High-dose sodium selenite can induce apoptosis of lymphoma cells in adult patients with non-Hodgkin's lymphoma

ATM/IKK alpha axis regulates the crosstalk between autophagy and apoptosis in selenite-treated Jurkat cells

Selenium is an essential trace element. High dosage of selenite exhibits a great potential in treating leukemia. Previous study discovered selenite could promote leukemia cells apoptosis through inducing DNA damage and cell cycle arrest, while the switch mechanisms of these events and autophagy were still unclear. Current study discovered selenite promoted autophagy and apoptosis of leukemia Jurkat cells. In this process, DNA damage related ATM/IKK alpha axis was activated. This axis could stabilize pro-apoptotic P73, and promote autophagy through regulating NF-kappaB signaling pathway. Moreover, survivin-2B was also confirmed to be necessary for the ATM-induced nuclear location of IKK alpha, and therefore stood at the node position of apoptosis and autophagy cascades inside Jurkat cells. Finally, our in vivo experiments proved that selenite exhibited some anti-tumor effects on Jurkat cells-bearing mice. Moreover, alterations of ATM and IKK alpha expression observed in vivo were similar to that identified in vitro. Therefore, our findings had fully confirmed survivin-2B dependent activation of ATM/IKK alpha axis might be another crosstalk between autophagy and apoptosis of selenite-treated leukemia cells.

Therapeutic Benefits of Selenium in Hematological Malignancies

Supplementing chemotherapy and radiotherapy with selenium has been shown to have benefits against various cancers. This approach has also been shown to alleviate the side effects associated with standard cancer therapies and improve the quality of life in patients. In addition, selenium levels in patients have been correlated with various cancers and have served as a diagnostic marker to track the efficiency of treatments or to determine whether these selenium levels cause or are a result of the disease. This concise review presents a survey of the selenium-based literature, with a focus on hematological malignancies, to demonstrate the significant impact of selenium in different cancers. The anti-cancer mechanisms and signaling pathways regulated by selenium, which impart its efficacious properties, are discussed. An outlook into the relationship between selenium and cancer is highlighted to guide future cancer therapy development.

The impact of selenium on regulatory T cell frequency and immune checkpoint receptor expression in patients with diffuse large B cell lymphoma (DLBCL)

For many decades, selenium (Se) has been known as a potential anti-cancer agent that can also improve the function of immune cells in a variety of solid tumors. However, there is no report on the role of Se on CD4⁺ T cell subsets like CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Tregs) in lymphoma patients. In this randomized clinical trial, we investigated the effect of 3-month Se consumption on the frequency of CD4⁺CD25⁺FOXP3⁺ Tregs and the expression of immune checkpoint receptors in thirty-two non-Hodgkin lymphoma (NHL) patients (16 patients with Se (Se+) and 16 without Se (Se-) consumption) with diffuse large B-cell lymphoma (DLBCL) subtype at stable remission. The change in the frequency of Tregs and expression of immune checkpoint receptors including CTLA-4, LAG-3, TIM-3, and PD-L1 genes were evaluated after 3 months in both groups using flow cytometry and SYBR Green Real-time PCR method, respectively. The results showed that the frequency of CD4⁺CD25⁺FOXP3⁺ Tregs and expression of immune checkpoint receptors did not significantly change after 3-month Se consumption in DLBCL patients. However, alteration in the frequency of CD4⁺CD25^-FOXP3⁺ Treg subsets was positively correlated with change in CTLA-4, LAG-3, and TIM-3 expression in the Se+ group. Three-month Se supplementation did not prevent relapse in Se+ group. Taken together, Se supplementation alone did not affect the frequency of CD4⁺CD25⁺FOXP3⁺ Tregs, expression of checkpoint receptors, and prevention of relapse in DLBCL patients at stable remission phase but might influence the functional properties of other Treg subsets like CD4⁺CD25^-FOXP3⁺ Tregs.

p53 controls the switch between autophagy and apoptosis through regulation of PLSCR1 in sodium selenite-treated leukemia cells

