Dietary selenite and azadeoxycytidine treatments affect dimethylhydrazine-induced aberrant crypt formation in rat colon and DNA methylation in HT-29 cells

Maternal Mineral Nutrition Regulates Fetal Genomic Programming in Cattle: A Review

Maternal mineral nutrition during the critical phases of fetal development may leave lifetime impacts on the productivity of an individual. Most research within the developmental origins of the health and disease (DOHaD) field is focused on the role of macronutrients in the genome function and programming of the developing fetus. On the other hand, there is a paucity of knowledge about the role of micronutrients and, specifically, minerals in regulating the epigenome of livestock species, especially cattle. Therefore, this review will address the effects of the maternal dietary mineral supply on the fetal developmental programming from the embryonic to the postnatal phases in cattle. To this end, we will draw a parallel between findings from our cattle model research with data from model animals, cell lines, and other livestock species. The coordinated role and function of different mineral elements in feto-maternal genomic regulation underlies the establishment of pregnancy and organogenesis and, ultimately, affects the development and functioning of metabolically important tissues, such as the fetal liver, skeletal muscle, and, importantly, the placenta. Through this review, we will delineate the key regulatory pathways involved in fetal programming based on the dietary maternal mineral supply and its crosstalk with epigenomic regulation in cattle.

Current challenges and future implications of exploiting the omics data into nutrigenetics and nutrigenomics for personalized diagnosis and nutrition-based care

Nutrigenetics and nutrigenomics, combined with the omics technologies, are a demanding and an increasingly important field in personalizing nutrition-based care to understand an individual's response to nutrition-guided therapy. Omics is defined as the analysis of the large data sets of the biological system featuring transcriptomics, proteomics, and metabolomics and providing new insights into cell regulation. The effect of combining nutrigenetics and nutrigenomics with omics will give insight into molecular analysis, as human nutrition requirements vary per individual. Omics measures modest intraindividual variability and is critical to exploit these data for use in the development of precision nutrition. Omics, combined with nutrigenetics and nutrigenomics, is instrumental in the creation of goals for improving the accuracy of nutrition evaluations. Although dietary-based therapies are provided for various clinical conditions such as inborn errors of metabolism, limited advancement has been done to expand the omics data for a more mechanistic understanding of cellular networks dependent on nutrition-based expression and overall regulation of genes. The greatest challenge remains in the clinical sector to integrate the current data available, overcome the well-established limits of self-reported methods in research, and provide omics data, combined with nutrigenetics and nutrigenomics research, for each individual. Hence, the future seems promising if a design for personalized, nutrition-based diagnosis and care can be implemented practically in the health care sector.

Higher blood selenium level is associated with lower risk of hyperhomocysteinemia in the elderly

BACKGROUND AND AIMS

Earlier studies have reported inconsistent association between selenium (Se) and homocysteine (Hcy) levels, while no evidence could be found from Chinese population. To fill this gap, we investigated the association between blood Se and hyperhomocysteinemia (HHcy) of rural elderly population in China.

METHODS

A cross-sectional study on 1823 participants aged 65 and older from four Chinese rural counties was carried out in this study. Whole blood Se and serum Hcy concentrations were measured in fasting blood samples. Analysis of covariance and restricted cubic spline models were used to examine the association between Se and Hcy levels. Logistic regression models were used to evaluate the risk of prevalent HHcy among four Se quartile groups after adjusting for covariates.

RESULTS

For this sample, the mean blood Se concentration was 156.34 (74.65) μg/L and the mean serum Hcy concentration was 17.25 (8.42) μmol/L. A significant non-linear relationship was found between blood Se and serum Hcy, the association was inverse when blood Se was less than 97.404 μg/L and greater than 156.919 μg/L. Participants in the top three blood Se quartile groups had significantly lower risk of prevalent HHcy compared with the lowest quartile group. When defined as Hcy> 10 μmol/L, the odds ratios and 95% confidence interval of HHcy were 0.600 (0.390, 0.924), 0.616 (0.398, 0.951) and 0.479 (0.314, 0.732) for Q2, Q3, and Q4 Se quartile groups compared with the Q1 group, respectively. When defined as Hcy≥ 15 μmol/L, the odds ratios and 95% confidence interval of HHcy were 0.833 (0.633, 1.098) and 0.827 (0.626, 1.092), 0.647 (0.489, 0.857) for Q2, Q3, and Q4 Se quartile groups compared with Q1 group.

CONCLUSIONS

Our findings suggest that higher blood Se level could be a protective factor for HHcy in the elderly.

Metabolism of Selenium, Selenocysteine, and Selenoproteins in Ferroptosis in Solid Tumor Cancers

A potential target of precision nutrition in cancer therapeutics is the micronutrient selenium (Se). Se is metabolized and incorporated as the amino acid selenocysteine (Sec) into 25 human selenoproteins, including glutathione peroxidases (GPXs) and thioredoxin reductases (TXNRDs), among others. Both the processes of Se and Sec metabolism for the production of selenoproteins and the action of selenoproteins are utilized by cancer cells from solid tumors as a protective mechanism against oxidative damage and to resist ferroptosis, an iron-dependent cell death mechanism. Protection against ferroptosis in cancer cells requires sustained production of the selenoprotein GPX4, which involves increasing the uptake of Se, potentially activating Se metabolic pathways such as the trans-selenation pathway and the TXNRD1-dependent decomposition of inorganic selenocompounds to sustain GPX4 synthesis. Additionally, endoplasmic reticulum-resident selenoproteins also affect apoptotic responses in the presence of selenocompounds. Selenoproteins may also help cancer cells adapting against increased oxidative damage and the challenges of a modified nutrient metabolism that result from the Warburg switch. Finally, cancer cells may also rewire the selenoprotein hierarchy and use Se-related machinery to prioritize selenoproteins that are essential to the adaptations against ferroptosis and oxidative damage. In this review, we discuss both the evidence and the gaps in knowledge on how cancer cells from solid tumors use Se, Sec, selenoproteins, and the Se-related machinery to promote their survival particularly via resistance to ferroptosis.

IRON-MEDIATED EPIGENETIC ACTIVATION OF NRF2 TARGETS

The toxic effects of excess dietary iron within the colonic lumen are well documented, particularly in the context of Inflammatory Bowel Disease (IBD) and Colorectal Cancer (CRC). Proposed mechanisms that underpin iron-associated intestinal disease include: i) the pro-inflammatory and ROS-promoting nature of iron, ii) gene-expression alterations, and iii) intestinal microbial dysbiosis. However, to date no studies have examined the effect of iron on the colonic epigenome. Here we demonstrate that chronic iron exposure of colonocytes leads to significant hypomethylation of the epigenome. Bioinformatic analysis highlights a significant epigenetic effect on NRF2 (nuclear factor erythroid 2-related factor 2) pathway targets (including NAD(P)H Quinone Dehydrogenase 1 [NQO1] and Glutathione peroxidase 2 [GPX2]); this demethylating effect was validated and subsequent gene and protein expression quantified. These epigenetic modifications were not observed upon the diminishment of cellular lipid peroxidation with endogenous glutathione and the subsequent removal of iron. Additionally, the induction of TET1 expression was found post-iron treatment, highlighting the possibility of an oxidative-stress induction of TET1 and subsequent hypomethylation of NRF2 targets. In addition, a strong time dependence on the establishment of iron-orchestrated hypomethylation was found which was concurrent with the increase in the intracellular labile iron pool (LIP) and lipid peroxidation levels. These epigenetic changes were further validated in murine intestinal mucosa in models administered a chronic iron diet, providing evidence for the likelihood of dietary-iron mediated epigenetic alterations in vivo. Furthermore, significant correlations were found between NQO1 and GPX2 demethylation and human intestinal tissue iron-status, thus suggesting that these iron-mediated epigenetic modifications are likely in iron-replete enterocytes. Together, these data describe a novel mechanism by which excess dietary iron is able to alter the intestinal phenotype, which could have implications in iron-mediated intestinal disease and the regulation of ferroptosis.

