Interactions between gut peptides and the central melanocortin system in the regulation of energy homeostasis

Role of Leptin in Obesity, Cardiovascular Disease, and Type 2 Diabetes

Diabetes mellitus (DM) is a highly prevalent disease worldwide, estimated to affect 1 in every 11 adults; among them, 90-95% of cases are type 2 diabetes mellitus. This is partly attributed to the surge in the prevalence of obesity, which has reached epidemic proportions since 2008. In these patients, cardiovascular (CV) risk stands as the primary cause of morbidity and mortality, placing a substantial burden on healthcare systems due to the potential for macrovascular and microvascular complications. In this context, leptin, an adipocyte-derived hormone, plays a fundamental role. This hormone is essential for regulating the cellular metabolism and energy balance, controlling inflammatory responses, and maintaining CV system homeostasis. Thus, leptin resistance not only contributes to weight gain but may also lead to increased cardiac inflammation, greater fibrosis, hypertension, and impairment of the cardiac metabolism. Understanding the relationship between leptin resistance and CV risk in obese individuals with type 2 DM (T2DM) could improve the management and prevention of this complication. Therefore, in this narrative review, we will discuss the evidence linking leptin with the presence, severity, and/or prognosis of obesity and T2DM regarding CV disease, aiming to shed light on the potential implications for better management and preventive strategies.

Gut peptide changes in patients with obstructive jaundice undergoing biliary drainage: A prospective case control study

BACKGROUND

Biliary obstruction is a relatively common condition that affects approximately 5 in 1000 people annually. Malnutrition is very common in patients with biliary obstruction and since it is associated with significant morbidity and mortality, it is important to identify factors and mechanisms involved in its development.

AIM

To determine the influence of obstructive jaundice on the hormones controlling appetite and nutritive status.

METHODS

This was a prospective case control study performed in a tertiary center in Zagreb, Croatia. Patients with biliary obstruction undergoing internal biliary drainage from September 2012 until August 2013 were enrolled. After excluding patients who developed procedure related complications or were lost in the follow-up, out of initial 73 patients, 55 patients were included in the analysis, including 34 with benign and 21 with malignant disease. Meanwhile, 40 non-jaundiced controls were also included. Appetite, nutritional status, and serum ghrelin, cholecystokinin (CCK), interleukin 6 (IL-6), and tumor necrosis factor α (TNF-α) were determined at admission, 48 h and 28 d after internal biliary drainage. Chi square test was used for categorical variables. Continuous variables were analysed for normality by Kolmogorov-Smirnov test and relevant non-parametric (Mann-Whitney, Kruskal-Wallis, and Friedman) or parametric (t-test and analysis of variance) tests were used.

RESULTS

Patients with obstructive jaundice were significantly malnourished compared to controls, regardless of disease etiology. Plasma ghrelin and CCK levels were significantly higher in patients with obstructive jaundice. Serum bilirubin concentrations were negatively correlated with ghrelin levels and positively correlated with TNF-α, but had no correlation with CCK concentrations. After internal biliary drainage, a significant improvement of nutritional status was observed although serum concentrations of ghrelin, IL-6, and TNF-α remained significantly elevated even 28 d after the procedure. CCK levels in patients without malnutrition remained elevated 28 d after the procedure, but in patients with malnutrition, CCK levels decreased to levels comparable with those in the control group. We have not established any correlation between appetite and serum levels of ghrelin, CCK, IL-6, and TNF-α before and after biliary drainage.

CONCLUSION

Possible abnormalities in ghrelin and CCK regulation may be associated with the development of malnutrition during the inflammatory response in patients with biliary obstruction.

Neurochemical Characterization of Brainstem Pro-Opiomelanocortin Cells

Genetic research has revealed pro-opiomelanocortin (POMC) to be a fundamental regulator of energy balance and body weight in mammals. Within the brain, POMC is primarily expressed in the arcuate nucleus of the hypothalamus (ARC), while a smaller population exists in the brainstem nucleus of the solitary tract (POMCNTS). We performed a neurochemical characterization of this understudied population of POMC cells using transgenic mice expressing green fluorescent protein (eGFP) under the control of a POMC promoter/enhancer (PomceGFP). Expression of endogenous Pomc mRNA in the nucleus of the solitary tract (NTS) PomceGFP cells was confirmed using fluorescence-activating cell sorting (FACS) followed by quantitative PCR. In situ hybridization histochemistry of endogenous Pomc mRNA and immunohistochemical analysis of eGFP revealed that POMC is primarily localized within the caudal NTS. Neurochemical analysis indicated that POMCNTS is not co-expressed with tyrosine hydroxylase (TH), glucagon-like peptide 1 (GLP-1), cholecystokinin (CCK), brain-derived neurotrophic factor (BDNF), nesfatin, nitric oxide synthase 1 (nNOS), seipin, or choline acetyltransferase (ChAT) cells, whereas 100% of POMCNTS is co-expressed with transcription factor paired-like homeobox2b (Phox2b). We observed that 20% of POMCNTS cells express receptors for adipocyte hormone leptin (LepRbs) using a PomceGFP:LepRbCre:tdTOM double-reporter line. Elevations in endogenous or exogenous leptin levels increased the in vivo activity (c-FOS) of a small subset of POMCNTS cells. Using ex vivo slice electrophysiology, we observed that this effect of leptin on POMCNTS cell activity is postsynaptic. These findings reveal that a subset of POMCNTS cells are responsive to both changes in energy status and the adipocyte hormone leptin, findings of relevance to the neurobiology of obesity.

