Isolation, identification, and chemical synthesis of 8 alpha,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3-one. A new metabolite of 25-hydroxyvitamin D3 produced by mouse myeloid leukemia cells (M1)

It is known that phagocytic cells such as monocyte-macrophages and myeloid leukemia cells metabolize 25-hydroxyvitamin D3 to 10-oxo-19-nor-25-hydroxyvitamin D3. Now we have found that phagocytic cells metabolize 25-hydroxyvitamin D3 not only to 10-oxo-19-nor-25-hydroxyvitamin D3 but also to a new metabolite eluted just after 24R,25-dihydroxyvitamin D3 on straight phase high pressure liquid chromatography with a 2-propanol-hexane solvent system. The new metabolite, produced by murine myeloid leukemia cells (M1), was isolated in pure form and identified as 8,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3-one on the basis of mass, ultraviolet, infrared, and proton magnetic resonance spectra. The 8 alpha-hydroxy epimer of the putative metabolite was chemically synthesized in two steps starting from 25-hydroxyvitamin D3. The spectral data and chromatographic behavior of chemically synthesized 8 alpha,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3-one coincided exactly with those of the isolated metabolite, indicating that the stereochemistry of the hydroxyl group at the 8-position is alpha. On the basis of the structural characteristics of the two metabolites produced from 25-hydroxyvitamin D3 (the present metabolite and 10-oxo-19-nor-25-hydroxyvitamin D3), it is suggested that dioxygenases are involved in the production of these metabolites from 25-hydroxyvitamin D3 in phagocytic cells.

The relationship between fusion and proliferation in mouse alveolar macrophages

We have reported that protein factors separated from conditioned media of Concanavalin A-stimulated spleen cell cultures induce growth and fusion of mouse alveolar macrophages. A macrophages growth factor (MGF) was purified and, at the final step of purification on HPLC, eluted at the same position as a colony-stimulating factor (CSF), suggesting that MGF is identical with CSF. In the present study, we examined the relationship between proliferation and fusion of macrophages using purified CSF (MGF) and 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)2D3]. The latter was used in place of a macrophage fusion factor which is supposed to be contained in the same conditioned medium, since a macrophage fusion factor has not yet been isolated. Adding less than 5% unfractionated conditioned medium from Concanavalin A-stimulated spleen cells markedly induced proliferation of alveolar macrophages without inducing fusion. In contrast, adding the same unfractionated conditioned medium at concentrations of 10% or more suppressed proliferation dose dependently, whereas it induced fusion reciprocally. Proliferation of macrophages was similarly enhanced by adding purified CSF or retinoic acid. Fusion of macrophages was induced by 1 alpha,25-(OH)2D3, but not by purified CSF or retinoic acid. Adding 1 alpha,25-(OH)2D3 together with purified CSF or retinoic acid completely suppressed the increase of proliferation induced by either growth factor, whereas that treatment rather potentiated the fusion induced by 1 alpha,25-(OH)2D3 alone. These results indicate that the fusion and proliferation of macrophages occur in a reciprocal fashion.

Phagocytic cells metabolize 25-hydroxyvitamin D3 to 10-oxo-19-nor-25-hydroxyvitamin D3 and a new metabolite, 8 alpha,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3-one

The metabolism of 25-hydroxyvitamin D3 [25(OH)D3] was examined in several phagocytic cells including alveolar macrophages and myeloid leukemia cells (M1, HL-60 and U937). Phagocytic cells converted 25(OH)D3 to 10-oxo-19-nor-25-hydroxyvitamin D3 and a new metabolite. The former metabolite was dominant in shorter incubation periods (1 h), whereas the latter dominated over longer incubation periods (24 h). The new metabolite was produced from 25(OH)D3 directly but not through 10-oxo-19-nor-25-hydroxyvitamin D3. The new metabolite was unequivocally identified as 8 alpha,25-dihydroxy-9-10-seco-4,6,10(19)-cholestatrien-3-one. These results suggest that phagocytic cells somehow promote oxidation of the triene part of vitamin D compounds.

