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

The role of the glucagon-FGF21 axis in improving beta cell function during glucose intolerance and SGLT2 inhibition

OBJECTIVE

Although primarily secreted by the liver, Fibroblast Growth Factor 21 (FGF21) is also expressed in the pancreas, where its function remains unclear. This study aims to elucidate the role of the glucagon-FGF21 interaction in the metabolic benefits of SGLT2 inhibition (SGLT2i) and hypothesizes it is key to enhancing glucose and lipid metabolism in individuals with glucose intolerance or type 2 diabetes (T2D).

METHODS

FGF21, FGF1R, and β-klotho expression in human pancreas was analysed by RNAscope, qPCR and immunofluorescent techniques. Glucose-stimulated insulin secretion (GSIS) assay was used to investigate the effects of recombinant FGF21 (rFGF21) on islets from donors with glucose intolerance or T2D. To explore the role of the glucagon-FGF21 axis in the benefits of SGLT2i, we used WT and Sglt2 knockout (KO) mice fed a chow diet (CD) or a high-fat diet (HFD) and chronically treated with vehicle or dapagliflozin.

RESULTS

Chronic rFGF21 treatment enhanced GSIS in islets from donors with glucose intolerance, with increased FGFR1 expression, suggesting FGF21's greater efficacy in the early stages of disease. In diet-induced insulin-resistant mice, dapagliflozin reduced postprandial glycaemia and elevated plasma glucagon and FGF21 levels. Sglt2 KO mice on a CD showed increased fasting plasma glucagon without changes in FGF21. In diet-induced insulin-resistant Sglt2 KO mice, elevated glucagon and FGF21 levels paralleled chronic dapagliflozin treatment, indicating similar metabolic adaptations in both models.

CONCLUSION

Our findings indicate FGF21 as a crucial mediator in liver-pancreas crosstalk, improving lipid and glucose metabolism, enhancing pancreatic function, and potentiating the therapeutic efficacy of SGLT2i, thereby representing a target for prediabetes treatment.

Free fatty acid receptor 4 modulates dietary sugar preference via the gut microbiota

Sugar preference is a key contributor to the overconsumption of sugar and the concomitant increase in the incidence of diabetes. However, the exact mechanism of its development remains ambiguous. Here we show that the expression of free fatty acid receptor Ffar4, a receptor for long-chain fatty acids, is decreased in patients and mouse models with diabetes, which is associated with high sugar intake. Deletion of intestinal Ffar4 in mice resulted in reduced gut Bacteroides vulgatus and its metabolite pantothenate, leading to dietary sugar preference. Pantothenate promoted the secretion of GLP-1 which inhibited sugar preference by stimulating hepatic FGF21 release, which in turn regulates energy metabolism. These findings uncover a previously unappreciated role of Ffar4 in negatively regulating sugar preference and suggest B. vulgatus-derived pantothenate as a potential therapeutic target for diabetes.

The Chimeric Peptide (GEP44) Reduces Body Weight, Energy Intake, and Energy Expenditure in Diet-Induced Obese Rats

We recently reported that a chimeric peptide (GEP44) targeting the glucagon-like peptide-1 receptor (GLP-1R) and neuropeptide Y1- and Y2-receptors decreased body weight (BW), energy intake and core temperature in diet-induced obese (DIO) male and female mice. Given that GEP44 was found to reduce core temperature (surrogate measure of energy expenditure (EE)) in DIO mice, we hypothesized that GEP44 would reduce EE in male and female high fat diet (HFD)-fed rats. To test this, rats were maintained on a HFD for at least 4 months to elicit DIO prior to undergoing a sequential 2-day vehicle period, 2-day GEP44 (50 nmol/kg) period and a minimum 2-day washout period and detailed measures of energy homeostasis. GEP44 (50 nmol/kg) reduced EE (indirect calorimetry), respiratory exchange ratio (RER), core temperature, activity, energy intake and BW in male and female rats. As in our previous study in mice, GEP44 reduced BW in male and female HFD-fed rats by 3.8 ± 0.2% and 2.3 ± 0.4%, respectively. These effects appear to be mediated by increased lipid oxidation and reductions of energy intake as GEP44 reduced RER and cumulative energy intake in male and female HFD-fed rats. The strong reduction of body weight in response to GEP44 is related to a robust reduction of energy intake, but not to stimulation of EE. The paradoxical finding that GEP44 reduced EE might be secondary to a reduction of diet-induced thermogenesis or might indicate an important mechanism to limit the overall efficacy of GEP44 to prevent further weight loss.

