Intracellular calcium homeostasis in patients with early stages of chronic kidney disease: effects of vitamin D3 supplementation.

BACKGROUND: Chronic renal failure has been referred to as a state of cellular calcium toxicity. The aim of this study was to investigate the status of free cytosolic calcium ([Ca(2+)](i)), intracellular calcium reserves and the capacitative calcium entry in peripheral blood mononuclear cells (PBMCs) of early-stage chronic kidney disease (CKD) patients, and to determine the effect of vitamin D(3) supplementation on these parameters. METHODS: The study involved 44 patients with CKD stages 2-3; 27 of them were treated with cholecalciferol (5000 IU/week) for 12 months. [Ca(2+)](i) was measured using Fluo-3 AM fluorimetry. Intracellular calcium reserves were emptied by the application of thapsigargin (Tg), a specific inhibitor of endoplasmic reticulum Ca(2+)-ATPase. 2-Aminoethyl-diphenyl borate (2APB) was used to examine the capacitative calcium entry. RESULTS: [Ca(2+)](i) of CKD patients was substantially higher in comparison with healthy subjects: 123 (115-127) versus 102 (98-103) nmol/l, P < 0.001. The calcium concentration of Tg-sensitive stores and the capacitative calcium entry were also significantly increased in CKD patients. After the 12-month vitamin D(3) supplementation, there was a marked decrease in [Ca(2+)](i) [105 (103-112) nmol/l, P < 0.001 versus baseline], independently of the increase in 25(OH)D(3) or the decrease in PTH levels. No significant changes in intracellular calcium reserves and the capacitative calcium entry were found. CONCLUSIONS: Our results demonstrate that (1) [Ca(2+)](i), intracellular calcium stores and the capacitative calcium entry were significantly increased already in early stages of CKD; (2) long-term vitamin D(3) supplementation normalized [Ca(2+)](i) without any effect on intracellular calcium reserves or the capacitative calcium entry.

Effects of long-term cholecalciferol supplementation on mineral metabolism and calciotropic hormones in chronic kidney disease.

BACKGROUND: Data on the efficacy and safety of long-term vitamin D supplementation in chronic kidney disease (CKD) are scarce. We assessed the effects of the 12-month vitamin D(3) treatment on mineral metabolism and calciotropic hormones in patients with CKD stages 2-4. METHODS: Eighty-seven patients (mean age 66 years, men/women 33/54) were randomized to cholecalciferol treatment with either 5,000 or 20,000 IU/week. Serum calcium, phosphate, 25(OH)D(3), 1,25(OH)(2)D(3), PTH and urinary mineral concentrations were obtained at baseline and after 4, 8 and 12 months. RESULTS: The median serum mineral concentrations were normal and not changed throughout the study. The number of hypercalciuric patients slightly increased with higher dose, but no sustained rise in calciuria was present. Vitamin D insufficiency/deficiency was revealed in 72 (83%) patients at baseline and 37 (43%) at month 12. The 25(OH)D(3) levels increased more with higher dose; a rise in 1,25(OH)(2)D(3) was less impressive. The parathyroid hormone (PTH) concentrations were reduced, but the number of subjects with PTH below the lower limit for CKD stage 3 increased equally with both doses. CONCLUSIONS: Vitamin D insufficiency/deficiency in CKD significantly improved after the 12-month cholecalciferol treatment, with higher dose being more effective and equally safe. Further studies of vitamin D(3) effects on bone metabolism are warranted.