20,23-dihydroxyvitamin D3, novel P450scc product, stimulates differentiation and inhibits proliferation and NF-kappaB activity in human keratinocytes

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.

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.

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 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 .

1,25(OH)2 D3 blocks IFNβ production through regulating STING in epithelial layer of oral lichen planus

Stimulator of interferon genes (STING) is reported to exert vital functions in inflammatory responses and autoimmune diseases. Nevertheless, the status and roles of STING in oral lichen planus (OLP) remain elusive. Here, we state that STING and its downstream cytokine interferon‐β (IFNβ) expression is boosted in the oral keratinocytes from patients suffering OLP in comparison with those from healthy participants. Mechanistically, transcription factor GATA‐binding protein 1 (GATA1) which is highly increased in diseased samples specifically interacts with its element in the promoter of STING to enhance STING transcripts. 1,25(OH)₂D₃, the active form of vitamin D, is capable of restricting STING and IFNβ increases in oral keratinocyte models resembling OLP in vitro. Moreover, there is a negative correlation between vitamin D receptor (VDR) and STING or IFNβ in human samples. Using plasmids and small interfering RNA transfection technologies, we find 1,25(OH)₂D₃ regulates STING and IFNβ through a mechanism controlled by the hypoxia‐inducible factor‐1α (HIF‐1α)‐GATA1 axis. Collectively, our findings unveil that 1,25(OH)₂D₃ lowers STING and IFNβ overexpression in the context of OLP.

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.

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.

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.

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.

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.

CYP11A1 Upregulation Leads to Trophoblast Oxidative Stress and Fetal Neurodevelopmental Toxicity That can be Rescued by Vitamin D

During normal pregnancy, the placental trophoblast secretes a variety of steroid hormones and participates in the regulation of maternal physiological functions and fetal development. The CYP11A1 gene encodes the cholesterol side-chain cleavage enzyme P450scc, which catalyzes the production of pregnenolone from cholesterol, which is the first step in the synthesis of all steroid hormones. Under the influence of genetic susceptibility and certain environmental factors, such as drugs and toxins, the expression of CYP11A1 can be upregulated, thereby affecting steroid metabolism and physiological functions in trophoblast cells, as well as fetal development. Here, we demonstrate that upregulation of CYP11A1 in the BeWo cell line triggers excessive mitochondrial oxidative stress, leads to mitochondrial damage and interleukin-6 release, and contributes to the inhibition of proliferation and DNA damage in neuronal stem cells (NSCs). Furthermore, oxidative stress and inflammation can be ameliorated by vitamin D₃ in a dose-dependent manner, thereby facilitating the rescue of NSC impairment. Our findings reveal the underlying mechanism in which upregulation of CYP11A1 is detrimental to the physiological function of trophoblasts and demonstrate the beneficial effects of vitamin D supplementation in preventing placental and neurodevelopmental damage associated with CYP11A1 upregulation during pregnancy.

Antifibrogenic Activities of CYP11A1-derived Vitamin D3-hydroxyderivatives Are Dependent on RORγ

Previous studies showed that noncalcemic 20(OH)D3, a product of CYP11A1 action on vitamin D3, has antifibrotic activity in human dermal fibroblasts and in a bleomycin mouse model of scleroderma. In this study, we tested the role of retinoic acid-related orphan receptor γ (RORγ), which is expressed in skin, in the action of CYP11A1-derived secosteroids using murine fibroblasts isolated from the skin of wild-type (RORγ +/+), knockout (RORγ -/-), and heterozygote (RORγ +/-) mice. CYP11A1-derived 20(OH)D3, 20,23(OH)2D3, 1,20(OH)2D3, and 1,20,23(OH)3D3 inhibited proliferation of RORγ +/+ fibroblasts in a dose-dependent manner with a similar potency to 1,25(OH)2D3. Surprisingly, this effect was reversed in RORγ +/- and RORγ -/- fibroblasts, with the most pronounced stimulatory effect seen in RORγ -/- fibroblasts. All analogs tested inhibited TGF-β1-induced collagen synthesis in RORγ +/+ fibroblasts and the expression of other fibrosis-related genes. This effect was curtailed or reversed in RORγ -/- fibroblasts. These results show that the antiproliferative and antifibrotic activities of the vitamin D hydroxy derivatives are dependent on a functional RORγ. The dramatic changes in the transcriptomes of fibroblasts of RORγ -/- versus wild-type mice following treatment with 20(OH)D3 or 1,20(OH)2D3 provide a molecular basis to explain, at least in part, the observed phenotypic differences.

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.

COVID-19 and Vitamin D: A lesson from the skin

The negative outcomes of COVID-19 diseases respiratory distress (ARDS) and the damage to other organs are secondary to a "cytokine storm" and to the attendant oxidative stress. Active hydroxyl forms of vitamin D are anti-inflammatory, induce antioxidative responses, and stimulate innate immunity against infectious agents. These properties are shared by calcitriol and the CYP11A1-generated non-calcemic hydroxyderivatives. They inhibit the production of pro-inflammatory cytokines, downregulate NF-κΒ, show inverse agonism on RORγ and counteract oxidative stress through the activation of NRF-2. Therefore, a direct delivery of hydroxyderivatives of vitamin D deserves consideration in the treatment of COVID-19 or ARDS of different aetiology. We also recommend treatment of COVID-19 patients with high-dose vitamin D since populations most vulnerable to this disease are likely vitamin D deficient and patients are already under supervision in the clinics. We hypothesize that different routes of delivery (oral and parenteral) will have different impact on the final outcome.

Pharmaceutic application of vitamin D3 on particle-induced fibrotic effects through induction of Nrf2 signals

Fine particulate matter, a major air pollutant across the world, causes a series of pulmonary diseases. Vitamin D is a typical vitamin with emerging roles in inflammation and fibrosis. Different situations and diseases need different doses and modes of vitamin D administration, which challenges the existing vitamin D supplementary rules. Thus, studies of vitamin D applications and their mechanisms in various diseases are important for its future therapeutic applications. In this study, the therapeutic application of vitamin D₃ in chronic particle-exposure-associated lung fibrosis and tissue remodeling was investigated. In vivo studies showed that vitamin D₃ significantly attenuated fibrosis effects by decreasing α-smooth muscle actin-regulated extracellular matrix deposition and restoring expressions of E-cadherin and N-cadherin. With the importance of activated macrophage in the regulation of local epithelium and fibroblast in the process of tissue fibrosis, two separate in vitro systems of co-culture of macrophages with lung epithelium or fibroblast were built. The results confirmed that vitamin D₃ promoted the proliferation of lung epithelium and depressed the fibrosis effects of fibroblasts as well. In addition, our results indicated that the therapeutic effects of vitamin D₃ were through Nrf2 signals. Our work provides convincing experimental evidence for vitamin D therapeutic application to promote tissue repair and improve particle-associated lung fibrosis.