Coordinated regulation of autophagy and apoptosis helps to enhance the antitumor effects of sodium selenite. However, the potential molecules that act as switch nodes in the crosstalk between autophagy and apoptosis is still elusive. Phospholipid scramblase 1 (PLSCR1) has been shown to regulate leukocyte differentiation, while its role in autophagy/apoptosis toggle switch remains unexplored. In this study, we showed that sodium selenite switched protective autophagy to apoptosis in p53-wild type NB4 cells without obvious caspase-8/apoptosis-inducing factor (AIF) axis activation, while induced autophagy-dependent caspase-8/AIF axis activation in p53-mutant Jurkat cells. Additionally, p53 was demonstrated as a positive regulator of PLSCR1. p53-dependent up-regulation of PLSCR1 accounted for the differential regulation of autophagy and apoptosis induced by sodium selenite. Furthermore, sodium selenite induced the release of AIF from mitochondria to cytosol with the facilitation of caspase-8 in Jurkat cells, while not in NB4 cells. The released AIF further enhanced autophagy flux through interacting with PLSCR1, which hereby resulting in the disassociation of PLSCR1 from Atg5-Atg12 complex. Our results indicate that PLSCR1 plays a critical role in p53-dependent regulation of autophagy and apoptosis in sodium selenite-treated leukemia cells. Manipulation of p53-PLSCR1 cascade might be beneficial to enhance the anti-tumor effects of sodium selenite.

Results from a Phase 1 Study of Sodium Selenite in Combination with Palliative Radiation Therapy in Patients with Metastatic Cancer

In preclinical studies, selenite had single agent activity and radiosensitized tumors in vivo. Here we report results from a Phase 1 trial in 15 patients with metastatic cancer treated with selenite (5.5 to 49.5 mg) orally as a single dose 2 hours before each radiation therapy (RT) treatment. Patients received RT regimens that were standard of care. The primary objective of the study was to assess the safety of this combination therapy. Secondary objectives included measurement of pharmacokinetics (PK) and evaluation of efficacy. Endpoints included assessment of PK, toxicity, tumor response, and pain before and after treatment. The half-life of selenite was 18.5 hours. There were no adverse events attributable to selenite until the 33 mg dose level, at which the primary toxicities were grade 1 GI side effects. One patient treated with 49.5 mg had grade 2 GI toxicity. Although this was not a DLT, it was felt that the highest acceptable dose in this patient population was 33 mg. Most patients had stabilization of disease within the RT fields, with some demonstrating objective evidence of tumor regression. Most patients had a marked improvement in pain and seven out of nine patients with prostate cancer had a decrease in PSA ranging from 11-78%. Doses up to 33 mg selenite were well tolerated in combination with RT. A randomized, well controlled study is needed at the 33 mg dose level to determine if selenite results in clinically meaningful improvements in the response to palliative RT.

Selenium as an adjuvant for modification of radiation response

Ionizing radiation plays a central role in several medical and industrial purposes. In spite of the beneficial effects of ionizing radiation, there are some concerns related to accidental exposure that could pose a threat to the lives of exposed people. This issue is also very critical for triage of injured people in a possible terror event or nuclear disaster. The most common side effects of ionizing radiation are experienced in cancer patients who had undergone radiotherapy. For complete eradication of tumors, there is a need for high doses of ionizing radiation. However, these high doses lead to severe toxicities in adjacent organs. Management of normal tissue toxicity may be achieved via modulation of radiation responses in both normal and malignant cells. It has been suggested that treatment of patients with some adjuvant agents may be useful for amelioration of radiation toxicity or sensitization of tumor cells. However, there are always some concerns for possible severe toxicities and protection of tumor cells, which in turn affect radiotherapy outcomes. Selenium is a trace element in the body that has shown potent antioxidant and radioprotective effects for many years. Selenium can potently stimulate antioxidant defense of cells, especially via upregulation of glutathione (GSH) level and glutathione peroxidase activity. Some studies in recent years have shown that selenium is able to mitigate radiation toxicity when administered after exposure. These studies suggest that selenium may be a useful radiomitigator for an accidental radiation event. Molecular and cellular studies have revealed that selenium protects different normal cells against radiation, while it may sensitize tumor cells. These differential effects of selenium have also been revealed in some clinical studies. In the present study, we aimed to review the radiomitigative and radioprotective effects of selenium on normal cells/tissues, as well as its radiosensitive effect on cancer cells.

