25 Hydroxyvitamin D 1 alpha-hydroxylase is required for optimal epidermal differentiation and permeability barrier homeostasis

Effects of vitamin D3 supplementation on the recovery of hospitalized burn patients: a randomized double-blind controlled trial

BACKGROUND

Burn patients, due to their damaged skin, may not be able to synthesize vitamin D. In this study, we aimed to evaluate the effects of vitamin D supplementation on the recovery of hospitalized burn patients.

METHODS

Fifty-four patients participated in a randomized controlled trial. Eighteen patients were randomly assigned to group C (control, received gelatin soft gel as placebo), 18 patients to group D1 (received 1000 IU/day vitamin D), and 18 patients to group D2 (received 3000 IU/day vitamin D). After supplementation, wound biopsy and blood samples were obtained from the patients. Weight, height, 25(OH)D level, wound healing, scar formation, quality of pain, and blood parameters were evaluated.

RESULTS

There were no significant differences in the serum vitamin D levels between the groups at admission (P = 0.52), and 81.5% of the participants were deficient, with a noteworthy increase during study in supplemented groups (P < 0.001). The Bates-Jensen Wound Assessment Tool demonstrated significant differences in wound healing between the C group and the D1 and D2 groups (P = 0.003), and the supplemented groups experienced greater improvement. The D2 group showed significant differences in thickness and total score on the Vancouver scar scale up to three months after discharge (P = 0.03). Moreover, there was a notable decrease in insulin requirements and the number of injected insulin units in the supplemented groups compared with those in group C (P = 0.006 and P = 0.01, respectively). In addition, shorter hospitalization was observed in group D2 (P = 0.04).

CONCLUSION

Supplementation with vitamin D at doses of 1000 and 3000 IU/day improved wound healing and decreased scar thickness as well as exogenous insulin requirements. Overall, at 3000 IU/day, better results were achieved than at 1000 IU/day.

TRIAL REGISTRATION

This article is registered in 24/04/2020 on the Iranian Randomized Clinical Trials Registry (trial registration number (IRCT, code: IRCT20200420047141N1.

Vitamin D beyond the blood: Tissue distribution of vitamin D metabolites after supplementation

Vitamin D3's role in mineral homeostasis through its endocrine function, associated with the main circulating metabolite 25-hydroxyvitamin D3, is well characterized. However, the increasing recognition of vitamin D3's paracrine and autocrine functions-such as cell growth, immune function, and hormone regulation-necessitates examining vitamin D3 levels across different tissues post-supplementation. Hence, this review explores the biodistribution of vitamin D3 in blood and key tissues following oral supplementation in humans and animal models, highlighting the biologically active metabolite, 1,25-dihydroxyvitamin D3, and the primary clearance metabolite, 24,25-dihydroxyvitamin D3. While our findings indicate significant progress in understanding how circulating metabolite levels respond to supplementation, comprehensive insight into their tissue concentrations remains limited. The gap is particularly significant during pregnancy, a period of drastically increased vitamin D3 needs and metabolic alterations, where data remains sparse. Within the examined dosage ranges, both human and animal studies indicate that vitamin D3 and its metabolites are retained in tissues selectively. Notably, vitamin D3 concentrations in tissues show greater variability in response to administered doses. In contrast, its metabolites maintain a more consistent concentration range, albeit different among tissues, reflecting their tighter regulatory mechanisms following supplementation. These observations suggest that serum 25-hydroxyvitamin D3 levels may not adequately reflect vitamin D3 and its metabolite concentrations in different tissues. Therefore, future research should aim to generate robust human data on the tissue distribution of vitamin D3 and its principal metabolites post-supplementation. Relating this data to clinically appropriate exposure metrics will enhance our understanding of vitamin D3's cellular effects and guide refinement of clinical trial methodologies.

Vitamin D Receptor Regulates the Expression of the Grainyhead-Like 1 Gene

Vitamin D plays an important pleiotropic role in maintaining global homeostasis of the human body. Its functions go far beyond skeletal health, playing a crucial role in a plethora of cellular functions, as well as in extraskeletal health, ensuring the proper functioning of multiple human organs, including the skin. Genes from the Grainyhead-like (GRHL) family code for transcription factors necessary for the development and maintenance of various epithelia. Even though they are involved in many processes regulated by vitamin D, a direct link between vitamin D-mediated cellular pathways and GRHL genes has never been described. We employed various bioinformatic methods, quantitative real-time PCR, chromatin immunoprecipitation, reporter gene assays, and calcitriol treatments to investigate this issue. We report that the vitamin D receptor (VDR) binds to a regulatory region of the Grainyhead-like 1 (GRHL1) gene and regulates its expression. Ectopic expression of VDR and treatment with calcitriol alters the expression of the GRHL1 gene. The evidence presented here indicates a role of VDR in the regulation of expression of GRHL1 and correspondingly a role of GRHL1 in mediating the actions of vitamin D.

Malignant Melanoma: An Overview, New Perspectives, and Vitamin D Signaling

Melanoma, originating through malignant transformation of melanin-producing melanocytes, is a formidable malignancy, characterized by local invasiveness, recurrence, early metastasis, resistance to therapy, and a high mortality rate. This review discusses etiologic and risk factors for melanoma, diagnostic and prognostic tools, including recent advances in molecular biology, omics, and bioinformatics, and provides an overview of its therapy. Since the incidence of melanoma is rising and mortality remains unacceptably high, we discuss its inherent properties, including melanogenesis, that make this disease resilient to treatment and propose to use AI to solve the above complex and multidimensional problems. We provide an overview on vitamin D and its anticancerogenic properties, and report recent advances in this field that can provide solutions for the prevention and/or therapy of melanoma. Experimental papers and clinicopathological studies on the role of vitamin D status and signaling pathways initiated by its active metabolites in melanoma prognosis and therapy are reviewed. We conclude that vitamin D signaling, defined by specific nuclear receptors and selective activation by specific vitamin D hydroxyderivatives, can provide a benefit for new or existing therapeutic approaches. We propose to target vitamin D signaling with the use of computational biology and AI tools to provide a solution to the melanoma problem.

Involvement of the secosteroid vitamin D in autoimmune rheumatic diseases and COVID-19

Evidence supporting the extra-skeletal role of vitamin D in modulating immune responses is centred on the effects of its final metabolite, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3, also known as calcitriol), which is regarded as a true steroid hormone. 1,25(OH)2D3, the active form of vitamin D, can modulate the innate immune system in response to invading pathogens, downregulate inflammatory responses and support the adaptive arm of the immune system. Serum concentrations of its inactive precursor 25-hydroxyvitamin D3 (25(OH)D3, also known as calcidiol) fluctuate seasonally (being lowest in winter) and correlate negatively with the activation of the immune system as well as with the incidence and severity of autoimmune rheumatic diseases such as rheumatoid arthritis, systemic lupus erythematosus and systemic sclerosis. Thus, a low serum concentration of 25(OH)D3 is considered to be a risk factor for autoimmune rheumatic diseases and vitamin D3 supplementation seems to improve the prognosis; moreover, long-term vitamin D3 supplementation seems to reduce their incidence (i.e. rheumatoid arthritis). In the setting of COVID-19, 1,25(OH)2D3 seems to downregulate the early viral phase (SARS-CoV-2 infection), by enhancing innate antiviral effector mechanisms, as well as the later cytokine-mediated hyperinflammatory phase. This Review provides an update of the latest scientific and clinical evidence concerning vitamin D and immune response in autoimmune rheumatic diseases and COVID-19, which justify the need for monitoring of serum 25(OH)D3 concentrations and for appropriate supplementation following clinical trial-based approaches.

Evidence-base for the beneficial effect of nutraceuticals in canine dermatological immune-mediated inflammatory diseases - A literature review

BACKGROUND

Immune-mediated inflammatory diseases (IMIDs) are associated with an abnormal immune response, resulting in a disturbed homeostasis and chronic inflammation. Most canine dermatological IMIDs (cDIMIDs), such as allergies, autoimmune and immune-mediated diseases, require long-term treatment with immunosuppressive drugs with potential adverse effects. In general, nutraceuticals are thought to be safe. As a result, there is a tendency for the more frequent use of nutraceuticals in veterinary medicine.

OBJECTIVES

The aim of this review was to present evidence-based proof for the use of various nutraceuticals in the treatment of cDIMIDs and, where possible, to provide conclusions to guide their use in veterinary dermatological practice.

