Predominant role of 25OHD in the negative regulation of PTH expression: Clinical relevance for hypovitaminosis D

Vitamin D and the Kidney: Two Players, One Console

Vitamin D belongs to the group of liposoluble steroids mainly involved in bone metabolism by modulating calcium and phosphorus absorption or reabsorption at various levels, as well as parathyroid hormone production. Recent evidence has shown the extra-bone effects of vitamin D, including glucose homeostasis, cardiovascular protection, and anti-inflammatory and antiproliferative effects. This narrative review provides an overall view of vitamin D’s role in different settings, with a special focus on chronic kidney disease and kidney transplant.

A rare combination of tumor-induced osteomalacia caused by sinonasal glomangiopericytoma and coexisting parathyroid adenoma: case report and literature review

BACKGROUND

Tumor-induced osteomalacia (TIO) is a rare, acquired disease of renal phosphate wasting and disturbed vitamin D homeostasis as a result of the action of a phosphaturic protein - FGF-23, produced by a neoplasm. Although the clinical and biochemical profile of the syndrome is characteristic, it remains underreported and unrecognized by clinicians. Hyperparathyroidism is rarely associated with oncogenic osteomalacia, but it should be considered because of potentially life-threatening hypophosphatemia caused by both conditions.

CASE PRESENTATION

We report a case of a 42-year-old woman admitted to the Department of Otolaryngology of the Military Institute of Medicine in Warsaw for the endoscopic resection of hormonally active glomangiopericytoma extending into the anterior skull base. She presented with a 5-year history of musculoskeletal pain and progressive weakness of the extremities which finally led her to become bedridden. After the excision of the tumor her symptoms and laboratory results gradually improved except increasing PTH serum levels. Further examination revealed a parathyroid proliferative tumor, which was surgically removed. The patient walked without aids at follow-up 16 months after the surgery.

CONCLUSIONS

This case is unusual because of tumor-induced osteomalacia and parathyroid adenoma occurring concomitantly. Further investigations of FGF-23 and PTH interplay should be conducted to elucidate the pathogenesis of hyperparathyroidism and tumorigenesis in some cases of TIO. By presenting this case, we wanted to remind clinicians of a rare and misdiagnosed paraneoplastic syndrome and highlight the importance of monitoring PTH concentrations during the follow-up of patients with TIO.

Lack of secondary hyperparathyroidism in sub-group of vitamin D deficient postmenopausal women: Is VDR gene polymorphism behind this mystery?

BACKGROUND AND AIMS

We aimed to determine the cause of non-secondary hyperparathyroidism (Non-SHPT) in Indian postmenopausal women.

MATERIALS & METHODS

334 apparently healthy postmenopausal women were assessed for bone mineral homeostaisis including Vitamin D, PTH and VDR polymorphism.

RESULTS

83% of the subjects had vitamin D deficiency further associated with VDR gene polymorphism (P 0.000). A sizable number of subjects (N = 83) did evoke SHPT despite low vitamin D levels. We observe that VDR gene polymorphism was strongly associated in the sub-group of non-SHPT.

CONCLUSION

lack of SHPT warrants researchers to study the pathophysiology of non-SHPT in detail to substantiate our findings.

Calcium-Sensing Receptors Control CYP27B1-Luciferase Expression: Transcriptional and Posttranscriptional Mechanisms

25-hydroxyvitamin D 1α-hydroxylase (encoded by CYP27B1), which catalyzes the synthesis of 1,25-dihydroxyvitamin D₃, is subject to negative or positive modulation by extracellular Ca²⁺ (Ca²⁺_o) depending on the tissue. However, the Ca²⁺ sensors and underlying mechanisms are unidentified. We tested whether calcium-sensing receptors (CaSRs) mediate Ca²⁺_o-dependent control of 1α-hydroxylase using HEK-293 cells stably expressing the CaSR (HEK-CaSR cells). In HEK-CaSR cells, but not control HEK-293 cells, cotransfected with reporter genes for CYP27B1-Photinus pyralis (firefly) luciferase and control Renilla luciferase, an increase in Ca²⁺_o from 0.5mM to 3.0mM induced a 2- to 3-fold increase in firefly luciferase activity as well as mRNA and protein levels. Surprisingly, firefly luciferase was specifically suppressed at Ca²⁺_o ≥ 5.0mM, demonstrating biphasic Ca²⁺_o control. Both phases were mediated by CaSRs as revealed by positive and negative modulators. However, Ca²⁺_o induced simple monotonic increases in firefly luciferase and endogenous CYP27B1 mRNA levels, indicating that the inhibitory effect of high Ca²⁺_o was posttranscriptional. Studies with inhibitors and the CaSR C-terminal mutant T888A identified roles for protein kinase C (PKC), phosphorylation of T888, and extracellular regulated protein kinase (ERK)_1/2 in high Ca²⁺_o-dependent suppression of firefly luciferase. Blockade of both PKC and ERK_1/2 abolished Ca²⁺_o-stimulated firefly luciferase, demonstrating that either PKC or ERK_1/2 is sufficient to stimulate the CYP27B1 promoter. A key CCAAT box (−74 bp to −68 bp), which is regulated downstream of PKC and ERK_1/2, was required for both basal transcription and Ca²⁺_o-mediated transcriptional upregulation. The CaSR mediates Ca²⁺_o-dependent transcriptional upregulation of 1α-hydroxylase and an additional CaSR-mediated mechanism is identified by which Ca²⁺_o can promote luciferase and possibly 1α-hydroxylase breakdown.

