Biosynthesis and function of selenocysteine-containing enzymes

Synthesis and Application of New Selanylfullerene Derivatives as Photosensitizers for Photodynamic Therapy

This study aims to describe the synthesis of a new class of selanylfullerene derivatives in a convergent strategy route, affording the desired products in a few steps and in good yields. C60 compounds were evaluated as photosensitizers to be used in photodynamic therapy (PDT) via the generation of singlet oxygen (1O2), using the chemical trapping method. The photooxidation of the chemical probe1,3-diphenylisobenzofuran (DPBF) sensitized by selanylfullerenes followed a first-order kinetic and the values of singlet oxygen quantum yields (ΦΔ) are appropriate for its use in PDT. The electronic absorption spectra, and the intersystem crossing tax rates for the most prominent synthesized compounds were calculated using the density functional theory and the Marcus electron transfer theory, with the theoretical results confirming the experimental findings.

Chemistry Related to the Catalytic Cycle of the Antioxidant Ebselen

The antioxidant drug ebselen has been widely studied in both laboratories and in clinical trials. The catalytic mechanism by which it destroys hydrogen peroxide via reduction with glutathione or other thiols is complex and has been the subject of considerable debate. During reinvestigations of several key steps, we found that the seleninamide that comprises the first oxidation product of ebselen underwent facile reversible methanolysis to an unstable seleninate ester and two dimeric products. In its reaction with benzyl alcohol, the seleninamide produced a benzyl ester that reacted readily by selenoxide elimination, with formation of benzaldehyde. Oxidation of ebselen seleninic acid did not afford a selenonium seleninate salt as previously observed with benzene seleninic acid, but instead generated a mixture of the seleninic and selenonic acids. Thiolysis of ebselen with benzyl thiol was faster than oxidation by ca. an order of magnitude and produced a stable selenenyl sulfide. When glutathione was employed, the product rapidly disproportionated to glutathione disulfide and ebselen diselenide. Oxidation of the S-benzyl selenenyl sulfide, or thiolysis of the seleninamide with benzyl thiol, afforded a transient thiolseleninate that also readily underwent selenoxide elimination. The S-benzyl derivative disproportionated readily when catalyzed by the simultaneous presence of both the thiol and triethylamine. The phenylthio analogue disproportionated when exposed to ambient or UV (360 nm) light by a proposed radical mechanism. These observations provide additional insight into several reactions and intermediates related to ebselen.

Nucleophilicities and Nucleofugalities of Thio- and Selenoethers

Rate constants for the reactions of dialkyl chalcogenides with laser flash photolytically generated benzhydrylium ions have been measured photometrically to integrate them into the comprehensive benzhydrylium‐based nucleophilicity scale. Combining these rate constants with the previously reported equilibrium constants for the same reactions provided the corresponding Marcus intrinsic barriers and made it possible to quantify the leaving group abilities (nucleofugalities) of dialkyl sulfides and dimethyl selenide. Due to the low intrinsic barriers, dialkyl chalcogenides are fairly strong nucleophiles (comparable to pyridine and N‐methylimidazole) as well as good nucleofuges; this makes them useful group‐transfer reagents.

Ex and In Situ Reactivity and Sorption of Selenium in Opalinus Clay in the Presence of a Selenium Reducing Microbial Community

79Se is a critical radionuclide concerning the safety of deep geological disposal of certain radioactive wastes in clay-rich formations. To study the fate of selenium oxyanions in clayey rocks in the presence of a selenium reducing microbial community, in situ tests were performed in the Opalinus Clay at the Mont Terri Rock Laboratory (Switzerland). Furthermore, biotic and abiotic batch tests were performed to assess Se(VI) and Se(IV) reactivity in the presence of Opalinus Clay and/or stainless steel, in order to support the interpretation of the in situ tests. Geochemical modeling was applied to simulate Se(VI) reduction, Se(IV) sorption and solubility, and diffusion processes. This study shows that microbial activity is required to transform Se(VI) into more reduced and sorbing Se species in the Opalinus Clay, while in abiotic conditions, Se(VI) remains unreactive. On the other hand, Se(IV) can be reduced by microorganisms but can also sorb in the presence of clay without microorganisms. In situ microbial reduction of Se oxyanions can occur with electron donors provided by the clay itself. If microorganisms would be active in the clay surrounding a disposal facility, microbial reduction of leached Se could thus contribute to the overall retention of Se in clayey host rocks.

Extremely low-frequency electromagnetic field induces a change in proliferative capacity and redox homeostasis of human lung fibroblast cell line MRC-5

Numerous studies have shown that extremely low-frequency electromagnetic field (ELF-EMF) by modulating oxidative-antioxidative balance in the cells achieved beneficial and harmful effects on living organisms. The aim of this study was to research changes of both proliferative capacity and redox homeostasis of human lung fibroblast cell line MRC-5 during exposure to ELF-EMF (50 Hz). The human lung fibroblast cell line MRC-5 were exposed to ELF-EMF once a day in duration of 1 h during 24 h (1 treatment 1 h/day), 48 h (2 treatments 1 h/day), 72 h (3 treatments 1 h/day), and 7 days (7 treatments 1 h/day). After 24 h of the last treatment, the proliferative capacity of the cells and the concentrations and activities of the components of the oxidative/antioxidative system were determined: superoxide anion (O₂^.-), hydrogen peroxide (H₂O₂), nitric oxide (NO), peroxynitrite (ONOO^-), reduced glutathione (GSH), oxidized glutathione (GSSG), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR), and glutathione-S-transferase (GST). The results of this study show that ELF-EMF may affect a cell cycle regulation of human lung fibroblast cell line MRC-5 through modulation of oxidative/antioxidative defense system. The effects of ELF-EMF on proliferation and redox balance of human lung fibroblast cell line MRC-5 depend on exposure time.

