Exendin-4, a GLP-1 receptor agonist, interacts with proteins and their products of digestion to suppress food intake in rats

The alpha-7 nicotinic acetylcholine receptor agonist GTS-21 does not affect food intake in rats

Obesity is a prevalent disease, but effective treatments remain limited. Agonists of the alpha-7 nicotinic acetylcholine receptor (α7nAChR) promote negative energy balance in mice, but these effects are not well-studied in rats. We tested the hypothesis that the α7nAChR agonist GTS-21 would decrease food intake and body weight in adult male Sprague Dawley rats. Contrary to our hypothesis, acute systemic administration of GTS-21 produced no significant effects on chow or high-fat diet (HFD) intake. Acute intracerebroventricular (ICV) GTS-21 also had no impact on chow intake, and actually increased body weight at the highest dose tested. Previous studies suggest that GTS-21 engages the food intake-suppressive glucagon-like peptide-1 (GLP-1) system in mice. As there are known species differences in GLP-1 physiology between mice and rats, we tested the ability of GTS-21 to elicit GLP-1 secretion in rats. Our results showed that plasma levels of total GLP-1 in rats were not significantly altered by peripheral GTS-21 injection. These results represent an advance in understanding how α7nAChR activation impacts energy balance control in rodents and suggest that there may be important differences between rats and mice in the ability of GTS-21/α7nAChR activation to increase secretion of GLP-1.

Milk whey from different animal species stimulates the in vitro release of CCK and GLP-1 through a whole simulated intestinal digestion

Milk whey is effective in enhancing satiety mainly due to its protein composition. Peptides and amino acids derived from digestion of whey protein can act as suppressants of appetite by stimulation of receptors of satiety gut hormones. But, the protein fraction of whey can vary depending on species of animal, season, lactation period, etc. The aim of this study is to evaluate the satiety effect of milk whey from different species of ruminants (cow, sheep, goat and a mixture of them) through a simulated in vitro digestion, which performed the whole gastrointestinal process, from oral digestion to colonic fermentation. The satiety effect of each sample was measured by the production of satiating hormones (CCK and GLP-1) secreted by enteroendocrine cell line (STC-1) after 2 hours of incubation with non-digested, digested and fermented whey. Digested samples have shown to be potent CCK and GLP-1 secretagogues followed by fermented and non-digested samples, showing that the last one showed a weak hormone stimulation. Digested goat whey was the most efficient stimulator of GLP-1 (86.33 ± 4.55 pg mL^-1) and fermented mixture whey produced the major release of CCK (80.78±1.81 pg mL^-1). This study demonstrates that milk whey is a suitable ingredient to stimulate satiety through the effect of peptides, amino acids produced from digestion, and metabolites released by fermentation.

Tryptophan Metabolites Along the Microbiota-Gut-Brain Axis: An Interkingdom Communication System Influencing the Gut in Health and Disease

The ‘microbiota-gut-brain axis’ plays a fundamental role in maintaining host homeostasis, and different immune, hormonal, and neuronal signals participate to this interkingdom communication system between eukaryota and prokaryota. The essential aminoacid tryptophan, as a precursor of several molecules acting at the interface between the host and the microbiota, is fundamental in the modulation of this bidirectional communication axis. In the gut, tryptophan undergoes 3 major metabolic pathways, the 5-HT, kynurenine, and AhR ligand pathways, which may be directly or indirectly controlled by the saprophytic flora. The importance of tryptophan metabolites in the modulation of the gastrointestinal tract is suggested by several preclinical and clinical studies; however, a thorough revision of the available literature has not been accomplished yet. Thus, this review attempts to cover the major aspects on the role of tryptophan metabolites in host-microbiota cross-talk underlaying regulation of gut functions in health conditions and during disease states, with particular attention to 2 major gastrointestinal diseases, such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), both characterized by psychiatric disorders. Research in this area opens the possibility to target tryptophan metabolism to ameliorate the knowledge on the pathogenesis of both diseases, as well as to discover new therapeutic strategies based either on conventional pharmacological approaches or on the use of pre- and probiotics to manipulate the microbial flora.

In vitro modulation of gut microbiota by whey protein to preserve intestinal health

The effect of several types of whey milk - cow, sheep, goat and a mixture of them (60 : 20 : 20, respectively) - was assessed in the human gut microbiota. The prebiotic potential of these substrates was evaluated through in vitro gastrointestinal digestion following faecal batch culture fermentations (mimicking colonic fermentation) for 48 hours, using faeces from normal-weight (NW) and obese (OB) donors. Throughout the fermentation process, pH, gas production, short chain and branched fatty acids (SCFA-BCFA) were measured, as well as the changes of microbiota using qPCR. The pH decreased in all whey samples during the fermentation process. Gas production was higher in all whey samples than in controls, especially at 12 hours (p < 0.05). The diversity of SCFA and BCFA production was significantly different between the donors, in particular cow and mixed whey. Whey milk had a strong prebiotic effect on the gut microbiota of NW and OB donors, showing a significant increase of Bifidobacterium (p < 0.05) with cow, sheep and mixed whey and increase in the Lactobacillus group, particularly in OB donors. Bacteria associated with obesity did not show an increase in any of the groups of donors. Therefore, supplementing a diet with these types of whey can selectively stimulate the growth of probiotic bacteria, enhancing SCFA production, which could improve intestinal disorders. In addition, it may be an interesting approach to the prevention of overweight and obesity and related diseases. Whey milk has a potent prebiotic effect. It can selectively stimulate desirable bacteria and SCFA profile, in both OB and NW donors, contributing to improved intestinal health and reducing obesity.

