S-glutathiolation in life and death decisions of the cell

Preparation, Characterization, and Antioxidant Activities of Extracts from Amygdalus persica L. Flowers

A novel water-soluble Amygdalus persica L. flowers polysaccharide (APL) was successfully isolated and purified from Amygdalus persica L. flowers by hot water extraction. Its chemical components and structure were analyzed by IR, GC-MS, and HPLC. APL consisted of rhamnose, arabinose, mannose and glucose in a molar ratio of 0.17:0.034:1.0:0.17 with an average molecular weight of approximately 208.53 kDa and 15.19 kDa. The antioxidant activity of APL was evaluated through radical scavenging assays using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 3-ethylbenzthiazoline-6-sulfonic acid (ABTS), Hydroxyl radical scavenging, Superoxide radical scavenging, and the reducing power activity was also determined in vitro. Besides, in vivo antioxidant experiment, zebrafish (Danio rerio) embryos were treated with different concentrations of APL and then exposed to LPS to induce oxidative stress. Treatment with APL at 50 or 100 µg/mL significantly reduced LPS-induced oxidative stress in the zebrafish, demonstrating the strong antioxidant activity of APL. Moreover, the effect of APL on zebrafish depigmentation was tested by analyzing the tyrosinase activity and melanin content of zebrafish embryos. APL showed a potential reduction in the total melanin content and tyrosinase activity after treatment. This work provided important information for developing a potential natural antioxidant in the field of cosmetics and food.

Modulation of Cell Death Pathways for Cellular Protection and Anti-Tumoral Activity: The Role of Thymus spp. Extracts and Their Bioactive Molecules

Natural products used for their health-promoting properties have accompanied the evolution of humanity. Nowadays, as an effort to scientifically validate the health-promoting effects described by traditional medicine, an ever-growing number of bioactivities are being described for natural products and the phytochemicals that constitute them. Among them, medicinal plants and more specifically the Thymus genus spp., arise as products already present in the diet and with high acceptance, that are a source of phytochemicals with high pharmacological value. Phenolic acids, flavonoid glycoside derivatives, and terpenoids from Thymus spp. have been described for their ability to modulate cell death and survival pathways, much-valued bioactivities in the pharmaceutical industry, that continually sought-after new formulations to prevent undesired cell death or to control cell proliferation. Among these, wound treatment, protection from endogenous/exogenous toxic molecules, or the induction of selective cell death, such as the search for new anti-tumoral agents, arise as main objectives. This review summarizes and discusses studies on Thymus spp., as well as on compounds present in their extracts, with regard to their health-promoting effects involving the modulation of cell death or survival signaling pathways. In addition, studies regarding the main bioactive molecules and their cellular molecular targets were also reviewed. Concerning cell survival and proliferation, Thymus spp. present themselves as an option for new formulations designed for wound healing and protection against chemicals-induced toxicity. However, Thymus spp. extracts and some of their compounds regulate cell death, presenting anti-tumoral activity. Therefore Thymus spp. is a rich source of compounds with nutraceutical and pharmaceutical value.

Effects of Panthenol and N-Acetylcysteine on Changes in the Redox State of Brain Mitochondria under Oxidative Stress In Vitro

The glutathione system in the mitochondria of the brain plays an important role in maintaining the redox balance and thiol–disulfide homeostasis, whose violations are the important component of the biochemical shifts in neurodegenerative diseases. Mitochondrial dysfunction is known to be accompanied by the activation of free radical processes, changes in energy metabolism, and is involved in the induction of apoptotic signals. The formation of disulfide bonds is a leading factor in the folding and maintenance of the three-dimensional conformation of many specific proteins that selectively accumulate in brain structures during neurodegenerative pathology. In this study, we estimated brain mitochondria redox status and functioning during induction of oxidative damage in vitro. We have shown that the development of oxidative stress in vitro is accompanied by inhibition of energy metabolism in the brain mitochondria, a shift in the redox potential of the glutathione system to the oxidized side, and activation of S-glutathionylation of proteins. Moreover, we studied the effects of pantothenic acid derivatives—precursors of coenzyme A (CoA), primarily D-panthenol, that exhibit high neuroprotective activity in experimental models of neurodegeneration. Panthenol contributes to the significant restoration of the activity of enzymes of mitochondrial energy metabolism, normalization of the redox potential of the glutathione system, and a decrease in the level of S-glutathionylated proteins in brain mitochondria. The addition of succinate and glutathione precursor N-acetylcysteine enhances the protective effects of the drug.

Thiol-based redox-active proteins as cardioprotective therapeutic agents in cardiovascular diseases

Thiol-based redox compounds, namely thioredoxins (Trxs), glutaredoxins (Grxs) and peroxiredoxins (Prxs), stand as a pivotal group of proteins involved in antioxidant processes and redox signaling. Glutaredoxins (Grxs) are considered as one of the major families of proteins involved in redox regulation by removal of S-glutathionylation and thereby reactivation of other enzymes with thiol-dependent activity. Grxs are also coupled to Trxs and Prxs recycling and thereby indirectly contribute to reactive oxygen species (ROS) detoxification. Peroxiredoxins (Prxs) are a ubiquitous family of peroxidases, which play an essential role in the detoxification of hydrogen peroxide, aliphatic and aromatic hydroperoxides, and peroxynitrite. The Trxs, Grxs and Prxs systems, which reversibly induce thiol modifications, regulate redox signaling involved in various biological events in the cardiovascular system. This review focuses on the current knowledge of the role of Trxs, Grxs and Prxs on cardiovascular pathologies and especially in cardiac hypertrophy, ischemia/reperfusion (I/R) injury and heart failure as well as in the presence of cardiovascular risk factors, such as hypertension, hyperlipidemia, hyperglycemia and metabolic syndrome. Further studies on the roles of thiol-dependent redox systems in the cardiovascular system will support the development of novel protective and therapeutic strategies against cardiovascular diseases.

Inflammation and apoptosis, two key events induced by hyperglycemia mediated reactive nitrogen species in RGC-5 cells

Nitrosative stress plays a critical role in retinal injury in high glucose (HG) environment of eye, but the mechanisms remain poorly understood. Here we tested the hypothesis that HG induced reactive nitrogen species (RNS) production acts as a key functional mediator of antioxidant depletion, mitochondrial dysfunction, biomolecule damage, inflammation and apoptosis. Our findings illustrated that exposure of cultured RGC-5 cells to HG significantly disrupts the antioxidant defense mechanism and mitochondrial machineries by increasing the loss of mitochondrial membrane potential (ΔѰM) and elevating mitochondrial mass. Furthermore, we used biochemical tools to analyze the changes in metabolites, sulfur amino acids (SAAs) such as L-glutathione (GSH) and L-cysteine (Cys), in the presence of HG environment. These metabolic changes were followed by an increase in glycolytic flux that is phosphofructokinase-2 (PFK-2) activity. Moreover, HG exposure results in a significant disruption of protein carbonylation (PC) and lipid peroxidation (LPO), downregulation of OGG1 and increase in 8-OHdG accumulations in RGC-5 cells. In addition, our results demonstrated that HG environment coinciding with increased expression of inflammatory mediators, cell cycle deregulation, decreased in cell viability and expression of FoxOs, increased lysosomal content leading to apoptosis. Pre-treatment of selective inhibitors of RNS significantly reduced the HG-induced cell cycle deregulation and apoptosis in RGC-5 cells. Collectively, these results illustrated that accumulated RNS exacerbates the antioxidant depletion, mitochondrial dysfunction, biomolecule damage, inflammation and apoptosis induced by HG exposure in RGC-5 cells. Treatment of pharmacological inhibitors attenuated the HG induced in retinal cells.

