Association between FGF23, α-Klotho, and Cardiac Abnormalities among Patients with Various Chronic Kidney Disease Stages

New Insights on Cardiac Arrhythmias in Patients With Kidney Disease

The risk of arrhythmia and its management become increasingly complex as kidney disease progresses. This presents a multifaceted clinical challenge. Our discussion addresses these specific challenges relevant to patients as their kidney disease advances. We highlight numerous opportunities for enhancing the current standard of care within this realm. Additionally, this review delves into research concerning early detection, prevention, diagnosis, and treatment of various arrhythmias spanning the spectrum of kidney disease.

Klotho and Clinical Outcomes in CKD: Findings From the Chronic Renal Insufficiency Cohort (CRIC) Study

RATIONALE & OBJECTIVE

Klotho deficiency may affect clinical outcomes in chronic kidney disease (CKD) through fibroblast growth factor-23 (FGF23)-dependent and -independent pathways. However, the association between circulating Klotho and clinical outcomes in CKD remains unresolved and was the focus of this study.

STUDY DESIGN

Prospective observational study.

SETTING & PARTICIPANTS

1,088 participants in the Chronic Renal Insufficiency Cohort (CRIC) Study with an estimated glomerular filtration rate (eGFR) of 20-70mL/min/1.73m2.

EXPOSURE

Plasma Klotho level at the year-1 study visit.

OUTCOMES

5-year risks of all-cause mortality, heart failure hospitalization, atherosclerotic cardiovascular events, and a composite kidney end point that comprised a sustained 50% decrease in eGFR, dialysis, kidney transplant, or eGFR<15mL/min/1.73m2.

ANALYTICAL APPROACH

We divided Klotho into 6 groups to account for its nonnormal distribution. We used Cox proportional hazards regression and subdistribution hazards models to compare survival and clinical outcomes, respectively, between Klotho groups. We sequentially adjusted for demographic characteristics, kidney function, cardiovascular risk factors, sample age, and FGF23.

RESULTS

Mean eGFR was 42mL/min/1.73m2, and median Klotho concentration was 0.31ng/mL (IQR, 0.10-3.27ng/mL). When compared with the lowest Klotho group, survival (HR, 0.77; 95% CI, 0.32-1.89), heart failure hospitalization (HR, 1.10; 95% CI, 0.38-3.17), atherosclerotic cardiovascular events (HR, 1.19; 95% CI, 0.57-2.52), and CKD progression (HR, 1.05; 95% CI, 0.58-1.91) did not differ in the high Klotho group. In contrast, FGF23 was significantly associated with mortality and heart failure hospitalization independent of Klotho levels.

LIMITATIONS

Despite adjustments, we cannot exclude the potential influence of residual confounding or sample storage on the results. A single measurement of plasma Klotho concentration may not capture Klotho patterns over time.

CONCLUSIONS

In a large, diverse, well-characterized CKD cohort, Klotho was not associated with clinical outcomes, and Klotho deficiency did not confound the association of FGF23 with mortality or heart failure hospitalization.

PLAIN-LANGUAGE SUMMARY

Klotho is a protein that is vital to mineral metabolism and aging and may protect against cardiovascular disease. Klotho levels decrease in chronic kidney disease (CKD), but the association between Klotho and clinical outcomes in CKD remains uncertain. In a prospective cohort study of more than 1,000 people with CKD, circulating Klotho levels were not associated with kidney disease progression, cardiovascular outcomes, or mortality. These results suggest that the decrease in circulating Klotho levels in CKD does not play a prominent role in the development of poor clinical outcomes.

FGF23 and klotho at the intersection of kidney and cardiovascular disease

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease (CKD). As CKD progresses, CKD-specific risk factors, such as disordered mineral homeostasis, amplify traditional cardiovascular risk factors. Fibroblast growth factor 23 (FGF23) regulates mineral homeostasis by activating complexes of FGF receptors and transmembrane klotho co-receptors. A soluble form of klotho also acts as a 'portable' FGF23 co-receptor in tissues that do not express klotho. In progressive CKD, rising circulating FGF23 levels in combination with decreasing kidney expression of klotho results in klotho-independent effects of FGF23 on the heart that promote left ventricular hypertrophy, heart failure, atrial fibrillation and death. Emerging data suggest that soluble klotho might mitigate some of these effects via several candidate mechanisms. More research is needed to investigate FGF23 excess and klotho deficiency in specific cardiovascular complications of CKD, but the pathophysiological primacy of FGF23 excess versus klotho deficiency might never be precisely resolved, given the entangled feedback loops that they share. Therefore, randomized trials should prioritize clinical practicality over scientific certainty by targeting disordered mineral homeostasis holistically in an effort to improve cardiovascular outcomes in patients with CKD.

Pathophysiological concepts and screening of cardiovascular disease in dialysis patients

Dialysis patients experience 10-20 times higher cardiovascular mortality than the general population. The high burden of both conventional and nontraditional risk factors attributable to loss of renal function can explain higher rates of cardiovascular disease (CVD) morbidity and death among dialysis patients. As renal function declines, uremic toxins accumulate in the blood and disrupt cell function, causing cardiovascular damage. Hemodialysis patients have many cardiovascular complications, including sudden cardiac death. Peritoneal dialysis puts dialysis patients with end-stage renal disease at increased risk of CVD complications and emergency hospitalization. The current standard of care in this population is based on observational data, which has a high potential for bias due to the paucity of dedicated randomized clinical trials. Furthermore, guidelines lack specific guidelines for these patients, often inferring them from non-dialysis patient trials. A crucial step in the prevention and treatment of CVD would be to gain better knowledge of the influence of these predisposing risk factors. This review highlights the current evidence regarding the influence of advanced chronic disease on the cardiovascular system in patients undergoing renal dialysis.

