Phagocytic cells synthesize 19-nor-10-keto-25-hydroxyvitamin D3, a metabolite that may induce differentiation of the human monoblastic cell line U937

Vitamin D3 induces pro-LL-37 expression in myeloid precursors from patients with severe congenital neutropenia

The innate immune system produces a number of effector molecules that are important for protection against bacterial infections. Neutrophils and antimicrobial peptides are major components of innate defense with the capacity of rapid bacterial killing. Patients with severe congenital neutropenia (SCN) experience recurrent and chronic infections despite recombinant G-CSF-mobilized neutrophils. We have shown previously that these neutrophils are deficient in that they lack the antimicrobial peptide LL-37. Here, we show that pro-LL-37 mRNA is not expressed in neutrophil precursors from patients with SCN, although the gene and promoter region for pro-LL-37, CAMP, does not display any mutations. The hormonal form of vitamin D3 [1,25(OH)2D3] induced the expression of pro-LL-37 in isolated neutrophil progenitors and in EBV-transformed B cells from patients with SCN, whereas all-trans retinoic acid only induced expression in transformed B cells. These results demonstrate that myeloid cells of patients with SCN can produce pro-LL-37, suggesting that other pathways are impaired.

Synthesis of active metabolite(s) from 1 alpha-hydroxyvitamin D3 by human monocytic leukemia cells

Synthesis of the biologically active metabolite(s) from 1 alpha-hydroxyvitamin D3 (1 alpha(OH)D3) was examined in various types of human leukemia cell lines. Untreated monocytoid leukemia cells (U937 and HEL/S) metabolized 1 alpha (OH)D3 to the active metabolite(s), possibly 1 alpha, 24- and/or 1 alpha, 25-dihydroxyvitamin D3, and these cells were efficiently induced to differentiate by treatment with 1 alpha (OH)D3. However, the other types of leukemia cells did not efficiently metabolize it and were not induced to differentiate by 1 alpha (OH)D3. The possible therapeutic advantage of 1 alpha (OH)D3 in the treatment of monocytic leukemia is discussed.

Metabolism of 25-OH-vitamin D3 by peritoneal macrophages from CAPD patients

The active metabolite of vitamin D, 1,25-dihydroxycholecalciferol (1,25(OH)2D3), is produced mainly by the kidney, but there is evidence for extrarenal production in certain circumstances. We studied whether peritoneal macrophages (PM) from CAPD patients were capable of metabolizing 25-OH-D3 to 1,25(OH)2D3. We found that PM were able to metabolize 25-OH-D3 in vitro; the main product following 16 hours of incubation was 19-nor, 10-oxo, 25-OH-D3 with smaller amounts of 1,25(OH)2D3. However, after shorter incubations of three and five hours a larger portion of 1,25(OH)2D3 was produced. The metabolism of 25-OH-D3 was greatly enhanced in PM harvested during episodes of peritonitis. This property was specific for PM of CAPD patients, and was not found in PM from normal subjects. However, incubation of control PM with peritoneal effluent from CAPD patients resulted in induction of the ability of these cells to metabolize 25-OH-D3. This induction was enhanced by preincubation with peritoneal effluent from CAPD patients suffering from peritonitis. Prostaglandin E2 was found to be involved in this synthesis: addition of PGE2 to normal PM induced metabolism of 25-OH-D3, and incubation of PM from CAPD patients with indomethacin decreased the metabolism of 25-OH-D3. The vitamin D metabolites produced by PM from CAPD patients could have a role in immunological resistance to peritoneal infections.

Constitutive expression of a vitamin D 1-hydroxylase in a myelomonocytic cell line: a model for studying 1,25-dihydroxyvitamin D production in vitro

