Regulation of matrix vesicle metabolism by vitamin D metabolites

Matrix vesicles are membrane organelles found in the extracellular matrix of calcifying cells. Vitamin D-responsive alkaline phosphatase specific activity has been localized to matrix vesicles in chondrocyte and osteoblast cultures. The effect of hormone is both metabolite and cell specific. Alkaline phosphatase in matrix vesicles produced by resting zone chondrocytes is stimulated by 24,25(OH)2D3 whereas alkaline phosphatase in matrix vesicles produced by growth zone chondrocytes is responsive to 1,25(OH)2D3. However, mesenchymal cell cultures, which exhibit a chondrogenic phenotype when exposed to bone inductive proteins in vitro, produce vesicles with alkaline phosphatase activity that is unaffected by either 1,25(OH)2D3 or 24,25(OH)2D3. Incorporation and release of arachidonic acid into phosphatidylethanolamine is also differentially regulated by 1,25(OH)2D3 and 24,25(OH)2D3 in chondrocytes. These data suggest that vitamin D metabolites may regulate endochondral ossification by altering matrix vesicle enzyme activities, perhaps through changes in membrane phospholipid metabolism.     

Evidence of functional vitamin D receptors in rat hippocampus

The steroid hormone vitamin D has important biological roles in calcium transport, cell growth, and cell differentiation. Its cellular activities are mediated by high affinity interaction with the vitamin D receptor. In brain, autoradiographic, immunohistologic, and messenger RNA expression studies implicate a number of neuronal systems, including the hippocampus, as potential targets of vitamin D. However, cellular distribution and protein expression, and binding of the receptor to vitamin D response elements have yet to be established in hippocampus. This investigation was undertaken to characterize the vitamin D receptor in rat hippocampus with western blot, immunocytochemistry, and gel shift analyses. The presence of the receptor protein in hippocampus extracts was revealed with western blotting using an anti-rat vitamin D receptor antiserum. In vivo and in vitro immunocytochemical results confirmed the presence of vitamin D receptor in neuronal and glial cells. In the hippocampus, the receptor was localized in pyramidal and granule cell layers, CA1, CA2, and CA3 subfields and in the dentate gyrus. Double labeling for the vitamin D receptor and glial fibrillary acidic protein revealed that glia also expressed the receptor protein. Gel shift analyses evaluated with the murine osteopontin vitamin D response element indicated a specific, bound receptor-containing complex from hippocampal extracts. Altogether, these findings clearly document the localization of vitamin D receptor in rat hippocampus and that hippocampus contains vitamin D receptors capable of specifically binding to DNA. In combination with reports of a neuroprotective role for vitamin D in hippocampal cell survival, these data suggest that the endogenous vitamin D receptor may mitigate processes related to cellular homeostasis, perhaps through a calcium buffering mechanism.     

Increased grooming behavior in mice lacking vitamin D receptors

Vitamin D is a neuroactive secosteroid with several important functions in the nervous system. Many human and animal findings link alterations in the vitamin D system to various neurological and behavioral disorders. Since grooming is an important element of animal behavior, here we studied whether genetic ablation of vitamin D receptors (VDR) in mice may be associated with altered grooming behaviors. Overall, VDR knockout (VDRko) mice presented longer duration and higher frequency of grooming when tested in the actimeter, open field, elevated plus maze, and horizontal rod tests. Increased grooming did not, however, correlate with unaltered general activity level (actimeter test), anxiety-like behaviors (hole board and elevated plus maze tests), and emotional reactivity index (defecation boli). In general, our results confirm the role of vitamin D and VDR in the regulation of behavior, including grooming, and suggest that increased grooming behavioral phenotype may be associated with genetic ablation of VDR in mutant mice.     

