DNA damage induced by phorbol ester-stimulated neutrophils is augmented by extracellular cofactors. Role of histidine and metals

Pleiotropic effects of 4-hydroxynonenal on oxidative burst and phagocytosis in neutrophils

Metabolic control of cellular function is significant in the context of inflammation-induced metabolic dysregulation in immune cells. Generation of reactive oxygen species (ROS) such as hydrogen peroxide and superoxide are one of the critical events that modulate the immune response in neutrophils. When activated, neutrophil NADPH oxidases consume large quantities of oxygen to rapidly generate ROS, a process that is referred to as the oxidative burst. These ROS are required for the efficient removal of phagocytized cellular debris and pathogens. In chronic inflammatory diseases, neutrophils are exposed to increased levels of oxidants and pro-inflammatory cytokines that can further prime oxidative burst responses and generate lipid oxidation products such as 4-hydroxynonenal (4-HNE). In this study we hypothesized that since 4-HNE can target glycolysis then this could modify the oxidative burst. To address this the oxidative burst was determined in freshly isolated healthy subject neutrophils using 13-phorbol myristate acetate (PMA) and the extracellular flux analyzer. Neutrophils pretreated with 4-HNE exhibited a significant decrease in the oxidative burst response and phagocytosis. Mass spectrometric analysis of alkyne-HNE treated neutrophils followed by click chemistry detected modification of a number of cytoskeletal, metabolic, redox and signaling proteins that are critical for the NADPH oxidase mediated oxidative burst. These modifications were confirmed using a candidate immunoblot approach for critical proteins of the active NADPH oxidase enzyme complex (Nox2 gp91phox subunit and Rac1 of the NADPH oxidase) and glyceraldehyde phosphate dehydrogenase, a critical enzyme in the metabolic regulation of oxidative burst. Taken together, these data suggest that 4-HNE-induces a pleiotropic mechanism to inhibit neutrophil function. These mechanisms may contribute to the immune dysregulation associated with chronic pathological conditions where 4-HNE is generated.

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Phagocytosis and glycolysis are inhibited in neutrophils by 4-hydroxynonenal.

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Click chemistry with alkyne-HNE identifies over 100 potential protein targets.

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Rac1, NOX2 and GAPDH are modified by 4-HNE.

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The 4-HNE-dependent inhibition of neutrophil function is mediated by a pleiotropic mechanism.

AID-deficient Bcl-xL transgenic mice develop delayed atypical plasma cell tumors with unusual Ig/Myc chromosomal rearrangements

Activation-induced cytidine deaminase (AID) is required for immunoglobulin (Ig) class switch recombination and somatic hypermutation, and has also been implicated in translocations between Ig switch regions and c-Myc in plasma cell tumors in mice. We asked if AID is required for accelerated tumor development in pristane-treated Bcl-xL transgenic BALB/c mice deficient in AID (pBxAicda−/−). pBxAicda^−/− mice developed tumors with a lower frequency (24 vs. 62%) and a longer mean latency (108 vs. 36 d) than AID-sufficient mice. The tumors appeared in oil granuloma tissue and did not form ascites. By interphase fluorescence in situ hybridization, six out of nine pBxAicda^−/− primary tumors had T(12;15) and one had T(6;15) chromosomal translocations. Two tumors were transplantable and established as stable cell lines. Molecular and cytogenetic analyses showed that one had an unusual unbalanced T(12;15) translocation, with IgH Cμ and Pvt-1 oriented head to tail at the breakpoint, resulting in an elevated expression of c-Myc. In contrast, the second was T(12;15) negative, but had an elevated N-Myc expression caused by a paracentric inversion of chromosome 12. Thus, novel mechanisms juxtapose Ig and Myc-family genes in AID-deficient plasma cell tumors.

Reactive oxygen species modify oligosaccharides of glycoproteins in vivo: a study of a spontaneous acute hepatitis model rat (LEC rat)

The Long-Evans Cinnamon (LEC) rat, an animal model of Wilson's disease, spontaneously develops hepatitis as the result of abnormal copper accumulation in liver. The findings of this study show that copper, hydrogen peroxide, and lipid peroxides accumulate to drastically high levels in LEC rat serum in acute hepatitis but not chronic hepatitis. The effect of these reactive oxygen species (ROS) on oligosaccharides of glycoproteins in the LEC rat serum was examined. Lectin blot and lectin ELISA analyses showed that sialic acid and galactose residues of serum glycoproteins including transferrin were decreased in acute hepatitis. Further analyses of oligosaccharide structures of transferrin demonstrated that di-sialylated and asialo-agalacto biantennary sugar chains, but not tri-sialylated sugar chain, exist on transferrin in the acute hepatitis rats. In addition, treatment of non-hepatitis rat serum with copper ions and hydrogen peroxide decreased tri-sialylated sugar chain of the normal transferrin and increased di-sialylated and asialo-agalacto biantennary sugar chains. This is the first evidence to show that ROS result in the cleavage of oligosaccharides of glycoproteins in vivo, and indicate this cleavage of oligosaccharides may contribute the development of acute hepatitis.

