Pancreatic polypeptide infusions reduce food intake in Prader-Willi syndrome

Hormonal regulators of appetite

Obesity is a significant cause of morbidity and mortality worldwide. There has been a significant worsening of the obesity epidemic mainly due to alterations in dietary intake and energy expenditure. Alternatively, cachexia, or pathologic weight loss, is a significant problem for individuals with chronic disease. Despite their obvious differences, both processes involve hormones that regulate appetite. These hormones act on specific centers in the brain that affect the sensations of hunger and satiety. Mutations in these hormones or their receptors can cause substantial pathology leading to obesity or anorexia. Identification of individuals with specific genetic mutations may ultimately lead to more appropriate therapies targeted at the underlying disease process. Thus far, these hormones have mainly been studied in adults and animal models. This article is aimed at reviewing the hormones involved in hunger and satiety, with a focus on pediatrics.

Role of gut hormones in obesity

A critical role for the gut in energy homeostasis has emerged. Gut hormones not only have a role in digestion but several of them have been found to modulate appetite in animals and humans. Current nonendocrine drugs for obesity are limited by their modest efficacies, and bariatric surgery is confined to use in severe cases. The discovery of important appetite-signaling pathways from the gut to the brain has led to the emergence of several gut hormone-derived drugs that are being investigated for clinical use. This article summarizes the physiology of the major gut hormones implicated in appetite regulation, and reviews clinical evidence that gives us insight into their potential as clinical treatments for obesity.

Gut hormones: a weight off your mind

The increasing prevalence of obesity and the associated morbidity and mortality has resulted in a major research effort to identify mechanisms that regulate appetite. It is well established that the hypothalamus and brain stem are major sites in the central nervous system (CNS) that regulate appetite. Until recently the missing element has been how information regarding food intake and energy stores is communicated to the CNS. Gut hormones have recently been found to be an important element in this regulation, communicating information regarding food intake to the CNS. Several gut hormones have been found to exert anorectic effects. These include members of the Pancreatic Polypeptide (PP)-fold family, namely PP itself and also peptide tyrosine-tyrosine (PYY), the first gut hormone shown to have appetite-inhibiting properties. The other main class of anorectic gut hormones are those derived by proteolytic processing from proglucagon, most importantly glucagon-like peptide-1 (GLP-1) and oxyntomodulin. All of these are currently being investigated as the basis of treatments to prevent the development of obesity. So far the only gastrointestinal hormone demonstrated to stimulate appetite is ghrelin. Potential sites and mechanisms of action and therapeutic use of these gastrointestinal hormones are discussed.

Leptin does not directly regulate the pancreatic hormones amylin and pancreatic polypeptide: interventional studies in humans

OBJECTIVE

Leptin and the pancreatic hormones amylin and pancreatic polypeptide are being evaluated alone or in combination for the treatment of obesity, but their physiological regulation has not yet been fully elucidated. Thus, we examined whether amylin and pancreatic polypeptide are regulated by caloric intake and/or short- and long-term energy deprivation and whether any potential regulation is mediated by changes in leptin levels.

RESEARCH DESIGN AND METHODS

We measured circulating levels of amylin and pancreatic polypeptide after 1) a 75-g glucose load in 28 healthy, normal-weight women, 2) 72-h complete energy deficiency (severe hypoleptinemia) with administration of either placebo or replacement-dose recombinant methionyl human leptin (r-metHuLeptin) in normal-weight men (n = 6) and women (n = 7), and 3) chronic mild energy deficiency (mild hypoleptinemia) in 7 women with hypothalamic amenorrhea before and after r-metHuLeptin administration for 3 months.

RESULTS

Amylin and pancreatic polypeptide levels increased 15 min after a 75-g glucose load and remained elevated at 60 and 120 min (P < 0.0001). Fasting for 72 h decreased leptin (to 21%) and amylin (to 67%) of baseline but not pancreatic polypeptide levels. Normalizing leptin levels with r-metHuLeptin did not alter the fasting-induced decrease in amylin and had no effect on pancreatic polypeptide levels. Neither amylin nor pancreatic polypeptide levels were different in leptin-deficient women with hypothalamic amenorrhea compared with weight-matched control subjects, and normalization of leptin levels with r-metHuLeptin treatment did not alter amylin or pancreatic polypeptide levels.

