Cytochrome P450-mediated metabolism of vitamin D Jones, Glenville; Prosser, David E.; Kaufmann, Martin
Journal of lipid research,
January 2014, 2014-Jan, 2014-01-00, 20140101, 2014-01-01, Letnik:
55, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The vitamin D signal transduction system involves a series of cytochrome P450-containing sterol hydroxylases to generate and degrade the active hormone, 1α,25-dihydroxyvitamin D3, which serves as a ...ligand for the vitamin D receptor-mediated transcriptional gene expression described in companion articles in this review series. This review updates our current knowledge of the specific anabolic cytochrome P450s involved in 25- and 1α-hydroxylation, as well as the catabolic cytochrome P450 involved in 24- and 23-hydroxylation steps, which are believed to initiate inactivation of the vitamin D molecule. We focus on the biochemical properties of these enzymes; key residues in their active sites derived from crystal structures and mutagenesis studies; the physiological roles of these enzymes as determined by animal knockout studies and human genetic diseases; and the regulation of these different cytochrome P450s by extracellular ions and peptide modulators. We highlight the importance of these cytochrome P450s in the pathogenesis of kidney disease, metabolic bone disease, and hyperproliferative diseases, such as psoriasis and cancer; as well as explore potential future developments in the field.
Bioactivation of vitamin D consists of two sequential hydroxylation steps to produce 1α,25-dihydroxyvitamin D ₃. It is clear that the second or 1α-hydroxylation step is carried out by a single ...enzyme, 25-hydroxyvitamin D 1α-hydroxylase CYP27B1. However, it is not certain what enzyme or enzymes are responsible for the initial 25-hydroxylation. An excellent case has been made for vitamin D 25-hydroxylase CYP2R1, but this hypothesis has not yet been tested. We have now produced Cyp2r1 ⁻/⁻ mice. These mice had greater than 50% reduction in serum 25-hydroxyvitamin D ₃. Curiously, the 1α,25-dihydroxyvitamin D ₃ level in the serum remained unchanged. These mice presented no health issues. A double knockout of Cyp2r1 and Cyp27a1 maintained a similar circulating level of 25-hydroxyvitamin D ₃ and 1α,25-dihydroxyvitamin D ₃. Our results support the idea that the CYP2R1 is the major enzyme responsible for 25-hydroxylation of vitamin D, but clearly a second, as-yet unknown, enzyme is another contributor to this important step in vitamin D activation.
Idiopathic infantile hypercalcemia (IIH) is characterized by severe hypercalcemia with failure to thrive, vomiting, dehydration, and nephrocalcinosis. Recently, mutations in the vitamin D ...catabolizing enzyme 25-hydroxyvitamin D3-24-hydroxylase (CYP24A1) were described that lead to increased sensitivity to vitamin D due to accumulation of the active metabolite 1,25-(OH)2D3. In a subgroup of patients who presented in early infancy with renal phosphate wasting and symptomatic hypercalcemia, mutations in CYP24A1 were excluded. Four patients from families with parental consanguinity were subjected to homozygosity mapping that identified a second IIH gene locus on chromosome 5q35 with a maximum logarithm of odds (LOD) score of 6.79. The sequence analysis of the most promising candidate gene, SLC34A1 encoding renal sodium-phosphate cotransporter 2A (NaPi-IIa), revealed autosomal-recessive mutations in the four index cases and in 12 patients with sporadic IIH. Functional studies of mutant NaPi-IIa in Xenopus oocytes and opossum kidney (OK) cells demonstrated disturbed trafficking to the plasma membrane and loss of phosphate transport activity. Analysis of calcium and phosphate metabolism in Slc34a1-knockout mice highlighted the effect of phosphate depletion and fibroblast growth factor-23 suppression on the development of the IIH phenotype. The human and mice data together demonstrate that primary renal phosphate wasting caused by defective NaPi-IIa function induces inappropriate production of 1,25-(OH)2D3 with subsequent symptomatic hypercalcemia. Clinical and laboratory findings persist despite cessation of vitamin D prophylaxis but rapidly respond to phosphate supplementation. Therefore, early differentiation between SLC34A1 (NaPi-IIa) and CYP24A1 (24-hydroxylase) defects appears critical for targeted therapy in patients with IIH.
