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Showing 1961–1980 of 2058 publications.
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Mohr, Detlef; Stocker, RolandOxidative modification of human low-density lipoprotein (LDL) has received much attention because of its suggested involvement in the early events of atherogenesis. In contrast, little data exist concerning the oxidation of human very-low-density lipoprotein (VLDL), although such modification promotes foam cell formation by these lipoproteins. We therefore investigated the radical-mediated oxidation of VLDL by using controlled oxidizing conditions and sensitive and specific methods to assess lipoprotein lipid oxidation and antioxidation. We observed that the ratio of ?-tocopherol to coenzyme Q<inf>10</inf> in VLDL was close to that of LDL, suggesting that these lipoproteins may transport some coenzyme Q<inf>10</inf> to extrahepatic tissues, as they do tocopherol. Most of the coenzyme Q<inf>10</inf> associated with VLDL was present in its reduced, antioxidant active form, ubiquinol-10. The small amounts of ubiquinol-10 in VLDL provided the lipoprotein lipids with a highly efficient antioxidant protection. Also, the kinetics of radical-mediated lipid peroxidation in VLDL resembled that in LDL and therefore also probably proceeded via the recently described tocopherol-mediated peroxidation mechanism. Oxidation competition experiments using aqueous radicals and physiological concentrations and molar ratios of LDL and VLDL indicated that in contrast to the situation with high-density lipoproteins, lipid peroxidation was initiated and detected simultaneously in the former two lipoprotein particles. However, once initiated, peroxidation propagated at an approximately twofold higher rate in VLDL than LDL. Our studies suggest that radical-mediated lipid (per)oxidation proceeds via similar mechanisms in isolated LDL and VLDL. We conclude that efficient LDL antioxidants are also likely to be effective protective agents for VLDL. 1994 American Heart Association Inc.
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Thomson, MurrayInteractions between glycosaminoglycans (GAGs) and low density lipoprotein (LDL) are thought to influence the progression of atherogenesis. In an effort to gauge whether macrophages mediate GAG-LDL interaction by GAG modification, we have investigated the endocytosis, degradation and retro-endocytosis of the GAG heparan sulfate (HS) by mouse peritoneal macrophages. Radiolabelled HS was produced by derivatization with sulfosuccinimidyl-3-(4-hydroxyphenyl) propionate and radio-iodination by the chloramine T method. The amount of 125I-HS internalized by cultures of thioglycollate-elicited macrophages rose over a 24 h time period in proportion to the amount of tracer added to the wells (2--2500 ng ml-1). Analysis of GAG molecular weight was performed using gel filtration chromatography and polyacrylamide gel electrophoresis. After a 24 h pulse period, the 125I-HS in the intracellular fraction of the cultured cells was of smaller molecular weight than for control material. During a 24 h cold chase, fragments of 125I-HS were released into the medium. These fragments had lower affinity for Polybrene-Sepharose but did not appear significantly N-desulfated as determined by low pH nitrous acid treatment. The NADPH oxidase inhibitor diphenylene iodonium, although minimizing basal and phorbol ester-triggered radical output, did not inhibit 125I-HS depolymerization. These data indicate that elicited macrophages can interact with and reduce the polymer length of HS without extensively desulfating the molecule. They are consistent with a mechanism by which the macrophage internalizes and partially degrades HS by endoglucuronidase activity rather than NADPH oxidase-generated free radicals, followed by release of the products into the extracellular milieu. 1994.
