Effects of central FGF21 infusion on the hypothalamus-pituitary-thyroid axis and energy metabolism in rats

Intracerebroventricular prokineticin 2 infusion may play a role on the hypothalamus-pituitary-thyroid axis and energy metabolism

AIM

The hypothesis of this study is to determine the effects of intracerebroventricular (icv) prokineticin 2 infusion on food consumption and body weight and to elucidate whether it has effects on energy expenditure via the hypothalamus-pituitary-thyroid (HPT) axis in adipose tissue.

MATERIAL AND METHODS

A total of 40 rats were used in the study and 4 groups were established: Control, Sham, Prokineticin 1.5 and Prokineticin 4.5 (n=10). Except for the Control group, rats were treated intracerebroventricularly via osmotic minipumps, the Sham group was infused with aCSF (vehicle), and the Prokineticin 1.5 and Prokineticin 4.5 groups were infused with 1.5 nMol and 4.5 nMol prokineticin 2, respectively. Food and water consumption and body weight were monitored during 7-day infusion in all groups. At the end of the infusion, the rats were decapitated and serum TSH, fT4 and fT3 levels were determined by ELISA. In addition, PGC-1α and UCP1 gene expression levels in white adipose tissue (WAT) and brown adipose tissue (BAT), TRH from rat hypothalamic tissue were determined by real-time PCR.

RESULTS

Icv prokineticin 2 (4.5 nMol) infusion had no effect on water consumption but reduced daily food consumption and body weight (p<0.05). Icv prokineticin 2 (4.5 nMol) infusion significantly increased serum TSH, fT4 and fT3 levels when compared to Control and Sham groups (p<0.05). Also, icv prokineticin 2 (4.5 nMol) infusion increased the expression of TRH in the hypothalamus tissue and expression of PGC-1α UCP1 in the WAT and BAT (p<0.05).

CONCLUSION

Icv prokineticin 2 (4.5 nMol) infusion may suppress food consumption via its receptors in the hypothalamus and reduce body weight by stimulating energy expenditure and thermogenesis in adipose tissue through the HPT axis.

Intracerebroventricular injection of spexin stimulates the hypothalamic-pituitary-testicular axis and increases the secretion of male reproductive hormones in rats

BACKGROUND

Male reproductive functions are regulated in the hypothalamic-pituitary-gonadal (HPG) axis. Any problem in this axis would lead to the deterioration of reproductive functions. The present study aimed to investigate the effects of intracerebroventricular (icv) Spexin (SPX) infusion on the HPG axis in detail.

METHODS

40 Wistar albino rats were divided into four groups: control, sham, SPX 30 nmol and SPX 100 nmol (n=10). 30 nmol/1 µl/hour SPX was administered icv to the rats in the SPX 30 nmol group for 7 days, while rats in the SPX 100 nmol group were administered 100 nmol/1 µl/hour SPX. On the 7th day, the rats were decapitated, blood and tissue samples were collected. Serum LH, FSH and testosterone levels were determined with the ELISA method, GnRH mRNA expression level was determined in hypothalamus with the RT-PCR method. Seminiferous tubule diameter and epithelial thickness were determined with the hematoxylin-eosin staining method.

RESULTS

SPX infusion was increased GnRH mRNA expression in the hypothalamus tissue independent of the dose (p<0.05). Serum LH, FSH and testosterone levels in the SPX groups were increased when compared to the control and sham groups independent of the dose (p <0.05). Histological analysis revealed that SPX infusion did not lead to any changes in seminiferous epithelial thickness, while the tubule diameter increased in the SPX groups (p<0.05).

CONCLUSION

The study findings demonstrated that icv SPX infusion stimulated the HPG axis and increased the secretion of male reproductive hormones.

Intracerebroventricular PROK2 infusion could increase the secretion of male reproductive hormones by stimulating the HPG axis

BACKGROUND

Prokineticin 2 (PROK2), an important neuropeptide that plays a key role in the neuronal migration of gonadotropin-releasing hormone (GnRH) in the hypothalamus, is known to have regulatory effects on the gonads. In the present study, the impact of intracerebroventricular (icv) PROK2 infusion on hypothalamic-pituitary-gonadal axis (HPG) hormones, testicular tissues, and sperm concentration was investigated.

