query: VgrG (Tssl) protein punctures membranes by forming a spike at the tip of the tube apparatus.

title: PAAR-repeat proteins sharpen and diversify the Type VI secretion system spike

text: The bacterial type VI secretion system (T6SS) is a large multicomponent, dynamic macromolecular machine that has an important role in the ecology of many Gram-negative bacteria. T6SS is responsible for translocation of a wide range of toxic effector molecules, allowing predatory cells to kill both prokaryotic as well as eukaryotic prey cells. The T6SS organelle is functionally analogous to contractile tails of bacteriophages and is thought to attack cells by initially penetrating them with a trimeric protein complex called the VgrG spike. Neither the exact protein composition of the T6SS organelle nor the mechanisms of effector selection and delivery are known. Here we report that proteins from the PAAR (proline-alanine-alanine-arginine) repeat superfamily form a sharp conical extension on the VgrG spike, which is further involved in attaching effector domains to the spike. The crystal structures of two PAAR-repeat proteins bound to VgrG-like partners show that these proteins sharpen the tip of the T6SS spike complex. We demonstrate that PAAR proteins are essential for T6SS-mediated secretion and target cell killing by Vibrio cholerae and Acinetobacter baylyi. Our results indicate a new model of the T6SS organelle in which the VgrG-PAAR spike complex is decorated with multiple effectors that are delivered simultaneously into target cells in a single contraction-driven translocation event.

title: A view to a kill: the bacterial type VI secretion system.

text: The bacterial type VI secretion system (T6SS) is an organelle that is structurally and mechanistically analogous to an intracellular membrane-attached contractile phage tail. Recent studies determined that a rapid conformational change in the structure of a sheath protein complex propels T6SS spike and tube components along with antibacterial and antieukaryotic effectors out of predatory T6SS(+) cells and into prey cells. The contracted organelle is then recycled in an ATP-dependent process. T6SS is regulated at transcriptional and posttranslational levels, the latter involving detection of membrane perturbation in some species. In addition to directly targeting eukaryotic cells, the T6SS can also target other bacteria coinfecting a mammalian host, highlighting the importance of the T6SS not only for bacterial survival in environmental ecosystems, but also in the context of infection and disease. This review highlights these and other advances in our understanding of the structure, mechanical function, assembly, and regulation of the T6SS.

title: Actin dynamics and cell-cell adhesion in epithelia.

text: Recent advances in the field of intercellular adhesion highlight the importance of adherens junction association with the underlying actin cytoskeleton. In skin epithelial cells a dynamic feature of adherens junction formation involves filopodia, which physically project into the membrane of adjacent cells, catalyzing the clustering of adherens junction protein complexes at their tips. In turn, actin polymerization is stimulated at the cytoplasmic interface of these complexes. Although the mechanism remains unclear, the VASP/Mena family of proteins seems to be involved in organizing actin polymerization at these sites. In vivo, adherens junction formation appears to rely upon filopodia in processes where epithelial sheets must be physically moved closer to form stable intercellular connections, for example, in ventral closure in embryonic development or wound healing in the postnatal animal.

title: A molecular framework for plant regeneration.

text: Plants and some animals have a profound capacity to regenerate organs from adult tissues. Molecular mechanisms for regeneration have, however, been largely unexplored. Here we investigate a local regeneration response in Arabidopsis roots. Laser-induced wounding disrupts the flow of auxin-a cell-fate-instructive plant hormone-in root tips, and we demonstrate that resulting cell-fate changes require the PLETHORA, SHORTROOT, and SCARECROW transcription factors. These transcription factors regulate the expression and polar position of PIN auxin efflux-facilitating membrane proteins to reconstitute auxin transport in renewed root tips. Thus, a regeneration mechanism using embryonic root stem-cell patterning factors first responds to and subsequently stabilizes a new hormone distribution.

title: The Ndc80 Kinetochore Complex Forms Load-Bearing Attachments to Dynamic Microtubule Tips via Biased Diffusion

text: Kinetochores couple chromosomes to the assembling and disassembling tips of microtubules, a dynamic behavior that is fundamental to mitosis in all eukaryotes but poorly understood. Genetic, biochemical, and structural studies implicate the Ndc80 complex as a direct point of contact between kinetochores and microtubules, but these approaches provide only a static view. Here, using techniques for manipulating and tracking individual molecules in vitro, we demonstrate that the Ndc80 complex is capable of forming the dynamic, load-bearing attachments to assembling and disassembling tips required for coupling in vivo. We also establish that Ndc80-based coupling likely occurs through a biased diffusion mechanism and that this activity is conserved from yeast to humans. Our findings demonstrate how an ensemble of Ndc80 complexes may provide the combination of plasticity and strength that allows kinetochores to maintain load-bearing tip attachments during both microtubule assembly and disassembly.

title: Dynamics of Microvillus Extension and Tether Formation in Rolling Leukocytes.

text: P-selectin glycoprotein ligand-1 (PSGL-1) binding to P-selectin mediates leukocyte rolling under conditions of flow. In human neutrophils, a type of leukocyte belonging to the innate immune system, PSGL-1 molecules are located on the neutrophil's surface ruffles, called microvilli. Each newly formed P-selectin-PSGL-1 bond can become load bearing, imposing on its microvillus a pulling force that deforms the microvillus. Depending on the magnitude of the bond force, a microvillus can be extended, or a thin membrane cylinder (a tether) can be formed at the tip of the microvillus. Here we propose a Kelvin-Voigt viscoelastic material as an improved model for microvillus extension. Using a modified version of our Event-Tracking Model of Adhesion (ETMA), we demonstrate how P-selectin-PSGL-1 load-bearing bonds shape microvillus deformation during neutrophil rolling at low shear (wall shear rate of 50 s(-1), P-selectin site density of 150 molecules μm(-2)). We also discuss the impact of microvillus deformability on neutrophil rolling. We find that the average microvillus extension constitutes 65% of the total microvillus-tether complex extension, and that the rolling neutrophil may never fully rest. A quantitative comparison with the corresponding non-deformable microvilli case supports a concept that the ability of the microvillus to deform stabilizes cell rolling.

title: Ultrasound imaging for lumbar punctures and epidural catheterisations: systematic review and meta-analysis.

text:
OBJECTIVE To determine whether ultrasound imaging can reduce the risk of failed lumbar punctures or epidural catheterisations, when compared with standard palpation methods, and whether ultrasound imaging can reduce traumatic procedures, insertion attempts, and needle redirections.
 DESIGN Systematic review and meta-analysis of randomised controlled trials.
 DATA SOURCES Ovid Medline, Embase, and Cochrane Central Register of Controlled Trials up to May 2012, without restriction by language or publication status.    REVIEW METHODS Randomised trials that compared ultrasound imaging with standard methods (no imaging) in the performance of a lumbar puncture or epidural catheterisation were identified.
 RESULTS 14 studies with a total of 1334 patients were included (674 patients assigned to the ultrasound group, 660 to the control group). Five studies evaluated lumbar punctures and nine evaluated epidural catheterisations. Six of 624 procedures conducted in the ultrasound group failed; 44 of 610 procedures in the control group failed. Ultrasound imaging reduced the risk of failed procedures (risk ratio 0.21 (95% confidence interval 0.10 to 0.43), P<0.001). Risk reduction was similar when subgroup analysis was performed for lumbar punctures (risk ratio 0.19 (0.07 to 0.56), P=0.002) or epidural catheterisations (0.23 (0.09 to 0.60), P=0.003). Ultrasound imaging also significantly reduced the risk of traumatic procedures (risk ratio 0.27 (0.11 to 0.67), P=0.005), the number of insertion attempts (mean difference -0.44 (-0.64 to -0.24), P<0.001), and the number of needle redirections (mean difference -1.00 (-1.24 to -0.75), P<0.001).
 CONCLUSIONS Ultrasound imaging can reduce the risk of failed or traumatic lumbar punctures and epidural catheterisations, as well as the number of needle insertions and redirections. Ultrasound may be a useful adjunct for these procedures.

title: Wnt5a functions in planar cell polarity regulation in mice.

text: Planar cell polarity (PCP) refers to the polarization of cells within the plane of a cell sheet. A distinctive epithelial PCP in vertebrates is the uniform orientation of stereociliary bundles of the sensory hair cells in the mammalian cochlea. In addition to establishing epithelial PCP, planar polarization is also required for convergent extension (CE); a polarized cellular movement that occurs during neural tube closure and cochlear extension. Studies in Drosophila and vertebrates have revealed a conserved PCP pathway, including Frizzled (Fz) receptors. Here we use the cochlea as a model system to explore the involvement of known ligands of Fz, Wnt morphogens, in PCP regulation. We show that Wnt5a forms a reciprocal expression pattern with a Wnt antagonist, the secreted frizzled-related protein 3 (Sfrp3 or Frzb), along the axis of planar polarization in the cochlear epithelium. We further demonstrate that Wnt5a antagonizes Frzb in regulating cochlear extension and stereociliary bundle orientation in vitro, and that Wnt5a(-/-) animals have a shortened and widened cochlea. Finally, we show that Wnt5a is required for proper subcellular distribution of a PCP protein, Ltap/Vangl2, and that Wnt5a interacts genetically with Ltap/Vangl2 for uniform orientation of stereocilia, cochlear extension, and neural tube closure. Together, these findings demonstrate that Wnt5a functions in PCP regulation in mice.

