Ferrous ion oxidation in the presence of xylenol orange for detection of lipid hydroperoxide in low density lipoprotein.

A simple and sensitive method for the direct measurement of lipid peroxides in lipoprotein and liposomes is described. The method is based on the principle of the rapid peroxide-mediated oxidation of Fe2+ to Fe3+ under acidic conditions. The latter, in the presence of xylenol orange, forms a Fe(3+)-xylenol orange complex which can be measured spectrophotometrically at 560 nm. Calibration with standard peroxides, such as hydrogen peroxide, linoleic hydroperoxide, t-butyl hydroperoxide, and cumene hydroperoxide gives a mean apparent extinction coefficient of 4.52 x 10(4) M-1 cm-1 consistent with a chain length of approximately 3 for ferrous ion oxidation by hydroperoxides. Endoperoxides are less reactive or unreactive in the assay. The assay has been validated in the study of lipid peroxidation of low density lipoprotein and phosphatidyl choline liposomes. By pretreatment with enzymes known to metabolize peroxides, we have shown that the assay measures lipid hydroperoxides specifically. Other methods for measuring peroxidation, such as the assessment of conjugated diene, thiobarbituric acid reactive substances and an iodometric assay have been compared with the ferrous oxidation-xylenol orange assay.     

Hyperoxia results in transient oxidative stress and an adaptive response by antioxidant enzymes in goldfish tissues

The effects of hyperoxia on the status of antioxidant defenses and markers of oxidative damage were evaluated in goldfish tissues. The levels of lipid peroxides, thiobarbituric acid reactive substances, carbonyl proteins and the activities of some antioxidant enzymes were measured in brain, liver, kidney and skeletal muscle of goldfish, Carassius auratus L., over a time course of 3-12 h of hyperoxia exposure followed by 12 or 36 h of normoxic recovery. Exposure to high oxygen resulted in an accumulation of protein carbonyls in tissues throughout hyperoxia and recovery whereas lipid peroxides and thiobarbituric acid reactive substances accumulated transiently under short-term hyperoxia stress (3-6 h) but were then strongly reduced. This suggests that hyperoxia stimulated an enhancement of defenses against lipid peroxidation or mechanisms for enhancing the catabolism of peroxidation products. The activities of principal antioxidant enzymes, superoxide dismutase and catalase, were not altered under hyperoxia but catalase increased during normoxic recovery; activities may rise in anticipation of further hyperoxic excursions. In most tissues, the activities of glutathione-utilizing enzymes (glutathione peroxidase, glutathione-S-transferase, glutathione reductase) as well as glucose-6-phosphate dehydrogenase, were not affected under hyperoxia but increased sharply during normoxic recovery. Correlations between some enzyme activities and oxidative stress markers were found, for example, an inverse correlation was seen between levels of thiobarbituric acid reactive substances and glutathione-S-transferase activity in liver and catalase and glucose-6-phosphate dehydrogenase in kidney. The results suggest that liver glutathione-S-transferase plays an important role in detoxifying end products of lipid peroxidation accumulated under hyperoxia stress.     

Critical role of peroxiredoxin 6 in the repair of peroxidized cell membranes following oxidative stress

Phospholipids are a major structural component of all cell membranes; their peroxidation represents a severe threat to cellular integrity and their repair is important to prevent cell death. Peroxiredoxin 6 (Prdx6), a protein with both GSH peroxidase and phospholipase A₂ (PLA₂) activity, plays a critical role in antioxidant defense of the lung and other organs. We investigated the role of Prdx6 in the repair of peroxidized cell membranes in pulmonary microvascular endothelial cells (PMVEC) and isolated mouse lungs treated with tert-butyl hydroperoxide and lungs from mice exposed to hyperoxia (100% O₂). Lipid peroxidation was evaluated by measurement of thiobarbituric acid reactive substances, oxidation of diphenyl-1-pyrenylphosphine, or ferrous xylenol orange assay. The exposure dose was varied to give a similar degree of lipid peroxidation at the end of exposure in the different models. Values for lipid peroxidation returned to control levels within 2 h after oxidant removal in wild-type PMVEC and perfused lungs but were unchanged in Pxdx6 null preparations. An intermediate degree of repair was observed with PMVEC and lungs that expressed only C47S or D140A mutant Prdx6; the former mutant does not have peroxidase activity, while the latter loses its PLA₂ activity. Prdx6 null mice showed markedly delayed recovery from lipid peroxidation during 20 h observation following exposure to hyperoxia. Thus, Prdx6 plays a critical role in the repair of peroxidized phospholipids in cell membranes and the recovery of lung cells from peroxidative stress; the peroxidase and PLA₂ activity each contribute to the recovery process.     

