Characterization of a vitamin D receptor knockout mouse as a model of colorectal hyperproliferation and DNA damage

Delineating the role of nuclear receptors in colorectal cancer, a focused review

Colorectal cancer (CRC) stands as one of the most prevalent form of cancer globally, causing a significant number of deaths, surpassing 0.9 million in the year 2020. According to GLOBOCAN 2020, CRC ranks third in incidence and second in mortality in both males and females. Despite extensive studies over the years, there is still a need to establish novel therapeutic targets to enhance the patients' survival rate in CRC. Nuclear receptors (NRs) are ligand-activated transcription factors (TFs) that regulate numerous essential biological processes such as differentiation, development, physiology, reproduction, and cellular metabolism. Dysregulation and anomalous expression of different NRs has led to multiple alterations, such as impaired signaling cascades, mutations, and epigenetic changes, leading to various diseases, including cancer. It has been observed that differential expression of various NRs might lead to the initiation and progression of CRC, and are correlated with poor survival outcomes in CRC patients. Despite numerous studies on the mechanism and role of NRs in this cancer, it remains of significant scientific interest primarily due to the diverse functions that various NRs exhibit in regulating key hallmarks of this cancer. Thus, modulating the expression of NRs with their agonists and antagonists, based on their expression levels, holds an immense prospect in the diagnosis, prognosis, and therapeutical modalities of CRC. In this review, we primarily focus on the role and mechanism of NRs in the pathogenesis of CRC and emphasized the significance of targeting these NRs using a variety of agents, which may represent a novel and effective strategy for the prevention and treatment of this cancer.

Long-Term Prognosis in Relation to Vitamin D Status in Pediatric Solid Tumor Patients

BACKGROUND

Hypovitaminosis D is associated with oncogenesis, and the initial level of Vitamin D may play a role in determining long-term prognosis, relapse-free survival (RFS) and overall survival (OS). The purpose of our study was to follow up pediatric cancer patients for a long time in terms of their baseline Vitamin D level and disease outcomes.

METHODS

We collected data on the initial 25(OH)D concentration in 117 children and examined their RFS and OS using Kaplan-Meier curves.

RESULTS

The initial 25(OH)D mean value in the relapsed group was 20.35 ng/mL (SE: 2.05) and in children without relapse it was 26.14 ng/mL (SE: 1.13). Both the relapse-free and overall Kaplan-Meier curves showed a tendency for children with lower serum Vitamin D concentrations to experience cancer recurrence or fatal outcomes sooner than patients with normal serum levels.

CONCLUSIONS

Our results indicated a possible correlation between higher pretreatment serum Vitamin D concentrations and improved overall and relapse-free survival.

Role of vitamin D in targeting cancer and cancer stem cell populations and its therapeutic implications

Cancer is recognized globally as the second-most dominating and leading cause of morbidities. Fighting the global health epidemic threat posed by cancer requires progress and improvements in imaging techniques, surgical techniques, radiotherapy, and chemotherapy. The existence of a small subpopulation of undifferentiated cells known as cancer stem cells has been supported by accumulating evidence and ongoing research. According to clinical data, cancer recurrence, tumor development, and metastasis are thought to be caused by CSCs. Nutritional or dietary supplements can help you to fight against cancer and cope with the treatment side effects. Vitamin D, sometimes known as the sunshine vitamin, is produced in the skin in reaction to sunlight. Vitamin D deficiency is hazardous to any degree, increasing the risk of diseases such as cancer and disorders like osteoporosis. Bioactive vitamin D, or calcitriol, regulates several biological pathways. Many modes of action of Vitamin D might be helpful in protecting somatic stem cells (e.g., DNA damage repair and oxidative stress protection) or restricting cancer stem cell growth (e.g., cell cycle arrest, cell apoptosis). Researchers have recently begun to investigate the inhibitory effects of dietary vitamin D on cancer stem cells. In this review, we investigated the therapeutic impact of vitamin D and its molecular processes to target cancer and cancer stem cells as well.

The predictive value of vitamin D follow-up and supplementation on recurrence in patients with colorectal cancer

Aim: Vitamin D has a role in carcinogenesis and may have effect on recurrence. Thus, we aim to analyze the prognostic effect of vitamin D levels at beginning and follow-up together with the contribution of vitamin D supplementation on patients with colorectal cancer (CRC). Materials & methods: CRC patients who underwent curative surgery were included. Patients' vitamin D values were assessed under four groups according to baseline and follow-up vitamin D values, and whether vitamin D supplementation was used. Survival distributions were compared for vitamin D groups. Results: Patients with a high follow-up vitamin D level and a high vitamin D level after supplementation presented with better disease-free survival and overall survival than patients with low vitamin D and low vitamin D levels after supplementation. Conclusion: Follow-up vitamin D values seems to be a good predictive biomarker and vitamin D supplementation may have a positive effect on survival.

Vitamin D as therapeutic modulator in cerebrovascular diseases: a mechanistic perspectives

Vitamin D deficiency has been linked to several major chronic diseases, such as cardiovascular and neurodegenerative diseases, diabetes, and cancer, linked to oxidative stress, inflammation, and aging. Vitamin D deficiency appears to be particularly harmful to the cardiovascular system, as it can cause endothelial dysfunctioning and vascular abnormalities through the modulation of various downstream mechanisms. As a result, new research indicates that therapeutic approaches targeting vitamin D inadequacies or its significant downstream effects, such as impaired autophagy, abnormal pro-inflammatory and pro-oxidant reactions, may delay the onset and severity of major cerebrovascular disorders such as stroke and neurologic malformations. Vitamin D modulates the various molecular pathways, i.e., Nitric Oxide, PI3K-Akt Pathway, cAMP pathway, NF-kB Pathway, Sirtuin 1, Nrf2, FOXO, in cerebrovascular disorder. The current review shows evidence for vitamin D's mitigating or slowing the progression of these cerebrovascular disorders, which are significant causes of disability and death worldwide.

Vitamin D Is Necessary for Murine Gastric Epithelial Homeostasis

Unlike other organs, the importance of VD in a normal stomach is unknown. This study focuses on understanding the physiological role of vitamin D in gastric epithelial homeostasis. C57BL/6J mice were divided into three groups that were either fed a standard diet and kept in normal light/dark cycles (SDL), fed a standard diet but kept in the dark (SDD) or fed a vitamin D-deficient diet and kept in the dark (VDD). After 3 months, sera were collected to measure vitamin D levels by LC-MS/MS, gastric tissues were collected for immunohistochemical and gene expression analyses and gastric contents were collected to measure acid levels. The VDD group showed a significant decrease in the acid-secreting parietal cell-specific genes Atp4a and Atp4b when compared with the controls. This reduction was associated with an increased expression of an antral gastrin hormone. VDD gastric tissues also showed a high proliferation rate compared with SDL and SDD using an anti-BrdU antibody. This study indicates the requirement for normal vitamin D levels for proper parietal cell functions.

Implications of Vitamin D Research in Chickens can Advance Human Nutrition and Perspectives for the Future

The risk of vitamin D insufficiency in humans is a global problem that requires improving ways to increase vitamin D intake. Supplements are a primary means for increasing vitamin D intake, but without a clear consensus on what constitutes vitamin D sufficiency, there is toxicity risk with taking supplements. Chickens have been used in many vitamin-D-related research studies, especially studies involving vitamin D supplementation. Our state-of-the-art review evaluates vitamin D metabolism and how the different hydroxylated forms are synthesized. We provide an overview of how vitamin D is absorbed, transported, excreted, and what tissues in the body store vitamin D metabolites. We also discuss a number of studies involving vitamin D supplementation with broilers and laying hens. Vitamin D deficiency and toxicity are also described and how they can be caused. The vitamin D receptor (VDR) is important for vitamin D metabolism; however, there is much more to understand about VDR in chickens. Potential research aims involving vitamin D and chickens should explore VDR mechanisms that could lead to newer insights into VDR. Utilizing chickens in future research to help elucidate vitamin D mechanisms has great potential to advance human nutrition. Finding ways to increase vitamin D intake will be necessary because the coronavirus disease 2019 (COVID-19) pandemic is leading to increased risk of vitamin D deficiency in many populations. Chickens can provide a dual purpose with addressing pandemic-caused vitamin D deficiency: 1) vitamin D supplementation gives chickens added-value with the possibility of leading to vitamin-D-enriched meat and egg products; and 2) using chickens in research provides data for translational research. We believe expanding vitamin-D-related research in chickens to include more nutritional aims in vitamin D status has great implications for developing better strategies to improve human health.

