Ebselen improves fungal keratitis through exerting anti-inflammation, anti-oxidative stress, and antifungal effects

Fungal keratitis is a severely vision-threatening corneal infection, where the prognosis depends on both fungal virulence and host immune defense. Inappropriate host responses can induce substantial inflammatory damage to the cornea. Therefore, in the treatment of fungal keratitis, it is important to concurrently regulate the immune response while efforts are made to eliminate the pathogen. Ebselen is a widely studied organo-selenium compound and has been demonstrated to have antifungal, antibacterial, anti-inflammatory, and oxidative stress-regulatory properties. The effectiveness of ebselen for the treatment of fungal keratitis remains unknown. In this study, ebselen was demonstrated to produce a marked inhibitory effect on Aspergillus fumigatus (A. fumigatus), including spore germination inhibition, mycelial growth reduction, and fungal biofilm disruption. The antifungal activity of ebselen was related to the cell membrane damage caused by thioredoxin (Trx) system inhibition-mediated oxidative stress. On the contrary, ebselen enhanced the antioxidation of Trx system in mammalian cells. Further, ebselen was proven to suppress the expressions of inflammatory mediators (IL-1β, IL-6, TNF-α, COX-2, iNOS, and CCL2) and reduce the production of oxidative stress-associated indicators (ROS, NO, and MDA) in fungi-stimulated RAW264.7 cells. In addition, ebselen regulated PI3K/Akt/Nrf2 and p38 MAPK signaling pathways, which contributed to the improvement of inflammation and oxidative stress. Finally, we verified the therapeutic effect of ebselen on mouse fungal keratitis. Ebselen improved the prognosis and reduced the fungal burden in mouse corneas. Expressions of inflammatory mediators, as well as the infiltration of macrophages and neutrophils in the cornea were also obviously decreased by ebselen. In summary, ebselen exerted therapeutic effects by reducing fungal load and protecting host tissues in fungal keratitis, making it a promising treatment for fungal infections.

An organometallic hybrid antibiotic of metronidazole with a Gold(I) N-Heterocyclic Carbene overcomes metronidazole resistance in Clostridioides difficile

Antimicrobial resistance (AMR) has been emerging as a major global health threat and calls for the development of novel drug candidates. Metal complexes have been demonstrating high efficiency as antibacterial agents that differ substantially from the established types of antibiotics in their chemical structures and their mechanism of action. One strategy to exploit this potential is the design of metal-based hybrid organometallics that consist of an established antibiotic and a metal-based warhead that contributes an additional mechanism of action different from that of the parent antibiotic. In this communication, we describe the organometallic hybrid antibiotic 2c, in which the drug metronidazole is connected to a gold(I) N-heterocyclic carbene warhead that inhibits bacterial thioredoxin reductase (TrxR). Metronidazole can be used for the treatment with the obligatory anaerobic pathogen Clostridioides difficile (C. difficile), however, resistance to the drug hampers its clinical success. The gold organometallic conjugate 2c was an efficient inhibitor of TrxR and it was inactive or showed only minor effects against eucaryotic cells and bacteria grown under aerobic conditions. In contrast, a strong antibacterial effect was observed against both metronidazole-sensitive and -resistant strains of C. difficile. This report presents a proof-of-concept that the design of metal-based hybrid antibiotics can be a viable approach to efficiently tackle AMR.

Engineering Whole-Cell Biosensors for Enhanced Detection of Environmental Antibiotics Using a Synthetic Biology Approach

Bacterial Two component systems have evolved with many intricate sensory apparatuses for external stimuli like light, temperature, oxygen, pH and chemical compounds. Recent studies have shown the potential of two-component regulatory systems (TCSs) of bacteria in creating synthetic regulatory circuits for several applications. Antimicrobial resistance is increasing globally in both developing and developed countries and it is one of the foremost global threats to public health. The resistance level to a broad spectrum of antibiotics is rising every year by 5-10%. In this context, TCSs controlling microbial physiology at the transcriptional level could be an appropriate candidate for monitoring the antibiotics present in the environment. This review provided a wide opportunity to gain knowledge about the TCSs available in diverse species to sense the antibiotics. Further, this review explored the EMeRALD (Engineered Modularized Receptors Activated via Ligand-induced Dimerization) based biosensors to repurpose the sensing modules from the microbial TCSs using the synthetic biology approach.

Silver Organometallics that are Highly Potent Thioredoxin and Glutathione Reductase Inhibitors: Exploring the Correlations of Solution Chemistry with the Strong Antibacterial Effects

The antibacterial activity of silver species is well-established; however, their mechanism of action has not been adequately explored. Furthermore, issues of low-molecular silver compounds with cytotoxicity, stability, and solubility hamper their progress to drug leads. We have investigated silver N-heterocyclic carbene (NHC) halido complexes [(NHC)AgX, X = Cl, Br, and I] as a promising new type of antibacterial silver organometallics. Spectroscopic studies and conductometry established a higher stability for the complexes with iodide ligands, and nephelometry indicated that the complexes could be administered in solutions with physiological chloride levels. The complexes showed a broad spectrum of strong activity against pathogenic Gram-negative bacteria. However, there was no significant activity against Gram-positive strains. Further studies clarified that tryptone and yeast extract, as components of the culture media, were responsible for this lack of activity. The reduction of biofilm formation and a strong inhibition of both glutathione and thioredoxin reductases with IC50 values in the nanomolar range were confirmed for selected compounds. In addition to their improved physicochemical properties, the compounds with iodide ligands did not display cytotoxic effects, unlike the other silver complexes. In summary, silver NHC complexes with iodide secondary ligands represent a useful scaffold for nontoxic silver organometallics with improved physicochemical properties and a distinct mechanism of action that is based on inhibition of thioredoxin and glutathione reductases.

Exploring Immune Redox Modulation in Bacterial Infections: Insights into Thioredoxin-Mediated Interactions and Implications for Understanding Host-Pathogen Dynamics

Bacterial infections trigger a multifaceted interplay between inflammatory mediators and redox regulation. Recently, accumulating evidence has shown that redox signaling plays a significant role in immune initiation and subsequent immune cell functions. This review addresses the crucial role of the thioredoxin (Trx) system in the initiation of immune reactions and regulation of inflammatory responses during bacterial infections. Downstream signaling pathways in various immune cells involve thiol-dependent redox regulation, highlighting the pivotal roles of thiol redox systems in defense mechanisms. Conversely, the survival and virulence of pathogenic bacteria are enhanced by their ability to counteract oxidative stress and immune attacks. This is achieved through the reduction of oxidized proteins and the modulation of redox-sensitive signaling pathways, which are functions of the Trx system, thereby fortifying bacterial resistance. Moreover, some selenium/sulfur-containing compounds could potentially be developed into targeted therapeutic interventions for pathogenic bacteria. Taken together, the Trx system is a key player in redox regulation during bacterial infection, and contributes to host-pathogen interactions, offering valuable insights for future research and therapeutic development.

Multimodal nanoimmunotherapy engages neutrophils to eliminate Staphylococcus aureus infections

The increasing prevalence of antimicrobial resistance in Staphylococcus aureus necessitates alternative therapeutic approaches. Neutrophils play a crucial role in the fight against S. aureus but suffer from deficiencies in function leading to increased infection. Here we report a nanoparticle-mediated immunotherapy aimed at potentiating neutrophils to eliminate S. aureus. The nanoparticles consist of naftifine, haemoglobin (Hb) and a red blood cell membrane coating. Naftifine disrupts staphyloxanthin biosynthesis, Hb reduces bacterial hydrogen sulfide levels and the red blood cell membrane modifies bacterial lipid composition. Collectively, the nanoparticles can sensitize S. aureus to host oxidant killing. Furthermore, in the infectious microenvironment, Hb triggers lipid peroxidation in S. aureus, promoting neutrophil chemotaxis. Oxygen supplied by Hb can also significantly enhance the bactericidal capability of the recruited neutrophils by restoring neutrophil respiratory burst via hypoxia relief. This multimodal nanoimmunotherapy demonstrates excellent therapeutic efficacy in treating antimicrobial-resistant S. aureus persisters, biofilms and S. aureus-induced infection in mice.

