Fibroblast growth factor-23: what we know, what we don't know, and what we need to know

FGF23 from bench to bedside

There is a strong association between elevated circulating fibroblast growth factor-23 (FGF23) levels and adverse outcomes in patients with chronic kidney disease (CKD) of all stages. Initially discovered as a regulator of phosphate and vitamin D homeostasis, FGF23 has now been implicated in several pathophysiological mechanisms that may negatively impact the cardiovascular and renal systems. FGF23 is purported to have direct (off-target) effects in the myocardium, as well as canonical effects on FGF receptor/α-klotho receptor complexes in the kidney to activate the renin-angiotensin-aldosterone system, modulate soluble α-klotho levels, and increase sodium retention, to cause left ventricular hypertrophy (LVH). Conversely, FGF23 could be an innocent bystander produced in response to chronic inflammation or other processes associated with CKD that cause LVH and adverse cardiovascular outcomes. Further exploration of these complex mechanisms is needed before modulation of FGF23 can become a legitimate clinical target in CKD.

Connecting heart failure with preserved ejection fraction and renal dysfunction: the role of endothelial dysfunction and inflammation

Renal dysfunction in heart failure with preserved ejection fraction (HFpEF) is common and is associated with increased mortality. Impaired renal function is also a risk factor for developing HFpEF. A new paradigm for HFpEF, proposing a sequence of events leading to myocardial remodelling and dysfunction in HFpEF, was recently introduced, involving inflammatory, microvascular, and cardiac components. The kidney might play a key role in this systemic process. Renal impairment causes metabolic and systemic derangements in circulating factors, causing an activated systemic inflammatory state and endothelial dysfunction, which may lead to cardiomyocyte stiffening, hypertrophy, and interstitial fibrosis via cross-talk between the endothelium and cardiomyocyte compartments. Here, we review the role of endothelial dysfunction and inflammation to explain the link between renal dysfunction and HFpEF, which allows for identification of new early risk markers, prognostic factors, and unique targets for intervention.

Counter-regulatory paracrine actions of FGF-23 and 1,25(OH)2 D in macrophages

Mechanisms underlying the association between fibroblastic growth factor 23 (FGF-23) and inflammation are uncertain. We found that FGF-23 was markedly up-regulated in LPS/INF-γ-induced proinflammatory M1 macrophages and Hyp mouse-derived peritoneal macrophages, but not in IL-4-induced M2 anti-inflammatory macrophages. NF-КB and JAK/STAT1 pathways mediated the increased transcription of FGF-23 in response to M1 polarization. FGF-23 stimulated TNF-α, but not IL-6, expression in M0 macrophages and suppressed Arginase-1 expression in M2 macrophages through FGFR-mediated mechanisms. 1,25(OH)2 D stimulated Arginase-1 expression and inhibited FGF-23 stimulation of TNF-α. FGF-23 has proinflammatory paracrine functions and counter-regulatory actions to 1,25(OH)2 D on innate immune responses.

Fibroblast growth factor 23 and parathyroid hormone predict extent of aortic valve calcifications in patients with mild to moderate chronic kidney disease

BACKGROUND

Cardiac valve calcifications are present in dialysis patients and regarded as dependent on a deranged mineral metabolism. Few data are available for patients with chronic kidney disease (CKD) not on dialysis. This study evaluates the potential association between the extent of cardiac valve calcification and levels of intact parathyroid hormone (i-PTH), phosphorus, calcium, 25-OH vitamin D, fibroblast growth factor 23 (FGF-23), Klotho and C-reactive protein (CRP) simultaneously measured in patients with mild to moderate CKD.

METHODS

Consecutive non-hospitalized patients referring to five nephrology units were evaluated. Inclusion criteria were age >18 years, CKD Stages 3-4, and the presence of aortic and/or mitral valve calcification assessed by echocardiography as routinely clinical evaluation. Patients underwent clinical examination and routine biochemistry. Baseline i-PTH, phosphorus, calcium, 25-OH vitamin D, FGF-23, Klotho and CRP were simultaneously ascertained.

RESULTS

Extent of aortic valve calcification (n = 100 patients) was moderate in 68 patients and mild in the remaining patients. Mitral valve calcification (n = 96 patients) score was 1, 2 and 3 in 61, 34 and 1 patients, respectively. In univariate analysis, no association was found between extent of mitral valve calcification and markers of mineral metabolism and CRP; aortic valve extent of calcification was positively associated with i-PTH (r(2) = 0.212; P = 0.03) and FGF-23 (r(2) = 0.272; P = 0.01), and negatively with Klotho (r(2) = -0.208; P = 0.04). In multivariable analysis, extent of aortic valve calcification was associated with FGF-23 (P = 0.01) and PTH (P = 0.01) levels.

