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T K Gray

Publications and source records attributed to T K Gray.

At least 37 records · Page 2Linked to original sources
PubMed1986

Mononuclear phagocytes secrete a protein that directly resorbs devitalized bone particles.

The radiolabelled bone particle assay was used as an in vitro model of bone resorption. Normal human peripheral blood monocytes and the monoblastic cell line, U937, increased 45Ca release from the devitalized bone particles. In contrast, normal human peripheral blood neutrophils, resting or stimulated, did not increase 45Ca release. Exposure of monocytes to gamma interferon (INF-gamma) stimulated secretion of hydrogen peroxide and inhibited 45Ca release from bone particles. U937 cells incubated with 1,25(OH)2D3 and lymphokines had increased secretion of oxygen reduction products and increased 45Ca release. Medium conditioned by incubation with U937 cells stimulated 45Ca release to the same extent as the U937 cells. The 45Ca releasing activity in the medium was resistant to extremes of temperature and acidification. This activity is not dependent on the presence of disulfide bonds and was not inhibited by collagenase or trypsin inhibitors. Exposure to a proteolytic agent reduced the activity by over 50%. These findings are consistent with the concept that mononuclear phagocytes secrete a substance, presumably a protein, which acts directly on the bone particles. The isolation and identification of this substance may increase our understanding of the mechanisms of bone loss associated with inflammatory processes.

Bone Resorption↗
PubMed1986

Acid phosphatase activity in mononuclear phagocytes and the U937 cell line: monocyte-derived macrophages express tartrate-resistant acid phosphatase.

Tartrate-resistant acid phosphatase (TRAcP) is used as a marker for osteoclasts, which are believed to be derived from phagocytic cells or phagocyte stem cell precursors. To further investigate the relationship between monocytic phagocytes and osteoclasts, acid phosphatase (AcP) activity was measured by three different techniques in human peripheral blood monocytes, monocyte-derived macrophages, and the U937 cell line. We found that cytochemistry and gel electrophoresis led to similar results, but that the colorimetric assay was inconsistent. Normal human peripheral monocytes expressed both tartrate-sensitive and -resistant AcP. In culture these cells formed polykaryons and expressed TRAcP activity that was further identified as an isoenzyme associated with bone tissue. In contrast, the U937 cells did not express TRAcP activity as measured by gel electrophoresis. Both U937 cells and monocytes possess material that interferes with interpretation of the colorimetric assay of AcP. The presence of TRAcP in monocyte-derived macrophages further supports the relationship between phagocytic cells and bone osteoclasts.

Acid Phosphatase↗
PubMed1985

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

Phagocytic cells, including normal human blood neutrophils and monocytes, metabolize 25-hydroxyvitamin D3 in vitro to more polar metabolites. Cells of the human monoblastic cell line U937 produced three metabolites when incubated with 25-hydroxyvitamin D3. One of these metabolites, previously designated peak III, has its maximal absorbance at 310 nm. Mass spectral analysis of the trimethylsilylated derivatives of peak III revealed a spectral pattern very similar to that published for the trimethylsilylated derivatives of 19-nor-10-keto-25-hydroxyvitamin D3. The biosynthetic 19-nor-10-keto-25-hydroxyvitamin D3 was active in the induction of differentiation of U937 cells.

Calcifediol↗
PubMed1985

Calcium requirement for the lymphokine and vitamin D mediated differentiation of monoblastic U937 cells.

The monocyte-osteoclast hypothesis states that osteoclasts are derived from the differentiation of monocytes. Recently we reported that the U937 cell line, a monoblastic cell of human origin, differentiated to an osteoclast precursor when cultured in the presence of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and lymphokines. Using this model of monocytic differentiation we have tested the role of calcium (Ca) in the culture medium by the addition of CaCl2 in the presence or absence of EGTA, a chelating agent, on the growth and differentiation of the U937 cells. Increasing the Ca concentration ([Ca]) to 2.0 mM inhibited the differentiation of resting or 1,25(OH)2D3 exposed cells, but had no effect on the cells exposed to lymphokines or lymphokines and 1,25 (OH)2D3. Reducing the [Ca] to 10(-7) M inhibited differentiation but also reduced cell viability. Addition of CaCl2 to medium containing EGTA to produce [Ca] in the range of 10(-5) M to 10(-3) M restored the cellular growth and viability. Inhibition of differentiation associated with the reduced calcium concentration over the range of 10(-5) M to 10(-3) M was not due to growth inhibition. These findings show the importance of the extracellular [Ca] in an in vitro model of monocytic differentiation induced by vitamin D and lymphokines.

Calcitriol↗
PubMed1985

Lymphokine-induced monocytic differentiation as a possible mechanism for hypercalcemia associated with adult T-cell lymphoma.

