Hydrogen Peroxide

The world rapidly growing demand for manganese has made it increasingly important to develop processes for economical recovery of manganese from low grade manganese ores and other secondary sources. Part I of this review outlines metallurgical processes for manganese production from various resources, particularly focusing on recent developments in direct hydrometallurgical leaching and recovery processes to identify potential sources of manganese and products which can be economically produced.

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.

Idiopathic pulmonary fibrosis (IPF) is thought to involve inflammatory infiltration of leukocytes, lung injury induced by reactive oxygen species (ROS), in particular superoxide anion, and fibrosis (collagen deposition). No treatment has been shown to improve definitively the prognosis for IPF patients. Superoxide dismutase (SOD) catalyzes the dismutation of superoxide anion to hydrogen peroxide, which is subsequently detoxified by catalase. Lecithinized SOD (PC-SOD) has overcome clinical limitations of SOD, including low tissue affinity and low stability in plasma. In this study, we examined the effect of PC-SOD on bleomycin-induced pulmonary fibrosis. Severity of the bleomycin-induced fibrosis in mice was assessed by various methods, including determination of hydroxyproline levels in lung tissue. Intravenous administration of PC-SOD suppressed the bleomycin-induced increase in the number of leukocytes in bronchoalveolar lavage fluid. Bleomycin-induced collagen deposition and incr...

Photosystem II reaction centers evolve 02 in the dark when H 202 is added as a substrate. Although some of this activity can be attributed to catalase, as much as 75% of the activity was not affected by the addition of 1 mM KCN. Several lines of evidence demonstrate that this KCN-insensitive 02 evolution from H 202 in the dark is catalyzed by the cycling of S states in the oxygen-evolving complex including: (1) inactivation of H2Oz-mediated 02 evolution by Ca/EDTA washing; (2) susceptibility of the activity to inhibition by amines like ammonia and Tris; (3) inhibition by CCCP which is known to accelerate the rate of deactivation of the S 2 state and; (4) a direct dependence of the rate of 02 evolution on the presence of calcium and (5) chloride.

h i g h l i g h t s We studied the acute effects of inhaled hydrogen peroxide in humans. Volunteers were exposed to 0 ppm, 0.5 ppm or 2.2 ppm hydrogen peroxide for 2 h. Our study suggests that hydrogen peroxide is slightly irritating at 2.2 ppm.

This study was designed to determine the predictive value of lipid hydroperoxide (LOOH) levels for adverse cardiovascular outcomes in patients with stable coronary artery disease (CAD). Oxidative modification of circulating lipids contributes to inflammation and endothelial dysfunction, which are hallmark features of atherosclerosis. A serum biomarker of oxidation is LOOH, which is a primary product of fatty acid peroxidation. Serum LOOH levels were measured and correlated with clinical events over a 3-year period in 634 patients with angiographic evidence of CAD. Baseline LOOH levels in the highest quartile were associated with hazard ratios of 3.24 (95% confidence interval [CI] 1.86 to 5.65; p = 0.0001) for nonfatal vascular events (n = 149), 1.80 (95% CI 1.13 to 2.88; p = 0.014) for major vascular procedures (n = 139), and 2.23 (95% CI 1.44 to 3.44; p = 0.0003) for all vascular events and procedures. Baseline LOOH levels correlated with serum levels of soluble intercellular adhesion molecule-1 (p = 0.001) and thiobarbituric acid reactive substances (p = 0.001) as well as the mean percent change in stenosis for large segments >50% stenosed (p = 0.048). A multivariate proportional hazards model, adjusted for traditional risk factors and inflammatory markers, showed an independent effect of LOOH on nonfatal vascular events, vascular procedures, and all events or procedures. Amlodipine treatment was associated with reduced cardiovascular events and changes in LOOH levels compared with placebo. Elevated LOOH levels were predictive of nonfatal vascular events and procedures in patients with stable CAD, independent of traditional risk factors and inflammatory markers.

