Effect of diphenyl diselenide, diphenyl ditelluride and ebselen on cerebral Na+, K+-ATPase activity in rats

Comparison of the antioxidant properties and the toxicity of p,p'-dichlorodiphenyl ditelluride with the parent compound, diphenyl ditelluride

The hypothesis to be tested in this study is whether the introduction of the chloro group into diphenyl ditelluride molecule (p,p'-dichlorodiphenyl ditelluride, compound 1b) alters the antioxidant and scavenging activity of diphenyl ditelluride (compound 1a) in vitro. The results revealed that 1a and 1b had a potent antioxidant activity in vitro. However, the introduction of a functional group, chloro, into diphenyl ditelluride molecule (1b) did not cause great alterations in the antioxidant action of diphenyl ditelluride against lipid peroxidation, protein carbonyl, and scavenging of 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) and 2,2'-diphenyl-1-picrylhydrazyl radicals. Based on the in vitro results, different doses (0.25 and 0.75 µmol/kg) of 1a and 1b or vehicle (canola oil, 1 ml/kg) were administered to rats to investigate if the presence of chloro into diphenyl ditelluride molecule reduces its toxicity. The data demonstrate that the chloro group introduced into diphenyl ditelluride molecule did not alter the acute oral toxicity in rats. The administration of compound 1a in rats only altered the urea level, while compound 1b caused alterations in all toxicological parameters analyzed (alanine aminotransferase and aspartate aminotransferase activities, urea and creatinine levels) in plasma of rats. The results of the present investigation support similar antioxidant and scavenging activities of 1a and 1b in rat liver homogenate in vitro. Furthermore, the presence of chloro into diphenyl ditelluride molecule did not alter the mortality index but increased toxicity of diphenyl ditelluride in rats.

Hydroxyl containing seleno-imine compound exhibits improved anti-oxidant potential and does not inhibit thiol-containing enzymes

Design and synthesis of organoselenium compounds with high thiol peroxidase (TPx) and low thiol oxidase (TOx) activities have been a difficult task and remains a synthetic-activity relationship dilemma. In this regard we are reporting for the first time a detail experimental data (both in vitro and in vivo) about the anti-oxidant and toxicological profile of an Imine (-N) containing organoselenium compound (Compound A). The TPx activity of Compound A was significantly higher than diphenyl diselenide (DPDS). Both Compound A and DPDS protected sodium nitropruside (SNP) induced thiobarbituric acid reactive species (TBARS) production in rats tissue homogenate with significantly higher activity observed for Compound A than DPDS (p<0.05). The Compound A also exhibited strong antioxidant activity in the DPPH and ABTS radical scavenging assays. This study reveals that an imine group close to selenium atom drastically enhances the catalytic activities in the aromatic thiol (PhSH) assay systems. The oxidation of biologically significant thiols reflects the toxicity of the compounds. However, the present data showed that treatment with Compound A at 0, 10, 25 or 50mg/kg was not associated with mortality or body weight loss. Similarly it did not inhibit α-ALA-D and Na(+1)/K(+1) ATPase (sulfhydryl group containing enzymes) activities after acute oral treatment; rather it enhanced non-protein thiols (NPSH) concentration. The Compound A did not cause any oxidative stress as measured by TBARS production in rat's tissue preparation. Our data also indicate that exposure to Compound A did not affect plasma transaminase activities or levels of urea and creatinine in rats. Ascorbic acid is always considered a marker of oxidative stress and the reduction of its content may indicate an increase in oxidative stress. Treatment with Compound A did not alter Ascorbic acid levels in rats. The conducted in vitro and in vivo tests show the versatile therapeutic potential of this compound in the area of free radical induced damages, will undoubtedly enhance our understanding of the mechanism of model compounds and may ultimately yield insights that result in improved GPx mimics.

An in vitro comparison of a new vinyl chalcogenide and sodium selenate on adenosine deaminase activity of human leukocytes

Selenium (Se) is a dietary essential trace element with important biological roles. Sodium selenate (Na(2)SeO(4)) is an inorganic Se compound used in human and animal nutrition that acts as precursor for selenoprotein synthesis. The organoselenium 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one (C(21)H(2)HOSe) is an α,β-unsaturated ketone functionalized vinyl chalcogenide that has been found as a potential tool in organic synthesis. Adenosine deaminase (ADA) is an important enzyme in the degradation of adenine nucleotides. In this study, we investigated the in vitro effects of both Se compounds on ADA activity and cell viability in leukocyte suspension (LS) of healthy donors (n=12). We first observed an inhibition of ADA activity using 0.1 μM of 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one, and an increase in cellular viability when 30 μM were used. However, we did not observe alterations in the presence of sodium selenate. Moreover, both Se compounds did not alter lactate dehydrogenase activity and thiobarbituric acid reactive substance levels. These results suggest that the inhibition of ADA activity caused by α,β-unsaturated ketone may affect the adenosine levels in LS and modulate cell viability, attenuating conditions that involve the activation of the immune system.