Quercetin ameliorates reactive oxygen species generation, inflammation, mucus depletion, goblet disintegration, and tumor multiplicity in colon cancer: Probable role of adenomatous polyposis coli, β-catenin

1,2 Dimethyl hydrazine (DMH), a cogent environmental toxicant, targets the colon. Previous reports suggest that DMH-mediated dysregulation of the Wnt/β-catenin pathway plays a vital role in the initial events of colon carcinogenesis. Our study was designed to investigate the effect of quercetin on DMH-mediated colon cancer by targeting adenomatous polyposis coli (APC) and β-catenin in Wistar rats. Animals were pretreated orally with quercetin at doses of either 25 or 50 mg/kg bodyweight (bw) and DMH at a dose of 20 mg/kg bw subcutaneously up to the 15th week and sacrificed after the 30th week. DMH administration leads to reactive oxygen species generation, resulting in an imbalance in redox homeostasis and causing membrane lipid peroxidation, which is also partly due to the decrease in the level of tissue antioxidant machinery. Increased inflammatory and proliferative proteins were observed in DMH-induced colon cancerous rats. DMH treatment also led to dysregulation in the apoptotic pathway with decreased Bax:Bcl-2 ratio. Quercetin pretreatment ameliorates DMH-induced proliferation, activities of detoxifying enzymes, and putative early markers (mucin depletion and goblet cell disintegration) in colonic tissue. It also significantly regulates APC and β-catenin expression and inhibits tumor incidence and multiplicity. Histological results further confirm the beneficial role of quercetin in averting DMH-induced pathological alterations.

Pharmacogenomics of 5-fluorouracil in colorectal cancer: review and update

BACKGROUND

Colorectal cancer (CRC) is a disease with high morbidity and mortality rates. 5-fluorouracil (5-FU) is the first-line recommended drug for chemotherapy in patients with CRC, and it has a good effect on a variety of other solid tumors as well. Unfortunately, however, due to the emergence of drug resistance the effectiveness of treatment may be greatly reduced. In the past decade, major progress has been made in the field of 5-FU drug resistance in terms of molecular mechanisms, pre-clinical (animal) models and clinical trials.

CONCLUSIONS

In this article we systematically review and update current knowledge on 5-FU pharmacogenomics related to drug uptake and activation, the expression and activity of target enzymes (DPD, TS and MTHFR) and key signaling pathways in CRC. Furthermore, a summary of drug combination strategies aimed at targeting specific genes and/or pathways to reverse 5-FU resistance is provided. Based on this, we suggest that causal relationships between genes, pathways and drug sensitivity should be systematically considered from a multidimensional perspective. In the design of research methods, emerging technologies such as CRISPR-Cas, TALENS and patient-derived xenograft models should be applied as far as possible to improve the accuracy of clinically relevant results.

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 Vitamin D Receptor as Tumor Suppressor in Skin

Cutaneous malignancies including melanomas and keratinocyte carcinomas (KC) are the most common types of cancer, occurring at a rate of over one million per year in the United States. KC, which include both basal cell carcinomas and squamous cell carcinomas, are substantially more common than melanomas and form the subject of this chapter. Ultraviolet radiation (UVR), both UVB and UVA, as occurs with sunlight exposure is generally regarded as causal for these malignancies, but UVB is also required for vitamin D synthesis in the skin. Keratinocytes are the major cell in the epidermis. These cells not only produce vitamin D but contain the enzymatic machinery to metabolize vitamin D to its active metabolite, 1,25(OH)₂D, and express the receptor for this metabolite, the vitamin D receptor (VDR). This allows the cell to respond to the 1,25(OH)₂D that it produces. Based on our own data and that reported in the literature, we conclude that vitamin D signaling in the skin suppresses UVR-induced epidermal tumor formation. In this chapter we focus on four mechanisms by which vitamin D signaling suppresses tumor formation. They are inhibition of proliferation/stimulation of differentiation with discussion of the roles of hedgehog, Wnt/β-catenin, and hyaluronan/CD44 pathways in mediating vitamin D regulation of proliferation/differentiation, regulation of the balance between oncogenic and tumor suppressor long noncoding RNAs, immune regulation, and promotion of DNA damage repair (DDR).

Mechanisms Underlying Bone Loss Associated with Gut Inflammation

Patients with gastrointestinal diseases frequently suffer from skeletal abnormality, characterized by reduced bone mineral density, increased fracture risk, and/or joint inflammation. This pathological process is characterized by altered immune cell activity and elevated inflammatory cytokines in the bone marrow microenvironment due to disrupted gut immune response. Gastrointestinal disease is recognized as an immune malfunction driven by multiple factors, including cytokines and signaling molecules. However, the mechanism by which intestinal inflammation magnified by gut-residing actors stimulates bone loss remains to be elucidated. In this article, we discuss the main risk factors potentially contributing to intestinal disease-associated bone loss, and summarize current animal models, illustrating gut-bone axis to bridge the gap between intestinal inflammation and skeletal disease.

Effect of Vitamin D Supplementation on Faecal Microbiota: A Randomised Clinical Trial

In animal studies, vitamin D supplementation has been shown to improve gut microbiota and intestinal inflammation. However, limited evidence exists on the effect of vitamin D supplementation on the human gut microbiota. We examined the effect of vitamin D supplementation on faecal microbiota in 26 vitamin D-deficient (25-hydroxyvitamin D (25(OH)D) ≤50 nmol/L), overweight or obese (BMI ≥25 kg/m²) otherwise healthy adults. Our study was ancillary to a community based double-blind randomised clinical trial, conducted between 2014 and 2016. The participants provided stool samples at baseline and after 100,000 international units (IU) loading dose of cholecalciferol followed by 4000 IU daily or matching placebo for 16 weeks. Faecal microbiota was analysed using 16S rRNA sequencing; V6-8 region. There was no significant difference in microbiome α-diversity between vitamin D and placebo groups at baseline and follow-up (all p > 0.05). In addition, no clustering was found based on vitamin D supplementation at follow-up (p = 0.3). However, there was a significant association between community composition and vitamin D supplementation at the genus level (p = 0.04). The vitamin D group had a higher abundance of genus Lachnospira, and lower abundance of genus Blautia (linear discriminate analysis >3.0). Moreover, individuals with 25(OH)D >75 nmol/L had a higher abundance of genus Coprococcus and lower abundance of genus Ruminococcus compared to those with 25(OH)D <50 nmol/L. Our findings suggest that vitamin D supplementation has some distinct effects on faecal microbiota. Future studies need to explore whether these effects would translate into improved clinical outcomes.

A network-based predictive gene expression signature for recurrence risks in stage II colorectal cancer

The current criteria for defining the recurrence risks of stage II colorectal cancer (CRC) are not robust; therefore, we aimed to explore novel gene signatures to predict recurrence risks and to reveal the underlying mechanisms of stage II CRC. First, the gene expression profiles of 124 patients with stage II CRC from The Cancer Genome Atlas (TCGA) database were obtained to screen differentially expressed genes (DEGs). A total of 202 DEGs, including 128 upregulated and 74 downregulated, were identified in the recurrence group (n = 24) compared to the nonrecurrence group (n = 100). Furthermore, the top 5 DEGs (ZNF561, WFS1, SLC2A1, MFI2, and PTGR1) were identified by random forest variable hunting, and four (ZNF561, WFS1, SLC2A1, and PTGR1) were selected to create a four‐gene recurrent model (GRM), with an area under the curve (AUC) of 0.882 according to the receiver operating characteristic curve, and the robust diagnostic effectiveness of the GRM was further validated with another gene expression profiling dataset (GSE12032), with an AUC of 0.943. The diagnostic effectiveness of the GRM regarding recurrence was associated with poor disease‐free survival in all stages of CRC. In addition, gene ontology functional annotation and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses revealed 18 enriched functions and 6 enriched pathways. Four genes, ABCG2, CACNA1F, CYP19A1, and TF, were identified as hub genes by the protein‐protein interaction network, which further validated that these genes were correlated with a poor pathologic stage and overall survival in all stages of CRC. In conclusion, the GRM can effectively classify stage II CRC into groups of high and low risks of recurrence, thereby making up for the prognostic value of the traditional clinicopathological risk factors defined by the National Comprehensive Cancer Network guidelines. The hub genes may be useful therapeutic targets for recurrence. Thus, the GRM and hub genes could offer clinical value in directing individualized and precision therapeutic regimens for stage II CRC patients.

