Singlet oxygen ((1)Delta(g)O(2)) as the principal oxidant in myeloperoxidase-mediated bacterial killing in neutrophil phagosome

Selenium vitaminology: The connection between selenium, vitamin C, vitamin E, and ergothioneine

Selenium is connected to three small molecule antioxidant compounds, ascorbate, α-tocopherol, and ergothioneine. Ascorbate and α-tocopherol are true vitamins, while ergothioneine is a "vitamin-like" compound. Here we review how selenium is connected to all three. Selenium and vitamin E work together as a team to prevent lipid peroxidation. Vitamin E quenches lipid hydroperoxyl radicals and the resulting lipid hydroperoxide is then converted to the lipid alcohol by selenocysteine-containing glutathione peroxidase. Ascorbate reduces the resulting α-tocopheroxyl radical in this reaction back to α-tocopherol with concomitant production of the ascorbyl radical. The ascorbyl radical can be reduced back to ascorbate by selenocysteine-containing thioredoxin reductase. Ergothioneine and ascorbate are both water soluble, small molecule reductants that can reduce free radicals and redox-active metals. Thioredoxin reductase can reduce oxidized forms of ergothioneine. While the biological significance of this is not yet realized, this discovery underscores the centrality of selenium to all three antioxidants.

Propofol metabolites and derivatives inhibit the oxidant activities of neutrophils and myeloperoxidase

In previous studies, propofol has shown immunomodulatory abilities on various in vitro models. As this anesthetic molecule is extensively used in intensive care units, its anti-inflammatory properties present a great interest for the treatment of inflammatory disorders like the systemic inflammatory response syndrome. In addition to its inhibition abilities on important neutrophils mechanisms (chemotaxis, reactive oxygen species (ROS) production, Neutrophil Extracellular Traps (NETs) formation, …), our group has shown that propofol is also a reversible inhibitor of the oxidant myeloperoxidase (MPO) activity. Propofol being subject to rapid metabolism, its derivatives could contribute to its anti-inflammatory action. First, propofol-β-glucuronide (PPFG), 2,6-diisopropyl-1,4-p-benzoquinone (PPFQ) and 3,5,3',5'-tetraisopropyl-(4,4')-diphenoquinone (PPFDQ) were compared on their superoxide (O₂^.-) scavenging properties and more importantly on their inhibitory action on the O₂^.- release by activated neutrophils using EPR spectroscopy and chemiluminescence assays. PPFQ and PPFDQ are potent superoxide scavengers and also inhibit the release of ROS by neutrophils. An Enzyme-Linked Immunosorbent Assay (ELISA) has also highlighted the ability of both molecules to significantly decrease the MPO degranulation process of neutrophils. Fluorescence enzymatic assays helped to investigate the action of the propofol derivatives on the peroxidase and chlorination activities of MPO. In addition, using SIEFED (Specific Immunological Extraction Followed by Enzyme Detection) assays and docking, we demonstrated the concentration-dependent inhibitory action of PPFQ and its ability to bind to the enzyme active site while PPFG presented a much weaker inhibitory action. Overall, the oxidation derivatives and metabolites PPFQ and PPFDQ can, at physiological concentrations, perpetuate the immunomodulatory action of propofol by acting on the oxidant response of PMN and MPO.

Singlet Molecular Oxygen Generation in the Reaction of Biological Haloamines of Amino Acids and Polyamines with Hydrogen Peroxide

Leucocytes generate hypohalous acids (HOCl and HOBr) to defend against pathogens. In cells, hypohalous acids react with amine-containing molecules, such as amino acids and polyamines, producing chloramines and bromamines, reservoirs of oxidizing power that can potentially damage host tissues at sites of inflammation. Hypohalous acids also react with H₂ O₂ to produce stoichiometric amounts of singlet molecular oxygen (¹ O₂ ), but its generation in leucocytes is still under debate. Additionally, it is unclear if haloamines generate ¹ O₂ following a reaction with H₂ O₂ . Herein, we provide evidence of the generation of ¹ O₂ in the reactions between amino acid-derived (taurine, N-α-acetyl-Lysine, and glycine) and polyamine-derived (spermine and spermidine) haloamines and H₂ O₂ in an aqueous solution. The unequivocal formation of ¹ O₂ was detected by monitoring its characteristic monomol light emission at 1270 nm in the near-infrared region. For amino acid-derived haloamines, the presence of ¹ O₂ was further confirmed by chemical trapping with anthracene-9,10-divinylsulfonate and HPLC-MS/MS detection. Altogether, photoemission and chemical trapping studies demonstrated that chloramines were less effective at producing ¹ O₂ than bromamines of amino acids and polyamines. Thus, ¹ O₂ formation via bromamines and H₂ O₂ may be a potential source of ¹ O₂ in non-illuminated biological systems.

Dehydromethionine is a common product of methionine oxidation by singlet molecular oxygen and hypohalous acids

Methionine is one of the main targets for biological oxidants. Its reaction with the majority of oxidants generates only methionine sulfoxide. However, when N-terminal methionine reacts with hypohalous acids (HOCl and HOBr) or singlet molecular oxygen (¹O₂), it can also generate a cyclic product called dehydromethionine (DHM). Previously, DHM was suggested as a biomarker of oxidative stress induced by hypohalous acids. However, DHM can also be generated by ¹O₂ -oxidation of methionine, and the contribution of this pathway of DHM formation in a context of a site-specific redox imbalance in an organism is unknown. In this work, a through comparison of the reactions of hypohalous acids and ¹O₂ with methionine, either free or inserted in peptides and proteins was undertaken. In addition, we performed methionine photooxidation in heavy water (H₂¹⁸O) to determine the influence of the pH in the mechanism of DHM formation. We showed that for free methionine, or methionine-containing peptides, the yields of DHM formation in the reactions with ¹O₂ were close to those achieved by HOBr oxidation, but much higher than the yields obtained with HOCl as the oxidant. This was true for all pH tested (5, 7.4, and 9). Interestingly, for the protein ubiquitin, DHM yields after reaction with ¹O₂ were higher than those obtained with both hypohalous acids. Our results indicate that ¹O₂ may also be an important source of DHM in biological systems.

