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Reaction of para-hydroxybenzoic acid esters with singlet oxygen in the presence of glutathione produces glutathione conjugates of hydroquinone, potent inducers of oxidative stress.

The determination and toxicological characterization of products of the reaction between p-hydroxybenzoic acid esters (parabens) and singlet oxygen ((1)O(2)) are very important because of the frequent use of parabens in cosmetics and possible generation of (1)O(2) in the skin. We observed (1)O(2)-dependent production of mono-, di-, and tri-substituted glutathione (GSH) conjugates of hydroquinone (HQ) during visible light-irradiation of a mixture of methyl or ethyl paraben and GSH in the presence of rose bengal (RB). 1,4-Benzoquinone (BQ) and HQ were produced during the irradiation in the absence of GSH. While a mixture of BQ and GSH produced only mono-substituted conjugate, irradiation of the mixture with RB produced mono-, di-, and tri-substituted conjugates. These observations indicate that (1)O(2) is involved both in the production of BQ and HQ from parabens and in the formation of multi-substituted GSH conjugates from mono-substituted conjugate. Tri-substituted conjugate generated larger amounts of hydrogen peroxide in an aqueous solution than mono-substituted conjugates or HQ did. Detection of semiquinone radical suggests that the autoxidation of conjugates is related to the generation of hydrogen peroxide. The results obtained in this study indicate that parabens may induce oxidative stress in the skin after conversion to GSH conjugates of HQ by reacting with (1)O(2) and GSH.

Chromatography, High Pressure Liquid↗

Quenching of singlet molecular oxygen by carnosine and related antioxidants. Monitoring 1270-nm phosphorescence in aqueous media.

In order to elucidate the biochemical roles of imidazol-containing dipeptides, we have studied quenching of singlet molecular oxygen (1O2) by carnosine (beta-alanyl-L-histidine), its structural components (L-histidine, imidazole, and beta-alanine), and related natural free-radical scavengers-L-anserine (beta-alanyl-1-methyl-histidine), ergothioneine (2-thiol-L-histidine-betaine), and taurine (2-aminoethanesulfonic acid) in aqueous (D2O, pD 7) solutions by using monitoring of 1O2-phosphorescence (1270-nm). The rate constants of 1O2 quenching (Kq) by carnosine, anserine, and ergothioneine were shown to be similar [(3 +/- 1) x 10(7) M-1s-1]. Their values resembled those of free-L-histidine [Kq = (4 +/- 1) x 10(7) M-1s-1] and imidazole [Kq = (2 +/- 1) x 10(7) M-1s-1]. Non-aromatic amino acids-taurine and beta-alanine-showed very low quenching activities (Kq < 3 x 10(3) M-1c-1). The Kq values did not correlate with the literature data on abilities of the tested compounds to stimulate muscle working capacities and inhibit myeloperoxidase-catalyzed oxygenation. Thus, the dipeptides can be used as potent water-soluble protectors against 1O2 attack whereas their natural biochemical functions are most probably determined by the processes of different nature.

Amino Acids↗

Inactivation of primary antioxidant enzymes in mouse keratinocytes by photodynamically generated singlet oxygen.

Cellular antioxidant enzymes protect against damage caused by exposure to endogenous or exogenous prooxidants. Singlet oxygen ((1)O(2)) is a reactive form of oxygen that can be produced in vivo either in normal and pathophysiologic conditions or by photosensitizing chemicals, as during photodynamic treatment. We hypothesized that photodynamically generated (1)O(2) would decrease the enzymatic activities of cellular antioxidants. To test this hypothesis, we treated cultured mouse epidermal keratinocytes with the photosensitizer Photofrin plus visible light to produce (1)O(2), and then measured CuZnSOD, MnSOD, and catalase activities with both ingel and spectrophotometric enzyme activity assays. Our results demonstrated that the enzymatic activities of cellular CuZnSOD, MnSOD, and catalase were significantly decreased after keratinocytes were treated with Photofrin plus visible light. By contrast, the enzymatic activities of cellular CuZnSOD, MnSOD, and catalase were unaffected in control cells treated with Photofrin only or visible light only. Despite the decreased levels of enzymatic activities, the protein levels of all three primary antioxidant enzymes remained constant after photodynamic treatment, as determined by Western blotting. L-Histidine, a (1)O(2) quencher, protected against the inactivation of cellular CuZnSOD, MnSOD, and catalase enzymes induced by photodynamically generated (1)O(2). The conclusion from these experiments is that the primary cellular antioxidant enzymes CuZnSOD, MnSOD, and catalase can be inactivated by photodynamically generated (1)O(2) in nucleated mammalian cells. These findings may be useful in the future development of antineoplastic adjuvant therapies that use photodynamic generation of (1)O(2) to inactivate antioxidant defenses with a goal of sensitizing tumor cells to prooxidant-generating drugs.