Meat proteins had different effects on oligopeptide transporter PEPT1 in the small intestine of young rats

The peptide transporter 1 (PEPT1) in the apical membrane of enterocytes is the central mechanism for regulating the absorption of di- and tripeptides. Dietary proteins may affect PEPT1 abundance and peptide absorption. The present study aimed to characterize changes in PEPT1 mRNA and PEPT1 protein levels in the duodenum and jejunum of young rats after 7-day diet intervention with casein (reference), soy, beef, pork, chicken and fish proteins and further evaluate the impact on the epithelial absorption capacity. RT-PCR and western blot analyses showed that: (1) PEPT1 protein level in duodenum was higher (p < 0.05) for soy protein group than that for casein group. However, no difference was observed in jejunal PEPT1 protein level between any two diet groups (p > 0.05). The soy protein group had lower crypt depth and higher V/C ratio in the jejunum (p < 0.05). (2) PEPT1 mRNA levels were lower (p < 0.05) in rat duodenum and jejunum in pork, chicken and fish protein groups, whose trend was contrary to the results of jejunual histological observation with lower crypt depth, greater villus height and higher V/C ratio. In conclusion, different meat proteins alter distinct PEPT1 expression level and absorption capacity as reflected by gut morphology in small intestine.

Milk-derived bioactive peptides inhibit human endothelial-monocyte interactions via PPAR-γ dependent regulation of NF-κB

Background

Milk-derived bioactive peptides retain many biological properties and have therapeutic effects in cardiovascular disorders such as atherosclerosis. Under inflammatory conditions the expression of endothelial cells adhesion molecules is induced, increasing monocyte adhesion to human vessel wall, a critical step in the pathogenesis of atherosclerosis. In the present work we explored the effects of milk-derived bioactive peptides on the expression of the inflammatory phenotype of human endothelial cells and their effects on monocyte adherence to endothelial cells.

Results

Treatment of endothelial cells with milk-derived hydrolysate inhibited their production of inflammatory proteins MCP-1 and IL-8 and expression of VCAM-1, ICAM-1 and E-selectin. Milk derived hydrolysate also attenuated the adhesion of human monocytes to activated endothelial cells. The effect was similar to that obtained in endothelial cells treated with troglitazone, a ligand of peroxisome proliferators-activator receptor-gamma (PPAR-γ). PPAR-γ is a transcription factor which when activated antagonises the pro-inflammatory capability of nuclear factor κB (NF-κB). We further examined whether the effects of milk-derived hydrolysates on endothelial cells may be mediated through NF-κB activation via a PPAR-γ dependent mechanism. The specific PPAR-γ inhibitor, GW9662 blocked the effects of the hydrolysate on the NF-κB-mediated chemokines and adhesion molecules expression in endothelial cells.

Conclusions

These results suggest that milk-derived bioactive peptides work as anti-atherogenic agents through the inhibition of endothelial-dependent adhesive interactions with monocytes by inhibiting the NF-κB pathway through a PPAR-γ dependent mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-014-0044-1) contains supplementary material, which is available to authorized users.

Bacterial metabolite indole modulates incretin secretion from intestinal enteroendocrine L cells

It has long been speculated that metabolites, produced by gut microbiota, influence host metabolism in health and diseases. Here, we reveal that indole, a metabolite produced from the dissimilation of tryptophan, is able to modulate the secretion of glucagon-like peptide-1 (GLP-1) from immortalized and primary mouse colonic L cells. Indole increased GLP-1 release during short exposures, but it reduced secretion over longer periods. These effects were attributed to the ability of indole to affect two key molecular mechanisms in L cells. On the one hand, indole inhibited voltage-gated K⁺ channels, increased the temporal width of action potentials fired by L cells, and led to enhanced Ca²⁺ entry, thereby acutely stimulating GLP-1 secretion. On the other hand, indole slowed ATP production by blocking NADH dehydrogenase, thus leading to a prolonged reduction of GLP-1 secretion. Our results identify indole as a signaling molecule by which gut microbiota communicate with L cells and influence host metabolism.

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Bacterial metabolite indole modulates secretion of incretin peptide GLP-1

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Indole widens the width of action potentials fired by L cells and elevates GLP-1

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Prolonged exposure to indole inhibits ATP production and thus GLP-1 secretion

Behavioural profile of exendin-4/naltrexone dose combinations in male rats during tests of palatable food consumption

RATIONALE

The glucagon-like peptide 1 receptor (GLP-1R) agonist exendin-4 potently suppresses food intake in animals and humans. However, little is known about the behavioural specificity of this effect either when administered alone or when co-administered with another anorectic agent.

