20-Hydroxyvitamin D3, a product of vitamin D3 hydroxylation by cytochrome P450scc, stimulates keratinocyte differentiation

Dual-Action Psoriasis Therapy: Antiproliferative and Immunomodulatory Effects via Self-Locking Microneedles

Psoriasis is a chronic, immune-mediated disorder characterized by immune regulation disorders and abnormal keratinocyte proliferation. Deucravacitinib (Deu), a selective oral Tyrosine Kinase 2 (TYK2) inhibitor, shows promise in treating psoriasis but may cause systemic side effects and fail to address persistent localized thickened lesions. Herein, a self-locking microneedle (MN) patch with a polyvinyl alcohol (PVA) inner ring loaded with Deu is developed, designed to penetrate the transdermal barriers and dissolve rapidly, downregulating the IL-23/IL-17 pathway and serve as the first line of defense against the spread of skin-originated inflammation. Additionally, Calcipotriol (Cal), a vitamin D derivative, is incorporated into a methacrylated hyaluronic acid (HAMA) backing layer and outer ring that mimics occlusive administration, maintaining localized skin surface retention for prolonged anti-proliferative therapy. The Deu@Cal MN demonstrates satisfactory adhesiveness due to swelling-mediated mechanical interlocking via the outer ring, ensuring targeted drug release at lesion site. Besides its effectiveness in alleviating both skin inflammation and proliferation, it inhibits the differentiation of Th17 cells in the spleen, suggesting potential to reduce systemic inflammation. These findings offer a new therapeutic approach for treating psoriasis and other autoimmune and inflammatory conditions.

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.

Vitamin D: sources, physiological role, biokinetics, deficiency, therapeutic use, toxicity, and overview of analytical methods for detection of vitamin D and its metabolites

Vitamin D has a well-known role in the calcium homeostasis associated with the maintenance of healthy bones. It increases the efficiency of the intestinal absorption of dietary calcium, reduces calcium losses in urine, and mobilizes calcium stored in the skeleton. However, vitamin D receptors are present ubiquitously in the human body and indeed, vitamin D has a plethora of non-calcemic functions. In contrast to most vitamins, sufficient vitamin D can be synthesized in human skin. However, its production can be markedly decreased due to factors such as clothing, sunscreens, intentional avoidance of the direct sunlight, or the high latitude of the residence. Indeed, more than one billion people worldwide are vitamin D deficient, and the deficiency is frequently undiagnosed. The chronic deficiency is not only associated with rickets/osteomalacia/osteoporosis but it is also linked to a higher risk of hypertension, type 1 diabetes, multiple sclerosis, or cancer. Supplementation of vitamin D may be hence beneficial, but the intake of vitamin D should be under the supervision of health professionals because overdosing leads to intoxication with severe health consequences. For monitoring vitamin D, several analytical methods are employed, and their advantages and disadvantages are discussed in detail in this review.

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 .

Machine learning-based phenotypic screening for postmitotic growth inducers uncover vitamin D3 metabolites as small molecule ribosome agonists

Objectives

To restore tissue growth without increasing the risk for cancer during aging, there is a need to identify small molecule drugs that can increase cell growth without increasing cell proliferation. While there have been numerous high‐throughput drug screens for cell proliferation, there have been few screens for post‐mitotic anabolic growth.

Materials and Methods

A machine learning (ML)‐based phenotypic screening strategy was used to discover metabolites that boost muscle growth. Western blot, qRT‐PCR and immunofluorescence staining were used to evaluate myotube hypertrophy/maturation or protein synthesis. Mass spectrometry (MS)‐based thermal proteome profiling‐temperature range (TPP‐TR) technology was used to identify the protein targets that bind the metabolites. Ribo‐MEGA size exclusion chromatography (SEC) analysis was used to verify whether the ribosome proteins bound to calcitriol.

