Hydrogen Peroxide

Human lymphocytes were either exposed to X-irradiation (25 to 200 rads) or treated with HzOz (9.1 to 291 u&f) at 4°C and the extent of DNA migration was measured using a singlecell microgel electrophoresis technique under alkaline conditions. Both agents induced a significant increase in DNA migration, beginning at the lowest dose evaluated. Migration patterns were relatively homogeneous among cells exposed to X-rays but heterogeneous among cells treated with HzOz. An analysis of repair kinetics following exposure to 200 rads X-rays was conducted with lymphocytes obtained from three individuals. The bulk of the DNA repair occurred within the first IS min, while all of the repair was essentially complete by 120 min after exposure. However, some cells demonstrated no repair during this incubation period while other cells demonstrated DNA migration patterns indicative of more damage than that induced by the initial irradiation with X-rays. This technique appears to be sensitive and useful for detecting damage and repair in single cells. @ IYXX Academic Press. Inc.

This review summarizes the multifaceted aspects of antioxidants and the basic kinetic models of inhibited autoxidation and analyzes the chemical principles of antioxidant capacity assays. Depending upon the reactions involved, these assays can roughly be classified into two types: assays based on hydrogen atom transfer (HAT) reactions and assays based on electron transfer (ET). The majority of HAT-based assays apply a competitive reaction scheme, in which antioxidant and substrate compete for thermally generated peroxyl radicals through the decomposition of azo compounds. These assays include inhibition of induced low-density lipoprotein autoxidation, oxygen radical absorbance capacity (ORAC), total radical trapping antioxidant parameter (TRAP), and crocin bleaching assays. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes color when reduced. The degree of color change is correlated with the sample's antioxidant concentrations. ET-based assays include the total phenols assay by Folin-Ciocalteu reagent (FCR), Trolox equivalence antioxidant capacity (TEAC), ferric ion reducing antioxidant power (FRAP), "total antioxidant potential" assay using a Cu(II) complex as an oxidant, and DPPH. In addition, other assays intended to measure a sample's scavenging capacity of biologically relevant oxidants such as singlet oxygen, superoxide anion, peroxynitrite, and hydroxyl radical are also summarized. On the basis of this analysis, it is suggested that the total phenols assay by FCR be used to quantify an antioxidant's reducing capacity and the ORAC assay to quantify peroxyl radical scavenging capacity. To comprehensively study different aspects of antioxidants, validated and specific assays are needed in addition to these two commonly accepted assays.

We explored genomic expression patterns in the yeast Saccharomyces cerevisiae responding to diverse environmental transitions. DNA microarrays were used to measure changes in transcript levels over time for almost every yeast gene, as cells responded to temperature shocks, hydrogen peroxide, the superoxide-generating drug menadione, the sulfhydryl-oxidizing agent diamide, the disulfide-reducing agent dithiothreitol, hyper-and hypo-osmotic shock, amino acid starvation, nitrogen source depletion, and progression into stationary phase. A large set of genes (ϳ 900) showed a similar drastic response to almost all of these environmental changes. Additional features of the genomic responses were specialized for specific conditions. Promoter analysis and subsequent characterization of the responses of mutant strains implicated the transcription factors Yap1p, as well as Msn2p and Msn4p, in mediating specific features of the transcriptional response, while the identification of novel sequence elements provided clues to novel regulators. Physiological themes in the genomic responses to specific environmental stresses provided insights into the effects of those stresses on the cell.

Glutathione (GSH) is a thiol-containing tripeptide, which plays central roles in the defence against oxidative damage and in signaling pathways. Upon oxidation, GSH is transformed to glutathione disulfide (GSSG). The concentrations of GSH and GSSG and their molar ratio are indicators of cell functionality and oxidative stress. Assessment of redox homeostasis in various clinical states and medical applications for restoration of the glutathione status are of growing importance. This review is intended to provide a state-of-the-art overview of issues relating to sample pretreatment and choices for the separation and detection of GSH and GSSG. High-performance liquid chromatography, capillary electrophoresis and gas chromatography (as techniques with a separation step) with photometric, fluorimetric, electrochemical and mass spectrometric detection are discussed, stress being laid on novel approaches.

