Serum FGF21 levels are increased in newly diagnosed type 2 diabetes with nonalcoholic fatty liver disease and associated with hsCRP levels independently

Relationship of postprandial fibroblast growth factor 21 with lipids, inflammation and metabolic dysfunction-associated fatty liver disease during oral fat tolerance test

Introduction

Metabolic dysfunction-associated fatty liver disease (MAFLD) is closely associated with serum fibroblast growth factor (FGF) 21; however, previous studies have typically focused on the static fasting state, and the relationships between postprandial FGF21 levels, postprandial metabolic status, and MAFLD remain unclear. Therefore, we measured postprandial lipids, inflammatory factors, and FGF21 levels in MAFLD and further analyzed their relationship using an oral fat tolerance test (OFTT).

Patients and methods

In total, 103 non-diabetic adult volunteers, including 46 patients with MAFLD, were included in this study. All participants underwent the OFTT. Venous blood samples were collected at 0, 2, 4, and 6 h. Circulating total cholesterol (TC), triglyceride (TG), free fatty acid (FFA), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), interleukin-6(IL-6), tumor necrosis factor-α(TNF-α), hypersensitive-C reactive protein(hs-CRP) and FGF21 were assessed.

Results

Serum FGF21 significantly increased in the fasting state (P < 0.05) and showed a biphasic change of first decreasing and then increasing in MAFLD during the OFTT. The postprandial levels of TG, TC, LDL-C, FFA, IL-6, TNF-α and hs-CRP were significantly increased in MAFLD (P < 0.05). After adjusting for multiple factors, the FGF21 incremental area under the curve (iAUC) was linearly correlated with the FFA iAUC, TG iAUC, and IL-6 iAUC (P < 0.05) and was an independent factor for MAFLD (P < 0.05, OR=1.403).

Conclusion

Dyslipidemia and excessive inflammation in MAFLD are associated to FGF21 levels in the postprandial period. An abnormal postprandial FGF21 response may be an important mechanism of MAFLD.

Metformin Improves the Prerequisites for FGF21 Signaling in Patients With Type 2 Diabetes

CONTEXT

Fibroblast growth factor (FGF) 21 acts as a metabolic regulator and its therapeutic use is under investigation. FGF21 signaling requires binding to surface receptors, FGFR1c and β-klotho. FGF21 resistance is observed in metabolic diseases and FGF21 signaling is regulated by fibroblast activation protein (FAP). Metformin is reported to influence expression and secretion of FGF21 in preclinical models, but the effect of metformin on FGF21 in a clinical trial remains unknown.

OBJECTIVE

To investigate how 12 weeks of treatment with metformin affects the FGF21 signaling pathway in patients with type 2 diabetes (T2D).

METHODS

Randomized, placebo-controlled study in patients with T2D (n = 24) receiving either metformin (1000 mg twice daily) or placebo. A control group of body mass index- and age-matched healthy individuals (n = 12) received a similar dose of metformin. Blood samples and muscle and fat biopsies were collected at study entry and after 12 weeks.

METHODS

Plasma levels of FGF21 (total and intact) and FAP (total and activity) were measured. Muscle and fat biopsies were analyzed for mRNA and protein expression of targets relevant for activation of the FGF21 signaling pathway.

RESULTS

Circulating FAP activity decreased after metformin treatment compared with placebo (P = .006), whereas FGF21 levels were unchanged. Metformin treatment increased gene and protein expression of β-klotho, FGFR1c, and pFGFR1c in adipose tissue. FGF21 mRNA expression increased in muscle tissue after metformin and the FGF21 protein, but not mRNA levels, were observed in adipose tissue.

CONCLUSION

Our findings suggest that metformin suppresses the circulating FAP activity and upregulates the expression of FGFR1c and β-klotho for increased FGF21 signaling in adipose tissue, thus improving peripheral FGF21 sensitivity.

Fibroblast Growth Factor-21 as a Potential Therapeutic Target of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a highly prevalent disease without any approved treatment to-date despite intensive research efforts by researchers and pharmaceutical industry. Fibroblast growth factor (FGF)-21 has been gaining increasing attention as a possible contributing factor and thus therapeutic target for obesity-related metabolic disorders, including NAFLD, mainly due to its effects on lipid and carbohydrate metabolism. Most animal and human observational studies have shown higher FGF-21 concentrations in NAFLD than non-NAFLD, implying that FGF-21 may be increased to counteract hepatic steatosis and inflammation. However, although Mendelian Randomization studies have revealed that variations of FGF-21 levels within the physiological range may have effects in hyperlipidemia and possibly nonalcoholic steatohepatitis, they also indicate that FGF-21, in physiological concentrations, may fail to reverse NAFLD and may not be able to control obesity and other diseases, indicating a state of FGF-21 resistance or insensitivity that could not respond to administration of FGF-21 in supraphysiological concentrations. Interventional studies with FGF-21 analogs (eg, pegbelfermin, efruxifermin, BOS-580) in humans have provided some favorable results in Phase 1 and Phase 2 studies. However, the definite effect of FGF-21 on NAFLD may be clarified after the completion of the ongoing clinical trials with paired liver biopsies and histological endpoints. The aim of this review is to critically summarize experimental and clinical data of FGF-21 in NAFLD, in an attempt to highlight existing knowledge and areas of uncertainty, and subsequently, to focus on the potential therapeutic effects of FGF-21 and its analogs in NAFLD.

Fibroblast growth factor 21 levels and liver inflammatory biomarkers in obese subjects after weight loss

INTRODUCTION

Previous studies have hypothesized fibroblast growth factor 21 (FGF-21) as a potential biomarker of the inflammation associated with liver diseases, which is also receiving considerable attention for its potential application concerning the management of obesity and co-morbidities. This study aimed to analyze the response of FGF-21 after a weight loss intervention and the relationships with other putative inflammatory liver biomarkers.

MATERIAL AND METHODS

Sixty-six obese participants from the RESMENA study were evaluated at baseline and following a 6-month energy restriction treatment. Anthropometric, body composition by DXA, routine laboratory measurements, which included transaminases and γ-glutamyl transferase (GGT) were analyzed by standardized methods. Moreover, FGF-21, M30 fragment (M30) and plasminogen activator inhibitor-1 (PAI-I) were analyzed as recognized liver inflammatory related biomarkers with specific ELISA kits.

RESULTS

Most measurements related to hepatic damage, inflammation and adiposity status improved at the end of the 6-month nutritional intervention. In addition, ΔFGF-21 shifts showed statistical relationships with changes in ΔM30, ΔGGT and ΔPAI. The reduction of M30 showed significant associations with changes in transaminases. Furthermore, PAI-I changes were associated with ΔM30 and ΔGGT regardless of weight loss. A linear regression model was set up to assess the influence of ΔPAI-I and ΔM30 on the variability of ΔFGF-21 (23.8%) adjusted by weight loss.

CONCLUSIONS

These results demonstrated interactions of some liver inflammatory mediators, specifically M30 and PAI-I with FGF-21. Thus, more investigation about FGF-21 is required given that this protein could be a biomarker of the obesity-inflammation-liver process.

The Nuanced Metabolic Functions of Endogenous FGF21 Depend on the Nature of the Stimulus, Tissue Source, and Experimental Model

Fibroblast growth factor 21 (FGF21) is a hormone that is involved in the regulation of lipid, glucose, and energy metabolism. Pharmacological FGF21 administration promotes weight loss and improves insulin sensitivity in rodents, non-human primates, and humans. However, pharmacologic effects of FGF21 likely differ from its physiological effects. Endogenous FGF21 is produced by many cell types, including hepatocytes, white and brown adipocytes, skeletal and cardiac myocytes, and pancreatic beta cells, and acts on a diverse array of effector tissues such as the brain, white and brown adipose tissue, heart, and skeletal muscle. Different receptor expression patterns dictate FGF21 function in these target tissues, with the primary effect to coordinate responses to nutritional stress. Moreover, different nutritional stimuli tend to promote FGF21 expression from different tissues; i.e., fasting induces hepatic-derived FGF21, while feeding promotes white adipocyte-derived FGF21. Target tissue effects of FGF21 also depend on its capacity to enter the systemic circulation, which varies widely from known FGF21 tissue sources in response to various stimuli. Due to its association with obesity and non-alcoholic fatty liver disease, the metabolic effects of endogenously produced FGF21 during the pathogenesis of these conditions are not well known. In this review, we will highlight what is known about endogenous tissue-specific FGF21 expression and organ cross-talk that dictate its diverse physiological functions, with particular attention given to FGF21 responses to nutritional stress. The importance of the particular experimental design, cellular and animal models, and nutritional status in deciphering the diverse metabolic functions of endogenous FGF21 cannot be overstated.

