ascorbic-acid and ebselen

The emerging and spreading of multi-drug resistant (MDR) bacteria have been becoming one of the most severe threats to human health. Enhancing oxidative stress as mimicking immune system was considered as a potential strategy to fight against infection of MDR bacteria. In this study, we investigated the antibacterial efficiency of such a strategy which combines silver nanoparticles (AgNPs) with ebselen. The results showed that AgNPs and ebselen combination had significant synergistic killing effects both on

Topics: Anti-Bacterial Agents; Ascorbic Acid; Azoles; Drug Resistance, Multiple; Drug Synergism; Escherichia coli; HeLa Cells; Humans; Isoindoles; Metal Nanoparticles; Microbial Sensitivity Tests; Organoselenium Compounds; Reactive Oxygen Species; Silver; Staphylococcus aureus

A series of test compounds were evaluated for an ability to reduce the toxicity of the nitrogen mustard mechlorethamine (HN2) in vitro. The test compounds included resveratrol, pterostilbene, vitamin C, ebselen, ebselen diselenide, and ebselen-sulfur. Among them, ebselen demonstrated the highest degree of protection against HN2 toxicity. To this end, pretreatment of the cells with ebselen offered protection against the toxicant whereas no protection was observed when cells were first incubated with HN2 and then treated with ebselen. Significant increases in caspase 3 and caspase 9 activities were observed in response to HN2, and ebselen was found to reduce these effects. Taken together, the data presented here indicate that ebselen is an effective countermeasure to nitrogen mustard in vitro, which is worthy of future investigation in vivo.

Topics: Antidotes; Antioxidants; Apoptosis; Ascorbic Acid; Azoles; Caspase 3; Caspase 9; Cell Line; Chemical Warfare Agents; Cytoprotection; Humans; Irritants; Isoindoles; Mechlorethamine; Organoselenium Compounds; Resveratrol; Stilbenes

Given their medical importance, proteases have been studied by diverse approaches and screened for small molecule protease inhibitors. Here, we present a multiplexed microsphere-based protease assay that uses high-throughput flow cytometry to screen for inhibitors of the light chain protease of botulinum neurotoxin type A (BoNTALC). Our assay uses a full-length substrate and several deletion mutants screened in parallel to identify small molecule inhibitors. The use of multiplex flow cytometry has the advantage of using full-length substrates, which contain already identified distal-binding elements for the BoNTALC, and could lead to a new class of BoNTALC inhibitors. In this study, we have screened 880 off patent drugs and bioavailable compounds to identify ebselen as an in vitro inhibitor of BoNTALC. This discovery demonstrates the validity of our microsphere-based approach and illustrates its potential for high-throughput screening for inhibitors of proteases in general.

Topics: Antigens, Bacterial; Azoles; Bacterial Toxins; Botulinum Toxins, Type A; Drug Evaluation, Preclinical; Flow Cytometry; Fluorescence Resonance Energy Transfer; High-Throughput Screening Assays; Isoindoles; Metalloproteases; Microspheres; Organoselenium Compounds; Protease Inhibitors

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.

Topics: Acetylcysteine; Antioxidants; Arginase; Arginine; Ascorbic Acid; Azoles; Catalase; Cell Death; Cell Line, Tumor; Cell Proliferation; Humans; Hydrogen Peroxide; Isoindoles; Leukemia; Organoselenium Compounds

This study was designed to examine if ebselen, an organoselenium compound with antioxidant and glutathione peroxidase-mimetic properties, attenuates testicular injury caused by intraperitoneal administration of CdCl(2). A number of toxicological parameters were evaluated in the testes of mice, such as delta-aminolevulinic acid dehydratase (delta-ALA-D) activity, lipid peroxidation, ascorbic acid levels and alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities. Ebselen attenuated lipid peroxidation levels altered by CdCl(2). delta-ALA-D activity inhibited by the highest dose of CdCl(2) was attenuated by ebselen. A significant negative correlation between lipid peroxidation levels and delta-ALA-D activity was observed. Ebselen restored ascorbic acid levels reduced by CdCl(2). A significant negative correlation between ascorbic acid levels and delta-ALA-D activity reinforces the idea that ebselen attenuated the damage induced by CdCl(2) via its antioxidant property. The significant correlation between ALT and delta-ALA-D activity supports the assumption that ebselen prevented damage caused by CdCl(2). The results show that ebselen attenuated oxidative stress, a process important for CdCl(2) toxicity.

