Ongoing prothrombotic state in patients with antiphospholipid antibodies: a role for increased lipid peroxidation.
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We measured the urinary excretion of Isoprostane F2alpha-III and Isoprostane-F2alpha-VI, two markers of in vivo lipid peroxidation, and the circulating levels of the prothrombin fragment F1+2, a marker of thrombin generation, in 18 antiphospholipid antibodies-positive patients, in 18 antiphospholipid antibodies-negative patients with systemic lupus erythematosus, and in 20 healthy subjects. Furthermore, 12 patients positive for antiphospholipid antibodies were treated with (n = 7) or without (n = 5) antioxidant vitamins (vitamin E at 900 IU/d and vitamin C at 2, 000 mg/d) for 4 weeks. Compared with antiphospholipid antibodies-negative patients, antiphospholipid antibodies-positive patients had higher urinary values of Isoprostane-F2alpha-III (P =. 0001), Isoprostane-F2alpha-VI (P =.006), and plasma levels of the prothrombin fragment F1+2 (P =.0001). In antiphospholipid-positive patients, F1+2 significantly correlated with Isoprostane-F2alpha-III (Rho =.56, P =.017) and Isoprostane-F2alpha-VI (Rho =.61, P =.008). After 4 weeks of supplementation with antioxidant vitamins, we found a significant decrease in F1+2 levels (P <.005) concomitantly with a significant reduction of both Isoprostane-F2alpha-III (P =.007) and Isoprostane-F2alpha-VI (P <.005). No change of these variables was observed in patients not receiving antioxidant treatment. This study suggests that lipid peroxidation might contribute to the activation of clotting system in patients positive for antiphospholipid antibodies. (+info)
Propofol prevents peroxide-induced inhibition of glutamate transport in cultured astrocytes.
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BACKGROUND: Glutamate transporters located in the plasma membrane of cerebral astrocytes take up excitatory neurotransmitters from the synaptic cleft. In diseases characterized by oxidative stress, the extracellular glutamate concentration increases and contributes to neuronal death. The authors wanted to determine whether propofol defends brain cells against oxidant-induced changes in their transport of glutamate. METHODS: Primary cultures of rat cerebral astrocytes were exposed to tert-butyl hydroperoxide (1 mM) to serve as an in vitro model of oxidative stress. Astrocytes were incubated with propofol for 2 h and tert-butyl hydroperoxide was added for the final hour. Alternatively, astrocytes were incubated with tert-butyl hydroperoxide for 30 min and then with propofol for another 30 min. Control cells received drug vehicle rather than propofol. The rate of uptake of glutamate, the efflux of the nonmetabolizable analog D-aspartate, and the intracellular concentration of the endogenous antioxidant glutathione were measured. RESULTS: Tert-butyl hydroperoxide decreased the glutathione concentration and inhibited glutamate uptake but had a negligible effect on D-aspartate efflux. At clinically relevant concentrations, propofol did not affect the glutathione concentration but did prevent the effect of tert-butyl hydroperoxide on glutamate transport. Furthermore, the addition of propofol after tert-butyl hydroperoxide reversed the inhibition of glutamate uptake. CONCLUSIONS: Propofol prevents and reverses the inhibition of excitatory amino acid uptake in astrocytes exposed to tert-butyl hydroperoxide. The ability of propofol to defend against peroxide-induced inhibition of glutamate clearance may prevent the pathologic increase in extracellular glutamate at synapses, and thus delay or prevent the onset of excitotoxic neuronal death. (+info)
Nitric oxide and lipid peroxidation.
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Nitric oxide can both promote and inhibit lipid peroxidation. By itself, nitric oxide acts as a potent inhibitor of the lipid peroxidation chain reaction by scavenging propagatory lipid peroxyl radicals. In addition, nitric oxide can also inhibit many potential initiators of lipid peroxidation, such as peroxidase enzymes. However, in the presence of superoxide, nitric oxide forms peroxynitrite, a powerful oxidant capable of initiating lipid peroxidation and oxidizing lipid soluble antioxidants. The role of nitric oxide in vascular pathology is discussed. (+info)
Antioxidant effect of dipyridamole and its derivative RA-25 in mitochondria: correlation of activity and location in the membrane.
