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Query: UMLS:C0004153 (atherosclerosis)
 77,401 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Uptake of oxidatively modified low-density lipoprotein (LDL) by cells in the arterial wall is believed to be an important early event in the development of atherosclerosis. Because vitamin E is the major antioxidant present in human lipoproteins, it has received much attention as a suppressor of LDL lipid oxidation and as an epidemiological marker for ischaemic heart disease. However, a careful examination of lipid peroxidation in LDL induced by a steady flux of aqueous peroxyl radicals has demonstrated that, following consumption of endogenous ubiquinol-10, the rate of peroxidation (i) declines as vitamin E is consumed, (ii) is faster in the presence of vitamin E than following its complete consumption, (iii) is substantially accelerated by enrichment of the vitamin in LDL, either in vitro or by diet, and (iv) is virtually independent of the applied radical flux. We propose that perodixation is propagated within lipoprotein particles by reaction of the vitamin E radical (i.e. alpha-tocopheroxyl radical) with polyunsaturated fatty acid moieties in the lipid. This lipid peroxidation mechanism, which can readily be rationalized by the known chemistry of the alpha-tocopheroxyl radical and by the radical-isolating properties of fine emulsions such as LDL, explains how reagents which reduce the alpha-tocopheroxyl radical (i.e. vitamin C and ubiquinol-10) strongly inhibit lipid peroxidation in vitamin E-containing LDL.
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PMID:Vitamin E in human low-density lipoprotein. When and how this antioxidant becomes a pro-oxidant. 146 40

LDL in the circulation is well protected against oxidation by the highly efficient antioxidant defense mechanisms of human plasma. LDL oxidation contributing to atherosclerosis, therefore, has been hypothesized to take place in the interstitial fluid of the arterial wall. We investigated the antioxidant composition and the capacity to inhibit LDL oxidation of human suction blister interstitial fluid (SBIF), a suitable representative of interstitial fluid. We found that the concentrations in SBIF of the aqueous small-molecule antioxidants ascorbate and urate were, respectively, significantly higher (P < 0.05) and identical to plasma concentrations. In contrast, lipoprotein-associated lipids and lipid-soluble antioxidants (alpha-tocopherol, ubiquinol-10, lycopene, and beta-carotene) were present at only 8-23% of the concentrations in plasma. No lipid hydroperoxides could be detected ( < 5 nM) in either fluid. The capacity of serum and SBIF to protect LDL from oxidation was investigated in three metal ion-dependent systems: copper, iron, and murine macrophages in Ham's F-10 medium. In all three systems, addition of > or = 6% (vol/vol) of either serum or SBIF inhibited LDL oxidation by > 90%. The concentration that inhibited macrophage-mediated LDL oxidation by 50% was as low as 0.3% serum and 0.7% SBIF. The enzymatic or physical removal of ascorbate or urate and other low molecular weight components did not affect the ability of either fluid to prevent LDL oxidation, and the high molecular weight fraction was as protective as whole serum or SBIF. These data demonstrate that both serum and SBIF very effectively protect LDL from metal ion-dependent oxidation, most probably because of a cumulative metal-binding effect of several proteins. Our data suggest that LDL in the interstitial fluid of the arterial wall is very unlikely to get modified by metal ion-mediated oxidation.
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PMID:Human suction blister interstitial fluid prevents metal ion-dependent oxidation of low density lipoprotein by macrophages and in cell-free systems. 756 88