CYP11A1-derived vitamin D3 products protect against UVB-induced inflammation and promote keratinocytes differentiation

UVB radiation mediates inflammatory responses causing skin damage and defects in epidermal differentiation. 1α,25-Dihydroxyvitamin D3 (1,25(OH)2D3) interacts with the vitamin D3 receptor (VDR) to regulate inflammatory responses. Additionally, 1,25(OH)2D3/VDR signaling represents a potential therapeutic target in the treatment of skin disorders associated with inflammation and poor differentiation of keratinocytes. Since the protective effect of 1,25(OH)2D3 against UVB-induced skin damage and inflammation is recognized, CYP11A1-derived vitamin D3-hydroxyderivatives including 20(OH)D3, 1,20(OH)2D3, 20,23(OH)2D3 and 1,20,23(OH)3D3 were tested for their anti-inflammatory and skin protection properties in UVB-irradiated human epidermal keratinocytes (HEKn). HEKn were treated with secosteroids for 24 h pre- and post-UVB (50 mJ/cm2) irradiation. Secosteroids modulated the expression of the inflammatory response genes (IL-17, NF-κB p65, and IκB-α), reducing nuclear-NF-κB-p65 activity and increasing cytosolic-IκB-α expression as well as that of pro-inflammatory mediators, IL-17, TNF-α, and IFN-γ. They stimulated the expression of involucrin (IVL) and cytokeratin 10 (CK10), the major markers of epidermal differentiation, in UVB-irradiated cells. We conclude that CYP11A1-derived hydroxyderivatives inhibit UVB-induced epidermal inflammatory responses through activation of IκB-α expression and suppression of NF-kB-p65 activity and its downstream signaling cytokines, TNF-α, and IFN-γ, as well as by inhibiting IL-17 production and activating epidermal differentiation.

Pathogenesis of psoriasis in the "omic" era. Part III. Metabolic disorders, metabolomics, nutrigenomics in psoriasis

Psoriasis is a systemic disease that is strictly connected with metabolic disorders (insulin resistance, atherogenic dyslipidemia, arterial hypertension, and cardiovascular diseases). It occurs more often in patients with a more severe course of the disease. Obesity is specially an independent risk factor and it is associated with a worse treatment outcome because of the high inflammatory activity of visceral fatty tissue and the production of inflammatory mediators involved in the development of both psoriasis and metabolic disorders. However, in psoriasis the activation of the Th17/IL-17 and the abnormalities in the Th17/Treg balance axis are observed, but this pathomechanism does not fully explain the frequent occurrence of metabolic disorders. Therefore, there is a need to look for better biomarkers in the diagnosis, prognosis and monitoring of concomitant disorders and therapeutic effects in psoriasis. In addition, the education on the use of a proper diet as a prophylaxis for the development of the above disorders is an important element of holistic care for a patient with psoriasis. Diet may affect gene expression due to epigenetic modification which encompasses interactions of environment, nutrition and diseases. Patients with psoriasis should be advised to adopt proper diet and dietician support.

Vitamin D receptor(s): In the nucleus but also at membranes?

The genomic actions of the vitamin D are mediated via its biologically most potent metabolite 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂ D₃ ) and the transcription factor vitamin D receptor (VDR). Activation of VDR by 1,25(OH)₂ D₃ leads to change in the expression of more 1000 genes in various human tissues. Based on (epi)genome, transcriptome and crystal structure data the molecular details of this nuclear vitamin D signalling pathway are well understood. Vitamin D is known for its role on calcium homeostasis and bone formation, but it also modulates energy metabolism, innate and adaptive immunity as well as cellular growth, differentiation and apoptosis. The observation of rapid, non-genomic effects of 1,25(OH)₂ D₃ at cellular membranes and in the cytosol initiated the question, whether there are alternative vitamin D-binding proteins in these cellular compartments. So far, the best candidate is the enzyme PDIA3 (protein disulphide isomerase family A member 3), which is found at various subcellular locations. Furthermore, also VDR seems to play a role in membrane-based responses to vitamin D. In this viewpoint, we will dispute whether these rapid, non-genomic pathways are a meaningful addition to the genome-wide effects of vitamin D.

Photoprotective Properties of Vitamin D and Lumisterol Hydroxyderivatives

We have previously described new pathways of vitamin D3 activation by CYP11A1 to produce a variety of metabolites including 20(OH)D3 and 20,23(OH)2D3. These can be further hydroxylated by CYP27B1 to produce their C1α-hydroxyderivatives. CYP11A1 similarly initiates the metabolism of lumisterol (L3) through sequential hydroxylation of the side chain to produce 20(OH)L3, 22(OH)L3, 20,22(OH)2L3 and 24(OH)L3. CYP11A1 also acts on 7-dehydrocholesterol (7DHC) producing 22(OH)7DHC, 20,22(OH)27DHC and 7-dehydropregnenolone (7DHP) which can be converted to the D3 and L3 configurations following exposure to UVB. These CYP11A1-derived compounds are produced in vivo and are biologically active displaying anti-proliferative, anti-inflammatory, anti-cancer and pro-differentiation properties. Since the protective role of the classical form of vitamin D3 (1,25(OH)2D3) against UVB-induced damage is recognized, we recently tested whether novel CYP11A1-derived D3- and L3-hydroxyderivatives protect against UVB-induced damage in epidermal human keratinocytes and melanocytes. We found that along with 1,25(OH)2D3, CYP11A1-derived D3-hydroxyderivatives and L3 and its hydroxyderivatives exert photoprotective effects. These included induction of intracellular free radical scavenging and attenuation and repair of DNA damage. The protection of human keratinocytes against DNA damage included the activation of the NRF2-regulated antioxidant response, p53-phosphorylation and its translocation to the nucleus, and DNA repair induction. These data indicate that novel derivatives of vitamin D3 and lumisterol are promising photoprotective agents. However, detailed mechanisms of action, and the involvement of specific nuclear receptors, other vitamin D binding proteins or mitochondria, remain to be established.

Noncalcemic Vitamin D Hydroxyderivatives Inhibit Human Oral Squamous Cell Carcinoma and Down-regulate Hedgehog and WNT/β-Catenin Pathways

BACKGROUND/AIM

The hormonally-active form of vitamin D, 1,25(OH)₂D₃, demonstrated activity against oral squamous cell carcinoma (OSCC). Cytochrome P450scc (CYP11A1)-derived vitamin D hydroxyderivatives, such as 20(OH)D₃ and 1,20(OH)₂D₃, have overlapping beneficial effects with 1,25(OH)₂D₃ without causing hypercalcemia. This study sought to determine (i) whether 20(OH)D₃ and 1,20(OH)₂D₃ exhibit antitumor effects against OSCC comparable to those of 1,25(OH)₂D₃ and (ii) whether these effects may stem from down-regulation of sonic hedgehog (SHH) or WNT/β-catenin signaling pathways.

