Enhanced Response of Acute Monocytic Leukemia Cells to Low-dose Cytarabine by 1,25-dihydroxyvitamin D3.

Low-dose cytarabine combined with differentiating or DNA hypomethylating agents, such as vitamin D compounds, is a potential regimen to treat acute myeloid leukemia (AML) patients who are unfit for high-intensity chemotherapy. The present study aimed to determine which subset of AML would be most responsive to low-dose cytarabine with the differentiating agent 1,25-dihydroxyvitamin D3 (1,25-D3). Here, firstly, cBioPortal database was used and we found out that vitamin D receptor (VDR) was highly expressed in acute monocytic leukemia (M5) and high VDR expression was associated with a poor survival of AML patients. Then, we confirmed that 1,25-D3 at clinical available concentration could induce more significant differentiation in acute monocytic leukemia cell lines (U937, MOLM-13, THP-1) and blasts from M5 patients than in non-monocytic cell lines (KGla and K562) and blasts from M2 patient. Finally, it was shown that the combination of 1,25-D3 and low-dose cytarabine further increased the differentiating rate, growth inhibition and G0/G1 arrest, while mild changes were found in the apoptosis in acute monocytic leukemia cell lines. Our study demonstrates that the enhanced response of acute monocytic leukemia cells to low-dose cytarabine by 1,25-D3 might indicate a novel therapeutic direction for patients with acute monocytic leukemia, especially for elderly and frail ones.

Lithocholic Acid Is a Vitamin D Receptor Ligand That Acts Preferentially in the Ileum.

The vitamin D receptor (VDR) is a nuclear receptor that mediates the biological action of the active form of vitamin D, 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], and regulates calcium and bone metabolism. Lithocholic acid (LCA), which is a secondary bile acid produced by intestinal bacteria, acts as an additional physiological VDR ligand. Despite recent progress, however, the physiological function of the LCA−VDR axis remains unclear. In this study, in order to elucidate the differences in VDR action induced by 1,25(OH)2D3 and LCA, we compared their effect on the VDR target gene induction in the intestine of mice. While the oral administration of 1,25(OH)2D3 induced the Cyp24a1 expression effectively in the duodenum and jejunum, the LCA increased target gene expression in the ileum as effectively as 1,25(OH)2D3. 1,25(OH)2D3, but not LCA, increased the expression of the calcium transporter gene Trpv6 in the upper intestine, and increased the plasma calcium levels. Although LCA could induce an ileal Cyp24a1 expression as well as 1,25(OH)2D3, the oral LCA administration was not effective in the VDR target gene induction in the kidney. No effect of LCA on the ileal Cyp24a1 expression was observed in the VDR-null mice. Thus, the results indicate that LCA is a selective VDR ligand acting in the lower intestine, particularly the ileum. LCA may be a signaling molecule, which links intestinal bacteria and host VDR function.

Associations Between Change in Total and Free 25-Hydroxyvitamin D With 24,25-Dihydroxyvitamin D and Parathyroid Hormone.

Context: The physiologic role of free 25-hydroxyvitamin D [25(OH)D] in humans is unclear. Objective: To assess whether rise in total vs free 25(OH)D is associated with change in downstream biomarkers of 25(OH)D entry into target cells in kidney and parathyroid: 24,25-dihyroxyvitamin D [24,25(OH)2D] and PTH, respectively. Design: 16-week randomized controlled trial. Intervention: 60 µg (2400 IU)/d of D3 or 20 µg/d of 25(OH)D3. Setting: Academic medical center. Participants: 35 adults age ≥18 years with 25(OH)D levels < 20 ng/mL. Main Outcome Measures: 24,25(OH)2D, 1,25-dihyroxyvitamin D [1,25(OH)2D] and PTH. Results: At baseline, participants [D3 and 25(OH)D3 groups combined] were 35.1 ± 10.6 years. Mean total 25(OH)D, free 25(OH)D, 24,25(OH)2D, and PTH were 16.6 ng/mL, 4.6 pg/mL, 1.3 ng/mL, and 37.2 pg/mL, respectively. From 0 to 4 weeks, rise in only free 25(OH)D was associated with a concurrent 24,25(OH)2D increase [P = 0.03, adjusted for change in 1,25(OH)2D and supplementation regimen] and PTH decrease (P = 0.01, adjusted for change in calcium and supplementation regimen). Between 4 and 8 weeks, and again from 8 to 16 weeks, rises in free and total 25(OH)D were associated with 24,25(OH)2D increase; in contrast, rise in neither total nor free 25(OH)D was associated with PTH decrease during these time periods. Conclusions: Early rise in free 25(OH)D during treatment of vitamin D deficiency was more strongly associated with changes in biomarkers of 25(OH)D entry into target kidney and parathyroid cells, suggesting a physiologic role of free 25(OH)D in humans.

