Selective ability of rat 7-Dehydrocholesterol reductase (DHCR7) to act on some 7-Dehydrocholesterol metabolites but not on lumisterol metabolites

Malignant Melanoma: An Overview, New Perspectives, and Vitamin D Signaling

Melanoma, originating through malignant transformation of melanin-producing melanocytes, is a formidable malignancy, characterized by local invasiveness, recurrence, early metastasis, resistance to therapy, and a high mortality rate. This review discusses etiologic and risk factors for melanoma, diagnostic and prognostic tools, including recent advances in molecular biology, omics, and bioinformatics, and provides an overview of its therapy. Since the incidence of melanoma is rising and mortality remains unacceptably high, we discuss its inherent properties, including melanogenesis, that make this disease resilient to treatment and propose to use AI to solve the above complex and multidimensional problems. We provide an overview on vitamin D and its anticancerogenic properties, and report recent advances in this field that can provide solutions for the prevention and/or therapy of melanoma. Experimental papers and clinicopathological studies on the role of vitamin D status and signaling pathways initiated by its active metabolites in melanoma prognosis and therapy are reviewed. We conclude that vitamin D signaling, defined by specific nuclear receptors and selective activation by specific vitamin D hydroxyderivatives, can provide a benefit for new or existing therapeutic approaches. We propose to target vitamin D signaling with the use of computational biology and AI tools to provide a solution to the melanoma problem.

Effects of Long-Term High-Ergosterol Intake on the Cholesterol and Vitamin D Biosynthetic Pathways of Rats Fed a High-Fat and High-Sucrose Diet

Dyslipidemia is a lifestyle-related (physical inactivity or obesity) disease; therefore, dietary foods that can easily be consumed in daily life is important to prevent dyslipidemia. Ergosterol, a precursor of vitamin D2, is a fungal sterol present in the membranes of edible mushrooms and other fungi. Ergosterol is converted to brassicasterol by 7-dehydrocholesterol reductase (DHCR7), a cholesterol biosynthesis enzyme that converts 7-dehydrocholesterol (a precursor of vitamin D3) into cholesterol. Previously, we reported that ergosterol increases 7-dehydrocholesterol, decreases cholesterol levels by competitive effect of DHCR7, and reduces DHCR7 mRNA and protein levels in human HepG2 hepatoma cells. Here, we investigated the effects of long-term high ergosterol intake on the cholesterol, vitamin D2, and D3 biosynthetic pathways of rats fed a high-fat and high-sucrose (HFHS) diet using GC-MS and LC with tandem mass spectrometry. In HFHS rats, oral ergosterol administration for 14 weeks significantly decreased plasma low-density lipoprotein cholesterol, total bile acid, and cholesterol precursor (squalene and desmosterol) levels and increased 7-dehydrocholesterol levels compared to HFHS rats without ergosterol. Ergosterol, brassicasterol, and vitamin D2 were detected, cholesterol levels were slightly decreased, and levels of vitamin D3 and its metabolites were slightly increased in rats fed HFHS with ergosterol. These results showed that ergosterol increased vitamin D2 levels, inhibited the cholesterol biosynthetic pathway, and possibly promoted vitamin D3 biosynthesis in vivo. Therefore, daily ergosterol intake may aid in the prevention of dyslipidemia.

