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PubMed1992

Singlet oxygen induced DNA damage.

Singlet oxygen generated by photoexcitation and by chemiexcitation selectively reacts with the guanine moiety in nucleosides (kq + kr about 5 x 10(6) M-1s-1) and in DNA. The oxidation products include 8-oxo-7-hydro-deoxyguanosine (8-oxodG; also called 8-hydroxydeoxyguanosine) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua). Singlet oxygen also causes alkali-labile sites and single-strand breaks in DNA. The biological consequences include a loss of transforming activity as studied with plasmids and bacteriophage DNA, and mutagenicity and genotoxicity. Employing shuttle vectors, it was shown that double-stranded vectors carrying singlet oxygen induced lesions seem to be processed in mammalian cells by DNA repair mechanisms efficient in preserving the biological activity of the plasmid but highly mutagenic in mammalian cells. Biological protection against singlet oxygen is afforded by quenchers, notably carotenoids and tocopherols. Major repair occurs by excision of the oxidized deoxyguanosine moieties by the Fpg protein, preventing mismatch of 8-oxodG with dA, which would generate G:C to T:A transversions.

Animals↗
PubMed1993

Effect of extracellularly generated singlet oxygen on gram-positive and gram-negative bacteria.

In the separated surface-sensitizer system, a photosensitizer is physically separated from the substrate by a thin air layer under such conditions that only singlet oxygen can reach and oxidize the substrate, preventing the competition by type I photosensitized processes. This method has been used to study the reaction of singlet oxygen with Gram-positive (Streptococcus faecium) and Gram-negative (Escherichia coli) bacterial strains. Studies on cell samples exposed to singlet oxygen for different periods of time show a drastic decrease in survival for S. faecium, while E. coli becomes sensitive only when the integrity of the outer membrane is altered by treatment with CaCl2 or tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetic acid (Tris-EDTA). Biochemical and ultrastructural analyses suggest that the cytoplasmic membrane and the genetic material are the main sites damaged by singlet oxygen.

Enterococcus faecium↗
PubMed2003

Singlet oxygen-mediated damage to proteins and its consequences.

Proteins comprise approximately 68% of the dry weight of cells and tissues and are therefore potentially major targets for oxidative damage. Two major types of processes can occur during the exposure of proteins to UV or visible light. The first of these involves direct photo-oxidation arising from the absorption of UV radiation by the protein, or bound chromophore groups, thereby generating excited states (singlet or triplets) or radicals via photo-ionisation. The second major process involves indirect oxidation of the protein via the formation and subsequent reactions of singlet oxygen generated by the transfer of energy to ground state (triplet) molecular oxygen by either protein-bound, or other, chromophores. Singlet oxygen can also be generated by a range of other enzymatic and non-enzymatic reactions including processes mediated by heme proteins, lipoxygenases, and activated leukocytes, as well as radical termination reactions. This paper reviews the data available on singlet oxygen-mediated protein oxidation and concentrates primarily on the mechanisms by which this excited state species brings about changes to both the side-chains and backbone of amino acids, peptides, and proteins. Recent work on the identification of reactive peroxide intermediates formed on Tyr, His, and Trp residues is discussed. These peroxides may be important propagating species in protein oxidation as they can initiate further oxidation via both radical and non-radical reactions. Such processes can result in the transmittal of damage to other biological targets, and may play a significant role in bystander damage, or dark reactions, in systems where proteins are subjected to oxidation.

Humans↗
PubMed1997

Singlet oxygen mediates the activation of JNK by UVA radiation in human skin fibroblasts.