Tellurium: an element with great biological potency and potential

Tellurium has long appeared as a nearly 'forgotten' element in Biology, with most studies focusing on tellurite, tellurate and a handful of organic tellurides. During the last decade, several discoveries have fuelled a renewed interest in this element. Bioincorporation of telluromethionine provides a new approach to add heavy atoms to selected sites in proteins. Cadmium telluride (CdTe) nanoparticles are fluorescent and may be used as quantum dots in imaging and diagnosis. The antibiotic properties of tellurite, long known yet almost forgotten, have attracted renewed interest, especially since the biochemical mechanisms of tellurium cytotoxicity are beginning to emerge. The close chemical relationship between tellurium and sulfur also transcends into in vitro and in vivo situations and provides new impetus for the development of enzyme inhibitors and redox modulators, some of which may be of interest in the field of antibiotics and anticancer drug design.

Acute exposure of rabbits to diphenyl diselenide: a toxicological evaluation

The simple organoselenium compound diphenyl diselenide (PhSe)(2) is a promising new pharmacological agent. However, few toxicological evaluations of this molecule have been reported. We evaluated the effects of acute administration of (PhSe)(2) on toxicological parameters in rabbits. Adult New Zealand rabbits were exposed to (PhSe)(2) (5-500 micromol kg(-1) , intraperitoneally) once a day for 5 days. Exposure to 500 micromol kg(-1) caused 85% mortality. Exposure to 50 micromol kg(-1) of (PhSe)(2) increased the glutathione levels in the hippocampus, kidney, heart, muscle and blood, whereas lipoperoxidation (TBARS) decreased in the cerebellum and kidney after exposure to 5 micromol kg(-1) . The activity of glutathione peroxidase increased in the heart and muscle of rabbits treated with 50 micromol kg(-1) of (PhSe)(2) and glutathione reductase activity was reduced in the cerebellum, cerebral cortex and kidney. Treatment with (PhSe)(2) reduced the activity of δ-aminolevulinate dehydratase in the hippocampus and increased this activity in the heart, but did not alter the activity of complexes I and II of the respiratory chain in the liver and brain. Hepatic and renal biochemical and histological parameters were not modified by (PhSe)(2) and apoptosis was not detected in these tissues; however, the hepatic cells tended to accumulate fat vacuoles. These results indicated that acute toxicology to (PhSe)(2) in rabbit is dependent on the dose, which should motivate further experiments on the therapeutic properties of this compound.

Effect of in vitro exposure of human serum to 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one on oxidative stress

The objective of this study was to verify the effect of the organochalcogen 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one on some parameters of oxidative stress in human serum. Serum of volunteers were incubated for 30 min in the presence or absence of 1, 10, or 30 microM of 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one and oxidative stress was measured. First, we tested the influence of the compound on 1,1-diphenyl-2-picrylhydrazyl (DPPH(*)) radical-scavenging and verified that the organotellurium did not have any antioxidant properties. The organochalcogen was capable to enhance TBARS but the compound was not able to alter carbonyl assay. Furthermore, the organochalcogen provoked a reduction of protein thiol groups measured by the sulfhydryl assay. Moreover, the organotellurium enhanced the activity of catalase and superoxide dismutase, inhibited the activity of glutathione peroxidase and did not modify the glutathione S-transferase activity. Furthermore, nitric oxide production and hydroxyl radical activity were not affected by the compound. Our findings showed that this organochalcogen induces oxidative stress in human serum, indicating that this compound is potentially toxic to human beings.

