Targeting the vitamin D endocrine system (VDES) for the management of inflammatory and malignant skin diseases: An historical view and outlook

Quantum Sensing Unravels Antioxidant Efficacy Within PCL/Matrigel Skin Equivalents

Skin equivalents (SE) that recapitulate biological and mechanical characteristics of the native tissue are promising platforms for assessing cosmetics and studying fundamental biological processes. Methods to achieve SEs with well-organized structure, and ideal biological and mechanical properties are limited. Here, the combination of melt electrowritten PCL scaffolds and cell-laden Matrigel to fabricate SE is described. The PCL scaffold provides ideal structural and mechanical properties, preventing deformation of the model. The model consists of a top layer for seeding keratinocytes to mimic the epidermis, and a bottom layer of Matrigel-based dermal compartment with fibroblasts. The compressive modulus and the biological properties after 3-day coculture indicate a close resemblance with the native skin. Using the SE, a testing system to study the damage caused by UVA irradiation and evaluate antioxidant efficacy is established. The effectiveness of Tea polyphenols (TPs) and L-ascorbic acid (Laa) is compared based on free radical generation. TPs are demonstrated to be more effective in downregulating free radical generation. Further, T1 relaxometry is used to detect the generation of free radicals at a single-cell level, which allows tracking of the same cell before and after UVA treatment.

Vitamin D in Melanoma: Potential Role of Cytochrome P450 Enzymes

Vitamin D is a promising anticancer agent for the prevention and treatment of several cancers, including melanoma. Low 25-hydroxyvitamin D levels, a routinely used marker for vitamin D, have been suggested as one of the factors in the development and progression of melanoma. The parent vitamin D needs activation by cytochrome P450 (CYP) enzymes to exert its actions via the vitamin D receptor (VDR). This review discusses the role of vitamin D in melanoma and how CYP-mediated metabolism can potentially affect the actions of vitamin D. Through interacting with the retinoid X receptor, VDR signaling leads to anti-inflammatory, antioxidative, and anticancer actions. Calcitriol, the dihydroxylated form of vitamin D3, is the most active and potent ligand of VDR. CYP27A1, CYP27B1, and CYP2R1 are involved in the activation of vitamin D, whereas CYP24A1 and CYP3A4 are responsible for the degradation of the active vitamin D. CYP24A1, the primary catabolic enzyme of calcitriol, is overexpressed in melanoma tissues and cells. Several drug classes and natural health products can modulate vitamin D-related CYP enzymes and eventually cause lower levels of vitamin D and its active metabolites in tissues. Although the role of vitamin D in the development of melanoma is yet to be fully elucidated, it has been proposed that melanoma prevention may be significantly aided by increased vitamin D signaling. Furthermore, selective targeting of the catabolic enzymes responsible for vitamin D degradation could be a plausible strategy in melanoma therapy. Vitamin D signaling can be improved by utilizing dietary supplements or by modulating CYP metabolism. A positive association exists between the intake of vitamin D supplements and improved prognosis for melanoma patients. Further investigation is required to determine the function of vitamin D supplementation and specific enzyme targeting in the prevention of melanoma.

Vitamin D in Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphoma (CTCL) is characterized by the proliferation of malignant T cells in inflamed skin lesions. Mycosis fungoides (MF)-the most common variant of CTCL-often presents with skin lesions around the abdomen and buttocks ("bathing suit" distribution), i.e., in skin areas devoid of sun-induced vitamin D. For decades, sunlight and vitamin D have been connected to CTCL. Thus, vitamin D induces apoptosis and inhibits the expression of cytokines in malignant T cells. Furthermore, CTCL patients often display vitamin D deficiency, whereas phototherapy induces vitamin D and has beneficial effects in CTCL, suggesting that light and vitamin D have beneficial/protective effects in CTCL. Inversely, vitamin D promotes T helper 2 (Th2) cell specific cytokine production, regulatory T cells, tolerogenic dendritic cells, as well as the expression of immune checkpoint molecules, all of which may have disease-promoting effects by stimulating malignant T-cell proliferation and inhibiting anticancer immunity. Studies on vitamin D treatment in CTCL patients showed conflicting results. Some studies found positive effects, others negative effects, while the largest study showed no apparent clinical effect. Taken together, vitamin D may have both pro- and anticancer effects in CTCL. The balance between the opposing effects of vitamin D in CTCL is likely influenced by treatment and may change during the disease course. Therefore, it remains to be discovered whether and how the effect of vitamin D can be tilted toward an anticancer response in CTCL.

Environmental Air Pollutants Affecting Skin Functions with Systemic Implications

The increase in air pollution worldwide represents an environmental risk factor that has global implications for the health of humans worldwide. The skin of billions of people is exposed to a mixture of harmful air pollutants, which can affect its physiology and are responsible for cutaneous damage. Some polycyclic aromatic hydrocarbons are photoreactive and could be activated by ultraviolet radiation (UVR). Therefore, such UVR exposure would enhance their deleterious effects on the skin. Air pollution also affects vitamin D synthesis by reducing UVB radiation, which is essential for the production of vitamin D3, tachysterol, and lumisterol derivatives. Ambient air pollutants, photopollution, blue-light pollution, and cigarette smoke compromise cutaneous structural integrity, can interact with human skin microbiota, and trigger or exacerbate a range of skin diseases through various mechanisms. Generally, air pollution elicits an oxidative stress response on the skin that can activate the inflammatory responses. The aryl hydrocarbon receptor (AhR) can act as a sensor for small molecules such as air pollutants and plays a crucial role in responses to (photo)pollution. On the other hand, targeting AhR/Nrf2 is emerging as a novel treatment option for air pollutants that induce or exacerbate inflammatory skin diseases. Therefore, AhR with downstream regulatory pathways would represent a crucial signaling system regulating the skin phenotype in a Yin and Yang fashion defined by the chemical nature of the activating factor and the cellular and tissue context.