Oxidized Forms of Ergothioneine Are Substrates for Mammalian Thioredoxin Reductase

Ergothioneine (EGT) is a sulfur-containing amino acid analog that is biosynthesized in fungi and bacteria, accumulated in plants, and ingested by humans where it is concentrated in tissues under oxidative stress. While the physiological function of EGT is not yet fully understood, EGT is a potent antioxidant in vitro. Here we report that oxidized forms of EGT, EGT-disulfide (ESSE) and 5-oxo-EGT, can be reduced by the selenoenzyme mammalian thioredoxin reductase (Sec-TrxR). ESSE and 5-oxo-EGT are formed upon reaction with biologically relevant reactive oxygen species. We found that glutathione reductase (GR) can reduce ESSE, but only with the aid of glutathione (GSH). The reduction of ESSE by TrxR was found to be selenium dependent, with non-selenium-containing TrxR enzymes having little or no ability to reduce ESSE. In comparing the reduction of ESSE by Sec-TrxR in the presence of thioredoxin to that of GR/GSH, we find that the glutathione system is 10-fold more efficient, but Sec-TrxR has the advantage of being able to reduce both ESSE and 5-oxo-EGT directly. This represents the first discovered direct enzymatic recycling system for oxidized forms of EGT. Based on our in vitro results, the thioredoxin system may be important for EGT redox biology and requires further in vivo investigation.

Role of myeloperoxidase and oxidant formation in the extracellular environment in inflammation-induced tissue damage

The heme peroxidase family generates a battery of oxidants both for synthetic purposes, and in the innate immune defence against pathogens. Myeloperoxidase (MPO) is the most promiscuous family member, generating powerful oxidizing species including hypochlorous acid (HOCl). Whilst HOCl formation is important in pathogen removal, this species is also implicated in host tissue damage and multiple inflammatory diseases. Significant oxidant formation and damage occurs extracellularly as a result of MPO release via phagolysosomal leakage, cell lysis, extracellular trap formation, and inappropriate trafficking. MPO binds strongly to extracellular biomolecules including polyanionic glycosaminoglycans, proteoglycans, proteins, and DNA. This localizes MPO and subsequent damage, at least partly, to specific sites and species, including extracellular matrix (ECM) components and plasma proteins/lipoproteins. Biopolymer-bound MPO retains, or has enhanced, catalytic activity, though evidence is also available for non-catalytic effects. These interactions, particularly at cell surfaces and with the ECM/glycocalyx induce cellular dysfunction and altered gene expression. MPO binds with higher affinity to some damaged ECM components, rationalizing its accumulation at sites of inflammation. MPO-damaged biomolecules and fragments act as chemo-attractants and cell activators, and can modulate gene and protein expression in naïve cells, consistent with an increasing cycle of MPO adhesion, activity, damage, and altered cell function at sites of leukocyte infiltration and activation, with subsequent tissue damage and dysfunction. MPO levels are used clinically both diagnostically and prognostically, and there is increasing interest in strategies to prevent MPO-mediated damage; therapeutic aspects are not discussed as these have been reviewed elsewhere.

Looking Back at the Early Stages of Redox Biology

The beginnings of redox biology are recalled with special emphasis on formation, metabolism and function of reactive oxygen and nitrogen species in mammalian systems. The review covers the early history of heme peroxidases and the metabolism of hydrogen peroxide, the discovery of selenium as integral part of glutathione peroxidases, which expanded the scope of the field to other hydroperoxides including lipid hydroperoxides, the discovery of superoxide dismutases and superoxide radicals in biological systems and their role in host defense, tissue damage, metabolic regulation and signaling, the identification of the endothelial-derived relaxing factor as the nitrogen monoxide radical (more commonly named nitric oxide) and its physiological and pathological implications. The article highlights the perception of hydrogen peroxide and other hydroperoxides as signaling molecules, which marks the beginning of the flourishing fields of redox regulation and redox signaling. Final comments describe the development of the redox language. In the 18th and 19th century, it was highly individualized and hard to translate into modern terminology. In the 20th century, the redox language co-developed with the chemical terminology and became clearer. More recently, the introduction and inflationary use of poorly defined terms has unfortunately impaired the understanding of redox events in biological systems.