METHODS

A comprehensive literature search on common cDIMIDs and nutraceuticals was performed. Only peer-reviewed articles published in English and related to the study topic were included. A total of 64 eligible publications were classified in five categories based on study design and substantively assessed on additional criteria such as standardisation of diets and number of included animals. For final appraisal, classification of major, minor or no evidence was used whereby efficacy was based on clinical outcome measurements.

CONCLUSIONS

Minor evidence for the beneficial use of several nutraceuticals, including essential fatty acids, niacinamide and probiotics, was found for treatment of specific cDIMIDs. These nutraceuticals may improve clinical signs or reduce the required dose of concurrent medication (e.g. drug-sparing effect) in some dogs. Some nutraceuticals also may be used for long-term maintenance therapy. Despite some promising findings, major evidence for the use of nutraceuticals in cDIMIDs is lacking, warranting further research.

Maternal Nutritional Status and Development of Atopic Dermatitis in Their Offspring

Atopic dermatitis (AD) is the leading chronic skin inflammatory disease and the initial manifestation of atopic march. Available evidence supports the notion that primary prevention early in life leads to a decreased incidence of AD, thus possibly decreasing the subsequent occurrence of atopic march. Nutritional status is essential to a proper functioning immune system and is valued for its important role in AD. Essential nutrients, which include carbohydrates, proteins, lipids, vitamins, and minerals, are transferred from the mother to the fetus through the placenta during gestation. Various nutrients, such as polyunsaturated fatty acids (PUFAs) and vitamin D, were studied in relation to maternal status and offspring allergy. However, no strong evidence indicates that a single nutrient or food in mothers' diet significantly affects the risk of childhood AD. In the light of current evidence, mothers should not either increase nor avoid consuming these nutrients to prevent or ameliorate allergic diseases in their offspring. Each essential nutrient has an important role in fetal development, and current government recommendations suggest specific intake amounts for pregnant women. This review discusses evidence on how various nutrients, including lipids (monounsaturated fatty acids, PUFAs, saturated fatty acids, and short-chain fatty acids), carbohydrates (oligosaccharides and polysaccharides), proteins, vitamins (A, B, C, D, and E), and trace minerals (magnesium, iron, zinc, copper, selenium, and strontium) in maternal status are associated with the development of AD and their possible mechanisms.

Cutaneous barrier dysfunction in allergic diseases

The fundamental defect(s) that drives atopic dermatitis (AD) remains controversial. "Outside in" proponents point to the important association of filaggrin gene mutations and other skin barrier defects with AD. The "inside out" proponents derive support from evidence that AD occurs in genetic animal models with overexpression of type 2 immune pathways in their skin, and humans with gain-of-function mutations in their type 2 response develop severe AD. The observation that therapeutic biologics, targeting type 2 immune responses, can reverse AD provides compelling support for the importance of "inside out" mechanisms of AD. In this review, we propose a central role for epithelial cell dysfunction that accounts for the dual role of skin barrier defects and immune pathway activation in AD. The complexity of AD has its roots in the dysfunction of the epithelial barrier that allows the penetration of allergens, irritants, and microbes into a cutaneous milieu that facilitates the induction of type 2 immune responses. The AD phenotypes and endotypes that result in chronic skin inflammation and barrier dysfunction are modified by genes, innate/adaptive immune responses, and different environmental factors that cause skin barrier dysfunction. There is also compelling evidence that skin barrier dysfunction can alter the course of childhood asthma, food allergy, and allergic rhinosinusitis. Effective management of AD requires a multipronged approach, not only restoring cutaneous barrier function, microbial flora, and immune homeostasis but also enhancing skin epithelial differentiation.

Topical Vitamin D Receptor Antagonist/Partial-Agonist Treatment Induces Epidermal Hyperproliferation via RARγ Signaling Pathways

Vitamin D and A derivatives are well-known endogenous substances responsible for skin homeostasis. In this study we topically treated shaved mouse skin with a vitamin D agonist (MC903) or vitamin D antagonist/partial agonist (ZK159222) and compared the changes with acetone (control treatment) treatment for 14 days. Topical treatment with ZK159222 resulted in increased expression of genes involved in retinoic acid synthesis, increased retinoic acid concentrations and increased expression of retinoid target genes. Clustering the altered genes revealed that heparin-binding epidermal growth factor-like growth factor, the main driver of epidermal hyperproliferation, was increased via RARγ-mediated pathways, while other clusters of genes were mainly decreased which were comparable to the changes seen upon activation of the RARα-mediated pathways. In summary, we conclude that epidermal hyperproliferation of mouse skin in response to a topically administered vitamin D receptor antagonist/partial agonist (ZK159222) is induced via increased retinoic acid synthesis, retinoic acid levels and increased RARγ-mediated pathways.

The association between vitamin D levels and burn factors in different burn types

Background

Patients with burns present with different clinical features depending on the types of burn injury and burn patients with lower levels of vitamin D have worse prognoses and more complications. The study aims to investigate the association between vitamin D levels and burn factors according to each burn type in relation to early intensive rehabilitation therapy initiated for inpatients with burns.

Methods

In this retrospective study, we enrolled 757 of 1716 inpatients who underwent rehabilitative therapy between May 2013 and April 2017. Burn types were divided into flame burn, electrical burn and other burns, including scalding, contact and chemical burns. Age, burned body surface area (BSA), wound healing time (WHT), length of hospital stay (LOS) and body mass index were analysed between vitamin D deficient and non-deficient patient groups using Student’s t-tests, or Mann-Whitney U test and among three burn types using one-way analysis of variance (ANOVA) or Kruskal-Wallis one-way ANOVA. The relationship between vitamin D levels and burn factors was evaluated using Pearson's or Spearman's correlation coefficient tests, and multiple linear regression analysis in different burn groups.

Results

In total, 88.9% patients were vitamin D deficient, and these patients had a larger burned BSA (p = 0.015) and longer WHT and LOS (all p < 0.001) than non-deficient patients. Burned BSA, WHT and vitamin D levels showed significant differences in their mean values according to three burn types (all p < 0.001). WHT was a communal factor significantly associated with vitamin D levels in all three burn types (p < 0.05). The WHT cut-off points to predict vitamin D deficiency were 55 days for flame burn (p < 0.001) and 62.5 days for electrical burn (p = 0.001).

Conclusions

WHT across all three burn types was a common factor associated with vitamin D levels for inpatients with burns who had undergone rehabilitative therapy. Electrical burn patients with vitamin D deficiency, even those with a low burned BSA percentage, showed prolonged wound healing over a two-month post-burn period. Independent of burned BSA, nutritional intervention concerning vitamin D in relation to burn wound healing should be considered to guide early initiation of intensive rehabilitation therapy.

Relevance of Vitamin D in Melanoma Development, Progression and Therapy

Melanoma is one of the most lethal types of skin cancer, with a poor prognosis once the disease enters metastasis. The efficacy of currently available treatment schemes for advanced melanomas is low, expensive, and burdened by significant side-effects. Therefore, there is a need to develop new treatment options. Skin cells are able to activate vitamin D via classical and non-classical pathways. Vitamin D derivatives have anticancer properties which promote differentiation and inhibit proliferation. The role of systemic vitamin D in patients with melanoma is unclear as epidemiological studies are not definitive. In contrast, experimental data have clearly shown that vitamin D and its derivatives have anti-melanoma properties. Furthermore, molecular and clinicopathological studies have demonstrated a correlation between defects in vitamin D signaling and progression of melanoma and disease outcome. Therefore, adequate vitamin D signaling can play a role in the treatment of melanoma.

The Vitamin D Receptor as Tumor Suppressor in Skin

Cutaneous malignancies including melanomas and keratinocyte carcinomas (KC) are the most common types of cancer, occurring at a rate of over one million per year in the United States. KC, which include both basal cell carcinomas and squamous cell carcinomas, are substantially more common than melanomas and form the subject of this chapter. Ultraviolet radiation (UVR), both UVB and UVA, as occurs with sunlight exposure is generally regarded as causal for these malignancies, but UVB is also required for vitamin D synthesis in the skin. Keratinocytes are the major cell in the epidermis. These cells not only produce vitamin D but contain the enzymatic machinery to metabolize vitamin D to its active metabolite, 1,25(OH)₂D, and express the receptor for this metabolite, the vitamin D receptor (VDR). This allows the cell to respond to the 1,25(OH)₂D that it produces. Based on our own data and that reported in the literature, we conclude that vitamin D signaling in the skin suppresses UVR-induced epidermal tumor formation. In this chapter we focus on four mechanisms by which vitamin D signaling suppresses tumor formation. They are inhibition of proliferation/stimulation of differentiation with discussion of the roles of hedgehog, Wnt/β-catenin, and hyaluronan/CD44 pathways in mediating vitamin D regulation of proliferation/differentiation, regulation of the balance between oncogenic and tumor suppressor long noncoding RNAs, immune regulation, and promotion of DNA damage repair (DDR).

