Regional variation of cancer mortality incidence and its relation to selenium levels in China

Laser Ablation ICP-MS Analysis of Chemically Different Regions of Rat Prostate Gland with Implanted Cancer Cells

The comparison of tissues analyzed by LA-ICP-MS is challenging in many aspects, both medical and mathematical. The concept of distinguishing regions of interest (ROIs) was proposed in the literature, allowing for data reduction and targeted comparative analysis. ROIs can be drawn before any analysis, by indicating the anatomical parts of tissue, or after the first step of analysis, by using elemental distribution maps and characteristic regions of enrichment in selected elements. A simple method for identifying different regions, without the manual extraction of image fragments, is highly needed in biological experiments, where large groups of individuals (with samples taken from each of them) is very common. In the present study, two ROIs were distinguished: (1) tissue-rich in fat (and tissue-poor in water); and (2) tissue-rich in water (and tissue-poor in fat). ROIs were extracted mathematically, using an algorithm based on the relationship between 13C and 23Na signal intensities. A cut-off point was indicated in the point of the simultaneous decrease in 13C and increase in 23Na signal intensity. Separate analyses of chemically different ROIs allow for targeted comparison, which is a great advantage of laser ablation over liquid introductions to ICP-MS. In the present experiment, tissues were provided from animals with implanted prostate cancer cells as well as supplemented with mineral compounds particularly important both for prostate gland functions (Zn and Se) and neoplastic processes (Ca, Fe, and Cu). One of the goals was to try to determine whether dietary supplementation qualitatively and quantitatively affects the mineral composition of the prostate gland.

The role of selenium and selected trace elements in the etiology of esophageal cancer in high risk Golestan province of Iran

Selenium (Se) deficiency is reported by some authors to be an important factor in the etiology of esophageal cancer (EC) in the Golestan province of Iran. In order to further investigate the role of Se and selected trace elements in the occurrence of EC disease, 663 samples including 206 cultivated soils, 247 sediments, 45 loess deposits and 165 grain samples from 45 villages in the Golestan province of Iran were collected and analyzed. Villages in the study area were classified into 2 groups according to the EC incidence in the local population. The results of this study demonstrate that, contrary to the expected trend, total Se concentrations in soil, grain, sediment, and loess samples increase from the low to the high EC areas suggesting that Se deficiency does not play a major role in the etiology of EC. On the other hand, antimony (Sb), and strontium (Sr) content in soil, grain, loess, and sediment samples is much higher in the high esophageal cancer area, which may be a significant factor. Total zinc (Zn) concentrations in soil, grain, loess, and sediment samples decrease from the low to the high cancer areas. Therefore, Zn deficiency may be a significant factor in EC incidence rate in the Golestan province.

Medical geology of arsenic, selenium and thallium in China

Arsenic (As), selenium (Se) and thallium (Tl) are three trace metals (metalloids) of high concern in China because deficiency or excess expose can cause a range of endemic diseases, such as endemic arsenism, selenosis, Keshan disease (KD), Kashin-Beck disease (KBD) and thallotoxicosis. These specific endemic diseases were attributable for overabundance or deficiency (mainly referring to selenium) of these three elements in the local environment as a result of natural geochemical processes and/or anthropologic activities. The geochemistry and human health impacts of these three trace elements have been intensively studied since the 1970s in China, in terms of geochemical sources, distribution, transportation, health impact pathways, and prevention/remediation measures. Endemic arsenism in China are induced from the exposures of high As in either drinking water or domestic combustion of As-rich coals. Both endemic selenium deficiency and selenosis occurred in China. The KD and KBD were related to the deficiency of Se in the low-Se geological belt with Se contents in soil less than 0.125mg/kg stretching from northeast to southwest of China. Endemic selenosis occurred in areas with high Se concentrations in soils derived from the Se-enriched black carbonaceous siliceous rocks, carbonaceous shale and slate. Endemic Tl poisoning occurred in southwestern China due to Tl contamination in local drinking water and vegetables surrounding the Tl-rich sulfide mineralized areas. Some measures have been taken to control and remedy the endemic diseases with significant effects in reducing health risk and damage of As, Se and Tl. However, the states of the endemic diseases of As, Se and Tl in China are still serious in some areas, and substantial research efforts regarding the health impacts of these elements are further required. This paper reviews the progress of medical geology of As, Se and Tl in China, and provides with some outlooks for future research directions.

Supplementation of selenium reduces chemical hepatocarcinogenesis in male Sprague-Dawley rats

Selenium is an essential micronutrient mineral found mainly in soils and has been shown to prevent certain cancers in humans and animals. However, the dose and effects of selenium on liver cancer are controversial. The aim of this study was to investigate the effects of sodium selenite (4 mg/kg in drinking water) on chemically induced hepatocarcinogenesis in rats. Hepatocarcinogenesis was induced by a single intraperitoneal injection of diethyl nitrosamine (DEN) (200 mg/kg body weight) and 2 weeks later, the carcinogenic effect was promoted by 2-acetylaminofluorene (2-AAF) (0.02%). 44 Sprague-Dawley rats were divided into 6 groups: negative control, positive control (DEN+2-AAF), pre-selenium group (sodium selenite for 4 weeks, then DEN+2-AAF), pre-selenium control group (sodium selenite for 4 weeks, no DEN or 2-AAF), post-selenium group (sodium selenite for 8 weeks after 4 weeks of DEN injection) and post-selenium control group (sodium selenite for 8 weeks, no DEN or 2-AAF). Hematoxylin and eosin plus Gordon and Sweet's methods were used to stain liver tissues. The results showed that the number and sizes of hepatic nodules in pre- and post-selenium treatment groups significantly decreased (P<0.05) compared with the positive control. Microscopic analysis of pre- and post-selenium groups showed that the majority of nodules were hyperplastic with preserved liver architecture, whereas the positive control was full of neoplastic nodules with a completely disrupted liver architecture. Hence, pre- and post-selenium treatments can reduce the extent of liver cancer on chemically induced hepatocarcinogenesis in rats.

