Ghrelin secretion is inhibited by either somatostatin or cortistatin in humans

The acromegaly lipodystrophy

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are essential to normal growth, metabolism, and body composition, but in acromegaly, excesses of these hormones strikingly alter them. In recent years, the use of modern methodologies to assess body composition in patients with acromegaly has revealed novel aspects of the acromegaly phenotype. In particular, acromegaly presents a unique pattern of body composition changes in the setting of insulin resistance that we propose herein to be considered an acromegaly-specific lipodystrophy. The lipodystrophy, initiated by a distinctive GH-driven adipose tissue dysregulation, features insulin resistance in the setting of reduced visceral adipose tissue (VAT) mass and intra-hepatic lipid (IHL) but with lipid redistribution, resulting in ectopic lipid deposition in muscle. With recovery of the lipodystrophy, adipose tissue mass, especially that of VAT and IHL, rises, but insulin resistance is lessened. Abnormalities of adipose tissue adipokines may play a role in the disordered adipose tissue metabolism and insulin resistance of the lipodystrophy. The orexigenic hormone ghrelin and peptide Agouti-related peptide may also be affected by active acromegaly as well as variably by acromegaly therapies, which may contribute to the lipodystrophy. Understanding the pathophysiology of the lipodystrophy and how acromegaly therapies differentially reverse its features may be important to optimizing the long-term outcome for patients with this disease. This perspective describes evidence in support of this acromegaly lipodystrophy model and its relevance to acromegaly pathophysiology and the treatment of patients with acromegaly.

Dynamic Tests in Pituitary Endocrinology: Pitfalls in Interpretation during Aging

Aging and age-related diseases represent hot topics of current research. Progressive damage in morphology and function of cells and tissue characterizes the normal process of aging that is influenced by both genetic and environmental factors. The ability of each individual to adapt to these stressors defines the type of aging and the onset of age-related diseases (i.e., metabolic syndrome, inflammatory disorders, cancer, and neurodegenerative diseases). The endocrine system plays a critical role in this process because of its complex relationships with brain, immune system, and skeletal muscle; thus, alterations in hormonal networks occur during aging to maintain homeostasis, with consequent under- or overactivity of specific hypothalamic-pituitary-peripheral hormone axes. On the other hand, the increase in life expectancy has led to increasing incidence of age-related diseases, including endocrine disorders, which may prompt assessment of endocrine function in aging individuals. In this context, there is growing awareness that natural changes of endocrine physiology and physiopathology occurring with increasing age may necessitate age-driven diagnostic cutoffs requiring validation in the elderly. This review aims to analyze the available literature on the hormone response to the most important dynamic tests currently used in the clinical practice for the screening of anterior pituitary-related diseases to underline pitfalls in interpretation during aging.

The inhibitory effect of somatostatin on gastric motility in Suncus murinus

Gastric contractions show two specific patterns in many species, migrating motor contractions (MMC) and postprandial contractions (PPCs), that occur in the fasted and fed states, respectively. In this study, we examined the role of somatostatin (SST) in gastric motility both in vivo and in vitro using the Asian house shrew (Suncus murinus). We performed in vivo recordings of gastric motility and in vitro organ bath experiments using S. murinus, which was recently established as a small laboratory animal for use in tests of gastrointestinal motility. SST (1.65 µg kg⁻¹ min⁻¹) was intravenously administered during phase II of MMC and PPCs. Next, the effect of SST on motilin-induced gastric contractions at phase I of MMC was measured. Cyclosomatostatin (CSST), an SST receptor antagonist, was administered at the peak of phase III of MMC. In addition, the effect of SST (10⁻¹¹–10⁻⁹ M) on motilin-induced gastric contractions was evaluated using an organ bath experiment in vitro. In conscious, free-moving S. murinus, the administration of SST decreased the occurrence of the spontaneous phase II of MMC and PPCs. Pretreatment with SST and octreotide suppressed the induction of motilin-induced gastric contractions both in vivo and in vitro. Administration of CSST before the peak of spontaneous phase III contractions had no effect on gastric contractions. Endogenous SST is not involved in the regulation of gastric MMC and PPCs, but exogenous SST suppresses spontaneous gastric contractions. Thus, SST would be good for treating abnormal gastrointestinal motility disorders.

Fructose-induced metabolic disturbances in rats and its impact on stomach endocrine cell number and smooth muscle contractility

Context: Gastric ghrelin-positive endocrine cells (GHR + EC) were most dense in the oxyntic mucosa.Objective: We evaluated ECs and contractile activity in rat stomach with metabolic disorders.Materials and methods: Male Wistar rats were divided into two groups: Control (n = 9) received tap water and Fructose (n = 9) drank 15% fructose solution for 12 weeks. Streptozotocin was applied in a dose of 20 mg/kg b.w. two weeks after the beginning of the experiment on Fructose group. Smooth-muscle strips from the stomach were influenced by Angiotensin II for analysis of parameters of contractions. Stomach samples were elaborated with immunohistochemistry for ghrelin, somatostatin, gastrin antibodies and with double immunofluorescence.Results: In treated animals, GHR + EC were significantly increased in the corpus where somatostatin-positive cells were decreased. Contractile activity was decreased.Conclusions: The increase number of GHR + EC was discussed in the context of Somatostatin and Gastrin-positive ECs variations and correlated with the decrease of smooth muscle contraction.

Cortistatin regulates glucose-induced electrical activity and insulin secretion in mouse pancreatic beta-cells

Although there is growing evidence that cortistatin regulates several functions in different tissues, its role in the endocrine pancreas is not totally known. Here, we aim to study the effect of cortistatin on pancreatic beta-cells and glucose-stimulated insulin secretion (GSIS). Exposure of isolated mouse islets to cortistatin inhibited GSIS. This effect was prevented using a somatostatin receptor antagonist. Additionally, cortistatin hyperpolarized the membrane potential and reduced glucose-induced action potentials in isolated pancreatic beta-cells. Cortistatin did not modify ATP-dependent K⁺ (K_ATP) channel activity. In contrast, cortistatin increased the activity of a small conductance channel with characteristics of G protein-coupled inwardly rectifying K⁺ (GIRK) channels. The cortistatin effects on membrane potential and GSIS were largely reduced in the presence of a GIRK channel antagonist and by down-regulation of GIRK2 with small interfering RNA. Thus, cortistatin acts as an inhibitory signal for glucose-induced electrical activity and insulin secretion in the mouse pancreatic beta-cell.

Multiple signaling pathways convey central and peripheral signals to regulate pituitary function: Lessons from human and non-human primate models

The anterior pituitary gland is a key organ involved in the control of multiple physiological functions including growth, reproduction, metabolism and stress. These functions are controlled by five distinct hormone-producing pituitary cell types that produce growth hormone (somatotropes), prolactin (lactotropes), adrenocorticotropin (corticotropes), thyrotropin (thyrotropes) and follicle stimulating hormone/luteinizing hormone (gonadotropes). Classically, the synthesis and release of pituitary hormones was thought to be primarily regulated by central (neuroendocrine) signals. However, it is now becoming apparent that factors produced by pituitary hormone targets (endocrine and non-endocrine organs) can feedback directly to the pituitary to adjust pituitary hormone synthesis and release. Therefore, pituitary cells serve as sensors to integrate central and peripheral signals in order to fine-tune whole-body homeostasis, although it is clear that pituitary cell regulation is species-, age- and sex-dependent. The purpose of this review is to provide a comprehensive, general overview of our current knowledge of both central and peripheral regulators of pituitary cell function and associated intracellular mechanisms, focusing on human and non-human primates.