Evaluating extended-release calcifediol as a treatment option for chronic kidney disease-mineral and bone disorder (CKD-MBD)

Introduction: Extended-release calcifediol (ERC) is an orally administered prohormone of active vitamin D (1,25-dihydroxyvitamin D [1,25D]) designed to safely and sufficiently increase serum total 25-hydroxyvitamin D (25D) to reduce elevated parathyroid hormone (PTH) in patients with non-dialysis-chronic kidney disease (ND-CKD). ERC is currently approved in the United States and Canada.Areas covered: Herein, key clinical data relating to the pharmacokinetics, pharmacodynamics, efficacy and safety of ERC are reviewed.Expert opinion: Currently available treatment options for secondary hyperparathyroidism (SHPT) in ND-CKD have limitations: the effectiveness of nutritional vitamin D supplements for reduction of PTH levels is unproven and active (1α-hydroxylated) vitamin D analogues elevate serum calcium, which increases the risk of hypercalcemia and vascular calcification. Clinical studies show that ERC is an effective, well tolerated treatment for SHPT in ND-CKD. ERC gradually raises serum 25D levels, resulting in physiologically regulated increases in serum 1,25D and sustained reductions in PTH, while avoiding clinically meaningful increases in serum phosphorus, calcium and fibroblast growth factor 23. ERC offers a new, effective and well tolerated treatment option for the early management of SHPT in patients with ND-CKD.

Vitamin D and the skin: what should a dermatologist know?

Although first discovered in 1931, vitamin D has seen an increased interest in the scientific community over the past decades, including the dermatology field. Vitamin D promotes calcium and phosphorus absorption; however, the actions of vitamin D are not confined to bone. Indeed, there is now overwhelming and compelling scientific data that vitamin D plays a crucial role in a plethora of cellular function and in extra-skeletal health. Except for fatty fish livers, very few foods naturally contain vitamin D; and the major source of vitamin D comes from skin exposure to sunlight via ultraviolet B. Keratinocytes are unique in the body as not only do they provide the primary source of vitamin D for the body, but they also possess both the enzymatic machinery to metabolize the vitamin D produced to active metabolites. This has been referred to as the photoendocrine vitamin D system. Vitamin D regulates keratinocytes proliferation and differentiation; and plays a role in the defense against opportunistic infections. Multiple factors are linked to vitamin D status; and a growing number of dermatologic diseases has been linked to vitamin D status such as atopic dermatitis, psoriasis, vitiligo, and cutaneous cancers. In this article, we reviewed the potential determinants of vitamin D status, as its implications in dermatologic diseases.

The Association Between Postburn Vitamin D Deficiency and the Biomechanical Properties of Hypertrophic Scars

Fibroblasts, keratinocytes, mast cells, and other cells participate in hypertrophic scar formation and express the vitamin D receptor. We investigated the association between vitamin D deficiency and the biomechanical properties of hypertrophic burn scars. This cross-sectional study analyzed 486 participants enrolled from May 1, 2013 to April 30, 2017. When complete wound healing was agreed with by the two opinions, blood sampling and scar evaluation were performed. The values of melanin and erythema, trans-epidermal water loss (TEWL), and scar distensibility and elasticity were measured using pigment- and TEWL-measuring devices and a suction skin elasticity meter. 25(OH) vitamin D deficiency was defined as plasma level of <20 ng/ml. The vitamin D-deficient patients had significantly higher mean values of scar melanin and TEWL (P = .032, P = .007), whereas scar erythema level was similar. They also showed significantly lower values of Uf (final distensibility; P < .001), Ua/Uf (gross elasticity; P < .001) and Ur/Uf (biological elasticity; P = .014), and higher value of Uv/Ue (viscoelasticity or potency against interstitial fluid shift; P = .016). In multiple linear regression analysis, Uf, Ua/Uf, Uv/Ue, and Ur/Uf were significantly affected by 25(OH)-vitamin D level in deficient patients (Uf, P = .017; Ua/Uf, P = .045; Uv/Ue, P = .024; Ur/Uf, P = .021). Our results demonstrated that vitamin D deficiency was significantly related to increased pigmentation, decreased skin barrier function, low scar distensibility and elasticity, and slow interstitial fluid movement in burn patients.

Myrtus Polyphenols, from Antioxidants to Anti-Inflammatory Molecules: Exploring a Network Involving Cytochromes P450 and Vitamin D

Inflammatory response represents one of the main mechanisms of healing and tissue function restoration. On the other hand, chronic inflammation leads to excessive secretion of pro-inflammatory cytokines involved in the onset of several diseases. Oxidative stress condition may contribute in worsening inflammatory state fall, increasing reactive oxygen species (ROS) production and cytokines release. Polyphenols can counteract inflammation and oxidative stress, modulating the release of toxic molecules and interacting with physiological defenses, such as cytochromes p450 enzymes. In this paper, we aimed at evaluating the anti-inflammatory properties of different concentrations of Myrtus communis L. pulp and seeds extracts, derived from liquor industrial production, on human fibroblasts. We determined ROS production after oxidative stress induction by H2O2 treatment, and the gene expression of different proinflammatory cytokines. We also analyzed the expression of CYP3A4 and CYP27B1 genes, in order to evaluate the capability of Myrtus polyphenols to influence the metabolic regulation of other molecules, including drugs, ROS, and vitamin D. Our results showed that Myrtus extracts exert a synergic effect with vitamin D in reducing inflammation and ROS production, protecting cells from oxidative stress damages. Moreover, the extracts modulate CYPs expression, preventing chronic inflammation and suggesting their use in development of new therapeutic formulations.

Epithelial barrier repair and prevention of allergy

Allergic diseases have in common a dysfunctional epithelial barrier, which allows the penetration of allergens and microbes, leading to the release of type 2 cytokines that drive allergic inflammation. The accessibility of skin, compared with lung or gastrointestinal tissue, has facilitated detailed investigations into mechanisms underlying epithelial barrier dysfunction in atopic dermatitis (AD). This Review describes the formation of the skin barrier and analyzes the link between altered skin barrier formation and the pathogenesis of AD. The keratinocyte differentiation process is under tight regulation. During epidermal differentiation, keratinocytes sequentially switch gene expression programs, resulting in terminal differentiation and the formation of a mature stratum corneum, which is essential for the skin to prevent allergen or microbial invasion. Abnormalities in keratinocyte differentiation in AD skin result in hyperproliferation of the basal layer of epidermis, inhibition of markers of terminal differentiation, and barrier lipid abnormalities, compromising skin barrier and antimicrobial function. There is also compelling evidence for epithelial dysregulation in asthma, food allergy, eosinophilic esophagitis, and allergic rhinosinusitis. This Review examines current epithelial barrier repair strategies as an approach for allergy prevention or intervention.

Vitamin D Receptor Deletion Leads to the Destruction of Tight and Adherens Junctions in Lungs

Vitamin D deficiency has been linked to various inflammatory diseases in lungs, including pneumonia, asthma and chronic obstructive pulmonary disease. However, the mechanisms by which vitamin D and vitamin D receptor reduce inflammation in lung diseases remain poorly understood. In this study, we investigated the expression and cell-specific distribution of tight and adherens junctions in the lungs of vitamin D receptor-deficient (VDR^-/-) mice. Our results demonstrated that mRNA and protein levels of claudin-2, claudin-4 and claudin-12 were significantly decreased in the lungs of VDR^-/- mice. Other tight and adherens junction proteins, such as ZO-1, occludin, claudin-10, β-catenin, and VE-cadherin, showed significant differences in expression in the lungs of VDR^-/- and wild-type mice. These data suggest that altered expression of tight and adherens junction molecules, especially of claudin-2, -4, -10, -12, and -18, after chronic pneumonia caused by VDR deletion could increase lung permeability.Therefore, VDR may play an important role in maintaining pulmonary barrier integrity. Further studies should confirm whether vitamin D/VDR is beneficial for the prevention or treatment of lung diseases.