title: Involvement of cortical fast-spiking parvalbumin-positive basket cells in epilepsy.

text: GABAergic interneurons of the parvalbumin-positive fast-spiking basket cells subtype (PV INs) are important regulators of cortical network excitability and of gamma oscillations, involved in signal processing and cognition. Impaired development or function of PV INs has been associated with epilepsy in various animal models of epilepsy, as well as in some genetic forms of epilepsy in humans. In this review, we provide an overview of some of the experimental data linking PV INs dysfunction with epilepsy, focusing on disorders of the specification, migration, maturation, synaptic function, or connectivity of PV INs. Furthermore, we reflect on the potential therapeutic use of cell-type specific stimulation of PV INs within active networks and on the transplantation of PV INs precursors in the treatment of epilepsy and its comorbidities.

title: PGAP2 mutations, affecting the GPI-anchor-synthesis pathway, cause hyperphosphatasia with mental retardation syndrome.

text: Recently, mutations in genes involved in the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor have been identified in a new subclass of congenital disorders of glycosylation (CDGs) with a distinct spectrum of clinical features. To date, mutations have been identified in six genes (PIGA, PIGL, PIGM, PIGN, PIGO, and PIGV) encoding proteins in the GPI-anchor-synthesis pathway in individuals with severe neurological features, including seizures, muscular hypotonia, and intellectual disability. We developed a diagnostic gene panel for targeting all known genes encoding proteins in the GPI-anchor-synthesis pathway to screen individuals matching these features, and we detected three missense mutations in PGAP2, c.46C>T, c.380T>C, and c.479C>T, in two unrelated individuals with hyperphosphatasia with mental retardation syndrome (HPMRS). The mutations cosegregated in the investigated families. PGAP2 is involved in fatty-acid GPI-anchor remodeling, which occurs in the Golgi apparatus and is required for stable association between GPI-anchored proteins and the cell-surface membrane rafts. Transfection of the altered protein constructs, p. Arg16Trp (NP_001243169.1), p. Leu127Ser, and p. Thr160Ile, into PGAP2-null cells showed only partial restoration of GPI-anchored marker proteins, CD55 and CD59, on the cell surface. In this work, we show that an impairment of GPI-anchor remodeling also causes HPMRS and conclude that targeted sequencing of the genes encoding proteins in the GPI-anchor-synthesis pathway is an effective diagnostic approach for this subclass of CDGs.

title: A conserved phosphatase cascade that regulates nuclear membrane biogenesis.

text: A newly emerging family of phosphatases that are members of the haloacid dehalogenase superfamily contains the catalytic motif DXDX(T/V). A member of this DXDX(T/V) phosphatase family known as Dullard was recently shown to be a potential regulator of neural tube development in Xenopus [Satow R, Chan TC, Asashima M (2002) Biochem Biophys Res Commun 295:85-91]. Herein, we demonstrate that human Dullard and the yeast protein Nem1p perform similar functions in mammalian cells and yeast cells, respectively. In addition to similarity in primary sequence, Dullard and Nem1p possess similar domains and show similar substrate preferences, and both localize to the nuclear envelope. Additionally, we show that human Dullard can rescue the aberrant nuclear envelope morphology of nem1Delta yeast cells, functionally replacing Nem1p. Finally, Nem1p, has been shown to deposphorylate the yeast phosphatidic acid phosphatase Smp2p [Santos-Rosa H, Leung J, Grimsey N, Peak-Chew S, Siniossoglou S (2005) EMBO J 24:1931-1941], and we show that Dullard dephosphorylates the mammalian phospatidic acid phosphatase, lipin. Therefore, we propose that Dullard participates in a unique phosphatase cascade regulating nuclear membrane biogenesis, and that this cascade is conserved from yeast to mammals.

title: Clathrin is required for the function of the mitotic spindle

text: Clathrin has an established function in the generation of vesicles that transfer membrane and proteins around the cell. The formation of clathrin-coated vesicles occurs continuously in non-dividing cells, but is shut down during mitosis, when clathrin concentrates at the spindle apparatus. Here, we show that clathrin stabilizes fibres of the mitotic spindle to aid congression of chromosomes. Clathrin bound to the spindle directly by the amino-terminal domain of clathrin heavy chain. Depletion of clathrin heavy chain using RNA interference prolonged mitosis; kinetochore fibres were destabilized, leading to defective congression of chromosomes to the metaphase plate and persistent activation of the spindle checkpoint. Normal mitosis was rescued by clathrin triskelia but not the N-terminal domain of clathrin heavy chain, indicating that stabilization of kinetochore fibres was dependent on the unique structure of clathrin. The importance of clathrin for normal mitosis may be relevant to understanding human cancers that involve gene fusions of clathrin heavy chain.

title: UV light-induced DNA synthesis arrest in HeLa cells is associated with changes in phosphorylation of human single-stranded DNA-binding protein.

text: We show that DNA replication activity in extracts of human HeLa cells decreases following UV irradiation. Alterations in replication activity in vitro parallel the UV-induced block in cell cycle progression of these cells in culture. UV irradiation also induces specific changes in the pattern of phosphorylation of the 34 kDa subunit of a DNA replication protein, human single-stranded DNA-binding protein (hSSB). The appearance of a hyperphosphorylated form of hSSB correlates with reduced in vitro DNA replication activity in extracts of UV-irradiated cells. Replication activity can be restored to these extracts in vitro by addition of purified hSSB. These results suggest that UV-induced DNA synthesis arrest may be mediated in part through phosphorylation-related alterations in the activity of hSSB, an essential component of the DNA replication apparatus.

title: Ionic protein-lipid interaction at the plasma membrane: what can the charge do?

text: Phospholipids are the major components of cell membranes, but they have functional roles beyond forming lipid bilayers. In particular, acidic phospholipids form microdomains in the plasma membrane and can ionically interact with proteins via polybasic sequences, which can have functional consequences for the protein. The list of proteins regulated by ionic protein-lipid interaction has been quickly expanding, and now includes membrane proteins, cytoplasmic soluble proteins, and viral proteins. Here we review how acidic phospholipids in the plasma membrane regulate protein structure and function via ionic interactions, and how Ca(2+) regulates ionic protein-lipid interactions via direct and indirect mechanisms.

title: Integrin beta1-mediated matrix assembly and signaling are critical for the normal development and function of the kidney glomerulus.

text: The human kidneys filter 180 l of blood every day via about 2.5 million glomeruli. The three layers of the glomerular filtration apparatus consist of fenestrated endothelium, specialized extracellular matrix known as the glomerular basement membrane (GBM) and the podocyte foot processes with their modified adherens junctions known as the slit diaphragm (SD). In this study we explored the contribution of podocyte beta1 integrin signaling for normal glomerular function. Mice with podocyte specific deletion of integrin beta1 (podocin-Cre beta1-fl/fl mice) are born normal but cannot complete postnatal renal development. They exhibit detectable proteinuria on day 1 and die within a week. The kidneys of podocin-Cre beta1-fl/fl mice exhibit normal glomerular endothelium but show severe GBM defects with multilaminations and splitting including podocyte foot process effacement. The integrin linked kinase (ILK) is a downstream mediator of integrin beta1 activity in epithelial cells. To further explore whether integrin beta1-mediated signaling facilitates proper glomerular filtration, we generated mice deficient of ILK in the podocytes (podocin-Cre ILK-fl/fl mice). These mice develop normally but exhibit postnatal proteinuria at birth and die within 15 weeks of age due to renal failure. Collectively, our studies demonstrate that podocyte beta1 integrin and ILK signaling is critical for postnatal development and function of the glomerular filtration apparatus.

title: Myogenic and morphogenetic defects in the heart tubes of murine embryos lacking the homeo box gene Nkx2-5.

text: The murine homeo box gene Nkx2-5 is expressed in precardiac mesoderm and in the myocardium of embryonic and fetal hearts. Targeted interruption of Nkx2-5 resulted in abnormal heart morphogenesis, growth retardation and embryonic lethality at approximately 9-10 days postcoitum (p.c.). Heart tube formation occurred normally in mutant embryos, but looping morphogenesis, a critical determinant of heart form, was not initiated at the linear heart tube stage (8.25-8.5 days p.c.). Commitment to the cardiac muscle lineage, expression of most myofilament genes and myofibrillogenesis were not compromised. However, the myosin light-chain 2V gene (MLC2V) was not expressed in mutant hearts nor in mutant ES cell-derived cardiocytes. MLC2V expression normally occurs only in ventricular cells and is the earliest known molecular marker of ventricular differentiation. The regional expression in mutant hearts of two other ventricular markers, myosin heavy-chain beta and cyclin D2, indicated that not all ventricle-specific gene expression is dependent on Nkx2-5. The data demonstrate that Nkx2-5 is essential for normal heart morphogenesis, myogenesis, and function. Furthermore, this gene is a component of a genetic pathway required for myogenic specialization of the ventricles.

title: Stress-dependent regulation of FOXO transcription factors by the SIRT1 deacetylase.