Selenium Deficiency Abrogates Inflammation-Dependent Plasma Cell Tumors in Mice

The role of the micronutrient, selenium, in human cancers associated with chronic inflammations and persistent infections is poorly understood. Peritoneal plasmacytomas (PCTs) in strain BALB/c (C), the premier experimental model of inflammation-dependent plasma cell transformation in mice, may afford an opportunity to gain additional insights into the significance of selenium in neoplastic development. Here, we report that selenium-depleted C mice (n = 32) maintained on a torula-based low-selenium diet (5-8 micro g of selenium/kg) were totally refractory to pristane induction of PCT. In contrast, 11 of 26 (42.3%) control mice maintained on a selenium adequate torula diet (300 micro g of selenium/kg) and 15 of 40 (37.5%) control mice fed standard Purina chow (440 micro g of selenium/kg) developed PCT by 275 days postpristane. Abrogation of PCT was caused in part by the striking inhibition of the formation of the inflammatory tissue in which PCT develop (pristane granuloma). This was associated with the reduced responsiveness of selenium-deficient inflammatory cells (monocytes and neutrophils) to chemoattractants, such as thioredoxin and chemokines. Selenium-deficient C mice exhibited little evidence of disturbed redox homeostasis and increased mutant frequency of a transgenic lacZ reporter gene in vivo. These findings implicate selenium, via the selenoproteins, in the promotion of inflammation-induced PCT and suggest that small drug inhibitors of selenoproteins might be useful for preventing human cancers linked with chronic inflammations and persistent infections.

Moderate Hypermutability of a TransgeniclacZReporter Gene inMyc-Dependent Inflammation-Induced Plasma Cell Tumors in Mice

Mutator phenotypes, a common and largely unexplained attribute of human cancer, might be better understood in mouse tumors containing reporter genes for accurate mutation enumeration and analysis. Previous work on peritoneal plasmacytomas (PCTs) in mice suggested that PCTs have a mutator phenotype caused by Myc-deregulating chromosomal translocations and/or phagocyte-induced mutagenesis due to chronic inflammation. To investigate this hypothesis, we generated PCTs that harbored the transgenic shuttle vector, pUR288, with a lacZ reporter gene for the assessment of mutations in vivo. PCTs exhibited a 5.5 times higher mutant frequency in lacZ (40.3 +/- 5.1 x 10(-5)) than in normal B cells (7.36 +/- 0.77 x 10(-5)), demonstrating that the tumors exhibit the phenotype of increased mutability. Studies on lacZ mutant frequency in serially transplanted PCTs and phagocyte-induced lacZ mutations in B cells in vitro indicated that mutant levels in tumors are not determined by exogenous damage inflicted by inflammatory cells. In vitro studies with a newly developed transgenic model of inducible Myc expression (Tet-off/MYC) showed that deregulated Myc sensitizes B cells to chemically induced mutations, but does not cause, on its own, mutations in lacZ. These findings suggested that the hypermutability of PCT is governed mainly by intrinsic features of tumor cells, not by deregulated Myc or chronic inflammation.

Cytotoxic effects of peroxynitrite, polymorphonuclear neutrophils, free-radical scavengers, inhibitors of myeloperoxidase, and inhibitors of nitric oxide synthase on bovine mammary secretory epithelial cells

OBJECTIVE

To determine cytotoxic effects of activated polymorphonuclear neutrophils (PMN) and peroxynitrite on bovine mammary secretory epithelial cells before and after addition of nitric oxide synthase inhibitors, myeloperoxidase (MPO) inhibitors, and free-radical scavengers.

SAMPLE POPULATION

Polymorphonuclear neutrophils from 3 lactating cows.

PROCEDURE

Cells from the bovine mammary epithelial cell line MAC-T were cultured. Monolayers were treated with activated bovine PMN, lipopolysaccharide (LPS), phorbol 12-myristate 13-acetate (PMA), 3-morpholino-sydnonimine (SIN-1), 4-amino-benzoic acid hydrazide (ABAH), NG-monomethyl-L-arginine, histidine, and superoxide dismutase (SOD). At 24 hours, activity of lactate dehydrogenase in culture medium was used as a relative index of cell death. Tyrosine nitration of proteins in MAC-T cell lysates was determined by visual examination of immunoblots.

RESULTS

Lipopolysaccharide, PMA, and < or = 0.1 mM SIN-1 were not toxic to MAC-T cells. Activated PMN, > or = 6 mg of histidine/ml, and 0.5 mM SIN-1 were toxic. Together, histidine and 500,000 activated PMN/ml also were toxic. NG-monomethyl-L-arginine did not have an effect, but ABAH decreased PMN-mediated cytotoxicity. Ten and 50 U of SOD/ml protected MAC-T cells from cytotoxic effects of 0.5 mM SIN-1. Compared with control samples, nitration of MAC-T tyrosine residues decreased after addition of 500,000 PMN/ml or > or = 6 mg of histidine/ml. Superoxide dismutase increased and SIN-1 decreased tyrosine nitration of MAC-T cell proteins in a dose-responsive manner.

CONCLUSIONS AND CLINICAL RELEVANCE

Peroxynitrite, MPO, and histidine are toxic to mammary secretory epithelial cells. Superoxide dismutase and inhibition of MPO activity mitigate these effects. Nitration of MAC-T cell tyrosine residues may be positively associated with viability.