Alteration of lipid metabolism associated with the activation of mouse alveolar macrophages induced by 1 alpha, 25-dihydroxyvitamin D3

We have reported that 1 alpha, 25-dihydroxyvitamin D3 [1 alpha, 25-(OH)2D3] directly induces fusion and tumoricidal activity (activation) in murine alveolar macrophages. In this study we examined lipid metabolism associated with the fusion and activation of alveolar macrophages induced by 1 alpha, 25-(OH)2D3. Treatment of alveolar macrophages with 12 nM 1 alpha, 25-(OH)2D3 for 48 h caused a marked increase in incorporation of [14C]acetic acid and [14C]oleic acid into triacylglycerol. The macrophages treated with the vitamin began to fuse and show cytotoxicity at 48 h, whereas incorporation of the radioactive compounds into triacylglycerol started as early as 12 h after 1 alpha, 25-(OH)2D3 was added. The triacylglycerol synthesis induced by 1 alpha, 25-(OH)2D3 was greatly increased when 14C-labeled unsaturated fatty acids were used as tracers compared with 14C-labeled saturated fatty acids. The activity of diacylglycerol acyltransferase, which catalyzes the last step of the three acylations in triacylglycerol synthesis, was significantly higher in the macrophages treated with 1 alpha, 25-(OH)2D3 than in the control macrophages. Like 1 alpha, 25-(OH)2D3, retinoic acid and lypopolysaccharides also activated alveolar macrophages, but not induce any fusion. The activated macrophages cultured with retinoic acid or lypopolysaccharides also induced synthesis of triacylglycerol. These results indicate that 1 alpha, 25-(OH)2D3 induces the synthesis of triacylglycerol by preferentially incorporating unsaturated fatty acids into diacylglycerol, and that the alteration of lipid metabolism is related to the activation, rather than the fusion, of alveolar macrophages.

Differentiation-inducing factor purified from conditioned medium of mitogen-treated spleen cell cultures stimulates bone resorption

Spleen cells treated with mitogens produce a potent bone-resorbing factor called osteoclast-activating factor (OAF). To examine the relationship between the bone-resorbing factor and other protein factors produced by spleen cells, the colony-stimulating factor (CSF), the differentiation-inducing factor (DIF), the macrophage fusion factor (MFF), and the macrophage growth factor (MGF) were purified from 2.68 liters of conditioned medium of mouse spleen cell cultures treated with concanavalin A. Purification was performed successively by DEAE-cellulose, Blue Sepharose, and Sephadex G-150 column chromatography and high-pressure liquid chromatography (HPLC). The DIF was successfully separated from CSF and MGF on HPLC. CSF coincided with MGF on HPLC, but MFF disappeared before application to HPLC. Only the DIF exhibited bone-resorbing activity, whereas CSF and MGF did not. The DIFs purified from L929 cells and Ehrlich ascites tumors similarly exhibited bone-resorbing activity. The DIFs purified from spleen cells and Ehrlich ascites tumor cells exhibited neither interleukin 1 (IL-1) activity nor tumor necrosis factor (TNF) activity, though the unfractionated conditioned medium from spleen cells did exhibit them. In the light of recent reports that IL-1 beta and TNF also stimulate bone resorption, the term OAF should refer to a generic activity rather than a single factor.

