Dual effects of fibroblast growth factor 21 on hepatic energy metabolism

The aim of this study was to investigate the mechanisms by which FGF21 affects hepatic integration of carbohydrate and fat metabolism in Siberian hamsters, a natural model of adiposity. Twelve aged matched adult male Siberian hamsters maintained in their long day fat state since birth were randomly assigned to one of two treatment groups and were continuously infused with either vehicle (saline; n=6) or recombinant human FGF21 protein (1 mg/kg/day; n=6) for 14 days. FGF21 administration caused a 40% suppression (P<0.05) of hepatic pyruvate dehydrogenase complex (PDC), the rate-limiting step in glucose oxidation, a 34% decrease (P<0.05) in hepatic acetylcarnitine accumulation, an index of reduced PDC flux, a 35% increase (P<0.05) in long-chain acylcarnitine content (an index of flux through β-oxidation) and a 47% reduction (P<0.05) in hepatic lipid content. These effects were underpinned by increased protein abundance of PD kinase-4 (a negative regulator of PDC), the phosphorylated (inhibited) form of acetyl-CoA carboxylase (ACC, a negative regulator of delivery of fatty acids into the mitochondria), and the transcriptional co-regulators of energy metabolism peroxisome proliferator activated receptor gamma co-activator alpha (PGC1 and sirtuin-1 (SIRT-1). These findings provide novel mechanistic basis to support the notion that FGF21 exerts profound metabolic benefits in the liver by modulating nutrient flux through both carbohydrate (mediated by a PDK4-mediated suppression of PDC activity) and fat (mediated by deactivation of ACC) metabolism, and therefore may be an attractive target for protection from increased hepatic lipid content and insulin resistance that frequently accompany obesity and diabetes

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.</p

Anorectic and aversive effects of GLP-1 receptor agonism are mediated by brainstem cholecystokinin neurons, and modulated by GIP receptor activation

This work was funded by an MRC Career Development Award (MR/ P009824/1 and MR/P009824/2) to GD’A, as well as an MRC grant to SML/GD’A (MR/T032669/1), a BBSRC grant to SML (BB/M001067/1), and an additional direct contribution from Eli Lilly. D.J.H. was sup- ported by MRC (MR/N00275X/1 and MR/S025618/1), Diabetes UK (17/ 0005681), and the European Research Council (ERC) under the Eu- ropean Union’s Horizon 2020 research and innovation programme (Starting Grant 715884 to D.J.H.). AC was supported for part of this project by a travel grant from the Italian Society of Pharmacology and a fellowship from the Veronesi Foundation (Italy).Peer reviewedPublisher PD

Colesevelam enhances the beneficial effects of brown fat activation on hyperlipidemia and atherosclerosis development

Aims Brown fat activation accelerates the uptake of cholesterol-enriched remnants by the liver and thereby lowers plasma cholesterol, consequently protecting against atherosclerosis development. Hepatic cholesterol is then converted into bile acids (BAs) that are secreted into the intestine and largely maintained within the enterohepatic circulation. We now aimed to evaluate the effects of prolonged brown fat activation combined with inhibition of intestinal BA reabsorption on plasma cholesterol metabolism and atherosclerosis development and results APOE∗3-Leiden.CETP mice with humanized lipoprotein metabolism were treated for 9 weeks with the selective b3-adrenergic receptor (AR) agonist CL316,243 to substantially activate brown fat. Prolonged b3-AR agonism reduced faecal BA excretion (-31%), while markedly increasing plasma levels of total BAs (258%), cholic acid-derived BAs (295%), and chenodeoxycholic acid-derived BAs (217%), and decreasing the expression of hepatic genes involved in BA production. In subsequent experiments, mice were additionally treated with the BA sequestrant Colesevelam to inhibit BA reabsorption. Concomitant intestinal BA sequestration increased faecal BA excretion, normalized plasma BA levels, and reduced hepatic cholesterol. Moreover, concomitant BA sequestration further reduced plasma total cholesterol (-49%) and non-high-density lipoprotein cholesterol (-56%), tended to further attenuate atherosclerotic lesion area (-54%). Concomitant BA sequestration further increased the proportion of lesion-free valves (34%) and decreased the relative macrophage area within the lesion (-26%), thereby further increasing the plaque stability index (44%). Conclusion BA sequestration prevents the marked accumulation of plasma BAs as induced by prolonged brown fat activation, thereby further improving cholesterol metabolism and reducing atherosclerosis development. These data suggest that combining brown fat activation with BA sequestration is a promising new therapeutic strategy to reduce hyperlipidaemia and cardiovascular diseases

