Hours Of Oxidation Research Articles

Immunoreactivity of apolipoprotein B-100 in oxidatively modified low density lipoprotein.

Thirteen monoclonal antibodies (MAbs) against apolipoprotein B-100 (apo B) were used to analyze changes in immunoreactivity of human LDL resulting from oxidation mediated by cupric ions and oxygen. Decrease in immunoreactivity of oxidized LDL was demonstrated by competitive ELISA with MAbs 5F8, BL3, Mb43, 2G8, B3, B5, and BL7 for which the epitopes are located within residues 1-1297, 4235-4355, 4027-4081, 3728-4306, 2239-2331, 1854-1878, and in the vicinity of residue 2331, respectively. Immunoreactivity of the epitope B6 (2239-2331) increased during first 4 hours of oxidation and then diminished gradually. Epitope B1 (405-539) had slightly reduced immunoreactivity during first 8 h of LDL oxidation and then its minor increase was observed. MAb 12G10, specific to the epitope within apo B thrombin-digest fragment T4 (1-1297), displayed either weak or strong binding to LDL. LDL with weak binding pattern demonstrated significant increase in immunoreactivity upon oxidation. In contrast, LDL with strong binding pattern showed little to no change. Epitopes Mb47 (3441-3569) and 8G4 (1-1297) remained unchanged in oxidized LDL. Immunoreactivity of apo B-100 epitope recognized by MAb 4C11 (residues 2377-2658) was shown to be a function of oxidation time: it increased progressively up to 16 h and was stabilized for another 24 h of LDL oxidation. This epitope may be unmasked by LDL oxidation and may provide a useful immunochemical marker to monitor the extent of LDL oxidation.

Identification of multiple dense LDL subfractions with enhanced susceptibility to in vitro oxidation among hypertriglyceridemic subjects. Normalization after clofibrate treatment.

The influence of different plasma triglyceride concentrations on the heterogeneity of low density lipoprotein (LDL) and on the susceptibility of LDL to copper oxidation was investigated. By density gradient ultracentrifugation, LDL subfractions were isolated from the plasma of 10 normolipidemic control subjects and 12 hypertriglyceridemic patients both before and after clofibrate treatment. In the plasma of control subjects three LDL subfractions were present: LDL1 (d = 1.030-1.033 g/mL), LDL2 (d = 1.033-1.040 g/mL), and LDL3 (d = 1.040-1.045 g/mL). In the plasma of nine moderately hypertriglyceridemic subjects up to five LDL subfractions could be detected: LDL1-LDL3, LDL4 (d = 1.045-1.049 g/mL), and LDL5 (d = 1.049-1.054 g/mL). This polydispersity of LDL was replaced by monodispersity with increasing plasma triglyceride concentrations in three subjects with chylomicronemia, in whom LDL was concentrated in the narrow LDL5 density range. Clofibrate treatment resulted in a lighter LDL subfraction pattern (LDL1-LDL4). In both the control and the moderately hypertriglyceridemic subjects, the small dense LDL subfractions appeared more prone to oxidative modification in vitro than the light LDL subfractions, as measured by the decreased lag time preceding the onset of lipid peroxidation. Furthermore, the dense LDL subfractions were more extensively modified over time, as shown by an increased oxidation rate and a greater number of dienes formed after 6 hours of oxidation. These results suggest an enhanced atherogenic potential of the small, dense LDL subfractions within each LDL subfraction profile. The hypertriglyceridemic LDL subfractions before therapy (LDL3-LDL5) were less resistant to in vitro oxidation than the light, control LDL subfractions (LDL1-LDL3).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of arterial proteoglycans and glycosaminoglycans on low density lipoprotein oxidation and its uptake by human macrophages and arterial smooth muscle cells.

