Endogenously produced nonclassical vitamin D hydroxy-metabolites act as "biased" agonists on VDR and inverse agonists on RORα and RORγ

RORα fine-tunes the circadian control of hepatic triglyceride synthesis and gluconeogenesis

Circadian rhythms play a fundamental role in hepatic metabolism, orchestrating lipid synthesis and glucose homeostasis. RORα, a nuclear receptor involved in circadian regulation, has been implicated in fine-tuning these metabolic processes. We previously showed a therapeutic potential of antagonizing RORα to reduce body fat in mice. Our current aim is to investigate the impact of the whole-body RORα deletion on hepatic lipid metabolism over a complete circadian cycle. Using RORα-knockout (staggerer) mice, this study reveals a time-dependent disruption in hepatic triglyceride synthesis, with reduced lipogenesis during the light-phase and altered transcriptional regulation of key metabolic genes, including Srebp1c and Insigs. Despite increased Srebp1c transcription at night, the anticipated rise in lipid synthesis was prevented by phase-shifted Insig expression, modulating precursor maturation. Moreover, core clock genes rhythmic expression was attenuated and phase-shifted for Reverbα. Pharmacological inhibition of RORα using an inverse agonist (SR3335) mirrored the metabolic effects observed in staggerer mice, further supporting the role of RORα as a crucial regulator of lipid and glucose homeostasis in mice fed a chow diet. These findings highlight the intricate interaction between the circadian clock and hepatic metabolism, situating RORα as a promising target to prevent metabolic disorders such as obesity and dyslipidemia.

Anticancer Activity of Vitamin D, Lumisterol and Selected Derivatives against Human Malignant Melanoma Cell Lines

Despite the recent development of improved methods of treating melanoma such as targeted therapy, immunotherapy or combined treatment, the number of new cases worldwide is increasing. It is well known that active metabolites of vitamin D3 and lumisterol (L3) exert photoprotective and antiproliferative effects on the skin, while UV radiation is a major environmental risk factor for melanoma. Thus, many natural metabolites and synthetic analogs of steroidal and secosteroidal molecules have been tested on various cancer cells and in animal models. In this study, we tested the anti-melanoma properties of several natural derivatives of vitamin D3 and L3 in comparison to 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). A significant decrease in melanoma cell proliferation and cell mobility was observed for selected derivatives, with (25R)-27-hydroxyL3 showing the highest potency (lowest IC50) in A375 cells but lower potency in SK-MEL-28 cells, whereas the parent L3 failed to inhibit proliferation. The efficacy (% inhibition) by 1,24,25(OH)3D3 and 1,25(OH)2D3 were similar in both cell types. 1,25(OH)2D3 showed higher potency than 1,24,25(OH)3D3 in SK-MEL-28 cells, but lower potency in A375 cells for the inhibition of proliferation. As for 1,25(OH)2D3, but not the other derivatives tested, treatment of melanoma cells with 1,24,25(OH)3D3 markedly increased the expression of CYP24A1, enhanced translocation of the vitamin D receptor (VDR) from the cytoplasm to the nucleus and also decreased the expression of the proliferation marker Ki67. The effects of the other compounds tested were weaker and occurred only under certain conditions. Our data indicate that 1,24,25(OH)3D3, which has undergone the first step in 1,25(OH)2D3 inactivation by being hydroxylated at C24, still shows anti-melanoma properties, displaying higher potency than 1,25(OH)2D3 in SK-MEL-28 cells. Furthermore, hydroxylation increases the potency of some of the lumisterol hydroxy-derivatives, as in contrast to L3, (25R)-27(OH)L3 effectively inhibits proliferation and migration of the human malignant melanoma cell line A375.

Biological Effects of CYP11A1-Derived Vitamin D and Lumisterol Metabolites in the Skin

Novel pathways of vitamin D3, lumisterol 3 (L3), and tachysterol 3 (T3) activation have been discovered, initiated by CYP11A1 and/or CYP27A1 in the case of L3 and T3. The resulting hydroxymetabolites enhance protection of skin against DNA damage and oxidative stress; stimulate keratinocyte differentiation; exert anti-inflammatory, antifibrogenic, and anticancer activities; and inhibit cell proliferation in a structure-dependent manner. They act on nuclear receptors, including vitamin D receptor, aryl hydrocarbon receptor, LXRα/β, RAR-related orphan receptor α/γ, and peroxisome proliferator-activated receptor-γ, with selectivity defined by their core structure and distribution of hydroxyl groups. They can activate NRF2 and p53 and inhibit NF-κB, IL-17, Shh, and Wnt/β-catenin signaling. Thus, they protect skin integrity and physiology.

Evolutionary formation of melatonin and vitamin D in early life forms: insects take centre stage

Melatonin, a product of tryptophan metabolism via serotonin, is a molecule with an indole backbone that is widely produced by bacteria, unicellular eukaryotic organisms, plants, fungi and all animal taxa. Aside from its role in the regulation of circadian rhythms, it has diverse biological actions including regulation of cytoprotective responses and other functions crucial for survival across different species. The latter properties are also shared by its metabolites including kynuric products generated by reactive oxygen species or phototransfomation induced by ultraviolet radiation. Vitamins D and related photoproducts originate from phototransformation of ∆5,7 sterols, of which 7-dehydrocholesterol and ergosterol are examples. Their ∆5,7 bonds in the B ring absorb solar ultraviolet radiation [290-315 nm, ultraviolet B (UVB) radiation] resulting in B ring opening to produce previtamin D, also referred to as a secosteroid. Once formed, previtamin D can either undergo thermal-induced isomerization to vitamin D or absorb UVB radiation to be transformed into photoproducts including lumisterol and tachysterol. Vitamin D, as well as the previtamin D photoproducts lumisterol and tachysterol, are hydroxylated by cyochrome P450 (CYP) enzymes to produce biologically active hydroxyderivatives. The best known of these is 1,25-dihydroxyvitamin D (1,25(OH)2D) for which the major function in vertebrates is regulation of calcium and phosphorus metabolism. Herein we review data on melatonin production and metabolism and discuss their functions in insects. We discuss production of previtamin D and vitamin D, and their photoproducts in fungi, plants and insects, as well as mechanisms for their enzymatic activation and suggest possible biological functions for them in these groups of organisms. For the detection of these secosteroids and their precursors and photoderivatives, as well as melatonin metabolites, we focus on honey produced by bees and on body extracts of Drosophila melanogaster. Common biological functions for melatonin derivatives and secosteroids such as cytoprotective and photoprotective actions in insects are discussed. We provide hypotheses for the photoproduction of other secosteroids and of kynuric metabolites of melatonin, based on the known photobiology of ∆5,7 sterols and of the indole ring, respectively. We also offer possible mechanisms of actions for these unique molecules and summarise differences and similarities of melatoninergic and secosteroidogenic pathways in diverse organisms including insects.

Cellular and Molecular Genetic Mechanisms of Lung Fibrosis Development and the Role of Vitamin D: A Review

Idiopathic pulmonary fibrosis remains a relevant problem of the healthcare system with an unfavorable prognosis for patients due to progressive fibrous remodeling of the pulmonary parenchyma. Starting with the damage of the epithelial lining of alveoli, pulmonary fibrosis is implemented through a cascade of complex mechanisms, the crucial of which is the TGF-β/SMAD-mediated pathway, involving various cell populations. Considering that a number of the available drugs (pirfenidone and nintedanib) have only limited effectiveness in slowing the progression of fibrosis, the search and justification of new approaches aimed at regulating the immune response, cellular aging processes, programmed cell death, and transdifferentiation of cell populations remains relevant. This literature review presents the key modern concepts concerning molecular genetics and cellular mechanisms of lung fibrosis development, based mainly on in vitro and in vivo studies in experimental models of bleomycin-induced pulmonary fibrosis, as well as the latest data on metabolic features, potential targets, and effects of vitamin D and its metabolites.

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.

Insight into vitamin D3 action within the ovary-Basic and clinical aspects

Vitamin D3 is a fat-soluble secosteroid predominantly synthesized in the skin or delivered with a diet. Nevertheless, recently it is considered more as a hormone than a vitamin due to its pleiotropic function within the organism ensured by widely distributed vitamin D receptors and metabolic enzymes. Besides the main role in calcium and phosphorus homeostasis, vitamin D3 was shown to regulate many cellular and metabolic processes in normal and cancerous tissues within the immune system, the cardiovascular system, the respiratory system and the endocrine system. The ovary is an important extraskeletal tissue of vitamin D3 action and local metabolism, indicating its role in the regulation of ovarian functions upon physiological and pathological conditions. This chapter reviews firstly the updated information about vitamin D3 metabolism and triggered intracellular pathways. Furthermore, the basic information about ovarian physiology and several aspects of vitamin D3 effects within the ovary are presented. Finally, the special attention is paid into possible mechanism of vitamin D3 action within ovarian pathologies such as premature ovarian failure, polycystic ovary syndrome, and ovarian cancer, considering its clinical application as alternative therapy.

