A comparative transcriptome analysis identifying FGF23 regulated genes in the kidney of a mouse CKD model

The endocrine FGFs axis: A systemic anti-fibrotic response that could prevent pulmonary fibrogenesis?

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal disease for which therapeutic options are limited, with an unmet need to identify new therapeutic targets. IPF is thought to be the consequence of repeated microlesions of the alveolar epithelium, leading to aberrant epithelial-mesenchymal communication and the accumulation of extracellular matrix proteins. The reactivation of developmental pathways, such as Fibroblast Growth Factors (FGFs), is a well-described mechanism during lung fibrogenesis. Secreted FGFs with local paracrine effects can either exert an anti-fibrotic or a pro-fibrotic action during this pathological process through their FGF receptors (FGFRs) and heparan sulfate residues as co-receptors. Among FGFs, endocrine FGFs (FGF29, FGF21, and FGF23) play a central role in the control of metabolism and tissue homeostasis. They are characterized by a low affinity for heparan sulfate, present in the cell vicinity, allowing them to have endocrine activity. Nevertheless, their interaction with FGFRs requires the presence of mandatory co-receptors, alpha and beta Klotho proteins (KLA and KLB). Endocrine FGFs are of growing interest for their anti-fibrotic action during liver, kidney, or myocardial fibrosis. Innovative therapies based on FGF19 or FGF21 analogs are currently being studied in humans during liver fibrosis. Recent data report a similar anti-fibrotic action of endocrine FGFs in the lung, suggesting a systemic regulation of the pulmonary fibrotic process. In this review, we summarize the current knowledge on the protective effect of endocrine FGFs during the fibrotic processes, with a focus on pulmonary fibrosis.

FGF23 as a Potential Pathophysiological Factor in Peripheral Arterial Disease Associated with Chronic Kidney Disease

Fibroblast growth factor 23 (FGF23) levels are often elevated in chronic kidney disease (CKD). FGF23 and inflammation are common characteristics in CKD, and both are associated with worse disease progression and the occurrence of complications. The existence of an interaction between FGF23 and inflammation has been suggested, each of which influences the expression and activity of the other, leading to a vicious feedback loop with adverse outcomes, including cardiovascular disease and mortality. In this work, we determined circulating FGF23 levels in a group of patients with CKD stages 3 and 4 subjected to elective femoral endarterectomy due to established peripheral artery disease (PAD), a condition resulting from an athero-inflammatory process, and we studied its associations with different inflammatory markers and mediators. We evaluated its association with serum tumor necrosis factor (TNF)α, interleukin (IL) 6, and IL10, as well as with the gene expression levels of these parameters and A disintegrin and metalloproteinase domain-containing protein (ADAM) 17 in femoral vascular tissue and peripheral blood circulating cells (PBCCs). We also analyzed its association with serum concentrations of C-reactive protein (CRP), the systemic immune inflammation index (SII), and the neutrophil-to-lymphocyte ratio (NLR). Finally, we determined the vascular immunoreactivity of protein TNFα in a subgroup of patients. FGF23 concentrations were independently associated with circulating and PBCC mRNA levels of TNFα. Worst kidney function and diabetes were also found to be contributing to FGF23 levels. Patients with higher levels of FGF23 also had greater vascular immunoreactivity for TNFα.

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.

Potential Role of Novel Cardiovascular Biomarkers in Pediatric Patients with Chronic Kidney Disease

BACKGROUND

Cardiovascular Disease is the leading cause of death in adult and pediatric patients with Chronic Kidney Disease (CKD) and its pathogenesis involves the interaction of multiple pathways. As Inflammatory mechanisms play a critical role in the vascular disease of CKD pediatric patients, there are several biomarkers related to inflammation strongly associated with this comorbidity.

OBJECTIVE

This review provides available evidence on the link between several biomarkers and the pathophysiology of heart disease in patients with CKD.

METHODS

The data were obtained independently by the authors, who carried out a comprehensive and non-systematic search in PubMed, Cochrane, Scopus, and SciELO databases. The search terms were "Chronic Kidney Disease", "Cardiovascular Disease", "Pediatrics", "Pathophysiology", "Mineral and Bone Disorder (MBD)", "Renin Angiotensin System (RAS)", "Biomarkers", "BNP", "NTproBNP", "CK-MB", "CXCL6", "CXCL16", "Endocan-1 (ESM-1)", "FABP3", "FABP4", h-FABP", "Oncostatin- M (OSM)", "Placental Growth Factor (PlGF)" and "Troponin I".

RESULTS

The pathogenesis of CKD-mediated cardiovascular disease is linked to inflammatory biomarkers, which play a critical role in the initiation, maintenance, and progression of cardiovascular disease. There are several biomarkers associated with cardiovascular disease in pediatric patients, including BNP, NTproBNP, CK-MB, CXCL6, CXCL16, Endocan-1 (ESM-1), FABP3, FABP4, Oncostatin- M (OSM), Placental Growth Factor (PlGF), and Troponin I.

CONCLUSION

The pathogenesis of CKD-mediated cardiovascular disease is not completely understood, but it is linked to inflammatory biomarkers. Further studies are required to elucidate the pathophysiological and potential role of these novel biomarkers.

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.

Exploring the implications of blocking renin-angiotensin-aldosterone system and fibroblast growth factor 23 in early left ventricular hypertrophy without chronic kidney disease

Background

Whether fibroblast growth factor 23 (FGF23) directly induces left ventricular hypertrophy (LVH) remains controversial. Recent studies showed an association between FGF23 and the renin-angiotensin-aldosterone system (RAAS). The aim of this study was to investigate changes in FGF23 levels and RAAS parameters and their influences on LVH.

Methods

In the first experiment, male C57BL/6J mice were divided into sham and transverse aortic constriction (TAC) groups. The TAC group underwent TAC at 8 weeks of age. At 1, 2, 3, and 4 weeks after TAC, the mice were sacrificed, and blood and urine samples were obtained. Cardiac expressions of FGF23 and RAAS-related factors were evaluated, and cardiac histological analyses were performed. In the second experiment, the sham and TAC groups were treated with vehicle, angiotensin-converting enzyme (ACE) inhibitor, or FGF receptor 4 (FGFR4) inhibitor and then evaluated in the same way as in the first experiment.

Results

In the early stage of LVH without chronic kidney disease, serum FGF23 levels did not change but cardiac FGF23 expression significantly increased along with LVH progression. Moreover, serum aldosterone and cardiac ACE levels were significantly elevated, and cardiac ACE2 levels were significantly decreased. ACE inhibitor did not change serum FGF23 levels but significantly decreased cardiac FGF23 levels with improvements in LVH and RAAS-related factors, while FGFR4 inhibitor did not change the values.

Conclusions

Not serum FGF23 but cardiac FGF23 levels and RAAS parameters significantly changed in the early stage of LVH without chronic kidney disease. RAAS blockade might be more crucial than FGF23 blockade for preventing LVH progression in this condition.

Fibroblast growth factor 23 but not copeptin is independently associated with kidney failure and mortality in patients with chronic kidney disease

Background

Copeptin and intact fibroblast growth factor 23 (iFGF23) increase early during chronic kidney disease (CKD) and may be predictive of unfavourable outcomes. The aim of this study was to evaluate their respective associations with renal and vital outcomes in CKD patients.

Methods

We included CKD patients from the NephroTest cohort with concomitant measurements of plasma copeptin and iFGF23 concentrations and isotopic glomerular filtration rate measurement (mGFR). The primary endpoint was a composite outcome including kidney failure (KF) (dialysis initiation, pre-emptive transplantation or a 57% decrease of mGFR, corresponding to doubling of serum creatinine) or death before KF. Hazard ratios (HRs) of the primary endpoint associated with log-transformed copeptin and iFGF23 concentrations were estimated by Cox models. The slope of mGFR over time was analysed using a linear mixed model.

