Decomposition Of Lipid Peroxides Research Articles

Amelioration of glucose induced hemolysis of human erythrocytes by vitamin E

Cells under aerobic condition are always threatened with the insult of reactive oxygen species, which are efficiently taken care of by the highly powerful antioxidant systems of the cell. The erythrocytes (RBCs) are constantly exposed to oxygen and oxidative stress but their metabolic activity is capable of reversing the injury under normal conditions. In vitro hemolysis of RBCs induced by 5, 10 and 20mM glucose was used as a model to study the free radical induced damage of biological membranes in hyperglycemic conditions and the protection rendered by vitamin E on the same. RBCs are susceptible to oxidative damage, peroxidation of the membrane lipids, release of hemoglobin (hemolysis) and alteration in activity of antioxidant enzymes catalase and superoxide dismutase. The glucose induced oxidative stress and the protective effect of vitamin E on cellular membrane of human RBCs manifested as inhibition of membrane peroxidation and protein oxidation and restoration of activities of superoxide dismutase and catalase, was investigated.Thiobarbituric acid reactive substances are generated from decomposition of lipid peroxides and their determination gives a reliable estimate of the amount of lipid peroxides present in the membrane. Vitamin E at 18μg/ml (normal serum level) strongly enhanced the RBC resistance to oxidative lysis leading to only 50–55% hemolysis in 24h, whereas RBCs treated with 10 and 20mM glucose without vitamin E leads to 70–80% hemolysis in 24h. Levels of enzymic antioxidants catalase, superoxide dismutase and nonenzymic antioxidants glutathione showed restoration to normal levels in presence of vitamin E. The study shows that vitamin E can protect the erythrocyte membrane exposed to hyperglycemic conditions and so a superior antioxidant status of a diabetic patient may be helpful in retarding the progressive tissue damage seen in chronic diabetic patients.

LOX-1 augments oxLDL uptake by lysoPC-stimulated murine macrophages but is not required for oxLDL clearance from plasma

Oxidized LDL (oxLDL) promotes lipid accumulation as well as growth and survival signaling in macrophages. OxLDL uptake is mainly due to scavenger receptors SR-AI/II and CD36. However, other scavenger receptors such as lectin-like oxLDL receptor-1 (LOX-1) may also play a role. We used mice with targeted inactivation of the LOX-1 gene to define the role of this receptor in the uptake of oxLDL and in activation of survival pathways. There was no difference in uptake or degradation of 125I-oxLDL in unstimulated macrophages from wild-type and LOX-1 knockout mice and no difference in the rate of clearance of oxLDL from plasma in vivo. However, when expression of LOX-1 was induced with lysophosphatidylcholine, oxLDL uptake and degradation increased 2-fold in wild-type macrophages but did not change in LOX-1 knockout macrophages. Macrophages lacking LOX-1 showed the same stimulation of PKB phosphorylation and enhancement of survival by oxLDL as wild-type cells. These data show that LOX-1 does not alter the uptake of oxLDL in unstimulated macrophages and is not essential for the pro-survival effect of oxLDL in these cells. However, LOX-1 expression is highly inducible by lysophosphatidylcholine and pro-inflammatory cytokines, and if that occurred in macrophages within atheromas, LOX-1 could substantially increase oxLDL uptake by lesion macrophages.

Serum neuron specific enolase and malondialdehyde in patients after out-of-hospital cardiac arrest.

Sudden cardiac arrest (CA) is a leading cause of death in Europe. The victims of CA need immediate cardiopulmonary resuscitation (CPR). Patients resuscitated due to CA have high mortality rate. Prognostic evaluation based on clinical observation is uncertain and would benefit from the use of biochemical markers of hypoxic brain damage. Multiple factors of brain origin can be measured in blood. The purpose of this study was to validate the use of the serum neuron-specific enolase (NSE) and malondialdehyde (MDA) concentrations for predicting in-hospital death, after resuscitation from out-of-hospital CA. Neuronal damage and impairment of the blood-brain-barrier integrity can be detected by the release of NSE into cerebrospinal fluid and eventually into the blood. MDA represents a product of lipid peroxide decomposition reactions. In a prospective study of 35 consecutive survivors of out-of-hospital CA, serum samples were obtained within 24, 72 and 168 h after the CA. NSE and MDA concentrations were measured, relationship between concentration in group of in-hospital death and survived patients were examined. Results There was a significant difference in NSE concentration between survivors and dead group on 1st day of measurement, marginally significant difference on 3rd day and no statistically significant difference in NSE on 7th day of measurement. There was marginally significant difference in MDA levels in both groups in all days of measurements. Estimation serum concentrations of NSE but not MDA seems to be a predictor of fate of patients after CA. The exact nature of oxidative stress can only be resolved by further studies.