Production and characterization of fully selenomethionine-labeled Saccharomyces cerevisiae

This paper reports, for the first time, a quantitative replacement of methionine (Met) by selenomethionine (SeMet) at >98% substitution, with up to 4940 microg of SeMet/g of yeast obtained for the entire protein pool of a wild-type yeast grown on a SeMet-containing medium. The incorporation of selenium in yeast proteins, in the form of selenomethionine, and the influence of various organic and inorganic Se and S sources present in the media were monitored during the growth of a wild-type Saccharomyces cerevisiae , which allowed the optimization of the composition of a fully defined synthetic growth medium that ensured maximum SeMet incorporation. Quantitation of SeMet and Met was performed by species-specific isotope dilution GC-MS. The use of ascorbic acid and a minimum concentration of cysteine (5 microg/L) was found to be beneficial to achieve incorporation by limiting the oxidative stress due to the presence of selenium. Except for small amounts of cysteine, no other sources of sulfur were necessary to achieve yeast growth. In a medium containing Se(VI), the maximum replacement of Met with SeMet was 50%, which is considerably higher than that obtained with the current commercial Se yeast formulations. For yeast grown in a Met-free defined medium, which was supplemented with SeMet, nearly total replacement of Met with SeMet could be achieved. The fully Se-labeled yeast could be an important tool for the study of eukaryotic protein structures both by mass spectrometry and by X-ray crystallography through selenomethionine single- and multiple-wavelength anomalous dispersion (SAD and MAD) phasing. In addition, a particular yeast strain, BY4741, that cannot synthesize Met using inorganic sulfur (met15Delta0) was shown to produce SeMet in the presence of inorganic selenium. This might indicate that the incorporation of inorganic selenium salts [Se(VI) and Se(IV)] is obviously not occurring exclusively through the same biological pathways as for sulfur. The reduction of inorganic Se to hydrogen selenide (H(2)Se), its reactions with organic compounds present in the yeast or in the media, and the possible metabolization through unspecific enzymatic pathways (such as transsulfuration) could also be of considerable importance in the production of selenoamino acids during yeast growth.

Extracellular Production of Hydrogen Selenide Accounts for Thiol-assisted Toxicity of Selenite against Saccharomyces cerevisiae

Administration of selenium in humans has anticarcinogenic effects. However, the boundary between cancer-protecting and toxic levels of selenium is extremely narrow. The mechanisms of selenium toxicity need to be fully understood. In Saccharomyces cerevisiae, selenite in the millimolar range is well tolerated by cells. Here we show that the lethal dose of selenite is reduced to the micromolar range by the presence of thiols in the growth medium. Glutathione and selenite spontaneously react to produce several selenium-containing compounds (selenodiglutathione, glutathioselenol, hydrogen selenide, and elemental selenium) as well as reactive oxygen species. We studied which compounds in the reaction pathway between glutathione and sodium selenite are responsible for this toxicity. Involvement of selenodiglutathione, elemental selenium, or reactive oxygen species could be ruled out. In contrast, extracellular formation of hydrogen selenide can fully explain the exacerbation of selenite toxicity by thiols. Indeed, direct production of hydrogen selenide with D-cysteine desulfhydrase induces high mortality. Selenium uptake by S. cerevisiae is considerably enhanced in the presence of external thiols, most likely through internalization of hydrogen selenide. Finally, we discuss the possibility that selenium exerts its toxicity through consumption of intracellular reduced glutathione, thus leading to severe oxidative stress.

Sodium selenite induces apoptosis in acute promyelocytic leukemia-derived NB4 cells by a caspase-3-dependent mechanism and a redox pathway different from that of arsenic trioxide

Two relatively recent discoveries stand behind our current effort to investigate the effects of the chemopreventive agent, selenium, on the proliferation and survival of NB4 cells. The first is that certain selenium compounds such as sodium selenite have pro-oxidant ability to catalyze the oxidation of thiols and simultaneously generate superoxide. The second lies in the exquisite susceptibility of NB4 cells to arsenic trioxide-induced, reactive oxygen species (ROS)-mediated apoptosis due to less efficiency of the cellular defense system. In this study, we demonstrated that sodium selenite could induce apoptosis in NB4 cells via the classic mitochondrial pathway involving caspase-3 activation and Bcl-2 cleavage. An increase in the basal cellular glutathione (GSH) content rendered NB4 cells resistant to arsenic trioxide, but could sensitize NB4 cells to sodium selenite. Moreover, combined treatment of NB4 cells with all- trans retinoic acid (ATRA) at low concentration and sodium selenite exhibited a synergistic effect on apoptosis induction. Together, our results suggest that selenite is a promising candidate for treatment of acute promyelocytic leukemia (APL) and the mechanism underlying its anticancer effects warrants further investigation.

Dietary supplementation with high-selenium soy protein reduces pulmonary metastasis of melanoma cells in mice

The effect of high-selenium (Se) soy protein on pulmonary metastasis of murine B16BL6 melanoma cells was investigated in male C57BL6 mice. Isolated soy proteins (ISP) from soybeans grown with and without Se foliar application during seed development were compared. Five diets were studied, a basal AIN-93G diet or a basal diet containing 10% low-Se ISP, 5% low-Se + 5% high-Se ISP, 10% high-Se ISP, or 10% low-Se ISP supplemented with Se equivalent to that of the 10% high-Se ISP diet. The Se concentrations of the 5 diets were 0.13, 0.13, 1.9, 3.6, and 3.0 microg/g, respectively. Mice were fed the diet for 2 wk before and 2 wk after an i.v. injection of 5 x 10(4) viable cells. At necropsy, the number and size of tumors that had developed in the lungs were determined. In the control group, 13/18 mice exhibited > or = 50 tumors. The numbers of mice with > or = 50 tumors were 8/18, 7/18, 3/18, and 6/17 in the ISP-fed groups, respectively. The differences between the 10% high-Se ISP group, the Se-supplemented 10% low-Se group, and the control were significant (P < 0.05). Dietary supplementation with 10% low-Se ISP significantly decreased the mean number of tumors per group and the tumor size compared with the control. A greater reduction in these variables occurred in mice fed the 10% high-Se ISP diet. The inhibition by the Se-supplemented 10% low-Se ISP diet was similar to that by the 10% high-Se ISP diet. The whole-blood Se concentration was inversely related to the tumor number (R = -0.87, P = 0.052), tumor cross-sectional area (R = -0.91, P < 0.05), and tumor volume (R = -0.93, P < 0.05). These findings suggest that Se is responsible for the greater antimetastatic effect of the high-Se ISP. We conclude that the high-Se soy protein has a greater inhibitory effect than the low-Se soy protein on pulmonary metastasis of melanoma cells in mice.