Upstream and downstream regulators of Klotho expression in chronic kidney disease

Klotho is a critical protein that protects the kidney. Klotho is severely downregulated in chronic kidney disease (CKD), and its deficiency is implicated in the pathogenesis and progression of CKD. Conversely, an increase in Klotho levels results in improved kidney function and delays CKD progression, supporting the notion that modulating Klotho levels could represent a possible therapeutic strategy for CKD treatment. Nevertheless, the regulatory mechanisms responsible for the loss of Klotho remain elusive. Previous studies have demonstrated that oxidative stress, inflammation, and epigenetic modifications can modulate Klotho levels. These mechanisms result in a decrease in Klotho mRNA transcript levels and reduced translation, thus can be grouped together as upstream regulatory mechanisms. However, therapeutic strategies that aim to rescue Klotho levels by targeting these upstream mechanisms do not always result in increased Klotho, indicating the involvement of other regulatory mechanisms. Emerging evidence has shown that endoplasmic reticulum (ER) stress, the unfolded protein response, and ER-associated degradation also affect the modification, translocation, and degradation of Klotho, and thus are proposed to be downstream regulatory mechanisms. Here, we discuss the current understanding of upstream and downstream regulatory mechanisms of Klotho and examine potential therapeutic strategies to upregulate Klotho expression for CKD treatment.

FGF23 in Chronic Kidney Disease: Bridging the Heart and Anemia

Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone produced mainly in osteocytes. In chronic kidney disease (CKD) FGF23 levels increase due to higher production, but also as the result of impaired cleavage and reduced excretion from the body. FGF23 has a significant role in disturbed bone and mineral metabolism in CKD, which leads to a higher cardiovascular risk and mortality in these patients. Current research has emphasized the expression of FGF23 in cardiac myocytes, fibroblasts, and endothelial cells, and in addition to the effects on the kidney, its primary role is in cardiac remodeling in CKD patients. Recent discoveries found a significant link between increased FGF23 levels and anemia development in CKD. This review describes the FGF23 role in cardiac hypertrophy and anemia in the setting of CKD and discusses the best therapeutical approach for lowering FGF23 levels.

Correlation study of FGF23/D-serine in maintenance hemodialysis patients with combined hearing impairment

BACKGROUND

Recent studies have reported an association between chronic renal failure and hearing impairment. Yet, the exact mechanism of action is still not fully understood. In this study, we investigated the expression of fibroblast growth factor 23 (FGF23) and D-serine in maintenance hemodialysis (MHD) patients with end-stage renal disease (ESRD) complicated with hearing impairment and further investigated the correlation between FGF23/D-serine and hearing impairment.

METHODS

A total of 90 subjects, including 30 MHD patients complicated with hearing impairment, 30 MHD patients with normal hearing, and 30 controls, were included in this case-control study. Relevant data were obtained by questionnaire survey, audiometric test, enzyme-linked immunosorbent assay (ELISA) to determine FGF23 level, and high-performance liquid chromatography to determine D-serine level.

RESULTS

MHD patients showed abnormally high expression of FGF23 and D-serine, where FGF23 and D-serine levels were significantly higher in the group with hearing impairment than in the group with normal hearing and normal controls (all P<0.01). Also, elevated FGF23 and D-serine were identified as risk factors for hearing impairment in ESRD, with ORs of 16.54 (95%CI, 2.75-99.55) and 15.22 (95%CI, 2.59-89.51), respectively. Further Person correlation analysis showed a moderate positive correlation between FGF23 and D-serine (r = 0.683, P<0.001).

CONCLUSION

This study provides potential biomarkers for the early detection of hearing impairment complicated by chronic renal failure, and the reduction of FGF23/D-serine may provide a potential target for the treatment of hearing impairment complicated by chronic renal failure.

Global longitudinal strain is superior to ejection fraction for detecting myocardial dysfunction in end-stage renal disease with hyperparathyroidism

BACKGROUND

The estimation of left ventricular ejection fraction (LVEF) by 2D echocardiography (2D-ECHO) is the most used tool to assess LV systolic function (LVSF). Global longitudinal strain (GLS) has recently been suggested as a superior method for several evaluations. This study explored the association and prevalence of LV systolic dysfunction (LVSD) by using these methods in patients with end-stage renal disease (ESRD) and severe hyperparathyroidism (SHPTH); both associated with cardiovascular events (CEs).

AIM

To evaluate the myocardial function in patients with ESRD and SHPTH by using the GLS and LVEF measured through conventional 2D-ECHO.

METHODS

In 62 patients with ESRD and SHPTH, asymptomatic, and without a history of CEs, LVSF was evaluated by 2D-ECHO, obtaining the EF, by the Simpson biplane method, and GLS by speckle tracking.

RESULTS

The total patients with ESRD had a preserved LVEF (> 50%) but abnormal GLS (< 13.55%). Additionally, multivariate analysis showed an independent association of GLS and serum parathyroid hormone (PTH), LV mass index, and hemoglobin. Also, PTH was independently associated with lateral e' wave and tricuspid regurgitation velocity.

CONCLUSION

In patients with SHPTH linked to ESRD, the use of GLS by 2D-ECHO is a more sensitive tool than LVEF for detecting LVSD.

Chronic Kidney Disease-Mineral Bone Disease biomarkers in kidney transplant patients

Background:

Chronic Kidney Disease associated with Mineral Bone Disease (CKD-MBD) is frequent in kidney transplant patients. Post-transplantation bone disease is complex, especially in patients with pre-existing metabolic bone disorders that are further affected by immunosuppressive medications and changes in renal allograft function. Main biochemical abnormalities of mineral metabolism in kidney transplantation (KTx) include hypophosphatemia, hyperparathyroidism (HPTH), insufficiency or deficiency of vitamin D, and hypercalcemia.

Objective:

This review aimed to summarize the pathophysiology and main biomarkers of CKD-MBD in KTx.

