AKR-001, an Fc-FGF21 Analog, Showed Sustained Pharmacodynamic Effects on Insulin Sensitivity and Lipid Metabolism in Type 2 Diabetes Patients

Development of Zalfermin, a Long-Acting Proteolytically Stabilized FGF21 Analog

Here, we describe the development of the FGF21 analog zalfermin (NNC0194-0499, 15), intended for once-weekly sc dosing. Protein engineering was needed to address inherent druggability issues of the natural FGF21 hormone. Thus, deamidation of Asp121 was solved by mutation to glutamine, and oxidation of Met168 was solved by mutation to leucine. N-terminal region degradation by dipeptidyl peptidase IV was prevented by alanine residue elongation. To prevent inactivating metabolism by fibroblast activation protein and carboxypeptidase-like activity in the C-terminal region, and to achieve t1/2 extension (53 h in cynomolgus monkeys), we introduced a C18 fatty diacid at the penultimate position 180. The fatty diacid binds albumin in a reversible manner, such that the free fraction of zalfermin potently activates the FGF-receptor complex and retains receptor selectivity compared with FGF21, providing strong efficacy on body weight loss in diet-induced obese mice. Zalfermin is currently being clinically evaluated for the treatment of metabolic dysfunction-associated steatohepatitis.

New advances in drug development for metabolic dysfunction-associated diseases and alcohol-associated liver disease

Metabolic disorders are currently threatening public health worldwide. Discovering new targets and developing promising drugs will reduce the global metabolic-related disease burden. Metabolic disorders primarily consist of lipid and glucose metabolic disorders. Specifically, metabolic dysfunction-associated steatosis liver disease (MASLD) and alcohol-associated liver disease (ALD) are two representative lipid metabolism disorders, while diabetes mellitus is a typical glucose metabolism disorder. In this review, we aimed to summarize the new drug candidates with promising efficacy identified in clinical trials for these diseases. These drug candidates may provide alternatives for patients with metabolic disorders and advance the progress of drug discovery for the large disease burden.

Defective FGFR1 Signaling Disrupts Glucose Regulation: Evidence From Humans With FGFR1 Mutations

Context

Activation of fibroblast growth factor receptor 1 (FGFR1) signaling improves the metabolic health of animals and humans, while inactivation leads to diabetes in mice. Direct human genetic evidence for the role of FGFR1 signaling in human metabolic health has not been fully established.

Objective

We hypothesized that individuals with naturally occurring FGFR1 variants ("experiments of nature") will display glucose dysregulation.

Methods

Participants with rare FGFR1 variants and noncarrier controls. Using a recall-by-genotype approach, we examined the β-cell function and insulin sensitivity of 9 individuals with rare FGFR1 deleterious variants compared to 27 noncarrier controls, during a frequently sampled intravenous glucose tolerance test at the Reproductive Endocrine Unit and the Harvard Center for Reproductive Medicine, Massachusetts General Hospital. FGFR1-mutation carriers displayed higher β-cell function in the face of lower insulin sensitivity compared to controls.

Conclusion

These findings suggest that impaired FGFR1 signaling may contribute to an early insulin resistance phase of diabetes pathogenesis and support the candidacy of the FGFR1 signaling pathway as a therapeutic target for improving the human metabolic health.

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.

Mesenchymal stem/stromal cells armored by FGF21 ameliorate alcohol-induced liver injury through modulating polarization of macrophages

BACKGROUND

Alcohol-associated liver disease (ALD) is a major health care challenge worldwide with limited therapeutic options. Although mesenchymal stem/stromal cells (MSCs) represent a newly emerging therapeutic approach to treat ALD, thus far, there have been extensive efforts to try and enhance their efficacy, including genetically engineering MSCs. FGF21, an endocrine stress-responsive hormone, has been shown to regulate energy balance, glucose, and lipid metabolism and to enhance the homing of MSCs toward injured sites. Therefore, the purpose of this study was to investigate whether MSCs that overexpress FGF21 (FGF21-MSCs) improve the therapeutic effect of MSCs in treating ALD.

METHODS

Human umbilical cord-derived MSCs served as the gene delivery vehicle for the FGF21 gene. Human umbilical cord-derived MSCs were transduced with the FGF21 gene using lentiviral vectors to mediate FGF21 overexpression. We utilized both chronic Lieber-DeCarli and Gao-binge models of ethanol-induced liver injury to observe the therapeutic effect of FGF21-MSCs. Liver injury was phenotypically evaluated by performing biochemical methods, histology, and inflammatory cytokine levels.

RESULTS

Compared with MSCs alone, administration of MSCs overexpressing FGF21(FGF21-MSCs) treatment significantly enhanced the therapeutic effect of ALD in mice, as indicated by the alleviation of liver injury with reduced steatosis, inflammatory infiltration, oxidative stress, and hepatic apoptosis, and the promotion of liver regeneration. Mechanistically, FGF21 could facilitate the immunomodulatory function of MSCs on macrophages by setting metabolic commitment for oxidative phosphorylation, which enables macrophages to exhibit anti-inflammatory inclination.

CONCLUSIONS

Our data elucidate that MSC modification by FGF21 could enhance their therapeutic effect in ALD and may help in the exploration of effective MSCs-based cell therapies for the treatment of ALD.

Targeting the FGF19-FGFR4 pathway for cholestatic, metabolic, and cancerous diseases

Human fibroblast growth factor 19 (FGF19, or FGF15 in rodents) plays a central role in controlling bile acid (BA) synthesis through a negative feedback mechanism. This process involves a postprandial crosstalk between the BA-activated ileal farnesoid X receptor and the hepatic Klotho beta (KLB) coreceptor complexed with fibrobalst growth factor receptor 4 (FGFR4) kinase. Additionally, FGF19 regulates glucose, lipid, and energy metabolism by coordinating responses from functional KLB and FGFR1-3 receptor complexes on the periphery. Pharmacologically, native FGF19 or its analogs decrease elevated BA levels, fat content, and collateral tissue damage. This makes them effective in treating both cholestatic diseases such as primary biliary or sclerosing cholangitis (PBC or PSC) and metabolic abnormalities such as nonalcoholic steatohepatitis (NASH). However, chronic administration of FGF19 drives oncogenesis in mice by activating the FGFR4-dependent mitogenic or hepatic regenerative pathway, which could be a concern in humans. Agents that block FGF19 or FGFR4 signaling have shown great potency in preventing FGF19-responsive hepatocellular carcinoma (HCC) development in animal models. Recent phase 1/2 clinical trials have demonstrated promising results for several FGF19-based agents in selectively treating patients with PBC, PSC, NASH, or HCC. This review aims to provide an update on the clinical development of both analogs and antagonists targeting the FGF19-FGFR4 signaling pathway for patients with cholestatic, metabolic, and cancer diseases. We will also analyze potential safety and mechanistic concerns that should guide future research and advanced trials.