24R,25-Dihydroxyvitamin D3 Protects against Articular Cartilage Damage following Anterior Cruciate Ligament Transection in Male Rats.

Osteoarthritis (OA) in humans is associated with low circulating 25-hydroxyvitamin D3 [25(OH)D3]. In vitamin D replete rats, radiolabeled 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] accumulates in articular cartilage following injection of [3H]-25(OH)D3. Previously, we showed that 24R,25(OH)2D3 blocks chondrocyte apoptosis via phospholipase D and p53, suggesting a role for 24R,25(OH)2D3 in maintaining cartilage health. We examined the ability of 24R,25(OH)2D3 to prevent degenerative changes in articular cartilage in an OA-like environment and the potential mechanisms involved. In vitro, rat articular chondrocytes were treated with IL-1ß with and without 24R,25(OH)2D3 or 1α,25(OH)2D3. 24R,25(OH)2D3 but not 1α,25(OH)2D3 blocked the effects of IL-1ß in a dose-dependent manner, and its effect was partially mediated through the TGF-ß1 signaling pathway. In vivo, unilateral anterior cruciate ligament transections were performed in immunocompetent rats followed by intra-articular injections of 24R,25(OH)2D3 or vehicle (t = 0, 7, 14, 21 days). Tissues were harvested on day 28. Joints treated with vehicle had changes typical of OA whereas joints treated with 24R,25(OH)2D3 had less articular cartilage damage and levels of inflammatory mediators. These results indicate that 24R,25(OH)2D3 protects against OA, and suggest that it may be a therapeutic approach for preventing trauma-induced osteoarthritis.

Anti-inflammatory effect of vitamin D on gingivitis: a dose-response randomised control trial.

PURPOSE: To assess the anti-inflammatory effect of vitamin D on gingivitis at various doses. MATERIALS AND METHODS: In this randomized controlled trial, daily oral vitamin D supplementation was given in doses of 2000 IU for group A, 1000 IU for group B, 500 IU for group C and a placebo for group D over a 3-month period. The changes in gingival scores were measured after the 1st, 2nd and 3rd months. RESULTS: The gingivitis score changed in direct proportion to the dose of vitamin D supplementation. In group A, the mean gingival scores were 2.4 (baseline), 1.7 after the first month, 0.8 after the second month and 0.3 after the third month. The group B mean baseline gingival score of 2.3 decreased to 2.0 in the first month, 1.1 after the second month and 0.5 after the third month. In group C, the baseline gingival scores were 2.2 and 1.9 after one month, 1.4 after two months and 0.8 by the last visit. Comparing baseline gingivitis scores with the later-visit score using the Wilcoxon paired test, the significant anti-inflammatory effect was seen in group A after one month, in group B at two months and in group C at three months after oral vitamin D supplementation (P < 0.0001). However, group D did not show a significant antiinflammatory effect. CONCLUSION: There is a dose-dependent anti-inflammatory effect of vitamin D on gingivitis. Vitamin D is a safe and effective anti-inflammatory agent in doses ranging from 500 IU to 2000 IU. Results are apparent earlier with the higher dose of 2000 IU.

[Comparative study 1,25-dihydroxycholecalciferols and 24,25-dihydroxycholecalciferols effect on ionized calcium level in blood plasma of patients with osteoporosis].

Comparative study results of vitamin's D active metabolites 1,25-dihydroxycholecalciferol (1,25(OH)2D3) and 24,25-dihydroxycholecalciferol (24,25(OH)2D3) effect on ionised calcium level in blood plasma of patients with postmenopause osteoporosis are described. Administration of 24,25(OH)2D3 for patients with osteoporosis leads to gradual stepped increase of ionised calcium level in blood plasma. This level remains normal and does not change in 2 weeks after cancelling of drug administration. Prescription of 1,25(OH)2D3 rapidly increases ionised calcium level in blood plasma and it's cancelling leads to normalisation of ionized calcium concentration in blood plasma during 1 week. Combination of two medicines causes summation of their effects. Administration of 24,25(OH)2D3 (10 mcg per 24 hours) and 1,25(OH)2D3 (0.5 mcg per 24 hours) doesn't cause any of incidental and allergic reactions.

