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PubMed1977

Binding of 25-hydroxycholecalciferol in tissues.

Evidence is presented that the 5.8 S 25-hydroxycholecalciferol-binding protein found in the cytosols of all nucleated rat tissues is formed from two macromolecular substances: a heat-stable 4.1 S 25-hydroxycholecalciferol-binding protein which behaves identically with the serum 25-hydroxycholecalciferol-binding protein, and a cytosolic heat-labile protein which appears to sediment around 4 S and does not show binding properties for 25-hydroxycholecalciferol. The 5.8 S complex is formed in vitro by incubating cytosols with appropriate amounts of serum. The complex is dissociated by heating, leaving the serum 25-hydroxycholecalciferol-binding protein. Complex formation also occurred with serum 25-hydroxycholecalciferol-binding proteins from other species. The widespread occurrence of the 4 S cytosolic component raises the possibility that the high affinity binding proteins for 25-hydroxycholecalciferol observed in nucleated tissues are largely the result of plasma contamination.

Animals↗

PubMed2003

Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol.

BACKGROUND: The cholecalciferol inputs required to achieve or maintain any given serum 25-hydroxycholecalciferol concentration are not known, particularly within ranges comparable to the probable physiologic supply of the vitamin. OBJECTIVES: The objectives were to establish the quantitative relation between steady state cholecalciferol input and the resulting serum 25-hydroxycholecalciferol concentration and to estimate the proportion of the daily requirement during winter that is met by cholecalciferol reserves in body tissue stores. DESIGN: Cholecalciferol was administered daily in controlled oral doses labeled at 0, 25, 125, and 250 micro g cholecalciferol for approximately 20 wk during the winter to 67 men living in Omaha (41.2 degrees N latitude). The time course of serum 25-hydroxycholecalciferol concentration was measured at intervals over the course of treatment. RESULTS: From a mean baseline value of 70.3 nmol/L, equilibrium concentrations of serum 25-hydroxycholecalciferol changed during the winter months in direct proportion to the dose, with a slope of approximately 0.70 nmol/L for each additional 1 micro g cholecalciferol input. The calculated oral input required to sustain the serum 25-hydroxycholecalciferol concentration present before the study (ie, in the autumn) was 12.5 micro g (500 IU)/d, whereas the total amount from all sources (supplement, food, tissue stores) needed to sustain the starting 25-hydroxycholecalciferol concentration was estimated at approximately 96 micro g (approximately 3800 IU)/d. By difference, the tissue stores provided approximately 78-82 micro g/d. CONCLUSIONS: Healthy men seem to use 3000-5000 IU cholecalciferol/d, apparently meeting > 80% of their winter cholecalciferol need with cutaneously synthesized accumulations from solar sources during the preceding summer months. Current recommended vitamin D inputs are inadequate to maintain serum 25-hydroxycholecalciferol concentration in the absence of substantial cutaneous production of vitamin D.

Administration, Oral↗

PubMed2001

Effects of the combined use of calcitonin and 1 alpha-hydroxycholecalciferol on vertebral bone loss and bone turnover in women with postmenopausal osteopenia and osteoporosis: a prospective study of long-term and continuous administration with low dose calcitonin.

OBJECTIVES: The present study investigates the effect of long-term and continuous treatment with low dose calcitonin in combination with 1 alpha-hydroxycholecalciferol on vertebral bone mass in early postmenopausal women. METHODS: A total of 202 postmenopausal women between 53 and 58 years of age were recruited individually and randomly assigned to one of four groups. Comparisons were made among groups of women receiving calcitonin alone (10 IU i.m. twice a month), 1 alpha-hydroxycholecalciferol alone (0.5 microg orally twice daily), a combination of the above two agents, or no treatment. Bone mineral density (BMD) of lumber spine (L2-4) was determined using Dual Energy X-ray Absorptiometry. The study was carried out prospectively over a 2-year period. RESULTS: We observed a significant increase in vertebral bone mass in the combined treatment regimen of calcitonin and 1 alpha-hydroxycholecalciferol (3.44% at 12 months in the combination group vs 1.40,0.92, and -0.70% in the calcitonin alone, 1 alpha-hydroxycholecalciferol alone, and control groups, respectively; 4.51% at 24 months in the combination group vs 2.21,1.04, and -3.61% in the calcitonin alone, 1 alpha-hydroxycholecalciferol alone, and control groups, respectively). Serum PTH, osteocalcin levels and alkaline phosphatase activity decreased significantly within 12 months whereas urinary pyridinoline/creatinine ratio decreased at 24 months in the combination group. We observed mild adverse effects in 25.0% (7/28) and 30.0% (6/20) of combination regimen and calcitonin treatment cases, respectively. CONCLUSIONS: The results of the study suggest that the combination treatment regimen increased vertebral bone loss in early postmenopausal women to a greater extent than did calcitonin alone or 1 alpha-hydroxycholecalciferol alone.

