An organotellurium compound with antioxidant activity against excitotoxic agents without neurotoxic effects in brain of rats

Catalytic system having an organotellurium ligand on graphene oxide: immobilization of Pd(0) nanoparticles and application in heterogeneous catalysis of cross-coupling reactions

First heterogeneous catalytic system, having a covalently linked hybrid bidentate organotellurium ligand [i.e., PhTe-CH2-CH2-NH2] on the surface of graphene oxide, has been synthesized with immobilized and stabilized Pd(0) nanoparticles. To the best of our knowledge, it is the first such catalytic system in which a heterogenized organotellurium ligand has been used. It has been well-characterized using different physicochemical characterization techniques viz. P-XRD, XPS, HR-TEM, EELS, FE-SEM, EDX, TGA, BET surface area analysis, FT-IR spectroscopy, and Raman spectroscopy. The Pd content of the final system has been quantified using ICP-OES. Its applications have been explored in Suzuki-Miyaura C-C cross coupling and C-O cross coupling reactions. Hot filtration experiments corroborate the heterogeneous nature of the catalysis. It is recyclable for up to five reaction cycles in Suzuki-Miyaura and C-O cross coupling with marginal loss in performance. It also catalyzes the reactions of chloroarenes such as chlorobenzene, 4-chloroaniline, 1-chloro-4-nitrobenzene, 4-chloroacetophenone, 4-chlorobenzophenone for Suzuki coupling, and 1-chloro-4-nitrobenzene, 4-chlorobenzonitrile, chlorobenzene, and 4-chlorotoluene for C-O coupling. P-XRD, FE-SEM, and EDX study reveals that the catalytic system retains its structural originality and functionality after recycling.

Hippocampal acetylcholinesterase activation induced by streptozotocin in mice is protected by an organotellurium compound without evidence of toxicity

The cognitive deficit, which is like Alzheimer's disease and is associated with oxidative damage, may be induced by exposure to streptozotocin. This study aimed to evaluate if the tellurium-containing organocompound, 3j, 5'-arylchalcogeno-3-aminothymidine derivative, interferes with the effects of streptozotocin, as well as to investigate its toxicity in adult mice. Cognitive deficit was induced by two doses of streptozotocin (2.25 mg/kg/day, 48 h interval) intracerebroventricularly. After, the mice were subcutaneously treated with 3j (8.62 mg/kg/day) for 25 days. The effects were assessed by evaluating hippocampal and cortical acetylcholinesterase and behavioral tasks. 3j toxicity was investigated for 10 (0, 21.55, or 43.10 mg/kg/day) and 37 (0, 4.31, or 8.62 mg/kg/day) days by assessing biometric parameters and glucose and urea levels, and alanine aminotransferase activity in blood plasma. 3j exposure did not alter the behavioral alterations induced by streptozotocin exposure. On the other hand, 3j exposure normalized hippocampus acetylcholinesterase activity, which is enhanced by streptozotocin exposure. Toxicity evaluation showed that the administration of 3j for either 10 or 37 days did not cause harmful effects on the biometric and biochemical parameters analyzed. Therefore, 3j does not present any apparent toxicity and reverts acetylcholinesterase activity increase induced by streptozotocin in young adult mice.

Selenoneine-inspired selenohydantoins with glutathione peroxidase-like activity

Chronic diseases such as cystic fibrosis, inflammatory bowel diseases, rheumatoid arthritis, and cardiovascular illness have been linked to a decrease in selenium levels and an increase in oxidative stress. Selenium is an essential trace element that exhibits antioxidant properties, with selenocysteine enzymes like glutathione peroxidase being particularly effective at reducing peroxides. In this study, a series of synthetic organoselenium compounds were synthesized and evaluated for their potential antioxidant activities. The new selenohydantoin molecules were inspired by selenoneine and synthesized using straightforward methods. Their antioxidant potential was evaluated and proven using classical radical scavenging and metal-reducing methods. The selenohydantoin derivatives exhibited glutathione peroxidase-like activity, reducing hydroperoxides. Theoretical calculations using Density Functional Theory (DFT) revealed the selenone isomer to be the only one occurring in solution, with selenolate as a possible tautomeric form in the presence of a basic species. Cytocompatibility assays indicated that the selenohydantoin derivatives were non-toxic to primary human aortic smooth muscle cells, paving the way for further biological evaluations of their antioxidant activity. The results suggest that selenohydantoin derivatives with trifluoro-methyl (-CF3) and chlorine (-Cl) substituents have significant activities and could be potential candidates for further biological trials. These compounds may contribute to the development of effective therapies for chronic diseases such cardiovascular diseases.

