The multiplicity of thioredoxin systems meets the specific lifestyles of Clostridia.

Cells are unceasingly confronted by oxidative stresses that oxidize proteins on their cysteines. The thioredoxin (Trx) system, which is a ubiquitous system for thiol and protein repair, is composed of a thioredoxin (TrxA) and a thioredoxin reductase (TrxB). TrxAs reduce disulfide bonds of oxidized proteins and are then usually recycled by a single pleiotropic NAD(P)H-dependent TrxB (NTR). In this work, we first analyzed the composition of Trx systems across Bacteria. Most bacteria have only one NTR, but organisms in some Phyla have several TrxBs. In Firmicutes, multiple TrxBs are observed only in Clostridia, with another peculiarity being the existence of ferredoxin-dependent TrxBs. We used Clostridioides difficile, a pathogenic sporulating anaerobic Firmicutes, as a model to investigate the biological relevance of TrxB multiplicity. Three TrxAs and three TrxBs are present in the 630Δerm strain. We showed that two systems are involved in the response to infection-related stresses, allowing the survival of vegetative cells exposed to oxygen, inflammation-related molecules and bile salts. A fourth TrxB copy present in some strains also contributes to the stress-response arsenal. One of the conserved stress-response Trx system was found to be present both in vegetative cells and in the spores and is under a dual transcriptional control by vegetative cell and sporulation sigma factors. This Trx system contributes to spore survival to hypochlorite and ensure proper germination in the presence of oxygen. Finally, we found that the third Trx system contributes to sporulation through the recycling of the glycine-reductase, a Stickland pathway enzyme that allows the consumption of glycine and contributes to sporulation. Altogether, we showed that Trx systems are produced under the control of various regulatory signals and respond to different regulatory networks. The multiplicity of Trx systems and the diversity of TrxBs most likely meet specific needs of Clostridia in adaptation to strong stress exposure, sporulation and Stickland pathways.

Purification and characterization of thioredoxin reductase enzyme from commercial Spirulina platensis tablets by affinity chromatography and investigation of the effects of some chemicals and drugs on enzyme activity.

Thioredoxin reductase (TrxR, enzyme code [E.C.] 1.6.4.5) is a widely distributed flavoenzyme that catalyzes nicotinamide adenine dinucleotide phosphate (NADPH)-dependent reduction of thioredoxin and many other physiologically important substrates. Spirulina platensis is a blue-green algae that is often used as a dietary supplement. S. platensis is rich in protein, lipid, polysaccharide, pigment, carotenoid, enzyme, vitamins and many other chemicals and exhibits a variety of pharmacological functions. In the present study, a simple and efficient method to purify TrxR from S. platensis tablets is reported. The extractions were carried out using two different methods: heat denaturation and 2',5'-adenosine diphosphate Sepharose 4B affinity chromatography. The enzyme was purified by 415.04-fold over the crude extract, with a 19% yield, and specific activity of 0.7640 U/mg protein. Optimum pH, temperature and ionic strength of the enzyme activity, as well as the Michaelis constant (Km ) and maximum velocity of enzyme (Vmax ) values for NADPH and 5,5'-dithiobis(2-nitrobenzoic acid) were determined. Tested metal ions, vitamins, and drugs showed inhibition effects, except Se4+ ion, cefazolin sodium, teicoplanin, and tobramycin that increased the enzyme activity in vitro. Ag+ , Cu2+ , Mg2+ , Ni2+ , Pb2+ , Zn2+ , Al3+ , Cr3+ , Fe3+ , and V4+ ions; vitamin B3 , vitamin B6 , vitamin C, and vitamin U and aciclovir, azithromycin, benzyladenine, ceftriaxone sodium, clarithromycin, diclofenac, gibberellic acid, glurenorm, indole-3-butyric acid, ketorolac, metformin, mupirocin, mupirocin calcium, paracetamol, and tenofovir had inhibitory effects on TrxR. Ag+ exhibited stronger inhibition than 1-chloro-2,4-dinitrobenzene (a positive control).

