Effect of CCK-1 receptor blockade on ghrelin and PYY secretion in men

The emerging role of gut hormones

The gut is traditionally recognized as the central organ for the digestion and absorption of nutrients, however, it also functions as a significant endocrine organ, secreting a variety of hormones such as glucagon-like peptide 1, serotonin, somatostatin, and glucocorticoids. These gut hormones, produced by specialized intestinal epithelial cells, are crucial not only for digestive processes but also for the regulation of a wide range of physiological functions, including appetite, metabolism, and immune responses. While gut hormones can exert systemic effects, they also play a pivotal role in maintaining local homeostasis within the gut. This review discusses the role of the gut as an endocrine organ, emphasizing the stimuli, the newly discovered functions, and the clinical significance of gut-secreted hormones. Deciphering the emerging role of gut hormones will lead to a better understanding of gut homeostasis, innovative treatments for disorders in the gut, as well as systemic diseases.

Yoyo Dieting, Post-Obesity Weight Loss, and Their Relationship with Gut Health

Excessive body weight is associated with many chronic metabolic diseases and weight loss, so far, remains the gold standard treatment. However, despite tremendous efforts exploring optimal treatments for obesity, many individuals find losing weight and maintaining a healthy body weight difficult. Weight loss is often not sustainable resulting in weight regain and subsequent efforts to lose weight. This cyclic pattern of weight loss and regain is termed "yoyo dieting" and predisposes individuals to obesity and metabolic comorbidities. How yoyo dieting might worsen obesity complications during the weight recurrence phase remains unclear. In particular, there is limited data on the role of the gut microbiome in yoyo dieting. Gut health distress, especially gut inflammation and microbiome perturbation, is strongly associated with metabolic dysfunction and disturbance of energy homeostasis in obesity. In this review, we summarise current evidence of the crosstalk between the gastrointestinal system and energy balance, and the effects of yoyo dieting on gut inflammation and gut microbiota reshaping. Finally, we focus on the potential effects of post-dieting weight loss in improving gut health and identify current knowledge gaps within the field, including gut-derived peptide hormones and their potential suitability as targets to combat weight regain, and how yoyo dieting and associated changes in the microbiome affect the gut barrier and the enteric nervous system, which largely remain to be determined.

Hunger and satiety responses to diets enriched with cottonseed oil vs. olive oil

Studies suggest that the type of dietary fat consumed habitually may modulate appetite and further influence weight management. The purpose of this study was to evaluate the impact of an 8-week diet intervention enriched with either cottonseed oil (CSO; polyunsaturated fat-rich) or olive oil (OO; monounsaturated fat-rich) on appetite responses in adults with high cholesterol. This was a parallel design, randomized partial outpatient feeding trial designed to provide approximately 60% of participants daily energy needs with ∼30% of energy needs as CSO (n = 21, BMI 27.3 ± 0.92 kg/m², age 53 ± 2y) or OO (n = 21, BMI 27.6 ± 1.20 kg/m², age 54 ± 2y). A high saturated fat meal challenge was completed at pre- and post-intervention visits with 5 h postprandial blood draws and visual analog scales (VAS) for cholecystokinin (CCK), peptide YY (PYY), ghrelin, and subjective appetite, respectively. Participants also completed VAS questionnaires hourly and recorded dietary intake after leaving the lab for the remainder of the day. There was a greater increase in fasting CCK (CSO: 0.54 ± 0.03 to 0.56 ± 0.04; OO: 0.63 ± 0.07 to 0.60 ± 0.06 ng/ml p = 0.05), a greater suppression of postprandial ghrelin (p < 0.01), and a greater increase in postprandial VAS fullness (p = 0.04) in CSO compared to OO. Additionally, there was a greater decrease in self-reported energy intake in CSO compared to OO (CSO: 2464 ± 123 to 2115 ± 123; OO: 2263 ± 147 to 2,434 ± 184 kcal/d p = 0.02). Only postprandial VAS prospective consumption showed greater suppression (p = 0.03) in OO vs. CSO. Altogether, these data show that CSO has a greater effect on appetite suppression than OO diet enrichment and may be beneficial for weight maintenance, especially in a population at-risk for chronic disease. Registered at clinicaltrials.gov: NCT04397055.

Gut peptide changes in patients with obstructive jaundice undergoing biliary drainage: A prospective case control study

BACKGROUND

Biliary obstruction is a relatively common condition that affects approximately 5 in 1000 people annually. Malnutrition is very common in patients with biliary obstruction and since it is associated with significant morbidity and mortality, it is important to identify factors and mechanisms involved in its development.

AIM

To determine the influence of obstructive jaundice on the hormones controlling appetite and nutritive status.

METHODS

This was a prospective case control study performed in a tertiary center in Zagreb, Croatia. Patients with biliary obstruction undergoing internal biliary drainage from September 2012 until August 2013 were enrolled. After excluding patients who developed procedure related complications or were lost in the follow-up, out of initial 73 patients, 55 patients were included in the analysis, including 34 with benign and 21 with malignant disease. Meanwhile, 40 non-jaundiced controls were also included. Appetite, nutritional status, and serum ghrelin, cholecystokinin (CCK), interleukin 6 (IL-6), and tumor necrosis factor α (TNF-α) were determined at admission, 48 h and 28 d after internal biliary drainage. Chi square test was used for categorical variables. Continuous variables were analysed for normality by Kolmogorov-Smirnov test and relevant non-parametric (Mann-Whitney, Kruskal-Wallis, and Friedman) or parametric (t-test and analysis of variance) tests were used.

RESULTS

Patients with obstructive jaundice were significantly malnourished compared to controls, regardless of disease etiology. Plasma ghrelin and CCK levels were significantly higher in patients with obstructive jaundice. Serum bilirubin concentrations were negatively correlated with ghrelin levels and positively correlated with TNF-α, but had no correlation with CCK concentrations. After internal biliary drainage, a significant improvement of nutritional status was observed although serum concentrations of ghrelin, IL-6, and TNF-α remained significantly elevated even 28 d after the procedure. CCK levels in patients without malnutrition remained elevated 28 d after the procedure, but in patients with malnutrition, CCK levels decreased to levels comparable with those in the control group. We have not established any correlation between appetite and serum levels of ghrelin, CCK, IL-6, and TNF-α before and after biliary drainage.

CONCLUSION

Possible abnormalities in ghrelin and CCK regulation may be associated with the development of malnutrition during the inflammatory response in patients with biliary obstruction.

Role of the gut-brain axis in energy and glucose metabolism

The gastrointestinal tract plays a role in the development and treatment of metabolic diseases. During a meal, the gut provides crucial information to the brain regarding incoming nutrients to allow proper maintenance of energy and glucose homeostasis. This gut-brain communication is regulated by various peptides or hormones that are secreted from the gut in response to nutrients; these signaling molecules can enter the circulation and act directly on the brain, or they can act indirectly via paracrine action on local vagal and spinal afferent neurons that innervate the gut. In addition, the enteric nervous system can act as a relay from the gut to the brain. The current review will outline the different gut-brain signaling mechanisms that contribute to metabolic homeostasis, highlighting the recent advances in understanding these complex hormonal and neural pathways. Furthermore, the impact of the gut microbiota on various components of the gut-brain axis that regulates energy and glucose homeostasis will be discussed. A better understanding of the gut-brain axis and its complex relationship with the gut microbiome is crucial for the development of successful pharmacological therapies to combat obesity and diabetes.