Ebselen: A Promising Repurposing Drug to Treat Infections Caused by Multidrug-Resistant Microorganisms

Bacterial multiresistance to drugs is a rapidly growing global phenomenon. New resistance mechanisms have been described in different bacterial pathogens, threatening the effective treatment of even common infectious diseases. The problem worsens in infections associated with biofilms because, in addition to the pathogen's multiresistance, the biofilm provides a barrier that prevents antimicrobial access. Several "non-antibiotic" drugs have antimicrobial activity, even though it is not their primary therapeutic purpose. However, due to the urgent need to develop effective antimicrobials to treat diseases caused by multidrug-resistant pathogens, there has been an increase in research into "non-antibiotic" drugs to offer an alternative therapy through the so-called drug repositioning or repurposing. The prospect of new uses for existing drugs has the advantage of reducing the time and effort required to develop new compounds. Moreover, many drugs are already well characterized regarding toxicity and pharmacokinetic/pharmacodynamic properties. Ebselen has shown promise for use as a repurposing drug for antimicrobial purposes. It is a synthetic organoselenium with anti-inflammatory, antioxidant, and cytoprotective activity. A very attractive factor for using ebselen is that, in addition to potent antimicrobial activity, its minimum inhibitory concentration is very low for microbial pathogens.

The erythromycin polyketide compound TMC-154 stimulates ROS generation to exert antibacterial effects against Streptococcus pyogenes

The erythromycin polyketide compound TMC-154 is a secondary metabolite that is isolated from the rhizospheric fungus Clonostachys rogersoniana associated with Panax notoginseng, which possesses antibacterial activity. However, its antibacterial mechanism has not been investigated thus far. In this study, proteomics coupled with bioinformatics approaches was used to explore the antibacterial mechanism of TMC-154. KEGG pathway enrichment analysis indicated that eight signaling pathways were associated with TMC-154, including oxidative phosphorylation, cationic antimicrobial peptide (CAMP) resistance, benzoate degradation, heme acquisition systems, glycine/serine and threonine metabolism, beta-lactam resistance, ascorbate and aldarate metabolism, and phosphotransferase system (PTS). Cell biology experiments confirmed that TMC-154 could induce reactive oxygen species (ROS) generation in Streptococcus pyogenes; moreover, TMC-154-induced antibacterial effects could be blocked by the inhibition of ROS generation with the antioxidant N-acetyl L-cysteine. In addition, TMC-154 combined with ciprofloxacin or chloramphenicol had synergistic antibacterial effects. These findings indicate the potential of TMC-154 as a promising drug to treat S. pyogenes infections. SIGNIFICANCE: Streptococcus pyogenes is a nearly ubiquitous human pathogen that causes a variety of diseases ranging from mild pharyngitis and skin infection to fatal sepsis and toxic heat shock syndrome. With the increasing incidence of known antibiotic resistance, there is an urgent need to find novel drugs with good antibacterial activity against S. pyogenes. In this study, we found that TMC-154, a secondary metabolite from the fungus Clonostachys rogersoniana, inhibited the growth of various bacteria, including Staphylococcus aureus, S. pyogenes, Streptococcus mutans, Pseudomonas aeruginosa and Vibrio parahemolyticus. Proteomic analysis combined with cell biology experiments revealed that TMC-154 stimulated ROS generation to exert antibacterial effects against S. pyogenes. This study provides potential options for the treatment of S. pyogenes infections in the future.

Repurposing ebselen as an inhalable dry powder to treat respiratory tract infections

Respiratory tract infections (RTIs) are one of the leading causes of death globally, lately exacerbated by the increasing prevalence of antimicrobial resistance. While antimicrobial resistance could be overcome by developing new antimicrobial agents, the use of a safe repurposed agent having potent antimicrobial activity against various RTIs can be an efficient and cost-effective alternative to overcome the long and complex process of developing and testing new drugs. Ebselen, a synthetic organoselenium drug originally developed to treat noise-inducing hearing problems, has shown promising antimicrobial activity in vitro against several respiratory pathogens including viruses (e.g., SARS-CoV-2, influenza A virus) and bacteria (e.g., Mycobacterium tuberculosis, Streptococcus pneumoniae, and Staphylococcus aureus). Inhaled drug delivery is considered a promising approach for treating RTIs, as it can ensure effective drug concentrations at a lower dose, thereby minimizing the side effects that are often encountered by using oral or injectable drugs. In this study, we developed inhalable ebselen dry powder formulations using a spray-drying technique. The amino acids leucine, methionine, and tryptophan were incorporated with ebselen to enhance the yield and aerosolization of the dry powders. The amino acid-containing ebselen dry powders showed a better yield (37-56.4 %) than the amino acid-free formulation (30.9 %). All dry powders were crystalline in nature. The mass median aerodynamic diameter (MMAD) was less than 5 µm for amino acids containing dry powders (3-4 µm) and slightly higher (5.4 µm) for amino acid free dry powder indicating their suitability for inhalation. The aerosol performance was higher when amino acids were used, and the leucine-containing ebselen dry powder showed the highest emitted dose (84 %) and fine particle fraction (68 %). All amino acid formulations had similar cytotoxicity as raw ebselen, tested in respiratory cell line (A549 cells), with half-maximal inhibitory concentrations (IC50) between 100 and 250 μg/mL. Raw ebselen and amino acid-containing dry powders showed similar potent antibacterial activity against the Gram-positive bacteria S. aureus and S. pneumoniae with minimum inhibitory concentrations of 0.31 μg/mL and 0.16 μg/mL, respectively. On the other hand, raw ebselen and the formulations showed limited antimicrobial activity against the Gram-negative pathogens Pseudomonas aeruginosa and Klebsiella pneumoniae. In summary, in this study we were able to develop amino-acid-containing inhalable dry powders of ebselen that could be used against different respiratory pathogens, especially Gram-positive bacteria, which could ensure more drug deposition in the respiratory tract, including the lungs. DPIs are generally used to treat lung (lower respiratory tract) diseases. However, DPIs can also be used to treat both upper and lower RTIs. The deposition of the dry powder in the respiratory tract is dependent on its physicochemical properties and this properties can be modulated to target the intended site of infection (upper and/or lower respiratory tract). Further studies will allow the development of similar formulations of individual and/or combination of antimicrobials that could be used to inhibit a number of respiratory pathogens.

Ebselen: A Review on its Synthesis, Derivatives, Anticancer Efficacy and Utility in Combating SARS-COV-2

Ebselen is a selenoorganic chiral compound with antioxidant properties comparable to glutathione peroxidase. It is also known as 2-phenyl-1,2-benzisoselenazol-3(2H)-one. In studies examining its numerous pharmacological activities, including antioxidant, anticancer, antiviral, and anti- Alzheimer's, ebselen has demonstrated promising results. This review's primary objective was to emphasize the numerous synthesis pathways of ebselen and their efficacy in fighting cancer. The data were collected from multiple sources, including Scopus, PubMed, Google Scholar, Web of Science, and Publons. The starting reagents for the synthesis of ebselen are 2-aminobenzoic acid and N-phenyl benzamide. It was discovered that ebselen has the ability to initiate apoptosis in malignant cells and prevent the formation of new cancer cells by scavenging free radicals. In addition, ebselen increases tumor cell susceptibility to apoptosis by inhibiting TNF-α mediated NF-kB activation. Ebselen can inhibit both doxorubicin and daunorubicin-induced cardiotoxicity. Allopurinol and ebselen administered orally can be used to suppress renal ototoxicity and nephrotoxicity. Due to excessive administration, diclofenac can induce malignancy of the gastrointestinal tract, which ebselen can effectively suppress. Recent research has demonstrated ebselen to inhibit viral function by binding to cysteinecontaining catalytic domains of various viral proteases. It was discovered that ebselen could inhibit the catalytic dyad function of Mpro by forming an irreversible covalent bond between Se and Cys145, thereby altering protease function and inhibiting SARS-CoV-2. Ebselen may also inhibit the activation of endosomal NADPH oxidase of vascular endothelial cells, which is believed to be required for thrombotic complications in COVID-19. In this review, we have included various studies conducted on the anticancer effect of ebselen as well as its inhibition of SARS-CoV-2.