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Bannon, Paul Gerard; Dawes, Joan; Dean, Roger T.[No abstract available]
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Iismaa, S. E.; Hu, Shengping; Kocher, Markus; Lackmann, Martin; Harrison, Craig A.; Thliveris, Soula; Geczy, Carolyn L.The S100 protein CP-10 (chemotactic protein, 10 kD), a potent chemotactic factor for murine and human polymorphonuclear cells (PMN) and murine monocytes, has been purified in small amounts from supernatants of activated murine spleen cells (Lackmann et al., 1992). To obtain a more abundant source of the protein, CP-10 was expressed in Escherichia coli as a fusion protein with glutathione S-transferase (GST). The property of S100 proteins to undergo calcium-dependent conformational changes was used in a novel approach to optimize the release of recombinant (r) CP-10 by thrombin cleavage. Purified rCP-10 was characterized by amino-terminal sequence analysis and bioassays. Optimal chemotactic activity of rCP-10 for murine PMN and WEHI-265 monocytoid cells was 10?11 M (native protein has optimal chemotactic activity between 10?11 and 10?13 M). Immunization of rabbits with the GST/CP-10 fusion protein bound to glutathione-agarose beads resulted in high titer, specific antibodies that neutralized CP-10-initiated chemotaxis and were suitable for immunoblotting. A combination of Western and Northern analyses identified CP-10 in murine peritoneal exudate PMN and macrophages, splenocytes, bone marrow cells, and WEHI-265 cells (all of myeloid origin), but not in thymus, liver, lung, 3T3 fibroblasts, EL4 lymphoma cells, or bEND 3 brain endothelial cells, indicating cell-specific regulation of CP-10 expression. 1994, Mary Ann Liebert, Inc. All rights reserved.
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Garner, Brett; Dean, Roger T.; Jessup, Wendy K.There is growing evidence that oxidatively modified low-density lipoprotein (LDL) accumulates in the atherosclerotic intima of arteries. Cells present in the intima (including the monocyte/macrophage) are capable of oxidizing LDL in vitro, but the mechanisms by which this occurs are unknown. Several reports have claimed a crucial role for superoxide as a cell-derived radical species capable of enhancing the rate of LDL oxidation. We have used a sensitive h.p.l.c. system with chemiluminescence detection to measure LDL cholesteryl ester hydroperoxides at early stages of LDL oxidation. During the initial stages of LDL oxidation, there is at least a 2 h delay before human monocyte-derived macrophages enhance this process. Stimulation of these cells to produce large fluxes of superoxide does not increase the rate of LDL oxidation or decrease the delay of its onset. Prior exposure of LDL to a high flux of superoxide does not increase its susceptibility to oxidation by human monocyte-derived macrophages. We also show that the thiobarbituric acid-reactive substances (TBARS) assay does not always correlate with more direct methods of assessing LDL oxidation and confirm recent reports that superoxide dismutase only partially inhibits cell-mediated LDL oxidation. We conclude that superoxide does not play a major role in human monocyte-derived macrophage-mediated LDL oxidation under the conditions that we describe.
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Hazell, Linda J.; van den Berg, J. J.M.; Stocker, RolandPeroxidation of low-density lipoprotein (LDL) lipid is generally thought to represent the initial step in a series of modification reactions that ultimately transform the protein moiety of the lipoprotein into a form recognized by receptors different from those that bind native LDL. Uptake of LDL via these alternative receptors can lead to the formation of lipid- laden cells, which are typical for the early stages of atherogenesis. We have studied the oxidative modification of LDL by hypochlorite (-OCl), a powerful oxidant produced from H<inf>2</inf>O<inf>2</inf> and chloride via the action of myeloperoxidase which is released from activated neutrophils and monocytes. Exposure of LDL to reagent or enzymically generated -OCl at 4 or 37 C resulted in immediate and preferential oxidation of amino acid residues of apolipoprotein B-100, the single protein associated with LDL. Lysine residues quantitatively represented the major target and, like tryptophan, were oxidized to approximately the same extent with reagent or enzymically generated -OCl. In contrast, LDL lipid oxidation was less favoured than protein oxidation, as judged by the amounts of lipid hydroperoxides, chlorohydrins, cholesterol or fatty acid oxidation products formed. Treatment with -OCl caused aggregation LDL, as shown by an increased turbidity of the oxidized LDL solution and elution from a size-exclusion h.p.l.c. column of high-molecular-mass LDL complexes. Chemical modification of lysine residues before oxidation with -OCl prevented aggregation, while it enhanched the extent of lipid peroxidation. Treatment of LDL with -OCl also caused the formation of carbonyl groups and release of ammonia; both these modifications were inhibited by lysine-residue modification before oxidation. These results demonstrate that aggregation reactions are dependent on initial lysine oxidation by -OCl, followed by deamination and carbonyl formation, but do not involve lipid (per)oxidation. We propose that the observed -OCl-mediated aggregation of LDL is caused, at least in part, by crosslinking of apoproteins by Schiff-base formation independently of lipid peroxidation.