Results

We discovered both the inactive cholecalciferol and the bioactive calcitriol are amongst the top hits that boost post‐mitotic growth. A large number of ribosomal proteins' melting curves were affected by calcitriol treatment, suggesting that calcitriol binds to the ribosome complex directly. Purified ribosomes directly bound to pure calcitriol. Moreover, we found that calcitriol could increase myosin heavy chain (MHC) protein translation and overall nascent protein synthesis in a cycloheximide‐sensitive manner, indicating that calcitriol can directly bind and enhance ribosomal activity to boost muscle growth.

Conclusion

Through the combined strategy of ML‐based phenotypic screening and MS‐based omics, we have fortuitously discovered a new class of metabolite small molecules that can directly activate ribosomes to promote post‐mitotic growth.

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.

Skin Immunosenescence and Type 2 Inflammation: A Mini-Review With an Inflammaging Perspective

Skin-resident stromal cells, including keratinocytes, fibroblasts, adipocytes, and immune cells including Langerhans cells, dendritic cells, T cells, and innate lymphoid cells, and their functional products work in concert to ensure the realization of skin barrier immunity. However, aging-induced immunosenescence predisposes the elderly to pruritic dermatoses, including type 2 inflammation-mediated. Inflammaging, characterized by chronic low level of pro-inflammatory cytokines released from senescent cells with the senescence-associated secretory phenotype (SASP), may drive immunosenescence and tangle with type 2 inflammatory dermatoses. The present mini-review summarizes current evidence on immunosenescence and type 2 inflammation in the skin and further focuses on future needs from an inflammaging perspective to clarify their complexity.

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.

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.

Knocking out the Vitamin D Receptor Enhances Malignancy and Decreases Responsiveness to Vitamin D3 Hydroxyderivatives in Human Melanoma Cells

Simple Summary

Active forms of vitamin D3, including 1,25(OH)₂D3, 20(OH)D3 and 1,20(OH)₂D3, inhibited cell proliferation, migration rate and the ability to form colonies and spheroids in the wild-type melanoma cell line, while cells with the vitamin D receptor (VDR) silenced showed an increased but not complete resistance to their action. Furthermore, silencing of the VDR in melanoma cells enhanced their proliferation as well as spheroid and colony formation and increased their migration rate. Previous clinicopathological studies have shown an inverse correlation between VDR expression, melanoma progression and poor outcome of the disease. Thus, the expression of VDR is not only necessary for the inhibition of melanoma growth by active forms of vitamin D, but the VDR can also function as a melanoma tumor suppressor gene.

Abstract

Vitamin D3 is not only involved in calcium and phosphate metabolism in humans, but it can also affect proliferation and differentiation of normal and cancer cells, including melanoma. The mechanism of the anti-cancer action of vitamin D3 is not fully understood. The nuclear vitamin D receptor (VDR) is crucial for the phenotypic effects of vitamin D hydroxyderivatives. VDR expression shows an inverse correlation with melanoma progression and poor outcome of the disease. In this study we knocked out the VDR in a human melanoma cell line using CRISPR methodology. This enhanced the proliferation of melanoma cells grown in monolayer culture, spheroids or colonies and their migration. Activated forms of vitamin D, including classical 1,25(OH)₂D3, 20(OH)D3 and 1,20(OH)₂D3, inhibited cell proliferation, migration rate and the ability to form colonies and spheroids in the wild-type melanoma cell line, while VDR KO cells showed a degree of resistance to their action. These results indicate that expression of VDR is important for the inhibition of melanoma growth induced by activated forms of vitamin D. In conclusion, based on our previous clinicopathological analyses and the current study, we suggest that the VDR can function as a melanoma tumor suppressor gene.

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.

