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• This is the first study on phytochemical profiling and enzyme inhibitory activities of C. corymbosum extracts. • Chlorogenic acid, rutin, and quercitrin were major compounds in the extracts. • The extracts have antioxidant and cytotoxic activities. • The extracts showed significant inhibitory effects on α-glucosidase and thioredoxin reductase. Cardopatium corymbosum (L.) Pers. (Asteraceae) has been used ethnomedicinally against intestinal worms, for skin diseases, and in wound treatment. This study investigated the phytochemical profile and biological activities of ethanol (CCE), methanol (CCM), and water (CCW) extracts of C. corymbosum. LC-MS/MS analysis revealed the presence of various metabolites. Antioxidant activities of the extracts were determined by measuring 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activities and ferric-reducing power (FRAP). The cytotoxicity against human breast cancer (MCF-7) and human umbilical vein endothelial (HUVEC) cell lines were determined using the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay. Enzyme inhibitory activities against α-amylase, α-glucosidase, acetylcholinesterase (AChE), butyrylcholinesterase (BChE), thioredoxin reductase (TrxR), and elastase were measured to assess potential antidiabetic, anti-Alzheimer's, anticancer, and antiaging/wound healing effects. CCM exhibited the highest total phenolic and flavonoid contents and antioxidant activity. Fumaric acid, chlorogenic acid, vanillic acid, and rutin were identified as major components in CCM. C. corymbosum extracts, particularly those from CCE and CCM, displayed significant cytotoxicity on MCF-7 cells while exhibiting lower toxicity towards HUVEC cells. Notably, CCM demonstrated potent α-glucosidase inhibitory activity, while no α-amylase inhibition was observed. All extracts showed weak inhibition of AChE, BChE, and elastase. Conversely, the extracts displayed moderate TrxR inhibitory activity. These findings suggest that C. corymbosum possesses significant antioxidant, enzyme inhibitory, and cytotoxic potential, highlighting its promise as a source of novel bioactive molecules. [ABSTRACT FROM AUTHOR]

Introduction Methods Results Conclusions Filifactor alocis is a newly appreciated member of the periodontal community with a strong periodontal disease correlation. Little is known about the survival mechanisms by which F. alocis copes with oxidative stress and establishes the infection within the local inflammatory microenvironment of the periodontal pocket. The aim of this study is to investigate if F. alocis putative peroxiredoxin/AhpC protein FA768 may constitute an alkyl hydroperoxide reductase system utilizing putative thioredoxin reductase protein FA608, and putative thioredoxin/glutaredoxin homolog FA1411/FA455.FA768, FA608, FA1411 and FA455 proteins from F. alocis were expressed and purified from Escherichia coli. Insulin and 5,5‐dithio‐bis‐2‐nitrobenzoic acid (DTNB) reduction assays were performed to determine if purified FA1411 and FA455 proteins could be a substrate for FA608. The peroxidase activity of FA768 was examined by measuring its ability to reduce hydrogen peroxide (H2O2) with FA608 and FA1411/FA455 provided as the reducing systems. Further, the hydroperoxide substrate specificity of FA768 was analyzed by monitoring the NADPH oxidation in the presence of different peroxides, including H2O2, cumyl hydroperoxide (CHP), and tert‐butyl hydroperoxide (t‐BHP).In this study, we have demonstrated the existence of a functioning thioredoxin‐dependent alkyl hydroperoxide system in F. alocis. This system is comprised of a thioredoxin reductase (FA608), a thioredoxin/glutaredoxin homolog (FA1411/FA455), and a typical 2‐cysteine peroxiredoxin/AhpC (FA768). FA608, together with FA1411/FA455, can function as a thioredoxin reductase system to reduce insulin, DTNB, and FA768. FA455 is a glutaredoxin‐like protein with thioredoxin functions in F. alocis. Both the FA768/FA608/FA1411 and FA768/FA608/FA455 reductase systems were NADPH‐dependent and exhibited specificity for broad hydroperoxide substrates H2O2, CHP, and t‐BHP.This is the first study of a thioredoxin dependent alkyl hydroperoxide system from a periodontal pathogen. This system is proposed to protect F. alocis against oxidative stress due to the likely absence of a catalase or an additional peroxiredoxin homolog. [ABSTRACT FROM AUTHOR]

Simple Summary: The utilisation of oxygen for cellular respiration and other metabolic pathways in aerobic organisms is inherently associated with the production of reactive oxygen species, a group of highly reactive and oxidising small molecules. Reactive oxygen species can cause oxidative modifications of biomolecules and cellular components, thus compromising their native structure and biological functions. The role of the antioxidant defence is to tightly control levels of reactive species by connecting diverse antioxidant small molecules and antioxidant enzymes. This review summarises the actual knowledge on the role of the crucial part of the antioxidant system in insects termed the thioredoxin system. It is composed of redox-active protein thioredoxin, which interacts with and reduces the oxidised forms of multiple proteins. It is assisted by the enzyme thioredoxin reductase, catalysing the reductive regeneration of thioredoxins. Recent advances have uncovered how the functions of the thioredoxin system extend beyond its primary function in controlling the cell redox state to diverse developmental processes and the regulation of stress and immune responses. Increased levels of reactive oxygen species (ROS) produced during aerobic metabolism in animals can negatively affect the intracellular redox status, cause oxidative stress and interfere with physiological processes in the cells. The antioxidant defence regulates ROS levels by interplaying diverse enzymes and non-enzymatic metabolites. The thioredoxin system, consisting of the enzyme thioredoxin reductase (TrxR), the redox-active protein thioredoxin (Trx) and NADPH, represent a crucial component of antioxidant defence. It is involved in the signalling and regulation of multiple developmental processes, such as cell proliferation or apoptotic death. Insects have evolved unique variations of TrxR, which resemble mammalian enzymes in overall structure and catalytic mechanisms, but the selenocysteine–cysteine pair in the active site is replaced by a cysteine–cysteine pair typical of bacteria. Moreover, the role of the thioredoxin system in insects is indispensable due to the absence of glutathione reductase, an essential enzyme of the glutathione system. However, the functions of the Trx system in insects are still poorly characterised. In the present review, we provide a critical overview of the current knowledge on the insect Trx system, focusing mainly on TrxR's role in the antioxidant and immune system of model insect species. [ABSTRACT FROM AUTHOR]

Background: Selenium and zinc are essential trace elements known to regulate cellular processes including redox homeostasis. During inflammation, circulating selenium and zinc concentrations are reduced in parallel, but underlying mechanisms are unknown. Accordingly, we modulated the zinc and selenium supply of HepG2 cells to study their relationship. Methods: HepG2 cells were supplied with selenite in combination with a short- or long-term zinc treatment to investigate intracellular concentrations of selenium and zinc together with biomarkers describing their status. In addition, the activation of the redox-sensitive transcription factor NRF2 was analyzed. Results: Zinc not only increased the nuclear translocation of NRF2 after 2 to 6 h but also enhanced the intracellular selenium content after 72 h, when the cells were exposed to both trace elements. In parallel, the activity and expression of the selenoprotein thioredoxin reductase 1 (TXNRD1) increased, while the gene expression of other selenoproteins remained unaffected or was even downregulated. The zinc effects on the selenium concentration and TXNRD activity were reduced in cells with stable NRF2 knockdown in comparison to control cells. Conclusions: This indicates a functional role of NRF2 in mediating the zinc/selenium crosstalk and provides an explanation for the observed unidirectional behavior of selenium and zinc. [ABSTRACT FROM AUTHOR]

Glioblastoma (GBM) is an incurable primary brain cancer characterized by increased reactive oxygen species (ROS) production. The redox-sensitive tumor suppressor gene TP53, wild-type (wt) for 70% of patients, regulates redox homeostasis. Glioblastoma stem cells (GSCs) increase thioredoxin (Trx) and glutathione (GSH) antioxidant systems as survival redox-adaptive mechanisms to maintain ROS below the cytotoxic threshold. Auranofin, an FDA-approved anti-rheumatoid drug, inhibits thioredoxin reductase 1 (TrxR1). L-buthionine sulfoximine (L-BSO) and the natural product piperlongumine (PPL) inhibit the GSH system. We evaluated the cytotoxic effects of Auranofin alone and in combination with L-BSO or PPL in GBM cell lines and GSCs with a known TP53 status. The Cancer Genome Atlas/GBM analysis revealed a significant positive correlation between wtp53 and TrxR1 expression in GBM. Auranofin induced ROS-dependent cytotoxicity within a micromolar range in GSCs. Auranofin decreased TrxR1 expression, AKT (Ser-473) phosphorylation, and increased p53, p21, and PARP-1 apoptotic cleavage in wtp53-GSCs, while mutant-p53 was decreased in a mutant-p53 GSC line. Additionally, p53-knockdown in a wtp53-GSC line decreased TrxR1 expression and significantly increased sensitivity to Auranofin, suggesting the role of wtp53 as a negative redox-sensitive mechanism in response to Auranofin in GSCs. The combination of Auranofin and L-BSO synergistically increased ROS, decreased IC50s, and induced long-term cytotoxicity irrespective of p53 in GBM cell lines and GSCs. Intriguingly, Auranofin increased the expression of glutathione S-transferase pi-1 (GSTP-1), a target of PPL. Combining Auranofin with PPL synergistically decreased IC50s to a nanomolar range in GSCs, supporting the potential to repurpose Auranofin and PPL in GBM. [ABSTRACT FROM AUTHOR]

