[Vitamin D and its positive effect on the PTH/vitamin D/calcium-FGF23/klotho/phosphorus axis in kidney transplant recipients].

Background: hypovitaminosis D is frequent in kidney transplant recipient (KTR) patients and is associated with deleterious effects both at the bone and extraosseous levels. Treatment with cholecalciferol is effective for the normalization of 25(OH)D, demonstrating a beneficial effect on the calcium-tropic axis in other populations; however, its effect on the PTH/vitamin D/calcium and FGF23/klotho/phosphorus axis in RTR has not been reported. The aim of this study was to evaluate the effect of normalization of serum 25(OH)D concentrations on the PTH/vitamin D/calcium-FGF23/klotho/phosphorus axis in KTR treated with cholecalciferol, as well as the association between the components of this axis. Methods: a prospective study in 23 KTR with hypovitaminosis D, with evolution from 1 to 12 months post-transplantation, an estimated glomerular filtration rate > 60 mL/min/1.73 m2 and a history of primary nephropathy treated with cholecalciferol, in whom the PTH/vitamin D/calcium and FGF23/klotho/phosphorus axis was evaluated during the state of hypovitaminosis D and at normalization of 25(OH)D. Results: at the normalization of 25(OH)D, a reduction in PTH [103 (58.5-123.9) vs 45.6 (30.1-65.1) pg/mL; p = 0.002] and an increase in serum phosphorus [3.1 (2.3-3.5) vs 3.3 (3-3.6) mg/dL; p = 0.01] were evident, with no differences in calcium, klotho and FGF23 concentrations. The time to achieve normalization of 25(OH)D was 12 weeks (RIC, 4-12), with a dose of 5000 IU/day (RIC, 4000-6000). A positive association between klotho and PTH was corroborated (r = 0.54; p = 0.008; linear regression, β = 0.421; B = 0.004; 95 % CI, 0.003-0.007; p = 0.045). Conclusions: treatment with cholecalciferol is effective for the normalization of 25(OH)D, with a beneficial effect on calcium-phosphotropic metabolism characterized by a reduction in PTH concentration, without significant changes in calcemia or calciuria, as well as an increase in phosphatemia, without modifications in FGF23 or klotho concentrations.