Fe2+Catalyzes Vitamin E-Induced Fragmentation of Hydroperoxy and Hydroxy Endoperoxides That Generates γ-Hydroxy Alkenals

The formation of cytotoxic γ-hydroxyalkenals has been generally viewed as the consequence of free radical-induced oxidation of polyunsaturated fatty acyls through the decomposition of lipid peroxides. Vitamin E (Vit E) would be expected to inhibit such autoxidation. In a model study, we now find that fragmentation of a hydroperoxy endoperoxide generated the lactone of a γ-hydroxyalkenal. With 1 equiv of Fe2+, or with a catalytic amount (0.1 equiv) of Fe2+ and 1 equiv of Vit E, the yields are 43−50%. However, Vit E alone did not promote the fragmentation, and a catalytic amount of Fe2+ alone only afforded a low yield (about 5%). Vit E could contribute to, as opposed to preventing, the formation of γ-hydroxyalkenals by converting redox-active metal ions into their reduced forms that promote the rapid fragmentation of hydroperoxy endoperoxides.

Reduction of oxidative changes in human spermatozoa by exogenous gangliosides

The effect of exogenous gangliosides, the sialic acid-containing glycosphingolipids, on oxidative changes in human spermatozoa was investigated. The incorporation of disialogangliosides or trisialogangliosides (GD1b and GT1b, respectively) into the iron/ascorbate promoter system for induction of lipid peroxidation decreased the release of malondialdehyde (MDA) from peroxidizing spermatozoa. The application of monosialogangliosides and disialogangliosides (GM1 and GD1a, respectively) did not have any effect under identical experimental conditions. GT1b, at a micromolar concentration, significantly inhibited the production of MDA, a breakdown product of lipid peroxide decomposition in spermatozoa of normozoospermic infertile men (P < 0.001; n = 51). An enhanced generation of MDA exhibited by the sperm population from the low-density Percoll fraction containing defective and/or immature spermatozoa was significantly reduced in the presence of GT1b. These results and the experiments on the influence of iron-chelating agent ethylenediamine tetraacetic acid (EDTA) as well as ferrous ion concentration itself on lipid peroxidation support the hypothesis that the protective effect of ganglioside against MDA generation could be the result of its chelating activity. Furthermore, superoxide anion release of phorbol myristate acetate-stimulated spermatozoa was significantly reduced in the presence of 50 and 100 micromol l(-1) GD1b (P < 0.05) and GT1b (P < 0.005). The inhibitory effect of 100 micromol l(-1) GT1b on spermatozoa from infertile normozoospermic men was statistically significant (P < 0.001; n = 21) and did not depend on the initial superoxide anion production. In conclusion, the protective action of GD1b and GT1b could be related to both scavenging of free radicals and metal-chelating properties, which might have relevance in the protection against oxidation-induced processes in human spermatozoa.

Lipid peroxidation in the postnatal rat brain. Formation of 4-hydroxynonenal in the supraventricular corpus callosum of postnatal rats.

Lipid peroxidation is known to be associated with many neurodegenerative diseases and with traumatic brain injury, but its occurrence in the normal developing brain has not been reported. The present study was carried out using a specific antibody that recognises proteins modified by the end-product of lipid peroxide decomposition, 4-hydroxynonenal (HNE), to evaluate evaluate possible lipid peroxidation products in the brains of developing rats by immunocytochemistry and electron microscopy. Moderately dense labelling was observed in the supraventricular corpus callosum in the 7- and 8-day-old rats, whilst very dense labelling was observed in the same region, in the 9- and 10-day-old rats. Very little immunoreactivity was observed at 14 days, and no staining was observed in the corpus callosum in adult rats. HNE staining was not observed in neuronal cell bodies that give rise to callosal axons in the overlying cerebral cortex. Electron microscopy showed dense HNE staining on the basal laminae of blood vessels and on the plasma membranes of unmyelinated axons. Large numbers of rounded cells with features of oligodendrocyte precursor cells were labelled by Perl's stain in the supraventricular corpus callosum at postnatal day 7 and postnatal day 10, i.e. at times corresponding to high levels of HNE immunoreactivity. In contrast, very few such cells were observed in the adult brain, corresponding to the very little or no Perl's staining in the adult. These results suggest that lipid peroxidation observed in the supraventricular corpus callosum at postnatal day 10 could result from an accumulation of iron in this region, at this time.