The role of reactive oxygen species, with the subsequent oxidative deterioration of biological macromolecules in the toxicities associated with transition metal ions, is reviewed. Recent studies have shown that metals, including iron, copper, chromium, and vanadium undergo redox cycling, while cadmium, mercury, and nickel, as well as lead, deplete glutathione and protein-bound sulfhydryl groups, resulting in the production of reactive oxygen species as superoxide ion, hydrogen peroxide, and hydroxyl radical. As a consequence, enhanced lipid peroxidation, DNA damage, and altered calcium and sulfhydryl homeostasis occur. Fenton-like reactions may be commonly associated with most membranous fractions including mitochondria, microsomes, and peroxisomes. Phagocytic cells may be another important source of reactive oxygen species in response to metal ions. Furthermore, various studies have suggested that the ability to generate reactive oxygen species by redox cycling quinones and related compounds may require metal ions. Recent studies have suggested that metal ions may enhance the production of tumor necrosis factor alpha (TNFα) and activate protein kinase C, as well as induce the production of stress proteins. Thus, some mechanisms associated with the toxicities of metal ions are very similar to the effects produced by many organic xenobiotics. Specific differences in the toxicities of metal ions may be related to differences in solubilities, absorbability, transport, chemical reactivity, and the complexes that are formed within the body. This review summarizes current studies that have been conducted with transition metal ions as well as lead, regarding the production of reactive oxygen species and oxidative tissue damage.

Mitochondria have been described as "the powerhouses of the cell" because they link the energy-releasing activities of electron transport and proton pumping with the energy conserving process of oxidative phosphorylation, to harness the value of foods in the form of ATP. Such energetic processes are not without dangers, however, and the electron transport chain has proved to be somewhat "leaky." Such side reactions of the mitochondrial electron transport chain with molecular oxygen directly generate the superoxide anion radical (O 2 •Ϫ ), which dismutates to form hydrogen peroxide (H 2 O 2 ), which can further react to form the hydroxyl radical (HO • ). In addition to these toxic electron transport chain reactions of the inner mitochondrial membrane, the mitochondrial outer membrane enzyme monoamine oxidase catalyzes the oxidative deamination of biogenic amines and is a quantitatively large source of H 2 O 2 that contributes to an increase in the steady state concentrations of reactive species within both the mitochondrial matrix and cytosol. In this article we review the mitochondrial rates of production and steady state levels of these reactive oxygen species. Reactive oxygen species generated by mitochondria, or from other sites within or outside the cell, cause damage to mitochondrial components and initiate degradative processes. Such toxic reactions contribute significantly to the aging process and form the central dogma of "The Free Radical Theory of Aging." In this article we review current understandings of mitochondrial DNA, RNA, and protein modifications by oxidative stress and the enzymatic removal of oxidatively damaged products by nucleases and proteases. The possible contributions of mitochondrial oxidative polynucleotide and protein turnover to apoptosis and aging are explored.

PPARg coactivator 1a (PGC-1a) is a potent stimulator of mitochondrial biogenesis and respiration. Since the mitochondrial electron transport chain is the main producer of reactive oxygen species (ROS) in most cells, we examined the effect of PGC-1a on the metabolism of ROS. PGC-1a is coinduced with several key ROS-detoxifying enzymes upon treatment of cells with an oxidative stressor; studies with RNAi or null cells indicate that PGC-1a is required for the induction of many ROS-detoxifying enzymes, including GPx1 and SOD2. PGC-1a null mice are much more sensitive to the neurodegenerative effects of MPTP and kainic acid, oxidative stressors affecting the substantia nigra and hippocampus, respectively. Increasing PGC-1a levels dramatically protects neural cells in culture from oxidativestressor-mediated death. These studies reveal that PGC-1a is a broad and powerful regulator of ROS metabolism, providing a potential target for the therapeutic manipulation of these important endogenous toxins.

