Therapeutic FGF19 promotes HDL biogenesis and transhepatic cholesterol efflux to prevent atherosclerosis

FGF-based drug discovery: advances and challenges

The fibroblast growth factor (FGF) family comprises 15 paracrine-acting and 3 endocrine-acting polypeptides, which govern a multitude of processes in human development, metabolism and tissue homeostasis. Therapeutic endocrine FGFs have recently advanced in clinical trials, with FGF19 and FGF21-based therapies on the cusp of approval for the treatment of primary sclerosing cholangitis and metabolic syndrome-associated steatohepatitis, respectively. By contrast, while paracrine FGFs were once thought to be promising drug candidates for wound healing, burns, tissue repair and ischaemic ailments based on their potent mitogenic and angiogenic properties, repeated failures in clinical trials have led to the widespread perception that the development of paracrine FGF-based drugs is not feasible. However, the observation that paracrine FGFs can exert FGF hormone-like metabolic activities has restored interest in these FGFs. The recent structural elucidation of the FGF cell surface signalling machinery and the formulation of a new threshold model for FGF signalling specificity have paved the way for therapeutically harnessing paracrine FGFs for the treatment of a range of metabolic diseases.

High plasma fibroblast growth factor 19 is associated with improved prognosis in patients with acute ischemic stroke

OBJECTIVE

To prospectively investigate the relationships between plasma fibroblast growth factor 19 (FGF-19) and clinical outcomes in patients with acute ischemic stroke.

METHODS

Plasma FGF-19 levels at baseline were measured for 3048 patients with ischemic stroke, and all patients were followed up at one year after stroke onset. The primary outcome was a combination of death and major disability (modified Rankin Scale score of ≥3) at one year after stroke onset, and secondary outcomes included major disability, death, recurrent stroke, vascular events and the combination of death and vascular events.

RESULTS

During the 1-year of follow-up, 682 (22.38 %) patients experienced the primary outcome; 503 had a major disability and 179 died. After multivariate adjustment, higher plasma FGF-19 was significantly associated with decreased risk of the primary outcome (odds ratio = 0.48, 95 % confidence interval = 0.36-0.66). Each 1-SD increase of log-transformed FGF-19 (0.93 pg/mL) was associated with 20 % decreased risk of the primary outcome. The addition of FGF-19 to the conventional risk factors significantly improved prediction of the primary outcome in ischemic stroke patients (net reclassification index = 25.10 %, p < 0.001; integrated discrimination improvement = 1.25 %, p < 0.001). Furthermore, patients with both high FGF-19 (≥573.7 pg/mL) and low FGF-21 (<740.1 pg/mL) levels had the lowest incidences of all study outcomes.

CONCLUSIONS

High plasma FGF-19 levels were associated with improved prognosis in patients with acute ischemic stroke, suggesting that FGF-19 may be a potential biomarker of good prognosis for ischemic stroke.

Fibroblast Growth Factors in Cardiovascular Disease

Despite advancements in managing traditional cardiovascular risk factors, many cardiovascular diseases (CVDs) persist. Fibroblast growth factors (FGFs) have emerged as potential diagnostic markers and therapeutic targets for CVDs. FGF1, FGF2, and FGF4 are primarily used for therapeutic angiogenesis. Clinical applications are being explored based on animal studies using approaches such as recombinant protein administration and adenovirus-mediated gene delivery, targeting patients with coronary artery disease and lower extremity arterial disease. Although promising results have been observed in animal models and early-stage clinical trials, further studies are required to assess their therapeutic potential. The FGF19 subfamily, consisting of FGF19, FGF21, and FGF23, act via endocrine signaling in various organs. FGF19, primarily expressed in the small intestine, plays important roles in glucose, lipid, and bile acid metabolism and has therapeutic potential for metabolic disorders. FGF21, found in various tissues, improves glucose metabolism and insulin sensitivity, suggesting potential for treating obesity and diabetes. FGF23, primarily secreted by osteocytes, regulates vitamin D and phosphate metabolism and serves as an important biomarker for chronic kidney disease and CVDs. Thus, FGFs holds promise for both therapeutic and diagnostic applications in metabolic and cardiovascular diseases. Understanding the mechanisms of FGF may pave the way for novel strategies to prevent and manage CVDs, potentially addressing the limitations of current treatments. This review explores the roles of FGF1, FGF2, FGF4, and the FGF19 subfamily in maintaining cardiovascular health. Further research and clinical trials are crucial to fully understand the therapeutic potential of FGFs in managing cardiovascular health.

A primer on the pleiotropic endocrine fibroblast growth factor FGF19/FGF15

Fibroblast Growth Factor 19 (FGF19) is a member of the Fibroblast Growth Factor (FGF) family, known for its role in various cellular processes including embryonic development and metabolic regulation. FGF19 functions as an endocrine factor, influencing energy balance, bile acid synthesis, glucose and lipid metabolism, as well as cell proliferation. FGF19 has a conserved structure typical of FGFs but exhibits unique features. Unlike most FGFs, which act locally, FGF19 travels through the bloodstream to distant targets including the liver. Its interaction with the β-Klotho (KLB) co-receptor and FGF Receptor 4 (FGFR4) in hepatocytes or FGFR1c in extrahepatic tissues initiates signaling cascades crucial for its biological functions. Although the mouse ortholog, FGF15, diverges significantly from human FGF19 in protein sequence and receptor binding, studies of FGF15-deficient mice have led to a better understanding of the proteins' role in bile acid regulation, metabolism, and embryonic development. Overexpression studies in transgenic mice have further revealed roles in not only ameliorating metabolic diseases but also in promoting hepatocyte proliferation and tumorigenesis. This review summarizes the gene and protein structure of FGF19/15, its expression patterns, phenotypes in mutant models, and implication in human diseases, providing insights into potential therapeutic strategies targeting the FGF19 signaling pathway.