CONCLUSIONS

Extent of aortic valve calcification is associated to FGF-23 and PTH in naïve CKD patients with mild to moderate CKD. Further studies should examine whether FGF-23 assay should be included in routine clinical evaluation of CKD as part of cardiovascular risk stratification.

Fibroblast Growth Factor 23 Is an Independent and Specific Predictor of Mortality in Patients With Heart Failure and Reduced Ejection Fraction

BACKGROUND

Strategies to improve risk prediction are of major importance in patients with heart failure (HF). Fibroblast growth factor 23 (FGF-23) is an endocrine regulator of phosphate and vitamin D homeostasis associated with an increased cardiovascular risk. We aimed to assess the prognostic effect of FGF-23 on mortality in HF patients with a particular focus on differences between patients with HF with preserved ejection fraction and patients with HF with reduced ejection fraction (HFrEF).

METHODS AND RESULTS

FGF-23 levels were measured in 980 patients with HF enrolled in the Ludwigshafen Risk and Cardiovascular Health (LURIC) study including 511 patients with HFrEF and 469 patients with HF with preserved ejection fraction and a median follow-up time of 8.6 years. FGF-23 was additionally measured in a second cohort comprising 320 patients with advanced HFrEF. FGF-23 was independently associated with mortality with an adjusted hazard ratio per 1-SD increase of 1.30 (95% confidence interval, 1.14-1.48; P<0.001) in patients with HFrEF, whereas no such association was found in patients with HF with preserved ejection fraction (for interaction, P=0.043). External validation confirmed the significant association with mortality with an adjusted hazard ratio per 1 SD of 1.23 (95% confidence interval, 1.02-1.60; P=0.027). FGF-23 demonstrated an increased discriminatory power for mortality in addition to N-terminal pro-B-type natriuretic peptide (C-statistic: 0.59 versus 0.63) and an improvement in net reclassification index (39.6%; P<0.001).

CONCLUSIONS

FGF-23 is independently associated with an increased risk of mortality in patients with HFrEF but not in those with HF with preserved ejection fraction, suggesting a different pathophysiologic role for both entities.

A single preoperative FGF23 measurement is a strong predictor of outcome in patients undergoing elective cardiac surgery: a prospective observational study

Introduction

Several scoring systems have been developed to predict postoperative mortality and complications in patients undergoing cardiac surgery. However, these computer-based calculations are time- and cost-intensive. A simple but highly predictive test for postoperative risk would be of clinical benefit with respect to increasingly scarce hospital resources. We therefore assessed the predictive power of fibroblast growth factor 23 (FGF23) measurement compared with an established scoring system.

Methods

We conducted a prospective interdisciplinary observational study at the Saarland University Medical Centre that included 859 patients undergoing elective cardiac surgery between January 2010 and March 2011 with a median follow-up after discharge of 822 days. We compared a single preoperative measurement of FGF23 as a prognostic tool with the 18 parameters comprising EuroSCORE II with respect to postoperative mortality, acute kidney injury, non-occlusive mesenteric ischemia, clinical course and long-term outcome.

Results

Preoperative FGF23 levels were highly predictive of postoperative outcome and complications. The predictive value of FGF23 for mortality in the receiver operating characteristic curve was greater than the EuroSCORE II (area under the curve: 0.800 versus 0.725). Moreover, preoperative FGF23 independently predicted postoperative acute kidney injury and non-occlusive mesenteric ischemia comparably to the EuroSCORE II. Finally, FGF23 was found to be an independent predictor of clinical course parameters, including duration of surgery, ventilation time and length of stay.

Conclusions

In patients undergoing elective cardiac surgery, a simple preoperative FGF23 measurement is a powerful indicator of surgical mortality, postoperative complications and long-term outcome. Its utility compares to the widely used EuroSCORE II.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0925-6) contains supplementary material, which is available to authorized users.

Associations of fibroblast growth factor-23 with markers of inflammation, insulin resistance and obesity in adults

Introduction

Elevated fibroblast growth factor-23 (FGF23) is an established marker of cardiovascular disease. The underlying reason(s) for the rise accompanying cardiovascular health decline are unclear. Prior studies have shown that FGF23 concentrations are associated with markers of inflammation and insulin resistance but they have been limited by a focus on persons with chronic kidney disease (CKD) and lack of race and sex diversity. The objective of this study was to examine the associations of FGF23 and markers of inflammation, insulin resistance, and anthropometrics in a large cohort of community-dwelling adults.

