Fibroblast growth factor 23 is not associated with and does not induce arterial calcification

FGF-23 and Long-term Outcome in Peripheral Artery Disease

Atherosclerotic peripheral artery disease (PAD) and chronic kidney disease (CKD) are highly interconnected diseases, while causes for excess mortality are not well-defined. Fibroblast growth-factor 23 (FGF-23) is elevated in mineral bone disease of CKD and was shown to be associated with higher mortality. However, it is not known if this association extends to PAD. FGF-23 was measured by ELISA in serum samples of 298 patients with stable PAD (Fontaine stage I-II) with an estimated glomerular filtration rate (eGFR) of 72 (58-85) ml/min. Mortality was assessed after a long-term follow-up of up to 10 years. FGF-23 showed significant associations with markers of metabolic syndrome (triglycerides r = .25, P < .001, high-density lipoprotein cholesterol (HDL-C) r = -.28, P < .001, c-reactive protein (CRP) r = .14, P = .016). Multivariable Cox-regression outcome analyses showed significant associations between FGF-23 and all-cause mortality (hazard ratio 1.35, 95% confidence interval 1.05-1.74) in PAD patients even after adjustment for traditional cardiovascular risk factors and renal excretory function. FGF-23 is associated with higher mortality in patients with PAD. Our findings indicate that FGF-23 has detrimental effects on patients with PAD that are independent of renal excretory function.

Serum calciprotein particle-to-phosphate ratio as a predictor of cardiovascular events in incident hemodialysis patients

INTRODUCTION

Recent studies have identified increased blood calciprotein particle (CPP) levels as risk factors for vascular calcification and cardiovascular events in patients undergoing maintenance hemodialysis. Although positively correlated with serum phosphate levels, serum CPP levels vary considerably among patients with similar serum phosphate levels. We investigated the capacity of the ratio of serum CPP levels to serum phosphate levels (CPP/Pi ratio) to predict cardiovascular events in incident hemodialysis patients compared to the serum calcification propensity test (T50).

METHODS AND RESULTS

The association between the CPP/Pi ratio and major adverse cardiac and cerebrovascular events (MACCE) was investigated in 174 incident hemodialysis patients. Multivariate analysis revealed that the CPP/Pi ratio was independently associated with MACCE [hazard ratio 1.60, 95% confidence interval (1.15-2.23), p = 0.006] but serum T50 levels were not.

CONCLUSIONS

The CPP/Pi ratio is a useful, novel biomarker for predicting the risk of cardiovascular events in patients undergoing incident hemodialysis.

The true cost of phosphate control in chronic kidney disease

The loss of kidney function entails the development of a positive phosphate balance. The burden of addressing elevated phosphate levels is high. Both parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) are increased to promote phosphaturia, thereby preventing the rise in serum phosphate. However, if the phosphate load is excessive, the corresponding phosphaturia is maximal, kidney function deteriorates and hyperphosphataemia becomes clinically evident in advanced stages of chronic kidney disease (CKD). In addition to its role in CKD progression, hyperphosphataemia has been linked to a multitude of adverse outcomes, including overt inflammation, vascular calcifications, endothelial dysfunction, cardiovascular disease, renal osteodystrophy and secondary hyperparathyroidism. Collectively, these factors contribute to the markedly elevated mortality rates observed among individuals with CKD. Furthermore, hyperphosphataemia has been identified as a significant contributor to the development of inflammatory processes, oxidative stress and fibrosis, which underlie the aetiology of numerous comorbidities. Additionally, elevated levels of PTH and FGF23 have been demonstrated to independently induce organ and tissue injury, which is associated with poor outcomes in CKD. This article provides a concise overview of the current understanding of phosphate handling by the kidney in the context of CKD. It outlines the detrimental effects of phosphate on various organs and the mechanisms through which it contributes to CKD progression. Additionally, we discuss the tools available for clinicians to identify patients at risk of an excessive phosphate load.

Non-Classical Effects of FGF23: Molecular and Clinical Features

This article reviews the role of fibroblast growth factor 23 (FGF23) protein in phosphate metabolism, highlighting its regulation of vitamin D, parathyroid hormone, and bone metabolism. Although it was traditionally thought that phosphate-calcium homeostasis was controlled exclusively by parathyroid hormone (PTH) and calcitriol, pathophysiological studies revealed the influence of FGF23. This protein, expressed mainly in bone, inhibits the renal reabsorption of phosphate and calcitriol formation, mediated by the α-klotho co-receptor. In addition to its role in phosphate metabolism, FGF23 exhibits pleiotropic effects in non-renal systems such as the cardiovascular, immune, and metabolic systems, including the regulation of gene expression and cardiac fibrosis. Although it has been proposed as a biomarker and therapeutic target, the inhibition of FGF23 poses challenges due to its potential side effects. However, the approval of drugs such as burosumab represents a milestone in the treatment of FGF23-related diseases.

Comparative Analysis of Vascular Calcification Risk Factors in Pre-Hemodialysis and Prevalent Hemodialysis Adult Patients: Insights into Calcification Biomarker Associations and Implications for Intervention Strategies in Chronic Kidney Disease

This retrospective study aimed to compare risk factors for vascular calcification (VC) between pre-hemodialysis (HD) and prevalent HD adult patients while investigating associations with calcification biomarkers. Baseline data from 30 pre-HD and 85 HD patients were analyzed, including iPTH, vitamin D, FGF 23, fetuin-A, sclerostin, and VC scores (Adragao method). Prevalence of VC was similar in both groups, but HD patients had more frequent VC scores ≥ 6. Pre-HD patients were older, with higher prevalence of hypertension and less frequent use of calcium phosphate binders. Both groups showed similar patterns of hyperphosphatemia, low vitamin D, and iPTH. Fetuin-A and sclerostin levels were higher in pre-HD, while FGF 23 was elevated in HD patients. Higher VC risk in pre-HD patients was associated with male gender, older age, lower fetuin-A and higher sclerostin, lower ferritin, and no vitamin D treatment, while in HD patients with higher sclerostin, FGF 23 and urea, and lower iPTH. Conclusion: Biomarkers could be measurable indicators of biological processes underlying VC in CKD patients that may serve as a potential guide for considering personalized therapeutic approaches. Further studies are needed to elucidate the underlying pathways.