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.

Transgenic shuttle vector assays for assessing oxidative B-cell mutagenesis in vivo

The recent development of transgenic mutagenicity assays provides new opportunities for evaluating mutagenic processes in vivo. To asses mutant frequencies in tissue B cells, we decided to take advantage of two such assays that utilize the transgenic shuttle vectors, lambda LIZ and pUR288. Our main interest in this research is to test two basic premises of inflammation-induced plasmacytoma development in genetically susceptible BALB/c mice; i.e., the possibility that plasmacytoma precursor cells may become targets of phagocyte-mediated oxidative mutagenesis in situ and the prospect that plasmacytoma susceptibility/resistance genes may contribute to these phenotypes by enhancing/reducing oxidative mutagenesis in B cells. Based on our preliminary experience with the lambda LIZ and pUR288 transgenic in vivo mutagenicity tests, we propose to employ these assays as broadly applicable tools for assessing overall mutagenesis during normal and aberrant (malignant) B-cell development. Furthermore, transgenic shuttle vector assays appear to lend themselves as ideal methods to associate general B-cell mutagenesis with the peculiar, B cell-typical somatic hypermutation processes that target the V(D)J gene segment, the proto-oncogene bcl-6 and perhaps other, still unknown loci.

Elevated mutant frequencies in gene lacI in splenic lipopolysaccharide blasts after exposure to activated phagocytes in vitro

The interaction of B lymphocytes with phagocytes is critical for shaping the humoral immune response, as well as various aspects of normal and malignant B cell development, and has therefore been studied by immunologists in great detail. However, one potential outcome of this confrontation is often neglected, namely the mutagenicity of phagocytes to B lymphocytes. We are interested in phagocyte-induced B cell mutagenesis and have conducted a feasibility study on the utility of a transgenic reporter assay to evaluate mutant frequencies in B cells that have encountered phagocytes. An in vitro co-incubation system was designed in which splenic lipopolysaccharide (LPS) blasts carrying a phage lambda-derived lacI transgene were exposed to pristane-elicited peritoneal exudate cells (PEC). Mutant frequencies in LPS blasts were significantly increased (up to 6-fold) when the cells were co-incubated with PEC that had been stimulated by phorbol myristate acetate to undergo an oxidative burst. The lacI-based transgenic mutation assay proved also useful for assessing mutagenicity in vivo, as demonstrated by the detection of elevated mutant frequencies in the spleen (3-fold) and the inflammatory granuloma (4.7-fold) obtained from pristane-treated mice. We propose to utilize the lacI-based transgenic mutagenesis assay as a tool to evaluate mutational levels during normal and aberrant B cell differentiation.

Levels of DNA strand breaks and superoxide in phorbol ester-treated human granulocytes

Phorbol ester treatment of granulocytes triggers release of superoxide (O2.-) and a concomitant burst of DNA strand breaks. The relationship between the amount of O2.- and the number of DNA breaks has not previously been explored. To quantify the relatively large amount of O2.- generated over a 40-min period by 1 x 10(6) granulocytes/mL, a discontinuous "10-min pulse" method employing cytochrome c was used; 140 nmol O2.- per 1 x 10(6) cells was detected. DNA strand breaks were quantified by fluorimetric analysis of DNA unwinding (FADU). To vary the level of O2.- released by cells, inhibitors of the respiratory burst were used. Sodium fluoride (1-10 mM) and staurosporine (2-10 nM) both inhibited O2.- production. In both cases, however, inhibition of strand breakage was considerably more pronounced than inhibition of O2.-. Zinc chloride (50-200 microM) inhibited both O2.- and DNA breaks, approximately equally. Dinophysistoxin-1 (okadaic acid) inhibited O2.- production more effectively than it inhibited DNA breaks. O2.- dismutes to H2O2, a reactive oxygen species known to cause DNA breaks. The addition of catalase to remove extracellular H2O2 had no effect on DNA breakage. Using pulse field gel electrophoresis, few double-stranded breaks were detected compared to the number detected by FADU, indicating that about 95% of breaks were single-stranded. The level of DNA breaks is not directly related to the amount of extracellular O2.- or H2O2 in PMA-stimulated granulocytes. We conclude that either an intracellular pool of these reactive oxygen species is involved in breakage or that the metabolic inhibitors are affecting a novel strand break pathway.

Synthesis of Cr(IV)-GSH, its identification and its free hydroxyl radical generation: a model compound for Cr(VI) carcinogenicity

