Detection of lipid radicals by electron paramagnetic resonance spin trapping using intact cells enriched with polyunsaturated fatty acid.

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.     

Photodegradation of hyaluronic acid: EPR and size exclusion chromatography study.

Photochemically induced radical reactions involving the lateral sequences and the end macromolecular chain groups of hyaluronic acid in aqueous solutions at 293K were studied by EPR spin trapping technique with DMPO (5,5-dimethylpyrroline-1-oxide). In the first 1-10 minutes of irradiation EPR indicates spin adducts of two carbon centered radicals with the splitting constants of aN = 1.60 mT, aH = 2.51 mT and aN = 1.56 mT, aH = 2.28 mT. After longer irradiation time (over 10 minutes) dominate two further DMPO adducts of radicals centered on hetero-atoms with splitting constants of aN = 1.44 mT, aH = 1.60 mT and of aN = 1.49 mT, aH = 1.49 mT. Simultaneously, molecular weight followed by SEC decreases, suggesting that UV irradiation leads to the breaking of interglycosidic bonds of hyaluronic acid main macromolecular chain.     

The NoH value in EPR spin trapping: a new parameter for the identification of 5,5-dimethyl-1-pyrroline-N-oxide spin adducts.

The ratio of the nitrogen to hydrogen hyperfine splittings (aN/aH) of spin adducts derived from the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) has been found to be a useful parameter for adduct identification. For example, this parameter makes it possible to distinguish between the superoxide (aN/aH = 1.22-1.26) and peroxyl (aN/aH = 1.33-1.40) radical adducts of DMPO in aqueous solution. Since the aN to aH ratio corrects for minor differences in EPR spectrometer calibration, it is a more reproducible parameter than the aN and aH values themselves.     

Alkyl free radicals from the beta-scission of fatty acid alkoxyl radicals as detected by spin trapping in a lipoxygenase system

2-Methyl-2-nitrosopropane (tNB)-radical adducts from incubation mixtures of fatty acids and soybean lipoxygenase in borate buffer (pH 9.0) were measured by electron paramagnetic resonance (EPR). In addition to the previously reported six-line signal of secondary carbon-centered radicals (RCHR'), a weak signal submerged in the baseline was detected after the peroxidation phase was finished. We propose that this radical is a decomposition product formed via beta-scission of fatty acid alkoxyl radicals. EPR spectra of tNB-radical adducts formed in mixtures of either linoleic acid, arachidonic acid, or 15-hydroperoxyeicosatetraenoic acid with lipoxygenase exhibited hyperfine structure characteristic of tNB/.CH2CH2-R with hyperfine coupling constants: aN = 17.1 G; aH beta = 11.2 G (2H); and aH gamma = 0.6 G (2H). In the case of linolenic acid, this radical tNB/.CH=CH-R' with hyperfine coupling constants: aN = 17.1 G; aH beta = 10.9 G (2H); aH gamma = 1.1 G; and aH delta = 0.5 G. In accord with the decomposition scheme of hydroperoxides derived from unsaturated fatty acids, the radical adducts tNB/.CH2CH2-R and tNB/.CH2-CH=CH-R' were assigned as the pentyl and 2-pentenyl radicals, respectively.     

Electron spin resonance and pulse radiolysis studies on the spin trapping of sulphur-centered radicals

Thiyl radicals are shown to be readily trapped with the spin traps 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (TMPO) giving characteristic spin adducts with hyperfine coupling constants aN 1.52-1.58, aH 1.52-1.80 mT, and g values in the range 2.0065-2.0067 for the DMPO adducts and aN 1.50-1.56, aH 1.70-1.92 mT, g 20049-2.0051 for the TMPO adducts. Kinetic data obtained from pulse radiolysis studies show that, in general, thiyl radicals react rapidly with these spin traps with rate constants of the order of 10(7)-10(8) dm3 mol-1 s-1. The tetramethylated spin trap TMPO though giving slightly less intense electron spin resonance (ESR) spectra, produces longer lived adducts, and is suggested to be of greater utility due to the more characteristic nature of the coupling constants of the observed adducts; reaction of certain thiyl radicals with DMPO produces adducts which are superficially similar to the hydroxyl radical adduct to the same trap.     

