The thioredoxin antioxidant system

Endoplasmic reticulum (ER) stress-induced reactive oxygen species (ROS) are detrimental for the fitness of a thioredoxin reductase mutant

The unfolded protein response (UPR) is constitutively active in yeast thioredoxin reductase mutants, suggesting a link between cytoplasmic thiol redox control and endoplasmic reticulum (ER) oxidative protein folding. The unique oxidative environment of the ER lumen requires tight regulatory control, and we show that the active UPR depends on the presence of oxidized thioredoxins rather than arising because of a loss of thioredoxin function. Preventing activation of the UPR by deletion of HAC1, encoding the UPR transcription factor, rescues a number of thioredoxin reductase mutant phenotypes, including slow growth, shortened longevity, and oxidation of the cytoplasmic GSH pool. This is because the constitutive UPR in a thioredoxin reductase mutant results in the generation of hydrogen peroxide. The oxidation of thioredoxins in a thioredoxin reductase mutant requires aerobic metabolism and the presence of the Tsa1 and Tsa2 peroxiredoxins, indicating that a complete cytoplasmic thioredoxin system is crucial for maintaining ER redox homeostasis.

Treatment of acetaminophen-induced liver injury with exogenous mitochondria in mice

Drug-induced liver injury shares a common feature of mitochondrial dysfunction. Mitochondrial therapy (mitotherapy), which replaces malfunctional mitochondria with functional exogenous mitochondria, may be a fundamental approach for treating drug-mediated hepatotoxicity. Here, we suggested that mitochondria isolated from human hepatoma cell could be used to treat acetaminophen (APAP)-induced liver injury in mice. When the mitochondria were added into the cell media, they could enter primarily cultured mouse hepatocyte. When the mitochondria were intravenously injected into mice, they distribute in several tissues, including liver. In the model mice of APAP-induced liver injury, mitochondria treatment increased hepatocyte energy supply, reduced oxidation stress, and consequently ameliorated tissue injury. The study suggests that exogenous mitochondria could be an effective therapeutic strategy in treating APAP-induced liver injury.

Cytoprotective effect of Streptococcus thermophilus against oxidative stress mediated by a novel peroxidase (EfeB)

Streptococcus thermophilus is one of the most important starter species used in the dairy industry and exhibits several beneficial properties for the hosts. However, knowledge of the mechanism of its beneficial effect is still limited. The objective of this study was to investigate the cytoprotective effect of S. thermophilus CGMCC 7.179 with a novel peroxidase (EfeB) against oxidative stress in human intestinal epithelial cells, HT-29. Previously, we identified EfeB in S. thermophilus CGMCC 7.179, which could provide protection when growing at aerobic conditions. Here, we found that, when exposed to 15 mM H₂O₂, the cell viability of the efeB mutant (ST1314) was much lower than that of strain CGMCC 7.179, and the 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity of strain ST1314 decreased by 15%. When co-incubated with HT-29 cells, strain CGMCC 7.179 stimulated the enhancement of the major antioxidant enzyme activities (superoxide dismutase, glutathione peroxidase, and catalase) in HT-29 cells under 2 mM H₂O₂-induced oxidative stress, whereas the active decrease of those antioxidant enzymes was observed in strain ST1314. In addition, the intracellular reactive oxygen species content in HT-29 cells co-incubated with strain CGMCC 7.179 was lower than that with strain ST1314 under the same oxidative stress. Furthermore, the protein content of nuclear factor erythroid 2-related factor 2 (Nrf2) in HT-29 cells following strain CGMCC 7.179 treatment was 1.4-fold higher than that with strain ST1314 treatment, and the increased transcription levels of Nrf2-related antioxidant enzyme genes were also observed in strain CGMCC 7.179 cells. All of these results demonstrated that S. thermophilus CGMCC 7.179 enhanced cellular antioxidant responses and endowed host cells with protective effects against oxidative stress mediated by the peroxidase EfeB.

Redox Pathways as Drug Targets in Microaerophilic Parasites

The microaerophilic parasites Entamoeba histolytica, Trichomonas vaginalis, and Giardia lamblia jointly cause hundreds of millions of infections in humans every year. Other microaerophilic parasites such as Tritrichomonas foetus and Spironucleus spp. pose a relevant health problem in veterinary medicine. Unfortunately, vaccines against these pathogens are unavailable, but their microaerophilic lifestyle opens opportunities for specifically developed chemotherapeutics. In particular, their high sensitivity towards oxygen can be exploited by targeting redox enzymes. This review focusses on the redox pathways of microaerophilic parasites and on drugs, either already in use or currently in the state of development, which target these pathways.

Designing aptamers which respond to intracellular oxidative stress and inhibit aggregation of mutant huntingtin

Targeted expression of a therapeutic agent is a major bottleneck in designing a drug delivery system. Protein aggregation and elevated oxidative stress are associated with the onset of many neurodegenerative disorders, including Huntington's disease (HD). An oxidative stress-inducible promoter, i.e. Thioredoxin 2, was employed to design a sensor for protein aggregation. RNA aptamers specific for mutant huntingtin were expressed only in cells where aggregation of mutant huntingtin occurred. A nine-fold increase in RNA expression was seen when aptamer sequences were cloned under the Trx2 promoter. Expression of aptamer resulted in reduced protein aggregation and decreased oxidative stress, which, in turn, reduced the expression of aptamers by two-fold. Reduction in aggregation led to increased cell survival. The aptamers were not expressed in cells expressing wild-type huntingtin in the soluble form. This rational and simple design will allow the use of this construct for the targeted expression of other therapeutic nucleic acid molecules as well.

Metabolic Reprogramming in Modulating T Cell Reactive Oxygen Species Generation and Antioxidant Capacity

A robust adaptive immune response requires a phase of proliferative burst which is followed by the polarization of T cells into relevant functional subsets. Both processes are associated with dramatically increased bioenergetics demands, biosynthetic demands, and redox demands. T cells meet these demands by rewiring their central metabolic pathways that generate energy and biosynthetic precursors by catabolizing and oxidizing nutrients into carbon dioxide. Simultaneously, oxidative metabolism also produces reactive oxygen species (ROS), which are tightly controlled by antioxidants and plays important role in regulating T cell functions. In this review, we discuss how metabolic rewiring during T cell activation influence ROS production and antioxidant capacity.

Toxicological effects of CdSe nanocrystals on the marine diatom Phaeodactylum tricornutum: The first mass spectrometry-based proteomic approach

In the marine environment, benthic diatoms from estuarine and coastal sediments are among the first targets of nanoparticle pollution whose potential toxicity on marine organisms is still largely unknown. It is therefore relevant to improve our knowledge of interactions between these new pollutants and microalgae, the key players in the control of marine resources. In this study, the response of P. tricornutum to CdSe nanocrystals (CdSe NPs) of 5 nm (NP5) and 12 nm (NP12) in diameter was evaluated through microscopic, physiological, biochemical and proteomic approaches. NP5 and NP12 affected cell growth but oxygen production was only slightly decreased by NP5 after 1-d incubation time. In our experimental conditions, a high CdSe NP dissolution was observed during the first day of culture, leading to Cd bioaccumulation and oxidative stress, particularly with NP12. However, after a 7-day incubation time, proteomic analysis highlighted that P. tricornutum responded to CdSe NP toxicity by regulating numerous proteins involved in protection against oxidative stress, cellular redox homeostasis, Ca²⁺ regulation and signalling, S-nitrosylation and S-glutathionylation processes and cell damage repair. These proteome changes allowed algae cells to regulate their intracellular ROS level in contaminated cultures. P. tricornutum was also capable to control its intracellular Cd concentration at a sufficiently low level to preserve its growth. To our knowledge, this is the first work allowing the identification of proteins differentially expressed by P. tricornutum subjected to NPs and thus the understanding of some molecular pathways involved in its cellular response to nanoparticles.

