Vitamin D: metabolism and biological actions

Correlation between serum vitamin D level and uterine volume in girls with idiopathic central precocious puberty

OBJECTIVES

Investigate serum vitamin D (vit D) levels' relation to uterine volume in idiopathic central precocious puberty (ICPP) girls and compare findings with normal peers.

METHODS

Analyzed 278 ICPP cases from January 2017 to September 2022 alongside 239 normally developing girls. Collected clinical data and lab markers and performed subgroup analysis based on vit D levels. Correlation and regression analyses were conducted.

RESULTS

The ICPP group exhibited elevated uterine volume and lower serum vit D compared to controls (p<0.05). A weak negative correlation was noted between vit D and uterine volume in ICPP (r=-0.193, p=0.004), and no such correlation in controls (r=-0.073, p=0.319). The ICPP vit D deficiency subgroup displayed higher uterine volume than the insufficiency and sufficiency subgroups (p<0.05). Uterine volume in the insufficiency subgroup exceeded the sufficiency subgroup (p<0.05). After adjusting for confounders, lower vit D is linked to increased ICPP uterine volume (non-standardized regression coefficient β=-25.55, 95 % CI= -46.23, -4.87, p=0.016). A Limited correlation between vit D and uterine volume was seen in girls with normal pubertal timing.

CONCLUSIONS

We demonstrated a correlation between vit D and uterine volume in ICPP girls, absent in normal peers. ICPP girls often exhibit lower vit D levels and increased uterine volume. Further research is vital for understanding vit D's role in ICPP pathogenesis and guiding prevention and treatment strategies.

Vitamin D status affects proteomic profile of HDL-associated proteins and inflammatory mediators in dyslipidemia

Vitamin D deficiency and dyslipidemia have substantial implications for human health globally. Vitamin D is essential for bone metabolism and immune modulation, and its insufficiency is linked to various chronic inflammatory conditions. Dyslipidemia, characterized by low levels of high-density lipoprotein (HDL) and elevated levels of low-density lipoprotein (LDL) and triglycerides, is also prevalent. Previous research has shown a connection between vitamin D deficiency and low HDL, but the precise mechanism by which vitamin D influences HDL production and its anti-inflammatory properties remains unclear. This study aimed to investigate the proteomic profiles of individuals with and without vitamin D deficiency and dyslipidemia, specifically focusing on the effects of vitamin D on HDL production, its anti-inflammatory potential, and the molecular pathways associated with vitamin D deficiency and dyslipidemia, particularly inflammation and cancer pathways. By analyzing the proteomic profiles of 274 participants from the Qatar Biobank database, we identified 1301 proteins. Our findings indicated a decrease in HDL-associated apolipoproteins (ApoM and ApoD) in individuals with both dyslipidemia and vitamin D deficiency. Conversely, participants with these conditions exhibited increased expression of acute-phase proteins (SAA1 and SOD1), which are associated with inflammation. Pathway enrichment analysis revealed heightened inflammatory activity in individuals with vitamin D deficiency and dyslipidemia, with notable enrichments in pathways such as MAPK, JAK-STAT, Ras signaling, cytokine-cytokine receptor interaction, AGE-RAGE, ErbB signaling, and cancer pathways. Overall, cases of vitamin D deficiency showed enrichment in inflammation pathways, while individuals with both vitamin D deficiency and dyslipidemia demonstrated enhanced activation of cancer and inflammation pathways.

Vitamin D in Diabetes: Uncovering the Sunshine Hormone's Role in Glucose Metabolism and Beyond

Over the last decades, epidemiology and functional studies have started to reveal a pivotal role of vitamin D in both type 1 and type 2 diabetes pathogenesis. Acting through the vitamin D receptor (VDR), vitamin D regulates insulin secretion in pancreatic islets and insulin sensitivity in multiple peripheral metabolic organs. In vitro studies and both T1D and T2D animal models showed that vitamin D can improve glucose homeostasis by enhancing insulin secretion, reducing inflammation, reducing autoimmunity, preserving beta cell mass, and sensitizing insulin action. Conversely, vitamin D deficiency has been shown relevant in increasing T1D and T2D incidence. While clinical trials testing the hypothesis that vitamin D improves glycemia in T2D have shown conflicting results, subgroup and meta-analyses support the idea that raising serum vitamin D levels may reduce the progression from prediabetes to T2D. In this review, we summarize current knowledge on the molecular mechanisms of vitamin D in insulin secretion, insulin sensitivity, and immunity, as well as the observational and interventional human studies investigating the use of vitamin D as a treatment for diabetes.

Role of Neural Stem Cells and Vitamin D Receptor (VDR)-Mediated Cellular Signaling in the Mitigation of Neurological Diseases

Specific stem cell-based therapies for treating Alzheimer's disease, Parkinson's disease, and schizophrenia are gaining importance in recent years. Accumulating data is providing further support by demonstrating the efficacy of neural stem cells in enhancing the neurogenesis in the aging brain. In addition to stem cells, recent studies have shown the efficacy of supplementing vitamin D in promoting neurogenesis and neuronal survival. Studies have also demonstrated the presence of mutational variants and single-nucleotide polymorphisms of the vitamin D receptor (VDR) in neurological disorders; however, implications of these mutations in the pathophysiology and response to drug treatment are yet to be explored. Hence, in this article, we have reviewed recent reports pertaining to the role of neural stem cells and VDR-mediated cellular signaling cascades that are involved in enhancing the neurogenesis through Wnt/β-catenin and Sonic Hedgehog pathways. This review benefits neurobiologists and pharmaceutical industry experts to develop stem cell-based and vitamin D-based therapies to better treat the patients suffering from neurological diseases.

Effect of Vitamin D Supplementation on the Fetal Growth Rate in Pregnancy Complicated by Fetal Growth Restriction

Background: Fetal growth restriction (FGR) increases the risk of intrauterine fetal death, infant death and complications in childhood, and diseases that appear in adulthood. Vitamin D may affect fetal vascular flow. The aim of the study was to check if the rate of fetal growth in pregnant women with FGR differs depending on whether the patient was supplemented with vitamin D in the recommended dose of 2000 IU, not supplemented at all, or supplemented with vitamin D in low doses. Methods: Patients were divided into two groups: suboptimal vitamin D dosage and an accurate dosage of 2000 IU. Fetal growth progress was observed for 14 days. Results: Fetal weight was higher at the beginning, after 1 and 2 weeks of observation in the optimal vit. D group compared with the suboptimal group. The analysis was adjusted to the mother’s age, gestational week, and the number of pregnancies. Conclusions: Greater fetal weight gain can be observed in women with FGR (fetal growth restriction) who intake vitamin D at the recommended dose of 2000 IU compared with women with FGR and with a vitamin D intake dosage lower than 500 IU.

