1α,25-dihydroxy-24-oxo-16-ene vitamin D3, a metabolite of a synthetic vitamin D3 analog, 1α,25-dihydroxy-16-ene vitamin D3, is equipotent to its parent in modulating growth and differentiation of human leukemic cells

Siu-Caldera, Mei-Ling; Clark, Jeffrey W.; Santos-Moore, Anabela; Peleg, Sara; Uskoković, Milan R.; Sharma, Surendra; Reddy, G. Satyanarayana

doi:10.1016/s0960-0760(96)00134-3

Cited by 30 publications

(20 citation statements)

References 22 publications

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“…The cells were then incubated with 1 µM 1␣,25(OH) 2 D 3 in serum-free medium for 24 h. Incubations were terminated by the addition of an equal volume of methanol containing 25-hydroxyvitamin D 3 as an internal standard to correct for recovery. Lipid extraction of both medium and cells was performed using the procedure described previously [Siu-Caldera et al, 1996]. The lipid extract was analyzed by straight-phase HPLC using a Zorbax-Sil column (4.6 mm ϫ 25 cm) eluted with four different solvent mixtures at a flow rate of 2 ml/min.…”

Section: Analysis Of 1␣25(oh) 2 D 3 Metabolitesmentioning

confidence: 99%

1?,25-Dihydroxy-3-Epi-vitamin D3, a natural metabolite of 1?,25-dihydroxyvitamin D3, is a potent suppressor of parathyroid hormone secretion

et al. 1999

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1Alpha,25(OH)2D3 is an important negative regulator of parathyroid hormone (PTH) gene transcription. In parathyroid cells, as in other target tissues, 1alpha,25(OH)2D3 is degraded by side chain oxidation by the inducible 24-hydroxylase. We have previously shown that one metabolite of this pathway, 1alpha,23(S),25-(OH)3-24-oxo-D3, potently suppresses PTH synthesis and secretion in cultured bovine parathyroid cells (bPTC). Further examination of the metabolites of 1alpha,25(OH)2D3 in bPTC has revealed another compound that is less polar than 1alpha,25(OH)2D3. By HPLC analysis and mass spectrometry, this metabolite was identified as 1alpha,25(OH)2-3-epi-D3. The activity of this metabol ite on PTH gene transcription was assessed by the steady-state PTH secretion by bPTC after 72-h treatment with concentrations from 10(-11) M to 10(-7) M. 1Alpha,25(OH)2-3-epi-D3 was found to be only slightly, but not significantly, less active than the native 1alpha,25(OH)2D3 in suppressing PTH secretion despite having 30 times lower affinity for the bPTC VDR. Both 1alpha,25(OH)2D3 and 1alpha,25(OH)2-3-epi-D3 maximally suppressed PTH secretion by 50%. Along with 1alpha,25(OH)2-3-epi-D3, the activities of the other two A-ring diastereomers were assessed. 1beta,25(OH)2D3 suppressed PTH only at 10(-7) M with a decrease of only 30%, in good agreement with its low VDR affinity. Surprisingly, 1beta,25(OH)2-3-epi-D3 stimulated PTH secretion by 30-50% at concentrations from 10(-11) M to 10(-8)M and fell to control (untreated) rates at 10(-7) M. The mechanism for this increase in PTH secretion is under investigation. Metabolism studies performed in bPTC cells using high concentrations of 1alpha,25(OH)2D3 substrate showed that in some incubations, the concentration of 1alpha,25(OH)2-3-epi-D3 was even higher than that of the parent substrate 1alpha,25(OH)2D3. This finding indicates a slower rate of metabolism for this diastereomer. Thus, production and accumulation of 1alpha,25(OH)2-3-epi-D3, as a major stable metabolite of 1alpha,25(OH)2D3 in parathyroid glands, may contribute to the prolonged suppressive effect of 1alpha,25(OH)2D3 on PTH gene transcription.

