Molecular actions of ebselen--an antiinflammatory antioxidant

Mitochondrial membrane potential in density-separated trout erythrocytes exposed to oxidative stress in vitro

Previous literature reports have demonstrated that nucleated trout erythrocytes in condition of oxidative stress are subjected to DNA and membrane damage, and inactivation of glutathione peroxidase. The present study was undertaken to investigate if mitochondrial membrane potential in stressed conditions was also influenced. Density-separated trout erythrocyte fractions, obtained using a discontinuous Percoll gradient, were submitted to stress conditions and the mitochondrial membrane potential was determined by means of cytofluorimetric analysis after incubation of each subfraction with JC-1, a mitochondrial specific fluorescent probe. The results clearly show that the mitochondrial membrane potential decreased significantly in all erythrocyte fractions, also if the oxidative effect on mitochondria is more severe with increased density (age) of the cell. Ebselen was very effective in preventing mitochondrial depolarization in young as well as in old erythrocytes.

Ebselen prevents early alcohol-induced liver injury in rats

Oxidants have been shown to be involved in alcohol-induced liver injury. Moreover, 2-phenyl-1,2-benzisoselenazole-3(2H)-one (ebselen), an organoselenium compound and glutathione peroxidase mimic, decreases oxidative stress and protects against stroke clinically. This study was designed to test the hypothesis that ebselen protects against early alcohol-induced liver injury in rats. Male Wistar rats were fed high-fat liquid diets with or without ethanol (10-16 g/kg/d) continuously for up to 4 weeks using the intragastric enteral feeding protocol developed by Tsukamoto and French. Ebselen (50 mg/kg twice daily, intragastrically) or vehicle (1% tylose) was administered throughout the experiment. Mean urine ethanol concentrations were not significantly different between treatment groups, and ebselen did not affect body weight gains or cyclic patterns of ethanol concentrations in urine. After 4 weeks, serum ALT levels were increased significantly about 4-fold over control values (37 +/- 5 IU/l) by enteral ethanol (112 +/- 7 IU/l); ebselen blunted this increase significantly (61 +/- 8 IU/l). Enteral ethanol also caused severe fatty accumulation, mild inflammation, and necrosis in the liver (pathology score: 4.3 +/- 0.3). In contrast, these pathological changes were blunted significantly by ebselen (pathology score: 2.5 +/- 0.4). While there were no significant effects of either ethanol or ebselen on glutathione peroxidase activity in serum or liver tissue, ebselen blocked the increase in serum nitrate/nitrite caused by ethanol. Furthermore, ethanol increased the activity of NF-kappaB over 5-fold, the number of infiltrating neutrophils 4-fold, and the accumulation of 4-hydroxynonenal over 5-fold. Ebselen blunted all of these effects significantly. These results indicate that ebselen prevents early alcohol-induced liver injury, most likely by preventing oxidative stress, which decreases inflammation.

Characterization and application of a gastric surface mucous cell line GSM06 established from temperature-sensitive simian virus 40 large T-antigen transgenic mice

It has been indicated that transgenic mouse harboring a temperature-sensitive simian virus 40 large T-antigen gene is useful for establishing cell lines from tissues that have proved difficult to culture in vitro. The gastric surface mucous cell line GSM06 was established from a primary culture of gastric fundic mucosal cells of the transgenic mice. GSM06 cells showed temperature-sensitive growth in culture and expressed large T-antigen at a permissive temperature (33 degrees C) but not at a nonpermissive temperature (39 degrees C). At 39 degrees C, the cells produced periodic acid-Schiff positive glycoconjugates that formed a mucous sheet like the gastric surface mucosa in the stomach. Insulin markedly increased the production of glycoconjugates. In addition, proprotein-processing endoprotease furin suppression retarded cell growth, but accelerated cell differentiation. An air-liquid interface promoted the differentiation of GSM06 cells in a reconstruction culture with nitrocellulose membrane and collagen gel. The gastric surface mucous cell line GSM06 with unique characteristics, therefore, should be useful as an in vitro model of the gastric mucosa for physiological and pharmacological investigations. Moreover, experiments using immortalized cells established in vitro and having specific functions may offer an alternative to experiments using living animals and thereby offer a solution to this ethical issue.

