Associations of FGF-23 and sKlotho with cardiovascular outcomes among patients with CKD stages 2-4

Lessons from Klotho mouse models to understand mineral homeostasis

AIM

Klotho, a key component of the endocrine fibroblast growth factor receptor-fibroblast growth factor axis, is a multi-functional protein that impacts renal electrolyte handling. The physiological significance of Klotho will be highlighted in the regulation of calcium, phosphate, and potassium metabolism.

METHODS

In this review, we compare several murine models with different renal targeted deletions of Klotho and the insights into the molecular and physiological function that these models offer.

RESULTS

In vivo, Klotho deficiency is associated with severely impaired mineral metabolism, with consequences on growth, longevity and disease development. Additionally, we explore the perspectives of Klotho in renal pathology and vascular events, as well as potential Klotho treatment options.

CONCLUSION

This comprehensive review emphasizes the use of Klotho to shed light on deciphering the renal molecular in vivo mechanisms in electrolyte handling, as well as novel therapeutic interventions.

Soluble Klotho, a Potential Biomarker of Chronic Kidney Disease-Mineral Bone Disorders Involved in Healthy Ageing: Lights and Shadows

Shortly after the discovery of Klotho, interest grew in its potential role in chronic kidney disease (CKD). There are three isoforms of the Klotho protein: αKlotho, βKlotho and γKlotho. This review will focus on αKlotho due to its relevance as a biomarker in CKD. αKlotho is synthesized mainly in the kidneys, but it can be released into the bloodstream and urine as soluble Klotho (sKlotho), which undertakes systemic actions, independently or in combination with FGF23. It is usually accepted that sKlotho levels are reduced early in CKD and that lower levels of sKlotho might be associated with the main chronic kidney disease-mineral bone disorders (CKD-MBDs): cardiovascular and bone disease. However, as results are inconsistent, the applicability of sKlotho as a CKD-MBD biomarker is still a matter of controversy. Much of the inconsistency can be explained due to low sample numbers, the low quality of clinical studies, the lack of standardized assays to assess sKlotho and a lack of consensus on sample processing, especially in urine. In recent decades, because of our longer life expectancies, the prevalence of accelerated-ageing diseases, such as CKD, has increased. Exercise, social interaction and caloric restriction are considered key factors for healthy ageing. While exercise and social interaction seem to be related to higher serum sKlotho levels, it is not clear whether serum sKlotho might be influenced by caloric restriction. This review focuses on the possible role of sKlotho as a biomarker in CKD-MBD, highlighting the difference between solid knowledge and areas requiring further research, including the role of sKlotho in healthy ageing.

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.

Short-term changes in klotho and FGF23 in heart failure with reduced ejection fraction-a substudy of the DAPA-VO2 study

The klotho and fibroblast growth factor 23 (FGF-23) pathway is implicated in cardiovascular pathophysiology. This substudy aimed to assess the changes in klotho and FGF-23 levels 1-month after dapagliflozin in patients with stable heart failure and reduced ejection fraction (HFrEF). The study included 29 patients (32.2% of the total), with 14 assigned to the placebo group and 15 to the dapagliflozin, as part of the double-blind, randomized clinical trial [DAPA-VO2 (NCT04197635)]. Blood samples were collected at baseline and after 30 days, and Klotho and FGF-23 levels were measured using ELISA Kits. Between-treatment changes (raw data) were analyzed by using the Mann-Whitney test and expressed as median (p25%-p75%). Linear regression models were utilized to analyze changes in the logarithm (log) of klotho and FGF-23. The median age was 68.3 years (60.8-72.1), with 79.3% male and 81.5% classified as NYHA II. The baseline medians of left ventricular ejection fraction, glomerular filtration rate, NT-proBNP, klotho, and FGF-23 were 35.8% (30.5-37.8), 67.4 ml/min/1.73 m2 (50.7-82.8), 1,285 pg/ml (898-2,305), 623.4 pg/ml (533.5-736.6), and 72.6 RU/ml (62.6-96.1), respectively. The baseline mean peak oxygen uptake was 13.1 ± 4.0 ml/kg/min. Compared to placebo, patients on dapagliflozin showed a significant median increase of klotho [Δ+29.5, (12.9-37.2); p = 0.009] and a non-significant decrease of FGF-23 [Δ-4.6, (-1.7 to -5.4); p = 0.051]. A significant increase in log-klotho (p = 0.011) and a decrease in log-FGF-23 (p = 0.040) were found in the inferential analysis. In conclusion, in patients with stable HFrEF, dapagliflozin led to a short-term increase in klotho and a decrease in FGF-23.

Klotho inversely relates with carotid intima- media thickness in atherosclerotic patients with normal renal function (eGFR ≥60 mL/min/1.73m2): a proof-of-concept study

Introduction

Klotho protein is predominantly expressed in the kidneys and has also been detected in vascular tissue and peripheral blood circulating cells to a lesser extent. Carotid artery intima-media thickness (CIMT) burden, a marker of subclinical atherosclerosis, has been associated with reductions in circulating Klotho levels in chronic kidney disease patients, who show reduced levels of this protein at all stages of the disease. However, the contribution of serum Klotho and its expression levels in peripheral blood circulating cells and in the carotid artery wall on the CIMT in the absence of kidney impairment has not yet been evaluated.

Methods

We conducted a single-center study in 35 atherosclerotic patients with preserved kidney function (eGFR≥60 mL/min/1.73m2) subjected to elective carotid surgery. Serum levels of Klotho and cytokines TNFa, IL6 and IL10 were determined by ELISA and transcripts encoding for Klotho (KL), TNF, IL6 and IL10 from vascular segments were measured by qRT-PCR. Klotho protein expression in the intima-media and adventitia areas was analyzed using immunohistochemistry.

Results

APatients with higher values of CIMT showed reduced Klotho levels in serum (430.8 [357.7-592.9] vs. 667.8 [632.5-712.9] pg/mL; p<0.001), mRNA expression in blood circulating cells and carotid artery wall (2.92 [2.06-4.8] vs. 3.69 [2.42-7.13] log.a.u., p=0.015; 0.41 [0.16-0.59] vs. 0.79 [0.37-1.4] log.a.u., p=0.013, respectively) and immunoreactivity in the intimal-medial area of the carotids (4.23 [4.15-4.27] vs. 4.49 [4.28-4.63] log µm2 p=0.008). CIMT was inversely related with Klotho levels in serum (r= -0.717, p<0.001), blood mRNA expression (r=-0.426, p=0.011), and with carotid artery mRNA and immunoreactivity levels (r= -0.45, p=0.07; r= -0.455, p= 0.006, respectively). Multivariate analysis showed that serum Klotho, together with the gene expression levels of tumor necrosis factor TNFa in blood circulating cells, were independent determinants of CIMT values (adjusted R2 = 0.593, p<0.001).

Discussion

The results of this study in subjects with eGFR≥60mL/min/1.73m2 show that patients with carotid artery atherosclerosis and higher values of CIMT present reduced soluble Klotho levels, as well as decreased KL mRNA expression in peripheral blood circulating cells and Klotho protein levels in the intima-media of the carotid artery wall.

Association between serum Klotho concentration and heart failure in adults, a cross-sectional study from NHANES 2007-2016

BACKGROUND

Limited data exist on the association between serum Klotho concentration and heart failure (HF).

METHODS AND RESULTS

We conducted a cross-sectional study of 13,625 participants aged 40-79 years in the National Health and Nutrition Examination Survey (NHANES) 2007-2016. Multivariable logistic regression models were used to examine the association between serum Klotho concentration (ln transformation) and HF. A total of 533 (2.9%) participants were identified to have HF, and participants with the lowest tertiles of serum Klotho concentration had the highest percentage of HF (T1: 3.8% vs. T2: 2.8% and T3: 2.1%, P < 0.001). After adjusting for potential confounders, ln (Klotho) was negatively and independently associated with the risk of HF (OR= 0.55, 95% CI 0.36-0.84). Meanwhile, compared with the T1 group, a higher serum Klotho concentration was associated with a lower risk of HF (tertile 2: OR = 0.93, 95% CI: 0.69-1.29, tertile 3: OR = 0.75, 95% CI: 0.52-1.09, P for trend 0.022). Finally, subgroup analyses indicated that lower Klotho concentrations significantly correlated with an increased risk of HF in half of the subgroups.

CONCLUSION

Serum Klotho concentration was consistently and negatively associated with the presence of HF among US middle-aged and older adults.

