Association between circulating fibroblast growth factor 21 and mortality in end-stage renal disease

Phosphate is associated with frailty in older patients with chronic kidney disease not on dialysis

PURPOSE

Frailty is common in older patients with chronic kidney disease (CKD) and has been considered an independent risk factor for adverse clinical outcomes in this population. CKD-associated mineral and bone metabolism (CKD-MBD) increases energy expenditure and causes malnutrition and inflammation leading to frailty. We investigated whether CKD-MBD markers and energy metabolism are associated with frailty in patients with advanced CKD on conservative management.

METHODS

In this cross-sectional study, we investigated factors associated with frailty in a sample of 75 patients ≥ 65 years, with stage 4 or 5 CKD. Collected data included age, sex, body mass index, physical activity status, educational level, Charlson Comorbidity Index, and laboratory markers. Frailty was evaluated according to Fried's classification.

RESULTS

Frailty was observed in 51.3% and pre-frailty in 47.3%. The frail population was significantly older, with a high proportion of females, more inactive, had lower educational levels, spent a long time sitting throughout the day, and had higher phosphate and fibroblast growth factor 21 (FGF-21). In the multivariate logistic analysis age (odds ratio 1.13, p = 0.026) and phosphate (odds ratio 3.38, p = 0.021) remained independently associated with frailty.

CONCLUSION

Serum phosphate seems to be a toxin associated with the frailty phenotype in older patients with CKD. Whether strategies to decrease serum phosphate would reduce the risk of frailty in this population deserves further evaluation.

Association of circulating fibroblast growth factor 21 levels with all-cause and cardiovascular mortality: The multi-ethnic study of atherosclerosis

BACKGROUND

Fibroblast growth factor 21 (FGF21) levels are often elevated in cardiovascular disease (CVD). However, no study has assessed its association with cardiovascular and all-cause mortality in a population free of clinically evident CVD.

METHODS

A total of 5543 Multi-Ethnic Study of Atherosclerosis (MESA) participants (mean age 62.7 years, 47.5 % male), free of clinically evident CVD at baseline, were studied. From baseline (2000-2002), 1606 deaths (including 387 CVD deaths) were observed over a median follow-up of 17.7 years. Multivariable Cox regression analysis was performed to assess the association of plasma FGF21 levels with mortality.

RESULTS

FGF21 levels at baseline were associated with all-cause mortality, even after adjustment for traditional risk factors, including demographic, socioeconomic and cardiovascular risk factors (adjusted hazard ratio 1.08 [95% confidence interval 1.01, 1.16] per 1 SD increase in ln-transformed levels; 1.27 for the highest vs, lowest quartile). Baseline FGF21 levels were significantly associated with both CVD and non-CVD mortality in unadjusted models. However, the association with non-CVD mortality, but not CVD mortality, remained statistically significant after adjusting for covariates. Similar results were obtained in FGF21 quartile analyses and also when using competing risk regression or matched case-control cohort in sensitivity analyses.

CONCLUSIONS

In subjects without clinically-evident CVD at baseline, over 17.7 years follow-up there is a modest association of baseline FGF21 levels with all-cause mortality. The finding that this is driven primarily by a significant association with non-CVD mortality over almost two decades merits further investigation.

Short-term hypercaloric carbohydrate loading increases surgical stress resilience by inducing FGF21

Dietary restriction promotes resistance to surgical stress in multiple organisms. Counterintuitively, current medical protocols recommend short-term carbohydrate-rich drinks (carbohydrate loading) prior to surgery, part of a multimodal perioperative care pathway designed to enhance surgical recovery. Despite widespread clinical use, preclinical and mechanistic studies on carbohydrate loading in surgical contexts are lacking. Here we demonstrate in ad libitum-fed mice that liquid carbohydrate loading for one week drives reductions in solid food intake, while nearly doubling total caloric intake. Similarly, in humans, simple carbohydrate intake is inversely correlated with dietary protein intake. Carbohydrate loading-induced protein dilution increases expression of hepatic fibroblast growth factor 21 (FGF21) independent of caloric intake, resulting in protection in two models of surgical stress: renal and hepatic ischemia-reperfusion injury. The protection is consistent across male, female, and aged mice. In vivo, amino acid add-back or genetic FGF21 deletion blocks carbohydrate loading-mediated protection from ischemia-reperfusion injury. Finally, carbohydrate loading induction of FGF21 is associated with the induction of the canonical integrated stress response (ATF3/4, NF-kB), and oxidative metabolism (PPARγ). Together, these data support carbohydrate loading drinks prior to surgery and reveal an essential role of protein dilution via FGF21.

Fibroblast growth factor 21 alleviates unilateral ureteral obstruction-induced renal fibrosis by inhibiting Wnt/β-catenin signaling pathway

Fibroblast growth factor 21 (FGF21) is a key regulator of energy metabolism. Recent studies suggested that serum FGF21 levels increase with declining renal function. However, the link between FGF21 and kidney diseases and the direct effect of FGF21 in renal fibrosis remains unclear. In this study, FGF21 was upregulated in unilateral ureteral obstruction (UUO)-induced renal fibrosis and cellular fibrosis induced by transforming growth factor-β, and renal expression of FGF21 was positively correlated with fibrosis markers. Additionally, FGF21 was regulated by Wnt/β-catenin signaling pathway. The knockdown and overexpression of FGF21 in mouse tubular epithelial cells demonstrated that FGF21 alleviates renal fibrosis by inhibiting the Wnt/β-catenin signaling pathway. To investigate the effect of FGF21 on renal fibrosis in vivo, we established an overexpression model by injecting the plasmid in mice and found that FGF21 overexpression relieved UUO-induced renal fibrosis and renal inflammatory response. Taken together, FGF21 is upregulated with the activation of Wnt/β-catenin signaling pathway and alleviates renal fibrosis by inhibiting the activation of Wnt/β-catenin signaling pathway in a negative feedback mode. These results provide a new understanding for the source of elevated serum FGF21 in patients with chronic kidney disease and prove that FGF21 is a direct inhibitor of the progression of renal fibrosis, thus providing novel therapeutic intervention insights for renal fibrosis.

Elevated serum FGF21 is an independent predictor for adverse events in hemodialysis patients from two large centers: a prospective cohort study

Introduction: We explored the relationship and the predictive value of serum fibroblast growth factor 21 (FGF21) with all-cause mortality, major adverse cardiovascular events (MACEs) and pneumonia in hemodialysis (HD) patients.Methods: A total of 388 Chinese HD patients from two HD centers were finally enrolled in this prospective cohort study (registration number: ChiCTR 1900028249) between January 2018 and December 2018. Serum FGF21 was detected. Patients were followed up with a median period of 47 months to record the MACEs and pneumonia until death or 31 December 2022.Results: The incidence of all-cause mortality, MACEs and pneumonia in HD patients were 20.6%, 29.6%, and 34.8%, respectively. The optimal cutoffs for FGF21 to predict all-cause mortality, MACEs and pneumonia were 437.57 pg/mL, 216.99 pg/mL and 112.79 pg/mL. Multivariate Cox regression analyses showed that FGF21, as a categorical variable, was an independent predictor for all-cause mortality, MACEs and pneumonia (HR, 3.357, 95% CI, 2.128-5.295, p < 0.001; HR, 1.575, 95% CI, 1.046-2.371, p = 0.029; HR, 1.784; 95% CI, 1.124-2.830; p = 0.014, respectively). The survival nomogram, MACEs-free survival nomogram and pneumonia-free survival nomogram based on FGF21 constructed for individualized assessment of HD patients had a high C-index with 0.841, 0.706 and 0.734.Conclusion: Higher serum FGF21 is an independent predictor of all-cause mortality, MACEs and pneumonia in HD patients.