Molecular characterization of the plasma membrane H(+)-ATPase, an antifungal target in Cryptococcus neoformans

The Cryptococcus neoformans PMA1 gene, encoding a plasma membrane H(+)-ATPase, was isolated from a genomic DNA library of serotype A strain ATCC 6352. An open reading frame of 3,380 nucleotides contains six introns and encodes a predicted protein consisting of 998 amino acids with a molecular mass of approximately 108 kDa. Plasma membranes were isolated, and the H(+)-ATPase was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be slightly larger than the S. cerevisiae H(+)-ATPase, consistent with its predicted molecular mass. The plasma membrane-bound enzyme exhibited a pH 6.5 optimum for ATP hydrolysis, K(m) and V(max) values of 0.5 mM and 3.1 micromol mg(-1) min(-1), respectively, and an apparent K(i) for vanadate inhibition of 1.6 microM. ATP hydrolysis in plasma membranes and medium acidification by whole cells were inhibited by ebselen, a nonspecific H(+)-ATPase antagonist which was also fungicidal. The predicted C. neoformans protein is 35% identical to proton pumps of both pathogenic and nonpathogenic fungi but exhibits more than 50% identity to PMA1 genes from plants. Collectively, this study provides the basis for establishing the Cryptococcus H(+)-ATPase as a viable target for antifungal drug discovery.

Ebselen lowers plasma interleukin-6 levels and glial heme oxygenase-1 expression after focal photothrombotic brain ischemia

Heme oxygenase-1, an inducible heat shock protein, is upregulated by oxidative stress, and its expression is modulated by proinflammatory cytokines such as IL-1 and IL-6. In the present study, we investigated the effects of postlesional, orally applied ebselen, a neuroprotective antioxidant, on serum levels of IL-6 and cerebral heme oxygenase-1 expression following focal ischemia induced by photothrombosis. Ebselen (50 mg/kg body weight) was given 30 min postlesion to male Wistar rats. Animals were divided into four groups: sham-operated vehicle control (n = 9), sham-operated ebselen control (n = 8), lesioned vehicle control (n = 14), and lesioned ebselen-treated (n = 17). Ebselen treatment resulted in a significant lowering of IL-6 plasma levels (26 +/- 5 pg/ml) as compared with that seen in lesioned vehicle controls (48 +/- 9 pg/ml) at 24 h postlesion. In sham-operated rats IL-6 was not detectable. Heme oxygenase-1-positive glial cells were quantitated within topographically determined perilesional brain regions. Within the 0.5-mm-wide rim region directly associated with the lesion core, no differences in the amount of heme oxygenase-1-positive glial cells were found. However, in the more remote ipsilateral perilesional cortex, significantly fewer heme oxygenase-1-positive glial cells were present within the supragranular cortical layers of lesioned ebselen-treated rats compared to lesioned vehicle controls (P < 0.001). In sham-operated rats, no glial heme oxygenase-1 induction occurred. The results indicate that postlesional ebselen treatment lowered plasma IL-6 levels subsequent to a photothrombotic lesion concomitant with a lowering of the heme oxygenase-1 response in glial cells.

The anti-oxidant ebselen antagonizes the release of the apoptogenic factor cytochrome c induced by Fe2+/citrate in rat liver mitochondria

We studied the effects of ebselen (a seleno-organic anti-oxidant), on the release of the apoptogenic factor, cytochrome c, in two different experimental situations damaging mitochondria: (1) Fe(2+)/citrate, known to induce lipid peroxidation consecutively to an oxidative stress; and (2) atractyloside, a ligand of the adenine nucleotide translocator. The effects of ebselen were compared to those of butylated hydroxytoluene (BHT, an inhibitor of lipid peroxidation), and cyclosporine A (CsA, a classical pore antagonist). Ebselen, like BHT, inhibited Fe(2+)/citrate-induced release of cytochrome c, whereas CsA was inactive. On the contrary, neither ebselen nor BHT inhibited atractyloside-induced release of cytochrome c, whereas CsA was potently active. The antioxidant properties of ebselen may protect mitochondria from the consequences of the release of cytochrome c. Thus, it is suggested that the neuroprotective effect of ebselen previously demonstrated in humans and in animals may be due, at least in part, to a mitochondrial protection.

Reactive oxygen and mechanisms of inflammatory liver injury

Reactive oxygen species (ROS) are important cytotoxic and signalling mediators in the pathophysiology of inflammatory liver diseases. They can be generated by resident and infiltrating phagocytes and/or intracellularly in every liver cell type after stimulation with cytokines. Although ROS are able to cause cell destruction by massive lipid peroxidation, in most cases, ROS are more likely to modulate signal transduction pathways by affecting redox-sensitive enzymes, organelles (e.g. mitochondria) and transcription factors. Thus, ROS can directly induce and/or regulate apoptotic and necrotic cell death. In addition, ROS can have indirect effects on the pathophysiology by supporting protease activity through inactivation of antiproteases and by modulating the formation of inflammatory mediators and adhesion molecules. Many of the effects of ROS may occur simultaneously or sequentially in the pathophysiology. Although mainly described in this review as detrimental, ROS are essential for host-defence functions of phagocytes and can modulate the formation of mediators involved in regulating sinusoidal blood flow and liver regeneration. Thus, continuous efforts are necessary to improve our understanding of the role of ROS in the pathophysiology of inflammatory liver diseases and to discover therapeutic interventions that selectively target the negative effects of reactive oxygen formation.