MATERIALS AND METHODS

Effects on CAL-27 cells were assessed by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt and spheroid assays. Signaling pathways were assessed by immunofluorescence and western blotting.

RESULTS

20(OH)D₃ and 1,20(OH)₂D₃ inhibited the growth of CAL-27 and demonstrated inhibition of WNT/β-catenin and the SHH signaling as evidenced by down-regulation of nuclear translocation of glioma-associated oncogene 1(GLI1) and β-catenin.

CONCLUSION

Noncalcemic vitamin D hydroxyderivatives demonstrated antitumor activities against OSCC comparable to those of 1,25(OH)₂D₃ Their activities against SHH and the WNT/β-catenin pathways provide insight for a possible target for OSCC treatment.

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-βHSD, 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 11βHSD1/2. 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.

Eldecalcitol (ED-71)-induced exosomal miR-6887-5p suppresses squamous cell carcinoma cell growth by targeting heparin-binding protein 17/fibroblast growth factor-binding protein-1 (HBp17/FGFBP-1)

Heparin-binding protein 17/fibroblast growth factor-binding protein-1 (HBp17/FGFBP-1) was purified from A431 cell-conditioned media based on its capacity to bind to fibroblast growth factor 1 and 2 (FGF-1 and FGF-2). HBp17/FGFBP-1 has been observed to induce the tumorigenic potential of epithelial cells and is highly expressed in oral cancer cell lines and tissues. HBp17/FGFBP-1 is also recognized as a pro-angiogenic molecule as a consequence of its interaction with FGF-2. We have previously reported that Eldecalcitol (ED-71), an analog of 1α,25(OH)₂D₃, downregulated the expression of HBp17/FGFBP-1 and inhibited the proliferation of squamous cell carcinoma (SCC) cells in vitro and in vivo through NF-κb inhibition. To explore the possibility of microRNA (miRNA) control of HBp17/FGFBP-1, we analyzed exosomal miRNAs from medium conditioned by A431 cells treated with ED-71. Microarray analysis revealed that 12 exosomal miRNAs were upregulated in ED-71-treated A431 cells. Among them, miR-6887-5p was identified to have a predicted mRNA target matching the 3' untranslated region (3'-UTR) of HBp17/FGFBP-1. The 3'-UTR of HBp17/FGFBP-1 was confirmed to be a direct target of miR-6887-5p in SCC/OSCC cells, as assessed with a luciferase reporter assay. Functional assessment revealed that overexpression of miR-6887-5p in SCC/OSCC cells inhibited cell proliferation and colony formation in vitro, and inhibited tumor growth in vivo compared with control. In conclusion, our present study supports a novel anti-cancer mechanism involving the regulation of HBp17/FGFBP-1 function by exosomal miR-6887-5p in SCC/OSCC cells, which has potential utility as a miRNA-based cancer therapy.

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.

Protective effects of novel derivatives of vitamin D3 and lumisterol against UVB-induced damage in human keratinocytes involve activation of Nrf2 and p53 defense mechanisms

We tested whether novel CYP11A1-derived vitamin D₃- and lumisterol-hydroxyderivatives, including 1,25(OH)₂D₃, 20(OH)D₃, 1,20(OH)₂D₃, 20,23(OH)₂D₃, 1,20,23(OH)₃D₃, lumisterol, 20(OH)L₃, 22(OH)L₃, 20,22(OH)₂L₃, and 24(OH)L₃, can protect against UVB-induced damage in human epidermal keratinocytes. Cells were treated with above compounds for 24 h, then subjected to UVB irradiation at UVB doses of 25, 50, 75, or 200 mJ/cm², and then examined for oxidant formation, proliferation, DNA damage, and the expression of genes at the mRNA and protein levels. Oxidant formation and proliferation were determined by the DCFA-DA and MTS assays, respectively. DNA damage was assessed using the comet assay. Expression of antioxidative genes was evaluated by real-time RT-PCR analysis. Nuclear expression of CPD, phospho-p53, and Nrf2 as well as its target proteins including HO-1, CAT, and MnSOD, were assayed by immunofluorescence and western blotting. Treatment of cells with the above compounds at concentrations of 1 or 100 nM showed a dose-dependent reduction in oxidant formation. At 100 nM they inhibited the proliferation of cultured keratinocytes. When keratinocytes were irradiated with 50–200 mJ/cm² of UVB they also protected against DNA damage, and/or induced DNA repair by enhancing the repair of 6-4PP and attenuating CPD levels and the tail moment of comets. Treatment with test compounds increased expression of Nrf2-target genes involved in the antioxidant response including GR, HO-1, CAT, SOD1, and SOD2, with increased protein expression for HO-1, CAT, and MnSOD. The treatment also stimulated the phosphorylation of p53 at Ser-15, increased its concentration in the nucleus and enhanced Nrf2 translocation into the nucleus. In conclusion, pretreatment of keratinocytes with 1,25(OH)₂D₃ or CYP11A1-derived vitamin D₃- or lumisterol hydroxy-derivatives, protected them against UVB-induced damage via activation of the Nrf2-dependent antioxidant response and p53-phosphorylation, as well as by the induction of the DNA repair system. Thus, the new vitamin D₃ and lumisterol hydroxy-derivatives represent promising anti-photodamaging agents.

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Vitamin D₃ and lumisterol derivatives stimulate antioxidative responses in skin.

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Vitamin D₃ and lumisterol derivatives protect against UVB-induced DNA damage.

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Vitamin D₃ and lumisterol derivatives target p53 and Nrf2-antioxidant pathways.

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Vitamin D₃ and lumisterol derivatives promise to be skin photoprotectors

