High Levels Of H2O2 Research Articles

The bicarbonate/carbon dioxide pair increases hydrogen peroxide-mediated hyperoxidation of human peroxiredoxin 1

2-Cys peroxiredoxins (Prxs) rapidly reduce H2O2, thereby acting as antioxidants and also as sensors and transmitters of H2O2 signals in cells. Interestingly, eukaryotic 2-Cys Prxs lose their peroxidase activity at high H2O2 levels. Under these conditions, H2O2 oxidizes the sulfenic acid derivative of the Prx peroxidatic Cys (CPSOH) to the sulfinate (CPSO2 -) and sulfonated (CPSO3 -) forms, redirecting the CPSOH intermediate from the catalytic cycle to the hyperoxidation/inactivation pathway. The susceptibility of 2-Cys Prxs to hyperoxidation varies greatly and depends on structural features that affect the lifetime of the CPSOH intermediate. Among the human Prxs, Prx1 has an intermediate susceptibility to H2O2 and was selected here to investigate the effect of a physiological concentration of HCO3 -/CO2 (25 mm) on its hyperoxidation. Immunoblotting and kinetic and MS/MS experiments revealed that HCO3 -/CO2 increases Prx1 hyperoxidation and inactivation both in the presence of excess H2O2 and during enzymatic (NADPH/thioredoxin reductase/thioredoxin) and chemical (DTT) turnover. We hypothesized that the stimulating effect of HCO3 -/CO2 was due to HCO4 -, a peroxide present in equilibrated solutions of H2O2 and HCO3 -/CO2 Indeed, additional experiments and calculations uncovered that HCO4 - oxidizes CPSOH to CPSO2 - with a second-order rate constant 2 orders of magnitude higher than that of H2O2 ((1.5 ± 0.1) × 105 and (2.9 ± 0.2) × 103 m-1·s-1, respectively) and that HCO4 - is 250 times more efficient than H2O2 at inactivating 1% Prx1 per turnover. The fact that the biologically ubiquitous HCO3 -/CO2 pair stimulates Prx1 hyperoxidation and inactivation bears relevance to Prx1 functions beyond its antioxidant activity.

A Tumor-Microenvironment-Activated Nanozyme-Mediated Theranostic Nanoreactor for Imaging-Guided Combined Tumor Therapy.

Activatable theranostic agents that can be activated by tumor microenvironment possess higher specificity and sensitivity. Here, activatable nanozyme-mediated 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) loaded ABTS@MIL-100/poly(vinylpyrrolidine) (AMP) nanoreactors (NRs) are developed for imaging-guided combined tumor therapy. The as-constructed AMP NRs can be specifically activated by the tumor microenvironment through a nanozyme-mediated "two-step rocket-launching-like" process to turn on its photoacoustic imaging signal and photothermal therapy (PTT) function. In addition, simultaneously producing hydroxyl radicals in response to the high H2 O2 level of the tumor microenvironment and disrupting intracellular glutathione (GSH) endows the AMP NRs with the ability of enhanced chemodynamic therapy (ECDT), thereby leading to more efficient therapeutic outcome in combination with tumor-triggered PTT. More importantly, the H2 O2 -activated and acid-enhanced properties enable the AMP NRs to be specific to tumors, leaving the normal tissues unharmed. These remarkable features of AMP NRs may open a new avenue to explore nanozyme-involved nanoreactors for intelligent, accurate, and noninvasive cancer theranostics.

A Minor Subpopulation of Mycobacteria Inherently Produces High Levels of Reactive Oxygen Species That Generate Antibiotic Resisters at High Frequency From Itself and Enhance Resister Generation From Its Major Kin Subpopulation.

