Role of gastrointestinal hormones in feeding behavior and obesity treatment

TM4SF5-mediated abnormal food-intake behavior and apelin expression facilitate non-alcoholic fatty liver disease features

Transmembrane 4 L six family member 5 (TM4SF5) engages in non-alcoholic steatohepatitis (NASH), although its mechanistic roles are unclear. Genetically engineered Tm4sf5 mice fed ad libitum normal chow or high-fat diet for either an entire day or a daytime-feeding (DF) pattern were analyzed for metabolic parameters. Compared to wild-type and Tm4sf5-/- knockout mice, hepatocyte-specific TM4SF5-overexpressing Alb-TGTm4sf5-Flag (TG) mice showed abnormal food-intake behavior during the mouse-inactive daytime, increased apelin expression, increased food intake, and higher levels of NASH features. DF or exogenous apelin injection of TG mice caused severe hepatic pathology. TM4SF5-mediated abnormal food intake was correlated with peroxisomal β-oxidation, mTOR activation, and autophagy inhibition, with triggering NASH phenotypes. Non-alcoholic fatty liver disease (NAFLD) patients' samples revealed a correlation between serum apelin and NAFLD activity score. Altogether, these observations suggest that hepatic TM4SF5 may cause abnormal food-intake behaviors to trigger steatohepatitic features via the regulation of peroxisomal β-oxidation, mTOR, and autophagy.

Potential for Improvement of Gut Microbiota Deterioration Caused by a High-fat, High-sucrose Diet through Administration of Acylated Steryl-β-glycosides

Consumption of a high-fat diet (HFD) is associated with an increased risk of metabolic diseases, cancer, and neurological disorders, which are major global health concerns. In the present study, mice were fed a HFD containing 40% fat and 0.5% or 1.0% acylated steryl-β-glucosides (ASG) and their gut microbiota was compared to that of mice fed with a low-fat diet (LFD). After 55 d, the epididymal fat weight was higher in the HFD and ASG groups than in the LFD group; however, the epididymal fat weight was lower in the ASG group than in the HFD group. The abundance of gut microbiota increased with HFD in obese micespecific Bacillota, but decreased when ASG was added to the HFD. The number of intestinal bacteria involved in the production of carcinogenic secondary bile acids was increased by the consumption of HFD, but decreased by the addition of ASG to HSD. This finding may indicate the gut bacteria-mediated health benefits of ASG.

GPR120 Regulates Pancreatic Polypeptide Secretion From Male Mouse Islets via PLC-Mediated Calcium Mobilization

The free fatty acid receptor G protein-coupled receptor 120 (GPR120) is expressed in pancreatic islets, but its specific cell distribution and function have not been fully established. In this study, a GPR120-IRES-EGFP knockin (KI) mouse was generated to identify GPR120-expressing cells with enhanced green fluorescence proteins (EGFP). EGFP-positive cells collected from KI mouse islets by flow cytometry had a significantly higher expression of pancreatic polypeptide (PP) evidenced by reverse transcriptase (RT)-quantitative polymerase chain reaction (qPCR). Single-cell RT-PCR and immunocytochemical double staining also demonstrated the coexpression of GPR120 with PP in mouse islets. The GPR120-specific agonist TUG-891 significantly increased plasma PP levels in mice. TUG-891 significantly increased PP levels in islet medium in vitro, which was markedly attenuated by GPR120 small interfering RNA treatment. TUG-891-stimulated PP secretion in islets was fully blocked by pretreatment with YM-254890 (a Gq protein inhibitor), U73122 (a phospholipase C inhibitor), or thapsigargin (an inducer of endoplasmic reticulum Ca2+ depletion), respectively. TUG-891 triggered the increase in intracellular free Ca2+ concentrations ([Ca2+]i) in PP cells, which was also eliminated by YM-254890, U73122, or thapsigargin. GPR120 gene expression was significantly reduced in islets of high-fat diet (HFD)-induced obese mice. TUG-891-stimulated PP secretion was also significantly diminished in vivo and in vitro in HFD-induced obese mice compared with that in normal-chow diet control mice. In summary, this study demonstrated that GPR120 is expressed in mouse islet PP cells and GPR120 activation stimulated PP secretion via the Gq/PLC-Ca2+ signaling pathway in normal-chow diet mice but with diminished effects in HFD-induced obese mice.

