The role of fibroblast growth factor-23 in cardiorenal syndrome

Rapid decline of kidney function increases fracture risk in the general population: Insights from TLGS

BACKGROUND

Although the association between Chronic Kidney Disease (CKD) and all-cause fractures was addressed in previous studies, the association between estimated glomerular filtration rate (eGFR) decline and fractures was poorly addressed. For the first time we examined the association between rapid kidney function decline (RKFD) and fracture incidence among Iranian general population.

METHODS

In a Tehranian community-based cohort, RKFD was defined as a 30 % decline in eGFR over 2-3 years. Cox proportional hazards models, adjusted for age, sex, current eGFR, diabetes mellitus, hypertension, dyslipidemia, current smoking, obesity status, waist circumference, prevalent cardiovascular diseases, aspirin, steroid use, education level, and marital status, were used to examine the association of RKFD with different fracture outcomes.

RESULTS

Among 5305 (3031 women) individuals aged ≥30 years, during the median follow-up of 9.62 years, 226 fracture events were observed. The multivariable hazard ratio of RKFD for any-fracture events, lower-extremity, and major osteoporotic fractures were 2.18 (95 % CI, 1.24-3.85), 2.32 (1.15-4.71), and 2.91 (1.29-6.58), respectively. These associations remained significant after accounting for the competing risk of death. The impact of RKFD on the development of incident all-cause fractures was not modified by gender [men: 2.64 (1.11-6.25) vs. women: 2.11 (1.00-4.47)] and according to current CKD status [without CKD: 2.34 (1.00-5.52) vs. with CKD: 2.59 (1.04-6.44)] (all P for interaction >0.5).

CONCLUSIONS

RKFD can increase the incidence of fractures among general population, the issue that was equally important among non-CKD individuals, emphasizing the need for early identification and management in those with rapidly declining eGFR.

Vitamin D3 Repletion Improves Vascular Function, as Measured by Cardiorenal Biomarkers in a High-Risk African American Cohort

Background: 25-hydroxy vitamin D (Vit D)-deficiency is common among patients with chronic kidney disease (CKD) and contributes to cardiovascular disease (CVD). African Americans (AAs) suffer disproportionately from CKD and CVD, and 80% of AAs are Vit D-deficient. The impact of Vit D repletion on cardio-renal biomarkers in AAs is unknown. We examined Vit D repletion on full-length osteopontin (flOPN), c-terminal fibroblast growth factor-23 (FGF-23), and plasminogen activator inhibitor-1 (PAI-1), which are implicated in vascular and kidney pathology. Methods: We performed a randomized, placebo-controlled study of high-risk AAs with Vit D deficiency, treated with 100,000 IU Vit D3 (cholecalciferol; n = 65) or placebo (n = 65) every 4 weeks for 12 weeks. We measured kidney function (CKD-EPI eGFR), protein-to-creatinine ratio, vascular function (pulse wave velocity; PWV), augmentation index, waist circumference, sitting, and 24-h-ambulatory blood pressure (BP), intact parathyroid hormone (iPTH) and serum calcium at baseline and study end, and compared Vit D levels with laboratory variables. We quantified plasma FGF-23, PAI-1, and flOPN by enzyme-linked immunosorbent assay. Multiple regression analyzed the relationship between log flOPN, FGF-23, and PAI-1 with vascular and renal risk factors. Results: Compared to placebo, Vit D3 repletion increased Vit D3 2-fold (p < 0.0001), decreased iPTH by 12% (p < 0.01) and was significantly correlated with PWV (p < 0.009). Log flOPN decreased (p = 0.03), log FGF-23 increased (p = 0.04), but log PAI-1 did not change. Multiple regression indicated association between log flOPN and PWV (p = 0.04) and diastolic BP (p = 0.02), while log FGF-23 was associated with diastolic BP (p = 0.05), and a trend with eGFR (p = 0.06). Conclusion: Vit D3 repletion may reduce flOPN and improve vascular function in high risk AAs with Vit D deficiency.