4-Hydroxynonenal induces oxidative stress and death of cultured spinal cord neurons

Primary spinal cord trauma can trigger a cascade of secondary processes leading to delayed and amplified injury to spinal cord neurons. Release of fatty acids, in particular arachidonic acid, from cell membranes is believed to contribute significantly to these events. Mechanisms of fatty acid-induced injury to spinal cord neurons may include lipid peroxidation. One of the major biologically active products of arachidonic acid peroxidation is 4-hydroxynonenal (HNE). The levels of HNE-protein conjugates in cultured spinal cord neurons increased in a dose-dependent manner after a 24-h exposure to arachidonic acid. To study cellular effects of HNE, spinal cord neurons were treated with different doses of HNE, and cellular oxidative stress, intracellular calcium, and cell viability were determined. A 3-h exposure to 10 microM HNE caused approximately 80% increase in oxidative stress and 30% elevation of intracellular calcium. Exposure of spinal cord neurons to HNE caused a dramatic loss of cellular viability, indicated by a dose-dependent decrease in MTS [3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-s ulfophenyl)- 2H-tetrazolium, inner salt] conversion. The cytotoxic effect of HNE was diminished by pretreating neurons with ebselen or N-acetylcysteine. These data support the hypothesis that formation of HNE may be responsible, at least in part, for the cytotoxic effects of membrane-released arachidonic acid to spinal cord neurons.

Interaction of peroxynitrite with selenoproteins and glutathione peroxidase mimics

Peroxynitrite is an oxidant generated under inflammatory conditions, acting in defense against invading microorganisms. There is a need for protection of the organism from damage inflicted by peroxynitrite. Selenium-containing compounds, notably ebselen, have a high second-order reaction rate constant (approx. 2 x 10(6) M(-1) s(-1)), which makes them candidates for efficient protection. This applies also for selenium in proteins, occurring as selenocysteine or selenomethionine residues. Glutathione peroxidases, thioredoxin reductase, and selenoprotein P have been shown to play a potential role in protection against peroxynitrite. Tellurium-containing compounds also react with peroxynitrite.

Screening of new antioxidant molecules using flow cytometry

We present a flow cytometry technique to evaluate the antioxidative properties of molecules on living cells, using a stable murine-murine hybridoma (Mark 3) cell line routinely cultured. Using this technique, intracellular superoxide anions and peroxides were evaluated with dihydrorhodamine (DHR-123) and dichlorofluorescein diacetate (DCFH-DA), respectively. When cells were first incubated for 10 min with either H(2)O(2) or the xanthine (X)/xanthine oxidase (XO) system, this flow cytometric technique was capable of evaluating the oxidative stress on cells. Twenty-one new analogues of ellipticine were synthesized and tested for their antioxidative properties compared to vitamin E and Ebselen used as references. A good statistical reflection of the antioxidative activities of these molecules was achieved by analyzing 35 000 cells in each experiment. Among them, the selenated molecule 18 was found to be 10 times more active than Ebselen but 10 000 times less active than vitamin E. Moreover, eight compounds showed glutathione peroxidase-like activities.

