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Background: Hyperphosphatemia confers adverse cardiovascular outcomes, and commonly occurs in late-stage CKD. Fibroblast growth factor 7 (FGF7) is a phosphaturic peptide which decreases renal phosphate transport in vitro and in vivo. Serum FGF7 concentrations are reduced in hyperphosphatemic patients with hypophosphatasia and are elevated in some hypophosphatemic patients with tumor-induced osteomalacia. No data, however, are available on whether circulating FGF7 concentrations increase to compensate for phosphate retention in CKD patients., Methods: This was a cross-sectional study performed among 85 adult patients with varying estimated glomerular filtration rates (eGFR). We measured serum intact FGF7 (iFGF7) concentration using an iFGF7 immunoassay and determined its associated factors. Relationships between eGFR and mineral metabolism biomarkers [phosphate, iFGF7, iFGF23, parathyroid hormone (PTH), and 1,25-dihydroxyvitamin D (1,25(OH) 2 D)] were explored., Results: For eGFRs of ≥ 60 (n = 31), 45-59 (n = 16), 30-44 (n = 11), 15-29 (n = 15), and < 15 mL/min/1.73 m 2 (n = 12), median (IQ25-75) iFGF7 concentrations were 46.1 (39.2-56.9), 43.1 (39.0-51.5), 47.3 (38.3-66.5), 47.7 (37.7-55.8), and 49.6 (42.5-65.6) pg/mL, respectively (P = 0.62). Significant increases in serum iFGF23, PTH, and phosphate were observed at eGFRs of < 33 (95 % CI, 26.40-40.05), < 29 (95 % CI, 22.51-35.36), and < 22 mL/min/1.73 m 2 (95 % CI, 19.25-25.51), respectively, while significant decreases in serum 1,25(OH) 2 D were observed at an eGFR of < 52 mL/min/1.73 m 2 (95 % CI, 42.57-61.43). No significant correlation was found between serum iFGF7 and phosphate, iFGF23, PTH or 1,25(OH) 2 D. In multivariable analyses, body mass index (per 5 kg/m 2 increase) was independently associated with the highest quartile of serum iFGF7 concentration (OR, 1.20; 95 % CI, 1.12-1.55)., Conclusions: Compensatory decreases in circulating 1,25(OH) 2 D and increases in circulating iFGF23 and PTH, but not iFGF7, facilitate normalization of serum phosphate concentration in early stages of CKD. Whether other circulating phosphaturic peptides change in response to phosphate retention in CKD patients deserves further study.

Objective: Supplementing lactating mothers with high doses of vitamin D 3 can adequately meet vitamin D requirements of the breastfed infant. We compared the effect of bolus versus daily vitamin D 3 dosing in lactating mothers on vitamin D 3 catabolism. We hypothesized that catabolism of 25(OH)D 3 to 24,25(OH) 2 D 3 would be greater in the bolus than in the daily dose group., Design, Setting and Patients: Randomized controlled trial (clinicaltrials.govNCT01240265) in 40 lactating women., Interventions: Subjects were randomized to receive vitamin D 3 orally, either a single dose of 150,000IU or 5000IU daily for 28days. Vitamin D metabolites were measured in serum and breast milk at baseline, 1, 3, 7, 14 and 28days., Main Outcome Measure: Temporal changes in the serum 24,25(OH) 2 D 3 /25(OH)D 3 ratio., Results: The concentration of serum 24,25(OH) 2 D 3 was directly related to that of 25(OH)D in both groups (r 2 =0.63; p<0.001). The mean (±SD) 24,25(OH) 2 D 3 /25(OH)D 3 ratio remained lower at all time points than baseline values in the daily dose group (0.093±0.024, 0.084±0.025, 0.083±0.024, 0.080±0.020, 0.081±0.023, 0.083±0.018 at baseline, 1, 3, 7, 14, and 28days, respectively). In the single dose group, the increase in 24,25(OH) 2 D 3 lagged behind that of 25(OH)D, but the 24,25(OH) 2 D 3 /25(OH)D 3 values (0.098±0.032, 0.067±0.019, 0.081±0.017, 0.092±0.024, 0.103±0.020, 0.106±0.024, respectively) exceeded baseline values at 14 and 28days and were greater than the daily dose group at 14 and 28days (p=0.003). The 24,25(OH) 2 D 3 /25(OH)D 3 ratio remained in the normal range with both dosing regimens. Greater breast milk vitamin D 3 values in the single dose group were inversely associated with the 24,25(OH) 2 D 3 /25(OH)D 3 ratio (r 2 =0.14, p<0.001), but not with daily dosing., Conclusions: After a 14-day lag, a single high dose of vitamin D led to greater production of 24,25(OH) 2 D 3 , presumably via induction of the 24-hydroxylase enzyme (CYP24A1), relative to the 25(OH)D 3 value than did daily vitamin D supplementation, and this effect persisted for at least 28days after vitamin D administration. A daily dose of vitamin D may have more lasting effectiveness in increasing 25(OH)D 3 with lesser diversion of 25(OH)D 3 to 24,25(OH) 2 D 3 than does larger bolus dosing., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Hypercalcemia occurs in up to 4% of the population in association with malignancy, primary hyperparathyroidism, ingestion of excessive calcium and/or vitamin D, ectopic production of 1,25-dihydroxyvitamin D [1,25(OH) 2 D], and impaired degradation of 1,25(OH) 2 D. The ingestion of excessive amounts of vitamin D 3 (or vitamin D 2 ) results in hypercalcemia and hypercalciuria due to the formation of supraphysiological amounts of 25-hydroxyvitamin D [25(OH)D] that bind to the vitamin D receptor, albeit with lower affinity than the active form of the vitamin, 1,25(OH) 2 D, and the formation of 5,6-trans 25(OH)D, which binds to the vitamin D receptor more tightly than 25(OH)D. In patients with granulomatous disease such as sarcoidosis or tuberculosis and tumors such as lymphomas, hypercalcemia occurs as a result of the activity of ectopic 25(OH)D-1-hydroxylase (CYP27B1) expressed in macrophages or tumor cells and the formation of excessive amounts of 1,25(OH) 2 D. Recent work has identified a novel cause of non-PTH-mediated hypercalcemia that occurs when the degradation of 1,25(OH) 2 D is impaired as a result of mutations of the 1,25(OH) 2 D-24-hydroxylase cytochrome P450 (CYP24A1). Patients with biallelic and, in some instances, monoallelic mutations of the CYP24A1 gene have elevated serum calcium concentrations associated with elevated serum 1,25(OH) 2 D, suppressed PTH concentrations, hypercalciuria, nephrocalcinosis, nephrolithiasis, and on occasion, reduced bone density. Of interest, first-time calcium renal stone formers have elevated 1,25(OH) 2 D and evidence of impaired 24-hydroxylase-mediated 1,25(OH) 2 D degradation. We will describe the biochemical processes associated with the synthesis and degradation of various vitamin D metabolites, the clinical features of the vitamin D-mediated hypercalcemia, their biochemical diagnosis, and treatment.