Antibiotic-exposed bacteria produce elevated levels of reactive oxygen species (ROS), to which either they succumb or get mutated genome-wide to generate antibiotic resisters. We recently showed that mycobacterial cultures contained two subpopulations, short-sized cells (SCs; ∼10%) and normal/long-sized cells (NCs; ∼90%). The SCs were significantly more antibiotic-susceptible than the NCs. It implied that the SCs might naturally be predisposed to generate significantly higher levels of ROS than the NCs. This in turn could make the SCs more susceptible to antibiotics or generate more resisters as compared to the NCs. Investigation into this possibility showed that the SCs in the actively growing mid-log phase culture naturally generated significantly high levels of superoxide, as compared to the equivalent NCs, due to the naturally high expression of a specific NADH oxidase in the SCs. This caused labile Fe2+ leaching from 4Fe-4S proteins and elevated H2O2 formation through superoxide dismutation. Thus, the SCs of both Mycobacterium smegmatis and Mycobacterium tuberculosis inherently contained significantly higher levels of H2O2 and labile Fe2+ than the NCs. This in turn produced significantly higher levels of hydroxyl radical through Fenton reaction, promoting enhanced antibiotic resister generation from the SCs than from the NCs. The SCs, when mixed back with the NCs, at their natural proportion in the actively growing mid-log phase culture, enhanced antibiotic resister generation from the NCs, to a level equivalent to that from the unfractionated whole culture. The enhanced antibiotic resister generation from the NCs in the reconstituted SCs-NCs natural mixture was found to be due to the high levels of H2O2 secreted by the SCs. Thus, the present work unveils and documents the metabolic designs of two mycobacterial subpopulations where one subpopulation produces high ROS levels, despite higher susceptibility, to generate significantly higher number of antibiotic resisters from itself and to enhance resister generation from its kin subpopulation. These findings show the existence of an inherent natural mechanism in both the non-pathogenic and pathogenic mycobacteria to generate antibiotic resisters. The presence of the SCs and the NCs in the pulmonary tuberculosis patients’ sputum, reported by us earlier, alludes to the clinical significance of the study.

Iron (III) oxide nanoparticles alleviate arsenic induced stunting in Vigna radiata

Iron nanoparticles (NPs) are widely used for the removal of arsenic from water. In this study, we evaluated the interaction between arsenate (AsO43−) and Fe2O3-NPs on early seedling growth of Vigna radiata. Seedlings were raised in AsO43− and Fe2O3-NPs, alone and in combination. While Fe2O3-NPs slightly promoted seedling growth, AsO43− reduced seedling growth drastically. AsO43--induced decline in the seedling growth was recovered by Fe2O3-NPs. In contrast, equivalent concentrations of FeCl3, alone and together with AsO43−, inhibited seed germination completely. Lower arsenic content in seedlings raised in the presence of Fe2O3-NPs indicated that Fe2O3-NPs restricted arsenic uptake. Ability of Fe2O3-NPs to restrict the arsenic uptake of the seedlings was due to adsorption of AsO43−, as revealed by transmission and scanning electron microscopy. Non-toxic levels of iron in seedlings were due to restriction of Fe2O3-NPs to root-surface. AsO43− enhanced the ferric chelate reductase activity of root which was recovered by Fe2O3-NPs. The AsO43--induced oxidative stress, evident from high levels of proline, H2O2 and malondialdehyde, and lowered root oxidisability was ameliorated by Fe2O3-NPs. AsO43-induced enhancement in total antioxidant capacity, superoxide dismutase and catalase activity, and decline in guaiacol peroxidase activity were antagonized by Fe2O3-NPs. Our findings reveal that Fe2O3-NPs provide effective resistance/amelioration to arsenic toxicity by reducing arsenic availability to plants.

The Ustilago maydis null mutant strains of the RNA-binding protein UmRrm75 accumulate hydrogen peroxide and melanin

