High Concentrations Of H2O2 Research Articles

Preincubation with a low-dose hydrogen peroxide enhances anti-oxidative stress ability of BMSCs

ObjectiveTo investigate the effects of low-concentration hydrogen peroxide pretreatment on the anti-oxidative stress of the bone marrow mesenchymal stem cells (BMSCs).MethodsRabbit BMSCs were isolated and cultured by density gradient centrifugation combined with the adherence method. Then, the third generation of well-grown BMSCs was continuously treated with 50-μM hydrogen peroxide (H2O2) for 8 h as the optimal pretreatment concentration and the BMSCs were continuously applied for 24 h with 500 μM H2O2, and the optimal damage concentration was determined as the oxidative stress cell model. The experiment was divided into three groups: control group, high-concentration H2O2 injury group (500 μM), and low-concentration H2O2 pretreatment group (50 μM + 500 μM). In each group, the DCFH-DA fluorescence probe was used to detect the reactive oxygen species (ROS). ELISA was used to detect the activity of superoxide dismutase (SOD) and catalase (CAT), and the TBA method was used to detect malondialdehyde (MDA). The mitochondrial membrane potential was detected by JC-1. The cell viability was detected by CCK-8 method, while flow cytometry and TUNEL/DAPI double staining were performed to detect cell apoptosis. Hence, the effect of H2O2 pretreatment on the anti-oxidative stress of BMSCs was investigated. One-way analysis of variance was performed using SPSS 19.0 statistical software, and P < 0.05 was considered statistically significant.ResultsA large number of typical BMSCs were obtained by density gradient centrifugation and adherent culture. The oxidative stress cell model was successfully established by 500-μM H2O2. Compared with the high-concentration H2O2 injury group, the low-concentration H2O2 pretreatment reduced the production of ROS [(62.33 ± 5.05), P < 0.05], SOD and CAT activities significantly increased (P < 0.05), and MDA levels significantly decreased (P < 0.05). The mitochondrial membrane potential fluorescence changes, the ratio of red/green fluorescence intensity of the high-concentration H2O2 injury group was less, and the ratio of the low-concentration H2O2 pretreatment group was significantly higher than that. The ratio of red/green increased by about 1.8 times (P < 0.05). The cell viability and survival rate of BMSCs were significantly increased in low-concentration H2O2 pretreatment group (P < 0.05), and the cell apoptosis rate was significantly decreased (P < 0.05).ConclusionPretreatment with low-concentration H2O2 can enhance the anti-oxidative stress ability and reduce their apoptosis of BMSCs under oxidative stress.

Synthesis of ‘dual-key-and-lock’ drug carriers for imaging and improved drug release

In this work, a ‘dual-key-and-lock’ drug carrier was designed to respond to the tumor microenvironment (TME). A core–shell Fe-MOF@ZIF-8 was synthesized, with ZIF-8 as the shell (the first lock) to encapsulate catalase (CAT), and the Fe metal–organic framework (MOF) as the core (the second lock) to encapsulate the anticancer drug doxorubicin (DOX). Fe-MOF@ZIF-8 takes advantage of the TME—which includes a high concentration of H2O2, a weakly acidic environment and hypoxia—to achieve efficient cancer therapy. With the pH response, ZIF-8 and Fe-MOF are degraded in turn to release CAT and DOX, just like ‘pH stimulation’, as a key to open the two locks in turn. The released CAT reacts with the rich H2O2 in the tumor to produce O2 to regulate hypoxia, thereby improving the anticancer efficiency of the released DOX. The different cytotoxicity to L-02 cells and HeLa cells of Fe-MOF@ZIF-8 shows Fe-MOF@ZIF-8 is only harmful to cancer cells and is not harmful to normal cells. The reason is that the Fe2+/Fe3+ in Fe-MOF interact with the rich H2O2 in cancer cells to generate hydroxyl radicals (ċOH), which is proved by the color of the solution of 3,3′,5,5′-tetramethylbenzidine turning blue. After loading of the drug and CAT, Fe-MOF@ZIF-8 can release CAT, DOX and ċOH in response to the TME, thus killing more HeLa cells. Therefore, synthesis of ‘dual-key-and-lock’ drug carriers responsive to the TME is a promising strategy for cancer treatment.