Obesity, Osteoarthritis, and Myokines: Balancing Weight Management Strategies, Myokine Regulation, and Muscle Health

Obesity and osteoarthritis (OA) are increasingly prevalent conditions that are intricately linked, with each exacerbating the other's pathogenesis and worsening patient outcomes. This review explores the dual impact of obesity on OA, highlighting the role of excessive weight in aggravating joint degeneration and the limitations OA imposes on physical activity, which further perpetuates obesity. The role of muscle tissue, particularly the release of myokines during physical activity, is examined in the context of OA and obesity. Myokines such as irisin, IL-6, and myostatin are discussed for their roles in metabolic regulation, inflammation, and tissue repair, offering insights into their potential therapeutic targets. This review emphasizes the importance of supervised weight management methods in parallel with muscle rehabilitation in improving joint health and metabolic balance. The potential for myokine modulation through targeted exercise and weight loss interventions to mitigate the adverse effects of obesity and OA is also discussed, suggesting avenues for future research and therapy development to reduce the burden of these chronic conditions.

FGF21 agonists: An emerging therapeutic for metabolic dysfunction-associated steatohepatitis and beyond

The worldwide epidemics of obesity, hypertriglyceridemia, dyslipidaemia, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease (MASLD)/metabolic dysfunction-associated steatohepatitis (MASH) represent a major economic burden on healthcare systems. Patients with at-risk MASH, defined as MASH with moderate or significant fibrosis, are at higher risk of comorbidity/mortality, with a significant risk of cardiovascular diseases and/or major adverse liver outcomes. Despite a high unmet medical need, there is only one drug approved for MASH. Several drug candidates have reached the phase III development stage and could lead to several potential conditional drug approvals in the coming years. Within the armamentarium of future treatment options, FGF21 analogues hold an interesting position thanks to their pleiotropic effects in addition to their significant effect on both MASH resolution and fibrosis improvement. In this review, we summarise preclinical and clinical data from FGF21 analogues for MASH and explore additional potential therapeutic indications.

FGF21 mediating the Sex-dependent Response to Dietary Macronutrients

Sex is key variable influencing body composition and substrate utilization. At rest, females maintain greater adiposity than males and resist the mobilization of fat. Males maintain greater lean muscle mass and mobilize fat readily. Determining the mechanisms that direct these sex-dependent effects is important for both reproductive and metabolic health. Here, we highlight the fundamental importance of sex in shaping metabolic physiology and assess growing evidence that the hepatokine fibroblast growth factor-21 (FGF21) plays a mechanistic role to facilitate sex-dependent responses to a changing nutritional environment. First, we examine the importance of sex in modulating body composition and substrate utilization. We summarize new data that point toward sex-biased effects of pharmacologic FGF21 administration on these endpoints. When energy is not limited, metabolic responses to FGF21 mirror broader sex differences; FGF21-treated males conserve lean mass at the expense of increased lipid catabolism, whereas FGF21-treated females conserve fat mass at the expense of reduced lean mass. Next, we examine the importance of sex in modulating the endogenous secretion of FGF21 in response to changing macronutrient and energy availability. During the resting state when energy is not limited, macronutrient imbalance increases the secretion of FGF21 more so in males than females. When energy is limited, the effect of sex on both the secretion of FGF21 and its metabolic actions may be reversed. Altogether, we argue that a growing literature supports FGF21 as a plausible mechanism contributing to the sex-dependent mobilization vs preservation of lipid storage and highlight the need for further research.