Animals↗

Involvement of Escherichia coli exonuclease III and endonuclease IV in the repair of singlet oxygen-induced DNA damage.

Singlet molecular oxygen (1O2) has been implicated in several biological processes that may lead to genetic damage. The relevance of various repair pathways in plasmid inactivation mediated by 1O2 was investigated. Plasmid treated with 1O2, chemically generated, was transfected into Escherichia coli strains deficient in genes implicated in the DNA repair of oxidative damage. The ability to transform bacteria is significantly reduced in the double mutant xth,nfo, deficient in both exonuclease III and endonuclease IV, although it was similar to wild-type cells in single mutants. The products of these two genes are able to cleave DNA damaged by 1O2 and to remove DNA polymerization blocks from 3'-termini generated either directly by 1O2 treatment or after the action of the formamidopyrimidine-DNA-N-glycosylase (Fpg protein). The results indicate that the exonuclease III and endonuclease IV participate in the excision of lethal lesions induced in DNA by 1O2.

DNA Damage↗

Singlet molecular oxygen induced mutagenicity in a mammalian SV40-based shuttle vector.

We have determined the deleterious effects of singlet oxygen (1O2), generated by thermal decomposition of the water-soluble endoperoxide 3,3'-(1,4-naphthylidene)dipropionate (NDPO2), on plasmid DNA. By following the electrophoretic mobility of DNA on agarose gels, we detected single and double strand breaks induced by treatment with NDPO2. The vector employed was a mammalian shuttle vector and the mutagenic consequences of these damages were investigated, using as mutation target the supF suppressor tRNA gene. A high increase of the mutation frequency, over the background, was observed in plasmids transfected in bacteria or after passage through mammalian cells. Trapping agents and quencher effects and other controls confirm the involvement of 1O2 in DNA damage and mutagenicity. These findings indicate that 1O2 can induce DNA lesions which are repaired by an error-prone process in prokaryotic and eukaryotic cells.

Animals↗

Efficiency of the photoprocesses leading to singlet oxygen (1 delta g) generation by alpha-terthienyl: optical absorption, optoacoustic calorimetry and infrared luminescence studies.

The triplet energy of alpha-terthienyl has been determined by heavy atom-induced optical absorption: the value of 39.7 +/- 1.5 kcal/mol is consistent with earlier energy transfer work. Combining this result with calorimetric data from optoacoustic calorimetry indicates that intersystem crossing occurs with at least 90% efficiency in polar and non-polar solvents. The quantum yields for singlet oxygen formation via energy transfer from triplet alpha-terthienyl have been obtained from time-resolved measurements of its IR phosphorescence: these yields are in the 0.6-0.8 range in non-polar and polar (hydroxylic and non-hydroxylic) solvents.

Calorimetry↗

The reaction of singlet oxygen with proteins, with special reference to crystallins.

Photosensitized oxidation of the eye lens proteins, the crystallins, is thought to lead to protein crosslinks and high molecular weight aggregates. Such protein modifications may be important factors in the formation of lens opacities or cataracts. We focus attention here on type 2 photo-oxidation involving the reaction of singlet oxygen (1O2) with crystallins and some "control" proteins. We find that: (1) trp residues are oxidized to N-formyl kynurenine and related products, but this in itself does not lead to the production of high molecular weight protein aggregates of the protein; (2) tyr residues react with 1O2 but we do not detect dihydroxyphenylalanine or bityrosine nor are protein crosslinks formed as a result; (3) oxidation of his residues appears necessary for high molecular weight protein covalent aggregates to form. Proteins devoid of his, e.g. melittin or bovine pancreatic trypsin inhibitor, do not form high molecular weight products upon reaction with 1O2. Prior reaction and blocking of his inhibits the crosslinking reactions. (4) The oxidized protein is seen to be more acidic than the parent and has an altered tertiary structure. (5) Among the crystallins, reactivity towards 1O2 varies in the order gamma greater than beta greater than alpha and also gamma A/E greater than gamma D greater than gamma B crystallin.