Mechanism of Microbicidal Action of E-101 Solution, a Myeloperoxidase-Mediated Antimicrobial, and Its Oxidative Products

E-101 solution is a first-in-class myeloperoxidase-mediated antimicrobial developed for topical application. It is composed of porcine myeloperoxidase (pMPO), glucose oxidase (GO), glucose, sodium chloride, and specific amino acids in an aqueous solution. Once activated, the reactive species hydrogen peroxide (H₂O₂), hypochlorous acid, and singlet oxygen are generated. We evaluated the treatment effects of E-101 solution and its oxidative products on ultrastructure changes and microbicidal activity against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli Time-kill and transmission electron microscopy studies were also performed using formulations with pMPO or GO omitted. The glutathione membrane protection assay was used to study the neutralization of reactive oxygen species. The potency of E-101 solution was also measured in the presence of serum and whole blood by MIC and minimal bactericidal concentration (MBC) determinations. E-101 solution demonstrated rapid bactericidal activity and ultracellular changes in MRSA and E. coli cells. When pMPO was omitted, high levels of H₂O₂ generated from GO and glucose demonstrated slow microbicidal activity with minimal cellular damage. When GO was omitted from the formulation, no antimicrobial activity or cellular damage was observed. Protection from exposure to E-101 solution reactive oxygen species in the glutathione protection assay was competitive and temporary. E-101 solution maintained its antimicrobial activity in the presence of inhibitory substances, such as serum and whole blood. E-101 solution is a potent myeloperoxidase enzyme system with multiple oxidative mechanisms of action. Our findings suggest that the primary site where E-101 solution exerts microbicidal action is the cell membrane, by inactivation of essential cell membrane components.

Ergothioneine stands out from hercynine in the reaction with singlet oxygen: Resistance to glutathione and TRIS in the generation of specific products indicates high reactivity

The candidate vitamin ergothioneine (ET), an imidazole-2-thione derivative of histidine betaine, is generally considered an antioxidant. However, the precise physiological role of ET is still unresolved. Here, we investigated in vitro the hypothesis that ET serves specifically to eradicate noxious singlet oxygen (¹O₂). Pure ¹O₂ was generated by thermolysis at 37°C of N,N'-di(2,3-dihydroxypropyl)-1,4-naphthalenedipropanamide 1,4-endoperoxide (DHPNO₂). Assays of DHPNO₂ with ET or hercynine (= ET minus sulfur) at pH 7.4 were analyzed by LC-MS in full scan mode to detect products. Based on accurate mass and product ion scan data, several products were identified and then quantitated as a function of time by selected reaction monitoring. All products of hercynine contained, after a [4+2] cycloaddition of ¹O₂, a carbonyl at position 2 of the imidazole ring. By contrast, because of the doubly bonded sulfur, we infer from the products of ET as the initial intermediates a 4,5-dioxetane (after [2+2] cycloaddition) and hydroperoxides at position 4 and 5 (after Schenck ene reactions). The generation of single products from ET, but not from hercynine, was fully resistant to a large excess of tris(hydroxymethyl)aminomethane (TRIS) or glutathione (GSH). This suggests that ¹O₂ markedly favors ET over GSH (at least 50-fold) and TRIS (at least 250-fold) for the initial reaction. Loss of ET was almost abolished in 5mM GSH, but not in 25mM TRIS. Regeneration of ET seems feasible, since some ET products - by contrast to hercynine products - decomposed easily in the MS collision cell to become aromatic again.

The importance of antioxidants which play the role in cellular response against oxidative/nitrosative stress: current state

Remarkable interest has risen in the idea that oxidative/nitrosative stress is mediated in the etiology of numerous human diseases. Oxidative/Nitrosative stress is the result of an disequilibrium in oxidant/antioxidant which reveals from continuous increase of Reactive Oxygen and Reactive Nitrogen Species production. The aim of this review is to emphasize with current information the importance of antioxidants which play the role in cellular responce against oxidative/nitrosative stress, which would be helpful in enhancing the knowledge of any biochemist, pathophysiologist, or medical personnel regarding this important issue. Products of lipid peroxidation have commonly been used as biomarkers of oxidative/nitrosative stress damage. Lipid peroxidation generates a variety of relatively stable decomposition end products, mainly α, β-unsaturated reactive aldehydes, such as malondialdehyde, 4-hydroxy-2-nonenal, 2-propenal (acrolein) and isoprostanes, which can be measured in plasma and urine as an indirect index of oxidative/nitrosative stress. Antioxidants are exogenous or endogenous molecules that mitigate any form of oxidative/nitrosative stress or its consequences. They may act from directly scavenging free radicals to increasing antioxidative defences. Antioxidant deficiencies can develop as a result of decreased antioxidant intake, synthesis of endogenous enzymes or increased antioxidant utilization. Antioxidant supplementation has become an increasingly popular practice to maintain optimal body function. However, antoxidants exhibit pro-oxidant activity depending on the specific set of conditions. Of particular importance are their dosage and redox conditions in the cell.

Singlet Oxygen Enhances Intrinsic Thrombolysis: The Intrinsic Oxidative Clot Lysis Assay (INOXCLA)

Granulocytes are important cells of inflammation and cellular thrombolysis. They produce urokinase (u-PA) and chloramines. In this study, u-PA/chloramine—mediated fibrinolysis is imitated in a microtiter-plate. Seventy-five microliters plasma are incubated with 50 μL 50% Pathromtin SL, 6% BSA, and 38 mM CaCl2 for 30 minutes (37°C). Then, 50 μL 10 mM chloramine-T in PBS are added. After 30 minutes (37°C), 50 μL 0, 100, or 10 IU/mL u-PA in 6% BSA-PBS are added and the turbidity is determined at 405 nm after 0, 3, or 16 hours. Clot lysis was increased more than tenfold by 0.5 to 1 μmoles chloramine (ED50 after 3h = about 0.25 μmoles = 2mM final concentration). The normal range for the present intrinsic oxidative clot lysis assay (INOXCLA) is 100% ± 25% (MV ± SD; 100 relative % of norm; the normal lysis being 60 absolute %; CVs < 10%). Fifty percent lysis of adherent microclots occurred after 0.75 hours, 2 hours, 14 hours, 13 days, or 17 days when using 1000, 100, 10, 1, or 0 IU/mL u-PA reagent. If the u-PA activity is quenched by PAI-2, no clot lysis appears. Chloramines are important physiologic generators of nonradical excited singlet oxygen and enhance u-PA—mediated lysis of plasma clots. Based on the u-PA/chloramines coaction, a new global fibrinolysis assay has been derived.

