Recent trends in glutathione biochemistry--glutathione-protein interactions: a molecular link between oxidative stress and cell proliferation?

Costunolide triggers apoptosis in human leukemia U937 cells by depleting intracellular thiols

We have previously demonstrated that costunolide, a biologically active compound that was isolated from the stem bark of Magnolia sieboldii, induced apoptosis in human cancer cells. In the present study, we investigated the underlying mechanisms and suggest that costunolide induces apoptosis in human promonocytic leukemia U937 cells by depleting the intracellular thiols. Costunolide treatment rapidly depleted the intracellular reduced glutathione (GSH) and protein thiols, and this preceded the occurrence of apoptosis. Pretreatment with sulfhydryl compounds such as GSH, N-acetyl-L-cysteine, dithiothreitol and 2-mercaptoethanol almost completely blocked the costunolide-induced apoptosis, highlighting the significance of the intracellular thiol level in the process. Furthermore, overexpression of Bcl-2 also significantly attenuated the effects of costunolide. The apoptosis-inducing activity of costunolide is likely to depend on the exomethylene moiety because derivatives in which this group was reduced, such as dihydrocostunolide and saussurea lactone, did not deplete the cellular thiols and showed no apoptotic activity. Taken together, the present study demonstrates that the costunolide-induced apoptosis depends on intracellular thiols contents, which are modulated by Bcl-2.

Characterization of an omega-class glutathione S-transferase from Schistosoma mansoni with glutaredoxin-like dehydroascorbate reductase and thiol transferase activities

Glutathione S-transferases (EC 2.5.1.18) (GSTs), are a family of multifunctional enzymes present in all living organisms whose main function is the detoxification of electrophilic compounds. GSTs are considered the most prominent detoxifying class II enzymes in helminths. We describe here the characterization of novel dehydroascorbate reductase and thiol transferase activities that reside in the human parasite Schistosoma mansoni GSTx. Protein sequence analysis of this parasite product showed lower identity to known GSTs. However, phylogenic analysis placed SmGSTx among the recently described omega class GSTs (GSTO1-1). We report here that SmGSTO protein is a 28-kDa polypeptide, detected in all life stages of the parasite, being highly expressed in adult worms. Like other omega class GSTs, SmGSTO showed very low activity toward classical GSTs substrates as 1-chloro-2,4-dinitrobenzene, and no binding affinity to glutathione-agarose matrix but showed some biochemical characteristics related with thioredoxins/glutaredoxins. Interestingly, SmGSTO was able to bind S-hexyl glutathione matrix and displayed significant glutathione-dependent dehydroascorbate reductase and thiol transferase enzymatic activities.

Glycation by ascorbic acid causes loss of activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and its increased susceptibility to proteases

Glycation is a process whereby sugar molecules form a covalent adduct with protein amino groups. In this study, we used ascorbic acid (AsA) as a glycating agent and purified cucumber (Cucumis sativus L.) ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) as a model protein in chloroplast tissues, and examined effects of glycation on the activity and susceptibility of Rubisco to proteases. Glycation proceeded via two phases during incubation with AsA and Rubisco in vitro at physiological conditions (10 mM AsA, pH 7.5, 25 degrees C in the presence of atmospheric oxygen). At the early stage of glycation (phase 1), the amount of AsA attaching to Rubisco increased at an almost linear rate (0.5-0.7 mol AsA incorporated (mol Rubisco)(-1) d(-1)). By Western blotting using monoclonal antibodies recognizing glycation adducts, a major glycation adduct, N( epsilon )-(carboxymethyl)lysine was detected. At the late stage of glycation (phase 2), incorporation of AsA reached saturation, and a glycation adduct, pentosidine mediating intramolecular cross-linking, was detected corresponding to formation of high molecular weight aggregates cross-linked between subunits. Glycation led to a decrease in Rubisco activity (half-life about 7-8 d). Furthermore, glycated Rubisco of phase 2 drastically increased protease susceptibility in contrast to unchanged susceptibility of glycated Rubisco of phase 1 compared to that of native Rubisco. Results obtained here suggest that AsA is possibly an important factor in the loss of activity and turnover of Rubisco.

Identification of S-glutathionylated cellular proteins during oxidative stress and constitutive metabolism by affinity purification and proteomic analysis

Redox modification of proteins is proposed to play a central role in regulating cellular function. However, high-throughput techniques for the analysis of the redox status of individual proteins in complex mixtures are lacking. The aim was thus to develop a suitable technique to rapidly identify proteins undergoing oxidation of critical thiols by S-glutathionylation. The method is based on the specific reduction of mixed disulfides by glutaredoxin, their reaction with N-ethylmaleimide-biotin, affinity purification of tagged proteins, and identification by proteomic analysis. The method unequivocally identified 43 mostly novel cellular protein substrates for S-glutathionylation. These include protein chaperones, cytoskeletal proteins, cell cycle regulators, and enzymes of intermediate metabolism. Comparisons of the patterns of S-glutathionylated proteins extracted from cells undergoing diamide-induced oxidative stress and during constitutive metabolism reveal both common protein substrates and substrates failing to undergo enhanced S-glutathionylation during oxidative stress. The ability to chemically tag, select, and identify S-glutathionylated proteins, particularly during constitutive metabolism, will greatly enhance efforts to establish posttranslational redox modification of cellular proteins as an important biochemical control mechanism in coordinating cellular function.

Protein S-glutathionylation correlates to selective stress gene expression and cytoprotection

During situations of oxidative stress phenotypic adaptation to altered redox state is achieved by changes in expression of selected genes. The mechanisms regulating this may involve reversible S-glutathionylation of cellular proteins. In this study we compared and contrasted changes in gene expression patterns in human type II lung epithelial A549 cells and human endothelial ECV304 cells in correlation to glutathione oxidation and the formation of glutathione-protein mixed disulphides, after exposure to subtoxic levels of hydrogen peroxide, formed in the medium by addition of glucose oxidase, or the thiol oxidant diamide. Both the number of specific mRNAs and their levels of induction were grossly correlated to the degree of S-glutathionylation of cellular protein. Thus, diamide induced the expression of a variety of protein and DNA chaperones and transcriptional regulators, particularly in ECV304 cells. On the other hand, the peroxide failed to induce many of these species, in association with only minimal disturbances to glutathione homeostasis. The induction of the chaperone responses at the level of mRNA was clearly shown to translate into a more resistant morphological phenotype in response to both heat shock and oxidative stress induced by the DNA-damaging pro-oxidant potassium bromate.

Antioxidants as treatment for neurodegenerative disorders

Oxidative stress is a ubiquitously observed hallmark of neurodegenerative disorders. Neuronal cell dysfunction and cell death due to oxidative stress may causally contribute to the pathogenesis of progressive neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease, as well as acute syndromes of neurodegeneration, such as ischaemic and haemorrhagic stroke. Neuroprotective antioxidants are considered a promising approach to slowing the progression and limiting the extent of neuronal cell loss in these disorders. The clinical evidence demonstrating that antioxidant compounds can act as protective drugs in neurodegenerative disease, however, is still relatively scarce. In the following review, the available data from clinical, animal and cell biological studies regarding the role of antioxidant neuroprotection in progressive neurodegenerative disease will be summarised, focussing particularly on Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. The general complications in developing potent neuroprotective antioxidant drugs directed against these long-term degenerative conditions will also be discussed. The major challenges for drug development are the slow kinetics of disease progression, the unsolved mechanistic questions concerning the final causalities of cell death, the necessity to attain an effective permeation of the blood-brain barrier and the need to reduce the high concentrations currently required to evoke protective effects in cellular and animal model systems. Finally, an outlook as to which direction antioxidant drug development and clinical practice may be leading to in the near future will be provided.

