Methylselenic Acid Research Articles

Assessment of Membrane and Electrochemical Technologies for the Treatment of a Selenium-Bearing Mine water: Technology Performance and Effect on Toxicity and Bioaccumulation

Nanofiltration (NF), reverse osmosis (RO), electrodialysis (ED), and electrocoagulation (EC), were all tested at the bench scale for removing selenium (Se) from mine water. All of these technologies reduced the concentration of total Se from 216 µg/L (i.e. 120.1 µg/L of selenate; 59.1 µg/L of selenite, and 0.6 µg/L methyl-selenic acid) in the raw mine water to about 2 µg/L or less in the treated water, equivalent to more than 99% removal. Electrodialysis was found to be the most effective, removing more than 99.5% of the Se. The untreated mine water was toxic to algae. In contrast, RO and NF reduced the toxicity of the mine water, allowing algae to grow between 15,000 to 25,000 cells/mL, while ED and EC did not allow algal growth, likely due to complete removal of essential minerals (ED) or the presence of other contaminants (EC), such as copper. The Se speciation did not change as a result of membrane filtration; however, selenite in the effluent was almost fully transformed to selenate in the brines from the ED and EC treatment processes. The effluent treated by NF and EC generated seleno-cyanate at 0.37 and 1.01 µg/L, respectively. Further testing is recommended at the pilot-scale with the same mine water as well as different mine water.

Antioxidant nutrients can increase high-dose Methotrexate efficacy in 4T1 breast tumor Model: An experimental study on Vitamin E Succinate and Methyl-selenic acid

BackgroundWe aimed to evaluate the anti-cancer and immune system enhancing properties of Vitamin E succinate (VES) and methylselenic acid (MSA) administration on 4T1 breast tumor model under high-dose methotrexate (HDMTX) therapy and folinic acid (FA) rescue. MethodsThirty six 4T1 mammary carcinoma bearing mice were randomly divided into six groups: control (untreated; n = 6), treatment-1 (T1 group; HDMTX; n = 6), T2 (T1 + FA; n = 6), T3 (T2 + MSA; n = 6), T4 (T2 + VES; n = 6) and T5 (T3 + VES; n = 6). On day 21 of the study, all surviving mice were sacrificed and primary tumors and peripheral tissues were examined for histological and gene expression assays. The expression of GATA Binding Protein-3 (GATA3), forkhead box-P3 (FOXP3), T-bet and Retinoic acid receptor-related orphan receptor γt (RORγt) were evaluated in tumors and spleens. Also, vascular endothelial growth factor-A (VEGF-A) and UL16-Binding Protein 1 (ULBP-1) expression were evaluated in tumors. ResultsThe control, T4 and T5 groups were able to complete the entire 21-day study period. Also, significant tumor shrinkage was occurred in T4 group (P < 0.05). Suppression of splenic FOXP3 and GATA3 were observed in the mice receiving T4 and T5 regimens. Also, induction of tumoral FOXP3 and GATA3 were achieved in the T4 and T5 groups, respectively (P < 0.05). No metastasis occurred in T4 receiving group; while, lung and liver metastasis were observed in T5 group. ConclusionIn this study, high and fixed dose of MTX was used. Further studies are needed to optimize MTX dose along with FA, VES and MSA.

Microbiome analysis and predicted relative metabolomic turnover suggest bacterial heme and selenium metabolism are altered in the gastrointestinal system of zebrafish (Danio rerio) exposed to the organochlorine dieldrin.

