Pharmacokinetics and Toxicity of Sodium Selenite in the Treatment of Patients with Carcinoma in a Phase I Clinical Trial: The SECAR Study

The Potential of Integrative Cancer Treatment Using Melatonin and the Challenge of Heterogeneity in Population-Based Studies: A Case Report of Colon Cancer and a Literature Review

Melatonin is a multifunctional hormone regulator that maintains homeostasis through circadian rhythms, and desynchronization of these rhythms can lead to gastrointestinal disorders and increase the risk of cancer. Preliminary clinical studies have shown that exogenous melatonin alleviates the harmful effects of anticancer therapy and improves quality of life, but the results are still inconclusive due to the heterogeneity of the studies. A personalized approach to testing clinical parameters and response to integrative treatment with nontoxic and bioavailable melatonin in patient-centered N-of-1 studies deserves greater attention. This clinical case of colon cancer analyzes and discusses the tumor pathology, the adverse effects of chemotherapy, and the dynamics of markers of inflammation (NLR, LMR, and PLR ratios), tumors (CEA, CA 19-9, and PSA), and hemostasis (D-dimer and activated partial thromboplastin time). The patient took melatonin during and after chemotherapy, nutrients (zinc, selenium, vitamin D, green tea, and taxifolin), and aspirin after chemotherapy. The patient's PSA levels decreased during CT combined with melatonin (19 mg/day), and melatonin normalized inflammatory markers and alleviated symptoms of polyneuropathy but did not help with thrombocytopenia. The results are analyzed and discussed in the context of the literature on oncostatic and systemic effects, alleviating therapy-mediated adverse effects, association with survival, and N-of-1 studies.

Nontoxic Levels of Se-Containing Compounds Increase Survival by Blocking Oxidative and Inflammatory Stresses via Signal Pathways Whereas High Levels of Se Induce Apoptosis

Selenium is a main group element and an essential trace element in human health. It was discovered in selenocysteine (SeC) by Stadtman in 1974. SeC is an encoded natural amino acid hailed as the 21st naturally occurring amino acid (U) present in several enzymes and which exquisitely participates in redox biology. As it turns out, selenium bears a U-shaped toxicity curve wherein too little of the nutrient present in biology leads to disorders; concentrations that are too great, on the other hand, pose toxicity to biological systems. In light of many excellent previous reviews and the corpus of literature, we wanted to offer this current review, in which we present aspects of the clinical and biological literature and justify why we should further investigate Se-containing species in biological and medicinal contexts, especially small molecule-containing species in biomedical research and clinical medicine. Of central interest is how selenium participates in biological signaling pathways. Several clinical medical cases are recounted; these reports are mainly pertinent to human cancer and changes in pathology and cases in which the patients are often terminal. Selenium was an option chosen in light of earlier chemotherapeutic treatment courses which lost their effectiveness. We describe apoptosis, and also ferroptosis, and senescence clearly in the context of selenium. Other contemporary issues in research also compelled us to form this review: issues with CoV-2 SARS infection which abound in the literature, and we described findings with human patients in this context. Laboratory scientific studies and clinical studies dealing with two main divisions of selenium, organic (e.g., methyl selenol) or inorganic selenium (e.g., sodium selenite), are discussed. The future seems bright with the research and clinical possibilities of selenium as a trace element, whose recent experimental clinical treatments have so far involved dosing simply and inexpensively over a set of days, amounts, and time intervals.

Sodium selenite inhibits proliferation of lung cancer cells by inhibiting NF-κB nuclear translocation and down-regulating PDK1 expression which is a key enzyme in energy metabolism expression

As a trace element that maintains homeostasis in human body, selenium has significant anti-tumor activity. However, its exact molecular mechanism remains to be elucidated. Sodium selenite (SSe) is the most widely-distributed inorganic selenium in nature. In this study, we selected SSe as the research object to explore its anti-tumor mechanism in lung cancer. In vitro experiment showed that SSe could inhibit the activation of NF-κB signaling pathway, knowing that NF-κB is an important intracellular nuclear transcription factor that regulates the expression of pyruvate dehydrogenase kinase 1 (PDK1), a key energy metabolism switch affecting the survival status of the whole cell.At the same time, Bay11-7082(NF-κB signaling pathway inhibitors) and SSe resulted in phosphorylation of p65 and IκBα, decreased expression of PDK1 and Bcl-2,and increased expression of Bax in lung cancer cells. Our further study demonstrated that the reduction of PDK1 activity inhibited lactate secretion, reduced mitochondrial membrane potential, caused the release of Cytochrome C (Cyto C), activated mitochondrial respiration, and promoted the apoptosis of lung cancer cells. The in vivo experiment revealed that SSe inhibited the activation of NF-κB signaling pathway, decreased the expression of PDK1, and induced lung cancer cell proliferation and apoptosis. All these findings indicated that SSe promoted lung cancer cell apoptosis by inhibiting the activation of NF-κB signaling pathway, down-regulating PDK1 and activating mitochondrial apoptosis pathway.

Selenite as a dual apoptotic and ferroptotic agent synergizes with EGFR and KRAS inhibitors with epigenetic interference

BACKGROUND

Selenium, an essential trace element, has previously been investigated as a pro-apoptotic and DNA demethylation agent. It sensitizes the response to chemotherapy in patients who were refractory to cytotoxic agents. Meanwhile, ferroptosis is a novel approach to cancer treatment by triggering cell death and reversing drug resistance. The role of selenium in treating cancer cells harboring druggable oncogenic alterations and its underlying mechanism are largely unknown.

RESULTS

We treated lung adenocarcinoma cell lines-EGFR-mutant H1975 (H1975 ^{EGFR p.L858R and p.T790M}) and KRAS-mutant H358 (H358 ^{KRAS p.G12C}), with sodium selenite to examine its effect on cell apoptosis, ferroptosis, and DNA methylation, as well as its interaction with existing targeted therapy, osimertinib, and adagrasib. We observed selenite to be a dual apoptotic and ferroptotic agent on lung cancer cells, associated with the activation of p38-ATF4-DDIT3 axis in the unfolded protein response. Ferroptosis induction was more remarkable in H1975 than H358. Selenite also altered cellular DNA methylation machinery through downregulating DNMT1 and upregulating TET1, though not as a major mechanism of its activity. Low-dose selenite synergized with osimertinib in EGFR-mutant H1975, and with adagrasib in KRAS-mutant H358, with stronger synergism observed in H1975.

CONCLUSION

These results suggest that selenite is a potential apoptotic and ferroptotic drug candidate for the treatment of especially EGFR- and potentially KRAS-mutant lung cancer.

Selenium Improves Bone Microenvironment-Related Hematopoiesis and Immunity in T-2 Toxin-Exposed Mice

The T-2 toxin is one of the most frequent contaminants in the environment and agricultural production globally. It exerts a wide range of toxic effects. Selenium (Se), as an antioxidant, has the potential to be widely used to antagonize mycotoxin toxicity. To investigate the protective effects of Se on bone microenvironment (BM)-related hematopoiesis and immunity after T-2 toxin exposure, 36 male mice were treated with the T-2 toxin (1 mg/kg) and/or Se (0.2 mg/kg) by intragastric administration for 28 days. The results showed that Se alleviated T-2 toxin-induced cytopenia and splenic extramedullary hematopoiesis. Se also significantly relieved T-2 toxin-induced immunosuppression, as assessed by immune factors and lymphocytes. Furthermore, Se also attenuated oxidative stress and apoptosis and improved the BM in T-2 toxin-exposed mice. Therefore, Se improves BM-related hematopoiesis and immunity after T-2 toxin exposure. This study provides references for identifying the toxic mechanism and screening potential therapeutic drugs of the T-2 toxin.

Intravenous Infusion of High Dose Selenite in End-Stage Cancer Patients: Analysis of Systemic Exposure to Selenite and Seleno-Metabolites

Cancer is one of the main causes of human death globally and novel chemotherapeutics are desperately required. As a simple selenium oxide, selenite is a very promising chemotherapeutic because of pronounced its dose-dependent tumor-specific cytotoxicity. We previously published a first-in-man systematic phase I clinical trial in patients with cancer (from IV to end-stage) (the SECAR trial) showing that selenite is safe and tolerable with an unexpectable high maximum tolerated dose (MTD) and short half-life. In the present study, we analyzed the selenium species in plasma samples, from the patients participating in the SECAR trial and from various time points and dose cohorts using LC-ICP-MS. In conclusion, selenite, selenosugars, and 1-2 unidentified peaks that did not correspond to any standard, herein denoted ui-selenium, were detected in the plasma. However, trimethylated selenium (trimethylselenonoium) was not detected. The unidentified ui-selenium was eluting close to the selenium-containing amino acids (selenomethionine and selenocysteine) but was not part of a protein fraction. Our data demonstrate that the major metabolite detected was selenosugar. Furthermore, the identification of selenite even long after the administration is remarkable and unexpected. The kinetic analysis did not support that dosing per the body surface area would reduce interindividual variability of the systemic exposure in terms of trough concentrations.

