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At least 109 records · Page 6Linked to original sources
PubMed1999

Comparison between in vitro lipid peroxidation in fresh sheep platelets and peroxidative processes during sheep platelet ageing under storage at 4 degrees C.

Incubation of sheep platelet crude membranes with xanthine oxidase (XO)/hypoxanthine/Fe(2+)-ADP revealed: (i) a fast peroxidative response - with a maximal linear rate of 14 nmol malondialdehyde (MDA) equivalents/mg protein, as evidenced by the thiobarbituric acid test - and a decrease in the polyunsaturated fatty acid (PUFA) content of the platelet crude membranes; (ii) a decrease in the lipid fluidity in the deep lipid core of the membranes but not at the membrane surface; (iii) a dramatic inhibitory effect on glucose 6-phosphatase (Glc-6-Pase) but not on acetylcholinesterase activity. Platelets were also aged by storage at 4 degrees C in their own plasma or in Seto additive solution. In these media, platelet aggregates were visible and the effects on platelet phospholipids, PUFA, lipid extract fluorescence, crude membrane fluidity and membrane-bound enzyme activities were assessed for comparison with those observed in in vitro lipid peroxidation. The sensitivity of membranes from stored platelets to lipid peroxidation was also assessed. Storage of platelets in plasma for 5 days was associated with different changes in their crude membranes such as decreases in arachidonic acid contents, the decrease not being avoided by the presence of phospholipase A(2) inhibitors, increases in MDA equivalents, conjugated dienes and lipid extract fluorescence, decreases in the amounts of MDA equivalents formed by platelet crude membranes treated with the oxidizing agents, changes in membrane fluidity and inhibition of Glc-6-Pase. All these alterations were less pronounced or even abolished after platelet storage in Seto. These findings suggest that platelet lipid peroxidation due to XO/hypoxanthine/Fe(2+)-ADP and platelet membrane alterations observed after platelet ageing under storage at 4 degrees C share common features. Also, as regards the prevention of peroxidative processes, Seto solution permits better storage of sheep platelets than plasma.

Acetylcholinesterase↗
PubMed2000

Kinetic analysis of copper-induced peroxidation of HDL, autoaccelerated and tocopherol-mediated peroxidation.

Comparison of the kinetic profiles of copper-induced peroxidation of HDL and LDL at different copper concentrations reveals that under all the studied experimental conditions HDL is more susceptible to oxidation than LDL. The mechanism responsible for HDL oxidation is a complex function of the copper/HDL ratio and of the tocopherol content of the HDL. At high copper concentrations, the kinetic profiles were similar to those observed for LDL oxidation, namely, relatively rapid accumulation of oxidation products, via an autoaccelerated, noninhibited mechanism, was preceded by an initial "lag phase." Under these conditions, the maximal peroxidation rate (V(max)) of HDL and LDL depended similarly on the molar ratio of bound copper/lipoprotein. Analysis of this dependency in terms of the binding characteristics of copper to lipoprotein, yielded similar dissociation constant (K = 10(-6) M) but different maximal binding capacities for the two lipoproteins (8 Cu(+2)/HDL as compared to 17 Cu(+2)/LDL). Given the size difference between HDL and LDL, these results imply that the maximal surface density of bound copper is at least 2-fold higher for HDL than for LDL. This difference may be responsible for the higher susceptibility of HDL to copper-induced oxidation in the presence of high copper concentrations. At relatively low copper concentrations, the kinetic profile of HDL oxidation was biphasic, similar to but more pronounced than the biphasic kinetics observed for the oxidation of LDL lipids at the same concentration of copper. Our results are consistent with the hypothesis that the first phase of rapid oxidation occurs via a tocopherol-mediated-peroxidation (TMP) mechanism. Accordingly, enrichment of HDL with tocopherol resulted in enhanced accumulation of hydroperoxides during the first phase of copper-induced oxidation. Notably, the maximal accumulation during the first phase decreased upon increasing the ratio of bound copper/HDL. This behavior can be predicted theoretically for peroxidation via a TMP mechanism, in opposition to autoaccelerated peroxidation. The possible pathophysiological significance of these findings is discussed.

Copper↗
PubMed1997

Characterization of hydrogen peroxide removal activities in mouse hemolysates: catalase activity and hydrogen peroxide removal activity by hemoglobin.