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Section: Analysis Of 1␣25(oh) 2 D 3 Metabolitesmentioning

confidence: 99%

1?,25-Dihydroxy-3-Epi-vitamin D3, a natural metabolite of 1?,25-dihydroxyvitamin D3, is a potent suppressor of parathyroid hormone secretion

et al. 1999

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“…Despite greater in vitro potency MC 1288 is predicted to be less useful in vivo due to rapid hepatic clearance, however, recent studies show it is metabolised to a stable 24-oxo intermediate which is almost as active as the parent compound in gene transactivation [270].…”

Section: Differential Modes and Cell Type-specific Metabolismmentioning

confidence: 99%

“…Ro 24-2637 is also metabolised to a stable, active intermediary 1,25-(OH) 2 -24-oxo-16-ene-D 3 via the C-24 oxidation pathway, both in a perfused rat kidney model and in the human myeloid leukemic cell line RWLeu-4 [270]. Ro 24-2637 and its 24-oxo metabolite display equipotent antiproliferative activity on RWLeu-4 cells and transactivational efficacy in ROS 17/2.8 cells and are equally effective in suppressing experimentally induced autoimmune encephaloyelitis in mice [213,270].…”

Section: Differential Modes and Cell Type-specific Metabolismmentioning

confidence: 99%

“…Ro 24-2637 and its 24-oxo metabolite display equipotent antiproliferative activity on RWLeu-4 cells and transactivational efficacy in ROS 17/2.8 cells and are equally effective in suppressing experimentally induced autoimmune encephaloyelitis in mice [213,270]. In contrast to the 24-oxo metabolite of calcitriol, the 24-oxo metabolite of Ro 24-2637 is resistant to subsequent hydroxylation by 23-hydroxylase.…”

Section: Differential Modes and Cell Type-specific Metabolismmentioning

confidence: 99%

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Molecular mechanism of vitamin D receptor action

Issa¹,

Leong²,

Eisman³

1998

Inflammation Research

109

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The vitamin D system is unique in that distinct calcium homeostatic functions and cell growth regulatory activities are mediated through a single ligand, calcitriol, acting through a specific receptor exhibiting ubiquitous tissue expression, the vitamin D receptor (VDR). The VDR is a member of a superfamily of nuclear steroid hormone receptors which regulate gene transcription by interacting with response elements in gene promoters. Structure-function analysis of the VDR protein has defined distinct domains involved in DNA binding, ligand binding, receptor dimerisation and gene transactivation, including a C-terminal activation function domain (AF-2) that is important for cofactor interaction. A model for regulation of gene transcription by the VDR is evolving and proposes VDR interaction with various components of the basal transcriptional machinery, including newly defined coactivators and corepressors, which may act to regulate gene transcription by altering histone acetylation and chromatin structure. This review describes the vitamin D endocrine system and the role of the VDR in regulating this system, including the molecular basis for the diverse actions of synthetic calcitriol analogues in the treatment of autoimmune disease and cancer.

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“…The in vivo result of CYP24A1 ablation is decreased viability, with 50% of mice not surviving beyond weaning because of hypercalcemia and nephrocalcinosis (8,10). Although it has been well established that calcitroic acid is the major biliary product of 1␣,25-(OH) 2 D 3 in the rat (11,12), there have been claims that intermediates of the C24 oxidation pathway retain some biological activity (13) and that the terminal product of 23-hydroxylation, namely 1␣,25-(OH) 2 D 3 -26,23-lactone, belongs to a family of potent VDR antagonists with potential for use in the treatment of Paget's disease (14,15).…”

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confidence: 99%

Single A326G mutation converts human CYP24A1 from 25-OH-D ₃ -24-hydroxylase into -23-hydroxylase, generating 1α,25-(OH) ₂ D ₃ -26,23-lactone

