An evaluation of the vitamin D3 content in fish: Is the vitamin D content adequate to satisfy the dietary requirement for vitamin D?

It has been suggested that the major source of vitamin D should come from dietary sources and not sun exposure. However, the major fortified dietary source of vitamin D is milk which often does not contain at least 80% of what is stated on the label. Fish has been touted as an excellent source of vitamin D especially oily fish including salmon and mackerel. Little is known about the effect of various cooking conditions on the vitamin D content in fish. We initiated a study and evaluated the vitamin D content in several species of fish and also evaluated the effect of baking and frying on the vitamin D content. Surprisingly, farmed salmon had approximately 25% of the vitamin D content as wild salmon had. The vitamin D content in fish varied widely even within species. These data suggest that the tables that list the vitamin D content are out-of-date and need to be re-evaluated.     

Where is the vitamin D receptor?

The vitamin D receptor (VDR) is a member of the nuclear receptor superfamily and plays a central role in the biological actions of vitamin D. VDR regulates the expression of numerous genes involved in calcium/phosphate homeostasis, cellular proliferation and differentiation, and immune response, largely in a ligand-dependent manner. To understand the global function of the vitamin D system in physiopathological processes, great effort has been devoted to the detection of VDR in various tissues and cells, many of which have been identified as vitamin D targets. This review focuses on the tissue- and cell type-specific distribution of VDR throughout the body.     

What is the optimal vitamin D status for health?

The most objectively substantiated health-related reason for tanning is that it improves vitamin D status. The serum 25-hydroxyvitamin D concentration (25(OH)D) is the measure of vitamin D nutrition status. Human biology was probably optimized through natural selection for a sun-rich environment that maintained serum 25(OH)D higher than 100 nmol/L. These levels are now only prevalent in people who spend an above-average amount of time outdoors, with the sun high in the sky. The best-characterized criteria for vitamin D adequacy are based on randomized clinical trials that show fracture prevention and preservation of bone mineral density. Based upon these studies, 25(OH)D concentrations should exceed 75 nmol/L. This concentration is near the upper end of the 25(OH)D reference ("normal") range for populations living in temperate climates, or for people who practice sun-avoidance, or who wear head coverings. Officially mandated nutrition guidelines restrict vitamin D intake from fortified food and supplements to less than 25 mcg/day, a dose objectively shown to raise serum 25(OH)D in adults by about 25 nmol/L. The combined effect of current nutrition guidelines and current sun-avoidance advice is to ensure that adults who follow these recommendations will have 25(OH)D concentrations lower than 75 nmol/L. Therefore, advice to avoid UVB light should be accompanied by encouragement to supplement with vitamin D in an amount that will correct for the nutrient deficit that sun-avoidance will cause.     

Systematic SAR study of the side chain of nonsecosteroidal vitamin D₃ analogs

A series of nonsecosteroidal vitamin D(3) analogs with carboxylic acid were explored. Through our systematic SAR studies on the side chain moiety, compound 6b was identified as the optimal compound showing excellent vitamin D receptor (VDR) agonistic activity. Compound 6b had the diethyl group in the terminal which was bound by (E)-olefin linker to the bisphenyl core. Calculating the volume of the side chain showed that the diethyl group in 6b filled the hydrophobic region of VDR with the ideal packing coefficient based on the 55% rule, and that this resulted in the most potent in vitro activity.     

Targeted delivery of vitamin D to the colon using β-glucuronides of vitamin D: therapeutic effects in a murine model of inflammatory bowel disease

1,25-Dihydroxyvitamin D(3) [1,25(OH)(2)D] has been shown to inhibit development of dextran sodium sulfate (DSS)-induced colitis in mice but can also cause hypercalcemia. The aim of this study was to evaluate whether β-glucuronides of vitamin D could deliver 1,25(OH)(2)D to the colon to ameliorate colitis while reducing the risk of hypercalcemia. Initial studies demonstrated that bacteria residing in the lower intestinal tract were capable of liberating 1,25(OH)(2)D from 1,25-dihydroxyvitamin D(3)-25-β-glucuronide [β-gluc-1,25(OH)(2)D]. We also determined that a much greater upregulation of the vitamin D-dependent 24-hydroxylase gene (Cyp24) was induced in the colon by treatment of mice with an oral dose of β-gluc-1,25(OH)(2)D than 1,25(OH)(2)D, demonstrating targeted delivery of 1,25(OH)(2)D to the colon. We then tested β-glucuronides of vitamin D in the mouse DSS colitis model in two studies. In mice receiving DSS dissolved in distilled water and treated with 1,25(OH)(2)D or β-gluc-1,25(OH)(2)D, severity of colitis was reduced. Combination of β-gluc-1,25(OH)(2)D with 25-hydroxyvitamin D(3)-25-β-glucuronide [β-gluc-25(OH)D] resulted in the greatest reduction of colitis lesions and symptoms in DSS-treated mice. Plasma calcium concentrations were lower in mice treated with β-gluc-1,25(OH)(2)D alone or in combination with β-gluc-25(OH)D than in mice treated with 1,25(OH)(2)D, which were hypercalcemic at the time of death. β-Glucuronides of vitamin D compounds can deliver 1,25(OH)(2)D to the lower intestine and can reduce symptoms and lesions of acute colitis in this model.     

