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

Vascular Effects of Obestatin in Lean and Obese Subjects

Obese patients have impaired vasodilator reactivity and increased endothelin 1 (ET-1)-mediated vasoconstriction, two abnormalities contributing to vascular dysfunction. Obestatin, a product of the ghrelin gene, in addition to favorable effects on glucose and lipid metabolism, has shown nitric oxide (NO)-dependent vasodilator properties in experimental models. Given these premises, we compared the effects of exogenous obestatin on forearm flow in lean and obese subjects and assessed its influence on ET-1-dependent vasoconstrictor tone in obesity. In both lean and obese participants, infusion of escalating doses of obestatin resulted in a progressive increase in blood flow from baseline (both P < 0.001). This vasodilation was predominantly mediated by enhanced NO activity, because N^G-monomethyl-l-arginine markedly blunted the flow response to obestatin in both groups (both P < 0.05 vs. saline). In obese subjects, antagonism of ET_A receptors by BQ-123 increased forearm flow during saline (P < 0.001) but did not induce additional vasodilation (P > 0.05) during obestatin. Circulating obestatin levels were not different between lean and obese participants (P = 0.41). Our findings indicate that obestatin causes NO-dependent vasodilation in the human circulation. This effect is preserved in obesity, where it is accompanied by reduced ET-1-mediated vasoconstriction. These latter observations make obestatin a promising target for vascular prevention in obesity and diabetes.

Obestatin stimulates glucose-induced insulin secretion through ghrelin receptor GHS-R

Orexigenic hormone ghrelin and anorexic hormone obestatin are encoded by the same preproghrelin gene. While it is known that ghrelin inhibits glucose-stimulated insulin secretion (GSIS), the effect of obestatin on GSIS is unclear. Ghrelin’s effect is mediated by its receptor Growth Hormone Secretagogue Receptor (GHS-R), but the physiologically relevant receptor of obestatin remains debatable. Here we have investigated the effect of obestatin on GSIS in vitro, in vivo and ex vivo, and tested whether obestatin regulates insulin secretion through GHS-R. We found that under hyperglycemic condition, obestatin augments GSIS in rat insulinoma cells (INS-1) and in pancreatic islets from ghrelin^−/− mice. Surprisingly, obestatin-induced GSIS was absent in β-cells in which GHS-R was suppressed. Obestatin-induced insulin secretion was abolished in the circulation of Ghsr^−/− mice, and in pancreatic islets isolated from Ghsr^−/− mice. We also found that obestatin-induced GSIS was attenuated in islets isolated from β-cell-specific Ghsr knockout MIP-Cre/ERT;Ghsr^f/f mice. Our data collectively demonstrate that obestatin is a potent insulin secretagogue under hyperglycemic condition, and obestatin’s effect on insulin secretion is mediated by GHS-R in pancreatic β-cells. Our findings reveal an intriguing insight that obestatin and ghrelin have opposing effects on insulin secretion, and both are mediated through ghrelin receptor GHS-R.

Clarifying the Ghrelin System's Ability to Regulate Feeding Behaviours Despite Enigmatic Spatial Separation of the GHSR and Its Endogenous Ligand

Ghrelin is a hormone predominantly produced in and secreted from the stomach. Ghrelin is involved in many physiological processes including feeding, the stress response, and in modulating learning, memory and motivational processes. Ghrelin does this by binding to its receptor, the growth hormone secretagogue receptor (GHSR), a receptor found in relatively high concentrations in hypothalamic and mesolimbic brain regions. While the feeding and metabolic effects of ghrelin can be explained by the effects of this hormone on regions of the brain that have a more permeable blood brain barrier (BBB), ghrelin produced within the periphery demonstrates a limited ability to reach extrahypothalamic regions where GHSRs are expressed. Therefore, one of the most pressing unanswered questions plaguing ghrelin research is how GHSRs, distributed in brain regions protected by the BBB, are activated despite ghrelin’s predominant peripheral production and poor ability to transverse the BBB. This manuscript will describe how peripheral ghrelin activates central GHSRs to encourage feeding, and how central ghrelin synthesis and ghrelin independent activation of GHSRs may also contribute to the modulation of feeding behaviours.

Plasma ghrelin level and plasma ghrelin/obestatin ratio are related to intestinal metaplasia in elderly patients with functional dyspepsia

Background

Whether plasma ghrelin/obestatin levels are associated with Helicobacter pylori (H. pylori) infection, subtypes of functional dyspepsia (FD), and gastric mucosal histology has not yet been established in elderly patients.

Objective

The aim of this study was to determine whether plasma ghrelin and obestatin levels are related to gastric mucosal histology, H. pylori infection, and FD subtypes in elderly patients with FD.

Methods

Ninety-two patients diagnosed with FD and older than 60 years (median age 69.4; range 60–88) were included. Clinical symptoms investigated included postprandial fullness, epigastric pain, epigastric soreness, nausea, and vomiting. According to the Rome III criteria, patients diagnosed with FD were divided into two subtypes: epigastric pain syndrome (EPS) and postprandial distress syndrome (PDS). Plasma ghrelin and obestatin levels were measured using enzyme immunoassay, and histological examination of gastric mucosa was performed. H. pylori infection was determined by histopathological examination of gastric mucosal biopsy and/or Campylobacter-like organism test.

Results

In our study, plasma ghrelin levels and plasma ghrelin/obestatin (G/O) ratio were significantly lower in subjects with intestinal metaplasia compared with those without intestinal metaplasia (ghrelin, p = 0.010; G/O ratio, p = 0.012). On the other hand, there were no significant differences in plasma ghrelin and obestatin levels between H. pylori–positive and H. pylori–negative groups. (ghrelin, p = 0.130; obestatin, p = 0.888). Similarly, no significant differences were detected between the EPS and PDS groups (ghrelin, p = 0.238; obestatin, p = 0.710).

Conclusions

Patients with intestinal metaplasia, a known precursor of gastric cancer, had significantly less plasma ghrelin levels and G/O ratio than those without intestinal metaplasia.

Ghrelin is a prognostic marker and a potential therapeutic target in breast cancer

Ghrelin and obestatin are gastrointestinal peptides, encoded by the same preproghrelin gene. Both are expressed in breast cancer tissue and ghrelin has been implicated in breast cancer tumorigenesis. Despite recent advances in breast cancer management the need for new prognostic markers and potential therapeutic targets in breast cancer remains high. We studied the prognostic impact of ghrelin and obestatin in women with node negative breast cancer.

