Dependence of the sister-chromatid exchange-inducing abilities of inorganic selenium compounds on the valence state of selenium

A 10 minute approach for the phase specific synthesis of Se nanoparticles with tunable morphology: their anticancer efficacy and the role of an ionic liquid

The current work demonstrates a rapid and highly facile controlled phase-specific synthesis of Se nanoparticles, their anticancer efficacy and the 3-in-1 role of a RTIL.

Investigating the Generalizability of the MultiFlow ® DNA Damage Assay and Several Companion Machine Learning Models With a Set of 103 Diverse Test Chemicals

The in vitro MultiFlow DNA Damage assay multiplexes p53, γH2AX, phospho-histone H3, and polyploidization biomarkers into 1 flow cytometric analysis (Bryce, S. M., Bernacki, D. T., Bemis, J. C., and Dertinger, S. D. (2016). Genotoxic mode of action predictions from a multiplexed flow cytometric assay and a machine learning approach. Environ. Mol. Mutagen. 57, 171-189). The work reported herein evaluated the generalizability of the method, as well as several data analytics strategies, to a range of chemical classes not studied previously. TK6 cells were exposed to each of 103 diverse chemicals, 86 of which were supplied by the National Toxicology Program (NTP) and selected based upon responses in genetic damage assays conducted under the Tox21 program. Exposures occurred for 24 h over a range of concentrations, and cell aliquots were removed at 4 and 24 h for analysis. Multiplexed response data were evaluated using 3 machine learning models designed to predict genotoxic mode of action based on data from a training set of 85 previously studied chemicals. Of 54 chemicals with sufficient information to make an a priori call on genotoxic potential, the prediction models' accuracies were 79.6% (random forest), 88.9% (logistic regression), and 90.7% (artificial neural network). A majority vote ensemble of the 3 models provided 92.6% accuracy. Forty-nine NTP chemicals were not adequately tested (maximum concentration did not approach assay's cytotoxicity limit) and/or had insufficient conventional genotoxicity data to allow their genotoxic potential to be defined. For these chemicals MultiFlow data will be useful in future research and hypothesis testing. Collectively, the results suggest the MultiFlow assay and associated data analysis strategies are broadly generalizable, demonstrating high predictability when applied to new chemicals and classes of compounds.

A Survey of Metal-induced Mutagenicity in Vitro and in Vivo

A survey of the literature shows that organic and inorganic compounds of 53 metals have been assayed for genotoxic effects in vitro and in vivo. It is found that there are great variations in the response obtained with different test systems and that a wide range of compounds of the different metals is positive in at least one of the short-term tests. Some of the variation observed could be due to differences in uptake mechanisms. This effect plus the wide variation in the quantity and quality of the data prevents any direct comparison of in vitro activity with in vivo potency of the various metallic species.

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Genotoxicity of selenite in diploid yeast

Selenite, a chemical of industrial importance and also an antimutagenic/anticarcinogenic agent, was tested for mutagenic and recombinogenic effects in 2 diploid yeast strains, Saccharomyces cerevisiae BZ 34 and D7. Selenite induced gene conversion and toxicity in BZ 34 and a variety of genetic events, viz. back-mutation, gene conversion, mitotic crossing-over, aberrant colony formation and also toxicity in the D7 strain. In both strains, the genetic effects of selenite showed a peak and a decline during 5 h of treatment while its toxicity increased marginally during 1-5 h. In the BZ 34 strain, the presence of glutathione (GSH) during selenite treatment greatly enhanced the convertogenic and toxic effects of selenite.

