Appetite-regulating Peptides Research Articles

Gender Differences for Ghrelin Levels in Alcohol‐Dependent Patients and Differences Between Alcoholics and Healthy Controls

Ghrelin is a 28-amino acid gut-brain peptide, mainly secreted by the gastric mucosa. Its effects are linked to energy homeostasis and particularly seem to increase hunger and food intake. In recent years, studies suggested that appetite-regulating peptides, such as ghrelin play a relevant role in alcoholism. Since data published to date on the potential role of ghrelin as state and/or trait marker in alcoholism and the association with craving are controversial, we aimed at further elucidating these aspects. One-hundred nine alcohol-dependent abstinent patients after withdrawal (27 f, 82 m), (ICD 10 F 10.25) and 45 healthy volunteers (12 f, 33 m) were included. Laboratory testing (Ghrelin RIA 90, Mediagnost Inc., Germany) was performed and several craving scales [Obsessive Compulsive Drinking Scale, Alcohol Urge Questionnaire and Visual Analogue Scale (VAS)] were applied at the beginning and at the end of the 3-week rehabilitation program. (1) Ghrelin levels are significantly higher in female alcohol-dependent patients as compared to controls, not, however, in men alcoholics. (2) In several statistical subanalyses, an association of craving and ghrelin was found. The results, however, remain heterogeneous. The data suggest gender-dependent ghrelin levels in alcohol-dependent patients. We therefore conclude, that it might be useful to perform statistical analyses gender-specific. With regard to a potential correlation of ghrelin and craving the results seem to depend on gender, duration of the abstinence period and the instrument used.

High altitude induced anorexia: Effect of changes in leptin and oxidative stress levels

High altitude (HA) exposure usually leads to a significant weight loss in non-acclimatized humans. Anorexia is believed to be the main cause of this body weight loss. Appetite regulatory peptides, i.e. leptin and neuropeptide Y play a key role in food intake and energy homeostasis. Recent studies suggests increased oxidative stress during HA exposure. In present study effect of HA exposure on levels of leptin and NPY was evaluated along with N-acetyl cysteine (NAC) and vitamin E supplementation in relation to food intake and body weight changes. The study was conducted on 30 healthy male volunteers (age 19 – 29 years). Subjects were divided randomly into three groups of 10 each. Group 1 (placebo) supplemented with 400 mg of calcium gluconate, group 2 and 3 were supplemented with 400 mg of NAC and 400 mg vitamin E, respectively per day. The study was conducted at low altitude (320 m, Phase I), at HA 3600 m (Phase II) and at an altitude of 4580 m (Phase III). On HA exposure significant reduction in plasma leptin levels was observed in all the groups on day 2 (Phase II) along with decrease in food intake and reduction in body weight. Statistically significant increase in blood malondialdehyde (MDA) levels was seen in all the groups on HA exposure (Phase II, Day 2), but the maximum increase was in case of placebo group (65.1%) on day 2 (Phase II) in comparison to low altitude values. The decrease in energy intake was almost same in all the groups indicating that antioxidant supplementation did not provide any protection against HA anorexia. From the study, it may be concluded that leptin and oxidative stress possibly are not the key players for HA anorexia.

Food-induced expression of orexin receptors in rat duodenal mucosa regulates the bicarbonate secretory response to orexin-A

