Ammonium-dependent hydrogen peroxide production by mitochondria

NADH-supported generation of H2O2 by permeabilized rat heart mitochondria was partially prevented by the specific complex I-directed inhibitor, NADH-OH, and was significantly stimulated by ammonium. Ammonium did not affect H2O2 production by complex I in coupled submitochondrial particles. The soluble mitochondrial matrix protein fraction catalyzed NADH-dependent H2O2 production, which was greatly (approximately 10-fold) stimulated by ammonium. We conclude that complex I is not the major contributor to mitochondrial superoxide (hydrogen peroxide) generation and that there are specific ammonium-sensitive NADH:oxygen oxidoreductase(s) in the mitochondrial matrix which are responsible for mitochondrial H2O2 production.     

Reversible oxidation of glyceraldehyde 3-phosphate dehydrogenase thiols in human lung carcinoma cells by hydrogen peroxide

Human lung carcinoma cells (A549) were oxidatively stressed with mildly-toxic or non-toxic amounts of hydrogen peroxide (H2O2, 0.1 mM to 120 mM) for 5 min. Hydrogen peroxide exposure resulted in a dose dependent inhibition of binding (pH 7) of the thiol reagent iodoacetic acid (IAA) to a 38 kDa cell protein. Incubation of cells in saline for 60 min following H2O2 removal restored the ability of IAA to bind to the protein. Treatment with 20 mM dithiothreitol or 2 M urea also restored IAA binding, but 10% Triton X102 or 1 mM Brij 58 had no effect. Increasing to pH 11 during the IAA binding also increased thiol availability. Glyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.12) has been identified as the protein undergoing thiol/disulfide redox status and enzymic activity changes.     

Antisteroidogenic actions of hydrogen peroxide on rat Leydig cells

It has been well known that reactive oxygen species (ROS) are produced in the steroidogenic pathway and spermatozoa. H2O2, one of ROS produced by spermatozoa, appears to be a primary toxic agent. In the present study, we examined the effects of H2O2 on the basal and evoked-testosterone release from primary Leydig cells, the protein expressions of cytochrome P450 side chain cleavage enzyme (P450scc) and steroidogenic acute regulatory (StAR) protein were also investigated. Our preparation was found to contain approximately 87% Leydig cells and very few macrophages. The results demonstrated that H2O2 (>1 x 10(-4) M) significantly inhibited the basal and hCG-stimulated testosterone release. H2O2 abolished forskolin- or 8-Br-cAMP-evoked testosterone release. In the presence of pregnenolone, progesterone, or androstenedione, the inhibitory effect of H2O2 on testosterone release was prevented. H2O2 also inhibited pregnenolone production in the presence of trilostane (an inhibitor of 3beta-hydroxysteroid dehydrogenase), therefore diminished the activity of P450scc in Leydig cells. In addition to the inhibition of hormone secretion, H2O2 also regulated steroidogenesis by diminishing protein expression of StAR. These results suggest that H2O2 acts directly on rat Leydig cells to diminish testosterone production by inhibiting P450scc activity and StAR protein expression.     

The hydrogen peroxide/copper ion system, but not other metal-catalyzed oxidation systems, produces protein-bound dityrosine

Dityrosine formation leads to the cross-linking of proteins intra- or intermolecularly. The formation of dityrosine in lens proteins oxidized by metal-catalyzed oxidation (MCO) systems was estimated by chemical and immunochemical methods. Among the four MCO systems examined (H(2)O(2)/Cu, H(2)O(2)/Fe-ethylenediaminetetraacetic acid (Fe-EDTA), ascorbate/Cu, ascorbate/Fe-EDTA), the treatment with H(2)O(2)/Cu preferentially caused dityrosine formation in the lens proteins. The success of oxidative protein modification with all the MCO systems was confirmed by carbonyl formation estimated using 2,4-dinitrophenylhydrazine. The loss of tyrosine by the MCO systems was partly due to the formation of protein-bound 3,4-dihydroxyphenylalanine. The formation of dityrosine specific to H(2)O(2)/Cu was confirmed by using poly-(Glu, Ala, Tyr) and N-acetyl-tyrosine as a substrate. The dissolved oxygen concentration in the H(2)O(2)/Cu system hardly affected the amount of dityrosine formation, suggesting that dityrosine generation by the H(2)O(2)/Cu system is independent of oxygen concentration. Moreover, the combination of copper ion with H(2)O(2) is the most effective system for dityrosine formation among various metal ions examined. The addition of reducing agents, glutathione or ascorbic acid, into the H(2)O(2)/Cu system suppressed the generation of the dityrosine moiety, suggesting effective quench of tyrosyl radicals by the reducing agents.     

