Research on the Effect and Mechanism of Selenium on Colorectal Cancer Through TRIM32

The intake of selenium (Se) in the human body is negatively correlated with the risk of colorectal cancer (CRC), but its mechanism in the occurrence and development of CRC is not clear. This study aimed to evaluate the therapeutic effect of Se on CRC, and explore the anti-tumor effect of Se supplementation on CRC and its molecular mechanism. In this study, we utilized colony formation assay, cell scratch test, Transwell migration, and flow cytometry to assess cell proliferation, migration, and apoptosis. Our findings demonstrate that Se effectively suppresses the growth and proliferation of CRC cell lines HCT116 and SW480 and promoting cellular apoptosis. In vivo experiments demonstrated a significant inhibitory effect of Se on tumor growth. CRC-related datasets were extracted from the Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus (GEO) databases for differential expression analysis of TRIM32 and survival analysis. We found that TRIM32 was highly expressed in tumor tissues of CRC patients and correlated with a poor prognosis. Furthermore, through RNA sequencing analysis, we identified TRIM32 as a gene that was significantly decreased after Se treatment in HCT116 cells. This finding was subsequently validated by Western blot results. Moreover, TRIM32 knockdown combined with Se treatment significantly inhibited cell growth proliferation and migration and further induced apoptosis of colorectal cancer cells. In conclusion, our findings provided evidence that Se inhibited the growth of colorectal cancer cells by down-regulating TRIM32.

Targeting beta-catenin signaling for prevention of colorectal cancer - Nutraceutical, drug, and dietary options

Progressive up-regulation of β-catenin signaling is very common in the transformation of colorectal epithelium to colorectal cancer (CRC). Practical measures for opposing such signaling hence have potential for preventing or slowing such transformation. cAMP/PKA activity in colon epithelium, as stimulated by COX-2-generated prostaglandins and β2-adrenergic signaling, boosts β-catenin activity, whereas cGMP/PKG signaling has the opposite effect. Bacterial generation of short-chain fatty acids (as supported by unrefined high-carbohydrate diets, berberine, and probiotics), dietary calcium, daily aspirin, antioxidants opposing cox-2 induction, and nicotine avoidance, can suppress cAMP production in colonic epithelium, whereas cGMP can be boosted via linaclotides, PDE5 inhibitors such as sildenafil or icariin, and likely high-dose biotin. Selective activation of estrogen receptor-β by soy isoflavones, support of adequate vitamin D receptor activity with UV exposure or supplemental vitamin D, and inhibition of CK2 activity with flavanols such as quercetin, can also oppose β-catenin signaling in colorectal epithelium. Secondary bile acids, the colonic production of which can be diminished by low-fat diets and berberine, can up-regulate β-catenin activity by down-regulating farnesoid X receptor expression. Stimulation of PI3K/Akt via insulin, IGF-I, TLR4, and EGFR receptors boosts β-catenin levels via inhibition of glycogen synthase-3β; plant-based diets can down-regulate insulin and IGF-I levels, exercise training and leanness can keep insulin low, anthocyanins and their key metabolite ferulic acid have potential for opposing TLR4 signaling, and silibinin is a direct antagonist for EGFR. Partially hydrolyzed phytate can oppose growth factor-mediated down-regulation of β-catenin by inhibiting Akt activation. Multifactorial strategies for safely opposing β-catenin signaling can be complemented with measures that diminish colonic mutagenesis and DNA hypomethylation - such as avoidance of heme-rich meat and charred or processed meats, consumption of phase II-inductive foods and nutraceuticals (e.g., Crucifera), and assurance of adequate folate status.

Artemisia argyi water extract promotes selenium uptake of peach seedlings

Soil in most areas of the world is selenium (Se) deficient, which results a low Se content in agricultural products. To improve the fruit tree Se accumulation, the effects of different Artemisia argyi water extract concentrations (0, 100, 200, 300, and 400-fold dilutions) on the growth and Se accumulation of peach seedlings were studied by a pot experiment. A 300- and 400-fold dilution of A. argyi water extract increased the root and shoot biomass (dry weight), leaf chlorophyll a content, superoxide dismutase (SOD) activity, and peroxidase (POD) activity of peach seedlings, but decreased the leaf chlorophyll a/b. Different A. argyi water extract concentrations had no significant effects on peach leaf chlorophyll a content of peach seedlings, but increased the leaf carotenoid content, catalase (CAT) activity, and soluble protein content. Different A. argyi water extract concentrations increased the total Se, inorganic Se, and organic contents in roots and shoots of peach seedlings to some extent. Furthermore, A. argyi water extract concentration exhibited a linear relationship with the root and shoot total Se contents. Compared with the control, the 100-, 200-, 300-, and 400-fold dilutions of A. argyi water extract increased the shoot total Se content by 18.95%, 31.31%, 39.32%, and 51.59%, respectively. Different A. argyi water extract concentrations also increased the leaf Se metabolism-related enzyme activities of peach seedlings, including the activities of adenosine triphosphate sulfurase (ATPS), adenosine 5'-phosphosulfate reductase (APR), and serine acetyltransferase (SAT), as well as selenocysteine methyltransferase (SMT) to some extent. Moreover, correlation and grey relational analyses revealed the root total Se content, CAT activity, and ATPS activity to be closely associated with the total shoot Se content. Therefore, applying A. argyi water extract can thus promote the growth and Se uptake of peach seedlings, and the future study should focus on the application effects of Se uptake in peach fruits.

The Associations of Selenoprotein Genetic Variants with the Risks of Colorectal Adenoma and Colorectal Cancer: Case–Control Studies in Irish and Czech Populations

Background: Selenium manifests its biological effects through its incorporation into selenoproteins, which play several roles in countering oxidative and inflammatory responses implicated in colorectal carcinogenesis. Selenoprotein genetic variants may contribute to colorectal cancer (CRC) development, as we previously observed for SNP variants in a large European prospective study and a Czech case–control cohort. Methods: We tested if significantly associated selenoprotein gene SNPs from these studies were also associated with CRC risk in case–control studies from Ireland (colorectal neoplasia, i.e., cancer and adenoma cases: 450, controls: 461) and the Czech Republic (CRC cases: 718, controls: 646). Genotyping of 23 SNPs (20 in the Irish and 13 in the Czechs) was performed by competitive specific allele-specific PCR (KASPar). Multivariable adjusted logistic regression was used to assess the associations with CRC development. Results: We found significant associations with an increased CRC risk for rs5859 (SELENOF) and rs2972994 (SELENOP) in the Irish cohort but only with rs4802034 (SELENOV) in the Czechs. Significant associations were observed for rs5859 (SELENOF), rs4659382 (SELENON), rs2972994 (SELENOP), rs34713741 (SELENOS), and the related Se metabolism gene variant rs2275129 (SEPHS1) with advanced colorectal neoplasia development. However, none of these findings retained significance after multiple testing corrections. Conclusions: Several SNPs previously associated with CRC risk were also associated with CRC or colorectal neoplasia development in either the Irish or Czech cohorts. Selenoprotein gene variation may modify CRC risk across diverse European populations, although the specific variants may differ.

Trace Element Selenium Effectively Alleviates Intestinal Diseases

Selenium (Se) is an essential trace element in the body. It is mainly used in the body in the form of selenoproteins and has a variety of biological functions. Intestinal diseases caused by chronic inflammation are among the most important threats to human health, and there is no complete cure at present. Due to its excellent antioxidant function, Se has been proven to be effective in alleviating intestinal diseases such as inflammatory bowel diseases (IBDs). Therefore, this paper introduces the role of Se and selenoproteins in the intestinal tract and the mechanism of their involvement in the mediation of intestinal diseases. In addition, it introduces the advantages and disadvantages of nano-Se as a new Se preparation and traditional Se supplement in the prevention and treatment of intestinal diseases, so as to provide a reference for the further exploration of the interaction between selenium and intestinal health.