1,25(OH)2D3 improves diabetic wound healing by modulating inflammation and promoting angiogenesis

Vitamin D was found to regulate inflammatory response and angiogenesis, which were often impaired in diabetic wound healing. This study aimed to investigate the effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on diabetic wound healing both in vivo and in vitro. Diabetes was induced by high-fat diet combined with streptozotocin. After four weeks of establishing diabetic mouse model, full-thickness excisional wounds were created on their dorsal skin. Then 1,25(OH)2D3 was administered via intraperitoneal injection for 14 consecutive days. Human umbilical vein endothelial cells (HUVECs) were cultured with normal glucose, high glucose, high glucose plus 1,25(OH)2D3. Cell proliferation, migration, tube formation, and expression levels of relevant pathway components were measured. Intervention with 1,25(OH)2D3 significantly increased wound closure rates of diabetic mice. During the inflammatory phase, 1,25(OH)2D3 alleviated excessive inflammation and promoted the transition of macrophages from M1 to M2 phenotype. Regarding vascular endothelial function, 1,25(OH)2D3 significantly up-regulated eNOS protein expression and inhibited Vcam-1 mRNA expression in diabetic mice (P < 0.05). As for angiogenesis, 1,25(OH)2D3 markedly increased CD31-positive area, the protein and mRNA expression of VEGF, VEGFR2, PDGF, and PDGFRβ, as well as the mRNA expression of Bfgf and Egfr (P < 0.05). In vitro, 1,25(OH)2D3 restored impaired cell proliferation, migration, and tube formation induced by high-glucose, and up-regulated expression of angiogenesis-related factors. These protective effects might be mediated through PI3K/AKT/HIF-1α pathway. These findings suggested that 1,25(OH)2D3 accelerated diabetic wound healing by modulating inflammation, restoring vascular endothelial dysfunction, and promoting angiogenesis.

Dissection of an impact of VDR and RXRA on the genomic activity of 1,25(OH)2D3 in A431 squamous cell carcinoma

BACKGROUND

Human skin is the natural source, place of metabolism, and target for vitamin D3. The classical active form of vitamin D3, 1,25(OH)2D3, expresses pluripotent properties and is intensively studied in cancer prevention and therapy. To define the specific role of vitamin D3 receptor (VDR) and its co-receptor retinoid X receptor alpha (RXRA) in genomic regulation, VDR or RXRA genes were silenced in the squamous cell carcinoma cell line A431 and treated with 1,25(OH)2D3 at long incubation time points 24 h/72 h. Extending the incubation time of A431 WT (wild-type) cells with 1,25(OH)2D3 resulted in a two-fold increase in DEGs (differentially expressed genes) and a change in the amount of downregulated from 37% to 53%. VDR knockout led to a complete loss of 1,25(OH)2D3-induced genome-wide gene regulation at 24 h time point, but after 72 h, 20 DEGs were found, of which 75% were downregulated, and most of them belonged to the gene ontology group "immune response". This may indicate the existence of an alternative, secondary response to 1,25(OH)2D3. In contrast, treatment of A431 ΔRXRA cells with 1,25(OH)2D3 for 24 h only partially affected DEGs, suggesting RXRA-independent regulation. Interestingly, overexpression of classic 1,25(OH)2D3 targets, like CYP24A1 (family 24 of subfamily A of cytochrome P450 member 1) or CAMP (cathelicidin antimicrobial peptide) was found to be RXRA-independent. Also, immunofluorescence staining of A431 WT cells revealed partial VDR/RXRA colocalization after 24 h and 72 h 1,25(OH)2D3 treatment. Comparison of transcriptome changes induced by 1,25(OH)2D3 in normal keratinocytes vs. cancer cells showed high cell type specific expression pattern with only a few genes commonly regulated by 1,25(OH)2D3. Activation of the genomic pathway at least partially reversed the expression of cancer-related genes, forming a basis for anti-cancer activates of 1,25(OH)2D3. In summary, VDR or RXRA independent genomic activities of 1,25(OH)2D3 suggest the involvement of alternative factors, opening new challenges in this field.

Sequential administration of paricalcitol followed by IL-17 blockade for progressive refractory IgA nephropathy patients

There is no established treatment for progressive IgA nephropathy refractory to steroids and immunosuppressant drugs (r-IgAN). Interleukin 17 (IL-17) blockade has garnered interest in immune-mediated diseases involving the gut-kidney axis. However, single IL-17A inhibition induced paradoxical effects in patients with Crohn's disease and some cases of de novo glomerulonephritis, possibly due to the complete Th1 cell response, along with the concomitant downregulation of regulatory T cells (Tregs). Seven r-IgAN patients were treated with at least six months of oral paricalcitol, followed by the addition of subcutaneous anti-IL-17A (secukinumab). After a mean follow-up of 28 months, proteinuria decreased by 71% (95% CI: 56-87), P < 0.001. One patient started dialysis, while the annual eGFR decline in the remaining patients [mean (95% CI)] was reduced by 4.9 mL/min/1.73 m2 (95% CI: 0.1-9.7), P = 0.046. Circulating Th1, Th17, and Treg cells remained stable, but Th2 cells decreased, modifying the Th1/Th2 ratio. Intriguingly, accumulation of circulating Th17.1 cells was observed. This novel sequential therapy appears to optimize renal advantages in patients with r-IgAN and elicit alterations in potentially pathogenic T helper cells.

Novel Vitamin D3 Hydroxymetabolites Require Involvement of the Vitamin D Receptor or Retinoic Acid-Related Orphan Receptors for Their Antifibrogenic Activities in Human Fibroblasts

We investigated multiple signaling pathways activated by CYP11A1-derived vitamin D3 hydroxymetabolites in human skin fibroblasts by assessing the actions of these molecules on their cognate receptors and by investigating the role of CYP27B1 in their biological activities. The actions of 20(OH)D3, 20,23(OH)2D3, 1,20(OH)2D3 and 1,20,23(OH)3D3 were compared to those of classical 1,25(OH)2D3. This was undertaken using wild type (WT) fibroblasts, as well as cells with VDR, RORs, or CYP27B1 genes knocked down with siRNA. Vitamin D3 hydroxymetabolites had an inhibitory effect on the proliferation of WT cells, but this effect was abrogated in cells with silenced VDR or RORs. The collagen expression by WT cells was reduced upon secosteroid treatment. This effect was reversed in cells where VDR or RORs were knocked down where the inhibition of collagen production and the expression of anti-fibrotic genes in response to the hydroxymetabolites was abrogated, along with ablation of their anti-inflammatory action. The knockdown of CYP27B1 did not change the effect of either 20(OH)D3 or 20,23(OH)2D3, indicating that their actions are independent of 1α-hydroxylation. In conclusion, the expression of the VDR and/or RORα/γ receptors in fibroblasts is necessary for the inhibition of both the proliferation and fibrogenic activity of hydroxymetabolites of vitamin D3, while CYP27B1 is not required.

Molecular Mechanism of Vitamin D Receptor Modulating Wnt/β-catenin Signaling Pathway in Gastric Cancer

Background: Gastric cancer is the most common gastrointestinal cancer worldwide. The latest data showed that it was the fourth leading cause of cancer-related death. The unobvious symptom and the difficulties lying in the early diagnosis largely affect the effect of the treatment. Therefore, it becomes particularly important to investigate the related genes and signal transduction pathways in gastric cancer. Our previous study found that the vitamin D receptor (VDR) gene FokI polymorphism may be associated with susceptibility to gastric cancer in the Chinese Han population. However, the mechanism of VDR affecting gastric cancer is unknown. In this study, we explored the molecular mechanism and the possible signaling pathway of VDR modulating carcinogenesis and progression of gastric cancer. Methods: The expression of VDR in gastric cancer cell lines was interfered by plasmid transfection and RNA interference technology. And then we analyzed the cell viability and invasive ability by MTT assay, colony formation assay, and transwell migration assay, and detected the expression of VDR and several signaling proteins in gastric cancer cells by SDS-PAGE and Western blotting. Results: The overexpression of VDR can significantly inhibit the viability and invasive ability of gastric cancer cells; on the contrary, when VDR siRNA inhibits the expression of VDR, the viability and invasive ability of gastric cancer cells enhanced. VDR expression levels in gastric cancer cells treated with 1,25 (OH) 2D3 showed a time-dependent increased expression; and with the increase of the VDR expression, the expression of β-catenin decreased gradually, but the expression of E-cadherin showed a time-dependent increase (P < 0.05). Compared with the mutant-type VDR gene(ff) cells, the degree of β-catenin decline was significantly enhanced after transfected with homozygous wild-type VDR gene (FF) plasmids (p<0.05). Conclusions: The results of this study indicate that VDR FokI polymorphism plays an important role in the malignant phenotype of gastric cancer cells, such as proliferation, invasion, and clone formation. When the VDR is activated by its ligand, it can prevent the nuclear import of β-catenin, affect the E-cadherin level, inhibit the proliferation of gastric cancer cells, which suggested that VDR FokI gene may play a role of cancer suppressor via Wnt/β-catenin signaling pathway.