Results

A total of 329 CKD patients (243 men, mean age 60.3 ± 14.6 years) were included. Among them, 301 with an mGFR >15 ml/min/1.73 m2 were included in survival and mGFR slope analyses. During a median follow-up of 4.61 years (quartile 1-quartile 3: 3.72-6.07), 61 KFs and 32 deaths occurred. Baseline iFGF23 concentrations were associated with the composite outcome after multiple adjustments {HR 2.72 [95% confidence interval (CI) 1.85-3.99]}, whereas copeptin concentrations were not [HR 1.01 (95% CI 0.74-1.39)]. Neither copeptin nor iFGF23 were associated with mGFR slope over time.

Conclusion

Our study shows for the first time in population of CKD patients an independent association between iFGF23 and unfavourable renal and vital outcomes and shows no such association regarding copeptin, encouraging the integration of iFGF23 measurement into the follow-up of CKD.

Renal FGF23 signaling depends on redox protein Memo1 and promotes orthovanadate-sensitive protein phosphotyrosyl phosphatase activity

Memo1 deletion in mice causes premature aging and an unbalanced metabolism partially resembling Fgf23 and Klotho loss-of-function animals. We report a role for Memo's redox function in renal FGF23-Klotho signaling using mice with postnatally induced Memo deficiency in the whole body (cKO). Memo cKO mice showed impaired FGF23-driven renal ERK phosphorylation and transcriptional responses. FGF23 actions involved activation of oxidation-sensitive protein phosphotyrosyl phosphatases in the kidney. Redox proteomics revealed excessive thiols of Rho-GDP dissociation inhibitor 1 (Rho-GDI1) in Memo cKO, and we detected a functional interaction between Memo's redox function and oxidation at Rho-GDI1 Cys79. In isolated cellular systems, Rho-GDI1 did not directly affect FGF23-driven cell signaling, but we detected disturbed Rho-GDI1 dependent small Rho-GTPase protein abundance and activity in the kidney of Memo cKO mice. Collectively, this study reveals previously unknown layers in the regulation of renal FGF23 signaling and connects Memo with the network of small Rho-GTPases.

Bone-derived C-terminal FGF23 cleaved peptides increase iron availability in acute inflammation

Inflammation leads to functional iron deficiency by increasing the expression of the hepatic iron regulatory peptide hepcidin. Inflammation also stimulates fibroblast growth factor 23 (FGF23) production by increasing both Fgf23 transcription and FGF23 cleavage, which paradoxically leads to excess in C-terminal FGF23 peptides (Cter-FGF23), rather than intact FGF23 (iFGF23) hormone. We determined that the major source of Cter-FGF23 is osteocytes and investigated whether Cter-FGF23 peptides play a direct role in the regulation of hepcidin and iron metabolism in response to acute inflammation. Mice harboring an osteocyte-specific deletion of Fgf23 showed a ∼90% reduction in Cter-FGF23 levels during acute inflammation. Reduction in Cter-FGF23 led to a further decrease in circulating iron in inflamed mice owing to excessive hepcidin production. We observed similar results in mice showing impaired FGF23 cleavage owing to osteocyte-specific deletion of Furin. We next showed that Cter-FGF23 peptides bind members of the bone morphogenetic protein (BMP) family, BMP2 and BMP9, which are established inducers of hepcidin. Coadministration of Cter-FGF23 and BMP2 or BMP9 prevented the increase in Hamp messenger RNA and circulating hepcidin levels induced by BMP2/9, resulting in normal serum iron levels. Finally, injection of Cter-FGF23 in inflamed Fgf23KO mice and genetic overexpression of Cter-Fgf23 in wild type mice also resulted in lower hepcidin and higher circulating iron levels. In conclusion, during inflammation, bone is the major source of Cter-FGF23 secretion, and independently of iFGF23, Cter-FGF23 reduces BMP-induced hepcidin secretion in the liver.

Fibroblast Growth Factor 23 Bone Regulation and Downstream Hormonal Activity

Mineral homeostasis of calcium and phosphate levels is one critical component to the maintenance of bone mineral density (BMD) and strength. Diseases that disrupt calcium and phosphate balanced have highlighted not only the role these minerals play in overall bone homeostasis, but also the factors, hormones and downstream transporters, responsible for mineral metabolism. The key phosphaturic hormone elucidated from studying rare heritable disorders of hypophosphatemia is Fibroblast Growth Factor 23 (FGF23). FGF23 is predominantly secreted from bone cells in an effort to maintain phosphate balance by directly controlling renal reabsorption and indirectly affecting intestinal uptake of this mineral. Multiple factors have been shown to enhance bone mRNA expression; however, FGF23 can also undergo proteolytic cleavage to control secretion of the biologically active form of the hormone. The review focuses specifically on the regulation of FGF23 and its secretion from bone as well as its hormonal actions under physiological and disease conditions.

Fibroblast Growth Factor 23: Potential Marker of Invisible Heart Damage in Diabetic Population

Two-dimensional speckle-tracking echocardiography (2DSTE) detects myocardial dysfunction despite a preserved left ventricular ejection fraction. Fibroblast growth factor 23 (FGF23) has become a promising biomarker of cardiovascular risk. This study aimed to determine whether FGF23 may be used as a marker of myocardial damage among patients with diabetes mellitus type 2 (T2DM) and no previous history of myocardial infarction. The study enrolled 71 patients with a median age of 70 years. Laboratory data were analyzed retrospectively. Serum FGF23 levels were determined using a sandwich enzyme-linked immunosorbent assay. All patients underwent conventional echocardiography and 2DSTE. Baseline characteristics indicated that the median time elapsed since diagnosis with T2DM was 19 years. All subjects were divided into two groups according to left ventricular diastolic function. Individuals with confirmed left ventricular diastolic dysfunction had significantly lower levels of estimated glomerular filtration rate and higher values of hemoglobin A1c. Global circumferential strain (GCS) was reduced in the majority of patients. Only an epicardial GCS correlated significantly with the FGF23 concentration in all patients. The study indicates that a cardiac strain is a reliable tool for a subtle myocardial damage assessment. It is possible that FGF23 may become an early diagnostic marker of myocardial damage in patients with T2DM.

Renal fibrosis in type 2 cardiorenal syndrome: An update on mechanisms and therapeutic opportunities

Cardiorenal syndrome (CRS) is a state of coexisting heart failure and renal insufficiency in which acute or chronic dysfunction of the heart or kidney lead to acute or chronic dysfunction of the other organ.It was found that renal fibrosis is an important pathological process in the progression of type 2 CRS to end-stage renal disease, and progressive renal impairment accelerates the deterioration of cardiac function and significantly increases the hospitalization and mortality rates of patients. Previous studies have found that Hemodynamic Aiteration, RAAS Overactivation, SNS Dysfunction, Endothelial Dysfunction and Imbalance of natriuretic peptide system contribute to the development of renal disease in the decompensated phase of heart failure, but the exact mechanisms is not clear. Therefore, in this review, we focus on the molecular pathways involved in the development of renal fibrosis due to heart failure and identify the canonical and non-canonical TGF-β signaling pathways and hypoxia-sensing pathways, oxidative stress, endoplasmic reticulum stress, pro-inflammatory cytokines and chemokines as important triggers and regulators of fibrosis development, and summarize the therapeutic approaches for the above signaling pathways, including SB-525334 Sfrp1, DKK1, IMC, rosarostat, 4-PBA, etc. In addition, some potential natural drugs for this disease are also summarized, including SQD4S2, Wogonin, Astragaloside, etc.

Renal Insufficiency Increases the Combined Risk of Left Ventricular Hypertrophy and Dysfunction in Patients at High Risk of Cardiovascular Diseases

BACKGROUND

The identification of asymptomatic structural and functional cardiac abnormalities can help us to recognize early and intervene in patients at pre-heart failure (HF). However, few studies have adequately evaluated the associations of renal function and left ventricular (LV) structure and function in patients at high risk of cardiovascular diseases (CVD).

METHODS

Patients undergoing coronary angiography and/or percutaneous coronary interventions were enrolled from the Cardiorenal ImprovemeNt II (CIN-II) cohort study, and their echocardiography and renal function were assessed at admission. Patients were divided into five groups according to their estimated glomerular filtration rate (eGFR). Our outcomes were LV hypertrophy and LV systolic and diastolic dysfunction. Multivariable logistic regression analyses were conducted to investigate the associations of eGFR with LV hypertrophy and LV systolic and diastolic dysfunction.

