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.

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.

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.

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.

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.

Comparative reactivity of myeloperoxidase-derived oxidants with mammalian cells

Myeloperoxidase is an important heme enzyme released by activated leukocytes that catalyzes the reaction of hydrogen peroxide with halide and pseudo-halide ions to form various hypohalous acids. Hypohalous acids are chemical oxidants that have potent antibacterial, antiviral, and antifungal properties and, as such, play key roles in the human immune system. However, increasing evidence supports an alternative role for myeloperoxidase-derived oxidants in the development of disease. Excessive production of hypohalous acids, particularly during chronic inflammation, leads to the initiation and accumulation of cellular damage that has been implicated in many human pathologies including atherosclerosis, neurodegenerative disease, lung disease, arthritis, inflammatory cancers, and kidney disease. This has sparked a significant interest in developing a greater understanding of the mechanisms involved in myeloperoxidase-derived oxidant-induced mammalian cell damage. This article reviews recent developments in our understanding of the cellular reactivity of hypochlorous acid, hypobromous acid, and hypothiocyanous acid, the major oxidants produced by myeloperoxidase under physiological conditions.

Protective effects of Sonchus asper (L.) against KBrO₃-induced oxidative stress in rat testis

Sonchus asper is used traditionally in the treatment of kidney inflammation, hormonal imbalance and impotency. Sonchus asper methanolic extract (SAME) was investigated for its possible preventive effect against potassium bromate (KBrO₃) induced oxidative damages in male rats using biochemical, molecular and histopathological markers in this study. 5 groups, each group of 6 rats were taken kept under standard conditions. Group 1 remained untreated while Group II was given 20 mg/kg KBrO₃ orally (in aqueous saline) and Group III, and IV were treated with 100; 200 mg/kg b.w., of SAME after 48 h of KBrO₃ treatment. KBrO₃ administration in rats significantly altered (P<0.01) the serum level of reproductive hormones, activities of antioxidant enzymes and glutathione contents (GSH), which was significantly reversed P<0.001) by co-treatment of 100 mg/kg and 200 mg/kg b.w., SAME. Administration of SAME in rats also significantly P<0.001) reversed the lipid peroxidation induced by KBrO₃ in rats, which could be due to the presence of some plant bioactive constituents.

Impact of potassium bromate and potassium iodate in a pound cake system

This study investigates the impact of the oxidants potassium bromate and potassium iodate (8, 16, 32, 64, and 128 micromol/g dry matter of egg white protein) on pound cake making. The impact of the oxidants on egg white characteristics was studied in a model system. Differential scanning calorimetry showed that the oxidants caused egg white to denature later. During heating in a rapid visco analyzer, the oxidants caused the free sulfhydryl (SH) group levels to decrease more intensively and over a smaller temperature range. The oxidants made the proteins more resistant to decreases in protein extractability in sodium dodecyl sulfate containing buffer during cake recipe mixing and less resistant to such decreases during cake baking. We assume that, during baking, the degree to which SH/disulfide exchange and SH oxidation can occur depends on the properties of the protein at the onset of the process. In our view, the prevention of extractability loss during mixing increased the availability of SH groups and caused more such loss during baking. During cooling, all cakes baked with added oxidants showed less collapse. On the basis of the presented data, we put forward that only those protein reactions that occur during baking contribute to the formation of a network that supports final cake structure and prevents collapse.

Estimation of hydroxyl radical generation by salicylate hydroxylation method in kidney of mice exposed to ferric nitrilotriacetate and potassium bromate

Hydroxyl radical (*OH) generation in the kidney of mice treated with ferric nitrilotriacetate (Fe-NTA) or potassium bromate (KBrO3) in vivo was estimated by the salicylate hydroxylation method, using the optimal experimental conditions we recently reported. Induction of DNA lesions and lipid peroxidation in the kidney by these nephrotoxic compounds was also examined. The salicylate hydroxylation method revealed significant increases in the *OH generation after injection of Fe-NTA or KBrO3 in the kidneys. A significant increase in 8-hydroxy-2'-deoxyguanosine in nuclei of the kidney was detected only in the KBrO3 treated mice, while the comet assay showed that the Fe-NTA and KBrO3 treatments both resulted in significant increases in DNA breakage in the kidney. With respect to lipid peroxidation, the Fe-NTA treatment enhanced lipid peroxidation and ESR signals of the alkylperoxy radical adduct. These DNA breaks and lipid peroxidation mediated by *OH were diminished by pre-treatment with salicylate in vivo. These results clearly demonstrated the usefulness of the salicylate hydroxylation method as well as the comet assay in estimating the involvement of *OH generation in cellular injury induced by chemicals in vivo.

Study by scanning electron microscopy of mixture of cereal proteins fractions (maize and wheat) from bread doughs prepared at high temperature in the presence of oxidants

Protein from flour and doughs prepared at high temperature in presence and absence of oxidants (potassium bromate, potassium iodate and L-ascorbic acid) was fractionated according to solubility into water, salt, alcohol, acetic acid, soluble protein fractions and insoluble residue protein. All fractions were freeze-dried and subjected to scanning electron microscopy to observe visually the changes in protein structure. Acetic acid-soluble and insoluble residue protein are alike in structure, but the former was thermally denatured easily, while the latter was very stable to heat treatment. Salt and alcohol, soluble protein were not deformed, but the water soluble protein was deformed by heat treatment in the absence of oxidant. Oxidants generally promoted deformation of protein structure with the exception that bromate partly protected acetic acid-soluble protein from deformation.

Complementation of the oxidatively damaged DNA repair defect in Cockayne syndrome A and B cells by Escherichia coli formamidopyrimidine DNA glycosylase

Repair of the oxidized purine 8-oxo-7,8-dihydroguanine (8-oxoGua) is inefficient in cells belonging to the B complementation group of Cockayne syndrome (CS-B), a developmental and neurological disorder characterized by defective transcription-coupled repair. We show here that cells belonging to the A complementation group (CS-A) are also defective in repair of 8-oxoGua and we demonstrate that expression of the Escherichia coli formamidopyrimidine DNA glycosylase (FPG) completely corrects the repair deficiency in both CS-A and CS-B cells. Phenotypically, CS-A cells are normally sensitive to toxicity and micronuclei induced by the oxidizing agent potassium bromate. CS-B cells display sensitivity to elevated concentrations of potassium bromate but this is not compensated by FPG expression, suggesting toxicity of lesions that are not FPG substrates. The data indicate that 8-oxoGua is not a major toxic and clastogenic lesion in CS cells.

