Bone Abstracts

Objectives: Fibroblast growth factor 23 (FGF23) is a bone-derived phosphaturic hormone. The main target organ is the kidney, where FGF23 suppresses renal phosphate reabsorption and vitamin D synthesis. It also stimulates calcium reabsorption in the kidney. FGF23 secretion is stimulated by 1,25(OH)2D and by increased extracellular phosphate concentration, thus forming a feedback loop between kidney and bone. The bioactive intact FGF23 contains 251 amino acids and is glycosylated and phosphorylated. Its activity is mediated by binding to FGFR/Klotho receptor complex at the target cell surface. FGF23 is cleaved between Arg179 and Ser180 to an inactive N- and C-terminal fragment. Increased serum concentrations of intact FGF23 are a hallmark of renal phosphate-wasting diseases such as ADHR, X-linked hypophosphatemia (XLH), tumor-induced osteomalacia, or autosomal recessive hypophosphatemic rickets.

Material: Here, we show the development, characterization and validation of a new ELISA for the determination of intact FGF23. The epitopes of the two monoclonal antibodies utilized in this assay were analyzed by overlapping linear peptides spotted to a microarray. The binding kinetics of the antibodies were determined with biolayer interferometry. The assay was validated according to standard quality guidelines regarding its specificity, precision, robustness, accuracy, and linearity. Assay performance as well as sample measurements of apparently healthy and diseased human subject were compared with other commercially available assays.

Results: The structural epitope of the coating antibody is within the N-terminal part of FGF23, whereas the labelled detection antibody detects a linear epitope at the C-terminal fragment. Both antibodies bind with high affinity to intact FGF23. The immunoassay generates highly specific signals for human intact FGF23 (>90%). Accuracy, parallelism, as well as intra- and inter-assay precision are within the standard of acceptance with 80–120% and <10% CV, respectively. The intact FGF23 ELISA correlates well with other existing commercial assays (R²>0.95), but shows a broader overall calibration range, a shorter sample incubation and can be used for the detection of FGF23 in human serum and plasma.

Conclusion: This well-characterized ELISA reliably detects intact FGF23 in human serum and plasma samples and may support further high-quality FGF23 research.

Disclosure: Association with Biomedica GmbH.