AAV-delivered muscone-induced transgene system for treating chronic diseases in mice via inhalation

Gene therapies provide treatment options for many diseases, but the safe and long-term control of therapeutic transgene expression remains a primary issue for clinical applications. Here, we develop a muscone-induced transgene system packaged into adeno-associated virus (AAV) vectors (AAVMUSE) based on a G protein-coupled murine olfactory receptor (MOR215-1) and a synthetic cAMP-responsive promoter (PCRE). Upon exposure to the trigger, muscone binds to MOR215-1 and activates the cAMP signaling pathway to initiate transgene expression. AAVMUSE enables remote, muscone dose- and exposure-time-dependent control of luciferase expression in the livers or lungs of mice for at least 20 weeks. Moreover, we apply this AAVMUSE to treat two chronic inflammatory diseases: nonalcoholic fatty liver disease (NAFLD) and allergic asthma, showing that inhalation of muscone-after only one injection of AAVMUSE-can achieve long-term controllable expression of therapeutic proteins (ΔhFGF21 or ΔmIL-4). Our odorant-molecule-controlled system can advance gene-based precision therapies for human diseases.

Artesunate treats obesity in male mice and non-human primates through GDF15/GFRAL signalling axis

Obesity, a global health challenge, is a major risk factor for multiple life-threatening diseases, including diabetes, fatty liver, and cancer. There is an ongoing need to identify safe and tolerable therapeutics for obesity management. Herein, we show that treatment with artesunate, an artemisinin derivative approved by the FDA for the treatment of severe malaria, effectively reduces body weight and improves metabolic profiles in preclinical models of obesity, including male mice with overnutrition-induced obesity and male cynomolgus macaques with spontaneous obesity, without inducing nausea and malaise. Artesunate promotes weight loss and reduces food intake in obese mice and cynomolgus macaques by increasing circulating levels of Growth Differentiation Factor 15 (GDF15), an appetite-regulating hormone with a brainstem-restricted receptor, the GDNF family receptor α-like (GFRAL). Mechanistically, artesunate induces the expression of GDF15 in multiple organs, especially the liver, in mice through a C/EBP homologous protein (CHOP)-directed integrated stress response. Inhibition of GDF15/GFRAL signalling by genetic ablation of GFRAL or tissue-specific knockdown of GDF15 abrogates the anti-obesity effect of artesunate in mice with diet-induced obesity, suggesting that artesunate controls bodyweight and appetite in a GDF15/GFRAL signalling-dependent manner. These data highlight the therapeutic benefits of artesunate in the treatment of obesity and related comorbidities.

Fructose-induced FGF21 secretion does not activate brown adipose tissue in Japanese young men: randomized cross-over and randomized controlled trials

BACKGROUND

Human brown adipose tissue (BAT) activity is associated with lower body fatness and favorable glucose metabolism. Previous studies reported that oral fructose loading induces postprandial fibroblast growth factor 21 (FGF21) secretion. FGF21 is a known inducer of adipose tissue thermogenesis; however, the effects of diet-induced FGF21 secretion on BAT thermogenesis remain to be elucidated.

METHODS

The effects of both single load and daily consumption of fructose on BAT activity were examined using a randomized cross-over trial and a 2-week randomized controlled trial (RCT), respectively. In the cross-over trial, 15 young men consumed a single dose of fructose solution or water and then consumed the other on a subsequent day. The RCT enrolled 22 young men, and the participants were allocated to a group that consumed fructose and a group that consumed water daily for 2 weeks. BAT activity was analyzed using thermography with cold exposure. Plasma FGF21 level was determined by enzyme-linked immunosorbent assay.

RESULTS

In the cross-over single-load trial, plasma FGF21 levels were significantly increased at 2 h after oral fructose load (p < 0.01); however, there was no significant difference in BAT activity between the fructose load and drinking water. The 2-week RCT revealed that both plasma FGF21 levels and BAT activity were not significantly increased by daily fructose consumption compared to water. Correlation analyses revealed that BAT activity at the baseline and the final measurements were strongly and positively associated with the RCT (r = 0.869, p < 0.001). Changes in BAT activity were significantly and negatively correlated with changes in plasma glucose levels during the 2-week intervention (r = - 0.497, p = 0.022).

CONCLUSIONS

Oral fructose load induces a temporary increase in circulating FGF21 levels; however, this does not activate BAT thermogenesis in healthy young men. Further studies are needed to elucidate the effect of endogenous FGF21 on physiological function.

TRIAL REGISTRATION

This study is registered with the University Hospital Medical Information Network in Japan (number 000051761, registered 1 August 2023, retrospectively registered, https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000052680 ).

Mitochondrial Stress and Mitokines: Therapeutic Perspectives for the Treatment of Metabolic Diseases

Mitochondrial stress and the dysregulated mitochondrial unfolded protein response (UPRmt) are linked to various diseases, including metabolic disorders, neurodegenerative diseases, and cancer. Mitokines, signaling molecules released by mitochondrial stress response and UPRmt, are crucial mediators of inter-organ communication and influence systemic metabolic and physiological processes. In this review, we provide a comprehensive overview of mitokines, including their regulation by exercise and lifestyle interventions and their implications for various diseases. The endocrine actions of mitokines related to mitochondrial stress and adaptations are highlighted, specifically the broad functions of fibroblast growth factor 21 and growth differentiation factor 15, as well as their specific actions in regulating inter-tissue communication and metabolic homeostasis. Finally, we discuss the potential of physiological and genetic interventions to reduce the hazards associated with dysregulated mitokine signaling and preserve an equilibrium in mitochondrial stress-induced responses. This review provides valuable insights into the mechanisms underlying mitochondrial regulation of health and disease by exploring mitokine interactions and their regulation, which will facilitate the development of targeted therapies and personalized interventions to improve health outcomes and quality of life.

Population Pharmacokinetics and Pharmacodynamics of Pegozafermin in Patients with Nonalcoholic Steatohepatitis

Pegozafermin is a long-acting glycoPEGylated analog of fibroblast growth factor 21 (FGF21) in development for the treatment of nonalcoholic steatohepatitis (NASH) and severe hypertriglyceridemia. In a phase Ib/IIa placebo-controlled, double-blind, multiple ascending dose study in patients with NASH (NCT04048135), administration of pegozafermin resulted in clinically meaningful reductions in hepatic fat fraction (HFF), with a favorable safety and tolerability profile. We aimed to characterize the relationship between pegozafermin dosing, exposure and effects on HFF reduction. We used pharmacokinetic (PK) and pharmacodynamic (PD) modeling of data from the phase Ib/IIa study to identify model parameters and covariates affecting the exposure-response relationship. Clinical simulations were performed to help support dose selection for larger studies. Pegozafermin exposure was adequately described by a one compartment PK model, with one additional transit absorption compartment. PK/PD modeling demonstrated that HFF reduction was significantly related to pegozafermin exposure. HFF outcomes were correlated with average pegozafermin concentrations regardless of weekly dosing (q.w.) or dosing every 2 weeks (q2w). The significant PK/PD model covariates included baseline body weight, alanine aminotransferase level, and liver volume. Simulations showed that the 30 mg q.w. dose approximated the full PD effect; almost all patients would benefit from a greater than or equal to 30% HFF reduction, suggesting fibrosis regression. Furthermore, 44 mg q2w dosing (~22 mg q.w.) appeared to be an effective regimen for HFF reduction. Our modeling supports the feasibility of q.w. and q2w dosing for achieving favorable treatment outcomes in patients with NASH, and provides the rationale for dose selection for the phase IIb ENLIVEN study (NCT04929483).