Patients with adult T-cell lymphoma frequently have hypercalcemia. Bone biopsies from these patients show increased numbers of osteoclasts. We hypothesized that substances produced by the malignant T-cell caused these phenomena by increasing the formation and/or activity of osteoclasts. To test this hypothesis, we cultured U937 cells in conditioned media from a clonal T-cell line derived from a patient with adult T-cell lymphoma and hypercalcemia. This conditioned media produced maturational changes in the U937 cells as evidenced by decreased proliferation, increased adherence, increased expression of complement receptors, and formation of multinucleated giant cells. These changes were synergistically enhanced by the addition of 1 alpha, 25-dihydroxyvitamin D3 which is known to promote monocyte differentiation. We also tested interleukin 2 and gamma- and alpha-interferon to see if they were responsible for the maturational changes. Although some effects were seen, these lymphokines could not account for all the changes induced by the T-cell conditioned media. These findings support the above hypothesis and suggest that other unidentified factors may promote the differentiation of osteoclast precursors and be involved in the pathogenesis of the hypercalcemia.

Calcitriol↗
PubMed1984

Phagocytic cells metabolize 25-hydroxyvitamin D3 in vitro.

Phagocytic cells are widely distributed in tissues known to be important in the metabolism of vitamin D. Incubation of human polymorphonuclear leukocytes and monocytes and resident rat peritoneal macrophages with 3H-labeled 25-hydroxyvitamin D3 leads to the formation of three radioactive peaks. Peak I is most consistent with a lactone derivative of 25-hydroxyvitamin D3, and peak II has been identified as putative 24,25-dihydroxyvitamin D3. Peak III is a novel metabolite of 25-hydroxyvitamin D3 unlike any of the synthetic standards available in our laboratories. Human neutrophils converted more substrate than did the other phagocytes examined. The stimulation of neutrophils by opsonized zymosan or phorbol myristate acetate led to a 4-fold increase in synthesis of the metabolites. These results suggest that vitamin D metabolism by phagocytic cells may play a role in the microenvironmental events that surround bony metabolism and calcium homeostasis.

Animals↗
PubMed1983

Rat kidney microsomes convert 25-hydroxyvitamin D3 to an unidentified metabolite.

Kidney microsomes from vitamin D-deficient rats and from thyroparathyroidectomized rats converted 25-hydroxyvitamin D3 to an unidentified metabolite. The addition of the cytosolic fraction enhanced microsomal synthesis of this metabolite two-fold. The kinetics of the conversion in the presence of the cytosolic fraction was allosteric, suggesting that the enzyme responsible for synthesis of this metabolite might serve some role in the regulation of vitamin D metabolism. Microsomes from vitamin D-fed thyroparathyroidectomized rats also produced a second metabolite, tentatively identified as 25,26-dihydroxyvitamin D3 because of its comigration with 25,26-dihydroxyvitamin D3 in three different chromatographic systems.

Animals↗
PubMed1983

Vitamin D metabolites change the phenotype of monoblastic U937 cells.

U937 is a human-derived lymphoma cell line that has monoblastic properties and high-affinity receptors for 1 alpha,-dihydroxyvitamin D3. Incubation of these cells with the vitamin D metabolite at 10 nM for 5 days produced marked stimulation in adherence and ingestion of Staphylococcus aureus (645% of control) and of C3b receptor (CR1) expression (292% of control) and a slight increase in hexose monophosphate shunt activity without changing cell growth rates or Fc fragment receptor expression. The changes in cellular association of S. aureus and the CR1 were detected as early as 48 hr of incubation and peaked between 3 and 5 days. Similar changes in the CR1 were induced by 25-hydroxy- and 24,25-dihydroxyvitamin D3 at micromolar concentrations. Dexamethasone, hydrocortisone, and progesterone had no effect on CR1 expression. U937 cells incubated in the presence of vitamin D metabolites exhibited a change in their phenotype. These results suggest that vitamin D metabolites may contribute to monocyte/macrophage differentiation.

Calcifediol↗
PubMed1982

Fluctuation of serum concentration of 1,25-dihydroxyvitamin D3 during the menstrual cycle.

The serum concentrations of total calcium and 1,25-dihydroxyvitamin D3 were measured in seven women during a menstrual cycle. A rise in the serum level of 1,25-dihydroxyvitamin D3 was observed on day 15 of the cycle without a detectable change in the serum calcium level. The level of 1,25-dihydroxyvitamin D3 on day 15 was double the value at days 1 and 8 of the cycle. The peak of 1,25-dihydroxyvitamin D3 on day 15 was not observed in five women ingesting oral contraceptives, suggesting that ovulation or its hormonal control was involved in the peak on day 15. A small but significant fall in the serum calcium concentration occurred in the women ingesting oral contraceptives. In view of these findings the serum concentrations of 1,25-dihydroxyvitamin D in women with functioning ovaries must be interpreted in the context of the stage of the menstrual cycle when the blood sample was obtained.

Adolescent↗
PubMed1982

Vitamin D deficiency in rats with normal serum calcium concentrations.