Selenium and its relationship to cancer: an update

Selenomethionine (Semet) is the major seleno-compound in cereal grains and enriched yeast whereas Se-methylselenocysteine (SeMCYS) is the major seleno-compound in Se-accumulator plants and some plants of economic importance such as garlic and broccoli exposed to excess Se. Animals can metabolize both Semet and SeMCYS. Epidemiological studies have indicated an inverse relationship between Se intake and the incidence of certain cancers. Blood or plasma levels of Se are usually lower in patients with cancer than those without this disorder, but inconsistent results have been found with toenail-Se values and the incidence of cancer. There have been eight trials with human subjects conducted on the influence of Se on cancer incidence or biomarkers, and except for one, all have shown a positive benefit of Se on cancer reduction or biomarkers of this disorder. This is consistent with about 100 small-animal studies where Se has been shown to reduce the incidence of tumours in most of these trials. Se-enriched yeast is the major form of Se used in trials with human subjects. In the mammary-tumour model, SeMCYS has been shown to be the most effective seleno-compound identified so far in reduction of tumours. Several mechanisms have been proposed on the mechanism whereby Se reduces tumours. Even though SeMCYS was shown to be the most effective seleno-compound in the reduction of mammary tumours, it may not be the most effective seleno-compound for reduction of colon tumours.

Selenite-induced survival of HuH7 hepatoma cells involves activation of focal adhesion kinase-phosphatidylinositol 3-kinase-Akt pathway and Rac1

Selenium has been shown to sustain the growth of selected human hepatocellular carcinoma cell lines under serum-free conditions, but the detailed mechanism remained undetermined. In the present study, the molecular mechanism(s) involving sodium selenite (Na2SO3, Se) as a survival agent were determined. Selenite not only protects HuH7 cells from serum deprivation-induced apoptosis, it also supports its long-term growth in sodium selenite (10(-7)m) supplemented serum-free medium. The anti-apoptotic effect correlates with activation of focal adhesion kinase and the phosphatidylinositol 3-kinase (PI3K)-Akt kinase pathway. Using HuH7 cells stably transfected with a constitutively active Akt kinase and PI3K inhibitor LY294002, selenite-induced cell survival was shown to be PI3K-Akt-dependent. Parallel changes included a significant reduction in the intracellular reactive oxygen species content, the reversal of DNA fragmentation, and the suppression of caspase and apoptosis signal-regulating kinase 1 activities. HuH7 cells stably expressing a Rac1 mutant N17 (Rac1N17-HuH7) are refractory to selenite treatment. In these cells selenite supplement neither triggers Akt activation nor supports cell proliferation. Participation of Rac1 activation in this event is supported by the fact that selenite treatment drastically enhanced activation of Rac1. The exact link between selenite treatment, Rac1 activation, and activation of the focal adhesion kinase-PI 3-kinase, however, remains to be characterized. The mitogenic signaling mediated by selenite may involve unconventional growth stimuli including higher glutathione peroxidase 1 activity and higher transcription levels of selenoprotein P. The selenium-HuH7 system we have established thus provides a unique tool that will allow the biological role of selenite in growth regulation of hepatocytes to be studied in detail.

Selenomethionine does not affect PSA secretion independent of its effect on LNCaP cell growth

BACKGROUND

Individuals supplemented with selenium have reduced incidence of prostate cancer. This study determines whether selenomethionine specifically affects the secretion of prostate specific antigen (PSA) in vitro.

METHODS

LNCaP cells were supplemented with selenomethionine for 7 days. PSA secretion was determined by ELISA. Cell proliferation was assessed by enumeration of trypan blue excluding cells. Colony formation was determined in soft agar. Cell cycle distribution was determined by FACS analysis of propidium iodide stained cells.

RESULTS

Selenomethionine at > or = 70 microM inhibited LNCaP cell growth and colony formation. 0-100 microM selenomethionine did not affect the secretion of PSA by LNCaP cells in cell culture supernatants when normalized to the number of cells in culture. At supra-nutritional concentrations of selenomethionine, LNCaP cells had longer G(0)/G(1) phase in agreement with the inhibitory effects on cell growth.

CONCLUSIONS

PSA secretion is not specifically inhibited by concentrations of selenomethionine corresponding to plasma selenium concentrations found in individuals supplemented with chemopreventive concentrations of selenized yeast. These data suggest that changes in serum PSA levels in individual patients during selenium supplementation is not an effect specific for PSA secretion, but rather may be a useful indicator for changes in disease progression in individual patients.

Effects of vitamin E and selenium supplementation on esophageal adenocarcinogenesis in a surgical model with rats

Two well-known antioxidative nutrients, vitamin E and selenium, were used in this study to investigate possible inhibitory action against the formation of esophageal adenocarcinoma (EAC) in rats. In this model, carcinogenesis is believed to be driven by oxidative stress. Male Sprague-Dawley rats (8 weeks old) were divided into four groups and received esophagoduodenal anastomosis (EDA) surgery plus iron supplementation (12 mg/kg/week). Vitamin E and selenium were supplemented in the diet in the forms of alpha-tocopheryl acetate (750 IU/kg) and sodium selenate (1.7 mg Se/kg), which were 10 times the regular amounts in the basic AIN93M diet. At 40 weeks after surgery, all the EDA groups had lower body weights than the non-operated control group. Iron nutrition (hemoglobin, total serum iron and transferrin saturation) was normal as a result of iron supplementation after EDA. Vitamin E supplementation maintained the normal plasma level of alpha-tocopherol in EDA rats, but not those of gamma-tocopherol and retinol. Selenium supplementation increased the serum and liver selenium contents of the EDA rats. Histopathological analysis showed that selenium supplementation increased the incidence of EAC and the tumor volume. The selenium level in the tumor is higher than that in the duodenum of the same animal. Vitamin E supplementation, however, inhibited carcinogenesis, especially in the selenium-supplemented group. We believe that vitamin E exerts its effect through its antioxidative properties, and a high dose of inorganic selenium may promote carcinogenesis by enhancing oxidative stress.

