Short-Term Effects of Cholecalciferol Supplementation on cFGF23 Levels in Children with Chronic Kidney Disease and Vitamin D Insufficiency

Emerging concepts on the FGF23 regulation and activity

Fibroblast growth factor 23 (FGF23) discovery has provided new insights into the regulation of Pi and Ca homeostasis. It is secreted by osteoblasts and osteocytes, and acts mainly in the kidney, parathyroid, heart, and bone. The aim of this review is to highlight the current knowledge on the factors modulating the synthesis of FGF23, the canonical and non-canonical signaling pathways of the hormone, the role of FGF23 in different pathophysiological conditions, and the anti-FGF23 therapy. This is a narrative review based on the search of PubMed database in the range of years 2000-2023 using the keywords local and systemic regulators of FGF23 synthesis, FGF23 receptors, canonical and non-canonical pathways, pathophysiological conditions and FGF23, and anti-FGF23 therapy, focusing the data on the molecular mechanisms. The regulation of FGF23 synthesis is complex and multifactorial. It is regulated by local factors and systemic regulators mainly involved in bone mineralization. The excessive FGF23 production is associated with different congenital diseases and with diseases occurring with a secondary high FGF23 production such as in chronic disease kidney and tumor-induced osteomalacia (TIO). The anti-FGF23 therapy appears to be useful to treat chromosome X-linked hypophosphatemia and TIO, but there are doubts about the handle of excessive FGF23 production in CKD. FGF23 biochemistry and pathophysiology are generating a plethora of knowledge to reduce FGF23 bioactivity at many levels that might be useful for future therapeutics of diseases associated with high-serum FGF23 levels.

Mineral Metabolism in Children: Interrelation between Vitamin D and FGF23

Fibroblast growth factor 23 (FGF23) was identified at the turn of the century as the long-sought circulating phosphatonin in human pathology. Since then, several clinical and experimental studies have investigated the metabolism of FGF23 and revealed its relevant pathogenic role in various diseases. Most of these studies have been performed in adult individuals. However, the mineral metabolism of the child is, to a large extent, different from that of the adult because, in addition to bone remodeling, the child undergoes a specific process of endochondral ossification responsible for adequate mineralization of long bones’ metaphysis and growth in height. Vitamin D metabolism is known to be deeply involved in these processes. FGF23 might have an influence on bones’ growth as well as on the high and age-dependent serum phosphate concentrations found in infancy and childhood. However, the interaction between FGF23 and vitamin D in children is largely unknown. Thus, this review focuses on the following aspects of FGF23 metabolism in the pediatric age: circulating concentrations’ reference values, as well as those of other major variables involved in mineral homeostasis, and the relationship with vitamin D metabolism in the neonatal period, in vitamin D deficiency, in chronic kidney disease (CKD) and in hypophosphatemic disorders.