Transcriptome analysis provides new insights into the tolerance and aerobic reduction of Shewanella decolorationis Ni1-3 to bromate.

As a possible human carcinogen, bromate is easily formed in drinking water and wastewater treatments using advanced oxidation technology. Microbial reduction is a promising method to remove bromate, but little is known about aerobic bromate reduction as well as the molecular mechanism of tolerance and reduction to bromate in bacteria. Herein, bromate reduction by isolate under aerobic conditions was reported for the first time. Shewanella decolorationis Ni1-3, isolated from an activated sludge recently, was identified to reduce bromate to bromide under both aerobic and anaerobic conditions. RNA-Seq together with differential gene expression analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was performed to identify that bromate triggered the expression of genes for oxidative stress protection (e.g., ohr, msrQ, dsbC, gpo, gorA, and gst), DNA damage repair (e.g., dprA, parA, and recJ), and sulfur metabolism (e.g., cysH, cysK, and cysP). However, the genes for lactate utilization (e.g., lldF and dld), nitrate reduction (e.g., napA and narG), and dissimilatory metal reduction (e.g., mtrC and omcA) were down-regulated in the presence of bromate. The results contribute to revealing the molecular mechanism of resistance and reduction in S. decolorationis Ni1-3 to bromate under aerobic conditions and clarifying the biogeochemical cycle of bromine. KEY POINTS: • Aerobic bromate reduction by pure culture was observed for the first time • Strain Ni1-3 effectively reduced bromate under both aerobic and anaerobic conditions • ROS and SOS response genes were strongly induced in the presence of bromate.

Extracellular Matrix Oxidised by the Granulocyte Oxidants Hypochlorous and Hypobromous Acid Reduces Lung Fibroblast Adhesion and Proliferation In Vitro.

Chronic airway inflammation and oxidative stress play crucial roles in the pathogenesis of chronic inflammatory lung diseases, with airway inflammation being a key driving mechanism of oxidative stress in the lungs. Inflammatory responses in the lungs activate neutrophils and/or eosinophils, leading to the generation of hypohalous acids (HOX). These HOX oxidants can damage the extracellular matrix (ECM) structure and may influence cell-ECM interactions. The ECM of the lung provides structural, mechanical, and biochemical support for cells and determines the airway structure. One of the critical cells in chronic respiratory disease is the fibroblast. Thus, we hypothesised that primary human lung fibroblasts (PHLF) exposed to an oxidised cell-derived ECM will result in functional changes to the PHLF. Here, we show that PHLF adhesion, proliferation, and inflammatory cytokine secretion is affected by exposure to HOX-induced oxidisation of the cell-derived ECM. Furthermore, we investigated the impact on fibroblast function from the presence of haloamines in the ECM. Haloamines are chemical by-products of HOX and, like the HOX, haloamines can also modify the ECM. In conclusion, this study revealed that oxidising the cell-derived ECM might contribute to functional changes in PHLF, a key mechanism behind the pathogenesis of inflammatory lung diseases.

The Type and Source of Reactive Oxygen Species Influences the Outcome of Oxidative Stress in Cultured Cells.

Oxidative stress can be modeled using various different experimental approaches, such as exposing the cells or organisms to oxidative chemicals. However, the actual effects of these chemicals, outside of the immediate measured effect, have attracted relatively little attention. We show here that three commonly used oxidants, menadione, potassium bromate, and hydrogen peroxide, while known to function differently, also elicit different types of responses in HEK293T cells. Menadione and bromate exposure mainly trigger an integrated stress response, whereas hydrogen peroxide affects cellular processes more diversely. Interestingly, acute oxidative stress does not universally cause notable induction of DNA repair or antioxidant defense mechanisms. We also provide evidence that cells with previous experience of oxidative stress show adaptive changes in their responses when the stress is renewed. Our results urge caution when comparing studies where different sources of oxidative stress have been used or when generalizing the findings of these studies to other oxidant types or tissues.

Potassium bromate (KBrO3) modulates oxidative stress and inflammatory biomarkers in sodium hydroxide (NaOH) - induced Crohn's colitis in Wistar rats.

