Intracellular messenger function of hydrogen peroxide and its regulation by peroxiredoxins

Hydrogen peroxide (H2O2) accumulates transiently in various cell types stimulated with peptide growth factors and participates in receptor signaling by oxidizing the essential cysteine residues of protein tyrosine phosphatases and the lipid phosphatase PTEN. The reversible inactivation of these phosphatases by H2O2 is likely required to prevent futile cycles of phosphorylation-dephosphorylation of proteins and phosphoinositides. The accumulation of H2O2 is possible even in the presence of large amounts of the antioxidant enzymes peroxiredoxin I and II in the cytosol, probably because of a built-in mechanism of peroxiredoxin inactivation that is mediated by H2O2 and reversed by an ATP-dependent reduction reaction catalyzed by sulfiredoxin.     

Green tea polyphenol blocks h(2)o(2)-induced interleukin-8 production from human alveolar epithelial cells

Reactive oxygen species (ROS) play crucial roles in ischemia-reperfusion (IR) injury of lung transplants. Reactive oxygen species may stimulate the production of neutrophil chemotactic factors such as interleukin-8 (IL-8), from alveolar epithelial cells, causing recruitment and activation of neutrophils in the reperfused tissue. Green tea polyphenol has potent anti-oxidative activities and anti-inflammatory effects by decreasing cytokine production. In the present study, we found that green tea polyphenol significantly inhibited IL-8 production induced by hydrogen peroxide (H(2)O(2)) in human lung alveolar epithelial cells (A549 line). It has been shown that mitogen activated protein kinases, such as Jun N-terminal kinase (JNK), p38 and p44/42, could mediate IL-8 production from a variety of cell types. We further investigated the effect of green tea polyphenol on these protein kinases, and demonstrated that H(2)O(2)-induced phosphorylation of JNK and p38 but not p44/42 was inhibited by green tea polyphenol in A549 cells. We speculate that green tea polyphenol may inhibit H(2)O(2)-induced IL-8 production from A549 cells through inactivation of JNK and p38.     

Hydrogen peroxide-induced carbonylation of key metabolic enzymes in Saccharomyces cerevisiae: the involvement of the oxidative stress response regulators Yap1 and Skn7

H(2)O(2) induces a specific protein oxidation in yeast cells, and the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (Tdh) is a major target. Using a 2D-gel system to study protein carbonylation, it is shown in this work that both Tdh2p and Tdh3p isozymes were oxidized during exposure to H(2)O(2). In addition, we identified two other proteins carbonylated and inactivated: Cu,Zn-superoxide dismutase and phosphoglycerate mutase. The oxidative inactivation of Cu,Zn-superoxide dismutase decreases the antioxidant capacity of yeast cells and probably contributes to H(2)O(2)-induced cell death. Cyclophilin 1 was also carbonylated, but CPH1 gene disruption did not affect peroxide stress sensitivity. The correlation between H(2)O(2) sensitivity and the accumulation of oxidized proteins was evaluated by assaying protein carbonyls in mutants deficient in the stress response regulators Yap1p and Skn7p. The results show that the high sensitivity of yap1delta and skn7delta mutants to H(2)O(2) was correlated with an increased induction of protein carbonylation. In wild-type cells, the acquisition of stress resistance by pre-exposure to a sublethal H(2)O(2) stress was associated with a lower accumulation of oxidized proteins. However, pre-exposure of yap1delta and skn7delta cells to 0.4 mM H(2)O(2) decreased protein carbonylation induced by 1.5 mM H(2)O(2), indicating that the adaptive mechanism involved in the protection of proteins from carbonylation is Yap1p- and Skn7p-independent.     