Lung cancer is a leading cause of cancer-related death worldwide that needs updated therapies to contrast both the serious side effects and the occurrence of drug resistance. A panel of non-small cell lung cancer (NSCLC) cells were herein employed as cancer models. Eight structurally related gold(I) and gold(III) complexes with NHC and halides or triphenylphosphane ligands were investigated as lung cancer cell growth inhibitors. As expected, gold compounds with PPh3 were found to be more cytotoxic than homoleptic [(NHC)2-Au(I)]X or heteroleptic NHC-Au(I)X or NHC-Au(III)X3 complexes. Mixed ligand gold(I) compounds exhibiting the linear NHC-AuPPh3 (compound 7) or the trigonal NHC-Au(Cl)PPh3 (compound 8) arrangements at the central metal were found to be the best lung cancer cytotoxic compounds. Analysis of the TrxR residual activity of the treated cells revealed that these compounds efficiently inhibit the most accredited molecular target for gold compounds, the TrxR, with compound 8 reaching more than 80% activity reduction in lung cells. Some of the current cancer lung therapy protocols consist of specific lung cancer cell cytotoxic agents combined with antifolate drugs; interestingly, the herein gold compounds are both TrxR and antifolate inhibitors. The human DHFR was inhibited with IC50 ranging between 10–21 µM, depending on substrate concentrations, proceeding by a likely allosteric mechanism only for compound 8. [ABSTRACT FROM AUTHOR]

Hepatocellular carcinoma (HCC), the predominant type of liver cancer, is an aggressive malignancy with limited therapeutic options. In this study, we assess a collection of newly designed gold(I) phosphine complexes. Remarkably, the compound GC002 exhibits the greatest toxicity to HCC cells and outperforms established medications, such as sorafenib and auranofin, in terms of antitumor efficacy. GC002 triggers irreversible necroptosis in HCC cells by increasing the intracellular accumulation of reactive oxygen species (ROS). Mechanistically, GC002 significantly suppresses the activity of thioredoxin reductase (TrxR), which plays a crucial role in regulating redox homeostasis and is often overexpressed in HCC by binding directly to the enzyme. Our in vivo xenograft study confirms that GC002 possesses remarkable antitumor activity against HCC without severe side effects. These findings not only highlight the novel mechanism of controlling necroptosis via TrxR and ROS but also identify GC002 as a promising candidate for the further development of antitumor agents targeting HCC.

Chuanjiang Dong,1,* Yueqing Wang,2,3,* Yi Cai,4,* Yuhuang Wu,2,3 Wei Chen,2,3 Lu Wang,2,3 Xiaowen Liu,2 Lili Zou,2,3 Jun Wang5 1Department of Urology, The First Dongguan Affiliated Hospital, Guangdong Medical University, Dongguan, Guangdong province, 523718, People’s Republic of China; 2Hubei Key Laboratory of Tumor Microenvironment and Immunotherapy, College of Basic Medical Science, China Three Gorges University, Yichang, Hubei Province, 443002, People’s Republic of China; 3Yichang Key Laboratory of Infection and Inflammation, College of Basic Medical Science, China Three Gorges University, Yichang, Hubei Province, 443002, People’s Republic of China; 4Department of Laboratory Medicine, Xiaogan Central Hospital, Xiaogan, Hubei Province, 432099, People’s Republic of China; 5The Second People’s Hospital of China Three Gorges University, Yichang, Hubei Province, 443002, People’s Republic of China*These authors contributed equally to this workCorrespondence: Lili Zou; Jun Wang, Email zoulili@ctgu.edu.cn; wangjfox@ctgu.edu.cnPurpose: Tuberculosis (TB) remains a major health threat worldwide, and the spread of drug-resistant (DR) TB impedes the reduction of the global disease burden. Ebselen (EbSe) targets bacterial thioredoxin reductase (bTrxR) and causes an imbalance in the redox status of bacteria. Previous work has shown that the synergistic action of bTrxR and sensitization to common antibiotics by EbSe is a promising strategy for the treatment of DR pathogens. Thus, we aimed to evaluate whether EbSe could enhance anti-TB drugs against Mycobacterium marinum (M. marinum) which is genetically related to Mycobacterium tuberculosis (Mtb) and resistant to many antituberculosis drugs.Methods: Minimum inhibitory concentrations (MIC) of isoniazid (INH), rifampicin (RFP), and streptomycin (SM) against M. marinum were determined by microdilution. The Bliss Independence Model was used to determine the adjuvant effects of EbSe over the anti-TB drugs. Thioredoxin reductase activity was measured using the DTNB assay, and its effects on bacterial redox homeostasis were verified by the elevation of intracellular ROS levels and intracellular GSH levels. The adjuvant efficacy of EbSe as an anti-TB drug was further evaluated in a mouse model of M. marinum infection. Cytotoxicity was observed in the macrophage cells Raw264.7 and mice model.Results: The results reveal that EbSe acts as an antibiotic adjuvant over SM on M. marinum. EbSe + SM disrupted the intracellular redox microenvironment of M. marinum by inhibiting bTrxR activity, which could rescue mice from the high bacterial load, and accelerated recovery from tail injury with low mammalian toxicity.Conclusion: The above studies suggest that EbSe significantly enhanced the anti-Mtb effect of SM, and its synergistic combination showed low mammalian toxicity in vitro and in vivo. Further efforts are required to study the underlying mechanisms of EbSe as an antibiotic adjuvant in combination with anti-TB drug MS.Keywords: Ebselen, antibiotic adjuvant, thioredoxin reductase, reactive oxygen species

Elevated cellular oxidative stress is a common marker of cancer cell dysregulation caused by malignant transformation. Thioredoxin reductase (TrxR, encoded by TXNRD) is a crucial enzyme that regulates cellular oxidative stress and the survival of many types of cancer cells. Therefore, targeting TrxR may lead to selective cell death in cancer cells. Pristimerin, a plant triterpenoid, increases the accumulation of reactive oxygen species (ROS) in cells, but its specific regulatory mechanism is unclear. Herein, we found that pristimerin selectively targets TrxR and subsequently induces apoptosis in human non-small cell lung cancer cells, and inhibits tumor growth in vivo with low toxicity to normal cells. Pristimerin was found to inhibit cancer cell growth primarily by inhibiting cellular TrxR, thereby compromising TrxR’s antioxidant function in cells and resulting in the accumulation of oxidized Trx. Furthermore, excessive ROS accumulation stimulated by pristimerin triggered tumor-specific amplification of oxidative stress in cancer cells and ultimately led to targeted destruction of cancer cells. Our data may support the development of potential therapeutic molecules as selective anticancer agents targeting highly enriched TrxR in cancer cells.

This study investigates the activity of novel gold(I) and copper(I)/zinc(II) heteronuclear complexes against colon cancer. The synthesised heteronuclear Au(I)-Cu(I) and Au(I)-Zn(II) complexes were characterised and evaluated for their anticancer activity using human colon cancer cell lines (Caco-2). The complexes exhibited potent cytotoxicity, with IC50 values in the low micromolar range, and effectively induced apoptosis in cancer cells. In the case of complex [Cu{Au(Spy)(PTA)}2]PF6 (2), its cytotoxicity is ×10 higher than its mononuclear precursor, while showing low cytotoxicity towards differentiated healthy cells. Mechanistic studies revealed that complex 2 inhibits the activity of thioredoxin reductase, a key enzyme involved in redox regulation, leading to an increase in reactive oxygen species (ROS) levels and oxidative stress, in addition to an alteration in DNA's tertiary structure. Furthermore, the complexes demonstrated a strong binding affinity to bovine serum albumin (BSA), suggesting the potential for effective drug delivery and bioavailability. Collectively, these findings highlight the potential of the investigated heteronuclear Au(I)-Cu(I) and Au(I)-Zn(II) complexes as promising anticancer agents, particularly against colon cancer, through their ability to disrupt redox homeostasis and induce oxidative stress-mediated cell death. [ABSTRACT FROM AUTHOR]

Auranofin (AF) is a gold-based compound with a well-known pharmacological and toxicological profile, currently used in the treatment of some severe forms of rheumatoid arthritis. Over the last twenty years, AF has also been repurposed as antiviral, antitumor, and antibacterial drug. In this review we focused on the antibacterial properties of AF, specifically researching the minimal inhibitory concentrations (MIC) of AF in both mono- and diderm bacteria reported so far in literature. AF proves to be highly effective against monoderm bacteria, while diderm are far less susceptible, probably due to the outer membrane barrier. We also reported the current mechanistic hypotheses concerning the antimicrobial properties of AF, although a conclusive description of its antibacterial mode of action is not yet available. Even if its mechanism of action has not been fully elucidated yet and further studies are required to optimize its delivery strategy, AF deserves additional investigation because of its unique mode of action and high efficacy against a wide range of pathogens, which could lead to potential applications in fighting antimicrobial resistance and improving therapeutic outcomes in infectious diseases. [ABSTRACT FROM AUTHOR]