Circulating levels of cortistatin are correlated with metabolic parameters in patients with newly diagnosed type 2 diabetes mellitus

Cortistatin (CST) is a recently discovered cyclic neuropeptide with multiple bioactive effects. The aim of this study was to investigate the relationship between plasma CST and various metabolic markers in patients with newly diagnosed type 2 diabetes mellitus (T2DM). For this study, 60 patients with newly diagnosed T2DM and 38 age- and gender-matched healthy controls were recruited. Fasting plasma glucose (FPG), serum insulin and hemoglobin A_1c (HbA_1c) levels and a blood lipid profile were obtained with commercially available diagnostic reagents. CST plasma levels were determined using an enzyme immunoassay kit. The results showed that the plasma levels of CST were substantially lower in patients with newly diagnosed T2DM compared with the healthy controls. Plasma CST levels were positively correlated with high-density lipoprotein and negatively related to FPG, serum insulin, the homeostasis model assessment of insulin resistance (HOMA-IR) and HbA_1c in all subjects. Further analysis showed that CST levels were positively correlated with systolic blood pressure and negatively correlated with FPG, serum insulin, HOMA-IR and HbA_1c in patients with newly diagnosed T2DM. Moreover, logistic regression analyses indicated that plasma CST was correlated with newly diagnosed T2DM. In conclusion, patients with newly diagnosed T2DM had significantly lower plasma levels of CST than healthy controls, and plasma CST was associated with glucose metabolism and insulin resistance, indicating a potential role of CST in the development of T2DM.

The Acylated/Unacylated Ghrelin Ratio Is Similar in Patients With Acromegaly During Different Treatment Regimens

BACKGROUND

Data on plasma acylated ghrelin (AG) and unacylated ghrelin (UAG) levels in acromegaly are limited. High AG/UAG ratios are linked with type 2 diabetes, obesity, and hyperphagia (e.g., in Prader-Willi syndrome).

OBJECTIVE

To assess fasting plasma AG and UAG levels, and the AG/UAG ratio in acromegaly patients receiving combination treatment of long-acting somatostatin analogs (LA-SSAs) and pegvisomant (PEGV; n = 60). We used as controls acromegaly patients whose disease was controlled with PEGV monotherapy and medically naïve patients with active acromegaly.

METHODS

Fasting venous blood samples were collected and directly stabilized to inhibit deacylation of AG. Plasma AG and UAG levels were determined by double-antibody sandwich enzyme immunoassay, and the AG/UAG ratio was calculated.

RESULTS

Plasma AG and UAG levels were significantly lower in patients with acromegaly receiving combination treatment [median, interquartile range (IQR): AG: 8.5 pg/mL, 2.9 to 21.1 pg/mL; UAG: 26.9 pg/mL, 11.2 to 42.1 pg/mL] compared with patients using PEGV alone [AG: 60.5 pg/mL (IQR, 58.8 to 77.4 pg/mL); UAG: 153.7 pg/mL (IQR, 127.3 to 196.0 pg/mL)] and medically naïve patients with acromegaly [AG: 24.0 pg/mL (IQR, 12.6 to 49.7 pg/mL); UAG: 56.3 pg/mL (IQR, 43.4 to 61.5 pg/mL)]. However, AG/UAG ratios were similar in all groups.

CONCLUSIONS

Although plasma AG and UAG are suppressed during combination treatment with LA-SSAs and PEGV, the AG/UAG ratio remained similar. This shows that SSAs decrease both AG and UAG levels, which suggests that they do not alter metabolism significantly in acromegaly patients.

Cortistatin: A new link between the growth hormone/prolactin axis, stress, and metabolism

Cortistatin is a neuropeptide originally identified in cortical brain regions, which displays a high structural and functional homology with somatostatin. However, cortistatin possesses distinct, unique functions, in the immune and central nervous systems, and it also shows specific endocrine effects, particularly on pituitary growth hormone, prolactin and adrenocorticotropin axes. Somatostatin and cortistatin bind similarly to the five native somatostatin receptors, sst1-sst5, whereas both compounds bind differentially to the recently discovered truncated variants of the sst subtype 5 (sst5TMD4, sst5TMD5); moreover, only cortistatin is able to bind other non-sst receptors (GHS-R and MrgX2). The non-overlapping tissue-specific distribution of each neuropeptide, together with the differential receptor binding profile, may be the cause of the singular effects of cortistatin. In this review we have provided and overview of the role of cortistatin on pituitary function by summarizing: 1) Its direct effect on pituitary cells using in vitro primary cultures derived from different species (from chicken to human); 2) Its putative physiological role revealed by in vivo assays, enabling to explore cortistatin effects on growth hormone, prolactin and adrenocorticotropin axes; and 3) The information provided by studying cortistatin knock-out mice. Altogether, these studies provide compelling evidence that cortistatin is a singular regulator of endocrine function, distinct from somatostatin.

Obesity- and gender-dependent role of endogenous somatostatin and cortistatin in the regulation of endocrine and metabolic homeostasis in mice

Somatostatin (SST) and cortistatin (CORT) regulate numerous endocrine secretions and their absence [knockout (KO)-models] causes important endocrine-metabolic alterations, including pituitary dysregulations. We have demonstrated that the metabolic phenotype of single or combined SST/CORT KO-models is not drastically altered under normal conditions. However, the biological actions of SST/CORT are conditioned by the metabolic-status (e.g. obesity). Therefore, we used male/female SST- and CORT-KO mice fed low-fat (LF) or high-fat (HF) diet to explore the interplay between SST/CORT and obesity in the control of relevant pituitary-axes and whole-body metabolism. Our results showed that the SST/CORT role in the control of GH/prolactin secretions is maintained under LF- and HF-diet conditions as SST-KOs presented higher GH/prolactin-levels, while CORT-KOs displayed higher GH- and lower prolactin-levels than controls under both diets. Moreover, the impact of lack of SST/CORT on the metabolic-function was gender- and diet-dependent. Particularly, SST-KOs were more sensitive to HF-diet, exhibiting altered growth and body-composition (fat/lean percentage) and impaired glucose/insulin-metabolism, especially in males. Conversely, only males CORT-KO under LF-diet conditions exhibited significant alterations, displaying higher glucose-levels and insulin-resistance. Altogether, these data demonstrate a tight interplay between SST/CORT-axis and the metabolic status in the control of endocrine/metabolic functions and unveil a clear dissociation of SST/CORT roles.

Ghrelin Expression and Actions: A Novel Peptide for an Old Cell Type of the Diffuse Endocrine System

Ghrelin is a gastric peptide involved in food intake control and growth hormone release. Its cell localization has been defined in distinct ghrelin cells of the gastric mucosa in humans and other mammals. Ghrelin production was also described in a number of other sites of the diffuse endocrine system, including the pituitary, thyroid, lung, pancreas, adrenal gland, and intestine. In addition, ghrelin cells were identified early during fetal life and in the placenta and gonads. Finally, endocrine growths and tumors of the diffuse endocrine system may present ghrelin-producing cells, and in a few cases high levels of circulating ghrelin were reported. Besides its well-defined orexigenic role, ghrelin is likely to exert a local paracrine role similar to other brain-gut axis hormones. This review aims to summarize recent data on ghrelin cell distribution in the diffuse endocrine system and discuss local and general ghrelin function during development, adulthood, and endocrine tumor development.