Lipocalin-2: a novel link between the injured kidney and the bone

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) excess is associated with left ventricular hypertrophy (LVH) and early mortality in patients with chronic kidney disease (CKD) and in animal models. Elevated Lipocalin-2 (LCN2), produced by the injured kidneys, contributes to CKD progression and might aggravate cardiovascular outcomes. The current review aims to highlight the role of LCN2 in CKD, particularly its interactions with FGF23.

RECENT FINDINGS

Inflammation, disordered iron homeostasis and altered metabolic activity are common complications of CKD, and are associated with elevated levels of kidney-produced LCN2 and bone-secreted FGF23. A recent study shows that elevated LCN2 increases FGF23 production, and contributes to cardiac injury in patients and animals with CKD, whereas LCN2 reduction in mice with CKD reduces FGF23, improves cardiovascular outcomes and prolongs lifespan.

SUMMARY

In this manuscript, we discuss the potential pathophysiological functions of LCN2 as a major kidney-bone crosstalk molecule, linking the progressive decline in kidney function to excessive bone FGF23 production. We also review associations of LCN2 with kidney, cardiovascular and bone and mineral alterations. We conclude that the presented data support the design of novel therapeutic approaches to improve outcomes in CKD.

Treatment of Anemia Associated with Chronic Kidney Disease with the HIF Prolyl Hydroxylase Inhibitor Enarodustat: A Review of the Evidence

Enarodustat, a newly developed hypoxia-inducible factor prolyl hydroxylase inhibitor, is used in clinical practice in Japan. Several clinical studies showed that enarodustat corrected and maintained hemoglobin (Hb) levels by stimulating endogenous erythropoietin production and improving iron utilization in anemic patients with chronic kidney disease, regardless of whether they were on dialysis. In addition, Phase III comparative studies demonstrated that enarodustat was non-inferior to darbepoetin alfa in controlling Hb levels. Furthermore, enarodustat was well tolerated during the treatment. Enarodustat is currently being developed in the Republic of Korea and China and is expected to be developed worldwide. This article reviews the data on enarodustat, including the findings from preclinical studies, pharmacokinetics/pharmacodynamics, and efficacy and safety results of clinical studies. This article is protected by copyright. All rights reserved.

FGF-23 (Fibroblast Growth Factor-23) and Cardiorenal Interactions

BACKGROUND

Animal models implicate FGF-23 (fibroblast growth factor-23) as a direct contributor to adverse cardiorenal interactions such as sodium avidity, diuretic resistance, and neurohormonal activation, but this has not been conclusively demonstrated in humans. Therefore, we aimed to evaluate whether FGF-23 is associated with parameters of cardiorenal dysfunction in humans with heart failure, independent of confounding factors.

METHODS

One hundred ninety-nine outpatients with heart failure undergoing diuretic treatment at the Yale Transitional Care Center were enrolled and underwent blood collection, and urine sampling before and after diuretics.

RESULTS

FGF-23 was associated with several metrics of disease severity such as higher home loop diuretic dose and NT-proBNP (N-terminal pro-B-type natriuretic peptide), and lower estimated glomerular filtration rate, serum chloride, and serum albumin. Multivariable analysis demonstrated no statistically significant association between FGF-23 and sodium avidity measured by fractional excretion of sodium, or proximal or distal tubular sodium reabsorption, either before diuretic administration or at peak diuresis (P≥0.11 for all). Likewise, FGF-23 was not independently associated with parameters of diuretic resistance (diuretic excretion, cumulative urine and sodium output, and loop diuretic efficiency [P≥0.33 for all]) or neurohormonal activation (plasma or urine renin [P≥0.36 for all]). Moreover, the upper boundary of the 95% CI of all the partial correlations were ≤0.30, supporting the lack of meaningful correlations. FGF-23 was not associated with mortality in multivariable analysis (P=0.44).