text: The Sir2 deacetylase modulates organismal life-span in various species. However, the molecular mechanisms by which Sir2 increases longevity are largely unknown. We show that in mammalian cells, the Sir2 homolog SIRT1 appears to control the cellular response to stress by regulating the FOXO family of Forkhead transcription factors, a family of proteins that function as sensors of the insulin signaling pathway and as regulators of organismal longevity. SIRT1 and the FOXO transcription factor FOXO3 formed a complex in cells in response to oxidative stress, and SIRT1 deacetylated FOXO3 in vitro and within cells. SIRT1 had a dual effect on FOXO3 function: SIRT1 increased FOXO3's ability to induce cell cycle arrest and resistance to oxidative stress but inhibited FOXO3's ability to induce cell death. Thus, one way in which members of the Sir2 family of proteins may increase organismal longevity is by tipping FOXO-dependent responses away from apoptosis and toward stress resistance.

title: Local, Efflux-Dependent Auxin Gradients as a Common Module for Plant Organ Formation

text: Plants, compared to animals, exhibit an amazing adaptability and plasticity in their development. This is largely dependent on the ability of plants to form new organs, such as lateral roots, leaves, and flowers during postembryonic development. Organ primordia develop from founder cell populations into organs by coordinated cell division and differentiation. Here, we show that organ formation in Arabidopsis involves dynamic gradients of the signaling molecule auxin with maxima at the primordia tips. These gradients are mediated by cellular efflux requiring asymmetrically localized PIN proteins, which represent a functionally redundant network for auxin distribution in both aerial and underground organs. PIN1 polar localization undergoes a dynamic rearrangement, which correlates with establishment of auxin gradients and primordium development. Our results suggest that PIN-dependent, local auxin gradients represent a common module for formation of all plant organs, regardless of their mature morphology or developmental origin.

title: Biochemical analysis of TssK, a core component of the bacterial Type VI secretion system, reveals distinct oligomeric states of TssK and identifies a TssK–TssFG subcomplex

text: Gram-negative bacteria use the Type VI secretion system (T6SS) to inject toxic proteins into rival bacteria or eukaryotic cells. However, the mechanism of the T6SS is incompletely understood. In the present study, we investigated a conserved component of the T6SS, TssK, using the antibacterial T6SS of Serratia marcescens as a model system. TssK was confirmed to be essential for effector secretion by the T6SS. The native protein, although not an integral membrane protein, appeared to localize to the inner membrane, consistent with its presence within a membrane-anchored assembly. Recombinant TssK purified from S. marcescens was found to exist in several stable oligomeric forms, namely trimer, hexamer and higher-order species. Native-level purification of TssK identified TssF and TssG as interacting proteins. TssF and TssG, conserved T6SS components of unknown function, were required for T6SS activity, but not for correct localization of TssK. A complex containing TssK, TssF and TssG was subsequently purified in vitro, confirming that these three proteins form a new subcomplex within the T6SS. Our findings provide new insight into the T6SS assembly, allowing us to propose a model whereby TssK recruits TssFG into the membrane-associated T6SS complex and different oligomeric states of TssK may contribute to the dynamic mechanism of the system.

title: The immunological synapse of CTL contains a secretory domain and membrane bridges.

text: Cytotoxic T lymphocytes (CTL) rapidly destroy their targets. Here we show that although target cell death occurs within 5 min of CTL-target cell contact, an immunological synapse similar to that seen in CD4 cells rapidly forms in CTL, with a ring of adhesion proteins surrounding an inner signaling molecule domain. Lytic granule secretion occurs in a separate domain within the adhesion ring, maintaining signaling protein organization during exocytosis. Live and fixed cell studies show target cell plasma membrane markers are transferred to the CTL as the cells separate. Electron microscopy reveals continuities forming membrane bridges between the CTL and target cell membranes, suggesting a possible mechanism for this transfer.


query: Vitamin D deficiency effects birth weight.

title: Association between maternal serum 25-hydroxyvitamin D level and pregnancy and neonatal outcomes: systematic review and meta-analysis of observational studies.

text:
OBJECTIVE To assess the effect of 25-hydroxyvitamin D (25-OHD) levels on pregnancy outcomes and birth variables.
 DESIGN Systematic review and meta-analysis.
 DATA SOURCES Medline (1966 to August 2012), PubMed (2008 to August 2012), Embase (1980 to August 2012), CINAHL (1981 to August 2012), the Cochrane database of systematic reviews, and the Cochrane database of registered clinical trials.    STUDY SELECTION Studies reporting on the association between serum 25-OHD levels during pregnancy and the outcomes of interest (pre-eclampsia, gestational diabetes, bacterial vaginosis, caesarean section, small for gestational age infants, birth weight, birth length, and head circumference).
 DATA EXTRACTION Two authors independently extracted data from original research articles, including key indicators of study quality. We pooled the most adjusted odds ratios and weighted mean differences. Associations were tested in subgroups representing different patient characteristics and study quality.
 RESULTS 3357 studies were identified and reviewed for eligibility. 31 eligible studies were included in the final analysis. Insufficient serum levels of 25-OHD were associated with gestational diabetes (pooled odds ratio 1.49, 95% confidence interval 1.18 to 1.89), pre-eclampsia (1.79, 1.25 to 2.58), and small for gestational age infants (1.85, 1.52 to 2.26). Pregnant women with low serum 25-OHD levels had an increased risk of bacterial vaginosis and low birthweight infants but not delivery by caesarean section.
 CONCLUSION Vitamin D insufficiency is associated with an increased risk of gestational diabetes, pre-eclampsia, and small for gestational age infants. Pregnant women with low 25-OHD levels had an increased risk of bacterial vaginosis and lower birth weight infants, but not delivery by caesarean section.

title: Vitamin D insufficiency and the blunted PTH response in established osteoporosis: the role of magnesium deficiency

text: Vitamin D insufficiency is common, however within individuals, not all manifest the biochemical effects of PTH excess. This further extends to patients with established osteoporosis. The mechanism underlying the blunted PTH response is unclear but may be related to magnesium (Mg) deficiency. The aims of this study were to compare in patients with established osteoporosis and differing degrees of vitamin D and PTH status : (1) the presence of Mg deficiency using the standard Mg loading test (2) evaluate the effects of Mg loading on the calcium-PTH endocrine axis (3) determine the effects of oral, short term Mg supplementation on the calcium-PTH endocrine axis and bone turnover. 30 patients (10 women in 3 groups) were evaluated prospectively measuring calcium, PTH, Mg retention (Mg loading test), dietary nutrient intake (calcium, vitamin D, Mg) and bone turnover markers (serum CTX & P1CP). Multivariate analysis controlling for potential confounding baseline variable was undertaken for the measured outcomes. All subjects, within the low vitamin D and low PTH group following the magnesium loading test had evidence of Mg depletion [mean(SD) retention 70.3%(12.5)] and showed an increase in calcium 0.06(0.01) mmol/l [95% CI 0.03, 0.09, p=0.007], together with a rise in PTH 13.3 ng/l (4.5) [95% CI 3.2, 23.4, p=0.016] compared to baseline. Following oral supplementation bone turnover increased: CTX 0.16 (0.06) mcg/l [95%CI 0.01, 0.32 p=0.047]; P1CP 13.1 (5.7) mcg/l [95% CI 0.29, 26.6 p=0.049]. In subjects with a low vitamin D and raised PTH mean retention was 55.9%(14.8) and in the vitamin replete group 36.1%(14.4), with little change in both acute markers of calcium homeostasis and bone turnover markers following both the loading test and oral supplementation. This study confirms that in patients with established osteoporosis, there is also a distinct group with a low vitamin D and a blunted PTH level and that Mg deficiency (as measured by the Mg loading test) is an important contributing factor.

title: Vitamin D: The "sunshine" vitamin.

text: Vitamin D insufficiency affects almost 50% of the population worldwide. An estimated 1 billion people worldwide, across all ethnicities and age groups, have a vitamin D deficiency (VDD). This pandemic of hypovitaminosis D can mainly be attributed to lifestyle (for example, reduced outdoor activities) and environmental (for example, air pollution) factors that reduce exposure to sunlight, which is required for ultraviolet-B (UVB)-induced vitamin D production in the skin. High prevalence of vitamin D insufficiency is a particularly important public health issue because hypovitaminosis D is an independent risk factor for total mortality in the general population. Current studies suggest that we may need more vitamin D than presently recommended to prevent chronic disease. As the number of people with VDD continues to increase, the importance of this hormone in overall health and the prevention of chronic diseases are at the forefront of research. VDD is very common in all age groups. As few foods contain vitamin D, guidelines recommended supplementation at suggested daily intake and tolerable upper limit levels. It is also suggested to measure the serum 25-hydroxyvitamin D level as the initial diagnostic test in patients at risk for deficiency. Treatment with either vitamin D2 or vitamin D3 is recommended for deficient patients. A meta-analysis published in 2007 showed that vitamin D supplementation was associated with significantly reduced mortality. In this review, we will summarize the mechanisms that are presumed to underlie the relationship between vitamin D and understand its biology and clinical implications.

title: Vitamin D status: measurement, interpretation, and clinical application.

