Isolation and identification of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone radical adducts formed by the decomposition of the hydroperoxides of linoleic acid, linolenic acid, and arachidonic acid by soybean lipoxygenase

Radical formation in individual aqueous solutions of some unsaturated fatty acids and in their mixtures

This study examines oxidizability in individual aqueous solutions of oleic acid, linoleic acid, α-linolenic acid, γ-linolenic acid and arachidonic acid, and in their mixtures. We used electron spin resonance (ESR), high performance liquid chromatography-electron spin resonance (HPLC-ESR) and high performance liquid chromatography-electron spin resonance-mass spectrometries (HPLC-ESR-MS). We detected 4-carboxybutyl radical derived from γ-linolenic acid, ethyl and 7-carboxyheptyl radicals derived from α-linolenic acid, and pentyl and 7-carboxyheptyl radicals derived from linoleic acid. HPLC-ESR analyses for the individual aqueous solutions of linoleic acid, α-linolenic acid, γ-linolenic acid and arachidonic acid showed less radical form for polyunsaturated fatty acids with more double bonds. On the other hand, HPLC-ESR peak height of 4-carboxybutyl radical, which form through hydrogen atom abstraction at the carbon close to the carboxy end, increased for linoleic acid/γ-linolenic acid, α-linolenic acid/γ-linolenic acid, and γ-linolenic acid/oleic acid mixtures compared to before mixing. Conversely, HPLC-ESR peak heights of ethyl, 7-carboxyheptyl and pentyl radicals, which form through hydrogen atom abstraction at the carbons close to the methyl end, decreased for linoleic acid/α-linolenic acid, linoleic acid/γ-linolenic acid, linoleic acid/oleic acid, linoleic acid/arachidonic acid, α-linolenic acid/γ-linolenic acid, and α-linolenic acid/oleic acid mixtures compared to before mixing.

A comparative study of the inhibitory effects by caffeic acid, catechins and their related compounds on the generation of radicals in the reaction mixture of linoleic acid with iron ions

Caffeic acid and (+)-catechin, which are abundantly contained in coffee and tea, are typical polyphenols. In order to know the relative magnitudes of antioxidant activity, effects by caffeic acid, (+)-catechin and their derivatives on the formation of 4-POBN/carbon-centered linoleic acid-derived radical adducts were examined in the control reaction mixture of linoleic acid with FeCl₃ at 30°C for 168 h. In the presence of 1.0 mM of the polyphenols, peak to peak heights of the third ESR signal resulted in 7.7 ± 2.4% (n = 3) (caffeic acid), 145 ± 13% (n = 3) (quinic acid), 4.4 ± 0.0% (n = 3) (chlorogenic acid), 104 ± 4.4% (n = 3) (ferulic acid), 4.3 ± 0.0% (n = 3) (noradrenaline), 12.5 ± 10.9% (n = 3) (gallic acid), 38.1 ± 7.1% (n = 3) [(+)-catechin], 47.9 ± 11.7% (n = 3) [(–)-epicatechin], 56.5 ± 1.6% (n = 3) (epigallocatechin), 13.5 ± 1.7% (n = 3) (catechol) and 83.7 ± 7.8% (n = 3) (resorcinol) of the control reaction mixture. All the compounds with catechol moiety exerted potent inhibitory effects on the radical formation except for (+)-catechin, (–)-epicatechin and epigallocatechin. (+)-Catechin, (–)-epicatechin and epigallocatechin may not exert the inhibitory effect as much possibly because they are less stable compared with caffeic acid. The resorcinol moiety in these molecules may also weaken their antioxidant activity.

Electron spin resonance. Part one: a diagnostic method in the biomedical sciences

A review is presented of some of the ways in which electron spin resonance (ESR) spectroscopy may be useful to investigate systems of relevance to the biomedical sciences. Specifically considered are: spin-trapping in biological media; the determination of antioxidant efficiencies; lipid-peroxidation; the use of nitroxides as probes of metabolic activity in cells and as structumral probes of cell-membranes; ESR coupled with materials for radiation-dosimetry; food- and drug-irradiation; studies of enzyme systems and ofcyclodextrins; diagnosis of cancer and rheumatoid arthritis; measurement of oxidative stress in synovial tissue in preparation for joint replacement; determination of oxidative species during kidney dialysis; measurement of biological oxygen concentrations (oximetry); trapping in living cells of the endothelium-derived relaxing factor nitric oxide (NO); measurement of hydrogen peroxide; determination of drugs of abuse (opiates); ESR measurements of whole blood and as a means to determine the age of bloodstains for forensic analysis are surveyed, and also a determination of the aqueous volume of human sperm cells is described, among other topics.

Identification of a radical formed in the reaction mixtures of ram seminal vesicle microsomes with arachidonic Acid using high performance liquid chromatography-electron spin resonance spectrometry and high performance liquid chromatography-electron spin resonance-mass spectrometry

The reaction of ram seminal vesicle (RSV) microsomes with arachidonic acid (AA) was examined using electron spin resonance (ESR), high performance liquid chromatography-electron spin resonance spectrometry (HPLC-ESR), and high performance liquid chromatography-electron spin resonance-mass spectrometry (HPLC-ESR-MS) combined use of spin trapping technique. A prominent ESR spectrum (alpha(N) = 1.58 mT and alpha(H)beta = 0.26 mT) was observed in the complete reaction mixture of ram seminal vesicle microsomes with arachidonic acid containing 2.0 mg protein/ml ram seminal vesicle (RSV) microsomal suspension, 0.8 mM arachidonic acid, 0.1 M 4-POBN, and 24 mM tris/HCl buffer (pH 7.4). The ESR spectrum was hardly observed for the complete reaction mixture without the RSV microsomes. The formation of the radical appears to be catalyzed by the microsomal components. In the absence of AA, the intensity of the ESR signal decreased to 16 +/- 15% of the complete reaction mixture, suggesting that the radical is derived from AA. For the complete reaction mixture with boiled microsomes, the intensity of the ESR signal decreased to 49 +/- 4% of the complete reaction mixture. The intensity of the ESR signal of the complete reaction mixture with indomethacin decreased to 74 +/- 20% of the complete reaction mixture, suggesting that cyclooxygenese partly participates in the reaction. A peak was detected on the elution profile of HPLC-ESR analysis of the complete reaction mixture. To determine the structure of the peak, an HPLC-ESR-MS analysis was performed. The HPLC-ESR-MS analysis of the peak showed two prominent ions, m/z 266 and m/z 179, suggesting that the peak is a 4-POBN/pentyl radical adduct. An HPLC-ESR analysis of the authentic 4-POBN/pentyl radical adduct comfirmed the identification.