Microbial Oxidation of Arsenite: Regulation, Chemotaxis, Phosphate Metabolism and Energy Generation

Arsenic (As) is a metalloid that occurs widely in the environment. The biological oxidation of arsenite [As(III)] to arsenate [As(V)] is considered a strategy to reduce arsenic toxicity and provide energy. In recent years, research interests in microbial As(III) oxidation have been growing, and related new achievements have been revealed. This review focuses on the highlighting of the novel regulatory mechanisms of bacterial As(III) oxidation, the physiological relevance of different arsenic sensing systems and functional relationship between microbial As(III) oxidation and those of chemotaxis, phosphate uptake, carbon metabolism and energy generation. The implication to environmental bioremediation applications of As(III)-oxidizing strains, the knowledge gaps and perspectives are also discussed.

Metabolic impairments, metal traffic, and dyshomeostasis caused by the antagonistic interaction of cadmium and selenium using organic and inorganic mass spectrometry

Cadmium (Cd) has become one of the most important environmental pollutants in the world, derived from natural and industrial sources, which is known to be accumulated in the human body, producing serious health effects. On the other hand, Selenium (Se) is an essential element for mammals, which is well known for its antagonistic interaction against Cd toxicity, such as the prevention of oxidative stress induced by this element. For this reason, the use of complementary analytical methods to study the homeostasis of metals, "traffic" between different organs and massive information about metabolites altered by the exposure, is of great interest. To this end, a metabolomic workflow based on the use of direct infusion mass spectrometry (DIMS) and gas chromatography mass spectrometry (GC-MS) was applied in mice serum. On the other hand, metal homeostasis and traffic between different organs and serum of mice exposed to Cd and Se have been evaluated by determining the concentration of metals by inductively coupled plasma mass spectrometry. This work demonstrates for the first time that Cd exposure causes a decrease of all the elements studied in the lung except itself. On the other hand, Se provokes As trafficking from metabolically less active organs (brain, lung, and testes) to others with greater metabolic activity (kidney), which also facilitates its excretion. Moreover, when mice are only exposed to Se, it provokes the accumulation of almost all the elements in the kidney, except Cd that increases also in the liver and brain. However, when both elements are simultaneously administered, Se increases Cd concentration in all the organs except in the serum and especially in the testis. On the other hand, important metabolic alterations have been detected in the energy and amino acid metabolism, as well as degradation of phospholipidic membranes, and in free fatty acids. In summary, the results show the high potential of the combined use of organic and inorganic mass spectrometry to establish Cd and Se interaction and the biological impairments caused and to provide information about metal traffic and metabolomic changes in exposure experiments.

Metabolic Impairments Caused by a "Chemical Cocktail" of DDE and Selenium in Mice Using Direct Infusion Triple Quadrupole Time-of-Flight and Gas Chromatography-Mass Spectrometry

Among organic contaminants, pesticides are one of the most important groups of chemicals due to their persistent character and toxicity. However, the biological systems are exposed to a complex environment in which the contaminants can interact in a synergistic/antagonistic fashion, and for this reason, the study of "chemical cocktails" is of great interest to fully understand the final biological effect. In this way, selenium is known for its antagonistic action against several toxicants. In this paper, metabolic impairments caused by the joint exposure of p,p'-dichloro diphenyl trichloroethane (DDE) and selenium (Se) have been issued for the first time. A metabolomic workflow was applied to mice fed DDE and DDE with Se diet, on the basis of the complementary use of two organic mass spectrometric techniques, combining direct infusion mass spectrometry (DI-ESI-QqQ-TOF MS) and gas chromatography-mass spectrometry (GC-MS). The results show a good classification between the studied groups caused by about 70 altered metabolites in the liver, kidney, or brain, including the pathways of energy metabolism, degradation of phospholipidic membrane, β-oxidation, and oxidative stress, which confirm the potential of combined metabolomic platforms in environmental studies.

Therapeutic potential of the mitochondria-targeted antioxidant MitoQ in mitochondrial-ROS induced sensorineural hearing loss caused by Idh2 deficiency

