Role of VGF-derived peptides in the control of food intake, body weight and reproduction

VGF is a 68-kDa polypeptide synthesized in neuronal and neuroendocrine cells. It is cleaved into a number of smaller peptides which are stored in dense core vesicles and are likely to be secreted products. The VGF gene is expressed abundantly in the brain, and in peripheral endocrine tissues including the pituitary gland, the adrenal glands and the pancreas but also in the gastrointestinal tract in both the myenteric plexus and in endocrine cells. Several lines of evidence including observation of changes in hypothalamic VGF expression in catabolic states, a hypermetabolic phenotype in transgenic mice lacking VGF signalling, and demonstration of bioactivity of various peptide fragments have led to the view that VGF and/or its derived peptides are involved in the regulation of both energy balance and reproduction.     

TLQP-21, a VGF-derived peptide, increases energy expenditure and prevents the early phase of diet-induced obesity

The vgf gene has been identified as an energy homeostasis regulator. Vgf encodes a 617-aa precursor protein that is processed to yield an incompletely characterized panel of neuropeptides. Until now, it was an unproved assumption that VGF-derived peptides could regulate metabolism. Here, a VGF peptide designated TLQP-21 was identified in rat brain extracts by means of immunoprecipitation, microcapillary liquid chromatography-tandem MS, and database searching algorithms. Chronic intracerebroventricular (i.c.v.) injection of TLQP-21 (15 mug/day for 14 days) increased resting energy expenditure (EE) and rectal temperature in mice. These effects were paralleled by increased epinephrine and up-regulation of brown adipose tissue beta2-AR (beta2 adrenergic receptor) and white adipose tissue (WAT) PPAR-delta (peroxisome proliferator-activated receptor delta), beta3-AR, and UCP1 (uncoupling protein 1) mRNAs and were independent of locomotor activity and thyroid hormones. Hypothalamic gene expression of orexigenic and anorexigenic neuropeptides was unchanged. Furthermore, in mice that were fed a high-fat diet for 14 days, TLQP-21 prevented the increase in body and WAT weight as well as hormonal changes that are associated with a high-fat regimen. Biochemical and molecular analyses suggest that TLQP-21 exerts its effects by stimulating autonomic activation of adrenal medulla and adipose tissues. In conclusion, we present here the identification in the CNS of a previously uncharacterized VGF-derived peptide and prove that its chronic i.c.v. infusion effected an increase in EE and limited the early phase of diet-induced obesity.     

PRL-releasing peptide interacts with leptin to reduce food intake and body weight.

PRL-releasing peptide (PrRP) is a novel anorexigen that reduces food intake and body weight gain in rats. In common with other anorexigens, PrRP mRNA expression is reduced during states of negative energy balance, i.e. lactation and fasting in female rats. In this study, we examined the interaction between PrRP and the adiposity signal, leptin, which interacts with a number of peptidergic systems in the brain to regulate energy homeostasis. Intracerebroventricular coadministration of 4 nmol PrRP and 1 microg leptin in rats resulted in additive reductions in nocturnal food intake and body weight gain and an increase in core body temperature compared with each peptide alone. We show also, by quantitative in situ hybridization, that PrRP mRNA is reduced in fasted male rats and obese Zucker rats, indicating that PrRP mRNA expression, like that of other anorexigens, may be regulated by leptin. Finally we show, using immunohistochemistry, that greater than 90% of PrRP neurons in all regions where PrRP is expressed contain leptin receptors. Thus, we provide evidence for PrRP neurons forming part of the leptin-sensitive brain circuitry involved in the regulation of food intake and energy homeostasis.     

