Vitamin D-binding protein directs monocyte responses to 25-hydroxy- and 1,25-dihydroxyvitamin D

Seasonal variation of total and bioavailable 25-hydroxyvitamin D [25(OH)D] in the healthy adult Slovenian population

Objective: The aim of our study was to compare the total 25(OH)D fraction, the bioavailable vitamin fraction, and the free vitamin D fraction in spring and fall in a group of healthy individuals. Methods: In our study, we collected blood samples from healthy participants at the end of both summer and winter, and measured serum levels of albumin, DBP, and 25(OH)D. Utilizing these data, we calculated the percentage of free and bioavailable vitamin D. Our cohort comprised 87 participants, with a male-to-female ratio of 14:73, aged 35.95 ± 12.55 years, ranging from 19 to 70 years. We employed the chemiluminescence method to determine the vitamin 25(OH)D levels, the ELISA method was utilized to determine DBP levels, the albumin BCP Assay was performed using the ADVIA biochemical analyzer (Siemens) and an online calculator was used to determine the free and bioavailable 25(OH)D levels. Results: Our findings indicate significantly lower 25(OH)D levels in winter (44.13 ± 17.82 nmol/L) compared to summer (74.97 ± 22.75 nmol/L; p < 0.001). For vitamin D binding protein there was no significant difference from summer (236.2 ± 164.39 mg/L) to winter (239.86 ± 141.9 mg/L; p = 0.77), albumin levels were significantly higher in summer (49.37 ± 4.15 g/L vs. 47.97 ± 3.91 g/L, p = 0.01), but the magnitude of the change may not be large enough to be solely responsible for the stability of vitamin D levels throughout the year. In the winter season a significantly lower calculated bioavailable 25(OH)D vitamin (7.45 ± 5.66 nmol/L against 13.11 ± 8.27 nmol/L; p < 0.001) was observed, and the free fraction also showed a significant decrease (17.3 ± 12.9 pmol/L versus 29.7 ± 19.1 pmol/L; p < 0.0001). We observed a moderately positive correlation between 25(OH)D and bioavailable percentage in winter (r = 0.680; p < 0.001), in contrast with a lower positive association in summer (r = 0.343; p < 0.001). Conclusion: Our data suggest a positive correlation between total and bioavailable 25(OH)D levels. In addition to the statistically significant variation in 25(OH)D between the two observation periods, there was an additional variation in the free vitamin D percentage. The summertime synthesis of vitamin D in the skin could contribute directly to the free fraction of vitamin D. Standardizing the measurement of free 25(OH)D and clinical studies is necessary to establish reference values before these methods can be implemented in clinical practice.

Relation of T Cell Profile with Vitamin D Receptor and Vitamin D-Binding Protein Gene Polymorphisms in Atopy

Atopic diseases, including atopic dermatitis (AD) and allergic asthma (AA), are characterized by complex immune responses involving various T cells subsets and their cytokine profiles. It is assumed that single nucleotide polymorphisms (SNPs) in the Vitamin D receptor (VDR) gene and the Vitamin D-binding protein (GC) gene are related to the action of Vitamin D and, consequently, play a role in regulating the immune response. However, there is not enough data to unequivocally support the hypothesis about the relationship between T cells profile and VDR or GC SNPs. Two hundred sixty-six subjects (aged > 18 years) were involved in the study: 100 patients with mild or moderate AD, 85 patients with mild or moderate AA, and 81 healthy individuals. Blood cell counts were determined by standard methods. Flow cytometric analysis was used to evaluate CD4+ T-helper (Th) cell subtypes: Th2, Th1, Th17, and T regulatory (Treg) cells in peripheral blood. Measurements of cytokines, total immunoglobulin E (IgE), and Vitamin D levels in serum were evaluated by ELISA. Significantly higher levels of Th1, Th2, and Th17 cells, along with lower levels of Tregs, were found in patients with atopic diseases compared to healthy individuals. Additionally, higher serum levels of interleukin (IL) 5, IL-17A, and transforming growth factor-β1 (TGF-β1), as well as lower levels of IL-10, were observed in patients with atopic diseases than in control. The study established associations between VDR SNPs and immune profiles: the AA genotype of rs731236 was associated with increased Th2 and Th17 cells and a higher Th1/Th2 ratio; the GG genotype of rs731236 was linked to decreased serum IL-10 and TGF-β1 levels; and the TT genotype of rs11168293 was associated with increased IL-10 levels. Additionally, the GG genotype of GC gene SNP rs4588 was associated with reduced Th2 and Th17 lymphocytes, while the TT genotype of rs4588 was linked to decreased IL-10 levels. Furthermore, the CC genotype of rs7041 was associated with higher levels of Th2, Th17, IL-10, and IL-35, as well as reduced levels of TGF-β1, while the GG genotype of rs3733359 was associated with reduced IL-10 levels. In conclusion, our study demonstrates that the Vitamin D receptor gene single nucleotide polymorphisms rs731236 and rs11168293, along with polymorphisms in the Vitamin D-binding protein gene (rs4588, rs7041, rs3733359), are significantly associated with variations in T cell profiles in atopy. These variations may play a crucial role in promoting inflammation and provide insight into the genetic factors contributing to the pathogenesis of atopy.

Vitamin D and its binding protein in patients with leiomyomas

AIM

This study examined the levels of VitD, VitD binding protein (DBP), and free VitD in leiomyomas patients and their association with the quantity, dimensions, and site of fibroid growths. Additionally, we evaluated the potentiality of employing these factors as a biomarker tool for the diagnosis and assessment of uterine fibroid progression.

METHODS

This study involved the participation of 55 women with leiomyomas and 50 healthy women. We utilized commercial ELISA kits to measure the levels of total VitD and DBP in their serum. Additionally, we calculated the levels of free VitD and the ratio of VitD to DBP. Moreover, we determined the number, size, and location of the leiomyomas in the patients.

RESULTS

There were no significant differences in the levels of total VitD between the groups. However, patients had significantly lower levels of free VitD and higher levels of DBP compared to the control group. The size of the largest leiomyomas showed a negative relationship with free VitD and a positive relationship with DBP. Receiver operating characteristic analyses, showed that the cut-off value for free VitD was 4.47 pg/mL, with a sensitivity of 75.6% and a specificity of 74.4%. The cut-off value for DBP was 256.2 μg/mL, with a sensitivity of 86% and a specificity of 70.3%.

CONCLUSIONS

Free VitD and DBP potentially contribute to the development of leiomyomas and are linked to the size of these tumors. The measurement of serum levels of these factors could serve as additional biomarkers for the diagnosis of leiomyomas.

Predicting comorbidities of pregnancy: A comparison between total and free 25(OH)D and their associations with parathyroid hormone

Pregnancy is a unique time when amplified sex steroid concentrations promote an escalation in vitamin D binding protein (DBP) synthesis, associated with increased total vitamin D and metabolites, including 25-hydroxyvitamin D (25(OH)D). Free 25(OH)D concentration increases disproportionately to total 25(OH)D during pregnancy, likely an adaptation to supply the woman and fetus with readily available 25(OH)D. Highlighting the importance of the calcium metabolic stress during pregnancy, the interactional relationship between serum 25(OH)D and PTH has been evaluated. Maternal total 25(OH)D and total 25(OH)D/iPTH are measures of vitamin D status and biomarkers for potential pregnancy complications. It has been proposed that free 25(OH)D and free 25(OH)D/iPTH could be better indicators of vitamin D status and predictors of pregnancy complications such as gestational diabetes (GDM), hypertensive disorders of pregnancy, and preterm delivery. This study aims to determine if free 25(OH)D and its association with PTH are more accurate predictors of comorbidities of pregnancy than total 25(OH)D and its association with PTH. In this post hoc analysis of the Kellogg Pregnancy Study, a double-blind randomized placebo-controlled trial, participants included 297 women with singleton pregnancies: 191 participants were randomized into a group receiving a daily prenatal (400 IU vitamin D3) while 196 received a prenatal plus extra supplementation (4400 IU vitamin D3). Blood and urine samples were collected monthly. 297 participants' serum total 25(OH)D concentrations were measured using radioimmunoassay at baseline (visit 1) and 5-7 months' gestation (visit 6-7). 93 participants' serum free 25(OH)D and PTH concentrations were measured using ELISA and immunoradiometric assay, respectively, at visit 1 and 6-7; 66 participants had paired samples and were included in this analysis. Data were analyzed using SAS 9.4, Cary, N.C. or SPSS v28, IBM Corporation, Armonk, N.Y. Results were considered significant with a p < 0.05. A significant relationship exists between the ratio of total 25(OH)D/iPTH and free 25(OH)D/iPTH grouped by total 25(OH)D ≥ 30 ng/mL and < 30 ng/mL as an indicator of maternal vitamin D status. There was a statistically significant relationship between lower mean free 25(OH)D/iPTH and the development of GDM at visit 1 (p = 0.0003) and at visit 6-7 (p = 0.001) while total 25(OH)D/iPTH and GDM were significantly related only at visit 1 (p = 0.029). In this exploratory cohort, neither free 25(OH)D/iPTH nor total 25(OH)D/iPTH were significantly associated with increased incidence of preterm delivery, hypertensive disorders, or combined comorbidities of pregnancy. An univariate logistic regression evaluating the outcome of gestational diabetes while independently controlling for independent factors showed the ratio of free 25(OH)D/iPTH was more closely associated with gestational diabetes than the ratio of total 25(OH)D/iPTH, although neither were significant. This proof-of-concept analysis suggests that the ratio of free 25(OH)D/iPTH is associated with the development of gestational diabetes throughout pregnancy while total 25(OH)D/iPTH is only associated with the outcome early in pregnancy. Further investigation is warranted to explore this relationship between calcium metabolic stress during pregnancy with a larger cohort to improve validity,reproducibility, and relevance to other pregnancy comorbidities.

