The Roles of Peroxiredoxin and Thioredoxin in Hydrogen Peroxide Sensing and in Signal Transduction

A challenge in the redox field is the elucidation of the molecular mechanisms, by which H2O2 mediates signal transduction in cells. This is relevant since redox pathways are disturbed in some pathologies. The transcription factor OxyR is the H2O2 sensor in bacteria, whereas Cys-based peroxidases are involved in the perception of this oxidant in eukaryotic cells. Three possible mechanisms may be involved in H2O2 signaling that are not mutually exclusive. In the simplest pathway, H2O2 signals through direct oxidation of the signaling protein, such as a phosphatase or a transcription factor. Although signaling proteins are frequently observed in the oxidized state in biological systems, in most cases their direct oxidation by H2O2 is too slow (10(1) M(-1)s(-1) range) to outcompete Cys-based peroxidases and glutathione. In some particular cellular compartments (such as vicinity of NADPH oxidases), it is possible that a signaling protein faces extremely high H2O2 concentrations, making the direct oxidation feasible. Alternatively, high H2O2 levels can hyperoxidize peroxiredoxins leading to local building up of H2O2 that then could oxidize a signaling protein (floodgate hypothesis). In a second model, H2O2 oxidizes Cys-based peroxidases that then through thiol-disulfide reshuffling would transmit the oxidized equivalents to the signaling protein. The third model of signaling is centered on the reducing substrate of Cys-based peroxidases that in most cases is thioredoxin. Is this model, peroxiredoxins would signal by modulating the thioredoxin redox status. More kinetic data is required to allow the identification of the complex network of thiol switches.

Synthetic cobalt clays for the storage and slow release of therapeutic nitric oxide

Nitric oxide (NO) is one of the smallest endogenous molecules with particularly interesting aspect roles in biological systems, despite its toxicological potential.

l-Histidine-based organoclays for the storage and release of therapeutic nitric oxide

Despite its toxicity, in low concentrations, nitric oxide (NO) is a small endogenous molecule with a particularly important role in the regulation of several biochemical pathways of the human body. The potential of l-histidine-modified clays (organoclays) for storage and therapeutic release of nitric oxide was assessed. Materials were characterized by powder X-ray diffraction, TG-DSC, IR spectroscopy, and nitrogen adsorption at -196 °C. The NO storage and release kinetics was studied both in the gas and liquid phases. For some materials, improvement was observed for both the released amounts and the release profile for the organoclays in relation to the respective raw clays. Assays with HeLa cells indicated that the materials have low cytotoxicity.

Estimation of kinetic parameters related to biochemical interactions between hydrogen peroxide and signal transduction proteins

The lack of kinetic data concerning the biological effects of reactive oxygen species is slowing down the development of the field of redox signaling. Herein, we deduced and applied equations to estimate kinetic parameters from typical redox signaling experiments. H2O2-sensing mediated by the oxidation of a protein target and the switch-off of this sensor, by being converted back to its reduced form, are the two processes for which kinetic parameters are determined. The experimental data required to apply the equations deduced is the fraction of the H2O2 sensor protein in the reduced or in the oxidized state measured in intact cells or living tissues after exposure to either endogenous or added H2O2. Either non-linear fittings that do not need transformation of the experimental data or linearized plots in which deviations from the equations are easily observed can be used. The equations were shown to be valid by fitting to them virtual time courses simulated with a kinetic model. The good agreement between the kinetic parameters estimated in these fittings and those used to simulate the virtual time courses supported the accuracy of the kinetic equations deduced. Finally, equations were successfully tested with real data taken from published experiments that describe redox signaling mediated by the oxidation of two protein tyrosine phosphatases, PTP1B and SHP-2, which are two of the few H2O2-sensing proteins with known kinetic parameters. Whereas for PTP1B estimated kinetic parameters fitted in general the present knowledge, for SHP-2 results obtained suggest that reactivity toward H2O2 as well as the rate of SHP-2 regeneration back to its reduced form are higher than previously thought. In conclusion, valuable quantitative kinetic data can be estimated from typical redox signaling experiments, thus improving our understanding about the complex processes that underlie the interplay between oxidative stress and redox signaling responses.