Neuroendocrine mechanisms regulating food intake and body weight

In the field of obesity research, two separate lines of study have emerged which explore the mechanism by which food intake is regulated: short‐term control of food intake, and the central regulation of energy balance. The former studies the satiety response during consumption of meals, whereby satiety signalling originating in the gut is transduced into a neural signal that modulates satiety pathways in the brainstem. This review describes a neuroanatomically based model in which leptin and insulin signalling in the hypothalamus governs long‐term regulation of energy balance via mechanisms that are integrated with satiety hormone signalling in the brainstem. The functional outcome of this integration is a cumulative meal‐to‐meal regulation of food intake, that over relatively long intervals serves to maintain stable adipose stores. Our model provides a context within which continued investigation of neuroendocrine mechanisms that control food intake and body weight can be explored, and has potential application to our current understanding of clinical obesity and its treatment.     

Sodium tungstate regulates food intake and body weight through activation of the hypothalamic leptin pathway

Aims: Sodium tungstate is an anti‐obesity drug targeting peripheral tissues. In vivo, sodium tungstate reduces body weight gain and food intake through increasing energy expenditure and lipid oxidation, but it also modulates hypothalamic gene expression when orally administered, raising the possibility of a direct effect of sodium tungstate on the central nervous system. Methods: Sodium tungstate was administered intraperitoneally (ip) to Wistar rats, and its levels were measured in cerebrospinal fluid through mass spectrometry. Body weight gain and food intake were monitored for 24 h after its administration in the third ventricle. Hypothalamic protein was obtained and subjected to western blot. In vitro, hypothalamic N29/4 cells were treated with 100 µM sodium tungstate or 1 nM leptin, and protein and neural gene expression were analysed. Results: Sodium tungstate crossed the blood–brain barrier, reaching a concentration of 1.31 ± 0.07 mg/l in cerebrospinal fluid 30 min after ip injection. When centrally administered, sodium tungstate decreased body weight gain and food intake and increased the phosphorylation state of the main kinases and proteins involved in leptin signalling. In vitro, sodium tungstate increased the phosphorylation of janus kinase‐2 (JAK2) and extracellular signal‐regulated kinase‐1/2 (ERK1/2), but the activation of each kinase did not depend on each other. It regulated c‐myc gene expression through the JAK2/STAT system and c‐fos and AgRP (agouti‐related peptide) gene expression through the ERK1/2 pathway simultaneously and independently. Conclusions: Sodium tungstate increased the activity of several kinases involved in the leptin signalling system in an independent way, making it a suitable and promising candidate as a leptin‐mimetic compound in order to manage obesity.     

Pulmonary delivery of peptide YY for food intake suppression and reduced body weight gain in rats

Aims: Peptide YY (PYY) is an endogenous anorectic gut‐secreted peptide that has been shown to suppress appetite in animals and humans, when given by injection. This study tested if needle‐free pulmonary delivery of PYY enables food intake suppression and reduced body weight gain in rats. The PYY pharmacokinetics and effects on brain neuropeptide levels were also examined. Methods: Rats received single or once‐daily 7‐day pulmonary administration of saline or PYYs. Food intake and body weight gain were monitored to study the effects of different doses (0.08–0.90 mg/kg) of PYY3‐36, PYY1‐36 and PYY13‐36. Plasma PYY pharmacokinetics were determined via enzyme‐linked immunosorbent assay. Changes in orexigenic neuropeptide Y (NPY) and c‐Fos protein levels in the hypothalamus arcuate nucleus (ARC) were measured by immunofluorescence microscopy. Results: PYY3‐36 caused dose‐dependent and 4‐ to 6‐h food intake suppression following pulmonary delivery. At 0.80 mg/kg, the effect was significant with 35.1 ± 5.7 and 19.7 ± 4.2% suppression at 4 and 6 h, respectively. Repeated administration for 7 days reduced cumulative body weight gain by 39.4 ± 11.0%. PYY1‐36, but not PYY13‐36, was equipotent to PYY3‐36 in food intake suppression. The plasma PYY concentration reached its peak at 10 min following pulmonary delivery with 12–14% of bioavailability. Increased c‐Fos and reduced NPY expressions were observed in the hypothalamus ARC, consistent with the magnitude of food intake suppression by each of the PYYs. Conclusions: Pulmonary delivery of PYY enabled significant 4‐ to 6‐h food intake suppression via 12–14% of lung absorption and hypothalamic ARC interaction, leading to reduced body weight gain in rats.     