Role of klotho and fibroblast growth factor 23 in arterial calcification, thickness, and stiffness: a meta-analysis of observational studies

This meta-analysis was conducted to clarify the role of klotho and fibroblast growth factor 23 (FGF-23) in human arterial remodeling across recent studies, in terms of arterial calcification, thickness, and stiffness. A systematic literature search was conducted on five databases for articles up to December 2023. Arterial calcification, thickness, and stiffness were determined using the calcification score and artery affected, carotid intima-media thickness (CIMT), and pulse wave velocity (PWV), respectively. Sixty-two studies with a total of 27,459 individuals were included in this meta-analysis. Most studies involved chronic kidney disease patients. Study designs were mostly cross-sectional with only one case-control and nine cohorts. FGF-23 was positively correlated with arterial calcification (r = 0.446 [0.254-0.611], p < 0.0001 and aOR = 1.36 [1.09-1.69], p = 0.006), CIMT (r = 0.188 [0.02-0.354], p = 0.03), and PWV (r = 0.235 [0.159-0.310], p < 0.00001). By contrast, Klotho was inversely correlated with arterial calcification (r = - 0.388 [- 0.578 to - 0.159], p = 0.001) and CIMT (r = - 0.38 [- 0.53 to - 0.207], p < 0.00001). In conclusion, FGF-23 and Klotho were associated with arterial calcification, thickness, and stiffness, clarifying their role in arterial remodeling processes.

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.

NT-proBNP Mediates the Association Between FGF23 and All-Cause Mortality in Individuals With Type 2 Diabetes

BACKGROUND

FGF23 (fibroblast growth factor 23) is associated with a higher mortality risk in type 2 diabetes, but the mechanism is unclear. We aimed to study whether NT-proBNP (N-terminal pro-brain natriuretic peptide) mediates the association between FGF23 and mortality.

METHODS AND RESULTS

We analyzed C-terminal FGF23 and NT-proBNP levels in 399 patients with type 2 diabetes. Cox regression analyses were performed, followed by mediation analyses using Structural Equation Modeling. During follow-up of 9.2 [7.6-11.3] years, 117 individuals died. FGF23 was associated with all-cause mortality, independent of potential confounders (fully adjusted hazard ratio [HR], 2.32 [95% CI, 1.21-4.43], P=0.01). The association was lost upon further adjustment for NT-proBNP (HR, 1.84; 95% CI, 0.91-3.73). NT-proBNP accounted for 26% of the mediation effect between FGF23 and all-cause mortality.

CONCLUSIONS

These findings suggest that a higher FGF23 level is associated with increased mortality in individuals with type 2 diabetes through an effect on volume homeostasis.

Vascular calcification: from the perspective of crosstalk

Vascular calcification (VC) is highly correlated with cardiovascular disease morbidity and mortality, but anti-VC treatment remains an area to be tackled due to the ill-defined molecular mechanisms. Regardless of the type of VC, it does not depend on a single cell but involves multi-cells/organs to form a complex cellular communication network through the vascular microenvironment to participate in the occurrence and development of VC. Therefore, focusing only on the direct effect of pathological factors on vascular smooth muscle cells (VSMCs) tends to overlook the combined effect of other cells and VSMCs, including VSMCs-VSMCs, ECs-VMSCs, Macrophages-VSMCs, etc. Extracellular vesicles (EVs) are a collective term for tiny vesicles with a membrane structure that are actively secreted by cells, and almost all cells secrete EVs. EVs docked on the surface of receptor cells can directly mediate signal transduction or transfer their contents into the cell to elicit a functional response from the receptor cells. They have been proven to participate in the VC process and have also shown attractive therapeutic prospects. Based on the advantages of EVs and the ability to be detected in body fluids, they may become a novel therapeutic agent, drug delivery vehicle, diagnostic and prognostic biomarker, and potential therapeutic target in the future. This review focuses on the new insight into VC molecular mechanisms from the perspective of crosstalk, summarizes how multi-cells/organs interactions communicate via EVs to regulate VC and the emerging potential of EVs as therapeutic methods in VC. We also summarize preclinical experiments on crosstalk-based and the current state of clinical studies on VC-related measures.

Targeting aging with the healthy skeletal system: The endocrine role of bone

Aging is an inevitable biological process, and longevity may be related to bone health. Maintaining strong bone health can extend one's lifespan, but the exact mechanism is unclear. Bone and extraosseous organs, including the heart and brain, have complex and precise communication mechanisms. In addition to its load bearing capacity, the skeletal system secretes cytokines, which play a role in bone regulation of extraosseous organs. FGF23, OCN, and LCN2 are three representative bone-derived cytokines involved in energy metabolism, endocrine homeostasis and systemic chronic inflammation levels. Today, advanced research methods provide new understandings of bone as a crucial endocrine organ. For example, gene editing technology enables bone-specific conditional gene knockout models, which allows the study of bone-derived cytokines to be more precise. We systematically evaluated the various effects of bone-derived cytokines on extraosseous organs and their possible antiaging mechanism. Targeting aging with the current knowledge of the healthy skeletal system is a potential therapeutic strategy. Therefore, we present a comprehensive review that summarizes the current knowledge and provides insights for futures studies.

Pathophysiology and Clinical Impacts of Chronic Kidney Disease on Coronary Artery Calcification

The global prevalence of chronic kidney disease (CKD) has increased in recent years. Adverse cardiovascular events have become the main cause of life-threatening events in patients with CKD, and vascular calcification is a risk factor for cardiovascular disease. Vascular calcification, especially coronary artery calcification, is more prevalent, severe, rapidly progressive, and harmful in patients with CKD. Some features and risk factors are unique to vascular calcification in patients with CKD; the formation of vascular calcification is not only influenced by the phenotypic transformation of vascular smooth muscle cells, but also by electrolyte and endocrine dysfunction, uremic toxin accumulation, and other novel factors. The study on the mechanism of vascular calcification in patients with renal insufficiency can provide a basis and new target for the prevention and treatment of this disease. This review aims to illustrate the impact of CKD on vascular calcification and to discuss the recent research data on the pathogenesis and factors involved in vascular calcification, mainly focusing on coronary artery calcification, in patients with CKD.

Kidney function, bone-mineral metabolism markers, and calcification of coronary arteries, aorta, and cardiac valves in older adults

BACKGROUND AND AIMS

The contribution of kidney dysfunction, especially at mild-to-moderate stages, and bone-mineral metabolism (BMM) markers to vascular calcification remains controversial or unclear. We comprehensively evaluated the association of kidney and BMM markers with coronary artery calcification (CAC) and extra-coronary calcification (ECC).

METHODS

In 1931 ARIC participants (age 73-95 years) without coronary heart disease at visit 7 (2018-19), we investigated the associations of estimated glomerular filtration rate (eGFR) (with creatinine, cystatin C, and both) and five serum BMM markers (calcium, fibroblast growth factor 23, magnesium, parathyroid hormone, and phosphorus) with high CAC and ECC (sex-race specific ≥75th vs. <75th percentile Agatston score) or any vs. zero CAC and ECC using multivariable logistic regression. For eGFR and BMM markers, we took their weighted cumulative averages from visit 1 (1987-89) to visit 5 (2011-13).