According to the World Health Organization (WHO), breast cancer (BC) is the deadliest and the most common type of cancer worldwide in women. Several factors associated with BC exert their effects by modulating the state of stress. They can induce genetic mutations or alterations in cell growth, encouraging neoplastic development and the production of reactive oxygen species (ROS). ROS are able to activate many signal transduction pathways, producing an inflammatory environment that leads to the suppression of programmed cell death and the promotion of tumor proliferation, angiogenesis, and metastasis; these effects promote the development and progression of malignant neoplasms. However, cells have both non-enzymatic and enzymatic antioxidant systems that protect them by neutralizing the harmful effects of ROS. In this sense, antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), thioredoxin reductase (TrxR), and peroxiredoxin (Prx) protect the body from diseases caused by oxidative damage. In this review, we will discuss mechanisms through which some enzymatic antioxidants inhibit or promote carcinogenesis, as well as the new therapeutic proposals developed to complement traditional treatments. [ABSTRACT FROM AUTHOR]

Salmonella enterica serovar Gallinarum biovar Gallinarum (SG) causes fowl typhoid, a notifiable infectious disease in poultry. However, the pathogenic mechanism of SG-induced systemic infection in chickens remains unclear. Thioredoxin reductase (TrxB) is a redox protein crucial for regulating various enzyme activities in Salmonella serovar, but the role in SG-induced chicken systemic infection has yet to be determined. Here, we constructed a mutant SG strain lacking the trxB gene (trxB::Cm) and used chicken embryo inoculation and chicken oral infection to investigate the role of trxB gene in the pathogenicity of SG. Our results showed that trxB::Cm exhibited no apparent differences in colony morphology and growth conditions but exhibited reduced tolerance to H2O2 and increased resistance to bile acids. In the chicken embryo inoculation model, there was no significant difference in the pathogenicity of trxB::Cm and wild-type (WT) strains. In the chicken oral infection, the WT-infected group exhibited typical clinical symptoms of fowl typhoid, with complete mortality between days 6 and 9 post infection. In contrast, the trxB::Cm group showed a 100% survival rate, with no apparent clinical symptoms or pathological changes observed. The viable bacterial counts in the liver and spleen of the trxB::Cm-infected group were significantly reduced, accompanied by decreased expression of cytokines and chemokines (IL-1β, IL-6, IL-12, CXCLi1, TNF-α, and IFN-γ), which were significantly lower than those in the WT group. These results show that the pathogenicity of the trxB-deficient strain was significantly attenuated, indicating that the trxB gene is a crucial virulence factor in SG-induced systemic infection in chickens, suggesting that trxB may become a potentially effective target for controlling and preventing SG infection in chickens. [ABSTRACT FROM AUTHOR]

ABSTRACT While highly effective at killing Gram-positive bacteria, auranofin lacks significant activity against Gram-negative species for reasons that largely remain unclear. Here, we aimed to elucidate the molecular mechanisms underlying the low susceptibility of the Gram-negative model organism Escherichia coli to auranofin when compared to the Gram-positive model organism Bacillus subtilis. The proteome response of E. coli exposed to auranofin suggests a combination of inactivation of thiol-containing enzymes and the induction of systemic oxidative stress. Susceptibility tests in E. coli mutants lacking proteins upregulated upon auranofin treatment suggested that none of them are directly involved in E. coli’s high tolerance to auranofin. E. coli cells lacking the efflux pump component TolC were more sensitive to auranofin treatment, but not to an extent that would fully explain the observed difference in susceptibility of Gram-positive and Gram-negative organisms. We thus tested whether E. coli’s thioredoxin reductase (TrxB) is inherently less sensitive to auranofin than TrxB from B. subtilis, which was not the case. However, E. coli strains lacking the low-molecular-weight thiol glutathione, but not glutathione reductase, showed a high susceptibility to auranofin. Bacterial cells expressing the genetically encoded redox probe roGFP2 allowed us to observe the oxidation of cellular protein thiols in situ. Based on our findings, we hypothesize that auranofin leads to a global disturbance in the cellular thiol redox homeostasis in bacteria, but Gram-negative bacteria are inherently more resistant due to the presence of drug export systems and high cellular concentrations of glutathione.IMPORTANCEAuranofin is an FDA-approved drug for the treatment of rheumatoid arthritis. However, it has also high antibacterial activity, in particular against Gram-positive organisms. In the current antibiotics crisis, this would make it an ideal candidate for drug repurposing. However, its much lower activity against Gram-negative organisms prevents its broad-spectrum application. Here we show that, on the level of the presumed target, there is no difference in susceptibility between Gram-negative and Gram-positive species: thioredoxin reductases from both Escherichia coli and Bacillus subtilis are equally inhibited by auranofin. In both species, auranofin treatment leads to oxidative protein modification on a systemic level, as monitored by proteomics and the genetically encoded redox probe roGFP2. The single largest contributor to E. coli’s relative resistance to auranofin seems to be the low-molecular-weight thiol glutathione, which is absent in B. subtilis and other Gram-positive species.

Thioredoxin Reductase (TrxR) functions to recycle thioredoxin (Trx) during hydroperoxide metabolism mediated by peroxiredoxins and is currently being targeted using the FDA-approved anti-rheumatic drug, auranofin (AF), to selectively sensitize cancer cells to therapy. AF treatment decreased TrxR activity and clonogenic survival in small cell lung cancer (SCLC) cell lines (DMS273 and DMS53) as well as the H727 atypical lung carcinoid cell line. AF treatment also significantly sensitized DMS273 and H727 cell lines in vitro to sorafenib, an FDA-approved multi-kinase inhibitor that depleted intracellular glutathione (GSH). The pharmacokinetic, pharmacodynamic, and safety profile of AF was examined in nude mice with DMS273 xenografts administered AF intraperitoneally at 2 mg/kg or 4 mg/kg (IP) once (QD) or twice daily (BID) for 1−5 d. Plasma levels of AF were 10–20 μM (determined by mass spectrometry of gold), and the optimal inhibition of TrxR activity was obtained at 4 mg/kg once daily, with no effect on glutathione peroxidase 1 activity. This AF treatment extended for 14 d, inhibited TrxR (>75%), and resulted in a significant prolongation of median overall survival from 19 to 23 d (p = .04, N = 30 controls, 28 AF). In this experiment, there were no observed changes in animal bodyweight, complete blood counts (CBCs), bone marrow toxicity, blood urea nitrogen, or creatinine. These results support the hypothesis that AF effectively inhibits TrxR both in vitro and in vivo in SCLC, sensitizes NETs and SCLC to sorafenib, and could be repurposed as an adjuvant therapy with targeted agents that induce disruptions in thiol metabolism.

Alzheimer's disease (AD) is the most common form of dementia and a public health problem. It exhibits significant oxidative stress and redox alterations. The antioxidant enzyme systems defend the cellular environment from oxidative stress. One of the redox systems is the thioredoxin system (TS), which exerts decisive control over the cellular redox environment. We aimed to review the protective effects of TS, which include thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH. In the following, we discussed the physiological functioning and the role of the TS in maintaining the cellular redox-homeostasis in the AD-damaged brain. Trx protects the cellular environment from oxidative stress, while TrxR is crucial for the cellular detoxification of reactive oxygen species in the brain. However, TS dysregulation increases the susceptibility to cellular death. The changes in Trx and TrxR levels are significantly associated with AD progression. Though the data from human, animal, and cellular models support the neuroprotective role of TS in the brain of AD patients, the translational potential of these findings to clinical settings is not yet applied. This review summarizes the current knowledge on the emerging role of the TrxR-Trx system in AD. [ABSTRACT FROM AUTHOR]

A dinuclear gold(I) complex featuring a strongly donating bis‐N‐heterocyclic imine ligand was synthesised and characterised by different methods, including single crystal X‐ray diffraction (SC‐XRD) analysis. The compound has been tested for its antiproliferative effects in a panel of human cancer cell lines in vitro, showing highly selective anticancer effects, particularly against human A549 non‐small cell lung cancer cells (NSCLC), with respect to non‐tumorigenic cells (VERO). The accumulation of the compound in A549 and VERO cells was studied by high‐resolution continuum source atomic absorption spectrometry (HRCS‐AAS), revealing that the anticancer effects are not particularly related to the different amounts of gold taken up by the cells over 72 h. Enzyme inhibition studies to evaluate the activity of the seleno‐enzyme thioredoxin reductase (TrxR) in cancer cell extracts show that the gold(I) compound is a potent inhibitor (IC50=0.567±0.208 μM), while the free ligand is ineffective. This result correlates with the observed compound's selectivity towards A549 cells overexpressing the enzyme. [ABSTRACT FROM AUTHOR]