CONCLUSIONS

FGF-23 was not meaningfully associated with any cardiorenal parameter in patients with heart failure. While our methods cannot rule out a small effect, FGF-23 is unlikely to be a primary driver of cardiorenal interactions.

Cardiorenal Syndrome: New Pathways and Novel Biomarkers

Cardiorenal syndrome (CRS) is a multi-organ disease characterized by the complex interaction between heart and kidney during acute or chronic injury. The pathogenesis of CRS involves metabolic, hemodynamic, neurohormonal, and inflammatory mechanisms, and atherosclerotic degeneration. In the process of better understanding the bi-directional pathophysiological aspects of CRS, the need to find precise and easy-to-use markers has also evolved. Based on the new pathophysiological standpoints and an overall vision of the CRS, the literature on renal, cardiac, metabolic, oxidative, and vascular circulating biomarkers was evaluated. Though the effectiveness of different extensively applied biomarkers remains controversial, evidence for several indicators, particularly when combined, has increased in recent years. From new aspects of classic biomarkers to microRNAs, this review aimed at a 360-degree analysis of the pathways that balance the kidney and the heart physiologies. In this delicate system, different markers and their combination can shed light on the diagnosis, risk, and prognosis of CRS.

Two long-term phase 3 studies of enarodustat (JTZ-951) in Japanese anemic patients with chronic kidney disease not on dialysis or on maintenance hemodialysis: SYMPHONY ND-Long and HD-Long studies

Enarodustat (JTZ‐951) is an oral hypoxia‐inducible factor prolyl hydroxylase inhibitor developed for treating anemia in chronic kidney disease. Two open‐label, uncontrolled phase 3 studies evaluated the 52‐week safety and efficacy of enarodustat in Japanese anemic patients with chronic kidney disease not on dialysis (n = 132) [SYMPHONY ND‐Long study] or on maintenance hemodialysis (n = 136) [SYMPHONY HD‐Long study]. The most frequent adverse events were viral upper respiratory tract infection (25.8%) followed by chronic kidney disease (8.3%) in the SYMPHONY ND‐Long study, and viral upper respiratory tract infection (49.3%) followed by contusion (16.9%) and diarrhea (16.9%) in the SYMPHONY HD‐Long study. The incidence of any adverse events did not increase over time. Mean hemoglobin levels and 95% confidence intervals were maintained within the target range (10.0–12.0 g/dl) over 52 weeks in both studies. The long‐term safety and efficacy of enarodustat were confirmed in Japanese anemic patients with chronic kidney disease.

Deciphering key genes in cardio-renal syndrome using network analysis

Cardio-renal syndrome (CRS) is a rapidly recognized clinical entity which refers to the inextricably connection between heart and renal impairment, whereby abnormality to one organ directly promotes deterioration of the other one. Biological markers help to gain insight into the pathological processes for early diagnosis with higher accuracy of CRS using known clinical findings. Therefore, it is of interest to identify target genes in associated pathways implicated linked to CRS. Hence, 119 CRS genes were extracted from the literature to construct the PPIN network. We used the MCODE tool to generate modules from network so as to select the top 10 modules from 23 available modules. The modules were further analyzed to identify 12 essential genes in the network. These biomarkers are potential emerging tools for understanding the pathophysiologic mechanisms for the early diagnosis of CRS. Ontological analysis shows that they are rich in MF protease binding and endo-peptidase inhibitor activity. Thus, this data help increase our knowledge on CRS to improve clinical management of the disease.

Should We Consider the Cardiovascular System While Evaluating CKD-MBD?