Phenyllactic acid (PLA) has recently been found in cultures of Lactobacillus plantarum that show antifungal activity in sourdough breads. The fungicidal activity of PLA and growth inhibition by PLA were evaluated by using a microdilution test and 23 fungal strains belonging to 14 species of Aspergillus, Penicillium, and Fusarium that were isolated from bakery products, flours, or cereals. Less than 7.5 mg of PLA ml ؊1 was required to obtain 90% growth inhibition for all strains, while fungicidal activity against 19 strains was shown by PLA at levels of <10 mg ml ؊1 . Levels of growth inhibition of 50 to 92.4% were observed for all fungal strains after incubation for 3 days in the presence of 7.5 mg of PLA ml ؊1 in buffered medium at pH 4, which is a condition more similar to those in real food systems. Under these experimental conditions PLA caused an unpredictable delaying effect that was more than 2 days long for 12 strains, including some mycotoxigenic strains of Penicillium verrucosum and Penicillium citrinum and a strain of Penicillium roqueforti (the most widespread contaminant of bakery products); a growth delay of about 2 days was observed for seven other strains. The effect of pH on the inhibitory activity of PLA and the combined effects of the major organic acids produced by lactic acid bacteria isolated from sourdough bread (PLA, lactic acid, and acetic acid) were also investigated. The ability of PLA to act as a fungicide and delay the growth of a variety of fungal contaminants provides new perspectives for possibly using this natural antimicrobial compound to control fungal contaminants and extend the shelf lives of foods and/or feedstuffs.

Resveratrol is a natural molecule with antioxidant action. Moreover, resveratrol is also considered to be a molecule with anti-inflammatory action, an effect attributed to suppression of prostaglandin (PG) biosynthesis. The aim of the present study was to investigate the effects of resveratrol, a polyphenol present in most red wines, on reactive oxygen species formation as well as on arachidonic acid (AA) release, cyclooxygenase expression, and PG synthesis in murine resident peritoneal macrophages. Results show that resveratrol exerted a strong inhibitory effect on superoxide radical (O2−) and hydrogen peroxide (H2O2) produced by macrophages stimulated by lipopolysaccharides (LPS) or phorbol esters (PMA). Resveratrol also significantly decreased [3H]AA release induced by LPS and PMA or by exposure to O2− or H2O2. Resveratrol treatment caused a significant impairment of cyclooxygenase-2 (COX-2) induction stimulated by LPS and PMA or by O2− or H2O2 exposure. These effects of resveratrol on [3H]AA release and COX-2 overexpression were correlated with a marked reduction of PG synthesis. Our results indicate that the antioxidant action of resveratrol affects AA mobilization and COX-2 induction.

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The development of cellular senescence both by replication and by oxidative stress is not homogenous in cultured primary human fibroblasts. To investigate whether this is due to the heterogeneity in the susceptibility of DNA in different phases of the cell cycle, we subjected synchronised cells to oxidative stress and examined the extent of DNA damage and its long-term effects on the induction of cellular senescence. Here, we first show marked heterogeneity in DNA damage as detected by markers of double strand breaks caused by oxidative stress in an asynchronous human fibroblast culture. Cell cycle synchronization followed by oxidative stress demonstrated that DNA in S-phase is most susceptible to oxidative stress whereas DNA in the quiescent phase is most resistant. DNA repair is an ongoing process after sensing DNA damage; reparable DNA damage is repaired even in cells that contain persistent DNA damage. The extent of persistent DNA damage is tightly correlated with permanent cessation of DNA replication and SA-␤-gal activity. Oxidative stress encountered by cells in S-phase resulted in more persistent DNA damage, more permanent cell cycle arrest and the induction of premature senescence.

A method is proposed for the simultaneous determination of tyrosine and tryptophan in solutions by differential spectrophotometry. The concentrations are calculated from the measurement of the absorbance of the amino acid mixture in an alkaline medium and from the differential absorbance of the alkaline solution against the acid solution a t 294.4 nm. A comparison with three other well-known methods is discussed. Keyphrases 0 Tyrosine-spectrophotometric analysis simultaneously with tryptophan in solutions Tryptophan-spectrophotometric analysis simultaneously with tyrosine in solutions 0 Spectrophotometry, differential-simultaneous analyses of tyrosine and tryptophan in solutions 0 Amino acids-tyrosine and tryptophan, simultaneous spectrophotometric analyses in solutions