Conundrum for Psoriasis and Thyroid Involvement

Strategies concerning thyroid anomalies in patients confirmed with psoriasis, either on clinical level or molecular levels, and their genetic findings remain an open issue. Identification of the exact subgroup of individuals that are candidates to endocrine assessments is also controversial. Our purpose in this work was to overview clinical and pathogenic data concerning psoriasis and thyroid comorbidities from a dual perspective (dermatologic and endocrine). This was a narrative review of English literature between January 2016 and January 2023. We included clinically relevant, original articles with different levels of statistical evidence published on PubMed. We followed four clusters of conditions: thyroid dysfunction, autoimmunity, thyroid cancer, and subacute thyroiditis. A new piece of information in this field was the fact that psoriasis and autoimmune thyroid diseases (ATD) have been shown to be related to the immune-based side effects of modern anticancer drugs-namely, immune checkpoint inhibitors (ICP). Overall, we identified 16 confirmatory studies, but with heterogeneous data. Psoriatic arthritis had a higher risk of positive antithyroperoxidase antibodies (TPOAb) (25%) compared to cutaneous psoriasis or control. There was an increased risk of thyroid dysfunction versus control, and hypothyroidism was the most frequent type of dysfunction (subclinical rather than clinical), among thyroid anomalies correlated with >2-year disease duration, peripheral > axial and polyarticular involvement. With a few exceptions, there was a female predominance. Hormonal imbalance included, most frequently, low thyroxine (T4) and/or triiodothyronine (T3) with normal thyroid stimulating hormone (TSH), followed by high TSH (only one study had higher total T3). The highest ratio of thyroid involvement concerning dermatologic subtypes was 59% for erythrodermic psoriasis. Most studies found no correlation between thyroid anomalies and psoriasis severity. Statistically significant odds ratios were as follows: hypothyroidism: 1.34-1.38; hyperthyroidism: 1.17-1.32 (fewer studies than hypo); ATD: 1.42-2.05; Hashimoto's thyroiditis (HT): 1.47-2.09; Graves' disease: 1.26-1.38 (fewer studies than HT). A total of 8 studies had inconsistent or no correlations, while the lowest rate of thyroid involvement was 8% (uncontrolled studies). Other data included 3 studies on patients with ATD looking for psoriasis, as well as 1 study on psoriasis and thyroid cancer. ICP was shown to potentially exacerbate prior ATD and psoriasis or to induce them both de novo (5 studies). At the case report level, data showed subacute thyroiditis due to biological medication (ustekinumab, adalimumab, infliximab). Thyroid involvement in patients with psoriasis thus remained puzzling. We observed significant data that confirmed a higher risk of identifying positive antibodies and/or thyroid dysfunction, especially hypothyroidism, in these subjects. Awareness will be necessary to improve overall outcomes. The exact profile of individuals diagnosed with psoriasis who should be screened by the endocrinology team is still a matter of debate, in terms of dermatological subtype, disease duration, activity, and other synchronous (especially autoimmune) conditions.

Vitamin D Signaling in Psoriasis: Pathogenesis and Therapy

Psoriasis is a systemic, chronic, immune-mediated disease that affects approximately 2–3% of the world’s population. The etiology and pathophysiology of psoriasis are still unknown, but the activation of the adaptive immune system with the main role of T-cells is key in psoriasis pathogenesis. The modulation of the local neuroendocrine system with the downregulation of pro-inflammatory and the upregulation of anti-inflammatory messengers represent a promising adjuvant treatment in psoriasis therapies. Vitamin D receptors and vitamin D-mediated signaling pathways function in the skin and are essential in maintaining the skin homeostasis. The active forms of vitamin D act as powerful immunomodulators of clinical response in psoriatic patients and represent the effective and safe adjuvant treatments for psoriasis, even when high doses of vitamin D are administered. The phototherapy of psoriasis, especially UVB-based, changes the serum level of 25(OH)D, but the correlation of 25(OH)D changes and psoriasis improvement need more clinical trials, since contradictory data have been published. Vitamin D derivatives can improve the efficacy of psoriasis phototherapy without inducing adverse side effects. The anti-psoriatic treatment could include non-calcemic CYP11A1-derived vitamin D hydroxyderivatives that would act on the VDR or as inverse agonists on RORs or activate alternative nuclear receptors including AhR and LXRs. In conclusion, vitamin D signaling can play an important role in the natural history of psoriasis. Selective targeting of proper nuclear receptors could represent potential treatment options in psoriasis.

CYP11A1‑derived vitamin D hydroxyderivatives as candidates for therapy of basal and squamous cell carcinomas

Hydroxyderivatives of vitamin D3, including classical 1,25(OH)2D3 and novel CYP11A1‑derived hydroxyderivatives, exert their biological activity by acting as agonists on the vitamin D receptor (VDR) and inverse agonists on retinoid‑related orphan receptors (ROR)α and γ. The anticancer activities of CYP11A1‑derived hydroxyderivatives were tested using cell biology, tumor biology and molecular biology methods in human A431 and SCC13 squamous (SCC)‑ and murine ASZ001 basal (BCC)‑cell carcinomas, in comparison with classical 1,25(OH)2D3. Vitamin D3‑hydroxyderivatives with or without a C1α(OH) inhibited cell proliferation in a dose‑dependent manner. While all the compounds tested had similar effects on spheroid formation by A431 and SCC13 cells, those with a C1α(OH) group were more potent in inhibiting colony and spheroid formation in the BCC line. Potent anti‑tumorigenic activity against the BCC line was exerted by 1,25(OH)2D3, 1,20(OH)2D3, 1,20,23(OH)3D3, 1,20,24(OH)3D3, 1,20,25(OH)3D3 and 1,20,26(OH)3D3, with smaller effects seen for 25(OH)D3, 20(OH)D3 and 20,23(OH)2D3. 1,25(OH)2D3, 1,20(OH)2D3 and 20(OH)D3 inhibited the expression of GLI1 and β‑catenin in ASZ001 cells. In A431 cells, these compounds also decreased the expression of GLI1 and stimulated involucrin expression. VDR, RORγ, RORα and CYP27B1 were detected in A431, SCC13 and ASZ001 lines, however, with different expression patterns. Immunohistochemistry performed on human skin with SCC and BCC showed nuclear expression of all three of these receptors, as well as megalin (transmembrane receptor for vitamin D‑binding protein), the level of which was dependent on the type of cancer and antigen tested in comparison with normal epidermis. Classical and CYP11A1‑derived vitamin D3‑derivatives exhibited anticancer‑activities on skin cancer cell lines and inhibited GLI1 and β‑catenin signaling in a manner that was dependent on the position of hydroxyl groups. The observed expression of VDR, RORγ, RORα and megalin in human SCC and BCC suggested that they might provide targets for endogenously produced or exogenously applied vitamin D hydroxyderivatives and provide excellent candidates for anti‑cancer therapy.