Diabetic Foot Ulcers and Vitamin D Status: A Literature Review

Approximately 15% of patients with diabetes mellitus (DM) are prone to developing diabetic foot ulcers (DFU) in their lifetime. The term vitamin D status or 25-hydroxyvitamin D (25(OH)D) levels is used interchangeably to represent the status of vitamin D in individuals throughout this article. Evidence suggests a relationship between 25(OH)D levels and DFU. However, very minimal data are available on the association between DFU and vitamin D deficiency. After a careful review of the literature, it was inferred that vitamin D could be associated with DFU and diabetic foot infections. Available evidence on vitamin D and DFU suggests a negative correlation between 25(OH)D levels and the presence of DFU. Evidence also supports a negative relationship between 25(OH)D levels and diabetic foot infections. Further large-scale randomized controlled studies need to be done to confirm the relationship between 25(OH)D levels and DFU including the use of vitamin D in the management of DFU and diabetic foot infections.

Vitamin D supplementation of initially vitamin D-deficient mice diminishes lung inflammation with limited effects on pulmonary epithelial integrity

In disease settings, vitamin D may be important for maintaining optimal lung epithelial integrity and suppressing inflammation, but less is known of its effects prior to disease onset. Female BALB/c dams were fed a vitamin D₃‐supplemented (2280 IU/kg, VitD⁺) or nonsupplemented (0 IU/kg, VitD⁻) diet from 3 weeks of age, and mated at 8 weeks of age. Male offspring were fed the same diet as their mother. Some offspring initially fed the VitD⁻ diet were switched to a VitD⁺ diet from 8 weeks of age (VitD^−/+). At 12 weeks of age, signs of low‐level inflammation were observed in the bronchoalveolar lavage fluid (BALF) of VitD⁻ mice (more macrophages and neutrophils), which were suppressed by subsequent supplementation with vitamin D₃. There was no difference in the level of expression of the tight junction proteins occludin or claudin‐1 in lung epithelial cells of VitD⁺ mice compared to VitD⁻ mice; however, claudin‐1 levels were reduced when initially vitamin D‐deficient mice were fed the vitamin D₃‐containing diet (VitD^−/+). Reduced total IgM levels were detected in BALF and serum of VitD^−/+ mice compared to VitD⁺ mice. Lung mRNA levels of the vitamin D receptor (VDR) were greatest in VitD^−/+ mice. Total IgG levels in BALF were greater in mice fed the vitamin D₃‐containing diet, which may be explained by increased activation of B cells in airway‐draining lymph nodes. These findings suggest that supplementation of initially vitamin D‐deficient mice with vitamin D₃ suppresses signs of lung inflammation but has limited effects on the epithelial integrity of the lungs.

On the role of classical and novel forms of vitamin D in melanoma progression and management

Melanoma represents a significant clinical problem affecting a large segment of the population with a relatively high incidence and mortality rate. Ultraviolet radiation (UVR) is an important etiological factor in malignant transformation of melanocytes and melanoma development. UVB, while being a full carcinogen in melanomagenesis, is also necessary for the cutaneous production of vitamin D3 (D3). Calcitriol (1,25(OH)2D3) and novel CYP11A1-derived hydroxyderivatives of D3 show anti-melanoma activities and protective properties against damage induced by UVB. The former activities include inhibitory effects on proliferation, plating efficiency and anchorage-independent growth of cultured human and rodent melanomas in vitro, as well as the in vivo inhibition of tumor growth by 20(OH)D3 after injection of human melanoma cells into immunodeficient mice. The literature indicates that low levels of 25(OH)D3 are associated with more advanced melanomas and reduced patient survivals, while single nucleotide polymorphisms of the vitamin D receptor or the D3 binding protein gene affect development or progression of melanoma, or disease outcome. An inverse correlation of VDR and CYP27B1 expression with melanoma progression has been found, with low or undetectable levels of these proteins being associated with poor disease outcomes. Unexpectedly, increased expression of CYP24A1 was associated with better melanoma prognosis. In addition, decreased expression of retinoic acid orphan receptors α and γ, which can also bind vitamin D3 hydroxyderivatives, showed positive association with melanoma progression and shorter disease-free and overall survival. Thus, inadequate levels of biologically active forms of D3 and disturbances in expression of the target receptors, or D3 activating or inactivating enzymes, can affect melanomagenesis and disease progression. We therefore propose that inclusion of vitamin D into melanoma management should be beneficial for patients, at least as an adjuvant approach. The presence of multiple hydroxyderivatives of D3 in skin that show anti-melanoma activity in experimental models and which may act on alternative receptors, will be a future consideration when planning which forms of vitamin D to use for melanoma therapy.

Physiologic and pathophysiologic roles of extra renal CYP27b1: Case report and review

Although the kidney was initially thought to be the sole organ responsible for the production of 1,25(OH)₂D via the enzyme CYP27b1, it is now appreciated that the expression of CYP27b1 in tissues other than the kidney is wide spread. However, the kidney is the major source for circulating 1,25(OH)₂D. Only in certain granulomatous diseases such as sarcoidosis does the extra renal tissue produce sufficient 1,25(OH)₂D to contribute to the circulating levels, generally associated with hypercalcemia, as illustrated by the case report preceding the review. Therefore the expression of CYP27b1 outside the kidney under normal circumstances begs the question why, and in particular whether the extra renal production of 1,25(OH)₂D has physiologic importance. In this chapter this question will be discussed. First we discuss the sites for extra renal 1,25(OH)₂D production. This is followed by a discussion of the regulation of CYP27b1 expression and activity in extra renal tissues, pointing out that such regulation is tissue specific and different from that of CYP27b1 in the kidney. Finally the physiologic significance of extra renal 1,25(OH)₂D₃ production is examined, with special focus on the role of CYP27b1 in regulation of cellular proliferation and differentiation, hormone secretion, and immune function. At this point the data do not clearly demonstrate an essential role for CYP27b1 expression in any tissue outside the kidney, but several examples pointing in this direction are provided. With the availability of the mouse enabling tissue specific deletion of CYP27b1, the role of extra renal CYP27b1 expression in normal and pathologic states can now be addressed definitively.

Vitamin D shows in vivo efficacy in a placebo-controlled, double-blinded, randomised clinical trial on canine atopic dermatitis

Atopic dermatitis (AD) in dogs is among the most common skin diseases in small animal practice. It is an inflammatory disease based on a genetic predisposition to develop hypersensitivity against environmental and food allergens and typical clinical signs up exposure. Treatment sometimes can be difficult and associated with adverse effects. Previous studies evaluating cholecalciferol as treatment for human AD have shown promising results. With canine AD being a good animal model for its human counterpart, it was hypothesised that cholecalciferol might have beneficial clinical effects in dogs, too. In this randomised, placebo-controlled, double-blinded eight-week cross-over study, 23 client-owned dogs received either systemic cholecalciferol (n=16), a vitamin D receptor analogue (n=8) or placebo (n=13). Blood samples for ionised calcium were obtained regularly during the study, and Canine Atopic Dermatitis Extent and Severity Index and pruritus scores, blood levels of vitamin D metabolites, measurements of skin pH and transepidermal water loss were determined before and after. Pruritus and lesion scores decreased significantly in the cholecalciferol group versus placebo. No differences in water loss or skin pH were observed. An increase in serum 25-hydroxycholecalciferol strongly correlated with a reduction in pruritus. Systemic cholecalciferol may be a viable treatment option for canine AD.

Genetic Diseases of Vitamin D Metabolizing Enzymes

Vitamin D metabolism involves 3 highly specific cytochrome P450 (CYP) enzymes (25-hydroxylase, 1α-hydroxylase, and 24-hydroxylase) involved in the activation of vitamin D₃ to the hormonal form, 1,25-(OH)₂D₃, and the inactivation of 1,25-(OH)₂D₃ to biliary excretory products. Mutations of the activating enzymes CYP2R1 and CYP27B1 cause lack of normal 1,25-(OH)₂D₃ synthesis and result in rickets whereas mutations of the inactivating enzyme CYP24A1 cause build-up of excess 1,25-(OH)₂D₃ and result in hypercalcemia, nephrolithiasis, and nephrocalcinosis. This article reviews the literature for 3 clinical conditions. Symptoms, diagnosis, treatment, and management of vitamin D-dependent rickets and idiopathic infantile hypercalcemia are discussed.