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)₂D, 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)₂D 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. Several examples are provided in this review that additional metabolites (eg, 24,25‐(OH)₂D₃, 25‐OH‐D₃‐26,23‐lactone, and 1,24,25‐(OH)₃D₃) or their ratios with the main forms offer valuable additional diagnostic information. This approach illustrates that biomarkers of disease can also include metabolites devoid of biological activity. Herein, a case is presented that the decision to switch to a LC‐MS/MS technology permits the measurement of a larger number of vitamin D metabolites simultaneously and does not need to lead to a dramatic increase in cost or complexity because the technique uses a highly versatile tandem mass spectrometer with plenty of reserve analytical capacity. Physicians are encouraged to consider adding this rapidly evolving technique aimed at evaluating the wider vitamin D metabolome toward streamlining their approach to calcium‐ and phosphate‐related disease states. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Investigation of Vitamin D2 and Vitamin D3 Hydroxylation by Kutzneria albida

The active vitamin D metabolites 25-OH-D and 1α,25-(OH)2 -D play an essential role in controlling several cellular processes in the human body and are potentially effective in the treatment of several diseases, such as autoimmune diseases, cardiovascular diseases and cancer. The microbial synthesis of vitamin D2 (VD2 ) and vitamin D3 (VD3 ) metabolites has emerged as a suitable alternative to established complex chemical syntheses. In this study, a novel strain, Kutzneria albida, with the ability to form 25-OH-D2 and 25-OH-D3 was identified. To further improve the conversion of the poorly soluble substrates, several solubilizers were tested. 100-fold higher product concentrations of 25-OH-D3 and tenfold higher concentrations of 25-OH-D2 after addition of 5 % (w/v) 2-hydroxypropyl β-cyclodextrin (2-HPβCD) were reached. Besides the single-hydroxylation products, the human double-hydroxylation products 1,25-(OH)2 -D2 and 1,25-(OH)2 -D3 and various other potential single- and double-hydroxylation products were detected. Thus, K. albida represents a promising strain for the biotechnological production of VD2 and VD3 metabolites.

Revised manuscript R2, clean version are serum levels of 25-hydroxy vitamin D reduced following orchiectomy in testicular cancer patients?

Background

The testis represents one place where the progenitor of vitamin D is converted into its active form. Loss of one testis was suggested to result in reduced vitamin D serum levels. Vitamin D deficiency would represent a significant health problem in the long-term course of patients with testicular germ cell tumors (GCTs) since most of them survive. The purpose of this study was to look to the serum 25(OH)-Vitamin D (25OHD) levels in patients with GCTs before and after orchiectomy. A total of 177 GCT patients underwent measurements of serum 25OHD levels, thereof 83 with preoperative measurements and 94 with measurements at six particular time-points from immediate postoperatively to >24 months. Longitudinal assessments of 25OHD serum levels were performed in individual patients with repeated measurements. A second analysis involved patient cohorts with measurements at six postoperative time-points. Serum levels of patients were also compared with 2 control groups, one consisting of 84 patients with non-neoplastic testicular diseases and another with 237 patients with non-neoplastic urologic diseases. We also looked to associations of 25OHD levels with levels of testosterone, follicle stimulating hormone (FSH), age, histology of GCT and season. Descriptive statistical methods were employed to compare groups and to analyze changes over time.

Results

Normal serum levels of 25OHD were found in 21.7%, 23.1%, 20.2%, 21.9% in GCT patients preoperatively, after >2 years, in control group 1 and control group 2, respectively. Levels were significantly higher in spring and summer, but no association was found with other parameters. We found a significant transient decrease of 25OHD levels with a nadir at 6-12 months after orchiectomy and a recovery thereafter.

Conclusion

Contrasting with previous studies we found no permanent reduction of serum 25OHD levels after orchiectomy but transient postoperative drop of 25OHD levels. There were no associations of 25OHD levels with age, and levels of testosterone or FSH. Our results may point to a particular role of the testis in vitamin D metabolism and may thus enhance the understanding of the diverse physiological roles of the testis.

A Review of Analytical Methods for Calcium Salts and Cholecalciferol in Dietary Supplements

Dietary supplements composed by the combination of a calcium salt with cholecalciferol (vitamin D₃) are widely used for improving bone health in conditions caused by the deficiency of these compounds in the body. Historically, these supplements have been linked to quality and safety issues. In the case of calcium salts, the presence of potentially toxic contaminants such as lead (Pb) has already been alerted by health authorities from different countries. Meanwhile, cholecalciferol is very unstable under inadequate manufacturing and storage conditions. The content of both compounds in commercial dietary supplements is often found to be in disagreement with the label claims, which can lead to a deficient or excessive nutrient intake by consumers. In this scenario, analyzing these compounds is still a difficult and time-consuming task, which usually requires specific pretreatment procedures and multiple analytical methods due to the inorganic nature of calcium and the organic nature of cholecalciferol. Therefore, this article reviews the analytical methods, described in official compendia and scientific literature, for the determination of calcium salts and cholecalciferol in dietary supplement formulations. We also approached the sample preparation procedures highly required due to the matrix complexity of these materials.

Systemic vitamin intake impacting tissue proteomes

The kinetics and localization of the reactions of metabolism are coordinated by the enzymes that catalyze them. These enzymes are controlled via a myriad of mechanisms including inhibition/activation by metabolites, compartmentalization, thermodynamics, and nutrient sensing-based transcriptional or post-translational regulation; all of which are influenced as a network by the activities of metabolic enzymes and have downstream potential to exert direct or indirect control over protein abundances. Considering many of these enzymes are active only when one or more vitamin cofactors are present; the availability of vitamin cofactors likely yields a systems-influence over tissue proteomes. Furthermore, vitamins may influence protein abundances as nuclear receptor agonists, antioxidants, substrates for post-translational modifications, molecular signal transducers, and regulators of electrolyte homeostasis. Herein, studies of vitamin intake are explored for their contribution to unraveling vitamin influence over protein expression. As a body of work, these studies establish vitamin intake as a regulator of protein abundance; with the most powerful demonstrations reporting regulation of proteins directly related to the vitamin of interest. However, as a whole, the field has not kept pace with advances in proteomic platforms and analytical methodologies, and has not moved to validate mechanisms of regulation or potential for clinical application.

In silico identification of novel transcription factors associated with CYP27B1 transcriptional regulation in LPS-challenged mononuclear phagocytes

Renal and extrarenal production of the active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)2D), is catalyzed by CYP27B1, an enzyme also called 1-α-hydroxylase. The overproduction of 1,25(OH)2D has been described in granulomatous diseases. High circulating concentrations of 1,25(OH)2D can lead to hypercalcemia. The aim of this work was to characterize the transcriptional regulation of CYP27B1 in human mononuclear phagocytes exposed to LPS due to its relevance to understanding the hypercalcemia and ectopic calcifications associated with chronic inflammatory diseases such as tuberculosis and other granulomatous diseases. The human CYP27B1 promoter analysis identified binding sites for published TF, SNPs, novel putative TFBS and conserved sites compared to mice. Then, using microarray data, a meta-analysis was performed to obtain a global view of the gene expression in LPS-challenged dendritic cells, monocytes and macrophages. Finally, two experiments, GSE40885 and time series GSE19765, were analyzed in-depth using differential expression analysis which permitted the identification of TF co-expressed with CYP27B1. This work allowed us to formulate a CYP27B1 transcriptional regulation model for LPS-challenged monocytes/macrophages. The importance of two TF families, NFKB and CEBPB, was confirmed. Data also suggests that PLAGL2 and STAT4 which are novel TF could participate in the CYP27B1 transcriptional regulation in cells exposed to LPS. These TF, in turn, would be interacting with regions that present polymorphisms in the general population which might explain the pathological phenotypes associated with altered vitamin D metabolism.

