Fibroblast growth factor 23 and left ventricular mass index in maintenance hemodialysis patients: standard versus long nocturnal hemodialysis

The anti-aging factor Klotho protects against acquired long QT syndrome induced by uremia and promoted by fibroblast growth factor 23

BACKGROUND

Chronic kidney disease (CKD) is associated with increased propensity for arrhythmias. In this context, ventricular repolarization alterations have been shown to predispose to fatal arrhythmias and sudden cardiac death. Between mineral bone disturbances in CKD patients, increased fibroblast growth factor (FGF) 23 and decreased Klotho are emerging as important effectors of cardiovascular disease. However, the relationship between imbalanced FGF23-Klotho axis and the development of cardiac arrhythmias in CKD remains unknown.

METHODS

We carried out a translational approach to study the relationship between the FGF23-Klotho signaling axis and acquired long QT syndrome in CKD-associated uremia. FGF23 levels and cardiac repolarization dynamics were analyzed in patients with dialysis-dependent CKD and in uremic mouse models of 5/6 nephrectomy (Nfx) and Klotho deficiency (hypomorphism), which show very high systemic FGF23 levels.

RESULTS

Patients in the top quartile of FGF23 levels had a higher occurrence of very long QT intervals (> 490 ms) than peers in the lowest quartile. Experimentally, FGF23 induced QT prolongation in healthy mice. Similarly, alterations in cardiac repolarization and QT prolongation were observed in Nfx mice and in Klotho hypomorphic mice. QT prolongation in Nfx mice was explained by a significant decrease in the fast transient outward potassium (K⁺) current (I_tof), caused by the downregulation of K⁺ channel 4.2 subunit (Kv4.2) expression. Kv4.2 expression was also significantly reduced in ventricular cardiomyocytes exposed to FGF23. Enhancing Klotho availability prevented both long QT prolongation and reduced I_tof current. Likewise, administration of recombinant Klotho blocked the downregulation of Kv4.2 expression in Nfx mice and in FGF23-exposed cardiomyocytes.

CONCLUSION

The FGF23-Klotho axis emerges as a new therapeutic target to prevent acquired long QT syndrome in uremia by minimizing the predisposition to potentially fatal ventricular arrhythmias and sudden cardiac death in patients with CKD.

Circulating FGF23 is not associated with cardiac dysfunction, atherosclerosis, infection or inflammation in hemodialysis patients

Fibroblast growth factor (FGF) 23 is a bone-derived hormone regulating serum inorganic phosphate (Pi) concentration. FGF23 is also involved in the development of chronic kidney disease (CKD)-mineral and bone disorder. Serum FGF23 concentration begins to increase early in the progression of CKD and can be remarkably high in hemodialysis patients with end-stage renal disease. It has been reported that high FGF23 concentration is a risk factor for cardiac dysfunction, atherosclerosis, infection or systemic inflammation in CKD patients. FGF23 was also shown to induce cardiac hypertrophy directly acting on cardiomyocytes. However, it is still controversial whether high FGF23 is causing cardiac dysfunction, atherosclerosis, infection or systemic inflammation in CKD patients. In the current study, we investigated whether FGF23 concentration is associated with cardiac dysfunction, atherosclerosis, infection or systemic inflammation in Japanese hemodialysis patients. We recruited 119 hemodialysis patients and examined the association between serum FGF23 concentration and several parameters concerning mineral metabolism, cardiac dysfunction, atherosclerosis, infection, and systemic inflammation. Serum FGF23 concentration was independently associated with serum calcium and Pi concentration (β = 0.276, p < 0.001; β = 0.689, p < 0.001). However, serum FGF23 concentration was not associated with parameters of cardiac dysfunction, atherosclerosis, infection, and systemic inflammation, either. Our results do not support the hypothesis that high FGF23 in dialysis patients is the cause of cardiac dysfunction, atherosclerosis, infection or systemic inflammation.

