Novel role of GLP-1 receptor signaling in energy expenditure during chronic high fat diet feeding in rats

Cotadutide (GLP-1/Glucagon dual receptor agonist) modulates hypothalamic orexigenic and anorexigenic neuropeptides in obese mice

The hypothalamic neuropeptides linked to appetite and satiety were investigated in obese mice treated with cotadutide (a dual receptor agonist of glucagon-like peptide 1 (GLP-1R)/Glucagon (GCGR)). Twelve-week-old male C57BL/6 mice were fed a control diet (C group, n = 20) or a high-fat diet (HF group, n = 20) for ten weeks. Each group was further divided, adding cotadutide treatment and forming groups C, CC, HF, and HFC for four additional weeks. The hypothalamic arcuate neurons were labeled by immunofluorescence, and protein expressions (Western blotting) for neuropeptide Y (NPY), proopiomelanocortin (POMC), agouti-related protein (AgRP), and cocaine- and amphetamine-regulated transcript (CART). Cotadutide enhanced POMC and CART neuropeptides and depressed NPY and AGRP neuropeptides. In addition, gene expressions (RT-qPCR) determined that Lepr (leptin receptor) and Calcr (calcitonin receptor) were diminished in HF compared to C but enhanced in CC compared to C and HFC compared to HF. Besides, Socs3 (suppressor of cytokine signaling 3) was decreased in HFC compared to HF, while Sst (somatostatin) was higher in HFC compared to HF; Tac1 (tachykinin 1) and Mc4r (melanocortin-4-receptor) were lower in HF compared to C but increased in HFC compared to HF. Also, Glp1r and Gcgr were higher in HFC compared to HF. In conclusion, the findings are compelling, demonstrating the effects of cotadutide on hypothalamic neuropeptides and hormone receptors of obese mice. Cotadutide modulates energy balance through the gut-brain axis and its associated signaling pathways. The study provides insights into the mechanisms underlying cotadutide's anti-obesity effects and its possible implications for obesity treatment.

Plant-based meat analogues enhance the gastrointestinal motility function and appetite of mice by specific volatile compounds and peptides

Eating behavior is critical for maintaining energy homeostasis. Previous studies have found that plant-based meat analogues increased diet intake in mice compared with animal meat under a free feeding mode, however the reasons were unclear. To explore the underlying mechanisms of plant-based meat analogues increasing diet intake, mice were fed animal or plant-based pork and beef analogue diets, respectively. Biochemical and histological analyses were performed to evaluate appetite-regulating hormones and gastrointestinal motility function. Peptiomics and GC-IMS were applied to identify key substances. We found that the intake of plant-based meat analogues significantly enhanced the gastrointestinal motility function of mice. The long-term intake (68 days) of plant-based meat analogues significantly increased the muscle layer thickness of the duodenum and jejunum of mice; the activity of gastrointestinal cells of Cajal were also promoted by upregulating the expression of c-kit related signals as compared to animal meat; plant-based meat analogues intake markedly enhanced the signal intensity of the intestinal neurotransmitter 5-hydroxytryptamine (5-HT) by upregulating the expression of 5-HT synthase and receptors but downregulating its transporter and catabolic enzyme in the intestine. Moreover, plant-based meat analogues intake significantly increased levels of appetite-stimulating factors in the peripheral or hypothalamus but reduced levels of appetite-suppressing factors compared with animal meat. Specific volatile compounds were significantly associated with appetite regulating factors. Among them, 7 substances such as linalool have a potential promoting effect on food intake. Besides, different digestive peptides in gastrointestinal tract may affect eating behavior mainly through the neuroactive ligand-receptor interaction pathway, exerting hormone-like effects or influencing endocrine cell secretion. These findings preliminarily clarified the mechanism of plant-based meat analogues promoting diet intake and provided a theoretical basis for a reasonable diet.