Humans with mutations of the sclerostin (SOST) gene, and knockout animals in which the Sost gene has been experimentally deleted, exhibit an increase in bone mass. We review the mechanisms by which Sost knockout mice are able to accrete increased amounts of calcium and phosphorus required for the maintenance of a high bone mass. Recently published information from our laboratory, shows that bone mass is increased in Sost-deficient mice through an increase in osteoblast and a decrease in osteoclast activity, which is mediated by activation of β-catenin and an increase in prostacyclin synthesis in osteocytes and osteoblasts. The increases in calcium and phosphorus retention required for enhanced bone mineral accretion are brought about by changes in the vitamin D endocrine system, parathyroid hormone (PTH) and fibroblast growth factor-23 (FGF-23). Thus, in Sost knockout mice, concentrations of serum 1,25-dihydroxyvitamin D (1,25(OH)2D) are increased and concentrations of FGF-23 are decreased thereby allowing a positive calcium and phosphorus balance. Additionally, in the absence of Sost expression, urinary calcium is decreased, either through a direct effect of sclerostin on renal calcium handling, or through its effect on the synthesis of 1,25(OH)2D. Adaptations in vitamin D, PTH and FGF-23 physiology occur in the absence of sclerostin expression and mediate increased calcium and phosphorus retention required for the increase in bone mineralization. This article is part of a Special Issue entitled '17th Vitamin D Workshop'., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The sterol hormone, 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃), regulates gene expression and messenger RNA (mRNA) concentrations in zebrafish in vivo. Since mRNA concentrations and translation are influenced by micro-RNAs (miRNAs), we examined the influence of 1α,25(OH)₂D₃ on miRNA expression in zebrafish in vivo with whole transcriptome RNA sequencing, searched for miRNA binding sites in 1α,25(OH)₂D₃-sensitive genes, and performed correlation analyses between 1α,25(OH)₂D₃-sensitive miRNAs and mRNAs. In vehicle- and 1α,25(OH)₂D₃-treated, 7-day postfertilization larvae, between 282 and 295 known precursor miRNAs were expressed, and in vehicle- and 1α,25(OH)₂D₃-treated fish, between 83 and 122 novel miRNAs were detected. Following 1α,25(OH)₂D₃ treatment, 31 precursor miRNAs were differentially expressed (p<0.05). The differentially expressed miRNAs are predicted to potentially alter mRNAs for metabolic enzymes, transcription factors, growth factors, and Jak-STAT signaling. We verified the role of a 1α,25(OH)₂D₃-sensitive miRNA, miR125b, by demonstrating alterations in the concentrations of the mRNA of a 1α,25(OH)₂D₃-regulated gene, Cyp24a1, following transfection of renal cells with a miR125b miRNA mimic. Changes in the Cyp24a1 mRNA concentration by the miR125b miRNA mimic were associated with changes in the protein for Cyp24a1. Our data show that 1α,25(OH)₂D₃ regulates miRNA in zebrafish larvae in vivo and could thereby influence vitamin D-sensitive mRNA concentrations.

Serum 25-hydroxyvitamin D (25[OH]D) concentrations are positively associated with pneumococcal antibody titers (PATs) in subjects with atopy or asthma. Little is known about the association of serum 25(OH)D concentrations and the waning of PATs over time in subjects with or without atopy. This study was designed to determine whether serum 25(OH)D concentrations are associated with waning of PATs and if such relationship is modified by atopic conditions. The study was designed as a prospective cohort study, which followed 20 asthmatic patients and 19 individuals without asthma for an average of 12 months. We measured PATs and serum 25(OH)D concentrations at baseline and at a subsequent follow-up visit. Asthma was ascertained by predetermined criteria. The association between serum 25(OH)D concentrations and PATs was determined by Pearson's correlation coefficient and a least square model. Of the 39 children and adults, 21(53%) were male subjects, all were white, and 6 (15%) were children. There was an overall negative correlation between serum 25(OH)D concentrations and the decrease of PATs during follow-up (r = -0.47; p = 0.004), suggesting that higher 25(OH)D concentrations were associated with a reduction in waning of PATs over time. Controlling for follow-up duration and pneumococcal colonization, these trends were significant among asthmatic patients but not in individuals without asthma. Similar trends were observed for individuals with or without other atopic conditions. Serum 25(OH)D concentrations are inversely associated with the waning of PATs over time, especially individuals with asthma and other atopy conditions. These study findings deserve further investigation.

