Interaction of peroxynitrite with selenoproteins and glutathione peroxidase mimics

An Update of Kaempferol Protection against Brain Damage Induced by Ischemia-Reperfusion and by 3-Nitropropionic Acid

Kaempferol, a flavonoid present in many food products, has chemical and cellular antioxidant properties that are beneficial for protection against the oxidative stress caused by reactive oxygen and nitrogen species. Kaempferol administration to model experimental animals can provide extensive protection against brain damage of the striatum and proximal cortical areas induced by transient brain cerebral ischemic stroke and by 3-nitropropionic acid. This article is an updated review of the molecular and cellular mechanisms of protection by kaempferol administration against brain damage induced by these insults, integrated with an overview of the contributions of the work performed in our laboratories during the past years. Kaempferol administration at doses that prevent neurological dysfunctions inhibit the critical molecular events that underlie the initial and delayed brain damage induced by ischemic stroke and by 3-nitropropionic acid. It is highlighted that the protection afforded by kaempferol against the initial mitochondrial dysfunction can largely account for its protection against the reported delayed spreading of brain damage, which can develop from many hours to several days. This allows us to conclude that kaempferol administration can be beneficial not only in preventive treatments, but also in post-insult therapeutic treatments.

Nicotinamide riboside, pterostilbene and ibudilast protect motor neurons and extend survival in ALS mice

Oxidative stress and neuroinflammation are major contributors to the pathophysiology of ALS. Nicotinamide riboside (a NAD+ precursor) and pterostilbene (a natural antioxidant) were efficacious in a human pilot study of ALS patients and in ALS SOD1G93A transgenic mice. Ibudilast targets different phosphodiesterases and the macrophage migration inhibitory factor, reduces neuroinflammation, and in early-phase studies improved survival and slowed progression in ALS patients. Using two ALS murine models (SOD1G93A, FUSR521C) the effects of nicotinamide riboside, pterostilbene, and ibudilast on disease onset, progression and survival were studied. In both models ibudilast enhanced the effects of nicotinamide riboside and pterostilbene on survival and neuromotor functions. The triple combination reduced microgliosis and astrogliosis, and the levels of different proinflammatory cytokines in the CSF. TNFα, IFNγ and IL1β increased H2O2 and NO generation by motor neurons, astrocytes, microglia and endothelial cells isolated from ALS mice. Nicotinamide riboside and pterostilbene decreased H2O2 and NO generation in all these cells. Ibudilast specifically decreased TNFα levels and H2O2 generation by microglia and endothelial cells. Unexpectedly, pathophysiological concentrations of H2O2 or NO caused minimal motor neuron cytotoxicity. H2O2-induced cytotoxicity was increased by NO via a trace metal-dependent formation of potent oxidants (i.e. OH and -OONO radicals). In conclusion, our results show that the combination of nicotinamide riboside, pterostilbene and ibudilast improve neuromotor functions and survival in ALS murine models. Studies on the underlying mechanisms show that motor neuron protection involves the decrease of oxidative and nitrosative stress, the combination of which is highly damaging to motor neurons.

Ebselen: A promising therapy protecting cardiomyocytes from excess iron in iron-overloaded thalassemia patients

Iron-overload-associated cardiomyopathy has been one of the primary causes of mortality in thalassemia patients with iron burden. There is growing evidence citing the beneficial effects of ebselen as an antioxidant selectively blocking the divalent metal transporter 1 (DMT-1) to deter iron ingress into cardiomyocytes, raising internets in viewing this component in this population in order to treat and even prevent cardiomyopathy occurring from iron surplus. In this article, we reviewed the potential advantageous effects of ebselen in thalassemia patients who suffer from iron excess, susceptible to cardiomyopathy induced by iron overload. A systematic search in several databases, including PubMed, Scopus, and Web of Science, was conducted to explore the role of ebselen in controlling iron-overload-related cardiomyopathy in thalassemia patients by the keywords of Ebselen AND iron. The inclusion criteria were English-written preclinical and clinical studies investigating the efficacy and side effects of ebselen in an iron-overload context. After searching the databases, 44 articles were found. Next, of 19 published articles, 3 were included in this article. After reviewing the references of the included studies, no articles were added. In conclusion ebselen can be a promising adjuvant therapy in patients with thalassemia alongside the standard treatment with iron chelators, particularly in severe cases with cardiomyopathy, due to falling iron inflow by inhibiting DMT-1 and increasing ferroportin-1 expression and antioxidant properties. However, clinical studies need to be carried out to reach a definite conclusion.

Effect of Organic Selenium on the Homeostasis of Trace Elements, Lipid Peroxidation, and mRNA Expression of Antioxidant Proteins in Mouse Organs

(1) In this study we determined the effect of long-term selenomethionine administration on the oxidative stress level and changes in antioxidant protein/enzyme activity; mRNA expression; and the levels of iron, zinc, and copper. (2) Experiments were performed on 4-6-week-old BALB/c mice, which were given selenomethionine (0.4 mg Se/kg b.w.) solution for 8 weeks. The element concentration was determined via inductively coupled plasma mass spectrometry. mRNA expression of SelenoP, Cat, and Sod1 was quantified using real-time quantitative reverse transcription. Malondialdehyde content and catalase activity were determined spectrophotometrically. (3) After long-term SeMet administration, the amount of Se increased by 12-fold in mouse blood, 15-fold in the liver, and 42-fold in the brain, as compared to that in the control. Exposure to SeMet decreased amounts of Fe and Cu in blood, but increased Fe and Zn levels in the liver and increased the levels of all examined elements in the brain. Se increased malondialdehyde content in the blood and brain but decreased it in liver. SeMet administration increased the mRNA expression of selenoprotein P, dismutase, and catalase, but decreased catalase activity in brain and liver. (4) Eight-week-long selenomethionine consumption elevated Se levels in the blood, liver, and especially in the brain and disturbed the homeostasis of Fe, Zn, and Cu. Moreover, Se induced lipid peroxidation in the blood and brain, but not in the liver. In response to SeMet exposure, significant up-regulation of the mRNA expression of catalase, superoxide dismutase 1, and selenoprotein P in the brain, and especially in the liver, was determined.