Simple Summary: This article reviews the biological importance of the Thioredoxin-1 system in different cells and organs. Redox balance, defined by an equilibrium between oxidized and reduced molecules, is crucial for proper cellular functions in health. Disruption of this balance may lead to cell death. Oxidation and reduction of cysteine residues in key signaling molecules changes their structural conformation and function. Thioredoxin-1 is a key regulatory protein that is used as a buffer to maintain the proteins in their optimal shape. In this review, we specifically focus on transgenic animal models related to the Thioredoxin-1 system. This review aims to showcase the specific roles of the Thioredoxin-1 system in maintaining balance in various organs and cell types. Redox balance is increasingly identified as a major player in cellular signaling. A fundamentally simple reaction of oxidation and reduction of cysteine residues in cellular proteins is the central concept in this complex regulatory mode of protein function. Oxidation of key cysteine residues occurs at the physiological levels of reactive oxygen species (ROS), but they are reduced by a supply of thiol antioxidant molecules including glutathione, glutaredoxin, and thioredoxin. While these molecules show complex compensatory roles in experimental conditions, transgenic animal models provide a comprehensive picture to pinpoint the role of each antioxidant. In this review, we have specifically focused on the available literature on thioredoxin-1 system transgenic models that include thioredoxin and thioredoxin reductase proteins. As the identification of thioredoxin protein targets is technically challenging, the true contribution of this system in maintaining cellular balance remains unidentified, including the role of this system in the brain. [ABSTRACT FROM AUTHOR]

Anti‐inflammatory and immune suppressive agents are required to moderate hyper‐activation of lymphocytes under disease conditions or organ transplantation. However, selective disruption of mitochondrial redox has not been evaluated as a therapeutic strategy for suppression of T‐cell‐mediated pathologies. Using mitochondrial targeted curcumin (MitoC), we studied the effect of mitochondrial redox modulation on T‐cell responses by flow cytometry, transmission electron microscopy, transcriptomics, and proteomics, and the role of Nrf2 was studied using Nrf2−/− mice. MitoC decreased mitochondrial TrxR activity, enhanced mitochondrial ROS (mROS) production, depleted mitochondrial glutathione, and suppressed activation‐induced increase in mitochondrial biomass. This led to suppression of T‐cell responses and metabolic reprogramming towards Treg differentiation. MitoC induced nuclear translocation and DNA binding of Nrf2, leading to upregulation of Nrf2‐dependent genes and proteins. MitoC‐mediated changes in mitochondrial redox and modulation of T‐cell responses are abolished in Nrf2−/− mice. Restoration of mitochondrial thiols abrogated inhibition of T‐cell responses. MitoC suppressed alloantigen‐induced lymphoblast formation, inflammatory cytokines, morbidity, and mortality in acute graft‐versus‐host disease mice. Disruption of mitochondrial thiols but not mROS increase inculcates an Nrf2‐dependent immune‐suppressive disposition in T cells for the propitious treatment of graft‐versus‐host disease. [ABSTRACT FROM AUTHOR]

Background/Aim: Chemoresistance in rhabdomyosarcoma (RMS) is associated with poor survival, necessitating the development of novel anticancer drugs. Auranofin (AUR), an anti-rheumatic drug, is a thioredoxin reductase (TXNRD) inhibitor with anticancer properties. Although patient-derived xenograft (PDX) models are essential for studying cancer biology, reports on sarcomas using the PDX model are scarce because of their rarity. This study aimed to investigate the effectiveness of AUR treatment in RMS using a PDX model to evaluate its impact on local progression. Materials and Methods: A 20-year-old woman who was diagnosed with alveolar RMS was used to generate the PDX model. RMS PDX tumors were implanted in nude mice and divided into non-treated (vehicle) and treated (AUR) groups. Tumor volume and weight were evaluated, and immunohistochemical staining was performed to evaluate local progression of the sarcoma. The relationship between the TXNRD-1 expression and survival probability of patients with RMS was evaluated using publicly available expression cohorts. Results: AUR significantly suppressed RMS tumor progression over time. It also significantly suppressed the tumor size and weight at the time of excision. Histological evaluation showed that AUR induced oxidative stress in the PDX mouse models and inhibited the local progression of RMS by inducing apoptosis. High TXNRD-1 expression was found to be a negative prognostic factor for overall survival in patients with RMS. Conclusion: AURinduced inhibition of TXNRDs can significantly impede the local progression of RMS through the oxidative stressapoptosis pathway as demonstrated in PDX models. Thus, targeting TXNRD inhibition may be a promising therapeutic strategy for the treatment of RMS. [ABSTRACT FROM AUTHOR]

Background: Lung adenocarcinoma (LUAD) is the primary form of lung cancer, yet the reliable biomarkers for early diagnosis remain insufficient. Thioredoxin reductase (TrxR) is strongly linked to the occurrence, development, and drug resistance of lung cancer, making it a potential biomarker. However, further research is required to assess its diagnostic value in LUAD. Methods: A retrospective analysis was performed on patients who underwent pulmonary nodule resection at our center from 2018 to 2022. Clinical data, including preoperative TrxR levels, imaging, and laboratory characteristics, were identified as study variables. Two prediction models were constructed using multiple logistic regression, and their prediction performance was evaluated comprehensively. Besides, bioinformatics analyses of TrxR coding genes including differential expression, functional enrichment, immune infiltration, drug sensitivity, and single-cell landscape were performed based on TCGA database, which were subsequently validated by Human Protein Atlas. Results: A total of 506 eligible patients (72 benign lesions, 77 AISs, 185 MIAs and 172 IACs) were identified in the clinical cohort. Two TrxR-based models were developed, which were able to distinguish between benign and malignant pulmonary nodules, as well as pathological subtypes of LUAD, respectively. The models exhibited good predictive ability with all AUC values ranging from 0.7 to 0.9. Based on calibration curves and clinical decision analysis, the nomogram models showed high reliability. Functional analysis indicated that TXNRD1 primarily participated in cell cycle and lipid metabolism. Immune infiltration analysis showed that TXNRD1 has a strong association with immune cells and could impact immunotherapy. Then, we identified small molecular compounds that inhibit TXNRD1 and confirmed TXNRD1 expression by single-cell landscape and immunohistochemistry. Conclusion: This study validated the diagnostic value of TrxR and TXNRD1 in clinical cohorts and transcriptional data, respectively. TrxR and TXNRD1 could be used in the risk diagnosis of early LUAD and facilitate personalized treatment strategies.

Background: Interstitial lung disease (ILD) treatment is a critical unmet need. Selenium is an essential trace element for human life and an antioxidant that activates glutathione, but the gap between its necessity and its toxicity is small and requires special attention. Whether selenium can be used in the treatment of ILD remains unclear. Methods: We investigated the prophylactic and therapeutic effects of selenite, a selenium derivative, in ILD using a murine model of bleomycin-induced idiopathic pulmonary fibrosis (IPF). We further elucidated the underlying mechanism using in vitro cell models and examined their relevance in human tissue specimens. The therapeutic effect of selenite in bleomycin-administered mice was assessed by respiratory function and histochemical changes. Selenite-induced apoptosis and reactive oxygen species (ROS) production in murine lung fibroblasts were measured. Results: Selenite, administered 1 day (inflammation phase) or 8 days (fibrotic phase) after bleomycin, prevented and treated deterioration of lung function and pulmonary fibrosis in mice. Mechanistically, selenite inhibited the proliferation and induced apoptosis of murine lung fibroblasts after bleomycin treatment both in vitro and in vivo. In addition, selenite upregulated glutathione reductase (GR) and thioredoxin reductase (TrxR) in murine lung fibroblasts, but not in lung epithelial cells, upon bleomycin treatment. GR and TrxR inhibition eliminates the therapeutic effects of selenite. Furthermore, we found that GR and TrxR were upregulated in the human lung fibroblasts of IPF patient samples. Conclusions: Selenite induces ROS production and apoptosis in murine lung fibroblasts through GR and TrxR upregulation, thereby providing a therapeutic effect in bleomycin-induced IPF.

Glioblastoma (GBM) is an incurable primary brain cancer characterized by increased reactive oxygen species (ROS) production. The redox-sensitive tumor suppressor gene TP53, wild-type (wt) for 70% of patients, regulates redox homeostasis. Glioblastoma stem cells (GSCs) increase thioredoxin (Trx) and glutathione (GSH) antioxidant systems as survival redox-adaptive mechanisms to maintain ROS below the cytotoxic threshold. Auranofin, an FDA-approved anti-rheumatoid drug, inhibits thioredoxin reductase 1 (TrxR1). L-buthionine sulfoximine (L-BSO) and the natural product piperlongumine (PPL) inhibit the GSH system. We evaluated the cytotoxic effects of Auranofin alone and in combination with L-BSO or PPL in GBM cell lines and GSCs with a known TP53 status. The Cancer Genome Atlas/GBM analysis revealed a significant positive correlation between wtp53 and TrxR1 expression in GBM. Auranofin induced ROS-dependent cytotoxicity within a micromolar range in GSCs. Auranofin decreased TrxR1 expression, AKT (Ser-473) phosphorylation, and increased p53, p21, and PARP-1 apoptotic cleavage in wtp53-GSCs, while mutant-p53 was decreased in a mutant-p53 GSC line. Additionally, p53-knockdown in a wtp53-GSC line decreased TrxR1 expression and significantly increased sensitivity to Auranofin, suggesting the role of wtp53 as a negative redox-sensitive mechanism in response to Auranofin in GSCs. The combination of Auranofin and L-BSO synergistically increased ROS, decreased IC50s, and induced long-term cytotoxicity irrespective of p53 in GBM cell lines and GSCs. Intriguingly, Auranofin increased the expression of glutathione S-transferase pi-1 (GSTP-1), a target of PPL. Combining Auranofin with PPL synergistically decreased IC50s to a nanomolar range in GSCs, supporting the potential to repurpose Auranofin and PPL in GBM.