OBJECTIVES

The present study characterises the effects of exendin-4, both alone and in combination with naltrexone, on behaviours displayed by male rats during tests with palatable mash.

METHODS

Experiment 1 examined the dose-response effects of exendin-4 (0.025-2.5 μg/kg, IP), while experiment 2 profiled the effects of low-dose combinations of the peptide (0.025 and 0.25 μg/kg) and naltrexone (0.1 mg/kg).

RESULTS

In experiment 1, exendin-4 dose dependently suppressed food intake as well as the frequency and rate of eating. However, these effects were accompanied by dose-dependent reductions in all active behaviours and, at 2.5 μg/kg, a large increase in resting and disruption of the behavioural satiety sequence (BSS). In experiment 2, while exendin-4 (0.25 μg/kg) and naltrexone each produced a significant reduction in intake and feeding behaviour (plus an acceleration in the BSS), co-treatment failed to produce stronger effects than those seen in response to either compound alone.

CONCLUSION

Similarities between the behavioural signature of exendin-4 and that previously reported for the emetic agent lithium chloride would suggest that exendin-4 anorexia is related to the aversive effects of the peptide. Furthermore, as low-dose combinations of the peptide with naltrexone failed to produce an additive/synergistic anorectic effect, this particular co-treatment strategy would not appear to have therapeutic significance.

Whey protein sweetened beverages reduce glycemic and appetite responses and food intake in young females

We hypothesized that whey protein (WP) will reduce the blood glucose spike, increase satiety, and reduce subsequent energy intake. The objective of the current study was to investigate WP-glucose mixed drinks relative to glucose or WP alone on glycemic response, appetite and energy intake (EI). In Experiment 1 sweetened beverages of 300-mL solution were given to 12 normal-weight females once a week after an overnight fast at 50 g or 75 g glucose, 25 g WP or 25 g WP with 50 g glucose. In Experiment 2 similar beverages were given to 15 normal-weight and 15 overweight females at 25 g glucose, 25 g WP alone or with 25 g glucose. Blood glucose and appetite were measured simultaneously at 0, 15, 30, 45, 60, 90, 120, 150 and 180 minutes in Experiment 1 and at the same time points but up to 120 minutes in Experiment 2. EI was calculated from a meal served at 180 minutes in Experiment 1. The blood glucose spike and hypoglycemia were reduced after WP and WP supplemented glucose in both normal-weight and overweight subjects resulting in smaller incremental area under the curves compared to the pure glucose (P < .05). EI was reduced after both WP drinks with or without glucose (P < .05). Changes in appetite and blood glucose at 180 minutes and blood glucose area under the curves were associated with EI. In conclusion, WP sweetened beverages attenuated blood glucose and appetite in both normal-weight and overweight females and reduced EI in normal-weight females at a 25 g level.

Appetite control and gastrointestinal hormonal behavior (CCK, GLP-1, PYY 1-36) following low doses of a whey protein-rich nutraceutic

Whey proteins represent the most satiating nutrients. In particular, their effects are due to enterohormonal changes (CCK, GLP-1 and PYY 1–36) observed after their exclusive ingestion. Glucomannan has important satiety property due to volume increase following gelification. The aim of the study is the evaluation of subjective rate of hunger and enterohormone concentrations (CCK, GLP-1, PYY 1–36) following oral loading of a mixture containing WP (8 g) or casein (8 g) plus glucomannan (1 g) (Colordiet^®, Inpha DUEMILA Srl Lecco, Italy). The study was conducted as a double-blind crossover with five healthy volunteers (BMI 22–26 kg/m² aging 18–65 years) in acute and a wash-out period of 1 week between the first and the second evaluation. From the analysis of the data, we observe that the load with WP induces a significant decrease in the desire to eat after 90 min (P < 0.0446) when compared with casein. As far as plasma hormones are concerned, there was a significant increase only in GLP-1 at 90 min after WP (P < 0.00166) and 180 min after casein (T0 vs. T180 P = 0.000129). There is a significant correlation between the increase in GLP-1 and decrease of desire to eat (R = −0.93). There is a tendency to the increasing of CCK after 90 min, which is not significant (P = 0.091). These results could be due to (a) the low number of cases or (b) the low dose of protein used. The present study suggests that a mixture of WP plus glucomannan exerts a decrease in the desire to eat which is correlated to enterohormonal modification (GLP-1 increase) despite the low content of protein (8 g) and the presence of glucomannan, which could reduce the fast absorption of WP in relation to the net forming during the gelification of the gastric environment.