Effects of retinoic acid on the activation and fusion of mouse alveolar macrophages induced by 1 alpha,25-dihydroxyvitamin D3

1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] directly induces both fusion and cytotoxicity in murine alveolar macrophages. Unlike 1 alpha,25(OH)2D3, retinoic acid per se did not induce fusion of alveolar macrophages, but it greatly enhanced the 1 alpha,25(OH)2D3-induced fusion every time the macrophages were treated simultaneously with the two vitamins. The giant cells induced by the two vitamins were much larger than those induced by 1 alpha,25(OH)2D3 alone. The macrophages treated with 1 alpha,25(OH)2D3 started to fuse 36 h after the addition of the vitamin, whereas the macrophages pretreated with retinoic acid for 24 h began to fuse immediately after 1 alpha,25(OH)2D3 was added. 1 alpha,25(OH)2D3 and retinoic acid activated alveolar macrophages similarly, measured by the enhancement of glucose consumption and the induction of cytotoxicity against tumor cells, though 1 alpha,25(OH)2D3 was 100 times more potent than retinoic acid on a molar basis. Simultaneous treatment with physiological concentrations of 1 alpha,25(OH)2D3 (0.12 nM) and retinoic acid (10 nM) induced cytotoxicity additively. Morphological examinations revealed that the treated cells were enlarged and flattened with numerous filopodia. These results clearly indicate that both 1 alpha,25(OH)2D3 and retinoic acid similarly activate alveolar macrophages, and the activated state is prerequisite to the fusion of macrophages induced by 1 alpha,25(OH)2D3.

Alternative differentiation of human promyelocytic leukemia cells (HL-60) induced selectively by retinoic acid and 1 alpha,25-dihydroxyvitamin D3

Induction of hematopoietic differentiation was investigated in human promyelocytic leukemia cells [HL-60] using two lipophilic vitamins, retinoic acid and 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3]. Both vitamins suppressed proliferation and induced differentiation of HL-60 cells, but 1 alpha,25(OH)2D3 was 70- to 100-fold more potent than was retinoic acid on a molar basis. Simultaneous treatment with suboptimal concentrations of 1 alpha,25(OH)2D3 (0.12 to 1.2 nM) and retinoic acid (10 to 100 nM) showed additive effects in reducing nitroblue tetrazolium, a common marker for monocyte-macrophage and granulocyte differentiation. For the study of alternative differentiation of the cells by the two vitamins, we used monoclonal antibodies specific for either human monocyte-macrophages or granulocytes and other markers specific for macrophage differentiation such as alpha-naphthyl acetate esterase activity and adherence to the dish surface. HL-60 cells were induced to differentiate alternatively into macrophages by 1 alpha,25(OH)2D3 or into granulocytes by retinoic acid. When HL-60 cells were treated with various concentrations of 1 alpha,25(OH)2D3 (1.2 to 120 nM) in the presence of 1000 nM retinoic acid which is a concentration sufficient to induce maximal granulocyte differentiation, the appearance of the markers for monocyte-macrophage differentiation by 1 alpha,25(OH)2D3 was not at all affected by the retinoic acid. These results indicate that 1 alpha,25(OH)2D3 and retinoic acid have additive effects in inducing differentiation of HL-60 cells, but monocyte-macrophage differentiation by 1 alpha,25(OH)2D3 occurs much more readily than does granulocyte differentiation by retinoic acid.

Syntheses and differentiating action of vitamin D endoperoxides. Singlet oxygen adducts of vitamin D derivatives in human myeloid leukemia cells (HL-60)