Animals↗

Oxidation of phosphatidylcholine membranes by singlet oxygen generated in the gas phase.

Singlet-oxygen (1O2) was generated in the gas phase by heterogeneous photosensitization and bubbled into suspensions of phosphatidylcholine (PC) liposomes. Lipid peroxidation and membrane lysis were observed, and were dependent on the 1O2 concentration and the degree of unsaturation of the liposome. An analysis based on large target diffusion theory indicates that approximately 5000, 2800, and 1600 interactions were required for the lysis of large dioleoylPC, dilinoleoylPC and dilinolenoylPC liposomes, respectively.

Kinetics↗

Singlet oxygen induced DNA damage and mutagenicity in a single-stranded SV40-based shuttle vector.

The effects of singlet oxygen (1O2), generated by the thermal decomposition of water soluble NDPO2 (endoperoxide of the disodium 3,3'-(1,4-naphthylidene) dipropionate), on a single-stranded shuttle vector were analysed. 1O2 induces a much higher level of breaks in the phosphodiester backbone of single-stranded than double-stranded DNA. This may be due to a higher accessibility of guanine residue, primarily damaged by 1O2. The damaged vector was transfected into monkey COS7 cells where single-stranded DNA was converted to the double-stranded replicative form DNA. After 3 days, extrachromosomal DNA was extracted and the plasmids rescued in E. coli to study mutagenesis. There is a significant increase in mutation frequency of damaged single-stranded DNA in comparison to untreated DNA. It is concluded that 1O2 induces breaks in the backbone of single-stranded DNA and that the 1O2-damaged molecules are mutated after passage through mammalian cells.

Animals↗

A test of the singlet oxygen mechanism of cationic dye photosensitization of mitochondrial damage.

Aromatic cationic dyes have a potential as photo-chemotherapeutic agents because they are selectively concentrated into the mitochondria of cancerous cells. The mechanism of cytophototoxicity has been proposed to be primarily due to dye sensitized photogeneration of highly toxic singlet oxygen (1O2) at the mitochondria. We tested this hypothesis by measuring the relative phototoxicity of a collection of aromatic cationic dyes towards respiring rat-liver mitochondria (RLM), upon addition of 514 nm laser light. Effectiveness of dye photosensitization towards destruction of RLM function was assayed by its effect on the RLM membrane potential. Three physical parameters of dye phototoxicity were independently measured and a relative phototoxicity calculated assuming adherence of mechanism to the 1O2 hypothesis. Quantum yields of dye sensitized 1O2 production were estimated, either from time-resolved luminescence measurements of photosensitized 1O2 formed, or by comparing rates of photobleaching of 1O2 trap; the relative partition of dye into mitochondrial lipid was determined gravimetrically; and the optical density of dye was determined in a lipid like Triton X-100 micellar environment. Under the assumption of the 1O2 hypothesis, these parameters were used to predict a relative phototoxicity which was compared with that observed. For 12 of the 14 dyes investigated, the observed and predicted phototoxicities were linearly correlated (r = 0.85) suggesting support of the 1O2 hypothesis. Carbocyanines DiOC2(3) and DiSC2(3) did not correlate and were found to be 10 and 1000 times more potent than predicted, suggesting an additional factor at play in their phototoxicity.

Animals↗

Photoperoxidation of cholesterol in homogeneous solution, isolated membranes, and cells: comparison of the 5 alpha- and 6 beta-hydroperoxides as indicators of singlet oxygen intermediacy.