A review of the critical role of vitamin D axis on the immune system

In recent years, the physiological and molecular functions of vitamin D (Vit-D) have been deeply investigated. At first, Vit-D was considered a regulator of mineral and skeletal homeostasis. However, due to the extensive-expression pattern of Vit-D receptor (VDR) in almost every non-skeletal cell, Vit-D is considered mainly a multifunctional agent with broad effects on various tissues, notably the immune system. The expression of VDR in immune cells such as dendritic cells, monocyte/macrophage, neutrophils, B cells and T cells has been well demonstrated. Besides, such immune cells are capable of metabolizing the active form of Vit-D which means that it can module the immune system in both paracrine and autocrine manners. Vit-D binding protein (DBP), that regulates the levels and homeostasis of Vit-D, is another key molecule capable of modulating the immune system. Recent studies indicate that dysregulation of Vit-D axis, variations in the DBP and VDR genes, and Vit-D levels might be risk factors for the development of autoimmune disease. Here, the current evidence regarding the role of Vit-D axis on the immune system, as well as its role in the development of autoimmune disease will be clarified. Further insight will be given to those studies that investigated the association between single nucleotide polymorphisms of DBP and VDR genes with autoimmune disease susceptibility.

Influence of Different Light Spectra on Melatonin Synthesis by the Pineal Gland and Influence on the Immune System in Chickens

It is well known that the pineal gland in birds influences behavioural and physiological functions, including those of the immune system. The purpose of this research is to examine the endocrine-immune correlations between melatonin and immune system activity. Through a description of the immune-pineal axis, we formulated the objective to determine and describe: the development of the pineal gland; how light influences secretory activity; and how melatonin influences the activity of primary and secondary lymphoid organs. The pineal gland has the ability to turn light information into an endocrine signal suitable for the immune system via the membrane receptors Mel1a, Mel1b, and Mel1c, as well as the nuclear receptors RORα, RORβ, and RORγ. We can state the following findings: green monochromatic light (560 nm) increased serum melatonin levels and promoted a stronger humoral and cellular immune response by proliferating B and T lymphocytes; the combination of green and blue monochromatic light (560-480 nm) ameliorated the inflammatory response and protected lymphoid organs from oxidative stress; and red monochromatic light (660 nm) maintained the inflammatory response and promoted the growth of pathogenic bacteria. Melatonin can be considered a potent antioxidant and immunomodulator and is a critical element in the coordination between external light stimulation and the body's internal response.

Role of Vitamin D in Head and Neck Cancer-Immune Function, Anti-Tumour Effect, and Its Impact on Patient Prognosis

Head and neck squamous cell carcinoma (HNSCC) describes a heterogeneous group of human neoplasms of the head and neck with high rates of morbidity and mortality, constituting about 3% of all cancers and ~1.5% of all cancer deaths. HNSCC constituted the seventh most prevalent human malignancy and the most common human cancer in the world in 2020, according to multi-population observations conducted by the GLOBOCAN group. Since approximately 60-70% of patients present with stage III/IV neoplastic disease, HNSCC is still one of the leading causes of death in cancer patients worldwide, with an overall survival rate that is too low, not exceeding 40-60% of these patients. Despite the application of newer surgical techniques and the implementation of modern combined oncological treatment, the disease often follows a fatal course due to frequent nodal metastases and local neoplastic recurrences. The role of micronutrients in the initiation, development, and progression of HNSCC has been the subject of considerable research. Of particular interest has been vitamin D, the pleiotropic biologically active fat-soluble family of secosteroids (vitamin-D-like steroids), which constitutes a key regulator of bone, calcium, and phosphate homeostasis, as well as carcinogenesis and the further development of various neoplasms. Considerable evidence suggests that vitamin D plays a key role in cellular proliferation, angiogenesis, immunity, and cellular metabolism. A number of basic science, clinical, and epidemiological studies indicate that vitamin D has multidirectional biological effects and influences anti-cancer intracellular mechanisms and cancer risk, and that vitamin D dietary supplements have various prophylactic benefits. In the 20th century, it was reported that vitamin D may play various roles in the protection and regulation of normal cellular phenotypes and in cancer prevention and adjunctive therapy in various human neoplasms, including HNSCC, by regulating a number of intracellular mechanisms, including control of tumour cell expansion and differentiation, apoptosis, intercellular interactions, angio- and lymphogenesis, immune function, and tumour invasion. These regulatory properties mainly occur indirectly via epigenetic and transcriptional changes regulating the function of transcription factors, chromatin modifiers, non-coding RNA (ncRNAs), and microRNAs (miRs) through protein-protein interactions and signalling pathways. In this way, calcitriol enhances intercellular communication in cancer biology, restores the connection with the extracellular matrix, and promotes the epithelial phenotype; it thus counteracts the tumour-associated detachment from the extracellular matrix and inhibits the formation of metastases. Furthermore, the confirmation that the vitamin D receptor (VDR) is present in many human tissues confirmed the physiopathological significance of vitamin D in various human tumours. Recent studies indicate quantitative associations between exposure to vitamin D and the incidence of HNC, i.e., cancer risk assessment included circulating calcidiol plasma/serum concentrations, vitamin D intake, the presence of the VDR gene polymorphism, and genes involved in the vitamin D metabolism pathway. Moreover, the chemopreventive efficacy of vitamin D in precancerous lesions of the head and neck and their role as predictors of mortality, survival, and recurrence of head and neck cancer are also widely discussed. As such, it may be considered a promising potential anti-cancer agent for developing innovative methods of targeted therapy. The proposed review discusses in detail the mechanisms regulating the relationship between vitamin D and HNSCC. It also provides an overview of the current literature, including key opinion-forming systematic reviews as well as epidemiological, prospective, longitudinal, cross-sectional, and interventional studies based on in vitro and animal models of HNSCC, all of which are accessible via the PubMed/Medline/EMBASE/Cochrane Library databases. This article presents the data in line with increasing clinical credibility.

Enzymatic activation in vitamin D signaling - Past, present and future

Vitamin D signaling is important in regulating calcium homeostasis essential for bone health but also displays other functions in cells of several tissues. Disturbed vitamin D signaling is linked to a large number of diseases. The multiple cytochrome P450 (CYP) enzymes catalyzing the different hydroxylations in bioactivation of vitamin D₃ are crucial for vitamin D signaling and function. This review is focused on the progress achieved in identification of the bioactivating enzymes and their genes in production of 1α,25-dihydroxyvitamin D₃ and other active metabolites. Results obtained on species- and tissue-specific expression, catalytic reactions, substrate specificity, enzyme kinetics, and consequences of gene mutations are evaluated. Matters of incomplete understanding regarding the physiological roles of some vitamin D hydroxylases are critically discussed and the authors will give their view of the importance of each enzyme for vitamin D signaling. Roles of different vitamin D receptors and an alternative bioactivation pathway, leading to 20-hydroxylated vitamin D₃ metabolites, are also discussed. Considerable progress has been achieved in knowledge of the vitamin D₃ bioactivating enzymes. Nevertheless, several intriguing areas deserve further attention to understand the pleiotropic and diverse activities elicited by vitamin D signaling and the mechanisms of enzymatic activation necessary for vitamin D-induced responses.