Methods:

A comprehensive and non-systematic search in PubMed was independently made with an emphasis on biomarkers in mineral bone disease in KTx.

Results:

CKD-MBD can be associated with numerous factors including secondary HPTH, metabolic dysregulations before KTx, and glucocorticoids therapy in post-transplant subjects. Fibroblast growth factor 23 (FGF23) reaches normal levels after KTx with good allograft function, while calcium, vitamin D and phosphorus, ultimately, result in hypercalcemia, persistent vitamin D insufficiency, and hypophosphatemia respectively. As for PTH levels, there is an initial tendency of a significant decrease, followed by a raise due to secondary or tertiary HPTH. In regard to sclerostin levels, there is no consensus in the literature.

Conclusion:

KTx patients should be continuously evaluated for mineral homeostasis and bone status, both cases with successful kidney transplantation and those with reduced functionality. Additional research on CKD-MBD pathophysiology, diagnosis, and management is essential to guarantee long-term graft function, better prognosis, good quality of life, and reduced mortality for KTx patients.

The Predialysis Serum Sodium Level Modifies the Effect of Hemodialysis Frequency on Left-Ventricular Mass: The Frequent Hemodialysis Network Trials

INTRODUCTION

The Frequent Hemodialysis Network (FHN) Daily and Nocturnal trials aimed to compare the effects of hemodialysis (HD) given 6 versus 3 times per week. More frequent in-center HD significantly reduced left-ventricular mass (LVM), with more pronounced effects in patients with low urine volumes. In this study, we aimed to explore another potential effect modifier: the predialysis serum sodium (SNa) and related proxies of plasma tonicity.

METHODS

Using data from the FHN Daily and Nocturnal Trials, we compared the effects of frequent HD on LVM among patients stratified by SNa, dialysate-to-predialysis serum-sodium gradient (GNa), systolic and diastolic blood pressure, time-integrated sodium-adjusted fluid load (TIFL), and extracellular fluid volume estimated by bioelectrical impedance analysis.

RESULTS

In 197 enrolled subjects in the FHN Daily Trial, the treatment effect of frequent HD on ∆LVM was modified by SNa. When the FHN Daily Trial participants are divided into lower and higher predialysis SNa groups (less and greater than 138 mEq/L), the LVM reduction in the lower group was substantially higher (-28.0 [95% CI -40.5 to -15.4] g) than in the higher predialysis SNa group (-2.0 [95% CI -15.5 to 11.5] g). Accounting for GNa, TIFL also showed more pronounced effects among patients with higher GNa or higher TIFL. Results in the Nocturnal Trial were similar in direction and magnitude but did not reach statistical significance.

DISCUSSION/CONCLUSION

In the FHN Daily Trial, the favorable effects of frequent HD on left-ventricular hypertrophy were more pronounced among patients with lower predialysis SNa and higher GNa and TIFL. Whether these metrics can be used to identify patients most likely to benefit from frequent HD or other dialytic or nondialytic interventions remains to be determined. Prospective, adequately powered studies studying the effect of GNa reduction on mortality and hospitalization are needed.

The Complexity of FGF23 Effects on Cardiomyocytes in Normal and Uremic Milieu

Fibroblast growth factor-23 (FGF23) appears to be one of the most promising biomarkers and predictors of cardiovascular risk in patients with heart disease and normal kidney function, but moreover in those with chronic kidney disease (CKD). This review summarizes the current knowledge of FGF23 mechanisms of action in the myocardium in the physiological and pathophysiological state of CKD, as well as its cross-talk to other important signaling pathways in cardiomyocytes. In this regard, current therapeutic possibilities and future perspectives are also discussed.

The effect of vitamin D supplementation on fibroblast growth factor-23 in patients with chronic kidney disease: A systematic review and meta-analysis

This is a meta-analysis of randomized controlled trials (RCTs) investigating the effects of oral vitamin D supplementation on serum fibroblast growth factor-23 (FGF23) concentrations in patients with chronic kidney disease (CKD). Manuscripts were extracted from PubMed/MEDLINE, Scopus, and ISI Web of Science through February 2020. Subgroup analyses, sensitivity analysis, and meta-regression assessments were performed. A total of eight clinical trials with nine treatment arms were included in the final analysis. The pooled results showed no significant changes in circulating FGF23 following vitamin D supplementation compared to the control group (Standardized mean difference (SMD): 0.24; 95% confidence intervals (CIs): -0.03 to 0.50, p > 0.05). Subgroup analyses found that studies which had participants with a body mass index (BMI) higher than 25 kg/m² , with an intervention duration shorter than 15 weeks, using phosphate binder medications, and trials that were on both patients with CKD undergoing hemodialysis and patients without hemodialysis treatment produced significant increases in FGF23 when concentration compared with the control group. This meta-analysis provides evidence that vitamin D supplementation does not have a significant effect on plasma FGF23 levels. However, further high-quality trials are required to identify the influence of oral vitamin D supplementation on FGF23 levels in patients with CKD.

High FGF23 Levels Failed to Predict Cardiac Hypertrophy in Animal Models of Hyperphosphatemia and Chronic Renal Failure

Increased fibroblast growth factor 23 (FGF23) levels are an independent predictor for adverse cardiac events suggesting a role as a link that drives cardiomyopathic changes in cardiorenal syndrome. The search for the underlying mechanism driving this interaction has led to the hypothesis that FGF23 causes pathogenic changes in the heart. Increased serum FGF23 has been independently shown to cause increased cardiac morbidity, mortality, and hypertrophy by signalling through FGF receptor 4. This mechanistic concept was based on preclinical studies demonstrating inhibition of FGF23 signaling through FGF4, which led to suppression of left ventricular hypertrophy and fibrosis in a 2-week rat 5/6 nephrectomy study and a 12-week (2%) high-phosphate diet mouse model in which FGF23 levels were markedly elevated. In this report, renal dysfunction was observed in the 5/6 nephrectomy model, and FGF23 levels were significantly elevated, whereas no changes in left ventricular hypertrophy were observed at 2 or 4 weeks postnephrectomy. Mice placed on a high-phosphate diet that did not cause significant renal dysfunction resulted in significantly elevated FGF23 but no changes in left ventricular hypertrophy. The in vivo studies reported here, which were performed to recapitulate the observations of FGF23 as a driver of cardiac hypertrophy, did not lend support to the FGF23-driven cardiac remodelling hypothesis.

