Vaccination against weight gain

Current trends in targeting the hormonal regulation of appetite and energy balance to treat obesity

With the eruption of the obesity pandemic over the past few decades, much research has been devoted to understanding the molecular mechanisms by which the human body regulates energy balance. These studies have revealed several mediators, including gut/pancreatic/adipose hormones and neuropeptides that control both short- and long-term energy balance by regulating appetite and/or metabolism. These endogenous mediators of energy balance have been the focus of many anti-obesity drug-development programs aimed at either amplifying endogenous anorexigenic/lipolytic signaling or blocking endogenous orexigenic/lipogenic signaling. Here, we discuss the efficacy and safety of targeting these pathways for the pharmacologic treatment of obesity.

Obesity treatment: novel peripheral targets

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

Central and peripheral molecular targets for antiobesity pharmacotherapy

Obesity has emerged as one of the principal worldwide health concerns of the modern era, and there exists a tremendous unmet clinical need for safe and effective therapies to combat this global pandemic. The prevalence of obesity and its associated comorbidities, including cardiovascular and metabolic diseases, has focused the attention of those in drug discovery and development on generating effective modalities for the treatment and prevention of obesity. Early efforts in the field of obesity pharmacotherapy centered on the development of agents with indeterminate mechanisms of action. This led to treatment paradigms characterized by significant off-target effects. In the past two decades, new insights have been made into the physiologic regulation of energy balance and the subordinate central and peripheral circuits coordinating appetite, metabolism, and lipogenesis. These studies have revealed previously unrecognized molecular targets for controlling appetite and managing weight from which has emerged a new wave of targeted pharmacotherapies to prevent and control obesity.

Ghrelin in diabetes and metabolic syndrome

Metabolic syndrome is a cluster of related risk factors for cardiovascular disease, type 2 diabetes and liver disease. Obesity, which has become a global public health problem, is one of the major risk factors for development of metabolic syndrome and type 2 diabetes. Obesity is a complex disease, caused by the interplay between environmental and genetic factors. Ghrelin is one of the circulating peptides, which stimulates appetite and regulates energy balance, and thus is one of the candidate genes for obesity and T2DM. During the last years both basic research and genetic association studies have revealed association between the ghrelin gene and obesity, metabolic syndrome or type 2 diabetes.

Inflammatory and autoimmune reactions in atherosclerosis and vaccine design informatics

Atherosclerosis is the leading pathological contributor to cardiovascular morbidity and mortality worldwide. As its complex pathogenesis has been gradually unwoven, the regime of treatments and therapies has increased with still much ground to cover. Active research in the past decade has attempted to develop antiatherosclerosis vaccines with some positive results. Nevertheless, it remains to develop a vaccine against atherosclerosis with high affinity, specificity, efficiency, and minimal undesirable pathology. In this review, we explore vaccine development against atherosclerosis by interpolating a number of novel findings in the fields of vascular biology, immunology, and bioinformatics. With recent technological breakthroughs, vaccine development affords precision in specifying the nature of the desired immune response—useful when addressing a disease as complex as atherosclerosis with a manifold of inflammatory and autoimmune components. Moreover, our exploration of available bioinformatic tools for epitope-based vaccine design provides a method to avoid expenditure of excess time or resources.

The role of gut hormones in the regulation of body weight and energy homeostasis

Obesity is one of the greatest public health challenges of the 21st century with 1.6 billion adults currently classified as being overweight and 400 million as obese. Obesity is causally associated with type 2 diabetes, hypertension, cardiovascular disease, obstructive sleep apnoea and certain forms of cancer and is now one of the leading causes of mortality and morbidity worldwide. The gastrointestinal tract is the largest endocrine organ in the body producing hormones that have important sensing and signaling roles in regulating body weight and energy expenditure. The last decade has witnessed a marked increase in our understanding of the role of gut hormones in energy homeostasis. Consequently, strategies aimed at modulating circulating gut hormone concentrations or targeting their receptors are being developed as potential pharmacotherapies for obesity. This review summarizes the current knowledge regarding the mechanisms, sites of action and effects of the anorectic gut hormones peptide tyrosine-tyrosine (PYY), pancreatic polypeptide (PP), oxyntomodulin, and amylin and of the unique orexigenic hormone, ghrelin.

