binds to specific receptors and has effects on glucose and medium-chain fatty acid uptake that are distinct from those of ghrelin. Real-time PCR indicated that expression levels of ghrelin O-acyltransferase RNA were comparable between HL-1 cells, human myocardial tissue, and human and murine stomach tissue, indicating the possibility of des-G conversion to ghrelin within our model.

Effects of glucose and insulin on acyl ghrelin and desacyl ghrelin, leptin, and adiponectin in pregnant women with diabetes

The aim of the study was to compare the regulation of ghrelin, leptin, and adiponectin by insulin and glucose during the second and third trimesters of pregnancy in women with diabetes. We studied 9 pregnant women with diabetes. All women were treated with insulin and omitted the morning dose on the day of the test. After collection of baseline fasting samples, we performed 3 successive glucose clamps: 2 euglycemic clamps (glucose, 5 mmol/L; insulin infusion at 20 and 40 mU m(-2) min(-1)) and 1 hyperglycemic clamp (glucose, 10 mmol/L; insulin infusion at 40 mU m(-2) min(-1)). We determined concentrations of acyl and desacyl ghrelin (using a double-antibody sandwich assay that recognizes the full-length molecule), leptin, and adiponectin. Fasting desacyl ghrelin concentrations decreased, whereas insulin and leptin concentrations increased, between the second and third trimesters of pregnancy (P < or = .011). During the clamp studies, desacyl ghrelin concentrations decreased by 33% (second trimester, P = .004) and 27% (third trimester, P = .09) with increasing glucose and insulin concentrations, whereas acyl ghrelin, leptin, and adiponectin concentrations were unaffected. Glucose and insulin regulate desacyl ghrelin concentrations in pregnant women with diabetes. Impaired desacyl ghrelin regulation may affect energy metabolism in pregnant women with poorly controlled diabetes.

Nesfatin-1--role as possible new potent regulator of food intake

Nesfatin-1 is an 82 amino acid peptide recently discovered in the brain which is derived from nucleobindin2 (NUCB2), a protein that is highly conserved across mammalian species. Nesfatin-1 has received much attention over the past two years due to its reproducible food intake-reducing effect that is linked with recruitment of other hypothalamic peptides regulating feeding behavior. A growing amount of evidence also supports that various stressors activate fore- and hindbrain NUCB2/nesfatin-1 circuitries. In this review, we outline the central nervous system distribution of NUCB2/nesfatin-1, and recent developments on the peripheral expression of NUCB2/nesfatin-1, in particular its co-localization with ghrelin in gastric X/A-like cells and insulin in ss-cells of the endocrine pancreas. Functional studies related to the characteristics of nesfatin-1's inhibitory effects on dark phase food intake are detailed as well as the central activation of NUCB2/nesfatin-1 immunopositive neurons in the response to psychological, immune and visceral stressors. Lastly, potential clinical implications of targeting NUCB2/nesfatin-1 signaling and existing gaps in knowledge to ascertain the role and mechanisms of action of nesfatin-1 are presented.

Neuronal circuits involving ghrelin in the hypothalamus-mediated regulation of feeding

Ghrelin, an n-octanoylated 28-amino acid brain-gut peptide, was first isolated from extracts of porcine stomach. Ghrelin is an endogenous ligand for the growth hormone secretagogue type 1a receptor (GHS-R1a), the functionally active form of GHS-R, and stimulates feeding and growth hormone secretion. Ghrelin is mainly produced in the A/X-like cells of the oxyntic glands of the stomach and is the main orexigenic circulating hormone that acts on the hypothalamus to affect feeding behavior and energy metabolism. Ghrelin-containing neuronal cell bodies are localized in the hypothalamic arcuate nucleus, a center that integrates signals for energy homeostasis. Ghrelin-containing nerve fibers are widely distributed in the brain. Accumulated evidence shows that hypothalamic neuropeptides such as neuropeptide Y (NPY), orexin and proopiomelanocortin (POMC) are involved in the regulation of feeding behavior and energy homeostasis via neuronal circuits in the hypothalamus. Ghrelin also forms part of the feeding-regulating neuronal circuitry in conjunction with other feeding-regulating peptide-containing neurons within the hypothalamus. In view of the fact that one decade has now passed since ghrelin was first discovered, we review advances that have been made in ghrelin research during that time and how this has impacted on our knowledge of feeding regulation in the hypothalamus. We also summarize our current understanding of the neuronal interactions between ghrelin and the different kinds of feeding-regulating peptide-containing neurons in the hypothalamus based on evidence at the ultrastructural level.

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.

