The effect of glucagon-like peptide 1 and glucagon-like peptide 1 receptor agonists on energy expenditure: A systematic review and meta-analysis

Diet induced thermogenesis, older and newer data with emphasis on obesity and diabetes mellitus - A narrative review

Obesity is a major public health problem with a prevalence increasing at an alarming rate worldwide. There is an urgent need for efficient approaches to weight management. Diet induced thermogenesis (DIT) is the process by which the body increases its energy expenditure in response to a meal. It is estimated to account for approximately 10 % of total energy expenditure and is considered a potentially modifiable component of energy expenditure. The palatability of food, meal's composition in macronutrients, the circadian rhythm and sleep, as well as individual's characteristics such as age, the presence of obesity or diabetes mellitus, and the proportion of physical activity are the main factors that affect DIT. However, studies examining DIT are mostly characterized by small sample size and the methodology varies considerably between studies. It seems that even today there is a lot of contradiction between the relative studies. Inspite of that, future research might lead to the modification of DIT in order to achieve some weight loss in obese people.

Pharmacological modulation of adaptive thermogenesis: new clues for obesity management?

BACKGROUND

Adaptive thermogenesis represents the main mechanism through which the body generates heat in response to external stimuli, a phenomenon that includes shivering and non-shivering thermogenesis. The non-shivering thermogenesis is mainly exploited by adipose tissue characterized by a brown aspect, which specializes in energy dissipation. A decreased amount of brown adipose tissue has been observed in ageing and chronic illnesses such as obesity, a worldwide health problem characterized by dysfunctional adipose tissue expansion and associated cardiometabolic complications. In the last decades, the discovery of a trans-differentiation mechanism ("browning") within white adipose tissue depots, leading to the generation of brown-like cells, allowed to explore new natural and synthetic compounds able to favour this process and thus enhance thermogenesis with the aim of counteracting obesity. Based on recent findings, brown adipose tissue-activating agents could represent another option in addition to appetite inhibitors and inhibitors of nutrient absorption for obesity treatment.

PURPOSE

This review investigates the main molecules involved in the physiological (e.g. incretin hormones) and pharmacological (e.g. β3-adrenergic receptors agonists, thyroid receptor agonists, farnesoid X receptor agonists, glucagon-like peptide-1, and glucagon receptor agonists) modulation of adaptive thermogenesis and the signalling mechanisms involved.

The association between gut hormones and diet-induced metabolic flexibility in metabolically healthy adults

OBJECTIVE

This study investigated whether interindividual variance in diet-induced metabolic flexibility is explained by differences in gut hormone concentrations.

METHODS

A total of 69 healthy volunteers with normal glucose regulation underwent 24-hour assessments of respiratory quotient (RQ) in a whole-room indirect calorimeter during eucaloric feeding (EBL; 50% carbohydrate, 30% fat) and then, in a crossover design, during 24-hour fasting and three normal-protein (20%) overfeeding diets (200% energy requirements). Metabolic flexibility was defined as the change in 24-hour RQ from EBL during standard (50% carbohydrate), high-fat (60%), and high-carbohydrate (75%) overfeeding diets. Plasma concentrations of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) after an overnight fast were measured prior to and after each diet.

RESULTS

Compared with EBL, on average, 24-hour RQ decreased by ~4% during high-fat overfeeding, whereas it increased by ~4% during standard overfeeding and by ~9% during high-carbohydrate overfeeding. During high-carbohydrate overfeeding, but not during any other overfeeding diet or fasting, increased GLP-1 concentration was associated with increased RQ (r = 0.44, p < 0.001), higher/lower carbohydrate/lipid oxidation rates (r = 0.34 and r = -0.51, both p < 0.01), respectively, and increased plasma insulin concentration (r = 0.38, p = 0.02).

CONCLUSIONS

Increased GLP-1 concentration following high-carbohydrate overfeeding associated with a greater shift to carbohydrate oxidation, suggesting that GLP-1 may be implicated in diet-induced metabolic flexibility to carbohydrate overload.