Identification of the Several New Radicals Formed in the Reaction Mixture of Oxidized Linoleic Acid with Ferrous Ions using HPLC-ESR and HPLC-ESR-MS

ESR, HPLC-ESR and HPLC-ESR-MS analyses were performed for the reaction mixtures of oxidized linoleic acid with ferrous ions combined use of spin trapping technique. More than 14 peaks were detected on the HPLC-ESR elution profile. In addition to 7-carboxyheptyl and pentyl radicals, several new radicals such as 7-carboxyldihydroxyheptyl, 1,5-dihydroxypentyl, 8-carboxy-1-hydroxyoctyl, 7-carboxy-1-hydroxyheptyl, 1-hydroxypentyl and 1-hydroxyhexyl were identified using HPLC-ESR and HPLC-ESR-MS.

Identification of radicals formed in the reaction mixture of bovine kidney microsomes with NADPH

In order to explore the mechanism of myoglobinuric renal toxicity, detection and identification of free radicals was performed for the reaction mixtures of bovine kidney microsomes. EPR measurements showed prominent signals for the control reaction mixture containing 2.0 mg protein/ml bovine kidney microsomes, 5 mM NADPH, 0.1 M 4-POBN and 29 mM phosphate buffer (pH 7.4). Addition of myoglobin (Mb) to the control reaction mixture resulted in increase of EPR peak height. The result indicates that Mb enhances the radical formation. An HPLC-EPR measurement showed three peaks with retention times of 29.4 min (P(1)), 32.4 min (P(2)) and 46.6 min (P(3)). HPLC-EPR-MS analyses of P(1) and P(2) gave ions at m/z 282. The results show that 4-POBN/hydroxypentyl radical adducts form in the reaction mixture. An HPLC-EPR-MS analysis of P(3) gave ions at m/z 266, indicating that 4-POBN/pentyl radical adduct forms in the reaction mixture.

Heme-mediated production of free radicals via preformed lipid hydroperoxide fragmentation

Electron spin resonance (ESR) spectroscopy and the spin-trapping technique were used to investigate the capacity of several hemoglobin (Hb) forms of rainbow trout (oxyHb and metHb), free hemin (oxidized form of heme group), and hemin complexed with bovine serum albumin (BSA) to promote formation of free radicals via fragmentation of preformed lipid hydroperoxides. Cumene hydroperoxide (CumOOH) was used as a model for lipid hydroperoxide, and free radicals were monitored by stabilizing with the spin traps alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Two different types of free radicals, hydroxyl and carbon-centered radicals, were identified as a result of the interaction of the heme-containing systems and CumOOH. Carbon-centered radicals were found to be mainly heme-mediated because the addition of the iron-chelating agent EDTA did not affect the formation of POBN/carbon-centered adducts. Hemin alone was the best promoter for the production of POBN/carbon-centered radicals in the presence of low hydroperoxide concentrations (below equimolar condition over heme group), whereas hemin/BSA and oxyHb were more active in generating radicals at high hydroperoxide concentrations or after successive interactions with hydroperoxides. This finding can be explained by the coexistence of two different facts: (i) the interaction between hemin and lipid hydroperoxides seems to be more efficient in the case of free hemin compared to heme-protein complexes and (ii) a faster degradation of hemin is produced without the presence of a protein fraction, globin or albumin. The comparison of oxyHb and metHb also suggested that both Hb redox states have similar capacities to generate oxidative stress via cleavage of preformed lipid hydroperoxides.

Enhancement by cigarette smoke extract of the radical formation in a reaction mixture of 13-hydroperoxide octadecadienoic acid and ferric ions

The effects of cigarette smoke extract on radical formation were examined in reaction mixtures containing 13-hydroperoxide octadecadienoic acid (13-HPODE), FeCl3, cigarette smoke extract, ethylenediaminetetraacetic acid (EDTA), alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN), and phosphate buffer (pH 7.4). Cigarette smoke extract enhanced the formation of both 7-carboxyheptyl and pentyl radicals in the reaction. Ferric ions were reduced in the reaction mixture, suggesting that cigarette smoke extract enhances the formation of 7-carboxyheptyl and pentyl radicals by reducing ferric irons. Although there is a large body of evidence supporting the involvement of radicals such as the semiquinone radical, hydroxyl radical, superoxide radical, nitric oxide radicals in smoking-related diseases, the enhancement by cigarette smoke of lipid-derived radical formation, which we first report here, may be one of the other causes of smoking-related diseases.

Interception of the radicals produced in electrophilic fluorination with radical traps (Tempo, Dmpo) studied by electrospray ionization mass spectrometry

The interaction of the nitroxide radical traps (Tempo and Dmpo) and radicals produced in the electrophilic fluorination of olefins (styrene and alpha-methylstyrene) and Selectfluor (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octanebis(tetrafluoroborate) (F-TEDA-BF(4)) (1)) was investigated by electrospray ionization mass spectrometry (ESI-MS). Tempo succeeded in intercepting the radical cationic intermediates and the radical adduct ions were detected at m/z 260 (for styrene) and m/z 274 (for alpha-methylstyrene). Dmpo could also intercept the fluorine radical and radical adduct ions were detected at m/z 131, 132 and 152. The interception of the radical cationic intermediates and fluorine radical is good evidence for the presence of a single-electron transfer mechanism in the electrophilic fluorination.