Effects of metals on chromosomes of higher organisms

An analysis of the available data on the clastogenic effects of metals and their compounds on higher organisms indicates some general trends. Following chronic exposure to subtoxic doses, a decrease in mitotic frequency and an increase in the number of chromosomal abnormalities are observed. These effects are usually directly proportional to the dose applied and the duration of treatment within the threshold limits. Recovery after acute treatment is inversely related to the dosage. The ultimate expression of the effects depends on certain factors, including the mode and vehicle of administration; the form administered; the test system used; the rate of detoxification, distribution, and retention in the different tissues; and interaction with foreign and endogenous substances as well as the mode of action with the biological macromolecules. In mammals, the clastogenic activity of the metals within each vertical group of the periodic table is directly proportional to the increase in atomic weight, electropositivity, and solubility of the metallic cations in water and lipids, except for Li and Ba. This pattern of inherent cytotoxicity increases with successive periods in the horizontal level. It is enhanced by the formation of covalent and coordinate covalent complexes by heavy metals with the biological macromolecules. In plants, the solubility of the metals in water is of much greater importance. The degree of dissociation of metallic salts and the rate of absorption affect significantly the frequency of chromosomal aberrations. In assessing the effects of environmental metal pollution, the presence of other metals and toxic chemicals and the level of nutrition should be taken into account, since in nature, metals occur in combination and these factors modify the cytotoxic effects to a significant extent.

Sister-chromatid exchange induction by sodium selenite: reduced glutathione converts Na2SeO3 to its SCE-inducing form

Sodium selenite (Na2SeO3) is an anticarcinogenic/antimutagenic agent that exhibits carcinogenic/mutagenic properties in some short-term test systems used for the detection of DNA-damaging agents. One such test system is sister-chromatid exchange (SCE) induction. Na2SeO3 induces SCEs only if red blood cells (RBCs) are present to 'activate' it to its SCE-inducing form. Here, the ability of reduced glutathione, a major component of RBCs, to serve as an RBC substitute in the activation of Na2SeO3 was determined. Reduced glutathione (10(-4) and 10(-3) M) was shown to be as capable as RBCs in activating Na2SeO3 (7.95 X 10(-6) M) to its SCE-inducing form. These data suggest strongly that the pathway normally utilized by RBCs in the metabolism of Na2SeO3 is the same as that in which Na2SeO3 is converted to its SCE-inducing form.

The influence of selenium and caffeine on chemical carcinogenesis in rats, mutagenesis in bacteria, and unscheduled DNA synthesis in human lymphocytes

The influence of sodium selenite (Na2SeO3) and caffeine on chemical carcinogenesis induced in rats by diethylnitrosamine (DEN), N-nitrosomorpholine (NM), andN-methyl-N-nitro-N-nitrosoguanidine (MNNG) was investigated. A dose-dependent inhibitory effect of Na2SeO3 (l-10 ppm) on hepatocarcinogenesis induced by DEN was demonstrated. Na2SeO3 also increased the latency period for stomach tumor formation in rats treated with MNNG. Combined treatment of rats with Na2SeO3 plus vitamin C added to the diet resulted in a slight inhibition of NM-induced liver carcinogenesis. Supplementation of diet with Na2SeO3 plus butylated hydroxytoluene, vitamin C, and vitamin E did not reveal any additive inhibitory effect compared to the inhibitory effect of Na2SeO3 given alone. Caffeine (600 rag/L) reduced the number of liver tumors induced in rats by DEN. Preliminary experiments have indicated that combined treatment of rats with selenium and caffeine could result in more effective inhibition of DEN-induced liver carcinogenesis.Further experiments are being conducted to study the influence of selenium and caffeine on mutagenic activity of 1-methyl-l-nitrosourea (MNU) inSalmonella typhimurium TA 1535. The pretreatment of bacteria cells with Na2SeO3 (3-10 p.g/mL) increased the mutagenic response of bacteria to MNU. A synergistic stimulation of mutagenic activity of MNU was observed in bacteria pretreated simultaneously with Na2SeO3 and caffeine.In addition the influence of Na2SeO3 on UDS induced by DEN in human lymphocytes was investigated. The trace element inhibited the UDS up to 82%.The possible role of potentiation by NazSeO3 of the cell killing effect of DEN in inhibition of liver carcinogenesis was discussed.