The capacity of the v-myc-transformed, chicken myelomonocytic cell line HD-11 to metabolize 25-hydroxyvitamin D3 (25-OHD3) was examined. HD-11 cells produced and secreted a metabolite of 25-OHD3 that was bound with high affinity by receptor for 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. On normal-phase HPLC, this metabolite cochromatographed with authentic 1,25-(OH)2D3 in both hexane- and methylene chloride-based solvent systems. The 25-OHD3 1-hydroxylation reaction was substrate saturable with a Km of 73 nM 25-OHD3 and a maximal velocity of 167 fmol per 10(6) cells per h. This reaction was inhibited by ketoconazole, a recognized inhibitor of cytochrome P450 mixed-function oxidases including the authentic, renal 25-OHD3 1-hydroxylase. On the other hand, HD-11 cell 1,25-(OH)2D3 production was not affected by the antioxidant DPPD, a known inhibitor of free radical-generated 1,25-(OH)2D3. In addition to synthesizing 1,25-(OH)2D3, this monocyte-macrophage cell line also has the potential to be a target for the hormone; HD-11 cells express high-affinity receptor for 1,25-(OH)2D3 (Kin = 0.06 nM).

Metabolism of the vitamin D3 derivative (24R)-hydroxycalcidiol by human promyelocytic leukemia cells (HL-60). Isolation and identification of (5Z) and (5E)-(24R)-19-nor-10-oxo-24-hydroxycalcidiol

Human promyelocytic leukemia cells (HL-60 cells) incubated with (24R)-hydroxy[26,27-methyl-3H]calcidiol (0.2 microCi) or non-radioactive (24R)-hydroxycalcidiol (370 micrograms) produced significant quantities of two new vitamin D3 (calciol) metabolites. The metabolites were isolated from HL-60 cell culture media by methanol/chloroform extraction and a series of chromatographic procedures. The two new metabolites were identified as (5Z)- and (5E)-(24R)-19-nor-10-oxo-24-hydroxycalcidiol by HPLC analysis, ultraviolet absorption spectrophotometry, mass spectrometry and Fourier-transform infrared spectrophotometry. According to the isolation and purification procedures, the total amounts of 3.04 micrograms (5Z)-(24R)-19-nor-10-oxo-24-hydroxycalcidiol (lambda max = 310 nm, epsilon = 17070 M-1 cm-1) and 8.89 micrograms (5E)-(24R)-19-nor-10-oxo-24-hydroxycalcidiol (lambda max = 312 nm, e = 24,500 M-1 cm-1) were calculated, assuming an Mr of 418. The activity of 19-nor-10-oxo-(24R)-hydroxycalcidiol to promote HL-60 cell differentiation was higher than the activity of the precursor (24R)-hydroxycalcidiol suggesting a possible biological action of this metabolite in HL-60 cells.

Biological activity of 19-nor, 10-keto, 25-hydroxyvitamin D3

19 nor, 10 keto, 25-hydroxyvitamin D3 (19/10-25OHD3) is a metabolite of 25-OHD3 produced in vitro by various phagocytes including normal human blood monocytes and transformed cell lines, U937 and HL-60. We recently reported that 19/10-25OHD3, induced differentiation of U937 cells. In these studies, 19/10-25OHD3 alone produced no detectable effect on the growth rates, surface adherence, and oxidative metabolism of U937 and HL-60 cells. When combined with lymphocyte-conditioned medium (LCM), 19/10-25OHD3 reduced proliferation, increased surface adherence and stimulated luminol-dependent luminescence (LDL) of the U937 cells. In contrast, the combination of 19/10-25OHD3 and LCM had no effect on the growth of HL-60 cells but did increase the surface adherence and the expression of a complement receptor component. 19/10-25OHD3 competed for tritium-labeled 1,25(OH)2D3 binding to receptors extracted from cultured human skin fibroblasts. This displacement capacity was 600 times weaker than that of unlabeled 1,25(OH)2D3. Incubation of human skin fibroblasts for 24 hr with 19/10-25OHD3 induced 25OHD3-24-hydroxylase activity in the fibroblasts. The inductive potency of 19/10-25OHD3 was 1/50 that of 1,25(OH)2D3. These results demonstrate bioactivity of 19/10-25OHD3 in several systems. At least one of these responses, the induction of 25OHD3-24-hydroxylase, is a receptor-mediated event. Some of the other responses may be independent of the cellular receptor for 1,25(OH)2D3. Interestingly, the potency of 19/10-25OHD3 was highest in the receptor-mediated response (1:50) and lower in the other parameters, ranging from 1:100 to 1:600 compared to 1,25(OH)2D3. This range of bioactivity in phagocytes and fibroblasts is presently explained.

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.