Presence of appetite-regulating peptides orexin-A and orexin-B in mucosal endocrine cells suggests a role in physiological control of the intestine. Our aim was to characterize orexin-induced stimulation of duodenal bicarbonate secretion and modulation of secretory responses and mucosal orexin receptors by overnight food deprivation. Lewis x Dark Agouti rats were anesthetized and proximal duodenum cannulated in situ. Mucosal bicarbonate secretion (pH stat) and mean arterial blood pressure were continuously recorded. Orexin-A was administered intra-arterially close to the duodenum, intraluminally, or into the brain ventricles. Total RNA was extracted from mucosal specimens, reverse transcribed to cDNA and expression of orexin receptors 1 and 2 (OX1 and OX2) measured by quantitative real-time PCR. OX1 protein was measured by Western blot. Intra-arterial orexin-A (60-600 nmol.h(-1).kg(-1)) increased (P < 0.01) the duodenal secretion in fed but not in fasted animals. The OX1 receptor antagonist SB-334867, which was also found to have a partial agonist action, abolished the orexin-induced secretory response but did not affect secretion induced by the muscarinic agonist bethanechol. Atropine, in contrast, inhibited bethanechol but not orexin-induced secretion. Orexin-A infused into the brain ventricles (2-20 nmol.kg(-1).h(-1)) or added to luminal perfusate (1.0-100 nM) did not affect secretion, indicating that orexin-A acts peripherally and at basolateral receptors. Overnight fasting decreased mucosal OX1 and OX2 mRNA expression (P < 0.01) as well as OX1 protein expression (P < 0.05). We conclude that stimulation of secretion by orexin-A may involve both receptor types and is independent of cholinergic pathways. Intestinal OX receptors and secretory responses are markedly related to food intake.

Role of Appetite‐Regulating Peptides in Alcohol Craving: An Analysis in Respect to Subtypes and Different Consumption Patterns in Alcoholism

A role of appetite-regulating peptides like leptin and ghrelin in the neurobiology of alcohol craving has been proposed by several studies. Aim of this analysis was to search for differences regarding an association between these peptides and alcohol craving with respect to different subtypes and beverage consumption patterns in patients with alcohol dependence. We analyzed a sample of 188 patients at admission for alcohol detoxification regarding leptin and ghrelin (n=117) serum levels. Craving was measured using the Obsessive Compulsive Drinking Scale (OCDS). Patients were classified according to Lesch's typology of alcohol dependence and according to their preferred type of alcoholic beverage (beer, wine, spirits). Using general linear models to analyze a possible interaction between subtypes and leptin/ghrelin levels with respect to craving, we found a significant positive association for leptin in patients of Lesch's types 1 and 2, and in patients consuming beer or wine. Ghrelin levels showed a significant trend regarding an association with craving in patients of Lesch's type 1. In the other subgroups we found no significant results. Our findings show that appetite-regulating peptides may be of special importance regarding alcohol craving in subtypes of patients. This may explicate at least in part previous contradictory findings.

Influence of photoperiod and gonadal status on food intake, adiposity, and gene expression of hypothalamic appetite regulators in a seasonal mammal

We studied the effects of photoperiod on metabolic profiles, adiposity, and gene expression of hypothalamic appetite-regulating peptides in gonad-intact and castrated Soay rams. Groups of five to six animals were studied 6, 18, or 30 wk after switching from long photoperiod (LP: 16 h of light) to short photoperiod (SP: 8 h of light). Reproductive and metabolic indexes were measured in blood plasma. Expression of neuropeptide Y (NPY), proopiomelanocortin (POMC), and leptin receptor (ObRb) in the arcuate nucleus was measured using in situ hybridization. Testosterone levels of intact animals were low under LP, increased to a peak at 16 wk under SP, and then declined. Voluntary food intake (VFI) was high under LP in both intact and castrated animals, decreased to a nadir at 12-16 wk under SP, and then recovered, but only in intact rams as the reproductive axis became photorefractory to SP. NPY gene expression varied positively and POMC expression varied negatively with the cycle in VFI, with differences between intact and castrate rams in the refractory phase. ObRb expression decreased under SP, unrelated to changes in VFI. Visceral fat weight also varied between the intact and castrated animals across the cycle. We conclude that 1) photoperiodic changes in VFI reflect changes in NPY and POMC gene expression, 2) changes in ObRb gene expression are not necessarily determinants of changes in VFI, 3) gonadal status affects the pattern of VFI that changes with photoperiod, and 4) in the absence of gonadal factors, animals can eat less but gain adiposity.

