A study of the radiation degradation of styrene/alkane and α-methylstyrene/alkane copolymers

The effects of copolymer composition and microstructure on the radiation chemistry of styrene/alkane and alpha-methylstyrene/alkane copolymers have been studied. The primary radical species formed on radiolysis of the copolymers at 77 K, and identified by ESR spectroscopy, are the same as those formed during radiolysis of the homopolymers. The yields of radicals for the copolymer are as predicted assuming that the cross-section is proportional to the electron density of each component; however, there is some evidence of radical migration to aromatic groups at 77 K. Changes in molecular structure on irradiation were detected by using C-13 NMR spectroscopy. Evidence of the consumption of terminal double bonds, and chain scission in alpha-methylstyrene/alkane copolymers was found. Measurements of viscosity supported the mechanism of cross-linking predominating in styrene/alkane copolymers, while in alpha-methylstyrene/alkane copolymers chain scission was the major result of irradiation. (C) 2003 Society of Chemical Industry.

A study of the radiation chemistry of poly(chlorotrifluoroethylene) by ESR spectroscopy

The ESR spectra of poly(chlorotrifluoroethylene) were recorded following gamma-radiolysis under vacuum at room temperature and 77 K. The very broad spectrum at 77 K revealed little fine structure with which to identity the radicals formed upon irradiation, but subsequent photobleaching and annealing studies, together with radiolytic studies at higher temperatures, afforded scope for making radical assignments. Both main-chain radicals and a range of chain-end radicals have been identified. The G-values for radical formation were 1.55, 0.36 and 0.32 at 77 K, 273 K and room temperature, respectively. (C) 2003 Elsevier Science Ltd. All rights reserved.

Molecular analysis of the pathway for the synthesis of thiol tripeptides in the model legume Lotus japonicus

The thiol tripeptides, glutathione (GSH) and homoglutathione (hGSH), perform multiple roles in legumes, including protection against toxicity of free radicals and heavy metals. The three genes involved in the synthesis of GSH and hGSH in the model legume, Lotus japonicus, have been fully characterized and appear to be present as single copies in the genome. The gamma-glutamylcysteine synthetase (gammaecs) gene was mapped on the long arm of chromosome 4 (70.0 centimorgans [cM]) and consists of 15 exons, whereas the glutathione synthetase (gshs) and homoglutathione synthetase (hgshs) genes were mapped on the long arm of chromosome 1 (81.3 cM) and found to be arranged in tandem, with a separation of approximately 8 kb. Both genes consist of 12 exons of exactly the same size (except exon 1, which is similar). Two types of transcripts were detected for the gshs gene, which putatively encode proteins localized in the plastids and cytosol. Promoter regions contain cis-acting regulatory elements that may be involved in the plant's response to light, hormones, and stress. Determination of transcript levels, enzyme activities, and thiol contents in nodules, roots, and leaves revealed that gammaecs and hgshs are expressed in all three plant organs, whereas gshs is significantly functional only in nodules. This strongly suggests an important role of GSH in the rhizobia-legume symbiosis.

Discoloration and mineralization of Reactive Red HE-3B by heterogeneous photo-Fenton reaction

Discoloration and mineralization of Reactive Red HE-3B were studied by using a laponite clay-based Fe nanocomposite (Fe-Lap-RD) as a heterogeneous catalyst in the presence of H2O2 and UV light. Our experimental results clearly indicate that Fe-Lap-RD mainly consists of Fe2O3 (meghemite) and Fe2Si4O10(OH)2 (iron silicate hydroxide) which have tetragonal and monoclinic structures, respectively, and has a high specific surface area (472m(2) / g) as well as a high total pore volume (0.547 cm(3)/g). It was observed that discoloration of HE-3B undergoes a much faster kinetics than mineralization of HE-3B. It was also found that initial HE-3B concentration, H2O2 concentration, UV light wavelength and power, and Fe-Lap-RD catalyst loading are the four main factors that can significantly influence the mineralization of HE-3B. At optimal conditions, complete discoloration of 100 mg/L HE-3B can be achieved in 30 min and the total organic carbon removal ratio can attain 76% in 120 min, illustrating that Fe-Lap-RD has a high photo-catalytic activity in the photo-assisted discoloration and mineralization of HE-3B in the presence of UV light (254nm) and H2O2. (C) 2003 Elsevier Science Ltd. All rights reserved.