Comparative Safety and Pharmacokinetic Evaluation of Three Oral Selenium Compounds in Cancer Patients

Selenium (Se) compounds have demonstrated anticancer properties in both preclinical and clinical studies, with particular promise in combination therapy where the optimal form and dose of selenium has yet to be established. In a phase I randomised double-blinded study, the safety, tolerability and pharmacokinetic (PK) profiles of sodium selenite (SS), Se-methylselenocysteine (MSC) and seleno-l-methionine (SLM) were compared in patients with chronic lymphocytic leukaemia and a cohort of patients with solid malignancies. Twenty-four patients received 400 μg of elemental Se as either SS, MSC or SLM for 8 weeks. None of the Se compounds were associated with any significant toxicities, and the total plasma Se AUC of SLM was markedly raised in comparison to MSC and SS. DNA damage assessment revealed negligible genotoxicity, and some minor reductions in lymphocyte counts were observed. At the dose level used, all three Se compounds are well-tolerated and non-genotoxic. Further analyses of the pharmacodynamic effects of Se on healthy and malignant peripheral blood mononuclear cells will inform the future evaluation of higher doses of these Se compounds. The study is registered under the Australian and New Zealand Clinical Trials Registry No: ACTRN12613000118707.

Whole Blood Selenium Levels and Selenium Supplementation in Patients Treated in a Family Doctor Practice in Golßen (State of Brandenburg, Germany): A Laboratory Study

Introduction: The supply of selenium (Se) varies widely in Germany. Therefore, a laboratory study was conducted in patients treated at a family doctor practice in Brandenburg, Germany, to determine whether there is a general Se deficiency in this area; specifically, whether Se concentrations differ with age, sex, or presence of cancer. Moreover, we tested the effects of a Se supplementation on whole blood Se levels (WBSL). Methods: In 2006, WBSL were analyzed in 871 patients (496 females, 375 males, median age: 67 years). Of these, 143 (78 females, 65 males) had cancer and were in an aftercare situation. From 2006 to 2012, 317 patients (76 with tumors, 241 without tumors) received continuous Se supplementation with sodium selenite (300 µg per day) and annual WBSL measurements. WBSL were compared by Student’s t test for paired and independent samples. Results: The initial WBSL of all patients was 97.2 ± 20.7 µg/L (mean ± SD). WBSL did not differ with regard to age or sex, but patients with cancer had the lowest WBSL. Se supplementation increased mean WBSL in both patients with (to 128.5 µg/L) and without (to 119.52 µg/L) cancer (P < .001). Discussion: Patients with cancer displayed significantly lower WBSL than patients without cancer, indicating a negative effect of tumors on Se uptake, absorption, or metabolism. Significant influences of age or sex were not observed. Selenite supplementation efficiently improved WBSL to concentrations considered necessary for health benefits.

The Interaction of Selenium with Chemotherapy and Radiation on Normal and Malignant Human Mononuclear Blood Cells

Selenium, a trace element with anticancer properties, can reduce harmful toxicities of chemotherapy and radiotherapy without compromising efficacy. However, the dose-response relationship in normal versus malignant human cells is unclear. We evaluated how methylseleninic acid (MSA) modulates the toxicity and efficacy of chemotherapy and radiation on malignant and non-malignant human mononuclear blood cells in vitro. We specifically investigated its effects on endoplasmic reticulum stress induction, intracellular glutathione concentration, DNA damage and viability of peripheral blood mononuclear cells and THP1 monocytic leukaemia cells in response to radiation, cytosine arabinoside or doxorubicin chemotherapy. MSA, at lower concentrations, induced protective responses in normal cells but cytotoxic effects in malignant cells, alone and in conjunction with chemotherapy or radiation. However, in normal cells higher concentrations of MSA were directly toxic and increased the cytotoxicity of radiation but not chemotherapy. In malignant cells higher MSA concentrations were generally more effective in combination with cancer treatments. Thus, optimal MSA concentrations differed between normal and malignant cells and treatments. This work supports clinical reports that selenium can significantly reduce dose-limiting toxicities of anticancer therapies and potentially improve efficacy of anticancer treatments. The optimal selenium compound and dose is not yet determined.