Biogenic Selenium Nanoparticles in Biomedical Sciences: Properties, Current Trends, Novel Opportunities and Emerging Challenges in Theranostic Nanomedicine

Selenium is an important dietary supplement and an essential trace element incorporated into selenoproteins with growth-modulating properties and cytotoxic mechanisms of action. However, different compounds of selenium usually possess a narrow nutritional or therapeutic window with a low degree of absorption and delicate safety margins, depending on the dose and the chemical form in which they are provided to the organism. Hence, selenium nanoparticles (SeNPs) are emerging as a novel therapeutic and diagnostic platform with decreased toxicity and the capacity to enhance the biological properties of Se-based compounds. Consistent with the exciting possibilities offered by nanotechnology in the diagnosis, treatment, and prevention of diseases, SeNPs are useful tools in current biomedical research with exceptional benefits as potential therapeutics, with enhanced bioavailability, improved targeting, and effectiveness against oxidative stress and inflammation-mediated disorders. In view of the need for developing eco-friendly, inexpensive, simple, and high-throughput biomedical agents that can also ally with theranostic purposes and exhibit negligible side effects, biogenic SeNPs are receiving special attention. The present manuscript aims to be a reference in its kind by providing the readership with a thorough and comprehensive review that emphasizes the current, yet expanding, possibilities offered by biogenic SeNPs in the biomedical field and the promise they hold among selenium-derived products to, eventually, elicit future developments. First, the present review recalls the physiological importance of selenium as an oligo-element and introduces the unique biological, physicochemical, optoelectronic, and catalytic properties of Se nanomaterials. Then, it addresses the significance of nanosizing on pharmacological activity (pharmacokinetics and pharmacodynamics) and cellular interactions of SeNPs. Importantly, it discusses in detail the role of biosynthesized SeNPs as innovative theranostic agents for personalized nanomedicine-based therapies. Finally, this review explores the role of biogenic SeNPs in the ongoing context of the SARS-CoV-2 pandemic and presents key prospects in translational nanomedicine.

The effects of selenium supplementation on blood lipids and blood pressure in adults: A systematic review and dose-response meta-analysis of randomized control trials

BACKGROUND

Previous studies evaluating the effects of selenium supplementation on lipid profile and blood pressure (BP) offer contradictory findings. This systematic review and meta-analysis assessed the effects of selenium supplementation on these lipid profile and BP.

METHODS

In order to identify interrelated clinical trials, we performed a comprehensive literature search in the online databases, including PubMed, Scopus, Embase, and ISI web of science, up to December 2021.

RESULTS

The analysis of the data established that selenium supplementation did not significantly affect TG level (WMD: -0.84 mg/dL; 95 % CI: -4.74, 3.05, p = 0.671), LDL-C (WMD: 0.86 mg/dL; 95 % CI: -1.21, 2.95, p = 0.416), and HDL-C (WMD: 0.3 mg/dL; 95 % CI: -0.66, 1.27, p = 0.535). however, there was a significant reduction in TC levels following selenium supplementation (WMD: -2.11 mg/dL; 95 % CI: -4.09, -0.13, p = 0.037). After subgroup analysis, when the baseline levels of LDL-C were < 130 mg/dL, selenium supplementation elicited a significant increase in LDL-C levels (WMD: 2.89 mg/dL; 95 % CI: 0.26, 5.51, p = 0.031). For BP, selenium supplementation significantly increased SBP (WMD: 2.02 mmHg; 95 % CI: 0.50, 3.55, p = 0.009), while it had no significant effect on DBP (WMD: 0.39 mmHg; 95 % CI: (-0.89, 1.68, p = 0.551)).

CONCLUSION

Although our findings suggest selenium may have possible therapeutic effects in improving TC and VLDL, because of its negative effects on LDL and BP, selenium supplementation for cardiovascular protection should be recommended with caution.

Potential Benefits of Selenium Supplementation in Reducing Insulin Resistance in Patients with Cardiometabolic Diseases: A Systematic Review and Meta-Analysis

BACKGROUND

Selenium is a trace element that has been reported to be effective in regulating glucose and lipid metabolism. However, there is conflicting evidence from different clinical trials of selenium supplementation in treating cardiometabolic diseases (CMDs).

OBJECTIVE

This meta-analysis aimed to identify the effects of selenium supplementation on insulin resistance, glucose homeostasis, and lipid profiles in patients with CMDs.

METHODS

Randomized controlled trials (RCTs) of selenium supplementation for treating CMDs were screened in five electronic databases. Insulin levels, homeostatic model assessment of insulin resistance (HOMA-IR), fasting plasma glucose (FPG), and glycosylated hemoglobin A1C (HbA1c) were defined as the primary outcome markers, and lipid profiles were considered the secondary outcome markers.

RESULTS

Ten studies involving 526 participants were included in the meta-analysis. The results suggested that selenium supplementation significantly reduced serum insulin levels (standardized men difference [SMD]: -0.53; 95% confidence interval [CI] [-0.84, -0.21], p = 0.001, I² = 68%) and HOMA-IR (SMD: -0.50, 95% CI [-0.86, -0.14], p = 0.006, I² = 75%) and increased high-density lipoprotein cholesterol (HDL-C) levels (SMD: 0.97; 95% CI [0.26, 1.68], p = 0.007, I² = 92%), but had no significant effect on FPG, total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and very low-density lipoprotein cholesterol (VLDL-C).

CONCLUSION

Current evidence supports the beneficial effects of selenium supplementation on reducing insulin levels, HOMA-IR, and increasing HDL-C levels. Selenium supplementation may be an effective strategy for reducing insulin resistance in patients with CMDs. However, more high-quality clinical studies are needed to improve the certainty of our estimates.

Selenocompounds and Sepsis-Redox Bypass Hypothesis: Part B-Selenocompounds in the Management of Early Sepsis

Significance: Endothelial barrier damage, which is in part caused by excess production of reactive oxygen, halogen and nitrogen species (ROHNS), especially peroxynitrite (ONOO^-), is a major event in early sepsis and, with leukocyte hyperactivation, part of the generalized dysregulated immune response to infection, which may even become a complex maladaptive state. Selenoenzymes have major antioxidant functions. Their synthesis is related to the need to limit deleterious oxidant redox cycling by small selenocompounds, which may be of therapeutic cytotoxic interest. Plasma selenoprotein-P is crucial for selenium transport from the liver to the tissues and for antioxidant endothelial protection, especially against ONOO^-. Above micromolar concentrations, sodium selenite (Na₂SeO₃) becomes cytotoxic, with a lower cytotoxicity threshold in activated cells, which has led to cancer research. Recent Advances: Plasma selenium (<2% of total body selenium) is mainly contained in selenoprotein-P, and concentrations decrease rapidly in the early phase of sepsis, because of increased selenoprotein-P binding and downregulation of hepatic synthesis and excretion. At low concentrations, Na₂SeO₃ acts as a selenium donor, favoring selenoprotein-P synthesis in physiology, but probably not in the acute phase of sepsis. Critical Issues: The cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes, especially the most immature forms that liberate ROHNS, may be beneficial, but they may also be harmful for activated endothelial cells. Endothelial protection against ROHNS by selenoprotein-P may reduce Na₂SeO₃ toxicity, which is increased in sepsis. Future Direction: The combination of selenoprotein-P for endothelial protection and the cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes may be a promising intervention for early sepsis. Antioxid. Redox Signal. 37, 998-1029.