text: Vitamin D, the sunshine vitamin, is now recognized not only for its importance in promoting bone health in children and adults but also for other health benefits, including reducing the risk of chronic diseases such as autoimmune diseases, common cancer, and cardiovascular disease. Vitamin D made in the skin or ingested in the diet is biologically inert and requires 2 successive hydroxylations first in the liver on carbon 25 to form 25-hydroxyvitamin D [25(OH)D], and then in the kidney for a hydroxylation on carbon 1 to form the biologically active form of vitamin D, 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. With the identification of 25(OH)D and 1,25(OH)(2)D, methods were developed to measure these metabolites in the circulation. Serum 25(OH)D is the barometer for vitamin D status. Serum 1,25(OH)(2)D provides no information about vitamin D status and is often normal or even increased as the result of secondary hyperparathyroidism associated with vitamin D deficiency. Most experts agree that 25(OH)D of <20 ng/mL is considered to be vitamin D deficiency, whereas a 25(OH)D of 21-29 ng/mL is considered to be insufficient. The goal should be to maintain both children and adults at a level >30 ng/mL to take full advantage of all the health benefits that vitamin D provides.

title: Environmental factors that influence the cutaneous production of vitamin D

text: All vertebrates, including humans, obtain most of their daily vitamin D requirement from casual exposure to sunlight. During exposure to sunlight, the solar ultraviolet B photons (290-315 nm) penetrate into the skin where they cause the photolysis of 7-dehydrocholesterol to precholecalciferol. Once formed, precholecalciferol undergoes a thermally induced rearrangement of its double bonds to form cholecalciferol. An increase in skin pigmentation, aging, and the topical application of a sunscreen diminishes the cutaneous production of cholecalciferol. Latitude, season, and time of day as well as ozone pollution in the atmosphere influence the number of solar ultraviolet B photons that reach the earth's surface, and thereby, alter the cutaneous production of cholecalciferol. In Boston, exposure to sunlight during the months of November through February will not produce any significant amounts of cholecalciferol in the skin. Because windowpane glass absorbs ultraviolet B radiation, exposure of sunlight through glass windows will not result in any production of cholecalciferol. It is now recognized that vitamin D insufficiency and vitamin D deficiency are common in elderly people, especially in those who are infirm and not exposed to sunlight or who live at latitudes that do not provide them with sunlight-mediated cholecalciferol during the winter months. Vitamin D insufficiency and deficiency exacerbate osteoporosis, cause osteomalacia, and increase the risk of skeletal fractures. Vitamin D insufficiency and deficiency can be prevented by encouraging responsible exposure to sunlight and/or consumption of a multivitamin tablet that contains 10 micrograms (400 IU) vitamin D.

title: Vitamin D and obesity: current perspectives and future directions.

text: In recent years, new functional roles of vitamin D beyond its traditional role in calcium homoeostasis and bone metabolism have emerged linking the fat-soluble vitamin to various non-communicable diseases. Vitamin D deficiency (25-hydroxyvitamin D (25(OH)D) < 25-30 nmol/l) and sub-optimal status (25(OH)D < 50-100 nmol/l) are increasingly associated with unfavourable metabolic phenotypes, including insulin resistance, type 2 diabetes and CVD; conditions also commonly linked with overweight and obesity. Early studies reported poor vitamin D status in the morbidly obese. More recently, it has been observed that a graded relationship between vitamin D status and BMI, or specifically adiposity, exists in the general population. A number of hypotheses have been proposed to explain the potential mechanisms whereby alterations in the vitamin D endocrine system occur in the obese state. Plausible explanations include sequestration in adipose tissue, volumetric dilution or negative feedback mechanisms from increased circulating 1,25-dihydroxyvitamin D3. Others hypothesise that heavier individuals may partake in less outdoor activity, may also cover-up and wear more clothing than leaner individuals, thus decreasing sun exposure and limiting endogenous production of cholecalciferol in the skin. Moreover, in some but not all studies, BMI and adiposity have been negatively associated with the change in vitamin D status following vitamin D supplementation. It therefore remains unclear if body size and/or adiposity should be taken into account when determining the dietary requirements for vitamin D. This review will evaluate the current evidence linking vitamin D status and supplementation to overweight and obesity, and discuss the implications for setting dietary requirements.

title: Lipid-based nutrient supplement increases the birth size of infants of primiparous women in Ghana.

text:
BACKGROUND The International Lipid-Based Nutrient Supplements Project developed a small-quantity (20 g/d) lipid-based nutrient supplement (LNS) for pregnant and lactating women.
 OBJECTIVE We evaluated the effects of prenatal LNS supplementation on fetal growth.
 DESIGN In a community-based, partially double-blind, individually randomized controlled trial, 1320 women ≤20 wk pregnant received 60 mg Fe/400 μg folic acid (IFA), or 1-2 Recommended Dietary Allowances of 18 micronutrients, including 20 mg Fe (MMN), or LNS with the same micronutrients as the MMN group, plus 4 minerals and macronutrients contributing 118 kcal (LNS) daily until delivery. Fetal growth was compared across groups by using intention-to-treat analysis. The primary outcome was birth length.
 RESULTS This analysis included 1057 women (IFA = 349, MMN = 354, LNS = 354). Groups did not differ significantly in mean birth length, length-for-age z score (LAZ), head circumference, or percentage low birth length but differed in mean birth weight (P = 0.044), weight-for-age z score (WAZ; P = 0.046), and BMI-for-age z score (BMIZ; P = 0.040), with a trend toward differences in low birth weight (P = 0.069). In pairwise comparisons, the LNS group had greater mean birth weight (+85 g; P = 0.040), WAZ (+0.19; P = 0.045), and BMIZ (+0.21; P = 0.035) and a lower risk of low birth weight (RR: 0.61, 95% CI: 0.39, 0.96; P = 0.032) than did the IFA group. The other group differences were not significant. The effect of intervention was modified by mother's parity, age, height, baseline hemoglobin, household food insecurity, and child sex, with parity being the most consistent modifier. Among primiparous women (IFA = 131; MMN = 110; LNS = 128), the LNS group had greater mean birth length (+0.91 cm; P = 0.001), LAZ (+0.47; P = 0.001), weight (+237 g; P < 0.001), WAZ (+0.56; P < 0.001), BMIZ (+0.52; P < 0.001), head circumference (0.50 cm; P = 0.017), and head circumference-for-age z score (+0.40; P = 0.022) than did the IFA group; similar differences were found when comparing the LNS and MMN groups among primiparous women, and no group differences were found among multiparous women.
 CONCLUSION Prenatal LNS supplementation can improve fetal growth among vulnerable women in Ghana, particularly primiparous women. This trial was registered at clinicaltrials.gov as NCT00970866.

title: Global vitamin D levels in relation to age, gender, skin pigmentation and latitude: an ecologic meta-regression analysis

text: We performed a meta-analysis of cross-sectional studies on serum 25(OH)D status globally. Serum 25(OH)D levels on average were 54 nmol/l, were higher in women than men, and higher in Caucasians than in non-Caucasians. There was no trend in serum 25(OH)D level with latitude. Vitamin D deficiency was widespread. We studied vitamin D status (expressed as serum 25-hydroxy-vitamin D [25(OH)D]) in native subjects worldwide. Meta-analysis and meta-regression of studies reporting on 25(OH)D in healthy subjects retrieved from Pubmed, Embase and Web of Science using the terms “serum”, “25-hydroxy-vitamin D”, “cholecalciferol”, and “human”. A total of 394 studies were included. The mean 25(OH)D level was 54 nmol/l (95% CI: 52–57 nmol/l). Women had borderline significantly higher 25(OH)D levels than men, and Caucasians had higher levels than non-Caucasians. 25(OH)D levels were higher in subjects aged >15 years than in younger subjects. Unadjusted there was no significant decrease in 25(OH)D with latitude (slope of curve −0.03 ± 0.12 nmol/l per degree latitude north or south of equator, p = 0.8). There was a significant decline with latitude for Caucasians (−0.69 ± 0.30 nmol/l per degree, p = 0.02), but not for non-Caucasians (0.03 ± 0.39 nmol/l per degree, p = 0.14). After adjustment for age, gender, and ethnicity, no overall correlation was present between 25(OH)D and latitude (−0.29 ± 0.24 nmol/l per degree, p = 0.23). There was no overall influence of latitude on 25(OH)D. However, in separate analyses 25(OH)D decreased with latitude in Caucasians but not in non-Caucasians. A widespread global vitamin D insufficiency was present compared with proposed threshold levels.

title: Genetic and environmental determinants of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels in Hispanic and African Americans.