Quantification of lipid alkyl radicals trapped with nitroxyl radical via HPLC with postcolumn thermal decomposition

Lipid alkyl radicals generated from polyunsaturated fatty acids via chemical or enzymatic H-abstraction have been a pathologically important target to quantify. In the present study, we established a novel method for the quantification of lipid alkyl radicals via nitroxyl radical spin-trapping. These labile lipid alkyl radicals were converted into nitroxyl radical-lipid alkyl radical adducts using 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-N-oxyl (CmdeltaP) (a partition coefficient between octanol and water is approximately 3) as a spin-trapping agent. The resulting CmdeltaP-lipid alkyl radical adducts were determined by HPLC with postcolumn online thermal decomposition, in which the adducts were degraded into nitroxyl radicals by heating at 100 degrees C for 2 min. The resulting nitroxyl radicals were selectively and sensitively detected by electrochemical detection. With the present method, we, for the first time, determined the lipid alkyl radicals generated from linoleic acid, linolenic acid, and arachidonic acid via soybean lipoxygenase-1 or the radical initiator 2,2'-azobis(2,4-dimethyl-valeronitrile).

Identification of linoleic acid free radicals and other breakdown products using spin trapping with liquid chromatography-electrospray tandem mass spectrometry

Linoleic acid radical products formed by radical reaction (Fenton conditions) were trapped using 5,5-dimethyl-1-pyrrolidine-N-oxide (DMPO) and analysed by reversed-phase liquid chromatography coupled to electrospray mass spectrometry (LC-MS). The linoleic acid radical species detected as DMPO spin adducts comprised oxidized linoleic acid and short-chain radical species that resulted from the breakdown of carbon and oxygen centred radicals. Based on the m/z values, the short-chain products were identified as alkyl and carboxylic acid DMPO radical adducts that exhibited different elution times. The ions identified as DMPO radical adducts were studied by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The LC-MS/MS spectra of linoleic acid DMPO radical adducts exhibited the fragment ion at m/z 114 and/or the loss of neutral molecule of 113 Da (DMPO) or 131 Da (DMPO + H2O), indicated to be DMPO adducts. The short-chain products identified allowed inference of the radical oxidation along the linoleic acid chain by abstraction of hydrogen atoms in carbon atoms ranging from C-8 to C-14. Other ions containing the fragment ion at m/z 114 in the LC-MS/MS spectra were attributed to DMPO adducts of unsaturated aldehydes, hydroxy-aldehydes and oxocarboxylic acids. The identification of aldehydic products formed by radical oxidation of linoleic acid peroxidation products, as short-chain product DMPO adducts, is a means of identifying lipid peroxidation products.

Synergistic production of lung free radicals by diesel exhaust particles and endotoxin

The present study tested the hypothesis that free radicals were involved in the pathogenesis of lung injury caused by diesel exhaust particles (DEP) and bacterial lipopolysaccharides (LPS). Intratracheal coinstillation of DEP and LPS in rat lungs resulted in synergistic enhancement of free radical generation in the lungs. The radical metabolites were characterized as lipid-derived by electron spin resonance (ESR). The free radical generation was paralleled by a synergistic increase in total protein and by infiltration of neutrophils in the bronchoalveolar lavage (BAL) fluid of the lungs. Experiments with NADP-reduced (NADPH) oxidase and iNOS knockout mice showed that NADPH oxidase and iNOS did not contribute to free radical generation. However, pretreatment with the macrophage toxicant GdCl(3), the xanthine oxidase (XO) inhibitor allopurinol, and the Fe(III) chelator Desferal resulted in a marked decrease in free radical generation, lung inflammation, and lung injury. These effects were concomitant with the inhibition of XO activity in BAL, suggesting that the activated macrophages and the activity of XO contributed to the generation of free radicals caused by DEP and LPS. This is the first demonstration that DEP and LPS work synergistically to enhance free radical generation in lungs, mediated by the activation of local XO.

ESR investigation of the oxidative damage in lungs caused by asbestos and air pollution particles

Exposure to asbestos and air pollution particles can be associated with increased human morbidity and mortality. However, the molecular mechanism of lung injuries remains unknown. It has been postulated that the in vivo toxicity results from the catalysis of free radical generation. Using electron spin resonance (ESR) in conjunction with the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) we previously investigated in vivo free radical production by rats treated with intratracheal instillation of asbestos (crocidolite fibers) and an emission source air pollution particle (oil fly ash). In this report we compare the effect of two different exposures on the type of free radicals they induce in in vivo animal model. Twenty-four hours after the exposure, ESR spectroscopy of the chloroform extract from lungs of animals exposed to either asbestos or oil fly ash gave a spectrum consistent with a carbon-centered radical adduct (aN = 15.01 G and aH = 2.46 G). To test whether free radical formation occurred in vivo and not in vitro, a number of control experiments were performed. Combinations (both individually and together) of asbestos or oil fly ash and 4-POBN were added to lung homogenate of unexposed rats prior to chloroform extraction. No detectable ESR signal resulted. To exclude the possibility of ex vivo free radical generation, asbestos or oil fly ash was added to lung homogenate of an animal treated with 4-POBN. Also, 4-POBN was added to lung homogenate from rats instilled with asbestos or oil fly ash. Neither system produced radical adducts, indicating that the ESR signal detected in the lung extracts of the treated animals must be produced in vivo and not ex vivo or in vitro. In conclusion, ESR analysis of lung tissue demonstrated that both exposures produce lipid-derived radical metabolites despite their different composition and structure. Analogously, both exposures provide evidence of in vivo enhanced lipid peroxidation. Furthermore, it is concluded that without the presence of a spin-trapping agent, no free radical metabolites could be detected directly by ESR in either exposure.

In vivo identification of aflatoxin-induced free radicals in rat bile

Aflatoxin B1 (AFB1) is a potent hepatocarcinogen. We have recently detected [via electron spin resonance (ESR) spectroscopy] free radicals in vivo in rat bile following AFB1 metabolism using the spin trapping [alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone (4-POBN)] technique. The aim of the present study was to identify the trapped free radical intermediates from the in vivo hepatic metabolism of AFB1. Rats were treated simultaneously with AFB1 (3 mg/kg i.p.) and the spin trapping agent 4-POBN (1 g/kg i.p.), and bile was collected over a period of 1 h at 20 min intervals. On-line high performance liquid chromatography (HPLC) coupled to ESR was used to identify an arachidonic acid-derived radical adduct of 4-POBN in rat bile, and a methyl adduct of 4-POBN from the reaction of hydroxyl radicals with carbon-13-labeled dimethyl sulfoxide ((13)C-DMSO). The effect of metabolic inhibitors, such as desferoxamine mesylate (DFO), an iron chelator, 2-dimethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF) 525A, a cytochrome P-450 inhibitor, and gadolinium chloride (GdCl(3)), a Kupffer cell inactivator, on in vivo aflatoxin-induced free radical formation were also studied. It was found that there was a significant decrease in radical formation as a result of DFO, SKF525A and GdCl(3) inhibition. Trapped 4-POBN radical adducts were also detected in rat bile following the in vivo metabolism of aflatoxin-M1, one of the hydroxylated metabolites of AFB1.