Cortistatin Is a Key Factor Regulating the Sex-Dependent Response of the GH and Stress Axes to Fasting in Mice

Cortistatin (CORT) shares high structural and functional similarities with somatostatin (SST) but displays unique sex-dependent pituitary actions. Indeed, although female CORT-knockout (CORT-KO) mice exhibit enhanced GH expression/secretion, Proopiomelanocortin expression, and circulating ACTH/corticosterone/ghrelin levels, male CORT-KO mice only display increased plasma GH/corticosterone levels. Changes in peripheral ghrelin and SST (rather than hypothalamic levels) seem to regulate GH/ACTH axes in CORT-KOs under fed conditions. Because changes in GH/ACTH axes during fasting provide important adaptive mechanisms, we sought to determine whether CORT absence influences GH/ACTH axes during fasting. Accordingly, fed and fasted male/female CORT-KO were compared with littermate controls. Fasting increased circulating GH levels in male/female controls but not in CORT-KO, suggesting that CORT can be a relevant regulator of GH secretion during fasting. However, GH levels were already higher in CORT-KO than in controls in fed state, which might preclude a further elevation in GH levels. Interestingly, although fasting-induced pituitary GH expression was elevated in both male/female controls, GH expression only increased in fasted female CORT-KOs, likely owing to specific changes observed in key factors controlling somatotrope responsiveness (ie, circulating ghrelin and IGF-1, and pituitary GHRH and ghrelin receptor expression). Fasting increased corticosterone levels in control and, most prominently, in CORT-KO mice, which might be associated with a desensitization to SST signaling and to an augmentation in CRH and ghrelin-signaling regulating corticotrope function. Altogether, these results provide compelling evidence that CORT plays a key, sex-dependent role in the regulation of the GH/ACTH axes in response to fasting.

Comprehensive Profiling of GPCR Expression in Ghrelin-Producing Cells

To determine the comprehensive G protein-coupled receptor (GPCR) expression profile in ghrelin-producing cells and to elucidate the role of GPCR-mediated signaling in the regulation of ghrelin secretion, we determined GPCR expression profiles by RNA sequencing in the ghrelin-producing cell line MGN3-1 and analyzed the effects of ligands for highly expressed receptors on intracellular signaling and ghrelin secretion. Expression of selected GPCRs was confirmed in fluorescence-activated cell-sorted fluorescently tagged ghrelin-producing cells from ghrelin-promoter CreERT2/Rosa-CAG-LSL-ZsGreen1 mice. Expression levels of GPCRs previously suggested to regulate ghrelin secretion including adrenergic-β1 receptor, GPR81, oxytocin receptor, GPR120, and somatostatin receptor 2 were high in MGN3-1 cells. Consistent with previous reports, isoproterenol and oxytocin stimulated the Gs and Gq pathways, respectively, whereas lactate, palmitate, and somatostatin stimulated the Gi pathway, confirming the reliability of current assays. Among other highly expressed GPCRs, prostaglandin E receptor 4 agonist prostaglandin E2 significantly stimulated the Gs pathway and ghrelin secretion. Muscarine, the canonical agonist of cholinergic receptor muscarinic 4, stimulated both the Gq and Gi pathways. Although muscarine treatment alone did not affect ghrelin secretion, it did suppress forskolin-induced ghrelin secretion, suggesting that the cholinergic pathway may play a role in counterbalancing the stimulation of ghrelin by Gs (eg, by adrenaline). In addition, GPR142 ligand tryptophan stimulated ghrelin secretion. In conclusion, we determined the comprehensive expression profile of GPCRs in ghrelin-producing cells and identified two novel ghrelin regulators, prostaglandin E2 and tryptophan. These results will lead to a greater understanding of the physiology of ghrelin and facilitate the development of ghrelin-modulating drugs.

A hypothesis for a possible synergy between ghrelin and exercise in patients with cachexia: Biochemical and physiological bases

This article reviews the biochemical and physiological observations underpinning the synergism between ghrelin and ghrelin agonists with exercise, especially progressive resistance training that has been shown to increase muscle mass. The synergy of ghrelin agonists and physical exercise could be beneficial in conditions where muscle wasting is present, such as that found in patients with advanced cancer. The principal mechanism that controls muscle anabolism following the activation of the ghrelin receptor in the central nervous system involves the release of growth hormone/insulin-like growth factor-1 (GH/IGF-1). GH/IGF-1 axis has a dual pathway of action on muscle growth: (a) a direct action on muscle, bone and fat tissue and (b) an indirect action via the production of both muscle-restricted mIGF-1 and anti-cachectic cytokines. Progressive resistance training is a potent inducer of the secretion the muscle-restricted IGF-1 (mIGF-1) that enhances protein synthesis, increases lean body mass and eventually leads to the improvement of muscle strength. Thus, the combination of ghrelin administration with progressive resistance training may serve to circumvent ghrelin resistance and further reduce muscle wasting, which are commonly associated with cachexia.

The regulation of circulating ghrelin - with recent updates from cell-based assays

Ghrelin is a stomach-derived orexigenic hormone with a wide range of physiological functions. Elucidation of the regulation of the circulating ghrelin level would lead to a better understanding of appetite control in body energy homeostasis. Earlier studies revealed that circulating ghrelin levels are under the control of both acute and chronic energy status: at the acute scale, ghrelin levels are increased by fasting and decreased by feeding, whereas at the chronic scale, they are high in obese subjects and low in lean subjects. Subsequent studies revealed that nutrients, hormones, or neural activities can influence circulating ghrelin levels in vivo. Recently developed in vitro assay systems for ghrelin secretion can assess whether and how individual factors affect ghrelin secretion from cells. In this review, on the basis of numerous human, animal, and cell-based studies, we summarize current knowledge on the regulation of circulating ghrelin levels and enumerate the factors that influence ghrelin levels.

Regulation of the Human Ghrelin Promoter Activity by Transcription Factors, NF-κB and Nkx2.2

To examine the gene expression of ghrelin, a growth hormone releasing and appetite stimulating hormone from stomach, we constructed human ghrelin promoter-reporter vectors and analyzed the promoter activity. The ghrelin promoter activity was high when cultured cells that express ghrelin mRNA endogenously like TT or ECC10 cells were used, indicating that these cells contain factors necessary for full expression of the human ghrelin gene. The human ghrelin promoter contains both positive and negative regulatory regions. A transient decrease of the promoter activity was found when the reporter vector with the -1600 fragment of the human ghrelin promoter was transfected into cultured cells. We then examined the effect of several transcription factors on the ghrelin promoter activity and found that NF-κB suppressed and that Nkx2.2, a homeodomain-containing transcription factor that is important for ghrelin cell development in pancreas, activates the promoter activity. These transcription factors may be possible targets for the control of ghrelin gene expression.