Counterregulatory response to hypoglycemia during a hypoglycemic clamp in people with type 2 diabetes treated with tirzepatide

IntroductionTo evaluate counterregulatory hormonal responses during a hypoglycemic clamp with tirzepatide.MethodsParticipants with type 2 diabetes (N=42) were randomized to tirzepatide (15 mg) or placebo for 12 weeks in a crossover design, with a wash-out period of 8–10 weeks. The primary objective was the change in glucagon response during clamp-induced hypoglycemia from plasma glucose (PG) 100 mg/dL to nadir PG (45 mg/dL). Secondary measures were changes in responses of other counterregulatory hormones during clamp-induced hypoglycemia. Time to recovery from the nadir to 72 mg/dL and hypoglycemic symptom scores using the 7-point Edinburgh Hypoglycemia Symptom scale were also assessed.ResultsAt 12 weeks, HbA1c change from baseline was -1.5% with tirzepatide versus +0.5% with placebo. During induced hypoglycemia, mean PG levels at nadir were 44.5 mg/dL with tirzepatide and 47.5 mg/dL with placebo. Increases in glucagon from PG 100 mg/dL to nadir PG and during recovery from the nadir to 72 mg/dL did not differ between treatments (p=0.756 and p=0.565, respectively). Growth hormone and adrenaline responses did not differ between treatments. Cortisol and noradrenaline responses were delayed with tirzepatide, consistent with lower hypoglycemic symptom scores at nadir observed during tirzepatide treatment periods versus placebo (p=0.007). The proportion of participants aware of hypoglycemia did not differ between treatments.DiscussionThe response of the key counterregulatory hormone glucagon to induced hypoglycemia was maintained with tirzepatide.Clinical trial registrationClinicalTrials.gov, identifier NCT04050553

Whole-body and adipose tissue-specific mechanisms underlying the metabolic effects of fibroblast growth factor 21 in the Siberian hamster

ObjectiveFibroblast growth factor 21 (FGF21) has been shown to rapidly lower body weight in the Siberian hamster, a preclinical model of adiposity. This induced negative energy balance mediated by FGF21 is associated with both lowered caloric intake and increased energy expenditure. Previous research demonstrated that adipose tissue (AT) is one of the primary sites of FGF21 action and may be responsible for its ability to increase the whole-body metabolic rate. The present study sought to determine the relative importance of white (subcutaneous WAT [sWAT], visceral WAT [vWAT]), and brown (interscapular brown AT [iBAT]) in governing FGF21-mediated metabolic improvements using the tissue-specific uptake of glucose and lipids as a proxy for metabolic activity.MethodsWe used positron emission tomography-computed tomography (PET-CT) imaging in combination with both glucose (18F-fluorodeoxyglucose) and lipid (18F-4-thiapalmitate) tracers to assess the effect of FGF21 on the tissue-specific uptake of these metabolites and compared responses to a control group pair-fed to match the food intake of the FGF21-treated group. In vivo imaging was combined with ex vivo tissue-specific functional, biochemical, and molecular analyses of the nutrient uptake and signaling pathways.ResultsConsistent with previous findings, FGF21 reduced body weight via reduced caloric intake and increased energy expenditure in the Siberian hamster. PET-CT studies demonstrated that FGF21 increased the uptake of glucose in BAT and WAT independently of reduced food intake and body weight as demonstrated by imaging of the pair-fed group. Furthermore, FGF21 increased glucose uptake in the primary adipocytes, confirming that these in vivo effects may be due to a direct action of FGF21 at the level of the adipocytes. Mechanistically, the effects of FGF21 are associated with activation of the ERK signaling pathway and upregulation of GLUT4 protein content in all fat depots. In response to treatment with FGF21, we observed an increase in the markers of lipolysis and lipogenesis in both the subcutaneous and visceral WAT depots. In contrast, FGF21 was only able to directly increase the uptake of lipid into BAT.ConclusionsThese data identify brown and white fat depots as primary peripheral sites of action of FGF21 in promoting glucose uptake and also indicate that FGF21 selectively stimulates lipid uptake in brown fat, which may fuel thermogenesis