Dual Roles of the Mineral Metabolism Disorders Biomarkers in Prevalent Hemodilysis Patients: In Renal Bone Disease and in Vascular Calcification

Background

Vascular calcification (VC) is highly prevalent in dialysis (HD) patients, and its mechanism is multifactorial. Most likely that systemic or local inhibitory factor is overwhelmed by promoters of VC in these patients. VC increased arterial stiffness, and left ventricular hypertrophy. Thus, the present study aimed to investigate the association of VC and myocardial remodeling and to analyze their relationship with VC promoters (fibroblast growth factor 23-FGF23, Klotho, intact parathormon-iPTH, vitamin D) in 56 prevalent HD patients (median values: age 54 yrs, HD vintage 82 months).

Methods

Besides routine laboratory analyzes, serum levels of FGF 23, soluble Klotho, iPTH, 1,25-dihydroxyvitamin D3; pulse wave velocity (PWV); left ventricular (LV) mass by ultrasound; and VCs score by Adragao method were measured.

Results

VC was found in 60% and LV concentric or eccentric hypertrophy in 50% patients. Dialysis vintage (OR 1.025, 95%CI 1.007–1.044, p=0.006) FGF23 (OR 1.006, 95% CI 0.992–1.012, p=0.029) and serum magnesium (OR 0.000, 95%CI 0.000–0.214, p=0.04) were associated with VC. Changes in myocardial geometry was associated with male sex (beta=-0.273, 95% CI -23.967 1.513, p=0.027), iPTH (beta 0.029, 95%CI -0.059–0.001, p=0.027) and vitamin D treatment (beta 25.49, 95%CI 11.325–39.667, p=0.001). Also, patients with the more widespread VC had the highest LV remodeling categories. PWV was associated patient’s age, cholesterol, diastolic blood pressure, LV mass (positively) and serum calcium (negatively), indicating potential link with atherosclerotic risk.

Conclusions

Despite to different risk factors for VC and myocardial remodeling, obtained results could indicate that risk factors intertwine in long-term treatment of HD patients and therefore careful and continuous correction of mineral metabolism disorders is undoubtedly of the utmost importance.

Vitamin D and Calcimimetics in Cardiovascular Disease

Cardiovascular disease has earned its place as one of the leading noncommunicable diseases that has become a modern-day global epidemic. The increasing incidence and prevalence of chronic kidney disease (CKD) has added to this enormous burden, given that CKD is now recognized as an established risk factor for accelerated cardiovascular disease. In fact, cardiovascular disease remains the leading cause of death in the CKD population, with significant prognostic implications. Alterations in vitamin D levels as renal function declines has been linked invariably to the development of cardiovascular disease beyond a mere epiphenomenon, and has become an important focus in recent years in our search for new therapies. Another compound, cinacalcet, which belongs to the calcimimetic class of agents, also has taken center stage over the past few years as a potential cardiovasculoprotective agent. However, given limited well-designed randomized trials to inform us, our clinical practice for the management of cardiovascular disease in CKD has not been adequately refined. This article considers the biological mechanisms, regulation, and current experimental, clinical, and trial data available to help guide the therapeutic use of vitamin D and calcimimetics in the setting of CKD and cardiovascular disease.

