Endocrine Abstracts

Introduction: Fibroblast growth factor (FGF)-23 is a peptid, released from bone tissue and osteogenic cells. Phosphatonins regulate phosphate homeostasis in some phosphate wasting disorders such as X-linked hypophosphatemia, otozomal dominant hypophosphatemic rickets, and tumor-induced osteomalacia.

FGF-23 is a possible phosphatonin: it regulates phosphate homeostasis by PTH independent actions.

Objective: In the present study, we aimed to determine the effect of serum FGF-23 levels before and after D Vitamin replacement therapy in Vitamin D deficient patients.

Materials and methods: Eighteen premenouposal female patients who had diagnosed as osteomalacia due to Vitamin D depletion were included to the study. Blood samples were collected before (Group 1: mean age 29.1±9.9 years) and 6 weeks after a standard treatment protocol (Group 2) (oral Vitamin D 150 000 IU once for all and subsequently 880 IU D3+1000 mg calcium carbonate for 6 weeks). Nineteen healthy premenouposal women who had normal levels of serum 25 OH D₃ Vitamin (>30 ng/ml) composed control group (Group 3; mean age 28.5±5.2 years). Serum levels of kreatinin, calcium, albumin, phosphate, alkaline phosphatase (ALP), intact parathyroid hormone (iPTH), bone alkaline phosphatase (BALP), 25(OH) D Vitamin, 1,25(OH)₂ D₃ Vitamin, FGF-23 and 24 h urine calcium, phosphorus, kreatinin were measured. The study was approved by local Ethical Committee and informed consent was obtained from each subject.

Results: After Vitamin D+calcium replacement, serum corrected calcium levels (9.0±0.3 vs 9.3±0.3 mg/dl; P<0.001), 1,25(OH)₂ D₃ Vitamin (41.6±15.2 vs 94.0±31.5 pmol/l; P<0.01), urine calcium excretion (145±110.8 vs 297±138.4 mg/day; P<0.01) were significantly increased. Serum BALP (27.8±29.6 vs 18.6±20.1 mg/l; P<0.05), iPTH (78.5±51.6 vs 44.8±15.1 pg/ml; P<0.01) and FGF-23 (33.6±43.0 vs 15.6±12.5 RU/ml; P<0.05). levels decreased significantly. In group 1, FGF-23 had positive correlation with serum calcium levels (P<0.05, r=0.30).

Conclusion: FGF 23 levels decrease while 1,25(OH)₂ D₃ Vitamin increase during Vitamin D replacement. The present study was supported by the Research Fund of Istanbul University (Project No: 573).