Distinct or Overlapping Areas of Mitochondrial Thioredoxin 2 May Be Used for Its Covalent and Strong Non-Covalent Interactions with Protein Ligands

In silico approaches were employed to examine the characteristics of interactions between human mitochondrial thioredoxin 2 (HsTrx2) and its 38 previously identified mitochondrial protein ligands. All interactions appeared driven mainly by electrostatic forces. The statistically significant residues of HsTrx2 for interactions were characterized as "contact hot spots". Since these were identical/adjacent to putative thermodynamic hot spots, an energy network approach identified their neighbors to highlight possible contact interfaces. Three distinct areas for binding emerged: (i) one around the active site for covalent interactions, (ii) another antipodal to the active site for strong non-covalent interactions, and (iii) a third area involved in both kinds of interactions. The contact interfaces of HsTrx2 were projected as respective interfaces for Escherichia coli Trx1 (EcoTrx1), 2, and HsTrx1. Comparison of the interfaces and contact hot spots of HsTrx2 to the contact residues of EcoTx1 and HsTrx1 from existing crystal complexes with protein ligands supported the hypothesis, except for a part of the cleft/groove adjacent to Trp30 preceding the active site. The outcomes of this study raise the possibility for the rational design of selective inhibitors for the interactions of HsTrx2 with specific protein ligands without affecting the entirety of the functions of the Trx system.

Combating planktonic and biofilm growth of Serratia marcescens by repurposing ebselen

AIM OF THE STUDY

The rising instances of multidrug-resistant pathogens are rapidly evolving into a global healthcare crisis. Identifying new ways of synthesis of antibiotics is both time-consuming and expensive. Repurposing existing drugs for the treatment of such antimicrobial-resistant pathogens has also been explored.

METHODS AND RESULTS

In the current study, ebselen was screened for antibacterial and antibiofilm activity against Serratia marcescens. Various antibacterial studies such as minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time-kill curves, intracellular reactive oxygen species (ROS) quantification, and colony-forming unit assays were performed. The antibiofilm potential was assayed by biofilm inhibition, cell surface hydrophobicity assay, eradication, quantification of extracellular DNA (eDNA), and extracellular polymeric substance (EPS) layer and scanning electron microscopy (SEM) analysis were performed. Anti-quorum sensing assay was validated by quantifying the virulence factors production. Further molecular docking of ebselen with two quorum sensing (QS) specific proteins was also carried out. Antibacterial susceptibility tests showed potent antimicrobial activity of ebselen against S. marcescens with MIC50 of 14 μg/mL. Ebselen's ability to disturb the redox environment by inducing significant ROS generation led to bacterial death. It also showed concentration-dependent bactericidal activity as indicated by reduced bacterial growth and colony-forming unit propagation. Ebselen was also found to prevent biofilm attachment by altering the cell surface hydrophobicity while also being effective against preformed biofilms as validated by scanning electron microscopy (SEM) analysis. Additionally, ebselen showed reduced virulence factors like urease enzyme activity and prodigiosin pigment production indicating its promising anti-quorum sensing potential. Molecular docking analysis validated the strong binding of ebselen with QS-specific proteins (1Joe and PigG) with binding energies of - 6.6 and - 8.1kj/mol through hydrogen bonds and aromatic interactions. These results show that ebselen has potent antibiofilm potential that can be explored to identify treatment against bacterial infections.

Antimicrobial and anti-viral effects of selenium nanoparticles and selenoprotein based strategies: COVID-19 and beyond

Deficiency of selenium (Se) has been described in a significant number of COVID-19 patients having a higher incidence of mortality, which makes it a pertinent issue to be addressed clinically for effective management of the COVID-19 pandemic. Se nanoparticles (SeNPs) provide a unique option for managing the havoc caused by the COVID-19 pandemic. SeNPs possess promising anti-inflammatory and anti-fibrotic effects by virtue of their nuclear factor kappa-light-chain-stimulator of activated B cells (NFκB), mitogen-activated protein kinase (MAPKs), and transforming growth factor-beta (TGF-β) modulatory activity. In addition, SeNPs possess remarkable immunomodulatory effects, making them a suitable option for supplementation with a much lower risk of toxicity compared to their elemental counterpart. Further, SeNPs have been shown to curtail viral and microbial infections, thus, making it a novel means to halt viral growth. In addition, it can be administered in the form of aerosol spray, direct injection, or infused thin-film transdermal patches to reduce the spread of this highly contagious viral infection. Moreover, a considerable decrease in the expression of selenoprotein along with enhanced expression of IL-6 in COVID-19 suggests a potential association among selenoprotein expression and COVID-19. In this review, we highlight the unique antimicrobial and antiviral properties of SeNPs and the immunomodulatory potential of selenoproteins. We provide the rationale behind their potentially interesting properties and further exploration in the context of microbial and viral infections. Further, the importance of selenoproteins and their role in maintaining a successful immune response along with their association to Se status is summarized.

Antimicrobial Coatings for Medical Textiles via Reactive Organo-Selenium Compounds

Bleached and cationized cotton fabrics were chemically modified with reactive organoselenium compounds through the nucleophilic aromatic substitution (SNAr) reaction, which allowed for organo-selenium attachment onto the surface of cotton fabrics via covalent bonds and, in the case of the cationized cotton fabric, additional ionic interactions. The resulting textiles exhibited potent bactericidal activity against S. aureus (99.99% reduction), although only moderate activity was observed against E. coli. Fabrics treated with reactive organo-selenium compounds also exhibited fungicidal activities against C. albicans, and much higher antifungal activity was observed when organo-selenium compounds were applied to the cationized cotton in comparison to the bleached cotton. The treatment was found to be durable against rigorous washing conditions (non-ionic detergent/100 °C). This paper is the first report on a novel approach integrating the reaction of cotton fabrics with an organo-selenium antimicrobial agent. This approach is attractive because it provides a method for imparting antimicrobial properties to cotton fabrics which does not disrupt the traditional production processes of a textile mill.

Novel gold(III)-dithiocarbamate complex targeting bacterial thioredoxin reductase: antimicrobial activity, synergy, toxicity, and mechanistic insights

Introduction

Antimicrobial resistance is a pressing global concern that has led to the search for new antibacterial agents with novel targets or non-traditional approaches. Recently, organogold compounds have emerged as a promising class of antibacterial agents. In this study, we present and characterize a (C^S)-cyclometallated Au(III) dithiocarbamate complex as a potential drug candidate.

Methods and results

The Au(III) complex was found to be stable in the presence of effective biological reductants, and showed potent antibacterial and antibiofilm activity against a wide range of multidrug-resistant strains, particularly gram-positive strains, and gram-negative strains when used in combination with a permeabilizing antibiotic. No resistant mutants were detected after exposing bacterial cultures to strong selective pressure, indicating that the complex may have a low propensity for resistance development. Mechanistic studies indicate that the Au(III) complex exerts its antibacterial activity through a multimodal mechanism of action. Ultrastructural membrane damage and rapid bacterial uptake suggest direct interactions with the bacterial membrane, while transcriptomic analysis identified altered pathways related to energy metabolism and membrane stability including enzymes of the TCA cycle and fatty acid biosynthesis. Enzymatic studies further revealed a strong reversible inhibition of the bacterial thioredoxin reductase. Importantly, the Au(III) complex demonstrated low cytotoxicity at therapeutic concentrations in mammalian cell lines, and showed no acute in vivo toxicity in mice at the doses tested, with no signs of organ toxicity.

Discussion

Overall, these findings highlight the potential of the Au(III)-dithiocarbamate scaffold as a basis for developing novel antimicrobial agents, given its potent antibacterial activity, synergy, redox stability, inability to produce resistant mutants, low toxicity to mammalian cells both in vitro and in vivo, and non-conventional mechanism of action.

Structure-Activity Relationships in NHC-Silver Complexes as Antimicrobial Agents

Silver has a long history of antimicrobial activity and received an increasing interest in last decades owing to the rise in antimicrobial resistance. The major drawback is the limited duration of its antimicrobial activity. The broad-spectrum silver containing antimicrobial agents are well represented by N-heterocyclic carbenes (NHCs) silver complexes. Due to their stability, this class of complexes can release the active Ag⁺ cations in prolonged time. Moreover, the properties of NHC can be tuned introducing alkyl moieties on N-heterocycle to provide a range of versatile structures with different stability and lipophilicity. This review presents designed Ag complexes and their biological activity against Gram-positive, Gram-negative bacteria and fungal strains. In particular, the structure-activity relationships underlining the major requirements to increase the capability to induce microorganism death are highlighted here. Moreover, some examples of encapsulation of silver-NHC complexes in polymer-based supramolecular aggregates are reported. The targeted delivery of silver complexes to the infected sites will be the most promising goal for the future.

