Abrogation of peripheral cholecystokinin-satiety in the capsaicin treated rat

CCK-sensitive C fibers activate NTS leptin receptor-expressing neurons via NMDA receptors

The hormone leptin reduces food intake through actions in the peripheral and central nervous systems, including in the hindbrain nucleus of the solitary tract (NTS). The NTS receives viscerosensory information via vagal afferents, including information from the gastrointestinal tract, which is then relayed to other central nervous system (CNS) sites critical for control of food intake. Leptin receptors (lepRs) are expressed by a subpopulation of NTS neurons, and knockdown of these receptors increases both food intake and body weight. Recently, we demonstrated that leptin increases vagal activation of lepR-expressing neurons via increased NMDA receptor (NMDAR) currents, thereby potentiating vagally evoked firing. Furthermore, chemogenetic activation of these neurons was recently shown to inhibit food intake. However, the vagal inputs these neurons receive had not been characterized. Here we performed whole cell recordings in brain slices taken from lepRCre × floxedTdTomato mice and found that lepR neurons of the NTS are directly activated by monosynaptic inputs from C-type afferents sensitive to the transient receptor potential vanilloid type 1 (TRPV1) agonist capsaicin. CCK administered onto NTS slices stimulated spontaneous glutamate release onto lepR neurons and induced action potential firing, an effect mediated by CCKR1. Interestingly, NMDAR activation contributed to the current carried by spontaneous excitatory postsynaptic currents (EPSCs) and enhanced CCK-induced firing. Peripheral CCK also increased c-fos expression in these neurons, suggesting they are activated by CCK-sensitive vagal afferents in vivo. Our results indicate that the majority of NTS lepR neurons receive direct inputs from CCK-sensitive C vagal-type afferents, with both peripheral and central CCK capable of activating these neurons and NMDARs able to potentiate these effects.

TRPV1 enhances cholecystokinin signaling in primary vagal afferent neurons and mediates the central effects on spontaneous glutamate release in the NTS

The gut peptide cholecystokinin (CCK) is released during feeding and promotes satiation by increasing excitation of vagal afferent neurons that innervate the upper gastrointestinal tract. Vagal afferent neurons express CCK1 receptors (CCK1Rs) in the periphery and at central terminals in the nucleus of the solitary tract (NTS). While the effects of CCK have been studied for decades, CCK receptor signaling and coupling to membrane ion channels are not entirely understood. Previous findings have implicated L-type voltage-gated calcium channels as well as transient receptor potential (TRP) channels in mediating the effects of CCK, but the lack of selective pharmacology has made determining the contributions of these putative mediators difficult. The nonselective ion channel transient receptor potential vanilloid subtype 1 (TRPV1) is expressed throughout vagal afferent neurons and controls many forms of signaling, including spontaneous glutamate release onto NTS neurons. Here we tested the hypothesis that CCK1Rs couple directly to TRPV1 to mediate vagal signaling using fluorescent calcium imaging and brainstem electrophysiology. We found that CCK signaling at high concentrations (low-affinity binding) was potentiated in TRPV1-containing afferents and that TRPV1 itself mediated the enhanced CCK1R signaling. While competitive antagonism of TRPV1 failed to alter CCK1R signaling, TRPV1 pore blockade or genetic deletion (TRPV1 KO) significantly reduced the CCK response in cultured vagal afferents and eliminated its ability to increase spontaneous glutamate release in the NTS. Together, these results establish that TRPV1 mediates the low-affinity effects of CCK on vagal afferent activation and control of synaptic transmission in the brainstem.NEW & NOTEWORTHY Cholecystokinin (CCK) signaling via the vagus nerve reduces food intake and produces satiation, yet the signaling cascades mediating these effects remain unknown. Here we report that the capsaicin receptor transient receptor potential vanilloid subtype 1 (TRPV1) potentiates CCK signaling in the vagus and mediates the ability of CCK to control excitatory synaptic transmission in the nucleus of the solitary tract. These results may prove useful in the future development of CCK/TRPV1-based therapeutic interventions.

Capsaicin for Weight Control: “Exercise in a Pill” (or Just Another Fad)?

Medical management of obesity represents a large unmet clinical need. Animal experiments suggest a therapeutic potential for dietary capsaicin, the pungent ingredient in hot chili peppers, to lose weight. This is an attractive theory since capsaicin has been a culinary staple for thousands of years and is generally deemed safe when consumed in hedonically acceptable, restaurant-like doses. This review critically evaluates the available experimental and clinical evidence for and against capsaicin as a weight control agent and comes to the conclusion that capsaicin is not a magic “exercise in a pill”, although there is emerging evidence that it may help restore a healthy gut microbiota.