"In vitro" effect of lipid peroxidation metabolites on elongation factor-2

Elongation Factor-2 (eEF-2) is the protein that catalyzes the translocation of the ribosome through mRNA. Not all oxidants affect eEF-2, which is extremely sensitive to oxidative stress caused mainly by lipid peroxidant compounds such as cumene hydroperoxide and t-butyl hydroperoxide. Lipid peroxides constitute a potential hazard to living organisms because of their direct reactivity with a variety of biomolecules and the ability to decompose into free radicals and reactive aldehydes. In this "in vitro" study, we show the effect of three of these aldehydes on the levels of hepatic eEF-2. The results suggest that the toxicity associated with prooxidant-mediated hepatic lipid peroxidation on protein synthesis can originate from the interaction of the aldehydic end products of lipid peroxidation with eEF-2.     

Effect of gossypol on tissue levels of glutathione and thiobarbituric acid reactive products in rats.

Gossypol was administered in pubertal and adult rats and lipid peroxide formation and GSH levels were estimated in different tissues like liver, testis, heart and kidney. Gossypol caused low generation of lipid peroxides, measured as thiobarbituric acid reactive products (TBAR), without causing significant changes in tissue glutathione (GSH) levels. This effect was more pronounced in liver and testis as compared to other tissues. In vitro effect of gossypol to inhibit lipid peroxidation as observed in vivo suggested that binding of gossypol to plasma membranes may result in inhibition of lipid peroxide generation.     

Studies on the properties of the singlet oxygen-like factor produced during lipid peroxidation

The singlet oxygen reaction product of various trapping agents is observed during enzymic and nonenzymic peroxidation of microsomes as well as during the peroxidation of pure lipids extracted from microsomes. We now wish to report that purified fatty acid hydroperoxide alone, as well as peroxidized microsomal lipid and cumene hydroperoxide also form the singlet oxygen reaction product with 2,5-diphenylfuran. The reaction product (cis-1,2-dibenzoylethylene) was observed to be formed in an anaerobic system, with or without EDTA. The data indicate that a reaction of hydroxyl radicals with 2,5-diphenylfuran cannot account for the formation of dibenzoylethylene in these systems. These results are consistent with a hypothesis that the singlet oxygen-like factor was formed from the lipid peroxides per se and, in addition, supports the possibility that either the peroxides can react directly with diphenylfuran to produce dibenzoylethylene or that the self-reaction of organic peroxides may form an intermediate product which can react directly with singlet oxygen-trapping agents to produce substances which are identical to a reaction of the trapping agents with singlets oxygen.     

Lipid hydroperoxide levels in plant tissues

Hydroperoxides are the primary oxygenated products of polyunsaturated fatty acids and are key intermediates in the octadecanoid signalling pathway in plants. Lipid hydroperoxides (LHPO) were determined spectrophotometrically based on their reaction with an excess of Fe(2+)at low pH in the presence of the dye xylenol orange. Triphenylphosphine-mediated hydroxide formation was used to authenticate the signal generated by the hydroperoxides. The method readily detected lipid peroxidation in Phaseolus: microsomes, senescing potato leaves and in a range of other plant tissues including Phaseolus hypocotyls (26+/-5 nmol g(-1) FW), Alstroemeria floral tissues (sepals 66+/-13 nmol g(-1) FW petals 49+/-6 nmol g(-1) FW), potato leaves (334+/-75 nmol g(-1) FW), broccoli florets (568+/-68 nmol g(-1) FW) and Chlamydomonas cells (602+/-40 nmol g(-1) FW). Relative to the total fatty acid content of the tissues, the % LHPO was within the range of 0.6-1.7% for all tissue types (photosynthetic and non-photosynthetic) and represents the basal oxidation level of membrane fatty acids in plant cells. In order to relate the levels of LHPO to specific signalling pathways, transgenic potato plant lines were used in which lipoxygenase (LOX) (responsible for hydroperoxide biosynthesis) and hydroperoxide lyase (a route of hydroperoxide degradation) activities were largely reduced by an antisense-mediated approach. While the LHPO levels were similar to wild type in the individual LOX antisensed plants, basal LHPO levels, by contrast, were elevated by 38% in transgenic potato leaves antisensed in hydroperoxide lyase, indicating a role for this enzyme in the maintenance of cellular levels of LHPOs.     