FGF23 AND ALTERED MINERAL HOMEOSTASIS IN KIDNEY DISEASE AND FOLLOWING INTRAVENOUS IRON

Fibroblast growth factor 23 (FGF23) is an endocrine hormone that stimulates renal phosphate excretion and suppresses circulating concentrations of 1,25-dihydroxyvitamin D (1,25D). These effects of FGF23 are most evident in rare diseases that are characterized by FGF23-mediated hypophosphatemic rickets-osteomalacia. More commonly, elevated FGF23 is a ubiquitous, early consequence of chronic kidney disease (CKD) in which it helps to maintain normal serum phosphate levels but causes secondary hyperparathyroidism by suppressing 1,25D, and directly promotes cardiovascular disease and death. Elevated FGF23 is also a common complication of intravenous administration of ferric carboxymaltose (FCM), which is widely used to treat iron deficiency anemia. Among patients with normal kidney function who receive FCM, the resulting increase in FGF23 and subsequent FGF23-mediated reduction of 1,25D and secondary hyperparathyroidism promote hypophosphatemia that can be symptomatic, severe, and associated with musculoskeletal complications. Ongoing research is needed to design novel therapeutic approaches to mitigate FGF23-related illnesses.

Association of α-klotho with subclinical carotid atherosclerosis in subjects with type 1 diabetes mellitus

Background

Compelling evidence suggests that the fibroblast growth factor 23 (FGF23) / α-klotho axis is impaired in subjects with diabetes mellitus. We examined the relationship between parameters related to calcium/phosphate homeostasis, including FGF23 and α-klotho, and subclinical carotid atherosclerosis burden in type 1 diabetes mellitus (T1D) subjects.

Methods

This cross-sectional study involved 226 subjects with T1D and 147 age-, sex- and plaque-matched, non-diabetic (non-T1D) subjects, both with normal renal function. Carotid ultrasound was performed to determine the presence and burden of atheromatous plaques. Concentrations of the intact form of FGF23 and α-klotho were assessed by ELISA. Calcium, phosphate, parathyroid hormone, and vitamin D levels were also determined. Negative binomial regression models were used to examine relationship between parameters studied and subclinical carotid atherosclerosis.

Results

Only FGF23 was increased in T1D compared with non-diabetic subjects (> 2-fold; p < 0.05). α-klotho was higher in subjects with subclinical carotid atherosclerosis (1.4-fold, p < 0.05). Regression analysis revealed that the log α-klotho concentration was positively associated with the presence of subclinical carotid atherosclerosis both in T1D subjects (incidence rate ratio [IRR]: 1.41; 95% confidence interval [CI], 1.06–1.89; p < 0.05) and in non-T1D subjects (IRR: 1.65; 95% CI, 1.02–2.75; p < 0.05). The models also showed that age, smoking and albuminuria-to-creatinine ratio were positively associated with subclinical carotid atherosclerosis in T1D subjects. Interestingly, sex-related protection against plaque was also revealed in T1D women.

Conclusion

Higher α-klotho was associated with subclinical carotid atherosclerotic in the absence of kidney dysfunction. This finding also points to a new pathophysiological pathway involved in the development and progression of this complication.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01640-3.

High-Dose Intravenous Iron with Either Ferric Carboxymaltose or Ferric Derisomaltose: A Benefit-Risk Assessment

The intravenous iron formulations ferric carboxymaltose (FCM) and ferric derisomaltose (FDI) offer the possibility of administering a large amount of iron in one infusion. This results in faster correction of anemia and the formulations being better tolerated than oral iron formulations. This triad of logistic advantages, improved patient convenience, and fast correction of anemia explains the fact that intravenous iron formulations nowadays are frequently prescribed worldwide in the treatment of iron deficiency anemia. However, these formulations may result in hypophosphatemia by inducing a strong increase in active fibroblast growth factor-23 (FGF-23), a hormone that stimulates renal phosphate excretion. This effect is much more pronounced with FCM than with FDI, and therefore the risk of developing hypophosphatemia is remarkably higher with FCM than with FDI. Repeated use of FCM may result in severe osteomalacia, which is characterized by bone pain, Looser zones (pseudofractures), and low-trauma fractures. Intravenous iron preparations are also associated with other adverse effects, of which hypersensitivity reactions are the most important and are usually the result of a non-allergic complement activation on nanoparticles of free labile iron-Complement Activation-Related Pseudo-Allergy (CARPA). The risk on these hypersensitivity reactions can be reduced by choosing a slow infusion rate. Severe hypersensitivity reactions were reported in < 1% of prospective trials and the incidence seems comparable between the two formulations. A practical guideline has been developed based on baseline serum phosphate concentrations and predisposing risk factors, derived from published cases and risk factor analyses from trials, in order to establish the safe use of these formulations.

The controversy of klotho as a potential biomarker in chronic kidney disease

Klotho is an identified longevity gene with beneficial pleiotropic effects on the kidney. Evidence shows that a decline in serum Klotho level occurs in early chronic kidney disease (CKD) and continues as CKD progresses. Klotho deficiency is associated with poor clinical outcomes and CKD mineral bone disorders (CKD-MBD). Klotho has been postulated as a candidate biomarker in the evaluation of CKD. However, the evidence for the clinical significance of the relationship between Klotho and kidney function, CKD stage, adverse kidney and/or non-kidney outcomes, and CKD-MBD remains inconsistent and in some areas, contradictory. Therefore, there is uncertainty as to whether Klotho is a potential biomarker in CKD; a general consensus regarding the clinical significance of Klotho in CKD has not been reached, and there is limited evidence synthesis in this area. To address this, we have systematically assessed the areas of controversy, focusing on the inconsistencies in the evidence base. We used a PICOM strategy to search for relevant studies and the Newcastle–Ottawa Scale scoring to evaluate included publications. We reviewed the inconsistent clinical findings based on the relationship of Klotho with CKD stage, kidney and/or non-kidney adverse outcomes, and CKD-MBD in human studies. Subsequently, we assessed the underlying sources of the controversies and highlighted future directions to resolve these inconsistencies and clarify whether Klotho has a role as a biomarker in clinical practice in CKD.

Klotho Levels and Their Relationship with Inflammation and Survival among Alcoholic Patients

α-Klotho (Klotho) is an antiaging hormone with anti-inflammatory and antioxidative properties. Some studies suggest that Klotho increases in response to enhanced oxidative damage and inflammation. Alcoholism is a proinflammatory condition. The aim of this study was to analyze the relationship between Klotho and the serum levels of the inflammatory markers in alcoholic liver disease and to assess its prognostic value. We included 184 alcoholics and 35 age- and sex-matched controls. We determined the serum levels of Klotho, the tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-8, and malondialdehyde (MDA), and routine laboratory variables. Patients were followed-up with during 16 ± 18 months; 67 patients died. Klotho levels were higher among cirrhotics (with KW = 37.00 and p < 0.001) and were related to the Child−Pugh score (with KW = 15.96 and p < 0.001) and to the TNF-α (ρ = 0.28; p < 0.001) and MDA (ρ = 0.21; p = 0.006). The child’s groups were associated with mortality, both in the univariate (with the log-rank = 13.56, p = 0.001, Breslow = 12.33, and p = 0.002) and multivariate (with β = 0.43, p = 0.02, and OR = 1.53 (1.07−2.15)) analyses, also introducing Klotho and the TNF-α as dichotomic variables. However, the independent prognostic value of the Child’s groups was displaced by Klotho when only cirrhotics were considered; Klotho, over the median (574.4 pg/mL), was associated with higher mortality (with p = 0.04 and OR = 2.68 (1.06−6.84)). We conclude that Klotho is increased in liver cirrhosis. It is directly related to TNF-α, MDA, and to mortality in cirrhotics.

In Vivo Cardiac-specific Expression of Adenylyl Cyclase 4 Gene Protects against Klotho Deficiency-induced Heart Failure

Klotho is an aging-suppressor gene. Klotho gene deficiency causes heart failure in Klotho-hypomorphic mutant (KL (-/-)) mice. RNA-seq and western blot analysis showed that adenylyl cyclase type IV (AC4) mRNA and protein expression was largely decreased in cardiomyocytes of KL (-/-) mice. The objective of this study was to investigate whether in vivo cardiac-specific expression of AC4 gene protects against Klotho deficiency-induced heart failure. Interestingly, in vivo AAV-based cardiac-specific AC4 gene expression increased left ventricular fractional shortening, ejection fraction, stroke volume, and left ventricular end-diastolic volume in KL (-/-) mice, suggesting that cardiac-specific AC4 gene expression improves Klotho deficiency-induced heart dysfunction. Cardiac-specific AC4 gene expression also decreased Klotho deficiency-induced cardiac hypertrophy. Cardiac-specific AC4 gene expression alleviated Klotho deficiency-induced cardiac fibrosis and calcification. Furthermore, cardiac-specific AC4 gene expression attenuated mitochondrial dysfunction, superoxide accumulation and cardiomyocyte apoptotic cell death. Thus, downregulation of AC4 may contribute to Klotho deficiency-induced heart failure. Mechanistically, AAV2/9-αMHC-AC4 increased cardiomyocytic cAMP levels and thus regulated the PKA-PLN-SERCA2 signal pathway, which is critical in modulating calcium flux and mitochondrial function. In conclusion, cardiac-specific AC4 gene expression protects against Klotho deficiency-induced heart failure through increasing cardiomyocytic cAMP levels, which alleviates cAMP-dependent mitochondrial dysfunction, superoxide accumulation and apoptotic cell death. AC4 regulates superoxide levels via the cAMP-PKA pathway. AC4 could be a potential therapeutic target for heart failure associated with Klotho deficiency. Heart failure is the major cause of mortality in patients with chronic kidney disease (CKD). A decrease in Klotho levels is linked to CKD.