Critical role of an endogenous gastric peroxidase in controlling oxidative damage in H. pylori-mediated and nonmediated gastric ulcer

The objective of the present study is to delineate the mechanism of oxidative damage in human gastric ulcerated mucosa despite the presence of some antioxidant enzymes. We report for the first time the critical role of an endogenous peroxidase, a major H(2)O(2) metabolizing enzyme, in controlling oxidative damage in gastric mucosa. Human gastric mucosa contains a highly active peroxidase in addition to the myeloperoxidase contributed by neutrophil. In both non-Helicobacter pylori (H. pylori)- and H. pylori-mediated gastric ulcer, when myeloperoxidase level increases due to neutrophil accumulation, gastric peroxidase (GPO) level decreases significantly. Moreover, gastric ulcer is associated with oxidative damage of the mucosa as evidenced by significant increase in lipid peroxidation, protein oxidation, and thiol depletion indicating accumulation of reactive oxygen metabolites (ROM). Mucosal total superoxide dismutase (Mn and Cu-Zn SOD) level also decreases significantly leading to increased accumulation of O(2)(*-). To investigate the plausible ROM-mediated inactivation of the GPO during ulceration, the enzyme was partially purified from the mucosa. When exposed to an in vitro ROM generating system, using Cu(2+), ascorbate, and H(2)O(2,) the enzyme gets inactivated, which is dependent on Cu(2+), ascorbate, or H(2)O(2). Insensitivity to SOD excludes inactivation by O(2)(*-). However, complete protection by catalase indicates that H(2)O(2) is essential for inactivation. Sensitivity to EDTA and hydroxyl radical *OH) scavengers indicates that GPO is inactivated most probably by *OH generated from H(2)O(2). We propose that GPO is inactivated in vivo by ROM generated by activated neutrophil. This leads to further accumulation of endogenous H(2)O(2) to cause more oxidative damage to aggravate the ulcer.     

Reconstitution of the mitochondrial PrxIII antioxidant defence pathway: general properties and factors affecting PrxIII activity and oligomeric state

The mitochondrial 2-Cys peroxiredoxin PrxIII serves as a thioredoxin-dependent peroxidase operating in tandem with its cognate partners, an organelle-specific thioredoxin (Trx2) and NADP-linked thioredoxin reductase (TRR2). This PrxIII pathway is emerging as a primary regulator of intracellular H(2)O(2) levels with dual roles in antioxidant defence and H(2)O(2)-mediated signalling. Here we describe the reconstitution of the mammalian PrxIII pathway in vitro from its purified recombinant components and investigate some of its overall properties. Employing the site-directed PrxIII mutants C47S, C66S and C168S, the putative N and C-terminal catalytic cysteine residues are shown to be essential for function whereas the C66S mutant retains full activity. The pathway attains maximal capacity at low H(2)O(2) concentrations (<10 microM) and is progressively inhibited in the range 0.1 mM to 1.0 mM peroxide. Damage to PrxIII caused by over-oxidation is confirmed by the appearance of abnormal oxidised species of PrxIII on SDS-PAGE at elevated H(2)O(2) levels. The presence of an N-terminal His-tag on PrxIII markedly enhances dodecamer stability, particularly apparent in its oxidised state. Its removal promotes oxidised PrxIII dissociation into dimers and leads to a 3.0-3.5-fold stimulation in peroxidase activity. The unusual concatenated crystal structure of PrxIII consisting of two-interlocked dodecameric rings is also evident in dilute solution employing transmission electron microscopy; however, it represents only 3-5% of the population with most molecules present as single toroids. Moreover, concatenated PrxIII C168S reverts to single toroids on crystal dissolution indicating that these higher-order structures are produced dynamically during the crystallisation process.     

Protein phosphatase 2A-mediated cross-talk between p38 MAPK and ERK in apoptosis of cardiac myocytes

Mitogen-activated protein kinases (MAPKs) play different regulatory roles in signaling oxidative stress-induced apoptosis in cardiac ventricular myocytes. The regulation and functional role of cross-talk between p38 MAPK and extracellular signal-regulated kinase (ERK) pathways were investigated in cardiac ventricular myocytes in the present study. We demonstrated that inhibition of p38 MAPK with SB-203580 and SB-239063 enhanced H(2)O(2)-stimulated ERK phosphorylation, whereas preactivation of p38 MAPK with sodium arsenite reduced H(2)O(2)-stimulated ERK phosphorylation. In addition, pretreatment of cells with the protein phosphatase 2A (PP2A) inhibitors okadaic acid and fostriecin increased basal and H(2)O(2)-stimulated ERK phosphorylation. We also found that PP2A coimmunoprecipitated with ERK and MAPK/ERK (MEK) in cardiac ventricular myocytes, and H(2)O(2) increased the ERK-associated PP2A activity that was blocked by inhibition of p38 MAPK. Finally, H(2)O(2)-induced apoptosis was attenuated by p38 MAPK or PP2A inhibition, whereas it was enhanced by MEK inhibition. Thus the present study demonstrated that p38 MAPK activation decreases H(2)O(2)-induced ERK activation through a PP2A-dependent mechanism in cardiac ventricular myocytes. This represents a novel cellular mechanism that allows for interaction of two opposing MAPK pathways and fine modulation of apoptosis during oxidative stress.     