The Role of Vitamin D in Health and Disease: A Narrative Review on the Mechanisms Linking Vitamin D with Disease and the Effects of Supplementation

Vitamin D insufficiency or deficiency (VDD) is a very prevalent condition in the general population. Vitamin D is necessary for optimal bone mineralization, but apart from the bone effects, preclinical and observational studies have suggested that vitamin D may have pleiotropic actions, whereas VDD has been linked to several diseases and higher all-cause mortality. Thus, supplementing vitamin D has been considered a safe and inexpensive approach to generate better health outcomes-and especially so in frail populations. Whereas it is generally accepted that prescribing of vitamin D in VDD subjects has demonstrable health benefits, most randomized clinical trials, although with design constraints, assessing the effects of vitamin D supplementation on a variety of diseases have failed to demonstrate any positive effects of vitamin D supplementation. In this narrative review, we first describe mechanisms through which vitamin D may exert an important role in the pathophysiology of the discussed disorder, and then provide studies that have addressed the impact of VDD and of vitamin D supplementation on each disorder, focusing especially on randomized clinical trials and meta-analyses. Despite there already being vast literature on the pleiotropic actions of vitamin D, future research approaches that consider and circumvent the inherent difficulties in studying the effects of vitamin D supplementation on health outcomes are needed to assess the potential beneficial effects of vitamin D. The evaluation of the whole vitamin D endocrine system, rather than only of 25-hydroxyvitamin D levels before and after treatment, use of adequate and physiologic vitamin D dosing, grouping based on the achieved vitamin D levels rather than the amount of vitamin D supplementation subjects may receive, and sufficiently long follow-up are some of the aspects that need to be carefully considered in future studies.

Vitamin D attenuates elevated oxidative DNA damage in scleroderma patients with organ involvement: A prospective study

Scleroderma is a rare autoimmune disease characterized by progressive fibrosis of the skin and internal organs. Oxidative damage to macromolecules has been reported to occur in scleroderma. Among the macromolecular damages, oxidative DNA damage is a sensitive and cumulative marker of oxidative stress and is of particular interest because of its cytotoxic and mutagenic effects. Vitamin D supplementation is an important part of treatment, as vitamin D deficiency is a common problem in scleroderma. Furthermore, the antioxidant role of vitamin D has been demonstrated in recent studies. In light of this information, the present study aimed to comprehensively investigate oxidative DNA damage in scleroderma at baseline and to evaluate the contribution of vitamin D supplementation to the attenuation of DNA damage in a prospectively designed study. In accordance with these objectives, oxidative DNA damage in scleroderma was evaluated by measurement of stable damage products (8-oxo-dG, S-cdA, and R-cdA) in urine by liquid chromatography-tandem mass spectrometry (LC-MS/MS); serum vitamin D levels were determined by high-resolution mass spectrometry (HR-MS); VDR gene expression and four polymorphisms in the VDR gene (rs2228570, rs1544410, rs7975232, and rs731236) were analyzed by RT-PCR and compared with healthy subjects. In the prospective part, the DNA damage and the VDR expression of the patients who received vitamin D were re-evaluated after the replacement. As a result of this study, we demonstrated that all DNA damage products were increased in scleroderma patients compared to healthy controls, whereas vitamin D levels and VDR expression were significantly lower (p < 0.05). After supplementation, statistical significance (p < 0.05) was reached for the decrease in 8-oxo-dG and the increase in VDR expression. Attenuated 8-oxo-dG after replacement in patients with lung, joint, and gastrointestinal system involvement demonstrated the efficacy of vitamin D in scleroderma patients with organ involvement. To the best of our knowledge, this is the first study to examine oxidative DNA damage in scleroderma comprehensively and to evaluate the effects of vitamin D on DNA damage using a prospective design.

Nongenomic Activities of Vitamin D

Vitamin D shows a variety of pleiotropic activities which cannot be fully explained by the stimulation of classic pathway- and vitamin D receptor (VDR)-dependent transcriptional modulation. Thus, existence of rapid and nongenomic responses to vitamin D was suggested. An active form of vitamin D (calcitriol, 1,25(OH)₂D₃) is an essential regulator of calcium-phosphate homeostasis, and this process is tightly regulated by VDR genomic activity. However, it seems that early in evolution, the production of secosteroids (vitamin-D-like steroids) and their subsequent photodegradation served as a protective mechanism against ultraviolet radiation and oxidative stress. Consequently, direct cell-protective activities of vitamin D were proven. Furthermore, calcitriol triggers rapid calcium influx through epithelia and its uptake by a variety of cells. Subsequently, protein disulfide-isomerase A3 (PDIA3) was described as a membrane vitamin D receptor responsible for rapid nongenomic responses. Vitamin D was also found to stimulate a release of secondary massagers and modulate several intracellular processes-including cell cycle, proliferation, or immune responses-through wingless (WNT), sonic hedgehog (SSH), STAT1-3, or NF-kappaB pathways. Megalin and its coreceptor, cubilin, facilitate the import of vitamin D complex with vitamin-D-binding protein (DBP), and its involvement in rapid membrane responses was suggested. Vitamin D also directly and indirectly influences mitochondrial function, including fusion-fission, energy production, mitochondrial membrane potential, activity of ion channels, and apoptosis. Although mechanisms of the nongenomic responses to vitamin D are still not fully understood, in this review, their impact on physiology, pathology, and potential clinical applications will be discussed.

Novel CYP11A1-Derived Vitamin D and Lumisterol Biometabolites for the Management of COVID-19

Vitamin D deficiency is associated with a higher risk of SARS-CoV-2 infection and poor outcomes of the COVID-19 disease. However, a satisfactory mechanism explaining the vitamin D protective effects is missing. Based on the anti-inflammatory and anti-oxidative properties of classical and novel (CYP11A1-derived) vitamin D and lumisterol hydroxymetabolites, we have proposed that they would attenuate the self-amplifying damage in lungs and other organs through mechanisms initiated by interactions with corresponding nuclear receptors. These include the VDR mediated inhibition of NFκβ, inverse agonism on RORγ and the inhibition of ROS through activation of NRF2-dependent pathways. In addition, the non-receptor mediated actions of vitamin D and related lumisterol hydroxymetabolites would include interactions with the active sites of SARS-CoV-2 transcription machinery enzymes (M^pro;main protease and RdRp;RNA dependent RNA polymerase). Furthermore, these metabolites could interfere with the binding of SARS-CoV-2 RBD with ACE2 by interacting with ACE2 and TMPRSS2. These interactions can cause the conformational and dynamical motion changes in TMPRSS2, which would affect TMPRSS2 to prime SARS-CoV-2 spike proteins. Therefore, novel, CYP11A1-derived, active forms of vitamin D and lumisterol can restrain COVID-19 through both nuclear receptor-dependent and independent mechanisms, which identify them as excellent candidates for antiviral drug research and for the educated use of their precursors as nutrients or supplements in the prevention and attenuation of the COVID-19 disease.

Vitamin D-Related Genes and Thyroid Cancer-A Systematic Review

Vitamin D, formerly known for its role in calcium-phosphorus homeostasis, was shown to exert a broad influence on immunity and on differentiation and proliferation processes in the last few years. In the field of endocrinology, there is proof of the potential role of vitamin D and vitamin D-related genes in the pathogenesis of thyroid cancer-the most prevalent endocrine malignancy. Therefore, the study aimed to systematically review the publications on the association between vitamin D-related gene variants (polymorphisms, mutations, etc.) and thyroid cancer. PubMed, EMBASE, Scopus, and Web of Science electronic databases were searched for relevant studies. A total of ten studies were found that met the inclusion criteria. Six vitamin D-related genes were analyzed (VDR-vitamin D receptor, CYP2R1-cytochrome P450 family 2 subfamily R member 1, CYP24A1-cytochrome P450 family 24 subfamily A member 1, CYP27B1-cytochrome P450 family 27 subfamily B member 1, DHCR7-7-dehydrocholesterol reductase and CUBN-cubilin). Moreover, a meta-analysis was conducted to summarize the data from the studies on VDR polymorphisms (rs2228570/FokI, rs1544410/BsmI, rs7975232/ApaI and rs731236/TaqI). Some associations between thyroid cancer risk (VDR, CYP24A1, DHCR7) or the clinical course of the disease (VDR) and vitamin D-related gene polymorphisms were described in the literature. However, these results seem inconclusive and need validation. A meta-analysis of the five studies of common VDR polymorphisms did not confirm their association with increased susceptibility to differentiated thyroid cancer. Further efforts are necessary to improve our understanding of thyroid cancer pathogenesis and implement targeted therapies for refractory cases.

