Inflammation regulates fibroblast growth factor 23 production

SPIKENET: An Evidence-Based Therapy for Long COVID

The COVID-19 pandemic has been one of the most impactful events in our lifetime, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Multiple SARS-CoV-2 variants were reported globally, and a wide range of symptoms existed. Individuals who contract COVID-19 continue to suffer for a long time, known as long COVID or post-acute sequelae of COVID-19 (PASC). While COVID-19 vaccines were widely deployed, both unvaccinated and vaccinated individuals experienced long-term complications. To date, there are no treatments to eradicate long COVID. We recently conceived a new approach to treat COVID in which a 15-amino-acid synthetic peptide (SPIKENET, SPK) is targeted to the ACE2 receptor binding domain of SARS-CoV-2, which prevents the virus from attaching to the host. We also found that SPK precludes the binding of spike glycoproteins with the receptor carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) of a coronavirus, murine hepatitis virus-1 (MHV-1), and with all SARS-CoV-2 variants. Further, SPK reversed the development of severe inflammation, oxidative stress, tissue edema, and animal death post-MHV-1 infection in mice. SPK also protects against multiple organ damage in acute and long-term post-MHV-1 infection. Our findings collectively suggest a potential therapeutic benefit of SPK for treating COVID-19.

Iloprost infusion reduces serological cytokines and hormones of hypoxia and inflammation in systemic sclerosis patients

INTRODUCTION

Systemic sclerosis (SSc) is characterized by microvascular damage of skin and internal organs with chronic hypoxia and release of cytokines and hormones such as neutrophil gelatinase-associated lipocalin (NGAL), fibroblast growth factor-23 (FGF-23) and Klotho. Aim of the study was to evaluate FGF-23, Klotho and NGAL serum levels in SSc patients and healthy controls (HC) and to evaluate serum levels changes of FGF-23, Klotho and NGAL after Iloprost.

METHODS

Twenty-one SSc patients and 20 HC were enrolled. In SSc patients, peripheral venous blood samples were collected at the first day before the autumn Iloprost infusion (t0), 60 min (t1) and 14 days after Iloprost infusion (t2).

RESULTS

SSc patients had higher serum level of FGF-23 [18.7 ± 6.4 pg/ml versus 3.6 ± 2.2 pg/ml, p < 0.001], Klotho [5.1 ± 0.8 pg/ml versus 2.3 ± 0.6 pg/ml, p < 0.001] and NGAL [20.9 ± 2.6 pg/ml versus 14.5 ± 1.7 pg/ml, p < 0.001] than HC. Iloprost infusion reduces serum level of FGF-23 (18.7 ± 6.4 pg/ml versus 10.4 ± 5.5 pg/ml, p < 0.001), Klotho (5.1 ± 0.8 pg/ml versus 2.5 ± 0.6 pg/ml, p < 0.001) and NGAL (20.9 ± 2.6 pg/ml versus 15.1 ± 2.3 pg/ml, p < 0.001) between t0 and t1. The Iloprost infusion reduces serum level of FGF-23 (18.7 ± 6.4 pg/ml versus 6.6 ± 5.1 pg/ml), Klotho (5.1 ± 0.8 pg/ml versus 2.3 ± 0.4 pg/ml) and NGAL (20.9 ± 2.6 pg/ml versus 15.5 ± 1.9 pg/ml) between t0 and t2.

CONCLUSIONS

SSc patients had higher FGF-23, Klotho and NGAL than HC. Iloprost reduces serum levels of FGF-23, Klotho and NGAL.

Reduced estrogen signaling contributes to bone loss and cardiac dysfunction in interleukin-10 knockout mice

Characterization of the interleukin (IL)-10 knockout (KO) mouse with chronic gut inflammation, cardiovascular dysfunction, and bone loss suggests a critical role for this cytokine in interorgan communication within the gut, bone, and cardiovascular axis. We sought to understand the role of IL-10 in the cross-talk between these systems. Six-week-old IL-10 KO mice and their wild type (WT) counterparts were maintained on a standard rodent diet for 3 or 6 months. Gene expression of proinflammatory markers and Fgf23, serum 17β-estradiol (E2), and cardiac protein expression were assessed. Ileal Il17a and Tnf mRNA increased while Il6 mRNA increased in the bone and heart by at least 2-fold in IL-10 KO mice. Bone Dmp1 and Phex mRNA were repressed at 6 months in IL-10 KO mice, resulting in increased Fgf23 mRNA (~4-fold) that contributed to increased fibrosis. In the IL-10 KO mice, gut bacterial β-glucuronidase activity and ovarian Cyp19a1 mRNA were lower (p < 0.05), consistent with reduced serum E2 and reduced cardiac pNOS3 (Ser1119 ) in these mice. Treatment of ileal lymphocytes with E2 reduced gut inflammation in WT but not IL-10 KO mice. In conclusion, our data suggest that diminished estrogen and defective bone mineralization increased FGF23 which contributed to cardiac fibrosis in the IL-10 KO mouse.

Hypophosphatemia in infants with severe bronchiolitis and association with length of mechanical ventilation

OBJECTIVES

Electrolyte disorders occurs frequently in children with bronchiolitis. The aim of the present study was to describe the frequency of hypophosphatemia and to evaluate its association with length of mechanical ventilation in infants admitted to a pediatric intensive care unit (PICU) with bronchiolitis.

METHODS

This retrospective cohort study included infants aged between 7 days and 3 months admitted to a PICU between September 2018 and March 2020 and diagnosed with severe acute bronchiolitis requiring respiratory support. Infants with a chronic condition that could potentially be a confounding factor were excluded. The primary outcome was the frequency of hypophosphatemia (<1.55 mmol/L); the secondary outcomes were the frequency of hypophosphatemia during the PICU stay, and the association with length of mechanical ventilation (LOMV).

RESULTS

Among the 319 infants admitted 178 had at least one phosphatemia value and were included in the study. The frequency of hypophosphatemia was 41% at PICU admission (61/148) and 46% during the PICU stay (80/172). The median [IQR] LOMV was significantly longer in children with hypophosphatemia at admission (109 [65-195] h vs. 67 [43-128] h, p = 0.007), and in multivariable linear regression lower phosphatemia at admission was associated with longer LOMV (p < 0.001) after controlling for severity (PELOD2 score) and weight.

CONCLUSION

Hypophosphatemia was frequent in infants with severe bronchiolitis admitted to a PICU and was associated with a longer LOMV.

Effect of Diosmin on Selected Parameters of Oxygen Homeostasis

Chronic venous disease (CVD) is a condition characterized by functional disturbances in the microcirculation of the superficial and deep veins, affecting up to 30% of the global population. Diosmin, a phlebotropic drug, is commonly used in the treatment of CVD, and its beneficial effects have been described in numerous clinical studies. However, the precise molecular mechanism underlying the activity of diosmin is not yet fully understood. Therefore, the objective of our study was to investigate whether diosmin has an impact on oxygen management, as cardiovascular diseases are often associated with hypoxia. In our study, patients were administered a daily dosage of 2 × 600 mg of diosmin for 3 months, and we evaluated several factors associated with oxygen management, angiogenesis, and inflammation using biochemical assays. Our findings indicate that diosmin reduced the levels of fibroblast growth factors (FGF) and vascular endothelial growth factor (VEGF-C), while increasing endostatin and angiostatin levels, suggesting a potential influence on angiogenesis regulation. Furthermore, diosmin exhibited anti-inflammatory properties by suppressing the levels of tumor necrosis factor-alpha (TNF-α), interleukin 1-beta (IL-1β), and interleukin 6 (IL-6), while promoting the production of interleukin 12 (IL-12). Additionally, diosmin significantly decreased the levels of hypoxia-inducible factor (HIF), anion gap (AG), and lactate, indicating its potential influence on the hypoxia-inducible factor pathway. These findings suggest that diosmin may play a crucial role in modulating oxygen management and inflammation in the context of chronic venous disease.