Ras signaling promotes simultaneously and independently [fig. S1L (7 )] three effects: activation of al and dlim1 at the very center, activation of Bar in nearby cells, and repression of bab from the whole area. Regarding tarsal segments 1 to 4, vn acts as the repressory element working in parallel to dac to restrict the activation of rn and bab to the middle of the Dll domain. Tarsal segments 1 to 4 are thus defined in those Dll-expressing cells not simultaneously exposed to either the dac protein or EGFR-Ras signaling triggered by vn ( ).

We have shown previously that the heavy metalresponsive transcriptional activator MTF-1 regulates the basal and heavy metal-induced expression of metallothioneins. To investigate the physiological function of MTF-1, we generated null mutant mice by targeted gene disruption. Embryos lacking MTF-1 die in utero at approximately day 14 of gestation. They show impaired development of hepatocytes and, at later stages, liver decay and generalized edema. MTF-1 -/embryos fail to transcribe metallothionein I and II genes, and also show diminished transcripts of the gene which encodes the heavy-chain subunit of the γ-glutamylcysteine synthetase, a key enzyme for glutathione biosynthesis. Metallothionein and glutathione are involved in heavy metal homeostasis and detoxification processes, such as scavenging reactive oxygen intermediates. Accordingly, primary mouse embryo fibroblasts lacking MTF-1 show increased susceptibility to the cytotoxic effects of cadmium or hydrogen peroxide. Thus, MTF-1 may help to control metal homeostasis and probably cellular redox state, especially during liver development. We also note that the MTF-1 null mutant phenotype bears some similarity to those of two other regulators of cellular stress response, namely c-Jun and NF-κB (p65/RelA). Keywords: glutathione biosynthesis/knockout mice/liver degeneration/metallothionein gene expression/ transcription factor MTF-1 sensitive and cisplatin-resistant human ovarian cancer cell lines. Cancer Res., 55, 4367-4374. Zheng,H., Liu,J., Liu,Y. and Klaasen,C.D. (1996) Hepatocytes from metallothionein-I and II knock-out mice are sensitive to cadmiumand tert-butylhydroperoxide-induced cytotoxicity.

Reactive oxygen species (ROS) play a multitude of signaling roles in different organisms from bacteria to mammalian cells. They were initially thought to be toxic byproducts of aerobic metabolism, but have now been acknowledged as central players in the complex signaling network of cells. In this review, we will attempt to address several key questions related to the use of ROS as signaling molecules in cells, including the dynamics and specificity of ROS signaling, networking of ROS with other signaling pathways, ROS signaling within and across different cells, ROS waves and the evolution of the ROS gene network.

To determine the role of reactive oxygen species in mammalian longevity, we generated transgenic mice that overexpress human catalase localized to the peroxisome, the nucleus, or mitochondria (MCAT). Median and maximum life spans were maximally increased (averages of 5 months and 5.5 months, respectively) in MCAT animals. Cardiac pathology and cataract development were delayed, oxidative damage was reduced, H 2 O 2 production and H 2 O 2induced aconitase inactivation were attenuated, and the development of mitochondrial deletions was reduced. These results support the free radical theory of aging and reinforce the importance of mitochondria as a source of these radicals.

Free radicals and other reactive oxygen species (ROS) are constantly formed in the human body. Free-radical mechanisms have been implicated in the pathology of several human diseases, including cancer, atherosclerosis, malaria, and rheumatoid arthritis and neurodegenerative diseases. For example, the superoxide radical (O 2 • −) and hydrogen peroxide (H 2 O 2) are known to be generated in the brain and nervous system in vivo, and several areas of the human brain are rich in iron, which appears to be easily mobilizable in a form that can stimulate free-radical reactions. Antioxidant defenses to remove O 2 • − and H 2 O 2 exist. Superoxide dismutases (SOD) remove O 2 • − by greatly accelerating its conversion to H 2 O 2. Catalases in peroxisomes convert H 2 O 2 into water and O 2 and help to dispose of H 2 O 2 generated by the action of the oxidase enzymes that are located in these organelles. Other important H 2 O 2-removing enzymes in human cells are the glutathione peroxidases. When produced in excess, ROS can cause tissue injury. However, tissue injury can itself cause ROS generation (e.g., by causing activation of phagocytes or releasing transition metal ions from damaged cells), which may (or may not, depending on the situation) contribute to a worsening of the injury. Assessment of oxidative damage to biomolecules by means of emerging technologies based on products of oxidative damage to DNA (e.g., 8-hydroxydeoxyguanosine), lipids (e.g., isoprostanes), and proteins (altered amino acids) would not only advance our understanding of the underlying mechanisms but also facilitate supplementation and intervention studies designed and conducted to test antioxidant efficacy in human health and disease.