Prediagnostic Blood Selenium Status and Mortality among Patients with Colorectal Cancer in Western European Populations

A higher selenium (Se) status has been shown to be associated with lower risk for colorectal cancer (CRC), but the importance of Se in survival after CRC diagnosis is not well studied. The associations of prediagnostic circulating Se status (as indicated by serum Se and selenoprotein P (SELENOP) measurements) with overall and CRC-specific mortality were estimated using multivariable Cox proportional hazards regression among 995 CRC cases (515 deaths, 396 from CRC) in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Se and SELENOP serum concentrations were measured on average 46 months before CRC diagnosis. Median follow-up time was 113 months. Participants with Se concentrations in the highest quintile (≥100 µg/L) had a multivariable-adjusted hazard ratio (HR) of 0.73 (95% CI: 0.52-1.02; Ptrend = 0.06) for CRC-specific mortality and 0.77 (95% CI: 0.57-1.03; Ptrend = 0.04) for overall mortality, compared with the lowest quintile (≤67.5 µg/L). Similarly, participants with SELENOP concentrations in the highest (≥5.07 mg/L) compared with the lowest quintile (≤3.53 mg/L) had HRs of 0.89 (95% CI: 0.64-1.24; Ptrend = 0.39) for CRC-specific mortality and 0.83 (95% CI: 0.62-1.11; Ptrend = 0.17) for overall mortality. Higher prediagnostic exposure to Se within an optimal concentration (100-150 µg/L) might be associated with improved survival among CRC patients, although our results were not statistically significant and additional studies are needed to confirm this potential association. Our findings may stimulate further research on selenium's role in survival among CRC patients especially among those residing in geographic regions with suboptimal Se availability.

Potential relationship between the selenoproteome and cancer

The role of the selenoproteome, which is the collection of all proteins containing selenium in an organism, in cancer development, growth and progression requires further investigation, due to the importance of selenium in both cancer and immune system function. Data about the selenoproteome, including its differential expression, single nucleotide variations, copy number variations, methylation, pathways and overall survival (OS) in five leading types of cancer are available from the GSCALite website. Subsequent to the analysis of these datasets, it was revealed that there was increased expression of GPX3 in stomach adenocarcinoma and lung squamous cell carcinoma, SELENOV in oesophageal carcinoma, GPX8 and GPX4 in colon adenocarcinoma, TXNRD1 and SEPHS1 in hepatocellular carcinoma and GPX8 in lung adenocarcinoma were associated with poor survival. Decreased gene expression of SELENOP was indicated in liver hepatocellular carcinoma and GPX3, and SELENOW, SELENOK, SELENBP1 and SECISBP2 in lung adenocarcinoma were associated with a poor prognosis. OS data suggested that hypermethylation of GPX4 in colon adenocarcinoma, GPX8 in lung squamous cell carcinoma, GPX1 in stomach adenocarcinoma and GPX3 in lung adenocarcinoma was associated with low survival, as is hypomethylation of GPX5 in lung adenocarcinoma. The selenoproteome is heterogeneous, especially in its effect on the OS of patients with cancer. The present study demonstrated that the roles of GPX4 in colon adenocarcinoma, SCLY and SELENOV in oesophageal carcinoma, SEPHS1 in liver hepatocellular carcinoma, SELENOK in lung cancer, as well as SELENOM and SELENOW in stomach adenocarcinoma requires further research. The present study may lead to the identification of novel biomarkers or potential therapeutic targets for use in the treatment of cancers, such as colon adenocarcinoma, oesophageal carcinoma, liver hepatocellular carcinoma, lung cancer and stomach adenocarcinoma.

Investigation of Different Selenium Sources and Supplying Methods for Selenium Enrichment of Basil Vegetable (A Case Study under Calcareous and Non-calcareous Soil Systems)

BACKGROUND

Selenium (Se) is a crucial component of selenoaminoacids and selenoproteins. Therefore, Se-enriched agricultural products can reduce health complications induced by Se deficiency.

OBJECTIVE

This research was carried out to investigate the effects of Se bio-enrichment on Basil grown in calcareous and non-calcareous soil systems and also to evaluate the changes in Se concentration in the soil after harvesting.

METHODS

The experiment executed in two calcareous and one non-calcareous soil systems, and different Se application methods (control, soil application, seed inoculation, foliar application, and soil + foliar application) were administered. Selenobacteria, a plant growth-promoting rhizobacteria (PGPR), derived from the soil was used as a biofertilizer, compared to the other Se sources.

RESULTS

The results showed that both soil types and the methods of Se application had significant effects (P ˂ 0.01) on root and shoot dry weights and concentrations of P, K, Zn, Fe, and Se in both of the root and shoot. Shoot dry weight of plants treated with foliar Se was maximum in the calcareous soil. Compared to the control treatment, foliar application of Se increased shoot Se content in both calcareous and non-calcareous soils by 242% and 204%, respectively. Furthermore, the increase in shoot Se concentration in calcareous soil induced by Se application increased the concentration of other nutrients in the shoot and root. Plant growth parameters and concentrations of nutrients were significantly increased by using selenobacter inoculum.

CONCLUSION

The application of Se-containing compounds can improve vegetable quality. Considering the daily requirement of the human body for minerals and nutrients, enriching basil with Se can play an important role in community health. Moreover, some patents have reported the effectiveness of endophyte bacteria.

Evaluation of SEPP1 and Selenoprotein S Gene Polymorphisms (rs7579 and rs34713741) in Relation to Colorectal Cancer Susceptibility in Subset of Iranian Population: A Case-control Study

Background

Colorectal cancer (CRC) is rated as the second cause of cancer death worldwide. Selenium (Se) has antioxidant activity and antitumor effect, especially in colon cancer. This important role occurs through selenoproteins. Low Se intake or low plasma Se and selenoproteins concentrations are associated with higher risk of CRC. rs7579 polymorphism in 3' untranslated region of the SEPP1 gene can effect on selenocysteine incorporation during protein synthesis and also effect on microRNA -messengerRNA interaction and sequentially change in SEPP1 expression. rs34713741 polymorphism as a promoter variant in selenoprotein S (SELS) gene can effect on SElS expression and finally lead to increased CRC risk.

Methods

A case-control study using 60 CRC patients and 74 noncancerous counterparts were undertaken in order to determine rs7579 and rs34713741 genotypes using real-time polymerase chain reaction high-resolution melting method.

Results

We found an association of borderline statistical significance between allele A for rs7579 in SEPP1 and CRC risk (adjusted odds ratio = 1.63; confidential interval = 0.99-2.07; P = 0.05). The frequency of genotypes rs34713741 of the mentioned polymorphisms was not significantly different between case and control groups (P = 0.23 and P = 0.93, respectively).

Conclusions

The results suggest that these polymorphisms probably has not a substantial role in Iranian CRC risk and is not a serious potential factor in risk assessment of mentioned disease among Iranians.