Pro-Inflammatory Proteins Associated with Frailty and Its Progression-A Longitudinal Study in Community-Dwelling Women

The complex pathophysiology underlying biological aging creates challenges for identifying biomarkers associated with frailty. This longitudinal, nontargeted proteomics study aimed to identify proteins associated with frailty, particularly the change from nonfrail to frail. The population-based Osteoporosis Prospective Risk Assessment cohort includes women all of whom are 75 years old at inclusion (n = 1044) and reassessed at 80 years (n = 715) and 85 years (n = 382). A deficits in health frailty index (FI) and 92 plasma proteins (Olink CVD-II panel) were available at all ages. The identical age facilitated differentiating chronological and biological aging. Bidirectional analyses, performed cross-sectionally and longitudinally, used regression models controlled for false discovery rate (FDR), across 5- and 10-year time windows and longitudinal mixed models. Frailty outcomes were frailty index, frailty status (frail defined as FI ≥ 0.25), change in frailty index, and change in frailty status, together with protein expression or change in protein expression. Elevated levels of 32 proteins were positively associated with the FI, cross-sectionally at all ages (range: β-coefficients 0.22-2.06; FDR 0.021-0.024), of which 18 were also associated with frailty status (range: odds ratios 1.40-5.77; FDR 0.022-0.016). Based on the accrued data, eight core proteins (CD4, FGF23, Gal-9, PAR-1, REN, TNFRSF10A TNFRSF11A, and TNFRSF10B) are proposed. A one-unit change in the FI was additively associated with increased protein expression over 5 and 10 years (range: β-coefficients 0.52-1.59; p < 0.001). Increments in baseline FI consistently associated with a change in protein expression over time (5 years, β-range 0.05-1.35; 10 years, β-range 0.51-1.48; all p < 0.001). A one-unit increase in protein expression was also associated with an increased probability of being frail (FI ≥ 0.25) (β-range: 0.14-0.61). Mirroring the multisystem deterioration that typifies frailty, the proteins and their associated biological pathways reflect pathologies, including the renal system, skeletal homeostasis, and TRAIL-activated apoptotic signaling. The core proteins are compelling candidates for understanding the development and progression of frailty with advancing age, including the intrinsic musculoskeletal component. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Fluid homeostasis induced by sodium-glucose cotransporter 2 inhibitors: novel insight for better cardio-renal outcomes in chronic kidney disease

Hypertension in chronic kidney disease (CKD) patients is a risk factor for end-stage renal disease, cardiovascular events, and mortality. Thus, the prevention and appropriate management of hypertension in these patients are essential strategies for better cardio-renal outcomes. In this review, we show novel risk factors for hypertension with CKD, several promising prognostic markers and treatment for cardio-renal outcomes. Of note, the clinical use of sodium-glucose cotransporter 2 (SGLT2) inhibitors has recently expanded to non-diabetic patients with CKD and heart failure as well as diabetic patients. SGLT2 inhibitors have an antihypertensive effect, but are also associated with a low risk of hypotension. This unique mechanism of blood pressure regulation by SGLT2 inhibitors may partially depend on body fluid homeostasis, which is mediated by the autoregulation property between "accelerator" (diuretic action) and "brake" (increase in anti-diuretic hormone vasopressin and fluid intake). Mineralocorticoid receptor (MR) blockers are used in the treatment of essential hypertension and hyperaldosteronism. Recently, a new MR blocker, finerenone, has been launched as a treatment for CKD with type 2 diabetes. These advances in relation to hypertension in CKD may contribute to the reduction of renal and cardiovascular events.

Endocrine manifestations of chronic kidney disease and their evolving management: A systematic review

BACKGROUND

Chronic Kidney Disease (CKD) shows a wide range of renal abnormalities including the excretory, metabolic, endocrine, and homeostatic function of the kidney. The prognostic impact of the 'endocrine manifestations' which are often overlooked by clinicians cannot be overstated.

METHODS AND OBJECTIVES

A systematic review was attempted to provide a comprehensive overview of all endocrine abnormalities of CKD and their evolving principles of management, searching databases of PubMed, Embase, and Scopus and covering the literature between 2002 and 2022.

RESULTS

The endocrine derangements in CKD can be attributed to a myriad of pathologic processes, in particular decreased clearance, impaired endogenous hormone production, uremia-induced cellular dysfunction, and activation of systemic inflammatory pathways. The major disorders include anemia, hyperprolactinemia, insulin resistance, reproductive hormone deficiency, thyroid hormone deficiency, and serum FGF (Fibroblast Growth Factor) alteration. Long-term effects of CKD also include malnutrition and increased cardiovascular risk. The recent times have unveiled their detailed pathogenesis and have seen an evolution in the principles of management which necessitates a revision of current guidelines.

CONCLUSION

Increased advertence regarding the pathology, impact, and management of these endocrine derangements can help in reducing morbidity as well as mortality in the CKD patients by allowing prompt individualized treatment. Moreover, with timely and appropriate intervention, a long-term reduction in complications, as well as an enhanced quality of life, can be achieved in patients with CKD.

Update on Hypertension Research in 2021

In 2021, 217 excellent manuscripts were published in Hypertension Research. Editorial teams greatly appreciate the authors' contribution to hypertension research progress. Here, our editorial members have summarized twelve topics from published work and discussed current topics in depth. We hope you enjoy our special feature, "Update on Hypertension Research in 2021".

Association between amorphous calcium-phosphate ratios in circulating calciprotein particles and prognostic biomarkers in hemodialysis patients

Calciprotein particles (CPPs) are circulating colloidal mineral-protein complexes containing crystalline and/or non-crystalline (amorphous) calcium-phosphate (CaPi). Serum CPP levels correlate with vascular stiffness and calcification in patients with chronic kidney disease (CKD). In vitro studies showed that CPPs containing crystalline CaPi were more arteriosclerogenic and inflammogenic than CPPs without containing crystalline CaPi. Thus, we hypothesized that not only the quantity but also the quality of CPPs (the phase of CaPi) might affect clinical outcomes. To test this hypothesis, we quantified amorphous CaPi ratio defined as the ratio of the amorphous CaPi amount to the total CaPi amount in serum CPPs from 183 hemodialysis patients and explored its possible correlation with serum parameters associated with prognosis of hemodialysis patients. Multivariate analysis revealed that the amorphous CaPi ratio correlated positively with hemoglobin and negatively with fibroblast growth factor-21 (FGF21), which remained significant after adjusting for the total CaPi amount. Because low hemoglobin and high FGF21 are associated with increased mortality, the present study warrants further studies to determine whether low amorphous CaPi ratio in circulating CPPs may be associated with poor prognosis in hemodialysis patients.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Serum Fibroblast Growth Factor 21 Level Is Associated with Aortic Stiffness in Patients on Maintenance Hemodialysis

Background. Fibroblast growth factor 21 (FGF-21) is a hormone that regulates glucose and lipid metabolism. High serum FGF-21 levels are associated with carotid atherosclerosis and coronary artery disease. This cross-sectional study aimed to assess the relationship between serum FGF-21 levels and carotid-femoral pulse wave velocity (cfPWV) in patients on maintenance hemodialysis (HD). Methods. Blood samples and baseline characteristics were collected from 130 HD patients. Serum FGF-21 concentrations were measured with an enzyme-linked immunosorbent assay kit. Aortic stiffness was defined as a carotid-femoral pulse wave velocity (cfPWV) of more than 10 m/s. Results. Of the 130 HD patients, aortic stiffness was diagnosed in 54 (41.5%). Serum FGF-21 levels were significantly higher in those with aortic stiffness than those without $\left(P<0.001\right)$ . The FGF-21 level was independently associated with aortic stiffness (odds ratio (OR): 1.008; 95% CI: 1.003–1.012; $P=0.001$ ) after adjusting for diabetes mellitus, age, hypertension, C-reactive protein, and body weight in multivariable logistic regression analysis. Multivariable forward stepwise linear regression analysis also confirmed that the logarithmically transformed FGF-21 level (β = 3.245, 95% CI: 1.593–4.987, $P<0.001$ ) was an independent predictor of cfPWV values. The area under the receiver operating characteristic (ROC) curve predicting aortic stiffness by the serum FGF-21 level was 0.693 (95% CI: 0.606–0.771, $P<0.001$ ). Conclusions. Serum FGF-21 level positively correlates with cfPWV and is also an independent predictor of aortic stiffness in maintenance HD patients.