Reactive oxygen species (ROS) have been proposed to function as second messengers in abscisic acid (ABA) signaling in guard cells. However, the question whether ROS production is indeed required for ABA signal transduction in vivo has not yet been addressed, and the molecular mechanisms mediating ROS production during ABA signaling remain unknown. Here, we report identi®cation of two partially redundant Arabidopsis guard cell-expressed NADPH oxidase catalytic subunit genes, AtrbohD and AtrbohF, in which gene disruption impairs ABA signaling. atrbohD/F double mutations impair ABA-induced stomatal closing, ABA promotion of ROS production, ABA-induced cytosolic Ca 2+ increases and ABAactivation of plasma membrane Ca 2+-permeable channels in guard cells. Exogenous H 2 O 2 rescues both Ca 2+ channel activation and stomatal closing in atrbohD/F. ABA inhibition of seed germination and root elongation are impaired in atrbohD/F, suggesting more general roles for ROS and NADPH oxidases in ABA signaling. These data provide direct molecular genetic and cell biological evidence that ROS are rate-limiting second messengers in ABA signaling, and that the AtrbohD and AtrbohF NADPH oxidases function in guard cell ABA signal transduction.

Endogenously produced pro-oxidant reactive species are essential to life, being involved in several biological functions. However, when overproduced (e.g. due to exogenous stimulation), or when the levels 0165-022X/$ -see front matter D of antioxidants become severely depleted, these reactive species become highly harmful, causing oxidative stress through the oxidation of biomolecules, leading to cellular damage that may become irreversible and cause cell death. The scientific research in the field of reactive oxygen species (ROS) associated biological functions and/or deleterious effects is continuously requiring new sensitive and specific tools in order to enable a deeper insight on its action mechanisms. However, reactive species present some characteristics that make them difficult to detect, namely their very short lifetime and the variety of antioxidants existing in vivo, capable of capturing these reactive species. It is, therefore, essential to develop methodologies capable of overcoming this type of obstacles. Fluorescent probes are excellent sensors of ROS due to their high sensitivity, simplicity in data collection, and high spatial resolution in microscopic imaging techniques. Hence, the main goal of the present paper is to review the fluorescence methodologies that have been used for detecting ROS in biological and non-biological media. D

We used genome-wide expression analysis to explore how gene expression in Saccharomyces cerevisiae is remodeled in response to various changes in extracellular environment, including changes in temperature, oxidation, nutrients, pH, and osmolarity. The results demonstrate that more than half of the genome is involved in various responses to environmental change and identify the global set of genes induced and repressed by each condition. These data implicate a substantial number of previously uncharacterized genes in these responses and reveal a signature common to environmental responses that involves ∼10% of yeast genes. The results of expression analysis with MSN2/MSN4 mutants support the model that the Msn2/Msn4 activators induce the common response to environmental change. These results provide a global description of the transcriptional response to environmental change and extend our understanding of the role of activators in effecting this response.