Purification of thioredoxin reductase from Spirulina platensis by affinity chromatography and investigation of kinetic properties.

The thioredoxin system consists of thioredoxin (Trx), thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). Spirulina platensis, which is one of the blue-green algae in the form of spiral rings, belongs to the cyanobacteria class. Spirulina platensis can produce Trx under stress conditions. If it can produce Trx, it also has TrxR activity. Therefore, in this study, the TrxR enzyme was purified for the first time from Spirulina platensis, an algae the most grown and also used as a nutritional supplement in the world. A two-step purification process was used: preparation of the homogenate and 2',5'-ADP sepharose 4B affinity chromatography. The enzyme was purified with a purification fold of 1059.51, a recovery yield of 9.7 %, and a specific activity of 5.77 U/mg protein. The purified TrxR was tested for purity by SDS-PAGE. The molecular weight of its subunit was found to be about 45 kDa. Optimum pH, temperature and ionic strength of the enzyme were pH 7.0, 40 °C and 750 mM in phosphate buffer respectively. The Michaelis constant (Km) and maximum velocity of enzyme (Vmax) values for NADPH and 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) are 5 µM and 2.2 mM, and 0.0033 U/mL and 0.0044 U/mL, respectively. Storage stability of the purified enzyme was determined at several temperatures. The inhibition effects of Ag+, Cu2+, Al3+ and Se4+ metal ions on the purified TrxR activity were investigated in vitro. While Se4+ ion increased the enzyme activity, other tested metal ions showed different type of inhibitory effects on the Lineweaver-Burk graphs.

Novel starting points for fragment-based drug design against mycobacterial thioredoxin reductase identified using crystallographic fragment screening.

The increasing number of people dying from tuberculosis and the existence of extensively drug-resistant strains has led to an urgent need for new antituberculotic drugs with alternative modes of action. As part of the thioredoxin system, thioredoxin reductase (TrxR) is essential for the survival of Mycobacterium tuberculosis (Mtb) and shows substantial differences from human TrxR, making it a promising and most likely selective target. As a model organism for Mtb, crystals of Mycobacterium smegmatis TrxR that diffracted to high resolution were used in crystallographic fragment screening to discover binding fragments and new binding sites. The application of the 96 structurally diverse fragments from the F2X-Entry Screen revealed 56 new starting points for fragment-based drug design of new TrxR inhibitors. Over 200 crystal structures were analyzed using FragMAXapp, which includes processing and refinement by largely automated software pipelines and hit identification via the multi-data-set analysis approach PanDDA. The fragments are bound to 11 binding sites, of which four are positioned at binding pockets or important interaction sites and therefore show high potential for possible inhibition of TrxR.

Identification and characterization of archaeal and bacterial F420 -dependent thioredoxin reductases.

The thioredoxin pathway is an antioxidant system present in most organisms. Electrons flow from a thioredoxin reductase to thioredoxin at the expense of a specific electron donor. Most known thioredoxin reductases rely on NADPH as a reducing cofactor. Yet, in 2016, a new type of thioredoxin reductase was discovered in Archaea which utilize instead a reduced deazaflavin cofactor (F420 H2 ). For this reason, the respective enzyme was named deazaflavin-dependent flavin-containing thioredoxin reductase (DFTR). To have a broader understanding of the biochemistry of DFTRs, we identified and characterized two other archaeal representatives. A detailed kinetic study, which included pre-steady state kinetic analyses, revealed that these two DFTRs are highly specific for F420 H2 while displaying marginal activity with NADPH. Nevertheless, they share mechanistic features with the canonical thioredoxin reductases that are dependent on NADPH (NTRs). A detailed structural analysis led to the identification of two key residues that tune cofactor specificity of DFTRs. This allowed us to propose a DFTR-specific sequence motif that enabled for the first time the identification and experimental characterization of a bacterial DFTR.

Hydrogen peroxide detoxification through the peroxiredoxin/thioredoxin antioxidant system: A look at the pancreatic ß-cell oxidant defense.