Lipid peroxidation and oxidative modification of low-density lipoprotein (LDL) have been implicated as causal factors in the pathogenesis of atherosclerosis, and prevention of LDL oxidation by antioxidants may be an effective strategy to inhibit the progression of the disease. We investigated the effects of the reduced form of vitamin C (L-ascorbic acid, AA) and its two-electron oxidation product (dehydro-L-ascorbic acid, DHA) upon metal ion-dependent oxidative modification of human LDL. We found that low micromolar concentrations of both AA and DHA protect LDL against oxidation induced by Cu2+ or by hemin and hydrogen peroxide. In a dose-dependent manner, AA and DHA prevented the initiation of lipid peroxidation in LDL, as determined by a sensitive and selective assay for lipid hydroperoxides utilizing HPLC with chemiluminescence detection. AA and DHA also preserved the LDL-associated antioxidants alpha-tocopherol, beta-carotene, and lycopene, but not ubiquinol-10. Furthermore, AA was able to stop propagation of lipid peroxidation in LDL, whereas DHA lacked this ability. The addition of 60 microM AA to LDL containing up to 38 nmol/mg protein of pre-formed lipid hydroperoxides led to their rapid disappearance; this activity of AA was dependent on the presence of redox-active copper, but did not lead to the formation of lipid hydroxides, the reduced form of lipid hydroperoxides. Our data show that in Cu(2+)-exposed LDL (i) vitamin C primarily spares, rather than regenerates, alpha-tocopherol and other endogenous antioxidants, except for AA and DHA prevent initiation of lipid peroxidation in LDL; and (iii) AA can terminate lipid peroxidation, thereby protecting partially oxidized LDL against further oxidative modification.
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PMID:Vitamin C prevents metal ion-dependent initiation and propagation of lipid peroxidation in human low-density lipoprotein. 764 4

Increased levels of blood cholesterol are considered as a major factor in the development of atherosclerosis. Simvastatin, a drug which blocks hydroxymethylglutaryl coenzyme A reductase (HMGCoAR), reduces plasma cholesterol and increases HDL-cholesterol in rats fed a hypercholesterolemic diet. Moreover, simvastatin produces a significant decrease of ubiquinol and dolichol in plasma and in liver.
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PMID:Effects of simvastatin on liver and plasma levels of cholesterol, dolichol and ubiquinol in hypercholesterolemic rats. 779 20

Oxidation of low density lipoprotein (LDL) may be involved in the development of atherosclerosis. It has recently been shown that alpha-tocopherol (alpha-TOH) can act either as an antioxidant or prooxidant for isolated low density lipoprotein (LDL). In the absence of an effective co-antioxidant, alpha-TOH is a prooxidant and this activity is evidently due to reaction of the alpha-tocopheroxyl radical (alpha-TO.) with the LDL's polyunsaturated lipids (Bowry, V. B., and Stocker, R. (1993) J. Am. Chem. Soc. 115, 6029-6045). Herein we examined the effectiveness of selected natural and synthetic radical scavengers as co-antioxidants for inhibiting peroxyl radical-induced peroxidation in LDL that is devoid of ubiquinol-10 (an effective endogenous co-antioxidant) but still contains most of its natural complement of alpha-TOH. Various quinols, catechols, and aminophenols, as well as ascorbate, 6-palmityl ascorbate, and bilirubin, were very effective co-antioxidants under our test conditions, whereas ordinary phenolic antioxidants, including short-tailed alpha-TOH homologues, were less effective. Reduced glutathione, urate, and Probucol were ineffective. These findings confirm that the prooxidant activity of alpha-TOH in LDL relies heavily on the segregation of water-insoluble radicals (particularly alpha-TO.) into individual LDL particles, since it was those compounds that are expected to either irreversibly reduce alpha-TO. or accelerate the diffusion of radicals between particles which most effectively inhibited the tocopherol-mediated phase of peroxidation. Theoretical and practical implications of these findings are discussed, as is their relevance to the "LDL oxidation" hypothesis of atherogenesis.
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PMID:Prevention of tocopherol-mediated peroxidation in ubiquinol-10-free human low density lipoprotein. 789 Jul 4