Methods

Associations of FGF23 with markers of inflammation [interleukin-6 (IL-6), IL-10, high sensitivity-CRP (hsCRP)], insulin utilization [resistin, adiponectin, homeostatic model assessment of insulin resistance (HOMA-IR)] and anthropometrics [BMI and waist circumference (WC)] were examined cross-sectionally in a 1,040 participants randomly selected from the Reason for Geographic and Racial Differences in Stroke (REGARDS) Study, a national study of black and white adults ≥45 years. Effect modification by race and CKD status was tested, and stratified models were analyzed accordingly.

Results

Median FGF23 concentration was 69.6 RU/ml (IQR: 53.2, 102.7). Higher quartiles of FGF23 were associated with higher mean concentrations of IL-6, IL-10, hsCRP and resistin (P_trend<0.001 for all). There were no significant differences in HOMA-IR, adiponectin concentrations, BMI, or WC across FGF23 quartiles in the crude analyses. CKD significantly modified the relationships between FGF23 and inflammatory markers, HOMA-IR, BMI and WC (P ≤ 0.01 for all). In linear regression models adjusted for sociodemographic and clinical variables, FGF23 was positively associated with IL-6, hsCRP, IL-10, HOMA-IR, BMI and WC in individuals without CKD, but not among individuals with CKD. Additionally, FGF23 was positively associated with resistin irrespective of CKD status.

Conclusions

Elevated FGF23 concentrations may be considered a biomarker for decline in metabolic function among individuals with normal kidney function.

Plasma fibroblast growth factor 23 and risk of cardiovascular disease: results from the EPIC-Germany case-cohort study

Increased fibroblast growth factor 23 (FGF23) concentrations have emerged as a novel risk factor for heart failure and stroke but not for myocardial infarction (MI). Yet, most studies on MI were conducted in coronary artery disease (CAD) patients and the elderly. Evidence is unclear in subjects without CAD and for stroke subtypes. We investigated the relationships between FGF23 and overall major cardiovascular endpoints, incident MI, ischemic (IS) and haemorrhagic stroke (HS) in middle-aged adults without pre-existing cardiovascular disease. We used a case-cohort study nested within the European Prospective Investigation into Cancer and Nutrition-Germany, including a randomly drawn subcohort (n = 1,978), incident MI (n = 463) and stroke cases (n = 359 IS; n = 88 HS) identified during a mean follow-up of 8.2 years. Compared with participants with FGF23 levels in the lowest quartile, those in the highest quartile had a 36% increased risk for cardiovascular events [hazard ratio: 1.36, 95% confidence interval (CI): 1.02-1.82] after adjustment for established cardiovascular risk factors, patahyroid hormone and 25-hydroxyvitamin D3 levels, dietary calcium and phosphorus intake, and kidney function. However, sub-analyses revealed significant relationships with risk of MI and HS, but not IS. Compared with the lowest quartile, individuals in the top two FGF23 quartiles had a 1.62 (95% CI 1.07-2.45) fold increased risk for MI and a 2.61 (95% CI 1.23-5.52) fold increase for HS. Increased FGF23 emerged as a risk factor for both MI and HS. Further studies are warranted to confirm these results and to identify underlying mechanisms.

[FGF23 and the heart]

The prevalence of chronic kidney disease (CKD) has now reached epidemic proportions and it is very likely that it will continue to rise with the increasing prevalence of juvenile diabetes mellitus, hypertension and aging population. CKD is a risk factor for cardiovascular disease (CVD) and cardiovascular disease can lead to CKD. It is also well known that patients with CKD have a higher risk of death from CVD than of progressing to end-stage renal disease that requires renal replacement therapy. In patients with CKD, there is a higher mortality from sudden cardiac death and congestive heart failure than coronary artery disease, which is not the case in the general population. The high prevalence of congestive heart failure in CKD is due to cardiac remodeling which progresses from concentric remodeling to concentric and eccentric hypertrophy, leading to left ventricular hypertrophy with both systolic and diastolic dysfunction. Recent studies have suggested that, in patients with chronic kidney disease, common traditional risk factors for cardiovascular disease such as hypertension, hyperlipidemia and obesity may not be the main determinants of cardiovascular disease. Among the various non-traditional cardiovascular risk factors present in patients with chronic kidney disease, abnormalities of CKD related mineral and bone disorder, which includes elevated fibroblast growth factor 23 (FGF23) have been one of the most extensively studied. However, after many years of research, the debate over the exact pathways by which FGF23 may lead to increased CVD still continues. FGF23 may have both direct and indirect effects on the cardiovascular system. Better understanding of the most relevant pathophysiologic pathways for FGF23 may lead to therapeutic interventions against cardiovascular disease in patients with CKD.