Detection of peroxyl and alkoxyl radicals produced by reaction of hydroperoxides with heme-proteins by electron spin resonance spectroscopy

ESR spin trapping using the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) has been used to directly detect alkoxyl radicals (with hyperfine coupling constants aN 1.488, aH 1.600 mT and aN 1.488, aH 1.504 mT for the tBuO. and PhC(CH3)2O. adducts, respectively) and peroxyl radicals (aN 1.448, aH 1.088, aH 0.130 mT and aN 1.456, aH 1.064, aH 0.128 mT for the tBuOO. and PhC(CH3)2OO. adducts, respectively) produced from t-butyl or cumene hydroperoxides by a variety of heme-containing substances (purified cytochrome P-450, metmyoglobin, oxyhemoglobin, methemoglobin, cytochrome c, catalase, horseradish peroxidase) and the model compound hematin. The observed species exhibit a complicated dependence on reagent concentrations and time, with maximum concentrations of the peroxyl radical adducts being observed immediately after mixing of the hydroperoxide with low concentrations of the heme-compound. Experiments with inhibitors (CN-, N3-, CO, metyrapone and imidazole) suggest that the major mechanism of peroxyl radical production involves high-valence-state iron complexes in a reaction analogous to the classical peroxidase pathway. The production of alkoxyl radicals is shown to arise mainly from the breakdown of peroxyl radical spin adducts, with direct production from the hydroperoxide being a relatively minor process.     

Trapping of free radicals with direct in vivo EPR detection: a comparison of 5,5-dimethyl-1-pyrroline-N-oxide and 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide as spin traps for HO* and SO4*-.

To spin trap hydroxyl radical (HO*) with in vivo detection of the resultant radical adducts, the use of two spin traps, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) (10 mmol/kg) has been compared. In mice treatment with 5-aminolevulinic acid and Fe3+ resulted in detection of adducts of hydroxyl radicals (HO*), but only with use of DEPMPO. Similarly, 'HO* adducts' generated via nucleophilic substitution of SO4*- adducts formed in vivo could be observed only when using DEPMPO as the spin trap. The reasons for the differences observed between DEPMPO and DMPO are likely due to different in vivo lifetimes of their hydroxyl radical adducts. These results seem to be the first direct in vivo EPR detection of hydroxyl radical adducts.     

Measurement of superoxide-derived free radicals in the reperfused heart. Evidence for a free radical mechanism of reperfusion injury

There has been considerable controversy regarding the role of oxygen free radicals as important mediators of cell damage in reperfused myocardium. This controversy regards whether superoxide and hydroxyl free radicals are generated on reperfusion and if these radicals actually cause impaired contractile function. In this study, EPR studies using the spin trap 5,5-dimethyl-1-pyroline-n-oxide (DMPO) demonstrate the formation of .OH and R. free radicals in the reperfused heart. EPR signals of DMPO-OH, aN = aH = 14.9 G, and DMPO-R aN = 15.8 G aH = 22.8 G are observed, with peak concentrations during the first minute of reperfusion. It is demonstrated that these radicals are derived from .O2- since reperfusion in the presence of enzymatically active recombinant human superoxide dismutase markedly reduced the formation of these signals while inactive recombinant human superoxide dismutase had no effect. On reperfusion with perfusate pretreated to remove adventitial iron, the concentration of the DMPO-OH signal was increased 2-fold and a 4-fold decrease in the DMPO-R signal was observed demonstrating that iron-mediated Fenton chemistry occurs. Hearts reperfused with recombinant human superoxide dismutase exhibited improved contractile function in parallel with the marked reduction in measured free radicals. In order to determine if the reperfusion free radical burst results in impaired contractile function, simultaneous measurements of free radical generation and contractile function were performed. A direct relationship between free radical generation and subsequent impaired contractile function was observed. These studies suggest that superoxide derived .OH and R. free radicals are generated in the reperfused heart via Fenton chemistry. These radicals appear to be key mediators of myocardial reperfusion injury.     