Kidney Damage in Long COVID: Studies in Experimental Mice

Signs and symptoms involving multiple organ systems which persist for weeks or months to years after the initial SARS-CoV-2 infection (also known as PASC or long COVID) are common complications of individuals with COVID-19. We recently reported pathophysiological changes in various organs post-acute infection of mice with mouse hepatitis virus-1 (MHV-1, a coronavirus) (7 days) and after long-term post-infection (12 months). One of the organs severely affected in this animal model is the kidney, which correlated well with human studies showing kidney injury post-SARS-CoV-2 infection. Our long-term post-infection pathological observation in kidneys includes the development of edema and inflammation of the renal parenchyma, severe acute tubular necrosis, and infiltration of macrophages and lymphocytes, in addition to changes observed in both acute and long-term post-infection, which include tubular epithelial cell degenerative changes, peritubular vessel congestion, proximal and distal tubular necrosis, hemorrhage in the interstitial tissue, and vacuolation of renal tubules. These findings strongly suggest the possible development of renal fibrosis, in particular in the long-term post-infection. Accordingly, we investigated whether the signaling system that is known to initiate the above-mentioned changes in kidneys in other conditions is also activated in long-term post-MHV-1 infection. We found increased TGF-β1, FGF23, NGAL, IL-18, HIF1-α, TLR2, YKL-40, and B2M mRNA levels in long-term post-MHV-1 infection, but not EGFR, TNFR1, BCL3, and WFDC2. However, only neutrophil gelatinase-associated lipocalin (NGAL) increased in acute infection (7 days). Immunoblot studies showed an elevation in protein levels of HIF1-α, TLR-2, and EGFR in long-term post-MHV-1 infection, while KIM-1 and MMP-7 protein levels are increased in acute infection. Treatment with a synthetic peptide, SPIKENET (SPK), which inhibits spike protein binding, reduced NGAL mRNA in acute infection, and decreased TGF-β1, BCL3 mRNA, EGFR, HIF1-α, and TLR-2 protein levels long-term post-MHV-1 infection. These findings suggest that fibrotic events may initiate early in SARS-CoV-2 infection, leading to pronounced kidney fibrosis in long COVID. Targeting these factors therapeutically may prevent acute or long-COVID-associated kidney complications.

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.

The relationship between FGF23 and body composition according to albuminuria stage in type 1 diabetes

AIMS

Fibroblast growth factor 23 (FGF23) and obesity are linked to kidney disease. However, the relationship between FGF23 and body composition is unclear. Associations between FGF23 and body composition were investigated in type 1 diabetes from the Finnish Diabetic Nephropathy Study according to albuminuria stages.

METHODS

Data were available from 306 adults with type 1 diabetes (229 normal albumin excretion rate, T1D^normo; 38 microalbuminuria, T1D^micro; 39 macroalbuminuria, T1D^macro), and 36 controls. Serum FGF23 was measured by ELISA. Body composition was assessed with dual-energy X-ray absorptiometry. Associations between body composition and serum FGF23 were investigated using linear regression models.

RESULTS

Compared with T1D^normo, individuals with more advanced kidney disease were older, had longer diabetes duration, higher serum hsCRP, and higher FGF23 concentration. However, FGF23 concentration was comparable between T1D^normo and controls. Adjusted for potential confounders, in T1D^micro, FGF23 was positively associated with the percentages of total fat, visceral fat, and android fat tissues, while negative associations between FGF23 and lean tissue were observed. FGF23 was not associated with body composition in T1D^normo, T1D^macro, and controls.

CONCLUSIONS

In type 1 diabetes, the relationship between FGF23 and body composition is dependent on albuminuria stages.

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.

Oxidative Stress and Natural Antioxidants in Osteoporosis: Novel Preventive and Therapeutic Approaches

This review reports in detail the cellular and molecular mechanisms which regulate the bone remodeling process in relation to oxidative stress (OS), inflammatory factors, and estrogen deficiency. OS is considered an important pathogenic factor of osteoporosis, inducing osteocyte apoptosis and varying levels of specific factors, such as receptor activator κB ligand (RANKL), sclerostin, and, according to recent evidence, fibroblast growth factor 23, with consequent impairment of bone remodeling and high bone resorption. Bone loss increases the risk of fragility fractures, and the most commonly used treatments are antiresorptive drugs, followed by anabolic drugs or those with a double effect. In addition, recent data show that natural antioxidants contained in the diet are efficient in preventing and reducing the negative effects of OS on bone remodeling and osteocytes through the involvement of sirtuin type 1 enzyme. Indeed, osteocytes and some of their molecular factors are considered potential biological targets on which antioxidants can act to prevent and reduce bone loss, as well as to promote bone anabolic and regenerative processes by restoring physiological bone remodeling. Several data suggest including antioxidants in novel therapeutic approaches to develop better management strategies for the prevention and treatment of osteoporosis and OS-related bone diseases. In particular, anthocyanins, as well as resveratrol, lycopene, oleuropein, some vitamins, and thiol antioxidants, could have protective and therapeutic anti-osteoporotic effects.

The Role of Uremic Retention Solutes in the MIA Syndrome in Hemodialysis Subjects

INTRODUCTION

In chronic kidney disease (CKD), the high morbidity and mortality risk for cardiovascular disease (CVD) are not easily explained only on the basis of traditional factors. Among nontraditional ones involved in CKD, malnutrition, inflammation, and atherosclerosis/calcification have been described as the "MIA syndrome."

METHODS

In this pilot study, we evaluated the association between the variation in serum levels of 27 uremic retention solutes plus 6 indexes related to the MIA syndrome processes in a population of dialysis patients.

RESULTS

As expected, we found a direct correlation between serum albumin and both phosphate and total cholesterol (r = 0.54 and 0.37, respectively; p < 0.05). Moreover, total cholesterol and phosphate directly correlate (r = 0.40, p < 0.05). The relationship between malnutrition and inflammation is highlighted by the correlation of serum cholesterol levels with serum alpha-1 acid glycoprotein and IL-6 levels (r = -0.56, r = -0.39, respectively; p < 0.05). Moreover, the relation between inflammation and atherosclerosis/calcification is supported by the correlation of IL-6 with VEGF levels and vascular smooth muscle cell high-Pi in vitro calcification (r = 0.81, r = 0.66, respectively; p < 0.01).

CONCLUSION

We found significant correlations between several uremic retention solutes and malnutrition, inflammation, and atherosclerosis/calcification. Our findings support the hypothesis of a central role of the uremic milieu in the MIA syndrome and ultimately in the pathogenesis of CKD-specific CVD risk factors.

Hypoxia-inducible factor signaling in vascular calcification in chronic kidney disease patients

Chronic kidney disease (CKD) affects approximately 15% of the adult population in high-income countries and is associated with significant comorbidities, including increased vascular calcifications which is associated with a higher risk for cardiovascular events. Even though the underlying pathophysiology is unclear, hypoxia-inducible factor (HIF) signaling appears to play a central role in inflammation, angiogenesis, fibrosis, cellular proliferation, apoptosis and vascular calcifications which is influenced by multiple variables such as iron deficiency anemia, serum phosphorus and calcium levels, fibroblast growth factor-23 (FGF-23) and Klotho. Along with the growing understanding of the pathology, potential therapeutic alternatives have emerged including HIF stabilizers and SGLT-2 inhibitors. The aim of this review is to discuss the role of HIF signaling in the pathophysiology of vascular calcification in CKD patients and to identify potential therapeutic approaches.

