alpha-(4-pyridyl-1-oxide)-n-tert-butylnitrone and 5-5-dimethyl-1-pyrroline-1-oxide

Topics: Animals; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Free Radicals; Humans; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Membrane Fluidity; Nitrogen Oxides; Oxidation-Reduction; Pyridines; Sensitivity and Specificity; Skin; Skin Diseases; Spin Labels; Ultraviolet Rays

The phenomena of stable and transient acoustic cavitation in liquids exposed to ultrasound are briefly explained. The role of micronuclei, resonant bubble size, and rectified diffusion in the initiation of transient cavitation is reviewed. In aqueous solutions transient cavitation initially generates hydrogen atoms and hydroxyl radicals that may recombine to form hydrogen and H2O2 or may react with solutes in the gas phase, at the gas-liquid boundary, or in the bulk of the solution. The analogies and differences between sonochemistry and ionizing radiation chemistry are explored. The use of spin trapping and electron spin resonance to conclusively identify hydrogen atoms and hydroxyl radicals and to detect cavitation produced by continuous wave and by pulsed ultrasound is described in detail.

Topics: Chemical Phenomena; Chemistry; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Free Radicals; Hydrogen; Hydrogen Peroxide; Hydroxides; Hydroxyl Radical; Nitrogen Oxides; Oxygen; Pyridines; Solutions; Spin Labels; Thermodynamics; Ultrasonics; Water

2-(3-Benzoylphenyl)propanoic acid (ketoprofen), one of the nonsteroidal anti-inflammatory drugs, causes photocontact dermatitis by ultraviolet (UV) light as a side effect. In this study, we examined radical reactions induced by ketoprofen in the lipid membranes under UV irradiation using egg yolk phosphatidylcholine (egg-PC) liposomal membranes containing 5- or 16-doxyl stearic acid (5- or 16-DSA), which carry nitroxyl radical at the 5- or 16-position of the fatty acid chain, respectively. When the suspension of liposomal membrane was mixed with ketoprofen and irradiated with UV, electron spin resonance signal of 5- and 16-DSA in the membrane decreased. The decay consisted of fast decay and subsequent slow decay. The overall decay for 5-DSA was faster than that for 16-DSA. The rate of slower decay of 16-DSA increased with ketoprofen concentration. The bulk lipid in the membrane affected the rate of slower decay of 5-DSA; the rate increased with the amount of egg-PC and decreased in the rigid membrane composed of dipalmitoylphosphatidylcholine. When spin trapping studies with α-(4-pyridyl 1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimetyl-1-pyrroline-N-oxide (DMPO) were performed in ketoprofen solution, C-centered radical adducts of POBN and superoxide anion radical adducts of DMPO were detected after UV irradiation. POBN suppressed the signal decay of 5-DSA in the liposomal membrane, whereas superoxide dismutase accelerated it. These results support that ketoprofen penetrates the lipid membrane and induces a radical reaction near the polar region in the membrane, and that ketoprofen-related C-centered radical is involved in the radical reaction.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Anti-Inflammatory Agents, Non-Steroidal; Cyclic N-Oxides; Egg Yolk; Free Radicals; Humans; Hydroxyl Radical; Ketoprofen; Phosphatidylcholines; Pyridines; Superoxide Dismutase; Superoxides; Ultraviolet Rays

Using a competitive spin trapping method, relative spin trapping rates were quantified for various short-lived radicals (methyl, ethyl, and phenyl radicals). High static pressure was applied to the competitive spin-trapping system by employing high-pressure electron spin resonance (ESR) equipment. Under high pressure (490 bar), spin trapping rate constants for alkyl and phenyl radicals increased by 10 to 40%, and the increase was dependent on the structure of nitrone spin traps. A maximum increase was obtained when tert-butyl(4-pyridinylmethylene)amine N-oxide (4-POBN) was used as a spin trap. Activation volumes (DeltaDeltaV(double dagger)) for the two spin trapping reactions were calculated to be -17-(-9) cm(3) mol(-1) for the 4-POBN system.