Dietary exposure to chemicals alters the diversity of microbiome communities and can lead to pathophysiological changes in the gastrointestinal system. The organochlorine pesticide dieldrin is a persistent environmental contaminant that bioaccumulates in fatty tissue of aquatic organisms. The objectives of this study were to determine whether environmentally-relevant doses of dieldrin altered gastrointestinal morphology and the microbiome of zebrafish. Adult zebrafish at ∼4 months of age were fed a measured amount of feed containing either a solvent control or one of two doses of dieldrin (measured at 16, and 163.5ng/g dry weight) for 4 months. Dieldrin body burden levels in zebrafish after four-month exposure were 0 (control), 11.47±1.13ng/g (low dose) and 18.32±1.32ng/g (high dose) wet weight [mean±std]. Extensive histopathology at the whole organism level revealed that dieldrin exposure did not induce notable tissue pathology, including the gastrointestinal tract. A repeated measure mixed model analysis revealed that, while fish gained weight over time, there were no dieldrin-specific effects on body weight. Fecal content was collected from the gastrointestinal tract of males and 16S rRNA gene sequencing conducted. Dieldrin at a measured feed dose of 16ng/g reduced the abundance of Firmicutes, a phylum involved in energy resorption. At the level of class, there was a decrease in abundance of Clostridia and Betaproteobacteria, and an increase in Verrucomicrobiae species. We used a computational approach called predicted relative metabolomic turnover (PRMT) to predict how a shift in microbial community composition affects exchange of metabolites. Dieldrin was predicted to affect metabolic turnover of uroporphyrinogen I and coproporphyrinogen I [enzyme]-cysteine, hydrogen selenide, selenite, and methyl-selenic acid in the fish gastrointestinal system. These pathways are related to bacterial heme biosynthesis and selenium metabolism. Our study demonstrates that dietary exposures to dieldrin can alter microbiota composition over 4 months, however the long-term consequences of such impacts are not well understood.

Expression of ER-resident selenoproteins and activation of cancer cells apoptosis mechanisms under ER-stress conditions caused by methylseleninic acid.

The aim of this work was to study changes in gene expression levels of 7 ER-resident selenoproteins under ER-stress caused by the action of a selenium-containing compound of organic nature, methylselenic acid using three human cancer cell lines DU 145 (prostate carcinoma), MCF 7 (breast adenocarcinoma)and HT-1080 (fibrosarcoma). According to the obtained results, we can speak of a synchronous changes in the expression of SELT and SEP15 mRNA depending on the concentration of MSA for 24h, while the pattern of SELM expression was completely opposite and was radically different from other selenoproteins. It should be noted that in HT-1080 cells, the expression pattern of SELM differed from the expression pattern in two other cancer cells, while the expression patterns of other ER-resident selenoproteins (SELT, SEP15, SELK, SELS, SELN and DIO2) differed slightly depending on the cell line. Also we investigated the molecular mechanisms of UPR caused by MSA-induced ER stress in three cancer cell lines. According to the obtained results, it can be assumed that in DU 145 cells, MSA promotes activation of the PERK signaling pathway of UPR. In fibrosarcoma cells MSA was promoted the activation of ATF-6 UPR signaling pathway. In MCF 7 cells, MSA promoted the activation of two pro-apoptotic UPR signaling pathways at once: IRE1 and ATF-6.The results of this work once again demonstrate that the mechanisms of ER-stress regulation caused by the same agent, in this case, MSA, lead to the activation of different UPR signaling pathways in different cancer cells, and about their relationship.

Instability of urinary excreted methyl-2-acetamido-2-deoxy-1-seleno-β-d-galactopyranoside (selenosugar 1), the main elimination product of human selenium metabolism, and measures for its stabilization

BackgroundThe urinary excreted selenium species selenosugar 1 (SeSug1) plays a key role for monitoring of supplemental selenium exposure, e.g. by occupational exposure. In order to reproduce its contents in the long term, the integrity of SeSug1 in the urine is essential. Studies on the stability of SeSug1 in urine samples stored at −20 °C have shown that degradation of SeSug 1 occurs, requiring adequate countermeasures. MethodsHere, we explored the long-term stability of SeSug1 under usual storage conditions at −20 °C. For this purpose, the simultaneous determination of selenosugar 1 and methylselenic acid (MeSeA) was used to explore the stabilizing of the SeSug1 content by applying sodium azide (NaN3) as a bactericide or/and 5 M ammonium acetate buffer for pH control. ResultsIn untreated urine, conversion of SeSug1 to MeSeA was evident within days. Differences in urine matrices clearly showed different impact, which could be attributed to different buffer strengths by the urine itself. For durability, various concentrations of sodium azide were first applied, followed by pH buffering. A combination of 0.1% NaN3 and pH of 5.5 kept the SeSug1 content stable for over 3 months. ConclusionThe formation of MeSeA as degradation product of SeSug1 could be confirmed. Based on the proportions, an oxidation-based decomposition pathway was proposed. The investigations revealed that the complex interaction of pH buffering and bactericidal activity must be taken into account in order to stabilize SeSug1 in the urine. The main effect was the addition of NaN3. However, the alkaline nature of NaN3 required a sufficient buffering of the urinary matrix at a pH of 5.5.