Structural aspects of Vitamin D endocrinology

1α,25-Dihydroxvitamin D₃ (1,25(OH)₂D₃) is the hormonally active form of vitamin D₃. Its synthesis and its metabolites, their transport and elimination as well as action on transcriptional regulation involves the harmonic cooperation of diverse proteins with vitamin D binding capacities such as vitamin D binding protein (DBP), cytochrome P450 enzymes or the nuclear vitamin receptor (VDR). The genomic mechanism of 1,25(OH)₂D₃ action involves its binding to VDR that functionally acts as a heterodimer with retinoid X receptor. The crystal structures of the most important proteins for vitamin D₃, VDR, DBP, CYP2R1 and CYP24A1, have provided identification of mechanisms of actions of these proteins and those mediating VDR-regulated transcription. This review will present the structural information on recognition of the vitamin D₃ and metabolites by CYP proteins and DBP as well as the structural basis of VDR activation by 1,25(OH)₂D₃ and metabolites. Additionally, we will describe, the implications of the VDR mutants associated with hereditary vitamin D-resistant rickets (HVDRR) that display impaired function.

Extraskeletal actions of vitamin D

The vitamin D receptor (VDR) is found in nearly all, if not all, cells in the body. The enzyme that produces the active metabolite of vitamin D and ligand for VDR, namely CYP27B1, likewise is widely expressed in many cells of the body. These observations indicate that the role of vitamin D is not limited to regulation of bone and mineral homeostasis, as important as that is. Rather, the study of its extraskeletal actions has become the major driving force behind the significant increase in research articles on vitamin D published over the past several decades. A great deal of information has accumulated from cell culture studies, in vivo animal studies, and clinical association studies that confirms that extraskeletal effects of vitamin D are truly widespread and substantial. However, randomized, placebo-controlled clinical trials, when done, have by and large not produced the benefits anticipated by the in vitro cell culture and in vivo animal studies. In this review, I will examine the role of vitamin D signaling in a number of extraskeletal tissues and assess the success of translating these findings into treatments of human diseases affecting those extracellular tissues.

Spotlight on vitamin D receptor, lipid metabolism and mitochondria: Some preliminary emerging issues

Transcriptional control and modulation of calcium fluxes underpin the differentiating properties of vitamin D (1,25(OH)₂D₃). In the latest years however few studies have pointed out the relevance of the mitochondrial effects of the hormone. It is now time to focus on the metabolic results of vitamin D receptor (VDR) action in mitochondria, which can explain the pleiotropic effects of 1,25(OH)₂D₃ and may elucidate few contrasting aspects of its activity. The perturbation of lipid metabolism described in VDR knockout mice and vitamin D deficient animals can be revisited based on the newly identified mechanism of action of 1,25(OH)₂D₃ in mitochondria. From the same point of view, the controversial role of 1,25(OH)₂D₃ in adipogenesis can be better interpreted.

Vitamin D signaling and melanoma: role of vitamin D and its receptors in melanoma progression and management

Ultraviolet B (UVB), in addition to having carcinogenic activity, is required for the production of vitamin D3 (D3) in the skin which supplies >90% of the body's requirement. Vitamin D is activated through hydroxylation by 25-hydroxylases (CYP2R1 or CYP27A1) and 1α-hydroxylase (CYP27B1) to produce 1,25(OH)₂D3, or through the action of CYP11A1 to produce mono-di- and trihydroxy-D3 products that can be further modified by CYP27B1, CYP27A1, and CYP24A1. The active forms of D3, in addition to regulating calcium metabolism, exert pleiotropic activities, which include anticarcinogenic and anti-melanoma effects in experimental models, with photoprotection against UVB-induced damage. These diverse effects are mediated through an interaction with the vitamin D receptor (VDR) and/or as most recently demonstrated through action on retinoic acid orphan receptors (ROR)α and RORγ. With respect to melanoma, low levels of 25(OH)D are associated with thicker tumors and reduced patient survival. Furthermore, single-nucleotide polymorphisms of VDR and the vitamin D-binding protein (VDP) genes affect melanomagenesis or disease outcome. Clinicopathological analyses have shown positive correlation between low or undetectable expression of VDR and/or CYP27B1 in melanoma with tumor progression and shorter overall (OS) and disease-free survival (DFS) times. Paradoxically, this correlation was reversed for CYP24A1 (inactivating 24-hydroxylase), indicating that this enzyme, while inactivating 1,25(OH)₂D3, can activate other forms of D3 that are products of the non-canonical pathway initiated by CYP11A1. An inverse correlation has been found between the levels of RORα and RORγ expression and melanoma progression and disease outcome. Therefore, we propose that defects in vitamin D signaling including D3 activation/inactivation, and the expression and activity of the corresponding receptors, affect melanoma progression and the outcome of the disease. The existence of multiple bioactive forms of D3 and alternative receptors affecting the behavior of melanoma should be taken into consideration when applying vitamin D management for melanoma therapy.

Treatment of Eczema: Corticosteroids and Beyond

Atopic dermatitis (AD) is a chronic inflammatory skin condition that requires a manifold approach to therapy. The goal of therapy is to restore the function of the epidermal barrier and to reduce skin inflammation. This can be achieved with skin moisturization and topical anti-inflammatory agents, such as topical corticosteroids and calcineurin inhibitors. Furthermore, proactive therapy with twice weekly use of both topical corticosteroids and calcineurin inhibitors in previously affected areas has been found to reduce the time to the next eczematous flare. Adjunctive treatment options include wet wrap therapy, anti-histamines, and vitamin D supplementation. Bacterial colonization, in particular Staphylococcus aureus, can contribute to eczematous flares and overt infection. Use of systemic antibiotics in infected lesions is warranted; however, empiric antibiotics use in uninfected lesions is controversial. Local antiseptic measures (i.e., bleach baths) and topical antimicrobial therapies can be considered in patients with high bacterial colonization. Difficult-to-treat AD is a complex clinical problem that may require re-evaluation of the initial diagnosis of AD, especially if the onset of disease occurs in adulthood. It may also necessitate evaluation for contact, food, and inhaled allergens that may exacerbate the underlying AD. There are a host of systemic therapies that have been successful in patients with difficult-to-treat AD, however, these agents are limited by their side effect profiles. Lastly, with further insight into the pathophysiology of AD, new biological agents have been investigated with promising results.

Bioactive forms of vitamin D selectively stimulate the skin analog of the hypothalamus-pituitary-adrenal axis in human epidermal keratinocytes

Ultraviolet radiation B stimulates both the production of vitamin D3 in the skin and the activation of the skin analog of the hypothalamic-pituitary-adrenal axis (HPA) as well as the central HPA. Since the role of vitamin D3 in the regulation of the HPA is largely unknown, we investigated the impact of 1,25(OH)2D3 and its noncalcemic analogs, 20(OH)D3 and 21(OH)pD, on the expression of the local HPA in human epidermal keratinocytes. The noncalcemic analogs showed similar efficacy to 1,25(OH)2D3 in stimulating the expression of neuropeptides, CRF, urocortins and POMC, and their receptors, CRFR1, CRFR2, MC1R, MC2R, MC3R and MC4R. Interestingly, unlike other secosteroids, the activity of 21(OH)pD did not correlate with induction of differentiation, suggesting a separate but overlapping mechanism of action. Thus, biologically active forms of vitamin D can regulate different elements of the local equivalent of the HPA with implications for the systemic HPA.