Anaphylaxis-induced atrial fibrillation and anesthesia: Pathophysiologic and therapeutic considerations

Atrial fibrillation is the most common cardiac arrhythmia in western society affecting more than 35 million individuals worldwide annually. It is a common postoperative complication and may also occur spontaneously during general and local anesthesia administration. Aging, diabetes mellitus, hypertension, and cardiovascular diseases including cardiomyopathies, congenital cardiac anomalies, heart failure, myocardial ischemia, pericarditis, previous cardiac surgery, vascular disease, and valvular heart disease are some correlated factors. Beyond age, increased incidence of atrial fibrillation has been correlated to autoimmune system activation as it is the underlying mechanism of persistent atrial fibrillation development. Current research supports an association between the complement system activation and lymphocyte-pro-inflammatory cytokines release with the cardiac conduction system and atrial fibrosis. The loss of CD28 antigen from CD4+ CD28+ T lymphocytes seems to play a major role in atrial fibrillation development and prognosis. Except atrial fibrillation, a variety of additional electrocardiographic changes, resembling those with digitalis intoxication may accompany anaphylaxis and particularly Kounis syndrome. Histamine is one well-known mediator in allergic and inflammatory conditions as physiologically regulates several cardiovascular and endothelial functions with arrhythmogenic potential. The increased oxidative stress, measured by the redox potentials of glutathione, has been correlated with atrial fibrillation incidence and prevalence. The use of antazoline, a first-generation antihistamine agent used for rapid conversion of recent-onset atrial fibrillation in patients with preserved left ventricular function and for rapid atrial fibrillation termination during accessory pathway ablation denotes that anaphylaxis-induced histamine production could be the cause of atrial fibrillation at least in some instances. The anaphylaxis diagnosis in anesthesia can be challenging owing to the absence of cutaneous manifestetions such as flushing, urticaria, or angioedema. Anticoagulation for stroke prevention, rate and rhythm control medications, invasive methods such as radiofrequency ablation or cryoablation of pulmonary veins as well surgical ablation constitute the treatment basis of atrial fibrillation. Understanding the underlying mechanisms of atrial fibrillation by cardiologists, anesthesiologists and surgeons, as well as potential treatments, to optimize care is of paramount importance.

Molecular and Supramolecular Structure of the Mitochondrial Oxidative Phosphorylation System: Implications for Pathology

Under aerobic conditions, mitochondrial oxidative phosphorylation (OXPHOS) converts the energy released by nutrient oxidation into ATP, the currency of living organisms. The whole biochemical machinery is hosted by the inner mitochondrial membrane (mtIM) where the protonmotive force built by respiratory complexes, dynamically assembled as super-complexes, allows the F1FO-ATP synthase to make ATP from ADP + Pi. Recently mitochondria emerged not only as cell powerhouses, but also as signaling hubs by way of reactive oxygen species (ROS) production. However, when ROS removal systems and/or OXPHOS constituents are defective, the physiological ROS generation can cause ROS imbalance and oxidative stress, which in turn damages cell components. Moreover, the morphology of mitochondria rules cell fate and the formation of the mitochondrial permeability transition pore in the mtIM, which, most likely with the F1FO-ATP synthase contribution, permeabilizes mitochondria and leads to cell death. As the multiple mitochondrial functions are mutually interconnected, changes in protein composition by mutations or in supercomplex assembly and/or in membrane structures often generate a dysfunctional cascade and lead to life-incompatible diseases or severe syndromes. The known structural/functional changes in mitochondrial proteins and structures, which impact mitochondrial bioenergetics because of an impaired or defective energy transduction system, here reviewed, constitute the main biochemical damage in a variety of genetic and age-related diseases.

Functional interplay among thiol-based redox signaling, metabolism, and ferroptosis unveiled by a genetic variant of TP53

The p53 tumor suppressor protein is a transcription factor and master stress response mediator, and it is subject to reduction-oxidation (redox)-dependent regulation. The P47S variant of TP53, which exists primarily in African-descent populations, associates with an elevated abundance of low molecular weight (LMW) thiols, including glutathione (GSH) and coenzyme A (CoA). Here we show that S47 and P47 cells exhibit distinct metabolic profiles, controlled by their different redox states and expression of Activating Transcription Factor-4 (ATF4). We find that S47 cells exhibit decreased catabolic glycolysis but increased use of the pentose phosphate pathway (PPP), and an enhanced abundance of the antioxidant, NADPH. We identify ATF4 as differentially expressed in P47 and S47 cells and show that ATF4 can reverse the redox status and rescue metabolism of S47 cells, as well as increase sensitivity to ferroptosis. This adaptive metabolic switch is rapid, reversible, and accompanied by thiol-mediated changes in the structures and activities of key glycolytic signaling pathway proteins, including GAPDH and G6PD. The results presented here unveil the important functional interplay among pathways regulating thiol-redox status, metabolic adaptation, and cellular responses to oxidative stress.

Cigarette smoke and glutathione: Focus on in vitro cell models

Cigarette smoke (CS) is one of the most important preventable risk factors for the development of respiratory diseases, cardiovascular diseases, stroke, and various types of cancer. Due to its high intracellular concentration and central role in maintaining the cellular redox state, glutathione (GSH) is one of the key players in several enzymatic and non-enzymatic reactions necessary for protecting cells against CS-induced oxidative stress. A plethora of in vitro cell models have been used over the years to assess the effects of CS on intracellular GSH and its disulphide forms, i.e. glutathione disulphide (GSSG) and S-glutathionylated proteins. In this review, we described the effects of cell exposure to CS on cellular GSH and formation of its oxidized forms and adducts (GSH-conjugates). We also discussed the limitations and relevance of in vitro cell models of exposure to CS and critically assessed the congruence between smokers and in vitro cell models. What emerges clearly is that results obtained in vitro should be interpreted with extreme caution, bearing in mind the limitations of the specific cell model used. Despite this, in vitro cell models remain important tools in the assessment of CS-induced oxidative damage.

Quercetin Triggers Induction of Apoptotic and Lysosomal Death of Sensitive and Multidrug Resistant Leukaemia HL60 Cells

Multidrug resistance (MDR) constitutes the major cause of the failure in anticancer therapy. One of the most important mechanisms leading to the occurrence of MDR is related to the modulation of cellular death pathways. The aim of this study was to determine the effect of quercetin (Q) on triggering the programed death of human promyelocytic leukemia sensitive cells HL60 as well as multidrug resistant HL60/VINC cells overexpressing P-glycoprotein and HL60/MX2 cells characterized by the presence of mutated α isoform of topoisomerase II and the absence of β isoform of this enzyme. Q exerted comparable cytotoxic activities toward sensitive HL60 cells and their MDR counterparts. It was also found that this compound modulated the cellular level of reactive oxygen species (ROS) and led to the marked decrease in cellular GSH level. Furthermore, it was demonstrated that Q used at IC₅₀ and IC₉₀ significantly increased the percentage of sub-G1 subpopulation of all studied leukemia cells causing oligonucleosomal DNA fragmentation. The present study also indicated that Q used at IC₉₀ triggers predominantly programed cell death of sensitive HL60 cells and their MDR counterparts by induction of apoptosis occurring with the involvement of caspase-3 and caspase-8 as well as by lysosome membrane permeabilization-dependent mechanisms.