Spin adducts of superoxide,alkoxyl, and lipid-derived radicals with EMPO and its derivatives

The compound 5-(ethoxycarbonyl)-5-methyl-1-pyrroline N-oxide (EMPO) is a hydrophilic cyclic nitrone spin trap, which, in contrast to DMPO, forms a relatively stable superoxide adduct (t(1/2)=8.6 min) with an EPR spectrum similar to the respective DMPO adduct. In order to find the optimal degree of lipophilicity of this novel type of spin trap with respect to the detection of radicals formed during lipid peroxidation, the ethoxy group of EMPO was replaced by alkoxy substituents of increasing chain length, leading to the methoxy- (MeMPO), 1-propoxy- (PrMPO), 1-butoxy- (BuMPO), and 1-octyloxy- (OcMPO) derivatives of EMPO. The stability of their superoxide adducts was found to be strongly dependent on the size of the alkoxycarbonyl group. Increasing chain length of the alkoxyl substituent decreased the stability of alkoxyl radical adducts of MeMPO, EMPO, and PrMPO, but increased the stability of OcMPO adducts. The stability of alkoxyl radical adducts of BuMPO, on the other hand, were practically independent of the size of the alkoxyl group. Detection of lipid alkoxyl radicals formed by peroxidizing linoleic acid in a stationary system was therefore only possible with the most lipophilic spin trap, OcMPO. However, with the more hydrophilic spin traps MeMPO, EMPO, PrMPO, and BuMPO optimal EPR signal intensity could be obtained when a slow-flow system was used. Thus, within this series EMPO is the best spin trap for the detection of superoxide; OcMPO, on the other hand, is most suitable for the detection of lipid alkoxyl radicals.     

Iron and free radical oxidations in cell membranes.

Brain tissue being rich in polyunsaturated fatty acids, is very susceptible to lipid peroxidation. Iron is well known to be an important initiator of free radical oxidations. We propose that the principal route to iron-mediated lipid peroxidations is via iron-oxygen complexes rather than the reaction of iron with hydrogen peroxide, the Fenton reaction. To test this hypothesis, we enriched leukemia cells (K-562 and L1210 cells) with docosahexaenoic acid (DHA) as a model for brain tissue, increasing the amount of DHA from approximately 3 mole % to 32 mole %. These cells were then subjected to ferrous iron and dioxygen to initiate lipid peroxidation in the presence or absence of hydrogen peroxide. Lipid-derived radicals were detected using EPR spin trapping with alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (POBN). As expected, lipid-derived radical formation increases with increasing cellular lipid unsaturation. Experiments with desferal demonstrate that iron is required for the formation of lipid radicals from these cells. Addition of iron to DHA-enriched L1210 cells resulted in significant amounts of radical formation; radical formation increased with increasing amount of iron. However, the exposure of cells to hydrogen peroxide before the addition of ferrous iron did not increase cellular radical formation, but actually decreased spin adduct formation. These data suggest that iron-oxygen complexes are the primary route to the initiation of biological free radical oxidations. This model proposes a mechanism to explain how catalytic iron in brain tissue can be so destructive.     

Spin trapping of lipid radicals with DEPMPO-derived spin traps: detection of superoxide, alkyl and alkoxyl radicals in aqueous and lipid phase

The spin trap 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO) forms a superoxide adduct with a half-life of almost 15 min. DEPMPO is very hydrophilic and its use for the detection of radicals in the lipid phase (lipid-derived radicals and superoxide generated in the lipid phase) is therefore limited due to its very low concentration in the lipid phase. For the detection of lipid-derived radicals, three derivatives of DEPMPO with increasing degree of lipid solubility have been investigated: 5-(di-n-propoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DPPMPO), 5-(di-n-butoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DBPMPO), and 5-(bis-(2-ethylhexyloxy)phosphoryl)-5-methyl-1-pyrroline N-oxide (DEHPMPO). As compared with the spin trap DMPO, the half-lives of the respective superoxide adducts were clearly higher in aqueous solutions of the spin traps, which facilitates qualitative ESR measurements. The stability of the superoxide spin adducts formed with the various lipophilic spin traps in aqueous buffer were similar to those observed with DEPMPO (half-life: 7-11 min.). In model experiments using Fe(3+)-catalyzed nucleophilic addition of methanol or tert-butanol to the respective spin trap the respective alkoxyl radical adducts were formed in aqueous solution as transient species in the presence of high concentrations of the alcohol. Upon dilution with water the alkoxyl group was substituted by water, giving the respective hydroxyl adduct of the spin trap. Care must therefore be taken when Fenton-type reactions are used for the generation of radicals such as the use of Fe(2+) complexes with phosphate or DTPA or inactivation of iron by addition of "Desferal" (Novarti's Pharma GmbH, Vienna, Austria) after a short incubation time. Addition of Fe(2+) under anaerobic conditions to an aqueous suspension of linoleic acid hydroperoxide and the spin trap resulted in the detection of three different species: a carbon-centered radical adduct, an acyl radical adduct, and the hydroxyl adduct. In the presence of oxygen a different species was observed with DEPMPO, DPPMPO, and DBPMPO, which was only slightly suppressed upon the addition of SOD, possibly the respective spin adduct of either the alkylperoxyl radical or, in analogy to DMPO, a secondary alkoxyl radical.     