Selenium in Radiation Oncology-15 Years of Experiences in Germany

Introduction: Se measurement and supplementation in radiation oncology is a controversial issue. The German Working Group Trace Elements and Electrolytes in Oncology (AKTE) has conducted a number of studies on this issue, which are summarized in this review. Strategies have been tested and developed, aiming to stratify the patients with a potential need for supplemental Se and how best to monitor Se supplementation with respect to health effects and risks. Methods: We analyzed blood and tissue Se-levels of different tumor patients (n = 512). Two randomized phase III clinical studies were conducted for testing a potential radioprotective effect of supplemental Se during radiation therapy in patients with uterine cancer (n = 81) and head and neck tumor patients (n = 39). Results: A relative Se deficit in whole blood or serum was detected in the majority of tumor patients (carcinomas of the uterus, head and neck, lung, rectal or prostate cancer). In prostate cancer, tissue Se concentrations were relatively elevated in the carcinoma centre as compared to the surrounding compartment or as compared to tumor samples from patients with benign prostatic hyperplasia. Adjuvant Se supplementation successfully corrected Se-deficiency in the patients analyzed and decreased radiotherapy-induced diarrhea in a randomized study of radiotherapy patients with carcinomas of the uterus. Survival data imply that Se supplementation did not interfere with radiation success. Some positive effects of supplemental Se in the prevention of ageusia (loss of taste) and dysphagia due to radiotherapy were noted in a second randomized trial in patients with head and neck cancer. We have not observed any adverse effects of supplemental Se in our studies. Conclusions: Se supplementation yielded promising results concerning radioprotection in tumor patients and should be considered as a promising adjuvant treatment option in subjects with a relative Se deficit.

Double-ratiometric fluorescence imaging of H2Se and O2˙− under hypoxia for exploring Na2SeO3-induced HepG2 cells' apoptosis

Sodium selenite (Na₂SeO₃), as an anti-tumor drug for inducing tumor cells' apoptosis, has been widely studied under normoxic conditions and has been shown to exhibit oxidative stress process-induced apoptosis. However, since the real tumor environment is hypoxic, the actual mechanism is still unclear. Hence, considering the main metabolite of Na₂SeO₃ in the metabolic process to be hydrogen selenide (H₂Se) and also that it can be converted to superoxide anion (O₂˙⁻) instantaneously in the presence of oxygen, a dual-ratiometric fluorescence imaging system for simultaneous monitoring of the changes of H₂Se and O₂˙⁻ induced by Na₂SeO₃-guided tumor cell apoptosis under hypoxic conditions was constructed. Two molecular probes NIR-H₂Se and dihydroethidium were used to detect H₂Se and O₂˙⁻, respectively, whereas Rhodamine 110 was used as the reference fluorophore. Notably, H₂Se levels significantly increased under hypoxic conditions, but there was no change in the level of O₂˙⁻, which is inconsistent with the results of the previous researches. Therefore, we hypothesize that the mechanism of Na₂SeO₃-induced apoptosis for tumor cells is caused by reductive stress; also, this method can be applied for the future study of other anti-cancer selenium compounds.

Sodium selenite (Na₂SeO₃), as an anti-tumor drug for inducing tumor cells' apoptosis, has been widely studied under normoxic conditions and has been shown to exhibit oxidative stress process-induced apoptosis.

Randomized phase II trial of selenomethionine as a modulator of efficacy and toxicity of chemoradiation in squamous cell carcinoma of the head and neck

AIM: To investigate whether selenomethionine (SLM) reduces mucositis incidence in patients with head and neck squamous cell cancer (HNSCC) undergoing concurrent chemoradiation (CRT).

METHODS: In this multi-institutional, randomized, double-blind phase II trial, patients with Stage III or IV HNSCC received SLM 3600 μg/m² or placebo twice daily for 7 d prior to CRT, once daily during CRT, and daily for 3 wk following CRT. CRT consisted of 70 Gy at 2 Gy per fraction with cisplatin 100 mg/m² IV on days 1, 22, and 43.