Vitamin D receptor and vitamin D binding protein gene polymorphisms in patients with asthma: a pilot study

BACKGROUND

The effects of vitamin D are exerted by interaction with the vitamin D receptor (VDR) and vitamin D binding protein (VDBP). Polymorphisms in VDR or VDBP genes may affect vitamin D levels, influencing the pathogenesis of asthma and atopy. The aim of this study was to investigate the possible association of VDR and VDBP gene single-nucleotide polymorphisms (SNP), 25-hydroxyvitamin D (25(OH)D), blood eosinophils and total IgE level in subjects with asthma in comparison with healthy individuals.

METHODS

This case-control study enrolled 63 subjects with asthma (45 allergic and 18 non-allergic) and 32 healthy subjects were involved in the study. Sensitization of subjects to inhaled allergens was determined by a skin prick test, lung function was evaluated by spirometry. Blood eosinophil count was determined by standard methods. Serum 25(OH)D and total IgE levels were evaluated by ELISA. Polymorphisms in the VDR and VDBP genes on the 12q13.11 and 4q13.3 chromosomal region were analyzed using TaqMan SNP Genotyping Assay probes.

RESULTS

In asthma patients with vitamin D deficiency (< 20 ng/ml) the allele G of rs11168293 of VDR was more common than in those having insufficiency (20-30 ng/ml) of vitamin D (63% and 31%, p < 0.05). Moreover, asthmatic subject with rs11168293 G allele has significant higher blood eosinophil count compared to asthmatic without the rs11168293 G allele (8.5 ± 12.3% vs. 5.1 ± 1.5%, p < 0.05). Significantly higher IgE level was found in subjects with allergic asthma with the allele A of rs7041 on VDBP gene than in those without this allele (540 ± 110 and 240 ± 80 IU/ml, p < 0.05).

CONCLUSIONS

The association of polymorphisms in VDBP and VDR gene, the rs11168293 G allele and the rs7041 A allele, with 25(OH)D, blood eosinophil and total IgE level in asthma, let us suggest that vitamin D, VDR and VDBP gene polymorphisms are important in pathogenesis of asthma despite its form in relation to atopy.

Impact of Common Vitamin D-Binding Protein Isoforms on Supplemental Vitamin D3 and/or Calcium Effects on Colorectal Adenoma Recurrence Risk: A Secondary Analysis of a Randomized Clinical Trial

Importance

Variants in the vitamin D-binding protein (DBP) gene (GC) encode DBP isoforms that may affect vitamin D metabolism. However, whether these isoforms modify the effects of vitamin D3 and/or calcium supplementation on colorectal adenoma recurrence is unclear. We hypothesized that supplementation effects may be stronger among those with the DBP2 isoform (encoded by the rs4588*A allele), which is associated with vitamin D deficiency and modified the associations of circulating vitamin D with risk for colorectal neoplasms in observational studies.

Objective

To estimate supplemental vitamin D3 and/or calcium effects on colorectal adenoma recurrence according to 3 common DBP isoforms (DBP1s, DBP1f, DBP2) encoded by 2 missense variants: rs7041 (NG_012837.3:g.57904T>G NP_001191235.1:p.Asp432Glu) and rs4588 (NG_012837.3:g.57915C>A NP_001191235.1:p.Thr436Lys).

Design, Setting, and Participants

Secondary analysis of a randomized, double-blind, placebo-controlled clinical trial of 2259 participants with a recently diagnosed adenoma and no remaining polyps after complete colonoscopy in the US from July 1, 2004, to August 31, 2013. The current analyses were performed from August 12, 2019, to July 16, 2022.

Interventions

Daily vitamin D3 (1000 IU), calcium (1200 mg), both, or placebo.

Main Outcomes and Measures

One or more adenomas diagnosed during 3 to 5 years of follow-up. Treatment effects were estimated according to DBP isoform as risk ratios (RRs) and 95% CIs using Poisson regression analysis.

Results

Of the 2259 participants randomized (mean [SD] age, 58 [6.8] years; 1033 [64%] men), 1604 non-Hispanic White participants (chosen to avoid population stratification bias) were included in the analysis. Among those with the DBP2 isoform (rs4588*AC or AA), the RRs (95% CI) for adenoma recurrence were 0.84 (0.72-1.00) with vitamin D3 relative to no vitamin D3, 0.83 (95% CI, 0.70-0.99) with calcium relative to no calcium, and 0.76 (95% CI, 0.59-0.98) with both agents relative to neither agent. Conversely, among those without DBP2 (rs4588*CC), the corresponding values were 1.08 (95% CI, 0.93-1.26; P = .03 for interaction) with vitamin D3 relative to no vitamin D3, 0.98 (95% CI, 0.84-1.14; P = .37 for interaction) with calcium relative to no calcium, and 1.09 (0.88-1.36; P = .03 for interaction) with both agents relative to neither agent. Among DBP2 homozygotes (rs4588*AA), the RR for adenoma recurrence was 0.57 (95% CI, 0.31-1.08) with both agents relative to neither agent.

Conclusions and Relevance

The findings of this secondary analysis of a randomized clinical trial suggest that individuals with the DBP2 isoform-encoding rs4588*A allele may particularly benefit from vitamin D3 and/or calcium supplementation for colorectal adenoma prevention.

Trial Registration

ClinicalTrials.gov Identifier: NCT00153816.

Vitamin D and COVID-19: where are we now?

The pandemic caused by the SARS-CoV-2 virus has triggered great interest in the search for the pathophysiological mechanisms of COVID-19 and its associated hyperinflammatory state. The presence of prognostic factors such as diabetes, cardiovascular disease, hypertension, obesity, and age influence the expression of the disease's clinical severity. Other elements, such as 25-hydroxyvitamin D (25(OH)D3) concentrations, are currently being studied. Various studies, mostly observational, have sought to demonstrate whether there is truly a relationship between 25(OH)D3 levels and the acquisition and/or severity of the disease. The objective of this study was to carry out a review of the current data that associate vitamin D status with the acquisition, evolution, and/or severity of infection by the SARS-CoV-2 virus and to assess whether prevention through vitamin D supplementation can prevent infection and/or improve the evolution once acquired. Vitamin D system has an immunomodulatory function and plays a significant role in various bacterial and viral infections. The immune function of vitamin D is explained in part by the presence of its receptor (VDR) and its activating enzyme 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1) in immune cells. The vitamin D, VDR, and Retinoid X Receptor complex allows the transcription of genes with antimicrobial activities, such as cathelicidins and defensins. COVID-19 characteristically presents a marked hyperimmune state, with the release of proinflammatory cytokines such as IL-6, TNF-α, and IL-1β. Thus, there are biological factors linking vitamin D to the cytokine storm, which can herald some of the most severe consequences of COVID-19, such as acute respiratory distress syndrome. Hypovitaminosis D is widespread worldwide, so the prevention of COVID-19 through vitamin D supplementation is being considered as a possible therapeutic strategy easy to implement. However, more-quality studies and well-designed randomized clinical trials are needed to address this relevant question.

High-Throughput CAMP Assay (HiTCA): A Novel Tool for Evaluating the Vitamin D-Dependent Antimicrobial Response

Vitamin D is known to modulate human immune responses, and vitamin D deficiency is associated with increased susceptibility to infection. However, what constitutes sufficient levels or whether vitamin D is useful as an adjuvant therapeutic is debated, much in part because of inadequate elucidation of mechanisms underlying vitamin D's immune modulatory function. Cathelicidin antimicrobial peptide (CAMP) has potent broad-spectrum activity, and the CAMP gene is regulated in human innate immune cells by active 1,25(OH)2D3, a product of hydroxylation of inactive 25(OH)D3 by CYP27B1-hydroxylase. We developed a CRISPR/Cas9-edited human monocyte-macrophage cell line containing the mCherry fluorescent reporter gene at the 3' end of the endogenous CAMP gene. The High Throughput CAMP Assay (HiTCA) developed here is a novel tool for evaluating CAMP expression in a stable cell line that is scalable for a high-throughput workflow. Application of HiTCA to serum samples from a small number of human donors (n = 10) showed individual differences in CAMP induction that were not fully accounted for by the serum vitamin D metabolite status of the host. As such, HiTCA may be a useful tool that can advance our understanding of the human vitamin D-dependent antimicrobial response, which is being increasingly appreciated for its complexity.

The role of free vitamin D and vitamin D binding protein in SARS-Cov-2 infection in children

BACKGROUND

Many studies have discussed the effects of serum vitamin D deficiency in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) patients. This study aimed to investigate the relationship between SARS-CoV-2 infection severity and free vitamin D (FVD) and bioavailable vitamin D (BAVD) levels in children.

METHODS

A prospective case-control study design was used. Participants were divided into three groups based on the World Health Organization COVID-19 Clinical Progression Scale. Serum 25-hydroxyvitamin D (ng/mL), albumin (g/L), and vitamin D binding protein (ng/mL) levels were evaluated to investigate the relationship between disease severity and FVD and BAVD levels.

RESULTS

In total, 82 participants were included in the study. Of those, 24.4% were uninfected (n = 20), 50% had a mild case of SARS-CoV-2 (n = 41), and 25.6% had a moderate case (n = 21). There was a statistically significant difference in FVD and BAVD levels between the groups (p = 0.026). Median FVD (p = 0.007, Cohen's d = 0.84) and BAVD (p = 0.007, Cohen's d = 0.86) levels were significantly higher in the mild group compared to the moderate group. FVD and BAVD metabolites were moderately positively correlated with lymphocyte counts (FVD: r = 0.437, p < 0.001; BAVD: r = 0.439, p < 0.001).

CONCLUSIONS

This is the first study to demonstrate a relationship between SARS-CoV-2 symptom severity and FVD and BAVD levels. The relationship between FVD and BAVD levels and lymphocyte counts could play an important role in symptom severity and should be evaluated in further studies.

Bovine Immunity and Vitamin D3: An Emerging Association in Johne's Disease

Mycobacterium avium subspecies paratuberculosis (MAP) is an environmentally hardy pathogen of ruminants that plagues the dairy industry. Hallmark clinical symptoms include granulomatous enteritis, watery diarrhea, and significant loss of body condition. Transition from subclinical to clinical infection is a dynamic process led by MAP which resides in host macrophages. Clinical stage disease is accompanied by dysfunctional immune responses and a reduction in circulating vitamin D3. The immunomodulatory role of vitamin D3 in infectious disease has been well established in humans, particularly in Mycobacterium tuberculosis infection. However, significant species differences exist between the immune system of humans and bovines, including effects induced by vitamin D3. This fact highlights the need for continued study of the relationship between vitamin D3 and bovine immunity, especially during different stages of paratuberculosis.