Selenoprotein P - Selenium transport protein, enzyme and biomarker of selenium status

The habitual intake of selenium (Se) varies strongly around the world, and many people are at risk of inadequate supply and health risks from Se deficiency. Within the human organism, efficient transport mechanisms ensure that organs with a high demand and relevance for reproduction and survival are preferentially supplied. To this end, selenoprotein P (SELENOP) is synthesized in the liver and mediates Se transport to essential tissues such as the endocrine glands and the brain, where the "SELENOP cycle" maintains a privileged Se status. Mouse models indicate that SELENOP is not essential for life, as supplemental Se supply was capable of preventing the development of severe symptoms. However, knockout mice died under limiting supply, arguing for an essential role of SELENOP in Se deficiency. Many clinical studies support this notion, pointing to close links between health risks and low SELENOP levels. Accordingly, circulating SELENOP concentrations serve as a functional biomarker of Se supply, at least until a saturated status is achieved and SELENOP levels reach a plateau. Upon toxic intake, a further increase in SELENOP is observed, i.e., SELENOP provides information about possible selenosis. The SELENOP transcripts predict an insertion of ten selenocysteine residues. However, the decoding is imperfect, and not all these positions are ultimately occupied by selenocysteine. In addition to the selenocysteine residues near the C-terminus, one selenocysteine resides central within an enzyme-like environment. SELENOP proved capable of catalyzing peroxide degradation in vitro and protecting e.g. LDL particles from oxidation. An enzymatic activity in the intact organism is unclear, but an increasing number of clinical studies provides evidence for a direct involvement of SELENOP-dependent Se transport as an important and modifiable risk factor of disease. This interaction is particularly strong for cardiovascular and critical disease including COVID-19, cancer at various sites and autoimmune thyroiditis. This review briefly highlights the links between the growing knowledge of Se in health and disease over the last 50 years and the specific advances that have been made in our understanding of the physiological and clinical contribution of SELENOP to the current picture.

Delayed increase of plasma selenoproteins and absence of side effect induced by infusion of pharmacological dose of sodium selenite in septic shock: Secondary analysis of a multicenter, randomized controlled trial

BACKGROUND

In sepsis, neutrophil respiratory bursts participate in endothelium damage, the first step to multiple organ failure. In plasma two antioxidant selenoenzymes, which protect the endothelium, decrease: selenoprotein-P, and to a lesser extent glutathione peroxidase (GPX3). Sodium selenite (Na₂SeO₃) is a Se donor, but also an oxidant chemotherapy drug depending on its concentration. In a previous published study, Na₂SeO₃ continuous infusion in septic shock patients at a pharmacological dose of 4 mg¹ Se/day on day-1, followed by a high nutritional dose of 1 mg Se/day during 9 days, showed no beneficial effect on weaning of catecholamine nor on survival. In this ancillary study, we report clinical and biological effects of such continuous infusion of Na₂SeO_3. METHODS: This was a multicenter, placebo-controlled, double-blind study on 60 patients. Na₂SeO₃ or placebo in continuous infusion as described above. Evolution with time of plasma Se, selenoprotein-P, GPX3, Organ dysfunction (sequential organ failure assessment SOFA scores, including PaO2/FiO2, for respiratory failure, and plasma lactate) and quality of life at 6 months (by SF36 scores) were analyzed using two-way (time, treatment) non-parametric repeated-measures analysis of variance (Friedman test).

MAIN RESULTS

At baseline, plasma Se was about a quarter of reference values. From baseline to day-4 plasma Se, selenoprotein-P and GPX3 significantly increased by 3.9, 2.7 and 1.8 respectively in the Na₂SeO₃ group as compared with placebo and remained elevated by 2.3, 2.7 and 2.1 at day-14 respectively (p < 0.001). Na₂SeO₃ did not affect global and organ by organ SOFA Scores and plasma lactate concentration at day-1 and later up to day-14. The evolution of PaO2/FiO2 until day-14 was similar in the two groups. Quality of life in the surviving patients at 6 months was similar between the two groups.

CONCLUSION

Continuous infusion of Na₂SeO₃ at 4 mg Se at day-1 seems to have neither beneficial nor toxic effect at day-1 or later and induces a late increase of selenoprotein-P at day-4. Preclinical studies are required to confirm the use of Na₂SeO₃ as a cytotoxic drug against neutrophils and protection of the endothelium by selenoprotein-P.

Thioredoxin reductase selenoproteins from different organisms as potential drug targets for treatment of human diseases

Human thioredoxin reductase (TrxR) is a selenoprotein with a central role in cellular redox homeostasis, utilizing a highly reactive and solvent-exposed selenocysteine (Sec) residue in its active site. Pharmacological modulation of TrxR can be obtained with several classes of small compounds showing different mechanisms of action, but most often dependent upon interactions with its Sec residue. The clinical implications of TrxR modulation as mediated by small compounds have been studied in diverse diseases, from rheumatoid arthritis and ischemia to cancer and parasitic infections. The possible involvement of TrxR in these diseases was in some cases serendipitously discovered, by finding that existing clinically used drugs are also TrxR inhibitors. Inhibiting isoforms of human TrxR is, however, not the only strategy for human disease treatment, as some pathogenic parasites also depend upon Sec-containing TrxR variants, including S. mansoni, B. malayi or O. volvulus. Inhibiting parasite TrxR has been shown to selectively kill parasites and can thus become a promising treatment strategy, especially in the context of quickly emerging resistance towards other drugs. Here we have summarized the basis for the targeting of selenoprotein TrxR variants with small molecules for therapeutic purposes in different human disease contexts. We discuss how Sec engagement appears to be an indispensable part of treatment efficacy and how some therapeutically promising compounds have been evaluated in preclinical or clinical studies. Several research questions remain before a wider application of selenoprotein TrxR inhibition as a first-line treatment strategy might be developed. These include further mechanistic studies of downstream effects that may mediate treatment efficacy, identification of isoform-specific enzyme inhibition patterns for some given therapeutic compounds, and the further elucidation of cell-specific effects in disease contexts such as in the tumor microenvironment or in host-parasite interactions, and which of these effects may be dependent upon the specific targeting of Sec in distinct TrxR isoforms.

Drug-induced tumor-specific cytotoxicity in a whole tissue ex vivo model of human pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer. PDAC has a dismal prognosis and an inherent resistance to cytostatic drugs. The lack of reliable experimental models is a severe limitation for drug development targeting PDAC. We have employed a whole tissue ex vivo culture model to explore the effect of redox-modulation by sodium selenite on the viability and growth of PDAC. Drug-resistant tumors are more vulnerable to redox-active selenium compounds because of high metabolic activity and redox imbalance. Sodium selenite efficiently and specifically reduced PDAC cell viability (p <0.02) (n=8) and decreased viable de novo tumor cell outgrowth (p<0.05) while preserving non-neoplastic tissues. Major cellular responses (damaged tumor cells > 90%, tumor regression grades III-IV according to Evans) were observed for sodium selenite concentrations between 15-30 µM. Moreover, selenium levels used in this study were significantly below the previously reported maximum tolerated dose for humans. Transcriptome data analysis revealed decreased expression of genes known to drive PDAC growth and metastatic potential (CEMIP, DDR2, PLOD2, P4HA1) while the cell death-inducing genes (ATF3, ACHE) were significantly upregulated (p<0.0001). In conclusion, we report that sodium selenite has an extraordinary efficacy and specificity against drug-resistant pancreatic cancer in an organotypic slice culture model. Our ex vivo organotypic tissue slice culture model can be used to test a variety of drug candidates for swift and reliable drug responses to individual PDAC cases.

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.

Effect of Selenium on the Iron Homeostasis and Oxidative Damage in Brain and Liver of Mice

Selenium is an essential trace element that maintains normal brain function, mainly due its antioxidant properties. Although the amount of Se in the body is tightly regulated by the liver, both an excess of and deficiency in Se can modulate the cellular redox status and affect the homeostasis of other essential elements for both humans and animals. The aim of this study was to determine the effect of inorganic selenium excess on oxidative stress and iron homeostasis in brain and liver of laboratory BALB/c mice, which were supplemented with Na₂SeO₃ solution (0.2 mg and 0.4 mg Se/kg body weight) for 8 weeks. The content of the lipid peroxidation product malondialdehyde and antioxidant enzyme catalase activity/gene expression were used as markers of oxidative damage and were evaluated by spectrophotometric assays. Selenium and iron concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). Catalase gene expression was analyzed by qRT-PCR and ΔΔCt methods. Our results showed that doses of 0.2 mg Se and 0.4 mg Se caused a relatively low accumulation of Se in the brain of mice; however, it induced a 10-fold increase in its accumulation in the liver and also increased iron accumulation in both tested organs. Both doses of Se increased the content of malondialdehyde as well as decreased catalase activity in the liver, while the 0.4 mg Se dose has also activated catalase gene expression. Brain of mice exposed to 0.2 mg Se showed reduced lipid peroxidation; however, the exposure to 0.4 mg of Se increased the catalase activity as well as gene expression. One may conclude that exposure to both doses of Se caused the accumulation of this micronutrient in mice brain and liver and have also provided a disrupting effect on the levels of iron. Both doses of Se have triggered oxidative liver damage. In the brain, the effect of Se was dose dependent, where −0.2 mg of Se provided antioxidant activity, which was observed through a decrease in lipid peroxidation. On the contrary, the 0.4 mg dose increased brain catalase activity as well as gene expression, which may have contributed to maintaining brain lipid peroxidation at the control level.