Ghrelin effects on neuropeptides in the rat hypothalamus depend on fatty acid metabolism actions on BSX but not on gender

The orexigenic effect of ghrelin is mediated by neuropeptide Y (NPY) and agouti-related protein (AgRP) in the hypothalamic arcuate nucleus (ARC). Recent evidence also indicates that ghrelin promotes feeding through a mechanism involving activation of hypothalamic AMP-activated protein kinase (AMPK) and inactivation of acetyl-CoA carboxylase and fatty acid synthase (FAS). This results in decreased hypothalamic levels of malonyl-CoA, increased carnitine palmitoyltransferase 1 (CPT1) activity, and mitochondrial production of reactive oxygen species. We evaluated whether these molecular events are part of a unique signaling cascade or whether they represent alternative pathways mediating the orexigenic effect of ghrelin. Moreover, we examined the gender dependency of these mechanisms, because recent evidence has proposed that ghrelin orexigenic effect is reduced in female rats. We studied in both genders the effect of ghrelin on the expression of AgRP and NPY, as well as their transcription factors: cAMP response-element binding protein (CREB and its phosphorylated form, pCREB), forkhead box O1 (FoxO1 and its phosphorylated form, pFoxO1), and brain-specific homeobox transcription factor (BSX). In addition, to establish a mechanistic link between ghrelin, fatty acid metabolism, and neuropeptides, we evaluated the effect of ghrelin after blockage of hypothalamic fatty acid beta oxidation, by using the CPT1 inhibitor etomoxir. Ghrelin-induced changes in the AMPK-CPT1 pathway are associated with increased levels of AgRP and NPY mRNA expression through modulation of BSX, pCREB, and FoxO1, as well as decreased expression of endoplasmic reticulum (ER) stress markers in a gender-independent manner. In addition, blockage of hypothalamic fatty acid beta oxidation prevents the ghrelin-promoting action on AgRP and NPY mRNA expression, also in a gender-independent manner. Notably, this effect is associated with decreased BSX expression and reduced food intake. Overall, our data suggest that BSX integrates changes in neuronal metabolic status with ARC-derived neuropeptides in a gender-independent manner.

Integrating GHS into the Ghrelin System

Oligopeptide derivatives of metenkephalin were found to stimulate growth-hormone (GH) release directly by pituitary somatotrope cells in vitro in 1977. Members of this class of peptides and nonpeptidyl mimetics are referred to as GH secretagogues (GHSs). A specific guanosine triphosphatate-binding protein-associated heptahelical transmembrane receptor for GHS was cloned in 1996. An endogenous ligand for the GHS receptor, acylghrelin, was identified in 1999. Expression of ghrelin and homonymous receptor occurs in the brain, pituitary gland, stomach, endothelium/vascular smooth muscle, pancreas, placenta, intestine, heart, bone, and other tissues. Principal actions of this peptidergic system include stimulation of GH release via combined hypothalamopituitary mechanisms, orexigenesis (appetitive enhancement), insulinostasis (inhibition of insulin secretion), cardiovascular effects (decreased mean arterial pressure and vasodilation), stimulation of gastric motility and acid secretion, adipogenesis with repression of fat oxidation, and antiapoptosis (antagonism of endothelial, neuronal, and cardiomyocyte death). The array of known and proposed interactions of ghrelin with key metabolic signals makes ghrelin and its receptor prime targets for drug development.

