The serum level of the morphogenetic protein fibroblast growth factor 23 (FGF-23) as a marker for the efficiency of hyperphosphatemia therapy with phosphate-binding agents in chronic kidney disease

Abstract

To study whether the excessive production of serum fibroblast growth factor 23 (FGF-23) may be reduced with phosphate-binding agents to treat hyperphosphatemia in patients with Stage VD chronic kidney disease (CKD). The investigation enrolled 25 patients with Stage VD CKD on regular hemodialysis (HD) (12 patients with chronic glomerulonephritis, 8 with tubulointerstitial nephritis, and 5 with hypertensive nephrosclerosis); among them there were 15 men and 10 women at the age of 21 to 65 years; their mean age at inclusion in the study was 43±4.5 years. The clinical, laboratory, and instrumental examination similar to that in patients with the early stages of CKD was done. Serum FGF-23 levels (Human FGF-23 ELISA kit using monoclonal antibodies to the full FGF-23 molecule) were investigated in all the 25 patients. A whole blood sample was taken 2 days after the last session of HD before initiation of its regular procedure. The elevated serum FGF-23 concentrations in the patients on regular HD correlated with their HD duration (r=0.508; p<0.001). Along with this, a strong direct correlation (r=0.522; p<0.001) was found between the concentration of FGF-23 in the serum and inorganic phosphorus; at the same time hyperphosphatemia was less significantly associated with higher serum intact parathyroid hormone (PTH) levels (r=0.398; p<0.05). Lower FGF-23 and PHT levels were noted in a group of patients who could achieve and maintain the target serum inorganic phosphorus level (0.9-1.45 mmol/l) compared to that of patients with uncorrected hyperphosphatemia (>1.45 mmol/l) (p<0.01). A decrease in FGF-23 and PHT levels was achieved chiefly in the patients who had used phosphate-binders that contained no calcium (sevelamer hydrochloride). Lower FGF-23 levels were observed in the patients with CHD on regular HD who can achieve and maintain the target serum inorganic phosphorus level when using phosphate-binders that do not contain calcium than in those with uncorrected hyperphosphatemia (p<0.01).