Low vitamin D-modulated calcium-regulating proteins in psoriasis vulgaris plaques: S100A7 overexpression depends on joint involvement

Psoriasis is an inflammatory skin disease with or without joint involvement. In this disease, the thickened epidermis and impaired barrier are associated with altered calcium gradients. Calcium and vitamin D are known to play important roles in keratinocyte differentiation and bone metabolism. Intracellular calcium is regulated by calcium-sensing receptor (CASR), calcium release-activated calcium modulator (ORAI) and stromal interaction molecule (STIM). Other proteins modulated by vitamin D play important roles in calcium regulation e.g., calbindin 1 (CALB1) and transient receptor potential cation channel 6 (TRPV6). In this study, we aimed to investigate the expression of calcium-regulating proteins in the plaques of patients with psoriasis vulgaris with or without joint inflammation. We confirmed low calcium levels, keratinocyte hyperproliferation and an altered epidermal barrier. The CASR, ORAI1, ORAI3, STIM1, CALB1 and TRPV6 mRNA, as well as the sterol 27-hydroxylase (CYP27A1), 25-hydroxyvitamin D3 1-α-hydroxylase (CYP27B1) and 1,25-dihydroxyvitamin D3 24-hydroxylase (CYP24A1) protein levels were low in the plaques of patients with psoriasis. We demonstrated S100 calcium-binding protein A7 (S100A7) overexpression in the plaques of patients with psoriasis vulgaris with joint inflammation, compared with those without joint involvement. We suggest an altered capacity to regulate the intracellular Ca2+ concentration ([Ca2+]i), characterized by a reduced expression of CASR, ORAI1, ORAI3, STIM1, CALB1 and TRPV6 associated with diminished levels of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], which may be associated with an altered balance between keratinocyte proliferation and differentiation in the psoriatic epidermis. Additionally, differences in S100A7 expression depend on the presence of joint involvement.

Effects of Osteoporosis-Inducing Drugs on Vitamin D-Related Gene Transcription and Mineralization in MG-63 and Saos-2 Cells

Vitamin D₃ is important for calcium and phosphate homeostasis. To exert its effects, vitamin D₃ has to be enzymatically activated into 1,25D₃ (1,25-dihydroxyvitamin D₃ ). Regulation by endogenous vitamin D metabolites of the activation and inactivation of 1,25D₃ is important to maintain adequate amounts of active vitamin D₃ . Vitamin D deficiency and low bone mineral density have been linked to treatments with antiretroviral drugs and glucocorticoids. However, the causes of drug-induced osteoporosis remain unclear. The antiretroviral drugs efavirenz and ritonavir as well as the glucocorticoid dexamethasone were included in this study. Their effects on transcription of vitamin D-regulating enzymes in MG-63 cells were investigated. Ritonavir and dexamethasone both induced transcription of CYP27B1, the enzyme responsible for the formation of 1,25D₃ . Efavirenz, however, suppressed CYP27B1 expression. When administered together with endogenous vitamin D metabolites, dexamethasone and efavirenz counteracted the 1,25D₃ -mediated up-regulation of CYP24A1, which inactivates 1,25D₃ . This suggests that the drugs may interfere with local regulation of the vitamin D metabolizing system in osteoblasts. Studies on mineralization were performed in MG-63 cells and Saos-2 cells by measuring calcium concentrations accumulated over time. The effects of efavirenz, ritonavir and dexamethasone and/or vitamin D metabolites were examined. 1,25D₃ induced mineralization in both cell lines. Efavirenz administered alone did not affect mineralization but suppressed the inducing effects of 1,25D₃ on mineralization in both MG-63 cells and Saos-2 cells. In summary, the results suggest that antiretroviral drugs and glucocorticoids may adversely affect bone by interference with the vitamin D system in osteoblasts.

The Transient Role for Calcium and Vitamin D during the Developmental Hair Follicle Cycle

The role for 1,25-dihydroxyvitamin D3 and/or calcium in hair follicle cycling is not clear despite their impact on keratinocyte differentiation. We found that calbindin-D9k null (knockout) pups generated from calbindin-D9k knockout females fed a vitamin D-deficient, low-calcium (0.47%) diet develop transient alopecia. The pups appear phenotypically normal until 13 days of age, after which the hair progressively sheds in a caudocephalic direction, resulting in truncal alopecia totalis by 20-23 days, with spontaneous recovery by 28 days. Histological studies showed markedly dystrophic hair follicles, loss of hair shafts with increased apoptosis, and hyperplastic epidermis during this time. Ha1 expression is lost during catagen in all mice but recovers more slowly in the knockout pups on the vitamin D-deficient, low-calcium diet. Keratin 1 expression is reduced throughout days 19-28. The expressions of involucrin, loricrin, and cathepsin L is initially increased by day 19 but subsequently falls below those of controls by day 23, as does that of desmoglein 3. Feeding the mothers a high-vitamin D/high-calcium (2%)/lactose (20%) diet lessens the phenotype, and knockout pups fostered to mothers fed a normal diet do not develop alopecia. Our results show that in calbindin-D9k knockout pups, a maternal vitamin D-deficient/low-calcium diet leads to transient noncicatricial alopecia.

PTH and Vitamin D

PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.

Admission vitamin D status is associated with discharge destination in critically ill surgical patients

BACKGROUND

Discharge destination after critical illness is increasingly recognized as a valuable patient-centered outcome. Recently, vitamin D status has been shown to be associated with important outcomes such as length of stay (LOS) and mortality in intensive care unit (ICU) patients. Our goal was to investigate whether vitamin D status on ICU admission is associated with discharge destination.

METHODS

We performed a retrospective analysis from an ongoing prospective cohort study of vitamin D status in critical illness. Patients were recruited from two surgical ICUs at a single teaching hospital in Boston, Massachusetts. All patients had 25-hydroxyvitamin D (25OHD) levels measured within 24 h of ICU admission. Discharge destination was dichotomized as non-home or home. Locally weighted scatterplot smoothing (LOWESS) was used to graph the relationship between 25OHD levels and discharge destination. To investigate the association between 25OHD level and discharge destination, we performed logistic regression analyses, controlling for age, sex, race, body mass index, socioeconomic status, acute physiology and chronic health evaluation II score, need for emergent vs. non-emergent surgery, vitamin D supplementation status, and hospital LOS.

RESULTS

300 patients comprised the analytic cohort. Mean 25OHD level was 19 (standard deviation 8) ng/mL and 41 % of patients had a non-home discharge destination. LOWESS analysis demonstrated a near-inverse linear relationship between vitamin D status and non-home discharge destination to 25OHD levels around 10 ng/mL, with rapid flattening of the curve between levels of 10 and 20 ng/mL. Overall, 25OHD level at the outset of critical illness was inversely associated with non-home discharge destination (adjusted OR, 0.88; 95 % CI 0.82-0.95). When vitamin D status was dichotomized, patients with 25OHD levels <20 ng/mL had an almost 3-fold risk of a non-home discharge destination (adjusted OR, 2.74; 95 % CI 1.23-6.14) compared to patients with 25OHD levels ≥20 ng/mL.

CONCLUSIONS

Our results suggest that vitamin D status may be a modifiable risk factor for non-home discharge destination in surgical ICU patients. Future randomized, controlled trials are needed to determine whether vitamin D supplementation in surgical ICU patients can improve clinical outcomes such as the successful rate of discharge to home after critical illness.

Mitochondrial and lipogenic effects of vitamin D on differentiating and proliferating human keratinocytes

Even in cells that are resistant to the differentiating effects of vitamin D, the activated vitamin D receptor (VDR) can downregulate the mitochondrial respiratory chain and sustain cell growth through enhancing the activity of biosynthetic pathways. The aim of this study was to investigate whether vitamin D is effective also in modulating mitochondria and biosynthetic metabolism of differentiating cells. We compared the effect of vitamin D on two cellular models: the primary human keratinocytes, differentiating and sensitive to the genomic action of VDR, and the human keratinocyte cell line HaCaT, characterized by a rapid growth and resistance to vitamin D. We analysed the nuclear translocation and features of VDR, the effects of vitamin D on mitochondrial transcription and the consequences on lipid biosynthetic fate. We found that the negative modulation of respiratory chain is a general mechanism of action of vitamin D, but at high doses, the HaCaT cells became resistant to mitochondrial effects by upregulating the catabolic enzyme CYP24 hydroxylase. In differentiating keratinocytes, vitamin D treatment promoted intracellular lipid deposition, likewise the inhibitor of respiratory chain stigmatellin, whereas in proliferating HaCaT, this biosynthetic pathway was not inducible by the hormone. By linking the results on respiratory chain and lipid accumulation, we conclude that vitamin D, by suppressing respiratory chain transcription in all keratinocytes, is able to support both the proliferation and the specialized metabolism of differentiating cells. Through mitochondrial control, vitamin D can have an essential role in all the metabolic phenotypes occurring in healthy and diseased skin.