Ebselen: prospective therapy for cerebral ischaemia

Stroke occurs due to haemorrhage or occlusive injury and results in ischaemia and reperfusion injury. A variety of destructive mechanisms are involved including oxygen radical generation, calcium overload, cytotoxicity and apoptosis as well as the generation of inflammatory mediators. Ebselen, 2-phenyl-1, 2-benzisoselenazol-3(2H)-one (PZ 51, DR3305), is a mimic of GSH peroxidase which also reacts with peroxynitrite and can inhibit enzymes such as lipoxygenases, NO synthases, NADPH oxidase, protein kinase C and H(+)/K(+)-ATPase. Ebselen is in a late stage of development for the treatment of stroke. The molecular actions of ebselen contribute to its anti-inflammatory and anti-oxidant properties, which have been demonstrated in a variety of in vivo models. Numerous in vitro experiments using isolated LDL, liposomes, microsomes, isolated cells and organs have established that ebselen protects against oxidative challenge. Unlike many inorganic and aliphatic selenium compounds, ebselen has low toxicity as metabolism of the compound does not liberate the selenium moiety, which remains within the ring structure. Subsequent metabolism involves methylation, glucuronidation and hydroxylation. Experimental studies in rats and dogs have revealed that ebselen is able to inhibit both vasospasm and tissue damage in stroke models, which correlates with its inhibitory effects on oxidative processes. Results from randomised, placebo-controlled, double-blind clinical studies on the neurological consequences of acute ischaemic stroke, subarachnoid haemorrhage and acute middle cerebral artery occlusion, have revealed that ebselen significantly enhances outcome in patients who have experienced occlusive cerebral ischaemia of limited duration. The benefit achieved with ebselen is closely related to the rapidity with which the treatment is initiated, following the onset of the stroke attack. Safety and tolerability are good and no adverse effects have become apparent. Ebselen is currently at the pre-registration stage for subarachnoid haemorrhage and stroke in Japan.

Ebselen induces apoptosis in HepG(2) cells through rapid depletion of intracellular thiols

Ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)-one, is a synthetic seleno-organic compound with antioxidant capability. In the present study, we systematically examined the ability of ebselen to induce apoptosis in a human hepatoma cell line, HepG(2). Ebselen-induced apoptosis was evaluated by (i) TdT-mediated dUTP nick end labeling assay; (ii) analysis of sub-G1 cells; (iii) cell morphology, including cell size and granularity examination; and (iv) DNA gel electrophoresis. The results showed that ebselen was able to induce typical apoptosis in HepG(2) cells in a dose- and time-dependent manner. In order to explore the possible mechanisms involved in ebselen-induced apoptosis, the effect of ebselen on intracellular thiol concentrations including reduced glutathione (GSH) and protein thiols and the effect of N-acetylcysteine (NAC) and buthionine sulfoximine (BSO) pretreatment on ebselen-induced apoptosis were investigated. It was found that (i) ebselen rapidly depleted intracellular GSH and protein thiols, moreover, the depletion preceded the occurrence of apoptosis; (ii) NAC, a precursor of intracellular GSH synthesis, significantly alleviated ebselen-induced apoptosis; and (iii) BSO, a specific inhibitor of intracellular GSH synthesis, augmented ebselen-induced apoptosis significantly. Taken together, the present study demonstrates that ebselen is able to induce apoptosis in HepG(2) cells, most probably through rapid depletion of intracellular thiols.

Effect of three diaryl tellurides, and an organoselenium compound in trout erythrocytes exposed to oxidative stress in vitro

Previous literature reports have demonstrated that nucleated trout erythrocytes in conditions of oxidative stress are subjected to DNA and membrane damage, and inactivation of glutathione peroxidase. The present study was undertaken to evaluate the ability of three diaryl tellurides and the organoselenium compound ebselen to protect trout (Salmo irideus) erythrocytes against oxidative stress, induced thermally and by a variation of pH. The antioxidant ability of these molecules was evaluated through chemiluminescence. Impairment of DNA was assessed using the comet assay, a rapid and sensitive single cell gel electrophoresis technique, used to detect primary DNA damage in individual cells. At low concentrations (<10 microM), all the compounds used presented a protective effect on DNA damage without altering the hemolysis rate. In higher concentrations, they accelerated the hemolysis rate and two of the diaryl tellurides were strongly genotoxic.

Ebselen as protection against ethanol-induced toxicity in rat stomach

The mucosal protective effect of ebselen was examined in an ethanol-induced rat gastric lesion model. Examination of gastric tissue samples by light microscopy showed that i.g. exposure to 50% ethanol induced gastric injury, which was more prominent in female rats. Ethanol did not effect the gastric acid secretion examined by means of H(+)-K+ATPase, the increment of which might be harmful in the stomach. But ebselen with or without ethanol kept H(+)-K+ATPase below control levels. Gastric alcohol dehydrogenase (ADH) was mainly responsible for oxidation of ethanol in the stomach before it enters the bloodstream. I.g. ethanol exposure inhibited the ADH activity but ebselen eliminated the ethanol-induced inhibition of this enzyme. Therefore, ebselen exhibited a beneficial effect by increasing the gastric ethanol metabolism and by ameliorating the possible tissue toxicity of ethanol. Consistently, we also found that ebselen diminished the blood ethanol level. A gender difference in the blood ethanol levels existed following the same dose of ethanol but there was no difference in ADH activity. Histologically, mucosal injury following ebselen exposure together with ethanol was less severe compared with ethanol treatment alone. We concluded that the decrease in ethanol-induced mucosal injury following ebselen may have contributed to the inhibition of H(+)-K+ATPase and the activation of ADH by ebselen.

