Inhibition of tropoelastin expression by 1,25-dihydroxyvitamin D3.

Elastin production is modulated by steroid hormones and is dependent on calcium. Because vitamin D3 is involved in the regulation of calcium metabolism and influences the expression of various extracellular matrix proteins, we investigated whether vitamin D3 influences tropoelastin expression. Three elastin-producing, bovine cell types, auricular chondroblasts, nuchal ligament fibroblasts and arterial smooth muscle cells, were treated with the principal active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25[OH]2D3), and with 24,25 dihydroxyvitamin D3 (24,25[OH]2D3). Tropoelastin levels in culture media and cell layers, as measured by an enzyme-linked immunoassay, decreased in a dose and exposure dependent manner after treatment with 1,25(OH)2D3; 24,25(OH)2D3 had no effect on tropoelastin production relative to solvent-treated controls. The maximal effective dose of 1,25(OH)2D3 was 10(-7) M for 48 hr, which resulted in a severalfold reduction of tropoelastin production, and decreased tropoelastin levels were detected at 8 hr after treatment. Reduction of tropoelastin protein production was paralleled by a decrease of equal magnitude in the steady-state levels of tropoelastin mRNA. Vitamin D3 metabolites had no effect on DNA or total protein synthesis. These results suggest that vitamin D3 may be an important modulator of elastin expression.     

Phosphatemic action of 1,25-dihydroxyvitamin D3.

The action of a single intraperitoneal injection of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) was investigated in thyroparathyroidectomized (TPTX) vitamin D-deficient phosphate-depleted rats. After 14 h, plasma inorganic phosphorus (Pi) was significantly greater in animals receiving 1,25(OH)2D3 than in D-deficient controls, but urinary Pi excretion was very low in both groups and not significantly different in the rats given 1,25(OH)2D3. Clearance studies indicated that the D-deficient controls reabsorbed more than 99% of their filtered Pi. Avid Pi reabsorption continued even after the infusion of sufficient phosphate to raise the plasma and filtered Pi to approximately 3 times normal. Fractional calcium excretion (FECa) exceeded fractional sodium excretion (FENa) by severalfold, but FECa decreased strikingly during phosphate infusion. In animals that manifested a substantial elevation of plasma Pi after 1,25(OH)2D3, FECa was significantly less than in D-deficient controls. Therefore, the increase in plasma Pi following 1,25(OH)2D3 administration occurs independently of any effect on renal Pi reabsorption and may be responsible, at least in part, for the amelioration of hypercalciuria after 1,25(OH)2D3 treatment.     

On the regulation of differentiation and function of rat macrophages by 1,25-dihydroxyvitamin D3 and dexamethasone

Rat bone marrow macrophage progenitor cells develop in vitro in the presence of rat embryo fibroblast conditioned medium into colonies and clusters. 1 alpha,25-Dihydroxyvitamin D3 (1,25(OH)2D3) (0.12-12 nM) was found to enhance the formation of macrophage colonies and the proliferation of mononuclear phagocytes in liquid cultures of bone marrow cells (ED50 0.12-1.0 nM). Fractionation of bone marrow cells by centrifugal elutriation showed that: a) macrophage progenitors are heterogeneous in size; b) the progenitors eluted at early fractions have a lower proliferative capacity (form mainly small clusters) than those eluting at later fractions (higher counterflow velocities) which develop into macrophage colonies and c) that 1,25(OH)2D3 (at 12 nM) augments the expression of colony forming cells enriched in late eluting fractions while having a suppressive effect on expression of low proliferative potential cluster forming cells enriched in early eluting fractions. Dexamethasone was found to suppress the clonal growth of macrophage progenitor cells as well as their proliferation in liquid cultures (ED50 about 1 nM). Both dexamethasone and 1,25(OH)2D3 induced in mononuclear phagocytes of 4 d cultures an increased phagocytic capability. The data suggest a regulatory role for 1,25(OH)2D3 and glucocorticosteroids in myelopoietic processes in the rat. Furthermore, when compared with our recent findings with mouse bone marrow cells, the effects, their magnitude and concentration dependence imply genuine species differences in the responses of mice and rats to these hormones.     