Selenium and cancer: some nutritional aspects

The level of selenium in cancer patients is lower than that in control subjects. However, low selenium levels in body fluids can be due to the malnutrition observed in these patients. There is evidence from epidemiologic studies that high dietary selenium intakes and high selenium status in people are associated with lower cancer mortality. However, contradictory information has been found in some prospective studies. The presence of other nutrients in selenium-rich foods can influence the role of the selenium in cancer etiology. Therefore, there are selenium antagonistic elements that inhibit the anticarcinogenic effects of selenium and other antioxidant micronutrients such as ascorbic acid, retinol, beta-carotene, alpha-tocopherol, and some other elements have a synergistic effect on the prevention of cancer.

Selenium-enriched Agaricus bisporus mushrooms suppress 7,12-dimethlybenz[a]anthracene bioactivation in mammary tissue

The present studies compared dietary Se (1.0 microg/g) when provided as either fortified Agaricus bisporus mushrooms, or sodium selenite on the in vivo metabolism of 7,12-dimethylbenz(a)anthracene (DMBA). Dietary addition of Se unenriched A. bisporus mushrooms at 2% did not alter the occurrence of DMBA induced DNA adducts or the activity of glutathione S-transferase (GST). However, the addition of Se as enriched mushrooms, or as selenite, significantly increased both liver and mammary GST activity. Providing sodium selenite, or enriched mushrooms also significantly reduced total and anti-3,4-dihydrodiol-1,2-epoxide-deoxyguanosine adducts compared to feeding the basal diet (P < 0.05). These investigations provide evidence that Se enriched mushrooms can be used as an effective method to retard chemically induced tumors.

Expression pattern of gastrointestinal selenoproteins--targets for selenium supplementation

There is experimental and epidemiological evidence for an association between low selenium levels and gastrointestinal cancer incidence, prevalence, and mortality. To identify targets for selenium supplementation in the human digestive tract, we examined mRNA expression of various selenocysteine-containing proteins in normal mucosa biopsy specimens. Tissue samples from the esophagus and from different sites of the stomach, small bowel, and colon were obtained during endoscopies of the upper and lower gastrointestinal tract. Northern blot analyses revealed a lack of cytosolic glutathione peroxidase mRNA but a differential mRNA expression pattern of gastrointestinal and plasma glutathione peroxidase, selenoprotein P, and thioredoxin reductase. Glutathione peroxidase and thioredoxin reductase activities were detected in the mucosa of all biopsies, but the differential pattern did not reflect the differential mRNA steady-state levels. In addition to gastrointestinal glutathione peroxidase, which was found to play a role in colon cancer resistance, we identified further gastrointestinal selenoproteins, which may be involved in gastrointestinal cell defense and cell differentiation.

Lessons from basic research in selenium and cancer prevention

The article reviews the progress in basic research of selenium and cancer prevention during the past decade. Special emphasis is placed on the following four major areas of discussion: 1) chemical forms of selenium and anticarcinogenic activity; 2) selenium-enriched food; 3) in vitro effects of selenite vs. monomethylated selenium; and 4) aromatic selenium compounds. It is clear that basic research has contributed new knowledge to our understanding of selenium biochemistry, anticancer efficacy and regulation of cell growth. Some of this information could be ready for incorporation into the design of a second-generation selenium trial in humans.

Chemopreventive agents: selenium

The element selenium (Se) was recognized only 40 years ago as being essential in the nutrition of animals and humans. It is recognized as being an essential component of a number of enzymes, in which it is present as the amino acid selenocysteine. Se compounds have also been found to inhibit tumorigenesis in a variety of animal models, and recent studies indicate that supplemental Se in human diets may reduce cancer risk. The antitumorigenic activities have been associated with Se intakes that correct nutritionally deficient status in animals, as well as higher intakes that are substantially greater than those associated with maximal expression of the selenocysteine-containing enzymes. Therefore, it is proposed that while some cancer protection, particularly that involving antioxidant protection, involves selenoenzymes, specific Se metabolites, which are produced in significant amounts at relatively high Se intakes, also discharge antitumorigenic functions. According to this two-stage model of the roles of Se in cancer prevention, individuals with nutritionally adequate Se intakes may benefit from Se supplementation. Evidence for chemoprevention by Se and for the apparent mechanisms underlying these effects is reviewed to the end of facilitating the development of the potential of Se compounds as cancer chemopreventive agents.

Selenium, calcium channel blockers, and cancer risk--the Yin and Yang of apoptosis?

It is increasingly clear that apoptosis plays a crucial role in the promotional phase of cancer development. Initiated pre-neoplastic clones in rat liver experience a high rate of apoptosis, and this rate has an important impact on the survival and growth of these clones. Suppression of apoptosis appears to be a universal property of cancer promoters, suggesting conversely that agents which inhibit cancer induction during the promotional phase increase the rate of apoptosis in initiated cells. Modulation of apoptosis is a likely explanation for recent striking evidence that use of calcium channel blockers substantially increases, whereas supplemental selenium substantially decreases, human cancer incidence. Non-genotoxic measures which are likely to upregulate apoptosis in pre-neoplastic/neoplastic cells--and thus may be useful in prevention and/or therapy--include selenium, retinoids/carotenoids, green tea polyphenols, caloric restriction, downregulation of IGF-I activity, high-dose tamoxifen and other protein kinase C antagonists, withdrawal or blockade of trophic hormones, isoflavones, limonene, vitamin D and cholecalciferol analogs, dietary fiber/sodium butyrate, hyperthermia, benzaldehyde derivatives, and creatine.

