Should ebselen be considered for the treatment of mercury intoxication? A minireview

Mercury is a ubiquitous environmental contaminant and can be found in inorganic (Hg0, Hg+ and Hg2+) and organic forms (chiefly CH3Hg+ or MeHg+). The main route of human, mammals and bird exposure occurs via predatory fish ingestion. Occupational exposure to Hg0 (and Hg2+) can also occur; furthermore, in gold mining areas the exposure to inorganic Hg can also be high. The toxicity of electrophilic forms of Hg (E+Hg) is mediated by disruption of thiol (-SH)- or selenol (-SeH)-containing proteins. The therapeutic approaches to treat methylmercury (MeHg+), Hg0 and Hg2+ are limited. Here we discuss the potential use of ebselen as a potential therapeutic agent to lower the body burden of Hg in man. Ebselen is a safe drug for humans and has been tested in clinical trials (for instance, brain ischemia, noise-induce hearing loss, diabetes complications, bipolar disorders) at doses varying from 400 to 3600 mg per day. Two clinical trials with ebselen in moderate and severe COVID are also approved. Ebselen can be metabolized to an intermediate with -SeH (selenol) functional group, which has a greater affinity to electrophilic Hg (E+Hg) forms than the available thiol-containing therapeutic agents. Accordingly, as observed in vitro and rodent models in vivo, Ebselen exhibited protective effects against MeHg+, indicating its potential as a therapeutic agent to treat MeHg+ overexposure. The combined use of ebselen with thiol-containing molecules (e.g. N-acetylcysteine and enaramide)) is also commented, because they can have synergistic protective effects against MeHg+.

Oxidative stress in rat brain during experimental status epilepticus: effect of antioxidants

Antioxidants have been proposed as a treatment for diseases of the central nervous system. However, few studies actually studied their effects in the brain. To test central actions of antioxidants, we used the lithium-pilocarpine (Li-Pilo) model of status epilepticus (SE) in the rat in which seizures are accompanied by significant oxidative stress. We used in vivo microdialysis to determine isoprostane levels during SE in real time and brain homogenates for other measures of oxidative stress. Six different antioxidants were tested in acute and preventive experiments (vitamin C, vitamin E, ebselen, resveratrol, n-tert-butyl-α-phenylnitrone and coenzyme Q10). None of the antioxidants had an effect when given acutely during SE. In contrast, when antioxidants were given for 3 days prior to seizure induction, vitamins C and E reduced isoprostane formation by 58% and 65%, respectively. Pretreatment with the other antioxidants was ineffective. In brain homogenates prepared after 90 min of seizures, SE decreased the ratio of reduced vs. oxidized glutathione (GSH/GSSG ratio) from 60.8 to 7.50 and caused a twofold increase of 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels and protein carbonyls. Pretreatment with vitamin C or vitamin E mitigated these effects and increased the GSH/GSSG ratio to 23.9 and 28.3, respectively. Again, the other antioxidants were not effective. We conclude that preventive treatment with vitamin C or vitamin E ameliorates seizure-induced oxidative damage in the brain. Several well-studied antioxidants were inactive, possibly due to limited brain permeability or a lack of chain-breaking antioxidant activity in hydrophilic compounds.

Ebselen Inhibits the Growth of Lung Cancer Cells via Cell Cycle Arrest and Cell Death Accompanied by Glutathione Depletion

Ebselen is a glutathione (GSH) peroxidase (GPx) mimic originally developed to reduce reactive oxygen species (ROS). However, little is known about its cytotoxicological effects on lung cells. Therefore, this study aimed to investigate the effects of Ebselen on the cell growth and cell death of A549 lung cancer cells, Calu-6 lung cancer cells, and primary normal human pulmonary fibroblast (HPF) cells in relation to redox status. The results showed that Ebselen inhibited the growth of A549, Calu-6, and HPF cells with IC50 values of approximately 12.5 μM, 10 μM, and 20 μM, respectively, at 24 h. After exposure to 15 μM Ebselen, the proportions of annexin V-positive cells were approximately 25%, 65%, and 10% in A549, Calu-6, and HPF cells, respectively. In addition, Ebselen induced arrest at the S phase of the cell cycle in A549 cells and induced G2/M phase arrest in Calu-6 cells. Treatment with Ebselen induced mitochondrial membrane potential (MMP; ΔΨm) loss in A549 and Calu-6 cells. Z-VAD, a pan-caspase inhibitor, did not decrease the number of annexin V-positive cells in Ebselen-treated A549 and Calu-6 cells. Intracellular ROS levels were not significantly changed in the Ebselen-treated cancer cells at 24 h, but GSH depletion was efficiently induced in these cells. Z-VAD did not affect ROS levels or GSH depletion in Ebselen-treated A549 or Ebselen-treated Calu-6 cells. In conclusion, Ebselen inhibited the growth of lung cancer and normal fibroblast cells and induced cell cycle arrest and cell death in lung cancer cells with GSH depletion.

Spray-Dried Inhalable Microparticles Combining Remdesivir and Ebselen against SARS-CoV-2 Infection

There is a continuous effort to develop efficient treatments for coronavirus disease 2019 (COVID-19) and other viral respiratory diseases. Among the different strategies, inhaled treatment is considered one of the most logical and efficient approaches to treating COVID-19, as the causative "SARS-CoV-2 virus RNA" predominantly infects the respiratory tract. COVID-19 treatments initially relied on repurposed drugs, with a few additional strategies developed during the last two years, and all of them are based on monotherapy. However, drug combinations have been found to be more effective than monotherapy in other viral diseases such as HIV, influenza, and hepatitis C virus. In the case of SARS-CoV-2 infection, in vitro studies have shown synergistic antiviral activity combining remdesivir with ebselen, an organoselenium compound. Therefore, these drug combinations could ensure better therapeutic outcomes than the individual agents. In this study, we developed a dry powder formulation containing remdesivir and ebselen using a spray-drying technique and used L-leucine as an aerosolization enhancer. The prepared dry powders were spherical and crystalline, with a mean particle size between 1 and 3 µm, indicating their suitability for inhalation. The emitted dose (ED) and fine particle fraction (FPF) of remdesivir- and ebselen-containing dry powders were ~80% and ~57% when prepared without L-leucine. The ED as well as the FPF significantly increased with values of >86% and >67%, respectively, when L-leucine was incorporated. More importantly, the single and combinational dry powder of remdesivir and ebselen showed minimal cytotoxicity (CC50 > 100 μM) in Calu-3 cells, retaining their anti-SARS-CoV-2 properties (EC50 2.77 to 18.64 μM). In summary, we developed an inhalable dry powder combination of remdesivir and ebselen using a spray-drying technique. The spray-dried inhalable microparticles retained their limited cytotoxicity and specific antiviral properties. Future in vivo studies are needed to verify the potential use of these remdesivir/ebselen combinational spray-dried inhalable microparticles to block the SARS-CoV-2 replication in the respiratory tract.

Ebselen and Diphenyl Diselenide Inhibit SARS-CoV-2 Replication at Non-Toxic Concentrations to Human Cell Lines

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was the causative agent of the COVID-19 pandemic, a global public health problem. Despite the numerous studies for drug repurposing, there are only two FDA-approved antiviral agents (Remdesivir and Nirmatrelvir) for non-hospitalized patients with mild-to-moderate COVID-19 symptoms. Consequently, it is pivotal to search for new molecules with anti-SARS-CoV-2 activity and to study their effects in the human immune system. Ebselen (Eb) is an organoselenium compound that is safe for humans and has antioxidant, anti-inflammatory, and antimicrobial properties. Diphenyl diselenide ((PhSe)₂) shares several pharmacological properties with Eb and is of low toxicity to mammals. Herein, we investigated Eb and (PhSe)₂ anti-SARS-CoV-2 activity in a human pneumocytes cell model (Calu-3) and analyzed their toxic effects on human peripheral blood mononuclear cells (PBMCs). Both compounds significantly inhibited the SARS-CoV-2 replication in Calu-3 cells. The EC₅₀ values for Eb and (PhSe)₂ after 24 h post-infection (hpi) were 3.8 µM and 3.9 µM, respectively, and after 48 hpi were 2.6 µM and 3.4 µM. These concentrations are safe for non-infected cells, since the CC₅₀ values found for Eb and (PhSe)₂ on Calu-3 were greater than 200 µM. Importantly, the concentration rates tested on viral replication were not toxic to human PBMCs. Therefore, our findings reinforce the efficacy of Eb and demonstrate (PhSe)₂ as a new candidate to be tested in future trials against SARS-CoV-2 infection/inflammation conditions.