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Christison, Julie K.; Sies, Helmult; Stocker, RolandEbselen, a glutathione peroxidase mimic capable of reducing simple as well as complex hydroperoxides, including those of phospholipids and cholesteryl esters in intact oxidized low-density lipoprotein (LDL(ox)), requires the presence of low-molecular-mass thiols to be active. In plasma, the drug is thought to be transported as an inactive albumin complex. As formation of LDL(ox) is likely to occur extracellularly, we tested under which conditions ebselen can support reduction of LDL(ox)-associated cholesteryl ester hydroperoxides outside cells. We observed that addition of albumin-bound ebselen to whole blood, but not plasma, resulted in reduction of LDL(ox)-associated cholesteryl linoleate hydroperoxides to the corresponding hydroxides. The observed reduction was rapid and its extent increased with increasing concentrations of ebselen. Physical contact of blood cells with LDL(ox) was not required for this reducing activity. These results demonstrate that, in the presence of blood cells, extracellular ebselen is catalytically active. They suggest that ebselen may be considered as a drug for extracellular targets.
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Thomas, Stephen; Brake, Brigitte A.; Luzio, J. Paul; Stanley, Keith K.; Banting, George S.Immunoscreening a rat liver cDNA expression library has led to the isolation of a full-length cDNA clone encoding a novel isoform of rat inositol 1,4,5-trisphosphate 3-kinase (IP<inf>3</inf> 3-kinase). Sequence comparison shows it (i) to be 93% identical to human hippocampus IP<inf>3</inf> 3-kinase B over 468 residues at the protein level, and (ii) to encode a protein 204 amino acids larger than the published sequence of its human homologue. 1994.
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Newton, Rebecca A.; Raftos, David Andrew; Raison, Robert L.; Geczy, Carolyn L.The chemotactic responses of hagfish leucocytes were tested using a variety of chemoattractants. Leucocyte migration was significantly enhanced by purified mammalian complement anaphylotoxin (C5a) and LPS-activated hagfish plasma. Checkerboard analyses confirmed that the responses of leucocytes to both of these chemoattractants were directed along concentration gradients (chemotaxis) and did not result from accelerated random movement (chemokinesis). Chemotaxis was undertaken by leucocyte fractions that were enriched in granulocytes, the predominant phagocytic cells of hagfish. The data suggest that chemotactic mechanisms may have been conserved during evolution to such a degree that mammalian chemoattractants can bind and activate chemotactic receptors on hagfish leucocytes. Moreover, hagfish appear to express plasma proteins that are structurally and functionally homologous to mammalian complement anaphylotoxins. 1994.
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Brieger, David B.; Dawes, JoanIt is widely reported that persistent anti-Xa activity follows administration of low molecular weight heparins. To identify the effectors of this activity we have injected 125I-labelled Enoxaparin sodium into rabbits and subsequently analysed the circulating radiolabelled material and anti-Xa activity by affinity and size exclusion chromatography. Antithrombin III-binding material derived from the injected drug was responsible for all the anti-Xa amidolytic activity. At early times after injection additional anticoagulant activity which was largely attributable to tissue factor pathway inhibitor was measured by the Heptest clotting assay after removal of glycosaminoglycans from plasma samples. Small radiolabelled fragments, including penta/hexasaccharide with affinity for antithrombin III, were detectable in the circulation 1 week later, and sulphated oligosaccharides persisted for 3-4 weeks. Significant quantities of radiolabel remained in the liver and kidney several weeks post-injection, these organs may sequester some of the injected drug and give rise to circulating biologically active material by degradation and secretion of catabolic products into the plasma.
