Voltage-dependent ebselen and diorganochalcogenides inhibition of 45Ca2+ influx into brain synaptosomes

Acute exposure to diphenyl ditelluride causes oxidative damage in rat lungs

The present study evaluated the effect of acute exposure to diphenyl ditelluride [(PhTe)(2)] on oxidative status in lungs of rats. Rats were exposed to a single subcutaneous application of (PhTe)(2) at the doses of 0.3, 0.6, 0.9 μmol/kg or vehicle. After 72 h of exposure to (PhTe)(2), biochemical parameters of oxidative stress were carried out in lungs of rats. The lungs of rats exposed to (PhTe)(2) showed an increase in the levels of lipid peroxidation, reactive species and non-protein thiol. Alterations in superoxide dismutase activity were observed at all tested doses. (PhTe)(2) caused an increase in catalase activity and a reduction in ascorbic acid levels at the dose of 0.9 μmol/kg. The oxidative damage was more pronounced in animals treated with the highest dose of (PhTe)(2). Thus, this study demonstrated that acute exposure to (PhTe)(2) induced oxidative damage and an adaptive response of antioxidants in pulmonary tissue of rats.

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.

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.

45Ca2+ Influx in Rat Brain: Effect of Diorganylchalcogenides Compounds

In nervous tissue, the calcium (Ca(2+)) release induces neurotransmitter exocytosis and synaptic plasticity in neurons and is essential for Ca(2+) waves and oscillations in astrocytes. In this work, we have investigated the effect of organocalchogens on calcium influx in synaptosomal preparations under basal and depolarizing conditions. Acute administration of ebselen caused a significant increase of 34% (p < 0.05) Ca(2+) influx, when under basal conditions but showed no effect on potassium stimulated calcium conditions by brain synaptosomes. Diphenyl ditelluride (PhTe)(2) increased (45)Ca(2+) influx by 40% (p < 0.05) under depolarizing conditions, while diphenyl diselenide (PhSe)(2) had no effect on the brain synaptosomes studied. In addition, we characterized an "in vitro" model with the purpose of studying Ca(2+) movements in slices. In this model, we examined the effect of diorganylchalcogenides using brain hippocampal slices, which showed the decrease of calcium influx with the three drugs studied. These findings showed that there are different effects of diorganylchalcogenides in the different models evaluated. It is possible that these differential effects result from the action of neural signal transduction pathways at different levels, possibly involving neurotransmitter release and channel targeting.

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.

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.

Exposure of mothers to diphenyl ditelluride during the suckling period changes behavioral tendencies in their offspring

The long-lasting possible influence of maternal exposure to 0.03 mg/kg of diphenyl ditelluride during the first 14 days of lactational period on later offspring behavior was examined in Wistar rats. Open-field locomotor activity, spontaneous alternation in the T-maze, behavior in the elevated plus-maze, motor coordination in the coat-hanger and rotorod tasks were evaluated in 30 day old pups. There were no significant specific overt signs of maternal intoxication. There were a small (less than 5%) but significant transitory differences in the body weight gain of pups between exposed and control groups, which were apparent from day 30 of suckling. Locomotor activity in the open-field task was similar between telluride and control groups. In the coat-hanger test, the latency before falling for the tellurium group was higher than that of the control group. However, the behavior of both groups was similar in the rotorod test and spontaneous alternation in the T-maze. Tellurium-treated pups presented a higher number of entries and spent more time in the open arms of the elevated plus-maze than control pups. The behavioral alterations observed here after tellurium exposure can be cautiously interpreted as an indication of behavioral disinhibition. In conclusion, this study demonstrated that dam exposure to diphenyl ditelluride can cause subtle behavioral changes in the offspring, which can be related to neurotoxic effects of diphenyl ditelluride.

Ebselen protects glutamate uptake inhibition caused by methyl mercury but does not by Hg2+

Alterations of the neurotransmitter release systems in CNS have been reported in a variety of neuropathological processes associated with heavy metal toxicity. Neurotoxic effects of mercurials were investigated in vitro in cerebral cortex slices from young rats. The present study indicates that: (i) the environmental contaminants methylmercury (MeHg) and mercuric chloride (Hg2+) (50 microM) inhibited the glutamate net uptake from the cerebral cortex of 17-day-old rats; (ii) ebselen (10 microM) reverted the MeHg-induced inhibition of glutamate net uptake but did not protect the inhibition caused by Hg2+. At same time, we investigated another diorganochalcogenide, diphenyl diselenide (PhSe)2 and it was observed that this compound did not revert the action of MeHg or Hg2+; (iii) in addition, we observed that exposure of slices to 50 microM MeHg and Hg2+ for 30 min followed by Trypan blue exclusion assay resulted in 58.5 and 67.5% of staining cells, respectively, indicating a decrease in cell viability. Ebselen protected slices from the deleterious effects of MeHg, but not of Hg2+ on cell viability. Conversely, ebselen did not modify the reduction of MTT caused by MeHg and Hg2+; (iv) the protective effect of ebselen on MeHg-induced inhibition of glutamate net uptake seems to be related to its ability in maintaining cell viability.

