Cellular recovery of glyceraldehyde-3-phosphate dehydrogenase activity and thiol status after exposure to hydroperoxides

In Situ Raman Study of Neurodegenerated Human Neuroblastoma Cells Exposed to Outer-Membrane Vesicles Isolated from Porphyromonas gingivalis

The aim of this study was to elucidate the chemistry of cellular degeneration in human neuroblastoma cells upon exposure to outer-membrane vesicles (OMVs) produced by Porphyromonas gingivalis (Pg) oral bacteria by monitoring their metabolomic evolution using in situ Raman spectroscopy. Pg-OMVs are a key factor in Alzheimer's disease (AD) pathogenesis, as they act as efficient vectors for the delivery of toxins promoting neuronal damage. However, the chemical mechanisms underlying the direct impact of Pg-OMVs on cell metabolites at the molecular scale still remain conspicuously unclear. A widely used in vitro model employing neuroblastoma SH-SY5Y cells (a sub-line of the SK-N-SH cell line) was spectroscopically analyzed in situ before and 6 h after Pg-OMV contamination. Concurrently, Raman characterizations were also performed on isolated Pg-OMVs, which included phosphorylated dihydroceramide (PDHC) lipids and lipopolysaccharide (LPS), the latter in turn being contaminated with a highly pathogenic class of cysteine proteases, a key factor in neuronal cell degradation. Raman characterizations located lipopolysaccharide fingerprints in the vesicle structure and unveiled so far unproved aspects of the chemistry behind protein degradation induced by Pg-OMV contamination of SH-SY5Y cells. The observed alterations of cells' Raman profiles were then discussed in view of key factors including the formation of amyloid β (Aβ) plaques and hyperphosphorylated Tau neurofibrillary tangles, and the formation of cholesterol agglomerates that exacerbate AD pathologies.

Origin of Elevated S-Glutathionylated GAPDH in Chronic Neurodegenerative Diseases

H2O2-oxidized glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalytic cysteine residues (Cc(SH) undergo rapid S-glutathionylation. Restoration of the enzyme activity is accomplished by thiol/disulfide SN2 displacement (directly or enzymatically) forming glutathione disulfide (G(SS)G) and active enzyme, a process that should be facile as Cc(SH) reside on the subunit surface. As S-glutathionylated GAPDH accumulates following ischemic and/or oxidative stress, in vitro/silico approaches have been employed to address this paradox. Cc(SH) residues were selectively oxidized and S-glutathionylated. Kinetics of GAPDH dehydrogenase recovery demonstrated that glutathione is an ineffective reactivator of S-glutathionylated GAPDH compared to dithiothreitol. Molecular dynamic simulations (MDS) demonstrated strong binding interactions between local residues and S-glutathione. A second glutathione was accommodated for thiol/disulfide exchange forming a tightly bound glutathione disulfide G(SS)G. The proximal sulfur centers of G(SS)G and Cc(SH) remained within covalent bonding distance for thiol/disulfide exchange resonance. Both these factors predict inhibition of dissociation of G(SS)G, which was verified by biochemical analysis. MDS also revealed that both S-glutathionylation and bound G(SS)G significantly perturbed subunit secondary structure particularly within the S-loop, region which interacts with other cellular proteins and mediates NAD(P)+ binding specificity. Our data provides a molecular rationale for how oxidative stress elevates S-glutathionylated GAPDH in neurodegenerative diseases and implicates novel targets for therapeutic intervention.

Determination of Phosphofructokinase and Enolase Activities in Cultured Mouse Neuroblastoma Cells: Application to the In Vitro Detection of Neurotoxic Effects

Simple methods for the determination of phosphofructokinase (PFK) and total enolase (END activities in cultured mouse neuroblastoma cells have been developed. The influences of changes in glucose metabolism, induced by chlorpromazine, cycloheximide, 2,4-dinitrophenol and iodoacetic acid, on PFK and ENL activities in vitro were compared as a practical application of the methods. Mouse neuroblastoma cell cultures (Neuro-2a) were exposed for 24 hours and cytotoxic effects were evaluated. All the determinations were carried out in the same 96-well tissue culture plates in which exposure took place. Chlorpromazine and cycloheximide produced opposite effects on both PFK and ENL activities. While chlorpromazine increased PFK activity by 50% and decreased ENL activity by 30%, cycloheximide inhibited PFK activity by 50% and increased ENL activity by 45%. The response to dinitrophenol was quite different; both PFK and ENL activities were increased, by 45% and 35% respectively. After exposure of the cells to iodoacetic acid, neither PFK nor ENL activities showed statistically significant differences from the levels in control cells. The different responses elicited by the four toxicants suggest that the two enzymes selected are useful for differentiating among diverse types of mechanism of action.

Enzyme production ofd-gluconic acid and glucose oxidase: successful tales of cascade reactions

This review mainly focuses on the use of glucose oxidase in the production ofd-gluconic acid, which is a reactant of undoubtable interest in different industrial areas. As example of diverse enzymatic cascade reactions.

Mitochondrial DNA density homeostasis accounts for a threshold effect in a cybrid model of a human mitochondrial disease

Mitochondrial dysfunction is involved in a wide array of devastating diseases, but the heterogeneity and complexity of the symptoms of these diseases challenges theoretical understanding of their causation. With the explosion of omics data, we have the unprecedented opportunity to gain deep understanding of the biochemical mechanisms of mitochondrial dysfunction. This goal raises the outstanding need to make these complex datasets interpretable. Quantitative modelling allows us to translate such datasets into intuition and suggest rational biomedical treatments. Taking an interdisciplinary approach, we use a recently published large-scale dataset and develop a descriptive and predictive mathematical model of progressive increase in mutant load of the MELAS 3243A>G mtDNA mutation. The experimentally observed behaviour is surprisingly rich, but we find that our simple, biophysically motivated model intuitively accounts for this heterogeneity and yields a wealth of biological predictions. Our findings suggest that cells attempt to maintain wild-type mtDNA density through cell volume reduction, and thus power demand reduction, until a minimum cell volume is reached. Thereafter, cells toggle from demand reduction to supply increase, up-regulating energy production pathways. Our analysis provides further evidence for the physiological significance of mtDNA density and emphasizes the need for performing single-cell volume measurements jointly with mtDNA quantification. We propose novel experiments to verify the hypotheses made here to further develop our understanding of the threshold effect and connect with rational choices for mtDNA disease therapies.

Adaptive Posttranslational Control in Cellular Stress Response Pathways and Its Relationship to Toxicity Testing and Safety Assessment

Although transcriptional induction of stress genes constitutes a major cellular defense program against a variety of stressors, posttranslational control directly regulating the activities of preexisting stress proteins provides a faster-acting alternative response. We propose that posttranslational control is a general adaptive mechanism operating in many stress pathways. Here with the aid of computational models, we first show that posttranslational control fulfills two roles: (1) handling small, transient stresses quickly and (2) stabilizing the negative feedback transcriptional network. We then review the posttranslational control pathways for major stress responses-oxidative stress, metal stress, hyperosmotic stress, DNA damage, heat shock, and hypoxia. Posttranslational regulation of stress protein activities occurs by reversible covalent modifications, allosteric or non-allosteric enzymatic regulations, and physically induced protein structural changes. Acting in feedback or feedforward networks, posttranslational control may establish a threshold level of cellular stress. Sub-threshold stresses are handled adequately by posttranslational control without invoking gene transcription. With supra-threshold stress levels, cellular homeostasis cannot be maintained and transcriptional induction of stress genes and other gene programs, eg, those regulating cell metabolism, proliferation, and apoptosis, takes place. The loss of homeostasis with consequent changes in cellular function may lead to adverse cellular outcomes. Overall, posttranslational and transcriptional control pathways constitute a stratified cellular defense system, handling stresses coherently across time and intensity. As cell-based assays become a focus for chemical testing anchored on toxicity pathways, examination of proteomic and metabolomic changes as a result of posttranslational control occurring in the absence of transcriptomic alterations deserves more attention.