Within a cohort of women with breast cancer with tumor size ≤ 50 mm, no lymph node metastases and no initiation of adjuvant chemotherapy, 190 women were identified who died from breast cancer and randomly selected 190 women alive at the corresponding time as controls. Tumor tissues were immunostained with antibodies versus the peptides.

Ghrelin expression was associated with better breast cancer specific survival in univariate analyses (OR 0.55, 95% CI 0.36–0.84) and in multivariate models, adjusted for endocrine treatment and age (OR 0.57, 95% CI 0.36–0.89). Obestatin expression was non-informative (OR 1.2, 95% CI 0.60–2.46). Ghrelin expression is independent prognostic factor for breast cancer death in node negative patients—halving the risk for dying of breast cancer. Our data implies that ghrelin could be a potential therapeutic target in breast cancer treatment.

Interaction between prenatal pesticide exposure and a common polymorphism in the PON1 gene on DNA methylation in genes associated with cardio-metabolic disease risk-an exploratory study

BACKGROUND

Prenatal environmental conditions may influence disease risk in later life. We previously found a gene-environment interaction between the paraoxonase 1 (PON1) Q192R genotype and prenatal pesticide exposure leading to an adverse cardio-metabolic risk profile at school age. However, the molecular mechanisms involved have not yet been resolved. It was hypothesized that epigenetics might be involved. The aim of the present study was therefore to investigate whether DNA methylation patterns in blood cells were related to prenatal pesticide exposure level, PON1 Q192R genotype, and associated metabolic effects observed in the children.

METHODS

Whole blood DNA methylation patterns in 48 children (6-11 years of age), whose mothers were occupationally unexposed or exposed to pesticides early in pregnancy, were determined by Illumina 450 K methylation arrays.

RESULTS

A specific methylation profile was observed in prenatally pesticide exposed children carrying the PON1 192R-allele. Differentially methylated genes were enriched in several neuroendocrine signaling pathways including dopamine-DARPP32 feedback (appetite, reward pathways), corticotrophin releasing hormone signaling, nNOS, neuregulin signaling, mTOR signaling, and type II diabetes mellitus signaling. Furthermore, we were able to identify possible candidate genes which mediated the associations between pesticide exposure and increased leptin level, body fat percentage, and difference in BMI Z score between birth and school age.

CONCLUSIONS

DNA methylation may be an underlying mechanism explaining an adverse cardio-metabolic health profile in children carrying the PON1 192R-allele and prenatally exposed to pesticides.

Changes in obestatin gene and GPR39 receptor expression in peripheral tissues of rat models of obesity, type 1 and type 2 diabetes

BACKGROUND

Obestatin has a role in regulating food intake and energy expenditure, but the roles of obestatin and the GPR39 receptor in obesity and type 1 and type 2 diabetes mellitus (T1DM and T2DM, respectively) are not well understood. The aim of the present study was to investigate changes in obestatin and GPR39 in pathophysiological conditions like obesity, T1DM, and T2DM.

METHODS

Using rat models of diet-induced obesity (DIO), T1DM and T2DM (n = 14 per group), obestatin, its precursor protein preproghrelin, and GPR39 expression was investigated in tissues involved in glucose and lipid homeostasis regulation. Furthermore, serum obestatin and ghrelin concentrations were determined.

RESULTS

Serum obestatin concentrations were positively correlated with glucagon (r = 0.6456; P < 0.001) and visfatin (r = 0.5560; P < 0.001), and negatively correlated with insulin (r = -0.4362; P < 0.05), adiponectin (r = -0.3998; P < 0.05), and leptin (r = -0.4180; P < 0.05). There were differences in GPR39 and preproghrelin expression in the three animal models. Hepatic GPR39 and preproghrelin mRNA expression was greater in T1DM, T2DM, and obese rats than in lean controls, whereas pancreatic GPR39 mRNA and protein and preproghrelin mRNA expression was decreased in T1DM, T2DM, and DIO rats. Higher GPR39 and preproghrelin protein and mRNA levels were found in adipose tissues of T1DM compared with control. In adipose tissues of T2DM and DIO rats, GPR39 protein levels were lower than in lean or T1DM rats. Preproghrelin mRNA was higher in adipose tissues of T1DM, T2DM, and DIO than lean rats.

CONCLUSION

We hypothesize that changes in obestatin, GPR39, and ghrelin may contribute to metabolic abnormalities in T1DM, T2DM, and obesity.

The Zn2+-sensing receptor, ZnR/GPR39, upregulates colonocytic Cl- absorption, via basolateral KCC1, and reduces fluid loss

Administration of zinc, as a complement to oral rehydration solutions, effectively diminishes duration and severity of diarrhea, but it is not known whether it merely fulfills a nutritional deficiency, or if zinc has a direct role of regulating solute absorption. We show that Zn2+ acts via a specific receptor, ZnR/GPR39, to reduce fluid loss. Intestinal fluid secretion triggered by cholera toxin (CTx) was lower in WT mice compared to ZnR/GPR39 KO. In the absence of dietary Zn2+ we observed similar fluid accumulation in WT and ZnR/GPR39 KO mice, indicating that Zn2+ and ZnR/GPR39 are both required for a beneficial effect of Zn2+ in diarrhea. In primary colonocytes and in Caco-2 colonocytic cells, activation of ZnR/GPR39 enhanced Cl- transport, a critical factor in diarrhea, by upregulating K+/Cl- cotransporter (KCC1) activity. Importantly, we show basolateral expression of KCC1 in mouse and human colonocytes, thus identifying a novel Cl- absorption pathway. Finally, inhibition of KCC-dependent Cl- transport enhanced CTx-induced fluid loss. Altogether, our data indicate that Zn2+ acting via ZnR/GPR39 has a direct role in controlling Cl- absorption via upregulation of basolateral KCC1 in the colon. Moreover, colonocytic ZnR/GPR39 and KCC1 reduce water loss during diarrhea and may therefore serve as effective drug targets.