Inactivating mutations of the SOST (sclerostin) gene are associated with overgrowth and sclerosis of the skeleton. To determine mechanisms by which increased amounts of calcium and phosphorus are accreted to enable enhanced bone mineralization in the absence of sclerostin, we measured concentrations of calciotropic and phosphaturic hormones, and urine and serum calcium and inorganic phosphorus in mice in which the sclerostin (sost) gene was replaced by the β-D-galactosidase (lacZ) gene in the germ line. Knockout (KO) (sost(-/-)) mice had increased bone mineral density and content, increased cortical and trabecular bone thickness, and greater net bone formation as a result of increased osteoblast and decreased osteoclast surfaces compared with wild-type (WT) mice. β-Galactosidase activity was detected in osteocytes of sost KO mice but was undetectable in WT mice. Eight-week-old, male sost KO mice had increased serum 1α,25-dihydroxyvitamin D, decreased 24,25-dihydroxyvitamin D, decreased intact fibroblast growth factor 23, and elevated inorganic phosphorus concentrations compared with age-matched WT mice. 25-Hydroxyvitamin D 1α-hydroxylase cytochrome P450 (cyp27B1) mRNA was increased in kidneys of sost KO mice compared with WT mice. Treatment of cultured proximal tubule cells with mouse recombinant sclerostin decreased cyp27B1 mRNA transcripts. Urinary calcium and renal fractional excretion of calcium were decreased in sost KO mice compared with WT mice. Sost KO and WT mice had similar serum calcium and parathyroid hormone concentrations. The data show that sclerostin not only alters bone mineralization, but also influences mineral metabolism by altering concentrations of hormones that regulate mineral accretion.

The biological role of vitamin D receptors (VDR), which are abundantly expressed in developing zebrafish (Danio rerio) as early as 48 h after fertilization, and before the development of a mineralized skeleton and mature intestine and kidney, is unknown. We probed the role of VDR in developing zebrafish biology by examining changes in expression of RNA by whole transcriptome shotgun sequencing (RNA-seq) in fish treated with picomolar concentrations of the VDR ligand and hormonal form of vitamin D(3), 1α,25-dihydroxyvitamin D(3) [1α,25(OH)(2)D(3))].We observed significant changes in RNAs of transcription factors, leptin, peptide hormones, and RNAs encoding proteins of fatty acid, amino acid, xenobiotic metabolism, receptor-activator of NFκB ligand (RANKL), and calcitonin-like ligand receptor pathways. Early highly restricted, and subsequent massive changes in more than 10% of expressed cellular RNA were observed. At days post fertilization (dpf) 2 [24 h 1α,25(OH)(2)D(3)-treatment], only four RNAs were differentially expressed (hormone vs. vehicle). On dpf 4 (72 h treatment), 77 RNAs; on dpf 6 (120 h treatment) 1039 RNAs; and on dpf 7 (144 h treatment), 2407 RNAs were differentially expressed in response to 1α,25(OH)(2)D(3). Fewer RNAs (n = 481) were altered in dpf 7 larvae treated for 24 h with 1α,25(OH)(2)D(3) vs. those treated with hormone for 144 h. At dpf 7, in 1α,25(OH)(2)D(3)-treated larvae, pharyngeal cartilage was larger and mineralization was greater. Changes in expression of RNAs for transcription factors, peptide hormones, and RNAs encoding proteins integral to fatty acid, amino acid, leptin, calcitonin-like ligand receptor, RANKL, and xenobiotic metabolism pathways, demonstrate heretofore unrecognized mechanisms by which 1α,25(OH)(2)D(3) functions in vivo in developing eukaryotes.

The kidney is essential for the maintenance of normal calcium and phosphorus homeostasis. Calcium and inorganic phosphorus are filtered at the glomerulus, and are reabsorbed from tubular segments by transporters and channels which are regulated by 1α,25-dihydroxyvitamin (1α,25(OH)(2)D) and parathyroid hormone (PTH). The kidney is the major site of the synthesis of 1α,25(OH)(2)D under physiologic conditions, and is one of the sites of 24,25-dihydroxyvitamin D (24,25(OH)(2)D) synthesis. The activity of the 25(OH)D-1α-hydroxylase, the mixed function oxidase responsible for the synthesis of 1α,25(OH)(2)D, is regulated by PTH, 1α,25(OH)(2)D, fibroblast growth factor 23 (FGF23), inorganic phosphorus and other growth factors. Additionally, the vitamin D receptor which binds to, and mediates the activity of 1α,25(OH)(2)D, is widely distributed in the kidney. Thus, the kidney, by regulating multiple transport and synthetic processes is indispensible in the maintenance of mineral homeostasis in physiological states., (Published by Elsevier Inc.)