The mitochondrial respiratory chain is a major source of reactive oxygen species (ROS) under pathological conditions including myocardial ischemia and reperfusion. Limitation of electron transport by the inhibitor rotenone immediately before ischemia decreases the production of ROS in cardiac myocytes and reduces damage to mitochondria. We asked if ROS generation by intact mitochondria during the oxidation of complex I substrates (glutamate, pyruvate/malate) occurred from complex I or III. ROS production by mitochondria of Sprague-Dawley rat hearts and corresponding submitochondrial particles was studied. ROS were measured as H 2 O 2 using the amplex red assay. In mitochondria oxidizing complex I substrates, rotenone inhibition did not increase H 2 O 2 . Oxidation of complex I or II substrates in the presence of antimycin A markedly increased H 2 O 2 . Rotenone prevented antimycin A-induced H 2 O 2 production in mitochondria with complex I substrates but not with complex II substrates. Catalase scavenged H 2 O 2 . In contrast to intact mitochondria, blockade of complex I with rotenone markedly increased H 2 O 2 production from submitochondrial particles oxidizing the complex I substrate NADH. ROS are produced from complex I by the NADH dehydrogenase located in the matrix side of the inner membrane and are dissipated in mitochondria by matrix antioxidant defense. However, in submitochondrial particles devoid of antioxidant defense ROS from complex I are available for detection. In mitochondria, complex III is the principal site for ROS generation during the oxidation of complex I substrates, and rotenone protects by limiting electron flow into complex III.

The purity of wafer surfaces is an essential requisite for the successful fabrication of VLSI and ULSI silicon circuits. Wafer cleaning chemistry has remained essentially unchanged in the past 25 years and is based on hot alkaline and acidic hydrogen peroxide solutions, a process known as "RCA Standard Clean." This is still the primary method used in the industry. What has changed is its implementation with optimized equipment: from simple immersion to centrifugal spraying, megasonic techniques, and enclosed system processing that allow simultaneous removal of both contaminant films and particles. Improvements in wafer drying by use of isopropanol vapor or by "slow-pull" out of hot deionized water are being investigated. Several alternative cleaning methods are also being tested, including choline solutions, chemical vapor etching, and UV/ozone treatments. The evolution of silicon wafer cleaning processes and technology is traced and reviewed from the 1950s to August 1989.

Cell survival requires multiple factors, including appropriate proportions of molecular oxygen and various antioxidants. Although most oxidative insults can be overcome by the cell's natural defenses, sustained perturbation of this balance may result in either apoptotic or necrotic cell death. Numerous, recent studies have shown that the mode of cell death that occurs depends on the severity of the insult. Oxidants and antioxidants can not only determine cell fate, but can also modulate the mode of cell death. Effects of oxidative stress on components of the apoptotic machinery may mediate this modulation. This review will address some of the current paradigms for oxidative stress and apoptosis, and discuss the potential mechanisms by which oxidants can modulate the apoptotic pathway.

The purpose of this position paper is to present a critical analysis of the challenges and limitations of the most widely used fluorescent probes for detecting and measuring reactive oxygen and nitrogen species. Where feasible, we have made recommendations for the use of alternate probes and appropriate analytical techniques that measure the specific products formed from the reaction between fluorescent probes and reactive oxygen and nitrogen species.

When titanium dioxide (TiO(2)) is irradiated with near-UV light, this semiconductor exhibits strong bactericidal activity. In this paper, we present the first evidence that the lipid peroxidation reaction is the underlying mechanism of death of Escherichia coli K-12 cells that are irradiated in the presence of the TiO(2) photocatalyst. Using production of malondialdehyde (MDA) as an index to assess cell membrane damage by lipid peroxidation, we observed that there was an exponential increase in the production of MDA, whose concentration reached 1.1 to 2.4 nmol. mg (dry weight) of cells(-1) after 30 min of illumination, and that the kinetics of this process paralleled cell death. Under these conditions, concomitant losses of 77 to 93% of the cell respiratory activity were also detected, as measured by both oxygen uptake and reduction of 2,3,5-triphenyltetrazolium chloride from succinate as the electron donor. The occurrence of lipid peroxidation and the simultaneous losses of both me...

