High serum phosphorus and FGF 23 levels are associated with progression of coronary calcifications

FGF-23 as a Biomarker for Carotid Plaque Vulnerability: A Systematic Review

BACKGROUND/OBJECTIVES

Carotid artery disease is a condition affecting 3% of the general population which significantly contributes to the development of cerebrovascular events. Fibroblast Growth Factor-23 (FGF-23) is a hormone that has been linked to atherosclerosis and increased cardiovascular risk, including stroke and myocardial infarction. This review explores the association of FGF-23 with carotid artery disease progression in an endarterectomy clinical context.

METHODS

Based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), a search was performed relying on MEDLINE, Scopus and Web of Science, identifying publications focused on the correlation between serum FGF-23 and carotid artery disease. Assessment of study quality was made using National Heart, Lung and Blood Institute Study Quality Assessment Tool (NHLBI).

RESULTS

Three observational studies, comprising 1039 participants, were included. There was considerable heterogeneity among the populations from the different studies. Elevated FGF-23 levels were consistently associated with unstable plaque features, including intraplaque neovascularization, as identified through Superb Microvascular Imaging (SMI). Plasma levels of inflammatory mediators, such as Interleukin-6 (Il-6), Monocyte Chemoattractant Protein-1 (MCP-1), and Osteoprotegerin (OPG), positively correlated with carotid artery disease, but their link to unstable plaques is conflicting. None of the studies investigated clinical complications following carotid endarterectomy.

CONCLUSIONS

FGF-23 is a potential biomarker for plaque vulnerability in carotid disease. Despite promising findings, limitations such as small sample sizes and lack of longitudinal data suggest the need for larger and more diverse studies to improve risk stratification and inform personalized treatment strategies for carotid atherosclerosis.

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.

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.

Iron Sucrose: A Double-Edged Sword in High Phosphate Media-Induced Vascular Calcification

The high incidence of vascular calcification (VC) in patients with chronic kidney disease (CKD) has become an important clinical subject. Hyperphosphatemia is a primary cause of CKD-related VC. Intravenous iron sucrose (IS) is commonly used to treat anemia in CKD patients, and is effective and well tolerated worldwide. However, the interaction between iron and VC remains controversial, and the underlying mechanisms are yet to be clarified. In the present study, ex vivo normal rat aortic rings were cultured with various concentrations of phosphate and IS, and the levels of calcium and iron depositions, oxidative injury, as well as phenotypic marker genes were detected. To the best of our knowledge, the present study is the first to report that IS is a double-edged sword in high phosphate media-induced VC which not only alleviates VC in a dose-dependent manner but also leads to iron overload in vasculature when in high concentration. IS is a promising agent for VC prevention in patients with hyperphosphatemia and iron deficiency. Meanwhile, the appropriate blood concentration of IS in patients with hyperphosphatemia needs to be explored clinically.

FGF23: A Review of Its Role in Mineral Metabolism and Renal and Cardiovascular Disease

FGF23 is a hormone secreted mainly by osteocytes and osteoblasts in bone. Its pivotal role concerns the maintenance of mineral ion homeostasis. It has been confirmed that phosphate and vitamin D metabolisms are related to the effect of FGF23 and its excess or deficiency leads to various hereditary diseases. Multiple studies have shown that FGF23 level increases in the very early stages of chronic kidney disease (CKD), and its concentration may also be highly associated with cardiac complications. The present review is limited to some of the most important aspects of calcium and phosphate metabolism. It discusses the role of FGF23, which is considered an early and sensitive marker for CKD-related bone disease but also as a novel and potent cardiovascular risk factor. Furthermore, this review gives particular attention to the reliability of FGF23 measurement and various confounding factors that may impact on the clinical utility of FGF23. Finally, this review elaborates on the clinical usefulness of FGF23 and evaluates whether FGF23 may be considered a therapeutic target.

Vascular Calcification: The Evolving Relationship of Vascular Calcification to Major Acute Coronary Events

Calcification in a coronary artery is accepted as definite evidence of coronary atherosclerosis. The extent and density of calcification, as combined in the Agatston score, is associated with the risk of a patient experiencing a major acute coronary event. Atherosclerosis occurs because damaged endothelial cells allow low-density lipoprotein cholesterol (LDLc) to leak into subintimal tissue. Proteoglycans in subendothelial collagen have a high affinity for LDLc, retaining the lipoprotein cholesterol complex. As the endothelial damage is repaired, the subintimal LDLc is trapped. Retained LDLc induces an inflammatory response in the overlying endothelium, causing the endothelium to express chemotactic peptides. Chemotactic peptides attract circulating monocytes, which follow the concentration gradient, enter the tissue, and become tissue macrophages to phagocytize and digest the irritating LDLc in the atheroma. In the process of digesting LDLc, enzymes in the macrophages oxidize the LDLc complex. Oxidized LDL is toxic to macrophages; when present in sufficient quantity, it may cause death of macrophages, contributing to inflammation in the atheroma. In a necrotic inflammatory lesion, the regulatory mechanisms that control tissue concentrations of calcium and phosphorus are lost, allowing the solubility product of calcium phosphate to be exceeded, resulting in the formation of microscopic calcium-phosphate crystals. With ongoing inflammation, additional calcium-phosphate crystals are formed, which may aggregate. When these aggregated calcium phosphate crystals exceed 1 mm, the lesions become visible on clinical CT as coronary calcifications. Serial gated CT scans of the heart have demonstrated that once formed, CT-visible calcifications do not decrease significantly in size but may increase.