Vitamin D: a new player in kidney transplantation?

Vitamin D is a hormone with pleiotropic effects. It mainly regulates calcium and phosphate metabolism through interactions with FGF23 and its receptor klotho. In addition, it has been shown that Vitamin D also regulates the immune response and has protective effects from cardiovascular disease, cancer and infections. Most renal transplant recipients have overt Vitamin D deficiency, a condition that may be associated with a decline in graft function and other complications. After kidney transplantation, elevated levels of FGF23 may predict increased risks of death and allograft loss. Theoretically, an optimal Vitamin D supplementation might favor operational tolerance and protect transplant recipients from the triad cardiovascular disease-cancer-infection. However, more solid data are needed to confirm this and to set the optimal level of serum Vitamin D supplementation in order to attain the best clinical outcome.

Calpain 1 inhibitor BDA-410 ameliorates α-klotho-deficiency phenotypes resembling human aging-related syndromes

Taking good care of elderly is a major challenge of our society, and thus identification of potential drug targets to reduce age-associated disease burden is desirable. α-klotho^-/- (α-kl) is a short-lived mouse model that displays multiple phenotypes resembling human aging-related syndromes. Such ageing phenotype of α-kl^-/- mice is associated with activation of a proteolytic enzyme, Calpain-1. We hypothesized that uncontrolled activation of calpain-1 might be causing age-related phenotypes in α-kl-deficient mice. We found that daily administration of BDA-410, a calpain-1 inhibitor, strikingly ameliorated multiple aging-related phenotypes. Treated mice showed recovery of reproductive ability, increased body weight, reduced organ atrophy, and suppression of ectopic calcifications, bone mineral density reduction, pulmonary emphysema and senile atrophy of skin. We also observed ectopic expression of FGF23 in calcified arteries of α-kl^-/- mice, which might account for the clinically observed association of increased FGF23 level with increased risk of cardiovascular mortality. These findings allow us to propose that modulation of calpain-1 activity is a potential therapeutic option for delaying age-associated organ pathology, particularly caused by the dysregulation of mineral ion homeostasis.

Vitamin D resistance in chronic kidney disease (CKD)

BACKGROUND

Previous studies have shown that treatment with ergocalciferol in patients with CKD stage 3 + 4 is not effective with less than 33% of patients achieving a 25-OH vitamin D target of >30 ng/ml. The aim of this study was to test the response to cholecalciferol in CKD. We attempted to replete 25-OH vitamin D to a target level of 40-60 ng/ml using the response to treatment and PTH suppression as an outcome measure.

METHODS

This retrospective cohort study identified patients (Stages 2-5 and Transplant) from 2001-2010 who registered at the Chronic Kidney Disease Clinic. Patients received cholecalciferol 10,000 IU capsules weekly as initial therapy. When levels above 40 ng/ml were not achieved, doses were titrated up to a maximum of 50,000 IU weekly. Active vitamin D analogs were also used in some Stage 4-5 CKD patients per practice guidelines. Patients reaching at least one level of 40 ng/mL were designated RESPONDER, and if no level above 40 ng/mL they were designated NON-RESPONDER. Patients were followed for at least 6 months and up to 5 years.

RESULTS

352 patients were included with a mean follow up of 2.4 years. Of the CKD patients, the initial 25-OH vitamin D in the NON-RESPONDER group was lower than the RESPONDER group (18 vs. 23 ng/ml) (p = 0.03). Among all patients, the initial eGFR in the RESPONDER group was significantly higher than the NON-RESPONDER group (36 vs. 30 ml/min/1.73 m2) (p < 0.001). Over time, the eGFR of the RESPONDER group stabilized or increased (p < 0.001). Over time, the eGFR in the NON-RESPONDER group decreased toward a trajectory of ESRD. Proteinuria did not impact the response to 25-OH vitamin D replacement therapy. There were no identifiable variables associated with the response or lack of response to cholecalciferol treatment.

CONCLUSIONS

CKD patients treated with cholecalciferol experience treatment resistance in raising vitamin D levels to a pre-selected target level. The mechanism of vitamin D resistance remains unknown and is associated with progressive loss of eGFR. Proteinuria modifies but does not account for the vitamin D resistance.

Treatment of phosphate retention: The earlier the better?