CONCLUSIONS

Circulating amylin levels increase after a glucose load and decrease in response to short-term complete fasting, but these changes are not mediated by leptin.

Central and peripheral neuroendocrine peptides and signalling in appetite regulation: considerations for obesity pharmacotherapy

Appetite and satiety are mediated by complex neuroendocrine signalling pathways involving over 40 hormones, neuropeptides, enzymes, other chemical messengers and their receptors. Research efforts continue to expand understanding of the role of signalling molecules between central hypothalamic nuclei and peripheral enteroendocrine cells; and discoveries of novel networks and messengers provide new biological insights on how to manipulate appetite-satiety pathways. Despite the vast array of peptides that are potentially useful for anti-obesity drug development, only four classes of agents are approved: (i) catecholamine stimulants; (ii) serotonin and noradrenaline reuptake inhibitors; (iii) lipase inhibitors; and (iv) more recently cannabinoid-1 receptor antagonists. Clinical effects of these drugs confer modest improvements, and side effects negatively impact long-term treatment course. This paper suggests single target pharmacological interventions are possibly hampered by the myriad of alternate orexigenic peptidic signals that drive hyperphagia, hence a multiple target model or combination treatment approach is proposed to offer greater therapeutic potential in modulating appetite and managing weight.

Neuropeptide y receptor selective ligands in the treatment of obesity

Obesity is a serious public health problem throughout the world, affecting both developed societies and developing countries. The central nervous system has developed a meticulously interconnected circuitry in order to keep us fed and in an adequate nutritional state. One of these consequences is that an energy-dense environment favors the development of obesity. Neuropeptide Y (NPY) is one of the most abundant and widely distributed peptides in the central nervous system of both rodents and humans and has been implicated in a variety of physiological actions. Within the hypothalamus, NPY plays an essential role in the control of food intake and body weight. Centrally administered NPY causes robust increases in food intake and body weight and, with chronic administration, can eventually produce obesity. NPY activates a population of at least six G protein-coupled Y receptors. NPY analogs exhibit varying degrees of affinity and specificity for these Y receptors. There has been renewed speculation that ligands for Y receptors may be of benefit for the treatment of obesity. This review highlights the therapeutic potential of Y(1), Y(2), Y(4), and Y(5) receptor agonists and antagonists as additional intervention to treat human obesity.

Gut hormones and appetite control

Many peptides are synthesized and released from the gastrointestinal tract. Although their roles in the regulation of gastrointestinal function have been known for some time, it is now evident that they also physiologically influence eating behavior. Our understanding of how neurohormonal gut-brain signaling regulates energy homeostasis has advanced significantly in recent years. Ghrelin is an orexigenic peptide produced by the stomach, which appears to act as a meal initiator. Satiety signals derived from the intestine and pancreas include peptide YY, pancreatic polypeptide, glucagon-like peptide 1, oxyntomodulin, and cholecystokinin. Recent research suggests that gut hormones can be manipulated to regulate energy balance in humans, and that obese subjects retain sensitivity to the actions of gut hormones. Gut hormone-based therapies may thus provide an effective and well-tolerated treatment for obesity.

Y2, Y4 receptors and obesity

The neuropeptide Y system - comprising neuropeptide Y, peptide YY, pancreatic polypeptide and the Y receptors through which they act (Y1, Y2, Y4, Y5 and y6) - has been at the center of attention with regards to regulation of feeding behavior and its possible involvement in obesity. In the past, research has focused mainly on the orexigenic and obesogenic action of this system, with Y1 and Y5 receptors being prime candidates as mediators of neuropeptide Y-induced hyperphagia and obesity. However, in recent years, the role of other members of the neuropeptide Y family, peptide YY, pancreatic polypeptide and the Y2 and Y4 receptors through which they predominantly act, have commanded increasing attention on account of their effects to mediate satiety and promote weight loss via actions in key brain structures, such as the arcuate nucleus of the hypothalamus and the brain stem. This review focuses on the role of peptide YY- and pancreatic polypeptide-like compounds as possible antiobesity drugs, taking into account their effects, not only on energy balance, but also in the regulation of bone formation, and highlights potential benefits of using Y2 and/or Y4 antagonists (as opposed to agonists such as peptide YY or pancreatic polypeptide) in the treatment of obesity.

