ESR and HPLC-EC analysis of the interaction of hydroxyl radical with DMSO: rapid reduction and quantification of POBN and PBN nitroxides

DNA-binding, photocleavage and anti-cancer activity of tin(IV) corrole

A new tin(IV) corrole, 5,10,15-tris(4-methoxycarbonylphenyl) corrole tin(IV) (1-Sn) was synthesized and characterized. The DNA binding, photocleavage and anti-cancer activity were studied and compared with its free-base. The interaction of 1-Sn and its free-base 1 with calf thymus DNA had been investigated by spectroscopic methods, viscosity measurements and molecular docking analysis. The results revealed that 1-Sn and 1 could interact with calf thymus DNA via an outside groove binding mode. Furthermore, although 1 displayed no photonuclease activity, 1-Sn exhibited good photonuclease activity as indicated by agarose gel electrophoresis, and superoxide anion might be the active intermediate for the DNA scission. Finally, 1 was nontoxic but 1-Sn displayed cytotoxicity towards A549 tumor cell lines.

Ratiometric detection of hydroxy radicals based on functionalized europium(III) coordination polymers

A ratiometric fluorescent probe is described that is based on a functionalized europium(III) coordination polymer (Eu/DPA-TA). It can be fabricated by using dipicolinic acid (DPA) as a bridging ligand (to sensitize the Eu³⁺ fluorescence) and terephthalic acid (TA) acting as a functional ligand to recognize the hydroxy radical (^•OH). The quenching of Eu³⁺ fluorescence (measured at excitation/emission wavelengths of 288/615 nm) by water is strongly reduced in the presence of TA. This leads to a significant enhancement in the emission lifetime and intensity of Eu³⁺. Upon the addition of ^•OH, the fluorescence of Eu/DPA-TA showed ratiometric changes in that the TA sensitized fluorescence (peaking at 445 nm) is switched on, while the plain Eu³⁺ fluorescence (peaking at 615 nm) decreases. This finding led to a method for the ratiometric (2-wavelength) detection of OH˙ with a 0.5 μM detection limit. The method also allows OH˙ to be detected with bare eyes at OH˙ concentrations as low as 10 μM. In our perception, this study paves the way towards the design of new functionalized lanthanide coordination polymers for fluorometric assays and biomedical imaging. Graphical abstract Schematic of a ratiometric fluorescent assay for the detection of hydroxy radical (^•OH) based on the use of a europium(III)/dipicolinic acid coordination polymer (Eu/DPA CP) functionalized with terephthalic acid (TA). A gradual color change from red to blue can be observed and correlated to ^•OH concentrations.

Dual-emissive fluorescence measurements of hydroxyl radicals using a coumarin-activated silica nanohybrid probe

This work reports a novel dual-emissive fluorescent probe based on dye hybrid silica nanoparticles for ratiometric measurement of the hydroxyl radical (˙OH). In the probe sensing system, the blue emission of coumarin dye (coumarin-3-carboxylic acid, CCA) immobilized on the nanoparticle surface is selectively enhanced by ˙OH due to the formation of a coumarin hydroxylation product with strong fluorescence, whereas the emission of red fluorescent dye encapsulated in the silica nanoparticle is insensitive to ˙OH as a self-referencing signal, and so the probe provides a good quantitative analysis based on ratiometric fluorescence measurement with a detection limit of 1.65 μM. Moreover, the probe also shows high selectivity for ˙OH determination against metal ions, other reactive oxygen species and biological species. More importantly, it exhibits low cytotoxicity and high biocompatibility in living cells, and has been successfully used for cellular imaging of ˙OH, showing its promising application for monitoring of intracellular ˙OH signaling events.

