25-Hydroxylation of vitamin D3 in the human hepatoma cell lines Hep G2 and Hep 3B

Syntheses of 25-Adamantyl-25-alkyl-2-methylidene-1α,25-dihydroxyvitamin D3 Derivatives with Structure-Function Studies of Antagonistic and Agonistic Active Vitamin D Analogs

The active form of vitamin D₃, 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], is a major regulator of calcium homeostasis through activation of the vitamin D receptor (VDR). We have previously synthesized vitamin D derivatives with large adamantane (AD) rings at position 24, 25, or 26 of the side chain to study VDR agonist and/or antagonist properties. One of them-ADTK1, with an AD ring and 23,24-triple bond-shows a high VDR affinity and cell-selective VDR activity. In this study, we synthesized novel vitamin D derivatives (ADKM1-6) with an alkyl group substituted at position 25 of ADTK1 to develop more cell-selective VDR ligands. ADKM2, ADKM4, and ADKM6 had VDR transcriptional activity comparable to 1,25(OH)₂D₃ and ADTK1, although their VDR affinities were weaker. Interestingly, ADKM2 has selective VDR activity in kidney- and skin-derived cells-a unique phenotype that differs from ADTK1. Furthermore, ADKM2, ADKM4, and ADKM6 induced osteoblast differentiation in human dedifferentiated fat cells more effectively than ADTK1. The development of vitamin D derivatives with bulky modifications such as AD at position 24, 25, or 26 of the side chain is useful for increased stability and tissue selectivity in VDR-targeting therapy.

Differential effects of vitamin D3 vs vitamin D2 on cellular uptake, tissue distribution and activation of vitamin D in mice and cells

To combat vitamin D deficiency, vitamin D₃ and vitamin D₂ are commonly used as a supplement or to fortify food sources. Human data show that the response of 25-hydroxyvitamin D (25(OH)D) to supplementation with vitamin D₃ is higher than to vitamin D₂. To elucidate the metabolic route of both vitamers, we conducted a study with vitamin D-depleted mice, which were allotted into three groups (n = 12) and received equal doses of either deuterated vitamin D₃, deuterated vitamin D₂ or both for 4 weeks. To further investigate the hepatic uptake and hydroxylation of both D-vitamers to 25(OH)D, we conducted cell culture experiments with murine and human hepatoma cells (Hepa1-6 and HepG2). The vitamin D metabolite concentrations in serum, tissues and cells were analyzed by LC-MS/MS or ELISA. In mice, vitamin D₂ resulted in lower serum and tissue concentrations of vitamin D (P < 0.001) than vitamin D₃, while the group which received both D-vitamers showed values in between. Interestingly, vitamin D₂ fed mice had 1.9-times and 2.9-times higher serum concentrations of total and free 25(OH)D (P < 0.001) than mice fed vitamin D₃, while the concentration of 1,25-dihydroxyvitamin D (1,25(OH)₂D) was 1.8-times lower (P < 0.001). The gene and protein expression of enzymes, involved in the hydroxylation and renal uptake of vitamin D remained largely unaffected by the D-vitamer. In contrast to the mice data, hepatoma cells preferred vitamin D₃ for 25-hydroxylation over vitamin D₂ (P < 0.001). In general, the formation of 25(OH)D was much more pronounced in human than in murine hepatoma cells (P < 0.001). To conclude, in contrast to humans, vitamin D₂ was more efficient in increasing 25(OH)D than vitamin D₃ in mice, although this difference was not caused by a preferential hydroxylation of vitamin D₂ in the liver. The metabolic routes of D₃ and D₂ in mice differ, showing lower circulating 1,25(OH)₂D and tissue vitamin D concentrations in D₂- than in D₃-fed mice.

Intake of ergosterol increases the vitamin D concentrations in serum and liver of mice