Development of high cell density Limosilactobacillus reuteri KUB-AC5 for cell factory using oxidative stress reduction approach

BACKGROUND

Expression systems for lactic acid bacteria have been developed for metabolic engineering applications as well as for food-grade recombinant protein production. But the industrial applications of lactic acid bacteria as cell factories have been limited due to low biomass formation resulted in low efficiency of biomanufacturing process. Limosilactobacillus reuteri KUB-AC5 is a safe probiotic lactic acid bacterium that has been proven as a gut health enhancer, which could be developed as a mucosal delivery vehicle for vaccines or therapeutic proteins, or as expression host for cell factory applications. Similar to many lactic acid bacteria, its oxygen sensitivity is a key factor that limits cell growth and causes low biomass production. The aim of this study is to overcome the oxidative stress in L. reuteri KUB-AC5. Several genes involved in oxidative and anti-oxidative stress were investigated, and strain improvement for higher cell densities despite oxidative stress was performed using genetic engineering.

RESULTS

An in-silico study showed that L. reuteri KUB-AC5 genome possesses an incomplete respiratory chain lacking four menaquinone biosynthesis genes as well as a complete biosynthesis pathway for the production of the precursor. The presence of an oxygen consuming enzyme, NADH oxidase (Nox), leads to high ROS formation in aerobic cultivation, resulting in strong growth reduction to approximately 25% compared to anaerobic cultivation. Recombinant strains expressing the ROS scavenging enzymes Mn-catalase and Mn-superoxide dismutase were successfully constructed using the pSIP expression system. The Mn-catalase and Mn-SOD-expressing strains produced activities of 873 U/ml and 1213 U/ml and could minimize the ROS formation in the cell, resulting in fourfold and sevenfold higher biomass formation, respectively.

CONCLUSIONS

Expression of Mn-catalase and Mn-SOD in L. reuteri KUB-AC5 successfully reduced oxidative stress and enhanced growth. This finding could be applied for other lactic acid bacteria that are subject to oxidative stress and will be beneficial for applications of lactic acid bacteria for cell factory applications.

Target- and prodrug-based design for fungal diseases and cancer-associated fungal infections

Invasive fungal infections (IFIs) are emerging as a serious threat to public health and are associated with high incidence and mortality. IFIs also represent a frequent complication in patients with cancer who are undergoing chemotherapy. However, effective and safe antifungal agents remain limited, and the development of severe drug resistance further undermines the efficacy of antifungal therapy. Therefore, there is an urgent need for novel antifungal agents to treat life-threatening fungal diseases, especially those with new mode of action, favorable pharmacokinetic profiles, and anti-resistance activity. In this review, we summarize new antifungal targets and target-based inhibitor design, with a focus on their antifungal activity, selectivity, and mechanism. We also illustrate the prodrug design strategy used to improve the physicochemical and pharmacokinetic profiles of antifungal agents. Dual-targeting antifungal agents offer a new strategy for the treatment of resistant infections and cancer-associated fungal infections.

Optimized Ebselen-Based Inhibitors of Bacterial Ureases with Nontypical Mode of Action

Screening of 25 analogs of Ebselen, diversified at the N-aromatic residue, led to the identification of the most potent inhibitors of Sporosarcina pasteurii urease reported to date. The presence of a dihalogenated phenyl ring caused exceptional activity of these 1,2-benzisoselenazol-3(2H)-ones, with K_i value in a low picomolar range (<20 pM). The affinity was attributed to the increased π-π and π-cation interactions of the dihalogenated phenyl ring with αHis323 and αArg339 during the initial step of binding. Complementary biological studies with selected compounds on the inhibition of ureolysis in whole Proteus mirabilis cells showed a very good potency (IC₅₀ < 25 nM in phosphate-buffered saline (PBS) buffer and IC₉₀ < 50 nM in a urine model) for monosubstituted N-phenyl derivatives. The crystal structure of S. pasteurii urease inhibited by one of the most active analogs revealed the recurrent selenation of the Cys322 thiolate, yielding an unprecedented Cys322-S-Se-Se chemical moiety.

Antibacterial Activity of Ebselen

Ebselen is a low-molecular-weight organoselenium compound that has been broadly studied for its antioxidant, anti-inflammatory, and cytoprotective properties. These advantageous properties were initially associated with mimicking the activity of selenoprotein glutathione peroxidase, but the biomedical impact of this compound appear to be far more complex. Ebselen serves as a substrate or inhibitor with multiple protein/enzyme targets, whereas inhibition typically originates from the covalent modification of cysteine residues by opening the benzisoselenazolone ring and S-Se bond formation. The inhibition of enzymes of various classes and origins has been associated with substantial antimicrobial potential among other activities. In this contribution, we summarize the current state of the art regarding the antibacterial activity of ebselen. This activity, alone and in combination with commercial pharmaceuticals, against pathogens, including those resistant to drugs, is presented, together with the molecular mechanism behind the reactivity. The specific inactivation of thioredoxin reductase, bacterial toxins, and other resistance factors is considered to have certain therapeutic implications. Synergistic action and sensitization to common antibiotics assisted with the use of ebselen appear to be promising directions in the treatment of persistent infections.

Inhibition of planktonic growth and biofilm formation of Staphylococcus aureus by entrectinib through disrupting the cell membrane

Over the last few decades, Staphylococcus aureus infection remain a major medical challenge and health concern worldwide. Biofilm formation and antibiotic resistance caused by S. aureus make it difficult to be eradicated from bacterial infections in clinics. In this study, our data demonstrated the antibacterial and excellent anti-biofilm activity of entrectinib against S. aureus. Entrectinib also exhibited the good safety, suggesting no toxicity with antibacterial concentration of entrectinib toward the erythrocytes and mammalian 239 T cells. Moreover, entrectinib significantly reduced the bacterial burden of septic tissue in a murine model of MRSA infection. Global proteomic analysis of S. aureus treated with entrectinib showed significant changes in the expression levels of ribosomal structure-related (rpmC, rpmD, rplX, and rpsT) and oxidative stress-related proteins (Thioredoxin system), suggesting the possible inhibition of bacterial protein biosynthesis with entrectinib exposure. The increased production of reactive oxygen species (ROS) was demonstrated in the entrectinib-treated S. aureus, supported the impact of entrectinib on the expression changes of ROS-correlated proteins involved in oxidative stress. Furthermore, entrectinib-induced resistant S. aureus clone was selected by in vitro induction under entrectinib exposure and 3 amino acid mutations in the entrectinib-induced resistant S. aureus strain, 2 of which were located in the gene encoding Type II NADH: quinoneoxidoreductase and one were found in GTP pyrophosphokinase family protein. Finally, the bactericidal action of entrectinib on S. aureus were confirmed by disrupting the bacterial cell membrane. Conclusively, entrectinib exhibit the antibacterial and anti-biofilm activity by destroying cell membrane against S. aureus.

The synergistic activity of SBC3 in combination with Ebselen against Escherichia coli infection

Escherichia coli ranks as the number one clinical isolate in the past years in China according to The China Antimicrobial Surveillance Network (CHINET), and its multidrug-resistant (MDR) pathogenic strains account for over 160 million cases of dysentery and one million deaths per year. Here, our work demonstrates that E. coli is highly sensitive to the synergistic combination of SBC3 [1,3-Dibenzyl-4,5-diphenyl-imidazol-2-ylidene silver (I) acetate] and Ebselen, which shows no synergistic toxicity on mammalian cells. The proposed mechanism for the synergistic antibacterial effect of SBC3 in combination with Ebselen is based on directly inhibiting E. coli thioredoxin reductase and rapidly depleting glutathione, resulting in the increase of reactive oxygen species that cause bacterial cell death. Furthermore, the bactericidal efficacy of SBC3 in combination with Ebselen has been confirmed in mild and acute peritonitis mice. In addition, the five most difficult to treat Gram-negative bacteria (including E. coli, Acinetobacter baumannii, Enterobacter cloacae, Klebsiella pneumoniae, and Pseudomonas aeruginosa) are also highly sensitive to a synergistic combination of SBC3 and Ebselen. Thus, SBC3 in combination with Ebselen has potential as a treatment for clinically important Gram-negative bacterial infections.