The role of thiols in antioxidant systems

The sulfur biochemistry of the thiol group endows cysteines with a number of highly specialized and unique features that enable them to serve a variety of different functions in the cell. Typically highly conserved in proteins, cysteines are predominantly found in functionally or structurally crucial regions, where they act as stabilizing, catalytic, metal-binding and/or redox-regulatory entities. As highly abundant low molecular weight thiols, cysteine thiols and their oxidized disulfide counterparts are carefully balanced to maintain redox homeostasis in various cellular compartments, protect organisms from oxidative and xenobiotic stressors and partake actively in redox-regulatory and signaling processes. In this review, we will discuss the role of protein thiols as scavengers of hydrogen peroxide in antioxidant enzymes, use thiol peroxidases to exemplify how protein thiols contribute to redox signaling, provide an overview over the diverse set of low molecular weight thiol-based redox systems found in biology, and illustrate how thiol-based redox systems have evolved not only to protect against but to take full advantage of a world full of molecular oxygen.

The garlic compound ajoene covalently binds vimentin, disrupts the vimentin network and exerts anti-metastatic activity in cancer cells

BACKGROUND

Garlic has been used for centuries for its flavour and health promoting properties that include protection against cancer. The vinyl disulfide-sulfoxide ajoene is one of the phytochemicals found in crushed cloves, hypothesised to act by S-thiolating reactive cysteines in target proteins.

METHODS

Using our fluorescently labelled ajoene analogue called dansyl-ajoene, ajoene's protein targets in MDA-MB-231 breast cancer cells were tagged and separated by 2D electrophoresis. A predominant band was identified by MALDI-TOF MS/MS to be vimentin. Target validation experiments were performed using pure recombinant vimentin protein. Computational modelling of vimentin bound to ajoene was performed using Schrödinger and pKa calculations by Epik software. Cytotoxicity of ajoene in MDA-MB-231 and HeLa cells was measured by the MTT assay. The vimentin filament network was visualised in ajoene-treated and non-treated cells by immunofluorescence and vimentin protein expression was determined by immunoblot. The invasion and migration activity was measured by wound healing and transwell assays using wildtype cells and cells in which the vimentin protein had been transiently knocked down by siRNA or overexpressed.

RESULTS

The dominant protein tagged by dansyl-ajoene was identified to be the 57 kDa protein vimentin. The vimentin target was validated to reveal that ajoene and dansyl-ajoene covalently bind to recombinant vimentin via a disulfide linkage at Cys-328. Computational modelling showed Cys-328 to be exposed at the termini of the vimentin tetramer. Treatment of MDA-MB-231 or HeLa cells with a non-cytotoxic concentration of ajoene caused the vimentin filament network to condense; and to increase vimentin protein expression. Ajoene inhibited the invasion and migration of both cancer cell lines which was found to be dependent on the presence of vimentin. Vimentin overexpression caused cells to become more migratory, an effect that was completely rescued by ajoene.

CONCLUSIONS

The garlic-derived phytochemical ajoene targets and covalently modifies vimentin in cancer cells by S-thiolating Cys-328. This interaction results in the disruption of the vimentin filament network and contributes to the anti-metastatic activity of ajoene in cancer cells.

Molecular Mechanisms of Glutaredoxin Enzymes: Versatile Hubs for Thiol-Disulfide Exchange between Protein Thiols and Glutathione

The tripeptide glutathione (GSH) and its oxidized form glutathione disulfide (GSSG) constitute a key redox couple in cells. In particular, they partner protein thiols in reversible thiol-disulfide exchange reactions that act as switches in cell signaling and redox homeostasis. Disruption of these processes may impair cellular redox signal transduction and induce redox misbalances that are linked directly to aging processes and to a range of pathological conditions including cancer, cardiovascular diseases and neurological disorders. Glutaredoxins are a class of GSH-dependent oxidoreductase enzymes that specifically catalyze reversible thiol-disulfide exchange reactions between protein thiols and the abundant thiol pool GSSG/GSH. They protect protein thiols from irreversible oxidation, regulate their activities under a variety of cellular conditions and are key players in cell signaling and redox homeostasis. On the other hand, they may also function as metal-binding proteins with a possible role in the cellular homeostasis and metabolism of essential metals copper and iron. However, the molecular basis and underlying mechanisms of glutaredoxin action remain elusive in many situations. This review focuses specifically on these aspects in the context of recent developments that illuminate some of these uncertainties.

Oxidative Signaling Response to Cadmium Exposure

Changes in the intracellular thiol-disulfide balance are considered major determinants in the redox status/signaling of the cell. Cellular signaling is very sensitive to both exogenous and intracellular redox status and respond to many exogenous pro-oxidative or oxidative stresses. Redox status has dual effects on upstream signaling systems and downstream transcription factors. Redox signaling pathways use reactive oxygen species (ROS) to transfer signals from different sources to the nucleus to regulate such functions as growth, differentiation, proliferation, and apoptosis. Mitogen-activated protein kinases are activated by numerous cellular stresses and ligand-receptor bindings. An imbalance in the oxidant/antioxidant system, either resulting from excessive ROS/reactive nitrogen species production and/or antioxidant system impairment, leads to oxidative stress. Glutathione (GSH) is known to play a critical role in the cellular defense against unregulated oxidative stress in mammalian cells and involvement of large molecular antioxidants include classical antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR). Cadmium (Cd), a potent toxic heavy metal, is a widespread environmental contaminant. It is known to cause renal dysfunction, hepatic toxicity, genotoxicity, and apoptotic effects depending on the dose, route, and duration of exposure. This review examines the signaling pathways and mechanisms of activation of transcription factors by Cd-induced oxidative stress thus representing an important basis for understanding the mechanisms of Cd effect on the cells.

Glutaredoxins employ parallel monothiol-dithiol mechanisms to catalyze thiol-disulfide exchanges with protein disulfides

Glutaredoxins were demonstrated to be a family of versatile enzymes capable of catalyzing thiol–disulfide exchange involving GSSG/GSH via different catalytic routes either alone or in parallel.