RESULTS

A total of 5610 patients (mean age: 61.6 ± 10.6 years; 27.3% female) were included in the final analysis. The prevalence of LV hypertrophy assessed by echocardiography was 29.0%, 34.8%, 51.9%, 66.7%, and 74.3% for the eGFR categories >90, 61-90, 31-60, 16-30, and ≤15 mL/min per 1.73 m² or for patients needing dialysis, respectively. Multivariate logistic regression analysis showed that subjects with eGFR levels of ≤15 mL/min per 1.73 m2 or needing dialysis (OR: 4.66, 95% CI: 2.96-7.54), as well as those with eGFR levels of 16-30 (OR: 3.87, 95% CI: 2.43-6.24), 31-60 (OR: 2.00, 95% CI: 1.64-2.45), and 61-90 (OR: 1.23, 95% CI: 1.07-1.42), were significantly associated with LV hypertrophy. This reduction in renal function was also significantly associated with LV systolic and diastolic dysfunction (all P for trend <0.001). In addition, a per one unit decrease in eGFR was associated with a 2% heightened combined risk of LV hypertrophy and systolic and diastolic dysfunction.

CONCLUSIONS

Among patients at high risk of CVD, poor renal function was strongly associated with cardiac structural and functional abnormalities. In addition, the presence or absence of CAD did not change the associations. The results may have implications for the pathophysiology behind cardiorenal syndrome.

Raised FGF23 Correlates to Increased Mortality in Critical Illness, Independent of Vitamin D

BACKGROUND

Fibroblast Growth Factor (FGF23) is an endocrine hormone classically associated with the homeostasis of vitamin D, phosphate, and calcium. Elevated serum FGF23 is a known independent risk factor for mortality in chronic kidney disease (CKD) patients. We aimed to determine if there was a similar relationship between FGF23 levels and mortality in critically ill patients.

METHODS

Plasma FGF23 levels were measured by ELISA in two separate cohorts of patients receiving vitamin D supplementation: critical illness patients (VITdAL-ICU trial, n = 475) and elective oesophagectomy patients (VINDALOO trial, n = 76). Mortality data were recorded at 30 and 180 days or at two years, respectively. FGF23 levels in a healthy control cohort were also measured (n = 27).

RESULTS

Elevated FGF23 (quartile 4 vs. quartiles 1-3) was associated with increased short-term (30 and 180 day) mortality in critical illness patients (p < 0.001) and long-term (two-year) mortality in oesophagectomy patients (p = 0.0149). Patients who died had significantly higher FGF23 levels than those who survived: In the critical illness cohort, those who died had 1194.6 pg/mL (range 0-14,000), while those who survived had 120.4 pg/mL (range = 15-14,000) (p = 0.0462). In the oesophagectomy cohort, those who died had 1304 pg/mL (range = 154-77,800), while those who survived had 644 pg/mL (range = 179-54,894) (p < 0.001). This was found to be independent of vitamin D or CKD status (critical illness p = 0.3507; oesophagectomy p = 0.3800). FGF23 levels in healthy controls were similar to those seen in oesophagectomy patients (p = 0.4802).

CONCLUSIONS

Elevated baseline serum FGF23 is correlated with increased mortality in both the post-oesophagectomy cohort and the cohort of patients with critical illness requiring intensive care admission. This was independent of vitamin D status, supplementation, or CKD status, which suggests the presence of vitamin D-independent mechanisms of FGF23 action during the acute and convalescent stages of critical illness, warranting further investigation.

FGF23 in Chronic Kidney Disease: Bridging the Heart and Anemia

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

Fibroblast growth factor 23 in children with or without heart failure: a prospective study

BACKGROUND

Elevated fibroblast growth factor 23 (FGF23) levels have been associated with mortality in adults with heart failure (HF), but data on FGF23 levels in paediatric HF are limited. In this prospective cohort study, we aimed to assess the prognostic value of FGF23 in children with chronic HF.

METHODS

We prospectively enrolled 40 children with chronic HF and 20 matched healthy controls. In each patient, a complete diagnostic workup was performed, including transthoracic echocardiography to evaluate cardiac systolic and diastolic functions. Serum FGF23, renal function tests, parathyroid hormone, serum calcium and phosphate were measured in patients and controls. N-terminal probrain natriuretic peptide (NT-proBNP) was measured in patients. The severity of symptoms was assessed using the modified Ross HF classification for children. Patients were followed for 1 year, and clinical worsening events such as death and HF hospitalisation were recorded.

RESULTS

Patients with HF had significantly higher FGF23 levels compared with controls (355.68±97.27 pg/mL and 60.20±11.04 pg/mL, respectively; p<0.001). Three patients died and 11 were admitted with HF. In comparison with patients without clinical worsening events, these 14 patients exhibited significantly higher FGF23 levels (320.04±89.56 pg/mL and 421.86±75.50 pg/mL, respectively; p<0.001). FGF23 was positively correlated with NT-proBNP and left ventricular end-diastolic diameter and negatively correlated with ejection fraction and fractional shortening. The ability of FGF23 to predict clinical worsening events in patients was analysed using a receiver operating characteristic curve. The optimal cut-off point was 375 pg/mL, with 85.71% sensitivity, 84.62% specificity, positive predictive value of 75.0, negative predictive value of 91.7 and area under the curve (AUC) of 0.878. Multivariable regression analysis revealed that FGF23 is the only independent predictor of clinical worsening events in children with chronic HF.

CONCLUSION

FGF23 levels were elevated in children with chronic HF and increased significantly as Ross score class increased. FGF23 levels increased in patients who experienced clinical worsening events.

Hypertension and cardiomyopathy associated with chronic kidney disease: epidemiology, pathogenesis and treatment considerations

Chronic kidney disease (CKD) is a complex condition with a prevalence of 10-15% worldwide. An inverse-graded relationship exists between cardiovascular events and mortality with kidney function which is independent of age, sex, and other risk factors. The proportion of deaths due to heart failure and sudden cardiac death increase with progression of chronic kidney disease with relatively fewer deaths from atheromatous, vasculo-occlusive processes. This phenomenon can largely be explained by the increased prevalence of CKD-associated cardiomyopathy with worsening kidney function. The key features of CKD-associated cardiomyopathy are increased left ventricular mass and left ventricular hypertrophy, diastolic and systolic left ventricular dysfunction, and profound cardiac fibrosis on histology. While these features have predominantly been described in patients with advanced kidney disease on dialysis treatment, patients with only mild to moderate renal impairment already exhibit structural and functional changes consistent with CKD-associated cardiomyopathy. In this review we discuss the key drivers of CKD-associated cardiomyopathy and the key role of hypertension in its pathogenesis. We also evaluate existing, as well as developing therapies in the treatment of CKD-associated cardiomyopathy.

A protective erythropoietin evolutionary landscape, NLRP3 inflammasome regulation, and multisystem inflammatory syndrome in children

The low incidence of pediatric severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and the associated multisystem inflammatory syndrome (MIS-C) lack a unifying pathophysiological explanation, impeding effective prevention and therapy. Activation of the NACHT, LRR, and PYD domains-containing protein (NLRP) 3 inflammasome in SARS-CoV-2 with perturbed regulation in MIS-C, has been reported. We posit that, early age physiological states and genetic determinants, such as certain polymorphisms of renin-angiotensin aldosterone system (RAAS) molecules, promote a controlled RAAS hyperactive state, and form an evolutionary landscape involving an age-dependent erythropoietin (EPO) elevation, mediating ancestral innate immune defenses that, through appropriate NLRP3 regulation, mitigate tissue injury and pathogen invasion. SARS-CoV-2-induced downregulation of angiotensin-converting enzyme (ACE)2 expression in endothelial cells (EC), impairment of endothelial nitric oxide (NO) synthase (eNOS) activity and downstream NO bioavailability, may promote a hyperactive RAAS with elevated angiotensin II and aldosterone that, can trigger, and accelerate NLRP3 inflammasome activation, while EPO-eNOS/NO abrogate it. Young age and a protective EPO evolutionary landscape may successfully inhibit SARS-CoV-2 and contain NLRP3 inflammasome activation. By contrast, increasing age and falling EPO levels, in genetically susceptible children with adverse genetic variants and co-morbidities, may lead to unopposed RAAS hyperactivity, NLRP3 inflammasome dysregulation, severe endotheliitis with pyroptotic cytokine storm, and development of autoantibodies, as already described in MIS-C. Our haplotype estimates, predicted from allele frequencies in population databases, are in concordance with MIS-C incidence reports in Europeans but indicate lower risks for Asians and African Americans. Targeted Mendelian approaches dissecting the influence of relevant genetic variants are needed.

