Selection of a novel FGF23-binding peptide antagonizing the inhibitory effect of FGF23 on phosphate uptake

Association of serum soluble α‑klotho with risk of kidney stone disease: a population-based cross-sectional study

BACKGROUND

The aim of the study was to explore the association of serum soluble klotho with kidney stone disease (KSD) in the general population over the age of 40 years in the United States.

METHODS

We integrated the data in National Health and Nutrition Examination Survey from 2007 to 2016 years. The relationship between serum soluble α‑klotho and prevalence of KSD was analyzed by constructing weighted multivariable logistic regression model, restricted cubic spline (RCS) curve, and subgroup analyses.

RESULTS

In the study, a total of 13,722 individuals were included in our study. A U-shaped association between serum soluble klotho and the risk of KSD was shown by the RCS curve (P value for nonlinear < 0.05). In the full adjusted model, compared with the lowest quartile of serum soluble α‑klotho, the adjusted odd ratios (95% confidence intervals) for KSD across the quartiles were (0.999 (0.859, 1.164), 1.005 (0.858, 1.176), and 1.061 (0.911, 1.235)). Subgroup analyses also showed that the U-shaped association of serum soluble α‑klotho with KSD was found among subjects who were age < 60 years, female or male, with or without hypertension, and BMI ≥ 30 kg/m2.

CONCLUSIONS

Our findings suggested that serum klotho levels had a U-shaped correlation with risk of KSD. When the Klotho level is at 818.66 pg/mL, prevalence of KSD is lowest. Therefore, maintaining a certain level of serum soluble α‑klotho could prevent the occurrence of KSD.

Fibroblast growth factor 23: a biomarker of fibrosis and prognosis in heart failure with preserved ejection fraction

AIMS

Besides regulating calcium-phosphate metabolism, fibroblast growth factor 23 (FGF-23) has been associated with incident heart failure (HF) and left ventricular hypertrophy. However, data about FGF-23 in HF and preserved ejection fraction (HFpEF) remain limited. The aim of this study was to assess the association between FGF-23 levels, clinical and imaging characteristics, particularly diffuse myocardial fibrosis, and prognosis in HFpEF patients.

METHODS AND RESULTS

We prospectively included 143 consecutive HFpEF patients (78 ± 8 years, 61% female patients) and 31 controls of similar age and gender (75 ± 6 years, 61% female patients). All subjects underwent a complete two-dimensional echocardiography and cardiac magnetic resonance with extracellular volume (ECV) assessment by T1 mapping. FGF-23 was measured at baseline. Among the patients, differences in clinical and imaging characteristics across tertiles of FGF-23 levels were analysed with a trend test across the ordered groups. Patients were followed over time for a primary endpoint of all-cause mortality and first HF hospitalization and a secondary endpoint of all-cause mortality. Median FGF-23 was significantly higher in HFpEF patients compared with controls of similar age and gender (247 [115; 548] RU/mL vs. 61 [51; 68] RU/mL, P < 0.001). Among HFpEF patients, higher FGF-23 levels were associated with female sex, higher incidence of atrial fibrillation, lower haemoglobin, worse renal function, and higher N terminal pro brain natriuretic peptide levels (P for trend < 0.05 for all). Regarding imaging characteristics, patients with higher FGF-23 levels had greater left atrial volumes, worse right ventricular systolic function, and more fibrosis estimated by ECV (P for trend < 0.05 for all). FGF-23 was moderately correlated with ECV (r = 0.46, P < 0.001). Over a mean follow-up of 30 ± 8 months, 43 patients (31%) died and 69 patients (49%) were hospitalized for HF. A total of 87 patients (62%) reached the primary composite endpoint of all-cause mortality and/or first HF hospitalization. In multivariate Cox regression analysis for the primary endpoint, FGF-23 (HR: 3.44 [2.01; 5.90], P < 0.001) and E wave velocities (HR: 1.01 [1.00; 1.02], P = 0.034) were independent predictors of the primary composite endpoint. In multivariate Cox regression analysis for the secondary endpoint, ferritin (HR: 1.02 [1.01; 1.03], P < 0.001), FGF-23 (HR: 2.85 [1.26; 6.44], P = 0.012), and ECV (HR: 1.26 [1.03; 1.23], P = 0.008) were independent predictors of all-cause mortality.