Administration, Oral↗

PubMed2003

Prevention of postmenopausal bone loss with exchange for short-term HRT for 1alpha-hydroxycholecalciferol.

OBJECTIVE: The present study investigated bone turnover with exchange of hormone replacement therapy (HRT) by treatment with 1alpha-hydroxycholecalciferol in early postmenopausal women. METHODS: Subjects included a total of 75 postmenopausal women between 49 and 59 years of age who visited the Department of Obstetrics and Gynecology at Osaka Medical College Hospital for regular gynecological checkups and menopausal disorder, postmenopausal osteoporosis or hyperlipidemia, and were diagnosed with menopausal disorder or osteopenia. Changes in bone turnover and vertebral bone mineral density (BMD) in 28 patients who had undergone HRT; conjugated equine estrogen 0.625 mg daily and medroxyprogesterone acetate 2.5 mg daily) for at least 2 years and then switched to 1alpha-hydroxycholecalciferol (0.5 microg orally twice daily) and in 26 patients who were observed without drug administration after discontinuation of HRT were compared with those in 37 patients who continued HRT. BMD of the lumbar spine (L2-4) was determined using Dual Energy X-ray Absorptiometry. RESULTS: While we observed a significant decrease in vertebral bone mass in the HRT-no medication group at 12 months (P=0.049) and 18 months (P=0.013), there was no significant decrease in vertebral bone mass in either the continuous HRT group or the group with change of HRT to 1alpha-hydroxycholecalciferol. In the group with change of HRT to 1alpha-hydroxycholecalciferol, although urinary pyridinoline level increased significantly from the baseline level throughout the study period (P<0.05), serum propeptide of type-1 procollagen (P1CP) level also increased significantly from the baseline level throughout this period (P<0.001). Furthermore, significant increase from the baseline value (P<0.01) was observed in serum osteocalcin level at 6, 12 and 18 months. CONCLUSIONS: These results indicate that switching to 1alpha-hydroxycholecalciferol therapy after short-term HRT increased both bone resorption and bone formation, and permitted maintenance of increase in bone mass due to HRT for at least 18 months, though this switching accelerated bone turnover. This may have occurred because stimulation of bone formation induced by HRT was maintained by 1alpha-hydroxycholecalciferol, though bone turnover was slightly promoted because of withdrawal of HRT. This method was thus found to be very effective in preventing bone loss in patients who have discontinued HRT and are considered relatively contraindicated for use of estrogen.

Absorptiometry, Photon↗

PubMed1973

Biological activity of 1alpha-hydroxycholecalciferol, a synthetic analog of the hormonal form of vitamin D3.

1,25-Dihydroxycholecalciferol, the apparent active hormonal form of cholecalciferol (vitamin D(2)), is formed from cholecalciferol by specific and sequential hydroxylations of the sterol at carbons 25 and 1. Recently, 1alpha-hydroxycholecalciferol was synthesized and we report on its biological activity in rachitic chicks. 1alpha-Hydroxycholecalciferol is identical in potency to 1,25-dihydroxycholecalciferol in stimulation of intestinal calcium absorption; either sterol elicits a near maximal effect at a dose of 0.3-0.6 nmol. The time-course of action of 1alpha-hydroxycholecalciferol also parallels that of the active metabolite 1,25-dihydroxycholecalciferol with a maximal increase in calcium transport occurring 5-10 hr after administration of sterol to vitamin D-deficient chicks. 6.5 nmol of 1alpha-hydroxycholecalciferol causes a doubling in calcium absorption in only 2-3 hr, which is the most rapid physiologic response yet detected for a vitamin D-sterol. 1alpha-Hydroxycholecalciferol is active also in enhancing bone calcium resorption and, like 1,25-dihydroxycholecalciferol, is at least 10 times as active as cholecalciferol in mobilizing bone calcium and raising plasma calcium concentration. It is concluded that 1alpha-hydroxycholecalciferol represents a synthetic analog of 1,25-dihydroxycholecalciferol that can be used both to study the mechanism of action of this hormone and as a therapeutic agent in the treatment of patients with certain metabolic bone diseases.

Animals↗

PubMed1979

[Effect of 1 alpha-hydroxycholecalciferol on cellular calcium metabolism of kidney cortex (author's transl)].