The Association of Dietary Intake of Calcium and Vitamin D to Colorectal Cancer Risk among Iranian Population

Background:

Vitamin D and Calcium have a possible protective impact versus rectal neoplasm. Vitamin D, an important nutrient, is vital to regulate the absorption of calcium and bone mineralization; nevertheless, in a case-control study in Iran, we investigated the relationship among the dietary intake of vitamin D and calcium with the hazard of rectal neoplasm.

Methods:

363 subjects (162 cases and 201 controls) participated in the case- control Study from March 2017 to November 2018. Dietary intake of Calcium and Vitamin D was calculated using a 148-items food-frequency questionnaire.

Results:

Since altering the strong confounding agents, the multivariate risk proportion within the dietary vitamin D intake was OR=0.2, 95%CI 0.1-0.5, P-value <0.001 among cases. There was no association in case of calcium and rectal cancer.

Conclusions:

Taken together, a possible reduction in the hazard of rectal neoplasm with dietary intake of Vitamin D within Iranian patients was observed.

Vitamin D attenuates gentamicin-induced acute renal damage via prevention of oxidative stress and DNA damage

Background:

Despite being one of the most nephrotoxic drugs, gentamicin (GM) remains a mainstay as a first-choice agent in a vast variety of clinical situations owing to its superlative efficiency as a broad-spectrum antibiotic in treating several life-threatening bacterial infections. This urgently calls for the need for in-depth analysis of the mechanisms governing GM-induced nephrotoxicity and entails the necessity of presenting novel protective agents capable of ameliorating those renal deleterious effects. The reactive oxygen species and redox-sensitive transcription factors in GM-induced nephrotoxicity have recently called attention.

Purpose:

This study has been designed to shed light on the possible mechanisms of GM-induced nephrotoxicity and to provide a consensus set of histopathological, immunohistochemical, genetic and biochemical parameters elucidating the protective role of vitamin D against this nephrotoxicity.

Methods:

Twenty-four adult male albino rats were equally divided into four groups: group I (control group), group II (GM), group III (GM + vitamin D) and group IV (vitamin D only). Kidney function tests, histopathological examination, gene expression of nuclear factor 2, nuclear factor kappa beta (NF-κB) and western blot of NF-κB p65, assessment of glutathione peroxidase and nicotinamide adenine dinucleotide phosphate oxidase (NADPH) oxidase by ELISA, as well as immunohistochemical evaluation of inducible nitric oxide, malondialdehyde, 8-hydroxy 2 deoxyguanine and vitamin D receptor, have been carried out.

Results:

The kidney function deterioration, tissue oxidative stress development and the histopathological changes induced by GM were significantly attenuated by vitamin D administration.

Conclusion:

Vitamin D attenuates GM nephrotoxicity through its antioxidant properties and prevention of DNA damage.

Vitamin D receptor FokI polymorphism and the risks of colorectal cancer, inflammatory bowel disease, and colorectal adenoma

Based on an inverse association between vitamin D levels and the risks of colorectal diseases, a functional start codon polymorphism in the vitamin D receptor (VDR) gene is speculated to affect the risks for these diseases. To validate this hypothesis, we first conducted a case-control study of 695 colorectal cancer patients and 1,397 controls. The association of VDR FokI polymorphism with colorectal cancer risk was analyzed using a logistic regression model. In the present case-control study, compared to the F allele, the f allele seemed to be associated with lower risks of colon cancer and advanced colorectal cancer. Additionally, a meta-analysis of 27 studies was conducted to combine findings from previous studies investigating the association of FokI polymorphism with colorectal disease using a random effects model. In the present meta-analysis, the f allele was positively associated with the risk of inflammatory bowel disease, including Crohn’s disease and ulcerative colitis. However, this allele was inversely associated with colon cancer and was not associated with the risk of rectal cancer or colorectal adenoma. In conclusion, the findings from this study imply that the role of VDR FokI polymorphism may differ based on the type and severity of colorectal disease.

Thioredoxin-Interacting Protein (TXNIP) in Cerebrovascular and Neurodegenerative Diseases: Regulation and Implication

Neurological diseases, including acute attacks (e.g., ischemic stroke) and chronic neurodegenerative diseases (e.g., Alzheimer's disease), have always been one of the leading cause of morbidity and mortality worldwide. These debilitating diseases represent an enormous disease burden, not only in terms of health suffering but also in economic costs. Although the clinical presentations differ for these diseases, a growing body of evidence suggests that oxidative stress and inflammatory responses in brain tissue significantly contribute to their pathology. However, therapies attempting to prevent oxidative damage or inhibiting inflammation have shown little success. Identification and targeting endogenous "upstream" mediators that normalize such processes will lead to improve therapeutic strategy of these diseases. Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of the thioredoxin (TRX) system, a major cellular thiol-reducing and antioxidant system. TXNIP regulating redox/glucose-induced stress and inflammation, now is known to get upregulated in stroke and other brain diseases, and represents a promising therapeutic target. In particular, there is growing evidence that glucose strongly induces TXNIP in multiple cell types, suggesting possible physiological roles of TXNIP in glucose metabolism. Recently, a significant body of literature has supported an essential role of TXNIP in the activation of the NOD-like receptor protein (NLRP3)-inflammasome, a well-established multi-molecular protein complex and a pivotal mediator of sterile inflammation. Accordingly, TXNIP has been postulated to reside centrally in detecting cellular damage and mediating inflammatory responses to tissue injury. The majority of recent studies have shown that pharmacological inhibition or genetic deletion of TXNIP is neuroprotective and able to reduce detrimental aspects of pathology following cerebrovascular and neurodegenerative diseases. Conspicuously, the mainstream of the emerging evidences is highlighting TXNIP link to damaging signals in endothelial cells. Thereby, here, we keep the trend to present the accumulative data on CNS diseases dealing with vascular integrity. This review aims to summarize evidence supporting the significant contribution of regulatory mechanisms of TXNIP with the development of brain diseases, explore pharmacological strategies of targeting TXNIP, and outline obstacles to be considered for efficient clinical translation.

Vitamin D Receptor Signaling and Cancer

The vitamin D receptor (VDR) binds the secosteroid hormone 1,25(OH)₂D₃ with high affinity and regulates gene programs that control a serum calcium levels, as well as cell proliferation and differentiation. A significant focus has been to exploit the VDR in cancer settings. Although preclinical studies have been strongly encouraging, to date clinical trials have delivered equivocal findings that have paused the clinical translation of these compounds. However, it is entirely possible that mining of genomic data will help to refine precisely what are the key anticancer actions of vitamin D compounds and where these can be used most effectively.

Vitamin D receptor and calcium-sensing receptor polymorphisms and colorectal cancer survival in the Newfoundland population

Background:

Increased serum levels of vitamin D and calcium have been associated with lower risks of colorectal cancer (CRC) incidence and mortality. These inverse associations may be mediated by the vitamin D receptor (VDR) and the calcium-sensing receptor (CASR). We investigated genetic variants in VDR and CASR for their relevance to CRC prognosis.