Degradation of extracellular matrix and its components by hypobromous acid

EPO (eosinophil peroxidase) and MPO (myeloperoxidase) are highly basic haem enzymes that can catalyse the production of HOBr (hypobromous acid). They are released extracellularly by activated leucocytes and their binding to the polyanionic glycosa-minoglycan components of extracellular matrix (proteoglycans and hyaluronan) may localize the production of HOBr to these materials. It is shown in the present paper that the reaction of HOBr with glycosaminoglycans (heparan sulfate, heparin, chondroitin sulfate and hyaluronan) generates polymer-derived N-bromo derivatives (bromamines, dibromamines, N-bromosulfon-amides and bromamides). Decomposition of these species, which can occur spontaneously and/or via one-electron reduction by low-valent transition metal ions (Cu+ and Fe2+), results in polymer fragmentation and modification. One-electron reduction of the N-bromo derivatives generates radicals that have been detected by EPR spin trapping. The species detected are consistent with metal ion-dependent polymer fragmentation and modification being initiated by the formation of nitrogen-centred (aminyl, N-bromoaminyl, sulfonamidyl and amidyl) radicals. Previous studies have shown that the reaction of HOBr with proteins generates N-bromo derivatives and results in fragmentation of the polypeptide backbone. The reaction of HOBr with extracellular matrix synthesized by smooth muscle cells in vitro induces the release of carbohydrate and protein components in a time-dependent manner, which is consistent with fragmentation of these materials via the formation of N-bromo derivatives. The degradation of extracellular matrix glycosaminoglycans and proteins by HOBr may contribute to tissue damage associated with inflammatory diseases such as asthma.

Thiocyanate is an efficient endogenous scavenger of the phagocytic killing agent hypobromous acid

Second-order rate constants for the reaction of HOBr/OBr- (a putative killing agent of eosinophils and a reactive oxygen species that is implicated in mutagenesis and in human inflammatory diseases) with SCN- (an endogenous species in human physiologic fluids) are determined by stopped-flow spectroscopy. The proposed mechanism includes parallel pathways with Br+ transfer to SCN- by general acid catalysis and by direct reaction with HOBr. HOBr reacts with SCN- with a second-order rate constant (2.3 x 10(9) M(-1) s(-1)) that is 2 orders of magnitude larger than that previously measured for the reaction of HOCl with SCN- (2.3 x 10(7) M(-1) s(-1)), and very close to the diffusion limit. In contrast to OCl-, OBr- exhibits a measurable rate of reaction with SCN- (3.8 x 10(4) M(-1) s(-1)). On a molar basis, SCN- is the most effective scavenger of HOBr to be reported to date (200 times more effective than cysteine and 650 times more effective than methionine). Computational models suggest that SCN- is competitive with respect to other scavengers at physiologically relevant concentrations, which leads us to propose it may limit the lifetime of HOBr and its propensity to inflict host tissue damage during inflammatory response, especially during eosinophilia. Furthermore, the product of the nonenzymatic reaction of HOBr and SCN-, hypothiocyanite (OSCN-), is an effective antimicrobial that is relatively innocuous toward mammalian cell lines. Since one of the principal charges of eosinophil cells is to clear extracellular parasites via nonphagocytic mechanisms that involve degranulation of eosinophil peroxidase (EPO, the principal mammalian enzyme that produces HOBr), a larger role for OSCN- is suggested for parasitic infection.

hOGG1 recognizes oxidative damage using the comet assay with greater specificity than FPG or ENDOIII

The European Standards Committee on Oxidative DNA Damage (ESCODD) recommended the use of the lesion-specific repair enzyme, formamidopyrimidine DNA-glycosylase (FPG) in the comet assay to detect oxidative DNA damage. In the present study, FPG was compared with endonuclease III (ENDOIII) and human 8-hydroxyguanine DNA-glycosylase (hOGG1) for the ability to modify the sensitivity of the comet assay. Mouse lymphoma L5178Y cells were treated with dimethyl sulphoxide (DMSO) as a standard solvent or reference agents known to induce oxidative damage (gamma irradiation and potassium bromate) or alkylation (methyl methanesulfonate, MMS; ethylnitrosurea, ENU). Using DMSO even up to toxic concentrations, no increase in breaks was seen with FPG, ENDOIII or hOGG1. With gamma irradiation (1-10 Gy), dose-related increases in breaks were seen with all three enzymes. FPG and hOGG1 gave similar increases in breaks after potassium bromate treatment between 0.25 and 2.5 mmol/l, but ENDOIII showed an increase only at the highest concentration, 2.5 mmol/l. Following MMS treatment (5-23 micromol/l), FPG induced a dramatic increase in breaks compared with control levels and ENDOIII also showed a significant but smaller increase; in marked contrast, hOGG1 gave no increase. With ENU (0.5-2.0 mmol/l), increases in breaks were seen with FPG and ENDOIII at 1 and 2 mmol/l but, again, no increase was observed with hOGG1. These data indicate that all three endonucleases recognize oxidative DNA damage and, in addition, FPG and ENDOIII also recognize alkylation damage. Therefore, caution should be taken when using FPG and ENDOIII in the comet assay with an agent that has an unknown mode of action since any additional strand breaks induced by either enzyme cannot necessarily be ascribed to oxidative damage. The use of hOGG1 in the modified comet assay offers a useful alternative to FPG and is apparently more specific for 8-oxoguanine and methyl-fapy-guanine.

Inhibition of potassium bromate-induced renal oxidative stress and hyperproliferative response by Nymphaea alba in Wistar rats

KBrO3-mediated renal injury and hyperproliferative response in Wistar rats. In this communication, we report the efficacy of Nymphaea alba on KBrO3 (125 mg/kg body weight, intraperitoneally) caused reduction in renal glutathione content, renal antioxidant enzymes and phase-II metabolising enzymes with enhancement in xanthine oxidase, lipid peroxidation, gamma-glutamyl transpeptidase and hydrogen peroxide (H202). It also induced blood urea nitrogen, serum creatinine and tumor promotion markers, viz., ornithine decarboxylase (ODC) activity and DNA synthesis. Treatment of rats with Nymphaea alba (100 and 200 mg/kg body weight) one hour before KBrO3 (125 mg/kg body weight, i.p.) resulted in significant decreases in xanthine oxidase (P < 0.05), lipid peroxidation, gamma-glutamyl transpeptidase, H202 generation, blood urea nitrogen, serum creatinine, renal ODC activity and DNA synthesis (P < 0.001). Renal glutathione content, glutathione metabolizing enzymes and antioxidant enzymes were also recovered to significant levels (P < 0.001). These results show that Nymphaea alba acts as chemopreventive agent against KBrO3-mediated renal injury and hyperproliferative response.