Bacterial redox response factors in the management of environmental oxidative stress

Bacteria evolved to survive in the available environmental chemosphere via several cellular mechanisms. A rich pool of antioxidants and stress regulators plays a significant role in the survival of bacteria in unfavorable environmental conditions. Most of the microbes exhibit resistant phenomena in toxic environment niches. Naturally, bacteria possess efficient thioredoxin reductase, glutaredoxin, and peroxiredoxin redox systems to handle environmental oxidative stress. Further, an array of transcriptional regulators senses the oxidative stress conditions. Transcription regulators, such as OxyR, SoxRS, PerR, UspA, SsrB, MarA, OhrR, SarZ, etc., sense and transduce bacterial oxidative stress responses. The redox-sensitive transcription regulators continuously recycle the utilized antioxidant enzymes during oxidative stress. These regulators promote the expression of antioxidant enzymes such as superoxide dismutase, catalase, and peroxides that overcome oxidative insults. Therefore, the transcriptional regulations maintain steady-state activities of antioxidant enzymes representing the resistance against host cell/environmental oxidative insults. Further, the redox system provides reducing equivalents to synthesize biomolecules, thereby contributing to cellular repair mechanisms. The inactive transcriptional regulators in the undisturbed cells are activated by oxidative stress. The oxidized transcriptional regulators modulate the expression of antioxidant and cellular repair enzymes to survive in extreme environmental conditions. Therefore, targeting these antioxidant systems and response regulators could alter cellular redox homeostasis. This review presents the mechanisms of different redox systems that favor bacterial survival in extreme environmental oxidative stress conditions.

Enzyme-Responsive COF-Based Thiol-Targeting Nanoinhibitor for Curing Bacterial Infections

Pathogen infections impose severe challenges in clinical practice, especially for patients infected with antibiotic-resistant microbes. The thioredoxin (Trx) system in Gram-positive bacteria serves as an ideal antimicrobial target for novel medicine design due to the structural differences from corresponding system in mammals. However, a backup thiol-dependent antioxidant glutathione (GSH) system limits the effectiveness of drugs in many Gram-negative bacteria. Herein, we synthesize a thiol-targeting nanoinhibitor based on an enzyme-responsive covalent organic framework (COF) coloaded with silver nanoparticles (AgNPs) and ebselen (EBS) (Ag-TA-CON@EBS@PEG) to exert synergistic antibacterial effects. Since azoreductase can dissociate the enzyme-responsive COF, we adopt this strategy to achieve the accurate release of EBS and Ag⁺ at infection sites. Our research identifies that the functionalized nanoinhibitor shows excellent bactericidal performance for Gram-positive and Gram-negative bacteria in vitro and exhibits low toxicity to normal cells. Besides, the nanoinhibitor presents favorable biocompatibility, anti-inflammatory property, and effective wound healing ability in mice. This paper provides a promising clinical strategy for synergistic antibacterial therapy and enhanced wound healing properties via an optimized combination of the targeted nanomedicines with an intelligent drug conveying platform.

NO news: S-(de)nitrosylation of cathepsins and their relationship with cancer

Tumor formation and progression have been much of a study over the last two centuries. Recent studies have seen different developments for the early diagnosis and treatment of the disease; some of which even promise survival of the patient. Cysteine proteases, mainly cathepsins have been unequivocally identified as putative worthy players of redox imbalance that contribute to the premonition and further progression of cancer by interfering in the normal extracellular and intracellular proteolysis and initiating a proteolytic cascade. The present review article focuses on the study of cancer so far, while establishing facts on how future studies focused on the cellular interrelation between nitric oxide (NO) and cancer, can direct their focus on cathepsins. For a tumor cell to thrive and synergize a cancerous environment, different mutations in the proteolytic and signaling pathways and the proto-oncogenes, oncogenes, and the tumor suppressor genes are made possible through cellular biochemistry and some cancer-stimulating environmental factors. The accumulated findings show that S-nitrosylation of cathepsins under the influence of NO-donors can prevent the invasion of cancer and cause cancer cell death by blocking the activity of cathepsins as well as the major denitrosylase systems using a multi-way approach. Faced with a conundrum of how to fill the gap between the dodging of established cancer hallmarks with cathepsin activity and gaining appropriate research/clinical accreditation using our hypothesis, the scope of this review also explores the interplay and crosstalk between S-nitrosylation and S-(de)nitrosylation of this protease and highlights the utility of charging thioredoxin (Trx) reductase inhibitors, low-molecular-weight dithiols, and Trx mimetics using efficient drug delivery system to prevent the denitrosylation or regaining of cathepsin activity in vivo. In foresight, this raises the prospect that drugs or novel compounds that target cathepsins taking all these factors into consideration could be deployed as alternative or even better treatments for cancer, though further research is needed to ascertain the safety, efficiency and effectiveness of this approach.

Enzymatic basis of the Fc-selective intra-chain disulfide reduction and free thiol content variability in an antibody produced in Escherichia coli

Background

Escherichia coli (E. coli) is a promising host for production of recombinant proteins (including antibodies and antibody fragments) that don’t require complex post-translational modifications such as glycosylation. During manufacturing-scale production of a one-armed antibody in E. coli (periplasmic production), variability in the degree of reduction of the antibody’s disulfide bonds was observed. This resulted in variability in the free thiol content, a potential critical product quality attribute. This work was initiated to understand and prevent the variability in the total free thiol content during manufacturing.

Results

In this study, we found that the reduction in antibody’s disulfide bonds was observed to occur during homogenization and the ensuing homogenate hold step where in the antibody is exposed to redox enzymes and small molecule reductants present in homogenate. Variability in the downstream processing time between the start of homogenization and end of the homogenate hold step resulted in variability in the degree of antibody disulfide bond reduction and free thiol content. The disulfide bond reduction in the homogenate is catalyzed by the enzyme disulfide bond isomerase C (DsbC) and is highly site-specific and occurred predominantly in the intra-chain disulfide bonds present in the Fc CH2 region. Our results also imply that lack of glycans in E. coli produced antibodies may facilitate DsbC accessibility to the disulfide bond in the Fc CH2 region, resulting in its reduction.

Conclusions

During E. coli antibody manufacturing processes, downstream processing steps such as homogenization and subsequent processing of the homogenate can impact degree of disulfide bond reduction in the antibody and consequently product quality attributes such as total free thiol content. Duration of the homogenate hold step should be minimized as much as possible to prevent disulfide bond reduction and free thiol formation. Other approaches such as reducing homogenate temperature, adding flocculants prior to homogenization, using enzyme inhibitors, or modulating redox environments in the homogenate should be considered to prevent antibody disulfide bond reduction during homogenization and homogenate processing steps in E. coli antibody manufacturing processes.

Helicobacter pylori Thioredoxin1 May Play a Highly Pathogenic Role via the IL6/STAT3 Pathway

Background

Recent studies have shown that CagA is considered highly pathogenic to helicobacter pylori (HP) in Western populations. However, in East Asia, CagA positive HP can be up to 90%, but not all patients will lead to gastric cancer. Our research group has found that HP thioredoxin1 (Trx1) may be a marker of high pathogenicity. Here, we investigate whether HP Trx1 exerts high pathogenicity and its internal molecular mechanism.

Materials and Methods

We constructed the coculture system of high-Trx1 HP and low-Trx1 HP strains with gastric epithelial cell lines separately and detected the influence of HP strains. The cells were stained by AM/PI, and the cell's mortality was assessed by fluorescence microscope. The cell's supernatants or precipitates were collected to detect the expression of IL6. In addition, the cell's precipitates were collected, and the expression of p-STAT3 was detected by western blot. Furthermore, the cell's supernatants were collected for detecting the expression of 8-OHDG to investigate the extent of DNA damage.