A role for pancreatic polypeptide in feeding and body weight regulation

PP administration induces negative energy balance by suppressing food intake and gastric emptying while increasing energy expenditure in rodents. The mechanism of PP actions involves the changes in the expression of hypothalamic feeding-regulatory peptides and the activity of the vago-vagal and vago-sympathetic reflex arc. PP-overexpressing mice we developed exhibited the thin phenotype with decreased food intake and gastric emptying rate. Plasma cholecystokinin (CCK) concentrations were increased in the transgenic mice and CCK-1 receptor antagonist improved the anorexia of the animals. These results, together with the previous notion of PP as an anti-CCK hormone in pancreatic exocrine secretion and gallbladder contraction, indicate that PP-CCK interactions may be either antagonistic or synergistic and the transgenic mice may exhibit the mixed phenotype by overproduction of PP and CCK.

The obesity pipeline: current strategies in the development of anti-obesity drugs

This review provides a summary of currently available pharmaceutical therapies for the treatment of obesity, along with an overview of the pipeline of products currently in development, and the key mechanisms on which the major development candidates are based. In particular, the recent increase in understanding of the role of gut peptides in energy homeostasis is highlighted as a promising source of potential future obesity therapies.

Up-regulation of neuropeptide Y Y4 receptor mRNA expression in the brainstem of refed rats following 48 h of food deprivation: effect of leptin

Neuropeptide Y (NPY) Y4 receptor (Y4R) in rat brainstem has been implicated in the signaling of satiety. In this study, we investigated the effects of leptin, and refeeding-induced satiety on Y4R mRNA expression in rat brainstem. Y4R receptor-specific primers were used to amplify the mRNA obtained from hypothalamus and brainstem utilizing conventional RT-PCR and quantitative real-time RT-PCR. No PCR product for Y4R was obtained from entire hypothalamic mRNA. Real-time RT-PCR showed a significant two-fold increase in the relative quantity of Y4R mRNA in brainstem of refed rats in comparison to food deprived or ad lib fed rats. Consistently, plasma leptin level was elevated in refed rats in comparison to food deprived rats. Similarly, leptin-treated rats exhibited a significant increase in Y4R mRNA in brainstem as compared to saline-injected rats. Plasma leptin was significantly elevated in leptin-treated rats. These results suggest that refeeding stimulates the expression of Y4R gene in the brainstem and that leptin may be one of the peripheral factors involved in this anorectic signaling mechanism.

Pancreatic signals controlling food intake; insulin, glucagon and amylin

The control of food intake and body weight by the brain relies upon the detection and integration of signals reflecting energy stores and fluxes, and their interaction with many different inputs related to food palatability and gastrointestinal handling as well as social, emotional, circadian, habitual and other situational factors. This review focuses upon the role of hormones secreted by the endocrine pancreas: hormones, which individually and collectively influence food intake, with an emphasis upon insulin, glucagon and amylin. Insulin and amylin are co-secreted by B-cells and provide a signal that reflects both circulating energy in the form of glucose and stored energy in the form of visceral adipose tissue. Insulin acts directly at the liver to suppress the synthesis and secretion of glucose, and some plasma insulin is transported into the brain and especially the mediobasal hypothalamus where it elicits a net catabolic response, particularly reduced food intake and loss of body weight. Amylin reduces meal size by stimulating neurons in the hindbrain, and there is evidence that amylin additionally functions as an adiposity signal controlling body weight as well as meal size. Glucagon is secreted from A-cells and increases glucose secretion from the liver. Glucagon acts in the liver to reduce meal size, the signal being relayed to the brain via the vagus nerves. To summarize, hormones of the endocrine pancreas are collectively at the crossroads of many aspects of energy homeostasis. Glucagon and amylin act in the short term to reduce meal size, and insulin sensitizes the brain to short-term meal-generated satiety signals; and insulin and perhaps amylin as well act over longer intervals to modulate the amount of fat maintained and defended by the brain. Hormones of the endocrine pancreas interact with receptors at many points along the gut-brain axis, from the liver to the sensory vagus nerve to the hindbrain to the hypothalamus; and their signals are conveyed both neurally and humorally. Finally, their actions include gastrointestinal and metabolic as well as behavioural effects.