Maize Sep15-like functions in endoplasmic reticulum and reactive oxygen species homeostasis to promote salt and osmotic stress resistance

In animals, the Sep15 protein participates in disease resistance, growth, and development, but the function of its plant homologues remains unclear. Here, the function of maize Sep15 was analysed by characterization of two independent Sep15-like loss-of-function mutants. In the absence of ZmSep15-like, seedling tolerance to both water and salinity stress was compromised. The mutants experienced a heightened level of endoplasmic reticulum stress, and over-accumulated reactive oxygen species, resulting in leaf necrosis. Characterization of Arabidopsis thaliana atsep15 mutant as well as like with ectopic expression of ZmSep15-like indicated that ZmSep15-like contributed to tolerance of both osmotic and salinity stress. ZmSep15-like interacted physically with UDP-glucose: glycoprotein glucosyltransferase1 (UGGT1). When the interaction was disrupted, the response to both osmotic and salinity stresses was impaired in maize or Arabidopsis. Co-expressing ZmUGGT1 and ZmUGGT2 enhanced the tolerance of A. thaliana to both stressors, indicating a functional interaction between them. Together, the data indicated that plants Sep15-like proteins promote osmotic and salinity stress resistance by influencing endoplasmic reticulum stress response and reactive oxygen species level.

Association of Selenoprotein and Selenium Pathway Genotypes with Risk of Colorectal Cancer and Interaction with Selenium Status

Selenoprotein genetic variations and suboptimal selenium (Se) levels may contribute to the risk of colorectal cancer (CRC) development. We examined the association between CRC risk and genotype for single nucleotide polymorphisms (SNPs) in selenoprotein and Se metabolic pathway genes. Illumina Goldengate assays were designed and resulted in the genotyping of 1040 variants in 154 genes from 1420 cases and 1421 controls within the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Multivariable logistic regression revealed an association of 144 individual SNPs from 63 Se pathway genes with CRC risk. However, regarding the selenoprotein genes, only TXNRD1 rs11111979 retained borderline statistical significance after adjustment for correlated tests (PACT = 0.10; PACT significance threshold was P < 0.1). SNPs in Wingless/Integrated (Wnt) and Transforming growth factor (TGF) beta-signaling genes (FRZB, SMAD3, SMAD7) from pathways affected by Se intake were also associated with CRC risk after multiple testing adjustments. Interactions with Se status (using existing serum Se and Selenoprotein P data) were tested at the SNP, gene, and pathway levels. Pathway analyses using the modified Adaptive Rank Truncated Product method suggested that genes and gene x Se status interactions in antioxidant, apoptosis, and TGF-beta signaling pathways may be associated with CRC risk. This study suggests that SNPs in the Se pathway alone or in combination with suboptimal Se status may contribute to CRC development.

Expression of Selenoprotein Genes and Association with Selenium Status in Colorectal Adenoma and Colorectal Cancer

Dietary selenium (Se) intake is essential for synthesizing selenoproteins that are important in countering oxidative and inflammatory processes linked to colorectal carcinogenesis. However, there is limited knowledge on the selenoprotein expression in colorectal adenoma (CRA) and colorectal cancer (CRC) patients, or the interaction with Se status levels. We studied the expression of seventeen Se pathway genes (including fifteen of the twenty-five human selenoproteins) in RNA extracted from disease-normal colorectal tissue pairs, in the discovery phase of sixty-two CRA/CRC patients from Ireland and a validation cohort of a hundred and five CRC patients from the Czech Republic. Differences in transcript levels between the disease and paired control mucosa were assessed by the Mann-Whitney U-test. GPX2 and TXNRD3 showed a higher expression and GPX3, SELENOP, SELENOS, and SEPHS2 exhibited a lower expression in the disease tissue from adenomas and both cancer groups (p-values from 0.023 to <0.001). In the Czech cohort, up-regulation of GPX1, SELENOH, and SOD2 and down-regulation of SELENBP1, SELENON, and SELENOK (p-values 0.036 to <0.001) was also observed. We further examined the correlation of gene expression with serum Se status (assessed by Se and selenoprotein P, SELENOP) in the Irish patients. While there were no significant correlations with both Se status markers, SELENOF, SELENOK, and TXNRD1 tumor tissue expression positively correlated with Se, while TXNRD2 and TXNRD3 negatively correlated with SELENOP. In an analysis restricted to the larger Czech CRC patient cohort, Cox regression showed no major association of transcript levels with patient survival, except for an association of higher SELENOF gene expression with both a lower disease-free and overall survival. Several selenoproteins were differentially expressed in the disease tissue compared to the normal tissue of both CRA and CRC patients. Altered selenoprotein expression may serve as a marker of functional Se status and colorectal adenoma to cancer progression.

Selenium at the redox interface of the genome, metabolome and exposome

Selenium (Se) is a redox-active environmental mineral that is converted to only a small number of metabolites and required for a relatively small number of mammalian enzymes. Despite this, dietary and environmental Se has extensive impact on every layer of omics space. This highlights a need for global network response structures to provide reference for targeted, hypothesis-driven Se research. In this review, we survey the Se research literature from the perspective of the responsive physical and chemical barrier between an organism (functional genome) and its environment (exposome), which we have previously termed the redox interface. Recent advances in metabolomics allow molecular phenotyping of the integrated genome-metabolome-exposome structure. Use of metabolomics with transcriptomics to map functional network responses to supplemental Se in mice revealed complex network responses linked to dyslipidemia and weight gain. Central metabolic hubs in the network structure in liver were not directly linked to transcripts for selenoproteins but were, instead, linked to transcripts for glucose transport and fatty acid β-oxidation. The experimental results confirm the survey of research literature in showing that Se interacts with the functional genome through a complex network response structure. The results imply that systematic application of data-driven integrated omics methods to models with controlled Se exposure could disentangle health benefits and risks from Se exposures and also serve more broadly as an experimental paradigm for exposome research.

Selenoproteins in colon cancer

Selenocysteine-containing proteins (selenoproteins) have been implicated in the regulation of various cell signaling pathways, many of which are linked to colorectal malignancies. In this in-depth excurse into the selenoprotein literature, we review possible roles for human selenoproteins in colorectal cancer, focusing on the typical hallmarks of cancer cells and their tumor-enabling characteristics. Human genome studies of single nucleotide polymorphisms in various genes coding for selenoproteins have revealed potential involvement of glutathione peroxidases, thioredoxin reductases, and other proteins. Cell culture studies with targeted down-regulation of selenoproteins and studies utilizing knockout/transgenic animal models have helped elucidate the potential roles of individual selenoproteins in this malignancy. Those selenoproteins, for which strong links to development or progression of colorectal cancer have been described, may be potential future targets for clinical interventions.

The Regulation of Pathways of Inflammation and Resolution in Immune Cells and Cancer Stem Cells by Selenium

Cancer is a complex disease where cancer stem cells (CSCs) maintain unlimited replicative potential, but evade chemotherapy drugs through cellular quiescence. CSCs are able to give rise to bulk tumor cells that have the capability to override antiproliferative signals and evade apoptosis. Numerous pathways are dysregulated in tumor cells, where increased levels of prooxidant reactive oxygen and nitrogen species can lead to localized inflammation to exacerbate all three stages of tumorigenesis: initiation, progression, and metastasis. Modulation of cellular metabolism in tumor cells as well as immune cells in the tumor microenvironment (TME) can impact inflammatory networks. Altering these pathways can potentially serve as a portal for therapy. It is well known that selenium, through selenoproteins, modulates inflammatory pathways in addition to regulating redox homeostasis in cells. Therefore, selenium has the potential to impact the interaction between tumor cells, CSCs, and immune cells. In the sections later, we review the current status of knowledge regarding this interaction, with reference to leukemia stem cells, and the importance of selenium-dependent regulation of inflammation as a potential mechanism to affect the TME and tumor cell survival.