Results

The high-Trx1 HP can cause higher mortality of GES-1 cells compared with the low-Trx1 HP group (high-Trx1 HP (4.53 ± 0.56) %, low-Trx1 HP (0.39 ± 0.10) %, P < 0.001). The mRNA and protein level of IL-6 in AGS and GES-1 cells were increased during HP infection, and the expression of IL-6 in the High-Trx1 HP group was much higher than the low-Trx1 HP group. Besides, the expression of p-STAT3 was higher in the HP-positive gastric mucosa. And the expression of p-STAT3 in the high-Trx1 HP group was significantly upregulated compared with the low-Trx1 HP group. Furthermore, the expression of 8-OHDG in the high-Trx1 group was much higher than the low-Trx1 group (high-Trx1 HP (5.47 ± 1.73) ng/ml, low-Trx1 HP (2.89 ± 1.72) ng/ml, P < 0.05).

Conclusion

HP Trx1 may play as a marker of high pathogenicity, and the high-Trx1 HP could mediate the pathogenic process of HP infection via the IL6/STAT3 pathway.

The Assessment on Synergistic Activity of Ebselen and Silver Ion Against Yersinia pseudotuberculosis

Yersinia pseudotuberculosis is a foodborne zoonotic bacterium that is pathogenic to guinea pigs, rabbits, and mice. It also causes pseudotuberculosis in humans. However, it still lacked the scientific basis for control. Here, we found out that Ebselen (EbSe) exhibited synergistic antibacterial activity with silver nitrate (Ag⁺) against Y. pseudotuberculosis YpIII strain with high efficacy in vitro using UV-visible light absorption spectrum, 5,5’-dithiobis-(2-nitrobenzoic acid), laser scanning confocal microscope, flow cytometry, transmission electron microscopy and Western blotting assays. The depletion of total glutathione (GSH) amount and inhibition of thioredoxin reductase (TrxR) activity in thiol-dependent redox system revealed the destructiveness of EbSe-Ag⁺-caused intracellular oxidative stress. Furthermore, a YpIII-caused mice gastroenteritis model was constructed. EbSe-Ag⁺ significantly reduced bacterial loads with low toxicity. It also down-regulated the expression levels of interferon (IL)-1β and tumor necrosis factor-α, up-regulated the expression level of IL-10 on-site. All the in vivo results demonstrated the antibacterial activity and immune-modulatory property of EbSe-Ag⁺. Collectively, these results provided academic fundament for further analysis and development of EbSe-Ag⁺ as the antibacterial agents for pseudotuberculosis control.

Genetic validation of Aspergillus fumigatus phosphoglucomutase as a viable therapeutic target in invasive aspergillosis

Aspergillus fumigatus is the causative agent of invasive aspergillosis, an infection with mortality rates of up to 50%. The glucan-rich cell wall of A. fumigatus is a protective structure that is absent from human cells and is a potential target for antifungal treatments. Glucan is synthesized from the donor uridine diphosphate glucose, with the conversion of glucose-6-phosphate to glucose-1-phosphate by the enzyme phosphoglucomutase (PGM) representing a key step in its biosynthesis. Here, we explore the possibility of selectively targeting A. fumigatus PGM (AfPGM) as an antifungal treatment strategy. Using a promoter replacement strategy, we constructed a conditional pgm mutant and revealed that pgm is required for A. fumigatus growth and cell wall integrity. In addition, using a fragment screen, we identified the thiol-reactive compound isothiazolone fragment of PGM as targeting a cysteine residue not conserved in the human ortholog. Furthermore, through scaffold exploration, we synthesized a para-aryl derivative (ISFP10) and demonstrated that it inhibits AfPGM with an IC50 of 2 μM and exhibits 50-fold selectivity over the human enzyme. Taken together, our data provide genetic validation of PGM as a therapeutic target and suggest new avenues for inhibiting AfPGM using covalent inhibitors that could serve as tools for chemical validation.

Molecular Connectivity between Extracytoplasmic Sigma Factors and PhoP Accounts for Coupled Mycobacterial Stress Response

Mycobacterium tuberculosis encounters numerous stress conditions within the host, but how it is able to mount a coupled stress response remains unknown. Growing evidence suggests that under acidic pH, M. tuberculosis modulates redox homeostasis. In an attempt to dissect the mechanistic details of responses to multiple stress conditions, here we studied the significance of connectivity of extracytoplasmic sigma factors with PhoP. We show that PhoP impacts the mycothiol redox state, and the H37Rv ΔphoP deletion mutant strain displays a significantly higher susceptibility to redox stress than the wild-type bacilli. To probe how the two regulators PhoP and redox-active sigma factor SigH contribute to redox homeostasis, we show that SigH controls expression of redox-active thioredoxin genes, a major mycobacterial antioxidant system, and under redox stress, SigH, but not PhoP, is recruited at the target promoters. Consistent with these results, interaction between PhoP and SigH fails to impact redox-dependent gene expression. This is in striking contrast to our previous results showing PhoP-dependent SigE recruitment within acid-inducible mycobacterial promoters to maintain pH homeostasis. Our subsequent results demonstrate reduced PhoP-SigH interaction in the presence of diamide and enhanced PhoP-SigE interaction under low pH. These contrasting results uncover the underlying mechanism of the mycobacterial adaptive program, coupling low pH with maintenance of redox homeostasis. IMPORTANCE M. tuberculosis encounters reductive stress under acidic pH. To investigate the mechanism of coupled stress response, we show that PhoP plays a major role in mycobacterial redox stress response. We observed a strong correlation of phoP-dependent redox-active expression of thioredoxin genes, a major mycobacterial antioxidant system. Further probing of functioning of regulators revealed that while PhoP controls pH homeostasis via its interaction with SigE, direct recruitment of SigH, but not PhoP-SigH interaction, controls expression of thioredoxin genes. These strikingly contrasting results showing enhanced PhoP-SigE interaction under acidic pH and reduced PhoP-SigH interaction under redox conditions uncover the underlying novel mechanism of the mycobacterial adaptive program, coupling low pH with maintenance of redox homeostasis.

Gold Nanoclusters as Nanoantibiotic Auranofin Analogues

Auranofin, a gold(I)-complex with tetraacetylated thioglucose (Ac4 GlcSH) and triethylphosphine ligands, is an FDA-approved drug used as an anti-inflammatory aid in the treatment of rheumatoid arthritis. In repurposing auranofin for other diseases, it was found that the drug showed significant activity against Gram-positive but was inactive against Gram-negative bacteria. Herein, the design and synthesis of gold nanoclusters (AuNCs) based on the structural motif of auranofin are reported. Phosphine-capped AuNCs are synthesized and glycosylated, yielding auranofin analogues with mixed triphenylphosphine monosulfonate (TPPMS)/Ac4 GlcSH ligand shells. These AuNCs are active against both Gram-negative and Gram-positive bacteria, including multidrug-resistant pathogens. Notably, an auranofin analogue, a mixed-ligand 1.6 nm AuNC 4b, is more active than auranofin against Pseudomonas aeruginosa, while exhibiting lower toxicity against human A549 cells. The enhanced antibacterial activity of these AuNCs is characterized by a greater uptake of Au by the bacteria compared to AuI complexes. Additional factors include increased oxidative stress, moderate inhibition of thioredoxin reductase (TrxR), and DNA damage. Most intriguingly, the uptake of AuNCs are not affected by the bacterial outer membrane (OM) barrier or by binding with the extracellular proteins. This contrasts with AuI complexes like auranofin that are susceptible to protein binding and hindered by the OM barrier.