Singlet oxygen (1O2) can react with cholesterol (Ch) to give three possible ene-addition hydroperoxides: 3 beta-hydroxy-5 alpha-cholest-6-ene-5-hydroperoxide (5 alpha-OOH), 3 beta-hydroxycholest-4-ene-6 alpha-hydroperoxide (6 alpha-OOH), and 3 beta-hydroxycholest-4-ene-6 beta-hydroperoxide (6 beta-OOH). The rates of dye-sensitized photogeneration and also the fates of 5 alpha-OOH and 6 beta-OOH in membrane bilayers have been studied and compared. Irradiation of unilamellar [14C]Ch/phospholipid vesicles in the presence of aluminum phthalocyanine tetrasulfonate or merocyanine 540 resulted in formation of 5 alpha-OOH and 6 beta-OOH, as determined by high performance liquid chromatography with radiochemical or electrochemical detection. The initial rate of 6 beta-OOH formation was 30-35% that of 5 alpha-OOH in a variety of liposomal systems. However, after a lag, 5 alpha-OOH invariably decayed via allylic rearrangement to 7 alpha-OOH (also known to be a free radical product), whereas 6 beta-OOH accumulated in unabated fashion until Ch depletion became limiting. Photooxidation of Ch in an isolated natural membrane (erythrocyte ghost) or in L1210 leukemia cells gave similar results. When the reaction was carried out in pyridine or methanol, the rate of 6 beta-OOH formation relative to 5 alpha-OOH was reduced by approximately half, with essentially no isomerization of the latter to 7 alpha-OOH.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Influence of the peptide bond on the singlet molecular oxygen-mediated (O2[1 delta g]) photooxidation of histidine and methionine dipeptides. A kinetic study.

The dye-sensitized photooxidation of L-histidine (His) and L-methionine (Met) and their simplest dipeptides with glycine (Gly) (His-Gly, Gly-His Gly-Met) and Met-methyl ester (Met-ME) mediated by singlet molecular oxygen (O2[1 delta g]) was studied. The overall rate constants in acetonitrile-H2O (kt) for O2(1 delta g) quenching were measured by time-resolved phosphorescence detection. In H2O a competitive kinetic method was employed. In both solvents the reactive rate constants (kr) were determined to discriminate between the overall and physical contributions to the quenching. The kinetic and mechanistic aspects of the interaction are discussed. For His-Gly, the peptide bond has practically no effect on the kinetics of photooxidation. For Gly-His the overall rate constant is much higher than that for His and His-Gly, in both H2O and acetonitrile-H2O. The main contribution to kt (for Gly-His) is the physical quenching of O2(1 delta g). In water the kt/kr ratio for free His and His-Gly is 1.0, reaching a value of 2.0 in the organic solvent-H2O mixture. The rates of -NH2 loss upon sensitized photooxidation in all cases parallel the trend of kr values. The main results for the His series indicate that: (1) a polar environment favors autoprotection (i.e. an increase in the contribution of physical quenching) against photodynamic effects; (2) only the rate constant for reactive interaction with O2(1 delta g) does not depend on the location of the peptide bond involving His. For Met derivatives the kt values are higher in both solvents than that for free Met.(ABSTRACT TRUNCATED AT 250 WORDS)

Dipeptides↗

Singlet oxygen generation by porphyrins and the kinetics of 9,10-dimethylanthracene photosensitization in liposomes.

Two new sensitizers are introduced for a potential use in photodynamic therapy: Zn(2+)- and MG(2+)-tetrabenzoporphyrin (ZnTBP and MgTBP). A comparative study of the quantum yields of singlet oxygen generation (phi delta) of hematoporphyrin derivative (HpD), Photofrin II (PF-II), Zn(2+)-phthalocyanine tetrahydroxyl [ZnPC(OH)4] and the newly introduced sensitizers ZnTBP and MgTBP in liposomes, as well as the kinetics of a photochemical reaction sensitized by them, was made by employing the fluorescent membrane probe 9,10-dimethylanthracene (DMA). We followed the photosensitization of DMA in real time by monitoring its fluorescence decrease at 457 nm and found that DMA's photosensitization is oxygen mediated. The kinetic traces of the photosensitization reactions were fitted to an analytical function, and the phi delta values were evaluated. At 10 microM sensitizer in an aqueous suspension of 2 mg/mL egg phosphatidylcholine (EPC), HpD was found to have the largest value of phi delta (0.215), followed by PF-II (0.191), ZnTBP (0.023), MgTBP (0.019) and ZnPC(OH)4 (0.005). As a test of the method, phi delta for methylene blue in ethanol was measured and found to be 0.45 as compared to 0.52 reported in the literature. Due to difference in the sensitizers' absorbances at the laser's wavelength, the reaction photosensitized by ZnTBP was the fastest with a time constant of 6.7 min, followed by MgTBP (8.7), PF-II (11.9), HpD (17.1) and ZnPC(OH)4 (31.2), all at equal sensitizers' concentrations and laser intensities. The binding constants of the sensitizers to EPC liposomes are also reported.