Effect of dietary supplementation of selenite on pulmonary metastasis of melanoma cells in mice

The purpose of the present study was to determine the effect of dietary supplementation of selenite on experimental pulmonary metastasis of B16BL6 murine melanoma cells in C57BL/6 mice by means of an intravenous injection model. Three groups of mice were fed a basal AIN-93G diet containing 0.1 ppm selenium (control group) or the basal diet supplemented with 2 or 4 ppm selenium as selenite (experimental groups). Mice were fed the diet for two weeks before and after the intravenous injection of 0.75 x 10(5) viable tumor cells. At necropsy the number of tumors that developed in the lungs and their cross-sectional area were determined, and tumor volume was calculated. In the control group, 12 of the 15 mice had > or = 1 lung tumors. In contrast, only 4 of the 15 mice in each of the selenite-supplemented groups had > or = 11 tumors. The incidence of metastasis in mice fed the control and the 2- and 4-ppm selenium diets was 93%, 73%, and 53%, respectively. The median number of lung tumors was 53, 1, and 1 in mice fed the basal and the 2- and 4-ppm selenium diets, respectively. Tumor cross-sectional area and tumor volume were significantly decreased in selenite-supplemented groups. These results demonstrate that dietary supplementation of selenite reduced pulmonary metastasis of B16BL6 melanoma cells in C57BL/6 mice and also inhibited the growth of the metastatic tumors that developed in the lungs. It is concluded that selenite may be a useful adjuvant to prevent metastatic diseases in cancer patients.

Up-regulation of IGF binding protein-1 as an anticarcinogenic strategy: relevance to caloric restriction, exercise, and insulin sensitivity

The mitotic rate of stem cells is a major determinant of cancer risk. Insulin-like growth factors (IGFs) are virtually obligate stimulants of cell turnover in nearly every tissue. IGF activity is subject to rapid modulation by hepatic release of IGF binding protein-1 (IGFBP-1), a factor whose synthesis is suppressed by insulin and increased by glucagon. Up-regulation of IGFBP-1 production can be expected to decrease IGF activity and thereby diminish cancer risk. Measures that sensitize peripheral tissues to insulin, and thereby down-regulate insulin secretion, can be expected to increase IGFBP-1 synthesis, provided that they do not unduly sensitize hepatocytes as well. Prolonged aerobic exercise and caloric restriction also increase IGFBP-1 production. Since IGF-1 suppresses hepatic synthesis of sex hormone binding globulin (SHBG), down-regulation of IGF activity will increase SHBG levels and thus diminish the availability of free sex hormones--an effect that should further decrease cancer risk in sex hormone-responsive tissues. These considerations rationalize many findings in animal and epidemiologic studies, and suggest that non-diabetic insulin resistance may be a significant cancer risk factor. Increased IGF activity associated with insulin resistance may also promote benign hyperplasias-most notably atherosclerosis. Hyperinsulinemia stimulates intimal hyperplasia indirectly, via IGF.

natural antimutagenic agents may prolong efficacy of human immunodeficiency virus drug therapy

The long-term efficacy of new combination drug therapies for human immunodeficiency virus infection may be limited by the tendency of transfected human immunodeficiency virus to mutate to drug-resistant forms. This argues for the use of safe antimutagenic measures as adjuvants to such therapies. Certain nutrients and food factors-notably selenium, green-tea polyphenols, and cruciferous phytochemicals-can suppress cancer initiation and mutagenesis in animal and cell culture models; epidemiological studies suggest that ambient variations in consumption of these food factors can have an important impact on human cancer rates. Low-fat diets may reduce deoxyribonucleic acid base damage in human leukocytes, whereas increased body iron stores are likely to increase mutation rates. Thus, ample but safe intakes of selenium, green-tea polyphenols, and cruciferous vegetables, in the context of a diet low in fat and assimilable iron, can be expected to prolong the efficacy of drug therapy in subjects infected with the human immunodeficiency virus. These measures can also be recommended for cancer prevention in the general population.

Up-regulation of intracellular signalling pathways may play a central pathogenic role in hypertension, atherogenesis, insulin resistance, and cancer promotion--the 'PKC syndrome'

The modern diet is greatly different from that of our paleolithic forebears' in a number of respects. There is reason to believe that many of these dietary shifts can up-regulate intracellular signalling pathways mediated by free intracellular calcium and protein kinase C, particularly in vascular smooth muscle cells; this disorder of intracellular regulation is given the name 'PKC syndrome'. PKC syndrome may entail either a constitutive activation of these pathways, or a sensitization to activation by various agonists. The modern dietary perturbations which tend to induce PKC syndrome may include increased dietary fat and sodium, and decreased intakes of omega-3 fats, potassium, calcium, magnesium and chromium. Insulin resistance may be both a cause and effect of PKC syndrome, and weight reduction and aerobic training should act to combat this disorder. PKC syndrome sensitizes vascular smooth muscle cells to both vasoconstrictors and growth factors, and thus promotes both hypertension and atherogenesis. In platelets, it induces hyperaggregability, while in the microvasculature it may be a mediator of diabetic microangiopathy. In vascular endothelium, intimal macrophages, and hepatocytes, increased protein kinase C activity can be expected to increase cardiovascular risk. Up-regulation of protein kinase C in stem cells may also play a role in the promotion of 'Western' fat-related cancers. Practical guidelines for combatting PKC syndrome are suggested.

Selenium in human lactation

The primary factor determining selenium concentration in human milk is the maternal selenium intake. A significant correlation between selenium in human milk and maternal selenium intake has been reviewed in papers from different regions of the world. Infants fed human milk have higher selenium intake than those fed commercially available formula milk or baby foods. Selenium compounds found in breast milk seem to be more biologically available for infant nutrition than those in formulas. Increased requirements of selenium have been observed in pregnant and lactating women. Supplementation of lactating and pregnant women with different selenium compounds has been assayed, and selenium supplementation of soil and cows has been used to increase the selenium status of children fed infant formula made from cow's milk.