Distribution of hydroxynonenal-modified proteins in the kainate-lesioned rat hippocampus: evidence that hydroxynonenal formation precedes neuronal cell death

Decomposition of lipid peroxides gives rise to a wide range of aldehydes. 4-Hydroxyalkenals and in particular 4-hydroxynonenal (HNE) are often the most toxic products. Frequently, it is unclear at which stage in the tissue injury process HNE is formed, i.e., is it a late stage or an early stage in which HNE contributes to subsequent cell death? The present study was carried out using an antibody to HNE-modified proteins to elucidate the time course and distribution of HNE in the lesioned hippocampus after kainate injections. HNE was absent from normal neurons, but dense staining to HNE was observed in degenerating neurons after kainate injection. The increase in HNE staining occurred as early as 1 d postinjection, at a time when there was no histological evidence of cell death. HNE immunoreactivity was observed in the degenerating CA1 and CA3 fields at 3 d and 1 week postinjection, but was confined to a cluster of neurons at the edge of the degenerating CA fields, at 2 and 3 weeks postinjection. These observations suggest that HNE formation is an early event after this tissue injury, and may contribute to later cell death.

When and why a water-soluble antioxidant becomes pro-oxidant during copper-induced low-density lipoprotein oxidation: a study using uric acid

The inclusion of uric acid in the incubation medium during copper-induced low-density lipoprotein (LDL) oxidation exerted either an antioxidant or pro-oxidant effect. The pro-oxidant effect, as mirrored by an enhanced formation of conjugated dienes, lipid peroxides, thiobarbituric acid-reactive substances and increase in negative charge, occurred when uric acid was added late during the inhibitory or lag phase and during the subsequent extensive propagation phase of copper-stimulated LDL oxidation. The pro-oxidant effect of uric acid was specific for copper-induced LDL oxidation and required the presence of copper as either Cu(I) or Cu(II). In addition, it became much more evident when the copper to LDL molar ratio was below a threshold value of approx. 50. In native LDL, the shift between the antioxidant and the pro-oxidant activities was related to the availability of lipid hydroperoxides formed during the early phases of copper-promoted LDL oxidation. The artificial enrichment of isolated LDL with alpha-tocopherol delayed the onset of the pro-oxidant activity of uric acid and also decreased the rate of stimulated lipid peroxidation. However, previous depletion of alpha-tocopherol was not a prerequisite for unmasking the pro-oxidant activity of uric acid, since this became apparent even when alpha-tocopherol was still present in significant amounts (more than 50% of the original values) in LDL. These results suggest, irrespective of the levels of endogenous alpha-tocopherol, that uric acid may enhance LDL oxidation by reducing Cu(II) to Cu(I), thus making more Cu(I) available for subsequent radical decomposition of lipid peroxides and propagation reactions.

Principales métodos para la determinación de la oxidación lipídica Main methods used in lipid oxidation determination

Main spectrophotometric and chromatographic methods for determination of lipid oxidation in foods and biological systems are reviewed. A new classification, according to the compounds produced in the oxidation phases, is suggested as follows: measurement of oxygen absorption, conjugated dienes, peroxide values, and decomposition of lipid peroxides. Both conjugated dienes (propagation phase) and thiobarbituric acid (termination phase) methods are the most used, despite their interferences; however, chromatographic methods are more precise and selective. Determination of bioavailability and metabolic pathway of the antioxidants in the human body are problems to be solved in the devel opment of new biological antioxidants.

Free radical-mediated lipid peroxidation induced by T-2 toxin in yeast ( Kluyveromyces marxianus)

Lipid peroxidation may be one of the main manifestations of cellular damage in the toxicity of several mycotoxins. A species of yeast, Kluyveromyces marxianus, was used in this study to determine the oxidative damage induced by T-2 toxin (T-2). Malondialdehyde (MDA), produced from the decomposition of lipid peroxides, was monitored using the thiobarbituric acid reaction. The yeast showed a high sensitivity to T-2 because the addition of 25 ng T-2/mL medium greatly reduced the multiplication rate of yeast. In addition, the MDA content increased when the concentration of T-2 was increased in the growth medium. Preincubation of the yeast with linoleic and linolenic acids in the medium enhanced the effects of T-2. The addition of the antioxidant dl-α-tocopherol acetate completely quenched the effects of T-2 whereas ascorbic acid and reduced glutathione (GSH) acted as prooxidants in this system. Electron paramagnetic resonance (EPR) spin trapping technique using lipid soluble N- tert-butyl-α-phenylnitrone (PBN) or more water soluble α-(4-pyridyl-1-oxide)-N- tert-butylnitrone (4-POBN) as free radical spin traps showed that free radical production was promoted by T-2. Vitamin E effectively quenched the EPR signals of the spin adducts. The observed spin adduct hyperfine splitting constants were consistent with those of α-hydroxyethyl radicals. The spin trapping data strongly suggest that initially generated hydroxyl radicals react with ethanol that is present in the samples, and the α-hydroxyethyl radicals formed in this process are then trapped. These data demonstrate that T-2 stimulates lipid peroxidation in a biological system due to an increased generation of hydroxyl radicals.