Hydrogen peroxide removal activities in normal and acatalasemic mouse hemolysates were examined to determine the optimal temperature of catalase. From thermal stability of the removal activities in hemolysates, the removal activities were divided into two activities. The removal activity deactivated at lower temperature was catalase, and the 50% inactivation was observed after 10 min incubation at 47.2 +/- 0.5 degrees C for normal hemolysates and 34.0 +/- 0.8 degrees C for acatalasemic ones. The removal activity deactivated at a higher temperature remained after the addition of sodium azide, and the 50% inactivation was observed at 63.5 +/- 1.4 degrees C. After separation of the removal activities by carboxymethyl-cellulose column chromatography, the removal activity deactivated at higher temperature was attributed to the activity by hemoglobin. From Lineweaver-Burk plot analysis of the removal rates by hemoglobin at 37 degrees C, the Michaelis constant for hydrogen peroxide and the maximum velocity were 201 +/- 53 microM and 5.37 +/- 1.39 micromol/s per g of Hb, respectively. Removal rates by hemoglobin in mouse hemolysates at 37 degrees C in 70 microM hydrogen peroxide were 1.32 +/- 0.12 micromol/s per g of Hb. Catalase activity (k/g Hb: rate constant related to the hemoglobin content) in normal mouse hemolysates was 104 +/- 12 at 25 degrees C and 117 +/- 10 at 37 degrees C, and that in acatalasemic hemolysates was 10.5 +/- 1.7 at 25 degrees C. These results indicate that activity of hydrogen peroxide removal by hemoglobin is substantial and the activity in acatalasemic hemolysates is predominant at low concentration of hydrogen peroxide.

Acatalasia↗
PubMed2005

Lipid peroxides in obese patients and effects of weight loss with orlistat on lipid peroxides levels.

OBJECTIVE: Obesity is a well-known risk factor of atherosclerosis. Recent studies showed that obesity is associated with enhanced lipid peroxidation. The aim of this study is to investigate the effect of weight reduction with orlistat treatment on lipid peroxidation levels. We assessed lipid peroxidation by measuring the concentration of plasma malondialdehyde (MDA). DESIGN: A randomized, controlled, open-label 6-month study. SUBJECTS: In total, 36 obese (body mass index (BMI) >30 kg/m2) and 11 healthy age-matched control subjects were enrolled in the study. MEASUREMENTS: Fasting glucose, triglyceride, total cholesterol, HDL cholesterol and LDL cholesterol and MDA levels were measured in both groups. Obese subjects received orlistat, 120 mg three times daily together with hypocaloric diet. After 6 months of treatment laboratory tests were repeated. RESULTS: MDA levels were significantly higher in obese patients than the control group (P<0.0001). After 6 months of treatment in obese subjects, the mean weight of the patients decreased by 6.8 kg, the BMI by 3.2 kg/m2. Plasma MDA levels were significantly reduced by weight loss from 2+/-0.77 to 0.89+/-0.41 nmol/ml (P<0.001). BMI correlated with MDA levels at baseline (r=0.6, P<0.0001). Changes in BMI was positively associated with plasma MDA level reduction (r=0.36, P<0.05). CONCLUSION: These results indicate that obesity is associated with increases in endogenous lipid peroxides. Our data show that the indicator of lipid peroxidation-MDA-falls markedly in association with weight loss with orlistat. The demonstration of decreased free radical generation has important implications for oxidative mechanism underlying obesity-associated disorders.

Adult↗
PubMedDate not supplied

Effects of vitamin E deficiency and nitrogen dioxide exposure on lung lipid peroxidation: use of lipid epoxides and malonaldehyde as measures of peroxidation.

The effect of vitamin E deficiency in male Sprague-Dawley rats upon lipid peroxidation in lung tissue was examined by measuring malonaldehyde and lipid epoxide production. In addition to controls, some animals were also exposed to 3 +/- 0.1 ppm NO2 continuously for 7 d in order to study the effects of oxidant stress on lung lipid peroxidation and vitamin E content. The observed changes in malonaldehyde and epoxide content could serve as good indices of lipid peroxidation, particularly under conditions of vitamin E deprivation. The responses measured indicated an inverse relation in the lung between tissue vitamin E content and quantity of lipid peroxidation products. Measurement of lipid epoxides served as a reliable indicator of lung tissue lipid peroxidation. Finally, NO2 inhalation appeared to elicit a response characterized by increased assimilation of vitamin E into lung tissue.