Dependence of leukemic cell proliferation and survival on H2O2 and L-arginine

The proliferation and/or survival of a variety of cells is dependent on cellular hydrogen peroxide (H(2)O(2)) production. We tested whether this was true of leukemic cells, using cell lines from leukemic patients (CEM, 697, Mn-60, and Tanoue). We found that addition of catalase inhibited proliferation of all cell lines and induced death in two. However, this turned out to be due to arginase contamination of the catalase. Pure arginase inhibited cell proliferation and survival, which was reversible by adding L-arginine, demonstrating the L-arginine dependency of these cells. The glutathione peroxidase mimetic ebselen killed the cells by a novel, rapid form of death, preceded by cell blebbing and prevented by N-acetylcysteine, suggesting toxicity is not due to ebselen's antioxidant activity. Addition of N-acetylcysteine to remove endogenous H(2)O(2) stimulated survival and proliferation, suggesting that basal levels of H(2)O(2) promoted cell death. Consistent with this, leukemic cell death was induced by adding as little as 5 microM H(2)O(2). Ascorbic acid, even at 100 microM, induced death through H(2)O(2) production. Thus H(2)O(2) does not promote proliferation and survival, rather the opposite, and previous literature may have misinterpreted the effects of antioxidants. Arginase, H(2)O(2), ascorbic acid, and ebselen might be useful in the treatment of leukemia.

Anticonvulsant and antioxidant effects of 3-alkynyl selenophene in 21-day-old rats on pilocarpine model of seizures

This study investigated the anticonvulsant effect of 3-alkynyl selenophene (3-ASP) on pilocarpine (PC)-, pentylenetetrazole (PTZ)- and kainic acid (KA)-induced seizures and mortality in 21-day-old rats. Rats were pretreated by oral route (p.o.) with 3-ASP (10, 25 and 50mg/kg) before intraperitoneal (i.p.) administration of PC (400mg/kg), PTZ (80 mg/kg) or KA (45 mg/kg). 3-ASP increased the latency to the seizure onset on PTZ and KA models. At the dose of 50mg/kg, 3-ASP avoided the death caused by PTZ and KA. 3-ASP (50mg/kg) abolished seizures and death induced by PC in rats. To investigate the antioxidant effect of 3-ASP on rats exposed to PC, the activity of glutathione peroxidase (GPx), glutathione-S-transferase (GST), acetylcholinesterase (AChE), Na(+)K(+)ATPase, superoxide dismutase (SOD) and catalase (CAT) as well as the levels of reactive species (RS) and ascorbic acid (AA) were determined in brains of rats. 3-ASP protected against the increase in RS levels and CAT activity induced by PC in brains of rats. The decrease in the levels of AA and inhibition of Na(+)K(+)ATPase, SOD and AChE activities caused by PC were protected by 3-ASP. Subeffective doses of 3-ASP plus diazepam, 5S,10R-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) or 6,7-dinitroquinoxaline-2,3-dione (DNQX) increased the latency to the seizure onset induced by PC, suggesting the involvement of ionotropic glutamatergic and GABAergic receptors in anticonvulsant action of 3-ASP. The anticonvulsant and antioxidant effects of 3-ASP in 21-day-old rats on PC model were demonstrated.

Structural modifications into diphenyl diselenide molecule do not cause toxicity in mice

The aim of the present study was to evaluate toxicological parameters of following compounds: 1a (4,4'-dichloro-diphenyl diselenide [(ClPhSe)(2)]), 1b (3,3'-ditrifluoromethyl-diphenyl diselenide [(F(3)CPhSe)(2)]) and 1c (4,4'-dimethoxyl-diphenyl diselenide [(CH(3)OPhSe)(2)]). Calculated lethal dose (LD(50)) values for mice exposed, by oral route, to a single application of compounds 1a, 1b or 1c were estimated to be >381, 278 and >372mg/kg, respectively. Compounds 1a and 1b significantly reduced body weight gain as well as food and water intake in mice. δ-Aminolevulinate dehydratase (δ-ALA-D) and catalase activities were inhibited in mice which received the highest dose of compounds 1a or 1b. Exposure to compounds 1a, 1b and 1c did not modify lipid peroxidation, vitamin C levels, cerebral Na(+)/K(+)-ATPase activity and the biochemical parameters evaluated. The important point for medicinal chemistry is that the structural modifications are not introducing toxicity for the compounds in mice.

Antioxidant effect of a novel class of telluroacetilene compounds: studies in vitro and in vivo

AIMS

The effect of telluroacetylenes a-d on pharmacological assays was investigated in vitro. A second objective of this study was to investigate the antioxidant action of compound b against the oxidative damage induced by sodium nitroprusside (SNP) in mouse brain.