Cardiac hypertrophy elevates serum levels of fibroblast growth factor 23

Several experimental studies have shown that fibroblast growth factor 23 (FGF23) induces left ventricular hypertrophy (LVH). However, the opposite directional relationship, namely a potential effect of LVH on FGF23, remains uncertain. Here we evaluated the effects of LVH on FGF23 using cardiomyocyte-specific calcineurin A transgenic mice. At six weeks, these mice showed severe LVH, with elevated levels of serum intact FGF23. FGF23 levels were elevated in cardiomyocytes, but not osteocytes, of the transgenic animals. Moreover, transverse aortic constriction also upregulated myocardial FGF23 expression in wild type mice. The promoter region of the FGF23 gene contains two putative nuclear factors of activated T cells (NFAT)-binding sites, with NFAT1 activating the promoter in a proximal NFAT-binding site dependent manner. Neither serum, urinary, or fractional excretion values of calcium and phosphate nor serum levels of 1,25(OH)₂ vitamin D were different between wild type and transgenic mice. Moreover, the renal expression of FGF receptors and α-Klotho was comparable. However, plasma levels of antidiuretic hormone were significantly increased in the transgenic mice, and aquaporin-2 immunohistochemical staining was mainly positive in the apical membrane of the collecting duct, compared to a primarily cytoplasmic staining in wild type mice. Real-time PCR analyses of kidney CYP27B1 and CYP24A1 expression in wild type mice showed that exogenous antidiuretic hormone blocked FGF23's actions on these vitamin D activating or inactivating enzymes. Finally, the renal resistance of transgenic mice to FGF23 was partly overcome by tolvaptan. Thus, LVH in transgenic mice is associated with an increase in myocardial and serum intact FGF23, with the kidneys being protected against FGF23 excess by elevated antidiuretic hormone levels.

Clearance of Sclerostin, Osteocalcin, Fibroblast Growth Factor 23, and Osteoprotegerin by Dialysis

INTRODUCTION

Fibroblast growth factor (FGF23), sclerostin, osteocalcin, and osteoprotegerin are important factors that control mineral bone metabolism. End-stage renal disease is associated with the pronounced dysregulation of mineral bone metabolism; however, the impact and clearance of mineral bone metabolism factors during dialysis remain largely undescribed.

METHODS

In a cross-sectional study, 10 chronic hemodialysis patients were treated with hemodialysis for 8 h using a high-flux filter and a dialysate bath of 50% calculated total body water continuously recycled at a rate of 500 mL/min. Plasma and dialysate concentrations of FGF23, sclerostin, osteoprotegerin, and osteocalcin were measured at 1, 2, 4, 6, and 8 h permitting the estimation of dialysis clearance.

RESULTS

Clearance of FGF23 was 7.7 mL/min, of sclerostin was 7.6 mL/min, of osteoprotegerin was 1.2 mL/min, and of osteocalcin was 19.7 mL/min. Clearance of FGF23 was correlated to sclerostin and osteoprotegerin clearance and also to the ultrafiltration rate. Although, osteocalcin blood concentrations decreased during dialysis, they rebounded within 6 h. Overall, no significant changes in blood concentrations of the measure mineral bone metabolism factors were observed.

CONCLUSIONS

The intradialytic clearance of osteocalcin, FGF23, sclerostin, and osteoprotegerin occurs; however, only clearance of FGF23 is directly correlated with the ultrafiltration rate. The effects of dialytic clearance on mineral bone metabolism are, however, uncertain and intradialytic plasma concentrations of the studied substrates remained largely unchanged.

Patients with FGF23-related hypophosphatemic rickets/osteomalacia do not present with left ventricular hypertrophy

PURPOSE

Fibroblast growth factor 23 (FGF23) is a hormone regulating phosphate metabolism. Excessive actions of FGF23 cause several types of FGF23-related hypophosphatemic rickets/osteomalacia. Recently, it was reported that FGF23 levels were independently correlated with left ventricular hypertrophy (LVH) in patients with chronic kidney disease (CKD). In addition, FGF23 was also shown to cause cardiac hypertrophy directly acting on cardiomyocytes. However, there is no study indicating the correlation between FGF23 and LVH in adult patients with FGF23-related hypophosphatemic rickets/osteomalacia. Therefore, we examined the existence of LVH in these patients.

MATERIALS AND METHODS

We recruited consecutive 24 patients with FGF23-related hypophosphatemic diseases. Their serum intact FGF23 levels and the parameters associated with LVH, including left ventricular mass index (LVMI), relative wall thickness (RWT), Sokolow-Lyon voltage, and Cornell product, were measured. The correlations between FGF23 and these parameters were examined.