Methods:

A population-based cohort of 531 CRC patients diagnosed from 1999 to 2003 in Newfoundland and Labrador, Canada, was followed for mortality and cancer recurrence until April 2010. Germline DNA samples were genotyped with the Illumina Omni-Quad 1 Million chip. Multivariate Cox models assessed 41 tag single-nucleotide polymorphisms and relative haplotypes on VDR and CASR in relation to all-cause mortality (overall survival, OS) and disease-free survival (DFS).

Results:

Gene-level associations were observed between VDR and the DFS of rectal cancer patients (P=0.037) as well as between CASR and the OS of colon cancer patients (P=0.014). Haplotype analysis within linkage blocks of CASR revealed the G-G-G-G-G-A-C haplotype (rs10222633-rs10934578-rs3804592-rs17250717-A986S-R990G-rs1802757) to be associated with a decreased OS of colon cancer (HR, 3.15; 95% CI, 1.66–5.96). Potential interactions were seen among prediagnostic dietary calcium intake with the CASR R990G (P_int=0.040) and the CASR G-T-G-G-G-G-C haplotype for rs10222633-rs10934578-rs3804592-rs17250717-A986S-R990G-rs1802757 (P_int=0.017), with decreased OS time associated with these variants limited to patients consuming dietary calcium below the median, although the stratified results were not statistically significant after correction for multiple testing.

Conclusions:

Polymorphic variations in VDR and CASR may be associated with survival after a diagnosis of CRC.

Extraskeletal actions of vitamin D

The vitamin D receptor (VDR) is found in nearly all, if not all, cells in the body. The enzyme that produces the active metabolite of vitamin D and ligand for VDR, namely CYP27B1, likewise is widely expressed in many cells of the body. These observations indicate that the role of vitamin D is not limited to regulation of bone and mineral homeostasis, as important as that is. Rather, the study of its extraskeletal actions has become the major driving force behind the significant increase in research articles on vitamin D published over the past several decades. A great deal of information has accumulated from cell culture studies, in vivo animal studies, and clinical association studies that confirms that extraskeletal effects of vitamin D are truly widespread and substantial. However, randomized, placebo-controlled clinical trials, when done, have by and large not produced the benefits anticipated by the in vitro cell culture and in vivo animal studies. In this review, I will examine the role of vitamin D signaling in a number of extraskeletal tissues and assess the success of translating these findings into treatments of human diseases affecting those extracellular tissues.

Murine Pancreatic Acinar Cell Carcinoma Growth Kinetics Are Independent of Dietary Vitamin D Deficiency or Supplementation

Vitamin D has been proposed as a therapeutic strategy in pancreatic cancer, yet evidence for an effect of dietary vitamin D on pancreatic cancer is ambiguous, with conflicting data from human epidemiological and intervention studies. Here, we tested the role of dietary vitamin D in the in vivo context of the well-characterized Ela1-TAg transgenic mouse model of pancreatic acinar cell carcinoma. Through longitudinal magnetic resonance imaging of mice under conditions of either dietary vitamin D deficiency (<5 IU/kg vitamin D) or excess (76,500 IU/kg vitamin D), compared to control diet (1,500 IU/kg vitamin D), we measured the effect of variation of dietary vitamin D on tumor kinetics. No measurable impact of dietary vitamin D was found on pancreatic acinar cell carcinoma development, growth or mortality, casting further doubt on the already equivocal data supporting potential therapeutic use in humans. The lack of any detectable effect of vitamin D, within the physiological range of dietary deficiency or supplementation, in this model further erodes confidence in vitamin D as an effective antitumor therapeutic in pancreatic acinar cell carcinoma.

Vitamin D Receptor-Dependent Signaling Protects Mice From Dextran Sulfate Sodium-Induced Colitis

Low vitamin D status potentiates experimental colitis, but the vitamin D-responsive cell in colitis has not been defined. We hypothesized that vitamin D has distinct roles in colonic epithelial cells and in nonepithelial cells during colitis. We tested this hypothesis by using mice with vitamin D receptor (VDR) deletion from colon epithelial cells (CEC-VDRKO) or nonintestinal epithelial cells (NEC-VDRKO). Eight-week-old mice were treated with 1.35% dextran sulfate sodium (DSS) for 5 days and then euthanized 2 or 10 days after removal of DSS. DSS induced body weight loss and increased disease activity index and spleen size. This response was increased in NEC-VDRKO mice but not CEC-VDRKO mice. DSS-induced colon epithelial damage and immune cell infiltration scores were increased in both mouse models. Although the epithelium healed between 2 and 10 days after DSS administration in control and CEC-VDRKO mice, epithelial damage remained high in NEC-VDRKO mice 10 days after removal of DSS, indicating delayed epithelial healing. Gene expression levels for the proinflammatory, M1 macrophage (Mɸ) cytokines tumor necrosis factor-α, nitric oxide synthase 2, and interleukin-1β were significantly elevated in the colon of NEC-VDRKO mice at day 10. In vitro experiments in murine peritoneal Mɸs demonstrated that 1,25 dihydroxyvitamin D directly inhibited M1 polarization, facilitated M2 polarization, and regulated Mɸ phenotype switching toward the M2 and away from the M1 phenotype. Our data revealed unique protective roles for vitamin D signaling during colitis in the colon epithelium as well as nonepithelial cells in the colon microenvironment (i.e., modulation of Mɸ biology).

Vitamin D and colorectal cancer: molecular, epidemiological and clinical evidence

In many cells throughout the body, vitamin D is converted into its active form calcitriol and binds to the vitamin D receptor (VDR), which functions as a transcription factor to regulate various biological processes including cellular differentiation and immune response. Vitamin D-metabolising enzymes (including CYP24A1 and CYP27B1) and VDR play major roles in exerting and regulating the effects of vitamin D. Preclinical and epidemiological studies have provided evidence for anti-cancer effects of vitamin D (particularly against colorectal cancer), although clinical trials have yet to prove its benefit. In addition, molecular pathological epidemiology research can provide insights into the interaction of vitamin D with tumour molecular and immunity status. Other future research directions include genome-wide research on VDR transcriptional targets, gene-environment interaction analyses and clinical trials on vitamin D efficacy in colorectal cancer patients. In this study, we review the literature on vitamin D and colorectal cancer from both mechanistic and population studies and discuss the links and controversies within and between the two parts of evidence.

Vitamin D Signaling Modulators in Cancer Therapy

The antiproliferative and pro-apoptotic effects of 1α,25-dihydroxycholecalciferol (1,25(OH)2D3, 1,25D3, calcitriol) have been demonstrated in various tumor model systems in vitro and in vivo. However, limited antitumor effects of 1,25D3 have been observed in clinical trials. This may be attributed to a variety of factors including overexpression of the primary 1,25D3 degrading enzyme, CYP24A1, in tumors, which would lead to rapid local inactivation of 1,25D3. An alternative strategy for improving the antitumor activity of 1,25D3 involves the combination with a selective CYP24A1 inhibitor. The validity of this approach is supported by numerous preclinical investigations, which demonstrate that CYP24A1 inhibitors suppress 1,25D3 catabolism in tumor cells and increase the effects of 1,25D3 on gene expression and cell growth. Studies are now required to determine whether selective CYP24A1 inhibitors+1,25D3 can be used safely and effectively in patients. CYP24A1 inhibitors plus 1,25D3 can cause dose-limiting toxicity of vitamin D (hypercalcemia) in some patients. Dexamethasone significantly reduces 1,25D3-mediated hypercalcemia and enhances the antitumor activity of 1,25D3, increases VDR-ligand binding, and increases VDR protein expression. Efforts to dissect the mechanisms responsible for CYP24A1 overexpression and combinational effect of 1,25D3/dexamethasone in tumors are underway. Understanding the cross talk between vitamin D receptor (VDR) and glucocorticoid receptor (GR) signaling axes is of crucial importance to the design of new therapies that include 1,25D3 and dexamethasone. Insights gained from these studies are expected to yield novel strategies to improve the efficacy of 1,25D3 treatment.