The serum vitamin D metabolome: What we know and what is still to discover

Vitamin D, referring to the two forms, D2 from the diet and D3 primarily derived from phototransformation in the skin, is a prohormone important in human health. The most hormonally active form, 1α,25-dihydroxyvitamin D (1α,25(OH)₂D), formed from vitamin D via 25-hydroxyvitamin D (25(OH)D), is not only important for regulating calcium metabolism, but has many pleiotropic effects including regulation of the immune system and has anti-cancer properties. The major circulating form of vitamin D is 25(OH)D and both D2 and D3 forms are routinely measured by LC/MS/MS to assess vitamin D status, due to their relatively long half-lives and much higher concentrations compared to 1α,25(OH)₂D. Inactivation of both 25(OH)D and 1α,25(OH)₂D is catalyzed by CYP24A1 and 25-hydroxyvitamin D3 3-epimerase. Initial products from these enzymes acting on 25(OH)D3 are 24R,25(OH)₂D3 and 3-epi-25(OH)D3, respectively, and both of these can also be measured routinely in some clinical laboratories to further document vitamin D status. With advances in LC/MS/MS and its increased availability, and with the help of studies with recombinant vitamin D-metabolizing enzymes, many other vitamin D metabolites have now been detected and in some cases quantitated, in human serum. CYP11A1 which catalyzes the first step in steroidogenesis, has been found to also act on vitamins D3 and D2 hydroxylating both at C20, but with some secondary metabolites produced by subsequent hydroxylations at other positions on the side chain. The major vitamin D3 metabolite, 20S-hydroxyvitamin D3 (20S(OH)D3), shows biological activity, often similar to 1α,25(OH)₂D3 but without calcemic effects. Using standards produced enzymatically by purified CYP11A1 and characterized by NMR, many of these new metabolites have been detected in human serum, with semi-quantitative measurement of 20S(OH)D3 indicating it is present at comparable concentrations to 24R,25(OH)₂D3 and 3-epi-25(OH)D3. Recently, vitamin D-related hydroxylumisterols derived from lumisterol3, a previtamin D3 photoproduct, have also been measured in human serum and displayed biological activity in initial in vitro studies. With the current extensive knowledge on the reactions and pathways of metabolism of vitamin D, especially those catalyzed by CYP24A1, CYP27A1, CYP27B1, CYP3A4 and CYP11A1, it is likely that many other of the resulting hydroxyvitamin D metabolites will be measured in human serum in the future, some contributing to a more detailed understanding of vitamin D status in health and disease.

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.

Properties of purified CYP2R1 in a reconstituted membrane environment and its 25-hydroxylation of 20-hydroxyvitamin D3

Recent studies indicate that CYP2R1 is the major 25-hydroxylase catalyzing the first step in vitamin D activation. Since the catalytic properties of CYP2R1 have been poorly studied to date and it is a membrane protein, we examined the purified enzyme in a membrane environment. CYP2R1 was expressed in E. coli and purified by nickel affinity- and hydrophobic interaction-chromatography and assayed in a reconstituted membrane system comprising phospholipid vesicles plus purified human NADPH-P450 oxidoreductase. CYP2R1 converted vitamin D3 in the vesicle membrane to 25-hydroxyvitamin D3 [25(OH)D3] with good adherence to Michaelis-Menten kinetics. The kinetic parameters for 25-hydroxylation of vitamin D3 by the two major vitamin D 25-hydroxylases, CYP2R1 and CYP27A1, were examined in vesicles under identical conditions. CYP2R1 displayed a slightly lower k_cat than CYP27A1 but a much lower K_m for vitamin D3, and thus an overall 17-fold higher catalytic efficiency (k_cat/K_m), consistent with CYP2R1 being the major vitamin D 25-hydroxylase. 20-Hydroxyvitamin D3 [20(OH)D3], the main product of vitamin D3 activation by an alternative pathway catalyzed by CYP11A1, was metabolized by CYP2R1 to 20,25-dihydroxyvitamin D3 [20,25(OH)₂D3], with catalytic efficiency similar to that for the 25-hydroxylation of vitamin D3. 20,25(OH)₂D3 retained full, or somewhat enhanced activity compared to the parent 20(OH)D3 for the inhibition of the proliferation of melanocytes and dermal fibroblasts, with a potency comparable to 1,25-dihydroxyvitamin D3 [1,25(OH)₂D3]. The 20,25(OH)₂D3 was also able to act as an inverse agonist on retinoic acid-related orphan receptor α, like its parent 20(OH)D3. Thus, the major findings of this study are that CYP2R1 can metabolize substrates in a membrane environment, the enzyme displays higher catalytic efficiency than CYP27A1 for the 25-hydroxylation of vitamin D, it efficiently hydroxylates 20(OH)D3 at C25 and this product retains the biological activity of the parent compound.

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

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

Noncalcemic 20-hydroxyvitamin D3 inhibits human melanoma growth in in vitro and in vivo models

A novel pathway of vitamin D₃ (D₃) metabolism, initiated by C20-hydroxylation of D₃ by CYP11A1, has been confirmed to operate in vivo. Its major product, 20(OH)D₃, exhibits antiproliferative activity in vitro comparable to that of 1,25(OH)₂D₃, but is noncalcemic in mice and rats. To further characterize the antimelanoma activity of 20(OH)D₃, we tested its effect on colony formation of human melanoma cells in monolayer culture and anchorage-independent growth in soft agar. The migratory capabilities of the cells and cell-cell and cell-extracellular matrix interactions were also evaluated using transwell cell migration and spheroid toxicity assays. To assess the antimelanoma activity of 20(OH)D₃in vivo, age-matched immunocompromised mice were subcutaneously implanted with luciferase-labelled SKMel-188 cells and were randomly assigned to be treated with either 20(OH)D₃ or vehicle (n=10 per group). Tumor size was measured with caliper and live bioimaging methods, and overall health condition expressed as a total body score scale. The following results were observed: (i) 20(OH)D₃ inhibited colony formation both in monolayer and soft agar conditions, (ii) 20(OH)D₃ inhibited melanoma cells in both transwell migration and spheroid toxicity assays, and (iii) 20(OH)D₃ inhibited melanoma tumor growth in immunocompromised mice without visible signs of toxicity. However, although the survival rate was 90% in both groups, the total body score was higher in the treatment group compared to control group (2.8 vs. 2.55). In conclusion, 20(OH)D₃, an endogenously produced secosteroid, is an excellent candidate for further preclinical testing as an antimelanoma agent.

Investigation of 20S-hydroxyvitamin D3 analogs and their 1α-OH derivatives as potent vitamin D receptor agonists with anti-inflammatory activities

20S-hydroxyvitamin D₃ [20S(OH)D₃] is anti-inflammatory and not hypercalcemic, suggesting its potential as a lead compound. In this study, side chain modified 20S(OH)D₃ analogs (4, 13, 23 and 33) together with their 1α-OH derivatives were synthesized and their metabolism and biological activities tested. 4, 13 and 23 are good substrates for CYP27B1, enabling enzymatic synthesis of their 1α-OH derivatives 5, 14 and 24. However, 33 could not be hydroxylated by CYP27B1 and acts as an inhibitor. All analogs were poorer substrates for CYP24A1 than calcitriol, indicating improved catabolic stability. While the parent analogs showed minimal VDR stimulating activity, their 1α-OH derivatives were potent VDR agonists. 4, 5, 14 and 24 significantly upregulated the expression of CYP24A1 at the mRNA level, consistent with their VDR activation abilities and indicating that 1α-hydroxylation is required to produce analogs with strong activity. These analogs have anti-inflammatory activities that are influenced by side chain composition and by 1α-hydroxylation. To understand their molecular interactions with the VDR, 20S(OH)D₃, 4 and 33 were co-crystalized with the VDR ligand binding domain, which revealed subtle differences to the calcitriol-bound receptor. This study demonstrates the potential of the 20S(OH)D₃ scaffold for the development of novel anti-inflammatory agents.