Singlet oxygen adducts of various vitamin D derivatives, 6,19-dihydro-6,19-epidioxyvitamin D (vitamin D endoperoxides, 2 and 2'), were chemically synthesized, and their biological activity in inducing differentiation of a human myeloid leukemia cell line (HL-60 cells) was examined. The potency of the endoperoxides derived from vitamin D derivatives possessing the 1 alpha-hydroxyl group such as 1 alpha, 25-dihydroxyvitamin D3 endoperoxides (2b and 2b') was markedly (10(-2)) diminished relative to the respective parent vitamin D compounds. In contrast, 25-hydroxyvitamin D3 endoperoxides [25-(OH)D3 endoperoxides, 2a and 2a'] and their analogues fluorinated at the 24- or 26- and 27-positions were 2.5-10 times more potent than 25-hydroxyvitamin D3 (1a) in spite of the absence of the conjugated triene structure typical of vitamin D compounds. The potency of these vitamin D endoperoxides (2 and 2'), especially those lacking the 1 alpha-hydroxyl group, in inducing differentiation of HL-60 cells was not correlated with their activity in binding to the cytosol receptor for 1 alpha, 25-dihydroxyvitamin D3 (1b). The binding efficiency to the receptor was relatively lower than the differentiating activity. To examine the action of vitamin D endoperoxides, carbon analogues of 25-(OH)D3 endoperoxides, two C-6 epimers of 25-hydroxy-6,19-dihydro-6,19-ethanovitamin D3 (6 and 6'), were synthesized. The carbon analogues (6 and 6') had no potential to induce differentiation of HL-60 cells. These results suggest that vitamin D endoperoxides (2 and 2') express their biological activity probably after being converted to some other compounds.

Mechanism of the differentiating action of 25-hydroxyvitamin D3 endoperoxides in human myeloid leukemia cells (HL-60)

The action of 25-hydroxy-6,19-dihydro-6,19-epidioxyvitamin D3 [25-(OH)D3 endoperoxides, 2a and 3a] in inducing differentiation of human myeloid leukemia cells (HL-60) was studied by using their radioactive derivatives (2a' and 3a'). When HL-60 cells were incubated with the labeled endoperoxides (2a' and 3a') in serum-free RPMI 1640 medium, no radioactivity was incorporated into either the cytosol or the chromatin fraction of the cells. When the radioactive endoperoxide (2a') was incubated in the culture medium for 3 days, with or without HL-60 cells, about 45% of the compound was similarly converted to 19,25-dihydroxy-6,19-dihydro-6,19-epoxyvitamin D3 (4a) and about 10% to 25-hydroxy-6,19-epoxyvitamin D3 (6a). These two new vitamin D derivatives were synthesized chemically and tested for their biological activities. Both compounds (4a and 6a) were about 2 times as active as 25-(OH)D3 endoperoxides (2a and 3a) and about 7 times as active as 25-hydroxyvitamin D3 (1a) in inducing differentiation of HL-60 cells. The differentiating activity of these compounds was well correlated with their activity in binding to the cytosol receptor for 1 alpha, 25-dihydroxyvitamin D3 in HL-60 cells. The in vitro bone-resorbing activity of 25-hydroxy-6,19-epoxyvitamin D3 (6a) and 25-(OH)D3 endoperoxide (2a) was higher than that of 25-hydroxyvitamin D3 (1a), indicating that the differentiating activity also paralleled the bone-resorbing activity in these vitamin D derivatives. These results suggest that 25-(OH)D3 endoperoxides (2a and 3a) induce differentiation of HL-60 cells and bone resorption after being converted to these two compounds.

Activation and fusion induced by 1 alpha,25-dihydroxyvitamin D3 and their relation in alveolar macrophages

1 alpha,25-Dihydroxyvitamin D3 [1 alpha,25-(OH)2D3] induces fusion of murine alveolar macrophages. This effect was observed in growth medium containing 5% human serum but not in the medium with 5% fetal bovine serum. Unlike 1 alpha,25-(OH)2D3, bacterial lipopolysaccharides (LPS) did not induce fusion of alveolar macrophages. However, both 1 alpha,25-(OH)2D3 and LPS activated alveolar macrophages, as measured by glucose consumption, increase in Fc receptors, and induction of cytotoxicity. The number of Fc receptors on the surface of multinucleated giant cells induced by 1 alpha,25-(OH)2D3 was much smaller than that on the surface of mononuclear macrophages treated with the hormone. These results indicate that 1 alpha,25-(OH)2D3 induces both fusion and activation of alveolar macrophages, whereas LPS elicits activation only.