EHDP-induced rachitic syndrome in rats is not reversed by vitamin D metabolites

To examine whether either of the two known active vitamin D metabolites 1,25(OH)2D3 or 24,25(OH)2D3 could reverse the mineralization defect induced by 1-hydroxyethylidene-1,1-bis phosphonate (EHDP), a model of EHDP-induced rickets was used. Rats at the age of 31 days were injected for 10 consecutive days with EHDP (10 mg/kg). Other littermates were treated with a combination of EHDP and either 1,25(OH)2D3 or 24,25(OH)2D3 or were treated following 10 days of EHDP, with either of the vitamin D metabolites for an additional 72 hr. Samples of cartilage fluid (Cfl) and of blood were removed prior to sacrifice for biochemical studies of some parameters of calcification. These parameters were correlated with the results of light and electron microscope studies of growth plate cartilage and bone. EHDP-treated rats revealed signs of typical rickets, manifested by widened growth plates and impaired bone mineralization. Transmission electron microscope (TEM) examination revealed matrix vesicles distributed throughout the growth plate; however, there appeared to be an arrest of the spread of the crystals at the provisional zone of calcification. Treatment with either 1,25(OH)2D3 or 24,25(OH)2D3 failed to reverse the rachitic condition of the animals. Serum calcium blood levels were elevated in the 1,25(OH)2D3 and EHDP-treated group. 1,25(OH)2D3 and 24,25(OH)2/D3 further increased the already elevated serum alkaline phosphatase levels observed in EHDP rats, although the increase observed with 1,25(OH)2D3 was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Membrane receptors for soluble defense collagens

Membrane receptors for the soluble 'defense collagens' - naturally occurring chimeric molecules that contain a recognition domain contiguous with a collagen-like triple helical domain and play a role in protecting the host from pathogens entering the blood, lung and other tissues - are being isolated. These receptors are key to understanding the mechanisms by which defense collagens influence cellular responses in order to either provide rapid 'stealth clearance' of cellular debris or to initiate the responses that lead to the destruction of harmful microbes.     

Intestinal Ca and phosphate transport: differential responses to vitamin D3 metabolites

The transport of Ca and inorganic phosphate (Pi) was studied in the absence of electrochemical gradients across rat intestine in vitro. 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) increased the active absorption of both Ca and Pi in all segments of the small intestine, with changes occurring only in absorptive fluxes, whereas secretory fluxes were unaffected. Active Ca absorption was greatest in the duodenum (greater than jejunum greater than ileum) and active Pi absorption was highest in jejunum (greater than duodenum greater than ileum), in agreement with earlier reports. 24R,25-dihydroxy-vitamin2D3 had similar effects on transport but was less potent. The ratios of Pi absorptive fluxes to Ca absorptive fluxes remained remarkably constant during 80-200% increases in absorption produced by 1,25(OH)2D3, suggesting coupled Ca-Pi transport or coordinate stimulation of Ca and Pi absorptive processes by hormonally active metabolites of vitamin D. The results seem most compatible with a differential distribution of vitamin D-responsive Ca and Pi absorptive cells with a predominance of cells with Ca absorptive sites occurring in duodenum, more Pi absorbing cells in jejunum, and a nearly equal ratio of each type in ileum.     

The effects of different vitamin D-states on intestinal absorption of vitamin D3 and its metabolites in rats

Rats were kept on a diet deficient in vitamin D for 2 months and were then randomly assigned to one of three groups with different supplies of vitamin D for 9 days. At the end of this period [3H]-cholecalciferol (5 microCi) was administered intragastrically and the serum radioactivity was recorded after various periods of time. The animals were kept in metabolic cages and urine and faeces were collected. After 3 days the animals were killed and the liver, kidney and fat tissue were investigated for radioactivity. The radioactivity was separated into different fractions of vitamin D by means of chromatography. The animals with vitamin D deficiency displayed higher levels of serum radioactivity, which were to a great extent confined to the fractions of the more polar metabolites (25(OH)D3 and 1,25(OH)2D3). There was significantly less radioactivity in the 3-day faecal collection from these animals. In general, there was a low urinary excretion of radioactivity. In the rats with sufficient vitamin D, most of the radioactivity remained as the parent substance and was also detected in increased amounts in the liver, kidney and fat tissue. The results suggest a discriminatory enterohepatic cycling of vitamin D and its more polar metabolites leading to an increased faecal loss of the pro-hormone in animals with a vitamin D surplus. It is proposed that the selectively effective enterohepatic reabsorption of the different metabolites may serve as a protective mechanism when body stores of vitamin D are overloaded.     

