Relative effectiveness of vitamin D metabolites in increasing bone mineral solubility

Summary Weanling rats were given a vitamin D-deficient diet containing 1.4% calcium and 1.0% phosphorus. After 4 weeks these deficient animals were injected for 7 days with selected doses of one of the following vitamin D metabolites: 25(OH)D₃, 1,25(OH)₂D₃, 24,25(OH)₂D₃, 25,26(OH)₂D₃ or the ethanol vehicle. A vitamin D-replete group was placed on the same diet but injected with 50 IU of vitamin D₃ once a week for the entire 5-week period. By the use of a modified Ussing chamber [1], the measurements of calcium fluxes into and from the rat calvaria were possible. These data enabled the apparent mineral solubilities to be derived. After 5 weeks on this diet the vitamin D-deficient rats had low levels of serum calcium (1.41 mM) and decreased mineral solubility when compared to the vitamin D-replete group. The apparent solubility of the bone mineral increased toward the vitamin D-replete level in calvaria from vitamin D metabolite-treated rats. However, these changes did not directly reflect the alterations in the level of serum calcium. At any given dose level, 1,25(OH)₂D₃ was the most effective metabolite in increasing serum calcium. In fact, the high dose (250 pmoles/day) was hypercalcemic. Next in effectiveness was 25(OH)D₃. These two metabolites were equally effective in increasing mineral solubility. At a 10 times higher dose, the 24,25(OH)₂D₃ metabolite was able to normalize serum calcium and improve but not normalize mineral solubility. At the high dose (260 pmoles/day), the 25,26(OH)₂D₃ metabolite caused no effect on mineral solubility and minimal increases in serum calcium.     

The role of vitamin D metabolites in bone resorption

Two metabolites of vitamin D₃, 25-hydroxycholecalciferol (25-OHD₃) and 1,25-dihydroxy-cholecalciferol (1,25-(OH)₂D₃) are potent stimulators of bone resorption in two test systems whereas vitamin D₃ itself is inactive. These substances were tested (a) by directly comparing their action on bone explants of mouse half-calvariain vitro, and (b) by injecting them into young mice and measuring the degree of resorptionin vitro when explants were made 18 hours atter the injection. In both tests the 1,25-metabolite was about 100 times more potent than 25-OHD₃. The dose-response curve for 1,25-(OH)₂D₃ indicates that doses above about 0.2 ng/g body weight are capable of inducing an increase in bone resorption in normal young mice. These data show that 1,25-(OH)₂D₃ is one of the most potent substances known that affects bone metabolism. The results are discussed in relation to the possible role of 1,25-(OH)₂D₃ in the normal mobilization of calcium from bone.

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Zusammenfassung Bei Anwendung zweier verschiedener Versuchsanordnungen konnte gezeigt werden, daß die beiden Vitamin D₃-Metaboliten 25-Hydroxycholecalciferol (25-OHD₃) und 1,25-Dihydroxycholecalciferol (1,25-(OH)₂D₃) als starke Stimulatoren der Knochenresorption wirken, während sich Vitamin D₃ selbst inaktiv verhält. Diese Substanzen wurden folgendermaßen geprüft: a) durch direkten Vergleich ihrer Wirkung auf Knochenexplantate (Hälften von Mäusecalvarien)in vitro und b) indem die Metaboliten jungen Mäusen injiziert wurden und der Resorptionsgrad an Explantaten 18 Std nach Injektionin vitro gemessen wurde. Bei beiden Versuchsanordnungen war der 1,25-Metabolit etwa 100mal wirksamer als der 25-OHD₃-Metabolit. Aus der Dosiswirkungskurve für 1,25-(OH)₂D₃ geht hervor, daß es möglich ist, mit Dosen über ca. 0,2 ng/g Körpergewicht bei normalen jungen Mäusen bereits eine erhöhte Knochenresorption auszulösen. Diese Resultate zeigen, daß 1,25-(OH)₂D₃ eine der wirksamsten bisher bekannten Substanzen ist, die auf den Knochenmetabolismus einwirken können. Die Ergebnisse werden im Zusammenhang mit der Rolle, die das 1,25-(OH)₂D₃ bei der normalen Freisetzung von Calcium aus dem Knochen spielt, besprochen.