RESULTS

Lower eGFR, regardless of equations used, was not robustly associated with high CAC or ECC. Among BMM markers, only higher phosphorus levels, even within the normal range, showed robust associations with high CAC (only when modeled continuously) and ECC, independently of kidney function (e.g., odds ratio 1.94 [95%CI 1.38-2.73] for high aortic valve calcification, in the highest vs. lowest quartile). Results were generally consistent when analyzing any CAC or ECC, although cystatin C-based eGFR <60 mL/min/1.73 m2 became significantly associated with mitral valve calcification (odds ratio 1.69 [1.10-2.60]).

CONCLUSIONS

Among kidney and BMM measures tested, only serum phosphorus demonstrated robust associations with both CAC and ECC, supporting a key role of phosphorus in the pathophysiology of vascular calcification.

Correlation of Serum FGF23 and Chronic Kidney Disease-Mineral and Bone Abnormality Markers With Cardiac Structure Changes in Maintenance Hemodialysis Patients

Background

CKD-MBD is a mineral and bone metabolism syndrome caused by chronic kidney disease. FGF23 is an important factor regulating phosphorus and is the main influencer in the CKD-MBD process. In this study, we observed the correlation among serum FGF23 and calcium, phosphorus and parathyroid hormone, and the correlation between FGF23 levels and cardiac structural changes in MHD patients.

Methods

We examined serum FGF23 concentrations in 107 cases of MHD patients using the ELISA method, recorded demographic information and biochemical data, and analyzed the correlation between serum FGF23 levels and blood calcium and blood phosphorus and PTH levels. All patients were evaluated by cardiac color ultrasound, and we finally analyzed the association between the FGF23 level and cardiac structural changes.

Results

In 107 cases of MHD patients, serum FGF23 levels were linearly associated with serum calcium (r = 0.27 P < 0.01) and parathyroid hormone levels (r = 0.25, P < 0.05). FGF 23 was negatively correlated with age (r = -0.44, P < 0.01).Serum FGF23 levels were correlated with right atrial hypertrophy in HD patients (P < 0.05). No correlation was found among FGF23, left ventricular hypertrophy/enlargement, and valve calcification stenosis (P > 0.05).

Conclusion

Serum FGF23 showed a positive correlation among blood calcium levels and PTH levels in hemodialysis patients, and FGF23 levels can affect the incidence of right atrial hypertrophy in MHD patients.

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.

Genetic Evidence for a Causal Role of Serum Phosphate in Coronary Artery Calcification: The Rotterdam Study

Background

Hyperphosphatemia has been associated with coronary artery calcification (CAC) mostly in chronic kidney disease, but the association between phosphate levels within the normal phosphate range and CAC is unclear. Our objectives were to evaluate associations between phosphate levels and CAC among men and women from the general population and assess causality through Mendelian randomization.

Methods and Results

CAC, measured by electron‐beam computed tomography, and serum phosphate levels were assessed in 1889 individuals from the RS (Rotterdam Study). Phenotypic associations were tested through linear models adjusted for age, body mass index, blood pressure, smoking, prevalent cardiovascular disease and diabetes, 25‐hydroxyvitamin D, total calcium, C‐reactive protein, glucose, and total cholesterol : high‐density lipoprotein cholesterol ratio. Mendelian randomization was implemented through an allele score including 8 phosphate‐related single‐nucleotide polymorphisms. In phenotypic analyses, serum phosphate (per 1 SD) was associated with CAC with evidence for sex interaction (P_interaction=0.003) (men β, 0.44 [95% CI, 0.30–0.59]; P=3×10⁻⁹; n=878; women β, 0.24 [95% CI, 0.08–0.40]; P=0.003; n=1011). Exclusion of hyperphosphatemia, chronic kidney disease (estimated glomerular filtration rate <60 mL/min per 1.73 m²) and prevalent cardiovascular disease yielded similar results. In Mendelian randomization analyses, instrumented phosphate was associated with CAC (total population β, 0.93 [95% CI: 0.07–1.79]; P=0.034; n=1693), even after exclusion of hyperphosphatemia, chronic kidney disease and prevalent cardiovascular disease (total population β, 1.23 [95% CI, 0.17–2.28]; P=0.023; n=1224).

Conclusions

Serum phosphate was associated with CAC in the general population with stronger effects in men. Mendelian randomization findings support a causal relation, also for serum phosphate and CAC in subjects without hyperphosphatemia, chronic kidney disease, and cardiovascular disease. Further research into underlying mechanisms of this association and sex differences is needed.

The direct effect of fibroblast growth factor 23 on vascular smooth muscle cell phenotype and function

BACKGROUND

In chronic kidney disease (CKD) patients, increased levels of fibroblast growth factor 23 (FGF23) are associated with cardiovascular mortality. The relationship between FGF23 and heart hypertrophy has been documented, however, it is not known whether FGF23 has an effect on vasculature. Vascular smooth muscle cells VSMCs may exhibit different phenotypes; our hypothesis is that FGF23 favours a switch from a contractile to synthetic phenotype that may cause vascular dysfunction. Our objective was to determine whether FGF23 may directly control a change in VSMC phenotype.

METHODS

This study includes in vitro, in vivo and ex vivo experiments and evaluation of patients with CKD stages 2-3 studying a relationship between FGF23 and vascular dysfunction.

RESULTS

In vitro studies show that high levels of FGF23, by acting on its specific receptor FGFR1 and Erk1/2, causes a change in the phenotype of VSMCs from contractile to synthetic. This change is mediated by a downregulation of miR-221/222, which augments the expression of MAP3K2 and PAK1. miR-221/222 transfections recovered the contractile phenotype of VSMCs. Infusion of recombinant FGF23 to rats increased vascular wall thickness, with VSMCs showing a synthetic phenotype with a reduction of miR-221 expression. Ex-vivo studies on aortic rings demonstrate also that high FGF23 increases arterial stiffening. In CKD 2-3 patients, elevation of FGF23 was associated with increased pulse wave velocity and reduced plasma levels of miR-221/222.

CONCLUSION

In VSMCs, high levels of FGF23, through the downregulation of miR-221/222, causes a change to a synthetic phenotype. This change in VSMCs increases arterial stiffening and impairs vascular function, which might ultimately worsen cardiovascular disease.