Mitochondrial NADP⁺-dependent isocitrate dehydrogenase 2 (IDH2) is a major NADPH-producing enzyme which is essential for maintaining the mitochondrial redox balance in cells. We sought to determine whether IDH2 deficiency induces mitochondrial dysfunction and modulates auditory function, and investigated the protective potential of an antioxidant agent against reactive oxygen species (ROS)-induced cochlear damage in Idh2 knockout (Idh2^−/−) mice. Idh2 deficiency leads to damages to hair cells and spiral ganglion neurons (SGNs) in the cochlea and ultimately to apoptotic cell death and progressive sensorineural hearing loss in Idh2^−/− mice. Loss of IDH2 activity led to decreased levels of NADPH and glutathione causing abnormal ROS accumulation and oxidative damage, which might trigger apoptosis signal in hair cells and SGNs in Idh2^−/− mice. We performed ex vivo experiments to determine whether administration of mitochondria-targeted antioxidants might protect or induce recovery of cells from ROS-induced apoptosis in Idh2-deficient mouse cochlea. MitoQ almost completely neutralized the H₂O₂-induced ototoxicity, as the survival rate of Idh2^−/− hair cells were restored to normal levels. In addition, the lack of IDH2 led to the accumulation of mitochondrial ROS and the depolarization of ΔΨ_m, resulting in hair cell loss. In the present study, we identified that IDH2 is indispensable for the functional maintenance and survival of hair cells and SGNs. Moreover, the hair cell degeneration caused by IDH2 deficiency can be prevented by MitoQ, which suggests that Idh2^−/− mice could be a valuable animal model for evaluating the therapeutic effects of various antioxidant candidates to overcome ROS-induced hearing loss.

Delivery of selenium to selenophosphate synthetase for selenoprotein biosynthesis

BACKGROUND

Selenophosphate, the key selenium donor for the synthesis of selenoprotein and selenium-modified tRNA, is produced by selenophosphate synthetase (SPS) from ATP, selenide, and H₂O. Although free selenide can be used as the in vitro selenium substrate for selenophosphate synthesis, the precise physiological system that donates in vivo selenium substrate to SPS has not yet been characterized completely.

SCOPE OF REVIEW

In this review, we discuss selenium metabolism with respect to the delivery of selenium to SPS in selenoprotein biosynthesis.

MAJOR CONCLUSIONS

Glutathione, selenocysteine lyase, cysteine desulfurase, and selenium-binding proteins are the candidates of selenium delivery system to SPS. The thioredoxin system is also implicated in the selenium delivery to SPS in Escherichia coli.

GENERAL SIGNIFICANCE

Selenium delivered via a protein-bound selenopersulfide intermediate emerges as a central element not only in achieving specific selenoprotein biosynthesis but also in preventing the occurrence of toxic free selenide in the cell. This article is part of a Special Issue entitled "Selenium research in biochemistry and biophysics - 200 year anniversary".

Mutual detoxification of mercury and selenium in unicellular Tetrahymena

Selenium (Se) is commonly recognized as a protective element with an antagonistic effect against mercury (Hg) toxicity. However, the mechanisms of this Hg-Se antagonism are complex and remain controversial. To gain insight into the Hg-Se antagonism, a type of unicellular eukaryotic protozoa (Tetrahymena malaccensis, T. malaccensis) was selected and individually or jointly exposed to two Hg and three Se species. We found that Se species showed different toxic effects on the proliferation of T. malaccensis with the toxicity following the order: selenite (Se(IV))>selenomethionine (SeMeth)>selenate (Se(VI)). The Hg-Se antagonism in Tetrahymena was observed because the joint toxicity significantly decreased under co-exposure to highly toxic dosages of Hg and Se versus individual toxicity. Unlike Se(IV) and Se(VI), non-toxic dosage of SeMeth significantly decreased the Hg toxicity, revealing the influence of the Se species and dosages on the Hg-Se antagonism. Unexpectedly, inorganic divalent Hg (Hg²⁺) and monomethylmercury (MeHg) also displayed detoxification towards extremely highly toxic dosages of Se, although their detoxifying efficiency was discrepant. These results suggested mutual Hg-Se detoxification in T. malaccensis, which was highly dependent on the dosages and species of both elements. As compared to other species, SeMeth and MeHg promoted the Hg-Se joint effects to a higher degree. Additionally, the Hg contents decreased for all the Hg-Se co-exposed groups, revealing a sequestering effect of Se towards Hg in T. malaccensis.

Trace minerals intake: Risks and benefits for cardiovascular health

Minerals play a major role in regulating cardiovascular function. Imbalances in electrolyte minerals are frequent and potentially hazardous occurrences that may lead to the development of cardiovascular diseases (CVDs). Transition metals, such as iron, zinc, copper and selenium, play a major role in cell metabolism. However, there is controversy over the effects of dietary and supplemental intake of these metals on cardiovascular risk factors and events. Since their pro-oxidant or antioxidant functions can have different effects on cardiovascular health. While deficiency of these trace elements can cause cardiovascular dysfunction, several studies have also shown a positive association between metal serum levels and cardiovascular risk factors and events. Thus, a J- or U-shaped relationship between the transition minerals and cardiovascular events has been proposed. Given the existing controversies, large, well-designed, long-term, randomized clinical trials are required to better examine the effects of trace mineral intake on cardiovascular events and all-cause mortality in the general population. In this review, we discuss the role of dietary and/or supplemental iron, copper, zinc, and selenium on cardiovascular health. We will also clarify their clinical applications, benefits, and harms in CVDs prevention.

