L«,25-dihydroxyvitamin

Other vitamin D analogs available in the United States include paricalcitol (19-nor-l,25-dihydroxyvitamin D2, Zemplar by Abbott Laboratories, North Chicago, IL) and doxercalciferol (1 -a-hydroxyvitamin D2, Hectoral by Bone Care International, Middleton, WI). Alfacalcidiol (1-a-hydroxyvitamin D3) is only available outside the United States. Paricalcitol has less effect on vitamin D receptors in the intestines, decreasing the effects on... 

Kao PC, Heser DW. Simultaneous determination of 25-hydroxy- and l,25-dihydroxyvitamin D from a single sample by dual-cartridge extraction. Chn Chem 1984 30 56-61. 

Osteocalcin (OCN) is one of the most prevalent non-collagenous intraosseous proteins, and it is predominantly localized to osteoblasts. This 9-kD cytoplasmic protein contains abundant gamma carboxyglutamic acid residues. Its expression is down-regulated by helix-loop-helix-type transcription factors and up-regulated by vitamin D analogs such as 1,25 dihydroxyvita-min D2 and 24-epi-l,25 dihydroxyvitamin D2 in the final steps of osteoblastic differentiation and osteoid formation. ... 

Meyer, M.B., Watanuki, M., Kim, S., et al. 2006. The human transient receptor potential vanilloid type 6 distal promoter contains multiple vitamin D receptor binding sites that mediate activation by l,25-dihydroxyvitamin D, in intestinal cells. Mol. Endocrinol. 20 1447-61. 

Prehn, J. L., Fagan, D. L., Jordan, S. C., Adams, J. S. 1992. Potentiation of lipopolysacchaiide-induced tumor necrosis factor-alpha expression by l,25-dihydroxyvitamin D3. Blood 80 2811-16... 

Lawrence JA, Akman SA, Melin SA, Case LD, Schwartz GG. Oral paricalcitol (19-nor-l,25-dihydroxyvitamin D2) in women receiving chemotherapy for metastatic breast cancer a feasibility trial. Gancer Biol Ther June 2013 14(6) 476-80. 

The steroid hormone l/ ,25-dihydroxyvitamin D3 (l/ ,25-(OH)2-D3, calcitriol, 158) is the bioactive metabolite of vitamin D3. This B-ring-seco-steroid plays an important role in the regulation of mineral metabolism and finds application in the treatment of osteodystrophy due to renal failure, rickets, osteoporosis, and psoriasis. The bromoolefin 156 was subjected to sequential metallation and transmetallation to give the corresponding... 

Liu, Y., Chang, R.L., Cui, X.X., Newmark, H.L. and Conney, A.H. 1997. Synergistic effects of curcumin on all-trans retinoic acid- and 1 alpha,25-dihydroxyvitamin D3-induced differentiation in human promyelocytic leukemia HL-60 cells. Oncol Res 9 19-29. 

L The answer is e. (Kalzang, pp 744, 748J Vitamin is hydroxylated to 2.5-0ITDj (calcifediol). Calcifediol is then hydroxylated in the kidney to the most active form of vitamin D, which is 1,25-dihydroxyvitamin D (cal-citriol). Calcitriol has a rapid onset of action and a short half-life. The administration of calcitriol causes the elevation of serum Ca levels by enhancing the intestinal absorption of Ca. Calcitriol is indicated in vitamin D deficiency,... 

Pattanaungkul, S., Riggs, B. L., Yergey, A. L., Vieira, N. E., O Eallon, W. M., and Khosla, S. (2000). Relationship of intestinal calcium absorption to 1,25-dihydroxyvitamin D [1,25 (0H)2D] levels in young versus elderly women Evidence for age-related intestinal resistance to l,25(OH)2D action. /. Clin. Endocrinol. Metab. 85,4023M027. 