Possible role of milk-derived bioactive peptides in the treatment and prevention of metabolic syndrome

The growing prevalence of metabolic syndrome as well as its impact on public health has garnered increased attention in recent years. As a result, metabolic syndrome is now considered one of the world's leading public health problems. Bioactive peptides deriving from milk proteins may play an important role in the prevention and treatment of metabolic syndrome and its complications via several mechanisms, such as the satiety response, the regulation of insulinemia levels and blood pressure, the uptake of free radicals, and alteration of the lipid profile. These peptides can be incorporated into functional foods or administered via nutraceuticals to decrease the risk of obesity, atherogenesis, arterial hypertension, and type 2 diabetes. Recent findings have generated considerable scientific and commercial interest in milk-derived bioactive peptides, leading to numerous publications on the effectiveness of these substances. This review summarizes the current knowledge on bioactive peptides derived from milk proteins and examines the potential value of these peptides in the treatment and prevention of metabolic syndrome and its complications.

Intragastric infusion of pea-protein hydrolysate reduces test-meal size in rats more than pea protein

Because protein hydrolysates are digested faster than the corresponding proteins, they may increase or hasten the acute eating-inhibitory effect of protein. Potential mediating mechanisms include accelerated or greater release of satiating gut peptides and activation of metabolic signals that inhibit eating. We tested these hypotheses in adult male rats that were surgically equipped with intragastric (IG) cannulas and adapted to 30-min test meals at dark onset after 14-h food deprivation. Equiosmotic 12 ml loads of saline-urea control (C), 13.6% pea protein (PP), or 13.6% PP hydrolysate (PPH, DSM/DFS, Delft, The Netherlands) solutions were IG infused in 1 min just before test meals. PPH reduced test-meal size compared to C more than PP (-3.8±0.3 g vs. -2.6±0.4 g; P<0.0001). Plasma glutamate increased more after PPH than PP (P<0.0001). Plasma lactate, alanine, insulin, glucagon, GLP-1 and paracetemol (an index of gastric emptying) all increased similarly, and glucose decreased similarly, after PPH or PP. Finally, PPH still reduced test-meal size more than PP (-4.6±0.3 g vs. -3.1±0.4 g; P<0.001) in rats after subdiaphragmatic vagal deafferentation, indicating that abdominal vagal afferents are not necessary for the eating-inhibitory effects of PP and PPH and, by extension, that gut peptides whose satiating effects depend on intact vagal afferents (e.g., CCK and glucagon) do not play crucial roles. Thus, PPH reduced short-term food intake more than PP under our conditions, but the mechanism(s) involved remain unclear.

Dietary proteins as determinants of metabolic and physiologic functions of the gastrointestinal tract

Dietary proteins elicit a wide range of nutritional and biological functions. Beyond their nutritional role as the source of amino acids for protein synthesis, they are instrumental in the regulation of food intake, glucose and lipid metabolism, blood pressure, bone metabolism and immune function. The interaction of dietary proteins and their products of digestion with the regulatory functions of the gastrointestinal (GI) tract plays a dominant role in determining the physiological properties of proteins. The site of interaction is widespread, from the oral cavity to the colon. The characteristics of proteins that influence their interaction with the GI tract in a source-dependent manner include their physico-chemical properties, their amino acid composition and sequence, their bioactive peptides, their digestion kinetics and also the non-protein bioactive components conjugated with them. Within the GI tract, these products affect several regulatory functions by interacting with receptors releasing hormones, affecting stomach emptying and GI transport and absorption, transmitting neural signals to the brain, and modifying the microflora. This review discusses the interaction of dietary proteins during digestion and absorption with the physiological and metabolic functions of the GI tract, and illustrates the importance of this interaction in the regulation of amino acid, glucose, lipid metabolism, and food intake.

The potential role of milk-derived peptides in cardiovascular disease

Bioactive peptides derived from milk proteins are of particular interest to the food industry due to the potential functional and physiological roles that they demonstrate, particularly in relation to cardiovascular disease (CVD). By 2020 it is estimated that heart disease and stroke will become the leading cause of death and disability worldwide. Acute and chronic cardiovascular events may result from alterations in the activity of the renin-angiotensin aldosterone system and activation of the coagulation cascade and of platelets. Medications that inhibit angiotensin converting enzyme (ACE) are widely prescribed in the treatment and prevention of cardiovascular disease. ACE inhibitory peptides are of particular interest due to the presence of encrypted inhibitory peptide sequences. In particular, Ile-Pro-Pro and Val-Pro-Pro are fore runners in ACE inhibition, and have been incorporated into commercial products. Additionally, studies to identify additional novel peptides with similar bio-activity and the ability to withstand digestion during transit through the gastrointestinal tract are ongoing. The potential sources of such peptides in cheese and other dairy products are discussed. Challenges to the bio-availability of such peptides in the gastro intestinal tract are also reviewed. Activation of platelets and the coagulation cascade play a central role in the progression of cardiovascular disease. Platelets from such patients show spontaneous aggregation and an increased sensitivity to agonists which results in vascular damage and endothelial dysfunction associated with CVD. Peptide sequences exhibiting anti-thrombotic activity have been identified from fermented milk products. Studies on such peptides are reviewed and their effects on platelet function are discussed. Finally the ability of food derived peptides to decrease the formation of blood clots (thrombi) is reviewed. In conclusion, due to the widespread nature of cardiovascular disease, the identification of food derived compounds that exhibit a beneficial effect in such widespread areas of CVD regulation will have strong clinical potential. Due to the perception that food derived products have an acceptable risk profile they have the potential for widespread acceptance by the public. In this review, selected biological effects relating to CVD are discussed with a view to providing essential information to researchers.