Fibroblast growth factor 23 (Fgf23) levels and their relationship with disease activity, bone mineral density, and radiological damage score in patients with rheumatoid arthritis: a single center case–control study

Background

There is limited and conflicting information on Fgf23 levels and their relationship with bone loss and disease activity in rheumatoid arthritis (RA). The aim of this study was to compare Fgf23 levels in RA patients with a healthy population and to evaluate the relationship between Fgf23 levels in RA with disease activity, bone mineral density (BMD), and radiological damage score.

Results

The median Fgf23 levels in patients with RA and in hospital staff were 20.06 (11.2–51.0) and 26.40 (12.6–49.5) pg/ml (P < 0.001), respectively. RA patients were divided into active (DAS28 > 3.2) and inactive (DAS28 ≤ 3.2) subgroups. The median Fgf23 levels in active and inactive RA patients were 22.12 (13.90–51.02) and 17.71 (11.20–31.19) pg/ml, respectively (P = 0.001). BMD of RA patients was evaluated with dual-energy X-ray absorptiometry and radiological damage scores were evaluated independently by two investigators using the modified Sharp score (MSS). In RA patients, Fgf23 values correlated with DAS28 and with erosion score of observer-2 (r = 0.297, P = 0.036), but not with erosion score of observer-1 (r = 0.252, P = 0.077). No correlation was found between DAS28 and femur and lumbar vertebra BMD.

Conclusion

In RA, Fgf23 is not associated with BMD but may be associated with local bone loss and disease activity.

MCP1 Could Mediate FGF23 and Omega 6/Omega 3 Correlation Inversion in CKD

Fibroblast growth factor 23 (FGF23) concentrations rise after the early stages of chronic kidney disease (CKD). FGF23 is involved in inflammatory reactions closely associated with an incremented risk of cardiovascular disease (CVD). There is growing evidence that omega-6 (n-6) and n-3 polyunsaturated fatty acids (PUFA) can modulate inflammation through several mediators producing an opposite effect on cardiovascular (CV) risks. In this study, we explore whether there is any correlation between PUFA, FGF23, and inflammation in CKD patients. We evaluated, cross-sectionally, 56 patients at different stages of CKD. Monocyte chemoattractant protein 1 (MCP1), and intact and c-terminal FGF23 (iFGF23, cFGF23) were quantified by the ELISA, and the fatty acids (FA) profile was analyzed by gas chromatography. Concurrently with an eGFR decrease (p < 0.01) and an MCP1 increase (p = 0.031), we observed an inversion of the correlation between FGF23 and the n-6/n-3 ratio. This last correlation was inversed in CKD stage 3 (r2 (−) 0.502 p = 0.029) and direct in stage 5 (r2 0.657 p = 0.020). The increase in MCP1 seems to trigger events in the inversion of the correlation between FGF23 and the n-6/n-3 PUFA ratio. This result strongly encourages future studies on basal pathways, on possible pharmacological interventions, and on managing kidney transplant patients treated with immunosuppressive therapy.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Phosphate in the Context of Cognitive Impairment and Other Neurological Disorders Occurrence in Chronic Kidney Disease

The nervous system and the kidneys are linked under physiological states to maintain normal body homeostasis. In chronic kidney disease (CKD), damaged kidneys can impair the central nervous system, including cerebrovascular disease and cognitive impairment (CI). Recently, kidney disease has been proposed as a new modifiable risk factor for dementia. It is reported that uremic toxins may have direct neurotoxic (astrocyte activation and neuronal death) and/or indirect action through vascular effects (cerebral endothelial dysfunction, calcification, and inflammation). This review summarizes the evidence from research investigating the pathophysiological effects of phosphate toxicity in the nervous system, raising the question of whether the control of hyperphosphatemia in CKD would lower patients’ risk of developing cognitive impairment and dementia.

Function of PHEX mutations p.Glu145* and p.Trp749Arg in families with X-linked hypophosphatemic rickets by the negative regulation mechanism on FGF23 promoter transcription

X-linked hypophosphatemic rickets (XLH) is characterized by increased circulating fibroblast growth factor 23 (FGF23) concentration caused by PHEX (NM_000444.5) mutations. Renal tubular resorption of phosphate is impaired, resulting in rickets and impaired bone mineralization. By phenotypic-genetic linkage analysis, two PHEX pathogenic mutations were found in two XLH families: c.433 G > T, p.Glu145* in exon 4 and c.2245 T > C, p.Trp749Arg in exon 22. Immunofluorescence showed that the localization of p.Glu145* and p.Trp749Arg mutant and secretory PHEX (secPHEX) changed, with decreased expression. In a HEK293T cell model co-transfected with PHEX, secPHEX, and FGF23, wild-type PHEX, secPHEX, and FGF23 proteins were distributed in the cell membrane or endoplasmic reticulum, while the mutant was located in the nuclear membrane and cytoplasm. qPCR of p.Glu145* revealed decreased PHEX and secPHEX mRNA expression in cells, with no difference in mRNA expression of p.Trp749Arg. Both mutations decreased intracellular PHEX endopeptidase activity. Western blot analysis showed decrease in mutant and secPHEX protein expression and no FGF23 protein expression in single-transfected PHEX and secPHEX cells. In cells co-transfected with FGF23, PHEX and secPHEX mutation promoted FGF23 expression. Dual-luciferase reporter gene was used to detect the effect of PHEX on FGF23 promoter. The dual-luciferase reporter gene showed that after PHEX overexpression, the activity of mutant firefly luciferase was significantly higher than that of wild type. The regulatory mechanism between PHEX and FGF23 is still unclear, but we found that PHEX is a direct transcriptional inhibitor of FGF23 and affects the expression of FGF23. This study verified the pathogenicity of the two variants and revealed the possible regulatory mechanism between PHEX and FGF23.

Physiological and pathophysiological role of endocrine fibroblast growth factors

The endocrine subfamily of fibroblast growth factors (FGF) includes three factors: FGF19, FGF21, FGF23. They act on distal tissues through FGF receptors (FGFRs). The FGFR activation requires two cofactors: α- and β-Klotho, which are structurally related single-pass transmembrane proteins. The endocrine FGFs regulate various metabolic processes involved in the regulation of glucose and lipid metabolism as well as bile acid circulation, vitamin D modulation, and phosphate homeostasis. The FGF-FGFR dysregulation is widely implicated in the pathogenesis of various disorders. Significant alterations in plasma FGF concentration are associated with the most prevalent chronic diseases, including dyslipidemia, type 2 diabetes, cardiovascular diseases, obesity, non-alcoholic fatty liver disease, diseases of the biliary tract, chronic kidney disease, inflammatory bowel disease, osteomalacia, various malignancies, and depression. Therefore, the endocrine FGFs may serve as disease predictors or biomarkers, as well as potential therapeutic targets. Currently, numerous analogues and inhibitors of endocrine FGFs are under development for treatment of various disorders, and recently, a human monoclonal antibody against FGF23 has been approved for treatment of X-linked hypophosphatemia. The aim of this review is to summarize the current data on physiological and pathophysiological actions of the endocrine FGF subfamily and recent research concerning the therapeutic potential of the endocrine FGF pathways.

Impact of Overhydration on Left Ventricular Hypertrophy in Patients With Chronic Kidney Disease

Objective

Volume overload is a frequent feature related to left ventricular hypertrophy (LVH) in dialysis patients, but its influence on patients with chronic kidney disease (CKD) not on dialysis has not been accurately uncovered. This article was to examine the relationship between overhydration (OH) and LVH in patients with CKD not yet on dialysis.

Methods

A total of 302 patients with CKD stages 1–4 were included. Participants were divided into different subgroups according to occurring LVH or not, and OH tertiles. Clinical and laboratory parameters were compared among groups. Spearman correlation analyses were adopted to explore the relationships of echocardiographic findings with the clinical and laboratory characteristics. Binary logistic regression models were performed to estimate the odds ratios (ORs) for the associations between OH and LVH. Restricted cubic splines were implemented to assess the possible non-linear relationship between OH and LVH. LVH was defined as left ventricular mass index (LVMI) &gt;115 g/m2 in men and &gt;95 g/m2 in women.