Gastrointestinal hormones regulating appetite

The role of gastrointestinal hormones in the regulation of appetite is reviewed. The gastrointestinal tract is the largest endocrine organ in the body. Gut hormones function to optimize the process of digestion and absorption of nutrients by the gut. In this capacity, their local effects on gastrointestinal motility and secretion have been well characterized. By altering the rate at which nutrients are delivered to compartments of the alimentary canal, the control of food intake arguably constitutes another point at which intervention may promote efficient digestion and nutrient uptake. In recent decades, gut hormones have come to occupy a central place in the complex neuroendocrine interactions that underlie the regulation of energy balance. Many gut peptides have been shown to influence energy intake. The most well studied in this regard are cholecystokinin (CCK), pancreatic polypeptide, peptide YY, glucagon-like peptide-1 (GLP-1), oxyntomodulin and ghrelin. With the exception of ghrelin, these hormones act to increase satiety and decrease food intake. The mechanisms by which gut hormones modify feeding are the subject of ongoing investigation. Local effects such as the inhibition of gastric emptying might contribute to the decrease in energy intake. Activation of mechanoreceptors as a result of gastric distension may inhibit further food intake via neural reflex arcs. Circulating gut hormones have also been shown to act directly on neurons in hypothalamic and brainstem centres of appetite control. The median eminence and area postrema are characterized by a deficiency of the blood-brain barrier. Some investigators argue that this renders neighbouring structures, such as the arcuate nucleus of the hypothalamus and the nucleus of the tractus solitarius in the brainstem, susceptible to influence by circulating factors. Extensive reciprocal connections exist between these areas and the hypothalamic paraventricular nucleus and other energy-regulating centres of the central nervous system. In this way, hormonal signals from the gut may be translated into the subjective sensation of satiety. Moreover, the importance of the brain-gut axis in the control of food intake is reflected in the dual role exhibited by many gut peptides as both hormones and neurotransmitters. Peptides such as CCK and GLP-1 are expressed in neurons projecting both into and out of areas of the central nervous system critical to energy balance. The global increase in the incidence of obesity and the associated burden of morbidity has imparted greater urgency to understanding the processes of appetite control. Appetite regulation offers an integrated model of a brain-gut axis comprising both endocrine and neurological systems. As physiological mediators of satiety, gut hormones offer an attractive therapeutic target in the treatment of obesity.

Gut peptides and the regulation of appetite

There is a growing worldwide epidemic of obesity. Obese people have a higher incidence of type 2 diabetes and cardiovascular disease, and hence present increasing social, financial and health burdens. Weight loss is always difficult to achieve through lifestyle changes alone, and currently licensed anti-obesity drug treatments, such as orlistat and sibutramine, if tolerated, only achieve modest weight loss. Therefore, there is a need to identify more potent pharmacological targets. In the last 10 years, discoveries of new hormones such as leptin and ghrelin, together with greater understanding of previously described hormones such as cholecystokinin (CCK), pancreatic polypeptide (PP), peptide YY (PYY) and glucagon-like peptide 1 (GLP-1), have led to a rapid increase in our knowledge of the regulation of energy balance. Among the most important factors, controlling appetite and satiety are peptide hormones released from the gut. In this paper, we provide a full up-to-date overview of the current state of knowledge of this field, together with the potential of these peptides as drugs, or as other therapeutic targets, in the treatment of obesity. Finally, we propose an integrated model to describe the complex interplay of these hormones in the broader physiology of energy balance.