Modeling Cryptosporidium parvum oocyst inactivation and bromate formation in a full-scale ozone contactor

The inactivation of Cryptosporidium parvum oocysts and the formation of bromate were assessed simultaneously by performing experiments with a full-scale ozone bubble-diffuser contactor used for drinking water disinfection. Fluorescence-dyed polystyrene microspheres were used as surrogates for C. parvum oocysts. Semi-batch ozonation experiments were performed to determine the fluorescence-intensity decay of individual microspheres, which was measured by flow cytometry. The results obtained with the microspheres were correlated to the inactivation kinetics of C. parvum oocysts by choosing an appropriate threshold fluorescence intensity below which microspheres were considered to be equivalent to nonviable oocysts. A mathematical model was then used to predict the inactivation efficiency and bromate formation. The contactor hydrodynamics were characterized by running tracer tests, and the kinetic parameters for ozone decomposition and bromate formation were obtained by performing batch experiments. Model predictions were in good agreement with full-scale experimental results. Additional model simulations revealed that ozone contactors should be designed with the lowest possible backmixing so that the target inactivation efficiency can be achieved with the lowest possible formation of bromate.

Quantitation of dityrosine in wheat flour and dough by liquid chromatography-tandem mass spectrometry

A method for the quantitation of dityrosine in wheat flour and dough by high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) using an isotope dilution assay with the internal standard 3,3'-(13)C(2)-dityrosine in the single-reaction monitoring mode was developed. The method consisted of the release of protein-bound dityrosine by hydrolysis in 4 mol/L hydrochloric acid/8.9 mol/L propionic acid for 24 h at 110 degrees C after addition of the internal standard, cleanup by C(18) solid-phase extraction, and HPLC-MS/MS. The limit of detection of dityrosine was 80 ng/g of sample (0.22 nmol/g), and the limit of quantitation was 270 ng/g of sample (0.75 nmol/g). The method was sensitive enough to analyze wheat flour and dough and to study the effect of flour improvers on the dityrosine content. Furthermore, the effect of the mixing time was studied. The dityrosine concentration in the flour was 0.66 nmol/g. After we mixed a dough to peak consistency, the dityrosine concentration doubled and remained constant on further mixing. Overdoses of hydrogen peroxide and hexose oxidase (HOX, E.C. 1.1.3.5) resulted in a strongly increased dityrosine content, whereas no increase of the dityrosine concentration was found after the addition of ascorbic acid and potassium bromate. Calculation of the percentage of dimeric tyrosine showed that less than 0.1% of the tyrosine residues of wheat protein were cross-linked. Therefore, dityrosine residues seem to play only a very minor role in the structure of wheat gluten.

Endogenous formation of novel halogenated 2'-deoxycytidine. Hypohalous acid-mediated DNA modification at the site of inflammation

A potential role of DNA damage by leukocyte-derived reactive species in carcinogenesis has been suggested. Leukocyte-derived peroxidases, such as myeloperoxidase and eosinophil peroxidase, use hydrogen peroxide and halides (Cl- and Br-) to generate hypohalous acids (HOCl and HOBr), halogenating intermediates. It has been suggested that these oxidants lead to the formation of halogenated products upon reaction with nucleobases. To verify the consequences of phagocyte-mediated DNA damage at the site of inflammation, we developed a novel monoclonal antibody (mAb2D3) that recognizes the hypohalous acid-modified DNA and found that the antibody most significantly recognized HOCl/HOBr-modified 2'-deoxycytidine residues. The immunoreactivity of HOCl-treated oligonucleotide was attenuated by excess methionine, suggesting that chloramine-like species may be the plausible epitopes of the antibody. On the basis of further characterization combined with mass spectrometric analysis, the epitopes of mAb2D3 were determined to be novel N4,5-dihalogenated 2'-deoxycytidine residues. The formation of the dihalogenated 2'-deoxycytidine in vivo was immunohistochemically demonstrated in the lung and liver nuclei of mice treated with lipopolysaccharides, an experimental inflammatory model. These results strongly suggest that phagocyte-derived oxidants, hypohalous acids, endogenously generate the halogenated DNA bases such as a novel dihalogenated 2'-deoxycytidine in vivo. Halogenation (chlorination and/or bromination) of DNA therefore may constitute one mechanism for oxidative DNA damage at the site of inflammation.

Microelectrochemical approach to induce local cell adhesion and growth on substrates

The nature of an albumin-coated substrate that blocks protein adsorption and cell adhesion was rapidly switched to cell-adhesive by exposure to an oxidizing agent such as HBrO. This finding has enabled cellular pattern drawing even on a single-cell level by closely scanning a microelectrode above the substrate and electrochemically producing the agent at the tip of the electrode. The present microelectrochemical cell patterning is applicable even for a previously cell-patterned substrate and for a grooved substrate. These unique technical features will have impacts on a variety of cell-based studies that require the analysis of heterotypic cell-cell interactions and cellular arrangement on an uneven surface such as semiconductor devices.

Effects of the brominated phenol, lanosol, on cytochrome P-450 and glutathione transferase activities in Haliotis rufescens and Katharina tunicata

The relationship between biochemical transformation mechanisms and dietary preferences has been little studied among marine herbivores. Here we report on basal activities and kinetic parameters of steroid hydroxylase and glutathione transferase from digestive gland tissue of the marine molluscan generalist herbivores Haliotis rufescens and Katharina tunicata and the differential effects of the brominated phenol lanosol [1,2-dihydroxy-3,4-dibromo-5-(hydroxymethyl)-benzene] on the activity of these enzymes. Lanosol and other brominated aromatic compounds are prevalent among filamentous red algae frequently consumed by K. tunicata and have been shown to deter feeding in species of Haliotis. Animals were gavaged daily with 10 mg of lanosol per kg of wet mass for 3 days. Mean basal levels of estradiol and testosterone hydroxylase and glutathione transferase specific activities were higher in digestive gland tissue from H. rufescens relative to that of K. tunicata, and only K. tunicata glutathione transferase specific activity was affected by lanosol treatment. Apparent enzyme kinetic parameters (K(m) and V) for the substrate estradiol were higher in K. tunicata, and glutathione transferase from H. rufescens showed a higher efficiency of turnover compared with glutathione transferase from K. tunicata based on V/K(m) ratios. These results suggest a potential relationship between detoxification enzyme induction mechanisms and feeding behaviors among marine herbivores.