MAIN METHODS

In in vitro experiments, lipid peroxidation (LP) and protein carbonyl (PC) levels and delta-aminolevulinate dehydratase (delta-ALA-D) activity were carried out in rat brain homogenate. The thiol peroxidase-like activity and DPPH radical scavenging of telluroacetylenes a-d were investigated. In in vivo experiments, mice received SNP (0.335 micromol per site) intra cerebroventricular (i.c.v.) thirty minutes after oral administration of telluroacetylene b (10 mg/kg). After 1 h, animals were euthanized. The levels of LP and delta-ALA-D, catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST) activities were carried out in mouse brain homogenate.

KEY FINDINGS

Telluroacetylenes a-d, at low muM range, reduced LP and PC levels in rat brain homogenate. Telluroacetylenes a-d showed effect of scavenging DPPH radicals. delta-ALA-D activity was inhibited by telloruacetylenes a-d, at high muM range, in rat brain homogenate. Brains of mice treated with SNP showed an increase in LP and the reduction in delta-ALA-D, GR and GST activities. Telluroacetylene b protected against the oxidative stress caused by SNP in brain of rats.

SIGNIFICANCE

The results support an antioxidant effect of telluroacetylenes a-d in vitro. Telluroacetylene b protected against oxidative damage caused by SNP in mouse brain, suggesting an antioxidant effect of this compound.

Exposure to diphenyl ditelluride, via maternal milk, causes oxidative stress in cerebral cortex, hippocampus and striatum of young rats

The present study evaluated the effect of diphenyl ditelluride [(PhTe)(2)] exposure to mothers on the cerebral oxidative status of their offspring. The dams received (PhTe)(2) or canola oil via subcutaneous injection once daily during the first 14 days of lactational period. At post natal day 28, biochemical parameters of oxidative stress were evaluated in cerebral structures-cortex, hippocampus and striatum-of young rats. Exposure to (PhTe)(2) increased lipid peroxidation levels and inhibited delta-ALA-D, catalase and SOD activities in hippocampus and striatum of young rats. (PhTe)(2) induced changes in the levels of non-enzymatic antioxidant defenses in cortex and striatum of young rats. The exposure to (PhTe)(2), via maternal milk, caused oxidative stress in cerebral structures of young rats. Thus, the possible role of disrupted prooxidant/antioxidant balance in (PhTe)(2) toxicity was demonstrated. These results highlighted a possible molecular mechanism involved in toxicity caused by (PhTe)(2).

Opposing effects of coupled and uncoupled NOS activity on the Na+-K+ pump in cardiac myocytes

Pharmacological delivery of nitric oxide (NO) stimulates the cardiac Na(+)-K(+) pump. However, effects of NO synthesized by NO synthase (NOS) often differ from the effects of NO delivered pharmacologically. In addition, NOS can become "uncoupled" and preferentially synthesize O(2)(.-), which often has opposing effects to NO. We tested the hypothesis that NOS-synthesized NO stimulates Na(+)-K(+) pump activity, and uncoupling of NOS inhibits it. To image NO, we loaded isolated rabbit cardiac myocytes with 4,5-diaminofluorescein-2 diacetate (DAF-2 DA) and measured fluorescence with confocal microscopy. L-arginine (L-arg; 500 micromol/l) increased DAF-2 DA fluorescence by 51% compared with control (n = 8; P < 0.05). We used the whole cell patch-clamp technique to measure electrogenic Na(+)-K(+) pump current (I(p)). Mean I(p) of 0.35 +/- 0.03 pA/pF (n = 44) was increased to 0.48 +/- 0.03 pA/pF (n = 7, P < 0.05) by 10 micromol/l L-Arg in pipette solutions. This increase was abolished by NOS inhibition with radicicol or by NO-activated guanylyl cyclase inhibition with 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one. We next examined the effect of uncoupling NOS using paraquat. Paraquat (1 mmol/l) induced a 51% increase in the fluorescence intensity of O(2)(.-)-sensitive dye dihydroethidium compared with control (n = 9; P < 0.05). To examine the functional effects of uncoupling, we measured I(p) with 100 micromol/l paraquat included in patch pipette solutions. This decreased I(p) to 0.28 +/- 0.03 pA/pF (n = 12; P < 0.001). The paraquat-induced pump inhibition was abolished by superoxide dismutase (in pipette solutions). We conclude that NOS-mediated NO synthesis stimulates the Na(+)-K(+) pump, whereas uncoupling of NOS causes O(2)(.-)-mediated pump inhibition.

