Vitamin D: metabolism and biological actions

Activity of ornithine decarboxylase and creatine kinase in soft and hard tissue of vitamin D-deficient chicks following parenteral application of 1,25-dihydroxyvitamin D3 or 24R,25-dihydroxyvitamin D3

We investigated the stimulation of creatine kinase (CK) and ornithine decarboxylase (ODC) by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] in doses ranging from 1.625 to 6500 pmol in 4-week-old vitamin D-deficient chicks. Enzyme activities were monitored for 72 h. 1,25(OH)2D3 but not 24R,25(OH)2D3 enhanced the activity of ODC in duodenum and bone. The time course of ODC activity in bone was biphasic, with an increase after 1 h and a higher peak after 24 h. Diaphyses and epiphyses responded equally well after a dose of 6500 pmol. The kidney, liver, and lung showed 1.5-3.8-fold increase in CK activity following 1,25(OH)2D3, reaching a maximum between 3-5 h. However, sustained stimulation of CK activity could still be demonstrated after 72 h, and the 48-h levels in the lung even exceeded the 5-h values. No change of activity of either enzyme was noted in heart and brain after application of 1,25(OH)2D3. There was no coincidence of stimulation of ODC and CK by 1,25(OH)2D3 in the same tissue, and the dose-responsiveness of both enzymes differed considerably. Near maximum activities of ODC were achieved with 19.5 pmol 1,25(OH)2D3 in duodenum and pancreas, while maximum responses of CK occurred in the liver at 195 pmol and in lung and kidney at 6500 pmol. 24R,25(OH)2D3 failed to produce any consistent effects of either enzyme in all tissues examined. These results, particularly the lack of response to 24R,25(OH)2D3, are different from those reported in rats.

Effect of ketoconazole and miconazole on 25-hydroxyvitamin D3 metabolism by cultured chick kidney cells

The antifungal imidazoles, ketoconazole and miconazole, were tested for effects on 25-hydroxyvitamin D3 metabolism in primary cultures of chick kidney cells. Both behave as competitive inhibitors of 1-hydroxylation of 25-OH-D3 with approximate Ki's of 0.8 and 5.0 microM for ketoconazole and miconazole, respectively. Ketoconazole was as effective when added at the same time as the substrate as when the cells were preincubated with the compound. Ketoconazole also inhibited the production of 24,25(OH)2D3 in cells in which this activity was induced by 1,24(OH)2D3. The data suggest that therapeutic doses of these antifungal imidazoles could affect vitamin D status and calcium metabolism.

Effects of specific nutrients on the immune response. Selected clinical applications

The importance of diet in multiple aspects of the immune response is inescapable. Although only a few trials have attempted to apply knowledge derived from in-vitro and animal data to humans, the ability to modulate or "reset" the immune response by manipulating dietary intake will surely continue to be studied in the future. The role of various nutrients in immunity is reviewed and clinical applications are noted.