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 ß, 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 .

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.

Vitamin D and lumisterol novel metabolites can inhibit SARS-CoV-2 replication machinery enzymes.

Vitamin D deficiency significantly correlates with the severity of SARS-CoV-2 infection. Molecular docking-based virtual screening studies predict that novel vitamin D and related lumisterol hydroxymetabolites are able to bind to the active sites of two SARS-CoV-2 transcription machinery enzymes with high affinity. These enzymes are the main protease (Mpro) and RNA-dependent RNA polymerase (RdRP), which play important roles in viral replication and establishing infection. Based on predicted binding affinities and specific interactions, we identified 10 vitamin D3 (D3) and lumisterol (L3) analogs as likely binding partners of SARS-CoV-2 Mpro and RdRP and, therefore, tested their ability to inhibit these enzymes. Activity measurements demonstrated that 25(OH)L3, 24(OH)L3, and 20(OH)7DHC are the most effective of the hydroxymetabolites tested at inhibiting the activity of SARS-CoV-2 Mpro causing 10%-19% inhibition. These same derivatives as well as other hydroxylumisterols and hydroxyvitamin D3 metabolites inhibited RdRP by 50%-60%. Thus, inhibition of these enzymes by vitamin D and lumisterol metabolites may provide a novel approach to hindering the SARS-CoV-2 infection.NEW & NOTEWORTHY Active forms of vitamin D and lumisterol can inhibit SARS-CoV-2 replication machinery enzymes, which indicates that novel vitamin D and lumisterol metabolites are candidates for antiviral drug research.

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.

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.

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-ß1-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-ß1 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-ß1-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-ß1 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.

Extra-adrenal glucocorticoid biosynthesis: implications for autoimmune and inflammatory disorders.

Glucocorticoid synthesis is a complex, multistep process that starts with cholesterol being delivered to the inner membrane of mitochondria by StAR and StAR-related proteins. Here its side chain is cleaved by CYP11A1 producing pregnenolone. Pregnenolone is converted to cortisol by the enzymes 3-ßHSD, CYP17A1, CYP21A2, and CYP11B1. Glucocorticoids play a critical role in the regulation of the immune system and exert their action through the glucocorticoid receptor (GR). Although corticosteroids are primarily produced in the adrenal gland, they can also be produced in a number of extra-adrenal tissue including the immune system, skin, brain, and intestine. Glucocorticoid production is regulated by ACTH, CRH, and cytokines such as IL-1, IL-6, and TNFα. The bioavailability of cortisol is also dependent on its interconversion to cortisone, which is inactive, by 11ßHSD1/2. Local and systemic glucocorticoid biosynthesis can be stimulated by ultraviolet B, explaining its immunosuppressive activity. In this review, we want to emphasize that dysregulation of extra-adrenal glucocorticoid production can play a key role in a variety of autoimmune diseases including multiple sclerosis (MS), lupus erythematosus (LE), rheumatoid arthritis (RA), and skin inflammatory disorders such as psoriasis and atopic dermatitis (AD). Further research on local glucocorticoid production and its bioavailability may open doors into new therapies for autoimmune diseases.

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.

Hydroxylumisterols, Photoproducts of Pre-Vitamin D3, Protect Human Keratinocytes against UVB-Induced Damage.