Tissue-engineered parathyroid gland and its regulatory secretion of parathyroid hormone

Parathyroid glands (PTGs) are important endocrine organs being mainly responsible for the secretion of parathyroid hormone (PTH) to regulate the balance of calcium (Ca) /phosphorus (P) ions in the body. Once PTGs get injured or removed, their resulting defect or loss of PTH secretion should disturb the level of Ca/P in blood, thus damaging other related organs (bone, kidney, etc.) and even causing death. Recently, tissue-engineered PTGs (TE-PTGs) have attracted lots of attention as a potential treatment for the related diseases of PTGs caused by hypoparathyroidism and hyperparathyroidism, including tetany, muscle cramp, nephrolithiasis, nephrocalcinosis, and osteoporosis. Although great progress has been made in the establishment of TE-PTGs with an effective strategy to integrate the key factors of cells and biomaterials, its regulatory secretion of PTH to mimic its natural rhythms in the body remains a huge challenge. This review comprehensively describes an overview of PTGs from physiology and pathology to cytobiology and tissue engineering. The state of the arts in TE-PTGs and the feasible strategies to regulate PTH secretion behaviors are highlighted to provide an important foundation for further investigation.

Significance of urinary C-megalin excretion in vitamin D metabolism in pre-dialysis CKD patients

Serum 1,25(OH)₂D and 24,25(OH)₂D are decreased in CKD. Megalin in proximal tubular epithelial cells reabsorbs glomerular-filtered 25(OH)D-DBP complex to convert 25(OH)D to 1,25(OH)₂D and 24,25(OH)₂D. Urinary C-megalin excretion is increased via exocytosis from injured nephrons overloaded with megalin-mediated protein metabolism. This study investigated the significance of urinary C-megalin excretion in vitamin D metabolism in 153 pre-dialysis CKD patients. Urinary C-megalin was positively associated with urinary protein, β₂MG and α₁MG, and exhibited negative correlations with serum 25(OH)D, 1,25(OH)₂D and 24,25(OH)₂D. Multiple regression analysis showed that urinary C-megalin had a significantly negative association with 25(OH)D. Serum 1,25(OH)₂D and 24,25(OH)₂D, as well as 1,25(OH)₂D/25(OH)D and 24,25(OH)₂D/25(OH)D ratios, showed positive correlations with eGFR. Additionally, wholePTH was positively associated with 1,25(OH)₂D/25(OH)D and 1,25(OH)₂D/24,25(OH)₂D, while FGF23 was positively associated with 24,25(OH)₂D/25(OH)D and negatively with 1,25(OH)₂D/24,25(OH)₂D. Urinary C-megalin emerged as an independent factor positively associated with 1,25(OH)₂D/25(OH)D and 1,25(OH)₂D/24,25(OH)₂D. Although 1,25(OH)₂D and 24,25(OH)₂D are decreased in CKD patient serum, our findings suggest that PTH and FGF23 retain their effects to regulate vitamin D metabolism even in the kidneys of these patients, while production of 1,25(OH)₂D and 24,25(OH)₂D from 25(OH)D is restricted due to either impairment of megalin-mediated reabsorption of the 25(OH)D-DBP complex or reduced renal mass.

