Investigating the effect of testosterone by itself and in combination with letrozole on 1,25-dihydroxy vitamin D and FGF23 in male rats.

BACKGROUND: Testosterone deficiency might be associated with vitamin D levels in hypogonadal men, but it is not clear whether testosterone can affect vitamin D and fibroblast growth factor-23 (FGF23), either directly or indirectly via aromatization to estradiol. We aimed to investigate the role of testosterone on vitamin D metabolism and serum FGF23 in male rats. METHODS: A total of 48 male rats were divided into 4 equal groups: sham; O, orchiectomy; O + T, orchiectomized rats treated with testosterone; and O + T + L, orchiectomized rats treated with combination of testosterone and letrozole. We compare the vitamin D metabolism biochemical parameters in these four groups, before and after the study. RESULTS: We detected a significant reduction in 25-hydroxyvitamin D (25(OH)D), vitamin D binding protein (DBP), FGF23, and 1,25-dihydroxyvitamin D (1,25(OH)2D) serum level in O group compared to sham group (p = 0.004, p = 0.009, p < 0.001 and p < 0.001, respectively), and a significant increase in serum phosphorus, parathyroid hormone (PTH), and alkaline phosphatase (ALP) levels in orchiectomized rats in comparison to sham group (p < 0.001, p = 0.022, and p = 0.006, respectively). However, these changes were corrected by testosterone replacement in O + T and O + T + L groups. In addition, we found that DBP and 1,25(OH)2D serum levels were significantly higher in O + T group in comparison to O + T + L group (p = 0.030 and p = 0.026, respectively). CONCLUSIONS: Testosterone plays a significant role on regulating 25(OH)D, DBP, FGF23, phosphate (Phos), PTH, and 1,25(OH)2D serum levels in male rats. Also, testosterone has a potent effect on 1,25(OH)2D and DBP by its conversion to estradiol.

Effect of Cholecalciferol therapy on serum FGF23 in vitamin D deficient patients: a randomized clinical trial.

INTRODUCTION: Fibroblast growth factor-23 plays an important role in regulating systemic phosphate homeostasis, and vitamin D metabolism. However, the effect of Cholecalciferol therapy on FGF23 serum level in patients with vitamin D deficiency has not been studied, yet. MATERIALS AND METHODS: This is a double-blind, randomized clinical trial on 119 vitamin D deficient patients in 2016. Biochemical variables of treatment and placebo groups were analyzed after 12 weeks of 50,000 IU of Cholecalciferol vs. placebo therapy once a week, by SPSS18. RESULTS: After Cholecalciferol therapy, delta of serum PTH in treatment group was less than the controls (P < 0.001). However, delta values of serum 25(OH)D3, 1,25(OH)2D3 and FGF23 in vitamin D treated group were more than the placebo-treated ones (P < 0.001, P = 0.002, and P = 0.04, respectively). Moreover, FGF23 serum level in treatment group was associated with serum calcium (P = 0.005, r = -0.256), and serum 1,25(OH)2D3 (P < 0.001, r = 0.529). CONCLUSIONS: We propose that in these patients 1,25(OH)2D3 has a positive association with serum FGF23, and hypostasized that serum calcium might be a down regulator of serum FGF23.