Hepatic function of glucagon-like peptide-1 and its based diabetes drugs

Incretins are gut-produced peptide-hormones that potentiate insulin secretion, especially after food intake. The concept of incretin was formed more than 100 years ago, even before insulin was isolated and utilized in the treatment of subjects with type 1 diabetes. The first incretin, glucose-dependent insulinotropic polypeptide (GIP), was identified during later 1960's and early 1970's; while the second one, known as glucagon-like peptide-1 (GLP-1), was recognized during 1980's. Today, GLP-1-based therapeutic agents [also known as GLP-1 receptor (GLP-1R) agonists, GLP-1RAs] are among the first line drugs for type 2 diabetes. In addition to serving as incretin, extra-pancreatic functions of GLP-1RAs have been broadly recognized, including those in the liver, despite the absence of GLP-1R in hepatic tissue. The existence of insulin-independent or gut-pancreas-liver axis-independent hepatic function of GLP-1RAs explains why those therapeutic agents are effective in subjects with insulin resistance and their profound effect on lipid homeostasis. Following a brief review on the discovery of GLP-1, we reviewed literature on the exploration of hepatic function of GLP-1 and GLP-1RAs and discussed recent studies on the role of hepatic hormone fibroblast growth factor 21 (FGF21) in mediating function of GLP-1RAs in animal models. This was followed by presenting our perspective views.

A combination of Citrus aurantifolia fruit rind and Theobroma cacao seed extracts supplementation enhances metabolic rates in overweight subjects: a randomized, placebo-controlled, cross-over study

Background and objective

LN19183 is a proprietary, synergistic combination of Citrus aurantifolia fruit rind and Theobroma cacao seed extracts that increased resting energy expenditure (REE) in high-fat diet (HFD)-fed obese rats. The objective of this study was to validate the thermogenic potential of LN19183 in obese Sprague Dawley (SD) rats and to assess its clinical efficacy in a proof-of-concept, randomized, placebo-controlled, cross-over human trial.

Methods

In the rat study, HFD-fed obese rats were supplemented with either HFD alone or with 45, 90, or 180 mg LN19183 per kg body weight (BW) for 28 days. In the human study, 60 overweight adults (male and female, aged 20-39 years) were randomized. Subjects took LN19183 (450 mg) or a matched placebo capsule on two consecutive days in phases one and two of the study, separated by a 10-day washout period. In each phase, on day 1, REE at pre-dose, 60-, 120-, and 180-min post-dose, and on day 2, metabolic rates at pre-dose and post-dose during and 20 min after exercise were measured using indirect calorimetry.

Results

In rats, LN19183 significantly increased REE, reduced BW gain and fat masses, and increased fat and carbohydrate metabolism marker proteins including beta 3 adrenergic receptor (β3-AR), phospho-AMP-activated protein kinase (AMPK), glucagon-like peptide-1 receptor (GLP-1R) in the liver, and serum adiponectin levels. Furthermore, LN19183-supplemented human volunteers increased (P < 0.05, vs. placebo) the metabolic rates at rest and with exercise; their fat oxidation was increased (P < 0.05, vs. placebo) at rest and 20 min post-exercise. The groups' systolic and diastolic blood pressure (BP), heart rates (HR), and safety parameters were comparable.

Conclusion

These observations suggest that LN19183 is a thermogenic botanical composition with no stimulatory effects on BP and HR.

Weight-loss maintenance is accompanied by interconnected alterations in circulating FGF21-adiponectin-leptin and bioactive sphingolipids

Weight loss is often followed by weight regain. Characterizing endocrine alterations accompanying weight reduction and regain may disentangle the complex biology of weight-loss maintenance. Here, we profile energy-balance-regulating metabokines and sphingolipids in adults with obesity undergoing an initial low-calorie diet-induced weight loss and a subsequent weight-loss maintenance phase with exercise, glucagon-like peptide-1 (GLP-1) analog therapy, both combined, or placebo. We show that circulating growth differentiation factor 15 (GDF15) and C16:0-C18:0 ceramides transiently increase upon initial diet-induced weight loss. Conversely, circulating fibroblast growth factor 21 (FGF21) is downregulated following weight-loss maintenance with combined exercise and GLP-1 analog therapy, coinciding with increased adiponectin, decreased leptin, and overall decrements in ceramide and sphingosine-1-phosphate levels. Subgroup analyses reveal differential alterations in FGF21-adiponectin-leptin-sphingolipids between weight maintainers and regainers. Clinically, cardiometabolic health outcomes associate with selective metabokine-sphingolipid remodeling signatures. Collectively, our findings indicate distinct FGF21, GDF15, and ceramide responses to diverse phases of weight change and suggest that weight-loss maintenance involves alterations within the metabokine-sphingolipid axis.