Molecular profiling of hepatotoxicity induced by a aminoguanidine carboxylate in the rat: gene expression profiling

The hepatotoxicity of the aminoguanidine carboxylate 2-[1-[hydrazino(imino)methyl]hydrazino]acetic acid was characterized using oligonucleotide micro arrays, with the goal to select compounds from the same class with lower toxicity potential. The approach included a 14-day repeated- and a single-dose study in the rat as well as in vitro studies. Common gene expression changes could be followed from in vivo to in vitro studies. Anyhow, comparing the in vivo and in vitro response of the compound on gene expression, significant discrepancies were detected. Many of the genes whose mRNA levels were increased/decreased in the livers of the animals treated with toxic doses of the compound, were expressed at higher/lower levels in control hepatocytes than in control liver. The expression of the majority of these genes was not affected by in vitro treatment. These data question the use of gene expression analysis as a marker for drug response in vitro and illustrate the need of a careful characterization of in vitro systems. The results presented show that array-based gene expression analysis can lead to a better understanding of the molecular basis of drug-induced liver injury and, potentially, be used in the selection process for compounds and in the design of safer drugs.

A549 subclones demonstrate heterogeneity in toxicological sensitivity and antioxidant profile

In A549 cell culture, significant variability was found in sensitivity to actinomycin D. Using limiting dilution, actinomycin D-susceptible (G4S) and -resistant (D3R) subclones were isolated. G4S cells were also susceptible to protein synthesis inhibitors, a redox cycling quinone, and an electrophile with concomitant activation of caspases 3 and 9. D3R cells were resistant to these agents without caspase activation. Antioxidant profiles revealed that D3R cells had significantly higher glutathione and glutathione reductase activity but markedly lower catalase, glutathione peroxidase, and aldehyde reductase activities than G4S cells. Thus A549 cells contain at least two distinct subpopulations with respect to predisposition to cell death and antioxidant profile. Because sensitivities to agents and the antioxidant profile were inconsistent, mechanisms independent of antioxidants, including the apparent inability to activate caspases in D3R cells, may play an important role. Regardless, the results suggest that antioxidant profiles of asymmetrical cell populations cannot predict sensitivity to oxidants and warn that the use of single subclones is advisable for mechanistic studies using A549 or other unstable cell lines.

CxxS: fold-independent redox motif revealed by genome-wide searches for thiol/disulfide oxidoreductase function

Redox reactions involving thiol groups in proteins are major participants in cellular redox regulation and antioxidant defense. Although mechanistically similar, thiol-dependent redox processes are catalyzed by structurally distinct families of enzymes, which are difficult to identify by available protein function prediction programs. Herein, we identified a functional motif, CxxS (cysteine separated from serine by two other residues), that was often conserved in redox enzymes, but rarely in other proteins. Analyses of complete Escherichia coli, Campylobacter jejuni, Methanococcus jannaschii, and Saccharomyces cerevisiae genomes revealed a high proportion of proteins known to use the CxxS motif for redox function. This allowed us to make predictions in regard to redox function and identity of redox groups for several proteins whose function previously was not known. Many proteins containing the CxxS motif had a thioredoxin fold, but other structural folds were also present, and CxxS was often located in these proteins upstream of an alpha-helix. Thus, a conserved CxxS sequence followed by an alpha-helix is typically indicative of a redox function and corresponds to thiol-dependent redox sites in proteins. The data also indicate a general approach of genome-wide identification of redox proteins by searching for simple conserved motifs within secondary structure patterns.

Glutathione regulates the expression of gamma-glutamylcysteine synthetase via the Met4 transcription factor

Our previous studies have shown that glutathione is an essential metabolite in the yeast Saccharomyces cerevisiae because a mutant deleted for GSH1, encoding the first enzyme in gamma-l-glutamyl-l-cysteinylglycine (GSH) biosynthesis, cannot grow in its absence. In contrast, strains deleted for GSH2, encoding the second step in GSH synthesis, grow poorly as the dipeptide intermediate, gamma-glutamylcysteine, can partially substitute for GSH. In this present study, we identify two high copy suppressors that rescue the poor growth of the gsh2 mutant in the absence of GSH. The first contains GSH1, indicating that gamma-glutamylcysteine can functionally replace GSH if it is present in sufficiently high quantities. The second contains CDC34, encoding a ubiquitin conjugating enzyme, indicating a link between the ubiquitin and GSH stress protective systems. We show that CDC34 rescues the growth of the gsh2 mutant by inducing the Met4-dependent expression of GSH1 and elevating the cellular levels of gamma-glutamylcysteine. Furthermore, this mechanism normally operates to regulate GSH biosynthesis in the cell, as GSH1 promoter activity is induced in a Met4-dependent manner in a gsh1 mutant which is devoid of GSH, and the addition of exogenous GSH represses GSH1 expression. Analysis of a cis2 mutant, which cannot breakdown GSH, confirmed that GSH and not a metabolic product, serves as the regulatory molecule. However, this is not a general mechanism affecting all Met4-regulated genes, as MET16 expression is unaffected in a gsh1 mutant, and GSH acts as a poor repressor of MET16 expression compared with methionine. In summary, GSH biosynthesis is regulated in parallel with sulphate assimilation by activity of the Met4 protein, but GSH1-specific mechanisms exist that respond to GSH availability.

Glutathionylation of proteins by glutathione disulfide S-oxide

Aqueous solution of S-nitrosoglutathione (GSNO) underwent spontaneous chemical transformation that generated several glutathione derivatives including glutathione sulfonic acid (GSO3H), glutathione disulfide S-oxide (GS(O)SG), glutathione disulfide S-dioxide, and glutathione disulfide. Surprisingly, GS(O)SG (also called glutathione thiosulfinate), which was not identified as a metabolite of GSNO previously, was one of the major products derived from GSNO. This compound was very reactive toward any thiol and the reaction product was a mixed disulfide. The rate of reaction of GS(O)SG with 5-mercapto-2-nitro-benzoate was nearly 20-fold faster than that of GSNO. The mechanism for the formation of GS(O)SG was believed to involve the sulfenic acid (GSOH) and thiosulfinamide (GS(O)NH2) intermediates; the former underwent self-condensation and the latter reacted with GSH to form GS(O)SG. Many reactive oxygen and nitrogen species were also capable of oxidizing GSH or GSSG to form GS(O)SG, which likely played a central role in integrating both the oxidative and nitrosative cellular responses through thionylation of thiols. Treatments of rat brain tissue slices with oxidants resulted in an enhanced thionylation of proteins with a concomitant increase in cellular level of GS(O)SG, suggesting that this compound might play a second messenger role for stimuli that produced a variety of oxidative species.

Cell signalling and the glutathione redox system

The reduction/oxidation (redox) state of the cell is a consequence of the balance between the levels of oxidising and reducing equivalents. A reducing intracellular environment is often associated with cell survival; however, redox unbalance is necessary since it represents a regulatory sensor for several nuclear transcription factors. Activator protein 1 (AP-1), nuclear factor-kappaB (NF-kappaB) and protein tyrosine phosphatases 1-B (PTP-1B) are some of the well-known molecular factors for which a redox modulation of their activity has been demonstrated. The glutathione buffer system modulates cell response to redox changes induced by either external or intracellular stimuli. This paper summarises recent knowledge on the role played by several redox modulators in inducing signalling events that finally regulate cell cycle progression.

Adaptive stress response of glutathione and uric acid metabolism in man following controlled exercise and diet

Ergometer cycling performance as well as acute exercise-induced changes in the metabolism of energy-intermediates and glutathione (GSH) were investigated in skeletal muscle (SM) of 15 healthy young male subjects (VO(2max) approximately 54.7 mL kg(-1) min(-1), age approximately 25 years), before and after 3 days of controlled 'ìoverload-training' in combination with either high (62% of energy intake) or low (26% of energy intake) dietary intake of carbohydrates. The intake of a carbohydrate-rich diet clearly reduced the depletion of SM glycogen following the short-term training period, paralleled with a positive effect on the endurance performance, but not on high-intensity work-performance. An 'delayed over-reaching effect', defined as impaired work-performance, was observed after 2.5 days of recovery from the short-term training period, irrespective of the carbohydrate content of the diet and basal glycogen level in SM. Taken together, the main and novel findings of present investigation are: (1) an acute decrease of reduced GSH content and altered thiol-redox homeostasis in SM induced by strenuous high-intensity exercise; (2) an adaptive elevation of basal GSH level following the short-term training period; (3) an adaptive decrease of basal GSH level following 2.5 days recovery from training; (4) evidence of a relationship between the SM fibre type, physical performance capacity and GSH turnover during acute bouts of exercise; and (5) no evident effect of the level of carbohydrate intake on metabolism of GSH or energy intermediates. Furthermore, the induction of acute oxidative stress in exercising human SM and the adaptive responses to training are suggested to provide a protective antioxidant phenotype to the exercising SM during periods with repeated intense intermittent training.

