Gut hormone PYY(3-36) physiologically inhibits food intake. Nature. 2002;418:650-654. [PMID: 12167864 DOI: 10.1038/nature02666]

Interaction between the gut microbiota and colonic enteroendocrine cells regulates host metabolism

Nutrient handling is an essential function of the gastrointestinal tract. Hormonal responses of small intestinal enteroendocrine cells (EECs) have been extensively studied but much less is known about the role of colonic EECs in metabolic regulation. To address this core question, we investigated a mouse model deficient in colonic EECs. Here we show that colonic EEC deficiency leads to hyperphagia and obesity. Furthermore, colonic EEC deficiency results in altered microbiota composition and metabolism, which we found through antibiotic treatment, germ-free rederivation and transfer to germ-free recipients, to be both necessary and sufficient for the development of obesity. Moreover, studying stool and blood metabolomes, we show that differential glutamate production by intestinal microbiota corresponds to increased appetite and that colonic glutamate administration can directly increase food intake. These observations shed light on an unanticipated host-microbiota axis in the colon, part of a larger gut-brain axis, that regulates host metabolism and body weight.

PYY3-36 infused systemically or directly into the VTA attenuates fentanyl seeking in male rats

More effective treatments for fentanyl use disorder are urgently needed. An emerging literature indicates that glucagon-like peptide-1 receptor (GLP-1R) agonists attenuate voluntary opioid taking and seeking in rodents. However, GLP-1R agonists produce adverse malaise-like effects that may limit patient compliance. Recently, we developed a dual agonist of GLP-1Rs and neuropeptide Y2 receptors (Y2Rs) that attenuates fentanyl taking and seeking at doses that do not produce malaise-like effects in opioid-experienced rats. Whether activating Y2Rs alone is sufficient to reduce opioid taking and seeking, however, is not known. Here, we investigated the efficacy of the Y2R ligand PYY3-36 to reduce fentanyl self-administration and the reinstatement of fentanyl-seeking behavior, a model of relapse in humans. Male rats were allowed to self-administer fentanyl (2.5 μg/kg, i.v.) for 21 days on a fixed-ratio 5 (FR5) schedule of reinforcement. Rats were then pretreated with vehicle or PYY3-36 (50 μg/kg s.c.; 0.1 and 1.0 μg/100 nL intra-VTA) prior to fentanyl self-administration test sessions. There were no effects of systemic or intra-VTA PYY3-36 on intravenous fentanyl self-administration. Opioid taking was then extinguished. Prior to subsequent reinstatement test sessions, rats were pretreated with vehicle or PYY3-36 (50 μg/kg s.c.; 0.1 and 1.0 μg/100 nL intra-VTA). Both systemic and intra-VTA administration of PYY3-36 attenuated fentanyl reinstatement in male rats at doses that did not affect food intake or produce adverse malaise-like effects. These findings indicate that Y2R agonism alone is sufficient to decrease fentanyl-seeking behavior during abstinence in opioid-experienced rats and further support strategies aimed at targeting Y2Rs for treating opioid use disorders.

The Gut-Brain Axis and Its Role in Controlling Eating Behavior in Intestinal Inflammation

Malnutrition represents a major problem in the clinical management of the inflammatory bowel disease (IBD). Presently, our understanding of the cross-link between eating behavior and intestinal inflammation is still in its infancy. Crohn's disease patients with active disease exhibit strong hedonic desires for food and emotional eating patterns possibly to ameliorate feelings of low mood, anxiety, and depression. Impulsivity traits seen in IBD patients may predispose them to palatable food intake as an immediate reward rather than concerns for future health. The upregulation of enteroendocrine cells (EEC) peptide response to food intake has been described in ileal inflammation, which may lead to alterations in gut-brain signaling with implications for appetite and eating behavior. In summary, a complex interplay of gut peptides, psychological, cognitive factors, disease-related symptoms, and inflammatory burden may ultimately govern eating behavior in intestinal inflammation.