Inhibition of aflatoxin B1-induced cell injury by selenium: an in vitro study

Dietary selenium is an essential trace element in human nutrition. Selenium has been shown in animal studies to inhibit aflatoxin hepatocarcinogenesis. However, the cellular mechanism responsible for the inhibition has not been thoroughly studied. This study examines the effect of two selenium compounds, namely, sodium selenite and selenium-enriched yeast extract (SeY), on the cytotoxicity, DNA-binding and mutagenicity of aflatoxin B1 (AFB1) in cultured Chinese hamster ovary (CHO) cells. CHO cells, after treatment with 2 micrograms ml-1 selenite or 80 micrograms ml-1 SeY, exhibited increased resistance to AFB1-induced cell killing. At a concentration of 50 micrograms ml-1 AFB1, cell survival, measured by the clonogenicity assay, was increased by 21- and 10-fold in selenite- and SeY-treated cells, respectively. However, selenium treatment did not appear to affect AFB1-DNA binding. Similarly, no effect was observed on AFB1 mutagenicity, as determined by the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene mutation assay. The results showed that selenium could effectively protect cells from AFB1 cytotoxicity in cultured cells but had no effect on AFB1-DNA adduct formation or mutagenesis. It is suggested that there are multiple pathways of AFB1 toxicity and that selenium can modulate AFB1-induced cell killing independent of its genotoxicity.

Selenium--its biological perspectives

Selenium is an essential trace element at lower concentrations and toxic at higher concentration. Animals can metabolize both inorganic and organic forms and convert non methylated Se to mono--or di--or tri--methylated forms, of which, mono-methylated forms are most toxic. Glutathione reductase converts selenoglutathione to H2S in liver and erythrocytes and is ultimately excreted. Se effects the toxicities of xenobiotic agents, provides antagonistic effect to Sulphur and co-administration with Zn increase Se retention in certain organs. At its toxic level (4-8 ppm) it increases Cu contents of heart, liver and kidney and has detoxifying or protecting effect against Cd and Hg. It is a prosthetic group of several seleno metalloenzymes. The concentration of the element is decreased in serum/plasma or erythrocytes of patients of AIDS, trisomy-21, Crohn's and Down's syndrome, phenylketonurea, Keshan's disease and cancer. Rather, the element has antiproliferative and cancer protecting effect. Se content of testes increases considerably during pubertal maturation and, during Se deficiency, the supply to the testes has priority over the other tissues. The element is localized in the mitochondrial capsule protein (MCP) and is involved in biosynthesis of testosterone. Neither the age of mother nor the concentration of Se during pregnancy has any effect on weight of baby or the length of pregnancy. Se levels in human milk is affected by maternal intake and its requirements by infants and young children are higher for their rapid growth. Clinical symptoms of its toxicity include severe irritations of respiratory system, metallic taste in mouth, formication of nose, signs of rhinitis, lung edema and brancho-pneumonia. The typical garlic odour of breath and sweat is due to dimethyl-selenide.

Levels of selenium in plasma and glutathione peroxidase in erythrocytes and the risk of breast cancer. A case-control study

Plasma selenium and glutathione peroxidase in erythrocytes were analyzed in a case-control study encompassing 441 cases with breast cancer and 191 controls with benign breast disease. No difference in mean serum selenium level between cases and controls on supplementary selenium intake was seen. If only individuals without supplementary intake, 278 cases and 135 controls, were considered a preventive effect was found increasing with selenium level. This finding was significant among women 50 years old or more with Mantel-Haenszel odds ratio = 0.16 for individuals with serum selenium > 1.21 mumol/L. Also for subjects with serum selenium in the range 1.00-1.21 mumol/L a significant preventive effect was seen with odds ratio = 0.38. For women under 50 years of age a nonsignificant preventive effect was seen. Glutathione peroxidase in erythrocytes did not correlate well with serum selenium and was not a marker for the risk of breast cancer.

Selenium deficiency in Yugoslavia and possible effects on health

New data on Se-deficiency in Yugoslavia are presented. The results include Se contents of soils, cereal crops and garlic grown in the investigated soils, and human serum and scalp hair from several towns and regions in this country. All data indicate a serious Se-deficiency. Analyses of human tissues show a very low Se-status of the Yugoslav population. In some regions, Se contents of garlic, grains and human serum and hair are approaching those in the low-selenium zone in China. It is assumed that the very low Se-status of the human population could be a risk factor for the endemic nephropathy and the urinary tract tumours in endemic areas.

Selenium content and distribution in bovine and human milk from different regions of Poland

Human milk and bulk cow's milk samples from 3 different areas of central Poland were analyzed for their Se content. Cow's milk specimens were also analyzed for Se distribution and GSH-Px activity. Mature human milk contained 34-68% more Se than bulk cow's milk obtained from analogous areas of central Poland. Comparison of literature values suggest, that human and cow's milk from vicinity of Warsaw and Piotrków Trubunalski were Se-adequate but milk from Siedlce area was Se-deficient. Glutathione peroxidase activity accounted for 25-31% of the total peroxidase activity of cow's milk. The majority of the Se was found in the whey fraction. It was suggested that the participation of the casein fraction in total milk selenium increased faster than milk Se content. Cow's milk obtained near Warsaw had a 2-times higher concentration of Se than in milk from Siedlce but the content of this microelement in the casein fraction (pellet) was 3-times higher.

Selenium deficiency in Yugoslavia

Data on selenium (Se) deficiency in Yugoslavia are presented. The results include Se content of soil, cereal crops, and garlic grown in these soils, and human serum and scalp hair from several towns and regions. All data indicate a serious Se deficiency: soil (n = 140), the mean value of 200 +/- 69.6 micrograms/kg Se; wheat, (58) mean = 20.5 +/- 12.4 micrograms/kg; corn, (79) mean = 13.7 +/- 13.6 micrograms/kg; and garlic, (66) mean = 13.7 +/- 17.1 micrograms/kg Se. Analyses of human tissue show a very low Se status of the Yugoslav population: serum, (n = 875) mean = 50.0 +/- 18.0 micrograms/L and scalp hair, (388) mean = 94 +/- 16 micrograms/kg Se. In some regions, Se contents of grain, garlic, and human serum and hair are approaching those in the low-Se belt in China. It is assumed that very low Se status of a human population could be a risk factor in the development of Balkan Endemic Nephropathy (BEN) and in a high incidence of urinary tract tumors (UTT) in endemic areas.