Exploring the inhibition mechanism of SARS-CoV-2 main protease by ebselen: A molecular docking, molecular dynamics simulation and DFT approach

The main protease (Mpro) of SARS-CoV-2 plays an essential role in the virus life cycle and is considered a key target for therapeutic development. This study explores the inhibition mechanism of SARS-CoV-2 Mpro by ebselen, an organoselenium drug that shows potent inhibitory activity. By using a combination of multiple computational methods including molecular docking, molecular dynamics simulations, and density functional theory calculations, the complete covalent inhibition process of ebselen is simulated for the first time. Two possible pathways with different bound conformations of ebselen are identified. The hydrolysis of the enzyme-ebselen adduct is found to be the rate-determining step. The simulation results show that the behavior of water molecules at the hydrolysis site is crucial to distinguish the two paths energetically. Our simulations, which are in agreement with existing experimental results, provide a theoretical basis for the rational design and mechanism exploration of ebselen-based inhibitors.

Chemistry Related to the Catalytic Cycle of the Antioxidant Ebselen

The antioxidant drug ebselen has been widely studied in both laboratories and in clinical trials. The catalytic mechanism by which it destroys hydrogen peroxide via reduction with glutathione or other thiols is complex and has been the subject of considerable debate. During reinvestigations of several key steps, we found that the seleninamide that comprises the first oxidation product of ebselen underwent facile reversible methanolysis to an unstable seleninate ester and two dimeric products. In its reaction with benzyl alcohol, the seleninamide produced a benzyl ester that reacted readily by selenoxide elimination, with formation of benzaldehyde. Oxidation of ebselen seleninic acid did not afford a selenonium seleninate salt as previously observed with benzene seleninic acid, but instead generated a mixture of the seleninic and selenonic acids. Thiolysis of ebselen with benzyl thiol was faster than oxidation by ca. an order of magnitude and produced a stable selenenyl sulfide. When glutathione was employed, the product rapidly disproportionated to glutathione disulfide and ebselen diselenide. Oxidation of the S-benzyl selenenyl sulfide, or thiolysis of the seleninamide with benzyl thiol, afforded a transient thiolseleninate that also readily underwent selenoxide elimination. The S-benzyl derivative disproportionated readily when catalyzed by the simultaneous presence of both the thiol and triethylamine. The phenylthio analogue disproportionated when exposed to ambient or UV (360 nm) light by a proposed radical mechanism. These observations provide additional insight into several reactions and intermediates related to ebselen.

High-resolution structural study on pyridin-3-yl ebselen and its N-methylated tosylate and iodide derivatives

The crystal structure of the pyridine-substituted benzisoselenazolinone 2-(pyridin-3-yl)-2,3-dihydro-1,2-benzoselenazol-3-one (C₁₂H₈N₂OSe, 2), related to the antioxidant ebselen [systematic name: 2-phenyl-1,2-benzoselenazol-3(2H)-one, 1], is characterized by strong intermolecular N...Se(-N) chalcogen bonding, where the N...Se distance of 2.3831 (6) Å is well within the sum of the van der Waals radii for N and Se (3.34 Å). This strong interaction results in significant lengthening of the internal N-Se distance, consistent with significant population of the Se-N σ* antibonding orbital. Much weaker intermolecular O...Se chalcogen bonding occurs between the amide-like O atom in 2 and the less polarized C-Se bond in this structure. Charge density analysis of 2 using multipole refinement of high-resolution data allowed the electrostatic surface potential for 2 to be mapped, and clearly reveals the σ-hole at the extension of the Se-N bond as an area of positive electrostatic potential. Topological analysis of the electron-density distribution in 2 was carried out within the Quantum Theory of Atoms in Molecules (QTAIM) framework and revealed bond paths and (3,-1) bond critical points (BCPs) for the N...Se-N moiety consistent with a closed-shell interaction; however, the potential energy term is suggestive of electron sharing. Analysis of the electron localization function (ELF) for the strong N...Se and the weak O...Se chalcogen-bonding interactions in the structure of 2 suggest significant electron sharing in the former interaction, and a largely electrostatic interaction in the latter. Conversion of 2 to its N-methylated derivatives by reaction with methyl iodide [1-methyl-3-(3-oxo-2,3-dihydro-1,2-benzoselenazol-2-yl)pyridin-1-ium iodide, C₁₃H₁₁N₂OSe⁺·I^-] and methyl tosylate [1-methyl-3-(3-oxo-2,3-dihydro-1,2-benzoselenazol-2-yl)pyridin-1-ium toluenesulfonate trihydrate, C₁₃H₁₁N₂OSe⁺·C₇H₇O₃S^-·3H₂O] removes the possibility of N...Se chalcogen bonding and instead structures are obtained where the iodide and tosylate counter-ions fulfill the role of chalcogen-bond acceptors, with a strong I^-...Se interaction in the iodide salt and a weaker p-Tol-SO₃^-...Se interaction in the tosylate salt.

Detailed Insights into the Inhibitory Mechanism of New Ebselen Derivatives against Main Protease (Mpro) of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2)

SARS-CoV-2 main protease (M^pro/3CL^pro) is a crucial target for therapeutics, which is responsible for viral polyprotein cleavage and plays a vital role in virus replication and survival. Recent studies suggest that 2-phenylbenzisoselenazol-3(2H)-one (ebselen) is a potent covalent inhibitor of M^pro, which affects its enzymatic activity and virus survival. Herein, we synthesized various ebselen derivatives to understand the mechanism of M^pro inhibition by ebselen. Using ebselen derivatives, we characterized the detailed interaction mechanism with M^pro. We discovered that modification of the parent ebselen inhibitor with an electron-withdrawing group (NO₂) increases the inhibition efficacy by 2-fold. We also solved the structure of an M^pro complex with an ebselen derivative showing the mechanism of inhibition by blocking the catalytic Cys145 of M^pro. Using a combination of crystal structures and LC-MS data, we showed that M^pro hydrolyzes the new ebselen derivative and leaves behind selenium (Se) bound with Cys145 of the catalytic dyad of M^pro. We also described the binding profile of ebselen-based inhibitors using molecular modeling predictions supported by binding and inhibition assays. Furthermore, we have also solved the crystal structure of catalytically inactive mutant H41N-M^pro, which represents the inactive state of the protein where the substrate binding pocket is blocked. The inhibited structure of H41N-M^pro shows gatekeeper residues in the substrate binding pocket responsible for blocking the substrate binding; mutation of these gatekeeper residues leads to hyperactive M^pro.

Small-Molecule Ebselen Binds to YTHDF Proteins Interfering with the Recognition of N 6-Methyladenosine-Modified RNAs

YTHDF proteins bind the N 6-methyladenosine (m6A)-modified mRNAs, influencing their processing, stability, and translation. Therefore, the members of this protein family play crucial roles in gene regulation and several physiological and pathophysiological conditions. YTHDF proteins contain a hydrophobic pocket that accommodates the m6A embedded in the RRACH consensus sequence on mRNAs. We exploited the presence of this cage to set up an m6A-competitive assay and performed a high-throughput screen aimed at identifying ligands binding in the m6A pocket. We report the organoselenium compound ebselen as the first-in-class inhibitor of the YTHDF m6A-binding domain. Ebselen, whose interaction with YTHDF proteins was validated via orthogonal assays, cannot discriminate between the binding domains of the three YTHDF paralogs but can disrupt the interaction of the YTHDF m6A domain with the m6A-decorated mRNA targets. X-ray, mass spectrometry, and NMR studies indicate that in YTHDF1 ebselen binds close to the m6A cage, covalently to the Cys412 cysteine, or interacts reversibly depending on the reducing environment. We also showed that ebselen engages YTHDF proteins within cells, interfering with their mRNA binding. Finally, we produced a series of ebselen structural analogs that can interact with the YTHDF m6A domain, proving that ebselen expansion is amenable for developing new inhibitors. Our work demonstrates the feasibility of drugging the YTH domain in YTHDF proteins and opens new avenues for the development of disruptors of m6A recognition.

Investigating the Metabolic Mechanisms of Butaselen, An Ebselen Analog

BACKGROUND

Butaselen is an ebselen analog that is under clinical trials for treating hepatic and pulmonary fibrosis. Our previous studies showed that butaselen is mainly present in human plasma in the form of M2, a free Se-methylated metabolite.

OBJECTIVE

This study aimed to investigate the metabolic mechanisms of butaselen.