Glutathione oxidation in calcium- and p38 MAPK-dependent membrane blebbing of endothelial cells

Under conditions where apoptosis is prevented, peroxides disrupt the endothelial monolayer by inducing cytoskeletal rearrangements, cell retraction and formation of arrays of membrane blebs. In human umbilical vein endothelial cells (HUVEC), the H(2)O(2)-induced membrane blebbing was found to be a transient process executed by two parallel signaling mechanisms: (i) mobilization of cytosolic [Ca(2+)](i) through a pathway requiring oxidation of reduced glutathione (GSH), and (ii) activation of p38 mitogen-activated protein kinases (MAPK) independently of GSH oxidation and Ca(2+) mobilization. In the HUVEC, membrane blebbing was thus blocked by inhibition of GSH oxidation, Ca(2+) mobilization or p38 MAPK activation. Stimulation of GSH peroxidation with ebselen potentiated the H(2)O(2)-induced oscillating Ca(2+) response and the bleb formation, but not p38 phosphorylation. Chelation of [Ca(2+)](i) abolished the blebbing process but not p38 activation. In addition, in the GSH peroxidase-resistant cell line ECV304, H(2)O(2) was unable to promote membrane blebbing or significant Ca(2+) release, while p38 became phosphorylated. However, [Ca(2+)](i) was increased and blebs were formed, when the ECV304 were treated with ebselen before H(2)O(2). Together, this leads to a model where oxidative stress, through both Ca(2+)-dependent and p38 kinase-mediated phosphorylation events, causes reassembly of the actin cytoskeleton and subsequent appearance of membrane blebs at the plasma membrane.

Lipid peroxide-induced redox imbalance differentially mediates CaCo-2 cell proliferation and growth arrest

Dietary oxidants like lipid hydroperoxides (LOOH) can perturb cellular glutathione/glutathione disulphide (GSH/GSSG) status and disrupt mucosal turnover. This study examines the effect of LOOH on GSH/GSSG balance and phase transitions in the human colon cancer CaCo-2 cell. LOOH at 1 or 5 micro m were noncytotoxic, but disrupted cellular GSH/GSSG and stimulated proliferative activity at 6 h that paralleled increases in ornithine decarboxylase activity, thymidine incorporation, expression of cyclin D1/cyclin-dependent kinase 4, phosphorylation of retinoblastoma protein, and cell progression from G0/G1 to S. At 24 h, LOOH-induced sustained GSH/GSSG imbalance mediated growth arrest at G0/G1 that correlated with suppression of proliferative activity and enhanced oxidative DNA damage. LOOH-induced cell transitions were effectively blocked by N-acetylcysteine. Collectively, the study shows that subtoxic LOOH levels induce CaCo-2 GSH/GSSG imbalance that elicits time-dependent cell proliferation followed by growth arrest. These results provide insights into the mechanism of hydroperoxide-induced disruption of mucosal turnover with implications for understanding oxidant-mediated genesis of gut pathology.

Glutathionylation of human thioredoxin: a possible crosstalk between the glutathione and thioredoxin systems

To identify proteins undergoing glutathionylation (formation of protein-glutathione mixed disulfides) in human T cell blasts, we radiolabeled the glutathione pool with (35)S, exposed cells to the oxidant diamide, and analyzed cellular proteins by two-dimensional electrophoresis. One of the proteins undergoing glutathionylation was identified by molecular weight, isoelectric point, and immunoblotting as thioredoxin (Trx). Incubation of recombinant human Trx with glutathione disulfide or S-nitrosoglutathione led to the formation of glutathionylated Trx, identified by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. The glutathionylation site was identified as Cys-72. Glutathionylation of rhTrx abolished its enzymatic activity as insulin disulfide reductase in the presence of NADPH and Trx reductase. Activity was, however, regained with sigmoidal kinetics, indicating a process of autoactivation due to the ability of Trx to de-glutathionylate itself. These data suggest that the intracellular glutathione/glutathione disulfide ratio, an indicator of the redox state of the cell, can regulate Trx functions reversibly through thiol-disulfide exchange reactions.

The effects of ebselen on cisplatin and diethyldithiocarbamate (DDC) cytotoxicity in rat hippocampal astrocytes

Ebselen is a seleno-organic compound with documented cytoprotective properties. Little work has been done, however, demonstrating ebselen's cytoprotective properties in neural cell lines. In order to examine the effects of this compound and its mechanism of action, astrocytes were exposed to two known neurotoxicants, cisplatin and diethyldithiocarbamate (DDC). Cells were pretreated with 30 microM ebselen and subsequently treated with either 150 microM DDC for 1 h or 250 and 500 microM cisplatin for 24 h. Results indicate significant increases in viability in cells pretreated with ebselen and exposed to cisplatin. Ebselen pretreatment did not significantly increase viability in cells exposed to DDC. Light and scanning electron microscopy studies confirm the viability studies. Gross morphological damage was seen in cells treated with cisplatin, however, cells pretreated with ebselen and then exposed to cisplatin, appeared similar to controls. No differences were noted in cells pretreated with ebselen and then exposed to DDC or cells treated with DDC alone. In order to examine the mechanism of protection of this compound, glutathione status was examined. Results show that ebselen does not significantly increase reduced or oxidized glutathione (GSH, GSSG). All cell groups treated with cisplatin showed an increase in GSH levels. Ebselen showed protection in glutathione depleted cells at the 250 microM cisplatin dose. DDC treatment showed no significant increase in either reduced or oxidized glutathione. We conclude that ebselen significantly protects against cisplatin, but not DDC toxicity. We further conclude that this protection is not related to changes in glutathione status in the rat hippocampal cell line as has been reported in other cell types.

Regulation of protein S-thiolation by glutaredoxin 5 in the yeast Saccharomyces cerevisiae

The irreversible oxidation of cysteine residues can be prevented by protein S-thiolation, a process by which protein -SH groups form mixed disulfides with low molecular weight thiols such as glutathione. We report here that this protein modification is not a simple response to the cellular redox state, since different oxidants lead to different patterns of protein S-thiolation. SDS-polyacrylamide gel electrophoresis shows that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is the major target for modification following treatment with hydroperoxides (hydrogen peroxide or tert-butylhydroperoxide), whereas this enzyme is unaffected following cellular exposure to the thiol oxidant diamide. Further evidence that protein S-thiolation is tightly regulated in response to oxidative stress is provided by the finding that the Tdh3 GAPDH isoenzyme, and not the Tdh2 isoenzyme, is S-thiolated following exposure to H(2)O(2) in vivo, whereas both GAPDH isoenzymes are S-thiolated when H(2)O(2) is added to cell-free extracts. This indicates that cellular factors are likely to be responsible for the difference in GAPDH S-thiolation observed in vivo rather than intrinsic structural differences between the GAPDH isoenzymes. To begin to search for factors that can regulate the S-thiolation process, we investigated the role of the glutaredoxin family of oxidoreductases. We provide the first evidence that protein dethiolation in vivo is regulated by a monothiol-glutaredoxin rather than the classical glutaredoxins, which contain two active site cysteine residues. In particular, glutaredoxin 5 is required for efficient dethiolation of the Tdh3 GAPDH isoenzyme.

Identification by redox proteomics of glutathionylated proteins in oxidatively stressed human T lymphocytes

Formation of mixed disulfides between glutathione and the cysteines of some proteins (glutathionylation) has been suggested as a mechanism through which protein functions can be regulated by the redox status. The aim of this study was to identify the proteins of T cell blasts that undergo glutathionylation under oxidative stress. To this purpose, we radiolabeled cellular glutathione with (35)S, exposed T cells to oxidants (diamide or hydrogen peroxide), and performed nonreducing, two-dimensional electrophoresis followed by detection of labeled proteins by phosphorimaging and their identification by mass spectrometry techniques. We detected several proteins previously not recognized to be glutathionylated, including cytoskeletal proteins (vimentin, myosin, tropomyosin, cofilin, profilin, and the already known actin), enzymes (enolase, aldolase, 6-phosphogluconolactonase, adenylate kinase, ubiquitin-conjugating enzyme, phosphoglycerate kinase, triosephosphate isomerase, and pyrophosphatase), redox enzymes (peroxiredoxin 1, protein disulfide isomerase, and cytochrome c oxidase), cyclophilin, stress proteins (HSP70 and HSP60), nucleophosmin, transgelin, galectin, and fatty acid binding protein. Based on the presence of several protein isoforms in control cells, we suggest that enolase and cyclophilin are heavily glutathionylated under basal conditions. We studied the effect of glutathionylation on some of the enzymes identified in the present study and found that some of them (enolase and 6-phosphogluconolactonase) are inhibited by glutathionylation, whereas the enzymatic activity of cyclophilin (peptidylprolyl isomerase) is not. These findings suggest that protein glutathionylation might be a common mechanism for the global regulation of protein functions.