The Emerging Role of Nutritional Vitamin D in Secondary Hyperparathyroidism in CKD

In chronic kidney disease (CKD), hyperphosphatemia induces fibroblast growth factor-23 (FGF-23) expression that disturbs renal 1,25-dihydroxy vitamin D (1,25D) synthesis; thereby increasing parathyroid hormone (PTH) production. FGF-23 acts on the parathyroid gland (PTG) to increase 1α-hydroxylase activity and results in increase intra-gland 1,25D production that attenuates PTH secretion efficiently if sufficient 25D are available. Interesting, calcimimetics can further increase PTG 1α-hydroxylase activity that emphasizes the demand for nutritional vitamin D (NVD) under high PTH status. In addition, the changes in hydroxylase enzyme activity highlight the greater parathyroid 25-hydroxyvitmain D (25D) requirement in secondary hyperparathyroidism (SHPT); the higher proportion of oxyphil cells as hyperplastic parathyroid progression; lower cytosolic vitamin D binding protein (DBP) content in the oxyphil cell; and calcitriol promote vitamin D degradation are all possible reasons supports nutritional vitamin D (NVD; e.g., Cholecalciferol) supplement is crucial in SHPT. Clinically, NVD can effectively restore serum 25D concentration and prevent the further increase in PTH level. Therefore, NVD might have the benefit of alleviating the development of SHPT in early CKD and further lowering PTH in moderate to severe SHPT in dialysis patients.

High-dose vitamin D supplementation is associated with an improvement in several cardio-metabolic risk factors in adolescent girls: a nine-week follow-up study

Background Vitamin D deficiency is a prevalent and important global health problem. Because of its role in growth and development, vitamin D status is likely to be particularly important in adolescent girls. Here, we explored the effects of high-dose vitamin D supplementation on cardio-metabolic risk factors. Methods We have examined the effects of vitamin D supplementation on cardio-metabolic risk factors in 988 healthy adolescent girls in Iran. Fasting blood samples and anthropometric measurements were obtained at baseline and after supplementation with high-dose vitamin D. All individuals took a capsule of 50,000 IU vitamin D/week for nine weeks. The study was completed by 940 participants. Results The prevalence of vitamin D deficiency was 90% at baseline, reducing to 16.3% after vitamin D supplementation. Vitamin supplementation was associated with a significant increase in serum concentrations of 25 (OH) vitamin D and calcium. There were significant reductions in diastolic blood pressure, heart rate, waist circumference and serum fasting blood glucose, total- and low-density lipoprotein-cholesterol after the nine-week period on vitamin D treatment, but no significant effects were observed on body mass index, systolic blood pressure or serum high-density lipoprotein cholesterol and triglyceride. Conclusion Vitamin D supplementation had beneficial effects on cardio-metabolic profile in adolescent girls.

Longitudinal Assessment of PTH in Community-Dwelling Older Women-Elevations Are Not Associated With Mortality

Context:

In older women, the magnitude of elevated parathyroid hormone (PTH) and its consequence is unclear.

Objective:

To describe normal PTH profiles over time and the association with mortality.

Design and Participants:

There were 1044 community-dwelling women in the Malmö Osteoporosis Prospective Risk Assessment cohort (OPRA) who attended baseline (age 75 years). Follow-ups were attended by 715 (age 80 years) and 382 (age 85 years).

Main Outcome Measures:

PTH, estimated glomerular filtration rate (eGFR), 25-hydroxyvitamin D (25OHD) and mortality.

Results:

At age 75 years, PTH levels for most (n = 877, 88%) were within the normal reference range (NRR) (i.e., <6.9 pmol/L). Longitudinally, between ages 75 and 80 years, PTH increased in 60% of all women (n = 390) but increases of up to 50% above baseline values (64%; n=250) still resulted in PTH levels within the NRR. These women had lower 25OHD levels (74 vs 83 nmol/L, P = 0.001). Only when increases were >50% was PTH elevated beyond the NRR (mean 7.1 ± 3.3). Here, a pronounced decline in eGFR (56 vs 61 mL/min/1.73 m², P = 0.002) was found, despite no further changes in 25OHD. Extending the observational period until age 85 years gave similar results. Baseline PTH levels above NRR were associated with mortality (hazard ratio, 1.4; 95% confidence interval (CI), 1.1-1.8; P = 0.007), although not after adjustment for covariates (P = 0.082).

Conclusions:

Most women remained within normal PTH ranges despite large increases of up to 50%. PTH elevated above normal is not independently associated with mortality; impaired kidney function and low 25OHD status may be more prognostic in the very old.