Ghrelin gene products and the regulation of food intake and gut motility

A breakthrough using "reverse pharmacology" identified and characterized acyl ghrelin from the stomach as the endogenous cognate ligand for the growth hormone (GH) secretagogue receptor (GHS-R) 1a. The unique post-translational modification of O-n-octanoylation at serine 3 is the first in peptide discovery history and is essential for GH-releasing ability. Des-acyl ghrelin, lacking O-n-octanoylation at serine 3, is also produced in the stomach and remains the major molecular form secreted into the circulation. The third ghrelin gene product, obestatin, a novel 23-amino acid peptide identified from rat stomach, was found by comparative genomic analysis. Three ghrelin gene products actively participate in modulating appetite, adipogenesis, gut motility, glucose metabolism, cell proliferation, immune, sleep, memory, anxiety, cognition, and stress. Knockdown or knockout of acyl ghrelin and/or GHS-R1a, and overexpression of des-acyl ghrelin show benefits in the therapy of obesity and metabolic syndrome. By contrast, agonism of acyl ghrelin and/or GHS-R1a could combat human anorexia-cachexia, including anorexia nervosa, chronic heart failure, chronic obstructive pulmonary disease, liver cirrhosis, chronic kidney disease, burn, and postsurgery recovery, as well as restore gut dysmotility, such as diabetic or neurogenic gastroparesis, and postoperative ileus. The ghrelin acyl-modifying enzyme, ghrelin O-Acyltransferase (GOAT), which attaches octanoate to serine-3 of ghrelin, has been identified and characterized also from the stomach. To date, ghrelin is the only protein to be octanylated, and inhibition of GOAT may have effects only on the stomach and is unlikely to affect the synthesis of other proteins. GOAT may provide a critical molecular target in developing novel therapeutics for obesity and type 2 diabetes.

Ghrelin, des-acyl ghrelin and nesfatin-1 in gastric X/A-like cells: role as regulators of food intake and body weight

Numerous peptides released from endocrine cells in the intestinal mucosa were established early on to be involved in the physiological regulation of food intake with a prominent role in termination of food ingestion when nutrients pass along the intestinal tract. Recently, peptides released from X/A-like endocrine cells of the gastric oxyntic mucosa were recognized as additional key players in the regulation of feeding and energy expenditure. Gastric X/A-like cells release the octanoylated peptide, ghrelin, the only known peripherally produced hormone stimulating food intake through interaction with growth hormone secretagogue 1a receptor (GHS-R1a). Additionally, non-octanoylated (des-acyl) ghrelin present in the circulation at higher levels than ghrelin is currently discussed as potential modulator of food intake by opposing ghrelin's action independent from GHS-R1a although the functional significance remains to be established. Obestatin, a ghrelin-associated peptide was initially reported as anorexigenic modulator of ghrelin's orexigenic action. However, subsequent reports did not support this contention. Interesting is the recent identification of nesfatin-1, a peptide derived from the nucleobindin2 gene prominently expressed in gastric X/A-like cells in different vesicles than ghrelin. Circulating nesfatin-1 levels vary with metabolic state and peripheral or central injection inhibits dark phase feeding in rodents. Overall, these data point to an important role of gastric X/A-like cells in food intake regulation through the expression of the orexigenic peptide ghrelin along with des-acyl ghrelin and nesfatin-1 capable of reducing food intake upon exogenous injection although their mechanisms of action and functional significance remain to be established.

Ontogeny of acylated ghrelin degradation in the rat

Ghrelin circulates as acylated (AG) and unacylated (or desacyl) ghrelin (UAG). We aimed at clarifying the effect of age and sex on plasma deacylation and degradation of AG in vivo and in vitro in the rat. In vivo, we compared AG and UAG concentrations following administration of 1 microg AG intraperitoneally in rat neonates during the first 3h of life. AG administration caused a 2-3 times increase in plasma AG concentrations contrasting with a approximately 1000 times increase in UAG concentrations suggesting rapid deacylation of AG into UAG. In vitro, we demonstrated that AG degradation was greater in the fetus (97% over 30 min) and decreased progressively to 57% in adult animals (P<0.001). Carboxylesterase and butyrylcholinesterase activities were determined during the fetal (day 21 of pregnancy) and postnatal period (days 1, 6, 13, 21 and 28) and in the adult rat and were found to increase with age (P<0.001). While inhibition of carboxylesterase and butyrylcholinesterase did not affect AG deacylation, serine protease inhibitors decreased AG degradation in the adult rat (from 59% to 23%) and, to a lesser extent, in the rat neonate (from 92% to 57%) by reducing both deacylation and degradation into non-UAG metabolites. Our data suggest that degradation of AG into UAG and non-UAG metabolites is much faster in the fetus and in the rat neonate compared to the adult. We speculate that this process allows for fine tuning of the physiological effects of both AG and UAG.

