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At least 451 records · Page 25Linked to original sources
PubMed2005

Lifetime and diffusion of singlet oxygen in a cell.

In time- and spatially resolved experiments, singlet molecular oxygen, O(2)(a(1)Delta(g)), was created in a single nerve cell upon irradiation of a sensitizer incorporated in the cell nucleus using a focused laser beam. The singlet oxygen thus produced was detected by its infrared phosphorescence. Data obtained indicate that, contrary to common perception, this reactive species can be quite long-lived in a cell and, as such, can diffuse over appreciable distances including across the cell membrane into the extra-cellular environment. These results provide a new perspective for mechanistic studies of photoinduced cell death and intracellular signaling.

Diffusion↗
PubMed1998

Inhibition by singlet oxygen quenchers of oxidative damage to DNA produced in cultured cells by exposure to a quinolone antibiotic and ultraviolet A irradiation.

The photogenotoxicity mechanism of quinolone antibiotics was investigated by measuring oxidative DNA damage in lomefloxacin- and UVA-exposed cultured liver-derived cells. The combination of lomefloxacin and UVA irradiation produced a dose-dependent increase in 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG) in cell DNA. This DNA damage was substantially inhibited by co-incubation with sodium azide (NaN3) or 2,2,6,6-tetramethyl-4-piperadone (TMP), chemicals that specifically quench singlet oxygen. No significant reduction of 8-oxo-dG formation was produced by N-t-butyl-alpha-phenylnitrone (TBP) or alpha-tocopherol, which primarily scavenge hydroxyl radicals. We conclude that the photodynamic generation of 8-oxo-dG by quinolones is mediated, at least in part, by singlet oxygen.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2002

Mitochondrial permeability transition induced by chemically generated singlet oxygen.

Pure singlet molecular oxygen (1O2) generated by thermal decomposition of the 3,3'-(1,4-naphthylidene) dipropionate endoperoxide (NDPO2), inhibited respiration of isolated rat liver mitochondria supported by NADH-linked substrates or succinate, but not by N,N,N,N-tetramehyl-p-phenylene-diamine (TMPD)/ascorbate. Under the latter conditions, mitochondria treated with 2.7 mM NDPO2 exhibited a decrease in transmembrane potential (deltapsi) in manner dependent on NDPO2 exposure time. This process was sensitive to the mitochondrial permeability transition inhibitors EGTA, dithiothreitol, ADP, and cyclosporin A. The presence of deuterium oxide (D2O), that increases 1O2 lifetime, significantly enhanced NDPO2-promoted mitochondrial pereabilization. In addition, NDPO2-induced mitochondrial permeabilization was accompanied by DTT or ADP-sensitive membrane protein thiol oxidation. Taken together, these results provide evidence that mitochondrial permeability transition induced by chemically generated singlet oxygen is mediated by the oxidation of membrane protein thiols.

Animals↗
PubMed2002

Determination of the singlet oxygen quantum yield of bacteriochlorin a: a comparative study in phosphate buffer and aqueous dispersion of dimiristoyl-L-alpha-phosphatidylcholine liposomes.

The production of singlet oxygen (1O2) by bacteriochlorin a (BCA) was studied in phosphate buffer and in dimyristoyl-L-alpha-phosphatidylcholine (DMPC) unilamellar liposomes. The comparative method used to measure 1O2 production was a quantitative analysis of photooxidation reactions leading to the loss of absorbance of the water-soluble specific probe: anthracene-9,10-dipropionic acid. Rose Bengal, whose 1O2 quantum yield (phi(RB)) is well known in alcohols and phosphate buffer, was used as the standard for the quantification of the BCA singlet oxygen production. Our results confirm quantitatively that solubilization of BCA in liposomes leads to an increase in 1O2 production. Indeed, the quantum yield of 1O2 production by BCA (phi(BCA)) is 0.05 in phosphate buffer and 0.33 in DMPC liposomes. Furthermore, the diffusion characteristics of 1O2 produced by BCA bound to liposome were also examined using the isotopic lifetime enhancement effect of D2O. It was shown that 1O2 spent at least 70% of its lifetime in the vesicular environment.

Buffers↗
PubMed2002

A new look into the reaction between ergosterol and singlet oxygen in vitro.

