Regulation of immune function continues to be one of the most well recognised extra-skeletal actions of vitamin D. This stemmed initially from the discovery that antigen presenting cells such as macrophages could actively metabolise precursor 25-hydroxyvitamin D (25D) to active 1,25-dihydroxyvitamin D (1,25D). Parallel observation that activated cells from the immune system expressed the intracellular vitamin D receptor (VDR) for 1,25D suggested a potential role for vitamin D as a localised endogenous modulator of immune function. Subsequent studies have expanded our understanding of how vitamin D exerts effects on both the innate and adaptive arms of the immune system. At an innate level, intracrine synthesis of 1,25D by macrophages and dendritic cells (DC) stimulates expression of antimicrobial proteins such as cathelicidin, as well as lowering intracellular iron concentrations via suppression of hepcidin. By potently enhancing autophagy, 1,25D may also play an important role in combatting intracellular pathogens such as M. tuberculosis and viral infections. Local synthesis of 1,25D by macrophages and DC also appears to play a pivotal role in mediating T cell responses to vitamin D, leading to suppression of inflammatory T helper (Th)1 and Th17 cells, and concomitant induction of immunotolerogenic T regulatory (Treg) responses. The aim of this review is to provide an update on our current understanding of these prominent immune actions of vitamin D, as well as highlighting new, less well-recognised immune effects of vitamin D. The review also aims to place this mechanistic basis for the link between vitamin D and immunity with studies in vivo that have explored a role for vitamin D supplementation as a strategy for improved immune health. This has gained prominence in recent months with the global COVID-19 health crisis and highlights important new objectives for future studies of vitamin D and immune function. This article is protected by copyright. All rights reserved.

https://asbmr.onlinelibrary.wiley.com/doi/pdf/10.1002/jbm4.10405

Vitamin D and immune regulation: antibacterial, antiviral, anti-inflammatory.

Multiple sclerosis (MS) is a chronic inflammatory demyelinating and neurodegenerative disease of the central nervous system (CNS). In recent years, vitamin D has gained attention, as low serum levels are suspected to increase the risk for MS. Cholecalciferol supplementation has been tested in several clinical trials, since hypovitaminosis D was linked to higher disease activity and may even play a role in long-term outcome. Here, we review the current understanding of the molecular effects of vitamin D beyond calcium homeostasis, the potential beneficial action in MS and hazards including complications of chronic and high-dose therapy. In clinical trials, doses of up to 40,000 IU/day were tested and appeared safe as add-on therapy for short-term periods. A recent meta-analysis of a randomized, double-blind, placebo-controlled clinical trial investigating vitamin D as add-on therapy in MS, however, suggested that vitamin D had no therapeutic effect on disability or relapse rate. We recognize a knowledge gap for chronic and high-dose therapy, which can lead to life-threatening complications related to vitamin D toxicity including renal failure, cardiac arrythmia and status epilepticus. Moreover, vitamin D toxicity may manifest as fatigue, muscle weakness or urinary dysfunction, which may mimic the natural course of progressive MS. Given these limitations, vitamin D supplementation in MS is a sensitive task which needs to be supervised by physicians. While there is strong evidence for vitamin D deficiency and the development of MS, the risk-benefit profile of dosage and duration of add-on supplementation needs to be further clarified.

Vitamin D Supplementation in Multiple Sclerosis: A Critical Analysis of Potentials and Threats.

Over the last decades, a central role for vitamin D in immune modulation has been well established. The active form of vitamin D, i.e., 1,25-dihydroxyvitamin D, through the interaction with vitamin D receptor, exerts different activities on the innate and adaptive immune system, among which suppression of inflammation and promotion of tolerogenic responses. Vitamin D insufficiency has been linked to autoimmune disorders that commonly display significant differences between females and males due to genetic, epigenetic, hormonal, and environmental factors. Notably, a number of studies recently showed a cross-talk between vitamin D and the sex hormone estrogen. Estrogen-mediated effects on immune response may favor a Th1 profile or a Th2 profile, depending on hormone concentration. Thus, estrogen-mediated effects appear to be variable on autoimmunity depending on its concentration but also on the pathogenic mechanisms underlying the different autoimmune diseases (i.e., Th1- or Th2-mediated diseases). Notably, estrogen has been demonstrated to enhance vitamin D function favoring its accumulation, and increasing the expression of vitamin D receptor, thus resulting in a more potent anti-inflammatory response in females than males. On the other hand, vitamin D has been shown to downregulate in immune cells the expression of aromatase, which converts testosterone to estrogen, leading to a decrease in estrogen level. Overall, available data allow us to hypothesize a higher protective effect of vitamin D-based therapeutic approaches in women, at least in fertile age, than in men. Future studies are needed to expand current knowledge on the immunomodulatory role of vitamin D in a sex and gender perspective, paving the way to a more personalized therapeutic approach in autoimmune diseases.

/pdf/the-role-of-vitamin-d-in-autoimmune-diseases-could-sex-make-79m11xjj4z.pdf

The role of vitamin D in autoimmune diseases: could sex make the difference?