Use of FGF21 analogs for the treatment of metabolic disorders: a systematic review and meta-analysis

FGF21 is a hormone produced primarily by the liver with several metabolic functions, such as induction of heat production, control of glucose homeostasis, and regulation of blood lipid levels. Due to these actions, several laboratories have developed FGF21 analogs to treat patients with metabolic disorders such as obesity and diabetes. Here, we performed a systematic review and meta-analysis of randomized controlled trials that used FGF21 analogs and analyzed metabolic outcomes. Our search yielded 236 articles, and we included eight randomized clinical trials in the meta-analysis. The use of FGF21 analogs exhibited no effect on fasting blood glucose, glycated hemoglobin, HOMA index, blood free fatty acids or systolic blood pressure. However, the treatment significantly reduced fasting insulinemia, body weight and total cholesterolemia. None of the included studies were at high risk of bias. The quality of the evidence ranged from moderate to very low, especially due to imprecision and indirection issues. These results indicate that FGF21 analogs can potentially treat metabolic syndrome. However, more clinical trials are needed to increase the quality of evidence and confirm the effects seen thus far.

Aberrant expression of AKR1B1 indicates poor prognosis and promotes gastric cancer progression by regulating the AKT-mTOR pathway

Gastric cancer (GC) is a common malignant tumor in the digestive tract and a major cause of global cancer death. Due to the limited access to early screening, many patients are diagnosed with advanced GC. Therefore, postoperative radiotherapy and chemotherapy possess limited efficacy in treating GC. AKR1B1 has been associated with tumorigenesis and metastasis across various tumors, becoming a potential therapeutic target for GC. However, its role and mechanism in GC remain unclear. In this study, AKR1B1 was elevated in GC tissue, depicting a poor prognosis. AKR1B1 is closely related to age, vascular and neural invasion, lymph node metastasis, and the TNM stage of GC. The developed survival prediction model suggested that AKR1B1 expression level is crucial in the prognosis of GC patients. Moreover, the expression level of AKR1B1 in GC tissues is closely associated with the AKT-mTOR pathway. In vitro and in vivo assays functional assays helped determine the oncogenic role of AKR1B1. Additionally, the knockdown of AKR1B1 expression level in GC cell lines could effectively suppress the AKT-mTOR pathway and inhibit the proliferation and migration of tumor cells. In conclusion, this study provides a theoretical basis to establish the potential association and regulatory mechanism of AKR1B1 while offering a new strategy for GC-targeted therapy.

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).

Fibroblast growth factor 21 in metabolic syndrome

Metabolic syndrome is a complex metabolic disorder that often clinically manifests as obesity, insulin resistance/diabetes, hyperlipidemia, and hypertension. With the development of social and economic systems, the incidence of metabolic syndrome is increasing, bringing a heavy medical burden. However, there is still a lack of effective prevention and treatment strategies. Fibroblast growth factor 21 (FGF21) is a member of the human FGF superfamily and is a key protein involved in the maintenance of metabolic homeostasis, including reducing fat mass and lowering hyperglycemia, insulin resistance and dyslipidemia. Here, we review the current regulatory mechanisms of FGF21, summarize its role in obesity, diabetes, hyperlipidemia, and hypertension, and discuss the possibility of FGF21 as a potential target for the treatment of metabolic syndrome.

Pharmaceutical Strategies to Improve Druggability of Potential Drug Candidates in Nonalcoholic Fatty Liver Disease Therapy

Nonalcoholic fatty liver disease (NAFLD) has become globally prevalent and is the leading cause of chronic liver disease. Although NAFLD is reversible without medical intervention in the early stage, the condition could be sequentially worsened to nonalcoholic steatohepatitis (NASH) and, eventually, cirrhosis and hepatic cancer. The progression of NAFLD is related to various factors such as genetics, pre-disposed metabolic disorders, and immunologic factors. Thankfully, to date, there have been accumulating research efforts and, as a result, different classes of potent drug candidates have been discovered. In addition, there have also been various attempts to explore pharmaceutical strategies to improve the druggability of drug candidates. In this review, we provided a brief overview of the drug candidates that have undergone clinical trials. In the latter part, strategies for developing better drugs are discussed.

The FGF21 analog pegozafermin in severe hypertriglyceridemia: a randomized phase 2 trial

Pegozafermin, a long-acting glycopegylated analog of human fibroblast growth factor 21, is in development for the treatment of severe hypertriglyceridemia (SHTG) and nonalcoholic steatohepatitis. Here we report the results of a phase 2, double-blind, randomized, five-arm trial testing pegozafermin at four different doses (n = 67; 52 male) versus placebo (n = 18; 12 male) for 8 weeks in patients with SHTG (triglycerides (TGs), ≥500 mg dl-1 and ≤2,000 mg dl-1). Treated patients showed a significant reduction in median TGs for the pooled pegozafermin group versus placebo (57.3% versus 11.9%, difference versus placebo -43.7%, 95% confidence interval (CI): -57.1%, -30.3%; P < 0.001), meeting the primary endpoint of the trial. Reductions in median TGs ranged from 36.4% to 63.4% across all treatment arms and were consistent regardless of background lipid-lowering therapy. Results for secondary endpoints included significant decreases in mean apolipoprotein B and non-high-density lipoprotein cholesterol concentrations (-10.5% and -18.3% for pooled doses compared to 1.1% and -0.6% for placebo (95% CI: -21.5%, -2.0%; P = 0.019 and 95% CI: -30.7%, -5.1%; P = 0.007, respectively), as well as a significant decrease in liver fat fraction for pooled treatment (n = 17) versus placebo (n = 6; -42.2% pooled pegozafermin, -8.3% placebo; 95% CI: -60.9%, -8.7%; P = 0.012), as assessed in a magnetic resonance imaging sub-study. No serious adverse events were observed to be related to the study drug. If these results are confirmed in a phase 3 trial, pegozafermin could be a promising treatment for SHTG (ClinicalTrials.gov registration: NCT0441186).

Efruxifermin, an investigational treatment for fibrotic or cirrhotic non-alcoholic steatohepatitis (NASH)

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease and strongly associated with metabolic disorders: obesity, type 2 diabetes (T2D), cardiovascular disease. Persistent metabolic injury results in inflammatory processes leading to nonalcoholic steatohepatitis (NASH), liver fibrosis and ultimately cirrhosis. To date, no pharmacologic agent is approved for the treatment of NASH. Fibroblast growth factor 21 (FGF21) agonism has been linked to beneficial metabolic effects ameliorating obesity, steatosis and insulin resistance, supporting its potential as a therapeutic target in NAFLD.

AREAS COVERED

Efruxifermin (EFX, also AKR-001 or AMG876) is an engineered Fc-FGF21 fusion protein with an optimized pharmacokinetic and pharmacodynamic profile, which is currently tested in several phase 2 clinical trials for the treatment of NASH, fibrosis and compensated liver cirrhosis. EFX improved metabolic disturbances including glycemic control, showed favorable safety and tolerability, and demonstrated antifibrotic efficacy according to FDA requirements for phase 3 trials.