METHODS AND RESULTS

Rats were randomly divided into four groups: control, sham, PROK2 1.5 and PROK2 4.5. Rats in the PROK2 1.5 and PROK2 4.5 groups were administered 1.5 nmol and 4.5 nmol PROK2 intracerebroventricularly for 7 days via an osmotic mini pump (1 µl/h), respectively. Rat blood serum follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone hormone levels were determined with the ELISA method in the blood samples after 7 days of infusion. GnRH mRNA expression was determined with the RT-PCR in hypothalamus tissues. analyze Sperm concentration was determined, and testicular tissue was examined histologically with the hematoxylin-eosin staining method. It was observed that GnRH mRNA expression increased in both PROK2 infusion groups. Serum FSH, LH and testosterone hormone levels also increased in these groups. Although sperm concentration increased in PROK2 infusion groups when compared to the control and sham, the differences were not statistically significant. Testicular tissue seminiferous epithelial thickness was higher in the PROK2 groups when compared to the control and sham groups.

CONCLUSION

The present study findings demonstrated that icv PROK2 infusion induced the HPG axis. It could be suggested that PROK2 could be a potential agent in the treatment of male infertility induced by endocrinological defects.

Fibroblast growth factor 21: An emerging pleiotropic regulator of lipid metabolism and the metabolic network

Fibroblast growth factor 21 (FGF21) was originally identified as an important metabolic regulator which plays a crucial physiological role in regulating a variety of metabolic parameters through the metabolic network. As a novel multifunctional endocrine growth factor, the role of FGF21 in the metabolic network warrants extensive exploration. This insight was obtained from the observation that the FGF21-dependent mechanism that regulates lipid metabolism, glycogen transformation, and biological effectiveness occurs through the coordinated participation of the liver, adipose tissue, central nervous system, and sympathetic nerves. This review focuses on the role of FGF21-uncoupling protein 1 (UCP1) signaling in lipid metabolism and how FGF21 alleviates non-alcoholic fatty liver disease (NAFLD). Additionally, this review reveals the mechanism by which FGF21 governs glucolipid metabolism. Recent research on the role of FGF21 in the metabolic network has mostly focused on the crucial pathway of glucolipid metabolism. FGF21 has been shown to have multiple regulatory roles in the metabolic network. Since an adequate understanding of the concrete regulatory pathways of FGF21 in the metabolic network has not been attained, this review sheds new light on the metabolic mechanisms of FGF21, explores how FGF21 engages different tissues and organs, and lays a theoretical foundation for future in-depth research on FGF21-targeted treatment of metabolic diseases.

Intracerebroventricular BDNF infusion may reduce cerebral ischemia/reperfusion injury by promoting autophagy and suppressing apoptosis

Here, it was aimed to investigate the effects of intracerebroventricular (ICV) Brain Derived Neurotrophic Factor (BDNF) infusion for 7 days following cerebral ischemia (CI) on autophagy in neurons in the penumbra. Focal CI was created by the occlusion of the right middle cerebral artery. A total of 60 rats were used and divided into 4 groups as Control, Sham CI, CI and CI + BDNF. During the 7-day reperfusion period, aCSF (vehicle) was infused to Sham CI and CI groups, and BDNF infusion was administered to the CI + BDNF group via an osmotic minipump. By the end of the 7th day of reperfusion, Beclin-1, LC3, p62 and cleaved caspase-3 protein levels in the penumbra area were evaluated using Western blot and immunofluorescence. BDNF treatment for 7 days reduced the infarct area after CI, induced the autophagic proteins Beclin-1, LC3 and p62 and suppressed the apoptotic protein cleaved caspase-3. Furthermore, rotarod and adhesive removal test times of BDNF treatment started to improve from the 4th day, and the neurological deficit score from the 5th day. ICV BDNF treatment following CI reduced the infarct area by inducing autophagic proteins Beclin-1, LC3 and p62 and inhibiting the apoptotic caspase-3 protein while its beneficial effects were apparent in neurological tests from the 4th day.