Proteome analysis of the left ventricle in the vitamin D₃ and nicotine-induced rat vascular calcification model

Vitamin D? and nicotine (VDN) serve as an animal model of arterial calcification. The vascular calcification induced by the VDN model is always accompanied by compensatory left ventricular (LV) hypertrophy and impaired cardiac performance. To determine the possible mechanisms that are responsible for the effects of VDN on the LV, a 2-DE based proteomics approach was used to evaluate the changes in protein expression of the left ventricle in VDN rats, to our knowledge, for the first time. We identified sixteen proteins that were markedly altered and involved in mitochondrial function, heat shock protein activity, myocyte cytoskeleton composition and enzyme activity for energy metabolism. We describe, for the first time, a novel pathway (NDPK) that is involved in LV hypertrophy and enzyme activities of three of the sixteen clinical identified proteins: lactate dehydrogenase (LDH), SOD [Mn] and GST.     

Intrinsic requirement for the vitamin D receptor in the development of CD8αα-expressing T cells

Vitamin D and vitamin D receptor (VDR) deficiency results in severe symptoms of experimental inflammatory bowel disease in several different models. The intraepithelial lymphocytes of the small intestine contain large numbers of CD8αα(+) T cells that have been shown to suppress the immune response to Ags found there. In this study, we determined the role of the VDR in the development of CD8αα(+) T cells. There are fewer total numbers of TCRαβ(+) T cells in the gut of VDR knockout (KO) mice, and that reduction was largely in the CD8αα(+) TCRαβ(+) cells. Conversely TCRγδ(+) T cells were normal in the VDR KO mice. The thymic precursors of CD8αα(+) TCRαβ(+) cells (triple-positive for CD4, CD8αα, and CD8αβ) were reduced and less mature in VDR KO mice. In addition, VDR KO mice had a higher frequency of the CD8αα(+) TCRαβ(+) precursors (double-negative [DN] TCRαβ(+) T cells) in the gut. The proliferation rates of the DN TCRαβ(+) gut T cells were less in the VDR KO compared with those in wild type. Low proliferation of DN TCRαβ(+) T cells was a result of the very low expression of the IL-15R in this population of cells in the absence of the VDR. Bone marrow transplantation showed that the defect in VDR KO CD8αα(+) TCRαβ(+) cells was cell intrinsic. Decreased maturation and proliferation of CD8αα(+) TCRαβ(+) cells in VDR KO mice results in fewer functional CD8αα(+) TCRαβ(+) T cells, which likely explains the increased inflammation in the gastrointestinal tract of VDR KO and vitamin D-deficient mice.     

Does vitamin D protect against DNA damage?

Vitamin D is a secosteroid best known for its role in maintaining bone and muscle health. Adequate levels of vitamin D may also be beneficial in maintaining DNA integrity. This role of vitamin D can be divided into a primary function that prevents damage from DNA and a secondary function that regulates the growth rate of cells. The potential for vitamin D to reduce oxidative damage to DNA in a human has been suggested by clinical trial where vitamin D supplementation reduced 8-hydroxy-2'-deoxyguanosine, a marker of oxidative damage, in colorectal epithelial crypt cells. Studies in animal models and in different cell types have also shown marked reduction in oxidative stress damage and chromosomal aberrations, prevention of telomere shortening and inhibition of telomerase activity following treatment with vitamin D. The secondary function of vitamin D in preventing DNA damage includes regulation of the poly-ADP-ribose polymerase activity in the DNA damage response pathway involved in the detection of DNA lesions. It is also able to regulate the cell cycle to prevent the propagation of damaged DNA, and to regulate apoptosis to promote cell death. Vitamin D may contribute to prevention of human colorectal cancer, though there is little evidence to suggest that prevention of DNA damage mediates this effect, if real. Very limited human data mean that the intake of vitamin D required to minimise DNA damage remains uncertain.     

Modulation of the immune system by UV radiation: more than just the effects of vitamin D?