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Devery, Jannine M.; Milborrow, Barry V.Carotene-15,15 -dioxygenase (EC 1.13.11.21; ?-carotene dioxygenase) activity in extracts from guinea-pig intestinal mucosa was assayed by supplying [15,15'-14C2]- or [15,15-3H2]?-carotene dissolved in Tween 80. Methods were developed to minimize the breakdown of labelled ?-carotene and ?-carotene cleavage products during the isolation procedure. Antioxidants and unlabelled carriers were added to extracting solvents and C18 Sep-Pak cartridges were used to isolate the remaining ?-carotene and retinaldehyde, which was the only cleavage product detected. The labelled material produced by the enzyme was analysed by either normal-phase TLC or reversed-phase HPLC and characterized chemically as retinaldehyde. The lack of other labelled apo-carotenals isolated in these experiments and the formation of between 15 and 2 mol retinaldehyde/mol ?-carotene consumed confirm the central cleavage mechanism for the enzyme's action. More ?-carotene dioxygenase activity was obtained from guinea-pig mucosa than from chicken or pig intestinal mucosa. The ?-carotene dioxygenase was obtained as a soluble enzyme which was partially purified by gel filtration and ion-exchange chromatography to a specific activity of 0 6 nmol retinaldehyde formed/mg protein per h. The formation of a lipid-protein aggregate containing the ?-carotene dioxygenase activity, which has been reported to be present in the exclusion volume of Sephadex columns, was avoided if the mucosal scrapings were homogenized in buffer at a proportion of 1:4 (w/v). 1994, The Nutrition Society. All rights reserved.
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Christen, Stephan; Thomas, Shane R.; Garner, Brett; Stocker, RolandIn this study we examined the potential inhibition by interferon-? (IFN?) of the early stages of low density lipoprotein (LDL) oxidation mediated by human peripheral blood mononuclear cells (PBMC) and monocyte-derived macrophages (MDM) in Ham's F-10 medium supplemented with physiological amounts of L-tryptophan (Trp). We assessed LDL oxidation by measuring the consumption of LDL's major antioxidant (i.e., ?-tocopherol) and targets for oxidation (cholesteryllinoleate and cholesterylarachidonate), together with the accumulation of cholesterylester hydroperoxides and the increase in relative electrophoretic mobility of the lipoprotein particle. Exposure of PBMC or MDM to IFN? induced the degradation of extracellular Trp with concomitant accumulation of kynurenine, anthranilic and 3-hydroxyanthranilic acid (3HAA) in the culture medium. Formation of 3HAA, but neither Trp degradation nor formation of kynurenine and anthranilic acid, was inhibited by low amounts of diphenylene iodonium (DPI) in a concentration-dependent manner. In contrast to oxidative Trp metabolism, exposure of human PBMC or MDM to IFN? failed to induce degradation of arginine, and nitrite was not detected in the cell supernatant, indicating that nitric oxide synthase was not induced under these conditions. Incubation of LDL in Trp-supplemented F-10 medium resulted in a time-dependent oxidation of the lipoprotein that was accelerated in the presence of PBMC or MDM but inhibited strongly in the presence of both cells and IFN?, i.e., when Trp degradation and formation of 3HAA were induced. In contrast, when IFN? was added to PBMC or MDM in F-10 medium that was virtually devoid of Trp, inhibition of cell-accelerated LDL oxidation was not observed. Exogenous 3HAA added to PBMC or purified monocytes in the absence of IFN? also strongly and in a concentration-dependent manner inhibited LDL oxidation. Selective inhibition of IFN?-induced formation of 3HAA by DPI caused reversion of the inhibitory action of this cytokine on both PBMC- and MDM-mediated LDL oxidation. These results show that IFN? treatment of human PBMC or MDM in vitro attenuates the extent of LDL oxidation caused by these cells, and indicate that Trp degradation with formation of 3HAA is a major contributing factor to this inhibitory activity.