Regulation of systemic metabolism by the autonomic nervous system consisting of afferent and efferent innervation

Autonomic nerves, sympathetic and parasympathetic, innervate organs and modulate their functions. It has become evident that afferent and efferent signals of the autonomic nervous system play important roles in regulating systemic metabolism, thereby maintaining homeostasis at the whole-body level. Vagal afferent nerves receive signals, such as nutrients and hormones, from the peripheral organs/tissues including the gastrointestinal tract and adipose tissue then transmit these signals to the hypothalamus, thereby regulating feeding behavior. In addition to roles in controlling appetite, areas in the hypothalamus serves as regulatory centers of both sympathetic and parasympathetic efferent fibers. These efferent innervations regulate the functions of peripheral organs/tissues, such as pancreatic islets, adipose tissues and the liver, which play roles in metabolic regulation. Furthermore, recent evidence has unraveled the metabolic regulatory systems governed by autonomic nerve circuits. In these systems, afferent nerves transmit metabolic information from peripheral organs to the central nervous system (CNS) and the CNS thereby regulates the organ functions through the efferent fibers of autonomic nerves. Thus, the autonomic nervous system regulates the homeostasis of systemic metabolism, and both afferent and efferent fibers play critical roles in its regulation. In addition, several lines of evidence demonstrate the roles of the autonomic nervous system in regulating and dysregulating the immune system. This review introduces variety of neuron-mediated inter-organ cross-talk systems and organizes the current knowledge of autonomic control/coordination of systemic metabolism, focusing especially on a liver-brain-pancreatic β-cell autonomic nerve circuit, as well as highlighting the potential importance of connections with the neuronal and immune systems.

Gochujang prepared using rice and wheat koji partially alleviates high-fat diet-induced obesity in rats

The aim of this study was to compare whether gochujang products prepared using giant embryo rice koji (rice gochujang, RG) and wheat koji (wheat gochujang, WG) have anti-obesity effects on rats fed a high-fat diet (HFD), who served as a model for obesity. The nutritional composition of RG and WG including proximate constituents, amino acid and fatty acid compositions were investigated. Consequently, the secondary fermented metabolites were analyzed in RG and WG by ultrahigh-performance liquid chromatography and mass spectrometry. Rats were fed a HFD containing 10% RG powder (HFD-RG) or 10% WG powder (HFD-WG) for 8 weeks. Body weight gain, weights of liver, epididymal, retroperitoneal, perirenal, and total white fat pads, and levels of serum triglyceride (TG), total cholesterol, low-density lipoprotein cholesterol, and leptin were lower in all gochujang groups than in the HFD group. Furthermore, RG and WG treatment decreased the hepatic TG content and lipid accumulation and significantly reduced the size of epididymal adipocytes. These effects are probably mediated through inhibition of hepatic fatty acid synthase, acetyl CoA carboxylase, malic enzyme, and adipose tissue lipoprotein lipase activities. The anti-obesity effect was slightly greater in the HFD-RG group than in the HFD-WG group. This effect may be attributed to secondary metabolites, such as capsaicin, genistein, daidzein, soyasaponin, and lysophosphatidylcholines, contained in gochujang prepared using giant embryo rice or wheat koji.

Non-sulfated cholecystokinin-8 reduces meal size and prolongs the intermeal interval in male Sprague Dawley rats

The current study measured seven feeding responses by non-sulfated cholecystokinin-8 (NS CCK-8) in freely fed adult male Sprague Dawley rats. The peptide (0, 0.5, 1, 3, 5 and 10 nmol/kg) was given intraperitoneally (ip) prior to the onset of the dark cycle, and first meal size (MS), second meal size, intermeal interval (IMI) length, satiety ratio (SR = IMI/MS), latency to first meal, duration of first meal, number of meals and 24-hour food intake were measured. We found that NS CCK-8 (0.5 and 1.0 nmol/kg) reduced MS, prolonged IMI length and increased SR during the dark cycle. Furthermore, the specific CCK-B receptor antagonist L365, 260 (1 mg/kg, ip) attenuated these responses. These results support a possible role for NS CCK-8 in regulating food intake.

The metabolic role of vagal afferent innervation

The regulation of energy and glucose balance contributes to whole-body metabolic homeostasis, and such metabolic regulation is disrupted in obesity and diabetes. Metabolic homeostasis is orchestrated partly in response to nutrient and vagal-dependent gut-initiated functions. Specifically, the sensory and motor fibres of the vagus nerve transmit intestinal signals to the central nervous system and exert biological and physiological responses. In the past decade, the understanding of the regulation of vagal afferent signals and of the associated metabolic effect on whole-body energy and glucose balance has progressed. This Review highlights the contributions made to the understanding of the vagal afferent system and examines the integrative role of the vagal afferent in gastrointestinal regulation of appetite and glucose homeostasis. Investigating the integrative and metabolic role of vagal afferent signalling represents a potential strategy to discover novel therapeutic targets to restore energy and glucose balance in diabetes and obesity.