Effect of 1,25-dihydroxyvitamin D3 on the Wnt pathway in non-malignant colonic cells

Epidemiological studies suggest a correlation between vitamin D deficiency and colorectal cancer (CRC) incidence. The majority of sporadic tumors develop from premalignant lesions with aberrant activation of the Wnt/β-catenin signaling pathway. The adenoma cell line LT97 harbors an adenomatous polyposis coli (APC) mutation leading to constitutively active Wnt signaling. In these cells, expression of Wnt target genes leads to increased survival capacity. We hypothesized that 1,25-dihydroyvitamin D3 (1,25-D3), the active form of vitamin D3, promotes differentiation by modulating β-catenin/T-cell factor (TCF) 4-mediated gene transcription. The effect of dietary vitamin D on colonic Wnt signaling was investigated in mice fed either with 100 IU or 2500 IU vitamin D/kg diet. We examined the effect of 1,25-D3 on differentiation by measuring alkaline phosphatase activity. We analyzed mRNA expression of Wnt target genes by real time qRT-PCR. The impact of 1,25-D3 on β-catenin and TCF4 protein expression was assessed by western blot and immunohistochemistry. In LT97 cells, 1,25-D3 increased cellular differentiation and reduced nuclear β-catenin levels. Further, 1,25-D3 decreased mRNA expression of the Wnt target genes BCL-2, Cyclin D1, Snail1, CD44 and LGR5. In healthy colon of mice fed with high vitamin D diet, the mRNA levels of Wnt5a and ROR2, that promote degradation of β-catenin, were upregulated whereas β-catenin and TCF4 protein expression were decreased. In conclusion, 1,25-D3 inhibits Wnt signaling even in nonmalignant cells underlining its importance in protection against colorectal tumorigenesis and early tumor progression. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Impaired Vitamin D Signaling in Endothelial Cell Leads to an Enhanced Leukocyte-Endothelium Interplay: Implications for Atherosclerosis Development

Endothelial cell activation leading to leukocyte recruitment and adhesion plays an essential role in the initiation and progression of atherosclerosis. Vitamin D has cardioprotective actions, while its deficiency is a risk factor for the progression of cardiovascular damage. Our aim was to assess the role of basal levels of vitamin D receptor (VDR) on the early leukocyte recruitment and related endothelial cell-adhesion-molecule expression, as essential prerequisites for the onset of atherosclerosis. Knockdown of VDR in endothelial cells (shVDR) led to endothelial cell activation, characterized by upregulation of VCAM-1, ICAM-1 and IL-6, decreased peripheral blood mononuclear cell (PBMC) rolling velocity and increased PBMC rolling flux and adhesion to the endothelium. shVDR cells showed decreased IκBα levels and accumulation of p65 in the nucleus compared to shRNA controls. Inhibition of NF-κB activation with super-repressor IκBα blunted all signs of endothelial cell activation caused by downregulation of VDR in endothelial cells. In vivo, deletion of VDR led to significantly larger aortic arch and aortic root lesions in apoE^-/- mice, with higher macrophage content. apoE^-/-VDR^-/-mice showed higher aortic expression of VCAM-1, ICAM-1 and IL-6 when compared to apoE^-/-VDR^+/+ mice. Our data demonstrate that lack of VDR signaling in endothelial cells leads to a state of endothelial activation with increased leukocyte-endothelial cell interactions that may contribute to the more severe plaque accumulation observed in apoE^-/-VDR^-/- mice. The results reveal an important role for basal levels of endothelial VDR in limiting endothelial cell inflammation and atherosclerosis.

Restoration of the anti-proliferative and anti-migratory effects of 1,25-dihydroxyvitamin D by silibinin in vitamin D-resistant colon cancer cells

Colorectal carcinoma (CRC) is the third most common cancer in developed countries. A large fraction of cases are linked to chronic intestinal inflammation, with concomitant increased TNF-α release and elevated Snail1/Snail2 levels. These transcription factors in turn suppress vitamin D receptor (VDR) expression, resulting in loss of responsiveness to the protective anti-proliferative and anti-migratory effects of 1,25-dihydroxyvitamin D (1,25D). Experimental and epidemiologic evidence support the use of natural products to target CRC. Here we show that the flavonolignan silibinin reverses the TNF-α-induced upregulation of Snail1 and Snail2 in the 1,25D-resistant human colon carcinoma cells HT-29. These silibinin effects are accompanied by an increase in VDR levels; Snail1 overexpression reverses these silibinin effects. Silibinin also restores promoter activity from a vitamin D-response element (VDRE) reporter construct. While 1,25D had no significant effect on HT-29 and SW480-R cell proliferation and migration, co-treatment with silibinin restored 1,25D responsiveness. In addition, co-treatment with silibinin plus 1,25D decreased proliferation and migration at doses where silibinin alone had no effect. These findings demonstrate that this combination may present a novel approach to target CRC in conditions of chronic colonic inflammation.

Role of local bioactivation of vitamin D by CYP27A1 and CYP2R1 in the control of cell growth in normal endometrium and endometrial carcinoma

Vitamin D (VD) deficiency has been suggested as a risk factor for cancer. One recognized mechanism is that the low-serum 25-hydroxyvitamin D (25(OH)D) of VD deficiency reduces intratumoral 25(OH)D conversion to 1α,25-dihydroxyvitamin D (1,25D, the hormonal form of VD), compromising 1,25D-VD receptor (VDR) antitumoral actions. Reduced tumoral VDR and increased CYP24A1, the enzyme that degrades 1,25D and 25(OH)D, further worsen cancer progression. Importantly, in cells expressing CYP27A1 and/or CYP2R1, which convert inert VD into 25(OH)D, low-serum VD may reduce intratumoral 25(OH)D synthesis thereby compromising VDR antitumoral actions because 25(OH)D can activate the VDR directly and enhance 1,25D-VDR action. Therefore, this study examined whether abnormal endometrial expression of CYP27A1 and/or CYP2R1 may impair VDR-antiproliferative properties in endometrial carcinoma (EC). Immunohistochemical analysis of tissue microarrays of normal human endometrium (NE; n=60) and EC (n=157) showed the expected lower VDR expression in EC (P=0.0002). Instead, CYP24A1 expression was lower in EC compared with NE, while CYP27A1 and CYP2R1 expressions were higher (P=0.0002; P=0.03). Furthermore, in NE and EC, CYP2R1 and CYP27A1 expression correlated directly with nuclear VDR levels, an indicator of ligand-induced VDR activation, and inversely with the proliferation marker Ki67. Accordingly, in the endometrioid carcinoma cell lines IK, RL95/2 and HEC1-A, which express VDR, CYP27A1, and CYP2R1, VD efficaciously reduced cell viability and colony number, with a time course that paralleled actual increases in both intracellular 25(OH)D and nuclear VDR levels. Thus, VD may protect from EC progression in part through increased intratumoral 25(OH)D production by CYP27A1 and CYP2R1 for autocrine/paracrine enhancement of 1,25D-VDR-antiproliferative actions.

Lack of vitamin D receptor causes stress-induced premature senescence in vascular smooth muscle cells through enhanced local angiotensin-II signals

OBJECTIVES

The inhibition of the renal renin-angiotensin system by the active form of vitamin D contributes to the cardiovascular health benefits of a normal vitamin D status. Local production of angiotensin-II in the vascular wall is a potent mediator of oxidative stress, prompting premature senescence. Herein, our objective was to examine the impact of defective vitamin D signalling on local angiotensin-II levels and arterial health.

METHODS

Primary cultures of aortic vascular smooth muscle cells (VSMC) from wild-type and vitamin D receptor-knockout (VDRKO) mice were used for the assessment of cell growth, angiotensin-II and superoxide anion production and expression levels of cathepsin D, angiotensin-II type 1 receptor and p57(Kip2). The in vitro findings were confirmed histologically in aortas from wild-type and VDRKO mice.

RESULTS

VSMC from VDRKO mice produced more angiotensin-II in culture, and elicited higher levels of cathepsin D, an enzyme with renin-like activity, and angiotensin-II type 1 receptor, than wild-type mice. Accordingly, VDRKO VSMC showed higher intracellular superoxide anion production, which could be suppressed by cathepsin D, angiotensin-II type 1 receptor or NADPH oxidase antagonists. VDRKO cells presented higher levels of p57(Kip2), impaired proliferation and premature senescence, all of them blunted upon inhibition of angiotensin-II signalling. In vivo studies confirmed higher levels of cathepsin D, angiotensin-II type 1 receptor and p57(Kip2) in aortas from VDRKO mice.