Differential epithelial and mesenchymal regulation of tooth-specific matrix proteins expression by 1,25-dihydroxyvitamin D3 in vivo

Enamel defects have been reported in rickets and related to disturbed expression of amelogenin in ameloblasts. The present study is devoted to amelogenin, enamelin, ameloblastin, and dentin sialophosphoprotein (DSPP) expression in both the epithelium and mesenchyme of vitamin D-deficient rat incisors. Quantitative Northern blotting analysis (relatively to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA steady-state levels) was performed on microdissected cells of rachitic (-D) and control (+D) 56 day old rats. Steady-state levels of amelogenin and enamelin mRNA were significantly reduced in the -D epithelium versus the +D epithelium ones. In contrast, ameloblastin expression was slightly increased in -D epithelium. In the same samples, DSPP mRNA levels remained unchanged in -D dental mesenchyme. Comparative electron microscopy studies between +D and -D animals showed a dramatic decrease of intraprismatic enamel (amelogenin and enamelin immunoreactive) consistent with our molecular results. In conclusion, tooth formation results from the coordinated expression of several matrix proteins that may be controlled by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3].     

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.     

1,25-dihydroxyvitamin D3 and development of tuberculosis in cattle

This report describes the presence and activity of 1,25-dihydroxyvitamin D3 (1,25-D3) in experimental bovine tuberculosis. Animals that went on to develop tuberculous lesions exhibited a rapid transient increase in serum 1,25-D3 within the first 2 weeks following infection with Mycobacterium bovis. 1,25-D3-positive mononuclear cells were later identified in all tuberculous granulomas by immunohistochemical staining of postmortem lymph node tissue. These results suggest a role for 1,25-D3 both at the onset of infection and in the development of the granuloma in these infected animals. Using a monoclonal antibody to the vitamin D receptor (VDR) as a VDR agonist, we confirmed that activation of the vitamin D pathway profoundly depresses antigen-specific, but not mitogenic, bovine peripheral blood T-cell responses (proliferation and gamma interferon production). Investigation of the mechanism of this suppression showed that the VDR antibody modified the expression of CD80 by accessory cells, such that a significant positive correlation between T-cell proliferation and accessory cell CD80 emerged.     

Inhibition of production and function of interleukin-6 by 1,25-dihydroxyvitamin D3

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) has been shown to interfere with immunoglobulin production and lymphocyte proliferation in vitro. These lymphocyte functions are influenced by interleukin (IL)-6 produced by antigen presenting cells. Hence, the ability of 1,25-(OH)2D3 to interfere with the production and function of IL-6 was investigated. 1,25-(OH)2D3 and the analogue MC 903 inhibited IL-6 production by LPS-stimulated human mononuclear cells. The precursor 25-OH D3 was ineffective. Likewise, 1,25-(OH)2D3 but not 25-OH D3 inhibited rIL-6-driven as well as rIL-1 alpha/beta-driven proliferation of murine thymocytes. This effect of 1,25-(OH)2D3 was partially or totally overcome by larger concentrations of rIL-6 as well as by rIL-2 and ionomycin. Consistently, the production of IL-6 and IL-2 in rIL-1 driven thymocyte cultures were found to be reduced by 1,25-(OH)2D3. Inhibition of production and function of IL-6 may therefore be involved in 1,25-(OH)2D3-mediated regulation of lymphocyte functions in vitro.     

Apparent [3H]1,25-dihydroxyvitamin D3 uptake by canine and rodent brain

The brain uptake of [3H]1,25-dihydroxyvitamin D3 ([3H]1,25(OH)2D3) was studied during steady-state conditions using the multiple-indicator dilution technique in dogs. The fractional [3H]1,25(OH)2D3 uptake was evaluated at 0.8 +/- 0.15% during a single passage through the dog brain. Evaluation of the [3H]1,25(OH)2D3 uptake by the vitamin D-replete and vitamin D-depleted rat brain indicated that 30 min after its injection, the fractional uptake was not influenced by the vitamin D status of the animals or by the amount of [3H]-1,25(OH)2D3 injected. In the rodent the fractional [3H]-1,25(OH)2D3 brain accumulation was between 0.16 and 0.20%, whereas the brain-to-serum ratio varied between 5 and 6%. Protein-binding studies of serum [3H]1,25(OH)2D3 indicated that, at 37 degrees C, 94.8 +/- 0.4% of the hormone was protein bound 30 min after its intravenous injection. These observations suggest that 1,25(OH)2D3 is able to cross the blood-brain barrier. However, its limited brain uptake in relation to its serum concentration suggests that the hormone does not penetrate freely into the central nervous system and that its brain uptake may be related to the free circulating 1,25(OH)2D3 concentration perfusing the blood-brain barrier.     