Spexin may induce mitochondrial biogenesis in white and brown adipocytes via the hypothalamus-pituitary-thyroid (HPT) axis

AIM

The present study aimed to investigate the effect of the intracerebroventricular (icv) administration of spexin on the hypothalamus-pituitary-thyroid (HPT) axis (TRH, TSH, T4 and T3 hormones) and energy expenditure (PGC-1α and UCP1 genes) in white adipose (WAT) and brown adipose tissues (BAT) in rats. Furthermore, the study aimed to determine the effects of spexin on food-water consumption and body weight of rats.

MATERIAL AND METHOD

The study was conducted with 40 male rats that were divided into 4 groups: Control, Sham, Spexin 30 and Spexin 100 (n = 10). Spexin (1 μl/hour) was administered to rats other than those in the control group for 7 days with osmotic minipumps intracerebroventricularly, artificial cerebrospinal fluid (vehicle) was administered to the Sham group, and 30 nMol and 100 nMol spexin was infused to the Spexin 30 and Spexin 100 groups, respectively. Food-water consumption and body weight of the rats were monitored during the experiments. After the seven-day infusion, the rats were decapitated and serum TSH, fT4 and fT3 levels were determined with ELISA on rat blood samples. Also, TRH gene expression levels from the hypothalamus tissues and PGC-1α and UCP1 expression levels from WAT and BAT were determined by real-time PCR.

FINDINGS

It was determined that icv spexin infusion reduced daily food consumption and body weight without leading to a significant change in water consumption (p < 0.05). Icv spexin infusion significantly decreased serum TSH, and increased fT4 and fT3 levels when compared to control and sham groups (p < 0.05). Moreover, icv spexin infusion increased the TRH expressions in the hypothalamus tissues and PGC-1α UCP1 in the WAT and BAT (p < 0.05).

CONCLUSION

Icv Spexin infusion may have effects on food consumption and body weight as well as, thyroid hormones and energy metabolism.

Fibroblast growth factor receptor 1/Klothoβ agonist BFKB8488A improves lipids and liver health markers in patients with diabetes or NAFLD: A phase 1b randomized trial

BACKGROUND AND AIMS

BFKB8488A is a bispecific antibody targeting fibroblast growth factor receptor 1c and Klothoβ. This phase 1b study assessed safety, tolerability, pharmacokinetics, immunogenicity, and pharmacodynamics of BFKB8488A in patients with type 2 diabetes mellitus (T2DM) or NAFLD.

APPROACH AND RESULTS

Patients were randomized to receive multiple doses of BFKB8488A at various dose levels and dosing intervals (weekly, every 2 weeks, or every 4 weeks) or placebo for 12 weeks. The primary outcome was the safety of BFKB8488A. Overall, 153 patients (T2DM: 91; NAFLD: 62) were enrolled and received at least one dose of treatment. Of these, 102 patients (62.7%) reported at least one adverse event (BFKB8488A: 83 [68.6%]; placebo: 19 [59.4%]). BFKB8488A exhibited nonlinear pharmacokinetics, with greater than dose-proportional increases in exposure. The treatment-emergent antidrug antibody incidence was 22.7%. Overall, trends in exposure-dependent increases in high-density lipoprotein (HDL) and decreases in triglyceride levels were observed. Decreases in alanine aminotransferase and aspartate aminotransferase were 0.7% and 9.2% for medium exposure and 7.3% and 11.2% for high-exposure tertiles, compared with increases of 7.5% and 17% in the placebo group, respectively, at Day 85. In patients with NAFLD, the mean decrease from baseline liver fat was 13.0%, 34.5%, and 49.0% in the low-, medium-, and high-exposure tertiles, respectively, compared with 0.1% with placebo at Day 85.

CONCLUSIONS

BFKB8488A was adequately tolerated in patients with T2DM or NAFLD, leading to triglyceride reduction, HDL improvements, and trends in improvement in markers of liver health for both populations and marked liver fat reduction in patients with NAFLD. ( ClinicalTrials.gov : NCT03060538).