Much evidence indicates that superoxide is generated from Oz in a cyanide-sensitive reaction involving a reduced component of complex III of the mitochondrial respiratory chain, particularly when antimycin A is present. Although it is generally believed that ubisemiquinone is the electron donor to Oz, little experimental evidence supporting this view has been reported. Experiments with succinate as electron donor in the presence of antimycin A in intact rat heart mitochondria, which contain much superoxide dismutase but little catalase, showed that myxothiazol, which inhibits reduction of the Rieske iron-sulfur center, prevented formation of hydrogen peroxide, determined spectrophotometrically as the HzOz-peroxidase complex. Similarly, depletion of the mitochondria of their cytochrome c also inhibited formation of Hz02, which was restored by addition of cytochrome c. These observations indicate that factors preventing the formation of ubisemiquinone also prevent Hz02 formation. They also exclude ubiquinol, which remains reduced under these conditions, as the reductant of Oz. Since cytochrome b also remains fully reduced when myxothiazol is added to succinate-and antimycin A-supplemented mitochondria, reduced cytochrome b may also be excluded as the reductant of OZ. These observations, which are consistent with the Q-cycle reactions, by exclusion of other possibilities leave ubisemiquinone as the only reduced electron carrier in complex III capable of reducing Oz to 0;. o 1985 Academic Press, Inc.

portant tool for studying phagocyte function. The ini-The enzymatic determination of hydrogen peroxide tial product of NADPH oxidase-mediated oxygen can be accomplished with high sensitivity and specificreduction is primarily superoxide anion. Subsequently, ity using N-acetyl-3,7-dihydroxyphenoxazine (Amplex superoxide is converted to H 2 O 2 either spontaneously Red), a highly sensitive and chemically stable fluoroor by superoxide dismutase. Because of its stability and genic probe for the enzymatic determination of H 2 O 2 . membrane permeability, H 2 O 2 is usually chosen as an Enzyme-catalyzed oxidation of Amplex Red, which is a analyte among other oxidants to quantitate the extracolorless and nonfluorescent derivative of dihydrorescellular release of reactive oxygen reduction products orufin, produces highly fluorescent resorufin, which in phagocytes. H 2 O 2 is also a coproduct of a variety of has an excitation maximum at 563 nm and emission oxidases, and its detection is the basis for measuring maximum at 587 nm. The reaction stoichiometry of the activity of these oxidases (1, 2). Both chromogenic Amplex Red and H 2 O 2 was determined to be 1:1. This and fluorogenic substrates are currently used to meaprobe allows detection of 5 pmol H 2 O 2 in a 96-well fluosure the activity of NADPH oxidase, HRP, 1 and other rescence microplate assay. When applied to the meaoxidases. While assays using chromogenic substrates surement of NADPH oxidase activation, the Amplex require only a regular spectrophotometer, they are usu-Red assay can detect H 2 O 2 release from as few as 2000 ally less sensitive than assays that use fluorogenic phorbol myristate acetate-stimulated neutrophils with substrates. Absorption-and fluorescence-detecting a sensitivity 5-to 20-fold greater than that attained in microplate readers, which are particularly useful inthe scopoletin assay under the same experimental construments for enzyme assays, are now available in ditions. Furthermore, the oxidase-catalyzed assay usmany research and clinical laboratories.

It is now clear that hydrogen peroxide (H 2 O 2 ) and nitric oxide (NO) function as signalling molecules in plants. A wide range of abiotic and biotic stresses results in H 2 O 2 generation, from a variety of sources. H 2 O 2 is removed from cells via a number of antioxidant mechanisms, both enzymatic and nonenzymatic. Both biotic and abiotic stresses can induce NO synthesis, but the biosynthetic origins of NO in plants have not yet been resolved. Cellular responses to H 2 O 2 and NO are complex, with considerable cross-talk between responses to several stimuli. In this review the potential roles of H 2 O 2 and NO during various stresses and the signalling pathways they activate are discussed. Key signalling components that might provide targets for enhancing crop production are also identified.

Hydrogen peroxide was discovered in 1818 and has been used in bleaching for over a century [1]. H 2 O 2 on its own is a relatively weak oxidant under mild conditions: It can achieve some oxidations unaided, but for the majority of applications it requires activation in one way or another. Some activation methods, e.g., Fenton's reagent, are almost as old . However, by far the bulk of useful chemistry has been discovered in the last 50 years, and many catalytic methods are much more recent.