A systematic review and meta-analysis of dietary fat effects on reproductive performance of sows and growth performance of piglets

Effects of added fat in sow diets on the sows’ reproductive performance and offspring growth performance are influenced by multiple factors such as genetics, nutrition, parity, ambient temperatures, and farm management. Individual studies cannot cover all these factors. With the view to address this challenge, we searched all studies that were published from 1986 to 2020, and performed a systematic review and meta-analysis on the fat effect. In total, 19 papers were collected and analyzed. Fat supplementation in sow diets during late gestation and lactation decreased average daily feed intake (ADFI, P < 0.05) and tended to increase average daily energy intake (ADEI, P = 0.11). It had no impact on litter weights at birth (P = 0.40) or weaning (P = 0.46). It increased total numbers of piglets at birth (P = 0.07), but had no effect on liveborn per litter (P = 0.90) or survival rate (P = 0.48) of piglets to weaning. Fat supplementation had no significant effect on sow body weight loss (P = 0.67) or backfat thickness changes (P = 0.66), but sows fed diets with added fat had increased milk fat concentration (P = 0.03) and shorter wean to estrus intervals (WEI, P = 0.01). In specific circumstances, fat supplementation tended to improve growth performance of piglets with low litter weights at birth (P = 0.14), or when the sows lost large amounts of body weight during lactation (P = 0.11). The level of supplemented fat was 10% and higher would decrease liveborn per litter at neutral temperature (P = 0.10). The meta-analysis revealed that fat supplementation to sows diet during late gestation and lactation can be beneficial for sow reproductive performance and litter growth performance.

Medium-chain triglycerides inhibit long-chain triglyceride-induced GIP secretion through GPR120-dependent inhibition of CCK

Long-chain triglycerides (LCTs) intake strongly stimulates GIP secretion from enteroendocrine K cells and induces obesity and insulin resistance partly due to GIP hypersecretion. In this study, we found that medium-chain triglycerides (MCTs) inhibit GIP secretion after single LCT ingestion and clarified the mechanism underlying MCT-induced inhibition of GIP secretion. MCTs reduced the CCK effect after single LCT ingestion in wild-type (WT) mice, and a CCK agonist completely reversed MCT-induced inhibition of GIP secretion. In vitro studies showed that medium-chain fatty acids (MCFAs) inhibit long-chain fatty acid (LCFA)-stimulated CCK secretion and increase in intracellular Ca²⁺ concentrations through inhibition of GPR120 signaling. Long-term administration of MCTs reduced obesity and insulin resistance in high-LCT diet-fed WT mice, but not in high-LCT diet-fed GIP-knockout mice. Thus, MCT-induced inhibition of GIP hypersecretion reduces obesity and insulin resistance under high-LCT diet feeding condition.

Administration of hydro-alcoholic extract of spinach improves oxidative stress and inflammation in high-fat diet-induced NAFLD rats

Background

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide. The aim of this study was to evaluate the effects of hydro-alcoholic extract of spinach (HES) on hepatic and serum measurements of NAFLD in a rat model.

Methods

In the prevention phase, 18 Sprague–Dawley rats were fed a high-fat diet, a high-fat diet plus 400 mg/kg HES, or a chow diet for seven weeks. For the treatment phase, after the induction of NAFLD, they were fed a high-fat diet, a high-fat diet plus 400 mg/kg HES, a chow diet, or a chow diet plus 400 mg/kg HES for four weeks (n = 6).

Results

Administration of HES combined with high-fat diet in rats was associated with decreased food intake (P < 0.01), weight loss (P = 0.01), and increased superoxide dismutase (SOD) (P = 0.02) enzyme activity in the liver, at the end of the prevention phase. hs-CRP (P < 0.05), PTX-3 (P < 0.05), and TNF-α (P < 0.05) gene expression in the liver were decreased and PPAR-γ (P < 0.05) gene expression in the liver was increased by spinach intake, both in the prevention and treatment phases. Furthermore, administration of spinach in the treatment phase increased serum TAC (P = 0.03) and hepatic GPX (P = 0.01) enzyme activity.

Conclusion

Taking into account the potential beneficial effects of HES on prevention and treatment of NAFLD in the present study, to confirm these findings, we propose that further clinical trials be conducted on human subjects with NAFLD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03396-x.

The regulation of gastric ghrelin secretion

Ghrelin is a gastric hormone with multiple physiological functions, including the stimulation of food intake and adiposity. It is well established that circulating ghrelin levels are closely associated with feeding patterns, rising strongly before a meal and lowering upon food intake. However, the mechanisms underlying the modulation of ghrelin secretion are not fully understood. The purpose of this review is to discuss current knowledge on the circadian oscillation of circulating ghrelin levels, the neural mechanisms stimulating fasting ghrelin levels and peripheral mechanisms modulating postprandial ghrelin levels. Furthermore, the therapeutic potential of targeting the ghrelin pathway is discussed in the context of the treatment of various metabolic disorders, including obesity, type 2 diabetes, diabetic gastroparesis and Prader-Willi syndrome. Moreover, eating disorders including anorexia nervosa, bulimia nervosa and binge-eating disorder are also discussed.

Gut Hormones in Health and Obesity: The Upcoming Role of Short Chain Fatty Acids

We are currently facing an obesity pandemic, with worldwide obesity rates having tripled since 1975. Obesity is one of the main risk factors for the development of non-communicable diseases, which are now the leading cause of death worldwide. This calls for urgent action towards understanding the underlying mechanisms behind the development of obesity as well as developing more effective treatments and interventions. Appetite is carefully regulated in humans via the interaction between the central nervous system and peripheral hormones. This involves a delicate balance in external stimuli, circulating satiating and appetite stimulating hormones, and correct functioning of neuronal signals. Any changes in this equilibrium can lead to an imbalance in energy intake versus expenditure, which often leads to overeating, and potentially weight gain resulting in overweight or obesity. Several lines of research have shown imbalances in gut hormones are found in those who are overweight or obese, which may be contributing to their condition. Therefore, this review examines the evidence for targeting gut hormones in the treatment of obesity by discussing how their dysregulation influences food intake, the potential possibility of altering the circulating levels of these hormones for treating obesity, as well as the role of short chain fatty acids and protein as novel treatments.

Effects of thylakoid intake on appetite and weight loss: a systematic review

BACKGROUND

Previous studies have shown thylakoids, the membrane proteins which are extracted from green leaves like spinach, can induce satiety through homeostatic and non-homeostatic pathways. In this study, we reviewed the current human literature on thylakoids' characteristics and their relationship to satiety regulation and weight loss.