Expression profiling indicating low selenium-sensitive microRNA levels linked to cell cycle and cell stress response pathways in the CaCo-2 cell line

Se is an essential micronutrient for human health, and fluctuations in Se levels and the potential cellular dysfunction associated with it may increase the risk for disease. Although Se has been shown to influence several biological pathways important in health, little is known about the effect of Se on the expression of microRNA (miRNA) molecules regulating these pathways. To explore the potential role of Se-sensitive miRNA in regulating pathways linked with colon cancer, we profiled the expression of 800 miRNA in the CaCo-2 human adenocarcinoma cell line in response to a low-Se (72 h at <40 nm) environment using nCounter direct quantification. These data were then examined using a range of in silico databases to identify experimentally validated miRNA-mRNA interactions and the biological pathways involved. We identified ten Se-sensitive miRNA (hsa-miR-93-5p, hsa-miR-106a-5p, hsa-miR-205-5p, hsa-miR-200c-3p, hsa-miR-99b-5p, hsa-miR-302d-3p, hsa-miR-373-3p, hsa-miR-483-3p, hsa-miR-512-5p and hsa-miR-4454), which regulate 3588 mRNA in key pathways such as the cell cycle, the cellular response to stress, and the canonical Wnt/β-catenin, p53 and ERK/MAPK signalling pathways. Our data show that the effects of low Se on biological pathways may, in part, be due to these ten Se-sensitive miRNA. Dysregulation of the cell cycle and of the stress response pathways due to low Se may influence key genes involved in carcinogenesis.

Supplementation with Brazil nuts and green tea extract regulates targeted biomarkers related to colorectal cancer risk in humans

Se and green tea have been shown in epidemiological, observational and preclinical studies to be inversely related to the risk of developing colorectal cancer (CRC). However, there are limited studies to evaluate their regulatory effects on genes/proteins that relate to CRC oncogenesis in human subjects, such as selenoproteins, WNT signalling pathway, inflammation and methylation. This study examined the effects of supplementation of Se using Brazil nuts and green tea extract (GTE) capsules, alone and in combination, on targeted biomarkers. In total, thirty-two volunteers (>50 years of age) with plasma Se≤1·36 µmol/l were randomised to one of three treatment groups: nine to Se (approximately 48 µg/d) as six Brazil nuts, eleven to four GTE capsules (800 mg (-)-epigallocatechin-3-gallate) and twelve to a combination of Brazil nuts and GTE. Blood and rectal biopsies were obtained before and after each intervention. Plasma Se levels, rectal selenoprotein P (SePP) and β-catenin mRNA increased significantly in subjects consuming Brazil nuts alone or in combination, whereas rectal DNA methyltransferase (DNMT1) and NF-κB mRNA were reduced significantly in subjects consuming GTE alone or in combination. None of the interventions significantly affected rectal acetylated histone H3 or Ki-67 expression at the protein level or plasma C-reactive protein. Effects of the combination of Brazil nuts and GTE did not differ from what would be expected from either agent alone. In conclusion, supplementation of Brazil nuts and/or GTE regulates targeted biomarkers related to CRC oncogenesis, specifically genes associated with selenoproteins (SePP), WNT signalling (β-catenin), inflammation (NF-κB) and methylation (DNMT1). Their combination does not appear to provide additional effects compared with either agent alone.

Trace Elements and Chemotherapy Sensitivity

Trace elements might be associated with the development of hepatocellular carcinoma (HCC) and the efficacy of chemotherapy against HCC. Therefore, this study aimed to explore the association between trace elements and efficacy of chemotherapy in patients with HCC. Cancer, cancer-adjacent, and cancer-free tissues were collected intraoperatively from 55 patients with HCC between January 2001 and April 2004 at the Affiliated Tumor Hospital of Guangxi Medical University in Guangxi (China), a high HCC incidence area in the world. Trace element levels were analyzed by atomic absorption spectrophotometry. In vitro sensitivity of cancer cells to five chemotherapeutic drugs (5-fluorouracil, doxorubicin, cisplatin, carboplatin, and mitomycin) was tested using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in cancer cells from 32 patients. Zinc, copper, manganese, and selenium levels had the same gradient distribution in different liver tissues: cancer < cancer-adjacent < cancer-free tissues. Copper levels of cancer tissues were negatively correlated with body weight (r = -0.278, P = 0.027), while manganese and selenium levels were negatively correlated with age (r = -0.297, P = 0.015; r = -0.285, P = 0.018, respectively). Simple correlation analyses revealed that the carboplatin sensitivity was negatively correlated with selenium levels of cancer tissues, while doxorubicin sensitivity was negatively correlated with manganese levels (r = -0.497, P = 0.004). Partial correlation analyses showed that doxorubicin sensitivity only was negatively correlated with manganese levels (r = -0.450, P = 0.014). These results suggest that the selenium and manganese content in primary HCC tissues could influence the response of the HCC cells to carboplatin and doxorubicin. These preliminary results provide a basis for future studies.

Selenoproteins: Antioxidant selenoenzymes and beyond

Adequate intake of the essential trace element and micronutrient selenium is thought to be beneficial for maintaining human health. Selenium may modulate a broad spectrum of key biological processes, including the cellular response to oxidative stress, redox signalling, cellular differentiation, the immune response, and protein folding. Biochemical and cellular effects of selenium are achieved through activities of selenocysteine-containing selenoproteins. This small yet essential group comprises proteins encoded by 25 genes in humans, e.g. oxidoreductases such as glutathione peroxidases (GPx) and thioredoxin reductases (TrxR), as well as the iodothyronine deiodinases (DIO) and the plasma selenium transport protein, selenoprotein P (SePP1). Synthetic selenoorganic compounds, including the GPx mimetic ebselen, have also been applied in biological systems in vitro and in vivo; antioxidant and anti-inflammatory actions of ebselen and its history as a drug candidate are summarised here. Furthermore, we discuss several aspects of selenoprotein biochemistry, ranging from their well-known importance for cellular protection against oxidative damage to more recent data that link selenoprotein expression/activity to enterocyte and adipocyte differentiation and function and to (dys)regulation of insulin action and secretion.

Factors impacting the aminoglycoside-induced UGA stop codon readthrough in selenoprotein translation

Aminoglycosides (AG) are oligosaccharide antibiotics that interfere with the small ribosomal subunit in aerobic, Gram-negative bacteria, causing pathogen-destructing error rates in their protein biosynthesis. Aminoglycosides also induce mRNA misinterpretation in eukaryotic cells, especially of the UGA (Opal)-stop codon, albeit to a lower extent. UGA recoding is essentially required for the incorporation of selenocysteine (Sec) into growing selenoproteins during translation. Selenocysteine incorporation requires the presence of a selenoprotein-specific stem-loop structure within the 3'-untranslated region of the mRNA, the so-called Sec-insertion sequence (SECIS) element. Interestingly, selenoprotein genes differ in their SECIS-element sequence and in their UGA base context. We hypothesized that the SECIS-element and the specific codon context synergize in controlling the effects of AG on stop codon readthrough. To this end, the SECIS-elements of glutathione peroxidase 1, glutathione peroxidase 4 and selenoprotein P transcripts were cloned into a reporter system and analyzed in combination with different UGA codon contexts. Our results indicate that a cytosine in position 4 (directly downstream of UGA) confers strongest effects on both the Se- and AG-dependent readthrough. Overall selenoprotein biosynthesis rate depends on the Se-status, AG concentration and the specific SECIS-element present in the transcript. These findings help to get a better understanding for the susceptibility of different transcripts towards AG-mediated interference with the biosynthesis of functional Se-containing selenoproteins, and highlight the importance of the Se-status for successful selenoprotein biosynthesis under antibiotic therapy.