Results

Of the enrolled patients with CKD, the mean age was 45.03 ± 15.14 years old, 165 (54.6%) cases were men, and 65 (21.5%) cases had LVH. Spearman correlation analyses revealed that OH was positively correlated with LVMI (r = 0.263, P &lt; 0.001). After adjustment for age, gender, diabetes, body mass index (BMI), systolic blood pressure (SBP), hemoglobin, serum albumin, estimated glomerular filtration rate (eGFR), and logarithmic transformation of urinary sodium and urinary protein, multivariate logistic regression analyses demonstrated that both the middle and highest tertile of OH was associated with increased odds of LVH [OR: 3.082 (1.170–8.114), P = 0.023; OR: 4.481 (1.332–15.078), P = 0.015, respectively], in comparison to the lowest tierce. Restricted cubic spline analyses were employed to investigate the relationship between OH and LVH, which unfolded a significant non-linear association (P for non-linear = 0.0363). Furthermore, patients were divided into two groups according to CKD stages. The multivariate logistic regression analyses uncovered that increased odds of LVH were observed in the middle and the highest tertile of OH [OR: 3.908 (0.975–15.670), P = 0.054; OR: 6.347 (1.257–32.054), P = 0.025, respectively] in patients with stages 1–2.

Conclusion

These findings suggest that a higher level of OH was associated with a higher occurrence of LVH in patients with CKD not on dialysis, especially in patients with CKD stages 1–2.

Effect of Oxidative Stress-Induced Apoptosis on Active FGF23 Levels in MLO-Y4 Cells: The Protective Role of 17-β-Estradiol

The discovery that osteocytes secrete phosphaturic fibroblast growth factor 23 (FGF23) has defined bone as an endocrine organ. However, the autocrine and paracrine functions of FGF23 are still unknown. The present study focuses on the cellular and molecular mechanisms involved in the complex control of FGF23 production and local bone remodeling functions. FGF23 was assayed using ELISA kit in the presence or absence of 17β–estradiol in starved MLO-Y4 osteocytes. In these cells, a relationship between oxidative stress-induced apoptosis and up-regulation of active FGF23 levels due to MAP Kinases activation with involvement of the transcriptional factor (NF-kB) has been demonstrated. The active FGF23 increase can be due to up-regulation of its expression and post-transcriptional modifications. 17β–estradiol prevents the increase of FGF23 by inhibiting JNK and NF-kB activation, osteocyte apoptosis and by the down-regulation of osteoclastogenic factors, such as sclerostin. No alteration in the levels of dentin matrix protein 1, a FGF23 negative regulator, has been determined. The results of this study identify biological targets on which drugs and estrogen may act to control active FGF23 levels in oxidative stress-related bone and non-bone inflammatory diseases.

Vitamin D Actions: The Lung Is a Major Target for Vitamin D, FGF23, and Klotho

Vitamin D is well known for its role as a calcium regulator and in maintenance of phosphate homeostasis in musculoskeletal health, and fibroblast growth factor 23 (FGF23) and its coreceptor α-klotho are known for their roles as regulators of serum phosphate levels. However, apart from these classical actions, recent data point out a relevant role of vitamin D and FGF23/klotho in lung health. The expression of the vitamin D receptor by different cell types in the lung and the fact that those cells respond to vitamin D or can locally produce vitamin D indicate that the lung represents a target for vitamin D actions. Similarly, the presence of the four FGF receptor isoforms in the lung and the ability of FGF23 to stimulate pulmonary cells support the concept that the lung is a target for FGF23 actions, whereas the contribution of klotho is still undetermined. This review will give an overview on how vitamin D or FGF23/klotho may act on the lung and interfere positively or negatively with lung health. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

The Multiple Roles of Fibroblast Growth Factor in Diabetic Nephropathy

Diabetic nephropathy (DN) is a common microvascular complication in the late stages of diabetes. Currently, the etiology and pathogenesis of DN are not well understood. Even so, available evidence shows its development is associated with metabolism, oxidative stress, cytokine interaction, genetic factors, and renal microvascular disease. Diabetic nephropathy can lead to proteinuria, edema and hypertension, among other complications. In severe cases, it can cause life-threatening complications such as renal failure. Patients with type 1 diabetes, hypertension, high protein intake, and smokers have a higher risk of developing DN. Fibroblast growth factor (FGF) regulates several human processes essential for normal development. Even though FGF has been implicated in the pathological development of DN, the underlying mechanisms are not well understood. This review summarizes the role of FGF in the development of DN. Moreover, the association of FGF with metabolism, inflammation, oxidative stress and fibrosis in the context of DN is discussed. Findings of this review are expected to deepen our understanding of DN and generate ideas for developing effective prevention and treatments for the disease.

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.

Physiology and Inflammation Driven Pathophysiology of Iron Homeostasis-Mechanistic Insights into Anemia of Inflammation and Its Treatment

Anemia is very common in patients with inflammatory disorders. Its prevalence is associated with severity of the underlying disease, and it negatively affects quality of life and cardio-vascular performance of patients. Anemia of inflammation (AI) is caused by disturbances of iron metabolism resulting in iron retention within macrophages, a reduced erythrocyte half-life, and cytokine mediated inhibition of erythropoietin function and erythroid progenitor cell differentiation. AI is mostly mild to moderate, normochromic and normocytic, and characterized by low circulating iron, but normal and increased levels of the storage protein ferritin and the iron hormone hepcidin. The primary therapeutic approach for AI is treatment of the underlying inflammatory disease which mostly results in normalization of hemoglobin levels over time unless other pathologies such as vitamin deficiencies, true iron deficiency on the basis of bleeding episodes, or renal insufficiency are present. If the underlying disease and/or anemia are not resolved, iron supplementation therapy and/or treatment with erythropoietin stimulating agents may be considered whereas blood transfusions are an emergency treatment for life-threatening anemia. New treatments with hepcidin-modifying strategies and stabilizers of hypoxia inducible factors emerge but their therapeutic efficacy for treatment of AI in ill patients needs to be evaluated in clinical trials.

The relationship between FGF23 and anemia in HD and renal transplant patients

PURPOSE

Recent studies claim that FGF23 is also associated with anemia and inflammation. In this study, the relationship between FGF23 and anemia in hemodialysis (HD) and renal transplantation patients (RTx patients) patients was investigated.

METHODS

This was a cross-sectional study involving 40 RTx patients (13 females, 27 males; mean age, 45.93 ± 12.49 years) who had transplantation at least 6 months before, 25 HD patients (12 females, 13 males; mean age, 54.72 ± 15.5 years), and 20 healthy control subjects (13 females, 7 males; mean age, 36.7 ± 9.38 years). FGF23 was studied using Elisa method. Parameters such as iron, ferritin, total iron binding capacity, and transferrin saturation were assessed.

RESULTS

FGF23 level was significantly higher in HD patients when compared with the RTx patients and control groups. In the bivariate correlation analysis, hemoglobin was positively correlated with albumin (r = 0.681, p = 0.000), ferritin (r = 0.446, p = 0.043), and negatively correlated with CRP (r = - 0.476, p = 0.016) and FGF23 (r = 0.493, p = 0.043). FGF23 was found to be an independent predictor of decreased hemoglobin in HD patients. In addition, this association was observed to disappear after transplantation.

CONCLUSION

While FGF23 is closely related to hemoglobin levels in HD patients, we have shown that this relationship disappears after transplantation.