Non-mitogenic FGF19 mRNA-based therapy for the treatment of experimental metabolic dysfunction-associated steatotic liver disease (MASLD)

Metabolic dysfunction-associated steatohepatitis (MASH) represents a global health threat. MASH pathophysiology involves hepatic lipid accumulation and progression to severe conditions like cirrhosis and, eventually, hepatocellular carcinoma. Fibroblast growth factor (FGF)-19 has emerged as a key regulator of metabolism, offering potential therapeutic avenues for MASH and associated disorders. We evaluated the therapeutic potential of non-mitogenic (NM)-FGF19 mRNA formulated in liver-targeted lipid nanoparticles (NM-FGF19-mRNAs-LNPs) in C57BL/6NTac male mice with diet-induced obesity and MASH (DIO-MASH: 40% kcal fat, 20% kcal fructose, 2% cholesterol). After feeding this diet for 21 weeks, NM-FGF19-mRNAs-LNPs or control (C-mRNA-LNPs) were administered (0.5 mg/kg, i.v.) weekly for another six weeks, in which diet feeding continued. NM-FGF19-mRNAs-LNPs treatment in DIO-MASH mice resulted in reduced body weight, adipose tissue depots, and serum transaminases, along with improved insulin sensitivity. Histological analyses confirmed the reversal of MASH features, including steatosis reduction without worsening fibrosis. NM-FGF19-mRNAs-LNPs reduced total hepatic bile acids (BAs) and changed liver BA composition, markedly influencing cholesterol homeostasis and metabolic pathways as observed in transcriptomic analyses. Extrahepatic effects included the down-regulation of metabolic dysfunction-associated genes in adipose tissue. This study highlights the potential of NM-FGF19-mRNA-LNPs therapy for MASH, addressing both hepatic and systemic metabolic dysregulation. NM-FGF19-mRNA demonstrates efficacy in reducing liver steatosis, improving metabolic parameters, and modulating BA levels and composition. Given the central role played by BA in dietary fat absorption, this effect of NM-FGF19-mRNA may be mechanistically relevant. Our study underscores the high translational potential of mRNA-based therapies in addressing the multifaceted landscape of MASH and associated metabolic perturbations.

The role of FGF19 in metabolic regulation: insights from preclinical models to clinical trials

Fibroblast growth factor 19 (FGF19) is a hormone synthesized in enterocytes in response to bile acids. This review explores the pivotal role of FGF19 in metabolism, addressing the urgent global health concern of obesity and its associated pathologies, notably type 2 diabetes. The intriguing inverse correlation between FGF19 and body mass or visceral adiposity, as well as its rapid increase following bariatric surgery, emphasizes its potential as a therapeutic target. This article meticulously examines the impact of FGF19 on metabolism by gathering evidence primarily derived from studies conducted in animal models or cell lines, using both FGF19 treatment and genetic modifications. Overall, these studies demonstrate that FGF19 has antidiabetic and antiobesogenic effects. A thorough examination across metabolic tissues, including the liver, adipose tissue, skeletal muscle, and the central nervous system, is conducted, unraveling the intricate interplay of FGF19 across diverse organs. Moreover, we provide a comprehensive overview of clinical trials involving an FGF19 analog called aldafermin, emphasizing promising results in diseases such as nonalcoholic steatohepatitis and diabetes. Therefore, we aim to foster a deeper understanding of FGF19 role and encourage further exploration of its clinical applications, thereby advancing the field and offering innovative approaches to address the escalating global health challenge of obesity and related metabolic conditions.

Pharmacological modulation of cholesterol 7α-hydroxylase (CYP7A1) as a therapeutic strategy for hypercholesterolemia

Despite the availability of many therapeutic options, the prevalence of hypercholesterolemia remains high. There exists a significant unmet medical need for novel drugs and/or treatment combinations to effectively combat hypercholesterolemia while minimizing adverse reactions. The modulation of cholesterol 7α-hydroxylase (CYP7A1) expression via perturbation of the farnesoid X receptor (FXR) - dependent pathways, primarily FXR/small heterodimer partner (SHP) and FXR/ fibroblast growth factor (FGF)-19/ fibroblast growth factor receptor (FGFR)-4 pathways, presents as a potential option to lower cholesterol levels. This paper provides a comprehensive review of the important role that CYP7A1 plays in cholesterol homeostasis and how its expression can be exploited to assert differential control of bile acid synthesis and cholesterol metabolism. Additionally, the paper also summarizes the current therapeutic options for hypercholesterolemia, and positions modulators of CYP7A1 expression, namely FGFR4 inhibitors and FXR antagonists, as emerging and distinct pharmacological agents to complement and diversify the treatment regime. Their mechanistic and clinical considerations are also extensively described to interrogate the benefits and risks associated with using FXR-mediating agents, either singularly or in combination with recognised agents such as statins to target hypercholesterolemia.

Endocrine FGFs and their signaling in the brain: Relevance for energy homeostasis

Since their discovery in 2000, there has been a continuous expansion of studies investigating the physiology, biochemistry, and pharmacology of endocrine fibroblast growth factors (FGFs). FGF19, FGF21, and FGF23 comprise a subfamily with attributes that distinguish them from typical FGFs, as they can act as hormones and are, therefore, referred to as endocrine FGFs. As they participate in a broad cross-organ endocrine signaling axis, endocrine FGFs are crucial lipidic, glycemic, and energetic metabolism regulators during energy availability fluctuations. They function as powerful metabolic signals in physiological responses induced by metabolic diseases, like type 2 diabetes and obesity. Pharmacologically, FGF19 and FGF21 cause body weight loss and ameliorate glucose homeostasis and energy expenditure in rodents and humans. In contrast, FGF23 expression in mice and humans has been linked with insulin resistance and obesity. Here, we discuss emerging concepts in endocrine FGF signaling in the brain and critically assess their putative role as therapeutic targets for treating metabolic disorders.