Effects of Strain and Kinetics on the H2O2-Assisted Reconstruction of Ag-Au-Ag Nanorods.

Morphology of Ag nanocrystals (NCs) is essential to the NC application in catalysis, optics, and as antibacterial agents. Therefore, it is important to develop synthetic methods and understand the evaluation of NC morphology in different chemical environments. In this study, we report interesting findings of the morphological change of fivefold-twinned Ag–Au–Ag nanorods (NRs) under the effect of H2O2 both as an oxidant (etchant) and a reductant. At low H2O2 concentration, the reconstruction of Ag–Au–Ag NRs was dominated by the growth along the longitudinal direction of NRs. With the increase of H2O2 concentration, the reconstruction also occurs in the transverse direction, and a clear change in particle morphology was observed. We further systematically studied the mechanism of the reaction. The results showed that the transition of the morphology was a two-step process: (1) the etching of Ag on the seeds and (2) the reduction of Ag2O. In the second step, the reaction kinetics was highly affected by H2O2 concentration. At low H2O2 concentration, the growth mainly occurs along ⟨110⟩. However, at high H2O2 concentration, the reduction of Ag was not facet-selective. Using the developed method, we can prepare various bimetallic NCs (high aspect ratio NRs with abundant pinholes, nanoplates, and other NCs). The effect of the reconstruction process on the surface-enhanced Raman scattering (SERS) performance of NCs was investigated.

Degradation and toxicity evaluation of azo dye Direct red 83:1 by an advanced oxidation process driven by pulsed light

Water contamination by dyes is an ecological problem that can be alleviated by advanced oxidation processes (AOPs). A common AOP uses hydroxyl radicals generated by splitting H2O2 using UV light. Pulsed light (PL) technology can be used as light source in AOPs having the advantage of producing fast effects. Direct red 83:1 (DR) is an azo dye that is being used to study the elimination of dyes from wastewaters but details about its degradation by a PL/H2O2 process are missed. In this work, the effect of H2O2 and dye concentrations, pH and salts on the decolourization of DR were determined by spectrophotometry. The PL/H2O2 process was able to degrade nearly 80 % of the dye after 45 light pulses. Absence of photolysis and inhibition by hydroxyl scavenging indicate that the degradation was due to oxidation hydroxyl radicals. The decolouration was higher at low dye concentration, high H2O2 concentration and alkaline conditions, and was inhibited by salts. These results are useful for the further use of DR as model dye to study the potential of PL as an alternative light source in AOPs for dye degradation. Further studies are recommended to estimate the treatment conditions required for enhancing toxicity abatement.

The direct synthesis of hydrogen peroxide from H2 and O2 using Pd-Ni/TiO2 catalysts.

The direct synthesis of hydrogen peroxide (H2O2) from molecular H2 and O2 offers an attractive, decentralized alternative to production compared to the current means of production, the anthraquinone process. Herein we evaluate the performance of a 0.5%Pd-4.5%Ni/TiO2 catalyst in batch and flow reactor systems using water as a solvent at ambient temperature. These reaction conditions are considered challenging for the synthesis of high H2O2 concentrations, with the use of sub-ambient temperatures and alcohol co-solvents typical. Catalytic activity was observed to be stable to prolonged use in multiple batch experiments or in a flow system, with selectivities towards H2O2 of 97% and 85%, respectively. This study was carried out in the absence of halide or acid additives that are typically used to inhibit sequential H2O2 degradation reactions showing that this Pd-Ni catalyst has the potential to produce H2O2 selectively. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

An Enzymatically Driven Hydrogen Peroxide Exposure To Human Hepatocytes And Its Effects On Iron Homeostatic Proteins