Characterization of new conjugated metabolites in bile of rats administered 24,25-dihydroxyvitamin D(3) and 25-hydroxyvitamin D(3).

The characterization of new conjugated vitamin D metabolites in rat bile was performed using HPLC, liquid chromatography/tandem mass spectrometry combined derivatization, and GC-MS. After the administration of 24,25-dihydroxyvitamin D(3) to rats, 23, 25-dihydroxy-24-oxovitamin D(3) 23-glucuronide, 3-epi-24, 25-dihydroxyvitamin D(3) 24-glucuronide, and 24,25-dihydroxyvitamin D(3) 3-sulfate were obtained as new biliary metabolites together with 24,25-dihydroxyvitamin D(3) 3- and 24-glucuronides. The above metabolites, except 24,25-dihydroxyvitamin D(3) 3-glucuronide, were obtained from rats dosed with 25-hydroxyvitamin D(3). 23, 25-Dihydroxyvitamin D(3) 23-glucuronide was also obtained from the bile of rats administered 25-hydroxyvitamin D(3) in addition to its 3-glucuronide, 25-glucuronide, and 3-sulfate. Thus, it was found that 24,25-dihydroxyvitamin D(3) and 25-hydroxyvitamin D(3) were directly conjugated as glucuronide and sulfate, whereas at the C-23 position, they were hydroxylated and then conjugated. Furthermore, we found that the C-3 epimerization acts as one of the important pathways in vitamin D metabolism.

24,25-dihydroxyvitamin D3 in combination with 1,25-dihydroxyvitamin D3 ameliorates renal osteodystrophy in rats with chronic renal failure.

AIMS: This study compares the effects of 1,25(OH)2D3 and 24,25(OH)2D3 alone or in combination on renal osteodystrophy in rats with chronic renal failure (CRF). MATERIAL AND METHOD: One month subsequent to 5/6 nephrectomy animals were divided into four groups and treated for one or four weeks with either vehicle, 1,25(OH)2D3, 24,25(OH)2D3 or 1,25(OH)2D3 + 24,25(OH)2D3. A sham-operated group with normal renal function matched for age and weight was used as control. At the termination of the study blood chemistry, parathyroid hormone (PTH) level and bone histomorphometry were analyzed. RESULTS: The main findings were: amelioration of 1,25(OH)2D3-induced hypercalcemia by 24,25(OH)2D3, and similar suppression of PTH by the two metabolites of vitamin D when administered alone or in combination. Bone histomorphometry showed that 1,25(OH)2D3 alone exerts a potent proliferative effect on the osteoblasts but severely depresses their mineralizing capacity in a dose- and time-dependent manner. By contrast, 24,25(OH)2D3 improved the mineralizing activity with only a limited effect on osteoblast proliferation. Addition of 24,25(OH)2D3 potentiated the beneficial effect of 1,25(OH)2D3 on bone-resorbing parameters and corrected the mineralization failure. CONCLUSIONS: Based on the above observations we suggest that the combined treatment with 1,25(OH)2D3 and 24,25(OH)2D3 markedly improves the morphologic and metabolic abnormalities of renal osteodystrophy.

A highly sensitive method for large-scale measurements of 1,25-dihydroxyvitamin D.

A quantitative method for measuring 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) was developed utilizing a luciferase reporter gene under the control of the highly inducible 25-hydroxyvitamin D3 24-hydroxylase promoter in a stably transfected cell line. Transient transfections with constructs containing the 24-hydroxylase gene promoter 5' to a luciferase reporter were first performed in cell lines with high levels of vitamin D receptor, i.e., the rat osteosarcoma (ROS 17/2.8) and human breast cancer (T-47D) cell lines. ROS 17/2.8 cells, stably transfected with the plasmid, gave a 60-fold stimulation with 10(-10) M 1,25-(OH)2D3. A standard curve was constructed showing a large range of response to 1,25-(OH)2D3 (1 pg to 1 ng). The assay was adapted to microtiter plates, which permits a large number of samples to be assayed simultaneously. Other metabolites of vitamin D and analogs such as 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, and 1 alpha-hydroxyvitamin D3 have negligible effects on the detection of 1,25-(OH)2D3, thus eliminating the need for purification of sample. The sensitivity of the method permitted the use of 100 microliters of serum with excellent results. Comparison of this method with a commercially available assay demonstrates that it gives higher sensitivity, simpler manipulations, and comparable results.