Accumulation of overoxidized Peroxiredoxin III in aged rat liver mitochondria

Overoxidation and subsequent inactivation of Peroxiredoxin III (PrxIII), a mitochondrial H₂O₂ scavenging enzyme, have been reported in oxidative stress conditions. No data are available in the literature about the presence of overoxidized forms of PrxIII in aged tissues. Liver mitochondria from 12-month-old rats and 28-month-old rats were here analyzed by two-dimensional gel electrophoresis. A spot corresponding to the native form of PrxIII was present in adult and old rats with the same volume, whereas an additional, more acidic spot, of the same molecular weight of the native form, accumulated only in old rats. The acidic spot was identified, by MALDI-MS analysis, as a form of PrxIII bearing the cysteine of the catalytic site overoxidized to sulphonic acid. This modified PrxIII form corresponds to the irreversibly inactivated enzyme, here reported, for the first time, in aging. Three groups of 28-month-old rats treated with acetyl-l-carnitine were also examined. Reduced accumulation of the overoxidized PrxIII form was found in all ALCAR-treated groups.     

Mechanism of inactivation of Escherichia coli and Lactobacillus leichmannii ribonucleotide reductases by 2'-chloro-2'-deoxynucleotides: evidence for generation of 2-methylene-3(2H)-furanone

Incubation of 2'-chloro-2'-deoxy[3'-3H]uridine 5'-diphosphate ([3'-3H]ClUDP) with Escherichia coli ribonucleotide reductase (RDPR) and use of thioredoxin-thioredoxin reductase as reductants result in release of 4.7 equiv of 3H2O/equiv of B1 protomer, concomitant with enzyme inactivation. Inactivation is accompanied by the production of 6 equiv of inorganic pyrophosphate [Stubbe, J. A., & Kozarich, J.W. (1980) J. Am. Chem. Soc. 102, 2505-2507] and by the release of uracil as previously shown [Thelander, L., Larsson, A., Hobbs, J., & Eckstein, F. (1976) J. Biol. Chem. 251, 1398-1405]. Reisolation of RDPR by Sephadex chromatography and analysis by scintillation counting indicate that 0.96 equiv of 3H is bound per protomer of the B1 subunit of the inactivated enzyme. Incubation of [5'-3H]ClUDP with RDPR followed by similar analysis indicates that 4.6 mol of 3H is bound per protomer of the B1 subunit of the inactivated enzyme. No 3H2O is released, and 6 equiv of inorganic pyrophosphate is produced during the inactivation. RDPR is protected against inactivation when dithiothreitol (DTT) is used as a reductant in place of thioredoxin-thioredoxin reductase. Incubation of [5'-3H]ClUDP with RDPR and DTT results in the isolation of CHCl3-extractable material that exhibits infrared absorptions at 1710 and 1762 cm-1. The infrared spectrum and the NMR spectrum of the CHCl3-extracted material are very similar to model compounds prepared by the interaction of 2-methylene-3(2H)-furanone with ethanethiol. Incubation of ribonucleoside-triphosphate reductase (RTPR) from Lactobacillus leichmannii with [3'-3H]ClUTP and 3 mM DTT also results in time-dependent 3H2O release concomitant with enzyme inactivation. Reisolation of the inactive protein by Sephadex chromatography followed by radiochemical analysis indicates that 0.4 equiv of 3H is bound covalently per mol of inactivated enzyme. Similar studies with [5'-3H]ClUTP indicate that 2.9 equiv of 3H is bound covalently per mol of inactivated enzyme. No 3H2O is released. High concentrations of DTT protect the enzyme against inactivation. Extraction of the enzymatic reaction mixture with CHCl3 and analysis of the isolated products result in an infrared spectrum and an NMR spectrum remarkably similar to those observed with the E. coli RDPR. Data presented are consistent with the proposal that both the E. coli and L. leichmannii enzymes are able to catalyze the breakdown of the appropriate 2'-chloro-2'-deoxynucleotide to a 3'-keto-2'-deoxynucleotide that can collapse to form the reactive sugar intermediate 2-methylene-3(2H)-furanone.(ABSTRACT TRUNCATED AT 400 WORDS)     