Molecular mechanisms and therapeutic effects of different vitamins and minerals in COVID-19 patients

COVID-19 is a rapidly spreading disease, which has caught the world by surprise. Millions of people suffer from illness, and the mortality rates are dramatically high. Currently, there is no specific and immediate treatment for this disease. Remedies are limited to supportive regiments and few antiviral and anti-inflammatory drugs. The lack of a definite cure for COVID-19 is the reason behind its high mortality and global prevalence. COVID-19 can lead to a critical illness with severe respiratory distress and cytokine release. Increased oxidative stress and excessive production of inflammatory cytokines are vital components of severe COVID-19. Micronutrients, metalloids, and vitamins such as iron, manganese, selenium, Zinc, Copper, vitamin A, B family, and C are among the essential and trace elements that play a pivotal role in human nutrition and health. They participate in metabolic processes that lead to energy production. In addition, they support immune functions and act as antioxidants. Therefore, maintaining an optimal level of micronutrients intake, particularly those with antioxidant activities, is essential to fight against oxidative stress, modulate inflammation, and boost the immune system. Therefore, these factors could play a crucial role in COVID-19 prevention and treatment. In this review, we aimed to summarize antiviral properties of different vitamins and minerals. Moreover, we will investigate the correlation between them and their effects in COVID-19 patients.

Vitamin D: Before, during and after Pregnancy: Effect on Neonates and Children

A worldwide high prevalence of vitamin D (VD) deficiency has become of growing concern because of potential adverse effects on human health, including pregnant women and their offsprings. Beyond its classical function as a regulator of calcium and phosphate metabolism, together with its fundamental role in bone health in every stage of life, its deficiency has been associated to multiple adverse health effects. The classic effects of VD deficiency in pregnancy and neonates have been late hypocalcemia and nutritional rickets. Nevertheless, recent studies have linked VD to fertility and 25(OH)D with several clinical conditions in pregnancy: preeclampsia, gestational diabetes, higher incidence of cesarean section and preterm birth, while in infants, the clinical conditions are low birth weight, lower bone mass and possible relationship with the development of such diseases as bronchiolitis, asthma, type 1 diabetes, multiple sclerosis and autism included as VD non-classical actions. The supplementation with Vitamin D and achievement of optimal levels reduce maternal-fetal and newborn complications. Supplementation in children with VD deficiency reduces the risk of respiratory infections and possibly autoimmune diseases and autism. This review emphasizes the roles of Vitamin D deficiency and the consequences of intervention from preconception to infancy.

Autoimmune disease and interconnections with vitamin D

Vitamin D has well-documented effects on calcium homeostasis and bone metabolism but recent studies suggest a much broader role for this secosteroid in human health. Key components of the vitamin D system, notably the vitamin D receptor (VDR) and the vitamin D-activating enzyme (1α-hydroxylase), are present in a wide array of tissues, notably macrophages, dendritic cells and T lymphocytes (T cells) from the immune system. Thus, serum 25-hydroxyvitamin D (25D) can be converted to hormonal 1,25-dihydroxyvitamin D (1,25D) within immune cells, and then interact with VDR and promote transcriptional and epigenomic responses in the same or neighbouring cells. These intracrine and paracrine effects of 1,25D have been shown to drive antibacterial or antiviral innate responses, as well as to attenuate inflammatory T cell adaptive immunity. Beyond these mechanistic observations, association studies have reported the correlation between low serum 25D levels and the risk and severity of human immune disorders including autoimmune diseases such as inflammatory bowel disease, multiple sclerosis, type 1 diabetes and rheumatoid arthritis. The proposed explanation for this is that decreased availability of 25D compromises immune cell synthesis of 1,25D leading to impaired innate immunity and over-exuberant inflammatory adaptive immunity. The aim of the current review is to explore the mechanistic basis for immunomodulatory effects of 25D and 1,25D in greater detail with specific emphasis on how vitamin D-deficiency (low serum levels of 25D) may lead to dysregulation of macrophage, dendritic cell and T cell function and increase the risk of inflammatory autoimmune disease.

Evaluating the Evidence in Clinical Studies of Vitamin D in COVID-19

Laboratory evidence provides a biological rationale for the benefits of vitamin D in COVID-19, and vitamin D supplementation is associated with reduced risk of respiratory infections. Most of the clinical studies of vitamin D in COVID-19 have been observational, and the most serious problem with observational study design is that of confounding. Observational studies typically assess the relationship of 25(OH)D values with COVID-19 outcomes. Many conditions associated with low vitamin D status are also associated with worse COVID-19 outcomes. Randomized controlled trials (RCTs) overcome the problem of confounding, typically comparing outcomes between groups receiving vitamin D supplementation or placebo. However, any benefit of vitamin D in COVID-19 may be related to the dose, duration, daily vs. bolus administration, interaction with other treatments, and timing of administration prior to or during the illness. Serum 25(OH)D values >50 nmol/L have been associated with reduced infection rates, severity of COVID-19, and mortality in observational studies. Few RCTs of vitamin D supplementation have been completed, and they have shown no benefit of vitamin D in hospitalized patients. Vitamin D may benefit those with mild or asymptomatic COVID-19, and those with greater 25(OH)D values may have lower risk of acquiring infection. Because those at greatest risk of COVID-19 are also at greatest risk of vitamin D deficiency, it is reasonable to recommend vitamin D supplementation 15−20 mcg (600−800 IU) daily for the general population during the COVID-19 pandemic. Vitamin D doses greater than 100 mcg (4000 IU) daily should not be used without monitoring serum 25(OH)D and calcium.

The Action of Vitamin D in Adipose Tissue: Is There the Link between Vitamin D Deficiency and Adipose Tissue-Related Metabolic Disorders?

Adipose tissue plays an important role in systemic metabolism via the secretion of adipocytokines and storing and releasing energy. In obesity, adipose tissue becomes dysfunctional and characterized by hypertrophied adipocytes, increased inflammation, hypoxia, and decreased angiogenesis. Although adipose tissue is one of the major stores of vitamin D, its deficiency is detective in obese subjects. In the presented review, we show how vitamin D regulates numerous processes in adipose tissue and how their dysregulation leads to metabolic disorders. The molecular response to vitamin D in adipose tissue affects not only energy metabolism and adipokine and anti-inflammatory cytokine production via the regulation of gene expression but also genes participating in antioxidant defense, adipocytes differentiation, and apoptosis. Thus, its deficiency disturbs adipocytokines secretion, metabolism, lipid storage, adipogenesis, thermogenesis, the regulation of inflammation, and oxidative stress balance. Restoring the proper functionality of adipose tissue in overweight or obese subjects is of particular importance in order to reduce the risk of developing obesity-related complications, such as cardiovascular diseases and diabetes. Taking into account the results of experimental studies, it seemed that vitamin D may be a remedy for adipose tissue dysfunction, but the results of the clinical trials are not consistent, as some of them show improvement and others no effect of this vitamin on metabolic and insulin resistance parameters. Therefore, further studies are required to evaluate the beneficial effects of vitamin D, especially in overweight and obese subjects, due to the presence of a volumetric dilution of this vitamin among them.

Vitamin D Endocrine System and COVID-19

Preclinical data strongly suggest that the vitamin D endocrine system (VDES) may have extraskeletal effects. Cells of the immune and cardiovascular systems and lungs can express the vitamin D receptor, and overall these cells respond in a coherent fashion when exposed to 1,25-dihydroxyvitamin D, the main metabolite of the VDES. Supplementation of vitamin D-deficient subjects may decrease the risk of upper respiratory infections. The VDES also has broad anti-inflammatory and anti-thrombotic effects, and other mechanisms argue for a potential beneficial effect of a good vitamin D status on acute respiratory distress syndrome, a major complication of this SARS-2/COVID-19 infection. Activation of the VDES may thus have beneficial effects on the severity of COVID-19. Meta-analysis of observational data show that a better vitamin D status decreased the requirement of intensive care treatment or decreased mortality. A pilot study in Cordoba indicated that admission to intensive care was drastically reduced by administration of a high dose of calcifediol early after hospital admission for COVID-19. A large observational study in Barcelona confirmed that such therapy significantly decreased the odds ratio (OR) of mortality (OR = 0.52). This was also the conclusion of a retrospective study in five hospitals of Southern Spain. A retrospective study on all Andalusian patients hospitalized because of COVID-19, based on real-world data from the health care system, concluded that prescription of calcifediol (hazard ratio [HR] = 0.67) or vitamin D (HR = 0.75), 15 days before hospital admission decreased mortality within the first month. In conclusion, a good vitamin D status may have beneficial effects on the course of COVID-19. This needs to be confirmed by large, randomized trials, but in the meantime, we recommend (rapid) correction of 25 hydroxyvitamin D (25OHD) deficiency in subjects exposed to this coronavirus. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Vitamin D insufficiency in COVID-19 and influenza A, and critical illness survivors: a cross-sectional study

OBJECTIVES

The steroid hormone vitamin D has roles in immunomodulation and bone health. Insufficiency is associated with susceptibility to respiratory infections. We report 25-hydroxy vitamin D (25(OH)D) measurements in hospitalised people with COVID-19 and influenza A and in survivors of critical illness to test the hypotheses that vitamin D insufficiency scales with illness severity and persists in survivors.

DESIGN

Cross-sectional study.

SETTING AND PARTICIPANTS

Plasma was obtained from 295 hospitalised people with COVID-19 (International Severe Acute Respiratory and emerging Infections Consortium (ISARIC)/WHO Clinical Characterization Protocol for Severe Emerging Infections UK study), 93 with influenza A (Mechanisms of Severe Acute Influenza Consortium (MOSAIC) study, during the 2009-2010 H1N1 pandemic) and 139 survivors of non-selected critical illness (prior to the COVID-19 pandemic). Total 25(OH)D was measured by liquid chromatography-tandem mass spectrometry. Free 25(OH)D was measured by ELISA in COVID-19 samples.