Liraglutide Decreases Liver Fat Content and Serum Fibroblast Growth Factor 21 Levels in Newly Diagnosed Overweight Patients with Type 2 Diabetes and Nonalcoholic Fatty Liver Disease

PURPOSES

In this study, we aimed to verify plasma fibroblast growth factor 21 (FGF21) elevation in newly diagnosed overweight patients with type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD) and to evaluate the effectiveness of liraglutide on reducing liver fat content and serum (FGF21) levels in those patients.

METHODS

A 12-week, single-center, prospective study was conducted. Twenty newly diagnosed overweight patients with T2DM and NAFLD were recruited. Twenty healthy age, sex, and body mass index (BMI) matched subjects were enrolled as the control group. Enzyme-linked immunosorbent assay was used to measure serum FGF21 levels. Liver fat content was determined using the 3.0 T whole-body MRI scanner.

RESULTS

Those newly diagnosed overweight patients with T2DM and NAFLD had a BMI of 27.6 ± 0.5 kg/m². They had higher levels of FGF21 (159.6 ± 35.7 vs. 124.1 ± 42.9 pg/ml, P < 0.001) and increased liver fat content (19.3 ± 9.4 vs. 4.5 ± 0.6%, P < 0.001) compared to the controls. Liraglutide treatment for 12 weeks induced a significant 4.9 kg weight loss (95% confidence interval (CI): -6.1, -3.7, P < 0.001), which was equivalent to a relative reduction of 6.8% (95% CI: 5.3%, 8.3%, P < 0.001). FGF21 levels decreased after the 12-week liraglutide treatment (159.6 ± 35.7 vs. 124.2 ± 27.8 pg/ml, P = 0.006). There was a positive correlation between relative changes of liver fat content and relative change of FGF21 (r = 0.645, P = 0.002). FGF21 levels significantly decreased in patients who had a significant decrease in liver fat content (≥29%) (95% CI: -262.8, -55.1, P = 0.006); however, there was no significant change in the patients without a significant decrease in liver fat content (<29%) (95% CI: -60.0, 54.1, P = 0.899).

CONCLUSIONS

Liraglutide treatment reduced both liver fat content and FGF21 levels in newly diagnosed overweight patients with T2DM and NAFLD. FGF21 may be a potential biomarker for evaluating the effects of liraglutide treatment on hepatic fat and glucose metabolism.

Advances in Biological Functions and Clinical Studies of FGF21

Fibroblast growth factor 21 (FGF21) regulates many crucial biological processes in human and mammals, particularly metabolic modulation and protective effect after injury. Therefore, determining complex regulatory mechanisms and elucidating the signaling pathway may greatly promote the prevention, diagnosis, and treatment of related injury and metabolic diseases. This review focused on the metabolic modulation and protective effect of FGF21 and summarized the molecular mechanisms and clinical research developments.

Fibroblast growth factor 21 in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) encompasses a spectrum of pathologies ranging from uncomplicated hepatic fat accumulation to a state of lobular inflammation and hepatocyte ballooning, known as non-alcoholic steatohepatitis (NASH). Currently, there are no reliable biomarkers or effective therapeutic options established for NAFLD. Nevertheless, there are several molecular targets in the pipeline, of which fibroblast growth factor 21 (FGF21) is one. FGF21 is secreted primarily from liver and has a plethora of metabolic functions. Pre-clinical and epidemiological studies indicate a relationship between circulating FGF21 levels and hepatic fat content in both mice and humans. Moreover, animal studies have clearly shown that aberrant FGF21 signalling is a key pathological step in the development and progression of NAFLD. A recent Phase II clinical trial demonstrated that administration of an FGF21 analogue significantly reduced hepatic fat in subjects with NASH. As such, FGF21 provides a novel target for future biomarker and therapeutic studies. This review appraises preclinical data to outline the current understanding of FGF21 function in both normal hepatic function and NAFLD. Epidemiological evidence is explored to delineate the relationship between circulating FGF21 levels and NAFLD in humans. Finally, we review the therapeutic effects of FGF21 in the treatment of NAFLD.

Serum Fibroblast Growth Factor 21 Levels Are Positively Associated with Metabolic Syndrome in Patients with Type 2 Diabetes

BACKGROUND

Fibroblast growth factor 21 (FGF21) acts as a potent metabolic regulator. Serum FGF21 levels were significantly higher in obesity and type 2 diabetes mellitus (T2DM) populations. The aim of this study was to evaluate the relationship between serum FGF21 levels and metabolic syndrome (MetS) in T2DM patients.

METHODS

Fasting blood samples were obtained from 126 T2DM patients. MetS and its components were defined according to the diagnostic criteria from the International Diabetes Federation. Serum FGF21 concentrations were measured using a commercially available enzyme-linked immunosorbent assay.

RESULTS

Among these patients, 84 (66.7%) had MetS. Female gender, hypertension, systolic blood pressure (SBP), diastolic blood pressure (DBP), waist circumference (WC), body weight (BW), body mass index (BMI), body fat mass, fasting glucose, glycated hemoglobin level (HbA1c), triglyceride level (TG), urine albumin-to-creatinine ratio (UACR), insulin level, homeostasis model assessment of insulin resistance (HOMA-IR), and FGF21 levels were higher, whereas high-density lipoprotein cholesterol level (HDL-C) and estimated glomerular filtration rate (eGFR) were lower in DM patients with MetS. Univariate linear analysis revealed that hypertension, BMI, WC, body fat mass, SBP, DBP, logarithmically transformed TG (log-TG), low-density lipoprotein cholesterol (LDL-C) level, log-glucose, log-creatinine, log-UACR, log-insulin, and log-HOMA-IR positively correlated, whereas HDL-C and eGFR negatively correlated with serum FGF21 levels in T2DM patients. Multivariate forward stepwise linear regression analysis revealed that body fat mass (adjusted R 2 change = 0.218; P=0.008) and log-TG (adjusted R 2 change = 0.036; P < 0.001) positively correlated, whereas eGFR (adjusted R 2 change = 0.033; P=0.013) negatively correlated with serum FGF21 levels in T2DM patients.

CONCLUSIONS

This study showed that higher serum FGF21 levels were positively associated with MetS in T2DM patients and significantly positively related to body fat mass and TG but negatively related to eGFR in these subjects.

FGF21 and glycemic control in patients with T1D

PURPOSE

Fibroblast growth factor (FGF) 21 is a circulating hormone with an important role in metabolic regulation. FGF21 production in humans responds positively to glucose consumption and we hypothesize that serum FGF21 concentration is associated to glycemic control.

METHODS

We enrolled 31 patients with type 1 diabetes (T1D) based on their HbA1c (well-regulated (HbA1c <53 mmol/mol), (n = 18) or poorly-regulated (HbA1c >69 mmol/mol), (n = 13). Twelve patients (39%) were diagnosed with retinopathy. Twenty healthy individuals comparable for age and gender distribution were included as a reference group. Serum FGF21, intact FGF21, fibroblast activation protein (FAP), adiponectin, and C-Reactive Protein (CRP) were measured by immunoassays.