Reactive oxygen species (ROS), such as hydrogen peroxide, are formed when molecular oxygen obtains additional electrons, increasing its reactivity. While low concentrations of hydrogen peroxide are necessary for regulation of normal cellular signaling events, high concentrations can be toxic. To maintain this balance between beneficial and deleterious concentrations of hydrogen peroxide, cells utilize antioxidants. Our recent work supports a primary role for peroxiredoxin, thioredoxin, and thioredoxin reductase as the oxidant defense pathway used by insulin-producing pancreatic ß-cells. These three players work in an antioxidant cycle based on disulfide exchange, with oxidized targets ultimately being reduced using electrons provided by NADPH. Peroxiredoxins also participate in hydrogen peroxide-based signaling through disulfide exchange with redox-regulated target proteins. This chapter will describe the catalytic mechanisms of thioredoxin, thioredoxin reductase, and peroxiredoxin and provide an in-depth look at the roles these enzymes play in antioxidant defense pathways of insulin-secreting ß-cells. Finally, we will evaluate the physiological relevance of peroxiredoxin-mediated hydrogen peroxide signaling as a regulator of ß-cell function.

Analysis of Pleurotin binding to human thioredoxin reductase using docking and molecular dynamics simulation.

Thioredoxin reductase (TrxR) has been considered a potential target for cancer chemotherapy. It acts by controlling the redox homeostasis of human cells and, therefore, interfering in its function may trigger apoptosis, which is a crucial tumor suppression mechanism. Despite the great effort in the search for TrxR inhibitors, none was approved for human therapy. In the present study a virtual screening for natural organic compounds is discussed for a set of 72 compounds with known IC-50 for TrxR inhibition. The results suggest the Pleurotin, a naphthoquinone obtained from Hohenbuehelia grisea fungus, as a potential TrxR inhibitor, which acts by binding to the active site of the enzyme, between the N- and C-terminal domains. The presence of the ligand blocks the approximation of the C-terminal arm to the N-terminal, which is an essential step of the enzyme function. Besides, the two equivalent binding sites of TrxR were explored, by docking two ligands simultaneously. The results indicate that both sites have an allosteric correlation and, the presence of the ligand in one site may interfere, or even prevent, the binding of the second ligand at the other site. All these findings are quantitatively discussed based on the analysis of long molecular dynamics trajectories, which provides a full description of the ligand-receptor binding modes, average binding energies and conformational changes.Communicated by Ramaswamy H. Sarma.

Proteomic profiling of Deinococcus radiodurans with response to thioredoxin reductase inhibitor and ionizing radiation treatment.

This study explains the importance of cellular redox system in preserving the proteome of the radioresistant Deinococcus radiodurans. The thioredoxin reductase (TrxR) redox system was inhibited by ebselen (10 µM), and then the bacterium was exposed to 4 kGy of ionizing radiation. The differentially expressed proteins were analyzed using label-free quantitative (LFQ) proteomics. The 4 kGy radiation treatment increases the expression of stress response proteins like osmotically inducible protein OsmC, catalase, and metallophosphoesterase compared to control. Ebselen plus radiation treatment augments oxidoreductases proteins in D. radiodurans. Further, the proteins involved in glycolysis, tricarboxylic acetic acid (TCA) and proteins like proteases, peptidase, and peptide transporters were significantly decreased in the ebselen plus radiation group compared to radiation treated group. Further, ebselen plus radiation treatment increases the ATP-binding cassette (ABC) transporters involved in the efflux of toxic chemicals and nutrient uptake and the stress response related membrane protein like S-layer homology domain-containing protein in D. radiodurans. Thus, the results show that the altered redox status via inhibition of TrxR redox system significantly affects the expression of essential cellular proteins for the survival. The cellular content of D. radiodurans may be used to handle redox imbalances in the normal cells during cancer radiotherapy. SIGNIFICANCE: Deinococcus radiodurans is a popular radioresistance organism with efficient antioxidant systems and DNA repair mechanisms. There are many antioxidant systems and small molecules that responsible for its resistance. The importance of thiol based antioxidant systems in its resistance property has not fully studied yet. Thioredoxin reductase is an important disulfide containing protein that involved in maintaining redox homeostasis. The TrxR inhibition affects the cell survival and synthesis of molecules against ionizing radiation. In this study we are reporting the effects of TrxR inhibitor on proteome of D. radiodurans upon ionizing radiation. This study reveals the significance of TrxR antioxidant system on the proteome of D. radiodurans. The inhibition of TrxR antioxidant system and the subsequent disturbances in the proteome content makes the organism vulnerable to oxidative stress.