SIGNIFICANCE

The microalgae play a key role in the control of marine resources. Moreover, they produce 50% of the atmospheric oxygen. CdSe NPs are extensively used in the industry of renewable energies and it is regrettably expected that these pollutants will sometime soon appear in the marine environment through surface runoff, urban effluents and rivers. Since estuarine and coastal sediments concentrate pollutants, benthic microalgae which live in superficial sediments will be among the first targets of nanoparticle pollution. Thus, it is relevant to improve our knowledge of interactions between diatoms and nanoparticles. Proteomics is a powerful tool for understanding the molecular mechanisms triggered by nanoparticle exposure, and our study is the first one to use this tool to identify proteins differentially expressed by P. tricornutum subjected to CdSe nanocrystals. This work is fundamental to improve our knowledge about the defence mechanisms developed by algae cells to counteract damage caused by CdSe NPs.

Anti-stress effects of human placenta extract: possible involvement of the oxidative stress system in rats

BACKGROUND

Human placenta hydrolysate (hPH) has been utilized to improve menopausal, fatigue, liver function. Its high concentration of bioactive substances is known to produce including antioxidant, anti-inflammatory and anti-nociceptive activities. However, its mechanisms of stress-induced depression remain unknown.

METHODS

The present study examined the effect of hPH on stress-induced depressive behaviors and biochemical parameters in rats. hPH (0.02 ml, 0.2 ml or 1 ml/rat) was injected intravenously 30 min before the daily stress session in male Sprague-Dawley rats exposed to repeated immobilization stress (4 h/day for 7 days). The depressive-like behaviors of all groups were measured by elevated plus maze (EPM) and forced swimming test (FST). After the behavior tests, brain samples of all groups were collected for the analysis of glutathione peroxidase (GPx) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) staining.

RESULTS

Treatment with hPH produced a significant decrease of immobility time in the FST compared to the controls. Additionally, hPH treatment elicited a slightly decreasing trend in anxiety behavior on the EPM. Furthermore, hPH increased the level of GPx protein in the hippocampus, and decreased the expression of NADPH-d in the paraventricular nucleus (PVN).

CONCLUSION

This study demonstrated that hPH has anti-stress effects via the regulation of nitric oxide (NO) synthase and antioxidant activity in the brain. These results suggest that hPH may be useful in the treatment of stress-related diseases such as chronic fatigue syndrome.

Till Death Do Us Part: The Marriage of Autophagy and Apoptosis

Autophagy is a widely conserved catabolic process that is necessary for maintaining cellular homeostasis under normal physiological conditions and driving the cell to switch back to this status quo under times of starvation, hypoxia, and oxidative stress. The potential similarities and differences between basal autophagy and stimulus-induced autophagy are still largely unknown. Both act by clearing aberrant or unnecessary cytoplasmic material, such as misfolded proteins, supernumerary and defective organelles. The relationship between reactive oxygen species (ROS) and autophagy is complex. Cellular ROS is predominantly derived from mitochondria. Autophagy is triggered by this event, and by clearing the defective organelles effectively, it lowers cellular ROS thereby restoring cellular homeostasis. However, if cellular homeostasis cannot be reached, the cells can switch back and choose a regulated cell death response. Intriguingly, the autophagic and cell death machines both respond to the same stresses and share key regulatory proteins, suggesting that the pathways are intricately connected. Here, the intersection between autophagy and apoptosis is discussed with a particular focus on the role ROS plays.

Comparative Metatranscriptomics of Wheat Rhizosphere Microbiomes in Disease Suppressive and Non-suppressive Soils for Rhizoctonia solani AG8

The soilborne fungus Rhizoctonia solani anastomosis group (AG) 8 is a major pathogen of grain crops resulting in substantial production losses. In the absence of resistant cultivars of wheat or barley, a sustainable and enduring method for disease control may lie in the enhancement of biological disease suppression. Evidence of effective biological control of R. solani AG8 through disease suppression has been well documented at our study site in Avon, South Australia. A comparative metatranscriptomic approach was applied to assess the taxonomic and functional characteristics of the rhizosphere microbiome of wheat plants grown in adjacent fields which are suppressive and non-suppressive to the plant pathogen R. solani AG8. Analysis of 12 rhizosphere metatranscriptomes (six per field) was undertaken using two bioinformatic approaches involving unassembled and assembled reads. Differential expression analysis showed the dominant taxa in the rhizosphere based on mRNA annotation were Arthrobacter spp. and Pseudomonas spp. for non-suppressive samples and Stenotrophomonas spp. and Buttiauxella spp. for the suppressive samples. The assembled metatranscriptome analysis identified more differentially expressed genes than the unassembled analysis in the comparison of suppressive and non-suppressive samples. Suppressive samples showed greater expression of a polyketide cyclase, a terpenoid biosynthesis backbone gene (dxs) and many cold shock proteins (csp). Non-suppressive samples were characterised by greater expression of antibiotic genes such as non-heme chloroperoxidase (cpo) which is involved in pyrrolnitrin synthesis, and phenazine biosynthesis family protein F (phzF) and its transcriptional activator protein (phzR). A large number of genes involved in detoxifying reactive oxygen species (ROS) and superoxide radicals (sod, cat, ahp, bcp, gpx1, trx) were also expressed in the non-suppressive rhizosphere samples most likely in response to the infection of wheat roots by R. solani AG8. Together these results provide new insight into microbial gene expression in the rhizosphere of wheat in soils suppressive and non-suppressive to R. solani AG8. The approach taken and the genes involved in these functions provide direction for future studies to determine more precisely the molecular interplay of plant-microbe-pathogen interactions with the ultimate goal of the development of management options that promote beneficial rhizosphere microflora to reduce R. solani AG8 infection of crops.

The Function of Thioredoxin-Binding Protein-2 (TBP-2) in Different Diseases

Thioredoxin-binding protein-2 (TBP-2) has an important role in the redox system, but it plays a different role in many different diseases (e.g., various cancers, diabetes mellitus (DM), cardiovascular disease, and cataracts) by influencing cell proliferation, differentiation, apoptosis, autophagy, and metabolism. Distinct transcription factors (TFs) stimulated by different factors combine with binding sites or proteins to upregulate or downregulate TBP-2 expression, in order to respond to the change in the internal environment. Most research disclosed that the main function of TBP-2 is associating with thioredoxin (Trx) to inhibit the antioxidant capacity of Trx. Furthermore, the TBP-2 located in tissues, whether normal or abnormal, has the ability to cause the dysfunctioning of cells and even death through different pathways, such as shortening the cell cycle and inducing apoptosis or autophagy. Through these studies, we found that TBP-2 promoted the development of diseases which are involved in inflammatory and oxidative damage. To a certain extent, we believe that there is some hidden connection between the biological functions which TBP-2 participates in and some distinct diseases. This review presents only a summary of the roles that TBP-2 plays in cancer, DM, cataracts, and so on, as well as its universal mechanisms. Further investigations are needed for the cell signaling pathways of the effects caused by TBP-2. A greater understanding of the mechanisms of TBP-2 could produce potential new targets for the treatment of diseases, including cancer and diabetes, cardiovascular disease, and cataracts.

