Oxidative stress, resulting from an antioxidant/free radical imbalance, is considered to be an important etiologic factor in the patho-physiological changes associated with salt sensitive hypertension. An important unresolved issue in hypertension research is the mechanism for organ damage during the development of the syndrome. Reactive oxygen species (ROS) such as the superoxide radical (02) , hydrogen peroxide (H202), and the hydroxyl radical (OH), may playa critical role in the pathogenesis of hypertension by targeting the very tissue that is responsible for regulating blood pressure, during the hypertensive state. Thus, this study was undertaken to evaluate the antioxidant and free radical status in the DSS rat strain, which has been shown to be an excellent model of salt sensitive hypertension. The antioxidant status was evaluated on the basis of the vascular superoxide dismutase (SOD) and glutathione peroxidase (GPx) levels, and the free radical status was evaluated on the basis of the plasma H20 2 concentration. The levels of malonyldialdehyde (MDA), which is a bio-marker for lipid peroxidation was used to determine the level of oxidative stress in the kidney, liver and brain. The kidney and liver were also subjected to an induced free radical mediated lipid peroxidation, by exposing the tissue to increasing known concentrations of H202 (2.5mM - 15mM). The level of lipid peroxidation was used to assess the tissues antioxidant buffering capacity to an induced free radical "attack". The results have shown that the DSS strain may have a compensatory increase in vascular SOD levels, to counter an increase in 02-. SOD levels were significantly lower during salt loading. The GPx levels were significantly lower in the DSS strain, and showed a slight increase during salt loading. The results demonstrate that the DSS strain has a compromised antioxidant status compared to the DSR strain. The plasma H202concentration displayed non-significant changes in the DSS strain, however salt loading did result in a non-significant increase in the plasma H202 concentration in the DSS strain. The GPx : HZ02 ratio, demonstrated an inadequate increase in GPx levels during salt loading to neutralise this non-significant increase in HzOz concentration. The kidney showed an increased level of in vivo lipid peroxidation, which could implicate increased tissue damage, and thus confirm the kidney as being a target organ during the hypertensive state. The liver and brain showed non-significant differences in the level of in vivo lipid peroxidation and are therefore thought not to be target tissue in the hypertensive state. The kidney displayed a decreased antioxidant buffering capacity to the induced free radical "attack", thereby demonstrating the tissue's decreased ability to neutralise an increased free radical level. Although the liver displayed a "normal" level of in vivo lipid peroxidation, it also displayed a decreased antioxidant buffering capacity to an induced free radical "attack", showing that the liver is able to cope with in vivo free radical levels, but at higher free radical levels, its loses its ability to quench a free radical "attack" and thereby minimise lipid peroxidation. The in vivo lipid peroxidation levels of the kidney, liver and brain have shown that tissues have varying abilities to cope with tissue oxidative stress, and behave differently, in their free radical quenching abilities. These results have shown that a compromised free radical and antioxidant status results in oxidative damage to the tissue responsible for regulating blood pressure. / Thesis (M.Med.Sc.)-University of KwaZulu-Natal, Westville, 2006.

The studies described in this dissertation were performed with the goal of understandingthe function of antioxidant compounds delivered in vivo to rodents and the implication of theresults towards oxidative stress (OS)-related neurodegenerative disorders with particularemphasis on Alzheimer's disease (AD). OS has been implicated in AD and is characterized byextensive oxidative damage to protein, lipids and DNA. A major thrust of this dissertation workwas to gain insight into antioxidant properties of compounds used in the following studies andtheir efficacy as potential therapeutics for treatment of OS-related disorders.D609, a glutathione (GSH) mimetic is known to trap OH. Radicals, scavenge H2O2 andreduce the A?? (1-42)-induced OS and cytotoxicity in neurons. The present dissertation studyshowed in vivo protective effect of D609 in synaptosomes and mitochondria isolated fromgerbils against OS mediated by Fe2+/H2O2, AAPH, and A?? (1-42). Upon intraperitonial (i.p.)injection of gerbils, D609 showed protection of subsequently isolated brain moieties against OS.In vivo administration of D609 also modulates brain GSH levels and increases the activity of keyGSH-related enzymes, thereby likely provides a protection against OS.Adriamycin (ADR), a quinone-containing chemotherapeutic, is known to produce ROS inheart. Patients under treatment with ADR often show persistent changes in cognitive function(effect called as chemobrain by patients). Upon i.p. injection, ADR causes OS, increasesexpression of multidrug resistant protein-1 (MRP-1) in brain and alters GSH levels and itsrelated enzyme activities. ??-Glutamyl cysteinyl ethyl ester (GCEE) is known to increase GSHlevels in brain, in vivo. Research reported in this dissertation shows that in vivo GCEE reversesthe ADR-mediated OS in mice brain.N-acetylcysteine (NAC), a GSH precursor provides the limiting substrate cysteine inGSH synthesis. Previously, our laboratory showed increased GSH levels post i.p. injection ofNAC and reduces OS in synaptosomes treated with acrolein. The present study showed thatNAC given in drinking water to APP/PS-1 mice, a model of AD can significantly reduce OS.These results provide a potential therapeutic intervention by antioxidants that can modulateGSH in OS-mediated neurodegenerative disorders.