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.     

Physiology of food intake and regulation of body weight

Feeding is often influenced by competitive needs or by environmental factors. Nevertheless, in physiological conditions hunger is elicited by depletion of macronutrients. The first question is what specific signals cause food intake? Recent data suggest that the signal comes not from exclusive depletion of carbohydrates or of anyone type of the major macronutrients but from overall decreased cellular power production (hypoischymetric signal). Locomotion free metabolic rate has been shown to decrease preceding hunger and to increase in order to determine satiety. Satiation, which occurs largely before ingested nutrients can cross the intestinal barrier and replete the inner milieu, obeys a specific mechanism. Following the stimulation by ingestion of the oro-gastro-intestinal receptors metabolic hormones such as glucagon and insulin are released and enhance metabolism of endogenous reserves. The so-induced endogenous "meal" brings about an anticipatory hypermetabolism which inhibits further ingestion. Post-absorptive satiety subsequently will replace the pre-absorptive state of satiation. The long term regulation of body weight is more subtle. When the actual body weight exceeds its defended value, responsiveness towards signals of hunger diminishes. This hyporesponsiveness seems to be a consequent of an enlargement of the microscopic fat depot at the level of hypothalamic receptive structures which parallels the peripheral increase of the macroscopic fat depot. Thus, hunger promoting signals become less effective and feeding decreases. A symmetrical process takes place in case of body weight loss which results in central hyperresponsiveness to hunger related stimuli and thus facilitates feeding and body weight recovery.     

Melatonin regulates energy balance and attenuates fever in Siberian hamsters

Fever is considered an important host defense response but requires significant metabolic energy. During winter many animals must balance immune function with competing physiological demands (i.e. thermoregulation) to survive. Winterlike patterns of melatonin secretion induce a number of energy-saving adaptations. For instance, Siberian hamsters attenuate the duration of fever during simulated short winter day lengths, presumably to conserve energy. To determine the proximate role of melatonin in mediating this photoperiodic response, hamsters housed in long days were injected with saline or melatonin 4 h before lights off for either 1 or 6 wk and assessed for fever following injections of bacterial lipopolysaccharide. Fever duration was attenuated (32%) only in hamsters that decreased body mass, increased cortisol, and exhibited gonadal regression in response to 6 wk of melatonin. Because melatonin-treated hamsters lost significant body mass, fever was assessed in a second long-day group following ad libitum food intake, food restriction, or 24-h food deprivation. Food restriction sufficient to reduce body mass by approximately 25%, but not to reduce leptin, did not influence fever, and 24-h food deprivation virtually abolished fever. Our data suggest that long-term exposure to long-duration melatonin signals is required to induce the physiological changes necessary for short-day immune responses, perhaps involving interactions with hormones such as cortisol and leptin.     

Peripheral oxyntomodulin reduces food intake and body weight gain in rats

Oxyntomodulin (OXM) is a circulating gut hormone released post prandially from cells of the gastrointestinal mucosa. Given intracerebroventricularly to rats, it inhibits food intake and promotes weight loss. Here we report that peripheral (ip) administration of OXM dose-dependently inhibited both fast-induced and dark-phase food intake without delaying gastric emptying. Peripheral OXM administration also inhibited fasting plasma ghrelin. In addition, there was a significant increase in c-fos immunoreactivity, a marker of neuronal activation, in the arcuate nucleus (ARC). OXM injected directly into the ARC caused a potent and sustained reduction in refeeding after a fast. The anorectic actions of ip OXM were blocked by prior intra-ARC administration of the glucagon-like peptide-1 (GLP-1) receptor antagonist, exendin(9-39), suggesting that the ARC, lacking a complete blood-brain barrier, could be a potential site of action for circulating OXM. The actions of ip GLP-1, however, were not blocked by prior intra-ARC administration of exendin(9-39), indicating the potential existence of different OXM and GLP-1 pathways. Seven-day ip administration of OXM caused a reduction in the rate of body weight gain and adiposity. Circulating OXM may have a role in the regulation of food intake and body weight.     