Lipid hydroperoxides as a source of singlet molecular oxygen

Lipid hydroperoxides (LOOH) are formed in biological system by enzymatic and non-enzymatic pathways. These hydroperoxides exerts multiple damaging effects on cellular macromolecules and are also important regulators of cellular processes. Several classes of hydroperoxides including fatty acid, phospholipid, cholesterol and cholesteryl ester hydroperoxides have been detected and characterized both in vitro and in vivo. Although cells are normally endowed with enzymatic defenses capable to reduce LOOH to less reactive hydroxides, LOOH may accumulate in several pathological conditions and attention has been focused on elucidating their pathophysiological role. In the last years we have demonstrated the generation of singlet molecular oxygen (O2 (1)Δg or (1)O2) in several reactions involving LOOH. The generation of (1)O2 was directly evidenced by spectroscopic detection and characterization of its light emission at 1,270 nm. Moreover, using 18-oxygen labeled hydroperoxides (L(18)O(18)OH) we could detect the formation of (18)O-labeled (1)O2 by chemical trapping with anthracene derivatives followed by detection of the corresponding labeled endoperoxides by HPLC coupled to tandem mass spectrometry. The experimental evidences indicate that (1)O2 is generated at a yield close to 10 % by the Russell mechanism from LOOH, either free or in membranes, in the presence of biologically relevant oxidants, such as metal ions, peroxynitrite, HOCl and cytochrome c.

Antibody-catalyzed water-oxidation pathway

The intrinsic ability of all antibodies to generate hydrogen peroxide (H2O2) from singlet dioxygen (1O2*) via the antibody-catalyzed water-oxidation pathway (ACWOP) has triggered a rethink of the potential role of antibodies both in immune defense, inflammation, and disease. It has been shown that photochemical activation of this pathway is highly bactericidal. More recently, cholesterol oxidation by-products that may arise from the ACWOP have been discovered in vivo and are receiving a great deal of attention as possible key players in atherosclerosis and diseases of protein misfolding, such as Alzheimer's disease and Parkinson's disease.

Singlet oxygen potentiates thrombolysis

Activated polymorphonuclear neutrophils (PMN) participate in physiologic thrombolysis. PMN produce large amounts of urokinase (u-PA) and oxidants of the hypochlorite/chloramine-type that generate nonradical excited singlet oxygen ((1)O(2)). The u-PA/(1)O(2)-mediated thrombolysis was imitated in vitro. One hundred microliters microclots of normal human plasma were oxidized with 25 microL 0 to 5.0 micromoles of chloramine-T in physiol. NaCl in the absence or presence of 100 microL 6% bovine serum albumin or 100 microL normal plasma. Twenty-five microliters 0 to 167 IU/mL (related to 150 microL added supernatant) u-PA or 0 to 2.08 microg/mL t-PA were added. The absorbance at 405 nm was determined after 0 to 27 hours (37 degrees C). The specific clot turbidity was calculated, subtracting the 100% lysis absorbance from the respective measured absorbance. The chloramine-effective dose 50% (ED(50)) after 27 hours was determined in the presence of 2.6 IU/mL u-PA. The plasminogen activator-ED(25) was determined after 2 hours (37 degrees C), and the ET(25); i.e., the time needed to lyse a microclot by 25%, was determined for each respective clot-oxidation. The ED(25) of u-PA depends on the oxidation of the microclots: 1.25 micromoles chloramine/100 microL clot enhances thrombolysis approximately 20-fold; here, 25% of clot lysis is achieved within 50 minutes (using approximately 20 IU/mL u-PA), whereas approximately 5 hours are needed to lyse an unoxidized microclot by 25%. The present global assay technique imitates the u-PA/(1)O(2) aspects of physiologic thrombolysis by PMN.

Singlet oxygen oxidation of isolated and cellular DNA: product formation and mechanistic insights

This survey focuses on recent aspects of the singlet oxygen oxidation of the guanine moiety of nucleosides, oligonucleotides, isolated and cellular DNA that has been shown to be the exclusive DNA target for this biologically relevant photogenerated oxidant. A large body of mechanistic data is now available from studies performed on nucleosides in both aprotic solvents and aqueous solutions. A common process to both reaction conditions is the formation of 8-oxo-7,8-dihydroguanine by reduction of 8-hydroperoxyguanine that arises from the rearrangement of initially formed endoperoxide across the 4,8-bond of the purine moiety. However, in organic solvent the hydroperoxide is converted as a major degradation pathway into a dioxirane that subsequently decomposes into a complex pattern of oxidation products. A different reaction that involved the formation of a highly reactive quinonoid intermediate consecutively to the loss of a water molecule from the 8-hydroperoxide has been shown to occur in aqueous solution. Subsequent addition of a water molecule at C5 leads to the generation of a spiroiminodihy-dantoin compound via a rearrangement that involves an acyl shift. However, in both isolated and cellular DNA the latter decomposition pathway is at the best a minor process, because only 8-oxo-7,8-dihydroguanine has been found to be generated. It is interesting to point out that singlet oxygen has been shown to contribute predominantly to the formation of 8-oxo-7,8-dihydroguanine in the DNA of bacterial and human cells upon exposure to UVA radiation. It may be added that the formation of secondary singlet-oxygen oxidation products of 8-oxo-7,8-dihydroguanine, including spiroiminodihydantoin and oxaluric acid that were characterized in nucleosides and oligonucleotide, respectively, have not yet been found in cellular DNA.