Factors that can modify the bioavailability of orally administered vitamin D are not yet widely known. Ergosterol is a common fungal sterol found in food which has a chemical structure comparable to that of vitamin D. This study aimed to investigate the effect of ergosterol on vitamin D metabolism. Therefore, 36 male wild type-mice were randomly subdivided into three groups (n = 12) and received a diet containing 25 μg vitamin D₃ and either 0 mg (control), 2 mg or 7 mg ergosterol per kg diet for 6 weeks. To elucidate the impact of ergosterol on hepatic hydroxylation of vitamin D, human hepatoma cells (HepG2) were treated with different concentrations of ergosterol. Concentrations of vitamin D₃ and 25-hydroxyvitamin D₃ (25(OH)D₃) in cells, livers and kidneys of mice and additionally 24,25-dihydroxyvitamin D₃ (24,25(OH)₂D₃) in serum were quantified by LC-MS/MS. The concentration of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) in serum was analyzed by commercially-available enzyme immuno assay. The concentrations of cholesterol and triglycerides were analyzed in livers of mice by photometric assays. Analyses revealed that mice receiving 7 mg/kg ergosterol with their diet had 1.3-, 1.7- and 1.5-times higher concentrations of vitamin D₃ in serum, liver and kidney, respectively, than control mice (P < 0.05), whereas no significant effects were observed in mice fed 2 mg/kg ergosterol. The hydroxylation of vitamin D remained unaffected by dietary ergosterol, since the concentration of 25-hydroxyvitamin D₃ in serum and tissues and the concentrations of 1,25(OH)₂D₃ and 24,25(OH)₂D₃ in serum were not different between the three groups of mice. The lipid concentrations in liver were also not affected by dietary ergosterol. Data from the cell culture studies showed that ergosterol did not influence the conversion of vitamin D₃ to 25(OH)D₃. To conclude, ergosterol appears to be a modulator of vitamin D₃ concentrations in the body of mice, without modulating the hydroxylation of vitamin D₃ in liver.

Vitamin D and melatonin protect the cell's viability and ameliorate the CCl4 induced cytotoxicity in HepG2 and Hep3B hepatoma cell lines

Carbon tetrachloride (CCl4) is widely used to induce liver toxicity in in vitro/in vivo models. Lipid peroxidation (LPO) begins with toxicity and affects cell viability. Recently, the beneficial effects of melatonin and Vitamin D on cell proliferation in human normal and cancer cells were found. This study was planned to evaluate antioxidant and cytoprotective activity of melatonin and Vitamin D in CCl4 induced cytotoxicity in HepG2 and Hep3B hepatoma cell lines. Based on the cytotoxicity assay, melatonin and Vitamin D were evaluated for cytotoprotective potential against CCl4 induced toxicity in HepG2 and Hep3B liver cell lines by monitoring cell viability, LPO and glutathione (GSH) level. Different dosages of CCl4 (0.1, 0.2, 0.3 and 0.4 % v/v) were applied to HepG2 and Hep3B cells in order to determine the most toxic dosage of it in a time dependent manner. The same experiments were repeated with exogenously applied melatonin (MEL) and Vitamin D to groups treated with/without CCL4. Cell viability was determined with MTT measurements at the 2nd, 24th and 48th h. GSH content and Malondialdehyde levels were measured from the cell lysates. As a result, both melatonin and Vitamin D administration during CCl4 exposure protected liver cells from CCl4 induced cell damage. Increase in LPO and decrease in GSH were found in the CCl4 groups of both cells. Contrary to these results administration of MEL and Vitamin D on cells exhibited results similar to the control groups. Therefore, melatonin and Vitamin D might be a promising therapeutic agent in several toxic hepatic diseases.

In vitro and in vivo inhibition of liver cancer cells by 1,25-dihydroxyvitamin D3

Inhibitory effects of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on the proliferation of a variety of cancer cell lines have been extensively reported. We have studied the effect of 1,25-(OH)2D3 (10(-11)-10(-6) M) on the proliferation of a number of human and rat liver cancer cell lines. Additionally, the effect of 1,25-(OH)2D3 (0.02-0.5 microg/kg per day) on the rate of growth of liver cancer cell line xenografts in nude mice was also investigated. In vitro, proliferation of Hep-3B, PLC/PRF/5, and SKHEP-1 cells was significantly inhibited by 1,25-(OH)2D3, while HTC and Novikoff cells were more resistant to the inhibitory effects of the drug. In vivo, treatment of SKHEP-1 tumor bearing nude mice with different doses of 1,25-(OH)2D3 significantly retarded tumor growth without the development of hypercalcemia.

Synergistic induction of HL60 cell differentiation by ketoconazole and 1-desoxy analogues of vitamin D3

BACKGROUND

The goal of differentiation therapy is to induce cancer cells to stop proliferating and to express characteristics of normal cells. Vitamin D analogues, such as the deltanoids, are being evaluated as differentiation agents in the treatment of several human cancers (e.g., myeloid leukemias); however, these compounds have a tendency to produce hypercalcemia in patients receiving therapy. A combination of a differentiation-inducing deltanoid with a compound that blocks entry of calcium into cells (e.g., ketoconazole) may offer a new approach to differentiation therapy and address the problem of hypercalcemia. We investigated whether various ketoconazole-deltanoid combinations would alter cellular differentiation or intracellular calcium homeostasis in comparison with deltanoids used alone.

METHODS

Cultured human leukemia HL60 cells were treated with ketoconazole-deltanoid combinations. Markers of differentiation (expression of CD11b and CD14 antigens and of non-specific esterase) were measured by flow cytometry and cytochemistry; cell cycle distribution was measured by flow cytometry of propidium iodide-stained cells. Expression of differentiation-related genes was assessed by northern blotting and immunoblotting, and changes in intracellular calcium homeostasis were monitored by fluorescence analysis of fura-2-containing cells.