Topics: Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Free Radicals; Molecular Structure; Nitrogen Oxides; Pressure; Pyridines; Solutions; Spin Labels; Spin Trapping

Topics: Animals; Antioxidants; Ascorbic Acid; Cyclic N-Oxides; Deferoxamine; Electron Spin Resonance Spectroscopy; Free Radicals; Humans; Mice; Mice, Hairless; Nitrogen Oxides; Oxidation-Reduction; Oxidative Stress; Pyridines; Skin; Spin Labels; Ultraviolet Rays

Acetaldehyde oxidation by enzymes and cellular fractions has been previously shown to produce radicals that have been characterized as superoxide anion, hydroxyl, and acetyl radicals. Here, we report that acetaldehyde metabolism by xanthine oxidase, submitochondrial particles and whole rats produces both the acetyl and the methyl radical, although only the latter was unambiguously identified in vivo. Electron paramagnetic resonance (EPR) characterization of both radicals was possible by the use of two spin traps, 5,5-dimethyl 1-pyrroline N-oxide (DMPO) and alpha-(4-pyridyl 1-oxide)-N-t-butylnitrone (POBN), and of acetaldehyde labeled with (13)C. The POBN-acetyl radical adduct proved to be unstable, but POBN was employed to monitor acetaldehyde metabolism by Sprague-Dawley rats because previous studies have shown its usefulness for in vivo spin trapping. EPR analysis of the bile collected from treated and control rats showed the presence of the POBN-methyl and of an unidentified, biomolecule-derived, POBN adduct. Because decarbonylation of the acetyl radical is one of the routes for methyl radical formation from acetaldehyde, detection of the latter in bile provides strong evidence for the production of both radicals in vivo. The results may be relevant to understanding the toxic effects of acetaldehyde itself and of its more relevant biological precursor, ethanol.

Topics: Acetaldehyde; Animals; Bile; Cattle; Cyclic N-Oxides; Edetic Acid; Electron Spin Resonance Spectroscopy; Ferric Compounds; Free Radicals; In Vitro Techniques; Male; Methane; Mitochondria, Heart; Nitrogen Oxides; Oxidation-Reduction; Pyridines; Rats; Rats, Sprague-Dawley; Spin Labels; Submitochondrial Particles; Xanthine Oxidase

In vivo spin trapping is potentially a very useful tool to investigate the role of free radicals in physiologic processes and disease development. Unfortunately, knowledge on the stability and distribution of spin traps in living systems is limited. Therefore, in our study, we selected 11 acyclic and cyclic nitrone spin traps with diverse properties to determine their pharmacokinetics in mice. At varying times after intraperitoneal administration, we measured the concentration of the spin traps in the liver, heart, and blood. Our results showed that most spin traps were rapidly absorbed and were approximately evenly distributed throughout the mouse body. It was also found that most of the traps were relatively stable in vivo with more than half of the injected amount still available for spin trapping free radicals after an hour. Two of the 11 tested spin traps, however, decomposed after injection. These results indicate that for a successful in vivo spin trapping experiment, the stability of the spin trap is not of major concern, but the time course of distribution may be important.

Topics: Animals; Chromatography, High Pressure Liquid; Cyclic N-Oxides; Mice; Mice, Inbred BALB C; Molecular Structure; Nitrogen Oxides; Pyridines; Spin Labels

Catechol estrogens are genotoxic, indirectly through redox cycling mechanisms leading to oxidative DNA damage and directly by formation of quinone-DNA adducts. Previously, we demonstrated that Cu2+ can oxidize estradiol (E2) catechols, establishing a copper redox cycle leading to the formation of DNA strand breaks. The goal of this study was to use electron spin resonance techniques to identify the free radical intermediates formed. The 2- and 4-OH catechols of E2 and ethinyl estradiol (EE) were oxidized to semiquinone intermediates, stabilized by Mg2+, when incubated with Cu2+. The 4-OH-EE semiquinone decayed more slowly than the 2-OH-EE semiquinone. Using the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone, 4-OH-E2 plus Cu2+ generated hydroxyl radicals at a greater rate than 2-OH-E2 plus Cu2+. Formation of hydroxyl and methyl radical adducts was detected, using 5,5-dimethyl-1-pyrroline-N-oxide as the spin trap, when 2-OH-E2 was incubated with Cu2+ and 1% dimethyl sulfoxide. This was inhibited by the Cu1+ chelator bathocuproinedisulfonic acid and catalase. These data demonstrate that the oxidation of estrogen catechols by Cu2+ leads to a Cu-dependent mechanism of hydroxyl radical production via a hydrogen peroxide intermediate and suggest a mechanism for estrogen-associated site-specific DNA damage and mutagenesis.

