The biphasic effect of calcium on lipid peroxidation

Mechanisms underlying Ca2+ effects on lipid peroxidation (LPO) induced in liposomes (from egg yolk lecithin) and ufasomes (from linolenic acid and methyl linolenate) with the aid of an O2-(.) -generating system (Fe2+ + ascorbate) were studied. It was shown that stimulation of LPO by low Ca2+ concentrations (10(-6)-10(-5)M) was due to its ability to release Fe2+ ions bound to negatively charged (phosphate or carboxylic) lipid groups (of lecithin or linolenic acid), thus increasing the concentration of catalytically active Fe2+. The inhibitory effect of high Ca2+ concentrations was caused by its interaction with superoxide anion radicals and was not observed in LPO systems independent of O2- generation (e.g., Fe2+ + cumol hydroperoxide).     

Mechanisms of the effects of Ca2+ ions on lipid peroxidation

Mechanisms underlying Ca2+ effects on lipid peroxidation (LPO) induced in liposomes (from egg yolk lecithin) and UFsomes (from linolenic acid, methyl linolenate) with the aid of O2- -system (Fe2+ + ascorbate) were studied. It was shown that stimulation of lipid peroxidation by low Ca2+ concentrations (10(-6)-10(-5) M) was due to its ability to release Fe2+-ions bound to negatively charged (phosphate, carboxylic) lipid groups (of licethin, linolenic acid), thus increasing the concentration of catalytically active Fe2+. The inhibitory effect of high Ca2+ concentrations was caused by its interaction with superoxide anion-radicals and was not observed in LPO-systems, independent of O2- generation (e. g. Fe2+ + cumol hydroperoxide).     

Regional differences in microsomal lipid peroxidation and antioxidant levels in the guinea pig adrenal cortex

Lipid peroxidation (LP) and antioxidant levels were studied in the chromatically distinct inner (zona reticularis) and outer (zona fasciculata + zona glomerulosa) zones of the guinea pig adrenal cortex. Ferrous ion (Fe2+) produced a concentration-dependent (10(-5) to 10(-3) M) stimulation of microsomal LP in both zones, but LP, as estimated by malonaldehyde production, was far greater in the inner zone. Although cytosolic ascorbic acid content was similar in the two zones, microsomal tocopherol levels were approx 4 times greater in the outer than inner zone. Subphysiological concentrations of ascorbic acid, like Fe2+, initiated LP to a greater extent in inner than outer zone microsomes; optimal stimulation of LP by ascorbic acid occurred at concentrations of 100-200 microM in both zones. Physiological concentrations of ascorbic acid (1-5 mM), by contrast, did not initiate LP and, in fact, markedly inhibited Fe2+-induced LP in both inner and outer zone microsomal preparations. Outer zone microsomes were more sensitive to the antioxidant effects of ascorbic acid than were inner zone preparations. Addition of alpha-tocopherol to inner zone microsomal suspensions inhibited Fe2+-induced LP. The results indicate that there are regional differences in adrenocortical LP which may be caused by differences in tocopherol content. alpha-Tocopherol may serve important antioxidant functions within the adrenal cortex, thereby contributing to the functional zonation of the gland.     

Formation of alpha-tocopherol radical and recycling of alpha-tocopherol by ascorbate during peroxidation of phosphatidylcholine liposomes. An electron paramagnetic resonance study

The events accompanying the inhibitory effect of alpha-tocopherol and/or ascorbate on the peroxidation of soybean L-alpha-phosphatidylcholine liposomes, which are an accepted model of biological membranes, were investigated by electron paramagnetic resonance, optical and polarographic methods. The presence of alpha-tocopherol radical in the concentration range 10(-8)-10(-7) M was detected from its EPR spectrum during the peroxidation of liposomes, catalysed by the Fe3+-triethylenetatramine complex. The alpha-tocopherol radical, generated in the phosphatidylcholine bilayer, is accessible to ascorbic acid, present in the aqueous phase at physiological concentrations. Ascorbic acid regenerates from it the alpha-tocopherol itself. A kinetic rate constant of about 2 X 10(5) M-1 X s-1 was estimated from the reaction as it occurs under the adopted experimental conditions. The scavenging effect of alpha-tocopherol on lipid peroxidation is maintained as long a ascorbic acid is present.     