Alpha-lipoic acid does not acutely affect resistance and conduit artery function or oxidative stress in healthy men

Aims Alpha-lipoic acid (ALA) is a thiol compound with antioxidant properties used in the treatment of diabetic polyneuropathy. ALA may also improve arterial function, but there have been scant human trials examining this notion. This project aimed to investigate the effects of oral and intra-arterial ALA on changes in systemic and regional haemodynamics, respectively. Methods In study 1, 16 healthy older men aged 58 +/- 7 years (mean +/- SD) received 600 mg of ALA or placebo, on two occasions 1 week apart, in a randomized cross-over design. Repeated measures of peripheral and central haemodynamics were then obtained for 90 min. Central blood pressure and indices of arterial stiffness [augmentation index (AIx) and estimated aortic pulse wave velocity] were recorded non-invasively using pulse wave analysis. Blood samples obtained pre- and post-treatments were analysed for erythrocyte antioxidant enzyme activity, plasma nitrite and malondialdehyde. In study 2 the effects of incremental cumulative doses (0.5, 1.0, 1.5 and 2.0 mg ml(-1) min(-1)) of intra-arterial ALA on forearm blood flow (FBF) were assessed in eight healthy subjects (aged 31 +/- 5 years) by conventional venous occlusion plethysmography. Results There were no significant changes on any of the central or peripheral haemodynamic measures after either oral or direct arterial administration of ALA. Plasma ALA was detected after oral supplementation (95% confidence intervals 463, 761 ng ml(-1)), but did not alter cellular or plasma measures of oxidative stress. Conclusions Neither oral nor intra-arterial ALA had any effect on regional and systemic haemodynamics or measures of oxidative stress in healthy men.

The impact of carboxy nitroxide antioxidants on irradiated ataxia telangiectasia cells

Three water-soluble carboxy nitroxide antioxidants, 5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl, 4-carboxy-2,2,6,6-tetramethylpiperidin-1-yloxyl, and 3-carboxy-2,2,5,5-tetramethylpyrrolidin-1-yloxyl, show significant impact on the postirradiation survival rates of ataxia telangiectasia (A-T) cells compared to normal cells, an assay which represents a model for understanding the impact of ROS damage on the A-T phenotype. The effects of these antioxidants are much more significant than those of vitamin E or Trolox (a water-soluble vitamin E analog), studied using the same cell survival model. (C) 2004 Elsevier Inc. All rights reserved.

Endurance exercise, plasma oxidation and cardiovascular risk

Objective-Although physical activity is beneficial to health, people who exercise at high intensities throughout their lifetime may have increased cardiovascular risk. Aerobic exercise increases oxidative stress and may contribute to atherogenesis by augmented oxidation of plasma lipoproteins. The aim of this study was to examine the relationship between aerobic power and markers of oxidative stress, including the susceptibility of plasma to oxidation. Methods and results-Aerobic power was measured in 24 healthy men aged 29 9 years (mean +/- SD). Plasma was analysed from subjects of high aerobic power (HAP; VO(2)max, 64.6 +/- 6.1 ml/kg/min) and lower aerobic power (LAP;VO(2)max, 45.1 +/- 6.3 ml/kg/min) for total antioxidant capacity (TAC), malondialdehyde (MDA) and susceptibility to oxidation. Three measures were used to quantify plasma oxidizability: (1) lag time to conjugated diene formation (lag time); (2) change in absorbance at 234 nm and; (3) slope of the oxidation curve during propagation (slope). The HAP subjects had significantly lowerTAC (1.38 +/- 0.04 versus 1.42 +/- 0.06 TEAC units; P < 0.05), significantly higher change in absorbance (1.55 +/- 0.21 versus 1.36 +/- 0.17 arbitrary units; P < 0.05), but no difference in MDA (P = 0.6), compared to LAP subjects. There was a significant inverse association between TAC and slope (r = -0.49; P < 0.05). Lipoprotein profiles and daily intake of nutrients did not differ between the groups. Conclusions-These findings suggest that people with high aerobic power, due to extreme endurance exercise, have plasma with decreased antioxidant capacity and higher susceptibility to oxidation, which may increase their cardiovascular risk.