High accumulation of oxidative DNA damage, 8-hydroxyguanine, in Mmh/Ogg1 deficient mice by chronic oxidative stress

8-Hydroxyguanine (8-OH-G) is a major pre-mutagenic lesion generated from reactive oxygen species. The Mmh/Ogg1 gene product plays a major role in maintaining genetic integrity by removing 8-OH-G by way of the base excision repair pathway. To investigate how oxidative stress influences the formation of 8-OH-G in Ogg1 mutant mice, a known oxidative agent, potassium bromate (KBrO(3)), was administered at a dose of 2 g/l in the drinking water to Ogg1(+/+), Ogg1(+/-) and Ogg1(-/-) mice for 12 weeks. Apurinic (AP) site lyase activity, measured by the excision of 8-OH-G from synthetic oligonucleotides, remained unchanged in kidney cell extracts isolated from Ogg1 mutant mice when the mice were pre-treated by KBrO(3). The levels of 8-OH-G in kidney DNA tremendously increased in a time-dependent manner following exposure of Ogg1(-/-) mice to KBrO(3). Of particular note, the amount of 8-OH-G in kidney DNA from Ogg1(-/-) mice treated with KBrO(3) was approximately 70 times that of KBrO(3)-treated Ogg1(+/+) mice. The accumulated 8-OH-G did not decrease 4 weeks after discontinuing treatment with KBrO(3). KBrO(3) treatment for 12 weeks gave rise to increased mutation frequencies at the transgenic gpt gene in Ogg1(+/+) mice kidney. Absence of the Ogg1 gene further enhanced the mutation frequency. Sequence data obtained from gpt mutants showed that the accumulated 8-OH-G caused mainly GC-->TA transversion and deletion. Other mutations including GC-->AT transition also showed a tendency to increase. These results indicate that 8-OH-G, produced by chronic exposure to exogenous oxidative stress agents, is not repaired to any significant extent within the overall genome of Ogg1(-/-) mice kidney.

Contribution of nitric oxide to potassium bromate-induced elevation of methaemoglobin concentration in mouse blood

Bromate, an inorganic oxyhalide disinfection by-product, is known to cause kidney damage, haemolysis and methaemoglobinemia. In potassium bromate (KBrO3)-treated mice (1.2 mmol/kg), elevation of methaemoglobin (MetHb) concentration in blood was observed simultaneously with an elevation of the NO concentration and attenuation of glutathione peroxidase (GPx) activity. Renal oxidative stress and kidney damage were also confirmed in the KBrO3-treated mice. A pre-administered GPx-mimic ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) dose-dependently diminished the KBrO3-induced changes in MetHb concentration and GPx activity. Renal oxidative stress and kidney damage caused by the KBrO3 administration were also dose-dependently suppressed by ebselen. On the other hand, ebselen did not suppress the KBrO3-induced elevation of the NO concentration. KBrO3-induced methaemoglobinemia, renal oxidative stress and kidney damage, consequently, seemed to result from the attenuation of GPx activity. Besides, the enhancement of NO production was not likely to be a result but a cause for the KBrO3-induced attenuation of GPx activity. In in vitro experiments, oxidation of human oxyhaemoglobin (HbO2) to MetHb was observed in a reaction mixture containing HbO2 and an NO donor, NOC-7 (1-hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene) or SIN-1 (3-(4-morpholinyl)sydnonimine), and this oxidation was inhibited by the NO scavenger carboxy-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide). However, no MetHb formation was observed in a reaction mixture containing HbO2 and KBrO3. These results suggest that KBrO3-induced methaemoglobinemia results from the reduction of GPx activity in blood by the KBrO3-induced increases in superoxide, NO and ONOO-.

DNA damage induced by hypochlorite and hypobromite with reference to inflammation-associated carcinogenesis

Hypohalites (OCl-, OBr-) are formed at inflammation sites as antimicrobial agents. OCl- is also used for the disinfection of water supplies and the association of drinking chlorinated water with cancer risk is pointed out. In this study, OCl- itself induced 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) formation, while OBr- damaged DNA only when glutathione (GSH) was added. OCl- caused oxidative DNA damage more efficiently than OBr-/GSH. In experiment with 32P-labeled DNA fragments, OCl- strongly caused piperidine-labile sites at guanine residues than piperidine-inert 8-oxodG, whereas OBr-/GSH caused no piperidine-labile sites. Endogenous OCl- may play a role in genotoxicity close to the site of inflammation.

Kolaviron modulates cellular redox status and impairment of membrane protein activities induced by potassium bromate (KBrO(3)) in rats

In this study, we examined the modulatory effects of kolaviron, a biflavonoid from Garcinia kola seeds on the antioxidant defense mechanisms, cellular redox status and oxidative stress in the kidney and liver of rats pretreated with potassium bromate (KBrO(3)) intragastrically as a single dose of 300 mg kg(-1)weight for 4 weeks. Treatment of rats with KBrO(3)resulted in an insignificant difference (P> 0.05) in body weight compared to controls. However, a significant increase in kidney/body weight ratio (P< 0.001) was observed in rats treated with KBrO(3)while liver/body weight ratio was not affected. KBrO(3)depressed the activities of superoxide dismutase, glutathione peroxidase and catalase (P< 0.001) in the kidney but not in the liver. Kolaviron (200 mg kg(-1)body weight) administered three times a week for 4 weeks inhibited the decrease mediated by KBrO(3)of these enzymes in the kidney by 29, 88 and 45%, respectively. Similarly, kolaviron reduced the KBrO(3)-induced decrease in the activities of gamma -glutamyltransferase and microsomal Ca(2+)ATPase by 73 and 63% in the kidney. In addition, the extract elicited a 27 and 25% decrease in the KBrO(3)-induced increase in malondialdehyde and lipid hydroperoxide formation in the kidney. Kolaviron also attenuated the KBrO(3)-decreased activities of glucose 6-phosphatase, 5 prime prime or minute nucleotidase and alkaline phosphatase (membrane enzymes) by 72, 57 and 25% respectively. The results of the present investigation indicate the antioxidative effect of kolaviron, a natural antioxidant, on drug-induced kidney toxicity. Kolaviron may therefore intervene in the cellular redox status and depression of membrane protein activities caused by KBrO(3)and other environmental carcinogens in the kidney.

