Merrill J. Christensen

High Selenium Reduces NF-κB-Regulated Gene Expression in Uninduced Human Prostate Cancer Cells

Abstract Nuclear factor kappa B (NF-κB) induces expression of antiapoptotic and pro-inflammatory genes and is constitutively activated in prostate cancer. We tested the hypothesis that a biologically and physiologically relevant form and concentration of selenium (Se) may alter NF-κ B activation in early prostate cancer cells in the absence of exogenously added inducers of the NF-κB pathway. LNCaP cells were cultured in medium without added tumor necrosis factor alpha or lipopolysaccharide but with methylseleninic acid added to provide final concentrations of Se of 30 nM–7.6 μM. Compared to 50 nM Se, treatment with 7.6 μM Se virtually eliminated NF-κB binding to its DNA response element and reduced transcription rates and mRNA levels by half for NF-κB-regulated genes. There were no differences due to Se in tyrosine phosphorylation, inhibitor of kappa B alpha (IκBα) levels, or NF-κB translocation from cytosol to nucleus. The observation in these basal, unstimulated cells of altered NF-κB binding to DNA in the absence of effects on the NF-κB activation pathway suggests an interaction of Se with the NF-κB protein or an effect on recruitment of NF-κB coactivators or corepressors. Inhibition of transcription factor binding and anti-apoptotic gene expression may be one mechanism for the chemopreventive effects of Se against prostate cancer.

Cell cycle arrest and differential gene expression in HT-29 cells exposed to an aqueous garlic extract

Epidemiological data show an inverse correlation between garlic consumption and the risk for colon cancer. To examine this relationship, HT-29 human adenocarcinoma cells were cultured in the presence and absence of an aqueous garlic extract. Garlic treatment resulted in a fraction of cells detaching from the culture flasks. These cells remained viable. Flow cell cytometry showed that untreated cells exhibited a normal distribution among phases of the cell cycle, with 12% of cells at the G2/M boundary. Of the garlic-treated cells remaining attached to the flask, 27% were present at the G2/M boundary. Treated cells that detached from the flask were found almost exclusively (89%) at the G2/M boundary. RNA fingerprinting and microarray analysis showed that expression of the gene for menin was twice as high in control cells as in detached treated cells. In contrast, expression of genes for epidermal growth factor receptor and integrin-α6 was nearly twice as high in detached treated cells as in control cells. These changes in gene expression were consistent with an arrest of the cell cycle at the G2/M boundary. Garlic=s arrest of the cell cycle in human adenocarcinoma cells may explain in part its anticarcinogenic properties.

Binding of nuclear proteins to transcription regulatory elements in selenium deficiency

Dietary selenium deficiency in rats increased binding of liver nuclear proteins to DNA regulatory sequences which activate transcription in response to oxidative stress. In contrast, binding to the activator protein-1 control sequence, which is inhibited by oxidation, was decreased in selenium deficiency.

Diets high in selenium and isoflavones decrease androgen-regulated gene expression in healthy rat dorsolateral prostate

BackgroundHigh dietary intake of selenium or soybean isoflavones reduces prostate cancer risk. These components each affect androgen-regulated gene expression. The objective of this work was to determine the combined effects of selenium and isoflavones on androgen-regulated gene expression in rat prostate.MethodsMale Noble rats were exposed from conception until 200 days of age to diets containing an adequate (0.33-0.45 mg/kg diet) or high (3.33-3.45 mg/kg) concentration of selenium as Se-methylselenocysteine and a low (10 mg/kg) or high (600 mg/kg) level of isoflavones in a 2 × 2 factorial design. Gene expression in the dorsolateral prostate was determined for the androgen receptor, for androgen-regulated genes, and for Akr1c9, whose product catalyzes the reduction of dihydrotestosterone to 5alpha-androstane-3alpha, 17beta-diol. Activity of hepatic glutathione peroxidise 1 and of prostatic 5alpha reductase were also assayed.ResultsThere were no differences due to diet in activity of liver glutathione peroxidase activity. Total activity of 5alpha reductase in prostate was significantly lower (p = 0.007) in rats fed high selenium/high isoflavones than in rats consuming adequate selenium/low isoflavones. High selenium intake reduced expression of the androgen receptor, Dhcr24 (24-dehydrocholesterol reductase), and Abcc4 (ATP-binding cassette sub-family C member 4). High isoflavone intake decreased expression of Facl3 (fatty acid CoA ligase 3), Gucy1a3 (guanylate cyclase alpha 3), and Akr1c9. For Abcc4 the combination of high selenium/high isoflavones had a greater inhibitory effect than either treatment alone. The effects of selenium on gene expression were always in the direction of chemopreventionConclusionThese results suggest that combined intake of high selenium and high isoflavones may achieve a greater chemopreventive effect than either compound supplemented individually.

Selenium and Prostate Cancer Prevention: What Next—If Anything?

Chemopreventive effects of the essential trace element selenium against prostate cancer have been shown in preclinical models and human observational studies, but results from clinical trials have been disappointing. It appears that there is a threshold selenium (Se) status below which improvement will decrease prostate cancer risk, but above which supplemental Se may be deleterious. Different forms of selenium have different effects, and genetic and other factors modify seleniums chemopreventive potential. Identification of men most likely to benefit from Se status improvement could have significant public health benefits. Cancer Prev Res; 7(8); 781–5. ©2014 AACR.