Glucagon resistance and metabolic-associated steatotic liver disease: a review of the evidence

Metabolic-associated steatotic liver disease (MASLD) is closely associated with obesity. MASLD affects over 1 billion adults globally but there are few treatment options available. Glucagon is a key metabolic regulator, and its actions include the reduction of liver fat through direct and indirect means. Chronic glucagon signalling deficiency is associated with hyperaminoacidaemia, hyperglucagonaemia and increased circulating levels of glucagon-like peptide 1 (GLP-1) and fibroblast growth factor 21 (FGF-21). Reduction in glucagon activity decreases hepatic amino acid and triglyceride catabolism; metabolic effects include improved glucose tolerance, increased plasma cholesterol and increased liver fat. Conversely, glucagon infusion in healthy volunteers leads to increased hepatic glucose output, decreased levels of plasma amino acids and increased urea production, decreased plasma cholesterol and increased energy expenditure. Patients with MASLD share many hormonal and metabolic characteristics with models of glucagon signalling deficiency, suggesting that they could be resistant to glucagon. Although there are few studies of the effects of glucagon infusion in patients with obesity and/or MASLD, there is some evidence that the expected effect of glucagon on amino acid catabolism may be attenuated. Taken together, this evidence supports the notion that glucagon resistance exists in patients with MASLD and may contribute to the pathogenesis of MASLD. Further studies are warranted to investigate the direct effects of glucagon on metabolism in patients with MASLD.

Current status and future perspectives of FGF21 analogues in clinical trials

Recent advances in fibroblast growth factor 21 (FGF21) biology and pharmacology have led to the development of several long-acting FGF21 analogues and antibody-based mimetics now in various phases of clinical trials for the treatment of obesity-related metabolic comorbidities. The efficacy of these FGF21 analogues/mimetics on glycaemic control and weight loss is rather mild and inconsistent; nevertheless, several promising therapeutic benefits have been reproducibly observed in most clinical studies, including amelioration of dyslipidaemia (particularly hypertriglyceridaemia) and hepatic steatosis, reduction of biomarkers of liver fibrosis and injury, and resolution of metabolic dysfunction-associated steatohepatitis (MASH). Evidence is emerging that combination therapy with FGF21 analogues and other hormones (such as glucagon-like peptide 1; GLP-1) can synergise their pharmacological benefits, thus maximising the therapeutic efficacy for obesity and its comorbidities.

Development of Syringaldehyde as an Agonist of the GLP-1 Receptor to Alleviate Diabetic Disorders in Animal Models

The phenolic aldehyde syringaldehyde (SA) has been shown to have an antihyperglycemic effect in diabetic rats due to increased glucose utilization and insulin sensitivity. To understand the direct effect of SA on the GLP-1 receptor, STZ-induced diabetic rats were used. The levels of pro-inflammatory cytokines, liver enzymes, and renal function were measured using specific ELISA kits. The mechanisms of SA effects were investigated using CHO-K1 cells, pancreatic Min-6 cells, and cardiomyocyte H9c2 cells. The results indicated that the antihyperglycemic effect of SA in diabetic rats was abolished by blocking the GLP-1 receptor with an antagonist. SA has a direct effect on the GLP-1 receptor when using CHO-K1 cells transfected with the exogenous GLP-1 receptor gene. In addition, SA stimulated insulin production in Min-6 cells by activating GLP-1 receptors. SA caused a dose-dependent rise in GLP-1 receptor mRNA levels in cardiac H9c2 cells. These in vitro results support the notion that SA has a direct effect on the GLP-1 receptor. Otherwise, SA inhibited the increase of pro-inflammatory cytokines, including interleukins and tumor TNF-α, in type 1 diabetic rats in a dose-dependent manner. Moreover, as with liraglutide, SA reduced plasma lipid profiles, including total cholesterol and triglyceride, in mixed diet-induced type 2 diabetic rats. Intriguingly, chronic treatment with SA (as with liraglutide) reversed the functions of both the liver and the kidney in these diabetic rats. SA displayed less efficiency in reducing body weight and food consumption compared to liraglutide. In conclusion, SA effectively activates GLP-1 receptors, resulting in a reduction in diabetic-related complications in rats. Therefore, it is beneficial to develop SA as a chemical agonist for clinical applications in the future.