The glucagon-like peptide-1 (GLP-1) analogue semaglutide reduces alcohol drinking and modulates central GABA neurotransmission

Growing evidence indicates that the glucagon-like peptide-1 (GLP-1) system is involved in the neurobiology of addictive behaviors, and GLP-1 analogues may be used for the treatment of alcohol use disorder (AUD). Here, we examined the effects of semaglutide, a long-acting GLP-1 analogue, on biobehavioral correlates of alcohol use in rodents. A drinking-in-the-dark procedure was used to test the effects of semaglutide on binge-like drinking in male and female mice. We also tested the effects of semaglutide on binge-like and dependence-induced alcohol drinking in male and female rats, as well as acute effects of semaglutide on spontaneous inhibitory postsynaptic currents (sIPSCs) from central amygdala (CeA) and infralimbic cortex (ILC) neurons. Semaglutide dose-dependently reduced binge-like alcohol drinking in mice; a similar effect was observed on the intake of other caloric/noncaloric solutions. Semaglutide also reduced binge-like and dependence-induced alcohol drinking in rats. Semaglutide increased sIPSC frequency in CeA and ILC neurons from alcohol-naive rats, suggesting enhanced GABA release, but had no overall effect on GABA transmission in alcohol-dependent rats. In conclusion, the GLP-1 analogue semaglutide decreased alcohol intake across different drinking models and species and modulated central GABA neurotransmission, providing support for clinical testing of semaglutide as a potentially novel pharmacotherapy for AUD.

Role of brain-gut-muscle axis in human health and energy homeostasis

The interrelationship between brain, gut and skeletal muscle plays a key role in energy homeostasis of the body, and is becoming a hot topic of research. Intestinal microbial metabolites, such as short-chain fatty acids (SCFAs), bile acids (BAs) and tryptophan metabolites, communicate with the central nervous system (CNS) by binding to their receptors. In fact, there is a cross-talk between the CNS and the gut. The CNS, under the stimulation of pressure, will also affect the stability of the intestinal system, including the local intestinal transport, secretion and permeability of the intestinal system. After the gastrointestinal tract collects information about food absorption, it sends signals to the central system through vagus nerve and other channels to stimulate the secretion of brain-gut peptide and produce feeding behavior, which is also an important part of maintaining energy homeostasis. Skeletal muscle has receptors for SCFAs and BAs. Therefore, intestinal microbiota can participate in skeletal muscle energy metabolism and muscle fiber conversion through their metabolites. Skeletal muscles can also communicate with the gut system during exercise. Under the stimulation of exercise, myokines secreted by skeletal muscle causes the secretion of intestinal hormones, and these hormones can act on the central system and affect food intake. The idea of the brain-gut-muscle axis is gradually being confirmed, and at present it is important for regulating energy homeostasis, which also seems to be relevant to human health. This article focuses on the interaction of intestinal microbiota, central nervous, skeletal muscle energy metabolism, and feeding behavior regulation, which will provide new insight into the diagnostic and treatment strategies for obesity, diabetes, and other metabolic diseases.

Vagal afferent cholecystokinin receptor activation is required for glucagon-like peptide-1-induced satiation

Peripheral glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK) are secreted from enteroendocrine cells, and their plasma concentrations increase in response to eating. While the satiating effect of gut-derived CCK on food-intake control is well documented, the effect of peripheral GLP-1 is less clear. There is evidence that native GLP-1 can inhibit food intake only in the fed state but not in the fasting state. We therefore hypothesized that other gut peptides released during a meal might influence the subsequent effect of endogenous GLP-1 and investigated whether CCK could do so. We found that intraperitoneal injection of CCK in food-restricted mice inhibited food intake during the first 30-minute segment of a 1-hour session of ad libitum chow intake and that mice compensated by increasing their intake during the second half of the session. Importantly, this compensatory behaviour was abolished by an intraperitoneal injection of GLP-1 administered following an intraperitoneal injection of CCK and prior to the 1-hour session. In vivo activation of the free fatty acid 1 (FFA1) receptor with orally administered TAK875 increased plasma CCK concentration and, consistent with the effect of exogenous CCK, we found that prior oral administration of TAK875 increased the eating inhibitory effect of peripherally administered GLP-1. To examine the role of the vagus nerve in this effect, we utilized a saporin-based lesioning procedure to selectively ablate the CCK receptor-expressing gastrointestinal vagal afferent neurones (VANs). We found that the combined anorectic effect of TAK875 and GLP-1 was significantly attenuated in the absence of CCK receptor expressing VANs. Taken together, our results indicate that endogenous CCK interacts with GLP-1 to promote satiation and that activation of the FFA1 receptor can initiate this interaction by stimulating the release of CCK.