The effects of fever on hormone ghrelins, immunoglobulins, and heat shock protein 70 expression after swine flu vaccinations

For analyzing the changes in immunoglobulins, HSP70, ghrelin levels in blood samples were collected from volunteers vaccinated against swine flu before the vaccinations and on days 3, and 15, and 1 and 2 months after the vaccination in the presence or absence of fever associated with the it. The study included 11 subjects having developed a fever, and 13 subjects not having a fever, and 20 control subjects. Immunoglobulins were measured by nephelometry, and HSP70 and ghrelins by appropriate ELISA tests. The level of ghrelin was reduced, while the level of HSP70 was significantly increased in subjects who developed fevers. When temperatures were normalized, both levels were found similar to the control group. These results indicate that the increase in serum immunoglobulins levels associated with vaccinations, along with, elevations in HSP70 and reduced ghrelin levels associated with fever, may be the important parameters in the clinical evaluation and follow-up of treatments with vaccines.

Regulated endocrine-specific protein 18 (RESP18) is localized to and regulated in A-like cells and G-cells in rat stomach

The regulated endocrine-specific protein 18 (RESP18) has previously been localized to different endocrine cells and neurons, in particular the pituitary gland and hypothalamus. It is found in the lumen of the endoplasmic reticulum and is degraded at the post-ER pre-Golgi compartment, and a role in processing of secreted peptides has been hypothesized. The present study examines localization of RESP18 in the gastrointestinal mucosa of rats by immunohistochemistry, and expression and regulation in response to hypergastrinemia induced by acid inhibition (pantoprazole), gastrin antagonism (YF476), fasting-refeeding and octreotide by mRNA measurements. RESP18 was mainly found in the gastric mucosa, but could also be detected in a few, scattered cells in the lower small intestine and in colon. In the antral mucosa, all RESP18 immunoreactivity was localized to ghrelin-producing A-like cells and gastrin-producing G-cells. In the corpus mucosa, a significant fraction, but not all of the RESP18 immunoreactive cells, were A-like cells. In both antrum and corpus, Resp18 mRNA seemed to vary similarly with the activation of the A-like cells, and in the antrum also with stimulation of the G-cells. This study demonstrates, for the first time, the localization of RESP18 to specific neuroendocrine cells of the gastrointestinal mucosa and that it seems to be regulated synchronously with the peptides secreted from these cells. This suggests that Resp18 may indeed have a functional role in the synthesis or storage of these gastrointestinal peptides.

Cysteamine improves growth performance and gastric ghrelin expression in preweaning piglets

The aim of the present study was to investigate the effect of cysteamine on growth performance of preweaning piglets and gastric expression of ghrelin mRNA in vivo and in vitro. Twelve litters of newborn piglets were allocated randomly to control and treatment groups. From 15 d of age, piglets in the control group were fed basal creep diet, whereas the treatment group received basal diet supplemented with 120 mg cysteamine per kg of diet until weaning on 35 d of age. Body weight gain, creep feed consumption, and diarrhea rates were recorded, and gastric mucosal tissues were collected for quantifying mRNA expression. To evaluate the direct effect of cysteamine on gastric ghrelin expression, primary cultures of gastric mucosal cells isolated from 35-d-old piglets were exposed to cysteamine for 20 h at 0, 1, 10, and 100 μg/mL, respectively. Dietary cysteamine increased (P < 0.05) average daily creep feed consumption and BW gain in preweaning pigs, which was accompanied by reduction in diarrhea rates. At 35 d of age, piglets treated with cysteamine showed increased (P < 0.05) ghrelin and gastrin and decreased (P < 0.05) somatostatin mRNA expression in gastric mucosa. Moreover, dietary cysteamine treatment increased serum concentration of gastrin (P < 0.05). In vitro, cysteamine significantly increased ghrelin mRNA expression in gastric mucosal cells at the concentration of 10 μg/mL. In conclusion, dietary cysteamine is effective in improving the growth performance and health condition of preweaning piglets, which is associated with its stimulatory effects on gastric ghrelin mRNA expression both in vivo and in vitro.

The migrating motor complex: control mechanisms and its role in health and disease

The migrating motor complex (MMC) is a cyclic, recurring motility pattern that occurs in the stomach and small bowel during fasting; it is interrupted by feeding. The MMC is present in the gastrointestinal tract of many species, including humans. The complex can be subdivided into four phases, of which phase III is the most active, with a burst of contractions originating from the antrum or duodenum and migrating distally. Control of the MMC is complex. Phase III of the MMC with an antral origin can be induced in humans through intravenous administration of motilin, erythromycin or ghrelin, whereas administration of serotonin or somatostatin induces phase III activity with duodenal origin. The role of the vagus nerve in control of the MMC seems to be restricted to the stomach, as vagotomy abolishes the motor activity in the stomach, but leaves the periodic activity in the small bowel intact. The physiological role of the MMC is incompletely understood, but its absence has been associated with gastroparesis, intestinal pseudo-obstruction and small intestinal bacterial overgrowth. Measuring the motility of the gastrointestinal tract can be important for the diagnosis of gastrointestinal disorders. In this Review we summarize current knowledge of the MMC, especially its role in health and disease.

Expression profiling identifies novel gene targets and functions for Pdx1 in the duodenum of mature mice

Transcription factor pancreatic and duodenal homeobox 1 (Pdx1) plays an essential role in the pancreas to regulate its development and maintain proper islet function. However, the functions of Pdx1 in mature small intestine are less known. We aimed to investigate the intestinal role of Pdx1 by profiling the expression of genes differentially regulated in response to inactivation of Pdx1 specifically in the intestinal epithelium. Pdx1 was conditionally inactivated in the intestinal epithelium of Pdx1(flox/flox);VilCre mice. Total RNA was isolated from the first 5 cm of the small intestine from mature Pdx1(flox/flox);VilCre and littermate control mice. Microarray analysis identified 86 probe sets representing 68 genes significantly upregulated or downregulated 1.5-fold or greater in Pdx(flox/flox);VilCre mice maintained under standard conditions. Ingenuity Pathway Analysis revealed that functions of the differentially expressed genes are significantly associated with metabolism of nutrients including lipids and iron. Network analysis examining the interactions among the differentially expressed genes further supports the notion that Pdx1 may modulate metabolism of lipids and iron from mature intestinal epithelium. Following forced oil feeding, Pdx1(flox/flox);VilCre mice showed diminished lipid staining in the duodenal epithelium and decreased serum triglyceride levels, indicating reduced lipid absorption compared with control duodenal epithelium. Blood samples from Pdx1(flox/flox);VilCre mice have significantly lower mean values for mean corpuscular volume and mean corpuscular hemoglobin, consistent with iron deficiency. The absence of nonheme iron in the villous epithelium and lamina propria of Pdx1(flox/flox);VilCre duodenum indicates that the duodenal epithelium lacking Pdx1 may have defects in importing iron through enterocytes, resulting in iron deficiency in Pdx1(flox/flox);VilCre mice.

Pepsinogen I/II ratio is related to glucose, triacylglycerol, and uric acid levels

OBJECTIVE

Under- and overnutrition are associated with a worse prognosis and constitute independent risk factors for morbidity and mortality. It is increasingly important to understand the factors that affect nutritional and metabolic statuses. The purpose of this study was to assess the relation between the pepsinogen I/II ratio and several biochemical markers.