The vitamin D metabolome: An update on analysis and function

Current understanding of vitamin D tends to be focussed on the measurement of the major circulating form 25-hydroxyvitamin D3 (25OHD3) and its conversion to the active hormonal form, 1α,25-dihydroxyvitamin D3 (1α,25(OH)₂ D3) via the enzyme 25-hydroxyvitamin D-1α-hydroxylase (CYP27B1). However, whilst these metabolites form the endocrine backbone of vitamin D physiology, it is important to recognise that there are other metabolic and catabolic pathways that are now recognised as being crucially important to vitamin D function. These pathways include C3-epimerization, CYP24A1 hydroxylase, CYP11A1 alternative metabolism of vitamin D3, and phase II metabolism. Endogenous metabolites beyond 25OHD3 are usually present at low endogenous levels and may only be functional in specific target tissues rather than in the general circulation. However, the technologies available to measure these metabolites have also improved, so that measurement of alternative vitamin D metabolic pathways may become more routine in the near future. The aim of this review is to provide a comprehensive overview of the various pathways of vitamin D metabolism, as well as describe the analytical techniques currently available to measure these vitamin D metabolites.

Vitamin D Resists Cyclophosphamide-Induced Genomic and DNA Damage in CHL Cells In Vitro and in Mice In Vivo

Vitamin D as an adjuvant therapy for cancer patients is hoped to have a beneficial outcome based on its physiological activity, but clinical trials so far by addition of vitamin D show unremarkable curative improvement, mechanism for explain this phenomena is not well-understood. The aim of this study was to determine whether vitamin D resists cyclophosphamide (CP)-induced genomic and DNA damage. In CHL cells in vitro, 1α,25-(OH)₂D₃ at 10, 50, and 100 nM was found to alleviate the frequency of chromosomal aberration with an alleviation range of 40.7-44.0%. There was a dose-dependent decrease for a proportion of γ-H2AX foci positive cells in response to an increase in 1α,25-(OH)₂D₃ concentration. Two vitamin D₃ injections of 1,000, 5,000, or 10,000 IU suppressed CP-induced micronucleus formation in mice BMCs with an alleviation range of 36.7-44.5%, mitigated lymphocytes DNA damage reflected by lower tail DNA, tail length and olive tail moment parameter in comet assay. Vitamin D showed an antagonistic effect on CP-induced genomic and DNA damage. Our data suggest that vitamin D as an adjuvant combine antineoplastic drug with genotoxicity administer to tumor patients is contraindicant.

Mechanical, Biochemical, and Structural Effects of Vitamin D Deficiency on the Chick Heart

The effects of vitamin D depriva tion on the chick heart were investi gated from three aspects: cardiac contractility (±dP/dT), intracellular high-energy phosphorus compounds, and structural differences. Four- week-old vitamin D-deficient chicks were divided into four groups: Group A served as the normal group and re ceived subcutaneous injections of cholecalciferol; Groups B and C were vitamin D-deficient hearts but per fused differently; Group D received daily subcutaneous injections of 5 μg of 1,25(OH) 2D3. When the isolated spontaneously beating hearts (modi fied Langendorff preparation) were perfused with Krebs-Henseleit (KH) solution containing a calcium concen tration of 2.5mM, the myocardial contractility of the vitamin D-defi cient hearts was significantly in creased when compared with group A. After the isolated heart had beaten for one hour, the myocardial contractility in the vitamin D-defi cient hearts was found to decline to significantly lower values. Presacri fice administration of 1,25(OH) 2D3 improved cardiac performance. Vita min D deficiency resulted in an en hanced rate of decline of the intracellular high-energy phosphorus compounds. No differences were found in the microscopic study. These observations suggest that vitamin D has a role in cardiac function.

The intervention effect of zuogui pill on chronic kidney disease-mineral and bone disorder regulatory factor

Chronic kidney disease-mineral and bone disorder (CKD-MBD) play a critical role in the pathogenesis of cardiovascular complications in patients with chronic kidney disease (CKD). Zuogui pill as a traditional Chinese herbal drug has been used for nourish kidney essence improve bone malnutrition of renal bone disease by regulating the metabolism of calcium and phosphorus and participating in osteoblast metabolism. In the present study, 5/6 nephrectomy rat model was used to reveal the mechanism of zuogui pill in treatment of CKD-MBD. Compared with sham rats, the levels of serum phosphorus, PTH, iPTH and creatinine were significantly decreased, while the serum calcium level was significantly increased, and the Cbfa1 protein level was significantly decreased and FGF23 protein level was significantly increased by Zuogui pill treatment. Compared with model rats, the BMD of rat was significantly increased by Zuogui pill treatment. Histological analysis revealed that the kidney injury of rats with CKD was significantly reduced by zuogui pill treatment. Compared with model rats, the CYP27B1 mRNA level was significantly increased, and the PTH mRNA level and NaPiIIa protein level were significantly decreased in the kidney by zuogui pill treatment. We inferred that zuogui pill exhibited potential therapeutic effects on CKD-MBD in the rats by regulating bone metabolism and nourish kidney.

Hepatic Transport of 25-Hydroxyvitamin D3 Conjugates: A Mechanism of 25-Hydroxyvitamin D3 Delivery to the Intestinal Tract

Vitamin D3 is an important prohormone critical for maintaining calcium and phosphate homeostasis in the body and regulating drug-metabolizing enzymes and transporters. 25-Hydroxyvitamin D3 (25OHD3), the most abundant circulating metabolite of vitamin D3, is further transformed to the biologically active metabolite 1α,25-dihydroxyvitamin D3 (1α,25-(OH)2D3) by CYP27B1 in the kidney and extrarenal tissues, and to nonactive metabolites by other cytochrome P450 enzymes. In addition, 25OHD3 undergoes sulfation and glucuronidation in the liver, forming two major conjugative metabolites, 25OHD3-3-O-sulfate (25OHD3-S) and 25OHD3-3-O-glucuronide (25OHD3-G), both of which were detected in human blood and bile. Considering that the conjugates excreted into the bile may be circulated to and reabsorbed from the intestinal lumen, deconjugated to 25OHD3, and then converted to 1α,25-(OH)2D3, exerting local intestinal cellular effects, it is crucial to characterize enterohepatic transport mechanisms of 25OHD3-S and 25OHD3-G, and thereby understand and predict mechanisms of interindividual variability in mineral homeostasis. In the present study, with plasma membrane vesicle and cell-based transport studies, we showed that 25OHD3-G is a substrate of multidrug resistance proteins 2 and 3, OATP1B1, and OATP1B3, and that 25OHD3-S is probably a substrate of breast cancer resistance protein, OATP2B1, and OATP1B3. We also demonstrated sinusoidal and canalicular efflux of both conjugates using sandwich-cultured human hepatocytes. Given substantial expression of these transporters in liver hepatocytes and intestinal enterocytes, this study demonstrates for the first time that transporters could play important roles in the enterohepatic circulation of 25OHD3 conjugates, providing an alternative pathway of 25OHD3 delivery to the intestinal tract, which could be critical for vitamin D receptor-dependent gene regulation in enterocytes.

