Decomposition Of Reactive Oxygen Species Research Articles

A macrocyclic quinol-containing ligand enables high catalase activity even with a redox-inactive metal at the expense of the ability to mimic superoxide dismutase.

Previously, we found that linear quinol-containing ligands could allow manganese complexes to act as functional mimics of superoxide dismutase (SOD). The redox activity of the quinol enables even Zn(ii) complexes with these ligands to catalyze superoxide degradation. As we were investigating the abilities of manganese and iron complexes with 1,8-bis(2,5-dihydroxybenzyl)-1,4,8,11-tetraazacyclotetradecane (H4qp4) to act as redox-responsive contrast agents for magnetic resonance imaging (MRI), we found evidence that they could also catalyze the dismutation of H2O2. Here, we investigate the antioxidant behavior of Mn(ii), Fe(ii), and Zn(ii) complexes with H4qp4. Although the H4qp4 complexes are relatively poor mimetics of SOD, with only the manganese complex displaying above-baseline catalysis, all three display extremely potent catalase activity. The ability of the Zn(ii) complex to catalyze the degradation of H2O2 demonstrates that the use of a redox-active ligand can enable redox-inactive metals to catalyze the decomposition of reactive oxygen species (ROS) besides superoxide. The results also demonstrate that the ligand framework can tune antioxidant activity towards specific ROS.

One-Pot Synthesis of MnOx-SiO2 Porous Composites as Nanozymes with ROS-Scavenging Properties.

The development of nanomaterials that mimic the activity of enzymes is a topic of interest, for the decomposition of reactive oxygen species (ROS). We report the preparation of a novel nanocomposite of MnOx needles covered with SiO2 porous material. The material was prepared in one pot with a two-step procedure. The material was characterized by EDX, SEM, TEM, XRD, nitrogen adsorption–desorption isotherms, and XPS. The synthesis protocol took advantage of the atrane method, favoring the nucleation and initial growth of manganese oxide needles that remained embedded and homogeneously dispersed in a mesoporous silica matrix. The final composite had a high concentration of Mn (Si/Mn molar ratio of ca. 1). The nanozyme presented bimodal porosity: intraparticle and interparticle association with the surfactant micelles and the gaps between silica particles and MnOx needles, respectively. The porosity favored the migration of the reagent to the surface of the catalytic MnOx. The nanozyme showed very efficient SOD and catalase activities, thus improving other materials previously described. The kinetics were studied in detail, and the reaction mechanisms were proposed. It was shown that silica does not play an innocent role in the case of catalase activity, increasing the reaction rate.

Increasing NADPH impairs fungal H2O2 resistance by perturbing transcriptional regulation of peroxiredoxin

NADPH provides the reducing power for decomposition of reactive oxygen species (ROS), making it an indispensable part during ROS defense. It remains uncertain, however, if living cells respond to the ROS challenge with an elevated intracellular NADPH level or a more complex NADPH-mediated manner. Herein, we employed a model fungus Aspergillus nidulans to probe this issue. A conditional expression of glucose-6-phosphate dehydrogenase (G6PD)-strain was constructed to manipulate intracellular NADPH levels. As expected, turning down the cellular NADPH concentration drastically lowered the ROS response of the strain; it was interesting to note that increasing NADPH levels also impaired fungal H2O2 resistance. Further analysis showed that excess NADPH promoted the assembly of the CCAAT-binding factor AnCF, which in turn suppressed NapA, a transcriptional activator of PrxA (the key NADPH-dependent ROS scavenger), leading to low antioxidant ability. In natural cell response to oxidative stress, we noticed that the intracellular NADPH level fluctuated “down then up” in the presence of H2O2. This might be the result of a co-action of the PrxA-dependent NADPH consumption and NADPH-dependent feedback of G6PD. The fluctuation of NADPH is well correlated to the formation of AnCF assembly and expression of NapA, thus modulating the ROS defense. Our research elucidated how A. nidulans precisely controls NADPH levels for ROS defense.Graphical

Regulation and distinct physiological roles of manganese in bacteria.