The reversible interaction of low density lipoprotein (LDL) with arterial chondroitin sulfate proteoglycans (CSPGs) or glycosaminoglycans (GAGs) selects LDL particles with a high affinity for sulfated GAGs and also induces modifications in apolipoprotein B (apo B) and the lipid organization of the lipoprotein. In the present work we studied the effect that the reversible interaction with sulfated polysaccharides has on the susceptibility of LDL to in vitro oxidation. For this purpose soluble, nonaggregated CSPG- or GAG-treated LDL was subjected to oxidation in the presence of 5 microM CuSO4 for as long as 48 hours. The rate of formation of thiobarbituric acid-reactive substances, the decrease in isoelectric point, the increase in relative electrophoretic mobility of LDL, the higher degradation rate by human macrophages, and the lower degradation rate by human arterial smooth muscle cells showed that LDLs exposed to CSPGs and GAGs were significantly more susceptible to oxidation than native LDL. Results from competition experiments indicate that C6S-treated LDL after 4 hours of oxidation is taken up via the acetylated LDL receptor in human macrophages. Coincubation of lipoproteins with human macrophages or human arterial smooth muscle cells for 24 hours also indicated that C6S-treated LDL was more susceptible to cell-induced modifications than native LDL. The occurrence in vivo of similar processes may contribute to focal retention, increased rate oxidation of LDL in the arterial intima, and foam cell formation during atherogenesis.

Enhanced susceptibility to in vitro oxidation of the dense low density lipoprotein subfraction in healthy subjects.

Oxidative modification of low density lipoprotein (LDL) has been implicated as a factor in the generation of macrophage-derived foam cells, the hallmark of atherosclerotic plaques. Because LDL consists of discrete subfractions with different physicochemical characteristics, the question arises as to whether these LDL subfractions differ in their susceptibility to oxidative modification. To answer this question, three LDL subfractions, LDL1, LDL2, and LDL3, were isolated from the plasmas of 11 healthy volunteers by density gradient ultracentrifugation. The LDL subfractions were oxidatively modified by incubation with copper ions. Differences in the subfractions' susceptibilities to lipid peroxidation were studied by measuring the formation of the 234-nm-absorbing oxidation products every 3 minutes on an ultraviolet spectrophotometer. A significant inverse linear relation was found between LDL subfractions and lag time (regression coefficient = -8.50, p less than 0.001), indicating that both the dense LDL3 and the light LDL2 were less well protected against oxidative modification than the very light LDL1. The LDL subfractions showed a positive linear relation with the rate of oxidation (regression coefficient = 0.46, p less than 0.001) and the amount of conjugated dienes formed in the LDL subfractions after 4 hours of oxidation (regression coefficient = 9.24, p less than 0.001). Thus, both LDL3 and LDL2 were more extensively modified in time than LDL1, which may be explained by the significantly higher concentration of polyunsaturated fatty acids in LDL3 (micromoles per gram LDL cholesterol) compared with LDL1 (Tukey's test, p less than 0.05). These results indicate that the more dense LDL subfractions, that is, LDL2 and LDL3, are more susceptible to oxidative modification and therefore may contribute more to foam cell formation than the less dense LDL subfraction LDL1.

Ion sputter rates of CrMnFe spinel oxides

AbstractThe oxide which forms on stainless steel is duplex in nature, with an outer spinel covering an inner rhombohedral Cr2O3. The thickness of the oxide is only a few micrometers, even after many thousands of hours of oxidation at high temperatures, and hence surface analytical techniques are required to characterize the oxide. In particular, depth analysis is obtained using the scanning Auger microprobe in conjunction with argon ion bombardment. The etch rates are at present assumed to be the same as that measured using a tantalum oxide standard. To obtain a more accurate measure of sputter rates on the spinel oxides 20%Cr/25%Ni/TiN‐strengthened steel has been oxidized and the thickness determined by independent means. These data have then been used to determine the etch rates, which are compared with that on tantalum pentoxide.

