[Fibroblast growth factor-23 (FGF-23). Part I. Significance in phosphate homeostasis and bone metabolism].

Fibroblast growth factor-23 (FGF-23) discovered in the last years, produced by osteocytes and osteoblast is hormone that lowers plasma phosphate level due to inhibition of renal tubule phosphate reabsorption (phosphaturic effect). It diminishes gut absorption of phosphate as a result of lowered kidney 1alpha-hydroxylase activity and respective decreased active vitamin D1,25(OH)2D synthesis. FGF-23 acts in the presence of the co-receptor Klotho protein which stabilizes its binding with receptor. The pathological states that are associated with increased FGF-23 synthesis in normal renal function lead to hypophosphatemia, while its deficiency may lead to severe hyperphosphatemia. The increased FGF-23 synthesis in patients with chronic kidney disease (CKD) allow to maintain phosphate concentration in spite of severe kidney dysfunction. This problem will be discussed in the II-nd part of this review.