METHODS

A cross-sectional study was performed in 1985 subjects who underwent a health screening test. Subjects had no medications for hyperuricemia, dyslipidemia, diabetes mellitus, or hypertension. All subjects were classified into two groups. Subjects with a pepsinogen I/II ratio below 3 were defined as having atrophic gastritis. The relations between the pepsinogen I/II ratio and several biochemical markers, including total cholesterol, triacylglycerol, uric acid, cholinesterase, and glucose levels, were evaluated.

RESULTS

The presence of atrophic gastritis was significantly associated with age, smoking status, alcohol consumption, body mass index, and triacylglycerol, uric acid, cholinesterase, and hemoglobin levels. Multiple linear regression analysis demonstrated that the pepsinogen I/II ratio was an independent determinant of glucose level (β = 0.104, P < 0.0001), triacylglycerol level (β = 0.072, P = 0.0014), uric acid level (β = 0.048, P = 0.0138), and hemoglobin (β = 0.037, P = 0.0429) after adjustments for age, sex, smoking status, alcohol consumption, and body mass index.

CONCLUSION

The pepsinogen I/II ratio was related to glucose, triacylglycerol, and uric acid levels. Such an association fosters the idea that a decreased pepsinogen I/II ratio seems favorable for the prevention of overnutrition.

Activation of somatostatin 2 receptors in the brain and the periphery induces opposite changes in circulating ghrelin levels: functional implications

Somatostatin is an important modulator of neurotransmission in the central nervous system and acts as a potent inhibitor of hormone and exocrine secretion and regulator of cell proliferation in the periphery. These pleiotropic actions occur through interaction with five G protein-coupled somatostatin receptor subtypes (sst(1) (-) (5)) that are widely expressed in the brain and peripheral organs. The characterization of somatostatin's effects can be investigated by pharmacological or genetic approaches using newly developed selective sst agonists and antagonists and mice lacking specific sst subtypes. Recent evidence points toward a divergent action of somatostatin in the brain and in the periphery to regulate circulating levels of ghrelin, an orexigenic hormone produced by the endocrine X/A-like cells in the rat gastric mucosa. Somatostatin interacts with the sst(2) in the brain to induce an increase in basal ghrelin plasma levels and counteracts the visceral stress-related decrease in circulating ghrelin. By contrast, stimulation of peripheral somatostatin-sst(2) signaling results in the inhibition of basal ghrelin release and mediates the postoperative decrease in circulating ghrelin. The peripheral sst(2)-mediated reduction of plasma ghrelin is likely to involve a paracrine action of D cell-derived somatostatin acting on sst(2) bearing X/A-like ghrelin cells in the gastric mucosa. The other member of the somatostatin family, named cortistatin, in addition to binding to sst(1) (-) (5) also directly interacts with the ghrelin receptor and therefore may simultaneously modulate ghrelin release and actions at target sites bearing ghrelin receptors representing a link between the ghrelin and somatostatin systems.

Hormonal appetite control is altered by shift work: a preliminary study

Shift work has been associated with a higher propensity for developing nutritional problems and obesity. However, the possible changes in leptin and ghrelin (2 hormones that contribute importantly to the central regulation of food intake) concentrations in this population are poorly described. The objective of the study was to evaluate the daily concentrations of leptin, nonacylated ghrelin, and acylated ghrelin and the appetite ratings in men working different shift schedules. Daily concentrations of nonacylated ghrelin, acylated ghrelin, and leptin and appetite were measured in 3 groups of subjects: workers on fixed night shifts (n = 9), fixed early morning shifts (n = 6), and fixed day shifts (n = 7). Appetite was evaluated by a validated questionnaire. Blood samples were collected every 4 hours over the course of 24 hours for a total of 6 samples. When comparing the 3 groups, leptin concentrations at 8:00 am and 4:00 pm for those workers on the day shift were significantly lower than for those on the early morning shift; and concentrations at noon for those workers on the day shift were significantly lower than for those on the night shift. Nonacylated and acylated ghrelin concentrations were significantly lower for those workers on the early morning shift than for those on the day shift. In general, appetite was the lowest in those working the early morning shift. Shift workers on the early morning shift have lower appetites and concentrations of leptin and nonacylated and acylated ghrelin than the workers on other shifts. Further studies are required to better understand the detailed needs of these individuals.

Ghrelin in neuroendocrine tumors

Ghrelin is a 28 amino acid peptide, primarily produced by the oxyntic mucosa X/A like neuroendocrine cells in the stomach. It is also found in the small intestine, hypothalamus, pituitary gland, pancreas, heart, adipose tissue, and immune system. In gastrointestinal neuroendocrine tumors (NETs) ghrelin release has been well documented. Ghrelin is a brain-gut circuit peptide with an important role in the physiological regulation of appetite, response to hunger and starvation, metabolic and endocrine functions as energy expenditure, gastric motility and acid secretion, insulin secretion and glucose homeostasis, as well as in the potential connection to the central nervous system. Recently, there has been a significant interest in the biological effects of ghrelin in NETs. In this article, we present a comprehensive review of ghrelin's expression and a brief summary of ghrelin's physiological role in NETs patients with carcinoids, type A chronic atrophic gastritis (CAG), with or without MEN-1, and with and without liver metastases. We hope, with the research reviewed here, to offer compelling evidence of the potential significance of ghrelin in NETs, as well as to provide a useful guide to the future work in this area.

Cortistatin is induced in brain tissue and exerts neuroprotection in a rat model of bacterial meningoencephalitis

There are fewer reports of brain infection by Klebsiella pneumoniae than there are in other organs, but an increase incidence and morbidity has been noted. We have previously developed a rat model of K. pneumoniae meningoencephalitis. Cortistatin (CST) is a recently discovered neuropeptide with endocrine activities in humans. In this study, we found that brain infection by K. pneumoniae increased endogenous prepro-CST messenger RNA expression, which occurred earlier than did leukocyte infiltration in vivo and also occurred in cultured neuron-glia. Postinfection treatment with CST (either intracerebroventricularly or intraperitoneally), but not somatostatin, reduced leukocyte recruitment and clinical illness as revealed by fever and clinical score in vivo. Postinfection increases of proinflammatory cytokine messenger RNA levels were attenuated by CST in neuron-glia cultures, further confirming a direct effect on neuroinflammation. Administration of CST resulted in less postinfection neuronal loss in vitro, suggesting a direct neuroprotective effect and potential as an adjuvant for treating bacterial meningoencephalitis.