It was previously shown that the addition of 1 equiv of a strong acid to [Mn IV (salpn)(µ-O)] 2 , 1, generates the oxo/hydroxo complex [{Mn IV (salpn)} 2 (µ-O,µ-OH)](CF 3 SO 3), 2, which emphasized the basicity of the µ 2-O 2units in the [Mn IV (µ-O)] 2 dimers. We now demonstrate the inherent nucleophilicity of those µ 2-O 2units by showing that the addition of methyl triflate to 1 results in formation of the oxo/methoxo-bridged Mn IV dimer [{Mn IV (salpn)} 2 (µ-O,µ-OCH 3)](CF 3 SO 3), 3. EXAFS analysis of 3 demonstrates that alkylation of an oxo bridge results in the same structural modification of the [Mn IV (µ-O)] 2 core as an oxo bridge protonation. Electrochemical and spectroscopic comparisons of 3 to 2 indicate that 3 is a good electronic structure analogue for 2 without the complication of proton lability and hydrogen bonding. Indeed, 2 and 3 react nearly identically with hydrogen peroxide and with strong acids. In contrast, the products of their reactions with amines, acetate, and triphenylphosphine are dramatically different. The proton lability of 2 results in simple proton transfer, circumventing the slower redox reactions of these substrates with 3. Isotopic labeling, kinetic, and EPR-monitored radical trap studies lead to a proposed reduction-oxidation mechanistic scheme for the reactions of 3 with amines and triphenylphosphine. The Mn III product of this reaction, [Mn III (salpn)(Ph 3 PO)](CF 3 SO 3), was isolated and crystallographically characterized as a dimerized complex. The redox nature of the reactions is confirmed by trapping of a reduced Mn intermediate which is identified by EPR spectroscopy. Comparison of the reactions of 2 and 3 demonstrates the dramatic effect of proton lability and hydrogen bonding on reactivity, and suggests how metalloenzymes may regulate active site reactivity to produce very different catalytic activities with similar active site structures. Furthermore, it also emphasizes that caution should be used when the reactivity of model compounds with easily and rapidly dissociable protons is assessed.

The combination of UV irradiation and hydrogen peroxide (UV–H2O2) was shown to be effective in treating water spiked with 2,2′,4,4′,5,5′-hexachlorobipheny (PCB 153), reducing its concentration by as much as 98%. To test the toxicity of the effluent, bioassays involving three species of primary producers were performed. Results showed the effluent exerting an adverse effect on the algae Scenedesmus bijugatus and

a-Mangostin is a xanthone with antioxidant properties isolated from mangosteen fruit. The reactive oxygen species (ROS) scavenging capacity and the potential protective effect of a-mangostin against the mitochondrial toxin 3-nitropropionic acid (3-NP) in primary cultures of cerebellar granule neurons (CGNs) were studied in the present work. It was found that a-mangostin was able to scavenge in a concentration-dependent way singlet oxygen, superoxide anion and peroxynitrite anion. In contrast, a-mangostin was unable to scavenge hydroxyl radicals and hydrogen peroxide. Furthermore, a-mangostin was able to ameliorate in a concentration-dependent way the neuronal death induced by 3-NP. This protective effect was associated with an amelioration of 3-NP-induced reactive oxygen species formation. It is concluded that a-mangostin is able to scavenge directly several ROS and has a neuroprotective effect against 3-NP in primary cultures of CGNs, which is associated with its ability to ameliorate 3-NP-induced ROS production.

Three hydroxyl-radical producing biomimetic systems, composed of Cu II , hydrogen peroxide and pyridine, glucaric or succinic acid, were able to perform decolorization of olive mill wastewaters (OMW) >85 % within 3 d combined with a significant removal of total phenols (>75 %). The systems consisting of 50 mmol/L succinic acid, 5-10 mmol/L CuSO 4 and 100 mmol/L H 2 O 2 were the most effective at OMW treatment, and led to the reduction of phenol contents to <1 % along with high decolorization (>88 %) and acceptable values of chemical oxygen demand.

Nitric oxide (NO) and reactive oxygen species (ROS) are emerging as important regulators of angiogenesis. NO enhances VEGF synthesis in several cell types and is required for execution of VEGF angiogenic effect in endothelial cells. Similarly, hydrogen peroxide induces VEGF synthesis and recent studies indicate the involvement of ROS in signaling downstream of VEGF stimulation. VEGF synthesis can not only be enhanced by gene transfer of VEGF but also by overexpression of NO synthase genes. Here, we examined the possibility of augmentation of VEGF production by gene transfer of copper/zinc superoxide dismutase (CuZnSOD, SOD1). Overexpression of human SOD1 in mouse NIH 3T3 fibroblasts increased SOD activity, enhanced intracellular generation of H 2 O 2 and significantly stimulated VEGF production as determined by increase in VEGF promoter activity, VEGF mRNA expression and VEGF protein synthesis. The stimulatory effect on VEGF synthesis induced by SOD1 gene transfer was reverted by overexpression of human catalase. The effect of H 2 O 2 produced by engineered cells is mediated by activation of hypoxia-inducible factor response element (HRE) as well as Sp1 recognition site of VEGF promoter. This data suggest the feasibility of stimulation of angiogenesis by overexpression of SOD1. (Mol Cell Biochem 264: [169][170][171][172][173][174][175][176][177][178][179][180][181] 2004)

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.

