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Showing 1801–1820 of 2058 publications.
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Dean, Roger T.[No abstract available]
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Al-Assaf, Saphwan; Hawkins, Clare L.; Parsons, Barry J.; Davies, Michael J.; Phillips, Glyn OwenThe reaction of hydroxyl radical s generated using a Ti(III)-H<inf>2</inf>O<inf>2</inf> redox couple with hyaluronan and cross-linked derivatives (hylan) has been studied using a rapid-flow electron paramagnetic resonance spectroscopy (EPR) system. Radical s were detected as a result of hydrogen atom abstraction from the carbohydrate at pH 3.6; these gave rise to both ralatively broad and sharp isotropic features. The broad signals are assigned to high-molecular-weight hyaluronan-derived radicals, whereas the isotropic features are due to rapidly tumbling radicals present either at the ends of the polymer or on low-molecular-weight fragments. These isotropic signals have been interpreted in terms of the presence of two major radicals; one of these gives rise to a doublet signal (a<inf>H</inf> 1.36 mT, g 2.0049), the other a doublet of doublets (a<inf>?-.H</inf> 1.86 mT, a<inf>?-H</inf> 0-81 mT, g 2.0035). The former signal has parameters identical to those observed for the radical generated as a result of hydrogen abstracti on from the C<inf>5</inf> position of the mode compound glucuronic acid, and is therefore assigned to this species on the polymer. The second signal, which has parameters characteristic of a radical with both ?-H and ?-H splittings, is believed to be generated as a result of hydrogen abstraction from C<inf>6</inf> on the N-acetyl-D-glucosamine monomer. Less intense signals were observed with the cross-linked material hylan, in accord with previous data which show that this material is less readily degraded than the linear polymer. These EPR data fully support the chai n scission processes previously proposed for aqueous hyaluronan and hylan systems, where each hydroxyl radical results in a singl e chain scission. 1999 Elsevier Science Ltd. All rights reserved.
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Silvester, Julie A.; Timmins, Graham S.; Davies, Michael J.Porphyrin-sensitized photoxidation of bovine serum albumin (BSA) results in oxidation of the protein at (at least) two different, specific sites: the Cys-34 residue giving rise to a thiyl radical (RS); and one or both of the tryptophan residues (Trp-134 and Trp-214) resulting in the formation of tertiary carbon-centred radicals and disruption of the tryptophan ring system. In the case of porphyrins such as hematoporphyrin, which bind at specific sites on BSA, these species appear to arise via long-range transfer of damage within the protein structure, as the binding site is some distance from the ultimate site of radical formation. This transfer of damage is shown to depend on a number of factors including the conformation of the protein, the presence of blocking groups and pH. Alteration of the protein conformation results in radical formation at additional (or alternative) sites, as does blocking of the preferred loci of radical formation. The formation of these thiyl and tryptophan-derived radicals does not lead to significant aggregation or fragmentation of the protein, though it does result in a dramatic enhancement in the susceptibility of the oxidised protein to proteolytic degradation by a range of proteases. The generation of protein-derived radicals also results in an enhancement of photobleaching of the porphyrin, suggesting that protein radical generation is linked to porphyrin photooxidation.
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Morin, Bicte; Davies, Michael J.; Dean, Roger T.A major product of hydroxy-radical addition to tyrosine is 3,4-dihydroxyphenylalanine (DOPA) which has reducing properties. Protein-bound DOPA (PB-DOPA) has been shown to be a major component of the stable reducing species formed during protein oxidation under several conditions. The aim of the present work was to investigate whether DOPA, and especially PB-DOPA, can mediate oxidative damage to DNA. We chose to generate PB-DOPA using mushroom tyrosinase, which catalyses the hydroxylation of tyrosine residues in protein. This permitted us to study the reactions of PB-DOPA in the virtual absence of other protein-bound oxidation products. The formation of two oxidation products of DNA, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8oxodG) and 5-hydroxy-2'-deoxycytidine (50HdC), were studied with a novel HPLC using gradient elution and an electrochemical detection method, which allowed the detection of both DNA modifications in a single experiment. We found that exposure of calf thymus DNA to DOPA or PB-DOPA resulted in the formation of 8oxodG and 50HdC, with the former predominating. The formation of these DNA oxidation products by either DOPA or PB-DOPA depended on the presence of oxygen, and also on the presence and on the concentration of transition metal ions, with copper being more effective than iron. The yields of 8oxodG and 50HdC increased with DOPA concentration in proteins. Thus PB-DOPA was able to promote further radical-generating events, which then transferred damage to other biomolecules such as DNA.