Caralluma fimbriata extract activity involves the 5-HT2c receptor in PWS Snord116 deletion mouse model

INTRODUCTION

In Prader-Willi syndrome (PWS), nonprotein coding small nucleolar (sno) RNAs are involved in the paternally deleted region of chromosome 15q11.2-q13, which is believed to cause the hyperphagic phenotype of PWS. Central to this is SnoRNA116. The supplement Caralluma fimbriata extract (CFE) has been shown to decrease appetite behavior in some individuals with PWS. We therefore investigated the mechanism underpinning the effect of CFE on food intake in the Snord116del mouse. Experiments utilized appetite stimulants which included a 5-hydroxytryptamine (5-HT) 2c receptor antagonist (SB242084), as the 5-HT2cR is implicated in central signaling of satiety.

METHODS

After 9-week chronic CFE treatment (33 mg or 100 mg kg^-1  day^-1 ) or placebo, the 14-week-old Snord116del (SNO) and wild-type mice (n = 72) were rotated through intraperitoneal injections of (a) isotonic saline; (b) 400 mg/kg of 2-deoxyglucose (2DG) (glucose deprivation); (c) 100 mglkg beta-mercaptoacetate (MA), fatty acid signaling; and (d) SB242084 (a selective 5HT2cR antagonist), with 5 days between reagents. Assessments of food intake were from baseline to 4 hr, followed by immunohistochemistry of neural activity utilizing c-Fos, neuropeptide Y, and alpha-melanocyte-stimulating hormone within hypothalamic appetite pathways.

RESULTS

Caralluma fimbriata extract administration decreased food intake more strongly in the SNO100CFE group with significantly stimulated food intake demonstrated during coadministration with SB242084. Though stimulatory deprivation was expected to stimulate food intake, 2DG and MA resulted in lower intake in the snord116del mice compared to the WT animals (p = <0.001). Immunohistochemical mapping of hypothalamic neural activity was consistent with the behavioral studies.

CONCLUSIONS

This study identifies a role for the 5-HT2cR in CFE-induced appetite suppression and significant stimulatory feeding disruptions in the snord116del mouse model.

Neural Programmatic Role of Leptin, TNFα, Melanocortin, and Glutamate in Blood Pressure Regulation vs Obesity-Related Hypertension in Male C57BL/6 Mice

Continuous nutritional surplus sets the stage for hypertension development. Whereas moderate dietary obesity in mice is normotensive, the homeostatic balance is disrupted concurrent with an increased risk of hypertension. However, it remains unclear how the obesity-associated prehypertensive state is converted into overt hypertension. Here, using mice with high-fat-diet (HFD)-induced moderate obesity vs control diet (CD)-fed lean mice, we comparatively studied the effects of central leptin and tumor necrosis factor-α (TNFα) as well as the involvement of the neuropeptide melanocortin pathway vs the neurotransmitter glutamate pathway. Compared with CD-fed lean mice, the pressor effect of central excess leptin and TNFα, but not melanocortin, was sensitized in HFD-fed mice. The pressor effect of central leptin in HFD-fed mice was strongly suppressed by glutamatergic inhibition but not by melanocortinergic inhibition. The pressor effect of central TNFα was substantially reversed by melanocortinergic inhibition in HFD-fed mice but barely in CD-fed mice. Regardless of diet, the hypertensive effects of central TNFα and melanocortin were both partially reversed by glutamatergic suppression. Hence, neural control of blood pressure is mediated by a signaling network between leptin, TNFα, melanocortin, and glutamate and changes in dynamics due to central excess leptin and TNFα mediate the switch from normal physiology to obesity-related hypertension.

Metabolic dysfunction following weight cycling in male mice

Background

Combatting over-weight or obesity can lead to large fluctuations in an individual’s body weight, often referred to as weight cycling or “yo-yo” dieting. Current evidence regarding the potentially damaging effects of these changes is conflicting.

Methods

Here, we assess the metabolic effects of weight cycling in a murine model, comprising three dietary switches to normal or high fat diets at 6 week intervals; male C57BL/6 mice were fed either a control (C) or high fat (F) diet for 6 weeks (n=140/group). C and F groups were then either maintained on their initial diet (CC and FF respectively) or switched to a high fat (CF) or control (FC) diet (n=35/group). For the final 6 week interval, CC and CF groups were returned to the control diet (CCC and CFC groups) while FC and FF groups were placed on a high fat diet (FCF and FFF) (n=28/group).

Results

For the majority of metabolic outcomes changes aligned with dietary switches; however assessment of neuropeptides and receptors involved in appetite regulation and reward signalling pathways reveal variable patterns of expression. Furthermore, we demonstrate that multiple cycling events leads to a significant increase in internal fat deposition, even when compared to animals maintained on a high fat diet (Internal Fat: FCF: 7.4 ± 0.2g vs. FFF: 5.6 ± 0.2g; p<0.01).

Conclusions

Increased internal adipose tissue is strongly linked to the development of metabolic syndrome associated conditions such as type 2 diabetes, cardiovascular disease and hypertension. While further work will be required to elucidate the mechanisms underlying the neuronal control of energy homeostasis, these studies provide a causative link between weight cycling and adverse health.

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.