Histone Lysine Methylation Modification and Its Role in Vascular Calcification

Histone methylation is an epigenetic change mediated by histone methyltransferase, and has been connected to the beginning and progression of several diseases. The most common ailments that affect the elderly are cardiovascular and cerebrovascular disorders. They are the leading causes of death, and their incidence is linked to vascular calcification (VC). The key mechanism of VC is the transformation of vascular smooth muscle cells (VSMCs) into osteoblast-like phenotypes, which is a highly adjustable process involving a variety of complex pathophysiological processes, such as metabolic abnormalities, apoptosis, oxidative stress and signalling pathways. Many researchers have investigated the mechanism of VC and related targets for the prevention and treatment of cardiovascular and cerebrovascular diseases. Their findings revealed that histone lysine methylation modification may play a key role in the various stages of VC. As a result, a thorough examination of the role and mechanism of lysine methylation modification in physiological and pathological states is critical, not only for identifying specific molecular markers of VC and new therapeutic targets, but also for directing the development of new related drugs. Finally, we provide this review to discover the association between histone methylation modification and VC, as well as diverse approaches with which to investigate the pathophysiology of VC and prospective treatment possibilities.

Improvement of Mineral and Bone Disorders After Renal Transplantation

BACKGROUND

Posttransplant mineral and bone diseases are causes of fractures, and their association with cardiovascular events is being studied.

METHODS

We analyzed the evolution of biochemical, histological, and imaging parameters pre- and 1 y post-renal transplantation in 69 patients and correlated mineral and bone findings with coronary calcifications. At inclusion and after 12 mo, clinical data and echocardiographic findings were recorded, and laboratory evaluations, radiography of the pelvis and hands, and bone biopsy were performed. Noncontrast cardiac computed tomography was performed during the second evaluation.

RESULTS

Serum levels of fibroblast growth factor 23 and sclerostin decreased in all patients, parathyroid hormone levels decreased in 89.8% of patients, bone alkaline phosphatase levels decreased in 68.1% of patients, and alpha-Klotho levels increased in 65.2% of patients. More than half of the patients presented with renal osteodystrophy at both biopsies, but histological findings improved: a significant transition from high to normal or low turnover and no significant differences in volume, mineralization defect, or cortical porosity at the 2 evaluations. Alpha-Klotho, sclerostin, and bone alkaline phosphatase shifts affect bone changes. Neither echocardiographic findings nor vascular calcification scores differed between the 2 points. Both the pretransplant period (dialysis vintage, sclerostin, and low bone volume at baseline) and the maintenance of abnormalities in the posttransplant period (high turnover posttransplant) were the most reliable predictors of the severity of the coronary calcification percentile.

CONCLUSIONS

Renal transplantation improved bone and mineral abnormalities. The pretransplant period determines the severity of calcification.

Deoxycholic Acid and Coronary Artery Calcification in the Chronic Renal Insufficiency Cohort

Background Deoxycholic acid (DCA) is a secondary bile acid that may promote vascular calcification in experimental settings. Higher DCA levels were associated with prevalent coronary artery calcification (CAC) in a small group of individuals with advanced chronic kidney disease. Whether DCA levels are associated with CAC prevalence, incidence, and progression in a large and diverse population of individuals with chronic kidney disease stages 2 to 4 is unknown. Methods and Results In the CRIC (Chronic Renal Insufficiency Cohort) study, we evaluated cross-sectional (n=1057) and longitudinal (n=672) associations between fasting serum DCA levels and computed tomographic CAC using multivariable-adjusted regression models. The mean age was 57±12 years, 47% were women, and 41% were Black. At baseline, 64% had CAC (CAC score >0 Agatston units). In cross-sectional analyses, models adjusted for demographics and clinical factors showed no association between DCA levels and CAC >0 compared with no CAC (prevalence ratio per 1-SD higher log DCA, 1.08 [95% CI, 0.91-1.26). DCA was not associated with incident CAC (incidence per 1-SD greater log DCA, 1.08 [95% CI, 0.85-1.39]) or CAC progression (risk for increase in ≥100 and ≥200 Agatston units per year per 1-SD greater log DCA, 1.05 [95% CI, 0.84-1.31] and 1.26 [95% CI, 0.77-2.06], respectively). Conclusions Among CRIC study participants, DCA was not associated with prevalent, incident, or progression of CAC.

The Role of Bone Volume, FGF23 and Sclerostin in Calcifications and Mortality; a Cohort Study in CKD Stage 5 Patients

Chronic kidney disease-mineral and bone disorder has been associated with increasing morbid-mortality. The aim of this study was to determine the prevalence and phenotype of bone disease before transplantation and to correlate FGF23 and sclerostin levels with bone histomorphometry, and study possible associations between FGF23, sclerostin, and bone histomorphometry with cardiovascular disease and mortality. We performed a cross-sectional cohort study of a sample of 84 patients submitted to renal transplant, which were prospectively followed for 12 months. Demographic, clinical, and echocardiographic data were collected, laboratory evaluation, bone biopsy, and X-ray of the pelvis and hands were performed. Patient and graft survival were recorded. We diagnosed low bone turnover in 16 patients (19.5%); high bone turnover in 22 patients (26.8%); osteomalacia in 1 patient (1.2%), and mixed renal osteodystrophy in 3 patients (3.7%). At the end of 12 months, 5 patients had graft failure (5.9%), 4 had a cardiovascular event (4.8%), and 4 died. Age was associated with low remodeling disease, whereas high BALP and phosphorus and low sclerostin with high turnover disease. Sclerostin was a risk factor for isolated low bone volume. High BALP, low phosphorus, and low FGF23 were risk factors for abnormal mineralization. FGF23 appears as an independent factor for severity of vascular calcifications and for cardiovascular events, whereas the presence of valve calcifications was associated with low volume and with turnover deviations. Sclerostin was associated a higher HR for death. Sclerostin and FGF23 seemed to provide higher cardiovascular risk, as well as low bone volume, which associated with extra-osseous calcifications.

Higher Serum Phosphorus Is Not an Independent Risk Factor of Mortality in Heart Failure with Reduced Ejection Fraction

Higher serum phosphorus has detrimental health effects. Even high-normal rage sP is associated with worse outcomes. The relationship of serum phosphorus with prognostic markers in heart failure remains unclear. We investigated the association of serum phosphorus with heart failure prognostic factors and risk of mortality related to serum phosphorus. In 1029 stable heart failure patients, we investigated the distribution of markers of more advanced heart failure stage across quintiles of serum phosphorus and estimated the relative risk of mortality in comparison to reference. Higher serum phosphorus levels sP were associated with markers of a worse outcome. The best survival was observed in low-normal serum levels. The unadjusted hazard ratio for mortality increased toward higher phosphorus quintiles but not to lower levels of sP. The correction for age, sex, BMI, percent weight loss, inflammation, kidney function, and LVEF did not modify the risk profile substantially. The adjustment for NYHA, natriuretic peptides, serum sodium, and treatment characteristics broke down the risk relationship completely. A higher serum phosphorus is associated with markers of a more risky profile of heart failure. Elevated serum levels of phosphorus sP does not provide independent prognostic information beyond the strongest markers of the severity of the syndrome. The potential involvement of higher serum phosphorus as a mediator in the pathophysiology of heart failure warrants further study.