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Gelissen, Ingrid C.; Hochgrebe, Tim T.; Wilson, Mark R.; Easterbrook-Smith, Simon B.; Jessup, Wendy K.; Dean, Roger T.; Brown, Andrew J.Apolipoprotein J (apo J) is a secreted glycoprotein of which the exact function remains a matter for speculation. Apo J has been implicated in such diverse processes as sperm maturation, regulation of complement activation, programmed cell death, tissue remodelling and lipid transport. In this study a possible role for apo J in lipid transport was explored. Mouse peritoneal macrophages were incubated with acetylated low-density lipoprotein (AcLDL) to produce foam cells containing cholesterol and cholesteryl esters. Incubation of the foam cells with physiological concentrations of purified apo J led to a dose-dependent export of cholesterol. The appearance of cholesterol in the medium was associated predominantly with a decline in intracellular cholesteryl esters rather than intracellular free cholesterol. The kinetics of cholesterol release to apo J were similar to apo A-I, an established promoter of cholesterol efflux. Apo J was also shown to induce phospholipid efflux from cells, whereas the cholesterol exported to the medium was associated with the apo J. Studies using foam cells from apo E-null mice showed that the cholesterol exported to the medium was independent of apo E production by the cells. These results present the first evidence that apo J can promote cholesterol efflux from foam cells and indicates that it might have a function in cellular cholesterol homoeostasis in both normal and pathological situations.
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Waldeck, A. Reginald; van Dam, Karel; Berden, Jan A.; Kuchel, Philip W. WilliamA non-equilibrium thermodynamics (NET) model describing the action of completely coupled or 'slipping' reconstituted Ca2+-ATPase is presented. Variation of the coupling stoichiometries with the magnitude of the electrochemical gradients, as the ATPase hydrolyzes ATP is an indication of molecular slip. However the Ca2+ and H+ membrane-leak conductances may also be a function of their respective gradients. Such non-ohmic leak typically yields 'flow-force' relationships that are similar to those that are obtained when the pump slips; hence, caution needs to be exercised when interpreting data of Ca2+-ATPase-mediated fluxes that display a non-linear dependence on the electrochemical proton (???(H)) and/or calcium gradients (???(Ca)). To address this issue, three experimentally verifiable relationships differentiating between membrane leak and enzymic slip were derived. First, by measuring ???(H) as a function of the rate of ATP hydrolysis by the enzyme. Second, by measuring the overall 'efficiency' of the pump as a function of ???(H). Third, by measuring the proton ejection rate by the pump as a function of its ATP hydrolysis rate.
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Hawkins, Clare L.; Davies, Michael J.Degradation of hyaluronic acid by oxidants such as HO and HOCl/ClO- is believed to be important in the progression of rheumatoid arthritis. While reaction of hyaluronic acid with HO has been investigated extensively, reaction with HOCl/ClO- is less well defined. Thus, little is known about the site(s) of HOCl/ClO- attack, the intermediates formed, or the mechanism(s) of polymer degradation. In this study reaction of HOCl/ClO- with amides, sugars, polysaccharides, and hyaluronic acid has been monitored by UV-visible (220-340 nm) and EPR spectroscopy. UV-visible experiments have shown that HOCl/ClO- reacts preferentially with N-acetyl groups. This reaction is believed to give rise to transient chloramide (R-NCl-C(O)-R') species, which decompose rapidly to give radicals via either homolysis (to produce N and Cl) or heterolysis (one-electron reduction, to give N and Cl-) of the N-Cl bond. The nature of the radicals formed has been investigated by EPR spin trapping. Reaction of HOCl/ClO- with hyaluronic acid, chondroitin sulphates A and C, N-acetyl sugars, and amides gave novel, carbon-centered, spin adducts, the formation of which is consistent with selective initial attack at the N-acetyl group. Thus, reaction with hyaluronic acid and chondroitin sulphate A, appears to be localized at the N- acetylglucosamine sugar rings. These carbon-centered radicals are suggested to arise from rapid rearrangement of initial nitrogen-centered radicals, formed from the N-acetyl chloramide, by reactions analogous to those observed with alkoxyl radicals. The detection of increasing yields of low-molecular- weight radical adducts from hyaluronic acid and chondroitin sulphate A with increasing HOCl/ClO- concentrations suggests that formation of the initial nitrogen-centered species on the N-acetylglucosamine rings, and the carbon- centered radicals derived from them, brings about polymer fragmentation.
