Fibroblast growth factor 23, high-sensitivity cardiac troponin, and left ventricular hypertrophy in CKD

Impact of Overhydration on Left Ventricular Hypertrophy in Patients With Chronic Kidney Disease

Objective

Volume overload is a frequent feature related to left ventricular hypertrophy (LVH) in dialysis patients, but its influence on patients with chronic kidney disease (CKD) not on dialysis has not been accurately uncovered. This article was to examine the relationship between overhydration (OH) and LVH in patients with CKD not yet on dialysis.

Methods

A total of 302 patients with CKD stages 1–4 were included. Participants were divided into different subgroups according to occurring LVH or not, and OH tertiles. Clinical and laboratory parameters were compared among groups. Spearman correlation analyses were adopted to explore the relationships of echocardiographic findings with the clinical and laboratory characteristics. Binary logistic regression models were performed to estimate the odds ratios (ORs) for the associations between OH and LVH. Restricted cubic splines were implemented to assess the possible non-linear relationship between OH and LVH. LVH was defined as left ventricular mass index (LVMI) >115 g/m2 in men and >95 g/m2 in women.

Results

Of the enrolled patients with CKD, the mean age was 45.03 ± 15.14 years old, 165 (54.6%) cases were men, and 65 (21.5%) cases had LVH. Spearman correlation analyses revealed that OH was positively correlated with LVMI (r = 0.263, P < 0.001). After adjustment for age, gender, diabetes, body mass index (BMI), systolic blood pressure (SBP), hemoglobin, serum albumin, estimated glomerular filtration rate (eGFR), and logarithmic transformation of urinary sodium and urinary protein, multivariate logistic regression analyses demonstrated that both the middle and highest tertile of OH was associated with increased odds of LVH [OR: 3.082 (1.170–8.114), P = 0.023; OR: 4.481 (1.332–15.078), P = 0.015, respectively], in comparison to the lowest tierce. Restricted cubic spline analyses were employed to investigate the relationship between OH and LVH, which unfolded a significant non-linear association (P for non-linear = 0.0363). Furthermore, patients were divided into two groups according to CKD stages. The multivariate logistic regression analyses uncovered that increased odds of LVH were observed in the middle and the highest tertile of OH [OR: 3.908 (0.975–15.670), P = 0.054; OR: 6.347 (1.257–32.054), P = 0.025, respectively] in patients with stages 1–2.

Conclusion

These findings suggest that a higher level of OH was associated with a higher occurrence of LVH in patients with CKD not on dialysis, especially in patients with CKD stages 1–2.

Cardiovascular remodeling as a result of fibroblast growth factor-23 (FGF-23)/Klotho imbalance in patients with CKD

BACKGROUND

In chronic kidney disease (CKD) cardiovascular remodeling (CVR) is very frequent compared with general population and, as suppose, may be associated with «new» renal risk factors. The aim of study was to estimate association of new serum biomarkers (FGF-23, Klotho) and traditional biomarker of cardiac damage-serum Troponin I (sTr-I) with signs of CVR.

METHODS

One hundred thirty CKD G1-5D patients without cardiovascular disease (CVD) clinical manifestation were included. We measured serum FGF-23, Klotho and sTr-I. The instrumental methods were: echocardiography, SphygmoCor test [Pulse Wave Velocity (PWV), Central (aortic) Blood Pressure (CBP), Subendocardial Blood Supply (SBS)].

RESULTS

FGF-23 level correlated with: sTr-I (r = 0.512; p < 0.01), eccentric left ventricular hypertrophy, LVH (r = 0.543; p < 0.01), SBS (r = - 0.499; p < 0.05). There were no differences of FGF-23 level in patients with normal and high CBP. Klotho correlated with concentric LVH (r = - 0.451; p < 0.01), PWV (r = - 0.667; p < 0.001), Cardiac Calcification Score, CCS (r = - 0.581; p < 0.01). Multivariate analysis revealed positive independent association of FGF-23 with eccentric LVH (OR = 1.036, 95% CI (1.004-1.068); p = 0.038). Klotho was a negative determinant for concentric LVH (OR = 0.990, 95% CI 0.987-0.994; p < 0.001), increased PWV (OR = 0.984, 95% CI (0.977-0.991); p < 0.001) and CCS (OR = 0.991, 95% CI (0.988-0.995); p < 0.001). In addition, multivariate analysis revealed a relationship between serum Klotho (OR = 0.980, 95% CI (0.964-0.996); p = 0.016), FGF-23 (OR = 3.145, 95% CI (1.020-9.695); p = 0.046) and troponin I level.

CONCLUSION

In CKD patients without CVD clinical manifestation increased serum FGF-23 level and decreased Klotho are associated with CVR: FGF-23 with eccentric LVH (independently of CBP), Klotho determinate concentric LVH, PWV and CCS. Moderately elevated sTr-I levels may be a manifestation of FGF-23/Klotho imbalance in CKD.

High-Sensitive Cardiac Troponin T for Prediction of Cardiovascular Outcomes in Stable Maintenance Hemodialysis Patients: A 3-Year Prospective Study

BACKGROUND

Hemodialysis patients, who are often excluded from cardiovascular (CV) clinical trials, are associated with higher CV morbidity and mortality. The risk stratification scheme for these patients is lacking. Therefore, this investigation examined the independent CV prognostic value of high-sensitive cardiac troponin T (hs-cTnT) and added prognostic value over echocardiographic parameters and other clinical risk predictors in asymptomatic stable maintenance hemodialysis (MHD) patients.