Vitamin D is a prohormone that serves as precursor to a number of biologically active metabolites (Figure 42-3). Vitamin D is first hydroxylated in the liver to form 25-hydroxyvitamin D (25[OH]D). This metabolite is further converted in the kidney to a number of other forms, the best studied of which are 1,25-dihydroxyvitamin D (l,25[OH]2D) and 24,25-dihydroxyvitamin D (24,25[OH]2D). Of the natural metabolites, only vitamin D and l,25(OH)2D (as calcitriol) are available for clinical use (Table 42-1). Moreover, a number of analogs of l,25(OH)2D are being synthesized to extend the... 

Doxercalciferol, the active ingredient in Hectorol, is a synthetic vitamin D analog that undergoes metabolic activation in vivo to form 1 (alpha),25-dihydroxyvitamin D2 (l(alpha),25-(OH)2D2), anaturally occurring, biologically active form of vitamin D2. Hectorol is available as soft... 

Canaff, L and Hendy, GN, 2002, Human calcium-sensing receptor gene. Vitamin D response elements in promoters PI and P2 confer transcriptional responsiveness to 1,25-dihydroxyvitamin D, J Biol Chem 277 30337-30350... 

Initially, 25-OH-D3 was considered to be the main biologically active metabolite of vitamin D. But soon it was discovered that physiological concentrations of 25-0H-D3, like vitamin D3, are incapable of stimulating either intestinal calcium transport or bone calcium jnobilization (108-110). Earlier work (111,112) with [la- H] vitamin D3 had shown that one of the unknown metabolites had lost its tritium from the C-l position. Fraser and Kodicek (113) established that this active metabolite is 1-oxygenated 25-OH-D3 and that it was produced in the kidney. A short time later Lawson et al. (114) identified this metabolite to be la, 25-dihydroxyvitamin D3 (1,25-(0H)2D3) which was confirmed by other investigators (115,116). 

Chemical Name 9,10-Secocholesta-5,7,10(19)-triene-l,3,25-triol Common Name la,25-Dihydroxycholecalciferol la,25-Dihydroxyvitamin D3 Structural Formula ... 

Although most biological activities of vitamin D3 are ascribed to l,25(OH)2D3, some activity has been associated with a second metabolite produced by the kidney, 24R,25-dihydroxyvitamin D3 [1], Thus, at the present time it is not clear whether l,25(OH)2D3 acting alone can produce all the biological responses supported by the parent vitamin D3 or whether in some instances the combined or sequential actions... 

Vitamin D that is taken up by the fiver is converted to 25-hydroxyvitamin D by a microsomal hydroxylase (Fig. 30-3). 25-Hydroxyvitamin D is the main circulating form of vitamin D in the serum and the best indicator of vitamin D status. Normal serum levels are 14-60 ng/mL (35-150 nmol/L). When serum calcium concentrations decline, 25-hydroxyvitamin D is converted to 1,25-dihydroxyvitmin D by la-hydroxylase, a mixed-function oxidase that is located in the inner mitochondrial membrane in kidney tissue and whose expression is regulated by parathyroid hormone (PTH). The main function of 1,25-dihydroxyvitamin D is to increase the intestinal absorption of dietary calcium and phosphorus. When serum concentrations of calcium and phosphorus are normal or when large doses of vitamin D are administered, 25-hydroxyvitamin D is metabolized to 24,25-dihydroxyvitamin D in the renal... 

Obeid, L.M., Linardic, C.M., Karolak, L.A., and Hannun, Y.A., 1993, Programmed cell death induced by ceramide, Science 259 1769-1771 Okazaki, T., Bell, R.M., and Hannun, Y.A., 1989, Sphingomyelin turnover induced by vitamin D3 in HL-60 cells. Role in cell differentiation. J. Biol. Chem. 264 19076-19080 Okazaki, T., Bielawska, A., Bell, R.M., and Hannun, Y. A., 1990, Role of ceramide as a lipid mediator of la, 25-dihydroxyvitamin D3-induced HL-60 cell differentiation. J. Biol. Chem. 265 15823-15831... 

Gregori S, GiarratanaN, Smiroldo S, Uskokovic M, Adorini L (2002) A 1 alpha,25-dihydroxyvitamin D(3) analog enhances regulatory T-cells and arrests autoimmune diabetes in NOD mice. Diabetes 51 1367-1374. 

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