Influence of vitamin D3 metabolites on the production of interleukins 1,2 and 3

We investigated the effect of vitamin D3 metabolites on the release of the three interleukins (IL) IL 1, IL 2 and IL 3 by mononuclear cells. Models for the production of these mediators were the release of IL 1 by the murine macrophage cell line P388D1, of IL2 by rat spleen cells, and of IL 3 by the murine WEHI-3 cell line. IL 1 production was significantly increased with 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) at 10(-10)M and above. 1,25(OH)2D3 did not stimulate cell proliferation as assessed with [methyl-3H]thymidine (3H-TdR) incorporation. 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) and 25-hydroxyvitamin D3 (25(OH)D3) were about 1000 times less effective than 1,25(OH)2D3. IL 2 production, by cultured rat spleen cells stimulated with Concanavalin A, was decreased by increasing concentrations of 1,25(OH)2D3. The minimal effective dose varied between experiments and ranged from 10(-11) to 10(-8) M. Moreover, proliferation (3H-TdR incorporation) of mouse thymocytes treated with phytohemagglutinin and IL 1 was decreased in a dose-dependent fashion by 1,25(OH)2D3 starting at 10-11) M. This effect might be secondary to a decrease of endogenous IL 2 production. IL 3 release by WEHI-3 cells was significantly increased with 10(-11)-10(-9) M 1,25(OH)2D3, whereas higher concentrations were less effective or decreased IL 3 production. These results show that 1,25(OH)2D3 and, to a lesser extent, 24,25(OH)2D3 and 25(OH)D3 have selective effects on lymphokine production. It is tempting to speculate that the actions of 1,25(OH)2D3 on bone might in part be mediated by lymphokines. Moreover, we suggest that 1,25(OH)2D3 might not be an immunoregulator per se, but makes use of the immune system to exert its influence on one of its classical targets, namely the bone, and possibly on other connective tissues.     

Effects of vitamin D metabolites and bisphosphonates on fibronectin release from monocyte-derived macrophages.

Fibronectin release from cultured macrophages, derived from human blood monocytes, was measured during incubation of the cells with increasing concentrations of vitamin D3 metabolites or of aminobutane bisphosphonate (AHButBP) or dichloromethylene bisphosphonate (Cl2MBP), two powerful inhibitors of bone resorption. The bisphosphonates significantly inhibited fibronectin release at 10(-8) M concentration and this inhibition was almost complete at 10(-5) M concentration. Opposite results were observed when the cells were incubated with vitamin D3 metabolites: the stimulation of fibronectin release was specific for 1,25-dihydroxyvitamin D3 relative to other vitamin D3 metabolites (1,25-dihydroxyvitamin D3 greater than 25-hydroxyvitamin D3 greater than 24,25-dihydroxyvitamin D3).     

维生素D对骨质疏松的影响及适宜补充量

维生素D缺乏在世界各地普遍存在,受到全球关注.近几年有很多相关文献报道补充足够的维生素D能增强肌力、减少跌倒相关风险以及预防骨质疏松和骨质疏松性骨折的风险,因此如何指导国人补充适量的维生素D以及研究体内维生素D的检测标准具有重要意义.     

Dendritic cells from human tissues express receptors for the immunoregulatory vitamin D3 metabolite, dihydroxycholecalciferol.

Dendritic cells have been isolated from human tonsillar tissue and shown to act as accessory cells in a mitogenic response. The dendritic cells will induced receptors for the active metabolite of vitamin D3, 1,25(OH)2D3, in the responder E+ T cells. The dendritic cells themselves constitutively express receptors for the metabolite, and this distinguishes them from other non-T cells in lymphomedullary tissue. Expression of the 1,25(OH)2D3 receptor may be a dendritic cell property that facilitates their accessory cell role within the tissue microenvironment.     

维生素D及其受体与毛发的关系

背景：越来越多的研究发现,维生素D及其受体与毛发有一定关系。 目的：全面阐述维生素D及其受体与毛囊干细胞、毛发生长周期、信号转导以及脱发性疾病等的关系。 方法：应用计算机以“维生素D、维生素D受体、毛发、脱发、基因多态性”或“vitamin D,vitamin D receptor,hair,alopecia,gene polymorphism”为检索词检索PubMed和CNKI数据库1990/2011-11发表的关于维生素D及其受体与毛发关系的文章,同一领域选择近期发表或发表在权威杂志上的文章。 结果与结论：初检得到152篇文献,根据纳入排除标准选择30篇文章进行综述。目前研究显示,维生素D及其受体在毛发中扮演重要角色,其异常可导致脱发等疾病的产生,为预防和治疗脱发性疾病提供新的可能,并有望在未来广泛应用。关键词：维生素D;维生素D受体;毛发;脱发;基因多态性;毛囊干细胞 doi:10.3969/j.issn.1673-8225.2012.14.035     

Treatment of hypoparathyroidism and pseudohypoparathyroidism with metabolites of vitamin D: evidence for impaired conversion of 25-hydroxyvitamin D to 1 alpha,25-dihydroxyvitamin D.