Control of Food Intake by Gastrointestinal Peptides: Mechanisms of Action and Possible Modulation in the Treatment of Obesity

This review focuses on the control of appetite by food intake-regulatory peptides secreted from the gastrointestinal tract, namely cholecystokinin, glucagon-like peptide 1, peptide YY, ghrelin, and the recently discovered nesfatin-1 via the gut-brain axis. Additionally, we describe the impact of external factors such as intake of different nutrients or stress on the secretion of gastrointestinal peptides. Finally, we highlight possible conservative—physical activity and pharmacotherapy—treatment strategies for obesity as well as surgical techniques such as deep brain stimulation and bariatric surgery also altering these peptidergic pathways.

Role of the vagus nerve in the development and treatment of diet-induced obesity

This review highlights evidence for a role of the vagus nerve in the development of obesity and how targeting the vagus nerve with neuromodulation or pharmacology can be used as a therapeutic treatment of obesity. The vagus nerve innervating the gut plays an important role in controlling metabolism. It communicates peripheral information about the volume and type of nutrients between the gut and the brain. Depending on the nutritional status, vagal afferent neurons express two different neurochemical phenotypes that can inhibit or stimulate food intake. Chronic ingestion of calorie-rich diets reduces sensitivity of vagal afferent neurons to peripheral signals and their constitutive expression of orexigenic receptors and neuropeptides. This disruption of vagal afferent signalling is sufficient to drive hyperphagia and obesity. Furthermore neuromodulation of the vagus nerve can be used in the treatment of obesity. Although the mechanisms are poorly understood, vagal nerve stimulation prevents weight gain in response to a high-fat diet. In small clinical studies, in patients with depression or epilepsy, vagal nerve stimulation has been demonstrated to promote weight loss. Vagal blockade, which inhibits the vagus nerve, results in significant weight loss. Vagal blockade is proposed to inhibit aberrant orexigenic signals arising in obesity as a putative mechanism of vagal blockade-induced weight loss. Approaches and molecular targets to develop future pharmacotherapy targeted to the vagus nerve for the treatment of obesity are proposed. In conclusion there is strong evidence that the vagus nerve is involved in the development of obesity and it is proving to be an attractive target for the treatment of obesity.

The subfornical organ: a novel site of action of cholecystokinin

The subfornical organ (SFO) is an important sensory circumventricular organ implicated in the regulation of fluid homeostasis and energy balance. We investigated whether the SFO is activated by the hormone cholecystokinin (CCK). CCK₁ and CCK₂ receptors were identified in the SFO by RT-PCR. Dissociated SFO neurons that responded to CCK (40/77), were mostly depolarized (9.2 ± 0.9 mV, 30/77), but some were hyperpolarized (-7.3 ± 1.1 mV, 10/77). We next examined the responses of SFO neurons in vivo to CCK (16 μg/kg ip), in the presence and absence of CCK₁ or CCK₂ receptor antagonists (devazepide; 600 μg/kg and L-365,260; 100 μg/kg, respectively), using the functional activation markers c-Fos and phosphorylated extracellular signal-related kinase (p-ERK). The nucleus of the solitary tract (NTS) served as a control for CCK-induced activity. There was a significant increase in c-Fos expression in the NTS (259.2 ± 20.8 neurons) compared with vehicle (47.5 ± 2.5). Similarly, in the SFO, c-Fos was expressed in 40.5 ± 10.6 neurons in CCK-treated compared with 6.6 ± 2.7 in vehicle-treated rats (P < 0.01). Devazepide significantly reduced the effects of CCK in the NTS but not in SFO. L-365,260 blocked the effects of CCK in both brain regions. CCK increased the number of p-ERK neurons in NTS (27.0 ± 4.0) as well as SFO (18.0 ± 4.0), compared with vehicle (8.0 ± 2.6 and 4.3 ± 0.6, respectively; P < 0.05). Both devazepide and L-365,260 reduced CCK-induced p-ERK in NTS, but only L-365,260 reduced it in the SFO. In conclusion, the SFO represents a novel brain region at which circulating CCK may act via CCK₂ receptors to influence central autonomic control.

The feeding responses evoked by cholecystokinin are mediated by vagus and splanchnic nerves

Total or selective branch vagotomy attenuates the reduction of cumulative food intake by cholecystokinin (CCK)-8 and CCK-33 respectively. However, the role of the sympathetic innervation of the gut and the role of the vagus nerve in feeding responses, which include meal size (MS) and intermeal interval (IMI), evoked by CCK-8 and CCK-33 have not been evaluated. Here, we tested the effects of total subdiaphragmatic vagotomy (VGX) and celiaco-mesenteric ganglionectomy (CMGX) on the previous feeding responses by CCK-8 and CCK-33 (0, 1, 3, and 5 nmol/kg given intraperitoneally). We found (1) that both peptides reduced meal size and CCK-8 (5 nmol) and CCK-33 (1 and 3 nmol) prolonged IMI, (2) that VGX attenuated the reduction of MS but failed to attenuate the prolongation of IMI by both peptides and (3) that CMGX attenuated the reduction of meal size by CCK-8 and the prolongation of IMI by both peptides. Therefore, the feeding responses evoked by CCK-8 require intact vagus and splanchnic nerves: the reduction of MS by CCK-33 requires an intact vagus nerve, and the prolongation of IMI requires the splanchnic nerve. These findings demonstrate the differential peripheral neuronal mediation of the feeding responses evoked by CCK-8 and CCK-33.