Elevation of serum fibroblast growth factor 23 level in a pediatric patient with lupus nephritis

Fibroblast growth factor 23 (FGF-23), a hormone mainly secreted by osteocytes and osteoblasts, regulates phosphate and vitamin D levels. However, the in vivo significance of FGF-23 is not fully elucidated. This case report describes a 12-year-old girl with systemic lupus erythematosus (SLE), lupus nephritis, and an elevated serum FGF-23 level. The patient was treated with active vitamin D and oral sodium phosphate medications to manage low serum phosphate levels (2.2 mg/dL). Magnetic resonance imaging (MRI) revealed a high-intensity area in the left femur, but somatostatin receptor scintigraphy images did not indicate tumor-induced osteomalacia. SLE treatment using mycophenolate mofetil (1500 mg/day) was initiated, and serum complements levels increased as FGF-23 level increased. Serum FGF-23 level gradually decreased as urinary protein levels decreased after treatment with steroids; however, there was no change in the high-intensity area on MRI. Recent studies have reported that serum FGF-23 level is associated with iron deficiency and inflammation; yet, the mechanism related to these associations is not fully elucidated. The findings from this case suggest that elevated serum FGF-23 levels noted in our patient were related to silent lupus nephritis and lupus nephritis activity.

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.

Interplay of erythropoietin, fibroblast growth factor 23, and erythroferrone in patients with hereditary hemolytic anemia

Recently, erythropoietin (EPO) was identified as regulator of fibroblast growth factor 23 (FGF23). Proteolytic cleavage of biologically active intact FGF23 (iFGF23) results in the formation of C-terminal fragments (cFGF23). An increase in cFGF23 relative to iFGF23 suppresses FGF receptor signaling by competitive inhibition. EPO lowers the i:cFGF23 ratio, thereby overcoming iFGF23-mediated suppression of erythropoiesis. We investigated EPO-FGF23 signaling and levels of erythroferrone (ERFE) in 90 patients with hereditary hemolytic anemia (www.trialregister.nl [NL5189]). We show, for the first time, the importance of EPO-FGF23 signaling in hereditary hemolytic anemia: there was a clear correlation between total FGF23 and EPO levels (r = +0.64; 95% confidence interval [CI], 0.09-0.89), which persisted after adjustment for iron load, inflammation, and kidney function. There was no correlation between iFGF23 and EPO. Data are consistent with a low i:cFGF23 ratio. Therefore, as expected, we report a correlation between EPO and ERFE in a diverse set of hereditary hemolytic anemias (r = +0.47; 95% CI, 0.14-0.69). There was no association between ERFE and total FGF23 or iFGF23, which suggests that ERFE does not contribute to the connection between FGF23 and EPO. These findings open a new area of research and might provide potentially new druggable targets with the opportunity to ameliorate ineffective erythropoiesis and the development of disease complications in hereditary hemolytic anemias.

Increased Osteocyte Lacunae Density in the Hypermineralized Bone Matrix of Children with Osteogenesis Imperfecta Type I

Osteocytes are terminally differentiated osteoblasts embedded within the bone matrix and key orchestrators of bone metabolism. However, they are generally not characterized by conventional bone histomorphometry because of their location and the limited resolution of light microscopy. OI is characterized by disturbed bone homeostasis, matrix abnormalities and elevated bone matrix mineralization density. To gain further insights into osteocyte characteristics and bone metabolism in OI, we evaluated 2D osteocyte lacunae sections (OLS) based on quantitative backscattered electron imaging in transiliac bone biopsy samples from children with OI type I (n = 19) and age-matched controls (n = 24). The OLS characteristics were related to previously obtained, re-visited histomorphometric parameters. Moreover, we present pediatric bone mineralization density distribution reference data in OI type I (n = 19) and controls (n = 50) obtained with a field emission scanning electron microscope. Compared to controls, OI has highly increased OLS density in cortical and trabecular bone (+50.66%, +61.73%; both p < 0.001), whereas OLS area is slightly decreased in trabecular bone (−10.28%; p = 0.015). Correlation analyses show a low to moderate, positive association of OLS density with surface-based bone formation parameters and negative association with indices of osteoblast function. In conclusion, hyperosteocytosis of the hypermineralized OI bone matrix associates with abnormal bone cell metabolism and might further impact the mechanical competence of the bone tissue.

Myostatin regulates the production of fibroblast growth factor 23 (FGF23) in UMR106 osteoblast-like cells

Myostatin is a signaling molecule produced by skeletal muscle cells (myokine) that inhibits muscle hypertrophy and has further paracrine and endocrine effects in other organs including bone. Myostatin binds to activin receptor type 2B which forms a complex with transforming growth factor-β type I receptor (TGF-βRI) and induces intracellular p38MAPK and NFκB signaling. Fibroblast growth factor 23 (FGF23) is a paracrine and endocrine mediator produced by bone cells and regulates phosphate and vitamin D metabolism in the kidney. P38MAPK and NFκB-dependent store-operated Ca²⁺ entry (SOCE) are positive regulators of FGF23 production. Here, we explored whether myostatin influences the synthesis of FGF23. Fgf23 gene expression was determined by qRT-PCR and FGF23 protein by ELISA in UMR106 osteoblast–like cells. UMR106 cells expressed activin receptor type 2A and B. Myostatin upregulated Fgf23 gene expression and protein production. The myostatin effect on Fgf23 was significantly attenuated by TGF-βRI inhibitor SB431542, p38MAPK inhibitor SB202190, and NFκB inhibitor withaferin A. Moreover, SOCE inhibitor 2-APB blunted the myostatin effect on Fgf23. Taken together, myostatin is a stimulator of Fgf23 expression in UMR106 cells, an effect at least partially mediated by downstream TGF-βRI/p38MAPK signaling as well as NFκB-dependent SOCE.

Evidence of a dysregulated vitamin D endocrine system in SARS-CoV-2 infected patient's lung cells

Although a defective vitamin D endocrine system has been widely suspected to be associated in SARS-CoV-2 pathobiology, the status of the vitamin D endocrine system and vitamin D-modulated genes in lung cells of patients infected with SARS-CoV-2 remains unknown. To understand the significance of the vitamin D endocrine system in SARS-CoV-2 pathobiology, computational approaches were applied to transcriptomic datasets from bronchoalveolar lavage fluid (BALF) cells of such patients or healthy individuals. Levels of vitamin D receptor, retinoid X receptor, and CYP27A1 in BALF cells of patients infected with SARS-CoV-2 were found to be reduced. Additionally, 107 differentially expressed, predominantly downregulated genes, as potentially modulated by vitamin D endocrine system, were identified in transcriptomic datasets from patient’s cells. Further analysis of differentially expressed genes provided eight novel genes with a conserved motif with vitamin D-responsive elements, implying the role of both direct and indirect mechanisms of gene expression by the dysregulated vitamin D endocrine system in SARS-CoV-2-infected cells. Protein–protein interaction network of differentially expressed vitamin D-modulated genes were enriched in the immune system, NF-κB/cytokine signaling, and cell cycle regulation as top predicted pathways that might be affected in the cells of such patients. In brief, the results presented here povide computational evidence to implicate a dysregulated vitamin D endocrine system in the pathobiology of SARS-CoV-2 infection.

Orphan nuclear receptor ERR-γ regulates hepatic FGF23 production in acute kidney injury

Bone is the main source of fibroblast growth factor 23 (FGF23), which is important for phosphate and vitamin D homeostasis. In acute kidney injury (AKI), high blood levels of FGF23 are positively correlated with disease progression and increased risk of mortality. Reducing adverse plasma FGF23 levels in AKI patients is favorable. We showed here that hepatocytes are the major source of circulating FGF23, and orphan nuclear receptor ERR-γ is a novel transcriptional regulator of hepatic FGF23 production in AKI. Liver-specific depletion of ERR-γ or ERR-γ inverse agonist, GSK5182, significantly reduced plasma levels of FGF23 in AKI. This study reveals liver is the source of FGF23 and a therapeutic strategy to control pathologically adverse plasma FGF23 levels in AKI.