Inhibition of Endothelial Cell Mediated Low-Density Lipoprotein Oxidation by Green Tea Extracts

Plant phenolics present in fruits and vegetables and that are particularly rich in tea and wine have received considerable attention because of their potential antioxidant activity. Two types of commercial green tea from Japan and two active components of green tea, catechin and epicatechin, were assessed for their relative abilities to inhibit the oxidation of low-density lipoprotein (LDL) mediated by human aortic endothelial cells (HAEC). The tea extracts, catechin and epicatechin, were incubated with HAEC and LDL for 12 h. After incubation, conjugated dienes were measured by spectrophotometry at 234 nm as an index of hydroperoxide formation, and hexanal was measured by static headspace gas chromatography as an index of hydroperoxide decomposition. On the basis of conjugated dienes and hexanal, inhibition of LDL oxidation was dose dependent for all compounds tested. LDL oxidation was inhibited 3.9−98% at concentrations ranging from 0.08 to 5 ppm of the green tea extracts. Both catechin and epicatechin inhibited oxidation by 0.5−97% at concentrations ranging from 0.08 to 5.00 μM. The pure compounds and the two tea extracts tested inhibited the formation of early lipid peroxidation products as well as the end stage lipid peroxide decomposition products. The polyphenolic components of green tea may have nutritional benefits as inhibitors of LDL oxidation. Keywords: Antioxidants; green tea; catechin; epicatechin; plant phenolics; human aortic endothelial cells; low-density lipoprotein (LDL) oxidation

Unexpected Dose Response of Copper Concentration on Lipoprotein Oxidation in Serum: Discovery of A Unique Peroxidase-Like Activity of Urate/Albumin in the Presence of High Copper Concentrations

Oxidative modification of low-density lipoprotein (LDL) may be an important factor in atherogenesis. The susceptibility of LDL to oxidation is usually determined in isolation by exposing LDL to oxidative stress induced by Cu ions or a free radical initiator. In these cases oxidation is carried out in the absence of water-soluble vitamins or serum proteins that may be present at the site of oxidation in vivo. We have examined the Cu 2+-induced oxidation of lipoproteins in diluted serum. When oxidizing isolated LDL, there is a decrease in lag time with increasing concentration of Cu 2+ until a minimum “lag time” is reached at a Cu:LDL ratio of about 50:1. In serum, we have shown an initial decrease in “lag time” with increasing Cu concentration up to 12.5 μM. However, with higher Cu concentrations “lag time” to oxidation increases, contrary to expectation, until a maximum is reached at about 50 μM Cu. This dose response observed for Cu oxidation of diluted serum was highly reproducible in a number of individual subjects. When serum was gel-filtered to remove low molecular weight compounds, the resulting filtrate behaved the same as isolated LDL. Uric acid was found to be an important component of the low molecular weight fraction responsible for the paradoxical effect of Cu concentration on serum oxidation. The same paradoxical effect was found when isolated LDL was incubated with uric acid in the presence of human serum albumin (HSA) and Cu. The incubation of HSA with reducing agents such as uric acid or bilirubin in the presence of high Cu concentrations, produces a “peroxidase-like” activity, capable of breaking down hydrogen peroxide as well as lipid hydroperoxides. The decomposition of lipid peroxides is a likely explanation for the longer serum oxidation lag times seen at higher Cu concentrations. Our study highlights the possible importance of interactions between uric acid and serum proteins in the presence of high metal ion concentrations.

Evidence for a relationship between the generation of reactive intermediates and the physicochemical characteristics of nickel oxides.