Antitumor effect of selenium-rich Brazil nuts and selenomethionine dietary supplementation on pre-existing 4T1 mammary tumor growth in mice

Selenium (Se) is an essential micronutrient known to play an important role in the antioxidant system that can potentially influence tumor growth. We aimed to investigate the effects of dietary Se supplementation after detection of 4T1 mammary tumor growth in BALB/c mice. Thirty female mice received subcutaneous inoculation of 4T1 cells. After five days, all animals presenting palpable tumors were randomly assigned to three groups: a control group (Se-control) receiving a diet with adequate Se (0.15 mg/kg) and two other groups that received Se-supplemented diets (1.4 mg/kg of total Se) with either Brazilian nuts (Se-Nuts) or selenomethionine (SeMet). Data were assessed by either One or Two-way ANOVA followed by Tukey's HSD or Bonferroni's post hoc tests, respectively. Both Se-supplemented diets reduced tumor volume from the thirteenth day of feeding compared with the Se-adequate (control) diet (p < 0.05). The SeMet group presented a higher Se blood concentration (p < 0.05) than the Se-control group, with the Se-Nuts group presenting intermediate values. Selenoprotein P gene expression in the liver was higher in the Se-Nuts group than in the Se-control group (p < 0.05), while the SeMet group presented intermediate expression. Dietary Se supplementation, starting after detection of 4T1 palpable lesions, reduced tumor volume in mice.

Emerging roles of selenium on metabolism and type 2 diabetes

Selenium is recognized as an essential element for human health and enters human body mainly via diet. Selenium is a key constituent in selenoproteins, which exert essential biological functions, including antioxidant and anti-inflammatory effects. Several selenoproteins including glutathione peroxidases, selenoprotein P and selenoprotein S are known to play roles in the regulation of type 2 diabetes. Although there is a close association between certain selenoproteins with glucose metabolism or insulin resistance, the relationship between selenium and type 2 diabetes is complex and remains uncertain. Here we review recent advances in the field with an emphasis on roles of selenium on metabolism and type 2 diabetes. Understanding the association between selenium and type 2 diabetes is important for developing clinical practice guidelines, establishing and implementing effective public health policies, and ultimately combating relative health issues.

Glutathione peroxidase-1 and neuromodulation: Novel potentials of an old enzyme

Glutathione peroxidase (GPx) acts in co-ordination with other signaling molecules to exert its own antioxidant role. We have demonstrated the protective effects of GPx,/GPx-1, a selenium-dependent enzyme, on various neurodegenerative disorders (i.e., Parkinson's disease, Alzheimer's disease, cerebral ischemia, and convulsive disorders). In addition, we summarized the recent findings indicating that GPx-1 might play a role as a neuromodulator in neuropsychiatric conditions, such as, stress, bipolar disorder, schizophrenia, and drug intoxication. In this review, we attempted to highlight the mechanistic scenarios mediated by the GPx/GPx-1 gene in impacting these neurodegenerative and neuropsychiatric disorders, and hope to provide new insights on the therapeutic interventions against these disorders.

The Thiol-Modifier Effects of Organoselenium Compounds and Their Cytoprotective Actions in Neuronal Cells

Most pharmacological studies concerning the beneficial effects of organoselenium compounds have focused on their ability to mimic glutathione peroxidase (GPx). However, mechanisms other than GPx-like activity might be involved on their biological effects. This study was aimed to investigate and compare the protective effects of two well known [(PhSe)₂ and PhSeZnCl] and two newly developed (MRK Picolyl and MRK Ester) organoselenium compounds against oxidative challenge in cultured neuronal HT22 cells. The thiol peroxidase and oxidase activities were performed using the glutathione reductase (GR)-coupled assay. In order to evaluate protective effects of the organoselenium compounds against oxidative challenge in neuronal HT22 cells, experiments based on glutamate-induced oxytosis and SIN-1-mediated peroxynitrite generation were performed. The thiol peroxidase activities of the studied organoselenium compounds were smaller than bovine erythrocytes GPx enzyme. Besides, (PhSe)₂ and PhSeZnCl showed higher thiol peroxidase and lower thiol oxidase activities compared to the new compounds. MRK Picolyl and MRK Ester, which showed lower thiol peroxidase activity, showed higher thiol oxidase activity. Both pre- or co-treatment with (PhSe)₂, PhSeZnCl, MRK Picolyl and MRK Ester protected HT22 cells against glutamate-induced cytotoxicity. (PhSe)₂ and MRK Picolyl significantly prevented peroxinitrite-induced dihydrorhodamine oxidation, but this effect was observed only when HT22 were pre-treated with these compounds. The treatment with (PhSe)₂ increased the protein expression of antioxidant defences (Prx3, CAT and GCLC) in HT22 cells. Taking together, our results suggest that the biological effects elicited by these compounds are not directly related to their GPx-mimetic and thiol oxidase activities, but might be linked to the up-regulation of endogenous antioxidant defences trough their thiol-modifier effects.

Preparation and spectroscopic identification of methyl-Se-nitrososelenol

Herein, we report, for the first time, the preparation, matrix-isolation, and spectroscopic characterization of the methyl selenyl radical and methyl-Se-nitrososelenol in combination with DFT and CASSCF/NEVPT2 computations. The latter proved to be highly photolabile, and upon irradiation with light at λ = 465 nm it leads to methyl selenyl and nitric oxide radical pairs. Upon λ > 730 nm irradiation it rearranges back to methyl-Se-nitrososelenol.

Role of glutathione peroxidase 1 in glucose and lipid metabolism-related diseases

Glutathione peroxidase 1 (GPX1) is a selenium-dependent enzyme that reduces intracellular hydrogen peroxide and lipid peroxides. While past research explored regulations of gene expression and biochemical function of this selenoperoxidase, GPX1 has recently been implicated in the onset and development of chronic diseases. Clinical data have shown associations of human GPX1 gene variants with elevated risks of diabetes. Knockout and overexpression of Gpx1 in mice may induce types 1 and 2 diabetes-like phenotypes, respectively. This review assembles the latest advances in this new field of selenium biology, and attempts to postulate signal and molecular mechanisms mediating the role of GPX1 in glucose and lipid metabolism-related diseases. Potential therapies by harnessing the beneficial effects of this ubiquitous redox-modulating enzyme are briefly discussed.