Fibroblast growth factor 23 level modulates the hepatocyte's alpha-2-HS-glycoprotein transcription through the inflammatory pathway TNFα/NFκB

Introduction

High serum levels of fibroblast growth factor 23 (FGF23) characterize chronic kidney disease (CKD) since its early stages and have been suggested to contribute to inflammation and cardiovascular disease. However, the mechanisms linking FGF23 with these pathological conditions remain still incompletely defined. The alpha-2-HS-glycoprotein (AHSG), a liver-produced anti-inflammatory cytokine, is highly modulated by inflammation itself, also through the TNFα/NFκB signaling pathway. In our previous study, we found that FGF23 modulates the production of AHSG in the liver in a bimodal way, with stimulation and inhibition at moderately and highly increased FGF23 concentrations, respectively.

Methods

The present study, aiming to gain further insights into this bimodal behavior, was performed in hepatocyte human cells line (HepG2), using the following methods: immunochemistry, western blot, chromatin immunoprecipitation, fluorescence in situ hybridization (FISH), qRT-PCR, and gene SANGER sequencing.

Results

We found that FGF23 at 400 pg/ml activates nuclear translocation of NFκB, possibly increasing AHSG transcription. At variance, at 1,200 pg/ml, FGF23 inactivates NFκB through the activation of two specific NFκB inhibitors (IκBα and NKIRAS2) and induces its detachment from the AHSG promoter, reducing AHSG transcription.

Conclusion

These results add another piece to the puzzle of FGF23 involvement in the multifold interactions between CKD, inflammation, and cardiovascular disease, suggesting the involvement of the NFκB pathway, which might represent a potential therapeutic target in CKD.

Mineral Bone Disorders in Kidney Disease Patients: The Ever-Current Topic

Chronic kidney disease (CKD) is a complex and multifactorial disease, and one of the most prevalent worldwide. Chronic kidney disease-mineral bone disorders (CKD-MBD) with biochemical and hormonal alterations are part of the complications associated with the progression of CKD. Pathophysiology of CKD-MBD focused on abnormalities in serum levels of several biomarkers (such as FGF-23, klotho, phosphate, calcium, vitamin D, and PTH) which are discussed in this review. We therefore examine the prognostic association between CKD-MBD and the increased risk for cardiovascular events, mortality, and CKD progression to end-stage kidney disease (ESKD). Lastly, we present specific treatments acting on CKD to prevent and treat the complications associated with secondary hyperparathyroidism (SHPT): control of hyperphosphatemia (with dietary restriction, intestinal phosphate binders, and adequate dialysis), the use of calcimimetic agents, vitamin D, and analogues, and the use of bisphosphonates or denosumab in patients with osteoporosis.

Long-Term Excessive Dietary Phosphate Intake Increases Arterial Blood Pressure, Activates the Renin-Angiotensin-Aldosterone System, and Stimulates Sympathetic Tone in Mice

Increased dietary phosphate intake has been associated with severity of coronary artery disease, increased carotid intima–media thickness, left ventricular hypertrophy (LVH), and increased cardiovascular mortality and morbidity in individuals with normal renal function as well as in patients suffering from chronic kidney disease. However, the underlying mechanisms are still unclear. To further elucidate the cardiovascular sequelae of long-term elevated phosphate intake, we maintained male C57BL/6 mice on a calcium, phosphate, and lactose-enriched diet (CPD, 2% Ca, 1.25% P, 20% lactose) after weaning them for 14 months and compared them with age-matched male mice fed a normal mouse diet (ND, 1.0% Ca, 0.7% P). Notably, the CPD has a balanced calcium/phosphate ratio, allowing the effects of elevated dietary phosphate intake largely independent of changes in parathyroid hormone (PTH) to be investigated. In agreement with the rationale of this experiment, mice maintained on CPD for 14 months were characterized by unchanged serum PTH but showed elevated concentrations of circulating intact fibroblast growth factor-23 (FGF23) compared with mice on ND. Cardiovascular phenotyping did not provide evidence for LVH, as evidenced by unchanged LV chamber size, normal cardiomyocyte area, lack of fibrosis, and unchanged molecular markers of hypertrophy (Bnp) between the two groups. However, intra-arterial catheterization revealed increases in systolic pressure, mean arterial pressure, and pulse pressure in mice fed the CPD. Interestingly, chronically elevated dietary phosphate intake stimulated the renin–angiotensin–aldosterone system (RAAS) as evidenced by increased urinary aldosterone in animals fed the CPD, relative to the ND controls. Furthermore, the catecholamines epinephrine, norepinephrine, and dopamine as well as the catecholamine metabolites metanephrine. normetanephrine and methoxytyramine as measured by mass spectrometry were elevated in the urine of mice on CPD, relative to mice on the ND. These changes were partially reversed by switching 14-month-old mice on CPD back to ND for 2 weeks. In conclusion, our data suggest that excess dietary phosphate induces a rise in blood pressure independent of secondary hyperparathyroidism, and that this effect may be mediated through activation of the RAAS and stimulation of the sympathetic tone.

Low Klotho/Fibroblast Growth Factor 23 Ratio Is an Independent Risk Factor for Renal Progression in Chronic Kidney Disease: Finding From KNOW-CKD

Background

We aimed to evaluate soluble Klotho and circulating fibroblast growth factor 23 (FGF23) ratio as a risk factor for renal progression, cardiovascular (CV) events, and mortality in chronic kidney disease (CKD).

Methods

We analyzed 2,099 subjects from a CKD cohort whose soluble Klotho and C-terminal FGF23 levels were measured at enrollment. The Klotho to FGF23 ratio was calculated as Klotho values divided by FGF23 values + 1 (hereinafter called the Klotho/FGF23 ratio). Participants were categorized into quartiles according to Klotho/FGF23 ratio. The primary outcome was renal events, defined as the doubling of serum creatinine, 50% reduction of estimated glomerular filtration rate from the baseline values, or development of end-stage kidney disease. The secondary outcomes consisted of CV events and death. Changes in CV parameters at the time of enrollment and during follow-up according to the Klotho/FGF23 ratio were also examined.

Results

During the follow-up period of 64.0 ± 28.2 months, 735 (35.1%) and 273 (13.0%) subjects developed renal events and composite outcomes of CV events and death, respectively. After adjustment, the first (HR: 1.36; 95% CI: 1.08–1.72, P = 0.010) and second (HR: 1.45; 95% CI: 1.15–1.83, P = 0.002) quartiles with regard to the Klotho/FGF23 ratio showed elevated risk of renal events as compared to the fourth quartile group. There was no significant association between Klotho/FGF23 ratio and the composite outcome of CV events and death. The prevalence of left ventricular hypertrophy and vascular calcification was higher in the low Klotho/FGF23 ratio quartiles at baseline and at the fourth-year follow-up.

Conclusions

Low Klotho/FGF23 ratio was significantly associated with increased renal events in the cohort of Korean predialysis CKD patients.