A synergistic protective effect of selenium and taurine against experimentally induced myocardial infarction in rats

This study investigated the protective effect of subacute pre-adminsitration of either selenium (Se), taurine (Tau), or both drugs in combination against experimentally induced myocardial infarction (MI) in rats and illustrates the possible mechanisms of action. While solely pre-administration of Se or Tau resulted in partial amelioration in all of the measured parameters in MI rats, concomitant administration of both drugs to MI rats significantly restored contractility function by increasing LVSP and decreasing LVEDP and significantly normalized serum levels of LDH, CK-MB and BNP and restored normal cardiac architecture. This concomitant treatment acted by increasing the activity of major antioxidant enzymes (SOD and GPx), decreasing the levels of inflammatory markers including TNF-α, IL-6 as well as levels of Bcl-2 and caspase-3 and downregulating mRNA levels of Bax and P53, markers of apoptosis. In conclusion, a combination of Se and Tau provides a new strategy to alleviate MI-induced cardiac dysfunction.

Selenium and Selenocysteine in Protein Chemistry

Selenocysteine, the selenium-containing analogue of cysteine, is the twenty-first proteinogenic amino acid. Since its discovery almost fifty years ago, it has been exploited in unnatural systems even more often than in natural systems. Selenocysteine chemistry has attracted the attention of many chemists in the field of chemical biology owing to its high reactivity and resulting potential for various applications such as chemical modification, chemical protein (semi)synthesis, and protein folding, to name a few. In this Minireview, we will focus on the chemistry of selenium and selenocysteine and their utility in protein chemistry.

Microbial transformations of selenite by methane-oxidizing bacteria

Methane-oxidizing bacteria are well known for their role in the global methane cycle and their potential for microbial transformation of wide range of hydrocarbon and chlorinated hydrocarbon pollution. Recently, it has also emerged that methane-oxidizing bacteria interact with inorganic pollutants in the environment. Here, we report what we believe to be the first study of the interaction of pure strains of methane-oxidizing bacteria with selenite. Results indicate that the commonly used laboratory model strains of methane-oxidizing bacteria, Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b, are both able to reduce the toxic selenite (SeO₃²⁻) but not selenate (SeO₄²⁻) to red spherical nanoparticulate elemental selenium (Se⁰), which was characterized via energy-dispersive X-ray spectroscopy (EDXS), X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The cultures also produced volatile selenium-containing species, which suggests that both strains may have an additional activity that can transform either Se⁰ or selenite into volatile methylated forms of selenium. Transmission electron microscopy (TEM) measurements and experiments with the cell fractions cytoplasm, cell wall and cell membrane show that the nanoparticles are formed mainly on the cell wall. Collectively, these results are promising for the use of methane-oxidizing bacteria for bioremediation or suggest possible uses in the production of selenium nanoparticles for biotechnology.

Effects of Dietary Selenium on Inflammation and Hydrogen Sulfide in the Gastrointestinal Tract in Chickens

Selenium (Se) is an essential trace element for humans and animals and is associated with many physiological functions. Previous studies have shown that low-Se diet may affect inflammatory cytokine productions and histology in the digestive system and that sulfide hydrogen (H₂S) may contribute to the protection against tissue injury and the inhibition of inflammation in the gastrointestinal tract. In this study, we investigated the relationship between Se deficiency-induced inflammation and H₂S production in the small intestine in chickens. One hundred twenty 1-day-old chickens were fed with diets with different Se concentrations (0.15 mg/kg in the control and 0.028 mg/kg in the low-Se-diet group). Chickens were euthanized and small intestinal tissues were extracted. We observed histology, measured H₂S concentration, and evaluated the mRNA expression of H₂S-producing enzymes cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3-MST), and inflammatory factors TNF-α, NF-κB p50, COX-2, and PTGES. Our results showed that chickens fed with low-Se diet exhibited histological changes, lower H₂S production, and lower mRNA expression of H₂S-producing enzymes (CSE, CBS, and 3-MST) whereas higher mRNA expression of intestinal inflammatory factors (TNF-α, NF-κB p50, COX-2, and PTGES) compared to controls. Our results indicate that low-Se diet could impact H₂S, H₂S-producing enzymes, and inflammatory factors in the small intestine, implying that Se is important in maintaining intestinal functions and H₂S production is downregulated in Se deficiency-induced inflammation. The downregulation exacerbates the inflammation and impacts H₂S-mediated intestinal functions.

Anaerobic Formate and Hydrogen Metabolism

Numerous recent developments in the biochemistry, molecular biology, and physiology of formate and H2 metabolism and of the [NiFe]-hydrogenase (Hyd) cofactor biosynthetic machinery are highlighted. Formate export and import by the aquaporin-like pentameric formate channel FocA is governed by interaction with pyruvate formate-lyase, the enzyme that generates formate. Formate is disproportionated by the reversible formate hydrogenlyase (FHL) complex, which has been isolated, allowing biochemical dissection of evolutionary parallels with complex I of the respiratory chain. A recently identified sulfido-ligand attached to Mo in the active site of formate dehydrogenases led to the proposal of a modified catalytic mechanism. Structural analysis of the homologous, H2-oxidizing Hyd-1 and Hyd-5 identified a novel proximal [4Fe-3S] cluster in the small subunit involved in conferring oxygen tolerance to the enzymes. Synthesis of Salmonella Typhimurium Hyd-5 occurs aerobically, which is novel for an enterobacterial Hyd. The O2-sensitive Hyd-2 enzyme has been shown to be reversible: it presumably acts as a conformational proton pump in the H2-oxidizing mode and is capable of coupling reverse electron transport to drive H2 release. The structural characterization of all the Hyp maturation proteins has given new impulse to studies on the biosynthesis of the Fe(CN)2CO moiety of the [NiFe] cofactor. It is synthesized on a Hyp-scaffold complex, mainly comprising HypC and HypD, before insertion into the apo-large subunit. Finally, clear evidence now exists indicating that Escherichia coli can mature Hyd enzymes differentially, depending on metal ion availability and the prevailing metabolic state. Notably, Hyd-3 of the FHL complex takes precedence over the H2-oxidizing enzymes.