The inhibition of mammalian 15-lipoxygenases by the anti-inflammatory drug ebselen: dual-type mechanism involving covalent linkage and alteration of the iron ligand sphere

Mammalian lipoxygenases have been implicated in inflammation and atherosclerosis and, thus, lipoxygenase inhibitors may be of pharmacological interest. In cells, lipoxygenases occur in a catalytically silent ground state that requires activation to become active. We found that the seleno-organic drug ebselen [2-phenyl-1, 2-benzisoselenazol-3(2H)-one], which exhibits anti-inflammatory properties, irreversibly inhibited pure rabbit 15-lipoxygenase, with an IC50 in the nM range when preincubated with the enzyme in the absence of fatty acid substrates. Subsequent dialysis, gel filtration, or substrate addition did not restore the enzyme activity, and experiments with [14C]ebselen indicated a covalent linkage of the drug. The presence of sulfhydryl compounds in the incubation mixture prevented both enzyme labeling and inactivation, but we did not see any reactivation when sulfhydryl compounds were added afterward. X-ray absorption studies indicated that ebselen did alter the geometry of the iron ligand sphere, and the data are consistent with an iron complexation by the drug. When fatty acid substrate was present during lipoxygenase-ebselen interaction, the inhibitory potency was strongly reduced and a competitive mode of action was observed. These data suggest that ebselen inactivated the catalytically silent ground-state lipoxygenase irreversibly by covalent linkage and alteration of the iron ligand sphere. In contrast, it functions as a competitive inhibitor of the catalytically active enzyme species. The pharmacological relevance of ebselen as a potential in vivo lipoxygenase inhibitor will be discussed.

Neuroprotective effects depend on the model of focal ischemia following middle cerebral artery occlusion

The purpose of the present study was to compare the characteristics of the photochemical-induced thrombotic occlusion model and the thermocoagulated occlusion model of the middle cerebral artery in rats. We evaluated the neuroprotective effects of a NMDA receptor antagonist, (+)-MK-801 (dizocilpine, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cycloheptan-5,10-imine), an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist, YM90K (6-(1H-imidazol-1-yl)-7-nitro-2,3(1H,4H)-quinoxalinedione monohydrochloride), a Ca2+ channel antagonist, S-312-d (S-(+)-methyl-4,7-dihydro-3-isobutyl-6-methyl-4-(3-nitrophenyl)-thieno[2 ,3-b]pyridine-5-carboxylate), the radical scavengers, MCI-186 (3-methyl-1-phenyl-2-pyrazolin-5-one) and EPC-K1 (L-ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyl-tridecyl)-2H-1-be nzopyran-6yl-hydrogen phosphate] potassium salt), and a calcineurin inhibitor, FK506 (tacrolimus, Prograf). Although all tested agents in the present study attenuated the brain damage in the photochemical-induced thrombotic occlusion model, the radical scavengers did not attenuate the brain damage in the thermocoagulated occlusion model. The time course of brain damage and brain edema formation in the two models was examined. The time course of brain damage was not different in the two models, but the time course of brain edema was quite different. Brain edema formation in the photochemical-induced thrombotic occlusion model was significantly greater (P < 0.01) than that in the thermocoagulated occlusion model at all time point studied until 24 h after occlusion of the middle cerebral artery. The present study suggests that the photochemical-induced thrombotic occlusion model has characteristics of both permanent ischemia and ischemia-reperfusion.

Differential effect of ebselen on compound 48/80- and anti-IgE-induced histamine release from rat peritoneal mast cells

2-Phenyl-1, 2-benzisoselenazol-3-(2H)one (ebselen), a nontoxic seleno-organic compound, exhibits anti-inflammatory activity through the inhibition of many enzymes involved in inflammation. In view of the role played by histamine in the pathophysiology of inflammation, we looked at the effect of ebselen on histamine secretion by rat peritoneal mast cells. It inhibited compound 48/80-induced histamine release in a concentration-dependent manner. Half-maximal and maximal (100%) inhibitory response occurred at 5.10(-7)M and 10(-5)M, respectively. In contrast, ebselen was without any effect on histamine release induced immunologically. Prevention of the inhibitory effect of ebselen by GSH suggests that it interacts with critical thiols involved in the compound 48/80 activation pathway.