Understanding the Stony Bridge between Osteoporosis and Vascular Calcification: Impact of the FGF23/Klotho axis

A relationship between osteoporosis (OP) and vascular calcification (VC) is now proposed. There are common mechanisms underlying the regulation of them. Fibroblast growth factor- (FGF-) 23 and Klotho are hormones associated with the metabolic axis of osteovascular metabolism. Most recently, it was suggested that the FGF23-klotho axis is associated with increasing incidence of fractures and is potentially involved in the progression of the aortic-brachial stiffness ratio. Herein, we discussed the potential role of the FGF23/Klotho axis in the pathophysiology of OP and VC. We want to provide an update review in order to allow a better understanding of the potential role of the FGF23/Klotho axis in comorbidity of OP and VC. We believe that a better understanding of the relationship between both entities can help in proposing new therapeutic targets for reducing the increasing prevalence of OP and VC in the aging population.

Role of Glycosylation in Vascular Calcification

Glycosylation is an important step in post-translational protein modification. Altered glycosylation results in an abnormality that causes diseases such as malignancy and cardiovascular diseases. Recent emerging evidence highlights the importance of glycosylation in vascular calcification. Two major types of glycosylation, N-glycosylation and O-glycosylation, are involved in vascular calcification. Other glycosylation mechanisms, which polymerize the glycosaminoglycan (GAG) chain onto protein, resulting in proteoglycan (PG), also have an impact on vascular calcification. This paper discusses the role of glycosylation in vascular calcification.

Reducing the burden of cardiovascular disease in children with chronic kidney disease: prevention vs. damage limitation

Cardiovascular disease (CVD) is a life-limiting condition in patients with chronic kidney disease (CKD) and is rapidly progressive, especially in those with stage 5 CKD and on dialysis. Cardiovascular mortality, although reducing, remains at least 30 times higher than in the general pediatric population. The American Heart Association guidelines for cardiovascular risk reduction in high-risk pediatric patients has stratified pediatric CKD patients in the "high risk" category for the development of CVD, with associated pathological and/or clinical evidence for manifest coronary disease before 30 years of age. While improving patient survival is a key priority, other patient-related outcomes, such as psychosocial development, quality of life and growth are of major importance to children and their caregivers. Once vascular damage or calcification has developed, there are no data to suggest that they can be reversed. Treatments such as intensified dialysis and transplantation may attenuate the progression of subclinical cardiovascular disease, but no treatment to date has shown that the inexorable progression of CVD in CKD can be reversed. Thus, our management must focus on early diagnosis and robust preventative strategies to give our patients the best chance of optimal cardiovascular health and survival. In this review, the pathophysiology and importance of preventing the development of CVD in CKD is discussed.

Phosphate and fibroblast growth factor 23 in diabetes

Diabetes is associated with a strongly elevated risk of cardiovascular disease, which is even more pronounced in patients with diabetic nephropathy. Currently available guideline-based efforts to correct traditional risk factors are only partly able to attenuate this risk, underlining the urge to identify novel treatment targets. Emerging data point towards a role for disturbances in phosphate metabolism in diabetes. In this review, we discuss the role of phosphate and the phosphate-regulating hormone fibroblast growth factor 23 (FGF23) in diabetes. We address deregulations of phosphate metabolism in patients with diabetes, including diabetic ketoacidosis. Moreover, we discuss potential adverse consequences of these deregulations, including the role of deregulated phosphate and glucose as drivers of vascular calcification propensity. Finally, we highlight potential treatment options to correct abnormalities in phosphate and FGF23. While further studies are needed to more precisely assess their clinical impact, deregulations in phosphate and FGF23 are promising potential target in diabetes and diabetic nephropathy.

A feline-focused review of chronic kidney disease-mineral and bone disorders - Part 2: Pathophysiology of calcium disorder and extraosseous calcification

Derangements in mineral metabolism are one of the main entities in chronic kidney disease-mineral and bone disorder (CKD-MBD). This is the second of a two-part review of the physiology and pathophysiology of calcium homeostasis in feline CKD-MBD. While dysregulation in calcium homeostasis is known to contribute to the development of vascular calcification in CKD, evidence characterising the relationship between serum calcium concentration and nephrocalcinosis and nephrolithiasis is limited. Recently, fibroblast growth factor 23 (FGF23) and α-Klotho have gained increased research interest and been shown to be important biomarkers for the prediction of CKD progression in human patients. However, conflicting evidence exists on their role in calcium homeostasis and vascular and soft tissue calcification. This review details the pathophysiology of calcium disorders associated with CKD-MBD and its implications on vascular and soft tissue mineralisation in human and feline patients. Further prospective studies investigating the clinical consequences of calcium disturbances in cats with CKD are warranted and this may provide additional insight into the pathophysiology of feline CKD-MBD.

Role of Matrix Gla Protein in the Complex Network of Coronary Artery Disease: A Comprehensive Review

Coronary artery disease (CAD) is widely recognized as one of the most important clinical entities. In recent years, a large body of accumulated data suggest that coronary artery calcification, a process highly prevalent in patients with CAD, occurs via well-organized biologic processes, rather than passively, as previously regarded. Matrix Gla protein (MGP), a vitamin K-dependent protein, emerged as an important inhibitor of both intimal and medial vascular calcification. The functionality of MGP hinges on two post-translational modifications: phosphorylation and carboxylation. Depending on the above-noted modifications, various species of MGP may exist in circulation, each with their respective level of functionality. Emerging data suggest that dysfunctional species of MGP, markedly, dephosphorylated-uncarboxylated MGP, might find its application as biomarkers of microvascular health, and assist in clinical decision making with regard to initiation of vitamin K supplementation. Hence, in this review we summarized the current knowledge with respect to the role of MGP in the complex network of vascular calcification with concurrent inferences to CAD. In addition, we discussed the effects of warfarin use on MGP functionality, with concomitant implications to coronary plaque stability.

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.

The Importance of Phosphate Control in Chronic Kidney Disease

A series of problems including osteopathy, abnormal serum data, and vascular calcification associated with chronic kidney disease (CKD) are now collectively called CKD-mineral bone disease (CKD-MBD). The pathophysiology of CKD-MBD is becoming clear with the emerging of αKlotho, originally identified as a progeria-causing protein, and bone-derived phosphaturic fibroblast growth factor 23 (FGF23) as associated factors. Meanwhile, compared with calcium and parathyroid hormone, which have long been linked with CKD-MBD, phosphate is now attracting more attention because of its association with complications and outcomes. Incidentally, as the pivotal roles of FGF23 and αKlotho in phosphate metabolism have been unveiled, how phosphate metabolism and hyperphosphatemia are involved in CKD-MBD and how they can be clinically treated have become of great interest. Thus, the aim of this review is reconsider CKD-MBD from the viewpoint of phosphorus, its involvement in the pathophysiology, causing complications, therapeutic approach based on the clinical evidence, and clarifying the importance of phosphorus management.