EXPERT OPINION

While some other FGF-21 agonists (e.g. pegbelfermin) are currently not further investigated, available evidence supports the development of EFX as a promising anti-NASH drug in fibrotic and cirrhotic populations. However, antifibrotic efficacy, long-term safety and benefits (i.e. cardiovascular risk, decompensation events, disease progression, liver transplantation, mortality) remain to be determined.

The potential effect of metformin on fibroblast growth factor 21 in type 2 diabetes mellitus (T2DM)

Fibroblast growth factor 21 (FGF21) is a peptide hormone mainly synthesized and released from the liver. FGF21 acts on FGF21 receptors (FGFRs) and β-Klotho, which is a transmembrane co-receptor. In type 2 diabetes mellitus (T2DM), inflammatory disorders stimulate the release of FGF21 to overcome insulin resistance (IR). FGF21 improves insulin sensitivity and glucose homeostasis. Metformin which is used in the management of T2DM may increase FGF21 expression. Accordingly, the objective of this review was to clarify the metformin effect on FGF21 in T2DM. FGF21 level and expression of FGF2Rs are dysregulated in T2DM due to the development of FGF21 resistance. Metformin stimulates the hepatic expression of FGF21/FGF2Rs by different signaling pathways. Besides, metformin improves the expression of β-Klotho which improves FGF21 sensitivity. In conclusion, metformin advances FGF21 signaling and decreases FGF21 resistance in T2DM, and this might be an innovative mechanism for metformin in the enhancement of glucose homeostasis and metabolic disorders in T2DM patients.

360-Degree Perspectives on Obesity

Alarming statistics show that the number of people affected by excessive weight has surpassed 2 billion, representing approximately 30% of the world's population. The aim of this review is to provide a comprehensive overview of one of the most serious public health problems, considering that obesity requires an integrative approach that takes into account its complex etiology, including genetic, environmental, and lifestyle factors. Only an understanding of the connections between the many contributors to obesity and the synergy between treatment interventions can ensure satisfactory outcomes in reducing obesity. Mechanisms such as oxidative stress, chronic inflammation, and dysbiosis play a crucial role in the pathogenesis of obesity and its associated complications. Compounding factors such as the deleterious effects of stress, the novel challenge posed by the obesogenic digital (food) environment, and the stigma associated with obesity should not be overlooked. Preclinical research in animal models has been instrumental in elucidating these mechanisms, and translation into clinical practice has provided promising therapeutic options, including epigenetic approaches, pharmacotherapy, and bariatric surgery. However, more studies are necessary to discover new compounds that target key metabolic pathways, innovative ways to deliver the drugs, the optimal combinations of lifestyle interventions with allopathic treatments, and, last but not least, emerging biological markers for effective monitoring. With each passing day, the obesity crisis tightens its grip, threatening not only individual lives but also burdening healthcare systems and societies at large. It is high time we took action as we confront the urgent imperative to address this escalating global health challenge head-on.

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.

Biological and pharmacological functions of the FGF19- and FGF21-coreceptor beta klotho

Beta klotho (KLB) is a fundamental component in fibroblast growth factor receptor (FGFR) signaling as it serves as an obligatory coreceptor for the endocrine hormones fibroblast growth factor 19 (FGF19) and fibroblast growth factor 21 (FGF21). Through the development of FGF19- and FGF21 mimetics, KLB has emerged as a promising drug target for treating various metabolic diseases, such as type 2 diabetes (T2D), non-alcoholic fatty liver disease (NAFLD), and cardiovascular disease. While rodent studies have significantly increased our understanding of KLB function, current clinical trials that test the safety and efficacy of KLB-targeting drugs raise many new scientific questions about human KLB biology. Although most KLB-targeting drugs can modulate disease activity in humans, individual patient responses differ substantially. In addition, species-specific differences in KLB tissue distribution may explain why the glucose-lowering effects that were observed in preclinical studies are not fully replicated in clinical trials. Besides, the long-term efficacy of KLB-targeting drugs might be limited by various pathophysiological conditions known to reduce the expression of KLB. Moreover, FGF19/FGF21 administration in humans is also associated with gastrointestinal side effects, which are currently unexplained. A better understanding of human KLB biology could help to improve the efficacy and safety of existing or novel KLB/FGFR-targeting drugs. In this review, we provide a comprehensive overview of the current understanding of KLB biology, including genetic variants and their phenotypic associations, transcriptional regulation, protein structure, tissue distribution, subcellular localization, and function. In addition, we will highlight recent developments regarding the safety and efficacy of KLB-targeting drugs in clinical trials. These insights may direct the development and testing of existing and future KLB-targeting drugs.

Adipokines as Clinically Relevant Therapeutic Targets in Obesity

Adipokines provide an outstanding role in the comprehensive etiology of obesity and may link adipose tissue dysfunction to further metabolic and cardiovascular complications. Although several adipokines have been identified in terms of their physiological roles, many regulatory circuits remain unclear and translation from experimental studies to clinical applications has yet to occur. Nevertheless, due to their complex metabolic properties, adipokines offer immense potential for their use both as obesity-associated biomarkers and as relevant treatment strategies for overweight, obesity and metabolic comorbidities. To provide an overview of the current clinical use of adipokines, this review summarizes clinical studies investigating the potential of various adipokines with respect to diagnostic and therapeutic treatment strategies for obesity and linked metabolic disorders. Furthermore, an overview of adipokines, for which a potential for clinical use has been demonstrated in experimental studies to date, will be presented. In particular, promising data revealed that fibroblast growth factor (FGF)-19, FGF-21 and leptin offer great potential for future clinical application in the treatment of obesity and related comorbidities. Based on data from animal studies or other clinical applications in addition to obesity, adipokines including adiponectin, vaspin, resistin, chemerin, visfatin, bone morphogenetic protein 7 (BMP-7) and tumor necrosis factor alpha (TNF-α) provide potential for human clinical application.

Looking ahead to potential incretin combination therapies for non-alcoholic steatohepatitis in patients with diabetes

INTRODUCTION

There are no drugs approved by regulatory agencies for the treatment of nonalcoholic fatty liver disease (NAFLD); incretin combination therapies are being developed for treatment of type 2 diabetes and research has moved to test their usefulness in NAFLD.

AREAS COVERED

We reviewed the literature on the effectiveness of dual and triple peptides combining receptor agonists of the glucagon-like peptide 1, the glucose-dependent insulinotropic peptide, and glucagon to treat NAFLD and its associated metabolic diseases, and/or the cardiovascular risk intimately connected with the cluster of the metabolic syndrome. Other combination peptides involved the glucagon-like peptide 2 receptor, the fibroblast growth factor 21, the cholecystokinin receptor 2, and the amylin receptor.

EXPERT OPINION

Both dual and triple agonists are promising, based on animal, pharmacokinetic and proof-of concept studies, showing effectiveness both in the presence and the absence of diabetes on a few validated surrogate NAFLD biomarkers, but the majority of studies are still in progress. Considering the long natural history of NAFLD, final proof of their efficacy on primary clinical liver outcomes might be also derived from the analysis of large databases of National Healthcare Systems or Insurance companies, when used in diabetes for improving glycemic control, after careful propensity-score matching.