Effects of central FGF21 infusion on the glucose homeostasis in rats (brain-pancreas axis)

INTRODUCTION

Glucose homeostasis is a physiological process mediated by a variety of hormones. Fibroblast growth factor (FGF) 21 is a protein expressed in the liver, adipose tissue, muscle and pancreas and exerts actions in multiple targets including adipose, liver, pancreas and hypothalamus. The aim of this study was to examine the possible involvement of FGF21 in pancreatic and central control of glucose by measuring reflective changes in the release of insulin and glucagon.

METHODS

Thirty adult male Wistar Albino rats were divided; Control, PD + aCSF, PD + FGF21 groups (n = 10). Effects of intracerebroventricular (icv) FGF21 administration to pancreatic denervated (PD) rats. Agouti-related protein (AgRP), Pro-opiomelanocortin (POMC) levels and blood glucose homeostasis were investigated.

RESULTS

Administration of FGF21 to 3rd ventricle increased food consumption but body weight didn't change significantly. AgRP level increased, pancreatic insulin levels increased, and glucagon level decreased.

CONCLUSION

Central FGF21 administration is effective in regulating blood glucose homeostasis by increasing the amount and efficiency of insulin and changing glucose use.

Advances in FGFs for diabetes care applications

BACKGROUND

Diabetes mellitus (DM) is an endocrine and metabolic disease caused by a variety of pathogenic factors, including genetic factors, environmental factors and behavior. In recent decades, the number of cases and the prevalence of diabetes have steadily increased, and it has become one of the most threatening diseases to human health in the world. Currently, insulin is the most effective and direct way to control hyperglycemia for diabetes treatment at a low cost. However, hypoglycemia is often a common complication of insulin treatment. Moreover, with the extension of treatment time, insulin resistance, considered the typical adverse symptom, can appear. Therefore, it is urgent to develop new targets and more effective and safer drugs for diabetes treatment to avoid adverse reactions and the insulin tolerance of traditional hypoglycemic drugs.

SCOPE OF REVIEW

In recent years, it has been found that some fibroblast growth factors (FGFs), including FGF1, FGF19 and FGF21, can safely and effectively reduce hyperglycemia and have the potential to be developed as new drugs for the treatment of diabetes. FGF23 is also closely related to diabetes and its complications, which provides a new approach for regulating blood glucose and solving the problem of insulin tolerance.

MAJOR CONCLUSIONS

This article reviews the research progress on the physiology and pharmacology of fibroblast growth factor in the treatment of diabetes. We focus on the application of FGFs in diabetes care and prevention.

Silencing of hypothalamic FGF11 prevents diet-induced obesity

Fibroblast growth factor 11 (FGF11) is a member of the intracellular fibroblast growth factor family. Here, we report the central role of FGF11 in the regulation of metabolism. Lentiviral injection of Fgf11 shRNA into the arcuate nucleus of the mouse hypothalamus decreased weight gain and fat mass, increased brown adipose tissue thermogenesis, and improved glucose and insulin intolerances under high-fat diet conditions. Fgf11 was expressed in the NPY–expressing neurons, and Fgf11 knockdown considerably decreased Npy expression and projection, leading to increased expression of tyrosine hydroxylase in the paraventricular nucleus. Mechanistically, FGF11 regulated Npy gene expression through the glycogen synthase kinase 3–cAMP response element-binding protein pathway. Our study defines the physiological significance of hypothalamic FGF11 in the regulation of metabolism in response to overnutrition such as high-fat diet.

Signaling pathways in obesity: mechanisms and therapeutic interventions

Obesity is a complex, chronic disease and global public health challenge. Characterized by excessive fat accumulation in the body, obesity sharply increases the risk of several diseases, such as type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and is linked to lower life expectancy. Although lifestyle intervention (diet and exercise) has remarkable effects on weight management, achieving long-term success at weight loss is extremely challenging, and the prevalence of obesity continues to rise worldwide. Over the past decades, the pathophysiology of obesity has been extensively investigated, and an increasing number of signal transduction pathways have been implicated in obesity, making it possible to fight obesity in a more effective and precise way. In this review, we summarize recent advances in the pathogenesis of obesity from both experimental and clinical studies, focusing on signaling pathways and their roles in the regulation of food intake, glucose homeostasis, adipogenesis, thermogenesis, and chronic inflammation. We also discuss the current anti-obesity drugs, as well as weight loss compounds in clinical trials, that target these signals. The evolving knowledge of signaling transduction may shed light on the future direction of obesity research, as we move into a new era of precision medicine.

