Calcitriol D6

The biologically active form of vitamin D3. Calcium regulator; vitamin (antirachitic); antihyperparathyroid; antineoplastic; antipsoriatic.

The vitamin D receptor (VDR) is expressed in skeletal muscle of male mice and modulates 25-hydroxyvitamin D (25OHD) uptake in myofibers.[Pubmed:24949660]

Endocrinology. 2014 Sep;155(9):3227-37.

Vitamin D deficiency is associated with a range of muscle disorders, including myalgia, muscle weakness, and falls. In humans, polymorphisms of the vitamin D receptor (VDR) gene are associated with variations in muscle strength, and in mice, genetic ablation of VDR results in muscle fiber atrophy and motor deficits. However, mechanisms by which VDR regulates muscle function and morphology remain unclear. A crucial question is whether VDR is expressed in skeletal muscle and directly alters muscle physiology. Using PCR, Western blotting, and immunohistochemistry (VDR-D6 antibody), we detected VDR in murine quadriceps muscle. Detection by Western blotting was dependent on the use of hyperosmolar lysis buffer. Levels of VDR in muscle were low compared with duodenum and dropped progressively with age. Two in vitro models, C2C12 and primary myotubes, displayed dose- and time-dependent increases in expression of both VDR and its target gene CYP24A1 after 1,25(OH)2D (1,25 dihydroxyvitamin D) treatment. Primary myotubes also expressed functional CYP27B1 as demonstrated by luciferase reporter studies, supporting an autoregulatory vitamin D-endocrine system in muscle. Myofibers isolated from mice retained tritiated 25-hydroxyvitamin D3, and this increased after 3 hours of pretreatment with 1,25(OH)2D (0.1 nM). No such response was seen in myofibers from VDR knockout mice. In summary, VDR is expressed in skeletal muscle, and vitamin D regulates gene expression and modulates ligand-dependent uptake of 25-hydroxyvitamin D3 in primary myofibers.

Determination of the vitamin D analog EB 1089 (seocalcitol) in human and pig serum using liquid chromatography-tandem mass spectrometry.[Pubmed:10798301]

J Chromatogr B Biomed Sci Appl. 2000 Mar 31;740(1):117-28.

A liquid chromatographic-tandem mass spectrometric assay in human and pig serum has been developed for quantitative analysis of EB 1089 (seocalcitol). EB 1089 is a novel vitamin D analog under development for the treatment of cancer. The analyte was extracted from serum after protein precipitation using an automated solid-phase extraction procedure involving both a reversed-phase and normal-phase procedure on a single C18 cartridge. The analytical chromatography was performed using a Symmetri C8 50x2.1 mm, 3.5 microm column. The mobile phase was a linear gradient from 75% to 99% methanol with a constant concentration of 2 mM ammonium acetate. EB 1089 and the internal standard [d6]-EB 1089 were detected by using MS-MS. The ion source was operated in the positive electrospray ionisation (ESI) mode. The assay is specific, sensitive, and has a capacity of more than 100 samples per day, with a limit of quantitation of 10 pg ml(-1) for a 1.0-ml sample aliquot. It is now used for routine analysis in connection with pharmacokinetic studies in humans and toxicokinetic studies in pigs.

1,25-Dihydroxyvitamin D3 stimulates avian and mammalian cartilage growth in vitro.[Pubmed:3213605]

J Bone Miner Res. 1988 Feb;3(1):87-91.

We addressed the question of whether 1,25-dihydroxyvitamin D3 (1,25-(OH)2D) could directly stimulate cartilage growth in vitro. Pelvic leaflets from chick embryos and scapular growth plates from fetal pigs were organ cultured in serum-free medium in the presence and absence of 1,25-(OH)2D. After 3 days of incubation, 1,25-(OH)2D had increased the pelvic cartilage wet weight 42% and the dry weight 32% above the weight of cartilages incubated in medium alone. 1,25-(OH)2D (10(-9) M-10(-12) M) caused a dose-dependent increase in weight, with maximal increases at 10(-9) M. Furthermore, two deuterized derivatives of 1,25-(OH)2D, 26,27-D6-1,25-(OH)2D3 and 24,26,27-D8-1,25-(OH)2D3, stimulated pelvic cartilage growth in vitro. 26,27-D6-1,25-(OH)2D stimulated increases in growth plate weight above growth plates incubated in medium alone. 26,27-D6-1,25-(OH)2D3 appeared to be potent at lower concentrations than 1,25-(OH)2D on growth plate cartilage. Thus, 1,25-(OH)2D stimulated in vitro growth in two growing cartilage models, the avian pelvic cartilage and the mammalian scapular growth plate cartilage.

Sensitive method for the determination of paricalcitol by liquid chromatography and mass spectrometry and its application to a clinical pharmacokinetic study.[Pubmed:25098404]

Biomed Chromatogr. 2015 Mar;29(3):452-8.

A highly sensitive, specific and rapid LC-ESI-MS/MS method has been developed and validated for the quantification of paricalcitol (PAR) in human plasma (500 muL) using paricalcitol-d6 (PAR-d6 ) as an internal standard (IS) as per regulatory guidelines. A liquid-liquid extraction method was used to extract the analyte and IS from human plasma. Chromatography was achieved on Zorbax SB C18 column using an isocratic mobile phase in a gradient flow. The total chromatographic run time was 6.0 min and the elution of PAR and PAR-d6 occurred at ~2.6 min. A linear response function was established for the range of concentrations 10-500 pg/mL in human plasma. The intra- and inter-day accuracy and precision values for PAR met the acceptance criteria. The validated assay was applied to quantitate PAR concentrations in human plasma following oral administration of 4 microg capsules to humans.

Calcitriol D6 is the deuterated form of Calcitriol(1,25-Dihydroxyvitamin D3; Rocaltrol ), which is the hormonally active form of vitamin D, Calcitriol is the active metabolite of vitamin D3 that activates the vitamin D receptor (VDR).

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