Antioxidants for hypertension

Increasing evidence implicates reactive oxygen species in the pathogenesis of hypertension and its cardiovascular complications. By altering the balance in the endothelium between vasoconstrictors such as thromboxane and isoprostanes and vasodilators such as nitric oxide, reactive oxygen species contribute to endothelium-dependent contractions and increased vascular resistance. Antioxidants can restore endothelial function and decrease blood pressure in several models of hypertension and in some, but not all, studies of humans with essential hypertension. The potential of antioxidant therapy for hypertension is considerable.

Ebselen, a selenium-containing redox drug, releases zinc from metallothionein

Selenium compounds oxidize the thiolate ligands in the zinc clusters of metallothionein and release zinc. This chemistry defines new cellular targets for biological forms of selenium and suggests important interactions between zinc and selenium, two biologically essential elements. In the course of delineating the redox chemistry of biological zinc complexes with thiolate ligands, we have found that the non-toxic experimental drug ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) releases zinc from metallothionein. The reaction follows a 1:1 stoichiometry for thiols, is very rapid (t1/2 < 1 min), and proceeds through the opening of the isoselenazol ring and formation of a selenodisulfide with metallothionein. Despite the fast reaction of ebselen with glutathione (t1/2 < 1 s), which proceeds past the stage of the selenodisulfide adduct to the selenol and diselenide derivatives, ebselen reacts with MT even in the presence of glutathione, suggesting that it can also react with MT in vivo. These findings reveal a new mode of action for ebselen and therefore suggest therapeutic applications in zinc-related medical disorders as well as a possible role of biological selenium compounds in zinc metabolism.

Neuroprotective efficacy of ebselen, an anti-oxidant with anti-inflammatory actions, in a rodent model of permanent middle cerebral artery occlusion

1. The aim of this study was to investigate whether delayed treatment with the anti-oxidant and anti-inflammatory agent ebselen reduces the volume of infarction in a rodent model of permanent focal cerebral ischaemia. 2. Ebselen (10 or 30 mg kg-1) or vehicle was administered by gavage 30 min and 12 h after the induction of cerebral ischaemia by permanent occlusion of the left middle cerebral artery (MCA). Animals were killed 24 h following MCA occlusion, and the volumes of ischaemic damage in the ebselen and control groups were evaluated by quantitative histopathology. 3. Ebselen was quickly absorbed following oral (gavage) administration and reached peak levels in the plasma by 1 h post-administration (plasma selenium level of 0.68 +/- 0.04 and 0.84 +/- 0.1 microgram ml-1 for 10 and 30 mg kg-1, respectively, compared to control level of 0.51 +/- 0.02 microgram kg-1). 4. Treatment with the lower dose of ebselen (10 mg kg-1) significantly (P < 0.01) reduced the volume of infarction in the cerebral hemisphere and cerebral cortex (by 31.8% and 36.7%, respectively compared with the placebo group). 5. The neuroprotective efficacy of the higher dose ebselen (30 mg kg-1) was less than that of the lower dose ebselen (10 mg kg-1). The volume of ischaemic damage in the cerebral hemisphere was reduced by 23.7% (P < 0.02), and cerebral cortex by 27.5% (P < 0.01). 6. Both doses of ebselen (10, 30 mg kg-1) had no therapeutic efficacy on the caudate nucleus, where ischaemia was most severe, in this model. 7. Free radical-mediated injury is normally associated with reperfusion of ischaemic tissue. The present results suggest that oxidative injury is also a significant contributor to brain damage in models of maintained (permanent) ischaemia and that ebselen is effective in attenuating this free radical-induced damage.

Modulation of cytokine production by a selenoorganic compound (AE-22) in hyperreactive or hyporeactive bronchoalveolar leukocytes of asthmatics or lung cancer patients

We have found that many synthetic selenoorganic compounds, including ebselen, have immunotropic activity. These studies were designed to assess the effect of the analog of ebselen bis[2-pyridyl (2-carbamoyl) phenyl]diselenide (AE-22) on human leukocytes that may express various activation states. The cells were obtained from bronchoalveolar lavage (BAL) cells of patients with various inflammatory lung diseases. The AE-22-treated BAL cells from patients with bronchial asthma (n = 6) and with small cell lung cancer (SCLC) (n = 6) were compared with these in the peripheral blood leukocytes (PBL) from the same donors. The control group comprised 5 patients who underwent diagnostic examination and were free of any cancer or concomitant diseases. Secretion of TNF-alpha, IL-6, and IFN-gamma was considered as a marker of BAL or PBL cell activation. Different response of the cells and various effects of AE-22 were observed in relation to the origin and functional state of leukocytes. It was established that AE-22 can induce TNF-alpha, IL-6, and IFN-gamma in a dose-dependent manner in BAL cells and PBL isolated from healthy individuals. However, BAL cells were found to be less reactive than PBL as cytokine producers. In contrast, AE-22 had no effect on BAL cells obtained from patients with lung cancer, which were found to be hyporeactive to phytohemagglutinin and bacterial lipopolysaccharide and did not produce TNF-alpha, IL-6, or IFN spontaneously. The spontaneous release of cytokines by BAL cells from bronchial asthma patients, but not by PBL from the same individuals, was significantly (p < 0.01) higher than that from the cultures of healthy control subjects. The high secretion of cytokines by the locally activated BAL cells was significantly (p < 0.01) reduced after administration of AE-22. The results suggest that AE-22 has immunomodulatory activity. AE-22 can downregulate the hyporeactive BAL cells from asthmatics, but it appears to be inactive in BAL cells of cancer patients who can tolerate the cytokine inducers.

