Biomedical subjects

H F DeLuca

Publications and source records attributed to H F DeLuca.

At least 307 records · Page 17Linked to original sources

PubMed1983

Biological activity of 24,24-difluoro-1 alpha, 25-dihydroxyvitamin D3 and 1 alpha, 25-dihydroxyvitamin D3-26,23-lactone in inducing differentiation of human myeloid leukemia cells.

Vitamin D compounds added to the culture medium induce differentiation of human myeloid leukemia cells (HL-60 cells) by binding to a specific cytosol receptor protein. This system provides a biologically relevant and technically simple assay to examine the relationship between molecular structure and biological activity of vitamin D compounds. Using this culture system, the biological activity of 24,24-F2-1 alpha,25(OH)2D3 and 1 alpha,25(OH)2D3-26,23-lactone was assayed. 24,24-F2-1 alpha,25(OH)2D3 was four to seven times more potent than 1 alpha,25(OH)2D3 in inducing phagocytosis and C3 rosette formation of HL-60 cells, though both compounds bound equally well to the cytosol receptor, suggesting that the defuorination at the 24-carbon position may stimulate membrane permeability of the compound. 1 alpha,25(OH)2D3-26,23-lactone, on the other hand, was only 1/200th as active as 1 alpha,25(OH)2D3. The binding affinity of the lactone for the cytosol receptor was identical with that of 1 alpha (OH)D3, suggesting that the lactone formation between the 26 and 23 positions masks the function of the 25-hydroxyl group. The binding affinity of vitamin D3 derivatives to the specific cytosol receptor of HL-60 cells was well correlated with that of intestinal cytosol protein specifically bound to 1 alpha,25(OH)2D3.

Calcitriol↗

PubMed1983

1 alpha,25-Dihydroxyvitamin D3 and 1 alpha-hydroxyvitamin D3 prolong survival time of mice inoculated with myeloid leukemia cells.

Syngeneic SL mice inoculated with murine myeloid leukemia cells (M1) all died of leukemia within 30 days. Treatment three times a week with 12.5-50 pmol per mouse of either 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3], the active form of vitamin D3, or its synthetic analog, 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3], considerably prolonged the survival time of mice inoculated with M1 cells. 1 alpha(OH)D3 was more effective than 1 alpha,25(OH)2D3 in increasing the survival time of the mice. 1 alpha(OH)D3 also increased the survival time of nude mice inoculated with M1 cells. The 1 alpha(OH)[3H]D3 administered intraperitoneally to tumor-bearing mice was converted very rapidly to 1 alpha,25(OH)2-[3H]D3. The chronic administration of 25 pmol of 1 alpha(OH)D3 to tumor-bearing mice for 30 days caused no appreciable hypercalcemia. These results indicate clearly that 1 alpha,25(OH)2D3 is effective not only in inducing differentiation of M1 cells in vitro, as previously reported [Abe, E., Miyaura, C., Sakagami, H., Takeda, M., Konno, K., Yamazaki, T., Yoshiki, S. & Suda, T. (1981) Proc. Natl. Acad. Sci. USA 78, 4990-4994], but also in prolonging the survival time of mice inoculated with M1 cells.

Animals↗

PubMed1983

Natural 25,26-dihydroxyvitamin D3 is an epimeric mixture.

Radiolabeled 25,26-dihydroxyvitamin D3 was prepared in vitro by using chicken kidney homogenates and in vivo in rats from [23,24-3H]-25-hydroxyvitamin D3. These compounds were mixed with synthetic (25S)- and (25R)-25,26-dihydroxyvitamin D3, converted to the corresponding (+)-alpha-methoxy-alpha-trifluoromethylphenylacetyl esters, and subjected to high-performance liquid chromatography that separates the derivatized epimers. The radiolabeled 25,26-dihydroxyvitamin D3 derivatives were a 1:1 mixture of the 25S and 25R isomers. Similarly unlabeled 25,26-dihydroxyvitamin D3 isolated from the plasma of rats given large amounts of vitamin D3 was shown to be a 1:1 mixture of the S and R isomers. Therefore, naturally occurring 25,26-dihydroxyvitamin D3 is a mixture of the 25R and 25S isomers and not just the S isomer reported previously.