Lumisterol (L3) is a stereoisomer of 7-dehydrocholesterol and is produced through the photochemical transformation of 7-dehydrocholesteol induced by high doses of UVB. L3 is enzymatically hydroxylated by CYP11A1, producing 20(OH)L3, 22(OH)L3, 20,22(OH)2L3, and 24(OH)L3. Hydroxylumisterols function as reverse agonists of the retinoic acid-related orphan receptors α and γ (RORα/γ) and can interact with the non-genomic binding site of the vitamin D receptor (VDR). These intracellular receptors are mediators of photoprotection and anti-inflammatory activity. In this study, we show that L3-hydroxyderivatives significantly increase the expression of VDR at the mRNA and protein levels in keratinocytes, both non-irradiated and after UVB irradiation. L3-hydroxyderivatives also altered mRNA and protein levels for RORα/γ in non-irradiated cells, while the expression was significantly decreased in UVB-irradiated cells. In UVB-irradiated keratinocytes, L3-hydroxyderivatives inhibited nuclear translocation of NFκB p65 by enhancing levels of IκBα in the cytosol. This anti-inflammatory activity mediated by L3-hydroxyderivatives through suppression of NFκB signaling resulted in the inhibition of the expression of UVB-induced inflammatory cytokines, including IL-17, IFN-γ, and TNF-α. The L3-hydroxyderivatives promoted differentiation of UVB-irradiated keratinocytes as determined from upregulation of the expression at the mRNA of involucrin (IVL), filaggrine (FLG), and keratin 14 (KRT14), downregulation of transglutaminase 1 (TGM1), keratins including KRT1, and KRT10, and stimulation of ILV expression at the protein level. We conclude that CYP11A1-derived hydroxylumisterols are promising photoprotective agents capable of suppressing UVB-induced inflammatory responses and restoring epidermal function through targeting the VDR and RORs.

Detection of 7-Dehydrocholesterol and Vitamin D3 Derivatives in Honey.

20(S)-Hydroxyvitamin D3 (20(OH)D3) is an endogenous metabolite produced by the action of CYP11A1 on the side chain of vitamin D3 (D3). 20(OH)D3 can be further hydroxylated by CYP11A1, CYP27A1, CYP24A1 and/or CYP27B1 to several hydroxyderivatives. CYP11A1 also hydroxylates D3 to 22-monohydroxyvitamin D3 (22(OH)D3), which is detectable in the epidermis. 20-Hydroxy-7-dehydrocholesterol (20(OH)-7DHC) has been detected in the human epidermis and can be phototransformed into 20(OH)D3 following the absorption of ultraviolet B (UVB) energy by the B-ring. 20(OH)D3 and its hydroxyderivatives have anti-inflammatory, pro-differentiation and anti-proliferative effects, comparable to 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Since cytochromes P450 with 20- or 25-hydroxylase activity are found in insects participating in ecdysone synthesis from 7-dehydrocholesterol (7DHC), we tested whether D3-hydroxyderivatives are present in honey, implying their production in bees. Honey was collected during summer in the Birmingham area of Alabama or purchased commercially and extracted and analyzed using LC-MS. We detected a clear peak of m/z = 423.324 [M + Na]+ for 20(OH)D3 corresponding to a concentration in honey of 256 ng/g. We also detected peaks of m/z = 383.331 [M + H - H2O]+ for 20(OH)-7DHC and 25(OH)D3 with retention times corresponding to the standards. We further detected species with m/z = 407.329 [M + Na]+ corresponding to the RT of 7DHC, D3 and lumisterol3 (L3). Similarly, peaks with m/z = 399.326 [M + H - H2O]+ were detected at the RT of 1,25(OH)2D3 and 1,20-dihydroxyvitamin D3 (1,20(OH)2D3). Species corresponding to 20-monohydroxylumisterol3 (20(OH)L3), 22-monohydroxyvitamin D3 (22(OH)D3), 20,23-dihydroxyvitamin D3 (20,23(OH)2D3), 20,24/25/26-dihydroxyvitamin D3 (20,24/25/26(OH)2D3) and 1,20,23/24/25/26-trihydroxyvitamin D3 (1,20,23/24/25/26(OH)3D3) were not detectable above the background. In conclusion, the presence of 7DHC and D3 and of species corresponding to 20(OH)-7DHC, 20(OH)D3, 1,20(OH)2D3, 25(OH)D3 and 1,25(OH)2D3 in honey implies their production in bees, although the precise biochemistry and photochemistry of these processes remain to be defined.

Catalytic properties of 25-hydroxyvitamin D3 3-epimerase in rat and human liver microsomes.