N-tert-butylmethanimine N-oxide is an efficient spin-trapping probe for EPR analysis of glutathione thiyl radical

The electron spin resonance (EPR) spin-trapping technique allows detection of radical species with nanosecond half-lives. This technique is based on the high rates of addition of radicals to nitrones or nitroso compounds (spin traps; STs). The paramagnetic nitroxides (spin-adducts) formed as a result of reactions between STs and radical species are relatively stable compounds whose EPR spectra represent “structural fingerprints” of the parent radical species. Herein we report a novel protocol for the synthesis of N-tert-butylmethanimine N-oxide (EBN), which is the simplest nitrone containing an α-H and a tertiary α′-C atom. We present EPR spin-trapping proof that: (i) EBN is an efficient probe for the analysis of glutathione thiyl radical (GS^•); (ii) β-cyclodextrins increase the kinetic stability of the spin-adduct EBN/^•SG; and (iii) in aqueous solutions, EBN does not react with superoxide anion radical (O₂^−•) to form EBN/^•OOH to any significant extent. The data presented complement previous studies within the context of synthetic accessibility to EBN and efficient spin-trapping analysis of GS^•.

New insights into the antioxidant activity of hydroxycinnamic and hydroxybenzoic systems: spectroscopic, electrochemistry, and cellular studies

A series hydroxycinnamic and gallic acids and their derivatives were studied with the aim of evaluating their in vitro antioxidant properties both in homogeneous and in cellular systems. It was concluded from the oxygen radical absorbance capacity-fluorescein (ORAC-FL), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and cyclic voltammetry data that some compounds exhibit remarkable antioxidant properties. In general, in homogeneous media (DPPH assay), galloyl-based cinnamic and benzoic systems (compounds 7-11) were the most active, exhibiting the lowest oxidation potentials in both dimethyl sulfoxide (DMSO) and phosphate buffer. Yet, p-coumaric acid and its derivatives (compounds 1-3) disclosed the highest scavenging activity toward peroxyl radicals (ORAC-FL assay). Interesting structure-property- activity relationships between ORAC-FL, or DPPH radical, and redox potentials have been attained, showing that the latter parameter can be a valuable antioxidant measure. It was evidenced that redox potentials are related to the structural features of cinnamic and benzoic systems and that their activities are also dependent on the radical generated in the assay. Electron spin resonance data of the phenoxyl radicals generated both in DMSO and phosphate buffer support the assumption that radical stability is related to the type of phenolic system. Galloyl-based cinnamic and benzoic ester-type systems (compounds 9 and 11) were the most active and effective compounds in cell-based assays (51.13 ± 1.27% and 54.90 ± 3.65%, respectively). In cellular systems, hydroxycinnamic and hydroxybenzoic systems operate based on their intrinsic antioxidant outline and lipophilic properties, so the balance between these two properties is considered of the utmost importance to ensure their performance in the prevention or minimization of the effects due to free radical overproduction.

Electronic paramagnetic resonance (EPR) for the study of ascorbyl radical and lipid radicals in marine organisms

Electron paramagnetic resonance (EPR) spectroscopy detects the presence of radicals of biological interest, such as ascorbyl radical (A(•)) and lipid radicals. A(•) is easily detectable by EPR even in aqueous solution at room-temperature. Under oxidative conditions leading to changes in total ascorbate (AH(-)) content, the A(•)/AH(-) ratio could be used to estimate early oxidative stress in the hydrophilic milieu. This methodology was applied to a wide range of aquatic systems including algae, sea urchin, limpets, bivalves and fish, under physiological and oxidative stress conditions as well. The A(•)/AH(-) ratio reflected the state of one part of the oxidative defense system and provided an early and simple diagnosis of environmental stressing conditions. Oxidative damage to lipids was assessed by the EPR-sensitive adduct formation that correlates well with cell membrane damage with no interference from other biological compounds. Probe instability, tissue metabolism, and lack of spin specificity are drawback factors for employing EPR for in vivo determination of free radicals. However, the dependability of this technique, mostly by combining it with other biochemical strategies, enhances the value of these procedures as contributors to the knowledge of oxidative condition in aquatic organisms.