RESULTS

No correlation between FGF21 concentration and HbA1c was found. Patients with T1D had lower levels of circulating FGF21 as compared with the reference group, but the difference was nonsignificant (p = 0.12). Dividing the patients according to retinopathy, we found that T1D patients with retinopathy had significantly lower FGF21 concentrations (10.0 ng/L) as compared with the healthy reference group (37.1 ng/L), (p = 0.02). We found significantly higher levels of the FGF21 cleaving enzyme, FAP, in patients with T1D (97.2 μg/L) as compared with the healthy control group (78.5 μg/L), (p = 0.006). Interestingly, serum FAP levels correlated significantly with circulating FGF21 levels in T1D patients, but this correlation was not found in the healthy controls.

CONCLUSIONS

We found no association between circulating FGF21 levels and HbA1c. T1D patients with retinopathy had significantly lower FGF21 levels as compared with healthy individuals, but it remains unclear if the lower levels of FGF21 are pathogenically related to the development of microvascular complications. Of note, serum FAP levels were significantly higher in all T1D patients as compared with the healthy individuals.

Fibroblast growth factor 21 in lipid metabolism and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases in several developed countries, ranging from simple non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH) and cirrhosis. Currently, NAFLD has been confirmed to be associated with dyslipidemia, insulin resistance, and pre-diabetes, which are always grouped together as metabolic syndrome. Fibroblast growth factor 21 (FGF21) plays an important role in liver pathophysiology with multiple metabolic functions. Accumulating evidence has shown that FGF21 could directly modulate lipid metabolism and reduce lipid accumulation in hepatocytes through an insulin-independent pathway, thus suppressing the pathogenesis of NAFLD. Furthermore, treatment with FGF21 could obviously reverse NAFLD and synergistically alleviate obesity and counteract insulin resistance. In this review, we summarize the current knowledge of FGF21 and the evidence of FGF21 as an important regulator in hepatic lipid metabolism. The mechanisms by which FGF21 affects the pathogenesis of NAFLD would also be proposed for the further understanding of FGF21.

Fibroblast growth factor 21 association with subclinical atherosclerosis and arterial stiffness in type 2 diabetes

AIM

To evaluate the association of serum FGF21 with subclinical atherosclerosis and pulse wave velocity, a marker of arterial stiffness, in type 2 diabetes Egyptian patients.

PATIENTS AND METHODS

Fasting serum FGF21 was measured in 120 type 2 diabetes patients without clinical atherosclerotic cardiovascular disease (mean age 51.1 ± 7.7 years; 63.3 women). In addition to basic laboratory tests, serum adiponectin and ultrasonographic examination of CIMT, ankle brachial index (ABI) and carotid-femoral pulse wave velocity (cfPWV) were performed.

RESULTS

Patients with subclinical atherosclerosis have higher serum FGF21 than those without (218 ± 66.8 pg/mL Vs 170 ± 43.1 pg/mL, P < 0.001). FGF21 correlated positively with CIMT and cfPWV (P < 0.001) regardless of patient gender. In logistic regression analysis, circulating FGF21 was found to be an independent predictor for subclinical atherosclerosis (P = 0.023) in addition to dyslipidemia, hypertension and adiponectin. FGF21 was also found to be an independent determinant of cfPWV in stepwise multiple regression analysis. ROC curve analysis was done and cutoff high risk FGF21 level of 184 pg/mL for the prediction of subclinical atherosclerosis with a sensitivity and specificity of 66.7%.

CONCLUSIONS

Serum FGF21 levels correlated with carotid intima media thickness and predict subclinical atherosclerosis. Serum FGF21 is also correlated positively with cfPWV and arterial stiffness in type 2 diabetes patients.

A nonalcoholic fatty liver disease model in human induced pluripotent stem cell-derived hepatocytes, created by endoplasmic reticulum stress-induced steatosis

Hepatic steatosis, a reversible state of metabolic dysregulation, can promote the onset of nonalcoholic steatohepatitis (NASH), and its transition is thought to be critical in disease evolution. The association between endoplasmic reticulum (ER) stress response and hepatocyte metabolism disorders prompted us to characterize ER stress-induced hepatic metabolic dysfunction in human induced pluripotent stem cell-derived hepatocytes (hiPSC-Hep), to explore regulatory pathways and validate a phenotypic in vitro model for progression of liver steatosis. We treated hiPSC-Hep with a ratio of unsaturated and saturated fatty acids in the presence of an inducer of ER stress to synergistically promote triglyceride accumulation and dysregulate lipid metabolism. We monitored lipid accumulation by high-content imaging and measured gene regulation by RNA sequencing and reverse transcription quantitative PCR analyses. Our results show that ER stress potentiated intracellular lipid accumulation by 5-fold in hiPSC-Hep in the absence of apoptosis. Transcriptome pathway analysis identified ER stress pathways as the most significantly dysregulated of all pathways affected. Obeticholic acid dose dependently inhibited lipid accumulation and modulated gene expression downstream of the farnesoid X receptor. We were able to identify modulation of hepatic markers and gene pathways known to be involved in steatosis and nonalcoholic fatty liver disease (NAFLD), in support of a hiPSC-Hep disease model that is relevant to clinical data for human NASH. Our results show that the model can serve as a translational discovery platform for the understanding of molecular pathways involved in NAFLD, and can facilitate the identification of novel therapeutic molecules based on high-throughput screening strategies.

Summary: Our study demonstrates expanded use of human induced pluripotent stem cell-derived hepatocytes for molecular studies and drug screening, to evaluate new therapeutics with an antisteatotic mechanism of action for nonalcoholic fatty liver disease.

Fibroblast Growth Factor 21-Metabolic Role in Mice and Men

Since its identification in 2000, the interest of scientists in the hepatokine fibroblast growth factor (FGF) 21 has tremendously grown, and still remains high, due to a wealth of very robust data documenting this factor's favorable effects on glucose and lipid metabolism in mice. For more than ten years now, intense in vivo and ex vivo experimentation addressed the physiological functions of FGF21 in humans as well as its pathophysiological role and pharmacological effects in human metabolic disease. This work produced a comprehensive collection of data revealing overlaps in FGF21 expression and function but also significant differences between mice and humans that have to be considered before translation from bench to bedside can be successful. This review summarizes what is known about FGF21 in mice and humans with a special focus on this factor's role in glucose and lipid metabolism and in metabolic diseases, such as obesity and type 2 diabetes mellitus. We highlight the discrepancies between mice and humans and try to decipher their underlying reasons.

Sex-specific association between fibroblast growth factor 21 and type 2 diabetes: a nested case-control study in Singapore Chinese men and women

Background

Fibroblast growth factor 21 (FGF-21) is mainly secreted by liver and has been reported to be involved in the pathogenesis of type 2 diabetes. Some prospective studies have shown a positive association between FGF-21 and diabetes risk. However, no study has examined whether the association differed by sex, which has been reported between FGF-21 and atherosclerosis. Therefore, we prospectively evaluated the sex-specific association between FGF-21 and diabetes in a Chinese population.

Methods

Serum FGF-21 concentration was measured in a case-control study comprising of 251 incident diabetes cases and 251 age-sex-matched controls nested within a prospective population-based cohort, the Singapore Chinese Health Study. At blood collection between 1999 and 2004, participants were free of diagnosed diabetes, cardiovascular disease, and cancer. Incident self-reported diabetes cases were identified at follow-up II interview (2006–2010). Odds ratio (OR) and 95% confidence interval (CI) were calculated using multivariable logistic regression models.

Results

After adjustment for risk biomarkers of diabetes including lipids, liver enzymes and inflammatory marker, the OR of type 2 diabetes with per one unit increment in log FGF-21 concentration was 1.16 (95% CI 0.90–1.50). Significant interaction was found with sex (P-interaction = 0.029): the OR (95% CI) was 1.50 (1.00-2.25) in women and 0.89 (0.52–1.53) in men.