Rats were provided a normal laboratory diet or a low Ca.vitamin D-deficient diet. After the administration of 1 alpha-hydroxycholecalciferol, mitochondria, microsomes and slices were prepared from kidney cortex of both control and treated rats. When 1 alpha-hydroxycholecalciferol was given to normal and low Ca.vitamin D-deficient rats, Ca accumulation in mitochondria was stimulated during 30 minutes and the high calcium content was maintained at the subsequent incubation. There was a significant decrease of mitochondrial Ca2+-ATPase and Mg2+-ATPase activities with low Ca.vitamin D depletion, but both enzyme activities were restored by 1 alpha-hydroxycholecalciferol treatment of the depleted rats. Ca2+-ATPase and Mg2+-ATPase activities of microsomes were not altered with the administration of 1 alha-hydroxycholecalciferol. In contrast to results of mitochondrial Ca transport, changes in Ca influx and efflux of slices were not significant in response to the treatment of low Ca.vitamin D-deficient rats with 1 alpha-hydroxycholecalciferol. The results of the present study suggest that 1 alpha-hydroxycholecalciferol plays a role in the process of Ca accumulation and ATP hydrolysis of mitochondria in kidney cortex.

Adenosine Triphosphatases↗

PubMed1987

Intestinal absorption of cholecalciferol and 25-hydroxycholecalciferol in chronic cholestatic liver disease.

We compared the absorption of cholecalciferol and 25-hydroxycholecalciferol in normal subjects and in patients with mild and severe cholestatic liver disease. 3H-cholecalciferol and 3H-25-hydroxycholecalciferol were given orally and serial blood samples were drawn for measurement of the serum level of radiolabeled vitamin. Absorption of 25-hydroxycholecalciferol peaked earlier and was greater than absorption of cholecalciferol at all times in all three groups. Patients with mild cholestasis (normal bilirubin and fecal fat excretion) absorbed both forms of the vitamin normally. Those with severe cholestasis (jaundice and steatorrhea) had minimal absorption of cholecalciferol but relatively preserved absorption of 25-hydroxycholecalciferol. Absorption of cholecalciferol and 25-hydroxycholecalciferol was inversely related to fecal fat excretion. The superior absorption of 25-hydroxycholecalciferol may partly explain its greater efficacy in oral treatment of vitamin D deficiency in patients with severe cholestasis.

Adult↗

PubMed1979

Pharmacokinetics and amounts of 25-hydroxycholecalciferol in sheep affected by osteodystrophy.

Amounts of 25-hydroxycholecalciferol in plasma were measured in two groups (A and B) of lambs (Experiment 1) and in two groups (C and D) of wethers (Experiment 2). Groups A (eight lambs) and C (nine wethers) consisted of animals born and raised in total confinement; these animals exhibited an osteodystrophic condition. Groups B (four lambs) and D (10 wethers) consisted of healthy animals born and raised in a conventional barn with free access to an open barn yard (i.e. exposure to sunshine). The 25-hydroxycholecalciferol in plasma of both groups of sick animals, Group A (12.9 ng/ml) and Group C (18.0 ng/ml), were lower than the amounts of the two corresponding groups of healthy animals. Group B (29.2 ng/ml and Group D (32.5 ng/ml). Pharmacokinetic analysis of 25-hydroxycholecalciferol in affected lambs following intramuscular injection of 1,000,000 IU vitamin D3 indicated that transport of vitamin D3 from the site of injection to the liver and its metabolism to 25-hydroxycholecalciferol were rapid. Peak 25-hydroxycholecalciferol occurred at .6 wk, and half-life was 3.1 wk.

Animals↗

PubMed1971

Inhibition of the metabolism of 25-hydroxycholecalciferol by actinomycin D and cycloheximide.

Actinomycin D (or cycloheximide) administered prior to radioactive 25-hydroxycholecalciferol blocks the metabolism of 25-hydroxycholecalciferol to polar metabolites that accumulate in intestinal tissue, while it does not prevent the 25-hydroxylation of vitamin D(3) in the liver. Actinomycin D given after radioactive 25-hydroxycholecalciferol does not inhibit 25-hydroxycholecalciferol metabolism. These results indicate that 25-hydroxycholecalciferol must interact with the nuclei of cells to bring about the production of an enzyme(s) that converts it to its polar metabolites.

Animals↗

PubMed1991

Intestinal absorption of cholecalciferol and 25-hydroxycholecalciferol in patients with both Crohn's disease and intestinal resection.