DNA methylation changes of apoptotic genes in organogenesis stage of mice embryos by maternal chlorpyrifos induction

The continued use of pesticides is one of the requirements of modern agriculture. Investigations have shown that pesticides can alter gene methylation and expression and subsequently may lead to abortion or birth of embryos with teratogenic disorders. In present study, 30 female NMRI mouse were divided in three experimental groups which in the CPF group, intraperitoneal chlorpyrifos was injected, in the sham group, DMSO was injected, and the control group without injection. The mice were mated and utinized 10 days' post gestation. The number of embryos in each fertilized female, maternal weight, and liver fibrosis was evaluated. The apoptosis pathway genes (caspase3, caspase9) and protein expressions (pro-caspase3, caspase3) of the embryos were evaluated with qRT-PCR and western blot, respectively. The DNA methylation of caspase3 and caspase9 were also assessed. The number of embryos and obtained maternal weight from the CPF group was significantly lower than other two groups. The mRNA expression of Caspase3 and Caspase9 were significantly higher in the CPF group. The protein expression evaluation confirmed the results achieved at the mRNA level. The percentage of Caspase9 DNA methylation in embryos collected from the CPF group was higher compared to the others. It can be considered that consumption of chlorpyrifos toxin can alter the DNA methylation and increase the expression of apoptotic genes. Therefore, continuous use of chlopyrifos may affect pregnancy by increasing the apoptosis pathway in the developing embryos which may lead to abortion or teratogenic disorders in newborn infants.

Role of Personalized Nutrition in Chronic-Degenerative Diseases

Human nutrition is a branch of medicine based on foods biochemical interactions with the human body. The phenotypic transition from health to disease status can be attributed to changes in genes and/or protein expression. For this reason, a new discipline has been developed called “-omic science”. In this review, we analyzed the role of “-omics sciences” (nutrigenetics, nutrigenomics, proteomics and metabolomics) in the health status and as possible therapeutic tool in chronic degenerative diseases. In particular, we focused on the role of nutrigenetics and the relationship between eating habits, changes in the DNA sequence and the onset of nutrition-related diseases. Moreover, we examined nutrigenomics and the effect of nutrients on gene expression. We perused the role of proteomics and metabolomics in personalized nutrition. In this scenario, we analyzed also how dysbiosis of gut microbiota can influence the onset and progression of chronic degenerative diseases. Moreover, nutrients influencing and regulating gene activity, both directly and indirectly, paves the way for personalized nutrition that plays a key role in the prevention and treatment of chronic degenerative diseases.

Selenium and Epigenetics in Cancer: Focus on DNA Methylation

Chemopreventive activity of selenium (Se) may influence epigenome. In this review, we have discussed two aspects of Se and epigenetics in cancer, related to (1) the association between Se and epigenetic regulation in cancer development and prevention; (2) epigenetic modification of selenoprotein-encoding genes in different cancers. In both issues, we focused on DNA methylation as the most investigated epigenetic mechanism. The existing evidence from experimental data in human cancer cell lines, rodents, and human studies in cancer-free subjects indicates that: high Se exposure leads to the inhibition of DNA methyltransferase expression/activity; the association between Se and global methylation remains unclear and requires further investigation with respect to the underlying mechanisms and possible nonlinear character of this relationship; Se affects methylation of specific tumor suppressor genes, possibly in a sex-dependent manner; and cancer phenotype is often characterized by altered methylation of selenoprotein-encoding genes, mainly glutathione peroxidase 3.

Effect of small molecules on cell reprogramming

The essential idea of regenerative medicine is to fix or replace tissues or organs with alive and patient-specific implants. Pluripotent stem cells are able to indefinitely self-renew and differentiate into all cell types of the body which makes them a potent substantial player in regenerative medicine. The easily accessible source of induced pluripotent stem cells may allow obtaining and cultivating tissues in vitro. Reprogramming refers to regression of mature cells to its initial pluripotent state. One of the approaches affecting pluripotency is the usage of low molecular mass compounds that can modulate enzymes and receptors leading to the formation of pluripotent stem cells (iPSCs). It would be great to assess the general character of such compounds and reveal their new derivatives or modifications to increase the cell reprogramming efficiency. Many improvements in the methods of pluripotency induction have been made by various groups in order to limit the immunogenicity and tumorigenesis, increase the efficiency and accelerate the kinetics. Understanding the epigenetic changes during the cellular reprogramming process will extend the comprehension of stem cell biology and lead to potential therapeutic approaches. There are compounds which have been already proven to be or for now only putative inducers of the pluripotent state that may substitute for the classic reprogramming factors (Oct3/4, Sox2, Klf4, c-Myc) in order to improve the time and efficiency of pluripotency induction. The effect of small molecules on gene expression is dosage-dependent and their application concentration needs to be strictly determined. In this review we analysed the role of small molecules in modulations leading to pluripotency induction, thereby contributing to our understanding of stem cell biology and uncovering the major mechanisms involved in that process.

Enhanced therapeutic efficacy and amelioration of cisplatin-induced nephrotoxicity by quercetin in 1,2-dimethyl hydrazine-induced colon cancer in rats

Objective:

The aim of quercetin treatment in combination of cisplatin (CP)-induced nephrotoxicity as well on 1,2-dimethyl hydrazine (DMH)-induced colon cancer.

Materials and Methods:

In this study, animals are exposed to DMH hydrochloride to induce colon cancer. In these groups, nephrotoxicity was assessed with the help of blood urea nitrogen, urea, and creatinine. The antitumor activity of quercetin and CP assessed with the help of number of aberrant crypts and foci formation. Tumor size in different treatment group determined with the help of vernier caliper.

Results:

CP is one of the most widely used antineoplastic drugs against colon cancer, but it has a major dose-limiting drawbacks of causing nephrotoxicity. Therefore, there is a need for a novel therapeutic regimen which will reduce the nephrotoxicity and enhance the anticancer activity of CP. The protective effect of quercetin on CP-induced nephrotoxicity is well-known. Moreover, quercetin is proven to have antitumor activity in colon cancer. Keeping all the facts in view, this study was conceived to evaluate the role of quercetin on therapeutic efficacy and nephrotoxicity of CP in DMH-induced colon cancer in male Sprague–Dawley rats. Treatment of quercetin with CP (7.5 mg/kg) prevents the CP-induced nephrotoxicity along with enhance the anticancer activity confirmed by the reduction of aberrant crypt foci number. Treatment of CP and quercetin alone leads to significant increase in the anticancer activity as compared to control colon tumor rats.

Conclusion:

In DMH-induced colon cancer model, combination of quercetin and CP ameliorates CP-induced nephrotoxicity as well as enhanced antitumor activity.

The interaction between epigenetics, nutrition and the development of cancer

Unlike the genome, the epigenome can be modified and hence some epigenetic risk markers have the potential to be reversed. Such modifications take place by means of drugs, diet or environmental exposures. It is widely accepted that epigenetic modifications take place during early embryonic and primordial cell development, but it is also important that we gain an understanding of the potential for such changes later in life. These “later life” epigenetic modifications in response to dietary intervention are the focus of this paper. The epigenetic modifications investigated include DNA methylation, histone modifications and the influence of microRNAs. The epigenotype could be used not only to predict susceptibility to certain cancers but also to assess the effectiveness of dietary modifications to reduce such risk. The influence of diet or dietary components on epigenetic modifications and the impact on cancer initiation or progression has been assessed herein.