Exendin-4 and exercise improve hepatic glucose homeostasis by promoting insulin signaling in diabetic rats

Recently, it has been reported that a long-acting glucagon-like peptide-1 (exendin-4) and physical exercise improve hepatic insulin action in diabetic rats. However, this phenomenon remains poorly understood. We investigated the long-term effect that exendin-4 and exercise had on hepatic insulin resistance through the modulation of hepatic and/or hypothalamic insulin signaling in 90% pancreatectomized diabetic rats fed 40% energy fat diets. The rats were divided into 4 groups: exendin-4 only, exendin-4 plus exercise training, saline (control), or exercise training only. Rats in the exendin-4 groups were administered with 150 pmol/kg exendin-4 twice a day for 8 weeks, whereas those in the exercise groups ran on an uphill treadmill with a 15 degrees incline at 20 m/min for 30 minutes 5 days a week. Exendin-4 reduced serum glucagon levels in overnight-fasted rats. Exendin-4 treatment by itself decreased hepatic glucose output at hyperinsulinemic states, and exercise without exendin-4 treatment also had the same effect. Exendin-4 promoted hepatic insulin signaling by potentiating tyrosine phosphorylation of the insulin receptor substrate-2 without changing hypothalamic insulin signaling. Exendin-4 also enhanced hypothalamic glucose sensing. However, exercise improved both hepatic and hypothalamic insulin signaling by activating the phosphorylation of cyclic adenosine monophosphate-responding element binding proteins to induce insulin receptor substrate-2 expression. Exendin-4 and exercise decreased the expression of phosphoenolpyruvate carboxykinase, which in turn reduced hepatic glucose output. Exendin-4 in combination with exercise had no additive effects. In conclusion, exendin-4 and exercise improve hepatic glucose homeostasis by promoting hepatic insulin signaling in diabetic rats.

GLP-1 secretion is enhanced directly in the ileum but indirectly in the duodenum by a newly identified potent stimulator, zein hydrolysate, in rats

Glucagon-like peptide-1 (GLP-1) is released from enteroendocrine cells (L cells) in response to food ingestion. The mechanism by which dietary peptides stimulate GLP-1 secretion in the gut is unknown. In the present study, we found that a hydrolysate prepared from zein, a major corn protein [zein hydrolysate (ZeinH)], strongly stimulates GLP-1 secretion in enteroendocrine GLUTag cells. Stimulatory mechanisms of GLP-1 secretion induced by ZeinH were investigated in the rat small intestine under anesthesia. Blood was collected through a portal catheter before and after ZeinH administration into different sites of the small intestine. The duodenal, jejunal, and ileal administration of ZeinH induced dose-dependent increases in portal GLP-1 concentration. GLP-1 secretion in response to the ileal administration of ZeinH was higher than that in the duodenal or jejunal administration. Capsaicin treatment on esophageal vagal trunks abolished the GLP-1 secretion induced by duodenal ZeinH but did not affect the secretion induced by jejunal or ileal ZeinH. These results suggest that ZeinH in the jejunum or ileum directly stimulates GLP-1 secretion but duodenal ZeinH indirectly stimulates GLP-1 secretion via the vagal afferent nerve. A direct blood sampling method from the duodenal vein and ileal mesenteric vein revealed that ZeinH administered into the ligated duodenal loop enhanced GLP-1 concentration in the ileal mesenteric vein but not in the duodenal vein. This confirmed that ZeinH in the duodenum induces GLP-1 secretion from L cells located in the ileum by an indirect mechanism. These results indicate that a potent GLP-1-releasing peptide, ZeinH, induces GLP-1 secretion by direct and indirect mechanisms in the rat intestine.

Multivitamin supplementation of Wistar rats during pregnancy accelerates the development of obesity in offspring fed an obesogenic diet

OBJECTIVE

The effect of gestational multivitamin supplementation on the development of obesity in rat offspring fed an obesogenic diet was investigated.

DESIGN

Pregnant Wistar rats (n=10 per group) were fed the AIN-93G diet with the recommended vitamin (RV) content or a 10-fold increase (high vitamin, HV). At weaning, 10 males and 10 females, from separate dams, and from each gestational diet group were weaned to the liquid obesogenic diet for 48 weeks post-weaning.

MEASUREMENTS

Body weight (BW) was measured weekly, and food intake over 24 h was measured once every 3 weeks for 24 weeks. Every 4 weeks, after an overnight fast, food intake over 1 h was measured 30 min after a gavage of water or glucose. An oral glucose tolerance test (OGTT) was carried out every 3-5 weeks. Post-weaning fasting glucose, insulin, ghrelin, glucagon-like peptide 1 (GLP-1), and systolic blood pressure (SBP) were measured.