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

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

Regulation of food intake: the gastric X/A-like endocrine cell in the spotlight

Nutritional status influences hormone secretion from specialized enteroendocrine cells within the gut mucosa. These hormones regulate food intake by mediating information to central neurocircuitries in the brainstem and forebrain (eg, hypothalamic nuclei). Intestinal enteroendocrine cells were believed to be the main source of gut peptides regulating food intake. However, recent evidence highlights a specific endocrine cell within the oxyntic glands of the stomach as an important player in appetite control. Acylated ghrelin is the only known orexigenic hormone peripherally produced in gastric X/A-like cells and centrally acting to stimulate food intake. Recent advances led to the assumption that des-acylated ghrelin, coreleased with acylated ghrelin, is also involved in regulating food intake. This, and the novel observation that nesfatin-1, which inhibits food intake, is expressed in ghrelin-producing cells of the stomach, supports an important role for gastric X/A-like cells in regulating food intake. Another peptide, obestatin, was initially described as a ghrelin gene product inhibiting food intake, but subsequent studies produced controversial data and its action as an anorexic factor is doubtful. Importantly, synergistic interactions between ghrelin and intestinal peptides seem to orchestrate food intake and body weight regulation, which may have implications for understanding mechanisms leading to the treatment of obesity.

Safety and efficacy trial of adipose-tissue derived oral preparation V-6 Immunitor (V-6): results of open-label, two-month, follow-up study

Background

Chronic inflammations, atherosclerosis and obesity, are major risk factors for cardiovascular diseases. Immune modulation of the inflammatory response has shown promise in animal models of atherogenesis and metabolic disease. Tableted dietary supplement, V-6, containing pooled antigens derived from pig adipose tissue has been administered daily to 12 volunteers for 2 months.

Results

No significant changes were observed in liver ALT and AST enzymes, i.e., 28 vs 23.8 IU and 22.6 vs 24.8 IU, with p = 0.07 and p = 0.49, respectively. Creatinine decreased; 0.88 vs 0.84 mg/dL (p = 0.05) while BUN moved upward; 14.5 vs 17.5 mg/dL (p = 0.01), but both values remained within normal range. Blood glucose remained within normal range; 96.1 vs 101.1 mg/dL (p = 0.04). Complete blood cell analysis has not revealed any change except slight increase in hemoglobin; 13.13 to 13.96 g/dL (p = 0.0002); hematocrit and red blood cells count 40.3 to 42.3% (p = 0.02) and 5.15 to 5.35 × 10⁶ cells/mm³ (p = 0.03) respectively. Blood pressure systolic and diastolic values were not affected, i.e., 116.1 vs 116.3 (p = 0.12) and 76.8 vs 76.6 (p = 0.99). Body weight and body mass index (BMI) remained same; 66.4 vs 66.3 kg (p = 0.47) and 25.7 vs 25.6 kg/m² (p = 0.2). Body fat deposit indices, such as abdomen; mid-arm; and thigh circumferences declined by 3.5 cm (p = 0.008); 1.2 cm (p = 0.004); and 3.0 cm (p = 0.0007) respectively. The total cholesterol and LDL levels did not change; 195.5 vs 195.1 (-0.2%; p = 0.8) and 113.4 vs 120.3 (6.1%; p = 0.08) respectively. Triglycerides have been reduced but not statistically significant; 168.1 vs 118 mg/dL (-29.8%; p = 0.2). In contrast, HDL content had risen by 29.7% from 39.4 to 51.1 mg/dL in all 12 patients (p = 0.000003). TG/HDL ratio - a marker of insulin resistance - was reduced from 4.78 to 2.56 (-46.5%; p = 0.04).

Conclusions

These results demonstrate that V-6 is safe and has a potential as an anti-atherogenic and overweight/obesity immune intervention.

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

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

Approved and Off-Label Uses of Obesity Medications, and Potential New Pharmacologic Treatment Options

Available anti-obesity pharmacotherapy options remain very limited and development of more effective drugs has become a priority. The potential strategies to achieve weight loss are to reduce energy intake by stimulating anorexigenic signals or by blocking orexigenic signals, and to increase energy expenditure. This review will focus on approved obesity medications, as well as potential new pharmacologic treatment options.