Phosphoinositide-specific inositol polyphosphate 5-phosphatase IV inhibits inositide trisphosphate accumulation in hypothalamus and regulates food intake and body weight

The enzyme phosphatidylinositol 3-kinase (PI3-kinase) exerts an important role in the transduction of the anorexigenic and thermogenic signals delivered by insulin and leptin to first-order neurons of the arcuate nucleus in the hypothalamus. The termination of the intracellular signals generated by the activation of PI3-kinase depends on the coordinated activity of specific inositol phosphatases. Here we show that phosphoinositide-specific inositol polyphosphate 5-phosphatase IV (5ptase IV) is highly expressed in neurons of the arcuate and lateral nuclei of the hypothalamus. Upon intracerebroventricular (ICV) treatment with insulin, 5ptase IV undergoes a time-dependent tyrosine phosphorylation, which follows the same patterns of canonical insulin signaling through the insulin receptor, insulin receptor substrate-2, and PI3-kinase. To evaluate the participation of 5ptase IV in insulin action in hypothalamus, we used a phosphorthioate-modified antisense oligonucleotide specific for this enzyme. The treatment of rats with this oligonucleotide for 4 d reduced the hypothalamic expression of 5ptase IV by approximately 80%. This was accompanied by an approximately 70% reduction of insulin-induced tyrosine phosphorylation of 5ptase IV and an increase in basal accumulation of phosphorylated inositols in the hypothalamus. Finally, inhibition of hypothalamic 5ptase IV expression by the antisense approach resulted in reduced daily food intake and body weight loss. Thus, 5ptase IV is a powerful regulator of signaling through PI3-kinase in hypothalamus and may become an interesting target for therapeutics of obesity and related disorders.     

Effects of manipulating hypothalamic triiodothyronine concentrations on seasonal body weight and torpor cycles in Siberian hamsters

Siberian hamsters display photoperiodically regulated annual cycles in body weight, appetite, and reproduction. Previous studies have revealed a profound up-regulation of type 3 deiodinase (DIO3) mRNA in the ventral ependyma of the hypothalamus associated with hypophagia and weight loss in short-day photoperiods. DIO3 reduces the local availability of T(3), so the aim of this study was to test the hypothesis that decreased hypothalamic T(3) availability underlies the short-day-induced catabolic state. The experimental approach was to determine whether a local increase in T(3) in the hypothalamus of hamsters exposed to short days could reverse the behavioral and physiological changes induced by this photoperiod. In study 1, microimplants releasing T(3) were placed bilaterally into the hypothalamus. This treatment rapidly induced a long-day phenotype including increased appetite and body weight within 3 wk of treatment and increased fat mass and testis size by the end of the 10-wk study period. In study 2, hypothalamic T(3) implants were placed into hamsters carrying abdominal radiotelemetry implants. Again body weight increased significantly, and the occurrence of winter torpor bouts was dramatically decreased to less than one bout per week, whereas sham-implanted hamsters entered torpor up to six times a week. Our findings demonstrate that increased central T(3) induces a long-day metabolic phenotype, but in neither study was the molt cycle affected, so we infer that we had not disrupted the initial detection of photoperiod. We conclude that hypothalamic thyroid hormone availability plays a key role in seasonal regulation of appetite, body weight, and torpor.     