Genetically encoded fluorescent indicator for intracellular hydrogen peroxide

We developed a genetically encoded, highly specific fluorescent probe for detecting hydrogen peroxide (H(2)O(2)) inside living cells. This probe, named HyPer, consists of circularly permuted yellow fluorescent protein (cpYFP) inserted into the regulatory domain of the prokaryotic H(2)O(2)-sensing protein, OxyR. Using HyPer we monitored H(2)O(2) production at the single-cell level in the cytoplasm and mitochondria of HeLa cells treated with Apo2L/TRAIL. We found that an increase in H(2)O(2) occurs in the cytoplasm in parallel with a drop in the mitochondrial transmembrane potential (DeltaPsi) and a change in cell shape. We also observed local bursts in mitochondrial H(2)O(2) production during DeltaPsi oscillations in apoptotic HeLa cells. Moreover, sensitivity of the probe was sufficient to observe H(2)O(2) increase upon physiological stimulation. Using HyPer we detected temporal increase in H(2)O(2) in the cytoplasm of PC-12 cells stimulated with nerve growth factor.     

Nitric oxide-induced resistance to hydrogen peroxide stress is a glutamate cysteine ligase activity-dependent process

Nitric oxide (*NO) is a reactive nitrogen species known to be involved in cytotoxic processes. Cells respond to cytotoxic injury by stress response induction leading to the development of cellular resistance. This report describes an *NO-induced stress response in Chinese hamster fibroblasts (HA1), which leads to glutathione synthesis-dependent resistance to H2O2-mediated oxidative stress. The development of resistance to H2O2 was completely abolished by the inhibition of glutamate cysteine ligase (GCL) during the first 8 h of recovery after *NO exposure. Altered thiol metabolism was observed immediately after *NO exposure as demonstrated by up to 75% decrease in intracellular thiol pools (glutathione, gamma-glutamylcysteine, and cysteine), which then reaccumulated during the *NO-mediated development of resistance. Immunoreactive protein and activity associated with GCL decreased immediately after exposure to *NO and then reaccumulated during the development of resistance to H2O2 challenge. Moreover, compared to N2 controls the activity levels of GCL in *NO-exposed cells increased approximately twofold 24 h after H2O2 challenge. These results demonstrate that *NO exposure is capable of inducing an adaptive response to H2O2-mediated oxidative stress in mammalian cells, which involves alterations in thiol metabolism and is dependent upon glutathione synthesis and increased GCL activity.     

The oxygen-evolving complex requires chloride to prevent hydrogen peroxide formation.

Illumination of PSII core preparations can cause the production of H2O2 at rates which approach 60 mumol of H2O2 (mg of Chl.h)-1. The rate of peroxide production is maximal at pH 7.2 at low sucrose concentrations and at concentrations of Cl- (1.5-3.0 mM) that limit the rate of the oxidation of water to O2. The rate of H2O2 production increased with pH from pH 6.8 to 7.2 and was inversely proportional to the oxidation of water to O2 from pH 6.8 to 7.5. While EDTA does not inhibit H2O2 production, this reaction is abolished by 5 mM NH2OH and inhibited by the same concentrations of NH3 that affect water oxidation which indicates that the oxygen-evolving complex is responsible for the production of peroxide generated upon illumination of PSII core preparations. These results support a mechanism in which bound Cl- in the S2 state is displaced by OH- ions which are then oxidized by the OEC to form H2O2. Thus, the OEC requires Cl- to prevent access to the active site of the OEC until four oxidizing equivalents can be generated to allow the oxidation of water to O2.     