Ghrelin in the regulation of body weight and metabolism

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

Ghrelin vaccination decreases plasma MCP-1 level in LDLR(-/-)-mice

Ghrelin is a novel peptide hormone having growth hormone releasing activity and many endocrine and metabolic functions. In rats and pigs, ghrelin immunizations have recently been shown to induce an antibody response against ghrelin simultaneously with a decrease in body weight gain. Our aim was to test the role of ghrelin immunization on atherosclerosis and weight gain in mice. LDLR(-/-)-mice (n=36) were immunized with ghrelin-PADRE, PADRE alone and PBS and then placed on a high fat diet for 22 weeks. Weight gain and food intake were followed throughout the study. Acylated and total ghrelin, cytokines and MCP-1 were analyzed from plasma using commercial kits. Stomach ghrelin was assessed using qRT-PCR and immunohistochemistry. Atherosclerosis was determined from aorta and cross-sections at the end of study. Mice immunized with ghrelin-PADRE developed high plasma IgG titers to ghrelin simultaneously with a significant increase in plasma acylated and total ghrelin levels. Plasma MCP-1 levels decreased in mice immunized with ghrelin-PADRE compared to mice immunized with PADRE and PBS. There were no differences in atherosclerosis determined from aorta and cross-sections as well as in body weights and food intake in LDLR(-/-)-mice between the different immunization groups. Our data indicates that ghrelin-PADRE vaccination induces a strong exclusive IgG response to ghrelin and increases plasma acylated and total ghrelin levels in mice. Ghrelin vaccination decreases plasma MCP-1 levels even though no effects on developing signs of atherosclerosis or weight gain in mice were observed.

21st century endocrinology

Recent developments in the field of diabetes and endocrinology have led to greater understanding of the body's complex hormonal axes. This article reviews the latest significant treatments which have the potential to impact greatly on a wide variety of disease states in the not too distant future.

Effect of reducing hypothalamic ghrelin receptor gene expression on energy balance

Central and peripheral injections of fghrelin potently stimulates food intake via its receptor, GHSR1a expressed in the brain. In this study, we explored the role of GHSR1a in the paraventricular nucleus of the hypothalamus (PVN) by reducing their gene expression using the RNA interference (RNAi). pSUPER plasmids inserted with sh (short hairpin)-GHSR1a were injected into the PVN to reduce its expression. The transfected rats were monitored daily for their food intake and body weight throughout the experimental period lasting 8 days. We found that knockdown of GHSR1a did not affect daily food intake but significantly reduced body weight and blood ghrelin levels. This suggests that the central ghrelin system could selectively regulate body weight without affecting energy intake.

Colocalization of ghrelin O-acyltransferase and ghrelin in gastric mucosal cells

Ghrelin is a peptide hormone with many known functions, including orexigenic, blood glucose-regulatory, and antidepressant actions, among others. Mature ghrelin is unique in that it is the only known naturally occurring peptide to be posttranslationally modified by O-acylation with octanoate. This acylation is required for many of ghrelin's actions, including its effects on promoting increases in food intake and body weight. GOAT (ghrelin O-acyltransferase), one of 16 members of the MBOAT family of membrane-bound O-acyltransferases, has recently been identified as the enzyme responsible for catalyzing the addition of the octanoyl group to ghrelin. Although the initial reports of GOAT have localized its encoding mRNA to tissues known to contain ghrelin, it is as yet unclear whether the octanoylation occurs within ghrelin-producing cells or in neighboring cells. Here, we have performed dual-label histochemical analysis on mouse stomach sections and quantitative PCR on mRNAs from highly enriched pools of mouse gastric ghrelin cells to demonstrate a high degree of GOAT mRNA expression within ghrelin-producing cells of the gastric oxyntic mucosa. We also demonstrate that GOAT is the only member of the MBOAT family whose expression is highly enriched within gastric ghrelin cells and whose whole body distribution mirrors that of ghrelin.

Lean mean fat reducing "ghrelin" machine: hypothalamic ghrelin and ghrelin receptors as therapeutic targets in obesity

Obesity has reached epidemic proportions not only in Western societies but also in the developing world. Current pharmacological treatments for obesity are either lacking in efficacy and/or are burdened with adverse side effects. Thus, novel strategies are required. A better understanding of the intricate molecular pathways controlling energy homeostasis may lead to novel therapeutic intervention. The circulating hormone, ghrelin represents a major target in the molecular signalling regulating food intake, appetite and energy expenditure and its circulating levels often display aberrant signalling in obesity. Ghrelin exerts its central orexigenic action mainly in the hypothalamus and in particular in the arcuate nucleus via activation of specific G-protein coupled receptors (GHS-R). In this review we describe current pharmacological models of how ghrelin regulates food intake and how manipulating ghrelin signalling may give novel insight into developing better and more selective anti-obesity drugs. Accumulating data suggests multiple ghrelin variants and additional receptors exist to play a role in energy metabolism and these may well play an important role in obesity. In addition, the recent findings of hypothalamic GHS-R crosstalk and heterodimerization may add to the understanding of the complexity of bodyweight regulation.