Pilot study on the bioactivity of vitamin d in the skin after oral supplementation

Laboratory studies suggest that vitamin D (VD) supplementation inhibits skin carcinogenesis. However, epidemiologic studies report mixed findings in the association between circulating VD levels and skin cancer risk. We conducted a clinical study to determine whether oral cholecalciferol supplementation would exert direct bioactivity in human skin through modulation of the VD receptor (VDR). We enrolled 25 individuals with serum 25-hydroxyvitamin-D levels <30 ng/mL and with skin photodamage to take 50,000 IU of cholecalciferol biweekly for 8 to 9 weeks. Then, we obtained baseline and end-of-study skin biopsies from photodamaged (PD) and photoprotected (PP) skin, and from benign nevi (BN) and tested for mRNA expression of VDR and cytochrome P450-24 (CYP24), and markers of keratinocytic differentiation. High-dose cholecalciferol supplementation significantly elevated circulating levels of 25-hydroxyvitamin-D (P < 0.0001) and 1,25-dihydroxyvitamin-D (P < 0.0001). VDR expression in PD- and PP-skin showed minimum changes after supplementation. CYP24 expression in PD- and PP-skin was increased after supplementation by 186%, P = 0.08, and 134%, P = 0.07, respectively. In BNs from 11 participants, a trend for higher VDR and CYP24 expression was observed (average of 20%, P = 0.08, and 544%, P = 0.09, respectively). Caspase-14 expression at the basal layer in PD skin samples was the only epidermal differentiation marker that was significantly increased (49%, P < 0.0001). High-dose cholecalciferol supplementation raised serum VD metabolite levels concurrently with CYP24 mRNA and caspase-14 levels in the skin. Our findings of significant variability in the range of VDR and CYP24 expression across study samples represent an important consideration in studies evaluating the role of VD as a skin cancer chemopreventive agent.

Role of micronutrients in skin health and function

Skin is the first line of defense for protecting our bodies against external perturbations, including ultraviolet (UV) irradiation, mechanical/chemical stress, and bacterial infection. Nutrition is one of many factors required for the maintenance of overall skin health. An impaired nutritional status alters the structural integrity and biological function of skin, resulting in an abnormal skin barrier. In particular, the importance of micronutrients (such as certain vitamins and minerals) for skin health has been highlighted in cell culture, animal, and clinical studies. These micronutrients are employed not only as active compounds in therapeutic agents for treating certain skin diseases, but also as ingredients in cosmetic products. Here, the author describes the barrier function of the skin and the general nutritional requirements for skin health. The goal of this review is to discuss the potential roles and current knowledge of selected micronutrients in skin health and function.

Novel mechanisms for the vitamin D receptor (VDR) in the skin and in skin cancer

The VDR acting with or without its principal ligand 1,25(OH)2D regulates two central processes in the skin, interfollicular epidermal (IFE) differentiation and hair follicle cycling (HFC). Calcium is an important co-regulator with 1,25(OH)2D at least of epidermal differentiation. Knockout of the calcium sensing receptor (CaSR) in addition to VDR accelerates the development of skin cancer in mice on a low calcium diet. Coactivators such as mediator 1 (aka DRIP205) and steroid receptor coactivator 3 (SRC3) regulate VDR function at different stages of the differentiation process, with Med 1 essential for hair follicle differentiation and early stages of epidermal differentiation and proliferation and SRC3 essential for the latter stages of differentiation including formation of the permeability barrier and innate immunity. The corepressor of VDR, hairless (HR), is essential for hair follicle cycling, although its effect on epidermal differentiation in vivo is minimal. In its regulation of HFC and IFE VDR controls two pathways-wnt/β-catenin and sonic hedgehog (SHH). In the absence of VDR these pathways are overexpressed leading to tumor formation. Whereas, VDR binding to β-catenin may block its activation of TCF/LEF1 sites, β-catenin binding to VDR may enhance its activation of VDREs. 1,25(OH)2D promotes but may not be required for these interactions. Suppression of SHH expression by VDR, on the other hand, requires 1,25(OH)2D. The major point of emphasis is that the role of VDR in the skin involves a number of novel mechanisms, both 1,25(OH)2D dependent and independent, that when disrupted interfere with IFE differentiation and HFC, predisposing to cancer formation. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Inferences from genetically modified mouse models on the skeletal actions of vitamin D

Vitamin D has pleiotropic extra-skeletal effects which have been noted in mouse models of deletion of either the 25-hydroxy vitamin D 1α-hydroxylase enzyme, cyp27b1 (1OHase(-/-) mice) or of the vitamin D receptor (Vdr(-/-) mice); these may be preventable or reversible by either restoring normal signaling of the 1,25(OH)2D/VDR system, or in some cases by restoring normal mineral homeostasis. However, effects on skeletal and mineral homeostasis are clearly the major phenotype observed in humans with loss-of-function mutations in either CYP27B1 or VDR. In mouse phenocopies of these human disorders, correction of hypocalcemia and hypophosphatemia reduce elevated circulating parathyroid hormone concentrations and normalize impaired bone mineralization, but restoration of normal 1,25(OH)2D/VDR signaling may be required for optimal bone formation. Induction of high endogenous 1,25(OH)2D concentrations in genetically modified mouse models may cause increased bone resorption and decreased mineralization. Transgenic Vdr overexpression and conditional Vdr deletion in cells of the osteoblastic lineage have also provided insights into the stages of osteoblast differentiation which may mediate these actions. These anabolic and catabolic effects of the 1,25(OH)2D system on bone may therefore be a function of both the ambient concentration of circulating 1,25(OH)2D and the stage of differentiation of the osteoblast. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Relationship between serum 25-hydroxyvitamin D and interleukin-31 levels, and the severity of atopic dermatitis in children

PURPOSE

Atopic dermatitis (AD) is a chronic inflammatory relapsing skin disorder. Vitamin D plays a pivotal role in the development of AD, and interleukin (IL) 31 is known to be related to pruritus in AD. The aim of our study was to determine whether 25-hydroxyvitamin D (25(OH)D) levels are related to IL-31 levels or to the severity of AD.

METHODS

We enrolled 91 children with AD and 32 control subjects without history or symptoms of allergic diseases. Blood was drawn to evaluate complete blood cell count, total eosinophil count (TEC), and total IgE, specific IgE to common allergens, 25(OH)D, and IL-31 levels. Serum 25(OH)D and IL-31 levels were measured using high-performance liquid chromatography and enzyme-linked immunosorbent assay, respectively. The scoring atopic dermatitis (SCORAD) index was used to evaluate the severity of AD.

RESULTS

The mean 25(OH)D level was significantly lower in the AD group than in the control group; 25(OH)D decreased greatly in the moderate and severe AD groups compared with the mild AD group. Children with atopic sensitization showed significantly lower 25(OH)D levels than nonatopic children. However, serum IL-31 levels were not related to AD group, SCORAD index, or 25(OH)D levels. The SCORAD index was inversely correlated with serum 25(OH)D level and positively correlated with TECs and total IgE levels. Children with moderate and severe AD had significantly higher TECs than children with mild AD.

CONCLUSION

Vitamin D is related to the severity of AD independently of IL-31.

Randomized trial of vitamin D supplementation for winter-related atopic dermatitis in children

BACKGROUND

Epidemiologic and preclinical data, and a small randomized trial in Boston, suggest that vitamin D supplementation may improve winter-related atopic dermatitis (AD).

OBJECTIVE

To determine the effect of vitamin D supplementation on winter-related AD.

METHODS

We performed a randomized, double-blind, placebo-controlled trial of Mongolian children with winter-related AD (clinicaltrials.gov identifier: NCT00879424). Baseline eligibility included age 2 to 17 years, AD score 10 to 72 using the Eczema Area and Severity Index (EASI), and winter-related AD (eg, history of AD worsening during the fall-to-winter transition). Subjects were enrolled in Ulaanbaatar during winter and randomly assigned to oral cholecalciferol (1000 IU/day) versus placebo for 1 month. All children and parents received emollient and patient education about AD and basic skin care. The main outcomes were changes in EASI score and in Investigator's Global Assessment.

RESULTS

The 107 enrolled children had a mean age of 9 years (SD 5), and 59% were male. Their median age of AD onset was 3 months (interquartile range 2 months to 1 year) and mean EASI score at baseline 21 (SD 9). One-month follow-up data were available for 104 (97%) children. Compared with placebo, vitamin D supplementation for 1 month produced a clinically and statistically significant improvement in EASI score (adjusted mean change: -6.5 vs -3.3, respectively; P = .04). Moreover, change in Investigator's Global Assessment favored vitamin D over placebo (P = .03). There were no adverse effects in either group.