Induction of sister chromatid exchange by various selenium compounds in Chinese hamster cells in the presence and absence of S9 mixture

This study was designed to investigate the effect of 3 selenium compounds, namely, sodium selenite, sodium selenide and sodium selenate on induction of sister chromatid exchange (SCE) in the Chinese hamster V79 cell line in the presence and absence of S9 mixture. The results indicated that the most potent SCE inducer in the presence of S9 mixture was sodium selenite and this was followed by sodium selenide, while in the absence of S9 mixture the most effective SCE inducer was sodium selenide which was then followed by sodium selenite. For sodium selenate, the data indicated no increase in SCE rate as compared to the control values both in the presence and absence of S9 mixture. In addition, it was observed that growth inhibition as measured by no sister chromatid differentiation or no metaphases was produced by certain doses of the compounds tested. Based on this, the compound that induced the most growth inhibition both in the presence and absence of S9 mixture was sodium selenide and this was followed by sodium selenite. For sodium selenate no growth inhibition was observed. The different capabilities of the selenium compounds tested to induce SCE were clearly demonstrated in the system employed in this study. It is felt that this effect is an important cytogenetic characteristic of these compounds, yet how this activity relates to the antimutagenic and anticarcinogenic properties of these agents is difficult to discern.

Sister-chromatid exchange induction by sodium selenite: plasma protein-bound selenium is not the active SCE-inducing metabolite of Na2SeO3

Sodium selenite (Na2SeO3) is an anticarcinogenic/antimutagenic/anticlastogenic agent that under certain incubation conditions induces sister-chromatid exchanges (SCEs), unscheduled DNA synthesis, and chromosome aberrations. Previous work has shown that SCE induction by Na2SeO3 depends on the presence of red blood cells (RBCs). Therefore, Na2SeO3 uptake and release by RBCs was studied in the present report as was the effect of plasma protein-bound selenium, the end product of Na2SeO3 metabolism by RBCs, on the SCE frequency of purified lymphocyte cultures. Na2SeO3 uptake by human whole blood, RBCs in plasma, RBCs in fetal calf serum, and RBCs in Hanks' balanced salt solution occurs rapidly, reaching a maximum after 2 min (37 degrees C). Release of Na2SeO3 from RBCs depends on the presence of plasma proteins to which the metabolized selenium becomes bound. In spite of the fact that plasma protein-bound selenium is the major product of Na2SeO3 metabolism by RBCs, the SCE frequency of purified lymphocyte cultures was unchanged when plasma protein-bound selenium (7.90 X 10(-6) and 1.19 X 10(-5) M) was added to the medium for the final 19 h of incubation. Further study showed that Na2SeO3 could induce SCEs in blood cultures that had been washed to remove plasma proteins and incubated in medium 199, a maintenance medium lacking fetal calf serum. These findings indicate that a Na2SeO3 metabolite other than plasma protein-bound selenium is responsible for Na2SeO3's SCE-inducing ability in human whole-blood cultures.

Selenite prevents the induction of sister-chromatid exchanges by methyl mercury and mercuric chloride in human whole-blood cultures

The protective effect of sodium selenite (Na2SeO3) against the cytogenetic toxicity of methyl mercury (CH3HgCl) and mercuric chloride (HgCl2) were investigated on human whole-blood cultures in relation to induction of sister-chromatid exchange (SCE). Both mercurials caused a dose-dependent increase in SCEs, methyl mercury being about 5 times more potent than mercuric chloride. Sodium selenite also induced SCEs. However, the simultaneous addition of selenite (1 x 10(-7) -3 x 10(-5) M) to cell cultures containing either methyl mercury (3 x 10(-6) M) or mercuric chloride (1 x 10(-5) M) prevented the induction of SCEs by the mercurial in a clear dose-related manner. When selenite and mercurial were simultaneously added at a molar ratio of 1:2 Na2SeO3:CH3HgCl, or 1:1 Na2SeO3:HgCl2, cells from treated cultures showed no increase in the SCE frequency. These results indicate that selenite and mercury mutually antagonize their ability to cause DNA damage leading to the formation of SCEs. The formation of bis(methylmercuric)selenide, (CH3Hg)2Se, from Na2SeO3 and CH3HgCl, or a high molecular complex consisting of glutathione-Se-Hg from Na2SeO3 and HgCl2 involving the participation of glutathione in RBCs might play a key role in this antagonism between mercury and selenium.