Is the Peroxiredoxin 2/Thioredoxin/Thioredoxin Reductase system in human erythrocytes designed for redox signaling?

In human erythrocytes H2O2 is mainly consumed by glutathione peroxidase, catalase and peroxiredoxin 2 (Prx2). Our previous analyses indicate that Prx2's peroxidase activity is subjected to a strong but quickly reversible inhibition (see companion abstract). If this activity is inhibited then the main role of Prx2 cannot be to eliminate H2O2. What functional advantages could then such an inhibition confer?We set up and validated a kinetic model of H2O2 metabolism human erythrocytes that shows quantitative agreement with extensive experimental observations. We then applied it to analyze the behavior of Prx2 and Trx under the H2O2 exposure dynamics that erythrocytes face in circulation. The significance of Prx2 inhibition was assessed by comparing the behavior of this model with that of an otherwise identical model lacking inhibition.Our analysis shows that Prx2 inhibition leads to 25-40% lower NADPH consumption under low to moderately high H2O2 supply (<0.8µM H2O2/s). Further, the inhibition extends the range where the concentrations of potential redox signaling readouts - H2O2, Prx2 sulfenic acid, Prx2 disulfide and Trx disulfide- show a proportional response to changes in H2O2 supply, covering practically the whole physiological range of the latter. This is desirable for analogic signal transduction and allows the Prx2/Trx/TrxR system to reliably transduce changes in H2O2 supply as changes in thiol oxidation. Finally, the inhibition allows other less abundant peroxiredoxins in the erythrocyte to be oxidized by H2O2 at physiological H2O2 supplies.Altogether, these results suggest that the postulated reversible inhibition of Prx2's peroxidase facilitates signal transduction by the peroxiredoxins and spares NADPH.We acknowledge: fellowship SFRH/BD/51199/2010, grants PEst-C/SAU/LA0001/2013-2014, PEst-OE/QUI/UI0612/2013, PEst-OE/QUI/UI0313/2014, and FCOMP-01-0124-FEDER-020978 co-financed by FEDER through the COMPETE program and by FCT (project PTDC/QUI-BIQ/119657/2010).

Is Peroxiredoxin II's peroxidase activity strongly inhibited in human erythrocytes?

H2O2 elimination in human erythrocytes is mainly carried out by catalase (Cat), glutathione peroxidase (GPx1) and the more recently discovered peroxiredoxin 2 (Prx2). However, the contribution of Prx2 to H2O2 consumption is still unclear. Prx2's high reactivity with H2O2 (kPrx2=10×10(7) M(-1)s(-1), kCat =7×10(7) M(-1)s(-1), kGPx1 =4×10(7) M(-1)s(-1)) and high abundance ([Prx2]= 570µM, [Cat]= 32µM, [GPx1]= 1µM) suggest that under low H2O2 supply rates it should consume >99% of the H2O2. However, extensive evidence indicates that in intact erythrocytes Prx2 contributes no more than Cat to H2O2 consumption. In order for this to be attained, Prx2's effective rate constant with H2O2would have to be just ~10(5) M(-1)s(-1), much lower than that determined in multiple experiments with the purified proteins. Nevertheless, nearly all Prx2 is oxidized within 1min of exposing erythrocytes to a H2O2 bolus, which is inconsistent with an irreversible inhibition. A mathematical model of the H2O2 metabolism in human erythrocytes [Benfeitas et al. (2014) Free Radic. Biol. Med.] where Prx2 either has a low kPrx2 or is subject to a strong (>99%) but readily reversible inhibition achieves quantitative agreement with detailed experimental observations of the responses of the redox status of Prx2 in human erythrocytes and suggests functional advantages of this design (see companion abstract). By contrast, a variant where Prx2 is fully active with kPrx2=10(8) M(-1)s(-1) shows important qualitative discrepancies. Altogether, these results suggest that Prx2's peroxidase activity is strongly inhibited in human erythrocytes. We acknowledge fellowship SFRH/BD/51199/2010, grants PEst-C/SAU/LA0001/2013-2014, PEst-OE/QUI/UI0612/2013, PEst-OE/QUI/UI0313/2014, and FCOMP-01-0124-FEDER-020978 (PTDC/QUI-BIQ/119657/2010) co-financed by FEDER through the COMPETE program and by FCT.

