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

Serum levels of leptin, ghrelin putative peptide YY-3 in patients with fetal alcohol spectrum disorders

Fetal alcohol spectrum disorders (FASD) are a severe developmental condition resulting from exposure to alcohol during pregnancy. The aim of this study was to examine the concentrations of hormones involved in appetite regulation-ghrelin, leptin, and putative peptide YY-3 (PYY)-in the serum of individuals with FASD. Additionally, we investigated the relationship between these hormone levels and clinical indicators. We conducted an enzyme-linked immunosorbent assay on samples collected from 62 FASD patients and 23 individuals without the condition. Our results revealed a significant decrease in leptin levels among FASD patients compared to the control group (5.124 vs. 6.838 ng/mL, p = 0.002). We revealed no statistically significant differences in the levels of other hormones studied (ghrelin and PYY). Comparisons of hormone levels were also conducted in three subgroups: FAS, neurobehavioral disorders associated with prenatal alcohol exposure and FASD risk, as well as by sex. Assignment to FASD subgroups indicated changes only for leptin. Sex had no effect on the levels of hormones. Moreover, the levels of leptin showed a negative correlation with cortisol levels and a positive correlation with BMI and proopiomelanocortin. Alterations in appetite regulation can contribute to the improper development of children with FASD, which might be another factor that should be taken into consideration in the proper treatment of patients.

Satiety Associated with Calorie Restriction and Time-Restricted Feeding: Peripheral Hormones

Calorie restriction (CR) is a common approach to inducing negative energy balance. Recently, time-restricted feeding (TRF), which involves consuming food within specific time windows during a 24-h day, has become popular owing to its relative ease of practice and potential to aid in achieving and maintaining a negative energy balance. TRF can be implemented intentionally with CR, or TRF might induce CR simply because of the time restriction. This review focuses on summarizing our current knowledge on how TRF and continuous CR affect gut peptides that influence satiety. Based on peer-reviewed studies, in response to CR there is an increase in the orexigenic hormone ghrelin and a reduction in fasting leptin and insulin. There is likely a reduction in glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and cholecystokinin (CCK), albeit the evidence for this is weak. After TRF, unlike CR, fasting ghrelin decreased in some TRF studies, whereas it showed no change in several others. Further, a reduction in fasting leptin, insulin, and GLP-1 has been observed. In conclusion, when other determinants of food intake are held equal, the peripheral satiety systems appear to be somewhat similarly affected by CR and TRF with regard to leptin, insulin, and GLP-1. But unlike CR, TRF did not appear to robustly increase ghrelin, suggesting different influences on appetite with a potential decrease of hunger after TRF when compared with CR. However, there are several established and novel gut peptides that have not been measured within the context of CR and TRF, and studies that have evaluated effects of TRF are often short-term, with nonuniform study designs and highly varying temporal eating patterns. More evidence and studies addressing these aspects are needed to draw definitive conclusions.

Whey-Adapted versus Natural Cow's Milk Formulation: Distinctive Feeding Responses and Post-Ingestive c-Fos Expression in Laboratory Mice

The natural 20:80 whey:casein ratio in cow’s milk (CM) for adults and infants is adjusted to reflect the 60:40 ratio of human milk, but the feeding and metabolic consequences of this adjustment have been understudied. In adult human subjects, the 60:40 CM differently affects glucose metabolism and hormone release than the 20:80 CM. In laboratory animals, whey-adapted goat’s milk is consumed in larger quantities. It is unknown whether whey enhancement of CM would have similar consequences on appetite and whether it would affect feeding-relevant brain regulatory mechanisms. In this set of studies utilizing laboratory mice, we found that the 60:40 CM was consumed more avidly than the 20:80 control formulation by animals motivated to eat by energy deprivation and by palatability (in the absence of hunger) and that this hyperphagia stemmed from prolongation of the meal. Furthermore, in two-bottle choice paradigms, whey-adapted CM was preferred against the natural 20:80 milk. The intake of the whey-adapted CM induced neuronal activation (assessed through analysis of c-Fos expression in neurons) in brain sites promoting satiation, but importantly, this activation was less pronounced than after ingestion of the natural 20:80 whey:casein CM. Activation of hypothalamic neurons synthesizing anorexigenic neuropeptide oxytocin (OT) was also less robust after the 60:40 CM intake than after the 20:80 CM. Pharmacological blockade of the OT receptor in mice led to an increase in the consumption only of the 20:80 CM, thus, of the milk that induced greater activation of OT neurons. We conclude that the whey-adapted CM is overconsumed compared to the natural 20:80 CM and that this overconsumption is associated with weakened responsiveness of central networks involved in satiety signalling, including OT.

