Metabolism of the cell differentiating agent 1alpha,25(OH)2-16-ene-23-yne vitamin D3 by leukemic cells

Dietary effect of Antrodia Camphorate extracts on immune responses in WEHI-3 leukemia BALB/c mice

Antrodia camphorata has been recognized to be a traditional Chinese medicine for abdominal pain, diarrhea, and to protect against hepatitis virus infection. Several ingredients derived from A. camphorata possess various pharmacological and biological activities such as antioxidant and anticancer. In this study, its ability to promote immune responses and to exhibited antileukemia activity in WEHI-3 leukemia BALB/c mice were investigated. The results indicated A. camphorata significantly prolonged the survival rate and prevented the body weight loss in leukemia mice. Four mg/kg of A. camphorata treatment significantly decreased the weight of the spleen. Both doses (2 and 4 mg/kg) of A. camphorata did not affect Mac-3 marker in leukocytes. However, the 4 mg/kg of A. camphorata decreased the levels of CD11b and both doses of treatment increased CD3 and CD19. With lipopolysaccharide stimulation, the 4 mg/kg of A. camphorata promoted the significant proliferation of leukocytes; but with concanavalin A stimulation, both doses promoted the significant proliferation of leukocytes. YAC-1 target cells were killed by NK cells from the mice after treatment with A. camphorata at 4 mg/kg in target cells at a ratio of 50:1. The percentage of macrophages with phagocyted at A. camphorata treatment increased, and these effects were in dose-dependent manners.

Benzyl isothiocyanate inhibits murine WEHI-3 leukemia cells in vitro and promotes phagocytosis in BALB/c mice in vivo

Many evidences have shown that dietary intake of cruciferous vegetables could protect against the risk of various types of malignancies. Benzyl isothiocyanate (BITC), one of the compounds from cruciferous vegetables, had shown induced cell cycle arrest and apoptosis in cancer cells. However, there is no available information to address that BITC affects murine leukemia cells in vitro and in vivo. Here, we investigated in vitro effects of BITC on murine leukemia WEHI-3 cells. BITC decreased the percentage of viable cells via G0/G1 arrest and apoptosis in WEHI-3 cells. BITC induced apoptosis through the dysfunction of mitochondria (decreased the levels of mitochondria membrane potential) and activation of caspase-3. Then we investigated in vivo effects of BITC on murine leukemia WEHI-3 cells and the results indicated that BITC decreased the weights of liver and spleen and it also decreased the percentage of CD11b and Mac-3 markers, indicating that the differentiation of the precursor of macrophage and B cells was inhibited. BITC promoted the activity of macrophage phagocytosis in cells which are isolated from PBMC and peritoneal (i.p.). Taken together, BITC can affect WEHI-3 cells in vitro and in vivo.

Importance of cytochrome P450-mediated metabolism in the mechanism of action of vitamin D analogs

The elucidation of the metabolic pathway for vitamin D, including the delineation of the specific cytochrome P450s (CYPs) involved in activation and catabolism, has emphasized the overall importance of metabolic considerations in vitamin D analog design. This short review attempts to summarize recent findings with isolated CYPs and animal models in which CYPs are genetically manipulated to draw attention to structural features of vitamin D analogs that make them more or less resistant to metabolic enzymes. We conclude by placing metabolic considerations in the context of the other important aspects of vitamin D analogs.

Activation of Vitamin D Receptor by the Wilms' Tumor GeneProduct Mediates Apoptosis of Renal Cells