Selective inhibitors of neuronal nitric oxide synthase--is no NOS really good NOS for the nervous system?

It is now ten years since NO was shown to account for the biological activity of endothelium-derived relaxing factor (EDRF). It is also the tenth anniversary of the identification of L-NG monomethyl arginine (L-NMMA) as the very first inhibitor of NO biosynthesis. That EDRF and NO were one and the same sparked an explosion of interest in the biochemistry and pharmacology of NO which has yet to subside. In contrast, the first ever nitric oxide synthase (NOS) inhibitor slipped seamlessly into the literature virtually without comment at the time. Over the following decade, L-NMMA (and like NOS inhibitors) have proved invaluable as tools for probing the biological roles of NO in health and disease and, in particular, have increased our understanding of the function of NO in the nervous system. Further advances in this important area now require the development of inhibitors selective for the neuronal isoform of NOS (nNOS). Here, Philip Moore and Rachel Handy provide an up-to-date account of the literature regarding the biochemical and pharmacological characterization of NOS inhibitors with particular reference to compounds with greater selectivity for the nNOS isoform.

Intramolecular Homolytic Substitution with Amidyl Radicals: A Free-Radical Synthesis of Ebselen and Related Analogues

Irradiation of a water-cooled benzene solution of pyridine-2-thioneoxycarbonyl (PTOC) imidate esters 9 derived from N-butyl-2-(benzylseleno)benzamide (6, R = Bu), 2-(benzylseleno)-N-hexylbenzamide (6, R = Hex), N-benzyl-2-(benzylseleno)benzamide (6, R = Bn), and 2-(benzylseleno)-N-cyclohexylbenzamide (6, R = c-Hex) with a 250-W low-pressure mercury lamp affords the corresponding 1,2-benzisoselenazol-3(2H)-ones (1) in yields of 81-91% (R = primary alkyl) and 45% (R = c-Hex). Presumably, these transformations involve formation of amidyl radicals 2 which undergo subsequent intramolecular homolytic substitution at the selenium atom with expulsion of a benzyl radical. PTOC imidate esters derived from 2-(benzylseleno)benzanilide (6, R = Ph) and 2-(benzylseleno)-N-tert-butylbenzamide (6, R = t-Bu) were unable to be prepared in this manner. 1,2-Benzisoselenazol-3(2H)-ones (1, R = Ph, Hex, i-Pr, t-Bu) could also be prepared in 76-85% yield by reaction of the corresponding 2,2'-diselenobis(benzamide) (15) with benzoyl or tert-butyl peroxide. The mechanisms of these transformations are discussed.

Are the reactive oxygen-derived species (ROS) interactive properties of the many therapeutic drugs from various categories pertinent to their beneficial effects?

Many pathologic states are known to involve the generation of reactive oxygen species, (ROS). It is not known at present to what extent these phenomena are due to ROS formation, or if their formation is a result of the disease. Many therapeutic drugs either scavenge ROS or inhibit their formation. The purpose of this review is to match the drugs used for certain diseases with their anti-ROS actions. This attempted correlation is made to try to give an answer to the title question.

Scavenging of hypochlorous acid by carvedilol and ebselen in vitro

1. The antihypertensive drug carvedilol and the antiinflammatory selenoorganic compound ebselen were tested for their ability to react with the reactive oxygen species hypochlorous acid (HOCl) in vitro. 2. Carvedilol scavenges HOCl at a rate sufficient to protect a model molecule catalase against inactivation by HOCl. 3. Ebselen was resistant to HOCl when its glutathione-peroxidase mimetic property was compared with that of glutathione peroxidase.