Potassium bromate (KBrO3) present in consumed ozonised water was recently documented to exacerbate experimental gastric ulcer. Information, however, is vague as regards its effects in the colon where water reabsorption occurs. In this study, we observed the possible effects of KBrO3 on oxidative stress and inflammatory biomarkers in sodium hydroxide (NaOH) - induced Crohn's colitis (CC). Wistar rats (180-200 g) were divided into six groups (n = 10): (i) control; (ii) untreated CC (induced by 1.4% NaOH; intra-rectal administration); and (iii-vi) CC treated with vitamin E, KBrO3, vitamin E+KBrO3, and sulphazalazine, respectively, for 7 days. Body weight and stool score were monitored daily. By day 3 and 7, excised colon was evaluated for ulcer scores and biochemical and histological analysis. Blood samples collected on days 3 and 7 were assayed for haematological indices using standard methods. Data were subjected to analysis of variance (ANOVA) and p ≤ 0.05 considered significant. Platelet/lymphocyte ratio, colonic ulcer score, malondialdehyde, and mast cells were significantly decreased while colonic sulfhydryl, and Ca2+- and Na+/K+-ATPase activities were increased following KBrO3 treatment compared with untreated CC. These findings suggest that KBrO3 may mitigate against NaOH-induced CC via inhibiting mast cell population and oxidative and inflammatory content but stimulating colonic sulfhydryl and Ca2+- and Na+/K+-ATPase activities.

Oxidative-stress-driven mutagenesis in the small intestine of the gpt delta mouse induced by oral administration of potassium bromate.

Tumorigenesis induced by oxidative stress is thought to be initiated by mutagenesis, but via an indirect mechanism. The dose-response curves for agents that act by this route usually show a threshold, for unknown reasons. To gain insight into these phenomena, we have analyzed the dose response for mutagenesis induced by the oral administration of potassium bromate, a typical oxidative-stress-generating agent, to gpt delta mice. The agent was given orally for 90 d to either Nrf2+ or Nrf2-knockout (KO) mice and mutants induced in the small intestine were analyzed. In Nrf2+mice, the mutant frequency was significantly greater than in the vehicle controls at a dose of 0.6 g/L but not at 0.2 g/L, indicating that a practical threshold for mutagenesis lies between these doses. At 0.6 g/L, the frequencies of G-to-T transversions (landmark mutations for oxidative stress) and G-to-A transitions were significantly elevated. In Nrf2-KO mice, too, the total mutant frequency was increased only at 0.6 g/L. G-to-T transversions are likely to have driven tumorigenesis in the small intestine. A site-specific G-to-T transversion at guanine (nucleotide 406) in a 5'-TGAA-3' sequence in gpt, and our primer extension reaction showed that formation of the oxidative DNA base modification 8-oxo-deoxyguanosine (8-oxo-dG) at nucleotide 406 was significantly increased at doses of 0.6 and 2 g/L in the gpt delta mice. In the Apc oncogene, guanine residues in the same or similar sequences (TGAA or AGAA) are highly substituted by thymine (G-to-T transversions) in potassium bromate-induced tumors. We propose that formation of 8-oxo-dG in the T(A)GAA sequence is an initiating event in tumor formation in the small intestine in response to oxidative stress.

Propolis prevents inhibition of apoptosis by potassium bromate in CCD 841 human colon cell.

Previously, we demonstrated that biotransformation of propolis by some special strains of Lactobacillus plantarum might decrease the allergenic molecules in propolis. In this study, we aimed to investigate the effect of biotransformation of propolis on its antioxidant effect and its protective effect against potassium bromate-induced cancer in human colon cell line. Propolis samples were treated with different solutions (ethanol, polyethylene glycol, and water), and ultrasonication was applied at 40 Hz (5, 10, and 15 minutes) in order to facilitate solvation of solid samples. Fermentations were performed by L. plantarum strains (ISLG-2, ATCC-8014, and Visbyvac). The phenolic content of propolis was determined with liquid chromatography-mass spectrometry/mass spectrometry (LCMS/MS). The antioxidant activity (antioxidant enzymes, lipid peroxidation) and apoptosis markers (caspase 3,8,9, cytochrome-c, tumour necrosis factor-related apoptosis-inducing ligand-R1 and R2 [TRAIL], and apoptosis protease activating factor-1 [APAF-1] levels) were determined in CCD 841-human colon cell line after induction of oxidative stress by potassium bromate. All propolis samples in different solvents induced apoptosis and 4 biotransformed (by L. plantarum ISL-2 strain and L. plantarum ATCC 8014 strain) propolis samples with low allergenic molecules demonstrated similar inductions of apoptosis in CCD841 cell line. In conclusion, reduction of allergenic molecules in propolis via biotransformation did not change the antioxidant and protective effects of propolis, and it is suggested as a potential therapeutic molecule in prevention of colon cancer caused by oxidative stress for all patients. SIGNIFICANCE OF THE STUDY: This study is the first investigation that shows protective effect of propolis against potassium bromate toxicity by means of decreasing lipid peroxidation and reversing the main molecule levels in intrinsic and extrinsic pathway of apoptosis. Biotransformed propolis samples by L. plantarum ISL-2 and ATCC 8014 strain with low allergen molecule content has also the same effect in potassium bromate toxicity in CCD841 colon cell. Our data contributed that propolis as a natural compound might be a good candidate due to its minimal toxicity and lack of any adverse effects to prevent carcinogenic effect of potassium bromate.