Analysis of the Core Genome and Pan-Genome of Autotrophic Acetogenic Bacteria

Acetogens are obligate anaerobic bacteria capable of reducing carbon dioxide (CO₂) to multicarbon compounds coupled to the oxidation of inorganic substrates, such as hydrogen (H₂) or carbon monoxide (CO), via the Wood-Ljungdahl pathway. Owing to the metabolic capability of CO₂ fixation, much attention has been focused on understanding the unique pathways associated with acetogens, particularly their metabolic coupling of CO₂ fixation to energy conservation. Most known acetogens are phylogenetically and metabolically diverse bacteria present in 23 different bacterial genera. With the increased volume of available genome information, acetogenic bacterial genomes can be analyzed by comparative genome analysis. Even with the genetic diversity that exists among acetogens, the Wood-Ljungdahl pathway, a central metabolic pathway, and cofactor biosynthetic pathways are highly conserved for autotrophic growth. Additionally, comparative genome analysis revealed that most genes in the acetogen-specific core genome were associated with the Wood-Ljungdahl pathway. The conserved enzymes and those predicted as missing can provide insight into biological differences between acetogens and allow for the discovery of promising candidates for industrial applications.

Microbial Transformations of Selenium Species of Relevance to Bioremediation

Selenium species, particularly the oxyanions selenite (SeO3 (2-)) and selenate (SeO4 (2-)), are significant pollutants in the environment that leach from rocks and are released by anthropogenic activities. Selenium is also an essential micronutrient for organisms across the tree of life, including microorganisms and human beings, particularly because of its presence in the 21st genetically encoded amino acid, selenocysteine. Environmental microorganisms are known to be capable of a range of transformations of selenium species, including reduction, methylation, oxidation, and demethylation. Assimilatory reduction of selenium species is necessary for the synthesis of selenoproteins. Dissimilatory reduction of selenate is known to support the anaerobic respiration of a number of microorganisms, and the dissimilatory reduction of soluble selenate and selenite to nanoparticulate elemental selenium greatly reduces the toxicity and bioavailability of selenium and has a major role in bioremediation and potentially in the production of selenium nanospheres for technological applications. Also, microbial methylation after reduction of Se oxyanions is another potentially effective detoxification process if limitations with low reaction rates and capture of the volatile methylated selenium species can be overcome. This review discusses microbial transformations of different forms of Se in an environmental context, with special emphasis on bioremediation of Se pollution.

The role of methoxy substituents in regulating the activity of selenides that serve as spirodioxyselenurane precursors and glutathione peroxidase mimetics

A series of o-(hydroxymethyl)phenyl selenides containing single or multiple methoxy substituents was synthesized, and the rate at which each compound catalyzed the oxidation of benzyl thiol to its disulfide with excess hydrogen peroxide was measured. This assay provided the means for comparing the relative abilities of the selenides to mimic the antioxidant selenoenzyme glutathione peroxidase. The mechanism for catalytic activity involves oxidation of the selenides to their corresponding selenoxides with hydrogen peroxide, cyclization to spirodioxyselenuranes, followed by reduction with two equivalents of thiol to regenerate the original selenide with concomitant disulfide formation. A single p-methoxy group on each aryl moiety afforded the highest catalytic activity, while methoxy groups in the meta position had little effect compared to the unsubstituted selenide, and o-methoxy groups suppressed activity. The installation of multiple methoxy groups on each aryl moiety provided no improvement. These results can be rationalized on the basis of dominating mesomeric and steric effects of the p- and o-substituents, respectively.

Reaction of low-molecular-mass organoselenium compounds (and their sulphur analogues) with inflammation-associated oxidants

Selenium is an essential trace element in mammals, with the majority specifically encoded as seleno-L-cysteine into a range of selenoproteins. Many of these proteins play a key role in modulating oxidative stress, via either direct detoxification of biological oxidants, or repair of oxidised residues. Both selenium- and sulphur-containing residues react readily with the wide range of oxidants (including hydrogen peroxide, radicals, singlet oxygen and hypochlorous, hypobromous, hypothiocyanous and peroxynitrous acids) that are produced during inflammation and have been implicated in the development of a range of inflammatory diseases. Whilst selenium has similar properties to sulphur, it typically exhibits greater reactivity with most oxidants, and there are considerable differences in the subsequent reactivity and ease of repair of the oxidised species that are formed. This review discusses the chemistry of low-molecular-mass organoselenium compounds (e.g. selenoethers, diselenides and selenols) with inflammatory oxidants, with a particular focus on the reaction kinetics and product studies, with the differences in reactivity between selenium and sulphur analogues described in the selected examples. These data provide insight into the therapeutic potential of low-molecular-mass selenium-containing compounds to modulate the activity of both radical and molecular oxidants and provide protection against inflammation-induced damage. Progress in their therapeutic development (including modulation of potential selenium toxicity by strategic design) is demonstrated by a brief summary of some recent studies where novel organoselenium compounds have been used as wound healing or radioprotection agents and in the prevention of cardiovascular disease.