RESULTS

Ketoconazole strongly potentiated the differentiating activity of the deltanoids, which exhibited low potency when used alone. Ketoconazole-deltanoid combinations had little effect on HL60 cell-cycle distribution, although the cells did stop proliferating and they differentiated. Ketoconazole-deltanoid combinations produced only minor changes in intracellular calcium homeostasis compared with changes produced by 1,25-dihydroxyvitamin D3, either alone or in combination with ketoconazole.

CONCLUSION

These results suggest that ketoconazole may be useful in combination with vitamin D analogues in the differentiation therapy for myeloid leukemias.

Polar metabolites of dihydrotachysterol3 in the rat. Comparison with in vitro metabolites of 1 alpha,25-dihydroxydihydrotachysterol3

The metabolism of 25-hydroxydihydrotachysterol3 (25-OH-DHT3) to more polar metabolites was investigated in vivo in the rat and compared with the in vitro metabolism of 1 alpha,25-dihydroxy-DHT3 (1 alpha,25-(OH)2DHT3) in the osteosarcoma cell line UMR 106. Rats were given 2 mg of DHT3 in divided doses at 0 and 6 hr. Plasma was collected 24 hr after the initial dose, extracted, separated, and polar metabolites purified by HPLC. A number of polar metabolites were formed in vivo with mass spectrometric characteristics which suggested that they were derived from a previously isolated metabolite of 25-OH-DHT3, T3/H. Of these, four were isolated and identified as 24-oxo-T3/H, 24-hydroxy-T3/H, 26-hydroxy-T3/H and the 26,23-lactone of T3/H. In view of the identification of T3/H as a mixture of 1 alpha- and 1 beta-hydroxylated 25-OH-DHT3, osteosarcoma cells (UMR 106) were incubated with chemically synthesized 1 alpha,25-(OH)2DHT3 in an attempt to determine from which component of the T3/H mixture these metabolites were derived. Again, more polar metabolites were formed and five of these were isolated by lipid extraction, purified by HPLC and identified as 24-oxo-1 alpha,25-(OH)2DHT3, 1 alpha,23,25-(OH)3DHT3, 24-oxo-1 alpha,23,25-(OH)3DHT3, 1 alpha,24,25-(OH)3DHT3 and 1 alpha,25,26-(OH)3DHT3. Three of the in vitro metabolites were similar to those found in rat plasma but only two of these metabolites were available in sufficient amounts to allow comparison. The chromatographic characteristics, using HPLC and gas chromatography, of these two pairs of metabolites (24-oxo and 24-hydroxy) were examined and it was demonstrated that they were not the same. It is therefore suggested that the polar metabolites formed in vivo are in fact metabolites of the T3/Hb component (1 beta,25-(OH)2DHT3) rather than the T3/Ha component (1 alpha,25-(OH)2DHT3). Supporting evidence for this suggestion was obtained when a small quantity of 1 beta,25-(OH)2DHT3, obtained from chemically synthesized 1 beta-OH-DHT3 by incubation with Hep 3B cells, was further incubated in the osteosarcoma UMR 106 system. Preliminary studies indicated that the putative 24-oxo and 24-hydroxy metabolites formed from 1 beta,25-(OH)2DHT3 had chromatographic and mass spectral properties almost indistinguishable from those of corresponding metabolites of T3/H formed in vivo. All the metabolites formed in vivo and in vitro are components of two metabolic pathways described previously for 25-hydroxyvitamin D3 and also for 25-OH-DHT3.

Metabolism of 25-hydroxydihydrotachysterol3 in bone cells in vitro

Dihydrotachysterol3, a reduced (or hydrogenated) analog of vitamin D3 in which the A ring has been rotate through 180 degrees , is, after hepatic 25-hydroxylation, converted in vivo to a dihydroxylated metabolite, termed peak H, which is at present unidentified but with good affinity for the vitamin D receptor. Although peak H is made in relatively large amounts in vivo, it has not yet been possible to synthesize it in vitro. Mass spectrometric evidence suggests that peak H is 25-hydroxylated and the presumption that it is a metabolite of 25-hydroxydihydrotachysterol3 was confirmed by the demonstration that radiolabeled peak H was formed in vivo in the rat after injection of 25-hydroxy-[10,19-3H]dihydrotachysterol3, produced from [10,19-3H]dihydrotachysterol3 in a hepatic cell model. The metabolism of 25-hydroxy-[10,19-3H]dihydrotachysterol3 was also studied in a rat osteosarcoma cell UMR-106, a known target cell for vitamin D, using high (11 microM) and low (10 nM) substrate concentrations. Metabolic products were isolated by lipid extraction, purified by high-performance liquid chromatography, and characterized by direct-probe mass spectrometry and gas chromatography/mass spectrometry. The formation of peak H from 25-hydroxydihydrotachysterol3 could not be demonstrated in UMR-106 cells. However, 25-hydroxydihydrotachysterol3 was metabolized to at least seven side-chain modified metabolites, each of which was extensively characterized and tentatively identified. It is concluded that the vitamin D enzyme system present in UMR-106 cells is able to metabolize dihydrotachysterol3 very efficiently to a series of metabolites but is incapable of producing peak H.