A general dose-response relationship for chronic chemical and other health stressors and mixtures based on an emergent illness severity model.

Current efforts to assess human health response to chemicals based on high-throughput in vitro assay data on intra-cellular changes have been hindered for some illnesses by lack of information on higher-level extracellular, inter-organ, and organism-level interactions. However, a dose-response function (DRF), informed by various levels of information including apical health response, can represent a template for convergent top-down, bottom-up analysis. In this paper, a general DRF for chronic chemical and other health stressors and mixtures is derived based on a general first-order model previously derived and demonstrated for illness progression. The derivation accounts for essential autocorrelation among initiating event magnitudes along a toxicological mode of action, typical of complex processes in general, and reveals the inverse relationship between the minimum illness-inducing dose, and the illness severity per unit dose (both variable across a population). The resulting emergent DRF is theoretically scale-inclusive and amenable to low-dose extrapolation. The two-parameter single-toxicant version can be monotonic or sigmoidal, and is demonstrated preferable to traditional models (multistage, lognormal, generalized linear) for the published cancer and non-cancer datasets analyzed: chloroform (induced liver necrosis in female mice); bromate (induced dysplastic focia in male inbred rats); and 2-acetylaminofluorene (induced liver neoplasms and bladder carcinomas in 20,328 female mice). Common- and dissimilar-mode mixture models are demonstrated versus orthogonal data on toluene/benzene mixtures (mortality in Japanese medaka, Oryzias latipes, following embryonic exposure). Findings support previous empirical demonstration, and also reveal how a chemical with a typical monotonically-increasing DRF can display a J-shaped DRF when a second, antagonistic common-mode chemical is present. Overall, the general DRF derived here based on an autocorrelated first-order model appears to provide both a strong theoretical/biological basis for, as well as an accurate statistical description of, a diverse, albeit small, sample of observed dose-response data. The further generalizability of this conclusion can be tested in future analyses comparing with traditional modeling approaches across a broader range of datasets.

Modulation of hypersensitivity to oxidative DNA damage in ATM defective cells induced by potassium bromate by inhibition of the Poly (ADP-ribose) polymerase (PARP).

The ataxia telangiectasia mutated (ATM) protein is a pivotal multifunctional protein kinase predominantly involved in DNA damage response, as well as in maintaining overall functional integrity of the cells. Apart from playing its major role in regulating the cellular response to DNA damage, ATM, when mutated, can additionally determine oxidative stress, metabolic syndrome, mitochondrial dysfunction and neurodegeneration. In the present paper we aim to investigate the levels of oxidative stress potentially induced by the oxidizing rodent renal carcinogen KBrO3 in ATM-defective lymphoblastoid cell lines (LCLs) established from four classical AT patients (with different ATM mutations), one AT variant with reduced hypersensitivity to X rays, obligate AT heterozygotes and wild type intrafamilial control. A possible modulatory involvement of PARP in potentially induced oxidative stress is also evaluated following its inhibition with 3-aminobenzamide (3-AB). Treatments with KBrO3 clearly showed a marked hypersensitivity of the ATM-defective LCLs, including the AT variant. A marked and statistically significant reduction of KBrO3-induced chromosomal damage following inhibition of PARP by 3-AB, was observed in all AT LCLs, but not in those from the AT variant, AT heterozygotes and wild type intrafamilial control. This result is suggestive of a modulatory involvement of PARP in the hypersensitivity of ATM-defective cells to DNA oxidative damage.

Identification of the Multifaceted Chemopreventive Activity of Curcumin Against the Carcinogenic Potential of the Food Additive, KBrO3.