Abstract. The Wilms' tumor transcription factor WT1 is required for kidney development, but little is known about WT1 downstream signaling in renal cells. This study reported an approximately fivefold upregulation of vitamin D receptor (VDR) mRNA and protein in human embryonic kidney (HEK) 293 cells that stably expressed WT1 at a level comparable to the developing kidney in vivo. Co-transfection of HEK 293 cells with expression plasmids encoding four different WT1 splicing variants stimulated mouse vdr promoter activity more than fourfold. A 201-bp fragment was identified in the proximal vdr promoter that was required for transactivation by WT1. This critical sequence contained a predicted WT1 consensus site, which bound to recombinant WT1 protein. Temporal changes of vdr and wt1 mRNA levels in developing rat kidneys were correlated closely. The active metabolite 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) strongly inhibited the proliferation of wt1-transfected HEK 293 cells. Exposure to 1,25-(OH)2D3 caused apoptosis of cultured wt1 immunopositive cells from mouse embryonic kidney cortex. These findings suggest that transcriptional activation of the VDR by WT1 can mediate programmed death of renal embryonic cells in response to 1,25-(OH)2D3. The results provide the first evidence for a role of the vitamin D endocrine system in renal cell growth and differentiation during development.

Metabolism of 1alpha,25-dihydroxyvitamin D(3) in human promyelocytic leukemia (HL-60) cells: in vitro biological activities of the natural metabolites of 1alpha,25-dihydroxyvitamin D(3) produced in HL-60 cells

The secosteroid hormone, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], induces differentiation of the human promyelocytic leukemia (HL-60) cells into monocytes/macrophages. At present, the metabolic pathways of 1alpha,25(OH)(2)D(3) and the biologic activity of its various natural intermediary metabolites in HL-60 cells are not fully understood. 1alpha,25(OH)(2)D(3) is metabolized in its target tissues via modifications of both the side chain and the A-ring. The C-24 oxidation pathway, the main side chain modification pathway initiated by hydroxylation at C-24 leads to the formation of the end product, calcitroic acid. The C-23 and C-26 oxidation pathways, the minor side chain modification pathways initiated by hydroxylations at C-23 and C-26 respectively together lead to the formation of the end product, 1alpha,25(OH)(2)D(3)-lactone. The C-3 epimerization pathway, the newly discovered A-ring modification pathway is initiated by epimerization of the hydroxyl group at C-3 to form 1alpha,25-dihydroxy-3-epi-vitamin-D(3). We performed the present study first to examine in detail the metabolism of 1alpha,25(OH)(2)D(3) in HL-60 cells and then to assess the ability of the various natural intermediary metabolites of 1alpha,25(OH)(2)D(3) in inducing differentiation and in inhibiting clonal growth of HL-60 cells. We incubated HL-60 cells with [1beta-(3)H] 1alpha,25(OH)(2)D(3) and demonstrated that these cells metabolize 1alpha,25(OH)(2)D(3) mainly via the C-24 oxidation pathway and to a lesser extent via the C-23 oxidation pathway, but not via the C-3-epimerization pathway. Three of the natural intermediary metabolites of 1alpha,25(OH)(2)D(3) derived via the C-24 oxidation pathway namely, 1alpha,24(R),25-trihydroxyvitamin D(3), 1alpha,25-dihydroxy-24-oxovitamin D(3) and 1alpha,23(S),25-trihydroxy-24-oxovitamin D(3) [1alpha,23(S),25(OH)(3)-24-oxo-D(3)] were almost as potent as 1alpha,25(OH)(2)D(3) in terms of their ability to differentiate HL-60 cells into monocytes/macrophages. We then selected 1alpha,23(S),25(OH)(3)-24-oxo-D(3) which has the least calcemic activity among all the three aforementioned natural intermediary metabolites of 1alpha,25(OH)(2)D(3) to examine further its effects on these cells. Our results indicated that 1alpha,23(S),25(OH)(3)-24-oxo-D(3) was also equipotent to its parent in inhibiting clonal growth of HL-60 cells and in inducing expression of CD11b protein. In summary, we report that 1alpha,25(OH)(2)D(3) is metabolized in HL-60 cells into several intermediary metabolites derived via both the C-24 and C-23 oxidation pathways but not via the C-3 epimerization pathway. Some of the intermediary metabolites derived via the C-24 oxidation pathway are found to be almost equipotent to 1alpha,25(OH)(2)D(3) in modulating growth and differentiation of HL-60 cells. In a previous study, the same metabolites when compared to 1alpha,25(OH)(2)D(3) were found to be less calcemic. Thus, the findings of our study suggest that some of the natural metabolites of 1alpha,25(OH)(2)D(3) may be responsible for the final expression of the noncalcemic actions that are presently being attributed to their parent, 1alpha,25(OH)(2)D(3).