The Effect of FGF23 on Cardiac Hypertrophy Is Not Mediated by Systemic Renin-Angiotensin- Aldosterone System in Hemodialysis

Fibroblast growth factor 23 (FGF23) is elevated in patients with chronic kidney disease and contributes to left ventricular hypertrophy (LVH). The aim of the analysis was to determine whether this effect is mediated by the renin-angiotensin-aldosterone system (RAAS) in hemodialysis. Serum samples from 62 randomized hemodialysis patients with LVH were analyzed for plasma renin activity (PRA-S), angiotensin II (AngII), and metabolites, angiotensin-converting enzyme-2 (ACE2) and aldosterone using a high throughput mass spectrometry assay. Compared to healthy individuals, levels of the RAAS parameters PRA-S, AngII and aldosterone were generally lower [median (IQR) PRA-S 130 (46–269) vs. 196 (98, 238) pmol/L; AngII 70 (28–157) vs. 137 (76, 201) pmol/L; Aldosterone 130 (54, 278) vs. 196 (98, 238) pmol/L]. We did not find an indication that the effect of FGF23 on LVH was mediated by RAAS parameters, with all estimated indirect effects virtually zero. Furthermore, FGF23 was not associated with RAAS parameter levels throughout the study. While there was a clear association between FGF23 levels and left ventricular mass index (LVMI) at the end of the study and in the FGF23 fold change and LVMI change analysis, no association between RAAS and LVMI was observed. Serum concentrations of PRA-S, AngII, and aldosterone were below the ranges measured in healthy controls suggesting that RAAS is not systemically activated in hemodialysis patients. The effect of FGF23 on LVMI was not mediated by systemic RAAS activity. These findings challenge the current paradigm of LVH progression and treatment with RAAS blockers in dialysis.

Renoprotective effects of ferric citrate in a mouse model of chronic kidney disease

In chronic kidney disease, ferric citrate has been shown to be an effective phosphate binder and source of enteral iron; however, the effects of ferric citrate on the kidney have been less well-studied. Here, in Col4α3 knockout mice—a murine model of progressive chronic kidney disease, we evaluated the effects of five weeks of 1% ferric citrate dietary supplementation. As expected, ferric citrate lowered serum phosphate concentrations and increased serum iron levels in the Col4α3 knockout mice. Consistent with decreased enteral phosphate absorption and possibly improved iron status, ferric citrate greatly reduced circulating fibroblast growth factor 23 levels. Interestingly, ferric citrate also lessened systemic inflammation, improved kidney function, reduced albuminuria, and decreased kidney inflammation and fibrosis, suggesting renoprotective effects of ferric citrate in the setting of chronic kidney disease. The factors mediating possible ferric citrate renoprotection, the mechanisms by which they may act, and whether ferric citrate affects chronic kidney disease progression in humans deserves further study.

Fibroblast growth factor-23 rs7955866 polymorphism and risk of chronic kidney disease

Background

A missense gain-of-function fibroblast growth factor-23 (FGF23) gene single nucleotide polymorphism (SNP) (rs7955866) has been associated with FGF23 hypersecretion, phosphaturia, and bone disease. Excess circulating FGF23 was linked with atherosclerosis, hypertension, initiation, and progression of chronic kidney disease (CKD).

Methods

The study included 72 CKD stage 2/3 Egyptian patients (27–71 years old, 37 females) and 26 healthy controls matching in age and sex. Repeated measures of blood pressure were used to quantify hypertension on a semiquantitative scale (grades 0 to 5). Fasting serum urea, creatinine, uric acid, total proteins, albumin, calcium, phosphorus, vitamin D3, intact parathyroid hormone (iPTH), and intact FGF23 (iFGF23) were measured. DNA extracted from peripheral blood leucocytes was used for genotyping of FGF23 rs7955866 SNP using the TaqMan SNP genotyping allelic discrimination method.

Results

Major causes of CKD were hypertension, diabetic kidney disease, and CKD of unknown etiology. There was no significant difference in minor allele (A) frequency between the studied groups (0.333 in GI and 0.308 in GII). Median (IQR) serum iFGF23 was significantly higher in GI [729.2 (531.9–972.3)] than in GII [126.1 (88.5–152.4)] pg/mL, P < 0.001. Within GI, the minor allele (A) frequency load, coded for codominant inheritance, had a significant positive correlation with both hypertension grade (r = 0.385, P = 0.001) and serum iFGF23 (r = 0.259, P = 0.028). Hypertension grade had a significant positive correlation with serum phosphorus and iFGF23.

Conclusions

For the first time in an Egyptian cohort, we report a relatively high frequency of the rs7955866 SNP. It may remain dormant or become upregulated in response to some environmental triggers, notably dietary phosphorus excess, leading to increased circulating iFGF23 with ensuing hypertension and/or renal impairment. Subjects with this SNP, particularly in the homozygous form, are at increased risk for CKD of presumably “unknown” etiology, with a tendency for early onset hypertension and increased circulating iFGF23 out of proportion with the degree of renal impairment. Large-scale population studies are needed to confirm these findings and explore the role of blockers of the renin–angiotensin–aldosterone system and sodium chloride cotransporters in mitigating hypertension associated with FGF23 excess.

Plasma Fibroblast Growth Factor 23 as a Predictor for Fosinopril Therapeutic Efficacy in Pediatric Primary Hypertension

Background

Plasma fibroblast growth factor 23 (FGF23) has been reported to be a predictive biomarker for therapeutic effectiveness of angiotensin‐converting enzyme inhibitors in heart failure. Higher plasma FGF23 levels have been shown in pediatric primary hypertension, but the predictive value of FGF23 for angiotensin‐converting enzyme inhibitors’ effectiveness in pediatric primary hypertension has not been documented.

Methods and Results

This is a prospective study. An exploratory study with 139 patients was first conducted to determine the cutoff value of FGF23 for the prediction of treatment responsiveness. After receiving fosinopril for 4 weeks, of all 139 patients, 91 responded, while 48 did not respond to the treatment, and the responders had a significantly higher baseline plasma FGF23 level than nonresponders (P<0.01). Multiple regression analysis revealed a significant impact of baseline plasma FGF23 levels on fosinopril responsiveness (P<0.05). The receiver operating characteristic curve analysis showed that the plasma FGF23 predicted the effectiveness of fosinopril treatment with an area under the curve of 0.784 (95% CI, 0.704–0.863) for a sensitivity and a specificity of 67.0% and 89.6%, respectively, for a cutoff value of 62.08 RU/mL. Subsequently, another group of 40 patients were recruited for validation. The blood pressure control rate in those (n=22) with baseline plasma FGF23 >62.08 RU/mL was significantly higher than that in children (n=18) with FGF23 ≤62.08 RU/mL (P<0.05).

Conclusions

Plasma FGF23 might be a valuable biomarker to guide fosinopril therapy for primary hypertension in children.

Hypophosphatemia related to a neuro-endocrine tumor of the pancreas: A case report

BACKGROUND

Tumor-induced osteomalacia (TIO) is a paraneoplastic syndrome characterized by hypophosphatemia associated with elevated fibroblast growth factor 23 (FGF23). TIO is primarily caused by benign mesenchymal tumors of the soft tissue and skeleton. Rarely, it is associated with a solid tumor or hematological malignancy. To date, no case of osteomalacia related to pancreatic cancer has been reported in the literature.

CASE REPORT

A 77-year-old woman was admitted to the rheumatology department (RD) of the Clermont-Ferrand University Hospital (France) for further evaluation of her hypophosphatemia. The patient reported bone pain, myalgia, and asthenia. Further laboratory tests revealed hyperphosphaturia, normocalcemia, low serum calcitriol, elevated serum alkaline phosphatase (ALP), and elevated plasma parathyroid hormone (PTH). A renal phosphate depletion disorder was suspected as an etiology for this hypophosphatemia. Finally, FGF23 levels were found to be significantly elevated, leading to a definitive diagnosis of pancreatic neuroendocrine tumor.

CONCLUSION

This is the first report of hypophosphatemic osteomalacia related to pancreatic cancer. Therefore, in the setting of hypophosphatemia associated with renal phosphate wasting and low calcitriol level, plasma FGF23 measurement should be considered.