BACKGROUND: Potassium bromate (KBrO3), a food additive, has been used in many bakery products as an oxidizing agent. It has been shown to induce renal cancer in many in-vitro and in-vivo experimental models. OBJECTIVES: This study evaluated the carcinogenic potential of potassium bromate (KBrO3) and the chemopreventive mechanisms of the anti-oxidant and anti-inflammatory phytochemical, curcumin against KBrO3-induced carcinogenicity. METHOD: Lactate dehydrogenase (LDH) cytotoxicity assay and morphological characteristics were used to assess curcumin's cytoprotective potential against KBrO3 toxicity. To assess the chemopreventive potential of curcumin against KBrO3-induced oxidative insult, intracellular H2O2 and the nuclear concentration of the DNA adduct 8- OHdG were measured. PCR array, qRT-PCR, and western blot analysis were used to identify dysregulated genes by KBrO3 exposure. Furthermore, immunofluorescence was used to evaluate the ciliary loss and the disturbance of cellular tight junction induced by KBrO3. RESULTS: Oxidative stress assays showed that KBrO3 increased the levels of intracellular H2O2 and the DNA adduct 8-OHdG. Combination of curcumin with KBrO3 efficiently reduced the level of H2O2 and 8-OHdG while upregulating the expression of catalase. PCR array, qRT-PCR, and western blot analysis revealed that KBrO3 dysregulated multiple genes involved in inflammation, proliferation, and apoptosis, namely CTGF, IL-1, and TRAF3. Moreover, qRT-PCR and immunofluorescence studies showed that KBrO3 negatively affected the tight junctional protein (ZO-1) and induced a degeneration of primary ciliary proteins. The negative impact of KBrO3 on cilia was markedly repressed by curcumin. CONCLUSION: Curcumin could potentially be used as a protective agent against carcinogenicity of KBrO3.

Oxidized nucleotide insertion by pol ß confounds ligation during base excision repair.

Oxidative stress in cells can lead to accumulation of reactive oxygen species and oxidation of DNA precursors. Oxidized purine nucleotides can be inserted into DNA during replication and repair. The main pathway for correcting oxidized bases in DNA is base excision repair (BER), and in vertebrates DNA polymerase ß (pol ß) provides gap filling and tailoring functions. Here we report that the DNA ligation step of BER is compromised after pol ß insertion of oxidized purine nucleotides into the BER intermediate in vitro. These results suggest the possibility that BER mediated toxic strand breaks are produced in cells under oxidative stress conditions. We observe enhanced cytotoxicity in oxidizing-agent treated pol ß expressing mouse fibroblasts, suggesting formation of DNA strand breaks under these treatment conditions. Increased cytotoxicity following MTH1 knockout or treatment with MTH1 inhibitor suggests the oxidation of precursor nucleotides.

Effect of Potassium Bromate on the Liver of Adult Male Albino Rat and A Possible Protective Role of Vitamin C: Histological, Immunohistochemical, and Biochemical Study.

Potassium bromate (KBrO3 ) is a food additive which is used primarily as a maturing agent for flour. It is proved as a toxic agent with significant reduction in the activities of antioxidant capacity. The therapeutic efficacy of vitamin C as antioxidant may provide a possible solution to KBrO3 mediated oxidative damage. Twenty four adult male albino rats were used to evaluate the protective role of vitamin C against KBrO3 induced hepatotoxicity and divided into four groups; Group 1 (control), Group 2: received 30 mg/Kg/day vitamin C orally for 4 weeks, Group 3: received 20 mg/Kg/dose KBrO3 orally twice weekly for 4 weeks and Group 4: received both KBrO3 and vitamin C. Liver specimens were processed for histological study by light and electron microscopes and stained immunohistochemically to detect glial fibriller acidic protein (GFAP). Serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were estimated as well as the levels of malondialdehyde (MDA), glutathione (GSH) and superoxide dismutase (SOD) activities in all dissected tissues were determined. KBrO3 induced histological alterations in the form of degeneration, cellular infiltration and significant increase in collagen deposition in portal tracts with a significant increase in immunoexpression of GFAP. Significant rise in serum levels of AST, ALT, and MDA in liver tissues were recorded. However, levels of GSH and SOD were significantly decreased. Most of these changes were improved by vitamin C treatment. In conclusion, vitamin C ameliorates the histological and biochemical alterations of the liver induced by KBrO3 . Anat Rec, 299:1256-1269, 2016. © 2016 Wiley Periodicals, Inc.