From cardiorenal syndromes to cardionephrology: a reflection by nephrologists on renocardiac syndromes

Cardiorenal syndromes (CRS) are broadly defined as disorders of the heart and kidneys whereby acute or chronic dysfunction in one organ may induce acute or chronic dysfunction of the other. CRS are currently classified into five categories, mostly based on disease-initiating events and their acuity or chronicity. CRS types 3 and 4 (also called renocardiac syndromes) refer to acute and chronic kidney dysfunction resulting in acute and chronic heart dysfunction, respectively. The notion of renocardiac syndromes has broadened interest in kidney-heart interactions but uncertainty remains in the nephrological community's understanding of the clinical diversity, pathophysiological mechanisms and optimal management approaches of these syndromes. This triple challenge that renocardiac syndromes (and likely other cardiorenal syndromes) pose to the nephrologist can only be faced through a specific and demanding training plan to enhance his/her cardiological scientific knowledge and through an appropriate clinical environment to develop his/her cardiological clinical skills. The first must be the objective of the subspecialty of cardionephrology (or nephrocardiology) and the second must be the result of collaboration with cardiologists (and other specialists) in cardiorenal care units. This review will first consider various aspects of the challenges that renocardiac syndromes pose to nephrologists and, then, will discuss those aspects of cardionephrology and cardiorenal units that can facilitate an effective response to the challenges.

Renal Function Mediates the Association Between Klotho and Congestive Heart Failure Among Middle-Aged and Older Individuals

Objective

Using a newly released National Health and Nutrition Examination Survey (NHANES) data of serum Klotho, this study aimed to explore the relationship between Klotho and specific cardiovascular diseases (CVD), as well as the mediation effect of renal function, among middle-aged and older individuals within the general population.

Methods

This nationally representative cross-sectional study analyzed data from the 2007–2016 NHANES. A total of 13,765 participants, who aged 40 years or older, from the general population were examined. Klotho were divided into four groups based on median and interquartile range. The associations among Klotho (exposure), congestive heart failure (CHF; outcome), and renal function markers [estimated glomerular filtration rate (eGFR), blood urea nitrogen (BUN), uric acid (UA), and urine albumin-to-creatinine ratio (UACR); mediators] were investigated using mediation analysis.

Results

In comparison to the lowest quartile, Klotho in the highest quartile was independently associated with the prevalence of CHF (OR 0.59; 95% CI 0.46–0.77, p for trend = 0.001), but not with other individual CVDs. Klotho had a significant direct effect on the prevalence of CHF (all p < 0.001), while eGFR, BUN, UA, and UACR partly mediated the indirect effect of Klotho on the prevalence of CHF (all p < 0.05), explaining 19.51, 6.98, 13.93, and 0.71% of the association between Klotho and CHF, respectively. Additionally, restricted cubic spline regression demonstrated a linear association and negative correlation between Klotho level and CHF.

Conclusion

These findings suggest that Klotho is closely linked to CHF and renal function may be a key mediator of this association.

Acute Effects of an Inorganic Phosphorus Additive on Mineral Metabolism and Cardiometabolic Risk Factors in Healthy Subjects

CONTEXT

Hyperphosphatemia and high levels of fibroblast growth factor 23 (FGF23) are risk factors for cardiovascular events in patients with chronic kidney diseases. However, the impact of an inorganic phosphorus additive in healthy people is largely unknown.

OBJECTIVE

We aimed to investigate the acute effect of excessive dietary phosphorus administered as sodium dihydrogen phosphate on the postprandial levels of Pi and FGF23 and the response to food.

METHODS

This study was a double-blind placebo-controlled crossover study with 29 healthy male and female participants from the general community who were administered a single dose of either 700 mg phosphorus (NaH2PO4) or a sodium-adjusted placebo in combination with a test meal. Postprandial plasma levels of Pi and FGF23 were measured.

RESULTS

Compared with placebo, oral phosphorus increased the plasma Pi level, which remained elevated during the ensuing 8 hours (at 480 minutes: 1.31 vs 1.16 mmol/l; P < 0.001), increased urinary Pi (iAUC0-480 789 vs 95 mmol/mmol; P < 0.001), reduced tubular Pi reabsorption (iAUC0-480 -31.5 vs -6.2; P < 0.001), decreased urinary calcium (iAUC0-240 30.6 vs 53.0 mmol/mmol; P = 0.009), and stimulated the release of parathyroid hormone (iAUC0-480 2212 vs 768 ng/l; P < 0.001). However, the FGF23 levels did not change. Postprandial levels of glucose, insulin, and lipids were not substantially affected by phosphorus vs placebo.

CONCLUSION

An oral phosphorus load can induce elevated postprandial levels of circulating Pi for hours in healthy subjects, despite rapid homeostatic counterreactions. FGF23 levels and the postprandial response to food were not affected.

The association of fibroblast growth factor 23 at mid-life and late-life with subsequent risk of cardiovascular disease: The Atherosclerosis Risk in Communities (ARIC) Study

Background

Fibroblast growth factor 23 (FGF-23) regulates phosphorus and is associated with cardiovascular disease (CVD), particularly in patients with chronic kidney disease. However, data are limited regarding its contribution to different CVD subtypes across wide age ranges in the general population.

Methods

Using data from ARIC, we evaluated the associations of FGF-23 with heart failure (HF), coronary heart disease (CHD), stroke, and composite CVD (any CVD event) in 12,039 participants at mid-life (visit 3 [1993-1995], mean age 60.0 [SD 5.7] years) and 5608 of the same participants at late-life (visit 5 [2011-2013], 75.5 [5.1] years).

Results

During a median of 9.0 years from visit 3 and 6.9 years from visit 5, we observed 1636 and 1137 composite CVD events, respectively. Higher FGF-23 at visit 5, but not necessarily at visit 3, was significantly associated with the risk of CVD independently of potential confounders including kidney function (adjusted HRs for top vs. bottom quartile, 1.56 [95% CI, 1.30-1.87] at visit 5 and 1.10 [95% CI, 0.95-1.27] at visit 3, p-for-difference < 0.001). We observed similar patterns in key demographic and clinical subgroups without interactions. Among CVD subtypes, HF was the only subtype robustly associated with higher FGF-23 at both visits.

Conclusion

Higher FGF-23 concentrations at late-life but not necessarily at mid-life were independently associated with the risk of CVD. Among CVD subtypes tested, only HF showed robust associations with FGF-23 at both mid-life and late-life.

Fibroblast Growth Factor-23-Klotho Axis in Cardiorenal Syndrome: Mediators and Potential Therapeutic Targets

Cardiorenal syndrome (CRS) is a complex disorder that refers to the category of acute or chronic kidney diseases that induce cardiovascular disease, and inversely, acute or chronic heart diseases that provoke kidney dysfunction. There is a close relationship between renal and cardiovascular disease, possibly due to the presence of common risk factors for both diseases. Thus, it is well known that renal diseases are associated with increased risk of developing cardiovascular disease, suffering cardiac events and even mortality, which is aggravated in those patients with end-stage renal disease or who are undergoing dialysis. Recent works have proposed mineral bone disorders (MBD) as the possible link between kidney dysfunction and the development of cardiovascular outcomes. Traditionally, increased serum phosphate levels have been proposed as one of the main factors responsible for cardiovascular damage in kidney patients. However, recent studies have focused on other MBD components such as the elevation of fibroblast growth factor (FGF)-23, a phosphaturic bone-derived hormone, and the decreased expression of the anti-aging factor Klotho in renal patients. It has been shown that increased FGF-23 levels induce cardiac hypertrophy and dysfunction and are associated with increased cardiovascular mortality in renal patients. Decreased Klotho expression occurs as renal function declines. Despite its expression being absent in myocardial tissue, several studies have demonstrated that this antiaging factor plays a cardioprotective role, especially under elevated FGF-23 levels. The present review aims to collect the recent knowledge about the FGF-23-Klotho axis in the connection between kidney and heart, focusing on their specific role as new therapeutic targets in CRS.