We compared the intestinal absorption of cholecalciferol and 25-hydroxycholecalciferol in patients with Crohn's disease and resections of the small bowel. Patients were subgrouped into those with small (less than 100 cm), intermediate (100-300 cm), and large (greater than 300 cm) resections. [3H]cholecalciferol or [3H]25-hydroxycholecalciferol were given orally and serial blood samples were taken for measurement of plasma radiolabeled vitamin. Absorption of both forms of the vitamin decreased with extent of resection but 25-hydroxycholecalciferol absorption was always greater than that of cholecalciferol. When compared with normal control subjects, 25-hydroxycholecalciferol absorption in these patients was better maintained than that of cholecalciferol. These data indicate that vitamin D malabsorption reflects the extent of distal small-bowel resection in Crohn's disease. Treatment with oral cholecalciferol is sufficient in those with small or moderate resections but oral 25-hydroxycholecalciferol supplementation may be preferred in those with a severe short-bowel syndrome.

Absorption↗

PubMed1973

The transporting proteins of cholecalciferol and 25-hydroxycholecalciferol in serum of chicks and other species. Partial purification and characterization of the chick proteins.

Chick serum contains two cholecalciferol-binding proteins, one of which binds mainly cholecalciferol (cholecalciferol-binding protein) and the other binds 25-hydroxycholecalciferol (25-hydroxycholecalciferol-binding protein). By means of Cohn fractionation, (NH(4))(2)SO(4) precipitation, gel filtration on Sephadex G-200, ion-exchange chromatography on DEAE-Sephadex and an additional gel-filtration step on Sephadex G-100, these two binding proteins were purified. Both proteins possess beta-globulin mobility on analytical polyacrylamide-disc-gel electrophoresis, a sedimentation coefficient of 3.5S and approximate molecular weights of 60000 for the cholecalciferol-binding protein and 54000 for the 25-hydroxycholecalciferol-binding protein. Sera obtained from rat, pig, human and monkey were shown to contain a single binding protein that is responsible for the transport of both cholecalciferol and 25-hydroxycholecalciferol. In the toad the lipoproteins are used for the transport of these two steroids.

Ammonium Sulfate↗

PubMed1978

Effect of oestrogen and 1,25-dihydroxycholecalciferol on 25-hydroxycholecalciferol metabolism in primary chick kidney-cell cultures.

Primary cultures of chick kidney cells convert 25-hydroxycholecalciferol into more-polar metabolites. Cells from vitamin D-deficient chicks have high 25-hydroxycholecalciferol 1 alpha-hydroxylase (1 alpha-hydroxylase) activity, but no 25-hydroxycholecalciferol 24-hydroxylase (24-hydroxylase) activity. Physiological concentrations of 1,25-dihydroxycholeclaciferol suppress 1 alpha-hydroxylase and induce 24-hydroxylase activity. The inhibition of 1 alpha-hydroxylase preceded the induction of 24-hydroxylase. In contrast, oestradiol-17 beta had no effect on the activity of either hydroxylase under a variety of experimental conditions. These results clearly demonstrate that 1,25-dihydroxycholecalciferol, but not oestrogen, acts directly on the kidney cells to regulate the metabolism of 25-hydroxycholecalciferol.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed1972

25-Hydroxycholecalciferol. A comparative study in deficiency rickets and different types of resistant rickets.

The effects of 25-hydroxycholecalciferol were studied in 4 children with deficiency rickets and 22 children with D-resistant rickets, including patients with hereditary hypophosphatemic D-resistant rickets, "pseudo-deficiency" rickets, and rickets secondary to cystinosis or to tyrosinosis. Three protocols were used. (a) 8 days after a single oral dose of 16,000 IU of 25-hydroxycholecalciferol, normalization of all biological parameters was observed in all cases of deficiency rickets. A complete lack of response was observed in the different types of resistant rickets. (b) Under prolonged administration of 2,640 IU/day for 2 months, clinical-biological symptoms and X-ray lesions disappeared, and a catch-up growth pattern was observed in deficiency rickets; no relapse of rickets occurred up to 5 months after therapy was stopped. The same dose had no significant effect in 10 patients with hereditary hypophosphatemic D-resistant rickets. A bone biopsy performed in one case showed the persistence of characteristic lesions. (c) With increasing doses of 25-hydroxycholecalciferol varying from 6,000 to 30,000 IU/day and a follow-up of 6 months up to 2 yr duration, clinical-biological-radiologic recovery and catch-up growht was obtained in all cases of "pseudo-deficiency" rickets. In hypophosphatemic hereditary D-resistant rickets, 5 out of 13 patients' serum concentration of phosphorus reached at least 30 mg/liter, but a catch-up growth pattern was not observed. These results indicate that (a) 25-hydroxycholecalciferol is highly active in deficiency rickets; (b) a defect in the conversion of vitamin D(3) to its active 25-hydroxy metabolite is probably not the metabolic defect in any of the different types of vitamin D-resistant rickets studied.