Extracellular calcium is involved in the mechanism of differentiation of mouse myeloid leukemia cells (M1) induced by 1 alpha, 25-dihydroxyvitamin D3

We have reported that 1 alpha, 25-dihydroxyvitamin D3 [1 alpha, 25(OH)2D3] suppresses proliferation and induces differentiation of murine myeloid leukemia cells (M1) into macrophages. In the current study, M1 cells were cultured either with 2.0 or 0.15 mM total calcium to examine the effect of calcium on the process of differentiation induced by the vitamin. The 0.15 mM calcium medium greatly enhanced 1 alpha, 25-dihydroxyvitamin D3 [1 alpha, 25(OH)2D3]-induced inhibition of cell growth and suppression of [3H]thymidine incorporation. Addition of Verapamil, a calcium antagonist, to the 2.0 mM calcium medium also elicited similar responses. The absolute number of cells with phagocytic activity induced by 1 alpha, 25(OH)2D3 was almost identical in media containing either concentration of calcium, and in cultures with or without Verapamil. Culture in the 0.15 mM calcium medium or addition of Verapamil to the 2.0 mM calcium medium did not suppress cell growth nor induce phagocytic activity in the absence of the vitamin. To confirm the preferential effect of calcium on cell growth, M1 cells were pretreated for 3 days with 1 alpha, 25(OH)2D3 in either the 2.0 or 0.15 mM calcium medium. Then the pretreated cells were washed and subcultured in the absence of 1 alpha, 25(OH)2D3 in either medium. The growth rate was inhibited much more effectively in the subculture with 0.15 mM calcium than with 2.0 mM calcium. These results suggest that the M1 cells' increased requirement of extracellular calcium, caused by the treatment with 1 alpha, 25(OH)2D3, is closely related to cell growth rather than differentiation.

Cooperative effect of 1 alpha,25-dihydroxyvitamin D3 and dexamethasone in inducing differentiation of mouse myeloid leukemia cells

Murine myeloid leukemia cells (MI) are induced to differentiate into macrophages by the metabolically active form of vitamin D3,1 alpha,25-dihydroxyvitamin D3[1 alpha,25(OH)2D3] (E. Abe et al., (1981) Proc. Natl. Acad. Sci. USA 78, 4990-4994). At 0.12-120 nM, 1 alpha,25(OH)2D3 suppressed cell growth in a dose-dependent manner and markedly induced phagocytic activity, lysozyme activity, and C3-receptor formation. The potency of 1 alpha,25(OH)2D3, at 0.12-120 nM, in inducing differentiation was nearly equivalent to that of 10-10,000 nM of dexamethasone, one of the most potent stimulators of Ml cells. Simultaneous treatment with low physiological plasma concentrations of 1 alpha,25(OH)2D3 (0.12 nM) and dexamethasone (10 nM) induced differentiation of Ml cells equivalent to the responses obtained only by using much higher concentrations of the respective steroids when used separately. In addition, two variant clones of Ml cells resistant to either 1 alpha,25(OH)2D3 or dexamethasone were isolated. One was resistant to 120 nM of 1 alpha,25(OH)2D3 but sensitive to 10-1000 nM of dexamethasone. The other was resistant to 1000 nM of dexamethasone but sensitive to 12 nM of 1 alpha,25(OH)2D3. This suggests that the mechanism of action of 1 alpha,25(OH)2D3 in inducing differentiation of Ml cells is different at least in part from that of dexamethasone, and that combination therapy by both steroids may be useful in reducing leukemogenicity of Ml cells in vivo.