Conclusions

Higher serum FGF-21 level was associated with an increased risk of diabetes in Chinese women but not in men. The sex difference in the association between FGF-21 and diabetes risk deserves further investigation and replication in other populations.

Electronic supplementary material

The online version of this article (10.1186/s12986-017-0216-0) contains supplementary material, which is available to authorized users.

Fibroblast Growth Factor 21 Mimetics for Treating Atherosclerosis

Fibroblast growth factor 21 (FGF21) is an atypical member of the FGF family. Acting in an endocrine fashion, it increases glucose uptake, modulates lipid metabolism, and sensitizes insulin response in metabolically active organs, including the liver and adipose tissue. Emerging evidence shows a strong correlation between circulating FGF21 levels and the incidence and severity of atherosclerosis. Animal studies have demonstrated a beneficial role of FGF21 in protecting against aberrant lipid profile, while recent development in FGF21 mimetics has provided further insight into the lipid-lowering effects of FGF21 signaling. The present review summarizes the physiological roles of FGF21, and discusses major breakthroughs and limitations of FGF21 mimetic-based therapeutic strategies for treating atherosclerosis.

The Role and Potential Therapeutic Implications of the Fibroblast Growth Factors in Energy Balance and Type 2 Diabetes

PURPOSE OF REVIEW

Obesity and its associated metabolic diseases have reached epidemic proportions worldwide, reducing life expectancy and quality of life. Several drugs have been tested to treat these diseases but many of them have damaging side effects. Consequently, there is an urgent need to develop more effective therapies. Recently, endocrine fibroblast growth factors (FGFs) have become attractive targets in the treatment of metabolic diseases. This review summarizes their most important functions as well as FGF-based therapies for the treatment of obesity and type 2 diabetes (T2D).

RECENT FINDINGS

Recent studies demonstrate that circulating levels of FGF19 are reduced in obesity. In fact, exogenous FGF19 administration is associated with a reduction in food intake as well as with improvements in glycaemia. In contrast, FGF21 levels are elevated in subjects with abdominal obesity, insulin resistance and T2D, probably representing a compensatory response. Additionally, elevated levels of circulating FGF23 in individuals with obesity and T2D are reported in most clinical studies. Finally, increased FGF1 levels in obese patients associated with adipogenesis have been described. FGFs constitute important molecules in the treatment of metabolic diseases due to their beneficial effects on glucose and lipid metabolism. Among all members, FGF19 and FGF21 have demonstrated the ability to improve glucose, lipid and energy homeostasis, along with FGF1, which was recently discovered to have beneficial effects on metabolic homeostasis. Additionally, FGF23 may also play a role in insulin resistance or energy homeostasis beyond mineral metabolism control. These results highlight the relevant use of FGFs as potential biomarkers for the early diagnosis of metabolic diseases. In this regard, notable progress has been made in the development of FGF-based therapies and different approaches are being tested in different clinical trials. However, further studies are needed to determine their potential therapeutic use in the treatment of obesity and obesity-related comorbidities.

Diabetes and dyslipidemia: characterizing lipoprotein metabolism

Premature atherosclerosis in diabetes accounts for much of the decreased life span. New treatments have reduced this risk considerably. This review explores the relationship among the disturbances in glucose, lipid, and bile salt metabolic pathways that occur in diabetes. In particular, excess nutrient intake and starvation have major metabolic effects, which have allowed us new insights into the disturbance that occurs in diabetes. Metabolic regulators such as the forkhead transcription factors, the farnesyl X transcription factors, and the fibroblast growth factors have become important players in our understanding of the dysregulation of metabolism in diabetes and overnutrition. The disturbed regulation of lipoprotein metabolism in both the intestine and the liver has been more clearly defined over the past few years, and the atherogenicity of the triglyceride-rich lipoproteins, and - in tandem - low levels of high-density lipoproteins, is seen now as very important. New information on the apolipoproteins that control lipoprotein lipase activity has been obtained. This is an exciting time in the battle to defeat diabetic atherosclerosis.

Chronic Over-expression of Fibroblast Growth Factor 21 Increases Bile Acid Biosynthesis by Opposing FGF15/19 Action

Pharmacological doses of fibroblast growth factor (FGF) 21 effectively normalize glucose, lipid and energy homeostasis in multiple animal models with many benefits translating to obese humans with type 2 diabetes. However, a role for FGF21 in the regulation of bile acid metabolism has not been reported. Herein, we demonstrate AAV-mediated FGF21 overexpression in mice increases liver expression of the key bile acid producing enzyme, Cyp7a1, resulting in an increased bile acid pool. Furthermore, in cholecystectomized mice, FGF21-mediated bile acid pool increase led to increased transit of bile acids into colon. We elucidate that the mechanism of FGF21 induced bile acid changes is mainly through antagonizing FGF15/19 function on liver βKlotho/FGFR4 receptor complex; thus inhibiting FGF15/19-mediated suppression of Cyp7a1 expression. In conclusion, these data reveal a previously unidentified role for FGF21 on bile acid metabolism and may be relevant to understand the effects of FGF21 analogs in clinical studies.

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Chronic FGF21 overexpression in mice leads to increases in bile acid production and bile acid pool.

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FGF21 mediates the bile acid changes at least in part through antagonizing FGF15/19 function.

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Cross-talk between FGF molecules may be a regulatory mechanism for their function.

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Effects of FGF21 on bile acid metabolism may be relevant to understand FGF21 clinical observations.

Pharmacological doses of FGF21 effectively normalize glucose, lipid and energy homeostasis in multiple animal models, and several FGF21 analogs are being evaluated in the clinic as potential therapies for type 2 diabetes. However, a role for FGF21 in the regulation of bile acid metabolism has not been reported. In the present study, we revealed a link between chronic FGF21 overexpression to increases in bile acid synthesis in mice and uncovered a new cross-talk mechanism between FGF molecules. These findings may highlight an importance aspect of FGF21's pharmacology for future clinical study considerations.

Fibroblast growth factor 21 - a key player in cardiovascular disorders?

Fibroblast growth factor 21 (FGF21) is a newly discovered adipokine, synthesized by several organs, mostly by the liver, which was introduced as a potent metabolic regulator and insulin-sensitizing factor. Numerous animal studies have demonstrated that FGF21 improves glucose and lipids metabolism and exerts anti-inflammatory effects. However, data obtained from human studies have shown contradictory results, in which circulating FGF21 levels were often elevated in obesity, dyslipidemia, type 2 diabetes (DM2) and other conditions connected with insulin resistance. This increase in basal FGF21 concentrations observed in patients with obesity and other conditions related to insulin resistance was being explained as a compensatory response to the underlying metabolic disturbances or tissue resistance to FGF21 action. Furthermore, the results of clinical trials have shown that increased FGF21 concentrations were associated with increased cardiovascular (CV) risk and had a prognostic value in CV outcomes. In recent years, it has been reported that FGF21 may exert cardioprotective effects. This mini-review aims to summarize the current state of knowledge about the role of FGF21 in CV disorders, and discuss the molecular mechanism underlying the anti-atherogenic properties of this compound.

NS5ATP6 modulates intracellular triglyceride content through FGF21 and independently of SIRT1 and SREBP1

The prevalence of nonalcoholic fatty liver disease (NAFLD) is rising strikingly in Western countries and China. The molecular biological mechanism of NAFLD remains unclear, with no effective therapies developed so far. Fibroblast growth factor 21 (FGF21) is a recently discovered hormone, with safe lipid lowering effects. FGF21 analogs are being developed for clinical application. Here we demonstrated that a novel gene, NS5ATP6, modulated intracellular triglyceride (TG) content independently of sirtuin1 (SIRT1) and sterol regulatory element binding protein 1 (SREBP1) in HepG2 cells. Interestingly, NS5ATP6 regulated FGF21 expression both at the mRNA and protein levels. The modulatory effects of NS5ATP6 on intracellular TG content depended upon FGF21. Further studies revealed that NS5ATP6 decreased the promoter activity of FGF21. In addition, NS5ATP6 regulated the expression of miR-577, which directly targeted and regulated FGF21. Therefore, miR-577 might be involved in NS5ATP6 regulation of FGF21 at the post-transcriptional level. In conclusion, NS5ATP6 regulates the intracellular TG level via FGF21, and independently of SIRT1 and SREBP1.