Lack of effects of selenium on N-nitrosomethylbenzylamine-induced tumorigenesis, DNA methylation, and oncogene expression in rats and mice

The effects of dietary selenium deficiency and excess on N-nitrosomethylbenzylamine-(NMBA) induced esophageal neoplasia in rats and forestomach tumors in mice and the effects of dietary selenium on DNA adduct formation and on the activities of DNA adduct-repairing enzyme and oncogene expression in rat esophagus were investigated. The esophageal and forestomach tumors were induced by administration of NMBA by gavage with a total dose of 39 mg/kg body wt in rats and 12 mg/kg body wt in mice. Neither selenium dietary deficiency (Se < 0.02 ppm) nor selenium excess (2.0 ppm) showed any significant effect on the incidence of tumors or number of tumors per tumor-bearing animal. For the DNA adduct formation studies, rats were given a dose of NMBA intraperitoneally after six weeks on the different selenium-containing diets. No significant difference in the amount of the DNA adduct O6-methyldeoxyguanosine was found among the different selenium-treated groups. In a parallel group of rats that did not receive NMBA, the levels of esophageal O6-methyldeoxyguanosine DNA methyltransferase were not significantly altered by dietary selenium levels. The c-myc oncogene expression in rat esophagus was induced by the administration of NMBA (3 mg/kg body wt) by gavage once a week for eight weeks. Dietary selenium did not show any effects on its expression. On the basis of the results of these studies, dietary selenium has no effects in the NMBA-induced tumor model.

Mineral insufficiency and cancer

There are excellent theoretical reasons why the mineral nutrients selenium, manganese, copper and zinc, known as the antioxidant minerals, may be involved in the prevention of cancer aetiogenesis. The biochemistry is discussed of the part played by the antioxidant minerals, in the wider context of the other dietary antioxidants vitamins A, E and C, and beta carotene, in preventing tissue damage caused by activated metabolites of oxygen. The likely part played by these oxygen metabolites is described and a detailed review given of the evidence that suggests a role for antioxidant minerals, notably selenium, in preventing carcinogenesis in a range of animal models. There follows a summary of the emerging epidemiological evidence that suggests clearly that low selenium intake is a risk factor in the aetiology of human cancer.

Selenium: clinical significance and analytical concepts

Selenium is an essential trace element in humans and animals. Its only established function in humans is the antioxidant activity of glutathione peroxidase, a selenoenzyme. Severe prolonged deficiency may cause a fatal cardiomyopathy. Iatrogenic causes of selenium deficiency include parenteral and enteral nutrition. Low plasma selenium is also found in malabsorption, cystic fibrosis, rheumatoid arthritis, neoplasia, and other varied clinical disorders. Death has resulted from a single massive ingestion of selenium, while chronic excessive intake causes skin, nail, and hair pathology. Extreme geographical variation in population blood and urine selenium levels and a marked age-specific variation in population reference intervals are important factors in understanding selenium nutrition. Nutritional requirements, biological availability, and metabolism are discussed in relation to geographical, age, and method variability. Sampling, processing procedures, and methods for selenium quantitation are reviewed. Selenium content in different biological matrices and reference values for pediatric, adult, and obstetric populations are provided.

The effect of income on selenium intake and status in Utah County, Utah

Foodstuffs produced and/or purchased locally were analyzed for Se. The effect of income and gender on Se intake and status of Utah County residents was evaluated by measurement of the following indicators: erythrocyte (RBC) and plasma Se concentration, and activity of Se-glutathione peroxidase (Se-GSH-Px) (EC 1.11.1.9) in RBCs, platelets, and plasma. A Random Digit Dialing procedure was employed to stratify subjects according to gender and annual family income (less than +10,000, +10,000-20,000, greater than +20,000) in a 2 x 3 factorial design, seven subjects per cell. The weekly consumption of 44 foods shown to contribute over 90% of the Se intake of U.S. subjects was recorded for each study participant. The estimated minimum daily intake for this sample was 76.0 +/- 4.5 micrograms Se/day (mean +/- SEM). Available grain products are not produced locally, and their Se content is lower than average values reported by the U.S.D.A. Locally produced meat and dairy products had higher than average Se contents. In spite of lower grain Se and higher meat Se concentrations, subjects in this study derived more Se from grain and dairy products, and less from meat products than did subjects in a nationwide sample. The Se status of Utah County residents is similar to several other populations in the United States. There were no significant differences in Se status or intake due to gender or income. The results suggest that consumption of other foods produced in a "high Se" area can maintain Se intake and status in spite of reduced consumption of meat products generally viewed as more reliable sources of dietary Se.

Selenium: geochemical distribution and associations with human heart and cancer death rates and longevity in China and the United States

The geochemistry of available soil Se varies enormously in different localities, and the corresponding amounts moving up through crops to food vary accordingly. In a belt extending from northeastern to south central China, the available soil Se was measured by human blood Se levels. Severe deficiency occurred at 8-26 ng/mL; subadequate amounts occurred in large areas with 32-83 ng/mL; adequate amounts of 200-300 ng/mL occurred in large cities; and toxic amounts of 3000-7800 ng/mL occurred in terrace areas where runoff from the uplands evaporated, and in certain other soils. Some heart deaths (Keshan Disease) occurred in children 1 to 10 yr of age in the most deficient areas, but were prevented by 230-900 micrograms/wk Se supplementation. One mg Se/wk was the adult dosage. In Se deficient areas, the life span of adults was lowered severely (35 to 45 yr), with heart muscle damage common at autopsy. Se and Zn deficiencies are apparently associated with stomach cancer. The geochemistry of Se in the USA is also highly variable, blood Se ranging from 100-350 ng/mL. Se data for individuals are limited; however, ischemic heart death correlated inversely with blood Se in 25 cities of 22 states (r = -.70; p less than .01). Counties of Wisconsin and Florida are highly variable in human heart death and cancer death rates, as are the 50 states, suggesting Se geographic variability.