OUTCOME MEASURES

Receipt of invasive mechanical ventilation (IMV) and in-hospital mortality.

RESULTS

Vitamin D insufficiency (total 25(OH)D 25-50 nmol/L) and deficiency (<25 nmol/L) were prevalent in COVID-19 (29.3% and 44.4%, respectively), influenza A (47.3% and 37.6%) and critical illness survivors (30.2% and 56.8%). In COVID-19 and influenza A, total 25(OH)D measured early in illness was lower in patients who received IMV (19.6 vs 31.9 nmol/L (p<0.0001) and 22.9 vs 31.1 nmol/L (p=0.0009), respectively). In COVID-19, biologically active free 25(OH)D correlated with total 25(OH)D and was lower in patients who received IMV, but was not associated with selected circulating inflammatory mediators.

CONCLUSIONS

Vitamin D deficiency/insufficiency was present in majority of hospitalised patients with COVID-19 or influenza A and correlated with severity and persisted in critical illness survivors at concentrations expected to disrupt bone metabolism. These findings support early supplementation trials to determine if insufficiency is causal in progression to severe disease, and investigation of longer-term bone health outcomes.

Macrophages Control the Bioavailability of Vitamin D and Vitamin D-Regulated T Cell Responses

The active form of vitamin D₃ (1,25(OH)₂D₃) has a great impact on T cell effector function. Thus, 1,25(OH)₂D₃ promotes T helper 2 (Th2) and regulatory T (Treg) cell function and concomitantly inhibits Th1 and Th17 cell function. Thus, it is believed that vitamin D exerts anti-inflammatory effects. However, vitamin D binding protein (DBP) strongly binds both 1,25(OH)₂D₃ and the precursor 25(OH)D₃, leaving only a minor fraction of vitamin D in the free, bioavailable form. Accordingly, DBP in physiological concentrations would be expected to block the effect of vitamin D on T cells and dendritic cells. In the present study, we show that pro-inflammatory, monocyte-derived M1 macrophages express very high levels of the 25(OH)D-1α-hydroxylase CYP27B1 that enables them to convert 25(OH)D₃ into 1,25(OH)₂D₃ even in the presence of physiological concentrations of DBP. Co-cultivation of M1 macrophages with T cells allows them to overcome the sequestering of 25(OH)D₃ by DBP and to produce sufficient levels of 1,25(OH)₂D₃ to affect T cell effector function. This study suggests that in highly inflammatory conditions, M1 macrophages can produce sufficient levels of 1,25(OH)₂D₃ to modify T cell responses and thereby reduce T cell-mediated inflammation via a vitamin D-mediated negative feed-back loop.

Total, Bioavailable, and Free 25-Hydroxyvitamin D Equally Associate with Adiposity Markers and Metabolic Traits in Mexican Adults

Epidemiological studies suggest a relationship between total 25-hydroxyvitamin D [25(OH)D], adiposity, and metabolic traits. The bioavailability of 25(OH)D is regulated by the albumin, vitamin D binding protein (VDBP), and variants of the GC gene. Therefore, it is not clear if bioavailable or free 25(OH)D offer additional benefits compared to total 25(OH)D when estimating the magnitude of these associations. Our aim was to evaluate the association between 25(OH)D (total, free and bioavailable) with adiposity and metabolic traits. This was a cross-sectional study of 1904 subjects from the Health Workers Cohort Study from Mexico. Free and bioavailable 25(OH)D were calculated based on VDBP and albumin determinations, using a formula adjusted for the GC gene diplotypes. Adiposity and metabolic traits were measured with standardized procedures. Free and bioavailable 25(OH)D levels correlated with total 25(OH)D, r = 0.71 and 0.70, respectively (p < 0.001). Total, bioavailable and free 25(OH)D levels were negatively associated with the adiposity marker (visceral adiposity index) and metabolic traits (metabolic syndrome, type 2 diabetes, triglycerides, triglycerides/HDL-c ratio, and triglycerides/glucose index) in multivariate regression models (ORs = 0.73 to 0.96). Our findings suggest that free and bioavailable 25(OH)D do not offer additional advantages over total 25(OH)D regarding its association with adiposity and several metabolic traits in Mexican adults.

Recent advances of vitamin D in immune, reproduction, performance for pig: a review

Vitamin D (VD) has been reported to play multiple and significant roles in improving pig health via modulating calcium and phosphorus homeostasis, skeletal muscle development and the immune system. Apart from food, photochemical action of 7-dehydrocholesterol in the skin is the main source of this molecule for pigs. The VD from dietary intake or photosynthesized via skin can be absorbed into the liver for hydroxylation, and further hydroxylated into the hormone form of VD (1,25-dihydroxyvitamin D3 or 1,25(OH)2D3) in the kidney. As a sterol hormone, 1,25(OH)2D3 is able to bind with the VD receptor (VDR), and this ligand-receptor complex (VDR/retinoic X receptor) translocates from the cytoplasm into the nucleus to regulate gene expression, thus modulating metabolism. In this review, we summarized the recent studies regarding the non-skeletal health benefits of VD for pigs, and focused on the recent advances in the cellular and molecular mechanisms of VD that affects the immune system and reproductive health. This review provides a reference for future research and application of VD in pigs.

Development of a LC-MS/MS method to measure serum 3-sulfate and 3-glucuronide 25-hydroxyvitamin D3 metabolites; comparisons to unconjugated 25OHD in pregnancy and polycystic ovary syndrome

Vitamin D status is routinely assessed by measuring circulating concentrations of 25-hydroxyvitamin D (25OHD2 or 25OHD3). However as deconjugation is not routinely incorporated into sample treatment prior to analysis, conjugated forms of 25OHD (particularly the more abundant 25OHD3) are often not considered in determining serum concentrations of total 25OHD. Two major circulating conjugated forms of 25OHD3 are 25-hydroxyvitamin D3-3-sulfate (25OHD3-S) and 25-hydroxyvitamin D3-3-glucuronide (25OHD3-G). Incorporating these two conjugated metabolites into the measurement of vitamin D status could improve our understanding of vitamin D status in health, particularly if there are changes in sulfation and glucuronidation activities. The aim of this study was to develop a liquid chromatography tandem-mass spectrometry (LC-MS/MS) targeted method for measurement of 25OHD3-S and 25OHD3-G in serum to enable comparisons with circulating levels of the free 25OHD3 form. We developed and validated a new LC-MS/MS method that measured both 25OHD3-S and 25OHD3-G following a solid phase extraction sample preparation method. Partial separation of analytes by LC, and the separation of analytes by the optimized multiple reaction monitoring transitions enabled the quantitation of both 25OHD3-S and 25OHD3-G in the single method. Serum concentrations of 25OHD3-S (24.7 ± 11.8 ng/mL) and 25OHD3-G (2.4 ± 1.2 ng/mL) were shown to be a significant proportion of circulating vitamin D metabolites in healthy donor serums. These levels of 25OHD3-S and 25OHD3-G closely associated with 25OHD3 concentrations, r = 0.728, p = 0.001 and r = 0.632, p = 0.006 respectively. However in serum from pregnant women and non-pregnant women with polycystic ovary syndrome (PCOS) significant differences in the ratios between conjugated and free 25OHD3 were observed between pregnancy groups (25OHD3/25OHD3-S and 25OHD3/25OHD3-G p < 0.001), and between healthy and PCOS subjects (25OHD3/25OHD3-G p < 0.050). Development of this novel high-throughput LC-MS/MS method indicates that 25OHD3-S and 25OHD3-G are substantial components of circulating vitamin D metabolites. The concentrations of these metabolites relative to conventional 25OHD3 may vary in different physiological and pathophysiological settings, and may therefore play an unrecognized but important role in the actions of vitamin D.

Vitamin D Inhibits Adipokine Production and Inflammatory Signaling Through the Vitamin D Receptor in Human Adipocytes

OBJECTIVE

The purpose of this study was to investigate the effects of vitamin D on adipokine expression and inflammation in human adipose tissues and adipocytes and evaluate the molecular mechanisms involved.

METHODS

Omental and abdominal subcutaneous human adipose tissues were treated with 1,25-dihydroxyvitamin D₃ (1,25(OH)₂ D₃ ), and adipokine levels were measured. Vitamin D effects were measured with or without dexamethasone because glucocorticoids are known to affect vitamin D actions. Using RNA interference, we examined whether the vitamin D receptor (VDR) mediated vitamin D actions on adipokine expression and inflammatory signaling pathways in human adipocytes.

RESULTS

mRNA levels and secretion of leptin and IL-6 were suppressed by 1,25(OH)₂ D₃ in omental adipose tissues. Cotreatment with dexamethasone did not affect these inhibitory actions but partially blocked CYP24A1 induction. Similar results were observed in the subcutaneous depot. In addition, 1,25(OH)₂ D₃ suppressed leptin and IL-6 expression as well as nuclear factor-κB and extracellular signal-regulated kinase-1/2 phosphorylation in human adipocytes. Adipokine expression also was decreased by 25-hydroxyvitamin D₃ (25(OH)D₃ ), but not vitamin D₃ . Knockdown of VDR increased the inflammatory signaling activity in the control condition and blocked the inhibitory effects of 1,25(OH)₂ D₃ on adipokine and inflammatory signaling pathways.

CONCLUSION

Vitamin D acts through VDR to inhibit inflammatory pathways and adipokine expression in human adipocytes. Increasing vitamin D status may ameliorate obesity-associated metabolic complications by decreasing adipose tissue inflammation.