The interaction between microbiome and host central nervous system: the gut-brain axis as a potential new therapeutic target in the treatment of obesity and cardiometabolic disease

INTRODUCTION

The role of the intestinal microbiota in host cardiometabolic health and disease has gained significant attention over recent decades. Previous studies have shown effects on metabolic health through gut microbiota modulation; this suggests diverse interaction pathways that constitute the communication between gut microbiota and host central nervous system, the so-called gut-brain axis.

AREAS COVERED

This article provides an overview of the various mechanisms that may mediate the gut-brain axis. It places an emphasis on cardiometabolic health, including effects of short-chain fatty acids (SCFA), alterations in neurotransmitters and gut peptides and microbial effects on chronic inflammation and immune function. Moreover, this paper sheds light on whether these mechanisms afford therapeutic targets to promote metabolic health. To this end, a PubMed search with the terms 'gut microbiota,' 'obesity' and 'insulin sensitivity' was performed.

EXPERT OPINION

Many properties of the human gut microbiome are associated with the central regulation of appetite and metabolic status. Some of these relationships are causal and there are positive effects from certain intervention methods. Microbial manipulation may offer a means to prevent or treat obesity and associated co-morbidities. However, to establish direct causal relations between altered gut microbiota and metabolic disease, clinical intervention studies are necessary.

Effects of synbiotic supplementation on energy and macronutrients homeostasis and muscle wasting of critical care patients: study protocol and a review of previous studies

BACKGROUND

An extreme and persistent dysbiosis occurs among critically ill patients, regardless of the heterogeneity of disease. Dysbiosis in critically ill patients may make them prone to hospital-acquired infections, sepsis, multi-organ failure (MOF), energy homeostasis disturbance, muscle wasting, and cachexia. Modulation of gut microbiota through synbiotics can be considered as a potential treatment for muscle wasting and macronutrient homeostasis disturbances.

METHODS

This is a prospective, single-center, double-blind, parallel randomized controlled trial with the aim to evaluate the effects of synbiotic supplementation on energy and macronutrient homeostasis and muscle wasting in critically ill patients. A total of 40 hemodynamically stable, adult, critically ill patients who receive enteral nutrition via a nasogasteric tube (NGT) in the 24-48 h after admission to critical care will be included in this study. Eligible patients will be randomly assigned to receive Lactocare (ZistTakhmir) capsules 500 mg every 12 h or a placebo capsule, which contains only the sterile maize starch and is similar to synbiotic capsules for 14 days. The synbiotic and placebo capsules will be given through the nasogastric tube, separately from gavage, after feeding.

DISCUSSION

Gut microbiota modulation through synbiotics is proposed to improve clinical prognosis and reduce infectious complications, ventilator dependency, and length of ICU stay by improving energy and macronutrient homeostasis and reducing muscle protein catabolism.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials, IRCT20190227042857N1. Registered on 17 March 2019.

A Metabolic Perspective on Reward Abnormalities in Anorexia Nervosa

Anorexia nervosa (AN) is the psychiatric disorder with the highest mortality rate; however, the mechanisms responsible for its pathogenesis remain largely unknown. Large-scale genome-wide association studies (GWAS) have identified genetic loci associated with metabolic features in AN. Metabolic alterations that occur in AN have been mostly considered as consequences of the chronic undernutrition state but until recently have not been linked to the etiology of the disorder. We review the molecular basis of AN based on human genetics, with an emphasis on the molecular components controlling energy homeostasis, highlight the main metabolic and endocrine alterations occurring in AN, and decipher the possible connection between metabolic factors and abnormalities of reward processes that are central in AN.

The Effect of 6 and 12 months Duodenal-Jejunal Bypass Liner Treatment on Obesity and Type 2 Diabetes: a Crossover Cohort Study

OBJECTIVE

The aim of this research was to study the duodenal-jejunal bypass liner (DJBL) treatment for obesity and type 2 diabetes mellitus (T2DM) in patients after dietary treatment in a cross-over design.

BACKGROUND

DJBL treatment has been proven effective for treatment of obesity and T2DM. However, data on safety and efficacy of a 12-month DJBL treatment is limited.