Activation of GPBAR1 attenuates vascular inflammation and atherosclerosis in a mouse model of NAFLD-related cardiovascular disease

While patients with nonalcoholic fatty liver disease (NAFLD) are at increased risk to develop clinically meaningful cardiovascular diseases (CVD), there are no approved drug designed to target the liver and CVD component of NAFLD. GPBAR1, also known as TGR5, is a G protein coupled receptor for secondary bile acids. In this study we have investigated the effect of GPBAR1 activation by BAR501, a selective GPBAR1 agonist, in Apolipoprotein E deficient (ApoE-/-) mice fed a high fat diet and fructose (Western diet), a validated model of NAFLD-associated atherosclerosis. Using aortic samples from patients who underwent surgery for abdominal aneurism, and ex vivo experiments with endothelial cells and human macrophages, we were able to co-localize the expression of GPBAR1 in CD14+ and PECAM1+ cells. Similar findings were observed in the aortic plaques from ApoE-/- mice. Treating ApoE-/- mice with BAR501, 30 mg/kg for 14 weeks, attenuated the body weight gain while ameliorated the insulin sensitivity by increasing the plasma concentrations of GLP-1 and FGF15. Activation of GPBAR1 reduced the aorta thickness and severity of atherosclerotic lesions and decreased the amount of plaques macrophages. Treating ApoE-/- mice reshaped the aortic transcriptome promoting the expression of anti-inflammatory genes, including IL-10, as also confirmed by tSNE analysis of spleen-derived macrophages. Feeding ApoE-/- mice with BAR501 redirected the bile acid synthesis and the composition of the intestinal microbiota. In conclusion, GPBAR1 agonism attenuates systemic inflammation and improve metabolic profile in a genetic/dietetic model of atherosclerosis. BAR501 might be of utility in the treatment for NAFLD-related CVD.

The metabolic adaptation of bile acids and cholesterol after biliary atresia in lamprey via transcriptome-based analysis

Lamprey underwent biliary atresia (BA) at its metamorphosis stage. In contrast to patients with BA who develop progressive disease, lamprey can grow and develop normally, suggesting that lamprey has several adaptations for BA. Here we show that adaptive changes in bile acid and cholesterol metabolism are produced after lamprey BA. Among 1102 differentially expressed genes (DGEs) after BA in lamprey, many are enriched in gene ontology (GO) terms and pathways related to steroid metabolism. We find that among the DGEs related to bile acids and cholesterol metabolism, the expression of cytochrome P450 family 7 subfamily A member 1 (CYP7A1), sodium-dependent taurine cotransport polypeptide (NTCP) are significantly downregulated, whereas nuclear receptor farnesoid X receptor (FXR), multidrug resistance-associated protein 3 (MRP3), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), sterol O-acyltransferase 1 (SOAT1), and ATP binding cassette subfamily A member 1 (ABCA1) are remarkably upregulated. The changes in expression level are also validated by RT-qPCR. Furthermore, the level of high-density lipoprotein-cholesterol (HDL-C) and low-density lipoprotein-cholesterol (LDL-C) in juvenile serum is higher compared to larvae. Taken together, the findings collectively indicate that after BA, lamprey may maintain bile acids and cholesterol homeostasis in liver tissue by inhibiting bile acids synthesis and uptake, promoting its efflux back to circulation, and enhancing cholesterol esterification for storage as lipid droplets and its egress to form nascent HDL (nHDL). Understanding the possible molecular mechanisms of lamprey metabolic adaptation sheds new light on the understanding of the development and treatment of diseases caused by abnormal bile acid and cholesterol metabolism in humans.

The interplay between nonalcoholic fatty liver disease and atherosclerotic cardiovascular disease

Therapeutic approaches that lower circulating low-density lipoprotein (LDL)-cholesterol significantly reduced the burden of cardiovascular disease over the last decades. However, the persistent rise in the obesity epidemic is beginning to reverse this decline. Alongside obesity, the incidence of nonalcoholic fatty liver disease (NAFLD) has substantially increased in the last three decades. Currently, approximately one third of world population is affected by NAFLD. Notably, the presence of NAFLD and particularly its more severe form, nonalcoholic steatohepatitis (NASH), serves as an independent risk factor for atherosclerotic cardiovascular disease (ASCVD), thus, raising interest in the relationship between these two diseases. Importantly, ASCVD is the major cause of death in patients with NASH independent of traditional risk factors. Nevertheless, the pathophysiology linking NAFLD/NASH with ASCVD remains poorly understood. While dyslipidemia is a common risk factor underlying both diseases, therapies that lower circulating LDL-cholesterol are largely ineffective against NASH. While there are no approved pharmacological therapies for NASH, some of the most advanced drug candidates exacerbate atherogenic dyslipidemia, raising concerns regarding their adverse cardiovascular consequences. In this review, we address current gaps in our understanding of the mechanisms linking NAFLD/NASH and ASCVD, explore strategies to simultaneously model these diseases, evaluate emerging biomarkers that may be useful to diagnose the presence of both diseases, and discuss investigational approaches and ongoing clinical trials that potentially target both diseases.

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.

Fibroblast Growth Factor 19 Improves LPS-Induced Lipid Disorder and Organ Injury by Regulating Metabolomic Characteristics in Mice

Sepsis is extremely heterogeneous pathology characterized by complex metabolic changes. Fibroblast growth factor 19 (FGF19) is a well-known intestine-derived inhibitor of bile acid biosynthesis. However, it is largely unknown about the roles of FGF19 in improving sepsis-associated metabolic disorder and organ injury. In the present study, mice were intravenously injected recombinant human FGF19 daily for 7 days followed by lipopolysaccharide (LPS) administration. At 24 hours after LPS stimuli, sera were collected for metabolomic analysis. Ingenuity pathway analysis (IPA) network based on differential metabolites (DMs) was conducted. Here, metabolomic analysis revealed that FGF19 pretreatment reversed the increase of LPS-induced fatty acids. IPA network indicated that altered linoleic acid (LA) and gamma-linolenic acid (GLA) were involved in the regulation of oxidative stress and mitochondrial function and were closely related to reactive oxygen species (ROS) generation. Further investigation proved that FGF19 pretreatment decreased serum malondialdehyde (MDA) levels and increased serum catalase (CAT) levels. In livers, FGF19 suppressed the expression of inducible NO synthase (iNOS) and enhanced the expression of nuclear factor erythroid 2-related factor 2 (NRF2) and hemeoxygenase-1 (HO-1). Finally, FGF19 pretreatment protected mice against LPS-induced liver, ileum, and kidney injury. Taken together, FGF19 alleviates LPS-induced organ injury associated with improved serum LA and GLA levels and oxidative stress, suggesting that FGF19 might be a promising target for metabolic therapy for sepsis.