Proteome Analysis and In Vitro Antiviral, Anticancer and Antioxidant Capacities of the Aqueous Extracts of Lentinula edodes and Pleurotus ostreatus Edible Mushrooms.

In this study, we examined aqueous extracts of the edible mushrooms Pleurotus ostreatus (oyster mushroom) and Lentinula edodes (shiitake mushroom). Proteome analysis was conducted using LC-Triple TOF-MS and showed the expression of 753 proteins by Pleurotus ostreatus, and 432 proteins by Lentinula edodes. Bioactive peptides: Rab GDP dissociation inhibitor, superoxide dismutase, thioredoxin reductase, serine proteinase and lectin, were identified in both mushrooms. The extracts also included promising bioactive compounds including phenolics, flavonoids, vitamins and amino acids. The extracts showed promising antiviral activities, with a selectivity index (SI) of 4.5 for Pleurotus ostreatus against adenovirus (Ad7), and a slight activity for Lentinula edodes against herpes simplex-II (HSV-2). The extracts were not cytotoxic to normal human peripheral blood mononuclear cells (PBMCs). On the contrary, they showed moderate cytotoxicity against various cancer cell lines. Additionally, antioxidant activity was assessed using DPPH radical scavenging, ABTS radical cation scavenging and ORAC assays. The two extracts showed potential antioxidant activities, with the maximum activity seen for Pleurotus ostreatus (IC50 µg/mL) = 39.46 ± 1.27 for DPPH; 11.22 ± 1.81 for ABTS; and 21.40 ± 2.20 for ORAC assays. This study encourages the use of these mushrooms in medicine in the light of their low cytotoxicity on normal PBMCs vis à vis their antiviral, antitumor and antioxidant capabilities.

Crystal structure of the cofactor-free form of thioredoxin reductase from Acinetobacter baumannii.

Thioredoxin reductase (TrxR) is a central component in the thioredoxin system by involving in catalyzing the reduction of thioredoxin, which is critical for organism survival. Because this system is essential, it is a promising target for novel antimicrobial agents. Herein, we solved the 1.9 Å high-resolution structure of TrxR from Acinetobacter baumannii Thioredoxin reductase (AbTrxR), which is a Gram-negative, pathogenic bacterium and a drug-resistant superbug. AbTrxR was cofactor-free and formed a dimer in solution. AbTrxR contained a longer dimerization loop2 and a shorter ß7 -ß8 connecting loop than other TrxRs. AbTrxR cofactor-free form exhibited a flavin-oxidizing (FO) conformation, whose NADPH domain was located close to the dimeric interface. This structural information might be helpful for development of new antibiotic agents targeting superbugs.

A Fluorescent Probe for the Specific Staining of Cysteine Containing Proteins and Thioredoxin Reductase in SDS-PAGE.

A naphthalimide-based fluorescent probe, Nap-I, with iodoacetamide as the alkylating group, has been synthesized, and its specific fluorescent staining of proteins containing cysteine (Cys) and selenocysteine (Sec) residues in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) has been evaluated. This molecule shows good fluorescence properties in the labeling of protein Cys/Sec residues, while reducing steric hindrance and minimizing changes in the water solubility of proteins. Reaction parameters, such as labeling time and pH, have been investigated, and the optimal labeling conditions for Cys-containing proteins have been determined. Thioredoxin reductase (TXNRD) is best stained at low pH. The probe Nap-I has been successfully used for the quantification of serum proteins and hemoglobin in Tan sheep serum, and TXNRD in Tan sheep liver and muscle has been labeled at low pH. Based on the probe Nap-I, we have also distinguished TXNRD1 and TXNRD2 by SDS-PAGE. The results showed that, compared with the normal microenvironment in which the protein resides, the lower the pH value, the greater the TXNRD activity.