Systematic Backbone Conformational Constraints on a Cyclic Melanotropin Ligand Leads to Highly Selective Ligands for Multiple Melanocortin Receptors

Human melanocortin receptors (hMCRs) have been challenging targets to develop ligands that are explicitly selective for each of their subtypes. To modulate the conformational preferences of the melanocortin ligands and improve the biofunctional agonist/antagonist activities and selectivities, we have applied a backbone N-methylation approach on Ac-Nle-c[Asp-His-D-Nal(2')-Arg-Trp-Lys]-NH2 (Ac-Nle(4)-c[Asp(5),D-Nal(2')(7),Lys(10)]-NH2), a nonselective cyclic peptide antagonist at hMC3R and hMC4R and an agonist at hMC1R and hMC5R. Systematic N-methylated derivatives of Ac-Nle(4)-c[Asp(5),D-Nal(2')(7),Lys(10)]-NH2, with all possible backbone N-methylation combinations, have been synthesized and examined for their binding and functional activities toward melanocortin receptor subtypes 1, 3, 4, and 5 (hMCRs). Several N-methylated analogues are selective and potent agonists or antagonists for hMC1R or hMC5R or have selective antagonist activity for hMC3R. The selective hMC1R ligands show strong binding for human melanoma cells. We have also discovered the first universal antagonist (compound 19) for all subtypes of hMCRs.

Central vagal afferent endings mediate reduction of food intake by melanocortin-3/4 receptor agonist

Injection of the melanocortin-3/4 receptor agonist melanotan-II (MTII) into the nucleus of the solitary tract (NTS) produces rapid and sustained reduction of food intake. Melanocortin-4 receptors (MC4Rs) are expressed by vagal afferent endings in the NTS, but it is not known whether these endings participate in MTII-induced reduction of food intake. In experiments described here, we evaluated the contribution of central vagal afferent endings in MTII-induced reduction of food intake. Examination of rat hindbrain sections revealed that neuronal processes expressing immunoreactivity for the endogenous MC4R agonist α-melanoctyte-stimulating hormone course parallel and wrap around anterogradely labeled vagal afferent endings in the NTS and thus are aptly positioned to activate vagal afferent MC4Rs. Furthermore, MTII and endogenous MC4R agonists increased protein kinase A (PKA)-catalyzed phosphorylation of synapsin I in vagal afferent endings, an effect known to increase synaptic strength by enhancing neurotransmitter release in other neural systems. Hindbrain injection of a PKA inhibitor, KT5720, significantly attenuated MTII-induced reduction of food intake and the increase in synapsin I phosphorylation. Finally, unilateral nodose ganglion removal, resulting in degeneration of vagal afferent endings in the ipsilateral NTS, abolished MTII-induced synapsin I phosphorylation ipsilateral to nodose ganglion removal. Moreover, reduction of food intake following MTII injection into the NTS ipsilateral to nodose ganglion removal was significantly attenuated, whereas the response to MTII was not diminished when injected into the contralateral NTS. Altogether, our results suggest that reduction of food intake following hindbrain MC4R activation is mediated by central vagal afferent endings.

The gut-brain axis in obesity

Currently the only effective treatment for morbid obesity with a proven mortality benefit is surgical intervention. The underlying mechanisms of these surgical techniques are unclear, but alterations in circulating gut hormone levels have been demonstrated to be at least one contributing factor. Gut hormones seem to communicate information from the gastrointestinal tract to the regulatory appetite centres within the central nervous system (CNS) via the so-called 'Gut-Brain-Axis'. Such information may be transferred to the CNS either via vagal or non-vagal afferent nerve signalling or directly via blood circulation. Complex neural networks, distributed throughout the forebrain and brainstem, are in control of feeding and energy homoeostasis. This article aims to review how appetite is potentially regulated by these gastrointestinal hormones. Identification of the underlying mechanisms of appetite and weight control may pave the way to develop better surgical techniques and new therapies in the future.

Modulation of orexigenic and anorexigenic peptides gene expression in the rat DVC and hypothalamus by acute immobilization stress

We studied the long term effects of a single exposure to immobilization stress (IS) (1 h) on the expression of anorexigenic (Pro-opiomelanocortin: POMC and cocaine amphetamine related transcript: CART) and orexigenic (neuropeptide Y:NPY, Agouti related peptide: AgRP) factors in hypothalamus and dorso vagal complex (DVC). We showed, by using RT-PCR that in the hypothalamus, that the mRNAs of POMC and CART were up-regulated at the end of IS and up to 24 h. This up regulation persists until 48–72 h after IS for CART only. In the DVC, their expressions peak significantly at 24 h post stress and decline afterwards; CART mRNA is down regulated after 48 h post stress. NPY and AgRP mRNAs show a gradual increase just after the end of IS. The up regulation is significant only at 24 h after stress for AgRP but remains significantly higher for NPY compared to controls. In DVC, the mRNAs of the two factors show generally a similar post stress pattern. A significant increase jut after the end of IS of rats which persists up to 24 h after is firstly noticed. The levels tend then to reach the basal levels although, they were slightly but significantly higher up to 72 h after stress for mRNA NPY. The comparison between the expression profiles of anorexigenic and the two orexigenic peptides investigated shows the presence of a parallelism between that of POMC and AgRP and that of CART and NPY when each brain region (hypothalamus and DVC) is considered separately. It seems that any surge in the expression of each anorexigenic factor stimulates the expression of those of corresponding and appropriated orexigenic one. These last reactions from orexigenic peptides tend to attenuate the anorexigenic effects of CART and POMC and by consequent to abolish the anorexia state generated by stress.