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

The classical pathway of vitamin D activation follows the sequence D3→25(OH)D3→1,25(OH)₂D3 with the final product acting on the receptor for vitamin D (VDR). An alternative pathway can be started by the action of CYP11A1 on the side chain of D3, primarily producing 20(OH)D3, 22(OH)D3, 20,23(OH)₂D3, 20,22(OH)₂D3 and 17,20,23(OH)₃D3. Some of these metabolites are hydroxylated by CYP27B1 at C1α, by CYP24A1 at C24 and C25, and by CYP27A1 at C25 and C26. The products of these pathways are biologically active. In the epidermis and/or serum or adrenals we detected 20(OH)D3, 22(OH)D3, 20,22(OH)₂D3, 20,23(OH)₂D3, 17,20,23(OH)₃D3, 1,20(OH)₂D3, 1,20,23(OH)₃D3, 1,20,22(OH)₃D3, 20,24(OH)₂D3, 1,20,24(OH)₃D3, 20,25(OH)₂D3, 1,20,25(OH)₃D3, 20,26(OH)₂D3 and 1,20,26(OH)₃D3. 20(OH)D3 and 20,23(OH)₂D3 are non-calcemic, while the addition of an OH at C1α confers some calcemic activity. Molecular modeling and functional assays show that the major products of the pathway can act as "biased" agonists for the VDR with high docking scores to the ligand binding domain (LBD), but lower than that of 1,25(OH)₂D3. Importantly, cell based functional receptor studies and molecular modeling have identified the novel secosteroids as inverse agonists of both RORα and RORγ receptors. Specifically, they have high docking scores using crystal structures of RORα and RORγ LBDs. Furthermore, 20(OH)D3 and 20,23(OH)₂D3 have been tested in a cell model that expresses a Tet-on RORα or RORγ vector and a RORE-LUC reporter (ROR-responsive element), and in a mammalian 2-hybrid model that test interactions between an LBD-interacting LXXLL-peptide and the LBD of RORα/γ. These assays demonstrated that the novel secosteroids have ROR-antagonist activities that were further confirmed by the inhibition of IL17 promoter activity in cells overexpressing RORα/γ. In conclusion, endogenously produced novel D3 hydroxy-derivatives can act both as "biased" agonists of the VDR and/or inverse agonists of RORα/γ. We suggest that the identification of large number of endogenously produced alternative hydroxy-metabolites of D3 that are biologically active, and of possible alternative receptors, may offer an explanation for the pleiotropic and diverse activities of vitamin D, previously assigned solely to 1,25(OH)₂D3 and VDR.

Characterization of a new pathway that activates lumisterol in vivo to biologically active hydroxylumisterols

Using LC/qTOF-MS we detected lumisterol, 20-hydroxylumisterol, 22-hydroxylumisterol, 24-hydroxylumisterol, 20,22-dihydroxylumisterol, pregnalumisterol, 17-hydroxypregnalumisterol and 17,20-dihydroxypregnalumisterol in human serum and epidermis, and the porcine adrenal gland. The hydroxylumisterols inhibited proliferation of human skin cells in a cell type-dependent fashion with predominant effects on epidermal keratinocytes. They also inhibited melanoma proliferation in both monolayer and soft agar. 20-Hydroxylumisterol stimulated the expression of several genes, including those associated with keratinocyte differentiation and antioxidative responses, while inhibiting the expression of others including RORA and RORC. Molecular modeling and studies on VDRE-transcriptional activity excludes action through the genomic site of the VDR. However, their favorable interactions with the A-pocket in conjunction with VDR translocation studies suggest they may act on this non-genomic VDR site. Inhibition of RORα and RORγ transactivation activities in a Tet-on CHO cell reporter system, RORα co-activator assays and inhibition of (RORE)-LUC reporter activity in skin cells, in conjunction with molecular modeling, identified RORα and RORγ as excellent receptor candidates for the hydroxylumisterols. Thus, we have discovered a new biologically relevant, lumisterogenic pathway, the metabolites of which display biological activity. This opens a new area of endocrine research on the effects of the hydroxylumisterols on different pathways in different cells and the mechanisms involved.

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.

Melatonin and its metabolites protect human melanocytes against UVB-induced damage: Involvement of NRF2-mediated pathways

Ultraviolet light (UV) is an inducer of reactive oxygen species (ROS) as well as 6-4-photoproducts and cyclobutane pyrimidine dimers (CPD) in the skin, which further cause damage to the skin cells. Irradiation of cultured human melanocytes with UVB stimulated ROS production, which was reduced in cells treated with melatonin or its metabolites: 6-hydroxymelatonin (6-OHM), N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), N-acetylserotonin (NAS), and 5-methoxytryptamine (5-MT). Melatonin and its derivatives also stimulated the expression of NRF2 (nuclear factor erythroid 2 [NF-E2]-related factor 2) and its target enzymes and proteins that play an important role in cell protection from different damaging factors including UVB. Silencing of NRF2 using siRNA diminished the protective effects of melatonin, while the membrane melatonin receptors (MT1 or MT2) did not change the activities of either melatonin or its derivatives. Melatonin and its metabolites enhanced the DNA repair in melanocytes exposed to UVB and stimulated expression of p53 phosphorylated at Ser-15. In conclusion, melatonin and its metabolites protect melanocytes from UVB-induced DNA damage and oxidative stress through activation of NRF2-dependent pathways; these actions are independent of an effect on the classic membrane melatonin receptors. Thus, melatonin and its derivatives can serve as excellent protectors of melanocytes against UVB-induced pathology.

Synthesis and Biological Evaluation of Vitamin D3 Metabolite 20S,23S-Dihydroxyvitamin D3 and Its 23R Epimer

The vitamin D3 metabolite, 20S,23S-dihydroxyvitamin D3, was chemically synthesized for the first time and identified to be the same as the enzymatically produced metabolite. The C23 absolute configurations of both 20S,23S/R-dihydroxyvitamin D3 epimers were unambiguously assigned by NMR and Mosher ester analysis. Their kinetics of CYP27B1 metabolism were investigated during the production of their 1α-hydroxylated derivatives. Bioactivities of these products were compared in terms of vitamin D3 receptor activation, anti-inflammatory, and antiproliferative activities.