Post-trapping derivatization of radical-derived EPR-silent adducts: application to free radical detection by HPLC/UV in chemical, biochemical, and biological systems and comparison with EPR spectroscopy

Free radicals are conventionally detected by electron paramagnetic resonance (EPR) spectroscopy after being trapped as spin adducts. Albeit this technique has demonstrated utmost efficacy in studying free radicals, its application to biological settings is intrinsically hampered by the inevitable bioreduction of radical-derived paramagnetic adducts. Herein, we describe a reliable technique to detect and quantify free radical metabolites, wherein reduced alkyl- and phenyl-5,5-dimethyl-1-pyrroline N-oxide (DMPO) adducts are converted into ultrastable N-naphthoate esters. To mimic the ubiquitous in vivo microenvironment, bioreductants, exogenous thiols, and sodium borohydride were studied. Nitroxyl reduction was confirmed using EPR and triphenyltetrazolium chloride. The formation of the N-naphthoyloxy derivatives was established by liquid chromatography/mass spectrometry (LC/MS). The derivatives were chromatographed using a binary eluent. HPLC and internal standards were synthesized using Grignard addition. The labeled DMPO adduct is (1) fluorescent, (2) stable as opposed to nitroxyl radical adducts, (3) biologically relevant, and (4) excellently chromatographed. Applications encompassed chemical, biochemical, and biological model systems generating C-centered radicals. Different levels of phenyl radicals produced in situ from whole blood were successfully determined. The method is readily applicable to the detection of hydroxyl radical. Analogously, DMPO, the spin trap, could be detected with extreme sensitivity suitable for in vivo applications. The developed method proved to be a viable alternative to EPR, where for the first time the reductive loss of paramagnetic signals of DMPO-trapped free radicals is transformed into fluorescence emission. We believe the proposed methodology could represent a valuable tool to probe free radical metabolites in vivo using DMPO, the least toxic spin trap.

Systemically administered tempol reduces neuronal activity in paraventricular nucleus of hypothalamus and rostral ventrolateral medulla in rats

OBJECTIVE

Systemic administration of the superoxide scavenger tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) reduces blood pressure (BP), heart rate (HR) and sympathetic nerve activity in normotensive and hypertensive animals. The global nature of the depressor response to tempol suggests an inhibitory influence on cardiovascular presympathetic regions of the brain. This study examined several possible mechanisms for such an effect.

METHODS AND RESULTS

In urethane anesthetized rats, as expected, intravenous tempol (120 microg mol/kg) reduced mean arterial pressure, HR and renal sympathetic nerve activity (RSNA). Concomitant central neuronal recordings revealed reduced spontaneous discharge (spikes/s) of neurons in the paraventricular nucleus of hypothalamus (from 2.9 +/- 0.4 to 0.8+/- 0.2) and the rostral ventrolateral medulla (RVLM; from 9.8 +/- 0.5 to 7.2 +/-0.4), two cardiovascular and autonomic regions of the brain. Baroreceptor-denervated rats had exaggerated sympathetic and cardiovascular responses. Pretreatment with the hydroxyl radical scavenger dimethyl sulfoxide (intravenous) attenuated the tempol-induced decreases in BP, HR and RSNA, but the nitric oxide synthesis inhibitor NG-nitro-L-arginine methyl ester (intravenous or intracerebroventricular) had no effect.

CONCLUSION

These findings suggest that systemically administered tempol acts upon neurons in paraventricular nucleus and RVLM to reduce BP, HR and RSNA, perhaps by reducing the influence of reactive oxygen species in those regions. The arterial baroreflex modulates the depressor responses to tempol. These central mechanisms must be considered in interpreting data from studies using systemically administered tempol to assess the role of reactive oxygen species in cardiovascular regulation.

Effects of soil cadmium on growth, oxidative stress and antioxidant system in wheat seedlings (Triticum aestivum L.)