Electron transfer in acetohydroxy acid synthase as a side reaction of catalysis. implications for the reactivity and partitioning of the carbanion/enamine form of (alpha-hydroxyethyl)thiamin diphosphate in a "nonredox" flavoenzyme

Acetohydroxy acid synthases (AHAS) are thiamin diphosphate- (ThDP-) and FAD-dependent enzymes that catalyze the first common step of branched-chain amino acid biosynthesis in plants, bacteria, and fungi. Although the flavin cofactor is not chemically involved in the physiological reaction of AHAS, it has been shown to be essential for the structural integrity and activity of the enzyme. Here, we report that the enzyme-bound FAD in AHAS is reduced in the course of catalysis in a side reaction. The reduction of the enzyme-bound flavin during turnover of different substrates under aerobic and anaerobic conditions was characterized by stopped-flow kinetics using the intrinsic FAD absorbance. Reduction of enzyme-bound FAD proceeds with a net rate constant of k' = 0.2 s(-1) in the presence of oxygen and approximately 1 s(-1) under anaerobic conditions. No transient flavin radicals are detectable during the reduction process while time-resolved absorbance spectra are recorded. Reconstitution of the binary enzyme-FAD complex with the chemically synthesized intermediate 2-(hydroxyethyl)-ThDP also results in a reduction of the flavin. These data provide evidence for the first time that the key catalytic intermediate 2-(hydroxyethyl)ThDP in the carbanionic/enamine form is not only subject to covalent addition of 2-keto acids and an oxygenase side reaction but also transfers electrons to the adjacent FAD in an intramolecular redox reaction yielding 2-acetyl-ThDP and reduced FAD. The detection of the electron transfer supports the idea of a common ancestor of acetohydroxy acid synthase and pyruvate oxidase, a homologous ThDP- and FAD-dependent enzyme that, in contrast to AHASs, catalyzes a reaction that relies on intercofactor electron transfer.

Defenses against oxidative stress in Neisseria gonorrhoeae and Neisseria meningitidis: Distinctive systems for different lifestyles

Defenses against oxidative stress are crucial for the survival of the pathogens Neisseria meningitidis and Neisseria gonorrhoeae. An Mn(II) uptake system is involved in manganese (Mn)-dependent resistance to superoxide radicals in N. gonorrhoeae. Here, we show that accumulation of Mn also confers resistance to hydrogen peroxide killing via a catalase-independent mechanism. An mntC mutant of N. meningitidis is susceptible to oxidative killing, but supplementation of growth media with Mn does not enhance the organism's resistance to oxidative killing. N. meningitidis is able to grow in the presence of millimolar levels of Mn ion, in contrast to N. gonorrhoeae, whose growth is retarded at Mn concentrations >100 mumol/L, indicating that Mn homeostasis in the 2 species is probably quite different. N. meningitidis superoxide dismutase B plays a role in protection against oxidative killing. However, a sodC mutant of N. meningitidis is no more sensitive to oxidative killing than is the wild type. A cytochrome c peroxidase (Ccp) is present in N. gonorrhoeae but not in N. meningitidis. Investigations of a ccp mutant revealed a role for Ccp in protection against hydrogen peroxide killing. These differences in oxidative defenses in the pathogenic Neisseria are most likely a result of their localization in different ecological niches.

Photodissociation of benzene under collision-free conditions: An ab initio/Rice-Ramsperger-Kassel-Marcus study

The ab initio/Rice-Ramsperger-Kassel-Marcus (RRKM) approach has been applied to investigate the photodissociation mechanism of benzene at various wavelengths upon absorption of one or two UV photons followed by internal conversion into the ground electronic state. Reaction pathways leading to various decomposition products have been mapped out at the G2M level and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for C6H5+H, C6H4+H-2, C4H4+C2H2, C4H2+C2H4, C3H3+C3H3, C5H3+CH3, and C4H3+C2H3 have been calculated subsequently using both numerical integration of kinetic master equations and the steady-state approach. The results show that upon absorption of a 248 nm photon dissociation is too slow to be observable in molecular beam experiments. In photodissociation at 193 nm, the dominant dissociation channel is H atom elimination (99.6%) and the minor reaction channel is H-2 elimination, with the branching ratio of only 0.4%. The calculated lifetime of benzene at 193 nm is about 11 mus, in excellent agreement with the experimental value of 10 mus. At 157 nm, the H loss remains the dominant channel but its branching ratio decreases to 97.5%, while that for H-2 elimination increases to 2.1%. The other channels leading to C3H3+C3H3, C5H3+CH3, C4H4+C2H2, and C4H3+C2H3 play insignificant role but might be observed. For photodissociation upon absorption of two UV photons occurring through the neutral hot benzene mechanism excluding dissociative ionization, we predict that the C6H5+H channel should be less dominant, while the contribution of C6H4+H-2 and the C3H3+C3H3, CH3+C5H3, and C4H3+C2H3 radical channels should significantly increase. (C) 2004 American Institute of Physics.