Hydrogen peroxide metabolism and sensing in human erythrocytes: a validated kinetic model and reappraisal of the role of peroxiredoxin II

Hydrogen peroxide (H2O2) metabolism in human erythrocytes has been thoroughly investigated, but unclear points persist. By integrating the available data into a mathematical model that accurately represents the current understanding and comparing computational predictions to observations we sought to (a) identify inconsistencies in present knowledge, (b) propose resolutions, and (c) examine their functional implications. The systematic confrontation of computational predictions with experimental observations of the responses of intact erythrocytes highlighted the following important discrepancy. The high rate constant (10(7)-10(8) M(-1) s(-1)) for H2O2 reduction determined for purified peroxiredoxin II (Prx2) and the high abundance of this protein indicate that under physiological conditions it consumes practically all the H2O2. However, this is inconsistent with extensive evidence that Prx2's contribution to H2O2 elimination is comparable to that of catalase. Models modified such that Prx2's effective peroxidase activity is just 10(5) M(-1) s(-1) agree near quantitatively with extensive experimental observations. This low effective activity is probably due to a strong but readily reversible inhibition of Prx2's peroxidatic activity in intact cells, implying that the main role of Prx2 in human erythrocytes is not to eliminate peroxide substrates. Simulations of the responses to physiological H2O2 stimuli highlight that a design combining abundant Prx2 with a low effective peroxidase activity spares NADPH while improving potential signaling properties of the Prx2/thioredoxin/thioredoxin reductase system.

Hydrogen peroxide sensing, signaling and regulation of transcription factors

The regulatory mechanisms by which hydrogen peroxide (H₂O₂) modulates the activity of transcription factors in bacteria (OxyR and PerR), lower eukaryotes (Yap1, Maf1, Hsf1 and Msn2/4) and mammalian cells (AP-1, NRF2, CREB, HSF1, HIF-1, TP53, NF-κB, NOTCH, SP1 and SCREB-1) are reviewed. The complexity of regulatory networks increases throughout the phylogenetic tree, reaching a high level of complexity in mammalians. Multiple H₂O₂ sensors and pathways are triggered converging in the regulation of transcription factors at several levels: (1) synthesis of the transcription factor by upregulating transcription or increasing both mRNA stability and translation; (ii) stability of the transcription factor by decreasing its association with the ubiquitin E3 ligase complex or by inhibiting this complex; (iii) cytoplasm–nuclear traffic by exposing/masking nuclear localization signals, or by releasing the transcription factor from partners or from membrane anchors; and (iv) DNA binding and nuclear transactivation by modulating transcription factor affinity towards DNA, co-activators or repressors, and by targeting specific regions of chromatin to activate individual genes. We also discuss how H₂O₂ biological specificity results from diverse thiol protein sensors, with different reactivity of their sulfhydryl groups towards H₂O₂, being activated by different concentrations and times of exposure to H₂O₂. The specific regulation of local H₂O₂ concentrations is also crucial and results from H₂O₂ localized production and removal controlled by signals. Finally, we formulate equations to extract from typical experiments quantitative data concerning H₂O₂ reactivity with sensor molecules. Rate constants of 140 M⁻¹ s⁻¹ and ≥1.3 × 10³ M⁻¹ s⁻¹ were estimated, respectively, for the reaction of H₂O₂ with KEAP1 and with an unknown target that mediates NRF2 protein synthesis. In conclusion, the multitude of H₂O₂ targets and mechanisms provides an opportunity for highly specific effects on gene regulation that depend on the cell type and on signals received from the cellular microenvironment.

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Complexity of redox regulation increases along the phylogenetic tree.

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Complex regulatory networks allow for a high degree of H₂O₂ biological plasticity.

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H₂O₂ modulates gene expression at all steps from transcription to protein synthesis.

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Fast response (s) is mediated by sensors with high H₂O₂ reactivity.

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Low reactivity H₂O₂ sensors may mediate slow (h) or localized H₂O₂ responses.