The reaction of ergosterol (ERGO) with singlet oxygen in vitro was studied by using different combinations of the photosensitizers (i.e. rose Bengal and eosine) and solvents (i.e. pyridine, ethanol and methyl tert-butyl ether) and all the products obtained were isolated and fully characterized (mp, Rf, UV, 1H-NMR, 13C-NMR, EI-MS, ESI-MS and HR-MS). In pyridine. together with the expected (22E)-5alpha,8alpha-epidioxyergosta-6,22-dien-3beta-ol, EEP, the keto derivative (22E)-3beta-hydroxyergosta-5,8(9),22-trien-7-one. KE, was obtained. In ethanol the expected EEP was obtained together with (22E)-5alpha,8alpha-epidioxyergosta-6,9,22-trien-3beta-ol, EEP9(11), and (22E)-ergosta-6,9,22-triene-3beta,5alpha,8alpha-triol, DHOE, as main products and (22E)-ergosta-5,7,9,22-tetraen-3beta-ol, DHE, in trace amounts In methyl tert-butyl ether, a complex mixture of EEP, KE, DHOE, EEP9(11), DHE, together with (22E)-7alpha-hydroperoxyergosta-5.8(9),22-trien-3beta-ol, EHP, and (22E)-ergosta-5,8(9),22-triene-3beta, 7alpha-diol, EH, was obtained. The minor products were characterized and showed strong dependence on the reaction medium. The regioselective and stereoselective character of the singlet oxygen attack on the ERGO diene moiety is discussed in terms of ERGO HOMO's properties.

Eosine Yellowish-(YS)↗
PubMed2003

Investigation of singlet oxygen reactivity towards propofol.

The reaction between the anaesthetic agent 2,6-diisopropylphenol (propofol, PPF) and singlet oxygen (1O2) has been investigated in aqueous solution by means of HPLC, GC, absorption spectroscopy and laser flash photolysis with infrared luminescence detection. The rate constants for the physical and chemical quenching of 1O2 by PPF (kPPF) are found to be 2.66 x 10(5) M(-1) s(-1) and approximately 3.2 x 10(6) M(-1) s(-1) in CD3OD and D2O-CD3OD (75:25 v/v), respectively. The reaction of propofol with singlet oxygen produced by light irradiation of Rose Bengal leads essentially to two reaction products, 2,6-diisopropyl-p-benzoquinone and 3,5,3',5'-tetraisopropyl-(4,4')-diphenoquinone that are unambiguously identified from comparison with authentic samples.

Anesthetics, Intravenous↗
PubMed2002

Inhibition of glyceraldehyde-3-phosphate dehydrogenase by peptide and protein peroxides generated by singlet oxygen attack.

Reaction of certain peptides and proteins with singlet oxygen (generated by visible light in the presence of rose bengal dye) yields long-lived peptide and protein peroxides. Incubation of these peroxides with glyceraldehyde-3-phosphate dehydrogenase, in the absence of added metal ions, results in loss of enzymatic activity. Comparative studies with a range of peroxides have shown that this inhibition is concentration, peroxide, and time dependent, with H2O2 less efficient than some peptide peroxides. Enzyme inhibition correlates with loss of both the peroxide and enzyme thiol residues, with a stoichiometry of two thiols lost per peroxide consumed. Blocking the thiol residues prevents reaction with the peroxide. This stoichiometry, the lack of metal-ion dependence, and the absence of electron paramagnetic resonance (EPR)-detectable species, is consistent with a molecular (nonradical) reaction between the active-site thiol of the enzyme and the peroxide. A number of low-molecular-mass compounds including thiols and ascorbate, but not Trolox C, can prevent inhibition by removing the initial peroxide, or species derived from it. In contrast, glutathione reductase and lactate dehydrogenase are poorly inhibited by these peroxides in the absence of added Fe2+-EDTA. The presence of this metal-ion complex enhanced the inhibition observed with these enzymes consistent with the occurrence of radical-mediated reactions. Overall, these studies demonstrate that singlet oxygen-mediated damage to an initial target protein can result in selective subsequent damage to other proteins, as evidenced by loss of enzymatic activity, via the formation and subsequent reactions of protein peroxides. These reactions may be important in the development of cellular dysfunction as a result of photo-oxidation.

Animals↗
PubMed1998

High sensitivity of Deinococcus radiodurans to photodynamically-produced singlet oxygen.

PURPOSE: To study the sensitivity of two bacterial cell systems to photodynamic treatment and X-ray irradiation as part of a project to establish efficient procedures for waste water disinfection. MATERIALS AND METHODS: Stationary-phase cells of Deinococcus radiodurans (Gram-positive) and Escherichia coli (Gram-negative) were exposed to visible light in a buffer solution containing up to 5 microg/ml sensitizer rose bengal (RB) and to X-rays at dose rates of 32.8 Gy/min or 14.6 Gy/min, respectively. RESULTS: Survival of both cell types decreased with increasing exposure time to visible light and increasing concentration of RB, and therefore with an increase in singlet oxygen production. Surprisingly, D. radiodurans, the most resistant cell system to ionizing radiation, was more sensitive to photodynamic treatment than E. coli by about a factor of 100. CONCLUSIONS: The main target of singlet oxygen reaction is the cell membrane. The repair of such damage in D. radiodurans is less effective than in E. coli.