Soluble PD-L1 Expression After Intravenous Treatment of Cancer Patients With Selenite in Phase I Clinical Trial

A high expression level of programmed death-ligand 1 (PD-L1) is observed in different types of cancers (particularly lung cancer). Soluble (s)PD-L1 may be used as a prognostic marker and a target for anti-cancer immunity, as well as, predicting gene therapy or systemic immunotherapy in blocking the PD-1 and PD-L1 checkpoint. Studies that evaluate the effects of the immune regulator selenium on PD-L1 expression show ambiguous results. Thus, we aimed to analyze sPD-L1 levels in samples from patients who underwent different dosages of selenite treatment in phase I clinical trial. We hypothesized that selenite modulates the sPD-L1 levels in the plasma as a consequence of the suggested mode of action of selenotherapy in cancer patients. In conclusion, our results support the view that selenotherapy does not substantially affect the PD-1/PD-L1 axis judged by sPD-L1 analysis. Furthermore, no significant correlation was observed between the survival and sPD-L1 expression nor sPD-L1 changes. However, due to a dynamic individual sPD-L1 profile and a high variation in survival, we suggest that further studies are needed to identify whether individual patients can be benefited from combinational seleno- and anti-PD-L1 therapy.

Selenium-enriched Polysaccharide: an Effective and Safe Selenium Source of C57 Mice to Improve Growth Performance, Regulate Selenium Deposition, and Promote Antioxidant Capacity

Selenium-enriched polysaccharide (SeEPS) was prepared by reducing Se(IV) to elemental selenium and organic selenium in polysaccharide medium by the obtained Enterobacter cloacae strain Z0206 under aerobic conditions. In the present study, we focused on investigating the role of short-term supplementation of SeEPS at supernutritional doses in the regulation of growth performance, liver damage, antioxidant capacity, and selenium (Se) accumulation in C57 mice. Thirty-two C57 mice were randomly divided into four groups: the control group was gavaged with equal volume of phosphate-buffered saline, while the sodium selenite (Na2SeO3), selenomethionine (SeMet), and SeEPS groups were gavaged with 0.5 mg Se/kg BW of Na2SeO3, SeMet, and selenium-enriched polysaccharide (n = 8), respectively. We examined liver injury indicators, antioxidant capacity in the serum and liver, selenium deposition at different sites, selenoprotein levels, and selenocysteine-synthesizing and degradation-associated gene expression in mouse livers. SeEPS supplementation dramatically increased average daily weight gain but reduced the feed-to-gain ratio (F/G) of mice (P < 0.05). Compared to Na2SeO3 and SeMet supplementation, SeEPS supplementation at supernutritional doses did not cause the liver damage. SeEPS supplementation also markedly enhanced total antioxidant capacity (T-AOC), catalase (CAT), glutathione peroxidase (GSH-PX), and total superoxide dismutase (T-SOD) activities but reduced malondialdehyde (MDA) levels in the liver and serum (P < 0.05), while significantly increasing selenocysteine-synthesizing and degradation-related gene (SEPHS2, SEPSECS, Secisbp, Scly) expression at the mRNA level (P < 0.05), thus upregulating the mRNA levels of selenoproteins (SELENOP, SELENOK) (P < 0.05). We suggest that SeEPS could be a potential replacement for inorganic selenium to improve animals' growth performance, promote antioxidant capacity, and regulate selenium deposition.

Glucose Limitation Sensitizes Cancer Cells to Selenite-Induced Cytotoxicity via SLC7A11-Mediated Redox Collapse

Simple Summary

Selenite, a representative inorganic form of selenium, is preferentially accumulated in tumors. The therapeutic potential of sodium selenite in tumors has received significant attention. However, the effect of sodium selenite in the treatment of established tumors is hampered by its systemic toxicities. In this study, we found selenite exerted a stronger lethality to the cancer cells under the condition of glucose limitation in vitro and an enhanced inhibitory effect on tumor growth when combined with intermittent fasting in vivo. In addition, this treatment showed no obvious toxicity to normal cells and mice. The findings of the present study provide an effective and practical approach for increasing the therapeutic window of selenite and imply that combination of selenite and fasting holds promising potential to be developed a clinically useful regimen for treating certain types of cancer.

Abstract

Combination of intermittent fasting and chemotherapy has been drawn an increasing attention because of the encouraging efficacy. In this study, we evaluated the anti-cancer effect of combination of glucose limitation and selenite (Se), a representative inorganic form of selenium, that is preferentially accumulated in tumors. Results showed that cytotoxic effect of selenite on cancer cells, but not on normal cells, was significantly enhanced in response to the combination of selenite and glucose limitation. Furthermore, in vivo therapeutic efficacy of combining selenite with fasting was dramatically improved in xenograft models of lung and colon cancer. Mechanistically, we found that SLC7A11 expression in cancer cells was up-regulated by selenite both in vitro and in vivo. The elevated SLC7A11 led to cystine accumulation, NADPH depletion and the conversion of cystine to cysteine inhibition, which in turn boosted selenite-mediated reactive oxygen species (ROS), followed by enhancement of selenite-mediated cytotoxic effect. The findings of the present study provide an effective and practical approach for increasing the therapeutic window of selenite and imply that combination of selenite and fasting holds promising potential to be developed a clinically useful regimen for treating certain types of cancer.

High dose supplementation of selenium in left ventricular assist device implant surgery - a double-blinded, randomized controlled, pilot trial

BACKGROUND

Systemic inflammation and oxidative stress remain the main cause of complications in heart failure patients receiving a left ventricular assist device (LVAD). Selenoproteins are a cornerstone of antioxidant defense mechanisms for improving inflammatory conditions.

METHODS

We conducted a monocentric double-blinded, randomized pilot trial. Patients scheduled for LVAD implantation were randomized to receive 300μg of selenium the evening before surgery orally, followed by high-dose intravenous selenium supplementation (3000μg after anesthesia induction, 1000 μg upon intensive care unit (ICU) admission, and 1000μg daily at ICU for a maximum of 14 days), or placebo. The main outcomes of this pilot study were feasibility and effectiveness in restoring serum selenium concentrations.

RESULTS

20 out of 21 randomized patients were included in the analysis. The average recruitment rate was 1.5 patients/month (0-3). The average duration of study intervention was 12.6 days (7-14) with a 97.7% dose compliance. No patient received open-label selenium. The supplementation strategy was effective in compensating low serum selenium concentration (before surgery: control: 63.5±11.9μg/L vs. intervention: 65.8±16.5μg/L, ICU admission: control: 49.0±9.8μg/L vs. intervention: 144.2±45.4μg/L). Comparing to the control group, the serum selenium concentrations in the intervention group were significantly higher during the observation period (baseline: mean of placebo (MoP):63.1 vs. mean of selenium (MoS):64.0; ICU admission: MoP:49.0 vs. MoS:144.6; day 1:MoP:44.9 vs. MoS: 102.4; day 3: MoP:43.6 vs. MoS:100.4; day 5: MoP:48.5 vs. MoS:114.7; day 7: MoP:44.4 vs.MoS:118.3; day 13:MoP:48.0 vs. MoS:131.0).

CONCLUSIONS

Selenium supplementation in patients receiving LVAD-implantation is feasible and effective to compensate a selenium deficiency. This article is protected by copyright. All rights reserved.

Antitumor Effects of Selenium

Functions of selenium are diverse as antioxidant, anti-inflammation, increased immunity, reduced cancer incidence, blocking tumor invasion and metastasis, and further clinical application as treatment with radiation and chemotherapy. These functions of selenium are mostly related to oxidation and reduction mechanisms of selenium metabolites. Hydrogen selenide from selenite, and methylselenol (MSeH) from Se-methylselenocyteine (MSeC) and methylseleninicacid (MSeA) are the most reactive metabolites produced reactive oxygen species (ROS); furthermore, these metabolites may involve in oxidizing sulfhydryl groups, including glutathione. Selenite also reacted with glutathione and produces hydrogen selenide via selenodiglutathione (SeDG), which induces cytotoxicity as cell apoptosis, ROS production, DNA damage, and adenosine-methionine methylation in the cellular nucleus. However, a more pronounced effect was shown in the subsequent treatment of sodium selenite with chemotherapy and radiation therapy. High doses of sodium selenite were effective to increase radiation therapy and chemotherapy, and further to reduce radiation side effects and drug resistance. In our study, advanced cancer patients can tolerate until 5000 μg of sodium selenite in combination with radiation and chemotherapy since the half-life of sodium selenite may be relatively short, and, further, selenium may accumulates more in cancer cells than that of normal cells, which may be toxic to the cancer cells. Further clinical studies of high amount sodium selenite are required to treat advanced cancer patients.