1 alpha,25-dihydroxyvitamin D3 induces differentiation of human promyelocytic leukemia cells (HL-60) into monocyte-macrophages, but not into granulocytes

The differentiating action of 1 alpha,25-dihydroxyvitamin D3 [1 alpha, 25-(OH)2D3] in hematopoietic cells was examined in 3 tumor cell lines. 1 alpha,25-(OH)2D3 induced common differentiation-associated properties in macrophages and granulocytes similarly in mouse myeloblastic leukemia cells (M1), human promyelocytic leukemia cells (HL-60) and human histiocytic monoblast-like lymphoma cells (U937). 1 alpha,25(OH)2D3 markedly induced alpha-naphthyl acetate esterase activity, a typical marker of monocyte-macrophages, in M1 and HL-60 cells. In HL-60 and U937 cells, the vitamin also induced binding of the monoclonal antibody MAS 072, specific for monocyte-macrophages, but not of MAS 067, specific for granulocytes. These results clearly indicate that 1 alpha, 25(OH)2D3 induces differentiation of all cell lines examined preferentially along the monocyte-macrophage pathway.

1 alpha,25-dihydroxyvitamin D3 promotes fusion of mouse alveolar macrophages both by a direct mechanism and by a spleen cell-mediated indirect mechanism

Extensive fusion was induced in mouse alveolar macrophages by treatment with conditioned media obtained from spleen cell cultures treated with 15 micrograms of phytohemagglutinin or concanavalin A per ml or with 12 nM 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3]. The fusion rate was 80-90% on day 3. In addition, 1 alpha,25(OH)2D3 added directly to alveolar macrophages induced fusion of about 35% of the cells on day 3, whereas direct addition of phytohemagglutinin and concanavalin A did not enhance fusion at all. When conditioned media from spleen cell or T cell cultures treated with 12 nM 1 alpha,25(OH)2D3 were applied to a Sephadex G-100 column, a fusion factor (Mr 37,000-70,000) could be separated from 1 alpha,25(OH)2D3. 1 alpha,25(OH)2D3 induced fusion at 0.012-120 nM in a dose-dependent manner both by direct action and by spleen cell-mediated indirect action, but the fusion rate was always much greater in the latter than in the former at each concentration of the vitamin. Of the vitamin D3 derivatives tested, 1 alpha,25(OH)2D3 was the most potent, followed successively by 1 alpha,24R,25-trihydroxyvitamin D3, 1 alpha-hydroxyvitamin D3, 25-hydroxyvitamin D3, and 24R,25-dihydroxyvitamin D3. These results clearly indicate that 1 alpha,25(OH)2D3 induces fusion of mouse alveolar macrophages by both a direct and an indirect mechanism, the latter mediated by spleen cells, probably by T cells.

Biological activity of 24,24-difluoro-1 alpha, 25-dihydroxyvitamin D3 and 1 alpha, 25-dihydroxyvitamin D3-26,23-lactone in inducing differentiation of human myeloid leukemia cells

Vitamin D compounds added to the culture medium induce differentiation of human myeloid leukemia cells (HL-60 cells) by binding to a specific cytosol receptor protein. This system provides a biologically relevant and technically simple assay to examine the relationship between molecular structure and biological activity of vitamin D compounds. Using this culture system, the biological activity of 24,24-F2-1 alpha,25(OH)2D3 and 1 alpha,25(OH)2D3-26,23-lactone was assayed. 24,24-F2-1 alpha,25(OH)2D3 was four to seven times more potent than 1 alpha,25(OH)2D3 in inducing phagocytosis and C3 rosette formation of HL-60 cells, though both compounds bound equally well to the cytosol receptor, suggesting that the defuorination at the 24-carbon position may stimulate membrane permeability of the compound. 1 alpha,25(OH)2D3-26,23-lactone, on the other hand, was only 1/200th as active as 1 alpha,25(OH)2D3. The binding affinity of the lactone for the cytosol receptor was identical with that of 1 alpha (OH)D3, suggesting that the lactone formation between the 26 and 23 positions masks the function of the 25-hydroxyl group. The binding affinity of vitamin D3 derivatives to the specific cytosol receptor of HL-60 cells was well correlated with that of intestinal cytosol protein specifically bound to 1 alpha,25(OH)2D3.