The Role of CYP3A in Health and Disease

CYP3A is an enzyme subfamily in the cytochrome P450 (CYP) superfamily and includes isoforms CYP3A4, CYP3A5, CYP3A7, and CYP3A43. CYP3A enzymes are indiscriminate toward substrates and are unique in that these enzymes metabolize both endogenous compounds and diverse xenobiotics (including drugs); almost the only common characteristic of these compounds is lipophilicity and a relatively large molecular weight. CYP3A enzymes are widely expressed in human organs and tissues, and consequences of these enzymes' activities play a major role both in normal regulation of physiological levels of endogenous compounds and in various pathological conditions. This review addresses these aspects of regulation of CYP3A enzymes under physiological conditions and their involvement in the initiation and progression of diseases.

Vitiligo: A Narrative Review Article

Vitiligo, a common depigmenting cutaneous condition, is thought to affect 0.5%-2% of the world's population. During this condition, melanocytes are selectively lost, resulting in non-scaly, chalky-white macules. Achromic macules and patches are side effects of the multifaceted disease vitiligo, defined as the absence of epidermal pigmentation. The causes of this disaster are three significant factors. A suppressed reaction to touch allergens is one of many abnormal activities of the hypopigmented epidermis, which has also been observed in hypopigmented rats. The white epidermis of people with albinism, which is the same color as vitiligo, is more vulnerable to skin carcinoma; the white epidermis of people with vitiligo does not develop non-melanoma skin carcinoma. The overall etiology of vitiligo, which is now categorically recognized as an immunological illness, has made significant strides in recent years. Even though vitiligo is frequently dismissed as an esthetic issue, it can have serious mental consequences and significantly interfere with daily life. A global consensus in 2011 classified segmental vitiligo separately from all other types of vitiligo. The term vitiligo has been repurposed to refer to various types of nonsegmental vitiligo. There are numerous pharmaceutical procedures available on the market that aim to stop the development of and induce epidermal repigmentation. Variable levels of skin pigmentation have been observed with such therapies, either alone or in combination, and their predominance was safe and efficient. There are few vitiligo treatments available, and none of them can reliably cause repigmentation in every individual. Individualized management is required depending on geography, physical appearance, and the presence of illness activities. The preceding study aims to provide insight into the potential prospects of vitiligo medication while also summarizing the current body of knowledge on the condition.

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 .

Vitamin D, Th17 Lymphocytes, and Breast Cancer

Simple Summary

The effect of vitamin D₃ on the development of breast cancer (favorable, ineffective, or even unfavorable) depends on many factors, such as age, menopausal status, or obesity. The immunomodulatory effect of vitamin D may be unfavorable in case of breast cancer progression. The effect of vitamin D on Th17 cells may depend on disease type and patients’ age. Our goal was to summarize the data available and to find indications of vitamin D treatment failure or success. Therefore, in this review, we present data describing the effects of vitamin D₃ on Th17 cells, mainly in breast cancer.

Abstract

Vitamin D₃, which is well known to maintain calcium homeostasis, plays an important role in various cellular processes. It regulates the proliferation and differentiation of several normal cells, including immune and neoplastic cells, influences the cell cycle, and stimulates cell maturation and apoptosis through a mechanism dependent on the vitamin D receptor. The involvement of vitamin D₃ in breast cancer development has been observed in numerous clinical studies. However, not all studies support the protective effect of vitamin D₃ against the development of this condition. Furthermore, animal studies have revealed that calcitriol or its analogs may stimulate tumor growth or metastasis in some breast cancer models. It has been postulated that the effect of vitamin D₃ on T helper (Th) 17 lymphocytes is one of the mechanisms promoting metastasis in these murine models. Herein we present a literature review on the existing data according to the interplay between vitamin D, Th17 cell and breast cancer. We also discuss the effects of this vitamin on Th17 lymphocytes in various disease entities known to date, due to the scarcity of scientific data on Th17 lymphocytes and breast cancer. The presented data indicate that the effect of vitamin D₃ on breast cancer development depends on many factors, such as age, menopausal status, or obesity. According to that, more extensive clinical trials and studies are needed to assess the importance of vitamin D in breast cancer, especially when no correlations seem to be obvious.

Vitamin D: A Potential Star for Treating Chronic Pancreatitis

Chronic pancreatitis (CP) is a chronic inflammatory and fibrotic disease of the pancreas. The incidence of CP is increasing worldwide but the effective therapies are lacking. Hence, it is necessary to identify economical and effective agents for the treatment of CP patients. Vitamin D (VD) and its analogues have been confirmed as pleiotropic regulators of cell proliferation, apoptosis, differentiation and autophagy. Clinical studies show that VD deficiency is prevalent in CP patients. However, the correlation between VD level and the risk of CP remains controversial. VD and its analogues have been demonstrated to inhibit pancreatic fibrosis by suppressing the activation of pancreatic stellate cells and the production of extracellular matrix. Limited clinical trials have shown that the supplement of VD can improve VD deficiency in patients with CP, suggesting a potential therapeutic value of VD in CP. However, the mechanisms by which VD and its analogues inhibit pancreatic fibrosis have not been fully elucidated. We are reviewing the current literature concerning the risk factors for developing CP, prevalence of VD deficiency in CP, mechanisms of VD action in PSC-mediated fibrogenesis during the development of CP and potential therapeutic applications of VD and its analogues in the treatment of CP.

Molecular and structural basis of interactions of vitamin D3 hydroxyderivatives with aryl hydrocarbon receptor (AhR): An integrated experimental and computational study

To better understand the molecular and structural basis underlying the interaction of vitamin D3 hydroxyderivatives with AhR, molecular simulation was used to probe the binding of 1,20(OH)₂D3, 1,25(OH)₂D3, 20,23(OH)₂D3 and 20(OH)D3 to AhR. qPCR showed that vitamin D3 derivatives stimulate expression of cyp1A1 and cyp1B1 genes that are downstream targets of AhR signaling. These secosteroids stimulated the translocation of the AhR to the nucleus, as measured by flow cytometry and western blotting. Molecular dynamics simulations were used to model the binding of vitamin D3 derivatives to AhR to examine their influence on the structure, conformation and dynamics of the AhR ligand binding domain (LBD). Binding thermodynamics, conformation, secondary structure, dynamical motion and electrostatic potential of AhR were analyzed. The molecular docking scores and binding free energy were all favorable for the binding of D3 derivatives to the AhR. These established ligands and the D3 derivatives are predicted to have different patterns of hydrogen bond formation with the AhR, and varied residue conformational fluctuations and dynamical motion for the LBD. These changes could alter the shape, size and electrostatic potential distribution of the ligand binding pocket, contributing to the different binding affinities of AhR for the natural ligands and D3 derivatives.

Analysis of the Seasonal Fluctuation of γδ T Cells and Its Potential Relation with Vitamin D3

In addition to its role in bone metabolism, vitamin D3 exerts immunomodulatory effects and has been proposed to contribute to seasonal variation of immune cells. This might be linked to higher vitamin D3 levels in summer than in winter due to differential sun exposure. γδ T cells comprise a numerically small subset of T cells in the blood, which contribute to anti-infective and antitumor immunity. We studied the seasonal fluctuation of γδ T cells, the possible influence of vitamin D3, and the effect of the active metabolite 1α,25(OH)2D3 on the in vitro activation of human γδ T cells. In a retrospective analysis with 2625 samples of random blood donors, we observed higher proportions of γδ T cells in winter when compared with summer. In a prospective study over one year with a small cohort of healthy adults who did or did not take oral vitamin D3 supplementation, higher proportions of γδ T cells were present in donors without oral vitamin D3 uptake, particularly in spring. However, γδ T cell frequency in blood did not directly correlate with serum levels of 25(OH)D3. The active metabolite 1α,25(OH)2D3 inhibited the in vitro activation of γδ T cells at the level of proliferation, cytotoxicity, and interferon-γ production. Our study reveals novel insights into the seasonal fluctuation of γδ T cells and the immunomodulatory effects of vitamin D3.