Acid Red 14 (AR14), commonly used as a textile dye, could be photocatalytically degraded using TiO 2 suspensions irradiated by a UV-C lamp (30 W). The experiments showed that TiO 2 and UV light had a negligible effect when they were used on their own. The semi-log plot of dye concentration versus time was linear, suggesting first order reaction (K = 1.41 × 10 −2 min −1 ). The effects of some parameters such as pH, the amount of TiO 2 and initial dye concentration were also examined.

In a recent publication , Science 320, 661-664), the authors described how replacing the endogenous mitochondrial DNA (mtDNA) in a weakly metastatic mouse tumor cell line with mtDNA from a highly metastatic cell line enhanced tumor progression through enhanced production of reactive oxygen species (ROS). The authors attributed the transformation from a low-metastatic cell line to a high-metastatic phenotype to overproduction of ROS (hydrogen peroxide and superoxide) caused by a dysfunction in mitochondrial complex I protein encoded by mtDNA transferred from the highly metastatic tumor cell line. In this critical evaluation, using the paper by Ishikawa et al. as an example, we bring to the attention of researchers in the free radical field how the failure to appreciate the complexities of dye chemistry could potentially lead to pitfalls, misinterpretations, and erroneous conclusions concerning ROS involvement. Herein we make a case that the authors have failed to show evidence for formation of superoxide and hydrogen peroxide, presumed to be generated from complex I deficiency associated with mtDNA mutations in metastatic cells.

BACKGROUND: Growing interest in the replacement of synthetic food antioxidants by natural ones has fostered research on vegetable sources and screening of raw materials to identify new antioxidants. The food-processing industry generates substantial quantities of phenolic-rich by-products that could be valuable natural sources of antioxidants. In this study the antioxidant properties and total phenolic, flavonoid and flavonol contents of three industrial by-products, sugar beet pulp, sesame cake and potato peel, extracted with various solvents were examined. Since different antioxidant compounds have different mechanisms of action, several methods were used to assess the antioxidant efficacy of extracts.RESULTS: Among the six solvents tested, methanol gave the highest extract yield of potato peel and sugar beet pulp, while diethyl ether gave the highest extract yield of sesame cake. Methanol exhibited the highest extraction ability for phenolic compounds, with total phenolics amounting to 2.91, 1.79 and 0.81 mg gallic acid equivalent g−1 dry weight in potato peel, sugar beet pulp and sesame cake extracts respectively, and also showed the strongest antioxidant capacity in the three assays used. All three methods proved that potato peel extract had the highest antioxidant activity owing to its high content of phenolic compounds and flavonoids.CONCLUSION: On the basis of the results obtained, potato peel, sugar beet pulp and sesame cake extracts could serve as natural antioxidants owing to their significant antioxidant activity. Therefore they could be used as preservative ingredients in the food and/or pharmaceutical industries. Copyright © 2009 Society of Chemical Industry

The electrochemical oxidation of organic pollutants is a promising process for substances which are recalcitrant to biological degradation. The anodic oxidation of coumaric acid, which is a biorefractory organic pollutant of olive oil manufacturing waste waters, was evaluated on a Pt-Ti electrode. The operating test conditions were compatible with direct discharge of the after-treatment effluent in natural water basins or rivers as regards the electrolyte salt content (Na 2 SO 4 =0.02 N). The effect of the applied current density, pH, temperature, initial coumaric acid concentration and of the type of DC feeder (a galvanostat or a simple current rectifier) over the oxidation rate was assessed through a series of batch runs performed in a pilot plant apparatus. Beyond direct oxidation at the Pt-electrode surface, bulk oxidation with hydrogen peroxide, generated through a persulfate-formation/hydrolysis route, was found to be a crucial step in coumaric acid degradation to more biodegradable non-aromatic products. Small quantities of Fe ions were helpful in accelerating the oxidation process. An analysis of the rather complex reaction schemes governing the process is proposed.