Pharmacological Support for the Treatment of Obesity-Present and Future

Obesity is a growing civilization problem, associated with a number of negative health consequences affecting almost all tissues and organs. Currently, obesity treatment includes lifestyle modifications (including diet and exercise), pharmacologic therapies, and in some clinical situations, bariatric surgery. These treatments seem to be the most effective method supporting the treatment of obesity. However, they are many limitations to the options, both for the practitioners and patients. Often the comorbidities, cost, age of the patient, and even geographic locations may influence the choices. The pharmacotherapy of obesity is a fast-growing market. Currently, we have at our disposal drugs with various mechanisms of action (directly reducing the absorption of calories-orlistat, acting centrally-bupropion with naltrexone, phentermine with topiramate, or multidirectional-liraglutide, dulaglutide, semaglutide). The drugs whose weight-reducing effect is used in the course of the pharmacotherapy of other diseases (e.g., glucose-sodium cotransporter inhibitors, exenatide) are also worth mentioning. The obesity pharmacotherapy is focusing on novel therapeutic agents with improved safety and efficacy profiles. These trends also include an assessment of the usefulness of the weight-reducing properties of the drugs previously used for other diseases. The presented paper is an overview of the studies related to both drugs currently used in the pharmacotherapy of obesity and those undergoing clinical trials, taking into account the individual approach to the patient.

Anti-Obesity Effects of Metformin: A Scoping Review Evaluating the Feasibility of Brown Adipose Tissue as a Therapeutic Target

Brown adipose tissue (BAT) is increasingly recognized as the major therapeutic target to promote energy expenditure and ameliorate diverse metabolic complications. There is a general interest in understanding the pleiotropic effects of metformin against metabolic complications. Major electronic databases and search engines such as PubMed/MEDLINE, Google Scholar, and the Cochrane library were used to retrieve and critically discuss evidence reporting on the impact of metformin on regulating BAT thermogenic activity to ameliorate complications linked with obesity. The summarized evidence suggests that metformin can reduce body weight, enhance insulin sensitivity, and improve glucose metabolism by promoting BAT thermogenic activity in preclinical models of obesity. Notably, this anti-diabetic agent can affect the expression of major thermogenic transcriptional factors such as uncoupling protein 1 (UCP1), nuclear respiratory factor 1 (NRF1), and peroxisome-proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α) to improve BAT mitochondrial function and promote energy expenditure. Interestingly, vital molecular markers involved in glucose metabolism and energy regulation such as AMP-activated protein kinase (AMPK) and fibroblast growth factor 21 (FGF21) are similarly upregulated by metformin treatment in preclinical models of obesity. The current review also discusses the clinical relevance of BAT and thermogenesis as therapeutic targets. This review explored critical components including effective dosage and appropriate intervention period, consistent with the beneficial effects of metformin against obesity-associated complications.

Fibroblast Growth Factor-Based Pharmacotherapies for the Treatment of Obesity-Related Metabolic Complications

The fibroblast growth factor (FGF) family, which comprises 22 structurally related proteins, plays diverse roles in cell proliferation, differentiation, development, and metabolism. Among them, two classical members (FGF1 and FGF4) and two endocrine members (FGF19 and FGF21) are important regulators of whole-body energy homeostasis, glucose/lipid metabolism, and insulin sensitivity. Preclinical studies have consistently demonstrated the therapeutic benefits of these FGFs for the treatment of obesity, diabetes, dyslipidemia, and nonalcoholic steatohepatitis (NASH). Several genetically engineered FGF19 and FGF21 analogs with improved pharmacodynamic and pharmacokinetic properties have been developed and progressed into various stages of clinical trials. These FGF analogs are effective in alleviating hepatic steatosis, steatohepatitis, and liver fibrosis in biopsy-confirmed NASH patients, whereas their antidiabetic and antiobesity effects are mildand vary greatly in different clinical trials. This review summarizes recent advances in biopharmaceutical development of FGF-based therapies against obesity-related metabolic complications, highlights major challenges in clinical implementation, and discusses possible strategies to overcome these hurdles.

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.

The potential function and clinical application of FGF21 in metabolic diseases

As an endocrine hormone, fibroblast growth factor 21 (FGF21) plays a crucial role in regulating lipid, glucose, and energy metabolism. Endogenous FGF21 is generated by multiple cell types but acts on restricted effector tissues, including the brain, adipose tissue, liver, heart, and skeletal muscle. Intervention with FGF21 in rodents or non-human primates has shown significant pharmacological effects on a range of metabolic dysfunctions, including weight loss and improvement of hyperglycemia, hyperlipidemia, insulin resistance, cardiovascular disease, and non-alcoholic fatty liver disease (NAFLD). Due to the poor pharmacokinetic and biophysical characteristics of native FGF21, long-acting FGF21 analogs and FGF21 receptor agonists have been developed for the treatment of metabolic dysfunction. Clinical trials of several FGF21-based drugs have been performed and shown good safety, tolerance, and efficacy. Here we review the actions of FGF21 and summarize the associated clinical trials in obesity, type 2 diabetes mellitus (T2DM), and NAFLD, to help understand and promote the development of efficient treatment for metabolic diseases via targeting FGF21.

Retinopathy of prematurity: Metabolic risk factors

At preterm birth, the retina is incompletely vascularized. Retinopathy of prematurity (ROP) is initiated by the postnatal suppression of physiological retinal vascular development that would normally occur in utero. As the neural retina slowly matures, increasing metabolic demand including in the peripheral avascular retina, leads to signals for compensatory but pathological neovascularization. Currently, only late neovascular ROP is treated. ROP could be prevented by promoting normal vascular growth. Early perinatal metabolic dysregulation is a strong but understudied risk factor for ROP and other long-term sequelae of preterm birth. We will discuss the metabolic and oxygen needs of retina, current treatments, and potential interventions to promote normal vessel growth including control of postnatal hyperglycemia, dyslipidemia and hyperoxia-induced retinal metabolic alterations. Early supplementation of missing nutrients and growth factors and control of supplemental oxygen promotes physiological retinal development. We will discuss the current knowledge gap in retinal metabolism after preterm birth.

Sitagliptin reduces FAP-activity and increases intact FGF21 levels in patients with newly detected glucose abnormalities

INTRODUCTION

Fibroblast growth factor 21 (FGF21), a hormone with pleiotropic metabolic effects, is inactivated by fibroblast activation protein (FAP), a member of the dipeptidyl peptidase-IV (DPP-IV) family. We investigate if sitagliptin (DPP-IV inhibitor) inhibits FAP-activity and increases intact FGF21.

METHODS

Patients with impaired glucose metabolism were randomized to 100 mg sitagliptin (n = 34) or placebo (n = 37) treatment for 12 weeks. Plasma samples obtained at study entry and at 12-weeks were analysed for FAP-activity, FAP, total FGF21 and intact FGF21.

RESULTS

Sitagliptin significantly inhibited FAP-activity (497 ± 553 vs. 48 ± 712 RFU/min, p < 0.01) and correspondingly increased intact FGF21 (253 ± 182 vs 141 ± 80 ng/L, p < 0.01) compared to placebo in plasma. Sitagliptin dose-dependently inhibited the FAP-activity in vitro. Intact FGF21 was higher in patients obtaining a normal glucose tolerance regardless of treatment (p = 0.03).