No description available.

Laser Magnetic Resonance (LMR) is a very sensitive, accurate and high resolution spectroscopic technique. Transitions of paramagnetic species are brought into coincidence with a fixed frequency laser using Zeeman tuning. Three different LMR spectrometers are described, two of which use the CO laser as a radiation source and the other used optically pumped far-infrared lasers. These LMR spectrometers have been used to study four radicals, germanium hydride (GeH), tellurium deuteride (TeD), iron hydride (FeH) and iron deuteride (FeD). Transitions in the fundamental and first hot bands of the GeH radical have been detected by CO LMR. The transitions occur within both ²Π_{¹andfrasl;₂} and ²Π_{³andfrasl;₂} manifolds. These data have been fitted with previously published data for GeH and GeD to determine the parameters of a single model effective Hamiltonian which describes all naturally occurring isotopomers. Details of the Hamiltonian are given. The same Hamiltonian was used to model transitions in the fundamental and first two hot bands of the TeD radical that were also recorded using CO LMR. Resonances from the seven most abundant isotopomers, including the two with I = ½, have been identified. Seven transitions in the fundamental band of FeH have been observed using Faraday CO LMR. Due to the complicated electronic structure for FeH it is not possible to model these data using a single model effective Hamiltonian. It has been possible to fit the parameters of a second order Zeeman expression to these FeH data and so determine accurate zerofield transition wavenumbers for six of these transitions. Pure rotational transitions in the ground state of FeD have been observed using FIR LMR. As for FeH the parameters of second order Zeeman expressions can be fitted to these transitions and zero field wavenumbers determined.

A liquid nitrogen cooled, carbon monoxide laser magnetic resonance spectrometer was used to study mid-infrared vibration-rotation transitions in the gaseous free radical NCO, in its ̅X²Π state, at very high resolution. The use of an intracavity absorption cell made possible the observation of some transitions with sub-Doppler resolution. Developments to the spectrometer extended the range of operation of the CO laser. Most importantly, a CO laser operating on overtone transitions, Δν = 2, was operated in Oxford. The Δν = 2 CO laser operates over the range 2450-3800cm^-1 (4.08-2.63 μm), and the Δν = 1 CO laser over the range 1200-2100 cm^-1 (8.33-4.76 μm). NCO exhibits a Renner-Teller effect in its ground electronic state, an interaction between the motion of the electrons and the bending motion of the nuclei. Vibration-rotation transitions were observed in a sequence of bands involving the excitation of the out-of-phase stretching vibration, in the region of 1900cm^-1. Some of the bands involved the excited bending vibration. The Zeeman effect behaviour of the molecular energy levels, particularly in the ²Σ vibronic states, clearly showed the manifestation of the Renner-Teller effect. The Zeeman effect in the ²Σ vibronic states was considered in detail. Many of the ²Σ LMR spectra were recorded at sub-Doppler resolution. NCO is complicated to model, and unassigned LMR spectra remain. A harmonic Renner-Teller model was developed for the analysis. It was implemented by constructing an explicit matrix representation of the single electronic state N² effective Hamiltonian, which was diagonalised exactly. A new term in this Hamiltonian, describing centrifugal distortion corrections to the Renner-Teller coupling term, was developed for the ²Σ vibronic states in order to account for anharmonic vibronic interactions.

o,o???-Dityrosine (dityrosine), an oxidation product of tyrosine produced by reaction between tyrosyl radicals, is becoming established as a biomarker of free radical oxidative protein damage in vivo. Attempts to measure dityrosine concentrations in various physiological and pathological systems have produced varied and often contradictory results. Dityrosine concentrations in urine, plasma, cerebrospinal fluid (CSF) and brain tissue varying over three orders of magnitude have been reported, together with inconsistent claims of significant dityrosine elevation in several ageing-related pathologies. Some of these findings have contributed to the implication of free radical activity in the pathology of several neurodegenerative disorders, vascular and ocular abnormalities and in phagocyte response to infection. The aim of this study was to test the hypothesis that dityrosine levels are elevated in ageing and ageing-related disease. The study also aims to determine the utility of dityrosine measurement as an index of oxidative damage, and elucidate possible explanations for the inconsistent levels reported. An assay for the quantification of dityrosine was developed using capillary HPLC with electrospray tandem quadrupole mass spectrometry (HPLC-MS/MS). The assay was highly specific for dityrosine and has the highest absolute sensitivity for dityrosine of any method reported to date, with a detection limit of 3 femtomoles of dityrosine on-column. Urine samples from volunteers of different age and from hospital patients with various pathologies were analysed. Plasma protein hydrolysates from control, Alzheimer???s and stroke subjects were analysed, together with hydrolysates of post mortem brain tissue from Alzheimer???s and control subjects. Urinary dityrosine level is elevated in states of acute infection and inflammation, but does not correlate with age or chronic disease. Protein dityrosine in four sections of Alzheimer???s brain was not significantly different from control sections. Dityrosine was present in human plasma and tissue proteins at approximately 5-35 residues per million tyrosine residues, and in normal urine at 5-25 micromol/mol creatinine or 20-200 nM. Most of the discrepancies in the literature relate to inadequate specificity of the analytical method. Interpretation of published data with critical appraisal of measurement technology specificity is essential in developing an accurate understanding of the role of free radicals in ageing and disease.