Physiological and pathophysiological role of endocrine fibroblast growth factors

The endocrine subfamily of fibroblast growth factors (FGF) includes three factors: FGF19, FGF21, FGF23. They act on distal tissues through FGF receptors (FGFRs). The FGFR activation requires two cofactors: α- and β-Klotho, which are structurally related single-pass transmembrane proteins. The endocrine FGFs regulate various metabolic processes involved in the regulation of glucose and lipid metabolism as well as bile acid circulation, vitamin D modulation, and phosphate homeostasis. The FGF-FGFR dysregulation is widely implicated in the pathogenesis of various disorders. Significant alterations in plasma FGF concentration are associated with the most prevalent chronic diseases, including dyslipidemia, type 2 diabetes, cardiovascular diseases, obesity, non-alcoholic fatty liver disease, diseases of the biliary tract, chronic kidney disease, inflammatory bowel disease, osteomalacia, various malignancies, and depression. Therefore, the endocrine FGFs may serve as disease predictors or biomarkers, as well as potential therapeutic targets. Currently, numerous analogues and inhibitors of endocrine FGFs are under development for treatment of various disorders, and recently, a human monoclonal antibody against FGF23 has been approved for treatment of X-linked hypophosphatemia. The aim of this review is to summarize the current data on physiological and pathophysiological actions of the endocrine FGF subfamily and recent research concerning the therapeutic potential of the endocrine FGF pathways.

Bromodomain Inhibition Reveals FGF15/19 As a Target of Epigenetic Regulation and Metabolic Control

Epigenetic regulation is an important factor in glucose metabolism, but underlying mechanisms remain largely unknown. Here we investigated epigenetic control of systemic metabolism by bromodomain-containing proteins (Brds), which are transcriptional regulators binding to acetylated histone, in both intestinal cells and mice treated with the bromodomain inhibitor JQ-1. In vivo treatment with JQ-1 resulted in hyperglycemia and severe glucose intolerance. Whole-body or tissue-specific insulin sensitivity was not altered by JQ-1; however, JQ-1 treatment reduced insulin secretion during both in vivo glucose tolerance testing and ex vivo incubation of isolated islets. JQ-1 also inhibited expression of fibroblast growth factor (FGF) 15 in the ileum and decreased FGF receptor 4-related signaling in the liver. These adverse metabolic effects of Brd4 inhibition were fully reversed by in vivo overexpression of FGF19, with normalization of hyperglycemia. At a cellular level, we demonstrate Brd4 binds to the promoter region of FGF19 in human intestinal cells; Brd inhibition by JQ-1 reduces FGF19 promoter binding and downregulates FGF19 expression. Thus, we identify Brd4 as a novel transcriptional regulator of intestinal FGF15/19 in ileum and FGF signaling in the liver and a contributor to the gut-liver axis and systemic glucose metabolism.

HDL maturation and remodelling

Cholesterol in the circulation is mostly transported in an esterified form as a component of lipoproteins. The majority of these cholesteryl esters are produced in nascent, discoidal high density lipoproteins (HDLs) by the enzyme, lecithin:cholesterol acyltransferase (LCAT). Discoidal HDLs are discrete populations of particles that consist of a phospholipid bilayer, the hydrophobic acyl chains of which are shielded from the aqueous environment by apolipoproteins that also confer water solubility on the particles. The progressive LCAT-mediated accumulation of cholesteryl esters in discoidal HDLs generates the spherical HDLs that predominate in normal human plasma. Spherical HDLs contain a core of water insoluble, neutral lipids (cholesteryl esters and triglycerides) that is surrounded by a surface monolayer of phospholipids with which apolipoproteins associate. Although spherical HDLs all have the same basic structure, they are extremely diverse in size, composition, and function. This review is concerned with how the biogenesis of discoidal and spherical HDLs is regulated and the mechanistic basis of their size and compositional heterogeneity. Current understanding of the impact of this heterogeneity on the therapeutic potential of HDLs of varying size and composition is also addressed in the context of several disease states.

Genetics and regulation of HDL metabolism

The inverse association between plasma HDL cholesterol (HDL-C) levels and risk for cardiovascular disease (CVD) has been demonstrated by numerous epidemiological studies. However, efforts to reduce CVD risk by pharmaceutically manipulating HDL-C levels failed and refused the HDL hypothesis. HDL-C levels in the general population are highly heterogeneous and are determined by a combination of genetic and environmental factors. Insights into the causes of HDL-C heterogeneity came from the study of monogenic HDL deficiency syndromes but also from genome wide association and Μendelian randomization studies which revealed the contribution of a large number of loci to low or high HDL-C cases in the general or in restricted ethnic populations. Furthermore, HDL-C levels in the plasma are under the control of transcription factor families acting primarily in the liver including members of the hormone nuclear receptors (PPARs, LXRs, HNF-4) and forkhead box proteins (FOXO1-4) and activating transcription factors (ATFs). The effects of certain lipid lowering drugs used today are based on the modulation of the activity of specific members of these transcription factors. During the past decade, the roles of small or long non-coding RNAs acting post-transcriptionally on the expression of HDL genes have emerged and provided novel insights into HDL regulation and new opportunities for therapeutic interventions. In the present review we summarize recent progress made in the genetics and the regulation (transcriptional and post-transcriptional) of HDL metabolism.