Free radicals: properties, sources, targets, and their implication in various diseases

Free radicals and other oxidants have gained importance in the field of biology due to their central role in various physiological conditions as well as their implication in a diverse range of diseases. The free radicals, both the reactive oxygen species (ROS) and reactive nitrogen species (RNS), are derived from both endogenous sources (mitochondria, peroxisomes, endoplasmic reticulum, phagocytic cells etc.) and exogenous sources (pollution, alcohol, tobacco smoke, heavy metals, transition metals, industrial solvents, pesticides, certain drugs like halothane, paracetamol, and radiation). Free radicals can adversely affect various important classes of biological molecules such as nucleic acids, lipids, and proteins, thereby altering the normal redox status leading to increased oxidative stress. The free radicals induced oxidative stress has been reported to be involved in several diseased conditions such as diabetes mellitus, neurodegenerative disorders (Parkinson's disease-PD, Alzheimer's disease-AD and Multiple sclerosis-MS), cardiovascular diseases (atherosclerosis and hypertension), respiratory diseases (asthma), cataract development, rheumatoid arthritis and in various cancers (colorectal, prostate, breast, lung, bladder cancers). This review deals with chemistry, formation and sources, and molecular targets of free radicals and it provides a brief overview on the pathogenesis of various diseased conditions caused by ROS/RNS.

Mesenchymal phenotype predisposes lung cancer cells to impaired proliferation and redox stress in response to glutaminase inhibition

Recent work has highlighted glutaminase (GLS) as a key player in cancer cell metabolism, providing glutamine-derived carbon and nitrogen to pathways that support proliferation. There is significant interest in targeting GLS for cancer therapy, although the gene is not known to be mutated or amplified in tumors. As a result, identification of tractable markers that predict GLS dependence is needed for translation of GLS inhibitors to the clinic. Herein we validate a small molecule inhibitor of GLS and show that non-small cell lung cancer cells marked by low E-cadherin and high vimentin expression, hallmarks of a mesenchymal phenotype, are particularly sensitive to inhibition of the enzyme. Furthermore, lung cancer cells induced to undergo epithelial to mesenchymal transition (EMT) acquire sensitivity to the GLS inhibitor. Metabolic studies suggest that the mesenchymal cells have a reduced capacity for oxidative phosphorylation and increased susceptibility to oxidative stress, rendering them unable to cope with the perturbations induced by GLS inhibition. These findings elucidate selective metabolic dependencies of mesenchymal lung cancer cells and suggest novel pathways as potential targets in this aggressive cancer type.

Target for diverse chemical modifications

The chapter begins with an historical perspective of GAPDH isozymes that is juxtaposed to the fact that there is only one somatic functional gene in humans that is virtually identical among the mammalian species. Over the many years of GAPDH research, dozens of labs have reported the existence of multiple forms of GAPDH, which mostly vary as a function of charge with an occasional report of truncated forms. These observations are in part due to GAPDH being a substrate for many enzymatically-controlled post-translational modifications. While target residues have been identified and predictive algorithms have implicated certain residues, this area of research appears to be in its infancy regarding GAPDH. Equally fascinating, the uniquely susceptible nature of GAPDH to non-enzymatic reactions, that typically are associated with cell stress, such as oxidation and nitration, is also discussed. Two metabolic gases, nitric oxide and hydrogen sulfide, which are enzymatically produced, appear to exert their signaling properties through non-enzymatic reaction with GAPDH. Models of cellular decline are also proposed, including the compelling hypothesis that states cell compromise occurs by the physically blocking the function of chaperonins (i.e. dual-ring multiple-subunit molecular chaperones) by the attachment of misfolded GAPDH.

High glucose-induced proteome alterations in retinal pigmented epithelium cells and its possible relevance to diabetic retinopathy

Diabetic retinopathy can cause poor vision and blindness. Previous research has shown that high blood glucose weakens retinal capillaries and induces glycoxidation. However, the detailed molecular mechanisms underlying the effects of high blood glucose on development of diabetic retinopathy have yet to be elucidated. In this study, we cultured a retinal pigmented epithelium cell line (ARPE-19) in mannitol-balanced 5.5 mM, 25 mM, and 100 mM d-glucose media, and evaluated protein expression and redox-regulation. We identified 56 proteins that showed significant changes in protein expression, and 33 proteins showing significant changes in thiol reactivity, in response to high glucose concentration. Several proteins that are involved in signal transduction, gene regulation, and transport showed significant changes in expression, whereas proteins involved in metabolism, transport, and cell survival displayed changes in thiol reactivity. Further analyses of clinical plasma specimens confirmed that the proteins lamin B2, PUMA, WTAP, ASGR1, and prohibitin 2 showed type 2 diabetic retinopathy-dependent alterations. In summary, in this study, we used a comprehensive retinal cell-based proteomic approach for the identification of changes in protein expression and redox-associated retinal markers induced by high glucose concentration. Some of the identified proteins have been validated with clinical samples and provide potential targets for the prognosis and diagnosis of diabetic retinopathy.

Glutathione depression by dihydropyrazine derivative

Dihydropyrazine (DHP), which is formed by nonenzymatic glycation, generates various radical species that lead to DNA damage and enzyme inhibition. In this study, we examined the reaction between DHP derivatives and glutathione (GSH). DHP exposure caused more intense growth inhibition of a GSH-deficient mutant Escherichia coli strain compared with the wild-type strain. DHP-exposed mouse fibroblasts showed a decrease in the cellular GSH level. The obtained data suggested that the reaction of DHP with GSH possibly potentiates cellular stress via the depletion of cellular GSH levels.

Dihydropyrazine-induced inactivation of glyceraldehyde-3-phosphate dehydrogenase

Dihydropyrazine (DHP), which is produced during the Maillard reaction, generates radicals that not only cause breakage of chromosomal DNA leading to mutagenic lesions but also induce oxidative damage to cellular proteins. In the present study, we show that three DHP derivatives, which generated superoxide anions, caused inhibition of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). SH-compounds, such as cysteine, dithiothreitol (DTT), 2-mercaptoethanol, 2-mercaptoethylamine, and N-acetyl-cysteine, suppressed the inhibition of GAPDH by DHP in vitro, although the effect of DHP on GAPDH was not reversed by DTT. In addition, DHP-exposed Escherichia coli showed almost unaffected growth on plates containing a rich medium, but poor growth on plates containing M9 synthetic medium with glucose as the sole carbon source. Furthermore, DHP-exposed E. coli exhibited reduced GAPDH activity. These findings indicate that DHP disturbs the glycolytic pathway by inhibiting GAPDH activity.

A new biomarker of protein oxidation degree and site using angiotensin as the target by MS

Hydroxyl radicals generated from Fenton reaction were used to damage the angiotensin. The oxidative damage degree and sites of peptides were measured by HPLC-MS and MS/MS. Experimental results proved that the oxidative damage degree increased with longer reaction time. The results also showed that the side chains of phenylalanine and tyrosine in angiotension can be attacked by hydroxyl radicals to form the oxidative products. A new strategy was established to monitor the oxidative degree and sites of peptides and laid the foundation for protein oxidation. This method can be used to investigate the mechanism of protein oxidative damage caused by oxidative stress which is induced by environmental pollutants and physiological activities. There will also be a wide application in the research of pathogenesis of some disease related to oxidative stress.

A systems biology perspective on Nrf2-mediated antioxidant response

Cells in vivo are constantly exposed to reactive oxygen species (ROS) generated endogenously and exogenously. To defend against the deleterious consequences of ROS, cells contain multiple antioxidant enzymes expressed in various cellular compartments to scavenge these toxic species. Under oxidative stresses, these antioxidant enzymes are upregulated to restore redox homeostasis. Such an adaptive response results from the activation of a redox-sensitive gene regulatory network mediated by nuclear factor E2-related factor 2. To more completely understand how the redox control system is designed by nature to meet homeostatic goals, we have examined the network from a systems perspective using engineering approaches. As with man-made control devices, the redox control system can be decomposed into distinct functional modules, including transducer, controller, actuator, and plant. Cells achieve specific performance objectives by utilizing nested feedback loops, feedforward control, and ultrasensitive signaling motifs, etc. Given that endogenously generated ROS are also used as signaling molecules, our analysis suggests a novel mode of action to explain oxidative stress-induced pathological conditions and diseases. Specifically, by adaptively upregulating antioxidant enzymes, oxidative stress may inadvertently attenuate ROS signals that mediate physiological processes, resulting in aberrations of cellular functions and adverse consequences. Lastly, by simultaneously considering the two competing cellular tasks-adaptive antioxidant defense and ROS signaling-we re-examine the premise that dietary antioxidant supplements is generally beneficial to human health. Our analysis highlights some possible adverse effects of these widely consumed antioxidants.