Effects of different concentrations of soil cadmium (0-33mg kg(-1)) on growth, oxidative stress, and antioxidant response of wheat seedlings (Triticum aestivum L.) were investigated using pot experiments. A slight stimulatory effect on seedling growth was observed, especially at low Cd concentrations (less than 3.3mg kg(-1)). Results of the electron paramagnetic resonance (EPR) determination showed a decrease in unstable free radical level in the leaves, followed by a significant increase with increasing Cd concentrations. Malondialdehyde (MDA) contents were significantly enhanced by a high Cd concentration. Activity levels of some antioxidant enzymes in the leaves, including superoxide dismutase (SOD, EC1.12.1.1), catalase (CAT, EC1.11.1.6), guaiacol peroxidase (GPX, EC1.11.1.7), ascorbate peroxidase (APX, EC1.11.1.11) and glutathione reductase (GR, EC1.6.4.2), did not change much at low Cd concentrations (less than 3.3mg kg(-1)), but fluctuated drastically at high Cd concentrations. GSH contents and GSH/GSSG ratios decreased at low Cd concentrations, then increased at high Cd concentrations. Wheat seedlings might overcompensate at low Cd concentrations, resulting in a low oxidative stress and a positive effect on growth. Changes in biochemical parameters would occur before any visible symptom of toxicity appeared, and the endpoint based on these parameters might be more sensitive or indicative than morphological observations in revealing the eco-toxicity of Cd. Based on the results of this study, we propose that the toxic critical value of soil Cd in inducing oxidative stress to wheat seedlings is between 3.3mg kg(-1) and 10mg kg(-1).

Unexpected reaction of the unsaturated cluster host and catalyst [Pd3(mu3-CO)(dppm)3]2+ with the hydroxide ion: spectroscopic and kinetic evidence of an inner-sphere mechanism

The title cluster, [Pd(3)(mu(3)-CO)(dppm)(3)](2+) (dppm=bis(diphenylphosphino)methane), reacts with one equivalent of hydroxide anions (OH(-)), from tetrabutylammonium hydroxide (Bu(4)NOH), to give the paramagnetic [Pd(3)(mu(3)-CO)(dppm)(3)](+) species. Reaction with another equivalent of OH(-) leads to the zero-valent compound [Pd(3)(mu(3)-CO)(dppm)(3)](0). From electron paramagnetic resonance analysis of the reaction medium using the spin-trap agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the 2-tetrahydrofuryl or methyl radicals, deriving from the tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO) solvent, respectively, were detected. For both [Pd(3)(mu(3)-CO)(dppm)(3)](2+) and [Pd(3)(mu(3)-CO)(dppm)(3)](+), the mechanism involves, in a first equilibrated step, the formation of a hydroxide adduct, [Pd(3)(mu(3)-CO)(dppm)(3)(OH)]((n-1)+) (n=1, 2), which reacts irreversibly with the solvent. The kinetics were resolved by means of stopped-flow experiments and are consistent with the proposed mechanism. In the presence of an excess of Bu(4)NOH, an electrocatalytic process was observed with modest turnover numbers (7-8). The hydroxide adducts [Pd(3)(mu(3)-CO)(dppm)(3)(OH)]((n-1)+) (n=1, 2), which bear important similarities to the well-known corresponding halide adducts [Pd(3)(mu(3)-CO)(dppm)(3)(mu(3)-X)](n) (X=Cl, Br, I), have been studied by using density functional theory (DFT). Although the optimised geometry for the cluster in its +2 and 0 oxidation states (i.e., cation and anion clusters, respectively) is the anticipated mu(3)-OH form, the paramagnetic species, [Pd(3)(mu(3)-CO)(dppm)(3)(OH)](0), shows a mu(2)-OH form; this suggests an important difference in electronic structure between these three species.

Determination of trace hydroxyl radicals by flow injection spectrofluorometry and its analytical application

On the basis of the fluorescence increase of the reaction of ninhydrin with hydroxyl radicals, a new method for the determination of trace amounts of hydroxyl radicals by flow injection spectrofluorometry is presented. The introduction of flow injection analysis brought better reproducibility and avoided the effect of oxygen and other substances in the environment on the reaction of ninhydrin with hydroxyl radicals. Under optimum experimental conditions, the hydroxylated product of ninhydrin had excitation and emission maxima at 300 and 406 nm, respectively. The linear range was 2.60 x 10(-7) to 4.00 x 10(-5) M, and the limit of detection was 7.91 x 10(-8) M. A high analysis rate of 22 samples per hour was obtained. The proposed method has been applied successfully to the determination of scavenging effects of thiourea and vitamin C on hydroxyl radicals as well as to the evaluation of antioxidant capacities of some natural food.