METHODS

A systematic search of literature published between January 1990 and May 2019 was conducted on the electronic databases; including WEB OF SCIENCE, Cochrane Library, MEDLINE, Scopus, and EMBASE databases. We included all clinical trials that addressed the effects of thylakoids or chloroplast intake on satiety and weight loss.

RESULTS

After excluding non-human studies, non-RCTs, duplications, studies with irrelevant data and interventions, eight studies were included in the qualitative synthesis. All studies supported this hypothesis that thylakoids reduce the feeling of hunger by increasing postprandial cholecystokinin and leptin and decreasing serum ghrelin, but the consequences of thylakoid intake on anthropometric characteristics were controversial.

CONCLUSION

In conclusion, our results may approve this postulation that receiving a thylakoid-enriched meal can decrease appetite and probably food intake in short term; however, more studies are needed to explore the effects of long term supplementation with thylakoids on weight loss in human subjects.

Intestinal sensing and handling of dietary lipids in gastric bypass-operated patients and matched controls

BACKGROUND

Altered meal-related gut hormone secretion seems important for weight loss and diabetes remission after Roux-en-Y gastric bypass (RYGB). Elucidating the responsible meal components and receptors could aid discovery of new treatments of obesity and diabetes. Enteroendocrine cells respond to digestion products of dietary triacylglycerol, especially long-chain fatty acids (LCFAs) and 2-oleoyl-glycerol (2-OG), but not medium-chain fatty acids (MCFAs).

OBJECTIVE

We examined the impact of olive oil (20 mL) and its derivates, LCFAs and 2-OG, on enteroendocrine secretions [glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), peptide YY (PYY), and neurotensin (NT)] and on glucose, lipid, and bile acid metabolism in RYGB-operated and unoperated individuals.

METHODS

In an exploratory randomized crossover design, 10 RYGB-operated patients and 10 matched controls ingested 3 equimolar triacylglycerol formulations on separate days: olive oil (digested to 2-OG + LCFAs), C8-dietary oil (2-OG + MCFAs), and tricaprylin (MCFAs; negative control). Hormone responses were calculated as area under the curve (AUC).

RESULTS

Independent of group status, olive oil had greater effects than C8-dietary oil on AUCs of plasma GLP-1 (+32%; 95% CI: 23%, 43%; P < 0.01), CCK (+53%, P < 0.01), and NT (+71%, P < 0.01), whereas the effect on GIP differed between groups (+90% in controls, P < 0.01; +24% in RYGB, P = 0.10). Independent of group status, C8-dietary oil had greater effects than tricaprylin on AUCs of plasma CCK (+40%, P < 0.01) and NT (+32%, P < 0.01), but not GLP-1 (+5%; 95% CI: -2.9%, 13%; P = 0.22), whereas the effect on GIP again differed between groups (+78% in controls, P < 0.01; +39% in RYGB, P = 0.01). Distal (GLP-1/PYY/NT), but not proximal (CCK/GIP), enteroendocrine responses were generally greater in RYGB patients than in controls.

CONCLUSIONS

The combination of LCFAs plus 2-OG was substantially more effective than 2-OG plus MCFAs in stimulating enteroendocrine secretion in RYGB-operated and matched control individuals. Distal lipid-induced gut hormone release was greater after RYGB.This trial was registered at clinicaltrials.gov as NCT03223389.

New Zealand Bitter Hops Extract Reduces Hunger During a 24 h Water Only Fast

Intermittent fasting improves metabolic and cardiac health. However, increased hunger towards the end of the fasting period may affect compliance and limit its application. Our aim was to determine the effect of anorexigenic agent co-therapy on subjective ratings of appetite during the 16–24 h period of a day-long water-only intermittent fast. Thirty adult men were recruited and required to fast for 24 h from 18:00 h to 18:00 h on the same day of the week for three subsequent weeks. Treatments of either a placebo or one of two doses (high dose; HD: 250 mg or low dose; LD: 100 mg) of a bitter hops-based appetite suppressant (Amarasate®) were given twice per day at 16 and 20 h into the fast. From 18–24 h of the 24 h fast, both the HD and LD treatment groups exhibited a statistically significant (p < 0.05) > 10% reduction in hunger. Additionally, the expected lunchtime increase in hunger that was present in the placebo group (12:00 h) was absent in both the HD and LD groups. These data suggest that appetite suppressant co-therapy may be useful in reducing hunger during intermittent fasting, and show that bitter compounds may regulate appetite independently of meal timing.

Pediatric Eating Behaviors as the Intersection of Biology and Parenting: Lessons from the Birds and the Bees

PURPOSE OF REVIEW

Current feeding advice to prevent pediatric obesity focuses on caregiver feeding behaviors. This review integrates newer data showing that child appetitive traits also have a genetic component.

RECENT FINDINGS

Caregiver feeding behaviors robustly correlate with child eating behaviors; however, there is also a strong heritable component. The satiety cascade delineates the biological drive underlying hunger, satiation, and satiety. Innate individual differences exist for the components of the satiety cascade, which may explain the heritability of child eating behaviors. However, given the correlation of caregiver feeding behaviors with child eating behaviors, any etiological model should include both genetic/biological components and environmental. Integrating the biological etiology of child eating behaviors into the current environmental model has implications for tailoring feeding advice which needs to move from a "one size fits all" approach to one that is tailored to individual differences in children's biological drives to appetite.

Hyperosmolar Duodenal Saline Infusion Lowers Circulating Ghrelin and Stimulates Intestinal Hormone Release in Young Men

CONTEXT

The mechanisms regulating the postprandial suppression of ghrelin secretion remain unclear, but recent observations in rats indicate that an increase in duodenal osmolarity is associated with a reduction in ghrelin levels. Several hormones have been implicated in the regulation of ghrelin.

OBJECTIVE

We hypothesized that intraduodenal infusion of a hyperosmolar solution would lower plasma ghrelin concentrations.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS

Eighteen healthy young men were studied after an overnight fast on two occasions in a randomized double-blinded fashion. A nasoduodenal catheter was positioned and isoosmolar (300 mOsm/L) or hyperosmolar (1500 mOsm/L) saline was infused intraduodenally (4 mL/min, t = 0 to 45 minutes). Venous blood was sampled at t = -45, -30, -15, 0, 15, 30, 45, 60, 75, 90, 120, and 180 minutes.

MAIN OUTCOME MEASURES

Plasma concentrations of ghrelin, glucagonlike peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), glucagon, pancreatic polypeptide (PP), neurotensin (NT), peptide YY (PYY), motilin, and glucose.

RESULTS

Ghrelin concentrations were suppressed with hyperosmolar when compared with isoosmolar saline, and remained lower until t = 180 minutes. CCK, NT, GLP-1, PYY, and glucagon all increased during hyperosmolar, but not isoosmolar, saline infusion (P < 0.01 for all), whereas GIP, PP, and motilin levels were not affected by either infusion.

CONCLUSIONS

Plasma ghrelin concentrations are lowered, whereas CCK, GLP-1, PYY, NT, and glucagon concentrations are augmented, by hyperosmolar duodenal content in healthy individuals. These observations have implications for the evaluation of studies comparing the effects of different types and loads of nutrients and chemicals on gut hormone secretion.