text:
CONTEXT Vitamin D deficiency is associated with many adverse health outcomes, yet little is known about the genetic epidemiology of vitamin D or its metabolites.
 OBJECTIVE Our objective was to examine the relationship among three vitamin D-related genes and levels of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] in Hispanics (HAs) and African Americans (AAs).
 DESIGN AND SETTING The cross-sectional Insulin Resistance Atherosclerosis Family Study recruited and examined subjects in: Los Angeles, California (AAs; 513 individuals from 42 families); San Luis Valley (SLV), Colorado (HAs; 513 individuals from 30 families); and San Antonio (SA), Texas (HAs; 504 individuals from 58 families).
 MAIN OUTCOME MEASURES Plasma levels of 25(OH)D and 1,25(OH)2D were measured.
 RESULTS Levels of 25(OH)D were highest in SLV-HAs [18.3 +/- 7.7 ng/ml (45.7 +/- 19.2 nmol/liter)], lower in SA-HAs [14.6 +/- 6.4 ng/ml (36.4 +/- 16.0 nmol/liter)], and lowest in AAs [11.0 +/- 5.4 ng/ml (27.5 +/- 13.5 nmol/liter)]. Levels of 1,25(OH)2D were similar in AAs [43.5 +/- 13.9 pg/ml (113.1 +/- 36.1 pmol/liter)] and SLV-HAs [43.2 +/- 13.3 pg/ml (112.3 +/- 34.6 pmol/liter)], but higher in SA-HAs [48.6 +/- 17.0 pg/ml (126.4 +/- 44.2 pmol/liter)]. After adjusting for gender and age within the site, two single nucleotide polymorphisms (SNPs) in the vitamin D binding protein gene (DBP), rs4588 and rs7041, were associated with 25(OH)D, and one SNP in the DBP, rs4588, was associated with 1,25(OH)2D at all three study centers.
 CONCLUSIONS SNPs in the DBP are associated with levels of 25(OH)D and 1,25(OH)2D in HA and AA participants in the Insulin Resistance Atherosclerosis Family Study.

title: Intracellular transport of fat-soluble vitamins A and E.

text: Vitamins are compounds that are essential for the normal growth, reproduction and functioning of the human body. Of the 13 known vitamins, vitamins A, D, E and K are lipophilic compounds and are therefore called fat-soluble vitamins. Because of their lipophilicity, fat-soluble vitamins are solubilized and transported by intracellular carrier proteins to exert their actions and to be metabolized properly. Vitamin A and its derivatives, collectively called retinoids, are solubilized by intracellular retinoid-binding proteins such as cellular retinol-binding protein (CRBP), cellular retinoic acid-binding protein (CRABP) and cellular retinal-binding protein (CRALBP). These proteins act as chaperones that regulate the metabolism, signaling and transport of retinoids. CRALBP-mediated intracellular retinoid transport is essential for vision in human. α-Tocopherol, the main form of vitamin E found in the body, is transported by α-tocopherol transfer protein (α-TTP) in hepatic cells. Defects of α-TTP cause vitamin E deficiency and neurological disorders in humans. Recently, it has been shown that the interaction of α-TTP with phosphoinositides plays a critical role in the intracellular transport of α-tocopherol and is associated with familial vitamin E deficiency. In this review, we summarize the mechanisms and biological significance of the intracellular transport of vitamins A and E.

title: Plasma vitamin D metabolites and risk of colorectal cancer in women.

text:
OBJECTIVE Experimental evidence suggests that 1,25-dihydroxyvitamin D and its precursor, 25-hydroxyvitamin D [25(OH)D], may aid in the prevention of colorectal cancer. We therefore examined risk in relation to plasma concentrations of these vitamin D metabolites.
 METHODS In a nested case-control study among women in the Nurses' Health Study, we identified 193 colorectal cancer cases, ages 46 to 78 years, diagnosed up to 11 years after blood collection. Two controls were matched per case on year of birth and month of blood draw. Odds ratios (OR) for risk of colorectal cancer were calculated using conditional logistic regression adjusted for body mass index, physical activity, smoking, family history, use of hormone replacement therapy, aspirin use, and dietary intakes.
 RESULTS We found a significant inverse linear association between plasma 25(OH)D and risk of colorectal cancer (P = 0.02). Among women in the highest quintile, the OR (95% confidence interval) was 0.53 (0.27-1.04). This inverse association remained strong when limited to women > or =60 years at blood collection (P = 0.006) but was not apparent among the younger women (P = 0.70). Benefit from higher 25(OH)D concentrations was observed for cancers at the distal colon and rectum (P = 0.02) but was not evident for those at the proximal colon (P = 0.81). In contrast to 25(OH)D, we did not observe an association between 1,25-dihydroxyvitamin D and colorectal cancer, although risk was elevated among the women in the highest quintile if they were also in the lower half of the 25(OH)D distribution (OR, 2.52; 95% confidence interval, 1.04-6.11).
 CONCLUSION From these results and supporting evidence from previous studies, we conclude that higher plasma levels of 25(OH)D are associated with a lower risk of colorectal cancer in older women, particularly for cancers at the distal colon and rectum.

title: Molecular Mechanisms of Vitamin D Action

text: The hormonal metabolite of vitamin D, 1α,25-dihydroxyvitamin D3 (1,25D), initiates biological responses via binding to the vitamin D receptor (VDR). When occupied by 1,25D, VDR interacts with the retinoid X receptor (RXR) to form a heterodimer that binds to vitamin D responsive elements in the region of genes directly controlled by 1,25D. By recruiting complexes of either coactivators or corepressors, ligand-activated VDR-RXR modulates the transcription of genes encoding proteins that promulgate the traditional functions of vitamin D, including signaling intestinal calcium and phosphate absorption to effect skeletal and calcium homeostasis. Thus, vitamin D action in a particular cell depends upon the metabolic production or delivery of sufficient concentrations of the 1,25D ligand, expression of adequate VDR and RXR coreceptor proteins, and cell-specific programming of transcriptional responses to regulate select genes that encode proteins that function in mediating the effects of vitamin D. For example, 1,25D induces RANKL, SPP1 (osteopontin), and BGP (osteocalcin) to govern bone mineral remodeling; TRPV6, CaBP9k, and claudin 2 to promote intestinal calcium absorption; and TRPV5, klotho, and Npt2c to regulate renal calcium and phosphate reabsorption. VDR appears to function unliganded by 1,25D in keratinocytes to drive mammalian hair cycling via regulation of genes such as CASP14, S100A8, SOSTDC1, and others affecting Wnt signaling. Finally, alternative, low-affinity, non-vitamin D VDR ligands, e.g., lithocholic acid, docosahexaenoic acid, and curcumin, have been reported. Combined alternative VDR ligand(s) and 1,25D/VDR control of gene expression may delay chronic disorders of aging such as osteoporosis, type 2 diabetes, cardiovascular disease, and cancer.

title: Estimation of the dietary requirement for vitamin D in healthy adults.

text:
BACKGROUND Knowledge gaps have contributed to considerable variation among international dietary recommendations for vitamin D.   OBJECTIVE We aimed to establish the distribution of dietary vitamin D required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above several proposed cutoffs (ie, 25, 37.5, 50, and 80 nmol/L) during wintertime after adjustment for the effect of summer sunshine exposure and diet.
 DESIGN A randomized, placebo-controlled, double-blind 22-wk intervention study was conducted in men and women aged 20-40 y (n = 238) by using different supplemental doses (0, 5, 10, and 15 microg/d) of vitamin D(3) throughout the winter. Serum 25(OH)D concentrations were measured by using enzyme-linked immunoassay at baseline (October 2006) and endpoint (March 2007).
 RESULTS There were clear dose-related increments (P < 0.0001) in serum 25(OH)D with increasing supplemental vitamin D(3). The slope of the relation between vitamin D intake and serum 25(OH)D was 1.96 nmol x L(-1) x microg(-1) intake. The vitamin D intake that maintained serum 25(OH)D concentrations of >25 nmol/L in 97.5% of the sample was 8.7 microg/d. This intake ranged from 7.2 microg/d in those who enjoyed sunshine exposure, 8.8 microg/d in those who sometimes had sun exposure, and 12.3 microg/d in those who avoided sunshine. Vitamin D intakes required to maintain serum 25(OH)D concentrations of >37.5, >50, and >80 nmol/L in 97.5% of the sample were 19.9, 28.0, and 41.1 microg/d, respectively.
 CONCLUSION The range of vitamin D intakes required to ensure maintenance of wintertime vitamin D status [as defined by incremental cutoffs of serum 25(OH)D] in the vast majority (>97.5%) of 20-40-y-old adults, considering a variety of sun exposure preferences, is between 7.2 and 41.1 microg/d.

title: Calcium absorption varies within the reference range for serum 25-hydroxyvitamin D.

text:
BACKGROUND Calcium absorption is generally considered to be impaired under conditions of vitamin D deficiency, but the vitamin D status that fully normalizes absorption is not known for humans.
 OBJECTIVE To quantify calcium absorption at two levels of vitamin D repletion, using pharmacokinetic methods and commercially marketed calcium supplements.
 DESIGN Two experiments performed in the spring of the year, one year apart. In the first, in which participants were pretreated with 25-hydroxyvitamin D (25OHD), mean serum 25OHD concentration was 86.5 nmol/L; and in the other, with no pretreatment, mean serum concentration was 50.2 nmol/L. Participants received 500 mg oral calcium loads as a part of a standard low calcium breakfast. A low calcium lunch was provided at mid-day. Blood was obtained fasting and at frequent intervals for 10 to 12 hours thereafter.
 METHODS Relative calcium absorption at the two 25OHD concentrations was estimated from the area under the curve (AUC) for the load-induced increment in serum total calcium.
 RESULTS AUC(9) (+/- SEM), was 3.63 mg hr/dL +/- 0.234 in participants pretreated with 25OHD and 2.20 +/- 0.240 in those not pretreated (P < 0.001). In brief, absorption was 65% higher at serum 25OHD levels averaging 86.5 nmol/L than at levels averaging 50 nmol/L (both values within the nominal reference range for this analyte).
 CONCLUSIONS Despite the fact that the mean serum 25OHD level in the experiment without supplementation was within the current reference ranges, calcium absorptive performance at 50 nmol/L was significantly reduced relative to that at a mean 25OHD level of 86 nmol/L. Thus, individuals with serum 25-hydroxyvitamin D levels at the low end of the current reference ranges may not be getting the full benefit from their calcium intake. We conclude that the lower end of the current reference range is set too low.