Effects of simulated microgravity on metabolic activities related to DNA damage and repair in lymphoblastoid cells

We adopted a simple experimental framework to follow the dependence of structural aberrations and the modifications in selected metabolic processes correlated with the exposure of cells to microgravity. Alterations to the cellular metabolism induced by exposure to microgravity are evidentiated in the modification of PARP activity (strongly dependent to the presence of DNA damages and to the altered gene expression), in the modification of the repair ability and in the cell's energy homeostasis (NAD and ATP). Cells are exposed continuously to microgravity in a Random Positioning Machine (RPM) in complete medium for 48 hours. At the end of this period a part of these cells are immediately analysed for the parameters reported above and the remaining were furtherly incubated in standard laboratory conditions to document eventual defects during the phases of the recovery process. A part of cells, just after exposure to microgravity, were also subjected to treatment with a strong damaging agent, KBrO3, and these cells were subsequently analyzed. This final treatment was meant to amplify the eventual deficiencies experienced by microgravity-exposed cells in the DNA repair process also in dependence with the alterated metabolic conditions resulting after the exposure to microgravity.

Comparison of low-density lipoprotein modification by myeloperoxidase-derived hypochlorous and hypobromous acids

Myeloperoxidase (MPO), a heme enzyme secreted by activated phagocytes, catalyzes the oxidation of halides to hypohalous acids. At plasma concentrations of halides, hypochlorous acid (HOCl) is the major strong oxidant produced. In contrast, the related enzyme eosinophil peroxidase preferentially generates hypobromous acid (HOBr). Since reagent and MPO-derived HOCl converts low-density lipoprotein (LDL) to a potentially atherogenic form, we investigated the effects of HOBr on LDL modification. Compared to HOCl, HOBr caused 2-3-fold greater oxidation of tryptophan and cysteine residues of the protein moiety (apoB) of LDL and 4-fold greater formation of fatty acid halohydrins from the lipids in LDL. In contrast, HOBr was 2-fold less reactive than HOCl with lysine residues and caused little formation of N-bromamines. Nevertheless, HOBr caused an equivalent increase in the relative electrophoretic mobility of LDL as HOCl, which was not reversed upon subsequent incubation with ascorbate, in contrast to the shift in mobility caused by HOCl. Similar apoB modifications were observed with HOBr generated by MPO/H(2)O(2)/Br(-). In the presence of equivalent concentrations of Cl(-) and Br(-), modifications of LDL by MPO resembled those seen in the presence of Br(-) alone. Interestingly, even at physiological concentrations of the two halides (100 mM Cl(-), 100 microM Br(-)), MPO utilized a portion of the Br(-) to oxidize apoB cysteine residues. MPO also utilized the pseudohalide thiocyanate to oxidize apoB cysteine residues. Our data show that even though HOBr has different reactivities than HOCl with apoB, it is able to alter the charge of LDL, converting it into a potentially atherogenic particle.

Reaction of acylated homoserine lactone bacterial signaling molecules with oxidized halogen antimicrobials

Oxidized halogen antimicrobials, such as hypochlorous and hypobromous acids, have been used extensively for microbial control in industrial systems. Recent discoveries have shown that acylated homoserine lactone cell-to-cell signaling molecules are important for biofilm formation in Pseudomonas aeruginosa, suggesting that biofouling can be controlled by interfering with bacterial cell-to-cell communication. This study was conducted to investigate the potential for oxidized halogens to react with acylated homoserine lactone-based signaling molecules. Acylated homoserine lactones containing a 3-oxo group were found to rapidly react with oxidized halogens, while acylated homoserine lactones lacking the 3-oxo functionality did not react. The Chromobacterium violaceum CV026 bioassay was used to determine the effects of such reactions on acylated homoserine lactone activity. The results demonstrated that 3-oxo acyl homoserine lactone activity was rapidly lost upon exposure to oxidized halogens; however, acylated homoserine lactones lacking the 3-oxo group retained activity. Experiments with the marine alga Laminaria digitata demonstrated that natural haloperoxidase systems are capable of mediating the deactivation of acylated homoserine lactones. This may illustrate a natural defense mechanism to prevent biofouling on the surface of this marine alga. The Chromobacterium violaceum activity assay illustrates that reactions between 3-oxo acylated homoserine lactone molecules and oxidized halogens do occur despite the presence of biofilm components at much greater concentrations. This work suggests that oxidized halogens may control biofilm not only via a cidal mechanism, but also by possibly interfering with 3-oxo acylated homoserine lactone-based cell signaling.

On the Oxidation of Cytochrome c by Hypohalous Acids

Oxidation of cytochrome c, a key protein in mitochondrial electron transport and a mediator of apoptotic cell death, by reactive halogen species (HOX, X2), i.e., metabolites of activated neutrophils, was investigated by stopped-flow. The fast initial reactions between FeIIIcytc and HOX species, with rate constants (at pH 7.6) of k > 3 x 10(6) M(-1) s(-1) for HOBr, k > 3 x 10(5) M(-1) s(-1) for HOCl, and k = (6.1+/-0.3) x 10(2) M(-1) s(-1) for HOI, are followed by slower intramolecular processes. All HOX species lead to a blue shift of the Soret absorption band and loss of the 695-nm absorption band, which is an indicator for the intact iron to Met-80 bond, and of the reducibility of FeIIIcytc. All HOX species do, in fact, persistently impair the ability of FeIIIcytc to act as electron acceptor, e.g., in reaction with ascorbate or O2*-. I2 selectively oxidizes the iron center of FeIIcytc, with a stoichiometry of 2 per I2, and with k(FeIIcytc + I2) approximately 4.6 x 10(4) M(-1) s(-1) and k(FeIIcytc + I2*-) = (2.9+/-0.4) x 10(8) M(-1) s(-1). Oxidation of FeIIcytc by HOX species is not selectively directed toward the iron center; HOBr and HOCl are considered to react primarily by N-halogenation of side chain amino groups, and HOI mainly by sulfoxidation. There is some evidence for the generation of HO* radicals upon reaction of HOCl with FeIIcytc. Chloramines (e.g., NH2Cl), bromamine (NH2Br), and cyclo-Gly2 chloramide oxidize FeIIcytc slowly and unselectively, but iodide efficiently catalyzes reactions of these N-halogens to yield fast selective oxidation of the iron center; this is due to generation of I2 by reaction of I- with the N-halogen and recycling of I- by reaction of I2 with FeIIcytc. Iodide also catalyzes methionine sulfoxidation and thiol oxidation by NH2Cl. The possible biological relevance of these findings is discussed.