Gene-Environment Interplay in Child Eating Behaviors: What the Role of "Nature" Means for the Effects of "Nurture"

PURPOSE OF REVIEW

This narrative review describes the evidence for both genetic and environmental influences on child appetitive traits and suggests ways of thinking about how these interact and correlate to influence how a child eats.

RECENT FINDINGS

Emerging evidence from social network analysis, and from longitudinal studies questioning the direction of association between parent feeding behaviors and child obesity risk, suggest that children's genes may shape the environmental risk for obesity that they are exposed to. There is strong evidence that child appetitive traits are both heritable and shaped by the environment. Instead of thinking about how genetic and environmental factors operate independently on each appetitive trait, research needs to expand the current paradigm to examine how genes and environments interact and shape each other.

Central Modulation of Energy Homeostasis and Cognitive Performance After Bariatric Surgery

In moderately or morbidly obese patients, bariatric surgery has been proven to be an effective therapeutic approach to control body weight and comorbidities. Surgery-mediated modulation of brain function via modified postoperative secretion of gut peptides and vagal nerve stimulation was identified as an underlying mechanism in weight loss and improvement of weight-related diseases. Increased basal and postprandial plasma levels of gastrointestinal hormones like glucagon-like peptide 1 and peptide YY that act on specific areas of the hypothalamus to reduce food intake, either directly or mediated by the vagus nerve, are observed after surgery while suppression of meal-induced ghrelin release is increased. Hormones released from the adipose tissue like leptin and adiponectin are also affected and leptin plasma levels are reduced in treated patients. Besides homeostatic control of body weight, surgery also changes hedonistic behavior in regard to food intake and cognitive performance involving the limbic system and prefrontal areas.

Effect of sterilization and of dietary fat and carbohydrate content on food intake, activity level, and blood satiety-related hormones in female dogs

Animal sterilization is suggested to promote food overconsumption, although it is unknown whether this effect is mediated by variations in satiety-related hormones, which are released in response to food intake. The aim of this study was to evaluate the effect of sterilization and of the main energy-delivery nutrients, fat and nonstructural carbohydrates, on food intake, blood concentration of satiety-related hormones, and activity level in dogs. In a 2-phase experiment (phase I [Ph.I], 74 d, and Ph.II, 84 d), 12 female Beagle dogs were assigned to a control group (intact in both phases) and a sterilization group (spayed 20 d before Ph.II). In each phase, dogs received a high-carbohydrate (HC) diet (313 and 105 g/kg DM starch and fat, respectively) and a high-fat (HF) diet (191 and 213 g/kg DM starch and fat, respectively), both high in total dietary fiber (>200 g/kg DM) and providing 27% ME as protein, in 2 consecutive periods following a crossover arrangement. During each period, dogs' voluntary DMI and activity level were recorded during 5 d. Then, energy allowance was restricted to 0.7 maintenance and the level of intake of a common challenge food offered 4 h after feeding the experimental diets (challenge food intake [ChFI]) was used as an index of the satiety state of dogs. Blood concentration of active ghrelin, cholecystokinin (CCK), total peptide YY (PYY), and insulin were determined before and 15, 60, 120, 240, and 360 min after feeding. Voluntary DMI was greater ( < 0.05) in HF-fed dogs, but ChFI did not differ between diets ( > 0.10). Dogs fed the HF diet showed a lower increase of CCK at 120 ( < 0.01) and 240 min ( < 0.05), resulting in a lower ( < 0.001) total area under the curve from 0 to 240 min (tAUC). A lower PYY elevation ( < 0.05) was also found in HF-fed dogs at 120 min. Only active ghrelin concentration at 240 min and insulin tAUC correlated ( < 0.05) with ChFI (r = 0.357 and r = -0.364, respectively), suggesting a role of these hormones in appetite. Dog sterilization did not affect voluntary DMI, ChFI, or blood hormones ( > 0.10) but led to a reduced activity level compared with control dogs ( < 0.05). In summary, dog sterilization was not associated with an impaired appetite control. Feeding dogs the HF diet led to energy overconsumption and to a lower blood elevation of CCK and PYY but was not associated with a weaker satiating effect 4 h later compared with the HC diet.

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Molecular cloning, characterization, and expression analysis of ghrelin and cholecystokinin in the pigeon (Columba livia)

Ghrelin and cholecystokinin (CCK) are multifunctional peptides. In the current study, complete sequences of ghrelin (800 bp) and CCK (739 bp) were firstly cloned in Columba livia by using rapid amplification of cDNA ends (RACE) method. The open reading frames of ghrelin (351bp) and CCK (393bp) encoded 116 amino acids and 130 amino acids, respectively. Sequence comparison indicated that pigeon ghrelin and CCK shared high identity with those reported in other avian species. Quantitative real-time PCR analysis found that ghrelin and CCK mRNAs expressed in three intestinal segments of pigeon during development. Both ghrelin and CCK showed generally higher expressions at days posthatch than embryonic periods regardless of intestinal segments. In duodenum and ileum, the expressions of ghrelin and CCK mRNA reached the peak values at 8 d posthatch. Jejunum CCK mRNA level increased linearly after hatching, and reached the highest point at posthatch 28 d. Based on documented effects of long chain fatty acids (LCFAs) on pigeon ghrelin and CCK expression were also investigated in vitro. Higher concentrations (50 μM or 250 μM) of linoleic acid, α-linolenic acid or arachidonic acid can significantly increase ghrelin mRNA level in pigeon jejunum. However, for oleic acid, the induction of ghrelin gene expressions needed a lower concentration (5 μM). 5 μM of linoleic acid, α-linolenic acid or arachidonic acid and 250 μM palmitic acid repressed CCK expression significantly. A higher concentration (250 μM) of oleic acid or α-linolenic acid can up-regulate CCK mRNA level significantly. Our results indicated that ghrelin and CCK may act key functions in pigeon intestine development and their expressions could be regulated by LCFAs.

Metabolic Actions of the Type 1 Cholecystokinin Receptor: Its Potential as a Therapeutic Target

Cholecystokinin (CCK) regulates appetite and reduces food intake by activating the type 1 CCK receptor (CCK1R). Attempts to develop CCK1R agonists for obesity have yielded active agents that have not reached clinical practice. Here we discuss why, along with new strategies to target CCK1R more effectively. We examine signaling events and the possibility of developing agents that exhibit ligand-directed bias, to dissociate satiety activity from undesirable side effects. Potential allosteric sites of modulation are also discussed, along with desired properties of a positive allosteric modulator (PAM) without intrinsic agonist action as another strategy to treat obesity. These new types of CCK1R-active drugs could be useful as standalone agents or as part of a rational drug combination for management of obesity.