ABSTRACTManganese (Mn2+) is an essential trace element within organisms spanning the entire tree of life. In this review, we provide an overview of Mn2+ transport and the regulation of its homeostasis in bacteria, with a focus on its functions beyond being a cofactor for enzymes. Crucial differences in Mn2+ homeostasis exist between bacterial species that can be characterized to have an iron- or manganese-centric metabolism. Highly iron-centric species require minimal Mn2+ and mostly use it as a mechanism to cope with oxidative stress. As a consequence, tight regulation of Mn2+ uptake is required, while organisms that use both Fe2+ and Mn2+ need other layers of regulation for maintaining homeostasis. We will focus in detail on manganese-centric bacterial species, in particular lactobacilli, that require little to no Fe2+ and use Mn2+ for a wider variety of functions. These organisms can accumulate extraordinarily high amounts of Mn2+ intracellularly, enabling the nonenzymatic use of Mn2+ for decomposition of reactive oxygen species while simultaneously functioning as a mechanism of competitive exclusion. We further discuss how Mn2+ accumulation can provide both beneficial and pathogenic bacteria with advantages in thriving in their niches.

Cytoprotective metal-organic frameworks for anaerobic bacteria

We report a strategy to uniformly wrap Morella thermoacetica bacteria with a metal-organic framework (MOF) monolayer of nanometer thickness for cytoprotection in artificial photosynthesis. The catalytic activity of the MOF enclosure toward decomposition of reactive oxygen species (ROS) reduces the death of strictly anaerobic bacteria by fivefold in the presence of 21% O2, and enables the cytoprotected bacteria to continuously produce acetate from CO2 fixation under oxidative stress. The high definition of the MOF-bacteria interface involving direct bonding between phosphate units on the cell surface and zirconium clusters on MOF monolayer, provides for enhancement of life throughout reproduction. The dynamic nature of the MOF wrapping allows for cell elongation and separation, including spontaneous covering of the newly grown cell surface. The open-metal sites on the zirconium clusters lead to 600 times more efficient ROS decomposition compared with zirconia nanoparticles.

Expression and characterization of recombinant bifunctional enzymes with glutathione peroxidase and superoxide dismutase activities

To balance the production and decomposition of reactive oxygen species, living organisms have generated antioxidant enzymes and non-enzymatic antioxidant defense systems. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) are two important antioxidant enzymes. Apart from their catalytic functions, they protect each other, resulting in more efficient removal of reactive oxygen species, protection of cells against injury, and maintenance of the normal metabolism of reactive oxygen species. SOD catalyzes the dismutation of the superoxide anion (O2•−) to oxygen (O2) and hydrogen peroxide (H2O2). H2O2 is then detoxified to water by GPx. In this study, human GPx1Ser and the Alvinella pompejana SOD (ApSOD) gene were used to design and generate several recombinant proteins with both GPx and SOD activities by combining traditional fusion protein technology, a cysteine auxotrophic expression system, and a single protein production (SPP) system. Among the fusion proteins, Se-hGPx1Ser-L-ApSOD exhibited the highest SOD and GPx activities. Additional research was conducted to better understand the properties of Se-hGPx1Ser-L-ApSOD. The synergism of Se-hGPx1Ser-L-ApSOD was evaluated by using an in vitro model. This research may facilitate future studies on the cooperation and catalytic mechanisms of GPx and SOD. We believe that the bifunctional enzyme has potential applications as a potent antioxidant.

The potential toxicological insights about the anti-HIV drug azidothymidine-derived monoselenides in human leukocytes: Toxicological insights of new selenium-azidothymidine analogs.

Acquired immunodeficiency syndrome (AIDS) is a worldwide disease characterized by impairments of immune function. AIDS can be associated with oxidative stress (OS) that can be linked to selenium (Se) deficiency. Se is fundamental for the synthesis of selenoproteins, such as glutathione peroxidase and thioredoxin reductase. These enzymes catalyze the decomposition of reactive oxygen species and contribute to maintain equilibrium in cell redox status. Literature data indicate that organoselenium compounds, such as ebselen and diphenyl diselenide, have antioxidant properties in vitro and in vivo models associated with OS. Nevertheless, selenocompounds can also react and oxidize thiols groups, inducing toxicity in mammals. Here, we tested the potential cytotoxic and genotoxic properties of six analogs of the prototypal anti-HIV drug azidothymidine (AZT) containing Se (5'-Se-(phenyl)zidovudine; 5'-Se-(1,3,5-trimethylphenyl)zidovudine; 5'-Se-(1-naphtyl)zidovudine; 5'-Se-(4-chlorophenyl)zidovudine) (C4); 5'-Se-(4-methylphenyl)zidovudine (C5); and 5'-(4-methylbenzoselenoate)zidovudine). C5 increased the rate of dithiothreitol oxidation (thiol oxidase activity) and C2-C4 and C6 (at 100 µM) increased DNA damage index (DI) in human leukocytes. Moreover, C5 (200 µM) decreased human leukocyte viability to about 50%. Taken together, these results indicated the low in vitro toxicity in human leukocytes of some Se-containing analogs of AZT.