Detection and characterization by mass spectrometry of radical adducts produced by linoleic acid oxidation

The formation of linoleic acid radical species under the oxidative conditions of the Fenton reaction (using hydrogen peroxide and Fe (II)) was monitored by FAB-MS and ES-MS using the spin trap 5,5-dimethyl-1-pyrrolidine-N-oxide, DMPO. Both the FAB and ES mass spectra were very similar and showed the presence of ions corresponding to carbon- and oxygen centered spin adducts (DMPO/L*, DMPO/LO*, and DMPO/LOO*). Cyclic structures, formed between the DMPO oxygen and the neighboring carbon of the fatty acid, were also observed. Electrospray tandem mass spectrometry of these ions was performed to confirm the proposed structure of these adducts. All MS/MS spectra showed an ion at m/z 114, correspondent to the [DMPO + H]+, and a fragment ion due to loss of DMPO (loss of 113 Da), confirming that they are DMPO adducts. ES-MS/MS spectra of alkoxyl radical adducts (DMPO/LO*) showed an additional ion at m/z 130 [DMPO - O + H]+, while ES MS/MS of peroxyl radical adducts (DMPO/LOO*) showed a fragment ion at m/z 146 [DMPO - OO + H]+, confirming both structures. Other fragment ions were observed, such as alkyl acylium radical ions, formed by cleavage of the alkyl chain after loss of water and the DMPO molecule. The identification of fragment ions observed in the MS/MS spectra of the different DMPO adducts suggests the occurrence of structural isomers containing the DMPO moiety both at C9 and C13. The use of ES tandem mass spectrometry, associated with spin trapping experiments, has been shown to be a valuable tool for the structural characterization of carbon and oxygen-centered spin adducts of lipid radicals.

Separation and identification of DMPO adducts of oxygen-centered radicals formed from organic hydroperoxides by HPLC-ESR, ESI-MS and MS/MS

Many electron spin resonance (ESR) spectra of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) radical adducts from the reaction of organic hydroperoxides with heme proteins or Fe(2+) were assigned to the adducts of DMPO with peroxyl, alkoxyl, and alkyl radicals. In particular, the controversial assignment of DMPO/peroxyl radical adducts was based on the close similarity of their ESR spectra to that of the DMPO/superoxide radical adduct in conjunction with their insensitivity to superoxide dismutase, which distinguishes the peroxyl adducts from the DMPO/superoxide adduct. Although recent reports assigned the spectra suggested to be DMPO/peroxyl radical adducts to the DMPO/methoxyl adduct based on independent synthesis of the adduct and/or (17)O-labeling, (17)O-labeling is extremely expensive, and both of these assignments were still based on hyperfine coupling constants, which have not been confirmed by independent techniques. In this study, we have used online high performance liquid chromatography (HPLC or LC)/ESR, electrospray ionization-mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) to separate and directly characterize DMPO oxygen-centered radical adducts formed from the reaction of Fe(2+) with t-butyl or cumene hydroperoxide. In each reaction system, two DMPO oxygen-centered radical adducts were separated and detected by online LC/ESR. The first DMPO radical adduct from both systems showed identical chromatographic retention times (t(R) = 9.6 min) and hyperfine coupling constants (a(N) = 14.51 G, a(H)(beta) = 10.71 G, and a(H)(gamma) = 1.32 G). The ESI-MS and MS/MS spectra demonstrated that this radical was the DMPO/methoxyl radical adduct, not the peroxyl radical adduct as was thought at one time, although its ESR spectrum is nearly identical to that of the DMPO/superoxide radical adduct. Similarly, based on their MS/MS spectra, we verified that the second adducts (a(N) = 14.86 G and a(H)(beta) = 16.06 G in the reaction system containing t-butyl hydroperoxide and a(N) = 14.60 G and a(H)(beta) = 15.61 G in the reaction mixture containing cumene hydroperoxide), previously assigned as DMPO adducts of t-butyloxyl and cumyloxyl radical, were indeed from trapping t-butyloxyl and cumyloxyl radicals, respectively.

Identification of oxidation products and free radicals of tryptophan by mass spectrometry

New oxidation products and free radicals derived from tryptophan (Trp) oxidation under Fenton reaction conditions were identified using mass spectrometry. After the oxidation of tryptophan using hydrogen peroxide and iron (II) system (Fenton reaction), mono- and dihydoxy tryptophans and N-formylkynurenine were identified using electrospray mass spectrometry (ES-MS) and ES-MS/MS. Besides these products, new products resulting from the reaction of tryptophan and oxidized tryptophan and 3-methyl indole derivatives were also identified. The 3-methyl indole derivatives resulted, most probably, from the oxidation process and not from in-source processes. A dimer formed by cross-linking between two Trp radicals (Trp-Trp), similar to the previously described tyrosine dimer was observed, as well as the corresponding monohydroxy-dimer (Trp-Trp-OH). Tandem mass spectrometry was used to identify the structures of these new oxidation products. Free radicals derived from tryptophan oxidation under Fenton reaction were detected using as spin trap the DMPO. The free radical species originated during the oxidation reaction formed stable adducts with the spin trap, and these adducts were identified by ES-MS. New adducts of oxidized tryptophan radicals, namely monohydroxy-tryptophan and dihydroxy-Trp dimer radicals, with one and two DMPO spin trap molecules where identified. Tandem mass spectrometry was used to confirm the proposed structure of the observed adducts.