Postprandial total ghrelin suppression is modulated by melanocortin signaling in humans

CONTENTS

Ghrelin is implicated in meal initiation because circulating levels increase before and fall after meal consumption. In rodents, ghrelin stimulates food intake via hypothalamic circuits expressing the melanocortin 4 receptor (MC4R).

OBJECTIVE

The aim of the study was to investigate the impact of central melanocortinergic tone on ghrelin secretion in humans. DESIGN/SETTING/PATIENTS/MAIN OUTCOME MEASURE: We measured plasma total ghrelin before and after 3 standardized meals in patients with MC4R mutations and obese and lean controls. Fasting total ghrelin, area under the curve, and early (30-min) and intermeal postprandial total ghrelin suppression (the percentage difference between the premeal and the 30-min postprandial or intermeal nadir total ghrelin concentration) were calculated.

RESULTS

Fasting total ghrelin concentrations and area under the curve for total ghrelin concentrations were significantly decreased in both obese groups compared to lean controls (fasting total ghrelin: lean controls, 1083 ± 203 pg/ml; and obese controls, 696 ± 81 pg/ml; MC4R: 609 ± 99 pg/ml, P < .05). Early and intermeal postprandial total ghrelin suppression was attenuated in MC4R-deficient patients compared to lean controls (P < .05); a similar pattern was observed for early postprandial suppression in comparison with obese controls, but this difference did not reach statistical significance (P = .09).

CONCLUSIONS

These findings are consistent with a role for central melanocortinergic signaling in modulating meal-related total ghrelin suppression.

Melanocortin system in cancer-related cachexia

The melanocortin system plays a pivotal role in the regulation of appetite and energy balance. It was recognized to play an important role in the development of cancer-related cachexia, a debilitating condition characterized by progressive body wasting associated with anorexia, increased resting energy expediture and loss of fat as well as lean body mass that cannot be simply prevented or treated by adequate nutritional support.

The recent advances in understanding of mechanisms underlying cancer-related cachexia led to consequent recognition of the melanocortin system as an important potential therapeutic target. Several molecules have been made available for animal experiments, including those with oral bioavailability, that act at various checkpoints of the melanocortin system and that might confer singificant benefits for the patients suffering from cancer-related cachexia. The application of melanocortin 4 receptor antagonists/agouti-related peptide agonists has been however restricted to animal models and more pharmacological data will be necessary to progress to clinical trials on humans. Still, pharmacological targeting of the melanocortin system seem to represent an elegant and promising way of treatment of cancer-related cachexia.

Bariatric surgery in a patient with complete MC4R deficiency

Bariatric surgery is often successful for treatment of severe obesity. The mechanisms of weight loss after bariatric surgery and the role of central energy homeostatic pathways in this weight loss process are not well understood. The study of individuals with complete loss of function of genes important in the leptin-melanocortin system may help establish the significance of these pathways for weight loss after bariatric surgery. We describe the outcome of bariatric surgery in an adolescent with compound heterozygosity and complete functional loss of both alleles of the melanocortin 4 receptor (MC4R). The patient underwent laparoscopic adjustable gastric banding and truncal vagotomy at years of age, which resulted in initial, but not long-term weight loss. Our experience with this patient suggests that complete MC4R deficiency impairs response to gastric banding and results in poor weight loss after this surgery.

Solid-phase peptide head-to-side chain cyclodimerization: discovery of C(2)-symmetric cyclic lactam hybrid α-melanocyte-stimulating hormone (MSH)/agouti-signaling protein (ASIP) analogues with potent activities at the human melanocortin receptors

A novel hybrid melanocortin pharmacophore was designed based on the pharmacophores of the agouti-signaling protein (ASIP), an endogenous melanocortin antagonist, and α-melanocyte-stimulating hormone (α-MSH), an endogenous melanocortin agonist. The designed hybrid ASIP/MSH pharmacophore was explored in monomeric cyclic, and cyclodimeric templates. The monomeric cyclic disulfide series yielded peptides with hMC3R-selective non-competitive binding affinities. The direct on-resin peptide lactam cyclodimerization yielded nanomolar range (25-120 nM) hMC1R-selective full and partial agonists in the cyclodimeric lactam series which demonstrates an improvement over the previous attempts at hybridization of MSH and agouti protein sequences. The secondary structure-oriented pharmacophore hybridization strategy will prove useful in development of unique allosteric and orthosteric melanocortin receptor modulators. This report also illustrates the utility of peptide cyclodimerization for the development of novel GPCR peptide ligands.