Current models of Cr(VI) carcinogenesis suggest an important role for Cr(IV) as an intermediate, toxic, carcinogenic species, but direct chemical evidence has been lacking. This is because Cr(IV) is a highly reactive oxidation state of Cr and few Cr(IV)-based compounds are known that can be used as a model compound containing a biological ligand. This study reports the isolation of such a stable Cr(IV) complex. The Cr(IV)-GSH complex has been synthesized through the reaction of Cr(VI) with GSH. Its electron paramagnetic resonance (EPR) spectrum exhibits g = 1.9629 and a peak-to-peak line width of 480 G in aqueous medium as well as in the powder form. Magnetic susceptibility measurements showed that the compound has a magnetic moment of 2.53 Bohr magneton per Cr, establishing that the Cr ion has two unpaired electrons, hence its identity as Cr(IV). The Cr(IV)-GSH complex is able to generate hydroxyl (.OH) radical in the presence of molecular oxygen in aqueous medium. Catalase inhibited the .OH radical generation while H2O2 enhanced it, indicating that the .OH radical was generated via a Fenton-like reaction, H2O2 being generated as an intermediate in the reduction of molecular oxygen. Metal ion chelators, deferoxamine and 1,10-phenanthroline, attenuated the generation of Cr(IV)-mediated .OH radical. In the case of deferoxamine, a deferoxamine-derived free radical was generated as shown by EPR measurements. The results imply that Cr(IV) may play an important role in the mechanism of Cr(VI)-induced carcinogenesis and Cr(IV)-GSH can be used as a model compound to study the role of Cr(IV) in this mechanism.

Tempol inhibits neutrophil and hydrogen peroxide-mediated DNA damage

Inflammatory conditions characterized by neutrophil activation are associated with a variety of chronic diseases. Reactive oxygen species are produced by activated neutrophils and produce DNA damage which may lead to tissue damage. Previous studies have shown that activated murine neutrophils induce DNA strand breaks in a target plasmacytoma cell, RIMPC 2394. We studied the effect of a water soluble nitroxide anti-oxidant, Tempol, on murine neutrophil induction of DNA strand breaks in this system. Murine neutrophils were isolated from the peritoneal cavity of BALB/cAn mice after an i.p. injection of pristane oil. Neutrophils were activated by the phorbol ester PMA and co-incubated with RIMPC 2394 cells. Control alkaline elution studies revealed progressive DNA strand breaks in RIMPC cells with time. The addition of Tempol to the incubation mixture prevented DNA damage in a dose dependent fashion. Five mM Tempol provided complete protection. Tempol protection against DNA strand breaks was similar for both stimulated neutrophils and exogenously added hydrogen peroxide. Measurement of hydrogen peroxide produced by stimulated neutrophils demonstrated that Tempol did not decrease hydrogen peroxide concentration. Oxidation of reduced metals, thereby interfering with the production of hydroxyl radical, is the most likely mechanism of nitroxide protection, although superoxide dismutase (SOD) like activity and scavenging of carbon-based free radicals may also account for a portion of the observed protection. The anti-oxidant activity of Tempol inhibited DNA damage by activated neutrophils. The nitroxides as a class of compounds may have a role in the investigation and modification of inflammatory conditions.

Low levels of hydrogen peroxide and L-histidine induce DNA double-strand breakage and apoptosis

The results presented in this study demonstrate that L-histidine triggers a lethal response in U937 cells exposed to nontoxic, albeit growth-inhibitory, levels of H2O2. Treatment for 1 h with the cocktail H2O2/L-histidine promotes the formation of a low level of DNA double-strand breaks that are rapidly rejoined, and this process is followed by secondary DNA fragmentation at about 7 h of post-treatment incubation, at which time cells are still viable. The appearance of oligonucleosomal DNA fragments associated with the detection of morphological changes typical of apoptosis strongly suggests that a portion of the cells was undergoing an apoptotic process. The relative level of cells with fragmented chromatin never exceeded 15-20% throughout the 20 h post-treatment incubation. Treatment with high concentrations of H2O2 in the presence of L-histidine was found to trigger necrotic cell death. The results presented in this paper provide further experimental evidence in support of the notion that DNA double-strand breaks mediate the lethal effects of the cocktail H2O2/L-histidine and suggest that this type of DNA lesion can promote both apoptotic and necrotic cell death, depending on the concentration of the oxidant.

Cytotoxicity and membrane damage in vitro by inclusion complexes between gamma-cyclodextrin and siloxanes

Inclusion complexes of gamma-cyclodextrin and octamethylcyclotetrasiloxane (D4), decamethyltetrasiloxane (M10TS), and 1,3,5,7-tetramethyltetravinylcyclotetra - siloxane (TMTV-D4) were prepared to compare the cytotoxic effects of siloxanes in vitro. In these preparations, the hydrophobic siloxanes are surrounded by a hydrophilic shell of eight circularly linked D-glucose molecules (gamma-cyclodextrin), and upon contact with plasma membranes the siloxane molecule can intercalate into the lipid bilayer of the cell membrane. XRPC24, 2-11 plasmacytoma, CH12.LX lymphoma and P388D1 macrophage-like cells were used as indicator cells in toxicity assays. Using an MTT tetrazolium reduction to formazan test, a colorimetric method to determine the number of viable cells, the 50% minimal lethal doses (CD50) for the siloxane compounds were found to range from 30 to 50 microM. Sublethal doses (e.g., 15 microM and lower) resulted in the loss of lactate dehydrogenase (LDH) and glutathione (GSH) from the cytosolic compartment of the target cells and thus indicated cytotoxicity. Treatment of macrophages with siloxanes resulted in a higher production of interleukin-6 (IL-6) than was exhibited by untreated macrophages. The B9 cell bioassay of these treated cells showed as much as a 10 fold higher production (500 U/ml) of IL-6 than did the untreated cells. The degree of increase was dependent on the compound and concentration used. The results of this study show that low molecular weight siloxanes produce lethal effects on B-lymphocyte derived target cells in vitro and permeabilize the plasma membranes at lower sublethal concentrations.