Chlorpyrifos alters expression of enzymes involved in vitamin D3 synthesis in skin cells

Skin acts as a mechanical barrier between human body and environment. Epidermal cells are regularly exposed to many physiological and environmental stressors, such as pesticides, like chlorpyrifos (CPS). It is recognised that CPS may affect metabolism of other exo- and endogenous substances by affecting enzyme activity and expression. This study aims to investigate the effect of CPS on expression of CYP27A1, CYP27B1 and CYP24A1, the enzymes involved in synthesis and metabolism of vitamin D_3, in human keratinocytes HaCaT and human fibroblasts BJ. Synthesis of vitamin D₃ in cells was initiated by irradiating with UVB. Expression of CYP27A1, CYP27B1 and CYP24A1 was evaluated by RT-qPCR and Western blot. Our experiments revealed that expression of all tested cytochrome P450 isoforms in cells exposed to CPS changed significantly. Exposure of HaCaT keratinocytes to CPS decreased CYP27A1 mRNA levels, but increased CYP27B1 and CYP24A1 mRNA levels. This was confirmed at the protein level, except for the CYP27A1 expression. Outcome for the BJ cells was however less conclusive. Though exposure to CPS decreased CYP27A1 and CYP27B1 mRNA levels, at protein level increasing concentration of CPS and UVB intensity induced expression of CYP27A1 and CYP24A1. The expression of CYP27B1 isoform decreased in line with mRNA level. Nevertheless, it can be concluded that CPS may therefore interrupt vitamin D₃ metabolism in skin cells, but further studies are required to better understand such mechanisms.

Non-Musculoskeletal Benefits of Vitamin D beyond the Musculoskeletal System

Vitamin D, a fat-soluble prohormone, is endogenously synthesized in response to sunlight or taken from dietary supplements. Since vitamin D receptors are present in most tissues and cells in the body, the mounting understanding of the role of vitamin D in humans indicates that it does not only play an important role in the musculoskeletal system, but has beneficial effects elsewhere as well. This review summarizes the metabolism of vitamin D, the research regarding the possible risk factors leading to vitamin D deficiency, and the relationships between vitamin D deficiency and numerous illnesses, including rickets, osteoporosis and osteomalacia, muscle weakness and falls, autoimmune disorders, infectious diseases, cardiovascular diseases (CVDs), cancers, and neurological disorders. The system-wide effects of vitamin D and the mechanisms of the diseases are also discussed. Although accumulating evidence supports associations of vitamin D deficiency with physical and mental disorders and beneficial effects of vitamin D with health maintenance and disease prevention, there continue to be controversies over the beneficial effects of vitamin D. Thus, more well-designed and statistically powered trials are required to enable the assessment of vitamin D’s role in optimizing health and preventing disease.

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.

Clinical Significance of Analysis of Vitamin D Status in Various Diseases

Vitamin D plays a role not only in the proper functioning of the skeletal system and the calcium-phosphate equilibrium, but also in the immune system, the cardiovascular system and the growth and division of cells. Although numerous studies have reported on the analysis of vitamin D status in various groups of patients, the clinical significance of measurements of vitamin D forms and metabolites remains ambiguous. This article reviews the reports analyzing the status of vitamin D in various chronic states. Particular attention is given to factors affecting measurement of vitamin D forms and metabolites. Relevant papers published during recent years were identified by an extensive PubMed search using appropriate keywords. Measurement of vitamin D status proved to be a useful tool in diagnosis and progression of metabolic syndrome, neurological disorders and cancer. High performance liquid chromatography coupled with tandem mass spectrometry has become the preferred method for analyzing the various forms and metabolites of vitamin D in biological fluids. Factors influencing vitamin D concentration, including socio-demographic and biochemical factors as well as the genetic polymorphism of the vitamin D receptor, along with vitamin D transporters and enzymes participating in vitamin D metabolism should be considered as potential confounders of the interpretation of plasma total 25(OH)D concentrations.

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.

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.

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.

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.