Spin trapping experiments have been carried out on solutions generated by the dissolution of nickel oxides, all of which contained NiO (bunsenite) as the predominant crystalline phase. Samples containing nickel (III), of low crystallinity, with small particle size and high surface areas can in the presence of H2O2, cause the generation of the hydroxyl radical (as detected by spin trapping with 5,5-dimethyl-1-pyrroline N-oxide or DMPO) and/or another highly reactive species capable of cleaving the C-S bond in dimethyl sulphoxide. In contrast samples which predominantly contain nickel (II), of high crystallinity, with a large particle size and low surface area cause the generation of alkyl and alkoxyl radicals, or another highly reactive species capable of causing the decomposition of lipid peroxides, but did not generate significant quantities of the hydroxy radical type. These findings help to explain the varied ability of nickel containing solids to cause DNA lesions in vivo and in vitro.

Immunological approach to investigating membrane cell damages induced by lipoperoxidative stress. Application to far UV-irradiated erythrocytes.

Oxygen-reactive species are being described as agents responsible for cell degeneration mechanisms resulting from membrane, enzyme, and nuclear alterations. Lipid peroxidation on its own is considered to be one of the consequences of the free radicals attack, and among the different reactive aldehydes that can be formed from the decomposition of lipid peroxides, the most extensively assayed have been malondialdehyde (MDA). However, the different techniques currently used for MDA assay (HPLC, GLC) are barely sensitive enough to follow its production at the cellular level. In order to develop an immunofluorescent technique able to detect cellular damages provoked by lipoperoxidation, polyclonal antibodies against lysozyme modified by MDA treatment have been raised in rabbits. We show that this immunserum recognizes specifically all the MDA-treated proteins tested, but not the intact proteins or the proteins treated by other aldehydes. Moreover, we demonstrate using an ELISA technique that the amount of immunoreactive proteins in MDA-treated membrane erythrocytes is proportional to the concentration of MDA applied, suggesting that this assay may represent a quantitative method of determination of lipoperoxidative alterations. In addition, when coupled to an indirect fluorophore antibody (FITC), the immunserum allows a precise location of these modified proteins within the membranes of erythrocytes in which lipid peroxidation was initiated by far UV irradiation. In summary, the interest of this work is to provide an immunological probe that can precociously detect membrane damages induced by MDA, regardless of the cell type and pro-oxidant (physiological or pathological) conditions.

Iron: Metabolism, toxicity and therapy

This paper is an overview on iron metabolism, iron toxicity and therapeutics against this toxicity. The attention has been focused on: i) the solubilization of iron by living organisms; ii) the iron metabolism in human; iii) the toxicity of iron (Fe-catalyzed reduction of oxygen, Fenton reaction, decomposition of lipid peroxides); iv natural protective mechanisms; v) the relations between iron, free radicals and human diseases; and vi) the iron overload and its treatment.

Formation and removal of active oxygen species and lipid peroxides in biological systems

The mechanisms of formation and removal of active oxygen species and lipid peroxides in biological systems have been briefly reviewed. Cytotoxic active oxygen species can be classified into two types: (a) radical species such as O2-. (superoxide) and HO. (hydroxyl radical) and (b) non-radical species such as H2O2 (hydrogen peroxide) and 1O2 (singlet oxygen). The direct or indirect attack of active oxygen species on polyunsaturated fatty acids, essential constituents of biological membranes, has been shown to result in the formation of a number of peroxidative lipid breakdown-products: LOOH (lipid hydroperoxide), LOO. (lipid peroxyl radical) and LO. (lipid alkoxyl radical). The lipid peroxide decomposition is probably dependent on the presence of ferric-ferrous ions. These processes are called lipid peroxidation reactions. In recent years, there has been a renewed interest in the role played by lipid peroxidation in many disease states. The multiple lines of defense against toxic oxygen intermediates consist of enzymatic systems, glutathione peroxidase, catalase and superoxide dismutase, and furthermore involves antioxidant capacities such as those of vitamin E and vitamin C. In biological systems, there are naturally occurring lipid-soluble (vitamin E and ubiquinone) and water-soluble (vitamin C, reduced glutathione and uric acid) antioxidants. Therefore, so long as homeostasis is maintained between the rate of radical generation and the rate of radical dissipation, the cellular generation of radicals may not be harmful. In contrast, this balance can be disturbed if cellular defenses are decreased or if there is a significant increase in the flux of radical generation. Once lipid peroxidation is initiated, the reactive intermediate formed induces cell damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of herbicidal injury by diphenyl ether herbicides oxyfluorfen and bifenox in Lemna pausicostata Hegelm.