24R,25-dihydroxyvitamin D3: an essential vitamin D3 metabolite for both normal bone integrity and healing of tibial fracture in chicks.

We tested the hypothesis that 24R,25-dihydroxyvitamin D3 [24R,25-(OH)2D3] is an essential vitamin D metabolite for the development of normal bone integrity and the healing of fractures. The natural 24R,25-(OH)2D3 and its synthetic epimer 24S,25-dihydroxyvitamin D3 [24S,25-(OH)2D3] were tested alone or in combination with 1alpha,25-dihydroxyvitamin D3 [1alpha,25-(OH)2D3], on normal bone development and other related variables of the Ca2+ homeostasis system [serum Ca2+, 25-hydroxyvitamin D3 (25OHD3), 24,25-(OH)2D3, and 1alpha,25-(OH)2D3 levels] in chicks. Mechanical testing of torsional strength was carried out on the femur. 24R,25-(OH)2D3 (80 nmol/kg diet) alone was sufficient for normal bone growth and integrity similar to that achieved by the vitamin D3-replete controls. Next, chicks were fed a 25OHD3-replete diet (75 nmol/kg diet) for 8 days after hatching, and then 25OHD3 was withdrawn to minimize any residual circulating metabolites before the imposition of standardized tibial fractures 14 days later. Vitamin D metabolites were administered for 2 weeks to determine their effects on the mechanical properties of healed tibia. 24S,25-(OH)2D3 combined with 1alpha,25-(OH)2D3 or 1alpha,25-(OH)2D3 alone resulted in poor healing [strength values of 0.158 +/- 0.011 and 0.123 +/- 0.009 Nm (Newton x meter), respectively] compared with that in the 25OHD3-treated control group (0.374 +/- 0.029 Nm). In contrast, the fractured tibia of the birds fed 24R,25-(OH)2D3 in combination with 1alpha,25-(OH)2D3 showed healing equivalent to that in the control group, with strength values of 0.296 +/- 0.043 Nm. These results suggest that when 24R,25-(OH)2D3 is present at normal physiological concentrations, it is an essential vitamin D3 metabolite for both normal bone integrity and healing of fracture in chicks.

24R,25-dihydroxyvitamin D3 promotes bone formation without causing excessive resorption in hypophosphatemic mice.

To clarify the differences in the action of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and 24,25-(OH)2D3 in hypophosphatemic (Hyp) mice, a model for familial X-linked hypophosphatemic rickets in humans, we carried out histomorphometric examinations of the effects of these agents in the lumbar vertebra of these mice. The Hyp mice received 1-1000 micrograms/kg.day 24,25-(OH)2D3, 0.01-0.1 micrograms/kg.day 1,25.(OH)2D3, or vehicle alone given daily for 28 days by ip injection. Histomorphometrically, 1,25-(OH)2D3 and 24,25-(OH)2D3 showed similar effects on bone formation. The parameters of bone formation, mineralized bone volume/bone volume, mineral apposition rate, and bone formation rate/bone surface, were improved to a similar extent in a dose-dependent manner by 1,25-(OH)2D3 and 24,25-(OH)2D3, but there were remarkable differences in the indexes of the bone resorption between these two metabolites. In 24,25-(OH)2D3-treated Hyp mice, osteoclast number/bone perimeter and osteoclast surface/bone surface, the parameters of bone resorption, increased to control levels and did not change according to the dose of 24,25-(OH)2D3. However, in 1,25-(OH)2D3-treated Hyp mice, these values increased remarkably, exceeding the control level. That is, 24,25-(OH)2D3 normalized bone resorption in the rachitic mice, whereas 1,25-(OH)2D3 caused excessive stimulation of bone resorption. This qualitative difference between the two compounds contributes to the superior effects exerted by 24,25-(OH)2D3 in improving the bone lesion in Hyp mice. At doses from 1-1000 micrograms/kg.day, 24,25-(OH)2D3 had dose-dependent effects in increasing bone formation without promoting excessive bone resorption, as shown by histomorphometric analysis.