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Dean, Roger T.; Nicholson, Philip L.Nine iron chelators were tested in five systems for their effects on radical-generation and conversion at chelator: iron molar ratios from 0.1 to 10. Stimulatory actions might distinguish toxic from safer chelators. Radical-generating reactions which represent different aspects of iron (ferrous and ferric) availability were studied: a) the reaction with hydrogen peroxide to hydroxylate benzoate; b) the oxidation of ascorbate; c) the reaction with hydrogen peroxide to fragment proteins; d) the reaction with hydrogen peroxide to permit amplified chemiluminescence; and e) the induction of peroxidation of mitochondrial membrane lipids. The compounds used were HBED, CP130, Desferal, EDTA, pyridine-hydrazone (CGP 43'902B), Ferrozine, CP 94 (CGP 46'700), LI (CGP 37 391) and rhodotorulic acid (CGP 45 274). Only the hexadentate compounds HBED, CP130 and Desferal were uniformly inhibitory ("protective" The protective compounds were also apparently more stable during radical fluxes than the other chelators. 1994 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.
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Stocker, RolandRecent epidemiological data suggest that dietary antioxidant vitamins reduce the risk from major diseases caused by aging, including heart disease and cancer. As a result, antioxidant vitamins, particularly E and C, have become fashionable. But how do these vitamins work in the body? Despite substantial advances in the 170s and 80s in understanding the basis for the chemical reactivity of vitamin E, we are only now beginning to understand how and why vitamin E efficiently protects biological lipids from oxidative damage.
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Kohar, Indrajati; Suarna, Cacang; Southwell-Keely, Peter T.Overoxidation of ?-tocopherol (1a) by silver nitrate produces tocored (9a) as a major product. The aim of the present work was to elucidate the pathway of formation of tocored using the ?-tocopherol model compound, 2,2,5,7,8-pentamethyl-6-chromanol (1b). Oxidation of 1b by silver nitrate in ethanol produces 2-(3-hydroxy-3-methylbutyl)-3,5,6-trimethyl-1,4-benzoquinone (6b) and 2,2,7,8-tetramethylchroman-5,6-dione (9b, the model compound of tocored) as major products. Formation of 6b is rapid and is accompanied by an equally rapid fall in pH. Formation of 9b only occurs after 6b has reached maximum concentration and has begun to decline. It appears that acid promotes the dehydration and recyclization of 6b into a quinone methide (2b), which is then rehydrated into 5-hydroxymethyl-2,2,7,8-tetramethyl-6-chromanol (5b), the phenolic isomer of the quinone 6b. Oxidative deformylation of 5b leads to 9b. It is also demonstrated that 6b, heated in ethanol in the presence of acid and in the absence of any oxidizing agent, is converted into 9b, 1b, 5-ethoxymethyl-2,2,7,8-tetramethyl-6-chromanol (4b) and 2-(3-hydroxy-3-methylbutyl)-3-ethoxymethyl-5,6-dimethyl-1,4-benzoquinone (7b). It seems that dehydration and recyclization of 6b into 5b occurs as above and that 6b then oxidizes 5b into 9b, while being reduced into the hydroquinone of 6b (6bH<inf>2</inf>). Compound 6bH<inf>2</inf> then cyclizes in acid to 1b. A possible alternative pathway from 6b to 9b that does not involve 5b is also discussed. These results suggest that 6b and, by implication, ?-tocopheryl quinone (6a), is not a stable compound and, in the presence of acid, is readily oxidized to 9b. 1993 American Oil Chemists' Society.