Selenazolidine: a selenium containing proline surrogate in peptide science

In the search for new peptide ligands containing selenium in their sequences, we investigated l-4-selenazolidine-carboxylic acid (selenazolidine, Sez) as a proline analog with the chalcogen atom in the γ-position of the ring. In contrast to proteinogenic selenocysteine (Sec) and selenomethionine (SeMet), the incorporation within a peptide sequence of such a non-natural amino acid has never been studied. There is thus a great interest in increasing the possibility of selenium insertion within peptides, especially for sequences that do not possess a sulfur containing amino acid (Cys or Met), by offering other selenated residues suitable for peptide synthesis protocols. Herein, we have evaluated selenazolidine in Boc/Bzl and Fmoc/tBu strategies through the synthesis of a model tripeptide, both in solution and on a solid support. Special attention was paid to the stability of the Sez residue in basic conditions. Thus, generic protocols have been optimized to synthesize Sez-containing peptides, through the use of an Fmoc-Xxx-Sez-OH dipeptide unit. As an example, a new analog of the vasopressin receptor-1A antagonist was prepared, in which Pro was replaced with Sez [3-(4-hydroxyphenyl)-propionyl-d-Tyr(Me)-Phe-Gln-Asn-Arg-Sez-Arg-NH2]. Both proline and such pseudo-proline containing peptides exhibited similar pharmacological properties and endopeptidase stabilities indicating that the presence of the selenium atom has minimal functional effects. Taking into account the straightforward handling of Sez as a dipeptide building block in a conventional Fmoc/tBu SPPS strategy, this result suggested a wide range of potential uses of the Sez amino acid in peptide chemistry, for instance as a viable proline surrogate as well as a selenium probe, complementary to Sec and SeMet, for NMR and mass spectrometry analytical purposes.

Transcriptomics and proteomics show that selenium affects inflammation, cytoskeleton, and cancer pathways in human rectal biopsies

Epidemiologic studies highlight the potential role of dietary selenium (Se) in colorectal cancer prevention. Our goal was to elucidate whether expression of factors crucial for colorectal homoeostasis is affected by physiologic differences in Se status. Using transcriptomics and proteomics followed by pathway analysis, we identified pathways affected by Se status in rectal biopsies from 22 healthy adults, including 11 controls with optimal status (mean plasma Se = 1.43 μM) and 11 subjects with suboptimal status (mean plasma Se = 0.86 μM). We observed that 254 genes and 26 proteins implicated in cancer (80%), immune function and inflammatory response (40%), cell growth and proliferation (70%), cellular movement, and cell death (50%) were differentially expressed between the 2 groups. Expression of 69 genes, including selenoproteins W1 and K, which are genes involved in cytoskeleton remodelling and transcription factor NFκB signaling, correlated significantly with Se status. Integrating proteomics and transcriptomics datasets revealed reduced inflammatory and immune responses and cytoskeleton remodelling in the suboptimal Se status group. This is the first study combining omics technologies to describe the impact of differences in Se status on colorectal expression patterns, revealing that suboptimal Se status could alter inflammatory signaling and cytoskeleton in human rectal mucosa and so influence cancer risk.-Méplan, C., Johnson, I. T., Polley, A. C. J., Cockell, S., Bradburn, D. M., Commane, D. M., Arasaradnam, R. P., Mulholland, F., Zupanic, A., Mathers, J. C., Hesketh, J. Transcriptomics and proteomics show that selenium affects inflammation, cytoskeleton, and cancer pathways in human rectal biopsies.

Update on selenoprotein biosynthesis

SIGNIFICANCE

Selenium is an essential trace element that is incorporated in the small but vital family of proteins, namely the selenoproteins, as the selenocysteine amino acid residue. In humans, 25 selenoprotein genes have been characterized. The most remarkable trait of selenoprotein biosynthesis is the cotranslational insertion of selenocysteine by the recoding of a UGA codon, normally decoded as a stop signal.

RECENT ADVANCES

In eukaryotes, a set of dedicated cis- and trans-acting factors have been identified as well as a variety of regulatory mechanisms, factors, or elements that control the selenoprotein expression at the level of the UGA-selenocysteine recoding process, offering a fascinating playground in the field of translational control. It appeared that the central players are two RNA molecules: the selenocysteine insertion sequence (SECIS) element within selenoprotein mRNA and the selenocysteine-tRNA([Ser]Sec); and their interacting partners.

CRITICAL ISSUES

After a couple of decades, despite many advances in the field and the discovery of many essential and regulatory components, the precise mechanism of UGA-selenocysteine recoding remains elusive and more complex than anticipated, with many layers of control. This review offers an update of selenoproteome biosynthesis and regulation in eukaryotes.

FUTURE DIRECTIONS

The regulation of selenoproteins in response to a variety of pathophysiological conditions and cellular stressors, including selenium levels, oxidative stress, replicative senescence, or cancer, awaits further detailed investigation. Clearly, the efficiency of UGA-selenocysteine recoding is the limiting stage of selenoprotein synthesis. The sequence of events leading Sec-tRNA([Ser]Sec) delivery to ribosomal A site awaits further analysis, notably at the level of a three-dimensional structure.

Macro- and micronutrients consumption and the risk for colorectal cancer among Jordanians

OBJECTIVE

Diet and lifestyle have been reported to be important risk factors for the development of colorectal cancer (CRC). However, the association between total energy and nutrient intake and the risk of developing CRC has not been clearly explained. The aim of our study is to examine the relationship between total energy intake and other nutrients and the development of CRC in the Jordanian population.

RESEARCH METHODS AND PROCEDURES

Dietary data was collected from 169 subjects who were previously diagnosed with CRC, and 248 control subjects (matched by age, gender, occupation and marital status). These control subjects were healthy and disease free. Data was collected between January 2010 and December 2012, using interview-based questionnaires. Logistic regression was used to evaluate the association between quartiles of total energy, macro- and micronutrient intakes with the risk of developing CRC in our study population.

RESULTS

Total energy intake was associated with a higher risk of developing CRC (OR = 2.60 for the highest versus lowest quartile of intake; 95% CI: 1.21-5.56, p-trend = 0.03). Intakes of protein (OR = 3.62, 95% CI: 1.63-8.05, p-trend = 0.002), carbohydrates (OR = 1.41, 95% CI: 0.67-2.99, p-trend = 0.043), and percentage of energy from fat (OR = 2.10, 95% CI: 0.38-11.70, p-trend = 0.009) significantly increased the risk for the development of CRC. Saturated fat, dietary cholesterol and sodium intake showed a significant association with the risk of developing CRC (OR = 5.23, 95% CI: 2.33-11.76; OR = 2.48, 95% CI: 1.18-5.21; and OR = 3.42, 95% CI: 1.59-7.38, respectively), while vitamin E and caffeine intake were indicative of a protective effect against the development of CRC, OR = 0.002 (95% CI: 0.0003-0.011) and 0.023 (95%CI: 0.008-0.067), respectively.

CONCLUSION

Our results suggest an increased risk for the development of CRC in subjects with high dietary intake of energy, protein, saturated fat, cholesterol, and sodium, and diets high in vitamin E and caffeine were suggestive of a protective effect against the risk of developing CRC.

IMPACT

This is the first study in Jordan to suggest that it may be possible to reduce CRC risk by adjusting the intake of some macro-and micronutrients.