Evidence for involvement of multiple iron species in DNA single-strand scission by H2O2 in HL-60 cells

Some of the properties of cellular iron species which react with H2O2 to cause DNA single-strand breaks in HL-60 cells were characterized in control cells and in cells made deficient of iron using 4,7-phenylsulfonyl-1,10-phenanthroline (bathophenanthroline disulfonic acid or BPS) and ascorbate. Single-strand breaks were measured using alkaline elution of DNA of cells treated at 4 degrees to minimize repair during treatment. Strand breakage in the presence of 10% serum was only 40% of that in the absence of serum. This effect was traced to reaction of H2O2 with metals, most likely iron, in serum. Dimethyl sulfoxide (Me2SO) inhibited a maximum of 65% of breaks in control cells. The diffusion distance from the site of generation of hydroxyl radicals to the site of reaction with DNA for the Me2SO-inhibitable fraction was 6.9 nm. There was no significant alteration in the fraction of Me2SO-inhibitable strand breaks or in diffusion distance in iron-deficient cells, though total strand breaks decreased by 70%. When the effect of extracellular iron in serum was taken into account, 60 microM orthophenanthroline (OP) inhibited a maximum of 85% of strand breaks. In cells pretreated with 60 microM OP, the Me2SO-inhibitable fraction of the remaining strand breaks decreased to 32%, while the diffusion distance decreased to 4.1 nm. These data indicate the existence of a number of different iron species, as characterized by overlapping but not coincidental inhibition by OP and Me2SO, and by differing diffusion distances.

The L-histidine-mediated enhancement of hydrogen peroxide-induced DNA double strand breakage and cytotoxicity does not involve metabolic processes

The cytotoxic response of Chinese hamster ovary (CHO) cells to challenge with hydrogen peroxide was highly dependent upon the temperature of exposure, being markedly higher at 37 degrees than at 4 degrees C. Increasing intracellular levels of L-histidine prior to challenge with hydrogen peroxide increased the toxicity elicited by the oxidant at both physiologic and ice-bath temperatures. The effect of the amino acid, however, was more pronounced under conditions at 4 degrees C, as compared to 37 degrees C. Indeed, at 4 degrees C the oxidant was nontoxic at submillimolar levels and pre-exposure to L-histidine restored cytotoxicity to levels slightly higher than those observed after treatment at 37 degrees C (in the micromolar range). Pre-exposure to the amino acid increased the production of DNA double-strand breaks (DSBs) elicited by treatment with the oxidant both at 37 degrees and 4 degrees C. A remarkable correlation was found when the level of this lesion was plotted against the cytotoxic response observed using different concentrations of L-histidine or hydrogen peroxide, or treating the cells with the oxidant either at 37 degrees or 4 degrees C, thus suggesting the existence of a cause-effect relationship. The overlapping correlation curves obtained with cells challenged with the oxidant at 4 degrees or 37 degrees C also suggest that similar molecular mechanisms mediate the formation of DNA DSBs under both experimental conditions. Two lines of evidence provide experimental support for this inference: (1) the kinetics of repair of DNA DSBs generated at 37 degrees or 4 degrees C were virtually superimposable; this would suggest that the same repair pathway(s) is/are responsible for the removal of DNA DSBs generated at the two temperatures; and (2) the size distribution of double-stranded DNA fragments produced under the two treatment conditions, resulting in a similar cytotoxic response, was basically identical. This is indicative of remarkable similarities in the topology of chromosomal domains where DSBs are generated. Overall, the results presented in this paper provide further experimental evidence supporting the notion that DNA DSBs are responsible for the L-histidine-mediated enhancement of hydrogen peroxide-induced cytotoxicity, and demonstrate that the mechanism whereby the amino acid enhances the ability of hydrogen peroxide to produce DNA double strand breakage and cell killing does not depend on cellular metabolism and/or energy-dependent reactions.

The effect of hydrogen peroxide/L-histidine-induced DNA single- vs. double-strand breaks on poly(ADP-ribose)polymerase

L-Histidine markedly increases the ability of hydrogen peroxide to induce DNA cleavage and this effect is associated with a 3-aminobenzamide-inhibitable decline in NAD+ levels, an event which very likely reflects an enhanced stimulation of the enzyme poly(ADP-ribose)polymerase. 3-Aminobenzamide slowed down the removal of alkaline elution-detected strand breaks induced by either H2O2 alone (producing only DNA single-strand breaks) or associated with L-histidine (resulting in the formation of both single-strand breaks and DNA double-strand breaks), and the extent of inhibition was similar under the two experimental conditions. 3-Aminobenzamide did not affect the rate of rejoining of DNA double-strand breaks generated by the cocktail H2O2/L-histidine. The above results suggest that these double-strand breaks have hardly any effect on the induction of poly(ADP-ribose)polymerase activity, a conclusion that is consistent with the observation that the activity of this enzyme appears to be basically identical under conditions that abolish the formation of DNA double-strand breaks, in the absence of measurable variations in the level of induction of DNA single-strand breaks (e.g. in the presence of an excess of L-glutamine, a competitive inhibitor of L-histidine uptake). Finally, 3-aminobenzamide did not affect the toxicity of the oxidant, both in the absence and presence of L-histidine.