Irreversible thiol oxidation in carbonic anhydrase III: protection by S-glutathiolation and detection in aging rats

Proteins with reactive sulfhydryls are central to many important metabolic reactions and also contribute to a variety of signal transduction systems. In this report, we examine the mechanisms of oxidative damage to the two reactive sulfhydryls of carbonic anhydrase III. Hydrogen peroxide (H2O2), peroxy radicals, or hypochlorous acid (HOCl) produced irreversibly oxidized forms, primarily cysteine sulfinic acid or cysteic acid, of carbonic anhydrase III if glutathione (GSH) was not present. When GSH was approximately equimolar to protein thiols, irreversible oxidation was prevented. H202 and peroxyl radicals both generated S-glutathiolated carbonic anhydrase III via partially oxidized protein sulfhydryl intermediates, while HOCl did not cause S-glutathiolation. Thus, oxidative damage from H202 or AAPH was prevented by protein S-glutathiolation, while a direct reaction between GSH and oxidant likely prevents HOCl-mediated protein damage. In cultured rat hepatocytes, carbonic anhydrase III was rapidly S-glutathiolated by menadione. When hepatocyte glutathione was depleted, menadione instead caused irreversible oxidation. We hypothesized that normal depletion of glutathione in aged animals might also lead to an increase in irreversible oxidation. Indeed, both total protein extracts and carbonic anhydrase III contained significantly more cysteine sulfinic acid in older rats compared to young animals. These experiments show that, in the absence of sufficient GSH, oxidation reactions lead to irreversible protein sulfhydryl damage in purified proteins, cellular systems, and whole animals.

Thalidomide modulates nuclear redox status and preferentially depletes glutathione in rabbit limb versus rat limb

Thalidomide produces numerous birth defects, the most notable being phocomelia. Mechanisms behind thalidomide-induced malformations have not been fully elucidated, although recent evidence suggests a role for reactive oxygen species. A thalidomide-resistant (rat) and -sensitive (rabbit) species were used to compare potential inherent differences related to oxidative stress that may provide a more definitive understanding of mechanisms of thalidomide embryopathy. Limb bud cells (LBCs) were removed from the rat and rabbit embryo, dissociated, and plated in culture for 24 h. A fluorescence (6-carboxy-2',7'-dichlorofluorescin diacetate; DCF) assay for oxidative stress was used with varying concentrations of thalidomide (5-100 microM). Thalidomide (100 microM) showed a 6-fold greater production of oxidative stress in rabbit cultures than in rat. Lower concentrations (50 and 25 microM) also showed a significant increase in reactive oxygen species. Confocal microscopy revealed DCF fluorescence preferentially in rabbit LBC nuclei compared with the uniform distribution of DCF fluorescence in rat LBC. Localization of glutathione (GSH) was determined using 5-chloromethylfluorescein diacetate fluorescent confocal microscopy. In rat cultures, significant thalidomide-induced GSH depletion was detected in the cytosol but the nuclei maintained its GSH content, but rabbit LBC showed significant GSH depletion in both compartments. GSH depletion was confirmed by high-performance liquid chromatography analysis. These observations provide evidence that thalidomide preferentially produces oxidative stress in the thalidomide-sensitive species but not the thalidomide-resistant species. Nuclear GSH content in the rabbit LBC is selectively modified and indicates a shift in the nuclear redox environment. Redox shifts in the nucleus may result in the misregulation of transcription factor/DNA interactions and cause defective growth and development.

Differentiation-specific alterations to glutathione synthesis in and hormonally stimulated release from human skeletal muscle cells

Muscle atrophy and cachexia are associated with many human diseases. These catabolic states are often associated with the loss of glutathione (GSH), which is thought to contribute to the induction of oxidative stress within the muscle. Glutathione synthesis and secretary characteristics were studied in human skeletal muscle myoblasts and myotube-like cells derived from the myoblasts by growth factor restriction. Differentiation was associated with a shift in the sulfur amino acid precursor specificity for synthesis of GSH from cystine to cysteine, as well as loss in ability to use extracellular glutathione and activation of methionine use. The thiol drug N-acetylcysteine was also shown to be an effective precursor irrespective of the state of differentiation. Additionally, myoblasts and myotube cultures were shown to secrete GSH continually, but only the differentiated cells responded to stress hormones such as glucagon, vasopressin, and phenylephrine, by increased secretion of the tripeptide. The data suggest that the skeletal muscle cells may provide an important hormonally regulated extra-hepatic source of systemic GSH and also shed light on the mechanisms of accelerated turnover of GSH operating during strenuous muscle activity and trauma. The data may also provide biochemical rationales for the nutritional and/or pharmacological manipulation of GSH with sulfur amino acid precursors during the treatment of muscle-specific oxidative stress and atrophy.

Differential effects of glucocorticoids and gonadal steroids on glutathione levels in neuronal and glial cell systems

The aim of the present study was to investigate the short- and long-term effects of glucocorticoids [corticosterone (CORT), dexamethasone (DEX), 6-methylprednisolone (6-MP)] and gonadal steroids [17beta-estradiol (E(2)), progesterone (PROG), testosterone (TEST)] on the levels of the antioxidant glutathione (GSH) in different cell systems of the CNS (neuronal hippocampal HT22 cells, primary hippocampal and neocortical brain cells, and C(6) glioma cells). In HT22 cells, steroids exerted mainly long-term effects. Significant increases of GSH levels were detectable after a 24 hr treatment with 10(-7) M of DEX (122% +/- 5%), 6-MP (208% +/- 32%), E(2) (134% +/- 10%), and TEST (155% +/- 17%). A significant decrease occurred after incubation with PROG for 24 hr (79% +/- 9%). In primary hippocampal cultures, a 24 hr treatment with DEX (140% +/- 8%), E(2) (123% +/- 6%), and PROG (118% +/- 5%) led to significant increases of the GSH levels, whereas, in neocortical primary cultures, only an incubation with E(2) increased GSH (149% +/- 8%). In C(6) cells, hormone treatment led to both significant short-term (1 hr: CORT 114% +/- 5%, DEX 90% +/- 3%, E(2) 88% +/- 3%; 3 hr: DEX 115% +/- 5%, E(2) 122% +/- 6%, TEST 78% +/- 4%) and significant long-term (24 hr: CORT 74% +/- 4%, 6-MP 84% +/- 5%, E(2) 115% +/- 6%, PROG 91% +/- 4%, TEST 116% +/- 5%) effects. In summary, we were able to demonstrate differential effects of steroids on GSH levels in different cellular CNS models, showing an important influence of steroids and especially E(2) on antioxidative cellular functions in neuronal and glial cells.