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Résumé Deux métabolites de la vitamine D₃, le 25-hydroxycholecalciferol (25-OHD₃) et 1,25-dihydroxycholecalciferol (1,25-(OH)₂D₃), stimulent la résorption osseuse dans deux systèmestests alors que la vitamine D₃ est inactive. Ces substances sont testées a) en comparant directement leur action dans les explants osseux de calottes craniennes de sourisin vitro et b) en les injectant dans de jeunes souris et en mesurant le degré de résorptionin vitro, lorsque les explants sont réalisés 18 heures après l'injection. Dans les deux tests, le métabolite 1,25 est environ 100 fois plus puissant que 25-OHD₃. La courbe dose-résponse de 1,25-(OH)₂D₃ indique que des doses au-dessus d'environ 0.2 ng/g de poids corporel sont capables d'induire une augmentation de la résorption osseuse chez de jeunes souris normales. Ces résultats montrent que 1,25-(OH)₂D₃ est une des substances connues les plus actives qui agit sur le métabolisme osseux. Le rôle possible de 1,25-(OH)₂D₃ sur la mobilisation normale du calcium osseux est envisagé.

     

The effect of short-term treatment with vitamin D metabolites on bone lipid and mineral composition in healing vitamin D-deficient rats

Vitamin D deficiency is known to cause alterations in the lipid and mineral components of bone and cartilage. In this study, second generation, normal phosphatemic, vitamin D-deficient rats, treated with low and high doses of three different vitamin D metabolites were sacrificed 24 h after treatment and their bones analyzed in order to determine which metabolites were most effective in altering the lipid composition. In the untreated vitamin D-deficient rats, tissues undergoing endochondral ossification (epimetaphyses), periosteal and endosteal bone formation (diaphyseal bone), and intramembranous bone formation (calvaria) all contained lower amounts of complexed acidic phospholipids, as well as decreased amounts of mineral. Twenty-four hours following treatment, the complexed acidic phospholipid content was significantly increased relative to both untreated and normal (vitamin D-replete) animals, the greatest increases occurring in animals treated with 1,25-dihydroxyvitamin D. All metabolites tested altered histomorphometric and/or mineral parameters, but only 1,25-dihydroxyvitamin D, in low and high doses, significantly increased the content of the complexed acidic phospholipids in all tissues studied. High doses of other metabolites increased complexed acidic phospholipid content in some tissues, perhaps due to their conversion to 1,25-dihydroxyvitamin D. Linear relationships between serum 1,25-dihydroxyvitamin D levels and tissue complexed acidic phospholipid content are reported. It is suggested that one way in which this metabolite may directly contribute to calcification is by facilitating formation of lipids involved in this process.     

Longitudinal study of vitamin D metabolites after long bone fracture

Animal models suggest a key role for dihydroxylated vitamin D metabolites in fracture healing, as evidenced by increases in serum concentration of 24R,25‐dihydroxyvitamin D (24R,25[OH]₂D) after long bone fracture. Human studies investigating the kinetics of serum concentrations of 24R,25[OH]₂D, 1,25‐dihydroxyvitamin D (1,25[OH]₂D) and their parent metabolite 25‐hydroxyvitamin D (25[OH]D) are lacking. We, therefore, conducted a longitudinal study to determine whether total, free, or bioavailable concentrations of these vitamin D metabolites fluctuate in humans after long bone fracture. Twenty‐eight patients with cross‐shaft (diaphyseal) long bone fracture presenting to an emergency department in London, UK, were studied. Serum concentrations of 25(OH)D, 24R,25(OH)₂D, 1,25(OH)₂D, vitamin D binding protein, albumin, and calcium were determined within 48 hours of fracture and again at 1 and 6 weeks postfracture. Concentrations of free and bioavailable vitamin D metabolites were calculated using standard equations. No changes in mean serum concentrations of 25(OH)D or 24R,25(OH)₂D were seen at either follow‐up time point versus baseline. In contrast, mean serum 1,25(OH)₂D concentration declined by 21% over the course of the study, from 68.5 pmol/L at baseline to 54.1 pmol/L at 6 weeks (p < 0.05). This decline was associated with an increase in mean serum corrected calcium concentration, from 2.32 mmol/L at baseline to 2.40 mmol/L at 1 week (p < 0.001) that was maintained at 6 weeks. No changes in free or bioavailable concentrations of any vitamin D metabolite investigated were seen over the course of the study. We conclude that serum 1,25(OH)₂D concentration declines after long bone fracture in humans but that the serum 24R,25(OH)₂D concentration does not fluctuate. The latter finding contrasts with those of animal models reporting increases in serum 24R,25(OH)₂D concentration after long bone fracture.     