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

Background:

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

Objective:

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

Methods:

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

Results:

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

Conclusion:

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

Changes of FGF23 and the Renin-Angiotensin-System in Male Mouse Models of Chronic Kidney Disease and Cardiac Hypertrophy

Serum fibroblast growth factor 23 (FGF23) levels and the renin-angiotensin-aldosterone system (RAAS) are elevated in chronic kidney disease (CKD) patients, and their association with left ventricular hypertrophy (LVH) has been reported. However, whether the FGF23 elevation is the cause or result of LVH remains unclear. At 10 weeks, male C57BL/6J mice were divided into 4 groups: sham, CKD (5/6 nephrectomy), LVH (transaortic constriction), and CKD/LVH group. At 16 weeks, the mice were euthanized, and blood and urine, cardiac expressions of FGF23 and RAAS-related factors, and cardiac histological analyses were performed. Heart weight, serum FGF23 levels, and cardiac expression of FGF23 and RAAS-related factors, except for angiotensin-converting enzyme 2, were more increased in the CKD/LVH group compared to the other groups. A significant correlation between LVH and cardiac expressions of FGF23 and RAAS-related factors was observed. Furthermore, there was a significantly close correlation of the cardiac expression of FGF23 with LVH and RAAS-related factors. The coexisting CKD and LVH increased serum and cardiac FGF23 and RAAS-related factors, and there was a significant correlation between them. A close correlation of cardiac, but not serum FGF23, with LVH and RAAS suggests that local FGF23 levels may be associated with LVH and RAAS activation.

Fibroblast Growth Factor 23 and Outcome Prediction in Patients with Acute Myocardial Infarction

(1) Background: Fibroblast growth factor 23 (FGF23) is associated with mortality in patients with heart failure (HF); however, less is known about mortality associations in patients with myocardial infarction (MI). (2) Methods: FGF23 was assessed in 180 patients with acute MI, 99 of whom presented with concomitant acute HF. Patients were followed up for one year, and outcome estimates by FGF23 were compared to GRACE score estimates. (3) Results: Log-transformed serum levels of intact FGF23 (logFGF23) did not differ between MI patients with and without HF, and no difference in logFGF23 was observed between 14 MI patients who died and those who survived. However, when only MI patients with concomitant HF were considered, logFGF23 was significantly higher among non-survivors compared to that in survivors. While logFGF23 was not associated with the outcome in the entire cohort, logFGF23 was fairly predictive for one-year mortality in patients with concomitant HF (AUC 0.78; 95%CI 0.61–0.95), where it outperformed GRACE score estimates (AUC 0.70; 95%CI 0.46–0.94). (4) Conclusions: FGF23 was associated with one-year mortality only in MI patients who concomitantly presented with HF, surpassing the predictive ability of GRACE score estimates. No associations were observed in patients without HF despite similar FGF23 levels at admission. Further studies are warranted to investigate whether FGF23 is causal for dismal outcome of HF.

FGF-23 (Fibroblast Growth Factor-23) and Cardiorenal Interactions

BACKGROUND

Animal models implicate FGF-23 (fibroblast growth factor-23) as a direct contributor to adverse cardiorenal interactions such as sodium avidity, diuretic resistance, and neurohormonal activation, but this has not been conclusively demonstrated in humans. Therefore, we aimed to evaluate whether FGF-23 is associated with parameters of cardiorenal dysfunction in humans with heart failure, independent of confounding factors.

METHODS

One hundred ninety-nine outpatients with heart failure undergoing diuretic treatment at the Yale Transitional Care Center were enrolled and underwent blood collection, and urine sampling before and after diuretics.

RESULTS

FGF-23 was associated with several metrics of disease severity such as higher home loop diuretic dose and NT-proBNP (N-terminal pro-B-type natriuretic peptide), and lower estimated glomerular filtration rate, serum chloride, and serum albumin. Multivariable analysis demonstrated no statistically significant association between FGF-23 and sodium avidity measured by fractional excretion of sodium, or proximal or distal tubular sodium reabsorption, either before diuretic administration or at peak diuresis (P≥0.11 for all). Likewise, FGF-23 was not independently associated with parameters of diuretic resistance (diuretic excretion, cumulative urine and sodium output, and loop diuretic efficiency [P≥0.33 for all]) or neurohormonal activation (plasma or urine renin [P≥0.36 for all]). Moreover, the upper boundary of the 95% CI of all the partial correlations were ≤0.30, supporting the lack of meaningful correlations. FGF-23 was not associated with mortality in multivariable analysis (P=0.44).

CONCLUSIONS

FGF-23 was not meaningfully associated with any cardiorenal parameter in patients with heart failure. While our methods cannot rule out a small effect, FGF-23 is unlikely to be a primary driver of cardiorenal interactions.

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.

Fibroblast growth factor 23-Klotho and hypertension: experimental and clinical mechanisms

Hypertension (HTN) and chronic kidney disease (CKD) are increasingly recognized in pediatric patients and represent risk factors for cardiovascular morbidity and mortality later in life. In CKD, enhanced tubular sodium reabsorption is a leading cause of HTN due to augmented extracellular fluid volume expansion. The renin-angiotensin-aldosterone system (RAAS) upregulates various tubular sodium cotransporters that are also targets of the hormone fibroblast growth factor 23 (FGF23) and its co-receptor Klotho. FGF23 inhibits the activation of 1,25-dihydroxyvitamin D that is a potent suppressor of renin biosynthesis. Here we review the complex interactions and disturbances of the FGF23-Klotho axis, vitamin D, and the RAAS relevant to blood pressure regulation and discuss the therapeutic strategies aimed at mitigating their pathophysiologic contributions to HTN.

How FGF23 shapes multiple organs in chronic kidney disease

Chronic kidney disease (CKD) is associated with distinct alterations in mineral metabolism in children and adults resulting in multiple organ dysfunctions. Children with advanced CKD often suffer from impaired bone mineralization, bone deformities and fractures, growth failure, muscle weakness, and vascular and soft tissue calcification, a complex which was recently termed CKD-mineral and bone disorder (CKD-MBD). The latter is a major contributor to the enhanced cardiovascular disease comorbidity and mortality in these patients. Elevated circulating levels of the endocrine-acting phosphaturic hormone fibroblast growth factor (FGF) 23 are the first detectable alteration of mineral metabolism and thus CKD-MBD. FGF23 is expressed and secreted from osteocytes and osteoblasts and rises, most likely due to increased phosphate load, progressively as kidney function declines in order to maintain phosphate homeostasis. Although not measured in clinical routine yet, CKD-mediated increased circulating levels of FGF23 in children are associated with pathological cardiac remodeling, vascular alterations, and increased cognitive risk. Clinical and experimental studies addressing other FGF23-mediated complications of kidney failure, such as hypertension and impaired bone mineralization, show partly conflicting results, and the causal relationships are not always entirely clear. This short review summarizes regulators of FGF23 synthesis altered in CKD and the main CKD-mediated organ dysfunctions related to high FGF23 levels.

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.

Lipocalin 2 stimulates bone fibroblast growth factor 23 production in chronic kidney disease

Bone-produced fibroblast growth factor 23 (FGF23) increases in response to inflammation and iron deficiency and contributes to cardiovascular mortality in chronic kidney disease (CKD). Neutrophil gelatinase-associated lipocalin (NGAL or lipocalin 2; LCN2 the murine homolog) is a pro-inflammatory and iron-shuttling molecule that is secreted in response to kidney injury and may promote CKD progression. We investigated bone FGF23 regulation by circulating LCN2. At 23 weeks, Col4a3^KO mice showed impaired kidney function, increased levels of kidney and serum LCN2, increased bone and serum FGF23, anemia, and left ventricular hypertrophy (LVH). Deletion of Lcn2 in CKD mice did not improve kidney function or anemia but prevented the development of LVH and improved survival in association with marked reductions in serum FGF23. Lcn2 deletion specifically prevented FGF23 elevations in response to inflammation, but not iron deficiency or phosphate, and administration of LCN2 increased serum FGF23 in healthy and CKD mice by stimulating Fgf23 transcription via activation of cAMP-mediated signaling in bone cells. These results show that kidney-produced LCN2 is an important mediator of increased FGF23 production by bone in response to inflammation and in CKD. LCN2 inhibition might represent a potential therapeutic approach to lower FGF23 and improve outcomes in CKD.