DNA damage in tissues and organs of mice treated with diphenyl diselenide

Diphenyl diselenide (DPDS) is an organoselenium compound with interesting pharmacological activities and various toxic effects. In previous reports, we demonstrated the pro-oxidant action and the mutagenic properties of this molecule in bacteria, yeast and cultured mammalian cells. This study investigated the genotoxic effects of DPDS in multiple organs (brain, kidney, liver, spleen, testes and urinary bladder) and tissues (bone marrow, lymphocytes) of mice using in vivo comet assay, in order to determine the threshold of dose at which it has beneficial or toxic effects. We assessed the mechanism underlying the genotoxicity through the measurement of GSH content and thiobarbituric acid reactive species, two oxidative stress biomarkers. Male CF-1 mice were given 0.2-200 micromol/kg BW DPDS intraperitonially. DPDS induced DNA damage in brain, liver, kidney and testes in a dose response manner, in a broad dose range at 75-200 micromol/kg with the brain showing the highest level of damage. Overall, our analysis demonstrated a high correlation among decreased levels of GSH content and an increase in lipid peroxidation and DNA damage. This finding establishes an interrelationship between pro-oxidant and genotoxic effects. In addition, DPDS was not genotoxic and did not increase lipid peroxidation levels in any organs at doses < 50 micromol/kg. Finally, pre-treatment with N-acetyl-cysteine completely prevented DPDS-induced oxidative damage by the maintenance of cellular GSH levels, reinforcing the positive relationship of DPDS-induced GSH depletion and DNA damage. In summary, DPDS induces systemic genotoxicity in mammals as it causes DNA damage in vital organs like brain, liver, kidney and testes.

Comparative Studies on Dicholesteroyl Diselenide and Diphenyl Diselenide as Antioxidant Agents and their Effect on the Activities of Na+/K+ ATPase and δ-Aminolevulinic acid Dehydratase in the Rat Brain

The present study sought to evaluate the effect of a newly synthesized selenium compound, dicholesteroyl diselenide (DCDS) and diphenyl diselenide (DPDS) on the activities of delta-aminolevulinate dehydratase and Na+/K+-ATPase in the rat brain. The glutathione peroxidase mimetic activity of the two compounds as well as their ability to oxidize mono- and di- thiols were also evaluated. The antioxidant effects were tested by measuring the ability of the compounds to inhibit the formation of thiobarbituric acid reactive species and also their ability to inhibit the formation of protein carbonyls. The results show that DPDS exhibited a higher glutathione peroxidase mimetic activity as well as increased ability to oxidize di-thiols than DCDS. In addition, while DPDS inhibited the formation of thiobarbituric acid reactive species and protein carbonyls, DCDS exhibited a prooxidant effect in all the concentration range (20-167 microM) tested. Also the activities of cerebral delta-aminolevulinate dehydratase and Na+/K+ ATPase were significantly inhibited by DPDS but not by DCDS. In addition, the present results suggested that the inhibition of Na+/K+ ATPase by organodiselenides, possibly involves the modification of the thiol group at the ATP binding site of the enzyme. In conclusion, the results of the present investigation indicated that the non-selenium moiety of the organochalcogens can have a profound effect on their antioxidant activity and also in their reactivity towards SH groups from low-molecular weight molecules and from brain proteins.

Repeated administration of diphenyl ditelluride induces hematological disorders in rats

In the present study, we investigated potential toxic effects of diphenyl ditelluride, as measured by biochemical and hematological parameters. Rats were given a daily dose of 0.3 micromol/kg diphenyl ditelluride by subcutaneous route and sacrificed at different times (24 and 48 h). Hepatic and renal TBARS levels were changed by diphenyl ditelluride exposure at the dose 0.9 micromol/Kg in rats. Diphenyl ditelluride exposure demonstrated an increase in AST (aspartate aminotransferase), ALT (alanine aminotransferase) and LDH (lactate dehydrogenase) activities. Plasma creatinine and urea levels increase after diphenyl ditelluride exposure. Diphenyl ditelluride also produced a significant decrease in plasma triglyceride and cholesterol levels. In contrast, this compound, at all doses tested, induced a marked increase in total leukocyte counts. The present study suggests that diphenyl ditelluride induces hematological disorders and provides evidence for renal and hepatic toxicity in rats.