Hematin- and peroxide-catalyzed peroxidation of phospholipid liposomes

The effect of hydroperoxides on hematin-catalyzed initiation and propagation of lipid peroxidation was examined utilizing soybean phosphatidylcholine liposomes as model membranes. Polarographic and spectrophotometric methods revealed a bimodal pseudocatalytic activity for hematin. A slow initiation phase of peroxidation was observed in the presence of low peroxide concentrations, whereas a fast propagative phase was observed at higher peroxide levels. Peroxide levels were manipulated enzymatically by the combination of phospholipase A2 and lipoxidase or by the direct addition of linoleic acid hydroperoxide, cumene hydroperoxide, or hydrogen peroxide. In addition, the effect of two different techniques for liposome preparation, i.e., sonication and extrusion, were compared on the basis of peroxidation kinetics. High pressure liquid chromatography analysis showed that sonicated liposomes contained higher levels of endogenous peroxides than the extruded ones. These sonicated liposomes also exhibited more rapid peroxidation following hematin addition. Extruded liposomes were more resistant to hematin-catalyzed peroxidation but became better substrates when exogenous hydroperoxides were added. All three peroxides reacted with hematin during which decomposition of peroxide and irreversible oxidation of hematin took place. Spectral analysis of hematin indicated that a higher oxidation state of hematin iron may be transiently formed during reaction with hydroperoxides and accounts for the propagation of lipid peroxidation when reactions proceed in the presence of soybean phosphatidylcholine liposomes. Of the three peroxides studied, linoleic acid hydroperoxide was most efficient in supporting hematin-catalyzed lipid peroxidation. The relevance of our findings is discussed in terms of the concentration dependence for lipid peroxides in determining the rate and extent of radical propagation chain reactions catalyzed by heme-iron catalysts such as hematin. Variation of hematin and linoleic hydroperoxide concentrations may provide an efficient and reproducible method for inducing and manipulating the rates and extent of lipid peroxidation through facilitation of the propagative phase of lipid peroxidation. In addition, we address a problem inherent to in vitro studies of heme-catalyzed lipid peroxidation where preparations of peroxide-free membranes should be of concern.     

Spectrophotometric measurement of hydroperoxides at increased sensitivity by oxidation of Fe2+ in the presence of xylenol orange

The method, developed by modifying the FOX methods described by Wolff (Methods Enzymol. 233, 182-189, 1994), involves the oxidation of Fe²⁺ by peroxides at low pH in the presence of both the ferric-complexing dye xylenol orange and sucrose, the amplifier of the reaction. The method proved to be a convenient, simple and efficient assay for the direct measurement of both water and lipid soluble peroxides. In fact it improves by about 60% the sensitivity of the FOX1 method for water soluble peroxides, and by 7-8 times that of the FOX2 method for lipid soluble peroxides. It allows the detection of 0.1 μM peroxide in the test solution. The method is suitable to measure the lipid hydroperoxides present in phosphatidylcholine liposomes and in human LDL. The data obtained allowed us to define a mathematical expression to calculate the lipid hydroperoxide content of liposomes knowing their oxidation index.     

Ultraviolet-treated lipoproteins as a model system for the study of the biological effects of lipid peroxides on cultured cell. I. Chemical modifications of ultraviolet-treated low-density lipoproteins

A new experimental model system constituted by ultraviolet-treated low-density lipoproteins (LDL) has been designed in order to investigate the biological effects of lipid peroxides entering the cell through the endocytotic pathway. This paper reports the chemical modifications of the lipid components and apolipoproteins of the ultraviolet-treated LDL. Human LDL were submitted to short ultraviolet radiations (254 nm, 0.5 mW/cm2, for variable periods of time) and compared to LDL peroxidized by iron. The lipid peroxidation was monitored by following the formation of the peroxidation products (conjugated dienes, thiobarbituric acid-reactive substances (TBARS) and fluorescent lipid-soluble products) and the change of the composition in polyunsaturated fatty acids, carotenes and vitamin E. Several parameters of the apo B-100 structure were investigated: molecular size (by SDS-PAGE) and TNBS-reactive amino groups (chemical determination by trinitrobenzene sulfonic acid). The most important feature was the absence of major modification of apo B-100 in ultraviolet-treated LDL: the molecular weight and the content in TNBS-reactive amino groups of apo B-100 were not modified. In contrast, iron-treated LDL exhibited a loss of the apo B-100 band and a decrease in the number of TNBS-reactive amino group. Both ultraviolet radiations and iron ions induced a significant decrease in the content of polyunsaturated fatty acids, carotenes and vitamin E together with a large formation of lipid peroxidation products. However, the time-course of the formation of conjugated dienes, TBARS and fluorescent lipid-soluble products was quite different using the two oxidative systems. These results demonstrate that ultraviolet radiations induced a strong peroxidation of the lipid content of LDL and no (or only minor) changes in the apolipoprotein moiety whereas iron-catalyzed peroxidation resulted in the formation fo lipid peroxidation products as well as apo B alterations.     