Fibroblast Growth Factor 21 Predicts and Promotes Vascular Calcification in Haemodialysis Patients

Background

Cardiovascular disease (CVD) is the leading cause of death in haemodialysis (HD) patients. Vascular calcification (VC) is dramatically accelerated and is strongly associated with CVD events and mortality in HD patients. VC coexists with osteoporosis in many studies. Fibroblast growth factor 21 (FGF21) which is known as an adipocytokine is a new hypoglycemic strategy and is inversely related to bone mineral density.

Methods

To evaluate the contribution of FGF21 to VC in HD patients, we detected circulating FGF21 levels and measured the whole thoracic aorta calcification scores (TACS) and calcification scores of the 3 segments of thoracic aorta, including ascending thoracic aorta (ATACS), aortic arch (AoACS), and descending thoracic aorta (DTACS) of our HD patients in this cross-sectional study. In addition, we pre-incubated human aortic endothelial cells (HAECs) with FGF21 in the presence or absence of parathyroid hormone (PTH) in vitro.

Results

The median serum FGF21 level in HD patients was 11-fold higher than that in healthy controls. Ln(FGF21) was positively correlated with Ln(TACS+1), Ln(ATACS+1), Ln(AoACS+1), and Ln(DTACS+1), respectively, in HD patients. Serum FGF21 was independently associated with TACS and ATACS, AoACS, and DTACS. FGF21 which was combined with age, calcium, and intact PTH demonstrated a high area under the curve of 0.84 with optimal sensitivity (84%) and specificity (71%) for the prediction of VC in HD patients. Our vitro results showed that FGF21 enhanced the calcification effect of PTH on HAECs by increasing calcium deposition and endothelial-to-mesenchymal transition.

Conclusions

Circulating FGF21 was notably higher and was a potential predictor and promoter of VC in HD patients.

Vascular calcification relationship to vascular biomarkers and bone metabolism in advanced chronic kidney disease

BACKGROUND

Vascular calcification (VC) and renal osteodystrophy are important complications of advanced chronic kidney disease (CKD). High resolution peripheral quantitative computed tomography (HRpQCT) is able to assess bone microstructure in renal osteodystrophy and lower leg arterial calcification (LLAC) is usually seen as an incidental finding. LLAC can be a useful quantitative assessment of VC in CKD but the relationship between LLAC and vascular biomarkers and bone is unknown. We aimed to assess the relationship between LLAC and biomarkers, bone turnover and microstructure.

METHODS

In this cross-sectional study, fasting blood samples were taken from 69 CKD stages 4-5D patients and 68 healthy controls. HRpQCT of distal tibia and radius were performed. 43 CKD patients had trans-iliac bone biopsy after tetracycline labelling.

RESULTS

LLAC was more severe in CKD than controls (median [IQR] 1.043 [0.05-16.52] vs 0 [0-0.55] mgHA, p < 0.001). CKD patients with diabetes (28%) had significantly higher LLAC compared to non-diabetic CKD (median [IQR] 24.07 [3.42-61.30] vs 0.23 [0-3.78] mgHA, p < 0.001). LLAC mass in CKD correlated with serum phosphate (rho = 0.29, p < 0.05), calcium x phosphate product (rho = 0.31, p < 0.05), intact parathyroid hormone (rho = 0.38, p < 0.01), intact fibroblast growth factor-23 (iFGF23) (rho = 0.40, p = 0.001), total alkaline phosphatase (rho = 0.41, p < 0.001), bone alkaline phosphatase (rho = 0.29, p < 0.05), osteocalcin (rho = 0.32, p < 0.05), osteoprotegerin (rho = 0.40, p = 0.001) and dephosphorylated-uncarboxylated matrix Gla protein (rho = 0.31, p < 0.05). LLAC in CKD also correlated with worse distal tibia cortical bone mineral density, thickness and porosity. No association was found between LLAC and bone turnover, mineralization or volume on biopsy in CKD. In multivariate analysis, only age, diabetes, iPTH and iFGF23 were independently associated with LLAC in CKD.

CONCLUSIONS

High levels of PTH and FGF23, along with older age and the presence of diabetes may all play independent roles in the development of LLAC in advanced CKD.

The role of AMP-activated protein kinase α1-mediated endoplasmic reticulum stress in alleviating the toxic effect of uremic toxin indoxyl sulfate on vascular endothelial cells by Klotho

Recently, the Klotho protein (Klotho) has received substantial attention as protective factor against cardiovascular complications of chronic kidney disease (CKD). However, the direct effect and mechanism of Klotho on endothelial cells injury are not well-known. In this study, we incubated human vein umbilical endothelial cells (HUVECs) with uremic toxin indoxyl sulfate (IS) to mimic CKD internal environment and investigated the direct effect of Klotho on the HUVECs injury induced by IS and to explore the mechanism in this process. We found IS inhibited cell viability, increased endoplasmic reticulum stress, and mediated apoptosis of HUVECs. Treatment with Klotho significantly attenuated IS-induced above effects. Furthermore, Klotho alleviated the IS toxic effect on HUVECs via promoting AMP-activated protein kinase (AMPK) α1 phosphorylation instead of directly upregulating AMPKα1, which could be partly blocked by AMPK pathway inhibitor-Compound C. In addition, Klotho also inhibited intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression induced by IS. Altogether, these results indicated that Klotho can protect HUVECs from IS-induced injury by alleviating AMPKα1-mediated endoplasmic reticulum stress.

High cut-off dialysis mitigates pro-calcific effects of plasma on vascular progenitor cells

Mortality of patients with end-stage renal disease tremendously exceeds that of the general population due to excess cardiovascular morbidity. Large middle-sized molecules (LMM) including pro-inflammatory cytokines are major drivers of uremic cardiovascular toxicity and cannot be removed sufficiently by conventional high-flux (HFL) hemodialysis. We tested the ability of plasma from 19 hemodialysis patients participating in a trial comparing HFL with high cut-off (HCO) membranes facilitating removal of LMM to induce calcification in mesenchymal stromal cells (MSC) functioning as vascular progenitors. HCO dialysis favorably changed plasma composition resulting in reduced pro-calcific activity. LMM were removed more effectively by HCO dialysis including FGF23, a typical LMM we found to promote osteoblastic differentiation of MSC. Protein-bound uremic retention solutes with known cardiovascular toxicity but not LMM inhibited proliferation of MSC without direct toxicity in screening experiments. We could not attribute the effect of HCO dialysis on MSC calcification to distinct mediators. However, we found evidence of sustained reduced inflammation that might parallel other anti-calcifying mechanisms such as altered generation of extracellular vesicles. Our findings imply protection of MSC from dysfunctional differentiation by novel dialysis techniques targeted at removal of LMM. HCO dialysis might preserve their physiologic role in vascular regeneration and improve outcomes in dialysis patients.