1 alpha,25-Dihydroxycholecalciferol and a human myeloid leukaemia cell line (HL-60)

Human promyelocytic leukaemia cells (HL-60) can be induced to differentiate into mature granulocytes in vitro by 1 alpha,25-dihydroxycholecalciferol [1 alpha,25(OH)2D3], the active form of cholecalciferol. The differentiation-associated properties, such as phagocytosis and C3 rosette formation, were induced by as little as 0.12 nM-1 alpha,25(OH)2D3, and, at 12 nM, about half of the cells exhibited differentiation on day 3 of incubation. Concomitantly the viable cell number was decreased to less than half of the control. Among various derivatives of cholecalciferol examined, 1 alpha,25(OH)2D3 and 1 alpha,24R-dihydroxycholecalciferol were the most potent in inducing differentiation, followed successively by 1 alpha,24S-dihydroxycholecalciferol, 1 alpha-hydroxycholecalciferol, 25-hydroxycholecalciferol and 24R,25-dihydroxycholecalciferol. A cytosol protein specifically bound to 1 alpha,25 (OH)2D3 was found in HL-60 cells. Its physical properties closely resembled those found in such target tissues as intestine and parathyroid glands. 1 alpha,25(OH)2D3 bound to the cytosol receptor was transferred quantitatively to the chromatin fraction. The specificity of various derivatives of cholecalciferol in inducing differentiation was well correlated with that of their association with the cytosol receptor. These results are compatible with the hypothesis that the active form of cholecalciferol induces differentiation of human myeloid leukaemia cells by a mechanism similar to that proposed for the classical concept of steroid hormone action.

Failure to demonstrate the stimulative effect of calcitonin on cyclic AMP accumulation in avian bone in vitro

The effect of calcitonin on the metabolism of calcium and cyclic AMP in the avian bone was examined in vitro. In the chick embryonic cortical bone, calcitonin affected neither the level of cyclic AMP nor the parathyroid hormone-induced stimulation of calcium release from bone. Also, the level of cyclic AMP in the cortical or medullary bone of Japanese quails was not increased by calcitonin. The medullary bone did not respond to calcitonin either in freshly prepared tissue or in tissue cultured for 48 hr in the absence of calcitonin. The activity of renal adenylate cyclase of Japanese quails was also calcitonin-insensitive. The inability of calcitonin to increase the level of cyclic AMP and to antagonize the parathyroid hormone-induced stimulation of calcium release from bone may account for the lack of hypocalcemic effect of calcitonin in birds as reported by other investigators.

Differentiation of mouse myeloid leukemia cells induced by 1 alpha,25-dihydroxyvitamin D3

Mouse myeloid leukemia cells can be induced to differentiate into macrophages in vitro by 1 alpha,25-dihydroxyvitamin D3, the active form of vitamin D3. The minimal concentration of 1 alpha,25-dihydroxyvitamin D3 to induce the cell differentiation was 0.12 nM. The degree of cell differentiation in various markers induced by 12 nM 1 alpha,25-dihydroxyvitamin D3 was nearly equivalent to that induced by 1 microM dexamethasone, the most potent known stimulator. Among several markers of the differentiation by 1 alpha,25-dihydroxyvitamin D3, phagocytic activity was induced within 24 hr, and this was followed by induction of lysozyme and locomotive activities. Similar changes were also induced by 0.01-1 microM 1 alpha-hydroxyvitamin D3. 25-Hydroxyvitamin D3 and 24R,25-dihydroxyvitamin D3 showed only weak inducing activity. These results suggest the possibility that, in addition to its wellknown biological activities in enhancing intestinal calcium transport and bone mineral mobilization, 1 alpha, 25-dihydroxyvitamin D3 is involved in the differentiation of bone marrow cells.