PTH and Vitamin D

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

Design, Synthesis and Biological Activities of Novel Gemini 20S-Hydroxyvitamin D3 Analogs

Vitamin D3 (D3) can be metabolized by cytochrome P450scc (CYP11A1) into 20S-hydroxyvitamin D3 (20D3) as a major metabolite. This bioactive metabolite has shown strong antiproliferative, antifibrotic, pro-differentiation and anti-inflammatory effects while being non-toxic (non-calcemic) at high concentrations. Since D3 analogs with two symmetric side chains (Gemini analogs) result in potent activation of the vitamin D receptor (VDR), we hypothesized that the chain length and composition of these types of analogs also containing a 20-hydroxyl group would affect their biological activities. In this study, we designed and synthesized a series of Gemini 20D3 analogs. Biological tests showed that some of these analogs are partial VDR activators and can significantly stimulate the expression of mRNA for VDR and VDR-regulated genes including CYP24A1 and transient receptor potential cation channel V6 (TRPV6). These analogs inhibited the proliferation of melanoma cells with potency comparable to that of 1α,25-dihydroxyvitamin D3. Moreover, these analogs reduced the level of interferon γ and up-regulated the expression of leukocyte associated immunoglobulin-like receptor 1 in splenocytes, indicating that they have potent anti-inflammatory activities. There are no clear correlations between the Gemini chain length and their VDR activation or biological activities, consistent with the high flexibility of the ligand-binding pocket of the VDR.

On the role of skin in the regulation of local and systemic steroidogenic activities

The mammalian skin is a heterogeneous organ/tissue covering our body, showing regional variations and endowed with neuroendocrine activities. The latter is represented by its ability to produce and respond to neurotransmitters, neuropeptides, hormones and neurohormones, of which expression and phenotypic activities can be modified by ultraviolet radiation, chemical and physical factors, as well as by cytokines. The neuroendocrine contribution to the responses of skin to stress is served, in part, by local synthesis of all elements of the hypothalamo-pituitary-adrenal axis. Skin with subcutis can also be classified as a steroidogenic tissue because it expresses the enzyme, CYP11A1, which initiates steroid synthesis by converting cholesterol to pregnenolone, as in other steroidogenic tissues. Pregnenolone, or steroidal precursors from the circulation, are further transformed in the skin to corticosteroids or sex hormones. Furthermore, in the skin CYP11A1 acts on 7-dehydrocholesterol with production of 7-dehydropregnolone, which can be further metabolized to other Δ7steroids, which after exposure to UVB undergo photochemical transformation to vitamin D like compounds with a short side chain. Vitamin D and lumisterol, produced in the skin after exposure to UVB, are also metabolized by CYP11A1 to several hydroxyderivatives. Vitamin D hydroxyderivatives generated by action of CYP11A1 are biologically active and are subject to further hydroxylations by CYP27B1, CYP27A1 and CP24A. Establishment of which intermediates are produced in the epidermis in vivo and whether they circulate on the systemic level represent a future research challenge. In summary, skin is a neuroendocrine organ endowed with steroid/secosteroidogenic activities.

Expression of Vitamin D Receptor (VDR) Positively Correlates with Survival of Urothelial Bladder Cancer Patients

Vitamin D3 shows tumoristatic and anticancer effects by acting through the vitamin D receptor (VDR), while hydroxylation of 25-hydroxyvitamin D3 at position 1α by CYP27B1 is an essential step in its activation. The expression of both the VDR and CYP27B1 has been found in many normal and cancer tissues, but there is a lack of information about its expression in human bladder cancers. The aim of the present research was to examine whether the expression of the VDR and CYP27B1 in bladder cancer was related to the prognostic markers and disease outcome. We analyzed VDR and CYP27B1 in samples of tumor and normal tissues obtained from 71 urinary bladder cancer patients. The highest VDR immunostaining was found in normal epithelium and was significantly lower in bladder cancer cells (p < 0.001 with Mann–Whitney U test). VDR expression was lowest in more advanced (pT2b–pT4) (p = 0.005 with Mann–Whitney U test) and metastasizing cancers (p < 0.05 and p = 0.004 with Mann–Whitney U test for nuclear and cytoplasmic VDR immunostaining, respectively). The lack of cytoplasmic and nuclear VDR was also related to shorter overall survival (for cytoplasmic VDR immunolocalization 13.3 vs. 55.3 months of survival, HR = 1.92, p = 0.04 and for nuclear VDR immunostaining 13.5 vs. 55.3 months of survival, HR = 2.47, p = 0.002 with Mantel-Cox test). In cases with the lack of high cytoplasmic VDR staining the non-classic differentiations (NDs) was observed in higher percentage of tumor area. CYP27B1 expression was lower in cancer cells than in normal epithelial cells (p = 0.03 with Mann–Whitney U test), but its expression did not correlate with tumor stage (pT), metastasizing, grade, mitotic activity or overall survival. In conclusion, expression of the VDR and CYP27B1 are deregulated in urothelial bladder cancers. Although our results showing a relationship between the decreased VDR expression and prognostic markers and survival time indicate potential usefulness of VDR as a new indicator of a poorer prognosis, further studies are needed in different patient cohorts by independent groups to validate this hypothesis. We also suggest that vitamin D-based therapies may represent an adjuvant strategy in treatment for bladder cancers expressing VDR.

Detection of novel CYP11A1-derived secosteroids in the human epidermis and serum and pig adrenal gland

To investigate whether novel pathways of vitamin D3 (D3) and 7-dehydrocholesterol (7DHC) metabolism initiated by CYP11A1 and previously characterized in vitro, occur in vivo, we analyzed samples of human serum and epidermis, and pig adrenals for the presence of intermediates and products of these pathways. We extracted human epidermis from 13 individuals and sera from 13 individuals and analyzed them by LC/qTOF-MS alongside the corresponding standards. Pig adrenal glands were also analyzed for these steroids and secosteroids. Epidermal, serum and adrenal samples showed the presence of D3 hydroxy-derivatives corresponding to 20(OH)D3, 22(OH)D3, 25(OH)D3, 1,25(OH)2D3, 20,22(OH)2D3, 20,23(OH)2D3, 20,24(OH)2D3, 20,25(OH)2D3, 20,26(OH)2D3, 1,20,23(OH)3D3 and 17,20,23(OH)3D3, plus 1,20(OH)2D3 which was detectable only in the epidermis. Serum concentrations of 20(OH)D3 and 22(OH)D3 were only 30- and 15-fold lower than 25(OH)D3, respectively, and at levels above those required for biological activity as measured in vitro. We also detected 1,20,24(OH)3D3, 1,20,25(OH)3D3 and 1,20,26(OH)3D3 in the adrenals. Products of CYP11A1 action on 7DHC, namely 22(OH)7DHC, 20,22(OH)27DHC and 7-dehydropregnenolone were also detected in serum, epidermis and the adrenal. Thus, we have detected novel CYP11A1-derived secosteroids in the skin, serum and adrenal gland and based on their concentrations and biological activity suggest that they act as hormones in vivo.

Chemical Synthesis and Biological Activities of 20S,24S/R-Dihydroxyvitamin D3 Epimers and Their 1α-Hydroxyl Derivatives

Bioactive vitamin D3 metabolites 20S,24S-dihydroxyvitamin D3 [20S,24S(OH)2D3] and 20S,24R-dihydroxyvitamin D3 [20S,24R(OH)2D3] were chemically synthesized and confirmed to be identical to their enzymatically generated counterparts. The absolute configurations at C24 and its influence on the kinetics of 1α-hydroxylation by CYP27B1 were determined. Their corresponding 1α-hydroxyl derivatives were subsequently produced. Biological comparisons of these products showed different properties with respect to vitamin D3 receptor activation, anti-inflammatory activity, and antiproliferative activity, with 1α,20S,24R(OH)2D3 being the most potent compound.

