Central GLP-1 receptor signalling accelerates plasma clearance of triacylglycerol and glucose by activating brown adipose tissue in mice

Adipose thermogenic mechanisms by cold, exercise and intermittent fasting: Similarities, disparities and the application in treatment

Given its nonnegligible role in metabolic homeostasis, adipose tissue has been the target for treating metabolic disorders such as obesity, diabetes and cardiovascular diseases. Besides its lipolytic function, adipose thermogenesis has gained increased interest due to the irreplaceable contribution to dissipating energy to restore equilibrium, and its therapeutic effects have been testified in various animal models. In this review, we will brief about the canonical cold-stimulated adipose thermogenic mechanisms, elucidate on the exercise- and intermittent fasting-induced adipose thermogenic mechanisms, with a focus on the similarities and disparities among these signaling pathways, in an effort to uncover the overlapped and specific targets that may yield potent therapeutic efficacy synergistically in improving metabolic health.

Doublecortin-like knockdown in mice attenuates obesity by stimulating energy expenditure in adipose tissue

Crosstalk between peripheral metabolic organs and the central nervous system is essential for body weight control. At the base of the hypothalamus, β-tanycytes surround the portal capillaries and function as gatekeepers to facilitate transfer of substances from the circulation into the cerebrospinal fluid and vice versa. Here, we investigated the role of the neuroplasticity gene doublecortin-like (DCL), highly expressed by β-tanycytes, in body weight control and whole-body energy metabolism. We demonstrated that DCL-knockdown through a doxycycline-inducible shRNA expression system prevents body weight gain by reducing adiposity in mice. DCL-knockdown slightly increased whole-body energy expenditure possibly as a result of elevated circulating thyroid hormones. In white adipose tissue (WAT) triglyceride uptake was increased while the average adipocyte cell size was reduced. At histological level we observed clear signs of browning, and thus increased thermogenesis in WAT. We found no indications for stimulated thermogenesis in brown adipose tissue (BAT). Altogether, we demonstrate an important, though subtle, role of tanycytic DCL in body weight control through regulation of energy expenditure, and specifically WAT browning. Elucidating mechanisms underlying the role of DCL in regulating brain-peripheral crosstalk further might identify new treatment targets for obesity.

Adipose tissue in older individuals: a contributing factor to sarcopenia

Sarcopenia is a geriatric syndrome characterized by a functional decline in muscle. The prevalence of sarcopenia increases with natural aging, becoming a serious health problem among elderly individuals. Therefore, understanding the pathology of sarcopenia is critical for inhibiting age-related alterations and promoting health and longevity in elderly individuals. The development of sarcopenia may be influenced by interactions between visceral and subcutaneous adipose tissue and skeletal muscle, particularly under conditions of chronic low-grade inflammation and metabolic dysfunction. This hypothesis is supported by the following observations: (i) accumulation of senescent cells in both adipose tissue and skeletal muscle with age; (ii) gut dysbiosis, characterized by an imbalance in gut microbial communities as the main trigger for inflammation, sarcopenia, and aged adipose tissue; and (iii) microbial dysbiosis, which could impact the onset or progression of a senescent state. Moreover, adipose tissue acts as an endocrine organ, releasing molecules that participate in intricate communication networks between organs. Our discussion focuses on novel adipokines and their role in regulating adipose tissue and muscle, particularly those influenced by aging and obesity, emphasizing their contributions to disease development. On the basis of these findings, we propose that age-related adipose tissue and sarcopenia are disorders characterized by chronic inflammation and metabolic dysregulation. Finally, we explore new potential therapeutic strategies involving specialized proresolving mediator (SPM) G protein-coupled receptor (GPCR) agonists, non-SPM GPCR agonists, transient receptor potential (TRP) channels, antidiabetic drugs in conjunction with probiotics and prebiotics, and compounds designed to target senescent cells and mitigate their pro-inflammatory activity.

GPCR-mediated regulation of beige adipocyte formation: Implications for obesity and metabolic health

Obesity and its associated complications pose a significant burden on health. The non-shivering thermogenesis (NST) and metabolic capacity properties of brown adipose tissue (BAT), which are distinct from those of white adipose tissue (WAT), in combating obesity and its related metabolic diseases has been well documented. However, beige adipose tissue, the third and relatively novel type of adipose tissue, which emerges in extensive presence of WAT and shares similar favorable metabolic properties with BAT, has garnered considerable attention in recent years. In this review, we focused on the role of G protein-coupled receptors (GPCRs), the largest receptor family and the most successful class of drug targets in humans, in the induction of beige adipocytes. More importantly, we highlight researchers' clinical treatment attempts to ameliorate obesity and other related metabolic diseases through the formation and activation of beige adipose tissue. In summary, this review provides valuable insights into the formation of beige adipose tissue and the involvement of GPCRs, based on the latest advancements in scientific research.

Do anti-obesity medical treatments have a direct effect on adipose tissue?

During the past years, several drugs have been developed for the treatment of obesity. Some are already used in clinical practice: orlistat, GLP-1 receptor agonists (RA), GLP-1/GIP biagonists and the melanocortin 4 receptor (MC4R) agonist, setmelanotide. Some should be available in the future: GLP-1/glucagon biagonists, GLP-1/GIP/glucagon triagonists. These drugs act mainly by reducing food intake or fat absorption. However, many of them show specific effects on the adipose tissue. All these drugs show significant reduction of fat mass and, more particularly of visceral fat. If most of the drugs, except orlistat, have been shown to increase energy expenditure in rodents with enhanced thermogenesis, this has not yet been clearly demonstrated in humans. However, biagonists or triagonist stimulating glucagon seem to a have a more potent effect to increase thermogenesis in the adipose tissue and, thus, energy expenditure. Most of these drugs have been shown to increase the production of adiponectin and to reduce the production of pro-inflammatory cytokines by the adipose tissue. GLP-1RAs reduce the size of adipocytes and promote their differentiation. GLP-1RAS and GLP-1/GIP biagonists reduce, in the adipose tissue, the expression of several genes involved in lipogenesis. Further studies are still needed to clarify the precise roles, on the adipose tissue, of these drugs dedicated for the treatment of obesity.

The effect of obesity pharmacotherapy on body composition, including muscle mass

Obesity pharmacotherapy represents a promising approach to treating obesity and may provide benefits beyond weight loss alone. Maintaining or even increasing muscle mass during weight loss is important to overall health, metabolic function and weight loss maintenance. Drugs such as liraglutide, semaglutide, tirzepatide, and naltrexone/bupropion have shown significant weight loss effects, and emerging evidence suggests they may also have effects on body composition, particularly a positive influence on muscle mass. However, further research is needed to fully understand the mechanism of action of these drugs and their effects on muscle mass. Clinicians should consider these factors when developing an obesity treatment plan for an individual patient.

Glucagon-Like Peptide-1: New Regulator in Lipid Metabolism

Glucagon-like peptide-1 (GLP-1) is a 30-amino acid peptide hormone that is mainly expressed in the intestine and hypothalamus. In recent years, basic and clinical studies have shown that GLP-1 is closely related to lipid metabolism, and it can participate in lipid metabolism by inhibiting fat synthesis, promoting fat differentiation, enhancing cholesterol metabolism, and promoting adipose browning. GLP-1 plays a key role in the occurrence and development of metabolic diseases such as obesity, nonalcoholic fatty liver disease, and atherosclerosis by regulating lipid metabolism. It is expected to become a new target for the treatment of metabolic disorders. The effects of GLP-1 and dual agonists on lipid metabolism also provide a more complete treatment plan for metabolic diseases. This article reviews the recent research progress of GLP-1 in lipid metabolism.

Cotadutide improves brown adipose tissue thermogenesis in obese mice

We studied the effect of cotadutide, a dual agonist glucagon-like peptide 1 (GLP1)/Glucagon, on interscapular brown adipose tissue (iBAT) remodeling and thermogenesis of obese mice. 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. Then, animals were redivided, adding cotadutide treatment: C, CC, HF, and HFC for four additional weeks. The multilocular brown adipocyte structure showed fat conversion (whitening), hypertrophy, and structural disarray in the HF group, which was reverted in cotadutide-treated animals. Cotadutide enhances the body temperature, thermogenesis, and sympathetic innervation (peroxisome proliferator-activated receptor-α, β3 adrenergic receptor, interleukin 6, and uncoupled protein 1), reduces pro-inflammatory markers (disintegrin and metallopeptidase domain, morphogenetic protein 8a, and neuregulin 4), and improves angiogenesis (vascular endothelial growth factor A, and perlecan). In addition, cotadutide enhances lipolysis (perilipin and cell death-inducing DNA fragmentation factor α), mitochondrial biogenesis (nuclear respiratory factor 1, transcription factor A mitochondrial, mitochondrial dynamin-like GTPase, and peroxisome proliferator-activated receptor gamma coactivator 1α), and mitochondrial fusion/fission (dynamin-related protein 1, mitochondrial fission protein 1, and parkin RBR E3 ubiquitin protein ligase). Cotadutide reduces endoplasmic reticulum stress (activating transcription factor 4, C/EBP homologous protein, and growth arrest and DNA-damage inducible), and extracellular matrix markers (lysyl oxidase, collagen type I α1, collagen type VI α3, matrix metallopeptidases 2 and 9, and hyaluronan synthases 1 and 2). In conclusion, the experimental evidence is compelling in demonstrating cotadutide's thermogenic effect on obese mice's iBAT, contributing to unraveling its action mechanisms and the possible translational benefits.