The herbicidal mode of action of diphenyl ethers oxyfluorfen (2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene) and bifenox (methyl-5-(2, 4-dichlorophenoxy)-2-nitrobenzoate) in Lemna pausicostata HEGELM. was investigated by monitoring an electrolyte leakage and a lipid peroxide decomposition product. Among the diphenyl ethers tested, these two herbicides caused intensive leakage in the plant after a lag period of 4-hr. Thiobarbituric acid-reacting material, product of lipid peroxide decomposition, content in a bathing solution was also increased. Light and oxygen were required for their action and by decreasing the light quantity, the effect of oxyfluorfen was delayed. Exogenously applied antioxidant α-tocopherol, and the scavengers of active oxygen species D-mannitol and hydroquinone partially protected from herbicidal injury. Protection was also partially afforded from phytotoxicity by the photosynthetic electron transport inhibitor, diuron. Although the mechanism of involvement of photosynthesis in the action is still unclear, active oxygen species were suggested to be involved in the initiation of lipid peroxidation.

Cooperation of quercetin with ascorbate in the protection of photosensitized lysis of human erythrocytes in the presence of hematoporphyrin.

Abstract— Quercetin(20–100 μM) suppressed photohemolysis sensitized by hematoporphyrin, while ascorbate(10–100 μM) stimulated it. However, in the presence of 40 μM quercetin, ascorbate promoted the suppression. The suppression by quercetin was due to scavenging of both singlet oxygen generated by a photosensitized reaction and radicals generated by decomposition of lipid peroxides formed by a singlet oxygen‐dependent reaction. In scavenging, quercetin was oxidized and the oxidation was suppressed by ascorbate. Ascorbate was oxidized by illumination in the presence of quercetin. It is suggested that the cooperation of quercetin with ascorbate in photohemolysis is due to reduction of oxidized quercetin by ascorbate regenerating the flavonol.

SPECTRAL AND TIME DEPENDENCE STUDIES OF THE ULTRA WEAK BIOLUMINESCENCE EMITTED BY THE BACTERIUM Escherichia coli

Abstract— Weak luminescence was detected using photon counting equipment, from oxygenated, liquid cultures of Escherichia coli during two stages of its growth cycle. The first period of emission occurred during the exponential phase of growth and comprised a UV(210–330 nm) band and a visible region(450–620 nm) band, the total intensity being (1.65 ± 0.12) x 103 counts s‐1. The second period of emission occurred during the stationary phase of growth and comprised only a visible region(450–620 nm) band of intensity (8.72 ± 0.15) x 103 counts s‐1. When the growth temperature was raised from 306.15 to 310.15 K, the above emission intensities were approximately halved, but the spectra were not changed significantly. No luminescence was observed at either temperature when the E. coli was grown anaerobically. The visible region luminescence was attributed to excited carbonyl groups and excited singlet O2 dimers formed during the decomposition of lipid peroxides. The UV component was tentatively assigned to oxidative side reactions accompanying the synthesis of proteins.

Oxidation of human low density lipoprotein results in derivatization of lysine residues of apolipoprotein B by lipid peroxide decomposition products.

Modification of low density lipoproteins (LDL) by oxidation has been shown to permit recognition by the acetyl-LDL receptor of macrophages. The extensive oxidation of LDL that is required before interaction occurs with this receptor produces major alterations in both the lipid and protein components of LDL. Several chemical modifications of LDL also lead to recognition by this receptor; all of these involve derivatization of lysine residues of apolipoprotein B by adducts that neutralize the positively charged epsilon-amino group. The present studies show that oxidation also results in derivatization of LDL lysine residues. Analysis of amino acid composition indicated that 32% of lysine residues were modified after oxidation of LDL by exposure to 5 microM CuSO4 for 20 h. About one-half of the derivatized lysines were labile under the conditions of acid hydrolysis. Fluorescence of LDL protein was greatly increased by oxidation, with excitation maximum at 350 nm and emission maximum at 433 nm. When LDL containing phosphatidylcholine with isotopically labeled arachidonic acid in the sn-2 position was oxidized, there was a 5-fold increase in radioactivity bound to protein compared to nonoxidized LDL or oxidized LDL labeled with 2-[1-14C]palmitoyl phosphatidylcholine. Prior methylation of LDL prevented the rapid uptake and degradation by macrophages that normally accompanies oxidation. These findings suggest that oxidation of LDL is accompanied by derivatization of lysine epsilon-amino groups by lipid products and that these adducts may be important in the interaction of oxidized LDL with the acetyl-LDL receptor.