Eating disorders and gastrointestinal peptides

PURPOSE OF REVIEW

Disturbances in gastrointestinal hormones have been implicated in the pathogenesis of eating disorders such as anorexia nervosa and bulimia nervosa. However, the contribution of these hormonal changes to the onset and maintenance of eating disorder remains unclear. We focus our review on a selective number of gastrointestinal hormones that are known to play a role in the regulation of short-term or long-term energy balance and examine their association with eating disorder in recently published literature.

RECENT FINDINGS

Several new studies reported differential changes of ghrelin isoforms during fasting and following nutrient ingestion. New findings on other appetite-regulating hormones (peptide YY, cholecystokinin, incretin hormones and pancreatic polypeptide) at different nutritional states and disease stage have also been reported in subtypes of eating disorder. Most of the changes in peripheral hormones disappeared or partially recovered after the restoration of weight with nutritional and behavioral therapy.

SUMMARY

Dysregulation of gastrointestinal hormones is more likely to contribute to the maintenance of the disordered eating behavior and related metabolic outcomes as well as the clinical course rather than causing them. A better understanding of this relationship also carries implications for developing targeted hormone-base treatment for eating disorder.

Obesity treatment: novel peripheral targets

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

Phytochemicals in the Control of Human Appetite and Body Weight

Since obesity has grown to epidemic proportions, its effective management is a very important clinical issue. Despite the great amount of scientific effort that has been put into understanding the mechanisms that lead to overconsumption and overweight, at the moment very few approaches to weight management are effective in the long term. On the other hand, modern society is also affected by the growing incidence of eating disorders on the other side of the spectrum such as anorexia and bulimia nervosa which are equally difficult to treat. This review will try to summarise the main findings available in the literature regarding the effect of plants or plant extracts (phytochemicals) on human appetite and body weight. The majority of plant extracts are not single compounds but rather a mixture of different molecules, therefore their mechanism of action usually targets several systems. In addition, since some cellular receptors tend to be widely distributed, sometimes a single molecule can have a widespread effect. This review will attempt to describe the main phytochemicals that have been suggested to affect the homeostatic mechanisms that influence intake and body weight. Clinical data will be summarised and scientific evidence will be reviewed.

Interactions of gastrointestinal peptides: ghrelin and its anorexigenic antagonists

Food intake behaviour and energy homeostasis are strongly regulated by a complex system of humoral factors and nerval structures constituting the brain-gut-axis. To date the only known peripherally produced and centrally acting peptide that stimulates food intake is ghrelin, which is mainly synthesized in the stomach. Recent data indicate that the orexigenic effect of ghrelin might be influenced by other gastrointestinal peptides such as cholecystokinin (CCK), bombesin, desacyl ghrelin, peptide YY (PYY), as well as glucagon-like peptide (GLP). Therefore, we will review on the interactions of ghrelin with several gastrointestinal factors known to be involved in appetite regulation in order to elucidate the interdependency of peripheral orexigenic and anorexigenic peptides in the control of appetite.

Gut hormones: implications for the treatment of obesity

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

Intracerebroventricular capsaicin influences the body weight increasing of rats

Adult rats were treated for ten days with capsaicin or with NaCl 0.9% directly injected into the lateral cerebral ventricles through a surgically implanted cannula. A third group of rats was implanted with the same cannula but did not receive any treatment. The food intake and the body weight were recorded for at least six weeks after stopping the treatment. The animals were always kept at constant ambient temperature of 22 °C. The body weight of the capsaicin-treated group was reduced by the treatment, and showed a regular but lower degree of recovery trend than the control groups after the treatment period. In fact the capsaicin treated animals never reached the body weight of the controls. Nevertheless, food intake did not significantly vary after the capsaicin treatment. On the basis of these and previous findings, we can assume that capsaicin injected into the cerebral ventricles to rats kept at constant ambient temperature can acts on hypothalamic neurons, but a permanent action on metabolic pathways can not be excluded.