Identification of Oxygen-Responsive Transcripts in the Silage Inoculant Lactobacillus buchneri CD034 by RNA Sequencing.

The Lactobacillus buchneri CD034 strain, known to improve the ensiling process of green fodder and the quality of the silage itself was transcriptionally analyzed by sequencing of transcriptomes isolated under anaerobic vs. aerobic conditions. L. buchneri CD034 was first cultivated under anaerobic conditions and then shifted to aerobic conditions by aeration with 21% oxygen. Cultivations already showed that oxygen was consumed by L. buchneri CD034 after aeration of the culture while growth of L. buchneri CD034 was still observed. RNA sequencing data revealed that irrespective of the oxygen status of the culture, the most abundantly transcribed genes are required for basic cell functions such as protein biosynthesis, energy metabolism and lactic acid fermentation. Under aerobic conditions, 283 genes were found to be transcriptionally up-regulated while 198 genes were found to be down-regulated (p-value < 0.01). Up-regulated genes i. a. play a role in oxygen consumption via oxidation of pyruvate or lactate (pox, lctO). Additionally, genes encoding proteins required for decomposition of reactive oxygen species (ROS) such as glutathione reductase or NADH peroxidase were also found to be up-regulated. Genes related to pH homeostasis and redox potential balance were found to be down-regulated under aerobic conditions. Overall, genes required for lactic acid fermentation were hardly affected by the growth conditions applied. Genes identified to be differentially transcribed depending on the aeration status of the culture are suggested to specify the favorable performance of the strain in silage formation.

Preventing UV induced cell damage by scavenging reactive oxygen species with enzyme-mimic Au–Pt nanocomposites

We have prepared enzyme-mimic Au-Pt nanocomposites (NCs) for catalyzing the decomposition of reactive oxygen species. After surface modification, the Au-Pt NCs can be readily internalized and retained by human skin cells and also can effectively reduce cellular oxidative stress. We have demonstrated that the active and biocompatible Au-Pt nanocomposites can be applied for preventing cell damages by scavenging cellular reactive oxygen species induced by ultraviolet irradiation, indicating potential uses for the prevention and therapy of ROS-mediated diseases.

Blood-Borne Macrophage–Neural Cell Interactions Hitchhike on Endosome Networks for Cell-Based Nanozyme Brain Delivery

Macrophage-carried nanoformulated catalase ('nanozyme') attenuates neuroinflammation and protects nigrostriatal neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication. This is facilitated by effective enzyme transfer from blood-borne macrophages to adjacent endothelial cells and neurons leading to the decomposition of reactive oxygen species. We examined the intra- and inter-cellular trafficking mechanisms of nanozymes by confocal microscopy. Improved neuronal survival mediated by nanozyme-loaded macrophages was demonstrated by fluorescence-activated cell sorting. In macrophages, nanozymes were internalized mainly by clathrin-mediated endocytosis then trafficked to recycling endosomes. The enzyme is subsequently released in exosomes facilitated by bridging conduits. Nanozyme transfer from macrophages to adjacent cells by endocytosis-independent mechanisms diffusing broadly throughout the recipient cells. In contrast, macrophage-free nanozymes were localized in lysosomes following endocytic entry. Facilitated transfer of nanozyme from cell to cell can improve neuroprotection against oxidative stress commonly seen during neurodegenerative disease processes.

Anthrolysin O and fermentation products mediate the toxicity of Bacillus anthracis to lung epithelial cells under microaerobic conditions