Silver-catalyzed synthesis of symmetrical diaryl tellurides from arylboronic acids and tellurium

The synthesis of symmetrical tellurides from different arylboronic acids and elemental tellurium using AgNO3 as a catalyst was performed.

Selenium Donors at the Junction of Inflammatory Diseases

Selenium is an essential non-metal trace element, and the imbalance in the bioavailability of selenium is associated with many diseases ranking from acute respiratory distress syndrome, myocardial infarction and renal failure (Se overloading) to diseases associated with chronic inflammation like inflammatory bowel diseases, rheumatoid arthritis, and atherosclerosis (Se unload). The only source of selenium is the diet (animal and cereal sources) and its intestinal absorption is limiting for selenocysteine and selenomethionine synthesis and incorporation in selenoproteins. In this review, after establishing the link between selenium and inflammatory diseases, we envisaged the potential of selenium nanoparticles and organic selenocompounds to compensate the deficit of selenium intake from the diet. With high selenium loading, nanoparticles offer a low dosage to restore selenium bioavailability whereas organic selenocompounds can play a role in the modulation of their antioxidant or antiinflammatory activities.

Spectroscopic identification of the phenyltelluryl radical and its reactivity toward molecular oxygen

The phenyltelluryl radical was prepared by high-vacuum flash pyrolysis of diphenyl ditelluride and was chacracterized by matrix isolation IR and UV/Vis spectroscopy. After doping the matrix with molecular oxygen and allowing bimolecular reactions, the hitherto unkown phenyltelluro peroxy radical formed and was identified via IR spectroscopy. Irradiation with light at λ = 436 nm leads to isomerization to the thermodynamically more stable novel phenyltelluroyl radical. All experimental findings agree well with density functional theory (UB3LYP/Def2QZVPP and UM06-2X/Def2QZVPP) computations.

Diphenyl Ditelluride: Redox-Modulating and Antiproliferative Properties

Tellurium is a rare element that has been regarded as a toxic, nonessential element, and its biological role is not clearly established. In addition, the biological effects of elemental tellurium and some of its organic and inorganic derivatives have been studied, leading to a set of interesting and promising applications. Diphenyl ditelluride (DPDT), an organic tellurium derivate, showed antioxidant, antigenotoxic, antimutagenic, and anticancer properties. The antioxidant and prooxidant properties of DPDT are complex and depend on experimental conditions, which may explain the contradictory reports of these properties. In addition, DPDT may exert its effects through different pathways, including distinct ones to those responsible for chemotherapy resistance phenotypes: transcription factors, membrane receptors, adhesion, structural molecules, cell cycle regulatory components, and apoptosis pathways. This review aims to present recent advances in our understanding of the biological effects, therapeutic potential, and safety of DPDT treatment. Moreover, original results demonstrating the cytotoxic effects of DPDT in different mammalian cell lines and systems biology analysis are included, and emerging approaches for possible future applications are inferred.

Synthesis of alkynyltellurides mediated by K3PO4 and DMSO

The reaction of diorganyl ditellurides with terminal alkynes is described using K₃PO₄ as a catalyst.

Telluric Acid Ameliorates Endotoxemic Kidney Injury in Mice: Involvement of TLR4, Nrf2, and PI3K/Akt Signaling Pathways

Being one of the most abundant trace elements in the human body, the therapeutic potential of tellurium-based compounds has been a target of interest. Recent reports denoted their redox-modulating and anti-inflammatory activities in experimental endotoxemia. However, their potential nephroprotective effect against endotoxemic kidney injury is yet to be elucidated. This study investigated the possible renoprotective effect of telluric acid (TEL) against lipopolysaccharide (LPS)-induced acute kidney injury (AKI) in mice, targeting toll-like receptor 4 (TLR4), phosphoinositide 3-kinase (PI3K)/Akt, and nuclear factor-erythroid 2-related factor-2 (Nrf2) pathways as possible mechanistic contributors to TEL's effect. AKI was induced by LPS (2 mg/kg). TEL (60 μg/kg; i.p.) was administered once daily for seven consecutive days before LPS injection. Pretreatment with TEL alleviated LPS-induced AKI as evidenced by the hampered serum levels of creatinine and cystatin C. TEL also opposed LPS-induced elevation in renal kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, nuclear factor-kappa B p65, interleukin-1β, and thiobarbituric acid-reactive substance contents. This was accompanied by a replenishment of renal glutathione, transcriptional upregulation of Nrf2, enhancement of heme oxygenase-1 activity, and a marked upregulation of phospho-PI3K and phospho-Akt protein expressions. Histopathological findings corroborated with the amendment of biochemical parameters. In view of these findings, we may conclude that TEL pretreatment purveyed novel nephroprotective effects against endotoxemic kidney injury, which might be partly attributed to the modulation of TLR4, PI3K/Akt, and Nrf2 signaling pathways and may hence provide a valuable asset for the management of endotoxemic renal complications.