Circulating fibroblast growth factor 21 links hemodynamics with kidney function in middle-aged and older adults: A mediation analysis

Altered hemodynamics are commonly observed in individuals with declining renal function; however, the pathophysiological mechanisms linking renal dysfunction and hemodynamics have not been fully elucidated. Fibroblast growth factor 21 (FGF21), which upregulates sympathetic nerve activity, can alter systemic hemodynamics, and its level can increase as renal function declines. This study aimed to determine the associations among circulating FGF21 levels, hemodynamics, and renal function in middle-aged and older adults. In a total of 272 middle-aged and older adults (age range: 46-83 years), estimated glomerular filtration rate (eGFR), hemodynamics (brachial and aortic blood pressure and aortic pulse wave velocity [PWV]), and serum FGF21 levels were measured. For mediation analysis, hemodynamic parameters were entered as outcomes. eGFR or log-transformed urinary albumin and creatinine ratio (UACR) and log-transformed serum FGF21 levels were set as the predictors and mediator, respectively. According to multivariable regression models after adjusting for potential covariates, serum FGF21 levels were significantly associated with brachial systolic blood pressure (β = 0.140), pulse pressure (β = 0.136), and aortic PWV (β = 0.144). Mediation analyses showed that serum FGF21 levels significantly mediated the relationship of eGFR with brachial systolic blood pressure (indirect effect [95% confidence interval]: -0.032 [-0.071, -0.002]), pulse pressure (-0.019 [-0.041, -0.001]), and aortic PWV (-0.457 [-1.053, -0.021]) and the relationship of UACR with aortic PWV (7.600 [0.011, 21.148]). These findings suggest that elevated circulating FGF21 levels partially mediate the association of elevated blood pressure and/or aortic stiffness with renal dysfunction in middle-aged and older adults.

Association of serum fibroblast growth factor 21 with kidney function in a population-based Chinese cohort

Fibroblast growth factor 21 (FGF21) plays a role in kidney disease. Circulating FGF21 levels are associated with kidney function and progression in patients with type 2 diabetes (T2D). However, the association between FGF21 and kidney function in the general population is still lacking. The aim of this study was to determine the association between FGF21 and kidney function and its progression in a Chinese cohort.A total of 2425 participants from a population-based survey of diabetes and metabolic syndrome in Pinggu, Beijing, were included in the baseline analysis. After a median follow-up of 12 months, 2402 participants with baseline estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2 were analyzed in the longitudinal study. The progression of kidney function was defined as an eGFR decline exceeding 3.3% per year. Serum FGF21 levels were measured using an enzyme-linked immunosorbent assay at baseline.Male sex, body mass index (BMI), homeostasis model assessment of insulin resistance, higher levels of low-density lipoprotein cholesterol (LDL-c), uric acid, and FGF21 were associated with increased odds of a lower eGFR at baseline. The association of FGF21 with lower eGFR was independent of all the potential confounders in multivariable logistic regression (odds ratio, 1.005; 95% confidence interval 1.002-1.008). However, FGF21 was not associated with eGFR decline in the longitudinal analysis (odds ratio, 1.000; 95% confidence interval 0.998-1.001).Increased serum FGF21 levels were independently associated with lower eGFR in this nonmedicated general population. FGF21 could be a biomarker of kidney function in the general population.

Fibroblast Growth Factor 21 and Its Association With Oxidative Stress and Lipid Profile in Type 2 Diabetes Mellitus

Introduction Cardiovascular diseases are the leading cause of mortality in diabetic patients. Oxidative stress and mitochondrial dysfunction lead to diabetic cardiomyopathy (DCM) characterized by impaired cardiac structure and function. Hyperglycemia causes oxidative stress, which can lead to microvascular complications, macrovascular complications, and atherosclerosis. Peripheral tissues produce fibroblast growth factor 21 (FGF-21), which has anti-inflammatory properties, increases oxidation of fatty acids, and improves insulin sensitivity. Its increased levels are found in metabolic syndrome and type 2 diabetes mellitus and may also lead to coronary heart disease. Our study sought to measure the serum FGF-21 levels and their associations with lipid profile parameters and oxidative stress in patients with type 2 diabetes mellitus. Methodology One-hundred fifty (150) patients of both genders with type 2 diabetes mellitus were recruited along with 150 controls. Simple random sampling was done. After taking relevant history and physical examination, we drew venous blood samples of each patient and sent them to the institutional laboratory for analysis of fasting blood sugar (FBS) levels, glycated hemoglobin (HbA1C), lipid profile, and FGF-21 serum levels. Oxidative stress parameter malondialdehyde (MDA) was estimated and the total antioxidant status by ferric reducing antioxidant power assay (FRAP) was assessed. Patients were followed up after three months to record the glycemic index, and the values were recorded. We used SPSS Software 25.0 (SPSS, Inc., Chicago, USA) to analyze the data. For consideration of results to be statistically significant, a 𝑃 value of < 0.05 was selected. Results The levels of serum cholesterol, triglycerides, and low-density lipoprotein (LDL) cholesterol were increased in diabetics compared to controls and were statistically significant (p<0.05). High-density lipoprotein (HDL) cholesterol was lower in diabetic patients as compared to the controls (p<0.05). There was a statistically significant increase in the level of MDA in diabetics compared to controls (p˂0.005). Serum levels of total antioxidant status (FRAP) were decreased in diabetics in comparison with controls (p˂0.005). Serum FGF-21 level was statistically increased in diabetics compared to controls (p˂0.005). FGF-21 and MDA are positively correlated and FGF-21 and FRAP are negatively correlated. Serum FGF-21 is positively correlated with total cholesterol, triglycerides, serum LDL cholesterol, and HDL cholesterol. Conclusion Our study concludes that there is a significant correlation between fibroblast growth factor 21, oxidative stress, and abnormal lipid profile in type 2 diabetic patients. FGF-21 could be the target of certain medications used to treat metabolic disorders and obesity.

Regulation and Potential Biological Role of Fibroblast Growth Factor 21 in Chronic Kidney Disease

Chronic kidney disease (CKD) is an incurable progressive disease with the progressive impairment of kidney function, which can accelerate the progression of cardiovascular disease, increase the risk of infection, and lead to related complications such as anemia and bone disease. CKD is to a great extent preventable and treatable, and it is particularly important to improve the early diagnosis, strengthen the research underlying the mechanism of disease occurrence and development, and innovate new intervention measures. Fibroblast growth factor 21 (FGF21) belongs to one of members of endocrine FGF subfamily with evolutionarily conserved functions and performs a vital role in the regulation of energy balance and adipose metabolism. FGF21 needs to rely on β-Klotho protein to specifically bind to FGF receptor (FGFR), which activates the FGF21 signaling exerting the biological function. FGF21 is deemed as an important regulatory factor extensively modulating many cellular functions under physiologic and pathologic conditions. Although the metabolic effect of FGF21 has been extensively studied, its potential biological role in the kidney has not been generally investigated. In this review, we summarize the biological characteristics, regulation and biological function of FGF21 based on the current studies, and briefly discuss the potential relationship with chronic kidney disease.