Topics: Benzoquinones; Copper; Cyclic N-Oxides; DNA Damage; Electron Spin Resonance Spectroscopy; Estradiol; Estrogens, Catechol; Ethinyl Estradiol; Free Radicals; Glutathione; Hydrogen Peroxide; Hydroxyl Radical; Molecular Structure; Mutagenesis; Nitrogen Oxides; Oxidation-Reduction; Phenanthrolines; Pyridines; Spin Labels

The focus of this investigation was to determine whether the nitrone spin-trapping compounds alpha-phenyl-N-tert-butylnitrone (PBN), 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) are radioprotectors. Two methods were used to assess for radioprotection: measurement of oxidative damage to DNA bases and mammalian cell survival assays. Oxidative damage to DNA was quantified by measuring the relative amounts of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) produced by the reaction of hydroxyl radicals (OH.) with 2-deoxyguanosine (dG) after irradiation. PBN, DMPO and POBN, when dissolved in aqueous solutions of either dG or naked salmon sperm DNA, reduced the formation of 8-OH-dG by 137Cs gamma irradiation significantly. The spin-trapping agents, especially PBN at lower concentrations, were more effective in preventing radiation-induced formation of 8-OH-dG in naked DNA than in free dG. These data suggest that PBN, DMPO and POBN act as free radical scavengers which may associate with DNA and afford protection against gamma rays. However, no enhancement of survival was observed when Chinese hamster ovary (CHO) cells were exposed to high non-toxic concentrations of PBN or POBN prior to and during irradiation with 60Co gamma rays and scored for clonogenic survival. DMPO provided only minimal protection from radiation-induced cell killing.

Topics: 8-Hydroxy-2'-Deoxyguanosine; Animals; Cell Survival; CHO Cells; Cricetinae; Cyclic N-Oxides; Deoxyguanosine; DNA Damage; Nitrogen Oxides; Pyridines; Radiation-Protective Agents; Spin Labels

The generation of free radicals during the lipid peroxidation of liposomes composed of 1-palmitoyl-2-arachidonoylphosphatidylcholine (PAPC-liposome) in Fe2+/ascorbic acid (AsA) solution was studied by the ESR spin trapping technique. A carbon-centered radical adduct was observed using alpha-(4-pyridyl-1-oxide)-N-tert-butyl-nitorone (4-POBN) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), but no oxygen-centered radicals such as .OH, LO., and LOO. were observed. The lipid peroxidation evaluated as 2-thiobarbituric acid reactive substances was inhibited by the addition of 4-POBN. The intensity of this inhibitory effect was dependent on the time when 4-POBN was added to the mixture of PAPC-liposomes and Fe2+/AsA solution, and no inhibitory effect could be observed after 4 min. The signal intensity of the carbon-centered radical adduct was dependent on the lipid concentration of PAPC-liposomes. These results suggest that the alkyl radicals generated from PAPC-liposome peroxidation induced by Fe2+/AsA were trapped by DMPO or 4-POBN at an earlier stage of lipid peroxidation.

Topics: Ascorbic Acid; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Ferrous Compounds; Free Radicals; Kinetics; Lipid Peroxidation; Liposomes; Nitrogen Oxides; Phospholipid Ethers; Pyridines; Solutions; Spin Labels; Thiobarbiturates

For greatest efficacy, it is desirable to use spin trapping agents in the highest concentrations possible. Fifty-four male Sprague-Dawley rats were used to explore the relative toxicity of four representative nitronyl spin traps at doses chosen on the basis of earlier lethality studies. Most studies were confined to the 3- to 6-h period following drug injection, because the behavioral signs of toxicity are most evident early after injection and because spin trapping studies would typically be performed within this time frame. Doses of spin trap were dissolved in a corn oil/buffer vehicle and injected intraperitoneally (i.p.). Toxic signs were recorded periodically, and at the time of euthanasia or spontaneous death a blood sample was collected by cardiac puncture for clinical chemistry analysis and a necropsy was performed. Both gross pathology and histopathological examination of the major organs were essentially negative in all cases, with no obvious evidence of cellular damage being observed. Neither DMPO (232 mg/100 g b.wt.) nor PBN (100 mg/100 g b.wt.) were lethal in the present study, while both M4PO (20 and 40 mg/ 100 g b.wt.) and PyOBN (100 and 200 mg/100 g b.wt.) were lethal. Abnormal clinical chemistry findings were generally confined to those animals that died spontaneously or were euthanized early for humane reasons. In most cases, death was associated with marked seizure activity and impaired respiration, and deaths occurred within a few min to a few hours. The mechanism of toxicity was unclear due to the lack of histopathological evidence and the wide range of abnormal serum analytes in those rats killed by either M4PO or PyOBN. In conclusion, during the first 6 h after IP administration there is little indication of tissue damage by the nitrone spin traps until the dose is increased to a lethal level, at which point an acute, rapidly occurring, wide-spread disruption of tissue integrity seems to occur.