Mechanisms underlying the weight loss effects of RYGB and SG: similar, yet different

The worldwide obesity epidemic continues unabated, adversely impacting upon global health and economies. People with severe obesity suffer the greatest adverse health consequences with reduced life expectancy. Currently, bariatric surgery is the most effective treatment for people with severe obesity, resulting in marked sustained weight loss, improved obesity-associated comorbidities and reduced mortality. Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB), the most common bariatric procedures undertaken globally, engender weight loss and metabolic improvements by mechanisms other than restriction and malabsorption. It is now clear that a plethora of gastrointestinal (GI) tract-derived signals plays a critical role in energy and glucose regulation. SG and RYGB, which alter GI anatomy and nutrient flow, impact upon these GI signals ultimately leading to weight loss and metabolic improvements. However, whilst highly effective overall, at individual level, post-operative outcomes are highly variable, with a proportion of patients experiencing poor long-term weight loss outcome and gaining little health benefit. RYGB and SG are markedly different anatomically and thus differentially impact upon GI signalling and bodyweight regulation. Here, we review the mechanisms proposed to cause weight loss following RYGB and SG. We highlight similarities and differences between these two procedures with a focus on gut hormones, bile acids and gut microbiota. A greater understanding of these procedure-related mechanisms will allow surgical procedure choice to be tailored to the individual to maximise post-surgery health outcomes and will facilitate the discovery of non-surgical treatments for people with obesity.

The Gut Microbiome, Obesity, and Weight Control in Women's Reproductive Health

The microbes residing in the human gut, referred to as the microbiome, are intricately linked to energy homeostasis and subsequently obesity. Integral to the origins of obesity, the microbiome is believed to affect not only health of the human gut but also overall health. This microbiome-obesity association is mediated through the process of energy extraction, metabolism, and cross talk between the brain and the gut microbiome. Host exposures, including diet, that potentially modify genetic predisposition to obesity and affect weight management are reviewed. The higher prevalence of obesity among women and recent evidence linking obesity during pregnancy with offspring health make this topic particularly relevant. Current limitations in microbiome research to address obesity and future advances in this field are described. Applications of this science with respect to applied nursing and overall health care in general are included, with emphasis on the reproductive health of women and their offspring.

Peptide hormones and lipopeptides: from self-assembly to therapeutic applications

This review describes the properties and activities of lipopeptides and peptide hormones and how the lipidation of peptide hormones could potentially produce therapeutic agents combating some of the most prevalent diseases and conditions. The self-assembly of these types of molecules is outlined, and how this can impact on bioactivity. Peptide hormones specific to the uptake of food and produced in the gastrointestinal tract are discussed in detail. The advantages of lipidated peptide hormones over natural peptide hormones are summarised, in terms of stability and renal clearance, with potential application as therapeutic agents. © 2017 The Authors Journal of Peptide Science published by European Peptide Society and John Wiley & Sons Ltd.

Polymorphic Variation in FFA Receptors: Functions and Consequences

Overfeeding of fat can cause various metabolic disorders including obesity and type 2 diabetes (T2D). Diet provided free fatty acids (FFAs) are not only essential nutrients, but they are also recognized as signaling molecules, which stimulate various important biological functions. Recently, several G protein-coupled receptors (GPCRs), including FFA1-4, have been identified as receptors of FFAs by various physiological and pharmacological studies. FFAs exert physiological functions through these FFA receptors (FFARs) depending on carbon chain length and degree of unsaturation. Functional analyses have revealed that several important metabolic processes, such as peptide hormone secretion, cell maturation and nerve activities, are regulated by FFARs and thereby FFARs contribute to the energy homeostasis through these physiological functions. Hence, FFARs are expected to be promising pharmacological targets for metabolic disorders since imbalances in energy homeostasis lead to metabolic disorders. In human, it is established that different responses of individuals to endogenous ligands and chemical drugs may be due to differences in the ability of such ligands to activate nucleotide polymorphic variants of receptors. However, the clear links between genetic variations that are involved in metabolic disorders and polymorphisms receptors have been relatively difficult to assess. In this review, I summarize current literature describing physiological functions of FFARs and genetic variations of those receptors to discuss the potential of FFARs as drug targets for metabolic disorders.

Ac-Trp-DPhe(p-I)-Arg-Trp-NH2, a 250-Fold Selective Melanocortin-4 Receptor (MC4R) Antagonist over the Melanocortin-3 Receptor (MC3R), Affects Energy Homeostasis in Male and Female Mice Differently