The biological activity of hydrogen peroxide. VI. Mechanism of the enhancing effects of L-histidine: the role of the formation of a histidine-peroxide adduct and membrane transport

Further details of the mechanism of the enhancing effects of L-histidine (L-His) on the clastogenic activities of hydrogen peroxide (H2O2) were investigated. The L-His-H2O2 adduct was prepared and its physicochemical properties and biological activities were compared with those of a mixture of L-His plus H2O2 and of H2O2 alone. When the stabilities of the three test samples against glucose were determined in terms of residual H2O2 content in solutions of various pH values over the course of 11 days, the adduct was found to be more stable than H2O2 alone and very similar in terms of stability to the mixture. The almost equivalent stability of the adduct and the mixture suggested formation of the adduct in the mixture even though the interaction between L-His and H2O2 in solution seems, from 13C-NMR analysis, to be rather weak. In cell-free DNA after lysis of cell membranes, the induction of single-strand breaks (SSB) by the adduct and by the mixture was less effective than by H2O2 alone. These results contrast with previous results obtained in intact cells (Oya et al., 1992) and demonstrate the indispensability of the cell membrane for the enhancing effects of L-His. In the presence of inhibitors of the active transport of L-His, namely, 10 different neutral amino acids, effective suppression of the clastogenic activity of the adduct and of the mixture was observed, whereas four acidic and basic amino acids had no effect. Thus, the participation of active transport in the enhancing effects of L-His was apparent. The formation of the adduct of L-His with H2O2 brings about the stabilization or reduces the reactivity of H2O2 and, as a result, the induction of SSB is prevented to some extent in cell-free DNA systems. By contrast, in a cellular system, the accumulation of the adduct in cells by active transport is potentiated by the enhancing effect of L-His, although the mediation of some factors that can generate hydroxyl radicals (*OH) from the adduct in cells must be postulated.

The L-histidine-mediated enhancement of hydrogen peroxide-induced cytotoxicity is a general response in cultured mammalian cell lines and is always associated with the formation of DNA double strand breaks

Micromolar concentrations of L-histidine increase the cytotoxicity of hydrogen peroxide in a number of cell lines including CHO (hamster), EAHY, McCoy's, U937 and CCRF-CEM (human), Vero (monkey) and SC-1 (mouse). Importantly, these cell lines displayed different degrees of sensitivity to H2O2 alone and the extent of enhancement elicited by the amino acid was more pronounced in resistant cell lines. The increased cytotoxicity was invariably associated with the formation of DNA DSBs and a remarkable correlation was found by plotting the level of DNA DSBs against the cytotoxic response. These results strongly support the hypothesis that the mechanism whereby L-histidine increases the toxicity elicited by H2O2 involves the formation of DNA DSBs and are consistent with the possibility that the amino acid might participate in the regulation of the physio-pathological response to oxidative stress in mammals.

L-histidine-mediated enhancement of hydrogen peroxide-induced cytotoxicity: relationships between DNA single/double strand breakage and cell killing

Results presented in this study demonstrate an association between the L-Histidine-mediated enhancement of H2O2-induced cytotoxicity and the formation of DNA double strand breakage (DSB), whereas no relationship exists between the increased cytotoxic response and DNA single strand breakage (SSB). Indeed, the higher lethality and the production of DNA DSB occurred in oxidatively-injured cells regardless of whether the exposure to L-Histidine was performed before or during challenge with the oxidant. In fact, the increased level of DNA SSB detected in cells simultaneously exposed to the oxidant and the amino acid was not observed in cells pre-treated with L-Histidine and then challenged with hydrogen peroxide. Further experiments have demonstrated an association between the kinetics of DNA DSB formation and the enhancement of the cytotoxic response. In conclusion, intracellular L-Histidine seems to mediate the formation of DNA DSB and the increased growth-inhibitory response elicited by the oxidant. In addition, these results suggest that the enhancement of DNA SSB is produced by the extracellular/plasma membrane fraction of the amino acid and not causally related to the L-Histidine-mediated increase of the growth-inhibitory response to H2O2-treated cells.

Activated murine neutrophils induce unscheduled DNA synthesis in B lymphocytes

Activated neutrophils induce DNA damage in neighboring cells by secreting reactive oxygen compounds into the extracellular milieu. Repair of this damage is required to prevent mutagenesis and neoplastic transformation. Conditions were established to detect the activation of excision-repair pathways (unscheduled DNA synthesis) by measuring stimulated thymidine uptake in target B lymphocytes exposed to activated neutrophils. Murine neutrophils were cocultured in serum-free medium with splenic B cells or with murine plasmacytoma cells for 2 h. Unscheduled DNA synthesis in the B cells was detected at neutrophil:target cell ratios of 1:1 to 4:1 when the neutrophils were activated with phorbol myristate acetate. Reagent H2O2 alone (> or = 6 microM) also induced UDS whereas HOCl (up to 4 mM) did not. No repair synthesis was observed within the neutrophils themselves. Control experiments indicated that the induction of UDS by neutrophils and H2O2 was not due to formation of a stable genotoxic compound from HU. On the contrary, scavenging of free H2O2 by HU probably lowered the levels of UDS that could be detected by these agents. Induction of unscheduled DNA synthesis by neutrophils and H2O2 occurred under conditions of less cytostasis than was found with other DNA-damaging agents such as 4-nitroquinoline 1-oxide or gamma-irradiation. This may reflect a heightened responsiveness of the cells to repair of damage from physiological oxidants. The results demonstrate that DNA damage induced by reactive oxygen intermediates can be repaired by nucleotide excision-repair pathways.