Fibroblast growth factor 1 levels are elevated in newly diagnosed type 2 diabetes compared to normal glucose tolerance controls

Fibroblast growth factor 1 (FGF1) has been recently characterized as a potent insulin sensitizer that regulates adipose tissue remodeling, but the physiological role of FGF1 remains unclear. This study measured serum FGF1 levels for the first time in patients with newly diagnosed type 2 diabetes mellitus (T2DM), and further explored the correlations between FGF1 levels and various metabolic parameters in T2DM. Serum FGF1 levels were determined using ELISA in age-, sex- and BMI- matched subjects with normal glucose tolerance (NGT) (n=80) and newly diagnosed T2DM (n=80). Oral glucose tolerance test (OGTT), glycosylated hemoglobin (HbA1C), blood lipids, and insulin secretion were also measured. Insulin resistance and pancreatic β-cell function were assessed by homeostasis model assessment of insulin resistance (HOMA-IR) and homeostasis model assessment of beta cell function (HOMA-β), respectively. Serum FGF1 levels were significantly higher in T2DM patients than in normal glucose tolerance subjects (74.52 [55.91∼101.34] vs. 60.31 [48.99∼83.91] pg/mL; P<0.05). In addition, serum FGF1 level positively correlated with body mass index (BMI), waist circumference (WC), waist to hip ratio (WHR), fasting plasma glucose (FPG), 2-h post-OGTT glucose (2h PG), and HbA1C (all P values <0.05) in T2DM subjects. Multivariate regression analyses showed that BMI and HbA1C were the independent factors influencing serum FGF1 levels. Logistic regression analyses demonstrated that serum FGF1 was significantly associated with type 2 diabetes (P<0.01). Circulating concentrations of FGF1 are significantly increased in T2DM patients. Our results suggest that FGF1 may play a role in the pathogenesis of T2DM.

Implications of Fibroblast growth factor/Klotho system in glucose metabolism and diabetes

Diabetes mellitus, especially type 2 diabetes, remains the dominant metabolic disease worldwide, with an expected increase in prevalence of over 50% in the next 20 years. Our knowledge about the pathophysiology of type 2 diabetes continues to be incomplete, with unmet medical need for new therapies. The characterization of the fibroblast growth factor (FGF) family and the discovery of endocrine FGFs provided new information on the mechanisms of regulation and homeostasis of carbohydrate metabolism. More specifically, FGF19 and FGF21 signaling pathways have been linked to different glucose metabolic processes, including hepatic glucose synthesis, glycogen synthesis, glucose uptake, and insulin sensitivity, among others, and these molecules have been further related to the pathophysiology of diabetes mellitus. In-depth comprehension of these growth factors may bring to light new potential therapeutic targets for the treatment of diabetes mellitus.

Patterns of Circulating Fibroblast Growth Factor 21 in Subjects with and without Type 2 Diabetes

Background

Fibroblast growth factor 21 (FGF21) exerts wide-range effects on carbohydrate and lipid metabolism. However, its perturbation in type 2 diabetes mellitus (T2DM) remains elusive. Besides, previous human studies in T2DM simply investigated fasting or stimulated levels of FGF21. The current study sought to evaluate the temporal changes of circulating FGF21 in subjects with and without T2DM.

Methods

Ten patients with T2DM and 16 normal controls (NC) were recruited. Participants were categorized as obese (BMI≥25 kg/m²) or lean (BMI<25 kg/m²). Blood samples were drawn every 30 min within 7 hours (8 a.m.-3 p.m.). Serum FGF21, blood glucose, insulin, free fatty acids (FFAs) and adiponectin were measured in all subjects.

Results

The peak levels of FGF21 were observed in the fasting state (8 a.m.) both in T2DM and NC groups (267.35 ±158.72 ng/L vs. 178.93±121.37 ng/L, P = 0.096). FGF21 AUC did not differ significantly between the two groups (T2DM: 949.4±471.47 ng/L; NC: 883.13±561.40 ng/L, P = 0.770). Obese subjects had higher FGF21 levels than lean ones in patients either with or without T2DM. The pattern of FFAs closely resembled that of FGF21. Correlation analysis showed that temporal levels of FGF21 were significantly related to FFAs (r = 0.749, P = 0.002),but not blood glucose, insulin or adiponectin (all P> 0.05).

Conclusions

These findings suggest that the pattern of circulating FGF21 does not differ significantly between T2DM and NC,although T2DM patients showed a trend toward higher fasting FGF21 than healthy subjects. The pattern of circulating FFAs is significantly associated with that of FGF21.

Fibroblast growth factors in cardiovascular disease: The emerging role of FGF21

Early detection of risk factors for enhanced primary prevention and novel therapies for treating the chronic consequences of cardiovascular disease are of the utmost importance for reducing morbidity. Recently, fibroblast growth factors (FGFs) have been intensively studied as potential new molecules in the prevention and treatment of cardiovascular disease mainly attributable to metabolic effects and angiogenic actions. Members of the endocrine FGF family have been shown to increase metabolic rate, decrease adiposity, and restore glucose homeostasis, suggesting a multiple metabolic role. Serum levels of FGFs have been associated with established cardiovascular risk factors as well as with the severity and extent of coronary artery disease and could be useful for prediction of cardiovascular death. Furthermore, preclinical investigations and clinical trials have tested FGF administration for therapeutic angiogenesis in ischemic vascular disease, demonstrating a potential role in improving angina and limb function. FGF21 has lately emerged as a potent metabolic regulator with multiple effects that ultimately improve the lipoprotein profile. Early studies show that FGF21 is associated with the presence of atherosclerosis and may play a protective role against plaque formation by improving endothelial function. The present review highlights recent investigations suggesting that FGFs, in particular FGF21, may be useful as markers of cardiovascular risk and may also serve as protective/therapeutic agents in cardiovascular disease.

The role of fibroblast growth factor 21 in diabetes and its complications: A review from clinical perspective

Fibroblast growth factor 21 (FGF21) has been well-recognized as a metabolic hormone and a promising target for treatment of metabolic diseases. The level of endogenous FGF21 is elevated in patients with impaired glucose tolerance and progressively increased from patients with overt type 2 diabetes to those with micro- and macro-vascular complications, presumably as a compensation or response to the deterioration of metabolic imbalance. A few exploratory in vivo studies, including a recent clinical trial, showed that exogenous FGF21 mimetics targeting FGF21 signaling can attain beneficial metabolic effects not with-standing the already elevated ambient FGF21 levels. In addition, some clinically available pharmacologic agents such as fenofibrates and metformin may modulate energy and macronutrients metabolism by acting through FGF21. This review mainly focuses on the role of FGF21 in development, progression and treatment of type 2 diabetes from a clinical perspective.

Serum fibroblast growth factor 21 levels is associated with lower extremity atherosclerotic disease in Chinese female diabetic patients

Background

Fibroblast growth factor 21 (FGF21) is an emerging metabolic regulator associated with glucose and lipid metabolism, and it is still unclear whether FGF21 is related to atherosclerosis. Here, we explored the potential link between FGF21 and lower extremity atherosclerotic disease (LEAD) in type 2 diabetic patients.

Methods

A cross-sectional study was conducted on 504 type 2 diabetic patients (283 men, 221 women). LEAD was defined by Ankle-brachial index (ABI) <0.9 and lower extremity arterial plaque evaluated by color Doppler ultrasound. Serum FGF21 concentrations were quantified by a sandwich enzyme-linked immunosorbent assay.