The Saga of Endocrine FGFs

Fibroblast growth factors (FGFs) are cell-signaling proteins with diverse functions in cell development, repair, and metabolism. The human FGF family consists of 22 structurally related members, which can be classified into three separate groups based on their action of mechanisms, namely: intracrine, paracrine/autocrine, and endocrine FGF subfamilies. FGF19, FGF21, and FGF23 belong to the hormone-like/endocrine FGF subfamily. These endocrine FGFs are mainly associated with the regulation of cell metabolic activities such as homeostasis of lipids, glucose, energy, bile acids, and minerals (phosphate/active vitamin D). Endocrine FGFs function through a unique protein family called klotho. Two members of this family, α-klotho, or β-klotho, act as main cofactors which can scaffold to tether FGF19/21/23 to their receptor(s) (FGFRs) to form an active complex. There are ongoing studies pertaining to the structure and mechanism of these individual ternary complexes. These studies aim to provide potential insights into the physiological and pathophysiological roles and therapeutic strategies for metabolic diseases. Herein, we provide a comprehensive review of the history, structure–function relationship(s), downstream signaling, physiological roles, and future perspectives on endocrine FGFs.

Combined ASBT Inhibitor and FGF15 Treatment Improves Therapeutic Efficacy in Experimental Nonalcoholic Steatohepatitis

BACKGROUND & AIMS

Pharmacologic agents targeting bile acid signaling show promise for treating nonalcoholic steatohepatitis (NASH). However, clinical findings suggest that new treatment strategies with enhanced therapeutic efficacy and minimized undesired effects are needed. This preclinical study investigates whether combining an apical sodium-bile acid transporter (ASBT) inhibitor GSK233072 (GSK672) and fibroblast growth factor-15 (FGF15) signaling activation improves anti-NASH efficacy.

METHODS

Mice with high fat, cholesterol, and fructose (HFCFr) diet-induced NASH and stage 2 fibrosis are used as a NASH model. GSK672 or AAV8-TBG-FGF15 interventions are administered alone or in combination to HFCFr diet-fed mice.

RESULTS

The combined treatment significantly enhances therapeutic efficacy against steatosis, inflammation, ballooning, and fibrosis than either single treatment. Mechanistically, the synergistic actions of GSK672 and FGF15 on inhibiting gut bile acid reuptake and hepatic bile acid synthesis achieve greater magnitude of bile acid pool reduction that not only decreases bile acid burden in NASH livers but also limits intestinal lipid absorption, which, together with FGF15 signaling activation, produces weight loss, reduction of adipose inflammation, and attenuated hepatocellular organelle stress. Furthermore, the combined treatment attenuates increased fecal bile acid excretion and repressed bile acid synthesis, which underlie diarrhea and hypercholesterolemia associated with ASBT inhibition and FGF19 analogue, respectively, in clinical settings.

CONCLUSIONS

Concomitant ASBT inhibition and FGF15 signaling activation produce metabolic changes that partially mimic the bariatric surgery condition whereby lipid malabsorption and increased FGF15/19 signaling synergistically mediate weight loss and metabolic improvement. Further clinical studies may be warranted to investigate whether combining ASBT inhibitor and FGF19 analogue enhances anti-NASH efficacy and reduced treatment-associated adverse events in humans.

Decreased serum fibroblast growth factor 19 level is a risk factor for type 1 diabetes

Background

Increasing evidence suggests that fibroblast growth factor 19 (FGF19) is a regulator of glucose metabolism and may provide a new therapeutic target for type 1 diabetes (T1D). However, the clinical relevance of FGF19 in T1D remains unclear. In this study, we examined the relationship between the serum FGF19 concentration and T1D.

Methods

This study included 81 newly diagnosed T1D patients and 80 sex- and age-matched healthy controls. The correlation between the FGF19 concentration and clinical characteristics of T1D patients and healthy controls was investigated. Logistic regression analysis was performed to determine whether levels of FGF19 were independently associated with T1D.

Results

The fasting serum FGF19 levels in the T1D group were significantly lower than those in the control group [159.9 (100.0–272.7) vs. 205.0 (126.9–307.9) pg/mL, P=0.008]. In all subjects, serum FGF19 levels were negatively correlated with fasting blood glucose (FBG) (r=−0.192, P=0.015). In the control group, serum FGF19 levels were positively correlated with total cholesterol (TC) (r=0.338, P=0.002) and low-density lipoprotein cholesterol (LDL-c) (r=0.300, P=0.007). In addition to sex and body mass index (BMI), FGF19 was an independent impact factor for T1D [odds ratio (OR) =0.541, P=0.023; adjusted for sex, age, BMI, presence of hypertension, and presence of dyslipidemia].

Conclusions

Low serum FGF19 level is associated with T1D, which could serve as a risk factor for T1D.

Nuclear hormone and peptide hormone therapeutics for NAFLD and NASH

Background

Non-alcoholic steatohepatitis (NASH) is a spectrum of histological liver pathologies ranging from hepatocyte fat accumulation, hepatocellular ballooning, lobular inflammation, and pericellular fibrosis. Based on early investigations, it was discovered that visceral fat accumulation, hepatic insulin resistance, and atherogenic dyslipidemia are pathological triggers for NASH progression. As these pathogenic features are common with obesity, type 2 diabetes (T2D), and atherosclerosis, therapies that target dysregulated core metabolic pathways may hold promise for treating NASH, particularly as first-line treatments.

Scope of Review

In this review, the latest clinical data on nuclear hormone- and peptide hormone-based drug candidates for NASH are reviewed and contextualized, culminating with a discovery research perspective on emerging combinatorial therapeutic approaches that merge nuclear and peptide strategies.

Major Conclusion

Several drug candidates targeting the metabolic complications of NASH have shown promise in early clinical trials, albeit with unique benefits and challenges, but questions remain regarding their translation to larger and longer clinical trials, as well as their utility in a more diseased patient population. Promising polypharmacological approaches can potentially overcome some of these perceived challenges, as has been suggested in preclinical models, but deeper characterizations are required to fully evaluate these opportunities.