Antioxidant Potential of Propolis, Bee Pollen, and Royal Jelly: Possible Medical Application

Honeybees products comprise of numerous substances, including propolis, bee pollen, and royal jelly, which have long been known for their medicinal and health-promoting properties. Their wide biological effects have been known and used since antiquity. Bee products are considered to be a potential source of natural antioxidants such as flavonoids, phenolic acids, or terpenoids. Nowadays, the still growing concern in natural substances capable of counteracting the effects of oxidative stress underlying the pathogenesis of numerous diseases, such as neurodegenerative disorders, cancer, diabetes, and atherosclerosis, as well as negative effects of different harmful factors and drugs, is being observed. Having regarded the importance of acquiring drugs from natural sources, this review is aimed at updating the current state of knowledge of antioxidant capacity of selected bee products, namely, propolis, bee pollen, and royal jelly, and of their potential antioxidant-related therapeutic applications. Moreover, the particular attention has been attributed to the understanding of the mechanisms underlying antioxidant properties of bee products. The influence of bee species, plant origin, geographic location, and seasonality as well as type of extraction solutions on the composition of bee products extracts were also discussed.

13 reasons why the brain is susceptible to oxidative stress

The human brain consumes 20% of the total basal oxygen (O2) budget to support ATP intensive neuronal activity. Without sufficient O2 to support ATP demands, neuronal activity fails, such that, even transient ischemia is neurodegenerative. While the essentiality of O2 to brain function is clear, how oxidative stress causes neurodegeneration is ambiguous. Ambiguity exists because many of the reasons why the brain is susceptible to oxidative stress remain obscure. Many are erroneously understood as the deleterious result of adventitious O2 derived free radical and non-radical species generation. To understand how many reasons underpin oxidative stress, one must first re-cast free radical and non-radical species in a positive light because their deliberate generation enables the brain to achieve critical functions (e.g. synaptic plasticity) through redox signalling (i.e. positive functionality). Using free radicals and non-radical derivatives to signal sensitises the brain to oxidative stress when redox signalling goes awry (i.e. negative functionality). To advance mechanistic understanding, we rationalise 13 reasons why the brain is susceptible to oxidative stress. Key reasons include inter alia unsaturated lipid enrichment, mitochondria, calcium, glutamate, modest antioxidant defence, redox active transition metals and neurotransmitter auto-oxidation. We review RNA oxidation as an underappreciated cause of oxidative stress. The complex interplay between each reason dictates neuronal susceptibility to oxidative stress in a dynamic context and neural identity dependent manner. Our discourse sets the stage for investigators to interrogate the biochemical basis of oxidative stress in the brain in health and disease.

The role of the thioredoxin/thioredoxin reductase system in the metabolic syndrome: towards a possible prognostic marker?

Mammalian thioredoxin reductase (TrxR) is a selenoprotein with three existing isoenzymes (TrxR1, TrxR2, and TrxR3), which is found primarily intracellularly but also in extracellular fluids. The main substrate thioredoxin (Trx) is similarly found (as Trx1 and Trx2) in various intracellular compartments, in blood plasma, and is the cell's major disulfide reductase. Thioredoxin reductase is necessary as a NADPH-dependent reducing agent in biochemical reactions involving Trx. Genetic and environmental factors like selenium status influence the activity of TrxR. Research shows that the Trx/TrxR system plays a significant role in the physiology of the adipose tissue, in carbohydrate metabolism, insulin production and sensitivity, blood pressure regulation, inflammation, chemotactic activity of macrophages, and atherogenesis. Based on recent research, it has been reported that the modulation of the Trx/TrxR system may be considered as a new target in the management of the metabolic syndrome, insulin resistance, and type 2 diabetes, as well as in the treatment of hypertension and atherosclerosis. In this review evidence about a possible role of this system as a marker of the metabolic syndrome is reported.

KH176 Safeguards Mitochondrial Diseased Cells from Redox Stress-Induced Cell Death by Interacting with the Thioredoxin System/Peroxiredoxin Enzyme Machinery

A deficient activity of one or more of the mitochondrial oxidative phosphorylation (OXPHOS) enzyme complexes leads to devastating diseases, with high unmet medical needs. Mitochondria, and more specifically the OXPHOS system, are the main cellular production sites of Reactive Oxygen Species (ROS). Increased ROS production, ultimately leading to irreversible oxidative damage of macromolecules or to more selective and reversible redox modulation of cell signalling, is a causative hallmark of mitochondrial diseases. Here we report on the development of a new clinical-stage drug KH176 acting as a ROS-Redox modulator. Patient-derived primary skin fibroblasts were used to assess the potency of a new library of chromanyl-based compounds to reduce ROS levels and protect cells against redox-stress. The lead compound KH176 was studied in cell-based and enzymatic assays and in silico. Additionally, the metabolism, pharmacokinetics and toxicokinetics of KH176 were assessed in vivo in different animal species. We demonstrate that KH176 can effectively reduce increased cellular ROS levels and protect OXPHOS deficient primary cells against redox perturbation by targeting the Thioredoxin/Peroxiredoxin system. Due to its dual activity as antioxidant and redox modulator, KH176 offers a novel approach to the treatment of mitochondrial (-related) diseases. KH176 efficacy and safety are currently being evaluated in a Phase 2 clinical trial.

Oxidative stress, aging, and diseases

Reactive oxygen and nitrogen species (RONS) are produced by several endogenous and exogenous processes, and their negative effects are neutralized by antioxidant defenses. Oxidative stress occurs from the imbalance between RONS production and these antioxidant defenses. Aging is a process characterized by the progressive loss of tissue and organ function. The oxidative stress theory of aging is based on the hypothesis that age-associated functional losses are due to the accumulation of RONS-induced damages. At the same time, oxidative stress is involved in several age-related conditions (ie, cardiovascular diseases [CVDs], chronic obstructive pulmonary disease, chronic kidney disease, neurodegenerative diseases, and cancer), including sarcopenia and frailty. Different types of oxidative stress biomarkers have been identified and may provide important information about the efficacy of the treatment, guiding the selection of the most effective drugs/dose regimens for patients and, if particularly relevant from a pathophysiological point of view, acting on a specific therapeutic target. Given the important role of oxidative stress in the pathogenesis of many clinical conditions and aging, antioxidant therapy could positively affect the natural history of several diseases, but further investigation is needed to evaluate the real efficacy of these therapeutic interventions. The purpose of this paper is to provide a review of literature on this complex topic of ever increasing interest.

Oxidative and cytotoxic stress induced by inorganic granular and fibrous particles

The hazards of granular and fibrous particles have been associated with the generation of reactive oxygen species (ROS), which in turn is often associated with physicochemical properties exhibited by these particles. In the present study, the ability of various types of fibrous and granular dusts to generate oxidative stress, and their cytotoxicity, was investigated. Biopersistent granular dusts employed in the present study included micro‑ and nanosized titanium dioxide with rutile or anatase crystal structure modifications. Additionally, glass fibres, chrysotile and crocidolite asbestos representative of fibrous dust were selected. Detailed characterisation of particles was performed using scanning electron microscopy, and the effect of exposure to these particles on cell viability and intracellular ROS generation was assessed by PrestoBlue and 2',7'‑dichlorofluorescein assays, respectively. A549 human lung epithelial adenocarcinoma cells were exposed to increasing concentrations (0.1‑10 µg/cm2) of particles and fibres for 24 h. Subsequently, the gene expression of X‑linked inhibitor of apoptosis (XIAP), superoxide dismutase (SOD)1 and SOD2 were analysed by reverse transcription‑quantitative polymerase chain reaction. All investigated granular particles induce ROS production in A549 lung carcinoma cells within 24 h. Hematite increased ROS production in a dose‑dependent manner. A concentration of >1 µg/cm2 TiO2 na with its disordered surface, demonstrated the greatest ability to generate ROS. Therefore, the crystalline surface structure of the particle may be considered as a determinant of the extent of ROS induction by the particle. Fibrous particle compared with granular particles were associated with a lower ability to generate ROS. Glass fibres did not significantly increase ROS production in A549 cells, but elevated gene expression of SOD2 was observed. The results demonstrated that in general, the ability of particles to generate ROS depends on their number and crystal phase. Therefore, the present study helps to understand the cause of particle toxicity.