Selenium status is associated with colorectal cancer risk in the European prospective investigation of cancer and nutrition cohort

Suboptimal intakes of the micronutrient selenium (Se) are found in many parts of Europe. Low Se status may contribute to colorectal cancer (CRC) development. We assessed Se status by measuring serum levels of Se and Selenoprotein P (SePP) and examined the association with CRC risk in a nested case-control design (966 CRC cases; 966 matched controls) within the European Prospective Investigation into Cancer and Nutrition. Se was measured by total reflection X-ray fluorescence and SePP by immunoluminometric sandwich assay. Multivariable incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were calculated using conditional logistic regression. Respective mean Se and SePP levels were 84.0 μg/L and 4.3 mg/L in cases and 85.6 μg/L and 4.4 mg/L in controls. Higher Se concentrations were associated with a non-significant lower CRC risk (IRR = 0.92, 95% CI: 0.82-1.03 per 25 μg/L increase). However, sub-group analyses by sex showed a statistically significant association for women (p(trend) = 0.032; per 25 μg/L Se increase, IRR = 0.83, 95% CI: 0.70-0.97) but not for men. Higher SePP concentrations were inversely associated with CRC risk (p(trend) = 0.009; per 0.806 mg/L increase, IRR = 0.89, 95% CI: 0.82-0.98) with the association more apparent in women (p(trend) = 0.004; IRR = 0.82, 95% CI: 0.72-0.94 per 0.806 mg/L increase) than men (p(trend) = 0.485; IRR = 0.98, 95% CI: 0.86-1.12 per 0.806 mg/L increase). The findings indicate that Se status is suboptimal in many Europeans and suggest an inverse association between CRC risk and higher serum Se status, which is more evident in women.

Selenium-fortified wheat: potential of microbes for biofortification of selenium and other essential nutrients

Selenium (Se) is an essential micronutrient for humans and animals, and Se deficiency is a worldwide problem. Plants are a main dietary source of Se for humans and livestock. In this study we investigated the effect of two selenium-tolerant bacterial strains Bacillus cereus-YAP6 and Bacillus licheniformis-YAP7, on the growth and Se uptake by wheat plants. The bacteria-inoculated plants exhibited a significant increase in spike length, shoot length and dry biomass. Inoculated Se-treated plants also showed increased stem Se, S, Ca and Fe concentrations, by up to 375%, 40%, 55%, and 104%, respectively, and increased kernel Se, S, Ca and Fe concentrations by up to 154%, 85%, 60%, and 240%, respectively, compared to un-inoculated Se-treated plants. In conclusion, inoculation with strains YAP6 andYAP7 is a good Se biofortification strategy for wheat. Both strains showed resistance to other toxic elements, i.e., As, Cd, Co, Cr, Cu, Mn and Zn. Optimal growth temperature and pH for both strains were 37°C and pH7, respectively, but both strains can grow very well at different temperatures (28-45°C) and at alkaline pH. Both strains have high Se reduction potential: strains YAP6 and YAP7 converted 92% and 32% of selenite into elemental Se within 48 h, respectively.

Association between maternal micronutrient status, oxidative stress, and common genetic variants in antioxidant enzymes at 15 weeks׳ gestation in nulliparous women who subsequently develop preeclampsia

Preeclampsia is a pregnancy-specific condition affecting 2-7% of women and a leading cause of perinatal and maternal morbidity and mortality. Deficiencies of specific micronutrient antioxidant activities associated with copper, selenium, zinc, and manganese have previously been linked to preeclampsia at the time of disease. Our aims were to investigate whether maternal plasma micronutrient concentrations and related antioxidant enzyme activities are altered before preeclampsia onset and to examine the dependence on genetic variations in these antioxidant enzymes. Predisease plasma samples (15±1 weeks׳ gestation) were obtained from women enrolled in the international Screening for Pregnancy Endpoints (SCOPE) study who subsequently developed preeclampsia (n=244) and from age- and BMI-matched normotensive controls (n=472). Micronutrient concentrations were measured by inductively coupled plasma mass spectrometry; associated antioxidant enzyme activities, selenoprotein-P, ceruloplasmin concentration and activity, antioxidant capacity, and markers of oxidative stress were measured by colorimetric assays. Sixty-four tag-single-nucleotide polymorphisms (SNPs) within genes encoding the antioxidant enzymes and selenoprotein-P were genotyped using allele-specific competitive PCR. Plasma copper and ceruloplasmin concentrations were modestly but significantly elevated in women who subsequently developed preeclampsia (both P<0.001) compared to controls (median (IQR), copper, 1957.4 (1787, 2177.5) vs 1850.0 (1663.5, 2051.5) µg/L; ceruloplasmin, 2.5 (1.4, 3.2) vs 2.2 (1.2, 3.0) µg/ml). There were no differences in other micronutrients or enzymes between groups. No relationship was observed between genotype for SNPs and antioxidant enzyme activity. This analysis of a prospective cohort study reports maternal micronutrient concentrations in combination with associated antioxidant enzymes and SNPs in their encoding genes in women at 15 weeks׳ gestation that subsequently developed preeclampsia. The modest elevation in copper may contribute to oxidative stress, later in pregnancy, in those women that go on to develop preeclampsia. The lack of evidence to support the hypothesis that functional SNPs influence antioxidant enzyme activity in pregnant women argues against a role for these genes in the etiology of preeclampsia.

Selenium and cancer: a story that should not be forgotten-insights from genomics

Selenium (Se) is an essential micronutrient that is incorporated into selenoproteins. Although epidemiological studies suggest that low Se intake is associated with increased risk of various cancers, the results of supplementation trials have been confusing. These conflicting results may be due to different baseline Se status and/or genetic factors. In addition, mechanistic links between Se intake, selenoproteins and carcinogenesis are not clear. In this article, we discuss the functional significance of single-nucleotide polymorphisms (SNP) in selenoprotein genes and the evidence as to whether or not they influence risk of colorectal, prostate, lung or breast cancers. Both in vitro and in vivo studies have shown that a small number of SNPs in genes encoding glutathione peroxidases 1 and 4, selenoprotein P, selenoprotein S and 15-kDa selenoprotein have functional consequences. Data from case-control studies suggest that a variant at codon 198 in glutathione peroxidase 1 influences the effect of Se status on prostate cancer and risk, and it has also been associated with breast cancer and lung cancer risk, whereas variants in glutathione peroxidase 4, selenoprotein P and selenoprotein S may influence the risk of colorectal cancer. In addition, the results of gene microarray (transcriptomic) studies have identified novel selenoprotein biomarkers of Se status and novel downstream Se-targeted pathways. The work highlights the need to take baseline Se status and genetic factors into account in the design of future intervention trials.

Naringin accelerates the regression of pre-neoplastic lesions and the colorectal structural reorganization in a murine model of chemical carcinogenesis

The aim of this study was to investigate the effect of Naringin on pre-neoplastic colorectal lesions induced by chemical carcinogen in rats. Female Wistar rats weighing 130.8±27.1 g received weekly one subcutaneous injection of 1,2-dimethylhydrazine (DMH, 20 mg/kg) for 10 weeks. The animals were divided into 5 groups with 6 animals in each group. Group 1: 0.9% saline; Group 2: DMH+0.9% saline; Group 3: DMH+Naringin (10 mg/kg); Group 4: DMH+Naringin (100 mg/kg); Group 5: DMH+Naringin (200 mg/kg). G2 and G3 showed a significant increase in ACF number, AgNOR/nucleus and mitosis compared to G1. G4 and G5 presented a significant reduction in these parameters compared to G2. The number of cells producing acidic and neutral mucins, red blood cells and the level of antioxidant minerals, such as copper, magnesium, selenium and zinc, were significantly reduced in G2 and G3, but similar in G4 and G5 compared to G1. Naringin, especially at 200 mg/kg, was effective in reducing the number of pre-neoplastic lesions in rats exposed to DMH. Some of these effects may be due to reduction in cellular proliferation and tissue levels of iron together with the recovery of antioxidant mineral levels induced by this flavonoid.