Antioxidant balance and free radical generation in vitamin e-deficient mice after dermal exposure to cumene hydroperoxide

Organic peroxides are widely used in the chemical industry as initiators of oxidation for the production of polymers and fiber-reinforced plastics, in the manufacture of polyester resin coatings, and pharmaceuticals. Free radical production is considered to be one of the key factors contributing to skin tumor promotion by organic peroxides. In vitro experiments have demonstrated metal-catalyzed formation of alkoxyl, alkyl, and aryl radicals in keratinocytes incubated with cumene hydroperoxide. The present study investigated in vivo free radical generation in lipid extracts of mouse skin exposed to cumene hydroperoxide. The electron spin resonance (ESR) spin-trapping technique was used to detect the formation of alpha-phenyl-N-tert-butylnitrone (PBN) radical adducts, following intradermal injection of 180 mg/kg PBN. It was found that 30 min after topical exposure, cumene hydroperoxide (12 mmol/kg) induced free radical generation in the skin of female Balb/c mice kept for 10 weeks on vitamin E-deficient diets. In contrast, hardly discernible radical adducts were detected when cumene hydroperoxide was applied to the skin of mice fed a vitamin E-sufficient diet. Importantly, total antioxidant reserve and levels of GSH, ascorbate, and vitamin E decreased 34%, 46.5%. 27%, and 98%, respectively, after mice were kept for 10 weeks on vitamin E-deficient diet. PBN adducts detected by ESR in vitamin E-deficient mice provide direct evidence for in vivo free radical generation in the skin after exposure to cumene hydroperoxide.

In vivo lipid-derived free radical formation by NADPH oxidase in acute lung injury induced by lipopolysaccharide: a model for ARDS

Intratracheal instillation of lipopolysaccharide (LPS) activates alveolar macrophages and infiltration of neutrophils, causing lung injury/acute respiratory distress syndrome. Free radicals are a special focus as the final causative molecules in the pathogenesis of lung injury caused by LPS. Although in vitro investigation has demonstrated radical generation after exposure of cells to LPS, in vivo evidence is lacking. Using electron spin resonance (ESR) and the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN), we investigated in vivo free radical production by rats treated with intratracheal instillation of LPS. ESR spectroscopy of lipid extract from lungs exposed to LPS for 6 h gave a spectrum consistent with that of a POBN/carbon-centered radical adduct (aN=14.94+/-0.07 G and abetaH=2.42+/-0.06 G) tentatively assigned as a product of lipid peroxidation. To further investigate the mechanism of LPS-initiated free radical generation, rats were pretreated with the phagocytic toxicant GdCl3, which significantly decreased the production of radical adducts with a corresponding decrease in neutrophil infiltration. NADPH oxidase knockout mice completely blocked phagocyte-mediated, ESR-detectable radical production in this model of acute lung injury. Rats treated intratracheally with LPS generate lipid-derived free radicals via activation of NADPH oxidase.

Identification of protein-derived tyrosyl radical in the reaction of cytochrome c and hydrogen peroxide: characterization by ESR spin-trapping, HPLC and MS

The reaction of cytochrome c and H(2)O(2) is known to form a protein-centred radical that can be detected with the spin trap 2-methyl-2-nitrosopropane (MNP). To characterize the MNP/tyrosyl adduct structure that had previously been determined incorrectly [Barr, Gunther, Deterding, Tomer and Mason (1996) J. Biol. Chem. 271, 15498-15503], we eliminated unreasonable structure models by ESR studies with a series of (13)C-labelled tyrosines, and photochemically synthesized an authentic MNP/tyrosyl adduct that has its trapping site on the C-3 position of the tyrosine phenyl ring. The observation of the identical ESR spectra for this radical adduct from the UV irradiation of 3-iodo-tyrosine and the adduct from the cytochrome c reaction demonstrated that the radical trapping site of MNP/tyrosyl is located on the equivalent C-3/C-5 positions instead of the C-1 position, as was proposed by Barr et al. In an on-line HPLC/ESR system, an identical retention time (17.7 min) was observed for the ESR-active HPLC peak of the MNP/tyrosyl adduct from the following three reactions: (i) the tyrosine oxidation via horseradish peroxidase/H(2)O(2); (ii) UV irradiation of 3-iodo-tyrosine and (iii) the reaction of cytochrome c with H(2)O(2). This result demonstrated that the radical adducts of all three reactions are most probably the same. The mass spectrometric analysis of the HPLC fractions from reactions (i) and (ii) showed an ion at m/z 267 attributed to the MNP/tyrosyl adduct. We conclude that the cytochrome c-derived tyrosyl radical was trapped by MNP, leading to a persistent radical adduct at the C-3/C-5 positions of the tyrosine phenyl ring.

Cytochrome c catalyses the formation of pentyl radical and octanoic acid radical from linoleic acid hydroperoxide

A reaction of 13-hydroperoxide octadecadienoic acid (13-HPODE) with cytochrome c was analysed using ESR, HPLC-ESR and HPLC-ESR-MS by the combined use of the spin-trapping technique. The ESR, HPLC-ESR and HPLC-ESR-MS analyses showed that cytochrome c catalyses formation of pentyl and octanoic acid radicals from 13-HPODE. On the other hand, only the alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone/octanoic acid radical adduct was detected in the elution profile of HPLC-ESR for a mixture of 13-HPODE with haematin, indicating that haematin catalyses the formation of octanoic acid radical. In addition, the reaction of 13-HPODE with cytochrome c was inhibited by chlorogenic acid, caffeic acid and ferulic acid via two possible mechanisms, i.e. reducing cytochrome c (chlorogenic acid and caffeic acid) and scavenging the radical intermediates (chlorogenic acid, caffeic acid and ferulic acid).

Production and chemiluminescent free radical reactions of glyoxal in lipid peroxidation of linoleic acid by the ligninolytic enzyme, manganese peroxidase

Glyoxal is a key compound involved in glyoxal oxidase (GLOX)-dependent production of glyoxylate, oxalate and H2O2 by lignin-degrading basidiomycetes. In this paper, we report that glyoxal was produced from a metabolite of ligninolytic fungi, linoleic acid, by manganese peroxidase (MnP)-dependent lipid peroxidation. In the absence of the parent substrate of linoleic acid, the dialdehyde was oxidized by MnP and Mn(III) chelate to start free radical reactions with emission of chemiluminescence at 700-710 nm. The spectroscopic profile of the light emission is distinguishable from (a) singlet oxygen, (b) triplet carbonyls from dioxetane and alpha-hydroxyperoxyl radicals, and (c) biacyl triplet formed by the coupling of two acyl radicals. The photon emission of glyoxal by MnP was activated by co-oxidation of tartrate. The MnP-dependent oxidation of glyoxal in tartrate buffers continued for 10 days without addition of exogenous H2O2. The importance of these results is discussed in relation to the free radical chemistry of lignin biodegradation by wood rot fungi.