Evidence for Inhibition of Topoisomerase 1A by Gold(III) Macrocycles and Chelates Targeting Mycobacterium tuberculosis and Mycobacterium abscessus

Mycobacterium tuberculosis and the fast-growing species Mycobacterium abscessus are two important human pathogens causing persistent pulmonary infections that are difficult to cure and require long treatment times. The emergence of drug-resistant M. tuberculosis strains and the high level of intrinsic resistance of M. abscessus call for novel drug scaffolds that effectively target both pathogens. In this study, we evaluated the activity of bis(pyrrolide-imine) gold(III) macrocycles and chelates, originally designed as DNA intercalators capable of targeting human topoisomerase types I and II (Topo1 and Topo2), against M. abscessus and M. tuberculosis We identified a total of 5 noncytotoxic compounds active against both mycobacterial pathogens under replicating in vitro conditions. We chose one of these hits, compound 14, for detailed analysis due to its potent bactericidal mode of inhibition and scalable synthesis. The clinical relevance of this compound was demonstrated by its ability to inhibit a panel of diverse M. tuberculosis and M. abscessus clinical isolates. Prompted by previous data suggesting that compound 14 may target topoisomerase/gyrase enzymes, we demonstrated that it lacked cross-resistance with fluoroquinolones, which target the M. tuberculosis gyrase. In vitro enzyme assays confirmed the potent activity of compound 14 against bacterial topoisomerase 1A (Topo1) enzymes but not gyrase. Novel scaffolds like compound 14 with potent, selective bactericidal activity against M. tuberculosis and M. abscessus that act on validated but underexploited targets like Topo1 represent a promising starting point for the development of novel therapeutics for infections by pathogenic mycobacteria.

Mutant p53 tunes the NRF2-dependent antioxidant response to support survival of cancer cells

NRF2 (NFE2L2) is one of the main regulators of the antioxidant response of the cell. Here we show that in cancer cells NRF2 targets are selectively upregulated or repressed through a mutant p53-dependent mechanism. Mechanistically, mutant p53 interacts with NRF2, increases its nuclear presence and resides with NRF2 on selected ARE containing gene promoters activating the transcription of a specific set of genes while leading to the transcriptional repression of others. We show that thioredoxin (TXN) is a mutant p53-activated NRF2 target with pro-survival and pro-migratory functions in breast cancer cells under oxidative stress, while heme oxygenase 1 (HMOX1) is a mutant p53-repressed target displaying opposite effects. A gene signature of NRF2 targets activated by mutant p53 shows a significant association with bad overall prognosis and with mutant p53 status in breast cancer patients. Concomitant inhibition of thioredoxin system with Auranofin and of mutant p53 with APR-246 synergizes in killing cancer cells expressing p53 gain-of-function mutants.

The Multifaceted Roles of DJ-1 as an Antioxidant

The DJ-1 protein was originally linked with Parkinson's disease and is now known to have antioxidant functions. The protein has three redox-sensitive cysteine residues, which are involved in its dimerisation and functional properties. A mildly oxidised form of DJ-1 is the most active form and protects cells from oxidative stress conditions. DJ-1 functions as an antioxidant through a variety of mechanisms, including a weak direct antioxidant activity by scavenging reactive oxygen species. DJ-1 also regulates a number of signalling pathways, including the inhibition of apoptosis signal-regulating kinase 1 (ASK1)-induced apoptosis under oxidative stress conditions. Other proteins regulated by DJ-1 include enzymes, chaperones, the 20S proteasome and transcription factors, including Nrf2. Once activated by oxidative stress, Nrf2 upregulates antioxidant gene expression including members of the thioredoxin and glutathione pathways, which in turn mediate an antioxidant protective function. Crosstalk between DJ-1 and both the thioredoxin and glutathione systems has also been identified. Thioredoxin reduces a cysteine residue on DJ-1 to modulate its activity, while glutaredoxin1 de-glutathionylates DJ-1, preventing degradation of DJ-1 and resulting in its accumulation. DJ-1 also regulates the activity of glutamate cysteine ligase, which is the rate-limiting step for glutathione synthesis. These antioxidant functions of DJ-1 are key to its role in protecting neurons from oxidative stress and are hypothesised to protect the brain from the development of neurodegenerative diseases such as Parkinson's disease (PD) and to protect cardiac tissues from ischaemic-reperfusion injury. However, DJ-1, as an antioxidant, also protects cancer cells from undergoing oxidative stress-induced apoptosis.

TXNIP in Metabolic Regulation: Physiological Role and Therapeutic Outlook

Background & Objective:

Thioredoxin-interacting protein (TXNIP) also known as thioredoxin binding protein-2 is a ubiquitously expressed protein that interacts and negatively regulates expression and function of Thioredoxin (TXN). Over the last few years, TXNIP has attracted considerable attention due to its wide-ranging functions impacting several aspects of energy metabolism. TXNIP acts as an important regulator of glucose and lipid metabolism through pleiotropic actions including regulation of β-cell function, hepatic glucose production, peripheral glucose uptake, adipogenesis, and substrate utilization. Overexpression of TXNIP in animal models has been shown to induce apoptosis of pancreatic β-cells, reduce insulin sensitivity in peripheral tissues like skeletal muscle and adipose, and decrease energy expenditure. On the contrary, TXNIP deficient animals are protected from diet induced insulin resistance and type 2 diabetes.

Summary:

Consequently, targeting TXNIP is thought to offer novel therapeutic opportunity and TXNIP inhibitors have the potential to become a powerful therapeutic tool for the treatment of diabetes mellitus. Here we summarize the current state of our understanding of TXNIP biology, highlight its role in metabolic regulation and raise critical questions that could help future research to exploit TXNIP as a therapeutic target.

Diabetic macular oedema: under-represented in the genetic analysis of diabetic retinopathy

Diabetic retinopathy, a complication of both type 1 and type 2 diabetes, is a complex disease and is one of the leading causes of blindness in adults worldwide. It can be divided into distinct subclasses, one of which is diabetic macular oedema. Diabetic macular oedema can occur at any time in diabetic retinopathy and is the most common cause of vision loss in patients with type 2 diabetes. The purpose of this review is to summarize the large number of genetic association studies that have been performed in cohorts of patients with type 2 diabetes and published in English-language journals up to February 2017. Many of these studies have produced positive associations with gene polymorphisms and diabetic retinopathy. However, this review highlights that within this large body of work, studies specifically addressing a genetic association with diabetic macular oedema, although present, are vastly under-represented. We also highlight that many of the studies have small patient numbers and that meta-analyses often inappropriately combine patient data sets. We conclude that there will continue to be conflicting results and no meaningful findings will be achieved if the historical approach of combining all diabetic retinopathy disease states within patient cohorts continues in future studies. This review also identifies several genes that would be interesting to analyse in large, well-defined cohorts of patients with diabetic macular oedema in future candidate gene association studies.