Chemical synthesis, biological activities and action on nuclear receptors of 20S(OH)D3, 20S,25(OH)2D3, 20S,23S(OH)2D3 and 20S,23R(OH)2D3

New and more efficient routes of chemical synthesis of vitamin D₃ (D₃) hydroxy (OH) metabolites, including 20S(OH)D₃, 20S,23S(OH)₂D₃ and 20S,25(OH)₂D₃, that are endogenously produced in the human body by CYP11A1, and of 20S,23R(OH)₂D₃ were established. The biological evaluation showed that these compounds exhibited similar properties to each other regarding inhibition of cell proliferation and induction of cell differentiation but with subtle and quantitative differences. They showed both overlapping and differential effects on T-cell immune activity. They also showed similar interactions with nuclear receptors with all secosteroids activating vitamin D, liver X, retinoic acid orphan and aryl hydrocarbon receptors in functional assays and also as indicated by molecular modeling. They functioned as substrates for CYP27B1 with enzymatic activity being the highest towards 20S,25(OH)₂D₃ and the lowest towards 20S(OH)D₃. In conclusion, defining new routes for large scale synthesis of endogenously produced D₃-hydroxy derivatives by pathways initiated by CYP11A1 opens an exciting era to analyze their common and differential activities in vivo, particularly on the immune system and inflammatory diseases.

PTEN: A novel target for vitamin D in melanoma

Melanoma is the most dangerous form of skin cancer, with poor prognosis in advanced stages. Vitamin D, also produced by ultraviolet radiation, is known for its anti-proliferative properties in some cancers including melanoma. While vitamin D deficiency has been associated with advanced melanoma stage and higher levels of vitamin D have been associated with better outcomes, the role for vitamin D in melanoma remains unclear. Vitamin D synthesis is initiated upon UVB exposure of skin cells and results in formation of the active metabolite 1,25-dihydroxyvitamin D3 (1,25D). We have previously demonstrated that 1,25D plays a role in protection against ultraviolet radiation-induced DNA damage, immune suppression, and skin carcinogenesis. In this study 1,25D significantly reduced cell viability and increased caspase levels in human melanoma cell lines. This effect was not present in cells that lacked both phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a well-known tumour suppressor, and the vitamin D receptor (VDR). PTEN is frequently lost or mutated in melanoma. Incubation of selected melanoma cell lines with 1,25D resulted in significant increases in PTEN levels and downregulation of the AKT pathway and its downstream effectors. This suggests that 1,25D may act to reduce melanoma cell viability by targeting PTEN.

Vitamin D as therapeutic modulator in cerebrovascular diseases: a mechanistic perspectives

Vitamin D deficiency has been linked to several major chronic diseases, such as cardiovascular and neurodegenerative diseases, diabetes, and cancer, linked to oxidative stress, inflammation, and aging. Vitamin D deficiency appears to be particularly harmful to the cardiovascular system, as it can cause endothelial dysfunctioning and vascular abnormalities through the modulation of various downstream mechanisms. As a result, new research indicates that therapeutic approaches targeting vitamin D inadequacies or its significant downstream effects, such as impaired autophagy, abnormal pro-inflammatory and pro-oxidant reactions, may delay the onset and severity of major cerebrovascular disorders such as stroke and neurologic malformations. Vitamin D modulates the various molecular pathways, i.e., Nitric Oxide, PI3K-Akt Pathway, cAMP pathway, NF-kB Pathway, Sirtuin 1, Nrf2, FOXO, in cerebrovascular disorder. The current review shows evidence for vitamin D's mitigating or slowing the progression of these cerebrovascular disorders, which are significant causes of disability and death worldwide.

The Role of Vitamin D in COVID-19 and the Impact of Pandemic Restrictions on Vitamin D Blood Content

Vitamin D is a hormone regulating the immune system and playing a pivotal role in responses to microbial infections. It regulates inflammatory processes by influencing the transcription of immune-response genes in macrophages, T cells, and dendritic cells. The proven role of vitamin D in many infectious diseases of the respiratory tract indicated that vitamin D should also play a role in SARS-CoV-2 infection. Vitamin D inhibits cytokine storm by switching the pro-inflammatory Th1 and Th17 to the anti-inflammatory Th2 and Treg response. Vitamin D is therefore expected to play a role in preventing, relieving symptoms, or treating SARS-CoV-2 infection symptoms, including severe pneumonia. There are several possible mechanisms by which vitamin D may reduce the risk of COVID-19 infection, such as induction of the transcription of cathelicidin and defensin. Also a nongenomic antiviral action of vitamin D and lumisterol, the molecule closely related to vitamin D, was reported. Despite this enormous progress, currently, there is still insufficient scientific evidence to support the claim that vitamin D supplementation may help treat COVID-19 infection. The pandemic restrictions were also shown to impact vitamin D uptake by limiting exposure to sunlight.

rs7041 and rs4588 Polymorphisms in Vitamin D Binding Protein Gene (VDBP) and the Risk of Diseases

The purpose of the study was to investigate the role of vitamin D binding protein (VDBP, DBP) and its polymorphism in the vitamin D pathway and human health. This narrative review shows the latest literature on the most popular diseases that have previously been linked to VDBP. Vitamin D plays a crucial role in human metabolism, controlling phosphorus and calcium homeostasis. Vitamin D binding protein bonds vitamin D and its metabolites and transports them to target tissues. The most common polymorphisms in the VDBP gene are rs4588 and rs7041, which are located in exon 11 in domain III of the VDBP gene. rs4588 and rs7041 may be correlated with differences not only in vitamin D status in serum but also with vitamin D metabolites. This review supports the role of single nucleotide polymorphisms (SNPs) in the VDBP gene and presents the latest data showing correlations between VDBP variants with important human diseases such as obesity, diabetes mellitus, tuberculosis, chronic obstructive pulmonary disease, and others. In this review, we aim to systematize the knowledge regarding the occurrence of diseases and their relationship with vitamin D deficiencies, which may be caused by polymorphisms in the VDBP gene. Further research is required on the possible influence of SNPs, modifications in the structure of the binding protein, and their influence on the organism. It is also important to mention that most studies do not have a specific time of year to measure accurate vitamin D metabolite levels, which can be misleading in conclusions due to the seasonal nature of vitamin D.

Modulation by 17,20S(OH)2pD of Fibrosis-Related Mediators in Dermal Fibroblast Lines from Healthy Donors and from Patients with Systemic Sclerosis

We previously demonstrated that the non-calcemic pregnacalciferol (pD) analog 17,20S (OH)₂pD suppressed TGF-β1-induced type I collagen production in cultured normal human dermal fibroblasts. In the present studies, we examined fibroblasts cultured from the lesional skin of patients with systemic sclerosis (scleroderma (SSc)) and assessed the effects of 17,20S(OH)₂pD on fibrosis-related mediators. Dermal fibroblast lines were established from skin biopsies from patients with SSc and healthy controls. Fibroblasts were cultured with either 17,20S(OH)₂pD or 1,25(OH)₂D₃ (positive control) with/without TGF-β1 stimulation and extracted for protein and/or mRNA for collagen synthesis and mediators of fibrosis (MMP-1, TIMP-1, PAI-1, BMP-7, PGES, GLI1, and GLI2). 1 7,20S(OH)₂pD (similar to 1,25(OH)₂D₃) significantly suppressed net total collagen production in TGF-β1-stimulated normal donor fibroblast cultures and in cultures of SSc dermal fibroblasts. 17,20S(OH)₂pD (similar to 1,25(OH)₂D₃) also increased MMP-1, BMP-7, and PGES and decreased TIMP-1 and PAI1 expression in SSc fibroblasts. Although 17,20S(OH)₂pD had no effect on Gli1 or Gli2 in SSc fibroblasts, it increased Gli2 expression when cultured with TGF-β1 in normal fibroblasts. These studies demonstrated that 17,20S(OH)₂pD modulates mediators of fibrosis to favor the reduction of fibrosis and may offer new noncalcemic secosteroidal therapeutic approaches for treating SSc and fibrosis.