Biochemical and structural characterizations of thioredoxin reductase selenoproteins of the parasitic filarial nematodes Brugia malayi and Onchocerca volvulus

Enzymes in the thiol redox systems of microbial pathogens are promising targets for drug development. In this study we characterized the thioredoxin reductase (TrxR) selenoproteins from Brugia malayi and Onchocerca volvulus, filarial nematode parasites and causative agents of lymphatic filariasis and onchocerciasis, respectively. The two filarial enzymes showed similar turnover numbers and affinities for different thioredoxin (Trx) proteins, but with a clear preference for the autologous Trx. Human TrxR1 (hTrxR1) had a high and similar specific activity versus the human and filarial Trxs, suggesting that, in vivo, hTrxR1 could possibly be the reducing agent of parasite Trxs once they are released into the host. Both filarial TrxRs were efficiently inhibited by auranofin and by a recently described inhibitor of human TrxR1 (TRi-1), but not as efficiently by the alternative compound TRi-2. The enzyme from B. malayi was structurally characterized also in complex with NADPH and auranofin, producing the first crystallographic structure of a nematode TrxR. The protein represents an unusual fusion of a mammalian-type TrxR protein architecture with an N-terminal glutaredoxin-like (Grx) domain lacking typical Grx motifs. Unlike thioredoxin glutathione reductases (TGRs) found in platyhelminths and mammals, which are also Grx–TrxR domain fusion proteins, the TrxRs from the filarial nematodes lacked glutathione disulfide reductase and Grx activities. The structural determinations revealed that the Grx domain of TrxR from B. malayi contains a cysteine (C22), conserved in TrxRs from clade IIIc nematodes, that directly interacts with the C-terminal cysteine-selenocysteine motif of the homo-dimeric subunit. Interestingly, despite this finding we found that altering C22 by mutation to serine did not affect enzyme catalysis. Thus, although the function of the Grx domain in these filarial TrxRs remains to be determined, the results obtained provide insights on key properties of this important family of selenoprotein flavoenzymes that are potential drug targets for treatment of filariasis.

A Fluorescent Probe to Detect Quick Disulfide Reductase Activity in Bacteria

The Trx and Grx systems, two disulfide reductase systems, play critical roles in various cell activities. There are great differences between the thiol redox systems in prokaryotes and mammals. Though fluorescent probes have been widely used to detect these systems in mammalian cells. Very few methods are available to detect rapid changes in the redox systems of prokaryotes. Here we investigated whether Fast-TRFS, a disulfide-containing fluorescent probe utilized in analysis of mammalian thioredoxin reductase, could be used to detect cellular disulfide reducibility in bacteria. Fast-TRFS exhibited good substrate qualities for both bacterial thioredoxin and GSH-glutaredoxin systems in vitro, with Trx system having higher reaction rate. Moreover, the Fast-TRFS was used to detect the disulfide reductase activity in various bacteria and redox-related gene null E. coli. Some glutaredoxin-deficient bacteria had stronger fast disulfide reducibility. The Trx system was shown to be the predominant disulfide reductase for fast disulfide reduction rather than the Grx system. These results demonstrated that Fast-TRFS is a viable probe to detect thiol-dependent disulfide reductases in bacteria. It also indicated that cellular disulfide reduction could be classified into fast and slow reaction, which are predominantly catalyzed by E. coli Trx and Grx system, respectively.

Structure-Guided Discovery of the Novel Covalent Allosteric Site and Covalent Inhibitors of Fructose-1,6-Bisphosphate Aldolase to Overcome the Azole Resistance of Candidiasis

Fructose-1,6-bisphosphate aldolase (FBA) represents an attractive new antifungal target. Here, we employed a structure-based optimization strategy to discover a novel covalent binding site (C292 site) and the first-in-class covalent allosteric inhibitors of FBA from Candida albicans (CaFBA). Site-directed mutagenesis, liquid chromatography-mass spectrometry, and the crystallographic structures of APO-CaFBA, CaFBA-G3P, and C157S-2a4 revealed that S268 is an essential pharmacophore for the catalytic activity of CaFBA, and L288 is an allosteric regulation switch for CaFBA. Furthermore, most of the CaFBA covalent inhibitors exhibited good inhibitory activity against azole-resistant C. albicans, and compound 2a11 can inhibit the growth of azole-resistant strains 103 with the MIC₈₀ of 1 μg/mL. Collectively, this work identifies a new covalent allosteric site of CaFBA and discovers the first generation of covalent inhibitors for fungal FBA with potent inhibitory activity against resistant fungi, establishing a structural foundation and providing a promising strategy for the design of potent antifungal drugs.

A fluorescent probe for specifically measuring the overall thioredoxin and glutaredoxin reducing activity in bacterial cells

Both bacterial thioredoxin and glutaredoxin systems can reduce TRFS-green selectively, which confers TRFS-green to be a remarkable probe to detect the dominant disulfide reductase activity with a slow reaction rate in bacteria, e. g. E. coli Grx2&3.

Ebselen Not Only Inhibits Clostridioides difficile Toxins but Displays Redox-Associated Cellular Killing

Ebselen, a reactive organoselenium compound, was shown to inhibit toxins TcdA and TcdB by covalently binding to their cysteine protease domains. It was suggested that ebselen lacked antimicrobial activity against Clostridioides difficile. However, this perception conflicts with C. difficile having essential cysteine-containing enzymes that could be potential targets and the reported antimicrobial activity of ebselen against other species. Hence, we reevaluated the anti-C. difficile properties of ebselen. Susceptibility testing revealed that its activity was either slightly reduced by pyruvate found in Wilkins-Chalgren agar or obliterated by blood in brucella agar. In brain heart infusion (BHI) agar, ebselen inhibited most C. difficile strains (MICs of 2 to 8 μg/ml), except for ribotype 078 that was intrinsically resistant (MIC = 32 to 128 μg/ml). Against C. difficile R20291, at concentrations below its minimal bactericidal concentration (MBC), 16 μg/ml, ebselen inhibited production of toxins and spores. Transcriptome analysis revealed that ebselen altered redox-associated processes and cysteine metabolism and enhanced expression of Stickland proline metabolism, likely to regenerate NAD⁺ from NADH. In cellular assays, ebselen induced uptake of cysteine, depleted nonprotein thiols, and disrupted the NAD⁺/NADH ratio. Taken together, killing of C. difficile cells by ebselen occurs by a multitarget action that includes disrupting intracellular redox, which is consistent with ebselen being a reactive molecule. However, the physiological relevance of these antimicrobial actions in treating acute C. difficile infection (CDI) is likely to be undermined by host factors, such as blood, which protect C. difficile from killing by ebselen.

IMPORTANCE We show that ebselen kills pathogenic C. difficile by disrupting its redox homeostasis, changing the normal concentrations of NAD⁺ and NADH, which are critical for various metabolic functions in cells. However, this antimicrobial action is hampered by host components, namely, blood. Future discovery of ebselen analogues, or mechanistically similar compounds, that remain active in blood could be drug leads for CDI or probes to study C. difficile redox biology in vivo.

Beneficial Effects of Green Tea EGCG on Skin Wound Healing: A Comprehensive Review

Epigallocatechin gallate (EGCG) is associated with various health benefits. In this review, we searched current work about the effects of EGCG and its wound dressings on skin for wound healing. Hydrogels, nanoparticles, micro/nanofiber networks and microneedles are the major types of EGCG-containing wound dressings. The beneficial effects of EGCG and its wound dressings at different stages of skin wound healing (hemostasis, inflammation, proliferation and tissue remodeling) were summarized based on the underlying mechanisms of antioxidant, anti-inflammatory, antimicrobial, angiogenesis and antifibrotic properties. This review expatiates on the rationale of using EGCG to promote skin wound healing and prevent scar formation, which provides a future clinical application direction of EGCG.

Ebselen, a multi-target compound: its effects on biological processes and diseases

Ebselen is a well-known synthetic compound mimicking glutathione peroxidase (GPx), which catalyses some vital reactions that protect against oxidative damage. Based on a large number of in vivo and in vitro studies, various mechanisms have been proposed to explain its actions on multiple targets. It targets thiol-related compounds, including cysteine, glutathione, and thiol proteins (e.g., thioredoxin and thioredoxin reductase). Owing to this, ebselen is a unique multifunctional agent with important effects on inflammation, apoptosis, oxidative stress, cell differentiation, immune regulation and neurodegenerative disease, with anti-microbial, detoxifying and anti-tumour activity. This review summarises the current understanding of the multiple biological processes and molecules targeted by ebselen, and its pharmacological applications.

Thioredoxin reductase as a pharmacological target

Thioredoxin reductases (TrxRs) belong to the pyridine nucleotide disulfide oxidoreductase family enzymes that reduce thioredoxin (Trx). The couple TrxR and Trx is one of the major antioxidant systems that control the redox homeostasis in cells. The thioredoxin system, comprised of TrxR, Trx and NADPH, exerts its activities via a disulfide-dithiol exchange reaction. Inhibition of TrxR is an important clinical goal in all conditions in which the redox state is perturbed. The present review focuses on the most critical aspects of the cellular functions of TrxRs and their inhibition mechanisms by metal ions or chemicals, through direct targeting of TrxRs or their substrates or protein interactors. To update the involvement of overactivation/dysfunction of TrxRs in various pathological conditions, human diseases associated with TrxRs genes were critically summarized by publicly available genome-wide association study (GWAS) catalogs and literature. The pieces of evidence presented here justify why TrxR is recognized as one of the most critical clinical targets and the growing current interest in developing molecules capable of interfering with the functions of TrxR enzymes.