In hypoparathyroidism and pseudohypoparathyroidism, pharmacologic doses of vitamin D correct hypocalcemia, but the mechanism is unknown. In two children with hypoparathyroidism and one with pseudohypoparathyroidism we tested the hypothesis that in these conditions there is a defect in synthesis of 1 alpha,25-dihydroxyvitamin D3, the principal active metabolite of vitamin D. In both conditions, minute doses of the metabolite (0.04 to 0.08 mug per kilogram of body weight per day) quickly corrected hypocalcemia and increased intestinal calcium absorption. On the other hand, the effective dose of 25-hydroxyvitamin D3 to maintain normocalcemia was 3 to 4 mug per kilogram per day in the two conditions. Thus, the dosage ratio of 25-hydroxyvitamin D3 to 1 alpha,25-dihydroxyvitamin D3 approximated 100:1. By contrast this ratio was approximately 3:1 in two infants with vitamin D deficiency, a condition in which optimal metabolism of vitamin D would be expected. These findings suggest an impaired conversion of 25-hydroxyvitamin D to 1 alpha,25-dihydroxyvitamin D in both hypoparathyroidism and pseudohypoparathyroidism.     

The quantification of vitamin D receptors in coronary arteries and their association with atherosclerosis

Objective

The activated vitamin D receptor (VDR) may have an important role in vascular health. The objective of this study was to determine whether there is an association between the expression of VDRs in coronary arteries and the extent of diet-induced atherosclerosis.

Methods

Utilizing a cohort of 39 postmenopausal female cynomolgus monkeys with varying stages of atherosclerosis, histologic sections of the left anterior descending artery (LAD) were analyzed for plaque cross-sectional area, plaque thickness, and VDR quantity using immunohistochemical H-score analysis. The quantities of VDRs were analyzed as a continuous variable and were divided at the median intimal H-score into high vs. low groupings.

Results

In the LAD, a significant negative correlation was observed between the quantity of VDR and plaque size (both cross-sectional area [p < 0.001] and plaque thickness [p < 0.001]). Monkeys in the low VDR group had a significantly greater cross-sectional plaque area (1.2 mm²) and greater plaque thickness (0.3 mm) than those in the high VDR group (0.4 mm², p = 0.005; 0.1 mm, p = 0.003, respectively).

Conclusions

Lower concentrations of VDRs in a main coronary artery were associated with greater atherosclerotic plaque size in postmenopausal female monkeys. Given that coronary artery atherosclerosis is a major cause of coronary heart disease in postmenopausal women, further research to ascertain the relationship between VDRs and atherosclerosis is warranted.     

Comparative abilities of various metabolites of vitamin D to protect cultured human macrophages against tubercle bacilli

Vitamin D metabolites have several biologic functions besides the best-known one of controlling mineral metabolism, one of which may be protection against tuberculosis. The chemical structures of the metabolites govern their functions. The most potent metabolite for regulating calcium metabolism is 1,25(OH)2-vitamin D3 (1,25-D3). This metabolite also is able to protect cultured human monocytes and macrophages (MP) against tubercle bacilli (TB). To determine whether these two functions are connected, 14 other analogs or metabolites of vitamin D were compared with 1,25-D3 for ability to protect cultured MP against TB. Blood-derived MP from 18 different donors were used in 70 experiments. The MP were infected with TB, then incubated for 7 days in medium containing 4 micrograms/ml of metabolite or synthesized analog. Growth of TB in the MP was measured by colony-forming unit counts from samples of lysed MP at 0, 4, and 7 days after infection. The metabolites, none of which inhibited TB in the absence of MP, varied from unprotective to bacteriostatic in the MP. Four of them were nearly as protective as 1,25-D3, and the metabolite 25S, 26(OH)2-vitamin D3 was consistently more protective. An analog synthetically designed for maximum ability to promote cell differentiation was unprotective. There was no correlation between metabolite ability to protect and known ability to stimulate calcium mobilization. These results suggest that antituberculosis protection of human MP by vitamin D metabolites or analogs can be separated from their functions of inducing cell differentiation and controlling mineral metabolism.