Loss of IDH2 Accelerates Age-related Hearing Loss in Male Mice

Isocitrate dehydrogenase (IDH) 2 participates in the TCA cycle and catalyzes the conversion of isocitrate to α-ketoglutarate and NADP⁺ to NADPH. In the mitochondria, IDH2 also plays a key role in protecting mitochondrial components from oxidative stress by supplying NADPH to both glutathione reductase (GSR) and thioredoxin reductase 2 (TXNRD2). Here, we report that loss of Idh2 accelerates age-related hearing loss, the most common form of hearing impairment, in male mice. This was accompanied by increased oxidative DNA damage, increased apoptotic cell death, and profound loss of spiral ganglion neurons and hair cells in the cochlea of 24-month-old Idh2^−/− mice. In young male mice, loss of Idh2 resulted in decreased NADPH redox state and decreased activity of TXNRD2 in the mitochondria of the inner ear. In HEI-OC1 mouse inner ear cell lines, knockdown of Idh2 resulted in a decline in cell viability and mitochondrial oxygen consumption. This was accompanied by decreased NADPH redox state and decreased activity of TXNRD2 in the mitochondria of the HEI-OC1 cells. Therefore, IDH2 functions as the principal source of NADPH for the mitochondrial thioredoxin antioxidant defense and plays an essential role in protecting hair cells and neurons against oxidative stress in the cochlea of male mice.

Linking Microbial Community Structure and Function During the Acidified Anaerobic Digestion of Grass

Harvesting valuable bioproducts from various renewable feedstocks is necessary for the critical development of a sustainable bioeconomy. Anaerobic digestion is a well-established technology for the conversion of wastewater and solid feedstocks to energy with the additional potential for production of process intermediates of high market values (e.g., carboxylates). In recent years, first-generation biofuels typically derived from food crops have been widely utilized as a renewable source of energy. The environmental and socioeconomic limitations of such strategy, however, have led to the development of second-generation biofuels utilizing, amongst other feedstocks, lignocellulosic biomass. In this context, the anaerobic digestion of perennial grass holds great promise for the conversion of sustainable renewable feedstock to energy and other process intermediates. The advancement of this technology however, and its implementation for industrial applications, relies on a greater understanding of the microbiome underpinning the process. To this end, microbial communities recovered from replicated anaerobic bioreactors digesting grass were analyzed. The bioreactors leachates were not buffered and acidic pH (between 5.5 and 6.3) prevailed at the time of sampling as a result of microbial activities. Community composition and transcriptionally active taxa were examined using 16S rRNA sequencing and microbial functions were investigated using metaproteomics. Bioreactor fraction, i.e., grass or leachate, was found to be the main discriminator of community analysis across the three molecular level of investigation (DNA, RNA, and proteins). Six taxa, namely Bacteroidia, Betaproteobacteria, Clostridia, Gammaproteobacteria, Methanomicrobia, and Negativicutes accounted for the large majority of the three datasets. The initial stages of grass hydrolysis were carried out by Bacteroidia, Gammaproteobacteria, and Negativicutes in the grass biofilms, in addition to Clostridia in the bioreactor leachates. Numerous glycolytic enzymes and carbohydrate transporters were detected throughout the bioreactors in addition to proteins involved in butanol and lactate production. Finally, evidence of the prevalence of stressful conditions within the bioreactors and particularly impacting Clostridia was observed in the metaproteomes. Taken together, this study highlights the functional importance of Clostridia during the anaerobic digestion of grass and thus research avenues allowing members of this taxon to thrive should be explored.

Antioxidant activity of nanomaterials

Nanomaterials represent one of the most promising frontiers in the research for improved antioxidants. Some nanomaterials, including organic (i.e. melanin, lignin) metal oxides (i.e. cerium oxide) or metal (i.e. gold, platinum) based nanoparticles, exhibit intrinsic redox activity that is often associated with radical trapping and/or with superoxide dismutase-like and catalase-like activities. Redox inactive nanomaterials can be transformed into antioxidants by grafting low molecular weight antioxidants on them. Herein, we propose a classification of nanoantioxidants based on their mechanism of action, and we review the chemical methods used to measure antioxidant activity by providing a rationale of the chemistry behind them.

Can dimedone be used to study selenoproteins? An investigation into the reactivity of dimedone toward oxidized forms of selenocysteine

Dimedone is a widely used reagent to assess the redox state of cysteine-containing proteins as it will alkylate sulfenic acid residues, but not sulfinic acid residues. While it has been reported that dimedone can label selenenic acid residues in selenoproteins, we investigated the stability, and reversibility of this label in a model peptide system. We also wondered whether dimedone could be used to detect seleninic acid residues. We used benzenesulfinic acid, benzeneseleninic acid, and model selenocysteine-containing peptides to investigate possible reactions with dimedone. These peptides were incubated with H₂ O₂ in the presence of dimedone and then the reactions were followed by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS). The native peptide, H-PTVTGCUG-OH (corresponding to the native amino acid sequence of the C-terminus of mammalian thioredoxin reductase), could not be alkylated by dimedone, but could be carboxymethylated with iodoacetic acid. However the "mutant peptide," H-PTVTGAUG-OH, could be labeled with dimedone at low concentrations of H₂ O₂ , but the reaction was reversible by addition of thiol. Due to the reversible nature of this alkylation, we conclude that dimedone is not a good reagent for detecting selenenic acids in selenoproteins. At high concentrations of H₂ O₂ , selenium was eliminated from the peptide and a dimeric form of dimedone could be detected using LCMS and ¹ H NMR. The dimeric dimedone product forms as a result of a seleno-Pummerer reaction with Sec-seleninic acid. Overall our results show that the reaction of dimedone with oxidized cysteine residues is quite different from the same reaction with oxidized selenocysteine residues.

An essential thioredoxin is involved in the control of the cell cycle in the bacterium Caulobacter crescentus

Thioredoxins (Trxs) are antioxidant proteins that are conserved among all species. These proteins have been extensively studied and perform reducing reactions on a broad range of substrates. Here, we identified Caulobacter crescentus Trx1 (CCNA_03653; CcTrx1) as an oxidoreductase that is involved in the cell cycle progression of this model bacterium and is required to sustain life. Intriguingly, the abundance of CcTrx1 varies throughout the C. crescentus cell cycle: although the expression of CcTrx1 is induced in stalked cells, right before DNA replication initiation, CcTrx1 is actively degraded by the ClpXP protease in predivisional cells. Importantly, we demonstrated that regulation of the abundance of CcTrx1 is crucial for cell growth and survival as modulating CcTrx1 levels leads to cell death. Finally, we also report a comprehensive biochemical and structural characterization of this unique and essential Trx. The requirement to precisely control the abundance of CcTrx1 for cell survival underlines the importance of redox control for optimal cell cycle progression in C. crescentus.

Balanced Regulation of Redox Status of Intracellular Thioredoxin Revealed by in-Cell NMR

To understand how intracellular proteins respond to oxidative stresses, the redox status of the target protein, as well as the intracellular redox potential ( E_GSH), which is defined by the concentrations of reduced and oxidized glutathione, should be observed simultaneously within living cells. In this study, we developed a method that can monitor the redox status of thioredoxin (Trx) and E_GSH by direct NMR observation of Trx and glutathione within living cells. Unlike the midpoint potential of Trx measured in vitro (∼ -300 mV), the intracellular Trx exhibited the redox transition at E_GSH between -250 and -200 mV, the range known to trigger the oxidative stress-mediated signalings. Furthermore, we quantified the contribution of Trx reductase to the redox status of Trx, demonstrating that the redox profile of Trx is determined by the interplay between the elevation of E_GSH and the reduction by Trx reductase and other endogenous molecules.