Effects of deranged metabolism on epigenetic changes in cancer

The concept of epigenetics is now providing the mechanisms by which cells transfer their new environmental-change-induced phenotypes to their daughter cells. However, how extracellular or cytoplasmic environmental cues are connected to the nuclear epigenome remains incompletely understood. Recently emerging evidence suggests that epigenetic changes are correlated with metabolic changes via chromatin remodeling. As many human complex diseases including cancer harbor both epigenetic changes and metabolic dysregulation, understanding the molecular processes linking them has huge implications for disease pathogenesis and therapeutic intervention. In this review, the impacts of metabolic changes on cancer epigenetics are discussed, along with the current knowledge on cancer metabolism and epigenetics.

Effects of selenium compounds on proliferation and epigenetic marks of breast cancer cells

Breast cancer is a global public health problem and the most frequent cause of cancer death among women. Mammary carcinogenesis is driven not only by genetic alterations but also by epigenetic disturbances. Because epigenetic marks are potentially reversible they represent promising molecular targets for breast cancer prevention interventions. Selenium is a promising anti-breast cancer trace element that has shown the modulation of DNA methylation and histone post-translational modifications in other malignancies. This study aimed to evaluate the effects of selenium compounds [methylseleninic acid (MSA) and selenite] on cell proliferation and death, expression of the tumor suppressor gene RASSF1A and epigenetic marks in MCF-7 human breast adenocarcinoma cells. Treatment with MSA or selenite markedly inhibited (P<0.05) in a dose-dependent manner the proliferation of MCF-7 cells. MSA induced (P<0.05) G2/M cell arrest while selenite presented the opposite effect. Regarding cell death induction, MSA acted mainly by inducing apoptosis (P<0.05), while selenite only induced necrosis (P<0.05). Furthermore selenite, but not MSA, markedly induced (P<0.05) cytotoxicity and increased (P<0.05) RASSF1A expression. Both selenium compounds inhibited (P<0.05) DNMT1 expression. MSA decreased (P<0.05) H3K9me3 and increased (P<0.05) H4K16ac, while selenite decreased (P<0.05) this latter histone mark. To the best of our knowledge this is the first report showing that selenite and MSA modulate epigenetic marks specifically in breast cancer cells. Our data reinforce the anti-breast cancer potential of selenium that is dependent on its chemical form. Furthermore the data show that epigenetic mechanisms represent relevant molecular targets involved in selenium inhibitory effects in breast cancer cells.

Natural products as potential cancer therapy enhancers: A preclinical update

Cancer is a multifactorial disease that arises as a consequence of alterations in many physiological processes. Recently, hallmarks of cancer were suggested that include sustaining proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, and activating invasion and metastasis, along with two emerging hallmarks including reprogramming energy metabolism and escaping immune destruction. Treating multifactorial diseases, such as cancer with agents targeting a single target, might provide partial treatment and, in many cases, disappointing cure rates. Epidemiological studies have consistently shown that the regular consumption of fruits and vegetables is strongly associated with a reduced risk of developing chronic diseases, such as cardiovascular diseases and cancer. Since ancient times, plants, herbs, and other natural products have been used as healing agents. Moreover, the majority of the medicinal substances available today have their origin in natural compounds. Traditionally, pharmaceuticals are used to cure diseases, and nutrition and herbs are used to prevent disease and to provide an optimal balance of macro- and micro-nutrients needed for good health. We explored the combination of natural products, dietary nutrition, and cancer chemotherapeutics for improving the efficacy of cancer chemotherapeutics and negating side effects.

TLR2-ICAM1-Gadd45α axis mediates the epigenetic effect of selenium on DNA methylation and gene expression in Keshan disease

Keshan disease (KD) is a fatal dilated cardiomyopathy with unknown etiology, and selenium deficiency is considered the main cause of KD. Several observations implicate a role for altered DNA methylation in selenium deficiency-related diseases. The aim of the present study was to investigate the epigenetic effects of selenium (Se) on DNA methylation and gene expression in Keshan disease. Using methylated DNA immunoprecipitation chip (MeDIP-Chip) and quantitative RT-PCR, we identified two inflammatory-related genes (TLR2 and ICAM1) that were differentially methylated and expressed between normal individuals and KD patients. Results from DNA methylation profile between KD patients and normal individuals showed that selenium deficiency decreased methylation of CpG islands in promoter regions of TLR2 and ICAM1 and upregulated messenger RNA (mRNA) and protein levels of TLR2 and ICAM1. In rat animal model of Keshan disease, selenite treatment could increase TLR2 and ICAM1 promoter methylation, suppress these genes expression, and reduce infiltration of myocardial inflammatory cells. In cell culture model of Keshan disease, we found 5-Aza-dC (DNMT1 inhibitor) treatment in the presence of selenium-reduced mRNA and protein levels of DNMT1 regardless of TLR2 and ICAM1 promoter methylation status and expression levels of these genes. Selenite treatment suppressed the expression of the Gadd45α, TLR2, and ICAM1 in a concentration-dependent manner, while selenium deficiency increased the expression of the Gadd45α, TLR2, and ICAM1 and decreased TLR2 and ICAM1 promoter methylation level in a time-dependent manner. Our results revealed that TLR2-ICAM1-Gadd45α axis might play an important role in gene-specific active DNA demethylation during inflammatory response in myocardium.

Selenium and selenoproteins in inflammatory bowel diseases and experimental colitis

Inadequate dietary intake of the essential trace element selenium (Se) is thought to be a risk factor for several chronic diseases associated with oxidative stress and inflammation. Biological actions of Se occur through low-molecular weight metabolites and through selenoproteins. Several key selenoproteins including glutathione peroxidases; selenoproteins M, P, and S; and selenium-binding protein 1 have been detected in the intestine. Interestingly, Se and antioxidant selenoproteins are known to modulate differentiation and function of immune cells and contribute to avoid excessive immune responses. This review discusses the role of Se and intestinal selenoproteins in inflammatory bowel diseases, based on data from human, animal, and in vitro studies. In humans, Se deficiency is commonly observed in patients with Crohn's disease. In animal models of experimental colitis, the Se status was negatively correlated with the severity of the disease. While the cause-effect relationship of these observations remains to be clarified, the beneficial outcome of dietary Se supplementation and an optimization of selenoprotein biosynthesis in murine inflammatory bowel disease models have led to investigations of targets and actions of Se in the gastrointestinal tract. The Se status affects gene expression, signaling pathways, and cellular functions in the small and large intestine as well as the gut microbiome composition. This data, particularly from animal experiments, hold promise that adequate dietary Se supply may counteract chronic intestinal inflammation in humans.

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.

Selenium and selenoprotein deficiencies induce widespread pyogranuloma formation in mice, while high levels of dietary selenium decrease liver tumor size driven by TGFα

Changes in dietary selenium and selenoprotein status may influence both anti- and pro-cancer pathways, making the outcome of interventions different from one study to another. To characterize such outcomes in a defined setting, we undertook a controlled hepatocarcinogenesis study involving varying levels of dietary selenium and altered selenoprotein status using mice carrying a mutant (A37G) selenocysteine tRNA transgene (Trsp(tG37) ) and/or a cancer driver TGFα transgene. The use of Trsp(tG37) altered selenoprotein expression in a selenoprotein and tissue specific manner and, at sufficient dietary selenium levels, separate the effect of diet and selenoprotein status. Mice were maintained on diets deficient in selenium (0.02 ppm selenium) or supplemented with 0.1, 0.4 or 2.25 ppm selenium or 30 ppm triphenylselenonium chloride (TPSC), a non-metabolized selenium compound. Trsp(tG37) transgenic and TGFα/Trsp(tG37) bi-transgenic mice subjected to selenium-deficient or TPSC diets developed a neurological phenotype associated with early morbidity and mortality prior to hepatocarcinoma development. Pathology analyses revealed widespread disseminated pyogranulomatous inflammation. Pyogranulomas occurred in liver, lungs, heart, spleen, small and large intestine, and mesenteric lymph nodes in these transgenic and bi-transgenic mice. The incidence of liver tumors was significantly increased in mice carrying the TGFα transgene, while dietary selenium and selenoprotein status did not affect tumor number and multiplicity. However, adenoma and carcinoma size and area were smaller in TGFα transgenic mice that were fed 0.4 and 2.25 versus 0.1 ppm of selenium. Thus, selenium and selenoprotein deficiencies led to widespread pyogranuloma formation, while high selenium levels inhibited the size of TGFα-induced liver tumors.

