SciCombinator

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Concept: Peroxide

150

There is still an important interest in controlling bacterial endospores. The use of chemical disinfectants and notably oxidising agents to sterilize medical devices is increasing. With this in mind hydrogen peroxide (H2O2) and peracetic acid (PAA) have been used in combination but until now there has been no explanation for the observed increased in sporicidal activity. This study provides information on the mechanism of synergistic interaction of PAA and H2O2 against bacterial spores. The investigations of the efficacy of different combinations, including pre-treatments with the two oxidisers were performed against wild-type and a range of spore mutants deficient in their spore coat or small acid-soluble spore proteins. The concentrations of the two biocides were also measured in the reaction vessels enabling the assessment of any shift from H2O2 to PAA formation. This study confirmed the synergistic activity of H2O2 and PAA combination. However, we observed that the sporicidal activity of the combination is largely due to PAA and not H2O2. Furthermore, we observed that the synergistic combination was based on H2O2 compromising the spore coat, which was the main spore resistance factor, likely allowing better penetration of PAA, resulting in the increased sporicidal activity.

Concepts: Oxygen, Hydrogen peroxide, Chlorine, Disinfectant, Peroxide, Disinfectants, Peracetic acid, Peroxy acid

25

Production of reactive oxygen species, including hydrogen peroxide (H2O2), is increased in diseased blood vessels. Although H2O2 leads to impairment of the nitric oxide (NO)/soluble guanylate cyclase (sGC)/cGMP signaling pathway, it is not clear whether this reactive molecule affects the redox state of sGC, a key determinant of NO bioavailability. To clarify this issue, mechanical responses of endothelium-denuded rat external iliac arteries to BAY 41-2272 (sGC stimulator), BAY 60-2770 (sGC activator), nitroglycerin (NO donor), acidified NaNO2 (exogenous NO), and 8-Br-cGMP (cGMP analog) were studied under exposure to H2O2. The relaxant response to BAY 41-2272 (pD2: 6.79 ± 0.10 and 6.62 ± 0.17), BAY 60-2770 (pD2: 9.57 ± 0.06 and 9.34 ± 0.15), or 8-Br-cGMP (pD2: 5.19 ± 0.06 and 5.24 ± 0.08) was not apparently affected by exposure to H2O2. In addition, vascular cGMP production stimulated with BAY 41-2272 or BAY 60-2770 in the presence of H2O2 was identical to that in its absence. On the other hand, nitroglycerin-induced relaxation was markedly attenuated by exposing the arteries to H2O2 (pD2: 8.73 ± 0.05 and 8.30 ± 0.05), which was normalized in the presence of catalase (pD2: 8.59 ± 0.05). Likewise, H2O2 exposure impaired the relaxant response to acidified NaNO2 (pD2: 6.52 ± 0.17 and 6.09 ± 0.16). These findings suggest that H2O2 interferes with the NO-mediated action, but the sGC redox equilibrium and the downstream target(s) of cGMP are unlikely to be affected in the vasculature.

Concepts: Oxygen, Blood, Blood vessel, Redox, Reactive oxygen species, Hydrogen peroxide, Nitric oxide, Peroxide

25

Hydrogen peroxide (H2O2) surface treatment of fiber posts has been reported to increase bond strength of fiber posts to resin cements. However, residual oxygen radicals might jeopardize the bonding procedure. This study examined the effect of three antioxidant agents on the bond strength of fiber posts to conventional and self-adhesive resin cements.

Concepts: Oxygen, Hydrogen, Oxidative stress, Reactive oxygen species, Carbon, Hydrogen peroxide, Bond, Peroxide

7

Host control of infections crucially depends on the capability to kill pathogens with reactive oxygen species (ROS). However, these toxic molecules can also readily damage host components and cause severe immunopathology. Here, we show that neutrophils use their most abundant granule protein, myeloperoxidase, to target ROS specifically to pathogens while minimizing collateral tissue damage. A computational model predicted that myeloperoxidase efficiently scavenges diffusible H2O2 at the surface of phagosomal Salmonella and converts it into highly reactive HOCl (bleach), which rapidly damages biomolecules within a radius of less than 0.1 μm. Myeloperoxidase-deficient neutrophils were predicted to accumulate large quantities of H2O2 that still effectively kill Salmonella, but most H2O2 would leak from the phagosome. Salmonella stimulation of neutrophils from normal and myeloperoxidase-deficient human donors experimentally confirmed an inverse relationship between myeloperoxidase activity and extracellular H2O2 release. Myeloperoxidase-deficient mice infected with Salmonella had elevated hydrogen peroxide tissue levels and exacerbated oxidative damage of host lipids and DNA, despite almost normal Salmonella control. These data show that myeloperoxidase has a major function in mitigating collateral tissue damage during antimicrobial oxidative bursts, by converting diffusible long-lived H2O2 into highly reactive, microbicidal and locally confined HOCl at pathogen surfaces.

Concepts: Oxygen, Antioxidant, Oxidative stress, Oxidative phosphorylation, Reactive oxygen species, Hydrogen peroxide, Chlorine, Peroxide

4

The direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 represents a potentially atom-efficient alternative to the current industrial indirect process. We show that the addition of tin to palladium catalysts coupled with an appropriate heat treatment cycle switches off the sequential hydrogenation and decomposition reactions, enabling selectivities of >95% toward H2O2. This effect arises from a tin oxide surface layer that encapsulates small Pd-rich particles while leaving larger Pd-Sn alloy particles exposed. We show that this effect is a general feature for oxide-supported Pd catalysts containing an appropriate second metal oxide component, and we set out the design principles for producing high-selectivity Pd-based catalysts for direct H2O2 production that do not contain gold.