METHODS

181 patients with end-stage renal disease undergoing MHD were eligible from the dialysis center of Tongren Hospital, Shanghai Jiao Tong University School of Medicine between October 2017 and September 2018. These patients were followed until September 2020 or until death. The median follow-up was 31 (IQR: 21-33) months. Outcome measures were all-cause mortality, first fatal or nonfatal CV events (CVEs), and 4-point composite major adverse CVEs (MACE). We performed multivariable Cox regression analysis using demographic, clinical, laboratory, and echocardiographic data to identify predictors of CV outcomes. We also evaluated the increased discriminative value associated with the addition of echocardiographic parameters and hs-cTnT using net reclassification improvement (NRI) and integrated discrimination improvement (IDI).

RESULTS

During follow-up, 37 patients died, 84 patients suffered one or more CVEs, and 78 patients developed 4-point MACE. In univariable analyses, age, dialysis vintage, diastolic blood pressure, parathyroid hormone concentrations, hs-cTnT, B-type natriuretic peptide, left ventricular mass index (LVMI), and E/E' predicted all end points. hs-cTnT remained a strong predictor for each end point in multivariate analysis, whereas LVMI and E/E' did not. The addition of hs-cTnT on top of clinical and echocardiographic variables was associated with improvements in reclassification for CVEs (NRI = 44.6% [15.9-74.3%], IDI = 15.9% [5.7-31.0%], all p < 0.001), all-cause mortality (NRI = 35.5% [10.1-50.2%], p < 0.001, IDI = 4.4% [1.3-8.5%], p = 0.005), and 4-point MACE (NRI = 47.2% [16.1-64.9%], p < 0.001, IDI = 16.9% [5.5-37.3%], p = 0.005). Adding echocardiographic variables on top of clinical variables and hs-cTnT was not associated with significant improvements in NRI and IDI (all p > 0.05).

CONCLUSIONS

Our data suggest that hs-cTnT is a powerful independent predictor of CV outcome and all-cause mortality in stable MHD patients. The additional use of echocardiography for improvement of risk stratification is not supported by our results.

Myocardial Hypertrophy and Fibrosis Are Associated with Cardiomyocyte Beta-Catenin and TRPC6/Calcineurin/NFAT Signaling in Spontaneously Hypertensive Rats with 5/6 Nephrectomy

BACKGROUND

Arterial hypertension (AH) is associated with heart and chronic kidney disease (CKD). However, the precise mechanisms of myocardial remodeling (MR) in the settings of CKD remain elusive. We hypothesized that TRPC6, calcineurin/NFAT, and Wnt/β-catenin signaling pathways are involved in the development of MR in the background of CKD and AH.

METHODS

Early CKD was induced by performing a 5/6 nephrectomy (5/6NE) in spontaneously hypertensive rats (SHR-NE). Sham-operated (SO) SHR (SHR-SO) and Wistar Kyoto (WKY-SO) rats served as controls. Systolic blood pressure (SBP), heart rate, myocardial mass index (MMI), serum creatinine, cardiomyocyte diameter (dCM), myocardial fibrosis (MF), serum and kidney α-Klotho levels, myocardial expression of calcineurin (CaN), TRPC6, and β-catenin were measured two months after 5/6NE or SO.

RESULTS

NE-induced kidney dysfunction corresponded to mild-to-moderate human CKD and was associated with an increase in FGF23 and a decrease in renal α-Klotho. The levels of SBP, MMI, dCM, and MF were higher in SHRs compared to WKY-SO as well as in SHR-NE vs. SHR-SO. The MR was associated with increased cardiomyocyte expression of CaN/NFAT and β-catenin along with its intracellular re-distribution. TRPC6 protein levels were substantially elevated in both SHR groups with higher Trpc6 mRNA expression in SHR-NE.

CONCLUSIONS

The Wnt/β-catenin and TRPC6/CaN/NFAT hypertrophic signaling pathways seem to be involved in myocardial remodeling in the settings of AH and CKD and might be mediated by FGF23 and α-Klotho axis.

Fibroblast growth factor 23: a biomarker of fibrosis and prognosis in heart failure with preserved ejection fraction

AIMS

Besides regulating calcium-phosphate metabolism, fibroblast growth factor 23 (FGF-23) has been associated with incident heart failure (HF) and left ventricular hypertrophy. However, data about FGF-23 in HF and preserved ejection fraction (HFpEF) remain limited. The aim of this study was to assess the association between FGF-23 levels, clinical and imaging characteristics, particularly diffuse myocardial fibrosis, and prognosis in HFpEF patients.

METHODS AND RESULTS

We prospectively included 143 consecutive HFpEF patients (78 ± 8 years, 61% female patients) and 31 controls of similar age and gender (75 ± 6 years, 61% female patients). All subjects underwent a complete two-dimensional echocardiography and cardiac magnetic resonance with extracellular volume (ECV) assessment by T1 mapping. FGF-23 was measured at baseline. Among the patients, differences in clinical and imaging characteristics across tertiles of FGF-23 levels were analysed with a trend test across the ordered groups. Patients were followed over time for a primary endpoint of all-cause mortality and first HF hospitalization and a secondary endpoint of all-cause mortality. Median FGF-23 was significantly higher in HFpEF patients compared with controls of similar age and gender (247 [115; 548] RU/mL vs. 61 [51; 68] RU/mL, P < 0.001). Among HFpEF patients, higher FGF-23 levels were associated with female sex, higher incidence of atrial fibrillation, lower haemoglobin, worse renal function, and higher N terminal pro brain natriuretic peptide levels (P for trend < 0.05 for all). Regarding imaging characteristics, patients with higher FGF-23 levels had greater left atrial volumes, worse right ventricular systolic function, and more fibrosis estimated by ECV (P for trend < 0.05 for all). FGF-23 was moderately correlated with ECV (r = 0.46, P < 0.001). Over a mean follow-up of 30 ± 8 months, 43 patients (31%) died and 69 patients (49%) were hospitalized for HF. A total of 87 patients (62%) reached the primary composite endpoint of all-cause mortality and/or first HF hospitalization. In multivariate Cox regression analysis for the primary endpoint, FGF-23 (HR: 3.44 [2.01; 5.90], P < 0.001) and E wave velocities (HR: 1.01 [1.00; 1.02], P = 0.034) were independent predictors of the primary composite endpoint. In multivariate Cox regression analysis for the secondary endpoint, ferritin (HR: 1.02 [1.01; 1.03], P < 0.001), FGF-23 (HR: 2.85 [1.26; 6.44], P = 0.012), and ECV (HR: 1.26 [1.03; 1.23], P = 0.008) were independent predictors of all-cause mortality.