Inflammation: a putative link between phosphate metabolism and cardiovascular disease

Dietary habits in the western world lead to increasing phosphate intake. Under physiological conditions, extraosseous precipitation of phosphate with calcium is prevented by a mineral buffering system composed of calcification inhibitors and tight control of serum phosphate levels. The coordinated hormonal regulation of serum phosphate involves fibroblast growth factor 23 (FGF23), αKlotho, parathyroid hormone (PTH) and calcitriol. A severe derangement of phosphate homeostasis is observed in patients with chronic kidney disease (CKD), a patient collective with extremely high risk of cardiovascular morbidity and mortality. Higher phosphate levels in serum have been associated with increased risk for cardiovascular disease (CVD) in CKD patients, but also in the general population. The causal connections between phosphate and CVD are currently incompletely understood. An assumed link between phosphate and cardiovascular risk is the development of medial vascular calcification, a process actively promoted and regulated by a complex mechanistic interplay involving activation of pro-inflammatory signalling. Emerging evidence indicates a link between disturbances in phosphate homeostasis and inflammation. The present review focuses on critical interactions of phosphate homeostasis, inflammation, vascular calcification and CVD. Especially, pro-inflammatory responses mediating hyperphosphatemia-related development of vascular calcification as well as FGF23 as a critical factor in the interplay between inflammation and cardiovascular alterations, beyond its phosphaturic effects, are addressed.

Utilizing image and caption information for biomedical document classification

Motivation

Biomedical research findings are typically disseminated through publications. To simplify access to domain-specific knowledge while supporting the research community, several biomedical databases devote significant effort to manual curation of the literature—a labor intensive process. The first step toward biocuration requires identifying articles relevant to the specific area on which the database focuses. Thus, automatically identifying publications relevant to a specific topic within a large volume of publications is an important task toward expediting the biocuration process and, in turn, biomedical research. Current methods focus on textual contents, typically extracted from the title-and-abstract. Notably, images and captions are often used in publications to convey pivotal evidence about processes, experiments and results.

Results

We present a new document classification scheme, using both image and caption information, in addition to titles-and-abstracts. To use the image information, we introduce a new image representation, namely Figure-word, based on class labels of subfigures. We use word embeddings for representing captions and titles-and-abstracts. To utilize all three types of information, we introduce two information integration methods. The first combines Figure-words and textual features obtained from captions and titles-and-abstracts into a single larger vector for document representation; the second employs a meta-classification scheme. Our experiments and results demonstrate the usefulness of the newly proposed Figure-words for representing images. Moreover, the results showcase the value of Figure-words, captions and titles-and-abstracts in providing complementary information for document classification; these three sources of information when combined, lead to an overall improved classification performance.

Availability and implementation

Source code and the list of PMIDs of the publications in our datasets are available upon request.

Pathophysiological Implications of Imbalances in Fibroblast Growth Factor 23 in the Development of Diabetes

Observational studies have associated the increase in fibroblast growth factor (FGF) 23 levels, the main regulator of phosphate levels, with the onset of diabetes. These studies open the debate on the plausible existence of undescribed diabetogenic mechanisms derived from chronic supraphysiological levels of FGF23, a prevalent condition in chronic kidney disease (CKD) and end-stage renal disease (ESRD) patients. These maladaptive and diabetogenic responses to FGF23 may occur at different levels, including a direct effect on the pancreatic ß cells, and an indirect effect derived from the stimulation of the synthesis of pro-inflammatory factors. Both mechanisms could be mediated by the binding of FGF23 to noncanonical receptor complexes with the subsequent overactivation of signaling pathways that leads to harmful effects. The canonical binding of FGF23 to the receptor complex formed by the receptor FGFR1c and the coreceptor αKlotho activates Ras/MAPK/ERK signaling. However, supraphysiological concentrations of FGF23 favor non-αKlotho-dependent binding of this molecule to other FGFRs, which could generate an undesired overactivation of the PLCγ/CN/NFAT pathway, as observed in cardiomyocytes and hepatocytes. Moreover, the decrease in αKlotho expression may constitute a contributing factor to the appearance of these effects by promoting the nonspecific activation of the PLCγ/CN/NFAT to the detriment of the αKlotho-dependent Ras/MAPK/ERK pathway. The description of these mechanisms would allow the development of new therapeutic targets susceptible to be modified by dietary changes or by pharmacological intervention.

Novel Small Molecule Fibroblast Growth Factor 23 Inhibitors Increase Serum Phosphate and Improve Skeletal Abnormalities in Hyp Mice

Excess fibroblast growth factor (FGF) 23 causes hereditary hypophosphatemic rickets, such as X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO). A small molecule that specifically binds to FGF23 to prevent activation of the fibroblast growth factor receptor/α-Klotho complex has potential advantages over the currently approved systemically administered FGF23 blocking antibody. Using structure-based drug design, we previously identified ZINC13407541 (N-[[2-(2-phenylethenyl)cyclopenten-1-yl]methylidene]hydroxylamine) as a small molecule antagonist for FGF23. Additional structure-activity studies developed a series of ZINC13407541 analogs with enhanced drug-like properties. In this study, we tested in a preclinical Hyp mouse homolog of XLH a direct connect analog [(E)-2-(4-(tert-butyl)phenyl)cyclopent-1-ene-1-carbaldehyde oxime] (8n), which exhibited the greatest stability in microsomal assays, and [(E)-2-((E)-4-methylstyryl)benzaldehyde oxime] (13a), which exhibited increased in vitro potency. Using cryo-electron microscopy structure and computational docking, we identified a key binding residue (Q156) of the FGF23 antagonists, ZINC13407541, and its analogs (8n and 13a) in the N-terminal domain of FGF23 protein. Site-directed mutagenesis and bimolecular fluorescence complementation-fluorescence resonance energy transfer assay confirmed the binding site of these three antagonists. We found that pharmacological inhibition of FGF23 with either of these compounds blocked FGF23 signaling and increased serum phosphate and 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations in Hyp mice. Long-term parenteral treatment with 8n or 13a also enhanced linear bone growth, increased mineralization of bone, and narrowed the growth plate in Hyp mice. The more potent 13a compound had greater therapeutic effects in Hyp mice. Further optimization of these FGF23 inhibitors may lead to versatile drugs to treat excess FGF23-mediated disorders. SIGNIFICANCE STATEMENT: This study used structure-based drug design and medicinal chemistry approaches to identify and optimize small molecules with different stability and potency, which antagonize excessive actions of fibroblast growth factor 23 (FGF23) in hereditary hypophosphatemic rickets. The findings confirmed that these antagonists bind to the N-terminus of FGF23 to inhibit its binding to and activation of the fibroblast growth factor receptors/α-Klotho signaling complex. Administration of these lead compounds improved phosphate homeostasis and abnormal skeletal phenotypes in a preclinical Hyp mouse model.

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

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

The bone is the major source of high circulating intact fibroblast growth factor-23 in acute murine polymicrobial sepsis induced by cecum ligation puncture

Fibroblast growth factor-23 (FGF23), a bone-produced hormone, plays a critical role in mineral homeostasis. Human diseases associated with excessive intact circulating FGF23 (iFGF23) result in hypophosphatemia and low vitamin D hormone in patients with normal kidney function. In addition, there is accumulating evidence linking FGF23 with inflammation. Based on these studies and the frequent observation of hypophosphatemia among septic patients, we sought to elucidate further the relationship between FGF23 and mineral homeostasis in a clinically relevant murine polymicrobial sepsis model. Medium-severity sepsis was induced by cecum ligation puncture (CLP) in adult CD-1 mice of both sexes. Healthy CD-1 mice (without CLP) were used as controls. Forty-eight hours post-CLP, spontaneous urine was collected, and serum, organs and bones were sampled at necropsy. Serum iFGF23 increased ~20-fold in CLP compared to control mice. FGF23 protein concentration was increased in the bones, but not in spleen or liver of CLP mice. Despite the ~20-fold iFGF23 increase, we did not observe any significant changes in mineral homeostasis or parathyroid hormone levels in the blood of CLP animals. Urinary excretion of phosphate, calcium, and sodium remained unchanged in male CLP mice, whereas female CLP mice exhibited lower urinary calcium excretion, relative to healthy controls. In line with renal FGF23 resistance, expression of phosphate-, calcium- and sodium-transporting proteins did not show consistent changes in the kidneys of male and female CLP mice. Renal expression of the co-receptor αKlotho was downregulated in female, but not in male CLP mice. In conclusion, our data demonstrate that the dramatic, sex-independent rise in serum iFGF23 post-CLP was mainly caused by an upregulation of FGF23 secretion in the bone. Surprisingly, the upsurge in circulating iFGF23 did not alter humoral mineral homeostasis in the acutely septic mice. Hence, the biological function of elevated FGF23 in sepsis remains unclear and warrants further studies.