A green and sustainable method for the oxidation of 1,3-dihydrobenzo[c] thiophenes to sulfones using metalloporphyrin complexes Two efficient methods are reported for the oxidation of 1,3-dihydrobenzo[c]thiophenes to sulfones in good to high yields using H 2 O 2 in the presence of catalytic amounts of porphyrin-based catalysts in ethanol or acetonitrile as solvents at room temperature. The presence of electron-donating or electron-withdrawing groups, in the benzene ring of 1,3-dihydrobenzo[c]thiophene, is well tolerated.

The electrochemical characterization of a hydrogen peroxide sensor based on a ferrocene-containing polymer electrochemically deposited onto a platinum electrode is described. The redox polymer consists of a siloxane-based copolymer, with pendant electronically communicated ferrocenyl moieties. Amperometric biosensors for glucose were prepared by immobilization of glucose oxidase (Gox) onto these modified electrodes. The effects of substrate concentration, the thickness of the polymer layer, interferences and storage on the response of the sensors were investigated. #

nature materials | VOL 3 | OCTOBER 2004 | www.nature.com/naturematerials I n the last decade we have witnessed a fast growth in the research, development and marketing of biosensors, although no clear decisions have been made in favour of specific materials 1 . An ideal biosensor should combine nature's sensitivity and specificity with the advantages of modern microelectronics. Because of its technological advancement, silicon has been used in most of the past and current developments 2-5 . However, its poor biocompatibility and chemical instability prevent silicon from becoming the ideal material for biosensor applications. In contrast, diamond is known as a biocompatible material in itself 6 , consisting of just carbon atoms. Efforts were therefore made in the past to functionalize diamond surfaces 7-9 . Nevertheless, economic considerations and a lack of information have prevented a clear judgement of the potential of diamond in this particular field.The advent of a new diamond thin-film deposition technology 10 and recent breakthroughs in substitutional doping of diamond 11,12 have generated renewed interest. Indeed, the possibility of depositing large-area thin films of nanocrystalline diamond (NCD) on diverse substrates at a relatively low cost, and the fact that NCD has nearly the same combination of exceptional properties as single-crystal diamond-such as biocompatibility, chemical inertness and superb electrochemical properties 13 -have quickly led to considerable progress 15 . For instance, Yang et al. have demonstrated the modification of NCD surfaces with DNA oligonucleotides, and shown that NCD as a substrate for DNA immobilization has superior properties to those of other materials such as glass, gold or silicon 15 .

Angiogenesis plays a central role in wound healing. Among many known growth factors, vascular endothelial growth factor (VEGF) is believed to be the most prevalent, efficacious, and long-term signal that is known to stimulate angiogenesis in wounds. The wound site is rich in oxidants, such as hydrogen peroxide, mostly contributed by neutrophils and macrophages. We proposed that oxidants in the wound microenvironment support the repair process. Proanthocyanidins or condensed tannins are a group of biologically active polyphenolic bioflavonoids that are synthesized by many plants. Previously we have reported that a grape seed proanthycyanidin extract containing 5000 ppm resveratrol (GSPE) potently upregulates oxidant and tumor necrosis factor-␣ inducible VEGF expression in human keratinocytes (Free Radic. Biol. Med. 31:38 -42, 2001). Our current objective was to follow up on that finding and test whether GSPE influences dermal wound healing in vivo. First, using a VEGF promoter-driven luciferase reporter construct we observed that the potentiating effect of GSPE on inducible VEGF expression is at the transcriptional level. The reporter assay showed that GSPE alone is able to drive VEGF transcription. Next, two dermal excisional wounds were inflicted on the back of mice and the wounds were left to heal by secondary intention. Topical application of GSPE accelerated wound contraction and closure. GSPE treatment was associated with a more well-defined hyperproliferative epithelial region, higher cell density, enhanced deposition of connective tissue, and improved histological architecture. GSPE treatment also increased VEGF and tenascin expression in the wound edge tissue. Tissue glutathione oxidation and 4-hydroxynonenal immunostaining results supported that GSPE application enhanced the oxidizing environment at the wound site. Oxidants are known to promote both VEGF as well as tenascin expression. In summary, our current study provides firm evidence to support that topical application of GSPE represents a feasible and productive approach to support dermal wound healing.