Organoselenium compounds as mimics of selenoproteins and thiol modifier agents

Selenium is an essential trace element for animals and its role in the chemistry of life relies on a unique functional group: the selenol (-SeH) group. The selenol group participates in critical redox reactions. The antioxidant enzymes glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) exemplify important selenoproteins. The selenol group shares several chemical properties with the thiol group (-SH), but it is much more reactive than the sulfur analogue. The substitution of S by Se has been exploited in organic synthesis for a long time, but in the last 4 decades the re-discovery of ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) and the demonstration that it has antioxidant and therapeutic properties has renovated interest in the field. The ability of ebselen to mimic the reaction catalyzed by GPx has been viewed as the most important molecular mechanism of action of this class of compound. The term GPx-like or thiol peroxidase-like reaction was previously coined in the field and it is now accepted as the most important chemical attribute of organoselenium compounds. Here, we will critically review the literature on the capacity of organoselenium compounds to mimic selenoproteins (particularly GPx) and discuss some of the bottlenecks in the field. Although the GPx-like activity of organoselenium compounds contributes to their pharmacological effects, the superestimation of the GPx-like activity has to be questioned. The ability of these compounds to oxidize the thiol groups of proteins (the thiol modifier effects of organoselenium compounds) and to spare selenoproteins from inactivation by soft-electrophiles (MeHg⁺, Hg²⁺, Cd²⁺, etc.) might be more relevant for the explanation of their pharmacological effects than their GPx-like activity. In our view, the exploitation of the thiol modifier properties of organoselenium compounds can be harnessed more rationally than the use of low mass molecular structures to mimic the activity of high mass macromolecules that have been shaped by millions to billions of years of evolution.

Selenoprotein P-neutralizing antibodies improve insulin secretion and glucose sensitivity in type 2 diabetes mouse models

Selenoprotein P (SeP) functions as a selenium (Se)-supply protein. SeP is identified as a hepatokine, promoting insulin resistance in type 2 diabetes. Thus, the suppression of Se-supply activity of SeP might improve glucose metabolism. Here, we develop an anti-human SeP monoclonal antibody AE2 as with neutralizing activity against SeP. Administration of AE2 to mice significantly improves glucose intolerance and insulin resistance that are induced by human SeP administration. Furthermore, excess SeP administration significantly decreases pancreas insulin levels and high glucose-induced insulin secretion, which are improved by AE2 administration. Epitope mapping reveals that AE2 recognizes a region of human SeP adjacent to the first histidine-rich region (FHR). A polyclonal antibody against the mouse SeP FHR improves glucose intolerance and insulin secretion in a mouse model of diabetes. This report describes a novel molecular strategy for the development of type 2 diabetes therapeutics targeting SeP.

Selenoprotein P is secreted by the liver and when present in excess it promotes development of type 2 diabetes. Here the authors develop neutralizing antibodies to target human and mouse selenoprotein P, and show that they improve insulin secretion and glucose tolerance in mouse models.

Immunobiology of Nitric Oxide and Regulation of Inducible Nitric Oxide Synthase

Nitric oxide (NO) is a bioactive gas that has multiple roles in innate and adaptive immune responses. In macrophages, nitric oxide is produced by inducible nitric oxide synthase upon microbial and cytokine stimulation. It is needed for host defense against pathogens and for immune regulation. This review will summarize the role of NO and iNOS in inflammatory and immune responses and will discuss the regulatory mechanisms that control inducible nitric oxide synthase expression and activity.

A role for Sel-Plex™, a source of organic selenium in selenised yeast cell wall protein, as a factor that influences meat stability

Selenium is an important mineral required in the antioxidant system in animals, which is involved with oxidative stability in tissues, particularly membranes, and is involved in various aspects of meat quality and stability on the shelf, due to its protective properties on lipids, preventing rancidity. Se can be supplied in an inorganic or chemically organic form, and it is well known that the latter has beneficial properties and improved functionality in physiological systems compared to the former. Research has shown that organic Se is associated with increased tenderness and the prevention of certain problems in pale exudative meat, discolouration and off-flavours and odours in meat, although this depends on other components of the antioxidant system, such as vitamin E, being present as well. The change in prominence of glutathione peroxidase forms in their interaction with vitamin E in cell membranes is also noted. The following review (the third in a series) details the research that has been conducted into the role of Se in meat stability and related factors, with specific focus on organic forms of Se, namely the commercial product Sel-Plex™ (Alltech Inc, Nicholasville, KY, USA), which is derived from yeast and in which selenium replaces sulphur in methionine forming selenomethionine in yeast protein.

Organic selenium in animal nutrition – utilisation, metabolism, storage and comparison with other selenium sources

The importance of selenium as a key component of antioxidant systems in animals is well recognised due to much research about this mineral in many species. Selenium is required as part of the antioxidant enzyme structure and plays a major role in various protective systems in animal physiology, including immunity, cellular stability and DNA protection. The following review is the first in a series of three which details the importance of selenium in animal nutrition, and how the chemically organic form, which is akin to the form of the mineral in natural feed materials, can provide increased benefits in utilisation, storage and metabolism compared to inorganic sources.

Evaluation of selenium on kidney function following ischemic injury in rats; protective effects and antioxidant activity

Introduction: Renal dysfunction is caused by ischemia-reperfusion (I/R) injury, which is a common problem in kidney surgery or kidney transplantation. The human body consists of enormous complex antioxidant systems, which inquires adequate selenium (Se) absorption for normal physiologic function. It is known that Se has some antioxidant effects. Objectives: In the present research, effects of the Se on damages caused by I/R injury investigated. Materials and Methods: In this experimental research, four groups of rats (weighing 220±10 g) used, include control group, I/R group, healthy group treated with Se for two weeks, and I/R group with two-week Se treatment. On the test day, I/R was treated in both right and left renal arteries for 45 minutes and the reperfusion was done for 24 hours. Results: In I/R group, the amount of urea and serum creatinine (Cr) was an injury indicator of the kidney cells which showed a significant increase compared with the control group. When the treatment with Se significantly reduced these indicators, glutathione (GSH) enzyme levels reduced significantly in the second group and the enzyme levels increased due to Se treatment in the fourth group. Furthermore, malondialdehyde (MDA) enzyme levels increased in I/R group due to the Se treatment in the fourth group which was significantly reduced. In addition, the tissue damage was reduced in the fourth group compared with I/R group. Conclusion: Se has a protective effect against the I/R injury. This effect might be due to the antioxidant properties of Se.