Animals↗

PubMed1983

1 alpha,25-dihydroxyvitamin D3 promotes fusion of mouse alveolar macrophages both by a direct mechanism and by a spleen cell-mediated indirect mechanism.

Extensive fusion was induced in mouse alveolar macrophages by treatment with conditioned media obtained from spleen cell cultures treated with 15 micrograms of phytohemagglutinin or concanavalin A per ml or with 12 nM 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3]. The fusion rate was 80-90% on day 3. In addition, 1 alpha,25(OH)2D3 added directly to alveolar macrophages induced fusion of about 35% of the cells on day 3, whereas direct addition of phytohemagglutinin and concanavalin A did not enhance fusion at all. When conditioned media from spleen cell or T cell cultures treated with 12 nM 1 alpha,25(OH)2D3 were applied to a Sephadex G-100 column, a fusion factor (Mr 37,000-70,000) could be separated from 1 alpha,25(OH)2D3. 1 alpha,25(OH)2D3 induced fusion at 0.012-120 nM in a dose-dependent manner both by direct action and by spleen cell-mediated indirect action, but the fusion rate was always much greater in the latter than in the former at each concentration of the vitamin. Of the vitamin D3 derivatives tested, 1 alpha,25(OH)2D3 was the most potent, followed successively by 1 alpha,24R,25-trihydroxyvitamin D3, 1 alpha-hydroxyvitamin D3, 25-hydroxyvitamin D3, and 24R,25-dihydroxyvitamin D3. These results clearly indicate that 1 alpha,25(OH)2D3 induces fusion of mouse alveolar macrophages by both a direct and an indirect mechanism, the latter mediated by spleen cells, probably by T cells.

Animals↗

PubMed1983

Quantitation of endogenously occupied and unoccupied binding sites for 1,25-dihydroxyvitamin D3 in rat intestine.

The quantitative reversible dissociation of the 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-receptor complex by the mercurial reagent mersalyl was used to develop an assay for endogenously occupied and unoccupied 1,25-(OH)2D3 binding sites. Incubation of intestinal cytosol preparations in buffer containing 50 mM Tris . HCl, 300 mM KCl, and 1.5 mM EDTA, pH 7.4, with 1 mM mersalyl for 60 min was effective in inhibiting 98% of 1,25-(OH)2D3 specific binding activity. Dissociation of bound 1,25-(OH)2[26,27-3H]D3 from the hormone-receptor complex approached completion by 180 min. In cytosol incubated with saturating levels of nonradioactive hormone, 96% of total binding activity was measurable with the hormone binding assay after displacement of bound nonradioactive ligand with 1 mM mersalyl. Endogenously occupied 1,25-(OH)2D3 binding sites contributed 0, 9, and 19% of total binding activity in rats with plasma 1,25-(OH)2D3 levels averaging 2, 121 +/- 36 and 516 +/- 92 pg/ml, respectively. Therefore, the major fraction of cytosolic 1,25-(OH)2D3 specific binding activity is unoccupied in rat intestine. The results suggest that only a small proportion of the measurable receptors are in the bound form to provide maximal 1,25-(OH)2D3-induced calcium transport.

Animals↗

PubMed1983

The effects of lactose on the absorption and retention of dietary lead.

Intubated lactose has been shown to facilitate the absorption and retention of radiolabeled tracer lead in weanling rats. The conditions under which this effect may be observed are specified here. In acute radiotracer studies with fasted rats, absorption of intubated lead from the intestines and lead uptake into kidney, liver, blood and brain were increased by lactose (3-6 mg/g, per os) in rats 22 and 26 days of age postpartum. However, neither absorption nor uptake by kidney and liver were affected in the suckling rat (less than 21 days postpartum), nor beyond the first week after weaning. The facilitation by lactose of lead absorption and uptake was inhibited by carrier lead concentrations of 100 and 1000 ppm. Lactose at 80 mM (the concentration in rat's milk) had no effect on absorption and uptake of lead, nor on excretion of parenterally administered lead. Chronic feeding of 80 mM lactose and lead (0, 10, or 100 ppm in diet) reduced the retention of lead in kidneys and bones of weanling rats, fed both a normal (0.47%) and a calcium-deficient (0.02%) diet. It is concluded that intubations of high concentrations of lactose into fasted weanling rats can cause an increase in the absorption and uptake of lead. When fed to weanling rats at physiological concentrations, however, lactose actually reduces the retention of lead in bone and kidney.