CONCLUSION

The beneficial effects of active vitamin D in vascular health could be a result of the attenuation of local production of angiotensin-II and downstream free radicals, thus preventing the premature senescence of VSMC.

Vitamin D and cancer: the promise not yet fulfilled

The negative association of the latitude where people live and the incidence of non cutaneous cancer in that population in North America have been demonstrated in many studies for many types of cancer. Since the intensity of UVB exposure decreases with increasing latitude, and UVB exposure provides the mechanism for vitamin D production in the skin, the hypothesis that increased vitamin D provides protection against the development of cancer has been proposed. This hypothesis has been tested in a substantial number of prospective and case control studies and in a few randomized clinical trials (RTC) assessing whether either vitamin D intake or serum levels of 25 hydroxyvitamin D (25OHD) correlate (inversely) with cancer development. Most of the studies have focused on colorectal, breast, and prostate cancer. The results have been mixed. The most compelling data for a beneficial relationship between vitamin D intake or serum 25OHD levels and cancer have been obtained for colorectal cancer. The bulk of the evidence also favors a beneficial relationship for breast cancer, but the benefit of vitamin D for prostate and skin cancer in clinical populations has been difficult to demonstrate. RTCs in general have been flawed in execution or too small to provide compelling evidence one way or the other. In contrast, animal studies have been quite consistent in their demonstration that vitamin D and/or its active metabolite 1,25 dihydroxyvitamin D (1,25(OH)2D) can prevent the development and/or treat a variety of cancers in a variety of animal models. Furthermore, 1,25(OH)2D has been shown to impact a number of cellular mechanisms that would be expected to underlie its anticancer effects. Thus, there is a dilemma-animal and cellular studies strongly support a role for vitamin D in the prevention and treatment of cancer, but the clinical studies for most cancers have not yet delivered compelling evidence that the promise from preclinical studies has been fulfilled in the clinic.

Vitamin D, steroid hormones, and autoimmunity

The endogenous serum metabolite of vitamin D (calcitriol, 1,25(OH)2 D3 ) is considered a true steroid hormone (D hormone), and like glucocorticoids (GCs) and gonadal hormones, may exert several immunomodulatory activities. Serum vitamin D deficiency (25(OH) D), and therefore reduced 1,25(OH)2 D3 availability, is considered a risk factor for several chronic/inflammatory or autoimmune conditions, including infectious diseases, type 1 diabetes, multiple sclerosis, and especially autoimmune rheumatic diseases (ARD). In ARD in particular, 1,25(OH)2 D3 regulates both innate and adaptive immunity, potentiating the innate response (antimicrobial activity) but reducing adaptive immunity (antigen presentation, T and B cell activities). Regarding a possible synergism between vitamin D and GCs, several studies show that 1,25(OH)2 D3 has significant additive effects on dexamethasone-mediated inhibition of human lymphocyte and monocyte proliferation. Conversely, vitamin D deficiency seems to play a role in increasing autoantibody production by B cells, and seasonal vitamin D declines may trigger flares in ARD, as recently shown. Finally, 1,25(OH)2 D3 seems to reduce aromatase activity and limit the negative effects related to increased peripheral estrogen metabolism (cell proliferation, B cell overactivity).

Vitamin D activates the Nrf2-Keap1 antioxidant pathway and ameliorates nephropathy in diabetic rats

BACKGROUND

Diabetic nephropathy is a major risk of end-stage kidney disease. Many complex factors relate to the progression of diabetic nephropathy. Using nonobese type 2 diabetes model rats, we confirmed that oxidative stress was a crucial factor. Because recent studies suggest that vitamin D could suppress oxidative stress, we explored whether the active vitamin D analog, maxacalcitol, could also attenuate oxidative stress and prevent the progression of diabetic nephropathy.

METHODS

Diabetic rats aged 20 weeks were divided into 3 groups and treated with insulin, maxacalcitol, and vehicle. At age 30 weeks, blood and urine analyses, renal histology, immunohistochemistry, real-time polymerase chain reaction, and western blot were performed.

RESULTS

Although maxacalcitol reduced albuminuria and mesangial matrix expansion, no significant differences were observed in blood pressure and creatinine clearance among the 3 treatment groups. Systemic and intrarenal oxidative stress was reduced by maxacalcitol therapy. Expressions of nuclear factor-κB and nicotinamide adenine dinucleotide phosphate oxidase in the kidney also decreased in the insulin-treated and maxacalcitol-treated groups but increased in the vehicle-alone group. In addition, the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) decreased and Kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated protein 1 (Keap1) increased in the vehicle-treated group; however, these expressions were restored in the maxacalcitol- and insulin-treated groups.

CONCLUSIONS

It is suggested that maxacalcitol attenuates the progression of diabetic nephropathy by suppression of oxidative stress and amelioration of the Nrf2-Keap1 pathway in nonobese type 2 diabetes without significant changes in blood pressure and glomerular filtration rate.

Vitamin D receptor regulates intestinal proteins involved in cell proliferation, migration and stress response

Background

Genome-wide association studies found low plasma levels of 25-hydroxyvitamin D and vitamin D receptor (VDR) polymorphisms associated with a higher prevalence of pathological changes in the intestine such as chronic inflammatory bowel diseases.

Methods

In this study, a proteomic approach was applied to understand the overall physiological importance of vitamin D in the small intestine, beyond its function in calcium and phosphate absorption.

Results

In total, 569 protein spots could be detected by two-dimensional-difference in-gel electrophoresis (2D-DIGE), and 82 proteins were considered as differentially regulated in the intestinal mucosa of VDR-deficient mice compared to that of wildtype (WT) mice. Fourteen clearly detectable proteins were identified by MS/MS and further analyzed by western blot and/or real-time RT-PCR. The differentially expressed proteins are functionally involved in cell proliferation, cell adhesion and cell migration, stress response and lipid transport. Mice lacking VDR revealed higher levels of intestinal proteins associated with proliferation and migration such as the 37/67 kDa laminin receptor, collagen type VI (alpha 1 chain), keratin-19, tropomyosin-3, adseverin and higher levels of proteins involved in protein trafficking and stress response than WT mice. In contrast, proteins that are involved in transport of bile and fatty acids were down-regulated in small intestine of mice lacking VDR compared to WT mice. However, plasma and liver concentrations of cholesterol and triglycerides were not different between the two groups of mice.

Conclusion

Collectively, these data imply VDR as an important factor for controlling cell proliferation, migration and stress response in the small intestine.

The molecular basis for the pharmacokinetics and pharmacodynamics of curcumin and its metabolites in relation to cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

Vitamin D Is a Multilevel Repressor of Wnt/b-Catenin Signaling in Cancer Cells

The Wnt/b-catenin signaling pathway is abnormally activated in most colorectal cancers and in a proportion of other neoplasias. This activation initiates or contributes to carcinogenesis by regulating the expression of a large number of genes in tumor cells. The active vitamin D metabolite 1a,25-dihydroxyvitamin D3 (1,25(OH)2D3) inhibits Wnt/b-catenin signaling by several mechanisms at different points along the pathway. Additionally, paracrine actions of 1,25(OH)2D3 on stromal cells may also repress this pathway in neighbouring tumor cells. Here we review the molecular basis for the various mechanisms by which 1,25(OH)2D3 antagonizes Wnt/b-catenin signaling, preferentially in human colon carcinoma cells, and the consequences of this inhibition for the phenotype and proliferation rate. The effect of the vitamin D system on Wnt/b-catenin signaling and tumor growth in animal models will also be commented in detail. Finally, we revise existing data on the relation between vitamin D receptor expression and vitamin D status and the expression of Wnt/b-catenin pathway genes and targets in cancer patients.