Evidence for Involvement of Nonclassical Pathways in the Protection From UV-Induced DNA Damage by Vitamin D-Related Compounds

The vitamin D hormone, 1,25dihydroxyvitamin D₃ (1,25(OH)₂D₃), and related compounds derived from vitamin D₃ or lumisterol as a result of metabolism via the enzyme CYP11A1, have been shown, when applied 24 hours before or immediately after UV irradiation, to protect human skin cells and skin from DNA damage due to UV exposure, by reducing both cyclobutane pyrimidine dimers (CPD) and oxidative damage in the form of 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine (8‐OHdG). We now report that knockdown of either the vitamin D receptor or the endoplasmic reticulum protein ERp57 by small, interfering RNA (siRNA) abolished the reductions in UV‐induced DNA damage with 20‐hydroxyvitamin D₃ or 24‐hydroxylumisterol_3, as previously shown for 1,25(OH)₂D₃. Treatment with 1,25(OH)₂D₃ reduced oxygen consumption rates in UV‐exposed and sham‐exposed human keratinocytes and reduced phosphorylation of cyclic AMP response binding element protein (CREB). Both these actions have been shown to inhibit skin carcinogenesis after chronic UV exposure, consistent with the anticarcinogenic activity of 1,25(OH)₂D₃. The requirement for a vitamin D receptor for the photoprotective actions of 1,25(OH)₂D₃ and of naturally occurring CYP11A1‐derived vitamin D–related compounds may explain why mice lacking the vitamin D receptor in skin are more susceptible to UV‐induced skin cancers, whereas mice lacking the 1α‐hydroxylase and thus unable to make 1,25(OH)₂D₃ are not more susceptible. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

1,25-Dihydroxyvitamin D3 and 20-Hydroxyvitamin D3 Upregulate LAIR-1 and Attenuate Collagen Induced Arthritis

Vitamin D plays a crucial role in regulation of the immune response. However, treatment of autoimmune diseases with 1,25-dihydroxyvitamin D3 [1,25(OH)₂D3] doses sufficient to be effective is prohibitive due to its calcemic and toxic effects. We use the collagen-induced arthritis (CIA) model to analyze the efficacy of the noncalcemic analog of vitamin D, 20S-hydroxyvitamin D3 [20S(OH)D3], as well as 1,25(OH)₂D3, to attenuate arthritis and explore a potential mechanism of action. Mice fed a diet deficient in vitamin D developed a more severe arthritis characterized by enhanced secretion of T cell inflammatory cytokines, compared to mice fed a normal diet. The T cell inflammatory cytokines were effectively suppressed, however, by culture of the cells with 20S(OH)D3. Interestingly, one of the consequences of culture with 1,25(OH)₂D3 or 20S(OH)D3, was upregulation of the natural inhibitory receptor leukocyte associated immunoglobulin-like receptor-1 (LAIR-1 or CD305). Polyclonal antibodies which activate LAIR-1 were also capable of attenuating arthritis. Moreover, oral therapy with active forms of vitamin D suppressed arthritis in LAIR-1 sufficient DR1 mice, but were ineffective in LAIR-1^−/− deficient mice. Taken together, these data show that the effect of vitamin D on inflammation is at least, in part, mediated by LAIR-1 and that non-calcemic 20S(OH)D3 may be a promising therapeutic agent for the treatment of autoimmune diseases such as Rheumatoid Arthritis.

Identification of the RORα Transcriptional Network Contributes to the Search for Therapeutic Targets in Atherosclerosis

The retinoic acid receptor-related orphan receptor α (RORα) is involved in the regulation of several physiological processes, including development, metabolism, and circadian rhythm. RORα-deficient mice display profound atherosclerosis, in which hypoalphalipoproteinemia is reportedly associated with decreased plasma levels of high-density lipoprotein, increased levels of inflammatory cytokines, and ischemia/reperfusion-induced damage. The recent characterization of endogenous ligands (including cholesterol, oxysterols, provitamin D₃, and their derivatives), mediators, and initiation complexes associated with the transcriptional regulation of these orphan nuclear receptors has facilitated the development of synthetic ligands. These findings have also highlighted the potential of application of RORα as a therapeutic target for several diseases, including diabetes, dyslipidemia, and atherosclerosis. In this review, the current literature related to the structure and function of RORα, its genetic inter-individual differences, and its potential as a therapeutic target in atherosclerosis is discussed.

Relevance of vitamin D3 in COVID-19 infection

SARS-CoV-2 virus, the main culprit for COVID-19 disaster, has triggered a gust of curiosity both in the mechanism of action of this infection as well as potential risk factors for disease generation and regimentation. The prime focus of the present review, which is basically a narrative one, is in utilizing the current concepts of vitamin D3 as an agent with myriad functions, one of them being immunocompetence and a promising weapon for both innate and adaptive immunity against COVID-19 infection. Some of the manifestations of SARS-CoV-2 virus such as Acute Respiratory Distress Syndrome (ARDS) overlap with the pathophysiological effects that are overcome due to already established role of vitamin D3 e.g., amelioration of cytokine outburst. Additionally, the cardiovascular complications due to COVID-19 infection may also be connected to vitamin D3 levels and the activity of its active forms. Eventually, we summarise the clinical, observational and epidemiological data of the respiratory diseases including COVID-19 disease and try to bring its association with the potential role of vitamin D3, in particular, the activity of its active forms, circulating levels and its supplementation, against dissemination of this disease.

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.

Impacts of deficiency in vitamin D derivatives on disease severity in adult bronchial asthma patients

Vitamin D affects innate and adaptive immunity processes that impact treatment, severity, and morbidity of acute asthma episodes. Several vitamin D forms may help modulate immunity, including vitamin D2 (D2), vitamin D3 (D3), 25-hydroxyvitamin D3 (25(OH)D3), and 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). This study assessed serum levels of vitamin D derivatives in bronchial asthma patients and their correlation with disease markers. One hundred thirteen subjects, divided into two groups, were enrolled. The first group included 73 asthmatic patients (57 males and 16 females), and the second included 40 healthy adults (31 males and 9 females) as a control group. All subjects were evaluated with a careful history and clinical examination, a chest X-ray with a posteroanterior view, routine laboratory examination, spirometry, and asthma control tests (ACT). Vitamin D serum levels were assessed using ultra-performance liquid chromatography (UPLC) with tandem mass spectrometry. Disease markers were assessed and correlated with serum levels of vitamin D forms. Markers included forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC%, peak expiratory flow (PEF), forced expiratory flow25-75% (FEF_25-75%), eosinophilic blood count, and total immunoglobulin E (IgE). Asthmatic patients had significantly lower serum levels of vitamin D than healthy controls (p ≤ 0.001). Further, serum vitamin D levels decreased significantly in uncontrolled asthmatic patients than partially controlled and controlled patients. Correlations for 25(OH)D3 and 1,25-(OH) 2D3 were stronger than for D2 and D3. There were negative correlations for eosinophilic blood count, total IgE, and ACT. Serum levels of all vitamin D forms were reduced in asthmatic patients with moderate to strong correlations with disease severity. Vitamin D deficiency or even insufficiency may thus play a role in disease severity.

Vitamin D3 and its hydroxyderivatives as promising drugs against COVID-19: a computational study

The epidemiologic correlation between the poor prognosis of SARS-CoV-2 infection and vitamin D deficiency has been observed worldwide, however, their molecular mechanisms are not fully understood. In this study, we used combined molecular docking, molecular dynamics simulations and binding free energy analyses to investigate the potentials of vitamin D3 and its hydroxyderivatives as TMPRSS2 inhibitor and to inhibit the SARS-CoV-2 receptor binding domain (RBD) binding to angiotensin-converting enzyme 2 (ACE2), as well as to unveil molecular and structural basis of 1,25(OH)2D3 capability to inhibit ACE2 and SARS-CoV-2 RBD interactions. The results show that vitamin D3 and its hydroxyderivatives are favorable to bind active site of TMPRSS2 and the binding site(s) between ACE2 and SARS-CoV2-RBD, which indicate that vitamin D3 and its biologically active hydroxyderivatives can serve as TMPRSS2 inhibitor and can inhibit ACE2 binding of SARS-CoV-2 RBD to prevent SARS-CoV-2 entry. Interaction of 1,25(OH)2D3 with SARS-CoV-2 RBD and ACE2 resulted in the conformation and dynamical motion changes of the binding surfaces between SARS-CoV-2 RBD and ACE2 to interrupt the binding of SARS-CoV-2 RBD with ACE2. The interaction of 1,25(OH)2D3 with TMPRSS2 also caused the conformational and dynamical motion changes of TMPRSS2, which could affect TMPRSS2 to prime SARS-CoV-2 spike proteins. Our results propose that vitamin D3 and its biologically active hydroxyderivatives are promising drugs or adjuvants in the treatment of COVID-19. Communicated by Ramaswamy H. Sarma.

20S-Hydroxyvitamin D3, a Secosteroid Produced in Humans, Is Anti-Inflammatory and Inhibits Murine Autoimmune Arthritis

The ability to use large doses of vitamin D3 (D3) to chronically treat autoimmune diseases such as rheumatoid arthritis (RA) is prohibitive due to its calcemic effect which can damage vital organs. Cytochrome P450scc (CYP11A1) is able to convert D3 into the noncalcemic analog 20S-hydroxyvitamin D3 [20S(OH)D3]. We demonstrate that 20S(OH)D3 markedly suppresses clinical signs of arthritis and joint damage in a mouse model of RA. Furthermore, treatment with 20S(OH)D3 reduces lymphocyte subsets such as CD4+ T cells and CD19+ B cells leading to a significant reduction in inflammatory cytokines. The ratio of T reg cells (CD4+CD25+Foxp3+ T cells) to CD3+CD4+ T cells is increased while there is a decrease in critical complement-fixing anti-CII antibodies. Since pro-inflammatory cytokines and antibodies against type II collagen ordinarily lead to destruction of cartilage and bone, their decline explains why arthritis is attenuated by 20(OH) D3. These results provide a basis for further consideration of 20S(OH)D3 as a potential treatment for RA and other autoimmune disorders.