Anthracenes↗

Microheterogeneity of singlet oxygen distributions in irradiated humic acid solutions.

Singlet oxygen (1O2) is a highly reactive species formed through solar irradiation of organic matter in environmental waters. Implicated in a range of reactions, it has proven difficult to quantify its spatial distribution in natural waters. We assessed the microheterogeneous distribution of 1O2 in irradiated solutions containing chromophoric dissolved organic matter (CDOM) by using molecular probes of varying hydrophobicity. The apparent 1O2 concentrations ([1O2]app), measured by recently developed hydrophobic trap-and-trigger chemiluminescent probe molecules, were orders of magnitude higher than those measured by the conventional hydrophilic probe molecule furfuryl alcohol. The differential [1O2]app values measured by these probes reflect a steep concentration gradient between the CDOM macromolecules and the aqueous phase. A detailed kinetic model based on the data predicts probabilistic 1O2 distributions under different solvent conditions.

Humic Substances↗

Plasmid DNA acquires immunogenicity on exposure to singlet oxygen.

In the present study, the effect of singlet oxygen (1O2) (generated by ultraviolet (UV) irradiation of methylene blue) on plasmid DNA has been analyzed by UV spectroscopy, fluorescence spectroscopy, and S1 nuclease digestibility. Both native and 1O2-modified plasmid DNA were treated with a number of restriction enzymes to map out the sites damaged by 1O2. It was also observed that, on exposure to 1O2, native plasmid DNA that is non-immunogenic acquired the ability to elicit an immune response in experimental animals. However, the induced antibodies exhibited appreciable cross reactivity with various polynucleotides and nucleic acids. The data indicate that the antibodies, though cross-reactive, preferentially bind 1O2-modified epitopes on plasmid DNA. Gel retardation assay further substantiated the enhanced recognition of 1O2-modified plasmid DNA over the native form. The antibodies developed were then subjected to competition ELISA with sera from various diseases such as systemic lupus erythematosus, rheumatoid arthritis, and cancer. These results suggest that upon exposure of DNA to 1O2, neo-epitopes are generated, which may be one of the factors for the induction of circulating autoantibodies in the three diseases.

Animals↗

Monitoring of singlet oxygen is useful for predicting the photodynamic effects in the treatment for experimental glioma.

PURPOSE: Singlet oxygen ((1)O(2)) generated in photodynamic therapy (PDT) plays a very important role in killing tumor cells. Using a new near-IR photomultiplier tube system, we monitored the real-time production of (1)O(2) during PDT and thus investigated the relationship between the (1)O(2) production and photodynamic effects. EXPERIMENTAL DESIGN: We did PDT in 9L gliosarcoma cells in vitro and in an experimental tumor model in vivo using 5-aminolevulinic acid and nanosecond-pulsed dye laser. During this time, we monitored (1)O(2) using this system. Moreover, based on the (1)O(2) monitoring, we set the different conditions of laser exposure and investigated whether they could affect the tumor cell death. RESULTS: We could observe the temporal changes of (1)O(2) production during PDT in detail. At a low fluence rate the (1)O(2) signal gradually decreased with a low peak, whereas at a high fluence rate it decreased immediately with a high peak. Consequently, the cumulative (1)O(2) at a low fluence rate was higher, which thus induced a strong photodynamic effect. The proportion of apoptosis to necrosis might therefore be dependent on the peak and duration of the (1)O(2) signal. A low fluence rate tended to induce apoptotic change, whereas a high fluence rate tended to induce necrotic change. CONCLUSIONS: The results of this study suggested that the monitoring of (1)O(2) enables us to predict the photodynamic effect, allowing us to select the optimal laser conditions for each patient.