METHODS AND RESULTS

Butaselen was incubated with human plasma. Butaselen immediately disappeared, and the butaselen-HSA (human serum albumin) adduct was detected by HPLC-HRMS, showing that butaselen covalently binds to HSA. The butaselen-HSA adduct was precipitated using acetonitrile and then incubated with PBS, Cys, and GSH for 1 hour. The product was M1, a reduced form of butaselen. The results indicated that HSA, Cys, and GSH can reduce the butaselen-HSA covalent bond. The binding site for butaselen could be the cysteine-34 residue of HSA through pronase and trypsin hydrolysis. Incubating butaselen with cysteine, butaselen-Cys, butaselen-2Cys, and M1 were generated, indicating the covalent binding and reduction of butaselen by cysteine. We incubated liver microsomes and cytosol with butaselen, 6.22 and 246 nM M2 were generated, respectively. The results demonstrated that cytosolic enzymes are mainly involved in M2 production. The amount of M2 in the liver cytosol decreased from 246 nM to 2.21 nM when 10 mM m-anisic acid (a specific TPMT enzyme inhibitor) was added, showing that TPMT is responsible for M2 formation.

CONCLUSION

Butaselen was covalently bound to HSA, and the binding site was the cysteine-34 residue of HSA. The butaselen-HSA adduct was reduced by free thiol compounds to generate M1. M1 was further metabolized to M2 by cytosolic TPMT. This study provides a basis for studying the pharmacokinetics of selenium-containing drugs.

Nano-based formulations as an approach for providing a novel identity for organoselenium compounds

The organoselenium compounds belong to a class of synthetic molecules that displays a remarkable spectrum of promising pharmacological properties. Despite the huge amount of preclinical data that supports a bright outlook for organoselenium compounds, some toxicity issues and physicochemical limitations delay the development of more advanced studies. Currently, several scientific reports demonstrated that the association of nanotechnology has emerged as an alternative to improve solubility and safety issues of these molecules as well as enhance pharmacological properties. Therefore, our main objective was to address studies that reported the development and biological evaluations of nano-based formulations to synthetic organoselenium compounds incorporation by constructing an integrative literature review. The data survey was performed using the Science Direct, PubMed, Web of Science, and SCOPUS online databases, covering studies that were published from January 2011 up to October 2021. In the last decade, there has been an exponential growth in research regarding the incorporation of synthetic organoselenium compounds into distinct nanocarrier systems such as nanocapsules, nanoemulsions, micelles, and others, reinforcing that the association of such molecules and nanotechnology is a promising alliance. The reports investigated many nanosystems containing selenium organic molecules intending oral, intravenous, and cutaneous applications. Besides that, these systems were evaluated in a variety of in vitro techniques and in vivo models, concerning their pharmacological potential, biodistribution profile, and safety. In summary, the findings indicate that the production of nano-based formulations containing organoselenium compounds either improved physicochemical and biological properties or minimize toxicological issues of compounds.

Protective effect of ebselen on bleomycin-induced lung fibrosis: analysis of the molecular mechanism of lung fibrosis mediated by oxidized diacylglycerol

The molecular mechanisms underlying the development of pulmonary fibrosis remain unknown, and effective treatments have not yet been developed. It has been shown that oxidative stress is involved in lung fibrosis. Oxidized diacylglycerol (DAG) produced by oxidative stress is thought to play an important role in lung fibrosis. This study assessed the effect of oxidized DAG in an animal model of pulmonary fibrosis induced by aspiration of bleomycin (BLM) into the lungs. The inhibitory effect of ebselen on pulmonary fibrosis was also investigated. In lung fibrotic tissue induced by BLM, an increase in lipid peroxides and collagen accumulation was observed. Moreover, the levels of oxidized DAG, which has strong protein kinase C (PKC) activation activity, were significantly increased over time following the administration of BLM. Western blotting showed that phosphorylation of PKCα and δ isoforms was increased by BLM. Oral administration of ebselen significantly suppressed the increase in oxidized DAG induced by BLM and improved lung fibrosis. PKCα and δ phosphorylation were also significantly inhibited. The mRNA expression of α-smooth muscle actin and collagen I (marker molecules for fibrosis), as well as the production of transforming growth factor-β and tumor necrosis factor-α(a potentially important factor in the fibrotic process), were increased by BLM and significantly decreased by ebselen. The administration of BLM may induce lipid peroxidation in lung tissue, while the oxidized DAG produced by BLM may induce overactivation of PKCα and δ, resulting in the induction of lung fibrosis.

The Potential Use of Ebselen in Treatment-Resistant Depression

Ebselen is an organoselenium compound developed as an antioxidant and subsequently shown to be a glutathione peroxidase (GPx) mimetic. Ebselen shows some efficacy in post-stroke neuroprotection and is currently in trial for the treatment and prevention of hearing loss, Meniere's Disease and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In vitro screening studies show that ebselen is also an effective inhibitor of the enzyme inositol monophosphatase (IMPase), which is a key target of the mood-stabilising drug lithium. Further, in animal experimental studies, ebselen produces effects on the serotonin system very similar to those of lithium and also decreases behavioural impulsivity. The antidepressant effects of lithium in treatment-resistant depression (TRD) have been attributed to its ability to facilitate presynaptic serotonin activity; this suggests that ebselen might also have a therapeutic role in this condition. Human studies utilising magnetic resonance spectroscopy support the notion that ebselen, at therapeutic doses, inhibits IMPase in the human brain. Moreover, neuropsychological studies support an antidepressant profile for ebselen based on positive effects on emotional processing and reward seeking. Ebselen also lowers a human laboratory measure of impulsivity, a property that has been associated with lithium's anti-suicidal effects in patients with mood disorders. Current clinical studies are directed towards assessment of the neuropsychological effects of ebselen in TRD patients. It will also be important to ascertain whether ebselen is able to lower impulsivity and suicidal behaviour in clinical populations. The objective of this review is to summarise the developmental history, pre-clinical and clinical psychopharmacological properties of ebselen in psychiatric disorders and its potential application as a treatment for TRD.

Structure-Activity Studies Reveal Scope for Optimisation of Ebselen-Type Inhibition of SARS-CoV-2 Main Protease

The reactive organoselenium compound ebselen is being investigated for treatment of coronavirus disease 2019 (COVID-19) and other diseases. We report structure-activity studies on sulfur analogues of ebselen with the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro ), employing turnover and protein-observed mass spectrometry-based assays. The results reveal scope for optimisation of ebselen/ebselen derivative- mediated inhibition of Mpro , particularly with respect to improved selectivity.

Discovery of Camellia sinensis catechins as SARS-CoV-2 3CL protease inhibitors through molecular docking, intra and extra cellular assays

BACKGROUND AND PURPOSE

Previous studies suggest that major Camellia sinensis (tea) catechins can inhibit 3-chymotrypsin-like cysteine protease (3CLpro), inspiring us to study 3CLpro inhibition of the recently discovered catechins from tea by our group.

METHODS

Autodock was used to dock 3CLpro and 16 tea catechins. Further, a 3CLpro activity detection system was used to test their intra and extra cellular 3CLpro inhibitory activity. Surface plasmon resonance (SPR) was used to analyze the dissociation constant (K_D) between the catechins and 3CLpro.

RESULTS

Docking data suggested that 3CLpro interacted with the selected 16 catechins with low binding energy through the key amino acid residues Thr24, Thr26, Asn142, Gly143, His163, and Gln189. The selected catechins other than zijuanin D (3) and (-)-8-(5''R)-N-ethyl-2-pyrrolidinone-3-O-cinnamoylepicatechin (11) can inhibit 3CLpro intracellularly. The extracellular 3CLpro IC₅₀ values of (-)-epicatechin 3-O-caffeoate (EC-C, 1), zijuanin C (2), etc-pyrrolidinone C and D (6), etc-pyrrolidinone A (9), (+)-gallocatechin gallate (GCG), and (-)-epicatechin gallate (ECG) are 1.58 ± 0.21, 41.2 ± 3.56, 0.90 ± 0.03, 46.71 ± 10.50, 3.38 ± 0.48, and 71.78 ± 8.36 µM, respectively. The K_D values of 1, 6, and GCG are 4.29, 3.46, and 3.36 µM, respectively.

CONCLUSION

Together, EC-C (1), etc-pyrrolidinone C and D (6), and GCG are strong 3CLpro inhibitors. Our results suggest that structural modification of catechins could be conducted by esterificating the 3-OH as well as changing the configuration of C-3, C-3''' or C-5''' to discover strong SARS-CoV-2 inhibitors.

In vitro and in silico studies of potential coronavirus-specific 3C-like protease inhibitors

We investigated similar compounds to ebselen and tideglusib, which exhibit strong activity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), using MACCS keys. Four candidate compounds were identified. One of them, phenyl-benzothiazol-3-one, showed coronavirus-specific 3C-like (3CL) protease inhibitory activity. The results indicated that a similarity score above 0.81 is a good indicator of activity for ebselen-and-tideglusib-like compounds. Subsequently, we simulated the ring-cleavage Michael reaction of ebselen at the Se center, which is responsible for its 3CL protease inhibitory activity, and determined the activation free energy of the reaction. The results showed that reaction simulation is a useful tool for estimating the activity of inhibitory compounds that undergo Michael addition reactions with the relevant cysteine S atom of 3CL proteases.