Gut hormones: implications for the treatment of obesity

Bariatric surgery is the only effective treatment for patients with morbid obesity. This is no solution to the present obesity pandemic however. Currently licensed non-surgical pharmaceuticals are of limited efficacy and alternatives are needed. Harnessing the body's own appetite-regulating signals is a desirable pharmacological strategy. The gastrointestinal tract has a prime role in sensing and signalling food intake to the brain. Gut hormones are key mediators of this information, including: peptide YY (PYY), pancreatic polypeptide (PP), glucagon-like peptide 1 (GLP-1), oxyntomodulin (OXM), ghrelin, amylin and cholecystokinin (CCK). This review summarises the latest knowledge regarding the physiological and pathophysiological role of gut hormones in regulating our food intake and how this knowledge could guide, or has guided, the development of weight-loss drugs. Up-to-date outcomes of clinical trials are evaluated and directions for the future suggested.

Regulation of feeding and anxiety by alpha-MSH reactive autoantibodies

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a stress-related neuropeptide involved in the regulation of motivated behavior, appetite and emotion including stimulation of satiety and anxiety. Although autoantibodies (autoAbs) reactive with alpha-MSH have been identified in human subjects and in rats, it remained unknown if these autoAbs are involved in the regulation of feeding and anxiety and if their production is related to stress. Here we show that repeated exposure of rats to anxiolytic mild stress by handling increases the levels and affinity of alpha-MSH reactive IgG autoAbs and that these changes are associated with adaptive feeding and anxiety responses during exposure of rats to a strong stress by food restriction. Importantly, an increase in affinity of alpha-MSH reactive autoAbs was associated with changes of their functional roles from stimulation to inhibition of alpha-MSH-mediated behavioural responses, suggesting that these autoAbs can be a carrier or a neutralizing molecule of alpha-MSH peptide, respectively. Using a model of passive transfer into the brain, we show that alpha-MSH autoAbs affinity purified from blood of rats exposed to repeated mild stress, but not from control rats, are able to increase acutely food intake, suppress anxiety and modify gene expression of hypothalamic neuropeptides in naïve rats. These data provide the first evidence that autoAbs reactive with alpha-MSH are involved in the physiological regulation of feeding and mood, supporting a further role of the immune system in the control of motivated behavior and adaptation to stress.

Vaccines in development to prevent and treat atherosclerotic disease

Coronary heart disease (CHD) remains the leading cause of death in the United States. Immune mechanisms have been recently proposed to play an important role in the development of atherosclerotic plaques in CHD. Heat shock proteins and oxidized low-density lipoprotein are proinflammatory substances that have been shown to have an important role in the pathogenesis of atherosclerosis, and are now targets for clinical vaccine development. In addition, a vaccine has been developed to inhibit cholesteryl ester transfer protein. It is now recognized that many medications used to combat plaque development and rupture have significant anti-inflammatory effects and these effects are critical for drug efficacy. The influenza vaccine is associated with an atheroprotective effect. In addition, a nicotine vaccine, an antiangiotensin vaccine, and an anti-obesity vaccine may play a therapeutic role in modifying known risk factors for the development of atherosclerosis and its complications. This article reviews these vaccines as possible additions to the armamentarium of atheroprotective treatment modalities.