Curcumin modulates DNA methylation in colorectal cancer cells

Aim

Recent evidence suggests that several dietary polyphenols may exert their chemopreventive effect through epigenetic modifications. Curcumin is one of the most widely studied dietary chemopreventive agents for colon cancer prevention, however, its effects on epigenetic alterations, particularly DNA methylation, remain unclear. Using systematic genome-wide approaches, we aimed to elucidate the effect of curcumin on DNA methylation alterations in colorectal cancer cells.

Materials and Methods

To evaluate the effect of curcumin on DNA methylation, three CRC cell lines, HCT116, HT29 and RKO, were treated with curcumin. 5-aza-2′-deoxycytidine (5-aza-CdR) and trichostatin A treated cells were used as positive and negative controls for DNA methylation changes, respectively. Methylation status of LINE-1 repeat elements, DNA promoter methylation microarrays and gene expression arrays were used to assess global methylation and gene expression changes. Validation was performed using independent microarrays, quantitative bisulfite pyrosequencing, and qPCR.

Results

As expected, genome-wide methylation microarrays revealed significant DNA hypomethylation in 5-aza-CdR-treated cells (mean β-values of 0.12), however, non-significant changes in mean β-values were observed in curcumin-treated cells. In comparison to mock-treated cells, curcumin-induced DNA methylation alterations occurred in a time-dependent manner. In contrast to the generalized, non-specific global hypomethylation observed with 5-aza-CdR, curcumin treatment resulted in methylation changes at selected, partially-methylated loci, instead of fully-methylated CpG sites. DNA methylation alterations were supported by corresponding changes in gene expression at both up- and down-regulated genes in various CRC cell lines.

Conclusions

Our data provide previously unrecognized evidence for curcumin-mediated DNA methylation alterations as a potential mechanism of colon cancer chemoprevention. In contrast to non-specific global hypomethylation induced by 5-aza-CdR, curcumin-induced methylation changes occurred only in a subset of partially-methylated genes, which provides additional mechanistic insights into the potent chemopreventive effect of this dietary nutraceutical.

Selenistasis: epistatic effects of selenium on cardiovascular phenotype

Although selenium metabolism is intricately linked to cardiovascular biology and function, and deficiency of selenium is associated with cardiac pathology, utilization of selenium in the prevention and treatment of cardiovascular disease remains an elusive goal. From a reductionist standpoint, the major function of selenium in vivo is antioxidant defense via its incorporation as selenocysteine into enzyme families such as glutathione peroxidases and thioredoxin reductases. In addition, selenium compounds are heterogeneous and have complex metabolic fates resulting in effects that are not entirely dependent on selenoprotein expression. This complex biology of selenium in vivo may underlie the fact that beneficial effects of selenium supplementation demonstrated in preclinical studies using models of oxidant stress-induced cardiovascular dysfunction, such as ischemia-reperfusion injury and myocardial infarction, have not been consistently observed in clinical trials. In fact, recent studies have yielded data that suggest that unselective supplementation of selenium may, indeed, be harmful. Interesting biologic actions of selenium are its simultaneous effects on redox balance and methylation status, a combination that may influence gene expression. These combined actions may explain some of the biphasic effects seen with low and high doses of selenium, the potentially harmful effects seen in normal individuals, and the beneficial effects noted in preclinical studies of disease. Given the complexity of selenium biology, systems biology approaches may be necessary to reach the goal of optimization of selenium status to promote health and prevent disease.

Selenium and sulindac are synergistic to inhibit intestinal tumorigenesis in Apc/p21 mice

Background

Both selenium and non-steroidal anti-inflammatory drug (NSAID) sulindac are effective in cancer prevention, but their effects are affected by several factors including epigenetic alterations and gene expression. The current study was designed to determine the effects of the combination of selenium and sulindac on tumor inhibition and the underlying mechanisms.

Results

We fed the intestinal tumor model Apc/p21 mice with selenium- and sulindac-supplemented diet for 24 weeks, and found that the combination of selenium and sulindac significantly inhibited intestinal tumorigenesis, in terms of reducing tumor incidence by 52% and tumor multiplicities by 80% (p<0.01). Mechanistic studies revealed that the combination of selenium and sulindac led to the significant induction of the expression of p27 and p53 and JNK1 phosphorylation, and led to the suppression of β-catenin and its downstream targets. Impressively, the data also showed that demythelation on p21 promoter was associated with tumor inhibition by the combination of selenium and sulindac.

Conclusions

The selenium is synergistic with sulindac to exert maximal effects on tumor inhibition. This finding provides an important chemopreventive strategy using combination of anti-cancer agents, which has a great impact on cancer prevention and has a promising translational potential.

Both selenium deficiency and modest selenium supplementation lead to myocardial fibrosis in mice via effects on redox-methylation balance

SCOPE

Selenium has complex effects in vivo on multiple homeostatic mechanisms such as redox balance, methylation balance, and epigenesis, via its interaction with the methionine-homocysteine cycle. In this study, we examined the hypothesis that selenium status would modulate both redox and methylation balance and thereby modulate myocardial structure and function.

METHODS AND RESULTS

We examined the effects of selenium-deficient (<0.025 mg/kg), control (0.15 mg/kg), and selenium-supplemented (0.5 mg/kg) diets on myocardial histology, biochemistry and function in adult C57/BL6 mice. Selenium deficiency led to reactive myocardial fibrosis and systolic dysfunction accompanied by increased myocardial oxidant stress. Selenium supplementation significantly reduced methylation potential, DNA methyltransferase activity and DNA methylation. In mice fed the supplemented diet, inspite of lower oxidant stress, myocardial matrix gene expression was significantly altered resulting in reactive myocardial fibrosis and diastolic dysfunction in the absence of myocardial hypertrophy.

CONCLUSION

Our results indicate that both selenium deficiency and modest selenium supplementation leads to a similar phenotype of abnormal myocardial matrix remodeling and dysfunction in the normal heart. The crucial role selenium plays in maintaining the balance between redox and methylation pathways needs to be taken into account while optimizing selenium status for prevention and treatment of heart failure.

Colorectal cancer cells Caco-2 and HCT116 resist epigenetic effects of isothiocyanates and selenium in vitro

PURPOSE

It is relatively unknown how different dietary components, in partnership, regulate gene expression linked to colon pathology. It has been suggested that the combination of various bioactive components present in a plant-based diet is crucial for their potential anticancer activities. This study employed a combinatorial chemopreventive strategy to investigate the impact of selenium and/or isothiocyanates on DNA methylation processes in colorectal carcinoma cell lines.

METHODS

To gain insights into the epigenetic-mediated changes in gene expression in response to these dietary constituents cultured Caco-2 and HCT116 cells were exposed for up to 12 days to different concentrations of selenium methylselenocysteine and selenite (ranging from 0.2 to 5 μM) either alone or in combination with sulforaphane and iberin (ranging from 6 to 8 μM), and changes to gene-specific (p16(INK4A) and ESR1), global (LINE-1) methylation and DNMT expression were quantified using real-time PCR-based assays.