Hyperphosphatemia and Chronic Kidney Disease: A Major Daily Concern Both in Adults and in Children

Hyperphosphatemia is common in chronic kidney disease (CKD). Often seen as the "silent killer" because of its dramatic effect on vascular calcifications, hyperphosphatemia explains, at least partly, the onset of the complex mineral and bone disorders associated with CKD (CKD-MBD), together with hypocalcemia and decreased 1-25(OH)₂ vitamin D levels. The impact of CKD-MBD may be immediate with abnormalities of bone and mineral metabolism with secondary hyperparathyroidism and increased FGF23 levels, or delayed with poor growth, bone deformities, fractures, and vascular calcifications, leading to increased morbidity and mortality. The global management of CKD-MBD has been detailed in international guidelines for adults and children, however, with difficulties to obtain an agreement on the ideal PTH targets. The clinical management of hyperphosphatemia is a daily challenge for nephrologists and pediatric nephrologists, notably because of the phosphate overload in occidental diets that is mainly due to the phosphate "hidden" in food additives. The management begins with a dietary restriction of phosphate intake, and is followed by the use of calcium-based and non-calcium-based phosphate binders, and/or the intensification of dialysis. The objective of this review is to provide an overview of the pathophysiology of hyperphosphatemia in CKD, with a focus on its deleterious effects and a description of the clinical management of hyperphosphatemia in a more global setting of CKD-MBD.

Rare diseases of phosphate and calcium metabolism: Crossing glances between nephrology and endocrinology

Rare diseases of phosphate/calcium metabolism correspond to a wide and heterogeneous spectrum of diseases. Recent knowledge in physiology and genetics has made it possible to better characterize them and to propose attractive therapeutic approaches based on the underlying pathophysiology. These diseases are often at the interface between nephrology and endocrinology. In this spirit of a multidisciplinary care, each specialty can bring its own critical point of view and its own specificities to improve patient care. The objective of this manuscript is to "read" with a nephrologist's point of view the main frameworks of diseases of phosphate/calcium metabolism, to illustrate the three crucial messages of nephro-protection sent to endocrinologists. First, calciuria must be interpreted both in absolute value (concentration hypercalciuria) and in ratio (flow hypercalciuria). Second, renal monitoring of therapies inducing hypercalciuria on kidneys with normal renal function (e.g. active vitamin D analogs or teriparatide) should be systematic. Last, hyperphosphatemia, often latent in hypoparathyroidism and pseudo-hypoparathyroidism, should be detected and at least benefit from dietary measures, in the context of Western diets rich in phosphate hidden in food additives.

Fibroblast Growth Factor 23 and Adverse Clinical Outcomes in Type 2 Diabetes: a Bitter-Sweet Symphony

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) is a key phosphate-regulating hormone that has been associated with adverse outcomes in patients with chronic kidney disease (CKD). Emerging data suggest that FGF23 plays a specific role in type 2 diabetes, partly independent of kidney function. We aimed to summarize current literature on the associations between FGF23 and outcomes in patients with type 2 diabetes with or without CKD.

RECENT FINDINGS

Several cohort studies have shown strong associations between plasma FGF23 and cardiovascular outcomes in diabetic CKD. Moreover, recent data suggest that FGF23 are elevated and may also be a risk factor for cardiovascular disease and mortality in type 2 diabetes patients without CKD, although the magnitude of the association is smaller than in CKD patients. Diabetes-related factors may influence plasma FGF23 levels, and a higher FGF23 levels seem to contribute to a higher cardiovascular and mortality risk in patients with type 2 diabetes. Although this risk may be relevant in diabetic individuals with preserved kidney function, it is strongly accentuated in diabetic nephropathy. Future studies should clarify if FGF23 is merely a disease severity marker or a contributor to adverse outcomes in type 2 diabetes and establish if antidiabetic medication can modify FGF23 levels.

Calcification Biomarkers, Subclinical Vascular Disease, and Mortality Among Multiethnic Dialysis Patients

Introduction

Vascular calcification and stiffness are associated with higher mortality and cardiovascular disease in hemodialysis patients, but the underlying mechanism is not well elucidated and previous studies have been contradictory. We sought to determine the association of circulating calcification biomarkers with calcification, stiffness, and mortality in a multiethnic incident dialysis population.

Methods

Among 391 incident hemodialysis participants enrolled in the Predictors of Arrhythmic and Cardiovascular Risk in End Stage Renal Disease (PACE) study, we examined the cross-sectional associations of baseline fibroblast growth factor 23 (FGF23), desphospho-uncarboxylated matrix Gla protein (dp-ucMGP), fetuin-A, and osteoprotegerin (OPG) according to total coronary artery calcium score (CAC, using the Agatston calcification criteria) at baseline, vascular stiffness (pulse wave velocity [PWV]) over 4 study visits, and all-cause mortality.

Results

Patients' mean age was 55 years; 40% were female, 72% were African American, and 58% had diabetes. Higher OPG and FGF23 were associated with a 1.09-fold (per 5-pmol/l increase in OPG; 95% confidence interval [CI]: 1.01-1.17) and 1.12-fold (per increase of 100 log RU/ml in FGF23; 95% CI: 1.02‒1.34) higher prevalence of CAC, independent of demographics, comorbidities, dialysis factors, and serum klotho levels. Higher OPG was associated with higher baseline PWV. Higher FGF23 was associated with lower PWV over follow-up. dp-ucMGP and fetuin-A were not associated with either CAC or vascular stiffness. After adjustment, circulating biomarkers were not associated with mortality risk.

Conclusion

Several circulating calcification biomarkers were only modestly associated with subclinical cardiovascular disease in an incident multiethnic hemodialysis population; none were associated with mortality. Understanding whether these associations persist in larger, diverse hemodialysis populations is warranted before planning trials.

Endocrine fibroblast growth factors as potential biomarkers for chronic kidney disease

INTRODUCTION

Among the family of fibroblast growth factors (FGFs), FGF19, FGF21, and FGF23 act as circulating hormones and are called endocrine FGFs. FGF19 and FGF21 regulate bile acid and energy homeostasis, respectively, whereas FGF23 regulates vitamin D and phosphate homeostasis. Accumulating evidence suggests that FGF23 plays a critical role in disturbed mineral metabolisms, left ventricular hypertrophy, immunosuppression, inflammation, among others in patients with chronic kidney disease (CKD), highlighting the potential both as a biomarker and a therapeutic target. Several studies have also examined the potential role of FGF19 and FGF21 in CKD patients.