Synthesis of symmetrical and unsymmetrical tellurides via silver catalysis

The cross-coupling reaction of diaryl ditellurides with aryl boronic acids is described using AgNO₃ as a catalyst.

Insights into the differential toxicological and antioxidant effects of 4-phenylchalcogenil-7-chloroquinolines in Caenorhabditis elegans

Organic selenium and tellurium compounds are known for their broad-spectrum effects in a variety of experimental disease models. However, these compounds commonly display high toxicity and the molecular mechanisms underlying these deleterious effects have yet to be elucidated. Thus, the need for an animal model that is inexpensive, amenable to high-throughput analyses, and feasible for molecular studies is highly desirable to improve organochalcogen pharmacological and toxicological characterization. Herein, we use Caenorhabdtis elegans (C. elegans) as a model for the assessment of pharmacological and toxicological parameters following exposure to two 4-phenylchalcogenil-7-chloroquinolines derivatives (PSQ for selenium and PTQ for tellurium-containing compounds). While non-lethal concentrations (NLC) of PTQ and PSQ attenuated paraquat-induced effects on survival, lifespan and oxidative stress parameters, lethal concentrations (LC) of PTQ and PSQ alone are able to impair these parameters in C. elegans. We also demonstrate that DAF-16/FOXO and SKN-1/Nrf2 transcription factors underlie the mechanism of action of these compounds, as their targets sod-3, gst-4 and gcs-1 were modulated following exposures in a daf-16- and skn-1-dependent manner. Finally, in accordance with a disturbed thiol metabolism in both LC and NLC, we found higher sensitivity of trxr-1 worm mutants (lacking the selenoprotein thioredoxin reductase 1) when exposed to PSQ. Finally, our study suggests new targets for the investigation of organochalcogen pharmacological effects, reinforcing the use of C. elegans as a powerful platform for preclinical approaches.

Glycerol as Precursor of Organoselanyl and Organotellanyl Alkynes

Herein we describe the synthesis of organoselanyl and organotellanyl alkynes by the addition of lithium alkynylchalcogenolate (Se and Te) to tosyl solketal, easily obtained from glycerol. The alkynylchalcogenolate anions were generated in situ and added to tosyl solketal in short reaction times, furnishing in all cases the respective products of substitution in good yields. Some of the prepared compounds were deprotected using an acidic resin to afford new water-soluble 3-organotellanylpropane-1,2-diols. The synthetic versatility of the new chalcogenyl alkynes was demonstrated in the iodocyclization of 2,2-dimethyl-1,3-dioxolanylmethyl(2-methoxyphenylethynyl)selane 3f, which afforded 3-iodo-2-(2,2-dimethyl-1,3-dioxolanylmethyl) selenanylbenzo[b]furan in 85% yield, opening a new way to access water-soluble Se-functionalized benzo[b]furanes.

Reactions of nitroxides 16. First nitroxides containing tellurium atom

Five- and six-membered nitroxides with a tellurium containing moiety were synthesized by the addition of nitroxyl amines to phenyltellanyl alkylene isothiocyanates.

Centella asiatica and Its Fractions Reduces Lipid Peroxidation Induced by Quinolinic Acid and Sodium Nitroprusside in Rat Brain Regions

Oxidative stress has been implicated in several pathologies including neurological disorders. Centella asiatica is a popular medicinal plant which has long been used to treat neurological disturbances in Ayurvedic medicine. In the present study, we quantified of compounds by high performance liquid chromatography (HPLC) and examined the phenolic content of infusion, ethyl acetate, n-butanolic and dichloromethane fractions. Furthermore, we analyzed the ability of the extracts from C. asiatica to scavenge the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) radical as well as total antioxidant activity through the reduction of molybdenum (VI) (Mo(6+)) to molybdenum (V) (Mo(5+)). Finally, we examined the antioxidant effect of extracts against oxidant agents, quinolinic acid (QA) and sodium nitroprusside (SNP), on homogenates of different brain regions (cerebral cortex, striatum and hippocampus). The HPLC analysis revealed that flavonoids, triterpene glycoside, tannins, phenolic acids were present in the extracts of C. asiatica and also the phenolic content assay demonstrated that ethyl acetate fraction is rich in these compounds. Besides, the ethyl acetate fraction presented the highest antioxidant effect by decreasing the lipid peroxidation in brain regions induced by QA. On the other hand, when the pro-oxidant agent was SNP, the potency of infusion, ethyl acetate and dichloromethane fractions was equivalent. Ethyl acetate fraction from C. asiatica also protected against thiol oxidation induced by SNP and QA. Thus, the therapeutic potential of C. asiatica in neurological diseases could be associated to its antioxidant activity.