High-Level Serum Fibroblast Growth Factor 21 Concentration Is Closely Associated With an Increased Risk of Cardiovascular Diseases: A Systematic Review and Meta-Analysis

Background: The association between fibroblast growth factor 21 (FGF21) and cardiovascular disease (CVD) risk remains unclear. We conducted this systematic review and meta-analysis to evaluate the association between FGF21 and CVDs, and relevant vascular parameters.

Methods: PubMed and Web of Science databases were systematically searched to identify relevant studies published before March 2021. The FGF21 concentration was compared between individuals with and without CVDs. The effect of FGF21 on CVD risk was assessed by using hazard ratio (HR) and odds ratio (OR). The association between FGF21 and vascular parameters was assessed by Pearson's r. Study quality was assessed using Newcastle–Ottawa Scale and Joanna Briggs Institution Checklist.

Results: A total of 29,156 individuals from 30 studies were included. Overall, the serum FGF21 concentration was significantly higher in CVD patients (p < 0.001), especially for coronary artery disease (CAD) (p < 0.001) and hypertension (p < 0.001). The pooled OR (p = 0.009) and HR (p < 0.001) showed that the risk of CVDs increased with FGF21. The linear association between FGF21 and vascular parameters, including pulse wave velocity (r = 0.32), carotid intima-media thickness (r = 0.21), ankle-brachial index (r = 0.33), systolic blood pressure (r = 0.13), and diastolic blood pressure (r = 0.05), was insignificant. The incidence of overall CVDs (p = 0.03) was significantly higher in individuals with higher FGF21 levels.

Conclusion: High-level serum FGF21 concentration is closely associated with an increased risk of CVDs, which may be independent of vascular parameters. A standard FGF21 classification threshold needs to be established before clinical use for CVD risk assessment.

Systematic Review Registration:https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=241968, identifier: CRD42021241968.

FGF21 prevents low-protein diet-induced renal inflammation in aged mice

Low-protein (LP) diets extend lifespan through a comprehensive improvement in metabolic health across multiple tissues and organs. Many of these metabolic responses to protein restriction are secondary to transcriptional activation and release of FGF21 from the liver. However, the effects of an LP diet on the kidney in the context of aging has not been examined. Therefore, the goal of the current study was to investigate the impact of chronic consumption of an LP diet on the kidney in aging mice lacking FGF21. Wild-type (WT; C57BL/6J) and FGF21 knockout (KO) mice were fed a normal protein diet (20% casein) or an LP (5% casein) diet ad libitum from 3 to 22 mo of age. The LP diet led to a decrease in kidney weight and urinary albumin-to-creatinine ratio in both WT and FGF21 KO mice. Although the LP diet produced only mild fibrosis and infiltration of leukocytes in WT kidneys, the effects were significantly exacerbated by the absence of FGF21. Accordingly, transcriptomic analysis showed that inflammation-related pathways were significantly enriched and upregulated in response to LP diet in FGF21 KO mice but not WT mice. Collectively, these data demonstrate that the LP diet negatively affected the kidney during aging, but in the absence of FGF21, the LP diet-induced renal damage and inflammation were significantly worse, indicating a protective role of FGF21 in the kidney.NEW & NOTEWORTHY Long-term protein restriction is not advantageous for an otherwise healthy, aging kidney, as it facilitates the development of renal tubular injury and inflammatory cell infiltration. We provide evidence using FGF21 knockout animals that FGF21 is essential to counteract the renal injury and inflammation during aging on a low-protein diet.

FGF21 and Chronic Kidney Disease

The global nephrology community recognizes the increasing burden of kidney disease and its poor health outcomes in the general population. Given this, strategies to establish early diagnosis, improve understanding of the natural course and develop novel therapeutic interventions to slow progression and reduce complications are encouraged. Fibroblast growth factor 21 (FGF21), a member of the endocrine FGF subfamily, has emerged as a master homeostasis regulator of local and systemic lipid, glucose and energy metabolism. In addition, FGF21 should be considered an autonomic and endocrine regulator of stress responses in general. Promising results has been shown in both dysmetabolic animal models and metabolic disease patients after pharmacological administration of FGF21 analogs. The association of FGF21 with renal function has been studied for more than ten years. However, the functional role of FGF21 in the kidney is still poorly understood. This review summarizes the biological effects of FGF21 and discusses what is currently known about this hormone and chronic kidney disease, highlighting important gaps that warrant further research.

Fibroblast Growth Factor 21 Predicts and Promotes Vascular Calcification in Haemodialysis Patients

Background

Cardiovascular disease (CVD) is the leading cause of death in haemodialysis (HD) patients. Vascular calcification (VC) is dramatically accelerated and is strongly associated with CVD events and mortality in HD patients. VC coexists with osteoporosis in many studies. Fibroblast growth factor 21 (FGF21) which is known as an adipocytokine is a new hypoglycemic strategy and is inversely related to bone mineral density.

Methods

To evaluate the contribution of FGF21 to VC in HD patients, we detected circulating FGF21 levels and measured the whole thoracic aorta calcification scores (TACS) and calcification scores of the 3 segments of thoracic aorta, including ascending thoracic aorta (ATACS), aortic arch (AoACS), and descending thoracic aorta (DTACS) of our HD patients in this cross-sectional study. In addition, we pre-incubated human aortic endothelial cells (HAECs) with FGF21 in the presence or absence of parathyroid hormone (PTH) in vitro.

Results

The median serum FGF21 level in HD patients was 11-fold higher than that in healthy controls. Ln(FGF21) was positively correlated with Ln(TACS+1), Ln(ATACS+1), Ln(AoACS+1), and Ln(DTACS+1), respectively, in HD patients. Serum FGF21 was independently associated with TACS and ATACS, AoACS, and DTACS. FGF21 which was combined with age, calcium, and intact PTH demonstrated a high area under the curve of 0.84 with optimal sensitivity (84%) and specificity (71%) for the prediction of VC in HD patients. Our vitro results showed that FGF21 enhanced the calcification effect of PTH on HAECs by increasing calcium deposition and endothelial-to-mesenchymal transition.

Conclusions

Circulating FGF21 was notably higher and was a potential predictor and promoter of VC in HD patients.

Aging and FGF23-klotho system

During the evolution of skeletons, vertebrates acquired the bone made of calcium phosphate. By keeping the extracellular fluid in a supersaturated condition regarding calcium and phosphate, vertebrates create the bone when and where they want simply by providing a cue for precipitation. To secure this strategy, a new endocrine system has evolved that strictly controls the extracellular phosphate concentration. In response to phosphate intake, fibroblast growth factor-23 (FGF23) is secreted from the bone and acts on the kidney through binding to its receptor Klotho to increase urinary phosphate excretion and maintain phosphate homeostasis. The FGF23-Klotho endocrine system, when disrupted, results in hyperphosphatemia and ectopic precipitation of calcium phosphate in mice and humans. In addition to disturbed phosphate homeostasis, mice lacking Klotho suffer from premature aging. They exhibit multiple organ atrophy, arteriosclerosis characterized by vascular calcification, cardiac hypertrophy, sarcopenia, cognition impairment, frailty, and a shortened life span associated with chronic non-infectious inflammation. Restoration of the phosphate balance by placing Klotho- or FGF23-deficient mice on low phosphate diet rescued them from the aging-like phenotypes, indicating that phosphate was responsible for the accelerated aging. The similar pathophysiology is universally observed in patients with chronic kidney disease (CKD), rendering advanced CKD a clinical model of accelerated aging. CKD patients bear colloidal nanoparticles containing calcium phosphate in the blood, which are termed calciprotein particles (CPPs). CPPs have the ability to induce cell damage and inflammation, potentially contributing to accelerated aging. Terrestrial vertebrates with the bone made of calcium phosphate may be destined to age due to ectopic calcium phosphate.