Inactivation in vivo of basic peroxidase and increased content of H2O2 in grapevine leaves post treatment with DTT and paraquat

Substantial differences in the in vivo effect of paraquat (Pq) and DTT on basic peroxidase (GBPx) activity and on H2O2 levels were found in grapevine leaves cv. Sultana. GBPx activity decreased and H2O2 levels increased in illuminated Pq treated leaf-discs. Inactivation of GBPx and accumulation of H2O2 depended on the duration and intensity of the illumination to which discs were exposed. Since GBPx was inactivated directly by H2O2 and not by Pq in leaf extracts, and since GBPx are cytosolic isoenzymes and H2O2 is a stable molecule that can easily permeate chloroplast membranes, we concluded that Pq inactivation of GBPx in vivo is mediated by H2O2. In contrast to the effect induced by Pq, DTT directly inactivated GBPx in leaf extracts. In leaf-discs, however, it reduced GBPx activity in the absence of light, although the levels of H2O2 increased only after exposure of the discs to high irradiance, suggesting that under excess of light, a significant fraction of the photosynthetically produced electrons are dissipated through the water-water cycle and H2O2 accumulates as a consequence of GBPx inactivation.     

Inhibition of PTPs by H(2)O(2) regulates the activation of distinct MAPK pathways

It has been shown that endogenous production of reactive oxygen species (ROS) during T cell activation regulates signaling events including MAPK activation. Protein tyrosine phosphatases (PTPs) have been regarded as targets of ROS which modify the catalytic cysteine residues of the enzymes. We have analyzed the interplay between the inhibition of PTPs and the activation of MAPK by H(2)O(2). Stimulation of Jurkat T cells with H(2)O(2) induces the phosphorylation of ERK, p38, and JNK members of MAPK family. H(2)O(2) stimulation of T cells was found to inhibit the PTP activity of CD45, SHP-1, and HePTP. Transfection of cells with wtSHP-1 decreased H(2)O(2)-induced ERK and JNK phosphorylation without affecting p38 phosphorylation. Transfection with wtHePTP inhibited H(2)O(2)-induced ERK and p38 phosphorylation without inhibiting JNK phosphorylation. The Src-family kinase inhibitor, PP2, inhibited the H(2)O(2)-induced phosphorylation of ERK, p38, and JNK. The phospholipase C (PLC) inhibitor, U73122, or the protein kinase C (PKC) inhibitor, Ro-31-8425, blocked H(2)O(2)-induced ERK phosphorylation, whereas the same treatment did not inhibit p38 or JNK phosphorylation. Taken together, these results suggest that inhibition of PTPs by H(2)O(2) contributes to the induction of distinct MAPK activation profiles via differential signaling pathways.     

Prevention of H2O2 generation by monoamine oxidase protects against CNS O2 toxicity.

Toxicity to the central nervous system (CNS) by hyperbaric oxygen (HBO) presumably relates to increased production of reactive oxygen species. The sites of generation of reactive oxygen species during HBO, however, have not been fully characterized in the brain. We investigated the relationship between regional generation of hydrogen peroxide (H2O2) in the brain in the presence of an irreversible inhibitor of catalase, aminotriazole (ATZ), and protection from CNS O2 toxicity by a monoamine oxidase (MAO) inhibitor, pargyline. At 6 ATA of oxygen, pargyline significantly protected rats from CNS O2 toxicity whereas ATZ enhanced O2 toxicity. In animals pretreated with ATZ, HBO inactivated 21-40% more catalase than air exposure in the six brain regions studied. Because ATZ-mediated inactivation of catalase was H2O2 dependent, the decrease in catalase activity during hyperoxia was proportional to the intracellular production of H2O2. Pargyline, administered 30 min before HBO, inhibited MAO by greater than 90%, prevented ATZ inhibition of catalase activity during HBO, and reversed the augmentation of CNS O2 toxicity by ATZ. These findings indicate that H2O2 generated by MAO during hyperoxia is important to the pathogenesis of CNS O2 toxicity in rats.     