Perspective: Vitamin D supplementation prevents rickets and acute respiratory infections when given as daily maintenance but not as intermittent bolus: implications for COVID-19

The value of vitamin D supplementation in the treatment or prevention of various conditions is often viewed with scepticism as a result of contradictory results of randomised trials. It is now becoming apparent that there is a pattern to these inconsistencies. A recent large trial has shown that high-dose intermittent bolus vitamin D therapy is ineffective at preventing rickets - the condition that is most unequivocally caused by vitamin D deficiency. There is a plausible biological explanation since high-dose bolus replacement induces long-term expression of the catabolic enzyme 24-hydroxylase and fibroblast growth factor 23, both of which have vitamin D inactivating effects. Meta-analyses of vitamin D supplementation in prevention of acute respiratory infection and trials in tuberculosis and other conditions also support efficacy of low dose daily maintenance rather than intermittent bolus dosing. This is particularly relevant during the current COVID-19 pandemic given the well-documented associations between COVID-19 risk and vitamin D deficiency. We would urge that clinicians take note of these findings and give strong support to widespread use of daily vitamin D supplementation.

Effects of vitamin D supplementation on circulating concentrations of growth factors and immune-mediators in healthy women during pregnancy

BACKGROUND

For the second aim of the Kellogg Foundation grant, this double-blind RCT investigated the impact of plasma vitamin D metabolite 25-hydroxyvitamin D (25(OH)D) on plasma immune-mediators during pregnancy. We hypothesized that higher 25(OH)D concentrations would associate with reduced pro-inflammatory and increased tolerogenic immune-mediator concentrations.

METHODS

Pregnant women enrolled at 10-14 weeks gestation were randomized to 400 or 4400 IU vitamin D₃/day. Data on health, safety, circulating 25(OH)D, and 9 immune-mediators were collected at each trimester. Associations between immune-mediators and 25(OH)D at baseline and at second and third trimesters were examined.

RESULTS

Baseline TGF-β and second and third trimesters IFN-γ and IL-2 were associated with baseline 25(OH)D. Baseline immune-mediators were associated with immune-mediators at second and third trimesters for all immune-mediators except IL-5 and IL-10. Race was associated with baseline TGF-β, VEGF and IL-10 and with IL-10 at second and third trimesters.

CONCLUSIONS

Both treatment groups had increased 25(OH)D at second and third trimesters, greatest in the 4400 IU group. Though associations between baseline 25(OH)D and baseline TGF-β and second and third trimester IFN-γ and IL-2 were noted, vitamin D supplementation throughout pregnancy did not impact immune-mediators at later trimesters. Supplementing with vitamin D before conception conceivably influences immune-mediator responses during pregnancy.

IMPACT

In this vitamin D supplementation clinical trial, baseline (first trimester) but not increasing plasma 25(OH)D concentration impacted select plasma immune-mediator profiles in pregnant women. Baseline 25(OH)D was associated with baseline TGF-β and with IFN-γ and IL-2 at second and third trimesters. Baseline IFN-γ, CRP, TGF-β, TNF-α, VEGF, IL-2, and IL-4 were associated with concentrations at second and third trimesters for respective immune-mediators; however, 25(OH)D concentration at second and third trimesters were not. Some racial differences existed in immune-mediator concentrations at baseline and at second and third trimesters. This study assesses the impact of vitamin D supplementation on multiple immune-mediators in pregnant women of different racial/ethnic groups using longitudinal data from a relatively large randomized controlled trial. This study found that race was associated with baseline TGF-β, VEGF, and IL-10 and with IL-10 at second and third trimesters, a novel finding that sheds light where relationships were less well defined. The results of this study suggest that vitamin D supplementation before conception or early in pregnancy, rather than during pregnancy, may be necessary to significantly impact immune-mediator response. This study sets premise for future clinical trials to evaluate the effect of vitamin D supplementation before conception or prior to pregnancy.

Inflammation Modulation by Vitamin D and Calcium in the Morphologically Normal Colorectal Mucosa of Patients with Colorectal Adenoma in a Clinical Trial

Increased COX-2 and decreased 15-hydroxyprostaglandin dehydrogenase (15-HPGD) expression promote prostaglandin-mediated inflammation and colorectal carcinogenesis. Experimental studies suggest that vitamin D and calcium may inhibit these pathways, but their effects on colorectal tissue COX-2 and 15-HPGD expression in humans are unknown. We tested the effects of supplemental vitamin D (1,000 IU/day) and/or calcium (1,200 mg/day) on COX-2 and 15-HPGD expression in the morphologically normal rectal mucosa from 62 paients with colorectal adenoma in a placebo-controlled chemoprevention trial. We measured biomarker expression using automated IHC and quantitative image analysis at baseline and 1-year follow-up, and assessed treatment effects using mixed linear models. The primary outcome was the COX-2/15-HPGD expression ratio, because these enzymes function as physiologic antagonists. After 1 year of treatment, the mean COX-2/15-HPGD expression ratio in full-length crypts proportionately decreased 47% in the vitamin D group (P = 0.001), 46% in the calcium group (P = 0.002), and 34% in the calcium + vitamin D group (P = 0.03), relative to the placebo group. Among individuals with the functional vitamin D-binding protein isoform DBP2 (GC rs4588*A), the COX-2/15-HPDG ratio decreased 70% (P = 0.0006), 75% (P = 0.0002), and 60% (P = 0.006) in the vitamin D, calcium, and combined supplementation groups, respectively, relative to placebo. These results show that vitamin D and calcium favorably modulate the balance of expression of COX-2 and 15-HPGD-biomarkers of inflammation that are strongly linked to colorectal carcinogenesis-in the normal-appearing colorectal mucosa of patients with colorectal adenoma (perhaps especially those with the DBP2 isoform). PREVENTION RELEVANCE: Supplemental calcium and vitamin D reduce indicators of cancer-promoting inflammation in normal colorectal tissue in humans, thus furthering our understanding of how they may help prevent colorectal cancer.

Perspective: Vitamin D deficiency and COVID-19 severity - plausibly linked by latitude, ethnicity, impacts on cytokines, ACE2 and thrombosis

BACKGROUND

SARS-CoV-2 coronavirus infection ranges from asymptomatic through to fatal COVID-19 characterized by a 'cytokine storm' and lung failure. Vitamin D deficiency has been postulated as a determinant of severity.

OBJECTIVES

To review the evidence relevant to vitamin D and COVID-19.

METHODS

Narrative review.

RESULTS

Regression modelling shows that more northerly countries in the Northern Hemisphere are currently (May 2020) showing relatively high COVID-19 mortality, with an estimated 4.4% increase in mortality for each 1 degree latitude north of 28 degrees North (P = 0.031) after adjustment for age of population. This supports a role for ultraviolet B acting via vitamin D synthesis. Factors associated with worse COVID-19 prognosis include old age, ethnicity, male sex, obesity, diabetes and hypertension and these also associate with deficiency of vitamin D or its response. Vitamin D deficiency is also linked to severity of childhood respiratory illness. Experimentally, vitamin D increases the ratio of angiotensin-converting enzyme 2 (ACE2) to ACE, thus increasing angiotensin II hydrolysis and reducing subsequent inflammatory cytokine response to pathogens and lung injury.

CONCLUSIONS

Substantial evidence supports a link between vitamin D deficiency and COVID-19 severity but it is all indirect. Community-based placebo-controlled trials of vitamin D supplementation may be difficult. Further evidence could come from study of COVID-19 outcomes in large cohorts with information on prescribing data for vitamin D supplementation or assay of serum unbound 25(OH) vitamin D levels. Meanwhile, vitamin D supplementation should be strongly advised for people likely to be deficient.

Association of prediagnostic vitamin D status with mortality among colorectal cancer patients differs by common, inherited vitamin D-binding protein isoforms

Lower prediagnostic circulating 25-hydroxyvitamin D (25[OH]D)-considered the best marker of total vitamin D exposure-is associated with higher mortality risk among colorectal cancer (CRC) patients. However, it is unknown whether this association differs by the vitamin D-binding protein (GC) isoform Gc2 (encoded by GC rs4588*C>A, Thr436Lys), which may substantially affect vitamin D metabolism and modify associations of 25(OH)D with colorectal neoplasm risk. Prediagnostic 25(OH)D-mortality associations according to Gc2 isoform were estimated using multivariable Cox proportional hazards regression among 1281 CRC cases (635 deaths, 483 from CRC) from two large prospective cohorts conducted in the United States (Cancer Prevention Study-II) and Europe (European Prospective Investigation into Cancer and Nutrition). 25(OH)D measurements were calibrated to a single assay, season standardized, and categorized using Institute of Medicine recommendations (deficient [<30], insufficient [30 - <50], sufficient [≥50 nmol/L]). In the pooled analysis, multivariable-adjusted hazard ratios (HRs) for CRC-specific mortality associated with deficient relative to sufficient 25(OH)D concentrations were 2.24 (95% CI 1.44-3.49) among cases with the Gc2 isoform, and 0.94 (95% CI 0.68-1.22) among cases without Gc2 (Pinteraction = .0002). The corresponding HRs for all-cause mortality were 1.80 (95% CI 1.24-2.60) among those with Gc2, and 1.12 (95% CI 0.84-1.51) among those without Gc2 (Pinteraction = .004). Our findings suggest that the association of prediagnostic vitamin D status with mortality among CRC patients may differ by functional GC isoforms, and patients who inherit the Gc2 isoform (GC rs4588*A) may particularly benefit from higher circulating 25(OH)D for improved CRC prognosis.