Alterations in gene expression in vitamin D-deficiency: Down-regulation of liver Cyp7a1 and renal Oat3 in mice

The vitamin D-deficient model, established in the C57BL/6 mouse after 8 weeks of feeding vitamin D-deficient diets in the absence or presence of added calcium, was found associated with elevated levels of plasma parathyroid hormone (PTH) and plasma and liver cholesterol, and a reduction in cholesterol 7α-hydroxylase (Cyp7a1, rate-limiting enzyme for cholesterol metabolism) and renal Oat3 mRNA/protein expression levels. However, there was no change in plasma calcium and phosphate levels. Appraisal of the liver revealed an up-regulation of mRNA expressions of the small heterodimer partner (Shp) and attenuation of Cyp7a1, which contributed to hypercholesterolemia in vitamin D-deficiency. When vitamin D-sufficient or D-deficient mice were further rendered hypercholesterolemic with 3 weeks of feeding the respective, high fat/high cholesterol (HF/HC) diets, treatment with 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂ D₃ ], active vitamin D receptor (VDR) ligand, or vitamin D (cholecalciferol) to HF/HC vitamin D-deficient mice lowered the cholesterol back to baseline levels. Cholecalciferol treatment partially restored renal Oat3 mRNA/protein expression back to that of vitamin D-sufficient mice. When the protein expression of protein kinase C (PKC), a known, negative regulator of Oat3, was examined in murine kidney, no difference in PKC expression was observed for any of the diets with/without 1,25(OH)₂ D₃ /cholecalciferol treatment, inferring that VDR regulation of renal Oat3 did not involve PKC in mice. As expected, plasma calcium levels were not elevated by cholecalciferol treatment of vitamin D-deficient mice, while 1,25(OH)₂ D₃ treatment led to hypercalcemia. In conclusion, vitamin D-deficiency resulted in down-regulation of liver Cyp7a1 and renal Oat3, conditions that are alleviated upon replenishment of cholecalciferol.

Shedding new light on female fertility: The role of vitamin D

In the last decades several studies suggested that vitamin D is involved in the modulation of the reproductive process in women due to the expression of VDR and 1α-hydroxylase in reproductive tissues such as ovary, uterus, placenta, pituitary and hypothalamus. Vitamin D has also a role in the regulation of sex hormone steroidogenesis. Increasing evidence suggests that vitamin D might have a regulatory role in polycystic ovary syndrome (PCOS)-associated symptoms, including ovulatory dysfunction, insulin resistance and hyperandrogenism. Vitamin D deficiency also has been reported to contribute to the pathogenesis of endometriosis due to its immunomodulatory and anti-inflammatory properties. Although most of the studies supported a role of vitamin D in the onset of these diseases, randomized controlled trials to assess the efficacy of vitamin D supplementation have never been performed. In this review we critically discuss the role of vitamin D in female fertility, starting from in vitro and in vivo studies, focusing our attention on the two most frequent causes of female infertility: PCOS and endometriosis.

Effect of endoplasmic reticulum stress on metabolic and stress signaling and kidney-specific functions in Madin-Darby bovine kidney cells

Recent studies demonstrated induction of endoplasmic reticulum (ER) stress in tissues of cows after parturition, but knowledge about the effect of ER stress on important cellular processes, such as critical signaling and metabolic pathways, in cattle is scarce. Thus, the present study aimed to investigate the effect of ER stress induction on nuclear factor-κB (NF-κB), nuclear factor E2-related factor 2 (Nrf2), and sterol regulatory element-binding protein (SREBF1) pathway in Madin-Darby bovine kidney (MDBK) cells, a widely used in vitro model in ruminant research. To consider the kidney origin of MDBK cells, the effect on renal distal tubular cell-specific functions, such as transport processes and regulation of 1,25(OH)₂D₃ levels, was also studied. Treatment of MDBK cells with 2 different ER stress inducers, thapsigargin (TG) and tunicamycin (TM), strongly induced ER stress as evident from induction of ER stress target genes, increased phosphorylation of PKR-like ER kinase, and enhanced splicing of X-box binding protein 1. The TM decreased the protein concentration of NF-κB p50 and the mRNA levels of the NF-κB target genes. Likewise, TG decreased the mRNA concentration of tumor necrosis factor and tended to decrease NF-κB p50 protein and mRNA levels of NF-κB target genes. The mRNA levels of most of the Nrf2 target genes investigated were reduced by TG and TM in MDBK cells. Both ER stress inducers reduced the mRNA levels of SREBF1 and its target genes in MDBK cells. Interestingly, TG decreased, but TM increased the mRNA level of the Ca²⁺ binding protein calbindin 1, whereas the mRNA level of the plasma membrane Ca²⁺-transporting ATPase 1 remained unchained. The mRNA level of the cytochrome P450 component 24A1 involved in 1α-hydroxylation of 25(OH)D₃ was strongly elevated, whereas the mRNA level of the cytochrome P450 component 27A1 catalyzing the breakdown of 1,25(OH)₂D₃ was markedly reduced by both ER stress inducers. The concentration of 1,25(OH)₂D₃ in the supernatant of MDBK cells was increased by approximately 15% by both TG and TM. The present study indicates that under conditions of ER stress, critical signaling pathways, such as NF-κB, Nrf2, and SREBF1, are inhibited, whereas the formation of 1,25(OH)₂D₃ is stimulated in bovine MDBK cells. Future studies are necessary to clarify the physiological relevance of these findings.

Quantifying the consequences of nutritional strategies aimed at decreasing phosphorus excretion from pig populations: a modeling approach

There is a global imperative to reduce phosphorous (P) excretion from pig systems. In this study, a previously validated deterministic model was modified to be stochastic, in order to investigate the consequences of different management strategies on P excretion by a group of growing pigs. The model predicts P digestion, retention and excretion from feed composition and growth parameters that describe a specified pig phenotype. Stochasticity was achieved by introducing random variation in the latter. The strategies investigated were: (1) changing feed composition frequently in order to match more closely pig digestible P (digP) requirements to feed composition (phase feeding) and (2) grouping pigs into light and heavy groups and feeding each group according to the requirements of their group average BW (sorting). Phase feeding reduced P excretion as the number of feeding phases increased. The effect was most pronounced as feeding phases increased from 1 to 2, with a 7.5% decrease achieved; the increase in phases from 2 to 3 was associated with a further 2.0% reduction. Similarly, the effect was more pronounced when the feed targeted the population requirements for digP at the average BW of the first third, rather than the average requirements at the mid-point BW of each feeding sequence plan. Increasing the number of feeding phases increased the percentage of pigs that met their digP requirements during the early stages of growth and reduced the percentage of pigs that were supplied <85% of their digP requirements at any stage of their growth; the latter may have welfare implications. Sorting of pigs reduced P excretion to a lesser extent; the reduction was greater as the percentage of pigs in the light group increased from 10% to 30% (from 1.5% to 3.0% reduction, respectively). This resulted from an increase in the P excreted by the light group, accompanied by a decrease in the P excreted by the remaining pigs. Sorting increased the percentage of light pigs that met their dig P requirements, but only slightly decreased the percentage of heavy pigs that met these requirements at any point of their growth. Exactly the converse was the case as far as the percentage of pigs that were supplied <85% of their digP requirements were concerned. The developed model is flexible and can be used to investigate the effectiveness of other management strategies in reducing P excretion from groups of pigs, including precision livestock feeding.