Fibroblast growth factor 23 decreases PDE4 expression in heart increasing the risk of cardiac arrhythmia; Klotho opposes these effects

The concentration of fibroblast growth factor 23 (FGF23) rises progressively in renal failure (RF). High FGF23 concentrations have been consistently associated with adverse cardiovascular outcomes or death, in chronic kidney disease (CKD), heart failure or liver cirrhosis. We identified the mechanisms whereby high concentrations of FGF23 can increase the risk of death of cardiovascular origin. We studied the effects of FGF23 and Klotho in adult rat ventricular cardiomyocytes (ARVMs) and on the heart of mice with CKD. We show that FGF23 increases the frequency of spontaneous calcium waves (SCWs), a marker of cardiomyocyte arrhythmogenicity, in ARVMs. FGF23 increased sarcoplasmic reticulum Ca²⁺ leakage, basal phosphorylation of Ca²⁺-cycling proteins including phospholamban and ryanodine receptor type 2. These effects are secondary to a decrease in phosphodiesterase 4B (PDE4B) in ARVMs and in heart of mice with RF. Soluble Klotho, a circulating form of the FGF23 receptor, prevents FGF23 effects on ARVMs by increasing PDE3A and PDE3B expression. Our results suggest that the combination of high FGF23 and low sKlotho concentrations decreases PDE activity in ARVMs, which favors the occurrence of ventricular arrhythmias and may participate in the high death rate observed in patients with CKD.

Serum hepcidin level, iron metabolism and osteoporosis in patients with rheumatoid arthritis

Hepcidin, a major regulator of iron metabolism and homeostasis, is regulated by inflammation. Recent studies have suggested that hepcidin and iron metabolism are involved in osteoporosis, and the aim of this study was to determine whether serum hepcidin levels are correlated with the degree of osteoporosis in patients with rheumatoid arthritis (RA). A total of 262 patients with RA (67.5 ± 11.4 years; 77.5% female) were enrolled. Serum iron, ferritin, and hepcidin levels were positively correlated each other. Multiple regression analyses revealed that the serum iron level was positively correlated with femoral T and Z scores, whereas the serum hepcidin level was not. Serum hepcidin level was correlated with the serum 25-hydroxy vitamin D level, which was in turn positively related to the femoral Z score. Serum hepcidin and serum iron were indirectly and directly related to osteoporosis in patients with RA.

Fibroblast growth factor 23 is associated with fractional excretion of sodium in patients with chronic kidney disease

BACKGROUND

Recent studies suggest that the phosphaturic hormone fibroblast growth factor 23 (FGF23) is involved in regulation of renal sodium excretion and blood pressure. There is evidence of both direct effects via regulation of the sodium-chloride symporter (NCC) in the distal tubule, and indirect effects through interactions with the renin-angiotensin-aldosterone system. However, clinical data on the association between FGF23 and renal sodium regulation is lacking. Herein, we investigated the associations of FGF23 with renal sodium handling and blood pressure in non-dialysis CKD patients.

METHODS

This was a cross-sectional study encompassing 180 CKD patients Stage 1-5, undergoing renal biopsy. Plasma intact FGF23, 24-h urinary sodium excretion, fractional excretion of sodium (FENa) and blood pressure were measured at baseline. The association between FGF23 and renal sodium handling was explored by multivariate regression analysis.

RESULTS

The median age was 52.8 years, 60.6% were men and the median estimated glomerular filtration rate (eGFR) was 50.6 mL/min/1.73 m2. In univariate analysis, FGF23 was positively associated with FENa (Spearman's rho = 0.47; P < 0.001) and systolic blood pressure (rho = 0.17, P < 0.05), but not with plasma sodium, 24-h urinary sodium excretion or mean arterial blood pressure. The association between FGF23 and FENa remained significant after adjustment for potential confounders (multivariable adjusted β coefficient 0.60, P < 0.001). This association was stronger among the 107 individuals with eGFR <60 mL/min/1.73 m2 (β = 0.47, P = 0.04) and in the 73 individuals on any diuretics (β = 0.88, P < 0.001). Adjustment for measured GFR instead of eGFR did not alter the relationship.

CONCLUSIONS

FGF23 is independently associated with increased FENa in non-dialysis CKD patients. These data do not support the notion that FGF23 causes clinically significant sodium retention. Further studies are warranted to explore the mechanism underlying this association.

Klotho/FGF23 and Wnt Signaling as Important Players in the Comorbidities Associated with Chronic Kidney Disease

Fibroblast Growth Factor 23 (FGF23) and Klotho play an essential role in the regulation of mineral metabolism, and both are altered as a consequence of renal failure. FGF23 increases to augment phosphaturia, which prevents phosphate accumulation at the early stages of chronic kidney disease (CKD). This effect of FGF23 requires the presence of Klotho in the renal tubules. However, Klotho expression is reduced as soon as renal function is starting to fail to generate a state of FGF23 resistance. Changes in these proteins directly affect to other mineral metabolism parameters; they may affect renal function and can produce damage in other organs such as bone, heart, or vessels. Some of the mechanisms responsible for the changes in FGF23 and Klotho levels are related to modifications in the Wnt signaling. This review examines the link between FGF23/Klotho and Wnt/β-catenin in different organs: kidney, heart, and bone. Activation of the canonical Wnt signaling produces changes in FGF23 and Klotho and vice versa; therefore, this pathway emerges as a potential therapeutic target that may help to prevent CKD-associated complications.

