Kidney deletions of Cyp27b1 fail to reduce serum 1,25(OH)D.

Vitamin D metabolism is controlled through the kidney mitochondrial P450 enzymes 1α-hydroxylase (CYP27B1) and 24-hydroxylase (CYP24A1) that activate and degrade the endocrine vitamin D hormone (1,25(OH)D), respectively. We recently demonstrated that extrarenal cells can make 1,25(OH)D with adequate vitamin D supplementation by targeted mass spectrometry imaging in our Cyp27b1 kidney enhancer deletion mouse model that lacks circulating 1,25(OH)D (M1/M21-DIKO mouse). Based on these observations, we selectively deleted Cyp27b1 (Cyp27b1) from the mouse kidney using the Six2- and Pax8-cre drivers that target tubule and nephron development to see if we could recapitulate the remarkable phenotype of the M1/M21-DIKO mice.

The impact of inducible-whole body or intestine-specific Cyp24a1 gene knockout on vitamin D metabolism in mice.

Expression of 25 hydroxyvitamin D 24 hydroxylase from the Cyp24a1 gene mediates 1,25 dihydroxyvitamin D (1,25(OH)D) catabolism but gaps exist in our understanding of this enzyme's physiologic importance. Here, we used tamoxifen to induce Cyp24a1 gene knockout (KO) in adult mice (50 mg Tamoxifen /g BW, ip, 5 d, at 11 wks of age) or intestinal-epithelial-cell-specific knock-out mice (IEC KO) to evaluate the role of CYP24A1 in adult mice and the contribution of the intestine to vitamin D (Vit D) metabolism. At 12-wks mice were euthanized and serum was analyzed for Vit D metabolites by LC MS/MS while duodenal (Dd) and kidney (Kd) mRNA levels were quantified using qPCR.

In Vivo Contribution of Cyp24a1 Promoter Vitamin D Response Elements.

CYP24A1 is a multifunctional, P450 mitochondrial enzyme that catabolizes the vitamin D hormone (calcitriol, 1,25(OH)2D3), its precursor (calcifediol, 25(OH)D3), and numerous vitamin D metabolites. In the kidney, Cyp24a1 is induced by 1,25(OH)2D3 and fibroblast growth factor 23 (FGF23) and potently suppressed by PTH to control the circulating levels of 1,25(OH)2D3. Cyp24a1 is controlled by a pair of promoter proximal (PRO) vitamin D response elements (VDREs) that are aided by distal, downstream (DS) enhancers.

contribution of promoter vitamin D response elements.

CYP24A1 is a multifunctional, P450 mitochondrial 24-hydroxylase enzyme that is responsible for catabolism of the most active vitamin D hormone (calcitriol, 1,25(OH)D), its precursor (calcifediol, 25(OH)D), and numerous other vitamin D metabolites at the 23- and 24-carbon positions. In the kidney, is induced by 1,25(OH)D, induced by FGF23, and potently suppressed by PTH to tightly control the circulating blood levels of 1,25(OH)D. This gene is believed to be under the control of a pair of classic promoter proximal (PRO) vitamin D response elements (VDREs) that are aided by distal, downstream (DS) containing enhancers that we identified more recently.

Vitamin D Metabolites in Mother-Infant Dyads and Associated Clinical Outcomes in a Population of Nigerian Women.

Low levels of vitamin D in maternal and cord blood have been associated with neonatal sepsis. This study assessed the association of vitamin D metabolites (25(OH)D, 3-epi-25(OH)D, and 24,25(OH)D) levels in maternal and cord blood with newborn sepsis evaluation in Nigerian mother-infant dyads. Maternal and cord blood from 534 mothers and 536 newborns were processed using liquid chromatography-tandem mass spectrometry.

Consensus Statement on Vitamin D Status Assessment and Supplementation: Whys, Whens, and Hows.

The 6th International Conference, "Controversies in Vitamin D," was convened to discuss controversial topics, such as vitamin D metabolism, assessment, actions, and supplementation. Novel insights into vitamin D mechanisms of action suggest links with conditions that do not depend only on reduced solar exposure or diet intake and that can be detected with distinctive noncanonical vitamin D metabolites. Optimal 25-hydroxyvitamin D (25(OH)D) levels remain debated.

Loss of maternal calcitriol reversibly alters early offspring growth and skeletal development in mice.

Ablation of Cyp27b1 eliminates calcitriol but does not disturb fetal mineral homeostasis or skeletal development. However, independent of fetal genotypes, maternal loss of Cyp27b1 altered fetal mineral and hormonal levels compared to offspring of WT dams. We hypothesized that these maternal influences would alter postnatal skeletal development.

A phase II dose evaluation pilot feasibility randomized controlled trial of cholecalciferol in critically ill children with vitamin D deficiency (VITdAL-PICU study).