Vitamin D and Placental-Decidual Function

The active form of vitamin D (1,25-dihydroxyvitamin D(3), 1,25[OH](2)D(3)) has well-established effects on bone metabolism and mineral homeostasis. However, recently it has become clear that 1,25(OH)(2)D(3) has potent antiproliferative and immunomodulatory actions that are not immediately linked to its role as a skeletal regulator. Both the nuclear receptor for 1,25(OH)(2)D(3) (vitamin D receptor, VDR) and the vitamin D-activating enzyme 1alpha-hydroxylase are expressed in a wide variety of nonclassic tissues, highlighting the potential for local autocrine-paracrine responses rather than traditional endocrine effects. Prominent among the tissues that express 1alpha-hydroxylase is the placenta-decidua, and this has raised important questions concerning the potential role of locally generated 1,25(OH)(2)D(3) as a modulator of fetal-placental development and function. When bound to the VDR, 1,25(OH)(2)D(3) regulates key target genes associated with implantation, such as HOXA10, whereas the potent immunosuppressive effects of 1,25(OH)(2)D(3) suggest a role in implantation tolerance. These observations are further supported by data from our group showing increased expression of 1alpha-hydroxylase and VDR in first-trimester trophoblast and decidua from human pregnancies. Studies by other groups have reported abnormal expression of 1alpha-hydroxylase in preeclamptic pregnancies, revealing a potential role for 1,25(OH)(2)D(3) as a regulator of placentation. The effect of vitamin D on reproduction has been further endorsed by murine gene knockout models for 1alpha-hydroxylase and VDR, both of which are infertile. These observations and others are discussed in this article in which we postulate an active role for 1,25(OH)(2)D(3) in placenta-decidua. In particular, we describe how induction of the vitamin D-activating enzyme 1alpha-hydroxylase in early gestation might provide a mechanism by which environmental or dietary vitamin D can influence fetal-placental development.

Vitamin D and the Promotion of Long-Term Metabolic Health from a Programming Perspective

Studies linking vitamin D and long-term metabolic health have generated much debate. Recommendations for the intake of vitamin D by the general public and by the health care professionals have been complicated by a number of inconsistencies in the literature. These caveats relate to the methodological approaches, differences in the populations (and the species) of study, and the definitions used for thresholds of vitamin D status. This review addresses current evidence available for assessing the potential programming of long-term metabolic health of offspring by maternal vitamin D status in pregnancy. It summarizes knowledge on the early origins of metabolic health and analyzes evidence for an association between the vitamin D status in pregnancy and maternal and fetal health status. In addition, we analyze the link between the regulation of inflammation and the vitamin D status in the general population to inform on the general mechanisms through which early vitamin D might affect the programming of long-term health. The evidence suggests an association between the vitamin D status in early life and the programming of long-term health. However, to the best of our knowledge, the current finding is insufficient to draw a final conclusion for evidence-based preventive actions. The data warrant replication in prospective studies and additional research substantiating the causal factors and pathways.

Vitamin D and the development of allergic disease: how important is it?

Vitamin D has known effects on lung development and the immune system that may be important in the development, severity, and course of allergic diseases (asthma, eczema, and food allergy). Vitamin D deficiency is prevalent worldwide and may partly explain the increases in asthma and allergic diseases that have occurred over the last 50-60 years. In this review, we explore past and current knowledge on the effect of vitamin D on lung development and immunomodulation and present the evidence of its role in allergic conditions. While there is growing observational and experimental evidence for the role of vitamin D, well-designed and well-powered clinical trials are needed to determine whether supplementation of vitamin D should be recommended in these disorders.

Regulation of hormone-sensitive renal phosphate transport

Phosphate is essential for growth and maintenance of the skeleton and for generating high-energy phosphate compounds. Evolutionary adaptation to high dietary phosphorous in humans and other terrestrial vertebrates involves regulated mechanisms assuring the efficient renal elimination of excess phosphate. These mechanisms prominently include PTH, FGF23, and Vitamin D, which directly and indirectly regulate phosphate transport. Disordered phosphate homeostasis is associated with pathologies ranging from kidney stones to kidney failure. Chronic kidney disease results in hyperphosphatemia, an elevated calcium×phosphate product with considerable morbidity and mortality, mostly associated with adverse cardiovascular events. This chapter highlights recent findings and insights regarding the hormonal regulation of renal phosphate transport along with imbalances of phosphate balance due to acquired or inherited diseases states.

Vitamin D3 potentiates the antitumorigenic effects of arsenic trioxide in human leukemia (HL-60) cells

Background

Arsenic trioxide (ATO) is a novel form of therapy that has been found to aid acute promyelocytic leukemia (APL) patients. Our laboratory has demonstrated that ATO-induced cytotoxicity in human leukemia (HL-60) cells is mediated by oxidative stress. Pro-oxidants have been known to play a role in free radical-mediated oxidative stress. Vitamin D₃, (Vit D₃) an active metabolite of vitamin D has been reported to inhibit the growth of number neoplasms such as prostate, breast, colorectal, leukemia, and skin cancers. The goal of the present research was to use (HL-60) cells as an in vitro test model to evaluate whether low doses of Vit D₃ potentiate the toxicity of ATO and whether this toxic action is mediated via apoptotic mechanisms.

Method

HL-60 cells were treated either with a pharmacologic dose of ATO alone and with several low doses of Vit D₃. Cell survival was determined by MTT assay. Cell apoptosis was measured both by flow cytometry assessment, and DNA laddering assay.

Results

MTT assay indicated that Vit D₃ co-treatment potentiates ATO toxicity in HL-60 cells in a dose dependent manner. A statistically significant and dose-dependent increase (p <0.05) was recorded in annexin V positive cells (apoptotic cells) with increasing doses of Vit D₃ in ATO-treated cells. This finding was confirmed by the result of DNA laddering assay showing clear evidence of nucleosomal DNA fragmentation in vitamin and ATO co-treated cells.

Conclusion

The present study indicates that Vit D₃ potentiates the antitumor effects of ATO. This potentiation is mediated at least in part, through induction of phosphatidylserine externalization and nucleosomal DNA fragmentation. These findings highlight the potential impact of Vit D₃ in promoting the pharmacological effect of ATO, suggesting a possible future role of Vit D₃/ATO combination therapy in patients with acute promyelocytic leukemia (APL).

Organic anion transporter 5 renal expression and urinary excretion in rats with vascular calcification

It has been described renal damage in rats with vascular calcification. The organic anion transporter 5 (Oat5) is only expressed in kidney, and its urinary excretion was proposed as potential early biomarker of renal injury. The aim of this study was to evaluate the Oat5 renal expression and its urinary excretion in an experimental model of vascular calcification in comparison with traditional markers of renal injury. Vascular calcification was obtained by the administration of an overdose of vitamin D₃ (300,000 IU/kg, b.w., i.m.) to male Wistar rats. Oat5 urinary abundance was evaluated by Western blotting. Traditional markers of renal injury, such as creatinine and urea plasma levels, urinary protein levels, and urinary alkaline phosphatase (AP) activity, were determined using commercial kits. Histology was assessed by hematoxylin/eosin staining. Oat5 renal expression was evaluated by Western blotting and by immunohistochemistry. An increased expression of Oat5 in renal homogenates, in apical membranes, and in its urinary excretion was observed in rats with vascular calcification. The traditional parameters used to evaluate renal function were not modified, with the exception of histology. It is possible to postulate the urinary excretion of Oat5 as a potential noninvasive biomarker of renal injury associated with vascular calcification.

Increased plasma concentrations of vitamin D metabolites and vitamin D binding protein in women using hormonal contraceptives: a cross-sectional study

Use of hormonal contraceptives (HC) may influence total plasma concentrations of vitamin D metabolites. A likely cause is an increased synthesis of vitamin D binding protein (VDBP). Discrepant results are reported on whether the use of HC affects free concentrations of vitamin D metabolites.

AIM

In a cross-sectional study, plasma concentrations of vitamin D metabolites, VDBP, and the calculated free vitamin D index in users and non-users of HC were compared and markers of calcium and bone metabolism investigated.