Changes in PYY and gastric emptying across the phases of the menstrual cycle and the influence of the ovarian hormones

Nutrition-related studies avoid the participation of pre-menopausal women due to the potential effect of the menstrual cycle (MC) on their appetite regulation. It is generally accepted that women increase their energy intake during the luteal phase (LPh) compared to the follicular (FPh), however what happens in the menstrual phase (MPh) and how this might be regulated remains uncertain. Although some research indicates changes in the gastric emptying (GE) velocity, whether PYY is affected by the MC phase, remains unknown. The aim of this study was to assess whether eating the same breakfast in each of the three MC phases would change the GE time, the PYY response and post-prandial satiety such that they might affect subsequent food intake. Furthermore, the aim was to associate any potential differences to the fluctuations in estradiol (E₂) and progesterone (P₄) within a MC. Nine naturally cycling women attended to the laboratory to consume a standardised breakfast on three occasions, each of them representing one of the MC phases. Breath samples to measure GE time, plasma samples to quantify PYY levels and hunger scores were collected for a total of 4 h after which food intake was assessed by an ad-libitum buffet lunch. GE and PYY levels changed significantly across the phases of the MC (p < 0.05). GE was correlated to P₄ and E₂-P₄ ratio (r = -0.5 and 0.4, respectively). To conclude, the appetite regulators PYY and GE time change depending upon the MC phases with GE time associated with the ovarian hormone levels which suggests the necessity of controlling the MC phase in studies looking at the appetite response.

Gut chemosensing mechanisms

The enteroendocrine system is the primary sensor of ingested nutrients and is responsible for secreting an array of gut hormones, which modulate multiple physiological responses including gastrointestinal motility and secretion, glucose homeostasis, and appetite. This Review provides an up-to-date synopsis of the molecular mechanisms underlying enteroendocrine nutrient sensing and highlights our current understanding of the neuro-hormonal regulation of gut hormone secretion, including the interaction between the enteroendocrine system and the enteric nervous system. It is hoped that a deeper understanding of how these systems collectively regulate postprandial physiology will further facilitate the development of novel therapeutic strategies.

Fat sensing and metabolic syndrome

Overconsumption of dietary fat contributes to the development of obesity and metabolic syndrome. Recent evidence suggests that high dietary fat may promote these metabolic states not only by providing calories but also by inducing impaired control of energy balance. In normal metabolic states, fat interacts with various organs or receptors to generate signals for the regulation of energy balance. Many of these interactions are impaired by high-fat diets or in obesity, contributing to the development or maintenance of obesity. These impairments may arise largely from fundamental alterations in the hypothalamus where all peripheral signals are integrated to regulate energy balance. This review focuses on various mechanisms by which fat is sensed at different stages of ingestion, circulation, storage, and utilization to regulate food intake, and how these individual mechanisms are altered by high-fat diets or in obesity.

Factors affecting circulating levels of peptide YY in humans: a comprehensive review

As obesity continues to be a global epidemic, research into the mechanisms of hunger and satiety and how those signals act to regulate energy homeostasis persists. Peptide YY (PYY) is an acute satiety signal released upon nutrient ingestion and has been shown to decrease food intake when administered exogenously. More recently, investigators have studied how different factors influence PYY release and circulating levels in humans. Some of these factors include exercise, macronutrient composition of the diet, body-weight status, adiposity levels, sex, race and ageing. The present article provides a succinct and comprehensive review of the recent literature published on the different factors that influence PYY release and circulating levels in humans. Where human data are insufficient, evidence in animal or cell models is summarised. Additionally, the present review explores the recent findings on PYY responses to different dietary fatty acids and how this new line of research will make an impact on future studies on PYY. Human demographics, such as sex and age, do not appear to influence PYY levels. Conversely, adiposity or BMI, race and acute exercise all influence circulating PYY levels. Both dietary fat and protein strongly stimulate PYY release. Furthermore, MUFA appear to result in a smaller PYY response compared with SFA and PUFA. PYY levels appear to be affected by acute exercise, macronutrient composition, adiposity, race and the composition of fatty acids from dietary fat.

Effects of acute and longer-term dietary restriction on upper gut motility, hormone, appetite, and energy-intake responses to duodenal lipid in lean and obese men

BACKGROUND

A 4-d 70% energy restriction enhances gastrointestinal sensitivity to nutrients associated with enhanced energy-intake suppression by lipid. To our knowledge, it is unknown whether these changes occur with 30% energy restriction and are sustained in the longer term.

OBJECTIVES

We hypothesized that 1) a 4-d 30% energy restriction would enhance effects of intraduodenal lipid on gastrointestinal motility, gut hormones, appetite, and energy intake in lean and obese men and 2) a 12-wk energy restriction associated with weight loss would diminish effects of acute energy restriction on responses to lipid in in obese men.

DESIGN

Twelve obese males were studied before (day 0) and after 4 d (day 5), 4 wk (week 4), and 12 wk (week 12), and 12 lean males were studied before and after 4 d of consumption of a 30% energy-restricted diet. On each study day, antropyloroduodenal pressures, gut hormones, and appetite during a 120-min (2.86-kcal/min) intraduodenal lipid infusion and energy intake at a buffet lunch were measured.

RESULTS

On day 5, fasting cholecystokinin was less, and ghrelin was higher, in lean (P < 0.05) but not obese men, and lipid-stimulated cholecystokinin and peptide YY and the desire to eat were greater in both groups (P < 0.05), with no differences in energy intakes compared with on day 0. In obese men, a 12-wk energy restriction led to weight loss (9.7 ± 0.7 kg). Lipid-induced basal pyloric pressures (BPPs), peptide YY, and the desire to eat were greater (P < 0.05), whereas the amount eaten was less (P < 0.05), at weeks 4 and 12 compared with day 0.

CONCLUSIONS

A 4-d 30% energy restriction modestly affects responses to intraduodenal lipid in health and obesity but not energy intake, whereas a 12-wk energy restriction, associated with weight-loss, enhances lipid-induced BPP and peptide YY and reduces food intake, suggesting that energy restriction increases gastrointestinal sensitivity to lipid. This trial was registered at the Australian New Zealand Clinical Trials Registry (www.anzctr.org.au) as 12609000943246.

Potential benefits of satiety to the consumer: scientific considerations

Foods and dietary patterns that enhance satiety may provide benefit to consumers. The aim of the present review was to describe, consider and evaluate research on potential benefits of enhanced satiety. The proposal that enhanced satiety could only benefit consumers by a direct effect on food intake should be rejected. Instead, it is proposed that there is a variety of routes through which enhanced satiety could (indirectly) benefit dietary control or weight-management goals. The review highlights specific potential benefits of satiety, including: providing appetite control strategies for consumers generally and for those who are highly responsive to food cues; offering pleasure and satisfaction associated with low-energy/healthier versions of foods without feeling 'deprived'; reducing dysphoric mood associated with hunger especially during energy restriction; and improved compliance with healthy eating or weight-management efforts. There is convincing evidence of short-term satiety benefits, but only probable evidence for longer-term benefits to hunger management, possible evidence of benefits to mood and cognition, inadequate evidence that satiety enhancement can promote weight loss, and no evidence on which consumers would benefit most from satiety enhancement. The appetite-reducing effects of specific foods or diets will be much more subtle than those of pharmaceutical compounds in managing hunger; nevertheless, the experience of pharmacology in producing weight loss via effects on appetite suggests that there is potential benefit of satiety enhancement from foods incorporated into the diet to the consumer.

