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PubMed1999

Oxidation of hypotaurine to taurine with photochemically generated singlet oxygen: the effect of azide.

Hypotaurine is oxidized to taurine by singlet oxygen (1O2) generated with methylene blue used as a photosensitizer. The oxidation rate increases in the presence of deuterium oxide as expected for the involvement of 1O2. Addition of the 1O2 quencher azide also produced an activating effect in contrast with the expected inhibition. Azidyl radicals produced by the oxidation of azide by the horseradish peroxidase/hydrogen peroxide system stimulate the oxidation of the added hypotaurine. It is concluded that azide competes with hypotaurine for 1O2 generating the azidyl radical which is a strong one-electron oxidant transfer of the radical to hypotaurine. The hypotaurine radical is then converted into taurine, possibly through the disulfone intermediate. Formation of the sulfonic hydroperoxide is the possible intermediate in the absence of azide. The finding that the azidyl radical efficiently oxidizes hypotaurine to its metabolic product taurine raises the expectation of hypotaurine being a valuable scavenger of endogenous and exogenous radicals.

Azides↗
PubMed1999

Role of ground and excited singlet state oxygen in the red light-induced stimulation of Escherichia coli cell growth.

Irradiation of selected Escherichia coli defective strains with red-light induces a stimulation of the cell growth rate. Such effect is wavelength-dependent and is accompanied by a transient increase of the cell volume and some enzymic activities. The presence of oxygen appears to be essential for the occurrence of a significant photostimulatory effect. The results obtained upon irradiation in the presence of quenchers (tryptophan, histidine, azide) or enhancers (deuterium oxide) of singlet oxygen (1O2) strongly suggest that this activated oxygen derivative is generated by excitation of endocellular chromophores (possibly cytochromes). The reaction of 1O2 with nearby cellular targets could induce a sublethal cell damage which in turn promotes an accelerated cell metabolism.

Azides↗
PubMed1999

Involvement of singlet oxygen in cytochrome P450-dependent substrate oxidations.

Cytochrome P450 (P450)-dependent p-hydroxylation of aniline and o-deethylation of 7-ethoxycoumarin were examined in rat liver microsomes in the presence of radical scavengers. The addition of beta-carotene, a quencher of singlet oxygen species ((1)O(2)), suppressed the aniline hydroxylation, while the addition of sodium azide (NaN(3)) ((1)O(2) quencher) enhanced the reaction. No other reactive oxygen scavengers or chelating agents such as superoxide dismutase, catalase, dimethylsulfoxide, or deferoxamine altered the reaction. In contrast, the microsomal o-deethylation of 7-ethoxycoumarin was suppressed by the addition of NaN(3). (1)O(2) was detectable during the reaction of microsomes and NADPH by ESR spin-trapping when 2,2,6,6-tetramethyl-4-piperidone (TMPD) was used as a spin trap, and the (1)O(2) was quenched by the additions of beta-carotene, NaN(3), aniline, and 7-ethoxycoumarin. The enhancement effect of NaN(3) in the hydroxylation of aniline appeared to be due to the conformational change of P450 protein, which in turn enhances the binding of aniline to P450 in terms of the spectral dissociation constant (K(s)). In contrast, (1)O(2) appeared to be active in the o-deethylation of 7-ethoxycoumarin. On the basis of the results, the involvement of (1)O(2) in P450-dependent substrate oxygenations is proposed.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1995

Interaction of singlet oxygen with 5'-nucleotidase in rat hearts.

This study was aimed to determine whether singlet oxygen (1O2) attenuates 5'-nucleotidase activity in the ischemic myocardium. Isolated rat hearts were exposed to either exogenous 1O2 produced by irradiating rose bengal or 40-min ischemia and reperfusion. Ecto-5'-nucleotidase activity was inhibited by exogenous 1O2 (3.74 +/- 0.38 mumol/min/g dry weight), when compared with normal control (7.52 +/- 0.41 mumol/min/g dry weight; P < 0.05). The enzymatic activity was significantly preserved by histidine (25 mM)--a 1O2 scavenger (7.04 +/- 0.61 mumol/min/g dry weight; P < 0.05 v rose bengal group). After ischemia, the activity of ecto-5'-nucleotidase was greatly reduced (2.51 +/- 0.25 mumol/min/g dry weight), when compared with normal control. Histidine significantly enhanced ecto-5'-nucleotidase activity (6.55 +/- 0.52 mumol/min/g dry weight, P < 0.05 v ischemic control). Adenosine release was consistent with ecto-5'-nucleotidase activity. The time course studies of effects of 1O2 on coronary flow, cardiac function, and LDH release revealed that the damage by 1O2 to ecto-5'-nucleotidase activity and adenosine release primarily accounted for impaired coronary flow, cardiac dysfunction, and impaired cardiac metabolism. Lipid peroxidation induced by exogenous 1O2 or ischemia was in parallel with ecto-5'-nucleotidase deactivation by 1O2. It is concluded that 1O2 causes inactivation of ecto-5'-nucleotidase and attenuation of adenosine release which could possibly be one of the important mechanisms of oxygen radical-mediated myocardial injury.