25-Hydroxyvitamin D3 3-epimerase catalyzes the 3ß â†’ 3α epimerization of 25-hydroxyvitamin D3 (25(OH)D3) producing 3-epi-25-hydroxyvitamin D3 (3-epi-25(OH)D3). 3-Epi-25(OH)D3 is one of the most abundant forms of vitamin D present in the serum. It can be converted to 3-epi-1α,25-dihydroxyvitamin D3 by CYP27B1 which generally displays lower biological activity than 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3). The 25(OH)D3 3-epimerase has been poorly characterized to date and the gene encoding it has not been identified. The 3-epimerase has been reported to be present in the microsomal fraction of cells, including liver cells, and to use NADPH as cofactor. It can also act on 1,25(OH)2D3 and 24,25(OH)2D3 forming the 3α-epimers. In this study we have characterized the activity of the 25(OH)D3 3-epimerase in rat and human liver microsomes, using 25(OH)D3 as substrate and HPLC to analyze product formation. For both rat and human liver microsomes the preferred cofactor was NADH, with the rat enzyme displaying a 6-fold greater catalytic efficiency (Vmax/Km) for NADH over that for NADPH. No activity was observed with oxidized cofactor, either NAD+ or NADP+. This was unexpected since the initial step in the epimerization, predicted to be the oxidation of the 3ß-OH to a ketone, would require oxidized cofactor. The rat 3-epimerase in microsomes gave a Km for 25(OH)D3 of 14 µM. The reverse reaction, conversion of 3-epi-25(OH)D3 to 25(OH)D3, was catalyzed by both rat and human liver microsomes but at lower rates than the forward reaction. In conclusion, both rat and human 25-hydroxyvitamin D3 3-epimerase catalyze the reversible interconversion of 25(OH)D3 and 3-epi-25(OH)D3, and use NADH as the preferred cofactor. The lack of requirement for exogenous NAD+ suggests that the enzyme has a tightly bound NAD+ in its active site that is released only upon its reduction.

Differential and Overlapping Effects of 20,23(OH)2D3 and 1,25(OH)2D3 on Gene Expression in Human Epidermal Keratinocytes: Identification of AhR as an Alternative Receptor for 20,23(OH)2D3.

A novel pathway of vitamin D activation by CYP11A has previously been elucidated. To define the mechanism of action of its major dihydroxy-products, we tested the divergence and overlap between the gene expression profiles of human epidermal keratinocytes treated with either CYP11A1-derived 20,23(OH)2D3 or classical 1,25(OH)2D3. Both secosteroids have significant chemical similarity with the only differences being the positions of the hydroxyl groups. mRNA was isolated and examined by microarray analysis using Illumina's HumanWG-6 chip/arrays and subsequent bioinformatics analyses. Marked differences in the up- and downregulated genes were observed between 1,25(OH)2D3- and 20,23(OH)2D3-treated cells. Hierarchical clustering identified both distinct, opposite and common (overlapping) gene expression patterns. CYP24A1 was a common gene strongly activated by both compounds, a finding confirmed by qPCR. Ingenuity pathway analysis identified VDR/RXR signaling as the top canonical pathway induced by 1,25(OH)2D3. In contrast, the top canonical pathway induced by 20,23(OH)2D3 was AhR, with VDR/RXR being the second nuclear receptor signaling pathway identified. QPCR analyses validated the former finding by revealing that 20,23(OH)2D3 stimulated CYP1A1 and CYP1B1 gene expression, effects located downstream of AhR. Similar stimulation was observed with 20(OH)D3, the precursor to 20,23(OH)2D3, as well as with its downstream metabolite, 17,20,23(OH)3D3. Using a Human AhR Reporter Assay System we showed marked activation of AhR activity by 20,23(OH)2D3, with weaker stimulation by 20(OH)D3. Finally, molecular modeling using an AhR LBD model predicted vitamin D3 hydroxyderivatives to be good ligands for this receptor. Thus, our microarray, qPCR, functional studies and molecular modeling indicate that AhR is the major receptor target for 20,23(OH)2D3, opening an exciting area of investigation on the interaction of different vitamin D3-hydroxyderivatives with AhR and the subsequent downstream activation of signal transduction pathways in a cell-type-dependent manner.