Ustilago maydis is a dimorphic fungus that has emerged as a model organism for the study of fungal phytopathogenicity and RNA biology. In a previous study, we isolated the U. maydis UmRrm75 gene. The deletion of the UmRrm75 gene affected morphogenesis and pathogenicity. UmRrm75 gene encodes a protein containing three RNA recognition motifs. Here we determined that UmRrm75 has chaperone activity in Escherichia coli using the transcription anti-termination assay. Subsequently, we analyzed the growth of ΔUmRrm75 mutants at 15 °C and 37 °C, observing that mutant strains had reduced growth in comparison to parental strains. UmRrm75 gene expression was induced under these non-optimal temperatures. ΔUmRrm75 mutant colonies displayed a dark-brown color at 28 °C, which was confirmed to be melanin based on spectroscopic analysis and spectrometric data. Furthermore, ΔUmRrm75 mutant strains showed the presence of peroxisomes, and increased H2O2 levels, even at 28 °C. The ΔUmRrm75 mutant strains displayed a higher expression of redox-sensor UmYap1 gene and increased catalase activity than the parental strains. Our data show that deletion of the UmRrm75 gene results in higher levels of H2O2, increased melanin content, and abiotic stress sensitivity.

Biochemical responses of rice roots to cold stress

BackgroundCold stress is the main factor that reduces rice yield in subtropical areas, especially at the seedling stage. Most of the current studies on cold stress focus the responses of rice shoots to cold stress. Limited studies are available on that of rice roots to cold stress. This study aimed to illustrate the biochemical responses of rice root under cold treatment, and subject to the establishment of cold stress-related biochemical traits for rice breeding or cropping-adjustment.ResultsOur results showed that the growth of rice seedling diminished under cold stress with difference extents among eight rice cultivars of most productive in Taiwan. Under cold treatments, the tested cultivars with higher growth rate had a higher level of hydrogen peroxide (H2O2) in the shoots but had a lower level in the roots. In contrast, the tested cultivates with low growth rate had higher levels of H2O2 in the roots but a lower level in the shoots. Meanwhile, higher MDA contents and higher cell-damage related electrolyte leakage were also found in the roots not in the shoots, suggesting that cold stress might induce oxidative stress in the roots, not in the shoots. Furthermore, the activity analysis of four antioxidant enzymes, namely superoxide dismutase (SOD), catalase (CAT), ascorbic peroxidase (APX), and glutathione reductase (GR), revealed that cold stress could increase SOD and CAT activities in the roots.ConclusionsIn summary, low H2O2 and low MDA contents along with lower SOD and CAT activities in rice root could be the biochemical traits of cold responses in rice seedlings. The results are hoping to have a contribution to the rice breeding or cropping-adjustment on cold tolerance.

Nitric oxide acts as an antioxidant and inhibits programmed cell death induced by aluminum in the root tips of peanut (Arachis hypogaea L.)

Aluminum (Al) causes programmed cell death (PCD) in plants. Our previous studies have confirmed that nitric oxide (NO) inhibits Al-induced PCD in the root tips of peanut. However, the mechanism by which NO inhibits Al-induced PCD is unclear. Here the effects of NO on mitochondrial reactive oxygen species (ROS), malondialdehyde (MDA), activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), expression of alternative oxidase (AhAOX) and cytochrome oxidase (AhCOX) were investigated in peanut (Arachis hypogaea L.) root tips treated with Al. The results showed that Al stress induced rapid accumulation of H2O2 and MDA and increased the ratio of SOD/APX. The up-regulation of AhAOX and AhCOX expressions was not enough to inhibit PCD occurrence. Sodium nitroprusside (SNP, a NO donor) decreased the ratio of SOD/APX and eliminated excess H2O2 and MDA, thereby inhibiting Al-induced PCD in the root tips of peanut. The expression of AhAOX and AhCOX was significantly enhanced in Al-induced PCD treated with SNP. But cPTIO (a NO specific scavenger) supply had the opposite effect. Taken together, these results suggested that lipid peroxidation induced by higher levels of H2O2 was an important cause of Al-induced PCD. NO-mediated inhibition of Al-induced PCD was related to a significant elimination of H2O2 accumulation by decreasing the ratio of SOD/APX and up-regulating the expression of AhAOX and AhCOX.

Enhanced Tumor-Specific Disulfiram Chemotherapy by In Situ Cu2+ Chelation-Initiated Nontoxicity-to-Toxicity Transition.