Relevance of peroxynitrite formation and 3-nitrotyrosine on spermatozoa physiology

HIGHLIGHTS

Male fertility decline has been attributed, in part, to increased oxidative stress.Here we will focus on spermatozoa ROS, namely O2•-, NO and ONOO- and their contribution to protein tyrosine nitration, namely by 3-NT formation.An in depth review will be made on the methods used to detect protein oxidation.Detecting 3-NT in sperm proteins will have a crucial clinical impact, namely on the follow up of anti-oxidant therapies.

ABSTRACT

Infertility is a clinical condition that affects around 15% of reproductive-aged couples worldwide. Around half of these cases are due to male factors, the most owing to idiopathic causes. The increase of reactive oxygen species (ROS), which leads to oxidative stress (OS), has been discussed in the last years as a possible cause of male idiopathic infertility. Superoxide anion (O2 •-) and nitric oxide (NO) can react with each other contributing to the formation of peroxynitrite (ONOO-). This molecule can then act on spermatozoa proteins, leading to nitration of protein tyrosines - addition of a nitro (NO2) group - that is then manifested by the formation of 3-nitrotyrosine (3-NT). In turn, 3-NT may be responsible for the alteration or inactivation of the protein function.This review will focus on the description of spermatozoa ROS, namely O2 •-, NO and ONOO- and in their contribution to protein tyrosine nitration, namely by 3-NT formation. Previous results about the effect of ONOO- and 3-NT in spermatozoa will be presented, as well as, the methods that can be performed to detect the protein oxidation by these species. The impact of measuring, at the clinical level, 3-NT, considered a marker of OS, in spermatozoa will be discussed.

Ebselen Decreases Oxygen Free Radical Production and Iron Concentrations in the Hearts of Chronically Iron-Overloaded Mice

Chronic iron overload is a major cause of cardiac failure throughout the world, but its pathogenesis remains to be clarified. It is conjectured that the toxicity of iron is due to its ability to catalyze the formation of oxygen free radicals (OFR), which can damage cellular membranes, proteins, and DNA. The authors report on the cardioprotective effects of the glutathione peroxidase (GPx) mimic ebselen on iron concentrations in the heart and GPx activity, and on the production of the cytotoxic aldehydes hexanal, 4-hydroxyl-2-nonenal (HNE), and malondialdehyde (MDA). Fifteen B6D2F1 mice were randomized to 1 of 3 treatment groups for a total of 20 treatments: 1) control (0.1 mL normal saline i.p. per mouse, per day); 2) iron-only (10 mg iron dextran i.p. per mouse, per day); 3) iron plus ebselen (25 mg/kg p.o. per mouse, per day). In comparison to iron-only treated mice, the authors’ findings show that supplementation with ebselen can decrease both cytotoxic aldehyde and iron concentrations in heart tissue. Additionally, mice supplemented with ebselen had an increase in GPx activity level in comparison to iron-only treated mice. To the authors’knowledge, this is the first study to examine the cardioprotective effects of ebselen against OFR damage in a model of chronic iron overload. These findings suggest that ebselen may have significance in the management of disorders of iron overload.

Helmut Sies and the compartmentation of hydroperoxide metabolism

The early work of Helmut Sies on mammalian hydroperoxide metabolism is reviewed with particular emphasis on the in situ function of catalase and glutathione peroxidase1. Starting out from a catalase-dominated thinking in the middle of the last century, Sies first demonstrated, by whole organ spectroscopy, that H2O2 is generated in rat liver and metabolized by catalase. In a joined effort with the author's group, he then worked out that glutathione peroxidase can kinetically compete with catalase in hydroperoxide metabolism in situ. In compartmentalized cells, however, the "competition" of the two enzymes turned out to be a mutual complementation because of their different subcellular location. The studies for the first time documented that the metabolism of freely diffusible hydroperoxides is compartmentalized and, thus, paved the way to a better understanding of oxidant challenges and redox regulation. The article, garnished with personal memories, is meant as a nostalgic journey though ancient times of biochemistry with their changing fashions and paradigms, revealing the roots of topical perspectives and controversies in redox biology.

Biological activity of selenorganic compounds at heavy metal salts intoxication

Possible mechanisms of the antitoxic action of organoselenium compounds in heavy metal poisoning have been considered. Heavy metal toxicity associated with intensification of free radical oxidation, suppression of the antioxidant system, damage to macromolecules, mitochondria and the genetic material can cause apoptotic cell death or the development of carcinogenesis. Organic selenium compounds are effective antioxidants during heavy metal poisoning; they exhibit higher bioavailability in mammals than inorganic ones and they are able to activate antioxidant defense, bind heavy metal ions and reactive oxygen species formed during metal-induced oxidative stress. One of promising organoselenium compounds is diacetophenonyl selenide (DAPS-25), which is characterized by antioxidant and antitoxic activity, under conditions including heavy metal intoxication

Production and characterization Te-peptide by induced autolysis of Saccharomyces cerevisiae

Recently, the interest in mimicking functions of chalcogen-based catalytic antioxidants like selenoenzymes, has been increased. Various attempts had been done with selenium, but very few attempts were carried out with tellurium. Bio-complex formation and characterization of tellurium was not tried earlier by using any organism. The present study was focused on tellurium peptide production, characterization, and bioactivity assessment especially Mimetic to glutathione peroxidase (GPx). The production was achieved by the autolysis of total proteins obtained from Saccharomyces cerevisiae ATCC 7752 grown with inorganic tellurium. The GPx-like activity of the hydrolyzed tellurium peptide was increased when prepared by autolysis, but decreased when prepared by acid hydrolysis. Tellurium peptide produced by autolysis of the yeast cell showed increased GPx-like activity as well as tellurium content. Tellurium peptide showed little toxicity, compared to highly toxic inorganic tellurium. The results showed the potential of tellurium peptide as an antioxidant that can be produced by simple autolysis of yeast cells.