RESULTS

No difference in BW at birth or litter size was observed. Males and females from HV dams gained 17% (P<0.05) and 37% (P<0.001) more BW at 48 weeks post-weaning, and consumed 18% (P=0.07) and 20% (P<0.05) more food. One-hour food intake after water and glucose preloads was 27% (P<0.01) and 34% (P<0.05) higher in males from HV dams. Fasting ghrelin and GLP-1 were 27 and 32% higher in males from HV dams at weaning (P<0.05). Blood glucose response to the OGTT was greater in both males and females from HV dams at 13 weeks post-weaning (P<0.05), and the insulin resistance index was 76 and 43% higher in females from HV dams at 14 and 28 weeks post-weaning (P<0.05). SBP was 23 and 16% higher at 44 weeks post-weaning in male and females (P<0.01).

CONCLUSION

High multivitamin intake during pregnancy increases the phenotypic expression of obesity and components of the metabolic syndrome in both female and male rats fed an obesogenic diet.

Caudal brainstem processing is sufficient for behavioral, sympathetic, and parasympathetic responses driven by peripheral and hindbrain glucagon-like-peptide-1 receptor stimulation

The effects of peripheral glucagon like peptide-1 receptor (GLP-1R) stimulation on feeding, gastric emptying, and energetic responses involve vagal transmission and central nervous system processing. Despite a lack of studies aimed at determining which central nervous system regions are critical for the GLP-1R response production, hypothalamic/forebrain processing is regarded as essential for these effects. Here the contribution of the caudal brainstem to the control of food intake, core temperature, heart rate, and gastric emptying responses generated by peripheral delivery of the GLP-1R agonist, exendin-4 (Ex-4), was assessed by comparing responses of chronic supracollicular decerebrate (CD) rats to those of pair-fed intact control rats. Responses driven by hindbrain intracerebroventricular (fourth i.c.v) delivery of Ex-4 were also evaluated. Intraperitoneal Ex-4 (1.2 and 3.0 microg/kg) suppressed glucose intake in both CD rats (5.0+/-1.2 and 4.4+/-1.1 ml ingested) and controls (9.4+/-1.5 and 7.7+/-0.8 ml ingested), compared with intakes after vehicle injections (13.1+/-2.5 and 13.2+/-1.7 ml ingested, respectively). Hindbrain ventricular Ex-4 (0.3 microg) also suppressed food intake in CD rats (4.7+/-0.6 ml ingested) and controls (11.0+/-2.9 ml ingested), compared with vehicle intakes (9.3+/-2.1 and 19.3+/-4.3 ml ingested, respectively). Intraperitoneal Ex-4 (0.12, 1.2, 2.4 microg/kg) reduced gastric emptying rates in a dose-related manner similarly for both CD and control rats. Hypothermia followed ip and fourth i.c.v Ex-4 in awake, behaving controls (0.6 and 1.0 C average suppression) and CD rats (1.5 and 2.5 C average suppression). Intraperitoneal Ex-4 triggered tachycardia in both control and CD rats. Results demonstrate that caudal brainstem processing is sufficient for mediating the suppression of intake, core temperature, and gastric emptying rates as well as tachycardia triggered by peripheral GLP-1R activation and also hindbrain-delivered ligand. Contrary to the literature, hypothalamic/forebrain processing and forebrain-caudal brainstem communication is not required for the observed responses.

Whey proteins in the regulation of food intake and satiety

Whey protein has potential as a functional food component to contribute to the regulation of body weight by providing satiety signals that affect both short-term and long-term food intake regulation. Because whey is an inexpensive source of high nutritional quality protein, the utilization of whey as a physiologically functional food ingredient for weight management is of current interest. At present, the role of individual whey proteins and peptides in contributing to food intake regulation has not been fully defined. However, Whey protein reduces short-term food intake relative to placebo, carbohydrate and other proteins. Whey protein affects satiation and satiety by the actions of: (1) whey protein fractions per se; (2) bioactive peptides; (3) amino-acids released after digestion; (4) combined action of whey protein and/or peptides and/or amino acids with other milk constituents. Whey ingestion activates many components of the food intake regulatory system. Whey protein is insulinotropic, and whey-born peptides affect the renin-angiotensin system. Therefore whey protein has potential as physiologically functional food component for persons with obesity and its co-morbidities (hypertension, type II diabetes, hyper- and dislipidemia). It remains unclear, however, if the favourable effects of whey on food intake, subjective satiety and intake regulatory mechanisms in humans are obtained from usual serving sizes of dairy products. The effects described have been observed in short-term experiments and when whey is consumed in much higher amounts.