Topics: Alanine Transaminase; Animals; Antioxidants; Ascorbic Acid; Aspartate Aminotransferases; Azoles; Biomarkers; Cadmium Chloride; Disease Models, Animal; Drug Antagonism; Injections, Intraperitoneal; Isoindoles; Lipid Peroxidation; Male; Mice; Organoselenium Compounds; Porphobilinogen Synthase; Testicular Diseases; Testis; Thiobarbituric Acid Reactive Substances

This study was designed to determine the effect of diphenyl diselenide and ebselen, synthetic organoselenium compounds with antioxidant properties, in diabetic rats. Diabetes was induced by the administration of streptozotocin (STZ) (45mg/kg, intravenous). In experimental trials, diphenyl diselenide, but not ebselen, caused a significant reduction in blood glucose levels of STZ-treated rats. This effect of diphenyl diselenide was accompanied by a reduction in the levels of glycated proteins. Diphenyl diselenide ameliorate superoxide dismutase activity (liver and erythrocytes) and Vitamin C levels (liver, kidney and blood), which were decreased in STZ-treated rats. In normal rats, diphenyl diselenide caused per se an increase in hepatic, renal and blood GSH levels. Similarly, treatment with diphenyl diselenide restored hepatic and renal GSH levels in STZ-treated rats. TBARS and protein carbonyl levels were not modified by STZ and/or diphenyl diselenide and ebselen treatments. Our findings suggest that diphenyl diselenide can be considered an anti-diabetogenic agent by exhibiting anti-hyperglycemic and antioxidant properties.

Topics: Alanine Transaminase; Aminolevulinic Acid; Animals; Antioxidants; Ascorbic Acid; Aspartate Aminotransferases; Azoles; Benzene Derivatives; Blood Glucose; Diabetes Mellitus, Experimental; Fructosamine; Glutathione; Glycated Hemoglobin; Hyperglycemia; Isoindoles; L-Lactate Dehydrogenase; Liver; Male; Organoselenium Compounds; Oxidative Stress; Random Allocation; Rats; Rats, Wistar; Sodium-Potassium-Exchanging ATPase; Superoxide Dismutase

This paper evaluates the ability of organoselenium compounds [ebselen, selenocystine N-ethyl-carbamate (SeCis), bis-4-isopropyl-2-oxazolinyl phenyl diselenide (AASe)] to prevent HgCl(2) toxicity. Rats were injected with HgCl(2) (0 or 17 micromol/kg, sc) 6 h after organoselenium compounds had been injected (0 or 50 micromol/kg, sc). In vivo, HgCl(2) inhibited renal ALA-D activity ( approximately 48%), increased TBARS level in kidney ( approximately 52%) and reduced the hepatic content of non-protein thiol groups ( approximately 40%), but organoselenium compounds did not prevent such effects. SeCis, per se, increased renal TBARS level ( approximately 42%), while AASe increased hepatic content of ascorbic acid ( approximately 38%). In vitro, renal and hepatic ALA-D activity was inhibited by HgCl(2) (>or=25 microM), ebselen (>or=12 microM) and SeCis (>or=4 microM). HgCl(2) (400 microM) significantly increased TBARS production in renal and hepatic tissue preparations in vitro, and this effect was completely or partially prevented by organoselenium compounds. Ebselen exhibited thiol peroxidase activity in our assay conditions, while SeCis exhibited thiol-oxidizing properties regardless of the presence of peroxide. AASe had no effect on thiol oxidation. Results suggest that organoselenium compounds could not prevent mercury toxicity in vivo. The protective effect of these compounds against mercury-induced increase of TBARS production in vitro is probably related to an antioxidant action rather than to mercury binding.