CONCLUSION

A sitagliptin-induced increase of intact FGF21 may contribute to an improved metabolic effect in patients with impaired glucose metabolism.

Fibroblast growth factor 21 and dietary interventions: what we know and what we need to know next

Dietary interventions include the change of dietary styles, such as fasting and dietary or nutrient restrictions; or the addition of plant-derived compounds (such as polyphenols known as curcumin, resveratrol, or anthocyanin, or other nutraceuticals) into the diet. During the past a few decades, large number of studies have demonstrated therapeutic activities of these dietary interventions on metabolic and other diseases in human subjects or various animal models. Mechanisms underlying those versatile therapeutic activities, however, remain largely unclear. Interestingly, recent studies have shown that fibroblast growth factor 21 (FGF21), a liver-derived hormone or hepatokine, mediates metabolic beneficial effects of certain dietary polyphenols as well as protein restriction. Here I have briefly summarized functions of FGF21, highlighted related dietary interventions, and presented literature discussions on role of FGF21 in mediating function of dietary polyphenol intervention and protein restriction. This is followed by presenting my perspective view, with the involvement of gut microbiota. It is anticipated that further breakthroughs in this field in the near future will facilitate conceptual merge of classical medicine and modern medicine.

Combination strategies for pharmacologic treatment of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is defined as hepatic steatosis, inflammation, and hepatocyte injury with or without fibrosis. It has emerged as the second leading indication for liver transplantation with a rising death rate in the non-transplantable population. While there are many drugs in evaluation, currently no approved therapies are on the market for this condition. Given this importance, the Food and Drug Administration has provided formal guidance regarding drug development for stopping or reversing NASH or NASH associated fibrosis. The complex pathogenesis of NASH and its bidirectional relationship with metabolic syndrome has highlighted multiple drugs of interest that address metabolic, inflammatory, and fibrotic factors. A few promising liver specific targets include farnesoid X receptor agonists and peroxisome proliferator-activated receptor agonists. Previously studied drug classes such as glucagon-like peptide-1 analogs or sodium/glucose transport protein 2 inhibitors have also demonstrated ability to improve hepatic steatosis. Here we discuss current rationale, scientific work, and preliminary data in combining multiple drugs for the purposes of a multimodal attack on the pathogenesis of NASH. We highlight multiple Phase 2 and Phase 3 studies that demonstrate the potential to achieve a response rate higher than previously assessed monotherapies for this condition. Ultimately, one of these combination strategies may rise above in its safety and efficacy to become a part of a standardized approach to NASH.

Multi-organ FGF21-FGFR1 signaling in metabolic health and disease

Metabolic syndrome is a chronic systemic disease that is particularly manifested by obesity, diabetes, and hypertension, affecting multiple organs. The increasing prevalence of metabolic syndrome poses a threat to public health due to its complications, such as liver dysfunction and cardiovascular disease. Impaired adipose tissue plasticity is another factor contributing to metabolic syndrome. Emerging evidence demonstrates that fibroblast growth factors (FGFs) are critical players in organ crosstalk via binding to specific FGF receptors (FGFRs) and their co-receptors. FGFRs activation modulates intracellular responses in various cell types under metabolic stress. FGF21, in particular is considered as the key regulator for mediating systemic metabolic effects by binding to receptors FGFR1, FGFR3, and FGFR4. The complex of FGFR1 and beta Klotho (β-KL) facilitates endocrine and paracrine communication networks that physiologically regulate global metabolism. This review will discuss FGF21-mediated FGFR1/β-KL signaling pathways in the liver, adipose, and cardiovascular systems, as well as how this signaling is involved in the interplay of these organs during the metabolic syndrome. Furthermore, the clinical implications and therapeutic strategies for preventing metabolic syndrome and its complications by targeting FGFR1/β-KL are also discussed.

Pathogenesis and Therapeutic Strategies Related to Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD), one of the most common types of chronic liver disease, is strongly correlated with obesity, insulin resistance, metabolic syndrome, and genetic components. The pathological progression of NAFLD, consisting of non-alcoholic fatty liver (NAFL), non-alcoholic steatohepatitis (NASH), and liver cirrhosis, is characterized by a broad spectrum of clinical phenotypes. Although patients with mild NAFL are considered to show no obvious clinical symptoms, patients with long-term NAFL may culminate in NASH and further liver fibrosis. Even though various drugs are able to improve NAFLD, there are no FDA-approved medications that directly treat NAFLD. In this paper, the pathogenesis of NAFLD, the potential therapeutic targets, and their underlying mechanisms of action were reviewed.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Hepatic Hedgehog Signaling Participates in the Crosstalk between Liver and Adipose Tissue in Mice by Regulating FGF21

The Hedgehog signaling pathway regulates many processes during embryogenesis and the homeostasis of adult organs. Recent data suggest that central metabolic processes and signaling cascades in the liver are controlled by the Hedgehog pathway and that changes in hepatic Hedgehog activity also affect peripheral tissues, such as the reproductive organs in females. Here, we show that hepatocyte-specific deletion of the Hedgehog pathway is associated with the dramatic expansion of adipose tissue in mice, the overall phenotype of which does not correspond to the classical outcome of insulin resistance-associated diabetes type 2 obesity. Rather, we show that alterations in the Hedgehog signaling pathway in the liver lead to a metabolic phenotype that is resembling metabolically healthy obesity. Mechanistically, we identified an indirect influence on the hepatic secretion of the fibroblast growth factor 21, which is regulated by a series of signaling cascades that are directly transcriptionally linked to the activity of the Hedgehog transcription factor GLI1. The results of this study impressively show that the metabolic balance of the entire organism is maintained via the activity of morphogenic signaling pathways, such as the Hedgehog cascade. Obviously, several pathways are orchestrated to facilitate liver metabolic status to peripheral organs, such as adipose tissue.

Acute Deletion of the FOXO1-dependent Hepatokine FGF21 Does not Alter Basal Glucose Homeostasis or Lipolysis in Mice

The hepatic transcription factor forkhead box O1 (FOXO1) is a critical regulator of hepatic and systemic insulin sensitivity. Previous work by our group and others demonstrated that genetic inhibition of FOXO1 improves insulin sensitivity both in genetic and dietary mouse models of metabolic disease. Mechanistically, this is due in part to cell nonautonomous control of adipose tissue insulin sensitivity. However, the mechanisms mediating this liver-adipose tissue crosstalk remain ill defined. One candidate hepatokine controlled by hepatic FOXO1 is fibroblast growth factor 21 (FGF21). Preclinical and clinical studies have explored the potential of pharmacological FGF21 as an antiobesity and antidiabetic therapy. In this manuscript, we performed acute loss-of-function experiments to determine the role of hepatocyte-derived FGF21 in glucose homeostasis and insulin tolerance both in control and mice lacking hepatic insulin signaling. Surprisingly, acute deletion of FGF21 did not alter glucose tolerance, insulin tolerance, or adipocyte lipolysis in either liver-specific FGF21KO mice or mice lacking hepatic AKT-FOXO1-FGF21, suggesting a permissive role for endogenous FGF21 in the regulation of systemic glucose homeostasis and insulin tolerance in mice. In addition, these data indicate that liver FOXO1 controls glucose homeostasis independently of liver-derived FGF21.