Metabolic activation of tachysterol3 to biologically active hydroxyderivatives that act on VDR, AhR, LXRs, and PPARγ receptors

CYP11A1 and CYP27A1 hydroxylate tachysterol3 , a photoproduct of previtamin D3 , producing 20S-hydroxytachysterol3 [20S(OH)T3 ] and 25(OH)T3 , respectively. Both metabolites were detected in the human epidermis and serum. Tachysterol3 was also detected in human serum at a concentration of 7.3 ± 2.5 ng/ml. 20S(OH)T3 and 25(OH)T3 inhibited the proliferation of epidermal keratinocytes and dermal fibroblasts and stimulated the expression of differentiation and anti-oxidative genes in keratinocytes in a similar manner to 1,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ]. They acted on the vitamin D receptor (VDR) as demonstrated by image flow cytometry and the translocation of VDR coupled GFP from the cytoplasm to the nucleus of melanoma cells, as well as by the stimulation of CYP24A1 expression. Functional studies using a human aryl hydrocarbon receptor (AhR) reporter assay system revealed marked activation of AhR by 20S(OH)T3 , a smaller effect by 25(OH)T3 , and a minimal effect for their precursor, tachysterol3 . Tachysterol3 hydroxyderivatives showed high-affinity binding to the ligan-binding domain (LBD) of the liver X receptor (LXR) α and β, and the peroxisome proliferator-activated receptor γ (PPARγ) in LanthaScreen TR-FRET coactivator assays. Molecular docking using crystal structures of the LBDs of VDR, AhR, LXRs, and PPARγ revealed high docking scores for 20S(OH)T3 and 25(OH)T3 , comparable to their natural ligands. The scores for the non-genomic-binding site of the VDR were very low indicating a lack of interaction with tachysterol3 ligands. Our identification of endogenous production of 20S(OH)T3 and 25(OH)T3 that are biologically active and interact with VDR, AhR, LXRs, and PPARγ, provides a new understanding of the biological function of tachysterol3 .

Deleterious side effects of nutritional supplements

Vitamin and mineral supplement consumption is widespread. They are taken for a variety of conditions, including dermatologic disorders. Although consumers often assume these supplements are safe, excessive consumption of supplements may have deleterious effects. Such vitamin supplements include vitamin A, niacin, biotin, vitamin D, and vitamin E, and specific mineral supplements include zinc, copper, and iron. These supplements may have a number of potential adverse effects.

The Impact of Vitamin D on Skin Aging

The active metabolites of vitamin D₃ (D₃) and lumisterol (L₃) exert a variety of antiaging and photoprotective effects on the skin. These are achieved through immunomodulation and include anti-inflammatory actions, regulation of keratinocytes proliferation, and differentiation programs to build the epidermal barrier necessary for maintaining skin homeostasis. In addition, they induce antioxidative responses, inhibit DNA damage and induce DNA repair mechanisms to attenuate premature skin aging and cancerogenesis. The mechanism of action would involve interaction with multiple nuclear receptors including VDR, AhR, LXR, reverse agonism on RORα and -γ, and nongenomic actions through 1,25D₃-MARRS receptor and interaction with the nongenomic binding site of the VDR. Therefore, active forms of vitamin D₃ including its canonical (1,25(OH)₂D₃) and noncanonical (CYP11A1-intitated) D₃ derivatives as well as L₃ derivatives are promising agents for the prevention, attenuation, or treatment of premature skin aging. They could be administrated orally and/or topically. Other forms of parenteral application of vitamin D₃ precursor should be considered to avoid its predominant metabolism to 25(OH)D₃ that is not recognized by CYP11A1 enzyme. The efficacy of topically applied vitamin D₃ and L₃ derivatives needs further clinical evaluation in future trials.

Immunological Aspects of Skin Aging in Atopic Dermatitis

The cutaneous immune response is important for the regulation of skin aging well as for the development of immune-mediated skin diseases. Aging of the human skin undergoes immunosenescence with immunological alterations and can be affected by environmental stressors and internal factors, thus leading to various epidermal barrier abnormalities. The dysfunctional epidermal barrier, immune dysregulation, and skin dysbiosis in the advanced age, together with the genetic factors, facilitate the late onset of atopic dermatitis (AD) in the elderly, whose cases have recently been on the rise. Controversial to the healthy aged skin, where overproduction of many cytokines is found, the levels of Th2/Th22 related cytokines inversely correlated with age in the skin of older AD patients. As opposed to an endogenously aged skin, the expression of the terminal differentiation markers significantly increases with age in AD. Despite the atenuated barrier disturbances in older AD patients, the aged skin carries an impairment associated with the aging process, which reflects the persistence of AD. The chronicity of AD in older patients might not directly affect skin aging but does not allow spontaneous remission. Thus, adult- and elderly subtypes of AD are considered as a lifelong disease.

Oral and Topical Vitamin D, Sunshine, and UVB Phototherapy Safely Control Psoriasis in Patients with Normal Pretreatment Serum 25-Hydroxyvitamin D Concentrations: A Literature Review and Discussion of Health Implications

Vitamin D, sunshine and UVB phototherapy were first reported in the early 1900s to control psoriasis, cure rickets and cure tuberculosis (TB). Vitamin D also controlled asthma and rheumatoid arthritis with intakes ranging from 60,000 to 600,000 International Units (IU)/day. In the 1980s, interest in treating psoriasis with vitamin D rekindled. Since 1985 four different oral forms of vitamin D (D2, D3, 1-hydroxyvitaminD3 (1(OH)D3) and 1,25-dihydroxyvitaminD3 (calcitriol)) and several topical formulations have been reported safe and effective treatments for psoriasis-as has UVB phototherapy and sunshine. In this review we show that many pre-treatment serum 25(OH)D concentrations fall within the current range of normal, while many post-treatment concentrations fall outside the upper limit of this normal (100 ng/mL). Yet, psoriasis patients showed significant clinical improvement without complications using these treatments. Current estimates of vitamin D sufficiency appear to underestimate serum 25(OH)D concentrations required for optimal health in psoriasis patients, while concentrations associated with adverse events appear to be much higher than current estimates of safe serum 25(OH)D concentrations. Based on these observations, the therapeutic index for vitamin D needs to be reexamined in the treatment of psoriasis and other diseases strongly linked to vitamin D deficiency, including COVID-19 infections, which may also improve safely with sufficient vitamin D intake or UVB exposure.