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Bartlett, Anna L.; Stanley, Keith K.Desialylation has been proposed as a natural modification of low density lipoprotein (LDL) increasing atherogenicity. The glactose (Gal)-specific lectin, Ricinus communis agglutinin I (RCA120), has been used to analyse LDL prepared by different methods and it was found that more than 96% of LDL binds to the lectin. The bound LDL could be eluted with Gal or Lactose (Lac), but not with sialic acid, mannose (Man), glucose (Glu) or sodium chloride, indicating that binding occurs via exposed Gal residues on the LDL particle. When freshly isolated whole plasma was loaded on an RCA<inf>120</inf> column, apo B- containing lipoproteins (including LDL) were quantitative bound, whereas other glycosylated serum proteins, like tranferrin, were not. Thus desialylation of LDL is not a consequence of its isolation from plasma, or a general property of all serum proteins. Analysis of apolipoprotein B from LDL indicates that only monodesialylated oligosaccharide chains are present, consistent with the rapid clearance of particles having biantennary Gal residues exposed.
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Thomas, Shane R.; Davies, Michael J.; Stocker, RolandAs peroxynitrite is implicated as an oxidant for low-density lipoprotein (LDL) in atherogenesis, we investigated this process using reagent peroxynitrite (ONOO-) and 3-morpholinosydnonimine (SIN-1, which produces peroxynitrite via generation of NO and O<inf>2</inf>-). LDL oxidation was assessed by the consumption of ubiquinol-10 (CoQ<inf>10</inf>H<inf>2</inf>) and ?-tocopherol (?-TOH), the accumulation of cholesteryl ester hydro(pero)xides, the loss of lysine (Lys) and tryptophan (Trp) residues, and the change in relative electrophoretic mobility. Exposure to ONOO- or SIN-1 resulted in rapid (<1 min) and time-dependent oxidation, respectively, of LDL's lipids and protein. Manipulating the ?-TOH content by in vivo or in vitro means showed that when ONOO- or SIN-1 was used at oxidant-to-LDL ratios of <100:1 the extent of LDL lipid peroxidation increased with increasing initial ?-TOH content. In contrast, in vivo enrichment with the co-antioxidant CoQ<inf>10</inf>H<inf>2</inf> decreased LDL lipid peroxidation induced by SIN-1. At oxidant-to-LDL ratios of > 200:1, ?- TOH enrichment decreased LDL lipid peroxidation for both SIN-1 and ONOO-. In contrast to lipid peroxidation, altering the ?-TOH content of LDL did not affect Trp or Lys loss, independent of the amounts of either oxidant added. Aqueous antioxidants inhibited ONOO-induced lipid and protein oxidation with the order of efficacy: 3-hydroxyanthranilate (3-HAA) > urate > ascorbate. With SIN-1, these antioxidants inhibited Trp consumption, while only the co- antioxidants ascorbate and 3-HAA prevented ?-TOH consumption and lipid peroxidation. Exposure of human plasma to SIN-1 resulted in the loss of ascorbate followed by loss of CoQ<inf>10</inf>H<inf>2</inf> and bilirubin. Lipid peroxidation was inhibited during this period, though proceeded as a radical-chain process after depletion of these antioxidants and in the presence of ?-TOH and urate. Bicarbonate at physiological concentrations decreased ONOO-induced lipid and protein oxidation, whereas it enhanced SIN-1-induced lipid peroxidation, Trp consumption, and ?-tocopheroxyl radical formation in LDL. These results indicate an important role for tocopherol-mediated peroxidation and co-antioxidation in peroxynitrite-induced lipoprotein lipid peroxidation, especially when peroxynitrite is formed time-dependently by SIN-1. The studies also highlight differences between ONOO- and SIN-1-induced LDL oxidation with regards to the effects of bicarbonate, ascorbate, and urate.