Fibroblast Growth Factor-23 and Heart Failure With Reduced Versus Preserved Ejection Fraction: MESA

Background

Higher fibroblast growth factor‐23 (FGF‐23) levels are associated with incident heart failure (HF) in MESA (the Multiethnic Study of Atherosclerosis). FGF‐23 is also associated with left ventricular hypertrophy. Whether the FGF‐23 association with HF is similar for heart failure with reduced ejection fraction (HFrEF) and heart failure with preserved ejection fraction (HFpEF) is not well established.

Methods and Results

We studied 6542 participants (mean age 62±10 years, 53% women, mean estimated glomerular filtration rate of 81±18 mL/min per 73 m²) from MESA who were free of cardiovascular disease at baseline (2000–2002). HF events were ascertained by an adjudication committee for a median follow‐up of 12.1 years. We classified HF events as HFrEF (ejection fraction [EF] <50%) or HFpEF [EF] ≥50%) at the time of diagnosis. Cox proportional hazard regression was used to compute hazard ratios and 95% confidence intervals for the association between baseline serum FGF‐23 and incident HFrEF and HFpEF. A total of 134 events were classified as HFpEF, 151 HFrEF, and 49 unknown EF. Following imputation, 149 were classified as HFpEF, 176 HFrEF, and 291 participants had HF (34 participants had HFpEF then HFrEF). In the fully adjusted model, higher FGF‐23 levels were associated with incident HFpEF but not with HFrEF (hazard ratio 1.29, 95% confidence interval, 1.08–1.54) versus (hazard ratio 1.04, 95% confidence interval, 0.84–1.29) for each 20 pg/mL higher serum FGF‐23 concentration.

Conclusions

FGF‐23 association with HF is driven by the association with HFpEF but not with HFrEF in a population‐based cohort. Further studies are needed to determine the pathological mechanisms mediating this association.

Chronic Kidney Disease as a Risk Factor for Heart Failure With Preserved Ejection Fraction: A Focus on Microcirculatory Factors and Therapeutic Targets

Heart failure (HF) and chronic kidney disease (CKD) co-exist, and it is estimated that about 50% of HF patients suffer from CKD. Although studies have been performed on the association between CKD and HF with reduced ejection fraction (HFrEF), less is known about the link between CKD and heart failure with preserved ejection fraction (HFpEF). Approximately, 50% of all patients with HF suffer from HFpEF, and this percentage is projected to rise in the coming years. Therapies for HFrEF are long established and considered quite successful. In contrast, clinical trials for treatment of HFpEF have all shown negative or disputable results. This is likely due to the multifactorial character and the lack of pathophysiological knowledge of HFpEF. The typical co-existence of HFpEF and CKD is partially due to common underlying comorbidities, such as hypertension, dyslipidemia and diabetes. Macrovascular changes accompanying CKD, such as hypertension and arterial stiffening, have been described to contribute to HFpEF development. Furthermore, several renal factors have a direct impact on the heart and/or coronary microvasculature and may underlie the association between CKD and HFpEF. These factors include: (1) activation of the renin-angiotensin-aldosterone system, (2) anemia, (3) hypercalcemia, hyperphosphatemia and increased levels of FGF-23, and (4) uremic toxins. This review critically discusses the above factors, focusing on their potential contribution to coronary dysfunction, left ventricular stiffening, and delayed left ventricular relaxation. We further summarize the directions of novel treatment options for HFpEF based on the contribution of these renal drivers.

Resveratrol and 1,25-dihydroxyvitamin D co-administration protects the heart against D-galactose-induced aging in rats: evaluation of serum and cardiac levels of klotho

The current study investigates the cooperative cardioprotective effect of calcitriol (active form of vitamin D) combined with resveratrol in a rat model of D-galactose (D.gal)-induced aging. Male Wistar rats received resveratrol (D.gal + Res), calcitriol (D.gal + Cal), or a combination of them (D.gal + Res + Cal). Intact animals served as control (Ctl). Blood pressure (BP) was recorded by cannulation of the left carotid artery. Fibrosis and cell size were assessed by Masson's trichrome and hematoxylin-eosin staining, respectively. Cardiac and serum level of antiaging protein, klotho, was measured by ELISA assay method. Gene expression was evaluated by real-time RT-PCR. Biochemical tests were performed according to the standardized method. In D.gal + Res + Cal group, BP, heart weight-to-body weight ratio, and cardiomyocytes size decreased significantly compared with D-gal group. The cardiac transcription levels of catalase and superoxide dismutase 1 and 2 were upregulated in D.gal + Res + Cal compared to the D.gal group (P < 0.001, P < 0.05, P < 0.05, respectively). Increased level of malondialdehyde was observed in D.gal group (P < 0.01 vs. Ctl) which was normalized partially in D.gal + Res + Cal group (P < 0.05). Catalase and superoxide dismutase activity also increased in D.gal + Res + Cal group (P < 0.01 vs. D.gal). Cardiac Klotho, as the antiaging protein, remained unchanged at mRNA and protein levels among the experimental groups. The serum level of Klotho did not change significantly in D.gal group; however, in D.gal + Res + Cal group, serum klotho concentration was increased (P < 0.05 vs. D.gal). It could be concluded that co-administration of resveratrol and vitamin D protects the heart against aging-induced damage by the modulation of hemodynamic parameters and antioxidant status of the heart. Furthermore, increased serum level of klotho could be a novel mechanism for antiaging effects of resveratrol and vitamin D.