RESULTS

No effects on the methylation of CpG islands in ESR1, p16(INK4A) or of LINE-1, a marker of global genomic methylation, were observed after exposure of Caco-2 and HCT116 cells to selenium or isothiocyanates. Only transient changes in DNMT mRNA expression, which occurred mostly in the treatment groups containing isothiocyanates, were observed, and these occurred only for specific DNMT transcripts and did not lead to the modification of the aberrant methylation status present in these cells.

CONCLUSION

These data suggest that treatment for colon cancer cells with selenium and/or isothiocyanates, either individually or in combination does not impact abnormal methylation patterns of key genes involved in the complex multistep process of colon carcinogenesis in vitro.

Epigenetics and lifestyle

The concept of 'lifestyle' includes different factors such as nutrition, behavior, stress, physical activity, working habits, smoking and alcohol consumption. Increasing evidence shows that environmental and lifestyle factors may influence epigenetic mechanisms, such as DNA methylation, histone acetylation and miRNA expression. It has been identified that several lifestyle factors such as diet, obesity, physical activity, tobacco smoking, alcohol consumption, environmental pollutants, psychological stress and working on night shifts might modify epigenetic patterns. Most of the studies conducted so far have been centered on DNA methylation, whereas only a few investigations have studied lifestyle factors in relation to histone modifications and miRNAs. This article reviews current evidence indicating that lifestyle factors might affect human health via epigenetic mechanisms.

Targeting the epigenome with bioactive food components for cancer prevention

Epigenetic processes participate in cancer development and likely influence cancer prevention. Global DNA hypomethylation, gene promoter hypermethylation and aberrant histone post-translational modifications are hallmarks of neoplastic cells which have been associated with genomic instability and altered gene expression. Because epigenetic deregulation occurs early in carcinogenesis and is potentially reversible, intervention strategies targeting the epigenome have been proposed for cancer prevention. Bioactive food components (BFCs) with anticancer potential, including folate, polyphenols, selenium, retinoids, fatty acids, isothiocyanates and allyl compounds, influence DNA methylation and histone modification processes. Such activities have been shown to affect the expression of genes involved in cell proliferation, death and differentiation that are frequently altered in cancer. Although the epigenome represents a promising target for cancer prevention with BFCs, few studies have addressed the influence of dietary components on these mechanisms in vivo, particularly on the phenotype of humans, and thus the exact mechanisms whereby diet mediates an effect on cancer prevention remains unclear. Primary factors that should be elucidated include the effective doses and dose timing of BFCs to attain epigenetic effects. Because diet-epigenome interactions are likely to occur in utero, the impact of early-life nutrition on cancer risk programming should be further investigated.

The antioxidants vitamins A and E and selenium do not reduce the incidence of asbestos-induced disease in a mouse model of mesothelioma

Epidemiological evidence indicates that supplementation with some dietary factors is associated with a lower incidence of cancer. An effective cancer prevention strategy for the millions of people worldwide who have been exposed to asbestos could have enormous benefit. We tested whether dietary supplementation of the antioxidants vitamin A, E, and selenium could alter the pattern of disease in the MexTAg transgenic mouse model, in which mice uniformly develop mesothelioma after asbestos exposure. We focused on antioxidants because one of the most widely accepted hypotheses for the mechanism by which asbestos fibers cause cancer proposes the involvement of reactive oxygen and nitrogen species. We compared the survival of MexTAg mice that had been inoculated with asbestos fed on diets supplemented with 250,000 IU/kg vitamin A (retinoic acid), or 1,000 mg/kg vitamin E (α-tocopherol acetate) or 3 mg/kg selenium, or both vitamin E and selenium concurrently and, additionally, diets deficient in each antioxidant. We found that neither the time to develop symptoms of disease nor overall survival times were altered by any of the diets. We conclude that the data do not support the notion that dietary antioxidants will moderate the rate of mesothelioma in asbestos-exposed populations.

The potential role of epigenetic responses to diet in ageing

Epigenetic changes may be causal in the ageing process and may be influenced by diet, providing opportunities to improve health in later life. The aim of this review is to provide an overview of several areas of research relevant to this topic and to explore a hypothesis relating to a possible role of epigenetic effects, mediated by sirtuin 1, in the beneficial effects of dietary restriction, including increased lifespan. Epigenetic features of ageing include changes in DNA methylation, both globally and at specific loci, which differ between individuals. A major focus of research on dietary influences on epigenetic status has been on nutrition in utero, because the epigenome is probably particularly malleable during this life-course window and because epigenetic marking by early exposures is a compelling mechanism underlying effects on lifelong health. We explore the potential of diet during adulthood, including the practice of dietary restriction, to affect the epigenetic architecture. We report progress with respect to deriving data to support our hypothesis that sirtuin 1 may mediate some of the effects of dietary restriction through effects on DNA methylation and note observations that resveratrol affects DNA methylation and other epigenetic features. Disentangling cause and effect in the context of epigenetic change and ageing is a challenge and requires better understanding of the underlying mechanisms and also the development of more refined experimental tools to manipulate the epigenetic architecture, to facilitate hypothesis-driven research to elucidate these links and thus to exploit them to improve health across the full life-course through dietary measures.

Cancer chemoprevention and nutriepigenetics: state of the art and future challenges

The term "epigenetics" refers to modifications in gene expression caused by heritable, but potentially reversible, changes in DNA methylation and chromatin structure. Epigenetic alterations have been identified as promising new targets for cancer prevention strategies as they occur early during carcinogenesis and represent potentially initiating events for cancer development. Over the past few years, nutriepigenetics - the influence of dietary components on mechanisms influencing the epigenome - has emerged as an exciting new field in current epigenetic research. During carcinogenesis, major cellular functions and pathways, including drug metabolism, cell cycle regulation, potential to repair DNA damage or to induce apoptosis, response to inflammatory stimuli, cell signalling, and cell growth control and differentiation become deregulated. Recent evidence now indicates that epigenetic alterations contribute to these cellular defects, for example epigenetic silencing of detoxifying enzymes, tumor suppressor genes, cell cycle regulators, apoptosis-inducing and DNA repair genes, nuclear receptors, signal transducers and transcription factors by promoter methylation, and modifications of histones and non-histone proteins such as p53, NF-κB, and the chaperone HSP90 by acetylation or methylation.The present review will summarize the potential of natural chemopreventive agents to counteract these cancer-related epigenetic alterations by influencing the activity or expression of DNA methyltransferases and histone modifying enzymes. Chemopreventive agents that target the epigenome include micronutrients (folate, retinoic acid, and selenium compounds), butyrate, polyphenols from green tea, apples, coffee, black raspberries, and other dietary sources, genistein and soy isoflavones, curcumin, resveratrol, dihydrocoumarin, nordihydroguaiaretic acid (NDGA), lycopene, anacardic acid, garcinol, constituents of Allium species and cruciferous vegetables, including indol-3-carbinol (I3C), diindolylmethane (DIM), sulforaphane, phenylethyl isothiocyanate (PEITC), phenylhexyl isothiocyanate (PHI), diallyldisulfide (DADS) and its metabolite allyl mercaptan (AM), cambinol, and relatively unexplored modulators of histone lysine methylation (chaetocin, polyamine analogs). So far, data are still mainly derived from in vitro investigations, and results of animal models or human intervention studies are limited that demonstrate the functional relevance of epigenetic mechanisms for health promoting or cancer preventive efficacy of natural products. Also, most studies have focused on single candidate genes or mechanisms. With the emergence of novel technologies such as next-generation sequencing, future research has the potential to explore nutriepigenomics at a genome-wide level to understand better the importance of epigenetic mechanisms for gene regulation in cancer chemoprevention.