Novel activities of CYP11A1 and their potential physiological significance

CYP11A1, found only in vertebrates, catalyzes the first step of steroidogenesis where cholesterol is converted to pregnenolone. The purified enzyme, also converts desmosterol and plant sterols including campesterol and β-sitosterol, to pregnenolone. Studies, initially with purified enzyme, reveal that 7-dehydrocholesterol (7DHC), ergosterol, lumisterol 3, and vitamins D3 and D2 also serve as substrates for CYP11A1, with 7DHC being better and vitamins D3 and D2 being poorer substrates than cholesterol. Adrenal glands, placenta, and epidermal keratinocytes can also carry out these conversions and 7-dehydropregnenolone has been detected in the epidermis, adrenal glands, and serum, and 20-hydroxyvitamin D3 was detected in human serum and the epidermis. Thus, this metabolism does appear to occur in vivo, although its quantitative importance and physiological role remain to be established. CYP11A1 action on 7DHC in vivo is further supported by detection of Δ(7)steroids in Smith-Lemli-Opitz syndrome patients. The activity of CYP11A1 is affected by the structure of the substrate with sterols having steroidal or Δ(7)-steroidal structures undergoing side chain cleavage following hydroxylations at C22 and C20. In contrast, metabolism of vitamin D involves sequential hydroxylations that start at C20 but do not lead to cleavage. Molecular modeling using the crystal structure of CYP11A1 predicts that other intermediates of cholesterol synthesis could also serve as substrates for CYP11A1. Finally, CYP11A1-derived secosteroidal hydroxy-derivatives and Δ(7)steroids are biologically active when administered in vitro in a manner dependent on the structure of the compound and the lineage of the target cells, suggesting physiological roles for these metabolites. This article is part of a special issue entitled 'SI: Steroid/Sterol signaling'.

A Proposed Molecular Mechanism of High-Dose Vitamin D3 Supplementation in Prevention and Treatment of Preeclampsia

A randomized prospective clinical study performed on a group of 74 pregnant women (43 presenting with severe preeclampsia) proved that urinary levels of 15-F(2t)-isoprostane were significantly higher in preeclamptic patients relative to the control (3.05 vs. 2.00 ng/mg creatinine). Surprisingly enough, plasma levels of 25-hydroxyvitamin D3 in both study groups were below the clinical reference range with no significant difference between the groups. In vitro study performed on isolated placental mitochondria and placental cell line showed that suicidal self-oxidation of cytochrome P450scc may lead to structural disintegration of heme, potentially contributing to enhancement of oxidative stress phenomena in the course of preeclampsia. As placental cytochrome P450scc pleiotropic activity is implicated in the metabolism of free radical mediated arachidonic acid derivatives as well as multiple Vitamin D3 hydroxylations and progesterone synthesis, we propose that Vitamin D3 might act as a competitive inhibitor of placental cytochrome P450scc preventing the production of lipid peroxides or excess progesterone synthesis, both of which may contribute to the etiopathogenesis of preeclampsia. The proposed molecular mechanism is in accord with the preliminary clinical observations on the surprisingly high efficacy of high-dose Vitamin D3 supplementation in prevention and treatment of preeclampsia.

Metabolism of 20-hydroxyvitamin D3 and 20,23-dihydroxyvitamin D3 by rat and human CYP24A1

CYP11A1 hydroxylates vitamin D3 producing 20S-hydroxyvitamin D3 [20(OH)D3] and 20S,23-dihydroxyvitamin D3 [20,23(OH)2D3] as the major and most characterized metabolites. Both display immuno-regulatory and anti-cancer properties while being non-calcemic. A previous study indicated 20(OH)D3 can be metabolized by rat CYP24A1 to products including 20S,24-dihydroxyvitamin D3 [20,24(OH)2D3] and 20S,25-dihydroxyvitamin D3, with both producing greater inhibition of melanoma colony formation than 20(OH)D3. The aim of this study was to characterize the ability of rat and human CYP24A1 to metabolize 20(OH)D3 and 20,23(OH)2D3. Both isoforms metabolized 20(OH)D3 to the same dihydroxyvitamin D species with no secondary metabolites being observed. Hydroxylation at C24 produced both enantiomers of 20,24(OH)2D3. For rat CYP24A1 the preferred initial site of hydroxylation was at C24 whereas the human enzyme preferred C25. 20,23(OH)2D3 was initially metabolized to 20S,23,24-trihydroxyvitamin D3 and 20S,23,25-trihydroxyvitamin D3 by rat and human CYP24A1 as determined by NMR, with both isoforms showing a preference for initial hydroxylation at C25. CYP24A1 was able to further oxidize these metabolites in a series of reactions which included the cleavage of C23-C24 bond, as indicated by high resolution mass spectrometry of the products, analogous to the catabolism of 1,25(OH)2D3 via the C24-oxidation pathway. Similar catalytic efficiencies were observed for the metabolism of 20(OH)D3 and 20,23(OH)2D3 by human CYP24A1 and were lower than for the metabolism of 1,25(OH)2D3. We conclude that rat and human CYP24A1 metabolizes 20(OH)D3 producing only dihydroxyvitamin D3 species as products which retain biological activity, whereas 20,23(OH)2D3 undergoes multiple oxidations which include cleavage of the side chain.

Novel non-calcemic secosteroids that are produced by human epidermal keratinocytes protect against solar radiation

CYP11A1 hydroxylates the side chain of vitamin D3 (D3) in a sequential fashion [D3→20S(OH)D3→20,23(OH)2D3→17,20,23(OH)3D3], in an alternative to the classical pathway of activation [D3→25(OH)D3→1,25(OH)2D3]. The products/intermediates of the pathway can be further modified by the action of CYP27B1. The CYP11A1-derived products are biologically active with functions determined by the lineage of the target cells. This pathway can operate in epidermal keratinocytes. To further define the role of these novel secosteroids we tested them for protective effects against UVB-induced damage in human epidermal keratinocytes, melanocytes and HaCaT keratinocytes, cultured in vitro. The secosteroids attenuated ROS, H2O2 and NO production by UVB-irradiated keratinocytes and melanocytes, with an efficacy similar to 1,25(OH)2D3, while 25(OH)D3 had lower efficacy. These attenuations were also seen to some extent for the 20(OH)D3 precursor, 20S-hydroxy-7-dehydrocholesterol. These effects were accompanied by upregulation of genes encoding enzymes responsible for defense against oxidative stress. Using immunofluorescent staining we observed that the secosteroids reduced the generation cyclobutane pyrimidine dimers in response to UVB and enhanced expression of p53 phosphorylated at Ser-15, but not at Ser-46. Additional evidence for protection against DNA damage in cells exposed to UVB and treated with secosteroids was provided by the Comet assay where DNA fragmentation was markedly reduced by 20(OH)D3 and 20,23(OH)2D3. In conclusion, novel secosteroids that can be produced by the action of CYP11A1 in epidermal keratinocytes have protective effects against UVB radiation. This article is part of a special issue entitled '17th Vitamin D Workshop'.