Selenium chemoprevention of liver cancer in animals and possible human applications

An inverse correlation between geographic distribution of liver cancer incidence and the selenium (Se) contents of whole blood and grains was observed in Qidong county, Jiangsu province, a high liver cancer area of the People's Republic of China. Animal experiments demonstrated that supplementation of Se reduced the incidence of liver cancer in rats exposed to aflatoxin B1. Se was also shown to inhibit the growth of transplanted tumors. A lower incidence of liver preneoplastic alterations and reduction of hepatitis B virus infection in ducks by Se-supplementation was observed, and three pilot studies for a Se-intervention trial on human liver cancer were carried out on the residents of Qidong county. A protective effect on the cellular DNA damage induced by aflatoxin B1 was observed in lympocytes from human with Se-supplements.

Differential Effects of selenium on the proliferation of human pulmonary adenocarcinoma cells and human embryonic lung diploid cells in vitro

The effect of different concentrations of Na2SeO3 on human pulmonary adenocarcinoma cells and human embryonic lung diploid cells in vitro was investigated. For human pulmonary adenocarcinoma cells, mitotic index and cell count decreased with increasing selenium concentrations. At 1 μg/mL sodium selenite, mitotic activity and growth of human lung cancer cells were partially inhibited, and the progression of human lung cancer cell cycle was partially arrested. When human embryonic lung diploid cells were treated with 1 μg/mL sodium selenite for five continuous days, cell counts of the treated group were closely parallel to those of the control group. After treating human embryonic lung diploid cells with 1-5μg/mL sodium selenite for 1-3 d, the mitotic index (MI), labeled index (LI), and average silver grain (SG) number per 20 labeled nuclei were the same as those of the control. In mixed cultures of human embryonic lung diploid cells and human pulmonary adenocarcinoma cells, treated with 3 and 5 μg/mL sodium selenite for 24 h, the lung diploid cells showed a normal fusiform morphology, whereas the lung cancer cells showed heavily vacuolated cytoplasms and distorted nuclei.

In vitro differential effects of sodium selenite on the growth of human hepatoma cells and human embryonic liver cells

The effects of various concentrations of Na2SeO3 on human hepatoma cells and human embryonic liver cells was investigated in vitro. For human hepatoma cells, mitotic index and cell count decreased with increasing selenium concentrations. At 1 μg/mL Na2SeO3, mitotic activity of human hepatoma cells were partially arrested. In human embryonic liver cells continuously treated with Na2SeO3, (1 μg/mL) cell count of the treated group decreased only by d 7; mitotic index, labeled index, and mean silver grain number per 50 labeled nuclei were the same as in the control group on exposure to 1, 3, and 5 μg/mL for up to 72 h. In mixed cultures of human hepatoma and embryonic liver cells treated with 3 and 5 μg/mL of Na2SeO3 for 24 h, hepatoma cells showed vacuolated cytoplasms, distorted nuclei, condensed chromatin, and even pyknosis, whereas the embryonic liver cells retained a normal morphology under the same treatment.

Some differentiating effects of selenium on the cultured human hepatoma cells and human pulmonary adenocarcinoma cells in vitro

Two human hepatoma cell lines, QGY-7703 and SMMC-7721, and two human pulmonary adenocarcinoma cell lines, LTEP-a-2 and SPC-A-1, were found to respond to 1 μg/mL Na2SeO3, 24 h, in-vitro treatment by decreasing its confluent saturation density. The same treatment was found to cause an increase in the adhesiveness of cells measured as resistance to detachment by trypsin/EDTA. The pathological features of tumors after heterotransplantation of treated and untreated cells were similar, but the size of tumor grown from treated cells was much smaller.

Serum selenium and risk of cancer. A prospective follow-up of nine years

The association between serum selenium concentration and the risk of cancer was studied in 1110 men aged 55 to 74 years in two rural areas of Finland. The men were followed-up prospectively for 9 years and there were 109 new cases of cancer, with the cases of the first follow-up year excluded. The serum selenium concentrations were adjusted for age, area, smoking, serum cholesterol, and alcohol intake. The patients had a slightly lower adjusted mean serum selenium than the subjects without cancer at the end of the follow-up (+/- standard error of mean) 53.9 +/- 1.5 and 55.3 +/- 0.5 micrograms/l, respectively. The relative risks of cancer were essentially the same when these were calculated in the tertiles of the serum selenium distribution. Thirty-seven men had a history of cancer at baseline or had cancer diagnosed during the first follow-up year and their adjusted mean serum selenium was 49.4 +/- 2.6 micrograms/l, which was significantly lower (P less than 0.05) than that of the subjects without cancer during the follow-up.

The role of micronutrient deficiency in carcinogenesis

Nutritional deficiencies are suspected to be contributing factors to several types of human cancers. Studies with laboratory animals have demonstrated that deficiencies in certain nutrients can enhance chemically induced carcinogenesis. In this review, we discuss several possible mechanisms for the involvement of nutritional deficiencies in carcinogenic processes, and note that different severities of deficiency may have varied effects on these processes. The relationship between results from studies with animals and the genesis of human cancer is discussed, and the application of the concept of nutrient density in relating experimental animal diets to human dietary conditions is emphasized. We also discuss in detail several recent studies that potentially may have a great impact on the prevention of human cancer. These include (1) the possible involvement of micronutrient deficiencies in carcinogenesis of the esophagus; (2) the effects of choline/methionine deprivation and calcium supplementation on liver carcinogenesis; and (3) the roles of low-calcium and high-fat intake on development of colon cancer. The possible mechanistic link between teratogenesis and carcinogenic processes is noted.