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Hawkins, Clare L.; Davies, Michael J.Stimulated monocytes and neutrophils generate hypochlorite (HOCl) via the release of the enzyme myeloperoxidase and hydrogen peroxide. HOCl damages proteins by reaction with amino acid side-chains or backbone cleavage. Little information is available about the mechanisms and intermediates involved in these reactions. EPR spin trapping has been employed to identify radicals on proteins, peptides and amino acids after treatment with HOCl. Reaction with HOCl gives both high- and low-molecular-mass nitrogen-centred, protein-derived radicals; the yield of the latter increases with both higher HOCl:protein ratios and enzymic digestion. These radicals, which arise from lysine side-chain amino groups, react with ascorbate, glutathione and Trolox. Reaction of HOCl-treated proteins with excess methionine eliminates radical formation, which is consistent with lysine-derived chloramines (via homolysis of N-Cl bonds) being the radical source. Incubation of HOCl-treated proteins, after removal of excess oxidant, gives rise to both nitrogen-centred radicals, over a period of hours, and time-dependent fragmentation of the protein. Treatment with excess methionine or antioxidants (Trolox, ascorbate, glutathione) protects against fragmentation; urate and bilirubin do not. Chloramine formation and nitrogen-centred radicals are therefore key species in HOCl-induced protein fragmentation.
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Neuil, Ji? Upston, Joanne M.; Witting, Paul Kenneth; Scott, Kieran F.; Stocker, RolandThe oxidation of low-density lipoprotein (LDL) is thought to contribute to atherogenesis. 15-Lipoxygenase (15LO) induces LDL oxidation, and phospholipase A<inf>2</inf> enhances this process [Sparrow, C. P., Parthasarathy, S., and Steinberg, D. (1988) J. Lipid Res. 29, 745-753]. As the underlying mechanism of the enhancing effect has not been investigated previously, we here show that in the presence of soybean 15LO (SLO) or human 15LO (rhLO), the addition of lipoprotein lipase, porcine pancreatic, or human type IIa secretory phospholipase A<inf>2</inf> (sPLA<inf>2</inf>) greatly enhanced the accumulation of hydro(pero)xides of all major classes of LDL's lipids. Hydroperoxides of free fatty acids accumulated exclusively as enzymic products with kinetics reflecting both the formation of free fatty acids and the initial 'build-up' of ?-tocopheroxyl radical. In contrast, hydroperoxides of cholesteryl esters and phosphatidylcholine accumulated linearly over comparatively longer periods of time and, in the case of rhLO, well beyond inactivation of the oxygenase. With SLO, formation of oxidized esterified lipids occurred nonenzymically, independent of the presence of lipase and despite the oxygenase remaining active until the end of the incubation. Enhancement of rhLO-induced LDL lipid peroxidation by sPLA<inf>2</inf> was eliminated by a neutralizing anti-sPLA<inf>2</inf> antibody, indicating that lipolytic activity was required for this effect. LDL depleted of ?-tocopherol was resistant to oxidation by 15LO alone, whereas lipase overcame this resistance, demonstrating that lipases enhance 15LO-induced enzymic and nonenzymic peroxidation of LDL lipids. This is likely due to provision of free fatty acid substrate, resulting in an enhanced rate of free radical formation which itself causes nonenzymic peroxidation of esterified lipids. As lipases and 15LO are present in atherosclerotic lesions, our findings could be of pathophysiological significance.