Animals↗
PubMed2000

Photosensitized formation of singlet oxygen by phycobiliproteins in neutral aqueous solutions.

Phycobiliproteins (PBPs) are a type of promising sensitizers for photodynamic therapy (PDT). Upon irradiation (lambda>500nm) of an oxygen-saturated aqueous solution of phycobiliproteins, particularly, C-phycocyanin (C-PC), allophycocyanin (APC) or R-phycoerythrin (R-PE), the formation of singlet oxygen (1O2) was detected by using imidazole in the presence of p-nitrosodimethylaniline (RNO). The bleaching of RNO caused by the presence of imidazole in our system showed typical concentration dependence with a maximum at about 8mM imidazole, which is in agreement with the formation of 1O2. In addition, the generation of 1O2 was verified further in the presence of D2O and specific singlet oxygen quencher 1,4-diazabicyclo [2,2,2] octane (DABCO) and sodium azide (NaN3). Our experimental results indicated that APC possesses high ability to generate reactive oxygen species and the relative quantum yields of photogeneration of 1O2 by PBPs are as follows: APC > C-PC > R-PE.

Aniline Compounds↗
PubMed2001

Photogeneration of singlet oxygen (1O2) and free radicals (Sen*-, O2*-) by tetra-brominated hypocrellin B derivative.

To improve photodynamic activity of the parent hypocrellin B (HB), a tetra-brominated HB derivative (compound 1) was synthesized in high yield. Compared with HB, compound 1 has enhanced red absorption and high molar extinction coefficients. The photodynamic action of compound 1, especially the generation mechanism and efficiencies of active species (Sens*-, O2*- and 1O2) were studied using electron paramagnetic resonance (EPR) and spectrophotometric methods. In the deoxygenated DMSO solution of compound 1, the semiquinone anion radical of compound 1 is photogenerated via the self-electron transfer between the excited and ground state species. The presence of electron donor significantly promotes the reduction of compound 1. When oxygen is present, superoxide anion radical (O2*-) is formed via the electron transfer from Sens*- to the ground state molecular oxygen. The efficiencies of Sens*- and O2*- generation by compound 1 are about three and two times as much as that of HB, respectively. Singlet oxygen (1O2) can be produced via the energy transfer from triplet compound 1 to ground state oxygen molecules. The quantum yield of singlet oxygen (1O2) is 0.54 in CHCl3 similar to that of HB. Furthermore, it was found that the accumulation of Sens*- would replace that of O2*- or 1O2 with the depletion of oxygen in the sealed system.

Benzoquinones↗
PubMed1990

Involvement of singlet oxygen in photoactivation of aflatoxins B1 and B2 to DNA-binding forms in vitro.

UVA-activated aflatoxin B1 (AFB1) and AFB2 bound covalently to DNA. The rate of binding increased in D2O versus H2O and decreased by diazabicyclo-octane, azide, aniline, 2-naphthylamine and by efficient stripping of oxygen. Similarly to DNA-binding, singlet oxygen (1O2) formation increased in D2O and was inhibited by singlet scavengers, as judged by the formation of malonaldehyde from linolenic acid. The above argue for the involvement of 1O2 in aflatoxin photoactivation to DNA-binding species. A model for the mechanism is proposed.

2-Naphthylamine↗
PubMed2006

Tocopherol is the scavenger of singlet oxygen produced by the triplet states of chlorophyll in the PSII reaction centre.

Recent developments on the role of tocopherol in the antioxidant network of the chloroplast and, in particular, in the protection of PSII in high light are summarized. The origin and conditions for singlet oxygen production in the reaction centre via P680 triplet formation are discussed, as well as the scavenging of this singlet oxygen by tocopherol. This is probably the obligatory function of tocopherol in the plant in high light acclimation. Furthermore, tocopherol is part of the modulation system of ROS in stress signalling.

Antioxidants↗
PubMed1990

Enzymatic recognition of DNA modifications induced by singlet oxygen and photosensitizers.

DNA modifications induced either by photosensitization (illumination in the presence of methylene blue) or by chemically generated singlet oxygen (thermal decomposition of an 1,4-etheno-2,3-benzodioxin) are recognized and incised by repair endonucleases present in crude bacterial cell extracts. Only a small fraction of the incised modifications are sites of base loss (AP-sites) sensitive to exonuclease III, endonuclease IV from E. coli or to the UV-endonuclease from M. luteus. Cell extracts from E. coli strains overproducing or defective in endonuclease III recognize the modifications induced by illumination in the presence of methylene blue just as well as do those from wild-type E. coli strains. This indicates that dihydropyrimidine derivatives, which are characteristic of hydroxyl radical-induced DNA modifications, are absent. In contrast, most of the modifications induced are not recognized by a cell extract from a fpg strain defective in formamidopyrimidine-DNA glycosylase FPG protein). Furthermore, incision by a cell extract from an E. coli strain overproducing FPG protein takes place at much lower protein concentration than with the wild-type strain. Experiments with purified FPG protein confirm that this enzyme is responsible for the recognition of singlet oxygen-induced DNA base modifications.