Plasma thiobarbituric acid reactivity: reaction conditions and the role of iron, antioxidants and lipid peroxy radicals on the quantitation of plasma lipid peroxides

The effects of Fe3+, lipid peroxy radicals and the antioxidant butylated hydroxytoluene on the 2-thiobarbituric (TBA) acid quantitation of plasma lipid peroxides were investigated. Whole plasma and plasma fractions prepared by trichloroacetic acid (TCA) protein precipitation and lipid extraction, demonstrated markedly differing TBA reactivities in the presence or absence of added Fe3+. Examination of the spectral profiles of the TBA reacted whole plasma and TCA precipitated fractions demonstrated the presence of interfering compounds which gave rise to an artifactual increase in lipid peroxide concentrations. In contrast the TBA reacted lipid extracts had low levels of interfering compounds that could be removed by our previously described high pressure liquid chromatographic method (Wade, Jackson and van Rij (1985) Biochem. Med. 33, 291-296). Further characterization of the TBA reactivity of the lipid extract showed that Fe3+ at an optimal concentration of 0.5 mM was necessary for the quantitative decomposition of the lipid peroxides to the TBA reactive product malondialdehyde (MDA). However the presence of Fe3+ resulted in further peroxidation of any unsaturated lipids present. Butylated hydroxytoluene (BHT) at an optimal concentration of 1.4 mM inhibited Fe3+ stimulated peroxidation without affecting the formation of the MDA-TBA chromogen. Using a standardized TBA test with plasma lipid extracts and the addition of optimal concentrations of Fe3+ and BHT, we have determined the mean concentration of lipid peroxides in 30 healthy human subjects to be 102.7 +/- 20.0 ngm/ml.     

Lipoprotein Oxidation and Induction of Ferroxidase Activity in Stored Human Extracellular Fluids

It was observed that during the storage of human extracellular fluids at – 20°C the azide-inhibitable ferroxidase activity of caeruloplasmin declined, whilst a new azide-resistant ferroxidase activity (ARFA) developed. The literature suggested that storage-induced ARFA might be due to either a poorly defined enzymatic activity of a low density lipoprotein (LDL) or to lipid peroxides formed within the different lipoprotein fractions. To study this further, the major lipoprotein classes were separated from human serum by density gradient centrifugation. After storage of the lipoprotein fractions, it was found that the LDL fraction had the highest specific activity of ARFA and the highest content of lipid peroxidation products, as assessed by diene conjugates. The ARFA of LDL correlated with its content of diene conjugates and TBA reactive material, which initially suggested that the Fe(II) oxidising activity of peroxidised LDL arose from the reduction of peroxides by Fe(II) in the classical reaction between the metal ion and free radical reduction of lipid peroxides. However. steady state kinetic analysis indicated an enzymic role of LDL in Fe(II) oxidation, with lipid peroxides acting as a substrate for the enzyme. These results indicate that LDL may contain a peroxidase activity. catalysing the oxidation of Fe(II) by lipid peroxides, as well as a ferrous oxidase activity where O₂ is the oxidising substrate.     

The effect of hyperbaric oxygenation on the antioxidant status of Xenopus laevis after its preliminary adaptation to oxygen]

We studied the level of lipid peroxidation and the activity of antioxidant enzymes (superoxide dismutase and catalase) in various tissues of adult Xenopus laevis after an initial exposure to hyperbaric oxygenation at the developmental stage 38. We have found that irrespective to the mode of treatment, the level of lipid peroxidation and activity of antioxidant enzymes in the brain, lungs, and blood of these animals were higher as compared to control animals. We demonstrate that, after the exposure of adult animals to hyperoxia, if they were earlier subjected to hyperbaric oxygenation (0.2 MPa) at stage 38, there was no intensification of lipid peroxidation or changes in the activity of superoxide dismutase and catalase. In adult animals initially subjected to hyperbaric oxygenation at the same stage of development but at the pressure--0.7 MPa, the second exposure to hyperoxia led to a drastic intensification of lipid peroxidation in the brain; in some animals, an increased level of lipid peroxidation products in the lungs was observed.     