Signaling mechanisms and disrupted cytoskeleton in the diphenyl ditelluride neurotoxicity

Evidence from our group supports that diphenyl ditelluride (PhTe)₂ neurotoxicity depends on modulation of signaling pathways initiated at the plasma membrane. The (PhTe)₂-evoked signal is transduced downstream of voltage-dependent Ca²⁺ channels (VDCC), N-methyl-D-aspartate receptors (NMDA), or metabotropic glutamate receptors activation via different kinase pathways (protein kinase A, phospholipase C/protein kinase C, mitogen-activated protein kinases (MAPKs), and Akt signaling pathway). Among the most relevant cues of misregulated signaling mechanisms evoked by (PhTe)₂ is the cytoskeleton of neural cells. The in vivo and in vitro exposure to (PhTe)₂ induce hyperphosphorylation/hypophosphorylation of neuronal and glial intermediate filament (IF) proteins (neurofilaments and glial fibrillary acidic protein, resp.) in different brain structures of young rats. Phosphorylation of IFs at specific sites modulates their association/disassociation and interferes with important physiological roles, such as axonal transport. Disrupted cytoskeleton is a crucial marker of neurodegeneration and is associated with reactive astrogliosis and apoptotic cell death. This review focuses the current knowledge and important results on the mechanisms of (PhTe)₂ neurotoxicity with special emphasis on the cytoskeletal proteins and their differential regulation by kinases/phosphatases and Ca²⁺-mediated mechanisms in developmental rat brain. We propose that the disrupted cytoskeletal homeostasis could support brain damage provoked by this neurotoxicant.

Seleno- and telluro-xylofuranosides attenuate Mn-induced toxicity in C. elegans via the DAF-16/FOXO pathway

Organochalcogens are promising pharmacological agents that possess significant biological activities. Nevertheless, because of the complexity of mammalian models, it has been difficult to determine the molecular pathways and specific proteins that are modulated in response to treatments with these compounds. The nematode worm Caenorhabditis elegans is an alternative experimental model that affords easy genetic manipulations, green fluorescent protein tagging and in vivo live analysis of toxicity. Abundant evidence points to oxidative stress in mediating manganese (Mn)-induced toxicity. In this study we challenged worms with Mn, and investigated the efficacy of inedited selenium- and tellurium-xylofuranosides in reversing and/or protecting the worms from Mn-induced toxicity. In addition, we investigated their putative mechanism of action. First, we determined the lethal dose 50% (LD50) and the effects of the xylofuranosides on various toxic parameters. This was followed by studies on the ability of xylofuranosides to afford protection against Mn-induced toxicity. Both Se- and Te-xylofuranosides increased the expression of superoxide dismutase (SOD-3). Furthermore, we observed that the xylofuranosides induced nuclear translocation of the transcription factor DAF-16/FOXO, which in the worm is known to regulate stress responsiveness, aging and metabolism. These findings suggest that xylofuranosides attenuate toxicity Mn-induced, by regulating the DAF-16/FOXO signaling pathway.

Main-Group Medicinal Chemistry Including Li and Bi*

Main-group element compounds were among the first developed in the modern era as pharmaceutical preparations for the treatment of a wide variety of human ailments; it is now recognized that many of these elements exist in traditional medicine of many societies, for example, arsenic. The use of main-group element compounds in contemporary medicine continues for the treatment of, for example, depression (Li), stomach ulcers (Bi), cancer (As and Ga), and leishmaniasis (Sb). Not surprisingly, new compounds of these elements, and other main-group elements, continue to be investigated for their potential use in new therapies. In this chapter, the use of main-group elements as therapeutic agents is outlined and also, where understood, comments on biological targets and mechanisms of action. Further, key advances in new potential applications of main-group element compounds in medicine are evaluated.