Animals↗
PubMedDate not supplied

Lipid peroxidation in autoimmune systemic vasculitides. Effect of corticoid treatment on lipid peroxidation. Antioxidant protection with vitamin E.

The effect of treatment with prednisone on lipid peroxidation and on lipid metabolism generally and the effect of vitamin E on plasma lipid peroxidation were studied in a group of patients with autoimmune systemic vasculitides. Vitamin E total plasma antioxidant capacity was determined to ascertain the antioxidant efficiency of vitamin E. Treatment with prednisone was found to induce disturbances of the lipid metabolism at the level of total cholesterol and of triglycerides. The increased values of the LDL/HDL ratio showed an increased risk of vascular disturbance in the patients investigated. The high level of lipid peroxides associated with a reduced activity of the endogenous antioxidant system was found to be uninfluenced by treatment with prednisone. Treatment with vitamin E reduced the process of lipid peroxidation but the endogenous deficiency of the antioxidant capacity prevented it to resume its normal values. In spite of the antiinflammatory and antioxidant treatment the high level of lipid peroxides might induce a self-maintained chronic process which, in time, might lead to the aggravation of the degenerative vascular changes.

Adult↗
PubMed1994

Effects of dietary oils and methyl ethyl ketone peroxide on in vivo lipid peroxidation and antioxidants in rat heart and liver.

Weanling male Sprague-Dawley rats were fed diets for four weeks which differed in their content of n-6 (corn oil; CO) and n-3 fatty acids (fish oil; FO), but were similar in their content of saturated and monounsaturated fatty acids and vitamin E. At the end of the four-week feeding period, each dietary group was subdivided into two groups. One group received a single placebo injection of alpha-tocopherol-stripped corn oil (TSCO); the other group received a single injection of the free radical generator; methyl ethyl ketone peroxide (MEKP), in TSCO. Twenty-four hours after injection, the effect of dietary oil and MEKP treatment on endogenous lipid peroxide (LPO) production (measured as methylene blue formed by the "Determiner LPO" assay), glutathione (GSH) and vitamin E content, and fatty acid composition of phosphatidylcholine and phosphatidylethanolamine in heart and liver from unfasted animals were measured. FO-fed rats had significantly heavier hearts and livers, increased levels of n-3 fatty acids in membrane phospholipids, and higher liver LPO levels than CO-fed rats. MEKP treatment resulted in significantly lower body weights and liver GSH levels. The data indicate that dietary n-3 fatty acids increase lipid peroxidation in liver somewhat more than in heart. The study also demonstrates that the effect of induced oxidative stress due to a single dose of MEKP on lipid peroxide formation and antioxidant status in tissues from unfasted animals was independent of the dietary oils.

Animals↗
PubMed1987

A nonenzymatic method for determination of hydrogen peroxide and organic peroxides.

Reduction of hydrogen peroxide and organic peroxides (t-butyl hydroperoxide and linoleic acid hydroperoxide) was achieved with homovanillic acid as hydrogen donor in the presence of the triethylenetetramine-Fe3+ complex. By the catalytic action of this complex, homovanillic acid is oxidized to its fluorescent dimer. Based on this reaction a fluorometric method for the measurement of the hydroperoxides mentioned above is described. The method can be extended to the determination of substrate-enzyme systems that produce hydrogen peroxide, e.g., glucose-glucose oxidase. The method allows the determination of substances such as hydrogen peroxide and t-butyl hydroperoxide with an accuracy and precision of less than 3%. Glucose can be determined with similar precision and an accuracy of 4.7%.

Glucose Oxidase↗
PubMed1985

Interaction of PGBx and peroxides with cytochrome c and inhibition of lipid peroxidation.