Repurposing Auranofin, Ebselen, and PX-12 as Antimicrobial Agents Targeting the Thioredoxin System

As microbial resistance to drugs continues to rise at an alarming rate, finding new ways to combat pathogens is an issue of utmost importance. Development of novel and specific antimicrobial drugs is a time-consuming and expensive process. However, the re-purposing of previously tested and/or approved drugs could be a feasible way to circumvent this long and costly process. In this review, we evaluate the U.S. Food and Drug Administration tested drugs auranofin, ebselen, and PX-12 as antimicrobial agents targeting the thioredoxin system. These drugs have been shown to act on bacterial, fungal, protozoan, and helminth pathogens without significant toxicity to the host. We propose that the thioredoxin system could serve as a useful therapeutic target with broad spectrum antimicrobial activity.

Peroxiredoxin as a functional endogenous antioxidant enzyme in pronuclei of mouse zygotes

Antioxidant mechanisms to adequately moderate levels of endogenous reactive oxygen species (ROS) are important for oocytes and embryos to obtain and maintain developmental competence, respectively. Immediately after fertilization, ROS levels in zygotes are elevated but the antioxidant mechanisms during the maternal-to-zygotic transition (MZT) are not well understood. First, we identified peroxiredoxin 1 (PRDX1) and PRDX2 by proteomics analysis as two of the most abundant endogenous antioxidant enzymes eliminating hydrogen peroxide (H₂O₂). We here report the cellular localization of hyperoxidized PRDX and its involvement in the antioxidant mechanisms of freshly fertilized oocytes. Treatment of zygotes at the pronuclear stage with H₂O₂ enhanced pronuclear localization of hyperoxidized PRDX in zygotes and concurrently impaired the generation of 5-hydroxymethylcytosine (5hmC) on the male genome, which is an epigenetic reprogramming event that occurs at the pronuclear stage. Thus, our results suggest that endogenous PRDX is involved in antioxidant mechanisms and epigenetic reprogramming during MZT.

Hyperoxidation of Peroxiredoxins: Gain or Loss of Function?

SIGNIFICANCE

In 2003, structural studies revealed that eukaryotic 2-Cys peroxiredoxins (Prx) have evolved to be sensitive to inactivation of their thioredoxin peroxidase activity by hyperoxidation (sulfinylation) of their peroxide-reacting catalytic cysteine. This was accompanied by the unexpected discovery, that the sulfinylation of this cysteine was reversible in vivo and the identification of a new enzyme, sulfiredoxin, that had apparently co-evolved specifically to reduce hyperoxidized 2-Cys Prx, restoring their peroxidase activity. Together, these findings have provided the impetus for multiple studies investigating the purpose of this reversible, Prx hyperoxidation. Recent Advances: It has been suggested that inhibition of the thioredoxin peroxidase activity by hyperoxidation can both promote and inhibit peroxide signal transduction, depending on the context. Prx hyperoxidation has also been proposed to protect cells against reactive oxygen species (ROS)-induced damage, by preserving reduced thioredoxin and/or by increasing non-peroxidase chaperone or signaling activities of Prx.

CRITICAL ISSUES

Here, we will review the evidence in support of each of these proposed functions, in view of the in vivo contexts in which Prx hyperoxidation occurs, and the role of sulfiredoxin. Thus, we will attempt to explain the basis for seemingly contradictory roles for Prx hyperoxidation in redox signaling.

FUTURE DIRECTIONS

We provide a rationale, based on modeling and experimental studies, for why Prx hyperoxidation should be considered a suitable, early biomarker for damaging levels of ROS. We discuss the implications that this has for the role of Prx in aging and the detection of hyperoxidized Prx as a conserved feature of circadian rhythms. Antioxid. Redox Signal. 28, 574-590.

Novel approach for evaluating pharmaceuticals toxicity using Daphnia model: analysis of the mode of cytochrome P450-generated metabolite action after acetaminophen exposure

Because of its widespread use, the pharmaceutical acetaminophen (APAP) is frequently detected in aquatic environments. APAP can have serious physiological effects, such as reduced reproduction, low growth rates, and abnormal behavior, in aquatic organisms. However, the methods available for evaluation of the aquatic toxicity of APAP are of limited usefulness. The present study aimed to develop reliable and sensitive markers for evaluation of APAP toxicity using Daphnia as a model organism. We focused on N-acetyl-p-benzoquinoneimine (NAPQI) production from APAP via cytochrome P450 metabolism because NAPQI causes APAP toxicity. Daphnia magna were exposed to APAP (0, 50, or 100 mg/L for 12 h or 24 h), and the total metabolites were extracted and analyzed for NAPQI. Direct detection of NAPQI was difficult because of its high reactivity, and its peak was close to that for APAP. Therefore, we tried to identify molecular and biochemical indicators associated with NAPQI generation, elimination, and its interactions with macromolecules. We identified changes in CYP370A13 gene expression, glutathione depletion, inhibition of thioredoxin reductase activity, and production of reactive oxygen species as indicators of D. magna exposure to APAP. These indicators could be used to develop sensitive and accurate techniques to evaluate the environmental toxicity of APAP.

Inhibition of thioredoxin activates mitophagy and overcomes adaptive bortezomib resistance in multiple myeloma

Background

Although current chemotherapy using bortezomib (Velcade) against multiple myeloma in adults has achieved significant responses and even remission, a majority of patients will develop acquired resistance to bortezomib. Increased thioredoxin level has been reported to be associated with carcinogenesis; however, the role of thioredoxin in bortezomib drug resistance of myeloma remains unclear.

Methods

We generated several bortezomib-resistant myeloma cell lines by serially passaging with increased concentrations of bortezomib over a period of 1.5 years. Thioredoxin expression was measured by real-time PCR and western blot.

Results

The role of thioredoxin in the survival of bortezomib-resistant myeloma cells was determined by specific shRNA knockdown in vitro and in vivo. Thioredoxin inhibitor (PX12) was used to determine the effectiveness of thioredoxin inhibition in the treatment of bortezomib-resistant myeloma cells. The effect of thioredoxin inhibition on mitophagy induction was examined. The correlation of thioredoxin expression with patient overall survival was interrogated. Thioredoxin expression was significantly upregulated in bortezomib-resistant myeloma cells and the change correlated with the increase of bortezomib concentration. Thioredoxin gene knockdown using specific shRNA sensitized bortezomib-resistant myeloma cells to bortezomib efficiency in vitro and in vivo. Similarly, pharmacological inhibition with PX12 inhibited the growth of bortezomib-resistant myeloma cells and overcame bortezomib resistance in vitro and in vivo. Furthermore, inhibition of thioredoxin resulted in the activation of mitophagy and blockage of mitophagy prevented the effects of PX12 on bortezomib-resistant myeloma cells, indicating that mitophagy is the important molecular mechanism for the induction of cell death in bortezomib-resistant myeloma cells by PX12. Moreover, inhibition of thioredoxin resulted in downregulation of phosphorylated mTOR and ERK1/2. Finally, thioredoxin was overexpressed in primary myeloma cells isolated from bortezomib-resistant myeloma patients and overexpression of thioredoxin correlated with poor overall survival in patients with multiple myeloma.

Conclusions

Our findings demonstrated that increased thioredoxin plays a critical role in bortezomib resistance in multiple myeloma through mitophagy inactivation and increased mTOR and ERK1/2 phosphorylation. Thioredoxin provides a potential target for clinical therapeutics against multiple myeloma, particularly for bortezomib-resistant/refractory myeloma patients.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0575-7) contains supplementary material, which is available to authorized users.

HuR silencing elicits oxidative stress and DNA damage and sensitizes human triple-negative breast cancer cells to radiotherapy

HuR is an mRNA-binding protein whose overexpression in cancer cells has been associated with poor prognosis and resistance to therapy. While reports on HuR overexpression contributing to chemoresistance exist, limited information is available on HuR and radioresistance especially in triple-negative breast cancer (TNBC).