Oleylethanolamide impairs glucose tolerance and inhibits insulin-stimulated glucose uptake in rat adipocytes through p38 and JNK MAPK pathways

Oleylethanolamide (OEA) is a lipid mediator that inhibits food intake and body weight gain and also exhibits hypolipemiant actions. OEA exerts its anorectic effects peripherally through the stimulation of C-fibers. OEA is synthesized in the intestine in response to feeding, increasing its levels in portal blood after the meal. Moreover, OEA is produced by adipose tissue, and a lipolytic effect has been found. In this work, we have examined the effect of OEA on glucose metabolism in rats in vivo and in isolated adipocytes. In vivo studies showed that acute administration (30 min and 6 h) of OEA produced glucose intolerance without decreasing insulin levels. Ex vivo, we found that 10 min of preincubation with OEA inhibited 30% insulin-stimulated glucose uptake in isolated adipocytes. Maximal effect was achieved at 1 microM OEA. The related compounds palmitylethanolamide and oleic acid had no effect, suggesting a specific mechanism. Insulin-stimulated GLUT4 translocation was not affected, but OEA promoted Ser/Thr phosphorylation of GLUT4, which may impair transport activity. This phosphorylation may be partly mediated by p38 and JNK kinases, since specific inhibitors (SB-203580 and SP-600125) partly reverted the inhibitory effect of OEA on insulin-stimulated glucose uptake. These results suggest that the lipid mediator OEA inhibits insulin action in the adipocyte, impairing glucose uptake via p38 and JNK kinases, and these effects may at least in part explain the glucose intolerance produced in rats in vivo. These effects of OEA may contribute to the anorectic effects induced by this mediator, and they might be also relevant for insulin resistance in adipose tissue.

Increased ATP content/production in the hypothalamus may be a signal for energy-sensing of satiety: studies of the anorectic mechanism of a plant steroidal glycoside

A steroidal glycoside with anorectic activity in animals, termed P57AS3 (P57), was isolated from Hoodia gordonii and found to have homologies to the steroidal core of cardiac glycosides. Intracerebroventricular (i.c.v.) injections of the purified P57AS3 demonstrated that the compound has a likely central (CNS) mechanism of action. There is no evidence of P57AS3 binding to or altering activity of known receptors or proteins, including Na/K-ATPase, the putative target of cardiac glycosides. The studies demonstrated that the compound increases the content of ATP by 50-150% in hypothalamic neurons. In addition, third ventricle (i.c.v.) administration of P57, which reduces subsequent 24-h food intake by 40-60%, also increases ATP content in hypothalamic slice punches removed at 24 h following the i.c.v. injections. In related studies, in pair fed rats fed a low calorie diet for 4 days, the content of ATP in the hypothalami of control i.c.v. injected animals fell by 30-50%, which was blocked by i.c.v. injections of P57AS3. With growing evidence of metabolic or nutrient-sensing by the hypothalamus, ATP may be a common currency of energy sensing, which in turn may trigger the appropriate neural, endocrine and appetitive responses as similar to other fundamental hypothalamic homeostatic centers for temperature and osmolarity.

Gastrointestinal mechanisms of satiation for food

Satiation for food comprises the physiological processes that result in the termination of eating. Satiation is evoked by physical and chemical qualities of ingested food, which trigger afferent signals to the brain from multiple sites in the GI tract, including the stomach, the proximal small intestine, the distal small intestine and the colon. The physiological nature of each signal's contribution to satiation and overall control of food intake is likely to vary, depending on the level of the GI tract from which the signal arises. This article is a critical, though non-exhaustive, review of our current understanding of the mechanisms and adaptive value of satiation signals from the stomach and intestine.

Effects of perivagal administration of capsaicin on post-surgical food intake

The vagus nerve has been related to the short-term control of food intake. This involvement has previously been explored by examining the food intake of animals after recovery from a vagotomy or immediately after the intervention, among other methods. In the present work, a study was conducted on the impact of the perivagal application of capsaicin (a specific neurotoxic treatment that destroys most of the vagal afferent pathways) on the intake of water and solid (experiment 1) or liquid (experiment 2) food presented after the surgery The results of experiment 1 showed that lesioned animals consume significantly larger amounts of food and water compared with controls at 6, 12, and 24 h (but not at 48 or 72 h) after the surgical intervention. Likewise, experiment 2 revealed a greater intake of liquid food by capsaicin-treated animals at the first post-surgical sessions. These data are discussed in terms of the role played by vagal afferent fibers in the control of short-term food intake.

An anorexic lipid mediator regulated by feeding

Oleylethanolamide (OEA) is a natural analogue of the endogenous cannabinoid anandamide. Like anandamide, OEA is produced in cells in a stimulus-dependent manner and is rapidly eliminated by enzymatic hydrolysis, suggesting a function in cellular signalling. However, OEA does not activate cannabinoid receptors and its biological functions are still unknown. Here we show that, in rats, food deprivation markedly reduces OEA biosynthesis in the small intestine. Administration of OEA causes a potent and persistent decrease in food intake and gain in body mass. This anorexic effect is behaviourally selective and is associated with the discrete activation of brain regions (the paraventricular hypothalamic nucleus and the nucleus of the solitary tract) involved in the control of satiety. OEA does not affect food intake when injected into the brain ventricles, and its anorexic actions are prevented when peripheral sensory fibres are removed by treatment with capsaicin. These results indicate that OEA is a lipid mediator involved in the peripheral regulation of feeding.

