Neutralization of Fibroblast Growth Factor-23 Alters Phosphate Requirement of Growing Chicks

Fibroblast growth factor 23 (FGF-23), a bone-derived hormone secreted by osteocytes/ osteoblasts, maintains blood phosphate homeostasis by inhibiting renal resorption of excreted phosphate. FGF-23 also indirectly inhibits intestinal phosphate absorption by reducing 1α-hydroxylase activity (hence reducing active 1,25(OH)₂D₃).  A study was conducted to determine if neutralization of FGF-23, using antibody, altered dietary phosphate requirements using a chick model. Laying hens were immunized with two peptide epitopes of FGF-23 to induce passive anti-peptide antibody transferred to the fertile eggs.  Chicks with passively transferred maternal antibody were hatched from hens immunized with the adjuvant control or anti-FGF-23 peptides. Chicks from the control and FGF-23 peptide-vaccinated hens were fed either a phosphate adequate or deficient diet for two weeks. Weekly chick weight and terminal blood samples (for plasma phosphate) were collected. Chicks with passive anti-FGF-23 (one of peptides studied) had a 23% increase in blood phosphate and a 11% increase in body weight gain when fed the low phosphate diet and compared to chicks with passive control antibody fed the low phosphate diet. Blood phosphate was not different due to passive antibody when chicks were fed the adequate phosphate diet. These data suggest that FGF-23 neutralization may decrease the phosphate requirements of a young growing animal. These results may also suggest that polymorphism of FGF-23 could alter the susceptibility of an animal to changes in dietary phosphate rendering them more susceptible to hyperphosphatemia.