RESULTS: Eighteen patients were randomized, 10 received SLM, and there were no differences in baseline factors. There was no difference in mucositis or patient-reported side effects between groups. There was no difference in overall or relapse-free survival at 12 mo.

CONCLUSION: Addition of SLM to CRT for HNSCC was well-tolerated but did not lower the incidence of severe mucositis or improve quality of life or survival outcomes.

Effects of selenomethionine on acute toxicities from concurrent chemoradiation for inoperable stage III non-small cell lung cancer

AIM

To prospectively determine the safety and tolerability of oral L-selenomethionine (SLM) with concurrent chemoradiation (CCRT) for Stage III non-small cell lung cancer (NSCLC) and estimate if the incidence and/or severity of adverse events could be reduced by its use.

METHODS

Sixteen patients with stage III NSCLC were accrued to this single arm, phase II study. CCRT consisted of radiation given at 2 Gy per fraction for 30-33 fractions, 5 d per week with concurrent weekly IV paclitaxel 50 mg/m(2) followed by carboplatin dosed at an area under the time-concentration curve of 2. SLM was dosed in a loading phase at 4800 μg twice daily for one week prior to CCRT followed by once daily dosing during treatment.

RESULTS

No selenium-related toxicity was observed. Analysis revealed grade 3 or higher esophagitis in 3 of 16 patients (19%), pneumonitis in 0, leukopenia in 2 (12.5%), and anemia in 1 (6%); the latter two were significantly reduced when compared to the protocol-stated expected rate of 35% (P = 0.045 for leukopenia, and P < 0.01 for anemia). Median overall survival was 14.9 mo and median failure-free survival was 9 mo (95%CI: 3.3-21.5).

CONCLUSION

There may be some protective benefit of selenium in the setting of CCRT for inoperable NSCLC. The data suggests decreased rates of myelosuppression when compared to similarly-treated historical and contemporary controls. Further evaluation of selenium in this setting may be warranted.

Redox-active selenium compounds--from toxicity and cell death to cancer treatment

Selenium is generally known as an antioxidant due to its presence in selenoproteins as selenocysteine, but it is also toxic. The toxic effects of selenium are, however, strictly concentration and chemical species dependent. One class of selenium compounds is a potent inhibitor of cell growth with remarkable tumor specificity. These redox active compounds are pro-oxidative and highly cytotoxic to tumor cells and are promising candidates to be used in chemotherapy against cancer. Herein we elaborate upon the major forms of dietary selenium compounds, their metabolic pathways, and their antioxidant and pro-oxidant potentials with emphasis on cytotoxic mechanisms. Relative cytotoxicity of inorganic selenite and organic selenocystine compounds to different cancer cells are presented as evidence to our perspective. Furthermore, new novel classes of selenium compounds specifically designed to target tumor cells are presented and the potential of selenium in modern oncology is extensively discussed.

The selenium metabolite methylselenol regulates the expression of ligands that trigger immune activation through the lymphocyte receptor NKG2D

For decades, selenium research has been focused on the identification of active metabolites, which are crucial for selenium chemoprevention of cancer. In this context, the metabolite methylselenol (CH3SeH) is known for its action to selectively kill transformed cells through mechanisms that include increased formation of reactive oxygen species, induction of DNA damage, triggering of apoptosis, and inhibition of angiogenesis. Here we reveal that CH3SeH modulates the cell surface expression of NKG2D ligands. The expression of NKG2D ligands is induced by stress-associated pathways that occur early during malignant transformation and enable the recognition and elimination of tumors by activating the lymphocyte receptor NKG2D. CH3SeH regulated NKG2D ligands both on the transcriptional and the posttranscriptional levels. CH3SeH induced the transcription of MHC class I polypeptide-related sequence MICA/B and ULBP2 mRNA. However, the induction of cell surface expression was restricted to the ligands MICA/B. Remarkably, our studies showed that CH3SeH inhibited ULBP2 surface transport through inhibition of the autophagic transport pathway. Finally, we identified extracellular calcium as being essential for CH3SeH regulation of NKG2D ligands. A balanced cell surface expression of NKG2D ligands is considered to be an innate barrier against tumor development. Therefore, our work indicates that the application of selenium compounds that are metabolized to CH3SeH could improve NKG2D-based immune therapy.