Overview of structurally homologous flavoprotein oxidoreductases containing the low Mr thioredoxin reductase-like fold - A functionally diverse group.

Structural studies show that enzymes have a limited number of unique folds, although structurally related enzymes have evolved to perform a large variety of functions. In this review, we have focused on enzymes containing the low molecular weight thioredoxin reductase (low Mr TrxR) fold. This fold consists of two domains, both containing a three-layer ßßα sandwich Rossmann-like fold, serving as flavin adenine dinucleotide (FAD) and, in most cases, pyridine nucleotide (NAD(P)H) binding-domains. Based on a search of the Protein Data Bank for all published structures containing the low Mr TrxR-like fold, we here present a comprehensive overview of enzymes with this structural architecture. These range from TrxR-like ferredoxin/flavodoxin NAD(P)+ oxidoreductases, through glutathione reductase, to NADH peroxidase. Some enzymes are solely composed of the low Mr TrxR-like fold, while others contain one or two additional domains. In this review, we give a detailed description of selected enzymes containing only the low Mr TrxR-like fold, however, catalyzing a diversity of chemical reactions. Our overview of this structurally similar, yet functionally distinct group of flavoprotein oxidoreductases highlights the fascinating and increasing number of studies describing the diversity among these enzymes, especially during the last decade(s).

Inhibition of thioredoxin reductase (TrxR) triggers oxidative stress-induced apoptosis in filarial nematode Setaria cervi channelized through ASK-1-p38 mediated caspase activation.

Inhibition of an imperative antioxidant enzyme with subsequent death is a victorious and widely accepted strategy to combat various infectious diseases. Among different antioxidant enzymes, thioredoxin reductase (TrxR) is an exclusive one. Studies have revealed that direct inhibition of TrxR by different classes of chemical moieties promptly results in the death of an organism. Especially the structural as well as biochemical modifications of the enzyme upon inhibition project serious threat towards the subject organism. Herein, an attempt was made to inhibit TrxR of filarial species by administering Auranofin, 1 chloro 2,4 dinitrobenzene (CDNB), Curcumin, and a novel carbamo dithioperoxo(thioate) derivative (4a). Our study has revealed that inhibition of TrxR resulted in the induction of the classical CED pathway of apoptosis along with the intrinsic and extrinsic pathways of apoptosis (Caspase mediated) routed through the ASK-1/p38 axis. Druggability analysis of filarial TrxR for the selected compounds was performed in silico through molecular docking studies. Therefore, this study attempts to decipher the mechanism of apoptosis induction following TrxR inhibition. The safety of those four compounds in terms of dose and toxicity was taken under consideration. Thitherto, the mechanism of TrxR mediated initiation of cell death in filarial parasite has remained undercover, and therefore, it is a maiden report on the characterization of apoptosis induction upon TrxR inhibition which will eventually help in generating effective antifilarial drugs in the future.

Functional metagenomics of the thioredoxin superfamily.