Behavior of hydrogen peroxide in electrolyzed anode water

Oxygen electrodes and spectrophotometric analysis have been used to evaluate the contribution of H2O2, in addition to available chlorine, to the high redox potential of electrolyzed anode water (EAW) with potassium chloride as an electrolyte. H2O2 was added externally to EAW, and the reaction between H2O2 and the available chlorine in the water was examined. EAW has a low pH (2.5), a high concentration of dissolved oxygen, and extremely high redox potentials (19 mg/l and 1,319 mV) when the available chlorine is at the concentration of about 580 microM. The addition of H2O2 to EAW led to H2O2 decomposition, and the amount of oxygen produced was equivalent to the amount of available chlorine. Oxygen production was reduced by ascorbic acid, and completely inhibited by 600 microM ascorbate. The rate of oxygen production was much affected by pH, and was slowest at or near pH 5.0. Rates were particularly high in alkaline solution. Absorbance at 235 nm (pH 3.0 and 5.0) and 292 nm (pH 10.0) decreased when H2O2 was added to the EAW at these pHs, and the extent of decrease was similar pH dependency to that of the oxygen production rate. Oxygen was not produced after H2O2 was added to EAW at pH 2.6 when available chlorine was absent, but oxygen was produced after potassium hypochlorite was added to such EAW. The oxygen production rates in EAW without available chlorine at pH 5.0 and 2.0, pH adjustment with KOH and HCl, respectively, were faster than the rate at pH 2.6, and fastest at pH 2.0. These results suggest that H2O2 or hydroxyl radicals derived from Fenton's reaction did not contribute to the high redox potential of EAW prepared with chlorine compounds as an electrolyte, so that the decomposition of H2O2 occurred rapidly with the reactions of chlorine and hypochlorite ions in EAW.     

Oxidation and generation of hydrogen peroxide by thiol compounds in commonly used cell culture media

Many studies have examined the effects of thiol compounds upon cells in culture (e.g., upon signal transduction and regulation of gene expression), but few have considered how thiols can interact with cell culture media. A wide range of thiols (cysteine, GSH, N-acetylcysteine, gamma-glutamylcysteine, cysteinylglycine, cysteamine, homocysteine) were found to interact with three commonly used cell culture media (RPMI, MEM, DMEM) to generate hydrogen peroxide with complex concentration-dependencies. Thiols added to these media rapidly disappeared, although less H(2)O(2) was generated on a molar basis than the amount of thiol lost. Studies on cellular effects of thiols, especially those on redox regulation of gene expression or protein function, need to take into account that thiols are rapidly lost, and that their oxidation generates H(2)O(2), which can have multiple concentration-dependent effects on cell metabolism.     

Glutathione oxidation and PTPase inhibition by hydrogen peroxide in Caco-2 cell monolayer

The role of H(2)O(2) and protein thiol oxidation in oxidative stress-induced epithelial paracellular permeability was investigated in Caco-2 cell monolayers. Treatment with a H(2)O(2) generating system (xanthine oxidase + xanthine) or H(2)O(2) (20 microM) increased the paracellular permeability. Xanthine oxidase-induced permeability was potentiated by superoxide dismutase and prevented by catalase. H(2)O(2)-induced permeability was prevented by ferrous sulfate and potentiated by deferoxamine and 1,10-phenanthroline. GSH, N-acetyl-L-cysteine, dithiothreitol, mercaptosuccinate, and diethylmaleate inhibited H(2)O(2)-induced permeability, but it was potentiated by 1,3-bis(2-chloroethyl)-1-nitrosourea. H(2)O(2) reduced cellular GSH and protein thiols and increased GSSG. H(2)O(2)-mediated reduction of GSH-to-GSSG ratio was prevented by ferrous sulfate, GSH, N-acetyl-L-cysteine, diethylmaleate, and mercaptosuccinate and potentiated by 1,10-phenanthroline and 1, 3-bis(2-chloroethyl)-1-nitrosourea. Incubation of soluble fraction of cells with GSSG reduced protein tyrosine phosphatase (PTPase) activity, which was prevented by coincubation with GSH. PTPase activity was also lower in H(2)O(2)-treated cells. This study indicates that H(2)O(2), but not O(2)(-). or.OH, increases paracellular permeability of Caco-2 cell monolayer by a mechanism that involves oxidation of GSH and inhibition of PTPases.     

Environmental influences on competitive hydrogen peroxide production in Streptococcus gordonii

Streptococcus gordonii is an important member of the oral biofilm. One of its phenotypic traits is the production of hydrogen peroxide (H2O2). H2O2 is an antimicrobial component produced by S. gordonii that is able to antagonize the growth of cariogenic Streptococcus mutans. Strategies that modulate H2O2 production in the oral cavity may be useful as a simple therapeutic mechanism to improve oral health, but little is known about the regulation of H2O2 production. The enzyme responsible for H2O2 production is pyruvate oxidase, encoded by spxB. The functional studies of spxB expression and SpxB abundance presented in this report demonstrate a strong dependence on environmental oxygen tension and carbohydrate availability. Carbon catabolite repression (CCR) modulates spxB expression carbohydrate dependently. Catabolite control protein A (CcpA) represses spxB expression by direct binding to the spxB promoter, as shown by electrophoretic mobility shift assays (EMSA). Promoter mutation studies revealed the requirement of two catabolite-responsive elements (CRE) for CcpA-dependent spxB regulation, as evaluated by spxB expression and phenotypic H2O2 production assays. Thus, molecular mechanisms for the control of S. gordonii spxB expression are presented for the first time, demonstrating the possibility of manipulating H2O2 production for increased competitive fitness.     