Multicenter, phase III trial comparing selenium supplementation with observation in gynecologic radiation oncology: follow-up analysis of the survival data 6 years after cessation of randomization

PURPOSE

In 2010, we reported that selenium (Se) supplementation during radiation therapy (RT) is effective for increasing blood Se levels in Se-deficient cervical and uterine cancer patients, and reduced the number of episodes and severity of RT-induced diarrhea. In the current study, we examine whether of Se supplementation during adjuvant RT affects long-term survival of these patients.

PATIENTS AND METHODS

Former patients were identified and questioned with respect to their health and well-being.

RESULTS

A total of 81 patients were randomized in the initial supplementation study, 39 of whom received Se (selenium group, SeG) and 42 of whom served as controls (control group, CG). When former patients were reidentified after a median follow-up of 70 months (range = 0-136), the actuarial 10-year disease-free survival rate in the SeG was 80.1% compared to 83.2% in the CG (P = .65), and the actuarial 10-year overall survival rate of patients in the SeG was 55.3% compared to 42.7% in the CG (P = .09).

CONCLUSIONS

Our extended follow-up analysis demonstrates that Se supplementation had no influence on the effectiveness of the anticancer irradiation therapy and did not negatively affect patients' long-term survival. In view of its positive effects on RT-induced diarrhea, we consider Se supplementation to be a meaningful and beneficial adjuvant treatment in Se-deficient cervical and uterine cancer patients while undergoing pelvic radiation therapy.

Impact of treatment planning target volumen (PTV) size on radiation induced diarrhoea following selenium supplementation in gynecologic radiation oncology--a subgroup analysis of a multicenter, phase III trial

Background

In a previous analysis (Int J Radiat Oncol Biol Phys 70:828-835,2010), we assessed whether an adjuvant supplementation with selenium (Se) improves Se status and reduces the radiation-induced side-effects of patients treated by adjuvant radiotherapy (RT) for cervical and uterine cancer. Now, a potential relation between the planning target volume (PTV) of the RT and the Se effect concerning radiation induced diarrhoea was evaluated in detail.

Methods

Whole blood Se concentrations had been measured in patients with cervical (n=11) and uterine cancer (n=70) after surgical treatment, during, and at the end of RT. Patients with initial Se concentrations of less than 84 μg/l were categorized as Se-deficient and randomized before RT to receive Se (as sodium selenite) per os on the days of RT, or to receive no supplement during RT. Diarrhoea was graded according to the Common Toxicity Criteria system (CTC, Version 2a). The evaluation of the PTV of the RT was ascertained with the help of a specialised computer-assisted treatment planning software used for radiation planning procedure.

Results

A total of 81 patients had been randomized for the initial supplementation study, 39 of which received Se [selenium group, SeG] and 42 serving as controls [control group, CG]. Mean Se levels did not differ between SeG and CG upon study initiation, but were significantly higher in the SeG compared to the CG at the end of RT. The actuarial incidence of at least CTC 2 radiation induced diarrhoea in the SeG was 20.5% compared to 44.5% in the CG (p=0.04). The median PTV in both groups was 1302 ml (916–4608). With a PTV of <= 1302 ml (n=41) the actuarial incidence of at least CTC 2 diarrhoea in the SeG was 22.3% (4 of 18 patients) compared to 34.8% (8 of 23 patients) in the CG (p=0.50). In patients with a PTV of > 1302 ml (n=40) the actuarial incidence of at least CTC 2 diarrhoea in the SeG was 19.1% (4 of 21 patients) versus 52.6% (10 of 19 patients) in the CG (p=0.046).

Conclusions

Se supplementation during RT was effective to improve blood Se status in Se-deficient cervical and uterine cancer patients, and reduces episodes and severity of RT-induced diarrhoea. This effect was most pronounced and significant in patients with large PTV (> 1302 ml).