Thiol-based redox switches in eukaryotic proteins

For many years, oxidative thiol modifications in cytosolic proteins were largely disregarded as in vitro artifacts, and considered unlikely to play significant roles within the reducing environment of the cell. Recent developments in in vivo thiol trapping technology combined with mass spectrometric analysis have now provided convincing evidence that thiol-based redox switches are used as molecular tools in many proteins to regulate their activity in response to reactive oxygen and nitrogen species. Reversible oxidative thiol modifications have been found to modulate the function of proteins involved in many different pathways, starting from gene transcription, translation and protein folding, to metabolism, signal transduction, and ultimately apoptosis. This review will focus on three well-characterized eukaryotic proteins that use thiol-based redox switches to influence gene transcription, metabolism, and signal transduction. The transcription factor Yap1p is a good illustration of how oxidative modifications affect the function of a protein without changing its activity. We use glyeraldehyde-3-phosphate dehydrogenase to demonstrate how thiol modification of an active site cysteine re-routes metabolic pathways and converts a metabolic enzyme into a pro-apoptotic factor. Finally, we introduce the redox-sensitive protein tyrosine phosphatase PTP1B to illustrate that reversibility is one of the fundamental aspects of redox-regulation.

Identification of proteins targeted by the thioredoxin superfamily in Plasmodium falciparum

The malarial parasite Plasmodium falciparum possesses a functional thioredoxin and glutathione system comprising the dithiol-containing redox proteins thioredoxin (Trx) and glutaredoxin (Grx), as well as plasmoredoxin (Plrx), which is exclusively found in Plasmodium species. All three proteins belong to the thioredoxin superfamily and share a conserved Cys-X-X-Cys motif at the active site. Only a few of their target proteins, which are likely to be involved in redox reactions, are currently known. The aim of the present study was to extend our knowledge of the Trx-, Grx-, and Plrx-interactome in Plasmodium. Based on the reaction mechanism, we generated active site mutants of Trx and Grx lacking the resolving cysteine residue. These mutants were bound to affinity columns to trap target proteins from P. falciparum cell extracts after formation of intermolecular disulfide bonds. Covalently linked proteins were eluted with dithiothreitol and analyzed by mass spectrometry. For Trx and Grx, we were able to isolate 17 putatively redox-regulated proteins each. Furthermore, the approach was successfully established for Plrx, leading to the identification of 21 potential target proteins. In addition to confirming known interaction partners, we captured potential target proteins involved in various processes including protein biosynthesis, energy metabolism, and signal transduction. The identification of three enzymes involved in S-adenosylmethionine (SAM) metabolism furthermore suggests that redox control is required to balance the metabolic fluxes of SAM between methyl-group transfer reactions and polyamine synthesis. To substantiate our data, the binding of the redoxins to S-adenosyl-L-homocysteine hydrolase and ornithine aminotransferase (OAT) were verified using BIAcore surface plasmon resonance. In enzymatic assays, Trx was furthermore shown to enhance the activity of OAT. Our approach led to the discovery of several putatively redox-regulated proteins, thereby contributing to our understanding of the redox interactome in malarial parasites.

Protection from oxidative stress and efficient redox regulation are essential for malarial parasites which have to grow and multiply rapidly in various environments. As shown by glucose-6 phosphate dehydrogenase deficiency, a genetic variation protecting from malaria, the parasite–host cell unit is very susceptible to disturbances in redox equilibrium. This is the major reason why redox active proteins of Plasmodium currently belong to the most attractive antimalarial drug targets. The dithiol-containing redox proteins thioredoxin (Trx) and glutaredoxin (Grx), as well as plasmoredoxin (Plrx), which is exclusively found in Plasmodium species, represent central players in the redox network of malarial parasites. To extend our knowledge of interacting partners and the functions of these proteins, we carried out pull-down assays with immobilized active site mutants of Trx, Grx, and Plrx and whole cell parasite lysate. After elution of bound proteins and mass spectrometric identification, about 20 interacting partners were identified for each of the redox proteins. Data was supported using BIAcore surface plasmon resonance. The identified interacting proteins, which are likely to be redox-regulated, are involved in important cellular processes including protein biosynthesis, energy metabolism, polyamine synthesis, and signal transduction. Our results contribute to our understanding of the redox interactome in malarial parasites.

Human glyceraldehyde-3-phosphate dehydrogenase plays a direct role in reactivating oxidized forms of the DNA repair enzyme APE1

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has diverse biological functions including its nuclear translocation in response to oxidative stress. We show that GAPDH physically associates with APE1, an essential enzyme involved in the repair of abasic sites in damaged DNA, as well as in the redox regulation of several transcription factors. This interaction allows GAPDH to convert the oxidized species of APE1 to the reduced form, thereby reactivating its endonuclease activity to cleave abasic sites. The GAPDH variants C152G and C156G retain the ability to interact with but are unable to reactivate APE1, implicating these cysteines in catalyzing the reduction of APE1. Interestingly, GAPDH-small interfering RNA knockdown sensitized the cells to methyl methane sulfonate and bleomycin, which generate lesions that are repaired by APE1, but showed normal sensitivity to 254-nm UV. Moreover, the GAPDH knockdown cells exhibited an increased level of spontaneous abasic sites in the genomic DNA as a result of diminished APE1 endonuclease activity. Thus, the nuclear translocation of GAPDH during oxidative stress constitutes a protective mechanism to safeguard the genome by preventing structural inactivation of APE1.

Regulation of plant cytosolic glyceraldehyde 3-phosphate dehydrogenase isoforms by thiol modifications

Cytosolic NAD-dependent glyceraldehyde 3-P dehydrogenase (GAPDH; GapC; EC 1.2.1.12) catalyzes the oxidation of triose phosphates during glycolysis in all organisms, but additional functions of the protein has been put forward. Because of its reactive cysteine residue in the active site, it is susceptible to protein modification and oxidation. The addition of GSSG, and much more efficiently of S-nitrosoglutathione, was shown to inactivate the enzymes from Arabidopsis thaliana (isoforms GapC1 and 2), spinach, yeast and rabbit muscle. Inactivation was fully or at least partially reversible upon addition of DTT. The incorporation of glutathione upon formation of a mixed disulfide could be shown using biotinylated glutathione ethyl ester. Furthermore, using the biotin-switch assay, nitrosylated thiol groups could be shown to occur after treatment with nitric oxide donors. Using mass spectrometry and mutant proteins with one cysteine lacking, both cysteines (Cys-155 and Cys-159) were found to occur as glutathionylated and as nitrosylated forms. In preliminary experiments, it was shown that both GapC1 and GapC2 can bind to a partial gene sequence of the NADP-dependent malate dehydrogenase (EC 1.2.1.37; At5g58330). Transiently expressed GapC-green fluorescent protein fusion proteins were localized to the nucleus in A. thaliana protoplasts. As nuclear localization and DNA binding of GAPDH had been shown in numerous systems to occur upon stress, we assume that such mechanism might be part of the signaling pathway to induce increased malate-valve capacity and possibly other protective systems upon overreduction and initial formation of reactive oxygen and nitrogen species as well as to decrease and protect metabolism at the same time by modification of essential cysteine residues.

Hyperoxidized Peroxiredoxins and Glyceraldehyde-3-Phosphate Dehydrogenase Immunoreactivity and Protein Levels are Changed in the Gerbil Hippocampal CA1 Region After Transient Forebrain Ischemia

Oxidative stress is a major pathogenic event occurring in several brain disorders and is a major cause of brain damage due to ischemia/reperfusion. Thiol proteins are easily oxidized in cells exposed to reactive oxygen species (ROS). In the present study, we investigated transient ischemia-induced chronological changes in hyperoxidized peroxiredoxins (Prx-SO3) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH-SO3) immunoreactivity and protein levels in the gerbil hippocampus induced by 5 min of transient forebrain ischemia. Weak Prx-SO3 immunoreactivity is detected in the hippocampal CA1 region of the sham-operated group. Prx-SO3 immunoreactivity was significantly increased 12 h and 1 day after ischemia/reperfusion, and the immunoreactivity was decreased to the level of the sham-operated group 2 days after ischemia/reperfusion. Prx-SO3 immunoreactivity in the 4 days post-ischemia group was increased again, and the immunoreactivity was expressed in glial components for 5 days after ischemia/reperfusion. GAPDH-SO3 immunoreactivity was highest in the CA1 region 1 day after ischemia/reperfusion, the immunoreactivity was decreased 2 days after ischemia/reperfusion. Four days after ischemia/reperfusion, GAPDH-SO3 immunoreactivity increased again, and the immunoreactivity began to be expressed in glial components from 5 days after ischemia/reperfusion. Prx-SO3 and GAPDH-SO3 protein levels in the ischemic CA1 region were also very high 12 h and 1 day after ischemia/reperfusion and returned to the level of the sham-operated group 3 days after ischemia/reperfusion. Their protein levels were increased again 5 days after ischemia/reperfusion. In conclusion, Prx-SO3 and GAPDH-SO3 immunoreactivity and protein levels in the gerbil hippocampal CA1 region are significantly increased 12 h-24 h after ischemia/reperfusion and their immunoreactivity begins to be expressed in glial components from 4 or 5 days after ischemia/reperfusion.