Obestatin modulates ghrelin's effects on the basal and stimulated testosterone secretion by the testis of rat: an in vitro study

The functional antagonism between obestatin and ghrelin in the testis is under investigation. We investigated the ability of obestatin to counteract the inhibitory effect of ghrelin on basal and stimulated testosterone (T) secretion in vitro. Testicular strips from adult rats were incubated with 10 ng/ml and 100 ng/ml of obestatin alone, ghrelin alone and obestatin + ghrelin. Obestatin modulation of stimulated T secretion was evaluated by incubation of testicular samples with 10 ng/ml and 100 ng/ml obestatin, ghrelin and obestatin + ghrelin in the absence and presence of 10 IU of human chorionic gonadotrophin (hCG). T concentrations in the hCG treated groups were significantly (P<0.0001) higher than those in the control groups. Obestatin caused a significant increase in basal T secretion in a dose-dependent manner; however, obestatin at the both 10 ng/ml and 100 ng/ml significantly (P<0.0001) increased hCG-stimulated T secretion. In contrast, ghrelin in a dose-dependent manner significantly (P<0.001) decreased both basal and hCG-induced T secretion by testicular slices. Obestatin opposed the inhibitory effect of ghrelin on T secretion under both basal and hCG-stimulated conditions at all doses tested. In conclusions, administration of obestatin was able to antagonize the inhibitory effect of ghrelin on testosterone secretion in vitro.

[Ghrelin: a gastric hormone at the crossroad between growth and appetite regulation]

Ghrelin is a 28 amino acid peptide hormone synthesized within the gastrointestinal tract. Initially identified as the endogenous ligand of the GHS-R1a (Growth Hormone Secretagogue Receptor 1a), ghrelin is a powerful stimulator of growth hormone (GH) secretion. At the crossroad between nutrition, growth and long-term energy metabolism, ghrelin also plays a unique role as the first identified gastric hormone increasing appetite and adiposity. However, the role of the ghrelin/GHS-R system in the physiology of growth, feeding behaviour and energy homeostasis needs to be better understood. Utilization of pharmacological tools and complementary animal models with deficiency in preproghrelin, ghrelin-O-acyl-transferase (GOAT - the enzyme that acylates ghrelin -) or GHS-R in situations of chronic undernutrition or high fat diet gives a more precise overview of the role of ghrelin in the pathophysiology of eating and metabolic disorders.

Is Ghrelin Synthesized in the Central Nervous System?

Ghrelin is an octanoylated peptide that acts via its specific receptor, the growth hormone secretagogue receptor type 1a (GHSR-1a), and regulates a vast variety of physiological functions. It is well established that ghrelin is predominantly synthesized by a distinct population of endocrine cells located within the gastric oxyntic mucosa. In addition, some studies have reported that ghrelin could also be synthesized in some brain regions, such as the hypothalamus. However, evidences of neuronal production of ghrelin have been inconsistent and, as a consequence, it is still as a matter of debate if ghrelin can be centrally produced. Here, we provide a comprehensive review and discussion of the data supporting, or not, the notion that the mammalian central nervous system can synthetize ghrelin. We conclude that no irrefutable and reproducible evidence exists supporting the notion that ghrelin is synthetized, at physiologically relevant levels, in the central nervous system of adult mammals.

The role of ghrelin in the regulation of glucose homeostasis

Ghrelin is a 28-amino acid (aa) stomach-derived peptide discovered in 1999 as the endogenous ligand for growth hormone secretagogue-receptor (GHS-R). Ghrelin-producing cells constitute a distinct group of endocrine cells dispersed throughout the gastric mucosa and to a lesser extent in the small intestine and the endocrine pancreas. Ghrelin plasma levels rise during fasting and chronic caloric restriction to stimulate food intake and fat storage and to prevent life-threatening falls in blood glucose. Plasma ghrelin levels decrease after a meal is consumed and in conditions of energy surplus (such as obesity). Ghrelin has emerged as a key player in the regulation of appetite and energy homeostasis. Ghrelin achieves these functions through binding the ghrelin receptor GHS-R in appetite-regulating neurons and in peripheral metabolic organs including the endocrine pancreas. Ghrelin levels are negatively correlated with body mass index (BMI) and insulin resistance. In addition, ghrelin secretion is impaired in obesity and insulin resistance. Several studies highlight an important role for ghrelin in glucose homeostasis. Genetic, immunological, and pharmacological blockade of ghrelin signaling resulted in improved glucose tolerance and insulin sensitivity. Furthermore, exogenous ghrelin administration was shown to decrease glucose-induced insulin release and increase glucose level in both humans and rodents. GHS-R was shown to be expressed in pancreatic β-cells and ghrelin suppressed insulin release via a Ca2+-mediated pathway. In this review, we provide a detailed summary of recent advances in the field that focuses on the role of insulin and insulin resistance in the regulation of ghrelin secretion and on the role of ghrelin in glucose-stimulated insulin secretion (GSIS).

A potential role for the secretogranin II-derived peptide EM66 in the hypothalamic regulation of feeding behaviour

EM66 is a conserved 66-amino acid peptide derived from secretogranin II (SgII), a member of the granin protein family. EM66 is widely distributed in secretory granules of endocrine and neuroendocrine cells, as well as in hypothalamic neurones. Although EM66 is abundant in the hypothalamus, its physiological function remains to be determined. The present study aimed to investigate a possible involvement of EM66 in the hypothalamic regulation of feeding behaviour. We show that i.c.v. administration of EM66 induces a drastic dose-dependent inhibition of food intake in mice deprived of food for 18 hours, which is associated with an increase of hypothalamic pro-opiomelanocortin (POMC) and melanocortin-3 receptor mRNA levels and c-Fos immunoreactivity in the POMC neurones of the arcuate nucleus. By contrast, i.c.v. injection of EM66 does not alter the hypothalamic expression of neuropeptide Y (NPY), or that of its Y1 and Y5 receptors. A 3-month high-fat diet (HFD) leads to an important decrease of POMC and SgII mRNA levels in the hypothalamus, whereas NPY gene expression is not affected. Finally, we show that a 48 hours of fasting in HFD mice decreases the expression of POMC and SgII mRNA, which is not observed in mice fed a standard chow. Taken together, the present findings support the view that EM66 is a novel anorexigenic neuropeptide regulating hypothalamic feeding behaviour, at least in part, by activating the POMC neurones of the arcuate nucleus.