RESULTS

The participants did not show LVH on the whole. In addition, no significant correlation was observed by these examinations.

CONCLUSION

It seems unlikely that FGF23 levels are the apparent determinant of the cardiac mass in patients with FGF23-related hypophosphatemic rickets/osteomalacia.

Coronary artery calcification in CKD-5D patients is tied to adverse cardiac function and increased mortality

Background: Coronary artery calcification (CAC) is common in patients with chronic kidney disease on hemodialysis (CKD-5D) and is an important predictor of mortality. However, cardiac functional links between CAC and mortality have not been well established. This study tested the hypothesis that CAC increases mortality by adversely affecting cardiac function. Methods: Patients were recruited from 37 regional dialysis centers. 2-D and Doppler echocardiographic analyses were performed, and CAC was measured using 64-slice computed tomography. Relationships between CAC and echocardiographic measures of left ventricular (LV) function were analyzed. Survival was assessed with median follow-up of 37 months. Results: There were 157 patients: 59% male, 46% Caucasian, 48% diabetic. Median age was 55 years, and median duration of CKD-5D was 45 months. Agatston CAC scores > 100 were found in 69% of patients, with 51% having a score > 400. CAC was associated with measures of LV systolic and diastolic function (global longitudinal strain (GLS; rho = 0.270, p = 0.004)), peak LV systolic velocity (rho = –0.259, p = 0.004), and estimate of LV filling pressure (E:E’; rho = 0.286, p = 0.001). Multivariate regression confirmed these relationships after adjustment for age, gender, LV ejection fraction, and coronary artery disease. Valvular calcification varied linearly with CAC (p < 0.05). Both LV diastolic and systolic functional measures were significant predictors of mortality, the strongest of which was LV diastolic dysfunction. Conclusions: These findings show a link between CAC, cardiac function, and mortality in CKD-5D. LV diastolic function (E:E’), peak LV systolic velocity, and GLS are independent predictors of mortality. Valvular calcification may be an important marker of CAC in CKD-5D. These effects on cardiac function likely explain the high mortality with CKD-5D and describe a potentially-valuable role for echocardiography in the routine management of these patients.

Association of serum intact fibroblast growth factor 23 with left ventricular mass and different echocardiographic findings in patients on hemodialysis

OBJECTIVES

To determine the association of fibroblast growth factor 23 (FGF23) with left ventricular hypertrophy (LVH) through the assessment of left ventricular (LV) mass and left ventricular mass index (LVMI) in patients on hemodialysis, this study was done.

METHODS

All patients on hemodialysis who are older than 18 years and in whom hemodialysis vintage was at least 6 months were enrolled. All patients were on hemodialysis thrice a week for 4 h using low-flux dialysis filters, polysulfone membranes, reverse osmosis purified water, and bicarbonate-base hemodialysis solution. The exclusion criteria were any respiratory illness or pulmonary infection, cigarette smoking, and the presence of pericarditis or pericardial effusion. Additionally, patients with a known coronary artery disease, any form of cardiac arrhythmias, any cardiomyopathy or severe valvular heart disease diagnosed by echocardiography, acute congestive heart failure (CHF), and acute myocardial infarction were not included. Echocardiography was conducted by an experienced operator for all the enrolled patients using the ACUSON SC2000™ ultrasound system transducer (Siemens), with a frequency bandwidth of: 1.5-3.5 MHz. Patients were considered to have LVH if the LVMI was greater than 134 g/m² for men and greater than 110 g/m² for women.