Previous data in our lab has shown that high concentration (200 μM) H2O2 exposure induces iron dysregulation in muscle cells. It is known that following strenuous exercise, oxidative stress is induced in tissues, leading to iron dysregulation, and generation of reactive oxygen species. Due to the unstable nature of H2O2 in solution and the critical role of the liver in iron homeostasis, we sought to see how human hepatocytes would respond to a 12-hour low-dose H2O2 exposure that mimics the concentration of neutrophils during the inflammatory response using glucose oxidase (GOX) and Catalase (CAT) PURPOSE: To determine the effects of a low-concentration, H2O2 exposure on the iron regulatory proteins such as TfR, and Ferritin Light-Chain (FLC) in HepG2 cells. METHODS: When HepG2 cells reached 80% confluency, iron treatments of 10, 50, and 100 μM were imposed for 24 hours using an FeCl3 solution diluted in media. Groups that received both iron and H2O2 treatments were exposed to 12 hours of iron, followed by 12-hour incubation with media that included both iron and a GOX-CAT cocktail. Western blots were carried out to measure protein content relative to controls. Cell viability was assessed using an MTT assay. RESULTS: MTT assays for both FeCl3, and FeCl3 + H2O2 groups did not show any significant cell death. Treatment with FeCl3 alone resulted in a significant decrease in TfR for all three groups when compared against controls (C=1±0.1 SEM vs. 0.71±.1; p<0.01; n=12). We observed a significant increase in FTL, but only in the 10 μM group (C=1± 0.1 vs. 1.6±0.2; p<0.01; n=11). We saw no significant change in FTL at 50 and 100 μM. H2O2 treatments driven by GOX and CAT produced concentrations of 5-10 μM, mimicking neutrophils during inflammatory response. The addition of a low concentration H2O2 stress resulted in a 9-fold increase of FTL content at all iron exposure concentrations (C=1±0.3 vs 9.3 ±0.9 10 μM; p<0.01; n=4). Groups of 50 and 100 μM also showed similar results, with an increasing trend. CONCLUSION: A low concentration exposure of H2O2 and iron to human hepatocytes results in a significant increase in FTL when compared to iron exposure alone. This suggests that liver cells have a robust defense against iron-dysregulation induced by oxidative stress. We are still evaluating changes that occur in other iron regulatory proteins.

Enhanced O2−[rad] and HO[rad] via in situ generating H2O2 at activated graphite felt cathode for efficient photocatalytic fuel cell

The use of a photocatalytic fuel cell (PFC) in wastewater treatment is an intensively researched topic because the device integrates organic pollutant degradation and chemical energy recovery. Herein, we proposed a strategy to enhance PFC performance by increasing the concentrations of hydroxyl radical (HO) and superoxide radical (O2−) produced from H2O2 generated in situ using an activated graphite felt (GF) cathode. This cathode was prepared by H2SO4 treatment to introduce oxygen-containing functional groups on its surface that would serve as surface-active sites and facilitate the two-electron pathway of H2O2 production. Remarkably, the peak current density of the activated GF cathode (−1.25 mA/cm2) was more than thrice that of the original GF cathode (−0.40 mA/cm2), and its Faradaic efficiency significantly improved from 20.01% to 74.09%. The PFC equipped with the activated GF cathode harvested 2.69 times the maximum power density (JVmax) and 5.15 times the degradation rate of the traditional Pt black-PFC system. This was because the O2− and HO concentrations, respectively, were 2.87 (23.98 × 10−5 M) and 2.48 times (13.00 × 10−4 M) as high as those in the Pt black-PFC system. These results were attributed to the high concentration of H2O2 generated in situ at the activated GF cathode, which was 25.13 times (0.402 mM) as high as that generated at the Pt black cathode. Thus, the proposed PFC system demonstrates the feasibility of improving organic pollutant degradation and energy recovery by enhancing H2O2 production.