Bacillus amyloliquefaciens ameliorates high-carbohydrate diet-induced metabolic phenotypes by restoration of intestinal acetate-producing bacteria in Nile Tilapia

Poor utilisation efficiency of carbohydrate always leads to metabolic phenotypes in fish. The intestinal microbiota plays an important role in carbohydrate degradation. Whether the intestinal bacteria could alleviate high-carbohydrate diet (HCD)-induced metabolic phenotypes in fish remains unknown. Here, a strain affiliated to Bacillus amyloliquefaciens was isolated from the intestine of Nile tilapia. A basal diet (CON), HCD or HCD supplemented with B. amy SS1 (HCB) was used to feed fish for 10 weeks. The beneficial effects of B. amy SS1 on weight gain and protein accumulation were observed. Fasting glucose and lipid deposition were decreased in the HCB group compared with the HCD group. High-throughput sequencing showed that the abundance of acetate-producing bacteria was increased in the HCB group relative to the HCD group. Gas chromatographic analysis indicated that the concentration of intestinal acetate was increased dramatically in the HCB group compared with that in the HCD group. Glucagon-like peptide-1 was also increased in the intestine and serum of the HCB group. Thus, fish were fed with HCD, HCD supplemented with sodium acetate at 900 mg/kg (HLA), 1800 mg/kg (HMA) or 3600 mg/kg (HHA) diet for 8 weeks, and the HMA and HHA groups mirrored the effects of B. amy SS1. This study revealed that B. amy SS1 could alleviate the metabolic phenotypes caused by HCD by enriching acetate-producing bacteria in fish intestines. Regulating the intestinal microbiota and their metabolites might represent a powerful strategy for fish nutrition modulation and health maintenance in future.

Incretin Hormones in Obesity and Related Cardiometabolic Disorders: The Clinical Perspective

The prevalence of obesity continues to grow rapidly worldwide, posing many public health challenges of the 21st century. Obese subjects are at major risk for serious diet-related noncommunicable diseases, including type 2 diabetes mellitus, cardiovascular disease, and non-alcoholic fatty liver disease. Understanding the mechanisms underlying obesity pathogenesis is needed for the development of effective treatment strategies. Dysregulation of incretin secretion and actions has been observed in obesity and related metabolic disorders; therefore, incretin-based therapies have been developed to provide new therapeutic options. Incretin mimetics present glucose-lowering properties, together with a reduction of appetite and food intake, resulting in weight loss. In this review, we describe the physiology of two known incretins—glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and their role in obesity and related cardiometabolic disorders. We also focus on the available and incoming incretin-based medications that can be used in the treatment of the above-mentioned conditions.

Liraglutide Activates Glucagon-Like Peptide 1 Receptor to Attenuate Hyperglycemia through Endogenous Beta-Endorphin in Diabetic Rats

Liraglutide, an acylated analog of glucagon-like peptide 1 (GLP-1), could improve glycemic control in diabetes. Moreover, endogenous opioid peptides play a role in blood sugar regulation. Since GLP-1 receptors are also expressed in extra-pancreatic tissues, this study investigates the effect of liraglutide on endogenous opioid secretion in type 1-like diabetes. The endogenous opioid level was determined by enzyme-linked immunosorbent assay. The direct effect of liraglutide on endogenous opioid secretion was determined in the isolated adrenal medulla. Acute treatment with liraglutide dose-dependently attenuated hyperglycemia, and increased the plasma opioid neuropeptide, beta-endorphin (BER) levels in diabetic rats. These effects have been blocked by GLP-1 receptor antagonist, naloxone. Additionally, the effects of liraglutide were markedly reduced in adrenalectomized diabetic rats. In the isolated adrenal medulla, liraglutide induced BER secretion and increased the BER mRNA levels. Subcellular effects of liraglutide on the adrenal gland were further identified to mediate through the exchange proteins directly activated by cAMP, mainly using the pharmacological blockade. After repeatedly administering liraglutide, metabolic changes in diabetic rats were investigated, and genes associated with gluconeogenesis in the liver were downregulated. Naloxone pretreatment inhibited these effects of liraglutide, indicating the involvement of endogenous opioids. The present study indicated that liraglutide had an acute effect of reducing hyperglycemia by regulating endogenous opioid BER and modifying the glucose homeostasis.