Vitamin D and melanoma: state of the art and possible therapeutic uses

Despite the presence of several studies in literature, the real connection between vitamin D serological levels, vitamin D receptor and melanoma remains unclear, probably because of the complex correlation between vitamin D and melanoma. Indeed, UV radiations are not reported as the main risk factor for melanoma in non-sun-exposed, while systemic immunosuppression, anatomical and physiological features may contribute to malignancy. Therefore, the correlation between melanoma cells in sun-exposed areas and vitamin D, as well as vitamin D receptor could be different from the one in melanoma of sun-shielded sites. These differences may also explain the controversial results reported in the literature regarding the correlation between melanoma and vitamin D, as well as the different outcomes in melanoma patients treated with vitamin D as adjuvant therapy. The aim of this review is to highlight the most recent findings about vitamin D and melanoma, focusing on the anatomic site of the primary tumor as well as on the possible therapeutic uses of vitamin D in melanoma patients.

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.

1α,20S-Dihydroxyvitamin D3 Interacts with Vitamin D Receptor: Crystal Structure and Route of Chemical Synthesis

1α,20S-Dihydroxyvitamin D3 [1,20S(OH)₂D₃], a natural and bioactive vitamin D3 metabolite, was chemically synthesized for the first time. X-ray crystallography analysis of intermediate 15 confirmed its 1α-OH configuration. 1,20S(OH)₂D₃ interacts with the vitamin D receptor (VDR), with similar potency to its native ligand, 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] as illustrated by its ability to stimulate translocation of the VDR to the nucleus, stimulate VDRE-reporter activity, regulate VDR downstream genes (VDR, CYP24A1, TRPV6 and CYP27B1), and inhibit the production of inflammatory markers (IFNγ and IL1β). However, their co-crystal structures revealed differential molecular interactions of the 20S-OH moiety and the 25-OH moiety to the VDR, which may explain some differences in their biological activities. Furthermore, this study provides a synthetic route for the synthesis of 1,20S(OH)₂D₃ using the intermediate 1α,3β-diacetoxypregn-5-en-20-one (3), and provides a molecular and biological basis for the development of 1,20S(OH)₂D₃ and its analogs as potential therapeutic agents.

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.

Effect of 1,25(OH)2 D3 and 20(OH)D3 on interleukin-1β-stimulated interleukin-6 and -8 production by human gingival fibroblasts

BACKGROUND AND OBJECTIVE

Vitamin D-1,25(OH)₂ D₃ or 1,25D3-maintains healthy osseous tissue, stimulates the production of the antimicrobial peptide cathelicidin and has anti-inflammatory effects, but it can cause hypercalcemia. Evidence links diminished serum levels of 1,25D3 with increased gingival inflammation. Periodontitis progression is associated with increased local production of inflammatory mediators by immune cells and gingival fibroblasts. These include interleukin (IL)-6, a regulator of osteoclastic bone resorption, and the neutrophil chemoattractant IL-8, both regulated by signaling pathways, including NF-κB and MAPK/AP-1. The objectives were to determine the effects of 1,25D3 or a non-calcemic analog, 20-hydroxyvitamin D₃ -20(OH)D₃ or 20D3-on IL-1β-stimulated IL-6 and IL-8 production, and NF-κB and MAPK/AP-1 activation, by human gingival fibroblasts.

MATERIAL AND METHODS

Human gingival fibroblasts were incubated ± IL-1β, with or without exposure to 1,25D3 or 20D3. IL-6 and IL-8 in culture supernatants were measured by enzyme-linked immunosorbent assay. NF-κB (p65) and AP-1 (phospho-cJun) and were measured in nuclear extracts via binding to specific oligonucleotides. Data were analyzed using ANOVA and Scheffe's F procedure for post hoc comparisons.

RESULTS

IL-1β-stimulated IL-6 and IL-8 levels were both significantly inhibited (40%-60%) (P<.045) by 1,25D3, but not 20D3 (0%-15% inhibition, not statistically significant). Both 1,25D3 and 20D3 significantly and similarly inhibited IL-1β-stimulated nuclear levels of p65 and phospho-cJun (P<.02).