Glutaredoxins (Grxs) are a family of glutathione (GSH)-dependent thiol–disulfide oxidoreductases. They feature GSH-binding sites that directly connect the reversible redox chemistry of protein thiols to the abundant cellular nonprotein thiol pool GSSG/GSH. This work studied the pathways for oxidation of protein dithiols P(SH)₂ and reduction of protein disulfides P(SS) catalyzed by Homo sapiens HsGrx1 and Escherichia coli EcGrx1. The metal-binding domain HMA4n(SH)₂ was chosen as substrate as it contains a solvent-exposed CysCys motif. Quenching of the reactions with excess iodoacetamide followed by protein speciation analysis via ESI-MS allowed interception and characterization of both substrate and enzyme intermediates. The enzymes shuttle between three catalytically-competent forms (Grx(SH)(S^–), Grx(SH)(SSG) and Grx(SS)) and employ conserved parallel monothiol and dithiol mechanisms. Experiments with dithiol and monothiol versions of both Grx enzymes demonstrate which monothiol (plus GSSG or GSH) or dithiol pathways dominate a specific oxidation or reduction reaction. Grxs are shown to be a class of versatile enzymes with diverse catalytic functions that are driven by specific interactions with GSSG/GSH.

Assessment of glutathione/glutathione disulphide ratio and S-glutathionylated proteins in human blood, solid tissues, and cultured cells

Glutathione (GSH) is the major non-protein thiol in humans and other mammals, which is present in millimolar concentrations within cells, but at much lower concentrations in the blood plasma. GSH and GSH-related enzymes act both to prevent oxidative damage and to detoxify electrophiles. Under oxidative stress, two GSH molecules become linked by a disulphide bridge to form glutathione disulphide (GSSG). Therefore, assessment of the GSH/GSSG ratio may provide an estimation of cellular redox metabolism. Current evidence resulting from studies in human blood, solid tissues, and cultured cells suggests that GSH also plays a prominent role in protein redox regulation via S -glutathionylation, i.e., the conjugation of GSH to reactive protein cysteine residues. A number of methodologies that enable quantitative analysis of GSH/GSSG ratio and S-glutathionylated proteins (PSSG), as well as identification and visualization of PSSG in tissue sections or cultured cells are currently available. Here, we have considered the main methodologies applied for GSH, GSSG and PSSG detection in biological samples. This review paper provides an up-to-date critical overview of the application of the most relevant analytical, morphological, and proteomics approaches to detect and analyse GSH, GSSG and PSSG in mammalian samples as well as discusses their current limitations.

Stress-Induced Protein S-Glutathionylation and S-Trypanothionylation in African Trypanosomes-A Quantitative Redox Proteome and Thiol Analysis

AIMS

Trypanosomatids have a unique trypanothione-based thiol redox metabolism. The parasite-specific dithiol is synthesized from glutathione and spermidine, with glutathionylspermidine as intermediate catalyzed by trypanothione synthetase. In this study, we address the oxidative stress response of African trypanosomes with special focus on putative protein S-thiolation.

RESULTS

Challenging bloodstream Trypanosoma brucei with diamide, H₂O₂ or hypochlorite results in distinct levels of reversible overall protein S-thiolation. Quantitative proteome analyses reveal 84 proteins oxidized in diamide-stressed parasites. Fourteen of them, including several essential thiol redox proteins and chaperones, are also enriched when glutathione/glutaredoxin serves as a reducing system indicating S-thiolation. In parasites exposed to H₂O₂, other sets of proteins are modified. Only three proteins are S-thiolated under all stress conditions studied in accordance with a highly specific response. H₂O₂ causes primarily the formation of free disulfides. In contrast, in diamide-treated cells, glutathione, glutathionylspermidine, and trypanothione are almost completely protein bound. Remarkably, the total level of trypanothione is decreased, whereas those of glutathione and glutathionylspermidine are increased, indicating partial hydrolysis of protein-bound trypanothione. Depletion of trypanothione synthetase exclusively induces protein S-glutathionylation. Total mass analyses of a recombinant peroxidase treated with T(SH)₂ and either diamide or hydrogen peroxide verify protein S-trypanothionylation as stable modification.

INNOVATION

Our data reveal for the first time that trypanosomes employ protein S-thiolation when exposed to exogenous and endogenous oxidative stresses and trypanothione, despite its dithiol character, forms protein-mixed disulfides.

CONCLUSION

The stress-specific responses shown here emphasize protein S-trypanothionylation and S-glutathionylation as reversible protection mechanism in these parasites. Antioxid. Redox Signal. 27, 517-533.

Resveratrol Modulation of Protein Expression in parkin-Mutant Human Skin Fibroblasts: A Proteomic Approach

In this study, we investigated by two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS) analysis the effects of resveratrol treatment on skin primary fibroblasts from a healthy subject and from a parkin-mutant early onset Parkinson's disease patient. Parkin, an E3 ubiquitin ligase, is the most frequently mutated gene in hereditary Parkinson's disease. Functional alteration of parkin leads to impairment of the ubiquitin-proteasome system, resulting in the accumulation of misfolded or aggregated proteins accountable for the neurodegenerative process. The identification of proteins differentially expressed revealed that resveratrol treatment can act on deregulated specific biological process and molecular function such as cellular redox balance and protein homeostasis. In particular, resveratrol was highly effective at restoring the heat-shock protein network and the protein degradation systems. Moreover, resveratrol treatment led to a significant increase in GSH level, reduction of GSSG/GSH ratio, and decrease of reduced free thiol content in patient cells compared to normal fibroblasts. Thus, our findings provide an experimental evidence of the beneficial effects by which resveratrol could contribute to preserve the cellular homeostasis in parkin-mutant fibroblasts.

Redox regulation of the actin cytoskeleton and its role in the vascular system

The actin cytoskeleton is critical for form and function of vascular cells, serving mechanical, organizational and signaling roles. Because many cytoskeletal proteins are sensitive to reactive oxygen species, redox regulation has emerged as a pivotal modulator of the actin cytoskeleton and its associated proteins. Here, we summarize work implicating oxidants in altering actin cytoskeletal proteins and focus on how these alterations affect cell migration, proliferation and contraction of vascular cells. Finally, we discuss the role of oxidative modification of the actin cytoskeleton in vivo and highlight its importance for vascular diseases.

Association between oxidative stress and atrial fibrillation

BACKGROUND

Oxidative stress (OS) may be a key mechanism underlying the development of atrial fibrillation (AF) in experimental studies, but data in humans remain limited.

OBJECTIVE

Systemic OS can be estimated by measurements of circulating levels of the aminothiols including glutathione, cysteine, and their oxidized products. We tested the hypothesis that the redox potentials of glutathione (E_hGSH) and cysteine will be associated with prevalent and incident AF.

METHODS

Plasma levels of aminothiols were measured in 1439 patients undergoing coronary angiography, of whom 148 (10.3%) had a diagnosis of AF. After a median follow-up of 6.3 years, 104 of 917 patients (11.5%) developed incident AF. Multivariate logistic regression and Cox regression models were used to determine whether OS markers were independent predictors of prevalent and incident AF after adjustment for traditional risk factors, heart failure, coronary artery disease, and high-sensitivity C-reactive protein level.

RESULTS

For each 10% increase in E_hGSH, the odds of prevalent AF was 30% higher (odds ratio [OR] 1.3; 95% confidence interval [CI] 1.1-1.7; P = .02) and 90% higher (OR 1.9; 95% CI 1.3-2.7; P = .004) when the median was used as a cutoff. The E_hGSH level above the median was more predictive of chronic AF (OR 4.0; 95% CI 1.3-12.9; P = .01) than of paroxysmal AF (OR 1.7; 95% CI 1.1-2.7; P = .03). Each 10% increase in E_hGSH level was associated with a 40% increase in the risk of incident AF (hazard ratio 1.4; 95% CI 1.1-1.7; P = .01).