CONCLUSION

Vitamin D supplementation improved winter-related AD among Mongolian children, a population likely to have vitamin D deficiency in winter.

A humanized mouse model of hereditary 1,25-dihydroxyvitamin D-resistant rickets without alopecia

The syndrome of hereditary 1,25-dihydroxyvitamin D-resistant rickets (HVDRR) is a genetic disease of altered mineral homeostasis due to mutations in the vitamin D receptor (VDR) gene. It is frequently, but not always, accompanied by the presence of alopecia. Mouse models that recapitulate this syndrome have been prepared through genetic deletion of the Vdr gene and are characterized by the presence of rickets and alopecia. Subsequent studies have revealed that VDR expression in hair follicle keratinocytes protects against alopecia and that this activity is independent of the protein's ability to bind 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. In the present study, we introduced into VDR-null mice a human VDR (hVDR) bacterial artificial chromosome minigene containing a mutation that converts leucine to serine at amino acid 233 in the hVDR protein, which prevents 1,25(OH)2D3 binding. We then assessed whether this transgene recreated features of the HVDRR syndrome without alopecia. RT-PCR and Western blot analysis in one strain showed an appropriate level of mutant hVDR expression in all tissues examined including skin. The hVDR-L233S mutant failed to rescue the aberrant systemic and skeletal phenotype characteristic of the VDR null mouse due to the inability of the mutant receptor to activate transcription after treatment with 1,25(OH)2D3. Importantly, however, neither alopecia nor the dermal cysts characteristic of VDR-null mice were observed in the skin of these hVDR-L233S mutant mice. This study confirms that we have created a humanized mouse model of HVDRR without alopecia that will be useful in defining additional features of this syndrome and in identifying potential novel functions of the unoccupied VDR.

Vitamin D signaling regulates oral keratinocyte proliferation in vitro and in vivo

The secosteroidal hormone 1,25-dihyroxyvitamin D [1,25(OH)₂D₃] and its receptor, the vitamin D receptor (VDR), are crucial regulators of epidermal proliferation and differentiation. However, the effects of 1,25(OH)₂D₃-directed signaling on oral keratinocyte pathophysiology have not been well studied. We examined the role of 1,25(OH)₂D₃ in regulating proliferation and differentiation in cultured oral keratinocytes and on the oral epithelium in vivo. Using lentiviral-mediated shRNA to silence VDR, we generated an oral keratinocyte cell line with stable knockdown of VDR expression. VDR knockdown significantly enhanced proliferation and disrupted calcium- and 1,25(OH)₂D₃-induced oral keratinocyte differentiation, emphasizing the anti-proliferative and pro-differentiation effects of 1,25(OH)₂D₃ in oral keratinocytes. Using vitamin D₃-deficient diets, we induced chronic vitamin D deficiency in mice as evidenced by decreased serum 25-hydroxyvitamin D (25OHD) concentrations. The vitamin D-deficient mice manifested increased proliferation of the tongue epithelium, but did not develop any morphological or histological abnormalities in the oral epithelium, suggesting that vitamin D deficiency alone is insufficient to alter oral epithelial homeostasis and provoke carcinogenesis. Immunohistochemical analyses of human and murine oral squamous cell carcinomas showed increased VDR expression. Overall, our results provide strong support for a crucial role for vitamin D signaling in oral keratinocyte pathophysiology.

Vitamin D deficiency rickets in an adolescent with severe atopic dermatitis

Atopic dermatitis (AD) affects 10% to 20% of children worldwide. Its severity may be inversely correlated with 25-hydroxyvitamin D (25OHD) levels. Although low levels of vitamin D (VD) can cause rickets in infants, VD deficiency rickets is an unusual presentation in teenagers. We report the case of a 14-year-old girl with severe AD and fish allergy since early childhood. She lived at high latitude (with less sun exposure) and, because of her atopic disorders, avoided sunlight and fish. Laboratory studies showed elevated alkaline phosphatase and parathyroid hormone levels and low serum calcium; her serum 25OHD level was <12 nmol/L. A radiograph of the wrist showed a radiolucent band in the distal metaphysis of the radius with marginal sclerosis. She was diagnosed as having hypocalcemic rickets due to VD deficiency. Treatment with VD increased her 25OHD level to 44 nmol/L, with normalization of alkaline phosphatase, parathyroid hormone, and calcium. Moreover, we observed a dramatic improvement in her AD severity with VD treatment. This case demonstrates the complex interaction between VD deficiency, AD, and food allergy. We advise a high index of suspicion of VD deficiency rickets in children of all ages with AD, particularly during accelerated growth periods and in the presence of other risk factors such as darker skin, living at high latitude, sun avoidance, and low intake of VD-rich foods. The concomitant improvement in bone-related parameters and AD severity may reflect a double benefit of VD treatment, a possibility that warrants research on VD as potential treatment for AD.

Low vitamin D levels are associated with atopic dermatitis, but not allergic rhinitis, asthma, or IgE sensitization, in the adult Korean population

BACKGROUND

The effect of vitamin D on allergic conditions is unclear. In particular, large-scale, population-based studies examining this relationship in adult Asian populations are lacking.

OBJECTIVE

To evaluate the association between serum vitamin D levels and allergic conditions in the general adult Korean population.

METHODS

A cross-sectional study was performed by using data collected from 15,212 individuals 19 years or older who participated in the Korean National Health and Nutrition Examination Survey from 2008 to 2010. The confounder-adjusted mean serum 25-hydroxyvitamin D (25[OH]D) levels of participants with and without allergic conditions (including atopic dermatitis, asthma, allergic rhinitis, and increased total and allergen-specific serum IgE) were compared by using multiple linear regression analyses. Multiple logistic regression analyses with confounder adjustment estimated the odds ratios (ORs) for developing each condition according to adequate, inadequate, or deficient serum 25(OH)D levels.

RESULTS

After adjusting for potential confounders, mean serum 25(OH)D levels were significantly lower in participants diagnosed with atopic dermatitis than in those without this diagnosis (mean ± SE, 18.58 ± 0.29 ng/mL vs 19.20 ± 0.15 ng/mL; P = .02). Compared with participants with adequate vitamin D levels (≥20 ng/mL), confounder-adjusted ORs of atopic dermatitis were significantly higher in those with inadequate (12-19.99 ng/mL) or deficient (<12 ng/mL) levels (OR [95% CI], 1.50 [1.10-2.06] and 1.48 [1.04-2.12], respectively; P = .02). This relationship was not observed in participants with the other allergic conditions.

CONCLUSION

Vitamin D-insufficient adult individuals within the general Korean population have an increased likelihood of atopic dermatitis, but not asthma, allergic rhinitis, or IgE sensitization.

Barrier repair therapy in atopic dermatitis: an overview

Atopic eczema or dermatitis (AD) is a chronically relapsing dermatitis associated with pruritus, sleep disturbance, psychosocial symptoms, and impaired quality of life. It affects 10-20 % of school-aged children, and there is evidence to suggest that this prevalence is increasing. Filaggrin (filament-aggregating protein) has an important function in epidermal differentiation and barrier function. Null mutations within the filaggrin gene cause ichthyosis vulgaris and appear to be a major risk factor for developing AD. The affected skin of atopic individuals is deficient in filaggrin degradation products or ceramides. Avoidance of triggering factors, optimal skin care, topical corticosteroids, and calcineurin inhibitors are the mainstays of therapy for AD. Proper moisturizer therapy can reduce the frequency and intensity of flares, as well as the need for topical corticosteroids or topical calcineurin inhibitors. Recent advances in the understanding of the pathophysiological process of AD involving filaggrin and ceramides has led to the concept of barrier therapy and the production of new moisturizers and topical skin products targeted to correct reduced amounts of ceramides and natural moisturizing factors in the skin with natural moisturizing factors, ceramides, and pseudoceramide products. Emollients, both creams and ointments, improve the barrier function of the stratum corneum by providing it with water and lipids. Studies on AD and barrier repair treatment show that adequate lipid replacement therapy reduces the inflammation and restores epidermal function. We reviewed 12 randomized trials and 11 cohort studies and found some evidence that certain products had therapeutic efficacy in improving clinical and/or biophysical parameters of patients with AD. Nevertheless, study methods were often flawed and sample sizes were small. Additional research is warranted to better understand the optimal formulary compositions. Also, long-term studies would be important to evaluate whether lipid barrier replacement therapy reduces bacterial colonization or prevents progression of the atopic march.