RESULTS

A total of 61 patients (19 female and 42 male) were enrolled to the study. Mean (± SD) age of the patients was 59.6 ± 13.1 years. The median duration of hemodialysis was 23 (range: 6-120) months. The median predialysis level of FGF23 was 1,977 pg/mL (range: 155-8,870). LVH was seen in 73.8% of the patients (n = 45) and of them 66.7% were male. There was a statistically significant direct correlation between FGF23 and left ventricle diameter in end systole (LVDs) (r = 0.29, P = 0.027). However, the association of FGF23 with LV mass, LVMI, and left ventricular ejection fraction (LVEF) was not significant.

CONCLUSION

This study does not show the correlation between FGF23 and LV mass in stable hemodialysis patients.

A 4-month programme of in-centre nocturnal haemodialysis was associated with improvements in patient outcomes

BACKGROUND

Extended periods of haemodialysis (HD) can improve patient outcomes. In-centre nocturnal haemodialysis (INHD) should be explored as a method of offering extended periods of HD to patients unsuitable for or unable to perform home therapy.

METHODS

Ten self-selecting, prevalent HD patients started an INHD programme to assess feasibility and patient satisfaction. Quality-of-life (QOL) measures were evaluated at enrolment and after 4 months of INHD using the EQ-5D, the Hospital Anxiety and Depression Scale (HADS) and the SF-12 questionnaires. Demographic, biochemical and haematological data and data on dialysis adequacy were collected before starting INHD and after 4 months.

RESULTS

Three of the 10 patients failed to complete the 2-week run-in period. Seven patients completed the 4-month programme, with mean dialysis time of 355 ± 43.92 min throughout the period. The EQ-5D visual analogue score improved from 48 ± 16.89 to 72 ± 13.2 (P = 0.003) and the HADS anxiety score decreased from 9 ± 5.83 to 3.57 ± 3.04 (P = 0.029). The urea reduction ratio improved from 71.57 ± 2.29% to 80.43 ± 3.101% (P < 0.001), with improvements in phosphate control, reducing to within the target range from 1.73 ± 0.6 to 1.2 ± 0.2 (P = 0.08). Ultrafiltration (UF) volumes increased during the study from 2000 ± 510 to 2606 ± 343 mL (P = 0.015); there was a significant reduction in mean UF rate adjusted for body weight from 6.47 ± 1.71 to 4.61 ± 1.59 mL/kg/h (P = 0.032). Sensitivity analyses confirmed the significance of these results.

CONCLUSIONS

This single-centre study showed a 4-month programme of extended hours INHD is safe and associated with improvements in QOL measures, decreased UF rates and measures of dialysis adequacy. These data have been used to expand our service and inform the design of future randomized controlled trials to examine medical endpoints.

Non-Linear Heart Rate Variability Indices in the Frequent Hemodialysis Network Trials of Chronic Hemodialysis Patients

BACKGROUND

Non-linear heart rate variability (HRV) indices were hypothesized to correlate with cardiac function, fluid overload and physical performance in hemodialysis patients.

METHODS

Twenty-four-hour Holter electrocardiograms were recorded in patients enrolled in the Frequent Hemodialysis Network (FHN) Daily Dialysis Trial. Correlations between non-linear HRV indices and left ventricular ejection fraction (LVEF), left ventricular end-diastolic volume (LVEDV), extracellular volume (ECV)/total body water (TBW) ratio, the SF-36 Physical Health Composite (PHC) and Physical Functioning (PF) scores were tested.

RESULTS

We studied 210 subjects (average age 49.8 ± 13.5 years, 62% men, 42% diabetics). In non-diabetic patients, multiscale entropy (MSE) slope sample entropy (SampEn) and approximate entropy (ApEn) correlated positively with LVEF, PF and PHC and inversely with LVEDV and ECV/TBW. Spectral power slope correlated positively with ECV/TBW (r = 0.27). Irregularity measures (MSE ApEn and MSE SampEn) correlated positively with LVEDV (r = 0.19 and 0.20).

CONCLUSION

Non-linear HRV indices indicated an association between a deteriorated heart rate regulatory system and impaired cardiac function, fluid accumulation and poor physical condition.