Superoxide and hydrogen peroxide formation during enzymatic oxidation of DOPA by phenoloxidase

Generation of superoxide anion and hydrogen peroxide during enzymatic oxidation of 3-(3,4-dihydroxyphenyl)-DL-alanine (DOPA) has been studied. The ability of DOPA to react with O2*- has been revealed. EPR spectrum of DOPA-semiquinone formed upon oxidation of DOPA by O2*- was observed using spin stabilization technique of ortho-semiquinones by Zn2+ ions. Simultaneously, the oxidation of DOPA by O2*- was found to produce hydrogen peroxide (H2O2). The analysis of H2O2 formation upon oxidation of DOPA by O2*- using 1-hydroxy-3-carboxy-pyrrolidine (CP-H), and SOD as competitive reagents for superoxide provides consistent values of the rate constant for the reaction between DOPA and O2*- being equal to (3.4+/-0.6)x10(5) M(-1) s(-1).The formation of H2O2 during enzymatic oxidation of DOPA by phenoloxidase (PO) has been shown. The H2O2 production was found to be SOD-sensitive. The inhibition of H2O2 production by SOD was about 25% indicating that H2O2 is produced both from superoxide anion and via two-electron reduction of oxygen at the enzyme. The attempts to detect superoxide production during enzymatic oxidation of DOPA using a number of spin traps failed apparently due to high value of the rate constant for DOPA interaction with O2*-.     

Superoxide, hydrogen peroxide and singlet oxygen in hematoporphyrin derivative-cysteine, -NADH and -light systems

Hematoporphyrin derivative and light in the presence of cysteine or glutathione were found to convert oxygen to superoxide and hydrogen peroxide at pH less than approx. 6.5, while at pH greater than 6.5 no superoxide or hydrogen peroxide production was observed. However, at pH values greater than 6.5 the rate of oxygen consumption increased. This rate paralleled the acid dissociation curve of the cysteine thiol group and is consistent with the chemical quenching of 1O2 by cysteine. The superoxide and hydrogen peroxide formation observed below pH 6.5 appeared not to be related to the singlet oxygen production of hematoporphyrin derivative. In addition, superoxide and hydrogen peroxide production was observed with hematoporphyrin derivative and light in the presence of NADH, both above and below pH 6.5. Direct detection of singlet oxygen luminescence at 1268 nm in the hematoporphyrin derivative-light system (2H2O as solvent) revealed an apparent linear increase in the singlet oxygen emission intensity as the p2H was raised from 7.0 to 10.0. Azide efficiently quenched this observed emission. In addition, at p2H 7.4, 1 mM cysteine resulted in a 40% reduction of the singlet oxygen luminescence, while at p2H 9.4 the signal was quenched by over 95% (under the experimental conditions employed). In total, we interpret these results as consistent with the chemical quenching of 1O2 by the ionized thiol group of cysteine.     

The sensitivity of ABI2 to hydrogen peroxide links the abscisic acid-response regulator to redox signalling

ABI1 and ABI2 are two protein serine/threonine phosphatases of type 2C (EC 3.1.3.16) that act as key regulators in the responses of Arabidopsis thaliana (L.) Heynh. to abscisic acid (ABA). They are involved in the control of ABA-mediated seed dormancy, stomatal closure and vegetative growth inhibition. Analysis of the enzymatic properties of ABI2 revealed high sensitivities towards protons and unsaturated fatty acids. Furthermore, the protein phosphatase activity of ABI2 is very sensitive to H2O2, which has recently emerged as a secondary messenger of ABA signalling. Upon H2O2 challenge, ABI2 is rapidly inactivated with an IC50 value of 50 microM in the presence of reduced glutathione. Inhibitor studies with phenylarsine oxide and manipulation of the redox status of ABI2 in vitro indicate that oxidation of critical cysteine residue(s) is responsible for inactivation. The levels of the major cellular thiol compounds cysteine and glutathione in leaves and seedlings of A. thaliana are compatible with a physiological role of H2O2 in regulating ABI2 activity. ABI2 is considered to exert negative regulation on ABA action. Thus, transient inactivation of this protein phosphatase by H2O2 would allow or enhance the ABA-dependent signalling process. In conclusion, ABI2 represents a likely target for redox-regulation of a hormonal signalling pathway in higher plants.     