Triosephosphate isomerase- and glyceraldehyde-3-phosphate dehydrogenase-reactive autoantibodies in the cerebrospinal fluid of patients with multiple sclerosis

Our previous results revealed that Igs in lesions and single chain variable fragment Abs (scFv-Abs) generated from clonal B cells in the cerebrospinal fluid (CSF) from patients with multiple sclerosis (MS) bind to axons in MS brains. To study the axonal Ags involved in MS, we identified the glycolytic enzymes, triosephosphate isomerase (TPI) and GAPDH, using Igs from the CSF and scFv-Abs generated from clonal B cells in the CSF and in lesions from MS patients. Elevated levels of CSF-Abs to TPI were observed in patients with MS (46%), clinically isolated syndrome (CIS) suggestive of MS (40%), other inflammatory neurological diseases (OIND; 29%), and other noninflammatory neurological diseases (ONIND; 31%). Levels of GAPDH-reactive Abs were elevated in MS patients (60%), in patients with CIS (10%), OIND (14%), and ONIND (8%). The coexistence of both autoantibodies was detected in 10 MS patients (29%), and 1 CIS patient (3%), but not in patients with OIND/ONIND. Two scFv-Abs generated from the CSF and from lesions of a MS brain showed immunoreactivity to TPI and GAPDH, respectively. The findings suggest that TPI and GAPDH may be candidate Ags for an autoimmune response to neurons and axons in MS.

Reversible post-translational modification of proteins by nitrated fatty acids in vivo

Nitric oxide ((*)NO)-derived reactive species nitrate unsaturated fatty acids, yielding nitroalkene derivatives, including the clinically abundant nitrated oleic and linoleic acids. The olefinic nitro group renders these derivatives electrophilic at the carbon beta to the nitro group, thus competent for Michael addition reactions with cysteine and histidine. By using chromatographic and mass spectrometric approaches, we characterized this reactivity by using in vitro reaction systems, and we demonstrated that nitroalkene-protein and GSH adducts are present in vivo under basal conditions in healthy human red cells. Nitro-linoleic acid (9-, 10-, 12-, and 13-nitro-9,12-octadecadienoic acids) (m/z 324.2) and nitro-oleic acid (9- and 10-nitro-9-octadecaenoic acids) (m/z 326.2) reacted with GSH (m/z 306.1), yielding adducts with m/z of 631.3 and 633.3, respectively. At physiological concentrations, nitroalkenes inhibited glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which contains a critical catalytic Cys (Cys-149). GAPDH inhibition displayed an IC(50) of approximately 3 microM for both nitroalkenes, an IC(50) equivalent to the potent thiol oxidant peroxynitrite (ONOO(-)) and an IC(50) 30-fold less than H(2)O(2), indicating that nitroalkenes are potent thiol-reactive species. Liquid chromatography-mass spectrometry analysis revealed covalent adducts between fatty acid nitroalkene derivatives and GAPDH, including at the catalytic Cys-149. Liquid chromatography-mass spectrometry-based proteomic analysis of human red cells confirmed that nitroalkenes readily undergo covalent, thiol-reversible post-translational modification of nucleophilic amino acids in GSH and GAPDH in vivo. The adduction of GAPDH and GSH by nitroalkenes significantly increased the hydrophobicity of these molecules, both inducing translocation to membranes and suggesting why these abundant derivatives had not been detected previously via traditional high pressure liquid chromatography analysis. The occurrence of these electrophilic nitroalkylation reactions in vivo indicates that this reversible post-translational protein modification represents a new pathway for redox regulation of enzyme function, cell signaling, and protein trafficking.

Proteomic detection of hydrogen peroxide-sensitive thiol proteins in Jurkat cells

Thiol proteins are important in cellular antioxidant defenses and redox signalling. It is postulated that reactive oxidants cause selective thiol oxidation, but relative sensitivities of different cell proteins and critical targets are not well characterized. We exposed Jurkat cells to H2O2 for 10 min and measured changes in reversibly oxidized proteins by labelling with iodoacetamidofluorescein and two-dimensional electrophoresis. At 200 microM H2O2, which caused activation of the MAP (mitogen-activated protein) kinase ERK (extracellular-signal-regulated kinase), growth arrest and apoptosis, relatively few changes were seen. A total of 28 spots were reversibly oxidized (increased labelling intensity) and 24 decreased. The latter included isoforms of peroxiredoxins 1 and 2, which were irreversibly oxidized. Oxidation of GAPDH (glyceraldehyde-3-phosphate dehydrogenase) was striking, and other affected proteins included glutathione S-transferase P1-1, enolase, a regulatory subunit of protein kinase A, annexin VI, the mitotic checkpoint serine/threonine-protein kinase BUB1beta, HSP90beta (heat-shock protein 90beta) and proteosome components. At 20 microM H2O2, changes were fewer, but GAPDH and peroxiredoxin 2 were still modified. Dinitrochlorobenzene treatment, which inhibited cellular thioredoxin reductase and partially depleted GSH, caused reversible oxidation of several proteins, including thioredoxin 1 and peroxiredoxins 1 and 2. Most changes were distinct from those with H2O2, and changes with H2O2 were scarcely enhanced by dinitrochlorobenzene. Relatively few proteins, including deoxycytidine kinase, nucleoside diphosphate kinase and a proteosome activator subunit, responded only to the combined treatment. Thus most of the effects of H2O2 were not linked to thioredoxin oxidation. Our study has identified peroxiredoxin 2 and GAPDH as two of the most oxidant-sensitive cell proteins and has highlighted how readily peroxiredoxins undergo irreversible oxidation.

Amyloid‐β induces disulfide bonding and aggregation of GAPDH in Alzheimer's disease

GAPDH is a redox-sensitive glycolytic enzyme that also promotes apoptosis when translocated to the nucleus and associates with aggregate-prone proteins involved in neurodegenerative disorders. Recent evidence indicates that polymorphic variation within GAPDH genes is associated with an elevated risk of developing Alzheimer's disease (AD). We previously demonstrated that GAPDH readily undergoes disulfide bonding following oxidant exposure, although the consequence of disulfide bonding on GAPDH activity or function is unknown. Here we show that increased GAPDH disulfide bonding is observed in detergent-insoluble extracts from AD patient and transgenic AD mouse brain tissue compared with age-matched controls. Exposure of primary rat cortical neurons to the pro-oxidant amyloid beta peptide promotes nuclear accumulation of a disulfide-linked form of GAPDH, which becomes detergent-insoluble. Disulfide bonding leads to a reduction in GAPDH enzymatic activity and correlates with the appearance of punctate aggregate-like GAPDH staining within the cytoplasm of both oxidant-treated HT22 cells and amyloid beta-treated primary cortical neurons. Our findings suggest that disulfide bonding of GAPDH and subsequent protein aggregate formation may have relevance to the pathophysiology of AD.