Effect of vitamin E supplementation or alfalfa grazing on fatty acid composition and expression of genes related to lipid metabolism in lambs

The aim of this study was to investigate the effects of vitamin E (VE) supplementation and alfalfa grazing during fattening on fatty acid composition and mRNA expression of genes related to lipid metabolism in the LM of Rasa Aragonesa light lambs. After weaning, 48 lambs were kept indoors and fed a commercial concentrate and a VE supplemented concentrate (480 mg DL-α-tocopheryl acetate/kg DM) for 0 (control [CON]), 10 (VE10d), 20 (VE20d), and 30 d (VE30d) before slaughtering at 22 to 24 kg. Simultaneously, 8 unweaned lambs grazed in alfalfa (154 mg α-tocopherol/kg DM) paddocks with their dams and supplemented with the commercial concentrate (ALF). Immediately after slaughter, LM was sampled to determine gene expression. After 24 h of cooling at 4°C, LM was extracted to determine intramuscular fat (IMF) content and fatty acid composition. The IMF content did not differ with the dietary treatment ( = 0.212). Unweaned grazing alfalfa lambs had greater concentration of rumenic acid (C18:2 c9,t11; P < 0.001) and lower oleic acid (C18:1 c9; = 0.001) content and PUFA n-6:n-3 ratio (P < 0.001) but similar expression of genes implicated in lipid metabolism compared to the concentrate-fed lambs. Vitamin E supplementation did not modify muscle fatty acid composition; however, it increased the expression of FADS2 and ELOVL6, which are involved in desaturation of long-chain fatty acid and the elongation of SFA and MUFA. The results showed that a short period of VE supplementation, especially 10 (VE10d) and 20 d (VE20d), modified gene expression. Overall, the results showed that VE may be acting as a regulatory factor for transcriptional control of genes related to lipid metabolism in the muscle of Rasa Aragonesa light lambs (22-24 kg live weight and younger than 90 d old).

PTH and Vitamin D

PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.

Hepatocellular carcinoma cells express 25(OH)D-1α-hydroxylase and are able to convert 25(OH)D to 1α,25(OH)₂D, leading to the 25(OH)D-induced growth inhibition

Hepatocellular carcinoma (HCC) is the most diagnosed liver cancer without effective treatments available for advanced HCC. Vitamin D is getting popular due to its anti-cancer characteristics. However, the clinical application of 1α,25(OH)2D, the active form of vitamin, is hampered by its hypercalcemia side effect. 1α,25(OH)2D is converted from 25(OH)D, the index of serum vitamin D status, by CYP27B1, which is originally found in kidneys but recently detected in non-renal tissues. 25(OH)D has been shown to repress some cancers expressing CYP27B1 due to the local conversion of 25(OH)D to 1α,25(OH)2D, which works in a intra-, auto-, or paracrine manner and thus minimizes the risk of hypercalcemia. In this study, we found CYP27B1 expression in human hepatocyte, HCC, and HepG2 cells. As we treated HepG2 cells with 25(OH)D, the 1α,25(OH)2D target gene CYP24A1 expression was increased and was further upregulated as CYP27B1 transfection or downregulated as CYP27B1 knockdown. Other 1α,25(OH)2D target genes in HepG2 cells, p21 and p27 were also stimulated by 25(OH)D after CYP27B1 transfection. Further, 25(OH)D could inhibit HepG2 cells growth, which was potentiated by CYP27B1 transfection. Collectively, we showed for the first time that HCC expressed CYP27B1 and was able to covert 25(OH)D to 1α,25(OH)2D in vitro, thus responsive to 25(OH)D treatment. Our data justifies the application of 25(OH)D and CYP27B1 gene transfection therapy in further HCC treatment studies.

Effect of finishing period length with α-tocopherol supplementation on the expression of vitamin E-related genes in the muscle and subcutaneous fat of light lambs

The aim of this study was to investigate how different finishing period lengths with α-tocopherol supplementation or alfalfa grazing affect mRNA expression levels of genes related to vitamin E metabolism in L. thoracis (LT) muscle and subcutaneous fat (SF) from lambs of the Rasa Aragonesa breed. Indoors, concentrate-fed light lambs (n=48) were supplemented with 500 dl-α-tocopheryl acetate/kg concentrate for an average finishing period length of 0 (C), 10.7 (VE10d), 21.2 (VE20d) and, 32.3 (VE30d) days before slaughtering. Simultaneously, 8 lambs with their dams were alfalfa-grazed. The α-tocopherol affected in a short-term the expression of genes in LT muscle (ABCA1, LPL, APOE, and SREBP1) and SF (ABCA1, SCARB1, LPL, and PPARG). On the contrary, PPARA gene expression showed a long-term α-tocopherol effect because the highest levels of PPARA mRNA were found in the VE30d.