The effectiveness of popular, non-prescription weight loss supplements

OBJECTIVES

To review the evidence for the effectiveness of popular, non-prescription weight loss supplements.

DATA SOURCES

A detailed literature search including all relevant medical and supplementary medicine databases and evidence submitted from manufacturers.

DATA SYNTHESIS

The theoretical basis and rationale for the use of each substance is considered along with available research in the published literature on effectiveness and potential risks. We classified the level of evidence represented by the main research studies on each substance.

CONCLUSIONS

There is no good evidence for any weight loss benefits from most of the substances reviewed here. There is some support for mild effects of capsaicin, caffeine and fibre, but only in whole foods. In some cases (e.g., chitosan), there is a plausible theoretical basis for the product, but no supporting proof of effect in humans in the absence of a calorie-controlled diet. Possible synergistic effects of different ingredients cannot be dismissed, but cannot be assessed from current data. There is an absence of good quality research on many substances, which means that advertising claims may be misleading.

Capsaicin-sensitive fibers are required for the anorexic action of systemic but not central bombesin

Bombesin (BN) suppresses food intake in rats whether given centrally or systemically. Although the brain BN-sensitive receptors are known to be essential for the anorexic effect of systemic BN, the mode of communication between the gut and the brain remains unclear. This study assessed whether the anorexic effect of systemic BN is mediated humorally or via neural circuits. Afferent neurons were lesioned using capsaicin (50 mg/kg sc) on postnatal day 2, and responses to BN were assessed during adulthood. Capsaicin treatment decreased body weight gain significantly from postnatal age 4-7 wk. Peripheral BN (4-16 micrograms/kg ip) dose dependently suppressed food intake in control animals. However, this effect was completely blocked in capsaicin-treated rats. In contrast to systemic effects, feeding-suppressant effects of centrally administered BN (0.01-0.5 microgram icv) were not affected by capsaicin treatment. This research suggests that peripheral BN communicates with the brain via a neuronal system(s) whose afferent arm is constituted of capsaicin-sensitive C and/or Adelta-fibers, whereas the efferent arm of this satiety- and/or anorexia-mediating circuitry is capsaicin resistant.

Time-course of the pancreatic changes following long-term stimulation or inhibition of the CCK-A receptor

Cholecystokinin (CCK) reportedly induces both hyperplastic and hypertrophic changes in the pancreas. Blockade of the CCK receptor results in decreased pancreatic secretion and atrophy. The aim of this study was to evaluate the time-course of the effects of stimulation and inhibition of the CCK-A receptor in the rat exocrine pancreas. Male rats had infusion of sulfated CCK-8, the CCK-A receptor antagonist devazepide, or sodium chloride by osmotic minipumps. After 36 h, 3, 7, or 28 d the rats had ip injections of thymidine, and 1 h later they were sacrificed. The pancreas was excised, weighed, and its content of protein, DNA, water, and enzymes was analyzed. Histologic samples were prepared for autoradiography. Pancreatic weight, protein, and DNA were increased at 36 h after the start of CCK infusion and throughout the study period. CCK stimulation also increased the content of trypsin at days 3 and 28. The labeling index of pancreatic acinar cells was increased at 36 h. Blockade of endogenous CCK by the receptor antagonist devazepide led to decreased pancreatic weight from the third day of infusion, whereas the protein content was decreased from the seventh day. At day 28, the DNA content was decreased by devazepide. However, the labeling index of acinar cells decreased transiently already at 36 h. Neither CCK nor devazepide caused any changes of protein content:DNA content ratio during the study. Continuous infusion of CCK caused pancreatic hyperplasia already after 36 h. Stimulation up to 28 d did not cause any further effects. The adverse changes found after blockade of the CCK-A receptor showed much of the same time-course.

Neonatal capsaicin treatment (NCT) alters the metabolic activity of the rat somatosensory cortex in response to mechanical deflection of the mystacial vibrissae

Capsaicin, a selective neurotoxin of unmyelinated C-fibers, was administered to neonatal rat pups at birth. Following a recovery period of 10 days, pups were injected with 2-deoxy-glucose (2DG) and subjected to repetitive mechanical stimulation to the left whiskerpad. Their brains were then harvested for autoradiography. The observed changes in 2DG uptake in the somatosensory cortex of capsaicin-treated rats were compared to vehicle-treated rats. The cross-sectional area and density of 2DG uptake by the primary and the secondary somatosensory cortex (SSI and SSII, respectively) were measured. Capsaicin-treated rats significantly exhibited a reduction in area of activation and a decrease of 2DG uptake in both structures. The present data indicates that neonatal capsaicin affects the functional activity of the rat somatosensory cortex. It is suggested that unmyelinated sensory afferents play a role in the development of the rat somatosensory system.

