title: Effects of iron deficiency anemia and its treatment on fibroblast growth factor 23 and phosphate homeostasis in women.
abstract: Fibroblast growth factor 23 (FGF23) is an osteocyte-derived hormone that regulates phosphate and vitamin D homeostasis. Through unknown mechanisms, certain intravenous iron preparations induce acute, reversible increases in circulating FGF23 levels that lower serum phosphate in association with inappropriately low levels of calcitriol, similar to genetic diseases of primary FGF23 excess. In contrast, studies in wild-type mice suggest that iron deficiency stimulates fgf23 transcription but does not result in hypophosphatemia because FGF23 is cleaved within osteocytes by an unknown catabolic system. We tested the association of iron deficiency anemia with C-terminal FGF23 (cFGF23) and intact FGF23 (iFGF23) levels in 55 women with a history of heavy uterine bleeding, and assessed the longitudinal biochemical response over 35 days to equivalent doses of randomly-assigned, intravenous elemental iron in the form of ferric carboxymaltose (FCM) or iron dextran. Iron deficiency was associated with markedly elevated cFGF23 (807.8 ± 123.9 relative units [RU]/mL) but normal iFGF23 (28.5 ± 1.1 pg/mL) levels at baseline. Within 24 hours of iron administration, cFGF23 levels fell by approximately 80% in both groups. In contrast, iFGF23 transiently increased in the FCM group alone, and was followed by a transient, asymptomatic reduction in serum phosphate <2.0 mg/dL in 10 women in the FCM group compared to none in the iron dextran group. Reduced serum phosphate was accompanied by increased urinary fractional excretion of phosphate, decreased calcitriol levels, and increased parathyroid hormone levels. These findings suggest that iron deficiency increases cFGF23 levels, and that certain iron preparations temporarily increase iFGF23 levels. We propose that intravenous iron lowers cFGF23 in humans by reducing fgf23 transcription as it does in mice, whereas carbohydrate moieties in certain iron preparations may simultaneously inhibit FGF23 degradation in osteocytes leading to transient increases in iFGF23 and reduced serum phosphate.
authors.affiliation: Division of Nephrology and Hypertension, University of Miami Miller School of Medicine, Miami, FL 33136, USA. mwolf2@med.miami.edu
authors.forename: Myles
authors.initials: M
authors.lastname: Wolf
authors.forename: Todd A
authors.initials: TA
authors.lastname: Koch
authors.forename: David B
authors.initials: DB
authors.lastname: Bregman
mesh_terms: D000328:Adult; D018798:Anemia, Iron-Deficiency / Q000097:blood* / Q000188:drug therapy* / Q000503:physiopathology / Q000652:urine; D000818:Animals; D002118:Calcium / Q000097:blood; D003710:Demography; D004920:Erythropoiesis / Q000187:drug effects; D005260:Female; D005290:Ferric Compounds / Q000009:adverse effects / Q000494:pharmacology / Q000627:therapeutic use; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D007501:Iron / Q000378:metabolism; D007505:Iron-Dextran Complex / Q000009:adverse effects / Q000494:pharmacology / Q000627:therapeutic use; D008320:Maltose / Q000009:adverse effects / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D051379:Mice; D008954:Models, Biological; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood* / Q000652:urine; D014807:Vitamin D / Q000097:blood
chemical_list: C000717427:FGF23 protein, human; D005290:Ferric Compounds; C000717428:Fgf23 protein, mouse; D010281:Parathyroid Hormone; D010710:Phosphates; D014807:Vitamin D; D005346:Fibroblast Growth Factors; C522335:ferric carboxymaltose; D008320:Maltose; D000089703:Fibroblast Growth Factor-23; D007505:Iron-Dextran Complex; D007501:Iron; D002118:Calcium
keywords: FGF23; IRON; PHOSPHATE; PTH; VITAMIN D