Myokines and Heart Failure: Challenging Role in Adverse Cardiac Remodeling, Myopathy, and Clinical Outcomes

Heart failure (HF) is a global medical problem that characterizes poor prognosis and high economic burden for the health system and family of the HF patients. Although modern treatment approaches have significantly decreased a risk of the occurrence of HF among patients having predominant coronary artery disease, hypertension, and myocarditis, the mortality of known HF continues to be unacceptably high. One of the most important symptoms of HF that negatively influences tolerance to physical exercise, well-being, social adaptation, and quality of life is deep fatigue due to HF-related myopathy. Myopathy in HF is associated with weakness of the skeletal muscles, loss of myofibers, and the development of fibrosis due to microvascular inflammation, metabolic disorders, and mitochondrial dysfunction. The pivotal role in the regulation of myocardial and skeletal muscle rejuvenation, attenuation of muscle metabolic homeostasis, and protection against ischemia injury and apoptosis belongs to myokines. Myokines are defined as a wide spectrum of active molecules that are directly synthesized and released by both cardiac and skeletal muscle myocytes and regulate energy homeostasis in autocrine/paracrine manner. In addition, myokines have a large spectrum of pleiotropic capabilities that are involved in the pathogenesis of HF including cardiac remodeling, muscle atrophy, and cardiac cachexia. The aim of the narrative review is to summarize the knowledge with respect to the role of myokines in adverse cardiac remodeling, myopathy, and clinical outcomes among HF patients. Some myokines, such as myostatin, irisin, brain-derived neurotrophic factor, interleukin-15, fibroblast growth factor-21, and growth differential factor-11, being engaged in the regulation of the pathogenesis of HF-related myopathy, can be detected in peripheral blood, and the evaluation of their circulating levels can provide new insights to the course of HF and stratify patients at higher risk of poor outcomes prior to sarcopenic stage.

Prognostic value of plasma fibroblast growth factor 21 among patients with acute ischemic stroke

BACKGROUND AND PURPOSE

To evaluate the association between plasma fibroblast growth factor 21 (FGF-21) and clinical outcomes in patients with acute ischemic stroke.

METHODS

A total of 3412 acute ischemic stroke patients from the China Antihypertensive Trial in Acute Ischemic Stroke with plasma FGF-21 measurements were included in this analysis. The primary outcome was a combination of death or major disability (modified Rankin Scale score ≥3) within 1 year after stroke.

RESULTS

During the 1-year of follow-up, 745 (21.83%) patients experienced the primary outcome; 550 had a major disability and 195 died. After multivariate adjustment, higher plasma FGF-21 was significantly associated with increased risk of the primary outcome (odds ratio = 1.52, 95% confidence interval = 1.11-1.29). Each 1-SD increase of log-transformed FGF-21 (0.67 pg/ml) was associated with 19%, 3%, and 33% increased risk of the primary outcome, major disability, and death, respectively. The addition of FGF-21 to the conventional risk factors significantly improved prediction of the primary outcome in ischemic stroke patients (net reclassification index = 10.8%, p = 0.011; integrated discrimination improvement = 0.3%, p = 0.038).

CONCLUSIONS

Higher plasma FGF-21 was associated with poor prognosis in acute ischemic stroke patients, suggesting that FGF-21 may be a prognostic marker for ischemic stroke.

Current understanding and controversies on the clinical implications of fibroblast growth factor 21

Metabolic functions of the hepatic hormone fibroblast growth factor 21 (FGF21) have been recognized for more than a decade in studying the responses of human subjects and rodent models to nutritional stresses such as fasting, high-fat diet or ketogenic diet consumption, and ethanol intake. Our interest in the beneficial metabolic effects of FGF21 has risen due to its potential ability to serve as a therapeutic agent for various metabolic disorders, including type 2 diabetes, obesity, and fatty liver diseases, as well as its potential to act as a diagnostic or prognostic biomarker for metabolic and other disorders. Here, we briefly review the FGF21 gene and protein structures, its expression pattern, and cellular signaling cascades that mediate FGF21 production and function. We mainly focus on discussing experimental and clinical literature pertaining to FGF21 as a therapeutic agent. Furthermore, we present several lines of investigation, including a few studies conducted by our team, suggesting that FGF21 expression and function can be regulated by dietary polyphenol interventions. Finally, we discuss the literature debating FGF21 as a potential biomarker in various disorders.

Relationship between physical activity and circulating fibroblast growth factor 21 in middle-aged and older adults

OBJECTIVE

Circulating levels of fibroblast growth factor 21 (FGF21) increase with advancing age and may lead to the development of cardiometabolic diseases via impaired lipid and glucose metabolism. While physical activity can reduce these risks of cardiometabolic dysfunction, it remains obscure whether circulation FGF21 levels are influenced by physical activity. The purpose of this study was to investigate the relations between daily physical activities and circulating FGF21 levels in middle-aged and older adults.

METHODS

In this cross-sectional study with 110 middle-aged and 102 older adults, circulating (serum) FGF21 levels were evaluated by enzyme-linked immunosorbent assay, and the time spent in light-intensity physical activity (LPA) and moderate-to-vigorous-intensity physical activity (MVPA) was assessed using a uniaxial accelerometer.

RESULTS

Serum FGF21 levels in the older group (158 pg/mL) were significantly higher than those in the middle-aged group (117 pg/mL). When we examined the joint association of age (middle-aged or older) and MVPA (lower or higher than the median) groups, serum FGF21 levels in the older and higher MVPA group (116 pg/mL) were significantly lower than those in the older and lower MVPA group (176 pg/mL). However, there was no difference in serum FGF21 levels between the lower and higher MVPA groups in the middle-aged group. In multivariable liner regression analysis, serum FGF21 levels were independently determined by MVPA time after adjusting for potential covariates in older adults (β = -0.209).

CONCLUSIONS

These cross-sectional study findings indicate that the time spent in MVPA is an independent determinant of circulating FGF21 levels, and that an age-related increase in serum FGF21 levels may be attenuated by habitually performing MVPA. (250/250 words).

l-carnitine supplementation vs cycle ergometer exercise for physical activity and muscle status in hemodialysis patients: A randomized clinical trial

Serum carnitine is decreased in hemodialysis patients, which induces muscle atrophy. Thus, we examined the different effects of l-carnitine and exercise on exercise activity and muscle status in hemodialysis patients. Twenty patients were divided into l-carnitine and cycle ergometer groups and were followed for 3 months. Muscle and fat mass, physical activities, and muscle status were evaluated by an impedance, physical function test, and magnetic resonance imaging, respectively. The l-carnitine significantly increased muscle mass (P = .023) and thigh circumference (P = .027), decreased fat mass (P = .007), and shortened chair stand-up time (P = .002) and 10-m walk test (P = .037). The fat fraction was improved by the l-carnitine (P = .047). Compared with the exercise group, l-carnitine improved the changes in 10-m walk test (P = .026), chair stand-up time (P = .014), and thigh circumference (P = .022). Baseline fibroblast growth factor-21 and myostatin levels predicted the l-carnitine-associated changes in exercise activities. l-carnitine, rather than exercise, improved physical activity and muscle status in hemodialysis patients.

FGF/FGFR signaling in health and disease

Growing evidences suggest that the fibroblast growth factor/FGF receptor (FGF/FGFR) signaling has crucial roles in a multitude of processes during embryonic development and adult homeostasis by regulating cellular lineage commitment, differentiation, proliferation, and apoptosis of various types of cells. In this review, we provide a comprehensive overview of the current understanding of FGF signaling and its roles in organ development, injury repair, and the pathophysiology of spectrum of diseases, which is a consequence of FGF signaling dysregulation, including cancers and chronic kidney disease (CKD). In this context, the agonists and antagonists for FGF-FGFRs might have therapeutic benefits in multiple systems.