Glucose-lowering drugs with cardiovascular benefits as modifiers of critical elements of the human life history

The life history theory assumes that all organisms are under selective pressure to harvest external resources and allocate them to maximise fitness: only organisms making the best use of energy obtain the greatest fitness benefits. The trade-off of energy spans four functions: maintenance, growth, reproduction, and defence against pathogens. The innovative antihyperglycaemic agents glucagon-like peptide 1 (GLP-1) receptor agonists and sodium-glucose cotransporter 2 (SGLT2) inhibitors decrease bodyweight and have the potential to counter low-grade inflammation. These key activities could rewire two components of the life history theory operative in adulthood-ie, maintenance and defence. In this Personal View, we postulate that the benefits of these medications on the cardiovascular system, beyond their glucose-lowering effects, could be mediated by the reduction of the maintenance cost driven by obesity and efforts spent on blunting low-grade inflammation.

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.

The Longer-Term Benefits and Harms of Glucagon-Like Peptide-1 Receptor Agonists: a Systematic Review and Meta-Analysis

BACKGROUND

Previous meta-analyses of the benefits and harms of glucagon-like peptide-1 receptor agonists (GLP1RAs) have been limited to specific outcomes and comparisons and often included short-term results. We aimed to estimate the longer-term effects of GLP1RAs on cardiovascular risk factors, microvascular and macrovascular complications, mortality, and adverse events in patients with type 2 diabetes, compared to placebo and other anti-hyperglycemic medications.

METHODS

We searched PubMed, Scopus, and clinicaltrials.gov (inception-July 2019) for randomized controlled trials ≥ 52 weeks' duration that compared a GLP1RA to placebo or other anti-hyperglycemic medication and included at least one outcome of interest. Outcomes included cardiovascular risk factors, microvascular and macrovascular complications, all-cause mortality, and treatment-related adverse events. We performed random effects meta-analyses to give summary estimates using weighted mean differences (MD) and pooled relative risks (RR). Risk of bias was assessed using the Cochrane Collaboration risk of bias in randomized trials tool. Quality of evidence was summarized using the Grading of Recommendations, Assessment, Development, and Evaluation approach. The study was registered a priori with PROSPERO (CRD42018090506).

RESULTS

Forty-five trials with a mean duration of 1.7 years comprising 71,517 patients were included. Compared to placebo, GLP1RAs reduced cardiovascular risk factors, microvascular complications (including renal events, RR 0.85, 0.80-0.90), macrovascular complications (including stroke, RR 0.86, 0.78-0.95), and mortality (RR 0.89, 0.84-0.94). Compared to other anti-hyperglycemic medications, GLP1RAs only reduced cardiovascular risk factors. Increased gastrointestinal events causing treatment discontinuation were observed in both comparisons.

DISCUSSION

GLP1RAs reduced cardiovascular risk factors and increased gastrointestinal events compared to placebo and other anti-hyperglycemic medications. GLP1RAs also reduced MACE, stroke, renal events, and mortality in comparisons with placebo; however, analyses were inconclusive for comparisons with other anti-hyperglycemic medications. Given the high costs of GLP1RAs, the lack of long-term evidence comparing GLP1RAs to other anti-hyperglycemic medications has significant policy and clinical practice implications.

Novel equation for estimating resting energy expenditure in patients with chronic kidney disease

BACKGROUND

In chronic kidney disease (CKD), determining energy expenditure is the precondition for recommending energy intake in nutrition management.

OBJECTIVES

We aimed to develop and validate a resting energy expenditure (REE) equation for patients with CKD.

METHODS

This cross-sectional study enrolled 300 patients with CKD (stages 3-5) according to inclusion and exclusion criteria. Stepwise linear regression analysis was used to derive a new REE equation (eREE-CKD) according to actual REE (aREE) measured using indirect calorimetry in the development dataset. The eREE-CKD value was then validated with aREE in the validation dataset and compared with values from existing equations obtained in general populations, namely, the Harris-Benedict, Mifflin, WHO, and Schofield equations in terms of bias, precision, and accuracy.

