title: Regulatory mechanisms of circulating fibroblast growth factor 23 in parathyroid diseases.
abstract: Fibroblast growth factor-23 (FGF-23) is a circulating factor regulating phosphate and vitamin D homeostasis. Phosphate intake and an administration of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) increase circulating FGF-23 levels, and elevated FGF-23 prevents hyperphosphatemia and vitamin D toxicity by hyperphosphaturia and suppression of circulating 1,25(OH)(2)D level, comprising a feedback loop to maintain phosphate and vitamin D homeostasis. Excess secretion of parathyroid hormone (PTH), another phosphaturic factor, elevates the serum calcium level in primary hyperparathyroidism. PTH also elevates circulating FGF-23 level, which cooperatively enhances the phosphaturia, resulting in hypophosphatemia. The circulating FGF-23 level increases as renal function declines in chronic kidney disease (CKD), and it exhibits significant and positive correlations with serum phosphate, calcium, and PTH in CKD patients on maintenance hemodialysis, suggesting that these parameters regulate circulating FGF-23 level. Tight associations between circulating FGF-23 and calcium levels were observed both in patients with primary hyperparathyroidism and in CKD patients on maintenance hemodialysis, suggesting the role of serum calcium on FGF-23 regulatory mechanisms. FGF-23 may have a physiological role in preventing tissue damage such as ectopic calcifications, partly via suppressing the serum calcium x phosphate product by accelerating urinary phosphate excretion and suppressing vitamin D activation.
authors.affiliation: Department of Metabolism, Endocrinology and Molecular Medicine, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka, Japan. imanishi@med.osaka-cu.ac.jp
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Imanishi
authors.forename: Keisuke
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Takehisa
authors.initials: T
authors.lastname: Kawata
authors.forename: Masaaki
authors.initials: M
authors.lastname: Inaba
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Nishizawa
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D017674:Hypophosphatemia / Q000503:physiopathology; D010279:Parathyroid Diseases / Q000503:physiopathology*; D010281:Parathyroid Hormone / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism / Q000494:pharmacology
chemical_list: C000717427:FGF23 protein, human; D010281:Parathyroid Hormone; D010710:Phosphates; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D002117:Calcitriol; D002118:Calcium