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.

Progress in the contrary effects of glucagon-like peptide-1 and chemerin on obesity development

Glucagon-like peptide-1 (GLP-1), secreted by intestinal L-cells, plays a pivotal role in the modulation of β-cell insulin secretion in a glucose-dependent manner, concurrently promoting β-cell survival and β-cell mass. Notably, GLP-1 has emerged as an effective second-line treatment for type 2 diabetes mellitus, gaining further prominence for its pronounced impact on body weight reduction, positioning it as a potent antiobesity agent. However, the mechanism by which GLP-1 improves obesity remains unclear. Some reports suggest that this mechanism may be associated with the regulation of adipokine synthesis within adipose tissue. Chemerin, a multifunctional adipokine and chemokine, has been identified as a pivotal player in adipocyte differentiation and the propagation of systemic inflammation, a hallmark of obesity. This review provides a comprehensive overview of the mechanisms by which GLP-1 and chemerin play crucial roles in obesity and obesity-related diseases. It discusses well-established aspects, such as their effects on food intake and glycolipid metabolism, as well as recent insights, including their influence on macrophage polarization and adipose tissue thermogenesis. GLP-1 has been shown to increase the population of anti-inflammatory M2 macrophages, promote brown adipose tissue thermogenesis, and induce the browning of white adipose tissue. In contrast, chemerin exhibits opposite effects in these processes. In addition, recent research findings have demonstrated the promising potential of GLP-1-based therapies in directly or indirectly regulating chemerin expression. In an intriguing reciprocal relationship, chemerin has also been newly identified as a negative regulator of GLP-1 in vivo. This review delineates the intricate interplay between GLP-1 and chemerin, unraveling their mutual inhibitory interactions. To the best of our knowledge, no previous reviews have focused on this specific topic, making this review particularly valuable in expanding our understanding of the endocrine mechanisms of obesity and providing potential strategies for the treatment of obesity and related diseases.

Combined GIP receptor and GLP1 receptor agonism attenuates NAFLD in male APOE∗3-Leiden.CETP mice

BACKGROUND

Combined glucose-dependent insulinotropic polypeptide receptor (GIPR) and glucagon-like peptide-1 receptor (GLP1R) agonism is superior to single GLP1R agonism with respect to glycemic control and weight loss in obese patients with or without type 2 diabetes. As insulin resistance and obesity are strong risk factors for nonalcoholic fatty liver disease (NAFLD), in the current study we investigated the effects of combined GIPR/GLP1R agonism on NAFLD development.

METHODS

Male APOE∗3-Leiden.CETP mice, a humanized model for diabetic dyslipidemia and NAFLD when fed a high-fat high-cholesterol diet, received subcutaneous injections with either vehicle, a GIPR agonist, a GLP1R agonist, or both agonists combined every other day.

FINDINGS

GIPR and GLP1R agonism reduced body weight and additively lowered fasting plasma levels of glucose, triglycerides and total cholesterol. Strikingly, we report an additive reduction in hepatic steatosis as evidenced by lower hepatic lipid content and NAFLD scores. Underlying the lipid-lowering effects were a reduced food intake and intestinal lipid absorption and an increased uptake of glucose and triglyceride-derived fatty acids by energy-combusting brown adipose tissue. Combined GIPR/GLP1R agonism also attenuated hepatic inflammation as evidenced by a decreased number of monocyte-derived Kupffer cells and a reduced expression of inflammatory markers. Together, the reduced hepatic steatosis and inflammation coincided with lowered markers of liver injury.

INTERPRETATION

We interpretate that GIPR and GLP1R agonism additively attenuate hepatic steatosis, lower hepatic inflammation, ameliorate liver injury, together preventing NAFLD development in humanized APOE∗3-Leiden.CETP mice. We anticipate that combined GIPR/GLP1R agonism is a promising strategy to attenuate NAFLD progression in humans.

FUNDING

This work was supported by a grant from the Netherlands CardioVascular Research Initiative: the Dutch Heart Foundation, Dutch Federation of University Medical Centers, the Netherlands Organization for Health Research and Development, and the Royal Netherlands Academy of Sciences [CVON-GENIUS-II] to P.C.N.R., a Lilly Research Award Program [LRAP] Award to P.C.N.R. and S.K., a Dutch Heart Foundation [2017T016] grant to S.K., and an NWO-VENI grant [09150161910073] to M.R.B.; J.F.D.B. is supported by the Nutrition and Health initiative of the University of Groningen; Z.Y. is supported by a full-time PhD scholarship from the China Scholarship Council (201806850094 to Z.Y.).

Treatment of obesity-related diabetes: significance of thermogenic adipose tissue and targetable receptors

Diabetes mellitus is mainly classified into four types according to its pathogenesis, of which type 2 diabetes mellitus (T2DM) has the highest incidence rate and is most relevant to obesity. It is characterized by high blood glucose, which is primarily due to insulin resistance in tissues that are responsible for glucose homeostasis (such as the liver, skeletal muscle, and white adipose tissue (WAT)) combined with insufficiency of insulin secretion from pancreatic β-cells. Treatment of diabetes, especially treatment of diabetic complications (such as diabetic nephropathy), remains problematic. Obesity is one of the main causes of insulin resistance, which, however, could potentially be treated by activating thermogenic adipose tissues, like brown and beige adipose tissues, because they convert energy into heat through non-shivering thermogenesis and contribute to metabolic homeostasis. In this review, we summarize the function of certain anti-diabetic medications with known thermogenic mechanisms and focus on various receptor signaling pathways, such as previously well-known and recently discovered ones that are involved in adipose tissue-mediated thermogenesis and could be potentially targeted to combat obesity and its associated diabetes, for a better understanding of the molecular mechanisms of non-shivering thermogenesis and the development of novel therapeutic interventions for obesity-related diabetes and potentially diabetic complications.

Fibroblast growth factor-21 is required for weight loss induced by the glucagon-like peptide-1 receptor agonist liraglutide in male mice fed high carbohydrate diets

OBJECTIVE

Glucagon-like peptide-1 receptor (GLP-1R) agonists (GLP-1RA) and fibroblast growth factor-21 (FGF21) confer similar metabolic benefits. GLP-1RA induce FGF21, leading us to investigate mechanisms engaged by the GLP-1RA liraglutide to increase FGF21 levels and the metabolic relevance of liraglutide-induced FGF21.

METHODS

Circulating FGF21 levels were measured in fasted male C57BL/6J, neuronal GLP-1R knockout, β-cell GLP-1R knockout, and liver peroxisome proliferator-activated receptor alpha knockout mice treated acutely with liraglutide. To test the metabolic relevance of liver FGF21 in response to liraglutide, chow-fed control and liver Fgf21 knockout (LivFgf21-/-) mice were treated with vehicle or liraglutide in metabolic chambers. Body weight and composition, food intake, and energy expenditure were measured. Since FGF21 reduces carbohydrate intake, we measured body weight in mice fed matched diets with low- (LC) or high-carbohydrate (HC) content and in mice fed a high-fat, high-sugar (HFHS) diet. This was done in control and LivFgf21-/- mice and in mice lacking neuronal β-klotho (Klb) expression to disrupt brain FGF21 signaling.

RESULTS

Liraglutide increases FGF21 levels independently of decreased food intake via neuronal GLP-1R activation. Lack of liver Fgf21 expression confers resistance to liraglutide-induced weight loss due to attenuated reduction of food intake in chow-fed mice. Liraglutide-induced weight loss was impaired in LivFgf21-/- mice when fed HC and HFHS diets but not when fed a LC diet. Loss of neuronal Klb also attenuated liraglutide-induced weight loss in mice fed HC or HFHS diets.

CONCLUSIONS

Our findings support a novel role for a GLP-1R-FGF21 axis in regulating body weight in a dietary carbohydrate-dependent manner.