Direct synthesis of 4-organylsulfenyl-7-chloro quinolines and their toxicological and pharmacological activities in Caenorhabditis elegans

We describe herein our results on the synthesis and biological properties in Caenorhabditis elegans of a range of 4-organylsulfenyl-7-chloroquinolines. This class of compounds have been easily synthesized in high yields by direct reaction of 4,7-dichloroquinoline with organylthiols using DMSO as solvent at room temperature under air atmosphere and tolerates a range of substituents in the organylsulfenyl moiety. We have performed a toxicological and pharmacological screening of the synthesized 4-organylsulfenyl-7-chloroquinolines in vivo in C. elegans acutely exposed to these compounds, under per se and stress conditions. Hence, we determined the lethal dose 50% (LD50), in order to choose a nonlethal concentration (10 μM) and verified that at that concentration some of the compounds depicted protective action against the induced damage inflicted by paraquat, a superoxide generator. Two compounds (3c and 3h) reduced the toxicity inflicted by paraquat above survival, reproduction and longevity of the worms, at least in part, by reducing the reactive oxygen species (ROS) generated by the toxicant exposure. Besides, these compounds increased the quantities of superoxide dismutase (SOD-3::GFP) and catalase (CTL-1,2,3::GFP), antioxidant enzymes. We concluded that the protective effects of the compounds observed in this study might have been a hormetic response dependent of the transcriptional factor DAF-16/FOXO, causing a non-lethal oxidative stress that protects against the subsequently damage induced by paraquat.

Role of vitamin C in the function of the vascular endothelium

SIGNIFICANCE

Vitamin C, or ascorbic acid, has long been known to participate in several important functions in the vascular bed in support of endothelial cells. These functions include increasing the synthesis and deposition of type IV collagen in the basement membrane, stimulating endothelial proliferation, inhibiting apoptosis, scavenging radical species, and sparing endothelial cell-derived nitric oxide to help modulate blood flow. Although ascorbate may not be able to reverse inflammatory vascular diseases such as atherosclerosis, it may well play a role in preventing the endothelial dysfunction that is the earliest sign of many such diseases.

RECENT ADVANCES

Beyond simply preventing scurvy, evidence is mounting that ascorbate is required for optimal function of many dioxygenase enzymes in addition to those involved in collagen synthesis. Several of these enzymes regulate the transcription of proteins involved in endothelial function, proliferation, and survival, including hypoxia-inducible factor-1α and histone and DNA demethylases. More recently, ascorbate has been found to acutely tighten the endothelial permeability barrier and, thus, may modulate access of ascorbate and other molecules into tissues and organs.

CRITICAL ISSUES

The issue of the optimal cellular content of ascorbate remains unresolved, but it appears that low millimolar ascorbate concentrations are normal in most animal tissues, in human leukocytes, and probably in the endothelium. Although there may be little benefit of increasing near maximal cellular ascorbate concentrations in normal people, many diseases and conditions have either systemic or localized cellular ascorbate deficiency as a cause for endothelial dysfunction, including early atherosclerosis, sepsis, smoking, and diabetes.

FUTURE DIRECTIONS

A key focus for future studies of ascorbate and the vascular endothelium will likely be to determine the mechanisms and clinical relevance of ascorbate effects on endothelial function, permeability, and survival in diseases that cause endothelial dysfunction.

Neuroprotective effect of ebselen against intracerebroventricular streptozotocin-induced neuronal apoptosis and oxidative stress in rats

The goal of this study was to examine the neuroprotective effect of ebselen against intracerebroventricular streptozotocin (ICV-STZ)-induced oxidative stress and neuronal apoptosis in rat brain. A total of 30 adult male Sprague-Dawley rats were randomly divided into 3 groups of 10 animals each: control, ICV-STZ, and ICV-STZ treated with ebselen. The ICV-STZ group rats were injected bilaterally with ICV-STZ (3 mg/kg) on days 1 and 3, and ebselen (10 mg/kg/day) was administered for 14 days starting from 1st day of ICV-STZ injection to day 14. Rats were killed at the end of the study and brain tissues were removed for biochemical and histopathological investigation. Our results demonstrated, for the first time, the neuroprotective effect of ebselen on Alzheimer's disease (AD) model in rats. Our present study, in ICV-STZ group, showed significant increase in tissue malondialdehyde levels and significant decrease in enzymatic antioxidants superoxide dismutase and glutathione peroxidase in the frontal cortex tissue. The histopathological studies in the brain of rats also supported that ebselen markedly reduced the ICV-STZ-induced histopathological changes and well preserved the normal histological architecture of the frontal cortex tissue. The number of apoptotic neurons was increased in frontal cortex tissue after ICV-STZ administration. Treatment of ebselen markedly reduced the number of degenerating apoptotic neurons. The study demonstrates the effectiveness of ebselen, as a powerful antioxidant, in preventing the oxidative damage and morphological changes caused by ICV-STZ in rats. Thus, ebselen may have a therapeutic value for the treatment of AD.