Seven transmembrane G protein-coupled receptor repertoire of gastric ghrelin cells

The molecular mechanisms regulating secretion of the orexigenic-glucoregulatory hormone ghrelin remain unclear. Based on qPCR analysis of FACS-purified gastric ghrelin cells, highly expressed and enriched 7TM receptors were comprehensively identified and functionally characterized using in vitro, ex vivo and in vivo methods. Five Gαs-coupled receptors efficiently stimulated ghrelin secretion: as expected the β1-adrenergic, the GIP and the secretin receptors but surprisingly also the composite receptor for the sensory neuropeptide CGRP and the melanocortin 4 receptor. A number of Gαi/o-coupled receptors inhibited ghrelin secretion including somatostatin receptors SSTR1, SSTR2 and SSTR3 and unexpectedly the highly enriched lactate receptor, GPR81. Three other metabolite receptors known to be both Gαi/o- and Gαq/11-coupled all inhibited ghrelin secretion through a pertussis toxin-sensitive Gαi/o pathway: FFAR2 (short chain fatty acid receptor; GPR43), FFAR4 (long chain fatty acid receptor; GPR120) and CasR (calcium sensing receptor). In addition to the common Gα subunits three non-common Gαi/o subunits were highly enriched in ghrelin cells: GαoA, GαoB and Gαz. Inhibition of Gαi/o signaling via ghrelin cell-selective pertussis toxin expression markedly enhanced circulating ghrelin. These 7TM receptors and associated Gα subunits constitute a major part of the molecular machinery directly mediating neuronal and endocrine stimulation versus metabolite and somatostatin inhibition of ghrelin secretion including a series of novel receptor targets not previously identified on the ghrelin cell.

Effects of dietary fatty acid composition from a high fat meal on satiety

The composition of fats within a high-fat (HF) meal may differentially affect hunger and satiety.

PURPOSE

Compare HF meals rich in either monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), or saturated fatty acids (SFAs) on the satiety hormone, peptide YY (PYY), and subjective feelings of hunger and fullness.

METHODS

Fifteen normal weight women (18-45 year) were randomized in a crossover design to complete three study visits. The three treatments (three visits) were HF meals (70% of energy from fat) rich in MUFAs (42% of total energy), PUFAs (42% of total energy), or SFAs (45% of total energy). At each visit, subjects consumed a HF meal and eight blood draws were collected over a 5 h period. A visual analog scale (VAS) was completed at the same time as each blood draw for subjective feelings of hunger and fullness.

RESULTS

The postprandial PYY response (area under the curve) was significantly lower (p<0.05) for the MUFA-rich meal (MUFA: 534.5±27.2 pg/mL/5 h) vs. the SFA-rich or PUFA-rich meals (SFA: 607.3±51.6 pg/mL/5h, PUFA: 633.1±35.8 pg/mL/5 h). The SFA-rich meal elicited greater subjective feelings of fullness compared to MUFA- and PUFA-rich meals (288.1±9.6 vs. 236.8±7.9 and 220.9±7.4 mm/5 h; p=0.04, for 5h AUC for SFA, MUFA, and PUFA, respectively). The only significant correlations between PYY levels and VAS measures were found with the SFA-rich meal.

CONCLUSION

Our data shows that liquid meals rich in MUFAs may elicit a weaker satiety response based on PYY levels compared to liquid meals rich in PUFAs or SFAs in normal weight women.

Dietary lipids and functional gastrointestinal disorders

There is convincing evidence that patients with functional gastrointestinal disorders (FGIDs) exhibit dysfunctions of the gut involving hypersensitivity and abnormal reflexes, so that physiological, normally unperceived, stimuli induce symptoms. The type of symptoms depends on the specific sensory-reflex pathways and region(s) affected. Fat modulates the responses of the gut to various stimuli, and some of these modulatory mechanisms are abnormal in patients with FGIDs. Indeed, laboratory-based studies have shown that the symptoms experienced by these patients can be induced, or exacerbated, by administration of lipids in amounts that are well tolerated by healthy controls, and, thus, demonstrate a hypersensitivity to lipid. Very few studies have evaluated dietary patterns and eating behavior in these patients, with often-conflicting outcomes, and no studies have been performed to evaluate the role of targeted dietary interventions for the relief of symptoms. Given the evidence from laboratory studies, as well as patient experience, such studies, in large cohorts of patients, are needed with the view to develop personalized, cost-effective treatment approaches.

Role of peptide YY(3-36) in the satiety produced by gastric delivery of macronutrients in rats

Peptide YY(3-36) [PYY(3-36)] is postulated to act as a hormonal signal from gut to brain to inhibit food intake. PYY(3-36) potently reduces food intake when administered systemically or into the brain. If action of endogenous PYY(3-36) is necessary for normal satiation to occur, then pharmacological blockade of its receptors should increase food intake. Here, we determined the effects of iv infusion of Y1, Y2, and Y5 receptor antagonists (BIBP 3226, BIIE 0246, CGP 71683) during the first 3 h of the dark period on food intake in non-food-deprived rats. Our results showed that 1) Y2 receptor blockade reversed the anorexic response to iv infusion of PYY(3-36) but did not increase food intake when administered alone; 2) Y1 and Y5 receptor antagonists neither attenuated PYY(3-36)-induced anorexia nor altered food intake when given alone; and 3) Y2 receptor blockade attenuated anorexic responses to gastric infusions of casein hydrolysate and long-chain triglycerides, but not maltodextrin. Previous work showed that Y2 antagonist BIIE 0246 does not penetrate the blood-brain barrier. Together, these results support the hypothesis that gut PYY(3-36) action at Y2 receptors peripheral to the blood brain barrier plays an essential role in mediating satiety responses to gastric delivery of protein and long-chain triglycerides, but not polysaccharide.

Oral administration of omega-7 palmitoleic acid induces satiety and the release of appetite-related hormones in male rats

We have analyzed the effect of palmitoleic acid on short-term food intake in male rats. Administration of omega-7 palmitoleic acid by oral gavage significantly decreased food intake compared to palmitic acid, omega-9 oleic acid, or a vehicle control. Palmitoleic acid exhibited a dose-dependent effect in this context and did not cause general malaise. A triglyceride form of palmitoleate also decreased food intake, whereas olive oil, which is rich in oleic acid, did not. Palmitoleic acid accumulated within the small intestine in a dose-dependent fashion and elevated levels of the satiety hormone cholecystokinin (CCK). Both protein and mRNA levels of CCK were affected in this context. The suppression of food intake by palmitoleic acid was attenuated by intravenous injection of devazepide, a selective peripheral CCK receptor antagonist. Palmitoleic acid did not alter the expression of peroxisome proliferator-activated receptor alpha (PPARα) target genes, and a PPARα antagonist did not affect palmitoleic acid-induced satiety. This suggests that the PPARα pathway might not be involved in suppressing food intake in response to palmitoleic acid. We have shown that orally administered palmitoleic acid induced satiety, enhanced the release of satiety hormones in rats.