Chloroplastic ascorbate peroxidase is the primary target of methylviologen-induced photooxidative stress in spinach leaves: its relevance to monodehydroascorbate radical detected with in vivo ESR

Methylviologen (MV) induces oxidative damages in leaves. In order to understand its mechanism we studied initial biochemical events under light in MV-fed spinach leaves. When isolated chloroplasts were illuminated in the presence of MV, both stromal and thylakoid-bound ascorbate peroxidases (APX) were inactivated rapidly at the same rates, and their inactivation was retarded by ascorbate (AsA) at higher concentrations. Since MV accelerates the photoproduction of O2- in Photosystem (PS) I and simultaneously inhibits the photoreduction of monodehydroascorbate (MDA) to AsA, the inactivation of APX was attributed to the loss of AsA and accumulation of H2O2 in the stroma. Following APX, superoxide dismutase and NADP(+)-glyceraldehyde 3-phosphate dehydrogenase, both of which are vulnerable to H2O2, were inactivated by MV plus light. Dehydroascorbate reductase, monodehydroascorbate reductase, PS II, PS I and ferredoxin-NADP(+) reductase were far less sensitive to the treatment. In the treated leaves, cytosolic APX and guaiacol-specific peroxidase were also inactivated, but slower than chloroplastic APXs were. Catalase was not inactivated. Thus the MV-induced photooxidative damages of leaves are initiated with the inactivation of chloroplastic APXs and develop via the inactivation of other H2O2-sensitive targets. The decay half-life of the MDA signal after a short illumination in the leaves, as determined by in vivo electron spin resonance spectrometry (ESR), was prolonged when the H2O2-scavenging capacity of the leaf cells was abolished by the inactivation of chloroplastic and cytosolic APXs. The measurement of MDA in leaves by ESR, therefore, allows to estimate in vivo cellular capacity to scavenge the photoproduced H2O2.     

Timed maternal melatonin treatment reverses circadian disruption of the fetal adrenal clock imposed by exposure to constant light

Surprisingly, in our modern 24/7 society, there is scant information on the impact of developmental chronodisruption like the one experienced by shift worker pregnant women on fetal and postnatal physiology. There are important differences between the maternal and fetal circadian systems; for instance, the suprachiasmatic nucleus is the master clock in the mother but not in the fetus. Despite this, several tissues/organs display circadian oscillations in the fetus. Our hypothesis is that the maternal plasma melatonin rhythm drives the fetal circadian system, which in turn relies this information to other fetal tissues through corticosterone rhythmic signaling. The present data show that suppression of the maternal plasma melatonin circadian rhythm, secondary to exposure of pregnant rats to constant light along the second half of gestation, had several effects on fetal development. First, it induced intrauterine growth retardation. Second, in the fetal adrenal in vivo it markedly affected the mRNA expression level of clock genes and clock-controlled genes as well as it lowered the content and precluded the rhythm of corticosterone. Third, an altered in vitro fetal adrenal response to ACTH of both, corticosterone production and relative expression of clock genes and steroidogenic genes was observed. All these changes were reversed when the mother received a daily dose of melatonin during the subjective night; supporting a role of melatonin on overall fetal development and pointing to it as a 'time giver' for the fetal adrenal gland. Thus, the present results collectively support that the maternal circadian rhythm of melatonin is a key signal for the generation and/or synchronization of the circadian rhythms in the fetal adrenal gland. In turn, low levels and lack of a circadian rhythm of fetal corticosterone may be responsible of fetal growth restriction; potentially inducing long term effects in the offspring, possibility that warrants further research.     

