The vitamin D receptor is present in caveolae-enriched plasma membranes and binds 1 alpha,25(OH)2-vitamin D3 in vivo and in vitro

Genomic and non-genomic action of vitamin D on ion channels - Targeting mitochondria

Recent studies revealed that mitochondria are not only a place of vitamin D3 metabolism but also direct or indirect targets of its activities. This review summarizes current knowledge on the regulation of ion channels from plasma and mitochondrial membranes by the active form of vitamin D3 (1,25(OH)2D3). 1,25(OH)2D3, is a naturally occurring hormone with pleiotropic activities; implicated in the modulation of cell differentiation, and proliferation and in the prevention of various diseases, including cancer. Many experimental data indicate that 1,25(OH)2D3 deficiency induces ionic remodeling and 1,25(OH)2D3 regulates the activity of multiple ion channels. There are two main theories on how 1,25(OH)2D3 can modify the function of ion channels. First, describes the involvement of genomic pathways of response to 1,25(OH)2D3 in the regulation of the expression of the genes encoding channels, their auxiliary subunits, or additional regulators. Interestingly, intracellular ion channels, like mitochondrial, are encoded by the same genes as plasma membrane channels. Therefore, the comprehensive genomic regulation of the channels from these two different cellular compartments we analyzed using a bioinformatic approach. The second theory explores non-genomic pathways of vitamin D3 activities. It was shown, that 1,25(OH)2D3 indirectly regulates enzymes that impact ion channels, change membrane physical properties, or directly bind to channel proteins. In this article, the involvement of genomic and non-genomic pathways regulated by 1,25(OH)2D3 in the modulation of the levels and activity of plasma membrane and mitochondrial ion channels was investigated by an extensive review of the literature and analysis of the transcriptomic data using bioinformatics.

Vitamin D and reproductive disorders: a comprehensive review with a focus on endometriosis

Vitamin D is a fat-soluble steroid hormone that was initially known only for regulating calcium and phosphorus levels and maintaining bone health. However, it was later discovered that many organs express vitamin D metabolizing enzymes and have a ligand for vitamin D, which regulates the expression of an extensive assortment of genes. As a result, vitamin D is indispensable for the proper function of organs, and its deficiency is believed to be a critical factor in symptoms and disorders such as cardiovascular diseases, autoimmune diseases, and cancers. The significance of vitamin D in reproductive tissues was recognized later, and studies have revealed its crucial role in male and female fertility, as well as proper reproductive function during pregnancy. Vitamin D deficiency has been identified as a risk factor for infertility, gonadal cancers, pregnancy complications, polycystic ovary syndrome, and endometriosis. However, data investigating the association between vitamin D levels and reproductive disorders, including endometriosis, have encountered inconsistencies. Therefore, the present study aims to review existing research on the effect of vitamin D on proper reproductive function, and the role of deficiency in reproductive diseases and specifically focuses on endometriosis.

The vitamin D receptor agonist EB1089 can exert its antiviral activity independently of the vitamin D receptor

Vitamin D has been shown to have antiviral activity in a number of different systems. However, few studies have investigated whether the antiviral activity is exerted through the vitamin D receptor (VDR). In this study, we investigated whether the antiviral activity of a vitamin D receptor agonist (EB1089) towards dengue virus (DENV) was modulated by VDR. To undertake this, VDR was successively overexpressed, knocked down and retargeted through mutation of the nuclear localization signal. In no case was an effect seen on the level of the antiviral activity induced by EB1089, strongly indicating that the antiviral activity of EB1089 is not exerted through VDR. To further explore the antiviral activity of EB1089 in a more biologically relevant system, human neural progenitor cells were differentiated from induced pluripotent stem cells, and infected with Zika virus (ZIKV). EB1089 exerted a significant antiviral effect, reducing virus titers by some 2Log10. In support of the results seen with DENV, no expression of VDR at the protein level was observed. Collectively, these results show that the vitamin D receptor agonist EB1089 exerts its antiviral activity independently of VDR.

Vitamin D receptor (VDR) on the cell membrane of mouse macrophages participates in the formation of lipopolysaccharide tolerance: mVDR is related to the effect of artesunate to reverse LPS tolerance

It is unclear whether membrane vitamin D receptor (mVDR) exists on the macrophage membrane or whether mVDR is associated with lipopolysaccharide (LPS) tolerance. Herein, we report that interfering with caveolae and caveolae-dependent lipid rafts inhibited the formation of LPS tolerance. VDR was detected as co-localized with membrane molecular markers. VDR was detected on the cell membrane and its level was higher in LPS-tolerant cells than that in only LPS treatment cells. Anti-VDR antibodies could abolish the effect of artesunate (AS) to reverse LPS tolerance, and the wild-type peptides (H397 and H305) of VDR, but not the mutant peptide (H397D and H305A), led to the loss of AS's effect. AS decreased the mVDR level in LPS-tolerant cells. In vivo, AS significantly reduced VDR level in the lung tissue of LPS-tolerant mice. In summary, mVDR exists on the cell membrane of macrophages and is closely associated with the formation of LPS tolerance and the effects of AS. Video Abstract.

Vitamin D-Mediated Regulation of Intestinal Calcium Absorption

Vitamin D is a critical regulator of calcium and bone homeostasis. While vitamin D has multiple effects on bone and calcium metabolism, the regulation of intestinal calcium (Ca) absorption efficiency is a critical function for vitamin D. This is necessary for optimal bone mineralization during growth, the protection of bone in adults, and the prevention of osteoporosis. Intestinal Ca absorption is regulated by 1,25 dihydroxyvitamin D (1,25(OH)₂ D), a hormone that activates gene transcription following binding to the intestinal vitamin D receptor (VDR). When dietary Ca intake is low, Ca absorption follows a vitamin-D-regulated, saturable pathway, but when dietary Ca intake is high, Ca absorption is predominately through a paracellular diffusion pathway. Deletion of genes that mediate vitamin D action (i.e., VDR) or production (CYP27B1) eliminates basal Ca absorption and prevents the adaptation of mice to low-Ca diets. Various physiologic or disease states modify vitamin-D-regulated intestinal absorption of Ca (enhanced during late pregnancy, reduced due to menopause and aging).

The role of bile acids in carcinogenesis

Bile acids are soluble derivatives of cholesterol produced in the liver that subsequently undergo bacterial transformation yielding a diverse array of metabolites. The bulk of bile acid synthesis takes place in the liver yielding primary bile acids; however, other tissues have also the capacity to generate bile acids (e.g. ovaries). Hepatic bile acids are then transported to bile and are subsequently released into the intestines. In the large intestine, a fraction of primary bile acids is converted to secondary bile acids by gut bacteria. The majority of the intestinal bile acids undergo reuptake and return to the liver. A small fraction of secondary and primary bile acids remains in the circulation and exert receptor-mediated and pure chemical effects (e.g. acidic bile in oesophageal cancer) on cancer cells. In this review, we assess how changes to bile acid biosynthesis, bile acid flux and local bile acid concentration modulate the behavior of different cancers. Here, we present in-depth the involvement of bile acids in oesophageal, gastric, hepatocellular, pancreatic, colorectal, breast, prostate, ovarian cancer. Previous studies often used bile acids in supraphysiological concentration, sometimes in concentrations 1000 times higher than the highest reported tissue or serum concentrations likely eliciting unspecific effects, a practice that we advocate against in this review. Furthermore, we show that, although bile acids were classically considered as pro-carcinogenic agents (e.g. oesophageal cancer), the dogma that switch, as lower concentrations of bile acids that correspond to their serum or tissue reference concentration possess anticancer activity in a subset of cancers. Differences in the response of cancers to bile acids lie in the differential expression of bile acid receptors between cancers (e.g. FXR vs. TGR5). UDCA, a bile acid that is sold as a generic medication against cholestasis or biliary surge, and its conjugates were identified with almost purely anticancer features suggesting a possibility for drug repurposing. Taken together, bile acids were considered as tumor inducers or tumor promoter molecules; nevertheless, in certain cancers, like breast cancer, bile acids in their reference concentrations may act as tumor suppressors suggesting a Janus-faced nature of bile acids in carcinogenesis.