Serum Fibroblast Growth Factor 21 Levels in Children and Adolescents with Hashimoto’s Thyroiditis before and after l-Thyroxin Medication: A Prospective Study

Backgrounds and Objectives: Fibroblast growth factor 21 (FGF-21) is a complex hormone, sharing common sites of action with thyroid hormones. We investigated the association among FGF-21 levels, resting metabolic rate (RMR), and l-thyroxin (LT4) treatment in children and adolescents with Hashimoto’s thyroiditis. Materials and Methods: A total of 60 youngsters with chronic autoimmune thyroiditis (AIT) (30 with subclinical hypothyroidism, 30 with euthyroidism) and 30 age and sex-matched healthy participants (5–18 years old) were enrolled in the study. Anthropometric, biochemical parameters, and RMR levels were assessed in all participants; serum FGF-21 levels were measured in the control group and the group with subclinical hypothyroidism before and six months after medication with LT4. Results: FGF-21 levels were lower in the treatment group compared with the healthy ones, but this difference was not statistically significant (p > 0.05); despite the increase in FGF-21 levels after six months of LT4 treatment, this difference was not statistically significant (p > 0.05). Free thyroxin (FT4) levels correlated well with FGF-21 levels (r = 0.399, p < 0.01), but further analysis revealed no interaction between these two variables. Both patient groups presented elevated triglyceride (TG) levels compared to controls (p < 0.05). LT4 treatment had no impact on RMR and lipid or liver or glycaemic parameters. An increase in fat mass and fat-free mass were reported, independently of FGF-21 levels. Conclusions: In youngsters with subclinical hypothyroidism due to Hashimoto’s thyroiditis, the serum FGF-21 levels are not significantly lower than in healthy individuals and increase after treatment with LT4 without a statistical significance. Further studies with a large number of young patients and severe hypothyroidism are recommended to confirm our results.

Efruxifermin, a long-acting Fc-fusion FGF21 analogue, reduces body weight gain but does not increase sympathetic tone or urine volume in Sprague Dawley rats

BACKGROUND AND PURPOSE

Analogues of fibroblast growth factor 21 (FGF21) demonstrate diverse metabolic benefits in preclinical models of type 2 diabetes, dyslipidaemia, and non-alcoholic steatohepatitis (NASH), but clinical responses with different analogues are inconsistent. Efruxifermin is an Fc-FGF21 fusion protein with prolonged half-life and enhanced receptor affinity compared to native human FGF21. Efruxifermin is in clinical trials for the treatment of NASH.

EXPERIMENTAL APPROACH

Efruxifermin was administered weekly to male and female Sprague Dawley rats for 4 or 26 weeks. Body and organ weights, macro- and microscopic pathology, clinical chemistry, blood cytology, and serum and urine biomarkers were analysed to characterise the pharmacodynamics of efruxifermin, and to investigate potential nonclinical toxicities following chronic administration of supra-pharmacological doses of efruxifermin.

KEY RESULTS

Efruxifermin significantly reduced body weight gain after 4 and 26 weeks, despite increasing food intake. Changes in tissue pathology, clinical chemistry and serum biomarkers generally appeared to be associated with weight loss, except for a significant decrease in urine volume in both males and females without perturbed electrolyte balance. Markers of sympathetic activation, urinary corticosterone, and ratio of adrenal-to-body weight were unchanged.

CONCLUSION AND IMPLICATIONS

Efruxifermin attenuated body weight gain, consistent with other FGF21 analogues. In contrast to at least one other FGF21 analogue, efruxifermin decreased rather than increased urine volume. The absence of an increase in sympathetic tone in rats mirrors the unchanged salivary cortisol and systemic blood pressure following efruxifermin treatment in humans.