Novel insight in distribution of nesfatin-1 and phospho-mTOR in the arcuate nucleus of the hypothalamus of rats

Recently, two proteins have been localized in the arcuate nucleus (ARC) and implicated in the regulation of food intake: the serine-threonine-kinase mammalian target of rapamycin (mTOR) as part of the TOR signaling complex 1 (TORC1), and nesfatin-1 derived from the precursor protein nucleobindin2. However, the exact cell types are not well described. Therefore, we performed double-labeling studies for NPY, CART, nesfatin-1 and pmTOR in the ARC. In this study, we showed that nesfatin-1 is not only intracellularly co-localized with cocaine- and amphetamine-regulated transcript (CART) peptide as reported before, but also with phospho-mTOR (pmTOR) and neuropeptide Y (NPY) in ARC neurons. Quantification revealed that 59+/-5% of the pmTOR-immunoreactive (ir) neurons were immunoreactive for nesfatin-1. Moreover, double labeling for nesfatin-1 and NPY exhibited that 19+/-5% of the NPY positive cells were also immunoreactive for nesfatin-1. Furthermore, we could also confirm results from previous studies, showing that the majority of nesfatin-1 neurons are also positive for CART peptide, whereas most of the pmTOR is co-localized with NPY and only to a lesser extent with CART.

Interactions of gastrointestinal peptides: ghrelin and its anorexigenic antagonists

Food intake behaviour and energy homeostasis are strongly regulated by a complex system of humoral factors and nerval structures constituting the brain-gut-axis. To date the only known peripherally produced and centrally acting peptide that stimulates food intake is ghrelin, which is mainly synthesized in the stomach. Recent data indicate that the orexigenic effect of ghrelin might be influenced by other gastrointestinal peptides such as cholecystokinin (CCK), bombesin, desacyl ghrelin, peptide YY (PYY), as well as glucagon-like peptide (GLP). Therefore, we will review on the interactions of ghrelin with several gastrointestinal factors known to be involved in appetite regulation in order to elucidate the interdependency of peripheral orexigenic and anorexigenic peptides in the control of appetite.

Regulation of food intake and body weight by recombinant proghrelin

Ghrelin is a 28-amino-acid hormone derived from the endoproteolytic processing of its prehormone proghrelin. Although ghrelin has been reported to regulate food intake and body weight, it is still unknown whether proghrelin exercises any biological function. Here we show that recombinant proghrelin alters food intake and energy metabolism in mice. After intraperitoneal administration of recombinant proghrelin (100 nmol/kg body wt), cumulative food intake was significantly increased at days 1, 2, and 3 (6 +/- 0.3, 13 +/- 0.5, and 20 +/- 0.8 g vs. 5 +/- 0.2, 10 +/- 0.2, and 16 +/- 0.3 g of the control mice receiving normal saline, respectively, n = 6, P < 0.05). Twelve-hour cumulative food intake in the light photo period in mice treated with proghrelin increased significantly relative to the control (2.1 +/- 0.04 vs. 1.3 +/- 0.2 g, n = 6, P < 0.05). No change in 12-h cumulative food intake in the dark photo period was observed between mice treated with proghrelin and vehicle (4.2 +/- 0.6 vs. 4.3 +/- 0.6 g, n = 6, P > 0.05). This is associated with a decrease in body weight (0.42 +/- 0.04 g) for mice treated with proghrelin, whereas control animals gained body weight (0.31 +/- 0.04 g). Mice treated with proghrelin demonstrate a significant decrease in respiratory quotient, indicating an increase in fat consumption. Recombinant proghrelin is functionally active with effects on food intake and energy metabolism.

The RAPID method for blood processing yields new insight in plasma concentrations and molecular forms of circulating gut peptides

The correct identification of circulating molecular forms and measurement of peptide levels in blood entails that the endocrine peptide being studied is stable and recovered in good yields during blood processing. However, it is not clear whether this is achieved in studies using standard blood processing. Therefore, we compared peptide concentration and form of 12 (125)I-labeled peptides using the standard procedure (EDTA-blood on ice) and a new method employing Reduced temperatures, Acidification, Protease inhibition, Isotopic exogenous controls, and Dilution (RAPID). During standard processing there was at least 80% loss for calcitonin-gene-related peptide and cholecystokinin-58 (CCK-58) and more than 35% loss for amylin, insulin, peptide YY forms (PYY((1-36)) and PYY((3-36))), and somatostatin-28. In contrast, the RAPID method significantly improved the recovery for 11 of 12 peptides (P < 0.05) and eliminated the breakdown of endocrine peptides occurring after standard processing as reflected in radically changed molecular forms for CCK-58, gastrin-releasing peptide, somatostatin-28, and ghrelin. For endogenous ghrelin, this led to an acyl/total ghrelin ratio of 1:5 instead of 1:19 by the standard method. These results show that the RAPID method enables accurate assessment of circulating gut peptide concentrations and forms such as CCK-58, acylated ghrelin, and somatostatin-28. Therefore, the RAPID method represents an efficacious means to detect circulating variations in peptide concentrations and form relevant to the understanding of physiological function of endocrine peptides.