There is ample evidence implicating reactive oxygen species in a number of human degenerative diseases such as atherosclerosis and haemochromatosis. Although lipid peroxidation underlies many of the toxic effects of oxidative stress, there is a lack of a sensitive and reliable method for its assessment in vivo. To understand the implications of oxidative stress in vivo, we have used dietary iron overload (IO) in the rat. Oxidant status in these animals was determined by assessing depletion of endogenous antioxidants and formation of various lipid peroxidation products, including acylated F2-isoprostanes, a novel class of free-radical-derived prostaglandin-F2-like compounds. IO led to a significant decrease in the concentration of the antioxidants alpha-tocopherol and ascorbic acid in plasma, and alpha-tocopherol, beta-carotene and ubiquinol-10 in liver. Whereas there was no significant lipid peroxidation in plasma, hepatic F2-isoprostane levels were moderately but significantly increased in IO. In addition, IO caused a significant increase in plasma total and high-density lipoprotein cholesterol levels, an effect that was correlated with depletion of plasma ascorbic acid but not alpha-tocopherol. The data demonstrate that IO causes lipid metabolism disturbances and oxidative stress which is associated with substantial depletion of endogenous antioxidants and moderate lipid peroxidative damage.
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PMID:The effect of iron overload on rat plasma and liver oxidant status in vivo. 801 Sep 63

F2-isoprostanes are prostaglandin F2-like compounds that are known to be formed in vivo by free radical oxidation of arachidonyl-containing lipids, and their plasma levels have been suggested as indicators of in vivo oxidative stress. As oxidation of LDL, a likely causal factor in atherosclerosis, involves lipid peroxidation, we investigated whether F2-isoprostanes are formed in plasma and LDL exposed to oxidative stress, and how F2-isoprostane formation is related to endogenous antioxidant status. In plasma exposed to aqueous peroxyl radicals, lipid hydroperoxides and esterified F2-isoprostanes were formed simultaneously after endogenous ascorbate and ubiquinol-10 had been exhausted, despite the continued presence of urate, alpha-tocopherol, beta-carotene, and lycopene. In isolated LDL exposed to aqueous peroxyl radicals or Cu2+, consumption of endogenous ubiquinol-10 and alpha-tocopherol was followed by rapid formation and subsequent breakdown of lipid hydroperoxides and esterified F2-isoprostanes, and a continuous increase in LDL's electronegativity, indicative of atherogenic modification. In Cu(2+)-exposed LDL, the decrease in esterified F2-isoprostane levels was paralleled by the appearance of free F2-isoprostanes, suggesting that hydrolysis by an LDL-associated activity had occurred. Our data suggest that F2-isoprostanes are useful markers of LDL oxidation in vivo. As F2-isoprostanes are potent vasoconstrictors and can modulate platelet aggregation, their formation in LDL demonstrated here may also have important implications for the etiology of cardiovascular disease.
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PMID:Formation of non-cyclooxygenase-derived prostanoids (F2-isoprostanes) in plasma and low density lipoprotein exposed to oxidative stress in vitro. 813 86

Oxidative modification of low density lipoprotein (LDL) has been suggested to play a casual role in human atherosclerosis, and prevention of LDL oxidation may be an effective strategy to prevent or slow the progression of this disease. It is important, therefore, to identify the factors that determine LDL's susceptibility to oxidation. We have analyzed 62 human LDL samples for content of antioxidants, preformed lipid hydroperoxides, and cholesterol. To investigate their oxidative susceptibility, the LDL samples were exposed to either a metal ion-dependent (Cu2+) or -independent (aqueous peroxyl radicals) oxidizing system; the length of the lag phase of inhibited lipid peroxidation was measured, as well as the rate of lipid peroxidation during the lag and ensuing propagation phases. The susceptibility of LDL to metal ion-dependent oxidation was not related to its susceptibility to metal ion-independent oxidation. A strong predictor of an increased susceptibility of LDL to metal ion-dependent oxidation was a decreased vitamin E-to-cholesterol ratio, in contrast to the vitamin E-to-protein ratio. Elevated levels of performed lipid hydroperoxides in LDL and an increased cholesterol content were also associated with an increased susceptibility of the lipoprotein to Cu(2+)-induced oxidation. Remarkably, a strong predictor of an increased susceptibility of LDL to metal ion-independent oxidation was an increased, rather than decreased, vitamin E content relative to protein. An increased cholesterol content also was associated with an increased oxidative susceptibility of LDL to aqueous peroxyl radicals, while preformed lipid hydroperoxides showed no significant correlation. Ubiquinol-10, beta-carotene, and lycopene, whether quantitated relative to cholesterol or protein, did not show significant protective effects against both metal ion-dependent and -independent oxidation of LDL. Our data suggest that a high lipid content of LDL, relative to its protein content, renders the lipoprotein more susceptible to oxidative modification, while vitamin E may have either a protective or promoting effect on LDL oxidation, depending on the oxidative stress conditions. Other known antioxidants in LDL do not appear to play a significant role in protecting LDL against oxidative modification.
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PMID:Content of antioxidants, preformed lipid hydroperoxides, and cholesterol as predictors of the susceptibility of human LDL to metal ion-dependent and -independent oxidation. 830 Dec 32