The antitumor activity of disulfiram (DSF), a traditional US Food and Drug Administration-approved drug for the treatment of "alcohol-dependence", is Cu2+-dependent, but the intrinsic anfractuous biodistribution of copper in the human body and copper toxicity induced by exogenous copper supply have severely hindered its in vivo application. Herein, we report an in situ Cu2+ chelation-enhanced DSF-based cancer chemotherapy technique, using a tumor-specific "nontoxicity-to-toxicity" transition strategy based on hollow mesoporous silica nanoparticles as the functional carrier. Cu2+-doped, DSF-loaded hollow mesoporous silica nanoparticles were constructed for the rapid release of Cu2+ ions induced by the mild acidic conditions of the tumor microenvironment. This resulted in the rapid biodegradation of the nanoparticles and accelerated DSF release once the particles were endocytosed into tumor cells. The resulting in situ chelation reaction between the coreleased Cu2+ ions and DSF generated toxic CuET products and concurrently, Fenton-like reactions between the generated Cu+ ions and the high levels of H2O2 resulted in the production of reactive oxygen species (ROS) in the acidic tumor microenvironment. Both in vitro cellular assays and in vivo tumor-xenograft experiments demonstrated the efficient Cu-enhanced and tumor-specific chemotherapeutic efficacy of DSF, with cocontributions from highly toxic CuET complexes and ROS generated within tumors. This work provides a conceptual advancement of nanoparticle-enabled "nontoxicity-to-toxicity" transformation in tumors, to achieving high chemotherapeutic efficacy and biosafety.

Cross talk between ROS homeostasis and antioxidative machinery contributes to salt tolerance of the xero-halophyte Haloxylon salicornicum

Salinity is a foremost environmental threat that challenges agriculture and food security worldwide. In the present work, physiological, biochemical and anatomical strategies adopted by the xero-halophyte Haloxylon salicornicum in response to salinity was investigated. H. salicornicum plant withstands a prolong treatment of salinity, even under high dose of NaCl (400 mM). Our results showed that both fresh and dry biomass of shoot, plant height, and shoot area increased under low salinity (100–200 mM NaCl), whereas these parameters remained unaffected under high salinity (300–400 mM NaCl). In H. salicornicum, shoot water content (SWC%) was maintained at all levels of salinity. Salt tolerance index of H. salicornicum did not decline with increasing doses of salinity indicating salt tolerance capability of the plant. Although, salinity caused an increase in Na+ content of shoot, but K+ content of shoot remained steady at all levels of salinity. The rate of photosynthesis (PN), stomatal conductance (gs), rate of transpiration (E), water use efficiency (WUE), quantum yield of PSII (ΦPSII), photochemical quenching (qP), and electron transport rate (ETR) remained at par to the control level under low salinity (100–200 mM NaCl) and then reduced significantly under high salinity (300–400 mM NaCl). Salinity had no significant impacts on maximum quantum efficiency of PSII (Fv/Fm) and non-photochemical quenching (NPQ) which implies that PS II remained unaffected by sanity-induced oxidative damage. The levels of H2O2 and NO increased significantly under salinity, whereas the level of O2•− remained unaffected under various levels of salinity. Higher level of H2O2 and NO indicates the signaling role of these molecules. Lipid peroxidation level remained unchanged under low salinity (0–300 mM NaCl), but increased significantly under extreme salinity (400 mM NaCl). Ratio of AsA/DHA (indicator of cellular redox potential) elevated under high salinity (300–400 mM NaCl). The activities of various enzymatic antioxidants like SOD, APX, POX, GR and CAT showed differential responses under salinity. The results propose that coordination between enzymatic and non-enzymatic antioxidative components regulates ROS levels in H. salicornicum and contribute in salt tolerance by maintaining water status, ion homeostasis, redox status of the cells, and efficient protection of PSII form salinity induced oxidative damage. Higher tolerance index, optimal growth and competent antioxidative system make this xero-halophyte a suitable candidate for reclamation of salt degraded agricultural lands and can be a potent genetic resource for the development of salinity tolerant crops.