CONCLUSION

Reduction of the activation of NF-κB and AP-1 alone is not able to inhibit strongly the IL-1β stimulated IL-6 and IL-8 gene expression. 1,25D3 but not 20D3 may affect some of the many other factors/processes/pathways that in turn regulate the expression of these genes. However, the results suggest that topical application of ligands of the vitamin D receptor may be useful in the local treatment of periodontitis while reducing adverse systemic effects.

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

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

Isolation of All CD44 Transcripts in Human Epidermis and Regulation of Their Expression by Various Agents

CD44, a cell surface proteoglycan, is involved in many biological events. CD44 transcripts undergo complex alternative splicing, resulting in many functionally distinct isoforms. To date, however, the nature of these isoforms in human epidermis has not been adequately determined. In this study, we isolated all CD44 transcripts from normal human epidermis, and studied how their expressions are regulated. By RT-PCR, we found that a number of different CD44 transcripts were expressed in human epidermis, and we obtained all these transcripts from DNA bands in agarose and acrylamide gels by cloning. Detailed sequence analysis revealed 18 CD44 transcripts, 3 of which were novel. Next, we examined effects of 10 different agents on the expression of CD44 transcripts in cultured human keratinocytes, and found that several agents, particularly epidermal growth factor, hydrogen peroxide, phorbol 12-myristate 13-acetate, retinoic acid, calcium and fetal calf serum differently regulated their expressions in various patterns. Furthermore, normal and malignant keratinocytes were found to produce different CD44 transcripts upon serum stimulation and subsequent starvation, suggesting that specific CD44 isoforms are involved in tumorigenesis via different CD44-mediated biological pathways.

25-Hydroxyvitamin D and Parathyroid Hormone Levels Are Independently Associated with the Hemoglobin A1c Level of Korean Type 2 Diabetic Patients: The Dong-Gu Study

In type 2 diabetic patients, the relationships between 25-hydroxyvitamin D and parathyroid hormone levels, and glycemic control, remain unclear. We evaluated associations between 25-hydroxyvitamin D, parathyroid hormone, and hemoglobin A_1c levels after adjusting for other covariates, including log transformed 25-hydroxyvitamin D levels and log transformed parathyroid hormone levels, in Korean patients with type 2 diabetes. In total, 1,175 patients with type 2 diabetes were selected from 8,857 individuals who completed the baseline survey of the Dong-gu study, conducted in Korea from 2007 to 2010. After adjusting for other covariates, we found that the mean hemoglobin A_1c level was inversely associated with the 25-hydroxyvitamin D level (Q1: 7.47% [7.30–7.63], Q2: 7.25% [7.09–7.40], Q3: 7.17% [7.02–7.32], Q4: 7.19% [7.02–7.35]; p for trend = 0.021, p for between groups = 0.050) and the parathyroid hormone level (Q1: 7.35% [7.19–7.51], Q2: 7.34% [7.19–7.50], Q3: 7.28% [7.13–7.43], Q4: 7.09% [6.94–7.24]; p for trend = 0.022, p for between groups = 0.048). However, the mean fasting glucose level was not associated with either the 25-hydroxyvitamin D or parathyroid hormone level. In conclusion, inverse associations were evident between hemoglobin A_1c, 25-hydroxyvitamin D and parathyroid hormone levels in Korean patients with type 2 diabetes. The associations remained significant after adjusting for other covariates, including the log transformed 25-hydroxyvitamin D levels and log transformed parathyroid hormone levels.