Regulation of GIP and Ghrelin in Healthy Subjects Fed on Sun-Dried Raisins: A Pilot Study with a Crossover Trial Design

The comparative effects of glucose and fructose on appetite and specifically on hormones regulating appetite remain controversial, and the role of different types of sugars has not been investigated broadly. To estimate the effect of raisins, a dried fruit rich in fructose, fibers, and phenolics, on hormones involved in the postprandial response. Ten healthy normal-weight subjects received in a crossover design 74 g raisins or 50 g glucose as reference food. Glucose, insulin, and appetite hormones were measured at time 0 and 60, 120, and 180 min after consumption. Glucose and insulin peaked significantly at 60 min in both trials with no difference in two trials. Gastric inhibitory peptide peaked significantly at 60 min in both trials and was found lower in raisin compared to glucose at 60 and 120 min postprandially. Ghrelin was lower in raisin compared to glucose at 120 and at 180 min postingestion. Ghrelin/obestatin ratio was lower at 120 min in raisin compared to glucose. No differences were reported for glucagon-like peptide-1, apelin, and obestatin in either trial. Raisin consumption could be favorable in terms of regulating appetite compared to refined sugars or glucose-based products in normal-weight healthy subjects.

The role of the obestatin/GPR39 system in human gastric adenocarcinomas

Obestatin, a 23-amino acid peptide encoded by the ghrelin gene, and the GPR39 receptor were reported to be involved in the control of mitogenesis of gastric cancer cell lines; however, the relationship between the obestatin/GPR39 system and gastric cancer progression remains unknown. In the present study, we determined the expression levels of the obestatin/GPR39 system in human gastric adenocarcinomas and explored their potential functional roles. Twenty-eight patients with gastric adenocarcinomas were retrospectively studied, and clinical data were obtained. The role of obestatin/GPR39 in gastric cancer progression was studied in vitro using the human gastric adenocarcinoma AGS cell line. Obestatin exogenous administration in these GPR39-bearing cells deregulated the expression of several hallmarks of the epithelial-mesenchymal transition (EMT) and angiogenesis. Moreover, obestatin signaling promoted phenotypic changes via GPR39, increasingly impacting on the cell morphology, proliferation, migration and invasion of these cells. In healthy human stomachs, obestatin expression was observed in the neuroendocrine cells and GPR39 expression was localized mainly in the chief cells of the oxyntic glands. In human gastric adenocarcinomas, no obestatin expression was found; however, an aberrant pattern of GPR39 expression was discovered, correlating to the dedifferentiation of the tumor. Altogether, our data strongly suggest the involvement of the obestatin/GPR39 system in the pathogenesis and/or clinical outcome of human gastric adenocarcinomas and highlight the potential usefulness of GPR39 as a prognostic marker in gastric cancer.

Obesity and diabetes: An update

The twin epidemic of obesity and diabetes is a major crisis globally. Several epidemiologic studies reveal the parallel escalation of obesity and diabetes. The term 'diabesity' expresses their close relationship to each other, wherein both these metabolic disorders are characterized by defects of insulin action. The pathophysiology connecting obesity and diabetes is chiefly attributed to two factors: insulin resistance and insulin deficiency. Recent years have seen an increasing body of work on the following metabolic defects common to both obesity and diabetes such as, impaired tissue perfusion, sleep disturbances, androgen dysfunction, altered Vitamin D levels and GI stress. The scope of this review is to present the most widely accepted theories that link the two diseases, provide an update on some proposed unifying metabolic defects and highlight current and future prevention and management strategies.

Intracerebroventricular injection of ghrelin decreases wheel running activity in rats

There is an increasing interest in elucidating the molecular mechanisms by which voluntary exercise is regulated. In this study, we examined how the central nervous system regulates exercise. We used SPORTS rats, which were established in our laboratory as a highly voluntary murine exercise model. SPORTS rats showed lower levels of serum ghrelin compared with those of the parental line of Wistar rats. Intracerebroventricular and intraperitoneal injection of ghrelin decreased wheel-running activity in SPORTS rats. In addition, daily injection of the ghrelin inhibitor JMV3002 into the lateral ventricles of Wistar rats increased wheel-running activity. Co-administration of obestatin inhibited ghrelin-induced increases in food intake but did not inhibit ghrelin-induced suppression of voluntary exercise in rats. Growth hormone secretagogue receptor (GHSR) in the hypothalamus and hippocampus of SPORTS rats was not difference that in control rats. We created an arcuate nucleus destruction model by administering monosodium glutamate (MSG) to neonatal SPORTS rats. Injection of ghrelin into MSG-treated rats decreased voluntary exercise but did not increase food intake, suggesting that wheel-running activity is not controlled by the arcuate nucleus neurons that regulate feeding. These results provide new insights into the mechanism by which ghrelin regulates voluntary activity independent of arcuate nucleus neurons.

Hypothalamic regulation of body growth and appetite by ghrelin-derived peptides during balanced nutrition or undernutrition

Among the gastrointestinal hormones that regulate food intake and energy homeostasis, ghrelin plays a unique role as the first one identified to increases appetite and stimulate GH secretion. This review highlights the latest mechanism by which ghrelin modulates body growth, appetite and energy metabolism by exploring pharmacological actions of the hormone and consequences of genetic or pharmacological blockade of the ghrelin/GHS-R (Growth Hormone Secretagogue Receptor) system on physiological responses in specific nutritional situations. Within the hypothalamus, novel mechanisms of action of this hormone involve its interaction with other ghrelin-derived peptides, such as desacyl ghrelin and obestatin, which are thought to act as functional ghrelin antagonists, and possible modulation of the GHS-R with other G-protein coupled receptors. During chronic undernutrition such as anorexia nervosa, variations of ghrelin-derived peptides may be an adaptative metabolic response to maintain normal glycemic control. Interestingly, some of ghrelin's metabolic actions are thought to be relayed through modulation of GH, an anabolic and hyperglycemic agent.