Fibroblast growth factor 21 (FGF21) in children and adolescents with chronic kidney disease

Fibroblast growth factor 21 (FGF21) is one of the members of endocrine arm of FGF family. Its actions as a glucose and lipids metabolism regulator are widely known. Although the mechanism of FGF21 action in kidneys is still under investigation, FGF21 was considered as a marker of early kidney function decline. While many researchers focused on adult subjects in this matter, there are no data regarding children. Therefore, we have investigated the relationship between plasma or urine FGF21 levels and kidney function in a group of 42 pediatric patients with chronic kidney disease (CKD). Anthropometrical parameters and blood pressure were taken, routine biochemical tests were performed. The concentration of FGF21 in serum and urine was determined by enzyme immunoassay. The results revealed significantly higher serum FGF21 concentration among children from CKD group. However, serum FGF21 level was not related to gender, proteinuria, eGFR or renal replacement therapy. Urine FGF21 concentration correlated negatively with albuminuria and positively with eGFR. Documented negative correlation of FGF21 fractional excretion and eGFR is not enough to support the role of FGF21 as a biomarker for predicting kidney disease progression in children and adolescents. Other mechanisms including local kidney FGF21 production or enhanced excretion due to higher extrarenal production may result in higher urine FGF21 concentrations.

Endocrine fibroblast growth factors as potential biomarkers for chronic kidney disease

INTRODUCTION

Among the family of fibroblast growth factors (FGFs), FGF19, FGF21, and FGF23 act as circulating hormones and are called endocrine FGFs. FGF19 and FGF21 regulate bile acid and energy homeostasis, respectively, whereas FGF23 regulates vitamin D and phosphate homeostasis. Accumulating evidence suggests that FGF23 plays a critical role in disturbed mineral metabolisms, left ventricular hypertrophy, immunosuppression, inflammation, among others in patients with chronic kidney disease (CKD), highlighting the potential both as a biomarker and a therapeutic target. Several studies have also examined the potential role of FGF19 and FGF21 in CKD patients.

AREAS COVERED

In this review, we present a brief overview of the biology of FGF19, FGF21, and FGF23, and summarize recent clinical and experimental studies on the pathophysiological roles of endocrine FGFs, mainly FGF23, in CKD patients.

EXPERT OPINION

Among the endocrine FGFs, FGF23 represents the most promising biomarker in CKD patients. If future studies confirm that FGF23 is directly toxic in CKD patients, FGF23 could be regarded as a therapeutic target and its measurement would be valuable if applied in clinical practice. Despite their potentially important roles, the clinical relevance of FGF19 and FGF21 in CKD patients is unclear, and much more studies are required.

Exercise-Released Myokines in the Control of Energy Metabolism

Physical activity reduces cardiometabolic risk, while physical inactivity increases chronic diseases risk. This led to the idea that exercise-induced muscle contraction contributes to metabolic regulation and health. It is now well established that skeletal muscle, through the release of endocrine factors, i.e., so-called myokines, crosstalk with metabolic organs such as adipose tissue, liver and pancreas. Recent advances suggested that a number of myokines are able to modulate adipose tissue metabolism and thermogenic activity, liver endogenous glucose production and β-cell insulin secretion. This novel paradigm offers a compelling hypothesis and molecular basis to explain the link between physical inactivity and chronic diseases. Herein, we review major findings and recent advances linking exercise, myokines secretion and inter-organ crosstalk. Identifying the molecular mediators linking physical activity to metabolic health could open the path toward novel therapeutic targets in metabolic diseases.

Fibroblast Growth Factor 21 Attenuates Diabetes-Induced Renal Fibrosis by Negatively Regulating TGF-β-p53-Smad2/3-Mediated Epithelial-to-Mesenchymal Transition via Activation of AKT

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) is required for renal fibrosis, which is a characteristic of diabetic nephropathy (DN). Our previous study demonstrated that fibroblast growth factor 21 (FGF21) prevented DN associated with the suppressing renal connective tissue growth factor expression, a key marker of renal fibrosis. Therefore, the effects of FGF21 on renal fibrosis in a DN mouse model and the underlying mechanisms were investigated in this study.

METHODS

Type 1 diabetes mellitus was induced in C57BL/6J mice by intraperitoneal injections of multiple low doses of streptozotocin. Then, diabetic and non-diabetic mice were treated with or without FGF21 in the presence of pifithrin-α (p53 inhibitor) or 10-[4'-(N,N-Diethylamino)butyl]-2-chlorophenoxazine hydrochloride (10-DEBC) hydrochloride (Akt inhibitor) for 4 months.

RESULTS

DN was diagnosed by renal dysfunction, hypertrophy, tubulointerstitial lesions, and glomerulosclerosis associated with severe fibrosis, all of which were prevented by FGF21. FGF21 also suppressed the diabetes-induced renal EMT in DN mice by negatively regulating transforming growth factor beta (TGF-β)-induced nuclear translocation of Smad2/3, which is required for the transcription of multiple fibrotic genes. The mechanistic studies showed that FGF21 attenuated nuclear translocation of Smad2/3 by inhibiting renal activity of its conjugated protein p53, which carries Smad2/3 into the nucleus. Moreover pifithrin-α inhibited the FGF21-induced preventive effects on the renal EMT and subsequent renal fibrosis in DN mice. In addition, 10-DEBC also blocked FGF21-induced inhibition of renal p53 activity by phosphorylation of mouse double minute-2 homolog (MDM2).

CONCLUSION

FGF21 prevents renal fibrosis via negative regulation of the TGF-β/Smad2/3-mediated EMT process by activation of the Akt/MDM2/p53 signaling pathway.

Serum Endocrine Fibroblast Growth Factors as Potential Biomarkers for Chronic Kidney Disease and Various Metabolic Dysfunctions in Aged Patients

Objective To prolong the health expectancy, it is important to prevent age-related diseases, such as osteoporosis and cerebrovascular disease, which are major causes of a bedridden state. Early predictable biomarkers for these diseases are urgently required in the clinical setting. Three members of the fibroblast growth factor (FGF) family - FGF19, FGF21, and FGF23 - are designated as endocrine FGFs and play crucial roles in various metabolic processes. We tried to clarify the clinical utility of endocrine FGFs as biomarkers for age-related diseases in elderly patients. Methods We examined the serum endocrine FGF levels and analyzed their association with various clinical parameters in 73 outpatients >60 years old as a single-center cross-sectional study. Results In a multivariable linear regression analysis, FGF19 was associated with ALT, a history of cardiovascular disease, and medication with active vitamin D₃. FGF21 was associated with the estimated glomerular filtration rate (eGFR), triglyceride level, and hypertension. FGF23 was associated with the eGFR and the serum levels of 1,25-dihydroxy vitamin D₃ and TRACP5b. In addition, a receiver operating characteristics analysis revealed that the measurement of FGF21 and FGF23 was useful for detecting chronic kidney disease (CKD) and its complications, including cardiovascular disease and metabolic bone disorder. Conclusion The measurement of FGF21 and FGF23 may be useful for evaluating CKD and its complications. Using serum endocrine FGFs as biomarkers for age-related conditions may help prevent elderly patients from entering a bedridden state.