The relationship between Fibroblast Growth Factor 23 (FGF23) and cardiac MRI findings following primary PCI in patients with acute first time STEMI

BACKGROUND

Fibroblast growth factor 23 (FGF23) is a regulator of mineral metabolism, that has been linked to myocardial remodeling including development of left ventricular (LV) hypertrophy and myocardial fibrosis. The aim of this study was to investigate the relationship between intact FGF23 (iFGF23), myocardial infarct size and LV remodeling following a first acute ST-elevation myocardial infarction (STEMI).

METHODS AND RESULTS

Forty-two consecutive patients with first-time STEMI, single vessel disease, successfully treated with primary percutaneous coronary intervention were included. Cardiac magnetic resonance (CMR) imaging was performed at day 2, 1 week, 2 months and 1 year post MI, and blood samples were drawn at admittance and at the same time points as the CMRs. The cohort was divided according to the presence or not of heart failure post MI. In the total cohort, iFGF23 (mean ± SD) was significantly lower at day 0 (33.7 ± 20.6 pg/ml) and day 2 (31.5 ± 23.4 pg/ml) compared with a reference interval based on 8 healthy adults (43.9 pg/ml ± 19.0 pg/ml). iFGF23 increased to normal levels (55.8 ± 23.4 pg/ml) seven days post MI. In the subset of patients with signs of acute heart failure, FGF23 was higher at all measured timepoints, reaching significantly higher FGF23 levels at 2 months and 1 year following revascularization.

CONCLUSION

There was a reduction in iFGF23 levels during the acute phase of MI, with a normalization at seven days following revascularization. During one-year follow-up, there was a gradual increase in iFGF23 levels in patients with heart failure.

Renal Dnase1 expression is regulated by FGF23 but loss of Dnase1 does not alter renal phosphate handling

Fibroblast growth factor 23 (FGF23) is a bone-derived endocrine hormone that regulates phosphate and vitamin D metabolism. In models of FGF23 excess, renal deoxyribonuclease 1 (Dnase1) mRNA expression is downregulated. Dnase-1 is an endonuclease which binds monomeric actin. We investigated whether FGF23 suppresses renal Dnase-1 expression to facilitate endocytic retrieval of renal sodium dependent phosphate co-transporters (NaPi-IIa/c) from the brush border membrane by promoting actin polymerization. We showed that wild type mice on low phosphate diet and Fgf23^−/− mice with hyperphosphatemia have increased renal Dnase1 mRNA expression while in Hyp mice with FGF23 excess and hypophosphatemia, Dnase1 mRNA expression is decreased. Administration of FGF23 in wild type and Fgf23^−/− mice lowered Dnase1 expression. Taken together, our data shows that Dnase1 is regulated by FGF23. In 6-week-old Dnase1^−/− mice, plasma phosphate and renal NaPi-IIa protein were significantly lower compared to wild-type mice. However, these changes were transient, normalized by 12 weeks of age and had no impact on bone morphology. Adaptation to low and high phosphate diet were similar in Dnase1^−/− and Dnase1^+/+ mice, and loss of Dnase1 gene expression did not rescue hyperphosphatemia in Fgf23^−/− mice. We conclude that Dnase-1 does not mediate FGF23-induced inhibition of renal tubular phosphate reabsorption.

HBEGF: an EGF-like growth factor with FGF23-like activity?

Renal signaling networks downstream of FGF23 are not well delineated, but elucidating them may offer an opportunity to control target genes independent of FGF23 in states of dysregulated mineral metabolism. Ni et al. identify HBEGF as a paracrine/autocrine factor in the proximal tubules of mice that mimics the inductive effect of FGF23 on the vitamin D-catabolizing enzyme 24-hydroxylase through a common mitogen-activated protein kinase-dependent pathway. An understanding of how these findings relate to human disease is eagerly anticipated.

Roles for fibroblast growth factor-23 and α-Klotho in acute kidney injury

Acute kidney injury is a global disease with high morbidity and mortality. Recent studies have revealed that the fibroblast growth factor-23-α-Klotho axis is closely related to chronic kidney disease, and has multiple biological functions beyond bone-mineral metabolism. However, although dysregulation of fibroblast growth factor-23-α-Klotho has been observed in acute kidney injury, the role of fibroblast growth factor-23-α-Klotho in the pathophysiology of acute kidney injury remains largely unknown. In this review, we describe recent findings regarding fibroblast growth factor-23-α-Klotho, which is mainly involved in inflammation, oxidative stress, and hemodynamic disorders. Further, based on these recent results, we put forth novel insights regarding the relationship between the fibroblast growth factor-23-α-Klotho axis and acute kidney injury, which may provide new therapeutic targets for treating acute kidney injury.

Simultaneous management of disordered phosphate and iron homeostasis to correct fibroblast growth factor 23 and associated outcomes in chronic kidney disease

PURPOSE OF REVIEW

Hyperphosphatemia, iron deficiency, and anemia are powerful stimuli of fibroblast growth factor 23 (FGF23) production and are highly prevalent complications of chronic kidney disease (CKD). In this manuscript, we put in perspective the newest insights on FGF23 regulation by iron and phosphate and their effects on CKD progression and associated outcomes. We especially focus on new studies aiming to reduce FGF23 levels, and we present new data that suggest major benefits of combined corrections of iron, phosphate, and FGF23 in CKD.

RECENT FINDINGS

New studies show that simultaneously correcting iron deficiency and hyperphosphatemia in CKD reduces the magnitude of FGF23 increase. Promising therapies using iron-based phosphate binders in CKD might mitigate cardiac and renal injury and improve survival.

SUMMARY

New strategies to lower FGF23 have emerged, and we discuss their benefits and risks in the context of CKD. Novel clinical and preclinical studies highlight the effects of phosphate restriction and iron repletion on FGF23 regulation.

Excessive fibroblast growth factor 23 promotes renal fibrosis in mice with type 2 cardiorenal syndrome

Cardiorenal syndrome (CRS) has a high mortality, but its pathogenesis remains elusive. Fibroblast growth factor 23 (FGF23) is increased in both renal dysfunction and cardiac dysfunction, and FGF receptor 4 (FGFR4) has been identified as a receptor for FGF23. Deficiency of FGF23 causes growth retardation and shortens the lifespan, but it is unclear whether excess FGF23 is detrimental in CRS. This study sought to investigate whether FGF23 plays an important role in CRS-induced renal fibrosis. A mouse model of CRS was created by surgical myocardial infarction for 12 weeks. CRS mice showed a significant increase of circulatory and renal FGF23 protein levels, as well as an upregulation of p-GSK, active-β-catenin, TGF-β, collagen I and vimentin, a downregulation of renal Klotho expression and induction of cardiorenal dysfunction and cardiorenal fibrosis. These changes were enhanced by cardiac overexpression of FGF23 and attenuated by FGF receptor blocker PD173074 or β-catenin blocker IGC001. In fibroblasts (NRK-49F), expression of FGFR4 rather than Klotho was detected. Recombinant FGF23 upregulated the expression of p-GSK, active-β-catenin, TGF-β, collagen I and vimentin proteins. These changes were attenuated by FGFR4 blockade with BLU9931 or β-catenin blockade with IGC001. We concluded that FGF23 promotes CRS-induced renal fibrosis mediated by partly activating FGFR4/β-catenin signaling pathway.