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Adams, Mark R.; Robinson, Jacqui T.C.; McCredie, Robyn J.; Seale, John Paul; Sorensen, Keld Ejvind; Deanfield, John Eric; Celermajer, David S.Objectives. We sought to assess smooth muscle function in adults at risk for atherosclerosis. Background. Previous studies in subjects at risk for atherosclerosis have demonstrated arterial endothelial dysfunction, with reduced vasodilator responses after pharmacologic or physiologic stimulation of endothelial nitric oxide (NO). Most have also shown a slight but nonsignificant impairment of vasodilation in response to exogenous sources of NO, such as nitroglycerin (NTG). We hypothesized that NTG responses might be reduced in a large number of consecutively studied adults at risk for atherosclerosis, independent of any impaired endothelium-dependent responses, consistent with concomitant smooth muscle dysfunction. Methods. Using high resolution ultrasound, the dilator response of the brachial artery to 400 ?g of sublingual NTG was measured in 800 asymptomatic subjects. Subjects were also assessed for a history of vascular risk factors, blood pressure, total serum cholesterol and flow-mediated endothelium-dependent dilation (EDD). Results. We studied 317 men and 483 women, 38 17 years old (mean SD, range 15 to 76). The mean cholesterol level was 5.2 1.3 mmol/liter, and there were 126 smokers and ex-smokers (16 9 mean pack-years) and 105 diabetic subjects. On univariate analysis, a reduced vasodilator response to NTG was associated with high cholesterol, cigarette smoking, diabetes mellitus, increasing age, male gender, larger vessel size and reduced EDD (p ? 0.01 for all). On multivariate analysis, diabetes, larger vessel size and reduced EDD were all independently associated with impaired NTG-related vasodilation (p ? 0.001 for all). In the 574 nondiabetic subjects who had never smoked cigarettes, the independent relation between EDD and NTG responses was still observed (r = 0.24, p = 0.01). Conclusions. The vasodilator response to exogenous NO is impaired in asymptomatic subjects with reduced EDD, consistent with smooth muscle dysfunction in adults at risk for atherosclerosis.
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Fu, Shanlin; Davies, Michael J.; Stocker, Roland; Dean, Roger T.Oxidative damage might be important in atherogenesis. Oxidized lipids are present at significant concentrations in advanced human plaque, although tissue antioxidants are mostly present at normal concentrations. Indirect evidence of protein modification (notably derivatization of lysine) or oxidation has been obtained by immunochemical methods; the specificities of these antibodies are unclear. Here we present chemical determinations of six protein-bound oxidation products: dopa, o-tyrosine, m-tyrosine, dityrosine, hydroxyleucine and hydroxyvaline, some of which reflect particularly oxy-radical-mediated reaction pathways, which seem to involve mainly the participation of transition-metal ions. We compared the relative abundance of these oxidation products in normal intima, and in human carotid plaque samples with that observed after radiolytically generated hydroxyl radical attack on BSA in vitro. The close similarities in relative abundances in the latter two circumstances indicate that hydroxyl radical damage might occur in plaque. The relatively higher level of dityrosine in plaque than that observed after radiolysis suggests the additional involvement of HOC1-mediated reactions in advanced plaque.
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Brown, Andrew J.We set out to study the effects of acute cigarette smoking on plasma antioxidants and lipid oxidation and whether these effects could be ameliorated by prior supplementation with ascorbate. Blood samples were taken from 9 apparently healthy male smokers before and after a 1 h smoking test (3 cigarettes/h). The men were then randomly allocated to two groups in a double-blind cross-over design; either taking ascorbate (100 mg/d) or placebo. After 2 wk of supplementation, the men were given a fat meal to consume and after 3 h the smoking test was repeated. Blood samples were taken before the fat tolerance test and at 3 and 4 h postprandially. In response to ascorbate supplementation, total plasma ascorbate increased relative to the placebo period (mean SEM: 70 5 vs 46 9 ?mol/L, P = 0.01), with significantly less (P = 0.025) ascorbate in the oxidized form (dehydroascorbate). Contrary to the depletion of antioxidants reported by others when plasma is exposed to cigarette smoke in vitro, no change was observed in plasma antioxidants in response to acute smoking, apart from a paradoxical decrease in the plasma concentration of dehydroascorbate after acute smoking (6.8 1.1 vs 5.0 1.1 ?mol/L, P < 0.01). Plasma lipid peroxides (measured as thiobarbituric acid reactive substances) and copper- induced oxidizability of low-density lipoprotein showed no change after acute smoking. In response to a fat meal, plasma triglyceride concentrations peaked on average between 3 and 4 h postprandially and LDL's content of lipid- soluble antioxidants (mostly ?-tocopherol) decreased (8.1 0.4 vs 7.4 0.4 molecules/LDL particle, P = 0.023). This may render postprandial LDL more vulnerable to oxidation. The lack of effect of acute cigarette smoking on plasma antioxidant vitamins, apart from an apparent decrease in dehydroascorbate, suggests that compensatory mechanisms are at work in vivo with plasma ascorbate concentrations possibly replenished from other metabolic pools.