SEPP1 influences breast cancer risk among women with greater native american ancestry: the breast cancer health disparities study

Selenoproteins are a class of proteins containing a selenocysteine residue, many of which have been shown to have redox functions, acting as antioxidants to decrease oxidative stress. Selenoproteins have previously been associated with risk of various cancers and redox-related diseases. In this study we evaluated possible associations between breast cancer risk and survival and single nucleotide polymorphisms (SNPs) in the selenoprotein genes GPX1, GPX2, GPX3, GPX4, SELS, SEP15, SEPN1, SEPP1, SEPW1, TXNRD1, and TXNRD2 among Hispanic/Native American (2111 cases, 2597 controls) and non-Hispanic white (NHW) (1481 cases, 1586 controls) women in the Breast Cancer Health Disparities Study. Adaptive Rank Truncated Product (ARTP) analysis was used to determine both gene and pathway significance with these genes. The overall selenoprotein pathway P_ARTP was not significantly associated with breast cancer risk (P_ARTP = 0.69), and only one gene, GPX3, was of borderline significance for the overall population (P_ARTP =0.09) and marginally significant among women with 0-28% Native American (NA) ancestry (P_ARTP=0.06). The SEPP1 gene was statistically significantly associated with breast cancer risk among women with higher NA ancestry (P_ARTP=0.002) and contributed to a significant pathway among those women (P_ARTP=0.04). GPX1, GPX3, and SELS were associated with Estrogen Receptor-/Progesterone Receptor+ status (P_ARTP = 0.002, 0.05, and 0.01, respectively). Four SNPs (GPX3 rs2070593, rsGPX4 rs2074451, SELS rs9874, and TXNRD1 rs17202060) significantly interacted with dietary oxidative balance score after adjustment for multiple comparisons to alter breast cancer risk. GPX4 was significantly associated with breast cancer survival among those with the highest NA ancestry (P_ARTP = 0.05) only. Our data suggest that SEPP1 alters breast cancer risk among women with higher levels of NA ancestry.

Genetic variants in selenoprotein P plasma 1 gene (SEPP1) are associated with fasting insulin and first phase insulin response in Hispanics

CONTEXT

Insulin resistance is not fully explained on a molecular level, though several genes and proteins have been tied to this defect. Knockdowns of the SEPP1 gene, which encodes the selenoprotein P (SeP) protein, have been shown to increase insulin sensitivity in mice. SeP is a liver-derived plasma protein and a major supplier of selenium, which is a proposed insulin mimetic and antidiabetic agent.

OBJECTIVE

SEPP1 single nucleotide polymorphisms (SNPs) were selected for analysis with glucometabolic measures.

PARTICIPANTS AND MEASURES

The study included1424 Hispanics from families in the Insulin Resistance Atherosclerosis Family Study (IRASFS). Additionally, the multi-ethnic Insulin Resistance Atherosclerosis Study was used. A frequently sampled intravenous glucose tolerance test was used to obtain precise measures of acute insulin response (AIR) and the insulin sensitivity index (SI).

DESIGN

21 SEPP1 SNPs (tagging SNPs (n=12) from HapMap, 4 coding variants and 6 SNPs in the promoter region) were genotyped and analyzed for association.

RESULTS

Two highly correlated (r(2)=1) SNPs showed association with AIR (rs28919926; Cys368Arg; p=0.0028 and rs146125471; Ile293Met; p=0.0026) while rs16872779 (intronic) was associated with fasting insulin levels (p=0.0097). In the smaller IRAS Hispanic cohort, few of the associations seen in the IRASFS were replicated, but meta-analysis of IRASFS and all 3 IRAS cohorts (N=2446) supported association of rs28919926 and rs146125471 with AIR (p=0.013 and 0.0047, respectively) as well as rs7579 with SI (p=0.047).

CONCLUSIONS

Overall, these results in a human sample are consistent with the literature suggesting a role for SEPP1 in insulin resistance.

Selenium alters miRNA profile in an intestinal cell line: evidence that miR-185 regulates expression of GPX2 and SEPSH2

SCOPE

Intake of the essential micronutrient selenium (Se) has health implications. This work addressed whether some effects of Se on gene expression are exerted through microRNAs (miRNA).

METHODS AND RESULTS

Human colon adenocarcinoma cells (Caco-2) were grown in Se-deficient or Se-adequate medium for 72 h. RNA was extracted and subjected to analysis of 737 miRNA using microarray technology. One hundred and forty-five miRNA were found to be expressed in Caco-2 cells. Twelve miRNA showed altered expression after Se depletion: miR-625, miR-492, miR-373*, miR-22, miR-532-5p, miR-106b, miR-30b, miR-185, miR-203, miR1308, miR-28-5p, miR-10b. These changes were validated by quantitative real-time PCR (RT-qPCR). Transcriptomic analysis showed that Se depletion altered expression of 50 genes including selenoproteins GPX1, SELW, GPX3, SEPN1, SELK, SEPSH2 and GPX4. Pathway analysis identified arachidonic acid metabolism, glutathione metabolism, oxidative stress, positive acute phase response proteins and respiration of mitochondria as Se-sensitive pathways. Bioinformatic analysis identified 13 transcripts as targets for the Se-sensitive miRNA; three were predicted to be recognised by miR-185. Silencing of miR-185 increased GPX2 and SEPSH2 expression.

CONCLUSIONS

We propose that miR-185 plays a role in up-regulation of GPX2 and SEPHS2 expression. In the case of SEPHS2 this may contribute to maintaining selenoprotein synthesis. The data indicate that micronutrient supply can regulate the cell miRNA expression profile.

Toward understanding success and failures in the use of selenium for cancer prevention

SIGNIFICANCE

Adequate and supranutritional selenium (Se) intake, maintaining full expression of selenoproteins, has been assumed to be beneficial for human health with respect to prevention of cancer. Strikingly, the effectiveness of dietary Se supplementation depends on many factors: baseline Se status, age, gender, and genetic background of an individual; type of cancer; and time point of intervention in addition to metabolic conversion and dose of applied Se compounds.

RECENT ADVANCES

Se intake levels for optimization of plasma selenoproteins in humans have been delineated. Regulation, function, and genetic variants of several selenoproteins have been characterized in the intestine, where Se-mediated prevention of colorectal cancer appears to be particularly promising.

CRITICAL ISSUES

Numerous cell culture and animal studies indicate anticarcinogenic capacity of various Se compounds but, at present, the outcome of human studies is inconsistent and, in large part, disappointing. Moreover, supranutritional Se intake may even trigger adverse health effects, possibly increasing the risk for Type 2 diabetes in Se-replete populations.

FUTURE DIRECTIONS

To improve protocols for the use of Se in cancer prevention, knowledge on cellular and systemic actions of Se compounds needs to be broadened and linked to individual-related determinants such as the occurrence of variants in selenoprotein genes and the Se status. Based on better mechanistic insight, populations and individuals that may benefit most from dietary Se supplementation need to be defined and studied in suitably planned intervention trials.