Relationship between inflammation and metabolic regulation of energy expenditure by GLP-1 in critically ill children

BACKGROUND & AIMS

Critical illness is associated with derangement in the metabolic and inflammatory response. Previous investigators have highlighted the cross-link between feeding, inflammation and gut homeostasis. Glucagon like peptide-1 (GLP-1) is a gut derived hormone that plays an important role in the modulation of energy metabolism through appetite regulation and promotion of gastric motility. Growing evidence suggests that GLP-1 might influence energy expenditure. The aim of this study was to assess the relationship between inflammatory activation and metabolic regulation of energy expenditure by assessing cytokine release, levels of GLP-1 and energy expenditure in a cohort of critically ill children.

METHOD

This is a prospective study conducted in critically ill children. A blood sample was collected from each child during the first few days of critical illness, for the analysis of serum inflammatory cytokines (TNF-α, IL-10, IL-6 and IL-1β) and GLP-1 in 42 children. Indirect calorimetry (IC) measurements were performed concurrently in a subset of 21 children. The metabolic index was determined using the ratio of Measured Resting Energy Expenditure (MREE)/Predicted Resting Energy Expenditure (PREE) based on the Schofield equation. Correlation analysis was performed, followed by a stepwise linear regression analysis to assess factors affecting GLP-1 and the metabolic index.

RESULTS

A total of 42 children (0-14 years) were included in this study. The regression analysis indicated that CRP, TNF-α, IL-6 and IL-1β statistically influenced GLP-1 concentrations (p < 0.01). Where IC measurements were performed (N = 21), GLP-1 showed a statistically significant association with the metabolic index (p < 0.01). No evidence of statistical association was recorded between the inflammatory mediators and the metabolic index. Overall the results showed that circulating GLP-1 was increased in response to inflammatory stimuli in critically ill children. GLP-1 contributed to the changes observed in MREE induced by critical illness in our cohort.

CONCLUSION

Energy expenditure is extremely variable in critically ill children, our study suggests that changes in GLP-1 might contribute to a significant amount of this variation. If confirmed in larger studies, GLP-1 could be used as a correction factor for REE predictive equations in critically ill children.

Glucose-Dependent Insulinotropic Polypeptide Receptor-Expressing Cells in the Hypothalamus Regulate Food Intake

Ambiguity regarding the role of glucose-dependent insulinotropic polypeptide (GIP) in obesity arises from conflicting reports asserting that both GIP receptor (GIPR) agonism and antagonism are effective strategies for inhibiting weight gain. To enable identification and manipulation of Gipr-expressing (Gipr) cells, we created Gipr-Cre knockin mice. As GIPR-agonists have recently been reported to suppress food intake, we aimed to identify central mediators of this effect. Gipr cells were identified in the arcuate, dorsomedial, and paraventricular nuclei of the hypothalamus, as confirmed by RNAscope in mouse and human. Single-cell RNA-seq identified clusters of hypothalamic Gipr cells exhibiting transcriptomic signatures for vascular, glial, and neuronal cells, the latter expressing somatostatin but little pro-opiomelanocortin or agouti-related peptide. Activation of G_q-DREADDs in hypothalamic Gipr cells suppressed food intake in vivo, which was not obviously additive with concomitant GLP1R activation. These data identify hypothalamic GIPR as a target for the regulation of energy balance.