The role of CYP11A1 in the production of vitamin D metabolites and their role in the regulation of epidermal functions

Research over the last decade has revealed that CYP11A1 can hydroxylate the side chain of vitamin D3 at carbons 17, 20, 22 and 23 to produce at least 10 metabolites, with 20(OH)D3, 20,23(OH)2D3, 20,22(OH)2D3, 17,20(OH)2D3 and 17,20,23(OH)3D3 being the main products. However, CYP11A1 does not act on 25(OH)D3. The placenta, adrenal glands and epidermal keratinocytes have been shown to metabolize vitamin D3 via this CYP11A1-mediated pathway that is modified by the activity of CYP27B1, with 20(OH)D3 (the major metabolite), 20,23(OH)2D3, 1,20(OH)2D3, 1,20,23(OH)3D3 and 17,20,23(OH)3D3 being detected, defining these secosteroids as endogenous regulators/natural products. This is supported by the detection of a mono-hydroxyvitamin D3 with the retention time of 20(OH)D3 in human serum. In new work presented here we demonstrate that the CYP11A1-initiated pathways also occurs in Caco-2 colon cells. Our previous studies show that 20(OH)D3 and 20,23(OH)2D3 are non-calcemic at pharmacological doses, dependent in part on their lack of a C1α hydroxyl group. In epidermal keratinocytes, 20(OH)D3, 20(OH)D2 and 20,23(OH)2D3 inhibited cell proliferation, stimulated differentiation and inhibited NF-κB activity with potencies comparable to 1,25(OH)2D3, acting as partial agonists on the VDR. 22(OH)D3 and 20,22(OH)2D3, as well as secosteroids with a short or no side chain, showed antiproliferative and prodifferentiation effects, however, with lower potency than 20(OH)D3 and 20,23(OH)2D3. The CYP11A1-derived secosteroids also inhibited melanocyte proliferation while having no effect on melanogenesis, and showed anti-melanoma activities in terms of inhibiting proliferation and the ability to grow in soft agar. Furthermore, 20(OH)D3 and 20,23(OH)2D3 showed anti-fibrosing effects in vitro, and also in vivo for the former. New data presented here shows that 20(OH)D3 inhibits LPS-induced production of TNFα in the J774 line, TNFα and IL-6 in peritoneal macrophages and suppresses the production of proinflammatory Th1/Th17-related cytokines, while promoting the production of the anti-inflammatory cytokine IL-10 in vivo. In summary, CYP11A1 initiates new pathways of vitamin D metabolism in a range of tissues and products could have important physiological roles at the local or systemic level. In the skin, CYP11A1-derived secosteroids could serve both as endogenous regulators of skin functions and as excellent candidates for treatment of hyperproliferative and inflammatory skin disorders, and skin cancer. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Cytochromes p450 and skin cancer: role of local endocrine pathways

Skin is the largest body organ forming a metabolically active barrier between external and internal environments. The metabolic barrier is composed of cytochromes P450 (CYPs) that regulate its homeostasis through activation or inactivation of biologically relevant molecules. In this review we focus our attention on local steroidogenic and secosteroidogenic systems in relation to skin cancer, e.g., prevention, attenuation of tumor progression and therapy. The local steroidogenic system is composed of locally expressed CYPs involved in local production of androgens, estrogens, gluco- and mineralo-corticosteroids from cholesterol (initiated by CYP11A1) or from steroid precursors delivered to the skin, and of their metabolism and/or inactivation. Cutaneous 7-hydroxylases (CYP7A1, CYP7B1 and CYP39) potentially can produce 7-hydroxy/oxy-steroids/sterols with modifying effects on local tumorigenesis. CYP11A1 also transforms 7-dehydrocholesterol (7DHC)→22(OH)7DHC→20,22(OH)2-7DHC→7-dehydropregnenolone, which can be further metabolized to other 5,7- steroidal dienes. These 5,7-dienal intermediates are converted by ultraviolet radiation B (UVB) into secosteroids which show pro-differentiation and anti-cancer properties. Finally, the skin is the site of activation of vitamin D3 through two alternative pathways. The classical one involves sequential hydroxylation at positions 25 and 1 to produce active 1,25(OH)2D3, which is further inactivated through hydroxylation at C24. The novel pathway is initiated by CYP11A1 with predominant production of 20(OH)D3 which is further metabolized to biologically active but non-calcemic D3-hydroxyderivatives. Classical and non-classical (novel) vitamin D analogs show pro-differentiation, anti-proliferative and anticancer properties. In addition, melatonin is metabolized by local CYPs. In conclusion cutaneously expressed CYPs have significant effects on skin physiology and pathology trough regulation of its chemical milieu.

Melatonin and its metabolites ameliorate ultraviolet B-induced damage in human epidermal keratinocytes

We investigated the protective effects of melatonin and its metabolites: 6-hydroxymelatonin (6-OHM), N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), N-acetylserotonin (NAS), and 5-methoxytryptamine (5-MT) in human keratinocytes against a range of doses (25, 50, and 75 mJ/cm2) of ultraviolet B (UVB) radiation. There was significant reduction in the generation of reactive oxygen species (50-60%) when UVB-exposed keratinocytes were treated with melatonin or its derivatives. Similarly, melatonin and its metabolites reduced the nitrite and hydrogen peroxide levels that were induced by UVB as early as 30 min after the exposure. Moreover, melatonin and its metabolites enhanced levels of reduced glutathione in keratinocytes within 1 hr after UVB exposure in comparison with control cells. Using proliferation assay, we observed a dose-dependent increase in viability of UVB-irradiated keratinocytes that were treated with melatonin or its derivatives after 48 hr. Using the dot-blot technique and immunofluorescent staining we also observed that melatonin and its metabolites enhanced the DNA repair capacity of UVB-induced pyrimidine photoproducts (6-4)or cyclobutane pyrimidine dimers generation in human keratinocytes. Additional evidence for induction of DNA repair in cells exposed to UVB and treated with the indole compounds was shown using the Comet assay. Finally, melatonin and its metabolites further enhanced expression of p53 phosphorylated at Ser-15 but not at Ser-46 or its nonphosphorylated form. In conclusion, melatonin, its precursor NAS, and its metabolites 6-OHM, AFMK, 5-MT, which are endogenously produced in keratinocytes, protect these cells against UVB-induced oxidative stress and DNA damage.