Background: Selenium and zinc are essential trace elements known to regulate cellular processes including redox homeostasis. During inflammation, circulating selenium and zinc concentrations are reduced in parallel, but underlying mechanisms are unknown. Accordingly, we modulated the zinc and selenium supply of HepG2 cells to study their relationship. Methods: HepG2 cells were supplied with selenite in combination with a short- or long-term zinc treatment to investigate intracellular concentrations of selenium and zinc together with biomarkers describing their status. In addition, the activation of the redox-sensitive transcription factor NRF2 was analyzed. Results: Zinc not only increased the nuclear translocation of NRF2 after 2 to 6 h but also enhanced the intracellular selenium content after 72 h, when the cells were exposed to both trace elements. In parallel, the activity and expression of the selenoprotein thioredoxin reductase 1 (TXNRD1) increased, while the gene expression of other selenoproteins remained unaffected or was even downregulated. The zinc effects on the selenium concentration and TXNRD activity were reduced in cells with stable NRF2 knockdown in comparison to control cells. Conclusions: This indicates a functional role of NRF2 in mediating the zinc/selenium crosstalk and provides an explanation for the observed unidirectional behavior of selenium and zinc.

Thioredoxin reductase (TXNRD) is a selenoprotein that plays a crucial role in cellular antioxidant defense. Previously, a distinctive guiding bar motif was identified in TXNRD1, which influences the transfer of electrons. In this study, utilizing single amino acid substitution and Excitation-Emission Matrix (EEM) fluorescence spectrum analysis, we discovered that the guiding bar communicates with the FAD and modulates the electron flow of the enzyme. Differential Scanning Fluorimetry (DSF) analysis demonstrated that the aromatic amino acid in guiding bar is a stabilizer for TXNRD1. Kinetic analysis revealed that the guiding bar is vital for the disulfide reductase activity but hinders the selenocysteine-independent reduction activity of TXNRD1. Meanwhile, the guiding bar shields the selenocysteine residue of TXNRD1 from the attack of electrophilic reagents. We also found that the inhibition of TXNRD1 by caveolin-1 scaffolding domain (CSD) peptides and compound LCS3 did not bind to the guiding bar motif. In summary, the obtained results highlight new aspects of the guiding bar that restrict the flexibility of the C-terminal redox motif and govern the transition from antioxidant to pro-oxidant.

Thioredoxin reductase 1 (Txnrd1) is known to have prognostic significance in a subset of breast cancer patients. Despite the pivotal role of Txnrd1 in regulating several cellular and physiological processes in cancer progression and metastasis, its clinical significance is largely unrecognized. Here, we undertook a retrospective comprehensive meta-analysis of 13,322 breast cancer patients from 43 independent cohorts to assess prognostic and predictive roles of Txnrd1. We observed that Txnrd1 has a positive correlation with tumor grade and size and it is over-expressed in higher-grade and larger tumors. Further, hormone receptor-negative and HER2-positive tumors exhibit elevated Txnrd1 gene expression. Patients with elevated Txnrd1 expression exhibit significant hazards for shorter disease-specific and overall survival. While Txnrd1 has a positive correlation with tumor recurrence and metastasis, it has a negative correlation with time to recurrence and metastasis. Txnrd1High patients exhibit 2.5 years early recurrence and 1.3 years early metastasis as compared to Txnrd1Low cohort. Interestingly, patients with high Txnrd1 gene expression exhibit a pathologic complete response (pCR) to neoadjuvant chemotherapy, but they experience early recurrence after radiotherapy. Txnrd1High MDA-MB-231 cells exhibit significant ROS generation and reduced viability after doxorubicin treatment compared to Txnrd1Low MCF7 cells. Corroborating with findings from meta-analysis, Txnrd1 depletion leads to decreased survival, enhanced sensitivity to radiation induced killing, poor scratch-wound healing, and reduced invasion potential in MDA-MB-231 cells. Thus, Txnrd1 appears to be a potential predictor of recurrence, metastasis and therapy response in breast cancer patients.

Mammalian cytosolic thioredoxin reductase (TrxR1) serves as an antioxidant protein by transferring electrons from NADPH to various substrates. The action of TrxR1 is achieved via reversible changes between NADPH-reduced and non-reduced forms, which involves C-terminal selenolthiol/selenenylsulfide exchanges. TrxR1 may be released into extracellular environment, where TrxR1 is present mainly in the non-reduced form with active-site disulfide and selenenylsulfide bonds. The relationships between extracellular TrxR1 and tumor metastasis or cellular signaling have been discovered, but there are few reports on small-molecule compounds in targeted the non-reduced form of TrxR1. Using eight types of small-molecule thiol-reactive reagents as electrophilic models, we report that the selenenylsulfide bond in the non-reduced form of TrxR1 functions as a selector for the thiol-reactive reagents at pH 7.5. The non-reduced form of TrxR1 is resistant to hydrogen peroxide/oxidized glutathione, but is sensitive to certain electrophilic reagents in different ways. With 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) and S-nitrosoglutathione (GSNO), the polarized selenenylsulfide bond breaks, and selenolate anion donates electron to the dynamic covalent bond in DTNB or GSNO, forming TNB-S-Se-TrxR1 complex or ON-Se-TrxR1 complex. The both complexes lose the ability to transfer electrons from NADPH to substrate. For diamide, the non-reduced TrxR1 actually prevents irreversible damage by this oxidant. This is consistent with the regained activity of TrxR1 through removal of diamide via dialysis. Diamide shows effective in the presence of human cytosolic thioredoxin (hTrx1), Cys residue(s) of which is/are preferentially affected by diamide to yield disulfide, hTrx1 dimer and the mixed disulfide between TrxR1-Cys497/Sec498 and hTrx1-Cys73. In human serum samples, the non-reduced form of TrxR1 exists as dithiothreitol-reducible polymer/complexes, which might protect the non-reduced TrxR1 from inactivation by certain electrophilic reagents under oxidative conditions, because cleavage of these disulfides can lead to regain the activity of TrxR1. The details of the selective response of the selenenylsulfide bond to electrophilic reagents may provide new information for designing novel small-molecule inhibitors (drugs) in targeted extracellular/non-reduced TrxR1.

This study investigates the activity of novel gold(I) and copper(I)/zinc(II) heteronuclear complexes against colon cancer. The synthesised heteronuclear Au(I)-Cu(I) and Au(I)-Zn(II) complexes were characterised and evaluated for their anticancer activity using human colon cancer cell lines (Caco-2). The complexes exhibited potent cytotoxicity, with IC50 values in the low micromolar range, and effectively induced apoptosis in cancer cells. In the case of complex [Cu{Au(Spy)(PTA)}2]PF6 (2), its cytotoxicity is ×10 higher than its mononuclear precursor, while showing low cytotoxicity towards differentiated healthy cells. Mechanistic studies revealed that complex 2 inhibits the activity of thioredoxin reductase, a key enzyme involved in redox regulation, leading to an increase in reactive oxygen species (ROS) levels and oxidative stress, in addition to an alteration in DNA’s tertiary structure. Furthermore, the complexes demonstrated a strong binding affinity to bovine serum albumin (BSA), suggesting the potential for effective drug delivery and bioavailability. Collectively, these findings highlight the potential of the investigated heteronuclear Au(I)-Cu(I) and Au(I)-Zn(II) complexes as promising anticancer agents, particularly against colon cancer, through their ability to disrupt redox homeostasis and induce oxidative stress-mediated cell death.

Auranofin (AF) is a gold-based compound with a well-known pharmacological and toxicological profile, currently used in the treatment of some severe forms of rheumatoid arthritis. Over the last twenty years, AF has also been repurposed as antiviral, antitumor, and antibacterial drug. In this review we focused on the antibacterial properties of AF, specifically researching the minimal inhibitory concentrations (MIC) of AF in both mono- and diderm bacteria reported so far in literature. AF proves to be highly effective against monoderm bacteria, while diderm are far less susceptible, probably due to the outer membrane barrier. We also reported the current mechanistic hypotheses concerning the antimicrobial properties of AF, although a conclusive description of its antibacterial mode of action is not yet available. Even if its mechanism of action has not been fully elucidated yet and further studies are required to optimize its delivery strategy, AF deserves additional investigation because of its unique mode of action and high efficacy against a wide range of pathogens, which could lead to potential applications in fighting antimicrobial resistance and improving therapeutic outcomes in infectious diseases.