Effect of ozone produced from antibody-catalyzed water oxidation on pathogenesis of atherosclerosis

Recent studies have suggested that antibodies can catalyze the generation of unknown oxidants including hydrogen peroxide (H2O2) and ozone (O3) from singlet oxygen (1O2) and water. This study is aimed to detect the effect of antibody-catalyzed water oxidation on atherosclerosis. Our results showed that both H2O2 and O3 were produced in human leukemia THP-1 monocytes incubated with human immunoglobulin G and phorbol myristate acetate. In the THP-1 monocytes incubated with human immunoglobulin G, phorbol myristate acetate and low density lipoprotein, the intracellular total cholesterol, free cholesterol, cholesteryl ester and lipid peroxides clearly increased, and a larger number of foam cells were observed by oil red O staining. The accumulation of all intracellular lipids was significantly inhibited by vinylbenzoic acid, and only slightly affected by catalase. These findings suggested that the production of O3, rather than H2O2, might be involved in the pathogenesis of atherosclerosis through the antibody-catalyzed water oxidation pathway.

Oxidative burst of neutrophils against melanoma B16-F10

Intensive oxidative burst was determined by chemiluminescence of peripheral blood neutrophils of mice that were intramuscularly injected with melanoma B16-F10 and/or subcutaneously with Sephadex G-200. The neutrophils from papula developed at the site of Sephadex injection were cytotoxic for the B16-F10 cells in vitro. However, survival of Sephadex injected tumour-bearing mice was lower than of control animals bearing B16-F10, while their tumours grew faster and were less necrotic. Thus, it is likely that injection of Sephadex distracted the neutrophils from the tumour allowing faster progression of the tumour, indicating that neutrophils may have an important role in the host defence against malignant cells in the early stage of tumour development.

Suppression of the pro-apoptotic function of cytochrome c by singlet oxygen via a haem redox state-independent mechanism

Stimuli for apoptotic signalling typically induce release of cyt c (cytochrome c) from mitochondria. Cyt c then initiates the formation of the apoptosome, comprising Apaf-1 (apoptotic protease-activating factor 1), caspase-9 and other cofactors. The issue of whether the redox state of the haem in cyt c affects the initiation of the apoptotic pathway is currently a subject of debate. In a cell-free reconstitution system, we found that only oxidized cyt c was capable of activating the caspase cascade. Oxidized cyt c was reduced by the physiological reductants cysteine and glutathione, after which it was unable to activate the caspase cascade. It is thus likely that cyt c with oxidized haem is in a conformation capable of interaction with Apaf-1 and forming apoptosomes. When either oxidized or reduced cyt c was treated with submillimolar concentrations of endoperoxide, which affected less than 3% of the redox state of haem, the ability of the oxidized cyt c to activate the caspase cascade was abolished. Higher amounts of singlet oxygen were required to affect the optical spectral change of haem, suggesting that the suppressed pro-apoptotic function of oxidized cyt c is a mechanism that is separate from the redox state of haem. Oxidative protein modification of cyt c by singlet oxygen was evident, on the basis of elevated contents of carbonyl compounds. Our data suggest that singlet oxygen eliminates the pro-apoptotic ability of oxidized cyt c not via the reduction of haem, but via the modification of amino acid residues that are required for apoptosome formation.

An abortive apoptotic pathway induced by singlet oxygen is due to the suppression of caspase activation

Singlet oxygen causes the cytotoxic process of tumour cells in photodynamic therapy. The mechanism by which singlet oxygen damages cells is, however, not fully understood. To address this issue, we synthesized and used two types of endoperoxides, MNPE (1-methylnaphthalene-4-propionate endoperoxide) and NDPE (naphthalene-1,4-dipropionate endoperoxide), that generate defined amounts of singlet oxygen at 37 degrees C with similar half lives. MNPE, which is more hydrophobic than NDPE, induced the release of cytochrome c from mitochondria into the cytosol and exhibited cytotoxicity, but NDPE did not. RBL cells, a rat basophil leukaemia-derived line, that overexpress phospholipid hydroperoxide glutathione peroxidase in mitochondria were found to be highly resistant to the cytotoxic effect of MNPE. MNPE treatment induced much less DNA ladder formation and nuclear fragmentation in cells than etoposide treatment, even though these treatments induced a similar extent of cellular damage. Singlet oxygen inhibited caspase 9 and 3 activities directly and also suppressed the activation of the caspase cascade. Collectively, these data suggest that singlet oxygen triggers an apoptotic pathway by releasing cytochrome c from mitochondria via the peroxidation of mitochondrial components and results in cell death that is different from typical apoptosis, because of the abortive apoptotic pathway caused by impaired caspase activation.

