Abnormal DNA repair in selenium-treated human cells

Selenium exposure and urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine: Major effects of chemical species and sex

Selenium is an element present in trace amounts and different chemical forms. It may exert both beneficial and adverse effects on cellular redox status and on the generation of reactive oxygen species. 8-oxo-7,8-dihydro-2'deoxyguanosine (8-oxodG) is an oxidized derivative of deoxyguanosine, and a sensitive biomarker of oxidative stress and genotoxicity. The present study assessed the extent to which selenium status was associated with urinary 8-oxodG concentrations in a Northern Italian population. We recruited healthy, non-smoking blood donors living in the Reggio Emilia province during 2017-2019. We measured urinary 8-oxodG concentrations and used restricted cubic spline regression analyses to investigate the association between selenium status (estimated using food frequency questionnaires, urinary concentrations, and serum concentrations of selenium and selenium species) and 8-oxodG/g creatinine. Among 137 participants aged 30-60 years, median urinary selenium and 8-oxodG concentrations were 22.02 μg/L and 3.21 μg/g creatinine, respectively. Serum samples and selenium speciation analyses were available for 104 participants. Median total serum selenium levels and dietary intake were 116.5 μg/L and 78.7 μg/day, respectively. In spline regression analysis, there was little association between dietary, serum, or urinary selenium with 8-oxodG concentrations. In sex-specific analyses, urinary selenium showed a positive association with the endpoint among males. For single selenium species, we observed positive associations with urinary 8-oxodG for serum organic selenium species, and negative associations for inorganic selenium forms. In the most adjusted analysis, urinary 8-oxodG concentrations showed a strong positive association with selenomethione-bound selenium (Se-Met) and a negative association with inorganic tetravalent selenium, selenite. In sex-specific analyses, these associations were considerably stronger in males than in females. Overall, study findings indicate that selenium species exhibited very different patterns of associations with the biomarker of oxidative stress, and that these associations also depended on sex. Background exposure to Se-Met appears to be strongly and positively associated with oxidative stress.

Toxicological effects of nanoselenium in animals

The productivity and sustainability of livestock production systems are heavily influenced by animal nutrition. To maintain homeostatic balance in the body of the animal at different phases of life, the percentage of organically active minerals in livestock feed must be optimized. Selenium (Se) is a crucial trace mineral that is required for the maintenance of many functions of the body. Se nanoparticles (SeNPs) attracted considerable interest from researchers for a variety of applications a decade ago, owing to their extraordinary properties. SeNPs offer significant advantages over larger-sized materials, by having a comparatively wider surface area, increased surface energy, and high volume. Despite its benefits, SeNP also has toxic effects, therefore safety concerns must be taken for a successful application. The toxicological effects of SeNPs in animals are characterized by weight loss, and increased mortality rate. A safe-by-strategy to certify animal, human and environmental safety will contribute to an early diagnosis of all risks associated with SeNPs. This review is aimed at describing the beneficial uses and potential toxicity of SeNPs in various animals. It will also serve as a summary of different levels of SeNPs which should be added in the feed of animals for better performance.

Thiolated Chitosan Conjugated Liposomes for Oral Delivery of Selenium Nanoparticles

This study aimed to design a hybrid oral liposomal delivery system for selenium nanoparticles (Lip-SeNPs) to improve the bioavailability of selenium. Thiolated chitosan, a multifunctional polymer with mucoadhesive properties, was used for surface functionalization of Lip-SeNPs. Selenium nanoparticle (SeNP)-loaded liposomes were manufactured by a single step microfluidics-assisted chemical reduction and assembling process. Subsequently, chitosan-N-acetylcysteine was covalently conjugated to the preformed Lip-SeNPs. The Lip-SeNPs were characterized in terms of composition, morphology, size, zeta potential, lipid organization, loading efficiency and radical scavenging activity. A co-culture system (Caco-2:HT29-MTX) that integrates mucus secreting and enterocyte-like cell types was used as a model of the human intestinal epithelium to determine adsorption, mucus penetration, release and transport properties of Lip-SeNPs in vitro. Thiolated Lip-SeNPs were positively charged with an average size of about 250 nm. Thiolated Lip-SeNPs tightly adhered to the mucus layer without penetrating the enterocytes. This finding was consistent with ex vivo adsorption studies using freshly excised porcine small intestinal tissues. Due to the improved mucoadhesion and retention in a simulated microenvironment of the small intestine, thiolated Lip-SeNPs might be a promising tool for oral selenium delivery.