Cardiovascular (CV) disease is highly prevalent in the population with chronic kidney disease (CKD), where the risk of CV death in early stages far exceeds the risk of progression to dialysis. The presence of chronic kidney disease-mineral and bone disorder (CKD-MBD) has shown a strong correlation with CV events and mortality. As a non-atheromatous process, it could be partially explained why standard CV disease-modifying drugs do not provide such an impact on CV mortality in CKD as observed in the general population. We summarize the potential association of CV comorbidities with the older (parathyroid hormone, phosphate) and newer (FGF23, Klotho, sclerostin) CKD-MBD biomarkers.

Validation of a Novel Modified Aptamer-Based Array Proteomic Platform in Patients with End-Stage Renal Disease

End stage renal disease (ESRD) is characterized by complex metabolic abnormalities, yet the clinical relevance of specific biomarkers remains unclear. The development of multiplex diagnostic platforms is creating opportunities to develop novel diagnostic and therapeutic approaches. SOMAscan is an innovative multiplex proteomic platform which can measure >1300 proteins. In the present study, we performed SOMAscan analysis of plasma samples and validated the measurements by comparison with selected biomarkers. We compared concentrations of SOMAscan-measured prostate specific antigen (PSA) between males and females, and validated SOMAscan concentrations of fibroblast growth factor 23 (FGF23), FGF receptor 1 (FGFR1), and FGFR4 using Enzyme-Linked immunosorbent assay (ELISA). The median (25th and 75th percentile) SOMAscan PSA level in males and females was 4304.7 (1815.4 to 7259.5) and 547.8 (521.8 to 993.4) relative fluorescence units (p = 0.002), respectively, suggesting biological plausibility. Pearson correlation between SOMAscan and ELISA was high for FGF23 (R = 0.95, p < 0.001) and FGFR4 (R = 0.69, p < 0.001), indicating significant positive correlation, while a weak correlation was found for FGFR1 (R = 0.13, p = 0.16). In conclusion, there is a good to near-perfect correlation between SOMAscan and standard immunoassays for FGF23 and FGFR4, but not for FGFR1. This technology may be useful to simultaneously measure a large number of plasma proteins in ESRD, and identify clinically important prognostic markers to predict outcomes.

Clinical utility of bone markers in various diseases

Measurements of bone markers (BMs) in peripheral blood or urine are a pivotal part of bone research within modern clinical medicine. In recent years the use of BMs increased substantially as they can be useful either to diagnose bone (related) disease and to follow its natural history, but also to monitor the effects of interventions. However, the use of BMs is still complicated mainly due to (pre)analytical variability of these substances, limited accessibility of assays, variable cut-off values in different countries and laboratories and heterogeneous results with regard to clinical implications of measuring BMs in several studies. This review will provide the clinician with a practical guide, based on current evidence, in which circumstances to test which bone markers for optimal diagnostic purposes, in order to improve patient care in different areas of bone diseases including Paget's disease, primary osteoporosis, tumor induced osteomalacia, hypophosphatemic rickets, van Buchem disease, chronic kidney disease, rheumatoid arthritis, neoplasma/multiple myeloma, type 2 diabetes mellitus and primary hyperparathyroidism. The clinician should consider fasting state, recent fractures, aging, menopausal status, concomitant liver and kidney disease when ordering and interpreting BM measurements as these factors might result in misleading BM concentrations. We found that BMs are clearly useful in the current diagnosis of tumor induced osteomalacia, van Buchem disease, Paget's disease and hypophosphatemic rickets. In addition, BMs are useful to monitor disease activity in chronic kidney disease, Paget's disease and are useful to monitor treatment adherence in osteoporosis.

Inflammation regulates fibroblast growth factor 23 production

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) is a hormone secreted by osteocytes and osteoblasts that regulates phosphorus and vitamin D homeostasis. FGF23 levels increase progressively in chronic kidney disease (CKD), and FGF23 excess might be a causal factor of left ventricular hypertrophy, CKD progression and death. Therefore, understanding the molecular mechanisms that control FGF23 production is critical to design therapies to lower FGF23 levels. The present review focuses on the role of inflammatory stimuli on FGF23 regulation and summarizes recent studies that support a novel framework linking inflammation to FGF23 regulation.