Recent studies suggest that vitamin D modulates innate immunity and reduces the risk of microbial infections. Little is known about the role of vitamin D in antipneumococcal immunity in individuals with asthma. We determined the correlation between serum 25-hydroxyvitamin D (25[OH]D) levels and pneumococcal antibody levels in individuals with asthma, atopic dermatitis, or allergic rhinitis, and atopic sensitization status. A cross-sectional study was conducted for 21 subjects with asthma and 23 subjects without asthma. Pearson's correlation coefficient between serum 25(OH)D concentrations and the number of positive serotype-specific antibody levels was calculated among individuals with and without asthma, atopic dermatitis, and/or allergic rhinitis and atopic sensitization status. The overall correlation between serum 25(OH)D concentrations and positive pneumococcal antibody levels in all subjects regardless of asthma was not significant (r = -0.14; p = 0.38). Stratified analysis results showed that there was a positive correlation between serum 25(OH)D concentrations and positive pneumococcal antibody levels in asthmatic patients (r = 0.45; p < 0.05) and an inverse correlation was observed in nonasthmatic patients (r = -0.53; p < 0.05). These trends were similar for subjects with and without atopic dermatitis and/or allergic rhinitis (r = 0.58 and p = 0.008 versus r = -0.63 and p = 0.001). Despite similar trends in the correlation between serum 25(OH)D and pneumococcal antibody concentrations among those with and without atopic sensitization status (r = 0.27 and p = 0.19 versus r = -0.41 and p = 0.08), they did not reach statistical significance. The 25(OH)D may enhance humoral immunity against Streptococcus pneumonia in subjects with atopic conditions but not without atopic conditions. Atopic conditions may have an important effect modifier in the relationship between serum 25(OH)D concentrations and immune function.

Phosphorus plays a critical role in diverse biological processes, and, therefore, the regulation of phosphorus balance and homeostasis are critical to the well being of the organism. Changes in environmental, dietary, and serum concentrations of inorganic phosphorus are detected by sensors that elicit changes in cellular function and alter the efficiency by which phosphorus is conserved. Short-term, post-cibal responses that occur independently of hormones previously thought to be important in phosphorus homeostasis may play a larger role than previously appreciated in the regulation of phosphorus homeostasis. Several hormones and regulatory factors such as the vitamin D endocrine system, parathyroid hormone, and the phosphatonins (FGF-23, sFRP-4, MEPE) among others, may play a role only in the long-term regulation of phosphorus homeostasis. In this review, we discuss how organisms sense changes in phosphate concentrations and how changes in hormonal factors result in the conservation or excretion of phosphorus.

Patients with X-linked hypophosphatemia (XLH) and the hyp-mouse, a model of XLH characterized by a deletion in the Phex gene, manifest hypophosphatemia, renal phosphate wasting, and rickets/osteomalacia. Cloning of the PHEX/Phex gene and mutations in affected patients and hyp-mice established that alterations in PHEX/Phex expression underlie XLH. Although PHEX/Phex expression occurs primarily in osteoblast lineage cells, transgenic Phex expression in hyp-mouse osteoblasts fails to rescue the phenotype, suggesting that Phex expression at other sites underlies XLH. To establish whether abnormal Phex in osteoblasts and/or osteocytes alone generates the HYP phenotype, we created mice with a global Phex knockout (Cre-PhexDeltaflox/y mice) and conditional osteocalcin-promoted (OC-promoted) Phex inactivation in osteoblasts and osteocytes (OC-Cre-PhexDeltaflox/y). Serum phosphorus levels in Cre-PhexDeltaflox/y, OC-Cre-PhexDeltaflox/y, and hyp-mice were lower than those in normal mice. Kidney cell membrane phosphate transport in Cre-PhexDeltaflox/y, OC-Cre-PhexDeltaflox/y, and hyp-mice was likewise reduced compared with that in normal mice. Abnormal renal phosphate transport in Cre-PhexDeltaflox/y and OC-Cre-PhexDeltaflox/y mice was associated with increased bone production and serum FGF-23 levels and decreased kidney membrane type IIa sodium phosphate cotransporter protein, as was the case in hyp-mice. In addition, Cre-PhexDeltaflox/y, OC-Cre-PhexDeltaflox/y, and hyp-mice manifested comparable osteomalacia. These data provide evidence that aberrant Phex function in osteoblasts and/or osteocytes alone is sufficient to underlie the hyp-mouse phenotype.

Phosphate homeostasis is preserved during variations in phosphate intake by short-term intrinsic renal and intestinal adaptations in transport processes, and by more long-term hormonal mechanisms, which regulate the efficiency of phosphate transport in the kidney and intestine. Recently, several phosphaturic peptides such as fibroblast growth factor 23 (FGF-23), secreted frizzled-related protein-4 (sFRP-4), extracellular phosphoglycoprotein (MEPE) and fibroblast growth factor 7 (FGF-7) have been shown to play a pathogenic role in several hypophosphatemic disorders such as tumor-induced osteomalacia (TIO), autosomal dominant hypophosphatemic rickets (ADHR), X-linked hypophosphatemic rickets (XLH), the McCune-Albright syndrome (MAS) and fibrous dysplasia (FD). These proteins induce phosphaturia and hypophosphatemia in vivo, and inhibit sodium-dependent renal phosphate transport in cultured renal epithelial cells. Interestingly, despite the induction of hypophosphatemia by FGF-23 and sFRP-4 in vivo, serum 1, 25-dihydroxyvitamin D (1alpha,25(OH)(2)D) concentrations are decreased or remain inappropriately normal, suggesting an inhibitory effect of these proteins on 25-hydroxyvitamin D 1alpha-hydroxylase activity. In FGF-23 knockout mice, 25-hydroxyvitamin D 1alpha-hydroxylase expression is increased and elevated serum 1alpha,25(OH)(2)D levels cause significant hypercalcemia and hyperphosphatemia. MEPE, however, increases circulating 1alpha,25(OH)(2)D. Circulating or local concentrations of these peptides/proteins may regulate 25-hydroxyvitamin D 1alpha-hydroxylase activity in renal tissues under physiologic circumstances.