PTH-C1: a rat continuous cell line expressing the parathyroid phenotype

The lack of a continuous cell line of epithelial parathyroid cells able to produce parathyroid hormone (PTH) has hampered the studies on in vitro evaluation of the mechanisms involved in the control of parathyroid cell function and proliferation. The PT-r cell line was first established from rat parathyroid tissue in 1987, but these cells were known to express the parathyroid hormone-related peptide (Pthrp) gene, but not the Pth gene. In an attempt to subclone the PT-r cell line, a rat parathyroid cell strain was isolated and named PTH-C1. During 3 years, in culture, PTH-C1 cells maintained an epithelioid morphology, displaying a diploid chromosome number, a doubling time around 15 h during the exponential phase of growth, and parathyroid functional features. PTH-C1 cell line produces PTH and expresses the calcium sensing receptor (Casr) gene and other genes known to be involved in parathyroid function. Most importantly, the PTH-C1 cells also exhibit an in vitro secretory response to calcium. Altogether these findings indicate the uniqueness of the PTH-C1 cell line as an in vitro model for cellular and molecular studies on parathyroid physiopathology.

Vitamin D status and outcomes after renal transplantation

Kidney transplant recipients usually have low vitamin D levels, especially in the early posttransplantation period, but the association between vitamin D status with renal outcomes is not well described in this population. Here, we studied a prospective cohort of 634 kidney recipients who underwent transplantation at a single institution between January 2005 and June 2010. In this cohort, low 25-hydroxyvitamin D concentrations 3 months after transplantation did not predict early death or graft loss but were independently associated with lower measured GFR at 12 months (P=0.001) and higher risk for interstitial fibrosis and tubular atrophy (P=0.01). In contrast, levels of calcium, phosphorus, calcitriol, parathyroid hormone, or fibroblast growth factor-23 were not consistently associated with any of the studied outcomes. In conclusion, low 25-hydroxyvitamin D concentration measured 3 months after transplantation is an independent risk factor for interstitial fibrosis progression and is associated with a lower GFR 1 year after transplantation.

Extrarenal expression of the 25-hydroxyvitamin D-1-hydroxylase

Like the vitamin D receptor (VDR), the CYP27B1-hydroxylase is expressed widely in human tissues. This expression profile establishes the potential for interaction of the VDR with the product of the CYP27B1, 1,25-dihydroxyvitamin D (1,25-(OH)(2)D), in either an intracrine or paracrine mode. This expansive expression profile also suggests that the local production and action of 1,25-(OH)(2)D to regulate VDR-directed gene expression may be similarly wide-ranging and distinct from what occurs in the kidney; the proximal renal tubular epithelial cell is the richest source of the CYP27B1 and the site for production of 1,25-(OH)(2)D destined to function as a hormone. Existence of the CYP27B1 at extrarenal sites has been widely documented, although the functional impact of the enzyme in these tissues has yet to be fully demonstrated. Two notable exceptions are the disease-activated macrophage (e.g., in sarcoidosis or tuberculosis) and the placenta. These two tissues are capable of generating enough 1,25-(OH)(2)D so as to be detectable in the general circulation. As such, this review will focus on CYP27B1 expression only at these two sites, theorizing that 1,25-(OH)(2)D production at these sites is for the purpose of local immunoregulatory function, not for controlling calcium balance in the host or the fetus.

Vitamin D metabolism and activity in the parathyroid gland

Parathormone (PTH) and vitamin D are two critical hormonal regulators of calcium homeostasis. An important cross-talk exists between the PTH and vitamin D hormonal systems. PTH enhances vitamin D hydroxylation on carbon 1 in kidney cells thereby allowing the systemic release of 1-25-dihydroxy-vitamin D, which represents the fully active hormone. Conversely, parathyroid gland represents a direct target for vitamin D. Parathyroid cells express the vitamin D receptor and the 1-α-hydroxylase enzyme, which allows the local formation of 1-25-dihydroxy-vitamin D. Because of its potential implication in several diseases, including osteoporosis or chronic kidney disease, the interplay between PTH and vitamin D has received considerable attention these last two decades. The aim of this review is to summarize our current understanding of the molecular basis of vitamin D action and metabolism in parathyroid cells. The potential clinical implications of the recent advances made in this field will also be discussed.

