Adrian Oksa

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 D3 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)D3, 1,25(OH)2D3, 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)D3 levels increased more with higher dose; a rise in 1,25(OH)2D3 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 D3 effects on bone metabolism are warranted.

Effects of angiotensin-converting enzyme inhibitors on glucose and lipid metabolism in essential hypertension.

Summary Data of 52 patients, 29 women and 23 men aged 32–68 years (mean age 47 years) with essential hypertension, participating in three open therapeutic trials with either enalapril, lisinopril, or perindopril were evaluated to assess the effects of angiotensin-converting enzyme (ACE) inhibition on glucose and lipid metabolism. The 75-g oral glucose tolerance test (oGTT) was performed, and plasma glucose and insulin levels, as well as total cholesterol, high-density lipoprotein (HDL)-cholesterol, and triglycerides levels were determined before and after the 8− to 12-week treatment. Minor differences in the blood pressure (BP)-lowering effect and metabolic response were obtained with the ACE inhibitors studied; only lisinopril improved glucose tolerance significantly; blood lipids were not changed by any drug. The entire patient population showed only a slight reduction in 1-h postload glucose after treatment. More obvious improvement in glucose tolerance was evident in hypertensive patients who were glucose intolerant and/or insulin resistant (GI/IR, 53.8% of all), however. This subgroup also showed a slight but not significant increase in HDL-cholesterol and a decrease in triglycerides levels. Only a slight change or no change in plasma glucose, insulin, and lipid values was noted in hypertensive patients with normal glucose tolerance (NGT) and insulin sensitivity. These favorable effects were expressed only after ACE inhibitor monotherapy, but not when hydrochlorothiazide was added. The results indicate that a lack of stratification of hypertensive patients with regard to glucose tolerance or insulin sensitivity could be a confounding factor in evaluation of metabolic effects of ACE inhibitors.

Intracellular calcium homeostasis in patients with early stagesof 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.

Purinergic P2X7 receptors participate in disturbed intracellular calcium homeostasis in peripheral blood mononuclear cells of patients with chronic kidney disease.

Background: P2X₇ receptors intervene with lymphocyte activation and are responsible for multiple processes, including calcium influx. Here, we studied the participation of P2X₇ receptors in disturbed intracellular calcium homeostasis regulation in early-stage chronic kidney disease (CKD). Methods: The study involved 20 healthy volunteers and 20 CKD stage 2–3 patients. The free cytosolic calcium concentration ([Ca²⁺]_i) was measured using fluorimetry. The P2X₇ pore function was evaluated by the fluorescent dye ethidium bromide. Results: In peripheral blood mononuclear cells (PBMCs) of patients, [Ca²⁺]_i, intracellular calcium stores and the capacitative calcium entry were increased when compared with healthy subjects. The agonist of P2X₇ receptor BzATP caused a sustained increase in [Ca²⁺]_i in both groups, but the effect was smaller in patients. The antagonist at the P2X₇ receptor KN-62 reduced [Ca²⁺]_i in patients, but had no effect in healthy subjects. In patients, the permeability of ethidium bromide through P2X₇ pores, as well as through BzATP-activated and KN-62-inhibited pores, was distinct from permeability in healthy volunteers. Conclusions: These results demonstrate that the calcium signaling pathway in PBMCs of CKD patients is defective already in CKD stage 2–3, and the pore-forming P2X₇ receptors are involved in these pathophysiological processes.

The Impact of Vitamin D3 Supplementation on Mechanisms of Cell Calcium Signaling in Chronic Kidney Disease.

Intracellular calcium concentration in peripheral blood mononuclear cells (PBMCs) of patients with chronic kidney disease (CKD) is significantly increased, and the regulatory mechanisms maintaining cellular calcium homeostasis are impaired. The purpose of this study was to examine the effect of vitamin D3 on predominant regulatory mechanisms of cell calcium homeostasis. The study involved 16 CKD stages 2-3 patients with vitamin D deficiency treated with cholecalciferol 7000–14000 IU/week for 6 months. The regulatory mechanisms of calcium signaling were studied in PBMCs and red blood cells. After vitamin D3 supplementation, serum concentration of 25(OH)D3 increased (P < 0.001) and [Ca2+]i decreased (P < 0.001). The differences in [Ca2+]i were inversely related to differences in 25(OH)D3 concentration (P < 0.01). Vitamin D3 supplementation decreased the calcium entry through calcium release activated calcium (CRAC) channels and purinergic P2X7 channels. The function of P2X7 receptors was changed in comparison with their baseline status, and the expression of these receptors was reduced. There was no effect of vitamin D3 on P2X7 pores and activity of plasma membrane Ca2+-ATPases. Vitamin D3 supplementation had a beneficial effect on [Ca2+]i decreasing calcium entry via CRAC and P2X7 channels and reducing P2X7 receptors expression.