Update on Chronic Kidney Disease Mineral and Bone Disorder in Cardiovascular Disease

Chronic kidney disease mineral and bone disorder (MBD) encompasses changes in mineral ion and vitamin D metabolism that are widespread in the setting of chronic kidney disease and end-stage renal disease. MBD components associate with cardiovascular disease in many epidemiologic studies. Through impacts on hypertension, activation of the renin-angiotensin-aldosterone system, vascular calcification, endothelial function, and cardiac remodeling and conduction, MBD may be a direct and targetable cause of cardiovascular disease. However, assessment and treatment of MBD is rife with challenges owing to biological tensions between its many components, such as calcium and phosphorus with their regulatory hormones fibroblast growth factor 23 and parathyroid hormone; fibroblast growth factor 23 with its co-receptor klotho; and vitamin D with control of calcium and phosphorus. These complex interactions between MBD components hinder the simple translation to clinical trials, which ultimately are needed to prove the benefits of treating MBD. Deeper investigation using precision medicine tools and principles, including genomics and individualized risk assessment and therapy, may help move the field closer toward clinical applications. This review provides a high-level overview of conventional and precision epidemiology in MBD, potential mechanisms of cardiovascular disease pathogenesis, and guiding therapeutic principles for established and emerging treatments.

Plasmatic Klotho and FGF23 Levels as Biomarkers of CKD-Associated Cardiac Disease in Type 2 Diabetic Patients

Background: Research over the past decade has focused on the role of Klotho as a cardio protective agent that prevents the effects of aging on the heart and reduces the burden of cardiovascular disease CVD. The role of the interaction between fibroblast growth factor 23-(FGF-23)/Klotho in Klotho-mediated actions is still under debate. The main objective was to ascertain the potential use of plasmatic Klotho and FGF23 as markers for CKD-associated cardiac disease and mortality. Methods: This was a prospective analysis conducted in an outpatient diabetic nephropathy clinic, enrolling 107 diabetic patients with stage 2–3 CKD. Patients were divided into three groups according to their left ventricular mass index and relative wall thickness. Results: Multinomial regression analysis demonstrated that low Klotho and higher FGF-23 levels were linked to a greater risk of concentric hypertrophy. In the generalized linear model (GLM), Klotho, FGF-23 and cardiac geometry groups were statistically significant as independent variables of cardiovascular hospitalization (p = 0.007). According to the Cox regression model, fatal cardiovascular events were associated with the following cardiac geometric classifications; eccentric hypertrophy (p = 0.050); concentric hypertrophy (p = 0.041), and serum phosphate ≥ 3.6 mg/dL (p = 0.025), FGF-23 ≥ 168 (p = 0.0149), α-klotho < 313 (p = 0.044). Conclusions: In our population, Klotho and FGF23 are associated with cardiovascular risk in the early stages of CKD.

Comparison of echocardiographic changes in children with primary hypertension and hypertension due to mild to moderate chronic kidney disease

BACKGROUND

Chronic systemic hypertension has a well-known association with increased cardiovascular morbidity and mortality. One of the most important target organs affected in systemic hypertension is the heart. In addition, chronic kidney disease (CKD) further increases the mortality from cardiovascular disease. The aim of this study was to evaluate the differences in the cardiovascular changes in pediatric patients with primary hypertension (pHTN) vs. those with secondary hypertension from chronic kidney disease (CKD-HTN).

METHODS

This was a retrospective chart review of patients with CKD-HTN and pHTN. The medical records were reviewed for anthropometric data, biochemical assessment of renal function, and for cardiovascular changes on echocardiogram.

RESULTS

Twenty-three patients with pHTN and 29 patients with CKD-HTN were included in the study. There were no differences in age, gender, weight, height, body mass index, and blood pressure between the 2 groups. There was a high prevalence of left ventricular diastolic dysfunction among both the groups (CKD-HTN 25 vs. pHTN 26%). Reduced mitral valve inflow Doppler E/A ratio, a marker of left ventricular diastolic dysfunction in echocardiogram, was more pronounced in CKD-HTN patents, in comparison to those with pHTN (p = 0.042). Also, diastolic function worsened with declining glomerular filtration rate in patients with CKD-HTN. Similarly, patients with CKD-HTN had a larger aortic root dimension when compared to patients with pHTN (p = 0.049).

CONCLUSIONS

The prevalence of left ventricular diastolic dysfunction is similar in patients with pHTN and CKD-HTN. Patients with CKD-HTN appear to have more severe diastolic dysfunction and larger aortic root dimensions.

FGF23-klotho axis, bone fractures, and arterial stiffness in dialysis: a case-control study

We performed a case-control study on 130 age- and sex-matched hemodialysis patients. In multivariate analysis, we observed that FGF23 levels were associated with fracture incidence and that soluble α-klotho levels were associated with the aortic-brachial arterial stiffness ratio.

INTRODUCTION

New bone markers such as sclerostin, Dickkopf-related protein 1 (DKK1), fibroblast growth factor-23 (FGF23), and α-klotho have been identified as potential key players in bone and vascular abnormalities of chronic kidney disease. Therefore, we aimed to assess whether these markers are associated with fractures, bone metabolism, and vascular stiffness in dialysis patients.

METHODS

In a prospective hemodialysis cohort, where plasma samples and vascular assessment were performed at baseline, we matched patients who experienced a fracture during follow-up with sex- and age-matched non-fractured patients on a 1:4 ratio. Sclerostin, DKK1, α-klotho, FGF23, and markers of bone formation (alkaline phosphatase and procollagen type 1-N terminal propeptide [P1NP]) and bone resorption (tartrate-resistant acid phosphatase 5b [TRAP5b]) were measured in baseline plasma samples. Aortic-brachial pulse wave velocity ratio, a blood pressure independent measure of arterial stiffness, was used to assess vascular stiffness at baseline.

RESULTS

We included 130 hemodialysis patients (26 fractured, 104 non-fractured) with a median follow-up of 42 months and a median age of 72 years. In multivariate Cox regression models, high FGF23 levels were associated with increased fracture incidence (adjusted HR = 2.97; 95% CI 1.18, 7.43). α-Klotho levels were associated with bone formation but not resorption markers. In both univariate and multivariable adjusted models, α-klotho levels were inversely associated with the aortic-brachial pulse wave velocity ratio (β = - 0.070; 95% CI - 0.133, - 0.006).