Promotion of lipid oxidation by selenate and selenite and indicators of lipid peroxidation in the rat

The AIN-93 reformulation of the AIN-76A rodent diet includes a change in selenium supplement from sodium selenite to sodium selenate to reduce dietary lipid peroxidation. A change to selenate as the standard form of Se in rat diets would render results from previous work using selenite less relevant for comparison with studies using the AIN-93 formulation. To critically examine the rationale for the AIN-93 recommendation, we prepared Torula yeast basal diets patterned as closely as possible after the AIN-93 formulation and supplemented with 0, 0.15 (adequate), or 2.0 (high) mg selenium/kg diet as sodium selenite or sodium selenate. Livers isolated from male Sprague-Dawley rats fed these diets for 15 wk showed no differences in thiobarbituric acid-reactive substances or lipid hydroperoxides measured with the ferrous oxidation in xylenol orange method. Lipids isolated from samples of high-selenate and high-selenite diets showed no differences in conjugated dienes. The addition of selenate or selenite to soybean oil did not result in an altered Oil Stability Index. These results demonstrate that selenate is not less likely than selenite to cause oxidation of other dietary components. Benefits of selenate over selenite in the diets of rodents remain to be demonstrated.

Selenium regulates expression in rat liver of genes for proteins involved in iron metabolism

Suppression subtractive hybridization analysis in our laboratory recently revealed that transferrin mRNA may be elevated in Sedeficient rat liver. In this work, we compared expression in rat liver of genes for transferrin, transferrin receptor, ferritin light and heavy chains, and iron-regulatory proteins 1 and 2 in Se adequacy and deficiency. Weanling male Sprague-Dawley rats were fed Torula yeast diets supplemented with 0 or 0.15 µg Se/kg diet as sodium selenite for 15 wk. Activity of cellular glutathione peroxidase was virtually abolished in Se-deficient rat liver, whereas activity of glutathione S-transferase was 43% higher than in Se-adequate liver. There were no differences in hematocrit, hemoglobin, or liver iron content. To examine differential gene expression, we used a multiplex relative reverse transcriptase-polymerase chain reaction method. Three of the six genes examined showed modest but consistent upregulation in Se deficiency. Transferrin mRNA was 30% more abundant in Sedeficient than in Se-adequate liver. For the transferrin receptor, the difference was 32%, and for iron regulatory protein 1, it was 63%. No consistent differences were observed for iron regulatory protein 2 or for ferritin light or heavy chain. These findings suggest a possible role for dietary Se in moderating iron metabolism.

Combination effects of dietary soy and methylselenocysteine in a mouse model of prostate cancer.

High dietary intake of soy or selenium (Se) is associated with decreased risk of prostate cancer. Soy constituents and various chemical forms of Se have each been shown to downregulate expression of the androgen receptor (AR) and AR‐regulated genes in the prostate. We hypothesized that downregulation of AR and AR‐regulated genes by the combination of these dietary components would inhibit tumorigenesis in the TRansgenic Adenocarcinoma of Mouse Prostate (TRAMP) mouse.

A retail market study of organic and conventional potatoes (Solanum tuberosum): mineral content and nutritional implications

Whether or not all foods marketed to consumers as organic meet specified standards for use of that descriptor, or are nutritionally different from conventional foods, is uncertain. In a retail market study in a Western US metropolitan area, differences in mineral composition between conventional potatoes and those marketed as organic were analysed. Potatoes marketed as organic had more copper and magnesium (p < 0.0001), less iron (p < 0.0001) and sodium (p < 0.02), and the same concentration of calcium, potassium and zinc as conventional potatoes. Comparison of individual mineral concentrations between foodstuffs sold as organic or conventional is unlikely to establish a chemical fingerprint to objectively distinguish between organic and conventional produce, but more sophisticated chemometric analysis of multi-element fingerprints holds promise of doing so. Although statistically significant, these differences would only minimally affect total dietary intake of these minerals and be unlikely to result in measurable health benefits.

Soy Content of Basal Diets Determines the Effects of Supplemental Selenium in Male Mice

The effects of supplemental Se in rodent models may depend upon composition of the basal diet to which it is added. Wild-type male littermates of Transgenic Adenocarcinoma of Mouse Prostate mice were fed until 18 wk of age 1 of 2 Se-adequate stock diets high in soy (HS) or low in phytoestrogens (LP) or the same diets supplemented with 3.0 mg Se/kg diet as seleno-methylselenocysteine. Body and abdominal fat pad weights were lower (P < 0.01) in mice fed the HS diet. Supplemental Se reduced fat pad weights in mice receiving the LP diet but increased body and fat pad weights in mice consuming the HS formulation (P-interaction < 0.005). Serum free triiodothyronine concentrations were unaffected by supplemental Se in mice fed the LP diet but were decreased by Se supplementation of mice given the HS feed (P-interaction < 0.02). Free thyroxine concentrations were higher in mice consuming the HS diet regardless of Se intake (P < 0.001). Hepatic mRNA for iodothyronine deiodinase I was lower (P < 0.001) in mice fed the HS diet. Supplementation of Se increased this mRNA (P < 0.001) in both diet groups. Results from this study show a significant interaction between the composition of basal diets and the effects of supplemental Se with respect to body composition. These findings have important implications for future studies in rodent models of the effects of supplemental Se on heart disease, cancer, diabetes, and other conditions related to body weight and composition.