CONCLUSIONS

Fibroblast growth factor 23 (FGF-23) levels were significantly higher in HFpEF patients compared with controls of similar age and gender. FGF-23 was correlated with fibrosis evaluated by ECV. High levels of FGF-23 were significantly associated with signs of disease severity such as worse renal function, larger left atrial volumes, and right ventricular dysfunction. Moreover, FGF-23 was a strong predictor of poor outcome (mortality and first HF hospitalization).

A Control Region Near the Fibroblast Growth Factor 23 Gene Mediates Response to Phosphate, 1,25(OH)2D3, and LPS In Vivo

Fibroblast growth factor 23 (FGF23) is a bone-derived hormone involved in the control of phosphate (P) homeostasis and vitamin D metabolism. Despite advances, however, molecular details of this gene's regulation remain uncertain. In this report, we created mouse strains in which four epigenetically marked FGF23 regulatory regions were individually deleted from the mouse genome using CRISPR/Cas9 gene-editing technology, and the consequences of these mutations were then assessed on Fgf23 expression and regulation in vivo. An initial analysis confirmed that bone expression of Fgf23 and circulating intact FGF23 (iFGF23) were strongly influenced by both chronic dietary P treatment and acute injection of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. However, further analysis revealed that bone Fgf23 expression and iFGF23 could be rapidly upregulated by dietary P within 3 and 6 hours, respectively; this acute upregulation was lost in the FGF23-PKO mouse containing an Fgf23 proximal enhancer deletion but not in the additional enhancer-deleted mice. Of note, prolonged dietary P treatment over several days led to normalization of FGF23 levels in the FGF23-PKO mouse, suggesting added complexity associated with P regulation of FGF23. Treatment with 1,25(OH)2D3 also revealed a similar loss of Fgf23 induction and blood iFGF23 levels in this mouse. Finally, normal lipopolysaccharide (LPS) induction of Fgf23 expression was also compromised in the FGF23-PKO mouse, a result that, together with our previous report, indicates that the action of LPS on Fgf23 expression is mediated by both proximal and distal Fgf23 enhancers. These in vivo data provide key functional insight into the genomic enhancers through which Fgf23 expression is mediated.

Serum troponin-I as a marker of fibroblast growth factor-23 (FGF-23) cardiotoxic effect, in patients with chronic kidney disease

Aim. It has been established that an increased fibroblast growth factor (FGF-23) serum levels significantly contribute to the heart and blood vessels remodeling in patients with chronic kidney disease (CKD). But the precise mechanisms of the FGF-23 cardiac effect are currently being actively studied. At the same time, it is believed that the cardiac effects of FGF-23 may be due to the increasing deficit of Klotho protein as CKD progresses. In parallel with these changes, a number of studies indicate the persistence of the detectable troponins serum levels in CKD patients, even in the absence of clear clinical manifestations of cardiovascular diseases (CVD). The aim of the study was to confirm / exclude the existence of a causal relationship between elevated FGF-23, reduced Klotho and elevated troponin-I (as the most specific troponin in CKD). Materials and methods. The study included 130 CKD stages 1-5D patients without clinically pronounced symptoms of СVD (Coronary artery disease, CCS class 2-4, Chronic heart failure, NYHA 24, myocarditis, pericarditis, arrhythmias), as well as the severe arterial hypertension (BP >160/90 mm Hg), according to the laboratory and instrumental methods of examination. The selected group of patients was studied: serum levels of FGF-23 (Human FGF-23 ELISA kit), Klotho (Human soluble Klotho with antiklotho monoclonal antibodies), troponin-I (high - sensitive assay), and also data from instrumental examination methods: electrocardiography (ECG), echocardiography (left ventricular myocardial mass index (LVMI), cardiac (valvular) calcification score (CCS) using a semi - quantitative point scale), sphygmagraphy (augmentation (stiffness) indices of vessels (AI), pulse wave velocity (PWV), central (aortic) blood pressure (CBP), blood supply of subendocardium (BSE) - using "Shygmacor" device (Australia)). Results and discussion. The changes in serum levels of FGF-23, Klotho and troponin-I (Tr-I) depended on the stage of CKD. The following correlations were identified: FGF-23 and: Tr-I (r=0.601; p

FGF23: Clinical usefulness and analytical evolution

Fibroblast Growth Factor 23 (FGF23) is a key hormone for the regulation of phosphate homeostasis. Over the past decades, FGF23 was the subject of intense research in the fields of nephrology and the cardiology. It presents a remarkable correlation with well-established biomarkers of cardiovascular disorders in both chronic kidney disease (CKD) and heart failure (HF) patients. The interest of FGF23 lies in its early-onset in the primary course of CKD as well as in the incremental prognosis information it conveys in both CKD and HF. Different types of assays of FGF-23 testing exist, those targeting the intact form (iFGF23), the other one detecting terminal fragments (cFGF23). The issue is still pending which assay suits best for clinical use. Recently, the implementation of this biomarker on multianalyzer platforms, on which other markers of phospho-calcic balance are set up, allows a rapid turn-around-time and a potential financial gain. However, despite the good analytical performances of the automated methods, there is a poor harmonization between assays. The introduction of an international certified reference material should standardize the measurement and improve the harmonization of results from different laboratories. A deeper understanding of physio-pathological mechanisms and processing of FGF-23 should reinforce its clinical indications and might also identify new therapeutic targets for the treatment of CKD and HF.

