Activities of NAD-and NADP-specific isocitrate dehydrogenases in kidney mitochondria of rachitic rat

Effect of 1,25-dihydroxyvitamin D3 on proliferation in senescent IMR-90 human fibroblasts

The response of IMR-90 human fetal lung fibroblasts at high population doubling level (PDL > 42) to 1,25-dihydroxyvitamin D3[1,25(OH)2D3] was investigated to clarify whether some metabolic and molecular parameters of senescent cells are affected by the hormone treatment. Pyruvate kinase, lactate dehydrogenase and glucose-6-phosphate dehydrogenase activity significantly increased after treatment of confluent-phase cells with 10 nM 1,25(OH)2D3 for 24 h. Steroid specificity was established by the failure of 10 nM levels of 25-hydroxyvitamin D3 to affect the enzyme activities, while estradiol-17 beta and progesterone produced a slight increase in glucose-6-phosphate dehydrogenase and lactate dehydrogenase levels, respectively. 1,25(OH)2D3 also affected fibroblast proliferation, protein content/cell and DNA synthesis. The cell number significantly decreased after a 48 h incubation with 1,25(OH)2D3 at various concentrations (0.01-1 nM) when compared with control fibroblasts, while an increase in the protein content/cell was demonstrated. The same experiment, carried out by protracting the incubation with the hormone for 72 h, showed a similar trend, but 10 nM 1,25(OH)2D3 was also able to inhibit cell proliferation and to stimulate protein synthesis. The incorporation of [3H]thymidine into DNA increased after the treatment of high PDL fibroblasts with 0.01-1 nM of hormone for 48 h in comparison with controls.

1,25-dihydroxyvitamin D3 inhibits proliferation of IMR-90 human fibroblasts and stimulates pyruvate kinase activity in confluent-phase cells

This study tested the hypothesis that 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plays a role in regulating some aspects of metabolism in IMR-90 normal human fetal lung fibroblasts. Among the enzymes studied, only pyruvate kinase showed a significant increase after treatment of confluent-phase cells with 1,25(OH)2D3 at various concentrations (0.1-100 nM range) for 24 h. A parallel increase in lactate output was observed. Steroid specificity was established by the failure of 10 nM levels of 25-hydroxyvitamin D3, estradiol-17 beta and progesterone to affect pyruvate kinase activity. The determination of the time course of [3H]-2-deoxy-D-glucose transport indicated that the hormone did not influence the transmembrane transport system of D-glucose. The addition of the inhibitors cycloheximide and actinomycin D to the culture medium abolished, at least in part, the 1,25(OH)2D3 stimulation of pyruvate kinase activity, suggesting the probable dependence of the hormone effect on cellular RNA and protein synthesis. 1,25(OH)2D3 also affected fibroblast growth and DNA synthesis. Cell number significantly decreased after 2-5 days treatment with 10 nM hormone in comparison with control fibroblasts, and also the incorporation of [3H]thymidine into DNA decreased after treatment of the cells with 1 and 10 nM hormone for 48 h. In conclusion, these data demonstrate that 1,25(OH)2D3 stimulates pyruvate kinase activity in confluent-phase IMR-90 human fibroblasts by a mechanism probably dependent on de novo protein synthesis, and also affects cell growth and DNA synthesis in sub-confluent-phase cells.

Effect of vitamin D deficiency and 1,25-dihydroxyvitamin D3 on metabolism and D-glucose transport in rat cerebral cortex

We previously demonstrated that feeding rats Steenbock and Black's rickets-inducing diet produces remarkable changes in the metabolic pattern of the intestinal mucosa, kidney, and liver and in some membrane transport systems of intestinal mucosa and kidney. 1,25-Dihydroxyvitamin D3 administration to rachitic rats did not always prove to be effective in restoring normal values. We have now investigated the effect of 1,25-dihydroxyvitamin D3 on the levels of some metabolites in rat cerebral cortex, on the activity of some enzymes, and on the transport of 2-deoxy-D-glucose and D-glucose in synaptosomes. Our experiments were carried out on three rat groups: control, rachitic, and rachitic treated with 1,25-dihydroxyvitamin D3. The decrease in phosphorus content and the increase in citrate concentration observed in rachitic rat cerebral cortex were corrected by 1,25-dihydroxyvitamin D3 treatment. The activity of acetylcholinesterase, glucose-6-phosphate dehydrogenase, and acyl phosphatase significantly increased in rachitic rat synaptosomes, as well as NAD(+)-dependent isocitrate dehydrogenase in cerebral cortex mitochondria; the administration of 1,25-dihydroxyvitamin D3 to rachitic rats restored enzyme levels to normal. The transport of 2-deoxy-D-glucose and D-glucose in rachitic rat synaptosomes was lower than in the control group and returned to control values in consequence of 1,25-dihydroxyvitamin D3 treatment. The results reported here support the hypothesis of a participation of 1,25-dihydroxyvitamin D3 in some aspects of cerebral cortex metabolism.