Thrombus targeting aspirin particles for near infrared imaging and on-demand therapy of thrombotic vascular diseases

A blood clot (thrombus) is formed as a final product of the hemostatic process with two major components, a mesh of cross-linked fibrin and platelets activated by high concentration of hydrogen peroxide (H2O2). Thrombus formation impedes blood flow to brain and heart and is a principle cause of life-threatening diseases such as stroke and myocardial infarction. Aspirin has been widely used for the treatment and prevention of various cardiovascular diseases, but is unable to target a thrombus and scavenge a high level of H2O2. In this study, we report thrombus targeting aspirin polyconjugate particles (T-APP) as a near infrared imaging agent and on-demand therapeutic agent for thrombotic vascular diseases. T-APP were formulated from H2O2-activatable aspirin polyconjugate, fibrin-specific peptides and fluorescent IR780. In mouse models of tail bleeding and arterial thrombosis, T-APP targeted the thrombosed vessels rapidly with excellent specificity. T-APP also exerted highly strong antithrombotic activity in the thrombosed vessel by suppressing anti-inflammatory cytokines and inhibiting platelet activation. Based on the unique features such as specific thrombus targeting, H2O2 scavenging, and on-demand therapeutic actions, the rationally engineered T-APP have important ramifications on imaging and on-demand therapy of thrombotic disorders.

Salivary DNase II from Laodelphax striatellus acts as an effector that suppresses plant defence.

Extracellular DNA, released by damaged plant cells, acts as a damage-associated molecular pattern (DAMP). We demonstrated previously that the small brown planthopper (Laodelphax striatellus, SBPH) secreted DNase II when feeding on artificial diets. However, the function of DNase II in insect feeding remained elusive. The influences of DNase II on SBPHs and rice plants were investigated by suppressing expression of DNase II or by application of heterogeneously expressed DNase II. We demonstrated that DNase II is mainly expressed in the salivary gland and is responsible for DNA-degrading activity of saliva. Knocking down the expression of DNase II resulted in decreased performance of SBPH reared on rice plants. The dsDNase II-treated SBPH did not influenced jasmonic acid (JA), salicylic acid (SA), ethylene (ET) pathways, but elicited a higher level of H2 O2 and callose accumulation. Application of heterogeneously expressed DNase II in DNase II-deficient saliva slightly reduced the wound-induced defence response. We propose a DNase II-based invading model for SBPH feeding on host plants, and provide a potential target for pest management.

Hydrogen peroxide accelerated the lignification process of bamboo shoots by activating the phenylpropanoid pathway and programmed cell death in postharvest storage

Lignification is a typical characteristic of senescence of bamboo shoots during postharvest storage. In this study, exogenous hydrogen peroxide (H2O2) and diphenyliodonium iodide (DPI) were applied to postharvest bamboo shoots to explore the regulation of H2O2 in the lignification process. Bamboo shoots, soaked in 10 mM H2O2 or 5 mM DPI for 10 min, were stored at 20 ± 1 °C for 12 d. H2O2 treatment accelerated the accumulation of endogenous H2O2 by activating NADPH oxidase, while DPI treatment inhibited NADPH oxidase activity, leading to the decrease of endogenous H2O2. After 12 d of storage, the firmness and lignin content in H2O2-treated shoots was 4.79% and 5.14% higher, respectively, than in the control shoots. However, DPI treatment showed the opposite effects, with 10.88% less firmness and 19.23% less lignin content observed as compared with the control group. High level of endogenous H2O2 activated the activities of PAL, C4H and 4CL, thus promoting lignin biosynthesis. Also, H2O2 upregulated DNase, RNase and caspase 3-like activities, leading to the acceleration of the programmed cell death process, which finally contributed to the resulting lignification. Transmission electron microscopy further revealed thickened cell walls and the decompartmentalization of cellular structure in H2O2-treated shoots. Our results indicated that endogenous H2O2 may play a vital role in the lignification process of bamboo shoots.

Programmable Therapeutic Nanodevices with Circular Amplification of H2 O2 in the Tumor Microenvironment for Synergistic Cancer Therapy.