Lipid radicals: properties and detection by spin trapping

Unsaturated lipids are rapidly oxidized to toxic products such as lipid hydroperoxides, especially when transition metals such as iron or copper are present. In a Fenton-type reaction Fe2+ converts lipid hydroperoxides to the very short-lived lipid alkoxyl radicals. The reaction was started upon the addition of Fe2+ to an aqueous linoleic acid hydroperoxide (LOOH) emulsion and the spin trap in the absence of oxygen. Even when high concentrations of spin traps were added to the incubation mixture, only secondary radical adducts were detected, probably due to the rapid re-arrangement of the primary alkoxyl radicals. With the commercially available nitroso spin trap MNP we observed a slightly immobilized ESR spectrum with only one hydrogen splitting, indicating the trapping of a methinyl fragment of a lipid radical. With DMPO or 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO) adducts were detected with carbon-centered lipid radical, with acyl radical, and with the hydroxyl radical. We also synthesized lipophilic derivatives of the spin trap DEPMPO in order to detect lipid radical species generated in the lipid phase. With all spin traps studied a lipid-derived carbon-centered radical was obtained in the anaerobic incubation system Fe2+/LOOH indicating the trapping of a lipid radical, possibly generated as a secondary reaction product of the primary lipid alkoxyl radical formed. Under aerobic conditions an SOD-insensitive oxygen-centered radical adduct was formed with DEPMPO and its lipophilic derivatives. The observed ESR parameters were similar to those of alkoxyl radical adducts, which were independently synthesized in model experiments using Fe3+-catalyzed nucleophilic addition of methanol or t-butanol to the respective spin trap.     

Formation of acyl radical in lipid peroxidation of linoleic acid by manganese-dependent peroxidase from Ceriporiopsis subvermispora and Bjerkandera adusta.

Lipid peroxidation by managanese peroxidase (MnP) is reported to decompose recalcitrant polycyclic aromatic hydrocabon (PAH) and nonphenolic lignin models. To elucidate the oxidative process, linoleic acid and 13(S)-hydroperoxy-9Z,11E-octadecadienoic acid [13(S)-HPODE] were reacted with MnPs from Ceriporiopsis subvermispora and Bjerkandera adusta and the free radicals produced were analyzed by ESR. When the MnPs were reacted with 13(S)-HPODE in the presence of Mn(II), H2O2 and tert-nitrosobutane (t-NB), the ESR spectrum contained a sharp triplet of acyl radical (aN = 0.81 mT). Formation of acyl radical was also observed in the reactions of Mn(III)-tartrate with 13(S)-HPODE and with linoleic acid, but the latter reaction occurred explosively after an induction period of around 30 min. Reactions of MnP with linoleic acid in the presence of Mn(II), H2O2 and t-NB gave no spin adducts while addition of t-NB after preincubation of linoleic acid with MnP/Mn(II)/H2O2 for 2 h gave spin adducts of carbon-centered (aN = 1.53 mT, aH = 0.21 mT) and acyl (aN = 0.81 mT) radicals. In contrast to linoleic acid, methyl linoleate and oleic acid were not peroxidized by MnP and chelated Mn(III) within a few hours, indicating that structures containing both the 1,4-pentadienyl moiety and a free carboxyl group are necessary for inducing the peroxidation in a short reaction time. These results indicate that MnP-dependent lipid peroxidation is not initiated by direct abstraction of hydrogen from the bis-allylic position during turnover but proceeds by a Mn(III)-dependent hydrogen abstraction from enols and subsequent propagation reactions involving the formation of acyl radical from lipid hydroperoxide. This finding expands the role of chelated Mn(III) from a phenol oxidant to a strong generator of free radicals from lipids and lipid hydroperoxides in lignin biodegradation.     