Vitamin D in dairy cows: metabolism, status and functions in the immune system

The function of vitamin D in calcium homoeostasis in dairy cows, such as in other vertebrates, is known for many years. In recent years, new and interesting, non-classical functions of vitamin D have been elucidated, including effects on the immune system. The major aim of this review is to provide an overview of effects of vitamin D or its metabolites on the immune system in dairy cows. The first part of the review provides an overview of vitamin D metabolism, with particular reference to the role of various proteins (25- and 1-hydroxylases, vitamin D binding protein, vitamin D receptor) in vitamin D signalling. The second part deals with the role of the concentration of 25-hydroxyvitamin D [25(OH)D] in plasma as an indicator of the vitamin D status in dairy cows, and its dependence on sunlight exposure and dietary vitamin D supplementation. In this part also the "free hormone hypothesis" is discussed, indicating that the concentration of free 25(OH)D might be a more valid indicator of the vitamin D status than the concentration of total 25(OH)D. The third part deals with classical and the non-classical functions of vitamin D. Among the non-classical functions which are based on an autocrine vitamin D signalling, particular reference is given to the effects of vitamin D and vitamin D metabolites on the immune system in bovine immune cells and in dairy cows. Recent findings provide some indication that vitamin D or its metabolite 25(OH)D could enhance the immune function in dairy cows and be useful for the prevention and therapy of mastitis. However, the number of studies reported so far in this respect is very limited. Thus, much more research is required to yield clear concepts for an optimised usage of vitamin D to improve the immune system and prevent infectious diseases in dairy cows.

Reduced levels of serum 25(OH)D3 are associated with tuberculosis positive cattle under conditions of high natural exposure to Mycobacterium bovis

Serum vitamin D (25(OH)D₃) concentrations of < 30 ng/mL in cattle are insufficient to induce an adequate immune response against intracellular pathogens, which suggests that the efficacy of the immune response may be highly dependent on the bioavailability of 25(OH)D₃. This study shows an overview of both in vitro and in vivo 25(OH)D3-mediated immune modulation amongst dairy cattle naturally exposed to M. bovis. Tuberculin status was confirmed by interferon gamma release assay (IGRA), and natural exposure was demonstrated by polymerase chain reaction (PCR). Tuberculin (-) cattle have a higher serum concentration of 25(OH)D₃ (X¯= 87.12 ng/mL) when compared to tuberculin (+) cattle (X¯ = 45.86 ng/mL). Reduced serum 25(OH)D₃ levels are associated with the presence of bovine TB, and serum 25(OH)D₃ levels of > 80 ng/mL are necessary to counteract infection by M. bovis. Kill assays were performed to evaluate in vitro 25(OH)D₃ modulation of intracellular M. bovis growth in bovine macrophages, which showed that reduced serum 25(OH)D₃ levels are associated with diminished mycobactericidal capacity in this experimental model. On the other hand, increased 25(OH)D₃ in culture media enhances phagocytosis and nitric oxide production, which in turn improves capacity to combat M. bovis.

Vitamin D and Gut Health

Vitamin D is a conditionally required nutrient that can either be obtained from skin synthesis following UVB exposure from the diet. Once in the body, it is metabolized to produce the endocrine hormone, 1,25 dihydroxyvitamin D (1,25(OH)2D), that regulates gene expression in target tissues by interacting with a ligand-activated transcription factor, the vitamin D receptor (VDR). The first, and most responsive, vitamin D target tissue is the intestine. The classical intestinal role for vitamin D is the control of calcium metabolism through the regulation of intestinal calcium absorption. However, studies clearly show that other functions of the intestine are regulated by the molecular actions of 1,25(OH)2 D that are mediated through the VDR. This includes enhancing gut barrier function, regulation of intestinal stem cells, suppression of colon carcinogenesis, and inhibiting intestinal inflammation. While research demonstrates that there are both classical, calcium-regulating and non-calcium regulating roles for vitamin D in the intestine, the challenge facing biomedical researchers is how to translate these findings in ways that optimize human intestinal health.

Evolution of non-genomic nuclear receptor function

Nuclear receptors (NRs) are responsible for the regulation of diverse developmental and physiological systems in metazoans. NR actions can be the result of genomic and non-genomic mechanisms depending on whether they act inside or outside of the nucleus respectively. While the actions of both mechanisms have been shown to be crucial to NR functions, non-genomic actions are considered less frequently than genomic actions. Furthermore, hypotheses on the origin and evolution of non-genomic NR signaling pathways are rarely discussed in the literature. Here we summarize non-genomic NR signaling mechanisms in the context of NR protein family evolution and animal phyla. We find that NRs across groups and phyla act via calcium flux as well as protein phosphorylation cascades (MAPK/PI3K/PKC). We hypothesize and discuss a possible synapomorphy of NRs in the NR1 and NR3 families, including the thyroid hormone receptor, vitamin D receptor, ecdysone receptor, retinoic acid receptor, steroid receptors, and others. In conclusion, we propose that the advent of non-genomic NR signaling may have been a driving force behind the expansion of NR diversity in Cnidarians, Placozoans, and Bilaterians.

Evidence for Involvement of Nonclassical Pathways in the Protection From UV-Induced DNA Damage by Vitamin D-Related Compounds

The vitamin D hormone, 1,25dihydroxyvitamin D₃ (1,25(OH)₂D₃), and related compounds derived from vitamin D₃ or lumisterol as a result of metabolism via the enzyme CYP11A1, have been shown, when applied 24 hours before or immediately after UV irradiation, to protect human skin cells and skin from DNA damage due to UV exposure, by reducing both cyclobutane pyrimidine dimers (CPD) and oxidative damage in the form of 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine (8‐OHdG). We now report that knockdown of either the vitamin D receptor or the endoplasmic reticulum protein ERp57 by small, interfering RNA (siRNA) abolished the reductions in UV‐induced DNA damage with 20‐hydroxyvitamin D₃ or 24‐hydroxylumisterol_3, as previously shown for 1,25(OH)₂D₃. Treatment with 1,25(OH)₂D₃ reduced oxygen consumption rates in UV‐exposed and sham‐exposed human keratinocytes and reduced phosphorylation of cyclic AMP response binding element protein (CREB). Both these actions have been shown to inhibit skin carcinogenesis after chronic UV exposure, consistent with the anticarcinogenic activity of 1,25(OH)₂D₃. The requirement for a vitamin D receptor for the photoprotective actions of 1,25(OH)₂D₃ and of naturally occurring CYP11A1‐derived vitamin D–related compounds may explain why mice lacking the vitamin D receptor in skin are more susceptible to UV‐induced skin cancers, whereas mice lacking the 1α‐hydroxylase and thus unable to make 1,25(OH)₂D₃ are not more susceptible. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

1α,25-(OH)2 vitamin D3 prevents insulin resistance and regulates coordinated exocytosis and insulin secretion

Vitamin D₃ is associated with improvements in insulin resistance and glycemia. In this study, we investigated the short-term effect of 1α,25(OH)₂ Vitamin D₃ (1,25-D₃) and cholecalciferol (vitamin D₃) on the glycemia and insulin sensitivity of control and dexamethasone-induced insulin-resistance rats. ⁴⁵Ca²⁺ influx responses to 1,25-D₃ and its role in insulin secretion were investigated in isolated pancreatic islets from control rats. In vivo, 5 d treatment with 1,25-D₃ (i.p.) prevented insulin resistance in dexamethasone-treated rats. Treatment with 1,25-D₃ improved the activities of hepatic enzymes, serum lipids and calcium concentrations in insulin-resistant rats. 25-D₃ (o.g.) does not affect insulin resistance. In pancreatic islets, 1,25-D₃ increased insulin secretion and stimulated rapid response ⁴⁵Ca²⁺ influx. The stimulatory effect of 1,25-D₃ on ⁴⁵Ca²⁺ influx was decreased by diazoxide, apamine, thapsigargin, dantrolene, 2-APB, nifedipine, TEA, PKA, PKC, and cytoskeleton inhibitor, while it was increased by glibenclamide and N-ethylmaleimide. The stimulatory effect of 1,25-D₃ on ⁴⁵Ca²⁺ influx involves the activation of L-type VDCC, K⁺-ATP, K⁺-Ca^2+, and Kv channels, which augment cytosolic calcium. These ionic changes mobilize calcium from stores and downstream activation of PKC, PKA tethering vesicle traffic and fusion at the plasma membrane for insulin secretion. This is the first study highlighting the unprecedented role of 1,25-D₃ (short-term effect) in the regulation of glucose homeostasis and on prevention of insulin resistance. Furthermore, this study shows the intracellular β-cell signal transduction of 1,25-D₃ through the modulation of pivotal ionic channels and proteins exhibiting a coordinated exocytosis of vesicles for insulin secretion.