Animals↗

Biochemical requirements for singlet oxygen production by purified human myeloperoxidase.

The myeloperoxidase (MPO)-hydrogen peroxide (H2O2)-halide systems were found to produce chemiluminescence at 1,268 nm, a characteristic emission band for singlet oxygen (1O2). The emission was enhanced by a factor of 29 +/- 5 in deuterium oxide and was inhibited by the 1O2 quenchers, histidine and azide ion. Inactivation of MPO with heat or with cyanide ion prevented light production. The combined weight of all data strongly supported the production of 1O2 by these enzyme systems. The amount of 1O2 produced was sensitive to the conditions employed. Under optimal conditions at pH 5, the MPO-H2O2-bromide (Br-) system produced 0.42 +/- 0.03 mol 1O2/mol H2O2 consumed, close to the theoretical value of 0.5 that was predicted by the reaction stoichiometry. In contrast, the MPO-H2O2-chloride (Cl-) system was much less efficient. The maximum yield of 1O2 was 0.09 +/- 0.02 mol/mol H2O2 consumed and required pH 4 and 5 mM H2O2. At higher pH, the 1O2 production rapidly decreased. The yield at pH 7 was 0.0004 +/- 0.0002 mol/mol H2O2 consumed. Enzyme inactivation was a major factor limiting the yield of 1O2 with both Cl- and Br-. While the MPO-H2O2-halide systems can efficiently produce 1O2, the conditions required are not physiologic, which suggests that the chemiluminescence of the stimulated neutrophil does not derive from 1O2 generated by a MPO mechanism.

Chloride Peroxidase↗

The antithrombotic factor singlet oxygen/light (1O2/h nu).

Activated phagocytes (especially polymorphonuclear granulocytes (PMNs)) by respiratory oxidative/photonic burst (activation of NADPH-oxidase and myeloper-oxidase) generate large amounts of oxidants of the hypochlorite-/chloramine-type, which are physiologic sources for singlet oxygen (1O2), a nonradical-excited (photon (h nu) emitting) oxygen species [Weiss SJ, NEJM 1989;320:365-376]. In vitro experiments show that 1O2 (1) inhibits coagulation by inactivation of thrombocytes, fibrinogen, factor V, factor VIII, and factor X and (2) activates fibrinolysis by inactivation of the main fibrinolysis inhibitors plasminogen activator inhibitor (PAI)-1 and alpha-2-antiplasmin, and by activation of single-chain urokinase by plasmin and oxidized fibrin. Additionally, this work suggests that 1O2/h nu acts antithrombotically, inducing selective thrombolysis in vivo (i.e., thrombolysis induced by 0.1 to 0.5 mmol/l chloramine within 30 to 60 minutes without changes of the plasmatic hemostasis system). 1O2 might activate flowing to (on the endothelium) rolling PMN, increasing their chance to get in contact with fibrin/platelet aggregates deposited on the endothelial layer. Via 1O2 generation, the thrombus-activated phagocytes might call for (acute, physiologic) inflammation/fibrinolysis amplification, resulting in the "moving front" of PMN, which infiltrates and destroys the thrombus. 1O2 seems to (partially) participate in the reactivity of nitric oxide, another prooxidative agent. The inhibition of physiologic amounts of 1O2 by blood cholesterol might be involved in the pathogenesis of atherothrombosis. Consequently, it is suggested that activated PMNs modulate hemostasis, shifting it into an antithrombotic state; this cellular part of fibrinolysis seems to be of greater physiologic importance than the plasmatic one. Impaired PMN function (e.g., as occurring in patients with antineutrophil cytoplasmic antibodies or under cytostatic treatments) often results in serious thrombotic complications. Light is the only signal whose origin can be immediately recognized by a fast moving cell in the (dark) blood stream. The cell signal action of 1O2/h nu (e.g., released by chloramines such as taurine-chloramine or vancomycin, by fiberoptic, by photodynamic therapy, or by so-called redox-cycling drugs such as quinones or tetracyclines) might be a new and physiologic principle for pharmacologic intervention in atherothrombosis.

Animals↗