AREAS COVERED

In this review, we present a brief overview of the biology of FGF19, FGF21, and FGF23, and summarize recent clinical and experimental studies on the pathophysiological roles of endocrine FGFs, mainly FGF23, in CKD patients.

EXPERT OPINION

Among the endocrine FGFs, FGF23 represents the most promising biomarker in CKD patients. If future studies confirm that FGF23 is directly toxic in CKD patients, FGF23 could be regarded as a therapeutic target and its measurement would be valuable if applied in clinical practice. Despite their potentially important roles, the clinical relevance of FGF19 and FGF21 in CKD patients is unclear, and much more studies are required.

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.

Targeting Vascular Calcification in Chronic Kidney Disease

Cardiovascular (CV) disease remains an important cause of morbidity and mortality for patients with chronic kidney disease (CKD). Although clustering of traditional risk factors with CKD is well recognized, kidney-specific mechanisms are believed to drive the disproportionate burden of CV disease. One perturbation that is frequently observed at high rates in patients with CKD is vascular calcification, which may be a central mediator for an array of CV sequelae. This review summarizes the pathophysiological bases of intimal and medial vascular calcification in CKD, current strategies for diagnosis and management, and posits vascular calcification as a risk marker and therapeutic target.

Research Models for Studying Vascular Calcification

Calcification of the vessel wall contributes to high cardiovascular morbidity and mortality. Vascular calcification (VC) is a systemic disease with multifaceted contributing and inhibiting factors in an actively regulated process. The exact underlying mechanisms are not fully elucidated and reliable treatment options are lacking. Due to the complex pathophysiology, various research models exist evaluating different aspects of VC. This review aims to give an overview of the cell and animal models used so far to study the molecular processes of VC. Here, in vitro cell culture models of different origins, ex vivo settings using aortic tissue and various in vivo disease-induced animal models are summarized. They reflect different aspects and depict the (patho)physiologic mechanisms within the VC process.

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.

Treatment of hyperphosphatemia: the dangers of high PTH levels

The control of secondary hyperparathyroidism (SHPT) in pediatric chronic kidney disease is of utmost importance. Even though parathyroid hormone (PTH) is an important biomarker of mineral and bone disorders associated to CKD (CKD-MBD), calcium, phosphate, alkaline phosphatase, and vitamin D are also crucial and should be assessed together. In pediatric dialysis, high PTH levels have been associated with impaired longitudinal growth, bone disease, cardiovascular comorbidities, left ventricular hypertrophy, anemia, and even mortality (when PTH levels were above 500 pg/mL, i.e., 8.3-fold the upper normal limit (UNL)). As such, high PTH levels are for sure deleterious, but too low PTH levels have also been shown to impair growth and to promote vascular calcifications because of the underlying adynamic bone. This manuscript is part of a pros and cons debate for keeping PTH levels within the normal range in pediatric CKD, focusing on the pros. High bone turnover lesions can occur at lower PTH levels than "current" guidelines would suggest; thus, PTH alone is not a good predictor of the underlying osteodystrophy. PTH results can vary locally depending on the assay. Existing guidelines for PTH targets are conflicting and based on a very little evidence. However, the 120-180 pg/mL (2- to 3-fold the UNL) range is common to most of the guidelines; it seems to be a reasonable target in children undergoing dialysis, even though it does not correspond to "normal" PTH levels. As always, the philosophy of PTH levels in pediatric dialysis may be balanced, i.e., "not too low, not too high, and keep phosphate under control."

Paricalcitol regulatory effect on inflammatory, fibrotic and anticalcificating parameters in renal patiente. Far beyond mineral bone disease regulation

BACKWARD

Cardiovascular events are the major cause of morbidity and mortality in patients with chronic kidney disease (CKD). Inflammation and mineral-bone disorder are pathological conditions that have been associated with an increased cardiovascular risk.

OBJECTIVE

Show paricalcitol regulation overinflammatory, fibrotic and mineral disorder parameters in CKD.

MATERIAL AND METHODS

Prospective Study in 46 CKD stages III-V patients without dialysis patients whith elevated parathormone in which we introduced paricalcitol. We evaluated classic and newest mineral and bone metabolism serum parameters (calcium, phosphorus, parathormone, fibroblast growth factor-23 [FGF-23], Klotho, calcidiol), inflammatory-fibrosis and anticalcifying parameters (interleukin-6 and 10, tumor necrosis factor-a [TNF- α], transforming growth factor-b [TGF-β],bone morphogenic protein-7 [BMP-7] and fetuin-A) for four months.

RESULTS

At the end of study soluble Klotho increased (p=.001), FGF-23 remained stable, calcium and phosphorus levels were not increased, calcidiol increased (p=.010) and PTH decreased (p=.002). Inflammation-fibrosis and calcification parameters showed positive regulation after paricalcitol treatment: interleukin-6 decreased significantly (p=.001) and also TNF-α did (p=.005), on the contrary, interleukin-10 and fetuin-A increased (p=.001 for both). Anti-fibrosis marker BMP-7 increased (p=.001) and TGF-b decreased (p=.001). We did not find significant changes in renal function.

CONCLUSIONS

Paricalcitol treatment might be profitable in regulating inflammatory and anticalcificant parameters, unmodified calcium or phosphorus seric levels and preserving kidney function in renal patients with no dialysis. Our selected parameters could indicate paricalcitol effects in mineral and endothelial disorder related to renal disease.

Selected cardiovascular risk factors in early stages of chronic kidney disease

Cardiovascular diseases, including hypertension, congestive heart failure, myocardial infarction, stroke and atherosclerosis, are common in patients with chronic kidney disease. Aside from the standard biomarkers, measured to determine cardiovascular risk, new ones have emerged: markers of oxidative stress, apoptosis, inflammation, vascular endothelium dysfunction, atherosclerosis, organ calcification and fibrosis. Unfortunately, their utility for routine clinical application remains to be elucidated. A causal relationship between new markers and cardiovascular diseases in patients with chronic kidney disease remains to be established. First of all, there is a lack of large, randomized trials. Moreover, most studies focus on patients with end-stage renal disease as well as on dialysed patients. In such patients, cardiovascular diseases are already present and advanced while early detection of cardiovascular disease risk factor in patients with early-stages of chronic kidney disease would allow more precise prognosis and, as a result, changes in treatment algorithm. In this article, we conduct a comprehensive review of literature for publications relating to cardiovascular risk factors in patients with early-stages of chronic kidney disease. Overall, there are many encouraging advances in detection of cardiovascular risk factors that are making the future more promising for patients suffering from chronic kidney disease.