Acute cardiac overload does not induce cardiac or skeletal expression of fibroblast growth factor 23 in rats

Elevated fibroblast growth factor 23 (FGF23) is associated with cardiovascular events, particularly heart failure. Although FGF23 has been reported to induce cardiac hypertrophy, recent studies demonstrated that cardiac hypertrophy and myocardial infarction induce FGF23 production by cardiomyocytes. We aimed to explore whether acute cardiac overload increases cardiac and skeletal FGF23 expression and circulating FGF23 levels.

FGFR4 and Klotho Polymorphisms Are Not Associated with Cardiovascular Outcomes in Chronic Kidney Disease

INTRODUCTION

High plasma fibroblast growth factor 23 (FGF-23) predicts cardiovascular events in chronic kidney disease (CKD) patients. Experimental evidence suggests FGF receptor 4 (FGFR4) activation by FGF-23, and deficiency of the soluble form of its co-receptor Klotho promotes left-ventricular hypertrophy (LVH). To evaluate the clinical relevance of these findings, a Mendelian randomization study analyzed the association of genetic variants of FGFR4 and Klotho with echocardiographic parameters and cardiac events in CKD patients.

METHODS

The prospective Cardiovascular and Renal Outcome in CKD 2-4 Patients-The Fourth Homburg Evaluation study recruited CKD G2-G4 patients, of whom 519 consented to SNP genotyping (FGFR4: rs351855; Klotho: rs9536314). Echocardiographic examinations at baseline and 5 years later assessed prevalence of LVH by measurement of left-ventricular mass index (LVMI). Patients were followed for 5.1 ± 2.1 years for the primary endpoints of cardiac decompensation and atherosclerotic cardiovascular disease (ASCVD).

RESULTS

Carriers of the different alleles did neither differ in baseline LVMI (rs351855: p = 0.861; rs9536314: p = 0.379) nor in LVMI changes between baseline and follow-up (rs351855: p = 0.181; rs9536314: p = 0.995). Hundred and four patients suffered cardiac decompensation, and 144 patients had ASCVD. Time to cardiac decompensation (rs351855: p = 0.316; rs9536314: p = 0.765) and ASCVD (p = 0.508 and p = 0.800, respectively) did not differ between carriers of different alleles.

DISCUSSION/CONCLUSION

rs351855 and rs9536314 were not associated with LVMI or cardiac events. These findings do not provide evidence for a relevant clinical role of either FGFR4 stimulation or soluble form of Klotho deficiency in LVH development.

Longitudinal change in c-terminal fibroblast growth factor 23 and outcomes in patients with advanced chronic kidney disease

BACKGROUND

Fibroblast growth factor23 (FGF23) is elevated in CKD and has been associated with outcomes such as death, cardiovascular (CV) events and progression to Renal Replacement therapy (RRT). The majority of studies have been unable to account for change in FGF23 over time and those which have demonstrate conflicting results. We performed a survival analysis looking at change in c-terminal FGF23 (cFGF23) over time to assess the relative contribution of cFGF23 to these outcomes.

METHODS

We measured cFGF23 on plasma samples from 388 patients with CKD 3-5 who had serial measurements of cFGF23, with a mean of 4.2 samples per individual. We used linear regression analysis to assess the annual rate of change in cFGF23 and assessed the relationship between time-varying cFGF23 and the outcomes in a cox-regression analysis.

RESULTS

Across our population, median baseline eGFR was 32.3mls/min/1.73m², median baseline cFGF23 was 162 relative units/ml (RU/ml) (IQR 101-244 RU/mL). Over 70 months (IQR 53-97) median follow-up, 76 (19.6%) patients progressed to RRT, 86 (22.2%) died, and 52 (13.4%) suffered a major non-fatal CV event. On multivariate analysis, longitudinal change in cFGF23 was significantly associated with risk for death and progression to RRT but not non-fatal cardiovascular events.

CONCLUSION

In our study, increasing cFGF23 was significantly associated with risk for death and RRT.

The intersection of Mineralocorticoid Receptor (MR) activation and the FGF23 - Klotho cascade. A Duopoly that promotes renal and cardiovascular injury

The nexus of CKD and cardiovascular disease (CVD) amplifies the morbidity and mortality of CKD, emphasizing the need for defining and establishing therapeutic initiatives to modify and abrogate the progression of CKD and concomitant CV risks. In addition to the traditional CV risk factors, disturbances of mineral metabolism are specific risk factors that contribute to the excessive CV mortality in patients with CKD. These risk factors include dysregulations of circulating factors that modulate phosphate metabolism including fibroblast growth factor 23 (FGF23) and soluble Klotho. Reduced circulating levels and suppressed renal klotho expression may be associated with adverse outcomes in CKD patients. While elevated circulating concentrations or locally produced FGF23 in the strained heart exert pro-hypertrophic mechanisms on the myocardium, Klotho attenuates tissue fibrosis, progression of CKD, cardiomyopathy, endothelial dysfunction, vascular stiffness, and vascular calcification. Mineralocorticoid receptor (MR) activation in non-classical targets, mediated by aldosterone and other ligands, amplifies CVD in CKD. In concert, we detail how the interplay of elevated FGF23, activation of the MR, and concomitant reductions of circulating Klotho in CKD, may potentiate each other's deleterious effects on kidney and the heart, thereby contributing to the initiation and progression of kidney and cardiac functional deterioration, acting through multipronged albeit complementary mechanistic pathways.

Parathormone levels add prognostic ability to N-terminal pro-brain natriuretic peptide in stable coronary patients

AIMS

There are controversial data on the ability of the components of mineral metabolism (vitamin D, phosphate, parathormone [PTH], fibroblast growth factor-23 [FGF23], and klotho) to predict cardiovascular events. In addition, it is unknown whether they add any prognostic value to other well-known biomarkers.

METHODS AND RESULTS

In 969 stable coronary patients, we determined plasma levels of all the aforementioned components of mineral metabolism with a complete set of clinical and biochemical variables, including N-terminal pro-brain natriuretic peptide (NT-proBNP), high-sensitivity troponin I (hs-TnI), and high-sensitivity C-reactive protein. Secondary outcomes were ischaemic events (any acute coronary syndrome, stroke, or transient ischaemic attack) and heart failure or death. The primary outcome was a composite of the secondary outcomes. Median follow-up was 5.39 years. Age was 60 (52-72) years. Median glomerular filtration rate was 80.4 (65.3-93.1) mL/min/1.73 m2 . One-hundred and eighty-five patients developed the primary outcome. FGF23, PTH, hs-TnI, and NT-proBNP were directly related with the primary outcome on univariate Cox analysis, while Klotho and calcidiol were inversely related. On multivariate analysis, only PTH (HR 1.058 [CI 1.021-1.097]; P = 0.002) and NT-proBNP (HR 1.020 [CI 1.012-1.028]; P < 0.001) were independent predictors of the primary outcome but also for the secondary outcome of heart failure or death (HR 1.066 [CI 1.016-1.119]; P = 0.009 and HR 1.024 [CI 1.014-1.034]; P < 0.001, respectively). PTH was the only biomarker that predicted ischaemic events (HR 1.052 [1.010-1.096]; P = 0.016). Patients were divided in two subgroups according to FGF23 plasma levels. PTH retained its prognostic value only in patients with FGF23 levels above the median (>85.5 RU/mL) (P < 0.001) but not in patients with low FGF23 levels (P = 0.551). There was a significant interaction between FGF23 and PTH (P = 0.002). However, there was no significant interaction between PTH and both klotho and calcidiol levels.

CONCLUSIONS

Parathormone is an independent predictor of cardiovascular events in coronary patients, adding complimentary prognostic information to NT-proBNP plasma levels. This predictive value is restricted to patients with high FGF23 plasma levels. This should be considered in the design of future studies in this field.

A phosphate and calcium-enriched diet promotes progression of 5/6-nephrectomy-induced chronic kidney disease in C57BL/6 mice

C57BL/6 mice are known to be rather resistant to the induction of experimental chronic kidney disease (CKD) by 5/6-nephrectomy (5/6-Nx). Here, we sought to characterize the development of CKD and its cardiac and skeletal sequelae during the first three months after 5/6-Nx in C57BL/6 mice fed a calcium- and phosphate enriched diet (CPD) with a balanced calcium/phosphate ratio. 5/6-NX mice on CPD showed increased renal fibrosis and a more pronounced decrease in glomerular filtration rate when compared to 5/6-Nx mice on normal diet (ND). Interestingly, despite comparable levels of serum calcium, phosphate, and parathyroid hormone (PTH), circulating intact fibroblast growth factor-23 (FGF23) was 5 times higher in 5/6-Nx mice on CPD, relative to 5/6-Nx mice on ND. A time course experiment revealed that 5/6-Nx mice on CPD developed progressive renal functional decline, renal fibrosis, cortical bone loss, impaired bone mineralization as well as hypertension, but not left ventricular hypertrophy. Collectively, our data show that the resistance of C57BL/6 mice to 5/6-Nx can be partially overcome by feeding the CPD, and that the CPD induces a profound, PTH-independent increase in FGF23 in 5/6-Nx mice, making it an interesting tool to assess the pathophysiological significance of FGF23 in CKD.