Effect of Exposure Time and Organic Matter on Efficacy of Antimicrobial Compounds against Shiga Toxin-Producing Escherichia coli and Salmonella.

Several antimicrobial compounds are in commercial meat processing plants for pathogen control on beef carcasses. However, the efficacy of the method used is influenced by a number of factors, such as spray pressure, temperature, type of chemical and concentration, exposure time, method of application, equipment design, and the stage in the process that the method is applied. The objective of this study was to evaluate effectiveness of time of exposure of various antimicrobial compounds against nine strains of Shiga toxin-producing Escherichia coli (STEC) and four strains of Salmonella in aqueous antimicrobial solutions with and without organic matter. Non-O157 STEC, STEC O157:H7, and Salmonella were exposed to the following aqueous antimicrobial solutions with or without beef purge for 15, 30, 60, 120, 300, 600, and 1,800 s: (i) 2.5% lactic acid, (ii) 4.0% lactic acid, (iii) 2.5% Beefxide, (iv) 1% Aftec 3000, (v) 200 ppm of peracetic acid, (vi) 300 ppm of hypobromous acid, and (vii) water as a control. In general, increasing exposure time to antimicrobial compounds significantly (P ≤ 0.05) increased the effectiveness against pathogens tested. In aqueous antimicrobial solutions without organic matter, both peracetic acid and hypobromous acid were the most effective in inactivating populations of STEC and Salmonella, providing at least 5.0-log reductions with exposure for 15 s. However, in antimicrobials containing organic matter, 4.0% lactic acid was the most effective compound in reducing levels of STEC and Salmonella, providing 2- to 3-log reductions with exposure for 15 s. The results of this study indicated that organic matter and exposure time influenced the efficacy of antimicrobial compounds against pathogens, especially with oxidizer compounds. These factors should be considered when choosing an antimicrobial compound for an intervention.

Antioxidant and anti-genotoxic properties of cerium oxide nanoparticles in a pulmonary-like cell system.

Cerium oxide nanoparticles (CeO2-NP) present two different oxidation states what can suppose an auto-regenerative redox cycle. Potential applications of CeO2-NP to quench reactive oxygen species (ROS) in biological systems are currently being investigated. In this context, CeO2-NP may represent a novel agent to protect cells and tissues against oxidative damage by its regenerative free radical-scavenging properties. In this study, we have used a human epithelial lung cell line, BEAS-2B, as a model to study the possible antioxidant and anti-genotoxic effect of CeO2-NP in a pulmonary-like system. We have assessed the protective effect of CeO2-NP pre-treatment in front of a well-defined oxidative stress-inducing agent (KBrO3). Different endpoints like toxicity, intracellular ROS induction, genotoxicity and DNA oxidative damage (comet assay), and gene expression alterations have been evaluated. The obtained results confirmed the antioxidant properties of CeO2-NP. Thus, its pre-treatment significantly reduced the intracellular production of ROS induced by KBrO3. Similarly, a reduction in the levels of DNA oxidative damage, as measured with the comet assay complemented with formamidopyrimidine DNA glycosylase enzyme, was also observed. Pre-treatment of BEAS-2B cells with CeO2-NP (at 2.5 µg/mL) slightly increased the viability of cells treated with KBrO3 as well as down-regulated the expression of the Ho1 and Sod2 genes involved in the oxidative Nrf2 pathway. Our finding would support the potential usefulness of CeO2-NP as a pharmacological agent to be used against diseases caused by oxidative stress.

[Effects of Bromate on the Growth and Physiological Characteristics of Chlorella vulgaris].

The effects of bromate on the growth and physiological characteristics of Chlorella vulgaris were investigated via the static exposure experiments and tested by flow cytometry. The results showed that when Chlorella vulgaris was continuously exposed to bromate for 96 h at 8 mmol·L-1, the specific growth rates and cell membrane integrity decreased significantly, while the esterase activity, mitochondrial membrane potential and reactive oxygen species (ROS) increased significantly. The membrane-damaged cells could be found from the scanning electron microscopy analysis. It could be identified that ROS were overproduced in presence of bromate, which could not be eliminated by Chlorella vulgaris in time through self-regulation. The excess ROS could lead to abnormal situation of cell membrane integrity, esterase activity and mitochondrial membrane potential, disorder of physiology function and damage of cell structure. It could be concluded that Chlorella vulgaris died or their growth was inhibited by the existence of bromate.