The latency of peroxisomal catalase in terms of effectiveness factor for pancreatic and glioblastoma cancer cell lines in the presence of high concentrations of H2O2: Implications for the use of pharmacological ascorbate in cancer therapy

Previous research has identified variation in cancer cell line response to high levels of extracellular H2O2 (eH2O2) exposure. This directly contributes to our understanding cellular efficacy of pharmacological ascorbate (P-AscH-) therapy. Here we investigate the factors contributing to latency of peroxisomal catalase of a cell and the importance of latency in evaluating cell exposure to eH2O2. First, we develop a mathematical framework for the latency of catalase in terms of an effectiveness factor, ηeff, to describe the catalase activity in the presence of high levels of eH2O2. A simplified relationship emerges, ηeff=3mp/(k2CCatprp) when mprp/Dij≪1, where mp,rp, and k2CCatp are the experimentally determined peroxisome permeability, average peroxisome radius, and the pseudo first-order reaction rate constant, respectively. CCatp is the catalase concentration in the peroxisome and k2=1.7x107M−1s−1. Next, previously published parameters are used to determine the latency effect of the cell lines: normal pancreatic cells (H6c7), pancreatic cancer cells (MIA PaCa-2), and glioblastoma cells (LN-229, T98G, and U-87), all which vary in their susceptibility to exposure to high eH2O2. The results show that effectiveness is not significantly different except for the most susceptible, MIA PaCa-2 cell line, which is higher when compared to all other cell lines. This result is counterintuitive and further implies that latency, as a single parameter, is ineffective in forecasting cell line susceptibility to P-AscH- therapy equivalent eH2O. Thus, further research remains necessary to identify why cancer cells vary in susceptibility to P-AscH- therapy.

Dual-Functionalized Crescent Microgels for Selectively Capturing and Killing Cancer Cells.

In cancer therapy, the selective targeting of cancer cells while avoiding side effects to normal cells is still full of challenges. Here, we developed dual-functionalized crescent microgels, which selectively captured and killed lung cancer cells in situ without killing other cells. Crescent microgels with the inner surface of the cavity functionalized with antibody and containing glucose oxidase (GOX) in the gel matrix have been produced in a microfluidic device. These microgels presented high affinity and good selectivity to lung cancer cells and retained them inside the cavities for extended periods of time. Exposing the crescent hydrogels to physiological concentrations of glucose leads to the production of a locally high concentration of H2 O2 inside the microgels' cavities, due to the catalytic action by GOX inside the gel matrix, which selectively killed 90 % cancer cells entrapped in the microgel cavities without killing the cells outside. Our strategy to create synergy between different functions by incorporating them in a single microgel presents a novel approach to therapeutic systems, with potentially broad applications in smart materials, bioengineering and biomedical fields.

Dual‐Functionalized Crescent Microgels for Selectively Capturing and Killing Cancer Cells

AbstractIn cancer therapy, the selective targeting of cancer cells while avoiding side effects to normal cells is still full of challenges. Here, we developed dual‐functionalized crescent microgels, which selectively captured and killed lung cancer cells in situ without killing other cells. Crescent microgels with the inner surface of the cavity functionalized with antibody and containing glucose oxidase (GOX) in the gel matrix have been produced in a microfluidic device. These microgels presented high affinity and good selectivity to lung cancer cells and retained them inside the cavities for extended periods of time. Exposing the crescent hydrogels to physiological concentrations of glucose leads to the production of a locally high concentration of H2O2 inside the microgels’ cavities, due to the catalytic action by GOX inside the gel matrix, which selectively killed 90 % cancer cells entrapped in the microgel cavities without killing the cells outside. Our strategy to create synergy between different functions by incorporating them in a single microgel presents a novel approach to therapeutic systems, with potentially broad applications in smart materials, bioengineering and biomedical fields.