RESULTS

75 Caucasian women aged 25-35 years were included during winter season. Compared with non-users (n = 23), users of HC (n = 52) had significantly higher plasma concentrations of 25-hydroxyvitamin D (25OHD) (median 84 interquartile range: [67-111] vs. 70 [47-83] nmol/L, p = 0.01), 1,25-dihydroxyvitamin D (1,25(OH)2D) (198 [163-241] vs. 158 [123-183] pmol/L, p = 0.01) and VDBP (358 [260-432] vs. 271 [179-302] µg/mL, p < 0.001). However, the calculated free indices (FI-25OHD and FI-1,25(OH)2D) were not significantly different between groups (p > 0.10). There were no significant differences in indices of calcium homeostasis (plasma concentrations of calcium, parathyroid hormone, and calcitonin, p > 0.21) or bone metabolism (plasma bone specific alkaline phosphatase, osteocalcin, and urinary NTX/creatinine ratio) between groups.

IN CONCLUSION

Use of HC is associated with 13%-25% higher concentrations of total vitamin D metabolites and VDBP. This however is not reflected in indices of calcium or bone metabolism. Use of HC should be considered in the interpretation of plasma concentrations vitamin D metabolites.

Optimal vitamin D status: a critical analysis on the basis of evidence-based medicine

CONTEXT

Public health authorities around the world recommend widely variable supplementation strategies for adults, whereas several professional organizations, including The Endocrine Society, recommend higher supplementation.

METHODS

We analyzed published randomized controlled clinical trials to define the optimal intake or vitamin D status for bone and extraskeletal health.

CONCLUSIONS

The extraskeletal effects of vitamin D are plausible as based on preclinical data and observational studies. However, apart from the beneficial effects of 800 IU/d of vitamin D3 for reduction of falls in the elderly, causality remains yet unproven in randomized controlled trials (RCTs). The greatest risk for cancer, infections, cardiovascular and metabolic diseases is associated with 25-hydroxyvitamin D (25OHD) levels below 20 ng/mL. There is ample evidence from RCTs that calcium and bone homeostasis, estimated from serum 1,25-dihydroxyvitamin D and PTH, calcium absorption, or bone mass, can be normalized by 25OHD levels above 20 ng/mL. Moreover, vitamin D supplementation (800 IU/d) in combination with calcium can reduce fracture incidence by about 20%. Such a dose will bring serum levels of 25OHD above 20 ng/mL in nearly all postmenopausal women. Based on calculations of the metabolic clearance of 25OHD, a daily intake of 500-700 IU of vitamin D3 is sufficient to maintain serum 25OHD levels of 20 ng/mL. Therefore, the recommendations for a daily intake of 1500-2000 IU/d or serum 25OHD levels of 30 ng or higher for all adults or elderly subjects, as suggested by The Endocrine Society Task Force, are premature. Fortunately, ongoing RCTs will help to guide us to solve this important public health question.

Maternal serum 25-hydroxyvitamin D and measures of newborn and placental weight in a U.S. multicenter cohort study

CONTEXT

Inconsistent associations between maternal vitamin D status and fetal size have been published in small studies.

OBJECTIVE

Our objective was to examine the association between maternal 25-hydroxyvitamin D [25(OH)D] levels and measures of newborn and placental weight.

DESIGN AND SETTING

We measured maternal 25(OH)D in mothers from the Collaborative Perinatal Project, an observational cohort conducted in 12 U.S. medical centers from 1959 to 1965.

PARTICIPANTS

Women delivering singleton, term, live births with 25(OH)D measured at a gestation of 26 wk or less (n = 2146).

MAIN OUTCOME MEASURES

Birth weight, ponderal index, placental weight, the placental to fetal weight ratio, and small for gestational age were measured. Hypotheses were formulated after data collection.

RESULTS

After confounder adjustment, mothers with 25(OH)D of 37.5 nmol/liter or greater gave birth to newborns with 46 g [95% confidence interval (CI), 9-82 g] higher birth weights and 0.13 cm (0.01-0.25 cm) larger head circumferences compared with mothers with less than 37.5 nmol/liter. Birth weight and head circumference rose with increasing 25(OH)D up to 37.5 nmol/liter and then leveled off (P < 0.05). No association was observed between 25(OH)D and ponderal index, placental weight, or the placental to fetal weight ratio. Maternal 25(OH)D of 37.5 nmol/liter or greater vs. less than 37.5 nmol/liter in the first trimester was associated with half the risk of small for gestational age (adjusted odds ratio 0.5; 95% CI 0.3-0.9), but no second-trimester association was observed.

CONCLUSIONS

Maternal vitamin D status is independently associated with markers of physiological and pathological growth in term infants. Adequately powered randomized controlled trials are needed to test whether maternal vitamin D supplementation may improve fetal growth.

Vitamin D during pregnancy and maternal, neonatal and infant health outcomes: a systematic review and meta-analysis

Vitamin D has well-defined classical functions related to calcium metabolism and bone health but also has non-classical effects that may influence other aspects of health. There has been considerable recent interest in the role of vitamin D on outcomes related to pregnancy and young child health but few efforts have been made to systematically consolidate this evidence to inform the research and policy agenda for low-income countries. A systematic review was undertaken to identify intervention and observational studies of vitamin D supplementation, intake or status (25-hydroxy-vitamin D) during pregnancy on perinatal and infant health outcomes. Data from trials and observational studies isolating the effect of vitamin D supplementation and intake were extracted and study quality was evaluated. Meta-analysis was used to pool effect estimates. We identified five randomised trials with outcomes of relevance to our review. All had small sample size and dosage amount, duration and frequency varied as did the ability to correct deficiency. Pooled analysis of trials using fixed-effects models suggested protective effects of supplementation on low birthweight (three trials, risk ratio (RR) = 0.40 [95% confidence interval (CI) 0.23, 0.71]) and non-significant but suggestive effects of daily supplementation on small-for-gestational age (two trials, RR = 0.67 [0.40, 1.11]). No effect on preterm delivery (<37 weeks) was evident (two trials, RR = 0.77 [0.35, 1.66]). Little evidence from trials exists to evaluate the effect of vitamin D supplementation during pregnancy on maternal, perinatal or infant health outcomes. Based on both trials and observational studies, we recommend that future research explore small-for-gestational age, preterm delivery, pre-eclampsia, and maternal and childhood infections, as outcomes of interest. Trials should focus on populations with a high prevalence of vitamin D deficiency, explore the relevance of timing of supplementation, and the dosage used in such trials should be sufficient to correct deficiency.

Renal expression and function of oat1 and oat3 in rats with vascular calcification

BACKGROUND/AIMS

Calcium overload in vascular smooth muscle is a highly pathogenic event, which progresses with advancing age. Old patients are polymedicated, and several pharmacotherapeutic agents circulate in the plasma as organic anions. The organic anion transporters 1 and 3 (Oat1 and Oat3) are present in renal basolateral membranes, which transport organic anions of pharmacological and physiological interest. This study was designed to evaluate the renal expression and function of Oat1 and Oat3 in rats with vascular calcification.

METHODS

Vascular calcification was induced by administration of a single dose of vitamin D(3) (300,000 UI/ kg b.w., i.m.) to male Wistar rats 10 days before the experiments. Oat1 and Oat3 expression was assessed by immunoblotting, immunohistochemistry and reverse-transcriptase polymerase chain reaction. The renal clearance of p-aminohippurate (PAH, a prototypical organic anion, substrate of Oat1 and Oat3) was measured by conventional clearance techniques.