Age Factors↗

PubMed1983

Biological activity of 24,24-difluoro-25-hydroxycholecalciferol in chicks.

The biological activity of subcutaneously injected 24,24-difluoro-25-hydroxycholecalciferol was compared with that of 25-hydroxycholecalciferol in the vitamin D-deficient growing chick. 24,24-Difluoro-25-hydroxycholecalciferol is equal to 25-hydroxycholecalciferol in the stimulation of: 1) growth, 2) intestinal calcium absorption, 3) elevation of serum calcium and serum phosphorus, 4) healing of rachitic cartilage (radiography), and 5) mineralization of rachitic bone (bone ash). The response appears to be linear in the range of 13.0 to 325 pmol daily. Since 24,24-difluorocholecaliferol cannot be 24-hydroxylated to produce either 24,25-dihydroxycholecalciferol or 1,24,25-trihydroxycholecalciferol, while it can be 1 alpha-hydroxylated to produce 24,24-difluoro-1,25-dihydroxycholecalciferol, these results demonstrate that 24-hydroxylation is not required for the known functions of cholecalciferol in the chick.

Animals↗

PubMed1983

Vitamin D: recent advances.

The field of vitamin D metabolism and mechanism of action has continued to be very active. Autoradiography has shown specific nuclear localization of 1,25-(OH)2D3 in target organs prior to initiation of mechanism of action. Specific nuclear localization has also been demonstrated in a variety of other tissues not previously appreciated as targets of vitamin D action, suggesting the possibility that vitamin D carries out subtle functions previously unappreciated. A macromolecule believed to be a receptor that specifically binds 1,35-(OH)2D3 has been found in the cells showing nuclear localization and in a number of tumor and cancer cell lines. Since 1,25-(OH)2D3 has been found to cause differentiation of certain myeloid leukemia cells, a possible relationship between the vitamin D system and cancer has appeared. Substantial evidence exists that 1,25-(OH)2D3 functions in a nuclear-mediated process, although some evidence exists that not all of the actions of 1,25-(OH)2D3 are carried out through such a mechanism. Substantial advances in our understanding of the metabolism of vitamin D have also been made. The presence of significant amounts of 1 alpha-hydroxylase has been located in the placenta in addition to the kidney. Although there have been reports of extrarenal synthesis of 1,25-(OH)2D3, these sites, if they produce 1,25-(OH)2D3, produce it in insufficient amounts for function. The renal 1 alpha-hydroxylase has been solubilized and shown to be a three-component system. The 25-hydroxylase in the liver has also been solubilized and shown to be a two-component mixed-function monooxygenase. New pathways of vitamin D metabolism include a 23-oxidation to form 23,25-(OH)2D3 or a 23-hydroxylated form of 1,25-(OH)2D3. 23,25-(OH)2D3 is further oxidized to produce a 25-(OH)2D3-26,23-lactone. Although these pathways are of significant magnitude, their roles remain unknown since the products have low biological activity. Important analogs of the vitamin D metabolites include 24,24-F2-25-OH-D3 and the 26,26,26,27,27,27-F6-25-OH-D3. These have been used to show that the 24-hydroxylation, the 26-hydroxylation, and the lactone formation do not play a significant role in the function of vitamin D. Their 1-hydroxy analogs have also been prepared and shown to be extremely biologically active, being somewhere around ten times more active than the native 1,25-dihydroxyvitamin D3, illustrating that important analogs of the vitamin D system continue to be discovered.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed1983

Biological activity of 24,24-difluoro-1,25-dihydroxyvitamin D3.