In the past decade, changes have occurred in the spectrum of multiple sclerosis courses. The natural history of multiple sclerosis appears milder from the first sign of demyelinating disease to the progressive course, probably as a result of an interplay between several factors including changes in the diagnostic criteria, changes in the epidemiology of multiple sclerosis, impact of early and appropriate disease-modifying treatment and improvement of the general state of health in the population. It has been suggested to regard incidental findings of demyelinating lesions in MRI in individuals without any history of clinical symptoms consistent with neurological dysfunction, so-called radiological isolated syndrome, as the initial course of multiple sclerosis. New diagnostic criteria have enabled the multiple sclerosis diagnosis in many patients at the first clinical demyelinating event, clinically isolated syndrome. The remaining patients with clinically isolated syndrome have a more benign prognosis, and for relapsing-remitting multiple sclerosis, the prognosis has become more favourable. Reduced disease activity in patients with relapsing-remitting multiple sclerosis can partly be ascribed to more efficacious new disease-modifying therapies but decrease in disease activity has also be seen in placebo-treated patients in clinical trials. This may be explained by several factors: change in the diagnostic criteria, more explicit inclusion criteria, exclusion of high-risk patients e.g. patients with co-morbidities, and more rigorous definitions of relapses and disease worsening. However, these factors also make the disease course in patients treated with disease-modifying therapies seem more favourable. In addition, change in the therapeutic target to stable disease (no evidence of disease activity = no relapses, no disease worsening and no MRI activity) could by itself change the course in relapsing-remitting multiple sclerosis. The effectiveness of disease-modifying drugs has reduced the transition from relapsing-remitting to secondary progressive multiple sclerosis. The concept of progressive multiple sclerosis has also evolved from two very distinct categories (primary progressive and secondary progressive multiple sclerosis) to a unified category of progressive multiple sclerosis, which can then be split into the categories of active or inactive. Also, an increasing tendency to treat progressive multiple sclerosis with disease-modifying therapies may have contributed to change the course in progressive multiple sclerosis. In conclusion, during the past decade the entire course of multiple sclerosis from the first sign of a demyelinating disorder through the progressive course appears to be milder due to a complex interplay of several factors.

The apparently milder course of multiple sclerosis: changes in the diagnostic criteria, therapy and natural history.

Multiple sclerosis (MS) is characterized as an autoimmune disease affecting the central nervous system. It is one of the most common neurological disorders in young adults. Over the past decades, increasing evidence suggested that hypovitaminosis D is a contributing factor to the risk of developing MS. From different risk factors contributing to the development of MS, vitamin D status is of particular interest since it is not only a modifiable risk factor but is also associated with MS disease activity. MS patients with lower serum vitamin D concentrations were shown to have higher disease activity. However, this finding does not demonstrate causality. In this regard, prospective vitamin D supplementation studies missed statistical significance in its primary endpoints but showed promising results in secondary outcome measures or post hoc analyses. An explanation for missed primary endpoints may be underpowered trials. Besides vitamin D supplementation as a potential add-on to long-term immunotherapeutic treatment, a recent laboratory study of our group pointed toward a beneficial effect of vitamin D to improve the efficacy of glucocorticoids in relapse therapy. In the following article, we will briefly review the effects of vitamin D on MS by outlining its effects on the immune and nervous system and by reviewing the association between vitamin D and MS risk as well as MS disease activity. We will also review the effects of vitamin D supplementation on MS risk and MS disease activity.

/pdf/a-brief-review-of-the-effects-of-vitamin-d-on-multiple-29pyq1kje2.pdf

A Brief Review of the Effects of Vitamin D on Multiple Sclerosis.

Objective To evaluate the safety and efficacy of cholecalciferol in patients with relapsing-remitting MS (RRMS). Methods In this double-blind, placebo-controlled parallel-group, 2-year study, 181 patients with RRMS were randomized 1:1. Key inclusion criteria were a low serum 25-hydroxy vitamin D (25OHD) concentration ( Results The primary end point was not met. In patients who completed the 2-year follow-up (45 with cholecalciferol and 45 with placebo), all efficacy parameters favored cholecalciferol with an ARR reduction (p = 0.012), less new hypointense T1-weighted lesions (p = 0.025), a lower volume of hypointense T1-weighted lesions (p = 0.031), and a lower progression of EDSS (p = 0.026). The overall rate of adverse events was well balanced between groups. Conclusions Although the primary end point was not met, these data suggest a potential treatment effect of cholecalciferol in patients with RRMS already treated with interferon beta-1a and low serum 25OHD concentration. Together with the good safety profile, these data support the exploration of cholecalciferol treatment in such patients with RRMS. Clinicaltrials.gov identifier NCT01198132. Classification of evidence This study provides Class II evidence that for patients with RRMS and low serum 25OHD, cholecalciferol did not significantly affect ARRs.

https://nn.neurology.org/content/nnn/6/5/e597.full.pdf

Cholecalciferol in relapsing-remitting MS: A randomized clinical trial (CHOLINE)

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Cholecalciferol in relapsing-remitting MS: A randomized clinical trial (CHOLINE)