PGBx, a derivative of prostaglandin B1, stimulated the oxidation of cytochrome c in the presence of H2O2. Although the reaction was nonenzymatic, the apparent activation energies of 12 and 4.9 kcal above and below the transition at 21.5 degrees C were similar to those for oxidation by cytochrome oxidase. Depletion of H2O2 and oxidation of cytochrome c followed similar time courses, suggesting that H2O2 was consumed in the reaction. PGBx was a specific requirement, but organic hydroperoxides (ethyl and T-butyl) could replace H2O2. Low concentrations of ethyl or t-butyl hydroperoxide initially stimulated the oxidation of cytochrome c; this stimulation disappeared before completion of the oxidation, but was restored when the hydroperoxide concentration was renewed, suggesting that these hydroperoxides were probably also consumed in the reaction. The concentration of PGBx (8.9 microM) required for half-maximum stimulation of the oxidation was similar to the apparent Kd for its dissociation from oxidized cytochrome c (6.8 microM). Binding data and CD spectra suggested that a 1:1 complex between cytochrome c and PGBx was formed, altering the conformation of the heme region. This conformational change caused a shift of the Soret absorption peak from 410 to 406 nm and may be responsible for the enhanced oxidizability of the cytochrome c by H2O2. Cytochrome c inhibited lipid peroxidation in microsomes, an effect enhanced by the addition of PGBx. In the absence of lipid peroxidation, cytochrome c and PGBx stimulated NADPH oxidation via NADPH-cytochrome c reductase. Thus the inhibition of lipid peroxidation by cytochrome c and PGBx may involve either the removal of hydroperoxides or deviation of electron transfer away from the pathway for lipid peroxidation.

Animals↗
PubMed1985

Effects of formaldehyde, acetaldehyde, benzoyl peroxide, and hydrogen peroxide on cultured normal human bronchial epithelial cells.

The effects of several aldehydes and peroxides on growth and differentiation of normal human bronchial epithelial cells were studied. Cells were exposed to formaldehyde, acetaldehyde, benzoyl peroxide (BPO), or hydrogen peroxide (HPO). The effect of each agent on the following parameters was measured: (a) clonal growth rate; (b) squamous differentiation; (c) DNA damage; (d) ornithine decarboxylase activity; (e) nucleic acid synthesis; (f) aryl hydrocarbon hydroxylase activity; and (g) arachidonic acid and choline release. None of the agents were mitogenic, and their effects were assessed at concentrations which reduced growth rate (population doublings per day) to 50% of control. The 50% of control concentrations for the 6-h exposure were found to be 0.065 mM BPO, 0.21 mM formaldehyde, 1.2 mM HPO, and 30 mM acetaldehyde. BPO-exposed cells were smaller than controls (median cell planar area, 620 sq microns versus 1150 sq microns), and acetaldehyde-exposed cells were larger than controls (median cell planar area, 3200 sq microns). All agents increased the formation of cross-linked envelopes and depressed RNA synthesis more than DNA synthesis. HPO caused DNA single-strand breaks, while formaldehyde and BPO caused detectable amounts of both single-strand breaks and DNA-protein cross-links. Other effects included increased arachidonic acid and choline release due to HPO. The similarities and differences of the effects of these aldehydes and peroxides to those caused by tumor promoters are discussed.

Acetaldehyde↗
PubMed1985

Peroxidation of liposomes in the presence of human erythrocytes and induction of membrane damage of erythrocytes by peroxidized liposomes.

Hemolysis (Kobayashi, T., Takahashi, K., Yamada, A., Nojima, S. and Inoue, K. (1983) J. Biochem. 93, 675-680) and shedding of acetylcholinesterase-enriched membrane vesicles (diameter 150-200 nm) were observed when human erythrocytes were incubated with liposomes of phosphatidylcholine which contained polyunsaturated fatty acyl chains. These events occurring on erythrocyte membrane were inhibited by radical scavengers or incorporation of alpha-tocopherol into liposomes, suggesting that lipid peroxidation is involved in the process leading to membrane vesiculation and hemolysis. The idea was supported by findings that generation of chemiluminescence, formation of thiobarbituric acid reactive substance, accumulation of conjugated diene compounds in liposomes and decrease of polyunsaturated fatty acids in liposomes occurred concomitantly during incubation. Hemolysis was also suppressed by the addition of extra liposomes, insensitive to peroxidation, or of serum albumin even after the completion of peroxidation of liposomes. These results suggest that peroxidized lipids, responsible for vesiculation and hemolysis, may be formed first in liposomes and then gradually transferred to erythrocyte membranes. The accumulation of these lipids peroxides may eventually cause membrane vesiculation followed by hemolysis.

Egg Yolk↗
PubMed1979

Peroxidative breakdown of phospholipids in human spermatozoa, spermicidal properties of fatty acid peroxides, and protective action of seminal plasma.