维生素D受体在1,25(OH)2D3调节人骨肉瘤细胞系HOS-8603增殖中的作用

目的:研究维生素D₃受体(VDR)在1,25(OH)₂D₃及其类似物调节人骨肉瘤细胞系HOS-8603增殖中的作用。方法:用RT-PCR和免疫组织化学技术分别在mRNA和蛋白水平上明确HOS-8603细胞中是否有VDR表达;瞬时转染VDR报告基因技术观察HOS-8603细胞中VDR的功能活性;并进一步利用稳定表达VDR反义mRNA的细胞株VDRas3细胞研究VDR被阻断后细胞增殖以及基因转录的变化。结果:HOS-8603细胞有VDR表达,此内源性VDR具有激素依赖性的转录激活活性。在内源性VDR被阻断后,1,25(OH)₂D₃及其类似物对细胞增殖的抑制作用以及对VDR的靶基因p21mRNA表达的诱导作用均明显减弱。结论:1,25(OH)₂D₃及其类似物对HOS-8603细胞增殖抑制作用是由VDR介导的。     

Effect of 1,25-dihydroxyvitamin D3 on interferon gamma production in vitro

In recent years, receptors for calcitriol (the active form of vitamin D3) have been identified in monocytes and activated, but not resting, human B and T lymphocytes suggesting that it may be involved in immune regulation. Because lymphokines are central in the regulation and modulation of immune or inflammatory responses and since the calcium translocation is involved in the mitogen-induced activation of lymphocytes, we thought it interesting to study the role of calcitriol on interferon gamma (IFN-gamma) production in vitro. In this study, we report that calcitriol inhibits the IFN-gamma production by staphylococcal enterotoxin A-stimulated peripheral blood mononuclear cells (PBMC) in a dose-dependent fashion. The inhibitory effect was less potent in calcium ionophore A23187-stimulated PBMC and was absent in resting PBMC.     

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.     

Comparison of the effects of 1,25-dihydroxyvitamin D3 on T lymphocyte subpopulations

Previous studies have demonstrated that 1,25-dihydroxyvitamin D3 (calcitriol) is a potent inhibitor of human T lymphocyte proliferation. It has been reported that only CD4+ cells are sensitive to the anti-proliferative action of calcitriol. To further evaluate this observation, we first performed cell cycle analysis of unfractionated phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMC) in the absence or presence of calcitriol. The CD4/CD8 ratio was similar between control and treated cells for each phase of cycle (G0----G1, S, G2 + M), suggesting that calcitriol did not selectively block proliferation of either T cell subpopulation. Secondly, the growth-inhibitory activity of calcitriol on PBMC selectively depleted of either CD4+ or CD8+ cells was comparable to that observed with unfractionated PBMC. Furthermore, the induction of transferrin receptors was inhibited by calcitriol to a comparable degree in each T cell subset, suggesting that equivalent inhibition of transition into late G1 was observed. Finally, calcitriol inhibited the proliferation of highly purified T cell subsets (greater than 99% pure) to equivalent degrees. These data suggest that T cell subsets defined by either the CD4 or by the CD8 antigen are both sensitive to the growth inhibitory effects of calcitriol.     

Foreign body granulomatous inflammation increases the sensitivity of splenocytes to immunomodulation by 1,25-dihydroxyvitamin D3