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Neuil, Ji? Stocker, RolandOxidative damage to biological macromolecules has been implicated in a number of diseases. Much interest has focused on how non-proteinaceous, low-molecular weight antioxidants prevent oxidative damage to lipids, while comparatively little is known about protein antioxidation. Here we show that bilirubin (BR), the end-product of heme catabolism, when bound to bovine serum albumin (BSA), is oxidised by hydroxyl ('OH), hydroperoxyl (HO<inf>2</inf>), and Superoxide anion (Oxxx<inf>2</inf>) radicals to so far mostly uncharacterised products. The initial oxidation rates of BSA-bound BR decreased in the order OH ? HO <inf>2</inf> ? O-.<inf>2</inf> BR protected its carrier protein from oxidative damage inflicted by OH radicals. This protective action included a reduction in the OH-mediated cleavage of BSA, conversion of Trp into kynurenine and formation of 'bityrosine-specific' fluorescence. BR also strongly inhibited OH-mediated formation of protein carbonyls, whereas ascorbate and Trolox (a water-soluble analogue of vitamin E) were much less effective. These results support an antioxidant-protective function of BR and point towards significant differences in the efficacies of various antioxidants in the prevention of oxidative damage to lipids and proteins. 1993.
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Wagner, Richard J.; Motchnik, Paul A.; Stocker, Roland; Sies, Helmult; Ames, Bruce N.Human blood plasma and freshly isolated LDL were exposed to singlet oxygen (1O<inf>2</inf>) by thermal decomposition of synthetic endoperoxides. Exposure of blood plasma to 20 mM water-soluble 1O<inf>2</inf> generator resulted in the depletion of ascorbate (100%), urate (75%), ubiquinol-10 (65%), protein thiols (50%), and bilirubin (25%), whereas under these conditions the levels of ?-tocopherol, ?-carotene, and lycopene remained unchanged. The following rates of depletion were obtained by kinetic analysis (moles depleted per 100 mol of 1O<inf>2</inf> consumed): protein thiols (5), urate (5), ascorbate (4), bilirubin (1), and ubiquinol-10 (0.008). In contrast, the rates of depletion using the lipid-soluble 1O<inf>2</inf> generator were faster for bilirubin (13-fold), protein thiols (9-fold), ubiquinol-10 (8-fold), and ascorbate (5-fold), and slower for urate (2-fold). The formation of lipid hydroperoxides, including mostly cholesteryl linoleate hydroperoxide, was observed in 1O<inf>2</inf>-treated plasma (0.007-0.009 mol/100 mol 1O<inf>2</inf>) and LDL solutions (0.086 mol/100 mol 1O<inf>2</inf>). Based on competition kinetics, we estimate that 98% of 1O<inf>2</inf> generated in the aqueous phase of plasma is quenched by components in this phase, mostly by plasma protein (63%; 6% by protein thiols), urate (9%; 5% by chemical quenching), and bilirubin (5%; 1% by chemical quenching). Ascorbate and ubiquinol-10 do not contribute to 1O<inf>2</inf> quenching in plasma, and their oxidation is probably mediated secondary species. The remaining 1O<inf>2</inf> generated in plasma (2%) diffuses into lipoprotein leading to the formation of lipid hydroperoxides with an efficiency of about 100-fold greater than that compared to aqueous generated 1O<inf>2</inf>. The principal 1O<inf>2</inf> quenchers in LDL include apoB (42%), lycopene and ?-carotene (40%), and ?-tocopherol (17%). The importance of carotenoids in the quenching of 1O<inf>2</inf> in lipoprotein suggest that the beneficial effects of these compounds in health may in part be due to the elimination of this species in biology and medicine.