Protective effect of gypenosides against oxidative stress in phagocytes, vascular endothelial cells and liver microsomes

The action of gypenosides (GP, saponins of Gynostemma pentaphyllum, a Chinese medicinal herb) as an antioxidant was studied using various models of oxidant stress in phagocytes, liver microsomes and vascular endothelial cells. The results show that GP decreased superoxide anion and hydrogen peroxide content in human neutrophils and diminished chemiluminescent oxidative burst triggered by zymosan in human monocytes and murine macrophages. An increase of lipid peroxidation induced by Fe2+/cysteine, ascorbate/NADPH or hydrogen peroxide in liver microsomes and vascular endothelial cells was inhibited by GP. It was also found that GP protected biomembranes from oxidative injury by reversing the decreased membrane fluidity of liver microsomes and mitochondria, increasing mitochondrial enzyme activity in vascular endothelial cells and decreasing intracellular lactate dehydrogenase leakage from these cells. The extensive antioxidant effect of GP may be valuable to the prevention and treatment of various diseases such as atherosclerosis, liver disease and inflammation.

Modulation of the H2O2-induced SOS response in Escherichia coli PQ300 by amino acids, metal chelators, antioxidants, and scavengers of reactive oxygen species

The SOS chromotest is a simple colorimetric genotoxicity assay that monitors DNA repair by measuring the induction of the gene sfiA in Escherichia coli K-12. E. coli PQ300, a diagnostic SOS tester strain for the detection of oxidative genotoxins, carries a mutation in a key gene for antioxidative defense, oxyR. This mutation renders PQ300 more sensitive to oxidative genotoxins, particularly to H2O2. We found that induction of the SOS response by H2O2 in E. coli PQ300 is dependent on the composition of the incubation medium; a substantially reduced response was obtained in minimal phosphate buffered saline (PBS) as opposed to complex Luria broth (LB) medium. Supplementation of PBS with histidine or cysteine stimulated H2O2-induced SOS induction to levels exceeding those found in LB medium. Low concentrations of glutathione (20-70 microM) also enhanced the H2O2-induced SOS response in E. coli PQ300, whereas higher concentrations (> 150 microM) were protective. Preincubation of tester cells with the chelators o-phenanthroline, 2,2-dipyridyl, and ethylenediaminetetraacetic acid (EDTA) protected cells from the effects of H2O2, although EDTA was only partially effective. Pretreatment of PQ300 with the antioxidant ascorbic acid or the hydroxyl radical scavenger dimethyl sulfoxide also diminished the SOS response, whereas mannitol and glucose were ineffective. The results show that the net effect of H2O2-induced DNA damage is influenced by the balance of oxidative and antioxidative factors and, furthermore, can be modulated by constituents of the extracellular milieu.

L-glutamine prevents the L-histidine-mediated enhancement of hydrogen peroxide-induced cytotoxicity

Results presented in this study demonstrate that L-glutamine, a competitive inhibitor of L-histidine uptake, inhibits in a concentration-dependent fashion the L-histidine-mediated enhancement of H2O2-induced cytotoxicity. L-Glutamine also prevents the induction of DNA double strand breaks (DSB) but does not affect the enhancing effect of L-histidine on DNA single strand break induction by H2O2. Taken together, these data demonstrate that L-histidine, in order to allow the formation of DNA double strand breakage and increase the toxicity elicited by the oxidant, has to enter the cell. In addition, these results indicate that the enhancement of DNA single strand breakage is a consequence of the action of the amino acid at the extracellular level and/or outer surface of the plasma membrane and does not appear related to the mechanism whereby L-histidine increases the cytotoxic response to H2O2. The latter mechanism very likely involves the formation of DNA DSB.

Differential effect of the amino acid cystine in cultured mammalian and bacterial cells exposed to oxidative stress

The effect of cystine in the cytotoxic response of cultured Chinese hamster ovary and Escherichia coli cells to challenge with hydrogen peroxide has been investigated. It was found that this amino acid could either protect or sensitize cells, depending on the cellular system. In fact, although a reduction in the growth-inhibitory effect of hydrogen peroxide was observed in mammalian cells, a marked increase in the susceptibility to oxidative stress was induced by cystine in bacteria. None of the amino acid precursors of glutathione, e.g., glutamate, glycine or cysteine, afforded protection in the mammalian cell system, whereas cysteine, but not glycine or glutamate, markedly sensitized bacteria to hydrogen peroxide-induced cell killing. In mammalian cells, methionine, an amino acid which is converted to cysteine, was also unable to modify the oxidative response. The results presented indicate that cystine displays differential effects in oxidatively injured mammalian or bacterial cells and suggest that the mechanism whereby the amino acid modulates the lethal action of hydrogen peroxide differs in the two cellular systems.