Synthesis and characterization of vitamin D3-functionalized carbon dots for CRISPR/Cas9 delivery

Aim: To develop a novel nanovector for the delivery of genetic fragments and CRISPR/Cas9 systems in particular. Materials & methods: Vitamin D₃-functionalized carbon dots (D/CDs) fabricated using one-step microwave-aided methods were characterized by different microscopic and spectroscopic techniques. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and flow cytometry were employed to determine the cell viability and transfection efficiency. Results: D/CDs transfected CRISPR plasmid in various cell lines with high efficiency while maintaining their remarkable efficacy at high serum concentration and low plasmid doses. They also showed great potential for the green fluorescent protein disruption by delivering two different types of CRISPR/Cas9 systems. Conclusion: Given their high efficiency and safety, D/CDs provide a versatile gene-delivery vector for clinical applications.

Intestinal Calcium Absorption

In this article, we focus on mammalian calcium absorption across the intestinal epithelium in normal physiology. Intestinal calcium transport is essential for supplying calcium for metabolism and bone mineralization. Dietary calcium is transported across the mucosal epithelia via saturable transcellular and nonsaturable paracellular pathways, both of which are under the regulation of 1,25-dihydroxyvitamin D₃ and several other endocrine and paracrine factors, such as parathyroid hormone, prolactin, 17β-estradiol, calcitonin, and fibroblast growth factor-23. Calcium absorption occurs in several segments of the small and large intestine with varying rates and capacities. Segmental heterogeneity also includes differential expression of calcium transporters/carriers (e.g., transient receptor potential cation channel and calbindin-D_9k ) and the presence of favorable factors (e.g., pH, luminal contents, and gut motility). Other proteins and transporters (e.g., plasma membrane vitamin D receptor and voltage-dependent calcium channels), as well as vesicular calcium transport that probably contributes to intestinal calcium absorption, are also discussed. © 2021 American Physiological Society. Compr Physiol 11:1-27, 2021.

Matrix Vesicles: Role in Bone Mineralization and Potential Use as Therapeutics

Bone is a complex organ maintained by three main cell types: osteoblasts, osteoclasts, and osteocytes. During bone formation, osteoblasts deposit a mineralized organic matrix. Evidence shows that bone cells release extracellular vesicles (EVs): nano-sized bilayer vesicles, which are involved in intercellular communication by delivering their cargoes through protein–ligand interactions or fusion to the plasma membrane of the recipient cell. Osteoblasts shed a subset of EVs known as matrix vesicles (MtVs), which contain phosphatases, calcium, and inorganic phosphate. These vesicles are believed to have a major role in matrix mineralization, and they feature bone-targeting and osteo-inductive properties. Understanding their contribution in bone formation and mineralization could help to target bone pathologies or bone regeneration using novel approaches such as stimulating MtV secretion in vivo, or the administration of in vitro or biomimetically produced MtVs. This review attempts to discuss the role of MtVs in biomineralization and their potential application for bone pathologies and bone regeneration.

Mice lacking substance P have normal bone modeling but diminished bone formation, increased resorption, and accelerated osteopenia with aging

Substance P (SP) is a sensory neuropeptide that is expressed by the neurons innervating bone. There is considerable evidence that SP can regulate bone cell function in vitro, but it is unclear whether SP modulates bone modeling or remodeling in vivo. To answer this question we characterized the bone phenotype of mice with deletion of the Tac1 gene expressing SP. The phenotypes of 2-month-old and 5-month-old SP deficient mice and their wildtype controls were characterized by using μCT imaging, static and dynamic bone histomorphometry, and urinary deoxypyridinoline cross-links (DPD) measurement. No differences in bone phenotypes were observed between the 2 strains at 2 months of age. By 5 months both the wildtype and SP deficient mice had developed cancellous osteopenia, but relative to the wild-type mice the SP deficient mice had significantly greater cancellous bone loss. The SP deficient mice also exhibited decreased bone formation, increased osteoclast number, and increased urinary DPD levels. Cortical defect early repair was delayed in 5-month-old mice lacking SP. Collectively, these findings indicate that SP signaling is not required for bone modeling, but SP signaling reduces age-related osteopenia and accelerates cortical defect reparation, data supporting the hypothesis that SP is an anabolic physiologic regulator of bone metabolism.

Molecular distribution and localization of extracellular calcium-sensing receptor (CaSR) and vitamin D receptor (VDR) at three different laying stages in laying hens (Gallus gallus domesticus)

The extracellular calcium-sensing receptor (CaSR) and vitamin D receptor (VDR) play important roles in regulating calcium mobilization, calcium absorption, and calcium homeostasis, and they could be potential therapeutic targets to osteoporosis in laying hens. The present study investigated the molecular distribution of CaSR and VDR and the localization of CaSR in the kidney, proventriculus (true stomach), duodenum, jejunum, ileum, colon, cecum, shell gland, and tibia of laying hens at 3 different laying stages (19, 40, and 55 wk). The results showed that the relative mRNA abundance of CaSR in the kidney, ileum, proventriculus, duodenum, and colon was higher (P < 0.05) than the other tissues at 40 and 55 wk. The relative mRNA abundance of CaSR in the tibia was higher (P < 0.05) at 55 wk than at 40 wk. However, there were no significant differences in the relative protein abundance of CaSR among all tested tissues at peak production or in each tissue at the 3 different laying stages (P > 0.05). The relative mRNA abundance of VDR was higher (P < 0.05) in the small intestine (duodenum, jejunum, and ileum) when compared with other tissues at the 3 different laying stages. The relative protein abundance of VDR in the duodenum was higher (P < 0.05) than that in the proventriculus, colon, and cecum. There were no significant differences in the VDR expression among the tested tissues at the 3 different laying stages (P > 0.05). The immunohistochemical results showed that the positive staining was found widely in each tissue. Moreover, different laying stages did not affect the localization of CaSR except for the tibia tissue. In conclusion, similar to VDR, CaSR was widely expressed not only in the gut but also in the tibia and shell gland in laying hens. The expression level of CaSR and VDR in all tested tissues was unchanged at the different laying stages.

Role of nuclear and membrane estrogen signaling pathways in the male and female reproductive tract

Estrogen signaling through the main estrogen receptor, estrogen receptor 1 (ESR1; also known as ERα), is essential for normal female and male reproductive function. Historically, studies of estrogen action have focused on the classical genomic pathway. Although this is clearly the major pathway for steroid hormone actions, these hormones also signal through rapid non-classical effects involving cell membrane actions. Reports of rapid effects of estrogens extend for more than half a century, but recent results have expanded understanding of the identity, structure, function and overall importance of membrane receptors in estrogen responses. Key findings in this field were the immunohistochemical detection of ESR1 in cell membranes and demonstration that a portion of newly synthesized ESR1 is routed to the membrane by palmitoylation. These receptors in the membrane can then signal through protein kinases and other mechanisms following ligand binding to alter cell function. Another crucial advance in the field was development of transgenic mice expressing normal amounts of functional nuclear ESR1 (nESR1) but lacking membrane ESR1 (mESR1). Both male and female transgenic mice lacking mESR1 were infertile as adults, and both sexes had extensive reproductive abnormalities. Transgenic mice lacking mESR1 were highly protected from deleterious effects of neonatal estrogen administration, and estrogen effects on the histone methyltransferase Enhancer of Zeste homolog 2 that are mediated through mESR1 could have significant effects on epigenetic imprinting. In summary, signaling through mESR1 is essential for normal male and female reproductive function and fertility, and is a critical enabler of normal estrogen responses in vivo. Although the precise role of mESR1 in estrogen responses remains to be established, future research in this area should clarify its mechanism of action and lead to a better understanding of how mESR1 signaling works with classical genomic signaling through nESR1 to promote full estrogenic responses.