On the irreversible destruction of reduced nicotinamide nucleotides by hypohalous acids

Degradation of the reduced pyridine nucleotides NMNH and NADH by HOCl involves two distinct stages: a fast reaction, k = 4.2 x 10(5) M(-1) s(-1), leads to generation of stable pyridine products (Py/Cl) with a strong absorption band at 275 nm (epsilon = 12.4 x 10(3) M(-1) cm(-1) in the case of NMNH); secondarily, a subsequent reaction of HOCl, k = 3.9 x 10(3) M(-1) s(-1), leads to a complete loss of the aromatic absorption band of the pyridine ring. HOBr and HOI(I(2)) react similarly. Apparent rate constants of the primary reactions of HOX species with NMNH at pH 7.2 increase in the order HOCl (3 x 10(5) M(-1) s(-1)) < HOBr( approximately 4 x 10(6) M(-1) s(-1)) < HOI(I(2))( approximately 6.5 x 10(7) M(-1) s(-1)). HOBr reacts fast also with the primary product Py/Br, k approximately 9 x 10(5) M(-1) s(-1), while the reactions of HOI and I(2) with Py/I are slower, approximately 1.4 x 10(3) M(-1) s(-1) and >6 x 10(3) M(-1) s(-1), respectively. Halogenation of the amide group of NMN(+) by HOX species is many orders of magnitude slower than oxidation of NMNH. Taurine inhibits HOCl-induced oxidation of NADH, but HOBr-induced oxidation is not inhibited because the taurine monobromamine rapidly oxidizes NADH, and oxidation by HOI(I(2)) is not inhibited because taurine is inert toward HOI(I(2)). Also sulfur compounds (GSH, GSSG, and methionine) are less efficient in protecting NADH against oxidation by HOBr and HOI(I(2)) than against oxidation by HOCl. The results suggest that reactions of HOBr and HOI(I(2)) in a cellular environment are much more selectively directed toward irreversible oxidation of NADH than reactions of HOCl. It is noteworthy that the rather inert N-chloramines react with iodide to generate HOI(I(2)), i.e., the most reactive and selective oxidant of reduced pyridine nucleotides. NMR investigations show that the primary stable products of the reaction between NMNH and HOCl are various isomeric chlorohydrins originating from a nonstereospecific electrophilic addition of HOCl to the C5&dbond;C6 double bond of the pyridine ring. The primary products (Py/X) of NMNH all exhibit similar absorption bands around 275 nm and are hence likely to result from analogous addition of HOX to the C5&dbond;C6 bond of the pyridine ring. Since the Py/X species are stable and inert toward endogeneous reductants like ascorbate and GSH, they may generally be useful markers for assessing the contribution of hypohalous acids to inflammatory injury.

Activated leukocytes oxidatively damage DNA, RNA, and the nucleotide pool through halide-dependent formation of hydroxyl radical

A variety of chronic inflammatory conditions are associated with an increased risk for the development of cancer. Because of the numerous links between DNA oxidative damage and carcinogenesis, a potential role for leukocyte-generated oxidants in these processes has been suggested. In the present study, we demonstrate a novel free transition metal ion-independent mechanism for hydroxyl radical ((*)OH)-mediated damage of cellular DNA, RNA, and cytosolic nucleotides by activated neutrophils and eosinophils. The mechanism involves reaction of peroxidase-generated hypohalous acid (HOCl or HOBr) with intracellular superoxide (O(2)(*)(-)) forming (*)OH, a reactive oxidant species implicated in carcinogenesis. Incubation of DNA with either isolated myeloperoxidase (MPO) or eosinophil peroxidase (EPO), plasma levels of halides (Cl(-) and Br(-)), and a cell-free O(2)(*)(-) -generating system resulted in DNA oxidative damage. Formation of 8-hydroxyguanine (8-OHG), a mutagenic base which is a marker for (*)OH-mediated DNA damage, required peroxidase and halides and occurred in the presence of transition metal chelators (DTPA +/- desferrioxamine), and was inhibited by catalase, superoxide dismutase (SOD), and scavengers of hypohalous acids. Similarly, exposure of DNA to either neutrophils or eosinophils activated in media containing metal ion chelators resulted in 8-OHG formation through a pathway that was blocked by peroxidase inhibitors, hypohalous acid scavengers, and catalytically active (but not heat-inactivated) catalase and SOD. Formation of 8-OHG in target cells (HA1 fibroblasts) occurred in all guanyl nucleotide-containing pools examined following exposure to both a low continuous flux of HOCl (at sublethal doses, as assessed by [(14)C]adenine release and clonogenic survival), and hyperoxia (to enhance intracellular O(2)(*)(-) levels). Mitochondrial DNA, poly A RNA, and the cytosolic nucleotide pool were the primary targets for oxidation. Moreover, modest but statistically significant increases in the 8-OHG content of nuclear DNA were also noted. These results suggest that the peroxidase-H(2)O(2)-halide system of leukocytes is a potential mechanism contributing to the well-established link between chronic inflammation, DNA damage, and cancer development.

Comparison of mono- and dichlorinated tyrosines with carbonyls for detection of hypochlorous acid modified proteins

Hypochlorous acid is a potent oxidant capable of oxidizing and chlorinating proteins. Based on its indiscriminant reactivity, it is proposed to play a major role in tissue damage associated with a range of inflammatory diseases. We have determined the relative tendencies for formation of protein carbonyls, chlorinated tyrosine residues, and epitopes recognized by an antibody raised against hypochlorous acid oxidized protein (HOP-1) when albumin is treated with hypochlorous acid. We have also tested the specificity of the HOP-1 antibody by measuring how effectively it recognizes proteins oxidized by hypobromous acid. 3-Chlorotyrosine, along with a new marker of hypochlorous acid dependent protein modification, 3, 5-dichlorotyrosine, was formed at the lowest doses of hypochlorous acid that were capable of generating protein carbonyls. Comparatively high doses of hypochlorous acid were needed to generate epitopes recognized by HOP-1, which were also produced by hypobromous acid. Our study demonstrates that it is advantageous to measure protein carbonyls and HOP-1 epitopes in conjunction with chlorinated tyrosines when attempting to identify the oxidants responsible for inflammatory tissue damage.