The hypothalamus, hormones, and hunger: alterations in human obesity and illness

Obesity is a major global epidemic, with over 300 million obese people worldwide, and nearly 1 billion overweight adults. Being overweight carries significant health risks, reduced quality of life, and impaired socioeconomic success, with profound consequences for health expenditure. The most successful treatment for obesity is gastric bypass surgery, which acts in part by reducing appetite through alterations in gut hormones. Circulating gut hormones, secreted or suppressed after eating food, act in the brain, particularly the hypothalamus, to alter hunger and fullness. Stomach-derived ghrelin increases food intake even in those with anorexia from chronic illness, while pancreatic polypeptide (PP), intestinal peptide YY 3-36 (PYY), oxyntomodulin, and other hormones reduce food intake and appetite. While obese subjects have appropriate reductions in orexigenic ghrelin, other gut-hormone disturbances may contribute to obesity such as reduced anorexigenic PYY and PP. Prader-Willi syndrome (PWS) arises from the loss of paternally inherited genes on chromosome 15q11-13, leading to life-threatening insatiable hunger and obesity from early childhood, through developmental brain, particularly hypothalamic defects. The study of genetically homogenous causes of abnormal-feeding behavior helps our understanding of appetite regulation. PWS subjects have inappropriately elevated plasma ghrelin for their obesity, at least partly explained by preserved insulin sensitivity. It remains unproven if their hyperghrelinemia or other gut-hormone abnormalities contribute to the hyperphagia in PWS, in addition to brain defects. Postmortem human hypothalamic studies and generation of animal models of PWS can also provide insight into the pathophysiology of abnormal-feeding behavior. Changes in orexigenic NPY and AGRP hypothalamic neurons, or anorexigenic oxytocin neurons have been found in illness and PWS. Functional neuroimaging studies, using PET and fMRI, will also allow us to tease apart the hormonal and brain pathways responsible for controlling human appetite, and their defects in obesity.

Hormonal regulation of food intake

Our knowledge of the physiological systems controlling energy homeostasis has increased dramatically over the last decade. The roles of peripheral signals from adipose tissue, pancreas, and the gastrointestinal tract reflecting short- and long-term nutritional status are now being described. Such signals influence central circuits in the hypothalamus, brain stem, and limbic system to modulate neuropeptide release and hence food intake and energy expenditure. This review discusses the peripheral hormones and central neuronal pathways that contribute to control of appetite.

Pancreatic polypeptide is involved in the regulation of body weight in pima Indian male subjects

Pancreatic polypeptide (PP) is released from the pancreas in response to a meal. In humans, low-circulating PP levels have been observed in obesity, and administration of pharmacological doses of PP has been shown to decrease food intake. The aim of the present study was to investigate whether low circulating PP is associated with weight gain in Pima Indians. Plasma PP concentrations were measured after an overnight fast and 30 min after a standardized mixed meal in 33 nondiabetic male subjects who had a follow-up visit 4.9 +/- 2.5 years later. Cross-sectionally, fasting and postprandial PP levels were negatively associated with body size and adiposity. Prospectively, the change in PP response to the meal was negatively associated with the change in body weight (r = -0.53, P = 0.002). In contrast, a high fasting PP level was positively associated with change in body weight (r = 0.45, P = 0.009). In conclusion, our results provide evidence that, even within the physiological range, PP contributes to the regulation of energy balance in humans. However this contribution appears to be more complex than anticipated because of the opposite effect of fasting and postprandial PP on the risk of future weight gain.

Minireview: Gut peptides regulating satiety

The gastrointestinal tract and the pancreas release hormones regulating satiety and body weight. Ghrelin stimulates appetite, and glucagon-like peptide-1, oxyntomodulin, peptide YY, cholecystokinin, and pancreatic polypeptide inhibit appetite. These gut hormones act to markedly alter food intake in humans and rodents. Obesity is the current major cause of premature death in the United Kingdom, killing almost 1000 people per week. Worldwide, its prevalence is accelerating. There is currently no effective answer to the pandemic of obesity, but replacement of the low levels of peptide YY observed in the obese may represent an effective antiobesity therapy.

Gastrointestinal satiety signals III. Glucagon-like peptide 1, oxyntomodulin, peptide YY, and pancreatic polypeptide

Many peptides are synthesized and released from the gastrointestinal tract and pancreas, including pancreatic polypeptide (PP) and the products of the gastrointestinal L cells, glucagon-like peptide 1 (GLP-1), oxyntomodulin, and peptide YY (PYY). Whereas their roles in regulation of gastrointestinal function have been known for some time, it is now evident that they also influence eating behavior. This review considers the anorectic peptides PYY, PP, GLP-1, and oxyntomodulin, which decrease appetite and promote satiety in both animal models and humans.

Plasma ghrelin response following a period of acute overfeeding in normal weight men

BACKGROUND

Ghrelin, a 28 amino-acid peptide secreted primarily from the stomach has been identified as the endogenous ligand for the growth hormone secretagogue receptor. Ghrelin is suppressed in the postprandial state and has been linked to both type II diabetes and obesity.