The ability to protect refined metals from reactive environments is vital to many industrial and academic applications. Current solutions, however, typically introduce several negative effects, including increased thickness and changes in the metal physical properties. In this paper, we demonstrate for the first time the ability of graphene films grown by chemical vapor deposition to protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy from air oxidation. SEM, Raman spectroscopy, and XPS studies show that the metal surface is well protected from oxidation even after heating at 200 º C in air for up to 4 hours. Our work further shows that graphene provides effective resistance against

The gastrointestinal tract is a complex ecosystem that associates a resident microbiota and cells of various phenotypes lining the epithelial wall expressing complex metabolic activities. The resident microbiota in the digestive tract is a heterogeneous microbial ecosystem containing up to 1 Â 10 14 colony-forming units (CFUs) of bacteria. The intestinal microbiota plays an important role in normal gut function and maintaining host health. The host is protected from attack by potentially harmful microbial microorganisms by the physical and chemical barriers created by the gastrointestinal epithelium. The cells lining the gastrointestinal epithelium and the resident microbiota are two partners that properly and/or synergistically function to promote an efficient host system of defence. The gastrointestinal cells that make up the epithelium, provide a physical barrier that protects the host against the unwanted intrusion of microorganisms into the gastrointestinal microbiota, and against the penetration of harmful microorganisms which usurp the cellular molecules and signalling pathways of the host to become pathogenic. One of the basic physiological functions of the resident microbiota is that it functions as a microbial barrier against microbial pathogens. The mechanisms by which the species of the microbiota exert this barrier effect remain largely to be determined. There is increasing evidence that lactobacilli and bifidobacteria, which inhabit the gastrointestinal microbiota, develop antimicrobial activities that participate in the host's gastrointestinal system of defence. The objective of this review is to analyze the in vitro and in vivo experimental and clinical studies in which the antimicrobial activities of selected lactobacilli and bifidobacteria strains have been documented.

High dietary fat intake leads to insulin resistance in skeletal muscle, and this represents a major risk factor for type 2 diabetes and cardiovascular disease. Mitochondrial dysfunction and oxidative stress have been implicated in the disease process, but the underlying mechanisms are still unknown. Here we show that in skeletal muscle of both rodents and humans, a diet high in fat increases the H2O2-emitting potential of mitochondria, shifts the cellular redox environment to a more oxidized state, and decreases the redox-buffering capacity in the absence of any change in mitochondrial respiratory function. Furthermore, we show that attenuating mitochondrial H2O2 emission, either by treating rats with a mitochondrial-targeted antioxidant or by genetically engineering the overexpression of catalase in mitochondria of muscle in mice, completely preserves insulin sensitivity despite a high-fat diet. These findings place the etiology of insulin resistance in the context of mitochondrial bioenergetics by demonstrating that mitochondrial H2O2 emission serves as both a gauge of energy balance and a regulator of cellular redox environment, linking intracellular metabolic balance to the control of insulin sensitivity.

Oxidative stress markers characterize the neuropathology both of Alzheimer's disease and of amyloid-bearing transgenic mice. The neurotoxicity of amyloid A peptides has been linked to peroxide generation in cell cultures by an unknown mechanism. We now show that human A directly produces hydrogen peroxide (H 2 O 2 ) by a mechanism that involves the reduction of metal ions, Fe(III) or Cu(II), setting up conditions for Fenton-type chemistry. Spectrophotometric experiments establish that the A peptide reduces Fe(III) and Cu(II) to Fe(II) and Cu(I), respectively. Spectrochemical techniques are used to show that molecular oxygen is then trapped by A and reduced to H 2 O 2 in a reaction that is driven by substoichiometric amounts of Fe(II) or Cu(I). In the presence of Cu(II) or Fe(III), A produces a positive thiobarbituric-reactive substance (TBARS) assay, compatible with the generation of the hydroxyl radical (OH‚). The amounts of both reduced metal and TBARS reactivity are greatest when generated by A 1-42 . A 1-40 > rat A 1-40, a chemical relationship that correlates with the participation of the native peptides in amyloid pathology. These findings indicate that the accumulation of A could be a direct source of oxidative stress in Alzheimer's disease.