The therapeutic potential of FGF21 in metabolic diseases: from bench to clinic

Fibroblast growth factor 21 (FGF21) is a stress-inducible hormone that has important roles in regulating energy balance and glucose and lipid homeostasis through a heterodimeric receptor complex comprising FGF receptor 1 (FGFR1) and β-klotho. Administration of FGF21 to rodents or non-human primates causes considerable pharmacological benefits on a cluster of obesity-related metabolic complications, including a reduction in fat mass and alleviation of hyperglycaemia, insulin resistance, dyslipidaemia, cardiovascular disorders and non-alcoholic steatohepatitis (NASH). However, native FGF21 is unsuitable for clinical use owing to poor pharmacokinetic and biophysical properties. A large number of long-acting FGF21 analogues and agonistic monoclonal antibodies for the FGFR1-β-klotho receptor complexes have been developed. Several FGF21 analogues and mimetics have progressed to early phases of clinical trials in patients with obesity, type 2 diabetes mellitus and NASH. In these trials, the primary end points of glycaemic control have not been met, whereas substantial improvements were observed in dyslipidaemia, hepatic fat fractions and serum markers of liver fibrosis in patients with NASH. The complexity and divergence in pharmacology and pathophysiology of FGF21, interspecies variations in FGF21 biology, the possible existence of obesity-related FGF21 resistance and endogenous FGF21 inactivation enzymes represent major obstacles to clinical implementation of FGF21-based pharmacotherapies for metabolic diseases.

FGF21 Mimics a Fasting-Induced Metabolic State and Increases Appetite in Zebrafish

Fibroblast growth factor 21 (FGF21) is a member of the FGF superfamily that acts in an endocrine manner. FGF21 is a key regulator of energy balance and metabolism in mammals, and has emerged as a therapeutic potential for treating obesity and diabetes. Here, we report that mRNAs encoding FGF21 and its receptors are widely distributed within the zebrafish tissues and are importantly modulated by fasting (decreased in brain and liver, and increased in gut). FGF21 stimulates food intake in zebrafish, likely in part by modulating brain npy/agrp and nucb2/nesfatin-1 and gut ghrelin and cck mRNA expression. In accordance with this orexigenic role, the expression of FGF21 and its receptors were observed to increase preprandially and decrease post-feeding in the foregut and/or liver. Finally, we found important evidence in favor of a role for FGF21 in regulating glucose and lipid metabolism in the zebrafish liver in a way that mimics a fasting metabolic state.

Tanycytes Regulate Lipid Homeostasis by Sensing Free Fatty Acids and Signaling to Key Hypothalamic Neuronal Populations via FGF21 Secretion

The hypothalamus plays a key role in the detection of energy substrates to regulate energy homeostasis. Tanycytes, the hypothalamic ependymo-glia, are located at a privileged position to integrate multiple peripheral inputs. We observed that tanycytes produce and secrete Fgf21 and are located close to Fgf21-sensitive neurons. Fasting, likely via the increase in circulating fatty acids, regulates this central Fgf21 production. Tanycytes store palmitate in lipid droplets and oxidize it, leading to the activation of a reactive oxygen species (ROS)/p38-MAPK signaling pathway, which is essential for tanycytic Fgf21 expression upon palmitate exposure. Tanycytic Fgf21 deletion triggers an increase in lipolysis, likely due to impaired inhibition of key neurons during fasting. Mice deleted for tanycytic Fgf21 exhibit increased energy expenditure and a reduction in fat mass gain, reminiscent of a browning phenotype. Our results suggest that tanycytes sense free fatty acids to maintain body lipid homeostasis through Fgf21 signaling within the hypothalamus.

Effects of Short-Term Fasting and Different Overfeeding Diets on Thyroid Hormones in Healthy Humans