New Insights into the Role of FGF-23 and Klotho in Cardiovascular Disease in Chronic Kidney Disease Patients

Alterations of fibroblast growth factor 23 (FGF-23) and Klotho levels are considered to be the earliest biochemical abnormality of chronic kidney disease - mineral and bone disease (CKDMBD) syndrome. Moreover, emerging data suggests that the dysregulated FGF-23 and Klotho axis has many effects on the cardiovascular (CV) system and contributes significantly to the increased CV morbidity and mortality rates of CKD patients. This review examines recent evidence on the role of FGF-23 and Klotho in the development and progression of CV complications of uremia namely cardiac hypertrophy, uremic cardiomyopathy, and atherosclerotic and arteriosclerotic vascular lesions. Moreover, the available evidence on their associations with adverse clinical outcomes are summarized. Undoubtedly, more studies are needed to further elucidate the effects of FGF-23 and Klotho on the heart and vessels and to gain insights into their prognostic value as CV risk factors. Finally, large prospective studies are required to test the hypothesis that modification of their levels would have a favourable impact on the unacceptably high mortality rates of these patient populations.

Uraemic solutes as therapeutic targets in CKD-associated cardiovascular disease

Chronic kidney disease (CKD) is characterized by the retention of a myriad of solutes termed uraemic (or uremic) toxins, which inflict damage to several organs, including the cardiovascular system. Uraemic toxins can induce hallmarks of cardiovascular disease (CVD), such as atherothrombosis, heart failure, dysrhythmias, vessel calcification and dysregulated angiogenesis. CVD is an important driver of mortality in patients with CKD; however, reliance on conventional approaches to managing CVD risk is insufficient in these patients, underscoring a need to target risk factors that are specific to CKD. Mounting evidence suggests that targeting uraemic toxins and/or pathways induced by uraemic toxins, including tryptophan metabolites and trimethylamine N-oxide (TMAO), can lower the risk of CVD in patients with CKD. Although tangible therapies resulting from our growing knowledge of uraemic toxicity are yet to materialize, a number of pharmacological and non-pharmacological approaches have the potential to abrogate the effects of uraemic toxins, for example, by decreasing the production of uraemic toxins, by modifying metabolic pathways induced by uraemic toxins such as those controlled by aryl hydrocarbon receptor signalling and by augmenting the clearance of uraemic toxins.

mTOR inhibition improves mitochondria function/biogenesis and delays cardiovascular aging in kidney transplant recipients with chronic graft dysfunction

CVD remains the major cause of mortality with graft functioning in Kidney transplant recipients (KTRs), with an estimated risk of CV events about 50-fold higher than in the general population. Many strategies have been considered to reduce the CV risk such as the use of mTOR inhibitors. We evaluate whether chronic mTOR inhibition might influence CV aging in KTRs studying the molecular mechanisms involved in this effect. We retrospectively analyzed 210 KTRs with stable graft function on therapy with CNI and mycophenolic acid (Group A, 105 pts.), or with CNI and mTORi (Everolimus, Group B, 105 pts.). The presence of mTOR inhibitor in immunosuppressive therapy was associated to increase serum levels of Klotho with concomitant reduction in FGF-23, with a significant decrease in left ventricular mass. In addition, KTRs with mTORi improved mitochondrial function/biogenesis in PBMC with more efficient oxidative phosphorylation, antioxidant capacity and glutathione peroxidase activity. Finally, group B KTRs presented reduced levels of inflammaging markers such as reduced serum pentraxin-3 and p21ink expression in PBMC. In conclusion, we demonstrated that mTOR inhibition in immunosuppressive protocols prevents the occurrence and signs of CV aging in KTRs.

Serum levels of C-terminal FGF23 (cFGF23) are associated with 1-year-mortality in patients undergoing transcatheter aortic valve replacement (TAVR)

INTRODUCTION

Serum levels of FGF23 have been associated with adverse outcomes in cardiovascular diseases in patients with and without impaired renal function. Hence, this study aimed to explore the prognostic relevance of intact FGF23 (iFGF23) and its derivate C-terminal FGF23 (cFGF23) in patients undergoing transcatheter aortic valve replacement (TAVR) with regard to renal function.

METHODS

A total of 274 patients undergoing transfemoral TAVR were enrolled in this study. Blood samples were obtained preinterventionally and analyzed for iFGF23 and cFGF23 by means of enzyme linked immunosorbent assay (ELISA). Follow-up was obtained for 12 months.

RESULTS

Serum levels of cFGF23 and iFGF23 both correlated positively with serum creatinine and inversely with estimated glomerular filtration rate (eGFR). Cox regression analysis revealed a significant association of cFGF23 with 1-year-mortality in patients with eGFR ≥45ml/min/1.73m², but not in patients with an eGFR <45ml/min/1.73m². A cut-off was calculated for cFGF23 (6.82 pmol/l) and patients with eGFR ≥45ml/min/1.73m² were retrospectively divided into two groups (above/below cut-off). Patients above the cut-off had a significantly worse 1-year-mortality than patients below the cut-off (33.3% vs. 19.6%; OR 2.05 (95%CI 1.03-4.07), p= 0.038). The association of cFGF23 with 1-year-mortality in patients with eGFR ≥45ml/min/1.73m² remained statistically significant even after correction for possible confounders in a multivariate Cox regression analysis.

CONCLUSION

cFGF23 could be an individual risk factor for mortality in patients undergoing TAVR with an eGFR ≥45ml/min/1.73m².

Most exposed: the endothelium in chronic kidney disease

Accumulating evidence indicates that the pathological changes of the endothelium may contribute to the development of cardiovascular complications in chronic kidney disease (CKD). Non-traditional risk factors related to CKD are associated with the incidence of cardiovascular disease, but their role in uraemic endothelial dysfunction has often been disregarded. In this context, soluble α-Klotho and vitamin D are of importance to maintain endothelial integrity, but their concentrations decline in CKD, thereby contributing to the dysfunction of the endothelial lining. These hormonal disturbances are accompanied by an increment of circulating fibroblast growth factor-23 and phosphate, both exacerbating endothelial toxicities. Furthermore, impaired renal function leads to an increment of inflammatory mediators, reactive oxygen species and uraemic toxins that further aggravate the endothelial abnormalities and in turn also inhibit the regeneration of disrupted endothelial lining. Here, we highlight the distinct endothelial alterations mediated by the abovementioned non-traditional risk factors as demonstrated in experimental studies and connect these to pathological changes in CKD patients, which are driven by endothelial disturbances, other than atherosclerosis. In addition, we describe therapeutic strategies that may promote restoration of endothelial abnormalities by modulating imbalanced mineral homoeostasis and attenuate the impact of uraemic retention molecules, inflammatory mediators and reactive oxygen species. A clinical perspective on endothelial dysfunction in CKD may translate into reduced structural and functional abnormalities of the vessel wall in CKD, and ultimately improved cardiovascular disease.

Association of a single nucleotide polymorphism combination pattern of the Klotho gene with non-cardiovascular death in patients with chronic kidney disease

Background

Chronic kidney disease (CKD) is associated with an elevated risk of all-cause mortality, with cardiovascular death being extensively investigated. However, non-cardiovascular mortality represents the biggest percentage, showing an evident increase in recent years. Klotho is a gene highly expressed in the kidney, with a clear influence on lifespan. Low levels of Klotho have been linked to CKD progression and adverse outcomes. Single nucleotide polymorphisms (SNPs) of the Klotho gene have been associated with several diseases, but studies investigating the association of Klotho SNPs with non-cardiovascular death in CKD populations are lacking.

Methods

The main aim of this study was to assess whether 11 Klotho SNPs were associated with non-cardiovascular death in a subpopulation of the National Observatory of Atherosclerosis in Nephrology (NEFRONA) study (n = 2185 CKD patients).