Vitamin D3 analogs and salmon calcitonin partially reverse the development of renal osteodystrophy in rats.

We have previously established an uremic rat model which is suitable for investigating the effect of various treatment modalities on the progression of renal osteodystrophy [1]. Four months subsequent to 5/6 nephrectomy, animals were treated three times a week for 3 months with either vehicle, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], 1,25(OH)2D3 + 24,25-dihydroxyvitamin D3 [24,25(OH)2D3], 1,25(OH)2D3 + calcitonin (CT), or 1,25(OH)2D3 + 24,25(OH)2D3 + CT. At termination of the study, clinical chemistry, chemical composition, and mechanical properties of femurs, calvarial parathyroid hormone (PTH)-elicited adenylate cyclase (AC), and phospholipase C (PL-C) activities, femoral cross-sectional area, and bone histomorphometry were analyzed. The main findings were that 1,25(OH)2D3 +/- 24,25(OH)2D3 treatment enhanced elasticity as well as time to fracture at the femoral metaphysis. CT potentiated the increase in elasticity obtained by 1,25(OH)2D3 +/- 24,25(OH)2D3 treatment. Only 24,25(OH)2D3 administration rectified the supernormal PTH-stimulated uremic bone AC, and only 1,25(OH)2D3 medication normalized the diminished CT-elicited AC. The obliterated uremic bone PTH-sensitive PL-C was fully normalized by all drug regimens. Femoral shaft inner zone diameter was enhanced by uremia, however, all drug treatments normalized it. Ditto effect was registered with either drug treatment on the subnormal outer and inner zone widths. Histomorphometrical analyses showed that 1,25(OH)2D3 administration reduced both eroded and osteoid surfaces. Most prominently, adjuvant 24,25(OH)2D3 or CT administration potentiated the beneficial effect of 1,25(OH)2D3 on fibrosis and osteomalacia. We assert that vitamin D3 treatment markedly reverses the development of renal osteodystrophy, and CT potentiates the effect of vitamin D3.

Effects of 24R,25-dihydroxyvitamin D3 in combination with 1 alpha-hydroxyvitamin D3 in predialysis renal insufficiency: biochemistry and histomorphometry of cancellous bone.

The effect of combined administration of 24R,25-dihydroxyvitamin D3 (24,25-(OH)2D3) and 1 alpha-hydroxyvitamin D3 (1 alpha-(OH)D3) was studied in 24 non-dialyzed patients with chronic renal insufficiency (CRI), matched pairwise as to age, sex, and creatinine clearance (Cr.cl). Low Ca intake had been supplemented beforehand. Then, 1 alpha-(OH)D3 (mean dose 0.55 micrograms daily) was given orally to all patients for 3 months (T0 to T3). Subsequently, patients were assigned randomly to 6 months further treatment either with 1 alpha-(OH)D3 alone (Group A) or with 1 alpha-(OH)D3 plus a high dosage of 24,25-(OH)2D3 (50 micrograms orally, twice weekly) (Group B). Histomorphometry was performed at T0, T3, and T9. In both groups iPTH was equally suppressed, into the lower normal range. Whereas in Group A, serum Ca rose steadily and Cr.cl declined, in Group B both parameters levelled off between T6 and T9. At T9, in Group A the elevated resorption and osteoid indices had normalized markedly, but osteoblasts (Ob.Pm) and mineralizing boundaries (M.Bd) were depressed considerably between T3 and T9. In contrast, in Group B, preservation of Ob.Pm and improved mineralizing activity were observed (M.Bd at T9 > T3 > T0). Resorption indices hardly changed. In the patients with high Ob.Pm at T0, cancellous bone area increased significantly. This was not observed in Group A. Thus, in Group B, osteoblast recruitment appeared maintained and M.Bd appeared normalized. Decline of remodeling toward an adynamic state with an increased risk of hypercalcemia appeared prevented.

Gender-related effects of vitamin D metabolites on cartilage and bone.