Humans obtain most of their vitamin D through the exposure of skin to sunlight. The immunoregulatory properties of vitamin D have been demonstrated in studies showing that vitamin D deficiency is associated with poor immune function and increased disease susceptibility. The benefits of moderate ultraviolet (UV) radiation exposure and the positive latitude gradients observed for some immune-mediated diseases may therefore reflect the activities of UV-induced vitamin D. Alternatively, other mediators that are induced by UV radiation may be more important for UV-mediated immunomodulation. Here, we compare and contrast the effects of UV radiation and vitamin D on immune function in immunopathological diseases, such as psoriasis, multiple sclerosis and asthma, and during infection.     

Vitamin D regulation of immune function in the gut: why do T cells have vitamin D receptors?

Low vitamin D status is associated with an increased risk of immune-mediated diseases like inflammatory bowel disease (IBD) in humans. Experimentally vitamin D status is a factor that shapes the immune response. Animals that are either vitamin D deficient or vitamin D receptor (VDR) deficient are prone to develop IBD. Conventional T cells develop normally in VDR knockout (KO) mice but over-produce IFN-γ and IL-17. Naturally occurring FoxP3+ regulatory T cells are present in normal numbers in VDR KO mice and function as well as wildtype T regs. Vitamin D and the VDR are required for the development and function of two regulatory populations of T cells that require non-classical MHC class 1 for development. The two vitamin D dependent cell types are the iNKT cells and CD4/CD8αα intraepithelial lymphocytes (IEL). Protective immune responses that depend on iNKT cells or CD8αα IEL are therefore impaired in the vitamin D or VDR deficient host and the mice are more susceptible to immune-mediated diseases in the gut.     

The Orosomucoid 1 protein is involved in the vitamin D – mediated macrophage de-activation process

Orosomucoid 1 (ORM1), also named Alpha 1 acid glycoprotein A (AGP-A), is an abundant plasma protein characterized by anti-inflammatory and immune-modulating properties. The present study was designed to identify a possible correlation between ORM1 and Vitamin D3 (1,25(OH)2D3), a hormone exerting a widespread effect on cell proliferation, differentiation and regulation of the immune system. In particular, the data described here indicated that ORM1 is a 1,25(OH)2D3 primary response gene, characterized by the presence of a VDRE element inside the 1 kb sequence of its proximal promoter region. This finding was demonstrated with gene expression studies, Chromatin Immunoprecipitation and luciferase transactivation experiments and confirmed by VDR full length and dominant negative over-expression. In addition, several experiments carried out in human normal monocytes demonstrated that the 1,25(OH)2D3 – VDR – ORM1 pathway plays a functional role inside the macrophage de-activation process and that ORM1 may be considered as a signaling molecule involved in the maintenance of tissue homeostasis and remodeling.     

The role of the vitamin D receptor and ERp57 in photoprotection by 1α,25-dihydroxyvitamin D3

UV radiation (UVR) is essential for formation of vitamin D(3), which can be hydroxylated locally in the skin to 1α,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)]. Recent studies implicate 1,25-(OH)(2)D(3) in reduction of UVR-induced DNA damage, particularly thymine dimers. There is evidence that photoprotection occurs through the steroid nongenomic pathway for 1,25-(OH)(2)D(3) action. In the current study, we tested the involvement of the classical vitamin D receptor (VDR) and the endoplasmic reticulum stress protein 57 (ERp57), in the mechanisms of photoprotection. The protective effects of 1,25-(OH)(2)D(3) against thymine dimers were abolished in fibroblasts from patients with hereditary vitamin D-resistant rickets that expressed no VDR protein, indicating that the VDR is essential for photoprotection. Photoprotection remained in hereditary vitamin D-resistant rickets fibroblasts expressing a VDR with a defective DNA-binding domain or a mutation in helix H1 of the classical ligand-binding domain, both defects resulting in a failure to mediate genomic responses, implicating nongenomic responses for photoprotection. Ab099, a neutralizing antibody to ERp57, and ERp57 small interfering RNA completely blocked protection against thymine dimers in normal fibroblasts. Co-IP studies showed that the VDR and ERp57 interact in nonnuclear extracts of fibroblasts. 1,25-(OH)(2)D(3) up-regulated expression of the tumor suppressor p53 in normal fibroblasts. This up-regulation of p53, however, was observed in all mutant fibroblasts, including those with no VDR, and with Ab099; therefore, VDR and ERp57 are not essential for p53 regulation. The data implicate the VDR and ERp57 as critical components for actions of 1,25-(OH)(2)D(3) against DNA damage, but the VDR does not require normal DNA binding or classical ligand binding to mediate photoprotection.     

Ultraviolet exposure and vitamin D synthesis in a sun-dwelling and a shade-dwelling species of Anolis: are there adaptations for lower ultraviolet B and dietary vitamin D3 availability in the shade?