Age-dependence of alpha-MSH-induced anorexia

Long-term regulation of energy balance involves two major trends: first age-related obesity develops in the middle-aged, later it is followed by anorexia of aging (sarcopenia and/or cachexia). A dynamic balance between orexigenic and anorexigenic neuropeptides is essential for the regulation of energy homeostasis. Special imbalances of neuropeptide effects may be assumed corresponding to different age-periods. Anorexia induced by acute alpha-MSH (alpha-melanocyte stimulating hormone; endogenous melanocortin agonist) injections was analyzed in male Wistar rats aged 6-9 weeks (juvenile), 3-4 months (young adult), 6 or 12 months (two middle-aged groups), 18 months (aging) and 24-26 months (old). Alpha-MSH injected through a preimplanted intracerebroventricular (ICV) cannula (compared with saline injection) dose-dependently suppressed spontaneous food intake and also re-feeding following 24-h fasting, but the rate of suppression varied between age-groups. An ICV injection of 5 microg alpha-MSH attenuated the 2-h re-feeding by 21.9+/-3.2% in juvenile rats, strongly (68.7+/-2.5%) suppressed it in young adults, the suppression became progressively weaker in the two middle-aged groups (55.7+/-4.9%, vs. 26.4+/-4.9%, respectively), but it turned extreme in aging (94.7+/-4.2%) and old (74.3+/-4.5%) rats. Body composition also changed with age: unlike the tibialis anterior muscle, the epididymal and retroperitoneal fat pads increased until middle-age and remained large even in old animals, while the measured indicator of muscle mass decreased in the oldest group. The food intake suppressing and body weight decreasing effects of a 7-day-long ICV infusion of 1 microg/h alpha-MSH were weakest in the 12-month-old and most pronounced in the 24 month-old rats. In conclusion, responsiveness to the anorexic effect of alpha-MSH varies with age, with a nadir of the curve in the middle-aged, and a peak in the aging and old animals. This age-related nadir of melanocortin-responsiveness may promote obesity in middle-aged rats, while the tendency for anorexia and incipient sarcopenia of old (still obese) rats may result from age-related melanocortin-hypersensitivity rather than from adiposity.

Effects of meals high in carbohydrate, protein, and fat on ghrelin and peptide YY secretion in prepubertal children

CONTEXT

Ghrelin and peptide YY (PYY) are two hormones produced by the gastrointestinal tract that have effects on appetite. However, little is known about their secretion in response to meals high in individual macronutrients in prepubertal children.

OBJECTIVE

We sought to understand how meals high in carbohydrate, protein, and fat affect serum concentrations of total ghrelin and total PYY, hypothesizing that these macronutrients would exert differential effects on their secretion.

DESIGN AND SETTING

This was a cross-sectional study at one tertiary care center.

SUBJECTS

Subjects were 7- to 11-yr-old healthy normal-weight (NW) and obese (OB) volunteers recruited from local advertisements.

INTERVENTIONS

After an overnight fast, the subjects were given a breakfast high in carbohydrate, protein, or fat at 0800 h. Blood samples for total ghrelin and total PYY were taken at baseline, 30 min, and hourly from 0900 to 1200 h.

MAIN OUTCOME MEASURE

We assessed postprandial ghrelin suppression and PYY elevation, as well as changes in reported hunger and satiety, after the three test meals.

RESULTS

After the high-protein meal, ghrelin declined gradually in both groups over the study period without subsequent increase, whereas ghrelin suppressed more rapidly to a nadir at 60 min after the high-carbohydrate meal in both NW and OB children, followed by rebound in ghrelin levels. Similarly, after the high-protein meal, PYY concentrations increased steadily over the course of the morning in both groups without decline, whereas PYY levels peaked 30 min after the high-carbohydrate meal in both NW and OB subjects with significant decline thereafter. Ghrelin and PYY responses to the high-fat meal were somewhat intermediate between that observed with high carbohydrate and high protein. The OB children reported higher hunger and lower satiety after the high-carbohydrate meal compared to the NW subjects, whereas appetite ratings were similar between the groups after the high-protein and high-fat meals. Additionally, within the OB group, area under the curve (AUC) analysis revealed significantly greater PYY response, as well as lower AUC hunger and higher AUC satiety, to the high-protein meal than the high-carbohydrate and high-fat meals.

CONCLUSIONS

The patterns of secretion of ghrelin and PYY in our study of prepubertal children suggest that they may play a role in the effectiveness of high-protein/low-carbohydrate diets in promoting weight loss.

Pathogenesis of adolescent idiopathic scoliosis in girls - a double neuro-osseous theory involving disharmony between two nervous systems, somatic and autonomic expressed in the spine and trunk: possible dependency on sympathetic nervous system and hormones with implications for medical therapy

Anthropometric data from three groups of adolescent girls - preoperative adolescent idiopathic scoliosis (AIS), screened for scoliosis and normals were analysed by comparing skeletal data between higher and lower body mass index subsets. Unexpected findings for each of skeletal maturation, asymmetries and overgrowth are not explained by prevailing theories of AIS pathogenesis. A speculative pathogenetic theory for girls is formulated after surveying evidence including: (1) the thoracospinal concept for right thoracic AIS in girls; (2) the new neuroskeletal biology relating the sympathetic nervous system to bone formation/resorption and bone growth; (3) white adipose tissue storing triglycerides and the adiposity hormone leptin which functions as satiety hormone and sentinel of energy balance to the hypothalamus for long-term adiposity; and (4) central leptin resistance in obesity and possibly in healthy females. The new theory states that AIS in girls results from developmental disharmony expressed in spine and trunk between autonomic and somatic nervous systems. The autonomic component of this double neuro-osseous theory for AIS pathogenesis in girls involves selectively increased sensitivity of the hypothalamus to circulating leptin (genetically-determined up-regulation possibly involving inhibitory or sensitizing intracellular molecules, such as SOC3, PTP-1B and SH2B1 respectively), with asymmetry as an adverse response (hormesis); this asymmetry is routed bilaterally via the sympathetic nervous system to the growing axial skeleton where it may initiate the scoliosis deformity (leptin-hypothalamic-sympathetic nervous system concept = LHS concept). In some younger preoperative AIS girls, the hypothalamic up-regulation to circulating leptin also involves the somatotropic (growth hormone/IGF) axis which exaggerates the sympathetically-induced asymmetric skeletal effects and contributes to curve progression, a concept with therapeutic implications. In the somatic nervous system, dysfunction of a postural mechanism involving the CNS body schema fails to control, or may induce, the spinal deformity of AIS in girls (escalator concept). Biomechanical factors affecting ribs and/or vertebrae and spinal cord during growth may localize AIS to the thoracic spine and contribute to sagittal spinal shape alterations. The developmental disharmony in spine and trunk is compounded by any osteopenia, biomechanical spinal growth modulation, disc degeneration and platelet calmodulin dysfunction. Methods for testing the theory are outlined. Implications are discussed for neuroendocrine dysfunctions, osteopontin, sympathoactivation, medical therapy, Rett and Prader-Willi syndromes, infantile idiopathic scoliosis, and human evolution. AIS pathogenesis in girls is predicated on two putative normal mechanisms involved in trunk growth, each acquired in evolution and unique to humans.