The solvent and treatment regimen of sodium selenite cause its effects to vary on the radiation response of human bronchial cells from tumour and normal tissues

Sodium selenite is often given to moderate the side effects of cancer therapy to enhance the cellular defence of non-cancerous cells. To determine whether sodium selenite during radiotherapy protects not only normal cells but also cancer cells, which would imply a reduction of the desired effect of irradiation on tumour during radiotherapy, the effect of the combined treatment of irradiation and sodium selenite was investigated. Human bronchial cells from carcinoma (A549) and normal tissue (BEAS-2B) were treated with sodium selenite and effects on growth and in combination with radiation on metabolic activity and cell cycle distribution were studied. The influence on radiosensitivity was determined via colony forming assays using different solvents of sodium selenite and treatment schedules. It was shown that sodium selenite inhibits growth and influences cell cycle distribution of both normal and tumour cells. Metabolic activity of normal cells decreased more rapidly compared to that of cancer cells. The influence of sodium selenite on radiation response depended on the different treatment schedules and was strongly affected by the solvent of the agent. It could be shown that the effect of sodium selenite on radiation response is strongly dependent on the respective experimental in vitro conditions and ranges from lead to an initially suspected but ultimately no real radioprotection to radiosensitizing up to no effect in one and the same cell line. This might be a reason for controversially described cell responses to radiation under the influence of sodium selenite in studies so far.

Emerging Anticancer Potentials of Selenium on Osteosarcoma

Selenium is a trace element essential to humans and forms complexes with proteins, which exert physiological functions in the body. In vitro studies suggested that selenium possesses anticancer effects and may be effective against osteosarcoma. This review aims to summarise current evidence on the anticancer activity of inorganic and organic selenium on osteosarcoma. Cellular studies revealed that inorganic and organic selenium shows cytotoxicity, anti-proliferative and pro-apoptotic effects on various osteosarcoma cell lines. These actions may be mediated by oxidative stress induced by selenium compounds, leading to the activation of p53, proapoptotic proteins and caspases. Inorganic selenium is selective towards cancer cells, but can cause non-selective cell death at a high dose. This condition challenges the controlled release of selenium from biomaterials. Selenium treatment in animals inoculated with osteosarcoma reduced the tumour size, but did not eliminate the incidence of osteosarcoma. Only one study investigated the relationship between selenium and osteosarcoma in humans, but the results were inconclusive. In summary, although selenium may exert anticancer properties on osteosarcoma in experimental model systems, its effects in humans require further investigation.

Effect of the Interaction Between Selenium and Zinc on DNA Repair in Association With Cancer Prevention

Cancer is the most common cause of death worldwide. Annually, more than ten million new cancer cases are diagnosed, and more than six million deaths occur due to cancer. Nonetheless, over 80% of human cancer may be preventable through proper nutrition. Numerous nutritional compounds are effective in preventing cancer. Selenium and zinc are essential micronutrients that have important roles in reducing oxidative stress and protecting DNA from the attack of reactive oxygen species. Selenium is an essential trace element that possesses several functions in many cellular processes for cancer prevention. Meanwhile, zinc may have protective effects on tumor initiation and progression, and it is an essential cofactor of several mammalian proteins. Results show that both selenium and zinc provide an effective progression of DNA repair system; thus, cancer development that originated from DNA damage is decreased. Results mostly focus on the separate effects of these two elements on different cell types, tissues, and organs, and their combined effects are largely unknown. This review aimed to emphasize the joint role of selenium and zinc specifically on DNA repair for cancer prevention.