Orphan nuclear receptor ERR-γ regulates hepatic FGF23 production in acute kidney injury

Fibroblast growth factor 23 (FGF23), a hormone generally derived from bone, is important in phosphate and vitamin D homeostasis. In acute kidney injury (AKI) patients, high-circulating FGF23 levels are associated with disease progression and mortality. However, the organ and cell type of FGF23 production in AKI and the molecular mechanism of its excessive production are still unidentified. For insight, we investigated folic acid (FA)-induced AKI in mice. Interestingly, simultaneous with FGF23, orphan nuclear receptor ERR-γ expression is increased in the liver of FA-treated mice, and ectopic overexpression of ERR-γ was sufficient to induce hepatic FGF23 production. In patients and in mice, AKI is accompanied by up-regulated systemic IL-6, which was previously identified as an upstream regulator of ERR-γ expression in the liver. Administration of IL-6 neutralizing antibody to FA-treated mice or of recombinant IL-6 to healthy mice confirms IL-6 as an upstream regulator of hepatic ERR-γ-mediated FGF23 production. A significant (P < 0.001) interconnection between high IL-6 and FGF23 levels as a predictor of AKI in patients that underwent cardiac surgery was also found, suggesting the clinical relevance of the finding. Finally, liver-specific depletion of ERR-γ or treatment with an inverse ERR-γ agonist decreased hepatic FGF23 expression and plasma FGF23 levels in mice with FA-induced AKI. Thus, inverse agonist of ERR-γ may represent a therapeutic strategy to reduce adverse plasma FGF23 levels in AKI.

Diagnostic value of fibroblast growth factor 23 for abdominal aortic calcification in Indonesian hemodialysis patients

Objective:

Homeostasis of serum phosphorus and calcitriol level is regulated mainly by fibroblast growth factor 23 (FGF23). Studies show that elevated serum FGF23 level was significantly associated with aortic calcification severity, peripheral blood vessels, and a higher score of coronary artery calcification in patients undergoing hemodialysis. We did this cross-sectional study to determine the FGF23 diagnostic value for abdominal aortic calcification in Indonesian hemodialysis patients.

Materials and Methods:

This study included seventy-five, chronic hemodialysis patients. An enzyme-linked immunosorbent assay method was used to measure serum intact FGF23 level, and abdominal aortic calcification was detected by lateral lumbar X-ray. The diagnostic value of FGF23 was analyzed using receiver operating characteristic (ROC) curves.

Results:

fifty-one (68.0%) patients had abdominal aortic calcification (AAC). Serum intact FGF23 level ranged from 217 to 950 pg/mL with a median level of 328 pg/mL. The FGF23 levels in the serum of patients with AAC were significantly higher than those without AAC (P < 0.001). The best cutoff point was 277 pg/mL. The calculated area under the ROC curves was 0.959 (95% confidence interval, 0.912–1.00); sensitivity was 94.0% and specificity was 84.0% (P < 0.001).

Conclusion:

serum intact FGF23 level may be proposed as a proper tool for abdominal aortic calcification in Indonesian hemodialysis patients.

Myostatin and markers of bone metabolism in dermatomyositis

Background

In dermatomyostis (DM) patients, inflammation, reduced activity, and medication have a negative impact on the musculoskeletal system. Several endocrine factors are involved in muscle growth and bone turnover.

Objective: We aimed to investigate factors regulating myogenesis and bone metabolism and to evaluate possible associations between these endocrine factors, muscle strength, and functional tests in DM patients.

Methods

We conducted a cross-sectional study in 20 dermatomyositis patients. Serum levels of myostatin (MSTN), follistatin (FSTN), dickkopf 1 (Dkk1), sclerostin (SOST), periostin (PSTN), the receptor activator nuclear factor kB ligand (RANKL):osteoprotegerin (OPG) ratio and fibroblast growth factor 23 (FGF23) were determined. Physical function was evaluated by hand-held strength measurement, chair rising test, timed up and go test and the 3-min walking test.

Results

Serum MSTN and FGF23 levels (2.5 [1.9; 3.2] vs. 1.9 [1.6; 2.3] and 2.17 [1.45; 3.26] vs. 1.28 [0.79; 1.96], respectively; p <  0.05) were significantly higher in DM patients than in controls. Dkk1 was significantly lower (11.4 [6.9; 20.0] vs. 31.8 [14.3; 50.6], p <  0.01). Muscle strength and physical function tests correlated with each other (e.g. hip flexion – timed up and go test: r = − 0.748, p < 0.01).

Conclusion

In DM patients, biochemical musculo-skeletal markers are altered and physical function shows deficits. All these tests reflect independent of each other different deficits in long-term DM patients which is important for the assessment of DM patients as well as planning of therapeutic interventions in clinical routine.

Glucocorticoids dexamethasone and prednisolone suppress fibroblast growth factor 23 (FGF23)

Fibroblast growth factor 23 (FGF23) is a hormone mainly secreted by bone cells. Its most prominent effects are the regulation of renal phosphate reabsorption and calcitriol (active vitamin D, 1,25(OH)₂D₃) formation, effects dependent on its co-receptor αKlotho. Besides these actions, further paracrine and endocrine effects exist. The production of FGF23 is regulated by 1,25(OH)₂D₃, parathyroid hormone, dietary phosphate intake, iron status, as well as inflammation. Glucocorticoids are hormones with anti-inflammatory properties and are, therefore, widely used for acute and chronic inflammatory diseases, autoimmune disorders, and malignancies. The present study explored whether glucocorticoids influence the production of FGF23 in vitro as well as in mice. Fgf23 transcription was analyzed by semi-quantitative real-time PCR. Serum concentrations of FGF23 and 1,25(OH)₂D₃ were measured by ELISA. Urinary phosphate and Ca²⁺ excretion were determined in metabolic cages. As a result, in UMR106 rat osteoblast-like cells and in MC3T3-E1 cells, both, dexamethasone and prednisolone, downregulated Fgf23 transcription and FGF23 protein synthesis. Dexamethasone increased Dmp1 and Phex (encoding FGF23-regulating genes) as well as Nfkbia (encoding NFκB inhibitor IκBα) transcription in UMR106 cells. In mice, a single injection of dexamethasone or prednisolone was followed by a significant decrease of serum C-terminal and intact FGF23 concentration and bone Fgf23 mRNA expression within 12 h. These effects were paralleled by increased renal phosphate excretion and enhanced 1,25(OH)₂D₃ formation. We conclude that a single glucocorticoid treatment strongly downregulates the FGF23 plasma concentration. KEY MESSAGES: Glucocorticoids dexamethasone and prednisolone suppress the formation of bone-derived hormone fibroblast growth factor 23 (FGF23) in vitro. The effect is accompanied by an upregulation of Dmp1, Phex, and IκBα, negative regulators of FGF23, in UMR106 osteoblast-like cells. Glucocorticoid receptor antagonist RU-486 attenuates the effect of dexamethasone on FGF23, Dmp1, and Phex. In mice, a single glucocorticoid dose suppresses FGF23 and enhances 1,25(OH)₂D₃ (active vitamin D).