Gastrointestinal peptides in eating-related disorders

Food intake is tightly controlled by homeostatic signals sensitive to metabolic need for the regulation of body weight. This review focuses on the peripherally-secreted gastrointestinal peptides (i.e., ghrelin, cholecystokinin, glucagon-like peptide 1, and peptide tyrosine tyrosine) that contribute to the control of appetite and discusses how these peptides or the signals arising from their release are disrupted in eating-related disorders across the weight spectrum, namely anorexia nervosa, bulimia nervosa, and obesity, and whether they are normalized following weight restoration or weight loss treatment. Further, the role of gut peptides in the pathogenesis and treatment response in human weight conditions as identified by rodent models are discussed. Lastly, we review the incretin- and hormone-based pharmacotherapies available for the treatment of obesity and eating-related disorders.

Low Protein Diets and Energy Balance: Mechanisms of Action on Energy Intake and Expenditure

Low protein diets are associated with increased lifespan and improved cardiometabolic health primarily in rodents, and likely improve human health. There is strong evidence that moderate to severe reduction in dietary protein content markedly influences caloric intake and energy expenditure, which is often followed by a decrease in body weight and adiposity in animal models. While the neuroendocrine signals that trigger hyperphagic responses to protein restriction are better understood, there is accumulating evidence that increased sympathetic flux to brown adipose tissue, fibroblast growth factor-21 and serotonergic signaling are important for the thermogenic effects of low protein diets. This mini-review specifically focuses on the effect of low protein diets with variable carbohydrate and lipid content on energy intake and expenditure, and the underlying mechanisms of actions by these diets. Understanding the mechanisms by which protein restriction influences energy balance may unveil novel approaches for treating metabolic disorders in humans and improve production efficiency in domestic animals.

Effects of fasting and re-feeding on the expression of CCK, PYY, hypothalamic neuropeptides, and IGF-related genes in layer and broiler chicks

Cholecystokinin (CCK) and peptide YY (PYY) have been investigated as gut hormones that send satiation signals to the brain in mammals. There is evidence that chicken PYY mRNA expression was the highest in the pancreas compared to other tissues. We recently suggested that insulin-like growth factor (IGF)-1 and its binding proteins (IGFBPs) may be involved in the appetite regulation system in chicks. In the present study, in order to evaluate the possible roles of CCK, PYY, and IGF-related proteins in the appetite regulation system in chicks, we analyzed changes in the mRNA levels of these genes in response to fasting and re-feeding in layer and hyperphagic broiler chicks. In layer chicks, 12 h of fasting reduced the mRNA levels of intestinal CCK, PYY, Y2 receptor, and pancreatic PYY, and these changes were reversed by 12 h of re-feeding. On the other hand, in broiler chicks 12 h of fasting reduced the mRNA levels of intestinal PYY and Y2 receptor, but not intestinal CCK and pancreatic PYY, and these changes were reversed by 12 h of re-feeding. Hypothalamic NPY mRNA significantly increased by 12 h of fasting in both chicks, and these changes were reversed by re-feeding. Also, 12 h of fasting significantly increased the mRNA levels of hypothalamic agouti-related protein and reduced the mRNA levels of hepatic IGF-1 only in broiler chicks, and 12 h of re-feeding did not change these. IGFBP-1 and -2 mRNA levels were markedly increased by 12 h of fasting in both chicks, and these changes were reversed by re-feeding. IGFBP-3 mRNA levels were increased by 12 h of fasting only in layer chicks, while re-feeding reduced the mRNA levels of IGFBP-3 in both types of chicks. These results suggest that several peripheral hormones, such as pancreatic PYY and intestinal CCK, may not play important roles in the regulation of food intake in broiler chicks.