Increased fibroblast growth factor-21 in chronic kidney disease is a trade-off between survival benefit and blood pressure dysregulation

Circulating levels of fibroblast growth factor-21 (FGF21) start increasing in patients with chronic kidney disease (CKD) since early stages during the cause of disease progression. FGF21 is a liver-derived hormone that induces responses to stress through acting on hypothalamus to activate the sympathetic nervous system and the hypothalamus-pituitary-adrenal endocrine axis. However, roles that FGF21 plays in pathophysiology of CKD remains elusive. Here we show in mice that FGF21 is required to survive CKD but responsible for blood pressure dysregulation. When introduced with CKD, Fgf21^−/− mice died earlier than wild-type mice. Paradoxically, these Fgf21^−/− CKD mice escaped several complications observed in wild-type mice, including augmentation of blood pressure elevating response and activation of the sympathetic nervous system during physical activity and increase in serum noradrenalin and corticosterone levels. Supplementation of FGF21 by administration of an FGF21-expressing adeno-associated virus vector recapitulated these complications in wild-type mice and restored the survival period in Fgf21^−/− CKD mice. In CKD patients, high serum FGF21 levels are independently associated with decreased baroreceptor sensitivity. Thus, increased FGF21 in CKD can be viewed as a survival response at the sacrifice of blood pressure homeostasis.

The Klotho proteins in health and disease

The Klotho proteins, αKlotho and βKlotho, are essential components of endocrine fibroblast growth factor (FGF) receptor complexes, as they are required for the high-affinity binding of FGF19, FGF21 and FGF23 to their cognate FGF receptors (FGFRs). Collectively, these proteins form a unique endocrine system that governs multiple metabolic processes in mammals. FGF19 is a satiety hormone that is secreted from the intestine on ingestion of food and binds the βKlotho-FGFR4 complex in hepatocytes to promote metabolic responses to feeding. By contrast, under fasting conditions, the liver secretes the starvation hormone FGF21, which induces metabolic responses to fasting and stress responses through the activation of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system following binding to the βKlotho-FGFR1c complex in adipocytes and the suprachiasmatic nucleus, respectively. Finally, FGF23 is secreted by osteocytes in response to phosphate intake and binds to αKlotho-FGFR complexes, which are expressed most abundantly in renal tubules, to regulate mineral metabolism. Growing evidence suggests that the FGF-Klotho endocrine system also has a crucial role in the pathophysiology of ageing-related disorders, including diabetes, cancer, arteriosclerosis and chronic kidney disease. Therefore, targeting the FGF-Klotho endocrine axes might have therapeutic benefit in multiple systems; investigation of the crystal structures of FGF-Klotho-FGFR complexes is paving the way for the development of drugs that can regulate these axes.

Chronic Kidney Disease Is Associated with Increased Plasma Levels of Fibroblast Growth Factors 19 and 21

BACKGROUND

Chronic kidney disease (CKD) is the result of a reduced number of nephrons, in which adipose tissue and its metabolites play a significant role. Fibroblast growth factors, FGF19 and FGF21, are involved in lipid and carbohydrate metabolism. The aim of the study was to examine the concentrations of FGF19 and FGF21 in patients with CKD, as well as the correlation between FGF19 and FGF21 and selected biochemical parameters.

MATERIALS AND METHODS

The study included 178 subjects: 52 patients with CKD in stages 2-4, without haemodialysis (CKD), 47 haemodialysed patients with CKD (HD), 56 patients with CKD after a renal transplantation (Tx) and 23 healthy subjects as the control group (C).

RESULTS

The highest FGF19 serum concentrations were observed in CKD patients and the lowest were observed in the Tx group. Patients in the CKD group had significantly higher serum FGF21 concentrations. There were negative correlations between FGF19 and glomerular filtration rate (GFR), as well as high-density lipoprotein cholesterol levels in patients after kidney transplantation. Negative correlations were also found between serum FGF21 concentrations and GFR in patients after Tx, while positive correlations were observed between FGF21 concentrations and lean body mass in the CKD group, body mass index and total cholesterol in the HD group.

CONCLUSIONS

Our results suggest that increased concentrations of FGF19 and FGF21 in patients with CKD may be associated with the metabolism of lipids and carbohydrates. Our results also indicate that haemodialysis and transplantation results in the reduction of FGF19 and FGF21 concentrations in patients with CKD.

Fibroblast growth factor 21 in patients with cardiac cachexia: a possible role of chronic inflammation

Aims

Cardiac cachexia is a wasting syndrome characterized by chronic inflammation and high mortality. Fibroblast growth factor 21 (FGF‐21) and monocyte chemoattractant protein 1 (MCP‐1) are associated with cardiovascular disease and systemic inflammation. We investigated FGF‐21 and MCP‐1 in relations to cardiac function, inflammation, and wasting in patients with heart failure with reduced ejection fraction (HFrEF) and cardiac cachexia.

Methods and results

Plasma FGF‐21 and MCP‐1 were measured in a cross‐sectional study among the three study groups: 19 patients with HFrEF with cardiac cachexia, 19 patients with HFrEF without cachexia, and 19 patients with ischaemic heart disease and preserved ejection fraction. Patients with HFrEF and cardiac cachexia displayed higher FGF‐21 levels median (inter quantile range) 381 (232–577) pg/mL than patients with HFrEF without cachexia 224 (179–309) pg/mL and ischaemic heart disease patients 221 (156–308) pg/mL (P = 0.0496). No difference in MCP‐1 levels were found among the groups (P = 0.345). In a multivariable regression analysis, FGF‐21 (logarithm 2) was independently associated with interleukin 6 (logarithm 2) (P = 0.015) and lower muscle mass (P = 0.043), while no relation with N‐terminal pro‐hormone brain natriuretic peptide was observed.

Conclusions

Fibroblast growth factor 21 (FGF‐21) levels were elevated in patients with HFrEF and cardiac cachexia, which could be mediated by increased inflammation and muscle wasting rather than impaired cardiac function.

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.

FGF21 as Modulator of Metabolism in Health and Disease

Fibroblast growth factor 21 (FGF21) is a hormone that regulates important metabolic pathways. FGF21 is expressed in several metabolically active organs and interacts with different tissues. The FGF21 function is complicated and well debated due to its different sites of production and actions. Striated muscles are plastic tissues that undergo adaptive changes within their structural and functional properties in order to meet their different stresses, recently, they have been found to be an important source of FGF21. The FGF21 expression and secretion from skeletal muscles happen in both mouse and in humans during their different physiological and pathological conditions, including exercise and mitochondrial dysfunction. In this review, we will discuss the recent findings that identify FG21 as beneficial and/or detrimental cytokine interacting as an autocrine or endocrine in order to modulate cellular function, metabolism, and senescence.

Towards frailty biomarkers: Candidates from genes and pathways regulated in aging and age-related diseases

OBJECTIVE

Use of the frailty index to measure an accumulation of deficits has been proven a valuable method for identifying elderly people at risk for increased vulnerability, disease, injury, and mortality. However, complementary molecular frailty biomarkers or ideally biomarker panels have not yet been identified. We conducted a systematic search to identify biomarker candidates for a frailty biomarker panel.

METHODS

Gene expression databases were searched (http://genomics.senescence.info/genes including GenAge, AnAge, LongevityMap, CellAge, DrugAge, Digital Aging Atlas) to identify genes regulated in aging, longevity, and age-related diseases with a focus on secreted factors or molecules detectable in body fluids as potential frailty biomarkers. Factors broadly expressed, related to several "hallmark of aging" pathways as well as used or predicted as biomarkers in other disease settings, particularly age-related pathologies, were identified. This set of biomarkers was further expanded according to the expertise and experience of the authors. In the next step, biomarkers were assigned to six "hallmark of aging" pathways, namely (1) inflammation, (2) mitochondria and apoptosis, (3) calcium homeostasis, (4) fibrosis, (5) NMJ (neuromuscular junction) and neurons, (6) cytoskeleton and hormones, or (7) other principles and an extensive literature search was performed for each candidate to explore their potential and priority as frailty biomarkers.

RESULTS

A total of 44 markers were evaluated in the seven categories listed above, and 19 were awarded a high priority score, 22 identified as medium priority and three were low priority. In each category high and medium priority markers were identified.