An ESR and HPLC-EC assay for the detection of alkyl radicals

The correlation of lipid peroxidation with release of alkanes (RH) is considered a noninvasive method for the in vivo evaluation of oxidative stress. The formation of RH is believed to reflect a lipid hydroperoxide (LOOH)-dependent generation of alkoxyl radicals (LO*) that undergo beta-scission with release of alkyl radicals (R*). Alternatively, R* could be spin-trapped with a nitrone before the formation of RH and analyzed by ESR. Extracts from the liver and lung of CCl(4)- and asbestos-treated rats that were previously loaded with nitrones exhibited ESR spectra suggesting the formation of iso-propyl, n-butyl, ethyl, and pentyl radical-derived nitroxides. In biological systems, various nitroxides with indistinguishable ESR spectra could be formed. Hence, experiments with N-tert-butyl-alpha-phenylnitrone (PBN) for spin trapping of R* were carried out in which the nitroxides formed were separated and analyzed by HPLC with electrochemical detection (EC). The C(1-5) homologous series of PBN nitroxides and hydroxylamines were synthesized, characterized by ESR, GC-MS, and HPLC-EC, and used as HPLC standards. For in vivo generation and spin trapping of R*, rats were loaded with CCl(4) and PBN. The HPLC-EC chromatograms of liver extracts from CCl(4)-treated rats demonstrated the formation of both the nitroxide and hydroxylamine forms of PBN/*CCl(3), as well as the formation of a series of unidentified PBN nitroxides and hydroxylamines. However, formation of PBN adducts with retention times similar to these of the PBN/C(2-5) derivatives was not observed. In conclusion, we could not correlate the production of PBN-detectable alkyl radicals with the reported CCl(4)-dependent production of C(1-5) alkanes. We speculate that the major reason for this is the low steady-state concentrations of R* produced because only a small fraction of LO* undergo beta-scission to release R*.

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.

High-performance liquid chromatographic determination of linoleic acid peroxide-derived radicals using electrochemical detection

High-performance liquid chromatography-electrochemical detection (HPLC-ED) was applied to detect 13-hydroperoxide octadecadienoic acid (13-HPODE)-derived radicals such as the pentyl radical and octanoic acid radical. The 13-HPODE-derived radicals were successfully detected using HPLC-ED by the combined use of the spin-trapping technique with alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN). The 4-POBN-pentyl radical adduct was detected at the retention time of 18.2 +/- 0.3 min on the elution profile of HPLC-ED with an ODS column (15 cm x 4.6 mm I.D.) using a flow-rate of 1.0 ml/min with 50 mM ammonium acetate in 29% (v/v) aqueous acetonitrile. The 4-POBN-octanoic acid radical adduct was also detected at the retention time of 13.7 +/- 0.7 min using a flow-rate of 1.0 ml/min with 50 mM ammonium acetate in 14% (v/v) aqueous acetonitrile. The concentrations of the 4-POBN radical adducts were determined using HPLC-ED without an internal standard. HPLC-ED is 100 times as sensitive as HPLC-electron spin resonance (ESR) under the ESR and ED conditions employed here. Even 1.8 pmol of the 4-POBN-pentyl (or octanoic acid) radical adduct was detectable using

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.

Identification of free radical formation and F2-isoprostanes in vivo by acute Cr(VI) poisoning

We previously reported the detection of a carbon-centered radical adduct of alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (POBN) in the bile of rats acutely poisoned with Cr(VI) utilizing an electron spin resonance spin-trapping technique. These former studies suggested that the free radical metabolite was derived from a polyunsaturated fatty acid. The present studies were undertaken to further characterize this radical adduct and to determine whether its formation is associated with enhanced lipid peroxidation in vivo. This report demonstrates that electron spin resonance (ESR) spectra with hyperfine coupling constants aN of 15.71 G and of 2.90 G were present in bile from Cr(VI)-poisoned rats. We found out that virtually identical ESR spectra were obtained when authentic POBN-pentyl radical adducts generated from the reaction of POBN with either pentylhydrazine or linoleic or arachidonic acid with lipoxygenase were added to bile. The hyperfine coupling constants for the POBN-pentyl radical adducts added to bile were as follows: aN = 15.85 G and = 2.60 G for the reaction between pentylhydrazine and POBN; aN = 15.72 G and = 2.61 G for the reaction between arachidonic acid, lipoxygenase, and POBN; and aN = 15.85 G and = 2. 85 G for the reaction between linoleic acid, lipoxygenase, and POBN. In addition, the formation of this radical adduct was associated with lipid peroxidation as quantified by increases in F2-isoprostane levels in bile. These studies, therefore, provide additional evidence that acute Cr(VI) poisoning is associated with enhanced generation of F2-isoprostanes in vivo and tentatively identify the radical species that is produced as the POBN-pentyl radical adduct.

In vivo evidence of free radical formation after asbestos instillation: an ESR spin trapping investigation

It has been postulated that the in vivo toxicity of asbestos results from its catalysis of free radical generation. We examined in vivo radical production using electron spin resonance (ESR) coupled with the spin trap alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN); 180 day-old rats were intratracheally instilled with either 500 microg crocidolite or saline. Twenty-four hours later, histologic examination revealed a neutrophilic inflammatory response. ESR spectroscopy of the chloroform extract from lungs exposed to asbestos gave a spectrum consistent with a carbon-centered radical adduct, while those spectra from lungs instilled with saline revealed a much weaker signal. This same radical formation persisted and, even one month after instillation, could be detected in the lungs of rats exposed to asbestos. The 4-POBN adducts detected by ESR are very similar to, if not identical with, ethyl and pentyl radical adducts, providing evidence of in vivo lipid peroxidation resulting from asbestos exposure. We conclude that, after instillation of crocidolite in the rat, ESR analysis of lung tissue demonstrates in vivo free radical production.