Ultraviolet A (UVA: 320-400 nm) radiation activates c-Jun-N-terminal kinase (JNK 2) in human skin fibroblasts. Exposure of cells to UVA (300 kJ/m2) led to a 5-fold induction of JNK-activity which was significantly increased in the presence of D2O, an enhancer of the lifetime of singlet oxygen. Sodium azide, a quencher of singlet oxygen, abolished the activation of JNK. A hydroxyl radical scavenger, mannitol, had no effect. Furthermore, photochemically produced singlet oxygen (Rose Bengal plus white light) was found to induce JNK activity. This was enhanced by D2O and inhibited by azide. Thus, singlet oxygen activates and mediates the UVA-induced activation of JNK.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed2002

Kinetics and efficiency of excitation energy transfer from chlorophylls, their heavy metal-substituted derivatives, and pheophytins to singlet oxygen.

Time-resolved measurements of the singlet oxygen infrared (1269 nm) luminescence were used to follow the kinetics and efficiency of excitation energy transfer (EET) between chlorophyll (Chl) derivatives and oxygen in acetone. The studied pigments were Mg-Chl a and b and their heavy metal (Cu(2+) and Zn(2+))-substituted analogues, as well as pheophytin (Pheo) a and b. The efficiency of EET from chlorophyll to oxygen was highly dependent on the central ion in the pigment. Cu-Chl a and Cu-Chl b had the lowest efficiencies of singlet oxygen production, while Pheo a had a higher one, and Zn-Chl a had a similar one compared to Mg-Chl a. Also the side chain (position C-7, i.e. Chl a vs. Chl b) influenced the efficiency of singlet oxygen formation. In the case of square-planar complexes like Cu-Chl and Pheo, EET was more efficient in the Chl a derivatives than in those of Chl b; the opposite effect was observed in the case of the five- or six-coordinated Mg-Chl and Zn-Chl. As for the lifetime of the Chl triplet state, the most striking difference to Mg-Chl again was found in the case of Cu-Chls, which had much shorter lifetimes. Furthermore, the central ion in Chl affected the physical quenching of singlet oxygen: its efficiency was decreasing from Mg-Chl through Zn-Chl over Cu-Chl to Pheo. The results are discussed in the context of the oxidative stress accompanying heavy metal-induced stress in plants.

Chlorophyll↗
PubMed1999

New sensitive agents for detecting singlet oxygen by electron spin resonance spectroscopy.

Free radicals are well-established transient intermediates in chemical and biological processes. Singlet oxygen, though not a free radical, is also a fairly common reactive chemical species. It is rare that singlet oxygen is studied with the electron spin resonance (ESR) technique in biological systems, because there are few suitable detecting agents. We have recently researched some semiquinone radicals. Specifically, our focus has been on bipyrazole derivatives, which slowly convert to semiquinone radicals in DMSO solution in the presence of potassium tert-butoxide and oxygen. These bipyrazole derivatives are dimers of 3-methyl-1-phenyl-2-pyrazolin-5-one and have anti-ischemic activities and free radical scavenging properties. In this work, we synthesized a new bipyrazole derivative, 4,4'-bis(1p-carboxyphenyl-3-methyl-5-hydroxyl)-pyrazole, DRD156. The resulting semiquinone radical, formed by reaction with singlet oxygen, was characterized by ESR spectroscopy. DRD156 gave no ESR signals from hydroxyl radical, superoxide, and hydrogen peroxide. DRD156, though, gives an ESR response with hypochlorite. This agent, nevertheless, has a much higher ability to detect singlet oxygen than traditional agents with the ESR technique.

Dimethyl Sulfoxide↗
PubMed2000

Quenching of singlet oxygen (1deltag) by cobalt complexes with four nitrogen atoms in the equatorial plane.