title: Vitamin d deficiency in postmenopausal women - biological correlates.

text:
INTRODUCTION Low vitamin D (VD) is associated with secondary hyperparathyroidism and both contribute to deleterious consequences (reduced bone mineral density (BMD), risk of fractures and falls).
 OBJECTIVE To study the VD status and biological correlates in a group of postmenopausal women.    MATERIAL AND METHODS We studied 123 postmenopausal women evaluated in the C.I.Parhon National Institute of Endocrinology, the Pituitary and Neuroendocrine Diseases department. All cases had been reffered for the evaluation of BMD by the general practitioner. The evaluation included serum measurements of total and ionised calcium, phosphorus, alkaline phosphatase (ALP), 25 hydroxi vitaminD (25OHD), parathyroid hormone (PTH), osteocalcin, betacrosslaps. Central DXA osteodensitometry was performed.
 RESULTS 91.9% of cases had 25OHD serum levels below 30 ng/ml (74.8% had VD deficiency, 17.1% VD insufficiency). Only 8.1% had sufficient VD levels. A history of fragility fractures was present in 45.83% of the osteoporotic patients, 27.27% of the osteopenic ones and 15.15% of the women with normal BMD. 32 women (26%) were on VD supplementation at the time of evaluation. Among these subjects, the 25OHD level was significantly higher in those with prior fragility fractures (p=0.018) and osteoporosis (p=0.008). 25OHD concentration negatively correlated with PTH, alkaline phosphatase (ALP) and osteocalcin. The bone markers evaluated had a significant inverse correlation with the radius BMD, T and Z scores (p=0.004). 27.17% of the cases with VD deficiency had secondary hyperparathyroidism. The 25OHD concentration was significantly lower in these cases (p=0.000).
 CONCLUSIONS VD insufficiency is widely prevalent but still under-recognized and under-treated, possibly leading to secondary hyperparathyroidism. The compliance to VD supplementation is lower in subjects without osteoporosis or fragility fractures. Primary prevention measures should be more actively implemented.

title: Vitamin D and prevention of colorectal cancer.

text:
BACKGROUND Inadequate photosynthesis or oral intake of Vitamin D are associated with high incidence rates of colorectal cancer, but the dose-response relationship has not been adequately studied.
 METHODS Dose-response gradients from observational studies of Vitamin D intake and serum 25-hydroxyvitamin D were plotted as trend lines. The point on each linear trend line corresponding to an odds ratio of 0.50 provided the prediagnostic Vitamin D intake or 25-hydroxyvitamin D concentration associated with 50% lower risk compared to <100IU/day Vitamin D or <13ng/ml serum 25-hydroxyvitamin D. Medians of these values were determined.
 RESULTS Overall, individuals with >or=1000IU/day oral Vitamin D (p<0.0001) or >or=33ng/ml (82nmol/l) serum 25-hydroxyvitamin D (p<0.01) had 50% lower incidence of colorectal cancer compared to reference values.
 CONCLUSIONS Intake of 1000IU/day of Vitamin D, half the safe upper intake established by the National Academy of Sciences, was associated with 50% lower risk. Serum 25-hydroxyvitamin D of 33ng/ml, which is known to be safe, also was associated with 50% lower risk. Prompt public health action is needed to increase intake of Vitamin D(3) to 1000IU/day, and to raise 25-hydroxyvitamin D by encouraging a modest duration of sunlight exposure.

title: Relationship between serum parathyroid hormone levels, vitamin D sufficiency, and calcium intake.

text:
CONTEXT Adequate vitamin D status for optimum bone health has received increased recognition in recent years; however, the ideal intake is not known. Serum 25-hydroxyvitamin D is the generally accepted indicator of vitamin D status, but no universal reference level has been reached.
 OBJECTIVE To investigate the relative importance of high calcium intake and serum 25-hydroxyvitamin D for calcium homeostasis, as determined by serum intact parathyroid hormone (PTH).
 DESIGN, SETTING, AND PARTICIPANTS Cross-sectional study of 2310 healthy Icelandic adults who were divided equally into 3 age groups (30-45 years, 50-65 years, or 70-85 years) and recruited from February 2001 to January 2003. They were administered a semi-quantitative food frequency questionnaire, which assessed vitamin D and calcium intake. Participants were further divided into groups according to calcium intake (<800 mg/d, 800-1200 mg/d, and >1200 mg/d) and serum 25-hydroxyvitamin D level (<10 ng/mL, 10-18 ng/mL, and >18 ng/mL).
 MAIN OUTCOME MEASURE Serum intact PTH as determined by calcium intake and vitamin D.   RESULTS A total of 944 healthy participants completed all parts of the study. After adjusting for relevant factors, serum PTH was lowest in the group with a serum 25-hydroxyvitamin D level of more than 18 ng/mL but highest in the group with a serum 25-hydroxyvitamin D level of less than 10 ng/mL. At the low serum 25-hydroxyvitamin D level (<10 ng/mL), calcium intake of less than 800 mg/d vs more than 1200 mg/d was significantly associated with higher serum PTH (P = .04); and at a calcium intake of more than 1200 mg/d, there was a significant difference between the lowest and highest vitamin D groups (P = .04).
 CONCLUSIONS As long as vitamin D status is ensured, calcium intake levels of more than 800 mg/d may be unnecessary for maintaining calcium metabolism. Vitamin D supplements are necessary for adequate vitamin D status in northern climates.

title: Ascorbic-acid transporter Slc23a1 is essential for vitamin C transport into the brain and for perinatal survival

text: The only proven requirement for ascorbic acid (vitamin C) is in preventing scurvy, presumably because it is a cofactor for hydroxylases required for post-translational modifications that stabilize collagen. We have created mice deficient in the mouse ortholog (solute carrier family 23 member 1 or Slc23a1) of a rat ascorbic-acid transporter, Svct2 (ref. 4). Cultured embryonic fibroblasts from homozygous Slc23a1−/− mice had less than 5% of normal ascorbic-acid uptake. Ascorbic-acid levels were undetectable or markedly reduced in the blood and tissues of Slc23a1−/− mice. Prenatal supplementation of pregnant females did not elevate blood ascorbic acid in Slc23a1−/− fetuses, suggesting Slc23a1 is important in placental ascorbic-acid transport. Slc23a1−/− mice died within a few minutes of birth with respiratory failure and intraparenchymal brain hemorrhage. Lungs showed no postnatal expansion but had normal surfactant protein B levels. Brain hemorrhage was unlikely to be simply a form of scurvy since Slc23a1−/− mice showed no hemorrhage in any other tissues and their skin had normal skin 4-hydroxyproline levels despite low ascorbic-acid content. We conclude that Slc23a1 is required for transport of ascorbic acid into many tissues and across the placenta. Deficiency of the transporter is lethal in newborn mice, thereby revealing a previously unrecognized requirement for ascorbic acid in the perinatal period.

title: Mammographic density, plasma vitamin D levels and risk of breast cancer in postmenopausal women.

text: Mammographic density is a strong risk factor for breast cancer, but the underlying biology for this association is unknown. Studies suggest that vitamin D may reduce breast cancer risk and dietary vitamin D intake has been associated with reduced breast density. We conducted a case-control study nested within the Nurses' Health Study cohort consisting of 463 and 497 postmenopausal cases and controls, respectively. We examined the association between mammographic density and plasma levels of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. We assessed whether plasma vitamin D metabolites modify the association between breast density and breast cancer. Percent mammographic density was measured from digitized film mammograms. Generalized linear models were used to determine mean percent breast density per quartile of vitamin D metabolite. Logistic regression models were used to calculate relative risks and confidence intervals. All models were adjusted for matching variables and potential confounders. We found no cross-sectional association between circulating levels of 25(OH)D or 1,25(OH)(2)D with mammographic density. Women in the highest tertile of mammographic density and lowest tertile of plasma 25(OH)D had 4 times greater risk of breast cancer than women with the lowest mammographic density and highest plasma 25(OH)D levels (RR = 3.8; 95% CI: 2.0-7.3). The overall interaction between mammographic density and plasma 25(OH)D was nonsignificant (p-het = 0.20). These results indicate that the association between mammographic density and breast cancer is independent of plasma vitamin D metabolites in postmenopausal women. Further research examining vitamin D, mammographic density and breast cancer risk is warranted.

title: Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes.