The effect of mirabegron on energy expenditure and brown adipose tissue in healthy lean South Asian and Europid men

Aim: To compare the effects of cold exposure and the β3-adrenergic receptor agonist mirabegron on plasma lipids, energy expenditure and brown adipose tissue (BAT) activity in South Asians versus Europids. Materials and Methods: Ten lean Dutch South Asian (aged 18-30 years; body mass index [BMI] 18-25 kg/m2 ) and 10 age- and BMI-matched Europid men participated in a randomized, double-blinded, cross-over study consisting of three interventions: short-term (~ 2 hours) cold exposure, mirabegron (200 mg one dose p.o.) and placebo. Before and after each intervention, we performed lipidomic analysis in serum, assessed resting energy expenditure (REE) and skin temperature, and measured BAT fat fraction by magnetic resonance imaging. Results: In both ethnicities, cold exposure increased the levels of several serum lipid species, whereas mirabegron only increased free fatty acids. Cold exposure increased lipid oxidation in both ethnicities, while mirabegron increased lipid oxidation in Europids only. Cold exposure and mirabegron enhanced supraclavicular skin temperature in both ethnicities. Cold exposure decreased BAT fat fraction in both ethnicities. After the combination of data from both ethnicities, mirabegron decreased BAT fat fraction compared with placebo. Conclusions: In South Asians and Europids, cold exposure and mirabegron induced beneficial metabolic effects. When combining both ethnicities, cold exposure and mirabegron increased REE and lipid oxidation, coinciding with a higher supraclavicular skin temperature and lower BAT fat fraction.Diabetes Research Foundation Fellowship 2015.81.1808Netherlands CardioVascular Research Initiative: 'the Dutch Heart Foundation, Dutch Federation of University Medical Centers, the Netherlands Organisation for Health Research and Development and the Royal Netherlands Academy of Sciences' CVON2014-02 ENERGISE CVON2017-20 GENIUS-IIEuropean Union (EU) 602485European Research Council (NOMA-MRI) PCNR is an Established Investigator of the Netherlands Heart Foundation 2009T03

Fundamentals of FGF19 & FGF21 Action In Vitro and In Vivo

Fibroblast growth factors 19 (FGF19) and 21 (FGF21) have emerged as key regulators of energy metabolism. Several studies have been conducted to understand the mechanism of FGF19 and FGF21 action, however, the data presented has often been inconsistent and at times contradictory. Here in a single study we compare the mechanisms mediating FGF19/FGF21 actions, and how similarities/differences in actions at the cellular level between these two factors translate to common/divergent physiological outputs. Firstly, we show that in cell culture FGF19/FGF21 are very similar, however, key differences are still observed differentiating the two. In vitro we found that both FGF's activate FGFRs in the context of βKlotho (KLB) expression. Furthermore, both factors alter ERK phosphorylation and glucose uptake with comparable potency. Combination treatment of cells with both factors did not have additive effects and treatment with a competitive inhibitor, the FGF21 delta N17 mutant, also blocked FGF19's effects, suggestive of a shared receptor activation mechanism. The key differences between FGF21/FGF19 were noted at the receptor interaction level, specifically the unique ability of FGF19 to bind/signal directly via FGFR4. To determine if differential effects on energy homeostasis and hepatic mitogenicity exist we treated DIO and ob/ob mice with FGF19/FGF21. We find comparable efficacy of the two proteins to correct body weight and serum glucose in both DIO and ob/ob mice. Nevertheless, FGF21 and FGF19 had distinctly different effects on proliferation in the liver. Interestingly, in vivo blockade of FGF21 signaling in mice using ΔN17 caused profound changes in glycemia indicative of the critical role KLB and FGF21 play in the regulation of glucose homeostasis. Overall, our data demonstrate that while subtle differences exist in vitro the metabolic effects in vivo of FGF19/FGF21 are indistinguishable, supporting a shared mechanism of action for these two hormones in the regulation of energy balance