CONCLUSION

Increased OS measured by the redox potentials of glutathione is associated with prevalent and incident AF. Therapies that modulate OS need to be investigated to treat and prevent AF.

Protein Carbonylation in Human Smokers and Mammalian Models of Exposure to Cigarette Smoke: Focus on Redox Proteomic Studies

SIGNIFICANCE

Oxidative stress is one mechanism whereby tobacco smoking affects human health, as reflected by increased levels of several biomarkers of oxidative stress/damage isolated from tissues and biological fluids of active and passive smokers. Many investigations of cigarette smoke (CS)-induced oxidative stress/damage have been carried out in mammalian animal and cellular models of exposure to CS. Animal models allow the investigation of many parameters that are similar to those measured in human smokers. In vitro cell models may provide new information on molecular and functional differences between cells of smokers and nonsmokers. Recent Advances: Over the past decade or so, a growing number of researches highlighted that CS induces protein carbonylation in different tissues and body fluids of smokers as well as in in vivo and in vitro models of exposure to CS.

CRITICAL ISSUES

We review recent findings on protein carbonylation in smokers and models thereof, focusing on redox proteomic studies. We also discuss the relevance and limitations of these models of exposure to CS and critically assess the congruence between the smoker's condition and laboratory models.

FUTURE DIRECTIONS

The identification of protein targets is crucial for understanding the mechanism(s) by which carbonylated proteins accumulate and potentially affect cellular functions. Recent progress in redox proteomics allows the enrichment, identification, and characterization of specific oxidative protein modifications, including carbonylation. Therefore, redox proteomics can be a powerful tool to gain new insights into the onset and/or progression of CS-related diseases and to develop strategies to prevent and/or treat them. Antioxid. Redox Signal. 26, 406-426.

Mixed results with mixed disulfides

A period of research with Helmut Sies in the 1980s is recalled. Our experiments aimed at an in-depth understanding of metabolic changes due to oxidative challenges under near-physiological conditions, i.e. perfused organs. A major focus were alterations of the glutathione and the NADPH/NADP(+) system by different kinds of oxidants, in particular formation of glutathione mixed disulfides with proteins. To analyze mixed disulfides, a test was adapted which is widely used until today. The observations in perfused rat livers let us believe that glutathione-6-phosphate dehydrogenase (G6PDH), i.a. might be activated by glutathionylation. Although we did not succeed to verify this hypothesis for the special case of G6PDH, the regulation of enzyme/protein activities by glutathionylation today is an accepted posttranslational mechanism in redox biology in general. Our early experimental approaches are discussed in the context of present knowledge.

Determination of glutaredoxin enzyme activity and protein S-glutathionylation using fluorescent eosin-glutathione

Glutaredoxins catalyze glutathione-dependent disulfide oxidoreductions, particularly reduction of glutathione (GSH)-protein mixed disulfides. Mammalian glutaredoxins are present in the cytosol/nucleus as Grx1 or in mitochondria as Grx2a. Here we describe di-eosin-glutathione disulfide (Di-E-GSSG) as a new tool to study glutaredoxin (Grx) activity. Di-E-GSSG has almost no fluorescence in its disulfide form due to self-quenching, whereas the reduced form (E-GSH) has a large fluorescence emission at 545 nm after excitation at 520 nm. Di-E-GSSG was a very poor substrate for glutathione reductase, but we discovered that the molecule was an excellent substrate for glutaredoxin in a coupled assay system with GSH, nicotinamide adenine dinucleotide phosphate (NADPH), and glutathione reductase or with lipoamide, NADH, and lipoamide dehydrogenase. In addition, Di-E-GSSG was used to glutathionylate the free SH group of bovine serum albumin (BSA), yielding eosin-glutathionylated BSA (E-GS-BSA) readily observed in ultraviolet (UV) light. E-GS-BSA also displayed a quenched fluorescence, and its Grx-catalyzed reduction could be followed by the formation of E-GSH by fluorescence emission using microtiter plates. This way of measuring Grx activity provided an ultrasensitive method that detected Grx1 and Grx2 at picomolar levels. Human Grx1 was readily quantified in 40 μl of plasma and determined to be 680 ± 208 pM in healthy controls.

Increased TRPC5 glutathionylation contributes to striatal neuron loss in Huntington's disease

Aberrant glutathione or Ca(2+) homeostasis due to oxidative stress is associated with the pathogenesis of neurodegenerative disorders. The Ca(2+)-permeable transient receptor potential cation (TRPC) channel is predominantly expressed in the brain, which is sensitive to oxidative stress. However, the role of the TRPC channel in neurodegeneration is not known. Here, we report a mechanism of TRPC5 activation by oxidants and the effect of glutathionylated TRPC5 on striatal neurons in Huntington's disease. Intracellular oxidized glutathione leads to TRPC5 activation via TRPC5 S-glutathionylation at Cys176/Cys178 residues. The oxidized glutathione-activated TRPC5-like current results in a sustained increase in cytosolic Ca(2+), activated calmodulin-dependent protein kinase and the calpain-caspase pathway, ultimately inducing striatal neuronal cell death. We observed an abnormal glutathione pool indicative of an oxidized state in the striatum of Huntington's disease transgenic (YAC128) mice. Increased levels of endogenous TRPC5 S-glutathionylation were observed in the striatum in both transgenic mice and patients with Huntington's disease. Both knockdown and inhibition of TRPC5 significantly attenuated oxidation-induced striatal neuronal cell death. Moreover, a TRPC5 blocker improved rearing behaviour in Huntington's disease transgenic mice and motor behavioural symptoms in littermate control mice by increasing striatal neuron survival. Notably, low levels of TRPC1 increased the formation of TRPC5 homotetramer, a highly Ca(2+)-permeable channel, and stimulated Ca(2+)-dependent apoptosis in Huntington's disease cells (STHdh(Q111/111)). Taken together, these novel findings indicate that increased TRPC5 S-glutathionylation by oxidative stress and decreased TRPC1 expression contribute to neuronal damage in the striatum and may underlie neurodegeneration in Huntington's disease.

The Interplay Between Respiratory Supercomplexes and ROS in Aging

SIGNIFICANCE

The molecular mechanism of aging is still vigorously debated, although a general consensus exists that mitochondria are significantly involved in this process. However, the previously postulated role of mitochondrial-derived reactive oxygen species (ROS) as the damaging agents inducing functional loss in aging has fallen out of favor in the recent past. In this review, we critically examine the role of ROS in aging in the light of recent advances on the relationship between mitochondrial structure and function.

RECENT ADVANCES

The functional mitochondrial respiratory chain is now recognized as a reflection of the dynamic association of respiratory complexes in the form of supercomplexes (SCs). Besides providing kinetic advantage (channeling), SCs control ROS generation by the respiratory chain, thus providing a means to regulate ROS levels in the cell. Depending on their concentration, these ROS are either physiological signals essential for the life of the cell or toxic species that damage cell structure and functions.