Ghrelin and obestatin levels in end-stage renal disease

Malnutrition is fairly common in end-stage renal disease (ESRD) patients, persistent lack of appetite being a major symptom. Ghrelin and obestatin are two hormones that are involved in appetite and energy homeostasis. The present study examined ghrelin and obestatin levels in 24 ESRD patients undergoing haemodialysis and 24 age-matched healthy controls. Serum and saliva ghrelin and obestatin levels in the ESRD patients were significantly higher compared with controls, while saliva ghrelin and obestatin levels in all study participants were significantly higher than serum levels. Saliva ghrelin correlated with serum ghrelin and saliva obestatin correlated with serum obestatin in all study participants, although there was no correlation between ghrelin and obestatin levels. In conclusion, the results suggest that the kidneys may have a role in the metabolism and/or clearance of obestatin, as they do for ghrelin. Further studies are needed to determine if elevated levels of these hormones in ESRD patients contribute to the malnutrition that is common in these patients.

Is desacyl ghrelin a modulator of food intake?

Desacyl ghrelin is produced in the gastric mucosa and plasma by deacylation of ghrelin. It occurs in considerably larger amounts than ghrelin in various regions in the organisms of rats and mice. It exerts biological activities in vitro as different as stimulating adipogenesis or inhibiting glucose output in hepatocytes. In fasted rats, desacyl ghrelin levels decreased under catabolic metabolic conditions and in mice, high desacyl ghrelin concentrations went along with decreased food intake. These observations suggest an influence of the peptide on food intake and energy homeostasis. Behavioral studies led to controversial results, but several suggest an anorexigenic effect. Studies on desacyl ghrelin-induced modulation of food intake indicate the involvement of central nervous pathways, since it is said to cross the blood-brain barrier and to induce increased neuronal activity hypothalamic nuclei. It is likely to be involved in the regulation of the synthesis of anorexigenic hypothalamic mediators. Quite possibly, there might be means of interaction between desacyl ghrelin and its supposable precursor ghrelin.

A new anorexigenic protein, nesfatin-1

An anorexigenic peptide, nesfatin-1 was found in rat hypothalamus, and its expression in the paraventricular nucleus of the hypothalamus was reduced by starvation. Intracerebroventricular administration dose-dependently inhibited food intake for 6 h in male Wistar and leptin resistant, Zucker fatty rats. There may be a crosstalk between nesfatin-1 pathway and melanocortin pathway in the brain. Nesfatin-1 neurons co-express with oxytocin, vasopressin and melanin concentrating hormone in the hypothalamus. Intraperitoneal administration of nesfatin-1 and its mid-segment dose-dependently inhibited food intake for 3 h. Mid-segment of nesfatin-1 decreased food intake under leptin-resistant animal models of obesity. Intraperitoneal administration of the mid-segment of nesfatin-1 increased proopiomelanocortin and cocain- and amphetamine-related peptide mRNA expression in the nucleus of the solitary tract, but not in arcuate nucleus of the hypothalamus. In this review, we summarized recent progress in the research about the possible mechanism of nesfatin-1-induced anorexia.

Nesfatin-1: an overview and future clinical application

Nesfatin/nucleobindin 2 (NUCB2) is expressed in the appetite-control hypothalamic nuclei and brainstem nuclei. Nesfatin/NUCB2 expression in the paraventricular nucleus of the hypothalamus was modulated by starvation and refeeding. Intracerebroventricular administration of nesfatin-1 dose-dependently inhibited food intake for 6 hours in male Wistar and leptin resistant, Zucker fatty rats. Intraperitoneal administration of nesfatin-1 and its mid-segment (M30) dosedependentlyinhibited food intake for 3 hours in male ICR mice. Intraperitoneal administration of M30 also decreased foodintake in leptin-resistant, genetically obese (ob/ob), diabetic (db/db) mice and mice fed a 45% high fat diet for 28 days. Intraperitoneal administration of M30 increased proopiomelanocortin and cocaine- and amphetamine- related peptide mRNA expression in the nucleus of the solitary tract of mice. In addition, intranasal administration of nesfatin-1 significantly inhibited food intake for 6 hours in male Wistar rats. We summarize recent observations about nesfatin-1, and attempt to present future direction of nesfatin-1 research for developing a new anti-obesity treatment.