Salmonella enterica serovar Gallinarum biovar Gallinarum (SG) causes fowl typhoid, a notifiable infectious disease in poultry. However, the pathogenic mechanism of SG-induced systemic infection in chickens remains unclear. Thioredoxin reductase (TrxB) is a redox protein crucial for regulating various enzyme activities in Salmonella serovar, but the role in SG-induced chicken systemic infection has yet to be determined. Here, we constructed a mutant SG strain lacking the trxB gene (trxB::Cm) and used chicken embryo inoculation and chicken oral infection to investigate the role of trxB gene in the pathogenicity of SG. Our results showed that trxB::Cm exhibited no apparent differences in colony morphology and growth conditions but exhibited reduced tolerance to H2O2 and increased resistance to bile acids. In the chicken embryo inoculation model, there was no significant difference in the pathogenicity of trxB::Cm and wild-type (WT) strains. In the chicken oral infection, the WT-infected group exhibited typical clinical symptoms of fowl typhoid, with complete mortality between days 6 and 9 post infection. In contrast, the trxB::Cm group showed a 100% survival rate, with no apparent clinical symptoms or pathological changes observed. The viable bacterial counts in the liver and spleen of the trxB::Cm-infected group were significantly reduced, accompanied by decreased expression of cytokines and chemokines (IL-1β, IL-6, IL-12, CXCLi1, TNF-α, and IFN-γ), which were significantly lower than those in the WT group. These results show that the pathogenicity of the trxB-deficient strain was significantly attenuated, indicating that the trxB gene is a crucial virulence factor in SG-induced systemic infection in chickens, suggesting that trxB may become a potentially effective target for controlling and preventing SG infection in chickens.

Pulmonary fibrosis is highly lethal with limited treatments. Butaselen (BS) is an inhibitor of thioredoxin reductase (TrxR)/thioredoxin (Trx) with anti-tumor activity. However, its impact on pulmonary fibrosis and the involved mechanisms remain unclear. Here, we demonstrate that BS is a potential drug for the treatment of pulmonary fibrosis. Specifically, BS can inhibit pulmonary fibrosis both in vitro and in vivo, with comparable efficacy and enhanced safety when compared with pirfenidone. BS and dexamethasone display a synergistic effect in inhibiting pulmonary fibrosis both in vitro and in vivo. Mechanistic studies reveal that BS can inhibit the TrxR activity during pulmonary fibrosis. RNA-sequencing analysis identifies that genes of ECM-related signaling pathways are notably affected by BS. BS can not only inhibit the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and reduce pulmonary fibrosis-related inflammation, but also reduce NF-κB-activated transcriptional expression of transforming growth factor-β1 (TGF-β1), which leads to the inactivation of Smad2/Smad3 and decrease of collagen formation and fibrosis. Moreover, the knockdown of Trx1 with siRNA can also inhibit NF-κB/TGF-β1/Smads signaling. In conclusion, the TrxR/Trx inhibitor butaselen can suppress pulmonary fibrosis by inhibiting NF-κB/TGF-β1/Smads signaling.

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 (F420H2). 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 F420H2 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. [ABSTRACT FROM AUTHOR]

Targeting thioredoxin reductase (TXNRD) with low-weight molecules is emerging as a high-efficacy anti-cancer strategy in chemotherapy. Sanguinarine has been reported to inhibit the activity of TXNRD1, indicating that benzophenanthridine alkaloid is a fascinating chemical entity in the field of TXNRD1 inhibitors. In this study, the inhibition of three benzophenanthridine alkaloids, including chelerythrine, sanguinarine, and nitidine, on recombinant TXNRD1 was investigated, and their anti-cancer mechanisms were revealed using three gastric cancer cell lines. Chelerythrine and sanguinarine are more potent inhibitors of TXNRD1 than nitidine, and the inhibitory effects take place in a dose- and time-dependent manner. Site-directed mutagenesis of TXNRD1 and in vitro inhibition analysis proved that chelerythrine or sanguinarine is primarily bound to the Sec498 residue of the enzyme, but the neighboring Cys497 and remaining N-terminal redox-active cysteines could also be modified after the conjugation of Sec498. With high similarity to sanguinarine, chelerythrine exhibited cytotoxic effects on multiple gastric cancer cell lines and suppressed the proliferation of tumor spheroids derived from NCI-N87 cells. Chelerythrine elevated cellular levels of reactive oxygen species (ROS) and induced endoplasmic reticulum (ER) stress. Moreover, the ROS induced by chelerythrine could be completely suppressed by the addition of N-acetyl-L-cysteine (NAC), and the same is true for sanguinarine. Notably, Nec-1, an RIPK1 inhibitor, rescued the chelerythrine-induced rapid cell death, indicating that chelerythrine triggers necroptosis in gastric cancer cells. Taken together, this study demonstrates that chelerythrine is a novel inhibitor of TXNRD1 by targeting Sec498 and possessing high anti-tumor properties on multiple gastric cancer cell lines by eliciting necroptosis. [ABSTRACT FROM AUTHOR]

Mercury (Hg) exposure has not been examined in many recreational nearshore fish species that are commonly consumed around the Hawaiian Islands. Specific gene transcripts, such as metallothionein (MET) and thioredoxin reductase (TrxR), can be used to examine Hg exposure responses in aquatic organisms. This study measured total mercury (THg) in four species from two groups of Hawaiian nearshore fishes: giant trevally (Caranx ignobilis, n = 13), bluefin trevally (C. melampygus, n = 4), sharp jaw bonefish (Albula virgata, n = 2), and round jaw bonefish (A. glossodonta, n = 19). Total Hg accumulation and abundance profiles of MET and TrxR were evaluated for muscle, liver, and kidney tissues. Total Hg in round jaw bonefish and giant trevally tissues accumulated with length and calculated age. In round jaw bonefish tissues, mean THg was greater in kidney (1156 ng/g wet mass (wm)) than liver (339 ng/g wm) and muscle (330 ng/g wm). Giant trevally muscle (187 ng/g wm) and liver (277 ng/g wm) mean THg did not differ significantly. Fish species in this study were compared to commercial and local fish species with state and federal muscle tissue consumption advisories based on THg benchmarks developed by the U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA). Both bonefishes had mean muscle THg that exceeded benchmarks suggesting consumption advisories should be considered. MET transcript in round jaw bonefish kidney tissue and kidney THg exhibited a marginally significant positive correlation, while TrxR transcript in liver tissue negatively correlated with increasing liver THg. These results contribute to our understanding of Hg exposure associated health effects in fish. [ABSTRACT FROM AUTHOR]

Auranofin ([1-(thio-κS)-β-d-glucopyranose-2,3,4,6-tetraacetato](triethylphosphine)-gold) is a leading gold-based drug clinically used to treat arthritis. In the last years, it entered various drug reprofiling programs, and it has been found promising against various forms of tumor, including ovarian cancer. Evidence showed as its antiproliferative profile mainly depends on the inhibition of thioredoxin reductase (TrxR), being this mitochondrial system its main target. In this context, we report here the synthesis and biological evaluation of a novel complex designed as auranofin analogue obtained through the conjugation of a phenylindolylglyoxylamide ligand (which belongs to the so-called PIGA TSPO ligand family) with the auranofin-derived cationic fragment [Au(PEt3)]+. This complex is characterized by two parts. The phenylindolylglyoxylamide moiety, owing to its high affinity for TSPO (in the low nM range) should drive the compound to target mitochondria, whereas the [Au(PEt3)]+ cation is the actual anticancer-active molecular fragment. Overall, we wanted to offer the proof-of-concept that by coupling PIGA ligands to anticancer gold active moieties, it is possible to preserve and even improve anticancer effects, opening the avenue to a reliable approach for targeted therapy. [ABSTRACT FROM AUTHOR]

Simple Summary: The identification of biological targets is an essential step in deciphering the mechanism of action of anticancer drugs. In this review, we chose to study the relationship between the inhibition of thioredoxin reductase (TrxR), a key enzyme in maintaining the redox balance of cells, and the cytotoxic effects of two groups of organometallic complexes. The first group is essentially composed of Au(I) and Au(III) complexes and the second one comprises metallocifens (organometallic complexes derived from tamoxifen). The results show that these two groups interact differently with TrxR at the molecular level. Even if the contribution of TrxR inhibition to the cytotoxicity of complexes is clearly established for many of them, the number of complexes for which TrxR inhibition plays a predominant role appears quite limited. Eventually, the antiproliferative activity of most of the complexes appears to stem from the interaction with several targets, a favorable strategy to tackle MDR tumors. Cancers classified as multidrug-resistant (MDR) are a family of diseases with poor prognosis despite access to increasingly sophisticated treatments. Several mechanisms explain these resistances involving both tumor cells and their microenvironment. It is now recognized that a multi-targeting approach offers a promising strategy to treat these MDR tumors. Inhibition of thioredoxin reductase (TrxR), a key enzyme in maintaining redox balance in cells, is a well-identified target for this approach. Auranofin was the first inorganic gold complex to be described as a powerful inhibitor of TrxR. In this review, we will first recall the main results obtained with this metallodrug. Then, we will focus on organometallic complexes reported as TrxR inhibitors. These include gold(I), gold(III) complexes and metallocifens, i.e., organometallic complexes of Fe and Os derived from tamoxifen. In these families of complexes, similarities and differences in the molecular mechanisms of TrxR inhibition will be highlighted. Finally, the possible relationship between TrxR inhibition and cytotoxicity will be discussed and put into perspective with their mode of action. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Multiple sclerosis (MS) is one of the most prevalent chronic inflammatory autoimmune diseases. It causes the demyelination of neurons and the subsequent degeneration of the central nervous system (CNS). The infiltration of leukocytes of both myeloid and lymphoid origins from the systemic circulation into the CNS triggers autoimmune reactions through the release of multiple mediators. These mediators include oxidants, pro-inflammatory cytokines, and chemokines which ultimately cause the characteristic plaques observed in MS. Thioredoxin reductase (TrxR) and nuclear factor erythroid 2-related factor 2 (Nrf2) signaling plays a crucial role in the regulation of inflammation by modulating the transcription of antioxidants and the suppression of inflammatory cytokines. The gold compound auranofin (AFN) is known to activate Nrf2 through the inhibition of TrxR; however, the effects of this compound have not been explored in a mouse model of relapsing–remitting MS (RRMS). Therefore, this study explored the influence of AFN on clinical features, TrxR/Nrf2 signaling [heme oxygenase 1 (HO-1), superoxide dismutase 1 (SOD-1)] and oxidative/inflammatory mediators [IL-6, IL-17A, inducible nitric oxide synthase (iNOS), myeloperoxidase (MPO), nitrotyrosine] in peripheral immune cells and the CNS of mice with the RR type of EAE. Our results showed an increase in TrxR activity and a decrease in Nrf2 signaling in SJL/J mice with RR-EAE. The treatment with AFN caused the amelioration of the clinical features of RR-EAE through the elevation of Nrf2 signaling and the subsequent upregulation of the levels of antioxidants as well as the downregulation of oxidative/pro-inflammatory mediators in peripheral immune cells and the CNS. These data suggest that AFN may be beneficial in the treatment of RRMS. [ABSTRACT FROM AUTHOR]