The Role of Vitamin D in Small Animal Bone Metabolism

Dogs and cats have differences in vitamin D metabolism compared to other mammalian species, as they are unable to perform vitamin D cutaneous synthesis through sun exposure. Therefore, they are dependent on the dietary intake of this nutrient. The classic functions of vitamin D are to stimulate intestinal calcium and phosphate absorption, renal calcium and phosphate reabsorption and regulate bone mineral metabolism. Thus, it is an important nutrient for calcium and phosphorus homeostasis. This review highlights the evidence of the direct and indirect actions of vitamin D on bone mineral metabolism, the consequences of nutritional imbalances of this nutrient in small animals, as well as differences in vitamin D metabolism between different size dogs.

Vitamin D and Genetic Susceptibility to Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease affecting the central nervous system (CNS), resulting from the interaction among genetic, epigenetic, and environmental factors. Vitamin D is a secosteroid, and its circulating levels are influenced by environment and genetics. In the last decades, research data on the association between MS and vitamin D status led to hypothesize a possible role for hypovitaminosis D as a risk factor for MS. Some gene variants encoding proteins involved in vitamin D metabolism, transport, and function, which are responsible for vitamin D status alterations, have been related to MS susceptibility. This review explores the current literature on the influence of vitamin D-related genes in MS susceptibility, reporting all single-nucleotide polymorphisms (SNPs) investigated to date in 12 vitamin D pathway genes. Among all, the gene codifying vitamin D receptor (VDR) is the most studied. The association between VDR SNPs and MS risk has been reported by many Authors, with a few studies producing opposite results. Other vitamin D-related genes (including DHCR7/NADSYN1, CYP2R1, CYP27A1, CYP3A4, CYP27B1, CYP24A1, Megalin-DAB2-Cubilin, FGF-23, and Klotho) have been less investigated and achieved more conflicting evidence. Taken together, findings from the studies reviewed cannot clarify whether and to what extent vitamin D-related gene variants can influence MS risk.

Vitamin D and Polycystic Ovary Syndrome: a Narrative Review

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders of reproductive age women and contributes to metabolic dysfunctions including insulin resistance (IR) and dyslipidemia. Vitamin D is a steroid hormone, which is involved in calcium metabolism and bone structure and has a potential role in the prevention of many illnesses, including cancers, autoimmune disorders, hypertension, diabetes, and obesity. Recently, it has been reported that vitamin D deficiency was a common complication of PCOS and vitamin D status was associated with reproductive ability, metabolic alterations, and mental health of PCOS patients. This review summarizes the advances between vitamin D status and the pathophysiological process of PCOS. Vitamin D level was negatively associated with serum androgen level. Vitamin D treatment could reduce serum androgen and anti-MüllerianHormone (AMH) levels, and decrease endometrial thickness, which resulted in improvement of menstrual cycle and folliculogenesis of PCOS patients. Moreover, vitamin D concentrations were negatively correlated with parameters of IR and body fat mass. Vitamin D supplementation has beneficial effects on IR and lipid metabolism. In addition, a positive of vitamin D on mental health of PCOS patients was proposed. Understanding the relationship between vitamin D status and the symptoms of PCOS patients is of great clinical significance to treat and prevent the progression of PCOS.

Protection from Ultraviolet Damage and Photocarcinogenesis by Vitamin D Compounds

Exposure of skin cells to UV radiation results in DNA damage, which if inadequately repaired, may cause mutations. UV-induced DNA damage and reactive oxygen and nitrogen species also cause local and systemic suppression of the adaptive immune system. Together, these changes underpin the development of skin tumours. The hormone derived from vitamin D, calcitriol (1,25-dihydroxyvitamin D₃) and other related compounds, working via the vitamin D receptor and at least in part through endoplasmic reticulum protein 57 (ERp57), reduce cyclobutane pyrimidine dimers and oxidative DNA damage in keratinocytes and other skin cell types after UV. Calcitriol and related compounds enhance DNA repair in keratinocytes, in part through decreased reactive oxygen species, increased p53 expression and/or activation, increased repair proteins and increased energy availability in the cell when calcitriol is present after UV exposure. There is mitochondrial damage in keratinocytes after UV. In the presence of calcitriol, but not vehicle, glycolysis is increased after UV, along with increased energy-conserving autophagy and changes consistent with enhanced mitophagy. Reduced DNA damage and reduced ROS/RNS should help reduce UV-induced immune suppression. Reduced UV immune suppression is observed after topical treatment with calcitriol and related compounds in hairless mice. These protective effects of calcitriol and related compounds presumably contribute to the observed reduction in skin tumour formation in mice after chronic exposure to UV followed by topical post-irradiation treatment with calcitriol and some, though not all, related compounds.

Vitamin D Deficiency and the Risk of Cerebrovascular Disease

Vitamin D deficiency has been clearly linked to major chronic diseases associated with oxidative stress, inflammation, and aging, including cardiovascular and neurodegenerative diseases, diabetes, and cancer. In particular, the cardiovascular system appears to be highly sensitive to vitamin D deficiency, as this may result in endothelial dysfunction and vascular defects via multiple mechanisms. Accordingly, recent research developments have led to the proposal that pharmacological interventions targeting either vitamin D deficiency or its key downstream effects, including defective autophagy and abnormal pro-oxidant and pro-inflammatory responses, may be able to limit the onset and severity of major cerebrovascular diseases, such as stroke and cerebrovascular malformations. Here we review the available evidence supporting the role of vitamin D in preventing or limiting the development of these cerebrovascular diseases, which are leading causes of disability and death all over the world.

The Influence of Vitamin D on Neurodegeneration and Neurological Disorders: A Rationale for its Physio-pathological Actions

Vitamin D is a steroid hormone implicated in the regulation of neuronal integrity and many brain functions. Its influence, as a nutrient and a hormone, on the physiopathology of the most common neurodegenerative diseases is continuously emphasized by new studies. This review addresses what is currently known about the action of vitamin D on the nervous system and neurodegenerative diseases such as Multiple Sclerosis, Alzheimer's disease, Parkinson's disease and Amyotrophic Lateral Sclerosis. Further vitamin D research is necessary to understand how the action of this "neuroactive" steroid can help to optimize the prevention and treatment of several neurological diseases.

Translating vitamin D transcriptomics to clinical evidence: Analysis of data in asthma and chronic obstructive pulmonary disease, followed by clinical data meta-analysis

Vitamin D (VitD) continues to trigger intense scientific controversy, regarding both its bi ological targets and its supplementation doses and regimens. In an effort to resolve this dispute, we mapped VitD transcriptome-wide events in humans, in order to unveil shared patterns or mechanisms with diverse pathologies/tissue profiles and reveal causal effects between VitD actions and specific human diseases, using a recently developed bioinformatics methodology. Using the similarities in analyzed transcriptome data (c-SKL method), we validated our methodology with osteoporosis as an example and further analyzed two other strong hits, specifically chronic obstructive pulmonary disease (COPD) and asthma. The latter revealed no impact of VitD on known molecular pathways. In accordance to this finding, review and meta-analysis of published data, based on an objective measure (Forced Expiratory Volume at one second, FEV₁%) did not further reveal any significant effect of VitD on the objective amelioration of either condition. This study may, therefore, be regarded as the first one to explore, in an objective, unbiased and unsupervised manner, the impact of VitD levels and/or interventions in a number of human pathologies.

Ultrastructural characterization of vitamin D receptors and metabolizing enzymes in the lipid droplets of the fatty liver in rat

Vitamin D is a steroid hormone with numerous actions in the organism. There are strong evidences that relate vitamin D deficiency with liver lipid metabolism disturbances, but the mechanism of this action is still unknown. In our previous work we postulated the localization and accumulation of vitamin D receptor (VDR) in membrane of the lipid droplets (LDs) in hepatocytes. In this study, we applied the transmission electron microscopy (TEM) to confirm this hypothesis by using a long-term (6 months) high sucrose intake rat model that was previously found to be appropriate for research of the hepatic lipid accumulation. In addition to the VDR, we also found key vitamin D metabolizing enzymes, 1α-hydroxylase and CYP 24 associated with the membrane of the LDs. A light-microscopy data revealed significant increase in expression of VDR and CYP 24 in liver of high-sucrose treated rats, in comparison to controlones. According to the best of our knowledge, this is a first study confirming the presence of the VDR in the membrane of the LDs in general and also in particular in LDs of the hepatocytes that were accumulated as a consequence of the prolonged high sucrose intake. Moreover, we found association of main vitamin D metabolizing enzymes with LD membrane. These results provide a new insight in the possible relation of vitamin D signalling system with LD morphology and function and with the lipid metabolism in general.