Angiotensin II stimulates rapid serine phosphorylation of transcription factor Stat3

Lipid peroxidation (LPO) in rat testis and heart microsomes was compared using the ADP/Fe2+ as initiator with and without ascorbate at different concentrations. The extent of LPO was estimated by the levels of TBARS and PUFA. Without ascorbate, LPO was higher in heart than in testis despite elevated levels of catalase in heart. With increased ascorbate concentrations, a biphasic effect of LPO was observed. For a concentration 0.2 mM, ascorbate acted as pro-oxidant and increased TBARS correlated with decreased PUFA were observed both in testis and heart. Above 0.2 mM, ascorbate acts as antioxidant but differences in the rate of LPO were observed. In heart decreased TBARS correlated with increased PUFA whereas in testis TBARS only decreased, PUFA were not significantly modified. These results suggest different mechanisms in LPO initiation in the two organs. Increasing concentrations of H2O2 produced directly elevated TBARS levels in testis while a lag phase was observed in heart before the increase, suggesting that H2O2 was the essential ROS produced by ascorbate-ADP/Fe2+. The effects of scavengers such as catalase and ethanol showed an inhibitory effect on TBARS production only in testis, suggesting the role of H2O2/OH as an initiator of LPO. In heart, catalase produced a slight increase in TBARS levels whereas no modification was observed with ethanol, suggesting a possible direct activation by ADP/Fe2+ through a metal-oxo intermediate.     

Antiradical properties and antioxidant activity of ecdysterone]

Antiradical properties and total antioxidative activity of ecdysterone (10(-6)-10(-3)M were found on the model systems--photochemical one and that containing phosphatidylcholine liposomes oxidated with Fe2+ and Fe3+. The antioxidative activity of ecdysterone was shown to be comparable with that of the known inhibitors of peroxide oxidation of lipids--diethylparaphenylendiamine and ethylendiamine tetraacetate.     

Oxygen reduction and lipid peroxidation by iron chelates with special reference to ferric nitrilotriacetate

A certain iron chelate, ferric nitrilotriacetate (Fe3+-NTA) is nephrotoxic and also carcinogenic to the kidney in mice and rats, a distinguishing feature not shared by other iron chelates tested so far. Iron-promoted lipid peroxidation is thought to be responsible for the initial events. We examined its ability to initiate lipid peroxidation in vitro in comparison with that of other ferric chelates. Chelation of Fe2+ by nitrilotriacetate (NTA) enhanced the autoxidation of Fe2+. In the presence of Fe2+-NTA, lipid peroxidation occurred as measured by the formation of conjugated diene in detergent-dispersed linoleate micelles, and by the formation of thiobarbituric acid-reactive substances in the liposomes of rat liver microsomal lipids. Addition of ascorbic acid to Fe3+-NTA solution promoted dose-dependent consumption of dissolved oxygen, which indicates temporary reduction of iron. On reduction, Fe3+-NTA initiated lipid peroxidation both in the linoleate micelles and in the liposomes. Fe3+-NTA also initiated NADPH-dependent lipid peroxidation in rat liver microsomes. Although other chelators used (deferoxamine, EDTA, diethylenetriaminepentaacetic acid, ADP) enhanced autoxidation, reduction by ascorbic acid, or in vitro lipid peroxidation of linoleate micelles or liposomal lipids, NTA was the sole chelator that enhanced all the reactions.     

Cellular signalling and free-radical modulating activities of the novel peptidomimetic L-glutamyl-histamine.

A novel histamine-containing peptidomimetic, L-glutamyl-histamine (L-Glu-Hist), has been synthesized and characterized as a possible cytokine mimic which might lead to cellular responses of improved specificity. The energy-minimized 3-D conformations of L-Glu-Hist derived from its chemical structure stabilize Fe2+-chelating complexes. L-Glu-Hist concentration-dependently accelerates a decrease in ferrous iron in ferrous sulfate solution and shows ferroxidase-like activity at concentrations less than 3 mM in the phenanthroline assay, whereas in the concentration range 3-20 mM it restricts the availability of Fe2+ to phenanthroline by chelation of iron ions. At low concentrations (less than or about 1 mM), L-Glu-Hist stimulates peroxidation of phosphatidylcholine in liposomes catalyzed by a superoxide anion radical (O2)-generating system (Fe2+ + ascorbate) and, at high concentrations (*10 mM), it suppresses lipid peroxidation (LPO) in liposomes. The stimulation of LPO by L-Glu-Hist is related to its ability at low concentrations (*0.05 mM) to release O2 free radicals as determined by the superoxide dismutase-inhibitable reduction of cytochrome c. The release of O2 by L-Glu-Hist might result from its ferroxidase-like activity, while its inhibition of LPO is due to chelation of Fe2+, prevention of the formation of free radicals, and degradation of lipid hydroperoxides at 5-20 mM L-Glu-Hist concentrations. L-Glu-Hist releases O2 at concentrations which stimulate [3H]thymidine incorporation into DNA and proliferation of mouse spleen lymphocytes and also of mononuclear cells from human blood. The induction of lymphocyte proliferation by L-Glu-Hist is dose-dependent in the 0.01-0.05 mM concentration range, although the maximal stimulation of LPO in the O2-dependent system is observed at higher L-Glu-Hist concentrations (*1 mM). Thus, low concentrations of oxygen free radicals released by L-Glu-Hist may provide a very fast, specific, and sensitive trigger for lymphocyte proliferation and immunoregulation.     