Stress, inflammation, depression, and dementia associated with phosphate toxicity

Depression and dementia are predicted to increase within aging global populations. Pathophysiological effects of phosphate toxicity, dysregulated amounts of accumulated phosphorus in body tissue, are under-investigated in association with stress, inflammation, depression, and dementia. A comparative analysis of concepts in cited sources from the research literature was used to synthesize novel themes exploring the disease-oriented neuroscience effects of phosphate toxicity. Phosphate toxicity is associated with activation of cellular stress response systems and inflammation. Cortisol released by the hypothalamic-pituitary-adrenal axis responds to stress and inflammation associated with phosphate toxicity and depression. In a reciprocal interaction, phosphate toxicity is capable of harming adrenal gland function, possibly leading to adrenal insufficiency and depression. Furthermore, Alzheimer's disease is associated with hyperphosphorylated tau which self-assembles into neurofibrillary tangles from excessive amounts of phosphate in the brain and central nervous system. Future research should investigate dietary phosphate modification to reduce potential pathophysiological effects of phosphate toxicity in stress, inflammation, depression, and cognitive decline which affects global populations.

Vitamin A regulates fibroblast growth factor 23 (FGF23)

OBJECTIVES

Renal phosphate and vitamin D metabolism are regulated by proteohormone fibroblast growth factor 23 (FGF23), which is secreted by bone cells. FGF23 inhibits phosphate reabsorption and the production of calcitriol, active vitamin D (1,25(OH)₂D₃). FGF23 generated by other cells exerts further paracrine effects in the liver, heart, and immune system. The FGF23 plasma concentration is positively associated with the onset and progression of kidney and cardiovascular diseases, disclosing FGF23 as a potential disease biomarker. The effects of vitamin A on the expression of FGF23 are controversial. Vitamin A components, retinoids, are mainly effective through nuclear retinoic acid receptors (RAR) and exert different effects on bone. The aim of this study was to clarify whether vitamin A modulates the production of FGF23.

METHODS

We studied the relevance of vitamin A for FGF23 production. Fgf23 transcripts were determined by real-time quantitative polymerase chain reaction in UMR106 osteoblast-like cells and IDG-SW3 osteocytes. FGF23 protein in the cell culture supernatant was measured by enzyme-linked immunosorbent assay.

RESULTS

All-trans-retinoic acid, retinyl acetate, RAR agonist TTNPB (4-[(E)-2-(5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid), and 13-cis-retinoic acid downregulated the expression of the Fgf23 gene in a dose-dependent manner. This effect was significantly attenuated by RAR antagonist AGN193109 (4-[2-[5,6-Dihydro-5,5-dimethyl-8-(4-methylphenyl)-2-naphthalenyl]ethynyl]benzoic acid).

CONCLUSION

The present study demonstrated that vitamin A is a potent suppressor of FGF23 production through RAR.

Serum Levels of Fibroblast Growth Factor 23 in People Living with HIV

BACKGROUND

Fibroblast growth factor (FGF) 23 is a well-known phosphaturic hormone produced mainly by bone cells to maintain phosphate and mineral homeostasis. Serum FGF23 levels are elevated in patients with chronic kidney disease (CKD), and elevated FGF23 might increase the risk of cardiovascular disease (CVD). Several reports have documented an increased incidence of risk factors for osteopenia, CKD, and CVD in people living with HIV (PLWH). However, few reports related to FGF23 in PLWH have been published.

METHODS

Male HIV patients who presented to the outpatient clinic of Teikyo University Hospital, Tokyo, Japan, in 2015 and were treated with antiretroviral therapy (ART) for > 6 months were enrolled in the study. In addition to serum FGF23 measurements, the clinical factors assessed included age, ART regimens, and laboratory data. Spearman correlation and multiple regression analysis were performed to determine factors significantly associated with FGF23.

RESULTS

In total, 67 patients were enrolled in the present study. The median age was 43.7 years, the median CD4 count was 529 cells/μL, and the median serum FGF23 level was 36.0 pg/mL. Based on correlation and multiple regression analyses, serum FGF23 levels were significantly correlated with HIV RNA > 50 copies (correlation analysis: t = 3.4259, P = 0.0011 / multiple regression analysis: P = 0.00106) or abacavir (ABC)/lamivudine (3TC) use (t = 2.8618, P = 0.0057 / P = 0.02704).

CONCLUSION

Factors significantly associated with elevated serum FGF23 levels included poor virologic control and ABC/3TC use.

Carbonyl iron and iron dextran therapies cause adverse effects on bone health in juveniles with chronic kidney disease

Anemia is a frequent complication of chronic kidney disease (CKD), related in part to the disruption of iron metabolism. Iron therapy is very common in children with CKD and excess iron has been shown to induce bone loss in non-CKD settings, but the impact of iron on bone health in CKD remains poorly understood. Here, we evaluated the effect of oral and parenteral iron therapy on bone transcriptome, bone histology and morphometry in two mouse models of juvenile CKD (adenine-induced and 5/6-nephrectomy). Both modalities of iron therapy effectively improved anemia in the mice with CKD, and lowered bone Fgf23 expression. At the same time, iron therapy suppressed genes implicated in bone formation and resulted in the loss of cortical and trabecular bone in the mice with CKD. Bone resorption was activated in untreated CKD, but iron therapy had no additional effect on this. Furthermore, we assessed the relationship between biomarkers of bone turnover and iron status in a cohort of children with CKD. Children treated with iron had lower levels of circulating biomarkers of bone formation (bone-specific alkaline phosphatase and the amino-terminal propeptide of type 1 procollagen), as well as fewer circulating osteoblast precursors, compared to children not treated with iron. These differences were independent of age, sex, and glomerular filtration rate. Thus, iron therapy adversely affected bone health in juvenile mice with CKD and was associated with low levels of bone formation biomarkers in children with CKD.

FGF23: Is It Another Biomarker for Phosphate-Calcium Metabolism?

Fibroblast growth factor 23 (FGF23) is a protein produced by mature osteoblasts involved in mineral homeostasis by binding to its receptor complex FGFR/Klotho located mainly in the kidneys. Although this protein participates in numerous biological processes, increase in the levels of FGF23 is responsible for many pathologies, such as X-linked hypophosphataemia (XLH), chronic kidney disease, cardiovascular disease or even mortality. For this reason, both FGF23 and its receptors have become elements of interest for the development of treatments. However, FGF23 can be altered for many other reasons, such as inflammatory processes, iron, hypoxia, heart failure or erythropoietin, that negatively affect mortality. This article will review the role of FGF23 in phosphate homeostasis, its relationship to mortality, fractures and chronic renal failure, and how the levels of this factor can be reduced.

Peroxisome proliferator-activated receptor α (PPARα)-dependent regulation of fibroblast growth factor 23 (FGF23)

Bone cells secrete fibroblast growth factor 23 (FGF23), a hormone that inhibits the synthesis of active vitamin D (1,25(OH)₂D₃) and induces phosphate excretion in the kidney. In addition, it exerts paracrine effects on other cells including hepatocytes, cardiomyocytes, and immune cells. The production of FGF23 is controlled by different factors including parathyroid hormone, 1,25(OH)₂D₃, alimentary phosphate, insulin, inflammation, and AMP-dependent kinase (AMPK) regulation of store-operated Ca²⁺ entry (SOCE). Peroxisome proliferator-activated receptor α (PPARα) is a transcription factor with anti-inflammatory properties regulating lipid metabolism. Fibrates, PPARα agonists, are used in the treatment of dyslipidemia and activate AMPK. Here, we tested whether PPARα is a regulator of FGF23. Fgf23 gene expression was analyzed in UMR106 rat osteoblast-like cells by qRT-PCR, AMPK phosphorylation by Western blotting, and SOCE assessed by fluorescence optics. PPARα agonists fenofibrate and WY-14643 suppressed, whereas PPARα antagonist GW6471 and siRNA-mediated knockdown of PPARα induced Fgf23 gene expression. Fenofibrate induced AMPK activity in UMR106 cells and lowered SOCE. AMPK inhibitor compound C abrogated the PPARα effect on FGF23 in large part. Silencing of Orai-1 resulted in failure of PPARα to significantly influence Fgf23 expression. Taken together, PPARα is a potent regulator of FGF23. PPARα agonists down-regulate FGF23 formation at least in part through AMPK-mediated suppression of SOCE.