Environmental sequence data of microbial communities now makes up the majority of public genomic information. The assignment of a function to sequences from these metagenomic sources is challenging because organisms associated with the data are often uncharacterized and not cultivable. To overcome these challenges, we created a rationally designed expression library of metagenomic proteins covering the sequence space of the thioredoxin superfamily. This library of 100 individual proteins represents more than 22,000 thioredoxins found in the Global Ocean Sampling data set. We screened this library for the functional rescue of Escherichia coli mutants lacking the thioredoxin-type reductase (ΔtrxA), isomerase (ΔdsbC), or oxidase (ΔdsbA). We were able to assign functions to more than a quarter of our representative proteins. The in vivo function of a given representative could not be predicted by phylogenetic relation but did correlate with the predicted isoelectric surface potential of the protein. Selected proteins were then purified, and we determined their activity using a standard insulin reduction assay and measured their redox potential. An unexpected gel shift of protein E5 during the redox potential determination revealed a redox cycle distinct from that of typical thioredoxin-superfamily oxidoreductases. Instead of the intramolecular disulfide bond formation typical for thioredoxins, this protein forms an intermolecular disulfide between the attacking cysteines of two separate subunits during its catalytic cycle. Our functional metagenomic approach proved not only useful to assign in vivo functions to representatives of thousands of proteins but also uncovered a novel reaction mechanism in a seemingly well-known protein superfamily.

Can Selenoenzymes Resist Electrophilic Modification? Evidence from Thioredoxin Reductase and a Mutant Containing α-Methylselenocysteine.

Selenocysteine (Sec) is the 21st proteogenic amino acid in the genetic code. Incorporation of Sec into proteins is a complex and bioenergetically costly process that evokes the following question: "Why did nature choose selenium?" An answer that has emerged over the past decade is that Sec confers resistance to irreversible oxidative inactivation by reactive oxygen species. Here, we explore the question of whether this concept can be broadened to include resistance to reactive electrophilic species (RES) because oxygen and related compounds are merely a subset of RES. To test this hypothesis, we inactivated mammalian thioredoxin reductase (Sec-TrxR), a mutant containing α-methylselenocysteine [(αMe)Sec-TrxR], and a cysteine ortholog TrxR (Cys-TrxR) with various electrophiles, including acrolein, 4-hydroxynonenal, and curcumin. Our results show that the acrolein-inactivated Sec-TrxR and the (αMe)Sec-TrxR mutant could regain 25% and 30% activity, respectively, when incubated with 2 mM H2O2 and 5 mM imidazole. In contrast, Cys-TrxR did not regain activity under the same conditions. We posit that Sec enzymes can undergo a repair process via ß-syn selenoxide elimination that ejects the electrophile, leaving the enzyme in the oxidized selenosulfide state. (αMe)Sec-TrxR was created by incorporating the non-natural amino acid (αMe)Sec into TrxR by semisynthesis and allowed for rigorous testing of our hypothesis. This Sec derivative enables higher resistance to both oxidative and electrophilic inactivation because it lacks a backbone Cα-H, which prevents loss of selenium through the formation of dehydroalanine. This is the first time this unique amino acid has been incorporated into an enzyme and is an example of state-of-the-art protein engineering.

Chemistry and Chemical Biology of Selenenyl Sulfides and Thioseleninic Acids.

Significance: Selenenyl sulfides (RSeSRs) and thioseleninic acids (RSeSHs) are the monoselenium (Se) analogs of disulfides and persulfides that contain Se-S bonds. These bonds are found in several antioxidant-regenerating enzymes as derivatives of selenocysteine, making them an important player in redox biology as it pertains to sulfur redox regulation. Recent Advances: Mechanistic studies of redox-regulating selenoenzymes such as thioredoxin reductase and glutathione peroxidase suggest crucial Se-S bonds in the active sites. Peptide models and small-molecule mimics of these active sites have been prepared to study their fundamental chemistry. These advances help pave the road to better understand the functions of the Se-S bond in the body. Critical Issues: The Se-S bond is unstable at atmospheric temperatures and pressures. Therefore, studying their properties proposes a major challenge. Currently, there are no trapping reagents specific to RSeSRs or RSeSHs, making their presence, identity, and fates in biological environments difficult to track. Future Directions: Further understanding of the fundamental chemistry/biochemistry of RSeSRs and RSeSHs is needed to understand what their intracellular targets are and to what extent they impact signaling. Besides antioxidant regeneration and peroxide radical reduction, the roles of RSeSR and RSeSHs in other systems need to be further explored.

A Gold(I) Complex Containing an Oleanolic Acid Derivative as a Potential Anti-Ovarian-Cancer Agent by Inhibiting TrxR and Activating ROS-Mediated ERS.