Superoxide converts indigo carmine to isatin sulfonic acid: implications for the hypothesis that neutrophils produce ozone

Recently, it was proposed that neutrophils generate ozone (Wentworth, P. J., McDunn, J. E., Wentworth, A. D., Takeuchi, C., Nieva, J., Jones, T., Bautista, C., Ruedi, J. M., Gutierrez, A., Janda, K. D., Babior, B. M., Eschenmoser, A., and Lerner, R. A. (2002) Science 298, 2195-2199; Babior, B. M., Takeuchi, C., Ruedi, J., Gutierrez, A., and Wentworth, P. J. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 3031-3034). Evidence for the proposal was based largely on the chemistry of ozone reacting with indigo carmine to produce isatin sulfonic acid. In this investigation, we have examined the specificity of this reaction and whether it can be used as unequivocal evidence of ozone production by neutrophils. Stimulated neutrophils promoted the loss of indigo carmine and formation of isatin sulfonic acid in a reaction that was completely inhibited by superoxide dismutase. Methionine, which scavenges ozone, singlet oxygen, and hypochlorous acid, had no effect on the reaction. Neither did catalase or azide, which scavenge hydrogen peroxide and inhibit myeloperoxidase, respectively. From these results, it is apparent that superoxide was responsible for bleaching indigo carmine. Superoxide generated using xanthine oxidase and acetaldehyde also converted indigo carmine to isatin sulfonic acid in a reaction that was completely inhibited by superoxide dismutase and unaffected by catalase. When the xanthine oxidase reaction was carried out in H(2)(18)O, the proportion of (18)O incorporated into the isatin sulfonic acid was the same as that found for ozone. Thus, reactions of ozone and superoxide with indigo carmine are indistinguishable with respect to isatin sulfonic acid formation. We conclude that bleaching of indigo carmine cannot be used to invoke ozone production by neutrophils. Studies using indigo carmine to implicate ozone in other biological processes should also be interpreted with caution.

MCLA-dependent chemiluminescence suggests that singlet oxygen plays a pivotal role in myeloperoxidase-catalysed bactericidal action in neutrophil phagosomes

Bacteria ingested by a neutrophil are located in phagosomes in which H(2)O(2) is produced through the NADPH oxidase-dependent respiratory burst. Myeloperoxidase (MPO) plays important role in the bactericidal action of phagosomes. MPO catalyses the reaction of H(2)O(2) and Cl(-) to produce HClO. The chemical mechanism behind the bactericidal action of the MPO-H(2)O(2)-Cl(-) system is unclear. Bactericidal action may result from (a) the direct reactions of HOCl with biological components (through amine chlorination) or (b) (1)O(2), formed non-enzymatically from HOCl and H(2)O(2), that mainly works to kill microorganisms through bacterial respiratory chain injury. To answer this question, we developed a Cypridina luciferin analogue (MCLA)-dependent chemiluminescence method to determine the rate of formation of (1)O(2) from a (1)O(2) source at pH 4.5-9.0. Using the MCLA-dependent chemiluminescence method, we found that the rate of formation of (1)O(2) from the MPO-H(2)O(2)-Cl(-) system peaked at pH 7.0. Segal et al. (28) reported that almost all Staphylococcus aureus is killed 2 min after phagocytosis by neutrophils where the phagosomal pH is 7.4-7.75. However, amine chlorination by HOCl did not proceed at pH > 7.0. Moreover, the bactericidal activities of the MPO-H(2)O(2)-Cl(-) system with Escherichia coli at pH 4.5 and 8.0 were paralleled by the rate of formation of (1)O(2). Combining these observations and the results reported by Segal et al., we concluded that (1)O(2) is a major chemical species in the killing of bacteria in neutrophil phagosomes.

The physiology and pharmacology of singlet oxygen

Reactive oxygen species (ROS) are generated by many different cells. Singlet oxygen (1O(2)) and a reaction product of it, excited carbonyls (C=O*), are important ROS. 1O(2) and C=O* are nonradicalic and emit light (one photon/molecule) when returning to ground state oxygen. Especially activated polymorphonuclear neutrophil granulocytes (PMN) produce large amounts of 1O(2). Via activation of the respiratory burst (NADPH oxidase and myeloperoxidase) they synthesize hypochlorite (NaOCl) and chloramines (in particular N-chlorotaurine). Chloramines are selective and stable chemical generators of 1O(2). In the human organism, 1O(2) is both a signal and a weapon with therapeutic potency against very different pathogens, such as microbes, virus, cancer cells and thrombi. Chloramines at blood concentrations between 1 and 2 mmol/L inactivate lipid enveloped virus and chloramines at blood concentrations below 0.5 mmol/L, i.e. at oxidant concentrations that do not affect thrombocytes or hemostasis factors, act antithrombotically by activation of the physiologic PMN mediated fibrinolysis; this thrombolysis is of selective nature, i.e. it does not impair the hemostasis system of the patient allowing the antithrombotic treatment in patients where the current risky thrombolytic treatment is contraindicated. The action of 1O(2) might be compared to the signaling and destroying gunfire of soldiers directed against bandits at night, resulting in an autorecruitment of the physiological inflammatory response. Chloramines (such as the mild and untoxic oxidant chloramine T (N-chloro-p-toluene-sulfonamide)) and their signaling and destroying reaction product 1O(2) might be promising new therapeutic agents against a multitude of up to now refractory diseases.

Singlet oxygen (1O2)-oxidazable lipids in the HIV membrane, new targets for AIDS therapy?

Human immunodeficiency virus (HIV) is a lipid enveloped virus. The lipid envelope differs significantly from the lipid membrane of normal human cells: it contains high amounts of cholesterol, that is of importance for the virus-cell interaction (for entry and exit of the virus) at so-called lipid rafts. Cholesterol, as a R-C=C-R compound possesses an oxidazable carbenic bond. The present work suggests the inactivation of HIV by oxidation of viral cholesterol and/or unsaturated fatty acids. For oxidation, the relatively mild oxidant singlet oxygen (1O(2)) might be used. 1O(2) is generated by redoxcyclers (e.g., of the quinone type, such as vitamin K) or by chloramines (e.g., taurine-chloramine). At the 1O(2) concentrations necessary to inactivate lipid enveloped virus in human blood the oxidation-sensible critical hemostasis parameters such as thrombocytes and fibrinogen are only partly inactivated. Therefore, it is proposed to consider generators of 1O(2) as a new form of AIDS therapy.