RECENT FINDINGS

Inflammation and iron deficiency, which are common occurrences in CKD, have emerged as novel FGF23 regulators. Recent findings show that inflammation increases FGF23 production in bone through direct and iron-related indirect mechanisms. In these settings, hypoxia-inducible factor (HIF)-1α orchestrates FGF23 transcription in response to inflammation and is primarily responsible for coordinating FGF23 production and cleavage.

SUMMARY

We demonstrate that inflammation increases FGF23 production and may contribute to elevated FGF23 levels in CKD. Osseous HIF-1α may represent a therapeutic target to lower FGF23 levels in CKD patients and minimize the negative consequences associated with FGF23 excess.

Paracrine Effects of FGF23 on the Heart

Fibroblast growth factor (FGF) 23 is a phosphaturic hormone primarily secreted by osteocytes to maintain phosphate and mineral homeostasis. In patients with and without chronic kidney disease, enhanced circulating FGF23 levels associate with pathologic cardiac remodeling, i.e., left ventricular hypertrophy (LVH) and myocardial fibrosis and increased cardiovascular mortality. Experimental studies demonstrate that FGF23 promotes hypertrophic growth of cardiac myocytes via FGF receptor 4-dependent activation of phospholipase Cγ/calcineurin/nuclear factor of activated T cell signaling independent of its co-receptor klotho. Recent studies indicate that FGF23 is also expressed in the heart, and markedly enhanced in various clinical and experimental settings of cardiac remodeling and heart failure independent of preserved or reduced renal function. On a cellular level, FGF23 is expressed in cardiac myocytes and in other non-cardiac myocytes, including cardiac fibroblasts, vascular smooth muscle and endothelial cells in coronary arteries, and in inflammatory macrophages. Current data suggest that secreted by cardiac myocytes, FGF23 can stimulate pro-fibrotic factors in myocytes to induce fibrosis-related pathways in fibroblasts and consequently cardiac fibrosis in a paracrine manner. While acting on cardiac myocytes, FGF23 directly induces pro-hypertrophic genes and promotes the progression of LVH in an autocrine and paracrine fashion. Thus, enhanced FGF23 may promote cardiac injury in various clinical settings not only by endocrine but also via paracrine/autocrine mechanisms. In this review, we discuss recent clinical and experimental data regarding molecular mechanisms of FGF23's paracrine action on the heart with respect to pathological cardiac remodeling.

Progression of arterial stiffness is associated with changes in bone mineral markers in advanced CKD

Background

Arterial stiffness is an independent predictor of all-cause and cardiovascular mortality in patients with chronic kidney disease (CKD). There are limited prospective data however on progression of arterial stiffness in CKD, including evaluating associations with bone mineral markers such as fibroblast growth factor 23 (FGF23) and soluble α-klotho (sKl).

Methods

In this prospective, single-center, observational study, arterial stiffness [measured by pulse wave velocity (PWV)] and hormones influencing mineral homeostasis, including serum FGF23 and sKl, were compared between non-dialysis CKD stages 4/5 and healthy controls at baseline and 12 months (12 m). Abdominal aortic calcification (AAC) was quantitated using lateral lumbar radiography at baseline.

Results

Forty patients with CKD [mean estimated glomerular filtration rate (eGFR) 19.5 ± 6.7 mL/min/1.73m²] and 42 controls (mean eGFR 88.6 ± 12.9 mL/min/1.73m²) completed follow-up. There were no differences in age, gender and body mass index between groups. A significant increase in FGF23 [240.6 (141.9–1129.8) to 396.8 (160.3–997.7) pg/mL, p = 0.001] was observed in the CKD group but serum phosphate, corrected calcium, parathyroid hormone and sKl did not change significantly over 12 m. At baseline, CKD subjects had higher AAC prevalence [83.8% versus (vs.) 43.6%, p = 0.002] and higher aortic PWV [9.7(7.6–11.7) vs. 8.1 (7.2–9.7) m/s, p = 0.047] compared to controls. At 12 m, aortic PWV increased by 1.3 m/s (95% confidence interval, 0.56 to 2.08, p < 0.001) in the CKD cohort, with 30% of subjects showing progression from normal aortic elasticity to stiffening (PWV > 10 m/s). Serum FGF23 was associated with AAC, abnormal PWV and progression of PWV at 12 m.