Vitamin D Is a Multilevel Repressor of Wnt/b-Catenin Signaling in Cancer Cells

The Wnt/β-catenin signaling pathway is abnormally activated in most colorectal cancers and in a proportion of other neoplasias. This activation initiates or contributes to carcinogenesis by regulating the expression of a large number of genes in tumor cells. The active vitamin D metabolite 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) inhibits Wnt/β-catenin signaling by several mechanisms at different points along the pathway. Additionally, paracrine actions of 1,25(OH)₂D₃ on stromal cells may also repress this pathway in neighbouring tumor cells. Here we review the molecular basis for the various mechanisms by which 1,25(OH)₂D₃ antagonizes Wnt/β-catenin signaling, preferentially in human colon carcinoma cells, and the consequences of this inhibition for the phenotype and proliferation rate. The effect of the vitamin D system on Wnt/β-catenin signaling and tumor growth in animal models will also be commented in detail. Finally, we revise existing data on the relation between vitamin D receptor expression and vitamin D status and the expression of Wnt/β-catenin pathway genes and targets in cancer patients.

Molecular link between vitamin D and cancer prevention

The metabolite of vitamin D, 1α,25-dihydroxyvitamin D₃ (also known as calcitriol), is a biologically active molecule required to maintain the physiological functions of several target tissues in the human body from conception to adulthood. Its molecular mode of action ranges from immediate nongenomic responses to longer term mechanisms that exert persistent genomic effects. The genomic mechanisms of vitamin D action rely on cross talk between 1α,25-dihydroxyvitamin D₃ signaling pathways and that of other growth factors or hormones that collectively regulate cell proliferation, differentiation and cell survival. In vitro and in vivo studies demonstrate a role for vitamin D (calcitriol) in modulating cellular growth and development. Vitamin D (calcitriol) acts as an antiproliferative agent in many tissues and significantly slows malignant cellular growth. Moreover, epidemiological studies have suggested that ultraviolet-B exposure can help reduce cancer risk and prevalence, indicating a potential role for vitamin D as a feasible agent to prevent cancer incidence and recurrence. With the preventive potential of this biologically active agent, we suggest that countries where cancer is on the rise--yet where sunlight and, hence, vitamin D may be easily acquired--adopt awareness, education and implementation strategies to increase supplementation with vitamin D in all age groups as a preventive measure to reduce cancer risk and prevalence.

Vitamin D3 insufficiency and colorectal cancer

Traditionally the main recognized function of vitamin D has been calcium and phosphate homeostasis. Nevertheless, recent evidences have highlighted the importance of vitamin D3 as a protective agent against various cancers. The association between CRC and vitamin D3 was first suggested in ecologic studies, but further was confirmed by observational studies in humans and experimental studies in both animal models and cellular lines. The protective role of vitamin D3 against cancer has been attributed to its influence of on cell proliferation, differentiation, apoptosis, DNA repair mechanisms, inflammation and immune function. In its active (calcitriol) form (1,25-dihydroxyvitamin D3[1α,25-(OH)2D3]) vitamin D3 and the nuclear vitamin D receptor (VDR) regulate hundreds of genes including those coding for proteins involved in cell differentiation and cell proliferation. The current review addresses some of the key mechanisms that influence the biological actions of vitamin D and its metabolites. The insights derived from these mechanisms may aid in designing new uses for this hormone and its non-hypercalcemic derivatives in the treatment and/or prevention of CRC.

Role of calcium sensing receptor (CaSR) in tumorigenesis

The extracellular Ca(2+)-sensing receptor (CaSR) is a robust promoter of differentiation in colonic epithelial cells and functions as a tumor suppressor in colon cancer. CaSR mediates its biologic effects through diverse mechanisms. Loss of CaSR expression activates a myriad of stem cell-like molecular features that drive and sustain the malignant and drug-resistant phenotypes of colon cancer. This CaSR-null phenotype, however, is not irreversible and induction of CaSR expression in CaSR-null cells promotes cell death mechanisms and restores drug sensitivity. The CaSR also functions as a tumor suppressor in breast cancer and promotes cellular sensitivity to cytotoxic drugs. BRCA1 and CaSR functions intersect in breast cancer cells, and CaSR activation can rescue breast cancer cells from the deleterious effect of BRCA1 mutations.

Antineoplastic effects of 1,25(OH)2D3 and its analogs in breast, prostate and colorectal cancer

The active form of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), is mostly known for its importance in the maintenance of calcium and phosphate homeostasis. However, next to its classical effects on bone, kidney and intestine, 1,25(OH)2D3 also exerts antineoplastic effects on various types of cancer. The use of 1,25(OH)2D3 itself as treatment against neoplasia is hampered by its calcemic side effects. Therefore, 1,25(OH)2D3-derived analogs were developed that are characterized by lower calcemic side effects and stronger antineoplastic effects. This review mainly focuses on the role of 1,25(OH)2D3 in breast, prostate and colorectal cancer (CRC) and the underlying signaling pathways. 1,25(OH)2D3 and its analogs inhibit proliferation, angiogenesis, migration/invasion and induce differentiation and apoptosis in malignant cell lines. Moreover, prostaglandin synthesis and Wnt/b-catenin signaling are also influenced by 1,25(OH)2D3 and its analogs. Human studies indicate an inverse association between serum 25(OH)D3 values and the incidence of certain cancer types. Given the literature, it appears that the epidemiological link between vitamin D3 and cancer is the strongest for CRC, however more intervention studies and randomized placebo-controlled trials are needed to unravel the beneficial dose of 1,25(OH)2D3 and its analogs to induce antineoplastic effects.

Anti-oxidative effect of vitamin D analog on incipient vascular lesion in non-obese type 2 diabetic rats

BACKGROUND/AIMS

Vascular disease is one of the critical complications of diabetes. A growing body of evidence suggests that oxidative stress plays a key role for vascular disease progression. Recent studies have demonstrated a strong link between vitamin D and cardiovascular disease.

METHODS

We investigated the anti-oxidative effects of a vitamin D analog, 22-oxacalcitriol (maxacalcitol), on vascular lesions in type 2 diabetic rats. We used Spontaneously Diabetic Torii (SDT) rats, a model of non-obese type 2 diabetes. At 20 weeks of age, SDT rats were randomly divided into three groups: diabetes mellitus (DM, n = 10), DM + maxacalcitol (DM + D, n = 10), and DM + insulin (DM + I, n = 10). The rats were sacrificed at 30 weeks for the evaluation of blood and urine samples as well as histopathology and mRNA expression in the aorta.

RESULTS

Urinary 8-hydroxydeoxyguanosine (8-OHdG) excretion and the number of 8-OHdG-positive cells were significantly lower in the DM + I and DM + D groups than in the DM group. Real-time polymerase chain reaction analysis demonstrated that NADPH p22 phox and NADPH p47 phox mRNA levels were markedly decreased in the DM + I and DM + D groups compared with the DM group. Furthermore, the mRNA expression of MCP-1, ICAM-1 and VCAM-1 was significantly reduced in the DM + I and DM + D groups compared with the DM group.

CONCLUSION

Our results suggest that the vasoprotective effects of vitamin D are mediated by reducing oxidative stress.

Molecular mechanisms of vitamin D action

The hormonal metabolite of vitamin D, 1α,25-dihydroxyvitamin D(3) (1,25D), initiates biological responses via binding to the vitamin D receptor (VDR). When occupied by 1,25D, VDR interacts with the retinoid X receptor (RXR) to form a heterodimer that binds to vitamin D responsive elements in the region of genes directly controlled by 1,25D. By recruiting complexes of either coactivators or corepressors, ligand-activated VDR-RXR modulates the transcription of genes encoding proteins that promulgate the traditional functions of vitamin D, including signaling intestinal calcium and phosphate absorption to effect skeletal and calcium homeostasis. Thus, vitamin D action in a particular cell depends upon the metabolic production or delivery of sufficient concentrations of the 1,25D ligand, expression of adequate VDR and RXR coreceptor proteins, and cell-specific programming of transcriptional responses to regulate select genes that encode proteins that function in mediating the effects of vitamin D. For example, 1,25D induces RANKL, SPP1 (osteopontin), and BGP (osteocalcin) to govern bone mineral remodeling; TRPV6, CaBP(9k), and claudin 2 to promote intestinal calcium absorption; and TRPV5, klotho, and Npt2c to regulate renal calcium and phosphate reabsorption. VDR appears to function unliganded by 1,25D in keratinocytes to drive mammalian hair cycling via regulation of genes such as CASP14, S100A8, SOSTDC1, and others affecting Wnt signaling. Finally, alternative, low-affinity, non-vitamin D VDR ligands, e.g., lithocholic acid, docosahexaenoic acid, and curcumin, have been reported. Combined alternative VDR ligand(s) and 1,25D/VDR control of gene expression may delay chronic disorders of aging such as osteoporosis, type 2 diabetes, cardiovascular disease, and cancer.