Supplemental Dietary Selenohomolanthionine Improve Antioxidant Activity and Immune Function in Weaned Beagle Puppies

The purpose of this study was to investigate the effects of dietary Selenohomolanthionine (SeHLan) on antioxidant status and immune response in canine parvovirus (CPV) vaccinated puppies. In this study, 30 weaned puppies were randomly divided into six groups: control group (–Se/–Vacc), immunization group (–Se/+Vacc), supplementation of sodium selenite group (SS/+Vacc, 0.35 mg/kg DM), low-dose SeHLan group (SeHLan-L/+Vacc, 0.35 mg/kg DM), mid-dose SeHLan group (SeHLan-M/+Vacc, 1.0 mg/kg DM), and high-dose SeHLan group (SeHLan-H/+Vacc, 2.0 mg/kg DM). The puppies were fed for 42 days and vaccinated with Vanguard Plus 5 on day 0 and day 21. Blood samples were collected on 7, 14, 21, 28, 35, 42 days post-immunization (PI) for determination of antioxidant indicators, lymphocyte proliferation index, serum cytokine concentration (IL-2, IL-4), canine polymorphonuclear neutrophils (PMN) phagocytic function, and the level of CPV antibody titers. The results showed that SeHLan supplementation raised the serum Se concentration and glutathione peroxidase (GSH-Px) activity in a dose-dependent manner (P < 0.05). It also increased the activity of serum superoxide dismutase (SOD) and decreased serum malondialdehyde (MDA) content, especially in SeHLan-M/+Vacc group (1.0 mg/kg DM) (P < 0.01). SeHLan supplementation significantly increased lymphocyte proliferation, IL-2, and IL-4 levels in canine serum, and enhanced phagocytosis of PMN in vaccinated puppies (P < 0.05). Moreover, SeHLan supplementation shortened the CPV antibody production time and increased the CPV antibody titers (P < 0.05). Of note, the beneficial effects of SeHLan were superior to those of SS. In conclusion, dietary SeHLan supplementation improved antioxidant activity, increased CPV antibody titers, and enhanced immune function in puppies after weaning. An appropriate dosage of SeHLan (1~2 mg/kg DM) may confer nutritional benefits in puppies.

Preclinical Evaluation of Sodium Selenite in Mice: Toxicological and Tumor Regression Studies after Striatum Implantation of Human Glioblastoma Stem Cells

Glioblastoma (GBM) is the most aggressive malignant glioma, with a very poor prognosis; as such, efforts to explore new treatments and GBM’s etiology are a priority. We previously described human GBM cells (R2J-GS) as exhibiting the properties of cancer stem cells (growing in serum-free medium and proliferating into nude mice when orthotopically grafted). Sodium selenite (SS)—an in vitro attractive agent for cancer therapy against GBM—was evaluated in R2J-GS cells. To go further, we launched a preclinical study: SS was given orally, in an escalation-dose study (2.25 to 10.125 mg/kg/day, 5 days on, 2 days off, and 5 days on), to evaluate (1) the absorption of selenium in plasma and organs (brain, kidney, liver, and lung) and (2) the SS toxicity. A 6.75 mg/kg SS dose was chosen to perform a tumor regression assay, followed by MRI, in R2J-GS cells orthotopically implanted in nude mice, as this dose was nontoxic and increased brain selenium concentration. A group receiving TMZ (5 mg/kg) was led in parallel. Although not reaching statistical significance, the group of mice treated with SS showed a slower tumor growth vs. the control group (p = 0.08). No difference was observed between the TMZ and control groups. We provide new insights of the mechanisms of SS and its possible use in chemotherapy.

Selenium stimulates the antitumour immunity: Insights to future research

Selenium is an essential trace element for regulating immune functions through redox-regulating activity of selenoproteins (e.g. glutathione peroxidase), protecting immune cells from oxidative stress. However, in cancer, selenium has biological bimodal action depending on the concentration. At nutritional low doses, selenium, depending on its form, may act as an antioxidant, protecting against oxidative stress, supporting cell survival and growth, thus, plays a chemo-preventive role; while, at supra-nutritional higher pharmacological doses, selenium acts as pro-oxidant inducing redox signalling and cell death. To date, many studies have been conducted on the benefits of selenium intake in reducing the risk of cancer incidence at the nutritional level, indicating that likely selenium functions as an immunostimulator, i.e. reversing the immunosuppression in tumour microenvironment towards antitumour immunity by activating immune cells (e.g. M₁ macrophages and CD8⁺ T-lymphocytes) and releasing pro-inflammatory cytokines such as interferon-gamma; whereas, fewer studies have explored the effects of supra-nutritional or pharmacological doses of selenium in cancer immunity. This review, thus, systematically analyses the current knowledge about how selenium stimulates the immune system against cancer and lay the groundwork for future research. Such knowledge can be promising to design combinatorial therapies with Selenium-based compounds and other modalities like immunotherapy to lower the adverse effects and increase the efficacy of treatments.

Selenium Deficiency Due to Diet, Pregnancy, Severe Illness, or COVID-19-A Preventable Trigger for Autoimmune Disease

The trace element selenium (Se) is an essential part of the human diet; moreover, increased health risks have been observed with Se deficiency. A sufficiently high Se status is a prerequisite for adequate immune response, and preventable endemic diseases are known from areas with Se deficiency. Biomarkers of Se status decline strongly in pregnancy, severe illness, or COVID-19, reaching critically low concentrations. Notably, these conditions are associated with an increased risk for autoimmune disease (AID). Positive effects on the immune system are observed with Se supplementation in pregnancy, autoimmune thyroid disease, and recovery from severe illness. However, some studies reported null results; the database is small, and randomized trials are sparse. The current need for research on the link between AID and Se deficiency is particularly obvious for rheumatoid arthritis and type 1 diabetes mellitus. Despite these gaps in knowledge, it seems timely to realize that severe Se deficiency may trigger AID in susceptible subjects. Improved dietary choices or supplemental Se are efficient ways to avoid severe Se deficiency, thereby decreasing AID risk and improving disease course. A personalized approach is needed in clinics and during therapy, while population-wide measures should be considered for areas with habitual low Se intake. Finland has been adding Se to its food chain for more than 35 years-a wise and commendable decision, according to today's knowledge. It is unfortunate that the health risks of Se deficiency are often neglected, while possible side effects of Se supplementation are exaggerated, leading to disregard for this safe and promising preventive and adjuvant treatment options. This is especially true in the follow-up situations of pregnancy, severe illness, or COVID-19, where massive Se deficiencies have developed and are associated with AID risk, long-lasting health impairments, and slow recovery.

The Antitumor Activity of Sodium Selenite Alone and in Combination with Gemcitabine in Pancreatic Cancer: An In Vitro and In Vivo Study

Sodium selenite acts by depleting enzymes that protect against cellular oxidative stress. To determine its effect alone or in combination with gemcitabine (GMZ) in pancreatic cancer, we used PANC-1 and Pan02 cell lines and C57BL mice bearing a Pan02-generated tumor. Our results demonstrated a significant inhibition of pancreatic cancer cell viability with the use of sodium selenite alone and a synergistic effect when associated with GMZ. The molecular mechanisms of the antitumor effect of sodium selenite alone involved apoptosis-inducing factor (AIF) and the expression of phospho-p38 in the combined therapy. In addition, sodium selenite alone and in association with GMZ significantly decreased the migration capacity and colony-forming ability, reduced tumor activity in multicellular tumor spheroids (MTS) and decreased sphere formation of cancer stem cells. In vivo studies demonstrated that combined therapy not only inhibited tumor growth (65%) compared to the untreated group but also relative to sodium selenite or GMZ used as monotherapy (up to 40%), increasing mice survival. These results were supported by the analysis of C57BL/6 albino mice bearing a Pan02-generated tumor, using the IVIS system. In conclusion, our results showed that sodium selenite is a potential agent for the improvement in the treatment of pancreatic cancer and should be considered for future human clinical trials.

Selenite Induces Cell Cycle Arrest and Apoptosis via Reactive Oxygen Species-Dependent Inhibition of the AKT/mTOR Pathway in Thyroid Cancer

Thyroid cancer is the most common endocrine malignancy, and its incidence has increased in the past decades. Selenium has been shown to have therapeutic effects against several tumors. However, its role in thyroid cancer and its underlying molecular mechanism remains to be explored. In the present study, we demonstrated that sodium selenite significantly decreased cell viability and induced G0/G1 cell cycle arrest and apoptosis in thyroid cancer cells in a dose-dependent manner. Transcriptomics revealed that sodium selenite induced intracellular reactive oxygen species (ROS) by promoting oxidative phosphorylation. Increased intracellular ROS levels inhibited the AKT/mTOR signaling pathway and upregulated EIF4EBP3. Intracellular ROS inhibition by N-acetylcysteine (NAC) ameliorated the cellular effects of sodium selenite. The in vitro findings were reproduced in xenograft thyroid tumor models. Our data demonstrated that sodium selenite exhibits strong anticancer effects against thyroid cancer cells, which involved ROS-mediated inhibition of the AKT/mTOR pathway. This suggests that sodium selenite may serve as a therapeutic option for advanced thyroid cancer.