The Free Hormone Hypothesis: When, Why, and How to Measure the Free Hormone Levels to Assess Vitamin D, Thyroid, Sex Hormone, and Cortisol Status

The free hormone hypothesis postulates that only the nonbound fraction (the free fraction) of hormones that otherwise circulate in blood bound to their carrier proteins is able to enter cells and exert biologic effects. In this review, I will examine four hormone groups-vitamin D metabolites (especially 25OHD), thyroid hormones (especially thyroxine [T4]), sex steroids (especially testosterone), and glucocorticoids (especially cortisol)-that are bound to various degrees to their respective binding proteins-vitamin D-binding protein (DBP), thyroid-binding globulin (TBG), sex hormone-binding globulin (SHBG), and cortisol-binding globulin (CBG)-for which a strong case can be made that measurement of the free hormone level provides a better assessment of hormonal status than the measurement of total hormonal levels under conditions in which the binding proteins are affected in levels or affinities for the hormones to which they bind. I will discuss the rationale for this argument based on the free hormone hypothesis, discuss potential exceptions to the free hormone hypothesis, and review functions of the binding proteins that may be independent of their transport role. I will then review the complications involved with measuring the free hormone levels and the efforts to calculate those levels based on estimates of binding constants and levels of both total hormone and total binding protein. In this review, the major focus will be on DBP and free 25OHD, but the parallels and differences with the other binding proteins and hormones will be highlighted. Vitamin D and its metabolites, thyroid hormones, sex steroids, and glucocorticoids are transported in blood bound to serum proteins. The tightness of binding varies depending on the hormone and the binding protein such that the percent free varies from 0.03% for T4 and 25OHD to 4% for cortisol with testosterone at 2%. Although the major function of the primary carrier proteins (DBP, TBG, SHBG, and CBG) may be to transport their respective lipophilic hormones within the aqueous media that is plasma, these proteins may have other functions independent of their transport function. For most tissues, these hormones enter the cell as the free hormone presumably by diffusion (the free hormone hypothesis), although a few tissues such as the kidney and reproductive tissues express megalin/cubilin enabling by endocytosis protein-bound hormone to enter the cell. Measuring the free levels of these protein-bound hormones is likely to provide a better measure of the true hormone status than measuring the total levels in situations where the levels and/or affinities of the binding proteins are altered. Methods to measure free hormone levels are problematic as the free levels can be quite low, the methods require separation of bound and free that could disturb the steady state, and the means of separating bound and free are prone to error. Calculation of free levels using existing data for association constants between the hormone and its binding protein are likewise prone to error because of assumptions of linear binding models and invariant association constants, both of which are invalid. © 2020 The Author. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

MECHANISMS IN ENDOCRINOLOGY: Vitamin D and COVID-19

The SARS-CoV-2 virus responsible for the COVID-19 pandemic has generated an explosion of interest both in the mechanisms of infection leading to dissemination and expression of this disease, and in potential risk factors that may have a mechanistic basis for disease propagation or control. Vitamin D has emerged as a factor that may be involved in these two areas. The focus of this article is to apply our current understanding of vitamin D as a facilitator of immunocompetence both with regard to innate and adaptive immunity and to consider how this may relate to COVID-19 disease. There are also intriguing potential links to vitamin D as a factor in the cytokine storm that portends some of the most serious consequences of SARS-CoV-2 infection, such as the acute respiratory distress syndrome. Moreover, cardiac and coagulopathic features of COVID-19 disease deserve attention as they may also be related to vitamin D. Finally, we review the current clinical data associating vitamin D with SARS-CoV-2 infection, a putative clinical link that at this time must still be considered hypothetical.

Myogenic, genomic and non-genomic influences of the vitamin D axis in skeletal muscle

Despite vitamin D-deficiency clinically presenting with myopathy, muscle weakness and atrophy, the mechanisms by which vitamin D exerts its homeostatic effects upon skeletal muscle remain to be fully established. Recent studies have shown that the receptor by which 1α,25-dihydroxyvitamin D₃ (1,25[OH]₂ D₃ ) exerts its biological actions (ie, the vitamin D receptor, VDR) elicits both genomic and non-genomic effects upon skeletal muscle. The controversy surrounding skeletal muscle VDR mRNA/protein expression in post-natal muscle has been allayed by myriad recent studies, while dynamic expression of VDR throughout myogenesis, and association of higher VDR levels during muscle regeneration/immature muscle cells, suggests a role in myogenesis and perhaps an enrichment of VDR in satellite cells. Accordingly, in vitro studies have demonstrated 1,25(OH)₂ D₃ is anti-proliferative in myoblasts, yet pro-differentiation in latter stages of myogenesis. These effects involve modulation of gene expression (VDR as a transcriptional co-activator controls ~3% of the genome) and post-genomic intracellular signalling for example, via c-Src and alterations to intramuscular calcium homeostasis and proteostasis. The aim of this review is to consider the biomolecular role for the vitamin D/VDR axis in myogenesis, while also exploring global evidence for genomic and non-genomic mechanisms of action for 1,25(OH)₂ D₃ /VDR.

Comparison of Serum Free and Bioavailable 25-Hydroxyvitamin D Levels in Alzheimer's Disease and Healthy Control Patients

OBJECTIVE

Many studies have investigated lower 25-hydroxyvitamin D (25[OH]D) levels in patients with Alzheimer's disease (AD) compared with those in control patients. In the present study, we aimed to evaluate serum free and bioavailable 25(OH)D levels in patients with AD and in healthy control patients.

METHODS

The AD group consisted of 85 patients aged >60 years who were diagnosed with possible AD according to National Institute on Aging-Alzheimer's Association criteria and 85 healthy control patients. Serum levels of total 1,25-dihydroxyvitamin D, total 25(OH)D, vitamin D binding protein (VDBP), parathormone, calcium, phosphorus and albumin, free 25(OH)D, bioavailable 25(OH)D, and the bioavailable 25(OH)D/total 25(OH)D ratio were compared in both groups.

RESULTS

Total 25(OH)D, free 25(OH)D, bioavailable 25(OH)D, and the bioavailable 25(OH)D/total 25(OH)D ratio were significantly lower (P <.001, P <.001, P <.001, P <.05, respectively) in the AD group, whereas the VDBP level was significantly higher (P <.05) in the AD than in the control group.

CONCLUSION

Free and bioavailable 25(OH)D detected at lower levels in patients with AD limit the target central effects of 25(OH)D; this result suggests that reduced levels of the active free form of vitamin D may be a risk factor for AD and dementia.

Role of Vitamin D in Prevention of Food Allergy in Infants

The prevalence of food allergy is increasing over the last decades. The role of vitamin D in the prevention of food allergy has been largely investigated. Its role on the physiology of calcium and bone is known, but calcitriol (active form of the vitamin D) also influences the epithelial cells, T cells, B cells, macrophages, and dendritic cells. Almost all cells of the adaptive immune system express the vitamin D receptor, making them also capable of being vitamin responsive. Specifically considering the potential role of vitamins in food allergy, vitamin D has been shown to affect several mechanisms that promote immunologic tolerance, including the T regulatory cell function and the induction of tolerogenic dendritic cells. The target of our review is to evaluate the role of vitamin D in the prevention of food allergy in children. There are contradictory data on the relationship among the vitamin D deficiency and the developing of food allergy. Some studies associate lower exposure to sunlight to food allergy; on the other hand, further research has found that higher vitamin D levels could increase the likelihood of allergic sensitization and food allergy. Therefore, there is an urgent need for well-planned randomized controlled trials on vitamin D supplementation, with particular regard to the prevention of food allergy. The role of vitamin D beyond bone and calcium metabolism is not fully understood.

Vitamin D regulation of adipogenesis and adipose tissue functions

Vitamin D insufficiency is associated with obesity and its related metabolic diseases. Adipose tissues store and metabolize vitamin D and expression levels of vitamin D metabolizing enzymes are known to be altered in obesity. Sequestration of vitamin D in large amount of adipose tissues and low vitamin D metabolism may contribute to the vitamin D inadequacy in obesity. Vitamin D receptor is expressed in adipose tissues and vitamin D regulates multiple aspects of adipose biology including adipogenesis as well as metabolic and endocrine function of adipose tissues that can contribute to the high risk of metabolic diseases in vitamin D insufficiency. We will review current understanding of vitamin D regulation of adipose biology focusing on vitamin D modulation of adiposity and adipose tissue functions as well as the molecular mechanisms through which vitamin D regulates adipose biology. The effects of supplementation or maintenance of vitamin D on obesity and metabolic diseases are also discussed.

Scavenger Receptor Class B Type I is Required for 25-Hydroxycholecalciferol Cellular Uptake and Signaling in Myeloid Cells

SCOPE

Vitamin D₃ is a critical molecule for the properly controlled activity of the immune system. In myeloid-derived cells, vitamin D₃ induces the production of the antimicrobial and antitumor peptide cathelicidin. In this study, the mechanism of the entry of 25-hydroxycholecalciferol (25(OH)D) in myeloid-derived cells is explored.

METHODS AND RESULTS

Here, a novel regulatory pathway of vitamin D₃ biology is described. Using a polyclonal antibody, two different chemical inhibitors, and a high-density lipoprotein as a competing ligand, it is demonstrated here that the 25(OH)D signaling pathway in myeloid cells depends on scavenger receptor class B type I (SR-B1). This effect is observed in the THP-1 monocytic cell line and in human primary monocytes. SR-B1 blockade abrogates the cellular uptake of 25(OH)D leading to a general shut down of the gene transcription program modulated by 25(OH)D. The results obtained at the transcriptional level are confirmed at the protein and functional level for CD14 in the THP-1 cell line.

CONCLUSION

In conclusion, SR-B1 plays a critical role in vitamin D₃ biology, paving the way for novel therapeutic interventions.

New aspects of vitamin D metabolism and action - addressing the skin as source and target

Vitamin D has a key role in stimulating calcium absorption from the gut and promoting skeletal health, as well as many other important physiological functions. Vitamin D is produced in the skin. It is subsequently metabolized to its hormonally active form, 1,25-dihydroxyvitamin D (1,25(OH)₂D), by the 1-hydroxylase and catabolized by the 24-hydroxylase. In this Review, we pay special attention to the effect of mutations in these enzymes and their clinical manifestations. We then discuss the role of vitamin D binding protein in transporting vitamin D and its metabolites from their source to their targets, the free hormone hypothesis for cell entry and HSP70 for intracellular transport. This is followed by discussion of the vitamin D receptor (VDR) that mediates the cellular actions of 1,25(OH)₂D. Cell-specific recruitment of co-regulatory complexes by liganded VDR leads to changes in gene expression that result in distinct physiological actions by 1,25(OH)₂D, which are disrupted by mutations in the VDR. We then discuss the epidermis and hair follicle, to provide a non-skeletal example of a tissue that expresses VDR that not only makes vitamin D but also can metabolize it to its hormonally active form. This enables vitamin D to regulate epidermal differentiation and hair follicle cycling and, in so doing, to promote barrier function, wound healing and hair growth, while limiting cancer development.