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Dipyridamole (DIP), a coronary vasodilator, presents coactivator activity for a number of antitumor drugs as well as antioxidant activity in membrane systems. DIP and derivatives interact with membrane systems such as micelles, phospholipid monolayers and vesicles. The antioxidant effect of DIP and several derivatives upon iron-induced lipoperoxidation on mitochondria has been reported and a good correlation between the hydrophobicity and their protective effect was found (M.F. Nepomuceno et al., Free Radic. Biol. Med., 23 (1997) 1046-1054). In the present work an effort is made to better understand the role of DIP as inhibitor of Fe2+-induced lipid peroxidation in mitochondria. At low concentration, no significant effect on either state IV or state III respiration was found, discarding a possible direct interaction of DIP or RA-25 with the peripheral benzodiazepine receptor. The association constants for DIP and RA-25 in mitochondria were estimated, being 0.7 (mg/ml)-1 for DIP and 0.2 (mg/ml)-1 for RA-25. Oxygen consumption studies in the presence of FeSO4 showed that the antioxidant effect of DIP or RA-25 did not involved the initial step of Fe2+ oxidation. Our data strongly support the hypothesis that the antioxidant effect of both DIP and RA-25 is related to their partition in the lipid phase of the mitochondrial membrane and not to a specific interaction with membrane proteins. This protection may be due either to a direct inhibition of the propagation steps or a scavenger effect on the radicular species that would trigger the peroxidative process. (+info)
Formation of 9-hydroxy linoleic acid as a product of phospholipid peroxidation in diabetic erythrocyte membranes.
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The increased production of oxygen-derived free radicals (OFR) and lipid peroxidation may contribute to vascular complications in diabetes. Some lipid peroxidation products have already been reported to be formed via glucose-induced oxidative stress. We have identified 9-hydroxy linoleic acid (9-OH-C18:2) in the red cell membrane phospholipid of diabetic subjects. We hypothesized that 9-OH-C18:2 would be formed in hydroxyl radical reactions to linoleic acid (C18:2) during glucose-induced oxidative stress, and confirmed that the formation of 9-OH-C18:2 was induced by ultraviolet (UV)-C irradiation to the synthetic C18:2. UV-C light generates highly reactive hydroxy radicals. C18:2 is confirmed to be the precursor of 9-OH-C18:2. To estimate the degree of oxidative damage to red cell membrane phospholipids, we developed a selective ion monitoring gas chromatography-mass spectrometric measurement for C18:2 and 9-OH-C18:2, following methanolysis of red cell membrane phospholipids. The relative peak height ratio of C18:2 to 9-OH-C18:2 (9-OH-C18:2/C18:2) was measured in phospholipid extracts of red cell membranes from healthy (n=29, 3.1+/-1.9%) and diabetic (n=27, 20. 9+/-16.1%) subjects. It was confirmed that 9-OH-C18:2/C18:2 is significantly (P<0.001) elevated in patients with diabetes. The measurement of 9-OH-C18:2/C18:2 in red cell membranes should be useful for assessing oxidative damage to membrane phospholipids in diabetes. (+info)
Enhanced in vivo lipid peroxidation at elevated plasma total homocysteine levels.
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An elevated plasma total homocysteine level (tHcy) is considered an independent risk factor for atherosclerosis. The mechanisms by which hyperhomocysteinemia induces atherosclerosis are only partially understood, but promotion of LDL oxidation and endothelial injury have been suggested. The purpose of this study was to test the hypothesis that a high plasma tHcy is associated in men with increased in vivo lipid peroxidation, as measured by plasma F2-isoprostane concentrations. We investigated this association in a subset of the participants in the Antioxidant Supplementation in Atherosclerosis Prevention (ASAP) study. Of 256 male participants, a subsample of 100 consecutive men was selected for F2-isoprostane assays. The mean tHcy was 11.0 micromol/L, and the mean F2-isoprostanes was 29.6 ng/L. The simple correlation coefficient for association between tHcy and F2-isoprostane was 0.40 (P<0.001). In a linear regression model, the variables with the strongest associations with F2-isoprostane were tHcy (standardized coefficient 0.33, P<0.001), serum triglycerides (0.21, P=0.042), carbohydrate-deficient transferrin (0.15, P=0.132), and plasma lipid-standardized alpha-tocopherol (-0.11, P=0.252) (R2=0.24, P<0. 001 for model). Plasma F2-isoprostane levels increased linearly across quintiles of tHcy (P<0.001). The unadjusted mean (95% confidence interval) F2-isoprostanes was 47.5% greater in the highest tHcy quintile (37.4, 31.1 to 43.6 ng/L) than in the lowest quintile (25.3, 21.3 to 29.3 ng/L). Adjustment for the strongest other determinants of F2-isoprostane reduced this difference to 28. 2% (P=0.010). Our present data suggest that elevated fasting plasma tHcy is associated with enhanced in vivo lipid peroxidation in men. (+info)
Reduced postprandial serum paraoxonase activity after a meal rich in used cooking fat.