Phosphate and Cardiovascular Disease beyond Chronic Kidney Disease and Vascular Calcification

Phosphate is essential for life but its accumulation can be detrimental. In end-stage renal disease, widespread vascular calcification occurs as a result of chronic phosphate load. The accumulation of phosphate is likely to occur long before the rise in serum phosphate above the normal range since several observational studies in both general population and early-stage CKD patients have identified the relationship between high-normal serum phosphate and adverse cardiovascular outcomes. Consumption of food high in phosphate increases both fasting and postprandial serum phosphate and habitual intake of high phosphate diet is associated with aging, cardiac hypertrophy, endothelial dysfunction, and subclinical atherosclerosis. The decline in renal function and dietary phosphate load can increase circulating fibroblast growth factor-23 (FGF-23) which may have a direct impact on cardiomyocytes. Increased FGF-23 levels in both CKD and general populations are associated with left ventricular hypertrophy, congestive heart failure, atrial fibrillation, and mortality. Increased extracellular phosphate directly affects endothelial cells causing cell apoptosis and vascular smooth muscle cells (VSMCs) causing transformation to osteogenic phenotype. Excess of calcium and phosphate in the circulation can promote the formation of protein-mineral complex called calciprotein particles (CPPs). In CKD, these CPPs contain less calcification inhibitors, induce inflammation, and promote VSMC calcification.

Is there a role for newer biomarkers in chronic kidney disease-mineral and bone disorder management?

The current management of Chronic Kidney Disease-Mineral Bone Disorder (CKD-MBD) relies largely on clinical judgement and assessment of biochemical parameters including serum calcium, phosphate and intact parathyroid hormone concentrations. In the past two decades, there has been a leap in the understanding of the pathophysiology of CKD-MBD, leading to the discovery of novel biomarkers. The potential utility of these markers in this clinical setting is an area of intense investigation. In the absence of any guidelines aiding the clinician's understanding and application of these markers, we summarise the current available literature surrounding fibroblast growth factor-23, α-Klotho, sclerostin and serum calcification propensity testing and their respective assays in the context of CKD-MBD management.

FGF23 and Left Ventricular Hypertrophy in Children with CKD

BACKGROUND AND OBJECTIVES

High plasma concentration of fibroblast growth factor 23 (FGF23) is a risk factor for left ventricular hypertrophy (LVH) in adults with CKD, and induces myocardial hypertrophy in experimental CKD. We hypothesized that high FGF23 levels associate with a higher prevalence of LVH in children with CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed echocardiograms and measured plasma C-terminal FGF23 concentrations in 587 children with mild-to-moderate CKD enrolled in the Chronic Kidney Disease in Children (CKiD) study. We used linear and logistic regression to analyze the association of plasma FGF23 with left ventricular mass index (LVMI) and LVH (LVMI ≥95th percentile), adjusted for demographics, body mass index, eGFR, and CKD-specific factors. We also examined the relationship between FGF23 and LVH by eGFR level.

RESULTS

Median age was 12 years (interquartile range, 8-15) and eGFR was 50 ml/min per 1.73 m2 (interquartile range, 38-64). Overall prevalence of LVH was 11%. After adjustment for demographics and body mass index, the odds of having LVH was higher by 2.53 (95% confidence interval, 1.28 to 4.97; P<0.01) in participants with FGF23 concentrations ≥170 RU/ml compared with those with FGF23<100 RU/ml, but this association was attenuated after full adjustment. Among participants with eGFR≥45 ml/min per 1.73 m2, the prevalence of LVH was 5.4%, 11.2%, and 15.3% for those with FGF23 <100 RU/ml, 100-169 RU/ml, and ≥170 RU/ml, respectively (Ptrend=0.01). When eGFR was ≥45 ml/min per 1.73 m2, higher FGF23 concentrations were independently associated with LVH (fully adjusted odds ratio, 3.08 in the highest versus lowest FGF23 category; 95% confidence interval, 1.02 to 9.24; P<0.05; fully adjusted odds ratio, 2.02 per doubling of FGF23; 95% confidence interval, 1.29 to 3.17; P<0.01). By contrast, in participants with eGFR<45 ml/min per 1.73 m2, FGF23 did not associate with LVH.

CONCLUSIONS

Plasma FGF23 concentration ≥170 RU/ml is an independent predictor of LVH in children with eGFR≥45 ml/min per 1.73 m2.

John Sutton MG, Kusek JW, Isakova T, Wolf M, Keane MG. Racial/Ethnic Differences in Left Ventricular Structure and Function in Chronic Kidney Disease: The Chronic Renal Insufficiency Cohort

BACKGROUND

Chronic kidney disease (CKD) is associated with increased risk of cardiovascular disease (CVD) and it is especially common among Blacks. Left ventricular hypertrophy (LVH) is an important subclinical marker of CVD, but there are limited data on racial variation in left ventricular structure and function among persons with CKD.

METHODS

In a cross-sectional analysis of the Chronic Renal Insufficiency Cohort Study, we compared the prevalence of different types of left ventricular remodeling (concentric hypertrophy, eccentric hypertrophy, and concentric remodeling) by race/ethnicity. We used multinomial logistic regression to test whether race/ethnicity associated with different types of left ventricular remodeling independently of potential confounding factors.