Clinical evaluation of vitamin D status and its relationship with disease activity and changes of intestinal immune function in patients with Crohn's disease in the Chinese population

BACKGROUND

High prevalence of vitamin D deficiency has been found among Crohn's disease (CD) patients. Vitamin D probably participates in the pathogenesis of CD, but this idea remains controversial. This study was to investigate the levels of vitamin D in CD patients and analyze the relationship between vitamin D and intestinal inflammation.

METHODS

Vitamin D levels were measured by chemiluminescence immunoassay in 198 CD patients (96 in active, 102 in remission) and 100 healthy controls. The correlation between vitamin D levels and clinical parameters was analysed. The expression of intestinal tight junction (TJ) proteins in CD patients was measured by immunofluorescence staining. Treg and Th17 percentages in the peripheral blood were determined by flow cytometry.

RESULTS

CD patients exhibited significantly lower 25(OH)D levels than healthy controls, especially in active CD patients. Serum 25(OH)D levels in CD patients were negatively correlated with the CD activity index (CDAI), the simple endoscopic score for CD (SES-CD), and inflammatory markers, including erythrocyte sedimentation rate (ESR), platelet (PLT) count and faecal calprotectin (FC) levels. Moreover, in patients with vitamin D deficiency, the expression of TJ proteins (Occludin, claudin-1, ZO-1 and JAM-1) in the intestinal mucosa was reduced, and Treg cells in the peripheral blood were decreased, while Th17 cells were increased compared to those with vitamin D sufficiency and controls.

CONCLUSIONS

Vitamin D deficiency in CD patients is common. Vitamin D is associated with disease activity and intestinal inflammation, which may affect the Treg/Th17 balance and the expression of gut TJ proteins.

Is there a link between vitamin D status, SARS-CoV-2 infection risk and COVID-19 severity?

The outbreak of COVID-19 emerged in December 2019 rapidly spread across the globe and has become pandemic. Little is known about the protective factors of this infection, which is equally distributed between genders and different ages while severe and poor prognosis cases are strongly associated to old males and the presence of comorbidities. Thus, preventive measures aiming at reducing the number of infection and/or their severity are strongly needed. Vitamin D has got great attention and has been claimed as potentially protective against the infection since it may be associated with immunocompetence, inflammation, aging, and those diseases involved in determining the outcomes of COVID-19. This narrative review aims at collecting the literature available on the involvement of the vitamin D status in the pathogenesis of COVID-19 and the putative utility of vitamin D supplementation in the therapeutics. It emerges that a poor vitamin D status seems to associate with an increased risk of infection whereas age, gender and comorbidities seem to play a more important role in COVID-19 severity and mortality. While randomized control trials are needed to better inquire into this topic, vitamin D supplementation may be useful beside its potential effects on SARS-CoV-2 infection and COVID-19.

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.

Sunlight, UV Radiation, Vitamin D, and Skin Cancer: How Much Sunlight Do We Need?

Vitamin D is the sunshine vitamin for good reason. During exposure to sunlight, the ultraviolet B photons enter the skin and photolyze 7-dehydrocholesterol to previtamin D₃ which in turn is isomerized by the body's temperature to vitamin D₃. Most humans have depended on sun for their vitamin D requirement. Skin pigment, sunscreen use, aging, time of day, season, and latitude dramatically affect previtamin D₃ synthesis. Vitamin D deficiency was thought to have been conquered, but it is now recognized that more than 50% of the world's population is at risk for vitamin D deficiency. This deficiency is in part due to the inadequate fortification of foods with vitamin D and the misconception that a healthy diet contains an adequate amount of vitamin D. Vitamin D deficiency causes growth retardation and rickets in children and will precipitate and exacerbate osteopenia, osteoporosis and increase risk of fracture in adults. The vitamin D deficiency pandemic has other serious consequences including increased risk of common cancers, autoimmune diseases, infectious diseases, and cardiovascular disease. There needs to be a renewed appreciation of the beneficial effect of moderate sensible sunlight for providing all humans with their vitamin D requirement for health.

The Role of Classical and Novel Forms of Vitamin D in the Pathogenesis and Progression of Nonmelanoma Skin Cancers

Nonmelanoma skin cancers including basal and squamous cell carcinomas (SCC and BCC) represent a significant clinical problem due to their relatively high incidence, imposing an economic burden to healthcare systems around the world. It is accepted that ultraviolet radiation (UVR: λ = 290-400 nm) plays a crucial role in the initiation and promotion of BCC and SCC with UVB (λ = 290-320 nm) having a central role in this process. On the other hand, UVB is required for vitamin D3 (D3) production in the skin, which supplies >90% of the body's requirement for this prohormone. Prolonged exposure to UVB can also generate tachysterol and lumisterol. Vitamin D3 itself and its canonical (1,25(OH)2D3) and noncanonical (CYP11A1-intitated) D3 hydroxyderivatives show photoprotective functions in the skin. These include regulation of keratinocyte proliferation and differentiation, induction of anti-oxidative responses, inhibition of DNA damage and induction of DNA repair mechanisms, and anti-inflammatory activities. Studies in animals have demonstrated that D3 hydroxyderivatives can attenuate UVB or chemically induced epidermal cancerogenesis and inhibit growth of SCC and BCC. Genomic and non-genomic mechanisms of action have been suggested. In addition, vitamin D3 itself inhibits hedgehog signaling pathways which have been implicated in many cancers. Silencing of the vitamin D receptor leads to increased propensity to develop UVB or chemically induced epidermal cancers. Other targets for vitamin D compounds include 1,25D3-MARRS, retinoic orphan receptors α and γ, aryl hydrocarbon receptor, and Wnt signaling. Most recently, photoprotective effects of lumisterol hydroxyderivatives have been identified. Clinical trials demonstrated a beneficial role of vitamin D compounds in the treatment of actinic keratosis. In summary, recent advances in vitamin D biology and pharmacology open new exciting opportunities in chemoprevention and treatment of skin cancers.