Enhanced P450 fatty acid decarboxylase catalysis by glucose oxidase coupling and co-assembly for biofuel generation

Cytochrome P450 OleT is a fatty acid decarboxylase that uses hydrogen peroxide (H2O2) to catalyze the production of terminal alkenes, which are industrially important chemicals with biofuel and synthetic applications. Despite its requirement for large turnover levels, high concentrations of H2O2 may cause heme group degradation, diminishing enzymatic activity and limiting broad application for synthesis. Here, we report an artificial enzyme cascade composed of glucose oxidase (GOx) and OleTSA from Staphylococcus aureus for efficient terminal alkene production. By adjusting the ratio of GOx to OleTSA, the GOx-based tandem catalysis shows significantly improved product yield compared to the H2O2 injection method. Moreover, the co-assembly of the GOx/OleTSA enzymes with a polymer, forming polymer-dual enzymes nanoparticles, displays improved activity compared to the free enzyme. This dual strategy provides a simple and efficient system to transform a naturally abundant feedstock to industrially important chemicals.

In Situ Fabrication of Ultrasmall Gold Nanoparticles/2D MOFs Hybrid as Nanozyme for Antibacterial Therapy.

As one of the common reactive oxygen species, H2 O2 has been widely used for combating pathogenic bacterial infections. However, the high dosage of H2 O2 can induce undesired damages to normal tissues and delay wound healing. In this regard, peroxidase-like nanomaterials serve as promising nanozymes, thanks to their positive promotion toward the antibacterial performance of H2 O2 , while avoiding the toxicity caused by the high concentrations of H2 O2 . In this work, ultrasmall Au nanoparticles (UsAuNPs) are grown on ultrathin 2D metal-organic frameworks (MOFs) via in situ reduction. The formed UsAuNPs/MOFs hybrid features both the advantages of UsAuNPs and ultrathin 2D MOFs, displaying a remarkable peroxidase-like activity toward H2 O2 decomposition into toxic hydroxyl radicals (·OH). Results show that the as-prepared UsAuNPs/MOFs nanozyme exhibits excellent antibacterial properties against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria with the assistance of a low dosage of H2 O2 . Animal experiments indicate that this hybrid material can effectively facilitate wound healing with good biocompatibility. This study reveals the promising potential of a hybrid nanozyme for antibacterial therapy and holds great promise for future clinical applications.

Generation of localized highly concentrated hydrogen peroxide clusters in water by X-rays

The formation of highly concentrated hydrogen peroxide (H2O2) clusters (localized circumstance) in an aqueous solution during X-ray irradiation was demonstrated. The relationship between H2O2 concentration and hydrogen donor-independent reduction of nitroxyl radicals was examined. The method to measure the distance between the clusters (localized circumstance) was assessed by comparing the simulation and the experimental results. Reaction mixtures containing a nitroxyl redox probe, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl (CmP) at 0.1 mM were prepared containing several different concentrations (1.0 mM‒9.8 M) of H2O2. The reaction mixture was irradiated by 12000 μW/cm2 UVB for 2 min, and reduction of the electron paramagnetic resonance (EPR) signal of the nitroxyl radicals was measured. An aliquot (2 µL) of 200 mM K3[Fe(CN)6] or FeCl3 solution was added to 200 µL of the reaction mixture, and the time course of the EPR signal of the nitroxyl radicals was measured. To estimate the distance between the H2O2 clusters, a series of nitroxyl radical solutions with several different concentrations (0.06 μM‒2.28 mM) was irradiated with X-rays, and the degree of reduction of nitroxyl radicals in each sample was measured. UVB, K3[Fe(CN)6], or FeCl3-induced EPR signal loss of the nitroxyl radicals was observed with H2O2 concentrations greater than 10 mM or 100 mM, respectively. The EPR signal loss of nitroxyl radicals, TEMPOL or CmP, may occur in highly concentrated H2O2 circumstances after oxidative stimulation. Plotting the X-ray-induced reduction of nitroxyl radicals versus their density revealed the high-concentration H2O2 clusters to be separated by 40‒47 nm. Ionizing irradiation of an aqueous solution creates a localized highly concentrated H2O2 environment.

Exogenous Melatonin Enhances Rice Plant Resistance Against Xanthomonas oryzae pv. oryzae.