Impact of short and long exposure to cafeteria diet on food intake and white adipose tissue lipolysis mediated by glucagon-like peptide 1 receptor

Introduction

The modern food environment facilitates excessive calorie intake, a major driver of obesity. Glucagon-like peptide 1 (GLP1) is a neuroendocrine peptide that has been the basis for developing new pharmacotherapies against obesity. The GLP1 receptor (GLP1R) is expressed in central and peripheral tissues, and activation of GLP1R reduces food intake, increases the expression of thermogenic proteins in brown adipose tissue (BAT), and enhances lipolysis in white adipose tissue (WAT). Obesity decreases the efficiency of GLP1R agonists in reducing food intake and body weight. Still, whether palatable food intake before or during the early development of obesity reduces the effects of GLP1R agonists on food intake and adipose tissue metabolism remains undetermined. Further, whether GLP1R expressed in WAT contributes to these effects is unclear.

Methods

Food intake, expression of thermogenic BAT proteins, and WAT lipolysis were measured after central or peripheral administration of Exendin-4 (EX4), a GLP1R agonist, to mice under intermittent-short exposure to CAF diet (3 h/d for 8 days) or a longer-continuous exposure to CAF diet (24 h/d for 15 days). Ex-vivo lipolysis was measured after EX4 exposure to WAT samples from mice fed CAF or control diet for 12 weeks. .

Results

During intermittent-short exposure to CAF diet (3 h/d for 8 days), third ventricle injection (ICV) and intra-peritoneal administration of EX4 reduced palatable food intake. Yet, during a longer-continuous exposure to CAF diet (24 h/d for 15 days), only ICV EX4 administration reduced food intake and body weight. However, this exposure to CAF diet blocked the increase in uncoupling protein 1 (UCP1) caused by ICV EX4 administration in mice fed control diet. Finally, GLP1R expression in WAT was minimal, and EX4 failed to increase lipolysis ex-vivo in WAT tissue samples from mice fed CAF or control diet for 12 weeks. .

Discussion

Exposure to a CAF diet during the early stages of obesity reduces the effects of peripheral and central GLP1R agonists, and WAT does not express a functional GLP1 receptor. These data support that exposure to the obesogenic food environment, without the development or manifestation of obesity, can alter the response to GLP1R agonists. .

Brown Adipose Tissue: A New Potential Target for Glucagon-like Peptide 1 Receptor Agonists in the Treatment of Obesity

Adipose tissue can be divided into white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue, according to the differences in morphology. WAT acts as a buffer for increased energy intake and decreased energy expenditure during the development of obesity, resulting in visceral and ectopic WAT accumulation. These WAT depots are strongly associated with chronic systemic inflammation, insulin resistance, and cardiometabolic risk related to obesity. They represent a primary weight loss target in anti-obesity management. Second-generation anti-obesity medications glucagon-like peptide-1 receptor agonists (GLP-1RAs) cause weight loss and improve body composition by reducing visceral and ectopic fat depots of WAT, resulting in improved cardiometabolic health. Recently, the understanding of the physiological significance of BAT beyond its primary function in generating heat through non-shivering thermogenesis has been expanded. This has raised scientific and pharmaceutical interest in the manipulation of BAT to further enhance weight reduction and body weight maintenance. This narrative review focuses on the potential impact of GLP-1 receptor agonism on BAT, particularly in human clinical studies. It provides an overview of the role of BAT in weight management and highlights the need for further research to elucidate the mechanisms by which GLP-1RAs affect energy metabolism and weight loss. Despite encouraging preclinical data, limited clinical evidence supports the notion that GLP-1RAs contribute to BAT activation.

Combined glucose-dependent insulinotropic polypeptide receptor and glucagon-like peptide-1 receptor agonism attenuates atherosclerosis severity in APOE*3-Leiden.CETP mice

BACKGROUND AND AIMS

Combined agonism of the glucose-dependent insulinotropic polypeptide receptor (GIPR) and the glucagon-like peptide-1 receptor (GLP1R) is superior to single GLP1R agonism in terms of glycemic control and lowering body weight in individuals with obesity and with or without type 2 diabetes mellitus. As both GIPR and GLP1R signaling have also been implicated in improving inflammatory responses and lipid handling, two crucial players in atherosclerosis development, here we aimed to investigate the effects of combined GIPR/GLP1R agonism in APOE*3-Leiden.CETP mice, a well-established mouse model for human-like lipoprotein metabolism and atherosclerosis development.

METHODS

Female APOE*3-Leiden.CETP mice were fed a Western-type diet (containing 16% fat and 0.15% cholesterol) to induce dyslipidemia, and received subcutaneous injections with either vehicle, a GIPR agonist (GIPFA-085), a GLP1R agonist (GLP-140) or both agonists. In the aortic root area, atherosclerosis development was assessed.

RESULTS

Combined GIPR/GLP1R agonism attenuated the development of severe atherosclerotic lesions, while single treatments only showed non-significant improvements. Mechanistically, combined GIPR/GLP1R agonism decreased markers of systemic low-grade inflammation. In addition, combined GIPR/GLP1R agonism markedly lowered plasma triglyceride (TG) levels as explained by reduced hepatic very-low-density lipoprotein (VLDL)-TG production as well as increased TG-derived fatty acid uptake by brown and white adipose tissue which was coupled to enhanced hepatic uptake of core VLDL remnants.

CONCLUSIONS

Combined GIPR/GLP1R agonism attenuates atherosclerosis severity by diminishing inflammation and increasing VLDL turnover. We anticipate that combined GIPR/GLP1R agonism is a promising strategy to lower cardiometabolic risk in humans.

Brown Adipose Tissue-A Translational Perspective

Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.

Dietary butyrate ameliorates metabolic health associated with selective proliferation of gut Lachnospiraceae bacterium 28-4

Short-chain fatty acids, including butyrate, have multiple metabolic benefits in individuals who are lean but not in individuals with metabolic syndrome, with the underlying mechanisms still being unclear. We aimed to investigate the role of gut microbiota in the induction of metabolic benefits of dietary butyrate. We performed antibiotic-induced microbiota depletion of the gut and fecal microbiota transplantation (FMT) in APOE*3-Leiden.CETP mice, a well-established translational model for developing human-like metabolic syndrome, and revealed that dietary butyrate reduced appetite and ameliorated high-fat diet-induced (HFD-induced) weight gain dependent on the presence of gut microbiota. FMT from butyrate-treated lean donor mice, but not butyrate-treated obese donor mice, into gut microbiota-depleted recipient mice reduced food intake, attenuated HFD-induced weight gain, and improved insulin resistance. 16S rRNA and metagenomic sequencing on cecal bacterial DNA of recipient mice implied that these effects were accompanied by the selective proliferation of Lachnospiraceae bacterium 28-4 in the gut as induced by butyrate. Collectively, our findings reveal a crucial role of gut microbiota in the beneficial metabolic effects of dietary butyrate as strongly associated with the abundance of Lachnospiraceae bacterium 28-4.

GLP-1 receptor agonists for the treatment of obesity: Role as a promising approach

Obesity is a complex disease characterized by excessive fat accumulation which is caused by genetic, environmental and other factors. In recent years, there has been an increase in the morbidity, disability rate,and mortality due to obesity, making it great threat to people's health and lives, and increasing public health care expenses. Evidence from previous studies show that weight loss can significantly reduce the risk of obesity-related complications and chronic diseases. Diet control, moderate exercise, behavior modification programs, bariatric surgery and prescription drug treatment are the major interventions used to help people lose weight. Among them, anti-obesity drugs have high compliance rates and cause noticeable short-term effects in reducing obese levels. However, given the safety or effectiveness concerns of anti-obesity drugs, many of the currently used drugs have limited clinical use. Glucagon-like peptide-1 receptor (GLP-1R) agonists are a group of drugs that targets incretin hormone action, and its receptors are widely distributed in nerves, islets, heart, lung, skin, and other organs. Several animal experiments and clinical trials have demonstrated that GLP-1R agonists are more effective in treating or preventing obesity. Therefore, GLP-1R agonists are promising agents for the treatment of obese individuals. This review describes evidence from previous research on the effects of GLP-1R agonists on obesity. We anticipate that this review will generate data that will help biomedical researchers or clinical workers develop obesity treatments based on GLP-1R agonists.