The biological activity of 24,24-difluoro-1,25-dihydroxyvitamin D3 was compared with 1,25-dihydroxyvitamin D3 in the rat. The 24,24-difluoro-1,25-dihydroxyvitamin D3 has a potency of approximately 5-10 times that of 1,25-dihydroxyvitamin D3 in the known in vivo vitamin D responsive systems. These systems include intestinal calcium transport, bone calcium mobilization, calcification of epiphyseal plate cartilage, and elevation of plasma calcium and phosphorus concentrations. Thus, 24,24-difluoro-1,25-dihydroxyvitamin D3 is the first known analogue with higher potency than 1,25-dihydroxyvitamin D3 in vivo.

Animals↗

PubMed1983

Glucocorticoids and appearance of 1,25-dihydroxyvitamin D3 receptor in rat intestine.

The ontogenesis of the 1,25-dihydroxyvitamin D3 specific binding activity in intestine was examined in vitamin D-deficient and replete rats. The absence of binding activity in intestines during the first two postnatal weeks was not influenced by vitamin D supplementation. The concentration of binding sites peaked on day 18 in vitamin D-replete rats and preceded that in the deficient group by approximately 1 wk. The influence of glucocorticoids on 1,25-dihydroxyvitamin D3-binding protein levels was examined by sequential hydrocortisone administration and adrenalectomy. Subcutaneous hydrocortisone administration before day 14 postpartum did not induce binding activity. The concentration of binding sites was significantly increased to 369 +/- 60 fmol/mg of protein by hydrocortisone injections from days 15 to 17 postpartum when compared with an average of 182 +/- 16 fmol/mg of protein in littermate controls. Hydrocortisone administration did not further increase receptor levels in rats injected from days 19 to 21. Bilateral adrenalectomy on day 17 postpartum significantly decreased the concentration of binding sites. It is concluded that adrenal glucocorticoids play an important role in the developmental appearance of 1,25-dihydroxyvitamin D3 specific binding activity in the postnatal rat intestine.

Adrenalectomy↗

PubMed1983

1- but not 24-hydroxylation of vitamin D is required for growth and reproduction in rats.

This study examines whether 1,25-dihydroxyvitamin D3 or 24,24-difluoro-25-hydroxyvitamin D3, an analogue of 25-hydroxyvitamin D3 blocked from undergoing 24-hydroxylation, can maintain normal growth and reproduction in the female rat. Vitamin D-deficient weanling rats were maintained from weaning through mating, pregnancy, and lactation with either 1,25-dihydroxyvitamin D3 (given by continuous subcutaneous infusion), 24,24-difluoro-25-hydroxyvitamin D3, 25-hydroxyvitamin D3, or vehicle. Body weight, plasma calcium levels, estrous cycling time, ability to give birth to live pups, litter weight, number of pups per litter, dam plasma calcium level during lactation, and pup growth to 9 wk of age were recorded. No striking differences were observed between the 25-hydroxyvitamin D3 groups and either the 1,25-dihydroxyvitamin D3 group or the 24,24-difluoro-25-hydroxyvitamin D3 group. However, significant differences in most parameters were observed between the vitamin D-deficient and metabolite- or analogue-dosed rats. The results demonstrate that 1,25-dihydroxyvitamin D3 and/or one of its metabolites is sufficient to maintain normal growth, development, and reproductive functions in the female rat. Because 24,24-difluoro-25-hydroxyvitamin D3 cannot be hydroxylated at C-24, the 24-hydroxylation of 25-hydroxyvitamin D3 is not essential for normal growth, development, and reproduction in the female rat.

Animals↗

PubMed1983

1- but not 24-hydroxylation of vitamin D is required for skeletal mineralization in rats.