Catalytic antibody degradation of ghrelin increases whole-body metabolic rate and reduces refeeding in fasting mice

Obesity is a chronic, costly, and globally prevalent condition, with excess caloric intake a suspected etiologic factor. Nonsurgical treatments are modestly efficacious, and weight loss maintenance is hampered by anti-famine homeostatic mechanisms. Ghrelin, a gastric hormone linked to meal initiation, energy expenditure, and fuel partitioning, is hypothesized to facilitate weight gain and impede weight loss. Unique among known animal peptides, the serine-3 residue of ghrelin is posttranslationally acylated with an n-octanoic acid, a modification important for the peptide's active blood-brain transport and growth hormone secretagogue receptor-1 agonist activity. Pharmacological degradation of ghrelin would be hypothesized to reduce ghrelin's biological effects. To study endogenous ghrelin's role in appetite and energy expenditure, we generated antibodies that hydrolyze the octanoyl moiety of ghrelin to form des-acyl ghrelin. The most proficient antibody catalyst, GHR-11E11, was found to display a second-order rate constant of 18 M(-1) x s(-1) for the hydrolysis of ghrelin to des-acyl ghrelin. I.v. administration of GHR-11E11 (50 mg/kg) maintained a greater metabolic rate in fasting C57BL/6J mice as compared with mice receiving a control antibody and suppressed 6-h refeeding after 24 h of food deprivation. Indirect respiratory measures of metabolism after refeeding and relative fuel substrate utilization were unaffected. The results support the hypothesis that acylated ghrelin stimulates appetite and curbs energy expenditure during deficient energy intake, whereas des-acyl ghrelin does not potently share these functions. Catalytic anti-ghrelin antibodies might thereby adjunctively aid consolidation of caloric restriction-induced weight loss and might also be therapeutically relevant to Prader-Willi syndrome, characterized after infancy by hyperghrelinemia, hyperphagia, and obesity.

Ghrelin and ghrelin receptor inhibitors: agents in the treatment of obesity

BACKGROUND

Current medical treatment of obesity is highly ineffective. Soon after its discovery as the endogenous ligand for the growth hormone secretagogue-receptor (GHS-R), ghrelin was shown to stimulate food intake (including in humans) and promote body weight gain and adipogenesis.

OBJECTIVES

This review discusses the role of the ghrelin/GHS-R pathway in energy homeostasis regulation and its role as a novel molecular target for the treatment of obesity.

METHODS

Medline was searched for relevant articles published in English.

RESULTS/CONCLUSION

A large series of animal studies shows that inhibition of the ghrelin/GHS-R pathway reduces food intake, body weight and adiposity, through reduction of appetite and augmentation of energy expenditure and fat catabolism. This suggests that inhibition of this novel pathway may be used to treat/prevent obesity and its complications.

Central nervous system regulation of energy metabolism: ghrelin versus leptin

In this brief review, we introduce some major themes in the regulation of energy, lipid, and glucose metabolism by the central nervous system (CNS). Rather than comprehensively discussing the field, we instead will discuss some of the key findings made regarding the interaction of the hormones ghrelin and leptin with the CNS.

Introducing GOAT: a target for obesity and anti-diabetic drugs?

The acyltransferase that catalyzes ghrelin octanoylation has recently been identified as ghrelin O-acyltransferase (GOAT). GOAT belongs to a family of membrane-bound O-acyltransferases (MBOATs). GOAT covalently links a medium fatty-acid chain, typically octanoate, to the hydroxyl group of the third serine of ghrelin, a potent orexigenic peptide characterized by this unique post-translational modification. The discovery of GOAT raises important questions and reveals several therapeutical possibilities. Indeed, drugs that inhibit GOAT might be able to prevent diet-induced obesity and might be an effective therapy for type-2 diabetes, increasing insulin secretion and enhancing peripheral insulin sensitivity. Furthermore, research on GOAT is providing new insights into the pathophysiology of energy homeostasis and might lead to the identification of further therapeutic targets. Here, we review what is currently known about the regulatory role of GOAT and discuss the potential of this novel approach for treating obesity and type-2 diabetes.