Novel experimental and early investigational drugs for the treatment of bipolar disorder

INTRODUCTION

The quest toward more effective treatments for bipolar disorder (BD) solicits novel drugs and further research on the underpinning neurobiology. The present review aims to critically appraise the existing evidence about the pharmacological treatment of BD toward the development of novel treatment avenues.

AREAS COVERED

The present review appraises animal and human studies concerning both the currently available psychotropic drugs, and the general medicine drugs which may represent a path toward the development of novel drugs for BD. PubMed and Scopus were last accessed on February 20^th, 2021 for records indexed upon inception relevant to the pharmacological treatment of BD. Immune-modulating agents, anti-inflammatory agents, and glutamate antagonists represent the most intriguing potential targets for the development of new drugs for BD, thus receiving critical appraisal in the present text.

EXPERT OPINION

Regardless of the neurobiological pathways worthy of investigation toward the development of experimental drugs for BD, several unmet needs need to be addressed first. In particular, several biomarkers are altered in BD. However, it is the opinion herein expressed by the authors that it remains uncertain what comes first, that is peripheral changes or the disease.

Inhibition of iduronic acid biosynthesis by ebselen reduces glycosaminoglycan accumulation in mucopolysaccharidosis type I fibroblasts

Mucopolysaccharidosis type I (MPS-I) is a rare lysosomal storage disorder caused by deficiency of the enzyme alpha-L-iduronidase, which removes iduronic acid in both chondroitin/dermatan sulfate (CS/DS) and heparan sulfate (HS) and thereby contributes to the catabolism of glycosaminoglycans (GAGs). To ameliorate this genetic defect, the patients are currently treated by enzyme replacement and bone marrow transplantation, which have a number of drawbacks. This study was designed to develop an alternative treatment by inhibition of iduronic acid formation. By screening the Prestwick drug library, we identified ebselen as a potent inhibitor of enzymes that produce iduronic acid in CS/DS and HS. Ebselen efficiently inhibited iduronic acid formation during CS/DS synthesis in cultured fibroblasts. Treatment of MPS-I fibroblasts with ebselen not only reduced accumulation of CS/DS but also promoted GAG degradation. In early Xenopus embryos, this drug phenocopied the effect of downregulation of DS-epimerase 1, the main enzyme responsible for iduronic production in CS/DS, suggesting that ebselen inhibits iduronic acid production in vivo. However, ebselen failed to ameliorate the CS/DS and GAG burden in MPS-I mice. Nevertheless, the results propose a potential of iduronic acid substrate reduction therapy for MPS-I patients.

Selenium-Catalyzed Reduction of Hydroperoxides in Chemistry and Biology

Among the chalcogens, selenium is the key element for catalyzed H2O2 reduction. In organic synthesis, catalytic amounts of organo mono- and di-selenides are largely used in different classes of oxidations, in which H2O2 alone is poorly efficient. Biological hydroperoxide metabolism is dominated by peroxidases and thioredoxin reductases, which balance hydroperoxide challenge and contribute to redox regulation. When their selenocysteine is replaced by cysteine, the cellular antioxidant defense system is impaired. Finally, classes of organoselenides have been synthesized with the aim of mimicking the biological strategy of glutathione peroxidases, but their therapeutic application has so far been limited. Moreover, their therapeutic use may be doubted, because H2O2 is not only toxic but also serves as an important messenger. Therefore, over-optimization of H2O2 reduction may lead to unexpected disturbances of metabolic regulation. Common to all these systems is the nucleophilic attack of selenium to one oxygen of the peroxide bond promoting its disruption. In this contribution, we revisit selected examples from chemistry and biology, and, by using results from accurate quantum mechanical modelling, we provide an accurate unified picture of selenium's capacity of reducing hydroperoxides. There is clear evidence that the selenoenzymes remain superior in terms of catalytic efficiency.

Influence of Ce3+ Substitution on Antimicrobial and Antibiofilm Properties of ZnCexFe2-xO4 Nanoparticles (X = 0.0, 0.02, 0.04, 0.06, and 0.08) Conjugated with Ebselen and Its Role Subsidised with γ-Radiation in Mitigating Human TNBC and Colorectal Adenocarcinoma Proliferation In Vitro

Cancers are a major challenge to health worldwide. Spinel ferrites have attracted attention due to their broad theranostic applications. This study aimed at investigating the antimicrobial, antibiofilm, and anticancer activities of ebselen (Eb) and cerium-nanoparticles (Ce-NPs) in the form of ZnCexFe2-XO4 on human breast and colon cancer cell lines. Bioassays of the cytotoxic concentrations of Eb and ZnCexFe2-XO4, oxidative stress and inflammatory milieu, autophagy, apoptosis, related signalling effectors, the distribution of cells through the cell-cycle phases, and the percentage of cells with apoptosis were evaluated in cancer cell lines. Additionally, the antimicrobial and antibiofilm potential have been investigated against different pathogenic microbes. The ZOI, and MIC results indicated that ZnCexFe2-XO4; X = 0.06 specimen reduced the activity of a wide range of bacteria and unicellular fungi at low concentration including P. aeruginosa (9.5 mm; 6.250 µg/mL), S. aureus (13.2 mm; 0.390 µg/mL), and Candida albicans (13.5 mm; 0.195 µg/mL). Reaction mechanism determination indicated that after ZnCexFe2-xO4; X = 0.06 treatment, morphological differences in S.aureus were apparent with complete lysis of bacterial cells, a concomitant decrease in the viable number, and the growth of biofilm was inhibited. The combination of Eb with ZFO or ZnCexFe2-XO4 with γ-radiation exposure showed marked anti-proliferative efficacy in both cell lines, through modulating the oxidant/antioxidant machinery imbalance, restoring the fine-tuning of redox status, and promoting an anti-inflammatory milieu to prevent cancer progression, which may be a valuable therapeutic approach to cancer therapy and as a promising antimicrobial agent to reduce the pathogenic potential of the invading microbes.

Development of Tinnitus and Hyperacusis in a Mouse Model of Tobramycin Cochleotoxicity

Aminoglycosides (AG) antibiotics are a common treatment for recurrent infections in cystic fibrosis (CF) patients. AGs are highly ototoxic, resulting in a range of auditory dysfunctions. It was recently shown that the acoustic startle reflex (ASR) can assess behavioral evidence of hyperacusis and tinnitus in an amikacin cochleotoxicity mouse model. The goal of this study was to establish if tobramycin treatment led to similar changes in ASR behavior and to establish whether ebselen can prevent the development of these maladaptive neuroplastic symptoms. CBA/Ca mice were divided into three groups: Group 1 served as a control and did not receive tobramycin or ebselen, Group 2 received tobramycin (200 mg/kg/s.c.) and the vehicle (DMSO/saline/i.p.) daily for 14 continuous days, and Group 3 received the same dose/schedule of tobramycin as Group 2 and ebselen at (20 mg/kg/i.p.). Auditory brainstem response (ABR) and ASR hearing assessments were collected at baseline and 2, 6, 10, 14, and 18 weeks from the start of treatment. ASR tests included input/output (I/O) functions which assess general hearing and hyperacusis, and Gap-induced prepulse inhibition of the acoustic startle (GPIAS) to assess tinnitus. At 18 weeks, histologic analysis showed predominantly normal appearing hair cells and spiral ganglion neuron (SGN) synapses. Following 14 days of tobramycin injections, 16 kHz thresholds increased from baseline and fluctuated over the 18-week recovery period. I/O functions revealed exaggerated startle response magnitudes in 50% of mice over the same period. Gap detection deficits, representing behavioral evidence of tinnitus, were observed in a smaller subset (36%) of animals. Interestingly, increases in ABR wave III/wave I amplitude ratios were observed. These tobramycin data corroborate previous findings that AGs can result in hearing dysfunctions. We show that a 14-day course of tobramycin treatment can cause similar levels of hearing loss and tinnitus, when compared to a 14-day course of amikacin, but less hyperacusis. Evidence suggests that tinnitus and hyperacusis might be common side effects of AG antibiotics.