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Despite no approved treatments for NASH, several drug candidates have shown promise in early clinical trials.

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Therapies targeting metabolic pathologies of NASH have shown efficacy to reduce hepatic fat content and improve fibrosis.

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Many of these therapies have been rationally designed to mimic nuclear hormone or peptide hormone action.

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Despite provocative preclinical findings of nuclear and peptide hormone combination, clinical translation remains unproven.

DNA methylation microarrays identify epigenetically regulated lipid related genes in obese patients with hypercholesterolemia

BACKGROUND

Epigenetics can contribute to lipid disorders in obesity. The DNA methylation pattern can be the cause or consequence of high blood lipids. The aim of the study was to investigate the DNA methylation profile in peripheral leukocytes associated with elevated LDL-cholesterol level in overweight and obese individuals.

METHODS

To identify the differentially methylated genes, genome-wide DNA methylation microarray analysis was performed in leukocytes of obese individuals with high LDL-cholesterol (LDL-CH, ≥ 3.4 mmol/L) versus control obese individuals with LDL-CH, < 3.4 mmol/L. Biochemical tests such as serum glucose, total cholesterol, HDL cholesterol, triglycerides, insulin, leptin, adiponectin, FGF19, FGF21, GIP and total plasma fatty acids content have been determined. Oral glucose and lipid tolerance tests were also performed. Human DNA Methylation Microarray (from Agilent Technologies) containing 27,627 probes for CpG islands was used for screening of DNA methylation status in 10 selected samples. Unpaired t-test and Mann-Whitney U-test were used for biochemical and anthropometric parameters statistics. For microarrays analysis, fold of change was calculated comparing hypercholesterolemic vs control group. The q-value threshold was calculated using moderated Student's t-test followed by Benjamini-Hochberg multiple test correction FDR.

RESULTS

In this preliminary study we identified 190 lipid related CpG loci differentially methylated in hypercholesterolemic versus control individuals. Analysis of DNA methylation profiles revealed several loci engaged in plasma lipoprotein formation and metabolism, cholesterol efflux and reverse transport, triglycerides degradation and fatty acids transport and β-oxidation. Hypermethylation of CpG loci located in promoters of genes regulating cholesterol metabolism: PCSK9, LRP1, ABCG1, ANGPTL4, SREBF1 and NR1H2 in hypercholesterolemic patients has been found. Novel epigenetically regulated CpG sites include ABCG4, ANGPTL4, AP2A2, AP2M1, AP2S1, CLTC, FGF19, FGF1R, HDLBP, LIPA, LMF1, LRP5, LSR, NR1H2 and ZDHHC8 genes.

CONCLUSIONS

Our results indicate that obese individuals with hypercholesterolemia present specific DNA methylation profile in genes related to lipids transport and metabolism. Detailed knowledge of epigenetic regulation of genes, important for lipid disorders in obesity, underlies the possibility to influence target genes by changing diet and lifestyle, as DNA methylation is reversible and depends on environmental factors. These findings give rise for further studies on factors that targets methylation of revealed genes.

Dysregulated lipid metabolism links NAFLD to cardiovascular disease

Background

Non-alcoholic fatty liver disease (NAFLD) is rapidly becoming a global health problem. Cardiovascular diseases (CVD) are the most common cause of mortality in NAFLD patients. NAFLD and CVD share several common risk factors including obesity, insulin resistance, and type 2 diabetes (T2D). Atherogenic dyslipidemia, characterized by plasma hypertriglyceridemia, increased small dense low-density lipoprotein (LDL) particles, and decreased high-density lipoprotein cholesterol (HDL-C) levels, is often observed in NAFLD patients.

Scope of review

In this review, we highlight recent epidemiological studies evaluating the link between NAFLD and CVD risk. We further focus on recent mechanistic insights into the links between NAFLD and altered lipoprotein metabolism. We also discuss current therapeutic strategies for NAFLD and their potential impact on NAFLD-associated CVD risk.

Major conclusions

Alterations in hepatic lipid and lipoprotein metabolism are major contributing factors to the increased CVD risk in NAFLD patients, and many promising NASH therapies in development also improve dyslipidemia in clinical trials.

Gut-Pancreas-Liver Axis as a Target for Treatment of NAFLD/NASH

Non-alcoholic fatty liver disease (NAFLD) represents the most common form of chronic liver disease worldwide. Due to its association with obesity and diabetes and the fall in hepatitis C virus morbidity, cirrhosis in NAFLD is becoming the most frequent indication to liver transplantation, but the pathogenetic mechanisms are still not completely understood. The so-called gut-liver axis has gained enormous interest when data showed that its alteration can lead to NAFLD development and might favor the occurrence of non-alcoholic steatohepatitis (NASH). Moreover, several therapeutic approaches targeting the gut-pancreas-liver axis, e.g., incretins, showed promising results in NASH treatment. In this review, we describe the role of incretin hormones in NAFLD/NASH pathogenesis and treatment and how metagenomic/metabolomic alterations in the gut microbiota can lead to NASH in the presence of gut barrier modifications favoring the passage of bacteria or bacterial products in the portal circulation, i.e., bacterial translocation.