Effects of dipeptidyl peptidase IV on the satiety actions of peptide YY

Dipeptidyl peptidase IV (DP IV) inhibitors are currently being developed to prolong the biological activity of insulinotropic peptides as a novel approach in the treatment of diabetes. We hypothesised that DP IV inhibition could attenuate the satiety actions of peptide YY (PYY) by altering the conversion of PYY(1-36) to PYY(3-36). The effects of PYY delivered by osmotic mini-pumps were assessed in rats treated with a DP IV inhibitor and in a rat model deficient in DP IV. Pharmacological levels of total PYY were found in the circulation after the exogenous administration of PYY(3-36). While both PYY(1-36) and PYY(3-36) reduced food intake in normal rats, PYY(1-36) was ineffective in rats deficient in DP IV. When re-fed after a 24-h fast, DP IV-deficient rats exhibited higher food intake and weight gain than normal rats. Moreover, unlike controls, there was no postprandial increase in PYY levels in DP IV-deficient rats. Despite these findings, administration of a DP IV inhibitor, Pro-boroPro, did not alter the acute anorectic effects of exogenous PYY(1-36) in normal rats. This could be the result of the protection of other appetite regulatory peptides or the generation of PYY(3-36) by remaining DP IV activity or other dipeptidyl peptidases. Although DP IV inhibition with Pro-boroPro attenuated the generation of PYY(3-36), our results indicate that short-term DP IV inhibition does not eliminate the satiety actions of exogenously administered PYY(1-36) at the doses tested.

Neural interaction between galanin-like peptide (GALP)- and luteinizing hormone-releasing hormone (LHRH)-containing neurons

Galanin-like peptide (GALP), commonly known as an appetite-regulating peptide, has been shown to increase plasma luteinizing hormone (LH) through luteinizing hormone-releasing hormone (LHRH). This led us to investigate, using both light and electron microscopy, whether GALP-containing neurons in the rat brain make direct inputs to LHRH-containing neurons. As LHRH-containing neurons are very difficult to demonstrate immunohistochemically with LHRH antiserum without colchicine treatment, we used a transgenic rat in which LHRH tagged with enhanced green fluorescence protein facilitated the precise detection of LHRH-producing neuronal cell bodies and processes. This is the first study to report on synaptic inputs to LHRH-containing neurons at the ultrastructural level using this transgenic model. We also used immunohistochemistry to investigate the neuronal interaction between GALP- and LHRH-containing neurons. The experiments revealed that GALP-containing nerve terminals lie in close apposition with LHRH-containing cell bodies and processes in the medial preoptic area and the bed nucleus of the stria terminalis. At the ultrastructural level, the GALP-positive nerve terminals were found to make axo-somatic and axo-dendritic synaptic contacts with the EGFP-positive neurons in these areas. These results strongly suggest that GALP-containing neurons provide direct input to LHRH-containing neurons and that GALP plays a crucial role in the regulation of LH secretion via LHRH.

Novel functions of appetite-regulating peptides

Novel functions of appetite-regulating peptides

Reduction in Adiposity Affects the Extent of Afferent Projections to Growth Hormone-Releasing Hormone and Somatostatin Neurons and the Degree of Colocalization of Neuropeptides in Growth Hormone-Releasing Hormone and Somatostatin Cells of the Ovine Hypothalamus

Various neuropeptides and neurotransmitters affect GH secretion by acting on GHRH and somatostatin (SRIF) cells. GH secretion is also affected by alteration in adiposity, which could be via modulation of GHRH and SRIF cells. We quantified colocalization of neuropeptides in GHRH and SRIF cells and afferent projections to these cells in lean (food restricted) and normally fed sheep (n=4/group). The number of GHRH-immunoreactive (IR) cells in the arcuate nucleus was higher in lean animals, but the number of SRIF-IR cells in the periventricular nucleus was similar in the two groups. A subpopulation of GHRH-IR cells colocalized neuropeptide Y in lean animals, but this was not seen in normally fed animals. GHRH/galanin (GAL) colocalization was higher in lean animals with no difference in numbers of GHRH/tyrosine hydroxylase or GHRH/GAL-like peptide cells. SRIF/enkephalin colocalization was lower in lean animals. The percentage of GHRH neurons receiving SRIF input was similar in lean and normally fed animals, but more GHRH cells received input from enkephalin afferents in normally fed animals. The percentage of SRIF cells receiving GHRH, neuropeptide Y, GAL, and orexin afferents was higher in lean animals. These findings provide an anatomical evidence of central mechanism(s) by which appetite-regulating peptides and dopamine could regulate GH secretion. Increased input to SRIF cells in lean animals may be inhibitory and permissive of increased GH. The appearance of NPY in GHRH cells of lean animals may be a mechanism for regulation of increasing GH secretion with reduced adiposity.