Mechanisms by Which Skeletal Muscle Myokines Ameliorate Insulin Resistance

The skeletal muscle is the largest organ in the body and secretes circulating factors, including myokines, which are involved in various cellular signaling processes. Skeletal muscle is vital for metabolism and physiology and plays a crucial role in insulin-mediated glucose disposal. Myokines have autocrine, paracrine, and endocrine functions, serving as critical regulators of myogenic differentiation, fiber-type switching, and maintaining muscle mass. Myokines have profound effects on energy metabolism and inflammation, contributing to the pathophysiology of type 2 diabetes (T2D) and other metabolic diseases. Myokines have been shown to increase insulin sensitivity, thereby improving glucose disposal and regulating glucose and lipid metabolism. Many myokines have now been identified, and research on myokine signaling mechanisms and functions is rapidly emerging. This review summarizes the current state of the field regarding the role of myokines in tissue cross-talk, including their molecular mechanisms, and their potential as therapeutic targets for T2D.

FGF21: A Novel Regulator of Glucose and Lipid Metabolism and Whole-Body Energy Balance

Fibroblast growth factor (FGF) 21 is a recently recognized metabolic regulator that evokes interest due to its beneficial action of maintaining whole-body energy balance and protecting the liver from excessive triglyceride production and storage. Together with FGF19 and FGF23, FGF21 belongs to the FGF family with hormone-like activity. Serum FGF21 is generated primarily in the liver under nutritional stress stimuli like prolonged fasting or the lipotoxic diet, but also during increased mitochondrial and endoplasmic reticulum stress. FGF21 exerts its endocrine action in the central nervous system and adipose tissue. Acting in the ventromedial hypothalamus, FGF21 diminishes simple sugar intake. In adipose tissue, FGF21 promotes glucose utilization and increases energy expenditure by enhancing adipose tissue insulin sensitivity and brown adipose tissue thermogenesis. Therefore, FGF21 favors glucose consumption for heat production instead of energy storage. Furthermore, FGF21 specifically acts in the liver, where it protects hepatocytes from metabolic stress caused by lipid overload. FGF21 stimulates hepatic fatty acid oxidation and reduces lipid flux into the liver by increasing peripheral lipoprotein catabolism and reducing adipocyte lipolysis. Paradoxically, and despite its beneficial action, FGF21 is elevated in insulin resistance states, that is, fatty liver, obesity, and type 2 diabetes.

Hepatocyte-specific fibroblast growth factor 21 overexpression ameliorates high-fat diet-induced obesity and liver steatosis in mice

Fibroblast growth factor (FGF) 21 is an endocrine growth factor mainly secreted by the liver in response to a ketogenic diet and alcohol consumption. FGF21 signaling requires co-receptor β-klotho (KLB) co-acting with FGF receptors, which has pleiotropic metabolic effects, including induced hepatic fatty acid oxidation and ketogenesis, in human and animal models of obesity. We examined the hepatocyte-specific enhancer/promoter of FGF21 expression plasmids in high-fat diet-fed mice for 12 weeks. Hydrodynamic injection for FGF21 delivery every 6 weeks sustained high circulating levels of FGF21, resulting in marked reductions in body weight, epididymal fat mass, insulin resistance, and liver steatosis. FGF21-induced lipolysis in the adipose tissue enabled the liver to be flooded with fat-derived FFAs. The hepatic expression of Glut2 and Bdh1 was upregulated, whereas that of gluconeogenesis-related genes, G6p and Pepck, and lipogenesis-related genes, Srebp-1 and Srebp-2, was significantly suppressed. FGF21 induced the phosphorylation of AMPK at Thr172 and Raptor at ser792 and suppressed that of mTOR at ser2448, which downregulated mTORC1 signaling and reduced IRS-1 phosphorylation at ser1101. Finally, in the skeletal muscle, FGF21 increased Glut4 and Mct2, a membrane protein that acts as a carrier for ketone bodies. Enzymes for ketone body catabolism (Scot) and citrate cycle (Cs, Idh3a), and a marker of regenerating muscle (myogenin) were also upregulated via increased KLB expression. Thus, FGF21-induced lipolysis was continuously induced by a high-fat diet and fat-derived FFAs might cause liver damage. Hepatic fatty acid oxidation and ketone body synthesis may act as hepatic FFAs' disposal mechanisms and contribute to improved liver steatosis. Liver-derived ketone bodies might be used for energy in the skeletal muscle. The potential FGF21-related crosstalk between the liver and extraliver organs is a promising strategy to prevent and treat metabolic syndrome-related nonalcoholic steatohepatitis.

FGF21 (Fibroblast Growth Factor 21) Defines a Potential Cardiohepatic Signaling Circuit in End-Stage Heart Failure

BACKGROUND

Extrinsic control of cardiomyocyte metabolism is poorly understood in heart failure (HF). FGF21 (Fibroblast growth factor 21), a hormonal regulator of metabolism produced mainly in the liver and adipose tissue, is a prime candidate for such signaling.

METHODS

To investigate this further, we examined blood and tissue obtained from human subjects with end-stage HF with reduced ejection fraction at the time of left ventricular assist device implantation and correlated serum FGF21 levels with cardiac gene expression, immunohistochemistry, and clinical parameters.

RESULTS

Circulating FGF21 levels were substantially elevated in HF with reduced ejection fraction, compared with healthy subjects (HF with reduced ejection fraction: 834.4 [95% CI, 628.4-1040.3] pg/mL, n=40; controls: 146.0 [86.3-205.7] pg/mL, n=20, P=1.9×10-5). There was clear FGF21 staining in diseased cardiomyocytes, and circulating FGF21 levels negatively correlated with the expression of cardiac genes involved in ketone metabolism, consistent with cardiac FGF21 signaling. FGF21 gene expression was very low in failing and nonfailing hearts, suggesting extracardiac production of the circulating hormone. Circulating FGF21 levels were correlated with BNP (B-type natriuretic peptide) and total bilirubin, markers of chronic cardiac and hepatic congestion.

CONCLUSIONS

Circulating FGF21 levels are elevated in HF with reduced ejection fraction and appear to bind to the heart. The liver is likely the main extracardiac source. This supports a model of hepatic FGF21 communication to diseased cardiomyocytes, defining a potential cardiohepatic signaling circuit in human HF.

LLF580, an FGF21 Analog, Reduces Triglycerides and Hepatic Fat in Obese Adults With Modest Hypertriglyceridemia

PURPOSE

To evaluate the safety and potential efficacy of LLF580, a genetically engineered variant of human fibroblast growth factor-21, for triglyceride lowering, weight loss, and hepatic fat reduction.

METHODS

A multicenter, double-blind, parallel design trial in obese, mildly hypertriglyceridemic adults randomized (1:1) to LLF580 300 mg or placebo subcutaneously every 4 weeks for 3 doses.