Metabolic changes following 500 μg monthly administration of calcidiol: a study in normal females

This study was performed to investigate the effect of monthly oral administration of 500 μg of calcidiol (25-hydroxyvitamin D(3)) for 4 months on both serum vitamin D levels and sequential changes of parameters of calcium metabolism; 18 normal women aged 24-72 years were investigated. There was a significant increase of serum 25(OH)D after the first administration; thereafter all values persisted significantly higher compared to the basal value (P < 0.001). Mean 1,25(OH)(2)D serum levels peaked at day 3 and then tended to stabilize following day 30. During the first month, all mean values observed following the initial administration were significantly higher than basal values. The first calcidiol dose produced a significant reduction of serum PTH levels (P < 0.001), which then remained constant over time. Concerning serum calcium and phosphorus, we were not able to demonstrate any significant change during the entire observation period. Considering the single values for both serum ionized and total calcium, the values of Ca(2+) exceeded upper limits of normal on only two occasions. Regarding biochemical markers of bone remodeling, mean changes of serum bone isoenzyme of alkaline phosphatase activity showed a significant trend to decrease, starting at day 30. No significant changes of serum CTX values were noted. Overall, 24-h urinary excretion of calcium did not change, seven values exceeding the threshold of 4 mg/kg body weight. Monthly administration of 500 μg of 25-hydroxyvitamin D(3) may be considered an alternative for vitamin D repletion, without any detrimental effect.

Regulation of PTH secretion by 25-hydroxyvitamin D and ionized calcium depends on vitamin D status: a study in a large cohort of healthy subjects

INTRODUCTION

Previous papers investigating vitamin D status have often outlined the significant relationships between serum parathyroid hormone (PTH) and 25-hydroxyvitamin D (25OHD), but the influence of ionized calcium levels has not been concomitantly considered.

DESIGN

Cross-sectional.

MATERIALS AND METHODS

In 1050 healthy men (547) and women (503), serum ionized calcium (iCa), creatinine (Cr), albumin, 25OHD, and PTH were measured. After conventional analysis, a regression tree was fitted on the data set.

RESULTS

25OHD and PTH values showed significant opposite seasonal changes. 25OHD levels negatively correlated with PTH, which in turn negatively correlated with iCa. A regression tree was fitted to the whole data set using PTH as the response variable and 25OHD and iCa as covariates. PTH concentration depended on that of iCa only in subjects with 25OHD levels>16.35 ng/mL, while for 25OHD<16.35 ng/mL it depended on 25OHD values.

CONCLUSIONS

Our results indicated that PTH levels were highly conditioned by those of 25OHD in subjects with 25OHD values lower than 16.35 ng/mL and by those of iCa only for higher 25OHD concentration.

Involvement of GCMB in the transcriptional regulation of the human parathyroid hormone gene in a parathyroid-derived cell line PT-r: effects of calcium and 1,25(OH)2D3

Expression of the PTH gene is known to be under strict tissue-specific control and is also regulated by extracellular calcium and 1,25(OH)(2)D. However, the precise mode of transcriptional regulation remains to be elucidated, because of the unavailability of appropriate cell lines derived from the parathyroid gland. We tried to identify the transcription factor(s) regulating the human PTH gene transcription using the PT-r cell line. We found that PT-r cells endogenously express PTH and several parathyroid-related genes. Using the cells, we investigated the transcriptional regulation of human PTH gene. We found that GCMB binds to the PTH gene 5'-promoter (-390/-383 bp) and positively regulates its transcription. On the other hand, 1,25(OH)(2)D(3), and, in the presence of the calcium sensing receptor, high extracellular calcium, exerted inhibitory effects on PTH gene expression. These results indicate that GCMB and vitamin D receptor are involved in the positive and negative regulation of PTH gene expression, respectively. Our data also suggest that PT-r cells retain some of the characteristics of parathyroid cells.