Background: A greater decrease in 24-hour energy expenditure (EE) during fasting and a smaller increase in 24-hour EE during low-protein overfeeding (metabolic "thrifty" phenotype) predict weight gain. As thyroid hormones (TH) are implicated in energy intake and metabolism, we assessed whether: (i) TH concentrations are altered by 24-hour fasting or overfeeding diets with varying protein content and (ii) diet-related changes in TH correlate with concomitant changes in EE. Methods: Fifty-eight euthyroid healthy subjects with normal glucose regulation underwent 24-hour dietary interventions including fasting, eucaloric feeding, and five overfeeding diets in a crossover design within a whole-room indirect calorimeter to measure the 24-hour EE. Overfeeding diets (200% of energy requirements) included three diets with 20% protein, one diet with 3% protein (low-protein overfeeding diet [LPF]: 46% fat), and one diet with 30% protein (high-protein overfeeding diet [HPF]: 44% fat, n = 51). Plasma free thyroxine (fT4), free triiodothyronine (fT3), and fibroblast growth factor 21 (FGF21) concentrations were measured after overnight fast the morning of and after each diet. Results: On average, fT4 increased by 8% (+0.10 ng/dL, 95% confidence interval [CI 0.07-0.13], p < 0.0001) and fT3 decreased by 6% (-0.17 pg/mL [CI -0.27 to -0.07], p = 0.001) after 24-hour fasting, whereas both fT4 and fT3 decreased by 5% (-0.07 ng/dL [CI -0.11 to -0.04], p < 0.0001) and 4% (-0.14 pg/mL [CI -0.24 to -0.04], p = 0.008) following HPF, respectively. Greater decreases in fT3 after HPF are associated with larger decreases in FGF21 (r = 0.40, p = 0.005). Following LPF, the mean fT3 increased by 6% (+0.14 pg/mL [CI 0.05-0.2], p = 0.003) with no change in fT4 (p = 0.7). No changes in TH were observed after normal-protein overfeeding diets (all p > 0.1). No associations were observed between TH concentrations and diet-related changes in 24-hour EE during any diet (all p > 0.07). Conclusions: Acute (200%) short-term (24 hours) changes in food intake induce small changes in TH concentrations only after diets with low (0% fasting and 3% protein overfeeding) or high (30% protein overfeeding) protein content. The fT3-FGF21 association after high-protein overfeeding suggests a role for TH in inhibiting FGF21 secretion by the liver during protein excess. These results indicate that TH are involved in protein metabolism; however, they do not mediate the short-term EE response to diets that characterize the metabolic phenotypes and determine the individual susceptibility to weight gain.

Fibroblast growth factor 21: an endocrine inhibitor of sugar and alcohol appetite

Fibroblast growth factor 21 (FGF21) is a liver-derived hormone with pleiotropic metabolic effects. Its production is induced by various dietary imbalances in mice (including low-protein and ketogenic diets, fructose feeding and ethanol), hinting that it might influence food preference given the role of the liver in maintaining homeostatic levels of circulating nutrients. In 2016, it was shown that FGF21 selectively inhibits consumption of sugars and the primary product of their fermentation, ethanol, but not intake of fat, protein or complex carbohydrates. Since then, studies have sought to unravel this selectivity, its physiological purpose and translational relevance, as well as delineate the neural mechanisms involved. Initially found to impact ingestive behaviours in mice and non-human primates, FGF21 is also induced in humans by sugars and, far more dramatically, by acute alcohol intake. Genetic studies have revealed that patterns of weekly candy and alcohol consumption are associated with genetic variants in FGF21 and its co-receptor β-klotho (KLB), suggesting that liking for sugar, and fermented sugar, may be influenced by natural variation in FGF21 signal strength in humans. Herein, we discuss our nascent understanding of FGF21 as a selective negative regulator of sugar and alcohol appetite as well as reasons why such a peculiar system may have evolved in mammals. Uncovering the regulatory network governing sugar, and fermented sugar, intake could provide new opportunities to improve dietary choices in a population suffering from Western diet-induced diseases fuelled in part by a runaway sweet - and alcohol - tooth.

Small molecules for fat combustion: targeting thermosensory and satiety signals in the central nervous system

Brown adipose tissue (BAT) dissipates fatty acids as heat to maintain body temperature in cold environments. The existence of BAT and beige cells in human adults supplies a promising weight-reduction therapy. The central thermogenic regulation descends through an excitatory neural pathway from the hypothalamus, medullar and spine towards BAT. This sympathoexcitatory thermogenic circuit is controlled by GABAergic (γ-aminobutyric acid) signaling from the thermoregulatory center in the preoptic area and the satiety center in the ventromedial nucleus of the hypothalamus. This review summarizes recent research progresses in thermogenic regulators targeting thermosensory and satiety signals in the central nervous system, and speculates on their potential as antiobesity agents.