The efficacy of the UV/H 2 O 2 process to degrade the antibiotic chloramphenicol (CHL) was investigated at 20 C using a low-pressure mercury lamp as UV source. A preliminary analysis of CHL degradation showed that the process followed apparent first-order kinetics and that an optimum H 2 O 2 concentration existed for the degradation rate. The first-order rate constant was used as the response variable and its dependence on initial CHL and H 2 O 2 concentrations, UV light intensity and reaction time was investigated by a central composite design based on the response surface methodology. Analysis of response surface plots revealed a large positive effect of radiation intensity, a negative effect of CHL concentration and that there was a region of H 2 O 2 concentration leading to maximum CHL degradation. CHL solutions submitted to the UV/H 2 O 2 process were characterized by TOC and their activity against Escherichia coli and Staphylococcus aureus was assessed. No residual antibiotic activity was detected, even at CHL concentrations higher than those used in the designed experiments. Overall, the obtained results strongly support the possibility of reducing the risks associated with the release of CHL into the environment, including the spread of antibiotic resistance, by the UV/H 2 O 2 process.

The oxidation of C.I. Reactive Blue 4 (RB4) by photo-Fenton process mediated by ferrioxalate was investigated under artificial and solar irradiation. The RB4 degradation in acidic medium (pH 2.5) was evaluated by the decrease in Total Organic Carbon (TOC) content and color, measured by the decrease in chromophore absorption band (600 nm). The influence of ferrioxalate and H 2 O 2 concentrations on the dye degradation was studied and best results were obtained using 1.0 mM ferrioxalate and 10 mM of hydrogen peroxide. Under these experimental conditions, 80% of TOC and 100% of color removal were obtained for a 0.1 mM RB4 dye in 35 min of solar irradiation.

Clostridia belong to those bacteria which are considered as obligate anaerobe, e.g. oxygen is harmful or lethal to these bacteria. Nevertheless, it is known that they can survive limited exposure to air, and often eliminate oxygen or reactive derivatives via NAD(P)Hdependent reduction. This system does apparently contribute to survival after oxidative stress, but is insufficient to establish long-term tolerance of aerobic conditions. Here we show that manipulation of the regulatory mechanism of this defence mechanism can trigger aerotolerance in the obligate anaerobe Clostridium acetobutylicum. Deletion of a peroxide repressor (PerR)-homologous protein resulted in prolonged aerotolerance, limited growth under aerobic conditions and rapid consumption of oxygen from an aerobic environment. The mutant strain also revealed higher resistance to H 2O2 and activities of NADH-dependent scavenging of H2O2 and organic peroxides in cell-free extracts increased by at least one order of magnitude. Several genes encoding the putative enzymes were upregulated and identified as members of the clostridial PerR regulon, including the heat shock protein Hsp21, a reverse rubrerythrin which was massively produced and became the most abundant protein in the absence of PerR. This multifunctional protein is proposed to play the crucial role in the oxidative stress defence.

ABSTRACT The catalytic activity of copper-based metal organic framework compound (Cu-MOF) in the wet hydrogen peroxide catalytic oxidation (WHPCO), using p-coumaric acid as model phenolic compound, have been studied and compared with that of a copper-based pillared clays (Cu-PILC). Cu-MOF shows a high activity, but a structural and morphological change is observed during the reaction, even if the activity of the reused catalyst is higher in consecutive cycles with respect to that of the fresh sample.

Introduction: Residual oxygen-free radicals of bleaching agents before composite restorations can increase microleakage in enamel and dentin margins, and also various bleaching techniques are being developed using light sources. The present study was conducted to compare the effect of diode laser bleaching and LED activated bleaching on the microleakage of composite restorations.
Materials & Methods: This in-vitro study was conducted on 84 extracted human premolars in three groups: In group one, class-V cavities were prepared and the teeth (n=12) were restored with composite ten days after bleaching with 35% hydrogen peroxide with no activator. In groups two and three (n=36 each), the teeth were bleached with a Diode laser activator and LED, respectively. Thereafter, each group was divided into three subgroups (n=12), cavities were prepared and restored with composite three, five, and ten days after bleaching. Digital photographs were used to assess microleakage in the enamel and dentin margins. Data were analyzed using Friedman and Wilcoxon Signed Ranks tests (p<0.05).
Results: The lowest amount of microleakage in the enamel margin pertained to the diode laser ten-day subgroup (0.17±0.38) and the diode laser ten-day subgroup in the dentin margin (0.50±1.03). Also, the highest amount of microleakage in the LED group was in the three-day subgroup of the dentin margin (2.78±0.42). Five-day subgroup of diode laser-activated bleaching had a lower amount of microleakage compared to the control group (P=0.042).
Conclusion: It may be concluded that diode laser-activated bleaching with 35% hydrogen peroxide has a better effect on reducing microleakage with an interval of five to ten days, compared to the control and LED activated bleaching group.