The crosstalk between trace elements with DNA damage response, repair, and oxidative stress in cancer

DNA damage response (DDR) is a regulatory system responsible for maintaining genome integrity and stability, which can sense and transduce DNA damage signals. The severity of damage appears to determine DDRs, which can include damage repair, cell-cycle arrest, and apoptosis. Furthermore, defective components in DNA damage and repair machinery are an underlying cause for the development and progression of various types of cancers. Increasing evidence indicates that there is an association between trace elements and DDR/repair mechanisms. In fact, trace elements seem to affect mediators of DDR. Besides, it has been revealed that oxidative stress (OS) and trace elements are associated with cancer development. In this review, we discuss the role of some critical trace elements in the risk of cancer. In addition, we provide a brief introduction on DDR and OS in cancer. Finally, we will further review the interactions between some important trace elements including selenium, zinc, chromium, cadmium, and arsenic, and DDR, and OS in cancer.

The Adverse Effects of Se Toxicity on Inflammatory and Immune Responses in Chicken Spleens

Selenium (Se) is an essential trace element, but excessive intake of Se could induce Se poisoning, and result in various health problems. NF-κB regulated many molecules of the immune response and the inflammatory response, and Th1/Th2 balance played a key in the regulation of immune response. The aim of this study is to investigate the role of NF-κB pathway and Th1/Th2 imbalance in the adverse influence of Se poisoning on chicken spleens. In the current study, 90 chickens were randomly divided into two groups (n = 45 per group). The chickens were maintained either on a basal diet (the control group) containing 0.2 mg/kg Se or a high supplemented diet (the Se group) containing 15 mg/kg Se for 45 days. Then, we observed the pathohistology of spleen cells and detected NO content, iNOS activity, and the expression of NF-κB, iNOS, COX-2, PTGE, IL-6, TNF-α, Foxp3, IL-4, and IFN-γ in chicken spleens. In chicken spleens of the Se group, the result showed typical characteristics of inflammation: the content of NO and the activity of iNOS were increased, and the expression of NF-κB, iNOS, COX-2, PTGE, IL-6, TNF-α, and IL-4 was enhanced and that of Foxp3 and IFN-γ was decreased. Our study showed that Se toxicity could promote inflammation via NF-κB pathway, impairing the immune function, and changing Th1/Th2 balance in the chicken spleens.

Protective Effects of Selenium on Cyclophosphamide-Induced Oxidative Stress and Kidney Injury

Cyclophosphamide (CP) is a common anticancer drug, but its use in cancer treatment is limited due to its severe toxicities induced mainly by oxidative stress in normal cells. Reactive oxygen species (ROS) lead to multiple organ injuries, including the kidneys. Selenium (Se) is a nutritionally essential trace element with antioxidant properties. In the present study, the possible protective effect of Se on CP-induced acute nephrotoxicity was investigated. Forty-two Sprague-Dawley rats were equally divided into six groups of seven rats in each. The control group received saline, and other groups were injected with CP (150 mg/kg), Se (0.5 or 1 mg/kg), or CP + Se intraperitoneally. Total antioxidant capacity (TAC), total oxidant state (TOS), oxidative stress index (OSI), creatinine, and cystatin C (Cys C) levels were measured in the sera. In addition, kidney tissues were examined histologically. In the CP alone treated rats, creatinine, Cys C, TOS, and OSI levels increased, while TAC level decreased. CP-induced histological damages were decreased by co-treatment of Se and biochemical results supported the microscopic observations. In conclusion, our study points to the therapeutic potential of Se and indicates a significant role of ROS in CP-induced kidney toxicity.

