Segregating the effects of ferric citrate‐mediated iron utilization and FGF23 in a mouse model of CKD

• Published in: Physiological reports Vol. 10; no. 11; pp. e15307 - n/a
• Main Authors: Liesen, Michael P., Noonan, Megan L., Ni, Pu, Agoro, Rafiou, Hum, Julia M., Clinkenbeard, Erica L., Damrath, John G., Wallace, Joseph M., Swallow, Elizabeth A., Allen, Matthew R., White, Kenneth E.
• Format: Journal Article
• Language: English
• Published: United States John Wiley & Sons, Inc 01.06.2022; John Wiley and Sons Inc; Wiley
• Subjects: Anemia; Animals; Bone morphogenetic protein 6; Citric Acid; CKD; Clinical outcomes; Cortical bone; Dialysis; Diet; Disease; Disease Models, Animal; Electrolytes; Ferric citrate; Ferric Compounds; Fibroblast Growth Factor-23; Fibroblast Growth Factors - metabolism; Gene expression; Genotype & phenotype; Genotypes; GF23; Hemodialysis; Hepcidin; Humans; Interleukin 6; Iron; Iron - metabolism; Iron deficiency; kidney; Kidney diseases; klotho; Liver; Metabolism; Mice; Minerals; mRNA; Nutrient deficiency; Original; Patients; Physiology; Porosity; Raman spectroscopy; Renal Insufficiency, Chronic - metabolism; Rickets; RNA, Messenger - metabolism; Vitamin D; GF23; kidney; klotho; iron; ferric citrate; CKD
• DOI: 10.14814/phy2.15307

Ferric citrate (FC) is an approved therapy for chronic kidney disease (CKD) patients as a phosphate (Pi) binder for dialysis‐dependent CKD, and for iron deficiency anemia (IDA) in non‐dialysis CKD. Elevated Pi and IDA both lead to increased FGF23, however, the roles of iron and FGF23 during CKD remain unclear. To this end, iron and Pi metabolism were tested in a mouse model of CKD (0.2% adenine) ± 0.5% FC for 6 weeks, with and without osteocyte deletion of Fgf23 (flox‐Fgf23/Dmp1‐Cre). Intact FGF23 (iFGF23) increased in all CKD mice but was lower in Cre+ mice with or without FC, thus the Dmp1‐Cre effectively reduced FGF23. Cre+ mice fed AD‐only had higher serum Pi than Cre− pre‐ and post‐diet, and the Cre+ mice had higher BUN regardless of FC treatment. Total serum iron was higher in all mice receiving FC, and liver Tfrc, Bmp6, and hepcidin mRNAs were increased regardless of genotype; liver IL‐6 showed decreased mRNA in FC‐fed mice. The renal 1,25‐dihydroxyvitamin D (1,25D) anabolic enzyme Cyp27b1 had higher mRNA and the catabolic Cyp24a1 showed lower mRNA in FC‐fed mice. Finally, mice with loss of FGF23 had higher bone cortical porosity, whereas Raman spectroscopy showed no changes in matrix mineral parameters. Thus, FC‐ and FGF23‐dependent and ‐independent actions were identified in CKD; loss of FGF23 was associated with higher serum Pi and BUN, demonstrating that FGF23 was protective of mineral metabolism. In contrast, FC maintained serum iron and corrected inflammation mediators, potentially providing ancillary benefit. Chronic kidney disease (CKD) affects 10% of the world population and results in many patient complications, including iron deficiency and hyperphosphatemia, both potent stimulators of the phosphaturic hormone FGF23. An iron‐containing phosphate binder, ferric citrate (FC), was developed to alleviate these manifestations, however, the impact of FC on FGF23‐ and iron‐mediated effects in CKD are not completely understood. This study provides novel insight into the FGF23‐ and iron‐mediated effects in CKD. We demonstrate that FGF23 is necessary to control phosphate and disease progression (monitored by BUN) in CKD. This study also supports that FC may improve 1,25D metabolism independent of FGF23 and lower markers of inflammation due to iron repletion. Therefore, FC may provide ancillary benefits which could lead to improved CKD patient outcomes.