AIMS

To investigate the effects of a period of overfeeding with high-fat dietary supplements on plasma ghrelin levels in nonobese men.

METHODS

Six healthy males (21-34 y; BMI 21-24 kg/m(2)) underwent the dietary intervention after completing diet and exercise diaries for 7 days. For 3 further weeks subjects followed their own diet diary supplemented with 125 ml single cream and 50 g roasted peanuts (88 g fat, 15 g Protein, 8 g carbohydrate) every day. Oral fat tolerance tests (OFTT) were undertaken at baseline, 7, 14 and 21 days of fat supplementation. The diet was increased in energy by 3.9 MJ/day and from a mean of 29-45% energy intake from fat with a small weight gain noted each week (P=0.009).

RESULTS

Ghrelin concentrations were significantly reduced during the baseline OFTT. The postprandial ghrelin response (AUC) was significantly reduced following 2 weeks of dietary supplementation (P=0.005) increasing the suppression of plasma ghrelin by 18% despite only a 3% increase in body weight. Plasma triacylglycerol (P=0.009) and leptin (P=0.035) concentrations were also elevated and postprandial pancreatic polypeptide levels decreased (P=0.038) following dietary-supplementation.

CONCLUSIONS

These results suggest that the metabolic profile associated with obesity, including a reduction in plasma ghrelin levels, may be related to recent dietary energy intake and precedes the development of significant adiposity.

Prader-Willi syndrome: advances in genetics, pathophysiology and treatment

Prader-Willi syndrome (PWS) is a complex human genetic disease that arises from lack of expression of paternally inherited imprinted genes on chromosome 15q11-q13. Identification of the imprinting control centre, novel imprinted genes and distinct phenotypes in PWS patients and mouse models has increased interest in this human obesity syndrome. In this review I focus on: (i) the chromosomal region and candidate genes associated with PWS, and the possible links with individual PWS phenotypes identified using mouse models; (ii) the metabolic and hormonal phenotypes in PWS; (iii) postmortem studies of human PWS hypothalami; and (iv) current and potential advances in the management of PWS and its complications. This could have benefits for a wide spectrum of endocrine, paediatric and neuropsychiatric diseases.

Characterization of the effects of pancreatic polypeptide in the regulation of energy balance

BACKGROUND & AIMS

Pancreatic polypeptide (PP) belongs to a family of peptides including neuropeptide Y and peptide YY. We examined the role of PP in the regulation of body weight as well as the therapeutic potential of PP.

METHODS

We measured food intake, gastric emptying, oxygen consumption, and gene expression of hypothalamic neuropeptides, gastric ghrelin, and adipocytokines in mice after administering PP intraperitoneally. Peptide gene expression was also examined in PP-overexpressing mice. Vagal and sympathetic nerve activities were recorded after intravenous administration in rats. Effects of repeated administrations of PP on energy balance and on glucose and lipid metabolism were examined in both ob/ob obese mice and fatty liver Shionogi (FLS)-ob/ob obese mice.

RESULTS

Peripherally administered PP induced negative energy balance by decreasing food intake and gastric emptying while increasing energy expenditure. The mechanism involved modification of expression of feeding-regulatory peptides (decrease in orexigenic neuropeptide Y, orexin, and ghrelin along with an increase in anorexigenic urocortin) and activity of the vagovagal or vagosympathetic reflex arc. PP reduced leptin in white adipose tissue and corticotropin-releasing factor gene expression. The expression of gastric ghrelin and hypothalamic orexin was decreased in PP-overexpressing mice. Repeated administrations of PP decreased body weight gain and ameliorated insulin resistance and hyperlipidemia in both ob/ob obese mice and FLS-ob/ob obese mice. Liver enzyme abnormalities in FLS-ob/ob obese mice were also ameliorated by PP.

CONCLUSIONS

These observations indicate that PP may influence food intake, energy metabolism, and the expression of hypothalamic peptides and gastric ghrelin.