Discovery and Characterization of Novel GPR39 Agonists Allosterically Modulated by Zinc

In this study, we identified two previously described kinase inhibitors-3-(4-chloro-2-fluorobenzyl)-2-methyl-N-(3-methyl-1H-pyrazol-5-yl)-8-(morpholinomethyl)imidazo[1,2-b]pyridazin-6-amine (LY2784544) and 1H-benzimidazole-4-carboxylic acid, 2-methyl-1-[[2-methyl-3-(trifluoromethyl)phenyl]methyl]-6-(4-morpholinyl)- (GSK2636771)-as novel GPR39 agonists by unbiased small-molecule-based screening using a β-arrestin recruitment screening approach (PRESTO-Tango). We characterized the signaling of LY2784544 and GSK2636771 and compared their signaling patterns with a previously described "GPR39-selective" agonist N-[3-chloro-4-[[[2-(methylamino)-6-(2-pyridinyl)-4- pyrimidinyl]amino]methyl]phenyl]methanesulfonamide (GPR39-C3) at both canonical and noncanonical signaling pathways. Unexpectedly, all three compounds displayed probe-dependent and pathway-dependent allosteric modulation by concentrations of zinc reported to be physiologic. LY2784544 and GS2636771 at GPR39 in the presence of zinc were generally as potent or more potent than their reported activities against kinases in whole-cell assays. These findings reveal an unexpected role of zinc as an allosteric potentiator of small-molecule-induced activation of GPR39 and expand the list of potential kinase off-targets to include understudied G protein-coupled receptors.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

GPR39 is region-specifically expressed in mouse oviduct correlating with the Zn2+ distribution

G-protein-coupled receptor 39 (GPR39) plays a role in cellular and physiological processes, including insulin secretion, cell death inhibition, wound healing, and obesity. Increasing evidence suggests that GPR39 is potently stimulated by zinc ions (Zn²⁺) and is therefore considered a putative Zn²⁺ receptor. Given the importance of Zn²⁺ in the reproductive system, we proposed that GPR39 might have a functional role in the reproductive system. However, the localization of GPR39 in the reproductive system remains unknown. Here, we used mice expressing a Gpr39 promoter-driven LacZ reporter system to detect Gpr39 expression in the reproductive system at different phases of the estrous cycle and found an interesting region-specific distribution of Gpr39 in the mouse oviduct epithelium, with strong expression at the ampulla and weak expression at the isthmus, which was consistent with the results using reverse transcription polymerase chain reaction and immunofluorescence. Moreover, using ZnSe^AMG staining, we found that Zn²⁺, the putative ligand of GPR39, also found a distribution similar to GPR39 expression, suggesting that their potential interaction mediates fertilization and embryo transportation.

Ghrelin gene products rescue cultured adult rat hippocampal neural stem cells from high glucose insult

Adult hippocampal neurogenesis is decreased in type 2 diabetes, and this impairment appears to be important in cognitive dysfunction. Previous studies suggest that ghrelin gene products (acylated ghrelin (AG), unacylated ghrelin (UAG) and obestatin (OB)) promote neurogenesis. Therefore, we hypothesize that ghrelin gene products may reduce the harmful effects of high glucose (HG) on hippocampal neural stem cells (NSCs). The aim of this study was to investigate the role of these peptides on the survival of cultured hippocampal NSCs exposed to HG insult. Treatment of hippocampal NSCs with AG, UAG or OB inhibited HG-induced cell death and apoptosis. Exposure of cells to the growth hormone secretagogue receptor 1a antagonist abolished the protective effects of AG against HG toxicity, whereas those of UAG or OB were preserved. All three peptides attenuated HG-induced decrease in BrdU-labeled and phosphohistone-H3-labeled cells. We also investigated the effects of ghrelin gene products on the regulation of apoptosis at the mitochondrial level. AG, UAG or OB rescued hippocampal NSCs from HG insult by inhibiting intracellular and mitochondrial reactive oxygen species generation and stabilizing mitochondrial transmembrane potential. In addition, cells treated with ghrelin gene products showed an increased Bcl-2 and decreased Bax levels, thereby increasing the Bcl-2/Bax ratio, inhibiting cytochrome c release and preventing caspase-3 activation. Finally, AG-, UAG- or OB-mediated protection was dependent on the activities of adenosine monophosphate-activated protein kinase/uncoupling protein 2 pathway. Our data indicate that ghrelin gene products may act as survival factors that preserve mitochondrial function and inhibit oxidative stress-induced apoptosis.

The role of obestatin in Roux-en-Y gastric bypass surgery in the obese, type 2 diabetes Zucker rat

AIMS

Roux-en-Y gastric bypass (RYGB) is a novel therapy for diabetes and the exact mechanisms of this procedure remain unclear. Obestatin is an important gut hormone. We aimed to explore the role of obestatin in the therapeutic mechanism of RYGB.

METHODS

Twenty obese Zucker rats and twenty Wistar rats were randomly assigned to two groups: RYGB and sham surgery. We evaluated plasma obestatin and insulin levels pre- and post-RYGB. Additionally, obestatin expression levels in the gastrointestinal tract were assessed using immunohistochemical staining.

RESULTS

In Zucker rats, plasma obestatin and insulin levels gradually increased after RYGB. At post-operation week 7, plasma levels of obestatin were higher in the RYGB group than the sham operation group, and fasting plasma insulin levels were significantly increased the in RYGB group compared with the sham operation group. Furthermore, we observed a positive relationship between obestatin and insulin plasma levels. Among 10 zucker rats, high expression of obestatin was only seen in the jejunum of 2 rats before the operation; however, high expression of obestatin was seen in the Roux limb of 8 rats and in the ileum of 7 rats after RYGB. The expression of obestatin was significantly higher in the intestine in the RYGB group than the sham operation group postoperatively.

CONCLUSIONS

We propose that obestatin maybe a potential mediator to improve glucose homeostasis after RYGB. The increase of obestatin secretion may be an important mechanism through which RYGB alleviates obesity and type 2 diabetes mellitus.