The vitamin D endocrine system regulates mineral homeostasis through its activities in the intestine, kidney, and bone. Terminal activation of vitamin D3 to its hormonal form, 1α,25-dihydroxyvitamin ...D3 (1,25(OH)2D3), occurs in the kidney via the cytochrome P450 enzyme CYP27B1. Despite its importance in vitamin D metabolism, the molecular mechanisms underlying the regulation of the gene for this enzyme, Cyp27b1, are unknown. Here, we identified a kidney-specific control module governed by a renal cell-specific chromatin structure located distal to Cyp27b1 that mediates unique basal and parathyroid hormone (PTH)-, fibroblast growth factor 23 (FGF23)-, and 1,25(OH)2D3-mediated regulation of Cyp27b1 expression. Selective genomic deletion of key components within this module in mice resulted in loss of either PTH induction or FGF23 and 1,25(OH)2D3 suppression of Cyp27b1 gene expression; the former loss caused a debilitating skeletal phenotype, whereas the latter conferred a quasi-normal bone mineral phenotype through compensatory homeostatic mechanisms involving Cyp24a1. We found that Cyp27b1 is also expressed at low levels in non-renal cells, in which transcription was modulated exclusively by inflammatory factors via a process that was unaffected by deletion of the kidney-specific module. These results reveal that differential regulation of Cyp27b1 expression represents a mechanism whereby 1,25(OH)2D3 can fulfill separate functional roles, first in the kidney to control mineral homeostasis and second in extra-renal cells to regulate target genes linked to specific biological responses. Furthermore, we conclude that these mouse models open new avenues for the study of vitamin D metabolism and its involvement in therapeutic strategies for human health and disease.
Summary Background Routine prophylactic platelet transfusion is the standard of care for patients with severe thrombocytopenia. We assessed the effect of a new strategy of therapeutic platelet ...transfusion on the number of transfusions and safety in patients with hypoproliferative thrombocytopenia. Methods We did a multicentre, open-label, randomised parallel-group trial at eight haematology centres in Germany. Patients aged 16–80 years, who were undergoing intensive chemotherapy for acute myeloid leukaemia or autologous haemopoietic stem-cell transplantation for haematological cancers, were randomly assigned via a computer-generated randomisation sequence to receive either platelet transfusion when bleeding occurred (therapeutic strategy) or when morning platelet counts were 10×109 per L or lower (prophylactic strategy). Investigators undertaking interventions were not masked to group assignment. The primary endpoint was the number of platelet transfusions. Analysis was by intention to treat. This trial is registered, NCT00521664. Findings 197 patients were assigned the prophylactic strategy and 199 the therapeutic strategy. Of 391 patients analysed, the therapeutic strategy reduced the mean number of platelet transfusions by 33·5% (95% CI 22·2–43·1; p<0·0001) in all patients (2·44 2·22–2·67 in prophylactic group vs 1·63 1·42–1·83 in therapeutic group), 31·6% (18·6–42·6; p<0·0001) in those with acute myeloid leukaemia (2·68 2·35–3·01 vs 1·83 1·58–2·10), and 34·2% (6·6–53·7; p=0·0193) in those who had had autologous transplantation (1·80 1·45–2·15 vs 1·18 0·82–1·55. We noted no increased risk of major haemorrhage in patients who had undergone autologous transplantation. In those with acute myeloid leukaemia, risk of non-fatal grade 4 (mostly CNS) bleeding was increased. We recorded 15 cases of non-fatal haemorrhage: four retinal in each transfusion group, and one vaginal and six cerebral in the therapeutic group. 12 patients died in the study: two from fatal cerebral haemorrhages in the therapeutic group, and ten (five in each treatment group) unrelated to major bleeding. Interpretation The therapeutic strategy could become a new standard of care after autologous stem-cell transplantation; however, prophylactic platelet transfusion should remain the standard for patients with acute myeloid leukaemia. The new strategy should be used by some haematology centres only if the staff are well educated and experienced in the new approach and can react in a timely way to first signs of CNS bleeding. Funding Deutsche Krebshilfe eV (German Cancer Aid).