Background: Vitamin D deficiency (VDD) is highly prevalent in the pediatric intensive care unit (ICU) and associated with worse clinical course. Trials in adult ICU demonstrate rapid restoration of vitamin D status using an enteral loading dose is safe and may improve outcomes. There have been no published trials of rapid normalization of VDD in the pediatric ICU.

Epimeric vitamin D and cardiovascular structure and function in advanced CKD and after kidney transplantation.

Background: 25-hydroxyvitamin D can undergo C-3 epimerization to produce 3-epi-25(OH)D3. 3-epi-25(OH)D3 levels decline in chronic kidney disease (CKD), but its role in regulating the cardiovascular system is unknown. Herein, we examined the relationship between 3-epi-25(OH)D3, and cardiovascular functional and structural endpoints in patients with CKD.

Measurements of the Vitamin D Metabolome in the Calgary Vitamin D Study: Relationship of Vitamin D Metabolites to Bone Loss.

In a 36-month randomized controlled trial examining the effect of high-dose vitamin D on radial and tibial total bone mineral density (TtBMD), measured by high-resolution peripheral quantitative tomography (HR-pQCT), participants (311 healthy males and females aged 55-70 years with dual-energy X-ray absorptiometry T-scores > -2.5 without vitamin D deficiency) were randomized to receive 400 IU (N = 109), 4000 IU (N = 100), or 10,000 IU (N = 102) daily. Participants had HR-pQCT radius and tibia scans and blood sampling at baseline, 6, 12, 24, and 36 months.

Effect of Vitamin D Supplementation on Bone Mass in Infants With 25-Hydroxyvitamin D Concentrations Less Than 50 nmol/L: A Prespecified Secondary Analysis of a Randomized Clinical Trial.

Importance: The dose of supplemental vitamin D needed in infants born with serum 25-hydroxyvitamin D (25[OH]D) concentrations less than 50 nmol/L (ie, 20 ng/mL) is unclear.

Objective: To determine whether a higher dose (1000 IU vs 400 IU per day) is required in infants born with 25(OH)D concentrations less than 50 nmol/L for bone mineral accretion across infancy.

Design, Setting, And Participants: In this prespecified secondary analysis of a double-blinded randomized clinical trial, conducted from March 2016 to March 2019 in a single center in Greater Montreal, Quebec, Canada, a consecutive sample of 139 healthy term singletons were recruited from 866 infants screened for vitamin D status at birth.

The 1,24,25(OH)D metabolite in clinical and experimental CKD: Impact of calcitriol treatment.

Calcitriol, and other vitamin D receptor activators, remain a primary treatment for elevated parathyroid hormone levels in patients with end stage kidney disease. The objective of this study was to assess the 24-hydroxylation-mediated metabolism of 25(OH)D and 1,25(OH)D in rats with experimental kidney disease treated with calcitriol and in a cross-sectional analysis of patients requiring hemodialysis. Methods: Animals were stratified by creatinine into a time control group or calcitriol (20 ng/kg/day) for 3 weeks following CKD induction using a dietary adenine model (0.

Vitamin D and Diseases of Mineral Homeostasis: A R396W Humanized Preclinical Model of Infantile Hypercalcemia Type 1.

Infantile hypercalcemia type 1 (HCINF1), previously known as idiopathic infantile hypercalcemia, is caused by mutations in the 25-hydroxyvitamin D 24-hydroxylase gene, . The R396W loss-of-function mutation in is the second most frequent mutated allele observed in affected HCINF1 patients. We have introduced the site-specific R396W mutation within the murine gene in knock-in mice to generate a humanized model of HCINF1.

The metabolism of 1,25(OH)D in clinical and experimental kidney disease.

Chronic kidney disease (CKD) results in calcitriol deficiency and altered vitamin D metabolism. The objective of this study was to assess the 24-hydroxylation-mediated metabolism of 25(OH)D and 1,25(OH)D in a cross-sectional analysis of participants with a range of kidney function assessed by precise measured GFR (mGFR) (N = 143) and in rats with the induction and progression of experimental kidney disease. Vitamin D metabolites were assessed with LC-MS/MS.

Long-term Efficacy and Safety of Rifampin in the Treatment of a Patient Carrying a CYP24A1 Loss-of-Function Variant.

Background: Pharmacological therapy may be useful in the treatment of moderate to severe hypercalcemia in patients with infantile hypercalcemia-1 (HCINF1) due to pathogenic variants in the cytochrome P450 24 subfamily A member 1 (CYP24A1). Rifampin is an antituberculosis drug that is a potent inducer of cytochrome P450 3 subfamily A member 4, which is involved in an alternative catabolic pathway of vitamin D. The efficacy of rifampin in improving hypercalcemia was previously reported, but many questions remain on the long-term efficacy and safety.

Correction of neonatal vitamin D status using 1000 IU vitamin D/d increased lean body mass by 12 months of age compared with 400 IU/d: a randomized controlled trial.