RESULTS

We identified 1,164 non-Hispanic Black and 1,155 non-Hispanic White participants who completed Year 1 visits with echocardiograms that had sufficient data to categorize left ventricular geometry type. Compared to non-Hispanic Whites, non-Hispanic Blacks had higher mean left ventricular mass index (54.7 ± 14.6 vs. 47.4 ± 12.2 g/m2.7; P < 0.0001) and prevalence of concentric LVH (45.8% vs. 24.9%). In addition to higher systolic blood pressure and treatment with >3 antihypertensive medications, Black race/ethnicity was independently associated with higher odds of concentric LVH compared to White race/ethnicity (odds ratio: 2.73; 95% confidence interval: 2.02, 3.69).

CONCLUSION

In a large, diverse cohort with CKD, we found significant differences in left ventricular mass and hypertrophic morphology between non-Hispanic Blacks and Whites. Future studies will evaluate whether higher prevalence of LVH contribute to racial/ethnic disparities in cardiovascular outcomes among CKD patients.

Soluble ST2 does not change cardiovascular risk prediction compared to cardiac troponin T in kidney transplant candidates

BACKGROUND

Solubility of Tumorigenicity 2 (sST2) is a novel biomarker that better stratifies risk of cardiovascular events (CVE) compared to cardiac troponin T(cTnT) in heart failure. We assessed the association of sST2 with the composite outcome of CVE and/or mortality compared to cTnT in kidney transplant candidates.

METHODS

200 kidney transplant candidates between 2010 and 2013 were included. Elevated sST2 was defined as ≥30ng/ml, cTnT≥0.01 ng/ml.

RESULTS

Median age 53 (interquartile range (IQR) 42-61) years, 59.7% male and 82.0% white. 33.5% had history of CVE, 42.5% left ventricular hypertrophy (LVH) and 15.6% positive cardiac stress test. Elevated sST2 correlated with male gender, history of prior-transplants, CVE, positive stress test, LVH, elevated cTnT, anemia, hyperphosphatemia, increased CRP and non-transplanted status. Male gender, history of CVE and LVH were independent determinants of sST2. During 28 months (IQR 25.3-30), 7.5% died, 13.0% developed CVE and 19.0% developed the composite outcome. Elevated sST2 was associated with the composite outcome (hazard ratio = 1.76, CI 1.06-2.73, p = 0.029) on univariate analysis but not after adjusting for age, diabetes and cTnT (p = 0.068). sST2 did not change the risk prediction model for composite outcome after including age, diabetes, prior history of CVE and elevated cTnT.

CONCLUSIONS

Increased sST2 level is significantly associated with variables associated with CVE in kidney transplant candidates. sST2 was associated with increased risk of the composite outcome of CVE and/or death but not independent of cTnT. Larger studies are needed to confirm these findings and determine whether sST2 has added value in CV risk stratification in this cohort of patients.

Effects of klotho deletion from bone during chronic kidney disease

Klotho is a type I transmembrane protein that acts as a permissive co-receptor for FGF23 and helps to maintain proper mineral metabolism. Mice carrying a loss-of-function mutation in either the Klotho or Fgf23 gene develop many similar phenotypes including osteoporosis. Based on these observations it was hypothesized that the bone phenotypes in Klotho- and Fgf23-null mice may be mediated through a common signaling pathway. Recent improvements in antibody specificity have shown that osteoblasts and osteocytes, which produce FGF23, also express low amount of membrane Klotho. But, the role of Klotho in bone is still largely unclear. In this review we summarize the literature and show that Klotho has an FGF23 dependent and independent effect in bone.

Novel Faces of Fibroblast Growth Factor 23 (FGF23): Iron Deficiency, Inflammation, Insulin Resistance, Left Ventricular Hypertrophy, Proteinuria and Acute Kidney Injury

FGF23 is a hormone that appears as the core regulator of phosphate metabolism. Great deal of data has accumulated to demonstrate increased FGF23 secretion from the bone to compensate for even subtle increases in serum phosphorus long before intact PTH. However, recent evidence points to the fact that actions and interactions of FGF23 are not limited solely to phosphate metabolism. FGF23 may be implicated in iron metabolism and erythropoiesis, inflammation, insulin resistance, proteinuria, acute kidney injury and left ventricular hypertrophy. In this review, we will summarize latest experimental and clinical data examining impact of FGF23 on aforementioned pathophysiologic pathways/disorders.

Klotho expression in long bones regulates FGF23 production during renal failure

Circulating levels of bone-derived fibroblast growth factor 23 (FGF23) increase early during acute and chronic kidney disease and are associated with adverse outcomes. Membrane-bound Klotho acts as a permissive coreceptor for FGF23, and its expression was recently found in osteoblasts/osteocytes. We hypothesized that Klotho in bone cells is part of an autocrine feedback loop that regulates FGF23 expression during renal failure. Thus, we induced renal failure in mice with targeted deletion of Klotho in long bones. Uremic wild-type (KL^fl/fl ) and knockout (Prx1-Cre;KL^fl/fl ) mice both responded with reduced body weight, kidney atrophy, hyperphosphatemia, and increased bone turnover. Importantly, long bones of Prx1-Cre;KL^fl/fl mice but not their axial skeleton failed to increase FGF23 expression as observed in uremic KL^fl/fl mice. Consequently, Prx1-Cre;KL^fl/fl mice had significantly lower serum FGF23 and parathyroid hormone levels, and higher renal 1-α-hydroxylase expression, serum 1,25-dihydroxyvitamin D, and calcium levels than KL^fl/fl mice. These results were confirmed in two independent models of renal failure, adenine diet induced and 5/6 nephrectomy. Moreover, FGF23-treated bone cells required Klotho to increase FGF23 mRNA and ERK phosphorylation. In summary, our novel findings show that Klotho in bone is crucial for inducing FGF23 production upon renal failure. We propose the presence of an autocrine feedback loop in which Klotho senses the need for FGF23.-Kaludjerovic, J., Komaba, H., Sato, T., Erben, R. G., Baron, R., Olauson, H., Larsson, T. E., Lanske, B. Klotho expression in long bones regulates FGF23 production during renal failure.