Oxidative stress in phagocytes--"the enemy within"

Phagocytes represent a powerful defense system against invading microorganisms that threaten the life or functional integrity of the host. The capacity to generate and release substantial amounts of reactive oxygen species is a unique property of activated polymorphonuclear and mononuclear phagocytes. The crucial role of these molecules in killing microorganisms and their consecutive contribution to tissue damage during injury and inflammation is widely known. Although much research has been done to explore the molecular events involved in the interaction of oxygen intermediates with microbes or host tissue, surprisingly little attention has been paid to the effect of reactive metabolites on the phagocyte itself. This fact is especially surprising, since it is apparent that the activated phagocyte is directly exposed to its own toxic metabolites. The potential damage occurring during excessive radical formation might notably alter the vital functions of these primarily immunocompetent cells. Moreover, the critical role of oxygen radicals in apoptosis of leukocytes has been recently revealed. Apoptosis is now supposed to represent a key mechanism in neutrophil deactivation and resolution of inflammation. Therefore, this review will focus on the delicate balance between released oxidants and antioxidative protection within the phagocytes themselves. General and phagocyte-specific antioxidative mechanisms, which have co-evolved with the radical generating machinery of phagocytes, are discussed, since the outcome of local inflammation can directly depend on this antioxidative capacity and might range from adequate elimination of the pathogen with minimal acute tissue damage to progression towards a systemic inflammatory response syndrome.

Oxidative DNA damage in prostate cancer patients consuming tomato sauce-based entrees as a whole-food intervention

BACKGROUND

Human prostate tissues are vulnerable to oxidative DNA damage. The risk of prostate cancer is lower in men reporting higher consumption of tomato products, which contain high levels of the antioxidant lycopene. We examined the effects of consumption of tomato sauce-based pasta dishes on lycopene uptake, oxidative DNA damage, and prostate-specific antigen (PSA) levels in patients already diagnosed with prostate cancer.

METHODS

Thirty-two patients with localized prostate adenocarcinoma consumed tomato sauce-based pasta dishes for the 3 weeks (30 mg of lycopene per day) preceding their scheduled radical prostatectomy. Serum and prostate lycopene concentrations, serum PSA levels, and leukocyte DNA oxidative damage (ratio of 8-hydroxy-2'-deoxyguanosine [8-OHdG] to 2'-deoxyguanosine [dG]) were assessed before and after the dietary intervention. DNA oxidative damage was assessed in resected prostate tissue from study participants and from seven randomly selected prostate cancer patients. All statistical tests were two-sided.

RESULTS

After the dietary intervention, serum and prostate lycopene concentrations were statistically significantly increased, from 638 nM (95% confidence interval [CI] = 512 to 764 nM) to 1258 nM (95% CI = 1061 to 1455 nM) (P<.001) and from 0.28 nmol/g (95% CI = 0.18 to 0.37 nmol/g) to 0.82 nmol/g (95% CI = 0.57 to 1.11 nmol/g) (P <.001), respectively. Compared with preintervention levels, leukocyte oxidative DNA damage was statistically significantly reduced after the intervention, from 0.61 8-OHdG/10(5) dG (95% CI = 0.45 to 0.77 8-OHdG/10(5) dG) to 0.48 8-OHdG/ 10(5) dG (95% CI = 0.41 to 0.56 8-OHdG/10(5) dG) (P =.005). Furthermore, prostate tissue oxidative DNA damage was also statistically significantly lower in men who had the intervention (0.76 8-OHdG/10(5) dG [95% CI = 0.55 to 0.96 8-OHdG/10(5) dG]) than in the randomly selected patients (1.06 8-OHdG/10(5) dG [95% CI = 0.62 to 1.51 8-OHdG/10(5) dG]; P =.03). Serum PSA levels decreased after the intervention, from 10.9 ng/mL (95% CI = 8.7 to 13.2 ng/mL) to 8.7 ng/mL (95% CI = 6.8 to 10.6 ng/mL) (P<.001).

CONCLUSION

These data indicate a possible role for a tomato sauce constituent, possibly lycopene, in the treatment of prostate cancer and warrant further testing with a larger sample of patients, including a control group.

Singlet oxygen (1O(2)) disrupts platelet aggregates

INTRODUCTION

Important mediators of activated polymorphonuclear leukocytes (PMN) are the oxidants HOCl and chloramine, which generate the nonradical photon-emitting oxidant singlet oxygen (1O(2)). Since 1O(2) inhibits platelet aggregation, we became interested in a possible oxidant mediated reversibility of platelet aggregation.

METHODS

Chloramine T (CT) is a stable 1O(2) generator that mimics the natural chloramine N-chloro-taurine. Platelet-rich plasma (PRP) was incubated with CT 0-8 min after addition of the aggregation agonist (10 microM adenosine-5'-diphosphate, ADP, or 5 microg/ml collagen) and the aggregation was monitored. Platelet function was also analyzed by the platelet function analyzer, PFA-100. Fifty microliters of 200 micromol/l ADP was added to 400 microl PRP. After 1 min at 37 degrees C, 50 microl of 0 or 30 mmol/l CT was added, and after an incubation for 3 min at 37 degrees C, 50 microl of 25% glutaraldehyde was added. The samples were analyzed in a transmission microscope at x3000 and x7000 magnification.

