Hans P. Schilte

Erasmus Universiteit Rotterdam, Rotterdam, South Holland, Netherlands

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Publications (3)6.96 Total impact

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    ABSTRACT: The antifungal imidazole, ketoconazole, was tested for effects on 1,25-dihydroxyvitamin D-3 (1,25-(OH)2D3) metabolism and binding in intact osteoblast-like osteogenic sarcoma cells (UMR-106). Ketoconazole inhibited the C-24 oxidation of 1,25-(OH)2D3 in a dose-dependent manner. Furthermore, inhibition of 1,25-(OH)2D3 metabolism by ketoconazole resulted, after a lag time of 2 h, in a sharp increase of receptor-bound 1,25-(OH)2D3. The data suggest that the self-induced 1,25-(OH)2D3 metabolism may play an important role in controlling the intracellular levels of and, consequently, receptor occupancy by the active form of vitamin D. Furthermore the results are compatible with the existence of a homologous up-regulation of the 1,25-(OH)2D3-receptor.
    No preview · Article · Dec 1987 · Biochimica et Biophysica Acta
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    ABSTRACT: 1,25(OH)2D3 induced a dose-dependent increase of alkaline phosphatase activity in primary cultures of fetal rat osteoblast-like cells. A slight decrease in final DNA content was found in densely seeded cultures and at 10(-8) M 1,25(OH)2D3 only. Furthermore, 1,25(OH)2D3 treatment resulted in an attenuation of the cAMP response to PTH without an effect on the EC50 of PTH. On the other hand no change of the cAMP response to forskolin was observed. Forskolin partly restored the decline in the PTH-stimulated adenylate cyclase activity. The results indicate that physiological concentrations of 1,25(OH)2D3 have a stimulatory effect on the alkaline phosphatase of osteoblast-like cells and decrease the responsiveness of these cultures to PTH. We propose that the site of action of 1,25(OH)2D3 in the adenylate cyclase system is either at the level of the regulatory unit or on the interaction of the regulatory with the catalytic unit.
    No preview · Article · Nov 1986 · Bone and Mineral
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    ABSTRACT: Incubation of osteoblast-like cells with [3H]25-(OH)D3 and varying bovine serum albumin (BSA) concentrations resulted in a dramatic change in the accumulation of 1,25-(OH)2D3 and 24,25-(OH)2D3 in the medium. At 0.1% BSA 1,25-(OH)2D3 formation was transient and 24,25-(OH)2D3 was the main product after 3 h. At 2% BSA accumulation of 1,25-(OH)2D3 was sustained whereas 24,25-(OH)2D3 formation was suppressed. At low BSA levels added [3H]1,25-(OH)2D3 was rapidly metabolized to 1,24,25-(OH)3D3 and more polar metabolites. The effect of increasing BSA concentrations on 25-(OH)D3 metabolism was mimicked by addition of cycloheximide. This indicates that high BSA levels prevent the induction of 24-hydroxylase activity in this system, probably by lowering of the free 25-(OH)D3 concentration. The accumulation of 1,25-(OH)2D3 from 25-(OH)D3 not only depends on the 1 alpha-hydroxylase activity, but also on the further metabolism of 1,25-(OH)2D3 by 24-hydroxylation.
    No preview · Article · Dec 1984 · Biochemical and Biophysical Research Communications