In this study we investigated the role of HuR in radiation resistance in three TNBC (MDA-MB-231, MDA-MB-468 and Hs578t) cell lines. Endogenous HuR expression was higher in TNBC cells compared to normal cells. siRNA mediated knockdown of HuR (siHuR) markedly reduced HuR mRNA and protein levels compared to scrambled siRNA (siScr) treatment. Further, siHuR treatment sensitized TNBC cells to ionizing radiation at 2 Gy compared to siScr treatment as evidenced by the significant reduction in clonogenic cell survival from 59%, 49%, and 65% in siScr-treated cells to 40%, 33%, and 46% in siHuR-treated MDA-MB-231, MDA-MB-468 and Hs578t cells, respectively. Molecular studies showed increased ROS production and inhibition of thioredoxin reductase (TrxR) in HuR knockdown cells contributed to radiosensitization. Associated with increased ROS production was evidence of increased DNA damage, demonstrated by a significant increase (p < 0.05) in γ-H2AX foci that persisted for up to 24 h in siHuR plus radiation treated cells compared to control cells. Further, comet assay revealed that HuR-silenced cells had larger and longer-lasting tails than control cells, indicating higher levels of DNA damage. In conclusion, our studies demonstrate that HuR knockdown in TNBC cells elicits oxidative stress and DNA damage resulting in radiosensitization.

Oral engineered Bifidobacterium longum expressing rhMnSOD to suppress experimental colitis

In recent years, using genetic engineering and bioengineering techniques, Bifidobacterium as a carrier to express specific functions of the protein or polypeptide, has become a new treatment for disease. Ulcerative colitis (UC) is a type of inflammatory bowel diseases (IBD). Although the cause of this inflammatory disorder is still unknown, a large amount of evidence suggests that ulcerative colitis is associated with increased activity of reactive oxygen species (ROS), manganese superoxide dismutase (MnSOD) is a kind of superoxide dismutase (SOD) has been demonstrated to play a key role in the pathophysiology of colitis. Here, we explored the Bifidobacterium as a drug delivery system to orally deliver a potent anti-inflammatory but poor penetration and stability antioxidant enzymes human MnSOD, transported into cells by a penetratin PEP-1. We constructed an expression vector expressing PEP-1-hMnSOD fusion protein, and successfully expressed hMnSOD fusion protein in engineered Bifidobacterium. Then we identified the bioactivity of engineered Bifidobacterium in LPS-induced inflammatory cell model. Finally, we used Bifidobacterium expressing PEP-1-hMnSOD fusion protein against DSS-induced ulcerative colitis mice. B. longum-PEP-1-rhMnSOD can successfully express rhMnSOD in the colon. We found that levels of inflammatory cytokines TNF-α, IL-1β, IL-6 and IL-8 as well as histological damage in colonic tissues showed that engineered Bifidobacterium effectively reduced dextran sulfate sodium(DSS)-induced ulcerative colitis, we also tested the MPO, verified the above conclusions. These results suggest that oral Bifidobacterium expressing PEP-1-hMnSOD fusion protein can be treated as a new method of UC treatment.

Chemical Biology of H2S Signaling through Persulfidation

Signaling by H2S is proposed to occur via persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH). Persulfidation provides a framework for understanding the physiological and pharmacological effects of H2S. Due to the inherent instability of persulfides, their chemistry is understudied. In this review, we discuss the biologically relevant chemistry of H2S and the enzymatic routes for its production and oxidation. We cover the chemical biology of persulfides and the chemical probes for detecting them. We conclude by discussing the roles ascribed to protein persulfidation in cell signaling pathways.

Role of Thioredoxin in Age-Related Hypertension

PURPOSE OF REVIEW

Although the roles of oxidant stress and redox perturbations in hypertension have been the subject of several reviews, role of thioredoxin (Trx), a major cellular redox protein in age-related hypertension remains inadequately reviewed. The purpose of this review is to bring readers up-to-date with current understanding of the role of thioredoxin in age-related hypertension.

RECENT FINDINGS

Age-related hypertension is a major underlying cause of several cardiovascular disorders, and therefore, intensive management of blood pressure is indicated in most patients with cardiovascular complications. Recent studies have shown that age-related hypertension was reversed and remained lowered for a prolonged period in mice with higher levels of human Trx (Trx-Tg). Additionally, injection of human recombinant Trx (rhTrx) decreased hypertension in aged wild-type mice that lasted for several days. Both Trx-Tg and aged wild-type mice injected with rhTrx were normotensive, showed increased NO production, decreased arterial stiffness, and increased vascular relaxation. These studies suggest that rhTrx could potentially be a therapeutic molecule to reverse age-related hypertension in humans. The reversal of age-related hypertension by restoring proteins that have undergone age-related modification is conceptually novel in the treatment of hypertension. Trx reverses age-related hypertension via maintaining vascular redox homeostasis, regenerating critical vasoregulatory proteins oxidized due to advancing age, and restoring native function of proteins that have undergone age-related modifications with loss-of function. Recent studies demonstrate that Trx is a promising molecule that may ameliorate or reverse age-related hypertension in older adults.

Substrate-induced structural alterations of Mycobacterial mycothione reductase and critical residues involved

Redox homeostasis is a prerequisite for survival of the pathogen Mycobacterium tuberculosis (Mtb) which employs the low molecular weight thiol mycothiol (MSH). The Mycobacterial NADPH-dependent mycothione reductase (MtMtr), composed of an NADPH-, FAD-, and a dimerization-domain connected by linkers, regulates the balance of oxidized-reduced MSH. Here, we demonstrate by small-angle X-ray scattering, that NADPH-binding alters the oligomeric state equilibrium of the protein with no significant overall structural change after MSH-binding. Mutation of critical residues in the linker regions of MtMtr eliminate partially or totally the NADPH-induced oligomerization effect with simultaneous effect on enzyme activity. The data provide insight into the MtMtr linker regions involved in the novel oligomerization equilibrium of the Mycobacterial enzyme.

drFrnE Represents a Hitherto Unknown Class of Eubacterial Cytoplasmic Disulfide Oxido-Reductases

AIMS

Living cells employ thioredoxin and glutaredoxin disulfide oxido-reductases to protect thiol groups in intracellular proteins. FrnE protein of Deinococcus radiodurans (drFrnE) is a disulfide oxido-reductase that is induced in response to Cd²⁺ exposure and is involved in cadmium and radiation tolerance. The aim of this study is to probe structure, function, and cellular localization of FrnE class of proteins.

RESULTS

Here, we show drFrnE as a novel cytoplasmic oxido-reductase that could be functional in eubacteria under conditions where thioredoxin/glutaredoxin systems are inhibited or absent. Crystal structure analysis of drFrnE reveals thioredoxin fold with an alpha helical insertion domain and a unique, flexible, and functionally important C-terminal tail. The C-tail harbors a novel 239-CX₄C-244 motif that interacts with the active site 22-CXXC-25 motif. Crystal structures with different active site redox states, including mixed disulfide (Cys22-Cys244), are reported here. The biochemical data show that 239-CX₄C-244 motif channels electrons to the active site cysteines. drFrnE is more stable in the oxidized form, compared with the reduced form, supporting its role as a disulfide reductase. Using bioinformatics analysis and fluorescence microscopy, we show cytoplasmic localization of drFrnE. We have found "true" orthologs of drFrnE in several eubacterial phyla and, interestingly, all these groups apparently lack a functional glutaredoxin system. Innovation and Conclusion: We show that drFrnE represents a new class of hitherto unknown intracellular oxido-reductases that are abundantly present in eubacteria. Unlike other well-known oxido-reductases, FrnE harbors an additional dithiol motif that acts as a conduit to channel electrons to the active site during catalytic turnover. Antioxid. Redox Signal. 28, 296-310.