CRITICAL ISSUES

We propose that under physiological conditions the dynamic nature of SCs reversibly controls the generation of ROS as signals involved in mitochondrial-nuclear communication. During aging, there is a progressive loss of control of ROS generation so that their production is irreversibly enhanced, inducing a vicious circle in which signaling is altered and structural damage takes place.

FUTURE DIRECTIONS

A better understanding on the forces affecting SC association would allow the manipulation of ROS generation, directing these species to their physiological signaling role.

Glucose-induced glutathione reduction in mitochondria is involved in the first phase of pancreatic β-cell insulin secretion

Glucose can acutely reduce mitochondrial glutathione redox state in rat islets. However, whether glucose-stimulated mitochondrial glutathione redox state relates to glucose-stimulated insulin secretion (GSIS) remains unknown. We used genetically encoded redox-sensitive GFPs to target the mitochondria to monitor glutathione redox changes during GSIS in rat pancreatic β-cells. The results showed that mitochondrial glutathione was more reduced during GSIS, whereas inhibition of this glutathione reduction impaired insulin secretion. In isolated rat pancreatic islets glutathione reduction in mitochondria and the first phase of GSIS were concurrence at the early stage of glucose-stimulation. Our results suggest that the glucose-induced glutathione reduction in mitochondria is primarily required for the first phase of GSIS.

Analytical approaches to the diagnosis and treatment of aging and aging-related disease: redox status and proteomics

Basal levels of oxidants are indispensible for redox signaling to produce adaptive cellular responses such as vitagenes linked to cell survival; however, at higher levels, they are detrimental to cells, contributing to aging and to the pathogenesis of numerous age-related diseases. Aging is a complex systemic process and the major gap in aging research reminds the insufficient knowledge about pathways shifting from normal "healthy" aging to disease-associated pathological aging. The major complication of normal "healthy" aging is in fact the increasing risk of age-related diseases such as cardiovascular diseases, diabetes mellitus, and neurodegenerative pathologies that can adversely affect the quality of life in general, with enhanced incidences of comorbidities and mortality. In this context, global "omics" approaches may help to dissect and fully study the cellular and molecular mechanisms of aging and age-associated processes. The proteome, being more close to the phenotype than the transcriptome and more stable than the metabolome, represents the most promising "omics" field in aging research. In the present study, we exploit recent advances in the redox biology of aging and discuss the potential of proteomics approaches as innovative tools for monitoring at the proteome level the extent of protein oxidative insult and related modifications with the identification of targeted proteins.

Protein S-glutathionylation: from current basics to targeted modifications

The interaction between antioxidant glutathione and the free thiol in susceptible cysteine residues of proteins leads to reversible protein S-glutathionylation. This reaction ensures cellular homeostasis control (as a common redox-dependent post-translational modification associated with signal transduction) and intervenes in oxidative stress-related cardiovascular pathology (as initiated by redox imbalance). The purpose of this review is to evaluate the recent knowledge on protein S-glutathionylation in terms of chemistry, broad cellular intervention, specific quantification, and potential for therapeutic exploitation. The data bases searched were Medline and PubMed, from 2009 to 2014 (term: glutathionylation). Protein S-glutathionylation ensures protection of protein thiols against irreversible over-oxidation, operates as a biological redox switch in both cell survival (influencing kinases and protein phosphatases pathways) and cell death (by potentiation of apoptosis), and cross-talks with phosphorylation and with S-nitrosylation. Collectively, protein S-glutathionylation appears as a valuable biomarker for oxidative stress, with potential for translation into novel therapeutic strategies.

Novel study on N-nitrosamines as risk factors of cardiovascular diseases

Millions of people are exposed daily to N-nitrosamines from different environmental sources. The present study aims at investigating the role of N-nitrosamines in the alteration of homocysteine, lipid profile, oxidative stress, paraoxonase activity, antioxidant enzymes, and free radicals which are important risk factors for CVD. In addition, biomarkers of cardiovascular diseases such as creatine kinase MB activity (CK-MB) and lactate dehydrogenase (LDH) as well as protein expression of both glutathione peroxidase and glutathione S-transferase π isozyme were assayed after treatment of rats with 0.2 mg/kg body weight of N-nitrosodibutylamine (NDBA), N-nitrosoethylbutylamine (NEBA), N-nitrosobutylpropylamine (NBPA), N-nitrosodiethylamine (NDEA), N-nitrosodimethylamine (NDMA), and N-nitrosodiphenylamine (NDPA) as a daily dose for two weeks. LDL levels, paraoxonase activity, reduced glutathione levels, and glutathione reductase activities were increased, whereas HDL levels decreased after treatment of rats with most of N-nitrosamines compared to control group. Moreover, levels of free radicals and catalase activity increased, whereas protein expression of both glutathione peroxidase and glutathione S-transferase decreased after treatment of rats with some N-nitrosamines. The data showed that most N-nitrosamines increased CK-MB and LDH activities. It is concluded that N-nitrosamines increased levels of free radicals, and decreased the activity of antioxidant enzymes which may consequently increase the incidence of CVDs.

Mitochondrial energy metabolism and redox signaling in brain aging and neurodegeneration

SIGNIFICANCE

The mitochondrial energy-transducing capacity is essential for the maintenance of neuronal function, and the impairment of energy metabolism and redox homeostasis is a hallmark of brain aging, which is particularly accentuated in the early stages of neurodegenerative diseases.

RECENT ADVANCES

The communications between mitochondria and the rest of the cell by energy- and redox-sensitive signaling establish a master regulatory device that controls cellular energy levels and the redox environment. Impairment of this regulatory devise is critical for aging and the early stages of neurodegenerative diseases.

CRITICAL ISSUES

This review focuses on a coordinated metabolic network-cytosolic signaling, transcriptional regulation, and mitochondrial function-that controls the cellular energy levels and redox status as well as factors which impair this metabolic network during brain aging and neurodegeneration.

FUTURE DIRECTIONS

Characterization of mitochondrial function and mitochondria-cytosol communications will provide pivotal opportunities for identifying targets and developing new strategies aimed at restoring the mitochondrial energy-redox axis that is compromised in brain aging and neurodegeneration.

Interactive effects of in vitro binge-like alcohol and ATP on umbilical endothelial nitric oxide synthase post-translational modifications and redox modulation

Alcohol dysregulates the regulation of reproductive vascular adaptations. We herein investigated chronic in vitro binge-like alcohol effects on umbilical endothelial nitric oxide synthase (eNOS) multi-site phosphorylation and related redox switches under basal (unstimulated) and stimulated (with ATP) states. Alcohol decreased endothelial excitatory (Pser1177)eNOS (P<0.001), whereas excitatory (Pser635)eNOS exhibited a main effect of alcohol (↓P=0.016) and ATP (↑P<0.001). Alcohol decreased (Pthr495)eNOS (P=0.004) levels, whereas inhibitory (Pser116)eNOS exhibited an alcohol main effect in both basal and stimulated states (↑P=0.005). Total eNOS was reduced by alcohol (P=0.038). In presence of ATP, alcohol inhibited ERK activity (P=0.002), whereas AKT exhibited no alcohol effect. Alcohol main effect on S-nitroso-glutathione reductase (↓P=0.031) and glutathione-S-transferase (↓P=0.027) were noted. Increased protein glutathiolation was noted, whereas no alcohol effect on GSH, GSSG, NOX2 or SOD expression was noted. Thus, alcohol effects on multi-site post-translational modifications and redox switches related to vasodilatory eNOS underscore the necessity for investigating alcohol-induced gestational vascular dysfunction.