Concepts: Oxygen, Hydrogenation, Nitrogen, Hydrogen peroxide, Aluminium, Chlorine, Palladium, Peroxide

3

Reactive oxygen species regulate redox-signaling processes, but in excess they can cause cell damage, hence underlying the aetiology of several neurological diseases. Through its ability to down modulate reactive oxygen species, glutathione is considered an essential thiol-antioxidant derivative, yet under certain circumstances it is dispensable for cell growth and redox control. Here we show, by directing the biosynthesis of γ-glutamylcysteine-the immediate glutathione precursor-to mitochondria, that it efficiently detoxifies hydrogen peroxide and superoxide anion, regardless of cellular glutathione concentrations. Knocking down glutathione peroxidase-1 drastically increases superoxide anion in cells synthesizing mitochondrial γ-glutamylcysteine. In vitro, γ-glutamylcysteine is as efficient as glutathione in disposing of hydrogen peroxide by glutathione peroxidase-1. In primary neurons, endogenously synthesized γ-glutamylcysteine fully prevents apoptotic death in several neurotoxic paradigms and, in an in vivo mouse model of neurodegeneration, γ-glutamylcysteine protects against neuronal loss and motor impairment. Thus, γ-glutamylcysteine takes over the antioxidant and neuroprotective functions of glutathione by acting as glutathione peroxidase-1 cofactor.

Concepts: Oxygen, Bacteria, Adenosine triphosphate, Mitochondrion, Reactive oxygen species, Hydrogen peroxide, Glutathione, Peroxide

2

In brains of Alzheimer’s disease (AD), reactive oxygen species (ROS) levels are significantly higher than that of healthy brains. Evidence suggests that, during AD onset and progression, a vicious cycle revolves around amyloid beta (Aβ) production, aggregation, plaque formation, microglia/immunological responses, inflammation, and ROS production. In this cycle, ROS species play a central role, and H2O2 is one of the most important ROS species. In this report, we have designed a fluorescent imaging probe CRANAD-88, which is capable of cascade amplifying near infrared fluorescence (NIRF) signals at three levels upon interacting with H2O2 in AD brains. We demonstrated that the amplification was feasible in vitro and in vivo. Remarkably, we showed that, for the first time, it was feasible to monitor the changes of H2O2 concentrations in AD brains before and after treatment with an H2O2 scavenger. Our method opens new revenues to investigate H2O2 in AD brains and can be very instructive for drug development.

Concepts: Oxygen, Ultraviolet, Mitochondrion, Oxidative stress, Reactive oxygen species, Hydrogen peroxide, Beta amyloid, Peroxide

2

Hydrogen peroxide (H2O2), as a reactive oxygen species, is widely generated in many biological systems. It has been considered as an important signaling molecule that mediates various physiological and biochemical processes in plants. Normal metabolism in plant cells results in H2O2 generation, from a variety of sources. Also, it is now clear that nitric oxide (NO) and calcium (Ca(2+)) function as signaling molecules in plants. Both H2O2 and NO are involved in plant development and abiotic responses. A wide range of evidences suggest that NO could be generated under similar stress conditions and with similar kinetics as H2O2. The interplay between H2O2 and NO has important functional implications to modulate transduction processes in plants. Moreover, close interaction also exists between H2O2 and Ca(2+) in response to development and abiotic stresses in plants. Cellular responses to H2O2 and Ca(2+) signaling systems are complex. There is quite a bit of interaction between H2O2 and Ca(2+) signaling in responses to several stimuli. This review aims to introduce these evidences in our understanding of the crosstalk among H2O2, NO, and Ca(2+) signaling which regulates plant growth and development, and other cellular and physiological responses to abiotic stresses.

Concepts: Photosynthesis, Oxygen, Water, Oxidative stress, Reactive oxygen species, Hydrogen peroxide, Oxide, Peroxide

1

To describe a case of necroulcerative gastritis in a cat secondary to administration of 3% hydrogen peroxide as an emetic agent.

Concepts: Oxygen, Hydrogen peroxide, Cat, Peroxide

1

In-office tooth whitening using hydrogen peroxide (H2O2) has been practised in dentistry without significant safety concerns for more than a century. While few disputes exist regarding the efficacy of peroxide-based at-home whitening since its first introduction in 1989, its safety has been the cause of controversy and concern. This article reviews and discusses safety issues of tooth whitening using peroxide-based materials, including biological properties and toxicology of H2O2, use of chlorine dioxide, safety studies on tooth whitening, and clinical considerations of its use. Data accumulated during the last two decades demonstrate that, when used properly, peroxide-based tooth whitening is safe and effective. The most commonly seen side effects are tooth sensitivity and gingival irritation, which are usually mild to moderate and transient. So far there is no evidence of significant health risks associated with tooth whitening; however, potential adverse effects can occur with inappropriate application, abuse, or the use of inappropriate whitening products. With the knowledge on peroxide-based whitening materials and the recognition of potential adverse effects associated with the procedure, dental professionals are able to formulate an effective and safe tooth whitening regimen for individual patients to achieve maximal benefits while minimising potential risks.

Concepts: Immune system, Oxygen, Effectiveness, Hydrogen peroxide, Oxide, Chlorine, Patient safety, Peroxide