Determination of eleven small selenium species in human urine by chromatographic-coupled ICP-MS methods

BackgroundThe determination of various selenium species in urine enables a specific biomonitoring of the exposure to different selenium compounds. MethodsFor this task a coupling of three chromatographic techniques with ICP-MS was developed for the separate quantification of eleven species in urine. The first procedure was based on reverse phase chromatography and was designed for the separate determination of methyl-2-acetamido-2-deoxy-1-seleno-b-d-galactopyranoside (SeSug1), methyl-2-acetamido-2-deoxy-1-seleno-b-d-glucopyranoside (SeSug2), selenomethionine (SeMet), methylselenocysteine (MeSeC), seleno-D,L-ethionine (SeEt), methylselenic acid (MeSeA) and methylselenoglutathione (MeSeG); the second procedure was based on anion exchange chromatography and measured selenate (Se (VI)) and selenite (Se (IV)); the third procedure was based on cationic exchange chromatography and determined methyl-2-amino-2-deoxy-1-seleno-b-d-galactopyranoside (SeSug3) and the trimethylselenium ion (TMSe). A fourth method for the more sensitive determination of TMSe was upgraded by an on-line after-column reaction process. ResultsThe validation of the methods yielded sensitive detection limits of the species between 0.03 and 0.10 μg Se/L. For TMSe a detection limit of 0.02 μg Se/L resulted by the fourth method. An intra-day precision of 2.7–10.6% and a relative recovery between 87 % and 108 % confirm the robustness of the methods. ConclusionThe developed procedures enable a separate and sensitive determination of eleven selenium species in urine and thus permit the exploring of metabolic factors in the general population and particularly exposed individuals.

Methylselenol producing selenocompounds enhance the efficiency of mammaglobin-A peptide vaccination against breast cancer cells.

Previous phase I DNA-vaccine based clinical trials using Mammaglobin-A (Mam-A), a human breast tumor associated antigen (TAA), demonstrated that this agent was safe and efficient at treating patients with stage IV breast cancer. The long-term success of cancer vaccines is limited by the diminished expression of human leukocyte antigen (HLA) class I molecules in the tumor microenvironment. The current study assessed the impact of various selenocompounds on the expression of HLA class I molecules in THP-1 cells, an apparent proficient antigen that presents a human monocyte-like cell line, and their eventual activation of MamA2.1 (HLA-A2 immunodominant epitope of Mam-A) specific cytotoxic CD8+ T lymphocytes (CTLs). The results revealed that, following treatment with methylselenol producing compounds [methylselenic acid (MSA) and dimethylselenide (DMDSe)], the expression of HLA class-I was increased and components involved with the antigen presentation machinery of THP-1 cells were upregulated. Furthermore, CTLs activated by MamA2.1 peptide presenting THP-1 cells, pre-treated with MSA and DMDSe, demonstrated an enhanced cytotoxicity in HLA-A2+/Mam-A+ AU565 and UACC-812 breast cancer cell lines when compared with CTLs activated by THP-1 cells without drug treatment. However, no significant cytotoxicity was observed under similar conditions in HLA-A2+/Mam-A- MCF-7 and MDA-MB-231 breast cancer cell lines. The results indicated that treatment with methylselenol producing compounds retained antigen-dependent activation of CD8+ T cells. The data of the current study demonstrated that MSA and DMDSe potentiated effector cytotoxic responses following TAA specific activation of CTLs, indicating their future role as vaccine adjuvants in cancer immunotherapy.