Administration, Oral↗

PubMed1976

Human serum binding capacity and affinity for 25-hydroxyergocalciferol and 25-hydroxycholecalciferol.

25-Hydroxyvitamin D-binding capacity and affinity were studied in human cord, adult, and maternal sera, and in sera from women receiving oral contraceptives, by in vitro satuaration analyses employing dextran-coated charcoal to adsorb unbound sterol. 25-Hydroxyergocalciferol and 25-hydroxycholecalciferol were equipotent in their ability to displace 3H 25-hydroxycholecalciferol from human serum binding sites. At 0C, the apparent dissociation constant for the serum binding of 25-hydroxycholecalciferol was low (Kd=8x 10-10M). Cord and adult sera had a similar 25-hydroxycholecalciferol binding capacity (1.8 x 10-6M), but the binding capacity of maternal sera and the sera from women receiving oral contraceptives was significantly higher. At physiological serum concentrations of 25-hydroxyvitamin D (5 x 10-8M), only 2-3% of human serum 25-hydroxyvitamin D-bindig sites are occupied.

Adult↗

PubMed1990

Identification of 8 alpha,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3-one as a product of metabolism of 25-hydroxycholecalciferol by liver microsomes.

The ability of liver microsomes, sites of synthesis of 25-hydroxycholecalciferol, to further metabolize 25-hydroxycholecalciferol has been assessed. When liver microsomes were incubated with 25-hydroxycholecalciferol in the presence of cytosol, a metabolite was isolated that comigrated with 8 alpha,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3- one in three different chromatographic systems. The ultraviolet spectrum (220-350 nm) and mass spectrum of the purified metabolite were identical to that of synthetic 8 alpha,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3-one. This study indicates that liver microsomes convert 25-hydroxycholecalciferol to 8 alpha,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3-one. The significance of this metabolite, which has been shown previously by others to be produced by alveolar macrophages, has yet to be determined.

Animals↗

PubMed1992

22-oxacalcitriol suppresses 25-hydroxycholecalciferol-1 alpha-hydroxylase in rat kidney.

22-oxacalcitriol can decrease the serum level of 1,25-dihydroxycholecalciferol by increasing its metabolic clearance rate and decreasing its production rate. To determine whether 22-oxacalcitriol suppressed the renal 25-hydroxycholecalciferol-1 alpha- hydroxylase we treated rats with 200 ng of 22-oxacalcitriol daily for 1 week. Enzyme activity was measured in vitro by measurement of production of 1,25-dihydroxycholecalciferol by renal slices incubated with 25-hydroxycholecalciferol. 22-oxacalcitriol significantly decreased the 25-hydroxycholecalciferol-1 alpha-hydroxylase activity from 797 +/- 208 pg of 1,25-dihydroxycholecalciferol/g of kidney/h in the control group to 257 +/- 150 pg of 1,25-dihydroxycholecalciferol/g of kidney/h (p less than 0.05). This is the first demonstration of suppression of the renal 25-hydroxycholecalciferol-1 alpha-hydroxylase by the vitamin D3 analog, 22-oxacalcitriol.

Animals↗

PubMed2004

Effect of casein phosphopeptide and 25-hydroxycholecalciferol on tibial dyschondroplasia in growing broiler chickens.

1. An experiment was conducted to investigate the influence of dietary casein phosphopeptides and 25-hydroxycholecalciferol on the incidence of tibial dyschondroplasia (TD) in 14-d-old commercial broiler chickens. 2. Three hundred and twenty broiler chicks (one day old) were randomly allocated to one of 4 dietary treatments. A standard broiler diet was used as the control with the three experimental treatments receiving the control diet supplemented with 10 g casein phosphopeptide/kg, 14 g casein phosphopeptide/kg or 69 microg 25-hydroxycholecalciferol/kg. 3. Those birds fed the diets supplemented with 14g casein phosphopeptide/kg or 25-hydroxycholecalciferol had a lower incidence of TD than both the control and 10g casein phosphopeptide/kg treatments when assessed grossly. 4. The body weight of birds fed the 10 g casein phosphopeptide/kg diet or the 25-hydroxycholecalciferol diet was higher than birds fed the control diet. Although not significant, the body weight of birds fed the 14 g casein phosphopeptide/kg diet was also greater than the control birds. 5. The current experiment demonstrated that both casein phosphopeptide and 25-hydroxycholecalciferol can reduce the incidence of TD in the young broiler chicken. More research is required to explain the unexpected increase in body weight described above.

Animal Feed↗

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↗