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.

Fibroblast growth factor 23 correlates with volume status in haemodialysis patients and is not reduced by haemodialysis

BACKGROUND

Recent data suggest a role for fibroblast growth factor 23 (FGF-23) in volume regulation. In haemodialysis patients, a large ultrafiltration volume (UFV) reflects poor volume control, and both FGF-23 and a large UFV are risk factors for mortality in this population. We studied the association between FGF-23 and markers of volume status including UFV, as well as the intradialytic course of FGF-23, in a cohort of haemodialysis patients.

METHODS

We carried out observational, post hoc analysis of 109 prevalent haemodialysis patients who underwent a standardized, low-flux, haemodialysis session with constant ultrafiltration rate. We measured UFV, plasma copeptin and echocardiographic parameters including cardiac output, end-diastolic volume and left ventricular mass index at the onset of the haemodialysis session. We measured the intradialytic course of plasma C-terminal FGF-23 (corrected for haemoconcentration) and serum phosphate levels at 0, 1, 3 and 4 h after onset of haemodialysis and analysed changes with linear mixed effect model.

RESULTS

Median age was 66 (interquartile range: 51-75) years, 65% were male with a weekly Kt/V 4.3 ± 0.7 and dialysis vintage of 25.4 (8.5-52.5) months. In univariable analysis, pre-dialysis plasma FGF-23 was associated with UFV, end-diastolic volume, cardiac output, early diastolic velocity e' and plasma copeptin. In multivariable regression analysis, UFV correlated with FGF-23 (standardized β: 0.373, P < 0.001, model R(2): 57%), independent of serum calcium and phosphate. The association between FGF-23 and echocardiographic volume markers was lost for all but cardiac output upon adjustment for UFV. Overall, FGF-23 levels did not change during dialysis [7627 (3300-13 514) to 7503 (3109-14 433) RU/mL; P = 0.98], whereas phosphate decreased (1.71 ± 0.50 to 0.88 ± 0.26 mmol/L; P < 0.001).

CONCLUSIONS

FGF-23 was associated with volume status in haemodialysis patients. The strong association with UFV suggests that optimization of volume status, for example by more intensive haemodialysis regimens, may also benefit mineral homeostasis. A single dialysis session did not lower FGF-23 levels.

The fibroblast growth factor-23 and Vitamin D emerge as nontraditional risk factors and may affect cardiovascular risk

OBJECTIVES

Fibroblast growth factor-23 (FGF-23) and vitamin D are hormones involved in phosphate homoeostasis. They also directly influence cardiomyocyte hypertrophy. We examined whether the relationships between levels of vitamin D or FGF-23, cardiac phenotype and outcome were independent of established cardiac biomarkers in a large cohort of community-dwelling elderly subjects.

DESIGN AND SETTING

Plasma levels of FGF-23 and vitamin D were measured in 1851 men and women (65-84 years) resident in the Lazio region of Italy. Participants were referred to eight cardiology centres for clinical examination, electrocardiography, comprehensive Doppler echocardiography and blood sampling. All-cause mortality or hospitalizations were available after a median follow-up of 47 months with record linkage of administrative data.

RESULTS

Vitamin D deficiency (<20 ng mL(-1) ) was found in 72.3% of subjects, but FGF-23 levels were normal [74 (58-97) RU per mL]. After adjustment for cardiovascular risk factors and morbidities, low concentrations of vitamin D and high levels of FGF-23 were associated with a higher left ventricular (LV) mass index. Levels of FGF-23 [hazard ratio (HR) (95% confidence interval (CI)) 1.71 (1.28-2.28), P < 0.0001] but not vitamin D [0.76 (0.57-1.01), P = 0.08] were independently associated with mortality after adjustment for clinical risk factors and two cardiac markers together (N-terminal pro-brain natriuretic peptide and high-sensitivity cardiac troponin T), but did not predict hospital admission. People with above median values of FGF-23 and below median values of vitamin D had greater LV hypertrophy and higher mortality.

CONCLUSIONS

In community-dwelling elderly individuals with highly prevalent vitamin D deficiency, FGF-23 levels were associated with LV hypertrophy and predicted mortality independently of two robust cardiac biomarkers. A causal relationship was not demonstrated, but the hormones involved in mineral metabolism emerged as nontraditional risk factors and may affect cardiovascular risk.

Superior predictive value for NTproBNP compared with high sensitivity cTnT in dialysis patients: a pilot prospective observational study

BACKGROUND/AIMS

The clinical utility of the new biomarker, high sensitivity cardiac T troponin (hs-cTnT) is still unclear in dialysis patients. Furthermore, the prognostic value of combining N-terminal pro-B-type natriuretic peptide (NT-pro-BNP) and hs-cTnT has not been explored so far. The objective of this pilot study was to determine the utility of hs-cTnT alone versus hs-cTnT in combination with NT-proBNP for predicting death in a stable hemodialysis cohort.

METHODS

A prospective observational pilot study including 98 chronic asymptomatic hemodialysis patients with a follow up period of 24 months was designed. The cut-off values for NT-proBNP and hs-cTnT were calculated using receiver operating characteristic (ROC) analysis, using mortality as an end-point. Based on the cut-off values, the cohort was divided into four groups. Group 1--NT-proBNP < 14275 pg/ml and hs-cTnT < 69.48 ng/l; group 2--NT-proBNP < 14275 pg/ml and hs-cTnT > 69.48 ng/l; group 3--NT-proBNP > 14275 pg/ml and hs-cTnT < 69.48 ng/l; group 4--NT-proBNP > 14275 pg/ml and hs-cTnT > 69.48 ng/l. Survival for each group was determined using the Kaplan-Meier method and Cox regression analysis.