Spatial and temporal ontogenies of glutathione peroxidase and glutathione disulfide reductase during development of the prenatal rat

Spatial and temporal expression and regulation of the antioxidant enzymes, glutathione peroxidase (GSH-Px), glutathione disulfide reductase (GSSG-Rd) may be important in determining cell-specific susceptibility to embryotoxicants. Creation of tissue-specific ontogenies for antioxidant enzyme activities during development is an important first step in understanding regulatory relationships. Early organogenesis-stage embryos were grouped according to the somite number (GD 9-13), and fetuses were evaluated by gestational day (GD 14-21). GSH-Px activities in the visceral yolk sac (VYS) increased on consecutive days from GD 9 to GD 13, representing a 5.7-fold increase during this period of development. GSH-Px activities in VYS decreased after GD 13, ultimately constituting a 37% decrease at GD 21. Head, heart, and trunk specific activities generally increased from GD 9 to GD 13 albeit not to the same magnitude as detected in the VYS. GSSG-Rd activities showed substantial increases in the VYS from GD 9 to GD 13, 6.3-fold and decreased thereafter to 50% by GD 21. The greatest changes in enzyme activities were noted in the period between GD 10 and GD 11, where the embryo establishes an active cardiovascular system and begins to convert to aerobic metabolism. Generally, from GD 14-21, embryonic organ GSH-Px and GSSG-Rd activities either remained constant or increased as gestation progressed. These studies suggest the importance of the VYS in dealing with ROS and protecting the embryo. Furthermore, understanding the consequences of lower antioxidant activities during organogenesis may help to pinpoint periods of teratogenic susceptibility to xenobiotics and increased oxygen.

Protein glutathionylation: coupling and uncoupling of glutathione to protein thiol groups in lymphocytes under oxidative stress and HIV infection

We show here that exposure to oxidative stress induces glutathione (GSH) modification of protein cysteinyl residues (glutathionylation) in T cell blasts. Treating the cells with the oxidant diamide induces thiolation of a series of proteins that can be detected by 2D electrophoresis when 35S-cysteine is used to label the intracellular GSH pool. This thiolation is reversible, proteins are rapidly dethiolated and GSH is released from proteins once the oxidants are washed and the cells are allowed to recover. Dethiolation is dependent on the availability of GSH and thiols, since it is inhibited by GSH-depleting agents and improved by N-acetyl-L-cysteine (NAC). The capacity of these agents to reverse glutathionylation is diminished in T cell blasts infected in vitro with HIV, which is known to cause oxidative stress. Consistent with these findings, the activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an enzyme known to be inhibited by glutathionylation, is inhibited in diamide-treated cells and recovers rapidly when cells are allowed to dethiolate. Further, GAPDH activity is diminished by GSH-depleting agents and augmented by NAC. Thus, reversible glutathionylation of proteins can rapidly shift the activity of a key metabolic enzyme and thereby result in dramatic, reversible changes in cellular metabolism.

Thioredoxin and peptide methionine sulfoxide reductase: convergence of similar structure and function in distinct structural folds

Thioredoxin (Trx) and peptide methionine sulfoxide reductase (PMSR) are small thiol oxidoreductases implicated in antioxidant defense and redox regulation of cellular processes. Here we show that the structures of Trx and PMSR exhibit resemblance in their alphabeta core regions and that the active site cysteines in two proteins occupy equivalent positions downstream of a central beta-strand and at the N-terminus of an alpha-helix. Moreover, we identified a PMSR subfamily that contains an active site CxxC motif (two cysteines separated by two other amino acids) positioned similarly to the catalytic redox active CxxC motif in Trx. However, Trx and PMSR are characterized by distinct ancient folds that differ in both orientation of secondary structures and their patterns. Trx is a member of the Trx-fold superfamily, whereas PMSR has a unique fold not found in other proteins. The data suggest that similar structures and functions of Trx and PMSR were acquired independently during evolution and point to a general strategy of identifying new redox regulatory proteins.

Effect of H(2)O(2)on human lens epithelial cells and the possible mechanism for oxidative damage repair by thioltransferase

Human lens epithelial (HLE) B3 cells were used to study the oxidative damage and cellular repair with respect to the redox homeostasis, the oxidative defense enzymes and the glucose metabolic pathway. The effect of oxidative stress on cell growth was initially analyzed by culturing the cells with a bolus amount (0.02--0.1m M) of hydrogen peroxide (H(2)O(2)) in minimal essential medium (MEM) containing 20% fetal bovine serum (FBS) for 1 week. Concentration of H(2)O(2)greater than 0.03m M showed progressive inhibition of cell growth. However, the cells were also shown to tolerate H(2)O(2)concentrations up to 0.5m M by detoxifying the exogenous oxidant within 3hr without any detectable DNA damage. Therefore, this short-term H(2)O(2)exposure model was chosen to study the effect of oxidative stress on the cellular redox homeostasis. HLE B3 cells were first grown to confluence in MEM with 20% FBS. Approximately 1.6 million cells were gradually weaned off serum by subculturing in 2% FBS overnight, followed by serum-free medium for 30 min before subjecting to a bolus of 0.1m M H(2)O(2)for up to 180 min. These cells were used for biochemical analysis, which included H(2)O(2)detoxification (H(2)O(2)in the medium), glutathione (GSH) level and lactate production. Activity measurements were conducted on the oxidation defense enzymes: glutathione-S-transferase (GST), glutathione reductase (GR) and glutathione peroxidase (GPx); the dethiolating enzyme, thioltransferase (TTase); and a key glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (G-3PD). While the B3 cells were shown to tolerate and detoxify 0.1m M H(2)O(2)within 60 min, the GSH pool was transiently depleted in the first 60 min before fully recovered. GPx suffered more than 80% loss in activity and was unable to recover fully. GST showed slight inactivation but neither GR nor TTase was affected. G-3PD was inactivated to < 50% within 15 min of oxidative stress and was reactivated gradually to 80% of normal at the end of 180 min, concurrent with the transient loss of lactate production in the same cells. The reactivation of G-3PD was both temperature- and GSH-dependent, occurring only at physiological temperature and failing to reactivate when the intracellular GSH pool was depleted by BCNU (GR inhibitor) pretreatment. The inactivated cellular G-3PD in the cell extract could be partially reactivated by DTT (6m M) or by recombinant human lens thioltransferase (RHLT) but not by GSH (1m M), GR or GST. HLE cells cultured in the presence of L-(35)S-cystine and cycloheximide displayed an extra radiolabelled protein band on the autoradiograph in the H(2)O(2)treated cells. The labelled band was positively reacted with G-3PD antibody and could be removed by RHLT, indicating that S-thiolation of G-3PD occurred. The H(2)O(2)pre-exposed cells also transiently accumulated proteins modified by thiolation, including protein-S-S-glutathione (PSSG) and protein-S-S-cysteine (PSSC). It can be concluded that HLE could endure up to 0.1m M of H(2)O(2)oxidative stress since the cell could be protected by its effective repair systems, including dethiolating the inactivated key SH-sensitive enzymes. TTase may play a role in this. One of the mechanisms may be through preserving glucose metabolism and supplying ATP needed for maintaining cell viability.

Crystal structure of a soluble form of the intracellular chloride ion channel CLIC1 (NCC27) at 1.4-A resolution

CLIC1 (NCC27) is a member of the highly conserved class of chloride ion channels that exists in both soluble and integral membrane forms. Purified CLIC1 can integrate into synthetic lipid bilayers forming a chloride channel with similar properties to those observed in vivo. The structure of the soluble form of CLIC1 has been determined at 1.4-A resolution. The protein is monomeric and structurally homologous to the glutathione S-transferase superfamily, and it has a redox-active site resembling glutaredoxin. The structure of the complex of CLIC1 with glutathione shows that glutathione occupies the redox-active site, which is adjacent to an open, elongated slot lined by basic residues. Integration of CLIC1 into the membrane is likely to require a major structural rearrangement, probably of the N-domain (residues 1-90), with the putative transmembrane helix arising from residues in the vicinity of the redox-active site. The structure indicates that CLIC1 is likely to be controlled by redox-dependent processes.

Glutathione in blood of patients with Friedreich's ataxia

BACKGROUND

Oxidative stress and mitochondrial dysfunction have long been considered to play a role in Friedreich's ataxia, a neurodegenerative disease due to a GAA expansion in a gene coding for a mitochondrial protein (frataxin), implicated in the regulation of iron metabolism. Since glutathione is an important antioxidant whose role has been recently proposed in the pathogenesis of some neurodegenerative diseases, we investigated glutathione metabolism in the blood of 14 patients with Friedreich's ataxia by measuring total, free and protein-bound glutathione concentrations.

MATERIALS AND METHODS

Blood samples were obtained from 14 unrelated patients with Friedreich's ataxia (nine males, five females) and 20 age-matched healthy controls (10 males, 10 females). Total and free glutathione concentrations were determined by reverse-phase liquid chromatography with fluorescence detection; the glutathionyl-haemoglobin separation from healthy and pathological subjects was obtained by electrospray ionization-mass spectrometry.