Results

The total FGF21 levels of male and female patients had no significant differenence ((299.14(177.31-534.49) vs 362.50(214.01-578.73), P=0.516). Serum FGF21 levels in LEAD group were significantly higher than non-LEAD group in females (385.34(243.89-661.54) vs 313.13(156.38-485.79), P=0.006), while not in male patients (295.52(177.09-549.64) vs 342.09 (198.70-549.87), P=0.613). In diabetic women, subjects with LEAD had significantly higher serum FGF21 regardless of non-alcoholic fatty liver disease (NAFLD) (P < 0.05). And serum FGF21 levels were positively correlated with waist circumference and systolic blood pressure after adjusted for age and BMI (r=0.198, P=0.004; r=0.152, P=0.027; respectively). Moreover, FGF21 was independently tied to femoral intima-media thickness (FIMT) (β=0.208, P=0.031). After adjusted for other LEAD risk factors, FGF21 was demonstrated to be an independent risk factor for LEAD in type 2 diabetic women (OR, 1.106; 95%CI 1.008-1.223; P=0.028). In addition, FGF21 was negatively correlated with estradiol in premenopausal diabetic women (r=−0.368, P=0.009). After adjusted for estradiol, serum FGF21 levels were still positively associated with FIMT in premenopausal diabetic women (r=0.381, P=0.007). In diabetic men, serum FGF21 levels were correlated with triglyceride and C-reactive protein even after adjusted for age and BMI (r=0.204, P=0.001; r=0.312, P < 0.001; respectively). However, serum FGF21 was not an independent impact factor for LEAD in men (P > 0.05).

Conclusions

Serum FGF21 level independently and positively links LEAD in Chinese women with type 2 diabetes. The gender difference may be due to different estrogen levels.

Epicardial fat, body mass index, and triglyceride are independent contributors of serum fibroblast growth factor 21 level in obese premenopausal women

PURPOSE

The hormone fibroblast growth factor 21 (FGF-21) regulates carbohydrate and lipid homeostasis. FGF-21 represents an attractive novel therapy for obesity since administration of FGF-21 has been shown to improve metabolic abnormalities in obese animal models. We investigated FGF-21 and its relationship with epicardial fat thickness (EFT), metabolic parameters, and inflammatory markers in premenopausal obese women compared to controls with similar Systematic Coronary Risk Evaluation (SCORE) project risk profiles.

METHODS

Forty-five obese premenopausal women with body mass index (BMI) ≥30 kg/m(2) and 41 control premenopausal women with BMI <25 kg/m(2) with similar SCORE project risk profiles were included in this case-control study. EFT was evaluated by two-dimensional transthoracic echocardiography. Serum FGF-21 was measured with an ELISA kit.

RESULTS

FGF-21 and EFT were significantly higher in obese women compared to controls (p < 0.001). Multiple stepwise linear regression analysis showed that EFT, BMI, and triglycerides (TG) independently contributed to FGF-21 (R(2) = 0.757, p < 0.001). However, homeostasis model assessment of insulin resistance (HOMA-IR), visceral ectopic fat, and inflammatory markers were not found as a direct contributor to serum FGF-21 level (p > 0.05).

CONCLUSIONS

EFT, BMI, and TG may play an important role in predicting serum FGF-21 level which may be a potential therapeutic target in cardiometabolic disorders in the future.

The role of fibroblast growth factor 21 in the pathogenesis of non-alcoholic fatty liver disease and implications for therapy

Non-alcoholic fatty liver disease (NAFLD) includes a cluster of liver disorders ranging from simple fatty liver to non-alcoholic steatohepatitis (NASH) and cirrhosis. Due to its liver and vascular complications, NAFLD has become a public health problem with high morbidity and mortality. The pathogenesis of NAFLD is considered a "multi-hit hypothesis" that involves lipotoxicity, oxidative stress, endoplasmic reticulum stress, a chronic inflammatory state and mitochondrial dysfunction. Fibroblast growth factor 21 (FGF21) is a member of the fibroblast growth factor family with multiple metabolic functions. FGF21 directly regulates lipid metabolism and reduces hepatic lipid accumulation in an insulin-independent manner. Several studies have shown that FGF21 can ameliorate the "multi-hits" in the pathogenesis of NAFLD. The administration of FGF21 reverses hepatic steatosis, counteracts obesity and alleviates insulin resistance in rodents and nonhuman primates. Using several strategies, we show that the reversal of simple fatty liver and NASH is mediated by activation of the FGF21 signaling pathway. In this review, we describe the molecular mechanisms involved in the onset and/or progression of NAFLD, and review the current literature to highlight the therapeutic procedures associated with the FGF21 signaling pathway for simple fatty liver and NASH, which are the two most important types of NAFLD.

Serum levels of fibroblast growth factor-21 are increased in chronic and acute renal dysfunction

OBJECTIVE

Fibroblast growth factor (FGF)-21 has recently been introduced as a circulating adipokine which reverses insulin resistance and obesity in rodents. In this study, regulation of FGF-21 in renal dysfunction was elucidated in both chronic kidney disease (CKD) and acute kidney dysfunction (AKD).

STUDY DESIGN AND METHODS

Serum concentrations of total FGF-21 were quantified by enzyme-linked immunosorbent assay in 499 patients with CKD stages 1-5 (study population 1). Furthermore, total FGF-21 was determined before and within 30 h after unilateral nephrectomy, a model of AKD, in 32 patients (study population 2). FGF-21 levels were correlated to anthropometric and biochemical parameters of renal function, glucose and lipid metabolism, as well as inflammation, in both studies.

RESULTS

In study population 1, median [interquartile range] circulating FGF-21 adjusted for age, gender and body mass index was significantly different between CKD stages with highest values detectable in stage 5 (stage 1: 86·4 [132·9]; 2: 206·4 [223·1]; 3: 289·8 [409·3]; 4: 591·3 [789·0]; 5: 1918·1 [4157·0] ng/l). Furthermore, estimated glomerular filtration rate remained a strong independent and negative predictor of FGF-21. In study population 2, FGF-21 increased significantly postsurgically (325·0 [984·0] ng/l) as compared to presurgical values (255·5 [243·0] ng/l). Furthermore, relative changes of FGF-21 were independently and positively predicted by relative changes of creatinine.

CONCLUSIONS

We demonstrate that circulating FGF-21 is increased in both CKD and AKD. Our results suggest renal excretion as a major route for FGF-21 elimination. The pathophysiological significance of these findings needs to be elucidated in more detail.

Opposite alterations in FGF21 and FGF19 levels and disturbed expression of the receptor machinery for endocrine FGFs in obese patients

OBJECTIVE

Fibroblast growth factor (FGF)-21, and possibly FGF19, protect against type 2 diabetes mellitus (T2DM) and obesity in rodents. We investigated the circulating levels of FGF21 and FGF19 in obese patients with varying degrees of abnormal glucose homeostasis, and we determined gene expression for FGF receptors (FGFR1-4) and the co-receptor β-Klotho, in liver and adipose tissues.

SUBJECTS AND METHODS

We analyzed 35 lean healthy (71% men) and 61 obese patients (49% men, median body mass index (BMI): 40.5 kg m(-2), interquartile range: 34.7-46.2). Among obese patients, 36 were normoglycemic, 15 showed impaired glucose tolerance and 10 had T2DM. Biopsies from liver and visceral and subcutaneous fat from a subset of obese patients and controls were analyzed. FGF19 and FGF21 levels were measured using enzyme-linked immunosorbent assay, and tissue mRNA and protein levels by reverse transcription-polymerase chain reaction and immunoblotting.