Rats were raised after weaning on a vitamin D-deficient diet which used whole wheat and casein as the major protein source. For at least the first year of life, plasma calcium concentrations of these rats were the same as those of vitamin D-replete rats, and the rate of growth was normal for at least 6 months. The following evidence establishes the vitamin D deficiency of the rats (both male and female) on this diet: (i) plasma levels of 1,25-dihydroxycholecalciferol (1,25-dihydroxyvitamin D3) became undetectable after 6 weeks on the diet; (ii) by 4 months of age, the epiphyseal growth plates of the tibia were significantly enlarged and disorganized; (iii) when subjected to fracture in a dynamic torsion machine, the femur showed marked weakening as indicated by stress analysis; (iv) isolated kidney cells from the deficient rats showed a 3-fold increase in 25-hydroxyvitamin D 1-hydroxylase activity. When mother rats were placed on the vitamin D-deficient diet during lactation, plasma calcium values in the pups decreased and remained low throughout life and there was a stunted body growth pattern. It is concluded that hypocalcemia is not a necessary manifestation of vitamin D deficiency, that the onset of vitamin D deficiency during neonatal life influences the calcium homeostatic system, and that the normocalcemic, vitamin D-deficient animal provides an experimental model in which the effects of vitamin D deficiency can be studied independently of hypocalcemia.

Animals↗
PubMed1982

Serum concentrations of calcium and vitamin D metabolites in prosimians.

The concentrations of total calcium, 25-hydroxyvitamin D [25-(OH)D] and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] were measured in serum obtained from prosimians, the brown lemurs. The mean serum calcium level was 10.6 mg/dl in male and female lemurs. The mean serum mean 25-(OH)D concentration in serum from male and female lemurs was 27.1 and 31.0 ng/ml, respectively. The mean serum level of 1,25-(OH)2D3 in the female and male lemurs was 65.2 and 65.9 pg/ml, respectively. A small segment of the lemurs had hypercalcemia and elevated serum concentrations of 25-(OH)D or 1,25-(OH)2D3, suggesting the idea that the episodic ingestion of a large quantity of the calcium- and vitamin D-enriched diet normally provided ad libitum might cause hypercalcemia.

Animals↗
PubMed1981

25-Hydroxyvitamin D3 metabolism in the pregnant rat: maternal-fetal relationship.

Metabolism of 3H-25OHD3 was studied in pregnant, D-deprived rats and their fetuses at 21 days' gestation. Significant changes in the circulating levels of 3H-24,25(OH)2D3 and 3H-1,25(OH)2D3 in maternal and fetal plasma occurred from 4 to 12 h after the administration of 233 ng of 3H-25OHD3. 3H-1,25(OH)2D3 appeared before 3H-24,25(OH)2D3 in both the mother and fetuses. Maternal plasma contained more 3H-1,25(OH)2D3 than fetal plasma and, contrariwise, fetal plasma contained more 3H-24,25(OH)2D3 than maternal plasma. Maternal nephrectomy studies showed that the in vivo synthesis of 3H-24,25(OH)2D3 at 6 h was dependent on circulating levels of 3H-1,25(OH)2D3. These results revealed aspects of maternal-fetal metabolism of 25OHD3 similar to those in the non-pregnant state as well as others unique to pregnancy.

Animals↗
PubMed1981

Vitamin D and pregnancy: the maternal-fetal metabolism of vitamin D.

A model of the maternal-fetal metabolism of vitamin D3 is depicted in Fig. 2. 25-OHD3 of maternal origin is metabolized by the maternal kidneys to the potent metabolite, 1,25-(OH)2D3, which acts on the maternal intestine, kidneys, and skeleton. The maternal kidneys and other organs can produce 24,25-(OH)2D3, although this pathway may be suppressed near the end of gestation. The placenta has selective permeability to the vitamin D3 metabolites, with 25-OHD3 crossing from the mother to the fetus more readily than the dihydroxylated metabolites. The onset of the placental synthesis of 1,25-(OH)2D3 during gestation is unknown. Likewise the regulation of the placental 25-OHD3-1 alpha-hydroxylase is unknown. 1,25-(OH)2D3 of placental origin may enter the maternal or the fetal circulation or act locally on the placenta by inducing the synthesis of proteins involved in the cellular transport of Ca. Perhaps one placenta cell type synthesizes 1,25-(OH)2D3 and another cell type possessing a cytoplasmic receptor for 1,25-(OH)2D3 responds to this metabolite. The function of the 24,25-(OH)2D3 produced by the placenta is unknown. The concentration of free 25-OHD3 and free 1,25-(OH)2D3 in the fetal circulation exceeds the maternal levels due to the differences in the DBP concentrations of the two bloodstreams. The 1,25-(OH)2D3 in the fetal bloodstream may originate from either the placenta or the fetal kidneys. The latter site may not be active in utero due to the hypercalcemia and hyperphosphatemia relative to the maternal levels of these ions. 1,25-(OH)2D3 in the fetal bloodstream acts on those fetal tissues containing cytoplasmic receptors for this metabolite. The intestinal mucosa apparently lacks these receptors until sometime during neonatal life. In contrast, fetal bone cells possess receptors for the 1,25-(OH)2D3. The 24,25-(OH)2D3 in the fetal bloodstream may also be involved in the growth and differentiation of the fetal skeleton. However, the precise role of both metabolites in the fetus remains conjectural.

25-Hydroxyvitamin D 2↗