Conclusions

Arterial stiffness and serum FGF23, both of which are associated with increased cardiovascular risk, increased over one year in individuals with CKD. Additionally, a significant association was found between serum FGF23 and arterial calcification and stiffness. Larger clinical studies and further experimental work are warranted to delineate the temporal relationship as well as the pathological mechanisms linking FGF23 and vascular disease.

Electronic supplementary material

The online version of this article (10.1186/s12882-017-0705-4) contains supplementary material, which is available to authorized users.

The Association between Biomarker Profiles, Etiology of Chronic Kidney Disease, and Mortality

BACKGROUND

Prognosis in chronic kidney disease (CKD) for adverse outcomes differs substantially based on the etiology of CKD. We examined whether the biomarker profile differed based on CKD etiology and whether they were associated with mortality.

METHODS

Prospective observational study of 1,157 patients, 663 with diabetic kidney disease (DKD), 273 with glomerulonephritis (GN), and 221 with cystic/interstitial disease (polycystic kidney disease, pyelonephritis or chronic tubulointerstitial nephritis [PCK/TIN]) were identified in the Canadian Study of Prediction of Dialysis, Death and Interim Cardiovascular events over Time cohort. The outcome of interest was mortality before commencing dialysis. The biomarker profile consisted of N-terminal pro-brain natriuretic peptide (NT-proBNP), troponin I (TnI), asymmetric dimethylarginine (ADMA), interleukin (IL)-6, high sensitivity C-reactive protein, fibroblast growth factor-23 (FGF23), transforming growth factor-beta, 25-hydroxylvitamin D, and cystatin C (CysC).

RESULTS

The mean estimated glomerular filtration rate was 27 mL/min/1.73 m2 and median follow-up time was 44 months. Mortality before dialysis commencement was the greatest in DKD (20%), followed by PCK/TIN (13%), and was least in those GN (8%). The majority of deaths were cardiovascular in nature, 17, 9, and 5.5% for DKD, PCK/TIN, GN, respectively. Those with DKD had higher hazard for mortality, unadjusted (hazard ratio [HR] 2.7, 95% CI 1.7-4.3) and adjusted (HR 1.7, 95% CI 1.1-2.8). The biomarker profiles associated with mortality differed significantly by CKD etiology as follows: DKD was associated with CysC (HR 1.3, 95% CI 1.0-1.6), ADMA (HR 1.3, 95% CI 1.1-1.6), and NT-proBNP (HR 1.7, 95% CI 1.4-2.1), GN was associated with FGF23 (HR 1.8, 95% CI 1.1-2.8), TnI (HR 3.6, 95% CI 1.3-9.5), and transforming growth factor-beta (HR 0.6, 95% CI 0.4-0.9) and PCK/TIN was associated with ADMA (HR 1.5, 95% CI 1.3-1.8) and IL-6 (HR 2.1, 95% CI 1.5-3.1).

CONCLUSIONS

Biomarkers profiles differ according to the etiology of CKD and are associated with mortality.