Effects of the CCK receptor antagonist MK-329 on food intake in broiler chickens

The cholecystokinin (CCK) receptor antagonist MK-329 (previously L-364,718) was administered intraperitoneally to free-feeding broiler chickens and tested for conditioning effects using the colored food paradigm. The 8.0, 16.0, and 32.0 micrograms/kg doses of MK-329 did not exert any effect on food intake and failed to condition a color preference or aversion. When higher doses were used (90, 180, and 360 micrograms/kg) MK-329 caused a significant increase in food intake during the 2-h test period. Intravenously injected MK-329 (70, 140, and 280 micrograms/kg) produced an increase in food intake, with maximum increases occurring at a dose of 70 micrograms/kg. CCK (14 micrograms/kg) caused a reduction in feeding, and this effect was not blocked by pretreatment with intraperitoneal injection of MK-329 (32, 90, 180, and 360 micrograms/kg). The results question the role of endogenous CCK in satiety in chickens.

Weight loss induced by gastric implant in rats. Effects of capsaicin sensory denervation

To study the efficacy and mechanism of action of the intragastric bubble, 1- to 5-ml silicone bubbles were surgically implanted into the stomachs of 10- to 12-week-old female rats. To test the hypothesis that the satiety effects of the implant are mediated by visceral sensory nerves, a subgroup was treated as neonates with the sensory neurotoxin capsaicin, 50 mg/kg subcutaneously. In control animals, the implants caused a transient decrease in body weight, compared to sham-implanted animals, most evident at three days and abolished by 18 days after operation. In contrast, capsaicin-treated animals did not lose weight in response to gastric implantation. Substance P was decreased in the vagus nerves of capsaicin-treated animals, confirming sensory denervation. At autopsy, all gastric implanted rats had enlarged stomachs. We conclude that intact sensory innervation is essential for weight loss in response to the gastric bubble.

Effect of neonatal capsaicin treatment on cholecystokinin-(CCK8) satiety and axonal transport of CCK binding sites in the rat vagus nerve

Cholecystokinin (CCK) binding sites which accumulate at ligatures placed on the rat vagus nerve may mediate the satiety actions of CCK. Treatment of neonatal rats with capsaicin attenuated the satiety effect of injected CCK in adult life. Capsaicin pretreatment also reduced, but did not eliminate, the accumulation of CCK binding sites proximal and distal to ligatures on either cervical trunk. A similar effect was observed following ligation of subdiaphragmatic vagal trunks. The CCK receptor antagonists, MK-329 and L-365,260, inhibited binding to capsaicin- and vehicle-treated nerves to a similar degree. Densities of CCK binding sites in the nucleus tractus solitarius and area postrema were also markedly affected by neonatal capsaicin treatment.

Effects of a gastric implant on body weight and gastrointestinal hormones in cafeteria diet obese rats

In order to evaluate the effectiveness of a gastric implant in an animal model of dietary obesity, silicone implants (2.5 ml) were inserted into the stomachs of male rats maintained on a chow or "cafeteria" diet. At the time of implantation, the cafeteria fed rats weighed 14% more than chow fed controls. Overweight cafeteria fed animals lost weight in response to the gastric implant, whereas control chow fed animals did not. Both implant groups had significant increases in stomach weights in contrast to sham implant groups, but the increase was much less in the cafeteria diet group. The fasting plasma levels of the gastrointestinal hormones, gastrin and pancreatic polypeptide, and oxytocin (a marker of vagal afferent function) were measured by radioimmunoassay. Cafeteria fed sham or implanted animals had significantly higher fasting levels of plasma oxytocin and gastrin, and significantly lower plasma levels of pancreatic polypeptide than the chow fed groups. These studies demonstrate that the gastric implant has more effect on weight in overweight animals on a palatable mixed diet, perhaps related to both mechanical and neural factors.

Cholecystokinin

1. CCK-peptides are distributed throughout the whole brain with the exception of the cerebellum. 2. There is strong evidence that they act as neuromodulators on the noradrenergic, opioid and mainly dopaminergic system. 3. CCK reduces food-intake. However, tolerance occurs, when chronically given. Thus, potential benefits in the treatment of obesity seem unlikely. 4. CCK increases threshold and tolerance to electrically and thermally induced cutaneous pain. CCK yields relief of pain in colic and ischaemic pain. 5. To date, results about CCK-content in CSF and post-mortem-brain in various psychiatric and neurological diseases related to the dopaminergic system are equivocal. 6. Treatment studies do not provide evidence for beneficial effects of CCK-peptides in schizophrenia.