Ornithine decarboxylase activity in chick duodenum induced by 1 alpha, 25-dihydroxycholecalciferol

The effect of cholecalciferol and its metabolites on ornithine decarboxylase activity was investigated in the duodenal mucosa of vitamin D-deficient chicks. The duodenal ornithine decarboxylase activity decreased in animals fed a vitamin D-deficient diet and its retarded activity was increased dose-dependently by a single injection of cholecalciferol. Among various metabolites of cholecalciferol tested, 1 alpha, 25-dihydroxycholecalciferol [ 1 alpha, 25 (OH)2D3] was the most potent stimulator. Stimulation of the enzyme activity was detected as early as 2h after intravenous administration of 1 alpha, 25 (OH)2D3 and a maximal value was attained at 6 h. The maximal value was 27 times higher than the control. In addition, treatment with 1 alpha 25 (OH)2D3 affected the duodenal content of polyamines. The content of putrescine increased to a value of three times that of the control 6 h after the hormone administration. The spermidine content did not change appreciably. The enhancement of duodenal ornithine decarboxylase activity by 1 alpha, 25 (OH)2D3 occurred in parallel with the enhancement of calcium absorption, which was first detected 3 h after the hormone administration. The enhancement appeared to be tissue-specific. It was observed in every intestinal segment, but was highest in the duodenum. Enzyme activity in other tissues was not influenced appreciably by 1 alpha, 25 (OH)2D3. These results clearly indicate that the duodenal biosynthesis of polyamines is regulated by 1 alpha, 25 (OH)2D3, suggesting the possibility that duodenal ornithine decarboxylase may be involved in the calcium absorption mechanism.

Regulation and its refractoriness of 25-hydroxyvitamin D3 metabolism in vitamin D deficiency

The time course of change in plasma calcium levels and renal metabolism of 25-hydroxyvitamin D3 [25(OH)D3] was investigated in chicks maintained on a vitamin D-deficient diet for 4 weeks. Plasma calcium concentrations dropped sharply between the 7th and 14th day of the feeding period. Renal 25(OH)D3-1 alpha-hydroxylase activity was reciprocally enhanced concurrently with the decrease in plasma calcium levels. The elevated activity of 1 alpha-hydroxylase had declined significantly by the 21st and 28th days in spite of the more severe hypocalcemia. When graded amounts of vitamin D3 were administered to the chicks maintained on this diet for 14 or 28 days, there were considerable differences in the change of plasma calcium levels and 25(OH)D3 metabolism induced by vitamin D3 administration between the 14-day and 28-day birds. The minimal dose levels of vitamin D3 to completely suppress renal 1 alpha-hydroxylase activity were 25 micrograms in the 14-day, and 2.5 mg in the 28-day birds. These differences were not observed between the 14-day and 28-day birds when 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3] was administered. Renal adenylate cyclase activity induced by parathyroid hormone (PTH) was much lower in the 28-day chicks than that in 1-day-old and the 14-day birds. These results are explained by the hypersecretion of PTH and the subsequent refractoriness of the target organs in severe vitamin D deficiency. Plasma calcium levels per se did not appear to be a major factor in the regulation of 25(OH)D3 metabolism.

Effect of DL-alpha-tocopherol (vitamin E) on the differentiation of mouse myeloid leukemia cell

The effect of DL-alpha-tocopherol on the differentiation of the mouse myeloid leukemia cell line (M1) was investigated using fluorometry. The reliability of the fluorometric determination was verified by the mutual overlapping of the curves of disappearance of the radioactivity recovered as alpha-tocopherol and the loss of its fluorescence. alpha-Tocopherol solubilized into the culture medium was relatively stable (t1/2 = 147-168 hr). In corporation of alpha-tocopherol into M1 cells was time- and dose-dependent. Proliferation of M1 cells was never inhibited, but was slightly enhanced by treatment with alpha-tocopherol. alpha-Tocopherol caused a twofold increase in acid-phosphatase activity and slightly inhibited both the spontaneous- and dexamethasone-induced differentiation with respect to adhesion on glass and cell surface-rosette formation. alpha-Tocopherol also induced morphological change, making the shape of M1 cells rounder.