Results

After 48 months of follow-up, 62 cardiovascular deaths and 108 non-cardiovascular deaths were recorded. We identified a high non-cardiovascular death risk combination of SNPs corresponding to individuals carrying the most frequent allele (G) at rs562020, the rare allele (C) at rs2283368 and homozygotes for the rare allele (G) at rs2320762 (rs562020 GG/AG + rs2283368 CC/CT + rs2320762 GG). Among the patients with the three SNPs genotyped (n = 1016), 75 (7.4%) showed this combination. Furthermore, 95 (9.3%) patients showed a low-risk combination carrying all the opposite genotypes (rs562020 AA + rs2283368 TT + rs2320762 GT/TT). All the other combinations [n = 846 (83.3%)] were considered as normal risk. Using competing risk regression analysis, we confirmed that the proposed combinations are independently associated with a higher {hazard ratio [HR] 3.28 [confidence interval (CI) 1.51–7.12]} and lower [HR 6 × 10⁻⁶ (95% CI 3.3 × 10⁻⁷–1.1 × 10⁻⁵)] risk of suffering a non-cardiovascular death in the CKD population of the NEFRONA cohort compared with patients with the normal-risk combination.

Conclusions

Determination of three SNPs of the Klotho gene could help in the prediction of non-cardiovascular death in CKD.

Klotho in Clinical Nephrology: Diagnostic and Therapeutic Implications

αKlotho (called Klotho here) is a membrane protein that serves as the coreceptor for the circulating hormone fibroblast growth factor 23 (FGF23). Klotho is also cleaved and released as a circulating substance originating primarily from the kidney and exerts a myriad of housekeeping functions in just about every organ. The vital role of Klotho is shown by the multiorgan failure with genetic deletion in rodents, with certain features reminiscent of human disease. The most common causes of systemic Klotho deficiency are AKI and CKD. Preclinical data on Klotho biology have advanced considerably and demonstrated its potential diagnostic and therapeutic value; however, multiple knowledge gaps exist in the regulation of Klotho expression, release, and metabolism; its target organs; and mechanisms of action. In the translational and clinical fronts, progress has been more modest. Nonetheless, Klotho has potential clinical applications in the diagnosis of AKI and CKD, in prognosis of progression and extrarenal complications, and finally, as replacement therapy for systemic Klotho deficiency. The overall effect of Klotho in clinical nephrology requires further technical advances and additional large prospective human studies.

Fibroblast Growth Factor 23 and Mortality Among Prevalent Hemodialysis Patients in the Japan Dialysis Outcomes and Practice Patterns Study

INTRODUCTION

Elevated fibroblast growth factor 23 (FGF23) levels have been strongly associated with mortality in the predialysis and incident hemodialysis populations, but few studies have examined this relationship in a large cohort of prevalent hemodialysis patients and in particular among persons with high dialysis vintage. To address this, we analyzed data from the Japan Dialysis Outcomes and Practice Patterns Study (J-DOPPS).

METHODS

We included 1122 prevalent hemodialysis patients from the J-DOPPS phase 5 (2012-2015) who had FGF23 measurements. We evaluated the association of FGF23 levels with all-cause mortality and cardiovascular composite outcome using Cox regression adjusted for potential confounders.

RESULTS

At study enrollment, median dialysis vintage was 5.8 years (interquartile range, 2.7-12.4 years) and median FGF23 level was 2113 pg/ml (interquartile range, 583-6880 pg/ml). During 3-year follow-up, 154 of the 1122 participants died. In adjusted analyses, higher FGF23 was associated with a greater hazard of death (hazard ratio per doubling of FGF23, 1.12; 95% confidence interval, 1.03-1.21); however, the association became weaker as the dialysis vintage increased and finally disappeared in the highest tertile (>9.4 years). Similar patterns of effect modification by dialysis vintage were observed for cardiovascular composite outcome and in time-dependent models.

CONCLUSION

Elevated FGF23 was associated with mortality and cardiovascular events in prevalent hemodialysis patients, but the association was attenuated at longer dialysis vintages. This novel finding suggests that long-term hemodialysis patients may be less susceptible to the detrimental effects of FGF23 or correlated biological processes, and additional studies are needed to gain understanding of these possibilities.

Fibroblast Growth Factor 23 and α-Klotho Protein Are Associated with Adverse Clinical Outcomes in Non-Dialysis CKD Patients

BACKGROUND

Fibroblast growth factor 23 (FGF-23) and α-Klotho protein appear to have an important role in the pathogenesis of CKD-mineral and bone disorders. The aim of this study was to investigate the association of FGF-23 and α-Klotho levels with adverse clinical outcomes in patients with non-dialysis CKD.

MATERIALS AND METHODS

We conducted a prospective cohort study, enrolling participants with non-dialysis CKD from a single center in Greece. At enrollment, glomerular filtration rate (GFR) was measured (mGFR) and plasma levels of carboxyl terminal FGF-23 (cFGF-23) and soluble α-Klotho (sKlotho) were determined by enzyme-linked immunoassay. Participants were followed for up to 5 years or until the occurrence of the primary endpoint of initiation of renal replacement therapy or death. Multivariate regression tree analysis was used to identify informative baseline parameters in order to categorize participants. Also, using median values of cFGF-23 and sKlotho, participants were categorized into 4 groups, in whom survival was compared using Kaplan-Meier and Cox regression analysis.

RESULTS

128 participants were enrolled with a median mGFR of 41.5 mL/min/1.73 m2 (IQR = 28.2). Baseline mGFR correlated with cFGF-23 and sKlotho (r = -0.54 and r = 0.49, respectively; p < 0.0001 for both). cFGF-23 and sKlotho levels correlated negatively (r = -0.24, p = 0.006). Multivariate regression tree analysis resulted in 3 groups defined by cutoff values of mGFR (60.9 mL/min/1.73 m2) and phosphate (3.7 mg/dL). These groups correlated with CKD stage, cFGF-23, and sKlotho (p < 0.0001 for all). During a median follow-up of 36 months (IQR = 22), 40 (31.2%) participants reached the primary endpoint (31 initiated renal replacement therapy, 9 died). Survival to primary endpoint differed among the 4 groups formed using median values of both biomarkers, with the low FGF-23/high Klotho and high FGF-23/low Klotho having the longest and shortest survival, respectively. High FGF-23/low Klotho group, compared to the opposite one, had a significantly elevated risk of the primary outcome (HR, 6.8; 95% CI, 2.3-19.6; p = 0.0004).

CONCLUSIONS

In patients with CKD stages 1-5, the combination of higher cFGF-23 and lower sKlotho levels along with mGFR and serum phosphate was associated with adverse clinical outcomes. The utility of combinations of traditional and novel biomarkers to predict outcomes warrants further study.

Endothelial Dysfunction in Chronic Kidney Disease, from Biology to Clinical Outcomes: A 2020 Update

The vascular endothelium is a dynamic, functionally complex organ, modulating multiple biological processes, including vascular tone and permeability, inflammatory responses, thrombosis, and angiogenesis. Endothelial dysfunction is a threat to the integrity of the vascular system, and it is pivotal in the pathogenesis of atherosclerosis and cardiovascular disease. Reduced nitric oxide (NO) bioavailability is a hallmark of chronic kidney disease (CKD), with this disturbance being almost universal in patients who reach the most advanced phase of CKD, end-stage kidney disease (ESKD). Low NO bioavailability in CKD depends on several mechanisms affecting the expression and the activity of endothelial NO synthase (eNOS). Accumulation of endogenous inhibitors of eNOS, inflammation and oxidative stress, advanced glycosylation products (AGEs), bone mineral balance disorders encompassing hyperphosphatemia, high levels of the phosphaturic hormone fibroblast growth factor 23 (FGF23), and low levels of the active form of vitamin D (1,25 vitamin D) and the anti-ageing vasculoprotective factor Klotho all impinge upon NO bioavailability and are critical to endothelial dysfunction in CKD. Wide-ranging multivariate interventions are needed to counter endothelial dysfunction in CKD, an alteration triggering arterial disease and cardiovascular complications in this high-risk population.

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.

Uremic Toxins and Vascular Dysfunction

Vascular dysfunction is an essential element found in many cardiovascular pathologies and in pathologies that have a cardiovascular impact such as chronic kidney disease (CKD). Alteration of vasomotricity is due to an imbalance between the production of relaxing and contracting factors. In addition to becoming a determining factor in pathophysiological alterations, vascular dysfunction constitutes the first step in the development of atherosclerosis plaques or vascular calcifications. In patients with CKD, alteration of vasomotricity tends to emerge as being a new, less conventional, risk factor. CKD is characterized by the accumulation of uremic toxins (UTs) such as phosphate, para-cresyl sulfate, indoxyl sulfate, and FGF23 and, consequently, the deleterious role of UTs on vascular dysfunction has been explored. This accumulation of UTs is associated with systemic alterations including inflammation, oxidative stress, and the decrease of nitric oxide production. The present review proposes to summarize our current knowledge of the mechanisms by which UTs induce vascular dysfunction.