Neuroendocrine Peptides of the Gut and Their Role in the Regulation of Food Intake

The regulation of food intake encompasses complex interplays between the gut and the brain. Among them, the gastrointestinal tract releases different peptides that communicate the metabolic state to specific nuclei in the hindbrain and the hypothalamus. The present overview gives emphasis on seven peptides that are produced by and secreted from specialized enteroendocrine cells along the gastrointestinal tract in relation with the nutritional status. These established modulators of feeding are ghrelin and nesfatin-1 secreted from gastric X/A-like cells, cholecystokinin (CCK) secreted from duodenal I-cells, glucagon-like peptide 1 (GLP-1), oxyntomodulin, and peptide YY (PYY) secreted from intestinal L-cells and uroguanylin (UGN) released from enterochromaffin (EC) cells. © 2021 American Physiological Society. Compr Physiol 11:1679-1730, 2021.

Adjustment of Whey:Casein Ratio from 20:80 to 60:40 in Milk Formulation Affects Food Intake and Brainstem and Hypothalamic Neuronal Activation and Gene Expression in Laboratory Mice

Adjustment of protein content in milk formulations modifies protein and energy levels, ensures amino acid intake and affects satiety. The shift from the natural whey:casein ratio of ~20:80 in animal milk is oftentimes done to reflect the 60:40 ratio of human milk. Studies show that 20:80 versus 60:40 whey:casein milks differently affect glucose metabolism and hormone release; these data parallel animal model findings. It is unknown whether the adjustment from the 20:80 to 60:40 ratio affects appetite and brain processes related to food intake. In this set of studies, we focused on the impact of the 20:80 vs. 60:40 whey:casein content in milk on food intake and feeding-related brain processes in the adult organism. By utilising laboratory mice, we found that the 20:80 whey:casein milk formulation was consumed less avidly and was less preferred than the 60:40 formulation in short-term choice and no-choice feeding paradigms. The relative PCR analyses in the hypothalamus and brain stem revealed that the 20:80 whey:casein milk intake upregulated genes involved in early termination of feeding and in an interplay between reward and satiety, such as melanocortin 3 receptor (MC3R), oxytocin (OXT), proopiomelanocortin (POMC) and glucagon-like peptide-1 receptor (GLP1R). The 20:80 versus 60:40 whey:casein formulation intake differently affected brain neuronal activation (assessed through c-Fos, an immediate-early gene product) in the nucleus of the solitary tract, area postrema, ventromedial hypothalamic nucleus and supraoptic nucleus. We conclude that the shift from the 20:80 to 60:40 whey:casein ratio in milk affects short-term feeding and relevant brain processes.

PYY, a Therapeutic Option for Type 2 Diabetes?

Metabolic surgery leads to rapid and effective diabetes reversal in humans, by weight-independent mechanisms. The crucial improvement in pancreatic islet function observed after surgery is induced by alteration in several factors, including gut hormones. In addition to glucagon-like peptide 1 (GLP-1), increasing lines of evidence show that peptide tyrosine tyrosine (PYY) plays a key role in the metabolic benefits associated with the surgery, ranging from appetite regulation to amelioration of islet secretory properties and survival. Here, we summarize the current knowledge and the latest advancements in the field, which pitch a strong case for the development of novel PYY-based therapy for the treatment of diabetes.