Obesity, gut hormones, and bariatric surgery

Obesity is becoming the healthcare epidemic of this century. Bariatric surgery is the only effective treatment for morbid obesity. Gut hormones are key players in the metabolic mechanisms causing obesity. In this review we explore the role of these hormones as facilitators of appetite control and weight loss after bariatric surgery, and we describe the now established gut-brain axis.

Sir David Cuthbertson Medal Lecture. Bariatric surgery as a model to study appetite control

The obesity epidemic and its associated morbidity and mortality have led to major research efforts to identify mechanisms that regulate appetite. Gut hormones have recently been found to be an important element in appetite regulation as a result of the signals from the periphery to the brain. Candidate hormones include ghrelin, peptide YY, glucagon-like peptide-1 and gastric inhibitory polypeptide, all of which are currently being investigated as potential obesity treatments. Bariatric surgery is currently the most effective therapy for substantial and sustained weight loss. Understanding how levels of gut hormones are modulated by such procedures has greatly contributed to the comprehension of the underlying mechanisms of appetite and obesity. The present paper is a review of how appetite and levels of gastrointestinal hormones are altered after bariatric surgery. Basic principles of common bariatric procedures and potential mechanisms for appetite regulation by gut hormones are also addressed.

Role of central melanocortin pathways in energy homeostasis

The rise in the global prevalence of human obesity has emphasized the need for a greater understanding of the physiological mechanisms that underlie energy homeostasis. Numerous circulating nutritional cues and central neuromodulatory signals are integrated within the brain to regulate both short- and long-term nutritional state. The central melanocortin system represents a crucial point of convergence for these signals and, thus, has a fundamental role in regulating body weight. The melanocortin ligands, synthesized in discrete neuronal populations within the hypothalamus and brainstem, modulate downstream homeostatic signalling via their action at central melanocortin-3 and -4 receptors. Intimately involved in both ingestive behaviour and energy expenditure, the melanocortin system has garnered much interest as a potential therapeutic target for human obesity.

The STEDMAN project: biophysical, biochemical and metabolic effects of a behavioral weight loss intervention during weight loss, maintenance, and regain

The Study of the Effects of Diet on Metabolism and Nutrition (STEDMAN) Project uses comprehensive metabolic profiling to probe biochemical mechanisms of weight loss in humans. Measurements at baseline, 2 and 4 weeks, 6 and 12 months included diet, body composition, metabolic rate, hormones, and 80 intermediary metabolites measured by mass spectrometry. In 27 obese adults in a behavioral weight loss intervention, median weight decreased 13.9 lb over the first 6 months, then reverted towards baseline by 12 months. Insulin resistance (HOMA) was partially ameliorated in the first 6 months and showed sustained improvement at 12 months despite weight regain. Ghrelin increased with weight loss and reverted to baseline, whereas leptin and PYY fell at 6 months and remained persistently low. NPY levels did not change. Factors possibly contributing to sustained improvement in insulin sensitivity despite weight regain include adiponectin (increased by 12 months), IGF-1 (increased during weight loss and continued to increase during weight regain), and visceral fat (fell at 6 months but did not change thereafter). We observed a persistent reduction in free fatty acids, branched chain amino acids, and related metabolites that may contribute to improved insulin action. These findings provide evidence for sustained benefits of weight loss in obese humans and insights into mechanisms.

Changes in gut hormones after bariatric surgery

Bariatric surgery is one of the most effective treatments for achieving long-term weight loss in morbidly obese patients. Bariatric surgery causes weight loss through substantial decline of hunger and increased satiety. Recently our understanding of neuroendocrine regulation of food intake and weight gain, especially regarding the role of gut hormones, has significantly increased. The changes in these hormones following bariatric surgery can partly explain the mechanism behind weight loss achieved through these procedures. In this paper, we review the effect bariatric procedures have on different gut hormone levels and how they in turn can alter the complex neuroendocrine regulation of energy homeostasis.

The putative role of neuropeptide autoantibodies in anorexia nervosa

PURPOSE OF REVIEW

Anorexia nervosa remains a disease of unknown etiology. This situation explains the failure to develop effective therapy and emphasizes the fact that the neurobiological mechanisms of appetite and emotion are still incompletely understood. The present review is the first summary of recent research assigning to the immune system a new role in energy and emotional regulation by the production of autoantibodies directed against neuropeptides. The results of this research are promising to shed light on the etiology of eating disorders and open new fields for biological diagnosis and follow-up as well as designing new therapeutic strategies.