Coliphages↗
PubMed1992

Singlet oxygen induced mutation spectrum in mammalian cells.

In order to characterize the molecular nature of singlet oxygen (1O2) induced mutations in mammalian cells, a SV40-based shuttle vector (pi SVPC13) was treated with singlet oxygen arising from the thermal decomposition of the water-soluble endoperoxide of 3,3'-(1,4-naphthylidene) dipropionate (NDPO2). After the passage of damaged plasmid through monkey COS7 cells, the vector was shuffled into E. coli cells, allowing the screening of supF mutants. The mutation spectrum analysis shows that single and multiple base substitutions arose in 82.5% of the mutants, the others being rearrangements. The distribution of mutations within the supF gene is not random and some hotspots are evident. Most of the point mutations (98.4%) involve G:C base pairs and G:C to T:A transversion was the most frequent mutation (50.8%), followed by G:C to C:G transversion (32.8%). These results indicate that mutagenesis in mammalian cells, mediated by 1O2-induced DNA damage, is targeted selectively at guanine residues.

Animals↗
PubMed2002

Detection of singlet oxygen and superoxide with fluorescent sensors in leaves under stress by photoinhibition or UV radiation.

In order to understand the physiological functions of reactive oxygen species (ROS) generated in leaves, their direct measurement in vivo is of special importance. Here we report experiments with two dansyl-based ROS sensors, the singlet oxygen specific DanePy and HO-1889NH, which is reactive to both singlet oxygen and superoxide radicals. Here we report in vivo detection of (1)O(2) and O(2)(-*) by fluorescence quenching of two dansyl-based ROS sensors, the (1)O(2) specific DanePy and HO-1889NH, which was reactive with both (1)O(2) and O(2)(-*). The ROS sensors were administered to spinach leaves through a pinhole, and then the leaves were exposed to either excess photosynthetically active radiation or UV (280-360 nm) radiation. Microlocalization of the sensors' fluorescence and its ROS-induced quenching was followed with confocal laser scanning microscopy and with fluorescence imaging. These sensors were specifically localized in chloroplasts. Quenching analysis indicated that the leaves exposed to strong light produced (1)O(2), but hardly any O(2)(-*). On the other hand, the dominant ROS in UV-irradiated leaves was O(2)(-*), while (1)O(2) was minor.

Chloroplasts↗
PubMed1992

Calcium-mediated neuronal degeneration following singlet oxygen production.

NONINVASIVE photolytic injury to targeted neuronal subpopulations in vivo causes unique, slowly progressive neuronal degeneration. To examine the mechanisms of degeneration toward development and transplantation studies, cytosolic calcium levels were measured in vitro from neocortical neurons after incorporation of photoactive nanospheres and laser-activated singlet oxygen production within lysosomes. Cytosolic calcium increased irreversibly, predominantly from extracellular sources through channel-mediated mechanisms and increased membrane porosity. Propidium iodide studies demonstrated gradual loss of membrane integrity over hours to days. The calcium channel blocker nimodipine, or calcium-free medium, partially protected neurons from calcium flux and cell death. Results suggest calcium-dependent and independent mechanisms of neuronal degeneration following singlet oxygen production.

Animals↗
PubMed2002

Protection by isoprene against singlet oxygen in leaves.

Isoprene (2-methyl-1,3-butadiene) protection against effects of singlet oxygen was investigated in Myrtus communis and Rhamnus alaternus. In M. communis, singlet oxygen produced in the leaves by Rose Bengal (RB) led to a 65% decrease in net assimilation rates within 3 h, whereas isoprene emission rates showed either a 30% decrease at ambient CO2 concentrations or a 70% increase under high CO2. In both cases, these changes led to an increase in calculated internal isoprene concentrations. The isoprene protection effect was directly demonstrated by fumigation of young (non-emitting) leaves, treated with RB or bromoxynil (simulating photoinhibition). There was 42% and 29% reduction in the damage to net assimilation compared with non-fumigated leaves for RB or bromoxynil, respectively. In R. alaternus, similar effects of RB on net assimilation were observed, and additional fluorescence measurements showed a significantly smaller decrease in Fv/Fm in isoprene-fumigated young leaves treated with RB (from 0.78 to 0.52), compared with non-fumigated leaves (from 0.77 to 0.27). The internal isoprene concentrations used in this study and possible rate of 1O2 production in leaves indicate that the protective effects observed should be beneficial also under natural conditions.

Adaptation, Physiological↗