Imbalance between production and scavenging of hydroxyl radicals in patients maintained on hemodialysis

BACKGROUND

Reactive oxygen species are as being related to the pathophysiology of endstage renal disease (ESRD). We measured the plasma hydroxyl radical (.OH)-producing ability and .OH-scavenging activity in patients with ESRD to clarify the pathophysiological states involved.

METHODS

We used electron spin resonance to measure plasma N-t-butyl-alpha-phenylnitron radical spin adduct (pPBN rsa) as .OH-producing ability and plasma 3,3,5,5-tetramethyl-1-pyrroline-N-oxide radical spin adduct (pM4PO rsa) as .OH-scavenging activity. Oxidative injuries were evaluated by determining oxidised low-density lipoprotein (Ox-LDL).

RESULTS

The pPBN rsa of the ESRD patients was lower than that of the controls (1.83 vs 2.94 micromol/g protein). The pM4PO rsa of the ESRD patients was higher than that of the controls (3.85 vs 3.15 mmol L: -ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H-1-benzopyran-6-yl hydrogen phosphate] potassium salt (EPC-K1)/g protein). The pPBN rsa and pM4PO rsa were correlated, both in the ESRD patients and in the controls (r = 0.47 and r = 0.53). Ox-LDL was correlated with hemodialysis (HD) duration (r = 0.49) and was negatively correlated with pPBN rsa (r = -0.54), which indicates that oxidative stress was increased as HD therapy was prolonged and suppressed pPBN rsa.

CONCLUSIONS

There was an imbalance between .OH-producing ability and .OH-scavenging activity, in the ESRD patients, and this may be responsible for compromising the health of ESRD patients.

Probing the Hydroxyl Radical-Mediated Reactivity of Peroxynitrite by a Spin-Labeling Fluorophore

The decomposition of peroxynitrite at physiological pH yielded a hydroxyl radical, which reacted rapidly with dimethyl sulfoxide (DMSO) to produce a methyl radical (*CH3), which was then trapped by a spin-label fluorophore nitroxide-linked naphthalene (NTEMPO), a carbon-centered radical probe with a low fluorescence intensity, and transformed to a stable diamagnetic O-alkoxyamine, a high-fluorescence compound. The fluorescence increment was proportional to the concentration of the hydroxyl radical, and then to the concentration of peroxynitrite. NTEMPO therefore was demonstrated to be capable of detecting hydroxyl radicals generated from peroxynitrite, and the method was proved to be simple and sensitive. The hydroxyl radical-mediated reactivities of peroxynitrite to several amino acids, such as tyrosine, phenylalanine and histidine, were then evaluated by the spin-labeling fluorophore NTEMPO at pH 7.4 and, 37 degrees C. The obtained data were in good agreement with the reference values, respectively.

Effects of pH on the Cytotoxicity of Sodium Trioxodinitrate (Angeli's Salt)

Tumor tissues have an acidic microenvironment with a pH from 6.0 to 7.0, whereas the intra- and extracellular milieu of normal cells is 7.4. We have found that the hydrolysis of sodium trioxodinitrate (Angeli's salt; 1) to hydroxyl radical (*OH) was 10 times higher at pH = 6.0 than at pH = 7.4. It is hypothesized that the formation of *OH in solutions of 1 reflects the hydrolysis of the latter compound to nitroxyl (HNO) which dimerizes to cis-hyponitrous acid (HO-N=N-OH; 3) with concomitant azo-type homolytic fission to N(2) and *OH. In weakly acidified solutions, 1 exhibited strong toxicity to cancer cells that was inhibited by scavengers of hydroxyl radical, whereas no toxicity was observed at pH = 7.4. In a subcutaneous xenograft model of pheochromocytoma, 1 markedly inhibited tumor growth at a dose that was nontoxic to nude mice. These data suggest that the H(+)-amplified production of *OH from 1, and maybe other precursors of HNO, could be a selective mechanism for destruction cells with an acidic intra- or extracellular microenvironment.