5'-Nucleotidase↗
PubMed1994

Singlet oxygen quenching ability of naturally occurring carotenoids.

The singlet oxygen quenching ability of various naturally occurring carotenoids was examined by measuring toluidine blue-sensitized photooxidation of linoleic aci. To assess quenching, the oxidation of linoleic acid was followed by measuring oxygen consumption and ultraviolet absorbance at 235 nm. We found that oxygen quenching increased as the number of conjugated double bonds in the carotenoids increased, but quenching varied with chain structure and functional groups. Acyclic carotenoids enhanced quenching more than did cyclic carotenoids. Conjugated keto groups and the presence of a cyclopentane ring stimulated quenching, while hydroxy, epoxy and methoxy groups showed lesser effects. The photosynthetic bacterial carotenoids, spirilloxanthin and rhodopin, were found to be most effective as quenchers, followed by the cayenne carotenoid, capsorbin.

Animals↗
PubMed2007

New noncellular fluorescence microplate screening assay for scavenging activity against singlet oxygen.

In the present study, a new fluorescence microplate screening assay for evaluating scavenging activity against singlet oxygen (1O2) was implemented. The chemical generation of 1O2 was promoted using the thermodissociable endoperoxide of disodium 3,3'-(1,4-naphthalene)bispropionate (NDPO2). The detection of 1O2 was achieved using dihydrorhodamine 123 (DHR), a nonfluorescent molecule that is oxidizable to the fluorescent form rhodamine 123 (RH). The combined use of a 1O2-selective generator and a highly sensitive probe (DHR) was then successfully applied to perform a screening assay of the 1O2 scavenging activities of ascorbic acid, penicillamine, cysteine, N-acetylcysteine (NAC), methionine, reduced glutathione (GSH), dihydrolipoic acid, lipoic acid, and sodium azide. All of these antioxidants exhibited concentration-dependent 1O2 scavenging capacities. They could be ranked according to observed activity: ascorbic acid>cysteine>penicillamine>dihydrolipoic acid>GSH>NAC>sodium azide>lipoic acid (IC50 values of 3.0+/-0.2, 8.0+/-0.7, 10.9+/-0.8, 25.2+/-4.5, 57.4+/-5.9, 138+/-13, 1124+/-128, 2775+/-359 microM, mean+/-SEM, respectively)>methionine (35% of scavenging effect at 10 mM). In conclusion, the use of NDPO2 as a selective generator for 1O2 and its fluorescence detection by the highly sensitive probe DHR is shown to be a reliable and resourceful analytical alternative means to implement a microplate screening assay for scavenging activity against 1O2.

Antioxidants↗
PubMed2001

Thrombin converts singlet oxygen (1O2)-oxidized fibrinogen into a soluble t-PA cofactor. A new method for preparing a stimulator for functional t-PA assays.

Activated phagocytes, particularly polymorphonuclear leukocytes (neutrophils), by means of oxidative photonic burst, i.e., the combined activation of NADPH-oxidase and myeloperoxidase, generate large amounts of oxidants of the hypochlorite/chloramine type that are an important physiologic source for the nonradical, photon-emitting oxidant singlet oxygen (1O2), which (in the dark blood stream) is both a signal and an agent of defense against bacteria or fibrin. 1O2-oxidized fibrinogen or oxidized fibrin monomer has previously been shown to be unpolymerizable, and methionine to methionine sulfoxide-oxidized fibrinogen occurs in circulating blood. The present study demonstrates that thrombin converts oxidized fibrinogen into a soluble stimulator of tissue-type plasminogen activator (t-PA). After addition of 0.1 IU thrombin to 25 microl oxidized normal human plasma and an incubation time of 10 min (room temperature), t-PA activity increases about 20-fold when compared with oxidized plasma without the addition of thrombin. Thus, since oxidized fibrin monomer is a t-PA cofactor, thrombin-degraded oxidized fibrinogen can be used as a stimulator in functional t-PA assays.