The sensory-efferent function of capsaicin-sensitive sensory neurons

Capsaicin-sensitive sensory neurons convey to the central nervous system signals (chemical and physical) arising from viscera and the skin which activate a variety of visceromotor and neuroendocrine reflexes integrated at various levels (intramurally in peripheral organs, at level of prevertebral ganglia, spinal and supraspinal level). Much evidence is now available that peripheral terminals of certain sensory neurons, widely distributed in skin and viscera have the ability to release, upon adequate stimulation, their transmitter content. In addition to the well-known "axon reflex" arrangement, the capsaicin-sensitive sensory neurons have the ability to release the stored transmitter also from the same terminal which is excited by the environmental stimulus. The efferent function of these sensory neurons is realized through the direct and indirect (i.e. mediated by activation of other cells) effects of released mediators. The action of released transmitters on postjunctional elements covers a wide range of effects which may have a physiological or pathological relevance. Development of drugs capable of controlling the sensory-efferent functions of the capsaicin-sensitive sensory neurons represent a new and very promising area of research for pharmacological treatment of various human diseases.

The cholecystokinin receptor antagonist L364,718 increases food intake in the rat by attenuation of the action of endogenous cholecystokinin

1. To determine the role of endogenous cholecystokinin (CCK) in the regulation of food intake, the effects of the potent CCK receptor antagonist L364,718 were investigated on the intake of a palatable diet in non-deprived rats. The effect of a single dose of proglumide was also investigated for comparative purposes. In addition, the ability of L364,718 to antagonize the reduction in food intake produced by exogenous cholecystokinin-octapeptide (CCK8) or bombesin in food-deprived rats was determined. 2. L364,718 (10-100 micrograms kg-1, i.p.) increased the intake of palatable diet during the 30 min test period. Proglumide (300 mg kg-1, i.p.) also increased the intake of palatable diet. Conversely, CCK8 (0.5-5 micrograms kg-1, i.p.) produced a reduction in the intake of the diet. 3. In fasted rats, L364,718 (100 micrograms kg-1, i.p.) antagonized the reduction in food intake produced by CCK8 (10 micrograms kg-1, i.p.) but not that produced by bombesin (50 micrograms kg-1, i.p.). L364,718 did not increase food intake in these animals when measured over a 6 h period. 4. It is concluded that L364,718 is a potent, selective antagonist of the effects of CCK8 on food intake. The observation that L364,718 and proglumide increase the intake of a palatable diet provides some evidence that endogenous CCK is involved in the control of food intake in this model.

Cholecystokinin-octapeptide-induced hypothermia in rats: dose-effect and structure-effect relationships, effect of ambient temperature, pharmacological interactions and tolerance

Subcutaneous injection of cholecystokinin octapeptide (CCK-8) (0.005-1.25 mg/kg) elicited dose-dependent hypothermia in rats. The threshold of the response was between 0.01 and 0.05 mg/kg and the dose-response curve levelled off at doses larger than 0.2-0.5 mg/kg. Warm and cold ambient temperatures decreased and increased the response, respectively. Pretreatment with capsaicin, morphine, naloxone, atropine, haloperidol or propranolol did not affect the response to CCK-8, whereas pretreatment with phenoxybenzamine and a large dose of proglumide, an antagonist for CCK-receptors, attenuated the hypothermia. It seems that neither capsaicin-sensitive thermal and non-thermal afferents, nor opiate mechanisms are involved in the response, but alpha-adrenoceptors might be of some importance in the hypothermia. Non-sulphated-CCK-8, the C-terminal tetrapeptide and hexapeptide, [D-Ala4]-CCK-8 and [D-Met6]-CCK-8 were ineffective. Chronic treatment with CCK-8 resulted in the development of tolerance to the thermoregulatory effect, while the hypothermic responses to apomorphine and capsaicin were not affected. It seems that the tolerance cannot be attributed to conditioned homeostatic reactions.

Capsaicin and its effects upon meal patterns, and glucagon and epinephrine suppression of food intake

The neurotoxin capsaicin has been shown to selectively interfere with unmyelinated sensory fibers, as well as leading to depletions of substance P and other peptides. Meal pattern analysis was performed both before and after treatment with capsaicin in twelve adult male Sprague-Dawley rats. Capsaicin treatment only briefly altered feeding patterns. No long term effect on body weight was noted. These same animals were then tested for the appetite suppressing effects of IP injections of glucagon (125 micrograms/kg) and epinephrine (30 micrograms/kg). Capsaicin treated rats decreased their intake of sweetened condensed milk during a 30 minute test in response to glucagon and epinephrine. Controls failed to suppress intake in response to glucagon, but drank less milk after epinephrine than did capsaicin treated rats. Efficacy of capsaicin treatment was obtained using similarly treated animals subject to histological evaluation within 2 days of capsaicin treatment. These results suggest that peripherally generated information relayed to the CNS via small-diameter sensory neurons is not a necessary component of the normal hunger/satiety sequence, nor body weight regulation.