Tumor microenvironment activated nanodevices have remarkable superiority to enhance therapeutic efficacy and minimize side effects, but their practical applications are dramatically reduced by the low abundance and heterogeneous distribution of specific stimuli at the tumor site. Herein, programmable vesicular nanodevices based on the triblock copolymer containing poly(ethylene glycol) (PEG) and poly(caprolactone) (PCL) with peroxalate esters (PO) as hydrogen peroxide-responsive linkage (PEG-PO-PCL-PO-PEG), are developed for co-delivery of hypoxia-activated prodrug (AQ4N) and glucose oxidase (GOD). The obtained nanodevices (PAG) can be activated by the high level of H2 O2 in tumor microenvironment to improve the permeability of membranes for glucose entrance. Afterward, the oxidation of glucose catalyzed by GOD produces amplified H2 O2 amounts which in turn induce complete destruction of PAG for fast release of AQ4N and GOD. Ultimately, the PAG can exert programmable therapeutic effects from the following aspects: 1) starvation therapy by cutting off the energy supply from glucose through GOD catalysis; 2) oxidative cytotoxicity after H2 O2 amplification; 3) chemotherapy of AQ4N activated by the intensified tumor hypoxia microenvironment after oxygen consumption. The stimuli amplification, controlled drug release, synergistic therapy, and corresponding mechanisms of PAG are demonstrated. Therefore, the presented work could provide significant new insights for cancer treatment.

H2O2-activated oxidative stress amplifier capable of GSH scavenging for enhancing tumor photodynamic therapy.

Photodynamic therapy (PDT) is a clinically approved cancer treatment approach that relies on the generation of excess reactive oxygen species (ROS) to eradicate tumor cells by inducing oxidative stress. Unfortunately, if the tumor's endogenous glutathione (GSH) is overexpressed, it will eliminate the ROS and restrict the therapeutic efficacy of PDT. Herein, we report a H2O2-activated oxidative stress amplifier (OSA) for enhancing the ROS generation for PDT via GSH scavenging. Cinnamaldehyde (Cin) and chlorin e6 (Ce6) were applied as the GSH scavenger and photosensitizer, respectively, which were assembled with the ROS-responsive amphipathic polymer (DPL) to form DPL@CC micelles as the OSA. In the circulation of blood, the OSA can effectively protect the Cin from albumin binding to retain its GSH depletion ability. Once the OSA reached the tumor site, the high level of H2O2 triggered the degradation of DPL and led to the release of Cin and Ce6. Subsequently, the released Cin reacted with the intracellular GSH by Michael Addition and downregulated the GSH level to about 18.9%, versus untreated cells, to weaken the anti-oxidation ability of tumor cells. Thus, it provided a suitable environment for PDT to obtain an amplifying effect on oxidative stress and superior anti-cancer efficacy of 94% growth inhibition. The preparation of the H2O2-activated oxidative stress amplifier is a convincing strategy for promoting intracellular ROS generation and enhancing the tumor PDT efficacy, which could also augment the clinical application of PDT.

Differential regulation of cellular stress responses by the endoplasmic reticulum-resident Selenoprotein S (Seps1) in proliferating myoblasts versus myotubes.

The antioxidant Selenoprotein S (Seps1, Selenos) is an endoplasmic reticulum (ER)‐resident protein associated with metabolic and inflammatory disease. While Seps1 is highly expressed in skeletal muscle, its mechanistic role as an antioxidant in skeletal muscle cells is not well characterized. In C2C12 myotubes treated with palmitate for 24 h, endogenous Seps1 protein expression was upregulated twofold. Two different siRNA constructs were used to investigate whether decreased levels of Seps1 exacerbated lipid‐induced oxidative and ER stress in C2C12 myotubes and myoblasts, which differ with regards to cell cycle state and metabolic phenotype. In myoblasts, Seps1 protein knockdown of ~50% or ~75% exacerbated cellular stress responses in the presence of palmitate; as indicated by decreased cell viability and proliferation, higher H2O2 levels, a lower reduced to oxidized glutathione (GSH:GSSG) ratio, and enhanced gene expression of ER and oxidative stress markers. Even in the absence of palmitate, Seps1 knockdown increased oxidative stress in myoblasts. Whereas, in myotubes in the presence of palmitate, a ~50% knockdown of Seps1 was associated with a trend toward a marginal (3‐5%) decrease in viability (P = 0.05), decreased cellular ROS levels, and a reduced mRNA transcript abundance of the cellular stress marker thioredoxin inhibitory binding protein (Txnip). Furthermore, no enhancement of gene markers of ER stress was observed in palmitate‐treated myotubes in response to Seps1 knockdown. In conclusion, reduced Seps1 levels exacerbate nutrient‐induced cellular stress responses to a greater extent in glycolytic, proliferating myoblasts than in oxidative, differentiated myotubes, thus demonstrating the importance of cell phenotype to Seps1 function.