Electron Paramagnetic Resonance and Spin Trapping Study of Radicals Formed During Reaction of Aromatic Amines with isoAmyl Nitrite Under Aprotic Conditions

Diazotization of primary aromatic amines with isoamyl nitrite in benzene at room temperature was studied employing EPR and spin trapping techniques. Nitrosodurene (ND). 2-methyl-2-nitrosopropane (MNP). and 5,5-dimethyl-pyrroline N-oxide (DMPO) were used as spin trapping agents. Aryl radicals were detected employing ND and MNP. Using DMPO as a spin trap most of the amines produced EPR spectra ascribed to adducts with aniline-type radicals (N-centred radicals). The assignments were verified using ¹⁵JN-labeled anilines. Similar spectra of DMPO adducts were recorded from amines treated with benzoyl peroxide or benzophenone plus UV. Possible mechanisms of formation of these adducts (radical trapping versus nucleophilic addition to DMPO followed by oxidation) during treatment of the amines with isoamyl nitrite are discussed.     

Electron Paramagnetic Resonance and Spin Trapping Study of Radicals Formed During Reaction of Aromatic Amines with isoAmyl Nitrite Under Aprotic Conditions

Diazotization of primary aromatic amines with isoamyl nitrite in benzene at room temperature was studied employing EPR and spin trapping techniques. Nitrosodurene (ND). 2-methyl-2-nitrosopropane (MNP). and 5,5-dimethyl-pyrroline N-oxide (DMPO) were used as spin trapping agents. Aryl radicals were detected employing ND and MNP. Using DMPO as a spin trap most of the amines produced EPR spectra ascribed to adducts with aniline-type radicals (N-centred radicals). The assignments were verified using ¹⁵JN-labeled anilines. Similar spectra of DMPO adducts were recorded from amines treated with benzoyl peroxide or benzophenone plus UV. Possible mechanisms of formation of these adducts (radical trapping versus nucleophilic addition to DMPO followed by oxidation) during treatment of the amines with isoamyl nitrite are discussed.     

Spin trapping of polyunsaturated fatty acid-derived peroxyl radicals: reassignment to alkoxyl radical adducts

Polyunsaturated fatty acid (PUFA) peroxyl radicals play a crucial role in lipid oxidation. ESR spectroscopy with the spin-trapping technique is one of the most direct methods for radical detection. There are many reports of the detection of PUFA peroxyl radical adducts; however, it has recently been reported that attempted spin trapping of organic peroxyl radicals at room temperature formed only alkoxyl radical adducts in detectable amounts. Therefore, we have reinvestigated spin trapping of the linoleic, arachidonic, and linolenic acid-derived PUFA peroxyl radicals. The slow-flow technique allowed us to obtain well-resolved ESR spectra of PUFA-derived radical adducts in a mixture of soybean lipoxygenase, PUFA, and the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, interpretation of the ESR spectra was complicated by the overlapping of the PUFA-derived alkoxyl radical adduct spectra. In order to understand these spectra, PUFA-derived alkoxyl radical adducts were modeled by various alkoxyl radical adducts. For the first time, we synthesized a wide range of DMPO adducts with primary and secondary alkoxyl radicals. It was found that many ESR spectra previously assigned as DMPO/peroxyl radical adducts based on their close similarity to the ESR spectrum of the DMPO/superoxide radical adduct, in conjunction with their insensitivity to superoxide dismutase, are indeed alkoxyl radical adducts. We have reassigned the PUFA alkylperoxyl radical adducts to their corresponding alkoxyl radical adducts. Using hyperfine coupling constants of model DMPO/alkoxyl radical adducts, the computer simulation of DMPO/PUFA alkoxyl radical adducts was performed. It was found that the trapped, oxygen-centered PUFA-derived radical is a secondary, chiral alkoxyl radical. The presence of a chiral carbon atom leads to the formation of two diastereomers of the DMPO/PUFA alkoxyl radical adduct. Therefore, attempted spin trapping of the PUFA peroxyl radical by DMPO at room temperature leads to the formation of the PUFA alkoxyl radical adduct.     