Cytochrome P450 family 27 subfamily B member 1 (CYP27B1) and CYP24A1 function to maintain physiological levels of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in the kidney. Renal Cyp27b1 and Cyp24a1 ...expression levels are transcriptionally regulated in a highly reciprocal manner by parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and 1,25(OH)2D3. In contrast, Cyp24a1 regulation in nonrenal target cells (NRTCs) is limited to induction by 1,25(OH)2D3. Herein, we used ChIP-Seq analyses of mouse tissues to identify regulatory regions within the Cyp24a1 gene locus. We found an extended region downstream of Cyp24a1 containing a cluster of sites, termed C24-DS1, binding PTH-sensitive cAMP-responsive element–binding protein (CREB) and a cluster termed C24-DS2 binding the vitamin D receptor (VDR). VDR-occupied sites were present in both the kidney and NRTCs, but pCREB sites were occupied only in the kidney. We deleted each segment in the mouse and observed that although the overt phenotypes of both cluster deletions were unremarkable, RNA analysis in the C24-DS1–deleted strain revealed a loss of basal renal Cyp24a1 expression, total resistance to FGF23 and PTH regulation, and secondary suppression of renal Cyp27b1; 1,25(OH)2D3 induction remained unaffected in all tissues. In contrast, loss of the VDR cluster in the C24-DS2–deleted strain did not affect 1,25(OH)2D3 induction of renal Cyp24a1 expression yet reduced but did not eliminate Cyp24a1 responses in NRTCs. We conclude that a chromatin-based mechanism differentially regulates Cyp24a1 in the kidney and NRTCs and is essential for the specific functions of Cyp24a1 in these two tissue types.
Recommendations for vitamin D supplementation for preterm infants span a wide range of doses. Response to vitamin D supplementation and impact on outcomes in preterm infants is not well understood.
...Evaluate serum 25(OH)D3 concentration changes after 4 weeks in response to two different doses of vitamin D3 supplementation in a population of premature infants and quantify the impact on NICU outcomes.
32 infants born at 24-32 weeks gestation were prospectively randomized to receive 400 or 800 IU/day vitamin D3 supplementation. Serum 25(OH)D3 levels were measured every 4 weeks. The Wilcoxon signed rank test was used to compare serum levels of 25(OH)D3 at 4 weeks and each subsequent time point. A p-value of <0.05 was considered statistically significant.
Serum 25(OH)D3 levels at birth were 41.9 and 42.9 nmol/l for infants in the 400 IU group and 800 IU group, respectively (p = 0.86). Cord 25(OH)D3 concentrations significantly correlated with gestational age (r = 0.40, p = 0.04). After 4 weeks of D3 supplementation, median 25(OH)D3 levels increased in both groups (84.6vs. 105.3 nmol/l for 400 vs. 800 IU/day respectively, with significantly more improvement in the higher dose (p = 0.048). Infants in the 400 IU group were significantly more likely to have dual energy x-ray absorptiometry (DEXA) bone density measurements <10 percentile (56% vs 16%, p = 0.04).
Improvement in 25(OH)D3 levels at 4 weeks, bone density, and trends towards improvement in linear growth support consideration of a daily dose of 800 IU of vitamin D for infants <32 weeks cared for in the NICU.
Detection of the Doppler shift of airglow radiation in the middle and upper atmosphere is one of the most important methods for remote sensing of the atmospheric wind field. Laboratory and routine ...field calibration of an optical interferometer for wind measurement is very important. We report a novel calibration system that simulates a frequency shift of airglow emission lines introduced by wind in the middle and upper atmosphere for calibrating passive optical interferometers. The generator avoids the shortcomings of traditional motor-driven Doppler-shift generators in terms of stability and security while improving accuracy and simplifying assemblies. A simulated wind speed can be determined simultaneously using the light-beat method. The wind error simulated by the generator mainly comes from the light source, which is about 0.63 m/s. An experimental demonstration was conducted using a calibrated Fabry–Perot interferometer and showed that the root mean square of the measurement uncertainty is 0.91 m/s. The novel calibration system was applied to calibrate an asymmetric spatial heterodyne spectrometer (ASHS)-type interferometer successfully. The results demonstrate the feasibility of the system.
PDF