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

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

Impact of dietary selenium intake on cardiac health: experimental approaches and human studies

Selenium, a dietary trace mineral, essential for humans and animals, exerts its effects mainly through its incorporation into selenoproteins. Adequate selenium intake is needed to maximize the activity of selenoproteins, among which glutathione peroxidases have been shown to play a major role in cellular defense against oxidative stress initiated by excess reactive oxygen species. In humans, a low selenium status has been linked to increased risk of various diseases, including heart disease. The main objective of this review is to present current knowledge on the role of selenium in cardiac health. Experimental studies have shown that selenium may exert protective effects on cardiac tissue in animal models involving oxidative stress. Because of the narrow safety margin of this mineral, most interventional studies in humans have reported inconsistent findings. Major determinants of selenium status in humans are not well understood and several nondietary factors might be associated with reduced selenium status. In this review, we discuss recent studies regarding the role of selenoproteins in the cardiovascular system, the effect of dietary intake on selenium status, the impact of selenium status on cardiac health, and the cellular mechanisms that can be involved in the physiological and toxic effects of selenium.

Selenium in human health and disease

This review covers current knowledge of selenium in the environment, dietary intakes, metabolism and status, functions in the body, thyroid hormone metabolism, antioxidant defense systems and oxidative metabolism, and the immune system. Selenium toxicity and links between deficiency and Keshan disease and Kashin-Beck disease are described. The relationships between selenium intake/status and various health outcomes, in particular gastrointestinal and prostate cancer, cardiovascular disease, diabetes, and male fertility, are reviewed, and recent developments in genetics of selenoproteins are outlined. The rationale behind current dietary reference intakes of selenium is explained, and examples of differences between countries and/or expert bodies are given. Throughout the review, gaps in knowledge and research requirements are identified. More research is needed to improve our understanding of selenium metabolism and requirements for optimal health. Functions of the majority of the selenoproteins await characterization, the mechanism of absorption has yet to be identified, measures of status need to be developed, and effects of genotype on metabolism require further investigation. The relationships between selenium intake/status and health, or risk of disease, are complex but require elucidation to inform clinical practice, to refine dietary recommendations, and to develop effective public health policies.

Selenium: a double-edged sword for defense and offence in cancer

Selenium (Se) is an essential dietary component for animals including humans and is regarded as a protective agent against cancer. Although the mode of anticancer action of Se is not fully understood yet, several mechanisms, such as antioxidant protection by selenoenzymes, specific inhibition of tumor cell growth by Se metabolites, modulation of cell cycle and apoptosis, and effect on DNA repair have all been proposed. Despite the unsupported results of the last SELECT trial, the cancer-preventing activity of Se was demonstrated in majority of the epidemiological studies. Moreover, recent studies suggest that Se has a potential to be used not only in cancer prevention but also in cancer treatment where in combination with other anticancer drugs or radiation, it can increase efficacy of cancer therapy. In combating cancer cells, Se acts as pro-oxidant rather than antioxidant, inducing apoptosis through the generation of oxidative stress. Thus, the inorganic Se compound, sodium selenite (SeL), due to its prooxidant character, represents a promising alternative for cancer therapy. However, this Se compound is highly toxic compared to organic Se forms. Thus, the unregulated intake of dietary or pharmacological Se supplements mainly in the form of SeL has a potential to expose the body tissues to the toxic levels of Se with subsequent negative consequences on DNA integrity. Hence, due to a broad interest to exploit the positive effects of Se on human health and cancer therapy, studies investigating the negative effects such as toxicity and DNA damage induction resulting from high Se intake are also highly required. Here, we review a role of Se in cancer prevention and cancer therapy, as well as mechanisms underlying Se-induced toxicity and DNA injury. Since Saccharomyces cerevisiae has proven a powerful tool for addressing some important questions regarding Se biology, a part of this review is devoted to this model system.

Sodium selenite improves the in vitro follicular development by reducing the reactive oxygen species level and increasing the total antioxidant capacity and glutathione peroxide activity

BACKGROUND

The aim of this study was to investigate the effect of sodium selenite (SS) on reactive oxygen species (ROS) production, total antioxidant capacity (TAC) and glutathione peroxide (GPx) activity of cultured pre-antral follicles derived from vitrified and non-vitrified ovarian tissue.