Degradation of glyceraldehyde-3-phosphate dehydrogenase triggered by 4-hydroxy-2-nonenal and 4-hydroxy-2-hexenal

Lipid peroxidation products such as 4-hydroxy-2-nonenal (HNE) may be responsible for various pathophysiological events under oxidative stress, since they injure cellular components such as proteins and DNA. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which is a key enzyme of glycolysis and has been reported to be a multifunctional enzyme, is one of the enzymes inhibited by HNE. Previous studies showed that GAPDH is degraded when incubated with acetylleucine chloromethyl ketone (ALCK), resulting in the liberation of a 23-kDa fragment. In this study, we examined whether GAPDH incubated with HNE or other aldehydes of lipid peroxidation products are degraded similarly to that with ALCK. The U937 cell extract was incubated with these aldehydes at 37 degrees C and analyzed by Western blotting using anti-GAPDH antibodies. Incubation with HNE or 4-hydroxy-2-hexenal (HHE) decreased GAPDH activity and GAPDH protein level, and increased the 23-kDa fragment, in time- and dose-dependent manners, but that with other aldehydes did not. Gel filtration using the Superose 6 showed that the GAPDH-degrading activity was eluted in higher molecular fractions than proteasome activity. The enzyme activity was detected at the basic range of pH and inhibited by serine protease inhibitors, diisopropyl fluorophosphate and phenylmethylsulfonyl fluoride, but not by other protease inhibitors including a proteasome inhibitor, MG-132, and a tripeptidyl peptidase II (TPP II) inhibitor, AAF-CMK. These results suggest that GAPDH modified by HNE and HHE is degraded by a giant serine protease, releasing the 23-kDa fragment, not by proteasome or TPP II.

Protein disulfide bond formation in the cytoplasm during oxidative stress

The majority of disulfide-linked cytosolic proteins are thought to be enzymes that transiently form disulfide bonds while catalyzing oxidation-reduction (redox) processes. Recent evidence indicates that reactive oxygen species can act as signaling molecules by promoting the formation of disulfide bonds within or between select redox-sensitive proteins. However, few studies have attempted to examine global changes in disulfide bond formation following reactive oxygen species exposure. Here we isolate and identify disulfide-bonded proteins (DSBP) in a mammalian neuronal cell line (HT22) exposed to various oxidative insults by sequential nonreducing/reducing two-dimensional SDS-PAGE combined with mass spectrometry. By using this strategy, several known cytosolic DSBP, such as peroxiredoxins, thioredoxin reductase, nucleoside-diphosphate kinase, and ribonucleotide-diphosphate reductase, were identified. Unexpectedly, a large number of previously unknown DSBP were also found, including those involved in molecular chaperoning, translation, glycolysis, cytoskeletal structure, cell growth, and signal transduction. Treatment of cells with a wide range of hydrogen peroxide concentrations either promoted or inhibited disulfide bonding of select DSBP in a concentration-dependent manner. Decreasing the ratio of reduced to oxidized glutathione also promoted select disulfide bond formation within proteins from cytoplasmic extracts. In addition, an epitope-tagged version of the molecular chaperone HSP70 forms mixed disulfides with both beta4-spectrin and adenomatous polyposis coli protein in the cytosol. Our findings indicate that disulfide bond formation within families of cytoplasmic proteins is dependent on the nature of the oxidative insult and may provide a common mechanism used to control multiple physiological processes.

Target proteins of the cytosolic thioredoxins in Arabidopsis thaliana

Possible target proteins of cytosolic thioredoxin in higher plants have been investigated in the cell lysate of dark-grown Arabidopsis thaliana whole tissues. We immobilized a mutant of cytosolic thioredoxin, in which an internal cysteine at the active site was substituted with serine, on CNBr activated resin, and used the resin for the thioredoxin-affinity chromatography. By using this resin, the target proteins for thioredoxin in the higher plant cytosol were efficiently acquired. The obtained proteins were separated by two-dimensional gel electrophoresis and analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Thus we have identified proteins of the anti-oxidative stress system proteins (ascorbate peroxidase, germin-like protein, and monomeric type II peroxiredoxin), proteins involved in protein biosynthesis (elongation factor-2 and eukaryotic translation initiation factor 4A), proteins involved in protein degradation (the regulatory subunit of 26S proteasome), and several metabolic enzymes (alcohol dehydrogenase, fructose 1,6-bis phosphate aldolase-like protein, cytosolic glyceraldehyde 3-phosphate dehydrogenase, cytosolic malate dehydrogenase, and vitamin B(12)-independent methionine synthase) together with some chloroplast proteins (chaperonin 60-alpha and 60-beta, heat shock protein 70, and glutamine synthase). The results in this study and recent proteomics studies on the target proteins of chloroplast thioredoxin indicate the versatility and the physiological significance of thioredoxin as reductant in plant cell.

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.

Sodium pyruvate is better than sodium chloride as a resuscitation solution in a rodent model of profound hemorrhagic shock

Pyruvate is an energy substrate that has both inotropic and antioxidant properties. In this study, we tested the hypothesis that survivorship would be better after resuscitation with 1.7% sodium pyruvate than 0.9% sodium chloride in a profound hemorrhagic shock model. The study was performed in a blinded manner. Rats were randomly assigned into two groups (ten in each group), a sodium chloride resuscitation group and a sodium pyruvate resuscitation group. After a 60-min shock period, we infused 80 ml/kg of a resuscitation solution. We continuously monitored mean arterial pressure and heart rate for 50 min after resuscitation. We recognized death by the disappearance of blood pressure pulsation and precordial movement. We performed a comparison of survivorship at 50 min post resuscitation using a Z-test of proportions. Nine (90%) of the animals that received sodium pyruvate were living 50 min after resuscitation, whereas only three (30%) of the animals that received sodium chloride survived to the same time point. We conclude that sodium pyruvate is better than sodium chloride as a resuscitation solution in a model of profound hemorrhagic shock.

Estradiol protects against ATP depletion, mitochondrial membrane potential decline and the generation of reactive oxygen species induced by 3-nitroproprionic acid in SK-N-SH human neuroblastoma cells

Mitochondria are recognized as modulators of neuronal viability during ischemia, hypoxia and toxic chemical exposure, wherein mitochondria dysfunction leading to ATP depletion may be a common pathway of cell death. Estrogens have been reported to be neuroprotective and proposed to play a role in the modulation of cerebral energy/glucose metabolism. To address the involvement of 17beta-estradiol preservation of mitochondrial function, we examined various markers of mitochondrial activity in human SK-N-SH neuroblastoma cells exposed to 3-nitroproprionic acid (3-NPA), a succinate dehydrogenase inhibitor which uncouples oxidative phosphorylation. 3-NPA (10 mM) significantly increased ATP levels at 2 h then caused a 40% and a 50% decrease in ATP levels from baseline when treated for 12 h and 24 h, respectively. 3-NPA also induced significant increases in levels of cellular hydrogen peroxide and peroxynitrite at 2 h and a 60% decrease in mitochondrial membrane potential (MMP) at 12 h exposure. 17beta-Estradiol (17beta-E(2)) pretreatment restored the ATP level back to 80% at 12 h of that in control cells treated with 3-NPA but without E(2), blunted the effect of 3-NPA on MMP and reactive oxygen species levels. The present study indicates that 17beta-E(2) can preserve mitochondrial function in the face of inhibition of oxidative phosphorylation.

Eosinophil peroxidase oxidation of thiocyanate. Characterization of major reaction products and a potential sulfhydryl-targeted cytotoxicity system

Although the pseudohalide thiocyanate (SCN(-)) is the preferred substrate for eosinophil peroxidase (EPO) in fluids of physiologic halide composition, the product(s) of this reaction have not been directly identified, and mechanisms underlying their cytotoxic potential are poorly characterized. We used nuclear magnetic resonance spectroscopy (NMR), electrospray ionization mass spectrometry, and quantitative chemical analysis to identify the principal reaction products of both the EPO/SCN(-)/H(2)O(2) system and activated eosinophils as roughly equimolar amounts of OSCN(-) (hypothiocyanite) and OCN(-) (cyanate). Red blood cells exposed to increasing concentrations of OSCN(-)/OCN(-) are first depleted of glutathione, after which glutathione S-transferase and glyceraldehyde-3-phosphate dehydrogenase then ATPases undergo sulfhydryl (SH) reductant-reversible inactivation before lysing. OSCN(-)/OCN(-) inactivates red blood cell membrane ATPases 10-1000 times more potently than do HOCl, HOBr, and H(2)O(2). Exposure of glutathione S-transferase to [(14)C]OSCN(-)/OCN(-) causes SH reductant-reversible disulfide bonding and covalent isotope labeling. We propose that EPO/SCN(-)/H(2)O(2) reaction products comprise a potential SH-targeted cytotoxic system that functions in striking contrast to HOCl, the highly but relatively indiscriminantly reactive product of the neutrophil myeloperoxidase system.