FGF21 protects against hepatic lipotoxicity and macrophage activation to attenuate fibrogenesis in nonalcoholic steatohepatitis

Analogues of the hepatokine fibroblast growth factor 21 (FGF21) are in clinical development for type 2 diabetes and nonalcoholic steatohepatitis (NASH) treatment. Although their glucose-lowering and insulin-sensitizing effects have been largely unraveled, the mechanisms by which they alleviate liver injury have only been scarcely addressed. Here, we aimed to unveil the mechanisms underlying the protective effects of FGF21 on NASH using APOE*3-Leiden.CETP mice, a well-established model for human-like metabolic diseases. Liver-specific FGF21 overexpression was achieved in mice, followed by administration of a high-fat high-cholesterol diet for 23 weeks. FGF21 prevented hepatic lipotoxicity, accompanied by activation of thermogenic tissues and attenuation of adipose tissue inflammation, improvement of hyperglycemia and hypertriglyceridemia, and upregulation of hepatic programs involved in fatty acid oxidation and cholesterol removal. Furthermore, FGF21 inhibited hepatic inflammation, as evidenced by reduced Kupffer cell (KC) activation, diminished monocyte infiltration, and lowered accumulation of monocyte-derived macrophages. Moreover, FGF21 decreased lipid- and scar-associated macrophages, which correlated with less hepatic fibrosis as demonstrated by reduced collagen accumulation. Collectively, hepatic FGF21 overexpression limits hepatic lipotoxicity, inflammation, and fibrogenesis. Mechanistically, FGF21 blocks hepatic lipid influx and accumulation through combined endocrine and autocrine signaling, respectively, which prevents KC activation and lowers the presence of lipid- and scar-associated macrophages to inhibit fibrogenesis.

Liver Fibroblast Growth Factor 21 (FGF21) is Required for the Full Anorectic Effect of the Glucagon-Like Peptide-1 Receptor Agonist Liraglutide in Male Mice fed High Carbohydrate Diets

Glucagon-like peptide-1 receptor (GLP-1R) agonists and fibroblast growth factor 21 (FGF21) confer similar metabolic benefits. Studies report that GLP-1RA induce FGF21. Here, we investigated the mechanisms engaged by the GLP-1R agonist liraglutide to increase FGF21 levels and the metabolic relevance of liraglutide-induced FGF21. We show that liraglutide increases FGF21 levels via neuronal GLP-1R activation. We also demonstrate that lack of liver Fgf21 expression confers partial resistance to liraglutide-induced weight loss. Since FGF21 reduces carbohydrate intake, we tested whether the contribution of FGF21 to liraglutide-induced weight loss is dependent on dietary carbohydrate content. In control and liver Fgf21 knockout (Liv ^{Fgf21 -/-} ) mice fed calorically matched diets with low- (LC) or high-carbohydrate (HC) content, we found that only HC-fed Liv ^{Fgf21 -/-} mice were resistant to liraglutide-induced weight loss. Similarly, liraglutide-induced weight loss was partially impaired in Liv ^{Fgf21 -/-} mice fed a high-fat, high-sugar (HFHS) diet. Lastly, we show that loss of neuronal β-klotho expression also diminishes liraglutide-induced weight loss in mice fed a HC or HFHS diet, indicating that FGF21 mediates liraglutide-induced weight loss via neuronal FGF21 action. Our findings support a novel role for a GLP-1R-FGF21 axis in regulating body weight in the presence of high dietary carbohydrate content.

Degree of obesity and gastrointestinal adverse reactions influence the weight loss effect of liraglutide in overweight or obese patients with type 2 diabetes

Background

Liraglutide can effectively reduce the weight of patients with type 2 diabetes. Nonetheless, its weight loss effect was highly heterogeneous in different patients in the clinical practice.

Objective

To identify the factors most associated with the weight loss effect of liraglutide in obese or overweight patients with type 2 diabetes with poorly controlled oral medication in northeast China.

Design

A prospective study.

Methods

A prospective study was performed in subjects with type 2 diabetes who were taking oral medication and had a body mass index (BMI) of ⩾24 kg/m². Liraglutide was administered for at least 12 weeks, while the original hypoglycemic regimen was kept unchanged (Phase I). Later, liraglutide treatment was continued or stopped as necessary or as subjects thought fit in the 13-52 weeks that followed (Phase II), and the potential factors affecting the effect of weight loss of liraglutide were analyzed.

Results

Of the 127 recruited subjects, 90 had comprehensive follow-up data at week 12. In Phase I, the subjects' blood sugar levels and weight decreased significantly(P < 0.001). Among all the significant factors, the gastrointestinal adverse reactions score (GARS) was more correlated with BMI change (ΔBMI; r = 0.43) and waist circumference change (ΔWC; r = 0.32) than the baseline BMI (BMI₀) and WC (WC₀). At week 12, linear regression showed that BMI₀ independently affected ΔBMI and ΔWC, whereas WC₀ only affected ΔWC. The GARS was significantly associated with ΔBMI and ΔWC, and this association continued until week 52, even after most subjects had discontinued liraglutide treatment.

Conclusion

The degree of obesity and gastrointestinal adverse reactions were the most promising predictors of weight loss in liraglutide treatment.

Intestinal lipid absorption and transport in type 2 diabetes

Postprandial hyperlipidaemia is an important feature of diabetic dyslipidaemia and plays an important role in the development of cardiovascular disease in individuals with type 2 diabetes. Postprandial hyperlipidaemia in type 2 diabetes is secondary to increased chylomicron production by the enterocytes and delayed catabolism of chylomicrons and chylomicron remnants. Insulin and some intestinal hormones (e.g. glucagon-like peptide-1 [GLP-1]) influence intestinal lipid metabolism. In individuals with type 2 diabetes, insulin resistance and possibly reduced GLP-1 secretion are involved in the pathophysiology of postprandial hyperlipidaemia. Several factors are involved in the overproduction of chylomicrons: (1) increased expression of microsomal triglyceride transfer protein, which is a key enzyme in chylomicron synthesis; (2) higher stability and availability of apolipoprotein B-48; and (3) increased de novo lipogenesis. Individuals with type 2 diabetes present with disorders of cholesterol metabolism in the enterocytes with reduced absorption and increased synthesis. The increased production of chylomicrons in type 2 diabetes is also associated with a reduction in their catabolism, mostly because of a reduction in activity of lipoprotein lipase. Modification of the microbiota, which is observed in type 2 diabetes, may also generate disorders of intestinal lipid metabolism, but human data remain limited. Some glucose-lowering treatments significantly influence intestinal lipid absorption and transport. Postprandial hyperlipidaemia is reduced by metformin, pioglitazone, alpha-glucosidase inhibitors, dipeptidyl peptidase 4 inhibitors and GLP-1 agonists. The most pronounced effect is observed with GLP-1 agonists, which reduce chylomicron production significantly in individuals with type 2 diabetes and have a direct effect on the intestine by reducing the expression of genes involved in intestinal lipoprotein metabolism. The effect of sodium-glucose cotransporter 2 inhibitors on intestinal lipid metabolism needs to be clarified.

Recent Advances in the Emerging Therapeutic Strategies for Diabetic Kidney Diseases

Diabetic kidney disease (DKD) is one of the most common causes of end-stage renal disease worldwide. The treatment of DKD is strongly associated with clinical outcomes in patients with diabetes mellitus. Traditional therapeutic strategies focus on the control of major risk factors, such as blood glucose, blood lipids, and blood pressure. Renin–angiotensin–aldosterone system inhibitors have been the main therapeutic measures in the past, but the emergence of sodium–glucose cotransporter 2 inhibitors, incretin mimetics, and endothelin-1 receptor antagonists has provided more options for the management of DKD. Simultaneously, with advances in research on the pathogenesis of DKD, some new therapies targeting renal inflammation, fibrosis, and oxidative stress have gradually entered clinical application. In addition, some recently discovered therapeutic targets and signaling pathways, mainly in preclinical and early clinical trial stages, are expected to provide benefits for patients with DKD in the future. This review summarizes the traditional treatments and emerging management options for DKD, demonstrating recent advances in the therapeutic strategies for DKD.

Different Protein Sources Enhance 18FDG-PET/MR Uptake of Brown Adipocytes in Male Subjects

Background: The unique ability of brown adipocytes to increase metabolic rate suggests that they could be targeted as an obesity treatment. Objective: The objective of the study was to search for new dietary factors that may enhance brown adipose tissue (BAT) activity. Methods: The study group comprised 28 healthy non-smoking males, aged 21–42 years old. All volunteers underwent a physical examination and a 75 g oral glucose tolerance test (75g-OGTT). Serum atrial and brain natriuretic peptide (ANP, BNP), PRD1-BF1-RIZ1 homologous domain containing 16 (PRDM16) and eukaryotic translation initiation factor 4E (eIF4E) measurements were taken, and 3-day food intake diaries were completed. Body composition measurements were assessed using dual-energy X-ray absorptiometry (DXA) scanning and bioimpedance methods. An fluorodeoxyglucose-18 (FDG-18) uptake in BAT was assessed by positron emission tomography/magnetic resonance (PET/MR) in all participants after 2 h cold exposure. The results were adjusted for age, daily energy intake, and DXA lean mass. Results: Subjects with detectable BAT (BAT⁽⁺⁾) were characterized by a higher percentage of energy obtained from dietary protein and fat and higher muscle mass (p = 0.01, p = 0.02 and p = 0.04, respectively). In the BAT⁽⁺⁾ group, animal protein intake was positively associated (p= 0.04), whereas the plant protein intake negatively correlated with BAT activity (p = 0.03). Additionally, the presence of BAT was inversely associated with BNP concentration in the 2 h of cold exposure (p = 0.002). Conclusion: The outcomes of our study suggest that different macronutrient consumption may be a new way to modulate BAT activity leading to weight reduction.