Determination of Vitamin D Levels in Patients With Neurofibromatosis Type 1 in the Pediatric Age Group

Introduction:

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant genetic disorders. Some clinical manifestations are present at birth, while some develop during childhood, and others can occur at any age. Given the early age at which patients develop clinical features, diagnosis is often made during childhood. The most prevalent features of NF1 are café au lait spots, dermal and plexiform neurofibromas, and learning disability. A variety of skeletal problems may be seen in NF1, including scoliosis, short stature, and pseudoarthrosis. Reduced skeletal bone mass has been documented to be a common phenomenon in children and adults with NF1. Decreased serum 25-hydroxyvitamin D (vitamin D) levels have been noted in adults and children with NF1 and have been reported to be inversely correlated with the number of dermal neurofibromas in adults. However, the actual correlation of vitamin D level to bone density and dermal neurofibroma number in children with NF1 remains unclear.

Objectives:

The primary objective of this study was to evaluate vitamin D levels among children and adolescents with NF1. The secondary objective was to describe the levels of vitamin D among children and adolescents with NF1, to verify in which age group there is a higher frequency of vitamin D alterations, and to explore vitamin D level correlations between age, gender, sun exposure, number of neurofibromas, and number of plexiform neurofibromas.

Methods:

This was an observational, cross-sectional, hospital-based study. We obtained a convenience sample of individuals with confirmed diagnosis of NF1 from patients attending the Medical Genetics Service of the IPPMG-UFRJ and Santa Casa de Misericórdia of Rio de Janeiro over a 24-month period. We evaluated vitamin D levels in blood samples of patients with NF1 by a chemiluminescent immunoassay method, and we correlated the results with gender, age, number of neurofibromas, number of plexiform neurofibromas, and satisfactory sun exposure.

Results:

Of the 55 patients, 28 (50.9%) were female and 27 (49.1%) were male. Patient ages ranged from a minimum of 1.2 to a maximum of 19.6 years (mean age 10.95 years) and the median was 11.11 years. Median and mean body mass index (BMI; z score) were -0.09 (minimum value -1.63 and maximum of 4.62) and 0.16, respectively. The mean value of vitamin D was 30.82 ng/mL (±12.31) and the median was 29 ng/mL (minimum value of 10.40 ng/mL and maximum of 79.19 ng/mL).

Conclusions:

The levels of vitamin D did not differ according to gender, age group, or the presence or number of cutaneous neurofibromas. Among patients with adequate sun exposure, there was a higher incidence of sufficient serum vitamin D levels. Patients with cutaneous neurofibromas in the 0 to 11 age group had a greater tendency to vitamin D sufficiency in relation to patients aged 11 to 19 years.

Skeletal and Extraskeletal Actions of Vitamin D: Current Evidence and Outstanding Questions

The etiology of endemic rickets was discovered a century ago. Vitamin D is the precursor of 25-hydroxyvitamin D and other metabolites, including 1,25(OH)2D, the ligand for the vitamin D receptor (VDR). The effects of the vitamin D endocrine system on bone and its growth plate are primarily indirect and mediated by its effect on intestinal calcium transport and serum calcium and phosphate homeostasis. Rickets and osteomalacia can be prevented by daily supplements of 400 IU of vitamin D. Vitamin D deficiency (serum 25-hydroxyvitamin D <50 nmol/L) accelerates bone turnover, bone loss, and osteoporotic fractures. These risks can be reduced by 800 IU of vitamin D together with an appropriate calcium intake, given to institutionalized or vitamin D-deficient elderly subjects. VDR and vitamin D metabolic enzymes are widely expressed. Numerous genetic, molecular, cellular, and animal studies strongly suggest that vitamin D signaling has many extraskeletal effects. These include regulation of cell proliferation, immune and muscle function, skin differentiation, and reproduction, as well as vascular and metabolic properties. From observational studies in human subjects, poor vitamin D status is associated with nearly all diseases predicted by these extraskeletal actions. Results of randomized controlled trials and Mendelian randomization studies are supportive of vitamin D supplementation in reducing the incidence of some diseases, but, globally, conclusions are mixed. These findings point to a need for continued ongoing and future basic and clinical studies to better define whether vitamin D status can be optimized to improve many aspects of human health. Vitamin D deficiency enhances the risk of osteoporotic fractures and is associated with many diseases. We review what is established and what is plausible regarding the health effects of vitamin D.

Shedding light on the effects of 1,25-dihydroxyvitamin D3 on epidermal lipid barrier formation in three-dimensional human skin equivalents

Human skin equivalents (HSEs) are three dimensional models resembling native human skin (NHS) in many aspects. Despite the manifold similarities to NHS, a restriction in its applications is the altered in vitro lipid barrier formation, which compromises the barrier functionality. This could be induced by suboptimal cell culturing conditions, which amongst others is the diminished activation of the vitamin D receptor (VDR) signalling pathway. The active metabolite of this signalling pathway is 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃). An interacting role in the formation of the skin barrier has been ascribed to this pathway, although it remains unresolved to which extent this pathway contributes to the (mal-)formation of the epidermal barrier in HSEs. Our aim is to study whether cell culture medium enriched with 1,25(OH)₂D₃ affects epidermal morphogenesis and lipid barrier formation in HSEs. Addition of 20 nM 1,25(OH)₂D₃ resulted in activation of the VDR signalling pathway by inducing transcription of VDR target genes (CYP24A and LL37) in keratinocyte monocultures and in HSEs. Characterization of HSEs supplemented with 1,25(OH)₂D₃ using immunohistochemical analyses revealed a high similarity in epidermal morphogenesis and in expression of lipid processing enzymes. The barrier formation was assessed using state-of-the art techniques analysing lipid composition and organization. Addition of 1,25(OH)₂D₃ did not alter the composition of ceramides. Additionally, the lateral and lamellar organization of the lipids was similar, irrespective of supplementation. In conclusion, epidermal morphogenesis and barrier formation in HSEs generated in presence or absence of 1,25(OH)₂D₃ leads to a similar morphogenesis and comparable barrier formation in vitro.