CONCLUSIONS

These results suggest a role for FGF23/klotho axis on bone and vascular metabolism in dialysis populations.

Is FGF23 effective on insulin resistance in individuals with metabolic syndrome?

Purpose

Metabolic syndrome (MetS) is a polymetabolic syndrome has high morbidity and mortality rates. Insulin resistance (IR) plays a key role in the increasing frequency of this situation and has been cited as being an important etiologic factor in MetS. In this study, the relationship between IR and fibroblast growth factor-23 (FGF23), was investigated in a population with MetS.

Materials and methods

Forty patients with diagnosis of MetS and 40 healthy volunteers with an equal number of males and females were included in the study and classified as patient group and control group. Blood samples were obtained after 12-h fasting period to study FGF23 and other parameters. MetS, defined according to the International Diabetes Federation (IDF) guidelines, FGF23 was studied by Enzyme-Linked ImmunoSorbent Assay (ELISA) method and IR was calculated using the homeostatic model assessment-insulin resistance (HOMA-IR) formula.

Results

There was a statistically significant difference in HOMA-IR between the patient and control group as expected, while levels of FGF23 were similar. According to gender, levels of FGF23 was statistically significantly higher in male patients compared with controls (p = 0.037). A relationship was not detected between HOMA-IR and FGF23 in the correlation analysis.

Conclusion

Although there are many studies suggesting the correlation between FGF23 and IR in different populations, we did not find any statistically significant relationship between IR and FGF23 levels in MetS in this study.

The suppressive effect of soluble Klotho on fibroblastic growth factor 23 synthesis in UMR-106 osteoblast-like cells

Fibroblastic growth factor 23 (FGF23) is a hormone secreted primarily by bone. FGF23 is elevated in the serum of chronic kidney disease (CKD) patients, but the exact mechanism is not well known. Klotho is identified as an aging suppressor, which is mainly expressed in the kidney, and the level of soluble Klotho is negatively associated with FGF23 in CKD. The aim of this study was to investigate the effect and possible mechanism of Klotho on FGF23 synthesis in osteoblast-like UMR-106 cells. UMR-106 cells were divided into five groups: (i) control group; (ii) β-glycerophosphate (β-GP) group; (iii) β-GP + Klotho group; (iv) β-GP+ lithium chloride (LiCl, a Wnt/β-catenin pathway agonist) group; and (v) β-GP + Klotho + LiCl group. Subsequently, UMR-106 cells were cultured for 72 h, and the expression of FGF23, P-glycogen synthase kinase-3β (P-GSK-3β), and glycogen synthase kinase-3β(GSK-3β) were measured with Western blot analysis. The mRNA levels of FGF23 and the Wnt/β-catenin pathway target gene c-myc were determined with RT-qPCR. The results showed that β-GP induced increased expression of FGF23 mRNA and protein. Compared with the β-GP group, expression of FGF23 mRNA and protein expression were downregulated in the β-GP + Klotho group. In addition, β-GP induced increased expression of P-GSK-3β/GSK-3β and c-myc, which were all downregulated in the β-GP + Klotho group. Moreover, the expression of FGF23, P-GSK-3β/GSK-3β, and c-myc mRNA were upregulated when treated with LiCl. These results demonstrate that soluble Klotho suppresses FGF23 synthesis in osteoblast-like UMR-106 cells. The mechanism of this suppression may be partially through the inhibition of the Wnt/β-catenin pathway.

The association between soluble klotho and cardiovascular parameters in chronic kidney disease: results from the KNOW-CKD study

BACKGROUND

Klotho, a protein linked to aging, has emerged as a pivotal player in mineral bone metabolism and might explain the relationship between chronic kidney disease (CKD) and cardiovascular disease (CVD). The present study aimed to investigate the association between serum klotho and cardiac parameters from a large-scale Korean CKD cohort.

METHODS

We analyzed 2101 participants from KoreaN Cohort Study for Outcome in Patients With Chronic Kidney Disease (KNOW-CKD) cohort who had been measured for serum klotho levels. Left ventricular hypertrophy evaluated by left ventricular mass index (LVMI) and arterial stiffness measured by brachial-to-ankle pulse wave velocity (baPWV) were explored as cardiovascular parameters.

RESULTS

Patients were 53.6 ± 12.2 years old and 61.1% were male. The mean estimated glomerular filtration rate (eGFR) was 53.0 ± 30.7 mL/min/1.73m². The median serum klotho level was 536 (interquartile range [IQR]: 420-667) pg/mL. Advanced CKD stages were associated with lower serum klotho levels (P < 0.001, P for linear trend < 0.001). Ascending quartiles of klotho were significantly associated with decreased LMVI (P < 0.001, P for linear trend< 0.001). A multivariable linear regression model showed serum klotho had a significant inverse association with LVMI (β - 0.04; 95% CI [confidence interval] -0.004, - 0.00007; P = 0.041). However, there was no significant association between serum klotho and baPWV after adjustment (β 0.003; 95% CI -0.04, 0.05; P = 0.876).

TRIAL REGISTRATION

This trial was registered on ClinicalTrials.gov on 28 June 2012 ( NCT01630486 ).

CONCLUSIONS

Serum klotho was an independent biomarker of LVMI, but not arterial stiffness.

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.