Role of thermogenic adipose tissue in lipid metabolism and atherosclerotic cardiovascular disease: lessons from studies in mice and humans

Brown adipocytes within brown adipose tissue (BAT) and beige adipocytes within white adipose tissue dissipate nutritional energy as heat. Studies in mice have shown that activation of thermogenesis in brown and beige adipocytes enhances the lipolytic processing of triglyceride-rich lipoproteins (TRLs) in plasma to supply these adipocytes with fatty acids for oxidation. This process results in formation of TRL remnants that are removed from the circulation through binding of apolipoprotein E (ApoE) on their surface to the low-density lipoprotein receptor (LDLR) on hepatocytes, followed by internalization. Concomitantly, lipolytic processing of circulating TRLs leads to generation of excess surface phospholipids that are transferred to nascent high-density lipoproteins (HDL), increasing their capacity for reverse cholesterol transport. Activation of thermogenic adipocytes thus lowers circulating triglycerides and non-HDL-cholesterol, while it increases HDL-cholesterol. The combined effect is protection from atherosclerosis development, which becomes evident in humanized mouse models with an intact ApoE-LDLR clearance pathway only, and is additive to the effects of classical lipid-lowering drugs including statins and proprotein convertase subtilisin/kexin type 9 inhibitors. A large recent study revealed that the presence of metabolically active BAT in humans is associated with lower triglycerides, higher HDL-cholesterol and lower risk of cardiovascular diseases. This narrative review aims to provide leads for further exploration of thermogenic adipose tissue as a therapeutic target. To this end, we describe the latest knowledge on the role of BAT in lipoprotein metabolism and address, for example, the discovery of the β2-adrenergic receptor as the dominant adrenergic receptor in human thermogenic adipocytes.

The effects of glucagon-like peptide-1 receptor agonists on adipose tissues in patients with type 2 diabetes: A meta-analysis of randomised controlled trials

Aims

Glucagon‑like peptide 1 receptor agonist (GLP-1RA) treatment can improve adipose distribution. We performed this meta-analysis to investigate whether GLP-1RAs preferentially reduce visceral adipose tissue (VAT) over subcutaneous adipose tissue (SAT) in patients with type 2 diabetes.

Materials and methods

We searched MEDLINE and the Cochrane Library for randomised controlled trials explicitly reporting changes in VAT and SAT. A random-effects model was performed to estimate the weighted mean difference (MD) for VAT and SAT. Heterogeneity among the studies was assessed using I2 statistics, and publication bias was assessed using Egger’s tests. Meta-regression was performed to identify the correlation between changes in adipose tissues and changes in body weight and glycated haemoglobin level.

Results

Ten trials with 924 patients were enrolled in the meta-analysis. GLP-1RA treatment led to similar absolute area (cm2) reductions in VAT (MD -21.13 cm2, 95% CI [-29.82, -12.44]) and SAT (MD -22.89 cm2, 95% CI [-29.83, -15.95]). No significant publication bias was detected, and this result was stable in the sensitivity and subgroup analyses. Moreover, GLP-1RA treatment resulted in a greater reduction in VAT and SAT in the subgroup with a greater reduction in body weight. The absolute area reduction in VAT was significantly correlated with the reduction in body weight (r = 6.324, p = 0.035).

Conclusions

GLP-1RA treatment leads to significant and similar absolute reductions in VAT and SAT, and the reduction in adipose tissues may be correlated with the reduction in body weight.

Effect of glucagon-like peptide-1 (GLP-1) analogues on epicardial adipose tissue: A meta-analysis

BACKGROUND AND AIMS

Glucagon-like peptide-1 (GLP-1) analogues reduce body fat and cardiovascular events in patients with type 2 diabetes. Accumulation of epicardial adipose tissue (EAT) is associated with increased cardio-metabolic risks and coronary events in type 2 diabetes.

METHODS

A systematic review and meta-analysis were performed from Glucagon-like peptide-1 analogues therapy on type 2 diabetes patients, reporting data from changes in EAT, after searching the PubMed/MEDLINE, Embase, Science Direct, Scopus, Google Scholar, and Cochrane databases.

RESULTS

It has been found a limited number of studies, a total of 4 studies (n = 160 patients with GLP-1 analogues therapy) were included in the final analysis. Pooled analysis revealed that GLP-1 analogues reduce EAT (MD: 1.83 mm [-2.50; -1.10]; P < 0.01). Compared with the patients before the treatment, the patients after the treatment had a smaller HbA1c (MD -1.10%[-1.80; -0.30]; p = 0.0143) and body mass index was reduced (MD -2.20 kg/m²[-3.70; -0.60]; p = 0.0058), GLP-1 therapy reduced low-density lipoprotein levels (MD-13.53 mg/dL [-21.74; -5.31]; p = 0.001) and reduced triglycerides levels significantly (MD -18.32 -28.20 mg/dL; -8.50); p = 0.0003).

CONCLUSIONS

This meta-analysis suggests that the amount of EAT is significantly reduced in T2D patients with Glucagon-like peptide-1 analogues.

Physiological and pharmacological actions of glucagon like peptide-1 (GLP-1) in domestic animals

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GLP-1 improves peripheral glucose uptake in healthy dogs and cats.

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GLP-1 analogues administration in diabetic cats reduces exogenous insulin requirement.

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Dogs cardiomyocytes apoptosis is reduced by GLP-1-derived molecules action.

Analogues of glucagon like peptide-1 (GLP-1) and other drugs that increase this peptide half-life are used worldwide in human medicine to treat type 2 diabetes mellitus (DM) and obesity. These molecules can increase insulin release and satiety, interesting effects that could also be useful in the treatment of domestic animals pathologies, however their use in veterinary medicine are still limited. Considering the increasing incidence of DM and obesity in cats and dogs, the aim of this review is to summarize the available information about the physiological and pharmacological actions of GLP-1 in domestic animals and discuss about its potential applications in veterinary medicine. In diabetic dogs, the use of drugs based on GLP-1 actions reduced blood glucose and increased glucose uptake, while in diabetic cats they reduced glycemic variability and exogenous insulin administration. Thus, available evidence indicates that GLP-1 based drugs could become alternatives to DM treatment in domestic animals. Nevertheless, current data do not provide enough elements to recommend these drugs widespread clinical use.

GLP-1 receptor agonists in diabetic kidney disease: current evidence and future directions

With the emergence of various classes of blood glucose-lowering agents, choosing the appropriate drug for each patient is emphasized in diabetes management. Among incretin-based drugs, glucagon-like peptide 1 (GLP-1) receptor agonists are a promising therapeutic option for patients with diabetic kidney disease (DKD). Several cardiovascular outcome trials have demonstrated that GLP-1 receptor agonists have beneficial effects on cardiorenal outcomes beyond their blood glucose-lowering effects in patients with type 2 diabetes mellitus (T2DM). The renal protective effects of GLP-1 receptor agonists likely result from their direct actions on the kidney, in addition to their indirect actions that improve conventional risk factors for DKD, such as reducing blood glucose levels, blood pressure, and body weight. Inhibition of oxidative stress and inflammation and induction of natriuresis are major renoprotective mechanisms of GLP-1 analogues. Early evidence from the development of dual and triple combination agents suggests that GLP-1 receptor agonists will probably become popular treatment options for patients with T2DM.

Browning Epicardial Adipose Tissue: Friend or Foe?

The epicardial adipose tissue (EAT) is the visceral fat depot of the heart which is highly plastic and in direct contact with myocardium and coronary arteries. Because of its singular proximity with the myocardium, the adipokines and pro-inflammatory molecules secreted by this tissue may directly affect the metabolism of the heart and coronary arteries. Its accumulation, measured by recent new non-invasive imaging modalities, has been prospectively associated with the onset and progression of coronary artery disease (CAD) and atrial fibrillation in humans. Recent studies have shown that EAT exhibits beige fat-like features, and express uncoupling protein 1 (UCP-1) at both mRNA and protein levels. However, this thermogenic potential could be lost with age, obesity and CAD. Here we provide an overview of the physiological and pathophysiological relevance of EAT and further discuss whether its thermogenic properties may serve as a target for obesity therapeutic management with a specific focus on the role of immune cells in this beiging phenomenon.