Active Site Structures of CYP11A1 in the Presence of Its Physiological Substrates and Alterations upon Binding of Adrenodoxin.

The rate-limiting step in the steroid synthesis pathway is catalyzed by CYP11A1 through three sequential reactions. The first two steps involve hydroxylations at positions 22 and 20, generating 20(R),22(R)-dihydroxycholesterol (20R,22R-DiOHCH), with the third stage leading to a C20-C22 bond cleavage, forming pregnenolone. This work provides detailed information about the active site structure of CYP11A1 in the resting state and substrate-bound ferric forms as well as the CO-ligated adducts. In addition, high-quality resonance Raman spectra are reported for the dioxygen complexes, providing new insight into the status of Fe-O-O fragments encountered during the enzymatic cycle. Results show that the three natural substrates of CYP11A1 have quite different effects on the active site structure, including variations of spin state populations, reorientations of heme peripheral groups, and, most importantly, substrate-mediated distortions of Fe-CO and Fe-O2 fragments, as revealed by telltale shifts of the observed vibrational modes. Specifically, the vibrational mode patterns observed for the Fe-O-O fragments with the first and third substrates are consistent with H-bonding interactions with the terminal oxygen, a structural feature that tends to promote O-O bond cleavage to form the Compound I intermediate. Furthermore, such spectral data are acquired for complexes with the natural redox partner, adrenodoxin (Adx), revealing protein-protein-induced active site structural perturbations. While this work shows that Adx has an only weak effect on ferric and ferrous CO states, it has a relatively stronger impact on the Fe-O-O fragments of the functionally relevant oxy complexes.

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

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

RORα and ROR γ are expressed in human skin and serve as receptors for endogenously produced noncalcemic 20-hydroxy- and 20,23-dihydroxyvitamin D.

RORα and RORγ are expressed in human skin cells that produce the noncalcemic 20-hydroxyvitamin D3 [20(OH)D3] and 20,23-dihydroxyvitamin D3 [20,23(OH)2D3]. Chinese hamster ovary (CHO) cells stably expressing a Tet-on RORα or RORγ expression vector and a ROR-responsive element (RORE)-LUC reporter, and a mammalian 2-hybrid model examining the interaction between the ligand binding domain (LBD) of RORα or RORγ with an LBD-interacting LXXLL-peptide, were used to study ROR-antagonist activities. These assays revealed that 20(OH)D3 and 20,23(OH)2D3 function as antagonists of RORα and RORγ. Moreover, 20(OH)D3 inhibited the activation of the promoter of the Bmal1 and G6pase genes, targets of RORα, and 20(OH)D3 and 20,23(OH)2D3 inhibited Il17 promoter activity in Jurkat cells overexpressing RORα or RORγ. Molecular modeling using crystal structures of the LBDs of RORα and RORγ revealed docking scores for 20(OH)D3, 20,23(OH)2D3 and 1,25(OH)2D3 similar to those of the natural ligands, predicting good binding to the receptor. Notably, 20(OH)D3, 20,23(OH)2D3, and 1,25(OH)2D3 inhibited RORE-mediated activation of a reporter in keratinocytes and melanoma cells and inhibited IL-17 production by immune cells. Our study identifies a novel signaling pathway, in which 20(OH)D3 and 20,23(OH)2D3 act as antagonists or inverse agonists of RORα and RORγ, that opens new possibilities for local (skin) or systemic regulation.-Slominski, A. T., Kim, T.-K., Takeda, Y., Janjetovic, Z., Broz˙yna, A. A., Skobowiat, C., Wang, J., Postlethwaite, A., Li, W., Tuckey, R. C., Jetten, A. M. RORα and ROR γ are expressed in human skin and serve as receptors for endogenously produced noncalcemic 20-hydroxy- and 20,23-dihydroxyvitamin D.

Antitumor effects of vitamin D analogs on hamster and mouse melanoma cell lines in relation to melanin pigmentation.