Attenuation of cyclophosphamide-induced pulmonary toxicity in Swiss albino mice by naphthalimide-based organoselenium compound 2-(5-selenocyanatopentyl)-benzo[de]isoquinoline 1,3-dione

CONTEXT

The widely used antineoplastic drug cyclophosphamide causes pulmonary toxicity by inducing oxidative stress. Selenium, a dietary micronutrient, has been found to protect various organs from oxidative injuries.

OBJECTIVE

This study was designed to investigate the protective efficacy of an organoselenium compound 2-(5-selenocyanato-pentyl)-benzo[de]isoquinoline 1,3-dione against cyclophosphamide-induced pulmonary toxicity in Swiss albino mice.

MATERIALS AND METHODS

Cyclophosphamide (25 mg/kg b.w.) was administered intraperitoneally for 10 d and the organoselenium compound (3 mg/kg b.w.) was given by oral gavage in concomitant and pretreatment schedules. Various biochemical parameters related to oxidative stress and antioxidant enzymes along with histology of lungs were evaluated to assess the effect of the test compound.

RESULTS

The oral LD50 of the test compound was more than 1000 mg/kg b.w. in Swiss albino mice. The test compound substantially ameliorated cyclophosphamide-induced pulmonary injury by reducing the levels of reactive oxygen species, reactive nitrogen species, and lipid peroxidation, respectively, by 14.88, 18.54, and 21.10% in concomitant treatment schedule and by 23.89, 35.73, and 30.76% in the pretreatment schedule as well as by restoring the level of reduced glutathione and activities of glutathione-S-transferase, superoxide dismutase, catalase, and glutathione peroxidase, respectively, by 36.88, 42.43, 38.0, 35.0, and 34.06% in the concomitant treatment schedule and by 66.02, 59.29, 57.23, 71.59, and 57.22% in the pretreatment schedule. The test compound also attenuated cyclophosphamide-induced histological alterations of lung tissue.

DISCUSSION AND CONCLUSION

The test compound emerged as an efficient antioxidant protecting lungs tissue from cyclophosphamide-induced injury.

Redox control of GPx catalytic activity through mediating self-assembly of Fmoc-phenylalanine selenide into switchable supramolecular architectures

Artificial enzymes capable of achieving tunable catalytic activity through stimuli control of enzymatic structure transition are of significance in biosensor and biomedicine research. Herein we report a novel smart glutathione peroxidise (GPx) mimic with modulatory catalytic activity based on redox-induced supramolecular self-assembly. First, an amphiphilic Fmoc-phenylalanine-based selenide was designed and synthesized, which can self-assemble into nanospheres (NSs) in aqueous solution. The NSs demonstrate extremely low GPx activity. Upon the oxidation of hydroperoxides (ROOH), the selenide can be quickly transformed into the selenoxide form. The change of the molecular structure induces complete morphology transition of the self-assemblies from NSs to nanotubes (NTs), resulting in great enhancement in the GPx catalytic activity. Under the reduction of GSH, the selenoxide can be further reversibly reduced back into the selenide; therefore the reversible switch between the NSs and NTs can be successfully accomplished. The relationship between the catalytic activity and enzymatic structure was also investigated. The dual response nature makes this mimic play roles of both a sensor and a GPx enzyme at the same time, which can auto-detect the signal of ROOH and then auto-change its activity to achieve quick or slow/no scavenging of ROOH. The dynamic balance of ROOH is vital in organisms, in which an appropriate amount of ROOH does benefit to the metabolism, whereas surplus ROOH can cause oxidative damage of the cell instead and this smart mimic is of remarkable significance. We expect that such a mimic can be developed into an effective antioxidant drug and provide a new platform for the construction of intelligent artificial enzymes with multiple desirable properties.

Selenium attenuates high glucose-induced ROS/TLR-4 involved apoptosis of rat cardiomyocyte

The potential mechanism of high glucose-induced cardiomyocyte apoptosis and selenium's protective effects were investigated in this study. Myocytes isolated from neonate rats were cultured in high-glucose medium (25.5 mmol/L glucose) to mimic sustained hyperglycemia. Before high-glucose incubation, myocytes were pretreated by sodium selenite solution. Cell apoptosis was evaluated by annexin V/propidium iodide (PI) staining and caspase activation. Expression of Toll-like receptor 4 (TLR-4) and myeloid differentiation factor 88 (MyD-88) was examined at both mRNA and protein levels. The intracellular reactive oxygen species (ROS) production and glutathione peroxidase (GPx) activity in myocytes were also detected. We found high glucose-induced cell apoptosis and activation of TLR-4/MyD-88/caspase-8/caspase-3 signaling, accompanied by increased production of ROS. Selenium pretreatment attenuated apoptosis in high glucose-incubated myocytes, and mechanically, this protective effect was found to be associated with attenuating oxidative status by increasing activity of GPx, decreasing the generation of ROS, as well as inhibition of the activation of TLR-4/MyD-88/caspase-8/caspase-3 signaling in myocytes. These results suggest that activation of TLR-4/MyD-88 signaling pathway plays an important role in high glucose-induced cardiomyocyte apoptosis. Additionally, by modulating TLR-4/MyD-88 signaling pathway, which is linked to ROS formation, selenium exerts its antioxidative and antiapoptotic effects in high glucose-incubated myocytes.