Prosser

Kaufmann

O’Leary

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Studies of 25-hydroxyvitamin D3-24-hydroxylase (CYP24A1) have demonstrated that it is a bifunctional enzyme capable of the 24-hydroxylation of 1␣,25-(OH) 2D3, leading to the excretory form, calcitroic acid, and 23-hydroxylation, culminating in 1␣,25-(OH) 2D3-26,23-lactone. The degree to which CYP24A1 performs either 23-or 24-hydroxylation is species-dependent. In this paper, we show that the human enzyme that predominantly 24-hydroxylates its substrate differs from the opossum enzyme that 23-hydroxylates it at only a limited number of amino acid residues. Mutagenesis of the human form at a single substrate-binding residue (A326G) dramatically changes the regioselectivity of the enzyme from a 24-hydroxylase to a 23-hydroxylase, whereas other modifications have no effect. Ala-326 is located in the I-helix, close to the terminus of the docked 25-hydroxylated side chain in a CYP24A1 homology model, a result that we interpret indicates that substitution of a glycine at 326 provides extra space for the side chain of the substrate to move deeper into the pocket and place it in a optimal stereochemical position for 23-hydroxylation. We discuss the physiological ramifications of these results for species possessing the A326G substitution, as well as implications for optimal vitamin D analog design. (Fig. 1). Studies using CYP24A1-knockout (8) and VDR-knockout mice (8, 9) demonstrate the total absence of calcitroic acid and 1␣,25-(OH) 2 D 3 -26,23-lactone formation when the vitamin Dinducible, VDR-mediated CYP24A1 is not expressed. The in vivo result of CYP24A1 ablation is decreased viability, with 50% of mice not surviving beyond weaning because of hypercalcemia and nephrocalcinosis (8, 10). Although it has been well established that calcitroic acid is the major biliary product of 1␣,25-(OH) 2 D 3 in the rat (11, 12), there have been claims that intermediates of the C24 oxidation pathway retain some biological activity (13) and that the terminal product of 23-hydroxylation, namely 1␣,25-(OH) 2 D 3 -26,23-lactone, belongs to a family of potent VDR antagonists with potential for use in the treatment of Paget's disease (14, 15).The degree to which CYP24A1 performs either of these pathways varies with the species. It had been shown in the mid-1980s by using isolated kidney mitochondria from a variety of species, that the 24-hydroxylase and 23-hydroxylase activities copurify (16). Although both pathways are used in humans, certain species, such as the guinea pig (17, 18), were shown to 23-hydroxylate, whereas other species, such as the rat, primarily 24-hydroxylate the substrate, 25-OH-D 3 (16). These studies suggested that the two enzyme activities might have different kinetic parameters, but it was not clear whether the activities resided on a single or distinct polypeptide chains. With the cloning and expression of the recombinant protein from different species (19,20), it became clear that a single polypeptide chain was capable of both C23-and C24-hydroxylation activities (5-7).Recent studies of rat and human CYP24A1 hav...

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1α,25-dihydroxy-24-oxo-16-ene vitamin D3, a metabolite of a synthetic vitamin D3 analog, 1α,25-dihydroxy-16-ene vitamin D3, is equipotent to its parent in modulating growth and differentiation of human leukemic cells

Cited by 30 publications

References 22 publications

1?,25-Dihydroxy-3-Epi-vitamin D3, a natural metabolite of 1?,25-dihydroxyvitamin D3, is a potent suppressor of parathyroid hormone secretion

1?,25-Dihydroxy-3-Epi-vitamin D3, a natural metabolite of 1?,25-dihydroxyvitamin D3, is a potent suppressor of parathyroid hormone secretion

Molecular mechanism of vitamin D receptor action

Single A326G mutation converts human CYP24A1 from 25-OH-D ₃ -24-hydroxylase into -23-hydroxylase, generating 1α,25-(OH) ₂ D ₃ -26,23-lactone

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1α,25-dihydroxy-24-oxo-16-ene vitamin D3, a metabolite of a synthetic vitamin D3 analog, 1α,25-dihydroxy-16-ene vitamin D3, is equipotent to its parent in modulating growth and differentiation of human leukemic cells

Cited by 30 publications

References 22 publications

1?,25-Dihydroxy-3-Epi-vitamin D3, a natural metabolite of 1?,25-dihydroxyvitamin D3, is a potent suppressor of parathyroid hormone secretion

1?,25-Dihydroxy-3-Epi-vitamin D3, a natural metabolite of 1?,25-dihydroxyvitamin D3, is a potent suppressor of parathyroid hormone secretion

Molecular mechanism of vitamin D receptor action

Single A326G mutation converts human CYP24A1 from 25-OH-D 3 -24-hydroxylase into -23-hydroxylase, generating 1α,25-(OH) 2 D 3 -26,23-lactone

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Single A326G mutation converts human CYP24A1 from 25-OH-D ₃ -24-hydroxylase into -23-hydroxylase, generating 1α,25-(OH) ₂ D ₃ -26,23-lactone