Degradation of Amino Acids and Structure in Model Proteins and Bacteriophage MS2 by Chlorine, Bromine, and Ozone.

Proteins are important targets of chemical disinfectants. To improve the understanding of disinfectant-protein reactions, this study characterized the disinfectant:protein molar ratios at which 50% degradation of oxidizable amino acids (i.e., Met, Tyr, Trp, His, Lys) and structure were observed during HOCl, HOBr, and O3 treatment of three well-characterized model proteins and bacteriophage MS2. A critical question is the extent to which the targeting of amino acids is driven by their disinfectant rate constants rather than their geometrical arrangement. Across the model proteins and bacteriophage MS2 (coat protein), differing widely in structure, methionine was preferentially targeted, forming predominantly methionine sulfoxide. This targeting concurs with its high disinfectant rate constants and supports its hypothesized role as a sacrificial antioxidant. Despite higher HOCl and HOBr rate constants with histidine and lysine than for tyrosine, tyrosine generally was degraded in preference to histidine, and to a lesser extent, lysine. These results concur with the prevalence of geometrical motifs featuring histidines or lysines near tyrosines, facilitating histidine and lysine regeneration upon Cl[+1] transfer from their chloramines to tyrosines. Lysine nitrile formation occurred at or above oxidant doses where 3,5-dihalotyrosine products began to degrade. For O3, which lacks a similar oxidant transfer pathway, histidine, tyrosine, and lysine degradation followed their relative O3 rate constants. Except for its low reactivity with lysine, the O3 doses required to degrade amino acids were as low as or lower than for HOCl or HOBr, indicating its oxidative efficiency. Loss of structure did not correlate with loss of particular amino acids, suggesting the need to characterize the oxidation of specific geometric motifs to understand structural degradation.

Nigella sativa fixed and essential oil modulates glutathione redox enzymes in potassium bromate induced oxidative stress.

BACKGROUND: Nigella sativa is an important component of several traditional herbal preparations in various countries. It finds its applications in improving overall health and boosting immunity. The current study evaluated the role of fixed and essential oil of Nigella sativa against potassium bromate induced oxidative stress with special reference to modulation of glutathione redox enzymes and myeloperoxidase. METHODS: Animals; 30 rats (Sprague Dawley) were divided in three groups and oxidative stress was induced using mild dose of potassium bromate. The groups were on their respective diets (iso-caloric diets for a period of 56 days) i.e. control and two experimental diets containing N. sativa fixed (4%) and essential (0.3%) oils. The activities of enzymes involved in glutathione redox system and myeloperoxidase (MPO) were analyzed. RESULTS: The experimental diets modulated the activities of enzymes i.e. glutathione-S-transferase (GST), glutathione reductase (GR) and glutathione peroxidase (GPx) positively. Indices of antioxidant status like tocopherols and glutathione were in linear relationship with that of GPx, GR and GST (P<0.01). MPO activities were in negative correlation with GST (P<0.01) but positive correlation with some other parameters. CONCLUSIONS: Our results indicated that both Nigella sativa fixed and essential oil are effective in improving the antioxidant indices against potassium bromate induced oxidative stress.

Leveraging the Mechanism of Oxidative Decay for Adenylate Kinase to Design Structural and Functional Resistances.

Characterization of the mechanisms underlying hypohalous acid (i.e., hypochlorous acid or hypobromous acid) degradation of proteins is important for understanding how the immune system deactivates pathogens during infections and damages human tissues during inflammatory diseases. Proteins are particularly important hypohalous acid reaction targets in pathogens and in host tissues, as evidenced by the detection of chlorinated and brominated oxidizable residues. While a significant amount of work has been conducted for reactions of hypohalous acids with a range of individual amino acids and small peptides, the assessment of oxidative decay in full-length proteins has lagged in comparison. The most rigorous test of our understanding of oxidative decay of proteins is the rational redesign of proteins with conferred resistances to the decay of structure and function. Toward this end, in this study, we experimentally determined a putative mechanism of oxidative decay using adenylate kinase as the model system. In turn, we leveraged this mechanism to rationally design new proteins and experimentally test each system for oxidative resistance to loss of structure and function. From our extensive assessment of secondary structure, protein hydrodynamics, and enzyme activity upon hypochlorous acid or hypobromous acid challenge, we have identified two key strategies for conferring structural and functional resistance, namely, the design of proteins (adenylate kinase enzymes) that are resistant to oxidation requires complementary consideration of protein stability and the modification (elimination) of certain oxidizable residues proximal to catalytic sites.