Dietary selenomethionine increases exon-specific DNA methylation of the p53 gene in rat liver and colon mucosa

The regulation of site-specific DNA methylation of tumor suppressor genes has been considered as a leading mechanism by which certain nutrients exert their anticancer property. This study was to investigate whether selenium (Se) affects the methylation of globe genomic DNA and the exon-specific p53 gene. Three groups of rats (n = 6-7/group) were fed the AIN-93G basal diet supplemented with 0 [Se deficient (D)], 0.15 [Se adequate (A)], or 4 mg [Se supranutritional (S)] (Se as l-selenomethionine)/kg diet for 104 d, respectively. Rats fed the A or S diet had greater plasma and liver glutathione peroxidase activity, liver thioredoxin reductase activity, and plasma homocysteine concentration than those fed the D diet. However, compared with the A diet, rats fed the S diet did not further increase these Se-dependent enzyme activities or homocysteine concentration. In contrast, Se concentrations in kidney, liver, gastrocnemius muscle, and plasma were increased in a Se-dose-dependent manner. Interestingly, rats fed the S diet had significantly less global liver genomic DNA methylation than those fed the D diet. However, the S diet significantly increased the methylation of the p53 gene (exons 5-8) but not the β-actin gene (exons 2-3) DNA in liver and colon mucosa compared with those fed the D diet. Taken together, long-term Se consumption not only affects selenoprotein enzyme activities, homocysteine, tissue Se concentrations, and global genomic DNA methylation but also increases exon-specific DNA methylation of the p53 gene in a Se-dose-dependent manner in rat liver and colon mucosa.

The von Hippel-Lindau (VHL) tumor-suppressor gene is down-regulated by selenium deficiency in Caco-2 cells and rat colon mucosa

To test the hypothesis that selenium affects DNA methylation and hence gene regulation, we employed a methylation array (Panomics) in the human colonic epithelial Caco-2 cell model. The array profiles DNA methylation from promoter regions of 82 human genes. After conditioning cells to repeatedly reduced concentrations of fetal bovine serum, a serum-free culture was established. Se-methylselenocysteine (SeMSC) was added at 0 (deficient Se) or 250 (control Se) nM to cells maintained in DMEM. After 7 days, cells were collected and stored at -80 °C until analysis; experiments were replicated three times. Glutathione peroxidase activity was significantly decreased in cells grown in low SeMSC. Cells grown in 250 nM SeMSC had maximal GPx activity. Genomic DNA from cells grown in the low-SeMSC media and media containing 250 nM SeMSC was incubated with methylation-binding protein followed by isolation of methylated DNA. The methylated DNA was labeled with biotin and hybridized to the methylation array. Thus, genes with promoter methylation will produce a higher chemiluminescence signal than those genes with no promoter methylation. Of the genes profiled, the von Hippel-Lindau (VHL) gene was most different as indicated by quantification following chemiluminescence detection demonstrating that the promoter region of VHL was hypermethylated in cells from the low-SeMSC media. To determine whether promoter methylation affected transcription, we isolated RNA from replicate samples and performed real-time RT PCR. VHL (mRNA) was down-regulated (fold change significantly <1) in cells grown in low SeMSC compared to cells grown in 250 nM SeMSC (control; fold change = 1). We also show that (mRNA) Vhl expression is significantly reduced in mucosa from rats fed a diet deficient in Se. Our results suggest that low Se status affects DNA promoter region methylation and that this can result in down-regulation of the tumor suppressor gene VHL.

Induction of glutathione peroxidase 4 expression during enterocytic cell differentiation

Glutathione peroxidase 4 (GPx4), an abundant selenoenzyme, is ubiquitously expressed in a tissue-, cell- and differentiation-dependent manner, and it is localized in cytoplasmic, mitochondrial, and nuclear cellular compartments. Here, we report cytoplasmic and nuclear localization of GPx4 in Caco-2 intestinal epithelial cells. Enterocytic differentiation of Caco-2 cells triggers an increase in GPx4 mRNA and protein levels, mediated by enhanced promoter activity. We identified a combined cAMP response element (CREB) and CCAAT/enhancer binding protein (C/EBP) site as critical for the differentiation-triggered GPx4 promoter activity. Induction of GPx4 correlated with C/EBPα transcript levels during differentiation, suggesting a role of C/EBPα as regulator of enterocytic GPx4 expression. Consistent with the in vitro results, GPx4 protein was detected in cytoplasmic and nuclear compartments of enterocytes in human intestinal epithelia. GPx4 is uniformly expressed in colonic crypts and is differentially expressed along the crypt-to-villus axis in the small intestine with a more pronounced expression of GPx4 in the upper villi, which contain fully differentiated enterocytes. These data suggest that intestinal GPx4 expression is modulated by the enterocytic differentiation program, and the results support a direct role of nuclear GPx4 in the (selenium-dependent) prevention of oxidative damage in the gastrointestinal tract.

In utero life and epigenetic predisposition for disease

Regulatory regions of the human genome can be modified through epigenetic processes during prenatal life to make an individual more likely to suffer chronic diseases when they reach adulthood. The modification of chromatin and DNA contributes to a larger well-documented process known as "programming" whereby stressors in the womb give rise to adult onset diseases, including cancer. It is now well known that death from ischemic heart disease is related to birth weight; the lower the birth weight, the higher the risk of death from cardiovascular disease as well as type 2 diabetes and osteoporosis. Recent epidemiological data link rapid growth in the womb to metabolic disease and obesity and also to breast and lung cancers. There is increasing evidence that "marked" regions of DNA can become "unmarked" under the influence of dietary nutrients. This gives hope for reversing propensities for cancers and other diseases that were acquired in the womb. For several cancers, the size and shape of the placenta are associated with a person's cardiovascular and cancer risks as are maternal body mass index and height. The features of placental growth and nutrient transport properties that lead to adult disease have been little studied. In conclusion, several cancers have their origins in the womb, including lung and breast cancer. More research is needed to determine the epigenetic processes that underlie the programming of these diseases.

Selenium compounds activate ATM-dependent DNA damage response via the mismatch repair protein hMLH1 in colorectal cancer cells

Epidemiological and animal studies indicate that selenium supplementation suppresses risk of colorectal and other cancers. The majority of colorectal cancers are characterized by a defective DNA mismatch repair (MMR). Here, we have employed the MMR-deficient HCT 116 colorectal cancer cells and the MMR-proficient HCT 116 cells with hMLH1 complementation to investigate the role of hMLH1 in selenium-induced DNA damage response, a tumorigenesis barrier. The ATM (ataxia telangiectasia mutated) protein responds to clastogens and initiates DNA damage response. We show that hMLH1 complementation sensitizes HCT 116 cells to methylseleninic acid, methylselenocysteine, and sodium selenite via reactive oxygen species and facilitates the selenium-induced oxidative 8-oxoguanine damage, DNA breaks, G(2)/M checkpoint response, and ATM pathway activation. Pretreatment of the hMLH1-complemented HCT 116 cells with the antioxidant N-acetylcysteine or 2,2,6,6-tetramethylpiperidine-1-oxyl or the ATM kinase inhibitor KU55933 suppresses hMLH1-dependent DNA damage response to selenium exposure. Selenium treatment stimulates the association between hMLH1 and hPMS2 proteins, a heterodimer critical for functional MMR, in a manner dependent on ATM and reactive oxygen species. Taken together, the results suggest a new role of selenium in mitigating tumorigenesis by targeting the MMR pathway, whereby the lack of hMLH1 renders the HCT 116 colorectal cancer cells resistant to selenium-induced DNA damage response.

Could Sirt1-mediated epigenetic effects contribute to the longevity response to dietary restriction and be mimicked by other dietary interventions?