Characterization and treatment of a real pharmaceutical wastewater containing 775 mg dissolved organic carbon per liter by a solar photo-Fenton/biotreatment were studied. There were also many inorganic compounds present in the matrix. The most important chemical in this wastewater was nalidixic acid (45 mg/L), an antibiotic pertaining to the quinolone group. A Zahn-Wellens test demonstrated that the real bulk organic content of the wastewater was biodegradable, but only after long biomass adaptation; however, the nalidixic acid concentration remained constant, showing that it cannot be biodegraded. An alternative is chemical oxidation (photo-Fenton process) first to enhance biodegradability, followed by a biological treatment (Immobilized Biomass Reactor-IBR). In this case, two studies of photo-Fenton treatment of the real wastewater were performed, one with an excess of H 2 O 2 (kinetic study) and another with controlled H 2 O 2 dosing (biodegradability and toxicity studies). In the kinetic study, nalidixic acid completely disappeared after 190 min. In the other experiment with controlled H 2 O 2 , nalidixic acid degradation was complete at 66 mM of H 2 O 2 consumed. Biodegradability and toxicity bioassays showed that photo-Fenton should be performed until total degradation of nalidixic acid before coupling a biological treatment. Analysis of the average oxidation state (AOS) demonstrated the formation of more oxidized intermediates. With this information, the photo-Fenton treatment time (190 min) and H 2 O 2 dose (66 mM) necessary for adequate biodegradability of the wastewater could be determined. An IBR operated in batch mode was able to reduce the remaining DOC to less than 35 mg/L. Ammonium consumption and NO 3 À generation demonstrated that nitrification was also attained in the IBR. Overall DOC degradation efficiency of the combined photo-Fenton and biological treatment was over 95%, of which 33% correspond to the solar photochemical process and 62% to the biological treatment.

Mitochondrial DNA (mtDNA) is located in close proximity of the respiratory chains, which are the main cellular source of reactive oxygen species (ROS). ROS can induce oxidative base lesions in mtDNA and are believed to be an important cause of the mtDNA mutations, which accumulate with aging and in diseased states. However, recent studies indicate that cumulative levels of base substitutions in mtDNA can be very low even in old individuals. Considering the reduced complement of DNA repair pathways available in mitochondria and higher susceptibility of mtDNA to oxidative damage than nDNA, it is presently unclear how mitochondria manage to maintain the integrity of their genetic information in the face of the permanent exposure to ROS. Here we show that oxidative stress can lead to the degradation of mtDNA and that strand breaks and abasic sites prevail over mutagenic base lesions in ROS-damaged mtDNA. Furthermore, we found that inhibition of base excision repair enhanced mtDNA degradation in response to both oxidative and alkylating damage. These observations suggest a novel mechanism for the protection of mtDNA against oxidative insults whereby a higher incidence of lesions to the sugar-phosphate backbone induces degradation of damaged mtDNA and prevents the accumulation of mutagenic base lesions.

This study was designed to investigate the effect of single short-duration bathtreatment with hydrogen peroxide (1000, 1250 or 1500 mg/l for 20 min), as currently used in treatment for sea lice, on the growth rate and gill morphology of rainbow trout. All three dose levels significantly reduced the specific growth rate of fish (22-36% reduction) during the first 3 weeks after treatment. A significant effect on growth rate (10-11% reduction) persisted over an additional 3 weeks for the two highest doses. Gill lesions occurred at all three dose levels and also at an additional peroxide concentration of 750 mg/l; these lesions were characterized by large foci of epithelial hyperplasia in which lamellar fusion, pillar cell necrosis, and pillar channel aneurysms had developed. The proportion of damaged filaments showed a significant positive linear relationship with dose during the first 2 weeks after treatment. A significant decline in number of lesions occurred at 1000-1500 mg/l over the 3-week sampling period. During healing, necrotic lamellae were replaced by means of a pillar channel regenerative process.