The effects of tenapanor on serum fibroblast growth factor 23 in patients receiving hemodialysis with hyperphosphatemia

Background

Elevated serum fibroblast growth factor 23 (FGF23) is strongly associated with cardiovascular risk and mortality. Tenapanor, an inhibitor of gastrointestinal sodium/hydrogen exchanger isoform 3, decreased serum phosphate in a randomized, double-blind, placebo-controlled Phase 2 trial (ClinicalTrials.gov identifier NCT02081534) of patients receiving hemodialysis with hyperphosphatemia. Here, we report a secondary analysis of effects on serum FGF23 during that study.

Methods

After 1–3 weeks of washout of phosphate binders, 162 patients were randomized to receive 4 weeks of treatment with placebo or one of six tenapanor regimens (3 or 30 mg once daily, or 1, 3, 10 or 30 mg twice daily). Intact FGF23 concentrations were determined from serum samples collected at screening, post-washout and end of treatment, assayed in duplicate in a single batch at the end of the study.

Results

After phosphate-binder washout, serum FGF23 concentrations increased in all groups [range of geometric means: 1430–2605 pg/mL before, to 2601–6294 pg/mL after washout (P < 0.001 for all patients analyzed as a single group)]. Serum FGF23 concentrations subsequently decreased in tenapanor-treated patients (2030–3563 pg/mL), whereas they increased further in placebo-treated patients (6930 pg/mL). In an analysis of covariance, FGF23 decreased by 9.1–27.9% in tenapanor-treated patients and increased by 21.9% in placebo-treated patients (P ≤ 0.001–0.04).

Conclusions

Following a marked increase in serum FGF23 in response to withdrawal of phosphate binders, tenapanor significantly decreased serum FGF23 in patients receiving hemodialysis with hyperphosphatemia. Further studies are required to explore the long-term effects of controlling FGF23 with tenapanor.

CharXgen-Activated Bamboo Charcoal Encapsulated in Sodium Alginate Microsphere as the Absorbent of Uremic Toxins to Retard Kidney Function Deterioration

Indoxyl sulphate (IS) and p-cresyl sulphate (PCS) are two protein bound uraemic toxins accumulated in chronic kidney disease (CKD) and associated with adverse outcomes. The purpose of this study isto evaluate the effect of the new activated charcoal, CharXgen, on renal function protection and lowering serum uraemic toxins in CKD animal model. The physical character of CharXgen was analyzed before and after activation procedure by Scanning Electron Microscope (SEM) and X-ray diffractometer (XRD). The effect of CharXgen on biochemistry and lowering uremic toxins was evaluated by in vitro binding assay and CKD animal model. CharXgen have high interior surface area analyzed by SEM and XRD and have been produced from local bamboo after an activation process. CharXgen was able to effectively absorb IS, p-cresol and phosphate in an in vitro gastrointestinal tract simulation study. The animal study showed that CharXgen did not cause intestine blackening. Serum albuminand liver function did not change after feeding with CharXgen. Moreover, renal function was improved in CKD rats fed with CharXgen as compared to the CKD group, and there were no significant differences in the CKD and the CKD + AST-120 groups. Serum IS and PCS were higher in the CKD group and lower in rats treated with CharXgen and AST-120. In rats treated with CharXgen, Fibroblast growth factor 23 was significantly decreased as compared to the CKD group. This change cannot be found in rats fed with AST-120.It indicates that CharXgen is a new safe and non-toxic activated charcoal having potential in attenuating renal function deterioration and lowering protein-bound uraemic toxins. Whether the introduction of this new charcoal could further have renal protection in CKD patients will need to be investigated further.

Extra-Large Gα Protein (XLαs) Deficiency Causes Severe Adenine-Induced Renal Injury with Massive FGF23 Elevation

Fibroblast growth factor-23 (FGF23) is critical for phosphate and vitamin D homeostasis. Cellular and molecular mechanisms underlying FGF23 production remain poorly defined. The extra-large Gα subunit (XLαs) is a variant of the stimulatory G protein alpha-subunit (Gsα), which mediates the stimulatory action of parathyroid hormone in skeletal FGF23 production. XLαs ablation causes diminished FGF23 levels in early postnatal mice. Herein we found that plasma FGF23 levels were comparable in adult XLαs knockout (XLKO) and wild-type littermates. Upon adenine-rich diet-induced renal injury, a model of chronic kidney disease, both mice showed increased levels of plasma FGF23. Unexpectedly, XLKO mice had markedly higher FGF23 levels than WT mice, with higher blood urea nitrogen and more severe tubulopathy. FGF23 mRNA levels increased substantially in bone and bone marrow in both genotypes; however, the levels in bone were markedly higher than in bone marrow. In XLKO mice, a positive linear correlation was observed between plasma FGF23 and bone, but not bone marrow, FGF23 mRNA levels, suggesting that bone, rather than bone marrow, is an important contributor to severely elevated FGF23 levels in this model. Upon folic acid injection, a model of acute kidney injury, XLKO and WT mice exhibited similar degrees of tubulopathy; however, plasma phosphate and FGF23 elevations were modestly blunted in XLKO males, but not in females, compared to WT counterparts. Our findings suggest that XLαs ablation does not substantially alter FGF23 production in adult mice but increases susceptibility to adenine-induced kidney injury, causing severe FGF23 elevations in plasma and bone.

Mechanism of Action and Clinical Attributes of Auryxia® (Ferric Citrate)

Chronic kidney disease (CKD) is a major cause of morbidity and premature mortality and represents a significant global public health issue. Underlying this burden are the many complications of CKD, including mineral and bone disorders, anemia, and accelerated cardiovascular disease. Hyperphosphatemia and elevated levels of fibroblast growth factor 23 (FGF23) have been identified as key independent risk factors for the adverse cardiovascular outcomes that frequently occur in patients with CKD. Auryxia^® (ferric citrate; Keryx Biopharmaceuticals, Inc., Boston, MA, USA) is an iron-based compound with distinctive chemical characteristics and a mechanism of action that render it dually effective as a therapy in patients with CKD; it has been approved as a phosphate binder for the control of serum phosphate levels in adult CKD patients treated with dialysis and as an iron replacement product for the treatment of iron deficiency anemia in adult CKD patients not treated with dialysis. This review focuses on Auryxia, its mechanism of action, and the clinical attributes that differentiate it from other, non-pharmaceutical-grade, commercially available forms of ferric citrate and from other commonly used phosphate binder and iron supplement therapies for patients with CKD. Consistent with the chemistry and mechanism of action of Auryxia, multiple clinical studies have demonstrated its efficacy in both lowering serum phosphate levels and improving iron parameters in patients with CKD. Levels of FGF23 decrease significantly with Auryxia treatment, but the effects associated with the cardiovascular system remain to be evaluated in longer-term studies.

Iron Infusion and Induced Hypophosphatemia: The Role of Fibroblast Growth Factor-23

The mechanism of action of fibroblast growth factor-23 (FGF23) is becoming increasingly clearer as a result of studies that have defined its structure and pleiotropic effects. Furthermore, data are emerging on the effects exerted on this hormone by iron administration. Ten main iron formulations are recognized (with clear differences in composition and possible reactions of intolerance and anaphylaxis), which are indicated for iron deficiency anemia, including nephropathic subjects, as suggested by medical guidelines. With some types of iron formulation (especially iron carboxymaltose) a particular side effect has been observed: hypophosphatemia, mediated by FGF23. This review aims to draw attention to this correlation and the contradiction represented by the presence of both positive and negative modulation by FGF23, with the effects induced by its increase even after long-term treatment with iron formulation. However, more evidence is needed to understand the reasons for this differential stimulation.