RESULTS

The eREE-CKD equation: eREE-CKD (kcal) = (1 if male; 0 if female) × 106.0 - [1 if diabetes mellitus (DM); 0 if non-DM] × 51.6 - 4.7 × age (y) + 13.1 × weight (kg) + 645.5 (R2 = 0.779).The bias, precision, and accuracy (percentage of estimates that differed >20% from the measured REE) of the eREE-CKD equation were -0.4 (IQR: -29.8, 23.8) kcal, 98.4 (IQR: 79.5, 116.6) kcal, and 5.4%, respectively with indirect calorimetry as the reference method. Both bias and precision of the eREE-CKD were significantly better than the Harris-Benedict, WHO, and Schofield equations (P < 0.001) and similar to the Mifflin equation (P = 0.125 for bias and 0.268 for precision). Accuracy of the eREE-CKD was significantly better than the Harris-Benedict, WHO, Mifflin, and Schofield equations (P < 0.001). Bias, precision, and accuracy of the eREE-CKD equation were consistent when applied to subgroups categorized according to high-sensitivity C-reactive protein concentrations and CKD stages, respectively.

CONCLUSIONS

The eREE-CKD equation using age, sex, weight, and DM data could serve as a reliable tool for estimating REE in patients with CKD. This trial was registered at clinicaltrials.gov as NCT03377413.

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.

Weight Loss Outcomes Among Early High Responders to Exenatide Treatment: A Randomized, Placebo Controlled Study in Overweight and Obese Women

OBJECTIVE

As there is significant heterogeneity in the weight loss response to pharmacotherapy, one of the most important clinical questions in obesity medicine is how to predict an individual's response to pharmacotherapy. The present study examines patterns of weight loss among overweight and obese women who demonstrated early robust response to twice daily exenatide treatment compared to those treated with hypocaloric diet and matched placebo injections.

METHODS

We randomized 182 women (BMI 25-48 kg/m2) to treatment with exenatide alone or matched placebo injections plus hypocaloric diet. In both treatment groups, women who demonstrated ≥ 5% weight loss at 12 weeks were characterized as high responders and those who lost ≥10% of body weight were classified as super responders. Our primary outcome was long-term change in body weight among early high responders to either treatment. An exploratory metabolomic analysis was also performed.

RESULTS

We observed individual variability in weight loss with both exenatide and hypocaloric diet plus placebo injections. There was a trend toward a higher percentage of subjects who achieved ≥ 5% weight loss with exenatide compared to diet (56% of those treated with exenatide, 76% of those treated with diet, p = 0.05) but no significant difference in those who achieved ≥ 10% weight loss (23% of individuals treated with exenatide and 36% of those treated with diet, p = 0.55). In both treatment groups, higher weight loss at 3 months of treatment predicted super responder status (diet p=0.0098, exenatide p=0.0080). Both treatment groups also demonstrated similar peak weight loss during the study period. We observed lower cysteine concentrations in the exenatide responder group (0.81 vs 0.48 p < 0.0001) and a trend toward higher levels of serotonin, aminoisobutyric acid, anandamide, and sarcosine in the exenatide super responder group.

CONCLUSION

In a population of early high responders, longer term weight loss with exenatide treatment is similar to that achieved with a hypocaloric diet.

CLINICAL TRIAL REGISTRATION

www.clinicaltrialsgov, identifier NCT01590433.

Enteroendocrine Hormone Secretion and Metabolic Control: Importance of the Region of the Gut Stimulation

It is now widely appreciated that gastrointestinal function is central to the regulation of metabolic homeostasis. Following meal ingestion, the delivery of nutrients from the stomach into the small intestine (i.e., gastric emptying) is tightly controlled to optimise their subsequent digestion and absorption. The complex interaction of intraluminal nutrients (and other bioactive compounds, such as bile acids) with the small and large intestine induces the release of an array of gastrointestinal hormones from specialised enteroendocrine cells (EECs) distributed in various regions of the gut, which in turn to regulate gastric emptying, appetite and postprandial glucose metabolism. Stimulation of gastrointestinal hormone secretion, therefore, represents a promising strategy for the management of metabolic disorders, particularly obesity and type 2 diabetes mellitus (T2DM). That EECs are distributed distinctively between the proximal and distal gut suggests that the region of the gut exposed to intraluminal stimuli is of major relevance to the secretion profile of gastrointestinal hormones and associated metabolic responses. This review discusses the process of intestinal digestion and absorption and their impacts on the release of gastrointestinal hormones and the regulation of postprandial metabolism, with an emphasis on the differences between the proximal and distal gut, and implications for the management of obesity and T2DM.