Topics: Animals; Antioxidants; Ascorbic Acid; Azoles; Glutathione; Isoindoles; Kidney; Liver; Male; Mercury; Organoselenium Compounds; Oxidative Stress; Peroxidases; Porphobilinogen Synthase; Rats; Rats, Wistar; Sulfhydryl Compounds; Thiobarbituric Acid Reactive Substances

Ebselen is a selanazal drug recently revealed as a highly efficient peroxiredoxin mimic catalyzing the hydroperoxide reduction by the mammalian thioredoxin system [thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH]. The mammalian Trx system is a dehydroascorbic acid reductase recycling ascorbic acid essential for cell functions. Here we report that ebselen strongly facilitated the recycling of ascorbic acid by the TrxR both with and without Trx present. Reduction of dehydroascorbic acid by TrxR has a pH optimum of 6.4, and only approximately 55% of this activity at a physiological pH of 7.4. Ebselen at 6 microM enhances this reaction three-fold and with the same pH optimum of 6.4. The mechanism of the ebselen effect is suggested to involve reduction of dehydroascorbic acid by the ebselen selenol, a highly efficient two-electron reductant. Thus, ebselen acts as an antioxidant to lower the peroxide tone inside cells and to facilitate the recycling of dehydroascorbic acid to ascorbic acid, so as to increase the radical scavenging capacity of ascorbic acid directly or indirectly via vitamin E. The high ascorbic acid recycling efficiency of ebselen at pH 6.4 may play a major role in oxidatively stressed cells, where cytosol acidosis may trigger various responses, including apoptosis.

Topics: Animals; Antioxidants; Ascorbic Acid; Azoles; Cattle; Dehydroascorbic Acid; Humans; Hydrogen-Ion Concentration; Isoindoles; Kinetics; Organoselenium Compounds; Oxidation-Reduction; Oxidoreductases; Thioredoxin-Disulfide Reductase; Thioredoxins

There is evidence that LDL oxidation may render the lipoprotein atherogenic. The myeloperoxidase-hydrogen peroxide (MPO/H2O2) system of activated phagocytes may be involved in this process. Chloride is supposed to be the major substrate for MPO, generating reactive hypochlorous acid (HOCl), modifying LDL. The pseudo-halide thiocyanate (SCN-) has been shown to be a suitable substrate for MPO, forming reactive HOSCN/SCN*. As relatively abundant levels of SCN- are found in plasma of smokers--a well-known risk group for cardiovascular disease--the ability of SCN- to act as a catalyst of LDL atherogenic modification by MPO/H2O2 was tested. Measurement of conjugated diene and lipid hydroperoxide formation in LDL preparations exposed to MPO/H2O2 revealed that SCN- catalyzed lipid oxidation in LDL. Chloride did not diminish the effect of SCN- on lipid oxidation. Surprisingly, SCN inhibited the HOCl-mediated apoprotein modification in LDL. Nitrite--recently found to be a substrate for MPO--showed some competing properties. MPO-mediated lipid oxidation was inhibited by heme poisons (azide, cyanide) and catalase. Ascorbic acid was the most effective compound in inhibiting the SCN- -catalyzed reaction. Bilirubin showed some action, whereas tocopherol was ineffective. When LDL oxidation was performed with activated human neutrophils, which employ the MPO pathway, SCN- catalyzed the cell-mediated LDL oxidation. The MPO/H2O2/SCN- system may have the potential to play a significant role in the oxidative modification of LDL--an observation further pointing to the link between the long-recognized risk factors of atherosclerosis: elevated levels of LDL and smoking.

