FGF23 and the PTH response to paricalcitol in chronic kidney disease

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.

Paricalcitol and Extended-Release Calcifediol for Treatment of Secondary Hyperparathyroidism in Non-Dialysis Chronic Kidney Disease: Results From a Network Meta-Analysis

CONTEXT

Secondary hyperparathyroidism (SHPT) is a complication of chronic kidney disease (CKD) affecting mineral and bone metabolism and characterized by excessive parathyroid hormone (PTH) production and parathyroid hyperplasia.

OBJECTIVE

The objective of this analysis was to compare the efficacy and adverse effects of extended-release calcifediol (ERC) and paricalcitol (PCT) by assessing their effect on the biomarkers PTH, calcium, and phosphate in patients with non-dialysis CKD (ND-CKD).

METHODS

A systematic literature research was performed in PubMed to identify randomized control trials (RCTs). Quality assessment was done with the GRADE method. The effects of ERC vs PCT were compared using random effects in a frequentist setting.

RESULTS

Nine RCTs comprising 1426 patients were included in the analyses. The analyses were performed on 2 overlapping networks, due to nonreporting of outcomes in some of the included studies. No head-to-head trials were identified. No statistically significant differences in PTH reduction were found between PCT and ERC. Treatment with PCT showed statistically significant increases in calcium compared with ERC (0.2 mg/dL increase; 95% CI, -0.37 to -0.05 mg/dL). No differences in effects on phosphate were observed.

CONCLUSION

This network meta-analysis showed that ERC is comparable in lowering PTH levels vs PCT. ERC displayed avoidance of potentially clinically relevant increases in serum calcium, offering an effective and well-tolerated treatment option for the management of SHPT in patients with ND-CKD.

Elevated Fibroblast Growth Factor 23 Impairs Endothelial Function through the NF-κB Signaling Pathway

AIM

Roles of fibroblast growth factor 23 (FGF23) in endothelial dysfunction remain controversial, and evidence from population-based studies is lacking. The present study aimed to explore the effects of FGF23 on endothelial dysfunction on the basis of both clinical data of patients with coronary artery disease (CAD) and the in vitro research in human umbilical vein endothelial cells (HUVECs).

METHODS

A total of 321 CAD patients were enrolled after coronary angiography, brachial artery flow-mediated dilation (FMD) was assessed using ultrasound equipment. Serum FGF23, nitric oxide (NO), and endothelin-1 (ET-1) were detected via enzyme-linked immunosorbent assay. Apoptosis was determined using the annexin V-fluorescein isothiocyanate/propidium lodide apoptosis detection kit. Cell migration was evaluated by wound healing and transwell migration assays. Reactive oxide species levels were determined using fluorescent probes, and NF-κB p65 nuclear translocation was assessed via immunofluorescence.

RESULTS

Serum FGF23 was significantly increased in CAD patients combined with severe endothelial dysfunction (FMD ＜2%) compared to those with FMD ≥ 2% (P＜0.001). Furthermore, the levels of FGF23 were negatively correlated with NO, whereas positively correlated with ET-1 both in unadjusted analysis and multivariate-adjusted analysis. In HUVECs, FGF23 interfered with the bioavailability of NO via increased oxidative stress. Moreover, FGF23 directly impaired the endothelium by promoting HUVECs apoptosis and attenuating the migration of HUVECs. Additional experiments showed that FGF23 induced endothelial injury through activation of the NF-κB signaling pathway.

CONCLUSIONS

Elevated FGF23 is clinically associated with endothelial dysfunction in CAD patients, and FGF23 impairs endothelial function through activation of the NF-κB signaling pathway.

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

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

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.

Serum Fibroblast Growth Factor 23 Level and Liver Fat Content in MAFLD: A Community-Based Cohort

PURPOSE

Although fibroblast growth factor-23 (FGF23) is involved in the development of metabolic diseases, its association with metabolic-associated fatty liver disease (MAFLD) remains unknown. We explored the relationship between serum fibroblast growth factor-23 level, metabolic associated fatty liver disease, and liver fat content.

PATIENTS AND METHODS

Participants were enrolled from communities in Shanghai. Serum fibroblast growth factor-23 level was determined using two-side sandwich enzyme-linked immunosorbent assays. MAFLD was diagnosed using the international expert consensus (2020) criteria. Liver fat content was assessed using ultrasound.

RESULTS

We enrolled 1827 individuals aged 30-80 years (mean age, 59.4±7.3 years). MAFLD was diagnosed in 445/1393 (31.9%) non-diabetic participants and 245/434 (56.5%) diabetic participants. After adjusting for confounders, one standard deviation increase in serum FGF23 was associated with MAFLD in diabetic (odds ratio, 1.27; 95% confidence interval, 1.15-1.49; P<0.001) and non-diabetic (odds ratio, 1.28; 95% confidence interval, 1.07-1.74; P=0.030) groups. In a fully adjusted linear regression model, serum FGF23 emerged as a positive determinant of liver fat content in both diabetic and non-diabetic groups (P=0.039; P=0.034).

CONCLUSION

Participants with MAFLD had higher serum fibroblast growth factor-23 level than those without MAFLD, regardless of diabetes status. Serum fibroblast growth factor-23 was independently related to MAFLD and liver fat content.

Protective Role of Vitamin D in Renal Tubulopathies

Vitamin D is tightly linked with renal tubular homeostasis: the mitochondria of proximal convoluted tubule cells are the production site of 1α,25-dihydroxyvitamin D3. Patients with renal impairment or tubular injury often suffer from chronic inflammation. This alteration comes from oxidative stress, acidosis, decreased clearance of inflammatory cytokines and stimulation of inflammatory factors. The challenge is to find the right formula for each patient to correctly modulate the landscape of treatment and preserve the essential functions of the organism without perturbating its homeostasis. The complexity of the counter-regulation mechanisms and the different axis involved in the Vitamin D equilibrium pose a major issue on Vitamin D as a potential effective anti-inflammatory drug. The therapeutic use of this compound should be able to inhibit the development of inflammation without interfering with normal homeostasis. Megalin-Cubilin-Amnionless and the FGF23-Klotho axis represent two Vitamin D-linked mechanisms that could modulate and ameliorate the damage response at the renal tubular level, balancing Vitamin D therapy with an effect potent enough to contrast the inflammatory cascades, but which avoids potential severe side effects.