Comparison of metabolism of vitamins D2 and D3 in children with nutritional rickets

Children with calcium-deficiency rickets may have increased vitamin D requirements and respond differently to vitamin D(2) and vitamin D(3). Our objective was to compare the metabolism of vitamins D(2) and D(3) in rachitic and control children. We administered an oral single dose of vitamin D(2) or D(3) of 1.25 mg to 49 Nigerian children--28 with active rickets and 21 healthy controls. The primary outcome measure was the incremental change in vitamin D metabolites. Baseline serum 25-hydroxyvitamin D [25(OH)D] concentrations ranged from 7 to 24 and 15 to 34 ng/mL in rachitic and control children, respectively (p < .001), whereas baseline 1,25-dihydroxyvitamin D [1,25(OH)(2)D] values (mean ± SD) were 224 ± 72 and 121 ± 34 pg/mL, respectively (p < .001), and baseline 24,25-dihydroxyvitamin D [24,25(OH)(2)D] values were 1.13 ± 0.59 and 4.03 ± 1.33 ng/mL, respectively (p < .001). The peak increment in 25(OH)D was on day 3 and was similar with vitamins D(2) and D(3) in children with rickets (29 ± 17 and 25 ± 11 ng/mL, respectively) and in control children (33 ± 13 and 31 ± 16 ng/mL, respectively). 1,25(OH)(2)D rose significantly (p < .001) and similarly (p = .18) on day 3 by 166 ± 80 and 209 ± 83 pg/mL after vitamin D(2) and D(3) administration, respectively, in children with rickets. By contrast, control children had no significant increase in 1,25(OH)(2)D (19 ± 28 and 16 ± 38 pg/mL after vitamin D(2) and D(3) administration, respectively). We conclude that in the short term, vitamins D(2) and D(3) similarly increase serum 25(OH)D concentrations in rachitic and healthy children. A marked increase in 1,25(OH)(2)D in response to vitamin D distinguishes children with putative dietary calcium-deficiency rickets from healthy children, consistent with increased vitamin D requirements in children with calcium-deficiency rickets. © 2010 American Society for Bone and Mineral Research.

Emerging drugs for the management of cancer treatment induced bone loss

AREAS COVERED IN THIS REVIEW

We focus our attention on data on the efficacy of currently available and emerging drugs for the management of cancer treatment induced bone loss (CTIBL) found in a PubMed research from 1997 till today.

IMPORTANCE OF THE FIELD

One of the most common and severe safety issues of the antihormonal therapy in both sexes is the CTIBL and the related fragility fractures. In postmenopausal women with estrogenic receptor positive breast cancer, the third-generation aromatase inhibitors (AIs) are the standard therapy. Observational retrospective studies have found that AIs treated patients had a high rate of bone loss and fracture risk (RR 1.3). Also in men with prostate cancer receiving androgen deprivation therapy, the increase in bone turnover and the consequent bone loss are very rapid and sustained significantly increasing the fracture risk.

WHAT THE READER WILL GAIN

The aim of our review is to provide the current evidences for the management of bone loss and fracture risk in this subpopulation.

TAKE HOME MESSAGE

The very high rate of bone loss and the high incidence of fractures indicate that cancer patients at risk of CTIBL need to be carefully monitored and stratified for fracture risk. Although there is a strong evidence of efficacy in prevention of bone loss and reduction of fracture risk for many drugs approved for postmenopausal osteoporosis (PMO) and male osteoporosis, for CTIBL there are actually no drugs approved for this indication.

Effect of vitamin D on blood pressure: a systematic review and meta-analysis

OBJECTIVES

Vitamin D insufficiency has been linked to hypertension and cardiovascular events in observational studies. It is unclear whether vitamin D supplementation can reduce blood pressure, and, if so, by how much.

METHODS

We performed a systematic review and meta-analysis to examine whether vitamin D reduces blood pressure. Databases including MEDLINE, EMBASE, the Cumulative Index to Nursing and Allied Health Literature and the Cochrane library were searched, supplemented by searches of grey literature, unpublished trials and references from included studies. Studies were assessed by two reviewers independently according to a prespecified protocol. Interventions included activated vitamin D, unactivated vitamin D2 and D3 and ultraviolet B radiation.

RESULTS

Eleven randomized, controlled trials fulfilled the inclusion criteria. Studies were small and of variable methodological quality. Mean baseline blood pressure was more than 140/90 mmHg in eight studies. Meta-analysis of these eight studies showed a nonsignificant reduction in systolic blood pressure in the vitamin D group compared with placebo [-3.6 mmHg, 95% confidence interval (CI) -8.0 to 0.7]. A small, statistically significant reduction was seen in diastolic blood pressure (-3.1 mmHg, 95% CI -5.5 to -0.6). Subgroup analysis suggested that unactivated vitamin D produced a greater fall in systolic blood pressure than activated vitamin D (-6.2 mmHg, 95% CI -12.32 to -0.04, vs. +0.7 mmHg, 95% CI -4.8 to 6.2). No reduction in blood pressure was seen in studies examining patients who were normotensive at baseline.