Dietary restriction (DR) increases lifespan in a range of evolutionarily distinct species. The polyphenol resveratrol may be a dietary mimetic of some effects of DR. The pivotal role of the mammalian histone deacetylase (HDAC) Sirt1, and its homologue in other organisms, in mediating the effects of both DR and resveratrol on lifespan/ageing suggests it may be the common conduit through which these dietary interventions influence ageing. We propose the novel hypothesis that effects of DR relevant to lifespan extension include maintenance of DNA methylation patterns through Sirt1-mediated epigenetic effects, and proffer the view that dietary components, including resveratrol, may mimic these actions.

High dietary intake of sodium selenite does not affect gene mutation frequency in rat colon and liver

Our previous studies have shown that selenium (Se) is protective against dimethylhydrazine (DMH)-induced preneoplastic colon cancer lesions, and protection against DNA damage has been hypothesized to be one mechanism for the anticancer effect of Se. The present study was designed to determine whether dietary selenite affects somatic mutation frequency in vivo. We used the Big Blue transgenic model to evaluate the in vivo mutation frequency of the cII gene in rats fed either a Se-deficient (0 microg Se/g diet) or Se-supplemented diet (0.2 or 2 microg Se/g diet; n = 3 rats/diet in experiment 1 and n = 5 rats/group in experiment 2) and injected with DMH (25 mg/kg body weight, i.p.). There were no significant differences in body weight between the Se-deficient and Se-supplemented (0.2 or 2 microg Se/g diet) rats, but the activities of liver glutathione peroxidase and thioredoxin reductase and concentration of liver Se were significantly lower (p < 0.0001) in Se-deficient rats compared to rats supplemented with Se. We found no effect of dietary Se on liver 8-hydroxy-2'-deoxyguanosine. Gene mutation frequency was significantly lower in liver (p < 0.001) than that of colon regardless of dietary Se. However, there were no differences in gene mutation frequency in DNA from colon mucosa or liver from rats fed the Se-deficient diet compared to those fed the Se-supplemented (0.2 or 2 microg Se/g diet) diet. Although gene mutations have been implicated in the etiology of cancer, our data suggest that decreasing gene mutation is not likely a key mechanism through which dietary selenite exerts its anticancer action against DMH-induced preneoplastic colon cancer lesions in a Big Blue transgenic rat model.

Epigenetic and pharmacoepigenomic studies of major psychoses and potentials for therapeutics

Individuals with neuropsychiatric diseases have epigenetic programming disturbances, both in the brain, which is the primary affected organ, and in secondary tissues. Epigenetic modulations are molecular modifications made to DNA, RNA and proteins that fine-tune genotype into phenotype and do not include DNA base changes. For instance, gene-expression modulation is linked to epigenetic codes in chromatin that consist of post-replication DNA methylation and histone protein modifications (e.g., methylation, acetylation and so on), particularly in gene-promoter regions. Epigenetic coding is modulated globally, and in a gene-specific manner by environmental exposures that include nutrition, toxins, drugs and so on. Analysis of epigenetic aberrations in diseases helps to identify dysfunctional genes and pathways, establish more robust cause–effect relationships than genetic studies alone, and identify new pharmaceutical targets and drugs, including nucleic acid reagents such as inhibitory RNAs. The emerging science of pharmacoepigenomics can impact the treatment of psychiatric and other complex diseases. In fact, some therapeutics now in use target epigenetic programming. In the near future, epigenetic interventions should help stabilize affected individuals and lead to prevention strategies.

Aberrant expression of selenoproteins in the progression of colorectal cancer

Since damage to DNA and other cellular molecules by reactive oxygen species ranks high as a major culprit in the onset and development of colorectal cancer, the aim of the present study is to clarify the role of antioxidant seleonoproteins including glutathione peroxidase (GPx), thioredoxin reductase (TXR) and selenoprotein P (SePP), and the effect of oxidative stress on the progression of colorectal cancer. Expression of 14 oxidative stress-related molecules in both tumorous and non-tumorous tissues in 41 patients was examined by immunohistochemistry and Western blot analysis. Expression levels of proteins modified by 4-hydroxy-2-nonenal (4-HNE), malonyldialdehyde (MDA) and 4-hydroxy-2-hexenal (4-HHE), and the positive rate of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in tumorous tissues were much higher than those in non-tumorous tissues. Glutathione (GSH) content in tumor tissues was much lower than that in non-tumorous tissues. Expression level of selenoproteins such as GPx-1, GPx-3, and SePP, which are rapidly degraded during selenium deprivation, was significantly decreased in tumorous tissues, whereas that of GPx-2, which is resistant to selenium deprivation, was increased. Expression of SePP was decreased at stage III and IV, compared to that of stage II. These data suggest that contrasting expression pattern of the antioxidant selenoproteins plays an important role in the progression of colorectal cancer.

Environment, diet and CpG island methylation: epigenetic signals in gastrointestinal neoplasia

The epithelial surfaces of the mammalian alimentary tract are characterised by very high rates of cell proliferation and DNA synthesis, and in humans they are highly susceptible to cancer. The role of somatic mutations as drivers of carcinogenesis in the alimentary tract is well established, but the importance of gene silencing by epigenetic mechanisms is increasingly recognised. Methylation of CpG islands is an important component of the epigenetic code that regulates gene expression during development and normal cellular differentiation, and a number of genes are well known to become abnormally methylated during the development of tumours of the oesophagus, stomach and colorectum. Aberrant patterns of DNA methylation develop as a result of pathological processes such as chronic inflammation, and in response to various dietary factors, including imbalances in the supply of methyl donors, particularly folates, and exposure to DNA methyltransferase inhibitors, which include polyphenols and possibly isothiocyanates from plant foods. However the importance of these environmental interactions in human health and disease remains to be established. Recent moves to modify the exposure of human populations to folate, by mandatory supplementation of cereal foods, emphasise the importance of understanding the susceptibility of the human epigenome to dietary and other environmental effects.

Targeting aberrant chromatin structure in colorectal carcinomas

Epigenetic processes such as DNA methylation and histone modifications are now recognized as critical events for regulation of gene expression in mammalian cells and affect gene function without a change in coding sequence. Neoplastic cells often show profound epigenetic alterations that contribute to tumorigenesis by altering expression of critical genes. In colorectal tumorigenesis, detailed analysis led to a hypothesis on a critical role for epigenetic changes in age-related cancer susceptibility and separately identified a distinct phenotype termed the CpG island methylator phenotype. CpG island methylator phenotype-positive colorectal cancers have significant associations with female sex, older age, proximal location, mucinous histology, KRAS and BRAF mutations, wild-type p53, and microsatellite instability. Histone modifications that affect chromatin structures are also closely implicated in tumor suppressor gene inactivation and DNA methylation and histone modifications seem to form reinforcing networks for stable gene silencing. Much of the excitement in this field relates to the possibility of therapeutic reversal of epigenetic changes by chromatin-modifying drugs. In CpG island methylator phenotype-positive colorectal cancers, DNA methylation inhibitors restore key silenced pathways in vivo (eg, mismatch repair defects), and hypomethylation can largely abolish tumorigenesis in a mouse model. Drugs that inhibit DNA methylation and histone deacetylation are in use in the clinic and should be tested in colorectal malignancy.