Antioxidant properties of Taraxacum officinale fruit extract are involved in the protective effect against cellular death induced by sodium nitroprusside in brain of rats

CONTEXT

Taraxacum officinale Weber (Asteraceae), known as dandelion, is used for medicinal purposes due to its choleretic, diuretic, antitumor, antioxidant, antiinflammatory, and hepatoprotective properties.

OBJECTIVE

We sought to investigate the protective activity of T. officinale fruit extract against sodium nitroprusside (SNP)-induced decreased cellular viability and increased lipid peroxidation in the cortex, hippocampus, and striatum of rats in vitro. To explain the mechanism of the extract's antioxidant activity, its putative scavenger activities against NO, DPPH·, OH·, and H(2)O(2) were determined.

METHODS

Slices of cortex, hippocampus, and striatum were treated with 50 μM SNP and T. officinale fruit ethanolic extract (1-20 µg/mL) to determine cellular viability by MTT reduction assay. Lipid peroxidation was measure in cortical, hippocampal and striatal slices incubates with SNP (5 µM) and T. officinale fruit extract (1-20 µg/mL). We also determined the scavenger activities of T. officinale fruit extract against NO·, DPPH·, OH·, and H(2)O(2), as well as its iron chelating capacity.

RESULTS

The extract (1, 5, 10, and 20 μg/mL) protected against SNP-induced decreases in cellular viability and increases in lipid peroxidation in the cortex, hippocampus, and striatum of rats. The extract had scavenger activity against DPPH· and NO· at low concentrations and was able to protect against H(2)O(2) and Fe(2+)-induced deoxyribose oxidation.

CONCLUSION

T. officinale fruit extract has antioxidant activity and protects brain slices against SNP-induced cellular death. Possible mechanisms of action include its scavenger activities against reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are attributed to the presence of phenolic compounds in the extract.

Cooperation of non-effective concentration of glutamatergic system modulators and antioxidant against oxidative stress induced by quinolinic acid

Excessive formation of reactive oxygen species (ROS) and disruption of glutamate uptake have been hypothesized as key mechanisms contributing to quinolinic acid (QA)-induced toxicity. Thus, here we investigate if the use of diphenyl diselenide (PhSe)(2), guanosine (GUO) and MK-801, alone or in combination, could protect rat brain slices from QA-induced toxicity. QA (1 mM) increased ROS formation, thiobarbituric acid reactive substances (TBARS) and decreased cell viability after 2 h of exposure. (PhSe)(2) (1 μM) protected against this ROS formation in the cortex and the striatum and also prevented decreases in cell viability induced by QA. (PhSe)(2) (5 μM) prevented ROS formation in the hippocampus. GUO (10 and 100 μM) blocked the increase in ROS formation caused by QA and MK-801 (20 and 100 μM) abolished the pro-oxidant effect of QA. When the noneffective concentrations were used in combination produced a decrease in ROS formation, mainly (PhSe)(2) + GUO and (PhSe)(2) + GUO + MK-801. These results demonstrate that this combination could be effective to avoid toxic effects caused by high concentrations of QA. Furthermore, the data obtained in the ROS formation and cellular viability assays suggest different pathways in amelioration of QA toxicity present in the neurodegenerative process.

Organotellurium and organoselenium compounds attenuate Mn-induced toxicity in Caenorhabditis elegans by preventing oxidative stress

Organochalcogens have been widely studied given their antioxidant activity, which confers neuroprotection, antiulcer, and antidiabetic properties. Given the complexity of mammalian models, understanding the cellular and molecular effects of organochalcogens has been hampered. The nematode worm Caenorhabditis elegans is an alternative experimental model that affords easy genetic manipulations, green fluorescent protein tagging, and in vivo live analysis of toxicity. We previously showed that manganese (Mn)-exposed worms exhibit oxidative-stress-induced neurodegeneration and life-span reduction. Here we use Mn-exposed worms as a model for an oxidatively challenged organism to investigate the underlying mechanisms of organochalcogen antioxidant properties. First, we recapitulate in C. elegans the effects of organochalcogens formerly observed in mice, including their antioxidant activity. This is followed by studies on the ability of these compounds to afford protection against Mn-induced toxicity. Diethyl-2-phenyl-2-tellurophenyl vinyl phosphonate (DPTVP) was the most efficacious compound, fully reversing the Mn-induced reduction in survival and life span. Ebselen was also effective, reversing the Mn-induced reduction in survival and life span, but to a lesser extent compared with DPTVP. DPTVP also lowered Mn-induced increases in oxidant levels, indicating that the increased survival associated with exposure to this compound is secondary to a decrease in oxidative stress. Furthermore, DPTVP induced nuclear translocation of the transcriptional factor DAF-16/FOXO, which regulates stress responsiveness and aging in worms. Our findings establish that the organochalcogens DPTVP and ebselen act as antiaging agents in a model of Mn-induced toxicity and aging by regulating DAF-16/FOXO signaling and attenuating oxidative stress.