NADPH:thioredoxin reductase (TrxR) is considered a potential target for anticancer agents. Several nitroheterocyclic sulfones, such as Stattic and Tri-1, irreversibly inhibit TrxR, which presumably accounts for their antitumor activity. However, it is necessary to distinguish the roles of enzymatic redox cycling, an inherent property of nitroaromatics (ArNO2), and the inhibition of TrxR in their cytotoxicity. In this study, we calculated the previously unavailable values of single-electron reduction potentials of known inhibitors of TrxR (Stattic, Tri-1, and 1-chloro-2,4-dinitrobenzene (CDNB)) and inhibitors identified (nitrofuran NSC697923 and nitrobenzene BTB06584). These calculations were according to the rates of their enzymatic single-electron reduction (PMID: 34098820). This enabled us to compare their cytotoxicity with that of model redox cycling ArNO2. In MH22a and HCT-116 cells, Tri-1, Stattic, CDNB, and NSC697023 possessed at least 10-fold greater cytotoxicity than can be expected from their redox cycling activity. This may be related to TrxR inhibition. The absence of enhanced cytotoxicity in BTB06548 may be attributed to its instability. Another known inhibitor of TrxR, tetryl, also did not possess enhanced cytotoxicity, probably because of its detoxification by DT-diaphorase (NQO1). Apart from the reactions with NQO1, the additional mechanisms influencing the cytotoxicity of the examined inhibitors of TrxR are their reactions with cytochromes P-450. Furthermore, some inhibitors, such as Stattic and NSC697923, may also inhibit glutathione reductase. We suggest that these data may be instrumental in the search for TrxR inhibitors with enhanced cytotoxic/anticancer activity. [ABSTRACT FROM AUTHOR]

The modulation of numerous signaling pathways is orchestrated by redox regulation of cellular environments. Maintaining dynamic redox homeostasis is of utmost importance for human health, given the common occurrence of altered redox status in various pathological conditions. The cardinal component of the thioredoxin system, mammalian thioredoxin reductase (TrxR) plays a vital role in supporting various physiological functions; however, its malfunction, disrupting redox balance, is intimately associated with the pathogenesis of multiple diseases. Accordingly, the dynamic monitoring of TrxR of live organisms represents a powerful direction to facilitate the comprehensive understanding and exploration of the profound significance of redox biology in cellular processes. A number of classic assays have been developed for the determination of TrxR activity in biological samples, yet their application is constrained when exploring the real-time dynamics of TrxR activity in live organisms. Fluorescent probes offer several advantages for in situ imaging and the quantification of biological targets, such as non-destructiveness, real-time analysis, and high spatiotemporal resolution. These benefits facilitate the transition from a poise to a flux understanding of cellular targets, further advancing scientific studies in related fields. This review aims to introduce the progress in the development and application of TrxR fluorescent probes in the past years, and it mainly focuses on analyzing their reaction mechanisms, construction strategies, and potential drawbacks. Finally, this study discusses the critical challenges and issues encountered during the development of selective TrxR probes and proposes future directions for their advancement. We anticipate the comprehensive analysis of the present TrxR probes will offer some glitters of enlightenment, and we also expect that this review may shed light on the design and development of novel TrxR probes. [ABSTRACT FROM AUTHOR]

Entamoeba histolytica (E. histolytica) is a parasite in humans that provokes amoebiasis. The most employed drug is metronidazole (MTZ); however, some studies have reported that this drug induces genotoxic effects. Therefore, it is necessary to explore new compounds without toxicity that can eliminate E. histolytica. Flavonoids are polyphenolic compounds that have demonstrated inhibition of growth and dysregulation of amoebic proteins. Despite the knowledge acquired to date, action mechanisms are not completely understood. The present work evaluates the effect of kaempferol against E. histolytica trophozoites and in the interactions with neutrophils from hamster, which is a susceptibility model. Our study demonstrated a significant reduction in the amoebic viability of trophozoites incubated with kaempferol at 150 μM for 90 min. The gene expression analysis showed a significant downregulation of Pr (peroxiredoxin), Rr (rubrerythrin), and TrxR (thioredoxin reductase). In interactions with amoebae and neutrophils for short times, we observed a reduction in ROS (reactive oxygen species), NO (nitric oxide), and MPO (myeloperoxidase) neutrophil activities. In conclusion, we confirmed that kaempferol is an effective drug against E. histolytica through the decrease in E. histolytica antioxidant enzyme expression and a regulator of several neutrophil mechanisms, such as MPO activity and the regulation of ROS and NO. [ABSTRACT FROM AUTHOR]

Background: Our aim was to investigate the rationality and accuracy of plasma TrxR activity as an efficient tool in the early diagnosis of gastrointestinal malignancy, and whether TrxR can be used to evaluate the therapeutic efficacy of gastrointestinal malignancy. Methods: We enrolled a total of 5091 cases, including 3736 cases in gastrointestinal malignancy, 964 in benign diseases, and 391 cases in healthy controls. We also performed receiver operating characteristic (ROC) analysis to evaluate diagnostic efficiency of TrxR. Finally, we detected pre- and post-treatment level of TrxR and common tumor markers. Results: The plasma TrxR level in patients with gastrointestinal malignancy [8.4 (6.9, 9.7) U/mL] was higher than that in patients with benign disease [5.8 (4.6, 6.9) U/mL] and healthy control [3.5 (1.4, 5.4) U/mL]. Plasma TrxR showed a significant diagnostic advantage with an AUC of 0.897, compared with conventional tumor markers. In addition, the combination of TrxR and conventional tumor markers can further improve the diagnostic efficiency. We derived the optimal cut-off value of plasma TrxR as a diagnostic marker of gastrointestinal malignancy according to Youden index of 6.15 U/mL. After measuring the change trend of TrxR activity and conventional tumor markers before and after anti-tumor treatments, we found that their change trend was generally consistent, and the plasma TrxR activity was significantly decreased in patients treated with chemotherapy, targeted therapy and immunotherapy. Conclusions: Our findings recommend that plasma TrxR activity could be monitored as an efficient tool for the early diagnosis of gastrointestinal malignancy and as a feasible tool to evaluate the therapeutic effect. [ABSTRACT FROM AUTHOR]

Purpose: Cisplatin resistance is the major obstacle in the clinical treatment of ovarian cancer patients. Molecular mechanisms of cisplatin resistance are multifaceted. Gold(I)-compounds, i.e. N-heterocyclic carbene-gold(I)-complexes (NHC-Au(I)) has been regarded as promising cytotoxic drug candidates. However, their potential to overcome cisplatin resistance has hardly been addressed yet. Here we investigated the activity of the gold(I) drug auranofin and the NHC-Au(I)-compound MC3 in W1CR and A2780cis cisplatin-resistant ovarian cancer cells. Methods: Cytotoxicity of auranofin and MC3 was detected by MTT assay, correlated with intracellular gold(I) content, analyzed by AAS, and with flow cytometric detection of the cell cycle. Insight into cellular redox balance was provided by fluorimetric ROS-formation assay and western blotting thioredoxin (Trx) and Nrf2. The role of ERK was elucidated by using the inhibitor SCH772984 and its impact on cytotoxicity upon co-treatment with cisplatin and Au(I)-compounds, respectively. Results: MC3 overcomes cisplatin resistance in A2780cis and W1CR, and auranofin in W1CR cells completely, which is neither reflected by intracellular gold levels nor cell cycle changes. Upregulated redox balance appears as a basis for resistance. W1CR cells possess higher Trx levels, whereas A2780cis cells display strong Nrf2 expression as anti-oxidative protection. Nevertheless, overcoming redox balance appears not primary mode of activity comparing cisplatin and gold(I)-compounds. pERK emerges as a critical component and thus a promising target for overcoming resistance, regulating apoptosis differently in response to either gold(I) or cisplatin in A2780 cells. Conclusion: These data reflect the complexity of cisplatin resistance in cell models and emphasize NHC-Au(I)-complexes as prospective cytotoxic agents for further investigations in that respect. [ABSTRACT FROM AUTHOR]