Topics: Animals; Blood Glucose; Blood Proteins; Blood Urea Nitrogen; Cyclic N-Oxides; Electrolytes; Enzymes; Free Radicals; Injections, Intraperitoneal; Male; Nitrogen Oxides; Pyridines; Rats; Rats, Sprague-Dawley; Spin Labels

Metabolism of ethanol to 1-hydroxyethyl radicals by rat liver microsomes was studied with three nitrone spin trapping agents (POBN, PBN, and DMPO) under essentially comparable conditions. The data indicate that POBN was the superior spin trapping agent for 1-hydroxyethyl radicals, and that DMPO was least efficient. Addition of deferoxamine completely prevented detection of 1-hydroxyethyl radicals with PBN or DMPO, but caused only 50% decrease in EPR signals when POBN was the spin trap. However, superoxide dismutase only decreased 1-hydroxyethyl radical formation when POBN was the spin trap. Other experiments demonstrated that POBN was the most effective of these nitrones for reduction of Fe(III) in aqueous solutions. Furthermore, 1-hydroxyethyl radical adducts were formed when POBN was added to mixtures of ethanol, phosphate buffer, POBN and FeCl3, but this effect did not occur with either PBN or DMPO. Thus, these data indicate that undesirable effects of POBN on iron chemistry may influence results of spin trapping experiments, and complicate interpretation of the resulting data.

Topics: Animals; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Ethanol; Free Radicals; Male; Microsomes, Liver; Nitrogen Oxides; Pyridines; Rats; Rats, Sprague-Dawley; Spin Labels; Superoxide Dismutase

Free radicals react with nitrones to form stable nitroxides which can be identified by ESR spectroscopy. Unfortunately, little is known regarding the pharmacological properties of these compounds. In this study, three commonly used nitrones, 5,5-dimethylpyrroline-N-oxide (DMPO), alpha-phenyl-tert-butylnitrone (PBN), and alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (POBN), were found to induce relaxation of preconstricted isolated rat pulmonary artery rings. Additional experiments with PBN indicated that vasorelaxation could not be attributed to production of endothelial derived factors, prostaglandins, or free radicals. Patch-clamp techniques revealed reversible calcium channel blockade with PBN at a concentration below that needed to detect free radicals. Calcium channel blockade probably accounts for the vasorelaxation observed in the isolated ring preparations described here, and should be considered when using nitrone spin-traps both in in vivo and clinical studies.

Topics: Animals; Calcium Channels; Catalase; Cells, Cultured; Cyclic N-Oxides; Dose-Response Relationship, Drug; Endothelium, Vascular; Free Radicals; In Vitro Techniques; Male; Meclofenamic Acid; Methylene Blue; Muscle Relaxation; Muscle, Smooth, Vascular; Nitrogen Oxides; Pulmonary Artery; Pyridines; Rats; Rats, Sprague-Dawley; Spin Labels; Superoxide Dismutase

Electron paramagnetic resonance (EPR) spin trapping was used to detect lipid-derived free radicals generated by iron-induced oxidative stress in intact cells. Using the spin trap alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (POBN), carbon-centered radical adducts were detected. These lipid-derived free radicals were formed during incubation of ferrous iron with U937 cells that were enriched with docosahexaenoic acid (22:6n-3). The EPR spectra exhibited apparent hyperfine splittings characteristic of a POBN/alkyl radical, aN = 15.63 +/- 0.06 G and aH = 2.66 +/- 0.03 G, generated as a result of beta-scission of alkoxyl radicals. Spin adduct formation depended on the FeSO4 content of the incubation medium and the number of 22:6-enriched cells present; when the cells were enriched with oleic acid (18:1n-9), spin adducts were not detected. This is the first direct demonstration, using EPR, of a lipid-derived radical formed in intact cells in response to oxidant stress.