A Rat Model of Human Lipid Emulsion Digestion

A better understanding of how dietary lipids are processed by the human body is necessary to allow for the control of satiation and energy intake by tailored lipid systems. To examine whether rats are a valid model of human dietary lipid processing and therefore useful for further mechanistic studies in this context, we tested in rats three lipid emulsions of different stability, which alter satiety responses in humans. Different sets of 15 adult male Sprague Dawley rats, equipped with gastric catheters alone or combined with hepatic portal vein (HPV) and vena cava (VC) catheters were maintained on a medium-fat diet and adapted to an 8 h deprivation/16 h feeding schedule. Experiments were performed in a randomized cross-over study design. After gastric infusion of the lipid emulsions, we assessed gastric emptying by the paracetamol absorption test and recorded in separate experiments food intake and plasma levels of gastrointestinal hormones and metabolites in the HPV. For an acid stable emulsion, slower gastric emptying and an enhanced release of satiating gastrointestinal (GI) hormones were observed and were associated with lower short-term energy intake in rats and less hunger in humans, respectively. The magnitude of hormonal responses was related to the acid stability and redispersibility of the emulsions and thus seems to depend on the availability of lipids for digestion. Plasma metabolite levels were unaffected by the emulsion induced changes in lipolysis. The results support that structured lipid systems are digested similarly in rats and humans. Thus unstable emulsions undergo the same intragastric destabilization in both species, i.e., increased droplet size and creaming. This work establishes the rat as a viable animal model for in vivo studies on the control of satiation and energy intake by tailored lipid systems.

Peptide YY mediates the satiety effects of diets enriched with whey protein fractions in male rats

Dairy proteins-whey protein, in particular-are satiating and often recommended for weight control; however, little is known about the mechanisms by which whey protein and its components promote satiety and weight loss. We used diet-induced obese rats to determine whether the hypophagic effects of diets that are enriched with whey and its fractions, lactalbumin and lactoferrin, are mediated by the gut hormone, peptide YY (PYY). We demonstrate that high protein diets that contain whey, lactalbumin, and lactoferrin decreased food intake and body weight with a concurrent increase in PYY mRNA abundance in the colon and/or plasma PYY concentrations. Of importance, blockade of PYY neuropeptide Y receptor subtype 2 (Y2) receptors with a peripherally restricted antagonist attenuated the hypophagic effects of diets that are enriched with whey protein fractions. Diets that are enriched with whey fractions were less preferred; however, in a modified conditioned taste preference test, PYY Y2 receptor blockade induced hyperphagia of a lactoferrin diet, but caused a reduction in preference for Y2 antagonist-paired flavor, which suggested that PYY signaling is important for lactoferrin-induced satiety, but not essential for preference for lactoferrin-enriched diets. Taken together, these data provide evidence that the satiety of diets that are enriched with whey protein components is mediated, in part, via enhanced PYY secretion and action in obese male rats.-Zapata, R. C., Singh, A., Chelikani, P. K. Peptide YY mediates the satiety effects of diets enriched with whey protein fractions in male rats.

Identification, expression analysis, and functional characterization of peptide YY in chickens (Gallus gallus domesticus)

Peptide YY (PYY) functions as a postprandial satiety signal in mammals. However, the genomic information and physiological roles of chicken PYY have not yet been clarified, although PYY peptide was isolated from chicken intestines in 1992. In this study, we identified a full-length complementary DNA (cDNA) sequence encoding the chicken PYY precursor. The deduced amino acid sequence of chicken PYY was completely consistent with the previously identified peptide sequence. PYY mRNA was abundantly expressed in the small intestine compared with the large intestine. PYY mRNA levels in the jejunum were significantly higher during ad libitum feeding compared with fasting, suggesting that intestinal PYY expression is altered in response to nutritional status in chicks. Intravenous administration of PYY significantly suppressed food intake in chicks. Furthermore, neuropeptide Y receptor Y2, a possible target of PYY, was expressed in various brain regions including the appetite-regulating centers in chicks. This is the first evidence that the intestinal hormone PYY may function as an anorexigenic hormone in chicks.