Abstract 4088: Methylselenic acid inhibits the soluble and cell-surface bound NKG2D-ligand ULBP2 in melanoma

Abstract The secretion of the soluble NKG2D-ligand ULBP2 is a marker for poor prognosis in several types of cancer. NKG2D-ligands are normally directed to the cell surface of stressed, inflamed or pre-cancer cells and serve as targets for immune effector cells expressing the NKG2D receptor. The soluble NKG2D-ligands are devastating due to their chronic activation and thereby desensitization of NKG2D expressing immune effector cells. In fact this leads to severely compromised immune activation governing cancer development. The present study describes that methylselenic acid (MSA) is able to inhibit soluble ULBP2 in different primary melanoma cell lines. Moreover, MSA actively suppressed ULBP2 both from constitutively expressing tumors and after induction by HDAC-inhibitors. In the attempt to elucidate the mechanism of inhibition, real-time qPCR experiments were performed. MSA activated the promoter and the transcription of the ULBP2 gene at a level similar to HDAC-inhibitors. These findings strongly indicate that ULBP2 is post-transcriptional regulated. Selective blocking of ULBP2 from melanomas or other cancers that produces soluble immune suppressive ULBP2 is thus a new treatment strategy that also has the potential to be used in combination with existing treatment regimens. Citation Format: Franziska K. Uhlenbrock, Michael Hagemann Jensen, Stephanie Kehlet, Lars Andresen, Søren Skov. Methylselenic acid inhibits the soluble and cell-surface bound NKG2D-ligand ULBP2 in melanoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4088. doi:10.1158/1538-7445.AM2014-4088

The NKG2D ligand ULBP2 is specifically regulated through an invariant chain-dependent endosomal pathway.

Soluble ULBP2 is a marker for poor prognosis in several types of cancer. In this study we demonstrate that both soluble and cell surface-bound ULBP2 is transported via a so far unrecognized endosomal pathway. ULBP2 surface expression, but not MICA/B, could specifically be targeted and retained by affecting endosomal/lysosomal integrity and protein kinase C activity. The invariant chain was further essential for endosomal transport of ULBP2. This novel pathway was identified through screening experiments by which methylselenic acid was found to possess notable NKG2D ligand regulatory properties. The protein kinase C inhibitor methylselenic acid induced MICA/B surface expression but dominantly blocked ULBP2 surface transport. Remarkably, by targeting this novel pathway we could specifically block the production of soluble ULBP2 from different, primary melanomas. Our findings strongly suggest that the endosomal transport pathway constitutes a novel therapeutic target for ULBP2-producing tumors.

Se-methylselenocysteine sensitizes hypoxic tumor cells to irinotecan by targeting hypoxia-inducible factor 1α

Hypoxic tumor cells overexpressing hypoxia-inducible factor 1alpha (HIF-1alpha) are generally resistant to chemo/radiotherapy. We have reported that Se-methylselenocysteine (MSC) therapeutically enhances the efficacy and selectivity of irinotecan against human tumor xenografts. The aim of this study was to delineate the mechanism responsible for the observed efficacy targeting on HIF-1alpha and its transcriptionally regulated genes VEGF and CAIX. We investigated the mechanism of HIF-1alpha inhibition by MSC and its critical role in the therapeutic outcome by generating HIF-1alpha stable knockdown (KD) human head and neck squamous cell carcinoma, FaDu by transfecting HIF-1alpha short hairpin RNA. While cytotoxic efficacy in combination with methylselenic acid (MSA) with SN-38 (active metabolites of MSC and irinotecan) could not be confirmed in vitro against normoxic tumor cells, the hypoxic tumor cells were more sensitive to the combination. Reduction in HIF-1alpha either by MSA or shRNA knockdown resulted in significant increase in cytotoxicity of SN38 in vitro against hypoxic, but not the normoxic tumor cells. Similarly, in vivo, either MSC in combination with irinotecan treatment of parental xenografts or HIF-1alpha KD tumors treated with irinotecan alone resulted in comparable therapeutic response and increase in the long-term survival of mice bearing FaDu xenografts. Our results show that HIF-1alpha is a critical target for MSC and its inhibition was associated with enhanced antitumor activity of irinotecan. Inhibition of HIF-1alpha appeared to be mediated through stabilization of PHD2, 3 and downregulation of ROS by MSC. Thus, our findings support the development of MSC as a HIF-1alpha inhibitor in combination chemotherapy.