CONCLUSIONS

Fibroblast growth factor 23 (FGF-23) levels were significantly higher in HFpEF patients compared with controls of similar age and gender. FGF-23 was correlated with fibrosis evaluated by ECV. High levels of FGF-23 were significantly associated with signs of disease severity such as worse renal function, larger left atrial volumes, and right ventricular dysfunction. Moreover, FGF-23 was a strong predictor of poor outcome (mortality and first HF hospitalization).

FGF23: Clinical usefulness and analytical evolution

Fibroblast Growth Factor 23 (FGF23) is a key hormone for the regulation of phosphate homeostasis. Over the past decades, FGF23 was the subject of intense research in the fields of nephrology and the cardiology. It presents a remarkable correlation with well-established biomarkers of cardiovascular disorders in both chronic kidney disease (CKD) and heart failure (HF) patients. The interest of FGF23 lies in its early-onset in the primary course of CKD as well as in the incremental prognosis information it conveys in both CKD and HF. Different types of assays of FGF-23 testing exist, those targeting the intact form (iFGF23), the other one detecting terminal fragments (cFGF23). The issue is still pending which assay suits best for clinical use. Recently, the implementation of this biomarker on multianalyzer platforms, on which other markers of phospho-calcic balance are set up, allows a rapid turn-around-time and a potential financial gain. However, despite the good analytical performances of the automated methods, there is a poor harmonization between assays. The introduction of an international certified reference material should standardize the measurement and improve the harmonization of results from different laboratories. A deeper understanding of physio-pathological mechanisms and processing of FGF-23 should reinforce its clinical indications and might also identify new therapeutic targets for the treatment of CKD and HF.

Effects of phospho- and calciotropic hormones on electrolyte transport in the proximal tubule

Calcium and phosphate are critical for a myriad of physiological and cellular processes within the organism. Consequently, plasma levels of calcium and phosphate are tightly regulated. This occurs through the combined effects of the phospho- and calciotropic hormones, parathyroid hormone (PTH), active vitamin D ₃, and fibroblast growth factor 23 (FGF23). The organs central to this are the kidneys, intestine, and bone. In the kidney, the proximal tubule reabsorbs the majority of filtered calcium and phosphate, which amounts to more than 60% and 90%, respectively. The basic molecular mechanisms responsible for phosphate reclamation are well described, and emerging work is delineating the molecular identity of the paracellular shunt wherein calcium permeates the proximal tubular epithelium. Significant experimental work has delineated the molecular effects of PTH and FGF23 on these processes as well as their regulation of active vitamin D ₃ synthesis in this nephron segment. The integrative effects of both phospho- and calciotropic hormones on proximal tubular solute transport and subsequently whole body calcium-phosphate balance thus have been further complicated. Here, we first review the molecular mechanisms of calcium and phosphate reabsorption from the proximal tubule and how they are influenced by the phospho- and calciotropic hormones acting on this segment and then consider the implications on both renal calcium and phosphate handling as well as whole body mineral balance.

FGF23 regulation of renal tubular solute transport

PURPOSE OF REVIEW

Fibroblast growth factor-23 (FGF23) is a bone-derived hormone known to suppress phosphate reabsorption in the kidney. The purpose of this review was to highlight the recent advances in the area of FGF23-regulated solute transport in the kidney.

RECENT FINDINGS

Recent evidence suggests that FGF23 suppresses phosphate reabsorption in renal proximal tubular epithelium by a Klotho-dependent, FGF receptor (FGFR)-1 and FGFR4-mediated signaling mechanism that may also involve Janus kinase 3. Moreover, it was recently established that FGF23 signaling in the distal renal tubule targets with-no-lysine kinase-4 (WNK4), a key molecule in the regulation of solute transport in the distal nephron. By targeting WNK4, FGF23 has been shown to increase the membrane abundance of the epithelial calcium channel TRPV5 and of the sodium-chloride cotransporter NCC, resulting in augmented renal calcium and sodium reabsorption.

SUMMARY

Significant progress has been made in the further characterization of the signaling pathways involved in the FGF23-induced inhibition of phosphate transport in proximal tubular epithelium, and major new functions of FGF23 in solute transport have been discovered in distal renal tubules. The calcium- and sodium-conserving functions of FGF23 may have major implications for the pathophysiology of cardiovascular diseases. VIDEO ABSTRACT.