Clinical Pharmacokinetics of Oral Sodium Selenite and Dosing Implications in the Treatment of Patients with Metastatic Cancer

Background

Selenite is a radiosensitizer and inhibitor of androgen receptor expression and function. In a phase I study (NCT02184533) in 15 subjects with metastatic cancer receiving daily oral sodium selenite with palliative radiation therapy, disease stabilization was observed, as evidenced by tumor regression, marked reduction in pain symptoms, and decreased prostate-specific antigen levels (only patients with castrate-resistant prostate cancer).

Objective

The aim of this work was to characterize the pharmacokinetics of selenite to suggest dosing strategies and to propose a study design for further investigation.

Methods

With selenium plasma concentrations obtained from five dosing cohorts (5.5, 11, 16.5, 33, and 49.5 mg), a population pharmacokinetic model was constructed using NONMEM. The model described externally administered selenite (inorganic) with a baseline component for endogenous selenium levels. Using the pharmacokinetic model, simulations were performed to suggest dosing regimens that achieved in vitro target selenite levels, and optimal pharmacokinetic sampling times for a subsequent study were proposed using PopED.

Results

A one-compartment model characterized selenite pharmacokinetics. Parameter estimates were absorption rate constant (0.64 h⁻¹), apparent clearance (1.58 L/h), apparent volume of distribution (42.3 L), and baseline selenium amount (5270 μg). A logarithmic function characterized the inverse relationship between dose level and bioavailability. Four regimens to reach in vitro target selenite levels were proposed: 33 mg daily, 16.5 mg twice daily (BID), 11 mg BID, and 5.5 mg thrice daily (TID). Optimal sampling times were 1, 2, 6, and 24 h.

Discussion

The population model described the pharmacokinetic data well. Three regimens (33 mg daily, 11 mg BID, 5.5 mg TID) achieved in vitro target selenite levels after one dose. The model and optimal sampling times may inform future studies evaluating the efficacy of selenite for metastatic cancer treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40268-021-00340-9.

Toxicology and pharmacology of synthetic organoselenium compounds: an update

Here, we addressed the pharmacology and toxicology of synthetic organoselenium compounds and some naturally occurring organoselenium amino acids. The use of selenium as a tool in organic synthesis and as a pharmacological agent goes back to the middle of the nineteenth and the beginning of the twentieth centuries. The rediscovery of ebselen and its investigation in clinical trials have motivated the search for new organoselenium molecules with pharmacological properties. Although ebselen and diselenides have some overlapping pharmacological properties, their molecular targets are not identical. However, they have similar anti-inflammatory and antioxidant activities, possibly, via activation of transcription factors, regulating the expression of antioxidant genes. In short, our knowledge about the pharmacological properties of simple organoselenium compounds is still elusive. However, contrary to our early expectations that they could imitate selenoproteins, organoselenium compounds seem to have non-specific modulatory activation of antioxidant pathways and specific inhibitory effects in some thiol-containing proteins. The thiol-oxidizing properties of organoselenium compounds are considered the molecular basis of their chronic toxicity; however, the acute use of organoselenium compounds as inhibitors of specific thiol-containing enzymes can be of therapeutic significance. In summary, the outcomes of the clinical trials of ebselen as a mimetic of lithium or as an inhibitor of SARS-CoV-2 proteases will be important to the field of organoselenium synthesis. The development of computational techniques that could predict rational modifications in the structure of organoselenium compounds to increase their specificity is required to construct a library of thiol-modifying agents with selectivity toward specific target proteins.

Selenite Inhibits Notch Signaling in Cells and Mice

Selenium is an essential micronutrient with a wide range of biological effects in mammals. The inorganic form of selenium, selenite, is supplemented to relieve individuals with selenium deficiency and to alleviate associated symptoms. Additionally, physiological and supranutritional selenite have shown selectively higher affinity and toxicity towards cancer cells, highlighting their potential to serve as chemotherapeutic agents or adjuvants. At varying doses, selenite extensively regulates cellular signaling and modulates many cellular processes. In this study, we report the identification of Delta–Notch signaling as a previously uncharacterized selenite inhibited target. Our transcriptomic results in selenite treated primary mouse hepatocytes revealed that the transcription of Notch1, Notch2, Hes1, Maml1, Furin and c-Myc were all decreased following selenite treatment. We further showed that selenite can inhibit Notch1 expression in cultured MCF7 breast adenocarcinoma cells and HEPG2 liver carcinoma cells. In mice acutely treated with 2.5 mg/kg selenite via intraperitoneal injection, we found that Notch1 expression was drastically lowered in liver and kidney tissues by 90% and 70%, respectively. Combined, these results support selenite as a novel inhibitor of Notch signaling, and a plausible mechanism of inhibition has been proposed. This discovery highlights the potential value of selenite applied in a pathological context where Notch is a key drug target in diseases such as cancer, fibrosis, and neurodegenerative disorders.

Serum Selenium Status as a Diagnostic Marker for the Prognosis of Liver Transplantation

The trace element selenium (Se) is taken up from the diet and is metabolized mainly by hepatocytes. Selenoprotein P (SELENOP) constitutes the liver-derived Se transporter. Biosynthesis of extracellular glutathione peroxidase (GPx3) in kidney depends on SELENOP-mediated Se supply. We hypothesized that peri-operative Se status may serve as a useful prognostic marker for the outcome in patients undergoing liver transplantation due to hepatocellular carcinoma. Serum samples from liver cancer patients were routinely collected before and after transplantation. Concentrations of serum SELENOP and total Se as well as GPx3 activity were determined by standardized tests and related to survival, etiology of cirrhosis/carcinoma, preoperative neutrophiles, lymphocytes, thyrotropin (TSH) and Child-Pugh and Model for End-Stage Liver Disease (MELD) scores. A total of 221 serum samples from 79 transplanted patients were available for analysis. The Se and SELENOP concentrations were on average below the reference ranges of healthy subjects. Patients with ethanol toxicity-dependent etiology showed particularly low SELENOP and Se concentrations and GPx3 activity. Longitudinal analysis indicated declining Se concentrations in non-survivors. We conclude that severe liver disease necessitating organ replacement is characterized by a pronounced Se deficit before, during and after transplantation. A recovering Se status after surgery is associated with positive prognosis, and an adjuvant Se supplementation may, thus, support convalescence.

Regulation of Selenium/Sulfur Interactions to Enhance Chemopreventive Effects: Lessons to Learn from Brassicaceae

Selenium (Se) is an essential trace element, which represents an integral part of glutathione peroxidase and other selenoproteins involved in the protection of cells against oxidative damage. Selenomethionine (SeMet), selenocysteine (SeCys), and methylselenocysteine (MeSeCys) are the forms of Se that occur in living systems. Se-containing compounds have been found to reduce carcinogenesis of animal models, and dietary supplemental Se might decrease cancer risk. Se is mainly taken up by plant roots in the form of selenate via high-affinity sulfate transporters. Consequently, owing to the chemical similarity between Se and sulfur (S), the availability of S plays a key role in Se accumulation owing to competition effects in absorption, translocation, and assimilation. Moreover, naturally occurring S-containing compounds have proven to exhibit anticancer potential, in addition to other bioactivities. Therefore, it is important to understand the interaction between Se and S, which depends on Se/S ratio in the plant or/and in the growth medium. Brassicaceae (also known as cabbage or mustard family) is an important family of flowering plants that are grown worldwide and have a vital role in agriculture and populations’ health. In this review we discuss the distribution and further interactions between S and Se in Brassicaceae and provide several examples of Se or Se/S biofortifications’ experiments in brassica vegetables that induced the chemopreventive effects of these crops by enhancing the production of Se- or/and S-containing natural compounds. Extensive further research is required to understand Se/S uptake, translocation, and assimilation and to investigate their potential role in producing anticancer drugs.