Vitamin D derivatives enhance cytotoxic effects of H2O2 or cisplatin on human keratinocytes

Although the skin production of vitamin D is initiated by ultraviolet radiation type B (UVB), the role vitamin D plays in antioxidative or pro-oxidative responses remains to be elucidated. We have used immortalized human HaCaT keratinocytes as a model of proliferating epidermal cells to test the influence of vitamin D on cellular response to H2O2 or the anti-cancer drug, cisplatin. Incubation of keratinocytes with 1,25(OH)2D3 or its low calcemic analogues, 20(OH)D3, 21(OH)pD or calcipotriol, sensitized cells to ROS resulting in more potent inhibition of keratinocyte proliferation by H2O2 in the presence of vitamin D compounds. These results were supported by cell cycle and apoptosis analyses, and measurement of the mitochondrial transmembrane potentials (MMP), however some unique properties of individual secosteroids were observed. Furthermore, in HaCaT keratinocytes treated with H2O2, 1,25(OH)2D3, 21(OH)pD and calcipotriol stimulated the expression of SOD1 and CAT genes, but not SOD2, indicating a possible role of mitochondria in ROS-modulated cell death. 1,25(OH)2D3 also showed a short-term, protective effect on HaCaT keratinocytes, as exemplified by the inhibition of apoptosis and the maintenance of MMP. However, with prolonged incubation with H2O2 or cisplatin, 1,25(OH)2D3 caused an acceleration in the death of the keratinocytes. Therefore, we propose that lead vitamin D derivatives can protect the epidermis against neoplastic transformation secondary to oxidative or UV-induced stress through activation of vitamin D-signaling. Furthermore, our data suggest that treatment with low calcemic vitamin D analogues or the maintenance of optimal level of vitamin D by proper supplementation, can enhance the anticancer efficacy of cisplatin.

Hydroxylation of 20-hydroxyvitamin D3 by human CYP3A4

20S-Hydroxyvitamin D3 [20(OH)D3] is the biologically active major product of the action of CYP11A1 on vitamin D3 and is present in human plasma. 20(OH)D3 displays similar therapeutic properties to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], but without causing hypercalcaemia and therefore has potential for development as a therapeutic drug. CYP24A1, the kidney mitochondrial P450 involved in inactivation of 1,25(OH)2D3, can hydroxylate 20(OH)D3 at C24 and C25, with the products displaying more potent inhibition of melanoma cell proliferation than 20(OH)D3. CYP3A4 is the major drug-metabolising P450 in liver endoplasmic reticulum and can metabolise other active forms of vitamin D, so we examined its ability to metabolise 20(OH)D3. We found that CYP3A4 metabolises 20(OH)D3 to three major products, 20,24R-dihydroxyvitamin D3 [20,24R(OH)2D3], 20,24S-dihydroxyvitamin D3 [20,24S(OH)2D3] and 20,25-dihydroxyvitamin D3 [20,25(OH)2D3]. 20,24R(OH)2D3 and 20,24S(OH)2D3, but not 20,25(OH)2D3, were further metabolised to trihydroxyvitamin D3 products by CYP3A4 but with low catalytic efficiency. The same three primary products, 20,24R(OH)2D3, 20,24S(OH)2D3 and 20,25(OH)2D3, were observed for the metabolism of 20(OH)D3 by human liver microsomes, in which CYP3A4 is a major CYP isoform present. Addition of CYP3A family-specific inhibitors, troleandomycin and azamulin, almost completely inhibited production of 20,24R(OH)2D3, 20,24S(OH)2D3 and 20,25(OH)2D3 by human liver microsomes, further supporting that CYP3A4 plays the major role in 20(OH)D3 metabolism by microsomes. Since both 20,24R(OH)2D3 and 20,25(OH)2D3 have previously been shown to display enhanced biological activity in inhibiting melanoma cell proliferation, our results show that CYP3A4 further activates, rather than inactivates, 20(OH)D3.

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.

Total synthesis of biologically active 20S-hydroxyvitamin D3

A total synthetic strategy of 20S-hydroxyvitamin D3 [20S-(OH)D3] involving modified synthesis of key intermediates 7 and 12, Grignard reaction to stereoselectively generate 20S-OH and Wittig-Horner coupling to establish D3 framework, was completed in 16 steps with an overall yield of 0.4%. The synthetic 20S-(OH)D3 activated vitamin D receptor (VDR) and initiated the expression of downstream genes. In addition, 20S-(OH)D3 showed similar inhibitory potency as calcitriol [1,25(OH)2D3] on proliferation of melanoma cells.