The melanocortin-4 receptor (MC4R) has been indicated as a therapeutic target for metabolic disorders such as anorexia, cachexia, and obesity. The current study investigates the in vivo effects on energy homeostasis of a 15 nM MC4R antagonist SKY2-23-7, Ac-Trp-DPhe(p-I)-Arg-Trp-NH2, that is a 3700 nM melanocortin-3 receptor (MC3R) antagonist with minimal MC3R and MC4R agonist activity. When monitoring both male and female mice in TSE metabolic cages, sex-specific responses were observed in food intake, respiratory exchange ratio (RER), and energy expenditure. A 7.5 nmol dose of SKY2-23-7 increased food intake, increased RER, and trended toward decreasing energy expenditure in male mice. However, this compound had minimal effect on female mice's food intake and RER at the 7.5 nmol dose. A 2.5 nmol dose of SKY2-23-7 significantly increased female food intake, RER, and energy expenditure while having a minimal effect on male mice at this dose. The observed sex differences of SKY2-23-7 administration result in the discovery of a novel chemical probe for elucidating the molecular mechanisms of the sexual dimorphism present within the melanocortin pathway. To further explore the melanocortin sexual dimorphism, hypothalamic gene expression was examined. The mRNA expression of the MC3R and proopiomelanocortin (POMC) were not significantly different between sexes. However, the expression of agouti-related peptide (AGRP) was significantly higher in female mice which may be a possible mechanism for the sex-specific effects observed with SKY2-23-7.

Relative Effects of Sensory Modalities and Importance of Fatty Acid Sensitivity on Fat Perception in a Real Food Model

INTRODUCTION

Fat can be perceived through mouthfeel, odour and taste, but the influence of these modalities on fat perception remains undefined. Fatty acids are stimuli and individual sensitivity to fatty acids varies. Studies show association between fatty acid sensitivity, dietary intake and BMI, but results are conflicting. Therefore, this study examined this association, and the effect of modalities on fat perception.

METHODS

Two sub-studies were conducted. In study 1 (n = 46), fat intensity was assessed by milk/cream mixtures varying by five fat levels. Fat intensity was rated under four conditions: mouthfeel odour-masked, mouthfeel-masked, odour masked and with no masking. Mouthfeel masking was achieved using thickener and paraffin, odour masking using nose-clips. Fatty acid sensitivity was measured by 3-AFC staircase method using milk containing oleic acid (0.31-31.4 mM). In study 2 (n = 51), more fat levels were added into the intensity rating. A 2-AFC discrimination test was used to confirm whether fat levels could be distinguished. In the sensitivity test, a wider range of oleic acid was included.

RESULTS

Fat intensity was rated higher without nose clips (p < 0.0001), implying that odour increased fat perception. Mouthfeel-masked samples were rated higher, showing that increased viscosity and lubricity enhanced fat perception (p < 0.0001). Participants could distinguish fat levels based on "taste" in rating tests and 2-AFC tests. Participants were divided into high-/medium-/low-sensitivity groups. No significant difference was found in fat intensity between groups; however, the high-sensitivity group discriminated more fat levels. No association between sensitivity groups, nutrient intake or BMI was found.

CONCLUSION

Mouthfeel and odour can enhance fat perception. Fat level can be discriminated based on taste.

An in Vitro and in Vivo Investigation of Bivalent Ligands That Display Preferential Binding and Functional Activity for Different Melanocortin Receptor Homodimers

Pharmacological probes for the melanocortin receptors have been utilized for studying various disease states including cancer, sexual function disorders, Alzheimer's disease, social disorders, cachexia, and obesity. This study focused on the design and synthesis of bivalent ligands to target melanocortin receptor homodimers. Lead ligands increased binding affinity by 14- to 25-fold and increased cAMP signaling potency by 3- to 5-fold compared to their monovalent counterparts. Unexpectedly, different bivalent ligands showed preferences for particular melanocortin receptor subtypes depending on the linker that connected the binding scaffolds, suggesting structural differences between the various dimer subtypes. Homobivalent compound 12 possessed a functional profile that was unique from its monovalent counterpart providing evidence of the discrete effects of bivalent ligands. Lead compound 7 significantly decreased feeding in mice after intracerebroventricular administration. To the best of our knowledge, this is the first report of a melanocortin bivalent ligand's in vivo physiological effects.

Metabolic surgery: A paradigm shift in type 2 diabetes management

Obesity and type 2 diabetes mellitus (T2DM) are major public health issues globally over the past few decades. Despite dietary interventions, lifestyle modifications and the availability of several pharmaceutical agents, management of T2DM with obesity is a major challenge to clinicians. Metabolic surgery is emerging as a promising treatment option for the management of T2DM in the obese population in recent years. Several observational studies and a few randomised controlled trials have shown clear benefits of various bariatric procedures in obese individuals in terms of improvement or remission of T2DM and multiple other health benefits such as improvement of hypertension, obstructive sleep apnoea, osteoarthritis and non-alcoholic fatty liver disease. Uncertainties about the long-term implications of metabolic surgery such as relapse of T2DM after initial remission, nutritional and psychosocial complications and the optimal body mass index for different ethnic groups exist. The article discusses the major paradigm shift in recent years in the management of T2DM after the introduction of metabolic surgery.