Therapeutic potential of selenium and tellurium compounds: opportunities yet unrealised

Despite being disparaged for their malodorous and toxic demeanour, compounds of selenium, a bio-essential element, and tellurium, offer possibilities as therapeutic agents. Herein, their potential use as drugs, for example, as anti-viral, anti-microbial, anti-inflammatory agents, etc., will be surveyed along with a summary of the established biological functions of selenium. The natural biological functions of tellurium remain to be discovered.

Hepatoprotective activity of a vinylic telluride against acute exposure to acetaminophen

Acetaminophen (APAP) hepatotoxicity has been related with several cases of cirrhosis, hepatitis and suicides attempts. Notably, oxidative stress plays a central role in the hepatic damage caused by APAP and antioxidants have been tested as alternative treatment against APAP toxicity. In the present study, we observed the hepatoprotector activity of the diethyl-2-phenyl-2-tellurophenyl vinylphosphonate (DPTVP), an organotellurium compound with low toxicity and high antioxidant potential. When the dose of 200 mg/kg of APAP was used, we observed that all used doses of DPTVP were able to restore the -SH levels that were depleted by APAP. Furthermore, the increase in thiobarbituric acid reactive substances levels and in the seric alanine aminotransferase (ALT) activity and the histopathological alterations caused by APAP were restored to control levels by DPTVP (30, 50 and 100 μmol/kg). On the other hand, when the 300 mg/kg dose of APAP was used, DPTVP restored the non-proteic -SH levels and repaired the normal liver morphology of the intoxicated mice only at 50 μmol/kg. Our in vitro results point out to a scavenging activity of DPTVP against several reactive species, action that is attributed to its chemical structure. Taken together, our results demonstrate that the pharmacological action of DPTVP as a hepatoprotector is probably due to its scavenging activity related to its chemical structure.

Reduction of diphenyl diselenide and analogs by mammalian thioredoxin reductase is independent of their gluthathione peroxidase-like activity: a possible novel pathway for their antioxidant activity

Since the successful use of the organoselenium drug ebselen in clinical trials for the treatment of neuropathological conditions associated with oxidative stress, there have been concerted efforts geared towards understanding the precise mechanism of action of ebselen and other organoselenium compounds, especially the diorganyl diselenides such as diphenyl diselenide, and its analogs. Although the mechanism of action of ebselen and other organoselenium compounds has been shown to be related to their ability to generally mimic native glutathione peroxidase (GPx), only ebselen however has been shown to serve as a substrate for the mammalian thioredoxin reductase (TrxR), demonstrating another component of its pharmacological mechanisms. In fact, there is a dearth of information on the ability of other organoselenium compounds, especially diphenyl diselenide and its analogs, to serve as substrates for the mammalian enzyme thioredoxin reductase. Interestingly, diphenyl diselenide shares several antioxidant and neuroprotective properties with ebselen. Hence in the present study, we tested the hypothesis that diphenyl diselenide and some of its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxy-diphenyl diselenide, 4.4'-biscarboxydiphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could also be substrates for rat hepatic TrxR. Here we show for the first time that diselenides are good substrates for mammalian TrxR, but not necessarily good mimetics of GPx, and vice versa. For instance, bis-methoxydiphenyl diselenide had no GPx activity, whereas it was a good substrate for reduction by TrxR. Our experimental observations indicate a possible dissociation between the two pathways for peroxide degradation (either via substrate for TrxR or as a mimic of GPx). Consequently, the antioxidant activity of diphenyl diselenide and analogs can be attributed to their capacity to be substrates for mammalian TrxR and we therefore conclude that subtle changes in the aryl moiety of diselenides can be used as tool for dissociation of GPx or TrxR pathways as mechanism triggering their antioxidant activities.