Rice bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae, is one of the most serious diseases of rice. In this study we found that exogenous melatonin can increase rice resistance to BB. Treatment of rice plants with exogenous melatonin (20 µg/ml) increased nitrate reductase, nitric oxide synthase, and peroxidase activity, enabling high intracellular concentrations of melatonin, nitric oxide, and H2O2. The expression of NPR1, a key regulator in the salicylic acid signaling pathway, was upregulated more than 10-fold when the plants were challenged with melatonin. Similarly, the messenger RNA level of PDF1.2, a jasmonic acid-induced defense marker, was 15 times higher in the treated plants than in the control plants. Moreover, three pathogenesis-related proteins, PR1b, PR8a, and PR9, were upregulated 20-fold in the presence of melatonin. The application of melatonin (100 µg/ml) to soil-grown rice reduced the incidence of BB by 86.21%. Taken together, these results not only provide a better understanding of melatonin-mediated innate immunity to X. oryzae pv. oryzae in rice but also represent a promising cultivation strategy to protect rice against X. oryzae pv. oryzae infection.

The Effects of Hydrogen Peroxide on Plant Growth, Mineral Accumulation, as Well as Biological and Chemical Properties of Ficus deltoidea

Hydrogen peroxide (H2O2) is defined as a reactive oxygen species (ROS), able to cause damage to a variety of cellular structures. On the other hand, recent work has demonstrated that H2O2 can also act as a potent signaling molecule that mediates various physiological and biochemical processes in plants. This study was carried out to investigate the effects of H2O2 on the growth, mineral nutrient accumulation, as well as the biologic and chemical properties of Ficus deltoidea var. deltoidea. F. deltoidea plants were spray-treated with 0- (control), 8-, 16-, 30- and 60-mM H2O2 under field conditions. Plant height, leaf area, chlorophyll content, net photosynthetic rate, stomatal conductance and quantum yield of the F. deltoidea plants significantly increased after treatment with 16 and 30-mM H2O2. The results indicate that 60-mM H2O2 increased the accumulation of arsenic, iron and sodium content in the leaves of F. deltoidea. On the other hand, 8-mM H2O2 significantly enhanced the accumulation of arsenic, iron, calcium and potassium content in the syconium of F. deltoidea plants. In addition, H2O2 treatment did not produce any significant effects on antimony and magnesium accumulation in the leaves or the syconium of F. deltoidea plants. The results show that the F. deltoidea plant has strong antidiabetic properties and its α-glucosidase activity increased in treated plants compared to standard acarbose. Hydrogen peroxide, particularly in concentrations of 16 and 30 mM, increased the antioxidant activity, total phenolic and flavonoid content and the vitexin and isovitexin content. There was a positive correlation between antioxidant activity with total phenol and total flavonoid content in H2O2-treated plants. The quantitative analysis by HPTLC indicates that the amount of vitexin and isovitexin increased with the higher concentrations of H2O2. From this study, it can be concluded that spraying 16 and 30-mM H2O2 once a week enhances growth, mineral accumulation and stimulates bioactive compounds of the F. deltoidea plants.

Resveratrol attenuates hydrogen peroxide-induced oxidative stress in TM3 Leydig cells in vitro