Age-related changes in the response of intestinal cells to 1α,25(OH)2-vitamin D3

The hormonally active form of vitamin D(3), 1α,25(OH)(2)-vitamin D(3), acts in intestine, its major target tissue, where its actions are of regulatory and developmental importance: regulation of intracellular calcium through modulation of second messengers and activation of mitogenic cascades leading to cell proliferation. Several causes have been postulated to modify the hormone response in intestinal cells with ageing, among them, alterations of vitamin D receptor (VDR) levels and binding sites, reduced expression of G-proteins and hormone signal transduction changes. The current review summarizes the actual knowledge regarding the molecular and biochemical basis of age-impaired 1α,25(OH)(2)-vitamin D(3) receptor-mediated signaling in intestinal cells. A fundamental understanding why the hormone functions are impaired with age will enhance our knowledge of its importance in intestinal cell physiology.

Attenuation of constitutive DNA damage signaling by 1,25-dihydroxyvitamin D3

In addition to its traditional role in the regulation of calcium homeostasis and bone metabolism, vitamin D also exhibits immunomodulatory, anti-proliferative and cancer preventive activities. Molecular mechanisms that confer the chemo-preventive properties to vitamin D are poorly understood. We previously reported that constitutive phosphorylation of histone H2AX on Ser139 (γH2AX) and activation of ATM (Ser1981 phosphorylation), seen in untreated normal or tumor cells predominantly in S phase of the cell cycle, is to a large extent indicative of DNA replication stress occurring as a result of persistent DNA damage caused by endogenous oxidants, by-products of oxidative metabolism. In the present study we observed that exposure of mitogenically stimulated human lymphocytes, pulmonary carcinoma A549 and lymphoblastoid TK6 cells to 1,25-dihydroxyvitamin D3 (1,25-VD) reduced the level of constitutive expression of γH2AX and ATM-S1981^P. We also observed that the H₂O₂-induced rise in the level of γH2AX in lymphocytes was attenuated by 1,25-VD. Whereas in lymphocytes 1,25-VD reduced by 50-70% the level of endogenous oxidants as determined by their ability to oxidize 2,7-dichlorodihydrofluorescein (DCFH) in A549 and TK6 cells the attenuation of DNA damage signaling by 1,25-VD was seen in the absence of detectable reduction in DCFH oxidation. These findings suggest that while the anti-oxidant activity of 1,25-VD may contribute to a reduction in the intensity of DNA replication stress in lymphocytes, other factors play a role in the 1,25-VD effects seen in A549 and TK6 cells. The data are consistent with the recent report on the interaction between DNA damage signaling (ATM activation) and 1,25D receptor (VDR) phosphorylation that lead to enhancement of DNA repair efficiency, and provide further support for the chemo-preventive and anti-aging properties of this vitamin/hormone.

A 21st century evaluation of the safety of oral vitamin D

The safety of daily consumption of vitamin D was examined. A detailed literature search was conducted using the search term vitamin D; primary and secondary sources of original data and meta-analyses and systematic reviews were evaluated and summarized. A large body of scientific evidence demonstrates that long-term daily intakes of 600 to 800 IU of vitamin D are insufficient to achieve and sustain vitamin D adequacy (serum 25-hydroxyergocalciferol + 25-hydroxycholecalciferol concentration >75 nmol/L). Maximization of the physiologic benefits of vitamin D to the musculoskeletal system, the central and peripheral nervous systems, the heart and central and peripheral cardiovascular systems, the respiratory system, the skin, the eyes, dentition, glucoregulation, immunoregulation, and disease resistance requires daily vitamin D intakes of at least 1500 IU. Because long-term daily intakes up to and including 10 000 IU of vitamin D do not produce signs or symptoms of vitamin D toxicity and are safe for the entire general population of otherwise healthy adults, even daily vitamin D intakes of 2000 IU allow for the often-cited and excessively conservative five-fold safety factor. In conclusion, long-term daily intakes of up to and including 10 000 IU of vitamin D maximize physiologic benefits and are safe.

Cellular and molecular effects of vitamin D on carcinogenesis

Epidemiologic data suggest that the incidence and severity of many types of cancer inversely correlates with indices of vitamin D status. The vitamin D receptor (VDR) is highly expressed in epithelial cells at risk for carcinogenesis including those resident in skin, breast, prostate and colon, providing a direct molecular link by which vitamin D status impacts on carcinogenesis. Consistent with this concept, activation of VDR by its ligand 1,25-dihydroxyvitamin D (1,25D) triggers comprehensive genomic changes in epithelial cells that contribute to maintenance of the differentiated phenotype, resistance to cellular stresses and protection of the genome. Many epithelial cells also express the vitamin D metabolizing enzyme CYP27B1 which enables autocrine generation of 1,25D from the circulating vitamin D metabolite 25-hydroxyvitamin D (25D), critically linking overall vitamin D status with cellular anti-tumor actions. Furthermore, pre-clinical studies in animal models has demonstrated that dietary supplementation with vitamin D or chronic treatment with VDR agonists decreases tumor development in skin, colon, prostate and breast. Conversely, deletion of the VDR gene in mice alters the balance between proliferation and apoptosis, increases oxidative DNA damage, and enhances susceptibility to carcinogenesis in these tissues. Because VDR expression is retained in many human tumors, vitamin D status may be an important modulator of cancer progression in persons living with cancer. Collectively, these observations have reinforced the need to further define the molecular actions of the VDR and the human requirement for vitamin D in relation to cancer development and progression.

Vitamin D and colon cancer

The most active vitamin D metabolite, 1α,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), is a pleiotropic hormone with wide regulatory actions. Classically, vitamin D deficiency was known to alter calcium and phosphate metabolism and bone biology. In addition, recent epidemiological and experimental studies support the association of vitamin D deficiency with a large variety of human diseases, and particularly with the high risk of colorectal cancer. By regulating the expression of many genes via several mechanisms, 1,25(OH)(2)D(3) induces differentiation, controls the detoxification metabolism and cell phenotype, sensitises cells to apoptosis and inhibits the proliferation of cultured human colon carcinoma cells. Consistently, 1,25(OH)(2)D(3) and several of its analogues decrease intestinal tumourigenesis in animal models. Molecular, genetic and clinical data in humans are scarce but they suggest that vitamin D is protective against colon cancer. Clearly, the available evidence warrants new, well-designed, large-scale trials to clarify the role of vitamin D in the prevention and/or therapy of this important neoplasia.

Mechanism of action of vitamin D and the vitamin D receptor in colorectal cancer prevention and treatment

Vitamin D and its analogs are potent inhibitors of colorectal cancer growth and metastasis. A number of recent studies have defined the intersections between the β-catenin-TCF pathway (a known contributor to colorectal cancer progression) and the vitamin D receptor (VDR) pathway, shedding light on the underlying mechanisms. Vitamin D also regulates the innate immune response, and as such influences susceptibility to inflammatory bowel disease, a predisposing factor in colorectal cancer. Understanding the role of vitamin D in these different contexts will enable development of next generation vitamin D analogs that will serve as both chemopreventatives and cancer therapeutics, without the accompanying side effects of hypercalcemia usually associated with high vitamin D intake. This review summarizes the mechanisms of action of vitamin D and the VDR in the context of the gastrointestinal tract and colorectal carcinogenesis.