Protein oxidation

The oxidative modification of proteins by reactive species, especially reactive oxygen species, is implicated in the etiology or progression of a panoply of disorders and diseases. These reactive species form through a large number of physiological and non-physiological reactions. An increase in the rate of their production or a decrease in their rate of scavenging will increase the oxidative modification of cellular molecules, including proteins. For the most part, oxidatively modified proteins are not repaired and must be removed by proteolytic degradation, and a decrease in the efficiency of proteolysis will cause an increase in the cellular content of oxidatively modified proteins. The level of these modified molecules can be quantitated by measurement of the protein carbonyl content, which has been shown to increase in a variety of diseases and processes, most notably during aging. Accumulation of modified proteins disrupts cellular function either by loss of catalytic and structural integrity or by interruption of regulatory pathways.

Modulation of lens glycolytic pathway by thioltransferase

The observation that the level of S-thiolated proteins (protein-thiol mixed disulfides) was transiently increased in the lens epithelial cells correlation with the transient inactivation of glyceraldehyde-3-phosphate dehydrogenase (G-3PD), a key glycolytic enzyme, when the cells were treated with a bolus of hydrogen peroxide, prompted our speculation that G-3PD may have been transiently thiolated at the SH sensitive active center. In the meantime, thioltransferase (TTase), a thiol regulating enzyme, whose activity remained constant under the same condition, may be regulating G-3PD and other sulfhydryl-sensitive glycolytic enzymes through thiol-disulfide exchange reactions ( Lou et al., 1998 ). To prove this hypothesis, several purified glycolytic enzymes from a commercial source, including hexokinase (HK), G-3PD, pyruvate kinase (PK) and fructose 1,6-bisphosphatase (FBPase), an enzyme in gluconeogenesis, were made into protein-thiol mixed disulfide and used for this study. Glycolytic enzymes in cultured rabbit lens epithelial cells pre-exposed to H(2)O(2)(0.5 m M for 15 min) were also studied for this purpose. Recombinant human lens thioltransferase (RHLT), which was isolated and purified previously in this laboratory, reactivated these pure glycolytic enzymes inactivated by forming protein-S-S-gluthathione (PSSG), protein-S-S-cysteine (PSSC) or, protein-S-S-cysteamine after thiolating with oxidized glutathione, cystine or cystamine respectively. RHLT also reactivated these enzymes in the cell extract of cultured rabbit lens epithelial cells after being briefly exposed to 0.5 m M H(2)O(2). The S-thiolation and dethiolation of FBPase however, showed an opposite effect to that of glycolytic enzymes. These results suggest that TTase may participate in the repair process of glycolytic enzymes during oxidative stress and restore their activities in situ.

Pyruvate: metabolic protector of cardiac performance

Pyruvate, a metabolic product of glycolysis and an oxidizable fuel in myocardium, increases cardiac mechanical performance and energy reserves, especially when supplied at supraphysiological concentrations. The inotropic effects of pyruvate are most impressive in hearts that have been reversibly injured (stunned) by ischemia/reperfusion stress. Glucose appears to be an essential co-substrate for pyruvate's salutary effects in stunned hearts, but other fuels including lactate, acetate, fatty acids, and ketone bodies produce little or no improvement in postischemic function over glucose alone. In contrast to pharmacological inotropism by catecholamines, metabolic inotropism by pyruvate increases cardiac energy reserves and bolsters the endogenous glutathione antioxidant system. Pyruvate enhancement of cardiac function may result from one or more of the following mechanisms: increased cytosolic ATP phosphorylation potential and Gibbs free energy of ATP hydrolysis, enhanced sarcoplasmic reticular calcium ion uptake and release, decreased cytosolic inorganic phosphate concentration, oxyradical scavenging via direct neutralization of peroxides and/or enhancement of the intracellular glutathione/NADPH antioxidant system, and/or closure of mitochondrial permeability transition pores. This review aims to summarize evidence for each of these mechanisms and to consider the potential utility of pyruvate as a therapeutic intervention for clinical management of cardiac insufficiency.

Cytoprotective actions of estrogens against tert-butyl hydroperoxide-induced toxicity in hepatocytes

Estrogens are effective antioxidants in diverse biological systems. Despite their antioxidant activities, it is not known yet whether estrogens prevent or alleviate liver toxicity induced by oxidative stress. In the present work, we studied this possibility by examining in vitro the protective potential of different estrogen compounds (17beta-estradiol, 2-hydroxyestradiol, and diethylstilbestrol) against tert-butyl hydroperoxide-induced hepatocyte damage. Various parameters such as cell viability, lipid peroxidation, adenine nucleotide content, and thiol status were measured as an index of cytotoxicity. The protective effects of estrogens were compared to those of the iron chelator deferoxamine. The molecules tested prevented oxidant-induced cell death differently, showing variable degrees of protection. Deferoxamine was the most potent agent, followed by diethylstilbestrol and 2-hydroxyestradiol, 17beta-estradiol being the least efficient. The inhibitory effects on lipid and thiol oxidations paralleled the effects on cell viability. The molecules also reduced the oxidant-induced ATP depletion, except for 17beta-estradiol which had no effect on the decreased ATP levels. Our results suggest that the mechanisms of the preventive actions of estrogens may be related not only to their antioxidant activity against free radicals, but also and to a lesser extent to the maintenance of the normal redox status of the cell, which partially recovers the intracellular GSH levels.

Substrates of hexokinase, glucose-6-phosphate dehydrogenase, and glyceraldehyde-3-phosphate dehydrogenase prevent the inhibitory response induced by ascorbic acid/iron and dehydroascorbic acid in rabbit erythrocytes

Exposure of intact rabbit erythrocytes or erythrocyte lysates to ascorbic acid/FeCl3 in a glucose-free saline promoted a rapid decline in reduced glutathione and this response was paralleled by inactivation of hexokinase. Under the same conditions, the activity of the enzymes glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase did not show appreciablevariations in intact cells, but was severely inhibited in the cell-free system. Similar results were obtained by replacing ascorbic acid/FeCl3 with dehydroascorbic acid. In addition, both treatments effectively inhibited the activity of purified hexokinase as well as those of glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. Further studies using the cell-free system indicated that the inhibition of enzyme activities elicited by either of the two treatments was effectively counteracted by the specific substrates of these enzymes. The fact that the hexokinase substrate glucose freely permeates the plasma membrane, unlike the substrates of glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphatedehydrogenase, explains the selective inhibition of hexokinase observed in intact cells. The above results also indicate that dehydroascorbic acid is an inhibitor of these enzymes and strongly suggest that it is at least in part responsible for the effects mediated by the cocktail ascorbic acid/FeCl3.

Mitochondrial formation of hydrogen peroxide is causally linked to the antimycin A-mediated prevention of tert-butylhydroperoxide-induced U937 cell death

Antimycin A and 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), both of which bind to the same site of complex III, prevented U937 cell killing promoted by tert-butylhydroperoxide (tB-OOH). This cytoprotection was not directly caused by inhibition of electron transport or reduced formation of tB-OOH-derived toxic species, but rather appeared to be the consequence of a mechanism involving mitochondrial formation of hydrogen peroxide. Ubisemiquinone was most likely the electron donor allowing the formation of superoxides and, as a consequence, of hydrogen peroxide.