Topics: Antioxidants; Apoproteins; Ascorbic Acid; Azoles; Catalase; Catalysis; Chlorides; Cyclooxygenase Inhibitors; Dose-Response Relationship, Drug; Female; Free Radicals; Heme; Humans; Hydrogen Peroxide; Hypochlorous Acid; Isoindoles; Lipid Metabolism; Lipid Peroxidation; Lipids; Lipoproteins, LDL; Male; Neutrophils; Nitrites; Organoselenium Compounds; Oxygen; Peroxidase; Phagocytes; Phagocytosis; Risk Factors; Smoking; Thiocyanates; Time Factors; Ultracentrifugation

Transforming growth factor beta1 (TGF-beta1) stimulates cartilage extracellular matrix synthesis but, in excess, evokes synovial inflammation, hyperplasia, and osteophyte formation in arthritic joints. TGF-beta1 induces tissue inhibitor of metalloproteinases 3 (TIMP-3), an inhibitor of cartilage-damaging matrix metalloproteianases and aggrecanases. We investigated the role of reactive oxygen species (ROS) in TIMP-3 induction by TGF-beta1. In primary human and bovine chondrocytes, ROS scavenger and antioxidant N-acetylcysteine (NAC) inhibited TGF-beta1-induced TIMP-3 mRNA and protein increases. Ebselen and ascorbate also reduced this induction. TGF-beta1 time-dependently induced ROS production that was suppressed by NAC. Hydrogen peroxide, a ROS, induced TIMP-3 RNA. The TIMP-3 increase induced by TGF-beta1 was partly Smad2-dependent. TGF-beta1-stimulated Smad2 phosphorylation was inhibited by NAC. Reduced glutathione and L-cysteine also blocked Smad2 and TIMP-3 induction by TGF-beta1, whereas a nonthiol, N-acetylalanine, did not. Smad2 was not activated by H2O2. Smad2 phosphorylation was independent, and TIMP-3 expression was dependent, on new protein synthesis. TGF-beta-stimulated ERK and JNK phosphorylation was also inhibited by NAC. However, inhibitory actions of NAC were not mediated by ERK activation. Thus, ROS mediate TGF-beta1-induced TIMP-3 gene expression. Blocking TGF-beta1-induced gene expression by modulating cellular redox status with thiols can be potentially beneficial for treating arthritic and other disorders caused by excessive TGF-beta1.

Topics: Acetylcysteine; Animals; Ascorbic Acid; Azoles; Blotting, Northern; Blotting, Western; Cartilage, Articular; Cattle; Cells, Cultured; Chondrocytes; Culture Media, Serum-Free; Cycloheximide; DNA-Binding Proteins; Down-Regulation; Free Radicals; Growth Substances; Humans; Hydrogen Peroxide; Isoindoles; JNK Mitogen-Activated Protein Kinases; MAP Kinase Kinase 4; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinase Kinases; Oligonucleotides, Antisense; Organoselenium Compounds; Oxidation-Reduction; Phosphorylation; Reactive Oxygen Species; RNA; RNA, Messenger; Signal Transduction; Smad2 Protein; Species Specificity; Time Factors; Tissue Inhibitor of Metalloproteinase-3; Trans-Activators; Transfection; Transforming Growth Factor beta; Transforming Growth Factor beta1