RESULTS

During the follow-up period 16 patients died. According to the ROC curves analysis, the cut-off point for hs-cTnT and for NT-proBNP were 69.43 ng/l (AUC = 0.618; p = 0.04) and 14275 pg/ml (AUC = 0.722; p = 0.003), respectively. In univariate Cox analysis, both hs-cTnT (HR = 3.34; p = 0.016) and NT-proBNP (HR = 5.94; p = 0.01) were predictors of death. In the multivariable Cox proportional hazards model, only NT-pro-BNP levels above the cut-off value remained an independent predictor of all-cause mortality. The combined elevation of both biomarkers did not improve significantly the prognostic value compared with NT-proBNP alone (HR = 6.15 versus HR =4 .78; p = 0.338).

CONCLUSION

NT-pro-BNP is a strong predictor of overall mortality in asymptomatic hemodialysis patients. The addition of hs-cTnT did not improve the prognostic accuracy compared with NT proBNP alone.

Clinical relevance of biomarkers in heart failure and cardiorenal syndrome: the role of natriuretic peptides and troponin

In recent years, numerous biomarkers have been studied in heart failure to improve diagnostic accuracy and identify patients at higher risk. The overall outcome remains fairish despite improvements in therapy, with mean survival after first hospitalization, around 5 years. We therefore need surrogate end points to better understand the pathogenetic mechanisms of the disease, including interplays with other organs. The kidney plays an important role in the initiation and progression of HF, and around one-third of patients with HF show some degree of renal dysfunction. In addition, treatment for HF often worsens renal function, consequently to hemodynamic and clinical improvement do not correspond an effective improvement in HF prognosis. Association between HF and renal impairment (RI) is now classified as cardiorenal syndrome (CRS) pointing out the bidirectional nature of this vicious circle leading to a mutual and progressive damage of both organs. The clinicians can rely on circulating biomarkers that give insights into the underlying pathogenetic mechanisms and help in risk stratification. Recently, a multimarker strategy including biomarker tool to traditional risk scores has been purposed and applied: Although each biomarker provided incremental outcome benefit, the combination of multiple biomarkers should offer the greatest improvement in risk prediction. Natriuretic peptides (NP) and cardiac troponins (TN) are the two biomarkers most studied in this setting, probably because of their organ-specific nature. However, both NP and TN cutoffs in presence of renal dysfunction need to be revised and discussed in relation to age, gender and stage of RI. In this context, the biomarkers are a unique opportunity to elucidate pathophysiological mechanisms, tailor clinical management to the single patient and improve outcomes. Specific studies about the exact role of biomarkers as in HF as in CRS should be planned and considered for future trials.

The impact of arteriovenous fistulae on the myocardium: the impact of creation and ligation in the transplant era

Cardiac hypertrophy is a relatively common complication seen in patients with advanced chronic kidney disease (CKD) and end-stage renal disease (ESRD). Moreover, cardiac hypertrophy is even more frequently seen in patients with ESRD who have an arteriovenous (AV) access. There has been substantial evidence pertaining to the effects of AV access creation on the heart structure and function. Similarly, there is increasing evidence on the effects of AV access closure, flow reduction, transplantation, and immunosuppressive medication on both endpoints. In this review, we present the evidence available in the literature on these topics and open the dialog for further research in this interesting field.

The use of fibroblast growth factor 23 testing in patients with kidney disease

The emergence of fibroblast growth factor 23 as a potentially modifiable risk factor in CKD has led to growing interest in its measurement as a tool to assess patient risk and target therapy. This review discusses the analytical and clinical challenges faced in translating fibroblast growth factor 23 testing into routine practice. As for other bone mineral markers, agreement between commercial fibroblast growth factor 23 assays is poor, mainly because of differences in calibration, but also, these differences reflect the variable detection of hormone fragments. Direct comparison of readout from different assays is consequently limited and likely hampers setting uniform fibroblast growth factor 23-directed targets. Efforts are needed to standardize assay output to enhance clinical use. Fibroblast growth factor 23 is robustly associated with cardiovascular and renal outcomes in patients with CKD and adds value to risk assessments based on conventional risk factors. Compared with most other mineral markers, fibroblast growth factor 23 shows better intraindividual temporal stability, with minimal diurnal and week-to-week variability, but substantial interindividual variation, maximizing discriminative power for risk stratification. Conventional therapeutic interventions for the CKD-mineral bone disorder, such as dietary phosphate restriction and use of oral phosphate binders or calcimimetics, are associated with variable efficacy at modulating circulating fibroblast growth factor 23 concentrations, like they are for other mineral metabolites. Dual therapy with dietary phosphate restriction and noncalcium-based binder use achieves the most consistent fibroblast growth factor 23-lowering effect and seems best monitored using an intact assay. Additional studies are needed to evaluate whether strategies aimed at reducing levels or antagonizing its action have beneficial effects on clinical outcomes in CKD patients. Moreover, a better understanding of the mechanisms driving fibroblast growth factor 23 elevations in CKD is needed to inform the use of therapeutic interventions targeting fibroblast growth factor 23 excess. This evidence must be forthcoming to support the use of fibroblast growth factor 23 measurement and fibroblast growth factor 23-directed therapy in the clinic.

Phosphate wasting and fibroblast growth factor-23

PURPOSE OF REVIEW

The purpose of this study is to review the regulation of phosphate and recent progress in fibroblast growth factor-23 (FGF-23), a key phosphate regulatory hormone.

RECENT FINDINGS

Phosphate is required for mineralization of bone, muscle strength and a host of biologic functions. Phosphate is sensed by bone that responds with secretion of FGF-23. The major action of FGF-23 is to stimulate phosphaturia. Feedback loops between FGF-23, 1,25-dihydroxyvitamin D3 and parathyroid hormone maintain phosphate homeostasis. Information about FGF-23 has accumulated from studies in patients with oncogenic osteomalacia and inherited disorders of phosphate wasting rickets that explains the pathophysiology. Exciting new discoveries have highlighted FGF-23 as an independent risk factor for cardiovascular disease in patients with chronic kidney disease. The phosphate sensor triggering FGF-23 production remains to be identified.