1,25-dihydroxyvitamin D₃, the active metabolite of vitamin D, partially inhibits antigen and mitogen-driven lymphocyte stimulation. We studied the effect of granulomatous inflammation on the sensitivity of lymphocytes to 1,25-dihydroxyvitamin D₃in vitro, measuring the inhibitory effect of 1,25-dihydroxyvitamin D₃ on mitogenesis of splenocytes of mice with chronic inflammation induced by subcutaneous injection of talc. Systematic manifestations of the local inflammation included loss in body weight, splenomegaly, enhanced DNA synthesis by freshly isolated splenocytes and enhanced prostaglandin secretion by activated splenocytes. Splenocytes from animals with local inflammation were more susceptible to inhibition by 1,25-dihydroxyvitamin D₃, but not by prosaglandin E₂. This increased sensitivity to 1,25-dihydroxyvitamin D₃ was abolished by blocking prostaglandin synthesis in splenocyte cultures with indomethacin and was restored by adding prostaglandin E₂. This effect cannot be attributed to enhanced prostaglandin synthesis in the presence of 1,25-dihydroxyvitamin D₃, but is probably due to a qualitative change in the response of splenocytes from inflamed animals to the combined action of 1,25-dihydroxyvitamin D₃ and prostaglandin E₂.     

1,25-二羟基维生素D3协同转染反义端粒酶RNA诱导肝癌细胞凋亡的实验研究

目的观察在抑制肝癌细胞端粒酶活性表达情况下,1,25-二羟基维生素D3(1,25-VD3)对肝癌细胞凋亡的影响。方法经脂质体介导,将反义端粒酶RNA真核表达载体pBBS212/hTR导入维生素D3受体(VDR)阳性的肝癌细胞株SMMC7721细胞中培养。细胞克隆转移扩大培养,将其分为对照组、药物组、转染组和转染药物组。添加1,25-VD3,分别作用于转染药物组、药物组,用脱氧核糖核苷酸末端转移酶介导的缺口末端标记法(TUNEL)和电子显微镜检测肝癌细胞凋亡。结果转染组和对照组细胞的端粒酶活性分别为0.686和1.685,说明反义端粒酶RNA可显著降低肝癌细胞端粒酶活性。对照组、药物组、转染组和转染药物组细胞凋亡率分别为3.4%、12.2%、8.8%、23.6%;差异有显著统计学意义(P<0.01)。超微结构检查也证实存在凋亡发生。1,25-VD3或转染反义端粒酶RNA对肝癌细胞有促细胞凋亡作用,两者协同对肝癌细胞凋亡作用显著增强。结论转染反义端粒酶RNA,可降低肝癌细胞端粒酶活性,可显著增强1,25-VD3对肝癌细胞的促凋亡作用,并且对细胞的增殖也存在明显的抑制作用。     

25-hydroxyvitamin D, 24, 25-dihydroxyvitamin D and 1,25-dihydroxyvitamin D in human cerebrospinal fluid

Summary Samples of CSF and plasma were obtained simultaneously from 46 adult patients who had no endocrine disorders and were undergoing routine diagnostic lumbar puncture because of suspected or proved prolapse of a disc. Concentrations of 25-OHD, 24,25(OH)₂D and 1,25(OH)₂D were measured. The samples were purified by column chromatography and fractionated by HPLC. In the appropriate fractions the vitamin D metabolites were measured by PBA, and cytoreceptor assay. The results were as follows (median, range in brackets): 25-OHD in CSF 8.3 ng/ml (2.0–24.8), in plasma 14.5 ng/ml (7.0–36.0). 24,25(OH)₂D in CSF 1.8 ng/ml (0.3–4.6) and 2.5 ng/ml (0.4–4.7) in plasma. 1.25(OH)₂ D in CSF 25.0 pg/ml (2.2–39.0) and 31.0 pg/ml (10.1–55.0) in plasma. The correlations between plasma and CSF concentrations were as follows: 25-OHDr=0.479 (P<0.001); 24,25(OH)₂Dr=0.815 (P<0.001) and for 1.25(OH)₂Dr=0.497 (P<0.001).Our findings showed vitamin D metabolites to be present in human CSF.Abbreviations Ca Calcium - CSF Cerebrospinal fluid - Vitamin D₃ Cholecalciferol - CPM Counts per min - 24, 25 (OH)₂D 24, 25-dihydroxyvitamin D₃ - 1,25(OH)₂D 1,25-dihydroxyvitamin D₃ - Vitamin D₂ Ergocalciferol - HPLC High-pressure liquid chromatography - 25OHD 25-hydroxyvitamin D₃ - PTH Parathyroid hormone - PBA Protein binding assay - RIA Radioimmunoassay - D-CaBP Vitamin D dependent calcium-binding protein