Comparison of human red cell lysis by hypochlorous and hypobromous acids: insights into the mechanism of lysis

Human red blood cells are lysed by the neutrophil-derived oxidant hypochlorous acid (HOCl), although the mechanism of lysis is unknown. Hypobromous acid (HOBr), a similarly reactive oxidant, lysed red cells approx. 10-fold faster than HOCl. Therefore we compared the effects of these oxidants on thiols, membrane lipids and proteins to determine which reactions are associated with lysis. There was no difference in the loss of reduced glutathione or membrane thiols with either oxidant, but HOBr reacted more readily with membrane lipids and proteins. Bromohydrin derivatives of phospholipids and cholesterol were seen at approx. one-tenth the level of oxidant than chlorohydrins were. However, these products were detected only with high concentrations of HOCl or HOBr, which caused instant haemolysis. Membrane protein modification occurred at much lower doses of oxidant and was more closely correlated with lysis. SDS/PAGE analysis showed that band 3, the anion transport protein, was lost at the lowest dose of HOBr and at the higher concentrations of HOCl. Labelling the red cells with eosin 5-maleimide, a fluorescent label for band 3, suggested possible clustering of this protein in oxidant-exposed cells. There was also irreversible cross-linking of all the major membrane proteins; this reaction occurred more readily with HOBr. The results indicate that membrane protein modification is the reaction responsible for HOCl-mediated lysis. These effects, and particularly cross-link formation, might result in clustering of band 3 and other membrane and cytoskeletal proteins to form haemolytic pores.

Induction of oh8Gua glycosylase in rat kidneys by potassium bromate (KBrO3), a renal oxidative carcinogen

It has been suggested that 8-hydroxyguanine (oh8Gua), a DNA adduct formed by active oxygens, impairs the maintenance of genetic integrity, oh8Gua glycosylase removes oh8Gua residues as a free base from DNA strands. In E. coli, it has been demonstrated that oh8Gua glycosylase is induced in response to oxidative stress, but the oxidative inducibility in mammalian tissues has not yet been studied. In the present study, the inducibility of oh8Gua glycosylase was tested by comparing activity changes of this enzyme in the kidney and the liver of rats treated with potassium bromate (KBrO3). KBrO3 is known to cause oxidative damage to the kidney but not to other organs. With a single dose of KBrO3 (80 mg/kg, i.p.), activity in the kidney was found to increase significantly at 3 h compared to that at zero time. At 6 h, activity peaked, showing a 6-fold increase over that at zero time. Thereafter, it decreased and returned to its zero time level at 12 h. With increasing doses of KBrO3 (up to 160 mg/kg, i.p.), activity increased linearly with increased dosage, and over 40 mg/kg, i.p., activity increased to a level significantly higher than that in the control. In contrast to the time- and dose-dependent changes in activity in the kidney, no significant change was observed in the liver under the same conditions as above. These results show that oh8Gua glycosylase is also induced oxidatively in mammalian tissues. The induction in this tissue as well as in E. coli indicates that the adaptive response of this enzyme to oxidative stress is a general phenomenon in aerobic organisms and implies that the repair of oh8Gua residues in DNA is a process important for the survival of organisms in an aerobic environment.

Combination effects of clastogens in the mouse peripheral blood micronucleus assay

In order to study how two chemicals interact to induce micronuclei, simple ethylating agents [ethyl methanesulfonate (EMS), ethyl ethanesulfonate (EES) and N-ethyl-N-nitrosourea (ENU)], spindle poisons [vincristine sulfate (VINC) and colchicine (COL)] and an oxidizing agent [potassium bromate (KBrO3)] were used as model chemicals for combination treatments. The frequency of micronucleated reticulocytes (MNRETs) was evaluated in mice treated with two of these chemicals at a time. The combinations of ethylating agents (EMS and EES; EMS and ENU) and of spindle poisons (VINC and COL) induced more micronuclei than those expected on an additive basis. The apparent synergism was due to a 'combined dose' which could be calculated by the dosimetric conversion of one chemical to the other, when damage induced by each chemical was 'equivalent' in the induction of MNRETs. In contrast, no apparent synergism in induction of micronuclei was observed when two chemicals with different modes of clastogenic action (EMS and KBrO3 or EMS and VINC) were combined.

Susceptibility of Candida albicans to peroxidase-catalyzed oxidation products of thiocyanate, iodide and bromide

The susceptibility of Candida albicans (ATCC 10231 and wild strains) to hypo(pseudo)halous ions (OSCN-, OBr-, OI-) produced by the lactoperoxidase system was tested. Six strains of Candida albicans were isolated from swabs taken from the mouths of children with orthodontic appliances and selected on Sabouraud-Chloramphenicol-Actidione agar plates. The survival rate of Candida blastospores after a 30 min exposure to lactoperoxidase system ranged from 79 to 105% in the presence of 615 microM thiocyanate, from 56 to 88% in the presence of 345 microM bromide and from 0 to 4% in the presence of 250 microM iodide. Results showed that only OI- could exert a strong inhibiting effect in vitro on Candida albicans at physiological concentrations. Nevertheless, the activity of the hypoiodite generating system in saliva was found to be under the control of thiocyanate concentration.

Substitute anions and the chloride conductance of frog muscle: effects of chlorate and bromate on steady-state values and kinetics

Voltage-clamp experiments have been used to study the effects of external nitrate, chlorate and bromate on the chloride conductance of sarcolemma of Xenopus laevis. Nitrate reduces inward current (chloride efflux), but less potently than does thiocyanate [Vaughan (1987) Pflügers Arch 410:153-158] and does not affect conductance kinetics. As its concentration is increased the blocking effect of nitrate saturates; at a nitrate mole fraction of 0.6 the anion conductance is reduced to about 50% and further increases in nitrate concentration are without significant effect. Nitrate's influences are not voltage-dependent. Chlorate is a much less potent blocker than is nitrate, and its effects are voltage-dependent. With small hyperpolarizations, currents are sometimes seen to be larger than the control, but the degree of block (or the conversion of augmentation to reduction) increases with the size of the voltage step. Anomalous mole-fraction effects are observed in the range 0.4-0.6 mol/mol, in that in some cells the reduction of conductance is noticeably greater in the lower than in the higher concentration of the replacement ion. In the presence of chlorate, relaxation rates are significantly increased, and this influence is not anomalously dependent on the mole fraction. Similar effects are observed in bromate. The effect on kinetics is not pH-dependent. The main series of experiments was conducted at pH 5, but the same influence on kinetics was observed at pH 9. Using point voltage-clamp experiments, chlorate and thiocyanate were both seen to lower the contraction threshold voltage, but thiocyanate has no influence on conductance kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of 8-hydroxydeoxyguanosine formation in rat kidney to lipid peroxidation, glutathione level and relative organ weight after a single administration of potassium bromate