25-Dehydro-1alpha-hydroxyvitamin D3-26,23S-lactone antagonizes the nuclear vitamin D receptor by mediating a unique noncovalent conformational change

(23S)-25-dehydro-1alpha-Dihydroxyvitamin D3-26,23-lactone (TEI-9647; MK) has been reported to antagonize the 1alpha,25-dihydroxyvitamin D3 nuclear receptor (VDR)- mediated increase in transcriptional activity. Using a transient transfection system incorporating the osteocalcin VDRE (vitamin D response element) in Cos-1 cells, we found that 20 nM MK antagonizes VDR-mediated transcription by 50% when driven by 1 nM 1alpha,25(OH)2D3. Four analogs of 1alpha,25(OH)2D3, also at 1 nM, were antagonized 25 to 39% by 20 nM MK. However, analogs with 16-ene/23-yne or 20-epi modifications, which have a significantly lower agonist ED50 for the VDR than 1alpha,25(OH)2D3, were antagonized by 20 nM MK only at 100 pM or 10 pM, respectively. One possible mechanism for antagonism is that the 25-dehydro alkene of MK might covalently bind the ligand-binding site of the VDR rendering it inactive. Utilization of a ligand exchange assay, however, demonstrated that MK bound to VDR is freely exchanged with 1alpha,25(OH)2D3 in vitro. These data support the apparent correlation between VDR transcriptional activation by agonists and the effective range of MK antagonism by competition. Furthermore, protease sensitivity analysis of MK bound to VDR indicates the presence of a unique conformational change in the VDR ligand-binding domain, showing a novel doublet of VDR fragments centered at 34 kDa, whereas 1alpha,25(OH)2D3 as a ligand produces only a single 34-kDa fragment. In comparison, the natural metabolite 1alpha,25-dihydroxyvitamin D3-26,23-lactone yields only the 30-kDa fragment that is produced by all ligands to varying degrees. Collectively, these results support that MK is a potent partial antagonist of the VDR for 1alpha,25(OH)2D3 and its analogs when in appropriate excess of the agonist.

Current understanding of the molecular actions of vitamin D

The important reactions that occur to the vitamin D molecule and the important reactions involved in the expression of the final active form of vitamin D are reviewed in a critical manner. After an overview of the metabolism of vitamin D to its active form and to its metabolic degradation products, the molecular understanding of the 1alpha-hydroxylation reaction and the 24-hydroxylation reaction of the vitamin D hormone is presented. Furthermore, the role of vitamin D in maintenance of serum calcium is reviewed at the physiological level and at the molecular level whenever possible. Of particular importance is the regulation of the parathyroid gland by the vitamin D hormone. A third section describes the known molecular events involved in the action of 1alpha,25-dihydroxyvitamin D3 on its target cells. This includes reviewing what is now known concerning the overall mechanism of transcriptional regulation by vitamin D. It describes the vitamin D receptors that have been cloned and identified and describes the coactivators and retinoid X receptors required for the function of vitamin D in its genomic actions. The presence of receptor in previously uncharted target organs of vitamin D action has led to a study of the possible function of vitamin D in these organs. A good example of a new function described for 1alpha,25-dihydroxyvitamin D3 is that found in the parathyroid gland. This is also true for the role of vitamin D hormone in skin, the immune system, a possible role in the pancreas, i.e., in the islet cells, and a possible role in female reproduction. This review also raises the intriguing question of whether vitamin D plays an important role in embryonic development, since vitamin D deficiency does not prohibit development, nor does vitamin D receptor knockout. The final section reviews some interesting analogs of the vitamin D hormone and their possible uses. The review ends with possible ideas with regard to future directions of vitamin D drug design.