Serum Klotho in Living Kidney Donors and Kidney Transplant Recipients: A Meta-Analysis

α-Klotho is a known anti-aging protein that exerts diverse physiological effects, including phosphate homeostasis. Klotho expression occurs predominantly in the kidney and is significantly decreased in patients with chronic kidney disease. However, changes in serum klotho levels and impacts of klotho on outcomes among kidney transplant (KTx) recipients and kidney donors remain unclear. A literature search was conducted using MEDLINE, EMBASE, and Cochrane Database from inception through October 2019 to identify studies evaluating serum klotho levels and impacts of klotho on outcomes among KTx recipients and kidney donors. Study results were pooled and analyzed utilizing a random-effects model. Ten cohort studies with a total of 431 KTx recipients and 5 cohort studies with a total of 108 living kidney donors and were identified. After KTx, recipients had a significant increase in serum klotho levels (at 4 to 13 months post-KTx) with a mean difference (MD) of 243.11 pg/mL (three studies; 95% CI 67.41 to 418.81 pg/mL). Although KTx recipients had a lower serum klotho level with a MD of = -234.50 pg/mL (five studies; 95% CI -444.84 to -24.16 pg/mL) compared to healthy unmatched volunteers, one study demonstrated comparable klotho levels between KTx recipients and eGFR-matched controls. Among kidney donors, there was a significant decrease in serum klotho levels post-nephrectomy (day 3 to day 5) with a mean difference (MD) of -232.24 pg/mL (three studies; 95% CI -299.41 to -165.07 pg/mL). At one year following kidney donation, serum klotho levels remained lower than baseline before nephrectomy with a MD of = -110.80 pg/mL (two studies; 95% CI 166.35 to 55.24 pg/mL). Compared to healthy volunteers, living kidney donors had lower serum klotho levels with a MD of = -92.41 pg/mL (two studies; 95% CI -180.53 to -4.29 pg/mL). There is a significant reduction in serum klotho levels after living kidney donation and an increase in serum klotho levels after KTx. Future prospective studies are needed to assess the impact of changes in klotho on clinical outcomes in KTx recipients and living kidney donors.

Fibroblast growth factor 23: are we ready to use it in clinical practice?

Patients with chronic kidney disease (CKD) have a greatly enhanced risk of cardiovascular morbidity and mortality. Over the past decade it has come clear that a disturbed calcium-phosphate metabolism, with Fibroblast Growth Factor-23 as a key hormone, is partly accountable for this enhanced risk. Numerous studies have been performed unravelling FGF23s actions and its association with clinical conditions. As FGF23 is strongly associated with adverse outcome it may be a promising biomarker for risk prediction or, even more important, targeting FGF23 may be a strategy to improve patient outcome. This review elaborates on the clinical usefulness of FGF23 measurement. Firstly it discusses the reliability of the FGF23 measurement. Secondly, it evaluates whether FGF23 measurement may lead to improved patient risk classification. Finally, and possibly most importantly, this review evaluates if lowering of FGF23 should be a target for therapy. For this, the review discusses the current evidence indicating that FGF23 may be in the causal pathway to cardiovascular pathology, provides an overview of strategies to lower FGF23 levels and discusses the current evidence concerning the benefit of lowering FGF23.

Serum Klotho, Cardiovascular Events, and Mortality in Nondiabetic Chronic Kidney Disease

Background: Experimental studies indicate that Klotho deficiency is a pathogenic factor for CKD-related complications, including cardiovascular disease (CVD). However, the association between serum Klotho and clinical outcomes in nondiabetic CKD patients needs to be further clarified. We aimed to determine whether serum Klotho levels are associated with CVD events and mortality in predialysis CKD patients without diabetes. Methods: A total of 336 CKD stage 2–5 predialysis patients without diabetes were recruited and followed from the end of 2014 to January 2019 for CVD events and overall mortality. Serum Klotho was detected by ELISA and divided into quartiles (lowest, middle, second highest, and highest quartiles) according to their serum Klotho category. Results: After a median follow-up of 3.52 years (IQR 3.34–3.76), Kaplan-Meier analysis showed that, compared to participants with a Klotho level in the highest quartile (the reference category), those in the lowest Klotho quartile were associated with a higher all-cause mortality risk (HR = 7.05; 95% CI 1.59–31.25) and a higher CVD event risk (HR = 3.02; 95% CI 1.45–6.30). In addition, the middle Klotho quartile was also associated with CVD event risk (HR = 2.56; 95% CI 1.21–5.41). Moreover, in the multivariate-adjusted model, the lowest Klotho quartile remained significantly associated with all-cause mortality (HR = 5.17; 95% CI 1.07–24.96), and the middle Klotho quartile maintained a significant association with CVD event risk (HR = 2.32; 95% CI 1.03–5.21). Conclusion: These results suggest that lower serum Klotho levels are independently associated with overall mortality and CVD events in nondiabetic predialysis CKD patients.

Clinical Potential of Targeting Fibroblast Growth Factor-23 and αKlotho in the Treatment of Uremic Cardiomyopathy

Chronic kidney disease is highly prevalent, affecting 10% to 15% of the adult population worldwide and is associated with increased cardiovascular morbidity and mortality. As chronic kidney disease worsens, a unique cardiovascular phenotype develops characterized by heart muscle disease, increased arterial stiffness, atherosclerosis, and hypertension. Cardiovascular risk is multifaceted, but most cardiovascular deaths in patients with advanced chronic kidney disease are caused by heart failure and sudden cardiac death. While the exact drivers of these deaths are unknown, they are believed to be caused by uremic cardiomyopathy: a specific pattern of myocardial hypertrophy, fibrosis, with both diastolic and systolic dysfunction. Although the pathogenesis of uremic cardiomyopathy is likely to be multifactorial, accumulating evidence suggests increased production of fibroblast growth factor-23 and αKlotho deficiency as potential major drivers of cardiac remodeling in patients with uremic cardiomyopathy. In this article we review the increasing understanding of the physiology and clinical aspects of uremic cardiomyopathy and the rapidly increasing knowledge of the biology of both fibroblast growth factor-23 and αKlotho. Finally, we discuss how dissection of these pathological processes is aiding the development of therapeutic options, including small molecules and antibodies, directly aimed at improving the cardiovascular outcomes of patients with chronic kidney disease and end-stage renal disease.

Parathyroid Hormone and Plasma Phosphate Are Predictors of Soluble α-Klotho Levels in Adults of European Descent

CONTEXT

α-klotho is an integral membrane protein that serves as a coreceptor for fibroblast growth factor 23 (FGF23) in conjunction with cognate fibroblast growth factor receptors. Proteolytic cleavage sheds the ectodomain of α-klotho (soluble α-klotho) as an endocrine substance into blood, urine, and cerebrospinal fluid.

OBJECTIVE

To study the relationship of soluble α-klotho to mineral metabolism in the general population with mainly preserved kidney function.

DESIGN

Cross-sectional analysis of the associations between soluble α-klotho with laboratory markers of markers of mineral metabolism in a population-based cohort.

SETTING

Three centers in Switzerland including 1128 participants.

MEASURES

Soluble full-length α-klotho levels by a specific immunoassay and markers of mineral metabolism.

RESULTS

The median serum level of soluble α-klotho was 15.0 pmol/L. Multivariable analyses using α-klotho as the outcome variable revealed a sex-by-PTH interaction: In men, PTH was positively associated with α-klotho levels, whereas this association was negative in women. Plasma phosphate associated with soluble α-klotho levels in an age-dependent manner, changing from a positive association in young adults gradually to a negative association in the elderly. The decline of 1,25 (OH)2 vitamin D3 levels in parallel to the gradual impairment of kidney function was greatly attenuated in the setting of high circulating soluble α-klotho levels.

CONCLUSIONS

Soluble α-klotho level is associated with plasma phosphate in an age-dependent manner and with PTH in a sex-dependent manner. Furthermore, our data reveal soluble α-klotho as a modulator of 1,25 (OH)2 vitamin D3 levels in individuals with preserved renal function.

Nephrology and Public Policy Committee propositions to stimulate research collaboration in adults and children in Europe

The strengths and the limitations of research activities currently present in Europe are explored in order to outline how to proceed in the near future. Epidemiological and clinical research and public policy in Europe are generally considered to be comprehensive and successful, and the European Renal Association – European Dialysis and Transplant Association (ERA-EDTA) is playing a key role in the field of nephrology research. The Nephrology and Public Policy Committee (NPPC) aims to improve the current situation and translation into public policy by planning eight research topics to be supported in the coming 5 years by ERA-EDTA.

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

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

Stabilization of cell-cell junctions by active vitamin D ameliorates uraemia-induced loss of human endothelial barrier function

Background

Uraemia induces endothelial cell (EC) injury and impaired repair capacity, for which the underlying mechanism remains unclear. Active vitamin D (VD) may promote endothelial repair, however, the mechanism that mediates the effects of VD in chronic kidney disease are poorly understood. Thus, we investigated uraemia-induced endothelial damage and the protection against such damage by active VD.