CONCLUSION

We found weak evidence to support a small effect of vitamin D on blood pressure in studies of hypertensive patients.

FGF23 decreases renal NaPi-2a and NaPi-2c expression and induces hypophosphatemia in vivo predominantly via FGF receptor 1

Fibroblast growth factor-23 (FGF23) is a phosphaturic hormone that contributes to several hypophosphatemic disorders by reducing the expression of the type II sodium-phosphate cotransporters (NaPi-2a and NaPi-2c) in the kidney proximal tubule and by reducing serum 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] levels. The FGF receptor(s) mediating the hypophosphatemic action of FGF23 in vivo have remained elusive. In this study, we show that proximal tubules express FGFR1, -3, and -4 but not FGFR2 mRNA. To determine which of these three FGFRs mediates FGF23's hypophosphatemic actions, we characterized phosphate homeostasis in FGFR3(-/-) and FGFR4(-/-) null mice, and in conditional FGFR1(-/-) mice, with targeted deletion of FGFR1 expression in the metanephric mesenchyme. Basal serum phosphorus levels and renal cortical brush-border membrane (BBM) NaPi-2a and NaPi-2c expression were comparable between FGFR1(-/-), FGFR3(-/-), and FGFR4(-/-) mice and their wild-type counterparts. Administration of FGF23 to FGFR3(-/-) mice induced hypophosphatemia in these mice (8.0 +/- 0.4 vs. 5.4 +/- 0.3 mg/dl; p < or = 0.001) and a decrease in renal BBM NaPi-2a and NaPi-2c protein expression. Similarly, in FGFR4(-/-) mice, administration of FGF23 caused a small but significant decrease in serum phosphorus levels (8.7 +/- 0.3 vs. 7.6 +/- 0.4 mg/dl; p < or = 0.001) and in renal BBM NaPi-2a and NaPi-2c protein abundance. In contrast, injection of FGF23 into FGFR1(-/-) mice had no effects on serum phosphorus levels (5.6 +/- 0.3 vs. 5.2 +/- 0.5 mg/dl) or BBM NaPi-2a and NaPi-2c expression. These data show that FGFR1 is the predominant receptor for the hypophosphatemic action of FGF23 in vivo, with FGFR4 likely playing a minor role.

Short and long-term variations in serum calciotropic hormones after a single very large dose of ergocalciferol (vitamin D2) or cholecalciferol (vitamin D3) in the elderly

CONTEXT

In humans, few studies have compared the potencies of ergocalciferol and cholecalciferol in improving and maintaining vitamin D status.

OBJECTIVE

Our objective was to evaluate the effects of a single very large dose of both calciferols on serum changes of 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)(2)D], ionized calcium, and parathyroid hormone (PTH) at baseline, and at 3, 7, 30, and 60 d.

DESIGN

This was a prospective randomized intervention study.

SETTING

The study was performed in a nursing home residence.

PARTICIPANTS

A total of 32 elderly female patients (age range 66-97 yr), with vitamin D deficiency was included in the study.

INTERVENTION

Participants were randomized into four groups of eight to receive a single dose of 300,000 IU ergocalciferol or cholecalciferol by oral (os) or im route.

RESULTS

25(OH)D levels sharply increased at d 3 only when vitamins were given os. The 30-d basal difference in serum 25(OH)D was significantly greater after cholecalciferol os administration (47.8 +/- 7.3 ng/ml) compared with other forms (D(3) im: 15.9 +/- 11.3; D(2) os: 17.3 +/- 4.7; D(2) im: 5 +/- 4.4; all P < 0.001). The area under the curve (AUC) of the serum 25(OH)D against time (AUC(60)) was: D(3) os, 3193 +/- 759 ng x d/ml vs. D(2) os, 1820 +/- 512, P < 0.001; and D(3) im, 1361 +/- 492 vs. D(2) im, 728 +/- 195, P < 0.01. 25(OH)D significantly influences PTH levels at 3 (P < 0.03), 7 (P < 0.01), 30 (P < 0.01), and 60 d (P < 0.05). At 60 d, the form of vitamin (cholecalciferol) significantly lowers PTH levels (P = 0.037).

CONCLUSIONS

Cholecalciferol is almost twice as potent as ergocalciferol in increasing serum 25(OH)D, when administered either by mouth or im. 25(OH)D plays a role in modulating serum PTH.