RESULTS

Of 64 randomized study participants, 61 (mean ± SD: age 45 ± 11 years, 49% male, 80/15/5% Caucasian/African American/other, body mass index 36.1 ± 3.8 kg/m2) received LLF580 (n = 30) or placebo (n = 31) at 7 research sites in the United States. LLF580 lowered serum triglycerides by 54% (least square mean placebo adjusted change from baseline), total cholesterol 7%, low-density lipoprotein cholesterol 12%, and increased high-density lipoprotein cholesterol 36% compared with placebo (all P < 0.001) over 12 weeks. Substantial reduction of liver fat of 52% over placebo (P < 0.001) was also demonstrated in the setting of improved liver function tests including alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase, the composite enhanced liver fibrosis score, and N-terminal type III collagen propeptide (all P < 0.05). Insulin and C-peptide levels and insulin resistance by homeostatic model assessment for insulin resistance were all lower, and adiponectin higher with LLF580 treatment compared with placebo, whereas fasting glucose and glycated hemoglobin were unchanged. Reductions in biomarkers of bone formation without differences in markers of bone resorption were observed. LLF580 was generally safe and well tolerated, except for higher incidence of generally mild to moderate gastrointestinal adverse effects.

CONCLUSIONS

In obese, mildly hypertriglyceridemic adults, LLF580 was generally safe and demonstrated beneficial effects on serum lipids, liver fat, and biomarkers of liver injury, suggesting it may be effective for treatment of select metabolic disorders including hypertriglyceridemia and nonalcoholic fatty liver disease. Assessments of longer term safety and efficacy are warranted.

CLINICALTRIALS.GOV IDENTIFIER

NCT03466203.

FGF21 Is Released During Increased Lipogenesis State Following Rapid-Onset Radioiodine-Induced Hypothyroidism

BACKGROUND

FGF21 pharmacological treatment reverses fatty liver and lowers serum triglyceride concentration but FGF21 serum level is increased in hepatic steatosis. FGF21 secretion is induced by thyroid hormones in vitro.

PURPOSE

To determine the influence of thyroid hormones and metabolic changes secondary to thyroid dysfunction on FGF21 secretion in humans.

MATERIALS AND METHODS

This was a case-control study. 82 hyperthyroid and 15 hypothyroid patients were recruited together with 25 healthy controls. Of those with hyperthyroidism, 56 received radioiodine treatment and 42 of them achieved hypothyroidism and then euthyroidism within one year following therapy. Radioiodine-induced hypothyroidism developed abruptly within a six week interval between clinic visits. FGF21 serum levels were determined with an ELISA method.

RESULTS

Serum FGF21 levels did not differ in hyper- and hypothyroid patients in comparison to controls [median 103.25 (interquartile range, 60.90-189.48) and 86.10 (54.05-251.02) vs 85.20 (58.00-116.80) pg/mL P=0.200 and 0.503, respectively]. In hyperthyroid patients treated with radioiodine, serum FGF21 levels increased significantly in rapid-onset hypothyroidism in comparison to the hyperthyroid and euthyroid phase [median 160.55 (interquartile range, 92.48 - 259.35) vs 119.55 (67.78-192.32) and 104.43 (55.93-231.93) pg/mL, P=0.034 and 0.033, respectively]. The rising serum FGF21 level correlated positively with serum triglycerides (Spearman coefficient rs=0.36, P=0.017) and inversely with serum SHBG (rs=-0.41, P=0.007), but did not correlate with thyroid hormone levels.

CONCLUSIONS

There was a transient increase in FGF21 serum level during rapid-onset hypothyroidism following radioiodine treatment. There was no association between FGF21 serum level and thyroid hormones. In radioiodine-induced hypothyroidism, the rising serum FGF21 concentration correlated positively with rising serum triglycerides and negatively with falling SHBG, reflecting increased hepatic lipogenesis.

Mice with high FGF21 serum levels had a reduced preference for morphine and an attenuated development of acute antinociceptive tolerance and physical dependence

Because of increased opioid misuse, there is a need to identify new targets for minimizing opioid tolerance, and physical and psychological dependence. Previous studies showed that fibroblast growth factor 21 (FGF21) decreased alcohol and sweet preference in mice. In this study, FGF21-transgenic (FGF21-Tg) mice, expressing high FGF21 serum levels, and wildtype (WT) C57BL/6J littermates were treated with morphine and saline to determine if differences exist in their physiological and behavioral responses to opioids. FGF21-Tg mice displayed reduced preference for morphine in the conditioned place preference assay compared to WT littermates. Similarly, FGF21-Tg mice had an attenuation of the magnitude and rate of acute morphine antinociceptive tolerance development, and acute and chronic morphine physical dependence, but exhibited no change in chronic morphine antinociceptive tolerance. The ED50 values for morphine-induced antinociception in the 55 °C hot plate and the 55 °C warm-water tail withdrawal assays were similar in both strains of mice. Likewise, FGF21-Tg and WT littermates had comparable responses to morphine-induced respiratory depression. Overall, FGF21-Tg mice had a decrease in the development of acute analgesic tolerance, and the development of physical dependence, and morphine preference. FGF21 and its receptor have therapeutic potential for reducing opioid withdrawal symptoms and craving, and augmenting opioid therapeutics for acute pain patients to minimize tolerance development.

Insights into the molecular targets and emerging pharmacotherapeutic interventions for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease worldwide. With no Food and Drug Administration approved drugs, current treatment options include dietary restrictions and lifestyle modification. NAFLD is closely associated with metabolic disorders such as obesity, type 2 diabetes, and dyslipidemia. Hence, clinically various pharmacological approaches using existing drugs such as antidiabetic, anti-obesity, antioxidants, and cytoprotective agents have been considered in the management of NAFLD and nonalcoholic steatohepatitis (NASH). However, several pharmacological therapies aiming to alleviate NAFLD-NASH are currently being examined at various phases of clinical trials. Emerging data from these studies with drugs targeting diverse molecular mechanisms show promising outcomes. This review summarizes the current understanding of the pathogenic mechanisms of NAFLD and provides an insight into the pharmacological targets and emerging therapeutics with specific interventional mechanisms. In addition, we also discuss the importance and utility of new approach methodologies and regulatory perspectives for NAFLD-NASH drug development.

Hepatokines and Non-Alcoholic Fatty Liver Disease: Linking Liver Pathophysiology to Metabolism

The liver plays a key role in maintaining energy homeostasis by sensing and responding to changes in nutrient status under various metabolic conditions. Recently highlighted as a major endocrine organ, the contribution of the liver to systemic glucose and lipid metabolism is primarily attributed to signaling crosstalk between multiple organs via hepatic hormones, cytokines, and hepatokines. Hepatokines are hormone-like proteins secreted by hepatocytes, and a number of these have been associated with extra-hepatic metabolic regulation. Mounting evidence has revealed that the secretory profiles of hepatokines are significantly altered in non-alcoholic fatty liver disease (NAFLD), the most common hepatic manifestation, which frequently precedes other metabolic disorders, including insulin resistance and type 2 diabetes. Therefore, deciphering the mechanism of hepatokine-mediated inter-organ communication is essential for understanding the complex metabolic network between tissues, as well as for the identification of novel diagnostic and/or therapeutic targets in metabolic disease. In this review, we describe the hepatokine-driven inter-organ crosstalk in the context of liver pathophysiology, with a particular focus on NAFLD progression. Moreover, we summarize key hepatokines and their molecular mechanisms of metabolic control in non-hepatic tissues, discussing their potential as novel biomarkers and therapeutic targets in the treatment of metabolic diseases.