Sex steroid hormones are known to have gender-dependent effects on bone and cartilage in vivo and in vitro. To investigate whether this is a general property of steroids, or is specific to the sex steroid hormones, we examined whether the effects on bone of 1,25-(OH)2D3 and 24,25(OH)2D3, the two active metabolites of vitamin D, are also gender-dependent. One-month-old male and female rats were treated for 1 month with various doses of 1,25-(OH)2D3, 24,25-(OH)2D3, or a combination of both metabolites. The direct effects of both metabolites on the skeleton of the treated animals were similar in male and female rats. 24,25-(OH)2D3 alone or in combination with 1,25-(OH)2D3 increased bone calcium and phosphorus, while 1,25-(OH)2D3 slightly decreased bone mineral content. 24,25-(OH)2D3 also enhanced the differentiation of cartilage in the growth plate, increasing the size of the hypertrophic zone. In addition, an increased metaphyseal bone volume was observed following 24,25-(OH)2D3 treatment in rats of both sexes, but not with 1,25-(OH)2D3. Vitamin D metabolites affected the weight gain of the experimental animals in a gender-dependent manner; 1,25-(OH)2D3 increased weight gain of male rats and 24,25-(OH)2D3 decreased weight gain of female rats. In addition, 1,25-(OH)2D3 increased bone weight and ash weight in male animals. These gender-dependent effects of vitamin D metabolites may occur indirectly via effects of sex steroid hormones, the latter being a sex-related effect.

Treatment of secondary hyperparathyroidism with intermittent oral high doses of 1-alpha-OHD3 plus pharmacological dose of 24,25(OH)2D3.

The present study examined the effect of intermittent oral high doses of 1-alpha-OHD3 in combination with a pharmacological dose of 24,25(OH)2D3 on parathyroid hormone (PTH) secretion. Twenty hemodialysis (HD) patients (10 males, aged 26-72 years, on regular hemodialysis for 7-128 months) with secondary hyperparathyroidism resistant to long-term low-dose 1-alpha-OHD3 therapy were studied for 24 weeks. At the outset of the study they were randomly divided into two groups: group 1 received high-dose 1-alpha-OHD3 plus 24,25(OH)2D3 (2 x 5 micrograms/day) and group 2 was on monotherapy with 1-alpha-OHD3. 1-alpha-OHD3 was given three times a week in the evening before each HD in gradually increased doses from 1 to 4 micrograms adjusted to keep serum calcium levels below 2.6 mmol/L. During the therapy mean serum calcium and ionized calcium levels increased but remained in the normal ranges without differences between the two groups. However, the frequency of hypercalcemia episodes was different in the two groups. In the first 12 weeks the number of hypercalcemia episodes was significantly lower in group 1 than in group 2 (6 vs. 12; p < .05), allowing the use of significantly higher 1-alpha-OHD3 doses in group 1. In the second 12 weeks of the study the 1-alpha-OHD3 dose in group 1 had to be reduced due to more frequent appearance of hypercalcemia. So, the 1-alpha-OHD3 doses became similar in the two groups during the second 12 weeks of the study.(ABSTRACT TRUNCATED AT 250 WORDS)

[The metabolism of heavy metals depends on the vitamin-D status of the body]. / Obmen tiazhelykh metallov zavisit ot D-vitaminnogo statusa organizma.

The effect of vitamin D3 and its two metabolites 1,25(OH)2D3 and 24,25(OH)2D3 on the metabolism of heavy metals--Sr, Pb and Cd was studied. The experiments were carried out on chickens, the heavy metals were added to the chicken's ration. The results obtained demonstrated that vitamin D3 caused accumulation of those metals in tissues and their toxicity in organisms. When increasing the vitamin dose from 200 to 500 IU on 1 kg of ration that tendency was being heightened. On the three steroids which had been studied the metabolite 1,25(OH)2D3 displayed the greatest activity in accumulating metals in tissues, Pb in particular. The effect of 24,25(OH)2D3 on the indices being studied was comparable with that of vitamin D3.

Day time and night time effects of 24R,25-dihydroxycholecalciferol on renal alkaline phosphatase and gamma-glutamyltransferase activities in intact rats.

The effects of 24R,25-dihydroxycholecalciferol [24,25(OH)2 CC] on alkaline phosphatase (APA), gamma-glutamyltransferase (gamma-GT) and acid phosphatase (AP) activities were investigated on renal cortex slices of intact rats killed at 18h00 or at 06h00. At 06h00, three, six and nine hours after a single intraperitoneal injection of 24,25(OH)2 CC, APA activity was increased by 30%, 51% and 29%, respectively and gamma-GT activity, by 25%, 39% and 38%, as compared to their controls. AP on the other hand was not modified at all. These enzymatic stimulations were statistically higher than those measured at 18h00, respectively APA: 11%, 25%, 28% and gamma-GT: 2%, 20%, 22%. They can be explained by variations in new protein synthesis in relation with rat activity periods. Physiological significance of these renal effects remains to be elaborated.