Comparison of the anti-inflammatory and anti-nociceptive effects of cortistatin-14 and somatostatin-14 in distinct in vitro and in vivo model systems

We showed that somatostatin (SST) exerts anti-inflammatory and anti-nociceptive effects through somatostatin receptor subtypes 4 and 1 (sst(4)/sst(1)). Since cortistatin (CST) is a structurally similar peptide, we aimed at comparing the sst(1)- and sst(4)-binding and activating abilities, as well as the effects of SST-14 and CST-14 on inflammatory and nociceptive processes. CST-14 concentration-dependently displaced radiolabeled SST-14 binding, induced similar sst(1) and sst(4)-activation with a less potency, and exerted significantly greater inhibitory effect on endotoxin-stimulated interleukin (IL)-1β production of murine peritoneal macrophages. Capsaicin-induced calcitonin gene-related peptide release from peripheral sensory nerve terminals of isolated rat tracheae was significantly decreased by 2 μM CST and 100 nM SST, but concentration-response correlation was not found. Mustard oil-evoked acute neurogenic plasma protein extravasation in the rat hindpaw skin, carrageenan-induced mouse paw edema, mechanical hyperalgesia, and IL-1β, tumor necrosis factor-α production, as well as mild heat injury-evoked thermal hyperalgesia were similarly attenuated by both peptides. In the latter case, i.pl. and i.p. injections exerted equal inhibitory actions. CST-14 and SST-14 similarly diminish both acute neurogenic and cellular inflammatory processes, as well as mechanical and heat hyperalgesia, in which their inhibitory effect on sensory nerve endings is likely to be involved. However, CST-14 exerts remarkably greater inhibition on cytokine production.

Neural and hormonal control of food hoarding

Many animals hoard food, including humans, but despite its pervasiveness, little is known about the physiological mechanisms underlying this appetitive behavior. We summarize studies of food hoarding in humans and rodents with an emphasis on mechanistic laboratory studies of species where this behavior importantly impacts their energy balance (hamsters), but include laboratory rat studies although their wild counterparts do not hoard food. The photoperiod and cold can affect food hoarding, but food availability is the most significant environmental factor affecting food hoarding. Food-deprived/restricted hamsters and humans exhibit large increases in food hoarding compared with their fed counterparts, both doing so without overeating. Some of the peripheral and central peptides involved in food intake also affect food hoarding, although many have not been tested. Ad libitum-fed hamsters given systemic injections of ghrelin, the peripheral orexigenic hormone that increases with fasting, mimics food deprivation-induced increases in food hoarding. Neuropeptide Y or agouti-related protein, brain peptides stimulated by ghrelin, given centrally to ad libitum-fed hamsters, duplicates the early and prolonged postfood deprivation increases in food hoarding, whereas central melanocortin receptor agonism tends to inhibit food deprivation and ghrelin stimulation of hoarding. Central or peripheral leptin injection or peripheral cholecystokinin-33, known satiety peptides, inhibit food hoarding. Food hoarding markedly increases with pregnancy and lactation. Because fasted and/or obese humans hoard more food in general, and more high-density/high-fat foods specifically, than nonfasted and/or nonobese humans, understanding the mechanisms underlying food hoarding could provide another target for behavioral/pharmacological approaches to curb obesity.

Somatostatin and its receptors contribute in a tissue-specific manner to the sex-dependent metabolic (fed/fasting) control of growth hormone axis in mice

Somatostatin (SST) inhibits growth hormone (GH) secretion and regulates multiple processes by signaling through its receptors sst1-5. Differential expression of SST/ssts may contribute to sex-specific GH pattern and fasting-induced GH rise. To further delineate the tissue-specific roles of SST and sst1-5 in these processes, their expression patterns were evaluated in hypothalamus, pituitary, and stomach of male and female mice under fed/fasted conditions in the presence (wild type) or absence (SST-knockout) of endogenous SST. Under fed conditions, hypothalamic/stomach SST/ssts expression did not differ between sexes, whereas male pituitary expressed more SST and sst2A/2B/3/5A/5TMD2/5TMD1 and less sst1, and male pituitary cell cultures were more responsive to SST inhibitory actions on GH release compared with females. This suggests that local pituitary SST/ssts can contribute to the sexually dimorphic pattern of GH release. Fasting (48 h) reduced stomach sst2A/B and hypothalamic SST/sst2A expression in both sexes, whereas it caused a generalized downregulation of pituitary sst subtypes in male and of sst2A only in females. Thus, fasting can reduce SST sensitivity across tissues and SST input to the pituitary, thereby jointly contributing to enhance GH release. In SST-knockout mice, lack of SST differentially altered sst subtype expression levels in both sexes, supporting an important role for SST in sex-dependent control of GH axis. Evaluation of SST, IGF-I, and glucocorticoid effects on hypothalamic and pituitary cell cultures revealed that these hormones could directly account for alterations in sst2/5 expression in the physiological states examined. Taken together, these results indicate that changes in SST output and sensitivity can contribute critically to precisely define, in a tissue-dependent manner, the sex-specific metabolic regulation of the GH axis.

Obesity treatment: novel peripheral targets

Our knowledge of the complex mechanisms underlying energy homeostasis has expanded enormously in recent years. Food intake and body weight are tightly regulated by the hypothalamus, brainstem and reward circuits, on the basis both of cognitive inputs and of diverse humoral and neuronal signals of nutritional status. Several gut hormones, including cholecystokinin, glucagon-like peptide-1, peptide YY, oxyntomodulin, amylin, pancreatic polypeptide and ghrelin, have been shown to play an important role in regulating short-term food intake. These hormones therefore represent potential targets in the development of novel anti-obesity drugs. This review focuses on the role of gut hormones in short- and long-term regulation of food intake, and on the current state of development of gut hormone-based obesity therapies.

Establishment of a novel ghrelin-producing cell line

To establish a tool to study ghrelin production and secretion in vitro, we developed a novel ghrelin-producing cell line, MGN3-1 (mouse ghrelinoma 3-1) cells from a gastric ghrelin-producing cell tumor derived from ghrelin-promoter Simian virus 40-T-antigen transgenic mice. MGN3-1 cells preserve three essential characteristics required for the in vitro tool for ghrelin research. First, MGN3-1 cells produce a substantial amount of ghrelin at levels approximately 5000 times higher than that observed in TT cells. Second, MGN3-1 cell expressed two key enzymes for acyl modification and maturation of ghrelin, namely ghrelin O-acyltransferase for acylation and prohormone convertase 1/3 for maturation and the physiological acyl modification and maturation of ghrelin were confirmed. Third, MGN3-1 cells retain physiological regulation of ghrelin secretion, at least in regard to the suppression by somatostatin and insulin, which is well established in in vivo studies. Thus, MGN3-1 cells are the first cell line derived from a gastric ghrelin-producing cell preserving secretion of substantial amounts of ghrelin under physiological regulation. This cell line will be a useful tool for both studying the production and secretion of ghrelin and screening of ghrelin-modulating drugs.

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 cells in the gastrointestinal tract

Ghrelin is 28-amino-acid peptide that was discovered from the rat and human stomach in 1999. Since the discovery of ghrelin, various functions of ghrelin, including growth hormone release, feeding behavior, glucose metabolism, memory, and also antidepressant effects, have been studied. It has also been reported that ghrelin in the gastrointestinal tract has an important physiological effect on gastric acid secretion and gastrointestinal motility. Ghrelin has a unique structure that is modified by O-acylation with n-octanoic acid at third serine residues, and this modification enzyme has recently been identified and named ghrelin O-acyl transferase (GOAT). Ghrelin is considered to be a gut-brain peptide and is abundantly produced from endocrine cells in the gastrointestinal mucosa. In the gastrointestinal tract, ghrelin cells are most abundant in the stomach and are localized in gastric mucosal layers. Ghrelin cells are also widely distributed throughout the gastrointestinal tract. In addition, abundance of ghrelin cells in the gastric mucosa is evolutionally conserved from mammals to lower vertebrates, indicating that gastric ghrelin plays important roles for fundamental physiological functions. Ghrelin cells in the gastrointestinal tract are a major source of circulating plasma ghrelin, and thus understanding the physiology of these cells would reveal the biological significance of ghrelin.

