The Effects of Cholecalciferol Supplementation on FGF23 and α-Klotho in Hemodialysis Patients With Hypovitaminosis D: A Randomized, Double-Blind, Placebo-Controlled Trial

The Role of Daily Dialysate Calcium Exposure in Phosphaturic Hormones in Dialysis Patients

Managing mineral bone disease (MBD) could reduce cardiovascular risk and improve the survival of dialysis patients. Our study focuses on the impact of calcium bath exposure in dialysis patients by comparing peritoneal dialysis patients (PD, intervention group) and hemodialysis patients (HD, control group). We assessed various factors, including calcium, phosphorus, magnesium, PTH, vitamin D 25-OH, C-terminal telopeptide (CTX), and FGF-23 levels, as well as the calcium bath six hours before the blood sample and the length of daily calcium exposure. We enrolled 40 PD and 31 HD patients with a mean age of 68.7 ± 13.6 years. Our cohort had median PTH and FGF-23 levels of 194 ng/L (Interquartile range [IQR] 130-316) and 1296 pg/mL (IQR 396-2698), respectively. We identified the length of exposure to a 1.25 mmol/L calcium bath, phosphate levels, and CTX as independent predictors of PTH (OR 0.279, p = 0.011; OR 0.277, p = 0.012; OR 0.11, p = 0.01, respectively). In contrast, independent predictors of FGF-23 were phosphate levels (OR 0.48, p < 0.001) and serum calcium levels (OR 0.25, p = 0.015), which were affected by the calcium bath. These findings suggest that managing dialysate calcium baths impacts phosphaturic hormones and could be a critical factor in optimizing CKD-MBD treatment in PD patients, sparking a new avenue of research and potential interventions.

Interactions between FGF23 and vitamin D

Fibroblast growth factor-23 (FGF23) controls the homeostasis of both phosphate and vitamin D. Bone-derived FGF23 can suppress the transcription of 1α-hydroxylase (1α(OH)ase) to reduce renal activation of vitamin D (1,25(OH)2D3). FGF23 can also activate the transcription of 24-hydroxylase to enhance the renal degradation process of vitamin D. There is a counter-regulation for FGF23 and vitamin D; 1,25(OH)2D3 induces the skeletal synthesis and the release of FGF23, while FGF23 can suppress the production of 1,25(OH)2D3 by inhibiting 1α(OH)ase synthesis. Genetically ablating FGF23 activities in mice resulted in higher levels of renal 1α(OH)ase, which is also reflected in an increased level of serum 1,25(OH)2D3, while genetically ablating 1α(OH)ase activities in mice reduced the serum levels of FGF23. Similar feedback control of FGF23 and vitamin D is also detected in various human diseases. Further studies are required to understand the subcellular molecular regulation of FGF23 and vitamin D in health and disease.