The metabolism of dihydrotachysterols: renal side chain and non-renal nuclear hydroxylations in vivo and in vitro

The metabolism of dihydrotachysterol (DHT), a hydrogenated analogue of vitamin D, has been studied in vivo using man and rat and in vitro using the perfused rat kidney, and hepatoma (3B) and osteosarcoma (UMR-106) cell lines. In vivo a large number of metabolites appeared in the plasma of rats given DHT2 and DHT3. Of particular interest was a compound more polar than 25-hydroxy-DHT, which has been designated compound H. Further study of this compound showed that it was composed of two components, one (Ha) being in much lower concentration than the other (Hb). The production of T2/H (peak H from DHT2) was demonstrated in human plasma after administration of oral DHT2. Comparison of the metabolites formed in vivo with those isolated from the rat kidney perfused with 25-hydroxy-DHT3 in vitro showed that 25-hydroxy-DHT3 was metabolized along two metabolic pathways previously described for vitamin D, culminating in the production of 25-hydroxy-DHT3-23,26-lactone and 23,25-dihydroxy-24-oxo-DHT3. The osteosarcoma cell line metabolized 25-OH-DHT3 in vitro along the same two metabolic pathways already demonstrated in the perfused rat kidney. More polar metabolites than compound H seen in rat plasma in vivo were shown to be metabolites of compound H and similar metabolites were also produced in the osteosarcoma cell line from chemically synthesized 1 alpha,25-dihydroxy-DHT3. The hepatoma cell line 25-hydroxylated DHT and no feed-back inhibition was observed. Use of the hepatoma cell to 25-hydroxylate a number of chemically synthesized 1-hydroxy-DHTs indicated that compound Ha was indistinguishable from 1 alpha,25-dihydroxy-DHT whereas compound Hb is possibly 1 beta,25-dihydroxy-DHT. Studies with the VDR in both chick gut and calf thymus indicated that 1 alpha,25-dihydroxy-DHT is very effective in displacing radiolabelled 1 alpha,25-dihydroxyvitamin-D3 and is thus most likely to be the calcaemic metabolite of DHT.

Metabolism of a novel antitumor agent, crisnatol, by a human hepatoma cell line, Hep G2, and hepatic microsomes. Characterization of metabolites

Metabolism of the anticancer agent crisnatol was investigated using a human hepatoma cell line, Hep G2, and human liver microsomes. Crisnatol was metabolized extensively by both systems. The TLC/autoradiographic analysis showed that the crisnatol metabolite profile was similar for both systems and the major metabolites were shown to have structural characteristics similar to those formed by the rat. The Hep G2 cells formed three isomeric dihydrodiols; one of these has been identified by GC/MS and 1H-NMR as the crisnatol 1,2-dihydrodiol. Human liver microsomes also formed two isomeric dihydrodiols with 1,2-dihydrodiol as the major isomer and, in addition, produced 1-hydroxycrisnatol. Crisnatol concentrations of 1.3 micrograms/mL completely inhibited the replication of Hep G2 cells as measured by thymidine incorporation and cell growth kinetics and, at this concentration, cell viability decreased by only 35% as determined by vital staining of cells using neutral red dye.

Metabolism of a cyclopropane-ring-containing analog of 1 alpha-hydroxyvitamin D3 in a hepatocyte cell model. Identification of 24-oxidized metabolites

MC969 is an analog of the calcemic drug 1 alpha-hydroxyvitamin D3 (1 alpha-OH-D3) in which carbons 25,26, and 27 in the side chain are incorporated into a cyclopropane ring. Metabolites of MC 969 were generated in an in vitro human hepatocyte cell model, Hep 3B. The identity of the metabolites was established by comigration on HPLC with authentic standards, and by mass spectrometry of native and chemically modified metabolites. Unequivocal identification of the 24-keto- and the two epimeric 24-alcohol metabolites is provided. No 25-hydroxylated metabolites were detected. In competition studies, MC 969 was able to inhibit 25-hydroxylation of tritiated vitamin D3 more effectively than 1 alpha-OH-D3 itself, indicating that the vitamin D3-25-hydroxylase may be responsible for generation of one or more of the metabolites observed.