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Paraoxonase is an enzyme associated with HDL in human serum that hydrolyzes oxidized phospholipids and inhibits LDL oxidation, which is an important step in atherogenesis. In animals, addition of oxidized lipids to the circulation reduces paraoxonase activity, and diets rich in oxidized fat accelerate the development of atherosclerosis. The current randomized, crossover study was designed to compare the effect of a meal rich in oxidized lipids in the form of fat that had been used for deep-frying in a fast food restaurant and a control meal rich in the corresponding unused fat on postprandial serum paraoxonase (arylesterase) activity and peroxide content of LDL and its susceptibility to copper ion catalyzed oxidation in 12 healthy men. Four hours into the postprandial period, serum paraoxonase activity had decreased significantly after the used fat meal (-17%, P=0.005) and had increased significantly after the meal rich in unused fat (14%, P=0. 005). These changes were significantly (P=0.003) different. A time-course study indicated that serum paraoxonase activity remained lower than baseline for up to 8 hours after the used fat meal. Serum apoA1 concentration tended to decrease after the unused fat meal and tended to increase after the used fat meal. These changes were different at a marginal level of significance (P=0.07). Also, a significantly (P=0.03) greater decrease in apoA1 content of postprandial HDL was recorded after the unused fat meal. The peroxide content of LDL tended to decrease after the used fat meal and tended to increase after the control meal. These changes were significantly (P=0.04) different. Susceptibility of isolated LDL to copper ion oxidation and plasma levels of malondialdehyde were unchanged during the study. These data suggest that in the postprandial period after a meal rich in used cooking fat, the enzymatic protection of LDL against accumulation of peroxides and atherogenic oxidative modification may be reduced, possibly due to factors associated with apoA1, without acutely affecting the intrinsic resistance of LDL to in vitro oxidation. (+info)
Effects of native, triglyceride-enriched, and oxidatively modified LDL on plasminogen activator inhibitor-1 expression in human endothelial cells.
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Whereas VLDL has consistently been shown to induce a concentration-dependent increase in the expression of plasminogen activator inhibitor-1 (PAI-1) in human umbilical vein endothelial cells (HUVECs) and liver cells, variable effects have been reported for native and oxidatively modified LDL. In the present study, activation of PAI-1 protein and mRNA expression by native LDL (nLDL), UV-oxidized LDL (uvLDL), and triglyceride (TG)-enriched LDL was studied in HUVECs by using different incubation times and a wide range of lipoprotein concentrations. No significant increase of PAI-1 protein expression was observed after 4 hours of incubation with nLDL or uvLDL. However, PAI-1 protein secretion from HUVECs was markedly enhanced after 18 hours of incubation with uvLDL (200% increase at 10 microg/mL). Stimulation of PAI-1 protein expression in HUVECs by nLDL was seen, however, after increasing the TG content of the LDL particle. LDL enriched in phospholipid had no effect on PAI-1 secretion. PAI-1 mRNA levels on northern blot increased in parallel with the activation of PAI-1 protein expression by native and modified forms of LDL. Low concentrations of TG-enriched LDL (10 microg/mL) and higher concentrations of nLDL and uvLDL (100 microg/mL) were found to increase the binding of a VLDL-inducible transcription factor to the PAI-1 promoter. These results indicate that the TG content of the LDL particle influences PAI-1 expression in endothelial cells. Low concentrations of uvLDL enhanced PAI-1 protein and mRNA expression in the HUVECs after an 18-hour incubation but did not influence the VLDL-inducible transcription factor. This suggests that low levels of oxidized LDL increase PAI-1 expression by a different mechanism than VLDL and TG-enriched LDL. (+info)