Bacillus anthracis generates virulence factors such as lethal and edema toxins, capsule, and hemolytic proteins under conditions of reduced oxygenation. Here, we report on the acute cytotoxicity of culture supernatants (Sups) of six nonencapsulated B. anthracis strains grown till the stationary phase under static microaerobic conditions. Human small airway epithelial, umbilical vein endothelial, Caco-2, and Hep-G2 cells were found to be susceptible. Sups displayed a reduction of pH to 5.3–5.5, indicating the onset of acid anaerobic fermentation; however, low pH itself was not a major factor of toxicity. The pore-forming hemolysin, anthrolysin O (ALO), contributed to the toxicity in a concentration-dependent manner. Its effect was found to be synergistic with a metabolic product of B. anthracis, succinic acid. Cells exposed to Sups demonstrated cytoplasmic membrane blebbing, increased permeability, loss of ATP, mitochondrial membrane potential collapse, and arrest of cell respiration. The toxicity was reduced by inhibition of ALO by cholesterol, decomposition of reactive oxygen species, and inhibition of mitochondrial succinate dehydrogenase. Cell death appears to be caused by an acute primary membrane permeabilization by ALO, followed by a burst of reactive radicals from the mitochondria fuelled by the succinate, which is generated by bacteria in the hypoxic environment. This mechanism of metabolic toxicity is relevant to the late-stage conditions of hypoxia and acidosis found in anthrax patients and might operate at anatomical locations of the host deprived from oxygen supply.

Peroxisomes Are Oxidative Organelles

Peroxisomes are multifunctional organelles with an important role in the generation and decomposition of reactive oxygen species (ROS). In this review, the ROS-producing enzymes, as well as the antioxidative defense system in mammalian peroxisomes, are described. In addition, various conditions leading to disturbances in peroxisomal ROS metabolism, such as abnormal peroxisomal biogenesis, hypocatalasemia, and proliferation of peroxisomes are discussed. We also review the role of mammalian peroxisomes in some physiological and pathological processes involving ROS that lead to mitochondrial abnormalities, defects in cell proliferation, and alterations in the central nervous system, alcoholic cardiomyopathy, and aging. Antioxid.

A Novel Selenium and Copper-containing Peptide with Both Superoxide Dismutase and Glutathione Peroxidase Activities

Superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase (CAT) play crucial roles in balancing the production and decomposition of reactive oxygen species (ROS) in living organisms. These enzymes act cooperatively and synergistically to scavenge ROS. In order to imitate the synergism of these enzymes, we designed and synthesized a novel 32-mer peptide (32P) on the basis of the previous 15-mer peptide with GPX activity and a 17-mer peptide with SOD activity. Upon the selenation and chelation of copper, the 32-mer peptide is converted to a new Se- and Cu-containing 32-mer peptide (Se-Cu-32P) and displays both SOD and GPX activities and its kinetics was studied. Moreover, the novel peptide was demonstrated to be able to better protect vero cells from the injury induced by xanthine oxidase (XOD)/xanthine/Fe2+ damage system than its parents. Thus, this bifunctional enzyme imitated the synergism of SOD and GPX and could be a better candidate of therapeutic medicine.

Tuning Redox Potentials of Corrole Metal Complexes and their Catalytic Activity Regarding Decomposition of Reactive Oxygen Species

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A trifunctional enzyme with glutathione S-transferase, glutathione peroxidase and superoxide dismutase activity

Superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione S-transferase (GST) and glutathione reductase (GR) play crucial roles in balancing the production and decomposition of reactive oxygen species (ROS) in living organisms. These enzymes act cooperatively and synergistically to scavenge ROS, as not one of them can singlehandedly clear all forms of ROS. In order to imitate the synergy of the enzymes, we designed and generated a recombinant protein, which comprises of a Schistosoma japonicum GST (SjGST) and a bifunctional 35-mer peptide with SOD and GPX activities. The engineered protein demonstrated SOD, GPX and GST activities simultaneously. This trifunctional enzyme with SOD, GPX and GST activities is expected to be the best ROS scavenger.

Budding yeast Saccharomyces cerevisiae as a model to study oxidative modification of proteins in eukaryotes.

The budding yeast Saccharomyces cerevisiae is a well studied unicellular eukaryotic organism the genome of which has been sequenced. The use of yeast in many commercial systems makes its investigation important not only from basic, but also from practical point of view. Yeast may be grown under both aerobic and anaerobic conditions. The investigation of the response of eukaryotes to different kinds of stresses was pioneered owing to yeast and here we focus mainly on the so-called oxidative stress. It is a result of an imbalance between the formation and decomposition of reactive oxygen species increasing their steady-state concentration. Reactive oxygen species may attack any cellular component. In the present review oxidation of proteins in S. cerevisiae is analyzed. There are two connected approaches to study oxidative protein modification - characterization of the overall process and identification of individual oxidized proteins. Because all aerobic organisms possess special systems which defend them against reactive oxygen species, the involvement of so-called antioxidant enzymes, particularly superoxide dismutase and catalase, in the protection of proteins is also analyzed.