Thioltransferase is present in the lens epithelial cells as a highly oxidative stress-resistant enzyme

The redox homeostasis is controlled by several enzyme systems. Sulfhydryl groups in lens proteins are very sensitive to oxidative stress and can easily conjugate with nonprotein thiols (S-thiolation) to form protein-thiol mixed disulfides. We have observed an elevation of protein S-S-glutathione (PSSG) and protein-S-S-cysteine (PSSC) in cataractous lenses from humans and from animal models subjected to oxidative stress. We also observed that these protein-thiol mixed disulfides could be spontaneously dissociated and lowered to basal levels if the lens which was pre-exposed to H2O2 was subsequently cultured in H2O2-free medium. This suggests that the lens has a system to repair oxidative damage through dethiolation thereby restoring its redox homeostasis. In other tissues, an enzyme, thioltransferase (TTase), has been shown to be responsible for thiol/disulfide regulation. We recently demonstrated the presence of this enzyme in the lens and in cultured lens epithelial cells. Here, we investigated the response of TTase to H2O2 stress and its possible repair function in cultured lens epithelial cells. Rabbit lens epithelial cell line N/N 1003A was raised to confluence, trypsinized and plated at 0.8 million cells per 60 mm culture dish. The cells were incubated overnight in Eagle's minimum essential medium (MEM) with 1% rabbit serum and then in serum-free MEM for 30 min before a bolus of 0.5 mm H2O2 was added. At intervals of 5, 15, 30 min and up to 3 hr, the cells were harvested and used for enzyme assays for TTase, glutathione reductase (GR), glutathione peroxidase (GPx) and glyceraldehyde-3-phosphate dehydrogenase (G-3PD). Free GSH, total SH and PSSG and PSSC were also determined. Hydrogen peroxide in the medium was measured at each time point. Cells incubated without H2O2 were used as controls. The results showed that the H2O2 concentration was reduced to 50% within 30 min and was undetectable at 2 hr. Cellular GSH dropped to 40% within 5 min and stayed at this level before it began to increase at 90 min and completely recovered by 2 hr. The total SH groups were similar to free GSH. PSSG and PSSC increased 6.5 and 2 times respectively before 30 min and then decreased when GSH started to recover. G-3PD was most sensitive to H2O2 and lost 95% activity within 5 min. The activity was regained quickly when H2O2 diminished in the medium. A similar but less severe pattern was observed in both GPx (60% loss at 60 min) and GR (30% loss at 90 min). In contrast, TTase activity remained constant during the entire 3 hr. Only when a higher dose of H2O2 (0.8-1.0 mM) was used, did TTase activity show a brief loss (<30% at 60 min) and a swift recovery. Cells exposed to H2O2 exhibited a normal morphology with no evidence of DNA fragmentation. The lens epithelial cells showed a remarkable ability to repair the early damages induced by H2O2. The unusual oxidative stress-resistant property displayed by TTase, coupled with its known function suggest that it plays an important role in the repair of oxidative damage.

Glutathione involvement on the intestinal Na+-dependent D-glucose active transporter

Glutathione and its related enzymes are present in intestinal epithelium. Depletion or alteration of glutathione levels have been related to different physiological and pathological conditions. Glutathione also seems to be related to the regulation of some protein activities. The present study, by in vivo experiments, shows a specific relationship between D-glucose Na+-dependent active transporter activity in rat intestine brush-border membranes and reduced glutathione/oxidized glutathione ratio levels. Changes of the kinetic parameters show that an increase of this ratio is related to an increase of the affinity of glucose for its binding sites and a higher transport capacity of the transporter. Neither alteration in the activity of other substrate transport systems nor change in the specific activity of the key enzymes related to glutathione and glucose metabolism are found. These findings suggest the possibility that D-glucose transporter activity is modulated through the change in the redox status of glutathione.

The role of cysteine in the regulation of blood glutathione-protein mixed disulfides in rats treated with diamide

The kinetics of GSH, GSSG, and thiol-protein mixed disulfides (RS-SP) of GSH (GS-SP) and cysteine (CYS-SP) were studied in rat blood and liver in the time range 0-120 min after treatment with 100 and 200 mg/kg i.p. of diamide. Total consumption (10 min) and regeneration (120 min) of blood GSH, matched by parallel increases and decreases in RS-SP, were observed. GSSG did not change appreciably. No dose-effect relationship was obtained with either treatment. On the contrary, in vitro treatment of blood with 0.75 mM diamide provoked the same trends of GSH and RS-SP as in vivo (e.g., reversible modifications), whereas treatment with 1.5 mM caused drops and rises in GSH and RS-SP, respectively, without any subsequent return to control values. The presence of a hematic factor responsible for RS-SP regulation is hypothesized in the in vivo experiment. Successive experiments involving in vitro pretreatment with 2 mM diamide and treatment with 0.5 mM of various thiols indicated that cysteine (CYS), but not GSH or N-acetylcysteine, rapidly restored erythrocyte GSH and RS-SP to their basal levels. No evident sign of hemolysis was observed in these experiments. These results indicate that CYS is a diffusible thiol important for RS-SP regulation. Analysis of whole blood of rats treated with 100 mg/kg i.p. diamide and the presence of two reversible peaks (about 10 times the corresponding control level) of CYS-SP and free CYS confirmed the plausible role of CYS in maintaining the reversibility of the process. Preliminary results in liver of rats treated with 100 mg/kg diamide indicated that CYS may act by metabolic cooperation between organs. We suggest that CYS may have a role in the regulation of the intracellular redox state of rat erythrocytes during oxidative stress.

Evidence of oxidant-induced injury to epithelial cells during inflammatory bowel disease

Evidence of in vivo oxidant-induced injury in inflammatory bowel disease (IBD) is largely indirect. Colon epithelial crypt cells (CEC) from paired specimens of histologically normal and inflamed bowel from IBD patients with active disease were examined for altered protein thiol redox status as an indicator of oxidative damage. When CEC preparations from 22 IBD patients were labeled with the reduced-thiol-specific probe [14C]-iodoacetamide (IAM), there was decreased labeling of a number of proteins indicating oxidation of thiol groups in CEC from inflamed mucosa compared to paired normal mucosa, especially the loss of thiol labeling of a 37-kD protein which was almost completely lost. The loss of reduced protein thiol status for the 37-kD band was paralleled by loss of epithelial cell glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) enzyme activity, an enzyme known to contain an essential reduced cysteine (Cys149) at the active site. The identity of the 37-kD protein as GADPH monomer was confirmed by NH2-terminal amino acid sequence analysis. To examine whether this type of in vivo injury could be attributed to biologically relevant oxidants produced by inflammatory cells, CEC prepared from normal mucosa were exposed to H2O2, OCl-, nitric oxide (NO), and a model chloramine molecule chloramine T (ChT) in vitro. Dose-dependent loss of IAM labeling and GAPDH enzyme activity was observed. The efficacy (IC50) against IAM labeling was OCl- >> ChT > H2O2 > NO (52 +/- 3, 250 +/- 17, 420 +/- 12, 779 +/- 120 microM oxidant) and OCl- >> ChT > NO > H2O2 (89 +/- 17, 256 +/- 11, 407 +/- 105, 457 +/- 75 microM oxidant), respectively, for GAPDH enzyme activity. This study provides direct evidence of in vivo oxidant injury in CEC from inflamed mucosa of IBD patients. Oxidation and inhibition of essential protein function by inflammatory cells is a potential mechanism of tissue injury that may contribute to the pathogenesis of the disease and supports the exploration of compounds with antioxidant activity as new therapies for IBD.

Comparative effects of the metabolic inhibitors 2,4-dinitrophenol and iodoacetate on mouse neuroblastoma cells in vitro

The toxic effects of two metabolic inhibitors, dinitrophenol and iodoacetic acid, were compared. Mouse neuroblastoma cell cultures (Neuro-2a) were exposed to different concentrations of the toxic compounds for 24, 48 and 72 h to study basal toxicity effects (cell proliferation by quantification of total protein content (PR) and relative neutral red uptake (RNRU) by lysosomes). The following biochemical indicators assessed in the in vitro test system were: cytosolic phosphofructokinase (PFK) and enolase (ENL) activities in glycolysis; mitochondrial succinate dehydrogenase (SDH) activity in the citric acid cycle; lysosomal beta-galactosidase (GAL) activity; and neuronal acetylcholinesterase (AChE) activity. The effects of the two metabolic inhibitors on the various indicators differed. Iodoacetic acid was found to be far more toxic than dinitrophenol to neuroblastoma cell proliferation at 24 h exposure. Though 2,4-dinitrophenol and iodoacetic acid both inhibited cell proliferation of the neuroblastoma cells, their effects on the other endpoints were opposite. Dinitrophenol was a general activator of the metabolism, particularly affecting lysosomal function. Iodoacetic acid did not significantly alter general metabolism, but considerably modified lysosomal function and AChE activity. The modification of lysosomal function of Neuro-2a cells by the two compounds was quite different: dinitrophenol increased RNRU and GAL activity, and iodoacetic acid decreased both parameters.