Background: Intrauterine exposure to maternal vitamin D status <50 nmol/L of serum 25-hydroxyvitamin D [25(OH)D] may adversely affect infant body composition. Whether postnatal interventions can reprogram for a leaner body phenotype is unknown.

Objectives: The primary objective was to test whether 1000 IU/d of supplemental vitamin D (compared with 400 IU/d) improves lean mass in infants born with serum 25(OH)D <50 nmol/L.

100 YEARS OF VITAMIN D: Historical aspects of vitamin D.

Vitamin D has many physiological functions including upregulation of intestinal calcium and phosphate absorption, mobilization of bone resorption, renal reabsorption of calcium as well as actions on a variety of pleiotropic functions. It is believed that many of the hormonal effects of vitamin D involve a 1,25-dihydroxyvitamin D3-vitamin D receptor-mediated transcriptional mechanism involving binding to the cellular chromatin and regulating hundreds of genes in many tissues. This comprehensive historical review provides a unique perspective of the many steps of the discovery of vitamin D and its deficiency disease, rickets, stretching from 1650 until the present.

Maternal excess adiposity and serum 25-hydroxyvitamin D < 50 nmol/L are associated with elevated whole body fat mass in healthy breastfed neonates.

Background: Vitamin D status of pregnant women is associated with body composition of the offspring. The objective of this study was to assess whether the association between maternal vitamin D status and neonatal adiposity is modified by maternal adiposity preconception.

Methods: Healthy mothers and their term appropriate weight for gestational age (AGA) infants (n = 142; 59% male, Greater Montreal, March 2016-2019) were studied at birth and 1 month postpartum (2-6 weeks).

Maternal Vitamin D Status and Gestational Weight Gain as Correlates of Neonatal Bone Mass in Healthy Term Breastfed Young Infants from Montreal, Canada.

The implications of maternal gestational weight gain (GWG) and vitamin D status to neonatal bone health are unclear. We tested whether maternal 25-hydroxyvitamin D (25(OH)D) and GWG relate to neonatal bone mineral content (BMC) and bone mineral density (BMD). Healthy term appropriate for gestational age breastfed neonates ( = 142) and their mothers were recruited 24-36 h after delivery and followed at 1.

Diagnostic Aspects of Vitamin D: Clinical Utility of Vitamin D Metabolite Profiling.

The assay of vitamin D that began in the 1970s with the quantification of one or two metabolites, 25-OH-D or 1,25-(OH)D, continues to evolve with the emergence of liquid chromatography tandem mass spectrometry (LC-MS/MS) as the technique of choice. This highly accurate, specific, and sensitive technique has been adopted by many fields of endocrinology for the measurement of multiple other components of the metabolome, and its advantage is that it not only makes it feasible to assay 25-OH-D or 1,25-(OH)D but also other circulating vitamin D metabolites in the vitamin D metabolome. In the process, this broadens the spectrum of vitamin D metabolites, which the clinician can use to evaluate the many complex genetic and acquired diseases of calcium and phosphate homeostasis involving vitamin D.

Overlapping Phenotypes Associated With , , and Mutations: A Cohort Study of Patients With Hypersensitivity to Vitamin D.

Mutations in (vitamin D 24-hydroxylase) and (renal phosphate transporter NPT2a) cause autosomal recessive Infantile Hypercalcemia type 1 and 2, illustrating links between vitamin D and phosphate metabolism. Patients may present with hypercalciuria and alternate between chronic phases with normal serum calcium but inappropriately high 1,25-(OH)D and appropriately low PTH, and acute phases with hypercalcemia with suppressed PTH. Mutations in and have been associated with phosphate wasting without hypercalcemia.

CYP24A1 and SLC34A1 Pathogenic Variants Are Uncommon in a Canadian Cohort of Children with Hypercalcemia or Hypercalciuria.

Objectives: Biallelic pathogenic variants in CYPA24A1 and SLC34A1 are causes of idiopathic infantile hypercalcemia. Pathogenic variants in both may also give rise to hypercalciuria with nephrocalcinosis or nephrolithiasis without previous hypercalcemia (renal group). Our objective was to examine the frequency of CYP24A1 or SLC34A1 variants in children with early hypercalcemia or late-onset hypercalciuria.

Differential diagnosis of vitamin D-related hypercalcemia using serum vitamin D metabolite profiling.

Genetic causes of vitamin D-related hypercalcemia are known to involve mutation of 25-hydroxyvitamin D-24-hydroxylase CYP24A1 or the sodium phosphate co-transporter SLC34A1, which result in excessive 1,25-(OH) D hormonal action. However, at least 20% of idiopathic hypercalcemia (IH) cases remain unresolved. In this case-control study, we used precision vitamin D metabolite profiling based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) of an expanded range of vitamin D metabolites to screen German and French cohorts of hypercalcemia patients, to identify patients with altered vitamin D metabolism where involvement of CYP24A1 or SLC34A1 mutation had been ruled out and who possessed normal 25-OH-D :24,25-(OH) D ratios.