Biological markers of oxidative stress: Applications to cardiovascular research and practice

Oxidative stress is a common mediator in pathogenicity of established cardiovascular risk factors. Furthermore, it likely mediates effects of emerging, less well-defined variables that contribute to residual risk not explained by traditional factors. Functional oxidative modifications of cellular proteins, both reversible and irreversible, are a causal step in cellular dysfunction. Identifying markers of oxidative stress has been the focus of many researchers as they have the potential to act as an “integrator” of a multitude of processes that drive cardiovascular pathobiology. One of the major challenges is the accurate quantification of reactive oxygen species with very short half-life. Redox-sensitive proteins with important cellular functions are confined to signalling microdomains in cardiovascular cells and are not readily available for quantification. A popular approach is the measurement of stable by-products modified under conditions of oxidative stress that have entered the circulation. However, these may not accurately reflect redox stress at the cell/tissue level. Many of these modifications are “functionally silent”. Functional significance of the oxidative modifications enhances their validity as a proposed biological marker of cardiovascular disease, and is the strength of the redox cysteine modifications such as glutathionylation. We review selected biomarkers of oxidative stress that show promise in cardiovascular medicine, as well as new methodologies for high-throughput measurement in research and clinical settings. Although associated with disease severity, further studies are required to examine the utility of the most promising oxidative biomarkers to predict prognosis or response to treatment.

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Oxidative stress is a common mediator in pathobiology of risk factors for CVD.

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Oxidative modifications of proteins and lipids alter cellular function.

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Some oxidative biomarkers have been associated with severity of CVD.

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Pathophysiologically relevant biomarkers may integrate the effect of risk factors.

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Utility of oxidative biomarkers to guide prognosis/treatment merits further work.

Principles in redox signaling: from chemistry to functional significance

Reactive oxygen and nitrogen species are currently considered not only harmful byproducts of aerobic respiration but also critical mediators of redox signaling. The molecules and the chemical principles sustaining the network of cellular redox regulated processes are described. Special emphasis is placed on hydrogen peroxide (H(2)O(2)), now considered as acting as a second messenger, and on sulfhydryl groups, which are the direct targets of the oxidant signal. Cysteine residues of some proteins, therefore, act as sensors of redox conditions and are oxidized in a reversible reaction. In particular, the formation of sulfenic acid and disulfide, the initial steps of thiol oxidation, are described in detail. The many cell pathways involved in reactive oxygen species formation are reported. Central to redox signaling processes are the glutathione and thioredoxin systems controlling H(2)O(2) levels and, hence, the thiol/disulfide balance. Lastly, some of the most important redox-regulated processes involving specific enzymes and organelles are described. The redox signaling area of research is rapidly expanding, and future work will examine new pathways and clarify their importance in cellular pathophysiology.

Glutathione efflux and cell death

SIGNIFICANCE

Glutathione (GSH) depletion is a central signaling event that regulates the activation of cell death pathways. GSH depletion is often taken as a marker of oxidative stress and thus, as a consequence of its antioxidant properties scavenging reactive species of both oxygen and nitrogen (ROS/RNS).

RECENT ADVANCES

There is increasing evidence demonstrating that GSH loss is an active phenomenon regulating the redox signaling events modulating cell death activation and progression.

CRITICAL ISSUES

In this work, we review the role of GSH depletion by its efflux, as an important event regulating alterations in the cellular redox balance during cell death independent from oxidative stress and ROS/RNS formation. We discuss the mechanisms involved in GSH efflux during cell death progression and the redox signaling events by which GSH depletion regulates the activation of the cell death machinery.

FUTURE DIRECTIONS

The evidence summarized here clearly places GSH transport as a central mechanism mediating redox signaling during cell death progression. Future studies should be directed toward identifying the molecular identity of GSH transporters mediating GSH extrusion during cell death, and addressing the lack of sensitive approaches to quantify GSH efflux.

Mitochondrial thiols in the regulation of cell death pathways

SIGNIFICANCE

Regulation of mitochondrial H(2)O(2) homeostasis and its involvement in the regulation of redox-sensitive signaling and transcriptional pathways is the consequence of the concerted activities of the mitochondrial energy- and redox systems.

RECENT ADVANCES

The energy component of this mitochondrial energy-redox axis entails the formation of reducing equivalents and their flow through the respiratory chain with the consequent electron leak to generate [Formula: see text] and H(2)O(2). The mitochondrial redox component entails the thiol-based antioxidant system, largely accounted for by glutathione- and thioredoxin-based systems that support the activities of glutathione peroxidases, peroxiredoxins, and methionine sulfoxide reductase. The ultimate reductant for these systems is NADPH: mitochondrial sources of NADPH are the nicotinamide nucleotide transhydrogenase, isocitrate dehydrogenase-2, and malic enzyme. NADPH also supports the glutaredoxin activity that regulates the extent of S-glutathionylation of mitochondrial proteins in response to altered redox status.

CRITICAL ISSUES

The integrated network of these mitochondrial thiols constitute a regulatory device involved in the maintenance of steady-state levels of H(2)O(2), mitochondrial and cellular redox and metabolic homeostasis, as well as the modulation of cytosolic redox-sensitive signaling; disturbances of this regulatory device affects transcription, growth, and ultimately influences cell survival/death.

FUTURE DIRECTIONS

The modulation of key mitochondrial thiol proteins, which participate in redox signaling, maintenance of the bioenergetic machinery, oxidative stress responses, and cell death programming, provides a pivotal direction in developing new therapies towards the prevention and treatment of several diseases.

Protein-thiol oxidation and cell death: regulatory role of glutaredoxins

SIGNIFICANCE

Glutaredoxin (Grx) is the primary enzyme responsible for catalysis of deglutathionylation of protein-mixed disulfides with glutathione (GSH) (protein-SSG). This reversible post-translational modification alters the activity and function of many proteins important in regulation of critical cellular processes. Aberrant regulation of protein glutathionylation/deglutathionylation reactions due to changes in Grx activity can disrupt both apoptotic and survival signaling pathways.

RECENT ADVANCES

Grx is known to regulate the activity of many proteins through reversible glutathionylation, such as Ras, Fas, ASK1, NFκB, and procaspase-3, all of which play important roles in control of apoptosis. Reactive oxygen species and/or reactive nitrogen species mediate oxidative modifications of critical Cys residues on these apoptotic mediators, facilitating protein-SSG formation and thereby altering protein function and apoptotic signaling.

CRITICAL ISSUES

Much of what is known about the regulation of apoptotic mediators by Grx and reversible glutathionylation has been gleaned from in vitro studies of discrete apoptotic pathways. To relate these results to events in vivo it is important to examine changes in protein-SSG status in situ under natural cellular conditions, maintaining relevant GSH:GSSG ratios and using appropriate inducers of apoptosis.