Imaging of vitamin D in psoriatic skin using time-of-flight secondary ion mass spectrometry (ToF-SIMS): A pilot case study

Recently it has been recognized that there is a need of investigating in detail the vitamin D synthesis and metabolism directly in the skin with respect to its possible autocrine and paracrine actions. The potential effects the active metabolite of vitamin D exerts in pathological skin conditions like psoriasis needs to be clarified. Under ultraviolet B (UVB) irradiation skin can autonomously synthesize, activate and degrade vitamin D. In this pilot case study, we used for the first time Time-of-flight secondary ion mass spectrometry (ToF-SIMS) in the analysis of skin biopsies from a patient with psoriasis before and after UVB phototherapy. We were able to visualize vitamin D₃ and its metabolites in the skin and subcutaneous tissue. At the same time information about their localization at subcellular level and morphology of the skin was received. This study proves that ToF-SIMS is a promising powerful tool to be used when investigating vitamin D´s role in dermatological diseases through skin biopsies.

Vitamin D and its low calcemic analogs modulate the anticancer properties of cisplatin and dacarbazine in the human melanoma A375 cell line

Melanoma represents a significant challenge in cancer treatment due to the high drug resistance of melanomas and the patient mortality rate. This study presents data indicating that nanomolar concentrations of the hormonally active form of vitamin D, 1α,25-dihydroxyvitamin D3 [1α,25(OH)₂D3], its non-calcemic analogues 20S-hydroxyvitamin D3 and 21-hydroxypregnacalciferol, as well as the low-calcemic synthetic analog calcipotriol, modulate the efficacy of the anticancer drugs cisplatin and dacarbazine. It was observed that vitamin D analogs sensitized melanoma A375 cells to hydrogen peroxide used as an inducer of oxidative stress. On the other hand, only 1α,25(OH)₂D3 resulted in a minor, but significant effect on the proliferation of melanoma cells treated simultaneously with dacarbazine, but not cisplatin. Notably, cisplatin (300 µM) exhibited a higher overall antiproliferative activity than dacarbazine. Cisplatin treatment of melanoma cells resulted in an induction of apoptosis as demonstrated by flow cytometry (accumulation of cells at the subG₁ phase of the cell cycle), whereas dacarbazine caused G₁/G₀ cell cycle arrest, with the effects being improved by pre-treatment with vitamin D analogs. Treatment with cisplatin resulted in an initial increase in the level of reactive oxygen species (ROS). Dacarbazine caused transient stimulation of ROS levels and the mitochondrial membrane potential (Δψ_m) (after 1 or 3 h of treatment, respectively), but the effect was not detectable following prolonged (24 h) incubation with the drug. Vitamin D exhibited modulatory effects on the cells treated with dacarbazine, decreasing the half maximal inhibitory concentration (IC₅₀) for the drug, stimulating G₁/G₀ arrest and causing a marked decrease in Δψ_m. Finally, cisplatin, dacarbazine and 1α,25(OH)₂D3 displayed modulatory effects on the expression of ROS and vitamin D-associated genes in the melanoma A375 cells. In conclusion, nanomolar concentrations of 1,25(OH)₂D₃ only had minor effects on the proliferation of melanoma cells treated with dacarbazine, decreasing the relative IC₅₀ value. However, co-treatment with vitamin D analogs resulted in the modulation of cell cycle and ROS responses, and affected gene expression, suggesting possible crosstalk between the signaling pathways of vitamin D and the anticancer drugs used in this study.

Sex-specific correlation of IGFBP-2 and IGFBP-3 with vitamin D status in adults with obesity: a cross-sectional serum proteomics study

Objective

Subjects with low vitamin D levels are at risk of cardiometabolic disease. The aim of this study was to identify novel serological markers linking vitamin D status with cardiometabolic profile in non-diabetic adults with obesity.

Methods

For the discovery phase, we used quantitative serum proteomics in sex-matched, age-matched and BMI-matched subjects with obesity [BMI: 25–35 kg/m²] and low [25(OH)D < 50 nmol/L] vs. high vitamin D status [25(OH)D > 50 nmol/L] (n = 16). For the validation phase, we performed ELISA in a larger cohort with similar characteristics (n = 179).

Results

We identified 423 and 549 differentially expressed proteins in the high vs. low vitamin D groups of the male and female cohorts, respectively. The small molecule biochemistry protein networks and the glycolysis|gluconeogenesis pathway were significantly enriched in the DEPs of both sexes. As surrogate markers to these processes, the insulin-like growth factor binding protein -2  (IGFBP-2) was upregulated in males, whereas   IGFBP-3 was upregulated in females from the high Vitamin D status. This sex-specific trend  was confirmed using Luminex ELISA to an independent but clinically analogous cohort of males (n = 84, p = 0.002) and females (n = 95, p = 0.03).

Conclusions

The high Vitamin D status correlated with the serological upregulation of IGFBP-2 in males and IGFBP-3 in females with obesity and may constitute surrogate markers of risk reduction of cardiometabolic disease.

Antiproliferative Activity of Non-Calcemic Vitamin D Analogs on Human Melanoma Lines in Relation to VDR and PDIA3 Receptors

Vitamin D is a precursor for secosteroidal hormones, which demonstrate pleiotropic biological activities, including the regulation of growth and the differentiation of normal and malignant cells. Our previous studies have indicated that the inhibition of melanoma proliferation by a short side-chain, low calcemic analog of vitamin D—21(OH)pD is not fully dependent on the expression of vitamin D receptor (VDR). We have examined the effects of classic vitamin D metabolites, 1,25(OH)₂D₃ and 25(OH)D₃, and two low calcemic vitamin D analogs, (21(OH)pD and calcipotriol), on proliferation, mRNA expression and vitamin D receptor (VDR) translocation in three human melanoma cell lines: WM98, A375 and SK-MEL-188b (subline b of SK-MEL-188, which lost responsiveness to 1,25(OH)₂D₃ and became VDR^−/−CYP27B1^−/−). All tested compounds efficiently inhibited the proliferation of WM98 and A375 melanoma cells except SK-MEL-188b, in which only the short side-chain vitamin D analog—21(OH)pD was effective. Overall, 21(OH)pD was the most potent compound in all three melanoma cell lines in the study. The lack of responsiveness of SK-MEL-188b to 1,25(OH)₂D₃, 25(OH)D₃ and calcipotriol is explained by a lack of characteristic transcripts for the VDR, its splicing variants as well as for vitamin D-activating enzyme CYP27B1. On the other hand, the expression of VDR and its splicing variants and other vitamin D related genes (RXR, PDIA3, CYP3A4, CYP2R1, CYP27B1, CYP24A1 and CYP11A1) was detected in WM98 and A375 melanomas with the transcript levels being modulated by vitamin D analogs. The expression of VDR isoforms in WM98 cells was stimulated strongly by calcipotriol. The antiproliferative activities of 21(OH)pD appear not to require VDR translocation to the nucleus, which explains the high efficacy of this noncalcemic pregnacalciferol analog in SK-MEL-188b melanoma, that is, VDR^−/−. Therefore, we propose that 21(OH)pD is a good candidate for melanoma therapy, although the mechanism of its action remains to be defined.