Involvement of MsrB1 in the regulation of redox balance and inhibition of peroxynitrite-induced apoptosis in human lens epithelial cells

Methionine sulfoxide reductases (Msrs) in lens cells are important for the maintenance of lens cell viability and resistance to oxidative stress damage. Peroxynitrite (ONOO(-)), as a strong oxidizing and nitrating agent, occurred in diabetic retinopathy patients and diabetic model animal. In an attempt to shed light on the roles of MsrB1, known as selenoprotein R, in protecting human lens epithelial (HLE) cells against peroxynitrite damage, and contribution of loss of its normal activity to cataract, the influences of MsrB1 gene silencing on peroxynitrite-induced apoptosis in HLE cells were studied. The results showed that both exogenous peroxynitrite and MsrB1 gene silencing by short interfering RNA (siRNA) independently resulted in oxidative stress, endoplasmic reticulum (ER) stress, activation of caspase-3 as well as an increase of apoptosis in HLE cells; moreover, when MsrB1-gene-silenced cells were exposed to 300 μM peroxynitrite, these indexes were further aggravated at the same conditions and DNA strand breaks occurred. The results demonstrate that in HLE cells MsrB1 may play important roles in regulating redox balance and mitigating ER stress as induced by oxidative stress under physiological conditions; MsrB1 may also protect HLE cells against peroxynitrite-induced apoptosis by inhibiting the activation of caspase-3 and oxidative damage of DNA under pathological conditions. Our results imply that loss of its normal activity is likely to contribute to cataract.

Organotellurium and organoselenium compounds attenuate Mn-induced toxicity in Caenorhabditis elegans by preventing oxidative stress

Organochalcogens have been widely studied given their antioxidant activity, which confers neuroprotection, antiulcer, and antidiabetic properties. Given the complexity of mammalian models, understanding the cellular and molecular effects of organochalcogens has been hampered. The nematode worm Caenorhabditis elegans is an alternative experimental model that affords easy genetic manipulations, green fluorescent protein tagging, and in vivo live analysis of toxicity. We previously showed that manganese (Mn)-exposed worms exhibit oxidative-stress-induced neurodegeneration and life-span reduction. Here we use Mn-exposed worms as a model for an oxidatively challenged organism to investigate the underlying mechanisms of organochalcogen antioxidant properties. First, we recapitulate in C. elegans the effects of organochalcogens formerly observed in mice, including their antioxidant activity. This is followed by studies on the ability of these compounds to afford protection against Mn-induced toxicity. Diethyl-2-phenyl-2-tellurophenyl vinyl phosphonate (DPTVP) was the most efficacious compound, fully reversing the Mn-induced reduction in survival and life span. Ebselen was also effective, reversing the Mn-induced reduction in survival and life span, but to a lesser extent compared with DPTVP. DPTVP also lowered Mn-induced increases in oxidant levels, indicating that the increased survival associated with exposure to this compound is secondary to a decrease in oxidative stress. Furthermore, DPTVP induced nuclear translocation of the transcriptional factor DAF-16/FOXO, which regulates stress responsiveness and aging in worms. Our findings establish that the organochalcogens DPTVP and ebselen act as antiaging agents in a model of Mn-induced toxicity and aging by regulating DAF-16/FOXO signaling and attenuating oxidative stress.

Selenium and its' role in the maintenance of genomic stability

Selenium (Se) is an essential micronutrient for humans, acting as a component of the unusual amino acids, selenocysteine (Se-Cys) and selenomethionine (Se-Met). Where Se levels are low, the cell cannot synthesise selenoproteins, although some selenoproteins and some tissues are prioritised over others. Characterised functions of known selenoproteins, include selenium transport (selenoprotein P), antioxidant/redox properties (glutathione peroxidases (GPxs), thioredoxin reductases and selenoprotein P) and anti-inflammatory properties (selenoprotein S and GPx4). Various forms of Se are consumed as part of a normal diet, or as a dietary supplement. Supplementation of tissue culture media, animal or human diets with moderate levels of certain Se compounds may protect against the formation of DNA adducts, DNA or chromosome breakage, and chromosome gain or loss. Protective effects have also been shown on mitochondrial DNA, and on telomere length and function. Some of the effects of Se compounds on gene expression may relate to modulation of DNA methylation or inhibition of histone deacetylation. Despite a large number of positive effects of selenium and selenoproteins in various model systems, there have now been some human clinical trials that have shown adverse effects of Se supplementation, according to various endpoints. Too much Se is as harmful as too little, with animal models showing a "U"-shaped efficacy curve. Current recommended daily allowances differ among countries, but are generally based on the amount of Se necessary to saturate GPx enzymes. However, increasing evidence suggests that other enzymes may be more important than GPx for Se action, that optimal levels may depend upon the form of Se being ingested, and vary according to genotype. New paradigms, possibly involving nutrigenomic tools, will be necessary to optimise the forms and levels of Se desirable for maximum protection of genomic stability in all humans.

Glutathione peroxidase-1 in health and disease: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species, such as superoxide and hydrogen peroxide, are generated in all cells by mitochondrial and enzymatic sources. Left unchecked, these reactive species can cause oxidative damage to DNA, proteins, and membrane lipids. Glutathione peroxidase-1 (GPx-1) is an intracellular antioxidant enzyme that enzymatically reduces hydrogen peroxide to water to limit its harmful effects. Certain reactive oxygen species, such as hydrogen peroxide, are also essential for growth factor-mediated signal transduction, mitochondrial function, and maintenance of normal thiol redox-balance. Thus, by limiting hydrogen peroxide accumulation, GPx-1 also modulates these processes. This review explores the molecular mechanisms involved in regulating the expression and function of GPx-1, with an emphasis on the role of GPx-1 in modulating cellular oxidant stress and redox-mediated responses. As a selenocysteine-containing enzyme, GPx-1 expression is subject to unique forms of regulation involving the trace mineral selenium and selenocysteine incorporation during translation. In addition, GPx-1 has been implicated in the development and prevention of many common and complex diseases, including cancer and cardiovascular disease. This review discusses the role of GPx-1 in these diseases and speculates on potential future therapies to harness the beneficial effects of this ubiquitous antioxidant enzyme.