Fibroblast Growth Factor 19 Levels Predict Subclinical Atherosclerosis in Men With Type 2 Diabetes

Objective: Fibroblast growth factor 19 (FGF19) plays an indispensable role in regulating bile acid, glucose, and lipid metabolism, and alterations of its circulating concentration is associated with the development of type 2 diabetes (T2D). Atherosclerosis is directly related to the death-deriving diabetic macroangiopathy in T2D, yet relationships between FGF19 and atherosclerosis in T2D remain unclear. The aim of this study was to investigate the association of circulating FGF19 levels with the development of subclinical atherosclerosis (subAS) in patients with T2D in a 3-year prospective study. Methods: In the present study, 153 newly diagnosed T2D patients without subAS were recruited at baseline, and 137 of them completed a 3-year follow-up. FGF19 levels were measured in fasting serum samples collected at baseline and the third-year visits. Carotid, femoral, and iliac intima-media thickness (IMT) were detected by high-resolution B-mode ultrasound to determine the presence of subAS. Logistic regression analysis was applied to assess the relationship between serum FGF19 and subAS in patients with T2D. Results: At baseline, serum FGF19 levels were positively correlated with carotid IMT and iliac IMT in men (r = 0.239, P = 0.036; r = 0.309, P = 0.006). At the 3-year follow-up, 25 out of 153 patients developed subAS, and FGF19 levels in men were higher in the subAS group than in the non-subAS group [202.7 (177.9-373.6) vs. 133.4 (85.6-171.3) pg/ml, P = 0.028]. Furthermore, in men, higher baseline levels of FGF19 were independently associated with a greater risk of subAS at year 3 in patients with T2D with an odds ratio (OR) of 4.798 per 1 standard deviation (SD) of the FGF19 concentration [OR = 4.798 (95% CI, 1.680-13.706), P = 0.003]. Baseline FGF19 levels yielded an area under the receiver operating characteristic curve of 0.769 to predict the development of subAS at year 3 in men with T2D. Conclusions: Serum FGF19 levels could help in predicting the development of atherosclerosis in men with T2D.

Lipid efflux mechanisms, relation to disease and potential therapeutic aspects

Lipids are hydrophobic and amphiphilic molecules involved in diverse functions such as membrane structure, energy metabolism, immunity, and signaling. However, altered intra-cellular lipid levels or composition can lead to metabolic and inflammatory dysfunction, as well as lipotoxicity. Thus, intra-cellular lipid homeostasis is tightly regulated by multiple mechanisms. Since most peripheral cells do not catabolize cholesterol, efflux (extra-cellular transport) of cholesterol is vital for lipid homeostasis. Defective efflux contributes to atherosclerotic plaque development, impaired β-cell insulin secretion, and neuropathology. Of these, defective lipid efflux in macrophages in the arterial walls leading to foam cell and atherosclerotic plaque formation has been the most well studied, likely because a leading global cause of death is cardiovascular disease. Circulating high density lipoprotein particles play critical roles as acceptors of effluxed cellular lipids, suggesting their importance in disease etiology. We review here mechanisms and pathways that modulate lipid efflux, the role of lipid efflux in disease etiology, and therapeutic options aimed at modulating this critical process.

Regulation of Energy Metabolism by Receptor Tyrosine Kinase Ligands

Metabolic diseases, such as diabetes, obesity, and fatty liver disease, have now reached epidemic proportions. Receptor tyrosine kinases (RTKs) are a family of cell surface receptors responding to growth factors, hormones, and cytokines to mediate a diverse set of fundamental cellular and metabolic signaling pathways. These ligands signal by endocrine, paracrine, or autocrine means in peripheral organs and in the central nervous system to control cellular and tissue-specific metabolic processes. Interestingly, the expression of many RTKs and their ligands are controlled by changes in metabolic demand, for example, during starvation, feeding, or obesity. In addition, studies of RTKs and their ligands in regulating energy homeostasis have revealed unexpected diversity in the mechanisms of action and their specific metabolic functions. Our current understanding of the molecular, biochemical and genetic control of energy homeostasis by the endocrine RTK ligands insulin, FGF21 and FGF19 are now relatively well understood. In addition to these classical endocrine signals, non-endocrine ligands can govern local energy regulation, and the intriguing crosstalk between the RTK family and the TGFβ receptor family demonstrates a signaling network that diversifies metabolic process between tissues. Thus, there is a need to increase our molecular and mechanistic understanding of signal diversification of RTK actions in metabolic disease. Here we review the known and emerging molecular mechanisms of RTK signaling that regulate systemic glucose and lipid metabolism, as well as highlighting unexpected roles of non-classical RTK ligands that crosstalk with other receptor pathways.

Triglyceride to High-Density Lipoprotein Cholesterol Ratio is an Important Determinant of Cardiovascular Risk and Poor Prognosis in Coronavirus Disease-19: A Retrospective Case Series Study

BACKGROUND

Acute myocardial injury and heart failure characterized by elevated cardiac troponin and decreased heart pump function are significant clinical features and prognostic factors of coronavirus disease-19 (COVID-19). Triglyceride to high-density lipoprotein cholesterol (TG/HDL-C) ratio is an indicator of insulin resistance. This study aimed to explore the association of the TG/HDL-C ratio with cardiovascular risk and prognosis in COVID-19.

METHODS

Ninety-eight laboratory-confirmed patients with COVID-19 admitted in a tertiary teaching hospital in Wuhan, China, were enrolled in this retrospective study. Regression models were used to investigate the association between TG/HDL-C ratio with myocardial injury, heart failure, severity, and mortality in COVID-19.

RESULTS

Among the 98 patients, the mean age was 63.9±1.4 years, and male sex (58, 59%) was predominant. Forty-six patients (47%) were admitted to the intensive care unit (ICU), 32 (33%) and 46 (47%) patients suffered from myocardial injury and heart failure, respectively, and 36 (37%) patients died. The TG/HDL-C ratio was increased in patients with myocardial injury, heart failure, severe illness, and fatal outcome (P<0.05 for each). Baseline TG/HDL-C ratio significantly correlated with log transformed levels of plasma high-sensitivity cardiac troponin I (r=0.251, P=0.018), N-terminal brain natriuretic propeptide (r=0.274, P=0.008), glycated hemoglobin (r=0.239, P=0.038), and interleukin-6 (r=0.218, P=0.042). Multivariate logistic regression analysis showed that an increased TG/HDL-C ratio was independently associated with the risk of myocardial injury [odds ratio (OR)=2.73; P=0.013], heart failure (OR=2.64; P=0.019), disease severity (OR=3.01; P=0.032), and fatal outcome (OR=2.97; P=0.014).