Reduction of diphenyl diselenide and analogs by mammalian thioredoxin reductase is independent of their gluthathione peroxidase-like activity: a possible novel pathway for their antioxidant activity

Since the successful use of the organoselenium drug ebselen in clinical trials for the treatment of neuropathological conditions associated with oxidative stress, there have been concerted efforts geared towards understanding the precise mechanism of action of ebselen and other organoselenium compounds, especially the diorganyl diselenides such as diphenyl diselenide, and its analogs. Although the mechanism of action of ebselen and other organoselenium compounds has been shown to be related to their ability to generally mimic native glutathione peroxidase (GPx), only ebselen however has been shown to serve as a substrate for the mammalian thioredoxin reductase (TrxR), demonstrating another component of its pharmacological mechanisms. In fact, there is a dearth of information on the ability of other organoselenium compounds, especially diphenyl diselenide and its analogs, to serve as substrates for the mammalian enzyme thioredoxin reductase. Interestingly, diphenyl diselenide shares several antioxidant and neuroprotective properties with ebselen. Hence in the present study, we tested the hypothesis that diphenyl diselenide and some of its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxy-diphenyl diselenide, 4.4'-biscarboxydiphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could also be substrates for rat hepatic TrxR. Here we show for the first time that diselenides are good substrates for mammalian TrxR, but not necessarily good mimetics of GPx, and vice versa. For instance, bis-methoxydiphenyl diselenide had no GPx activity, whereas it was a good substrate for reduction by TrxR. Our experimental observations indicate a possible dissociation between the two pathways for peroxide degradation (either via substrate for TrxR or as a mimic of GPx). Consequently, the antioxidant activity of diphenyl diselenide and analogs can be attributed to their capacity to be substrates for mammalian TrxR and we therefore conclude that subtle changes in the aryl moiety of diselenides can be used as tool for dissociation of GPx or TrxR pathways as mechanism triggering their antioxidant activities.

NAD(P)H oxidase contributes to neurotoxicity in an excitotoxic/prooxidant model of Huntington's disease in rats: protective role of apocynin

Intrastriatal injection of quinolinic acid (QUIN) to rodents reproduces some biochemical, morphological, and behavioral characteristics of Huntington's disease. NAD(P)H oxidase is an enzymatic complex that catalyzes superoxide anion (O(2).(-)) production from O(2) and NADPH. The present study evaluated the role of NAD(P)H oxidase in the striatal damage induced by QUIN (240 nmol/microl) in adult male Wistar rats by means of apocynin (APO; 5 mg/kg i.p.), a specific NAD(P)H oxidase inhibitor. Rats were given APO 30 min before and 1 hr after QUIN injection or only 30 min after QUIN injection. NAD(P)H oxidase activity was measured in striatal homogenates by O2(*)(-) production. QUIN infusion to rats significantly increased striatal NAD(P)H oxidase activity (2 hr postlesion), whereas APO treatments decreased the QUIN-induced enzyme activity (2 hr postlesion), lipid peroxidation (3 hr postlesion), circling behavior (6 days postlesion), and histological damage (7 days postlesion). The addition of NADH to striatal homogenates increased NAD(P)H oxidase activity in striata from QUIN-treated animals but not from sham rats. Interestingly, O2(*)(-) production in QUIN-lesioned striata was unaffected by the addition of substrates for intramitochondrial O2(*)(-) production, xanthine oxidase and nitric oxide synthase, suggesting that NAD(P)H oxidase may be the main source of O2(*)(-) in QUIN-treated rats. Moreover, the administration of MK-801 to rats as a pretreatment resulted in a complete prevention of the QUIN-induced NAD(P)H activation, suggesting that this toxic event is completely dependent on N-methyl-D-aspartate receptor overactivation. Our results also suggest that NAD(P)H oxidase is involved in the pathogenic events linked to excitotoxic/prooxidant conditions.

A possible neuroprotective action of a vinylic telluride against Mn-induced neurotoxicity

Manganese (Mn) is a metal required by biological systems. However, environmental or occupational exposure to high levels of Mn can produce a neurological disorder called manganism, which has similarities to Parkinson's disease. Diethyl-2-phenyl-2-tellurophenyl vinylphosphonate (DPTVP) is an organotellurium compound with a high antioxidant activity, especially in the brain. The present study was designed to investigate the effects of long-term low-dose exposure to Mn in drinking water on behavioral and biochemical parameters in rats and to determine the effectiveness of vinylic telluride in attenuating the effects of Mn. After 4 months of treatment with MnCl(2) (13.7 mg/kg), rats exhibited clear signs of neurobehavioral toxicity, including a decrease in the number of rearings in the open field and altered motor performance in rotarod. The administration of DPTVP (0.150 micromol/kg, ip, 2 weeks) improved the motor performance of Mn-treated rats, indicating that the compound could be reverting Mn neurotoxicity. Ex vivo, we observed that Mn concentrations in the Mn-treated group were highest in the striatum, consistent with a statistically significant decrease in mitochondrial viability and [(3)H]glutamate uptake, and increased lipid peroxidation. Mn levels in the hippocampus and cortex were indistinguishable from controls, and no significant differences were noted in the ex vivo assays in these areas. Treatment with DPTVP fully reversed the biochemical parameters altered by Mn. Furthermore, DPTVP treatment was also associated with a reduction in striatal Mn levels. Our results demonstrate that DPTVP has neuroprotective activity against Mn-induced neurotoxicity, which may be attributed to its antioxidant activity and/or its effect on striatal Mn transport.