Ebselen and Analogues: Pharmacological Properties and Synthetic Strategies for Their Preparation

Ebselen is the leader of selenorganic compounds, and starting from its identification as mimetic of the key antioxidant enzyme glutathione peroxidase, several papers have appeared in literature claiming its biological activities. It was the subject of several clinical trials and it is currently in clinical evaluation for the treatment of COVID-19 patients. Given our interest in the synthesis and pharmacological evaluation of selenorganic derivatives with this review, we aimed to collect all the papers focused on the biological evaluation of ebselen and its close analogues, covering the timeline between 2016 and most of 2021. Our analysis evidences that, even if it lacks specificity when tested in vitro, being able to bind to every reactive cysteine, it proved to be always well tolerated in vivo, exerting no sign of toxicity whatever the administered doses. Besides, looking at the literature, we realized that no review article dealing with the synthetic approaches for the construction of the benzo[d][1,2]-selenazol-3(2H)-one scaffold is available; thus, a section of the present review article is completely devoted to this specific topic.

Interfering Reactive Cysteine Proteome in Covid-19 Disease

Although vaccination against SARS-CoV-2 infection has been initiated, effective therapies for severe Covid-19 disease are still needed. A promising therapeutic strategy is using FDA-approved drugs that have the biological potential to interfere with or modify some of the viral proteins capable of changing the disease's course. Recent studies highlight that some clinically safe drugs can suppress the viral life cycle while potentially promoting an adequate host inflammatory/immune response by interfering with the disease's cysteine proteome.

Efficacy of Ebselen Against Invasive Aspergillosis in a Murine Model

Invasive aspergillosis is one of the major causes of morbidity and mortality among invasive fungal infections. The search for new antifungal drugs becomes imperative when existing drugs are not able to efficiently treat these infections. Ebselen, is an organoselenium compound, already successfully approved in clinical trials as a repositioned drug for the treatment of bipolar disorder and prevention of noise-induced hearing loss. In this study, we aimed to reposition ebselen for the treatment of invasive aspergillosis by showing ebselen effectiveness in a murine model. For this, BALB/c mice were immunosuppressed and infected systemically with Aspergillus fumigatus. Animals were divided and treated with ebselen, voriconazole, or drug-free control, for four days. The kidneys were used for CFU count and, histopathological and cytokine analysis. Ebselen was able to significantly reduce the fungal burden in the kidneys of infected mice with efficacy comparable with voriconazole treatment as both had reductions to the same extent. The absence of hyphae and intact kidney tissue structure observed in the histopathological sections analyzed from treated groups corroborate with the downregulation of IL-6 and TNF. In summary, this study brings for the first time in vivo evidence of ebselen efficacy against invasive aspergillosis. Despite these promising results, more animal studies are warranted to evaluate the potential role of ebselen as an alternative option for the management of invasive aspergillosis in humans.

Modeling Secondary Iron Overload Cardiomyopathy with Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Excessive iron accumulation in the heart causes iron overload cardiomyopathy (IOC), which initially presents as diastolic dysfunction and arrhythmia but progresses to systolic dysfunction and end-stage heart failure when left untreated. However, the mechanisms of iron-related cardiac injury and how iron accumulates in human cardiomyocytes are not well understood. Herein, using human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we model IOC and screen for drugs to rescue the iron overload phenotypes. Human iPSC-CMs under excess iron exposure recapitulate early-stage IOC, including oxidative stress, arrhythmia, and contractile dysfunction. We find that iron-induced changes in calcium kinetics play a critical role in dysregulation of CM functions. We identify that ebselen, a selective divalent metal transporter 1 (DMT1) inhibitor and antioxidant, could prevent the observed iron overload phenotypes, supporting the role of DMT1 in iron uptake into the human myocardium. These results suggest that ebselen may be a potential preventive and therapeutic agent for treating patients with secondary iron overload.

Thioredoxin Reductase Is a Valid Target for Antimicrobial Therapeutic Development Against Gram-Positive Bacteria

There is a drought of new antibacterial compounds that exploit novel targets. Thioredoxin reductase (TrxR) from the Gram-positive bacterial antioxidant thioredoxin system has emerged from multiple screening efforts as a potential target for auranofin, ebselen, shikonin, and allicin. Auranofin serves as the most encouraging proof of concept drug, demonstrating TrxR inhibition can result in bactericidal effects and inhibit Gram-positive bacteria in both planktonic and biofilm states. Minimal inhibitory concentrations are on par or lower than gold standard medications, even among drug resistant isolates. Importantly, existing drug resistance mechanisms that challenge treatment of infections like Staphylococcus aureus do not confer resistance to TrxR targeting compounds. The observed inhibition by multiple compounds and inability to generate a bacterial genetic mutant demonstrate TrxR appears to play an essential role in Gram-positive bacteria. These findings suggest TrxR can be exploited further for drug development. Examining the interaction between TrxR and these proof of concept compounds illustrates that compounds representing a new antimicrobial class can be developed to directly interact and inhibit the validated target.

Ebselen prevents cigarette smoke-induced gastrointestinal dysfunction in mice

Gastrointestinal (GI) dysfunction is a common comorbidity of chronic obstructive pulmonary disease (COPD) for which a major cause is cigarette smoking (CS). The underlying mechanisms and precise effects of CS on gut contractility, however, are not fully characterised. Therefore, the aim of the present study was to investigate whether CS impacts GI function and structure in a mouse model of CS-induced COPD. We also aimed to investigate GI function in the presence of ebselen, an antioxidant that has shown beneficial effects on lung inflammation resulting from CS exposure. Mice were exposed to CS for 2 or 6 months. GI structure was analysed by histology and immunofluorescence. After 2 months of CS exposure, ex vivo gut motility was analysed using video-imaging techniques to examine changes in colonic migrating motor complexes (CMMCs). CS decreased colon length in mice. Mice exposed to CS for 2 months had a higher frequency of CMMCs and a reduced resting colonic diameter but no change in enteric neuron numbers. Ten days cessation after 2 months CS reversed CMMC frequency changes but not the reduced colonic diameter phenotype. Ebselen treatment reversed the CS-induced reduction in colonic diameter. After 6 months CS, the number of myenteric nitric-oxide producing neurons was significantly reduced. This is the first evidence of colonic dysmotility in a mouse model of CS-induced COPD. Dysmotility after 2 months CS is not due to altered neuron numbers; however, prolonged CS-exposure significantly reduced enteric neuron numbers in mice. Further research is needed to assess potential therapeutic applications of ebselen in GI dysfunction in COPD.

Mechanisms of ebselen as a therapeutic and its pharmacology applications

Ebselen is a synthetic organoselenium radical scavenger compound that possesses glutathione peroxidase-like activity and its own unique bioactivity by reacting with thiols, hydroperoxides and peroxynitrites. Owing to its high affinity toward several essential reactions, ebselen protects cellular components from oxidative and free radical damage, and it has been employed as a useful tool for studying redox-related mechanisms. Based on numerous in vitro and in vivo research, mechanisms are proposed to understand the biomedical and molecular actions of ebselen in health and disease, and it is currently under clinical trials for the prevention and treatment of various human disorders. Based on these outstanding discoveries, this review summarizes the current understanding of the biochemical and molecular characteristics, pharmacological applications and future directions of ebselen.

A Novel Mouse Model of Aminoglycoside-Induced Hyperacusis and Tinnitus

Aminoglycosides (AG) such as amikacin are commonly used in cystic fibrosis patients with opportunistic pulmonary infections including multi-drug resistant mycobacterium tuberculous and non-tuberculous mycobacterium. Unfortunately, this class of drugs is known to cause peripheral damage to the cochlea leading to hearing loss that can fluctuate and become permanent over time or multiple exposures. However, whether amikacin can lead to central auditory dysfunction like hyperacusis (increased sensitivity to sound) or tinnitus (perception of sound in the absence of acoustic stimulation) is not well-described in the literature. Thus, an animal model needs to be developed that documents these side effects in order to develop therapeutic solutions to reduce AG-induced auditory dysfunction. Here we present pioneer work in mice which demonstrates that amikacin can lead to fluctuating behavioral evidence of hyperacusis and tinnitus as assessed by the acoustic startle reflex. Additionally, electrophysiological assessments of hearing via auditory brainstem response demonstrate increased central activity in the auditory brainstem. These data together suggest that peripheral AG-induced dysfunction can lead to central hyperactivity and possible behavioral manifestations of hyperacusis and tinnitus. Importantly, we demonstrate that ebselen, a novel investigational drug that acts as both an antioxidant and anti-inflammatory, can mitigate AG-induced hyperacusis.