FUTURE DIRECTIONS

Apoptosis is a highly complex, tightly regulated process involving many different checks and balances. The influence of Grx activity on the interconnectivity among these various pathways remains unknown. Knowledge of the effects of Grx is essential for developing novel therapeutic approaches for treating diseases involving dysregulated apoptosis, such as cancer, heart disease, diabetes, and neurodegenerative diseases, where alterations in redox homeostasis are hallmarks for pathogenesis.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.

Sulfur mustard causes oxidative stress and depletion of antioxidants in muscles, livers, and kidneys of Wistar rats

Sulfur mustard (SM) is a chemical warfare agent with cytotoxic effect and a tight link to oxidative stress (OS). Depletion of antioxidants is considered as a cause of detrimental consequence and belongs to the important steps leading to cell death. The oxidative injury appearing after SM exposure is not well understood. Nevertheless, identification of the pathological processes would be a good opportunity to establish an efficient therapy. Here, we focused our effort on an estimation of reactive oxygen species homeostasis and apoptotic processes in Wistar rats exposed to 0-160 mg/kg of SM. We assayed antioxidant activity, thiobarbituric acid reactive substances, reduced glutathione/oxidized glutathione, metallothionein, glutathione reductase, glutathione peroxidase, glutathione S-transferase, caspase 3, and glucose in the livers, kidneys, and muscles of the animals. Significant OS, depletion of low-molecular-mass antioxidants, increase in caspase activity, and some other processes related to SM action were determined. Moreover, we infer a principal role of OS in the tested organs.

Leishmania TDR1 structure, a unique trimeric glutathione transferase capable of deglutathionylation and antimonial prodrug activation

Thiol-dependent reductase I (TDR1), an enzyme found in parasitic Leishmania species and Trypanosoma cruzi, is implicated in deglutathionylation and activation of antimonial prodrugs used to treat leishmaniasis. The 2.3 Å resolution structure of TDR1 reveals a unique trimer of subunits each containing two glutathione-S-transferase (GST) domains. The similarities of individual domains and comparisons with GST classes suggest that TDR1 evolved by gene duplication, diversification, and gene fusion; a combination of events previously unknown in the GST protein superfamily and potentially explaining the distinctive enzyme properties of TDR1. The deglutathionylation activity of TDR1 implies that glutathione itself has regulatory intracellular roles in addition to being a precursor for trypanothione, the major low mass thiol present in trypanosomatids. We propose that activation of antiparasite Sb(V)-drugs is a legacy of the deglutathionylation activity of TDR1 and involves processing glutathione adducts with concomitant reduction of the metalloid to active Sb(III) species.

S-Glutathionylation signaling in cell biology: progress and prospects

S-Glutathionylation is a mechanism of signal transduction by which cells respond effectively and reversibly to redox inputs. The glutathionylation regulates most cellular pathways. It is involved in oxidative cellular response to insult by modulating the transcription factor Nrf2 and inducing the expression of antioxidant genes (ARE); it contributes to cell survival through nuclear translocation of NFkB and activation of survival genes, and to cell death by modulating the activity of caspase 3. It is involved in mitotic spindle formation during cell division by binding cytoskeletal proteins thus contributing to cell proliferation and differentiation. Glutathionylation also interfaces with the mechanism of phosphorylation by modulating several kinases (PKA, CK) and phosphatases (PP2A, PTEN), thus allowing a cross talk between the two processes of signal transduction. Also, skeletal RyR1 channels responsible of muscle excitation-contraction coupling appear to be sensitive to glutathionylation. Members of the ryanodine receptor super family, responsible for Ca(2) release from endoplasmic reticulum stores, contain sulfhydryl groups that function as a redox "switch", which either induces or inhibits Ca(2) release. Finally, but very importantly, glutathionylation of proteins may also act on cell metabolism by modulating enzymes involved in glycosylation, in the Krebs cycle and in mitochondrial oxidative phosphorylation. In this review, we propose a greater role for glutathionylation in cell biology: not only a cellular response to oxidative stress, but an elegant and sensitive mechanism able to respond even to subtle changes in redox balance in the different cellular compartments. Given the wide spectrum of redox-sensitive proteins, we discuss the possibility that different pathways light up by glutathionylation under various pathological conditions. The feature of reversibility of this process also makes it prone to develop targeted drug therapies and monitor the pharmacological effectiveness once identified the sensor proteins involved.

Cytotoxic effects of Mn(III) N-alkylpyridylporphyrins in the presence of cellular reductant, ascorbate

Due to the ability to easily accept and donate electrons Mn(III)N-alkylpyridylporphyrins (MnPs) can dismute O(2)(·-), reduce peroxynitrite, but also generate reactive species and behave as pro-oxidants if conditions favour such action. Herein two ortho isomers, MnTE-2-PyP(5+), MnTnHex-2-PyP(5+), and a meta isomer MnTnHex-3-PyP(5+), which differ greatly with regard to their metal-centered reduction potential, E(1/2) (Mn(III)P/Mn(II)P) and lipophilicity, were explored. Employing Mn(III)P/Mn(II)P redox system for coupling with ascorbate, these MnPs catalyze ascorbate oxidation and thus peroxide production. Consequently, cancer oxidative burden may be enhanced, which in turn would suppress its growth. Cytotoxic effects on Caco-2, Hela, 4T1, HCT116 and SUM149 were studied. When combined with ascorbate, MnPs killed cancer cells via peroxide produced outside of the cell. MnTE-2-PyP(5+) was the most efficacious catalyst for peroxide production, while MnTnHex-3-PyP(5+) is most prone to oxidative degradation with H(2) , and thus the least efficacious. A 4T1 breast cancer mouse study of limited scope and success was conducted. The tumour oxidative stress was enhanced and its microvessel density reduced when mice were treated either with ascorbate or MnP/ascorbate; the trend towards tumour growth suppression was detected.

Reversible and irreversible protein glutathionylation: biological and clinical aspects

INTRODUCTION

Depending in part on the glutathione:glutathione disulfide ratio, reversible protein glutathionylation to a mixed disulfide may occur. Reversible glutathionylation is important in protecting proteins against oxidative stress, guiding correct protein folding, regulating protein activity and modulating proteins critical to redox signaling. The potential also exists for irreversible protein glutathionylation via Michael addition of an -SH group to a dehydroalanyl residue, resulting in formation of a stable, non-reducible thioether linkage.

AREAS COVERED

This article reviews factors contributing to reversible and irreversible protein glutathionylation and their biomedical implications. It also examines the possibility that certain drugs such as busulfan may be toxic by promoting irreversible glutathionylation. The reader will gain an appreciation of the protective nature and control of function resulting from reversible protein glutathionylation. The reader is also introduced to the recently identified phenomenon of irreversible protein glutathionylation and its possible deleterious effects.

EXPERT OPINION

The process of reversible protein glutathionylation is now well established but these findings need to be substantiated at the tissue and organ levels, and also with disease state. That being said, irreversible protein glutathionylation can also occur and this has implications in disease and aging. Toxicologists should consider this when evaluating the possible side effects of certain drugs such as busulfan that may generate a glutathionylating species in vivo.