RESULTS

We consistently found a reduction of free glutathione levels (0.55 +/- 0.06 nmol mg(-1) haemoglobin, vs. 8.4 +/- 1.79 nmol mg(-1) haemoglobin, P < 0.001) in the blood of patients with Friedreich's ataxia, a total glutathione concentration comparable to the controls (15 +/- 2.6 nmol mg(-1) haemoglobin, vs. 15.4 +/- 1.4 nmol mg(-1) haemoglobin), and a significant increase of glutathione bound to haemoglobin (15 +/- 1.5 vs. 8 +/- 1.8%, P < 0.05) in erythrocytes.

CONCLUSIONS

Our findings give evidence of an impairment in vivo of glutathione homeostasis in Friedreich's ataxia, suggesting a relevant role of free radical cytotoxicity in the pathophysiology of the disease; this study may also prove useful in the search for an oxidative stress marker in neurodegeneration.

The biochemistry of selenium and the glutathione system

In the context of defense against pro-oxidants, selenium and the glutathione (GSH) system play key functions. Major roles of GSH include direct interception of pro-oxidants, as well as a reduction of other antioxidants from their oxidized forms. Furthermore, GSH has ancillary functions, such as metabolism, cell signaling, and protein interactions, that can also mediate defense against oxidants. Protection by selenium in the mammalian cell is mediated by selenol-aminoacids, either as selenocysteine or selenomethionine. The active site of the potent glutathione peroxidases (GPx) contains selenocysteine residues. Furthermore, other selenoproteins (e.g. selenoprotein P and thioredoxin reductase) also have been shown to possess antioxidant properties. Synthetic organoselenium compounds (e.g. ebselen) have also shown promise as pharmacologic antioxidants in in vivo models of tissue damage due to oxidative stress. The specific function of selenoproteins and organoselenium compounds in defense against peroxynitrite, by reduction of this potent oxidizing and nitrating species to nitrite, is also discussed.

Expression of glutaredoxin in human coronary arteries: its potential role in antioxidant protection against atherosclerosis

Oxidative stress is considered an important factor in atherogenesis. Mammalian cells have a complex network of antioxidants such as catalase, superoxide dismutase, and glutathione peroxidase. However, the mechanisms that regulate the cellular redox state in the vessel wall remain unclear. Recent study has shown that thioredoxin, a thiol-disulfide oxidoreductase, is expressed in atherosclerotic plaques of human carotid arteries. In this study, we investigated the localization and expressional change of glutaredoxin and thioredoxin, two important members of the thiol-disulfide oxidoreductases, in autopsy samples of human coronary arteries. In nonatherosclerotic coronary arteries, glutaredoxin was expressed in endothelial cells, in fibroblasts of the adventitia, and most intensely in medial smooth muscle cells. Interestingly, in atherosclerotic lesions such as hypercellular lesions, the infiltrating macrophages highly expressed glutaredoxin. The expressional pattern of thioredoxin was quite similar to that of glutaredoxin. Western blot analysis demonstrated that hydrogen peroxide stimulated the expression of glutaredoxin in a time- and dose-dependent manner in cultured human coronary artery smooth muscle cells. Fluorescence microtopography with dihydroethidium demonstrated that the generation of reactive oxygen species was associated with the expression of glutaredoxin. These results suggest the possible involvement of thiol-disulfide oxidoreductases in antioxidant protection in human coronary arteries.

Identification and characterization of a new mammalian glutaredoxin (thioltransferase), Grx2

A thiol/disulfide oxidoreductase component of the GSH system, glutaredoxin (Grx), is involved in the reduction of GSH-based mixed disulfides and participates in a variety of cellular redox pathways. A single cytosolic Grx (Grx1) was previously described in mammals. We now report identification and characterization of a second mammalian Grx, designated Grx2. Grx2 exhibited 36% identity with Grx1 and had a disulfide active center containing the Cys-Ser-Tyr-Cys motif. Grx2 was encoded in the genomes of mammals and birds and expressed in a variety of cell types. The gene for human Grx2 consisted of four exons and three introns, spanned 10 kilobase pairs, and localized to chromosome 1q31.2-31.3. The coding sequence was present in all exons, with the first exon encoding a mitochondrial signal peptide. The mitochondrial leader sequence was also present in mouse and rat Grx2 sequences and was shown to direct either Grx2 or green fluorescent protein to mitochondria. Alternative splicing forms of mammalian Grx2 mRNAs were identified that differed in sequences upstream of exon 2. To functionally characterize the new protein, human and mouse Grx2 proteins were expressed in Escherichia coli, and the purified proteins were shown to reduce mixed disulfides formed between GSH and S-sulfocysteine, hydroxyethyldisulfide, or cystine. Grx1 and Grx2 were sensitive to inactivation by iodoacetamide and H(2)O(2) and exhibited similar pH dependence of catalytic activity. However, H(2)O(2)-inactivated Grx2 could only be reactivated with 5 mm GSH, whereas Grx1 could also be reactivated with dithiothreitol or thioredoxin/thioredoxin reductase. The Grx2 structural model suggested a common reaction mechanism for this class of proteins. The data provide the first example of a mitochondrial Grx and also indicate the occurrence of a second functional Grx in mammals.

Properties and biological activities of thioredoxins

The mammalian thioredoxins are a family of small (approximately 12 kDa) redox proteins that undergo NADPH-dependent reduction by thioredoxin reductase and in turn reduce oxidized cysteine groups on proteins. The two main thioredoxins are thioredoxin- 1, a cytosolic and nuclear form, and thioredoxin-2, a mitochondrial form. Thioredoxin-1 has been studied more. It performs many biological actions including the supply of reducing equivalents to thioredoxin peroxidases and ribonucleotide reductase, the regulation of transcription factor activity, and the regulation of enzyme activity by heterodimer formation. Thioredoxin-1 stimulates cell growth and is an inhibitor of apoptosis. Thioredoxins may play a role in a variety of human diseases including cancer. An increased level of thioredoxin-1 is found in many human tumors, where it is associated with aggressive tumor growth. Drugs are being developed that inhibit thioredoxin and that have antitumor activity.

Activation of matrix metalloproteinases by peroxynitrite-induced protein S-glutathiolation via disulfide S-oxide formation

Oxidative stress may cause tissue injury through activation of the precursors of matrix metalloproteinase (proMMPs). In this study, we observed glutathione (GSH)-dependent proMMP activation induced by peroxynitrite, a potent oxidizing agent formed during inflammatory processes. Peroxynitrite strongly activated all three types of purified human proMMPs (proMMP-1, -8, and -9) in the presence of similar concentrations of GSH. Of the potential reaction products between peroxynitrite and GSH, only S-nitroglutathione (GSNO(2)) caused proMMP activation. Extensive S-glutathiolation of the proMMP protein occurred during activation of proMMP by peroxynitrite and GSH, as shown by radiolabeling studies with [(35)S]GSH or [(3)H]GSH. Evidence of appreciable S-glutathiolation persisted even after dithiothreitol and protein-denaturing treatment, however, suggesting that some S-glutathiolation did not occur through formation of simple mixed disulfide. Matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry indicated that not only peroxynitrite plus GSH but also synthetic GSNO(2) produced dithiothreitol-resistant S-glutathiolation of the synthetic peptide PRCGVPD, which is a well conserved Cys-containing sequence of the propeptide autoinhibitory domain of proMMPs. PRCGVPD S-glutathiolation is presumed to be formed through glutathione disulfide S-oxide (GS(O)SR), based on the m/z 1064. Our results illustrate a unique mechanism of oxidative proMMP activation and oxidative tissue injury during inflammation.