To evaluate the importance of 1- and 24-hydroxylation of 25-hydroxyvitamin D3 on skeletal mineralization, male and female rats from vitamin D-deficient mothers were administered from weaning either 100 pmol/day of 25-hydroxyvitamin D3, 50 pmol/day of 1,25-dihydroxyvitamin D3, or 100 pmol/day of 24,24-difluoro-25-hydroxyvitamin D3 as their sole source of vitamin D. A separate group of rats did not receive any vitamin D. 1,25-Dihydroxyvitamin D3 was given by constant infusion at a dose that normalized plasma calcium concentrations and produced normal body weight gains. Skeletal mineralization was studied by determining femur organic and ash weights. Femurs were obtained from male rats 6 wk after weaning, from female rats at conception, at the end of lactation, and 6 wk after lactation, and from weanling pups born to the female rats. No striking differences in femur organic and ash weights were found between 25-hydroxyvitamin D3 groups and either the 1,25-dihydroxyvitamin D3 group or the 24,24-difluoro-25-hydroxyvitamin D3 group, whereas the vitamin D-deficient rats had poorly mineralized femurs. These results indicate that 1,25-dihydroxyvitamin D3 at a lower dose is as fully active as 25-hydroxyvitamin D3 in promoting skeletal mineralization in the rat and that preventing the 24-hydroxylation of 25-hydroxyvitamin D3 by administering 24,24-difluoro-25-hydroxyvitamin D3 does not elicit any obvious skeletal abnormality, especially on mineralization.

Aging↗

PubMed1983

Responsiveness of vitamin D-deficient fetal rat limb bones to parathyroid hormone in culture.

Radii and ulnae from 19-day fetal rats from normal or vitamin D-deficient mothers were treated with 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, or parathyroid hormone in vitro. Both sets of bones resorbed in response to all three agents. Statistical analysis indicated a purely additive model for the effects of vitamin D status and the bone-resorbing agents, with no evidence for interaction. The results suggest that the impaired calcemic response to parathyroid hormone seen in vitamin D-deficient animals in vivo is not the result of a specific unresponsiveness of vitamin D-deficient bone to parathyroid hormone.

Animals↗

PubMed1983

Stimulation of 24R,25-dihydroxyvitamin D3 synthesis by metabolites of vitamin D3.

Previously we have shown that the isolated perfused kidney from vitamin D-deficient rats converts [3H]25(OH)D3 into [3H]1 alpha,25(OH)2D3. When certain vitamin D metabolites were added to perfusate the same kidney began to synthesize [3H]24R,25(OH)2D3. In this study we investigated the structural requirements of the vitamin D molecule necessary to stimulate synthesis of [3H]24R,25(OH)2D3 in a 1-hydroxylating kidney. Kidneys were perfused with tracer [3H]25(OH)D3 (450 pM) alone and in the presence of a variety of hydroxylated metabolites and fluorinated analogues of vitamin D3 at concentrations of 450 pM to 25 microM. Tracer [3H]25(OH)D3 alone resulted in synthesis of only [3H]1 alpha,25(OH)2D3 during the 6-h perfusion period. 25-Hydroxylated metabolites [25(OH)D3, 25 nM; 1 alpha,25(OH)2D3, 25 nM; 24R,25(OH)2D3, 25 nM; 24(F)2,25(OH)D3, 50 nM] stimulated [3H]24R,25(OH)2D3 production at 2 h of perfusion. On the other hand, analogues without the 25-hydroxyl group [D3; 1 alpha(OH)D3; 25(F)D3; 1 alpha(OH),25(F)D3; 1 alpha(F)D3; 1 beta(F)D3]; did not stimulate [3H]24R,25(OH)2D3 synthesis. We conclude that the 25-hydroxyl group is an essential determinant of 24-hydroxylation.

24,25-Dihydroxyvitamin D 3↗

PubMed1983

Autoradiographic localization of 1,25-dihydroxyvitamin D3 in rat placenta and yolk sac.

After injection of 3H-1,25-(OH)-vitamin D3 into rats on days 18 and 20 of pregnancy, autoradiograms of placenta and fetal membranes show nuclear concentration of radioactivity in certain cells. This nuclear concentration is abolished when unlabeled 1,25-(OH)2-vitamin D3, but not 25-(OH)-vitamin D3, is injected prior to the labeled hormone. Nuclear labeling is observed in epithelial cells of visceral yolk sac and amnion, and in certain trophoblasts in basalis and labyrinth. The results suggest the presence of a specific receptor-like binding for 1,25-(OH)2-vitamin D3 and thus involvement of the target cells in calcium regulatory mechanisms during development.

Animals↗

PubMed1983

Target cells for 1,25-dihydroxyvitamin D3 in developing rat incisor teeth.