A neutralizing leptin receptor antibody mitigates hypertrophy and hemodynamic dysfunction in the postinfarcted rat heart

The 16 kDa adipokine leptin has been shown to exert direct hypertrophic effects on cultured cardiomyocytes although its role as an endogenous contributor to postinfarction remodeling and heart failure has not been determined. We therefore investigated the effect of leptin receptor blockade in vivo on hemodynamic function and cardiac hypertrophy following coronary artery ligation (CAL). Cardiac function and biochemical parameters were measured in rats subjected to 7 or 28 days of left main CAL in the presence and absence of a leptin receptor antibody. Animals subjected to an identical treatment in which the artery was not tied served as sham-operated controls. CAL produced myocardial hypertrophy, which was most pronounced 28 days postinfarction as demonstrated by increases in both left ventricular weight-to-body weight ratio and atrial natriuretic peptide gene expression, both of which were abrogated by leptin receptor antagonism. Leptin receptor blockade also significantly improved left ventricular systolic function, attenuated the increased left ventricular end-diastolic pressure, and reduced the expression of genes associated with extracellular matrix remodeling 28 days following CAL. In conclusion, the ability of a leptin receptor-neutralizing antibody to improve cardiac function offers evidence that endogenous leptin contributes to cardiac hypertrophy following CAL. The possibility exists that targeting the myocardial leptin receptor represents a viable and novel approach toward attenuating postinfarction remodeling.

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.

Ghrelin in pathological conditions

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

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

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

Autoantibodies against appetite-regulating peptide hormones and neuropeptides: putative modulation by gut microflora

Objective

Peptide hormones synthesized in gastrointestinal and adipose tissues in addition to neuropeptides regulate appetite and body weight. Previously, autoantibodies directed against melanocortin peptides were found in patients with eating disorders; however, it remains unknown whether autoantibodies directed against other appetite-regulating peptides are present in human sera and whether their levels are influenced by gut-related antigens.

Methods

Healthy women were studied for the presence of immunoglobulin (Ig) G and IgA autoantibodies directed against 14 key appetite-regulating peptides. The concept of molecular mimicry was applied to search in silico whether bacteria, viruses, or fungi contain proteins with amino acid sequences identical to appetite-regulating peptides. In addition, autoantibodies serum levels were studied in germ-free and specific pathogen-free rats.

Results

We found these IgG and IgA autoantibodies directed against leptin, ghrelin, peptide YY, neuropeptide Y, and other appetite-regulating peptides are present in human sera at levels of 100–900 ng/mL. Numerous cases of sequence homology with these peptides were identified among commensal and pathogenic micro-organisms including Lactobacilli, bacteroides, Helicobacter pylori, Escherichia coli, and Candida species. Decreased levels of IgA autoantibodies directed against several appetite-regulating peptides and increased levels of antighrelin IgG were found in germ-free rats compared with specific pathogen-free rats.

Conclusion

Healthy humans and rats display autoantibodies directed against appetite-regulating peptide hormones and neuropeptides, suggesting that these autoantibodies may have physiologic implications in hunger and satiety pathways. Gut-related antigens including the intestinal microflora may influence production of theses autoantibodies, suggesting a new link between the gut and appetite control.

Characterization of adult ghrelin and ghrelin receptor knockout mice under positive and negative energy balance

Ghrelin and the ghrelin receptor (GH secretagogue receptor, GHS-R), are believed to have important roles in energy homeostasis. We describe results from the first studies to be conducted in congenic (N10) adult ghrelin(-/-) and Ghsr(-/-) mice under conditions of both positive (high-fat diet) and negative (caloric restriction) energy balance. In contrast to results from young N2 mutant mice, changes in body weight and energy expenditure are not clearly distinguishable across genotypes. Although respiratory quotient was lower in mice fed a high-fat diet, no differences were evident between littermate wild-type and null genotypes. With normal chow, a modest decrease trend in respiratory quotient was detected in ghrelin(-/-) mice but not in Ghsr(-/-) mice. Under caloric restriction, the weight loss of ghrelin(-/-) and Ghsr(-/-) mice was identical to wild-type littermates, but blood glucose levels were significantly lower. We conclude that adult congenic ghrelin(-/-) and Ghsr(-/-) mice are not resistant to diet-induced obesity but under conditions of negative energy balance show impairment in maintaining glucose homeostasis. These results support our hypothesis that the primary metabolic function of ghrelin in adult mice is to modulate glucose sensing and insulin sensitivity, rather than directly regulate energy intake and energy expenditure.