Abstract This work investigates the kinetics of the emulsion polymerization of vinyl acetate. Several aspects of this system have been clarified, including the induced decomposition of persulfate, retardation by oxygen and entry by, and analysis of, the aqueous phase oligomeric radicals. It has been shown that the retardation period observed in the emulsion polymerization of VAc can be explained by the effect of traces of oxygen (< 10-6 M) on the entry efficiency of the initiator-derived aqueous-phase oligomeric radicals. Comparison of rates of polymerization in V and persulfate -initiated polymerizations together with electrospray mass spectrometry of aqueous phase oligomers, has shown that the mechanism for the induced decomposition of persulfate by vinyl acetate is chain transfer to initiator from aqueous-phase oligomeric radicals. A value has been determined for the rate coefficient for transfer to initiator, by fitting literature data to a model based on this mechanism. The reported independence of the rate of polymerization from the monomer concentration in the emulsion polymerization of vinyl acetate has been investigated. Possible explanations for this behaviour have been proposed and tested in this work, by measuring radical-loss rates directly with y-relaxation techniques. Although the Y relaxations were found to be affected by experimental artefacts, it has been demonstrated that rapid exit is not responsible for the high radical-loss rates in this system. The major artefact identified in the y relaxations was the significant effect of relatively small exotherms on relaxation behaviour, Methodologies were developed for correcting affected data and for avoiding exotherms under certain conditions. Arrhenius parameters were determined for the rate coefficient for chain transfer to monomer using the In^M method, which utilises the whole MWD. This section of the work is incomplete, for reasons detailed in chapter 5. However, as a preliminary indication it was found that the frequency factor was 106.38 M-1 s-1 and the activation energy was 38.8 kJ mol-1.

Doctor of Philosophy (PhD) / This thesis primarily details the application of high-level ab initio quantum chemistry techniques in order to understand aspects of free-radical mediated protein oxidation. Traditionally, product analysis and electron paramagnetic resonance (EPR) spectroscopy are the primary means for elucidating the chemistry of protein oxidation. However, in experiments involving relatively small proteins reacting with a controlled radical-flux, a vast array of compounds can be produced, which are often difficult to analyse. Quantum chemical techniques on the other hand, can calculate the properties of any particular species directly, without suffering from the problems associated with experiment, such as side-reactions and chain processes. The results presented in this thesis are aimed at elucidating mechanistic details of protein oxidation, which might otherwise be difficult to probe experimentally. Chapter 1 gives an overview of the free-radical hypothesis of disease and ageing. Protein-derived radicals can undergo a variety of reactions, with the particular reaction that occurs depending on numerous aspects. Many types of reactions have been identified through radiolysis experiments of amino acids, and these are detailed in this chapter. In addition, the key reactive species are characterized and their different chemistries explained. Chapter 2 details the theoretical tools used throughout this thesis. Species with unpaired electrons (radicals) present unique problems for quantum chemistry to handle, thus an appropriate choice of theoretical technique is needed. The approach taken in this thesis is to use high-level compound methods, many of which have been directly formulated to give improved results for radical species, to provide benchmark quality results by which other less demanding techniques can be assessed. During the course of this study, it became apparent there was a void in the armoury of tools that could be used for the theoretical chemistry calculations. Chapter 3 details the formulation of a new tool in an attempt to fill this gap. Historically, the formulation of this new procedure came after much of the work in this thesis had been carried out. Thus, for the study of many of the reactions of this thesis the new method has not been used. However, it is most appropriate to place its formulation after summarizing the current status of techniques in common use today. Chapters 4 and 5 detail computations carried out on models of peptides containing backbone carbon- and nitrogen-centered radicals. A number of different theoretical techniques are used in these chapters, ranging from the highly accurate and computationally intensive to the less reliable and less demanding. The highly accurate techniques are used to gauge the accuracy of the other less demanding theoretical techniques so that the latter can be used with confidence in larger systems. Not only is the choice of theoretical technique important but also the judicious choice of model is essential. With this in mind, models are incrementally built until convergence of the particular property of interest is reached. Chapters 6 and 7 detail the calculations of β-scission reactions of alkoxyl radicals, which are a particular class of reaction known to occur on peptide backbones. Alkoxyl radicals are particularly difficult for theory to describe correctly. Therefore, Chapter 6 extensively assesses and then identifies the theoretical methods needed to portray them. Chapter 7 uses the techniques identified in the previous chapter in order to predict how the preference for a particular type of β-scission reaction changes.

Thesis (Ph.D.)--McMaster University (Canada), 1992. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6173. Adviser: J. Warkentin.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 415-446).