It has been a little more than 20 years since the first appreciation that the biologically active hormonal form of the secosteroid vitamin D-classically categorized as a regulator of calcium/phosphorous metabolism and bone mineralization-can exert effects on cells of the immune system. Since then a substantial literature has accumulated to suggest that these effects are exerted on multiple immune cell types, are predominantly suppressive at pharmacologic levels, and are potent enough to have true therapeutic potential in the management or prevention of immune-mediated diseases. Less clear at present, however, are the physiological roles played by the vitamin D endocrine system in the regulation of normal and abnormal immune responses. In this review, an appraisal of the current understanding of vitamin D-mediated immune regulation is presented that emphasizes progress towards its clinical application as well as the manner in which emerging models of normal immune function may facilitate a more complete understanding of its physiologic significance.

1alpha,25-Dihydroxyvitamin D(3)(1alpha,25(OH)(2)D(3)), the active metabolite of vitamin D(3), mediates anti-proliferative effects in cells by regulating the expression of 1alpha,25(OH)(2)D(3)-responsive genes. The expression of the proliferation-promoting Immediate Early gene X-1 (IEX-1) is reduced by 1alpha,25(OH)(2)D(3) through unknown mechanisms. Here we report the presence of a novel inhibitory hexameric repeat DNA response element in the promoter of the human IEX-1 gene that mediates 1alpha,25(OH)(2)D(3)-associated IEX-1 gene repression. To localize a vitamin D sensitive DNA response element we transfected the keratinocyte-like cell line, HaCaT, (referred as HaCaT) with a series of plasmids containing full-length and truncated IEX-1 promoter elements fused to the luciferase reporter gene in the absence or presence of 1alpha,25(OH)(2)D(3), and we performed electrophoretic gel mobility assays in the presence of receptors for 1alpha,25(OH)(2)D(3) (vitamin D receptor, VDR) and 9-cis-retinoic acid (RXRalpha). We mapped a negative response element between nt -405 and -391(15 bp) of theIEX-1 promoter (5'-TGAACC AGG GAGTCA-3') that mediates transcriptional inhibition in response to 1alpha,25(OH)(2)D(3) and which requires expression of both nuclear receptors for 1alpha,25(OH)(2)D(3) and 9-cis-retinoic acid. Our data indicate that the physiological repression of IEX-1 gene expression by 1alpha,25(OH)(2)D(3) is directly mediated by nuclear VDR/RXRalpha heterodimers through a specific transcriptional element.

Previous studies have suggested that kidney donors may have abnormalities of mineral and bone metabolism typically seen in chronic kidney disease. This may have important implications for the skeletal health of living kidney donors and for our understanding of the pathogenesis of long-term mineral and bone disorders in chronic kidney disease. In this prospective study, 182 of 203 kidney donors and 173 of 201 paired normal controls had markers of mineral and bone metabolism measured before and at 6 and 36 months after donation (ALTOLD Study). Donors had significantly higher serum concentrations of intact parathyroid hormone (24.6% and 19.5%) and fibroblast growth factor-23 (9.5% and 8.4%) at 6 and 36 months, respectively, as compared to healthy controls, and significantly reduced tubular phosphate reabsorption (-7.0% and -5.0%) and serum phosphate concentrations (-6.4% and -2.3%). Serum 1,25-dihydroxyvitamin D3 concentrations were significantly lower (-17.1% and -12.6%), while 25-hydroxyvitamin D (21.4% and 19.4%) concentrations were significantly higher in donors compared to controls. Moreover, significantly higher concentrations of the bone resorption markers, carboxyterminal cross-linking telopeptide of bone collagen (30.1% and 13.8%) and aminoterminal cross-linking telopeptide of bone collagen (14.2% and 13.0%), and the bone formation markers, osteocalcin (26.3% and 2.7%) and procollagen type I N-terminal propeptide (24.3% and 8.9%), were observed in donors. Thus, kidney donation alters serum markers of bone metabolism that could reflect impaired bone health. Additional long-term studies that include assessment of skeletal architecture and integrity are warranted in kidney donors.