Changes in Serum Fibroblast Growth Factor 23 in Patients With Acute Myocardial Infarction

BACKGROUND

Fibroblast growth factor 23 (FGF23) induces cardiac remodeling. We investigated the changes in serum FGF23 levels in patients diagnosed with acute myocardial infarction (AMI).Methods and Results:A total of 44 patients diagnosed with AMI were included in the current study. All patients underwent emergency percutaneous coronary intervention (PCI). The median of peak creatine kinase (CK) and CKMB values was 1,816 U/L and 159 U/L, respectively. Serum levels of FGF23, calcium, and inorganic phosphate (iP) were measured before PCI, and on days 1, 3, 5, 7 after PCI. Serum FGF23 levels showed a slight, but significant decrease on days 1 and 3 after PCI, and a 1.5- and 2.0-fold increase on days 5 and 7, respectively, after PCI. As compared with propensity score-matched patients without AMI, serum FGF23 was significantly lower among the current cohort of AMI patients. In 22 subjects who underwent a follow-up echocardiographic examination at 6 months after the onset of AMI, the log-transformed relative increase in FGF23 on day 7 significantly and negatively correlated with changes between LVEF on admission and that at 6 months afterward.

CONCLUSIONS

After a slight decrease on days 1 and 3 after admission, serum FGF23 increased significantly on days 5 and 7. The underlying mechanism and potential clinical importance of these observations require further investigation.

Plasma s-Klotho is related to kidney function and predicts adverse renal outcomes in patients with advanced chronic kidney disease

To investigate whether the soluble Klotho (s-Klotho) level in patients with chronic kidney disease (CKD) is related to kidney function and whether a low s-Klotho level can predict adverse renal outcomes or CKD progression in patients with advanced CKD. 112 patients with CKD stages 3-5 and 30 healthy volunteers were enrolled. Blood samples were collected to measure serum creatinine, calcium, phosphorus, intact parathyroid hormone, and hemoglobin. s-Klotho and fibroblast growth factor 23 (FGF23) were determined by ELISA. We first conducted a cross-sectional study to investigate correlations between s-Klotho and estimated glomerular filtration rate (eGFR) and other parameters. Patients were then followed prospectively for 20.1±10.1 months according to s-Klotho median level until serum creatinine doubled, or initiation of renal replacement therapy, or death. s-Klotho levels inpatients with CKD were significantly lower than that in the control group. For patients with CKD, there were no differences in age distribution among subgroups. However, s-Klotho level differed significantly across CKD stages, and it was lower in the advanced CKD group compared with the moderate CKD group. Correlation analysis revealed that s-Klotho was positively associated with eGFR, but inversely associated with FGF23. During the follow-up of 20.1±10.1 months, patients with higher s-Klotho levels showed a reduced risk of kidney adverse outcomes, including serum creatinine doubling and initiation of renal replacement therapy. Cox regression analysis revealed that low s-Klotho was an independent risk factor for CKD progression. s-Klotho level was closely correlated with kidney function, further, low s-Klotho level could predict adverse kidney disease outcomes in patients with progressive CKD.

Relationship between plasma xanthine oxidoreductase activity and left ventricular ejection fraction and hypertrophy among cardiac patients

Background and purpose

Xanthine oxidoreductase (XOR), which catalyzes purine catabolism, has two interconvertible forms, xanthine dehydrogenase and xanthine oxidase, the latter of which produces superoxide during uric acid (UA) synthesis. An association between plasma XOR activity and cardiovascular and renal outcomes has been previously suggested. We investigated the potential association between cardiac parameters and plasma XOR activity among cardiology patients.

Methods and results

Plasma XOR activity was measured by [¹³C₂,¹⁵N₂]xanthine coupled with liquid chromatography/triplequadrupole mass spectrometry. Among 270 patients who were not taking UA-lowering drugs, XOR activity was associated with body mass index (BMI), alanine aminotransferase (ALT), HbA1c and renal function. Although XOR activity was not associated with serum UA overall, patients with chronic kidney disease (CKD), those with higher XOR activity had higher serum UA among patients without CKD. Compared with patients with the lowest XOR activity quartile, those with higher three XOR activity quartiles more frequently had left ventricular hypertrophy. In addition, plasma XOR activity showed a U-shaped association with low left ventricular ejection fraction (LVEF) and increased plasma B-type natriuretic peptide (BNP) levels, and these associations were independent of age, gender, BMI, ALT, HbA1C, serum UA, and CKD stages.

Conclusions

Among cardiac patients, left ventricular hypertrophy, low LVEF, and increased BNP were significantly associated with plasma XOR activity independent of various confounding factors. Whether pharmaceutical modification of plasma XOR activity might inhibit cardiac remodeling and improve cardiovascular outcome should be investigated in future studies.

Is Serum Uric Acid Independently Associated With Left Ventricular Mass Index, Ejection Fraction, and B-Type Natriuretic Peptide Among Female and Male Cardiac Patients?

Mean serum uric acid (SUA) levels are higher in men than women. In addition, recent studies have suggested that the SUA threshold at which the cardiovascular risk might increase may vary between women and men. In the current retrospective study, by analyzing the data from 219 female and 519 male patients who were free from uric acid-lowering medication, we investigated whether SUA is associated with left ventricular mass index (LVMI), left ventricular ejection fraction (LVEF), and plasma levels of B-type natriuretic peptide (BNP) independent of confounding factors, such as serum calcium, inorganic phosphate, and fibroblast growth factor 23 (FGF23), in a gender-specific manner.In multivariate stepwise linear regression analysis in which age, blood pressure, eGFR, corrected calcium, inorganic phosphate, and FGF23 were entered as potential covariates, SUA was selected as a factor significantly associated with LVEF, LVMI, and plasma levels of BNP in both genders. On the other hand, however, after adding diuretic use as a potential covariate, the association between SUA and LVEF lost statistical significance in both genders, and that between SUA and BNP lost significance among female patients. These findings suggest that diuretic use is a non-negligible confounder in understanding the observed association between SUA and cardiac dysfunction and heart failure.In summary, SUA is associated with left ventricular hypertrophy independent of confounding factors including FGF23 and diuretic use in female and male patients. Whether lowering SUA can influence the progression of cardiac remodeling awaits further investigation.