Assessing the Continuation of Glucagon-Like Peptide-1 Receptor Agonists When Weight and HBA1C Are Not Reduced

Background: Glucagon-like peptide-1 agonists (GLP-1) reportedly lower HbA1c and promote weight reduction and improve cardiovascular outcomes. The primary objective of this study was to evaluate the use of GLP-1 agents in patients and changes in HbA1c, weight loss, blood pressure, and lipoid profiles. Methods: Patient information was extracted from a regional Veteran Affairs data mart. Patients were included if they had prescriptions for at least 90 days of a GLP-1 between April 1, 2005, and December 1, 2016, and HbA1Cs and weights at both baseline and within first 15 months of therapy. Blood pressure and lipids were also measured. Pearson's correlation and multiple regression analysis were used. Results: Three hundred twenty-two patients met inclusion criteria. Average HbA1c decreased by 0.81% and weight by 4.4 kg. At 1 year, 160 patients had both weight and HbA1c measured, and of those, 92 (58%) patients had HbA1c reduction of at least 0.5% and 94 (59%) patients had <-2 kg change in weight. Fifty-seven (36%) patients met both of those outcomes. Veterans who met both weight and HbA1c outcomes were slightly, but significantly, older than those who did not meet both. No correlation was found between weight and HbA1c change at each quarter (P > 0.05); however, weight change was correlated with systolic blood pressure change (P = 0.03). Multiple regression for meeting weight and HbA1c target outcomes, and changes at quarters 1-3, all correlated to success at 1 year (P < 0.05). Conclusions: Weight change was independent of HbA1c changes in patients receiving GLP-1s for diabetes control. Weight loss was associated with decreases in systolic BP.

Role of endogenous glucagon-like peptide-1 enhanced by vildagliptin in the glycaemic and energy expenditure responses to intraduodenal fat infusion in type 2 diabetes

AIM

To evaluate the effects of the dipeptidyl peptidase-4 (DPP-4) inhibitor vildagliptin on glycaemic and energy expenditure responses during intraduodenal fat infusion, as well as the contribution of endogenous glucagon-like peptide-1 (GLP-1) signalling, in people with type 2 diabetes (T2DM).

METHODS

A total of 15 people with T2DM managed by diet and/or metformin (glycated haemoglobin 49.3 ± 2.1 mmol/mol) were studied on three occasions (two with vildagliptin and one with placebo) in a double-blind, randomized, crossover fashion. On each day, vildagliptin 50 mg or placebo was given orally, followed by intravenous exendin (9-39) 600 pmol/kg/min, on one of the two vildagliptin treatment days, or 0.9% saline over 180 minutes. At between 0 and 120 minutes, a fat emulsion was infused intraduodenally at 2 kcal/min. Energy expenditure, plasma glucose and glucose-regulatory hormones were evaluated.

RESULTS

Intraduodenal fat increased plasma GLP-1 and glucose-dependent insulinotropic polypeptide (GIP), insulin and glucagon, and energy expenditure, and decreased plasma glucose (all P < 0.05). On the two intravenous saline days, plasma glucose and glucagon were lower, plasma intact GLP-1 was higher (all P < 0.05), and energy expenditure tended to be lower after vildagliptin (P = 0.08) than placebo. On the two vildagliptin days, plasma glucose, glucagon and GLP-1 (both total and intact), and energy expenditure were higher during intravenous exendin (9-39) than saline (all P < 0.05).

CONCLUSIONS

In well-controlled T2DM during intraduodenal fat infusion, vildagliptin lowered plasma glucose and glucagon, and tended to decrease energy expenditure, effects that were mediated by endogenous GLP-1.