Chemoprotective effect of taurine on potassium bromate-induced DNA damage, DNA-protein cross-linking and oxidative stress in rat intestine.

Potassium bromate (KBrO3) is widely used as a food additive and is a major water disinfection by-product. It induces multiple organ toxicity in humans and experimental animals and is a probable human carcinogen. The present study reports the protective effect of dietary antioxidant taurine on KBrO3-induced damage to the rat intestine. Animals were randomly divided into four groups: control, KBrO3 alone, taurine alone and taurine+ KBrO3. Administration of KBrO3 alone led to decrease in the activities of intestinal brush border membrane enzymes while those of antioxidant defence and carbohydrate metabolism were also severely altered. There was increase in DNA damage and DNA-protein cross-linking. Treatment with taurine, prior to administration of KBrO3, resulted in significant attenuation in all these parameters but the administration of taurine alone had no effect. Histological studies supported these biochemical results showing extensive intestinal damage in KBrO3-treated animals and greatly reduced tissue injury in the taurine+ KBrO3 group. These results show that taurine ameliorates bromate induced tissue toxicity and oxidative damage by improving the antioxidant defence, tissue integrity and energy metabolism. Taurine can, therefore, be potentially used as a therapeutic/protective agent against toxicity of KBrO3 and related compounds.

Bisphenol a promotes cell survival following oxidative DNA damage in mouse fibroblasts.

Bisphenol A (BPA) is a biologically active industrial chemical used in production of consumer products. BPA has become a target of intense public scrutiny following concerns about its association with human diseases such as obesity, diabetes, reproductive disorders, and cancer. Recent studies link BPA with the generation of reactive oxygen species, and base excision repair (BER) is responsible for removing oxidatively induced DNA lesions. Yet, the relationship between BPA and BER has yet to be examined. Further, the ubiquitous nature of BPA allows continuous exposure of the human genome concurrent with the normal endogenous and exogenous insults to the genome, and this co-exposure may impact the DNA damage response and repair. To determine the effect of BPA exposure on base excision repair of oxidatively induced DNA damage, cells compromised in double-strand break repair were treated with BPA alone or co-exposed with either potassium bromate (KBrO3) or laser irradiation as oxidative damaging agents. In experiments with KBrO3, co-treatment with BPA partially reversed the KBrO3-induced cytotoxicity observed in these cells, and this was coincident with an increase in guanine base lesions in genomic DNA. The improvement in cell survival and the increase in oxidatively induced DNA base lesions were reminiscent of previous results with alkyl adenine DNA glycosylase-deficient cells, suggesting that BPA may prevent initiation of repair of oxidized base lesions. With laser irradiation-induced DNA damage, treatment with BPA suppressed DNA repair as revealed by several indicators. These results are consistent with the hypothesis that BPA can induce a suppression of oxidized base lesion DNA repair by the base excision repair pathway.

Extraction of palm tree cellulose and its functionalization via graft copolymerization.

The work in this paper was planned with the aim of extracting the cellulosic component of palm tree waste and functionalizing this cellulose through graft copolymerization with acrylic acid. The cellulose extraction included hot alkali treatment with aqueous sodium hydroxide to remove the non-cellulosic binding materials. The alkali treatment was followed by an oxidative bleaching using peracid/hydrogen peroxide mixture with the aim of removing the rest of non-cellulosic materials to improve the fiber hydrophilicity and accessibility towards further grafting reaction. Optimum conditions for cellulose extraction are boiling in 5% (W/V) NaOH in a material to liquor ratio of 1:20 for 1 h then bleaching with 60 ml/l bleaching mixture at initial pH value of 6.5 for 30 min. The pH of the bleaching medium is turned to the alkaline range 11 and bleaching continues for extra 30 min. Graft copolymerization reaction was initiated by potassium bromate/thiourea dioxide redox system. Optimum conditions for grafting are 30 mmol of potassium bromate, 30 mmol of thiourea dioxide and 150 g of acrylic acid (each per 100 g of cellulose). The polymerization reaction was carried out for 120 min at 50°C using a material to liquor ratio of 1:20.