Changes in bone mineral parameters,vitamin D metabolites,and PTH measurements with varying chronic kidney disease stages

Vitamin D deficiency is associated with an increased risk of many diseases (skeletal and nonskeletal). Emerging data also associate high concentrations of serum parathyroid hormone (PTH) with morbidity and increased mortality in patients both with and without known chronic kidney disease (CKD). Understanding the relationship between vitamin D and PTH and the determinants of PTH is therefore important. We performed a cross-sectional study of 203 patients with varying stages of CKD randomly recruited from the Renal Unit database at our institution. Detailed case review was performed, and samples of fasting blood were taken for biochemical analyses. We measured standard biochemistry, 25-hydroxyvitamin D (25-OHD), 1,25-OHD, and three PTH measurements [1–84 PTH, total PTH, and derived N-terminal truncated, 7–84 PTH (cPTH)]. Vitamin D deficiency was high, with 86% of patients having 25-OHD levels below 30 ng/ml. Estimated glomerular filtration rate (eGFR) was not associated with 25-OHD levels, whereas 1,25-OHD was lower in those with CKD stage 5 versus stage 4, who were not treated with vitamin D metabolites (18 vs. 65 pg/ml, respectively; P < 0.05). All three PTH measurements increased with worsening eGFR, with this finding being more pronounced in those patients who were not treated with vitamin D metabolites. The slope of the regression line of cPTH on eGFR tended to be steeper, –0.90, compared to –0.81 for total PTH and –0.80 for 1–84 PTH (P = 0.06). The ratio of total PTH to cPTH did decrease significantly through the range of CKD stages (P = 0.03). The determinants of PTH were similar for all three PTH measurements, with eGFR having a strong inverse relationship, with weaker relationships for 25-OHD and ionized calcium on multivariate analyses. We confirm that there is a complex relationship between 25-OHD, eGFR, and PTH. Total PTH, 1–84 PTH, and cPTH increase with increasing CKD stages, with a relatively greater increase in cPTH, although the clinical significance of this finding remains uncertain. The three PTH measurements had similar correlations with the biochemical and clinical variables studied, suggesting that either total PTH or 1–84 PTH can be used in clinical practice when evaluating vitamin D and PTH status.     

Effects on bone mineral density of calcium and vitamin D supplementation in elderly women with vitamin D deficiency

OBJECTIVE: Calcium and vitamin D deficiency is common in older individuals, particularly those who live in nursing homes, and increases the risk of osteoporosis and fractures. METHODS: We conducted a randomized double-blind placebo-controlled study of combined supplementation with 500 mg of elemental calcium, as carbonate, and 400 IU of vitamin D bid for 12 months in women older than 65 years of age with vitamin D deficiency, defined as serum 25(OH)D concentrations 相似文献   

Effects of vitamin D3 metabolites on bone cell calcium transport

Summary The vitamin D₃ metabolite, 25-hydroxycholecalciferol, at concentrations of 0.01 to 10.0 g/ml, decreased calcium uptake by isolated bone cells. The effect occurred within 1 min after the simultaneous addition of metabolite and⁴⁵Ca. Lactic acid and ATP production by the cells was not affected. 24(R), 25-dihydroxycholecalciferol produced a similar decrease in calcium uptake. Vitamin D₃ had no effect at concentrations from 0.01 to 10.0 g/ml. No effect of 1,25-dihydroxycholecalciferol on calcium uptake was observed with concentrations from 0.1 to 100 ng/ml and various preincubation periods extending to 2 h. None of the agents had any effect on calcium efflux. The effects of 25-hydroxycholecalciferol and 24(R), 25-dihydroxycholecalciferol on calcium uptake were not seen in isolated fetal rat skin cell preparations.     

Association between vitamin D and bone mineral density in Iranian postmenopausal women

The role of vitamin-D in determining bone mineral density (BMD), especially in less severe vitamin D deficiency, is still unclear. To investigate the possible association between 25-hydroxyvitamin D [25(OH)D] and BMD, 245 healthy free-living postmenopausal women, aged between 40 and 80, were randomly selected from participants of a population-based study. BMD was measured at the lumbar spine and hip by dual X-ray absorptiometry (Lunar DPXMD 7164). Serum 25(OH)D, parathyroid hormone (PTH), calcium, phosphorus, total and bone alkaline phosphatases, and urine deoxypyridinoline were measured. PTH was logarithmically transformed (LnPTH). Linear regression models were developed to determine the association between serum 25(OH)D and BMD at different sites. Means of age and duration of menopause were 57.7 +/- 7 and 9.4 +/- 6.8 years, respectively. Mean 25(OH)D was 73.0 +/- 62.3 nmol/l; 5.3% (n = 13) had 25(OH)D < 25 nmol/l and 37.6% (n = 92) had 25(OH)D between 25 and 50 nmol/l. Eleven percent of the women (n = 27) were osteoporotic in femoral neck and 25.3% of them (n = 62) were osteoporotic in lumbar spine sites. 25(OH)D correlated inversely with LnPTH (r = -0.25, P < 0.01). In the multivariate analyses, no association was found between 25(OH)D and BMD at any of the skeletal sites after adjusting for age, duration of menopause, body mass index, calcium, and LnPTH. However, BMD was associated inversely with LnPTH only in femoral neck but not in the other sites. This study did not show any association between 25(OH)D and BMD in free-living Iranian postmenopausal women.     