Topics: Cell Line; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Fatty Acids, Unsaturated; Free Radicals; Humans; Leukemia, Myeloid; Nitrogen Oxides; Pyridines; Spin Labels

Extracellular free radicals were detected in rat striatal perfusate samples by intracerebral microdialysis coupled to the spin trapping technique. Five Sprague-Dawley rats were subjected to 30 min of global ischemia followed by reperfusion; throughout the experimental period the intrastriatal dialysing probe was perfused with Ringer's solution containing the spin trap agent pyridyl-N-oxide-t-butylnitrone (100 mM) together with the iron chelating agent diethylentriaminepentacetic acid (100 microM). A radical adduct occurred during ischemia and early reperfusion, but not in basal conditions; the spin adduct was characterized as a carbon centered radical, consistent with the presence of an oxidative attack on membrane lipids. The direct evidence of the formation of free radicals supports the hypothesis that free radicals play a role in the pathogenesis of the histological damage during brain ischemia.

Topics: Animals; Brain Ischemia; Cyclic N-Oxides; Dialysis; Free Radicals; Nitrogen Oxides; Pyridines; Rats; Rats, Inbred Strains; Reperfusion; Spin Labels; Thiobarbiturates

Adriamycin (ADR) is known to exert a severe negative inotropic effect on isolated myocardial preparations; a role for free radical generation has been hypothesized. Spin-trapping of free radicals has been extensively exploited in ESR studies, both in cell-free systems and in intact tissues. The interaction between spin-traps and free radicals should in principle stop the reaction cascade leading to cellular damage. Based on this hypothesis, the possible cardioprotective action of three spin-trapping agents, 5,5-dimethyl-l-pyrroline-N-oxide (DMPO), N-tert-butyl-alpha-phenylnitrone (PBN) and alpha-(4-pyridyl 1-oxide) N-tert-butylnitrone (POBN), was tested on isolated rat atria incubated in the presence of ADR; maximal non-cardiotoxic concentrations were used (50, 10 and 50 mM respectively) in order to achieve a maximal spin-trapping effect. A varying degree of protection was observed with the three compounds, directly correlated to their hydrophobicity, as assessed by chloroform/water partition coefficients. It is proposed that ADR-induced free radical generation is responsible for the acute cardiotoxic effects of the drug; this seems to be a site-specific mechanism restricted to one or more hydrophobic cellular compartment/s, since only lipophilic spin-trapping agents are able to prevent the development of the negative inotropic effect of ADR.

Topics: Animals; Cardiomyopathies; Cyclic N-Oxides; Depression, Chemical; Doxorubicin; Female; Free Radicals; Kinetics; Myocardial Contraction; Nitrogen Oxides; Pyridines; Rats; Rats, Inbred Strains; Spin Labels

Cr(III), which is thought to be relatively non-toxic, was reduced to Cr(II) ion by biological reductants such as L-cysteine and NADH and Cr(II) thus formed could easily react with hydrogen peroxide (H2O2) to yield very reactive active oxygen species, hydroxyl radical (.OH). The formation of hydroxyl radical was detected by water-soluble spin-traps, alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). This result indicates that non-toxic Cr(III) compounds have the possibility of causing dangerous effects to living organism in the presence of biological reductants.

Topics: Chromium; Cyclic N-Oxides; Cysteine; Cystine; Electron Spin Resonance Spectroscopy; Hydrogen Peroxide; Hydroxides; Hydroxyl Radical; NAD; Nitrogen Oxides; Oxidation-Reduction; Pyridines; Spin Labels

Electron spin resonance (ESR) measurements provide direct evidence for the involvement of Cr(V) in the reduction of Cr(VI) by NAD(P)H. Addition of hydrogen peroxide (H2O2) to NAD(P)H-Cr(VI) reaction mixtures suppresses the Cr(V) signal and generates hydroxyl (.OH) radicals (as detected via spin trapping), suggesting that Cr(V) reacts with H2O2 to generate the .OH radicals. Reaction between H2O2 and a Cr(V)-glutathione complex, and between H2O2 and several Cr(V)-carboxylato complexes also produces .OH radicals. These results suggest that Cr(V) complexes catalyze the generation of .OH radicals from H2O2, and that .OH radicals might play a significant role in the mechanism of Cr(VI) cytotoxicity.