Electrophoresis, Polyacrylamide Gel↗
PubMed2005

The glutathione peroxidase homologous gene Gpxh in Chlamydomonas reinhardtii is upregulated by singlet oxygen produced in photosystem II.

The expression of the glutathione peroxidase homologous gene Gpxh, known to be specifically induced by the formation of singlet oxygen (1O2), was analyzed in cells of Chlamydomonas reinhardtii exposed to environmental conditions causing photoinhibition. Illumination with high light intensities, leading to an increased formation of 1O2 in photosystem II, continuously induced the expression of Gpxh in cell for at least 2 h. Phenolic herbicides like dinoterb, raise the rate of 1O2 formation by increasing the probability of charge recombination in photosystem II via the formation of the primary radical pair and thereby 3P680 formation (Fufezan C et al. 2002, FEBS Letters 532, 407-410). In the presence of dinoterb the light-induced loss of the D1 protein in C. reinhardtii was increased and the high light-induced Gpxh expression was further stimulated. DCMU, a urea-type herbicide, causing reduced 1O2 generation in photosystem II, protected the D1 protein slightly against degradation and downregulated the expression of the Gpxh gene compared to untreated cells exposed to high light intensities. This indicates that the Gpxh expression is induced by 1O2 under environment conditions causing photoinhibition.

Animals↗
PubMed1990

Physical and chemical scavenging of singlet molecular oxygen by tocopherols.

Singlet molecular oxygen (1O2) arising from the thermal decomposition of the endoperoxide of 3,3'-(1,4-naphthylidene) dipropionate was used to assess the effectiveness of alpha-, beta-, gamma-, and delta-tocopherol in the physical quenching as well as the chemical reaction of 1O2. The relative physical quenching efficiencies of the tocopherol homologs were found to decrease in the order of alpha greater than or equal to beta greater than gamma greater than delta-tocopherol. The ability of physical quenching depends on a free hydroxyl group in position 6 of the chromane ring. Chemical reactivity of the tocopherol homologs with 1O2 was low, accounting for 0.1-1.5% of physical quenching with beta-tocopherol showing particularly low reactivity, resulting in the sequence alpha greater than gamma greater than delta greater than beta-tocopherol. Tocopheryl quinones were products of all tocopherol homologs, and in addition a quinone epoxide was a major product from gamma-tocopherol. This quinone epoxide was not cleaved by rat liver microsomal epoxide hydrolase; however, it reacted further with 1O2. It is concluded that methylation in position 5 of the chromane ring enhances physical quenching of 1O2, whereas chemical reactivity is favored by a methylated position 7. In view of the fact that beta-tocopherol is as effective as alpha-tocopherol in physical quenching of 1O2 but shows very low chemical reactivity, this tocopherol homolog might be particularly suitable for biological conditions in which an accumulation of oxidation products might weaken the antioxidant defense.

Kinetics↗
PubMed1996

Comparison of photosensitized plasma membrane damage caused by singlet oxygen and free radicals.

The efficiency and selectivity of photosensitized damage to membrane functions may be influenced strongly by the identity of the initial reactive species formed by the photosensitizer. To test this possibility, a photosensitizer, rose bengal (RB), was used that resides in the plasma membrane and which generates singlet molecular oxygen (1O2*) upon excitation with visible light, and radicals plus 1O2* upon excitation with UV radiation. With this approach, 1O2* and radicals are formed at the same locations in the plasma membrane. The response of three plasma membrane functions, namely, proline transport, membrane potential, and membrane impermeability to charged dye molecules, was assessed. The efficiencies of the responses in the presence and absence of oxygen were compared per photon absorbed by RB at two wavelengths, 355 nm (UV excitation) and 532 nm (visible excitation). The efficiency of oxygen removal before irradiation was assessed by measuring the RB triplet lifetime. The three membrane functions were inhibited more efficiently at 355 nm than at 532 nm in the presence of oxygen indicating that the radicals are more effective at initiating damage to membrane components than 1O2*. The ratio of photosensitized effects at the two wavelengths in the presence of oxygen was the same for two membrane functions but not for the third suggesting that 1O2* and radicals initiate a common mechanistic pathway for damage to some membrane functions but not to others. Removing oxygen reduced the efficiency of 355 nm-induced photosensitization by factors of 1.4 to 7. The sensitivity of the three membrane functions to 1O2*-initiated damage varied over a factor of 50 whereas radical initiated damage only varied by a factor of 15. In summary, these results indicate that radicals and 1O2* formed at the same locations in the plasma membrane vary in their efficiency and specificity for membrane damage but may, in some cases, operate by a common secondary damage mechanism in the presence of oxygen.