Ironing out the cross talk between FGF23 and inflammation

The bone-secreted hormone fibroblast growth factor 23 (FGF23) has an essential role in phosphate homeostasis by regulating expression of the kidney proximal tubule sodium-phosphate cotransporters as well as parathyroid hormone levels. Induction of FGF23 early in chronic kidney disease (CKD) helps to maintain normal phosphorous levels. However, high FGF23 levels become pathological as kidney disease progresses and are associated with an increased risk of CKD progression, cardiovascular events, and death. The factors responsible for increasing FGF23 levels early in CKD are unknown, but recent work has proposed a role for inflammation and disordered iron homeostasis. Notably, FGF23 has recently been shown to elicit an inflammatory response and to display immunomodulatory properties. Here, we will review emerging evidence on the cross talk between inflammation, iron, FGF23, and bone and mineral metabolism and discuss the relevance for CKD patients.

Type 4 cardiorenal syndrome

The Acute Dialysis Quality Initiative consensus conference proposed a classification of cardiorenal syndrome (CRS), aiming for a better delineation of each subtype. Although the exact pathophysiology of type 4 CRS is not completely understood, the mechanisms involved are probably multifactorial. There is growing evidence that oxidative stress is a major connector in the development and progression of type 4 CRS. Giving its complexity, poor prognosis and increasing incidence, type 4 CRS is becoming a significant public health problem. Patients with chronic kidney disease are particularly predisposed to cardiac dysfunction, due to the high prevalence of traditional cardiovascular risk factors in this population, but the contribution of risk factors specific to chronic kidney disease should also be taken into account. Much remains to be elucidated about type 4 CRS: despite progress over the last decade, there are still significant questions regarding its pathophysiology and there is as yet no specific therapy. A better understanding of the mechanisms involved may provide potential targets for intervention. The present review will provide a brief description of the definition, epidemiology, diagnosis, prognosis, biomarkers and management strategies of type 4 CRS, and the pathophysiological mechanisms and risk factors presumably involved in its development will be particularly highlighted.

Association of Fibroblast Growth Factor-23 Levels and Angiotensin-Converting Enzyme Inhibition in Chronic Systolic Heart Failure

OBJECTIVES

The aim of this study was to evaluate the association of fibroblast growth factor (FGF)-23 with clinical and laboratory findings, the prognostic value of FGF-23, and the relationship between angiotensin-converting enzyme inhibitor (ACEi) therapy, FGF-23 levels, and outcomes in patients with chronic systolic heart failure (HF).

BACKGROUND

FGF-23 is a bone-derived hormone regulating mineral metabolism. Higher FGF-23 levels are associated with an increased risk of cardiovascular mortality or HF development. Mechanisms leading to increased FGF-23 and its prognostic value have not been thoroughly studied in HF.

METHODS

FGF-23 was measured in 369 patients (mean age 59 ± 11 years, 84% male) with systolic HF. Patients were followed for adverse events (e.g., death, urgent heart transplantation, ventricular assist device implantation).

RESULTS

Tricuspid regurgitation severity, chronic kidney disease (CKD), alkaline phosphatase concentrations, inferior vena cava dilation, and absence of ACEi therapy were independently associated with FGF-23. FGF-23 was independently associated with outcomes in patients without CKD (hazard ratio [HR]: 1.43, 95% confidence interval [CI]: 1.14 to 1.78), but not in CKD patients (HR: 1.12, 95% CI: 0.87 to 1.45). In patients without CKD and with FGF-23 in the highest tertile, ACEi therapy was associated with a lower risk of adverse events (HR: 0.42, 95% CI: 0.21 to 0.81), whereas no association was seen in the remaining patients (HR: 1.18, 95% CI: 0.52 to 2.70).

CONCLUSIONS

In systolic HF, elevated FGF-23 is an independent predictor of adverse events, particularly in patients with preserved renal function. The association of FGF-23 with adverse events likely reflects early alterations of renal hemodynamics and renin-angiotensin system activation. Increased FGF-23 may identify a subset of HF patients benefiting from ACEi therapy.

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.