Dietary selenium affects homocysteine metabolism differently in Fisher-344 rats and CD-1 mice

In our previous work with rats, plasma and tissue homocysteine concentrations were decreased by selenium deprivation. The purpose of this study was to follow up and expand on that work by determining the effects of selenium status (deficient, adequate, and supranutritional) on several aspects of homocysteine metabolism involving methionine recycling and transsulfuration. A 2nd objective was to determine whether there are differences in how selenium status affects homocysteine metabolism in rats and mice. Male weanling Fischer-344 rats and male weanling CD-1 mice were fed diets containing 0, 0.2, or 2.0 microg selenium (as sodium selenite)/g for 72 d or 60 d, respectively. Plasma homocysteine and cysteine were significantly decreased by feeding rats or mice the selenium-deficient diet compared with feeding adequate or supranutritional selenium. On the other hand, plasma glutathione was increased by selenium deficiency only in rats. Also, the specific activities of liver betaine homocysteine methyltransferase and glycine N-methyltransferase were decreased by selenium deficiency in rats, but were unaffected by selenium status in mice. Real-time RT-PCR was used to determine the expression of the subunits of glutamate-cysteine ligase, which catalyzes the rate-limiting step in glutathione biosynthesis. The expression of Gclc, the catalytic subunit of glutamate-cysteine ligase, was upregulated by selenium deprivation in both rat and mouse liver. Gclm, the modifier subunit of glutamate-cysteine ligase, was downregulated in rats fed 2 microg Se/g compared with rats fed adequate or deficient selenium. Based on these findings, it is evident that selenium deficiency has different outcomes in mice and rats. These variables are all related to methionine/methyl metabolism. Although only one strain of rat was compared with one strain of mouse, this work suggests that differences between species may prove vital in determining which animal model is used in studies of selenium deficiency or in studies that are designed to ascertain chemopreventive mechanisms of selenium.

Dietary selenium intake, aldehyde dehydrogenase-2 and X-ray repair cross-complementing 1 genetic polymorphisms, and the risk of esophageal squamous cell carcinoma

BACKGROUND

To the authors' knowledge, few studies have been conducted to date regarding dietary selenium and the potential gene-nutrient interactions with single-nucleotide polymorphisms (SNPs) in different pathways on the risk of esophageal cancer.

METHODS

The authors investigated the role of dietary selenium intake and its interplay with SNPs of the ALDH2 (glutamic acid [Glu] 487 lysine [Lys]) and the X-ray repair cross-complementing 1 (XRCC1) (arginine [Arg] 399 glutamine [Gln]) genes on the risk of esophageal squamous cell carcinoma (ESCC) in a population-based, case-control study in China. In total, 218 patients with ESCC and 415 healthy population control participants were interviewed. Dietary selenium intake was estimated from a food frequency questionnaire with 97 food items. ALDH2 and XRCC1 polymorphisms were detected with a polymerase chain reaction-restriction fragment length polymorphism assay.

RESULTS

The adjusted odds ratio (OR) for the highest quintile of dietary selenium intake, compared with the lowest quintile of intake, was 0.48 (95% confidence interval [95% CI], 0.25-0.89), with a strong dose-response relation (P for trend, <.01). The ALDH2 Lys and XRCC1 Gln variant alleles were associated with an increased risk of ESCC with adjusted ORs of 1.91 (95% CI, 0.96-3.80) and 1.67 (95% CI, 1.08-2.59), respectively. An elevation of the risk for ESCC was pronounced most among carriers of ALDH2 Lys/Lys and XRCC1 399Gln/Gln or Gln/Arg who consumed a low level of dietary selenium (adjusted OR, 4.16; 95% CI, 1.14-15.12).

CONCLUSIONS

To the authors' knowledge, this is the first in-depth study to suggest that genetic susceptibility may modify the association between selenium intake and the risk of ESCC. The findings indicated that individuals with low dietary selenium intake and ALDH2 Lys/Lys and XRCC1 399Gln/Gln or Gln/Arg genotypes were associated with an increased ESCC risk, especially in the presence of exposure to tobacco and alcohol carcinogens.

Both selenoproteins and low molecular weight selenocompounds reduce colon cancer risk in mice with genetically impaired selenoprotein expression

Selenium has cancer protective effects in a variety of experimental systems. Currently, it is not known whether selenoproteins or low molecular weight selenocompounds are responsible for this activity. To evaluate the contribution of selenoproteins to the cancer protective effects of selenium, we used transgenic mice that carry a mutant selenocysteine transfer RNA gene, which causes reduced selenoprotein synthesis. Selenium homeostasis was characterized in liver and colon of wild-type and transgenic mice fed selenium-deficient diets supplemented with 0, 0.1, or 2.0 microg selenium (as selenite)/g diet. (75)Se-labeling, Western blot analysis, and enzymatic activities revealed that transgenic mice have reduced (P < 0.05) liver and colon glutathione peroxidase expression, but conserved thioredoxin reductase expression compared with wild-type mice, regardless of selenium status. Transgenic mice had more (P < 0.05) selenium in the nonprotein fraction of the liver and colon than wild-type mice, indicating a greater amount of low molecular weight selenocompounds. Compared with wild-type mice, transgenic mice had more (P < 0.05) azoxymethane-induced aberrant crypt formation (a preneoplastic lesion for colon cancer). Supplemental selenium decreased (P < 0.05) the number of aberrant crypts and aberrant crypt foci in both wild-type and transgenic mice. These results provide evidence that a lack of selenoprotein activity increases colon cancer susceptibility. Furthermore, low molecular weight selenocompounds reduced preneoplastic lesions independent of the selenoprotein genotype. These results are, to our knowledge, the first to provide evidence that both selenoproteins and low molecular weight selenocompounds are important for the cancer-protective effects of selenium.

Allelic loss of the gene for the GPX1 selenium-containing protein is a common event in cancer

Selenium has been shown to reduce cancer incidence in animal models and more recent data indicate that it may be protective in humans as well. However, little is known about the mechanism by which selenium prevents cancer. Cytosolic glutathione peroxidase (GPX1), a selenium-containing antioxidant enzyme, has been implicated in the development of cancer of the head and neck, lung, and breast, in part because of allelic loss at the GPX1 locus. The study of allelic loss at the GPX1 locus in colon cancer was investigated by examining loss of heterozygosity (LOH) in DNA extracted from both tumor and adjacent histopathologically normal tissue obtained by laser capture microdissection. Tissue samples were obtained from 53 colon cancer patients. Two highly polymorphic markers, alanine codon repeats and a proline-leucine polymorphism (198P/L) present in the GPX1 gene, were used to examine LOH at this locus. Analysis of both polymorphisms identified LOH at GPX1 in a significant percentage of colorectal cancer (42%). These results indicated that LOH at the GPX1 locus is a common event in cancer development and that GPX1 or other tightly linked genes may be involved in the etiology of this disease.

Antimutagenicity of selenium-enriched rice on mice exposure to cyclophosphamide and mitomycin C

The in vivo antimutagenicity of Se-enriched rice was evaluated by bone marrow micronucleus and testicle chromosomal aberrations assay in mice exposed to cyclophosphamide (CP) and mitomycin C (MMC). Regular rice did not alter the occurrence of chemical-induced mutation. However, the addition of Se-enriched rice or selenite significantly inhibited the incidence of CP-induced micronuclei and MMC-induced chromosomal aberration in mice and the effect was dose-dependent. Providing selenite or Se-enriched rice also significantly increased the activity of glutathione peroxidase in liver and the selenium concentration in blood compared to regular rice. No significant differences were found in mice body weight gain. These results revealed the antimutagenic potential of Se-enriched rice against chemical-induced mutation.

Aging, cancer and nutrition: the DNA methylation connection

Cancer and aging are two coupled developmental processes as reflected by the higher incidence of cancer in the elderly human population group. Genetic mutations accumulate in somatic cells with age, which may explain in part the association of age with cancer. Epigenetic mechanisms are also frequently involved in controlling gene functions during development and tumorigenesis. A common molecular feature associated with both aging and tumorigenesis is global hypomethylation of the genomic DNA. The contributing mechanisms underlying this hypomethylation are not yet well understood. Epigenetic investigation of cancer and aging has recently emerged as a fruitful area of study and has added exciting insights into some of the mysteries surrounding aging and cancer. Recent studies have also shown that dietary factors can modulate DNA methylation and thereby contribute to aging and tumorigenesis. Thus, DNA methylation provides an important common link between aging, cancer and nutrition.