Solution structure of Escherichia coli glutaredoxin-2 shows similarity to mammalian glutathione-S-transferases

Glutaredoxin 2 (Grx2) from Escherichia coli is distinguished from other glutaredoxins by its larger size, low overall sequence identity and lack of electron donor activity with ribonucleotide reductase. However, catalysis of glutathione (GSH)-dependent general disulfide reduction by Grx2 is extremely efficient. The high-resolution solution structure of E. coli Grx2 shows a two-domain protein, with residues 1 to 72 forming a classical "thioredoxin-fold" glutaredoxin domain, connected by an 11 residue linker to the highly helical C-terminal domain, residues 84 to 215. The active site, Cys9-Pro10-Tyr11-Cys12, is buried in the interface between the two domains, but Cys9 is solvent-accessible, consistent with its role in catalysis. The structures reveal the hither to unknown fact that Grx2 is structurally similar to glutathione-S-transferases (GST), although there is no obvious sequence homology. The similarity of these structures gives important insights into the functional significance of a new class of mammalian GST-like proteins, the single-cysteine omega class, which have glutaredoxin oxidoreductase activity rather than GSH-S-transferase conjugating activity. E. coli Grx 2 is structurally and functionally a member of this new expanding family of large glutaredoxins. The primary function of Grx2 as a GST-like glutaredoxin is to catalyze reversible glutathionylation of proteins with GSH in cellular redox regulation including stress responses.

Cloning and expression of a novel human glutaredoxin (Grx2) with mitochondrial and nuclear isoforms

Glutaredoxin (Grx) is a glutathione-dependent hydrogen donor for ribonucleotide reductase. Today glutaredoxins are known as a multifunctional family of GSH-disulfide-oxidoreductases belonging to the thioredoxin fold superfamily. In contrast to Escherichia coli and yeast, a single human glutaredoxin is known. We have identified and cloned a novel 18-kDa human dithiol glutaredoxin, named glutaredoxin-2 (Grx2), which is 34% identical to the previously known cytosolic 12-kDa human Grx1. The human Grx2 sequence contains three characteristic regions of the glutaredoxin family: the dithiol/disulfide active site, CSYC, the GSH binding site, and a hydrophobic surface area. The human Grx2 gene, located at chromosome 1q31.2--31.3, consisted of five exons that were transcribed to a 0.9-kilobase human Grx2 mRNA ubiquitously expressed in several tissues. Two alternatively spliced Grx2 mRNA isoforms that differed in their 5' region were identified. These corresponded to alternative proteins with a common 125-residue C-terminal Grx domain but with different N-terminal extensions of 39 and 40 residues, respectively. The 125-residue Grx domain and the two full-length variants were expressed in E. coli and exhibited GSH-dependent hydroxyethyl disulfide and dehydroascorbate reducing activities. Western blot analysis of subcellular fractions from Jurkat cells with a specific anti-Grx2 antibody showed that human Grx2 was predominantly located in the nucleus but also present in the mitochondria. We further showed that one of the mRNA isoforms corresponding to Grx2a encoded a functional N-terminal mitochondrial translocation signal.

Spatial glutathione and cysteine distribution and chemical modulation in the early organogenesis-stage rat conceptus in utero

Glutathione (GSH), cysteine, and other low-molecular-weight thiols (LMWT) play a vital role in the detoxication of xenobiotics and endogenous chemicals. Differential alterations of LMWT status in various cell types of the developing embryo may underlie cell-specific sensitivity or resistance to xenobiotics and contribute to embryotoxicity. This study describes the spatial and temporal distribution of LMWTs in rat conceptuses and alterations produced by the non-teratogenic GSH modulator, acetaminophen (APAP). Pregnant female rats were given 125, 250, or 500 mg/kg APAP (po) on gestational day 9. Conceptal LMWT was localized histochemically using mercury orange in cryosections, and GSH and cysteine concentrations were measured by HPLC analysis. Mercury orange histofluorescence revealed a non-uniform distribution of LMWT in untreated conceptal tissues, with strongest staining observed in the ectoplacental cone (EPC), visceral yolk sac (VYS), and embryonic heart. Less intense staining was observed in the neuroepithelium. Following treatment with APAP, tissue-associated LMWT decreased dramatically except in the EPC, while exocoelomic fluid LMWT, and LMWT within embryonic lumens, increased. Exposure to 250 mg/kg APAP decreased embryonic GSH after 6 and 24 h by 46% and 38%, respectively. Acetaminophen (500 mg/kg) decreased embryonic and VYS cysteine content by 54% and 83%, respectively, after 24 h. Acetaminophen alters the spatial distribution of LMWT in rat conceptuses, particularly with respect to cysteine. The mobilization of cysteine following chemical insult may influence the ability of conceptal cells to maintain normal GSH status due to reduced availability of cysteine for de novo GSH synthesis.

Properties and biological activities of thioredoxins

The mammalian thioredoxins are a family of small (approximately 12 kDa) redox proteins that undergo NADPH-dependent reduction by thioredoxin reductase and in turn reduce oxidized cysteine groups on proteins. The two main thioredoxins are thioredoxin-1, a cytosolic and nuclear form, and thioredoxin-2, a mitochondrial form. Thioredoxin-1 has been studied more. It performs many biological actions including the supply of reducing equivalents to thioredoxin peroxidases and ribonucleotide reductase, the regulation of transcription factor activity, and the regulation of enzyme activity by heterodimer formation. Thioredoxin-1 stimulates cell growth and is an inhibitor of apoptosis. Thioredoxins may play a role in a variety of human diseases including cancer. An increased level of thioredoxin-1 is found in many human tumors, where it is associated with aggressive tumor growth. Drugs are being developed that inhibit thioredoxin and that have antitumor activity.

Glutathione oxidation by hypochlorous acid in endothelial cells produces glutathione sulfonamide as a major product but not glutathione disulfide

Treatment of cells with hypochlorous acid (HOCl) at sublethal doses causes a concentration-dependent loss in reduced glutathione (GSH) levels. We have investigated the products of the reaction of HOCl with GSH in human umbilical vein endothelial cells. Despite a complete loss of GSH, there were only very small increases in intracellular and extracellular glutathione disulfide and glutathione sulfonic acid after exposure to HOCl. (35)S labeling of the GSH pool showed only a minimal increase in protein-bound GSH, suggesting that S-thiolation was not a major contributor to HOCl-mediated loss of GSH in endothelial cells. Rather, the products of the reaction were mostly exported from cells and included a peak that co-eluted with the cyclic sulfonamide that is a product of the reaction of GSH with reagent HOCl. Evidence of this species in endothelial cell supernatants after HOCl treatment was also obtained using electrospray mass spectrometry. In conclusion, exposure to HOCl causes the irreversible loss of cellular GSH with the formation of novel products that are rapidly exported from the cell, and resynthesis of GSH will be required to restore levels. The loss of GSH would alter the redox state of the cell and compromise its defenses against further oxidative stress.

Simultaneous determination of reduced and oxidized glutathione in peripheral blood mononuclear cells by liquid chromatography-electrospray mass spectrometry

We developed a sensitive and specific liquid chromatography-electrospray mass spectrometric (HPLC-ESI-MS) assay for the simultaneous determination of reduced and oxidized glutathione (GSH and GSSG) in peripheral blood mononuclear cells (PBMC). Following derivatization with N-ethylmaleimide to prevent GSH auto-oxidation, addition of thiosalicylic acid as internal standard, and protein precipitation with cold acetonitrile, the samples were injected into a diol column, eluted with acetonitrile-1% aqueous acetic acid (25:75) and detected by the ESI-MS system. The optimized method exhibited a good detection limit for both analytes (0.01 and 0.05 microM for GSH and GSSG, respectively). Good linearity was reached in the 0.01-20 microM range for GSH and 0.05-20 microM for GSSG. The mean recoveries of GSH and GSSG were 98.5-100.6% and 105.8-111.5%, respectively. The run-to-run repeatability for retention time and peak area was RSD% 0.06 and 1.75 for GSH and 0.18 and 2.50 for GSSG. The optimized method was applied to GSH and GSSG assay in PBMC analyzing 20 healthy individuals.