An ex vivo study of selenium, genistein on the morphological and nuclear changes in anticancer drug-induced apoptosis in human peripheral blood lymphocytes

Behavioral difference of cancer cells and normal cells to anticancer drugs is diverse. Debilitating side effects observed with certain chemotherapeutic and prophylactic anticancer drugs have lead to identification of natural agents that may offer protective role against the damage induced in normal cells. The present study aimed to determine the protective role of the micronutrient mineral selenium (Se) and plant product genistein (Gn) in synergy and single, against the apoptosis induced in human peripheral blood lymphocytes by the cytotoxic agents cisplatin and mitomycin C. We observed reduction in apoptotic potential of cisplatin and mitomycin C in lymphocytes by pre-treatment and post-treatment with selenium (30 μM) and genistein (100 μM). The intercellular interaction of Se + Gn in synergy is found to be more efficient in protecting lymphocytes than as individual. Moreover the beneficial results were well pronounced in pre-treatment than in post-treatment condition. The protective action of these natural compounds suggests that they might be useful immunomodulators during the course of chemotherapy and prophylaxis.

Protective efficacy of selenite against lead-induced neurotoxicity in Caenorhabditis elegans

Background

Selenium is an essential micronutrient that has a narrow exposure window between its beneficial and toxic effects. This study investigated the protective potential of selenite (IV) against lead (Pb(II))-induced neurotoxicity in Caenorhabditis elegans.

Principal Findings

The results showed that Se(IV) (0.01 µM) pretreatment ameliorated the decline of locomotion behaviors (frequencies of body bends, head thrashes, and reversal ) of C. elegans that are damaged by Pb(II) (100 µM) exposure. The intracellular ROS level of C. elegans induced by Pb(II) exposure was significantly lowered by Se(IV) supplementation prior to Pb(II) exposure. Finally, Se(IV) protects AFD sensory neurons from Pb(II)-induced toxicity.

Conclusions

Our study suggests that Se(IV) has protective activities against Pb(II)-induced neurotoxicity through its antioxidant property.

4-(5-Chloro-thio-phen-2-yl)-1,2,3-selenadiazole

In the title compound, C6H3ClN2SSe, the selenadiazole and chloro-thio-phene rings are almost coplanar [dihedral angle = 5.24 (15)°]. In the crystal, C-H⋯N inter-actions link the mol-ecules into chains extending along the b-axis direction. C-H⋯π inter-actions also occur.

Selenium deficiency is associated with insulin resistance in patients with hepatitis C virus-related chronic liver disease

The relationship between selenium (Se) deficiency and insulin resistance has not much been established in persistent hepatitis C virus (HCV) infection, although Se deficiency is often observed in patients with liver cirrhosis. We hypothesized that the decreased serum Se levels were associated with the severity of hepatic fibrosis or insulin resistance in patients with HCV-related chronic liver disease (CLD). To test the hypothesis, 52 patients with HCV-related CLD including chronic hepatitis and liver cirrhosis were enrolled in this study. The severity of hepatic fibrosis was divided into 4 categories (F(1) through F(4)) according to the new Inuyama classification. Insulin resistance was defined by the homeostasis model for assessment of insulin resistance value. Serum Se levels significantly declined in proportion to the severity of hepatic fibrosis and were positively correlated with serum albumin (r = 0.372, P = .0065) and zinc (r = 0.403, P = .0081) concentrations. Serum Se levels were also linked to glutathione peroxidase activities in the sera of the enrolled patients (r = 0.374, P = .0148). By contrast, serum Se levels were inversely correlated with the homeostasis model for assessment of insulin resistance values (r = -0.304, P = .0338). However, serum Se levels were independent of HCV genotype and loads of HCV-RNA. These findings suggest that Se deficiency was associated with the severity of hepatic fibrosis in patients with HCV-related CLD and that Se deficiency was likely to be one of the factors contributing to insulin resistance in those patients.

Ethyl 2-phenyl-3-(4-phenyl-1,2,3-selenadiazol-5-yl)-3-p-tolyl-propano-ate

In the title compound, C(26)H(24)N(2)O(2)Se, the selenadiazole ring is essentially planar [maximum deviation = 0.004 (3) Å]. The dihedral angle between the selenadiazole ring and the attached benzene ring is 50.17 (1)°. The crystal packing is stabilized by inter-molecular C-H⋯N inter-actions.

Genome-wide gene expression analysis suggests an important role of suppressed immunity in pathogenesis of Kashin-Beck disease

Objective

To investigate the differences between the gene expression profiles in peripheral blood mononuclear cells (PBMC) from normal controls and patients with Kashin-Beck disease (KBD).