text: Recent evidence suggests that vitamin D intakes above current recommendations may be associated with better health outcomes. However, optimal serum concentrations of 25-hydroxyvitamin D [25(OH)D] have not been defined. This review summarizes evidence from studies that evaluated thresholds for serum 25(OH)D concentrations in relation to bone mineral density (BMD), lower-extremity function, dental health, and risk of falls, fractures, and colorectal cancer. For all endpoints, the most advantageous serum concentrations of 25(OH)D begin at 75 nmol/L (30 ng/mL), and the best are between 90 and 100 nmol/L (36-40 ng/mL). In most persons, these concentrations could not be reached with the currently recommended intakes of 200 and 600 IU vitamin D/d for younger and older adults, respectively. A comparison of vitamin D intakes with achieved serum concentrations of 25(OH)D for the purpose of estimating optimal intakes led us to suggest that, for bone health in younger adults and all studied outcomes in older adults, an increase in the currently recommended intake of vitamin D is warranted. An intake for all adults of > or =1000 IU (25 microg) [DOSAGE ERROR CORRECTED] vitamin D (cholecalciferol)/d is needed to bring vitamin D concentrations in no less than 50% of the population up to 75 nmol/L. The implications of higher doses for the entire adult population should be addressed in future studies.


query: Vitamin D is an important factor in the relationship between calcium and parathyroid hormone.

title: Vitamin D: The "sunshine" vitamin.

text: Vitamin D insufficiency affects almost 50% of the population worldwide. An estimated 1 billion people worldwide, across all ethnicities and age groups, have a vitamin D deficiency (VDD). This pandemic of hypovitaminosis D can mainly be attributed to lifestyle (for example, reduced outdoor activities) and environmental (for example, air pollution) factors that reduce exposure to sunlight, which is required for ultraviolet-B (UVB)-induced vitamin D production in the skin. High prevalence of vitamin D insufficiency is a particularly important public health issue because hypovitaminosis D is an independent risk factor for total mortality in the general population. Current studies suggest that we may need more vitamin D than presently recommended to prevent chronic disease. As the number of people with VDD continues to increase, the importance of this hormone in overall health and the prevention of chronic diseases are at the forefront of research. VDD is very common in all age groups. As few foods contain vitamin D, guidelines recommended supplementation at suggested daily intake and tolerable upper limit levels. It is also suggested to measure the serum 25-hydroxyvitamin D level as the initial diagnostic test in patients at risk for deficiency. Treatment with either vitamin D2 or vitamin D3 is recommended for deficient patients. A meta-analysis published in 2007 showed that vitamin D supplementation was associated with significantly reduced mortality. In this review, we will summarize the mechanisms that are presumed to underlie the relationship between vitamin D and understand its biology and clinical implications.

title: Vitamin D insufficiency and the blunted PTH response in established osteoporosis: the role of magnesium deficiency

text: Vitamin D insufficiency is common, however within individuals, not all manifest the biochemical effects of PTH excess. This further extends to patients with established osteoporosis. The mechanism underlying the blunted PTH response is unclear but may be related to magnesium (Mg) deficiency. The aims of this study were to compare in patients with established osteoporosis and differing degrees of vitamin D and PTH status : (1) the presence of Mg deficiency using the standard Mg loading test (2) evaluate the effects of Mg loading on the calcium-PTH endocrine axis (3) determine the effects of oral, short term Mg supplementation on the calcium-PTH endocrine axis and bone turnover. 30 patients (10 women in 3 groups) were evaluated prospectively measuring calcium, PTH, Mg retention (Mg loading test), dietary nutrient intake (calcium, vitamin D, Mg) and bone turnover markers (serum CTX & P1CP). Multivariate analysis controlling for potential confounding baseline variable was undertaken for the measured outcomes. All subjects, within the low vitamin D and low PTH group following the magnesium loading test had evidence of Mg depletion [mean(SD) retention 70.3%(12.5)] and showed an increase in calcium 0.06(0.01) mmol/l [95% CI 0.03, 0.09, p=0.007], together with a rise in PTH 13.3 ng/l (4.5) [95% CI 3.2, 23.4, p=0.016] compared to baseline. Following oral supplementation bone turnover increased: CTX 0.16 (0.06) mcg/l [95%CI 0.01, 0.32 p=0.047]; P1CP 13.1 (5.7) mcg/l [95% CI 0.29, 26.6 p=0.049]. In subjects with a low vitamin D and raised PTH mean retention was 55.9%(14.8) and in the vitamin replete group 36.1%(14.4), with little change in both acute markers of calcium homeostasis and bone turnover markers following both the loading test and oral supplementation. This study confirms that in patients with established osteoporosis, there is also a distinct group with a low vitamin D and a blunted PTH level and that Mg deficiency (as measured by the Mg loading test) is an important contributing factor.

title: Calcium and peak bone mass.

text: On the basis of previous epidemiological, clinical and experimental studies, it was demonstrated that adequate calcium intake during growth may influence peak bone mass/density, and may be instrumental in preventing subsequent postmenopausal and senile osteoporosis. Calcium intake during adolescence appears to affect skeletal calcium retention directly, and a calcium intake of up to 1600 mg d-1 may be required. Therefore, adolescent females at the time of puberty probably represent the optimal population for early prevention of osteoporosis with calcium. Young individuals must be in positive calcium balance to provide the calcium necessary for skeletal modelling and consolidation, but the degree of positive balance required to achieve peak bone mass and density is unknown. To assess calcium requirements in young individuals, and also to evaluate the determinants of calcium metabolism during the period of acquisition of peak bone mass, 487 calcium balances from previously published reports have been collected and analysed according to developmental phase and calcium intake. The results of this analysis showed that calcium intake and skeletal modelling/turnover are the most important determinants of calcium balance during growth. The highest requirements for calcium are during infancy and adolescence, and then during childhood and young adulthood. Infants (adequate vitamin D supply) and adolescents have higher calcium absorption than children and young adults to meet their high calcium requirements. Calcium absorption during the periods of rapid bone modelling/turnover is probably mediated by Nicolaysen's endogenous factor. Urinary calcium increases with age, and reaches a maximum by the end of puberty. The results also show that calcium intake has little effect on urinary calcium excretion during the period of most rapid skeletal formation: a weak correlation is present in children and young adults. On the basis of the above studies it was suggested that the RDA for calcium should be higher than currently established for children, adolescents, and young adults, in order to ensure a level of skeletal retention of calcium sufficient for maximal peak bone mass. In addition to nutrition, heredity (both parents) and endocrine factors (sexual development) appear to have profound effects on peak bone mass formation. Most of the skeletal mass will be accumulated by late adolescence, indicating early timing of peak bone mass.

title: Folate and vitamin B6 from diet and supplements in relation to risk of coronary heart disease among women.

text:
CONTEXT Hyperhomocysteinemia is caused by genetic and lifestyle influences, including low intakes of folate and vitamin B6. However, prospective data relating intake of these vitamins to risk of coronary heart disease (CHD) are not available.
 OBJECTIVE To examine intakes of folate and vitamin B6 in relation to the incidence of nonfatal myocardial infarction (MI) and fatal CHD.
 DESIGN Prospective cohort study.
 SETTING AND PATIENTS In 1980, a total of 80082 women from the Nurses' Health Study with no previous history of cardiovascular disease, cancer, hypercholesterolemia, or diabetes completed a detailed food frequency questionnaire from which we derived usual intake of folate and vitamin B6.
 MAIN OUTCOME MEASURE Nonfatal MI and fatal CHD confirmed by World Health Organization criteria.
 RESULTS During 14 years of follow-up, we documented 658 incident cases of nonfatal MI and 281 cases of fatal CHD. After controlling for cardiovascular risk factors, including smoking and hypertension and intake of alcohol, fiber, vitamin E, and saturated, polyunsaturated, and trans fat, the relative risks (RRs) of CHD between extreme quintiles were 0.69 (95% confidence interval [CI], 0.55-0.87) for folate (median intake, 696 microg/d vs 158 microg/d) and 0.67 (95% CI, 0.53-0.85) for vitamin B6 (median intake, 4.6 mg/d vs 1.1 mg/d). Controlling for the same variables, the RR was 0.55 (95% CI, 0.41-0.74) among women in the highest quintile of both folate and vitamin B6 intake compared with the opposite extreme. Risk of CHD was reduced among women who regularly used multiple vitamins (RR=0.76; 95% CI, 0.65-0.90), the major source of folate and vitamin B6, and after excluding multiple vitamin users, among those with higher dietary intakes of folate and vitamin B6. In a subgroup analysis, compared with nondrinkers, the inverse association between a high-folate diet and CHD was strongest among women who consumed up to 1 alcoholic beverage per day (RR =0.69; 95% CI, 0.49-0.97) or more than 1 drink per day (RR=0.27; 95% CI, 0.13-0.58).
 CONCLUSION These results suggest that intake of folate and vitamin B6 above the current recommended dietary allowance may be important in the primary prevention of CHD among women.

title: Increased growth after long-term oral 1alpha,25-vitamin D3 in childhood renal osteodystrophy.