Aerobic incubation of human spermatozoa in the presence of catalytic amounts of ascorbate and ferrous ion results in rapid peroxidative breakdown of sperm phospholipids and fatty acids; most strongly affected are phosphatidyl ethanolamine, ethanolamine plasmalogen, and docosahexanoic acid. Both peroxidation of the endogenous sperm phospholipid and the concurrent loss of motility can be fully prevented, but not reversed, by an "antiperoxidant" factor present in human seminal plasma. Exogenously applied lipid peroxides are powerfully spermicidal. Washed human spermatozoa, at a concentration normally present in semen, treated with as little as 30 nmoles of lipid peroxide/ml become irreversibly immotile within a few minutes. The antiperoxidant factor present in human seminal plasma effectively counteracts the toxic effect of exogenous peroxidized fatty acids upon human spermatozoa, but is unable to restore motility lost by lipid peroxide action.

Chemical Phenomena↗
PubMed1988

Endotoxin causes hydrogen peroxide-induced lung lipid peroxidation and prostanoid production.

We studied the role of hydrogen peroxide release on endotoxin-induced lung injury in unanesthetized sheep with chronic lung lymph fistulas. We also further defined the relationship between endotoxin injury, lipid peroxidation, and prostaglandin production. Sheep were given endotoxin alone (1 microgram/kg) or pretreated with catalase (32,500 U/kg) or ibuprofen (12.5 mg/kg). Endotoxin alone resulted in an early prostanoid release, lipid peroxidation measured as circulating conjugated dienes both one and four hours after the administration of endotoxin, pulmonary hypertension, hypoxia, and increased protein permeability. Permeability was monitored by lymph flow and lymph protein content. Catalase pretreatment significantly attenuated all of these aspects of the endotoxin response. Ibuprofen prevented the early lung changes and blocked prostanoid release but did not attenuate the increased permeability. In addition, cyclo-oxygenase inhibition had a dual effect on lipid peroxidation, increasing initial conjugated diene levels while suppressing the later release. The initial effect was clearly related to cyclo-oxygenase blockade. The early conjugated diene release appears to be related to arachidonic acid metabolism and does not correspond to the degree of increased permeability. We conclude that H2O2 plays a major role in lung injury after endotoxin.

Animals↗
PubMed2000

TNF-alpha and IL-1alpha induce apoptosis in subconfluent rat mesangial cells. Evidence for the involvement of hydrogen peroxide and lipid peroxidation as second messengers.

Apoptosis of mesangial cells (MC) plays a role in glomerulonephritis (GN). In this study we investigated cytokine-induced apoptosis of cultured rat MC by morphological and biochemical features. TNF-alpha and IL-1alpha induced apoptosis in rat MC in a time- and concentration-dependent fashion. RT-PCR experiments revealed that MC express the TNF-receptor 1 (p60) gene constitutively. TNF-alpha as well as IL-1alpha stimulated the production of reactive oxygen species (ROS) and induced lipid peroxidation. Coincubation with catalase inhibited TNF-alpha and IL-1alpha induced apoptosis as well as lipid peroxidation. TNF-alpha, but not IL-1alpha increased the expression of c-jun. These results provide evidence that TNF-alpha and IL-1alpha induce apoptosis in rat MC with hydrogen peroxide and lipid peroxidation as second messengers. Increased c-jun expression may be a downstream intracellular signal of TNF-alpha-, but not IL-1alpha-induced apoptosis.

Animals↗
PubMed1989

tert-butyl hydroperoxide-dependent microsomal release of iron and lipid peroxidation. II. Evidence for the involvement of nonheme, nonferritin iron in lipid peroxidation.

In a previous study tert-butyl hydroperoxide (t-BOOH) was found to promote reductive release of nonheme, nonferritin iron from rat liver microsomes. The reaction was catalyzed by cytochrome P450 and was strictly contingent on the availability of ADP. In this study, t-BOOH was also found to promote microsomal lipid peroxidation, as evidenced by formation of malondialdehyde. t-BOOH-dependent lipid peroxidation was stimulated by ADP, and four lines of evidence suggested that such stimulation was mediated by reductive release and subsequent redox cycling of nonheme, nonferritin iron. First, lipid peroxidation was stimulated by the same concentration of ADP that promoted iron release. Second, depletion of nonheme, nonferritin iron by pretreatment of rats with phenobarbital decreased the stimulation of lipid peroxidation by ADP. Third, the effect of ADP was maximal when the concentration of t-BOOH was adjusted to values that yielded maximum iron release. Fourth, the effect of ADP was abolished by bathophenanthroline, which is known to chelate ferrous iron in a redox inactive form. These results suggest that the reductive release of nonheme, nonferritin iron exacerbates the deleterious effects of t-BOOH on microsomal lipids.