Animals↗
PubMed1984

Quenching of singlet oxygen by D-alpha-tocopherol in human granulocytes.

The ability of D-alpha-tocopherol to act as a quencher of (1)0(2) (singlet oxygen) was tested with a biological source of (1)0(2), namely the phagocytosis activated myeloperoxidase contained in the homogenate of human circulating polymorphonuclear leukocytes. With this system, the (1)0(2) quenching efficiency of exogenously added D-alpha-tocopherol was estimated from its inhibitory effect on the luminol amplified chemiluminescence. This inhibitory effect was dose dependent. D-alpha-tocopherol was also efficient in quenching the chemiluminescence generated through the H2O2-horseradish system. In both systems the quenching effect may be almost entirely "physical", since very little tocopherol was destroyed when compared to the relatively large amount of H2O2 consumed.

Humans↗
PubMed1992

Physico-chemical modeling of the role of free radicals in photo-dynamic therapy. I. Utilization of quantum yield data of singlet oxygen formation for the study of the interaction between excited photosensitizer and stable free radicals.

The measurement of the relative quantum yield of singlet oxygen formation, a simple process without tedious sample deoxygenation, is shown to furnish data on the interaction of the excited photosensitizer with any additive (in this case stable free radicals) given to the sample. The rate constants derived from such measurements are in good agreement with direct determination of the corresponding values.

Free Radicals↗
PubMed1993

Prevention of singlet oxygen-induced DNA damage by lipoate.

Among the several biologically and pharmacologically active sulfur compounds examined, only lipoic acid and dihydrolipoic acid provided protection to plasmid DNA against singlet molecular oxygen (1O2). 1O2 was generated in phosphate buffer by the thermal dissociation of the endoperoxide of 3,3'-(1,4-naphthylidene) dipropionate (NDPO2). The protecting effect of lipoic acid was time- and pH-dependent and significant protection was seen even at 50 microM. The antioxidant effect was adversely affected by temperatures above 45 degrees C. Superoxide dismutase and catalase marginally enhanced this effect. Metal chelation with EDTA decreased the protection by lipoate, indicating that metal ions may be involved. The protective effect was diminished when the disulfide was added after single-strand breaks were induced by 1O2. The formation of 8-oxoguanosine from guanosine upon exposure to NDPO2 was not altered by lipoate.

Catalase↗
PubMed1994

Diminution of singlet oxygen-induced DNA damage by curcumin and related antioxidants.

Curcumin, the natural antioxidant from turmeric, an Indian spice, and its derivatives have significant abilities to protect plasmid pBR322 DNA against single-strand breaks induced by singlet oxygen (1O2), a reactive oxygen species with potential genotoxic/mutagenic properties. 1O2 was generated at 37 degrees C in an aqueous buffer system by the thermal dissociation of the endoperoxide of 3,3'-(1,4-naphthylene)dipropionate (NDPO2). Among the compounds tested, curcumin was the most effective inhibitor of DNA damage followed by desmethoxycurcumin, bisdesmethoxycurcumin and other derivatives. The observed antioxidant activity was both time- and concentration-dependent. The protective ability of curcumin was higher than that of the well-known biological antioxidants lipoate, alpha-tocopherol and beta-carotene. However, the highest protective ability with saturating concentrations of curcumin did not exceed 50%. The ability of curcumin and its derivatives to protect DNA against 1O2 seems to be related to their structures and may at least partly explain the therapeutic and other beneficial effects of these compounds including anticarcinogenic and antimutagenic properties.

Antimutagenic Agents↗
PubMed1984

Studies on the possible involvement of singlet oxygen and superoxide anion radicals in the cyclo-oxygenase reaction.

The influence of several naphthalene and furan derivatives which are potent singlet oxygen (1O2) acceptors on two prostaglandin synthetase preparations derived from bovine seminal vesicles or rat kidney medulla was studied. Also the effects on the formation of superoxide anion radicals (O2-.) were measured to give further evidence for or against the possible involvement of 1O2 or O2-. in the cyclo-oxygenase reaction. The data we have attained make an essential role of these activated oxygen species as initiators of the cyclo-oxygenase reaction unlikely and thereby support the hypothesis that cyclo-oxygenation during prostaglandin biosynthesis is a lipoxygenase type of reaction.