Ca2+,Mg2+-ATPase of microsomal membranes from bovine aortic smooth muscle: effects of Sr2+ and Cd2+ on Ca2+ uptake and formation of the phosphorylated intermediate of the Ca2+,Mg2+-ATPase

The effects of various divalent cations on the Ca2+ uptake by microsomes from bovine aortic smooth muscle were studied. High concentrations (1 mM) of Co2+, Zn2+, Mn2+, Fe2+, and Ni2+ inhibited neither the Ca2+ uptake by the microsomes nor the formation of the phosphorylated intermediate (E approximately P) of the Ca2+,Mg2+-ATPase of the microsomes. The cadmium ion, however, inhibited both the Ca2+ uptake and the E approximately P formation by the microsomes. Dixon plot analysis indicated Cd2+ inhibited (Ki = 135 microM) the Ca2+ dependent E approximately P formation in a non-competitive manner. The inhibitory effect of Cd2+ was lessened by cysteine or dithiothreitol. The strontium ion inhibited the Ca2+ uptake competitively, while the E approximately P formation increased on the addition of Sr2+ at low Ca2+ concentrations. At a low Ca2+ concentration (1 microM), Sr2+ was taken up by the aortic microsomes in the presence of 1 mM ATP. It is thus suggested that Sr2+ replaces Ca2+ at the Ca2+ binding site on the ATPase.     

Antioxidative effect of α-tocopherol incorporation into lecithin liposomes on ascorbic acid-Fe2+-induced lipid peroxidation

The antioxidative effect of α-tocopherol incorporated into lecithin liposomes was studied. Lipid peroxidation of liposome membranes, assayed as malondialdehyde production, was catalyzed by ascorbic acid and Fe²⁺. The peroxidation reaction, which did not involve the formation of singlet oxygen, superoxide, hydrogen peroxide, or a hydroxyl radical, was inhibited by α-tocopherol and a model compound of α-tocopherol, 2,2,5,7,8-pentamethyl-6-hydroxy-chroman (TMC), but not by phytol, α-tocopherylquinone, or α-tocopheryl acetate. One mole of α-tocopherol completely prevented peroxidation of about 100 moles of polyunsaturated fatty acid. Decrease in membrane fluidity by lipid peroxidation, estimated as increase of fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) embedded in the membrane, was also inhibited by α-tocopherol and TMC, reflecting their antioxidant functions. Cholesterol did not act as an antioxidant, even when incorporated in large amount into the liposome membranes, but it increased the antioxidative efficiency of α-tocopherol. When a mixture of liposomes with and without α-tocopherol was incubated with Fe²⁺ and ascorbic acid, α-tocopherol did not protect the liposomes not containing α-tocopherol from peroxidation. However, preincubation of the mixture, or addition of Triton X-100 allowed the α-tocopherol to prevent peroxidation of the liposomes not containing α-tocopherol. In contrast, in similar experiments, liposomes containing TMC prevented peroxidation of those without TMC without preincubation. Tocopherol in an amount so small as to exhibit only a slight antioxidative effect was oxidized when incorporated in egg lecithin liposomes, but it mostly remained unoxidized when incorporated in dipalmitoyllecithin liposomes, indicating that oxygen activated by ascorbic acid-Fe²⁺ does not oxidize α-tocopherol directly. Thus, decomposition of α-tocopherol may be caused by its interaction with peroxy and/or alkoxyl radicals generated in the process of lipid peroxidation catalyzed by Fe²⁺ and ascorbic acid.     