Cardiovascular Disease in Children and Adolescents With Chronic Kidney Disease

The lifespan of children with advanced chronic kidney disease (CKD), although improved over the past 2 decades, remains low compared with the general pediatric population. Similar to adults with CKD, cardiovascular disease accounts for a majority of deaths in children with CKD because these patients have a high prevalence of traditional and uremia-related risk factors for cardiovascular disease. The cardiovascular alterations that cause these terminal events begin early in pediatric CKD. Initially, these act to maintain hemodynamic homeostasis. However, as the disease progresses, these modifications are unable to sustain cardiovascular function in the long term, leading to left ventricular failure, depressed cardiorespiratory fitness, and sudden death. In this review, we discuss the prevalence of the risk factors associated with cardiovascular disease in pediatric patients with CKD, the pathophysiology that stimulates these changes, the cardiac and vascular adaptations that occur in these patients, and management of the cardiovascular risk in these patients.

Deviations from the expected relationship between serum FGF23 and other markers in children with CKD: a cross-sectional study

BACKGROUND

High levels of fibroblast growth factor-23 (FGF23) are associated with mortality. In chronic kidney disease (CKD), FGF23 levels rise as renal function declines. We analyzed the contribution of laboratory values to the variance of FGF23 levels in relationship to a curve of expected FGF23 levels for a given GFR.

METHODS

Following approval by the research ethics boards, we measured FGF23, CysC eGFR, creatinine, urea, albumin, calcium, phosphate, vitamin D metabolites, PTH, alkaline phosphatase, CRP, and venous gases in 141 pediatric CKD patients (45, 37, 32, 13 and 14 CKD stages I, II, III, IV, and V, respectively). Data were expressed as median (25th, 75th percentile).

RESULTS

FGF23 correlated significantly with CysC, CysC eGFR, PTH, 1.25 (OH)₂ vitamin D, phosphate, and pH. The correlation of the latter three remained significant in the multivariate analysis. We calculated a formula for the expected FGF23 value for a given level of eGFR which reads Y = 1295 * e-0.07247*X + 38.35. Deviation by more than 20% from the curve also depended on phosphate, 1.25 (OH)₂ vitamin D and pH.

CONCLUSIONS

Our data emphasize the importance of phosphate and 1.25 (OH)₂ vitamin D levels. The impact of acidosis on FGF23 warrants further studies.

Extrarenal effects of FGF23

Chronic kidney disease (CKD) is associated with an increased risk of cardiovascular mortality, infections, and impaired cognitive function. It is characterized by excessively increased levels of the phosphaturic hormone fibroblast growth factor 23 (FGF23) and a deficiency of its co-receptor Klotho. Despite the important physiological effect of FGF23 in maintaining phosphate homeostasis, there is increasing evidence that higher FGF23 levels are a risk factor for mortality and cardiovascular disease. FGF23 directly induces left ventricular hypertrophy via activation of the FGF receptor 4/calcineurin/nuclear factor of activated T cells signaling pathway. By contrast, the impact of FGF23 on endothelial function and the development of atherosclerosis are poorly understood. The results of recent experimental studies indicate that FGF23 directly impacts on hippocampal neurons and may thereby impair learning and memory function in CKD patients. Finally, it has been shown that FGF23 interferes with the immune system by directly acting on polymorphonuclear leukocytes and macrophages. In this review, we discuss recent data from clinical and experimental studies on the extrarenal effects of FGF23 with respect to the cardiovascular, central nervous, and immune systems.

The role of bone in CKD-mediated mineral and vascular disease

Cardiovascular disease is the leading cause of death in pediatric patients with chronic kidney disease (CKD), and vascular calcifications start early in the course of CKD. Based on the growing body of evidence that alterations of bone and mineral metabolism and the therapies designed to treat the skeletal consequences of CKD are linked to cardiovascular calcifications, the Kidney Disease, Improving Global Outcomes (KDIGO) working group redefined renal osteodystrophy as a systemic disorder of mineral and bone metabolism due to CKD, and this newly defined disorder is now known as "chronic kidney disease-mineral bone disorder (CKD-MBD)". Elevated fibroblast growth factor 23 (FGF23), a bone-derived protein, is the first biochemical abnormality to be associated with CKD-MBD, and high FGF23 levels correlate with increased cardiovascular morbidity and mortality, suggesting that bone is central to both initiating and perpetuating the abnormal mineral metabolism and vascular disease in CKD. The current standard therapies for CKD-MBD affect FGF23 levels differently; non-calcium-based binders with or without concurrent use of dietary phosphate restriction reduce FGF23 levels, while calcium-based binders seem to either increase or have no effect on FGF23 levels. Active vitamin D sterols increase FGF23 levels, whereas therapy with calcimimetics decreases FGF23 levels. Thus, the appropriate therapy that will minimize the rise in FGF23 and prevent cardiovascular morbidity remains to be defined.