Differential role of superoxide and glutathione in S-nitrosoglutathione-mediated apoptosis: a rationale for mild forms of familial amyotrophic lateral sclerosis associated with less active Cu,Zn superoxide dismutase mutants

SH-SY5Y cells transfected with the enzymatically inactive Cu,Zn superoxide dismutase mutant H46R were more resistant to S-nitrosoglutathione (GSNO)-induced apoptosis. Cytochrome c release from mitochondria, caspase 3 activation, p53 up-regulation, p21 cleavage and Bcl-2 modulation, all involved in the apoptotic process, were significantly less altered with respect to untransfected cells. The H46R resistance to NO was associated with a higher content of reduced glutathione (GSH) and was abolished by blockage of glutathione synthesis. On the other hand, H46R cells were as sensitive as SH-SY5Y cells to puromycin-induced apoptosis; furthermore, they were more susceptible to apoptosis elicited by the superoxide-generating drug paraquat and to cell necrosis provoked by t-butyl hydroperoxide. These results confirm that the level of superoxide dismutase activity is fundamental for protecting cells against oxygen free radical challenge. Its impairment is not detrimental to cells exposed to NO, as long as the overall reducing power represented by GSH is assured. These results are relevant to explain a milder progression of the familial amyotrophic lateral sclerosis disease when associated with the H46R mutation.

Self-assembly and gelation of oxidized glutathione in organic solvents

The oxidized disulfide form of the ubiquitous tripeptide glutathione (gamma-glu-cys-gly) (GSSG) is shown to produce transparent, thermoreversible gels in aqueous solutions of dimethyl sulfoxide, dimethylformamide, and methanol, at GSSG concentrations as low as 1.5 mM. The gels bind Congo Red and exhibit dramatic green birefringence when observed between crossed polarizers, characteristic of amyloid structures. By transmission electron microscopy, the gels appear to consist of a network of fibrous structures about 75 nm in diameter. Several structurally related peptides, including the glutathione isomer glu-cys-gly and the aspartyl analogue of glutathione (beta-asp-cys-gly), failed to produce gels under similar conditions. These results suggest that the interactions which produce gelation are highly specific and that the unusual peptide geometry introduced by gamma-glu-cys linkage is critical to the gelation behavior. (1)H NMR indicates solvent-dependent perturbation of the gamma-glutamyl alpha- and beta-protons and circular dichroism reveals a shift in the geometry of the disulfide bond under conditions producing gelation. We propose that in appropriate organic solvents, GSSG self-assembles into an extended network of beta-sheetlike structures capable of immobilizing bulk solvent. While obviously speculative, it is interesting to consider possible physiological consequences of glutathione self-recognition in such processes as abnormal protein aggregation and the thiol-disulfide exchange which is believed to participate in protein folding.

Glutathiolation of the proteasome is enhanced by proteolytic inhibitors

The proteasome inhibitors lactacystin, clastro lactacystin beta-lactone, or tri-leucine vinyl sulfone (NLVS), in the presence of [(35)S]cysteine/methionine, caused increased incorporation of (35)S into cellular proteins, even when protein synthesis was inhibited by cycloheximide. This effect was blocked by incubation with the glutathione synthesis inhibitor buthionine sulfoximine. Proteasome inhibitors also enhanced total glutathione levels, increased reduced/oxidized glutathione ratio (GSH/GSSG) and upregulated gamma-glutamylcysteine synthetase (rate-limiting in glutathione synthesis). Micromolar concentrations of GSH, GSSG, or cysteine stimulated the chymotrypsin-like activity of purified 20S proteasome, but millimolar GSH or GSSG was inhibitory. Interestingly, GSH did not affect 20S proteasome's trypsin-like activity. Enhanced proteasome glutathiolation was verified when purified preparations of the 20S core enzyme complex were incubated with [(35)S]GSH after pre-incubation with any of the inhibitors. NLVS, lactacystin or clastro lactacystin beta-lactone may promote structural modification of the 20S core proteasome, with increased exposure of cysteine residues, which are prone to S-thiolation. Three main conclusions can be drawn from the present work. First, proteasome inhibitors alter cellular glutathione metabolism. Second, proteasome glutathiolation is enhanced by inhibitors but still occurs in their absence, at physiological GSH and GSSG levels. Third, proteasome glutathiolation seems to be a previously unknown mechanism of proteasome regulation in vivo.

Differential antioxidant enzyme activities and glutathione content between rat and rabbit conceptuses

Redox status regulates numerous cellular processes like transcription factor activation and binding, protein folding, and calcium sequestration. Because the most abundant reducing equivalent in the cell is glutathione (GSH), it could play a role for teratogens that cause oxidative stress and disrupt pathways involved in differentiation and proliferation. Investigation of the redox status of two species that have demonstrated differential sensitivity to teratogens represents a novel approach for determining the role of redox alteration in teratogenesis. Furthermore, examining specific regions of the embryo may also help to explain why certain tissues are uniquely sensitive, while others are resistant to oxidative insult. In the presented study, New Zealand White rabbit (GD 12) and Sprague Dawley rat embryos (GD 13) were removed from the uterus on days of similar development. Each embryo was dissected into three portions-the limbs, the head, and the trunk. Samples were placed in the appropriate buffers for the measurement of both direct and indirect redox status contributors-GSH, cysteine, thioredoxin, glutathione disulfide, protein-glutathione mixed disulfides, superoxide dismutase, glutathione peroxidase, and glutathione disulfide reductase. Species comparison of whole embryos indicated that the rabbit embryo possesses a higher redox potential (more oxidative) than the rat embryo. Findings, in general, show that the rabbit may be more sensitive to redox-altering teratogens because it is inherently more pro-oxidizing and may be more easily perturbed resulting in misregulation of cellular processes. Differences were most apparent in the limb as compared to the embryonic head and trunk, where the rabbit limb has a significantly more pro-oxidizing redox environment than the rat limb. Species comparisons like these may help in the understanding of how redox shifts affect cellular processes and would contribute to regulation of biochemical and molecular events that may be associated with mechanisms of teratogenesis. These may contribute to a more complete rationale for choosing a species for study and provide a better correlation with human developmental toxicants.

High glucose concentrations induce oxidative damage to mitochondrial DNA in explanted vascular smooth muscle cells

Oxidative stress is considered to be one of the mechanisms leading to atherosclerosis. It occurs in response to injury or to altered metabolic state. Alterations in cell growth (proliferation or apoptosis) can also contribute to the pathogenesis of atherosclerosis and is influenced by oxidative stress. Smooth muscle cells (SMC) from aortic explants of JCR:LA-cp homozygous cp/cp corpulent rats who are genetically predisposed to develop atherosclerosis exhibit increased SMC proliferation, which can be attenuated by exercise and food restriction. This study was conducted to characterize the effects fo oxidative stress and high glucose media on cell growth and its relationship to mitochondrial DNA integrity and gene expression in explanted aortic SMC from corpulent and lean JCR:LA-cp rats. The results show that SMC from the cp/cp rat appear to be resistant to oxidant-induced cell death and that they accumulate mitochondrial DNA mutations, probably as a result of a reduction in apoptosis. These data suggest that susceptibility to age- and glucose-related atherosclerosis may be related to alterations in redox signaling.

Responses of thiols to an oxidant challenge: differences between blood and tissues in the rat

Treatment of rats with diamide (100 mg/kg i.p.) altered the thiol components of the blood to a very different extent than in tissues (liver, kidney, lung, spleen, heart and testis). A total consumption (10 min) and regeneration (120 min) of blood glutathione (GSH), matched by a parallel increase and decrease in glutathione-protein mixed disulfides (GS-SP) was observed. In contrast, no modification of non-protein SH groups (NPSH) and protein SH groups (PSH), GS-SP and malondialdehyde (MDA) was observed in liver, kidney, lung, testis spleen and heart within same time range. In particular, only glutathione disulfide (GSSG) levels and some activities of antioxidant enzymes were modified to a small extent and in an opposite direction in some organs. For example, GSSG, and glucose-6-phosphate dehydrogenase (G-6-PDH) and catalase (CAT) activities appeared up-regulated in one tissue and down-regulated in another. The least modified organ was the liver, whereas lung and spleen were the most affected (lung, GSSG, significantly increased whereas G-6-PDH, glutaredoxin (GRX), GPX, superoxide dimutase (SOD) levels were significantly lowered; spleen, GSSG and the activity of glutathione reductase (GR), G-6-PDH and glutathione transferase (GST) were significantly decreased). The different responses of erythrocytes and organs to diamide were explained by the high affinity of hemoglobin and by the relatively high potential of thiol regeneration in organs. The rapid reversibility of the process of protein S-thiolation in blood and the small effects in organs leads us to propose the existence of an inter-organ cooperation in the rat that regulates protein S-thiolation in blood. Plasma thiols may well play a role in this process.