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Park, Jong-in; Grant, Chris M.; Davies, Michael J.; Dawes, Ian W.W.The involvement of oxidative stress in freeze-thaw injury to yeast cells was analyzed using mutants defective in a range of antioxidant functions, including Cu,Zn superoxide dismutase (encoded by SOD1), Mn superoxide dismutase (SOD2), catalase A, catalase T, glutathione reductase, ?- glutamylcysteine synthetase and Yap1 transcription factor. Only those affecting superoxide dismutases showed decreased freeze-thaw tolerance, with the sod1 mutant and the sod1 sod2 double mutant being most affected. This indicated that superoxide anions were formed during freezing and thawing. This was confirmed since the sod1 mutant could be made more resistant by treatment with the superoxide anion scavenger MnCl<inf>2</inf>, or by freezing in the absence of oxygen, or by the generation of a rho0 petite. Increased expression of SOD2 conferred freeze-thaw tolerance on the sod1 mutant indicating the ability of the mitochondrial superoxide dismutase to compensate for the lack of the cytoplasmic enzyme. Free radicals generated as a result of freezing and thawing were detected in cells directly using electron paramagnetic resonance spectroscopy with either ?-phenyl-N-tert- butylnitrone or 5,5-dimethyl-1-pyrroline-N-oxide as spin trap. Highest levels were formed in the sod1 and sod1 sod2 mutant strains, but lower levels were detected in the wild type. The results show that oxidative stress causes major injury to cells during aerobic freezing and thawing and that this is mainly initiated in the cytoplasm by an oxidative burst of superoxide radicals formed from oxygen and electrons leaked from the mitochondrial electron transport chain.
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Fu, Shanlin; Dean, Roger T.; Southan, Michael D.; Truscott, Roger John WillisCataract is the major cause of blindness; the most common form is age- related, or senile, cataract. The reasons for the development of cataract are unknown. Here we demonstrate that nuclear cataract is associated with the extensive hydroxylation of protein-bound amino acid residues, which increases with the development of cataract by up to 15-fold in the case of DOPA. The relative abundance of the oxidized amino acids in lens protein (assessed per parent amino acid) is DOPA > o- and m-tyrosine > 3-hydroxyvaline, 5- hydroxyleucine > dityrosine. Nigrescent cataracts, in which the normally transparent lens becomes black and opaque, contain the highest level of hydroxylated amino acids yet observed in a biological tissue: for example, per 1000 parent amino acid residues, DOPA, 15; 3-hydroxyvaline, 0.3; compared with dityrosine, 0.05. The products include representatives of the hydroperoxide and DOPA pathways of protein oxidation, which can give rise to secondary reactive species, radical and otherwise. The observed relative abundance corresponds closely with that of products of hydroxyl radical or metal-dependent oxidation of isolated proteins, and not with the patterns resulting from hypochlorite or tyrosyl-radical oxidation. Although very little light in the 300-400-nm range passes the cornea and the filter compounds of the eye, we nevertheless also demonstrate that photoxidation of lens proteins with light of 310 nm, the part of the spectrum in which protein aromatic residues have residual absorbance, does not give rise to the hydroxylated aliphatic amino acids. Thus the post-translational modification of crystallins by hydroxyl radicals/Fenton systems seems to dominate their in vivo oxidation, and it could explain the known features of such nuclear cataractogenesis.