Effect of bacterial lipopolysaccharide on the content of lipid peroxidation products in lungs and other organs of mice

The influence of lipopolysaccharide fromEscherichia coli (LPS, 17 mg/kg body weight) on the lipid peroxidation process in organs of mice was studied. The content of conjugated dienes (CD), lipid peroxides (LP), malondialdehyde (MDA) (all three lipid peroxidation by-products), peroxidase (PO) activity and wet-to-dry weight ratio in lungs, heart, spleen, kidneys and liver were determined 1.5 h after intravenous injection of LPS. Animals observed at this time-point had reduced activity and decreased body temperature by about 2°C, however, all analysed organs did not reveal any changes of wet-to-dry weight ratio comparing to organs from mice injected with sterile, pyrogen free 0,9% NaCl. Only extracts from heart and lungs showed significant increase in the tissue level of at least two lipid peroxidation products. The heart content of CD, MDA, and LP was about 1.5-, 1.3-, and 2.4-fold higher than in control group. In lungs CD and MDA increased 3.3- and 1.3-times but in spleen only content of LP was elevated. In these organs the suppression of PO activity was also observed. Liver and kidneys did not reveal any convincing enhancement of lipid peroxidation process and alterations of PO activity. Since free radical reactions are involved in lipid peroxidation process and inactivation of PO these results suggest that heart, lungs and spleen are the organs mostly exposed to oxidative stress during the first 1.5 h after single injection of LPS in mice.Abbreviations CD conjugated dienes - LP lipid peroxides - LPS lipopolysaccharide - MDA malondialdehyde - PMNL polymorphonuclear leukocytes - PO peroxidase - TBA thiobarbituric acid     

Decreased lipid peroxidation in the rat kidney during gestation

Renal malonaldehyde content and lipid peroxidation, induced by ascorbate, NADPH and cumene hydroperoxide, are significantly decreased during gestation in rats. Lipid peroxidation tends to reach normal levels in the kidney post partum. In the renal mitochondria lipid peroxidation without co-factors and that induced by cumene hydroperoxide, ascorbate and NADPH is decreased during pregnancy. However, in the microsomes, only lipid peroxidation induced by NADPH and cumene hydroperoxide is affected. The observed decrease in lipid peroxidation during gestation is reflected by low levels of total lipid and phospholipid. Endogenous inhibitors of lipid peroxidation also increase during pregnancy.     

The use of cis-parinaric acid to determine lipid peroxidation in human erythrocyte membranes. Comparison of normal and sickle erythrocyte membranes

The recently developed parinaric acid assay is shown to offer possibilities for studying peroxidation processes in biological membrane systems. Taking the human erythrocyte membrane as a model, several initiating systems were investigated, as well as the effect of residual hemoglobin in ghost membrane preparations. The effectivity of a radical generating system appeared to be strongly dependent upon whether radicals are generated at the membrane level or in the water phase. Thus, cumene hydroperoxide at concentrations of 1.0-1.5 mM was found to be a very efficient initiator of peroxidation in combination with submicromolar levels of hemin-Fe3+ as membrane-bound cofactor. In combination with cumene hydroperoxide, membrane-bound hemoglobin appeared to be about 6-times more effective in promoting peroxidation than hemoglobin in the water phase. Results comparing the behaviour of normal and sickle erythrocyte ghost suspensions in the peroxidation assay suggest that the increased oxidative stress on sickle erythrocyte membranes could be due to enhanced membrane binding of sickle hemoglobin, but also partly to a characteristically higher capability of sickle hemoglobin to promote peroxidation. The order of peroxidation-promoting capabilities that could be derived from the experiments was hemin greater than sickle hemoglobin greater than normal hemoglobin.     

Method for the simultaneous determination of free/protein malondialdehyde and lipid/protein hydroperoxides

A simple and sensitive method is presented for the simultaneous quantification (spectrophotometric and spectrofluorimetric) of the main lipid and protein peroxidation products after their initial fractionation: free malondialdehyde (FrMDA), protein-bound malondialdehyde (PrMDA), total hydroperoxides (LOOH), and protein hydroperoxides (PrOOH). FrMDA and PrMDA (released from proteins by alkaline hydrolysis) are measured after the reaction of MDA with thiobarbituric acid (TBA) under acidic conditions, by the specific fluorimetric quantification of the resulting MDA–(TBA)₂ adduct chromophore. The measurement of LOOH and PrOOH is based on the reaction of Fe³⁺ (resulting from the reaction of LOOH and PrOOH with Fe²⁺) with xylenol orange (XO) and the photometric quantification of the resulting XO–Fe complex. The sensitivity of the assays for FrMDA/PrMDA and LOOH/PrOOH is 20 and 100 pmol, respectively. The method was applied successfully on human plasma and can be used for the evaluation of oxidative stress in both basic and clinical research.     

