Impaired Response of FGF-23 to Oral Phosphate in Patients with Type 2 Diabetes: A Possible Mechanism of Atherosclerosis

Background: Fibroblast growth factor (FGF)-23, secreted from osteocytes/osteoblasts, plays major roles in phosphate (Pi)-mediated stimulation of PTH secretion and consequently in regulation of serum Pi. Osteocyte/osteoblast dysfunction develops in patients with type 2 diabetes mellitus (DM). Objective: Our objective was to examine whether increases in serum FGF-23 and PTH after oral Pi stimulation are impaired in type 2 DM. Design and Methods: The subjects were 10 DM and 10 non-DM patients without chronic kidney disease stage 3–5. Serum FGF-23, intact PTH (iPTH), and Pi were measured serially after oral Pi administration at a daily dose of 2.0 g. Results: Pi administration caused significant increases of FGF-23 by 2 h and iPTH by 4 h in non-DM patients. These increases were attenuated in DM patients. After 2 d of Pi stimulation, serum FGF-23 and iPTH remained elevated in non-DM patients but not in DM. In all subjects, initial changes of serum FGF-23 (0–2 h) and iPTH (0–4 h) were positively correlated (r = 0.528) and showed significant negative correlations with later changes in serum Pi (2–4 h) (r = −0.457 and r = −0.673, respectively). Serum Pi (2–4 h) significantly increased in DM patients, consistent with the lack of change in serum FGF-23 and iPTH, whereas serum Pi did not change significantly in non-DM patients. Conclusion: These results show that increases of serum FGF-23 and PTH in response to Pi stimulation are impaired in type 2 DM and that serum Pi is significantly increased thereafter. This may be a mechanism underlying advanced atherosclerosis in type 2 DM.