Over the last 15 years, our knowledge and understanding of the underlying mechanisms involved in the regulation of calcium and phosphate homeostasis in chronic kidney disease have advanced dramatically. Contrary to general opinion in the 20(th) century that moderate hypercalcemia and hyperphosphatemia were acceptable in treating secondary hyperparathyroidism, the calcium and phosphate load is increasingly perceived to be a major trigger of vascular and soft tissue calcification. The current treatment options are discussed in view of historical developments and the expectations of the foreseeable future, focusing on the early treatment of hyperphosphatemia. At present, we lack indisputable evidence that active intervention using currently available drugs is of benefit to patients in chronic kidney disease stages 3 and 4.

Evaluation of specific fecal protein biochips for the diagnosis of colorectal cancer

AIM: To develop and initially test a potential fecal protein biochip for the screening of colorectal cancer (CRC).

METHODS: Fecal protein from 20 colorectal cancer patients and 20 healthy controls were extracted from all of the fecal samples and screened for proteomic differences using a Biotin label-based protein array. Candidate proteins were then verified by ELISA. Finally, we will select out the significant protein and a seven-target multiplex fecal protein biochip was generated and tested for 20 fecal samples to determine the effectiveness of the biochip on identifying CRC. And the value of the protein biochip would be discussed.

RESULTS: After tested by protein biochip of the fecal protein from 20 colorectal cancer patients and 20 healthy controls and levels of calprotectin, M2-pyruvatekinase, angiopoietin-2, fibroblast growth factor-23 (FGF-23), proteins of the matrix metalloproteinase, thrombopoietin (TPO) and interleukin-13 (IL-13) were significantly different between CRC and healthy controls. The sensitivity of all the seven proteins combined was 0.7, specificity was 0.4, and area under the receiver operating characteristics was 0.729. The most promising combinations of test proteins were FGF-23, TPO, and IL-13, reaching a sensitivity of 0.7 and a specificity of 0.7. The combination of FGF-23 and TPO scored highest with sensitivity of 0.7 and specificity of 0.8. Its mean that the combination of FGF-23 and TPO has the highest value for the diagnosis of CRC in our study.

CONCLUSION: A protein biochip composed of proteins found to be elevated in the feces of colorectal cancer patients has great potential as a noninvasive diagnostic for colorectal cancer. The addition of new protein biomarkers and technologies, as they are discovered, is an excellent avenue of future research.

Effect of cholecalciferol recommended daily allowances on vitamin D status and fibroblast growth factor-23: an observational study in acute burn patients

OBJECTIVE

Burn patients are at risk of hypovitaminosis D. Optimal vitamin D (VD) intakes are not defined in burn nutrition guidelines and studies mostly focused on ergocalciferol (VD2) supplementation in burn children. Aim of our study was to describe adult burns VD status, to measure effects of our cholecalciferol (VD3) supplementation on VD metabolism during acute burn care, and to assess correlation between FGF23 and C-reactive protein (CRP).

DESIGN

Cohort study.

METHODS

From March 2012 to January 2013, patients >18 years, admitted within 24 h after injury with burn surface area (BSA) ≥10% were included. Patients daily received VD3 from oral or enteral nutrition (400-600 IU) and from oral or intravenous multivitamin complex (200-220 IU). Serum levels of 25(OH)-D, 1-25(OH)2-D, 3rd generation PTH, C-terminal FGF23, total calcium, phosphate, albumin and CRP were measured at admission (D0) and every week during 4 weeks of follow-up. Data are expressed as percentage or median (min-max). Paired data were compared using Wilcoxon test. Correlation between CRP and FGF23 was assessed using nonparametric Spearman test. A p value <0.05 was considered to be statistically significant.

RESULTS

We initially included 24 patients. Median age and BSA were, respectively, 46 [19-86] years and 15 [10-85]%. At D0, 75% presented a VD insufficiency (25(OH)-D 21-29 ng/ml) and 17% presented a deficiency (25(OH)-D ≤20 ng/ml). We followed 12 patients until day 28: 25(OH)-D was unchanged while 1-25(OH)2-D and FGF23 decreased without reaching significance. We observed a significant positive correlation between FGF23 and CRP (r=0.59, 95% CI: 0.22-0.82, p=0.0032).

CONCLUSIONS

Most of our adult burns presented hypovitaminosis D regardless of age. Nutrition supplemented with low dose of VD3 (intakes reaching recommended daily allowances) was insufficient to correct 25(OH)-D level. Moreover, an interesting correlation between CRP and FGF23 was found.