Lipid peroxide formation in microsomes. Relationship of hydroxylation to lipid peroxide formation

1. Metal ion-chelating agents such as EDTA, o-phenanthroline or desferrioxamine inhibit lipid peroxide formation when rat liver microsomes prepared from homogenates made in pure sucrose are incubated with ascorbate or NADPH. 2. Microsomes treated with metal ion-chelating agents do not form peroxide on incubation unless inorganic iron (Fe(2+) or Fe(3+)) in a low concentration is added subsequently. No other metal ion can replace inorganic iron adequately. 3. Microsomes prepared from sucrose homogenates containing EDTA (1mm) do not form lipid peroxide on incubation with ascorbate or NADPH unless Fe(2+) is added. Washing the microsomes with sucrose after preparation restores most of the capacity to form lipid peroxide. 4. Lipid peroxide formation in microsomes prepared from sucrose is stimulated to a small extent by inorganic iron but to a greater extent if adenine nucleotides, containing iron compounds as a contaminant, are added. 5. The iron contained in normal microsome preparations exists in haem and in non-haem forms. One non-haem component in which the iron may be linked to phosphate is considered to be essential for both the ascorbate system and NADPH system that catalyse lipid peroxidation in microsomes.     

Square-wave adsorptive voltammetry of dexamethasone: redox mechanism, kinetic properties, and electroanalytical determinations in multicomponent formulations

The electrochemical reduction behavior of dexamethasone at a hanging mercury drop electrode was investigated by cyclic and square-wave adsorptive voltammetries in a Britton–Robinson buffer at pH 2.0. The optimized experimental conditions consisted of a pulse potential frequency of 100 s⁻¹, a pulse amplitude of 15 mV, and a potential step height of 2 mV, with E_acc = −0.60 V and t_acc = 15 s. From these parameters, it was also possible to develop a detailed study about the kinetic and mechanistic events involved in the reduction process. Two well-defined peaks were observed in the cathodic scan, and peak 2 was used to obtain analytical curves. A linear range between 4.98 × 10⁻⁸ and 6.10 × 10⁻⁷ mol L⁻¹, with a detection limit of 2.54 × 10⁻⁹ mol L⁻¹ and a quantification limit of 8.47 × 10⁻⁹ mol L⁻¹, was observed. Moreover, it was possible to achieve a simple, selective, and versatile methodology adaptable to the quantification of dexamethasone because common excipients used in multicomponent commercial formulations caused no interference. The satisfactory recoveries and the low relative standard deviation data reflected the high accuracy and precision of the proposed method for the determination of dexamethasone in injectable eye drops and elixir samples.     

The peroxidase nature of cytochrome P-420 utilizing a lipid peroxide substrate

The peroxidase properties of cytochrome P-420, in its “high spin” and “low spin” forms, have been investigated using N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) as hydrogen donor, linoleic acid hydroperoxide (LAHPO) as substrate, and a preparation of cytochrome P-420 from hepatic microsomal “P-450 particles” as catalyst. The peroxidase reaction was found to be first order with respect to P-420 concentration and first order with respect to LAHPO concentration. Of the various hydroperoxides tested, only LAHPO was found to serve as a substrate for P-420.     

The effectiveness of a lipid peroxide in oxidizing protein and non-protein thiols

1. Thiol oxidation by a lipid peroxide or hydrogen peroxide was as efficient in denatured non-haem proteins as in small thiols. Both peroxides were relatively ineffective in oxidizing haemoprotein thiols, especially at low pH. Increased amounts of haematin decreased greatly the efficiency of GSH oxidation by peroxides especially at low pH. 2. Other than the haematin ring, the thiol group was found to be probably the group in proteins most sensitive to modification by peroxides. 3. At low concentrations, the fatty acid moiety of a lipid peroxide appeared to impede thiol oxidation in proteins, probably by hydrophobic bonding to the protein, rather than to stimulate thiol oxidation by denaturing the protein and thereby increasing the exposure and reactivity of the thiol group. 4. The relative rates of thiol oxidation by peroxides in the different thiols were: haemoprotein thiols>small thiols>other protein thiols. In all cases, thiol oxidation was much more rapid by the lipid peroxide than by hydrogen peroxide.     

Interaction between hydrogen peroxide and ferrous sulfate as a basis for glucose determinations

Summary The interaction between hydrogen peroxide and ferrous sulfate (Fenton's reaction) results in an increase in absorbance between the wavelengths of 240–400 nm. The greatest increase in absorbance occurs at 260 nm. Addition of glucose to a solution of glucose oxidase and ferrous sulfate results in an instantaneous increase in absorbance at 260 nm which is dependent upon glucose concentration and pH, with greatest increase occurring at pH 4.0. A solution of glucose oxidase and ferrous sulfate could be used as a reagent for manual glucose determinations.Operated by Martin Marietta Energy Systems, Inc., for the U.S. Department of Energy under Contract No. DE-ACO5-84OR21400.     