Ebselen and cytokine-induced nitric oxide synthase expression in insulin-producing cells

Interleukin-1 (IL-1) may be a mediator of beta-cell damage in insulin-dependent diabetes mellitus (IDDM). The IL-1 mechanism of action on insulin-producing cells probably includes activation of the transcription nuclear factor kappa B (NF-kappa B), increased transcription of the inducible form of nitric oxide synthase (iNOS) and the subsequent production of nitric oxide (NO). Reactive oxygen intermediates, particularly H2O2, have been proposed as second messengers for NF-kappa B activation. In the present study, we tested whether ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a glutathione peroxidase mimicking compound, could counteract the effects of IL-1 beta, H2O2 and alloxan in rat pancreatic islets and in the rat insulinoma cell line RINm5F (RIN cells). Some of these experiments were also reproduced in human pancreatic islets. Ebselen (20 microM) prevented the increase in nitrite production by rat islets exposed to IL-1 beta for 6 hr and induced significant protection against the acute inhibitory effects of alloxan or H2O2 exposure, as judged by the preserved glucose oxidation rates. However, ebselen failed to prevent the increase in nitrite production and the decrease in glucose oxidation and insulin release by rat islets exposed to IL-1 beta for 24 hr. Ebselen prevented the increase in nitrite production by human islets exposed for 14 hr to a combination of cytokines (IL-1 beta, tumor necrosis factor-alpha and interferon-gamma). In RIN cells, ebselen counteracted both the expression of iNOS mRNA and the increase in nitrite production induced by 6 hr exposure to IL-beta but failed to block IL-1 beta-induced iNOS expression following 24 hr exposure to the cytokine. Moreover, ebselen did not prevent IL-1 beta-induced NF-kappa B activation. As a whole, these data indicate that ebselen partially counteracts cytokine-induced NOS activation in pancreatic beta-cells, an effect not associated with inhibition of NF-kappa B activation.

Inhibition of copper- and peroxyl radical-induced LDL lipid oxidation by ebselen: antioxidant actions in addition to hydroperoxide-reducing activity

The effects of ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) on human LDL lipid oxidation induced by different fluxes of aqueous peroxyl radicals and cupric ion (at a Cu2+:LDL ratio of 17:1) were investigated. Addition of ebselen to LDL oxidised with Cu2+ prolonged the duration of the lag-phase typical for this oxidising condition, with the increase being proportional to the square of the ebselen concentration. Ebselen also prevented the formation of lipid hydroperoxides and inhibited the consumption of endogenous antioxidants during the early period of Cu(2+)-induced oxidation, during which time the drug was converted stoichiometrically into ebselen oxide (2-phenyl-1,2-benzisoselenazol-3(2H)-one-Se-oxide). Ebselen oxide itself was antioxidant inactive. Ebselen also inhibited formation of lipid-hydroperoxides and spared alpha-tocopherol during the initial stages of LDL oxidation mediated by low-flux of aqueous peroxyl radicals, where a lag-phase was not observed. When a higher flux of aqueous peroxyl radicals was used, ebselen increased the observed inhibited phase of peroxidation in a dose-dependent manner, though less pronounced than its prolongating effect on the lag-phase of Cu(2+)-induced LDL lipid oxidation. Ebselen was also able to directly interact with Cu1+, alkyl peroxyl radicals and alpha-tocopheroxyl radicals, demonstrating that the drug has a number of potential antioxidant activities in addition to its well-known hydroperoxide-reducing activity. We conclude that the antioxidant activities of ebselen are complex and that their relative importance likely vary depending on the experimental system used.

Ebselen-binding equilibria between plasma and target proteins

The antiinflammatory drug ebselen (2-phenyl-1,2-benzisoselenazo-3(2H)-one) is known to bind covalently to thiols to form seleno disulfides that, directly or indirectly, are responsible for its pharmacological effects. Due to its reactive thiol group and high plasma concentration, albumin is a preferred target of ebselen, which it binds covalently. Ebselen should not, then, be available for intracellular actions at other target proteins. We have addressed this question, and show by difference spectroscopy that the interaction of ebselen with albumin occurs stoichiometrically under ring opening, but is readily reversible in the presence of glutathione. With intact human polymorphonuclear leukocytes (PMN), a similar stoichiometric reaction with distinct spectral features was observed with ebselen that was completely abolished by pretreatment of PMN with N-ethylmaleimide, but not by selective depletion of cellular glutathione. Human platelets, again, exhibited different spectral changes upon addition of ebselen. In agreement with results reported in the literature, we show that 14C-ebselen is in dynamic equilibrium with all accessible thiol groups and, hence, despite mostly being bound covalently to albumin, it will exchange rapidly with other target proteins in PMN or platelets.