The development of novel and potent iron chelators as clinically useful antitumor agents is an area of active interest. Antiproliferative activity of chelators often relates to iron deprivation or stimulation of iron-dependent free radical damage. Recently, we showed that novel iron chelators of the di-2-pyridylketone isonicotinoyl hydrazone (PKIH) class have potent and selective antineoplastic activity (E. Becker, et al., Br. J. Pharmacol., 138: 819-30, 2003). In this study, we assessed the effects of the PKIH analogues on the redox activity of iron in terms of understanding their antitumor activity.. We tested the PKIH analogues for their ability to promote iron-mediated ascorbate oxidation, benzoate hydroxylation, and plasmid degradation. Subsequent experiments assessed their ability to bind DNA, inhibit topoisomerase I, and cause DNA damage. To measure intracellular reactive oxygen species, we used the redox-sensitive probe, 2',7'-dichloro-fluorescein-diacetate, to measure intracellular PKIH-dependent redox activity.. The PKIH analogues had relatively little effect on ascorbate oxidation in the presence of Fe(III) but stimulated benzoate hydroxylation and plasmid DNA degradation in the presence of Fe(II) and H2O2. These ligands could not inhibit DNA topoisomerase I or cause DNA damage in intact cells. PKIH markedly increased the intracellular generation of reactive oxygen species, and this was inhibited by catalase. This enzyme also decreased the antiproliferative effect of PKIH, indicating H2O2 played a role in its cytotoxic activity.. Our results suggest that the antiproliferative effects of these chelators relates to intracellular iron chelation, followed by the stimulation of iron-mediated free radical generation via the so-formed iron complex.

Topics: Antineoplastic Agents; Ascorbic Acid; Azoles; Catalase; Cell Line, Tumor; Chelating Agents; Coloring Agents; DNA; DNA Damage; DNA Topoisomerases, Type I; Dose-Response Relationship, Drug; Free Radicals; Humans; Hydrazones; Hydrogen Peroxide; Iron; Isoindoles; Ligands; Models, Chemical; Organoselenium Compounds; Oxidation-Reduction; Oxygen; Plasmids; Pyridines; Reactive Oxygen Species; Superoxide Dismutase; Tetrazolium Salts; Thiazoles

Amsacrine is an acridine derivative drug applied in haematological malignancies. It targets topoisomerase II enhancing the formation of a cleavable DNA-enzyme complex and leading to DNA fragmentation in dividing cancer cells. Little is known about other modes of the interaction of amsacrine with DNA, by which it could affect also normal cells. Using the alkaline comet assay, we showed that amsacrine at concentrations from the range 0.01 to 10 microM induced DNA damage in normal human lymphocytes, human promyelocytic leukemia HL-60 cells lacking the p53 gene and murine pro-B lymphoid cells BaF3 expressing BCR/ABL oncogene measured as the increase in percentage tail DNA. The effect was dose-dependent. Treated cells were able to recover within a 120-min incubation. Amifostine at 14 mM decreased the level of DNA damage in normal lymphocytes, had no effect on the HL-60 cells and potentiated the DNA-damaging effect of the drug in BCR/ABL-transformed cells. Vitamin C at 10 and 50 microM diminished the extent of DNA damage in normal lymphocytes, but had no effect in cancer cells. Pre-treatment of the cells with the nitrone spin trap, N-tert-butyl-alpha-phenylnitrone or ebselen, which mimics glutathione peroxidase, reduced the extent of DNA damage evoked by amsacrine in all types of cells. The cells exposed to amsacrine and treated with endonuclease III and 3-methyladenine-DNA glycosylase II, the enzymes recognizing oxidized and alkylated bases, respectively, displayed greater extent of DNA damage than those not treated with these enzymes. The results obtained suggest that free radicals may be involved in the formation of DNA lesions induced by amsacrine. The drug can also methylate DNA bases. Our results indicate that the induction of secondary malignancies should be taken into account as diverse side effects of amsacrine. Amifostine may potentate DNA-damage effect of amsacrine in cancer cells and decrease this effect in normal cells and Vitamin C can be considered as a protective agent against DNA damage in normal cells.