Bowels control brain: gut hormones and obesity

Peptide hormones are released from the gastrointestinal tract in response to nutrients and communicate information regarding the current state of energy balance to the brain. These hormones regulate appetite, energy expenditure and glucose homeostasis. They can act either via the circulation at target peripheral tissues, by activation of the vagus nerve or by acting on key brain regions implicated in energy homeostasis such as the hypothalamus and brainstem. This review gives an overview of the main gut hormones implicated in the regulation of food intake and how some of these are being targeted to develop anti obesity treatments.

Sulfated cholecystokinin-8 increases ghrelin secretion but does not affect oxyntomodulin in Holstein steers

The effect of appetite regulatory hormone cholecystokinin (CCK) on the secretions of oxyntomodulin (OXM) and ghrelin, and the effect of ghrelin on the secretions of CCK and OXM were studied in ruminants. Eight Holstein steers, 7 months old, 243 ± 7 kg body weight (BW), were arranged in an incomplete Latin square design (8 animals × 4 treatments × 4 days of sampling). Steers were intravenously injected with 10 µg of sulfated CCK-8/kg BW, 20 µg of acyl ghrelin/kg BW, 100 µg of des-acyl ghrelin/kg BW or vehicle. Blood samples were collected from -60 min to 120 min relative to time of injection. Plasma concentrations of ghrelin, sulfated CCK and OXM were measured by double-antibody radioimmunoassay. Plasma acyl ghrelin was increased to peak level (428.3 ± 6 pg/mL) at 60 min after injection of CCK compared with pre-injected levels (203.3 ± 1 pg/mL). These results showed for the first time, that intravenous bolus injection of CCK increased ghrelin secretion in ruminants. In contrast, injection of ghrelin did not change CCK secretion. Administration of ghrelin or CCK has no effect on plasma OXM concentrations. In conclusion, our results show that administration of CCK increased ghrelin secretion but did not affect OXM release in ruminants. Ghrelin did not affect the secretions of CCK and OXM.

Current and emerging concepts on the role of peripheral signals in the control of food intake and development of obesity

The gastrointestinal peptides are classically known as short-term signals, primarily inducing satiation and/or satiety. However, accumulating evidence has broadened this view, and their role in long-term energy homeostasis and the development of obesity has been increasingly recognised. In the present review, the recent research involving the role of satiation signals, especially ghrelin, cholecystokinin, glucagon-like peptide 1 and peptide YY, in the development and treatment of obesity will be discussed. Their activity, interactions and release profile vary constantly with changes in dietary and energy influences, intestinal luminal environment, body weight and metabolic status. Manipulation of gut peptides and nutrient sensors in the oral and postoral compartments through diet and/or changes in gut microflora or using multi-hormone 'cocktail' therapy are among promising approaches aimed at reducing excess food consumption and body-weight gain.

Intestinal feedback signaling and satiety

Peptidergic and neural signals arising from the presence of food in the gastrointestinal track provide feedback signals to the brain about the nature and quantity of consumed nutrients. Peptide secreting cells are differentially distributed along the gastrointestinal tract. How ingested nutrients activate or inhibit peptide secretion is complex and depends upon local, hormonal and neural mechanisms. The mode of action of the various peptides is equally complex involving endocrine, paracrine and neurocrine signaling. The success of bariatric surgical approaches to obesity treatment is secondary to alterations in gastrointestinal feedback signaling and roles of increased secretion of lower gut peptides such as peptide YY (PYY) and glucagon like peptide 1 (GLP-1) in mediating the superior effects of Roux-en-Y gastric bypass (RYGB) surgery are becoming evident. Direct nutrient delivery to jejunal sites that models the site of gastric-jejunal anastamosis in RYGB is especially effective at inhibiting food intake. Such infusions also stimulate the release of lower gut peptides suggesting a role for increased gut peptide signaling in sustaining such feeding inhibitions. Thus, gut peptides are clear targets for future obesity therapeutic developments.

Therapy for obesity based on gastrointestinal hormones

It has long been known that peptide hormones from the gastrointestinal tract have significant impact on the regulation of nutrient metabolism. Among these hormones, incretins have been found to increase insulin secretion, and thus incretin-based therapies have emerged as new modalities for the treatment of type 2 diabetes. In contrast to other antidiabetic treatments, these agents have a positive outcome profile on body weight. Worldwide there are 500 million obese people, and 3 million are dying every year from obesity-related diseases. Recently, incretin-based therapy was proposed for the treatment of obesity. Currently two different incretin therapies are widely used in the treatment of type 2 diabetes: 1) the GLP-1 receptor agonists which cause significant and sustained weight loss in overweight patients, and 2) dipeptidyl peptidase 4 (DPP-4) inhibitors being weight neutral. These findings have led to a greater interest in the physiology of intestinal peptides with potential weight-reducing properties. This review discusses the effects of the incretin-based therapies in obesity, and provides an overview of intestinal peptides with promising effects as potential new treatments for obesity.

The role of the gut/brain axis in modulating food intake

Peptide hormones released from the gastrointestinal tract communicate information about the current state of energy balance to the brain. These hormones regulate appetite and energy expenditure via the vagus nerve or by acting on key brain regions implicated in energy homeostasis such as the hypothalamus and brainstem. This review gives an overview of the main gut hormones implicated in the regulation of food intake. Research in this area has provided novel targets for the pharmacological treatment of obesity. This article is part of a Special Issue entitled 'Central Control Food Intake'

Chylomicron formation and glucagon-like peptide 1 receptor are involved in activation of the nutritional anti-inflammatory pathway

Enteral administration of lipid-enriched nutrition effectively attenuates inflammation via a cholecystokinin (CCK)-mediated vagovagal anti-inflammatory reflex. Cholecystokinin release and subsequent activation of the vagus are dependent on chylomicron formation and associated with release of additional gut peptides. The current study investigates the intestinal processes underlying activation of the CCK-mediated vagal anti-inflammatory pathway by lipid-enriched nutrition. Rats and mice were subjected to hemorrhagic shock (HS) or endotoxemia, respectively. Prior to the experimental procedures, animals were fasted or fed lipid-enriched nutrition. Pluronic L-81 (L-81) was added to the feeding to investigate involvement of chylomicron formation in activation of mesenteric afferent fibers and the immune-modulating potential of lipid-enriched nutrition. Ob/Ob mice and selective receptor antagonists were used to study the role of leptin, glucagon-like peptide 1 and peptide YY in activation of the nutritional reflex. Electrophysiological analysis of mesenteric afferents in mice revealed that lipid-enriched nutrition-mediated neural activation was abrogated by L-81 (P<.05). L-81 blunted the beneficial effects of lipid-enriched nutrition on systemic inflammation and intestinal integrity in both species (all parameters, P<.01). Ob/Ob mice required a higher dose of nutrition compared with wild-type mice to attenuate plasma levels of TNF-α and ileum-lipid binding protein, a marker for enterocyte damage (both P<.01), suggesting a higher stimulation threshold in leptin-deficient mice. Administration of a glucagon-like peptide 1-receptor antagonist, but not leptin or peptide YY antagonists, suppressed the effects of lipid-enriched nutrition. These data indicate that chylomicron formation is essential and activation of the glucagon-like peptide 1-receptor is involved in activation of the nutritional anti-inflammatory pathway by lipid-enriched nutrition.