RESULTS

Chloramines inhibit platelet function in PRP: about 1 mM CT suppresses 50% of the aggregatory capacity of thrombocytes in normal PRP (effective dose 50%, ED(50)=1 mM chloramine), which is identical to the ED(50) for CT in whole blood. The ADP- or collagen-induced platelet aggregation can be reversed by addition of CT: up to 2 min after the addition of ADP as the aggregation inducer, the aggregation is reversible to more than 70% by addition of a 1O(2) release-inducer (3 mM CT). In contrast, addition of CT 8 min after the addition of ADP results only in about 50% reversal of platelet aggregation. The electron microscopic images of platelets before ADP, after incubation for 4 min at 20 micromol/l ADP, after incubation for 1 min at 20 micromol/l ADP, and a further incubation for 3 min at 3 mmol/l CT demonstrate an ADP-dependent formation of platelet aggregates, which are disrupted by 1O(2) into the single platelets; a phenomenon comparable to the decomposition of a puzzle or the continental drift of the major earth plates. The morphology of oxidized and unoxidized platelets is similar.

CONCLUSION

This study demonstrates that 1O(2) inhibits and reverses platelet aggregation. The physiologic signal action and the direct anticoagulant action of 1O(2) might be a new principle for pharmacologic intervention in atherothrombosis.

Evaluation of the process for superoxide production by NADPH oxidase in human neutrophils: evidence for cytoplasmic origin of superoxide

We present an up-to-date insight into the function of NADPH oxidase in human neutrophils, the signalling pathways involved in activation of this enzyme and the process of association of its components with the cytoskeleton. We also discuss the functional implications of morphological studies revealing localization of the sites of NADPH oxidase activity. An original model of the process of superoxide (O2*-) production in human neutrophils is shown. Organization of NADPH oxidase is associated with several components. Upon stimulation, tri-phox cytosolic components of NADPH oxidase (p40-phox, p47-phox and p67-phox) bind to actin filaments. This process involves other actin-binding proteins, such as cofilin and coronin. Activated protein kinase C, translocated from the plasma membrane, phosphorylates cytosolic components at a scaffold of cytoskeleton. Subsequently, p40-phox, responsible for maintaining the resting state of NADPH oxidase, is separated from other two cytosolic phox proteins following an attachment of the active form of small GTP-binding protein Rac to p67-phox. Cytosolic duo-phox proteins (p47-phox and p67-phox) conjugate with membrane components (gp91-phox, p22-phox and Rapla) of NADPH oxidase residing within membranes of intracellular compartments. This chain of events triggers production of O2*-. Then, oxidant-producing intracellular compartments associate with the plasma membrane. Eventually, intracellularly produced O2*- is released to the extracellular environment through the orifice formed by fusion of oxidant-producing compartments with the plasma membrane. Intracellular movement of the oxidant-producing compartments may be regulated by myosin light chain kinase. The review emphasizes that functional assembly of NADPH oxidase and, therefore, generation of O2*- is accomplished essentially within the intracellular compartments. Upon neutrophil stimulation, intracellularly generated O2*- is transported to the plasma membrane to be released and to ensure host defense against infection.

Singlet oxygen inhibits agonist-induced P-selectin expression and formation of platelet aggregates

Major mediators of activated polymorphonuclear leukocytes (PMN) are the oxidants HOCl and chloramine, which are a source for the nonradical photon-emitting oxidant singlet oxygen (1O2). We were interested in a possible platelet-modulating activity of 1O2. As a stable 1O2 source we chose the mild oxidant chloramine T (CT), which mimics the natural chloramine N-chloro-taurine. Freshly drawn native whole blood from donors (n = 5) was incubated at 0 to 3 mM CT for 1 minute at 37 degrees C. Then saline. 10 microM adenosine diphosphate (ADP), 5 microg/mL collagen, or 6.25 microM thrombin receptor activator peptide (TRAP) were added and the mixtures were allowed to incubate for 3 minutes at 37 degrees C. Aliquots of activated blood were fixed in 1% para-formaldehyde. After removal of the fixative, platelets were labeled with anti-CD61-FITC and anti-CD62P-PE antibodies and analyzed by flow cytometry. An oxidant concentration-dependent decrease in the expression of P-selectin appeared (at 3 mM CT to 39, 23, and 20% of the 100% saline control level for ADP, collagen, and TRAP, respectively). There was also an oxidant concentration-dependent decrease in the formation of platelet aggregates (at 3 mM CT to 8, 12, and 13% of the 100% saline control level for ADP, collagen, and TRAP, respectively; the 50% effective dose was 1.0 to 1.5 mM chloramine). In ADP- and TRAP-stimulated platelets, an oxidant-mediated increase in platelet fragments appeared (at 3 mM CT: three- to fourfold of the initial value). The addition to the blood of 30 mM of the oxyradical scavenger mannitol in contrast to excess methionine did not antagonize these oxidative modulations of platelet activation. The results were confirmed using equimolar concentrations of NaOCI and N-chloro-taurine. This study shows that 1O2 inhibits platelets, decreasing the expression of CD62P and the formation of platelet aggregates. Activated PMN might modulate hemostasis, shifting it into an antithrombotic state. The physiologic signal action and the direct anticoagulant action of 1O2 (released by chloramines such as vancomycin) might be a new principle for pharmacologic intervention in atherothrombosis.

Antioxidants in health and disease

Free radical production occurs continuously in all cells as part of normal cellular function. However, excess free radical production originating from endogenous or exogenous sources might play a role in many diseases. Antioxidants prevent free radical induced tissue damage by preventing the formation of radicals, scavenging them, or by promoting their decomposition. This article reviews the basic chemistry of free radical formation in the body, the consequences of free radical induced tissue damage, and the function of antioxidant defence systems, with particular reference to the development of atherosclerosis.