Antagonism of ghrelin receptor reduces food intake and body weight gain in mice

BACKGROUND AND AIMS: Ghrelin, an endogenous ligand for growth hormone secretagogue receptor (GHS-R), is an appetite stimulatory signal from the stomach with structural resemblance to motilin. We examined the effects of the gastric peptide ghrelin and GHS-R antagonists on energy balance and glycaemic control in mice. MATERIALS AND METHODS: Body weight, fat mass, glucose, insulin, and gene expression of leptin, adiponectin, and resistin in white adipose tissue (WAT) were measured after repeated administrations of ghrelin under a high fat diet. Gastric ghrelin gene expression was assessed by northern blot analysis. Energy intake and gastric emptying were measured after administration of GHS-R antagonists. Repeated administration of GHS-R antagonist was continued for six days in ob/ob obese mice. RESULTS: Ghrelin induced remarkable adiposity and worsened glycaemic control under a high fat diet. Pair feeding inhibited this effect. Ghrelin elevated leptin mRNA expression and reduced resistin mRNA expression. Gastric ghrelin mRNA expression during fasting was increased by a high fat diet. GHS-R antagonists decreased energy intake in lean mice, in mice with diet induced obesity, and in ob/ob obese mice; it also reduced the rate of gastric emptying. Repeated administration of GHS-R antagonist decreased body weight gain and improved glycaemic control in ob/ob obese mice. CONCLUSIONS: Ghrelin appears to be closely related to excess weight gain, adiposity, and insulin resistance, particularly under a high fat diet and in the dynamic stage. Gastric peptide ghrelin and GHS-R may be promising therapeutic targets not only for anorexia-cachexia but also for obesity and type 2 diabetes, which are becoming increasingly prevalent worldwide.     

Regulation of food intake and body weight by cobalt porphyrins in animals.

Cobalt-substituted protoporphyrin administered subcutaneously to normal adult rats elicited prompt decreases in food intake and sustained decreases in body weight. Repetitive parenteral administration of small doses of this synthetic heme analogue resulted in dose-related diminutions of carcass fat content without changes in carcass protein content. Direct injection of the compound into the third ventricle of the brain produced changes in food intake and body weight that were quantitatively similar to those observed after parenteral treatment but required only 1-2% of the parenteral dose. The effects of intracerebroventricularly administered cobalt protoporphyrin on body weight were dose-related and were not produced by inorganic cobalt, heme, and a number of other metal-substituted protoporphyrins. Differential body weights between control and treated animals persisted for at least 300 days after intracerebroventricular injections of a single dose (0.2 or 0.4 mumol/kg of body weight) of the compound. Similar effects were observed after subcutaneous administration of the metalloporphyrin to genetically obese Zucker (fa/fa) rats and normal and genetically obese (ob/ob) mice as well as chickens and dogs. Cobalt-substituted mesoporphyrin elicited comparable effects on food intake and body weight. The results of these studies define a new biological action of cobalt protoporphyrin and demonstrate that this and certain other cobalt porphyrins can act, at least in part, in the central nervous system to regulate appetite and to produce long-sustained diminutions in body weight and carcass content of fat in animals.     

Liquid versus solid carbohydrate: effects on food intake and body weight

BACKGROUND: Beverages are contributing an increased proportion of energy to the diet. Because they elicit a weak compensatory dietary response, they may increase risk of positive energy balance. OBJECTIVES: This study aimed to document the differential effects of matched liquid and solid carbohydrate loads on diet and body weight. DESIGN: In a cross-over design, seven males and eight females consumed dietary carbohydrate loads of 1880 kJ/day as a liquid (soda) or solid (jelly beans) during two 4 week periods separated by a 4 week washout. Subjects were permitted to consume the loads however they chose. In addition to baseline measurements, diet records were obtained on random days throughout the study, body composition was measured weekly, physical activity was assessed before and after treatments and hunger was assessed during washout and midway through each treatment. RESULTS: Free-feeding energy intake during the solid period was significantly lower than intake prior to this period. Dietary energy compensation was precise (118%). No decrease in free-feeding energy intake occurred during the liquid period. Total daily energy intake increased by an amount equal to the load resulting in dietary compensation of -17%. Consequently, body weight and BMI increased significantly only during the liquid period. Physical activity and hunger were unchanged. CONCLUSIONS: This study indicates that liquid carbohydrate promotes positive energy balance, whereas a comparable solid carbohydrate elicits precise dietary compensation. Increased consumption of energy-yielding fluids may promote positive energy balance.