METHODS

In 2014, our research group reported on a multicenter randomized clinical trial. Patients were randomized to DJBL or dietary treatment (control group). Twenty-eight patients crossed over after their dietary treatment and received up to 12 months of DJBL treatment. Patient visits were conducted at baseline, during DJBL treatment (1 week, 1-6, 9, 12 months) and 6 months after removal of the liner. Patients underwent a standard physical examination, blood sampling, assessment of adverse events, nutritional and diabetes counseling, and a standardized meal tolerance test.

RESULTS

Of the 28 patients included in this study, 24 patients completed 6 months of treatment. Eighteen patients were extended to 12 months of DJBL treatment; 13 patients completed this treatment period. After 6 months of DJBL treatment, a significant increase in excess weight loss (EWL) and decrease in weight, BMI, HbA1c, fasting glucose, cholesterol, HDL and LDL improved significantly. After 12 months of DJBL treatment, these parameters stabilized.

CONCLUSIONS

The DJBL is an effective, minimally invasive treatment option. Even after successful treatment with dietary restrictions, the DJBL is still capable of significantly reducing weight and improving cardiovascular and type 2 diabetes mellitus parameters in obese patients.

Food Cues and Obesity: Overpowering Hormones and Energy Balance Regulation

PURPOSE OF REVIEW

In the modern obesogenic environment, food cues play a crucial role in the development of obesity by disrupting hormone and energy balance mechanisms. Thus, it is critical to understand the neurobiology of feeding behaviors and obesity in the context of ubiquitous food cues. The current paper reviews the physiology of feeding, hormonal regulation of energy balance, and food cue responses and discusses their contributions to obesity.

RECENT FINDINGS

Food cues have strong impact on human physiology. Obese individuals have altered food cue-elicited responses in the brain and periphery, overpowering hormone and energy balance regulation. Disrupted homeostasis during food cue exposure leads to continued food intake, unsuccessful weight management, and poor treatment outcomes, which further contributes to obesity epidemic. Findings from the review emphasize the crucial role of food cues in obesity epidemic, which necessitates multidimensional approaches to the prevention and treatment of obesity, including psychosocial interventions to reduce food cue reactivity, along with conventional treatment.

Drosophila mushroom bodies integrate hunger and satiety signals to control innate food-seeking behavior

The fruit fly can evaluate its energy state and decide whether to pursue food-related cues. Here, we reveal that the mushroom body (MB) integrates hunger and satiety signals to control food-seeking behavior. We have discovered five pathways in the MB essential for hungry flies to locate and approach food. Blocking the MB-intrinsic Kenyon cells (KCs) and the MB output neurons (MBONs) in these pathways impairs food-seeking behavior. Starvation bi-directionally modulates MBON responses to a food odor, suggesting that hunger and satiety controls occur at the KC-to-MBON synapses. These controls are mediated by six types of dopaminergic neurons (DANs). By manipulating these DANs, we could inhibit food-seeking behavior in hungry flies or promote food seeking in fed flies. Finally, we show that the DANs potentially receive multiple inputs of hunger and satiety signals. This work demonstrates an information-rich central circuit in the fly brain that controls hunger-driven food-seeking behavior.

Gut Microbiota and the Gut-Brain Axis: New Insights in the Pathophysiology of Metabolic Syndrome

OBJECTIVE

Emerging preclinical evidence has shown that the bidirectional signaling between the gastrointestinal (GI) tract and the brain, the so-called gut-brain axis, plays an important role in both host metabolism and behavior. In this review, we discuss the potential mechanisms of the brain-gut axis in relation to the pathophysiology of metabolic syndrome.

METHODS

A selective literature review was conducted to evaluate GI and brain interactions.

RESULTS

Evidence suggests reduced microbial diversity in obesity and metabolic dysregulation. However, findings of microbiota composition in obese individuals are inconsistent, and the investigation of causality between gut microbiota and energy homeostasis is complex because multiple variables contribute to the gut microbiota composition. The microbial metabolites short chain fatty acids are found to exert numerous physiologic effects, including energy homeostasis through the regulation of GI hormones such as cholecystokinin, glucagon-like peptide 1, peptide tyrosine-tyrosine, and leptin. Preclinical studies show that modifying rodents' microbiota through fecal transplantation results in alterations of these GI hormones and subsequently an altered metabolism and behavior. However, whether and to what extent preclinical findings translate to human metabolism is unclear.