[Effects of cadmium on vitamin D function involved in the regulation of phosphorus-calcium metabolism]. / Vliianie kadmiia na funktsiiu vitamina D po regulirovaniiu fosforno-kal'tsievogo obmena v éksperimente.

The role of vitamin D in regulation of phosphoric-calcium metabolism was evaluated in conditions of experimental cadmium intoxication induced by daily dietetic intake (100 micrograms/kg for 8 months) of cadmium in parallel with intake of calcium in diverse amounts. Daily requirements in vitamin D were provided in different groups of animals either with ergocalciferol (D2) or 24,25-dihydroxycholecalciferol (0.25 microgram per animal). The results of the trial suggested that despite regular supply of ergocalciferol, renal damage induced by cadmium intoxication was associated with phosphoric-calcium metabolic derangement which is likely to result from defects in renal synthesis of active vitamin D form. This was confirmed by the fact that the change of ergocalciferol for 24,25-dihydroxycholecalciferol did not produce any noticeable shifts in the phosphoric-calcium metabolism.

[The toxicity of different forms of 24,25-dihydroxycholecalciferol preparations in rats]. / Issledovanie toksichnosti razlichnykh form preparatov 24,25-dioksikholekal'tsiferola u krys.

The purpose of the study was to examine the toxicity of 24,25-DOXK on calcium-phosphorus metabolic parameters. The rats from experimental groups received enteral 50- and 1,000-fold physiological doses of 24,25-DOXK (Vitamins Research Production Association) as a combination of R- and S-epimers and homogeneous R-epimer in sunflower oil solutions or ethanol mixture (1:4 propylene glycol) during 3 and 7 days. Though there was a stable tendency for hyperphosphatemia and altered blood calcium concentrations, the 24,25-DOHK formulations under test, unlike 1-OXK and 1,25-DOXK, displayed no toxic properties on the kidney, heart and aorta and produced a mineralizing effect on bone tissue in the acute period. Comparison of the properties shown by 24R,25-DOXK and 24R,S-DOXK showed that a combination of 24,25-DOXK R- and S-epimers was preferable for practical application.

Bone turnover in rats treated with 1,25-dihydroxyvitamin D3, 25-hydroxyvitamin D3 or 24,25-dihydroxyvitamin D3.

Female rats were given 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), 0.25 microgram per 100 g body weight (bw), 25-hydroxyvitamin D3 (25(OH)D3), 1.7 micrograms/100 g bw or 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) 1.7 micrograms/100 g bw, subcutaneously three times a week for 12 weeks. Traditional variables pertaining to calcium homeostasis and growth, i.e. blood and urine calcium (Ca) and phosphate (P), serum levels of vitamin D3 metabolites parathyroid hormone, (PTH), calcitonin (CT), prolactin (PRL) and growth hormone (GH) were measured every four weeks. This data pool was correlated with bone matrix turnover parameters, i.e. serum levels of alkaline phosphatase (ALP) and urinary hydroxyproline (u-HYP) excretion. After 12 weeks of treatment, 1,25(OH)2D3 significantly enhanced serum total and ionized Ca, urine Ca and urine P, and also diminished urine cAMP due to reduced renal function (creatinine clearance). However, 25(OH)D3 administration had no such impact. 24,25(OH)2D3 opposed the effect of 1,25(OH)2D3 after 12 weeks by significantly augmenting serum P and diminishing serum levels of total Ca and ionized Ca. Cross sectional group analyses showed that circulating levels of ALP were directly related with serum 1,25(OH)2D3 and inversely related to serum 24,25(OH)2D3 and CT. Total u-HYP and per cent non-dialysable HYP (ndHYP) were reciprocally and positively correlated with serum PRL, respectively. However, no such relations were observed with serum GH. It appears that rats with elevated circulating levels of 1,25(OH)2D3 exhibit increased bone resorption, while augmented 24,25(OH)2D3 is associated with the opposite. Apparently, high bone turnover (i.e. reduced total urinary HYP and enhanced ndHYP) is associated with high serum PRL.