The objective of present study was to investigate in vitro protective potential of resveratrol in TM3 Leydig cells with induced oxidative stress using hydrogen peroxide (H2O2). Leydig cells experiencing oxidative stress exhibit reduced activities in androgens production, and become hypofunctional with age, which is also related to growing oxidative stress, while resveratrol has received growing attention as a cytoprotective agent. TM3 mouse Leydig cells were cultivated during 24 h in the presence of resveratrol (5, 10, 25, 50 and 100 μM) alone, or in combination with H2O2 (300/600 μM) to induce oxidative stress. Mitochondrial activity was evaluated using MTT test, triple assay was used in order to assess cell viability parameters, intracellular generation of superoxide was determined by the nitroblue-tetrazolium assay, and quantification of steroid hormones was performed by the enzyme- linked immunosorbent assay. Resveratrol alone treatment led to the most significantly improved values of all tested parameters in the cells of experimental group with addition of 10 μM of resveratrol in comparison to the control group. In the case of cells with induced oxidative stress (300 μM H2O2) resveratrol administration resulted in significantly increased (P < 0.05) metabolic activity, as well as cell membrane integrity at concentration 10 μM. Significantly improved (P < 0.001) lysosomal activity showed cells treated with 5 and 10 μM of resveratrol, and the level of both measured hormones was significantly higher (P < 0.05) in cells supplemented with 10 μM of resveratrol. Significant decline of superoxide radical production was observed in all experimental groups in comparison to the control exposed to H2O2 alone. With respect to cells exposed to higher concentration of H2O2 (600 μM), results showed positive effect of resveratrol only in biosynthesis of both androgens with significant increased values in experimental group treated with 5 μM (P < 0.05) and 10 μM (P < 0.01) of resveratrol, in addition, in the case of testosterone we recorded significant higher (P < 0.05) values in cells with addition of 25 and 50 μM resveratrol when compared to H2O2 control. More specific and systematic research focused especially on androgen biosynthesis is necessary related to the biological activity of resveratrol in male reproductive system due to inconsistent results of studies.

Protection from hydrogen peroxide stress relies mainly on AhpCF and KatA2 in Stenotrophomonas maltophilia

BackgroundAerobically-grown bacteria can be challenged by hydrogen peroxide stress from endogenous aerobic metabolism and exogenously generated reactive oxygen species. Catalase (Kat), alkyl hydroperoxidase (Ahp), and glutathione peroxidase (Gpx) systems are major adaptive responses to H2O2 stress in bacteria. Stenotrophomonas maltophilia is a ubiquitous Gram-negative bacterium equipped with four Kats (KatA1, KatA2, KatMn, and KatE), one Ahp (AhpCF), and three Gpxs (Gpx1, Gpx2, and Gpx3). Here, we systematically investigated how the eight H2O2 scavenging genes differentially contribute to the low-micromolar levels of H2O2 generated from aerobic metabolism and high-millimolar levels of H2O2 from exogenous sources.MethodsGene expression was assessed and quantified by reverse transcription-PCR (RT-PCR) and real time quantitative PCR (qRT-PCR), respectively. The contribution of these enzymes to H2O2 stress was assessed using mutant construction and functional investigation.ResultsOf the eight genes, katA2, ahpCF, and gpx3 were intrinsically expressed in response to low-micromolar levels of H2O2 from aerobic metabolism, and the expression of katA2 and ahpCF was regulated by OxyR. AhpCF and KatA2 were responsible for alleviating aerobic growth-mediated low concentration H2O2 stress and AhpCF played a critical role for stationary-phase cells. KatA2 was upregulated to compensate for AhpCF in the case of ahpCF inactivation. After exposure to millimolar levels of H2O2, katA2 and ahpCF were upregulated in an OxyR-dependent manner. KatA2 was the critical enzyme for dealing with high concentration H2O2. Loss-of-function of KatA2 increased bacterial susceptibility to high concentration H2O2.ConclusionsAhpCF and KatA2 are key enzymes protecting S. maltophilia from hydrogen peroxide stress.

Oxygen-Vacancy-Enhanced Peroxidase-like Activity of Reduced Co3O4 Nanocomposites for the Colorimetric Detection of H2O2 and Glucose.