Inflammation and functional iron deficiency regulate fibroblast growth factor 23 production

Circulating levels of fibroblast growth factor 23 (FGF23) are elevated in patients with chronic kidney disease (CKD), but the mechanisms are poorly understood. Here we tested whether inflammation and iron deficiency regulate FGF23. In wild-type mice, acute inflammation induced by single injections of heat-killed Brucella abortus or interleukin-1β (IL-1β) decreased serum iron within 6 h, and was accompanied by significant increases in osseous Fgf23 mRNA expression and serum levels of C-terminal FGF23, but no changes in intact FGF23. Chronic inflammation induced by repeated bacteria or IL-1β injections decreased serum iron, increased osseous Fgf23 mRNA, and serum C-terminal FGF23, but modestly increased biologically active, intact FGF23 serum levels. Chronic iron deficiency mimicked chronic inflammation. Increased osseous FGF23 cleavage rather than a prolonged half-life of C-terminal FGF23 fragments accounted for the elevated C-terminal FGF23 but near-normal intact FGF23 levels in inflammation. IL-1β injection increased Fgf23 mRNA and C-terminal FGF23 levels similarly in wildtype and Col4a3(ko) mice with CKD but markedly increased intact FGF23 levels only in the CKD mice. Inflammation increased Fgf23 transcription by activating Hif1α signaling. Thus, inflammation and iron deficiency stimulate FGF23 production. Simultaneous upregulation of FGF23 cleavage in osteocytes maintains near-normal levels of biologically active, intact circulating FGF23, whereas downregulated or impaired FGF23 cleavage may contribute to elevated intact serum FGF23 in CKD.

Cardiorenal Syndrome and the Role of the Bone-Mineral Axis and Anemia

The association between chronic kidney disease (CKD) and cardiovascular disease (CVD) is well established, and there is mounting evidence of interorgan cross talk that may accelerate pathologic processes and the progression of organ dysfunction in both systems. This process, termed cardiorenal syndrome (CRS) by the Acute Dialysis Quality Initiative, is considered a major health problem: patients with CKD and CVD are at much higher risk of mortality than patients with either condition alone. To date, the majority of CRS research has focused on neurohormonal mechanisms and hemodynamic alterations. However, mounting evidence suggests that abnormalities in the normal pathophysiology of the bone-mineral axis, iron, and erythropoietin play a role in accelerating CKD and CVD. The goal of this article is to review the role and interrelated effects of the bone-mineral axis and anemia in the pathogenesis of chronic CRS.

Effect of High-Flux Dialysis on Circulating FGF-23 Levels in End-Stage Renal Disease Patients: Results from a Randomized Trial

BACKGROUND

In patients undergoing maintenance hemodialysis (HD), increased levels of circulating fibroblast growth factor-23 (FGF-23) are independently associated with cardiovascular events and mortality. Interventional strategies aiming to reduce levels of FGF-23 in HD patients are of particular interest. The purpose of the current study was to compare the impact of high-flux versus low-flux HD on circulating FGF-23 levels.

METHODS

We conducted a post-hoc analysis of the MINOXIS study, including 127 dialysis patients randomized to low-flux (n = 62) and high-flux (n = 65) HD for 52 weeks. Patients with valid measures for FGF-23 investigated baseline and after 52 weeks were included.

RESULTS

Compared to baseline, a significant increase in FGF-23 levels after one year of low-flux HD was observed (Delta plasma FGF-23: +4026 RU/ml; p < 0.001). In contrast, FGF-23 levels remained stable in the high flux group (Delta plasma FGF-23: +373 RU/ml, p = 0.70). The adjusted difference of the absolute change in FGF-23 levels between the two treatment groups was statistically significant (p < 0.01).

CONCLUSIONS

Over a period of 12 months, high-flux HD was associated with stable FGF-23 levels, whereas the low-flux HD group showed an increase of FGF-23. However, the implications of the different FGF 23 time-trends in patients on high flux dialysis, as compared to the control group, remain to be explored in specifically designed clinical trials.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS) DRKS00007612.

[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.