Background: According to previous literatures, plasma thioredoxin reductase (TrxR) level was significantly elevated in various malignant tumors and serve as a potential biomarker for diagnosis and prognostic prediction. However, there is little awareness of the clinical value of plasma TrxR in gynecologic malignancies. In the present study, we aim to evaluate the diagnostic accuracy of plasma TrxR in gynecologic cancer and explore its role in treatment surveillance. Methods: We retrospectively enrolled 134 patients with gynecologic cancer and 79 patients with benign gynecologic disease. The difference of plasma TrxR activity and tumor markers level between two groups was compared using Mann-Whitney U test. By detecting pretreatment and post-treatment level of TrxR and conventional tumor markers, we further assessed the change trend of them with the Wilcoxon signed-ranks test. Results: Compared with benign control [5.7 (5, 6.6) U/mL], statistically significant increase of TrxR activity was observed in gynecologic cancer group [8.4 (7.25, 9.825) U/mL] (P <.0001), regardless of age and stage. On the basis of receiver operating characteristic (ROC) curves, we found plasma TrxR shows the highest diagnostic efficacy for distinguishing malignancy with benign disease, with an area under the curve (AUC) of 0.823 (95% confidence interval [CI] = 0.767-0.878), in the whole cohort. Besides, patients receiving treatment previously [8 (6.5, 9) U/mL] had a decreased TrxR level relative to treatment-native patients [9.9 (8.6, 10.85) U/mL]. Furthermore, follow-up data showed that plasma TrxR level would be evidently decreased after two courses of antitumor therapy (P <.0001), which is consistent with the downward trend of conventional tumor markers. Conclusion: Collectively, all these results demonstrated plasma TrxR is an effective parameter for gynecologic cancer diagnosis and concurrently acts as a promising biomarker for treatment response assessment. [ABSTRACT FROM AUTHOR]

Selenocysteine is a catalytic residue at the active site of all selenoenzymes in bacteria and mammals, and it is incorporated into the polypeptide backbone by a co-translational process that relies on the recoding of a UGA termination codon into a serine/selenocysteine codon. The best-characterized selenoproteins from mammalian species and bacteria are discussed with emphasis on their biological function and catalytic mechanisms. A total of 25 genes coding for selenoproteins have been identified in the genome of mammals. Unlike the selenoenzymes of anaerobic bacteria, most mammalian selenoenzymes work as antioxidants and as redox regulators of cell metabolism and functions. Selenoprotein P contains several selenocysteine residues and serves as a selenocysteine reservoir for other selenoproteins in mammals. Although extensively studied, glutathione peroxidases are incompletely understood in terms of local and time-dependent distribution, and regulatory functions. Selenoenzymes take advantage of the nucleophilic reactivity of the selenolate form of selenocysteine. It is used with peroxides and their by-products such as disulfides and sulfoxides, but also with iodine in iodinated phenolic substrates. This results in the formation of Se-X bonds (X = O, S, N, or I) from which a selenenylsulfide intermediate is invariably produced. The initial selenolate group is then recycled by thiol addition. In bacterial glycine reductase and D-proline reductase, an unusual catalytic rupture of selenium–carbon bonds is observed. The exchange of selenium for sulfur in selenoproteins, and information obtained from model reactions, suggest that a generic advantage of selenium compared with sulfur relies on faster kinetics and better reversibility of its oxidation reactions. [ABSTRACT FROM AUTHOR]

The efficacy of photodynamic therapy (PDT) is still limited by the inefficient utilisation of generated ROS in tumours due to cellular redox homeostasis. To improve the therapeutic efficacy for oral carcinoma, biomimetic cell membrane-coated mesoporous nanoplatform was tailored to interfere with cellular redox homeostasis for amplified PDT. In this study, CAL-27 cancer cell membrane (CM) was encapsulated onto the mesoporous silica NPs (MSN), which were preloaded with Chlorin e6 (Ce6) and Curcumin (Cur). The biomimetic nanoparticles displayed a size of around 120 nm, which had excellent cytotoxicity under a laser and increased uptake ability to tumour cell. After internalised by cancer cells, the released Cur could effectively disturb ROS-defence system by suppressing TrxR activity, and decreasing TrxR-2 expression (p < 0.05), leading to enhanced cancer cell killing ability of PDT. The biomimetic system was found to selectively accumulate in the tumour due to its homologous targeting capability and inhibit tumour growth significantly. In a word, the biomimetic nanoplatform apparently enhanced the therapeutic effect of PDT on tumours by Cur disturbing the ROS-defence system, which exhibited a new way to enhance PDT. [ABSTRACT FROM AUTHOR]

Simple Summary: Cutaneous melanoma is one of the deadliest forms of skin cancer. While advancements in systemic targeted therapies and immunotherapies have greatly improved melanoma survival in recent years, tumor resistance can limit the efficacy of these therapies. Targeting redox homeostasis in melanoma progression is a promising therapeutic approach, especially in cases of melanoma drug resistance. The role of oxidative stress in melanoma is paradoxical in that it promotes tumor initiation but prevents vertical growth and metastasis. As the disease progresses, melanoma employs adaptive mechanisms to decrease oxidative stress in the tumor environment. Thus, agents with antioxidant properties may have the greatest utility in chemoprevention whereas those with pro-oxidant properties may be better suited for treatment. The purpose of this review is to provide an overview of oxidative stress in melanoma, and how the antioxidant system may be manipulated in a therapeutic context for improved efficacy and survival. Cutaneous melanoma ranks as the fifth most common cancer in the United States and represents one of the deadliest forms of skin cancer. While recent advances in systemic targeted therapies and immunotherapies have positively impacted melanoma survival, the survival rate of stage IV melanoma remains at a meager 32%. Unfortunately, tumor resistance can impede the effectiveness of these treatments. Oxidative stress is a pivotal player in all stages of melanoma progression, with a somewhat paradoxical function that promotes tumor initiation but hinders vertical growth and metastasis in later disease. As melanoma progresses, it employs adaptive mechanisms to lessen oxidative stress in the tumor environment. Redox metabolic rewiring has been implicated in acquired resistance to BRAF/MEK inhibitors. A promising approach to enhance the response to therapy involves boosting intracellular ROS production using active biomolecules or targeting enzymes that regulate oxidative stress. The complex interplay between oxidative stress, redox homeostasis, and melanomagenesis can also be leveraged in a preventive context. The purpose of this review is to provide an overview of oxidative stress in melanoma, and how the antioxidant system may be manipulated in a therapeutic context for improved efficacy and survival. [ABSTRACT FROM AUTHOR]

The first regioselective syntheses of 1,2-thiaselenane-4-amine (TSA4) and 1,2-thiaselenane-5-amine (TSA5) are developed. Both are redox motifs with high value in chemical biology that until now were hindered by tedious synthesis. An aziridine intermediate and a kinetically controlled S-acylation were leveraged for regioselective chalcogen installations. Short, fast sequences were optimised with just one or two chromatographic steps that cheaply deliver these motifs on scale for high throughput inhibitor screening, and thus provide a robust methodology for assembling other selenenyl sulfides. [ABSTRACT FROM AUTHOR]

The purpose of the current study was to evaluate the effect of exogenous addition of vitamin E on the cellular uptake and transport of selenium (Se) across Caco-2 cell monolayer from wheat and pearl millet. Cellular bioavailability of Se was also determined by evaluating the activity of Se dependent enzymes such as glutathione peroxidase (GPx) and thioredoxin reductase (TR). Transport and uptake of Se was by passive diffusion (transcellular transport), which was time dependent. Uptake of selenomethionine (SeMet) and selenocysteine (SeCys2) by the Caco-2 cells incubated with wheat and pearl millet was significantly enhanced (p < 0.001) in the presence of vitamin E, which, however, was significantly decreased by heat processing (p < 0.001). The mRNA expression of the genes encoding the two Se dependant enzymes, GPx and TR was significantly upregulated in wheat and pearl millet respectively, upon the addition of vitamin E. The extent of upregulation ranged from 80 to 100%. [ABSTRACT FROM AUTHOR]

Inhibition of thioredoxin reductase (TrxR) is a crucial strategy for the discovery of antineoplastic drugs. 6-Shogaol (6-S), a primary bioactive compound in ginger, has high anticancer activity. However, its potential mechanism of action has not been thoroughly investigated. In this study, we demonstrated for the first time that 6-S, a novel TrxR inhibitor, promoted oxidative-stress-mediated apoptosis in HeLa cells. The other two constituents of ginger, 6-gingerol (6-G) and 6-dehydrogingerduone (6-DG), have a similar structure to 6-S but fail to kill HeLa cells at low concentrations. 6-Shogaol specifically inhibits purified TrxR1 activity by targeting selenocysteine residues. It also induced apoptosis and was more cytotoxic to HeLa cells than normal cells. The molecular mechanism of 6-S-mediated apoptosis involves TrxR inhibition, followed by an outburst of reactive oxygen species (ROS) production. Furthermore, TrxR knockdown enhanced the cytotoxic sensitivity of 6-S cells, highlighting the physiological significance of targeting TrxR by 6-S. Our findings show that targeting TrxR by 6-S reveals a new mechanism underlying the biological activity of 6-S and provides meaningful insights into its action in cancer therapeutics. [ABSTRACT FROM AUTHOR]