On the molecular mechanism of lactoperoxidase-catalyzed H2O2 metabolism and irreversible enzyme inactivation

Lactoperoxidase-catalyzed H2O2 metabolism proceeds through one of three different pathways, depending on the nature and the concentration of the second substrate as an e- donor and/or on pH conditions. In the lactoperoxidase (LPO)-H2O2 system, at low H2O2 concentrations and/or alkaline conditions the peroxidatic cycle involves ferric LPO----compound I----compound II----ferric LPO conversion, whereas high H2O2 concentrations and/or acidic conditions favor the ferric LPO----compound I----compound II----compound III----ferrous LPO----ferric LPO pathway. The compound III/ferroperoxidase states are associated with irreversible enzyme inactivation by cleavage of the heme moiety and liberation of iron. It is likely that either singlet oxygen or superoxide and hydroxyl radicals are involved in the attack on heme iron, because inactivation correlates with oxygen production and can be decreased to a certain degree by scavengers such as ethanol, 1-propanol, 2-propanol, or mannitol. In the LPO-H2O2-I- system, the enzyme may also be inactivated by I2 generated in the course of enzymatic I- oxidation (i.e. during ferric LPO----compound I----ferric LPO cycles).     

The Arabidopsis thaliana sulfiredoxin is a plastidic cysteine-sulfinic acid reductase involved in the photooxidative stress response

The 2-cysteine peroxiredoxins (2-Cys-Prxs) are antioxidants that reduce peroxides through a thiol-based mechanism. During catalysis, these ubiquitous enzymes are occasionally inactivated by the substrate-dependent oxidation of the catalytic cysteine to the sulfinic acid (-SO2H) form, and are reactivated by reduction by sulfiredoxin (Srx), an enzyme recently identified in yeast and in mammal cells. In plants, 2-Cys-Prxs constitute the most abundant Prxs and are located in chloroplasts. Here we have characterized the unique Srx gene in Arabidopsis thaliana (AtSrx) from a functional point of view, and analyzed the phenotype of two AtSrx knockout (AtSrx-) mutant lines. AtSrx is a chloroplastic enzyme displaying sulfinic acid reductase activity, as shown by the ability of the recombinant AtSrx to reduce the overoxidized 2-Cys-Prx form in vitro, and by the accumulation of the overoxidized Prx in mutant lines lacking Srx in vivo. Furthermore, AtSrx mutants exhibit an increased tolerance to photooxidative stress generated by high light combined with low temperature. These data establish that, as in yeast and in mammals, plant 2-Cys-Prxs are subject to substrate-mediated inactivation reversed by Srx, and suggest that the 2-Cys-Prx redox status and sulfiredoxin are parts of a signaling mechanism participating in plant responses to oxidative stress.     

p38 MAPK activation elevates serotonin transport activity via a trafficking-independent, protein phosphatase 2A-dependent process

Presynaptic, plasma membrane serotonin (5-hydroxytryptamine; 5-HT) transporters (SERTs) clear 5-HT following vesicular release and are regulated through trafficking-dependent pathways. Recently, we provided evidence for a trafficking-independent mode of SERT regulation downstream of adenosine receptor (AR) activation that is sensitive to p38 MAPK inhibitors. Here, we probe this pathway in greater detail, demonstrating elevation of 5-HT transport by multiple p38 MAPK activators (anisomycin, H(2)O(2), and UV radiation), in parallel with p38 MAPK phosphorylation, as well as suppression of anisomycin stimulation by p38 MAPK siRNA treatments. Studies with transporter-transfected Chinese hamster ovary cells reveal that SERT stimulation is shared with the human norepinephrine transporter but not the human dopamine transporter. Saturation kinetic analyses of anisomycin-SERT activity reveal a selective reduction in 5-HT K(m) supported by a commensurate increase in 5-HT potency (K(i)) for displacing surface antagonist binding. Anisomycin treatments that stimulate SERT activity do not elevate surface SERT surface density whereas stimulation is lost with preexposure of cells to the surface-SERT inactivating reagent, 2-(trimethylammonium)ethyl methane thiosulfonate. Guanylyl cyclase (1H-(1,2,4)-oxadiazolo[4,3-a]-quinoxalin-1-one) and protein kinase G inhibitors (H8, DT-2) block AR stimulation of SERT yet fail to antagonize SERT stimulation by anisomycin. We thus place p38 MAPK activation downstream of protein kinase G in a SERT-catalytic regulatory pathway, distinct from events controlling SERT surface density. In contrast, the activity of protein phosphatase 2A inhibitors (fostriecin and calyculin A) to attenuate anisomycin stimulation of 5-HT transport suggests that protein phosphatase 2A is a critical component of the pathway responsible for p38 MAPK up-regulation of SERT catalytic activity.