Ubiquinol-10, the reduced form of ubiquinone-10 (coenzyme Q10), is a potent lipophilic antioxidant present in nearly all human tissues. The exceptional oxidative lability of ubiquinol-10 implies that it may represent a sensitive index of oxidative stress. The present study was undertaken to assess the hypothesis that the level of ubiquinol-10 in human plasma can discriminate between healthy subjects and patients who are expected to be subjected to an increased oxidative stress in vivo. Using a newly developed method, we measured plasma ubiquinol-10 in 38 hyperlipidaemic patients with and without further complications, such as coronary heart disease, hypertension, or liver disease, and in 30 healthy subjects. The oxidizability of plasma samples obtained from hyperlipidaemic patients was found to be increased in comparison with control subjects, suggesting that the patients were subjected to a higher oxidative stress in vivo than the controls. Plasma ubiquinol-10, expressed as a percentage of total ubiquinol-10 + ubiquinone-10 or normalized to plasma lipids, was lower in the patients than in controls (P = 0.001 and 0.008, respectively). The proportion of ubiquinol-10 decreased in the order young controls > aged controls > hyperlipidaemic patients without complications > hyperlipidaemic patients with complications (P = 0.003). A negative correlation was found between the proportion of ubiquinol-10 and plasma triglycerides. The hyperlipidaemic patients with hypertension had a lower proportion of ubiquinol-10 than subjects without. When the study population was divided into smokers and non-smokers, plasma ubiquinol-10 was found to be reduced amongst smokers, independently of whether it was expressed as a percentage of total ubiquinol-10 + ubiquinone-10 (P = 0.006) or normalized to plasma lipids (P = 0.009). These data suggest that the level of ubiquinol-10 in human plasma may represent a sensitive index of oxidative stress in vivo especially indicative of early oxidative damage. Measuring plasma ubiquinol-10 can be proposed as a practical approach to assess oxidative stress in humans.
Atherosclerosis 1997 Feb 28
PMID:Plasma ubiquinol-10 is decreased in patients with hyperlipidaemia. 906 26

Oxidative modification of low-density lipoprotein (LDL), regarded an early event in atherogenesis, is associated with the depletion of the lipoprotein's antioxidants. We tested whether the levels of major lipophilic antioxidants in the blood of patients with advanced atherosclerosis are different to those in age-matched controls. On average, plasma ubiquinol-10, total coenzyme Q and coenzyme Q redox status were slightly lower whereas the levels of alpha-tocopherol were slightly higher in patients (63 +/- 11 years, n = 32) than controls (64 +/- 10 years, n = 24). However, these differences were not statistically significant (p > 0.05). The levels of antioxidants in LDL isolated from a subset of patients (n = 20) and controls (n = 15) were also indifferent, and hydroperoxides of cholesteryl esters were undetectable (detection limit 10 nM) in plasma of patients (n = 11) and controls (n = 10). The data suggests that plasma and LDL levels of lipophilic antioxidants are not depleted in patients suffering from severe atherosclerosis, and that neither parameter serves as a useful diagnostic indicator for this disease.
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PMID:Plasma and LDL levels of major lipophilic antioxidants are similar in patients with advanced atherosclerosis and age-matched controls. 925 29


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