Salicylic Acid and Hydrogen Peroxide Accumulation in Relation to Hydrolyte Leakage in Barley Plants Challenged with Cochliobolus sativus

Spot blotch (SB) caused by the hemibiotrophic fungal pathogen Cochliobolus sativus is a destructive disease of barley worldwide. To better understand the mechanisms of resistance to this disease, the involvements of salicylic acid (SA), hydrogen peroxide (H2O2) and ion fluxes during the interaction between resistant and susceptible barley seedlings and C. sativus were investigated. Early SA accumulation in leaf tissues was accompanied with an increase in H2O2 concentration in both compatible and incompatible interactions. The resistant cultivar constitutively contained higher levels of H2O2 and SA, as well as during the 72 h as compared with the un-infected control (0 h). However, levels increased rapidly upon infection in both cultivars. Moreover, a markedly greater increase in ion fluxes from the compatible material compared with the incompatible one was observed. Results suggest that SA and H2O2 accumulation are important during both compatible and incompatible barley-C. sativus interactions.

A comprehensive study on the main physiological and biochemical changes occurring during growth and on-tree ripening of two apple varieties with different postharvest behaviour

Apple quality and the storage potential likely depend on a range of physiological and biochemical events occurring throughout fruit development and ripening. In this study, we investigated the major physiological (ethylene production and respiration) and biochemical changes (related to sugar and malic acid content as well as antioxidant metabolism) occurring during growth and on-tree ripening of two apple varieties (‘Granny Smith’ (GS) and ‘Early Red One’ (ERO)) with known differences in their postharvest behaviour, mainly firmness loss and susceptibility to superficial scald. Our results demonstrate that the higher storability and the limited loss of firmness of ‘GS’ fruit was associated to a higher acid content, mainly malic acid, that seemed to be regulated already at fruit set (20 DAFB). The reduced loss of firmness during storage in ‘GS’ was also associated to the fruit inability to produce ethylene upon harvest resulting from very low 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) activity. Sugar accumulation, on the other hand, was similar among both varieties as was also observed for the rate of fruit growth or the fruit respiration pattern. In addition, the higher susceptibility of ‘GS’ if compared to ‘ERO’ to superficial scald was not associated to peroxidative damage (malondialdehyde accumulation) nor to higher levels of the sesquiterpene α-farnesene but rather mediated by a fruit antioxidant imbalance resulting from higher H2O2 levels and lower antioxidant (peroxidase) enzymatic capacity. The interplay between ethylene, respiration and antioxidants or sugars and organic acids during apple growth and development is further discussed.

Antioxidative, inflammatory and immune responses in hydrogen peroxide-induced liver injury of tilapia (GIFT, Oreochromis niloticus)

