2-methylselenobenzanilide and ebselen

Horseradish peroxidase (HRP) inhibition and glutathione peroxidase (GPx) activities of ebselen and some related derivatives are described. These studies show that ebselen and ebselen ditelluride (EbTe(2)) with significant antioxidant activity, inhibit the HRP-catalyzed oxidation reactions. In addition, inhibition of lipid peroxidation and singlet oxygen quenching studies were carried out. Although the inhibition of HRP by ebselen is comparable with that of EbTe(2), the inhibitory effect on gamma-radiation induced lipid peroxidation and the GPx activity of ebselen is found to be much higher than that of EbTe(2).

Topics: Anilides; Antioxidants; Azoles; Enzyme Activation; Enzyme Inhibitors; Glutathione Peroxidase; Horseradish Peroxidase; Isoindoles; Organoselenium Compounds; Structure-Activity Relationship

The oxidation of 2-(methylseleno)benzanilide and 2-selenylbenzanilide, metabolites of the antioxidant drug ebselen, was examined in reactions catalyzed by rat, pig, and guinea pig liver microsomes and in perfused rat liver. Microsomes from all three species catalyzed NADPH- and oxygen-dependent oxidation of the selenide and the selenol to thiol-reactive metabolites. The oxidation product of the selenide was similar in properties to the chemically synthesized selenoxide [2-(methylseleninyl)benzanilide]. The selenoxide oxidized GSH and thiocholine at rate constants of 1.2 x 10(2) and 7.2 x 10(2) M-1 s-1, respectively at pH 7.4, 37 degrees C. n-Octylamine stimulated the oxidation of the ring-opened metabolites of ebselen catalyzed by pig and guinea pig liver microsomes but it had essentially no effect on these activities in rat liver microsomes. The selenoxidase activity of microsomes from all three species was partially (30-50%) sensitive to N-benzylimidazole. The effects of n-octylamine and the imidazole suggest that the oxidation of the selenide was catalyzed primarily by enzymes with the properties of flavin-containing and P450-dependent monooxygenases, but the nature of enzymes responsible for a small fraction of the N-benzylimidazole-sensitive activity was not fully resolved. The 2-(methylseleno)benzanilide oxidase activity of pig liver microsomes sensitive to N-benzylimidazole was only partially sensitive to antisera to pig liver NADPH-cytochrome P450 reductase. While neither 2-(methylseleno)benzanilide nor ebselen affected bile flow, the biliary efflux of GSSG was stimulated about fourfold in rat liver perfused with either of these selenium compounds. The increased GSSG efflux produced by 5 microM ebselen or its methyl metabolite was abolished by N-benzylimidazole.

Topics: Anilides; Animals; Antioxidants; Azoles; Guinea Pigs; Isoindoles; Liver; Male; Methimazole; Microsomes, Liver; NADP; Organoselenium Compounds; Oxidation-Reduction; Perfusion; Rats; Rats, Sprague-Dawley; Rats, Wistar; Species Specificity; Sulfhydryl Compounds; Swine

Luminol chemiluminescence in phorbolester-activated cultured rat liver Kupffer cells was strongly inhibited by the selenoorganic compound ebselen (IC50 = 2 mumol/L). Ebselen (2-phenyl-1,2-benzisoselenazol-3[2H]one) also diminished reduction of ferricytochrome c (IC50 = 10 mumol/L), indicating a suppression of superoxide anion formation. Likewise, in lipopolysaccharide-pretreated Kupffer cells, ebselen proved to be a potent inhibitor of the conversion of oxyhemoglobin to methemoglobin (IC50 = 3 mumol/L) as a measure of nitric oxide formation. The sulfur-containing analog (2-phenyl-1,2-benzisothiazol-3[2H]one) and the ebselen derivative, methylselenobenzanilide, were inactive. These results indicate that ebselen is a potent inhibitor of NADPH oxidase in Kupffer cells, as has been reported for other macrophages and granulocytes. In addition, they suggest a novel characteristic of ebselen, namely very effective inhibition of nitric oxide synthase of macrophages. In line with its inhibitory effects on the release of reactive oxygen species by macrophages, complemented by its antioxidant properties, ebselen was potent in the prevention of reoxygenation injury of Kupffer cells (IC50 approximately 5 mumol/L).

Topics: Amino Acid Oxidoreductases; Anilides; Animals; Antioxidants; Azoles; Cell Hypoxia; Cell Survival; Cells, Cultured; Free Radicals; Isoindoles; Kupffer Cells; Macrophage Activation; Male; NADH, NADPH Oxidoreductases; NADPH Oxidases; Nitric Oxide; Nitric Oxide Synthase; Organoselenium Compounds; Oxygen; Rats; Rats, Inbred Strains; Superoxides; Thiazoles

Topics: Anilides; Anti-Inflammatory Agents, Non-Steroidal; Azoles; Blood Platelets; Calcium; Calcium Channels; Disulfides; Dose-Response Relationship, Drug; Fura-2; Heparin; Humans; Inositol 1,4,5-Trisphosphate; Inositol 1,4,5-Trisphosphate Receptors; Isoindoles; Microsomes; Organoselenium Compounds; Platelet Activation; Receptors, Cell Surface; Receptors, Cytoplasmic and Nuclear; Selenium; Sulfhydryl Compounds

Ebselen (PZ 51, 2-phenyl-1,2-benzoisoselenazol-3-(2H)-one) is a selenoorganic compound with anti-inflammatory properties. Its pharmacological action is thought to originate from its peroxidase activity which could lower the peroxide tonus required for cyclooxygenase and lipoxygenase activations. From experiments with aspirin-treated human platelets we now present evidence that ebselen also affects intracellular calcium homeostasis by inhibiting the agonist-triggered increase in intracellular calcium. Using Mn2+ entry to quench the fura-2 fluorescence after cell stimulation, we could exclude an interaction of ebselen with receptor-operated calcium channels and therefore an inhibition of extracellular calcium influx. It became evident from whole cell experiments and by using isolated platelet microsomal vesicles that ebselen inhibits the inositol 1,4,5-trisphosphate (IP3) induced calcium release. Besides this inhibitory effect of ebselen on the calcium release higher concentrations of the compound (greater than or equal to 5 microM) induced a calcium release from our microsomal vesicles which also could be reversed by dithiothreitol. An activation of inflammatory cells is usually associated with increased cytosolic calcium concentrations. An inhibition of such calcium movements by ebselen may account for an up to now unidentified anti-inflammatory mechanism of ebselen action which is linked to a direct effect of this compound rather than to its peroxidase-like activity.

Topics: Anilides; Anti-Inflammatory Agents, Non-Steroidal; Aspirin; Autoradiography; Azoles; Blood Platelets; Calcium; Dose-Response Relationship, Drug; Fluorescence; Homeostasis; Humans; Intracellular Fluid; Isoindoles; Microsomes; Organoselenium Compounds; Phosphorylation; Platelet Aggregation; Selenium; Thrombin