Biosensors for spatiotemporal detection of reactive oxygen species in cells and tissues

Redox biology has become a major issue in numerous areas of physiology. Reactive oxygen species (ROS) have a broad range of roles from signal transduction to growth control and cell death. To understand the nature of these roles, accurate measurement of the reactive compounds is required. An increasing number of tools for ROS detection is available; however, the specificity and sensitivity of these tools are often insufficient. Furthermore, their specificity has been rarely evaluated in complex physiological conditions. Many ROS probes are sensitive to environmental conditions in particular pH, which may interfere with ROS detection and cause misleading results. Accurate detection of ROS in physiology and pathophysiology faces additional challenges concerning the precise localization of the ROS and the timing of their production and disappearance. Certain ROS are membrane permeable, and certain ROS probes move across cells and organelles. Targetable ROS probes such as fluorescent protein-based biosensors are required for accurate localization. Here we analyze these challenges in more detail, provide indications on the strength and weakness of current tools for ROS detection, and point out developments that will provide improved ROS detection methods in the future. There is no universal method that fits all situations in physiology and cell biology. A detailed knowledge of the ROS probes is required to choose the appropriate method for a given biological problem. The knowledge of the shortcomings of these probes should also guide the development of new sensors.

Disulfide bond based polymeric drug carriers for cancer chemotherapy and relevant redox environments in mammals

Increasing numbers of disulfide linkage-employing polymeric drug carriers that utilize the reversible peculiarity of this unique covalent bond have been reported. The reduction-sensitive disulfide bond is usually employed as a linkage between hydrophilic and hydrophobic polymers, polymers and drugs, or as cross-linkers in polymeric drug carriers. These polymeric drug carriers are designed to exploit the significant redox potential difference between the reducing intracellular environments and relatively oxidizing extracellular spaces. In addition, these drug carriers can release a considerable amount of anticancer drug in response to the reducing environment when they reach tumor tissues, effectively improving antitumor efficacy. This review focuses on various disulfide linkage-employing polymeric drug carriers. Important redox thiol pools, including GSH/GSSG, Cys/CySS, and Trx1, as well as redox environments in mammals, will be introduced.

Expression of the methionine sulfoxide reductase lost during evolution extends Drosophila lifespan in a methionine-dependent manner

Accumulation of oxidized amino acids, including methionine, has been implicated in aging. The ability to reduce one of the products of methionine oxidation, free methionine-R-sulfoxide (Met-R-SO), is widespread in microorganisms, but during evolution this function, conferred by the enzyme fRMsr, was lost in metazoa. We examined whether restoration of the fRMsr function in an animal can alleviate the consequences of methionine oxidation. Ectopic expression of yeast fRMsr supported the ability of Drosophila to catalyze free Met-R-SO reduction without affecting fecundity, food consumption, and response to starvation. fRMsr expression also increased resistance to oxidative stress. Moreover, it extended lifespan of flies in a methionine-dependent manner. Thus, expression of an oxidoreductase lost during evolution can enhance metabolic and redox functions and lead to an increase in lifespan in an animal model. More broadly, our study exposes the potential of a combination of genetic and nutritional strategies in lifespan control.

Redox regulation of microRNAs in cancer

Dysregulation of microRNAs (miRNAs) has long been implicated in tumorigenesis, whereas the underlying mechanisms remain largely unknown. Oxidative stress is a hallmark of cancer that involved in multiple pathophysiological processes, including the aberrant regulation of miRNAs. Compelling evidences have implied complicated interplay between reactive oxygen species (ROS) and miRNAs. Indeed, ROS induces carcinogenesis through either reducing or increasing the miRNA level, leading to the activation of oncogenes or silence of tumor suppressors, respectively. In turn, miRNAs target ROS productive genes or antioxidant responsive elements to affect cellular redox balance, which contributes to establishing a microenvironment favoring cancer cell growth and metastasis. Both miRNAs and ROS have been identified as potential biomarkers and therapeutic targets in human malignancies, and comprehensive understanding of the molecular events herein will facilitate the development of novel cancer therapeutic strategies.

Low-Molecular-Weight Thiols and Thioredoxins Are Important Players in Hg(II) Resistance in Thermus thermophilus HB27

Mercury (Hg), one of the most toxic and widely distributed heavy metals, has a high affinity for thiol groups. Thiol groups reduce and sequester Hg. Therefore, low-molecular-weight (LMW) and protein thiols may be important cell components used in Hg resistance. To date, the role of low-molecular-weight thiols in Hg detoxification remains understudied. The mercury resistance (mer) operon of Thermus thermophilus suggests an evolutionary link between Hg(II) resistance and low-molecular-weight thiol metabolism. The mer operon encodes an enzyme involved in methionine biosynthesis, Oah. Challenge with Hg(II) resulted in increased expression of genes involved in the biosynthesis of multiple low-molecular-weight thiols (cysteine, homocysteine, and bacillithiol), as well as the thioredoxin system. Phenotypic analysis of gene replacement mutants indicated that Oah contributes to Hg resistance under sulfur-limiting conditions, and strains lacking bacillithiol and/or thioredoxins are more sensitive to Hg(II) than the wild type. Growth in the presence of either a thiol-oxidizing agent or a thiol-alkylating agent increased sensitivity to Hg(II). Furthermore, exposure to 3 μM Hg(II) consumed all intracellular reduced bacillithiol and cysteine. Database searches indicate that oah2 is present in all Thermus sp. mer operons. The presence of a thiol-related gene was also detected in some alphaproteobacterial mer operons, in which a glutathione reductase gene was present, supporting the role of thiols in Hg(II) detoxification. These results have led to a working model in which LMW thiols act as Hg(II)-buffering agents while Hg is reduced by MerA.IMPORTANCE The survival of microorganisms in the presence of toxic metals is central to life's sustainability. The affinity of thiol groups for toxic heavy metals drives microbe-metal interactions and modulates metal toxicity. Mercury detoxification (mer) genes likely originated early in microbial evolution in geothermal environments. Little is known about how mer systems interact with cellular thiol systems. Thermus spp. possess a simple mer operon in which a low-molecular-weight thiol biosynthesis gene is present, along with merR and merA In this study, we present experimental evidence for the role of thiol systems in mercury resistance. Our data suggest that, in T. thermophilus, thiolated compounds may function side by side with mer genes to detoxify mercury. Thus, thiol systems function in consort with mer-mediated resistance to mercury, suggesting exciting new questions for future research.

Role of protein carbonylation in diabetes

Diabetes mellitus is a metabolic disease characterized by, among others, elevated blood glucose levels. Hyperglycaemia as well as enhanced levels of glucose-derived reactive metabolites contribute to the development of diabetic complications partly via increased generation of reactive oxygen species (ROS). ROS are not only part of signaling pathways themselves but also lead to carbonylation of particular amino acid side chains by direct metal-catalyzed oxidation. In addition, carbonyl groups can be introduced into proteins indirectly by non-oxidative covalent adduction of reactive carbonyl species generated by the oxidation of lipids or carbohydrates. Both direct and indirect carbonylation mechanisms may affect protein conformation, activity, and function. Herein we introduce the different mechanisms of the carbonylation reaction, discuss degradation mechanisms, and the fate of proteins modified this way and how the overall degree of carbonylation affects protein homeostasis and function differently. The role of protein carbonylation in metabolic control systems and cell signaling are also summarized. Finally, current diagnostic and antioxidant therapeutic options in diabetes are discussed.