The GLP-1 agonist exendin-4 reduces food intake in nonhuman primates through changes in meal size

Exendin-4 (Ex4), a long-acting glucagon-like peptide-1 (GLP-1) receptor agonist, has been shown to reduce food intake and suppress gastric emptying in rodents and humans. In this study we investigated the effects of peripheral administration of Ex4 on food intake and meal patterns in adult male rhesus macaques. Rhesus macaques (n = 4) that had been trained to lever press for food pellets were injected intramuscularly 15 min before the start of their 6-h daily feeding period. Ex4 was given at doses of 0.10, 0.32, 0.56, 1.0, and 3.0 microg/kg. Ex4 suppressed food intake in a dose-dependent manner, with the 3.0 microg/kg dose completely preventing feeding during the 6-h period and the 0.10 microg/kg dose suppressing intake by 17%. Doses of 0.32, 0.56, 1.0, and 3.0 microg/kg caused significant reductions in cumulative intake at all six hourly time points. Ex4 inhibited food intake through a specific effect on meal size. Meal size was significantly reduced in a dose-dependent manner with significant reductions at the 0.32 and 1.0 microg/kg doses (P < 0.05). Day 2 and 3 intakes returned to baseline levels with no compensation for Ex4-induced feeding suppression. Administration of doses of 0.32 and 0.56 microg/kg Ex4 over 5 consecutive days led to sustained reductions in intake with no evidence of compensation. Again, these reductions were due to specific effects on meal size. These results demonstrate that activation of GLP-1 pathways has potent effects on the controls of meal size and overall food intake in a nonhuman primate model.

Antiobesity action of peripheral exenatide (exendin-4) in rodents: effects on food intake, body weight, metabolic status and side-effect measures

BACKGROUND

Exenatide (exendin-4) is an incretin mimetic currently marketed as an antidiabetic agent for patients with type 2 diabetes. In preclinical models, a reduction in body weight has also been shown in low-fat-fed, leptin receptor-deficient rodents.

OBJECTIVE

To more closely model the polygenic and environmental state of human obesity, we characterized the effect of exenatide on food intake and body weight in high-fat-fed, normal (those with an intact leptin signaling system) rodents. As glucagon-like peptide-1 receptor agonism has been found to elicit behaviors associated with visceral illness in rodents, we also examined the effect of peripheral exenatide on kaolin consumption and locomotor activity.

METHODS AND RESULTS

High-fat-fed C57BL/6 mice and Sprague-Dawley rats were treated with exenatide (3, 10 and 30 microg/kg/day) for 4 weeks via subcutaneously implanted osmotic pumps. Food intake and body weight were assessed weekly. At 4 weeks, body composition and plasma metabolic profiles were measured. Kaolin consumption and locomotor activity were measured in fasted Sprague-Dawley rats following a single intraperitoneal injection of exenatide (0.1-10 microg/kg). Exenatide treatment in mice and rats dose-dependently decreased food intake and body weight; significant reductions in body weight gain were observed throughout treatment at 10 and 30 microg/kg/day (P<0.05). Decreased body weight gain was associated with a significant decrease in fat mass (P<0.05) with sparing of lean tissue. Plasma cholesterol, triglycerides and insulin were also significantly reduced (P<0.05). Exenatide at 10 microg/kg significantly reduced food intake (P<0.05) but failed to induce kaolin intake. In general, locomotor activity was reduced at doses of exenatide that decreased food intake, although a slightly higher dose was required to produce significant changes in activity.

CONCLUSION

Systemic exenatide reduces body weight gain in normal, high-fat-fed rodents, a model that parallels human genetic variation and food consumption patterns, and may play a role in metabolic pathways mediating food intake.

Exendin-4 uses Irs2 signaling to mediate pancreatic beta cell growth and function

The insulin receptor substrate 2 (Irs2) branch of the insulin/insulin-like growth factor-signaling cascade prevents diabetes in mice because it promotes beta cell replication, function, and survival, especially during metabolic stress. Because exendin-4 (Ex4), a long acting glucagon-like peptide 1 receptor agonist, has similar effects upon beta cells in rodents and humans, we investigated whether Irs2 signaling was required for Ex4 action in isolated beta cells and in Irs2(-/-) mice. Ex4 increased cAMP levels in human islets and Min6 cells, which promoted Irs2 expression and stimulated Akt phosphorylation. In wild type mice Ex4 administered continuously for 28 days increased beta cell mass 2-fold. By contrast, Ex4 failed to arrest the progressive beta cell loss in Irs2(-/-) mice, which culminated in fatal diabetes; however, Ex4 delayed the progression of diabetes by 3 weeks by promoting insulin secretion from the remaining islets. We conclude that some short term therapeutic effects of glucagon-like peptide 1 receptor agonists can be independent of Irs2, but its long term effects upon beta cell growth and survival are mediated by the Irs2 branch of the insulin/insulin-like growth factor signaling cascade.