Hormone-based pharmacotherapy for metabolic dysfunction-associated fatty liver disease

Metabolic dysfunction-associated fatty liver disease (MAFLD) has reached epidemic proportions globally in parallel to the rising prevalence of obesity. Despite its significant burden, there is no approved pharmacotherapy specifically tailored for this disease. Many potential drug candidates for MAFLD have encountered setbacks in clinical trials, due to safety concerns or/and insufficient therapeutic efficacy. Nonetheless, several investigational drugs that mimic the actions of endogenous metabolic hormones, including thyroid hormone receptor β (THRβ) agonists, fibroblast growth factor 21 (FGF21) analogues, and glucagon-like peptide-1 receptor agonists (GLP-1RAs), showed promising therapeutic efficacy and excellent safety profiles. Among them, resmetirom, a liver-targeted THRβ-selective agonist, has met the primary outcomes in alleviation of metabolic dysfunction-associated steatohepatitis (MASH), the advanced form of MAFLD, and liver fibrosis in phase-3 clinical trials. These hormone-based pharmacotherapies not only exhibit varied degrees of therapeutic efficacy in mitigating hepatic steatosis, inflammation and fibrosis, but also improve metabolic profiles. Furthermore, these three hormonal agonists/analogues act in a complementary manner to exert their pharmacological effects, suggesting their combined therapies may yield synergistic therapeutic benefits. Further in-depth studies on the intricate interplay among these metabolic hormones are imperative for the development of more efficacious combination therapies, enabling precision management of MAFLD and its associated comorbidities.

Poly-Agonist Pharmacotherapies for Metabolic Diseases: Hopes and New Challenges

The use of glucagon-like peptide-1 (GLP-1) receptor-based multi-agonists in the treatment of type 2 diabetes and obesity holds great promise for improving glycaemic control and weight management. Unimolecular dual and triple agonists targeting multiple gut hormone-related pathways are currently in clinical trials, with recent evidence supporting their efficacy. However, significant knowledge gaps remain regarding the biological mechanisms and potential adverse effects associated with these multi-target agents. The mechanisms underlying the therapeutic efficacy of GLP-1 receptor-based multi-agonists remain somewhat mysterious, and hidden threats may be associated with the use of gut hormone-based polyagonists. In this review, we provide a critical analysis of the benefits and risks associated with the use of these new drugs in the management of obesity and diabetes, while also exploring new potential applications of GLP-1-based pharmacology beyond the field of metabolic disease.

Protein appetite as an integrator in the obesity system: the protein leverage hypothesis

Despite the large volume and extensive range of obesity research, there is substantial disagreement on the causes and effective preventative strategies. We suggest the field will benefit from greater emphasis on integrative approaches that examine how various potential contributors interact, rather than regarding them as competing explanations. We demonstrate the application of nutritional geometry, a multi-nutrient integrative framework developed in the ecological sciences, to obesity research. Such studies have shown that humans, like many other species, regulate protein intake more strongly than other dietary components, and consequently if dietary protein is diluted there is a compensatory increase in food intake-a process called protein leverage. The protein leverage hypothesis (PLH) proposes that the dilution of protein in modern food supplies by fat and carbohydrate-rich highly processed foods has resulted in increased energy intake through protein leverage. We present evidence for the PLH from a variety of sources (mechanistic, experimental and observational), and show that this mechanism is compatible with many other findings and theories in obesity research. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part II)'.