CONCLUSIONS

One of the major limitations and challenges in this field of research is interindividual variability of the microbiome. Future research needs to combine recent insights gained into tracking the dynamics of the microbiome as well as the metabolic responses. Furthermore, advanced mapping of the human microbiome is required to investigate the metabolic implications of the gut-brain axis to develop targeted interventions for obesity and metabolic syndrome.

Gut-Brain Glucose Signaling in Energy Homeostasis

Intestinal gluconeogenesis is a recently identified function influencing energy homeostasis. Intestinal gluconeogenesis induced by specific nutrients releases glucose, which is sensed by the nervous system surrounding the portal vein. This initiates a signal positively influencing parameters involved in glucose control and energy management controlled by the brain. This knowledge has extended our vision of the gut-brain axis, classically ascribed to gastrointestinal hormones. Our work raises several questions relating to the conditions under which intestinal gluconeogenesis proceeds and may provide its metabolic benefits. It also leads to questions on the advantage conferred by its conservation through a process of natural selection.

Central action of xenin affects the expression of lipid metabolism-related genes and proteins in mouse white adipose tissue

Xenin is a gastrointestinal hormone that reduces food intake when administered centrally and it has been hypothesized that central action of xenin participates in the regulation of whole-body metabolism. The present study was performed to address this hypothesis by investigating the central effect of xenin on the expression of genes and proteins that are involved in the regulation of lipid metabolism in white adipose tissue (WAT). Male obese ob/ob mice received intracerebroventricular (i.c.v.) injections of xenin (5μg) twice 12h apart. Food intake and body weight change during a 24-h period after the first injection were measured. Epididymal WAT was collected at the end of the 24-h treatment period and levels of lipid metabolism-related genes and proteins were measured. Xenin treatment caused significant reductions in food intake and body weight compared to control vehicle treatment. Levels of fatty acid synthase (FASN) protein were significantly reduced by xenin treatment, while levels of adipose triglyceride lipase (Atgl) and beta-3 adrenergic receptor (Adrb3) mRNA and phosphorylated hormone sensitive lipase (Ser⁶⁶⁰-pHSL and Ser⁵⁶³-pHSL) were significantly increased by xenin treatment. These findings suggest that central action of xenin causes alterations in lipid metabolism in adipose tissue toward reduced lipogenesis and increased lipolysis, possibly contributing to xenin-induced body weight reduction. Thus, enhancing central action of xenin and its downstream targets may be possible targets for the treatment of obesity by reducing the amount of stored fat in adipose tissue.

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

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

Gut Microbiota in Obesity and Undernutrition

Malnutrition is the result of an inadequate balance between energy intake and energy expenditure that ultimately leads to either obesity or undernutrition. Several factors are associated with the onset and preservation of malnutrition. One of these factors is the gut microbiota, which has been recognized as an important pathophysiologic factor in the development and sustainment of malnutrition. However, to our knowledge, the extent to which the microbiota influences malnutrition has yet to be elucidated. In this review, we summarize the mechanisms via which the gut microbiota may influence energy homeostasis in relation to malnutrition. In addition, we discuss potential therapeutic modalities to ameliorate obesity or undernutrition.

The Endocannabinoid System and Its Role in Regulating the Intrinsic Neural Circuitry of the Gastrointestinal Tract

Endocannabinoids are important neuromodulators in the central nervous system. They regulate central transmission through pre- and postsynaptic actions on neurons and indirectly through effects on glial cells. Cannabinoids (CBs) also regulate neurotransmission in the enteric nervous system (ENS) of the gastrointestinal (GI) tract. The ENS consists of intrinsic primary afferent neurons, interneurons, and motor neurons arranged in two ganglionated plexuses which control all the functions of the gut. Increasing evidence suggests that endocannabinoids are potent neuromodulators in the ENS. In this review, we will highlight key observations on the localization of CB receptors and molecules involved in the synthesis and degradation of endocannabinoids in the ENS. We will discuss endocannabinoid signaling mechanisms, endocannabinoid tone and concepts of CB receptor metaplasticity in the ENS. We will also touch on some examples of enteric neural signaling in relation neuromuscular, secretomotor, and enteroendocrine transmission in the ENS. Finally, we will briefly discuss some key future directions.