Methods

We applied electric cell-substrate impedance sensing (ECIS) to study real-time responses of human ECs exposed to pooled uraemic and non-uraemic plasma with or without the addition of active VD. The effects of indoxyl sulphate and p-cresol were tested in non-uraemic plasma. Structural changes for vascular endothelial (VE)-cadherin and F-actin were assessed by immunostaining and quantified.

Results

The exposure of ECs to uraemic media significantly decreased endothelial barrier function after 24 h. Cell migration after electrical wounding and recovery of the barrier after thrombin-induced loss of integrity were significantly impaired in uraemic-medium stimulated cells and cells exposed to indoxyl sulphate and p-cresol. This effect on ECIS was dependent on loss of cell-cell interaction. Mechanistically, we found that EC, exposed to uraemic media, displayed disrupted VE-cadherin interactions and F-actin reorganization. VD supplementation rescued both endothelial barrier function and cell-cell interactions in ECs exposed to uraemic media. These events were associated with an increment of VE-cadherin at intercellular junctions.

Conclusions

Our data demonstrate a potentially clinically relevant mechanism for uraemia-induced endothelial damage. Furthermore, active VD rescued the uraemic medium-induced loss of cell-cell adhesion, revealing a novel role of active VD in preservation of endothelial integrity during uraemia.

Limited role for fibroblast growth factor 23 in assessing prognosis in heart failure patients: data from the TIME-CHF trial

AIM

Fibroblast growth factor 23 (FGF23) is an intensively studied biomarker at the crossroads of cardiovascular disease, heart failure (HF) and chronic kidney disease. Independent associations between increasing FGF23 levels and cardiovascular events were found in many, but not all studies. By analysing data from the TIME-CHF cohort, we sought to investigate the prognostic value of FGF23 in an elderly, multimorbid HF patient cohort. We determined differences between intact (iFGF23) and C-terminal FGF23 (cFGF23) regarding their prognostic value and their levels over time in different HF subgroups according to left ventricular ejection fraction (LVEF).

METHODS AND RESULTS

In this multicentre trial of 622 patients with symptomatic HF aged ≥60 years, we determined iFGF23 and cFGF23 at baseline, 3, 6 and 12-month follow-up. In unadjusted analyses, cFGF23 significantly predicted all HF-related outcomes at all time points. The predictive value of iFGF23 was less and not statistically significant at baseline. After multivariable adjustments, the association between both cFGF23 and iFGF23 and outcome lost statistical significance apart from cFGF23 at month 3. Overall, patients with preserved and mid-range LVEF had higher levels of iFGF23 and cFGF23 than those with reduced LVEF. Levels decreased significantly during the first 3 months in mid-range and reduced LVEF patients, but did not significantly change over time in those with preserved LVEF.

CONCLUSIONS

Fibroblast growth factor 23 is of limited value regarding risk prediction in this elderly HF population. Potentially heterogeneous roles of FGF23 in different LVEF groups deserve further investigation.

Cystatin C for Risk Stratification in Patients After an Acute Coronary Syndrome

Background

Cystatin C (Cys‐C) is a marker of renal function that has shown prognostic value for cardiovascular risk stratification across different patient populations. The incremental value of Cys‐C beyond established cardiac and renal biomarkers remains incompletely explored.

Methods and Results

SOLID‐TIMI 52 (Stabilization of Plaques Using Darapladib‐Thrombolysis in Myocardial Infarction 52; http://www.clinicaltrials.gov, NCT01000727) randomized patients ≤30 days post–acute coronary syndrome were treated with darapladib or placebo. The association between Cys‐C and long‐term risk (median follow‐up 2.5 years) was assessed in 4965 individuals with adjustments made for clinical variables and other risk markers (eg, estimated glomerular filtration rate, high‐sensitivity troponin I, brain‐type natriuretic peptide, and fibroblast growth factor‐23). The prespecified outcome of interest was cardiovascular death (CVD) or heart failure hospitalization. Cys‐C was strongly correlated with creatinine (r=0.60) and estimated glomerular filtration rate (r=−0.68), moderately correlated with fibroblast growth factor‐23 (r=0.39), and weakly correlated with brain‐type natriuretic peptide (r=0.28) and high‐sensitivity troponin I (r=0.06) (all P<0.0001). After multivariate adjustment, increasing concentration of Cys‐C (per SD of log‐transformed Cys‐C) was significantly associated with a 28% higher hazard of CVD or heart failure hospitalization (hazard ratio [HR] 1.28, 95% confidence interval [CI] 1.12‐1.46, P<0.001), including CVD (HR 1.24, 95% CI 1.04‐1.47, P=0.01) and heart failure hospitalization (HR 1.42, 95% CI 1.19‐1.69, P<0.001). Cys‐C was also associated with a higher hazard of CVD, myocardial infarction, or stroke (HR 1.15, 95% CI 1.04‐1.28, P<0.01), including myocardial infarction (HR 1.17, 95% CI 1.02‐1.33, P=0.02). The addition of Cys‐C to a fully adjusted model without estimated glomerular filtration rate improved the C‐statistic from 0.80 to 0.81 (P=0.03) for CVD or heart failure hospitalization. In contrast, the addition of estimated glomerular filtration rate to a fully adjusted model without Cys‐C failed to improve model discrimination (P=0.17).

Conclusions

Cys‐C is associated with the risk of adverse outcomes in patients after acute coronary syndrome. This relationship is independent of established and novel biomarkers of the cardiorenal axis.

Early renal dysfunction and fibroblast growth factor-23 in patients with small vessel disease-related stroke

Interactions between cerebral small vessel disease (CSVD) and renal dysfunction (RD) have been reported, but previous studies were mostly retrospective and limited to measurements of estimated glomerular filtration rate (eGFR). In this prospective, longitudinal study of patients with CSVD-related recent small subcortical infarcts (RSSI), we aimed at a comprehensive exploration of markers of early RD and their association with microvascular brain damage. We investigated 101 stroke patients (mean age: 60.2 ± 10.7 years) with an MRI-confirmed RSSI who underwent follow-up brain MRI 15 months post-stroke. Besides serum creatinine and eGFR, we assessed urinary Albumin-Creatinine Ratio and fibroblast growth factor-23 (FGF-23). RD was classified according to recent Kidney Disease: Improving Global Outcomes criteria. We identified 24 patients with RD, only six patients revealed an eGFR <60 mL/min/1.73 m². RSSI patients with RD more often had severe white matter hyperintensities (WMH, 58% vs. 36%, p = 0.04). CSVD progression was not dependent on RD. However, patients in the highest FGF-23 quartile more frequently had new microangiopathic lesions on follow-up MRI (50% vs. 21%, p = 0.03). Early RD was found in a quarter of RSSI patients and associated with WMH severity, but not CSVD progression. High FGF-23 indicates an increased risk for ongoing microvascular brain damage, warranting further studies.

Albumin downregulates Klotho in tubular cells

Background

Kidney tubular cells are the main sources of Klotho, a protein with phosphaturic action. Genetic Klotho deficiency causes premature cardiovascular aging in mice. Human chronic kidney disease (CKD) is characterized by acquired Klotho deficiency. Despite the lack of uremic toxin accumulation, Category G1 CKD [(normal glomerular filtration rate (GFR)] is already associated with decreased Klotho and with premature cardiovascular aging.

Methods

We have explored whether albuminuria, a criterion to diagnose CKD when GFR is normal, may directly decrease Klotho expression in human CKD, preclinical models and cultured tubular cells.

Results

In a CKD cohort, albuminuria correlated with serum phosphate after adjustment for GFR, age and sex. In this regard, urinary Klotho was decreased in patients with pathological albuminuria but preserved GFR. Proteinuria induced in rats by puromycin aminonucleoside and in mice by albumin overload was associated with interstitial inflammation and reduced total kidney Klotho messenger ribonucleic acid (mRNA) expression. Western blot disclosed reduced kidney Klotho protein in proteinuric rats and mice and immunohistochemistry localized the reduced kidney Klotho expression to tubular cells in proteinuric animals. In cultured murine and human tubular cells, albumin directly decreased Klotho mRNA and protein expression. This was inhibited by trichostatin A, an inhibitor of histone deacetylases, but unlike cytokine-induced Klotho downregulation, not by inhibitors of nuclear factor kappa-light-chain-enhancer of activated B cells.

Conclusions

In conclusion, albumin directly decreases Klotho expression in cultured tubular cells. This may explain, or at least contribute to, the decrease in Klotho and promote fibroblast growth factor 23 resistance in early CKD categories, as observed in preclinical and clinical proteinuric kidney disease.