RESULTS

FGF21 serum levels were significantly increased in obese patients compared with controls (P<0.001), whereas FGF19 levels were decreased (P < 0.001). FGF21 levels were positively correlated with homeostasis model assessment of insulin resistance (P = 0.0002, r = 0.37) and insulin (P = 0.001, r = 0.32), whereas FGF19 levels were negatively correlated (P = 0.007, r = -0.27; P=0.003, r = -0.28; respectively). After adjusting for BMI, the correlations of FGF21 and FGF19 levels with indicators of abnormal glucose homeostasis were not significant. In obese patients, the hepatic expression of FGF21 was increased. (P = 0.04). β-Klotho transcript levels in visceral fat (P = 0.002) and β-Klotho protein levels in subcutaneous (P = 0.03) and visceral fat (P = 0.04) were significantly reduced in obese patients, whereas hepatic levels for β-Klotho (P = 0.03), FGFR1 (P = 0.04) and FGFR3 (P = 0.001) transcripts were significantly increased.

CONCLUSIONS

Obesity is characterized by reciprocal alterations in FGF19 (decrease) and FGF21 (increase) levels. Although worsened in diabetic obese patients, obesity itself appears as the predominant determinant of the abnormalities in FGF21 and FGF19 levels. Opposite changes in β-Klotho expression in fat and liver indicate potential tissue-specific alterations in the responsiveness to endocrine FGFs in obesity.

Artemisia scoparia extract attenuates non-alcoholic fatty liver disease in diet-induced obesity mice by enhancing hepatic insulin and AMPK signaling independently of FGF21 pathway

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is a common liver disease which has no standard treatment. In this regard, we sought to evaluate the effects of extracts of Artemisia santolinaefolia (SANT) and Artemisia scoparia (SCO) on hepatic lipid deposition and cellular signaling in a diet-induced obesity (DIO) animal model.

MATERIALS/METHODS

DIO C57/B6J mice were randomly divided into three groups, i.e. HFD, SANT and SCO. Both extracts were incorporated into HFD at a concentration of 0.5% (w/w). Fasting plasma glucose, insulin, adiponectin, and FGF21 concentrations were measured.

RESULTS

At the end of the 4-week intervention, liver tissues were collected for analysis of insulin, AMPK, and FGF21 signaling. SANT and SCO supplementation significantly increased plasma adiponectin levels when compared with the HFD mice (P<0.001). Fasting insulin levels were significantly lower in the SCO than HFD mice, but not in SANT group. Hepatic H&E staining showed fewer lipid droplets in the SCO group than in the other two groups. Cellular signaling data demonstrated that SCO significantly increased liver IRS-2 content, phosphorylation of IRS-1, IR β, Akt1 and Akt2, AMPK α1 and AMPK activity and significantly reduced PTP 1B abundance when compared with the HFD group. SCO also significantly decreased fatty acid synthase (FAS), HMG-CoA Reductase (HMGR), and Sterol regulatory element-binding protein 1c (SREBP1c), but not Carnitine palmitoyltransferase I (CPT-1) when compared with HFD group. Neither SANT nor SCO significantly altered plasma FGF21 concentrations and liver FGF21 signaling.

CONCLUSION

This study suggests that SCO may attenuate liver lipid accumulation in DIO mice. Contributing mechanisms were postulated to include promotion of adiponectin expression, inhibition of hepatic lipogenesis, and/or enhanced insulin and AMPK signaling independent of FGF21 pathway.

Serum fibroblast growth factor 21 is predictive of combined cardiovascular morbidity and mortality in patients with type 2 diabetes at a relatively short-term follow-up

AIMS

We hypothesised that serum fibroblast growth factor 21 (FGF-21), a novel adipokine with postulated insulin-sensitizing effects, may be predictive of cardiovascular (CV) events in patients with type 2 diabetes (DM2) at a relatively short-term follow-up.

METHODS

Serum FGF-21 levels were assessed in 87 DM2 patients, aged 57-66 years, with the median duration of diabetes of 10 years, who were referred to the Department of Endocrinology for routine annual metabolic assessment. During a follow-up of 24 months, overall mortality, CV mortality and CV nonfatal events were registered. Cox proportional hazards regression assessed adjusted differences in CV morbidity and mortality risk.

RESULTS

Patients stratified according to serum FGF-21 levels ≤ and > the median value of 240.7 pg/mL showed no significant differences at baseline in gender distribution, diabetes duration, insulin therapy, BMI, biochemical profiles and previous CV events. At 24-month follow-up, 21 (24.1%) patients experienced a nonfatal CV event. A significantly (P=0.0013) higher incidence of the combined end point of CV morbidity and mortality was observed in the FGF-21>240.7 pg/mL group. In the multivariate Cox proportional hazards regression model, the presence of FGF-21>the median value was associated with a significant increase in the risk of the combined end point of CV morbidity and mortality (HR: 4.7, 95% CI 1.67-13.24).

CONCLUSIONS

The obtained results support the prognostic value of FGF-21 in DM2 and may provide a useful tool for stratification of CV prognosis in DM2 patients.

Serum fibroblast growth factor-21 levels are associated with carotid atherosclerosis independent of established cardiovascular risk factors

OBJECTIVE

Serum levels of fibroblast growth factor-21 (FGF21), a metabolic hormone, have been shown to be elevated in subjects with adverse lipid profiles, obesity, metabolic syndrome, impaired glucose tolerance, type 2 diabetes mellitus, and hypertension. Recently, elevated serum FGF21 levels have also been reported in subjects with coronary heart disease or carotid artery plaques. However, whether serum FGF21 is independently associated with atherosclerotic diseases remains unclear. In this study, we examined the relationship between serum FGF21 levels and carotid intima-media thickness (IMT) in a large cohort of Southern Chinese subjects.

APPROACH AND RESULTS

The cohort consisted of 670 subjects who underwent carotid IMT measurement. Serum FGF21 levels were measured with an ELISA kit. Serum FGF21 levels positively correlated with carotid IMT in women (r=0.32; P<0.001), but not in men (r=0.06; P=0.305). On multiple linear regression analysis, elevated serum FGF21 level in women was an independent risk factor for increased carotid IMT (P=0.039), together with age (P<0.001) and hypertension (P=0.011), in a model comprising also waist circumference, smoking history, serum creatinine, high sensitive C-reactive protein, dysglycemia, and dyslipidemia (adjusted R(2)=35.8%; P<0.001). Elevated serum FGF21 levels were also a significant independent risk factor of carotid IMT on multiple stepwise regression analysis (P=0.01).

CONCLUSIONS

The present study is the first demonstration that elevated serum FGF21 levels are associated with carotid atherosclerosis in humans, independent of established risk factors including adverse lipid profiles and C-reactive protein. The role of FGF21 as a biomarker or therapeutic target of atherosclerotic diseases warrants further investigation.

Activation of Liver FGF21 in hepatocarcinogenesis and during hepatic stress

Background

FGF21 is a promising intervention therapy for metabolic diseases as fatty liver, obesity and diabetes. Recent results suggest that FGF21 is highly expressed in hepatocytes under metabolic stress caused by starvation, hepatosteatosis, obesity and diabetes. Hepatic FGF21 elicits metabolic benefits by targeting adipocytes of the peripheral adipose tissue through the transmembrane FGFR1-KLB complex. Ablation of adipose FGFR1 resulted in increased hepatosteatosis under starvation conditions and abrogation of the anti-obesogenic action of FGF21. These results indicate that FGF21 may be a stress responsive hepatokine that targets adipocytes and adipose tissue for alleviating the damaging effects of stress on the liver. However, it is unclear whether hepatic induction of FGF21 is limited to only metabolic stress, or to a more general hepatic stress resulting from liver pathogenesis and injury.

Methods

In this survey-based study, we examine the nature of hepatic FGF21 activation in liver tissues and tissue sections from several mouse liver disease models and human patients, by quantitative PCR, immunohistochemistry, protein chemistry, and reporter and CHIP assays. The liver diseases include genetic and chemical-induced HCC, liver injury and regeneration, cirrhosis, and other types of liver diseases.