CONCLUSION

Biomarker panels for frailty would be of high value and better than single markers. Based on our search we would propose a core panel of frailty biomarkers consisting of (1) CXCL10 (C-X-C motif chemokine ligand 10), IL-6 (interleukin 6), CX3CL1 (C-X3-C motif chemokine ligand 1), (2) GDF15 (growth differentiation factor 15), FNDC5 (fibronectin type III domain containing 5), vimentin (VIM), (3) regucalcin (RGN/SMP30), calreticulin, (4) PLAU (plasminogen activator, urokinase), AGT (angiotensinogen), (5) BDNF (brain derived neurotrophic factor), progranulin (PGRN), (6) α-klotho (KL), FGF23 (fibroblast growth factor 23), FGF21, leptin (LEP), (7) miRNA (micro Ribonucleic acid) panel (to be further defined), AHCY (adenosylhomocysteinase) and KRT18 (keratin 18). An expanded panel would also include (1) pentraxin (PTX3), sVCAM/ICAM (soluble vascular cell adhesion molecule 1/Intercellular adhesion molecule 1), defensin α, (2) APP (amyloid beta precursor protein), LDH (lactate dehydrogenase), (3) S100B (S100 calcium binding protein B), (4) TGFβ (transforming growth factor beta), PAI-1 (plasminogen activator inhibitor 1), TGM2 (transglutaminase 2), (5) sRAGE (soluble receptor for advanced glycosylation end products), HMGB1 (high mobility group box 1), C3/C1Q (complement factor 3/1Q), ST2 (Interleukin 1 receptor like 1), agrin (AGRN), (6) IGF-1 (insulin-like growth factor 1), resistin (RETN), adiponectin (ADIPOQ), ghrelin (GHRL), growth hormone (GH), (7) microparticle panel (to be further defined), GpnmB (glycoprotein nonmetastatic melanoma protein B) and lactoferrin (LTF). We believe that these predicted panels need to be experimentally explored in animal models and frail cohorts in order to ascertain their diagnostic, prognostic and therapeutic potential.

A high circulating FGF21 level as a prognostic marker in patients with acute myocardial infarction

OBJECTIVE

The purpose of this study was to examine the level of serum FGF21 in acute myocardial infarction (AMI) and to explore the association between serum FGF21 and major adverse cardiovascular events in AMI patients.

METHODS

A total of 238 Chinese patients were recruited for this study between January 2016 and June 2016, including 183 AMI patients and 55 patients without AMI were enrolled in this study. The level of serum FGF21 was measured by ELISA. Patients were followed-up after admission using a standardized protocol that included Outpatient follow-up and telephone contacts to record the Major Adverse Cardiovascular Events (MACEs). Finally, 165 patients were enrolled and followed up during the period of 24 months.

RESULTS

Circulating FGF21 level was elevated in the AMI patients compared to control (P < 0.05). Multivariate linear regression analysis showed that cTnI (β = -0.001, 95% CI = 0.021-0.001, P = 0.002), fibrinogen (β = -0.055, 95% CI = 0.098-0.013, P = 0.011) and hyperlipidemia (β = 0.129, 95% CI = 0.014-0.243, P = 0.011) were the independent risk factors for the serum of FGF21 in AMI patients. After follow-up, A Kaplan-Meier analysis showed that the all-cause mortality rate was not significantly different between the two groups (P = 0.4146). Meanwhile the rate of cardiovascular events was significantly higher in the high-FGF21 group than in the low-FGF21 group (P = 0.0399). In the multivariate Cox proportional hazards regression model suggested that the predictive independent risk factors for the occurrence of MACEs were FGF21 ≥ cut-off (HR: 1.637; 95% CI: 1.357-3.647, P = 0.029) and D-Dimer (HR: 1.420; 95% CI: 1.069-3.014, P = 0.046).

CONCLUSION

Circulating FGF21 level is elevated in the AMI patients. In AMI patients, cTnI, fibrinogen and hyperlipidemia are the inde pendent risk factors for the serum of FGF21. Higher circulating FGF21 level is associated with increased MACEs rate. This study suggests that circulating FGF21 level may be a predictive marker of the clinical outcomes in AMI patients.

Sex modulates the association of fibroblast growth factor 21 with end-stage renal disease in Asian people with Type 2 diabetes: a 6.3-year prospective cohort study

AIM

To study whether plasma fibroblast growth factor 21 independently predicts the risk of end-stage renal disease in Asian people with Type 2 diabetes.

METHODS

In this prospective cohort study, 1700 Asian people with Type 2 diabetes were followed for a mean of 6.3 years in a regional hospital in Singapore. Incident end-stage renal disease was identified by linkage with a national renal registry. The association of baseline fibroblast growth factor 21 levels with risk of progression to end-stage renal disease was studied using survival analyses.

RESULTS

Participants were aged 60 ± 10 years, with an average diabetes duration of 12 years. Their estimated GFR was 73 ± 28 ml/min/1.73 m² and 62% had albuminuria at baseline. A total of 179 incident end-stage renal disease cases were identified. Plasma fibroblast growth factor 21 interacted with sex in its association with end-stage renal disease (P_interaction = 0.003). A 1-sd increment in fibroblast growth factor 21 (natural log-transformed) was associated with a 1.32-fold (95% CI 1.05-1.66, P = 0.02) increased hazard for end-stage renal disease in women, after adjustment for traditional risk factors including estimated GFR and albuminuria. Taking death as a competing risk did not materially change the outcome [sub-distribution hazard ratio 1.35 (95% CI 1.11-1.66, P = 0.003)]. Fibroblast growth factor 21 did not predict end-stage renal disease risk in men after adjustment for baseline estimated GFR and albuminuria [hazard ratio 1.07 (95% CI 0.89-1.28, P = 0.49)].

CONCLUSIONS

Plasma fibroblast growth factor 21 level independently predicted risk of progression to end-stage renal disease in women with Type 2 diabetes. The pathophysiological relationships among FGF21, sex and renal progression warrant further study.

Fibroblast growth factor 21 in cardio-metabolic disorders: a systematic review and meta-analysis

BACKGROUND

Fibroblast growth factor 21 is a signalling protein involved in cell differentiation, morphogenesis, proliferation and metabolism. Recent studies have associated increased levels of FGF21 in the development of cardiovascular diseases, whereas others have reported no significant associations. Therefore, this systematic review and meta-analysis evaluated the value in predicting the risk of cardio-metabolic disorders and mortality.

METHODS

PubMed and EMBASE were searched until 5th September 2017 for studies that evaluated the roles of FGF21 levels in cardio-metabolic disorders.

RESULTS

A total of 183 and 301 entries were retrieved; 24 studies met the inclusion criteria. Four studies were identified by an additional search. Therefore, 28 studies were included in the final meta-analysis. High FGF21 levels significantly predicted the incidence of coronary artery disease (hazard ratio [HR]: 1.29; 95% confidence interval [CI]: 1.06-1.55; P < 0. 01; I² = 48%) and the risk of metabolic syndrome (HR: 1.70, 95% CI: 1.35-2.15; P < 0.0001 I² = 24%). In diabetes mellitus, FGF21 predicted disease incidence or progression (HR: 1.35, 95% CI: 1.06-1.72, P < 0.05, I² = 69%) and worsening renal failure (HR: 1.06, 95% CI: 1.03-1.09, P < 0.0001, I² = 47%). FGF21 also predicted all-cause mortality (HR: 3.00, 95% CI: 1.23-7.33; P < 0.05; I² = 51%), and cardiovascular mortality (HR: 2.33, 95% CI: 1.08-4.99, P < 0.05, I² = 75%).

CONCLUSION

FGF21 significantly predicts the incidence of coronary artery disease, the risks of metabolic syndrome, diabetes mellitus and renal progression in diabetes. It also predicted all-cause and cardiovascular mortality.