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/ß, 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/ß-catenin signaling. Thus, they protect skin integrity and physiology.

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

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

Metabolic activation of tachysterol3 to biologically active hydroxyderivatives that act on VDR, AhR, LXRs, and PPARγ receptors.

CYP11A1 and CYP27A1 hydroxylate tachysterol3 , a photoproduct of previtamin D3 , producing 20S-hydroxytachysterol3 [20S(OH)T3 ] and 25(OH)T3 , respectively. Both metabolites were detected in the human epidermis and serum. Tachysterol3 was also detected in human serum at a concentration of 7.3 ± 2.5 ng/ml. 20S(OH)T3 and 25(OH)T3 inhibited the proliferation of epidermal keratinocytes and dermal fibroblasts and stimulated the expression of differentiation and anti-oxidative genes in keratinocytes in a similar manner to 1,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ]. They acted on the vitamin D receptor (VDR) as demonstrated by image flow cytometry and the translocation of VDR coupled GFP from the cytoplasm to the nucleus of melanoma cells, as well as by the stimulation of CYP24A1 expression. Functional studies using a human aryl hydrocarbon receptor (AhR) reporter assay system revealed marked activation of AhR by 20S(OH)T3 , a smaller effect by 25(OH)T3 , and a minimal effect for their precursor, tachysterol3 . Tachysterol3 hydroxyderivatives showed high-affinity binding to the ligan-binding domain (LBD) of the liver X receptor (LXR) α and ß, and the peroxisome proliferator-activated receptor γ (PPARγ) in LanthaScreen TR-FRET coactivator assays. Molecular docking using crystal structures of the LBDs of VDR, AhR, LXRs, and PPARγ revealed high docking scores for 20S(OH)T3 and 25(OH)T3 , comparable to their natural ligands. The scores for the non-genomic-binding site of the VDR were very low indicating a lack of interaction with tachysterol3 ligands. Our identification of endogenous production of 20S(OH)T3 and 25(OH)T3 that are biologically active and interact with VDR, AhR, LXRs, and PPARγ, provides a new understanding of the biological function of tachysterol3 .

Safety Assessment of Vitamin D and Its Photo-Isomers in UV-Irradiated Baker's Yeast.

Vitamin D deficiency due to, e.g., nutritional and life style reasons is a health concern that is gaining increasing attention over the last two decades. Vitamin D3, the most common isoform of vitamin D, is only available in food derived from animal sources. However, mushrooms and yeast are rich in ergosterol. This compound can be converted into vitamin D2 by UV-light, and therefore act as a precursor for vitamin D. Vitamin D2 from UV-irradiated mushrooms has become an alternative source of vitamin D, especially for persons pursuing a vegan diet. UV-irradiated baker's yeast (Saccharomyces cerevisiae) for the production of fortified yeast-leavened bread and baked goods was approved as a Novel Food Ingredient in the European Union, according to Regulation (EC) No. 258/97. The Scientific Opinion provided by the European Food Safety Authority Panel on Dietetic Products, Nutrition, and Allergies has assessed this Novel Food Ingredient as safe under the intended nutritional use. However, recent findings on the formation of side products during UV-irradiation, e.g., the photoproducts tachysterol and lumisterol which are compounds with no adequate risk assessment performed, have only been marginally considered for this EFSA opinion. Furthermore, proceedings in analytics can provide additional insights, which might open up new perspectives, also regarding the bioavailability and potential health benefits of vitamin D-fortified mushrooms and yeast. Therefore, this review is intended to give an overview on the current status of UV irradiation in mushrooms and yeast in general and provide a detailed assessment on the potential health effects of UV-irradiated baker's yeast.

Degradation studies of cholecalciferol (vitamin D3) using HPLC-DAD, UHPLC-MS/MS and chemical derivatization.

In any food fortification program, the stability of added micronutrients is an important factor. Cholecalciferol or vitamin D3 is known to isomerise under various conditions, thereby making its analysis challenging. In the current study, the effects of different parameters, such as temperature, iodine, acidic conditions, and oxidation, on the isomerisation of vitamin D3 were studied using HPLC-DAD and UHPLC-MS/MS. Vitamin D3 thermally and reversibly transforms to pre-vitamin D3 type isomers. In the presence of iodine, cis/trans isomerisation of both cholecalciferol and pre-vitamin D3 takes place to form trans-vitamin D3 and tachysterol, respectively. Another isomer, isotachysterol, was formed under acidic conditions. The different rates of reaction of these products with a dienophile through the Diels-Alder reaction confirmed the formation of vitamin D3 isomerisation products. The derivatization enhanced the ionisation efficiency of vitamin D3 and its isomers in UHPLC-MS/MS and improved the separation and fragmentation enabling sensitive detection.

Environmental determinants of previtamin D synthesis in the United Arab Emirates.

Despite abundant sunshine throughout the year, vitamin D deficiency is endemic in the UAE. Solar radiation within the UVB range of the spectrum is required for the photosynthesis of previtamin D3 in the skin. Atmospheric transmission of UVB is strongly influenced by atmospheric conditions and solar zenith angle. We investigated the effects of diurnal and seasonal variation on the availability of sufficient UVB radiation for adequate previtamin D3 synthesis using an established in vitro model. Borosilicate ampoules of 7-dehydrocholesterol, the precursor of previtamin D3, in ethanol (50 µg/mL) were exposed to direct sunlight in an urban area of Abu Dhabi, at one hourly intervals between 0800 and 1700, on one day of each month over a period of one year. Conversion to previtamin D3, vitamin D3 and metabolically inactive photoisomers was analyzed using high performance liquid chromatography. The efficiency of 7-dehydrocholesterol conversion to previtamin D3 varied estimated UVB intensity. At the latitude of Abu Dhabi (24.2 N) previtamin D3 synthesis can occur throughout the year. However very little if any previtamin D3 was produced before 0900 hrs.and after 1600 hrs. Local conditions in Abu Dhabi are likely sufficient to maintain vitamin D levels throughout the year given adequate sun exposure.

Photoisomerization of Pre- and Provitamin D3 in EPA at 77 K: One-Bond-Twist, Not Hula-Twist.

The photoisomerizations of previtamin D3 (Pre) and provitamin D3 (Pro) in EPA at 77 K were monitored using fluorescence spectroscopy. In the glassy EPA medium equilibrated tachysterol (Tachy) exists as a mixture of three conformers, the major of which we assign to s-trans,s-cis- and s-cis,s-cis-conformers (tEc- and cEc-Tachy). By contrast, Pre exists exclusively as the s-cis,s-cis-conformer (cZc-Pre) and undergoes cis → trans photoisomerization to cEc-Tachy. Light-induced ring-opening of Pro gives three Pre conformers, the major of which is tZc-Pre instead of the expected cZc-Pre. Curve resolution based on singular value decomposition yields the fluorescence spectra of the conformers. Structural assignments are based on experimental and theoretical evidence showing that the s-cis,s-cis-conformers of Pre and Tachy absorb UV light to the red of s-trans-s-cis-conformers. The photoisomerizations of tZc- and cZc-Pre in EPA proceed by the one bond twist (OBT) mechanism to give tEc- and cEc-Tachy, respectively.