Influence of the prior oxide film on the growth and structure of oxides formed on Fe26Cr alloys at 600°C

A Fe26 Cr alloy has been oxidized at 600°C in 5 × 10 −3, 5 × 10 −2 and 5 × 10 −1 torr oxygen to examine the influence of the prior oxide film on the growth and structure of oxides formed at high temperature. Different prior oxides were produced either by electropolishing or by annealing the electropolished specimen in vacuum at 600°C. Auger electron spectroscopy (AES) showed the Cr content of the prior oxide film to be increased from ∼ 50 to ∼ 95% during annealing, and electron diffraction indicated a change in oxide structure from amorphous to crystalline. At 5 × 10 −3 torr, electropolished Fe26 Cr oxidizes faster than the vacuum annealed specimens because the amorphous prior oxide gives rise to a finer-grained cubic oxide with more grain boundary easy diffusion paths for cation transport. From AES and electron back-scattering Fe 57 Mössbauer spectroscopy it is concluded that this cubic oxide is a duplex layer of inner γ-Cr 2O 3 and outer Fe 3O 4. The oxidation rate slows markedly when nucleated α-Fe 2O 3 covers the cubic oxide. With increased oxidation time Fe 3O 4 converts to α-Fe 2O 3 and the γ-Cr 2O 2 to α-Cr 2O 3. Annealed Fe26 Cr oxidizes slower primarily because of a lower cation transport through a coarser-grained cubic oxide rather than because of a higher Cr content in the prior oxide. α-Fe 2O 3 nucleates at an earlier stage in the oxidation and essentially stifles the reaction. The extent of Cr incorporation into any of the Fe oxides produced in 5 × 10 −3 torr oxygen is small (⋞ 5%). Increasing the oxygen pressure from 5 × 10 −3 to 5 × 10 −2 and 5 × 10 −1 torr has little effect on the mechanism of oxidation of vacuum annealed Fe26 Cr, except that the overall extent of oxidation is less because of earlier α-Fe 2O 3 formation and, after a few hours of oxidation, up to ∼ 20% Cr is incorporated into the α-Fe 2O 3 lattice. On electropolished Fe26 Cr at 5 × 10 −2 and 5 × 10 −1 torr oxygen nodules of α-Cr 2O 3 form and continue to grow both at grain boundaries and within the grains. Possible mechanisms for this nodule formation, which is exclusive to electropolished specimens oxidized at the higher pressures, are considered.

Electrical properties of growing alumina scales

Scales growing on platinum 22 wt.% aluminum specimens at 1100°C were investigated by the following electrical techniques: open-circuit potential and short-circuit current as a function of time and oxygen pressure; current-voltage relationship at several oxygen pressures; transients in the short-circuit current on rapidly changing the oxygen pressure; changes in the growth rate with applied potential. The growth characteristics of the scale were also investigated using kinetic and metallographic techniques. The apparent parabolic rate constant of oxidation decreases in the first hours of oxidation and stabilizes after 20–30 hr at 2 × 10−13 g2·cm−4·sec−1. Transport in the scale is by lattice and grain-boundary diffusion and the changing kinetics are a consequence of changes in the oxide grain size. It was also determined that the electrical characteristics of the scale were affected by the hydrogen-water or carbon monoxide-carbon dioxide atmospheres used to obtain low oxygen pressures. Due to these complexities and to the difficulty in making a satisfactory oxide-gas electrode only qualitative observations could be made from the electrical measurements. These measurements are compatible with the scale having constant ionic conductivity in the pressure range 1 to 10−15 aim and predominantly electronic conductivity at lower oxygen pressures. The rate of oxidation can be accelerated or retarded by passing a current through the scale.

Oxidation of columbium (niobium) and coated columbium alloys

Oxidation of columbium alloys FS-85, SU-31, and a complex disilicide coating SU-31 and FS-85 alloy systems has been studied in the temperature range 1400–2700°F (760–1482°C) at 1 atm and 50 cm/s flow rate of air. For studies of the uncoated alloys, the flow rate and pressure dependence of the alloys was also investigated. The experimental methods included thermogravimetric measurements of oxidation rates and studies on reacted specimens by means of X-ray diffraction, metallographic techniques, and electron-microprobe analysis. Two anomalies in the temperature dependence of the oxidation rate were observed for both alloys and were related to the oxides formed. The SU-31 alloy has the best oxidation resistance. The oxidation mechanism of the alloys is discussed along with the mechanism of protection afforded by the complex disilicide coating system. The coating did not fail after 1000 hours of oxidation.