Modulation of food intake following deep brain stimulation of the ventromedial hypothalamus in the vervet monkey

Object

Deep brain stimulation (DBS) has become an effective therapy for an increasing number of brain disorders. Recently demonstrated DBS of the posterior hypothalamus as a safe treatment for chronic intractable cluster headaches has drawn attention to this target, which is involved in the regulation of diverse autonomic functions and feeding behavior through complex integrative mechanisms. In this study, the authors assessed the feasibility of ventromedial hypothalamus (VMH) DBS in freely moving vervet monkeys to modulate food intake as a model for the potential treatment of eating disorders.

Methods

Deep brain stimulation electrodes were bilaterally implanted into the VMH of 2 adult male vervet monkeys by using the stereotactic techniques utilized in DBS in humans. Stimulators were implanted subcutaneously on the upper back, allowing ready access to program stimulation parameters while the animal remained conscious and freely moving. In anesthetized animals, intraoperatively and 6–10 weeks postsurgery, VMH DBS parameters were selected according to minimal cardiovascular and autonomic nervous system responses. Thereafter, conscious animals were subjected to 2 cycles of VMH DBS for periods of 8 and 3 days, and food intake and behavior were monitored. Animals were then killed for histological verification of probe placement.

Results

During VMH DBS, total food consumption increased. The 3-month bilateral implant of electrodes and subsequent periods of high-frequency VMH stimulation did not result in significant adverse behavioral effects.

Conclusions

This is the first study in which techniques of hypothalamic DBS in humans have been applied in freely moving nonhuman primates. Future studies can now be conducted to determine whether VMH DBS can change hypothalamic responsivity to endocrine signals associated with adiposity for long-term modulation of food intake.

Ghrelin promotes thymopoiesis during aging

The decline in adaptive immunity, T lymphocyte output, and the contraction of the TCR repertoire with age is largely attributable to thymic involution. The loss of thymic function with age may be due to diminished numbers of progenitors and the loss of critical cytokines and hormones from the thymic microenvironment. We have previously demonstrated that the orexigenic hormone ghrelin is expressed by immune cells and regulates T cell activation and inflammation. Here we report that ghrelin and ghrelin receptor expression within the thymus diminished with progressive aging. Infusion of ghrelin into 14-month-old mice significantly improved the age-associated changes in thymic architecture and thymocyte numbers, increasing recent thymic emigrants and improving TCR diversity of peripheral T cell subsets. Ghrelin-induced thymopoiesis during aging was associated with enhanced early thymocyte progenitors and bone marrow-derived Lin(-)Sca1(+)cKit(+) cells, while ghrelin- and growth hormone secretagogue receptor-deficient (GHS-R-deficient) mice displayed enhanced age-associated thymic involution. Leptin also enhanced thymopoiesis in aged but not young mice. Our findings demonstrate what we believe to be a novel role for ghrelin and its receptor in thymic biology and suggest a possible therapeutic benefit of harnessing this pathway in the reconstitution of thymic function in immunocompromised subjects.

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

OBJECTIVES

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

RESEARCH METHODS AND PROCEDURES

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

RESULTS

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

DISCUSSION

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

Inter-organ metabolic communication involved in energy homeostasis: potential therapeutic targets for obesity and metabolic syndrome

The global rate of obesity is rising alarmingly, exerting a major adverse impact on human health by increasing the prevalences of disorders, such as diabetes, hypertension and heart disease. To maintain systemic energy homeostasis, metabolic information must be communicated among organs/tissues. Obesity-related disorders can be thought of as resulting from dysregulation of this vital inter-tissue communication. Remarkable advances in obesity research during this decade have shown humoral factors manufactured and secreted by adipose tissue (adipocytokines) to be of great importance. In addition to these humoral factors, such as nutrients (glucose, fatty acids and amino acids) and hormones (insulin, adipocytokines and so on), the functional significance of the autonomic nervous system has recently attracted research attention. Autonomic nerves are essential components of the endogenous system for maintaining energy homeostasis, making them potential therapeutic targets for obesity-related disorders. This review focuses on the therapeutic possibilities of targeting inter-organ communication systems.