Pro-oxidant action of diphenyl diselenide in the yeast Saccharomyces cerevisiae exposed to ROS-generating conditions

Organoselenium compounds have a potential thiol peroxidase-like activity. Diphenyl diselenide (DPDS) is an electrophilic reagent used in the synthesis of a variety of pharmacologically active organic selenium compounds. Using TRAP assay of chemiluminescense we have shown that diphenyl diselenide clearly possesses a pro-oxidant property. For an investigation on the mechanisms of this property, we used mutant strains of Saccharomyces cerevisiae defective in antioxidant defenses, i.e. in superoxide dismutase, in biosynthesis of glutathione, and the transcription factor yAP-1-lacking yap 1 mutant that cannot activate genes of the oxidative stress response. Exposure of growing cultures to the drug increased cell sensitivity to oxidizing agents. The pro-oxidant effect was independent of the metabolic condition or of the oxidative mutagen tested. N-acetylcysteine, a precursor of glutathione biosynthesis, could neutralize the pro-oxidant effects of diphenyl diselenide by stimulating an increase of endogenous glutathione biosynthesis or by directly binding to the drug. Vitamin E (Trolox), a known antioxidant, was also able to protect S. cerevisiae against the pro-oxidant effect of diphenyl diselenide. In vitro assays showed that diphenyl diselenide interacts non-enzymatically with the thiol group of glutathione.

Organoselenium compounds prevent hyperphosphorylation of cytoskeletal proteins induced by the neurotoxic agent diphenyl ditelluride in cerebral cortex of young rats

In this work we investigated the protective ability of the selenium compounds ebselen and diphenyl diselenide against the effect of diphenyl ditelluride on the in vitro incorporation of 32P into intermediate filament (IF) proteins from slices of cerebral cortex of 17-day-old rats. We observed that ditelluride in the concentrations of 1, 15 and 50 microM induced hyperphosphorylation of the high-salt Triton insoluble neurofilament subunits (NF-M and NF-L), glial fibrillary acidic protein (GFAP) and vimentin, without altering the immunocontent of these proteins. Concerning the selenium compounds, diselenide (1,15 and 50 microM) did not induce alteration of the in vitro phosphorylation of the IF proteins. Otherwise, ebselen induced an altered in vitro phosphorylation of the cytoskeletal proteins in a dose-dependent manner. At intermediate concentrations (15 and 30 microM) it increased the in vitro phosphorylation even though, at low (5 microM) or high (50 and 100 microM) concentrations this compound was ineffective in altering the activity of the cytoskeletal-associated phosphorylating system. In addition, 15 microM diselenide and 5 microM ebselen, presented a protective effect against the action of ditelluride, on the phosphorylation of the proteins studied. Considering that hyperphosphorylation of cytoskeletal proteins is associated with neuronal dysfunction and neurodegeneration, it is probable that the effects of ditelluride could be related to the remarkable neurotoxicity of this organic form of tellurium. Furthermore the neuroprotective action of selenium compounds against tellurium effects could be a promising route to be exploited for a possible treatment of organic tellurium poisoning.

Effect of ebselen and organochalcogenides on excitotoxicity induced by glutamate in isolated chick retina

In this study, we evaluated the effects of three simple organochalcogenides (diphenyl diselenide, diphenyl ditelluride and diphenyl telluride) and ebselen on the glutamate-driven 45Ca2+ influx into chick embryonic retinal cells, as well as their effects on the excitotoxic injury in retina cells. None of the compounds tested interfered with basal 45Ca2+ uptake. Diphenyl diselenide and diphenyl ditelluride had no effects on glutamate-driven 45Ca2+ influx. Diphenyl telluride (100-400 microM) decreased and ebselen (100-400 microM) completely blocked the glutamate-driven 45Ca2+ influx (P < 0.01) into chick retinal explants. The assessment of neural injury was made spectrophotometrically by quantification of cellularly reduced MTT (3(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide) 24 h after the beginning of glutamate exposure (8 h). Ebselen had no effects on retinal MTT reduction when co-incubated with glutamate for 8 h. However, when ebselen (100 and 400 microM) was co-incubated for 8 h with glutamate and remained in the incubation media until MTT evaluation (24 h after the beginning of incubation), it protected retinal cells against the decrease in MTT reduction induced by glutamate. These data indicate that besides its capacity of interacting with Ca2+ channels, other mechanisms are involved in the neuroprotection afforded by ebselen in this work, possibly its antioxidant properties.