RESULTS

Oat1 and Oat3 protein levels showed an increase in plasma membranes of renal proximal tubules of treated animals, where both transporters are functional. This could explain the increase observed in the renal clearance of PAH in treated rats.

CONCLUSIONS

These results suggest the relevance of considering the existence of vascular calcification, which is common in ageing, when organic anion drugs are prescribed.

Vitamin D: metabolism

The biologically active metabolite of vitamin D, 1,25(OH)(2)D(3), affects mineral homeostasis and has numerous other diverse physiologic functions including effects on growth of cancer cells and protection against certain immune disorders. This article reviews the role of vitamin D hydroxylases in providing a tightly regulated supply of 1,25(OH)(2)D(3). The role of extrarenal 1α(OH)ase in placenta and macrophages is also discussed, as well as regulation of vitamin D hydroxylases in aging and chronic kidney disease. Understanding specific factors involved in regulating the hydroxylases may lead to the design of drugs that can selectively modulate the hydroxylases. The ability to alter levels of these enzymes would have therapeutic potential for the treatment of various diseases, including bone loss disorders and certain immune diseases.

Vitamin D and fertility: a systematic review

BACKGROUND

Vitamin D has been well-known for its function in maintaining calcium and phosphorus homeostasis and promoting bone mineralization. There is some evidence that in addition to sex steroid hormones, the classic regulators of human reproduction, vitamin D also modulates reproductive processes in women and men.

AIM

The aim of this review was to assess the studies that evaluated the relationship between vitamin D and fertility in women and men as well as in animals.

METHODS

We performed a systematic literature search in Pubmed for relevant English language publications published until October 2011.

RESULTS AND DISCUSSION

The vitamin D receptor (VDR) and vitamin D metabolizing enzymes are found in reproductive tissues of women and men. Vdr knockout mice have significant gonadal insufficiency, decreased sperm count and motility, and histological abnormalities of testis, ovary and uterus. Moreover, we present evidence that vitamin D is involved in female reproduction including IVF outcome (clinical pregnancy rates) and polycystic ovary syndrome (PCOS). In PCOS women, low 25-hydroxyvitamin D (25(OH)D) levels are associated with obesity, metabolic, and endocrine disturbances and vitamin D supplementation might improve menstrual frequency and metabolic disturbances in those women. Moreover, vitamin D might influence steroidogenesis of sex hormones (estradiol and progesterone) in healthy women and high 25(OH)D levels might be associated with endometriosis. In men, vitamin D is positively associated with semen quality and androgen status. Moreover, vitamin D treatment might increase testosterone levels. Testiculopathic men show low CYP21R expression, low 25(OH)D levels, and osteoporosis despite normal testosterone levels.

Simultaneous measurement of plasma vitamin D(3) metabolites, including 4β,25-dihydroxyvitamin D(3), using liquid chromatography-tandem mass spectrometry

Simultaneous and accurate measurement of circulating vitamin D metabolites is critical to studies of the metabolic regulation of vitamin D and its impact on health and disease. To that end, we have developed a specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method that permits the quantification of major circulating vitamin D(3) metabolites in human plasma. Plasma samples were subjected to a protein precipitation, liquid-liquid extraction, and Diels-Alder derivatization procedure prior to LC-MS/MS analysis. Importantly, in all human plasma samples tested, we identified a significant dihydroxyvitamin D(3) peak that could potentially interfere with the determination of 1α,25-dihydroxyvitamin D(3) [1α,25(OH)(2)D(3)] concentrations. This interfering metabolite has been identified as 4β,25-dihydroxyvitamin D(3) [4β,25(OH)(2)D(3)] and was found at concentrations comparable to 1α,25(OH)(2)D(3). Quantification of 1α,25(OH)(2)D(3) in plasma required complete chromatographic separation of 1α,25(OH)(2)D(3) from 4β,25(OH)(2)D(3). An assay incorporating this feature was used to simultaneously determine the plasma concentrations of 25OHD(3), 24R,25(OH)(2)D(3), 1α,25(OH)(2)D(3), and 4β,25(OH)(2)D(3) in healthy individuals. The LC-MS/MS method developed and described here could result in considerable improvement in quantifying 1α,25(OH)(2)D(3) as well as monitoring the newly identified circulating metabolite, 4β,25(OH)(2)D(3).

Defective renal maintenance of the vitamin D endocrine system impairs vitamin D renoprotection: a downward spiral in kidney disease

In kidney disease, the progressive loss of renal capacity to produce calcitriol, the vitamin D hormone, is a key contributor to elevations in parathyroid hormone (PTH) and mineral and skeletal disorders predisposing to renal and cardiovascular damage, ectopic calcifications, and high mortality rates. Thus, the safe correction of calcitriol deficiency to suppress PTH has been the treatment of choice for decades. However, recent epidemiological and experimental data suggest that calcitriol replacement may improve outcomes through renal and cardioprotective actions unrelated to PTH suppression. Furthermore, a striking incidence of vitamin D deficiency occurs in kidney disease and associates more strongly than calcitriol deficiency with a higher risk for kidney disease progression and death. Despite the translational relevance of these findings, no prospective trials are currently available in support of the efficacy of vitamin D supplementation and/or calcitriol replacement to safely halt/moderate renal disease progression. This review updates the pathophysiology behind the vicious cycle by which kidney injury impairs the maintenance of normal vitamin D and calcitriol levels, which in turn impedes vitamin D/calcitriol renoprotective actions, a requirement for the design of prospective trials to improve current recommendations for vitamin D interventions at all stages of kidney disease.

Vitamin D and primary hyperparathyroidism (PHPT)

Vitamin D deficiency and PHPT are two common conditions, especially in postmenopausal women. Vitamin D deficiency is said to be even more frequent in PHPT patients than in the general population due to an accelerated conversion of 25OHD into calcitriol or 24-hydroxylated compounds. Although several studies have reported worsening of PHPT phenotype (larger tumours, higher PTH levels, more severe bone disease) when vitamin D deficiency coexists whereas vitamin D supplementation in PHPT patients with a serum calcium level<3 mmol/L has been shown to be safe (no increase in serum or urinary calcium) and to decrease serum PTH concentration, that many physicians are afraid to give vitamin D to already hypercalcemic PHPT patients. On the other hand, it is possible that, in some patients, a persistent vitamin D deficiency induces, in the long-term, an autonomous secretion of PTH (i.e. tertiary hyperparathyroidism). The mechanism by which this could occur is unclear however. Finally, as many, otherwise normal, subjects with vitamin D insufficiency may have an increased serum PTH level we believe that those with vitamin D insufficiency should be excluded from a reference population for serum PTH levels. By doing that, we found that the upper normal limit for serum PTH was 25-30% lower than in the whole population.

Vitamin D: metabolism

The biologically active metabolite of vitamin D, 1,25(OH)(2)D(3), affects mineral homeostasis and has numerous other diverse physiologic functions including effects on growth of cancer cells and protection against certain immune disorders. This article reviews the role of vitamin D hydroxylases in providing a tightly regulated supply of 1,25(OH)(2)D(3). The role of extrarenal 1alpha(OH)ase in placenta and macrophages is also discussed, as well as regulation of vitamin D hydroxylases in aging and chronic kidney disease. Understanding specific factors involved in regulating the hydroxylases may lead to the design of drugs that can selectively modulate the hydroxylases. The ability to alter levels of these enzymes would have therapeutic potential for the treatment of various diseases, including bone loss disorders and certain immune diseases.