Combination of Selenomethionine and N-Acetylcysteine Alleviates the Joint Toxicities of Aflatoxin B1 and Ochratoxin A by ERK MAPK Signal Pathway in Porcine Alveolar Macrophages

Our previous studies showed that aflatoxin B1 (AFB1) and ochratoxin A (OTA) could trigger joint immune toxicity. Little is known about the combined effects of selenomethionine (SeMet) and N-acetylcysteine (NAC) on the joint toxicities of the two toxins. In this study, results showed that SeMet or NAC alone or in combination significantly alleviated the downswing of cell viability, glutathione production, and phagorytosis induced by AFB1 and OTA in porcine alveolar macrophages. The uptrend of lactate dehydrogenase activities, apoptosis, reactive oxygen species levels, and the relative mRNA of inflammatory cytokines triggered by the two toxins was decreased. Combination of them was more effective than single application. Knockdown of p38, c-JUN N-terminal kinase (JNK), or extracellular signal-regulated kinase (ERK) via use of the corresponding specific siRNA could alleviate the joint toxicities of AFB1 and OTA. However, the ERK but not p38 or JNK pathway was involved in the protection of SeMet and NAC against the immunotoxicity. In conclusion, combination of SeMet and NAC might be a new therapeutic orientation for preventing the joint toxicities induced by AFB1 and OTA.

Effect of Selenium Supplementation on Apoptosis and Cell Cycle Blockage of Renal Cells in Broilers Fed a Diet Containing Aflatoxin B1

The aim of the study was to investigate the competency of selenium (Se) in counteracting the adverse effects of aflatoxin B1 (AFB1) on apoptosis, cell cycle, and proliferation of nephritic cells. Two hundred forty 1-day-old healthy male avian broilers were randomly divided into four groups and fed basal diet (control group), 0.3 mg/kg AFB1 diet (AFB1 group), 0.4 mg/kg Se diet (+Se group), and 0.3 mg/kg AFB1 + 0.4 mg/kg Se diet (AFB1 + Se group), respectively. Compared to the control group, the number of apoptotic renal cells and expressions of Bax and caspase-3 messenger RNA (mRNA) were significantly increased, while the expression of Bcl-2 was significantly decreased in the AFB1 and the +Se groups (p < 0.01). A significantly decreased proliferating cell nuclear antigen (PCNA) expression and arrested G0/G1 phases of the cell cycle were also seen in the AFB1 and the +Se groups when compared with those of the control group. Moreover, these parameters were restored to the control group levels in the AFB1 + Se group. These results suggested that sodium selenite supplied in the diet could effectively inhibit AFB1-induced apoptosis and cell cycle blockage in renal cells of broiler.

Arsenic and selenium toxicity and their interactive effects in humans

Arsenic (As) and selenium (Se) are unusual metalloids as they both induce and cure cancer. They both cause carcinogenesis, pathology, cytotoxicity, and genotoxicity in humans, with reactive oxygen species playing an important role. While As induces adverse effects by decreasing DNA methylation and affecting protein 53 expression, Se induces adverse effects by modifying thioredoxin reductase. However, they can react with glutathione and S-adenosylmethionine by forming an As-Se complex, which can be secreted extracellularly. We hypothesize that there are two types of interactions between As and Se. At low concentration, Se can decrease As toxicity via excretion of As-Se compound [(GS3)2AsSe](-), but at high concentration, excessive Se can enhance As toxicity by reacting with S-adenosylmethionine and glutathione, and modifying the structure and activity of arsenite methyltransferase. This review is to summarize their toxicity mechanisms and the interaction between As and Se toxicity, and to provide suggestions for future investigations.

Determination of protective role of selenium against aflatoxin B1-induced DNA damage

Selenium is an essential mineral for a healthy life. Appropriate doses of it may undertake a protective role in the organism. In this study, the protective role of selenium (Se(4+)) against aflatoxin B1 (AFB1)-induced DNA damage was determined using random amplified polymorphic DNA on two plants including Vicia faba and Zea mays. It was observed that the concentrations of 0.1, 0.2 and 0.4 ppm of AFB1 have increased polymorphism value, total chlorophyll inhibition rate (IRc, %) and total protein IR (IRp, %). Unlike protein, chlorophyll contents and genomic template stability were decreased. With the addition of different concentrations (0.8 and 80 ppm) of Se(4+) to the treated samples with AFB1, the values return to normal. An 800-ppm concentration of Se(4+), on the contrary, could not inhibit the toxicity of AFB1 but caused an increase in toxicity level of AFB1/enhanced the toxicity level of AFB1. Results suggested that Se(4+) has an antagonistic effect against AFB1 toxicity and that the degree of antagonistic effect of Se(4+) against AFB1 was related to its concentration.