Diphenyl diselenide, a simple organoselenium compound, decreases methylmercury-induced cerebral, hepatic and renal oxidative stress and mercury deposition in adult mice

Oxidative stress has been pointed out as an important molecular mechanism in methylmercury (MeHg) intoxication. At low doses, diphenyl diselenide ((PhSe)2), a structurally simple organoselenium compound, has been shown to possess antioxidant and neuroprotective properties. Here we have examined the possible in vivo protective effect of diphenyl diselenide against the potential pro-oxidative effects of MeHg in mouse liver, kidney, cerebrum and cerebellum. The effects of MeHg exposure (2 mg/(kg day) of methylmercury chloride 10 ml/kg, p.o.), as well as the possible antagonist effect of diphenyl diselenide (1 and 0.4 mg/(kg day); s.c.) on body weight gain and on hepatic, cerebellar, cerebral and renal levels of thiobarbituric acid reactive substances (TBARS), non-protein thiols (NPSH), ascorbic acid content, mercury concentrations and activities of antioxidant enzymes (glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD)) were evaluated after 35 days of treatment. MeHg caused an increase in TBARS and decreased NPSH levels in all tissues. MeHg also induced a decrease in hepatic ascorbic acid content and in renal GPx and CAT activities. Diphenyl diselenide (1 mg/kg) conferred protection against MeHg-induced hepatic and renal lipid peroxidation and at both doses prevented the reduction in hepatic NPSH levels. Diphenyl diselenide also conferred a partial protection against MeHg-induced oxidative stress (TBARS and NPSH) in liver and cerebellum. Of particular importance, diphenyl diselenide decreased the deposition of Hg in cerebrum, cerebellum, kidney and liver. The present results indicate that diphenyl diselenide can protect against some toxic effects of MeHg in mice. This protection may be related to its antioxidant properties and its ability to reduce Hg body burden. We posit that formation of a selenol intermediate, which possesses high nucleophilicity and high affinity for MeHg, accounts for the ability of diphenyl diselenide to ameliorate MeHg-induced toxicity.

Antioxidant effects of different extracts from Melissa officinalis, Matricaria recutita and Cymbopogon citratus

Considering the important role of oxidative stress in the pathogenesis of several neurological diseases, and the growing evidence of the presence of compounds with antioxidant properties in the plant extracts, the aim of the present study was to investigate the antioxidant capacity of three plants used in Brazil to treat neurological disorders: Melissa officinalis, Matricaria recutita and Cymbopogon citratus. The antioxidant effect of phenolic compounds commonly found in plant extracts, namely, quercetin, gallic acid, quercitrin and rutin was also examined for comparative purposes. Cerebral lipid peroxidation (assessed by TBARS) was induced by iron sulfate (10 microM), sodium nitroprusside (5 microM) or 3-nitropropionic acid (2 mM). Free radical scavenger properties and the chemical composition of plant extracts were assessed by 1'-1' Diphenyl-2' picrylhydrazyl (DPPH) method and by Thin Layer Chromatography (TLC), respectively. M. officinalis aqueous extract caused the highest decrease in TBARS production induced by all tested pro-oxidants. In the DPPH assay, M. officinalis presented also the best antioxidant effect, but, in this case, the antioxidant potencies were similar for the aqueous, methanolic and ethanolic extracts. Among the purified compounds, quercetin had the highest antioxidant activity followed by gallic acid, quercitrin and rutin. In this work, we have demonstrated that the plant extracts could protect against oxidative damage induced by various pro-oxidant agents that induce lipid peroxidation by different process. Thus, plant extracts could inhibit the generation of early chemical reactive species that subsequently initiate lipid peroxidation or, alternatively, they could block a common final pathway in the process of polyunsaturated fatty acids peroxidation. Our study indicates that M. officinalis could be considered an effective agent in the prevention of various neurological diseases associated with oxidative stress.