Important role of hypothalamic Y2 receptors in body weight regulation revealed in conditional knockout mice

Neuropeptide Y is implicated in energy homeostasis, and contributes to obesity when hypothalamic levels remain chronically elevated. To investigate the specific role of hypothalamic Y2 receptors in this process, we used a conditional Y2 knockout model, using the Cre-lox system and adenoviral delivery of Cre-recombinase. Hypothalamus-specific Y2-deleted mice showed a significant decrease in body weight and a significant increase in food intake that was associated with increased mRNA levels for the orexigenic NPY and AgRP, as well as the anorexic proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) in the arcuate nucleus. These hypothalamic changes persisted until at least 34 days after Y2 deletion, yet the effect on body weight and food intake subsided within this time. Plasma concentrations of pancreatic polypeptide and corticosterone were 3- to 5-fold increased in hypothalamus-specific Y2 knockout mice. Germ-line Y2 receptor knockout also produced a significant increase in plasma levels of pancreatic polypeptide. However, these mice differed from conditional knockout mice in that they showed a sustained reduction in body weight and adiposity associated with increased NPY and AgRP but decreased POMC and CART mRNA levels in the arcuate nucleus. The transience of the observed effects on food intake and body weight in the hypothalamus-specific Y2 knockout mice, and the difference of this model from germ-line Y2 knockout mice, underline the importance of conditional models of gene deletion, because developmental, secondary, or extrahypothalamic mechanisms may mask such effects in germ-line knockouts.

Roles of pancreatic polypeptide in regulation of food intake

Pancreatic polypeptide (PP) is produced in pancreatic islets of Langerhans and released into the circulation after ingestion of a meal. Peripherally administered PP suppresses food intake and gastric emptying. On the other hand, central administration of PP elicits food intake and gastric emptying. Therefore, PP actions on food intake may be, in part, attributable to gastric emptying. PP transgenic mice exhibit decreases in both food intake and gastric emptying rate that were clearly reversed by anti-PP antiserum. PP is an anorexigenic signal in the periphery and an orexigenic signal in the central nervous system.

Peripheral signals conveying metabolic information to the brain: short-term and long-term regulation of food intake and energy homeostasis

Numerous peripheral signals contribute to the regulation of food intake and energy homeostasis. Mechano- and chemoreceptors signaling the presence and energy density of food in the gastrointestinal (GI) tract contribute to satiety in the immediate postprandial period. Changes in circulating glucose concentrations appear to elicit meal initiation and termination by regulating activity of specific hypothalamic neurons that respond to glucose. Other nutrients (e.g., amino acids and fatty acids) and GI peptide hormones, most notably cholecystokinin, are also involved in short-term regulation of food intake. However, the energy density of food and short-term hormonal signals by themselves are insufficient to produce sustained changes in energy balance and body adiposity. Rather, these signals interact with long-term regulators (i.e., insulin, leptin, and possibly the orexigenic gastric peptide, ghrelin) to maintain energy homeostasis. Insulin and leptin are transported into the brain where they modulate expression of hypothalamic neuropeptides known to regulate feeding behavior and body weight. Circulating insulin and leptin concentrations are proportional to body fat content; however, their secretion and circulating levels are also influenced by recent energy intake and dietary macronutrient content. Insulin and leptin concentrations decrease during fasting and energy-restricted diets, independent of body fat changes, ensuring that feeding is triggered before body energy stores become depleted. Dietary fat and fructose do not stimulate insulin secretion and leptin production. Therefore, attenuated production of insulin and leptin could lead to increased energy intake and contribute to weight gain and obesity during long-term consumption of diets high in fat and/or fructose. Transcription of the leptin gene and leptin secretion are regulated by insulin-mediated increases of glucose utilization and appear to require aerobic metabolism of glucose beyond pyruvate. Other adipocyte-derived hormones and proteins that regulate adipocyte metabolism, including acylation stimulating protein, adiponectin, diacylglycerol acyltransferase, and perilipin, are likely to have significant roles in energy homeostasis.

Effects of peptides on animal and human behavior: a review of studies published in the first twenty years of the journal Peptides

This review catalogs effects of peptides on various aspects of animal and human behavior as published in the journal Peptides in its first twenty years. Topics covered include: activity levels, addiction behavior, ingestive behaviors, learning and memory-based behaviors, nociceptive behaviors, social and sexual behavior, and stereotyped and other behaviors. There are separate tables for these behaviors and a short introduction for each section.