Topics: Adult; Amifostine; Amsacrine; Animals; Ascorbic Acid; Azoles; Cell Line, Transformed; Comet Assay; Cyclic N-Oxides; DNA Damage; DNA Repair; Dose-Response Relationship, Drug; Free Radical Scavengers; HL-60 Cells; Humans; In Vitro Techniques; Isoindoles; Lymphocytes; Male; Mice; Mutagens; Nitrogen Oxides; Organoselenium Compounds

Production of oxygen radicals by stimulated phagocytes followed by surfactant lipid peroxidation (LPO) and loss of surfactant function have all been implicated in the pathogenesis of acute lung injury. We studied the interactions between natural lung surfactant (Curosurf) and neutrophils in vitro, and compared various antioxidants; (superoxide dismutase (SOD), vitamin E, vitamin C, ebselen and melatonin), or combinations of them in duplicate and triplicate regarding their ability to decrease superoxide production and the peroxidation level of surfactant caused by activated phagocytes. The superoxide production of neutrophils activated by Candida albicans was measured with the nitroblue tetrazolium (NBT) test. The subsequent LPO was estimated as the content of malondialdehyde (MDA) and 4-hydroxyalkenals (4-HNE). We found that lung surfactant decreased the superoxide production by activated neutrophils (29.7%) and that Curosurf was peroxidized with elevated MDA/4-HNE values. With supplements of antioxidants (except vitamin C), superoxide radical production and the surfactant LPO level fell in a dose-dependent manner. The protective effect of the antioxidants differed in each test. SOD had a slight effect in both tests. The findings with vitamin E, melatonin and ebselen were similar. The best combination was that of a natural and a synthetic antioxidant (melatonin-ebselen) with a 60% decrease in comparison to the corresponding control. These findings suggest that antioxidants, particularly in combination, prevent LPO of lung surfactant.

Topics: Animals; Antioxidants; Ascorbic Acid; Azoles; Biological Products; Humans; In Vitro Techniques; Isoindoles; Lipid Peroxidation; Malondialdehyde; Melatonin; Neutrophil Activation; Neutrophils; Nitroblue Tetrazolium; Organoselenium Compounds; Oxidation-Reduction; Phagocytes; Phospholipids; Pulmonary Surfactants; Reactive Oxygen Species; Superoxide Dismutase; Swine; Vitamin E

Amyloid peptides (AbetaPs) are implicated in neuronal death associated with Alzheimer's disease. Their toxicity involves disruption cellular Ca(2+) homeostasis, leading to activation of caspases and cell death. Antioxidants can prevent such cell death and show beneficial clinical effects in Alzheimer's disease patients. Using the model neurosecretory cell line, PC12, we have shown that AbetaPs cause enhancement of evoked exocytosis via formation of a Cd(2+) -resistant Ca(2+) influx pathway, and also cause selective, functional up-regulation of current through L-type Ca(2+) channels. The involvement of reactive oxygen species (ROS) in these effects were investigated by examining the ability of various antioxidants to interfere with these responses. Both melatonin and ascorbic acid fully blocked the enhancement of catecholamine secretion caused by application of AbetaP((1-40)), as monitored in real time amperometrically, but inhibition of the transcriptional regulator NF-kappaB with SN-50 did not affect secretion. Enhanced immunofluorescence, observed in AbetaP-treated cells using a monoclonal antibody raised against the N-terminus of AbetaP, was also suppressed by melatonin. Ascorbic acid, melatonin and ebselen also fully prevented augmentation of whole-cell Ca(2+) currents caused by application of AbetaP((1-40)). By contrast, inhibitors of NF-kappaB (sulfasalazine and SN-50) were able to prevent AbetaP induced Ca(2+) channel current enhancement, whilst inhibitors of mitogen-activated protein kinase and protein kinase C could not. Our results indicate that augmentation or induction by AbetaPs of two important, distinct factors regulating Ca(2+) homeostasis is mediated by increased ROS production, but only one of these (up-regulation of native Ca(2+) channels) requires activation of NF-kappaB.