In vivo evidence of free radical formation in the rat lung after exposure to an emission source air pollution particle

Exposure to air pollution particles can be associated with increased human morbidity and mortality. The mechanism(s) of lung injury remains unknown. We tested the hypothesis that lung exposure to oil fly ash (an emission source air pollution particle) causes in vivo free radical production. Electron spin resonance (ESR) in conjunction with the spin trap alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN) was used to detect radical adducts. Rats were instilled with 500 micrograms of either oil fly ash or saline. Twenty-four hours later, ESR spectroscopy of the chloroform extract from lungs of animals exposed to the oil fly ash gave a spectrum consistent with a carbon-centered radical adduct (hyperfine coupling constants alpha N = 15.0 G and alpha H beta = 2.5 G), while those spectra from lungs instilled with saline revealed a much weaker signal. This signal was reproduced by instilling animals with the soluble fraction of the oil fly ash, which contains soluble metal compounds. The same signal was observed after instillation of either a mixture of vanadium, nickel, and iron sulfates or VOSO4 alone. We conclude that, after instillation of an air pollution particle in the rat, ESR analysis of lung tissue demonstrates in vivo free radical production. This generation of free radicals appears to be associated with soluble metals in the oil fly ash.

Evidence for a novel pentyl radical adduct of the cyclic nitrone spin trap MDL 101,002

3,4-Dihydro-3,3-dimethyl-isoquinoline-2-oxide (MDL 101,002) is a conformationally constrained cyclic analog of the known spin trap alpha-phenyl N-tert-butyl nitrone (PBN). Because of PBN's ability to scavenge free radicals, MDL 101,002 is currently being evaluated in stroke models as a means to ameliorate the oxidative insult associated with reperfusion injury. To augment our understanding of the radical scavenging mechanism of this potential drug, MDL 101,002 was incubated with soybean lipoxygenase in the presence of linoleic acid to study the interaction between MDL 101,002 and free radicals formed during lipid peroxidation. Analysis of the reaction mixture was performed by high performance liquid chromatography using normal phase conditions with detection by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Similar to the work by Iwahashi et al. [Arch. Biochem. Biophys., 1991, 285, 172], who studied the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone (4-POBN), an adduct that suggested the trapping of pentyl radicals by MDL 101,002 was observed. However, the apparent molecular ion for this adduct (246 Da) was 1 Da lower than would be predicted if a pentyl radical had simply added to MDL 101,002. In addition, the adduct exhibited significant absorbance at 304 nm, consistent with the unsaturated nitrone structure of MDL 101,002. To account for these observations, it is postulated that, after the initial capture of a pentyl radical, subsequent abstraction of a hydrogen atom by a neighboring radical occurs to regenerate a nitrone (1-pentyl analog of MDL 101,002). We present evidence for this adduct and offer a mechanism for its formation. These findings indicate that mass spectroscopic analysis of stable nitrone radical adducts may be useful in the identification of radical-dependent damage in vivo and possibly in clinical development of MDL 101,002 as an antioxidant pharmaceutical.

Studies on protective mechanisms of four components of green tea polyphenols against lipid peroxidation in synaptosomes

The comparison of the protective effects of four components of "green tea polyphenols' (GTP) - (-)-epigallocatechin gallate, EGCG; (-)-epicatechin gallate, ECG; (-)epigallocatechin, EGC; and (-)epicatechin, EC - against iron-induced lipid peroxidation in synaptosomes showed that: (1) the inhibitory effects of those compounds on TBA reactive materials from lipid peroxidation decreased in the order of EGCG > ECG > EGC > EC; (2) the scavenging effects of those compounds on lipid free radicals produced by lipid peroxidation could be classified as follows: ECG > EGCG > EC > EGC. Furthermore, we investigated the iron-chelating activity and the free radical scavenging activity of those compounds as their protective mechanisms against lipid peroxidation in synaptosomes. As for the iron-chelating activity, the ratio of EGC, EGCG, ECG or EC to iron(III) was 3:2, 2:1, 2:1 and 3:1, respectively. The hydroxyl radical (HO) scavenging activity of those compounds was investigated in a photolysis of the H2O2 system. It was found that their ability to scavenge hydroxyl radicals decreased in the order of ECG > EC > EGCG >> EGC. It was also found that they could scavenge lipid free radicals in the lecithin/lipoxidase system and their scavenging activity was classified as follows: ECG > EGCG >> EGC > EC. Moreover, we found that their antioxidant active positions were different from each other and the stability of the semiquinone free radicals produced by those compounds in NaOH solution decreased in the order of EGCG > ECG >> EC. The results indicated that the ability of those compounds to protect synaptosomes from the damage of lipid peroxidation initiated by Fe2+/Fe3+ was dependent not only on their iron-chelating activity and free-radical scavenging activity, but also on the stability of their semiquinone free radicals.

Identification of radical adducts formed in the reactions of unsaturated fatty acids with soybean lipoxygenase using continuous flow fast atom bombardment with tandem mass spectrometry

Structures of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) radical adducts formed in the reactions of soybean lipoxygenase with linoleic acid, linolenic acid, and arachidonic acid were determined using continuous flow fast atom bombardment (CF-FAB) combined with tandem mass spectrometry. The radical adducts of these lipoxygenase-dependent reactions were: n-octanoic acid radical, 12,13-dihydroxylinoleic acid radical, 12,13-epoxylinoleic acid radical, and n-pentyl radical from linoleic acid; n-octanoic acid radical, ethyl radical, and cis/trans and/or positional isomers (1- and 3-pentenyl) of pentenyl radical from linolenic acid; and 14,15-epoxyarachidonic acid radical and n-pentyl radical from arachidonic acid. Of these radical adducts, the n-octanoic acid radical from linoleic and linolenic acid, the ethyl radical from linolenic acid, and the 12,13-dihydroxylinoleic acid radical are identified for the first time in the reactions of soybean lipoxygenase. Thus the CF-FAB combined with tandem mass spectrometry employed here, by which both radical adducts and their fragment ions can be detected, is shown to be a powerful tool in the structural identification of free radicals.