FGF23 directly impairs endothelium-dependent vasorelaxation by increasing superoxide levels and reducing nitric oxide bioavailability

Fibroblast growth factor 23 (FGF23) is secreted primarily by osteocytes and regulates phosphate and vitamin D metabolism. Elevated levels of FGF23 are clinically associated with endothelial dysfunction and arterial stiffness in chronic kidney disease (CKD) patients; however, the direct effects of FGF23 on endothelial function are unknown. We hypothesized that FGF23 directly impairs endothelial vasorelaxation by hindering nitric oxide (NO) bioavailability. We detected expression of all four subtypes of FGF receptors (Fgfr1-4) in male mouse aortas. Exogenous FGF23 (90-9,000 pg/ml) did not induce contraction of aortic rings and did not relax rings precontracted with PGF2α. However, preincubation with FGF23 (9,000 pg/ml) caused a ∼36% inhibition of endothelium-dependent relaxation elicited by acetylcholine (ACh) in precontracted aortic rings, which was prevented by the FGFR antagonist PD166866 (50 nM). Furthermore, in FGF23-pretreated (9,000 pg/ml) aortic rings, we found reductions in NO levels. We also investigated an animal model of CKD (Col4a3(-/-) mice) that displays highly elevated serum FGF23 levels and found they had impaired endothelium-dependent vascular relaxation and reduced nitrate production compared with age-matched wild types. To elucidate a mechanism for the FGF23-induced impairment, we measured superoxide levels in endothelial cells and aortic rings and found that they were increased following FGF23 treatment. Crucially, treatment with the superoxide scavenger tiron reduced superoxide levels and also restored aortic relaxation to ACh. Therefore, our data suggest that FGF23 increases superoxide, inhibits NO bioavailability, and causes endothelial dysfunction in mouse aorta. Together, these data provide evidence that high levels of FGF23 contribute to cardiovascular dysfunction.

Roles of phosphate and fibroblast growth factor 23 in cardiovascular disease

Disturbances in phosphate homeostasis are common in patients with chronic kidney disease. As kidney function declines, circulating concentrations of phosphate and the phosphate-regulatory hormone, fibroblast growth factor (FGF)-23, rise progressively. Higher serum levels of phosphate and FGF-23 are associated with an increased risk of adverse outcomes, including all-cause mortality and cardiovascular events. The associations between higher FGF-23 levels and adverse cardiovascular outcomes are generally independent of serum phosphate levels, and might be strongest for congestive heart failure. Higher serum phosphate levels are also modestly associated with an increased risk of cardiovascular events even after accounting for FGF-23 levels. This observation suggests that FGF-23 and phosphate might promote distinct mechanisms of cardiovascular toxicity. Indeed, animal models implicate high serum phosphate as a mechanism of vascular calcification and endothelial dysfunction, whereas high levels of FGF-23 are implicated in left ventricular hypertrophy. These seemingly distinct, but perhaps additive, adverse effects of phosphate on the vasculature and FGF-23 on the heart suggest that future population-level and individual-level interventions will need to simultaneously target these molecules to reduce the risk of associated cardiovascular events.

Coronary artery calcification and cardiovascular disease in children with chronic kidney disease

PURPOSE OF REVIEW

Cardiovascular disease is the leading cause of death in children and young adults with end-stage renal disease (ESRD). As adults, children with advanced chronic kidney disease (CKD) have extremely high prevalence of traditional and uremia-related cardiovascular risk factors. Coronary artery calcification is one of the earliest cardiovascular markers detected in children with ESRD. The purpose of this review is to examine the new developments in pathogenesis of coronary artery calcification and to describe recently published studies on this topic in children with CKD.

RECENT FINDINGS

There is growing evidence that fibroblast growth factor 23 (FGF23) and Klotho factor play a key role in the development of coronary artery calcification in ESRD. Recent studies have shown that induction of vascular calcification begins in early normophosphatemic CKD by the reduction of vascular Klotho and increased FGF23 secretion. Pediatric studies confirmed the presence of abnormal FGF23 and Klotho metabolism and the association of increased circulating FGF23 with coronary artery calcification in children with CKD.

SUMMARY

New developments in our understanding of the mechanisms of vascular calcification in patients with early CKD require further investigation of whether control of FGF23/Klotho metabolism will prevent or delay the development of coronary artery calcification and other cardiovascular outcomes.