Mechanisms controlling hormone secretion in human gut and its relevance to metabolism

The homoeostatic regulation of metabolism is highly complex and involves multiple inputs from both the nervous and endocrine systems. The gut is the largest endocrine organ in our body and synthesises and secretes over 20 different hormones from enteroendocrine cells that are dispersed throughout the gut epithelium. These hormones include GLP-1, PYY, GIP, serotonin, and CCK, each of whom play pivotal roles in maintaining energy balance and glucose homeostasis. Some are now the basis of several clinically used glucose-lowering and weight loss therapies. The environment in which these enteroendocrine cells exist is also complex, as they are exposed to numerous physiological inputs including ingested nutrients, circulating factors and metabolites produced from neighbouring gut microbiome. In this review, we examine the diverse means by which gut-derived hormones carry out their metabolic functions through their interactions with different metabolically important organs including the liver, pancreas, adipose tissue and brain. Furthermore, we discuss how nutrients and microbial metabolites affect gut hormone secretion and the mechanisms underlying these interactions.

The functional impact of G protein-coupled receptor 142 (Gpr142) on pancreatic β-cell in rodent

We have recently shown that the G protein-coupled receptor 142 (GPR142) is expressed in both rodent and human pancreatic β-cells. Herein, we investigated the cellular distribution of GPR142 within islets and the effects of selective agonists of GPR142 on glucose-stimulated insulin secretion (GSIS) in the mouse islets and INS-1832/13 cells. Double-immunostaining revealed that GPR142 immunoreactivity in islets mainly occurs in insulin-positive cells. Potentiation of GSIS by GPR142 activation was accompanied by increased cAMP content in INS-1832/13 cells. PKA/Epac inhibition markedly suppressed the effect of GPR142 activation on insulin release. Gpr142 knockdown (Gpr142-KD) in islets was accompanied by elevated release of MCP-1, IFNγ, and TNFα during culture period and abolished the modulatory effect of GPR142 activation on the GSIS. Gpr142-KD had no effect on Ffar1, Ffar2, or Ffar3 mRNA while reducing Gpr56 and increasing Tlr5 and Tlr7 mRNA expression. Gpr142-KD was associated with an increased expression of Chrebp, Txnip, RhoA, and mitochondrial Vdac1 concomitant with a reduced Pdx1, Pax6, and mitochondrial Vdac2 mRNA levels. Long-term exposure of INS-1832/13 cells to hyperglycemia reduced Gpr142 and Vdac2 while increased Chrebp, Txnip, and Vdac1 mRNA expression. GPR142 agonists or Bt₂-cAMP counteracted this effect. Glucotoxicity-induced decrease of cell viability in Gpr142-KD INS-1 cells was not affected by GPR142-agonists while Bt₂-cAMP prevented it. The results show the importance of Gpr142 in the maintenance of pancreatic β-cell function in rodents and that GPR142 agonists potentiate GSIS by an action, which most likely is due to increased cellular generation of second messenger molecule cAMP.

Hypothalamic AMPK as a Mediator of Hormonal Regulation of Energy Balance

As a cellular energy sensor and regulator, adenosine monophosphate (AMP)-activated protein kinase (AMPK) plays a pivotal role in the regulation of energy homeostasis in both the central nervous system (CNS) and peripheral organs. Activation of hypothalamic AMPK maintains energy balance by inducing appetite to increase food intake and diminishing adaptive thermogenesis in adipose tissues to reduce energy expenditure in response to food deprivation. Numerous metabolic hormones, such as leptin, adiponectin, ghrelin and insulin, exert their energy regulatory effects through hypothalamic AMPK via integration with the neural circuits. Although activation of AMPK in peripheral tissues is able to promote fatty acid oxidation and insulin sensitivity, its chronic activation in the hypothalamus causes obesity by inducing hyperphagia in both humans and rodents. In this review, we discuss the role of hypothalamic AMPK in mediating hormonal regulation of feeding and adaptive thermogenesis, and summarize the diverse underlying mechanisms by which central AMPK maintains energy homeostasis.