Appetite regulatory peptides in Indian Antarctic expeditioners

Antarctica presents an inhospitable environment due to extreme low temperature, high wind velocity, low humidity, snowstorms, long polar days and nights, high level of UV radiations, magnetic storms and increased ionisation along with social isolation and sexual deprivation. Acclimatisation to any new condition is associated with certain metabolic changes along with alteration in nutritional requirements. There are reports of increased food intake and gain in body weight during past Indian Antarctic expeditions. Therefore, the present study was undertaken with the aim to assess the changes in appetite regulatory peptides i.e. leptin and neuropeptide Y in relation to energy intake and expenditure of the Antarctic expeditioners. The study was conducted in three phases viz. Phase I at Goa (basal), Phase II 48 h after reaching Antarctica and Phase III after one month of stay at Antarctica. Energy and nutrient intake were analysed from the duplicate plate samples of the expeditioners. Energy expenditure was computed using 24 h activity records for 7 days. Blood samples were collected in each phase for biochemical estimations. After reaching Antarctica, the expeditioners were active and the total energy expenditure (mean ± SEM, n = 10) was found to be 3120 ± 474 kcal/day. The actual energy intake was found to be 3911 ± 310 kcal/day. This indicates that the Antarctic expeditioners had very active life and weight gain during expedition could be due to positive energy balance. After 48 h of stay at Antarctica plasma leptin levels (mean ± SEM, n = 22) decreased from normal basal values 5.66 ( ± 0.59) ng/ml (Phase I) to 4.40 ( ± 0.37) ng/ml (Phase II), even though there was an increase in body fat. Increased level of plasma leptin was observed in Phase III as compared to phase I and II. Concomitantly there was increase in plasma neuropeptide Y levels from 0.303 ( ± 0.004) ng/ml to 1.211 ( ± 0. 27) ng/ml ( p

036. Nutritional programming, fetal growth and competence for life after birth

During the past decade there has been a world-wide series of epidemiological and clinical studies, which have demonstrated that there are associations between prenatal growth restriction and the risk of insulin resistance, central obesity, hypertension, type 2 diabetes and cardiovascular disease in adult life. More recently there has also been increasing interest in the consequences of exposure of the fetus to increased levels of maternal nutrition and whether maternal ‘overnutrition’ may program an ‘intergenerational cycle of obesity’. In this presentation, we review recent experimental evidence that highlights the impact of varying levels of fetal nutrition on the structural and functional development of the adipocyte, and on expression of a range of appetite regulatory peptides within the developing brain. The importance of the timing of nutritional perturbations and the different consequences of fetal undernutrition and overnutrition on subsequent gene expression within different fat depots and on the expression of appetite stimulatory and inhibitory neuropeptides will be reviewed. The importance of defining those critical windows during an individual’s lifespan when nutritional or other intervention strategies will have the maximum benefit in preventing the development of obesity and cardiovascular disease will also be considered.

The appetite-regulating peptide YY 3-36 (PYY3-36)* nasal spray may reduce intake of calories and facilitate weight loss,

The appetite-regulating peptide YY 3-36 (PYY3-36)* nasal spray may reduce intake of calories and facilitate weight loss,

Effects of lipopolysaccharide treatment on feeding of goldfish: role of appetite-regulating peptides

The gram-negative bacteria-derived endotoxin lipopolysaccharide (LPS) is known to play an important role in immune and neurological manifestations during bacterial infections. In mammals, peripheral or brain administration of LPS induces anorexia and is thought to exert its effects through activation of pro-inflammatory cytokines. In this study, we investigated the effects of peripheral (intraperitoneal, IP) and central (intracerebroventricular, ICV) injections of LPS on food intake of goldfish. Fish treated IP with 10, 25, 50, 100 or 250 ng/g LPS or ICV with 1, 10 and 100 ng/g LPS showed a significant dose-dependent decrease in food intake, compared to the saline-treated fish. We also examined the brain mRNA expression of several hypothalamic appetite-related neuropeptides in response to the administration of LPS. IP injections of LPS (100 ng/g) induced a decrease in NPY expression and an increase in CCK, CRF and CART expression. These results indicate that LPS is a potent anorexigenic factor in goldfish and that this endotoxin induces a reduction in appetite, at least in part, by influencing gene expression of appetite-related neuropeptides.