RECENT FINDINGS

Following the initial identification of autoantibodies against alpha-melanocyte-stimulating hormone, a key neuropeptide involved in the regulation of satiety and mood, in the plasma of patients with anorexia and bulimia nervosa, it has been further found that the serum levels of these autoantibodies correlated with psychopathological traits in individuals with eating disorders. Furthermore, recent findings show that autoantibodies against alpha-melanocyte-stimulating hormone and against some other appetite-regulating peptide hormones are normally present in the blood of humans and rats and their production may be influenced by stress and the gut microflora.

SUMMARY

Novel data provide evidence that autoantibodies against neuropeptides can be involved in the regulation of appetite and emotion and that alteration in autoantibody-mediated signaling pathways may be responsible for the development of eating disorders.

Mechanisms of disease: the role of gastrointestinal hormones in appetite and obesity

The obesity epidemic is fast becoming one of the leading causes of mortality and morbidity worldwide. Over the past 30 years, gastrointestinal hormones have been increasingly understood to have an important role as regulators of appetite and energy balance in obese individuals. The levels of these hormones are modulated by bariatric surgery, and understanding how they are affected by such procedures can contribute to our comprehension of the underlying mechanisms by which these hormones affect obesity and its treatment. In this Review, we consider several gastrointestinal hormones that can contribute to obesity by modulating the activity of the gut-brain axis, and examine their specific effects on appetite, hunger and energy balance. Better understanding of the mechanisms by which these peptides exert their effects may enable the development of improved weight-loss medications and new treatments for obesity.

The satiety hormone peptide YY as a regulator of appetite

Obesity is a major cause of premature death in the UK, and may contribute to as many as 30 000 deaths a year in the UK. Although effective treatment for obesity is still awaited, many developments have occurred to improve our understanding of neuroendocrine regulation of food intake and weight gain, especially regarding the role of gut hormones. One such gut hormone is peptide tyrosine-tyrosine also known as PYY where Y depicts the abbreviation for tyrosine. PYY is a 36 amino acid hormone, first isolated from porcine intestine. PYY, along with few other gut hormones, has been suggested as a potential therapeutic agent for obesity. This review examines the relationship of PYY to appetite regulation, energy homeostasis and the relevant neuroendocrine feedback mechanism.

Pathogenic potential of adipose tissue and metabolic consequences of adipocyte hypertrophy and increased visceral adiposity

When caloric intake exceeds caloric expenditure, the positive caloric balance and storage of energy in adipose tissue often causes adipocyte hypertrophy and visceral adipose tissue accumulation. These pathogenic anatomic abnormalities may incite metabolic and immune responses that promote Type 2 diabetes mellitus, hypertension and dyslipidemia. These are the most common metabolic diseases managed by clinicians and are all major cardiovascular disease risk factors. 'Disease' is traditionally characterized as anatomic and physiologic abnormalities of an organ or organ system that contributes to adverse health consequences. Using this definition, pathogenic adipose tissue is no less a disease than diseases of other body organs. This review describes the consequences of pathogenic fat cell hypertrophy and visceral adiposity, emphasizing the mechanistic contributions of genetic and environmental predispositions, adipogenesis, fat storage, free fatty acid metabolism, adipocyte factors and inflammation. Appreciating the full pathogenic potential of adipose tissue requires an integrated perspective, recognizing the importance of 'cross-talk' and interactions between adipose tissue and other body systems. Thus, the adverse metabolic consequences that accompany fat cell hypertrophy and visceral adiposity are best viewed as a pathologic partnership between the pathogenic potential adipose tissue and the inherited or acquired limitations and/or impairments of other body organs. A better understanding of the physiological and pathological interplay of pathogenic adipose tissue with other organs and organ systems may assist in developing better strategies in treating metabolic disease and reducing cardiovascular disease risk.

LRb signals act within a distributed network of leptin-responsive neurones to mediate leptin action

The adipose tissue-derived hormone, leptin, acts via its receptor (LRb) in the brain to regulate energy balance and neuroendocrine function. In order to understand leptin action we have explored the physiological function of LRb signalling pathways, defining important roles for signal transducer and activator of transcription-3 (STAT3) in positive signalling and for LRbTyr(985)-mediated feedback inhibition in leptin signal attenuation. As the cells on which leptin acts are not homogeneous, but rather represent a broadly distributed network of neurones with divergent projections and functions, it is also crucial to consider how each of these populations responds to LRb signals to contribute to leptin action. While well-known LRb-expressing neurones within the arcuate nucleus of the hypothalamus mediate crucial effects on satiety and energy expenditure, other populations of LRb-expressing neurones in the ventral tegmental area and elsewhere likely control the mesolimbic dopamine system. Additional populations of LRb-expressing neurones likely contribute to other aspects of neuroendocrine regulation. It will be important to define the molecular mechanisms by which leptin acts to regulate neurophysiology in each of these LRb-expressing neural populations in order to understand the totality of leptin action.