The quenching of singlet oxygen (1deltag) by cobalt(III)-bis-1,2-benzosemiquinone-diiminato complexes (general structure LCo(111)(BQDI)2ClO4) has been studied in different solvents by measuring the singlet oxygen phosphorescence decay in time-resolved experiments. The axial ligand (Ph3As, Ph3Sb, N-methyl-imidazole, pyrrolidine) has practically no influence on the quenching; however, the chlorinated benzosemiquinone-diiminato complex has a markedly lower quenching rate constant. The solvent effects can be fully explained by the difference in viscosity, which supports the assumption that the quenching is diffusion controlled. The reactive radius of the encounter pair has been estimated to be 0.3 nm, shorter than the radius of the complex itself, which points to the fact that singlet oxygen must approach the central cobalt atom at the (partially) open axial position. The significance of these results regarding the quenching of singlet oxygen by vitamin B12 derivatives is discussed.

Cobalt↗
PubMed2002

Bis-cyclometalated Ir(III) complexes as efficient singlet oxygen sensitizers.

We report the singlet oxygen sensitization properties of a series of bis-cyclometalated Ir(III) complexes (i.e., (bt)2Ir(acac), (bsn)2Ir(acac), and (pq)2Ir(acac); bt = 2-phenylbenzothiazole, bsn = 2-(1-naphthyl)benzothiazole, pq = 2-phenylquinoline, and acac = acetylacetonate). Complexes with acetylacetonate ancillary ligands give singlet oxygen quantum yields near unity (PhiDelta = (0.7-1.0) +/- 0.1), whether exciting the ligand-based state or the lowest energy excited state (MLCT + 3LC). The singlet oxygen quenching rates for these beta-diketonate complexes were found to be small [(5 +/- 2) x 105 to (6 +/- 0.2) x 106 M-1 s-1], roughly 3 orders of magnitude slower than the corresponding phosphorescence quenching rate. Similar complexes were prepared with glycine or pyridine tethered to the Ir(III) center (i.e., (bsn)2Ir(gly) and (bt)2Ir(py)Cl; gly = glycine and py = pyridine). The glycine and pyridine derivatives give high singlet oxygen yields (PhiDelta = (0.7-1.0) +/- 0.1).

Iridium↗
PubMed2000

Effects of singlet oxygen on membrane sterols in the yeast Saccharomyces cerevisiae.

Photodynamic treatment of the yeast Saccharomyces cerevisiae with the singlet oxygen sensitizer toluidine blue and visible light leads to rapid oxidation of ergosterol and accumulation of oxidized ergosterol derivatives in the plasma membrane. The predominant oxidation product accumulated was identified as 5alpha, 6alpha-epoxy-(22E)-ergosta-8,22-dien-3beta,7a lpha-diol (8-DED). 9(11)-dehydroergosterol (DHE) was identified as a minor oxidation product. In heat inactivated cells ergosterol is photooxidized to ergosterol epidioxide (EEP) and DHE. Disrupted cell preparations of S. cerevisiae convert EEP to 8-DED, and this activity is abolished in a boiled control indicating the presence of a membrane associated enzyme with an EEP isomerase activity. Yeast selectively mobilizes ergosterol from the intracellular sterol ester pool to replenish the level of free ergosterol in the plasma membrane during singlet oxygen oxidation. The following reaction pathway is proposed: singlet oxygen-mediated oxidation of ergosterol leads to mainly the formation of EEP, which is enzymatically rearranged to 8-DED. Ergosterol 7-hydroperoxide, a known minor product of the reaction of singlet oxygen with ergosterol, is formed at a much lower rate and decomposes to give DHE. Changes of physical properties of the plasma membrane are induced by depletion of ergosterol and accumulation of polar derivatives. Subsequent permeation of photosensitizer through the plasma membrane into the cell leads to events including impairment of mitochondrial function and cell inactivation.