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.

Sleeve gastrectomy: a new surgical approach for morbid obesity

While obesity and morbid obesity have reached epidemic proportions worldwide, bariatric surgeons continue to develop safer and more efficacious procedures to battle this lethal disease. Sleeve gastrectomy, a relative new surgical approach, was initially conceived as a restrictive component of the biliopancreatic diversion and duodenal switch in the era of open bariatric surgery. With the advent of minimally invasive surgery in the late 1980s, laparoscopic sleeve gastrectomy (LSG) has been proposed as a step procedure in high-risk patients, followed by a second step Roux-en-Y gastric bypass or biliopancreatic diversion and duodenal switch and, recently, as a standalone bariatric approach. This article reviews the literature and reports the results achieved with LSG performed either as the initial operation for high-risk, high body mass index patients followed by a definitive weight loss operation, or used as a final viable alternative to other well-established bariatric procedures. An extensive literature review was conducted and the information currently available surrounding LSG, such as history, indications and contraindications, mechanism of weight loss, technique and outcomes and controversial issues are discussed. LSG is an accepted procedure for the surgical management of morbid obesity. It is gaining popularity as a primary, staged and revisional operation for its proven safety and simplicity, as well as short-term and mid-term efficacy. Excess weight loss and remission of comorbidities have been reported to take place in a frequency comparable with other well-established procedures. Despite all of the above-mentioned factors, long-term results and larger series are pending.

Ghrelin in the regulation of body weight and metabolism

Ghrelin, a peptide hormone predominantly produced by the stomach, was isolated as the endogenous ligand for the growth hormone secretagogue receptor. Ghrelin is a potent stimulator of growth hormone (GH) secretion and is the only circulatory hormone known to potently enhance feeding and weight gain and to regulate energy homeostasis following central and systemic administration. Therapeutic intervention with ghrelin in catabolic situations may induce a combination of enhanced food intake, increased gastric emptying and nutrient storage, coupled with an increase in GH thereby linking nutrient partitioning with growth and repair processes. These qualities have fostered the idea that ghrelin-based compounds may have therapeutic utility in treating malnutrition and wasting induced by various sub-acute and chronic disorders. Conversely, compounds that inhibit ghrelin action may be useful for the prevention or treatment of metabolic syndrome components such as obesity, impaired lipid metabolism or insulin resistance. In recent years, the effects of ghrelin on glucose homeostasis, memory function and gastrointestinal motility have attracted considerable amount of attention and revealed novel therapeutic targets in treating a wide range of pathologic conditions. Furthermore, discovery of ghrelin O-acyltransferase has also opened new research opportunities that could lead to major understanding of ghrelin physiology. This review summarizes the current knowledge on ghrelin synthesis, secretion, mechanism of action and biological functions with an additional focus on potential for ghrelin-based pharmacotherapies.

Estimation of gastric ghrelin-positive cells activity in hyperthyroid rats

Ghrelin is a peptide of 28 amino acids that transmits appetite related signals from peripheral organs to the brain. The main source of ghrelin is stomach. The regulation of ghrelin secretion is still unknown. The finding that fasting and food intake, respectively increase and decrease the secretion of ghrelin suggests that this hormone may be a bridge connecting somatic growth with energy metabolism and appears to play an important role in the alteration of energy homeostasis and body weight in pathophisiological conditions. The purpose of this study was the evaluation of gastric ghrelin immunoreactivity and ghrelin plasma concentration in male Wistar rats with hyperthyroidism. Experimental model of hyperthyroidism was induced by intraperitoneal injection of levothyroxine at the dose of 80 microg/kg daily over 21 days. At the end of experiment the animals were anaesthetized, blood was taken from abdominal aorta to determinate plasma ghrelin concentration by RIA and then the animals underwent resection of distal part of stomach. Immunohistochemical study were performed using monoclonal specific antybodies against ghrelin. Hyperthyroidism was a reason of increase of gastric mucosal ghrelin - immunoreactivity, accompanied by a significant decreased of ghrelin plasma concentration. Those observations may indicate, that chronic administration of L-thyroxine cause the change of ghrelin plasma concentration in rats, probably via direct influence on gastric X/A-like cells, but this effect is not responsible for hyperphagia associated with hyperthyroidism.

The influence of the eradication of Helicobacter pylori on gastric ghrelin, appetite, and body mass index in patients with peptic ulcer disease

BACKGROUND AND AIM

Helicobacter pylori (H. pylori) infection has been known to influence the gastric leptin and ghrelin secretion, for which the exact pathogenic role has not been documented yet. This study was designed to investigate the influence of H. pylori eradication on plasma or gastric levels of ghrelin, body mass index (BMI), and resultant levels of appetite in patients with peptic ulcer disease.

METHODS

Twenty-two patients with H. pylori-associated active duodenal or gastric ulcer were treated with 7 weeks of antisecretory medication followed with 7 days of eradication regimen. The plasma and tissue ghrelin levels, tumor necrosis factor-alpha (TNF-alpha) mRNA, BMI, and appetite scale were checked before and after treatment. An additional endoscopic examination was conducted in 10 patients taking both ulcer treatment and H. pylori eradication.

RESULTS

Gastric ghrelin mRNA expression was significantly increased after either ulcer healing or H. pylori eradication, whereas gastric TNF-alpha mRNA expression was decreased after ulcer treatment and H. pylori eradication. In parallel with these changes, the visual analog scales for hunger and prospective food consumption were significantly increased after ulcer healing and H. pylori eradication. An increase in BMI was not statistically related to ulcer healing and H. pylori eradication therapy. In the subgroup analysis of 10 patients performed with additional endoscopic examination, ulcer treatment was associated with increased plasma ghrelin level and tissue ghrelin expression irrelevant to H. pylori eradication.

CONCLUSION

Restored tissue levels of ghrelin and improved status of appetite was achieved with gastric ulcer healing and H. pylori eradication.

Endogenous anti-inflammatory neuropeptides and pro-resolving lipid mediators: a new therapeutic approach for immune disorders

Identification of the factors that regulate the immune tolerance and control the appearance of exacerbated inflammatory conditions is crucial for the development of new therapies of inflammatory and autoimmune diseases. Although much is known about the molecular basis of initiating signals and pro-inflammatory chemical mediators in inflammation, it has only recently become apparent that endogenous stop signals are critical at early checkpoints within the temporal events of inflammation. Some neuropeptides and lipid mediators that are produced during the ongoing inflammatory response have emerged as endogenous anti-inflammatory agents that participate in the regulation of the processes that ensure self-tolerance and/or inflammation resolution. Here we examine the latest research findings, which indicate that neuropeptides participate in maintaining immune tolerance in two distinct ways: by regulating the balance between pro-inflammatory and anti-inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T-cell effectors. On the other hand, we also focus on lipid mediators biosynthesized from omega-3 and omega-6 polyunsaturated fatty-acids in inflammatory exudates that promote the resolution phase of acute inflammation by regulating leucocyte influx to and efflux from local inflamed sites. Both anti-inflammatory neuropeptides and pro-resolving lipid mediators have shown therapeutic potential for a variety of inflammatory and autoimmune disorders and could be used as biotemplates for the development of novel pharmacologic agents.