Identification of spin trapped carbon-centered radicals in soybean lipoxygenase-dependent peroxidations of omega-3 polyunsaturated fatty acids by LC/ESR,LC/MS,and tandem MS

With the combined techniques of on-line liquid chromatography/electron spin resonance (LC/ESR) and on-line liquid chromatography/mass spectrometry (LC/MS), we have previously characterized all classes of lipid-derived carbon-centered radicals (*Ld) formed from omega-6 polyunsaturated fatty acids (PUFAs: linoleic acid and arachidonic acid). In the present study, the carbon-centered radicals formed from two omega-3 PUFAs (linolenic acid and docosahexaenoic acid) resulting from their reactions with soybean lipoxygenase in the presence of alpha-[4-pyridyl 1-oxide]-N-tert-butylnitrone (POBN) were investigated using the combination of LC/ESR and LC/MS techniques. A total of 16 POBN trapped carbon-centered radicals formed from the peroxidation of linolenic acid and 11 formed from the peroxidation of docosahexaenoic acid were detected by LC/ESR, identified by LC/MS, and structurally confirmed by tandem mass analysis (MS/MS). The on-line ESR chromatograms and MS chromatograms obtained from two omega-3 PUFAs closely resembled each other not only because the four major beta-scission products, including an ethyl radical and three isomeric pentenyl radicals, were formed from each PUFA, but also because isomeric POBN adducts of lipid dihydroxyallylic radicals from both PUFAs had almost identical chromatographic retention times.     

Real-time continuous-flow spin trapping of hydroxyl free radical in the ischemic and post-ischemic myocardium

Real-time monitoring of spin-trapped oxygen-derived free radicals released by the isolated ischemic and reperfused rat heart has been achieved by ESR analysis of the coronary effluents using continuous flow detection and high-speed acquisition techniques. Two nitrone spin traps 5,5-dimethyl pyrroline 1-oxide (Me2PnO) and 3,3,5,5-tetramethyl pyrroline 1-oxide (MePnO) have been separately perfused at a concentration of 40 mM during a sequence of 50 min of low-flow ischemia (1 ml/min) followed by 30 min of global ischemia and subsequent reperfusion at the control flow rate (14 ml/min). ESR spectra were sequentially obtained in 5-min or 30-s blocks during low-flow ischemia and reperfusion, respectively. 1. The results show the formation of OH. free radicals in the ischemic and reperfused heart, as demonstrated by the observation of Me2PnO-OH (aN = aH = 14.9 G; g = 2.0053) and Me4PnO-OH (aN = 15.2 G, aH = 16.8 G; g = 2.0055) spin adducts. There is no evidence of significant biological carbon-centered or peroxyl free radicals spin-adduct formation in the coronary effluents or in lipid extracts analyzed after reflow. 2. The OH. generation began 15-20 min after the onset of ischemia and was moderate, peaking at 30-40 min. During reperfusion, an intense formation of OH. spin adducts was observed, with a maximum at 30-60 s and a further gradual decrease over the following 2 min. 3. Cumulative integrated values of the amount of spin adducts released during the ischemic period show a Me2PnO-OH level fourfold greater than that of Me4PnO-OH. It was 2.5 times greater during reflow, reflecting slower kinetics with the more stable Me4PnO. 4. The original ESR detection technique developed in this study allows accurate real-time quantitative monitoring of the oxygen-derived free radicals generated during myocardial injury. It might provide a quick and reliable new means for assessing the efficacy of free-radical inhibitors.     

Lymphocytes can produce respiratory burst and oxygen radicals as polymorphonuclear leukocytes.

The respiratory burst and production of oxygen radicals by lymphocytes stimulated with phorbol myristate acetate (PMA) was studied and compared with that of polymorphonuclear leukocytes (PMN) by electron paramagnetic resonance (EPR) and spin trapping technique. Superoxide anion and hydroxyl radicals spin adducts of DMPO were detected in the stimulated PMN system, but only hydroxyl radical spin adducts of DMPO were detected in the stimulated lymphocyte system. It was proved by superoxide dismutase (SOD) and catalase that the hydroxyl radicals produced in the stimulated lymphocyte system came from superoxide anions, just like the hydroxyl radicals produced in the stimulated PMN.     

Lymphocytes can produce respiratory burst and oxygen radicals as polymorphonuclear leukocytes

The respiratory burst and production of oxygen radicals by lymphocytes stimulated with phorbol myristate acetate (PMA) was studied and compared with that of polymorphonuclear leukocytes (PMN) by electron paramagnetic resonance (EPR) and spin trapping technique. Superoxide anion and hydroxyl radicals spin adducts of DMPO were detected in the stimulated PMN system, but only hydroxyl radical spin adducts of DMPO were detected in the stimulated lymphocyte system. It was proved by Superoxide dismutase (SOD) and catalase that the hydroxyl radicals produced in the stimulated lymphocyte system came from Superoxide anions, just like the hydroxyl radicals produced in the stimulated PMN.