Superoxide-mediated ferroptosis in human cancer cells induced by sodium selenite

Ferroptosis is a novel form of programmed cell death characterized by an iron-dependent increase in reactive oxygen species (ROS). However, the role of ROS in the regulation of ferroptosis remains elusive. In this study, for the first time, we demonstrate that sodium selenite (SS), a well-established redox-active selenium compound, is a novel inducer of ferroptosis in a variety of human cancer cells. Potent ferroptosis inhibitors, such as ferrostatin-1 (Fer-1) and deferoxamine (DFO), rescue cells from SS-induced ferroptosis. Furthermore, SS down-regulates ferroptosis regulators; solute carrier family 7 member 11 (SLC7A11), glutathione (GSH), and glutathione peroxidase 4 (GPx4), while it up-regulates iron accumulation and lipid peroxidation (LPO). These SS-induced ferroptotic responses are achieved via ROS, in particular superoxide (O₂•⁻) generation. Antioxidants such as superoxide dismutase (SOD) and Tiron not only scavenged O₂•⁻ production, but also markedly rescued SLC7A11 down-regulation, GSH depletion, GPx4 inactivation, iron accumulation, LPO, and ferroptosis. Moreover, iron chelator DFO significantly reduces the O₂•⁻ production, indicating a positive feedback regulation between O₂•⁻ production and iron accumulation. Taken together, we have identified SS as a novel ferroptosis inducing agent in various human cancer models.

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Sodium selenite selectively induces ferroptosis in multiple human cancer cells.

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Sodium selenite inhibits system X_c⁻ function and altered GSH homeostasis.

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Superoxide is the ROS molecule responsible for the sodium selenite-induced ferroptosis.

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Sodium selenite induces iron accumulation via superoxide dependent mechanism.

Pharmacokinetics of Sodium Selenite in Rat Plasma and Tissues After Intragastric Administration

The purpose of this research is to investigate the absorption, distribution, excretion, and pharmacokinetics of selenite in rats after intragastric administration, and thus illustrate the efficiency of selenium (Se) supplementation. After a single gavage of sodium selenite, a concentration of Se in plasma and tissues was determined by inductively coupled plasma mass spectrometry (ICP-MS) at different time points. Through fitting the data with the metabolic kinetic model, the corresponding kinetic parameters were determined for plasma and tissues, including kidney, liver, heart, muscle, and gonad. While the metabolic kinetics of sodium selenite in plasma, liver, and kidney of rats was well reflected by a two-compartment open model, that in heart and gonad was fitted to a one-compartment open model, and that in muscle was fitted to a one-compartment open model with a lag time. The results indicate that sodium selenite was absorbed by plasma and tissues quickly and was eliminated slowly after intragastric administration. Based on the results, we propose that multi-supplementation of Se with low dosage is superior to single supplementation with high dosage, in terms of avoiding selenosis.

The Effect of Methylselenocysteine and Sodium Selenite Treatment on microRNA Expression in Liver Cancer Cell Lines

The unique character of selenium compounds, including sodium selenite and Se-methylselenocysteine (MSC), is that they exert cytotoxic effects on neoplastic cells, providing a great potential for treating cancer cells being highly resistant to cytostatic drugs. However, selenium treatment may affect microRNA (miRNA) expression as the pattern of circulating miRNAs changed in a placebo-controlled selenium supplement study. This necessitates exploring possible changes in the expression profiles of miRNAs. For this, miRNAs being critical for liver function were selected and their expression was measured in hepatocellular carcinoma (HLE and HLF) and cholangiocarcinoma cell lines (TFK-1 and HuH-28) using individual TaqMan MicroRNA Assays following selenite or MSC treatments. For establishing tolerable concentrations, IC₅₀ values were determined by performing SRB proliferation assays. The results revealed much lower IC₅₀ values for selenite (from 2.7 to 11.3 μM) compared to MSC (from 79.5 to 322.6 μM). The treatments resulted in cell line-dependent miRNA expression patterns, with all miRNAs found to show fold change differences; however, only a few of these changes were statistically different in treated cells compared to untreated cells below IC₅₀. Namely, miR-199a in HLF, miR-143 in TFK-1 upon MSC treatment, miR-210 in HLF and TFK-1, miR-22, -24, -122, -143 in HLF upon selenite treatment. Fold change differences revealed that miR-122 with both selenium compounds, miR-199a with MSC and miR-22 with selenite were affected. The miRNAs showing minimal alterations included miR-125b and miR-194. In conclusion, our results revealed moderately altered miRNA expression in the cell lines (less alterations following MSC treatment), being miR-122, -199a the most affected and miR-125b, -194 the least altered miRNAs upon selenium treatment.

Serum selenium in critically ill patients: Profile and supplementation in a depleted region

BACKGROUND

General selenium supplementation to intensive care unit (ICU) patients in regions with selenium-rich soil does not improve outcomes. Still selenium supplementation may reduce morbidity and mortality in patients with low-serum selenium concentration (S-Se) in selenium-poor areas who respond to treatment. The primary aim of this observational study was to investigate S-Se in a selenium-deficient region at time of intensive care admission, and in addition to monitor S-Se during high-dose selenium supplementation for safety.

METHODS

We measured S-Se in 100 consecutive patients admitted to a tertiary general ICU. After initial sampling, high-dose intravenous (iv) selenium supplementation was administered up to 20 days.

RESULTS

At admission, in 95% of the cases, S-Se was below the saturation level for selenoenzymes, in 91%, below the Swedish reference level, and in 71%, below the level where selenoenzyme function may be impaired. At day 5 of substitution, all patients still remaining in the ICU (n = 26) were within the range for enzyme function, 12% were below reference, and 24% did not reach full enzymatic saturation. At day 10 and forward, all patients were within target for treatment. No patients were at risk for toxic S-Se concentration.

CONCLUSIONS

S-Se concentration was substantially lower compared to normal values at ICU admission in this cohort of unselected Swedish critical care patients. Selenium supplementation restituted S-Se to levels corresponding to enzymatic saturation and the Swedish reference interval for all subjects remaining in the ICU on day 5.

Understanding the Redox Biology of Selenium in the Search of Targeted Cancer Therapies

Selenium (Se) is an essential trace nutrient required for optimal human health. It has long been suggested that selenium has anti-cancer properties. However, clinical trials have shown inconclusive results on the potential of Se to prevent cancer. The suggested role of Se in the prevention of cancer is centered around its role as an antioxidant. Recently, the potential of selenium as a drug rather than a supplement has been uncovered. Selenium compounds can generate reactive oxygen species that could enhance the treatment of cancer. Transformed cells have high oxidative distress. As normal cells have a greater capacity to meet oxidative challenges than tumor cells, increasing the flux of oxidants with high dose selenium treatment could result in cancer-specific cell killing. If the availability of Se is limited, supplementation of Se can increase the expression and activities of Se-dependent proteins and enzymes. In cell culture, selenium deficiency is often overlooked. We review the importance of achieving normal selenium biology and how Se deficiency can lead to adverse effects. We examine the vital role of selenium in the prevention and treatment of cancer. Finally, we examine the properties of Se-compounds to better understand how each can be used to address different research questions.

Selenoprotein P as Biomarker of Selenium Status in Clinical Trials with Therapeutic Dosages of Selenite

Selenoprotein P (SELENOP) is an established biomarker of selenium (Se) status. Serum SELENOP becomes saturated with increasing Se intake, reaching maximal concentrations of 5–7 mg SELENOP/L at intakes of ca. 100–150 µg Se/d. A biomarker for higher Se intake is missing. We hypothesized that SELENOP may also reflect Se status in clinical applications of therapeutic dosages of selenite. To this end, blood samples from two supplementation studies employing intravenous application of selenite at dosages >1 mg/d were analyzed. Total Se was quantified by spectroscopy, and SELENOP by a validated ELISA. The high dosage selenite infusions increased SELENOP in parallel to elevated Se concentrations relatively fast to final values partly exceeding 10 mg SELENOP/L. Age or sex were not related to the SELENOP increase. Western blot analyses of SELENOP verified the results obtained by ELISA, and indicated an unchanged pattern of immunoreactive protein isoforms. We conclude that the saturation of SELENOP concentrations observed in prior studies with moderate Se dosages (<400 µg/d) may reflect an intermediate plateau of expression, rather than an absolute upper limit. Circulating SELENOP seems to be a suitable biomarker for therapeutic applications of selenite exceeding the recommended upper intake levels. Whether SELENOP is also capable of reflecting other supplemental selenocompounds in high dosage therapeutic applications remains to be investigated.