Short fasting dramatically decreases rat duodenal secretory responsiveness to orexin A but not to VIP or melatonin.

Orexins are involved in the central nervous control of appetite and behavior, and in addition, they are present in endocrine cells and/or neurons in the intestine. The role of these peptides in peripheral regulation of intestinal secretion has not been investigated. We thus compared the effects of orexin A and some established secretagogues on duodenal HCO3- secretion in fed rats with effects in rats exposed to short (overnight) food deprivation. Rats were anesthetized with thiobarbiturate, a 12-mm segment of proximal duodenum with intact blood supply was cannulated in situ, and the alkaline secretion was titrated by pH stat. Secretagogues were supplied specifically to the duodenum by close intra-arterial infusion. Orexin A (60-600 pmol x kg(-1) x h(-1)) caused marked and dose-dependent stimulation of the duodenal secretion in fed animals but did not affect secretion in overnight food-deprived animals. Similarly, short fasting caused a 100-fold increase in the amount of the muscarinic agonist bethanechol (from 50 to 5,000 nmol x kg(-1) x h(-1)) required for stimulation of the secretion. In contrast, the secretory responses to VIP (50-1,000 pmol x kg(-1) x h(-1)) and melatonin (20-200 nmol x kg(-1) x h(-1)) were not affected. The appetite-regulating peptide orexin A is thus a stimulant of intestinal secretion, but the response to this peptide as well as the muscarinic agonist bethanechol is markedly dependent on previous intake of food. Overnight fasting is a standard experimental procedure in studies of gastrointestinal function and pathophysiology in humans and animals. Studies made on neuroendocrine control of intestinal secretion may require reevaluation with respect to feeding status.

Photoperiod effects on gene expression for hypothalamic appetite-regulating peptides and food intake in the ram.

Relationship between voluntary food intake (VFI) and gene expression for appetite-regulating peptides was examined in the brains of Soay rams under contrasting photoperiods. Two groups (n = 8) were subjected to alternating block long-day (LD) and short-day photoperiods (SD) over a period of 42 wk to entrain long-term cycles in VFI. Five animals from each group were killed 18 wk into LD or SD, and the brains were collected for in situ hybridization studies. VFI was fourfold higher under LD compared with SD. Body weight, abdominal fat, or plasma leptin levels were similar under LD and SD. LD animals were in positive energy balance and sexually inactive, and SD animals were in negative energy balance and sexually active. Neuropeptide Y (NPY) mRNA levels were higher in the arcuate nucleus (ARC) under LD, and pro-opiomelanocortin expression was lower under LD. Leptin receptor (Ob-Rb) was higher in the ARC under LD. We conclude that photoperiod-induced increase in VFI correlates with expression of NPY, but not with expression of genes for other putative orexigenic peptides. Ob-Rb gene expression is regulated by photoperiod.

Alcohol intake, tumour necrosis factor-alpha, leptin and craving: factors of a possibly vicious circle?

Since the appetite-regulating peptide leptin was recently found to be highly correlated with both craving for alcohol and lifetime ethanol intake, the aim of our study was to test the hypothesis whether tumour necrosis factor-alpha (TNF-alpha) might be the factor that links alcohol intake with elevated leptin levels. TNF-alpha, leptin, and alcohol craving were assessed in male alcohol addicts at the onset of alcohol withdrawal and in matched controls. Increased leptin plasma levels in alcohol addicts correlated significantly with an enhanced secretion of TNF-alpha, which was itself related to the duration of alcohol misuse. Since leptin was shown to be associated with alcohol craving, a possible vicious circle is suggested, including the components: alcohol intake, increase of TNF-alpha, enhanced leptin secretion, enhanced alcohol craving, and consecutively increased alcohol intake.