Oral and gastrointestinal sensing of dietary fat and appetite regulation in humans: modification by diet and obesity

Dietary fat interacts with receptors in both the oral cavity and the gastrointestinal (GI) tract to regulate fat and energy intake. This review discusses recent developments in our understanding of the mechanisms underlying the effects of fat, through its digestive products, fatty acids (FAs), on GI function and energy intake, the role of oral and intestinal FA receptors, and the implications that changes in oral and small intestinal sensitivity in response to ingested fat may have for the development of obesity.

Bowels control brain: gut hormones and obesity

Food intake and energy expenditure are tightly regulated by the brain, in a homeostatic process that integrates diverse hormonal, neuronal and metabolic signals. The gastrointestinal tract is an important source of such signals, which include several hormones released by specialized enteroendocrine cells. These hormones exert powerful effects on appetite and energy expenditure. This Review addresses the physiological roles of peptide YY, pancreatic polypeptide, islet amyloid polypeptide, glucagon-like peptide 1, glucagon, oxyntomodulin, cholecystokinin and ghrelin and discusses their potential as targets for the development of novel treatments for obesity.

Pooled-data analysis identifies pyloric pressures and plasma cholecystokinin concentrations as major determinants of acute energy intake in healthy, lean men

BACKGROUND

The interaction of nutrients with the small intestine modulates gastropyloroduodenal motility, stimulates the release of gut hormones, and suppresses appetite and energy intake.

OBJECTIVE

We evaluated which, if any, of these variables are independent determinants of acute energy intake in healthy, lean men.

DESIGN

We pooled data from 8 published studies that involved a total of 67 healthy, lean men in whom antropyloroduodenal pressures, gastrointestinal hormones, and perceptions were measured during intraduodenal nutrient or intravenous hormone infusions. In all of the studies, the energy intake at a buffet lunch was quantified immediately after the infusions. To select specific motor, hormone, or perception variables for inclusion in a multivariable mixed-effects model for determination of independent predictors of energy intake, we assessed all variables for collinearity and determined within-subject correlations between energy intake and these variables by using bivariate analyses adjusted for repeated measures.

RESULTS

Although correlations were shown between energy intake and antropyloroduodenal pressures, plasma hormone concentrations, and gastrointestinal perceptions, only the peak number of isolated pyloric-pressure waves, peak plasma cholecystokinin concentration, and area under the curve of nausea were identified as independent predictors of energy intake (all P < 0.05), so that increases of 1 pressure wave, 1 pmol/L, and 1 mm . min were associated with reductions in energy intake of approximately 36, approximately 88, and approximately 0.4, respectively.

CONCLUSION

We identified specific changes in gastrointestinal motor and hormone functions (ie, stimulation of pyloric pressures and plasma cholecystokinin) and nausea that are associated with the suppression of acute energy intake.

Integrating GHS into the Ghrelin System

Oligopeptide derivatives of metenkephalin were found to stimulate growth-hormone (GH) release directly by pituitary somatotrope cells in vitro in 1977. Members of this class of peptides and nonpeptidyl mimetics are referred to as GH secretagogues (GHSs). A specific guanosine triphosphatate-binding protein-associated heptahelical transmembrane receptor for GHS was cloned in 1996. An endogenous ligand for the GHS receptor, acylghrelin, was identified in 1999. Expression of ghrelin and homonymous receptor occurs in the brain, pituitary gland, stomach, endothelium/vascular smooth muscle, pancreas, placenta, intestine, heart, bone, and other tissues. Principal actions of this peptidergic system include stimulation of GH release via combined hypothalamopituitary mechanisms, orexigenesis (appetitive enhancement), insulinostasis (inhibition of insulin secretion), cardiovascular effects (decreased mean arterial pressure and vasodilation), stimulation of gastric motility and acid secretion, adipogenesis with repression of fat oxidation, and antiapoptosis (antagonism of endothelial, neuronal, and cardiomyocyte death). The array of known and proposed interactions of ghrelin with key metabolic signals makes ghrelin and its receptor prime targets for drug development.

Role of fat hydrolysis in regulating glucagon-like Peptide-1 secretion

CONTEXT

Glucagon-like peptide-1 (GLP-1) is produced by specialized cells in the gut and secreted in response to carbohydrates and lipids. The mechanisms regulating fat-stimulated GLP-1 release have, however, not been clarified in detail.

AIM

We aimed to investigate the effect of intraduodenal (ID) fat hydrolysis on GLP-1 release and test whether the signal is mediated through cholecystokinin (CCK)-1 receptors.

DESIGN AND SETTING

Thirty-four healthy, male ambulatory volunteers were studied in three consecutive, randomized, double blind, crossover studies.

INTERVENTION

There were three interventions: 1) 12 subjects received an ID fat infusion with or without orlistat, an irreversible inhibitor of gastrointestinal lipases, in comparison with vehicle; 2) 12 subjects received ID sodium oleate (C18:1), ID sodium caprylate (C8:0), or ID vehicle; and 3) 10 subjects received ID sodium oleate with and without the CCK-1 receptor antagonist dexloxiglumide or ID vehicle plus iv saline (placebo). The effect of these treatments on GLP-1 concentrations and CCK release was quantified.

RESULTS

The following results were reached: 1) ID fat induced significant increase in GLP-1 concentrations (P < 0.004), and inhibition of fat hydrolysis by orlistat abolished this effect; 2) sodium oleate significantly stimulated GLP-1 release (P < 0.008), whereas sodium caprylate was ineffective compared with controls; and 3) dexloxiglumide administration abolished the effect of sodium oleate on GLP-1. ID fat or sodium oleate significantly stimulated plasma CCK (P < 0.006 and P < 0.004) compared with saline, whereas sodium caprylate did not.

CONCLUSION

Generation of long-chain fatty acids through hydrolysis of fat is a critical step for fat-induced stimulation of GLP-1 in humans; the signal is mediated via CCK release and CCK-1 receptors.

[Gastrointestinal hormones in food intake control]

The discovery of gut hormones regulating the energy balance has aroused great interest in the scientific community. Some of these hormones modulate appetite and satiety, acting on the hypothalamus or the solitary tract nucleus in the brainstem. In general, the endocrine signals generated in the gut have direct or indirect (through the autonomous nervous system) anorexigenic effects. Only ghrelin, a gastric hormone, has been consistently associated with the initiation of food intake and is regarded as the main orexigenic signal both in animal models and humans. In this review, we provide a brief description of the major gastrointestinal hormones implicated in the regulation of food intake. Given the increased importance of food intake disturbances, especially obesity, a better understanding of the underlying mechanisms of action of the gastrointestinal hormones might contribute to the development of new molecules that could increase the therapeutic arsenal for treating obesity and its associated comorbidities.

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.