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.

Formation of nitroxyl and hydroxyl radical in solutions of sodium trioxodinitrate: effects of pH and cytotoxicity

Despite its negative redox potential, nitroxyl (HNO) can trigger reactions of oxidation. Mechanistically, these reactions were suggested to occur with the intermediate formation of either hydroxyl radical (.OH) or peroxynitrite (ONOO-). In this work, we present further experimental evidence that HNO can generate.OH. Sodium trioxodinitrate (Na2N2O3), a commonly used donor of HNO, oxidized phenol and Me2SO to benzene diols and.CH3, respectively. The oxidation of Me2SO was O2-independent, suggesting that this process reflected neither the intermediate formation of ONOO- nor a redox cycling of transition metal ions that could initiate Fenton-like reactions. In solutions of phenol, Na2N2O3 yielded benzene-1,2-diol and benzene-1,4-diol at a ratio of 2:1, which is consistent with the generation of free.OH. Ethanol and Me2SO, which are efficient scavengers of.OH, impeded the hydroxylation of phenol. A mechanism for the hydrolysis of Na2N2O3 is proposed that includes dimerization of HNO to cis-hyponitrous acid (HO-N=N-OH) with a concomitant azo-type homolytic fission of the latter to N2 and.OH. The HNO-dependent production of.OH was with 1 order of magnitude higher at pH 6.0 than at pH 7.4. Hence, we hypothesized that HNO can exert selective toxicity to cells subjected to acidosis. In support of this thesis, Na2N2O3 was markedly more toxic to human fibroblasts and SK-N-SH neuroblastoma cells at pH 6.2 than at pH 7.4. Scavengers of.OH impeded the cytotoxicity of Na2N2O3. These results suggest that the formation of HNO may be viewed as a toxicological event in tissues subjected to acidosis.

Inactivation of the 2-oxo acid dehydrogenase complexes upon generation of intrinsic radical species

Self-regulation of the 2-oxo acid dehydrogenase complexes during catalysis was studied. Radical species as side products of catalysis were detected by spin trapping, lucigenin fluorescence and ferricytochrome c reduction. Studies of the complexes after converting the bound lipoate or FAD cofactors to nonfunctional derivatives indicated that radicals are generated via FAD. In the presence of oxygen, the 2-oxo acid, CoA-dependent production of the superoxide anion radical was detected. In the absence of oxygen, a protein-bound radical concluded to be the thiyl radical of the complex-bound dihydrolipoate was trapped by alpha-phenyl-N-tert-butylnitrone. Another, carbon-centered, radical was trapped in anaerobic reaction of the complex with 2-oxoglutarate and CoA by 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO). Generation of radical species was accompanied by the enzyme inactivation. A superoxide scavenger, superoxide dismutase, did not protect the enzyme. However, a thiyl radical scavenger, thioredoxin, prevented the inactivation. It was concluded that the thiyl radical of the complex-bound dihydrolipoate induces the inactivation by 1e- oxidation of the 2-oxo acid dehydrogenase catalytic intermediate. A product of this oxidation, the DMPO-trapped radical fragment of the 2-oxo acid substrate, inactivates the first component of the complex. The inactivation prevents transformation of the 2-oxo acids in the absence of terminal substrate, NAD+. The self-regulation is modulated by thioredoxin which alleviates the adverse effect of the dihydrolipoate intermediate, thus stimulating production of reactive oxygen species by the complexes. The data point to a dual pro-oxidant action of the complex-bound dihydrolipoate, propagated through the first and third component enzymes and controlled by thioredoxin and the (NAD+ + NADH) pool.