Metabolism of Lumisterol2 by CYP27A1

Lumisterol2 (L2) is a photoproduct of UVB action on the fungal membrane sterol, ergosterol. Like vitamin D2, it is present in edible mushrooms, especially after UV irradiation. Lumisterol3 is similarly produced in human skin from 7-dehydrocholesterol by UVB and can be converted to hydroxy-metabolites by CYP27A1 and CYP11A1. These products are biologically active on human cells with actions that include photoprotection and inhibition of proliferation. The aim of this study was to test the ability of CYP11A1 and CYP27A1 to metabolise L2. Purified CYP27A1 was found to efficiently metabolise L2 to three major products and several minor products, whilst CYP11A1 did not act appreciably on L2. The three major products of CYP27A1 action on L2 were identified by mass spectrometry and NMR as 24-hydroxyL2, 27-hydroxyL2 and 28-hydroxyL2. Minor products included two dihydroxy L2 species, one which was identified as 24,27(OH)2L2, and another metabolite with one oxo and one hydroxyl group added. A comparison on the kinetics of the metabolism of L2 by CYP27A1 with that of the structurally similar compounds, L3 and ergosterol, was carried out with substrates incorporated into phospholipid vesicles. CYP27A1 displayed a 12-fold lower Km with L2 as substrate compared to L3 and a 5-fold lower turnover number (kcat), resulting in a 2.2 fold higher catalytic efficiency (kcat/Km) for L2 metabolism. L2 was a much better substrate for CYP27A1 than its precursor, ergosterol, with a catalytic efficiency 18-fold higher. The major CYP27A1-derived hydroxy-L2 products, 24-hydroxyL2, 27-hydroxyL2 and 28-hydroxyL2, inhibited the proliferation of melanoma and epidermoid cancer cell lines. In conclusion, this study shows that L2 is not metabolized appreciably by CYP11A1, but it is a good substrate for CYP27A1 which hydroxylates its side chain to produce 3 major products that display anti-proliferative activity on skin-cancer cell lines.

The Over-Irradiation Metabolite Derivative, 24-Hydroxylumister-ol3, Reduces UV-Induced Damage in Skin

The hormonal form of vitamin D₃, 1,25(OH)₂D₃, reduces UV-induced DNA damage. UV exposure initiates pre-vitamin D₃ production in the skin, and continued UV exposure photoisomerizes pre-vitamin D₃ to produce "over-irradiation products" such as lumisterol₃ (L₃). Cytochrome P450 side-chain cleavage enzyme (CYP11A1) in skin catalyzes the conversion of L₃ to produce three main derivatives: 24-hydroxy-L₃ [24(OH)L₃], 22-hydroxy-L₃ [22(OH)L₃], and 20,22-dihydroxy-L₃ [20,22(OH)L₃]. The current study investigated the photoprotective properties of the major over-irradiation metabolite, 24(OH)L₃, in human primary keratinocytes and human skin explants. The results indicated that treatment immediately after UV with either 24(OH)L₃ or 1,25(OH)₂D₃ reduced UV-induced cyclobutane pyrimidine dimers and oxidative DNA damage, with similar concentration response curves in keratinocytes, although in skin explants, 1,25(OH)₂D₃ was more potent. The reductions in DNA damage by both compounds were, at least in part, the result of increased DNA repair through increased energy availability via increased glycolysis, as well as increased DNA damage recognition proteins in the nucleotide excision repair pathway. Reductions in UV-induced DNA photolesions by either compound occurred in the presence of lower reactive oxygen species. The results indicated that under in vitro and ex vivo conditions, 24(OH)L₃ provided photoprotection against UV damage similar to that of 1,25(OH)₂D₃.

DHCR7 promotes tumorigenesis via activating PI3K/AKT/mTOR signalling pathway in bladder cancer

Bladder cancer (BCa) is a common malignancy with uncertain molecular mechanism. 7-dehydrocholesterol reductase (DHCR7), the enzyme of mammalian sterol biosynthesis, plays important roles in several types of cancers but its specific function in BCa is still unknown. The current study aimed to determine the bioinformatic characteristics and biological functions of DHCR7 in BCa. Sequencing results and clinical data from online public databases, human BCa tissues and matched noncancerous tissues, xenograft nude mice, DHCR7 deficiency and overexpression BCa cell (T24 and EJ) models were used. Several bioinformatics analyses were made, qRT-PCR, Western-blotting, flow cytometry, immunohistochemistry (IHC), MTT assay, wound healing and cell invasion assays were performed. It was found that DHCR7 was upregulated in BCa as an independent risk factor, and the expression of DHCR7 was associated with BCa grade and stage, finally resulted in poor prognosis. We further demonstrated that DHCR7 overexpression could accelerate the G0/G1 phase to accelerate the growth of tumor cells, antagonize cell apoptosis, and enhance the invasion and migration capacity, as well as EMT process via PI3K/AKT/mTOR signalling pathway, which could be completely reversed by DHCR7 knockdown. Finally, DHCR7 deficiency significantly decreased tumorigenesis in vivo. Our novel data demonstrated that DHCR7 could modulate BCa tumorigenesis in vitro and in vivo via PI3K/AKT/mTOR signalling pathway. It is suggested that DHCR7 might become a molecular target for the diagnosis and treatment of BCa.

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 .

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.