Selenium Compounds Prevent the Effects of Methylmercury on the in Vitro Phosphorylation of Cytoskeletal Proteins in Cerebral Cortex of Young Rats

In this study we investigated the protective ability of the selenium compounds ebselen and diphenyldiselenide against the effect of methylmercury on the in vitro incorporation of 32P into intermediate filament (IF) proteins from the cerebral cortex of 17-day-old rats. We observed that methylmercury in the concentrations of 1 and 5 microM was able to inhibit the phosphorylating system associated with IF proteins without altering the immunocontent of these proteins. Concerning the selenium compounds, diselenide (1, 15, and 50 microM) did not induce alteration of the in vitro phosphorylation of IF proteins. Conversely, 15 microM diselenide was effective in preventing the toxic effects induced by methylmercury. Otherwise, ebselen induced an altered in vitro phosphorylation of the cytoskeletal proteins in a dose-dependent manner. Ebselen at intermediate concentrations (15 and 30 microM) increased the in vitro phosphorylation. However, at low (5 microM) or high (50 and 100 microM) concentrations it was ineffective in altering the cytoskeletal-associated phosphorylating system. Furthermore, 5 microM ebselen presented a protective effect against the action of methylmercury on the phosphorylating system. In conclusion, our results indicate that the selenium compounds ebselen and diselenide present protective actions toward the alterations of the phosphorylating system associated with the IF proteins induced by methylmercury in slices of the cerebral cortex of rats.

Ebselen and diphenyl diselenide change biochemical hepatic responses to overdosage with paracetamol

The toxicity of paracetamol is largely related to its conversion to the reactive intermediate alkylating metabolite N-acetyl-para-benzo-quinoneimine (NAPQI). δ-Aminolevulinate dehydratase (δ-ALA-D) is a sulfhydril containing enzyme which is extremely sensitive to oxidizing and alkylating agents. In the present study, we examined whether acute treatment with paracetamol changes δ-ALA-D activity. The influence of two organochalcogenides with glutathione peroxidase-like activity, diphenyl diselenide [(PhSe)(2)] and ebselen was also assessed as potential protecting agents against paracetamol toxicity. Paracetamol (1200mg/kg for three days 4h after the injection of DMSO, diphenyl diselenide (100μmol/kg) or ebselen (100μmol/kg) caused an inhibition of about 40% (P < 0.01) in hepatic δ-ALA-D. Ebselen restored enzyme activity to control values. Non-protein-SH and ascorbic acid were diminished to 50% of control value by paracetamol, independent of chalcogenides treatment (all P values <0.05). In view of the fact that paracetamol caused a massive reduction in non-protein-SH and ascorbic acid, we realize that the protective effect of ebselen on δ-ALA-D activity is mediated by its thiol peroxidase-like activity or by a direct interaction with NAPQI and other reactive species formed during paracetamol metabolism.

Teratogenic vulnerability of Wistar rats to diphenyl ditelluride

The effect of single maternal subcutaneous (s.c.) injection of 0.12 mg/kg diphenyl ditelluride, (PhTe)2, diluted in canola oil at days 6, 10 or 17 of gestation were evaluated in Wistar rats. The reduction of body weight gain was statistically significant at GD9, for the dams that received (PhTe)2, at GD6; at GD13, for the dams that received (PhTe)2, at GD10, and at GD20, for the dams that received (PhTe)2, at GD17, when compared to respective control groups. External and internal fetal soft tissues examination was performed on day 20 of gestation. Single maternal injection at day 10 of gestation resulted in appearance of malformation in fore- and hind-limbs, absent or short tail, subcutaneous blood clots, exophthalmia, hydrocephalus and absence of the cranial bone and cutaneous tissue in fetuses on day 20 of gestation. Besides, (PhTe)2 reduced fetal body and cerebral weight, kidney length, measurements of body dimension and provoked 73% of fetal mortality. Subcutaneous administration of (PhTe)2 on day 17 of gestation was associated with 94% mortality, hydrocephalus and edema. Histological evaluations of fetal brain demonstrated displaced brain tissue with absence of the cranial bone and cutaneous tissue when diphenyl ditelluride was administered in GD10. Histological evaluation of fetal head exposed at GD17 revealed a decrease of the brain volume with consequent dilation of the lateral ventricles and the adjacent tissues were thinner than that of control group tissues. No fetal changes were observed after administration of (PhTe)2 at day 6 of gestation. Thus, (PhTe)2 can be teratogenic to rat fetuses and toxic for dams. The late fetal stages of rat prenatal development appeared uniquely sensitive to organic tellurium exposure.

Cytometric analysis of adverse action of diphenyl ditelluride on rat thymocytes: cell shrinkage as a cytotoxic parameter

Despite the growing use of organotellurium compounds in the chemical and biomedical fields, there has been no great concern about their toxicity until now. To test the possibility that diphenyl ditelluride (DPDT) and tellurium chloride (TeCl2), organic and inorganic tellurium compounds, may exert adverse action on mammals, their effects on rat thymocytes were examined under in vitro conditions using a flow cytometer with fluorescent probes. Incubation of thymocytes with DPDT at 300 nM or more for 24 h significantly increased the populations of shrunken cells and of cells with hypodiploidal DNA. Z-VAD-FMK, a paninhibitor of caspases, greatly suppressed the DPDT-induced increase in the hypodiploidal cell population, suggesting the involvement of caspase activation in DPDT toxicity. Hence, it is possible that DPDT would increase the population of thymocytes undergoing apoptosis if the blood concentration in mammals reached at least 300 nM or more. TeCl2 was much less potent than DPDT in increasing the population of hypodiploidal cells.