Association of Circulating Vitamin D With Colorectal Cancer Depends on Vitamin D-Binding Protein Isoforms: A Pooled, Nested, Case-Control Study

BACKGROUND

Higher circulating 25-hydroxyvitamin-D [25(OH)D] concentrations are consistently inversely associated with colorectal cancer (CRC) risk in observational studies. However, it is unknown whether this association depends on the functional GC-rs4588*A (Thr436Lys) variant encoding the vitamin D-binding protein-2 (DBP2) isoform, which may affect vitamin D status and bioavailability.

METHODS

We analyzed data from 1710 incident CRC cases and 1649 incidence-density-matched controls nested within three prospective cohorts of mostly Caucasians. Study-specific incidence rate ratios (RRs) for associations of prediagnostic, season-standardized 25(OH)D concentrations according to DBP2 isoform with CRC were estimated using multivariable unconditional logistic regression and were pooled using fixed-effects models. All statistical significance tests were two-sided.

RESULTS

The odds of having 25(OH)D concentrations less than 50 nmol/L (considered insufficient by the Institute of Medicine) were 43% higher for each DBP2-encoding variant (rs4588*A) inherited (per DBP2 odds ratio [OR] = 1.43, 95% confidence interval [CI] = 1.27 to 1.62, P trend = 1.2 × 10-8). The association of 25(OH)D concentrations with CRC risk differed by DBP2: 25(OH)D concentrations considered sufficient (≥ 50 nmol/L), relative to deficient (< 30 nmol/L), were associated with a 53% lower CRC risk among individuals with the DBP2 isoform (RR = 0.47, 95% CI = 0.33 to 0.67), but with a non-statistically significant 12% lower risk among individuals without it (RR = 0.88, 95% CI = 0.61 to 1.27) (P heterogeneity = .01).

CONCLUSIONS

Our results suggest that the 25(OH)D-CRC association may differ by DBP isoform, and those with a DBP2-encoding genotype linked to vitamin D insufficiency may particularly benefit from adequate 25(OH)D for CRC prevention.

Vitamin D, Autoimmune Disease and Rheumatoid Arthritis

Vitamin D has been reported to influence physiological systems that extend far beyond its established functions in calcium and bone homeostasis. Prominent amongst these are the potent immunomodulatory effects of the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). The nuclear vitamin D receptor (VDR) for 1,25-(OH)2D3 is expressed by many cells within the immune system and resulting effects include modulation of T cell phenotype to suppress pro-inflammatory Th1 and Th17 CD4+ T cells and promote tolerogenic regulatory T cells. In addition, antigen-presenting cells have been shown to express the enzyme 1α-hydroxylase that converts precursor 25-hydroxyvitamin D3 (25-OHD3) to 1,25-(OH)2D3, so that immune microenvironments are able to both activate and respond to vitamin D. As a consequence of this local, intracrine, system, immune responses may vary according to the availability of 25-OHD3, and vitamin D deficiency has been linked to various autoimmune disorders including rheumatoid arthritis (RA). The aim of this review is to explore the immune activities of vitamin D that impact autoimmune disease, with specific reference to RA. As well as outlining the mechanisms linking vitamin D with autoimmune disease, the review will also describe the different studies that have linked vitamin D status to RA, and the current supplementation studies that have explored the potential benefits of vitamin D for prevention or treatment of RA. The overall aim of the review is to provide a fresh perspective on the potential role of vitamin D in RA pathogenesis and treatment.

Vitamin D-binding protein as a biomarker to confirm specific clinical diagnoses

Introduction: Vitamin D-binding protein (DBP) performs a variety of functions as a transporter for various ligands and takes part in a number of systemic and local physiological and pathological processes. The knowledge about the pathomechanisms of this protein involvement justifies its use as a biomarker to confirm specific clinical diagnoses suggested by nonspecific signs and symptoms.Areas covered: DBP has properties of both systemic laboratory parameters measured in the blood plasma and specific parameters measured in variety of physiological fluids to assess local changes in specific body organs. Articles published in English between 1993 and 2019 were searched for in PubMed using terms DBP, vitamin D, and metabolites, inflammation. DBP is a transport protein and a regulator of immune and inflammatory processes.Expert opinion: DBP capacity for transporting numerous ligands and co-involvement of DBP in immune and inflammatory processes suggest that DBP may be used in laboratory diagnostics as a specific parameter to confirm pathomechanisms of several systemic diseases and local conditions. Changes in the concentration of DBP present in a variety of clinical material may provide valuable information for use in assessing the severity and treatment of pathological processes.

Multiple Sclerosis Patients Show Lower Bioavailable 25(OH)D and 1,25(OH)2D, but No Difference in Ratio of 25(OH)D/24,25(OH)2D and FGF23 Concentrations

Vitamin D (VitD) insufficiency is common in multiple sclerosis (MS). VitD has possible anti-inflammatory effects on the immune system. The ratio between VitD metabolites in MS patients and the severity of the disease are suggested to be related. However, the exact effect of the bone-derived hormone fibroblast-growth-factor-23 (FGF23) and VitD binding protein (VDBP) on this ratio is not fully elucidated yet. Therefore, the aim is to study differences in total, free, and bioavailable VD metabolites and FGF23 between MS patients and healthy controls (HCs). FGF23, vitD (25(OH)D), active vitD (1,25(OH)₂D), inactive 24,25(OH)D, and VDBP were measured in 91 MS patients and 92 HCs. Bioavailable and free concentrations were calculated. No difference in FGF23 (p = 0.65) and 25(OH)D/24.25(OH)₂D ratio (p = 0.21) between MS patients and HCs was observed. Bioavailable 25(OH)D and bioavailable 1.25(OH)₂D were lower (p < 0.01), while VDBP concentrations were higher in MS patients (p = 0.02) compared with HCs, specifically in male MS patients (p = 0.01). In conclusion, FGF23 and 25(OH)D/24.25(OH)₂D did not differ between MS patients and HCs, yet bioavailable VitD concentrations are of potential clinical relevance in MS patients. The possible immunomodulating role of VDBP and gender-related differences in the VD-FGF23 axis in MS need further study.

The vitamin D metabolome: An update on analysis and function

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

Opposing effects of 25-hydroxy- and 1α,25-dihydroxy-vitamin D3 on pro-cachectic cytokine-and cancer conditioned medium-induced atrophy in C2C12 myotubes

AIM

Loss of skeletal muscle is one of the main features of cancer cachexia. Vitamin D (VD) deficiency is associated with impairment of muscle mass and performance and is highly prevalent in cachectic patients; therefore, VD supplementation has been proposed to counteract cancer cachexia-associated muscle loss. However, in both cachectic cancer patients and tumour-bearing animals, VD supplementation led to disappointing results, urging the need for a better understanding of VD activity on skeletal muscle.

METHODS

Cancer-associated muscle wasting was reproduced in vitro by treating C2C12 myotubes with cancer cell conditioned medium, a combination of TNF-α and IFNγ or IL-6 pro-cachectic cytokines. The biological effects and mechanisms of action of 1,25-dihydroxy VD (1,25 VD) and its precursor 25-hydroxy VD (25 VD) on myotubes were explored.

RESULTS

We demonstrated that only 25 VD was able to protect from atrophy by activating Akt signalling, inducing protein synthesis, and stimulating the autophagic flux, while 1,25 VD had an atrophic activity per se, increasing FoxO3 levels, inducing the expression of atrogenes, and blocking the autophagic flux. Furthermore, we showed that the contrasting activities of these VD metabolites on C2C12 myotubes depend on a differential induction of VD-24-hydroxylase and transformation of VD metabolites in pro-atrophic 24-hydroxylated products, as silencing of VD-24-hydroxylase reduced the atrophic activity of 1,25 VD.

CONCLUSIONS

Altogether these data might explain the lack of efficacy of VD treatment in vivo for the protection of muscle mass in cancer.

Which Risk Factors Causally Influence Dementia? A Systematic Review of Mendelian Randomization Studies

Background:

Numerous risk factors for dementia are well established, though the causal nature of these associations remains unclear.

Objective:

To systematically review Mendelian randomization (MR) studies investigating causal relationships between risk factors and global cognitive function or dementia.

Methods:

We searched five databases from inception to February 2017 and conducted citation searches including MR studies investigating the association between any risk factor and global cognitive function, all-cause dementia or dementia subtypes. Two reviewers independently assessed titles and abstracts, full-texts, and study quality.

Results:

We included 18 MR studies investigating education, lifestyle factors, cardiovascular factors and related biomarkers, diabetes related and other endocrine factors, and telomere length. Studies were of predominantly good quality, however eight received low ratings for sample size and statistical power. The most convincing causal evidence was found for an association of shorter telomeres with increased risk of Alzheimer’s disease (AD). Causal evidence was weaker for smoking quantity, vitamin D, homocysteine, systolic blood pressure, fasting glucose, insulin sensitivity, and high-density lipoprotein cholesterol. Well-replicated associations were not present for most exposures and we cannot fully discount survival and diagnostic bias, or the potential for pleiotropic effects.

Conclusions:

Genetic evidence supported a causal association between telomere length and AD, whereas limited evidence for other risk factors was largely inconclusive with tentative evidence for smoking quantity, vitamin D, homocysteine, and selected metabolic markers. The lack of stronger evidence for other risk factors may reflect insufficient statistical power. Larger well-designed MR studies would therefore help establish the causal status of these dementia risk factors.