Antisteroidogenic effects of hydrogen peroxide on rat granulosa cells

Rat granulosa cells (GCs) were treated with human chorionic gonadotropin (hCG), 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP), forskolin, phorbol 12-myristate 13-acetate (PMA), A23187 or pregnenolone in the absence or presence of hydrogen peroxide (H(2)O(2)). Different doses of trilostane were applied to GCs treated with steroidogenic precursors, that is, 25-hydroxy-cholesterol (25-OH-C) in the absence or presence of H(2)O(2). Results showed that all of the chemicals stimulated the progesterone (PG) release from rat GCs, but the stimulatory effects were inhibited by H(2)O(2) dose-dependently. 25-OH-C stimulated the PG release, which was inhibited by H(2)O(2) in the presence of trilostane. H(2)O(2) attenuated steroidogenic acute regulatory (StAR) protein expression, but did not alter the expression of cytochrome P450 side chain cleavage (P450scc) in Western blotting. This study indicated that H(2)O(2) inhibited PG production by GCs via cAMP pathway, protein kinase C (PKC) and the activities of intracellular calcium, P450scc and StAR protein.     

The oxidation of yeast alcohol dehydrogenase-1 by hydrogen peroxide in vitro

Yeast alcohol dehydrogenase (YADH) plays an important role in the conversion of alcohols to aldehydes or ketones. YADH-1 is a zinc-containing protein, and it accounts for the major part of ADH activity in growing baker's yeast. To gain insight into how oxidative modification of the enzyme affects its function, we exposed YADH-1 to hydrogen peroxide in vitro and assessed the oxidized protein by LC-MS/MS analysis of proteolytic cleavage products of the protein and by measurements of enzymatic activity, zinc release, and thiol/thiolate loss. The results illustrated that Cys43 and Cys153, which reside at the active site of the protein, could be selectively oxidized to cysteine sulfinic acid (Cys-SO2H) and cysteine sulfonic acid (Cys-SO3H). In addition, H2O2 induced the formation of three disulfide bonds: Cys43-Cys153 in the catalytic domain, Cys103-Cys111 in the noncatalytic zinc center, and Cys276-Cys277. Therefore, our results support the notion that the oxidation of cysteine residues in the zinc-binding domain of proteins can go beyond the formation of disulfide bond(s); the formation of Cys-SO2H and Cys-SO3H is also possible. Furthermore, most methionines could be oxidized to methionine sulfoxides. Quantitative measurement results revealed that, among all the cysteine residues, Cys43 was the most susceptible to H2O2 oxidation, and the major oxidation products of this cysteine were Cys-SO2H and Cys-SO3H. The oxidation of Cys43 might be responsible for the inactivation of the enzyme upon H2O2 treatment.     

Iron and hydrogen peroxide detoxification properties of DNA-binding protein from starved cells. A ferritin-like DNA-binding protein of Escherichia coli

The DNA-binding proteins from starved cells (Dps) are a family of proteins induced in microorganisms by oxidative or nutritional stress. Escherichia coli Dps, a structural analog of the 12-subunit Listeria innocua ferritin, binds and protects DNA against oxidative damage mediated by H(2)O(2). Dps is shown to be a Fe-binding and storage protein where Fe(II) oxidation is most effectively accomplished by H(2)O(2) rather than by O(2) as in ferritins. Two Fe(2+) ions bind at each of the 12 putative dinuclear ferroxidase sites (P(Z)) in the protein according to the equation, 2Fe(2+) + P(Z) --> [(Fe(II)(2)-P](FS)(Z+2) + 2H(+). The ferroxidase site (FS) bound iron is then oxidized according to the equation, [(Fe(II)(2)-P](FS)(Z+2) + H(2)O(2) + H(2)O --> [Fe(III)(2)O(2)(OH)-P](FS)(Z-1) + 3H(+), where two Fe(II) are oxidized per H(2)O(2) reduced, thus avoiding hydroxyl radical production through Fenton chemistry. Dps acquires a ferric core of approximately 500 Fe(III) according to the mineralization equation, 2Fe(2+) + H(2)O(2) + 2H(2)O --> 2Fe(III)OOH((core)) + 4H(+), again with a 2 Fe(II)/H(2)O(2) stoichiometry. The protein forms a similar ferric core with O(2) as the oxidant, albeit at a slower rate. In the absence of H(2)O(2) and O(2), Dps forms a ferrous core of approximately 400 Fe(II) by the reaction Fe(2+) + H(2)O + Cl(-) --> Fe(II)OHCl((core)) + H(+). The ferrous core also undergoes oxidation with a stoichiometry of 2 Fe(II)/H(2)O(2). Spin trapping experiments demonstrate that Dps greatly attenuates hydroxyl radical production during Fe(II) oxidation by H(2)O(2). These results and in vitro DNA damage assays indicate that the protective effect of Dps on DNA most likely is exerted through a dual action, the physical association with DNA and the ability to nullify the toxic combination of Fe(II) and H(2)O(2). In the latter process a hydrous ferric oxide mineral core is produced within the protein, thus avoiding oxidative damage mediated by Fenton chemistry.     