Temperature increase results in oxidative stress in goldfish tissues. 1. Indices of oxidative stress

Levels of lipid peroxides (LOOH), thiobarbituric-acid reactive substances (TBARS), protein carbonyls and low- and high-molecular weight thiols were measured in brain, liver, kidney, and white muscle of goldfish, Carassius auratus L., over 1-12 h of high temperature (35 degrees C) exposure followed by 4 or 24 h of lower (21 degrees C) temperature recovery. LOOH and TBARS contents increased during heat shock exposure with a maximal rise of 20-fold for liver TBARS, but both mainly reversed at recovery. Protein carbonyl content was unaffected by heat shock but rose in brain, liver, and kidney during recovery. Low-molecular weight thiol concentrations unexpectedly increased up to approximately 4-fold in brain, kidney and muscle under heat shock and remained high during recovery. Protein thiol contents also rose in liver and muscle during high temperature exposure by 2- and 3-fold, respectively, and decreased to control values or below in all tissues at late recovery. Low- and high-molecular weight thiol levels inversely correlated in liver (R2=0.87) suggesting that the former was used to reduce the latter over the experiment. It is concluded that the redox balance in goldfish tissues is strictly maintained probably contributing to the high tolerance of this species to heat shock.     

铝离子对二价铁离子启动的卵磷脂脂质体脂质过氧化的影响

利用化学发光、ＴＢＡ 反应与测量共轭二烯的方法观测了Ａｌ３ ＋ 对Ｆｅ２ ＋ 启动的卵磷脂脂质体脂质过氧化的影响。实验结果显示,在生理ｐＨ 条件下,Ａｌ３ ＋ 对Ｆｅ２ ＋ 启动的脂质过氧化有增强作用,表现为缩短潜伏期和加快脂质过氧化的反应速率, Ａｌ３ ＋ 的增强作用与脂质体中原先存在的过氧化物有关。这可能是因为在脂质体存在的条件下,Ａｌ３ ＋ 加速了Ｆｅ２ ＋ 的氧化,且加速作用与脂质体中原先存在的过氧化物的含量有关;另一方面,Ａｌ３ ＋ 可以引起脂质体的聚集,表现为浊度的增加;测量脂质体上标记的脂肪酸自旋标记物５ － Ｄｏｘｙｌ ｓｔｅａｒｉｃ ａｃｉｄ 的ＥＳＲ 波谱发现： Ａｌ３ ＋ 降低了脂质体的膜脂的流动性。研究表明： Ａｌ３ ＋ 对Ｆｅ２ ＋ 启动的卵磷脂脂质体的过氧化的增强作用可能与Ａｌ３ ＋ 加速了Ｆｅ２ ＋ 的氧化和改变了脂质体的物理状态有关     

Ferric(III) ions inhibits copper(II)/hydrogen peroxide-catalyzing lipid peroxidation in human erythrocyte membranes.

1. Effect of ferric ions (Fe3+) on the lipid peroxidation catalyzed by copper ions (Cu2+) and hydrogen peroxide (H2O2) was studied in human erythrocyte membranes. 2. The formation of thiobarbituric acid-reactive products elicited by CuCl2/H2O2 was inhibited by FeCl3 in a concentration-dependent manner; 0.25 mM FeCl3 were enough to cause 50% inhibition of the formation of peroxides. 3. The inhibitory effect of FeCl3 is not due to competition against Cu2+. 4. FeCl3 inhibited the initiation, but did not inhibit the propagation of Cu2+/H2O2-catalyzing lipid peroxidation. 5. In the heat- or trypsin-treated erythrocyte membranes, FeCl3 had no inhibitory effect on Cu2+/H2O2-catalyzing lipid peroxidation. 6. Sodium azide, an inhibitor of catalase, had no effect on the inhibitory effect of FeCl3. 7. These results suggest that a protein factor(s), which is not catalase, is involved in the inhibition of Cu2+/H2O2-catalyzing lipid peroxidation by Fe3+.