SUMMARY

Derangements in FGF-23 production, half-life or downstream response are responsible for several disorders of phosphate wasting, rickets and oncogenic osteomalacia. Very high levels of FGF-23 in renal failure are an independent risk for cardiovascular disease.

Fibroblast growth factor-23 and cardiovascular events in CKD

An elevated level of fibroblast growth factor-23 (FGF-23) is the earliest abnormality of mineral metabolism in CKD. High FGF-23 levels promote left ventricular hypertrophy but not coronary artery calcification. We used survival analysis to determine whether elevated FGF-23 is associated with greater risk of adjudicated congestive heart failure (CHF) and atherosclerotic events (myocardial infarction, stroke, and peripheral vascular disease) in a prospective cohort of 3860 participants with CKD stages 2-4 (baseline estimated GFR [eGFR], 44±15 ml/min per 1.73 m(2)). During a median follow-up of 3.7 years, 360 participants were hospitalized for CHF (27 events/1000 person-years) and 287 had an atherosclerotic event (22 events/1000 person-years). After adjustment for demographic characteristics, kidney function, traditional cardiovascular risk factors, and medications, higher FGF-23 was independently associated with graded risk of CHF (hazard ratio [HR], 1.45 per doubling [95% confidence interval (CI), 1.28 to 1.65]; HR for highest versus lowest quartile, 2.98 [95% CI, 1.97 to 4.52]) and atherosclerotic events (HR per doubling, 1.24 [95% CI, 1.09 to 1.40]; HR for highest versus lowest quartile, 1.76 [95% CI, 1.20 to 2.59]). Elevated FGF-23 was associated more strongly with CHF than with atherosclerotic events (P=0.02), and uniformly was associated with greater risk of CHF events across subgroups stratified by eGFR, proteinuria, prior heart disease, diabetes, BP control, anemia, sodium intake, income, fat-free mass, left ventricular mass index, and ejection fraction. Thus, higher FGF-23 is independently associated with greater risk of cardiovascular events, particularly CHF, in patients with CKD stages 2-4.

Predictors of high sensitivity cardiac troponin T in chronic kidney disease patients: a cross-sectional study in the chronic renal insufficiency cohort (CRIC)

Background

Cardiac troponin T is independently associated with cardiovascular events and mortality in patients with chronic kidney disease (CKD). Serum levels of high sensitivity cardiac troponin T (hs-TnT) reflect subclinical myocardial injury in ambulatory patients. We sought to determine the distribution and predictors of hs-TnT in CKD patients without overt cardiovascular disease (CVD).

Methods

We studied 2464 participants within the multi-ethnic Chronic Renal Insufficiency Cohort (CRIC) who did not have self-reported CVD. We considered renal and non-renal factors as potential determinants of hs-TnT, including demographics, comorbidities, left ventricular (LV) mass, serologic factors, estimated glomerular filtration rate (eGFR) and albumin to creatinine ratio.

Results

Hs-TnT was detectable in 81% of subjects, and the median (IQR) hs-TnT was 9.4 pg/ml (4.3-18.3). Analysis was performed using Tobit regression, adjusting for renal and non-renal factors. After adjustment, lower eGFR was associated with higher expected hs-TnT; participants with eGFR < 30 ml/min/1.73 m² had 3-fold higher expected hs-TnT compared to subjects with eGFR > 60. Older age, male gender, black race, LV mass, diabetes and higher blood pressure all had strong, independent associations with higher expected hs-TnT.

Conclusions

Knowledge of the determinants of hs-TnT in this cohort may guide further research on the pathology of heart disease in patients with CKD and help to stratify sub-groups of CKD patients at higher cardiovascular risk.

Associations between fibroblast growth factor 23 and cardiac characteristics in pediatric heart failure

BACKGROUND

In adults with heart failure, elevated levels of fibroblast growth factor 23 (FGF23) are associated with mortality. Data on FGF23 levels in pediatric heart failure are lacking.

PATIENTS AND METHODS

We conducted a cross-sectional study of 17 healthy children (mean age 13 years) and 20 pediatric patients with heart failure (mean age 12 years) who underwent echocardiography and for whom the following measurements were taken: plasma FGF23 and parathyroid hormone (PTH) and serum phosphate, creatinine and N-terminal prohormone brain natriuretic peptide (NT-proBNP). Symptom severity was assessed with the New York Heart Association and the Ross classification systems.

RESULTS

Of the 20 patients, 11 had dilated cardiomyopathy, four had congenital heart disease, three had hypertrophic cardiomyopathy, one had a failing heart transplant and one had pulmonary hypertension. Mean phosphate levels in these patients were within the reported reference range for healthy children. Median PTH levels were in the normal range in patients and controls. The median FGF23 level was higher in patients versus controls (110.9 vs. 66.4 RU/ml; P = 0.03) and higher in patients on diuretics versus other patients (222.4 vs. 82.1 RU/ml; P = 0.01). Levels of FGF23 and NT-proBNP were directly correlated (r = 0.47, P = 0.04), and patients with greater physical functional impairment had higher FGF23 levels (142.5 in those with moderate-severe limitation vs. 92.8 RU/ml in those with no limitation; P = 0.05). Among patients with dilated cardiomyopathy, higher FGF23 levels were associated with a greater left ventricular end-diastolic diameter (r = 0.63, P = 0.04).

CONCLUSION

FGF23 levels are elevated in children with heart failure and are associated with diuretic use, severity of heart failure and left ventricular dilation.