The flavonoid chrysin attenuates colorectal pathological remodeling reducing the number and severity of pre-neoplastic lesions in rats exposed to the carcinogen 1,2-dimethylhydrazine

Phenolic compounds are naturally occurring, bioactive substances with marked antioxidant and anti-inflammatory potential. The flavonoid chrysin, found in high levels in honey bee propolis, inhibits the activity of enzymes involved in carcinogenesis. We have investigated the effect of chrysin on pre-neoplastic colorectal lesions (ACF, aberrant crypt foci) in a rat model of chemical carcinogenesis induced by 1,2-dimethylhydrazine (DMH). Female Wistar rats weighing 137.2 ± 24.3 g received weekly one subcutaneous injection of DMH (20 mg/kg) for 10 weeks. The animals were divided into five groups each with seven animals: Group 1, 0.9% saline; Group 2, DMH+0.9% saline; Group 3, DMH+chrysin (10 mg/kg); Group 4, DMH+chrysin (100 mg/kg); Group 5, DMH+chrysin (200 mg/kg). Groups 2 and 3 showed a significant increase in ACF number, nucleolus organizer regions per enterocyte nucleus and nitrite/nitrate serum levels compared with Group 1. Groups 4 and 5 presented a significant reduction in all these parameters compared with Group 2. The levels of antioxidant minerals (copper, magnesium, selenium, zinc) and the number of enteroendocrine and mucin-producing cells were significantly reduced in Groups 2 and 3 but were similar in Groups 4 and 5 compared with Group 1. Chrysin, at 100 mg/kg and 200 mg/kg, was effective in attenuating pathological colorectal remodeling, reducing the number of pre-neoplastic lesions in rats exposed to DMH. Some of these effects might be attributable to the recovery of antioxidant mineral levels, a reduction in systemic nitrosative stress and an inhibition of the cellular proliferation induced by this flavonoid.

Selenium in bone health: roles in antioxidant protection and cell proliferation

Selenium (Se) is an essential trace element for humans and animals, and several findings suggest that dietary Se intake may be necessary for bone health. Such findings may relate to roles of Se in antioxidant protection, enhanced immune surveillance and modulation of cell proliferation. Elucidation of the mechanisms by which Se supports these cellular processes can lead to a better understanding of the role of this nutrient in normal bone metabolism. This article reviews the current knowledge concerning the molecular functions of Se relevant to bone health.

Friend or foe? The current epidemiologic evidence on selenium and human cancer risk

Scientific opinion on the relationship between selenium and the risk of cancer has undergone radical change over the years, with selenium first viewed as a possible carcinogen in the 1940s then as a possible cancer preventive agent in the 1960s-2000s. More recently, randomized controlled trials have found no effect on cancer risk but suggest possible low-dose dermatologic and endocrine toxicity, and animal studies indicate both carcinogenic and cancer-preventive effects. A growing body of evidence from human and laboratory studies indicates dramatically different biological effects of the various inorganic and organic chemical forms of selenium, which may explain apparent inconsistencies across studies. These chemical form-specific effects also have important implications for exposure and health risk assessment. Overall, available epidemiologic evidence suggests no cancer preventive effect of increased selenium intake in healthy individuals and possible increased risk of other diseases and disorders.

Glutathione peroxidases

BACKGROUND

With increasing evidence that hydroperoxides are not only toxic but rather exert essential physiological functions, also hydroperoxide removing enzymes have to be re-viewed. In mammals, the peroxidases inter alia comprise the 8 glutathione peroxidases (GPx1-GPx8) so far identified.

SCOPE OF THE REVIEW

Since GPxs have recently been reviewed under various aspects, we here focus on novel findings considering their diverse physiological roles exceeding an antioxidant activity.

MAJOR CONCLUSIONS

GPxs are involved in balancing the H2O2 homeostasis in signalling cascades, e.g. in the insulin signalling pathway by GPx1; GPx2 plays a dual role in carcinogenesis depending on the mode of initiation and cancer stage; GPx3 is membrane associated possibly explaining a peroxidatic function despite low plasma concentrations of GSH; GPx4 has novel roles in the regulation of apoptosis and, together with GPx5, in male fertility. Functions of GPx6 are still unknown, and the proposed involvement of GPx7 and GPx8 in protein folding awaits elucidation.

GENERAL SIGNIFICANCE

Collectively, selenium-containing GPxs (GPx1-4 and 6) as well as their non-selenium congeners (GPx5, 7 and 8) became key players in important biological contexts far beyond the detoxification of hydroperoxides. This article is part of a Special Issue entitled Cellular functions of glutathione.

Glutathione peroxidase 4 has a major role in protecting mitochondria from oxidative damage and maintaining oxidative phosphorylation complexes in gut epithelial cells

Intake of the micronutrient selenium, which is incorporated into 25 selenoproteins in humans, has been implicated in affecting risk of colorectal cancer. A genetic variant in the gene encoding the selenoprotein glutathione peroxidase 4 (GPX4) has been reported to influence colorectal cancer risk. In this study GPX4 expression was knocked down by 60% using RNA silencing and the effects were investigated using an unbiased transcriptomic analysis. Microarray analysis of the total Caco-2 cell transcriptome was carried out using Illumina HumanHT-12v3 beadchips and the data were validated by real-time PCR. Ingenuity Pathway Analysis showed that the major canonical pathways affected by GPX4 knockdown were oxidative phosphorylation, ubiquinone biosynthesis, and mitochondrial dysfunction and the top two toxicological lists were mitochondrial dysfunction and oxidative stress. Western blotting and real-time PCR confirmed that knockdown affected target genes encoding components of respiratory complexes I, IV, and V as well as the protein apoptosis-inducing factor (AIF). GPX4 knockdown increased levels of mitochondrial reactive oxygen species and oxidized lipid and decreased mitochondrial adenosine triphosphate levels and mitochondrial membrane potential. Time-course experiments showed that changes in AIF expression preceded those in the respiratory complexes. We conclude that in Caco-2 gut epithelial cells GPx4, through effects on AIF, plays a major role in maintaining the oxidative phosphorylation system and protecting mitochondria from oxidative damage.

Genetic variation in selenoprotein genes, lifestyle, and risk of colon and rectal cancer

Background

Associations between selenium and cancer have directed attention to role of selenoproteins in the carcinogenic process.

Methods

We used data from two population-based case-control studies of colon (n = 1555 cases, 1956 controls) and rectal (n = 754 cases, 959 controls) cancer. We evaluated the association between genetic variation in TXNRD1, TXNRD2, TXNRD3, C11orf31 (SelH), SelW, SelN1, SelS, SepX, and SeP15 with colorectal cancer risk.

Results

After adjustment for multiple comparisons, several associations were observed. Two SNPs in TXNRD3 were associated with rectal cancer (rs11718498 dominant OR 1.42 95% CI 1.16,1.74 pACT 0.0036 and rs9637365 recessive 0.70 95% CI 0.55,0.90 pACT 0.0208). Four SNPs in SepN1 were associated with rectal cancer (rs11247735 recessive OR 1.30 95% CI 1.04,1.63 pACT 0.0410; rs2072749 GGvsAA OR 0.53 95% CI 0.36,0.80 pACT 0.0159; rs4659382 recessive OR 0.58 95% CI 0.39,0.86 pACT 0.0247; rs718391 dominant OR 0.76 95% CI 0.62,0.94 pACT 0.0300). Interaction between these genes and exposures that could influence these genes showed numerous significant associations after adjustment for multiple comparisons. Two SNPs in TXNRD1 and four SNPs in TXNRD2 interacted with aspirin/NSAID to influence colon cancer; one SNP in TXNRD1, two SNPs in TXNRD2, and one SNP in TXNRD3 interacted with aspirin/NSAIDs to influence rectal cancer. Five SNPs in TXNRD2 and one in SelS, SeP15, and SelW1 interacted with estrogen to modify colon cancer risk; one SNP in SelW1 interacted with estrogen to alter rectal cancer risk. Several SNPs in this candidate pathway influenced survival after diagnosis with colon cancer (SeP15 and SepX1 increased HRR) and rectal cancer (SepX1 increased HRR).

Conclusions

Findings support an association between selenoprotein genes and colon and rectal cancer development and survival after diagnosis. Given the interactions observed, it is likely that the impact of cancer susceptibility from genotype is modified by lifestyle.