Cellular polarity in aging: role of redox regulation and nutrition

Cellular polarity concerns the spatial asymmetric organization of cellular components and structures. Such organization is important not only for biological behavior at the individual cell level, but also for the 3D organization of tissues and organs in living organisms. Processes like cell migration and motility, asymmetric inheritance, and spatial organization of daughter cells in tissues are all dependent of cell polarity. Many of these processes are compromised during aging and cellular senescence. For example, permeability epithelium barriers are leakier during aging; elderly people have impaired vascular function and increased frequency of cancer, and asymmetrical inheritance is compromised in senescent cells, including stem cells. Here, we review the cellular regulation of polarity, as well as the signaling mechanisms and respective redox regulation of the pathways involved in defining cellular polarity. Emphasis will be put on the role of cytoskeleton and the AMP-activated protein kinase pathway. We also discuss how nutrients can affect polarity-dependent processes, both by direct exposure of the gastrointestinal epithelium to nutrients and by indirect effects elicited by the metabolism of nutrients, such as activation of antioxidant response and phase-II detoxification enzymes through the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In summary, cellular polarity emerges as a key process whose redox deregulation is hypothesized to have a central role in aging and cellular senescence.

Interplay between apoptosis and autophagy, a challenging puzzle: new perspectives on antitumor chemotherapies

Autophagy is a mechanism of protection against various forms of human diseases, such as cancer, in which autophagy seems to have an extremely complex role. In cancer, there is evidence that autophagy may be oncogenic in some contexts, whereas in others it clearly contributes to tumor suppression. In addition, studies have demonstrated the existence of a complex relationship between autophagy and cell death, determining whether a cell will live or die in response to anticancer therapies. Nevertheless, we still need to complete the autophagy-apoptosis puzzle in the tumor context to better address appropriate chemotherapy protocols with autophagy modulators. Generally, tumor cell resistance to anticancer induced-apoptosis can be overcome by autophagy inhibition. However, when an extensive autophagic stimulus is activated, autophagic cell death is observed. In this review, we discuss some details of autophagy and its relationship with tumor progression or suppression, as well as role of autophagy-apoptosis in cancer treatments.

Toxicity of organic and inorganic nanoparticles to four species of white-rot fungi

The rapid development of nanoparticles (NP) for industrial applications and large-volume manufacturing, with its subsequent release into the environment, raised the need to understand and characterize the potential effects of NP to biota. Accordingly, this work aimed to assess sublethal effects of five NP to the white-rot fungi species Trametes versicolor, Lentinus sajor caju, Pleurotus ostreatus, and Phanerochaete chrysosporium. Each species was exposed to serial dilutions of the following NP: organic-vesicles of SDS/DDAB and of Mo/NaO; gold-NP, quantum dot CdSe/ZnS, and Fe/Co. Fungi growth rate was monitored every day, and at the end of assay the mycelium from each replicate was collected to evaluate possible changes in its chemical composition. For all NP-suspensions the following parameters were characterized: hydrodynamic diameter, surface charge, aggregation index, zeta potential, and conductivity. All tested NP tended to aggregate when suspended in aqueous media. The obtained results showed that gold-NP, CdSe/ZnS, Mo/NaO, and SDS/DDAB significantly inhibited the growth of fungi with effects on the mycelium chemical composition. Among the tested NP, gold-NP and CdSe/ZnS were the ones exerting a higher effect on the four fungi. Finally to our knowledge, this is the first study reporting that different types of NP induce changes in the chemical composition of fungi mycelium.

A quantitative study of the cell-type specific modulation of c-Rel by hydrogen peroxide and TNF-α

Hydrogen peroxide (H₂O₂) at moderate steady-state concentrations synergizes with TNF-α, leading to increased nuclear levels of NF-κB p65 subunit and to a cell-type specific up-regulation of a limited number of NF-κB-dependent genes. Here, we address how H₂O₂ achieves this molecular specificity. HeLa and MCF-7 cells were exposed to steady-state H₂O₂ and/or TNF-α and levels of c-Rel, p65, IκB-α, IκB-β and IκB-ε were determined. For an extracellular concentration of 25 µM H₂O₂, the intracellular H₂O₂ concentration is 3.7 µM and 12.5 µM for respectively HeLa and MCF-7 cells. The higher cytosolic H₂O₂ concentration present in MCF-7 cells may be a contributing factor for the higher activation of NF-κB caused by H₂O₂ in this cell line, when compared to HeLa cells. In both cells lines, H₂O₂ precludes the recovery of TNF-α-dependent IκB-α degradation, which may explain the observed synergism between H₂O₂ and TNF-α concerning p65 nuclear translocation. In MCF-7 cells, H₂O₂, in the presence of TNF-α, tripled the induction of c-Rel triggered either by TNF-α or H₂O₂. Conversely, in HeLa cells, H₂O₂ had a small antagonistic effect on TNF-α-induced c-Rel nuclear levels, concomitantly with a 50 % induction of IκB-ε, the preferential inhibitor protein of c-Rel dimers. The 6-fold higher c-Rel/IκB-ε ratio found in MCF-7 cells when compared with HeLa cells, may be a contributing factor for the cell-type dependent modulation of c-Rel by H₂O₂.