Efeitos contrastantes da vitamina D sobre a resposta imune inata e adquirida e seu impacto na recuperação da tuberculose

A vitamina D é um hormônio essencial para o organismo, podendo ser obtida da dieta ou, principalmente, gerada pela pele após exposição à luz solar ultravioleta B. Na sua forma ativa (1,25(OH)2D) ela controla a absorção de cálcio e fósforo do intestino para a corrente sanguínea e participa de diversos processos celulares e fisiológicos. A ligação da 1,25(OH)2D ao receptor da vitamina D (VDR) presente em diversas células, como as células do sistema imunológico, induz a transcrição de genes que podem, por exemplo, modular a resposta imune inata e adquirida. A deficiência de vitamina D ou do VDR é associada a problemas de saúde como desordens esqueléticas, hipertensão, doenças cardiovasculares, diabetes mellitus, dislipidemias, doenças autoimunes e doenças infecciosas. Neste sentido, a suplementação com vitamina D tem sido proposta como uma possível medida preventiva, podendo ser aplicada em muitas patologias, em especial na tuberculose. Principal causa de morte por um único agente infeccioso, a tuberculose é responsável por cerca de 1,3 milhões de óbitos por ano no mundo. Publicações recentes apontam efeitos diversos da vitamina D na resposta imune inata e adquirida. A 1,25(OH)2D3 na presença do interferon (IFN)-γ é capaz de aumentar a atividade bactericida do macrófago contra o M. tuberculosis, aumentando a produção de peptídios antimicrobianos e estimulando a autofagia, favorecendo assim a lise de bacilos localizados em fagossomos. Por outro lado, a vitamina D em linfócitos T mostra efeito tolerogênico que favorece o controle de respostas inflamatórias excessivas. Neste trabalho de revisão são apresentados estudos recentes envolvendo efeitos da vitamina D na resposta imune inata e adquirida. Além disso, considerações sobre deficiência de vitamina D e maior risco de contrair tuberculose, e efeitos contrastantes da suplementação com vitamina D na prevenção e tratamento da TB, são discutidos.

The Role of Vitamin D in Inflammatory Bowel Disease: Mechanism to Management

Vitamin D has been linked to human health benefits that extend far beyond its established actions on calcium homeostasis and bone metabolism. One of the most well studied facets of extra-skeletal vitamin D is its activity as an immuno-modulator, in particular its potent anti-inflammatory effects. As a consequence, vitamin D deficiency has been associated with inflammatory diseases including inflammatory bowel disease (IBD). Low serum levels of the major circulating form of vitamin D, 25-hydroxyvitamin D (25-OH-D) are significantly more prevalent in patients with IBD, particularly in the winter and spring months when UV-induced synthesis of vitamin D is lower. Dietary malabsorption of vitamin D may also contribute to low serum 25(OH)D in IBD. The benefits of supplementation with vitamin D for IBD patients are still unclear, and improved vitamin D status may help to prevent the onset of IBD as well as ameliorating disease severity. Beneficial effects of vitamin D in IBD are supported by pre-clinical studies, notably with mouse models, where the active form of vitamin D, 1,25-dihydroxyvitamin D (1,25-(OH)2D) has been shown to regulate gastrointestinal microbiota function, and promote anti-inflammatory, tolerogenic immune responses. The current narrative review aims to summarise the different strands of data linking vitamin D and IBD, whilst also outlining the possible beneficial effects of vitamin D supplementation in managing IBD in humans.

Free versus total serum 25-hydroxyvitamin D in a murine model of colitis

Inflammatory bowel diseases (IBD) such as ulcerative colitis and Crohn's disease have been linked to vitamin D-deficiency. Using a dextran sodium sulphate (DSS)-induced model of IBD we have shown previously that mice raised on vitamin D-deficient diets from weaning have lower serum 25-hydroxyvitamin D (25OHD) levels and develop more severe colitis compared to vitamin D-sufficient counterparts. We have also shown in vitro that immune responses to 25OHD may depend on 'free' rather than total serum concentrations of 25OHD. To investigate the possible effects of free versus total 25OHD on anti-inflammatory immune responses in vivo we have studied DSS-induced colitis in wild type C57BL/6 mice raised from weaning on diets containing vitamin D2 (D2) or vitamin D3 (D3) only (both 1000 IU/kg feed). 25OHD2 has lower binding affinity for the vitamin D binding protein than 25OHD3 which results in higher levels of free 25OHD2 relative to free 25OHD3 in mice raised on a D2-only diet. Total serum 25OHD concentrations, measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS), showed that D2 mice had significantly lower levels of 25OHD than D3 mice (6.85 ± 2.61 nmol/L vs. 49.16 ± 13.8 nmol/L for D2 and D3 respectively). Despite this, direct ELISA measurement showed no difference in free serum 25OHD levels between D2 and D3 mice (13.62 ± 2.26 pmol/L vs. 14.11 ± 2.24 pmol/L for D2 and D3 respectively). Analysis of DSS-induced colitis also showed no difference in weight loss or disease progression between D2 and D3 mice. These data indicate that despite D2-fed mice being vitamin D-deficient based on serum total 25OHD concentrations, these mice showed no evidence of increased inflammatory colitis disease relative to vitamin D-sufficient D3 mice. We therefore propose that free, rather than total serum 25OHD, may be a better marker of immune responses to vitamin D in vivo.

Maternal and Newborn Vitamin D-Binding Protein, Vitamin D Levels, Vitamin D Receptor Genotype, and Childhood Type 1 Diabetes

OBJECTIVE

Circumstantial evidence links 25-hydroxy vitamin D [25(OH)D], vitamin D-binding protein (DBP), vitamin D-associated genes, and type 1 diabetes (T1D), but no studies have jointly analyzed these. We aimed to investigate whether DBP levels during pregnancy or at birth were associated with offspring T1D and whether vitamin D pathway genetic variants modified associations between DBP, 25(OH)D, and T1D.

RESEARCH DESIGN AND METHODS

From a cohort of >100,000 mother/child pairs, we analyzed 189 pairs where the child later developed T1D and 576 random control pairs. We measured 25(OH)D using liquid chromatography-tandem mass spectrometry, and DBP using polyclonal radioimmunoassay, in cord blood and maternal plasma samples collected at delivery and midpregnancy. We genotyped mother and child for variants in or near genes involved in vitamin D metabolism (GC, DHCR7, CYP2R1, CYP24A1, CYP27B1, and VDR). Logistic regression was used to estimate odds ratios (ORs) adjusted for potential confounders.

RESULTS

Higher maternal DBP levels at delivery, but not in other samples, were associated with lower offspring T1D risk (OR 0.86 [95% CI 0.74-0.98] per μmol/L increase). Higher cord blood 25(OH)D levels were associated with lower T1D risk (OR = 0.87 [95% CI 0.77-0.98] per 10 nmol/L increase) in children carrying the VDR rs11568820 G/G genotype (P _interaction = 0.01 between 25(OH)D level and rs11568820). We did not detect other gene-environment interactions.

CONCLUSIONS

Higher maternal DBP level at delivery may decrease offspring T1D risk. Increased 25(OH)D levels at birth may decrease T1D risk, depending on VDR genotype. These findings should be replicated in other studies. Future studies of vitamin D and T1D should include VDR genotype and DBP levels.

In vitro metabolic activation of vitamin D3 by using a multi-compartment microfluidic liver-kidney organ on chip platform

Organ-on-chip platforms provide models that allow the representation of human physiological processes in cell-based miniaturized systems. Potential pre-clinical applications include drug testing and toxicity studies. Here we describe the use of a multi-compartment micro-fluidic chip to recapitulate hepatic vitamin D metabolism (vitamin D to 25-hydroxyvitamin D) and renal bio-activation (25-hydroxyvitamin D to 1,25-dihydroxyvitamin D) in humans. In contrast to cultivation in conventional tissue culture settings, on-chip cultivation of HepG2 and RPTEC cells in interconnected chambers, used to mimic the liver and kidneys, respectively, resulted in the enhanced expression of vitamin D metabolizing enzymes (CYP2R1, CYP27B1 and CYP24A1). Pump-driven flow of vitamin D3-containing medium through the microfluidic chip produced eluate containing vitamin D3 metabolites. LC-MSMS showed a strong accumulation of 25-hydroxyvitamin D. The chip eluate induced the expression of differentiation markers in HL-60 (acute myeloid leukemia) cells, assessed by qPCR and FACS analysis, in a manner similar to treatment with reference standards indicating the presence of fully activated 1,25 dihydroxyvitamin D, although the latter was not detected in the eluate by LC-MSMS. Interestingly, 25-hydroxyvitamin D by itself led to weak activation of HL-60 cells suggesting that 25-hydroxyvitamin D is also an active metabolite. Our experiments demonstrate that complex metabolic interactions can be reconstructed outside the human body using dedicated organ-on-chip platforms. We therefore propose that such systems may be used to mimic the in vivo metabolism of various micronutrients and xenobiotics.

Serum and synovial fluid vitamin D metabolites and rheumatoid arthritis

Vitamin D-deficiency has been linked to inflammatory diseases including rheumatoid arthritis (RA). Studies to date have focused on the impact of serum 25-hydroxyvitamin D3 (25(OH)D3), an inactive form of vitamin D, on RA disease activity and progression. However, anti-inflammatory actions of vitamin D are likely to be mediated at sites of RA disease, namely the inflamed joint, and may involve other vitamin D metabolites notably the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). In the current study serum and synovial fluid samples from n = 20 patients with persistent RA and n = 7 patients with reactive arthritis (ReA) were analysed for multiple vitamin D metabolites. Serum data for RA and ReA patients were compared to healthy controls (HC). There was no significant difference between RA or ReA patients relative to HC for 25(OH)D3, 24,25(OH)2D3, 1,25(OH)2D3 or 25(OH)D2. However, 3-epi-25(OH)D3 was significantly lower in RA and ReA patients compared to HC (p < 0.05). All vitamin D metabolites, apart from 25(OH)D2, were lower in SF compared to serum, and SF 1,25(OH)2D3 was unquantifiable in 13/20 RA and 4/7 ReA samples. SF 25(OH)D3, 3-epi-25(OH)D3 and DBP correlated inversely with swollen joint score, and serum 25(OH)D2 and SF DBP correlated directly with C-reactive protein levels. These data indicate that serum 25(OH)D3 provides only limited insight into the role of vitamin D in RA. Alternative serum metabolites such as 3-epi-25(OH)2D3, and SF metabolites, notably lack of SF 1,25(OH)2D3, may be more closely linked to RA disease severity and progress.