Mouse pancreatic polypeptide modulates food intake, while not influencing anxiety in mice

This study was designed to investigate the effects of synthetic mouse pancreatic polypeptide (mPP) on feeding and anxiety in mice. The intracerebroventricular (i.c.v.) injection of mPP (0.003-3 nmol) dose-dependently increased food intake. A significant increase was observed 20 min after i.c.v. injection and continued for 4 h. The intraperitoneal (i.p.) injection of mPP (0.03-30 nmol) dose-dependently decreased food intake. A significant decrease was observed 20 min after i.p. injection and continued for 4 h. In the elevated plus maze test, the i.c.v. injection of mPP (0.003-3 nmol) did not affect anxiety behavior. These results suggest that mPP modulates food intake and the Y4 receptor in the brain may contribute to the regulation of feeding, whereas appearing not to influence anxiety in mice.

Decreased food intake and body weight in pancreatic polypeptide-overexpressing mice

BACKGROUND & AIMS

Pancreatic polypeptide (PP) is a 36-amino acid hormone produced by F cells within the pancreatic islets and the exocrine pancreas. The definitive function of PP in mammalian physiology remains to be determined. This study examined the effects of chronic overexpression of PP through the development of PP transgenic mice.

METHODS

PP transgenic mice were created by using mouse PP complementary DNA under the control of the cytomegalovirus immediate early enhancer-chicken beta-actin hybrid promoter (pCAGGS expression vector).

RESULTS

A unique line of transgenic mice was created that overexpresses PP in the pancreatic islets with low levels of expression in other tissues including the brain. Plasma PP concentrations were more than 20 times higher than those of control littermates. However, PP overproduction led to postnatal lethality in half of the pups because of markedly decreased milk intake. The remaining PP transgenic mice gained less weight with specifically reduced food intake and fat mass compared with controls, a result that was more evident in male than in female mice. The transgenic mice exhibited a reduced rate of gastric emptying of a solid meal but had normal oxygen consumption and fasting leptin levels. Immunoneutralization with anti-PP antiserum reversed the phenotypic changes of transgenic animals.

CONCLUSIONS

PP could be involved in feeding and body weight regulation partly through regulation of gastric emptying.

Food intake in Prader-Willi syndrome and controls with obesity after administration of a benzodiazepine receptor agonist

Benzodiazepine receptor (BZR) agonists, used extensively for their anxiolytic effects, have been shown to increase food intake in many mammalian species. Little information, however, is available on the effects of BZR agonists on feeding behaviors of humans. Food intake was evaluated in a 60-minute free-feeding standardized test after the acute administration of the BZR agonist chlordiazepoxide (CDP, Librium; 5 mg or 20 mg) or placebo. Subjects were 12 individuals with the Prader-Willi syndrome (PWS), a disorder characterized by extreme hyperphagia and morbid obesity, and 11 controls with obesity. PWS subjects showed the characteristic hyperphagia associated with the appetite disorder, consuming more than six times as many sandwiches as controls with obesity. Results revealed no significant effect of either dose of CDP on the food intake of either group. Serum assays revealed that dose-dependent, clinically effective levels of CDP and active metabolites were achieved. These results suggest that acute administration of the BZR agonist CDP, at the therapeutic levels used, may not increase food intake in populations with obesity. However, the chronic effects of CDP on appetite in human populations still need to be explored.

Passage of peptides across the blood-brain barrier: pathophysiological perspectives

Blood-borne peptides are capable of affecting the central nervous system (CNS) despite being separated from the CNS by the blood-brain barrier (BBB), a monolayer comprised of brain endothelial and ependymal cells. Blood-borne peptides can directly affect the CNS after they cross the BBB by nonsaturable and saturable transport mechanisms. The ability of peptides to cross the BBB to a meaningful degree suggests that the BBB may act as a modulatory pathway in the exchange of informational molecules between the brain and the peripheral circulation. The permeability of the BBB to peptides is a regulatory process affected by developmental, physiological, and pathological events. This regulation sets the stage for the relation between peptides and the BBB to be involved in pathophysiological events. For example, some of the classic actions of melanocortins on the CNS are explained by their abilities to cross the BBB, whereas aspects of feeding and alcohol-related behaviors are associated with the passage of other specific peptides across the BBB. The BBB should no longer be considered a static barrier but should be recognized as a regulatory interface controlling the exchange of informational molecules, such as peptides, between the blood and CNS.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.