Our results suggest that H₂O₂ might have an important cell-type specific role in the regulation of c-Rel-dependent processes, e.g. cancer or wound healing.

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Selective modulation of individual NF-κB-dependent genes expression by H₂O₂.

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In MCF-7 cells H₂O₂ tripled the TNF-α 4-fold induction of c-Rel nuclear levels.

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In HeLa cells, H₂O₂ had an antagonistic effect on TNF-α induced c-Rel translocation.

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c-Rel dimers bind chiefly to IκB-α/IκB-ε in MCF-7 cells and to IκB-ε in HeLa cells.

Cateterismo posterior do plexo braquial em cão: estudo radiológico e avaliação de três protocolos anestésicos na duração do bloqueio motor e sensitivo

Avaliou-se a eficiência do cateterismo posterior do plexo braquial em cães para promover bloqueio motor e sensitivo, por meio de três protocolos anestésicos. Foram utilizados nove cães, machos e fêmeas, sem distinção de raça e idade, com peso variando de 6 a 15kg, distribuídos em três grupos de três animais por grupo. Após a confirmação do correto posicionamento do cateter pela via posterior do plexo braquial por meio do exame radiográfico, foram aplicadas as medicações de acordo com os grupos. No grupo 1, a solução anestésica de bupivacaína 0,5% sem vasoconstrictor, na dose de 2mg.kg-1, foi usada isoladamente. No grupo 2, a solução anestésica de bupivacaína foi associada ao butorfanol na dose de 0,25mg.kg-1 . No grupo 3, o fentanil, na dose de 0,005mg.kg¹, foi associado à solução anestésica de bupivacaína. Não houve diferença estatística significante entre os grupos. Observou-se que a duração dos bloqueios motor e sensitivo foi clinicamente maior no grupo 2. O cateterismo posterior do plexo braquial permite a aplicação de fármacos mais próximos do plexo nervoso, promovendo analgesia complementar nos membros anteriores.

Impairment of locomotor activity induced by the novel N-acylhydrazone derivatives LASSBio-785 and LASSBio-786 in mice

The N-acylhydrazone (NAH) analogues N-methyl 2-thienylidene 3,4-benzoylhydrazine (LASSBio-785) and N-benzyl 2-thienylidene 3,4-benzoylhydrazine (LASSBio-786) were prepared from 2-thienylidene 3,4-methylenedioxybenzoylhydrazine (LASSBio-294). The ability of LASSBio-785 and LASSBio-786 to decrease central nervous system activity was investigated in male Swiss mice. LASSBio-785 or LASSBio-786 (30 mg/kg, ip) reduced locomotor activity from 209 ± 26 (control) to 140 ± 18 (P < 0.05) or 146 ± 15 crossings/min (P < 0.05), respectively. LASSBio-785 (15 or 30 mg/kg, iv) also reduced locomotor activity from 200 ± 15 to 116 ± 29 (P < 0.05) or 60 ± 16 crossings/min (P < 0.01), respectively. Likewise, LASSBio-786 (15 or 30 mg/kg, iv) reduced locomotor activity from 200 ± 15 to 127 ± 10 (P < 0.01) or 96 ± 14 crossings/min (P < 0.01), respectively. Pretreatment with flumazenil (20 mg/kg, ip) prevented the locomotor impairment induced by NAH analogues (15 mg/kg, iv), providing evidence that the benzodiazepine (BDZ) receptor is involved. This finding was supported by the structural similarity of NAH analogues to midazolam. However, LASSBio-785 showed weak binding to the BDZ receptor. LASSBio-785 or LASSBio-786 (30 mg/kg, ip, n = 10) increased pentobarbital-induced sleeping time from 42 ± 5 (DMSO) to 66 ± 6 (P < 0.05) or 75 ± 4 min (P < 0.05), respectively. The dose required to achieve 50% hypnosis (HD₅₀) following iv injection of LASSBio-785 or LASSBio-786 was 15.8 or 9.5 mg/kg, respectively. These data suggest that both NAH analogues might be useful for the development of new neuroactive drugs for the treatment of insomnia or for use in conjunction with general anesthesia.