The other view: the trace element selenium as a micronutrient in thyroid disease, diabetes, and beyond

Antibiotics are provided for infections caused by bacteria, and statins help to control hypercholesterolemia. When hungry, you need to eat, and when you are deficient in a particular nutrient, the diet should be chosen wisely to provide what is missing. In the matter of providing the essential trace element selenium (Se), there are two different but partly overlapping views on its nature and requirements. Some consider it a medication that should be given to a subset of more or less well-defined (thyroid) patients only, in order to alleviate symptoms, to improve the course of the disease or even to provide a cure, alone or in an adjuvant mode. Such treatment attempts are conducted for a short time period, and potential medical benefits and side effects are evaluated thoroughly. One could also approach Se in medicine in a more holistic way and evaluate primarily the nutritional status of the patient before considering supplementation. The available evidence for positive health effects of supplemental Se can be interpreted as the consequence of correcting deficiency instead of speculating on a direct pharmaceutical action. This short review provides a novel view on Se in (thyroid) disease and beyond and offers an alternative explanation for its positive health effects, i.e., its provision of the substrate needed for allowing adequate endogenous expression of those selenoproteins that are required in certain conditions. In Se deficiency, the lack of the trace element constitutes the main limitation for the required adaptation of selenoprotein expression to counteract health risks and alleviate disease symptoms. Supplemental Se lifts this restriction and enables the full endogenous response of selenoprotein expression. However, since Se does not act as a pharmacological medication per se, it should not be viewed as a dangerous drug, and, importantly, current data show that supplemental Se does not cause diabetes.

Investigating the Potential of Conjugated Selenium Redox Folic Acid as a Treatment for Triple Negative Breast Cancer

Previous studies have demonstrated that redox selenium compounds arrest cancer cell viability in vitro through their pro-oxidative activity by generating superoxide (O₂^•−). Currently, there are no efficacious treatment options for women with Triple Negative Breast Cancer (TNBC). However, the association between the over-expression of the Folate Receptor Alpha (FRA) in TNBC and other cancer cells, has led to the possibility that TNBCs might be treated by targeting the FRA with redox selenium covalent Folic Acid conjugates. The present study reports the synthesis of the redox active vitamer, Selenofolate, generating superoxide. Superoxide (O₂^•−) catalytic generation by Selenofolate was assessed by an in vitro chemiluminescence (CL) assay and by a Dihydroethidium (DHE) in vivo assay. Cytotoxicity of Selenofolate was assessed against the TNBC cell line MDA-MB-468 and an immortalized, mammary epithelial cell line, HME50-5E. Cytotoxicity of Selenofolate was compared to Folic Acid and sodium selenite, in a time and dose dependent manner. Selenofolate and selenite treatments resulted in greater inhibition of MDA-MB-468 cell proliferation than HME50-5E as evaluated by Trypan Blue exclusion, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) metabolic assay and Annexin V apoptosis assays. Folate receptor alpha (FRA) protein expression was assessed by Western blotting, with the experimental results showing that redox active Selenofolate and selenite, but not Folic Acid, was cytotoxic to MDA-MB-468 cells in vitro, suggesting a possible clinical option for treating TNBC and other cancers over-expressing FRA.

Sodium Selenite Accentuates the Therapeutic Effect of Adriamycin Prodrug (PADM) against Gastric Cancer

Selenium has remained a controversial character in cancer research. While its antitumor effects have been widely demonstrated, further evidence is required to establish it as a robust treatment regime. Sodium selenite (SS), an inorganic selenium, reportedly affected the proliferation and redifferentiation of gastric cancer cells, but whether it could act as a complement to conventional chemotherapeutic drugs for combination therapy is uncertain. Herein, SGC-7901 and MGC-803 gastric cancer cells were treated with PADM (Ac-Phe-Lys-PABC-ADM), a prodrug of doxorubicin/adriamycin (ADM), and the combined antitumor effects of the two drugs were evaluated. Characterization after treatment revealed that although PADM exhibited antitumor effects individually by inhibiting the proliferation and migration of gastric cancer cells and inducing apoptosis, the addition of SS significantly amplified these effects. Furthermore, gastric cancer cell apoptosis triggered by the combined treatment of SS and PADM may involve the participation of mitochondrial apoptosis, as evidenced by the changes in mitochondrial morphology and occurrence of mitochondrial fission. Collectively, SS could be a strong complementary drug that accentuates the therapeutic potential of PADM in gastric cancer treatment and management, and its significance could contribute to unique and innovative anticancer strategies.

Extracellular Albumin Covalently Sequesters Selenocompounds and Determines Cytotoxicity

Selenocompounds (SeCs) are well-known nutrients and promising candidates for cancer therapy; however, treatment efficacy is very heterogeneous and the mechanism of action is not fully understood. Several SeCs have been reported to have albumin-binding ability, which is an important factor in determining the treatment efficacy of drugs. In the present investigation, we hypothesized that extracellular albumin might orchestrate SeCs efficacy. Four SeCs representing distinct categories were selected to investigate their cytotoxicity, cellular uptake, and species transformation. Concomitant treatment of albumin greatly decreased cytotoxicity and cellular uptake of SeCs. Using both X-ray absorption spectroscopy and hyphenated mass spectrometry, we confirmed the formation of macromolecular conjugates between SeCs and albumin. Although the conjugate was still internalized, possibly via albumin scavenger receptors expressed on the cell surface, the uptake was strongly inhibited by excess albumin. In summary, the present investigation established the importance of extracellular albumin binding in determining SeCs cytotoxicity. Due to the fact that albumin content is higher in humans and animals than in cell cultures, and varies among many patient categories, our results are believed to have high translational impact and clinical implications.

Nutraceutical Effect of Trace Elements as Additional Injectable Doses to Modulate Oxidant and Antioxidant Status, and Improves the Quality of Lamb Meat

Our study aimed to evaluate whether zinc, copper, selenium, and manganese subcutaneous mineral application (trace elements) reduced mortality, improved performance, and modulated oxidant and antioxidant balance in lamb meat, thereby improving its quality. We divided the 110 newborn Lacaune lambs into two groups: non-treated (control), and treated (application of minerals) with three doses of 0.33 mL/kg of body weight mineral complex on days of life 1, 30, and 60. All animals were weighed on day of life 1, 30, 60, 90, and 150. At the end of the experiment, 12 animals were slaughtered for physical and chemical analysis of meat, oxidant, and antioxidant status, and for allometric analysis. Mineral-application animals had greater live-weight (P < 0.05) on days of life 60 and 90. There was an increase in fat thickness (P = 0.004); pH levels (P = 0.002) were lower in mineral-application animal meat than in that of the control group. Meat was paler (according to lightness (L color)) in the control group (P = 0.04). Weight loss from cooking was greater in control animals (P = 0.004). Shear strength values were lower in the meat of treated lambs (P = 0.008) suggesting that mineral application was associated with increased meat tenderness. In addition, catalase and superoxide dismutase activities were higher (P = 0.01) in mineral-treated animals, associated with a reduction in reactive oxygen species levels (P < 0.01), and lipid peroxidation products (P = 0.02). These data suggest that mineral application modulated oxidant and antioxidant status, reflecting better meat quality.

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 in Cardiac Surgery

Selenium (Se) is an essential trace element that plays a pivotal role in many of the body's regulatory and metabolic functions, especially during times of stress. After uptake, Se is incorporated into several Se-dependent proteins, which have potent anti-inflammatory and antioxidant capacities. Several observational clinical studies have demonstrated that Se deficiency can cause chronic cardiovascular diseases and aggravate organ dysfunction after cardiac surgery and that low levels of Se may be independently associated with the development of organ dysfunction after cardiac surgery. Based on these findings, several studies have investigated the effects of a perioperative Se supplementation strategy. Therefore, the present review describes in depth the pathophysiology and harmful stimuli during cardiac surgery, how Se may counteract these injuries, the different types of Se supplementation strategies that have been evaluated, and current evidence of its clinical significance.

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.

The Cell Culture Medium Affects Growth, Phenotype Expression and the Response to Selenium Cytotoxicity in A549 and HepG2 Cells

Selenium compounds influence cell growth and are highly interesting candidate compounds for cancer chemotherapy. Over decades an extensive number of publications have reported highly efficient growth inhibitory effects with a number of suggested mechanisms f especially for redox-active selenium compounds. However, the studies are difficult to compare due to a high degree of variations in half-maximal inhibitor concentration (IC₅₀) dependent on cultivation conditions and methods to assess cell viability. Among other factors, the variability in culture conditions may affect the experimental outcome. To address this, we have compared the maintenance effects of four commonly used cell culture media on two cell lines, A549 and HepG2, evaluated by the toxic response to selenite and seleno-methylselenocysteine, cell growth and redox homeostasis. We found that the composition of the cell culture media greatly affected cell growth and sensitivity to selenium cytotoxicity. We also provided evidence for change of phenotype in A549 cells when maintained under different culture conditions, demonstrated by changes in cytokeratin 18 (CK18) and vimentin expression. In conclusion, our results have shown the importance of defining the cell culture medium used when comparing results from different studies.