Animals↗
PubMed1985

Comparison of the DNA-damaging property of photosensitised riboflavin via singlet oxygen (1O2) and superoxide radical O2-. mechanisms.

Riboflavin was found to generate singlet oxygen (1O2) and superoxide anion radicals O2-. on exposure to UV-A (320-400 nm) and UV-B (290-320 nm) light. Studies with deoxyguanosine (dGuo) showed that 1O2 was largely responsible for riboflavin-sensitised photodegradation of the guanine base of DNA and RNA. Azide ions (N-3) and 1,4 diazabicyclo-[2.2.2]-octane (DABCO) produced over 90% inhibition of dGuo photo oxidation, whereas superoxide dismutase did not show any noticeable quenching effect under similar conditions. Photo oxidation of dGuo by riboflavin and UV radiation is of significant importance from the point of view of cell-damaging reactions by activated oxygen species produced by the synergistic action of sunlight and chemical agents. It is now known that activated oxygen species are responsible for skin photosensitisation, tumor promotion and carcinogenic properties.

DNA↗
PubMed1992

Interaction of singlet oxygen with DNA and biological consequences.

To study the interaction of singlet oxygen (1O2) with DNA and the biological consequences of 1O2-induced DNA damage, we used the thermodissociable endoperoxide of 3,3'-(1,4 naphthalidene) dipropionate (NDPO2) as a generator of free 1O2 in reactions with (1) 2'-deoxynucleoside 3'-monophosphates (dNps), (2) an oligonucleotide (16-mer) having one deoxyguanine (dG), (3) native and denaturated rat kidney DNA and (4) single-stranded (ss) and double-stranded (ds) bacteriophage M13mp10 DNA. Using both anion exchange and reversed phase HPLC and 32P-postlabeling analyses, it was found that exposure of the various dNps to chemically generated 1O2 led to a detectable reaction with dGp and not with dAp, dCp, d5mCp or Tp. The reaction with dGp led to degradation of this nucleotide and the formation of a large number of reaction products, one of which could be identified as 7-hydro-8-oxo-2'-deoxyguanosine 3'-monophosphate (8-oxo-dGp). A second product could tentatively be identified as a formamido pyrimidine derivative of dGp (Fapy-dGp). When ss DNA, ds DNA or the oligonucleotide were exposed to 1O2, the formation of 8-oxo-dG could also be demonstrated. With the oligonucleotide, we found a so far unidentified reaction product. Under the same reaction conditions the yield of 8-oxo-dG was about 8-fold higher in ss DNA than in ds DNA. In ss DNA 8-oxo-dG seemed to be a more prominent product than in the case of reaction of 1O2 with free dGp. Reaction of 1O2 with ss or ds M13mp10 DNA led to biological inactivation of these DNAs, ss DNA being at least 100-fold more sensitive than ds DNA. It could be concluded that inactivation of the ss DNA must be largely due to 1O2-induced DNA lesions other than 8-oxo-dG. In agreement with the observed preferential reaction of 1O2 with dG most of the so far sequenced mutations, induced by 1O2 in a 144 bp mutation target sequence inserted in the lacZ alpha gene of ss or ds M13mp10 DNA, occurred at a G or G/C base pair respectively. A preference for G(C) to T(A) transversions can be observed for which 8-oxo-dG might have been responsible. In ss DNA a significant number of the mutations are characterized by the fact that a G is deleted.

Animals↗
PubMed1990

Photophysical studies of pheophorbide a and pheophytin a. Phosphorescence and photosensitized singlet oxygen luminescence.

The triplet states of pheophorbide a and pheophytin a were studied in several environments by direct measurement of the phosphorescence of the pigments and photosensitized singlet oxygen (1O2) luminescence. The spectra, lifetimes and quantum yields of phosphorescence and the quantum yields of 1O2 generation were determined. These parameters are similar for monomeric molecules of both pigments in all the environments studied. Aggregation of the pigment molecules leads to a strong decrease in the phosphorescence and 1O2 luminescence intensities, which is probably due to a large decrease in the triplet lifetime and triplet quantum yield in the aggregates. The results obtained for pheophorbide a and pheophytin a are compared with those previously reported for chlorophyll alpha. The data suggest that the photodynamic activity of the pigments in living tissues is probably determined by the monomeric pigment molecules formed in hydrophobic cellular structures. Aggregated molecules seem to have a much lower activity.

Chlorophyll↗