Synergistic action of gastrin and ghrelin on gastric acid secretion in rats

Gastrin and ghrelin are secreted from G cells and X/A-like cells in the stomach, respectively, and respective hormones stimulate gastric acid secretion by acting through histamine and the vagus nerve. In this study, we examined the relationship between gastrin, ghrelin and gastric acid secretion in rats. Intravenous (iv) administration of 3 and 10 nmol of gastrin induced transient increases of ghrelin levels within 10 min in a dose-dependent manner. Double immunostaining for ghrelin and gastrin receptor revealed that a proportion of ghrelin cells possess gastrin receptors. Although (iv) administration of gastrin or ghrelin induced significant gastric acid secretion, simultaneous treatment with both hormones resulted in a synergistic, rather than additive, increase of gastric acid secretion. This synergistic increase was not observed in vagotomized rats. These results suggest that gastrin may directly stimulate ghrelin release from the stomach, and that both hormones may increase gastric acid secretion synergistically.

Ghrelin in pathological conditions

The recently identified gastric hormone ghrelin was initially described as a natural Growth Hormone Secretagogue Receptor ligand. Apart from ghrelin's first discovered action, which was the stimulation of Growth Hormone release, implications for many other functions have been reported. It seems that ghrelin exhibits an important role in conditions related to processes regulating nutrition, body composition and growth, as well as heart, liver, thyroid or kidney dysfunction. In this review, current available knowledge about ghrelin's role in various pathological conditions is presented.

Pharmacological profile of somatostatin and cortistatin receptors

Somatostatin (SRIF) and cortistatin (CST) are two endogenous peptides with high sequence similarities that act as hormones/neurotransmitters both in the CNS and the periphery; their genes although distinct result from gene duplication. Their receptors appear to be common, since the five known SRIF receptors (sst1-sst5) have similar subnanomolar affinity for SRIF and CST, whether the short (SRIF-14, CST-14, CST-17) or the long versions (SRIF-28, CST-29) of the peptides. Whether CST targets specific receptors not shared by SRIF, is still debated: MrgX2 has been described as a selective CST receptor, with submicromolar affinity for CST but devoid of affinity for SRIF; however the distribution of CST and MrgX2 is largely different, and there is no MrgX2 in rodents. A similar situation arises with the GHS receptor GHS-R1a, which displays some preferential affinity for CST over SRIF, but for which there is no evidence that it is activated by CST in vivo. In both cases, one may argue that submicromolar affinity is not the norm of a GPCR for its endogenous neuropeptide. On the other hand, all receptors known to bind SRIF have similar high affinity for CST and both peptides act as potent agonists at the sst1-sst5 receptors, whichever transduction pathway is considered. In addition, [(125)I][Tyr(10)]CST(14) labels sst1-sst5 receptors with subnanomolar affinity, and [(125)I][Tyr(10)]CST(14) binding in the brain is overlapping with that of [(125)I][Tyr(0)]SRIF(14). The functional differences reported that distinguish CST from SRIF, have not been explained convincingly and may relate to ligand-driven transductional selectivity, and other complicating factors such as receptor dimerisation, (homo or heterodimerisation), and/or the influence of accessory proteins (GIPs, RAMPS), which remain to be studied in more detail.

Endocrine actions of cortistatin: in vivo studies

Cortistatin (CST) shares high structural homology with somatostatin (SST) and binds all SST-receptors (SST-R) subtypes with similar affinity. However, CST actions, tissue expression patterns and regulation do not fully overlap with those of SST, and, moreover, CST, but not SST, also binds and activates proadrenomedullin N-terminal peptide receptor (MrgX2) and shows binding affinity to ghrelin receptor (GHS-R1a). Several studies performed to clarify the endocrine actions of CST, compared with SST, showed that, in humans, CST and SST share the same endocrine actions, i.e. inhibition of GH and insulin secretion in physiological conditions and in acromegaly. A similar inhibitory effect on PRL and ACTH secretion was shown in acromegaly, prolactinoma or in Cushing's disease. This identity of endocrine actions by CST and SST suggests that SST-R activation by CST overrides any other independent action of this peptide mediated by other receptors. Thus, in terms of endocrine actions, CST can well be considered a natural alternative to SST.

Cortistatin--functions in the central nervous system

Cortistatin (CST) is a neuropeptide from the somatostatin (SRIF)/urotensin (UII) family named after its predominantly cortical expression and ability to depress cortical activity, which was discovered a decade ago. In vitro assays show CST is able to bind all five cloned somatostatin receptors and shares many pharmacological and functional properties with SRIF. However, distinct from SRIF, CST has been shown to induce slow-wave sleep, reduce locomotor activity, and activate cation selective currents not responsive to somatostatin. Different lines of evidence also indicate that CST, like SRIF, is involved in learning and memory processes. CST-14 may also function as an endogenous anti-convulsant. In addition to its role in cortical synchronization, CST-14 has emerged as an important mediator of immunity and inflammation. This review will cover some of the basic properties of CST in the brain, and will discuss new data on the role of CST in cortical activity.

Cortistatin-8, a synthetic cortistatin-derived ghrelin receptor ligand, does not modify the endocrine responses to acylated ghrelin or hexarelin in humans

Cortistatin (CST), a neuropeptide with high structural homology with somatostatin (SST), binds all SST receptor (SST-R) subtypes but, unlike SST, also shows high binding affinity to ghrelin receptor (GHS-R1a). CST exerts the same endocrine activities of SST in humans, suggesting that the activation of the SST-R might mask the potential interaction with ghrelin system. CST-8, a synthetic CST-analogue devoid of any binding affinity to SST-R but capable to bind the GHS-R1a, has been reported able to exert antagonistic effects on ghrelin actions either in vitro or in vivo in animals. We studied the effects of CST-8 (2.0 microg/kg i.v. as a bolus or 2.0 microg/kg/h i.v. as infusion) on both spontaneous and ghrelin- or hexarelin- (1.0 microg/kg i.v. as bolus) stimulated GH, PRL, ACTH and cortisol secretion in 6 normal volunteers. During saline, no change occurred in GH and PRL levels while a spontaneous ACTH and cortisol decrease was observed. As expected, both ghrelin and hexarelin stimulated GH, PRL, ACTH and cortisol secretion (p<0.05). CST-8, administered either as bolus or as continuous infusion, did not modify both spontaneous and ghrelin- or hexarelin-stimulated GH, PRL, ACTH and cortisol secretion. In conclusion, CST-8 seems devoid of any modulatory action on either spontaneous or ghrelin-stimulated somatotroph, lactotroph and corticotroph secretion in humans in vivo. These negative results do not per se exclude that, even at these doses, CST-8 might have some neuroendocrine effects after prolonged treatment or that, at higher doses, may be able to effectively antagonize ghrelin action in humans. However, these data strongly suggest that CST-8 is not a promising candidate as GHS-R1a antagonist for human studies to explore the functional interaction between ghrelin and cortistatin systems.