Hyperglycemia after protein ingestion concurrent with injection of a GLP-1 receptor agonist in rats: a possible role for dietary peptides

Protein ingestion after injection of the glucagon-like peptide-1 receptor agonist Exendin-4 (Ex-4) causes hyperglycemia in rats. The objectives of this study were to determine the components of protein digestion responsible for this effect and to associate it with changes in the concentrations of other metabolites and hormones. Two experiments were conducted. In the first experiment, food-deprived rats were gavaged with intact whey (WP) or albumin protein, their hydrolysates, amino acid mixtures (1 g/2.5 ml), or water 5 min after injection of either PBS or Ex-4 (0.5 μg/rat). Tail vein blood was analyzed for glucose over 2 h. In the second experiment, food-deprived rats were gavaged with WP with or without Ex-4. Groups of conscious rats were killed by decapitation either before, or at selected times after gavage. Plasma concentrations of glucose, amino acids, free fatty acids (FFA), glycerol, insulin, glucagon, and leptin were measured. In experiment 1, blood glucose was higher when intact proteins and protein hydrolysates, but not amino acid mixtures, were given with than without Ex-4 ( P < 0.05). In experiment 2, concentrations of glucose, FFA, and the ratio of tyrosine to branched-chain amino acid were higher ( P < 0.01), but leptin and essential amino acid concentrations were lower ( P < 0.05), and insulin, glucagon, and glycerol were similar when WP was given with or without Ex-4. We conclude that the hyperglycemia caused by the administration of Ex-4 concurrently with dietary protein arises from the action of peptides released during digestion and their interaction with Ex-4 in the regulation of glucose, fatty acid, and amino acid metabolism.

Intravenous infusion of glucagon-like peptide-1 potently inhibits food intake, sham feeding, and gastric emptying in rats

Glucagon-like peptide-1(7-36)-amide (GLP-1) is postulated to act as a hormonal signal from gut to brain to inhibit food intake and gastric emptying. A mixed-nutrient meal produces a 2 to 3-h increase in plasma GLP-1. We determined the effects of intravenous infusions of GLP-1 on food intake, sham feeding, and gastric emptying in rats to assess whether GLP-1 inhibits food intake, in part, by slowing gastric emptying. A 3-h intravenous infusion of GLP-1 (0.5-170 pmol.kg(-1).min(-1)) at dark onset dose-dependently inhibited food intake in rats that were normally fed with a potency (mean effective dose) and efficacy (maximal % inhibition) of 23 pmol.kg(-1).min(-1) and 82%, respectively. Similar total doses of GLP-1 administered over a 15-min period were less potent and effective. In gastric emptying experiments, GLP-1 (1.7-50 pmol.kg(-1).min(-1)) dose-dependently inhibited gastric emptying of saline and ingested chow with potencies of 18 and 6 pmol.kg(-1).min(-1) and maximal inhibitions of 74 and 83%, respectively. In sham-feeding experiments, GLP-1 (5-50 pmol.kg(-1).min(-1)) dose-dependently reduced 15% aqueous sucrose intake in a similar manner when gastric cannulas were closed (real feeding) and open (sham feeding). These results demonstrate that intravenous infusions of GLP-1 dose-dependently inhibit food intake, sham feeding, and gastric emptying with a similar potency and efficacy. Thus GLP-1 may inhibit food intake in part by reducing gastric emptying, yet can also inhibit food intake independently of its action to reduce gastric emptying. It remains to be determined whether intravenous doses of GLP-1 that reproduce postprandial increases in plasma GLP-1 are sufficient to inhibit food intake and gastric emptying.

Protein source, quantity, and time of consumption determine the effect of proteins on short-term food intake in young men

The objective of these 4 studies was to describe the effects of protein source, time of consumption, quantity, and composition of protein preloads on food intake in young men. Young men were fed isolates of whey, soy protein, or egg albumen in sweet and flavored beverages (400 mL) and provided a pizza meal 1-2 h later. Compared with the water control, preloads (45-50 g) of whey and soy protein, but not egg albumen, suppressed food intake at a pizza meal consumed 1 h later. Meal energy intake after egg albumen and soy, but not after control or whey treatments, was greater when the treatments were given in the late morning (1100 h) compared with earlier (0830-0910 h). Suppression of food intake after whey protein, consumed as either the intact protein or as peptides, extended to 2 h. Altering the composition of the soy preload (50 g) by reducing the soy protein content to 25 g and by adding 25 g of either glucose or amylose led to a loss in suppression of food intake by the preload. Egg albumen, in contrast to whey and soy preloads, increased cumulative energy intake (sum of the energy content of the preload plus that in the test meal) relative to the control. We conclude that protein source, time of consumption, quantity, and composition are all factors determining the effect of protein preloads on short-term food intake in young men.

Dietary proteins in the regulation of food intake and body weight in humans

This review presents 4 lines of evidence supporting a role for proteins in the regulation of food intake and maintenance of healthy body weights. It is concluded that the protein content of food, and perhaps its source, is a strong determinant of short-term satiety and of how much food is eaten. Although the role of protein in the regulation of long-term food intake and body weight is less clear, the evidence reviewed suggests that further research to define its role is merited. Such research has the potential to lead to new functional foods, food formulations, and dietary recommendations for achieving healthy body weights.