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.

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.

Differential antitumor effects of vitamin D analogues on colorectal carcinoma in culture

Colorectal cancer (CRC) is an emerging global problem with the rapid increase in its incidence being associated with an unhealthy lifestyle. Epidemiological studies have shown that decreased levels of vitamin D3 significantly increases the risk of CRC. Furthermore, negative effects of vitamin D3 deficiency can be compensated by appropriate supplementation. Vitamin D3 was shown to inhibit growth and induce differentiation of cancer cells, however, excessive vitamin D3 intake leads to hypercalcemia. Thus, development of efficient vitamin D3 analogues with limited impact on calcium homeostasis is an important scientific and clinically relevant task. The aims of the present study were to compare the antiproliferative potential of classic vitamin D3 metabolites (1α,25(OH)2D3 and 25(OH)D3) with selected low calcemic analogues (calcipotriol and 20(OH)D3) on CRC cell lines and to investigate the expression of vitamin D-related genes in CRC cell lines and clinical samples. Vitamin D3 analogues exerted anti-proliferative effects on all CRC cell lines tested. Calcipotriol proved to be as potent as 1α,25(OH)2D3 and had more efficacy than 20-hydroxyvitamin D3. In addition, the analogs tested effectively inhibited the formation of colonies in Matrigel. The expression of genes involved in 1α,25(OH)2D3 signaling and metabolism varied in cell lines analysed, which explains in part their different sensitivities to the various analogues. In CRC biopsies, there was decreased VDR expression in tumor samples in comparison to the surgical margin and healthy colon samples (p<0.01). The present study indicates that vitamin D3 analogues which have low calcemic activity, such as calcipotriol or 20(OH)D3, are very promising candidates for CRC therapy. Moreover, expression profiling of vitamin D-related genes is likely to be a powerful tool in the planning of anticancer therapy. Decreased levels of VDR and increased CYP24A1 expression in clinical samples underline the importance of deregulation of vitamin D pathways in the development of CRC.

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'.

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.

CYP11A1 in skin: an alternative route to photoprotection by vitamin D compounds

Topical 1,25-dihydroxyvitamin D (1,25D) and other vitamin D compounds have been shown to protect skin from damage by ultraviolet radiation (UVR) in a process that requires the vitamin D receptor. Yet, while mice which do not express the vitamin D receptor are more susceptible to photocarcinogenesis, mice unable to 1α-hydroxylate 25-hydroxyvitamin D to form 1,25D do not show increased susceptibility to UVR-induced skin tumors. A possible explanation is that an alternative pathway, which does not involve 1α-hydroxylation, may produce photoprotective compounds from vitamin D. The cholesterol side chain cleavage enzyme CYP11A1 is expressed in skin and produces 20-hydroxyvitamin D3 (20OHD) as a major product of vitamin D3. We examined whether topical 20OHD would affect UVR-induced DNA damage, inflammatory edema or immune suppression produced in Skh:hr1 mice. Photoprotection by 20OHD at 23 or 46pmol/cm(2) against cyclobutane pyrimidine dimers (DNA lesions) after UVR in mice was highly effective, up to 98±0.8%, (p<0.001) and comparable to that of 1,25D. Sunburn edema measured as skinfold thickness 24h after UVR was also significantly reduced by 20OHD (p<0.001). In studies of contact hypersensitivity (CHS), which is suppressed by UVR, topical application of 20OHD to mice protected against UVR-induced immunosuppression (p<0.05), similar to the effect of 1,25D at similar doses (46±0.6% protection with 20OHD, 44±0.5% with 1,25D). Both UVR-induced DNA damage and immunosuppression contribute to increased susceptibility to UVR-induced skin tumors. This study indicates a potentially anti-photocarcinogenic role of the naturally occurring vitamin D metabolite, 20OHD, which does not depend on 1α-hydroxylation for generation. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

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'.

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.

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'.