CONCLUSION

Increased TG/HDL-C ratio was independently associated with myocardial injury, heart failure, disease severity, and mortality in patients with COVID-19, and it may be a useful marker for early identification of patients with high risk and poor outcome.

Association of serum fibroblast growth factor 19 levels with arteriosclerosis parameters assessed by arterial stiffness and atherogenic index of plasma in patients with type 2 diabetes

BACKGROUND

The role of serum fibroblast growth factor 19 (FGF19) in arteriosclerosis is not well known. In the present study, we aimed to explore whether serum FGF19 levels were related to arteriosclerosis parameters, including arterial stiffness and atherogenic index of plasma (AIP), in patients with type 2 diabetes (T2D).

METHODS

A total of 200 patients with type 2 diabetes and 50 healthy controls were recruited for this study from Apr 2017 to Oct 2018. Serum FGF19 levels, arterial stiffness assessed by brachial ankle pulse wave velocity (baPWV), and AIP assessed by the triglyceride to high-density lipoprotein cholesterol (TG/HDL-c) ratio were measured in those subjects. In addition, other relevant clinical data were also collected.

RESULTS

Serum FGF19 levels in T2D patients were significantly lower than those in healthy controls (p < 0.05). The arteriosclerosis parameters, including baPWV and AIP, significantly decreased across ascending tertiles of serum FGF19 levels (all p for trend < 0.001). Moreover, the baPWV and AIP were all inversely correlated with serum FGF19 levels (r = - 0.351 and - 0.303, respectively, p < 0.001). Furthermore, after adjusting for other clinical covariates by multiple linear regression analyses, the serum FGF19 levels were independently associated with baPWV (β = - 0.20, t = - 2.23, p = 0.029) and AIP (β = - 0.28, t = - 2.66, p = 0.010).

CONCLUSIONS

The serum FGF19 levels were independently and inversely associated with baPWV and AIP, which indicate that serum FGF19 may have a protective role in atherosclerosis in patients with T2D.

Angiopoietin-1 aggravates atherosclerosis by inhibiting cholesterol efflux and promoting inflammatory response

OBJECTIVE

Angiopoietin-1 (Ang-1), a secreted protein, mainly regulates angiogenesis. Ang-1 has been shown to promote the development of atherosclerosis, whereas little is known about its effects on lipid metabolism and inflammation in this process.

METHOD

Ang-1 was transfected into ApoE^-/- mice via lentiviral vector or incubated with THP-1 derived macrophages. Oil red O and HE staining were performed to measure the size of atherosclerotic plaques in ApoE^-/- mice. Immunofluorescence was employed to show the expression of target proteins in aorta. [³H] labeled cholesterol was performed to examine the efficiency of cholesterol efflux and reverse cholesterol transport (RCT) both in vivo and vitro. Western blot and qPCR were used to quantify target proteins both in vivo and vitro. ELISA detected the levels of pro-inflammatory cytokines in mouse peritoneal macrophage.

RESULTS

Our data showed that Ang-1 augmented atherosclerotic plaques formation and inhibited cholesterol efflux. The binding of Ang-1 to Tie2 resulted in downregulation of LXRα, ABCA1 and ABCG1 expression via inhibiting the translocation of TFE3 into nucleus. In addition, Ang-1 decreased serum HDL-C levels and reduced reverse cholesterol transport (RCT) in ApoE-/- mice. Furthermore, Ang-1 induced lipid accumulation followed by increasing TNF-α, IL-6, IL-1β，and MCP-1 produced by MPMs, as well as inducing M1 phenotype macrophage marker iNOS and CD86 expression in aorta of ApoE^-/- mice.

CONCLUSION

Ang-1 has an adverse effect on cholesterol efflux by decreasing the expression of ABCA1 and ABCG1 via Tie2/TFE3/LXRα pathway, thereby promoting inflammation and accelerating atherosclerosis progression.

Impaired Chylomicron Assembly Modifies Hepatic Metabolism Through Bile Acid-Dependent and Transmissible Microbial Adaptations

The mechanisms by which alterations in intestinal bile acid (BA) metabolism improve systemic glucose tolerance and hepatic metabolic homeostasis are incompletely understood. We examined metabolic adaptations in mice with conditional intestinal deletion of the abetalipoproteinemia (ABL) gene microsomal triglyceride transfer protein (Mttp-IKO), which blocks chylomicron assembly and impairs intestinal lipid transport. Mttp-IKO mice exhibit improved hepatic glucose metabolism and augmented insulin signaling, without weight loss. These adaptations included decreased BA excretion, increased pool size, altered BA composition, and increased fibroblast growth factor 15 production. Mttp-IKO mice absorb fructose normally but are protected against dietary fructose-induced hepatic steatosis, without weight loss or changes in energy expenditure. In addition, Mttp-IKO mice exhibit altered cecal microbial communities, both at baseline and following fructose feeding, including increased abundance of Bacteroides and Lactobacillus genera. Transplantation of cecal microbiota from chow-fed Mttp-IKO mice into antibiotic-treated wild-type recipients conferred transmissible protection against fructose-induced hepatic steatosis in association with a bloom in Akkermansia and increased Clostridium XIVa genera, whose abundance was positively correlated with fecal coprostanol and total neutral sterol excretion in recipient mice. However, antibiotic-treated Mttp-IKO mice were still protected against fructose-induced hepatic steatosis, suggesting that changes in microbiota are not required for this phenotype. Nevertheless, we found increased abundance of fecal Akkermansia from two adult ABL subjects with MTTP mutations compared to their heterozygous parents and within the range noted in six healthy control subjects. Furthermore, Akkermansia abundance across all subjects was positively correlated with fecal coprostanol excretion. Conclusion: The findings collectively suggest multiple adaptive pathways of metabolic regulation following blocked chylomicron assembly, including shifts in BA signaling and altered microbial composition that confer a transmissible phenotype.