text: We evaluated oral 1,25-vitamin D3 for as long as 26 months in six prepubescent children with renal osteodystrophy previously treated with vitamin D2. Therapy was given at 14 to 41 ng per kilogram per day to correct hypocalcemia and reverse bone disease. Serum levels of 1,25-vitamin D3 were initially reduced at 15 +/- 5 pg per milliliter (mean +/- S.E.M.) and after treatment rose to 54 +/- 13. Serum calcium rose from 7.5 +/- 1.6 mg per deciliter (mean +/- S.D.) to 9.8 +/- 0.6 after one month (P less than 0.02). Alkaline phosphatase activity fell from 536 +/- 298 to 208 +/- 91 IU per liter after 12 months (P less than 0.05). Serum immunoreactive parathyroid levels fell from 900 +/- 562 microliter eq per milliliter 411 +/- 377. Healing of rickets and subperiosteal erosions was found. Remineralization of bone was demonstrated by the photon absorption technic. In four patients growth velocity, evaluated for 12 months before and after therapy, increased from 2.6 +/- 0.8 to 8.0 +/- 3.2 cm per year. Growth velocity per year increased from less than third percentile in each to the 10th to 97th percentile after therapy. Height increment ranged from 27 to 113 per cent of that expected for change in chronologic age and 40 to 114 per cent expected for change in bone age after therapy. This trial demonstrates that oral 1,25-vitamin D3 can reverse renal bone disease and increase growth in uremic children.

title: [Vitamin D and latitude as environmental factors in multiple sclerosis].

text: Multiple sclerosis (MS) shows a multifold increase in prevalence with an increase in latitudes, both north and south of the equator. One of the potential factors related to the difference of the prevalence is vitamin D, because the strength of ambient ultraviolet light, which is essential for vitamin D production, decreases with increasing latitude. It is known that vitamin D has immunomodulatory functions and suppresses an animal model of MS. It is also considered that vitamin D-related genes are critical susceptible genes for MS. An approach from environmental and genetic aspects is needed to investigate the association between vitamin D and MS.

title: Parathyroid hormone induces E4bp4 messenger ribonucleic acid expression primarily through cyclic adenosine 3',5'-monophosphate signaling in osteoblasts.

text: PTH binding to its receptor activates protein kinase A (PKA), protein kinase C (PKC), and calcium signaling to induce transcription of primary response genes in osteoblasts. Adenovirus E4 promoter-binding protein/nuclear factor regulated by IL-3 (E4BP4/NFIL3), a transcriptional repressor, is a PTH-induced primary response gene in primary mouse osteoblasts (MOBs). Here we investigate the signaling pathway(s) that lead to PTH induction of E4bp4 mRNA expression. Ten and 100 nm PTH induced maximum E4bp4 expression in MOBs. Forskolin (FSK), an adenylate cyclase inducer, 8-bromo-cAMP, a cAMP analog, and phorbol myristate acetate, a PKC activator, increased E4bp4 mRNA levels, whereas ionomycin, a calcium ionophore, had no effect. Pretreatment of cells with 30 microm H89, a PKA inhibitor, strongly inhibited PTH- and FSK-induced E4bp4 expression. In contrast, overnight pretreatment with 1 microm phorbol myristate acetate to down-regulate PKC signaling did not alter PTH and FSK effects. Moreover, PTH (3-34) that does not activate cAMP signaling did not increase E4bp4 expression. Prostaglandin E(2), which signals through cAMP, increased E4bp4 mRNA at all doses, whereas prostaglandin F(2alpha) that primarily activates PKC and calcium signaling, induced E4bp4 only at high doses and fluprostenol that only activates PKC and calcium signaling, had no effect. Finally, 80 microg/kg PTH (1-34) ip injection induced E4bp4 mRNA expression at 1 h in mice. In contrast, 80 microg/kg PTH (3-34) had no effect. Our data suggest that PTH-induced E4bp4 mRNA expression is mediated primarily through cAMP-PKA signaling in vitro and in vivo. In conjunction with our previous report, we hypothesize that E4bp4 attenuates transcription of osteoblastic genes possessing E4bp4 promoter binding sites.

title: Psychobiological Protective Factors Modifying the Association Between Age and Sexual Health in Men: Findings From the Men’s Health 40+ Study

text: Sexual health severely decreases with age. For males older than 40 years, erectile dysfunction (ED) is the most common sexual disorder. Although physical and psychological risk factors for ED have been identified, protective factors are yet to be determined. To date, no study has examined endocrine and psychosocial factors in parallel with regard to their modifying effect on the age-related increase in ED. Two hundred and seventy-one self-reporting healthy men aged between 40 and 75 years provided both psychometric data on sexual function and a set of potential psychosocial protective factors, and saliva samples for the analysis of steroid hormones and proinflammatory cytokines. Around 35% of the participants reported at least a mild form of ED. Direct associations with ED were identified for perceived general health, emotional support, relationship quality, intimacy motivation but not for steroid hormones or proinflammatory markers. Moderation analyses for the association between age and ED revealed positive effects for testosterone (T), dehydroepiandrosterone (DHEA), perceived general health, emotional support, intimacy motivation, and a negative effect for interleukin-6 (all p < .05; f2 > .17). Group differences between older men with and without ED emerged for T, DHEA, and psychometric measures such as perceived general health, emotional support, satisfaction with life, and intimacy motivation (all p < .05; d > .3). Both psychosocial and endocrine parameters moderated the association between age and sexual health. Perceived general health, emotional support, intimacy motivation, and relationship quality emerged as psychosocial protective factors against ED. Higher T and DHEA and lower interleukin-6 levels also buffered against an age-related increase in ED.

title: Subcellular steroid/nuclear receptor dynamics.

text: Steroid hormones, thyroid hormones, retinoic acids, and vitamin D bind to their receptors, which are now called steroid/nuclear receptors, and liganded receptors translocate either intracellularly or intranuclearly and form large protein complexes with cofactors to induce or repress gene transcription. Therefore, steroid/nuclear receptors are ligand-dependent transcription factors. With the advent of green fluorescent protein (GFP) and its color variants, the subcellular distribution of many steroid/nuclear receptors has been found to be much more dynamic than previously thought, with some of the receptors shuttling between the cytoplasm and nucleus. Steroid/nuclear receptors can be divided into three categories based on their unliganded distribution: those that are primarily in the nucleus, those in the cytoplasm, and those with mixed cytoplasmic and nuclear distributions. However, in all cases, the addition of a ligand leads to almost complete nuclear translocation of the receptors. Hormonal stimulation induces intranuclear receptor distribution from a homogeneous pattern to a heterogeneous dot-like image. Ligand binding to steroid/nuclear receptors leads to the recruitment of many proteins including cofactors to provoke the redistribution of receptor complexes in the nucleus. This focal organization could involve more complex events than simple DNA binding sites for transcription. Protein activities and interactions of steroid/nuclear receptors can be imaged and localized in a single cell.

title: Vitamin D status: measurement, interpretation, and clinical application.

text: Vitamin D, the sunshine vitamin, is now recognized not only for its importance in promoting bone health in children and adults but also for other health benefits, including reducing the risk of chronic diseases such as autoimmune diseases, common cancer, and cardiovascular disease. Vitamin D made in the skin or ingested in the diet is biologically inert and requires 2 successive hydroxylations first in the liver on carbon 25 to form 25-hydroxyvitamin D [25(OH)D], and then in the kidney for a hydroxylation on carbon 1 to form the biologically active form of vitamin D, 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. With the identification of 25(OH)D and 1,25(OH)(2)D, methods were developed to measure these metabolites in the circulation. Serum 25(OH)D is the barometer for vitamin D status. Serum 1,25(OH)(2)D provides no information about vitamin D status and is often normal or even increased as the result of secondary hyperparathyroidism associated with vitamin D deficiency. Most experts agree that 25(OH)D of <20 ng/mL is considered to be vitamin D deficiency, whereas a 25(OH)D of 21-29 ng/mL is considered to be insufficient. The goal should be to maintain both children and adults at a level >30 ng/mL to take full advantage of all the health benefits that vitamin D provides.

title: Differential Requirement of the Extracellular Domain in Activation of Class B G Protein-coupled Receptors.

text: G protein-coupled receptors (GPCRs) from the secretin-like (class B) family are key players in hormonal homeostasis and are important drug targets for the treatment of metabolic disorders and neuronal diseases. They consist of a large N-terminal extracellular domain (ECD) and a transmembrane domain (TMD) with the GPCR signature of seven transmembrane helices. Class B GPCRs are activated by peptide hormones with their C termini bound to the receptor ECD and their N termini bound to the TMD. It is thought that the ECD functions as an affinity trap to bind and localize the hormone to the receptor. This in turn would allow the hormone N terminus to insert into the TMD and induce conformational changes of the TMD to activate downstream signaling. In contrast to this prevailing model, we demonstrate that human class B GPCRs vary widely in their requirement of the ECD for activation. In one group, represented by corticotrophin-releasing factor receptor 1 (CRF1R), parathyroid hormone receptor (PTH1R), and pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1R), the ECD requirement for high affinity hormone binding can be bypassed by induced proximity and mass action effects, whereas in the other group, represented by glucagon receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R), the ECD is required for signaling even when the hormone is covalently linked to the TMD. Furthermore, the activation of GLP-1R by small molecules that interact with the intracellular side of the receptor is dependent on the presence of its ECD, suggesting a direct role of the ECD in GLP-1R activation.