Characterization of the initial carbon-centered pentadienyl radical and subsequent radicals in lipid peroxidation: identification via on-line high performance liquid chromatography/electron spin resonance and mass spectrometry

The previously reported combination of an on-line high-performance liquid chromatography (LC)/electron spin resonance (ESR) system with mass spectrometric analysis (MS) created a unique technique to identify a variety of lipid-derived radicals ((.)L(d)) formed from in vitro lipid peroxidation (Iwahashi et al. [20]). To improve the sensitivity, resolution, and reliability of this method for in vitro and in vivo studies, we have investigated the effects of mobile phase pH, modifiers, and columns on the chromatographic separation of linoleic acid-derived radical adducts. Using tetrahydrofuran (THF) and 0.1% glacial acetic acid (HOAc) in an H(2)O/acetonitrile (ACN) mobile phase greatly increased the resolution and retention reproducibility of lipid radical adducts in LC/ESR. In addition, these modifications allowed the elimination of an ESR tuning problem and the synchronization of UV and ESR detection of radical adducts in on-line LC/ESR, neither of which had been possible previously. Analyte purity was therefore increased, thus increasing the reliability of radical detection via on-line LC/ESR as well as radical identification via MS analysis. For the first time, POBN adducts of linoleic carbon-centered pentadienyl radicals (L(.)) were detected and identified. The optimization of chromatography in the LC/ESR and MS combination provided a reliable and sensitive way for the detection and identification of expected radical adducts in vitro and in vivo.

The influence of additives on beer stability investigated by EPR spectroscopy

In thermally-accelerated aging followed by EPR spectroscopy of beer samples of various stabilities, free radical 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPOL) was shown to be an effective indicator of the breakdown of a sample's stability, comparable to the commonly used spin trapping agent alpha-phenyl-N-tert-butylnitrone (PBN). Both indicators were then employed to investigate the influence of additives on beer stability. The addition of L-ascorbic acid (ASC) to the beer samples accelerated the radical processes and a lower stability was found. DL-alpha-tocopherol (alpha-TOC) did not influence beer stability significantly (probably due to its limited solubility). Na2SO3, described as a very effective stabilizer in experiments with the PBN spin trap, was found not to be effective using the TEMPOL indicator. This is probably due to inhibition in the formation of spin adducts or their degradation by Na2SO3.

Bupivacaine hydrochloride induces muscle fiber necrosis and hydroxyl radical formation-dimethyl sulphoxide reduces hydroxyl radical formation

We induced acute skeletal muscle necrosis in rats using bupivacaine hydrochloride and found that both 2,5- and 2,3-dihydroxybenzoic acid significantly increased in skeletal muscle. A single administration of dimethyl sulphoxide, a free radical scavenger, significantly lowered concentrations of 2,5- and 2,3-dihydroxybenzoic acid. These results suggest that dimethyl sulphoxide is an effective hydroxyl radical scavenger and may be useful in the treatment of myopathy.

Botrytis cinerea induces the formation of free radicals in fruits of Capsicum annuum at positions remote from the site of infection

Free radical adducts of the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone have been observed by electron paramagnetic resonance spectroscopy in detached fruits of Capsicum annuum investigated 5 days after infection with Botrytis cinerea. The spectra of these adducts were at a maximum within the soft rot lesion, but they could also be detected at distances up to 50 mm from the edge of the lesion in samples following main vascular bundles. At distances greater than 40 mm, the spectrum of the ascorbate radical was also seen, and at greater distances from the lesion it was the only radical detected. With samples taken from parenchyma tissue adjacent to the vascular bundles there was little adduct formation and the ascorbate radical could be detected, albeit with reduced intensity compared to healthy tissue, at distances as small as 10 mm from the edge of the lesion. This observation of chemical changes at considerable distances from the infected tissue is in contrast to previous observations on the behaviour of other markers of oxidative stress (e.g., 4-hydroxynonenal, malondialdehyde, single-peak free radical, and Fe(III) (g = 4.27) electron paramagnetic resonance signals), where their levels decreased rapidly outside of the soft rot.