Vitamin D and Multiple Sclerosis: An Open-Ended Story

Multiple Sclerosis (MS) is a chronic inflammatory autoimmune disease of the Central Nervous System (CNS). Genetic, epigenetic and environmental factors interact together, contributing to the complex pathogenesis of the disease. In the last decades, the role of hypovitaminosis D on MS risk was hypothesised. Several factors drive the regulation of vitamin D status, including genetics. The current review summarises the literature evidence on the association between vitamin D and MS, with a focus on the genetic polymorphisms in vitamin D-related genes. The variants of the genes codifying Vitamin D Receptor (VDR), Vitamin D Binding Protein (VDBP) and CYP enzymes have been investigated, but the findings are controversial. Only a few studies have addressed the role of DHCR7 polymorphisms in MS risk.

The association between vitamin D status and infectious diseases of the respiratory system in infancy and childhood

PURPOSE

Respiratory tract infections (RTIs) are a major cause of illness worldwide and the most common cause of hospitalization for pneumonia and bronchiolitis. These two diseases are the leading causes of morbidity and mortality among children under 5 years of age. Vitamin D is believed to have immunomodulatory effects on the innate and adaptive immune systems by modulating the expression of antimicrobial peptides, like cathelicidin, in response to both viral and bacterial stimuli. The aim of this review is to summarize the more recently published data with regard to potential associations of 25-hydroxyvitamin D [25(OH)D] with infectious respiratory tract diseases of childhood and the possible health benefits from vitamin D supplementation.

METHODS

The literature search was conducted by using the PubMed, Scopus, and Google Scholar databases, with the following keywords: vitamin D, respiratory tract infection, tuberculosis, influenza, infancy, and childhood.

RESULTS

Several studies have identified links between inadequate 25(OH)D concentrations and the development of upper or lower respiratory tract infections in infants and young children. Some of them also suggest that intervention with vitamin D supplements could decrease both child morbidity and mortality from such causes.

CONCLUSIONS

Most studies agree in that decreased vitamin D concentrations are prevalent among most infants and children with RTIs. Also, normal to high-serum 25(OH)D appears to have some beneficial influence on the incidence and severity of some, but not all, types of these infections. However, studies with vitamin D supplementation revealed conflicting results as to whether supplementation may be of benefit, and at what doses.

A single mega dose of vitamin D3 improves selected physical variables in vitamin D-deficient young amateur soccer players: a randomized controlled trial

This randomized controlled trial aimed to test whether vitamin D (VD) supplementation affects measures of physical performance in VD-deficient, mildly trained children. Thirty-six recreationally soccer player boys were randomly assigned to single dose (200 000 IU) of VD3 (n = 19) or placebo (n = 17). Plasma 25-hydroxyvitamin D (25-OHD) was assessed and measures of physical performance (i.e., vertical and standing broad jumps, triple hop, 10-m and 30-m sprints, shuttle run) were performed before and 12 weeks after the loading dose. Mixed ANCOVA models were performed and effect size was estimated by partial eta squared (η_p²). Baseline 25-OHD and physical variables were equivalent in the 2 groups. Twelve weeks after VD loading, plasma 25-OHD increased and physical variables improved only in the VD group. There was a significant interaction effects for group by time for vertical jump (F = 14.9, p = 0.001, η_p² = 0.394), triple hop jump (F = 24.2, p < 0.001, η_p² = 0.513), 10-m (F = 4.46, p = 0.046, η_p² = 0.162) and 30-m (F = 6.56, p = 0.017, η_p² = 0.222) sprints, and shuttle run (F = 13.4, p = 0.001, η_p² = 0.369). In conclusion, a single bolus of VD3 resulted in significant improvements in jumping ability, agility, and running speed in mildly trained children that are deficient in VD. The findings suggest that correcting VD deficit might be beneficial for physical performance. Novelty A mega dose of VD3 improves jumping ability, agility, and running speed in VD-deficient, mildly trained children. Effect of VD on measures of physical performance is noticeable 3 months after the loading dose.

Mechanisms of vitamin D action in skeletal muscle

Vitamin D receptor expression and associated function have been reported in various muscle models, including C2C12, L6 cell lines and primary human skeletal muscle cells. It is believed that 1,25-hydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D, has a direct regulatory role in skeletal muscle function, where it participates in myogenesis, cell proliferation, differentiation, regulation of protein synthesis and mitochondrial metabolism through activation of various cellular signalling cascades, including the mitogen-activated protein kinase pathway(s). It has also been suggested that 1,25(OH)2D3 and its associated receptor have genomic targets, resulting in regulation of gene expression, as well as non-genomic functions that can alter cellular behaviour through binding and modification of targets not directly associated with transcriptional regulation. The molecular mechanisms of vitamin D signalling, however, have not been fully clarified. Vitamin D inadequacy or deficiency is associated with muscle fibre atrophy, increased risk of chronic musculoskeletal pain, sarcopenia and associated falls, and may also decrease RMR. The main purpose of the present review is to describe the molecular role of vitamin D in skeletal muscle tissue function and metabolism, specifically in relation to proliferation, differentiation and protein synthesis processes. In addition, the present review also includes discussion of possible genomic and non-genomic pathways of vitamin D action.

The Prevalence of Dysphonia and Dysphagia in Patients with Vitamin D Deficiency

OBJECTIVE

To investigate the prevalence of phonatory and swallowing symptoms in patients with hypovitaminosis D.

METHODS/DESIGN

All patients presenting to the endocrinology clinic and investigated for vitamin D deficiency between January 2018 and April 2018 were asked to participate in this study. Demographic data included age, gender, allergy, and history of smoking. Patients filled Voice handicap Index (VHI-10) and Eating Assessment Tool (EAT-10).

RESULTS

A total of 136 consecutive subjects presenting to the endocrinology clinic for vitamin D testing were included: 60 with hypovitaminosis D and 76 with no hypovitaminosis D. The mean vitamin D level in the study group and controls was 13.25 ng/mL and 31.91 ng/mL, respectively. There was no significant difference in the mean score of VHI-10, nor in the mean score of EAT-10 in patients with hypovitaminosis D versus those with no hypovitaminosis D (P value >0.05).

CONCLUSION

There was no significant difference in the prevalence of phonatory and dysphagia symptoms using VHI-10 and EAT-10 questionnaires between subjects with hypovitaminosis D and those with normal serum vitamin D levels.

Alternative binding sites at the vitamin D receptor and their ligands

In recent decades, the majority of ligands developed for the vitamin D receptor (VDR) bind at its deeply buried genomic ligand binding pocket. Theses ligands can be categorized into agonists and partial agonists/antagonists. A limited number of ligands, most of them peptides, bind the VDR‒coactivator binding site that is formed in the presence of an agonist and inhibit coactivator recruitment, and therefore transcription. Another solvent exposed VDR‒ligand binding pocket was identified for lithocholic acid, improving the overall stability of the VDR complex. Additional proposed interactions with VDR are discussed herein that include the alternative VDR‒ligand binding pocket that may mediate both non-genomic cellular responses and binding function 3 that was identified for the androgen receptor. Many VDR ligands increase blood calcium levels at therapeutic concentrations in vivo, thus the identification of alternative VDR‒ligand binding pockets might be crucial to develop non-calcemic and potent ligands for VDR to treat cancer and inflammatory disease.