Recent developments in the pathophysiology of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder, the pathophysiology of which is not completely known, although it has been shown that genetic/social learning factors, diet, intestinal microbiota, intestinal low-grade inflammation, and abnormal gastrointestinal endocrine cells play a major role. Studies of familial aggregation and on twins have confirmed the heritability of IBS. However, the proposed IBS risk genes are thus far nonvalidated hits rather than true predisposing factors. There is no convincing evidence that IBS patients suffer from food allergy/intolerance, with the effect exerted by diet seemingly caused by intake of poorly absorbed carbohydrates and fiber. Obesity is a possible comorbidity of IBS. Differences in the microbiota between IBS patients and healthy controls have been reported, but the association between IBS symptoms and specific bacterial species is uncertain. Low-grade inflammation appears to play a role in the pathophysiology of a major subset of IBS, namely postinfectious IBS. The density of intestinal endocrine cells is reduced in patients with IBS, possibly as a result of genetic factors, diet, intestinal microbiota, and low-grade inflammation interfering with the regulatory signals controlling the intestinal stem-cell clonogenic and differentiation activities. Furthermore, there is speculation that this decreased number of endocrine cells is responsible for the visceral hypersensitivity, disturbed gastrointestinal motility, and abnormal gut secretion seen in IBS patients.

Obesity and dyslipidemia

Dyslipidemia associated with obesity and the metabolic syndrome is one of the central features contributing to the increased CV risk in these patients. In view of the pandemic of the metabolic syndrome, it is imperative to fully understand the mechanisms leading to the metabolic lipid phenotype before embarking upon optimal treatment strategies. The traditional concept that insulin resistance causes increased FFA flux via increased TG hydrolysis in adipose tissue is still of a central theme in the general hypothesis. The combination of increased hepatic VLDL secretion with impaired LPL-mediated TG clearance explains the hypertriglyceridemia phenotype of the metabolic syndrome. Hence, central IR may be an important factor contributing to peripheral hypertriglyceridemia. Recently recognized regulatory systems include the profound impact of the hypothalamus on TG secretion and glucose control. In addition, dysfunctional (or inflamed) intra abdominal adipose tissue has emerged as a potent regulator of dyslipidemia and IR. It will be a challenge to design novel treatment modalities that target “dysfunctional” fat or central IR to attempt to prevent the epidemic of CV disease secondary to the metabolic syndrome.

Obesity and dyslipidemia

The alarming and still increasing prevalence of obesity and associated cardiovascular risk raises much concern. The increase in cardiovascular risk depends to a significant extent on the changes in lipid profiles as observed in obesity. These changes are decreased high-density lipoprotein cholesterol and increased triglyceride levels. Much effort has already been expended into the elucidation of the mechanisms behind these obesity-associated lipid changes. Insulin resistance certainly plays a central role and, in addition, both hormonal and neurologic pathways have recently been found to play an important role. This article focuses on the mechanisms involved in the development of the proatherogenic lipid changes associated with obesity.

Common neuropeptide Y2 receptor gene variant is protective against obesity among Swedish men

BACKGROUND

Gut hormones and their receptors are considered important in the control of feeding behavior. The gut hormone peptide-YY (PYY) has anorexic effects via the inhibitory neuropeptide Y2 receptor (Y2R) highly expressed in orexigenic NPY/AGRP neurons within the arcuate nucleus, a major integrator of appetite control in the hypothalamus.

DESIGN

Genetic case-control association study of single nucleotide polymorphisms (SNPs) in Y2R and PYY.

SUBJECTS

Swedish Caucasians comprising 148 lean, 129 overweight/obese and 226 morbidly obese men.

MEASUREMENTS

Genotypes of the common, silent and conserved SNP Y2R 585T>C and the common SNP PYY Arg72Thr, as well as various obesity-related clinical parameters.

RESULTS

Obese men had a lower allele and homozygosity frequency of the common allele 585T>C:T which was particularly evident comparing morbidly obese with lean men (P = 0.002), and analyzing dependence between continuous body mass index (BMI) and genotype (P = 0.002). In agreement, systolic blood pressure tended to be lower in those homozygous for allele T, which was not explained by the BMI - genotype dependence. We found no association to obesity for the PYY Arg72Thr polymorphism, which is located nearby the essential carboxy terminal.

CONCLUSION

A common and conserved variant of the PYY and NPY receptor Y2R is less prevalent among obese compared to among lean Swedish men. This suggests that the common Y2R variant is protective against obesity. Our findings further implicate Y2R in food intake regulation.