Results

We found that mouse FGF21 is induced in response to chemical (DEN treatment) and genetic-induced hepatocarcinogenesis (disruptions in LKB1, p53, MST1/2, SAV1 and PTEN). It is also induced in response to loss of liver mass due to partial hepatectomy followed by regeneration. The induction of FGF21 expression is potentially under the control of stress responsive transcription factors p53 and STAT3. Serum FGF21 levels correlate with FGF21 expression in hepatocytes. In patients with hepatitis, fatty degeneration, cirrhosis and liver tumors, FGF21 levels in hepatocytes or phenotypically normal hepatocytes are invariably elevated compared to normal health subjects.

Conclusion

FGF21 is an inducible hepatokine and could be a biomarker for normal hepatocyte function. Activation of its expression is a response of functional hepatocytes to a broad spectrum of pathological changes that impose both cellular and metabolic stress on the liver. Taken together with our recent data, we suggest that hepatic FGF21 is a general stress responsive factor that targets adipose tissue for normalizing local and systemic metabolic parameters while alleviating the overload and damaging effects imposed by the pathogenic stress on the liver. This study therefore provides a rationale for clinical biomarker studies in humans.

Control of lipid metabolism by adipocyte FGFR1-mediated adipohepatic communication during hepatic stress

Background

Endocrine FGF19 and FGF21 exert their effects on metabolic homeostasis through fibroblast growth factor receptor (FGFR) and co-factor betaKlotho (KLB). Ileal FGF19 regulates bile acid metabolism through specifically FGFR4-KLB in hepatocytes where FGFR1 is not significant. Both FGF19 and FGF21 activate FGFR1-KLB whose function predominates in adipocytes. Recent studies using administration of FGF19 and FGF21 and genetic ablation of KLB or adipocyte FGFR1 indicate that FGFR1-KLB mediates the response of adipocytes to both FGF21 and FGF19. Here we show that adipose FGFR1 regulates lipid metabolism through direct effect on adipose tissue and indirect effects on liver under starvation conditions that cause hepatic stress.

Methods

We employed adipocyte-specific ablations of FGFR1 and FGFR2 genes in mice, and analyzed metabolic consequences in adipose tissue, liver and systemic parameters under normal, fasting and starvation conditions.

Results

Under normal conditions, the ablation of adipose FGFR1 had little effect on adipocytes, but caused shifts in expression of hepatic genes involved in lipid metabolism. Starvation conditions precipitated a concurrent elevation of serum triglycerides and non-esterified fatty acids, and increased hepatic steatosis and adipose lipolysis in the FGFR1-deficient mice. Little effect on glucose or ketone bodies due to the FGFR1 deficiency was observed.

Conclusions

Our results suggest an adipocyte-hepatocyte communication network mediated by adipocyte FGFR1 that concurrently dampens hepatic lipogenesis and adipocyte lipolysis. We propose that this serves overall to mete out and extend lipid reserves for neural fuels (glucose and ketone bodies), while at the same time governing extent of hepatosteatosis during metabolic extremes and other conditions causing hepatic stress.

Identification of a support vector machine-based biomarker panel with high sensitivity and specificity for nonalcoholic steatohepatitis

BACKGROUND

Although liver biopsy remains the best diagnostic standard for nonalcoholic steatohepatitis (NASH), non-invasive tests are eagerly awaited. In this study, we sought to develop a support vector machine (SVM) algorithm to discriminate with high accuracy between subjects with NASH and controls using a blood-based biomarker panel.

METHODS

A total of 17 biomarkers were measured by commercially available enzyme-linked immunosorbent assays in 136 serum samples from patients with biopsy-proven NASH (n = 60) and subjects with normal ALT and no evidence of fatty liver on ultrasound (n = 76). The database was randomly divided (1:1 fashion) into a discovery set for classification training and in a validation set of the chosen biomarkers in blinded samples. Multivariate analysis was performed by means of SVM.

RESULTS

After the identification of a group of three most discriminative biomarkers (osteoprotegerin, fibroblast growth factor 21, and M30) in the discovery set, the application of SVM to the validation test resulted in a 92.5% sensitivity and 84.1% specificity for distinguishing subjects with NASH from controls.

CONCLUSIONS

A targeted biomarker profiling combined with a SVM-based pattern identification approach may allow the identification of patients with NASH with clinically relevant accuracy and validity.

Metabolic actions of fibroblast growth factor 21

PURPOSE OF REVIEW

FGF21 has emerged as a hormone involved in energy homeostasis. A large number of recent reports have expanded the role of FGF21 from a response factor to prolonged fasting to a key hormone that regulates free fatty acid (FFAs) levels. The therapeutic role of recombinant human FGF21 for type 2 diabetes and dyslipidemia is under study.

RECENT FINDINGS

Recent evidence suggests that supraphysiological concentrations of FFAs induce FGF21 secretion (i.e., starvation and intense physical activity) through the peroxisome proliferator-activated receptor alpha (PPARα) pathway. The rise in FGF21 levels is aimed at improving energy production (ketogenesis) and utilization (oxidation) of FFAs. FGF21 increment may protect against chronic exposure to high concentrations of FFAs, which causes lipotoxicity in muscle, pancreas, and liver. In addition, FGF21 induces appetite and inhibits growth, probably as part of the adaptive starvation response. The autocrine function of FGF21 in adipose tissue increases PPARγ activity and glucose uptake. Increased plasma FGF21 levels have been found in insulin resistance states in humans. However, the reason for this rise in FGF21 values is still under study.

SUMMARY

We propose that FGF21 serves as a defense mechanism against supraphysiological concentrations of FFAs. In addition, FGF21 might have a therapeutic indication in humans.

Decrease in circulating fibroblast growth factor 21 after an oral fat load is related to postprandial triglyceride-rich lipoproteins and liver fat

BACKGROUND

Elevated levels of circulating fibroblast growth factor 21 (FGF21) are commonly encountered in type 2 diabetes, dyslipidemia, and non-alcoholic fatty liver disease, all of which share exaggerated postprandial lipemia as a common proatherogenic feature. How FGF21 responds to an oral fat load in man is unknown.

METHODS

We measured liver fat contents and subcutaneous and visceral fat volumes in 47 healthy subjects, who also underwent an oral fat load with measurements of plasma FGF21 and free fatty acid (FFA). Triglyceride (TG), apolipoprotein B-48 (apoB-48), and apoB-100 concentrations were measured in triglyceride-rich lipoprotein (TRL) fractions.

RESULTS

When compared with fasting levels, the concentration of FGF21 decreased significantly at 4 h (P < 0.05) and tended to return to fasting levels at 8 h after an oral fat load. Fasting and postprandial FGF21 correlated significantly with liver fat as well as with TRLs in the chylomicron and especially in very low-density lipoprotein 1 (VLDL1) and VLDL2 fractions representing remnant particles, but not with FFA. Subjects with increased liver fat (>5%, n = 12) showed impaired suppression of FGF21 at 4 h (P < 0.05) and at 8 h (P=0.01) and demonstrated higher postprandial TG area under the curve in plasma and TRL fractions (P ≤ 0.032) compared with those with normal liver fat (≤ 5%, n = 35).

CONCLUSIONS

We observed a significant decrease of FGF21 concentration after an oral fat load. Fasting and postprandial FGF21 levels were closely related to large VLDL and remnants, but not to plasma FFA. Our pilot findings suggest that the postprandial accumulation of TRL remnants and liver fat may modulate postprandial FGF21 levels.

Endocrine fibroblast growth factors 15/19 and 21: from feast to famine

We review the physiology and pharmacology of two atypical fibroblast growth factors (FGFs)-FGF15/19 and FGF21-that can function as hormones. Both FGF15/19 and FGF21 act on multiple tissues to coordinate carbohydrate and lipid metabolism in response to nutritional status. Whereas FGF15/19 is secreted from the small intestine in response to feeding and has insulin-like actions, FGF21 is secreted from the liver in response to extended fasting and has glucagon-like effects. FGF21 also acts in an autocrine fashion in several tissues, including adipose. The pharmacological actions of FGF15/19 and FGF21 make them attractive drug candidates for treating metabolic disease.