Regulation of prohormone convertases in hypothalamic neurons: implications for prothyrotropin-releasing hormone and proopiomelanocortin

Recent evidence demonstrated that posttranslational processing of neuropeptides is critical in the pathogenesis of obesity. Leptin or other physiological changes affects the biosynthesis and processing of many peptides hormones as well as the regulation of the family of prohormone convertases responsible for the maturation of these hormones. Regulation of energy balance by leptin involves regulation of several proneuropeptides such as proTRH and proopiomelanocortin. These proneuropeptide precursors require for their maturation proteolytic cleavage by the prohormone convertases 1 and 2 (PC1/3 and PC2). Because biosynthesis of mature peptides in response to leptin requires prohormone processing, it is hypothesized that leptin might regulate hypothalamic PC1/3 and PC2 expression, ultimately leading to coordinated processing of prohormones into mature peptides. Leptin has been shown to increase PC1/3 and PC2 promoter activities, and starvation of rats, leading to low serum leptin levels, resulted in a decrease in PC1/3 and PC2 gene and protein expression in the paraventricular and arcuate nucleus of the hypothalamus. Changes in nutritional status also changes proopiomelanocortin processing in the nucleus of the solitary tract, but this is not reversed by leptin. The PCs are also physiologically regulated by states of hyperthyroidism, hyperglycemia, inflammation, and suckling, and a recently discovered nescient helix-loop-helix-2 transcription factor is the first one to show an ability to regulate the transcription of PC1/3 and PC2. Therefore, the coupled regulation of proneuropeptide/processing enzymes may be a common process, by which cells generate more effective processing of prohormones into mature peptides.

Bang-bang control of feeding: role of hypothalamic and satiety signals

Rats, people, and many other omnivores eat in meals rather than continuously. We show by experimental test that eating in meals is regulated by a simple bang-bang control system, an idea foreshadowed by Le Magnen and many others, shown by us to account for a wide range of behavioral data, but never explicitly tested or tied to neurophysiological facts. The hypothesis is simply that the tendency to eat rises with time at a rate determined by satiety signals. When these signals fall below a set point, eating begins, in on-off fashion. The delayed sequelae of eating increment the satiety signals, which eventually turn eating off. Thus, under free conditions, the organism eats in bouts separated by noneating activities. We report an experiment with rats to test novel predictions about meal patterns that are not explained by existing homeostatic approaches. Access to food was systematically but unpredictably interrupted just as the animal tried to start a new meal. A simple bang-bang model fits the resulting meal-pattern data well, and its elements can be identified with neurophysiological processes. Hypothalamic inputs can provide the set point for longer-term regulation carried out by a comparator in the hindbrain. Delayed gustatory and gastrointestinal aftereffects of eating act via the nucleus of the solitary tract and other hindbrain regions as neural feedback governing short-term regulation. In this way, the model forges real links between a functioning feedback mechanism, neuro-hormonal data, and both short-term (meals) and long-term (eating-rate regulation) behavioral data.

Differential effects of fasting and leptin on proopiomelanocortin peptides in the arcuate nucleus and in the nucleus of the solitary tract

The alpha-melanocyte-stimulating hormone (alpha-MSH), derived from proopiomelanocortin (POMC), is generated by a posttranslational processing mechanism involving the prohormone convertases (PCs) PC1/3 and PC2. In the brain, alpha-MSH is produced in the arcuate nucleus (ARC) of the hypothalamus and in the nucleus of the solitary tract (NTS) of the medulla. This peptide is key in controlling energy balance, as judged by changes observed at transcriptional level. However, little information is available regarding the biosynthesis of the precursor POMC and the production of its processed peptides during feeding, fasting, and fasting plus leptin in the ARC compared with the NTS in conjunction with the PC activity. In this study we found that, in the ARC, pomc mRNA, POMC-derived peptides, and PC1/3 all decreased during fasting, and administration of leptin reversed these effects. In contrast, in the NTS, where there is a large amount of a 28.1-kDa peptide similar in size to POMC, the 28.1-kDa peptide and other POMC-derived peptides, including alpha-MSH, were further accumulated in fasting conditions, whereas pomc mRNA decreased. These changes were not reversed by leptin. We also observed that, during fasting, PC2 levels decreased in the NTS. These data suggest that, in the NTS, fasting induced changes in POMC biosynthesis, and processing is independent of leptin. These observations indicate that changes in energy status affect POMC in the brain in a tissue-specific manner. This represents a novel aspect in the regulation of energy balance and may have implications in the pathophysiology of obesity.

Integrative capacity of the caudal brainstem in the control of food intake

The caudal brainstem nucleus of the solitary tract (NTS) is the initial central nervous system (CNS) terminus for a variety of gastrointestinal mechanical, nutrient chemical and gut peptide signals that limit the amount of food consumed during a meal. It receives neuroanatomical projections from gut vagal and non-vagal visceral afferents that mediate the CNS representation of these meal-stimulated gut feedback signals, and is reciprocally connected to a range of hypothalamic and limbic system sites that play significant roles in the neural processing of meal-related stimuli and in determining food consumption. Neurons in the NTS also contains elements of leptinergic and melanocortinergic signalling systems, presenting the possibility that the brainstem actions of these neuropeptides affect both the NTS processing of meal-stimulated gut afferent neural activity and its behavioural potency. Taken together, these features suggest that the NTS is ideally situated to integrate central and peripheral signals that determine meal size. This manuscript will review recent support from molecular genetic, neurophysiological and immunocytochemical studies that begin to identify and characterize the types of integrative functions performed within the NTS, and highlight the extent to which they are consistent with a causal role for NTS integration of peripheral gut and central neuropeptide signals important in the control of food intake.