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Stocker, Roland; Suarna, CacangUbiquinol-10 (CoQ<inf>10</inf>H<inf>2</inf>) is present in human low density lipoproteins (LDL) where it contributes significantly to the antioxidant defenses against radical-mediated oxidative damage. As CoQ<inf>10</inf>H<inf>2</inf> becomes oxidized to ubiquinone-10 (CoQ<inf>10</inf>) during the earliest stages of in vitro oxidation of LDL, we investigated a possible cellular recycling of oxidized CoQ<inf>10</inf>H<inf>2</inf>, adding CoQ<inf>10</inf> or its ambiphilic, short-chain analogue ubiquinone-1 (CoQ<inf>1</inf>), to cells that are exposed to LDL in vivo. Whole blood, isolated red blood cells and human hepatoma Hep G2 cells (used as a model of hepatocytes) rapidly and efficiently reduced added CoQ<inf>1</inf> to ubiquinol-1 (CoQ<inf>1</inf>H<inf>2</inf>) detectable outside the cells. In whole blood the same steady-state level of CoQ<inf>1</inf>H<inf>2</inf> was reached whether an equimolar amount of CoQ<inf>1</inf> or CoQ<inf>1</inf>H<inf>2</inf> was added. Red cell membranes also showed some reducing activity, whereas CoQ<inf>1</inf> added to human blood plasma remained largely in its oxidized form. Cell- and membrane-mediated reduction of CoQ<inf>1</inf> was enhanced by NADH, FAD, or human plasma. In comparison to this rapid reduction of extracellular CoQ<inf>1</inf>, formation of CoQ<inf>10</inf>H<inf>2</inf> from CoQ<inf>10</inf> incorporated into human LDL by red blood and Hep G2 cells was slow. Our results show that although human blood cells and Hep G2 cells are endowed with a highly reducing activity for CoQ<inf>1</inf>, the natural CoQ<inf>10</inf> does not appear to represent an efficient substrate for this activity. 1993.
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Kritharides, Leonard; Jessup, Wendy K.; Gifford, J.; Dean, Roger T.A new high-performance liquid chromatographic system for the identification of some of the lipid oxidation products of low-density lipoprotein (LDL) oxidized by copper is described. Using a reversed-phase C-18 column and an isocratic solvent system of acetonitrile/isopropanol/water (44/54/2, v/v/v), a number of oxidized lipid moieties were resolved and detected simply by their 234-nm absorbance. The nature of several of these compounds was determined by chromatographic criteria, chemiluminescence, and mass spectrometry. The production of compounds within 4 h oxidation corresponded to the production of lipid hydroperoxides, the quantitatively most important of which is cholesterol linoleate hydroperoxide, and to the rapid decrease in the cholesterol ester content of LDL detected at 210 nm. More prolonged copper oxidation (up to 48 h) of LDL resulted in decreased quantities of lipid hydroperoxide moieties and increased amounts of a number of other, nonhydroperoxide, compounds. 7-Ketocholesterol and cholesterol linoleate hydroxide are two of the major products of prolonged oxidation. The detection of oxidation products correlates with the modification of LDL protein, permits a four-stage definition of metal-mediated LDL oxidation, and enables the calculation of a quantitative index of oxidation (lipoprotein oxidation index). This method will be generally applicable to cell-and copper-mediated oxidation, and will enable standardization of, and direct comparison between, different preparations of oxidized LDL. 1993 Academic Press, Inc.
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Iheanacho, Eugene N.; Stocker, Roland; Hunt, Nicholas H.As oxidative mechanisms have been suggested to be part of the host immune reaction against malarial parasites, we investigated the redox metabolism of the antioxidant vitamin C in the blood of control and malaria-infected mice. At the peak of infection (day 6) with the malaria parasite P. vinckei, plasma levels of ascorbate (AH-) were 10.8 0.9 ?g/ml compared to 5.7 0.7 ?g/ml in control mice, though no significant change was observed in the plasma concentration of dehydroascorbate (DHA). The plasma redox ratio of vitamin C, [AH-]:[DHA], was 7.4 in control mice and 18.5 in infected mice on day 6 post-inoculation. The increased AH- level in plasma of P. vinckei-infected mice was not due to differences in stabilities of either AH- or DHA in plasmas from control or P. vinckei-infected mice. DHA added to plasma was lost rapidly. In contrast, when added to whole blood, DHA was rapidly taken up and reduced to AH- by blood cells from both normal mice and P. vinckei-infected mice. Most of the intracellular AH- derived from the exogenously added DHA was released into the plasma by blood cells from the infected but not normal mice. The observed release of AH- into the plasma by blood cells from infected mice was not caused by a plasma factor. Depletion of leukocytes from erythrocytes had no effect on the uptake and reduction of DHA by red blood cells, but the subsequent release of intracellular AH- occurred more rapidly. The increased propensity of erythrocytes from infected animals to release AH- could in part explain the higher levels of AH- observed in P. vinckei infection. 1993.