Deregulated melanogenesis is involved in melanomagenesis and melanoma progression and resistance to therapy. Vitamin D analogs have anti-melanoma activity. While the hypercalcaemic effect of the active form of Vitamin D (1,25(OH)2D3) limits its therapeutic use, novel Vitamin D analogs with a modified side chain demonstrate low calcaemic activity. We therefore examined the effect of secosteroidal analogs, both classic (1,25(OH)2D3 and 25(OH)D3), and novel relatively non-calcemic ones (20(OH)D3, calcipotriol, 21(OH)pD, pD and 20(OH)pL), on proliferation, colony formation in monolayer and soft-agar, and mRNA and protein expression by melanoma cells. Murine B16-F10 and hamster Bomirski Ab cell lines were shown to be effective models to study how melanogenesis affects anti-melanoma treatment. Novel Vitamin D analogs with a short side-chain and lumisterol-like 20(OH)pL efficiently inhibited rodent melanoma growth. Moderate pigmentation sensitized rodent melanoma cells towards Vitamin D analogs, and altered expression of key genes involved in Vitamin D signaling, which was opposite to the effect on heavily pigmented cells. Interestingly, melanogenesis inhibited ligand-induced Vitamin D receptor translocation and ligand-induced expression of VDR and CYP24A1 genes. These findings indicate that melanogenesis can affect the anti-melanoma activity of Vitamin D analogs in a complex manner.

Cutaneous glucocorticosteroidogenesis: securing local homeostasis and the skin integrity.

Human skin has the ability to synthesize glucocorticoids de novo from cholesterol or from steroid intermediates of systemic origin. By interacting with glucocorticoid receptors, they regulate skin immune functions as well as functions and phenotype of the epidermal, dermal and adnexal compartments. Most of the biochemical (enzyme and transporter activities) and regulatory (neuropeptides mediated activation of cAMP and protein kinase A dependent pathways) principles of steroidogenesis in the skin are similar to those operating in classical steroidogenic organs. However, there are also significant differences determined by the close proximity of synthesis and action (even within the same cells) allowing para-, auto- or intracrine modes of regulation. We also propose that ultraviolet light B (UVB) can regulate the availability of 7-dehydrocholesterol for transformation to cholesterol with its further metabolism to steroids, oxysterols or ∆7 steroids, because of its transformation to vitamin D3. In addition, UVB can rearrange locally produced ∆7 steroids to the corresponding secosteroids with a short- or no-side chain. Thus, different mechanisms of regulation occur in the skin that can be either stochastic or structuralized. We propose that local glucocorticosteroidogenic systems and their regulators, in concert with cognate receptors operate to stabilize skin homeostasis and prevent or attenuate skin pathology.

CYP24A1 expression inversely correlates with melanoma progression: clinic-pathological studies.

The major role of 24-hydroxylase (CYP24A1) is to maintain 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) homeostasis. Recently, it has been discovered that CYP24A1 also catalyses the hydroxylation of 20(OH)D3, producing dihydroxy-derivatives that show very effective antitumorigenic activities. Previously we showed a negative correlation of vitamin D receptor (VDR) and CYP27B1 expression with progression, aggressiveness and overall or disease-free survivals of skin melanomas. Therefore, we analyzed CYP24A1 expression in relation to clinicopathomorphological features of nevi, skin melanomas and metastases. In melanocytic tumors, the level of CYP24A1 was higher than in the normal epidermis. The statistically highest mean CYP24A1 level was found in nevi and early stage melanomas. With melanoma progression, CYP24A1 levels decreased and in advanced stages were comparable to the normal epidermis and metastases. Furthermore, the CYP24A1 expression positively correlated with VDR and CYP27B1, and negatively correlated with mitotic activity. Lower CYP24A1 levels correlated with the presence of ulceration, necrosis, nodular type and amelanotic phenotypes. Moreover, a lack of detectable CYP24A1 expression was related to shorter overall and disease-free survival. In conclusion, the local vitamin D endocrine system affects melanoma behavior and an elevated level of CYP24A1 appears to have an important impact on the formation of melanocytic nevi and melanomagenesis, or progression, at early stages of tumor development.

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.

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.