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McCredie, Robyn J.; McCrohon, Jane A.; Turner, Leo A.; Griffiths, Kaye A.; Handelsman, David J.; Celermajer, David S.Objective. To assess the vascular effects of high-dose androgen treatment in genetic females. Background. Male gender is an independent risk factor for coronary artery disease, suggesting either a protective effect of estrogens and/or a deleterious effect of androgens. We have recently demonstrated that androgen deprivation is associated with enhanced vascular reactivity in adult men, however, the effects of androgen excess on vascular function in humans has not been reported previously. Methods. We studied vascular reactivity in two groups of genetic females: 12 female-to-male transsexuals receiving long-term high-dose androgens, and 12 healthy female control subjects, matched for age and smoking history. Using external vascular ultrasound, brachial artery diameter was measured at rest, after flow increase (leading to flow-mediated dilatation [FMD], which depends on normal endothelial function)and after sublingual nitroglycerin (NTG), an endothelium-independent dilator. Results. Testosterone levels were higher (15.2 8.7 vs. 1.9 1.3 mmol/L, p < 0.001) and high-density lipoprotein cholesterol levels were lower (1.2 0.2 vs. 1.6 0.4 mmol/L, p = 0.02) in the transsexuals compared with the control subjects. In each group, nine of 12 subjects were current or ex- smokers, leading to impaired FMD in both groups (5.1 3.7% in the transsexuals vs. 6.9 4.1% in controls, p = 0.28). The NTG response was significantly decreased in the transsexuals (15.9 4.9% vs. 22 5.8% in controls, p = 0.01), independent of the effects of age, cholesterol or vessel size. Conclusions. Long-term treatment with high- dose androgens is associated with impaired Vascular reactivity in genetic females, consistent with a deleterious effect of androgen excess on arterial physiology.
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Davies, Michael J.; Mathieu, Christel; Puppo, Alain[No abstract available]
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Dass, Crispin R.; Walker, Todd L.; Burton, M.Solid tumours comprise a majority of human cancers. While a tumour emerges from parent normal tissue, there exist genetic and hence, biological, physiological and immunological differences between the tumour and its surrounding normal tissues. While some differences such as acquired resistance against chemotherapeutic drugs make it difficult to treat solid tumours, others such as an aberrant tumour vascular system may be exploited for targeting drug delivery with such vehicles as microspheres or liposomes. This review discusses the possibilities of enhancing tumour therapy with intravascularly-delivered agents.
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Morin, dicte; Bubb, William A.; Davies, Michael J.; Dean, Roger T.; Fu, Shanlin?-Irradiation of several amino acids (Val, Leu, Ile, Lys, Pro, and Glu) in the presence of O<inf>2</inf> generates hydroperoxides. We have previously isolated and characterized valine and leucine hydroperoxides, and hydroxides, and have detected these products in both isolated systems [e.g., bovine serum albumin (BSA) and human low-density lipoprotein (LDL)] and diseased human tissues (atherosclerotic plaques and lens cataractous proteins). This work was aimed at investigating oxidized lysine as a sensitive marker for protein oxidation, as such residues are present on protein surfaces, and are therefore likely to be particularly susceptible to oxidation by radicals in bulk solution. HOattack on lysine in the presence of oxygen, followed by NaBH<inf>4</inf> reduction, is shown to give rise to (2S)-3-hydroxylysine [(2S)-2,6-diamino-3- hydroxyhexanoic acid], (2S)-4-hydroxylysine [(2S)-2,6-diamino-4- hydroxyhexanoic acid], (2S,5R)5-hydroxylysine [(2S,5R)-2,6-diamino-5- hydroxyhexanoic acid], and (2S,5S)-5-hydroxylysine [(2S,5S)-2,6-diamino-5- hydroxyhexanoic acid]. 5-Hydroxylysines are natural products formed by lysyl oxidase and are therefore not good markers of radical-mediated oxidation. The other hydroxylysines are however useful markers, with HPLC analysis of 9- fluorenylmethyl chloroformate (FMOC) derivatives providing a sensitive and accurate method for quantitative measurement. Hydroxylysines have been detected in the hydrolysates of peptides (Gly-Lys-Gly and Lys-Val-Ile-Leu- Phe) and proteins (BSA and histone H1) exposed to HO/O<inf>2</inf>, and subsequently treated with NaBH<inf>4</inf>. Quantification of the hydroxylysines yields, and comparison with hydroxyvalines and hydroxyleucines, supports the hypothesis that surface residues give higher yields of oxidized products than the hydrophobic leucines and valines, at least with globular proteins such as BSA. Hydroxylysines, and particularly 3-hydroxylysine, may therefore be sensitive and useful markers of radical-mediated protein oxidation in biological systems.