Cell Membrane↗
PubMed2000

p38 mitogen-activated protein kinase mediates bid cleavage, mitochondrial dysfunction, and caspase-3 activation during apoptosis induced by singlet oxygen but not by hydrogen peroxide.

p38 mitogen-activated protein kinase is activated and involved in cleavage of caspase-3 during apoptosis induced by a number of stimuli. However, the signaling events triggered by p38 that result in caspase-3 activation are still unknown. In human leukemia cells, two reactive oxygen species, singlet oxygen and hydrogen peroxide (H(2)O(2)), selectively stimulated the phosphorylation of p38. Preincubation of cells with SB203580, a specific inhibitor of p38, dose dependently inhibited DNA fragmentation induced by singlet oxygen but not by H(2)O(2). Protection from apoptosis by SB203580 correlated with inhibition of caspase-3, and several events that are associated with caspase-3 activation, including Bid cleavage, decrease in mitochondrial transmembrane potential and release of cytochrome c from mitochondria, whereas caspase-8 cleavage was not affected by this inhibitor. In contrast, blockade of caspase-8 with Ile-Glu-Thr-Asp-fluoromethyl ketone is sufficient to prevent formation of DNA fragments and to inhibit all the above signaling events, with exception of p38 phosphorylation, in both singlet oxygen- and H(2)O(2)-treated cells. These data suggest that caspase-3 activation is regulated through redundant signaling pathways that involve p38 and caspase-8 acting upstream of Bid during singlet oxygen-induced apoptosis, whereas the activation of caspase-3 by H(2)O(2) is only governed by a caspase-8-mediated apoptotic pathway.

Apoptosis↗
PubMed2000

Singlet oxygen induces oxidation of cellular DNA.

The aim of the present work was to evaluate the potential for (1)O(2) to induce oxidation of cellular DNA. For this purpose cells were incubated in the presence of a water-soluble endoperoxide whose thermal decomposition leads to the formation of singlet oxygen. Thereafter, DNA was extracted and the level of several modified DNA bases was determined by HPLC analysis coupled to a tandem mass spectrometric detection. A significant increase in the level of 8-oxo-7,8-dihydro-2'-deoxyguanosine was observed upon incubation of the cells with the chemical generator of (1)O(2), whereas the level of the other DNA bases measured remained unchanged. To demonstrate that singlet oxygen is directly involved in the formation of 8-oxo-7, 8-dihydro-2'-deoxyguanosine, the corresponding (18)O-labeled endoperoxide was used. Incubation of the cells with such a generator of (18)O-labeled singlet oxygen results in the formation of (18)O-labeled 8-oxo-7,8-dihydro-2'-deoxyguanosine in the nuclear DNA. This result clearly demonstrates that singlet oxygen, when released within cells, is able to directly oxidize cellular DNA.

8-Hydroxy-2'-Deoxyguanosine↗
PubMedDate not supplied

Pro-oxidating properties of melatonin in the in vitro interaction with the singlet oxygen.

In an aqueous system, the oxidation of the erythrocyte membrane by the singlet oxygen formed during the photoactivation of the rose bengal coloring was examined. The effects of the singlet oxygen on lipids and proteins were studied through the simultaneous quantification of peroxidation products, lipoperoxides and carbonyl groups, the oxidation of protein SH groups and the activity of the glyceraldehyde 3-phosphate dehydrogenase (G3PD) associated with the erythrocyte membrane. The antioxidant activity of melatonin was tested and compared to that of two antioxidants in extreme cases of hydrosolubility, ascorbate and beta-carotene, with the purpose of comparing the protective ability of melatonin against singlet oxygen. The results show the expected effect even at low (0.125-0.75 mM; 0.015-0.90 mM, respectively) for ascorbate and beta-carotene, antioxidants known to possess important antioxidant qualities against singlet oxygen. It is shown that melatonin, under the conditions described, and at the concentrations at which the other two compounds are efficacious, not only confers little antioxidant protection, but that a pro-oxidant tendency was proven both on lipids and proteins, as well as on G3PD enzymatic activity. The results show that the antioxidant protective effect that melatonin can exert on biological systems is probably not by a direct interaction with oxidant species, but probably, as has been previously proposed, through the regulation of antioxidant defense systems. The formation of secondary oxidation products, such as melatonin-derived endoperoxides, may explain the evidence found on pro-oxidant qualities of this molecule.