Formation of adducts between 13-oxooctadecadienoic acid (13-OXO) and protein-derived thiols, in vivo and in vitro

Linoleic acid is metabolized by numerous tissues to oxidized derivatives possessing biological activity. In the current experiments, we have investigated the reaction of 13-oxooctadecadienoic acid (13-OXO) and the metabolic precursor 13-hydroxyoctadecadienoic acid (13-HODE) with cellular macromolecules and model cellular nucleophiles. Colonic mucosal explants from Sprague-Dawley rats were incubated in the presence of [1-14C]-13-OXO or [1-14C]-13-HODE. The binding of radiolabel to the protein and nucleic acid fractions was analyzed by isopycnic centrifugation in Cs2SO4. Cellular homogenates incubated with either 13-OXO or 13-HODE resulted in the binding of radiolabel to cellular protein. No significant amounts of reaction with cellular RNA or DNA were observed. To assess possible modes of reaction with cellular constituents, the oxidized fatty acids were incubated in vitro with oxygen, sulfur, or nitrogen, nucleophiles including, serine, cysteine, glutathione, methionine, lysine, adenosine, and guanosine. Under physiologic conditions, in the absence of cellular homogenates, only 13-OXO was reactive. In addition, only the sulfur-containing compounds cysteine and glutathione showed significant rates of reaction. Furthermore, treatment of colonic homogenates with N-ethlymaleimide reduced the binding of [1-14C]-13-OXO to cellular protein. These data support the suggestion that 13-HODE requires metabolic activation, by dehydrogenation to 13-OXO, prior to binding to cellular protein and that protein-derived thiol groups are involved in the binding reactions.

Mechanism of toxicity of precocene II in rat hepatocyte cultures

Precocene II was more toxic in 24 hour cultures than in 72 hour cultures of rat hepatocytes. In 24 hour cultures, there was no observable toxicity at 75 microM precocene II after exposure for 6 hours, but after 24 hours, 65% of the cells were dead. In contrast, although 794 microM killed 50% of the cells in the 72 hour cultures after a 24 hour exposure, 1 mM killed 96% of the cells within 6 hours. In both 24 and 72 hour cultures, cell death was preceded by a rapid, early loss of mitochondrial membrane potential, followed by decreases in glutathione, reduced pyridine nucleotide status, and plasma membrane Na+/K+-ATPase activity. There was also a rapid loss of ATP in the 72 hour cultures but not in the 24 hour cultures; therefore, onset of cell death may be closely linked to loss of ATP. Inhibition of cytochrome P-450 prevented the toxicity, and partially protected against the loss of membrane potential and glutathione, in 24 hour cultures but was ineffective in 72 hour cultures. Therefore, in addition to depletion of glutathione, precocene II appears to damage mitochondria and plasma membrane functions and can do so by more than one pathway.

Diamide-induced alterations of intracellular thiol status and the regulation of glucose metabolism in the developing rat conceptus in vitro

Direct oxidation of embryonic reduced glutathione (GSH) by a thiol oxidant, diamide, has been demonstrated to result in increased glutathione disulfide (GSSG) and protein-glutathione mixed disulfide (protein-S-SG) formation, which is accompanied by embryotoxicity and reductions in amniotic fluid volume. The altered functions of critical proteins or enzymes caused by the formation of protein-S-SG perturb cellular metabolism and may be involved in the embryotoxicity produced by GSH oxidation. The present study investigates changes in the metabolism of glucose through glycolysis and the pentose phosphate shunt pathways (PPP) and their related enzymes under the oxidative conditions produced by diamide exposure in organogenesis-stage rat conceptus (gestational day 10) in vitro. The metabolism of glucose via the PPP, measured as amounts of CO2 production from D-[1-14C]-glucose, was significantly increased in the conceptus exposed to 100-500 microM diamide to levels 2.5-3-fold those of controls. It was found that these substantial increases in the PPP activity did not correlate well with a moderate activation of glucose 6-phosphate dehydrogenase (G6PD) activity, the key enzyme in the PPP pathway. Changes in glycolysis due to diamide treatment were also determined by measurements of lactate production from D-[U-14C]-glucose. Production of lactate by the conceptus exposed to 250-500 microM diamide for 60 min was reduced (to approximately 54% of control values) concomitantly with a significant inhibition of the glycolytic enzymes, glyceraldehyde 3-phosphate dehydrogenase (GPD) and phosphofructokinase (PFK), indicating an overall decrease in glycolysis. Diamide was found to produce a differential effect on the enzymatic activities determined in this study, with greater degrees of inhibition seen in the tissue supernatants from the visceral yolk sac (VYS) compared to those from the embryo. Activities of GPD and PFK were decreased to approximately 22% and 43% control values, respectively, when determined in the supernatants from the VYS of the conceptus exposed to 500 microM diamide for 60 min. In addition, more than 90% of the GPD activity in the VYS, but not the embryo, was rapidly inhibited by the thiol alkylating agent N-ethylmaleimide (NEM, 100 microM) within 15 min of the exposure. In contrast to diamide and NEM, no alterations in lactate production were seen in the conceptus treated with the GSH depletor L-buthionine-S,R-sulfoximine (1 mM) for 5 hr in the culture media. Further experiments demonstrated that the activity of the GPD, inhibited by a 30-min incubation with 500 microM diamide, can be reversed after removal of diamide and that this effect was potentiated by subsequent treatment with dithiothreitol (30 mM), a thiol reducing agent. These results indicated the involvement of thiol/disulfide status in regulation of the metabolism of glucose in the developing conceptus and support the hypothesis that GSH oxidation and protein-S-SG formation could be a critical event associated with mechanisms of embryotoxicity elicited by oxidative stress. It was suggested in this study that, under these experimental conditions, embryotoxicity induced by diamide is primarily mediated via altered VYS functions, including disrupted energy production (glycolysis).

Protection by pyruvate against inhibition of Na+, K(+)-ATPase by a free radical generating system containing t-butylhydroperoxide

Global tissue damage due to oxygen-derived free radicals has been implicated in several pathological processes including exposure to ionizing radiation, and postischemic reperfusion of the heart or kidney. Recently pyruvate, a hydroperoxide scavenger, has been shown to protect against functional damage during postischemic reperfusion of the heart and in acute renal failure. In the present study, pyruvate was found to protect against inactivation of partially purified guinea pig renal and rat cardiac Na+,K(+)-ATPase which occurred when microsomal membranes were assayed for 1 hr at 37 degrees C (pH 7.5) in the presence of a free radical generating system (FRGS) containing 0.3 mM t-butylhydroperoxide and horseradish peroxidase. The presence of the FRG system inhibited the guinea pig renal Na+,K(+)-ATPase activity by 48.2 +/- 4.8% (N = 10, P < .05) and the presence of 0.2 to 20 mM pyruvate partially protected the Na+,K(+)-ATPase. At 5 mM pyruvate Na+,K(+)-ATPase was inhibited by only 18.8 +/- 2.5% (N = 10, P < .05) but increasing the pyruvate concentration gave no further protection. Equimolar concentrations of glucose, mannitol or lactate were without effect. The protection appeared to require an alpha-keto acid since alpha- but not beta-ketoglutarate was also effective and the mechanism is most probably the scavenging of t-BHO2. The results of the present study therefore support the hypothesis that, if free radical damage to native Na+,K(+)-ATPase does contribute to global tissue injury in certain pathological processes, pyruvate, in addition to being a powerful metabolic effector of recovery, may also protect against oxidative damage.

Cloning of the gene for phosphoglycerate kinase from Schistosoma mansoni and characterization of its gene product

As molecules on the surface or associated with the outer covering (tegument) of Schistosoma mansoni are a major focus as potential vaccine candidates, affinity purified antibodies which are specific to the tegumental antigens were used to immunoscreen a lambda gt11 S. mansoni cercarial cDNA library. One of the identified clones was found to encode the glycolytic enzyme phosphoglycerate kinase (PGK, EC 2.7.2.3). The 1.5-kb cDNA clone has a single open reading frame encoding 416 amino acids and exhibits over 60% identity to PGKs from a number of eukaryotic species. Recombinant S. mansoni PGK (SmPGK) was overexpressed in Escherichia coli, purified, and shown to have PGK enzyme activity. Native protein affinity purified from S. mansoni adult worms was shown by microsequencing to have the same amino-acid sequence as deduced from the cDNA sequence, thus confirming the cDNA clone we identified encodes S. mansoni phosphoglycerate kinase. Antibodies localize the native SmPGK to various tissues including the tegument of 3-h schistosomula and 42-day adult worms.