Maternal serum 25-hydroxyvitamin D concentrations are associated with small-for-gestational age births in white women

Maternal vitamin D deficiency has been associated with numerous adverse health outcomes, but its association with fetal growth restriction remains uncertain. We sought to elucidate the association between maternal serum 25-hydroxyvitamin D [25(OH)D] concentrations in early pregnancy and the risk of small-for-gestational age birth (SGA) and explore the association between maternal single nucleotide polymorphisms (SNP) in the vitamin D receptor (VDR) gene and the risk of SGA. We conducted a nested case-control study of nulliparous pregnant women with singleton pregnancies who delivered SGA infants (n = 77 white and n = 34 black) or non-SGA infants (n = 196 white and n = 105 black). Women were followed from <16 wk gestation to delivery. Women's banked sera at <22 wk were newly measured for 25(OH)D and DNA extracted for VDR genotyping. SGA was defined as live-born infants that were <10th percentile of birth weight according to nomograms based on gender and gestational age. After confounder adjustment, there was a U-shaped relation between serum 25(OH)D and risk of SGA among white mothers, with the lowest risk from 60 to 80 nmol/L. Compared with serum 25(OH)D 37.5-75 nmol/L, SGA odds ratios (95% CI) for levels <37.5 and >75 nmol/L were 7.5 (1.8, 31.9) and 2.1 (1.2, 3.8), respectively. There was no relation between 25(OH)D and SGA risk among black mothers. One SNP in the VDR gene among white women and 3 SNP in black women were significantly associated with SGA. Our results suggest that vitamin D has a complex relation with fetal growth that may vary by race.

Vitamin D may be a link to black-white disparities in adverse birth outcomes

In the United States, significant, intractable disparities exist in rates of major pregnancy outcomes between non-Hispanic black and non-Hispanic white women. A previously unexplored candidate influence on the black-white disparity in adverse birth outcomes is maternal vitamin D status. This review summarizes the evidence relating maternal vitamin D to preeclampsia, spontaneous preterm birth, gestational diabetes, and fetal growth restriction, and addresses gaps in our understanding of the contribution of vitamin D to the intractable black-white disparity in these conditions. The literature reviewed highlights strong biologic plausibility of role for vitamin D in the pathophysiology of these poor pregnancy outcomes. Data also suggest that maternal vitamin D deficiency may increase the risk of preeclampsia and fetal growth restriction. Less research has been done in support of relations with spontaneous preterm birth and gestational diabetes, and fetal and infant survival have rarely been studied. Few trials of vitamin D supplementation have been conducted in pregnant women with adequate power to test effects on birth outcomes. Importantly, black pregnant women have rarely been studied in vitamin D-birth outcomes research. Although vitamin D is a promising candidate influence on black-white disparities in preeclampsia, spontaneous preterm birth, fetal growth restriction, and gestational diabetes, these associations require further study in large samples of black US women. Because vitamin D deficiency is widespread and black-white disparities in pregnancy outcomes and infant survival have been resistant to previous interventions, research to test vitamin D as a causal factor is of major public health significance.

TARGET AUDIENCE

Obstetricians & Gynecologist, Family Physicians.

LEARNING OBJECTIVES

After completion of this educational activity, the reader will be able to appreciate risk factors for inadequate vitamin D status. Understand the basic aspects of vitamin D metabolism. Become aware of recent literature linking inadequate vitamin D status and adverse pregnancy outcomes such as preeclampsia and preterm birth.

Effect of paricalcitol and cinacalcet on serum phosphate, FGF-23, and bone in rats with chronic kidney disease

Calcimimetics activate the calcium-sensing receptor (CaR) and reduce parathyroid hormone (PTH) by increasing the sensitivity of the parathyroid CaR to ambient calcium. The calcimimetic, cinacalcet, is effective in treating secondary hyperparathyroidism in dialysis patients [chronic kidney disease (CKD 5)], but little is known about its effects on stage 3-4 CKD patients. We compared cinacalcet and paricalcitol in uremic rats with creatinine clearances "equivalent" to patients with CKD 3-4. Uremia was induced in anesthetized rats using the 5/6th nephrectomy model. Groups were 1) uremic control, 2) uremic + cinacalcet (U+Cin; 15 mg x kg(-1) x day(-1) po for 6 wk), 3) uremic + paricalcitol (U+Par; 0.16 microg/kg, 3 x wk, ip for 6 wk), and 4) normal. Unlike U+Par animals, cinacalcet promoted hypocalcemia and marked hyperphosphatemia. The Ca x P in U+Cin rats was twice that of U+Par rats. Both compounds suppressed PTH. Serum 1,25-(OH)(2)D(3) was decreased in both U+Par and U+Cin rats. Serum FGF-23 was increased in U+Par but not in U+Cin, where it tended to decrease. Analysis of tibiae showed that U+Cin, but not U+Par, rats had reduced bone volume. U+Cin rats had similar bone formation and reduced osteoid surface, but higher bone resorption. Hypocalcemia, hyperphosphatemia, low 1,25-(OH)(2)D(3), and cinacalcet itself may play a role in the detrimental effects on bone seen in U+Cin rats. This requires further investigation. In conclusion, due to its effects on bone and to the hypocalcemia and severe hyperphosphatemia it induces, we believe that cinacalcet should not be used in patients with CKD without further detailed studies.

Multi-organ damage induced by anabolic steroid supplements: a case report and literature review

Introduction

The use of anabolic supplements and other related drugs for body building and to enhance athletic performance is nowadays widespread and acutely pervasive all around the world. This alarming increase in the use of anabolic and amino acid supplements has been linked to a diverse array of pathologies. As previously reported, the abuse of androgenic steroids is not without severe physiological, psychiatric and physical costs. The case we report here describes multi-organ damage resulting from the abuse and uncontrolled use of anabolic steroid supplements, mainly testosterone.

Case presentation

A 24-year-old white man presented with abdominal pain concomitant with nausea and vomiting. Laboratory analysis revealed hypercalcemia, elevated liver enzymes and high levels of amylase, lipase and creatine protein kinase.

Conclusion

Amino acid as well as anabolic supplements may lead to abnormal functioning of many organs, which could be fatal in some instances. This mandates worldwide and concerted efforts to educate the public, especially the youth, about the dangers of these increasingly abused drugs.

Plasma 25-hydroxyvitamin D levels and risk of incident hypertension among young women

Numerous cross-sectional studies demonstrate an inverse association between plasma 25-hydroxyvitamin D [25(OH)D] and blood pressure or hypertension. Prospective data, however, are limited. Among 1484 women aged 32 to 52 years who did not have hypertension at baseline, we prospectively analyzed the association between plasma levels of 25(OH)D and the odds of incident hypertension using a nested case-control study design. We matched cases and controls on age, race, and month of blood collection and further adjusted for body mass index, physical activity, family history of hypertension, oral contraceptive use, and plasma levels of parathyroid hormone, calcium, phosphorous, creatinine, and uric acid. Median plasma 25(OH)D levels were lower in the cases (25.6 ng/mL) than in the controls (27.3 ng/mL; P<0.001). Women in the lowest compared with highest quartile of plasma 25(OH)D had an adjusted odds ratio for incident hypertension of 1.66 (95% CI: 1.11 to 2.48; P for trend=0.01). Compared with women with sufficient levels, those with vitamin D deficiency (<30 ng/mL; 65.7% of the study population) had a multivariable odds ratio of 1.47 (95% CI: 1.10 to 1.97). Plasma 25(OH)D levels are inversely and independently associated with the risk of developing hypertension.