Structure-based identification of natural compound inhibitor against M. tuberculosis thioredoxin reductase: insight from molecular docking and dynamics simulation

Antioxidant systems of M. tuberculosis (Mtb) play an important role in providing resistance in the hostile environment of mononuclear phagocytes. Thioredoxin system is a known antioxidant system that consists of three copies of thioredoxins (Trxs) and a single copy of thioredoxin reductase (TrxR). TrxR has been validated as an essential gene known to be involved in the reduction of peroxides, dinitrobenzenes and hydroperoxides, and is crucial in maintaining the survival of Mtb in macrophages. Recently, it has been demonstrated to be a druggable target. In this study, molecular docking was applied to screen more than 20,000 natural compounds from the Traditional Chinese Medicine database. Theoretical calculation of ΔGbinding by the Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) methods indicated two top-hit compounds that bind with a high affinity to the allosteric site, consisting of a hinge region, of TrxR. Further, stability and binding analysis of both compounds were carried out with molecular dynamics simulation. An analysis of conformational variation by principal component analysis (PCA) and protein contact network (PCN) uncovered the conformational changes in the compound-bound forms of protein. The NADPH domain formed many new interactions with the FAD domain in the compound-bound form, signifying that the binding may render an effect on the protein structure and function. Our results suggest that these two compounds could potentially be used for structure-based lead inhibitors against TrxR. The inhibitor selected as lead compound will be used further as a scaffold to optimize as novel anti-tuberculosis therapeutic.Communicated by Ramaswamy H. Sarma.

Gold(I) and Gold(III) N-Heterocyclic Carbene Complexes as Antibacterial Agents and Inhibitors of Bacterial Thioredoxin Reductase

A series of (NHC)Au(I)Cl monocarbene complexes and their gold(III) analogues (NHC)Au(III)Cl₃ were prepared and investigated as antibacterial agents and inhibitors of bacterial TrxR. The complexes showed stronger antibacterial effects against the Gram-positive MRSA and E. faecium strains than against several Gram-negative bacteria. All complexes were efficient inhibitors of bacterial thioredoxin reductase, indicating that inhibition of this enzyme might be involved in their mechanism of action. The efficacy of gold(I) and gold(III) analogues was comparable in most of the assays. The cytotoxicity of the gold NHC compounds against cancer and human cells was overall weaker than the activity against the Gram-positive bacteria, suggesting that their optimization as antibacterials warrants further investigation.

Evaluation of Ruthenium(II) N-Heterocyclic Carbene Complexes as Antibacterial Agents and Inhibitors of Bacterial Thioredoxin Reductase

A series of ruthenium(II) complexes with N-heterocyclic carbene (NHC) ligands of the general type (arene)(NHC)Ru(II)X2 (where X = halide) was prepared, characterized, and evaluated as antibacterial agents in comparison to the respective metal free benzimidazolium cations. The ruthenium(II) NHC complexes generally triggered stronger bacterial growth inhibition than the metal free benzimidazolium cations. The effects were much stronger against Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) than against Gram-negative bacteria (Escherichia coli, Acinetobacter baumannii, Pseudomonas aeruginosa), and all complexes were inactive against the fungus Candida albicans. Moderate inhibition of bacterial thioredoxin reductase was confirmed for selected complexes, indicating that inhibition of this enzyme might be a contributing factor to the antibacterial effects.

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.

Inhibition of Pseudomonas aeruginosa Alginate Synthesis by Ebselen Oxide and Its Analogues

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that is frequently found in the airways of cystic fibrosis (CF) patients due to the dehydrated mucus that collapses the underlying cilia and prevents mucociliary clearance. During this life-long chronic infection, P. aeruginosa cell accumulates mutations that lead to inactivation of the mucA gene that results in the constitutive expression of algD-algA operon and the production of alginate exopolysaccharide. The viscous alginate polysaccharide further occludes the airways of CF patients and serves as a protective matrix to shield P. aeruginosa from host immune cells and antibiotic therapy. Development of inhibitors of alginate production by P. aeruginosa would reduce the negative impact from this viscous polysaccharide. In addition to transcriptional regulation, alginate biosynthesis requires allosteric activation by bis (3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) binding to an Alg44 protein. Previously, we found that ebselen (Eb) and ebselen oxide (EbO) inhibited diguanylate cyclase from synthesizing c-di-GMP. In this study, we show that EbO, Eb, ebsulfur (EbS), and their analogues inhibit alginate production. Eb and EbS can covalently modify the cysteine 98 (C98) residue of Alg44 and prevent its ability to bind c-di-GMP. However, P. aeruginosa with Alg44 C98 substituted with alanine or serine was still inhibited for alginate production by Eb and EbS. Our results indicate that EbO, Eb, and EbS are lead compounds for reducing alginate production by P. aeruginosa. Future development of these inhibitors could provide a potential treatment for CF patients infected with mucoid P. aeruginosa.

Selenium-Containing Polysaccharides—Structural Diversity, Biosynthesis, Chemical Modifications and Biological Activity

Selenosugars are a group of sugar derivatives of great structural diversity (e.g., molar masses, selenium oxidation state, and selenium binding), obtained as a result of biosynthesis, chemical modification of natural compounds, or chemical synthesis. Seleno-monosaccharides and disaccharides are known to be non-toxic products of the natural metabolism of selenium compounds in mammals. In the case of the selenium-containing polysaccharides of natural origin, their formation is also postulated as a form of detoxification of excess selenium in microorganisms, mushroom, and plants. The valency of selenium in selenium-containing polysaccharides can be: 0 (encapsulated nano-selenium), IV (selenites of polysaccharides), or II (selenoglycosides or selenium built into the sugar ring to replace oxygen). The great interest in Se-polysaccharides results from the expected synergy between selenium and polysaccharides. Several plant- and mushroom-derived polysaccharides are potent macromolecules with antitumor, immunomodulatory, antioxidant, and other biological properties. Selenium, a trace element of fundamental importance to human health, has been shown to possess several analogous functions. The mechanism by which selenium exerts anticancer and immunomodulatory activity differs from that of polysaccharide fractions, but a similar pharmacological effect suggests a possible synergy of these two agents. Various functions of Se-polysaccharides have been explored, including antitumor, immune-enhancement, antioxidant, antidiabetic, anti-inflammatory, hepatoprotective, and neuroprotective activities. Due to being non-toxic or much less toxic than inorganic selenium compounds, Se-polysaccharides are potential dietary supplements that could be used, e.g., in chemoprevention.

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.

Thioredoxin reductase inhibitors: updated patent review (2017-present)

Introduction: Thioredoxin reductase (TrxR) is a selenocysteine-containing enzyme which is responsible - as a part of the thioredoxin system - for maintaining redox homeostasis in cells. It is upregulated in cancerous state as a defense against oxidative stress. TrxR has been mostly considered an anticancer drug target although it has applications in other therapeutic areas such as neurodegeneration, inflammation, microbial infections, and neonatal hyperoxic lung injury.Areas covered: The present review covers the patent literature that appeared in the period 2017-2020, i.e. since the publication of the previous expert opinion patent review on TrxR inhibitors. The recent additions to the following traditional classes of inhibitors are discussed: metal complexes, Michael acceptors as well as arsenic and selenium compounds. At the same time, a novel group of nitro (hetero)aromatic compounds have emerged which likely acts via covalent inhibition mechanism. Several miscellaneous chemotypes are grouped under Miscellaneous subsection.Expert opinion: While specificity over glutathione reductase is achieved easily, TrxR is still moving toward the later stages of development at a very slow rate. Michael acceptors, particularly based on TRXR substrate-mimicking scaffolds, are gaining impetus and so are dual and hybrid compounds. The development prospects of the emerging nitro (hetero)aromatic chemotypes remain uncertain.