Ebselen and diorganylchalcogenides decrease in vitro glutamate uptake by RAT brain slices: Prevention by DTT and GSH

The purpose of this study was to investigate the possible involvement of the glutamatergic system in the neurotoxicity of diorganylchalcogenides or organochalcogenides from slices of cerebral cortex in different ages of development: 12- and 60-day-old rats. Glutamate uptake was evaluated in cortical slices of 12 and 60 days old rats. Cortex slices were incubated with three different organochalcogenides with or without reduced glutathione or dithiothreitol. At 100 microM, ebselen, diphenyl diselenide (PhSe)2 and diphenyl ditelluride (PhTe)2 in vitro inhibited the [3H]glutamate uptake in both age. Both 60-day-old rats and for 12-day-old rats, GSH and DTT prevented the (PhTe)2-induced inhibition of glutamate uptake but did not protect the inhibition caused by ebselen and (PhSe)2. These findings suggest that the neurotoxicity of organochalcogenides could be related to their effects on brain glutamate uptake, conceivably involving a redox modulation of reactive amino acids from the glutamate transporter proteins.

Previous treatment with ebselen and vitamin E alters adenine nucleotide hydrolysis in platelets from adult rats experimentally demyelinated with ethidium bromide

Many aspects of the relationship between the demyelinating pathology and platelet function need to be elucidated. Thus, the activity of NTPDase and 5'-nucleotidase enzymes was analyzed in platelets from rats demyelinated with ethidium bromide (EB) and previously treated with ebselen (Ebs) and vitamin E (Vit. E). The animals were divided into four groups: for ebselen, the groups were: I-control (saline), II-(saline and Ebs), III-(EB) and IV-(EB and Ebs); and for vitamin E, the groups were: I - control (saline), II-(saline and Vit. E), III-(EB) and IV-(EB and Vit. E). After 3 and 21 days, the blood was collected and the platelets were separated for enzymatic assays. For the treatment with Ebs, the NTPDase activity for ATP substrate was significantly lower in groups II, III and IV (p < 0.05) after 3 days, while after 21 days, a reduction was observed in group III (p < 0.05). ADP hydrolysis was reduced in group II (p < 0.05) and increased in group IV (p < 0.05) after 3 days, while after 21 days there was an increase in group IV (p < 0.05). In the treatment with Vit. E, ATP hydrolysis was lower in groups II, III and IV (p < 0.05) after 3 and 21 days. ADP hydrolysis was increased in group II (p < 0.05) after 3 days, and in group IV (p < 0.05) after 21 days. However, 5'-nucleotidase activity was not altered by the treatments. These findings demonstrate that NTPDase activity in platelets is diminished in demyelinating events and the treatments with Ebs and Vit. E modulated adenine nucleotide hydrolysis.

Involvement of oxidative stress in seizures induced by diphenyl diselenide in rat pups

In the present study the potential neurotoxicity of diphenyl diselenide, as measured by the manifestation of seizures in rat pups (postnatal days, PND, 12-14) was evaluated. The results suggest that the latency for the appearance of tonic-clonic seizures, characterized by rearing and falling of rat pups body, was dependent of the dose tested. Diphenyl diselenide at high doses induced seizure episodes in rat pups. The highest dose of diphenyl diselenide (500 mg/kg) increased the levels of lipid peroxidation and catalase activity as well as decreased delta-ALA-D (delta-aminolevulinate dehydratase) and Na(+), K(+) ATPase activity in the brain of rat pups. Our results indicate the possible involvement of free radical oxygen injury in diphenyl diselenide-induced seizures. The data obtained with the dose of 150 mg/kg in the brain of rats that exhibited seizures are: an increase in lipid peroxidation levels; the lack of effect on catalase activity; an inhibition of delta-ALA-D activity, supporting that the enzyme activity is more sensitive than other parameters analyzed as an indicator of oxidative stress. The lowest dose of diphenyl diselenide emphasizes the relationship between the appearance of seizures and the latency for the onset of the first episode. Taken together, this paper could add to our understanding of diphenyl diselenide neurotoxic effect demonstrated by the appearance of seizures which are, at least in part, related to the oxidative stress.