Background: Hyperphosphatemia confers adverse cardiovascular outcomes, and commonly occurs in late-stage CKD. Fibroblast growth factor 7 (FGF7) is a phosphaturic peptide which decreases renal phosphate transport in vitro and in vivo. Serum FGF7 concentrations are reduced in hyperphosphatemic patients with hypophosphatasia and are elevated in some hypophosphatemic patients with tumor-induced osteomalacia. No data, however, are available on whether circulating FGF7 concentrations increase to compensate for phosphate retention in CKD patients.Methods: This was a cross-sectional study performed among 85 adult patients with varying estimated glomerular filtration rates (eGFR). We measured serum intact FGF7 (iFGF7) concentration using an iFGF7 immunoassay and determined its associated factors. Relationships between eGFR and mineral metabolism biomarkers [phosphate, iFGF7, iFGF23, parathyroid hormone (PTH), and 1,25-dihydroxyvitamin D (1,25(OH)2D)] were explored.Results: For eGFRs of ≥ 60 (n = 31), 45-59 (n = 16), 30-44 (n = 11), 15-29 (n = 15), and < 15 mL/min/1.73 m2 (n = 12), median (IQ25-75) iFGF7 concentrations were 46.1 (39.2-56.9), 43.1 (39.0-51.5), 47.3 (38.3-66.5), 47.7 (37.7-55.8), and 49.6 (42.5-65.6) pg/mL, respectively (P = 0.62). Significant increases in serum iFGF23, PTH, and phosphate were observed at eGFRs of < 33 (95 % CI, 26.40-40.05), < 29 (95 % CI, 22.51-35.36), and < 22 mL/min/1.73 m2 (95 % CI, 19.25-25.51), respectively, while significant decreases in serum 1,25(OH)2D were observed at an eGFR of < 52 mL/min/1.73 m2 (95 % CI, 42.57-61.43). No significant correlation was found between serum iFGF7 and phosphate, iFGF23, PTH or 1,25(OH)2D. In multivariable analyses, body mass index (per 5 kg/m2 increase) was independently associated with the highest quartile of serum iFGF7 concentration (OR, 1.20; 95 % CI, 1.12-1.55).Conclusions: Compensatory decreases in circulating 1,25(OH)2D and increases in circulating iFGF23 and PTH, but not iFGF7, facilitate normalization of serum phosphate concentration in early stages of CKD. Whether other circulating phosphaturic peptides change in response to phosphate retention in CKD patients deserves further study. [ABSTRACT FROM AUTHOR]

Background: Elevated serum 1,25-dihydroxyvitamin D (1,25(OH)2D) concentrations have been reported among cohorts of recurrent calcium (Ca) kidney stone-formers and implicated in the pathogenesis of hypercalciuria. Variations in Ca and vitamin D metabolism, and excretion of urinary solutes among first-time male and female Ca stone-formers in the community, however, have not been defined. Methods: In a 4-year community-based study we measured serum Ca, phosphorus (P), 25-hydroxyvitamin D (25(OH)D), 1,25(OH)2D, 24,25-dihydroxyvitamin D (24,25(OH)2D), parathyroid hormone (PTH), and fibroblast growth factor-23 (FGF-23) concentrations in first-time Ca stone-formers and age- and gender frequency-matched controls. Results: Serum Ca and 1,25(OH)2D were increased in Ca stone-formers compared to controls (P = 0.01 and P = 0.001). Stone-formers had a lower serum 24,25(OH)2D/25(OH)D ratio compared to controls (P = 0.008). Serum PTH and FGF-23 concentrations were similar in the groups. Urine Ca excretion was similar in the two groups (P = 0.82). In controls, positive associations between serum 25(OH)D and 24,25(OH)2D, FGF-23 and fractional phosphate excretion, and negative associations between serum Ca and PTH, and FGF-23 and 1,25(OH)2D were observed. In SF associations between FGF-23 and fractional phosphate excretion, and FGF-23 and 1,25(OH)2D, were not observed. 1,25(OH)2D concentrations associated more weakly with FGF-23 in SF compared with C (P <0.05). Conclusions: Quantitative differences in serum Ca and 1,25(OH)2D and reductions in 24-hydroxylation of vitamin D metabolites are present in first-time SF and might contribute to first-time stone risk. [ABSTRACT FROM AUTHOR]

An association between low serum vitamin D levels and poorer melanoma survival has been reported. We have studied inheritance of a polymorphism of the GC gene, rs2282679, coding for the vitamin D-binding protein, which is associated with lower serum levels of vitamin D, in a meta-analysis of 3137 melanoma patients. The aim was to investigate evidence for a causal relationship between vitamin D and outcome ( Mendelian randomization). The variant was not associated with reduced overall survival (OS) in the UK cohort, per-allele hazard ratio ( HR) for death 1.23 (95% confidence interval (CI) 0.93, 1.64). In the smaller cohorts, HR in OS analysis was 1.07 (95% CI 0.88, 1.3) and for all cohorts combined, HR for OS was 1.09 (95% CI 0.93, 1.29). There was evidence of increased melanoma-specific deaths in the seven cohorts for which these data were available. The lack of unequivocal findings despite the large sample size illustrates the difficulties of implementing Mendelian randomization. [ABSTRACT FROM AUTHOR]

Two new clinical trials highlight refinements in the use of vitamin D and its analogs in the treatment of secondary hyperparathyroidism in end-stage renal disease (ESRD), and the treatment of proteinuria in diabetics. In patients with ESRD, alfacalcidol is as effective as paricalcitol in suppressing parathyroid hormone; the occurrence of hypercalcemia and hyperphosphatemia is infrequent and similar with the two analogs. Oral cholecalciferol reduces albuminuria and urinary transforming growth factor-β1 in patients with type 2 diabetes mellitus and proteinuria. [ABSTRACT FROM AUTHOR]