Adult↗
PubMed1990

Scavenging of singlet molecular oxygen by imidazole compounds: high and sustained activities of carboxy terminal histidine dipeptides and exceptional activity of imidazole-4-acetic acid.

Singlet molecular oxygen was generated by illumination of phenosafranin in phosphate buffer at pH 7.5. Relative efficiencies of various imidazole compounds to form endoperoxides were assayed by following at 25 degrees C the rate of light- and imidazole-dependent bleaching of N,N-dimethyl-4-nitrosoaniline. Of over 30 imidazole compounds tested, imidazole-4-acetic acid, a major catabolite of histamine in mammals, exhibited the highest activity. L-Carnosine (beta-alanyl-L-histidine), a natural dipeptide prevalent in striated muscle of mammals, possessed several properties important for a physiologically significant scavenger of singlet oxygen. On a molar basis, this readily water-soluble C-terminal histidine dipeptide reacted with singlet oxygen two- to four-fold faster than free L-histidine and approximately two-fold faster than the N-terminal L-histidine dipeptides tested. Furthermore scavenging ability of L-carnosine did not appreciably increase or decrease with time of reaction, in contrast to behaviors exhibited by a number of other imidazole compounds that included some other C-terminal L-histidine dipeptides. The fungal metabolite, ergothioneine, blocked singlet oxygen generation by illuminated phenosafranin.

Carnosine↗
PubMed1993

Direct exposure of mammalian cells to pure exogenous singlet oxygen (1 delta gO2).

Mammalian cells attached to membrane filters or deposited on filters without attachment were exposed to gas-phase singlet oxygen (1O2) in the absence of any other reactants. Cells were exposed in a monolayer or less, in the absence of external medium, during steady-state 1O2 generation, ensuring that singlet oxygen impinged directly and equally on all cells simultaneously. The current methodology for cell exposure ensures that 1O2 is initially the only reactive species to which the cells are exposed. Results seen with this system can therefore be attributed solely and unambiguously to events initiated by 1O2. Further, all cells in the sample receive the same magnitude of exposure per surface area per time interval, which supports calculations of the amount of 1O2 required for irreversible cell damage, based on measured 1O2 flux and exposed cell surface area. Exposure to pure 1O2 irreversibly damaged a variety of cell types, including rat basophilic leukemia, human squamous carcinoma and Chinese hamster lung fibroblast cell lines, and murine primary hepatocytes. Cell survival curves following exposure to 1O2 followed apparent first-order kinetics. A large number of singlet oxygen collisions (approximately 10(12)-10(13) were required to inactivate a cell, on average, indicating a low probability that singlet oxygen collision will reduce cell survival. Regardless of cell type or the survival endpoint measured, lethal toxicity required a fairly constant number of 1O2 collisions per cell. This poses a serious caveat in the assignment of causality in correlating 1O2-initiated cellular damage with mechanism of death, i.e. most damage observed will not be related to death.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Light emission resulting from hydroxylamine-induced singlet oxygen formation of oxidizing LDL particles.

Oxidation of low-density lipoprotein (LDL) by low amounts of cupric ions resulted in the formation of singlet oxygen (1O2, 1 delta g) when hydroxylamine (NH2OH) was added. Direct evidence on this excited species came from partial spectral resolution of the emitted light in the red spectral region (634 nm and 703 nm), which can be attributed to the dimol decay of singlet oxygen. Additional evidence for the existence of singlet oxygen came from the enhancing effect of deuterium oxide buffer (D2O) on chemiluminescence intensity and the quenching effect of sodium azide. A linear correlation between NH2OH-dependent chemiluminescence intensity and the amount of diene conjugates (DC) formed in this reaction was observed. Removal of adventitious transition metals by adequate chelators prevented chemiluminescence in this system; NH2OH was also found to efficiently decrease metabolites of lipid peroxidation (LPO). Our findings are consistent with a sequence of reactions in which NH2OH first converts transition metals to their reduced state, thereby stimulating the formation of alkoxy- and peroxyradicals. Peroxyradicals decompose in a bimolecular Russel reaction to hydroxyl compounds and singlet oxygen while the majority of alkoxy radicals are eliminated by a secondary reaction with NH2OH. Identical effects were observed when reducing antioxidants such as ascorbic acid or trolox C were used instead of hydroxylamine.