Adenosine Diphosphate↗
PubMed1984

Superoxide and hydrogen peroxide-dependent lipid peroxidation in intact and triton-dispersed erythrocyte membranes.

Isolated erythrocyte membranes incubated with xanthine, xanthine oxidase, and Fe(III) underwent lipid peroxidation, as indicated by the thiobarbituric acid reaction and iodometric determination of hydroperoxides. In detergent-free medium (phosphate buffered saline) peroxidation was inhibited by superoxide dismutase, catalase, and EDTA; but was promoted by OH. scavangers, eg. mannitol. Generation of OH. in the system via iron-catalyzed reduction of H2O2 by O-2 was demonstrated by EPR spectrometry using spin trapping. In membranes treated with Triton X-100 lipid peroxidation was stimulated by EDTA and suppressed by OH. traps. This and other evidence suggests that OH. in the medium was an effective initiator of lipid peroxidation in detergent-dispersed membranes, but not in intact membranes.

Catalase↗
PubMed1994

Spectral characterization of lipid peroxidation in rabbit lens membranes induced by hydrogen peroxide in the presence of Fe2+/Fe3+ cations: a site-specific catalyzed oxidation.

The role of free-radical-induced lipid peroxidation (LPO) in relation to lens opacity is investigated using Fourier transform infrared spectroscopy. Phospholipids extracted from nuclear and cortical regions of the rabbit lens membranes are subjected to oxidative-damage induced by hydrogen peroxide and Fe2+/Fe3+ cations. Vibrational data suggest a homolytic decomposition of the unsaturated membrane hydrocarbon chains at cis-double bonds, as well as structural modifications at the carbonyl and phosphate-oxygen sites of the fiber cell membranes upon metal oxidation. This is also evident from a substantial induction of the carbonyl groups and a significant dephosphorylation of the phosphate groups in lens phospholipids. These covalent modifications and/or alterations of the carbonyl and phosphate groups, and specificity of certain vibrational modes only to iron oxidation, may serve as a diagnostic probe of the metal-catalyzed LPO in lens membranes. Despite covalent modifications of the hydrophilic part of the lens membranes, hydrocarbon chain region remains largely intact at physiological concentrations of hydrogen peroxide. However, at elevated concentrations of hydrogen peroxide, a substantial breakdown of the acyl chains occurs. Striking similarities observed between the spectral features of the oxidized rabbit lens phospholipids and those of the cataractous human lenses suggest that the mechanism and pathways of lipid oxidation in model animal membranes and in human lenses are similar. Differences in the nuclear or cortical regions are also evident upon metal oxidation. Nuclear lipids experience increased effects of the metal oxidation compared to cortical lipids. Both the nuclear or the cortical lipids indicate effective penetration of the bilayer water creating segregated membrane domains, possibly through breakdown of headgroup-specific lipid-water interactions. This could effectively alter the lens membrane permeability and fluidity, rendering it susceptible to a host of toxic oxidants present in the eye. These findings also demonstrate that LPO can lead to acyl chain degradation that may effectively derange the lens membrane function, which could be a contributing factor in cataractogenesis.

Animals↗
PubMed1981

Hydrogen peroxide and hematin in microsomal lipid peroxidation.

Lipids of rat liver microsomes underwent peroxidation with production of malondialdehyde in the presence of H2O2 and hematin. Rates of peroxidation of 27-33 nmol of MDA formed/mg of microsomal protein/30 min were measured with 5 mM H2O2 and 10 microM hematin at 22 degrees C. Histidine (0.01 M) caused a 55% inhibition. Hematin could be added to the reaction mixtures either simultaneously with H2O2 or afterwards, when all H2O2 had been destroyed by catalase present in the microsomal preparation. Catalase was necessary for formation of MDA. Indeed, when heat-denatured microsomes were employed, incubation with H2O2 and the iron complex led to formation of lipid hydroperoxides; however, no production of MDA was observed, unless exogenous catalase was added together with H2O2 and hematin to the reaction mixture. The role of H2O2 in microsomal lipid peroxidation is that of promoting the formation of fatty acid hydroperoxides. These are decomposed in the presence of hematin, with formation of free radicals, bicyclic endoperoxides and MDA. Catalase is necessary to remove H2O2, which, after starting the peroxidation process, blocks the decomposition of lipid hydroperoxides, apparently by binding to the iron complex.

Animals↗