Liraglutide Activates Type 2 Deiodinase and Enhances β3-Adrenergic-Induced Thermogenesis in Mouse Adipose Tissue

Aims

Liraglutide is a long-acting glucagon-like peptide 1 (GLP-1) receptor agonist used as an anti-hyperglycemic agent in type 2 diabetes treatment and recently approved for obesity management. Weight loss is attributed to appetite suppression, but therapy may also increase energy expenditure. To further investigate the effect of GLP-1 signaling in thermogenic fat, we assessed adipose tissue oxygen consumption and type 2 deiodinase (D2) activity in mice treated with liraglutide, both basally and after β3-adrenergic treatment.

Methods

Male C57BL/6J mice were randomly assigned to receive liraglutide (400 μg/kg, n=12) or vehicle (n=12). After 16 days, mice in each group were co-treated with the selective β3-adrenergic agonist CL316,243 (1 mg/kg, n=6) or vehicle (n=6) for 5 days. Adipose tissue depots were assessed for gene and protein expression, oxygen consumption, and D2 activity.

Results

Liraglutide increased interscapular brown adipose tissue (iBAT) oxygen consumption and enhanced β3-adrenergic-induced oxygen consumption in iBAT and inguinal white adipose tissue (ingWAT). These effects were accompanied by upregulation of UCP-1 protein levels in iBAT and ingWAT. Notably, liraglutide increased D2 activity without significantly upregulating its mRNA levels in iBAT and exhibited additive effects to β3-adrenergic stimulation in inducing D2 activity in ingWAT.

Conclusions

Liraglutide exhibits additive effects to those of β3-adrenergic stimulation in thermogenic fat and increases D2 activity in BAT, implying that it may activate this adipose tissue depot by increasing intracellular thyroid activation, adding to the currently known mechanisms of GLP-1A-induced weight loss.

Lessons from bariatric surgery: Can increased GLP-1 enhance vascular repair during cardiometabolic-based chronic disease?

Type 2 diabetes (T2D) and obesity represent entangled pandemics that accelerate the development of cardiovascular disease (CVD). Given the immense burden of CVD in society, non-invasive prevention and treatment strategies to promote cardiovascular health are desperately needed. During T2D and obesity, chronic dysglycemia and abnormal adiposity result in systemic oxidative stress and inflammation that deplete the vascular regenerative cell reservoir in the bone marrow that impairs blood vessel repair and exacerbates the penetrance of CVD co-morbidities. This novel translational paradigm, termed 'regenerative cell exhaustion' (RCE), can be detected as the depletion and dysfunction of hematopoietic and endothelial progenitor cell lineages in the peripheral blood of individuals with established T2D and/or obesity. The reversal of vascular RCE has been observed after administration of the sodium-glucose cotransporter-2 inhibitor (SGLT2i), empagliflozin, or after bariatric surgery for severe obesity. In this review, we explore emerging evidence that links improved dysglycemia to a reduction in systemic oxidative stress and recovery of circulating pro-vascular progenitor cell content required for blood vessel repair. Given that bariatric surgery consistently increases systemic glucagon-like-peptide 1 (GLP-1) release, we also focus on evidence that the use of GLP-1 receptor agonists (GLP-1RA) during obesity may act to inhibit the progression of systemic dysglycemia and adiposity, and indirectly reduce inflammation and oxidative stress, thereby limiting the impact of RCE. Therefore, therapeutic intervention with currently-available GLP-1RA may provide a less-invasive modality to reverse RCE, bolster vascular repair mechanisms, and improve cardiometabolic risk in individuals living with T2D and obesity.

Non-shivering Thermogenesis Signalling Regulation and Potential Therapeutic Applications of Brown Adipose Tissue

In mammals, thermogenic organs exist in the body that increase heat production and enhance energy regulation. Because brown adipose tissue (BAT) consumes energy and generates heat, increasing energy expenditure via BAT might be a potential strategy for new treatments for obesity and obesity-related diseases. Thermogenic differentiation affects normal adipose tissue generation, emphasizing the critical role that common transcriptional regulation factors might play in common characteristics and sources. An understanding of thermogenic differentiation and related factors could help in developing ways to improve obesity indirectly or directly through targeting of specific signalling pathways. Many studies have shown that the active components of various natural products promote thermogenesis through various signalling pathways. This article reviews recent major advances in this field, including those in the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA), cyclic guanosine monophosphate-GMP-dependent protein kinase G (cGMP-AKT), AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), transforming growth factor-β/bone morphogenic protein (TGF-β/BMP), transient receptor potential (TRP), Wnt, nuclear factor-κ-light-chain-enhancer of activated B cells (NF-κΒ), Notch and Hedgehog (Hh) signalling pathways in brown and brown-like adipose tissue. To provide effective information for future research on weight-loss nutraceuticals or drugs, this review also highlights the natural products and their active ingredients that have been reported in recent years to affect thermogenesis and thus contribute to weight loss via the above signalling pathways.

Effective oral delivery of Exenatide-Zn2+ complex through distal ileum-targeted double layers nanocarriers modified with deoxycholic acid and glycocholic acid in diabetes therapy

The oral administration route is popular with T2DM patients because they need convenience in lifelong medication. At present, oral Exenatide is not available on the market and therefore the relevant studies are valuable. Herein, we constructed a novel dual cholic acid-functionalized nanoparticle for oral delivery of Exenatide, which was based on the functionalized materials of deoxycholic acid-low molecular weight protamine and glycocholic acid-poly (ethylene glycol)-b-polysialic acid. The hydrophobic deoxycholic acid strengthened the nanoparticles and the hydrophilic glycolic acid targeted to specific transporter. We first condensed Exenatide-Zn²⁺ complex with deoxycholic acid-low molecular weight protamine to prepare nanocomplexes with ζ-potentials of +8 mV and sizes of 95 nm. Then, we used glycocholic acid-poly (ethylene glycol)-b-polysialic acid copolymers masking the positive charge of nanocomplexes to prepare nanoparticles with negative charges of -22 mV and homogeneous sizes of 140 nm. As a result, this dual cholic acid-functionalized nanoparticle demonstrated enhanced uptake and transport of Exenatide, and a special targeting to apical sodium-dependent cholic acid transporter in vitro. Moreover, in vivo studies showed that the nanoparticle effectively accumulated in distal ileum, raised the plasma concentration of Exenatide, prolonged hypoglycemic effect, reduced blood lipid levels, and lightened organ lesions.

Direct Effect of the Synthetic Analogue of Glucagon-Like Peptide Type 1, Liraglutide, on Mature Adipocytes Is Realized through Adenylate-Cyclase-Dependent Enhancing of Insulin Sensitivity

Incretin hormones analogues, including glucagon-like peptide type 1 (GLP-1), exhibit complex glucose-lowering, anorexigenic, and cardioprotective properties. Mechanisms of action of GLP-1 and its analogues are well known for pancreatic β-cells, hepatocytes, and other tissues. Nevertheless, local effects of GLP-1 and its analogues in adipose tissue remain unclear. In the present work effects of the GLP-1 synthetic analogue, liraglutide, on adipogenesis and insulin sensitivity of the 3T3-L1 adipocytes were examined. Enhancement of insulin sensitivity of mature adipocytes by the GLP-1 synthetic analogue liraglutide mediated by adenylate cyclase was demonstrated. The obtained results imply existence of the positive direct insulin-sensitizing effect of liraglutide on mature adipocytes.

The Role of AMPK Signaling in Brown Adipose Tissue Activation

Obesity is becoming a pandemic, and its prevalence is still increasing. Considering that obesity increases the risk of developing cardiometabolic diseases, research efforts are focusing on new ways to combat obesity. Brown adipose tissue (BAT) has emerged as a possible target to achieve this for its functional role in energy expenditure by means of increasing thermogenesis. An important metabolic sensor and regulator of whole-body energy balance is AMP-activated protein kinase (AMPK), and its role in energy metabolism is evident. This review highlights the mechanisms of BAT activation and investigates how AMPK can be used as a target for BAT activation. We review compounds and other factors that are able to activate AMPK and further discuss the therapeutic use of AMPK in BAT activation. Extensive research shows that AMPK can be activated by a number of different kinases, such as LKB1, CaMKK, but also small molecules, hormones, and metabolic stresses. AMPK is able to activate BAT by inducing adipogenesis, maintaining mitochondrial homeostasis and inducing browning in white adipose tissue. We conclude that, despite encouraging results, many uncertainties should be clarified before AMPK can be posed as a target for anti-obesity treatment via BAT activation.