Mechanisms of lipid peroxide formation in animal tissues

1. Homogenates of rat liver, spleen, heart and kidney form lipid peroxides when incubated in vitro and actively catalyse peroxide formation in emulsions of linoleic acid or linolenic acid. 2. In liver, catalytic activity is distributed throughout the nuclear, mitochondrial and microsomal fractions and is present in the 100000g supernatant. Activity is weak in the nuclear fraction. 3. Dilute (0·5%, w/v) homogenates catalyse peroxidation over the range pH5·0–8·0 but concentrated (5%, w/v) homogenates inhibit peroxidation and destroy peroxide if the solution is more alkaline than pH7·0. 4. Ascorbic acid increases the rate of peroxidation of unsaturated fatty acids catalysed by whole homogenates of liver, heart, kidney and spleen at pH6·0 but not at pH7·4. 5. Catalysis of peroxidation of unsaturated fatty acids by the mitochondrial and microsomal fractions of liver is inhibited by ascorbic acid at pH7·4 but the activity of the supernatant fraction is enhanced. 6. Inorganic iron or ferritin are active catalysts in the presence of ascorbic acid. 7. Lipid peroxide formation in linoleic acid or linolenic acid emulsions catalysed by tissue homogenates is partially inhibited by EDTA but stimulated by o-phenanthroline. 8. Cysteine or glutathione (1mm) inhibits peroxide formation catalysed by whole homogenates, mitochondria or haemoprotein. Inhibition increases with increase of pH.     

Lipid peroxidation and lipid peroxide detected by chemiluminescence

This article emphasizes the advantages of using a luminescence spectrometer based on photon counting techniques for the detection of lipid peroxidation. An overview is presented of how chemiluminescence can be stimulated in the luminol-cytochrome c heme peptide system as an assay for lipid hydroperoxides. This method is used for finding antioxidant drugs. The specificity and advantages of the chemiluminescent method for detecting lipid hydroperoxides is reviewed.     

Plasma and erythrocyte lipid peroxide levels in workers with occupational exposure to lead

The plasma and erythrocyte lipid peroxide levels were measured in a group of male subjects occupationally exposed to lead for an average period of 17 yr, and compared to those from an age-matched control group living in the same city in a similar socioeconomical environment. The blood lead and plasma zinc levels were measured by atomic absorption spectroscopy. The plasma and erythrocyte lipid peroxide levels were established by the malondialdehyde determination method. Significant differences were found in the blood lead levels in lead-exposed workers, 15.00±10.15 μg/dL as compared to controls, 2.37±0.89 μg/dL. The plasma (2.67±0.69 μM) and erythrocyte (27.53±6.28 nmol/g Hb) lipid peroxide levels in workers with occupational exposure to lead were significantly higher than controls, 1.23±0.61 μM and 14.35±2.08 nmol/g Hb, respectively. There were no significant differences of the zinc levels in both groups. The blood lead levels had a statistically significant positive correlation with age and with duration of exposure in both groups, but showed no relationship to the corresponding blood zinc levels. The results presented in this study indicate that the increase of plasma and erythrocyte lipid peroxide levels in workers exposed to lead may be related to the lead concentration, age and duration of exposure.     

Suitability and recovery of capillary blood plasma for lipid determinations]

Plasma lipid analysis, particularly in population screening, can be facilitated by the use of capillary blood. A system for serial collection of capillary plasma is described. The concentrations of total cholesterol, HDL-cholesterol and triglycerides in heparinized capillary plasma and venous blood, respectively, are compared. No significant differences were found. Using the KAPA-method hemolytic samples are a source of error. They occurred with a frequency of about 3% in mass screening.     

SD大鼠血液及某些组织过氧化脂质参考值的探讨

用SD大鼠检测正常血清及肝、肺和肠组织的黄嘌呤氧化酶(XOD)、还原谷光甘肽(GSH)和丙二醛(MDA)含量的变化,采用多指标测试的方法进行分析。通过上述指标检测．为大鼠有关过氧化脂质提供一些参考数据。     

Cytochrome c-catalyzed membrane lipid peroxidation by hydrogen peroxide.

Cytochrome c(3+)-catalyzed peroxidation of phosphatidylcholine liposomes by hydrogen peroxide (H2O2) was indicated by the production of thiobarbituric acid reactive substances, oxygen consumption, and emission of spontaneous chemiluminescence. The iron chelator diethylenetriaminepentaacetic acid (DTPA) only partially inhibited peroxidation when H2O2 concentrations were 200 microM or greater. In contrast, iron compounds such as ferric chloride, potassium ferricyanide, and hemin induced H2O2-dependent lipid peroxidation which was totally inhibitable by DTPA. Cyanide and urate, which react at or near the cytochrome-heme, completely prevented lipid peroxidation, while hydroxyl radical scavengers and superoxide dismutase had very little or no inhibitory effect. Changes in liposome surface charge did not influence cytochrome c3+ plus H2O2-dependent peroxidation, but a net negative charge was critical in favoring cytochrome c(3+)-dependent, H2O2-independent lipid auto-oxidative processes. These results show that reaction of cytochrome c with H2O2 promotes membrane oxidation by more than one chemical mechanism, including formation of high oxidation states of iron at the cytochrome-heme and also by heme iron release at higher H2O2 concentrations. Cytochrome c3+ could react with mitochondrial H2O2 to yield "site-specific" mitochondrial membrane lipid peroxidation during tissue oxidant stress.     

Serum lipid peroxide levels of albino rats administered naphthalene

When naphthalene was administered at a daily dose of 1 g/kg body weight to Wistar strain rats, their serum lipid peroxide levels were increased on the 4th day after the first administration and reached a maximum on the 7th day. This seems to be due to lipid peroxidation in the liver, in which lipid peroxide levels were increased in a similar pattern as those in the serum. The content of reduced glutathione in lenses of naphthalene-administered rats decreased on the 4th day. These results suggest that in naphthalene-induced cataract in albino rats increased lipid peroxides in the bloodstream may play a role in cataractogenesis.