The role of obestatin in roux-en-Y gastric bypass-induced remission of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a complex and multifactorial disease that is generally characterized by insulin resistance and loss of β-cell function that develops in adulthood. To date, more than 6% of the world's population is affected by T2DM. The main treatments of T2DM are dietary and lifestyle changes. However, only dependent on behaviour modification and oral hypoglycemics, many patients are unable to maintain glycemic control. Emerging evidence indicates that up to 80% of patients with T2DM undergoing Roux-en-Y gastric bypass (RYGB) experience complete remission of their T2DM and the majority of remissions occur almost immediately following the operation. Obestatin is a 23-amino-acid peptide, which is not only thought to suppress food intake and decrease gastric emptying but also found to exert survival effects in pancreatic β cells, increase glucose-stimulated insulin secretion, and reduce insulin resistance and inflammation. In addition, some researchers demonstrated that obestatin is a nutritional marker reflecting body adiposity and insulin resistance. Although results from previous studies were conflicting, the peripheral blood concentrations of obestatin were changed after RYGB. Therefore, regulation of obestatin level may be another mechanism for RYGB-induced remission of T2DM. In this article, we review briefly the effect of RYGB on T2DM in humans and offer an overview of the published data on the effects of RYGB on obestatin level in patients with T2DM. Furthermore, the possible roles of obestatin in the remission of T2DM following RYGB are also reviewed. Copyright © 2015 John Wiley & Sons, Ltd.

New Insights in Anorexia Nervosa

Anorexia nervosa (AN) is classically defined as a condition in which an abnormally low body weight is associated with an intense fear of gaining weight and distorted cognitions regarding weight, shape, and drive for thinness. This article reviews recent evidences from physiology, genetics, epigenetics, and brain imaging which allow to consider AN as an abnormality of reward pathways or an attempt to preserve mental homeostasis. Special emphasis is put on ghrelino-resistance and the importance of orexigenic peptides of the lateral hypothalamus, the gut microbiota and a dysimmune disorder of neuropeptide signaling. Physiological processes, secondary to underlying, and premorbid vulnerability factors-the "pondero-nutritional-feeding basements"- are also discussed.

An Evaluation of Acylated Ghrelin and Obestatin Levels in Childhood Obesity and Their Association with Insulin Resistance, Metabolic Syndrome, and Oxidative Stress

Background: Ghrelin is a 28-amino acid peptide with an orexigenic property, which is predominantly produced by the stomach. Acylated ghrelin is the active form of this hormone. Obestatin is a 23-amino acid peptide which is produced by post-translational modification of a protein precursor that also produces ghrelin. Obestatin has the opposite effect of ghrelin on food intake. The aim of this study was to evaluate acylated ghrelin and obestatin levels and their ratio in obese and normal-weight children and adolescents, and their association with metabolic syndrome (MetS) parameters. Methods: Serum acyl-ghrelin, obestatin, leptin, insulin, fasting plasma glucose (FPG), lipid profile, and malondialdehyde (MDA) were evaluated in 73 children and adolescents (42 obese and 31 control). Insulin resistance was calculated by a homeostasis model assessment of insulin resistance (HOMA-IR). MetS was determined according to IDF criteria. Results: Acyl-ghrelin levels were significantly lower in obese subjects compared to the control group and lower in obese children with MetS compared to obese subjects without MetS. Obestatin was significantly higher in obese subjects compared to that of the control, but it did not differ significantly among those with or without MetS. Acyl-ghrelin to obestatin ratio was significantly lower in obese subjects compared to that in normal subjects. Acyl-ghrelin showed significant negative and obestatin showed significant positive correlations with body mass index (BMI), BMI Z-score, leptin, insulin, and HOMA-IR. Acyl-ghrelin had a significant negative correlation with MDA as an index of oxidative stress. Conclusion: Ghrelin is decreased and obestatin is elevated in obesity. Both of these hormones are associated with insulin resistance, and ghrelin is associated with oxidative stress. The balance between ghrelin and obestatin seems to be disturbed in obesity.

Multi-species sequence comparison reveals conservation of ghrelin gene-derived splice variants encoding a truncated ghrelin peptide

The peptide hormone ghrelin is a potent orexigen produced predominantly in the stomach. It has a number of other biological actions, including roles in appetite stimulation, energy balance, the stimulation of growth hormone release and the regulation of cell proliferation. Recently, several ghrelin gene splice variants have been described. Here, we attempted to identify conserved alternative splicing of the ghrelin gene by cross-species sequence comparisons. We identified a novel human exon 2-deleted variant and provide preliminary evidence that this splice variant and in1-ghrelin encode a C-terminally truncated form of the ghrelin peptide, termed minighrelin. These variants are expressed in humans and mice, demonstrating conservation of alternative splicing spanning 90 million years. Minighrelin appears to have similar actions to full-length ghrelin, as treatment with exogenous minighrelin peptide stimulates appetite and feeding in mice. Forced expression of the exon 2-deleted preproghrelin variant mirrors the effect of the canonical preproghrelin, stimulating cell proliferation and migration in the PC3 prostate cancer cell line. This is the first study to characterise an exon 2-deleted preproghrelin variant and to demonstrate sequence conservation of ghrelin gene-derived splice variants that encode a truncated ghrelin peptide. This adds further impetus for studies into the alternative splicing of the ghrelin gene and the function of novel ghrelin peptides in vertebrates.

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

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

Bariatric Left Gastric Artery Embolization for the Treatment of Obesity: A Review of Gut Hormone Involvement in Energy Homeostasis

OBJECTIVE

The global population is becoming more overweight and obese, leading to increases in associated morbidity and mortality rates. Advances in catheter-directed embolotherapy offer the potential for the interventional radiologist to make a contribution to weight loss. Left gastric artery embolization reduces the supply of blood to the gastric fundus and decreases serum levels of ghrelin. Early evidence suggests that this alteration in gut hormone balance leads to changes in energy homeostasis and weight reduction. The pathophysiologic findings and current evidence associated with the use of left gastric artery embolization are reviewed.

CONCLUSION

The prevalence of obesity continues to increase at an alarming rate, and, thus far, advances in medical management have been relatively ineffective in slowing this trend. Lifestyle modifications such as diet and exercise are effective initially, but most patients regain the weight in the long term. Bariatric surgery is the most effective strategy for achieving long-term weight loss; however, as with all surgical procedures, it has potential complications.