Liraglutide improves lipid and carbohydrate metabolism of ovariectomized rats

Considering that post-menopausal women and ovariectomized rodents develop obesity associated with increased visceral fat, this study was developed to investigate if liraglutide, a glucagon-like peptide 1 (GLP1) analogue, could improve the metabolism of estrogen (E2) deficient females. Wistar rats were ovariectomized (OVX), and subdivided in four groups: sham saline, sham liraglutide, OVX saline, and OVX liraglutide. After sixty days, metabolic parameters of blood, heart, liver, brown (BAT) and white adipose tissue (WAT) visceral depots, and, heart oxidative homeostasis, were evaluated. Castration increased the animals' body weight, the relative weight of the WAT depots, hepatic triglycerides and cardiac glycogen content. Liraglutide treatment reversed these effects, decreased WAT depots weight and increased glucose oxidation and lipogenesis in BAT and WAT. In addition, liraglutide enhanced adrenalin (A) lipolytic effect. These results indicate that liraglutide may be a promising treatment to restore lipid homeostasis and prevent weight gain associated with E2 deficiency.

Pharmacological treatment with FGF21 strongly improves plasma cholesterol metabolism to reduce atherosclerosis

Aims 

Fibroblast growth factor (FGF) 21, a key regulator of energy metabolism, is currently evaluated in humans for treatment of type 2 diabetes and non-alcoholic steatohepatitis. However, the effects of FGF21 on cardiovascular benefit, particularly on lipoprotein metabolism in relation to atherogenesis, remain elusive.

Methods and results  

Here, the role of FGF21 in lipoprotein metabolism in relation to atherosclerosis development was investigated by pharmacological administration of a half-life extended recombinant FGF21 protein to hypercholesterolaemic APOE*3-Leiden.CETP mice, a well-established model mimicking atherosclerosis initiation and development in humans. FGF21 reduced plasma total cholesterol, explained by a reduction in non-HDL-cholesterol. Mechanistically, FGF21 promoted brown adipose tissue (BAT) activation and white adipose tissue (WAT) browning, thereby enhancing the selective uptake of fatty acids from triglyceride-rich lipoproteins into BAT and into browned WAT, consequently accelerating the clearance of the cholesterol-enriched remnants by the liver. In addition, FGF21 reduced body fat, ameliorated glucose tolerance and markedly reduced hepatic steatosis, related to up-regulated hepatic expression of genes involved in fatty acid oxidation and increased hepatic VLDL-triglyceride secretion. Ultimately, FGF21 largely decreased atherosclerotic lesion area, which was mainly explained by the reduction in non-HDL-cholesterol as shown by linear regression analysis, decreased lesion severity, and increased atherosclerotic plaque stability index.

Conclusion 

FGF21 improves hypercholesterolaemia by accelerating triglyceride-rich lipoprotein turnover as a result of activating BAT and browning of WAT, thereby reducing atherosclerotic lesion severity and increasing atherosclerotic lesion stability index. We have thus provided additional support for the clinical use of FGF21 in the treatment of atherosclerotic cardiovascular disease.

Effect of combined therapy of mesenchymal stem cells with GLP-1 receptor agonist, exenatide, on early-onset nephropathy induced in diabetic rats

Diabetic nephropathy is the principal cause of end-stage renal failure and current interventions for its recession remains unsatisfactory. Mesenchymal stem cells (MSCs) hold an attractive source for renovating injured tissues. Unfortunately, limited self-renewal and migration capacity of MSCs after transplantation hinder their clinical applicability which demands a new policy for enhancing their biological functions. This study aimed to investigate whether the renoprotective potential of adipose-derived MSCs (ADMSCs) in diabetic rats could be promoted by exenatide, a glucagon-like peptide-1 (GLP-1) analogue. These effects were studied in type 2 diabetes mellitus rats which were administrated ADMSCs, exenatide or their combination four weeks post-induction. Four weeks later, renal function parameters were evaluated. To address the possible underlying mechanisms, parameters indicating glycolipid metabolism tolerance and oxidative stress biomarkers were assessed in renal tissues alongside evaluation of protein expression of tumor necrosis factor-alpha, transforming growth factor-beta1 and cleaved caspase-3. The results showed that the combined therapy had superior renoprotective effect as evident by significant improvement in kidney function and renal architecture changes through rebalancing of inflammatory, fibrotic and apoptotic markers. Based on these outcomes, ADMSCs with exenatide were supposed to effectively ameliorate diabetic renal dysfunction compared to ADMSCs solely, presenting a promise therapy for diabetic nephropathy with further clinical studies warranted to validate this effect.

Free Thyroxine Levels are Associated with Cold Induced Thermogenesis in Healthy Euthyroid Individuals

Thyroid hormone (TH) is an important regulator of mammalian metabolism and facilitates cold induced thermogenesis (CIT) in brown adipose tissue (BAT). Profound hypothyroidism or hyperthyroidism lead to alterations in BAT function and CIT. In euthyroid humans the inter-individual variation of thyroid hormones is relatively large. Therefore, we investigated whether levels of free thyroxine (T4) or free triiodothyronine (T3) are positively associated with CIT in euthyroid individuals. We performed an observational study in 79 healthy, euthyroid volunteers (mean age 25.6 years, mean BMI 23.0 kg · m^-2). Resting energy expenditure (REE) was measured by indirect calorimetry during warm conditions (EE_warm) and after a mild cold stimulus of two hours (EE_cold). CIT was calculated as the difference between EE_cold and EE_warm. BAT activity was assessed by ¹⁸F-FDG-PET after a mild cold stimulus in a subset of 26 participants. EE_cold and CIT were significantly related to levels of free T4 (R² = 0.11, p=0.0025 and R² = 0.13, p=0.0011, respectively) but not to free T3 and TSH. Cold induced BAT activity was also associated with levels of free T4 (R² = 0.21, p=0.018). CIT was approximately fourfold higher in participants in the highest tertile of free T4 as compared to the lowest tertile. Additionally, free T4 was weakly, albeit significantly associated with outdoor temperature seven days prior to the respective study visit (R² = 0.06, p=0.037). These finding suggests that variations in thyroid hormone levels within the euthyroid range are related to the capability to adapt to cool temperatures and affect energy balance.

MS-275, a class 1 histone deacetylase inhibitor augments glucagon-like peptide-1 receptor agonism to improve glycemic control and reduce obesity in diet-induced obese mice

Given its glycemic efficacy and ability to reduce the body weight, glucagon-like peptide 1 receptor (GLP-1R) agonism has emerged as a preferred treatment for diabetes associated with obesity. We here report that a small-molecule Class 1 histone deacetylase (HDAC) inhibitor Entinostat (MS-275) enhances GLP-1R agonism to potentiate glucose-stimulated insulin secretion and decrease body weight in diet-induced obese (DIO) mice. MS-275 is not an agonist or allosteric activator of GLP-1R but enhances the sustained receptor-mediated signaling through the modulation of the expression of proteins involved in the signaling pathway. MS-275 and liraglutide combined therapy improved fasting glycemia upon short-term treatment and a chronic administration causes a reduction of obesity in DIO mice. Overall, our results emphasize the therapeutic potential of MS-275 as an adjunct to GLP-1R therapy in the treatment of diabetes and obesity.

Effect on Body Weight and Adipose Tissue by Cariprazine: A Head-to-Head Comparison Study to Olanzapine and Aripiprazole in Rats

Cariprazine (Car) is a recently approved second generation antipsychotic (SGA) with unique pharmacodynamic profile, being a partial agonist at both dopamine D2/3 receptor subtypes, with almost 10 times greater affinity towards D3. SGAs are known to increase body weight, alter serum lipids, and stimulate adipogenesis but so far, limited information about the adverse effects is available with this drug. In order to study this new SGA with such a unique mechanism of action, we compared Car to substances that are considered references and are well characterized: olanzapine (Ola) and aripiprazole (Ari). We studied the effects on body weight and also assessed the adipogenesis in rats. The drugs were self-administered in two different doses to female, adult, Wistar rats for six weeks. Weekly body weight change, vacuole size of adipocytes, Sterol Regulatory Element Binding Protein-1 (SREBP-1) and Uncoupling Protein-1 (UCP-1) expression were measured from the visceral adipose tissue (AT). The adipocyte’s vacuole size, and UCP-1 expression were increased while body weight gain was diminished by Car. by increasing UCP-1 might stimulate the thermogenesis, that could potentially explain the weight gain lowering effect through enhanced lipolysis.