Colorimetric assays have drawn increasing research interest with respect to the quantitative detection of hydrogen peroxide (H2O2) based on artificial enzymes because of their advantages with respect to natural enzymes, including design flexibility, low cost, and high stability. Regardless, the majority of the artificial enzymes exhibit low affinity to H2O2 with large Michaelis-Menten constants (Km). This indicates that the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to blue-colored oxTMB requires a high H2O2 concentration, hindering the sensitivity of the colorimetric assay. To address this problem, novel reduced Co3O4 nanoparticles (R-Co3O4) have been synthesized in this study via a step-by-step procedure using ZIF-67 as the precursor. R-Co3O4 exhibits a considerably enhanced peroxidase-like activity when compared with that exhibited by pristine Co3O4 (P-Co3O4). The catalytic process in the case of R-Co3O4 occurs in accordance with the typical Michaelis-Menten equation, and the affinity of R-Co3O4 to H2O2 is apparently higher than that of P-Co3O4. Furthermore, the density functional theory calculations revealed that the introduction of oxygen vacancies to R-Co3O4 enhances its H2O2 adsorption ability and facilitates the decomposition of H2O2 to produce ·OH radicals, resulting in improved peroxidase-like activity. A simple and convenient colorimetric assay has been established based on the excellent peroxidase-like activity of R-Co3O4 for detecting H2O2 in concentrations of 1-30 μM with a detection limit of 4.3 × 10-7 mol/L (S/N = 3). Furthermore, the R-Co3O4-based colorimetric method was successfully applied to glucose detection in human serum samples, demonstrating its potential for application in complex biological systems.

Using Box–Behnken experimental design to optimize the degradation of Basic Blue 41 dye by Fenton reaction

Degradation of a Basic Blue 41 dye using Fenton reagent was examined at laboratory scale in batch experiments using Box–Behnken statistical experiment design. Dyestuff, hydrogen peroxide (H2O2) and ferrous ion (Fe2+) concentrations were selected as independent factors. On the other hand, color and chemical oxygen demand (COD) removal were considered as the response functions. The value of coefficient of determination (R2) for both color and chemical oxygen demand removal with values 0.98 and 0.99 shows the best agreement between predicted value and experimental values. Perturbation plots indicated that iron dosage has the most effect on both color and COD removal. Normalized plot of residuals also indicated that the models were adequate to predict for both responses. Color and COD removal increased with increasing H2O2 and Fe2+ concentrations up to a certain level. High concentrations of H2O2 and Fe2+ did not result in better removal of color and COD due to hydroxyl radical being gradually consumed by both oxidant and catalyst. Percent color removal was higher than COD removal indicating the production of colorless compounds. The second-order polynomial model revealed optimal process factor ratio. The ratio of H2O2/Fe2+/dyestuff which gives a complete color removal and 95% COD removal was found to be 1195 mg/L/90 mg/L/255 mg/L.

Bacterial Detection and Elimination Using a Dual-Functional Porphyrin-Based Porous Organic Polymer with Peroxidase-Like and High Near-Infrared-Light-Enhanced Antibacterial Activity.

The efficient fabrication of multifunctional nanoplatforms for bacterial detection and elimination is of great importance in nanobiotechnology. A new porphyrin-based porous organic polymer, FePPOPBFPB, was synthesized via the reaction between pyrrole and 4-{2,2-bis[(4-formylphenoxy)methyl]-3-(4-formylphenoxy) propoxy} benzaldehyde (BFPB). The C-centric tetrahedral structure of BFPB promoted the formation of FePPOPBFPB with a 3D interconnected porous structure, high specific surface area, and plentiful surface catalytic active sites. The adjustable structural alkyl chain also enhanced the absorption capability of FePPOPBFPB in the long-wavelength visible and near-infrared regions (NIR). FePPOPBFPB exhibited excellent peroxidase-like activity toward a representative peroxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB) with H2O2. Utilizing these features, a rapid and visual detection of Staphylococcus aureus (S. aureus) based on FePPOPBFPB was established and exhibited high sensitivity and stability. Combining the catalysis with near-infrared-light (NIR) absorption, FePPOPBFPB can effectively catalyze the decomposition of biologically relevant concentrations of H2O2 to produce vast amounts of •OH radicals via the photo-Fenton reaction, which avoids the utilization of high toxic concentrations of H2O2. On the basis of these satisfactory features, FePPOPBFPB had a conspicuous bactericidal performance against S. aureus under NIR irradiation. To our knowledge, this is the first example of a porphyrin-based porous organic polymer antibacterial agent. The main reactive oxygen species (ROS) produced in this system and the possible antibacterial mechanism of FePPOPBFPB was also proposed through a series of experiments.