Topics: Amyloid beta-Peptides; Animals; Antioxidants; Ascorbic Acid; Azoles; Cadmium; Calcium; Calcium Channels, L-Type; Catecholamines; Enzyme Inhibitors; Exocytosis; Fluorescent Antibody Technique; Indoles; Isoindoles; Maleimides; Melatonin; NF-kappa B; Organoselenium Compounds; Patch-Clamp Techniques; PC12 Cells; Peptide Fragments; Peptides; Rats; Reactive Oxygen Species; Signal Transduction; Sulfasalazine

Topics: Animals; Antioxidants; Ascorbic Acid; Azoles; Ferrous Compounds; Glutathione Peroxidase; Isoindoles; Lipid Peroxidation; Mitochondria, Liver; Mitochondrial Swelling; Organoselenium Compounds; Rats

Ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)one, and its derivatives were compared for their ability to protect microsomal membranes against iron/ADP/ascorbate-induced lipid peroxidation, measured as low-level chemiluminescence and accumulation of thiobarbituric acid-reactive substances (TBARS). The concentrations of the compounds required to double the lag time of the control with no added antioxidants were 0.13 microM for ebselen, 0.5 microM for the N-pyridyl analog, 0.3-0.7 microM for the selenylsulfides, about 1.0 microM for the selenoxide derivative and 2.0 microM for the sulfur analog of ebselen. The open-chain seleno- and thioether derivatives, on the other hand, exhibited comparatively low abilities to protect the membrane, the lag doubling concentrations for these compounds being 100-1,000 fold higher than that for ebselen. The rate of loss of alpha-tocopherol in the microsomal membrane during peroxidation was significantly diminished in the presence of 0.1-0.5 microM ebselen, while the glutathione adduct of ebselen was equally effective in protecting the loss of alpha-tocopherol. The sulphur analogue and, the benzylated and methylated derivatives of ebselen did not afford protection. Ebselen was without effect in microsomes from vitamin E-deficient rats up to 20 microM, indicative of the dependence of its protective ability upon alpha-tocopherol.

Topics: Adenosine Diphosphate; Animals; Antioxidants; Ascorbic Acid; Azoles; Intracellular Membranes; Iron; Isoindoles; Kinetics; Lipid Peroxidation; Luminescent Measurements; Male; Microsomes; Organoselenium Compounds; Rats; Rats, Inbred Strains; Selenium; Thiobarbiturates; Vitamin E

The effects of ebselen(2-phenyl-1,2-benzoisoselenazol-3(2H)-one), a synthetic seleno-organic compound with glutathione peroxidase-like activity were investigated on lipid peroxidation in rat liver microsomes. Ebselen inhibited malondialdehyde production coupled to the lipid peroxidation stimulated by either ADP-iron-ascorbate or CCl4. The inhibitory activity of ebselen on each system was strongly increased by a 5-min preincubation with liver microsomes; the IC50 values against ADP-Fe-ascorbate-stimulated and CCl4-stimulated lipid peroxidation were 1.6 microM and 70 microM respectively. Ebselen also inhibited the endogenous lipid peroxidation with a NADPH-generating system, but it slightly stimulated the endogenous activity of ADP-Fe-ascorbate-stimulated lipid peroxidation (without a NADPH-generating system). Furthermore, ebselen inhibited oxygen uptake coupled to the lipid peroxidation by ADP-Fe-ascorbate and NADPH-ADP-iron; the IC50 values were 2.5 microM and 20.3 microM respectively. Ebselen also prolonged the lag-time of onset of ADP-Fe-ascorbate-stimulated lipid peroxidation significantly, but not that observed with NADPH-ADP-Fe-stimulated lipid peroxidation. These findings suggest that ebselen penetrates into the membrane lipid and acts as an effective antioxidant, and that there may be some differences between the modes of inhibitory action on the several types of lipid peroxidation.

Topics: Adenosine Diphosphate; Animals; Antioxidants; Ascorbic Acid; Azoles; Carbon Tetrachloride; In Vitro Techniques; Iron; Isoindoles; Lipid Peroxides; Male; Malondialdehyde; Microsomes, Liver; Organoselenium Compounds; Oxygen Consumption; Rats; Selenium