Anti-hemolytic and peroxyl radical scavenging activity of organoselenium compounds: an in vitro study

Selenium-containing amino acids, selenocystine (CysSeSeCys), methylselenocysteine (MeSeCys), and selenomethionine (SeMet) have been examined for anti-hemolytic and peroxyl radical scavenging ability. Effect of these compounds on membrane lipid peroxidation, release of hemoglobin, and loss of intracellular K(+) ion as a consequence of peroxyl radicals-induced oxidation of human red blood cells were used to evaluate their anti-hemolytic ability. The peroxyl radicals were generated from thermal degradation of 2,2'-azobis(2-methylpropionamidine) dihydrochloride. Significant delay (t(eff)) was observed in oxidative damage in the presence of the selenium compounds. From the IC(50) values for the inhibition of hemolysis, lipid peroxidation, and K(+) ion leakage, the relative anti-hemolytic ability of the compounds were found to be in the order of CysSeSeCys > MeSeCys > SeMet. The anti-hemolytic abilities of the compounds, when compared with sodium selenite (Na(2)SeO(3)) under identical experimental conditions, were found to be better than Na(2)SeO(3). Relative rate constants estimated for the reaction of MeSeCys and SeMet with peroxyl radicals by competition kinetics using ABTS(2-) as a reference confirmed that all the compounds are efficient peroxyl radical scavengers. Comparison of the GPx-like activity of these compounds, by NADPH-GSH reductase coupled assay, indicated that CysSeSeCys exhibits the highest activity. Based on these results, it is concluded that among the compounds examined, CysSeSeCys, possessing the ability to reduce peroxyl radicals and hydroperoxides showed efficient anti-hemolytic activity.

Reduction of diphenyl diselenide and analogs by mammalian thioredoxin reductase is independent of their gluthathione peroxidase-like activity: a possible novel pathway for their antioxidant activity

Since the successful use of the organoselenium drug ebselen in clinical trials for the treatment of neuropathological conditions associated with oxidative stress, there have been concerted efforts geared towards understanding the precise mechanism of action of ebselen and other organoselenium compounds, especially the diorganyl diselenides such as diphenyl diselenide, and its analogs. Although the mechanism of action of ebselen and other organoselenium compounds has been shown to be related to their ability to generally mimic native glutathione peroxidase (GPx), only ebselen however has been shown to serve as a substrate for the mammalian thioredoxin reductase (TrxR), demonstrating another component of its pharmacological mechanisms. In fact, there is a dearth of information on the ability of other organoselenium compounds, especially diphenyl diselenide and its analogs, to serve as substrates for the mammalian enzyme thioredoxin reductase. Interestingly, diphenyl diselenide shares several antioxidant and neuroprotective properties with ebselen. Hence in the present study, we tested the hypothesis that diphenyl diselenide and some of its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxy-diphenyl diselenide, 4.4'-biscarboxydiphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could also be substrates for rat hepatic TrxR. Here we show for the first time that diselenides are good substrates for mammalian TrxR, but not necessarily good mimetics of GPx, and vice versa. For instance, bis-methoxydiphenyl diselenide had no GPx activity, whereas it was a good substrate for reduction by TrxR. Our experimental observations indicate a possible dissociation between the two pathways for peroxide degradation (either via substrate for TrxR or as a mimic of GPx). Consequently, the antioxidant activity of diphenyl diselenide and analogs can be attributed to their capacity to be substrates for mammalian TrxR and we therefore conclude that subtle changes in the aryl moiety of diselenides can be used as tool for dissociation of GPx or TrxR pathways as mechanism triggering their antioxidant activities.

Reduction of diphenyl diselenide and analogs by mammalian thioredoxin reductase is independent of their gluthathione peroxidase-like activity: a possible novel pathway for their antioxidant activity

Since the successful use of the organoselenium drug ebselen in clinical trials for the treatment of neuropathological conditions associated with oxidative stress, there have been concerted efforts geared towards understanding the precise mechanism of action of ebselen and other organoselenium compounds, especially the diorganyl diselenides such as diphenyl diselenide, and its analogs. Although the mechanism of action of ebselen and other organoselenium compounds has been shown to be related to their ability to generally mimic native glutathione peroxidase (GPx), only ebselen however has been shown to serve as a substrate for the mammalian thioredoxin reductase (TrxR), demonstrating another component of its pharmacological mechanisms. In fact, there is a dearth of information on the ability of other organoselenium compounds, especially diphenyl diselenide and its analogs, to serve as substrates for the mammalian enzyme thioredoxin reductase. Interestingly, diphenyl diselenide shares several antioxidant and neuroprotective properties with ebselen. Hence in the present study, we tested the hypothesis that diphenyl diselenide and some of its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxy-diphenyl diselenide, 4.4'-biscarboxydiphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could also be substrates for rat hepatic TrxR. Here we show for the first time that diselenides are good substrates for mammalian TrxR, but not necessarily good mimetics of GPx, and vice versa. For instance, bis-methoxydiphenyl diselenide had no GPx activity, whereas it was a good substrate for reduction by TrxR. Our experimental observations indicate a possible dissociation between the two pathways for peroxide degradation (either via substrate for TrxR or as a mimic of GPx). Consequently, the antioxidant activity of diphenyl diselenide and analogs can be attributed to their capacity to be substrates for mammalian TrxR and we therefore conclude that subtle changes in the aryl moiety of diselenides can be used as tool for dissociation of GPx or TrxR pathways as mechanism triggering their antioxidant activities.

Antioxidants induce apoptosis of rat ovarian theca-interstitial cells

Regulation of growth of ovarian theca-interstitial tissues is essential for normal ovarian development and function. Reactive oxygen species are involved in modulation of signal transduction pathways, including regulation of tissue growth and apoptosis. Previously, we have demonstrated that antioxidants inhibit proliferation of theca-interstitial cells. This report evaluates the effects of antioxidants on apoptosis of rat theca-interstitial cells. The cells were cultured in chemically defined media without or with vitamin E succinate and ebselen. Apoptosis was evaluated by cytochemical assessment of nuclear morphology, activity of executioner caspases 3 and 7, and determination of staining with annexin V in combination with propidium iodide. Both tested antioxidants induced significant morphological changes consistent with apoptosis, including chromatin condensation, nuclear shrinkage, and pyknosis. Antioxidants also induced other hallmarks of apoptosis including increased activity of caspases 3/7 as well as increased staining with annexin V. The present findings demonstrate that antioxidants with distinctly different mechanisms of action induce a series of events consistent with the process of apoptosis in ovarian mesenchyme. These observations may be of translational-clinical relevance, providing mechanistic support for the use of antioxidants in the treatment of PCOS, a condition associated with excessive growth and activity of theca-interstitial cells.