Activation of Nrf2 by H2O2: de novo synthesis versus nuclear translocation

The most common mechanism described for the activation of the transcription factor Nrf2 is based on the inhibition of its degradation in the cytosol followed by its translocation to the nucleus. Recently, Nrf2 de novo synthesis was proposed as an additional mechanism for the rapid upregulation of Nrf2 by hydrogen peroxide (H2O2). Here, we describe a detailed protocol, including solutions, pilot experiments, and experimental setups, which allows exploring the role of H2O2, delivered either as a bolus or as a steady state, in endogenous Nrf2 translocation and synthesis. We also show experimental data, illustrating that H2O2 effects on Nrf2 activation in HeLa cells are strongly dependent both on the H2O2 concentration and on the method of H2O2 delivery. The de novo synthesis of Nrf2 is triggered within 5min of exposure to low concentrations of H2O2, preceding Nrf2 translocation to the nucleus which is slower. Evidence of de novo synthesis of Nrf2 is observed only for low H2O2 steady-state concentrations, a condition that is prevalent in vivo. This study illustrates the applicability of the steady-state delivery of H2O2 to uncover subtle regulatory effects elicited by H2O2 in narrow concentration and time ranges.

The plasma membrane-enriched fraction proteome response during adaptation to hydrogen peroxide in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, adaptation to hydrogen peroxide (H₂O₂) decreases plasma membrane permeability to H₂O₂, changes its lipid composition and reorganizes ergosterol-rich microdomains by a still unknown mechanism. Here we show, by a quantitative analysis of the H₂O₂-induced adaptation effect on the S. cerevisiae plasma membrane-enriched fraction proteome, using two-dimensional gel electrophoresis, that 44 proteins are differentially expressed. Most of these proteins were regulated at a post-transcriptional level. Fourteen of these proteins contain redox-sensitive cysteine residues and nine proteins are associated with lipid and vesicle traffic. In particular, three proteins found in eisosomes and in the eisosome-associated membrane compartment occupied by Can1p were up-regulated (Pil1p, Rfs1p and Pst2p) during adaptation to H₂O₂. Survival studies after exposure to lethal H₂O₂ doses using yeast strains bearing a gene deletion corresponding to proteins associated to lipid and vesicle traffic demonstrated for the first time that down-regulation of Kes1p, Vps4p and Ynl010wp and up-regulation of Atp1 and Atp2 increases resistance to H₂O₂. Moreover, for the pil1Δ strain, H₂O₂ at low levels produces a hormetic effect by increasing proliferation. In conclusion, these data further confirms the plasma membrane as an active cellular site during adaptation to H₂O₂ and shows that proteins involved in lipid and vesicle traffic are important mediators of H₂O₂ adaptation.

Theoretical analysis of the kinetic performance of laboratory- and full-scale composting systems

Composting research at laboratory-scale is critical for the development of optimized full-scale plants. Discrepancies between processes at laboratory-scale and full-scale systems have been investigated in terms of heat balances, but a kinetic analysis of this issue is still missing. In this study, the composting rate at laboratory-scale was, on average, between 1.9 and 5.7 times faster than in full-scale systems for a set of published studies using municipal solid waste, food waste or similar materials. Laboratory-scale performance and full-scale systems were limited to 71 and 46%, respectively, of their maximum potential due to poor management of environmental process conditions far from their optimum. The main limiting environmental factor was found to be moisture content, followed by temperature. Besides environmental factors, waste composition and particle size were identified as factors accounting for kinetic differences between laboratory- and full-scale systems. Overall, this study identifies those factors that affect the kinetics of the composting process most and revealed a significant margin for reducing process time in full-scale composting.