Topics: Chromium; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Free Radicals; Hydrogen Peroxide; Hydroxides; Hydroxyl Radical; NADP; Nitrogen Oxides; Oxidation-Reduction; Pyridines; Spin Labels

The involvement of free radicals in endurance to muscle effort is suggested by experimental and clinical data. Therefore, experiments have been performed to observe the effect of trapping free radicals on endurance to swimming in mice. Animals were injected intraperitoneally with each of three spin-trappers [N-tert-Butyl-alpha-Phenyl-Nitrone (PBN),alpha-4-Pyridyil-1-Oxide-N-tert-Butyl-Nitrone (POBN) and 5,5-Dimethyl-1-Pirrolyn-N-Oxide (DMPO): 0.2 ml of 10(-1) molar solution]. Each mouse was submitted to a swimming test to control resistance to exhaustion a) without any treatment, b) after administration of each spin-trapper in a random order c) after saline. Control experiments were performed with saline and with vitamin E. Endurance to swimming was greatly prolonged by pretreatment with all the spin-trappers (DMPO less than 0.0001; POBN less than 0.0001; PBN less than 0.001) and with Vitamin E. Experiments state that compared to treatment with spin-trappers or Vitamin E, administration of saline alone did not enhance time to exhaustion so that the increase in time to exhaustion with the various free radical scavengers was not the effect of training. Therefore, free radicals could be considered as one of the factors terminating muscle effort in mice.

Topics: Animals; Cyclic N-Oxides; Fatigue; Free Radicals; Male; Mice; Nitrogen Oxides; Physical Endurance; Pyridines; Spin Labels; Swimming; Vitamin E

[17O]oxygen hyperfine coupling constants are reported for the superoxide and hydroxyl radical adducts with the spin traps 5,5-dimethyl-1-pyrroline N-oxide, N-t-butyl-alpha-phenylnitrone and alpha-(4-pyridyl 1-oxide)-N-t-butylnitrone. These couplings provide spectroscopic evidence that the spin adducts have been correctly identified.

Topics: Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Free Radicals; Hydroxides; Nitrogen Oxides; Oxygen; Pyridines; Spin Labels; Superoxides

When diaziquone was irradiated with 500 nm visible light, hydroxyl free radicals as well as the diaziquone semiquinone were produced. The diaziquone semiquinone is a stable free radical that exhibits a characteristic 5-line electron spin resonance (ESR) spectrum. Since hydroxyl free radicals are short lived, and not observable by conventional ESR, the nitrone spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) was used to convert hydroxyl radicals into longer lived ESR detectable spin adducts. The formation of hydroxyl radicals was further confirmed by investigating reactions in which hydroxyl radical scavangers, sodium formate and dimethylsulfoxide, compete with the spin traps DMPO or POBN (alpha-(4-Pyridyl-1-oxide)-N- tert-butylnitrone) for hydroxyl free radicals. The products of these scavenging reactions were also trapped with DMPO or POBN. If drug free radicals and hydroxyl free radicals are important in the activity of quinone-containing antitumor agents, AZQ may have a potential in photoirradiation therapy or photodynamic therapy.

Topics: Aziridines; Azirines; Benzoquinones; Cyclic N-Oxides; Dimethyl Sulfoxide; Electron Spin Resonance Spectroscopy; Hydroxides; Hydroxyl Radical; Light; Nitrogen Oxides; Phototherapy; Pyridines; Quinones

The efficiency of 5,5-dimethylpyrroline-1-N-oxide (DMPO) and alpha-(4-pyridyl-1-oxide)-N-tert.-butylnitrone (POBN) to spin trap hydroxyl radicals and hydrogen atoms, respectively, was studied in gamma-irradiated solutions where the radical yields are accurately known. The effects of dose, spin trap concentration, and pH and of the stability of the spin adducts on the spin-trapping efficiency were investigated. In degassed or N2-saturated solutions the spin-trapping efficiencies were 35% for DMPO and hydroxyl radicals and 14% for POBN and hydrogen atoms. The low spin-trapping efficiencies were shown not to be due to the instability of the DMPO-OH and POBN-H spin adducts or to the effects of H2O2 or O2. The low spin-trapping efficiency of DMPO may be explained by the reaction of hydroxyl radicals to abstract hydrogen from the DMPO molecule to produce carbon radicals as well as addition to the N = C double bond to form nitroxide radicals. For POBN the low spin-trapping efficiency for hydrogen atoms is explained in terms of addition reactions of hydrogen atoms to the aromatic ring and the pyridinium and nitrone oxygens.

Topics: Cobalt Radioisotopes; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Free Radicals; Gamma Rays; Hydrogen; Hydroxides; Hydroxyl Radical; Nitrogen Oxides; Pyridines; Solutions; Spin Labels; Water