Phosphate ions are critical for normal bone mineralization, and phosphate plays a vital role in a number of other biological processes such as signal transduction, nucleotide metabolism, and enzyme regulation. The study of rare disorders associated with renal phosphate wasting has resulted in the discovery of a number of proteins [fibroblast growth factor 23 (FGF-23), secreted frizzled related protein 4 (sFRP-4), matrix extracellular phosphoglycoprotein, and FGF 7 (FGF-7)] that decrease renal sodium- dependent phosphate transport in vivo and in vitro. The "phosphatonins," FGF-23 and sFRP-4, also inhibit the synthesis of 1α,25-dihydroxyvitamin D, leading to decreased intestinal phosphate absorption and further reduction in phosphate retention by the organism. In this review, we discuss the biological properties of these proteins, alterations in their concentrations in various clinical disorders, and their possible physiological role. [ABSTRACT FROM AUTHOR]

The NF-κB component ReIB is essential for dendritic cell (DC) differentiation and maturation. The vitamin D receptor (VDR) is a nuclear receptor that mediates inhibition of DC maturation and transcriptional repression of ReIB after engagement of its ligand, 1α,25-dihydroxyvitamin D3, or related analogs (D3 analogs). Ligand-dependent ReIB suppression was abolished by a histone deacetylase (HDAC) inhibitor. Constitutive association of VDR with the ReIB promoter was demonstrated in DCs by chromatin immunoprecipitation. Promoter binding by VDR was enhanced by ligand and reduced by LPS. Association of HDAC3 and HDAC1 with the ReIB VDR-binding site was observed, but only HDAC3 was reciprocally modulated by D3 analog and LPS. Overexpression of HDAC3 caused ReIB promoter suppression, increased sensitivity to D3 analog, and resistance to LPS. Depletion of HDAC3 attenuated ReIB suppression by D3 analog. In vivo, D3 analog resulted in reduced ReIB in DCs from VDR WT mice but not VDR knockout mice. Other NF-κB family members were unaffected. In viva ReIB suppression was prevented by concomitant administration of HDAC inhibitor, which also resulted in up-regulation of ReIB and c-Rel in control animals. We conclude that vitamin D-regulated reIB transcription in DCs is controlled by chromatin remodeling by means of recruitment of complexes including HDAC3. [ABSTRACT FROM AUTHOR]

1α,25-Dihydroxyvitamin D[sub 3] , the hormonal form of vitamin D[sub 3] , is widely appreciated to play a central role in calcium and phosphorous homeostasis. It is becoming increasingly clear, however, that the sterol also plays an important role in the regulation of cellular growth, central nervous system function, and immune responsiveness. In this review, I will highlight some of the mechanisms by which 1α,25-dihydroxyvitamin D[sub 3] regulates cellular growth, alters central nervous system function, and immune function.Copyright © 2002 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Investigates the localization of the calcitriol receptor (VDR) and the 25-hydroxyvitamin D3 (25(OH)D3) 24-hydroxylase cytochrome P-450 in the human kidney. Production of polyclonal antibodies against VDR and 25(OH)D3 24-hydroxylase; Enzyme-linked immunosorbent assay of polyclonal antibodies; Immunohistochemistry; Relationship of calbindin D28k to VDR.

Editorial. Describes the metabolism of dihydroxyvitamin D[sub3] in humans and experimental animals. Chemical processes which account for the metabolism of dihydroxyvitamin D[sub3]; Excretion of dihydroxyvitamin D[sub3] metabolites; Factors involved in the genesis of calcium malabsorption and bone disorders in cholestatic liver disease.

Abstract: The immunological effects of vitamin D receptor (VDR) ligands include inhibition of dendritic cell (DC) maturation, suppression of T-helper type 1 (Th1) T-cell responses and facilitation of antigen-specific immune tolerance in vivo. While studying the molecular profile of DCs cultured in the presence of 1α,25(OH)D3 or synthetic D3 analogs we observed that expression of the NF-κB family member RelB, which plays an essential role in DC differentiation and maturation, is selectively suppressed by VDR ligands. Further in vitro and in vivo studies of VDR-mediated RelB suppression indicated that the mechanism for this effect involves direct binding of VDR/RXRα to a defined region of the relB promoter and assembly of a negative regulatory complex containing HDAC3, HDAC1, SMRT and, most likely, other factors. Interestingly, promoter engagement by VDR and HDAC3, but not the other identified components, is enhanced by addition of a VDR ligand and inhibited by a pro-maturational stimulus (LPS) that results in RelB upregulation. Promoter assays in a panel of cell lines suggest that the VDR ligand-dependent component of relB suppression may occur selectively in antigen presenting cells. Cell type-specific, ligand-enhanced negative transcriptional regulation represents a potentially novel paradigm for VDR-controlled genes. In this report we review the experimental data to support such a mechanism for relB regulation in DCs and present a model for the process. [Copyright &y& Elsevier]