Sodium selenite-induced apoptosis mediated by ROS attack in human osteosarcoma U2OS cells

Sodium selenite (Na(2)SeO(3), SSE) is an inorganic Se compound that is widely used in cancer chemoprevention studies. SSE has been shown to have anti-proliferative effects on several types of human cancer cells, but its effect on osteosarcoma cells has thus far not been reported. In this study, the cytotoxic effect of SSE on osteosarcoma cells U2OS was investigated in vitro and found to be higher than on comparable non-cancer cell lines 293 and L6. Treatment with SSE decreased cell growth in a dose- and time-dependent manner and altered cellular morphology. SSE also inhibited cell viability by inducing apoptosis, as evidenced by the formation of apoptotic bodies, generation of reactive oxygen species (ROS), and accumulation of cells during the advanced phase of apoptosis. SSE-induced apoptosis correlated with the activation of CASP 3, downregulation of BCL-2, and upregulation of P53 and PTEN in U2OS cells. These results indicated that SSE induces apoptosis in U2OS cells mainly through an ROS-mediated caspase pathway. This is the first report to show a possible mechanism of the anti-proliferative effect of SSE for the prevention of osteosarcoma in cell culture models.

Protective effects of selenium against sister chromatid exchange induced by AFG 1 in human lymphocytes in vitro

Aflatoxins have been shown to be hepatotoxic, carcinogenic, mutagenic and teratogenic to different species of animals. Besides, at low concentrations, Selenium (Se(4+)) is antimutagenic and anticarcinogenic while it is toxic, mutagenic and carcinogenic at high concentrations. In this study, we aimed to evaluate the effect of Se(4+) against aflatoxin GAFG(1) (AFG(1)) on blood cultures in relation to induction of sister chromatid exchange (SCE). The results showed that at 0.4 and 0.8 parts per million (ppm) concentration of AFG(1), the frequency of SCE increased in cultured human lymphocytes. When different concentration of Se(4+) (0.08 and 8 ppm) were added to AFG(1), the frequencies of SCE decreased. Howewer, when 800 ppm concentration of Se(4+) together with 0.08 ppm AFG(1) were added to cell division inhibited in the cultures. Results suggested that Se(4+) could effectively inhibit AFG(1)-induced SCE. Besides, the protective role of Se(4+) against AFG(1)-induced SCE is probably related to its doses.

Risk of chronic low-dose selenium overexposure in humans: insights from epidemiology and biochemistry

The latest developments of epidemiologic and biochemical research suggest that current upper limits of intake for dietary selenium and for overall selenium exposure may be inadequate to protect human health. In particular, recent experimental and observational prospective studies indicate a diabetogenic effect of selenium at unexpectedly low levels of intake. Experimental evidence from laboratory studies and veterinary medicine appears to confirm previous epidemiologic observations that selenium overexposure is associated with an increased risk of amyotrophic lateral sclerosis, and a recent large trial indicated no beneficial effect in preventing prostate cancer. Moreover, the pro-oxidant properties of selenium species and the observation that the selenium-containing enzymes glutathione peroxidases are induced by oxidative stress imply that the increase in enzymatic activity induced by this metalloid may represent at least in part a compensatory response. Taken together, the data indicate that the upper safe limit of organic and inorganic selenium intake in humans may be lower than has been thought and that low-dose chronic overexposure to selenium may be considerably more widespread than supposed.

Analysis of Saccharomyces cerevisiae null allele strains identifies a larger role for DNA damage versus oxidative stress pathways in growth inhibition by selenium