Combined liquid chromatography/mass spectrometry of the radical adducts of a fluorescamine-derivatized nitroxide

Dynamic liquid secondary ion mass spectrometry (dyn-LSIMS) was employed to acquire continuous, on-line mass spectral data from the effluent of a reversed-phase high-performance liquid chromatograph (HPLC) used to separate a broad suite of carbon-centered radicals trapped as the O-alkylhydroxylamine adducts of an amino nitroxide that was subsequently derivatized with fluorescamine. Data obtained by the use of these combined techniques (LC/MS) can be employed to elucidate radical adduct structures; elemental compositions of the adducts can be confirmed by acquiring mass spectra at high resolution. At low resolution, introduction into the source of < 1 pmol of adduct yielded usable spectra. The first application of this technique to the identification of photochemically generated radicals in natural water samples is presented.

Tandem mass spectrometry study of C-phenyl-N-tert-butyl nitrone spin adducts from in vitro rat liver microsomal metabolism of bromotrichloromethane and carbon tetrachloride

Electron ionization and thermospray were used in conjunction with tandem mass spectrometry methods to identify trichloromethyl/C-phenyl-N-tert-butyl nitrone (PBN) spin adducts produced in rat liver microsomal dispersions that had been treated with reduced nicotinamide adenine dinucleotide phosphate (NADPH)-generating system and BrCCl3 (or CCl4). In the identification of PBN spin adducts, a scan of precursors of m / z 57 was utilized to confirm the presence of PBN spin adducts, because PBN spin adducts produce m / z 57 from tert-butyl as a characteristic fragment. Use of deuterated PBN (PBN-d9 deuterated at tert-butyl; PBN-d 14 deuterated at both phenyl and tert-butyl) improved the recognition of PBN adducts in mixtures by precursor ion scans, because m / z 66 (which corresponds to the deuterated tert-butyl group) is characteristic and, unlike m / z 57, it is not a common fragment for any other compounds. Two new PBN spin adducts that were not detected before by electron paramagnetic resonance or mass spectrometry were identified by these methods for the first time.

Superoxide generation by lipoxygenase in the presence of NADH and NADPH

The ability of soybean lipoxygenase to mediate NAD(P)H oxidation and concomitant superoxide generation in the presence of linoleic acid was examined. At optimum pH of 8.3, lipoxygenase oxidized both NADH and NADPH in the presence of 700 microM linoleic acid. The oxidation of NAD(P)H was biphasic. The initial rates of NADH and NADPH oxidation were 130 and 140 nmoles/min/nmole of enzyme respectively and the corresponding final rates were 344 and 350 nmoles/min/nmole of enzyme. The apparent Km values calculated for NADH and NADPH oxidation were 13 microM and 117 microM respectively. NAD(P)H oxidation was accompanied by the reduction of either ferricytochrome c or nitroblue tetrazolium (NBT) which can be abolished (approx. 85%) by superoxide dismutase (SOD) suggesting the generation of superoxide anion radicals. Under optimal conditions, the rates of superoxide generation, measured as the SOD-inhibitable reduction of ferricytochrome c, were 325 and 235 nmoles/min/nmole of enzyme for NADH and NADPH respectively. Under identical experimental conditions, the SOD-inhibitable NBT reduction rates were 308 and 210 nmoles/min/nmole of enzyme for NADH and NADPH respectively. Both NADH and NADPH could be regenerated after oxidation using the appropriate dehydrogenases. These results strongly suggest that lipoxygenase not only generates lipid hydroperoxides but can also generate superoxide via oxidation of pyridine nucleotides and may, therefore, significantly contribute to oxidative stress in cells.

Fatty acid radical formation in rats administered oxidized fatty acids: in vivo spin trapping investigation

We report in vivo evidence for fatty acid-derived free radical metabolite formation in bile of rats dosed with spin traps and oxidized polyunsaturated fatty acids (PUFA). When rats were dosed with the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and oxidized PUFA, the DMPO thiyl radical adduct was formed due to a reaction between oxidized PUFA and/or its metabolites with biliary glutathione. In vitro experiments were performed to determine the conditions necessary for the elimination of radical adduct formation by ex vivo reactions. Fatty acid-derived radical adducts of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) were detected in vivo in bile samples collected into a mixture of iodoacetamide, desferrioxamine, and glutathione peroxidase. Upon the administration of oxidized 13C-algal fatty acids and 4-POBN, the EPR spectrum of the radical adducts present in the bile exhibited hyperfine couplings due to 13C. Our data demonstrate that the carbon-centered radical adducts observed in in vivo experiments are unequivocally derived from oxidized PUFA. This in vivo evidence for PUFA-derived free radical formation supports the proposal that processes involving free radicals may be the molecular basis for the previously described cytotoxicity of dietary oxidized PUFA.

Evidence against the 1:2:2:1 quartet DMPO spectrum as the radical adduct of the lipid alkoxyl radical

It was reported that the electron paramagnetic resonance (EPR) spectrum of 5,5-dimethyl-1-pyrroline N-oxide (DMPO)/lipid alkoxyl radical exhibited a quartet with 1:2:2:1 relative intensity that is identical to that of DMPO/hydroxyl radical (K. M. Schaich and D. C. Borg, 1990, Free Radicals Res. Commun. 9, 267-278). We repeated these EPR experiments using HPLC separation of radical adducts and isotope substitution. We found that the HPLC/EPR chromatogram of the radical adduct with a 1:2:2:1 quartet obtained by the reduction of methyl linoleate hydroperoxide (MLOOH) with Fe2+ exhibited identical retention time to that of the DMPO/OH radical adduct obtained from the Fenton reaction in two different solvent systems. Upon performing the same reaction in 17O-enriched water, the 17O-hyperfine coupling constants due to DMPO/17OH were identified. Ultimately, approximately 80-90% of the total DMPO/OH is derived from water by an iron-dependent nucleophilic addition reaction. Initially, a water-independent mechanism also significantly contributes to DMPO/OH formation. Regardless of its mechanism of formation, the 1:2:2:1 quartet radical adduct of DMPO formed during the reduction of MLOOH by Fe2+ is in fact DMPO/OH.