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.

Effects of solid-phase extraction of plasma in measuring gut metabolic hormones in fasted and fed blood of lean and diet-induced obese rats

Glucagon‐like peptide‐1 (GLP‐1), peptide YY (3‐36) [PYY(3‐36)], amylin, ghrelin, insulin, and leptin are thought to act as hormonal signals from periphery to brain to control food intake. Here, we determined the effects of solid‐phase extraction of plasma in measuring these hormones in blood of lean and diet‐induced obese rats. Individual enzyme‐linked immunoassays and a multiplex assay were used to measure active GLP‐1, total PYY, active amylin, active ghrelin, insulin, leptin, and total GIP in response to (1) addition of known amounts of the peptides to lean and obese plasma, (2) a large meal in lean and obese rats, and (3) intravenous infusions of anorexigenic doses of GLP‐1, PYY(3‐36), amylin, and leptin in lean rats. Extraction of lean and obese plasma prior to assays produced consistent recoveries across assays for GLP‐1, PYY, amylin, ghrelin, and insulin, reflecting losses inherent to the extraction procedure. Plasma extraction prior to assays generally revealed larger meal‐induced changes in plasma GLP‐1, PYY, amylin, ghrelin, and insulin in lean and obese rats. Plasma extraction and the multiplex assay were used to compare plasma levels of GLP‐1, PYY, and amylin after a large meal with plasma levels produced by IV infusions of anorexigenic doses of GLP‐1, PYY(3‐36), and amylin. Infusions produced dose‐dependent increases in plasma peptide levels, which were well above their postprandial levels. These results do not support the hypothesis that postprandial plasma levels of GLP‐1, PYY(3‐36), and amylin are sufficient to decrease food intake by an endocrine mechanism.

Low protein diets produce divergent effects on energy balance

Diets deficient in protein often increase food consumption, body weight and fat mass; however, the underlying mechanisms remain poorly understood. We compared the effects of diets varying in protein concentrations on energy balance in obesity-prone rats. We demonstrate that protein-free (0% protein calories) diets decreased energy intake and increased energy expenditure, very low protein (5% protein) diets increased energy intake and expenditure, whereas moderately low protein (10% protein) diets increased energy intake without altering expenditure, relative to control diet (15% protein). These diet-induced alterations in energy expenditure are in part mediated through enhanced serotonergic and β-adrenergic signaling coupled with upregulation of key thermogenic markers in brown fat and skeletal muscle. The protein-free and very low protein diets decreased plasma concentrations of multiple essential amino acids, anorexigenic and metabolic hormones, but these diets increased the tissue expression and plasma concentrations of fibroblast growth factor-21. Protein-free and very low protein diets induced fatty liver, reduced energy digestibility, and decreased lean mass and body weight that persisted beyond the restriction period. In contrast, moderately low protein diets promoted gain in body weight and adiposity following the period of protein restriction. Together, our findings demonstrate that low protein diets produce divergent effects on energy balance.

Role of capsaicin-sensitive peripheral sensory neurons in anorexic responses to intravenous infusions of cholecystokinin, peptide YY-(3-36), and glucagon-like peptide-1 in rats