Selenium toxicity is a growing environmental concern due to widespread availability of high-dose selenium supplements and the development of high-selenium agricultural drainage basins. To begin to analyze the effects of selenium toxicity at the genetic level, we have systematically determined which genes are involved in responding to high environmental selenium using a collection of viable haploid null allele strains of Saccharomyces cerevisiae representing three major stress pathways: the RAD9-dependent DNA repair pathway, the RAD6/RAD18 DNA damage tolerance pathway, and the oxidative stress pathway. A total of 53 null allele strains were tested for growth defects in the presence of a range of sodium selenite and selenomethionine (SeMet) concentrations. Our results show that approximately 64-72% of the strains lacking RAD9-dependent DNA repair or RAD6/RAD18 DNA damage tolerance pathway genes show reduced growth in sodium selenite versus approximately 28-36% in SeMet. Interestingly both compounds reduced growth in approximately 21-25% of the strains lacking oxidative stress genes. These data suggest that both selenite and SeMet are likely inducing DNA damage by generating reactive species. The anticipated effects of loss of components of the oxidative stress pathway were not observed, likely due to apparent redundancies in these gene products that may keep the damaging effects in check.

The effect of selenium, as selenomethionine, on genome stability and cytotoxicity in human lymphocytes measured using the cytokinesis-block micronucleus cytome assay

A supranutritional intake of selenium (Se) may be required for cancer prevention, but an excessively high dose could be toxic. Therefore, the effect on genome stability of seleno-L-methionine (Se-met), the most important dietary form of Se, was measured to determine its bioefficacy and safety limit. Peripheral blood lymphocytes were isolated from six volunteers and cultured with medium supplemented with Se-met in a series of Se concentrations (3, 31, 125, 430, 1880 and 3850 microg Se/litre) while keeping the total methionine (i.e. Se-met + L-methionine) concentration constant at 50 microM. Baseline genome stability of lymphocytes and the extent of DNA damage induced by 1.5-Gy gamma-ray were investigated using the cytokinesis-block micronucleus cytome assay after 9 days of culture in 96-microwell plates. High Se concentrations (>or=1880 microg Se/litre) caused strong inhibition of cell division and increased cell death (P < 0.0001). Baseline frequency of nucleoplasmic bridges and nuclear buds, however, declined significantly (P trend < 0.05) as Se concentration increased from 3 to 430 microg Se/litre. Se concentration (<or=430 microg Se/litre) had no significant effect on baseline frequency of micronuclei and had no protective effect against genome damage induced by exposure to 1.5-Gy gamma-ray irradiation. In conclusion, Se, as Se-met, may improve genome stability at concentrations up to 430 microg Se/litre, but higher doses may be cytotoxic. Therefore, a cautious approach to supplementation with Se-met is required to ensure that optimal genome health is achieved without cytotoxic effects.

Inhibition of cyclophoshamide-induced mutagenicity by microsized powder of selenium-enriched green tea in mice

Previously, the antioxidant activity of Se-enriched green tea extracts has been studied in vitro. In the present study, an in vivo micronuclei test was employed to assess the antimutagenic effect of microsized Se-enriched green tea powder (MSTP) in mice bone marrow. Pretreatments of MSTP, micrometer-sized regular tea powder (MRTP), selenite, and MRTP + selenite were given by gavage for 29 consecutive days prior to cyclophoshamide (CP) treatment. Certain key antioxidant enzymes were also investigated to elucidate the mechanism of antimutagenic effect. Results indicated that MSTP and MRTP or selenite alone did not significantly induce micronuclei at either concentration, confirming its nonmutagenicity. In the CP-treated groups, significant suppressions in the micronuclei were recorded following pretreatment with MSTP, MRTP, and selenite administration. The antimutagenic effect of MSTP was evidently observed by significant reduction in the frequencies of micronuclei in bone marrow cells when compared to a positive control group. The administration of MSTP, selenite, and MRTP + selenite also increased the levels of selenium concentration, glutathione peroxidase (GPx), and superoxide dismutase (SOD) enzymes in both blood and liver. However, no pronounced differences in activities of GPx and SOD were found among MSTP, selenite, and MRTP + selenite. The present findings demonstrate that the antimutagenic potential of MSTP could not be solely related to the enhancment of antioxidant enzymes of GPx and SOD.