Inhibition of dendritic cell (DC) maturity is an important immunomodulatory effect of 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) and related analogs (D3 analogs). The mechanisms underlying 1α,25(OH)2D3-mediated DC modulation are Vitamin D receptor (VDR)-dependent and likely involve direct or indirect regulation of multiple genes. Gene expression profiles of bone marrow-derived DCs (BMDCs) generated in the absence or presence of a potent D3 analog were analyzed using microarray technology. Results for D3 analog-conditioned DCs were also compared with glucocorticoid-conditioned BMDCs and with BMDCs conditioned with D3 analog and glucocorticoid combined. Of ∼12,000 gene products assayed, 52% were considered to have detectable expression in unconditioned BMDCs. Based on relative expression levels, 5.3% of these expressed genes were “silenced” or “suppressed” in D3 analog-conditioned BMDCs and 2.1% were “augmented”. In addition, 1.7% of gene products undetectable in control BMDCs were “induced” by D3 analog. Functional grouping of modulated genes demonstrated important effects of D3 analog on immunoreceptors, on chemokines and chemokine receptors, on growth factors/cytokines and related receptors, and on neuroendocrine hormones and related receptors. Many of these gene products were unaffected or differently regulated by glucocorticoid suggesting specific VDR-mediated regulatory effects. Confirmation of microarray analysis results for two differentially regulated chemokines (MIP-1α and RANTES) was obtained by RT-PCR and ELISA. The methodology provides novel insights into DC gene regulation by 1α,25(OH)2D3 agonists. [Copyright &y& Elsevier]

OBJECTIVE: To determine whether fibroblast growth factor 23 (FGF23) contributes to the hypophosphatemia of primary hyperparathyroidism. PATIENTS AND METHODS: Thirteen adult patients with primary hyperparathyroidism had serum collected before and after parathyroidectomy for analysis of inorganic phosphorus, calcium, 1α,25-dihydroxyvitamin D (1α,25[OH]2D), parathyroid hormone (PTH), FGF23, creatinine, and bone-specific alkaline phosphatase (BSAP). Patients were recruited between July 24, 2003, and February 11, 2004. RESULTS: Before surgery, patients had elevated serum calcium and PTH concentrations. Serum phosphorus concentration were in the low-normal range. The FGF23 concentrations were not elevated in patients with primary hyperparathyroidism compared with healthy controls. Within 24 hours of surgery, serum calcium, PTH, 1α,25(OH)2D, and BSAP concentrations were lower (P<.002 for all) and phosphorous concentrations were higher (P=.003) than in the preoperative state. The FGF23 concentrations were similar 1 day and 6 weeks after surgery. The FGF23 concentrations did not correlate with serum phosphorus, calcium PTH, 1α,25(OH)2D, creatinine, or BSAP concentrations in the preoperative or postoperative state. CONCLUSION: Parathyroid hormone is the major regulator of serum phosphorus concentrations in patients with primary hyperparathyroidism. Fibroblast growth factor 23 does not appear to play a role in phosphorus homeostatis in patients with surgically treated primary hyperparathyroidism. [ABSTRACT FROM AUTHOR]

The nuclear factor-κB (NF-κB) protein RelB plays a unique role in dendritic cell (DC) function and, as such, is an important regulator of antigen presentation and immune regulation. In this study, inhibition of RelB expression in DCs exposed to an analog of the active form of vitamin D[sub 3] (1α,25-dihydroxyvitamin D[sub 3] (1α,25(OH)[sub 2]D[sub 3])) was observed and shown to be mediated by the vitamin D receptor (VDR). Potential vitamin D response elements were identified within promoter regions of human and mouse relB genes. In gel shift experiments, these motifs specifically bound VDR. retinoid X receptor-α complexes. Reporter assays confirmed that transcriptional activity of human and mouse relB promoters was inhibited by 1α,25-(OH)[sub 2]D[sub 3] agonists in a DC derived cell line. The inhibition was abolished by mutagenesis of the putative vitamin D response elements and was enhanced by overexpression of VDR. Mutagenesis of NF-κB response elements within the relB promoter did not affect the magnitude of 1α,25-(OH)[sub 2]D[sub 3] analog-mediated inhibition, ruling out an indirect effect on NF-κB signaling. Glucocorticoid caused additional inhibition of relB promoter activity when combined with the 1α,25-(OH)[sub 2]D[sub 3] analog. This effect was dependent on the integrity of the NF-κB response elements, suggesting separate regulatory mechanisms for the two steroid pathways on this promoter. We conclude that relB is a direct target for 1α,25-(OH)[sub 2]D[sub 3]-mediated negative transcriptional regulation via binding of VDR·retinoid X receptor-α to discrete DNA motifs. This mechanism has important implications for the inhibitory effect of 1α,25-(OH)[sub 2]D[sub 3] on DC maturation and for the potential immunotherapeutic use of 1α,25-(OH)[sub 2]D[sub 3] analogs alone or combined with other agents. [ABSTRACT FROM AUTHOR]

Dendritic cell (DC) maturation plays a central role in regulating immunity. We show that glucocorticoid and 1α,25(OH)2D3 agonists modulate DCs via distinct and additive signaling pathways. Phenotypic and functional indices were examined in DCs treated with dexamethasone (DEX) and/or a 1α,25(OH)2D3 analog (D3 analog). DEX potently attenuated pro-inflammatory cytokines and chemokines but had modest, reversible effects on T-cell stimulatory capacity. D3 analog produced significantly greater inhibition of T-cell stimulation in vitro and in vivo and, unlike DEX, increased expression of the chemokines MCP-1 and MIP-1α. Both DEX and D3 analog were associated with reduced expression of the NF-κB proteins c-Rel and Rel B but not Rel A. Combined DEX and D3 analog treatment of DCs resulted in significant additive inhibition of pro-inflammatory cytokines, T-cell stimulation, chemokines, chemokine receptors, and NF-κB components. Additive inhibition was most striking for RANTES, CCR5, CCR7, and Rel B. The combined effects of the two hormonal pathways on DCs have unique immunomodulatory potential. [Copyright &y& Elsevier]