The concentration of radioactivity is observed in the nuclei of pulpal cells of maxillary and mandibular incisors of 20-day-old fetal rats, following injection of [3H]-1,25 (OH)2 vitamin D3. Cells in the odontoblast and ameloblast layers are essentially free of nuclear labeling. The radioactively labeled pulpal cells exist throughout the length of the incisors with the exception of the progenitor areas. The results indicate the presence of receptors for 1,25 (OH)2 vitamin D3 in pulpal cells, and suggest the effects of the hormone on these cells.

Ameloblasts↗

PubMed1983

Long-term influence of calcitriol (1,25-dihydroxyvitamin D) and supplemental phosphate in X-linked hypophosphatemic rickets.

Ten patients with hypophosphatemic rickets (eight with X-linked familial form) were treated with vitamin D2 (10,000 to 75,000 units per day) and oral phosphate (1.5 to 3.6 gm) for a total of 438 treatment months. Therapy was then changed to calcitriol (17 to 34 ng/kg/day) and the same phosphate dose. Patients served as their own controls, and significant biochemical changes noted were an increase in immunoreactive parathyroid hormone from 29 +/- 9 (SD) microliters Eq/ml (pre-phosphate) to 62 +/- 34 on vitamin D2 plus PO4, then decreasing to 40 +/- 20 on a regimen of 1,25-dihydroxyvitamin D (1,25(OH)2D) plus PO4; serum PO4 rose from 2.44 +/- 0.45 (SD) mg/100 ml to 3.06 +/- 0.79 and then to 3.43 +/- 0.76; alkaline phosphatase activity decreased from 677 +/- 298 (SD) IU/liter to 457 +/- 183 to 290 +/- 176. Serum calcium and creatinine levels were unchanged. Both urinary calcium excretion and calcium-creatinine ratio decreased after therapy with 1,25(OH)2D. Urinary phosphate excretion was higher after calcitriol administration. Serum 1,25(OH)2D levels were low in these vitamin D2-treated patients, and an inverse relationship between serum 25(OH)D and 1,25(OH)2D was found. Improved bone mineralization was evident from serial assessment by photon absorptiometry, and radial bone mineral content rose from 75.3% +/- 2.2% of expected to 82.2% +/- 1.4% (P less than .005). Stature was improved when assessed by standard deviation for chronologic age but did not reach statistical significance. Long-term 1,25(OH)2D plus phosphate therapy appears to be more efficacious than vitamin D2 in this form of rickets, particularly in improving phosphate homeostasis.

Adolescent↗

PubMed1983

Vitamin D metabolites in renal insufficiency and other vitamin D disorders of children.

Serum vitamin D metabolites were measured in relation to factors responsible for the synthesis of 1,25(OH)2D in children with renal disease and other disorders of vitamin D metabolism. Severe renal failure (CCr less than 15 ml/min/1.73 m2) was associated with a reduction in 1,25(OH)2D to 25% of mean normal levels, a very high PTH/1,25(OH)2D ratio of 75 (normal = 0.74), and a 60% reduction of serum 24,25(OH)2D. At CCr values between 15 and 50 ml/min 1.73 m2, 1,25(OH)2D was 50% of normal, despite a PTH/1,25(OH)2D ratio of 7 and a normal 24,25(OH)2D value. Above clearance values of 75 ml/min/1.73 m2, 1,25(OH)2D and the ratio were normal. Oral 1,25(OH)2D therapy in severe chronic renal insufficiency caused a fall in this ratio from 75 to 8. High PTH/1,25(OH)2D ratios were found in hypophosphatemic rickets and vitamin D-deficiency rickets, indicating reduced synthesis of 1,25(OH)2D relative to PTH. Low ratios were found in hypoparathyroidism and sarcoidosis, possibly indicating independence of PTH stimulation in 1,25(OH)2D production. The ratios of calcium/1,25(OH)2D and phosphate/1,25(OH)2D also provided useful information in each of these conditions, indicating that the use of such series of ratios in selected patients may promote a better understanding of pathogenic mechanisms and of the response to therapy.

Adolescent↗