The influence of dihydroxylated vitamin D metabolites on bone formation in the chick

Summary The ability of 1,25(OH)₂D₃ and of 24,25(OH)₂D₃ to prevent or to heal rickets in chicks was evaluated by studies of plasma biochemistry, growth plate histology, bone morphometry and microradiography, and bone mineralization. 1,25(OH)₂D₃ at a dose of 100 ng/day produced fewest abnormalities compared with vitamin D₃-treated control chicks. Bone growth was slightly greater than vitamin D₃-treated controls in chicks given a lower dose of this metabolite; the reverse was observed in chicks given a higher dose. 24,25(OH)₂D₃ was less effective than 1,25(OH)₂D₃ in preventing rickets even at doses as high as 400 ng/day. Treatment of rachitic chicks with doses of 24,25(OH)₂D₃ up to 300 ng/day produced no healing effect on the bone lesions, in marked contrast to the beneficial effects observed with 1,25(OH)₂D₃.     

Effects of vitamin D metabolites and analogs on bone collagen synthesis in vitro

Summary The effects of selected vitamin D₃ metabolites and analogs on bone collagen synthesis in vitro were examined in organ cultures of neonatal mouse calvarial bone. The incorporation of [³H]proline into the collagenase-digestible fraction of newly synthesized protein was progressively inhibited by 1α,25-dihydroxyvitamin D₃ (1α,25-(OH)₂D₃) (10⁻¹² M to 10⁻⁷ M) in 24-h cultures, and incorporation into noncollagen protein was also blunted at the higher doses employed. The synthetic analog 1α-hydroxyvitamin D₃ (1α-OHD₃) was almost 300-fold less potent an inhibitor of collagen synthesis than was 1α,25(OH)₂D₃, and the natural metabolites 25-hydroxyvitamin D₃ (25OHD₃) and 24R,25-dihydroxyvitamin D₃ (24R,25(OH)₂D₃), 1000-fold less potent, although the dose-response curve for each of these compounds was not parallel with that for 1α,25(OH)₂D₃. The 24S,25(OH)₂D₃ enantiomer was four-fold less potent than 24R,25-(OH)₂D₃ or 25OHD₃, and vitamin D₃ showed less than 2% the activity of 25OHD₃. The responses were unaffected by the substitution of 0.4% bovine albumin for 5% horse serum in the medium, and no stimulation of collagen synthesis was observed in response to 25-hydroxylated metabolites between 2×10⁻¹⁴ and 2×10⁻⁶ M or in cultures treated for up to 96 h with 24R,25(OH)₂D₃ (2×10⁻¹⁰M). The overall results emphasize the similarity of the structural requirements for the inhibition of matrix synthesis and the stimulation of resorption by active vitamin D metabolites in bone. In addition, these studies support the importance of the 1-hydroxyl function to the biologic activity of vitamin D in the skeleton.     

Effects of vitamin D insufficiency on bone mineral density in African American men

Summary  In African American men serum, 25-hydroxyvitamin D (25-OHD) was below 30 ng/ml in 89% of subjects. In overall group, there was no correlation between 25-OHD and bone mineral density (BMD). A subgroup analysis of subjects with 25-OHD ≤15 ng/ml showed that serum 25-OHD was positively associated with BMD. Introduction  This study examined the effects of low serum 25-hydroxyvitamin D (25-OHD) on bone mineral density (BMD) in African American (AA) men from the general medicine clinic at an inner city Veteran Administration medical center. Methods  The data for 112 AA males who had both 25-OHD levels and BMD of spine and hip were extracted and analyzed using SAS software. Results  AA men were aged 38 to 85 years, with mean age of 62 years. Levels of 25-OHD ranged from 4 to 45 ng/ml, with mean 17.5 ng/ml, 24% and 89% of the subjects had 25-OHD below 10 and 30 ng/ml, respectively. In the overall group, there was no correlation between 25-OHD and BMD at any site. In a subgroup analysis of subjects with 25-OHD ≤15 ng/ml, in multiple adjusted models, 25-OHD was positively associated with BMD of spine (r = 0.26, p = 0.05), total hip (r = 0.27, p < 0.05), ward’s triangle (r = 0.25, p = 0.05), and trochanter (r = 0.30, p < 0.05). Conclusions  The negative effect of vitamin D insufficiency on bone was observed only at very low levels of 25-OHD, suggesting that AA male skeleton is relatively resistant to the effects of secondary hyperparathyroidism.     