High-Throughput Screening for Inhibitors of the SARS-CoV-2 Protease Using a FRET-Biosensor

The global SARS-CoV-2 pandemic started late 2019 and currently continues unabated. The lag-time for developing vaccines means it is of paramount importance to be able to quickly develop and repurpose therapeutic drugs. Protein-based biosensors allow screening to be performed using routine molecular laboratory equipment without a need for expensive chemical reagents. Here we present a biosensor for the 3-chymotrypsin-like cysteine protease from SARS-CoV-2, comprising a FRET-capable pair of fluorescent proteins held in proximity by a protease cleavable linker. We demonstrate the utility of this biosensor for inhibitor discovery by screening 1280 compounds from the Library of Pharmaceutically Active Compounds collection. The screening identified 65 inhibitors, with the 20 most active exhibiting sub-micromolar inhibition of 3CL^pro in follow-up EC₅₀ assays. The top hits included several compounds not previously identified as 3CL^pro inhibitors, in particular five members of a family of aporphine alkaloids that offer promise as new antiviral drug leads.

Crystallization and structure of ebselen bound to Cys141 of human inositol monophosphatase

Inositol monophosphatase (IMPase) is inhibited by lithium, which is the most efficacious treatment for bipolar disorder. Several therapies have been approved, or are going through clinical trials, aimed at the replacement of lithium in the treatment of bipolar disorder. One candidate small molecule is ebselen, a selenium-containing antioxidant, which has been demonstrated to produce lithium-like effects both in a murine model and in clinical trials. Here, the crystallization and the first structure of human IMPase covalently complexed with ebselen, a 1.47 Å resolution crystal structure (PDB entry 6zk0), are presented. In the complex with human IMPase, ebselen in a ring-opened conformation is covalently attached to Cys141, a residue located away from the active site. IMPase is a dimeric enzyme and in the crystal structure two adjacent dimers share four ebselen molecules, creating a tetramer with approximate 222 symmetry. In the crystal structure presented in this publication, the active site in the tetramer is still accessible, suggesting that ebselen may function as an allosteric inhibitor or may block the binding of partner proteins.

Depletion of multidrug-resistant uropathogenic Escherichia coli BC1 by ebselen and silver ion

Ebselen, an organo‐selenium compound with well‐characterized toxicology and pharmacology, recently exhibited potent antibacterial activity against glutathione (GSH)‐negative bacteria by disrupting redox homeostasis. In this paper, we show that ebselen and silver ion in combination exert strong bactericidal activity against multidrug‐resistant (MDR) uropathogenic Escherichia coli (UPEC) BC1, a model MDR GSH‐positive bacterium. The mechanisms were found to involve consumption of total intracellular GSH and inhibition of thioredoxin reductase activity, which was highly related to reactive oxygen species up‐regulation. Furthermore, the therapeutic efficacy of ebselen and silver ion against UPEC‐induced cystitis was assessed in a mouse model. Treatment with ebselen and silver ion significantly reduced bacterial loads, down‐regulated the expression levels of tumour necrosis factor‐α (TNF‐α) and interferon‐γ (IFN‐γ) on‐site and decreased white/red blood cell counts in mild cystitis model mice, which demonstrated the anti‐inflammatory property of these agents. In addition, ebselen and silver ion also exhibited significantly high protective ability (100%) against acute cystitis infections. These results together may lay the foundation for further analysis and development of ebselen and silver ion as antibacterial agents for treatment of MDR UPEC infections.

Findings in redox biology: From H2O2 to oxidative stress

My interest in biological chemistry proceeded from enzymology in vitro to the study of physiological chemistry in vivo Investigating biological redox reactions, I identified hydrogen peroxide (H2O2) as a normal constituent of aerobic life in eukaryotic cells. This finding led to developments that recognized the essential role of H2O2 in metabolic redox control. Further research included studies on GSH, toxicological aspects (the concept of "redox cycling"), biochemical pharmacology (ebselen), nutritional biochemistry and micronutrients (selenium, carotenoids, flavonoids), and the concept of "oxidative stress." Today, we recognize that oxidative stress is two-sided. It has its positive side in physiology and health in redox signaling, "oxidative eustress," whereas at higher intensity, there is damage to biomolecules with potentially deleterious outcome in pathophysiology and disease, "oxidative distress." Reflecting on these developments, it is gratifying to witness the enormous progress in redox biology brought about by the science community in recent years.

Ebselen, disulfiram, carmofur, PX-12, tideglusib, and shikonin are non-specific promiscuous SARS-CoV-2 main protease inhibitors

There is an urgent need for vaccines and antiviral drugs to combat the COVID-19 pandemic. Encouraging progress has been made in developing antivirals targeting SARS-CoV-2, the etiological agent of COVID-19. Among the drug targets being investigated, the viral main protease (M pro ) is one of the most extensively studied drug targets. M pro is a cysteine protease that hydrolyzes the viral polyprotein at more than 11 sites and it is highly conserved among coronaviruses. In addition, M pro has a unique substrate preference for glutamine in the P1 position. Taken together, it appears that M pro inhibitors can achieve both broad-spectrum antiviral activity and a high selectivity index. Structurally diverse compounds have been reported as M pro inhibitors, with several of which also showed antiviral activity in cell culture. In this study, we investigated the mechanism of action of six previously reported M pro inhibitors, ebselen, disulfiram, tideglusib, carmofur, shikonin, and PX-12 using a consortium of techniques including FRET-based enzymatic assay, thermal shift assay, native mass spectrometry, cellular antiviral assays, and molecular dynamics simulations. Collectively, the results showed that the inhibition of M pro by these six compounds is non-specific and the inhibition is abolished or greatly reduced with the addition of reducing reagent DTT. In the absence of DTT, these six compounds not only inhibit M pro , but also a panel of viral cysteine proteases including SARS-CoV-2 papain-like protease, the 2A pro and 3C pro from enterovirus A71 (EV-A71) and EV-D68. However, none of the compounds inhibits the viral replication of EV-A71 or EV-D68, suggesting that the enzymatic inhibition potency IC 50 values obtained in the absence of DTT cannot be used to faithfully predict their cellular antiviral activity. Overall, we provide compelling evidence suggesting that ebselen, disulfiram, tideglusib, carmofur, shikonin, and PX-12 are non-specific SARS-CoV-2 M pro inhibitors, and urge the scientific community to be stringent with hit validation.

Targeting Bacterial Antioxidant Systems for Antibiotics Development

The emergence of multidrug-resistant bacteria has become an urgent issue in modern medicine which requires novel strategies to develop antibiotics. Recent studies have supported the hypothesis that antibiotic-induced bacterial cell death is mediated by Reactive Oxygen Species (ROS). The hypothesis also highlighted the importance of antioxidant systems, the defense mechanism which contributes to antibiotic resistance. Thioredoxin and glutathione systems are the two major thiol-dependent systems which not only provide antioxidant capacity but also participate in various biological events in bacteria, such as DNA synthesis and protein folding. The biological importance makes them promising targets for novel antibiotics development. Based on the idea, ebselen and auranofin, two bacterial thioredoxin reductase inhibitors, have been found to inhibit the growth of bacteria lacking the GSH efficiently. A recent study combining ebselen and silver exhibited a strong synergistic effect against Multidrug-Resistant (MDR) Gram-negative bacteria which possess both thioredoxin and glutathione systems. These drug-repurposing studies are promising for quick clinical usage due to their well-known profile.

Is Ebselen A Therapeutic Target in Fracture Healing?

Objective

We investigated the effect of ebselen on fracture healing in an experimental fracture model.

Materials and Methods

We divided rats into two groups, 6 rats in each: the experimental femur fracture control group and the ebselen treatment group with an experimental femur fracture. In the experimental femur fracture control group, we created only experimental femur fracture. In the ebselen treatment group, we administered ebselen treatment with creating an experimental femur fracture. We administered ebselen intraperitoneally at 5 mg/kg once daily for 1 month after the 1st day of experimental femur fracture in the ebselen treatment group. We evaluated the recovery status of fractured femurs at the end of 1st month with radiographic, histopathological, and immunohistochemical methods.

Results

According to the radiographic fracture healing scores, ebselen treatment increased the extent of new bone formation and fracture cartilage callus significantly compared to the control group. According to the histopathological recovery scores, ebselen treatment significantly improved healing scores compared to the control group. Ebselen treatment increased the expression scores of bone healing markers in the ebselen treatment group, such as vascular endothelial growth factor and osteocalcin, compared to the control group.

Conclusion

We demonstrated that ebselen treatment increases the formation of new bone in the femur in an experimentally created femoral fracture model. Ebselen has been shown to improve the bone fracture healing in a radiological and histopathological manner, and more detailed studies are needed.