Combination of vitamin E and selenium causes an induction of apoptosis of human prostate cancer cells by enhancing Bax/Bcl‐2 ratio

The Selenium and Vitamin E Chemoprevention Trial (SELECT) is aimed at determining the usefulness of a combination of vitamin E and selenium for Prostate cancer (PCa) prevention in humans. The aim of this study is to evaluate the efficacy and mechanistic basis of this combination. We determined the effect of vitamin E (+-alpha-tocopheryl succinate, VES) and selenium (methylselenic acid, MSA), alone and in combination, on the proliferation of LNCaP, DU145, and PC-3 cells as well as normal prostate PrEC cells. We also determined the involvement of Bcl-2 family proteins as a mechanism of the biological effects of vitamin E and selenium combination. VES or MSA alone led to a modest inhibition in the viability and growth of PCa cells. However, a combination of these two agents resulted in a dramatic increase in growth inhibition of PCa cells. Interestingly, VES and/or MSA were not found to have any effect on the growth or viability of normal PrEC cells. VES and MSA treatment to human PCa cells resulted in (i) induction of apoptosis, (ii) increase in Bax, Bak, and Bid proteins, and (iii) decrease in Bcl-2 protein. Furthermore, Bax knockdown via shRNA and Bcl-2 overexpression via Bcl-2 plasmid resulted in a rescue of PCa cells from apoptosis. Our study suggested that vitamin E and selenium combination may be more effective than either of these agents alone. Further, our data demonstrated a causal connection between Bax and Bcl-2 modulation and induction of apoptosis by VES and MSA combination.

Selenomethionine Induced Transcriptional Programs in Human Prostate Cancer Cells

We determined the effects of selenomethionine, the major organic selenium containing compound found in the diet and the form of selenium being used in the Selenium and Vitamin E Cancer Prevention Trial, on prostate cancer cells. We assessed global transcript profiles of selenomethionine treated LNCaP using cDNA microarrays and compared them to those of cells treated with methylselenic acid, a direct precursor of methylselenol, which is the active form of selenium in vivo. After treatment with selenomethionine 2,336 unique genes showed expression changes of at least 1.5-fold in at least 3 time points during 48 hours and 366 unique transcripts differed significantly between selenomethionine and methylselenic acid treated LNCaP. Approximately half of the 76 cell cycle regulated genes affected by selenomethionine were down-regulated and enriched for genes associated with the G2/M phase. Flow cytometry analysis showed that selenomethionine induced G2/M arrest in LNCaP at low concentrations. Selenomethionine also affected expression levels of 35 known androgen responsive genes and 18 of these transcripts showed changes that were the inverse of those seen after androgen stimulation. At high concentrations selenomethionine decreased prostate specific antigen promoter driven luciferase expression. Selenomethionine modulates transcript levels of genes involved in a number of biological processes, including cell cycle/apoptosis androgen signaling, signal transduction and transcriptional regulation. Although the pathways affected paralleled in many ways those that are modulated by methylselenic acid, distinct differences in transcript patterns and effects on cell cycle regulation suggest that different selenium compounds could exert unique effects in prostate cells.

Utilization of chromatographic and spectroscopic techniques to study the oxidation kinetics of selenomethionine.

Ion-exchange LC and spectroscopic supporting techniques have been successfully used to study the kinetics and mechanism of oxidation reactions of selenomethionine (SeMet). Oxidation of selenomethionine with both cyanogen bromide (CNBr) and hydrogen peroxide (H(2)O(2)) proceeds through a stable intermediate which undergoes cyclization and C-Se bond cleavage to form 2-amino-4-butyrolactone. This stable intermediate was identified by IR spectroscopy as methionine dihydroxy selenide. The CH(3)-Se moiety of SeMet formed methyl selenic acid upon reaction with H(2)O(2) and methyl selenocyanate (CH(3)SeCN), characterized by GC-MS, for the reaction with CNBr. Both reactions were of apparent first order with respect to the concentration of SeMet. A rate constant (k(1))of 4.0x10(-3) s(-1) for the reaction of SeMet with HO and 4.0x10(-3) s(-1) for the reaction with CNBr were determined at a temperature of 22 degrees C. Oxidation of methionine (Met) gives disparate kinetics and oxidation products from SeMet. Thus the differential rate method can be utilized to quantitatively separate SeMet in biological samples in the presence of much higher concentrations of Met.