Neuroendocrinological and Epigenetic Mechanisms Subserving Autonomic Imbalance and HPA Dysfunction in the Metabolic Syndrome

Impact of environmental stress upon pathophysiology of the metabolic syndrome (MetS) has been substantiated by epidemiological, psychophysiological, and endocrinological studies. This review discusses recent advances in the understanding of causative roles of nutritional factors, sympathomedullo-adrenal (SMA) and hypothalamic-pituitary adrenocortical (HPA) axes, and adipose tissue chronic low-grade inflammation processes in MetS. Disturbances in the neuroendocrine systems for leptin, melanocortin, and neuropeptide Y (NPY)/agouti-related protein systems have been found resulting directly in MetS-like conditions. The review identifies candidate risk genes from factors shown critical for the functioning of each of these neuroendocrine signaling cascades. In its meta-analytic part, recent studies in epigenetic modification (histone methylation, acetylation, phosphorylation, ubiquitination) and posttranscriptional gene regulation by microRNAs are evaluated. Several studies suggest modification mechanisms of early life stress (ELS) and diet-induced obesity (DIO) programming in the hypothalamic regions with populations of POMC-expressing neurons. Epigenetic modifications were found in cortisol (here HSD11B1 expression), melanocortin, leptin, NPY, and adiponectin genes. With respect to adiposity genes, epigenetic modifications were documented for fat mass gene cluster APOA1/C3/A4/A5, and the lipolysis gene LIPE. With regard to inflammatory, immune and subcellular metabolism, PPARG, NKBF1, TNFA, TCF7C2, and those genes expressing cytochrome P450 family enzymes involved in steroidogenesis and in hepatic lipoproteins were documented for epigenetic modifications.

Leptin regulates energy intake but fails to facilitate hibernation in fattening Daurian ground squirrels (Spermophilus dauricus)

Body fat storage before hibernation affects the timing of immergence in Daurian ground squirrels (Spermophilus dauricus). Leptin is an adipose signal and plays vital role in energy homeostasis mainly by action in brain. To test the hypothesis that leptin plays a role in facilitating the process of hibernation, squirrels were administrated with recombinant murine leptin (1μg/day) through intracerebroventricular (ICV) injection for 12 days during fattening. From day 7 to 12, animals were moved into a cold room (5±1°C) with constant darkness which functioned as hibernaculum. Energy intake, body mass and core body temperature (Tb) were continuously monitored throughout the course of experiment. Resting metabolic rate (RMR) was measured under both warm and cold conditions. At the end of leptin administration, we measured the serum concentration of hormones related to energy regulation, mRNA expression of hypothalamic neuropeptides and uncoupling protein 1 (UCP1) levels in brown adipose tissue (BAT). Our results showed that during leptin administration, the cumulative food intake and increase of body mass were suppressed while Tb and RMR were unaltered. The proportion of torpid squirrels was not different between two groups. At the end of leptin administration, the expressions of hypothalamic neuropeptide Y and agouti gene-related protein were suppressed. There were no differences in UCP1 mRNA expression or protein content in BAT between groups. Our data suggest that leptin can affect energy intake via hypothalamic neuropeptides, but is not involved in the initiation of hibernation in fattening Daurian ground squirrels.

GPR39 receptors and actions of trace metals on pancreatic beta cell function and glucose homoeostasis

AIMS

G-protein-coupled receptor 39 (GPR39) has been implicated in glucose homoeostasis, appetite control and gastrointestinal tract function.

METHODS

This study used clonal BRIN-BD11 cells and mouse pancreatic islets to assess the insulin-releasing actions of trace metals believed to act via GPR39, and the second messenger pathways involved in mediating their effects. Micromolar concentrations of Zn(2+), Cu(2+), Ni(2+) and Co(2+) were examined under normoglycaemic and hyperglycaemic conditions. Mechanistic studies investigated changes of intracellular Ca(2+), cAMP generation and assessment of cytotoxicity by LDH release. Cellular localisation of GPR39 was determined by double immunohistochemical staining.

RESULTS

All trace metals (7.8-500 µmol/l) stimulated insulin release with Cu(2+) being the most potent in isolated islets, with an EC50 value of 87 μmol/l. Zn(2+) was the most selective with an EC50 value of 125 μmol/l. Enhancement of insulin secretion was also observed with Ni(2+) (179 μmol/l) and Co(2+) (190 μmol/l). These insulin-releasing effects were confirmed using clonal BRIN-BD11 cells which exhibited enhanced intracellular Ca(2+) (p < 0.05-p < 0.001) and cAMP generation (p < 0.05-p < 0.001) in response to trace metals. Oral administration of Zn(2+), Ni(2+) and Cu(2+) (50 µmol/kg together with 18 mmol/kg glucose) decreased the glycaemic excursion (p < 0.05-p < 0.01) and augmented insulin secretion (p < 0.05-p < 0.01) in NIH Swiss mice.

CONCLUSIONS

This study has demonstrated the presence of GPR39 and the insulinotropic actions of trace metals on BRIN-BD11 cells and pancreatic beta cells, together with their antihyperglycaemic actions in vivo. These data suggest that development of agonists capable of specifically activating GPR39 may be a useful new therapeutic approach for diabetes management.

Ghrelin Receptor Mutations and Human Obesity

Growth hormone secretagogue receptor (GHSR) was originally identified as an orphan receptor in porcine and rat anterior pituitary membranes. In 1999, GHSR was deorphanized and shown to be a receptor for ghrelin, a peptide hormone secreted from the stomach. Therefore, GHSR is also called ghrelin receptor. In addition to regulating growth hormone secretion, ghrelin receptor regulates various physiological processes, including food intake and energy expenditure, glucose metabolism, cardiovascular functions, gastric acid secretion and motility, and immune function. Several human genetic studies conducted in populations originated from Europe, Africa, South America, and East Asia identified rare mutations and single nucleotide polymorphisms that might be associated with human obesity and short stature. Functional analyses of mutant GHSRs reveal multiple defects, including cell surface expression, ligand binding, and basal and stimulated signaling. With growing understanding in the functionality of naturally occurring GHSR mutations, potential therapeutic strategies including pharmacological chaperones and novel ligands could be used to correct the GHSR mutants.