Is Vitamin D Deficiency Related to Increased Cancer Risk in Patients with Type 2 Diabetes Mellitus?

There is mounting evidence that type 2 diabetes mellitus (T2DM) is related with increased risk for the development of cancer. Apart from shared common risk factors typical for both diseases, diabetes driven factors including hyperinsulinemia, insulin resistance, hyperglycemia and low grade chronic inflammation are of great importance. Recently, vitamin D deficiency was reported to be associated with the pathogenesis of numerous diseases, including T2DM and cancer. However, little is known whether vitamin D deficiency may be responsible for elevated cancer risk development in T2DM patients. Therefore, the aim of the current review is to identify the molecular mechanisms by which vitamin D deficiency may contribute to cancer development in T2DM patients. Vitamin D via alleviation of insulin resistance, hyperglycemia, oxidative stress and inflammation reduces diabetes driven cancer risk factors. Moreover, vitamin D strengthens the DNA repair process, and regulates apoptosis and autophagy of cancer cells as well as signaling pathways involved in tumorigenesis i.e., tumor growth factor β (TGFβ), insulin-like growth factor (IGF) and Wnt-β-Cathenin. It should also be underlined that many types of cancer cells present alterations in vitamin D metabolism and action as a result of Vitamin D Receptor (VDR) and CYP27B1 expression dysregulation. Although, numerous studies revealed that adequate vitamin D concentration prevents or delays T2DM and cancer development, little is known how the vitamin affects cancer risk among T2DM patients. There is a pressing need for randomized clinical trials to clarify whether vitamin D deficiency may be a factor responsible for increased risk of cancer in T2DM patients, and whether the use of the vitamin by patients with diabetes and cancer may improve cancer prognosis and metabolic control of diabetes.

The significance of CYP11A1 expression in skin physiology and pathology

CYP11A1, a member of the cytochrome P450 family, plays several key roles in the human body. It catalyzes the first and rate-limiting step in steroidogenesis, converting cholesterol to pregnenolone. Aside from the classical steroidogenic tissues such as the adrenals, gonads and placenta, CYP11A1 has also been found in the brain, gastrointestinal tract, immune systems, and finally the skin. CYP11A1 activity in the skin is regulated predominately by StAR protein and hence cholesterol levels in the mitochondria. However, UVB, UVC, CRH, ACTH, cAMP, and cytokines IL-1, IL-6 and TNFα can also regulate its expression and activity. Indeed, CYP11A1 plays several critical roles in the skin through its initiation of local steroidogenesis and specific metabolism of vitamin D, lumisterol, and 7-dehydrocholesterol. Products of these pathways regulate the protective barrier and skin immune functions in a context-dependent fashion through interactions with a number of receptors. Disturbances in CYP11A1 activity can lead to skin pathology.

Updates and new medical treatments for vitiligo (Review)

Vitiligo is a multifactorial disease characterized by the loss of skin pigment, which results in achromic macules and patches. There are currently several medical treatments available, which aim to arrest progression and induce skin repigmentation. These treatments alone or combined have exhibited varying degrees of pigmentation, and the majority are safe and effective. All therapies for vitiligo are limited, and no known treatment can consistently produce repigmentation in all patients. Individualized treatment is appropriate according to the location, clinical presentation and the presence of disease activity. The present review summarizes the medical treatments available for vitiligo: Systemic and topic pharmacological therapies, physical and depigmentation treatments. Several treatments are still underway and have not yet been approved. However, due to the promising preliminary results, these are also mentioned in the present review.

Simultaneous measurement of 13 circulating vitamin D3 and D2 mono and dihydroxy metabolites using liquid chromatography mass spectrometry

Objectives

Clinical evaluation of vitamin D status is conventionally performed by measuring serum levels of a single vitamin D metabolite, 25-hydroxyvitamin D predominantly by immunoassay methodology. However, this neglects the complex metabolic pathways involved in vitamin D bioactivity, including two canonical forms D3 and D2, bioactive 1,25-dihydroxy metabolites and inactive 24-hydroxy and other metabolites.

Methods

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) can measure multiple analytes in a sample during a single run with high sensitivity and reference level specificity. We therefore aimed to develop and validate a LC-MS/MS method to measure simultaneously 13 circulating vitamin D metabolites and apply it to 103 human serum samples.

Results

The LC-MS/MS method using a Cookson-type derivatization reagent phenyl-1,2,4-triazoline-3,5-dione (PTAD) quantifies 13 vitamin D metabolites, including mono and dihydroxy-metabolites, as well as CYP11A1-derived D3 and D2 metabolites in a single run. The lower limit of quantitation was 12.5 pg/mL for 1,25(OH)₂D3 with accuracy verified by analysis of National Institute of Standards and Technology (NIST) 972a standards. Quantification of seven metabolites (25(OH)D3, 25(OH)D2, 3-epi-25(OH)D3, 20(OH)D3, 24,25(OH)₂D3, 1,25(OH)₂D3 and 1,20S(OH)₂D3) was consistently achieved in human serum samples.

Conclusions

This profiling method can provide new insight into circulating vitamin D metabolite pathways forming the basis for improved understanding of the role of vitamin D in health and disease.

Identification of RORγ as a favorable biomarker for colon cancer

Objective

To evaluate the expression of retinoid-related orphan receptor gamma (RORγ) and its potential role in the prognosis of colon cancer.

Methods

The Cancer Genome Atlas and GSE117606 were used to evaluate to RORγ levels in colon cancer, and real-time quantitative polymerase chain reaction was applied for validation. UALCAN and MEXPRESS were used to analyze the associations of RORγ expression with clinical parameters. The survival analysis was conducted in GEPIA.

Results

RORγ expression was significantly lower in colon tumors than in adjacent normal mucosa tissues. RORγ expression was significantly associated with tumor stage, lymph node metastasis, and liver metastasis. The area under the curve for diagnosis was 0.71. Decreased RORγ expression was positively correlated with the incidence of lymphatic invasion, microsatellite instability, the presence of residual tumor, venous invasion, and copy number variation. Overall survival was longer in patients with higher RORγ expression, especially those with microsatellite instability-high features. Methylation analysis revealed that hypermethylation of the RORγ promoter was associated with the colon cancer stage.

Conclusions

RORγ downregulation could be a potential biomarker for colon cancer, especially for predicting prognosis. Decreased RORγ expression in colon tumor may be associated with promoter hypermethylation.

Vitamin D and lumisterol derivatives can act on liver X receptors (LXRs)

The interactions of derivatives of lumisterol (L3) and vitamin D3 (D3) with liver X receptors (LXRs) were investigated. Molecular docking using crystal structures of the ligand binding domains (LBDs) of LXRα and β revealed high docking scores for L3 and D3 hydroxymetabolites, similar to those of the natural ligands, predicting good binding to the receptor. RNA sequencing of murine dermal fibroblasts stimulated with D3-hydroxyderivatives revealed LXR as the second nuclear receptor pathway for several D3-hydroxyderivatives, including 1,25(OH)2D3. This was validated by their induction of genes downstream of LXR. L3 and D3-derivatives activated an LXR-response element (LXRE)-driven reporter in CHO cells and human keratinocytes, and by enhanced expression of LXR target genes. L3 and D3 derivatives showed high affinity binding to the LBD of the LXRα and β in LanthaScreen TR-FRET LXRα and β coactivator assays. The majority of metabolites functioned as LXRα/β agonists; however, 1,20,25(OH)3D3, 1,25(OH)2D3, 1,20(OH)2D3 and 25(OH)D3 acted as inverse agonists of LXRα, but as agonists of LXRβ. Molecular dynamics simulations for the selected compounds, including 1,25(OH)2D3, 1,20(OH)2D3, 25(OH)D3, 20(OH)D3, 20(OH)L3 and 20,22(OH)2L3, showed different but overlapping interactions with LXRs. Identification of D3 and L3 derivatives as ligands for LXRs suggests a new mechanism of action for these compounds.