Olfactory bulb-targeted quantum dot (QD) bioconjugate and Kv1.3 blocking peptide improve metabolic health in obese male mice

The olfactory system is a driver of feeding behavior, whereby olfactory acuity is modulated by the metabolic state of the individual. The excitability of the major output neurons of the olfactory bulb (OB) can be modulated through targeting a voltage-dependent potassium channel, Kv1.3, which responds to changes in metabolic factors such as insulin, glucose, and glucagon-like peptide-1. Because gene-targeted deletion or inhibition of Kv1.3 in the periphery has been found to increase energy metabolism and decrease body weight, we hypothesized that inhibition of Kv1.3 selectively in the OB could enhance excitability of the output neurons to evoke changes in energy homeostasis. We thereby employed metal-histidine coordination to self-assemble the Kv1.3 inhibitor margatoxin (MgTx) to fluorescent quantum dots (QDMgTx) as a means to label cells in vivo and test changes in neuronal excitability and metabolism when delivered to the OB. Using patch-clamp electrophysiology to measure Kv1.3 properties in heterologously expressed cells and native mitral cells in OB slices, we found that QDMgTx had a fast rate of inhibition, but with a reduced IC_50, and increased action potential firing frequency. QDMgTx was capable of labeling cloned Kv1.3 channels but was not visible when delivered to native Kv1.3 in the OB. Diet-induced obese mice were observed to reduce body weight and clear glucose more quickly following osmotic mini-pump delivery of QDMgTx/MgTx to the OB, and following MgTx delivery, they increased the use of fats as fuels (reduced respiratory exchange ratio). These results suggest that enhanced excitability of bulbar output neurons can drive metabolic responses.

Leucine Potentiates Glucose-mediated 18F-FDG Uptake in Brown Adipose Tissue via β-Adrenergic Activation

Significant depots of brown adipose tissue (BAT) have been identified in many adult humans through positron emission tomography (PET), with the amount of BAT being inversely correlated with obesity. As dietary activation of BAT has implications for whole body glucose metabolism, leucine was used in the present study to determine its ability to promote BAT activation resulting in increased glucose uptake. In order to assess this, 2-deoxy-2-(fluorine-18)fluoro-d-glucose (¹⁸F-FDG) uptake was measured in C57BL/6 mice using microPET after treatment with leucine, glucose, or both in interscapular BAT (IBAT). Pretreatment with propranolol (PRP) was used to determine the role of β-adrenergic activation in glucose and leucine-mediated ¹⁸F-FDG uptake. Analysis of maximum standardized uptake values (SUV_MAX) determined that glucose administration increased ¹⁸F-FDG uptake in IBAT by 25.3%. While leucine did not promote ¹⁸F-FDG uptake alone, it did potentiate glucose-mediated ¹⁸F-FDG uptake, increasing ¹⁸F-FDG uptake in IBAT by 22.5%, compared to glucose alone. Pretreatment with PRP prevented the increase in IBAT ¹⁸F-FDG uptake following the combination of glucose and leucine administration. These data suggest that leucine is effective in promoting BAT ¹⁸F-FDG uptake through β-adrenergic activation in combination with glucose.

Insights into incretin-based therapies for treatment of diabetic dyslipidemia

Derangements in triglyceride and cholesterol metabolism (dyslipidemia) are major risk factors for the development of cardiovascular diseases in obese and type-2 diabetic (T2D) patients. An emerging class of glucagon-like peptide-1 (GLP-1) analogues and next generation peptide dual-agonists such as GLP-1/glucagon or GLP-1/GIP could provide effective therapeutic options for T2D patients. In addition to their role in glucose and energy homeostasis, GLP-1, GIP and glucagon serve as regulators of lipid metabolism. This review summarizes the current knowledge in GLP-1, glucagon and GIP effects on lipid and lipoprotein metabolism and frames the emerging therapeutic benefits of GLP-1 analogs and GLP-1-based multiagonists as add-on treatment options for diabetes associated dyslipidemia.

Twelve weeks of exenatide treatment increases [18F]fluorodeoxyglucose uptake by brown adipose tissue without affecting oxidative resting energy expenditure in nondiabetic males

AIMS/HYPOTHESIS

Brown adipose tissue (BAT) improves energy metabolism by combusting glucose and lipids into heat. Agonism of the glucagon-like peptide-1 receptor (GLP-1R) within the central nervous system activates BAT in mice. Moreover, in patients with type 2 diabetes, GLP-1R agonism lowers body weight and improves glucose and lipid levels, possibly involving BAT activation. Interestingly, people from South Asian descent are prone to develop cardiometabolic disease. We studied the effect of GLP-1R agonism on BAT in humans, specifically in South Asians and Europids without obesity or type 2 diabetes.

METHODS

Twelve Dutch South Asian and 12 age- and BMI-matched Europid nondiabetic men received 12 weeks extended-release exenatide (Bydureon) in this single-arm prospective study. Before and after treatment, BAT was visualized by a cold-induced [¹⁸F]FDG-PET/CT scan and a thermoneutral MRI scan, and resting energy expenditure (REE), substrate oxidation, body composition and fasting plasma glucose and serum lipids were determined. Appetite was rated using a visual analogue scale.

RESULTS

Since the effect of exenatide on metabolic parameters did not evidently differ between ethnicities, data of all participants were pooled. Exenatide decreased body weight (-1.5 ± 0.4 kg, p < 0.01), without affecting REE or substrate oxidation, and transiently decreased appetite ratings during the first weeks. Exenatide also lowered triglycerides (-15%, p < 0.05) and total cholesterol (-5%, p < 0.05), and tended to lower glucose levels. Notably, exenatide increased BAT metabolic volume (+28%, p < 0.05) and mean standardized uptake value (+11%, p < 0.05) ([¹⁸F]FDG-PET/CT), without affecting supraclavicular adipose tissue fat fraction (MRI).

CONCLUSIONS/INTERPRETATION

We show for the first time that GLP-1R agonism increases [¹⁸F]FDG uptake by BAT in South Asian and Europid men without obesity or type 2 diabetes.

TRIAL REGISTRY

Clinicaltrials.gov NCT03002675.

Liraglutide decreases energy expenditure and does not affect the fat fraction of supraclavicular brown adipose tissue in patients with type 2 diabetes

BACKGROUND AND AIMS

Several studies have shown that glucagon-like peptide-1 (GLP-1) analogues can affect resting energy expenditure, and preclinical studies suggest that they may activate brown adipose tissue (BAT). The aim of the present study was to investigate the effect of treatment with liraglutide on energy metabolism and BAT fat fraction in patients with type 2 diabetes.

METHODS AND RESULTS

In a 26-week double-blind, placebo-controlled trial, 50 patients with type 2 diabetes were randomized to treatment with liraglutide (1.8 mg/day) or placebo added to standard care. At baseline and after treatment for 4, 12 and 26 weeks, we assessed resting energy expenditure (REE) by indirect calorimetry. Furthermore, at baseline and after 26 weeks, we determined the fat fraction in the supraclavicular BAT depot using chemical-shift water-fat MRI at 3T. Liraglutide reduced REE after 4 weeks, which persisted after 12 weeks and tended to be present after 26 weeks (week 26 vs baseline: liraglutide -52 ± 128 kcal/day; P = 0.071, placebo +44 ± 144 kcal/day; P = 0.153, between group P = 0.057). Treatment with liraglutide for 26 weeks did not decrease the fat fraction in supraclavicular BAT (-0.4 ± 1.7%; P = 0.447) compared to placebo (-0.4 ± 1.4%; P = 0.420; between group P = 0.911).

CONCLUSION

Treatment with liraglutide decreases REE in the first 12 weeks and tends to decrease this after 26 weeks without affecting the fat fraction in the supraclavicular BAT depot. These findings suggest reduction in energy intake rather than an increase in REE to contribute to the liraglutide-induced weight loss.

TRIAL REGISTRY NUMBER

NCT01761318.

A compendium of G-protein-coupled receptors and cyclic nucleotide regulation of adipose tissue metabolism and energy expenditure

With the ever-increasing burden of obesity and Type 2 diabetes, it is generally acknowledged that there remains a need for developing new therapeutics. One potential mechanism to combat obesity is to raise energy expenditure via increasing the amount of uncoupled respiration from the mitochondria-rich brown and beige adipocytes. With the recent appreciation of thermogenic adipocytes in humans, much effort is being made to elucidate the signaling pathways that regulate the browning of adipose tissue. In this review, we focus on the ligand-receptor signaling pathways that influence the cyclic nucleotides, cAMP and cGMP, in adipocytes. We chose to focus on G-protein-coupled receptor (GPCR), guanylyl cyclase and phosphodiesterase regulation of adipocytes because they are the targets of a large proportion of all currently available therapeutics. Furthermore, there is a large overlap in their signaling pathways, as signaling events that raise cAMP or cGMP generally increase adipocyte lipolysis and cause changes that are commonly referred to as browning: increasing mitochondrial biogenesis, uncoupling protein 1 (UCP1) expression and respiration.