Serum and bone vitamin D metabolites in elective patients and patients after fracture

Vitamin D metabolite levels were measured in serum and bone samples obtained from 27 patients undergoing elective bony procedures and from 28 patients operated on after a fracture. Serum 25 hydroxyvitamin D3 (25-OH-D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) did not differ significantly between the elective and fracture patients, but serum 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) was significantly reduced in the fracture patients. Very little 25-OH-D3 was found in bone, although it was the major vitamin D metabolite in serum (90%). In elective patients bone levels of 24,25(OH)2D3 and 1,25(OH)2D3 were similar to those in serum; however, in bone from around pertrochanteric fractures, but not from subcapital or patellar fractures, the concentrations of these compounds were considerably increased. These findings may shed light on the mechanism of callus formation and on the role of vitamin D metabolites in bone healing.     

Strong relationship between vitamin D status and bone mineral density in anorexia nervosa

BackgroundAnorexia nervosa (AN) is associated with impaired bone health and low bone mineral density (BMD) as a consequence of an inadequate peak bone mass in adolescence and bone loss in young adulthood. The vitamin D status with its implications for bone health in patients affected by AN has only been examined previously in small studies.ObjectiveTo evaluate the prevalence of vitamin D deficiency and test the hypothesis that patients with AN and vitamin D deficiency might have worse bone metabolism and lower bone density as compared with AN with adequate vitamin D repletion.DesignWe analysed the vitamin D status and bone metabolism in a large cohort (n = 89) of untreated patients affected by AN, with amenorrhoea.ResultsVitamin D deficiency is widespread in untreated patients with AN: 16.9% had 25OH vitamin D levels below 12 ng/ml, 36% below 20 ng/ml and 58.4% below 30 ng/ml. PTH values were higher and BMD at both femoral sites were lower in patients with vitamin D < 20 ng/ml. Progressively higher values of BMD were observed by 4 ranks of 25 OH vitamin D values (severe deficiency: < 12 ng/ml, deficiency: ≥ 12 ng/ml and < 20 ng/ml, insufficiency: ≥ 20 and < 30 ng/ml and normal: ≥ 30 ng/ml). In patients with severe vitamin D deficiency BMD at the hip were significantly lower than that measured in groups with values over 20 ng/ml (p < 0.001 for trend). The level of significance did not change for values adjusted for BMI or body weight.ConclusionWe found a strong relationship between vitamin D status and hip BMD values with additional benefits for those with 25OHD levels above 20 ng/ml. Our results support the design of a randomized placebo-controlled clinical trial on the effect of vitamin D on BMD in patients with AN. The second point, whether 25OHD should be above 20 or 30 ng/ml remains a discussion point.     

Serum vitamin D metabolites are not related to growth rate,bone mineral content,or serum alkaline phosphatase in male puberty

Summary Twenty boys were followed during their puberty for about 2 years with examinations every third month. At each examination we determined serum concentrations of 25OHD₃, 1,25(OH)₂D₃, 24,25(OH)₂D₃, 25.26(OH)₂D₃,alkaline phosphatase (AP) and testosterone together with bone mineral content (BMC) at the distal forearm. Highly significant increases in both BMC (P<0.001), serum AP (P<0.001), and peak height velocity (PHV) followed the increase in serum testosterone. The boys were grouped according to time of maximal increase in BMC, AP, and PHV. The serum levels of the vitamin D metabolites were related to these points. No significant changes in any of the serum vitamin D metabolites were found. Thus vitamin D metabolism does not seem to be significantly influenced during the period of life when both the linear growth and bone mineralization is maximal.     

维生素D受体基因型与骨密度

目的考察维生素D受体(VDR)基因多态性在我国汉族人群中的分布频率,分析VDR基因型与骨密度的关系.方法采用聚合酶链反应和限制性酶切技术检测100例绝经前健康妇女VDR基因多态性.应用双能X线骨密度仪检测受试者腰椎及髋部骨密度.结果VDR基因型分布频率为BB型4.0%,Bb型10.0%,bb型86.0%;而三种基因型受试者髋部及腰椎骨密度均表现出Bb＞bb＞BB,经F检验腰椎骨密度3基因型比较,P＜0.05,具有显著差异.结论绝经前妇女VDR基因型分布频率与西方及国内的一些报道不尽相同,且骨密度显示出Bb＞bb＞BB,亦与国内外一些研究结果不同.