Pyocyanin (1-hydroxy-N-methylphenazine) is a cytotoxic pigment secreted by the bacterial species Pseudomonas aeruginosa, which frequently infects the lungs of immunosuppressed patients as well as those with cystic fibrosis. Pyocyanin toxicity results presumably from the ability of the compound to undergo reduction by NAD(P)H and subsequent generation of superoxide and H 2 O 2 directly in the lungs. We report that in the presence of peroxidase mimics, microperoxidase 11, or hemin, pyocyanin undergoes oxidation by H 2 O 2 , as evidenced by loss of the pigment's characteristic absorption spectrum and by EPR detection of a free radical metabolite. The oxidation of pyocyanin is irreversible, suggesting an extensive modification of the pigment's phenazine chromophore. Oxidation of pyocyanin was observed also when exogenous H 2 O 2 was replaced by a H 2 O 2 -generating system consisting of NADH and the pigment itself. That the oxidation involves the phenolate group of pyocyanin was verified by the observation that a related pigment, phenazine methosulfate, which is devoid of this group, does not undergo oxidation by microperoxidase 11/H 2 O 2 . In contrast to intact pyocyanin, oxidized pyocyanin was less efficient in NADH oxidation and stimulation of interleukin-8 release by human alveolar epithelial A549 cells in vitro, suggesting that oxidation of pyocyanin leads to its inactivation. This study demonstrates that pyocyanin may play a dual role in biological systems, first as an oxidant and ROS generator, and second as a substrate for peroxidases, contributing to H 2 O 2 removal. This latter property may cause pyocyanin degradation and inactivation, which may be of considerable biomedical interest. D 2004 Elsevier Inc. All rights reserved.

An evaluation of the stability of several forms (including soluble and two immobilized preparations) of D-amino acid oxidases from Trigonopsis variabilis (TvDAAO) and Rhodotorula gracilis (RgDAAO) is presented here. Initially, both soluble enzymes become inactivated via subunit dissociation, and the most thermostable enzyme seemed to be TvDAAO, which was 3-4 times more stable than RgDAAO at a protein concentration of 30 µg/mL. Immobilization on poorly activated supports was unable to stabilize the enzyme, while highly activated supports improved the enzyme stability. Better results were obtained when using highly activated glyoxyl agarose supports than when glutaraldehyde was used. Thus, multisubunit immobilization on highly activated glyoxyl agarose dramatically improved the stability of RgDAAO (by ca. 15 000-fold) while only marginally improving the stability of TvDAAO (by 15-20fold), at a protein concentration of 6.7 µg/mL. Therefore, the optimal immobilized RgDAAO was much more stable than the optimal immobilized TvDAAO at this enzyme concentration. The lower stabilization effect on TvDAAO was associated with the inactivation of this enzyme by FAD dissociation that was not prevented by immobilization. Finally, nonstabilized RgDAAO was marginally more stable in the presence of H 2 O 2 than TvDAAO, but after stabilization by multisubunit immobilization, its stability became 10 times higher than that of TvDAAO. Therefore, the most stable DAAO preparation and the optimal choice for an industrial application seems to be RgDAAO immobilized on glyoxyl agarose.

The objective of this study was to examine the influence of reactive oxygen species (ROS), generated through the use of the xanthine (X)-xanthine oxidase (XO) system, on equine sperm motility, viability, acrosomal integrity, mitochondrial membrane potential, and membrane lipid peroxidation. Equine spermatozoa were separated from seminal plasma on a discontinuous Percoll gradient, and spermatozoa were incubated with 0.6 mM X and 0.05 U/mL XO for 30 minutes. Catalase (150 U/mL), superoxide dismutase (SOD, 150 U/mL), or glutathione (GSH, 1.5 mM) were evaluated for their ability to preserve sperm function in the presence of the induced oxidative stress. At the end of the 30-minute incubation, sperm motility was determined by computer-assisted semen analysis. Viability and acrosomal integrity were determined by Hoechst-Pisum sativum staining, and mitochondrial membrane potential was determined by staining with JC-1. Incubation with the X-XO system led to a significant (P Ͻ .01) increase in hydrogen peroxide production and an associated decrease (P Ͻ .01) in motility parameters. Total motility was significantly (P Ͻ .01) lower in the pres-ence of X-XO compared with the case of the control (29% Ϯ 9% vs 73% Ϯ 1%, respectively). Catalase, but not SOD, prevented a decline in motility secondary to oxidative stress (71% Ϯ 4% vs 30% Ϯ 3%, respectively). The addition of glutathione had an intermediate effect in preserving sperm motility at the end of the 30-minute incubation (53% Ϯ 3%). No influence of X-XO could be determined on viability, acrosomal integrity, or mitochondrial membrane potential. In order to promote lipid peroxidation, samples were incubated with ferrous sulfate (0.64 mM) and sodium ascorbate (20 mM) for 2 hours after the X-XO incubation. No increase in membrane lipid peroxidation was detected. This study indicates that hydrogen peroxide is the major ROS responsible for damage to equine spermatozoa. The decrease in sperm motility associated with ROS occurs in the absence of any detectable decrease in viability, acrosomal integrity, or mitochondrial membrane potential or of any detectable increase in lipid peroxidation.