Changes in kidney levels of 8-hydroxydeoxyguanosine (8-OH-dG), lipid peroxidation (LPO), glutathione (GSH) and relative organ weight were examined 6, 24, 48, 72 and 96 h after a single i.p. administration of potassium bromate (KBrO3) at a dose of 70 mg/kg to male F344 rats. The 8-OH-dG level was significantly increased 24 h after the treatment at this dose and thereafter gradually decreased. On the other hand, significant elevation in LPO level was observed from 6 h after the treatment with a continuous increase up to a plateau at 48 h and no subsequent drop. GSH level was significantly raised from 6 to 72 h, and relative kidney weight varied in almost the same manner as the 8-OH-dG level. Investigation of the dose-response relation revealed the 8-OH-dG and LPO levels to be significantly increased from a dose of 40 mg/kg KBrO3 in a dose-dependent manner. The results suggest that enhanced formation of 8-OH-dG in kidney DNA due to KBrO3 is closely related to the increase in LPO levels.

Gating in iodate-modified single cardiac Na+ channels

Elementary Na+ currents were recorded at 19 degrees C during 220-msec lasting step depolarizations in cell-attached and inside-out patches from cultured neonatal rat cardiocytes in order to study the modifying influence of iodate, bromate and glutaraldehyde on single cardiac Na+ channels. Iodate (10 mmol/liter) removed Na+ inactivation and caused repetitive, burst-like channel activity after treating the cytoplasmic channel surface. In contrast to normal Na+ channels under control conditions, iodate-modified Na+ channels attain two conducting states, a short-lasting one with a voltage-independent lifetime close to 1 msec and, likewise tested between -50 and +10 mV, a long-lasting one being apparently exponentially dependent on voltage. Channel modification by bromate (10 mmol/liter) and glutaraldehyde (0.5 mmol/liter) also included the occurrence of two open states. Also, burst duration depended apparently exponentially on voltage and increased when shifting the membrane in the positive direction, but there was no evidence for two bursting states. Chemically modified Na+ channels retain an apparently normal unitary conductance (12.8 +/- 0.5 pS). Of the two substates observed, one of them is remarkable in that it is mostly attained from full-state openings and is very short living in nature; the voltage-independent lifetime was close to 2 msec. Despite removal of inactivation, open probability progressively declined during membrane depolarization. The underlying deactivation process is strongly voltage sensitive but, in contrast to slow Na+ inactivation, responds to a voltage shift in the positive direction with a retardation in kinetics. Chemically modified Na+ channels exhibit a characteristic bursting state much shorter than in DPI-modified Na+ channels, a difference not consistent with the hypothesis of common kinetic properties in noninactivating Na+ channels.

Effects of sodium bromate on ionic concentrations and osmolalities of the cochlear fluids in guinea pigs

Effects of sodium bromate on cochlear potentials and electrolyte composition of the cochlear fluids in guinea pigs were investigated following administration of sodium bromate into the cochlea, using perilymphatic perfusion. Cochlear microphonics and the whole nerve action potential of the auditory nerve were markedly suppressed. The K+ and Cl- activities in the endolymph as well as the endocochlear dc potential (EP) decreased significantly and irreversibly, in proportion to the concentration of sodium bromate. A negative EP never developed during the monitoring of 120 min. Microsamples of the endolymph showed substantial decreases of K+ and Cl- concentrations and an increase in the concentration of Na+. Osmolality of the endolymph was much lower than that of the perilymph. The severe edema of the stria vascularis and collapse of Reissner's membrane were histologically evident. These events suggest a breakdown of the endolymph-perilymph barrier, coincident with an inhibition of the strial active transport, as a result of the ototoxic action of sodium bromate. The possible ion and water movement across the endolymph-perilymph barrier in the presence of sodium bromate is discussed.

Acute cytogenetic effects of potassium bromate on rat bone marrow cells in vivo

The acute cytogenetic effects of potassium bromate (KBrO3) on rat bone marrow cells in vivo were studied. The incidence of chromosome aberrations in bone marrow cells increased rapidly, reaching a maximum level 12 h after intraperitoneal injection and decreased within 24 h. Dose-response relationships were obtained for both intraperitoneal and oral administrations.

Dose-related enhancing effect of potassium bromate on renal tumorigenesis in rats initiated with N-ethyl-N-hydroxyethyl-nitrosamine

Dose-response studies were undertaken to investigate the enhancing activity of potassium bromate (KBrO3), a food additive, on renal tumorigenesis initiated by N-ethyl-N-hydroxyethylnitrosamine (EHEN). A total of 180 male 6-week-old F344 rats were divided into 12 groups. EHEN was given in the drinking water for the first 2 weeks at a concentration of 500 ppm for initiation of carcinogenesis. Thereafter, the rats were treated orally either with KBrO3 at a concentration of 500, 250, 125, 60, 30 or 15 ppm, or with potassium bromide (KBr) at a concentration of 1750 or 350 ppm for 24 weeks. The mean numbers of kidney dysplastic foci were significantly increased in a dose-related manner in rats treated with more than 30 ppm KBrO3. The mean number of renal cell tumors was significantly higher after treatment with KBrO3 at the highest concentration of 500 ppm. On the other hand, KBr had no effect. It was concluded that KBrO3 at doses higher than 30 ppm in the drinking water has an enhancing effect on renal tumorigenesis.

Nitrate uptake in Aspergillus nidulans and involvement of the third gene of the nitrate assimilation gene cluster

In Aspergillus nidulans, chlorate strongly inhibited net nitrate uptake, a process separate and distinct from, but dependent upon, the nitrate reductase reaction. Uptake was inhibited by uncouplers, indicating that a proton gradient across the plasma membrane is required. Cyanide, azide, and N-ethylmaleimide were also potent inhibitors of uptake, but these compounds also inhibited nitrate reductase. The net uptake kinetics were problematic, presumably due to the presence of more than one uptake system and the dependence on nitrate reduction, but an apparent Km of 200 microM was estimated. In uptake assays, the crnA1 mutation reduced nitrate uptake severalfold in conidiospores and young mycelia but had no effect in older mycelia. Several growth tests also indicate that crnA1 reduces nitrate uptake. crnA expression was subject to control by the positive-acting regulatory gene areA, mediating nitrogen metabolite repression, but was not under the control of the positive-acting regulatory gene nirA, mediating nitrate induction.