Molecular basis of vitamin D action in neurodegeneration: the story of a team perspective

Vitamin D, a secosteroid hormone, has, over the years, mainly been known for its classic role in the maintenance of calcium homeostasis of the human body. However, there is increasing understanding that vitamin D contributes to the regulation of Ca²⁺ homeostasis, especially via voltage-gated calcium channels, in another major organ that uses calcium, the brain. Almost 30 years ago, the role of dysregulation in the aging brain and in Alzheimer's disease (AD) gave rise to the Ca²⁺ hypothesis of brain aging and dementia. We thus made calcium homeostasis the starting point of our studies, proposing the notion that the consequences of long-term deficiency and/or inefficient utilization of vitamin D may cause the disruption of calcium homeostasis in neurons, this creating a vulnerability of neurons to aging and neurodegeneration. In this mini-review, we aim to describe the potential of vitamin D (cholecalciferol) as a neurosteroid based on our findings and conclusions.

Steroidal pheromones and their potential target sites in the vomeronasal organ

Steroids are important olfactory signals in most mammalian species. The vomeronasal organ has been suspected to be the primary target of pheromones. In rat vomeronasal sensory neurons express steroid binding proteins and nuclear receptors. Some binding globulins were found also in single ciliated cells of the non-sensory vomeronasal epithelium. Immunoelectron microscopy revealed VDR in olfactory microvilli and DPB in apical membrane protrusions of supporting sells within the sensory epithelium. Pilot behavioral studies with dogs showed increased sniffing duration upon exposure to low concentrations of vitamin D while higher concentrations were less effective. It has been shown that vitamin D has pheromone-like properties in lizards. Our histochemical and behavioral observations indicate that the mammalian vomeronasal organ may be a vitamin D target. Olfactory functions of vitamin D involve most likely rapid membrane mediated effects rather than actions through nuclear receptors.

Impaired vitamin D sensitivity

Resistance to vitamin D has been known for decades as vitamin D resistant rickets, caused by mutations of the gene encoding for vitamin D receptor (VDR). Findings of extra-skeletal effects of vitamin D and learning of the molecular mechanisms used by its biologically active metabolite calcitriol revealed other ways leading to its impaired sensitivity. Calcitriol takes advantage of both genomic and non-genomic mechanisms through its binding to vitamin D receptor, located not only in the cell nuclei but also in a perinuclear space. On the genomic level the complex of calcitriol bound to VDR binds to the DNA responsive elements of the controlled gene in concert with another nuclear receptor, retinoid X receptor, and expression of the VDR itself is controlled by its own ligand. These elements were found not only in the promotor region, but are scattered over the gene DNA. The gene expression includes a number of nuclear transcription factors which interact with the responsive elements and with each other and learning how they operate would further contribute to revealing causes of the impaired vitamin D sensitivity. Finally, the examples of major disorders are provided, associated with impairment of the vitamin D function and its receptor.

An active and selective molecular mechanism mediating the uptake of sex steroids by prostate cancer cells

Steroid hormones play important roles in normal physiological functions and diseases. Sex steroids hormones are important in the biology and treatment of sex hormone-related cancer such as prostate cancer and breast cancer. Cells may take up steroids using multiple mechanisms. The conventionally accepted hypothesis that steroids cross cell membrane through passive diffusion has not been tested rigorously. Experimental data suggested that cells may take up sex steroid using an active uptake mechanism. ³H-testosterone uptake by prostate cancer cells showed typical transporter-mediated uptake kinetic. Cells retained testosterone taken up from the medium. The uptake of testosterone was selective for certain steroid hormones but not others. Data also indicated that the active and selective uptake mechanism resided in cholesterol-rich membrane domains, and may involve ATP and membrane transporters. In summary, the present study provided strong evidence to support the existence of an active and selective molecular mechanism for sex steroid uptake.

Neuroprotective effects of vitamin D on high fat diet- and palmitic acid-induced enteric neuronal loss in mice

Background

The role of vitamin D in obesity and diabetes is debated. Obese and/or diabetic patients have elevated levels of free fatty acids, increased susceptibility to gastrointestinal symptoms and are suggested to have altered vitamin D balance. The enteric nervous system is pivotal in regulating gastrointestinal activity and high fat diet (HFD) has been shown to cause loss of enteric neurons in ileum and colon. This study investigates the effect of vitamin D on HFD- and palmitic acid-induced enteric neuronal loss in vivo and in vitro.

Methods

Mice were fed either a normal diet (ND) or HFD supplemented with varying levels of vitamin D (from 0x to 20x normal vitamin D level) for 19 weeks. Ileum and colon were analyzed for neuronal numbers and remodeling. Primary cultures of myenteric neurons from mouse small intestine were treated with palmitic acid (4x10^-4M) and/or 1α,25-hydroxy-vitamin D3 (VD, 10^-11- 10^-7M) with or without modulators of lipid metabolism and VD pathways. Cultures were analyzed by immunocyto- and histochemical methods.

Results

Vitamin D supplementation had no effect on enteric neuronal survival in the ND group. HFD caused substantial loss of myenteric neurons in ileum and colon. Vitamin D supplementation between 0-2x normal had no effect on HFD-induced neuronal loss. Supplementation with 20x normal, prevented the HFD-induced neuronal loss. In vitro supplementation of VD prevented the palmitic acid-induced neuronal loss. The VD receptor (VDR) was not identified in enteric neurons. Enteric glia expressed the alternative VD receptor, protein disulphide isomerase family A member 3 (PDIA3), but PDIA3 was not found to mediate the VD response in vitro. Inhibition of peroxisome proliferator-activated receptor gamma (PPARγ) and immune neutralization of isocitrate lyase prevented the VD mediated neuroprotection to palmitic acid exposure.

Conclusions

Results show that VD protect enteric neurons against HFD and palmitic acid induced neuronal loss. The mechanism behind is suggested to be through activation of PPARγ leading to improved neuronal peroxisome function and metabolism of neuronal lipid intermediates.

Antiproliferative Activity of Non-Calcemic Vitamin D Analogs on Human Melanoma Lines in Relation to VDR and PDIA3 Receptors

Vitamin D is a precursor for secosteroidal hormones, which demonstrate pleiotropic biological activities, including the regulation of growth and the differentiation of normal and malignant cells. Our previous studies have indicated that the inhibition of melanoma proliferation by a short side-chain, low calcemic analog of vitamin D—21(OH)pD is not fully dependent on the expression of vitamin D receptor (VDR). We have examined the effects of classic vitamin D metabolites, 1,25(OH)₂D₃ and 25(OH)D₃, and two low calcemic vitamin D analogs, (21(OH)pD and calcipotriol), on proliferation, mRNA expression and vitamin D receptor (VDR) translocation in three human melanoma cell lines: WM98, A375 and SK-MEL-188b (subline b of SK-MEL-188, which lost responsiveness to 1,25(OH)₂D₃ and became VDR^−/−CYP27B1^−/−). All tested compounds efficiently inhibited the proliferation of WM98 and A375 melanoma cells except SK-MEL-188b, in which only the short side-chain vitamin D analog—21(OH)pD was effective. Overall, 21(OH)pD was the most potent compound in all three melanoma cell lines in the study. The lack of responsiveness of SK-MEL-188b to 1,25(OH)₂D₃, 25(OH)D₃ and calcipotriol is explained by a lack of characteristic transcripts for the VDR, its splicing variants as well as for vitamin D-activating enzyme CYP27B1. On the other hand, the expression of VDR and its splicing variants and other vitamin D related genes (RXR, PDIA3, CYP3A4, CYP2R1, CYP27B1, CYP24A1 and CYP11A1) was detected in WM98 and A375 melanomas with the transcript levels being modulated by vitamin D analogs. The expression of VDR isoforms in WM98 cells was stimulated strongly by calcipotriol. The antiproliferative activities of 21(OH)pD appear not to require VDR translocation to the nucleus, which explains the high efficacy of this noncalcemic pregnacalciferol analog in SK-MEL-188b melanoma, that is, VDR^−/−. Therefore, we propose that 21(OH)pD is a good candidate for melanoma therapy, although the mechanism of its action remains to be defined.