Decomposition of reactive oxygen species by copper(II) bis(1-pyrazolyl)methane complexes

Two bis(1-pyrazolyl)alkane ligands, bis(3,5-dimethyl-1-pyrazolyl)methane and bis(4-iodo-3,5-dimethyl-1-pyrazolyl)methane, and their copper(II) complexes, bis(3,5-dimethyl-1-pyrazolyl)methanedinitratocopper(II) [CuL1(NO3)2] and bis(4-iodo-3,5-dimethyl-1-pyrazolyl)methanedinitratocopper(II) [CuL2(NO3)2] x 2H2O, were prepared. Physiochemical properties of the copper(II) complexes were studied by spectroscopic (UV-vis, IR, EPR) techniques and cyclic voltammetry. Spectroscopic analysis revealed a 1:1 stoichiometry of ligand:copper(II) ion and a bidentate coordination mode for the nitrate ions in both of the complexes. According to experimental and theoretical ab initio data, the copper(II) ion is located in an octahedral hexacoordinated environment. Both complexes were able to catalyze the dismutation of superoxide anion (O2*-) (pH 7.5) and decomposition of H2O2 (pH 7.5) and peroxynitrite (pH 10.9). In addition, both complexes exhibited superoxide dismutase (SOD) like activity toward extracellular and intracellular reactive oxygen species produced by activated human neutrophils in whole blood. Thus, these complexes represent useful SOD mimetics with a broad range of antioxidant activity toward a variety of reactive oxidants.

Protective effect of boldine on oxidative mitochondrial damage in streptozotocin-induced diabetic rats

Increased oxidative stress has been suggested to be involved in the pathogenesis and progression of diabetic tissue damage. Several antioxidants have been described as beneficial for oxidative stress-associated diseases. Boldine ([s]-2,9-dihydroxy-1,10-dimethoxyaporphine) is a major alkaloid found in the leaves and bark of boldo (Peumus boldus Molina), and has been shown to possess antioxidant activity and anti-inflammatory effects. From this point of view, the possible anti-diabetic effect of boldine and its mechanism were evaluated. The experiments were performed on male rats divided into four groups: control, boldine (100 mg kg−1, daily in drinking water), diabetic [single dose of 80 mg kg−1of streptozotocin (STZ), i.p.] and diabetic simultaneously fed with boldine for 8 weeks. Diabetic status was evaluated periodically with changes of plasma glucose levels and body weight in rats. The effect of boldine on the STZ-induced diabetic rats was examined with the formation of malondialdehydes and carbonyls and the activities of endogenous antioxidant enzymes (superoxide dismutase and glutathione peroxidase) in mitochondria of the pancreas, kidney and liver. The scavenging action of boldine on oxygen free radicals and the effect on mitochondrial free-radical production were also investigated. The treatment of boldine attenuated the development of hyperglycemia and weight loss induced by STZ injection in rats. The levels of malondialdehyde (MDA) and carbonyls in liver, kidney and pancreas mitochondria were significantly increased in STZ-treated rats and decreased after boldine administration. The activities of mitochondrial manganese superoxide dismutase (MnSOD) in the liver, pancreas and kidney were significantly elevated in STZ-treated rats. Boldine administration decreased STZ-induced elevation of MnSOD activity in kidney and pancreas mitochondria, but not in liver mitochondria. In the STZ-treated group, glutathione peroxidase activities decreased in liver mitochondria, and were elevated in pancreas and kidney mitochondria. The boldine treatment restored the altered enzyme activities in the liver and pancreas, but not the kidney. Boldine attenuated both STZ- and iron plus ascorbate-induced MDA and carbonyl formation and thiol oxidation in the pancreas homogenates. Boldine decomposed superoxide anions, hydrogen peroxides and hydroxyl radicals in a dose-dependent manner. The alkaloid significantly attenuated the production of superoxide anions, hydrogen peroxide and nitric oxide caused by liver mitochondria. The results indicate that boldine may exert an inhibitory effect on STZ-induced oxidative tissue damage and altered antioxidant enzyme activity by the decomposition of reactive oxygen species and inhibition of nitric oxide production and by the reduction of the peroxidation-induced product formation. Boldine may attenuate the development of STZ-induced diabetes in rats and interfere with the role of oxidative stress, one of the pathogeneses of diabetes mellitus.