Cholecystokinin (CCK)-induced suppression of feeding is mediated by vagal sensory neurons that are destroyed by the neurotoxin capsaicin (CAP). Here we determined whether CAP-sensitive neurons mediate anorexic responses to intravenous infusions of gut hormones peptide YY-(3-36) [PYY-(3-36)] and glucagon-like peptide-1 (GLP-1). Rats received three intraperitoneal injections of CAP or vehicle (VEH) in 24 h. After recovery, non-food-deprived rats received at dark onset a 3-h intravenous infusion of CCK-8 (5, 17 pmol·kg⁻¹·min⁻¹), PYY-(3-36) (5, 17, 50 pmol·kg⁻¹·min⁻¹), or GLP-1 (17, 50 pmol·kg⁻¹·min⁻¹). CCK-8 was much less effective in reducing food intake in CAP vs. VEH rats. CCK-8 at 5 and 17 pmol·kg⁻¹·min⁻¹ reduced food intake during the 3-h infusion period by 39 and 71% in VEH rats and 7 and 18% in CAP rats. In contrast, PYY-(3-36) and GLP-1 were similarly effective in reducing food intake in VEH and CAP rats. PYY-(3-36) at 5, 17, and 50 pmol·kg⁻¹·min⁻¹ reduced food intake during the 3-h infusion period by 15, 33, and 70% in VEH rats and 13, 30, and 33% in CAP rats. GLP-1 at 17 and 50 pmol·kg⁻¹·min⁻¹ reduced food intake during the 3-h infusion period by 48 and 60% in VEH rats and 30 and 52% in CAP rats. These results suggest that anorexic responses to PYY-(3-36) and GLP-1 are not primarily mediated by the CAP-sensitive peripheral sensory neurons (presumably vagal) that mediate CCK-8-induced anorexia.

Modulation of hunger and satiety: hormones and diet

PURPOSE OF REVIEW

To highlight recent research developments relating to the effects of, and interactions between, hormones and diet, as well as underlying mechanisms, on appetite, energy intake and body weight. For this purpose, clinically relevant English language articles were reviewed from October 2012 to April 2014.

RECENT FINDINGS

The mechanisms underlying nutrient-induced energy intake suppression differ between dietary protein and lipid. High-fat, energy-dense diets compromise the satiating effects of gut hormones, and, therefore, promote further overconsumption. These effects are mediated by changes in the signalling in both peripheral and central pathways, and may only be partially reversible by dietary restriction. Additional factors, including probiotics, meal-related factors (e.g., eating speed and frequency), circadian influences and gene polymorphisms, also modify energy intake and eating behaviour.

SUMMARY

Research continues to unravel the pathways and mechanisms underlying the nutrient-induced and diet-induced regulation of energy intake, as well as the changes, both peripherally and in the central nervous system, brought about by the consumption of high-fat, energy-dense diets. Much further work is required to translate this knowledge into novel, and effective, approaches for the management and treatment of obesity and associated metabolic disorders.

GLP-1 receptor signaling is not required for reduced body weight after RYGB in rodents

Exaggerated GLP-1 and PYY secretion is thought to be a major mechanism in the reduced food intake and body weight after Roux-en-Y gastric bypass surgery. Here, we use complementary pharmacological and genetic loss-of-function approaches to test the role of increased signaling by these gut hormones in high-fat diet-induced obese rodents. Chronic brain infusion of a supramaximal dose of the selective GLP-1 receptor antagonist exendin-9-39 into the lateral cerebral ventricle significantly increased food intake and body weight in both RYGB and sham-operated rats, suggesting that, while contributing to the physiological control of food intake and body weight, central GLP-1 receptor signaling tone is not the critical mechanism uniquely responsible for the body weight-lowering effects of RYGB. Central infusion of the selective Y2R-antagonist BIIE0246 had no effect in either group, suggesting that it is not critical for the effects of RYGB on body weight under the conditions tested. In a recently established mouse model of RYGB that closely mimics surgery and weight loss dynamics in humans, obese GLP-1R-deficient mice lost the same amount of body weight and fat mass and maintained similarly lower body weight compared with wild-type mice. Together, the results surprisingly provide no support for important individual roles of either gut hormone in the specific mechanisms by which RYGB rats settle at a lower body weight. It is likely that the beneficial effects of bariatric surgeries are expressed through complex mechanisms that require combination approaches for their identification.