1,1,2-Tris-organoselenide alkene derivatives, but not 1,2-bis-organoselenide alkene derivatives, inhibited δ-aminolevulinate dehydratase activity from human erythrocytic cells in vitro

Organochalcogens are important intermediates and useful reagents in organic synthesis. Recent data from our laboratory demonstrated that bis and tris-selenide alkene derivatives are attractive synthetic targets because of their chemio-, regio- and stereo-selective reactions. Since the erythrocytic delta-aminolevulinate dehydratase (delta-ALA-D) activity could be an important indicator of toxicity, this report investigated bis and tris-selenide alkene derivatives effects on blood delta-ALA-D in vitro. To investigate the mechanisms by which these compounds inhibit human blood delta-ALA-D activity, a thiol reducing agent or zinc chloride were used. 1,2-Bis-selenide alkene derivatives 1a (R=4-MeOC(6)H(4)), 1b (R=4-ClC(6)H(4)) and 1c (R=2,4,6-Me(3)C(6)H(2)) did not inhibit human blood delta-ALA-D activity. 1,1,2-Tris-selenide alkene derivative 2a (R=C(6)H(5)) was the most potent delta-ALA-D inhibitor. Compounds 2b (R=4-MeOC(6)H(4)) and 2c (R=4-ClC(6)H(4)) displayed similar inhibitory potency towards delta-ALA-D activity. Dithiothreitol, a hydrophobic SH-reducing agent, was able to restore and to protect delta-ALA-D activity inhibited by tris-selenide alkene derivatives. Conversely, ZnCl(2) did not alter the enzyme inhibition induced by tris-selenide alkene derivatives. From these findings we suggest that 1,1,2-tris-selenide alkene derivatives inhibited delta-ALA-D activity by an interaction with essential sulfhydryl groups for the enzyme activity.

A biochemical and toxicological study with diethyl 2-phenyl-2-tellurophenyl vinylphosphonate in a sub-chronic intraperitoneal treatment in mice

Diethyl-2-phenyl-2-tellurophenyl vinylphosphonate (DPTVP) is an organotellurium compound with low toxicity after subcutaneous administration in mice. This study evaluated possible in vivo and ex vivo toxicological effects of daily injections of DPTVP for 12 days in mice, using the intraperitoneal administration. This route potentially increases the pharmacokinetics of absorption, distribution, metabolism and toxicity of DPTVP. Treatment with DPTVP (0, 30, 50, 75, 100, 250, 350 or 500 micromol/kg) were not associated with mortality or body weight loss. Nevertheless, the liver and liver-to-body weight ratio increased in groups treated with 350 and 500 micromol/kg of DPTVP. However, plasmatic aspartate and alanine aminotransferase activities (classical markers of hepatotoxicity) were not increased after diethyl-2-phenyl-2-tellurophenyl vinylphosphonate administration. Hepatic, renal and cerebral thiobarbituric acid reactive substances (TBARS), delta-ALA-D activity and Vitamin C levels were not modified after DPTVP treatment. Renal and hepatic superoxide dismutase (SOD) and catalase (CAT) were unchanged after DPTVP treatment. Conversely, SOD activity significantly increased in brain in groups treated with 50, 75, 100 and 500 micromol/kg of DPTVP treated groups. Our findings corroborates that brain is a potential target for organochalcogen action. The absence of severe overt signs of toxicity after sub-chronic exposure to DPTVP reinforces the necessity for more detailed pharmacological studies concerning this new organotellurium compound.

Evaluation of the antimicrobial activity of ebselen: Role of the yeast plasma membrane H+-ATPase

Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) is a selenium-containing antioxidant demonstrating anti-inflammatory and cytoprotective properties in mammalian cells and cytotoxicity in lower organisms. The mechanism underlying the antimicrobial activity of ebselen remains unclear. It has recently been proposed that, in lower organisms like yeast, the plasma membrane H+-ATPase (Pma1p) could serve as a potential target for this synthetic organoselenium compound. Using yeast and bacteria, the present study found ebselen to inhibit microbial growth in a concentration- and time-dependent manner, and yeast and Gram-positive bacteria to be more sensitive to this action (IC50 approximately 2-5 microM) than Gram-negative bacteria (IC50 < 80 microM). Washout experiments and scanning electron microscopic analysis revealed ebselen to possess fungicidal activity. In addition, ebselen was found to inhibit medium acidification by PMA1-proficient haploid yeast in a concentration-dependent manner. Additional studies comparing PMA1 (+/-) and PMA1 (+/+) diploid yeast cells revealed the mutant to be more sensitive to treatment with ebselen than the wild type. Ebselen also inhibited the ATPase activity of Pma1p from S. cerevisiae in a concentration-dependent manner. The interaction of ebselen with the sulfhydryl-containing compounds L-cysteine and reduced glutathione resulted in the complete and partial prevention, respectively, of the inhibition of Pma1p ATPase activity by ebselen. Taken together, these results suggest that the fungicidal action of ebselen is due, at least in part, to interference with both the proton-translocating function and the ATPase activity of the plasma membrane H+-ATPase.