Neuroendocrine Regulation of Growth Hormone Secretion

This article reviews the main findings that emerged in the intervening years since the previous volume on hormonal control of growth in the section on the endocrine system of the Handbook of Physiology concerning the intra- and extrahypothalamic neuronal networks connecting growth hormone releasing hormone (GHRH) and somatostatin hypophysiotropic neurons and the integration between regulators of food intake/metabolism and GH release. Among these findings, the discovery of ghrelin still raises many unanswered questions. One important event was the application of deconvolution analysis to the pulsatile patterns of GH secretion in different mammalian species, including Man, according to gender, hormonal environment and ageing. Concerning this last phenomenon, a great body of evidence now supports the role of an attenuation of the GHRH/GH/Insulin-like growth factor-1 (IGF-1) axis in the control of mammalian aging.

A possible significant role of zinc and GPR39 zinc sensing receptor in Alzheimer disease and epilepsy

Zinc the essential trace element, plays a significant role in the brain development and in the proper brain functions at every stage of life. Misbalance of zinc (Zn(2+)) ions in the central nervous system is involved in the pathogenesis of numerous neurodegenerative disorders such as Alzheimer's disease, Depression, and Epilepsy. In brain, Zn(2+) has been identified as a ligand, capable of activating and inhibiting the receptors including the NMDA-type glutamate receptors (NMDARs), GABAA receptors, nicotinic acetylcholine receptors (nAChRs), glycine receptors (glyR) and serotonin receptors (5-HT3). Recently GPR39 has been identified as a zinc-specific receptor, widely expressed in brain tissues including the frontal cortex, amygdala, and hippocampus. GPR39, when binding with Zn(2+) has shown promising therapeutic potentials. This review presents current knowledge regarding the role of GPR39 zinc sensing receptor in brain, with a focus on Alzheimer's disease and Epilepsy. Although the results are encouraging, further research is needed to clarify zinc and GPR39 role in the treatment of Alzheimer's disease and Epilepsy.

Obestatin promotes proliferation and survival of adult hippocampal progenitors and reduces amyloid-β-induced toxicity

The ghrelin gene-derived peptide obestatin promotes survival in different cell types through a yet undefined receptor; however, its potential neuroprotective activities are still unknown. Here, obestatin effects were investigated on proliferation and survival of adult rat hippocampal progenitor cells (AHPs). Obestatin immunoreactivity was found in AHPs; moreover, obestatin binding to AHPs was displaced by the GLP-1R agonist Ex-4 and antagonist Ex-9. Furthermore, obestatin increased cell proliferation and survival in growth factor deprived medium and inhibited apoptosis; these effects were blocked by Ex-9. The underlying mechanisms involved Gαs/cAMP/PKA/CREB signaling, phosphorylation of ERK1/2 and PI3K/Akt, and the PI3K targets GSK-3β/β-catenin and mTOR. Obestatin also counteracted Aβ1-42-induced detrimental effects through inhibition of GSK-3β activity and Tau hyperphosphorylation, main hallmarks of neuronal death in Alzheimer's disease. These findings indicate a novel protective role for obestatin in AHPs and candidate this peptide as potential therapeutic target for increasing neurogenesis and for approaching neurodegenerative disorders.

β-Arrestin scaffolds and signaling elements essential for the obestatin/GPR39 system that determine the myogenic program in human myoblast cells

Obestatin/GPR39 signaling stimulates skeletal muscle repair by inducing the expansion of satellite stem cells as well as myofiber hypertrophy. Here, we describe that the obestatin/GPR39 system acts as autocrine/paracrine factor on human myogenesis. Obestatin regulated multiple steps of myogenesis: myoblast proliferation, cell cycle exit, differentiation and recruitment to fuse and form multinucleated hypertrophic myotubes. Obestatin-induced mitogenic action was mediated by ERK1/2 and JunD activity, being orchestrated by a G-dependent mechanism. At a later stage of myogenesis, scaffolding proteins β-arrestin 1 and 2 were essential for the activation of cell cycle exit and differentiation through the transactivation of the epidermal growth factor receptor (EGFR). Upon obestatin stimulus, β-arrestins are recruited to the membrane, where they functionally interact with GPR39 leading to Src activation and signalplex formation to EGFR transactivation by matrix metalloproteinases. This signalplex regulated the mitotic arrest by p21 and p57 expression and the mid- to late stages of differentiation through JNK/c-Jun, CAMKII, Akt and p38 pathways. This finding not only provides the first functional activity for β-arrestins in myogenesis but also identify potential targets for therapeutic approaches by triggering specific signaling arms of the GPR39 signaling involved in myogenesis.

Treatment of lean and diet-induced obesity (DIO) mice with a novel stable obestatin analogue alters plasma metabolite levels as detected by untargeted LC-MS metabolomics

INTRODUCTION

Obestatin is a controversial gastrointestinal peptide purported to have metabolic actions.

OBJECTIVES

This study investigated whether treatment with a stable obestatin analogue (PEG-OB(Cys¹⁰, Cys¹³)) changed plasma metabolite levels firstly in lean and subsequently in diet-induced obesity (DIO) C57BL6/J mice.

METHODS

Untargeted LC-HRMS metabolomics experiments were carried out in ESI + mode with plasma extracts from both groups of animals. Data were normalised, multivariate and univariate statistical analysis performed and metabolites of interest putatively identified.

RESULTS

In lean mice, 39 metabolites were significantly changed by obestatin treatment and the majority of these were increased, including various C16 and C18 moieties of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and monoacylglycerol, along with vitamin A, vitamin D3, tyrosine, acetylcarnitine and 2α-(hydroxymethyl)-5α-androstane-3β,17β-diol. Decreased concentrations of glycolithocholic acid, 3-dehydroteasterone and various phospholipids were observed. In DIO mice, 25 metabolites were significantly affected and strikingly, the magnitudes of changes here were generally much greater in DIO mice than in lean mice, and in contrast, the majority of metabolite changes were decreases. Four metabolites affected in both groups included glycolithocholic acid, and three different long-chain (C18) phospholipid molecules (phosphatidylethanolamine, platelet activating factor (PAF), and monoacylglycerol). Metabolites exclusively affected in DIO mice included various phosphatidylcholines, lysophosphatidylcholines and fatty acyls, as well as creatine and oxidised glutathione.

CONCLUSION

This investigation demonstrates that obestatin treatment affects phospholipid turnover and influences lipid homeostasis, whilst providing convincing evidence that obestatin may be acting to ameliorate diet-induced impairments in lipid metabolism, and it may influence steroid, bile acid, PAF and glutathione metabolism.