METHODS

Immature mouse ovaries were vitrified, and mechanically isolated pre-antral follicles from vitrified and non-vitrified samples were cultured in TCM 199 medium supplemented with different concentrations (0, 5 and 10 ng/ml) of SS. Follicular, oocyte and embryo development was assessed. In parallel, ROS, TAC and GPx levels were analyzed after 0, 12, 24, 48, 72 and 96 h of culture.

RESULTS

Development rates of follicles, oocytes and embryos were significantly higher in SS-supplemented groups (P < 0.005). ROS production was increased, and TAC levels and GPx activities were decreased after 24 h of culture of pre-antral follicles in vitrified and non-vitrified groups, whereas in the presence of SS, ROS production was decreased and TAC levels and selenium-dependent GPx-specific activities were increased after 96 h of culture. Vitrified and non-vitrified samples responded in a similar manner.

CONCLUSION

SS caused an increase in follicular TAC level and GPx activity and a decrease in ROS level, thus improving the in vitro development of follicles.

Selenium and glutathione peroxidase status in adult Egyptian patients with acute myeloid leukemia

This study was undertaken to evaluate selenium (Se) and glutathione peroxidase (GPX) status in patients with newly diagnosed acute myeloid leukemia (AML) before and after induction therapy. Twenty-five patients with newly diagnosed AML and 15 healthy age- and sex-matched control subjects were included in this study. Serum Se level by the graphite furnace atomic absorption spectrometric technique and GPX activity by an adaptation of Beutler method was performed for the patients before and after receiving the induction therapy. Serum Se level was significantly lower in patients with AML versus control subjects (63.1 ± 8.8 versus 77 ± 8.8 μg/L before therapy with a P value <0.01 and 69 ± 6.8 versus 77 ± 8.8 μg/L after therapy with a P value <0.01).GPX activity was significantly lower in patients with AML versus control subjects (1.6 ± 0.4 versus 3.4 ± 0.7 μ/g protein pretreatment with a P value <0.01 and 1.9 ± 0.6 versus 3.4 ± 0.7 μ/g protein post induction treatment with P value <0.01).Se level and GPX activity significantly increased in AML patients after treatment. Patients who accomplished complete remission after induction harbored significantly higher Se levels than resistant patients before and after treatment. There was no significant correlation between serum Se level and GPX activity. Decreased Se level and reduced GPX activity in AML patients support the association of carcinogenesis and subnormal Se states.

Phenotype-dependent apoptosis signalling in mesothelioma cells after selenite exposure

Background

Selenite is a promising anticancer agent which has been shown to induce apoptosis in malignant mesothelioma cells in a phenotype-dependent manner, where cells of the chemoresistant sarcomatoid phenotype are more sensitive.

Methods

In this paper, we investigate the apoptosis signalling mechanisms in sarcomatoid and epithelioid mesothelioma cells after selenite treatment. Apoptosis was measured with the Annexin-PI assay. The mitochondrial membrane potential, the expression of Bax, Bcl-XL, and the activation of caspase-3 were assayed with flow cytometry and a cytokeratin 18 cleavage assay. Signalling through JNK, p38, p53, and cathepsins B, D, and E was investigated with chemical inhibitors. Furthermore, the expression, nuclear translocation and DNA-binding activity of p53 was investigated using ICC, EMSA and the monitoring of p21 expression as a downstream event. Levels of thioredoxin (Trx) were measured by ELISA.

Results

In both cell lines, 10 μM selenite caused apoptosis and a marked loss of mitochondrial membrane potential. Bax was up-regulated only in the sarcomatoid cell line, while the epithelioid cell line down-regulated Bcl-XL and showed greater caspase-3 activation. Nuclear translocation of p53 was seen in both cell lines, but very little p21 expression was induced. Chemical inhibition of p53 did not protect the cells from apoptosis. p53 lost its DNA binding ability after selenite treatment and was enriched in an inactive form. Levels of thioredoxin decreased after selenite treatment. Chemical inhibition of MAP kinases and cathepsins showed that p38 and cathepsin B had some mediatory effect while JNK had an anti-apoptotic role.

Conclusion

We delineate pathways of apoptosis signalling in response to selenite, showing differences between epithelioid and sarcomatoid mesothelioma cells. These differences may partly explain why sarcomatoid cells are more sensitive to selenite.