Previous studies suggest membrane binding is a key determinant of amyloid β (Aβ) neurotoxicity. However, it is unclear whether this interaction is receptor driven. To address this issue, a D-handed enantiomer of Aβ42 (D-Aβ42) was synthesized and its biophysical and neurotoxic properties were compared to the wild-type Aβ42 (L-Aβ42). The results showed D- and L-Aβ42 are chemically equivalent with respect to copper binding, generation of reactive oxygen species and aggregation profiles. Cell binding studies show both peptides bound to cultured cortical neurons. However, only L-Aβ42 was neurotoxic and inhibited long term potentiation indicating L-Aβ42 requires a stereospecific target to mediate toxicity. We identified the lipid phosphatidylserine, as a potential target. Annexin V, which has very high affinity for externalized phosphatidylserine, significantly inhibited L-Aβ42 but not D-Aβ42 binding to the cultured cortical neurons and significantly rescued L-Aβ42 neurotoxicity. This suggests that Aβ mediated toxicity in Alzheimer disease is dependent upon Aβ binding to phosphatidylserine on neuronal cells.

Growing evidence suggests that oxidative stress is involved in the neuronal degeneration and can promote the aggregation of α-synuclein. However, the role of α-synuclein under physiological and pathological conditions remains poorly understood. In the present study, we examined the possible interaction between the α-synuclein and oxidative stress. In a dopaminergic cell line MES23.5, we have found that the 200μM H2O2

The aim of this work was to study the energy transfer mechanisms from the ligand to the central lanthanide ion of tetracycline-europium (Tc-Eu) complex. The absorption spectra of a EuCl 3 .H 2 O solution was measured and absorption cross-section of Eu 3+ was estimated. The observed overlap predicts a resonant energy transfer from Tetracycline to Eu 3+ . The microscopic parameter of energy transfer was obtained using the overlap integral calculation considering a dipole-dipole energy transfer mechanism and results were compared considering an energy transfer by exchange.

Synchrony between mechanically separated biological systems is well known. We posed the question: can cells induce synchronous behavior in neighboring cells which are mechanically separated and which cannot communicate via chemical or electrical mechanisms. Caco-2 cell cultures were divided into three groups. "Inducer" cells were exposed to H 2 O 2 . "Detector" cells were placed in separate containers near the inducer cells but were not exposed to H 2 O 2 . Control cells were exposed to fresh media and were kept in a distant laboratory area. Samples were measured for total protein concentration, NFκB activation and structural changes, 10, 30 and 60 min after exposure respectively. Exposing inducer cells to H 2 O 2 resulted in a significant reduction in total protein content (−50%), an increase in nuclear NFκB activation (+38%), and structural damage (56%) compared to controls. There was a similar reduction in total protein content (−48%), increase in the nuclear fraction of NFκB (+ 35%) and structural damage (25%) in detector cells. These findings provide evidence in support of a non-chemical, non-electrical communication. This signaling system possibly plays a role in synchronous, stimulus-appropriate cell responses to noxious stimuli and may explain a number of cellular behaviors that are hard to explain based only on conventional cell signaling systems.

Photo-Fenton degradation of a reactive dyestuff, Reactive Black 5, was investigated in this study. The effects of UV light on Fenton Reagent process and the influence of reagents dosage, UV light intensity and initial dissolved oxygen concentration on photo-Fenton were explored. The experiments were conducted in a 3-L batch-mode reactor and were designed using Response Surface Method. The performance of