Antioxidants↗
PubMed1992

Induction of glomerular injury by singlet oxygen.

The role of the reactive oxygen species (ROS) in the induction of tissue injury has been well documented. Regarding glomerular injury, the focus of past studies has been on superoxide, hydrogen peroxide, hydroxyl radical and C10-. However, whether singlet oxygen, an exceptionally reactive oxygen metabolite, may cause glomerular lesions has not been investigated. In the present study we documented the effects of locally generated singlet oxygen in the kidney. To generate singlet oxygen, kidneys were perfused with the pigment pheophorbide a, which was followed by exposure to light. One hour after irradiation, severe morphological damage of the glomerular cell had developed. Extensive deposits of fibrin and accumulation of platelets were seen in the glomerular capillary lumina. By contrast, kidneys not exposed to light showed no, or only minimal, abnormalities. Glomerular injury was not inhibited by pretreatment with superoxide dismutase. These results suggest that singlet oxygen produced by pheophorbide a by photodynamic reaction leads to tissue injury in vivo.

Animals↗
PubMed2002

Yeast thioredoxin peroxidase expression enhances the resistance of Escherichia coli to oxidative stress induced by singlet oxygen.

Singlet oxygen ((1)O(2)) is a highly reactive form of molecular oxygen that may harm living systems by oxidizing critical cellular macromolecules. A soluble protein from Saccharomyces cerevisiae specifically provides protection against a thiol-containing metal-catalyzed oxidation system (thiol/Fe(3+)/O(2)) but not against an oxidation system without thiol. This 25 kDa protein acts as a peroxidase but requires the NADPH-dependent thioredoxin system or a thiol-containing intermediate, and was named thioredoxin peroxidase (TPx). The role of TPx in the cellular defense against oxidative stress induced by singlet oxygen was investigated in Escherichia coli containing an expression vector with a yeast genomic DNA fragment that encodes TPx and mutant in which the catalytically essential amino acid cysteine (Cys-47) has been replaced with alanine by a site-directed mutagenesis. Upon exposure to methylene blue and visible light, which generates singlet oxygen, there was a distinct difference between the two strains in regard to growth kinetics, viability, the accumulation of oxidized proteins and lipids, and modulation of activities of superoxide dismutase and catalase. The results suggest that TPx may play an important protective role in a singlet oxygen-mediated cellular damage.

Cloning, Molecular↗
PubMed1991

Singlet oxygen production from the reactions of superoxide ion in aprotic solvents: implications for hydrophobic biochemistry.

A number of reactions of superoxide ion in aprotic solvents have been reported to produce singlet oxygen. There is strong evidence for singlet oxygen generation from the reactions of superoxide ion with chlorine-containing halocarbons, bromine-containing halocarbons, hexafluorobenzene, diacylperoxides, lead tetraacetate, iodobenzene diacetate, cerium (IV) cation and tetranitromethane. Earlier studies reporting singlet oxygen generation from the reactions of superoxide ion with iodine, ferricenium ion, thianthrene cation radical, tris (N,N'-dioxobipyridyl) manganese (III) cation and di-mu-oxo-bis[phenanthrolinato manganese (IV)] cation need to be repeated because of the methods used to detect singlet oxygen had low specificity. The results of studies of superoxide ion chemistry in aprotic solvents should not be uncritically extrapolated to hydrophobic biological microenvironments, such as the cell membrane.

Chemical Phenomena↗