Mechanisms involved in the antinociceptive effect caused by diphenyl diselenide in the formalin test

This study investigated the mechanisms involved in the antinociceptive action induced by diphenyl diselenide ((PhSe)2) in the formalin test. Mice were pre-treated with (PhSe)2 by the oral route (0.1–100 mg kg−1), 30 min before formalin injection. To address some of the mechanisms by which (PhSe)2 inhibits formalin-induced nociception mice were treated with different drugs. The antinociceptive effect of (PhSe)2 was shown in the first and second phases of the formalin test. The antinociceptive effect caused by (PhSe)2 (10 mg kg−1, p.o.) was prevented by intrathecal injection of K+ channel blockers such as apamin and charybdotoxin (small- and large-conductance Ca2+-activated K+ channel inhibitors, respectively) and tetraethylammonium (TEA, a non-selective voltage-dependent K+ channel inhibitor), but not glib-enclamide (an ATP-sensitive K+ channel inhibitor). The antinociceptive action caused by (PhSe)2 (10 mg kg−1, p.o.) was also blocked by a nitric oxide (NO) synthase inhibitor (Nω-nitro-l-arginine, L-NOARG) and the soluble guanylate cyclase inhibitors 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and methylene blue. These results suggest the participation of NO/cyclic GMP/Ca2+ and K+ channel pathways in the antinociceptive effect caused by (PhSe)2.

Mechanisms involved in the antinociceptive and anti-inflammatory effects of bis selenide in mice

Objectives

The present study examined the mechanisms involved in the antinociceptive effects of bis selenide [(Z)-2,3-bis(4-chlorophenylselanyl)prop-2-en-1-ol].

Methods

The effects of oral bis selenide were tested against licking behaviour and oedema in mice induced by formalin, serotonin, histamine, glutamate, phorbol 12-myristate 13-acetate (PMA), 8-bromoadenosine 3′,5′-cyclic monophosphate (8-BrcAMP) and pros-taglandin E2. The effects of a variety of receptor antagonists on the antinociceptive activity were tested to determine the likely mechanism of action of bis selenide.

Key findings

Bis selenide caused antinociception on the first and second phases of the formalin test, with mean ID50 values of 34.21 (29.66–39.45) and 15.86 (12.17–20.67) mg/kg and maximal inhibition of 65 ± 3% and 90 ± 1%, respectively. At 50 mg/kg bis selenide significantly inhibited (31 ± 2%) paw oedema induced by intraplantar injection of formalin. At 25 mg/kg given 5 min after the formalin injection, bis selenide caused a significant inhibition (42 ± 5%) in the second phase of the formalin test, whereas the prophylactic treatment caused more intense inhibition (64 ± 3%). Oral administration of bis selenide reduced licking and paw oedema induced by serotonin, histamine, glutamate, PGE2, PMA and 8-BrcAMP. The antinociceptive effect of bis selenide (25 mg/kg, p.o.) on the formalin test was reversed by i.p. administration of p-chlorophenylalanine methyl ester (an inhibitor of serotonin synthesis), ketanserin (a selective 5-HT2a receptor antagonist), ondansetron (a 5-HT3 receptor antagonist) and ranitidine (a histamine H2-receptor antagonist).

Conclusions

Glutamatergic, prostaglandin E2, serotonergic (5-HT2a and 5-HT3) and histamine H2 receptors are involved in the antinociceptive effects of bis selenide in mice. The interaction of bis selenide with protein kinase C and A signalling pathways was also demonstrated.

Expression of selenoprotein-coding genes SEPP1, SEP15 and hGPX1 in non-small cell lung cancer

Aim of the study was to investigate the mRNA expression level of selenoprotein P (SEPP1), 15-kDa selenoprotein (SEP15) and glutathione peroxidase 1 (hGPX1) in paired malignant and non-malignant tissue. To achieve this goal, the quantitative real-time PCR technique was utilized in paired tissue samples from 33 non-small cell lung cancer (NSCLC) patients. Simultaneously, the activity of glutathione peroxidases (GPX) and the level of thiobarbituric acid-reactive species (TBARS) in paired tissue specimens and the blood plasma selenium level was measured. We found significant down-regulation of SEPP1 expression level in tumorous lung tissue (2.732-fold; p<0.001). The expression of hGPX1 and SEP15 in tumorous tissue remained unchanged compared to healthy tissue. The level of TBARS in malignant tissue was significantly increased (p<0.005) and negatively correlated with SEPP1 expression level (R(S)=-0.3238; p<0.05). The activity of GPX in malignant tissue was significantly increased compared to the non-malignant one (p<0.005) and negatively correlated with the expression level of SEPP1. It seems possible, that the down-regulation of SEPP1 expression may lead to an increased oxidative stress possibly resulting in lung carcinogenesis. Increased activity of GPX in tumorous lung tissue seems to be a feedback mechanism.

Antioxidant activity of sulfur and selenium: a review of reactive oxygen species scavenging, glutathione peroxidase, and metal-binding antioxidant mechanisms

It is well known that oxidation caused by reactive oxygen species (ROS) is a major cause of cellular damage and death and has been implicated in cancer, neurodegenerative, and cardiovascular diseases. Small-molecule antioxidants containing sulfur and selenium can ameliorate oxidative damage, and cells employ multiple antioxidant mechanisms to prevent this cellular damage. However, current research has focused mainly on clinical, epidemiological, and in vivo studies with little emphasis on the antioxidant mechanisms responsible for observed sulfur and selenium antioxidant activities. In addition, the antioxidant properties of sulfur compounds are commonly compared to selenium antioxidant properties; however, sulfur and selenium antioxidant activities can be quite distinct, with each utilizing different antioxidant mechanisms to prevent oxidative cellular damage. In the present review, we discuss the antioxidant activities of sulfur and selenium compounds, focusing on several antioxidant mechanisms, including ROS scavenging, glutathione peroxidase, and metal-binding antioxidant mechanisms. Findings of several recent clinical, epidemiological, and in vivo studies highlight the need for future studies that specifically focus on the chemical mechanisms of sulfur and selenium antioxidant behavior.