Topical Therapeutic Efficacy of Ebselen Against Multidrug-Resistant Staphylococcus aureus LT-1 Targeting Thioredoxin Reductase

As a thiol-dependent enzyme, thioredoxin reductase (TrxR) is a promising antibacterial drug target. Ebselen, an organo-selenium with well-characterized toxicology and pharmacology, was recently reported to have potent antibacterial activity against Staphylococcus aureus. In this paper, we demonstrated that ebselen has strong bactericidal activity against multidrug-resistant (MDR) S. aureus based on taking TrxR as a major target and disruption of the redox microenvironment. Further, the topical therapeutic efficacy of ebselen for staphylococcal skin infections was assessed in a rat model. Treatment with ebselen significantly reduced the bacterial load and the expression of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1 beta (IL-1β) in S. aureus skin lesions; further, wound healing and pathological changes were obvious improved in ebselen-treated rats compare to controls. Finally, ebselen was found to sensitize S. aureus to curcumin, which may be due to their synergistic effects in inhibiting bacterial TrxR. Altogether, ebselen is an effective topical antibacterial agent in animal model of MDR S. aureus LT-1 skin infection. This may lay the foundation for further analysis and development of ebselen as an antibacterial agent for topical treatment of MDR staphylococcal infections.

Characterization of synergistic antibacterial effect of silver nanoparticles 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 Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in vitro, including model strains of China Veterinary Culture Collection and MDR clinical isolates, which is similar as the combination of silver ion and ebselen. AgNPs exhibited to be a strong inhibitor of bacterial thioredoxin reductase, same as a free silver ion. Ebselen mitigated the cytotoxicity of AgNPs to HeLa cells. However, in a bacteria-cell coexistence condition, the synergistic bactericidal effect was only observed on S. aureus (p<.05), while the temporary synergistic inhibitory effect on E. coli within 4 hours treatment (p<.01). In mice infection model, a combination of AgNPs and ebselen did not increase protection against the challenge of clinical E. coli CQ10 strain. Our data demonstrated that AgNPs and ebselen combination may be a promising strategy to fight against the increasingly MDR bacteria targeting bacterial thiol redox system.

Electrical Stimulation Degenerated Cochlear Synapses Through Oxidative Stress in Neonatal Cochlear Explants

Neurostimulation devices use electrical stimulation (ES) to substitute, supplement or modulate neural function. However, the impact of ES on their modulating structures is largely unknown. For example, recipients of cochlear implants using electroacoustic stimulation experienced delayed loss of residual hearing over time after ES, even though ES had no impact on the morphology of hair cells. In this study, using a novel model of cochlear explant culture with charge-balanced biphasic ES, we found that ES did not change the quantity and morphology of hair cells but decreased the number of inner hair cell (IHC) synapses and the density of spiral ganglion neuron (SGN) peripheral fibers. Inhibiting calcium influx with voltage-dependent calcium channel (VDCC) blockers attenuated the loss of SGN peripheral fibers and IHC synapses induced by ES. ES increased ROS/RNS in cochlear explants, but the inhibition of calcium influx abolished this effect. Glutathione peroxidase 1 (GPx1) and GPx2 in cochlear explants decreased under ES and ebselen abolished this effect and attenuated the loss of SGN peripheral fibers. This finding demonstrated that ES induced the degeneration of SGN peripheral fibers and IHC synapses in a current intensity- and duration-dependent manner in vitro. Calcium influx resulting in oxidative stress played an important role in this process. Additionally, ebselen might be a potential protector of ES-induced cochlear synaptic degeneration.

Micelle-embedded coating with ebselen for nitric oxide generation

Nitric oxide generation is considered to be a key factor to mimic endothelial function in terms of anti-coagulation and anti-hyperplasia. Herein, ebselen which could play the similar role as glutathion peroxidase-like was loaded into micelles and was further assembled into a layer-by-layer coating. The ability of nitric oxide generation and corresponding biological effect were investigated. Endothelial-mimetic surface has now attracted huge attention in blood-contacting materials, due to its inherent ability of secreting nitric oxide. Among those categories, nitric oxide generation surface is considered to be safe and tunable in the modification of vascular biomedical devices. How to adsorb or immobilize glutathion peroxidase-like catalyst and maintain sustained/safe nitric oxide generation is full of interest. This study aimed at developing a functional coating constructed via layer-by-layer assembly to introduce the catalyst into the coating by pre-loading ebselen in micelles. We firstly introduced phenylboronic acid moiety into the micelle molecule backbone and grafted catechol moiety to chitosan backbone. Then, chitosan, micelles (containing ebselen) and heparin were adopted as polyelectrolytes and then alternatively assembled onto the substrate via layer-by-layer protocol. The catechol was conjugated to the amine groups of chitosan by Schiff base reaction to synthesize chitosan-catechol. The hydrophobic cholesterol was conjugated to the one end of the hydrophilic hyaluronic acid, and the hydroxymethylphenylboronic acid was conjugated to the other end via the esterification of carboxyl (-COOH) and hydroxyl (-OH). The modified hyaluronic acid could spontaneously form micelles in aqueous solution. Ebselen was the loaded into the as-prepared micelles. Chitosan-catechol, heparin, and micelles were alternatively assembled onto the substrate layer by layer to form a micelle-embedded coating. The micelle-embedded coating with ebselen was successfully obtained and the nitric oxide generation ability was in a safe level which was close to healthy endothelial cells. The coating could effectively inhibit platelet adhesion and smooth muscle cell proliferation. The use of ebselen preloaded into micelles could provide a sustained release of catalyst for in situ nitric oxide generation. Besides, this method could also be used to load diverse drugs and regulate desired properties. The study was approved by the Institutional Review Board of the West China Hospital in Sichuan University on March 3, 2018, with approval No. K2018044.

Putative neuroprotective pharmacotherapies to target the staged progression of mental illness

AIM

Neuropsychiatric disorders including depression, bipolar and schizophrenia frequently exhibit a neuroprogressive course from prodrome to chronicity. There are a range of agents exhibiting capacity to attenuate biological mechanisms associated with neuroprogression. This review will update the evidence for putative neuroprotective agents including clinical efficacy, mechanisms of action and limitations in current assessment tools, and identify novel agents with neuroprotective potential.

METHOD

Data for this review were sourced from online databases PUBMED, Embase and Web of Science. Only data published since 2012 were included in this review, no data were excluded based on language or publication origin.

RESULTS

Each of the agents reviewed inhibit one or multiple pathways of neuroprogression including: inflammatory gene expression and cytokine release, oxidative and nitrosative stress, mitochondrial dysfunction, neurotrophin dysregulation and apoptotic signalling. Some demonstrate clinical efficacy in preventing neural damage or loss, relapse or cognitive/functional decline. Agents include: the psychotropic medications lithium, second generation antipsychotics and antidepressants; other pharmacological agents such as minocycline, aspirin, cyclooxygenase-2 inhibitors, statins, ketamine and alpha-2-delta ligands; and others such as erythropoietin, oestrogen, leptin, N-acetylcysteine, curcumin, melatonin and ebselen.

CONCLUSIONS

Signals of evidence of clinical neuroprotection are evident for a number of candidate agents. Adjunctive use of multiple agents may present a viable avenue to clinical realization of neuroprotection. Definitive prospective studies of neuroprotection with multimodal assessment tools are required.

Probing the Formation of a Seleninic Acid in Living Cells by the Fluorescence Switching of a Glutathione Peroxidase Mimetic

Glutathione peroxidase (GPx) is a selenoenzyme that protects cells against oxidative damage. Although the formation of a seleninic acid (-SeO₂ H) by this enzyme during oxidative stress has been proposed, a selenic acid has not been identified in cells. Herein, we report that the formation of a seleninic acid can be monitored in living cells by using a redox-active ebselen analogue with a naphthalimide fluorophore. The probe reacts with H₂ O₂ to generate the highly fluorescent seleninic acid. The electron withdrawing nature of the -SeO₂ H moiety and strong Se⋅⋅⋅O interactions, which prevent the photoinduced electron transfer, are responsible for the fluorescence.

Role of thymoquinone and ebselen in the prevention of sodium arsenite-induced nephrotoxicity in female rats

The aim of this study is to investigate the protective effects of thymoquinone (TQ) and ebselen (Eb) on arsenic (As)-induced renal toxicity in female rats. Sodium arsenite was orally administrated at a dose of 20 mg/kg body weight daily for 28 days, either alone or 1 h before TQ (10 mg/kg) or Eb (5 mg/kg) administration. Renal tissue As concentration and oxidative stress markers, including lipid peroxidation (LPO), nitrite/nitrate, and glutathione (GSH) levels, were determined. In addition to the oxidative stress response, antioxidant enzyme activities including that of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase were measured. Exposure to As elicited a significant increase in As concentration and significant modifications to the redox state of the kidney, as was evidenced by a significant elevation in LPO and nitrite/nitrate concentration, with a concomitant reduction in GSH content and antioxidant enzyme activity. The oxidant/antioxidant imbalance observed in As toxicity was associated with a significant elevation in renal tumor necrosis factor α, interleukin 6, B-cell lymphoma 2 (Bcl-2)-associated X protein, and caspase 3 levels, in addition to a significant decrease in Bcl-2 levels. Post-administration of TQ and Eb markedly prevented As-induced oxidative stress, inflammation, apoptosis, and As accumulation in the renal tissue and reduced histological renal damage. These findings demonstrate that TQ, the main bioactive phytochemical constituent of Nigella sativa seed oil, and Eb, an organoselenium compound, could significantly inhibit As-induced oxidative damage, apoptosis, and inflammation, and significantly attenuate the accumulation of As in renal tissues by facilitating As biomethylation and excretion.