Vitamin D Improves Neurogenesis and Cognition in a Mouse Model of Alzheimer's Disease

The impairment of hippocampal neurogenesis at the early stages of Alzheimer’s disease (AD) is believed to support early cognitive decline. Converging studies sustain the idea that vitamin D might be linked to the pathophysiology of AD and to hippocampal neurogenesis. Nothing being known about the effects of vitamin D on hippocampal neurogenesis in AD, we assessed them in a mouse model of AD. In a previous study, we observed that dietary vitamin D supplementation in female AD-like mice reduced cognitive decline only when delivered during the symptomatic phase. With these data in hand, we wondered whether the consequences of vitamin D administration on hippocampal neurogenesis are stage-dependent. Male wild-type and transgenic AD-like mice (5XFAD model) were fed with a diet containing either no vitamin D (0VD) or a normal dose of vitamin D (NVD) or a high dose of vitamin D (HVD), from month 1 to month 6 (preventive arm) or from month 4 to month 9 (curative arm). Working memory was assessed using the Y-maze, while amyloid burden, astrocytosis, and neurogenesis were quantified using immunohistochemistry. In parallel, the effects of vitamin D on proliferation and differentiation were assayed on primary cultures of murine neural progenitor cells. Improved working memory and neurogenesis were observed when high vitamin D supplementation was administered during the early phases of the disease, while a normal dose of vitamin D increased neurogenesis during the late phases. Conversely, an early hypovitaminosis D increased the number of amyloid plaques in AD mice while a late hypovitaminosis D impaired neurogenesis in AD and WT mice. The observed in vivo vitamin D-associated increased neurogenesis was partially substantiated by an augmented in vitro proliferation but not an increased differentiation of neural progenitors into neurons. Finally, a sexual dimorphism was observed. Vitamin D supplementation improved the working memory of males and females, when delivered during the pre-symptomatic and symptomatic phases, respectively. Our study establishes that (i) neurogenesis is improved by vitamin D in a male mouse model of AD, in a time-dependent manner, and (ii) cognition is enhanced in a gender-associated way. Additional pre-clinical studies are required to further understand the gender- and time-specific mechanisms of action of vitamin D in AD. This may lead to an adaptation of vitamin D supplementation in relation to patient’s gender and age as well as to the stage of the disease.

1α,25-Dihydroxyvitamin D3 promotes bone formation by promoting nuclear exclusion of the FoxO1 transcription factor in diabetic mice

1α,25-Dihydroxyvitamin D3 (1,25(OH)2D3) is the active form of vitamin D, which is responsible for reducing the risk for diabetes mellitus (DM), decreasing insulin resistance, and improving insulin secretion. Previous studies have shown that 1,25(OH)2D3 inhibited the activity of FoxO1, which has been implicated in the regulation of glucose metabolism. However, its function and mechanism of action in DM-induced energy disorders and also in bone development remains unclear. Here, using in vitro and in vivo approaches including osteoblast-specific, conditional FoxO1-knock-out mice, we demonstrate that 1,25(OH)2D3 ameliorates abnormal osteoblast proliferation in DM-induced oxidative stress conditions and rescues the impaired glucose and bone metabolism through FoxO1 nuclear exclusion resulting from the activation of PI3K/Akt signaling. Using alizarin red staining, alkaline phosphatase assay, Western blot, and real-time qPCR techniques, we found that 1,25(OH)2D3 promotes osteoblast differentiation and expression of osteogenic phenotypic markers (i.e. alkaline phosphatase (1), collagen 1 (COL-1), osteocalcin (OCN), and osteopontin (OPN)) in a high-glucose environment. Moreover, 1,25(OH)2D3 increased both total OCN secretion and levels of uncarboxylated OCN (GluOC) by phosphorylating FoxO1 and promoting its nuclear exclusion, indicated by Western blot and cell immunofluorescence analyses. Taken together, our findings confirm that FoxO1 is a key mediator involved in glucose homeostasis and indicate that 1,25(OH)2D3 improves glucose metabolism and bone development via regulation of PI3K/Akt/FoxO1/OCN pathway.

Vitamin D receptor and progesterone receptor protein and gene expression in papillary thyroid carcinomas: associations with histological features

PURPOSE

Vitamin D receptor (VDR) and progesterone receptor (PR) expression has been described in papillary thyroid carcinoma (PTC) but data regarding association with tumor histological characteristics and localization of the protein expression are scarce.

MATERIALS AND METHODS

Formalin-fixed, paraffin-embedded specimens from 45 patients with PTC (cases) were retrieved and tumor histological data were recorded. We analyzed gene and protein expression of VDR and PR and gene expression of vitamin D-inactivating 24-hyroxylase (CYP24A1) and the activating 1-alpha-hydroxylase (CYP27B1) enzymes in follicular cancer cells and the adjacent non-neoplastic thyroid tissue (NNTT).

RESULTS

VDR mRNA and protein expression was higher in PTC compared with NNTT (p < 0.05). The protein was globally localized in the cytoplasm and cell membranes of the neoplastic cells in all cases, with differences in intensity. Cytoplasmic positivity was stronger in the majority of cases. Membranous positivity was also evident in cases, whereas in NNTT was generally weak and in a low percentage of the cells. Expression of CYP 24A1, but not CYP27B1, was increased in approximately all PTC specimens and was associated with lymph node metastasis and extrathyroidal extension. PR mRNA was increased in 34% and protein expression was present in 57% of cases, and none of NNTT. PR, but not VDR, mRNA expression was significantly associated with the tumor size (r = 0.645, p = 0.007).

CONCLUSIONS

We provide evidence for the expression pattern of VDR, PR and CYP24A1 in the progression of PTC. Rapid anti-tumor responses of vitamin D in PTC may be blocked due to inactivation of local vitamin D metabolism.

Vitamin D receptor is present on the neuronal plasma membrane and is co-localized with amyloid precursor protein, ADAM10 or Nicastrin

Our recent study indicated that vitamin D and its receptors are important parts of the amyloid processing pathway in neurons. Yet the role of vitamin D receptor (VDR) in amyloid pathogenesis is complex and all regulations over the production of amyloid beta cannot be explained solely with the transcriptional regulatory properties of VDR. Given that we hypothesized that VDR might exist on the neuronal plasma membrane in close proximity with amyloid precursor protein (APP) and secretase complexes. The present study primarily focused on the localization of VDR in neurons and its interaction with amyloid pathology-related proteins. The localization of VDR on neuronal membranes and its co-localization with target proteins were investigated with cell surface staining followed by immunofluorescence labelling. The FpClass was used for protein-protein interaction prediction. Our results demonstrated the localization of VDR on the neuronal plasma membrane and the co-localization of VDR and APP or ADAM10 or Nicastrin and limited co-localization of VDR and PS1. E-cadherin interaction with APP or the γ-secretase complex may involve NOTCH1, NUMB, or FHL2, according to FpClass. This suggested complex might also include VDR, which greatly contributes to Ca⁺² hemostasis with its ligand vitamin D. Consequently, we suggested that VDR might be a member of this complex also with its own non-genomic action and that it can regulate the APP processing pathway in this way in neurons.

Role of CYP24A1, VDR and GC gene polymorphisms on deferasirox pharmacokinetics and clinical outcomes

β-Thalassemia patients develop deficiency in vitamin D absorption and liver hydroxylation, resulting in extremely low calcitriol levels. We explored the role of single-nucleotide polymorphisms (SNPs) involved in vitamin D metabolism, transport and activity on deferasirox pharmacokinetics and outcomes (effectiveness trough levels (C_trough) and the area under the curve (AUC) cutoffs of 20 μg ml^-1 and 360 μg ml^-1 h^-1, respectively; nonresponse AUC limit of 250 μg ml^-1 h^-1). Ninety-nine β-thalassemic patients were enrolled. Drug plasma C_trough and AUC were measured by the high-performance liquid chromatography system coupled with an ultraviolet determination method. Allelic discrimination for VDR, CYP24A1, CYP27B1 and GC gene SNPs was performed by real-time PCR. CYP24A1 22776 TT significantly influenced C_min and negatively predicted it in regression analysis. CYP24A1 3999 CC was associated with C_trough and C_min and was a negative predictor of T_max, whereas CYP24A1 8620 GG seemed to have a role in C_trough, AUC, t_1/2 and C_min, and was an AUC negative predictor factor. Considering treatment outcome, Cdx2 and GC 1296 were retained in regression analysis as AUC efficacy cutoff negative predictors.