Effect of lipophilic chelators on oxyradical-induced DNA strand breaks in human granulocytes: paradoxical effect of 1,10-phenanthroline

Strand breaks can be produced in the DNA of intact granulocytes by a flux of oxyradicals (O2- and H2O2) generated by tetradecanoylphorbol acetate (TPA) or by a flux of H2O2 generated by glucose oxidase. The mechanism by which such breaks are induced is still uncertain. Lipophilic chelators such as dipyridyl and 1,10-phenanthroline (OP) strongly inhibit strand breaks induced by H2O2, presumably because of their ability to chelate intracellular iron. We now report that dipyridyl also partially inhibits strand breaks in TPA-stimulated granulocytes while a "copper-specific" lipophilic chelator, neocuproine, has no effect. As opposed to these effects, OP increases the number of strand breaks in TPA-stimulated granulocytes. Superoxide dismutase (SOD) (but not catalase) partially blocks this increase. Both the cell-impermeable chelator, EDTA, and neocuproine strongly block the increase also. In fact, in the presence of EDTA, OP behaves like dipyridyl and inhibits strand breaks. Preformed OP2-copper(II) complex causes DNA breaks in TPA-stimulated granulocytes. The paradoxical effect of OP may be explained by assuming that OP may form two different metal complexes, a DNA-damaging complex with copper or an inhibitory complex with iron. If copper(II) and O2- are present, the first complex may form and the net effect may be an increase in strand breaks. If the formation of this complex is prevented by SOD, EDTA, or neocuproine, then OP may complex iron and the net effect may be (like dipyridyl) an inhibition of strand breaks. The source of the copper responsible for the formation of OP2-copper complex is unknown.

The role of extracellular medium components and specific amino acids in the cytotoxic response of Escherichia coli and Chinese hamster ovary cells to hydrogen peroxide

A concentration of H2O2 resulting in mode one killing of Escherichia coli is more toxic when exposure to the oxidant is performed in complete medium (K medium), as compared to a saline (M9 salts). Inorganic salts (MgSO4 and CaCl2), thiamine or glucose, when added separately, or combined, to M9 salts had no effect on the cytotoxic response to H2O2. In contrast, the lethality of the oxidant was highly dependent on the presence of the amino acids in the incubation medium. The addition of glucose further enhanced this response. Among the seventeen amino acids which are present in the complete amino acid mixture, only two, i.e. L-histidine and L-cystine, were found to increase the toxicity of H2O2. Again, glucose augmented this response. The effect of these amino acids on the growth inhibitory action of hydrogen peroxide was also tested in Chinese Hamster Ovary cells. It was found that L-histidine was capable of increasing the toxicity of the oxidant whereas all the other amino acids did not affect the toxicity of the oxidant. Glucose only slightly augmented this effect of L-histidine. DNA single strand breakage produced by H2O2 was increased by L-histidine and was not significantly modified by the other amino acids. DNA double strand breakage was also shown to occur in cells exposed to H2O2-L-histidine, and this effect was independent on the presence of glucose. These results demonstrate that the cytotoxic response of bacterial and mammalian cells to challenge with H2O2 is highly dependent on the composition of the extracellular milieu.(ABSTRACT TRUNCATED AT 250 WORDS)

Does hydrogen peroxide exist "free" in biological systems?

Hydrogen peroxide (H2O2) can diffuse far from the site of production to intracellular locations where biological effects may be greater. The diffusion range is extended by H2O2 carriers formed spontaneously by hydrogen bonding with monomeric and polymeric compounds, including amino and dicarboxylic acids, peptides, proteins, nucleic acid bases, and nucleosides. Hydrogen peroxide adducts (HPAs) are readily synthesized, e.g., crystalline histidine (His)-H2O2 adducts. An equilibrium exists between an adduct-forming compound and H2O2. The detection and relative stabilities of HPAs are measured by the degree of decomposition of H2O2 as influenced by test compounds in buffered solution competing with glucose or fructose for H2O2. The HPAs delay decomposition of H2O2 up to several hundredfold. The overall charge on an HPA, i.e., its ability to penetrate cell membranes, influences the cytotoxic and clastogenic effects of H2O2. Growth inhibition of Salmonella typhimurium LT2 by H2O2 is enhanced by neutral HPAs but decreased by anionic HPAs. Addition of catalase 1, 10, or 30 min after inoculation of S. typhimurium LT2 reduces or nearly eliminates partial growth inhibition by H2O2, but a neutral HPA, especially His-H2O2, transported H2O2 into the cells within 1 min, and in about 10 min completely inhibited growth. The stability of HPAs decreases with increasing pH or increasing temperature, while added Fe(II) in the presence and absence of EDTA accelerates H2O2 and HPA decomposition. Calculations indicate H2O2 hydrogen bonds with nucleic acid-base pairs with no apparent bond strain and energy stabilization comparable to normal hydrogen bonding.