Identification of proteins containing cysteine residues that are sensitive to oxidation by hydrogen peroxide at neutral pH

A procedure for detecting proteins that contain H(2)O(2)-sensitive cysteine (or selenocysteine) residues was developed as a means with which to study protein oxidation by H(2)O(2) in cells. The procedure is based on the facts that H(2)O(2) and biotin-conjugated iodoacetamide (BIAM) selectively and competitively react with cysteine residues that exhibit a low pK(a), and that the decrease in the labeling of cell lysate proteins with BIAM caused by prior exposure of cells to H(2)O(2) or to an agent that induces H(2)O(2) production can be monitored by streptavidin blot analysis. This procedure was applied to rat pheochromocytoma PC12 cells directly treated with H(2)O(2), mouse hippocampal HT22 cells in which H(2)O(2) production was induced by glutamate, and human erythroleukemia K562 cells in which H(2)O(2) production was induced by phorbol myristate acetate. It revealed that several cell proteins contain cysteine or selenocysteine residues that are selectively oxidized by H(2)O(2). Three of these H(2)O(2)-sensitive proteins were identified as a member of the protein disulfide isomerase family, thioredoxin reductase, and creatine kinase, all of which were previously known to contain at least one reactive cysteine or selenocysteine at their catalytic sites. This procedure should thus prove useful for the identification of proteins that are oxidized by H(2)O(2) generated in response to a variety of extracellular agents.     

Vascular endothelial cell killing by combinations of membrane-active agents and hydrogen peroxide

Previous studies have demonstrated that a number of membrane-active agents are capable of binding to the surface of polymorphonuclear leukocytes (PMN) resulting in an augmentation of superoxide anion and hydrogen peroxide (H2O2) production in response to soluble stimuli. It is now demonstrated that these same membrane-active agents can bind to the surface of endothelial cells and enhance their susceptibility to killing by H2O2. Membrane-active agents which are capable of synergizing with H2O2 include cationic proteins, cationic poly-amino acids, lysophosphatides and enzymes which are capable of degrading membrane phospholipids (e.g., phospholipase C, phospholipase A2 and streptolysin S). In each case, treatment of the target cells with the membrane-active agent and H2O2 produces greater damage than the sum of the damage produced by either agent separately. Since inflammatory lesions, particularly sites of bacterial infection, may contain a rich mixture of cationic substances, phospholipases and phospholipid breakdown products, these substances may contribute to the tissue damage observed at sites of inflammation by enhancing endothelial cell sensitivity to PMN-generated H2O2 as well as by augmenting the generation of H2O2 by PMNs.     

Fragmentation of human ceruloplasmin induced by hydrogen peroxide

We investigated the fragmentation of human ceruloplasmin induced by H2O2 to study its oxidative damage. When ceruloplasmin was incubated with H2O2, the frequency of the protein fragmentation increased in a proportion to the concentration of H2O2. It also increased in a time-dependent manner and was accompanied by gradual loss of the oxidase activity. Hydroxyl radical scavengers such as azide and mannitol inhibited the fragmentation of ceruloplasmin. The deoxyribose assay showed that hydroxyl radicals were generated in the reaction of ceruloplasmin with H2O2. Incubation of ceruloplasmin with H2O2 resulted in a time-dependent release of copper ions. The released copper ion may participate in a Fenton-like reaction to produce hydroxyl radical, which enhanced the fragmentation. The protection of the fragmentation by copper chelators such as diethylenetriaminepentaacetic acid and bathocuproine indicates a role for copper ion in the reaction. These results suggest that the fragmentation of ceruloplasmin induced by H2O2 is due to hydroxyl radicals formed by a copper-dependent Fenton-like reaction.