Continuous feeding of a combined high-fat and high-sucrose diet, rather than an individual high-fat or high-sucrose diet, rapidly enhances the glucagon-like peptide-1 secretory response to meal ingestion in diet-induced obese rats

OBJECTIVES

Glucagon-like peptide-1 (GLP-1) is secreted by enteroendocrine L-cells in response to nutrient ingestion. To date, GLP-1 secretion in diet-induced obesity is not well characterized. We aimed to examine GLP-1 secretion in response to meal ingestion during the progression of diet-induced obesity and determinewhether a combined high-fat and high-sucrose (HFS) diet, an individual high-fat (HiFat), or a high-sucrose (HiSuc) diet affect adaptive changes in the postprandial GLP-1 response.

METHODS

Rats were fed a control, HiFat diet (30% weight), HiSuc diet (40% weight), or HFS (30% fat and 40% sucrose) diet for 5 wk. Meal tolerance tests were conducted to determine postprandial glucose, insulin, and GLP-1 responses to standard (control) diet ingestion every 2 wk.

RESULTS

After 5 wk, body weight gain of the HiFat (232.3 ± 7.8 g; P = 0.021) and HFS groups (228.0 ± 7.8; P = 0.039), but not the HiSuc group (220.3 ± 7.9; P = 0.244), were significantly higher than that of the control group (200.7 ± 5.4 g). In meal tolerance tests after 2 wk, GLP-1 concentration was significantly elevated in the HFS group only (17.2 ± 2.6 pM; P < 0.001) in response to meal ingestions, but the HiFat group (16.6 ± 3.7 pM; P = 0.156) had a similar response as the HFS group. After 4 wk, GLP-1 concentrations were similarly elevated at 15min in the HFS (14.1 ± 4.4; P = 0.010), HiFat (13.2 ± 2.0; P < 0.001), and HiSuc (13.0 ± 3.3; P = 0.016) groups, but the HFS (9.8 ± 1.0; P = 0.019) and HiFat (8.3 ± 1.5; P = 0.010) groups also had significant elevation at 30min.

CONCLUSIONS

These results demonstrate that the continuous ingestion of excessive fat and sucrose rapidly enhances the GLP-1 secretory response to luminal nutrients, and the HiFat diet may have a potent effect compared with the HiSuc diet on GLP-1 secretory responses. The increment of postprandial GLP-1 and insulinsecretion may have a role in normalizing postprandial glycaemia and slowing the establishment of glucose intolerance.

Oleoylethanolamide modulates glucagon-like peptide-1 receptor agonist signaling and enhances exendin-4-mediated weight loss in obese mice

Long-acting glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) agonists (GLP-1RA), such as exendin-4 (Ex4), promote weight loss. On the basis of a newly discovered interaction between GLP-1 and oleoylethanolamide (OEA), we tested whether OEA enhances GLP-1RA-mediated anorectic signaling and weight loss. We analyzed the effect of GLP-1+OEA and Ex4+OEA on canonical GLP-1R signaling and other proteins/pathways that contribute to the hypophagic action of GLP-1RA (AMPK, Akt, mTOR, and glycolysis). We demonstrate that OEA enhances canonical GLP-1R signaling when combined with GLP-1 but not with Ex4. GLP-1 and Ex4 promote phosphorylation of mTOR pathway components, but OEA does not enhance this effect. OEA synergistically enhanced GLP-1- and Ex4-stimulated glycolysis but did not augment the hypophagic action of GLP-1 or Ex4 in lean or diet-induced obese (DIO) mice. However, the combination of Ex4+OEA promoted greater weight loss in DIO mice than Ex4 or OEA alone during a 7-day treatment. This was due in part to transient hypophagia and increased energy expenditure, phenotypes also observed in Ex4-treated DIO mice. Thus, OEA augments specific GLP-1RA-stimulated signaling but appears to work in parallel with Ex4 to promote weight loss in DIO mice. Elucidating cooperative mechanisms underlying Ex4+OEA-mediated weight loss could, therefore, be leveraged toward more effective obesity therapies.