Association of Vitamin D3 Level with Breast Cancer Risk and Prognosis in African-American and Hispanic Women

Background: This study investigated the association of vitamin D3 levels with breast cancer risk and progression in African-Americans and Hispanics. Methods: A total of 237 African-American (Cases = 119, Control = 118) and 423 Hispanic women (Cases = 124, Control = 299) were recruited in the study. Blood samples were collected at the time of breast cancer screening and prior to cancer treatment for 4 weeks on average for the cases. The serum 25-hydroxyvitamin D (25(OH)D3) was measured at a Quest-Diagnostics facility. Results: The results showed that 69.2% of African-Americans and 37.8% of Hispanics had 25(OH)D3 levels below 20 ng/mL. The 25(OH)D3 level below 20 ng/mL was significantly associated with breast cancer in both African-Americans (OR = 2.5, 95% CI = 1.3-4.8) and Hispanics (OR = 1.9, 95% CI = 1.1-3.0). However, the predicted probabilities of breast cancer in African-Americans were significantly higher than in Hispanics (p < 0.001). The 25(OH)D3 below 20 ng/mL was significantly associated with triple negative breast cancer (TNBC) in African-Americans (OR = 5.4, p = 0.02, 95% CI = 1.4-15), but not in Hispanics in our cohort of participants. Levels of 25(OH)D3 below 26 ng/mL predicts a decrease in disease-free survival, but it was not an independent predictor. Conclusions: Our data shows an association between 25(OH)D3 levels and the risk of breast cancer. Further studies on the relationship between 25(OH)D3 level and breast cancer risk are warranted.

Beneficial effects of bile acid receptor agonists in pulmonary disease models

INTRODUCTION

Bile acids act as steroid hormones, controlling lipid, glucose and energy metabolism, as well as inflammation and fibrosis. Their actions are implemented through activation of nuclear (FXR, VDR, PXR) and membrane G protein-coupled (TGR5, S1PR2) receptors. Areas covered: This review discusses the potential of FXR and TGR5 as therapeutic targets in the treatment of pulmonary disorders linked to metabolism and/or inflammation. Obeticholic acid (OCA) is the most clinically advanced bile acid-derived agonist for FXR-mediated anti-inflammatory and anti-fibrotic effects. It therefore represents an attractive pharmacological approach for the treatment of lung conditions characterized by vascular and endothelial dysfunctions. Expert opinion: Inflammation, vascular remodeling and fibrotic processes characterize the progression of pulmonary arterial hypertension (PAH) and idiopathic pulmonary fibrosis (IPF). These processes are only partially targeted by the available therapeutic options and still represent a relevant medical need. The results hereby summarized demonstrate OCA efficacy in preventing experimental lung disorders, i.e. monocrotaline-induced PAH and bleomycin-induced fibrosis, by abating proinflammatory and vascular remodeling progression. TGR5 is also expressed in the lung, and targeting the TGR5 pathway, using the TGR5 agonist INT-777 or the dual FXR/TGR5 agonist INT-767, could also contribute to the treatment of pulmonary disorders mediated by inflammation and fibrosis.

Endocrine actions of vitamin D in skin: Relevance for photocarcinogenesis of non-melanoma skin cancer, and beyond

The skin represents a pivotal organ for the human body's vitamin D endocrine system, being both the site of ultraviolet (UV)-B-induced vitamin D synthesis and a target tissue for the pluripotent effects of 1,25(OH)₂D₃ and other biologically active vitamin D metabolites. As many other steroid hormones, 1,25(OH)₂D₃ exerts its effects via two independent signal transduction pathways: the classical genomic and the non-genomic pathway. While non-genomic effects of 1,25(OH)₂D₃ are in part exerted via effects on intracellular calcium, genomic effects are mediated by the vitamin D receptor (VDR). Recent findings convincingly support the concept of a new function of the VDR as a tumor suppressor in skin, with key components of the vitamin D endocrine system, including VDR, CYP24A1, CYP27A1, and CYP27B1 being strongly expressed in non-melanoma skin cancer (NMSC). It has now been shown that anti-tumor effects of VDR, that include some of its ligand-induced growth-regulatory effects, are at least in part mediated by interacting in a highly coordinated manner with the p53 family (p53/p63/p73) in response to a large number of alterations in cell homeostasis, including UV-induced DNA damage, a hallmark for skin photocarcinogenesis. Considering the relevance of the vitamin D endocrine system for carcinogenesis of skin cancer, it is not surprising that low 25(OH)D serum concentrations and genetic variants (SNPs) of the vitamin D endocrine system have been identified as potential risk factors for occurrence and prognosis of skin malignancies. In conclusion, an increasing body of evidence now convincingly supports the concept that the vitamin D endocrine system is of relevance for photocarcinogenesis and progression of NMSC and that its pharmacologic modulation by vitamin D, 1,25(OH)₂D_3, and analogs represents a promising new strategy for prevention and/or treatment of these malignancies.

The role of vitamin D in the endocrinology controlling calcium homeostasis

Vitamin D and its' metabolites are a crucial part of the endocrine system that controls whole body calcium homeostasis. The goal of this hormonal control is to regulate serum calcium levels so that they are maintained within a very narrow range. To achieve this goal, regulatory events occur in coordination at multiple tissues, e.g. the intestine, kidney, bone, and parathyroid gland. Production of the vitamin D endocrine hormone, 1,25 dihydroxyvitamin D (1,25(OH)2 D) is regulated by habitual dietary calcium intake and physiologic states like growth, aging, and the menopause. The molecular actions of 1,25(OH)2 D on calcium regulating target tissues are mediated predominantly by transcription controlled by the vitamin D receptor. A primary role for 1,25(OH)2 D during growth is to increase intestinal calcium absorption so that sufficient calcium is available for bone mineralization. However, vitamin D also has specific actions on kidney and bone.

Effect of Vitamin D Deficiency on Voice

PURPOSE

The purpose of this article was to investigate the relationship between low level of vitamin D, phonatory symptoms, and acoustic findings.

METHOD

A total of 38 subjects presenting to the endocrinology clinic were enrolled in 2 groups: 19 with vitamin D deficiency who were not on treatment, and 19 with normal vitamin D level who were on treatment. Demographic data included age, gender, and history of smoking. All patients were asked about the presence or absence of dysphonia, degree of phonatory effort, and vocal fatigue. Acoustic analysis and perceptual evaluation using the grade, roughness, breathiness, asthenia, and strain scale were performed on all subjects.

RESULTS

The mean age of the total group was 47.29 ± 13.52 years. The difference in the mean and frequency of phonatory effort, vocal fatigue, and dysphonia, and in the mean of the acoustic variables, perceptual parameters, and the score of the Voice Handicap Index-10 was not statistically significant between patients with low vitamin D levels compared with controls.

CONCLUSION

The results of this study revealed no significant difference in the prevalence of phonatory symptoms in patients with vitamin D deficiency compared with patients with no vitamin D deficiency. A larger study is needed to substantiate the difference in the prevalence of phonatory systems between the 2 groups.

Role of vitamin D pathway gene polymorphisms on rifampicin plasma and intracellular pharmacokinetics

AIM

We retrospectively evaluate the pharmacogenetic role of single nucleotide polymorphisms involved in rifampicin transport (SLCO1B1, MDR1 and PXR genes) and vitamin D (VDR, CYP24A1 and CYP27B1 genes) metabolism and activity on drug plasma and intracellular concentrations.

PATIENTS & METHODS

Rifampicin C_max and C_trough were measured at weeks 2 and 4 using Ultra-Performance Liquid Chromatography-tandem mass spectroscopy methods. Allelic discrimination was performed by real-time polymerase chain reaction.

RESULTS

Twenty-four patients were enrolled. At week 2, OATP1B1 521TT and CYP27B1 +2838CC/CT considering plasma and BsmIAA for intraperipheral blood mononuclear cells C_max, remained in regression analysis. Concerning week 4, TaqITC/CC and CYP24A1 22776CT/TT were retained in plasma C_max regression model.

CONCLUSION

This study confirms the role of SLCO1B1 and it suggests the involvement of vitamin D pathway gene polymorphisms in rifampicin pharmacokinetics.