Many cancer cells critically rely on antioxidant systems for cell survival and are vulnerable to further oxidative impairment triggered by agents generating reactive oxygen species (ROS). Therefore, the classical design and development of inhibitors that target antioxidant defense enzymes such as thioredoxin reductase (TrxR) can be a promising anticancer strategy. Herein, it is shown that a gold(I) complex containing an oleanolic acid derivative (4 b) induces apoptosis of ovarian cancer A2780 cells by activating endoplasmic reticulum stress (ERS). It can inhibit TrxR enzyme activity to elevate ROS, mediate ERS and mitochondrial dysfunction, and finally leads to cell cycle arrest and apoptosis of A2780 cells. Notably, this complex inhibits A2780 xenograft tumor growth accompanied by increased ERS level and decreased TrxR activity in tumor tissues.

The Thioredoxin System: A Promising Target for Cancer Drug Development.

The thioredoxin system is highly conserved system found in all living cells and comprises NADPH, thioredoxin, and thioredoxin reductase. This system plays a critical role in preserving a reduced intracellular environment, and its involvement in regulating a wide range of cellular functions makes it especially vital to cellular homeostasis. Its critical role is not limited to healthy cells, it is also involved in cancer development, and is overexpressed in many cancers. This makes the thioredoxin system a promising target for cancer drug development. As such, over the last decade, many inhibitors have been developed that target the thioredoxin system, most of which are small molecules targeting the thioredoxin reductase C-terminal redox center. A few inhibitors of thioredoxin have also been developed. We believe that more efforts should be invested in developing protein/peptide-based inhibitors against both thioredoxin reductase and/or thioredoxin.

Cytotoxic Ag(I) and Au(I) NHC-carbenes bind DNA and show TrxR inhibition.

A silver(I) and a gold(I) complex of the fluorescent N-heterocyclic carbenic (NHC) ligand 1-(9-anthracenylmethyl)-3-(3-trimethylsilyl-2-propynil)-benzimidazol-2-ylidene have been synthesized and characterized. These compounds show cytotoxicity in the micromolar range and higher antiproliferative properties than cisplatin (CDDP) against several tumour cell lines such as SW480 (colon), A549 (lung) and HepG2 (liver). Both metal complexes are successfully internalized by SW480 cells being the silver compound the most accumulated. Subsequently, they were evaluated as inhibitors of the selenoenzyme Thioredoxin reductase (TrxR) and as DNA binders. Fluorescence microscopy confirmed that both protein and DNA binding could be involved in the biological activity of the compounds. The silver carbene was the most effective enzyme inhibitor with an IC50 in the nanomolar range. Also, interaction studies with natural double stranded DNA highlight a strong stabilisation of the double helix after binding to the Ag(I) carbene, indicating its potential suitability as dual-targeting anticancer active molecule.

A review on the druggability of a thiol-based enzymatic antioxidant thioredoxin reductase for treating filariasis and other parasitic infections.

Understanding and elucidating the mechanism of host-pathogen interactions are the major area of interest among the Parasitologists all around the globe. Starting from the origin on mother earth parasites have searched for successful strategies to invade their respective host for the sake of survivability and eventually succeeded to manage in the unfriendly environment inside the host's body. Parasite-generated antioxidants are potent enough to combat the oxidative challenges inside the host body and within its own as well. Antioxidant enzymes are tremendously important as they are directly related to the survival of the parasites. The thiol-based antioxidant enzymes (glutathione reductase and thioredoxin reductase) have dragged much attention of the researchers to date. In this regard, among the thiol-based antioxidants, particularly the Thioredoxin reductase (TrxR), is known to be present in a number of parasitic organisms have pulled the researchers. Therefore, selective targeting of TrxR can emerge as a novel capital for developing suitable adulticidal candidate for treating filariasis and other helminth infections. This review tries to assemble the existing knowledge of the parasitic TrxR and how these can be utilized as a druggable target in cases of filariasis and other helminth infections has been discussed.