We compared the natural ultraviolet B (UV-B) exposure, dietary vitamin D, and skin-generated vitamin D synthesis for adult males of two species of Jamaican anoles. The more shade-tolerant and thermal-conforming Anolis lineotopus merope, rarely exposed to full sun, experienced less UV-B irradiation in its shady environment than the more heliophilic and thermophilic Anolis sagrei, which frequently basked in full sun during the morning hours (0800-1100 hours). Both species obtained detectable levels of vitamin D(3) in their diet, but the heliophilic A. sagrei obtained more. To compensate for less availability of UV-B and dietary vitamin D, the skin of A. lineotopus merope seems to have acquired a greater sensitivity than that of A. sagrei regarding UV-B-induced vitamin D(3) photobiosynthesis. We assessed this by observing a greater conversion of provitamin D to photoproducts in skin exposed to UV-B from a sunlamp. The reduced skin sensitivity of A. sagrei regarding vitamin D photobiosynthesis may reflect a correlated response associated with less need for vitamin D photobiosynthesis and greater need for UV-B screening capacity as an adaptation to a more damaging UV-B environment. However, the possibility that adaptations for photobiosynthesis of vitamin D and for protection from skin damage could involve independent mechanisms needs investigation. Also, the ability to behaviorally regulate UV-B exposure, as shown for the panther chameleon, would benefit both species of Anolis and should be investigated.     

Simultaneous production of β-carotene, vitamin E and vitamin C by the aerial microalga Trentepohlia aurea

The biomass production and antioxidant accumulation of the aerial microalga Trentepohlia aurea were examined. Using ammonium chloride as nitrogen source for growth in liquid medium, the growth rate was exponential and accompanied by a marked fall in the pH of the medium. The highest growth rate of 152 mg L^-1 day^-1 (logarithmic phase) was attained when T. aurea was cultured with aeration of 5% CO₂-enriched air in medium buffered with HEPES. The growth rate and antioxidant content were enhanced under 5% CO₂ by switching the light intensity from 43 to 143 μmol photon m^-2 s^-1 for the two-stage culture. As a result, T. aurea cells accumulated 2.1 mg β-carotene, 0.3 mg L-ascorbic acid and 2.4 mg tocopherols, respectively, per g dry cell. The simultaneous production of useful materials, such as β-carotene, vitamin E and vitamin C, was demonstrated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Seasonal variation in vitamin D₃ levels is paralleled by changes in the peripheral blood human T cell compartment

It is well-recognized that vitamin D₃ has immune-modulatory properties and that the variation in ultraviolet (UV) exposure affects vitamin D₃ status. Here, we investigated if and to what extent seasonality of vitamin D₃ levels are associated with changes in T cell numbers and phenotypes. Every three months during the course of the entire year, human PBMC and whole blood from 15 healthy subjects were sampled and analyzed using flow cytometry. We observed that elevated serum 25(OH)D₃ and 1,25(OH)₂D₃ levels in summer were associated with a higher number of peripheral CD4⁺ and CD8⁺ T cells. In addition, an increase in naïve CD4⁺CD45RA⁺ T cells with a reciprocal drop in memory CD4⁺CD45RO⁺ T cells was observed. The increase in CD4⁺CD45RA⁺ T cell count was a result of heightened proliferative capacity rather than recent thymic emigration of T cells. The percentage of Treg dropped in summer, but not the absolute Treg numbers. Notably, in the Treg population, the levels of forkhead box protein 3 (Foxp3) expression were increased in summer. Skin, gut and lymphoid tissue homing potential was increased during summer as well, exemplified by increased CCR4, CCR6, CLA, CCR9 and CCR7 levels. Also, in summer, CD4⁺ and CD8⁺ T cells revealed a reduced capacity to produce pro-inflammatory cytokines. In conclusion, seasonal variation in vitamin D₃ status in vivo throughout the year is associated with changes in the human peripheral T cell compartment and may as such explain some of the seasonal variation in immune status which has been observed previously. Given that the current observations are limited to healthy adult males, larger population-based studies would be useful to validate these findings.     

Is thioredoxin the physiological vitamin K epoxide reducing agent?

E. coli thioredoxin plus thioredoxin reductase have previously been shown to replace dithiothreitol as the electron donor for mammalian liver microsomal vitamin K epoxide reduction in vitro. Such activity is dependent on detergent disruption of the microsomal membrane integrity. A previously characterized salicylate-inhibitable pathway for electron transfer from endogenous cytosolic reducing agents to the microsomal epoxide reducing warfarin-inhibitable enzyme is not inhibited by known alternate substrates and inhibitors of the thioredoxin system nor by antibodies against thioredoxin.