Oxidative stress has been implicated in the pathogenesis of many liver diseases in fish, but the molecular mechanism is still obscure. Here, we used hydrogen peroxide (H2O2) as a reactive oxygen species (ROS) to induce liver injury and assess underlying molecular mechanism linking oxidative stress and liver injury in fish. Tilapia were injected with various concentrations of H2O2 (0, 40, 120, 200, 300 and 400 mM) for 72 h. The blood and liver were collected to assay biochemical parameters and genes expression after 24, 48 and 72 h of injection. The results showed that treatments with higher H2O2 levels (300 and/or 400 mM) significantly increased the levels of GPT, GOT, AKP and MDA, and apparently decreased the levels of TP, ALB, SOD, GSH, CAT, GST and T-AOC throughout of the 72 h. The gene expression data showed that treatments with 200, 300 and/or 400 H2O2 suppressed Nrf2/keap1 pathway and its downstream genes including ho-1, nqo1 and gsta, activated inflammatory response via enhancing the mRNA levels of nf-κb, tnf-α, il-1β and il-8, and attenuating il-10 mRNA level, and caused immunotoxicity through downregulating the genes expression of c3, hep, lzm and Igm for 24, 48 and/or 72 h. Additionally, there was a mild or strong increase in levels of nrf2 and its subsequent antioxidant genes or enzymes such as ho-1, nqo1, gst, CAT and SOD in treatments with lower concentrations of H2O2 (40 or 120 mM) for 24 and/or 48 h. Overall results suggested that H2O2 hepatotoxicity was mainly concerned with lipid peroxidation, impairment antioxidant defense systems, inflammatory response and immunotoxicity, and Nrf2/Keap1 and NF-κB signaling pathways played important roles in oxidative stress-induced liver injury in fish.

Glutathione and H2O2 consumption promoted photodynamic and chemotherapy based on biodegradable MnO2–Pt@Au25 nanosheets

Photodynamic therapy (PDT) has become a significant anticancer method by making full use of reactive oxygen species (ROS) to kill cancer cells. However, high concentration of reductive glutathione (GSH) in tumor site is an enemy, which can decrease the PDT efficacy due to ROS consumption property of reductive GSH. To overcome the problem, here we design an innovative nanoplatform, which could integrate PDT, chemotherapy and magnetic resonance imaging (MRI) in one nanosystem. In this platform, MnO2 nanosheets were employed as the carrier by conjugating photosensitizer (Au25 nanoclusters) with platinum(IV) (Pt(IV)) prodrugs for synergistic PDT and chemotherapy. Interestingly, GSH can reduce MnO2 nanosheets and Pt(IV) prodrugs simultaneously. Consequently, the concentration of intercellular GSH has been greatly decreased. More importantly, Mn2+ reduced from MnO2 nanosheets remarkably improves both T1– and T2–weighted MRI owing to high level of GSH and H2O2 in acidic tumor microenvironment, and Pt(II) reduced from Pt(IV) gives rise to high chemotoxicity to cancer cells. Combined with high PDT efficiency by consuming large amount of intercellular GSH, this nanoplatform has successfully achieved the MRI guided synergistic therapy, which is promising for potential clinic applications in cancer therapy.

Pore Diameter of Mesoporous Silica Modulates Oxidation of H2O2-Sensing Chromophore in a Porous Matrix.

Hydrogen peroxide (H2O2) is an attractive chemical because of its bleaching properties in paper and pulp industry and as a disinfectant in the food, water, and medical industries. However, it is important to monitor the residual H2O2 level after its usage and prevent any unintended health problems or chemical reactions. Most H2O2 sensors often utilize fluorophores or electrical circuitry that requires an additional irradiation or a digital display. To this end, this study presents a 3,3',5,5'-tetramethylbenzidine (TMB)/horseradish peroxidase (HRP)-loaded patch that alerts the presence of high H2O2 levels by generating a visible blue color. We hypothesized that water-insoluble TMB immobilized within mesoporous silica particles of proper pore diameter and structure would act as a colorimetric indicator through the H2O2-mediated oxidation within a cross-linked patch. We examined this hypothesis by immobilizing TMB molecules in mesoporous silica particles with 2 and 7 nm diameter cylindrical pores as well as on nonporous silica particles. Then, we loaded these TMB-silica particles and HRP in a porous alginate patch via sequential in situ cross-linking reaction and lyophilization. In the presence of 25-5000 μM H2O2, which simulate H2O2 concentrations found in residual disinfecting fluids, the patch loaded with TMB-mesoporous silica particles with 7 nm diameter pores generated a distinct blue color with varying intensities depending on the H2O2 concentration. The design principles demonstrated in this study should be applicable to a broad array of sensors to be integrated into a moldable, three-dimensional matrix.