Structure, Mechanism, and Inhibition of Aspergillus fumigatus Thioredoxin Reductase

Aspergillus fumigatus infections are associated with high mortality rates and high treatment costs. Limited available antifungals and increasing antifungal resistance highlight an urgent need for new antifungals. Thioredoxin reductase (TrxR) is essential for maintaining redox homeostasis and presents as a promising target for novel antifungals. We show that ebselen [2-phenyl-1,2-benzoselenazol-3(2H)-one] is an inhibitor of A. fumigatus TrxR (K_i = 0.22 μM) and inhibits growth of Aspergillus spp., with in vitro MIC values of 16 to 64 µg/ml. Mass spectrometry analysis demonstrates that ebselen interacts covalently with a catalytic cysteine of TrxR, Cys148. We also present the X-ray crystal structure of A. fumigatus TrxR and use in silico modeling of the enzyme-inhibitor complex to outline key molecular interactions. This provides a scaffold for future design of potent and selective antifungal drugs that target TrxR, improving the potency of ebselen toward inhbition of A. fumigatus growth.

Use of ebselen as a neuroprotective agent in rat spinal cord subjected to traumatic injury

Spinal cord injury (SCI) causes disturbances of motor skills. Free radicals have been shown to be essential for the development of spinal cord trauma. Despite some progress, until now no effective pharmacological therapies against SCI have been verified. The purpose of our experiment was to investigate the neuroprotective effects of ebselen on experimental SCI. Twenty-two rats subjected to SCI were randomly subjected to SCI with no further treatment (n = 10) or intragastric administration of ebselen (10 mg/kg) immediately and 24 hours after SCI. Behavioral changes were assessed using the Basso, Beattie, and Bresnahan locomotor scale and footprint test during 12 weeks after SCI. Histopathological and immunohistochemical analyses of spinal cords and brains were performed at 12 weeks after SCI. Magnetic resonance imaging analysis of spinal cords was also performed at 12 weeks after SCI. Rats treated with ebselen presented only limited neurobehavioral progress as well as reduced spinal cord injuries compared with the control group, namely length of lesions (cysts/scars) visualized histopathologically in the spinal cord sections was less but cavity area was very similar. The same pattern was found in T2-weighted magnetic resonance images (cavities) and diffusion-weighted images (scars). The number of FluoroGold retrogradely labeled neurons in brain stem and motor cortex was several-fold higher in ebselen-treated rats than in the control group. The findings suggest that ebselen has only limited neuroprotective effects on injured spinal cord. All exprimental procedures were approved by the Local Animal Ethics Committee for Experiments on Animals in Katowice (Katowice, Poland) (approval No. 19/2009).

Ebselen protects rat hearts against myocardial ischemia-reperfusion injury

Ebselen is an organoselenium compound that has demonstrated potent antioxidant and anti-inflammatory effects in previous studies. The present study was conducted to evaluate the effect of ebselen on myocardial ischemia-reperfusion (I/R) injury in a rat model and to elucidate the related mechanisms. Myocardial infarct size was assessed using triphenyltetrazolium chloride staining. Myocardial injury was evaluated according to the histopathological and ultrastructural alterations of rat hearts and the serum activity levels of cardiac enzymes, including creatine kinase (CK), CK-MB isoenzyme and lactate dehydrogenase (LDH). Cardiomyocyte apoptosis was detected using the terminal dUTP nick end-labelling (TUNEL) assay. In addition, the expression of apoptosis-associated proteins was measured using western blot analysis. In heart tissue specimens the activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx), and levels of malondialdehyde (MDA) and protein carbonyl (PC) were also detected. The results indicated that ebselen reduced I/R-induced increase in myocardial infarct size and prevented the I/R-induced decreases in ejection fraction and fractional shortening. Further of note, ebselen improved I/R-induced rat heart injury. This was indicated by attenuation of histological and ultrastructural changes; reduction of serum CK, CK-MB and LDH activity levels; and decreased cell apoptosis on TUNEL staining, which was verified by decreased expression of cleaved (C)-Caspase-8, C-Caspase-3, B-cell lymphoma 2 (Bcl-2)-associated X protein and C-PARP, and increased expression of Bcl-2. Additionally, SOD and GPx activity levels were significantly higher, while MDA and PC levels were significantly lower in the ebselen + I/R group compared with in the I/R group. In conclusion, the present results suggested that ebselen serves an important role in protecting against myocardial I/R injury. The underlying mechanism may involve suppression of cardiomyocyte apoptosis and promotion of antioxidant activity.

The putative lithium-mimetic ebselen reduces impulsivity in rodent models

BACKGROUND

Deficits in impulse control feature in many psychiatric conditions including bipolar disorder, suicidality and addictions. Lithium lowers impulsivity in clinical populations and decreases pathological gambling in experimental medicine studies, but suffers from adverse effects, poor compliance and a low therapeutic index.

AIMS

Recently we identified that the neuroprotective agent ebselen, which is reportedly safe in humans, inhibited inositol monophosphatase (IMPase), a candidate lithium mechanism. Ebselen also reduced 5-HT receptor (5-HT_2A) function which predicts impulsivity lowering properties. Here we investigated the effect of ebselen in rat models of impulsive behaviour.

METHODS

Ebselen was tested in two models of impulsivity with human analogues: the five-choice serial reaction time task (5-CSRTT) and rodent gambling task (rGT). The main outcome measures were premature responses (5-CSRTT and rGT) and choice behaviour (rGT), which model motor impulsivity and choice impulsivity, respectively.

RESULTS

At doses that decreased 5-HT_2A receptor function (DOI-induced wet dog shakes), ebselen decreased premature responding in the 5-CSRTT both in the absence and presence of cocaine. The 5-HT_2A receptor antagonist MDL 100,907 also reduced premature responding in the 5-CSRTT although not in the presence of cocaine. In the rGT ebselen showed a tendency to reduce premature responding but had no effect on choice behaviour.

CONCLUSIONS

These findings suggest that ebselen preferentially reduces motor impulsivity over choice impulsivity, and that inhibition of 5-HT_2A receptor function is a contributing mechanism. Collectively, these data support the repurposing of ebselen as an anti-impulsive treatment and fast-tracking to clinical trials in patient groups characterised by poor impulse control.

Exploring the simultaneous σ-hole/π-hole bonding characteristics of a Br⋯π interaction in an ebselen derivative via experimental and theoretical electron-density analysis

In this study, the nature and characteristics of a short Br⋯π interaction observed in an ebselen derivative, 2-(2-bromophenyl)benzo[d][1,2]selenazol-3(2H)-one, has been explored. The electronic nature of this Br⋯π interaction was investigated via high-resolution X-ray diffraction and periodic density functional theory calculations using atoms-in-molecules (AIM) analysis. This study unravels the simultaneous presence of σ-hole and π-hole bonding characteristics in the same interaction. The dual characteristics of this unique Br⋯π interaction are further established via molecular electrostatic potentials (MESPs) and natural bond orbitals (NBOs).

Ebselen inhibits the activity of acetylcholinesterase globular isoform G4 in vitro and attenuates scopolamine-induced amnesia in mice

There is a well-known relationship between the cholinergic system and learning, memory, and other common cognitive processes. The process for researching and developing new drugs has lead researchers to repurpose older ones. This study investigated the effects of ebselen on the activity of acethylcholinesterase (AChE) isoforms in vitro and in an amnesia model induced by scopolamine in Swiss mice. In vitro, ebselen at concentrations equal or higher than 10 μM inhibited the activity of cortical and hippocampal G4/AChE, but not G1/AChE isoform. Treatment of mice with ebselen (50 mg/kg, i.p.) was effective against impairment of spatial recognition memory in both Y-maze and novel object recognition tests induced by scopolamine (1 mg/kg, i.p.). Ebselen (50 mg/kg) inhibited hippocampal AChE activity in mice. The present study demonstrates that ebselen inhibited the G4/AChE isoform in vitro and elicited an anti-amnesic effect in a mouse model induced by scopolamine. These findings reveal ebselen as a potential compound in terms of opening up valid therapeutic avenues for the treatment of memory impairment diseases.