The bacterial response to the chalcogen metalloids Se and Te

Microbial metabolism of inorganics has been the subject of interest since the 1970s when it was recognized that bacteria are involved in the transformation of metal compounds in the environment. This area of research is generally referred to as bioinorganic chemistry or microbial biogeochemistry. Here, we overview the way the chalcogen metalloids Se and Te interact with bacteria. As a topic of considerable interest for basic and applied research, bacterial processing of tellurium and selenium oxyanions has been reviewed a few times over the past 15 years. Oddly, this is the first time these compounds have been considered together and their similarities and differences highlighted. Another aspect touched on for the first time by this review is the bacterial response in cell-cell or cell-surface aggregates (biofilms) against the metalloid oxyanions. Finally, in this review we have attempted to rationalize the considerable amount of literature available on bacterial resistance to the toxic metalloids tellurite and selenite.

Vicia root-mirconucleus and sister chromatid exchange assays on the genotoxicity of selenium compounds

Selenium (Se) is an important metalloid with industrial, environmental, biological and toxicological significance. Excessive selenium in soil and water may contribute to environmental selenium pollution, and affect plant growth and human health. By using Vicia faba micronucleus (MN) and sister chromatid exchange (SCE) tests, possible genotoxicity of sodium selenite and sodium biselenite was evaluated in this study. The results showed that sodium selenite, at concentrations from 0.01 to 10.0mg/L, induced a 1.9-3.9-fold increase in MN frequency and a 1.5-1.6-fold increase in SCE frequency, with a statistically significantly difference from the control (P<0.05 and 0.01, respectively). Sodium selenite also caused mitotic delay and a 15-80% decrease in mitotic indices (MI), but at the lowest concentration (0.005mg/L), it slightly stimulated mitotic activity. Similarly, the frequencies of MN and SCE also increased significantly in sodium biselenite treated samples, with MI decline only at relatively higher effective concentrations. Results of the present study suggest that selenite is genotoxic to V. faba root cells and may be a genotoxic risk to human health.

Effects of selenium supplementation on expression of glutathione peroxidase isoforms in cultured human lung adenocarcinoma cell lines

Selenium is an essential nutrient, a component of several anti-oxidant enzymes, and a possible factor in cancer risk, including lung cancer. We determined the subtoxic range of selenium concentration (as sodium selenite) required to increase and maintain the expression of anti-oxidant selenoproteins gluthathione peroxidases GPX1 and GPX4 at a constant level in cultures of human lung adenocarcinoma cell lines (H460, H1703 and H1944) and in HPL1D, a non-transformed lung epithelial cell line. Selenium dose-dependently increased GPX1 protein expression 1.8-fold in HPL1D cells and approximately 40-fold in H460 and H1944 cancer cells, with maximum effects at 20-40 nM. GPX4 protein was also increased, but more so in HPL1D (five-fold) than in H460 or H1944 cells (two- to three-fold). GPX1 mRNA showed similar patterns but differences of lesser magnitude. GPX1 protein and activity level was not consistently detectable in H1703 cells, with or without Se supplementation; its mRNA was present but very low. GPX4 protein level was also low in H1703 cells, but was markedly increased by selenium supplementation (48-fold). These results confirm a role for selenium in risk of lung cancer and the independent regulation of GPX1 and GPX4. Characterization of individual tumors with regard to GPX1 and GPX4 levels and regulation might be useful for interpretation of clinical studies on effects of selenium in lung cancer risk.

Selenium: From cancer prevention to DNA damage

Selenium (Se) is a dietary essential trace element with important biological roles. Accumulating evidence indicates that Se compounds possess anticancer properties. Se is specifically incorporated into proteins in the form of selenocysteine and non-specifically incorporated as selenomethionine in place of methionine. The effects of Se compounds on cells are strictly compositional and concentration-dependent. At supranutritional dietary levels, Se can prevent the development of many types of cancer. At higher concentrations, Se compounds can be either cytotoxic or possibly carcinogenic. The cytotoxicity of Se is suggested to be associated with oxidative stress. Accordingly, sodium selenite, an inorganic Se compound, was reported to induce DNA damage, particularly DNA strand breaks and base damage. In this review we summarize the various activities of Se compounds and focus on their relation to DNA damage and repair. We discuss the use of Saccharomyces cerevisiae for identification of the genes involved in Se toxicity and resistance.