Effect of dexamethasone on 25-hydroxyvitamin D3 metabolism by chick kidney cell cultures

The hypercalcemic Walker carcinosarcoma 256 of the rat causes an increase in serum 1,25-dihydroxyvitamin D3

We have studied vitamin D metabolism in rats with the transplantable hypercalcemic Walker carcinosarcoma 256, which is a well characterized animal model for humoral hypercalcemia of malignancy. 25-Hydroxyvitamin D3 (25(OH)D3) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) concentrations were determined in blood samples obtained from parathyroidectomized (PTX) female rats at different time intervals after intramuscular tumor cell inoculation. We observed a dramatic increase in serum 1,25(OH)2D3 (280 +/- 184 vs. 98 +/- 31 pmol/l) 6 days after tumor cell injection and 4 days after the initial rise of serum calcium, whereas 25(OH)D3 tended to decrease. In a separate control experiment we compared this to the effect of exogenous parathyroid hormone in PTX rats and found similar results. In contrast, rats exhibited no change in vitamin D metabolite blood concentration after inoculation of the normocalcemic Yoshida sarcoma, which obviously does not interfere with vitamin D metabolism. We conclude that the humoral bone-resorbing agent produced by the Walker tumor cells causes elevation of serum 1,25(OH)2D3 concentration by this fulfilling an additional criterion of PTH-like activity.

Modulation of cell-cell and cell-antigen interactions by 1,25-dihydroxyvitamin D3 and vitamin D3 sulfate in vitro: a study on pregnancy lymphocytes and hybridoma cells

The effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) was investigated in single cell cytotoxicity assays, using K-562 target cells. The action of vitamin D3 sulfate (VD3S) in natural cytotoxicity assays as well as its effect on the antigen-specific adherence of hybridoma cells has also been studied. In the single cell cytotoxicity assay 1,25(OH)2D3 dose-dependently and significantly increased the binding of PBMC to target, the number of lysed target cells and NK activity. RU486, a compound known as a potent blocker of progesterone and glucocorticoid receptors, suppressed the effect of 1,25(OH)2D3 in all systems. VD3S dose-dependently decreased the natural cytotoxicity of PBMC and the binding of hybridoma cells to antigen immobilized on plastic surfaces. The results suggest that both 1,25(OH)2D3 and VD3S are potent modulatory agents in cell-cell and cell-antigen interactions.

The effects of short-term, high-dose treatment with prednisone on the nuclear uptake of 1,25-dihydroxyvitamin D3 in monocytes from normal human subjects

Animal and cell culture studies indicate glucocorticoid regulation of 1,25-dihydroxyvitamin D3 receptors and interference with cellular effects of vitamin D. These investigations prompted us to examine the effects of prednisone on the nuclear uptake of 1,25-dihydroxyvitamin D3 in freshly isolated human monocytes. Eighteen normal subjects were studied in a randomized, double-blind, placebo-controlled study. Analysis of receptor kinetics revealed that the maximal nuclear uptake (Bmax) of (3H)-1,25-dihydroxyvitamin D3 in monocytes decreased 40% (P less than .001) after prednisone treatment. In the group treated with prednisone (40 mg/d for 5 days) s-1,25-dihydroxyvitamin D increased 46% (P less than .01). S-25-Hydroxyvitamin D, S-phosphat, S-calcium, and S-iPTH remained unchanged. Osteoblastic production of the matrix protein, bone gla protein (BGP) is stimulated by 1,25-dihydroxyvitamin D3. However, despite increased serum levels of 1,25-dihydroxyvitamin D3, the prednisone-treated group revealed a 75% reduction in s-BGP. The present data indicate that corticosteroids decrease the nuclear uptake of 1,25-dihydroxyvitamin D3 in human monocytes. Further investigations are necessary, however, to elucidate the biologic mechanism for this observation and whether the mechanism is operative in other human tissues including bone.

Inhibitory and stimulatory effects of dexamethasone and 1,25-dihydroxyvitamin D3 on chick intestinal calbindin-D28K and its mRNA

The present study examined the interactions of the synthetic glucocorticoid, dexamethasone, with the regulation of chick intestinal calbindin-D28K (a 28,000 Da vitamin D-dependent calcium binding protein, CaBP) and its mRNA by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Dexamethasone (0-500 nmol) had a neutral impact on calbindin levels in the rachitic chick intestine when measured 12 h later. However, dexamethasone appeared to exert a significant, though modest, stimulatory influence upon calbindin-mRNA accumulation in the vitamin D-deficient (-D) intestine when measured 12 h after administration. 1,25(OH)2D3 also stimulated calbindin-mRNA accumulation in the -D chick intestine; half-maximal (ED50) doses were 1.1 nmol (7.6-fold) and 12.6 nmol (4.3-fold stimulation) for 1,25(OH)2D3 and dexamethasone respectively. In contrast, when both 1,25(OH)2D3 and dexamethasone were administered simultaneously, the stimulatory effect of 1,25(OH)2D3 (and that of the glucocorticoid) was lost in terms of calbindin and calbindin-mRNA accumulation. Dexamethasone treatment of vitamin D-replete (+D) chicks resulted in a depression of calbindin-mRNA accumulation; levels were depressed to baseline with 250 nmol/bird. Dexamethasone (1.25 mumol per day for 3 days) also induced an apparent 'down-regulation' of the 1,25(OH)2D3 receptor population in the -D chick intestine but failed to influence the binding of 1,25(OH)2D3 to its receptor in vitro. Taken collectively, these data indicate that glucocorticoids are able to influence the receptor-mediated action of 1,25(OH)2D3, possibly at the level of calbindin-D28K gene expression.