Methods

Twenty KBD patients and 12 normal subjects were selected from a KBD-endemic area and divided into four pairs of KBD vs. control (KBD, n = 5 per pair; control, n = 3 per pair). RNAs were respectively isolated from KBD PBMCs and normal PBMCs. Gene expression profiles were analyzed by oligonucleotide microarray. The gene expression profiles in PBMCs from KBD patients and normal controls were compared and the differentially expressed genes were identified. The obtained microarray data was further confirmed by using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR).

Results

Approximately 501 genes, corresponding to 2.4% of the total probe transcripts, showed a 2-fold change in differential expression. 19.4% (97 out of 501)of the differentially expressed genes were commonly detected in all the four pairs. Among the 97 differentially expressed genes, 83 genes were up-regulated and 14 genes were down-regulated, compared with those in the normal controls. Some differentially expressed genes were found to be related to functions such as immunity, metabolism, apoptosis, cystoskeleton and cell movement, and extracellular matrix. The validity of our microarray data were supported by the results of qRT-PCR assay.

Conclusion

Differences in the PBMC gene expression profile between the KBD patients and the normal controls exhibited a similar pattern among all the four pairs of microarrays examined, indicating that the suppressed immunity may play an important role in the pathogenesis of KBD.

Life and death with arsenic. Arsenic life: an analysis of the recent report "A bacterium that can grow by using arsenic instead of phosphorus"

Arsenic and phosphorus are group 15 elements with similar chemical properties. Is it possible that arsenate could replace phosphate in some of the chemicals that are required for life? Phosphate esters are ubiquitous in biomolecules and are essential for life, from the sugar phosphates of intermediary metabolism to ATP to phospholipids to the phosphate backbone of DNA and RNA. Some enzymes that form phosphate esters catalyze the formation of arsenate esters. Arsenate esters hydrolyze very rapidly in aqueous solution, which makes it improbable that phosphorous could be completely replaced with arsenic to support life. Studies of bacterial growth at high arsenic:phosphorus ratios demonstrate that relatively high arsenic concentrations can be tolerated, and that arsenic can become involved in vital functions in the cell, though likely much less efficiently than phosphorus. Recently Wolfe-Simon et al. [1 ] reported the isolation of a microorganism that they maintain uses arsenic in place of phosphorus for growth. Here, we examine and evaluate their data and conclusions.

Curcumin protects against hepatic and renal injuries mediated by inducible nitric oxide synthase during selenium-induced toxicity in Wistar rats

The aim of this study is to evaluate the effect of curcumin in protecting against selenium-induced toxicity in liver and kidney of Wistar rats. Light microscopy evaluation of selenium alone administered rats showed liver to be infiltrated with mononuclear cells, vacuolation, necrosis, and pronounced degeneration. Control liver sections showed a regular morphology of parenchymal cells with intact hepatocytes and sinusoids. Kidney from selenium alone administered rats showed vacuolar degeneration changes in the epithelial cells, cellular proliferation with fibrosis, thickening of capillary walls, and glomerular tuft atrophy. Such changes were also observed in rats administered with selenium and curcumin simultaneously and rats administered first with selenium and then curcumin 24 h later. Interestingly, such degenerative changes observed in liver and kidney induced by selenium were not seen in rats that were administered with curcumin first and selenium 24 h later. This clearly suggests the protective nature of curcumin against selenium toxicity. To understand the probable mechanism of action of curcumin, we analyzed inducible nitric oxide synthase (iNOS) expression by immunohistochemistry, and the results showed an increased iNOS expression in selenium-alone induced liver and kidney. Such high iNOS levels were inhibited in liver and kidney of rats pretreated with curcumin and then with selenium 24 h later. Based on the histological results, it can be concluded that curcumin functions as a protective agent against selenium-induced toxicity in liver as well as kidney, and this action is probably by the regulatory role of curcumin on iNOS expression.

Homoselenocysteine — An oxygen or selenium acid in the gas phase?

The potential energy surface of l-homoselenocysteine (HSEC) has been explored through the use of B3LYP/6-311+G(d,p) calculations. In this survey, seventy-seven different conformers have been located. These local minima can be classified in four groups, A–D. Structures A, B, and D are stabilized by intramolecular hydrogen bonds (IMHBs) with the amino group acting as the hydrogen bond (HB) donor and the carbonyl group (structures A and D) or the hydroxyl group (structure B) as HB acceptors. The structures in set C present an IMHB with the amino group acting as the HB acceptor and the hydroxyl group as the HB donor. The stability order decreases in the following order: A > B > C > D. From their relative stabilities it can be concluded that only three of these conformers, namely A1, A4, and A5, would exist in the gas phase at room temperature. The most stable deprotonated form corresponds to a Se-deprotated species stabilized by a strong IMHB between the hydroxyl group and the Se atom. However, a direct deprotonation of the most stable neutrals lead to O-deprotonated species, which eventually isomerize to yield the global minimum. Hence, we can conclude that, quite unexpectedly, HSEC behaves as a Se acid in the gas phase, its intrinsic acidity being 1374 kJ mol–1at the B3LYP/6-311++G(3df,2p) level of theory. The most stable protonated forms are systematically the N-protonated ones, the global minimum being a structure stabilized through an IMHB involving the protonated amino group as the HB donor and the SeH group as the HB acceptor. The calculated gas-phase proton affinity (PA) at the B3LYP/6-311++G(3df,2p) level of theory is 930 kJ mol–1.