Small-molecule screening identifies the selanazal drug ebselen as a potent inhibitor of DMT1-mediated iron uptake

HEK293T cells overexpressing divalent metal transporter-1 (DMT1) were established to screen for small-molecule inhibitors of iron uptake. Using a fluorescence-based assay, we tested 2000 known bioactive compounds to find 3 small molecules that potently block ferrous iron uptake. One of the inhibitors, ebselen, is a seleno compound used in clinical trials as a protective agent against ischemic stroke. Ebselen inhibited Fe(II) uptake (IC(50) of approximately 0.22 microM), but did not influence Fe(III) transport or DMT1-mediated manganese uptake. An unrelated antioxidant, pyrrolidine dithiobarbamate (PDTC), also inhibited DMT1 activity (IC(50) of approximately 1.54 microM). Both ebselen and PDTC increased cellular levels of reduced glutathione. These observations indicate that Fe(II) transport by DMT1 can be modulated by cellular redox status and suggest that ebselen may act therapeutically to limit iron-catalyzed damage due to transport inhibition.

Ebselen effects on MPTP-induced neurotoxicity

We evaluated the effect of ebselen on human SH-SY5Y dopaminergic neuronal cells and determined whether ebselen, a glutathione peroxidase-mimetic, protected against MPTP-induced dopamine depletion in mice. Ebselen (10-100 microM) inhibited the proliferation of SH-SY5Y cells dose-dependently. Ebselen did not induce any behavioral changes and did not block MPTP-induced tremor and akinesia. Ebselen had no effect on the monoamine oxidase activity and did not protect against MPTP-induced dopamine depletion in striatum.

Evaluation of antioxidant activity and potential toxicity of 1-buthyltelurenyl-2-methylthioheptene

The aim of the present study was to evaluate pharmacological and toxicological properties of 1-buthyltelurenyl-2-methylthioheptene (compound 1). In vitro, compound 1 at 1 microM was effective in reducing lipid peroxidation induced by Fe/EDTA. Compound 1 presented neither thiol peroxidase nor thiol oxidase activity and did not change delta-ALA-D (delta-aminolevulinate dehydratase) activity (10-400 microM). Calculated LD(50) of compound 1, administered by oral route, was 65.1 micromol/kg. Rats treated with compound 1 did not reveal any motor impairment in the open field. Hepatic, renal and cerebral lipid peroxidation in treated rats did not differ from those in control rats. Conversely, 0.5 micromol/kg of compound 1 decreased lipid peroxidation in spleen. Delta-ALA-D activity in liver and spleen was inhibited in rats treated with the higher dose of compound 1 but no significant differences were detected in renal delta-ALA-D activity. AST (aspartate aminotransferase) and ALT (alanine aminotransferase) activities as well as urea and creatinine levels were increased by high doses of compound 1 (50-75 micromol/kg). Compound 1 induced a significant decrease in plasma triglyceride levels but none of the doses tested changed the cholesterol level. This is a promising compound for more detailed pharmacological studies involving organotellurium compounds.

Diphenyl diselenide changes behavior in female pups

Diphenyl diselenide, (PhSe)(2), is an organoselenium compound that affects a number of neuronal processes. The effect of maternal subcutaneous (s.c.) injection of 25 mg/kg (PhSe)(2) once daily during early postnatal development (from PND 1 to 21) was evaluated in offspring of Wistar rats. The physical and neural reflexes were recorded at pre-weaning period. The behavioral changes in the elevated plus-maze (EPM), open-field and rotarod tasks were performed in 28-day-old pups. Selenium brain status was significantly increased ( approximately 41%) in rat pups. Statistically significant decreases in body weight were observed during lactation period in male and female pups exposed to 25 mg/kg (PhSe)(2). There were no dose-related changes on landmarks indicative of physical and reflexologic parameters of development in rats. (PhSe)(2) induced a disinhibitory effect in EPM behavior according to gender. Specifically, exposure to (PhSe)(2) increased entries and duration in the open arms of the EPM in females but not in males. Locomotor activity and rearing increased by (PhSe)(2) exposure in both male and female offspring in the open field. Both groups were similar in response to motor coordination in the rotarod. We concluded that maternal (PhSe)(2) exposure during lactation increased selenium levels in the pup brain and caused changes on developmental and behavioral parameters of Wistar rat offspring.