Evidence of vitamin D synthesis in insects exposed to UVb light

Vertebrates obtain the prohormone vitamin D primarily by endogenous cutaneous synthesis under ultraviolet b (UVb) exposure. To date, endogenous synthesis of vitamin D in insects has never been investigated. In an initial experiment, we exposed four insect species which differ in ecology and morphology (migratory locusts, house crickets, yellow mealworms and black soldier fly larvae (BSFL)) to a low irradiance UVb source. In a second experiment we exposed these species to a higher UV irradiance, and in a third we tested the effect of exposure duration on vitamin D concentrations in yellow mealworms. Low irradiance UVb tended to increase vitamin D3 levels in house crickets, vitamin D2 levels in BSFL and vitamin D2 and D3 in yellow mealworms. Higher UVb irradiance increased vitamin D3 levels in all species but BSFL. Both BSFL and migratory locusts had increased vitamin D2 levels. Longer UVb exposure of yellow mealworms increased vitamin D2 and increased vitamin D3 until a plateau was reached at 6400 IU/kg. This study shows that insects can synthesize vitamin D de novo and that the amounts depend on UVb irradiance and exposure duration.

Challenge and perspective: the relevance of ultraviolet (UV) radiation and the vitamin D endocrine system (VDES) for psoriasis and other inflammatory skin diseases

During evolution, the ability of many organisms to synthesize vitamin D photochemically represented, and still represents, a major driving factor for the development of life on earth. In humans because not more than 10-20% of the requirement of vitamin D can be satisfied by the diet (under most living conditions in the US and Europe), the remaining 80-90% need to be photochemically synthesized in the skin through the action of solar or artificial ultraviolet-B (UV-B) radiation. The skin is a key organ of the human body's vitamin D endocrine system (VDES), representing both the site of vitamin D synthesis and a target tissue for biologically active vitamin D metabolites. Human keratinocytes contain the enzymatic machinery (CYP27B1) for the synthesis of the biologically most active natural vitamin D metabolite 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), representing an autonomous vitamin D₃ pathway. Cutaneous production of 1,25(OH)₂D₃ may mediate intracrine, autocrine and paracrine effects on keratinocytes and on neighboring cells. Many skin cells (including keratinocytes, sebocytes, fibroblasts, melanocytes, macrophages and other skin immune cells) express the vitamin D receptor (VDR), an absolute pre-requisite for exerting genomic effects of 1,25(OH)₂D₃ and analogs. The VDR is a member of the superfamily of trans-acting transcriptional regulatory factors, which also contains the steroid and thyroid hormone receptors as well as the retinoid-X receptors (RXR) and retinoic acid receptors (RAR). A large body of evidence, including cDNA microarray analyses of mRNAs, indicates that as many as 500-1000 genes may be controlled by VDR ligands that regulate a broad variety of cellular functions including growth, differentiation, and apoptosis. Clinical and laboratory investigations, including the observation that 1,25(OH)₂D₃ is very effective in inducing the terminal differentiation and in inhibiting the proliferation of cultured human keratinocytes have resulted in the use of 1,25(OH)₂D₃ and analogs for the treatment of psoriasis. Focussing on the UV-induced cutaneous synthesis of vitamin D, this review gives an update on the relevance of the VDES and of UV radiation for the management of psoriasis and other inflammatory skin diseases.

Endocrine actions of vitamin D in skin: Relevance for photocarcinogenesis of non-melanoma skin cancer, and beyond

The skin represents a pivotal organ for the human body's vitamin D endocrine system, being both the site of ultraviolet (UV)-B-induced vitamin D synthesis and a target tissue for the pluripotent effects of 1,25(OH)₂D₃ and other biologically active vitamin D metabolites. As many other steroid hormones, 1,25(OH)₂D₃ exerts its effects via two independent signal transduction pathways: the classical genomic and the non-genomic pathway. While non-genomic effects of 1,25(OH)₂D₃ are in part exerted via effects on intracellular calcium, genomic effects are mediated by the vitamin D receptor (VDR). Recent findings convincingly support the concept of a new function of the VDR as a tumor suppressor in skin, with key components of the vitamin D endocrine system, including VDR, CYP24A1, CYP27A1, and CYP27B1 being strongly expressed in non-melanoma skin cancer (NMSC). It has now been shown that anti-tumor effects of VDR, that include some of its ligand-induced growth-regulatory effects, are at least in part mediated by interacting in a highly coordinated manner with the p53 family (p53/p63/p73) in response to a large number of alterations in cell homeostasis, including UV-induced DNA damage, a hallmark for skin photocarcinogenesis. Considering the relevance of the vitamin D endocrine system for carcinogenesis of skin cancer, it is not surprising that low 25(OH)D serum concentrations and genetic variants (SNPs) of the vitamin D endocrine system have been identified as potential risk factors for occurrence and prognosis of skin malignancies. In conclusion, an increasing body of evidence now convincingly supports the concept that the vitamin D endocrine system is of relevance for photocarcinogenesis and progression of NMSC and that its pharmacologic modulation by vitamin D, 1,25(OH)₂D_3, and analogs represents a promising new strategy for prevention and/or treatment of these malignancies.

The vitamin D receptor: contemporary genomic approaches reveal new basic and translational insights

The vitamin D receptor (VDR) is the single known regulatory mediator of hormonal 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in higher vertebrates. It acts in the nucleus of vitamin D target cells to regulate the expression of genes whose products control diverse, cell type-specific biological functions that include mineral homeostasis. In this Review we describe progress that has been made in defining new cellular sites of action of this receptor, the mechanisms through which this mediator controls the expression of genes, the biology that ensues, and the translational impact of this receptor on human health and disease. We conclude with a brief discussion of what comes next in understanding vitamin D biology and the mechanisms that underlie its actions.