Mitochondrial ATP Synthase--a Possible Target Protein in the Regulation of Energy Metabolism In Vitro and In Vivo

The increasing prevalence of obesity in the Western world has stimulated an intense search for mechanisms regulating food intake and energy balance. A number of appetite-regulating peptides have been identified, their receptors cloned and the intracellular events characterized. One possible energy-dissipating mechanism is the mitochondrial uncoupling of ATP-synthesis from respiratory chain oxidation through uncoupling proteins, whereby energy derived from food could be dissipated as heat, instead of stored as ATP. The exact role of the uncoupling proteins in energy balance is, however, uncertain. We show here that mitochondrial F1F0-ATP synthase itself is a target protein for an anorectic peptide, enterostatin, demonstrated both after affinity purification of rat brain membranes and through a direct physical interaction between enterostatin and purified F1-ATP synthase. In insulinoma cells (INS-1) enterostatin was found to target F1F0-ATP synthase, causing an inhibition of ATP production, an increased thermogenesis and increased oxygen consumption. The experiments suggest a role of mitochondrial F1F0-ATP synthase in the suppressed insulin secretion induced by enterostatin. It could be speculated that this targeting mechanism is involved in the decreased energy efficiency following enterostatin treatment in rat.

The role of NPY in the mediation of orexin-induced hypothermia

The mediation of orexin-A-induced hypothermia was investigated. Different doses of orexin-A (140–560 pmol) were administered intracerebroventricularly (i.c.v.) to adult male rats, and the colon temperature was used as an index of the thermoregulatory action. Orexin-A decreased both the basal colon temperature and the lipopolysaccharide-induced fever and exhibited a bell-shaped dose–response curve. I.c.v. pretreatment with neuropeptide Y (NPY) antiserum 24 h before orexin administration significantly decreased the hypothermic effect of orexin-A. These data strengthen the hypothesis that this appetite-regulating peptide might also play a role in thermoregulation, and its hypothermic effect seems to be mediated at least partially by NPY.

Sex and season are major determinants of voluntary food intake in sheep.

Seasonal changes in voluntary food intake (VFI) are seen in various species, including sheep. This paper reviews recent work in this area, especially in relation to alterations in the expression of appetite-regulating peptides in the brain of the sheep. Work in the hamster is also reviewed because this is another species in which VFI is regulated by photoperiod. In normally grazing sheep, appetite is maximal in the late summer/early autumn and minimal in spring. This appears to be owing to increased expression of the orexigenic peptide, neuropeptide Y. Similar results are obtained in sheep that are subjected to controlled photoperiod. The same does not appear to be true for hamsters. Further work in sheep has shown that there is a seasonal pattern of responsiveness to leptin that is more pronounced in females than in males. In particular, the effect of leptin to reduce food intake is maximal in female sheep in the spring; reasons for the sex difference are discussed.

Effects of Orexins on the Hypothalamic‐Pituitary‐Adrenal System

The effects of the recently identified neuropeptides orexin-A and orexin-B on the hypothalamic-pituitary-adrenal (HPA) system were investigated. An in vivo system was used to assess the central effects of both orexin-A and orexin-B. Different doses of the orexins (2.8-560 pmol) were administered intracerebroventricularly (i.c.v.) to adult male rats, and plasma corticosterone was used as an index of the degree of the activation of the HPA system. Both peptides exhibited a clear dose-response action, although orexin-B proved to be less effective than orexin-A. Pretreatment with the corticotropin-releasing hormone (CRH) antagonist alpha-helical CRH9-41 completely prevented the action of the orexins. Orexin-A, orexin-B or adrenocorticotropic hormone (ACTH) was further administered intraperitoneally (i.p.). While ACTH evoked a significant adrenal response, the orexins did not influence the basal secretion. Adrenal slices, oxygenized and perifused with Krebs' solution, were also treated with orexin-A, orexin-B or ACTH. Both orexins failed to modify the release of corticosterone, but ACTH induced a marked adrenal response. This study suggests that these appetite-regulating peptides might activate the HPA system at a central level but neither orexin-A nor orexin-B appears to modulate directly the adrenal corticosterone release.