Mutation in mitochondrial DNA as a cause of presbyacusis

Much of the hearing loss that occurs in old age is likely to be due to the long-term deterioration of the mitochondria in the different structures of the cochlea. The current review surveys some of the basic information on mitochondria and mitochondrial DNA, as a background to their possible involvement in presbyacusis. It is likely that oxygen radicals damage mitochondrial DNA and other components of the mitochondria, such as their proteins and lipids. This further compromises both oxidative phosphorylation and the repair processes in mitochondria, setting up a vicious cycle of degradation. Evidence is presented from inherited point mutations on the possibly most critical sites for mutations in mitochondrial DNA associated with hearing loss. It is suggested that random sorting and clonal expansion of mutations both maintain the integrity of the pool of mitochondrial DNA molecules and give rise to the apoptosis that leads to loss of vulnerable cells, and hence to deafness. It is moreover suggested that apoptosis of the vulnerable cells of the inner ear may to some extent be preventable, or at least delayed. Copyright (C) 2004 S. Karger AG, Basel.

Caveolins in the repair phase of acute renal failure after oxidative stress

Ischaemia-reperfusion and toxic injury are leading causes of acute renal failure (ARF). Both of these injury initiators use secondary mediators of damage in oxygen-derived free radicals. Several recent publications about ischaemia-reperfusion and toxin-induced ARF have indicated that plasma membrane structures called caveolae, and their proteins, the caveolins, are potential participants in protecting or repairing renal tissues. Caveolae and caveolins have previously been ascribed many functions, a number of which may mediate cell death or survival of injured renal cells. This review proposes possible pathophysiological mechanisms by which altered caveolin-1 expression and localization may affect renal cell survival following oxidative stress.

Role of oxidative stress in age-associated chronic kidney pathologies

The kidneys exhibit age-associated deterioration in function via a loss of 20% to 25% kidney mass, particularly from the renal cortex and increased fibrosis. Oxidative stress has been found to mediate age-associated renal cell injury and cell death, particularly apoptosis. Oxidative stress results from an imbalance between the levels of free radicals generated during aerobic metabolism, inflammation, and infection and the safe breakdown of these species by endogenous and exogenous scavengers. Other factors may influence these pathologies. For example, growth hormone and caloric restriction have been shown to influence life span, although neither method of prolonging life is likely to find general acceptance in humans. Some genetic knockout models offer promise; for example, knockout of the p66 isoform of the Shc gene in mice increases life span by 30%, but appetite, size, and fertility are retained. Whether the increase in life span is via increased kidney health is not yet clear, but decreasing the age-related renal pathologies will no doubt aid in increasing life span and health in general. This review looks at the role and modulation of factors that influence life span, in particular modulation of oxidative stress, with particular relevance to age-related renal pathologies. (C) 2005 by the National Kidney Foundation, Inc.

Neuroprotectant effects of iso-osmolar D-mannitol to prevent Pacific ciguatoxin-1 induced alterations in neuronal excitability: A comparison with other osmotic agents and free radical scavengers

The basis for the neuroprotectant effect of D-mannitol in reducing the sensory neurological disturbances seen in ciguatera poisoning, is unclear. Pacific ciguatoxin-1 (P-CTX-1), at a concentration 10 nM, caused a statistically significant swelling of rat sensory dorsal root ganglia (DRG) neurons that was reversed by hyperosmolar 50 MM D-mannitol. However, using electron paramagnetic resonance (EPR) spectroscopy, it was found that P-CTX-1 failed to generate hydroxyl free radicals at concentrations of toxin that caused profound effects on neuronal excitability. Whole-cell patch-clamp recordings from DRG neurons revealed that both hyper- and iso-osmolar 50 MM D-mannitol prevented the membrane depolarisation and repetitive firing of action potentials induced by P-CTX-1. In addition, both hyper- and iso-osmolar 50 MM D-mannitol prevented the hyperpolarising shift in steady-state inactivation and the rise in leakage current through tetrodotoxin (TTX)-sensitive Na-v channels, as well as the increased rate of recovery from inactivation of TTX-resistant Nav channels induced by P-CTX-1. D-Mannitol also reduced, but did not prevent, the inhibition of peak TTX-sensitive and TTX-resistant I-Na amplitude by P-CTX-1. Additional experiments using hyper- and isoosmolar D-sorbitol, hyperosmolar sucrose and the free radical scavenging agents Trolox (R) and L-ascorbic acid showed that these agents, unlike D-mannitol, failed to prevent the effects of P-CTX-1 on spike electrogenesis and Na-v channel gating. These selective actions of D-mannitol indicate that it does not act purely as an osmotic agent to reduce swelling of nerves, but involves a more complex action dependent on the Nav channel subtype, possibly to alter or reduce toxin association. (c) 2005 Elsevier Ltd. All rights reserved.