1α,25(OH) 2D3 Sensitive Cytosolic pH Regulation and Glycolytic Flux in Human Endometrial Ishikawa Cells

BACKGROUND/AIMS

Tumor cell proliferation is modified by 1,25-Dihydroxy-Vitamin D3 (1,25(OH)2D3), a steroid hormone predominantly known for its role in calcium and phosphorus metabolism. Key properties of tumor cells include enhanced glycolytic flux with excessive consumption of glucose and formation of lactate. As glycolysis is highly sensitive to cytosolic pH, maintenance of glycolysis requires export of H+ ions and lactate, which is in part accomplished by Na+/H+ exchangers, such as NHE1 and monocarboxylate transporters, such as MCT4. An effect of 1,25(OH)2D3 on those transport processes has, however, never been reported. As cytosolic pH impacts on apoptosis, the study further explored the effect of 1,25(OH)2D3 on apoptosis and on the apoptosis regulating kinase AKT, transcription factor Forkhead box O-3 (FOXO3A) and B-cell lymphoma protein BCL-2.

METHODS

In human endometrial adenocarcinoma (Ishikawa) cells, cytosolic pH (pHi) was determined utilizing (2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein [BCECF] fluorescence, Na+/H+ exchanger activity from Na+ dependent realkalinization after an ammonium pulse, NHE1 and MCT4 transcript levels using qRT-PCR, NHE1, MCT4, total & phospho AKT, total & phospho-FOXO3A and BCL-2 protein abundance by Western blotting, lactate concentration in the supernatant utilizing a colorimetric enzyme assay and cell death quantification using CytoTox 96®, Annexin V and Propidium Iodide staining.

RESULTS

A 24 hours treatment with 1,25(OH)2D3 (100 nM) significantly increased cytosolic pH (pHi), significantly decreased Na+/H+ exchanger activity, NHE1 and MCT4 transcript levels as well as protein abundance and significantly increased lactate concentration in the supernatant. Treatment of Ishikawa cells with 1,25(OH)2D3 (100 nM) further triggered apoptosis, an effect paralleled by decreased phosphorylation of AKT and FOXO3A as well as decreased abundance of BCL-2.

CONCLUSIONS

In Ishikawa cells 1,25(OH)2D3 is a powerful stimulator of glycolysis, an effect presumably due to cytosolic alkalinization. Despite stimulation of glycolysis, 1,25(OH)2D3 stimulates slightly but significantly suicidal cell death, an effect presumably in part due to decreased activation of AKT with decreased inhibition of pro-apoptotic transcription factor FOXO3A and downregulation of the anti-apoptotic protein BCL-2.

The quantification of reproductive hormones in the hair of captive adult brown bears and their application as indicators of sex and reproductive state

Recognizing the potential value of steroid hormone measurements to augment non-invasive genetic sampling, we developed procedures based on enzyme-linked immunoassays to quantify reproductive steroid hormone concentrations in brown bear (Ursus arctos) hair. Then, using 94 hair samples collected from eight captive adult bears over a 2-year period, we evaluated (i) associations between hair concentrations of testosterone, progesterone, estradiol and cortisol; (ii) the effect of collecting by shaving vs. plucking; and (iii) the utility of reproductive hormone profiles to differentiate sex and reproductive state. Sample requirements (125 mg of guard hair) to assay all hormones exceeded amounts typically obtained by non-invasive sampling. Thus, broad application of this approach will require modification of non-invasive techniques to collect larger samples, use of mixed (guard and undercoat) hair samples and/or application of more sensitive laboratory procedures. Concentrations of hormones were highly correlated suggesting their sequestration in hair reflects underlying physiological processes. Marked changes in hair hormone levels during the quiescent phase of the hair cycle, coupled with the finding that progesterone concentrations, and their association with testosterone levels, differed markedly between plucked and shaved hair samples, suggests steroids sequestered in hair were likely derived from various sources, including skin. Changes in hair hormone concentrations over time, and in conjunction with key reproductive events, were similar to what has been reported concerning hormonal changes in the blood serum of brown bears. Thus, potential for the measurement of hair reproductive hormone levels to augment non-invasive genetic sampling appears compelling. Nonetheless, we are conducting additional validation studies on hair collected from free-ranging bears, representative of all sex, age and reproductive classes, to fully evaluate the utility of this approach for brown bear conservation and research.

Role of Vitamin D in the Hygiene Hypothesis: The Interplay between Vitamin D, Vitamin D Receptors, Gut Microbiota, and Immune Response

The hygiene hypothesis postulates that higher levels of cleanliness and improper exposure to microorganisms early in childhood could disturb the intestinal microbiome resulting in abnormal immune responses. Recently, more attention has been put on how a lack of sun exposure and consequently vitamin D deficiency could lead to less immune tolerance and aberrant immune responses. Moreover, vitamin D receptor (VDR) function has been positioned to be a critical aspect of immune response and gut homeostasis. Therefore, this review focuses on the role that the interaction between vitamin D, VDR function, and gut microbiome might have on autoimmune diseases in the context of the hygiene hypothesis. Literature shows that there is a high correlation between vitamin D deficiency, VDR dysfunction, gut microbiota composition, and autoimmune diseases. The biologically active form of vitamin D, 1,25(OH)₂D₃, serves as the primary ligand for VDRs, which have been shown to play a fundamental role in reducing autoimmune disease symptoms. Although the biological functions of VDR, the effects of its genetic variants, and the effects of epigenetic profiles in its promoter region are largely unknown in humans, studies in murine models are increasingly demonstrating that VDRs play a crucial role in attenuating autoimmune disease symptoms by regulating autophagy and the production of antimicrobial peptides, such cathelicidin and β-defensin, which are responsible for modifying the intestinal microbiota to a healthier composition. Remarkably, evidence shows that hormonal compounds and byproducts of the microbiota such as secondary bile acids might also activate VDR. Therefore, understanding the interaction between VDR and gut microbiota is of the utmost importance toward understanding the rise in autoimmune diseases in Western countries. We have gained insights on how the VDR functions affects inflammation, autophagy, and microbiota composition that could lead to the development of pathogenesis of autoimmune diseases, while confirming the role vitamin D and VDRs have in the context of hygiene hypothesis.