Antioxidant protection of phospholipid bilayers by alpha-tocopherol. Control of alpha-tocopherol status and lipid peroxidation by ascorbic acid and glutathione

Factors affecting the balance between pro- and antioxidant effects of ascorbic acid and glutathione were studied in soybean phosphatidylcholine liposomes challenged with Fe2+/H2O2. Effective antioxidant protection by alpha-tocopherol appeared to be due to efficient reaction with lipid oxy-radicals in the bilayer rather than to interception of initiating oxygen radicals. At concentrations above a threshold level of approximately 0.2 mol % (based on phospholipid content), alpha-tocopherol completely suppressed lipid oxy-radical propagation, which was measured as malondialdehyde production. Both ascorbic acid and glutathione, alone or in combination, enhanced lipid oxy-radical propagation. Alpha-Tocopherol, incorporated into liposomes at concentrations above its threshold protective level, reversed the pro-oxidant effects of 0.1-1.0 mM ascorbic acid but not those of glutathione. Ascorbic acid also prevented alpha-tocopherol depletion. The combination of ascorbic acid and subthreshold levels of alpha-tocopherol only temporarily suppressed lipid oxy-radical propagation and did not maintain the alpha-tocopherol level. Glutathione antagonized the antioxidant action of the alpha-tocopherol/ascorbic acid combination regardless of alpha-tocopherol concentration. These observations indicate that membrane alpha-tocopherol status can control the balance between pro- and antioxidant effects of ascorbic acid. The data also provide the most direct evidence to date that ascorbic acid interacts directly with components of the phospholipid bilayer.     

Anti- and pro-oxidative effects of flavonoids on metal-induced lipid hydroperoxide-dependent lipid peroxidation in cultured hepatocytes loaded with α-linolenic acid

Lipid hydroperoxide (LOOH)–dependent lipid peroxidation was induced in α-linolenic acid (LNA)-loaded hepatocytes by adding Fe, Cu, V, or Cd ions at concentrations from 20 to 500 μM. The effects of structurally related flavonoids at concentrations from 10 to 500 μM on the lipid peroxidation were examined. The results with regard to each flavonoid subclass are as follows: (i) Flavonols such as myricetin, quercetin, fisetin, and kaempferol, but not morin, showed dose-dependent antioxidative activity against metal-induced lipid peroxidation at all metal concentrations. Myricetin, quercetin, and fisetin were the most effective antioxidants, although their efficacies depended on the metal ion. Kaempferol and morin had antioxidative activity equal to the other flavonols in the presence of Cu ions, but were much less effective for the other three metal ions. (ii) Flavones, luteolin, apigenin, and chrysin were antioxidative at low Fe concentrations, but were pro-oxidative at high Fe concentrations. Luteolin exhibited antioxidative activity similar to that of catechol-containing flavonols in the presence of the other three metal ions. Apigenin and chrysin also acted as pro-oxidants with V or with all metal ions, respectively. (iii) Taxifolin, a flavanone, also showed both anti- and prooxidative activity, depending on Fe concentrations, but with other metal showed only antioxidative activity ions. (iv) Epigallocatechin, a flavanol, was antioxidative with all metal ions, and its activity was similar to that of catechol-containing flavonols. The various effects of flavonoids on metal-induced lipid peroxidation in LNA-loaded hepatocytes is discussed with regard to the change in redox potential of flavonoid–metal complexes.     

Antioxidative activity of flavonoids in various systems of lipid peroxidation

The antioxidant action of flavonols in different systems of lipid peroxidation (LPO) was studied. Quercetin and rutin were found to inhibit NADPH and CCl4-dependent LPO in rat liver microsomes, however, in the case of CCl4-dependent LPO, rutin had a very poor antioxidant effect. Study of flavonols oxidation by products of the cytochrome c catalyzed destruction of linoleic acid hydroperoxide demonstrated that the differences in the antioxidant offects of quercetin and rutin can be due to their different capability to terminate free radical chain reactions. The antioxidant effect of rutin was shown to be largely due to the chelating properties of this compound.     

Purification and characterization of a purple acid phosphatase from rat spleen

An acid phosphatase species which is activated by Fe2+ was purified 3,700-fold from rat spleen by chromatography on columns containing Blue-Sepharose, concanavalin A-Sepharose, Sephadex G-100, and CM-Sephadex. The enzyme hydrolyzed aryl phosphates, nucleoside di- and triphosphates, phosphoproteins, and thiamine pyrophosphate with Km values of 10(-4) to 10(-3) M at an optimal pH of 5.0-5.8. Co-purification of the acid phosphatase and acid phosphoprotein phosphatase indicated that they were identical. The purified enzyme was glycoprotein in nature, showing four heterogeneous forms on acid polyacrylamide gel electrophoresis (pI values, 7.8, 8.0, 8.3, and 8.5), but it gave a molecular weight of 33,000 on sodium dodecyl sulfate-gel electrophoresis and gel permeation chromatography. The enzyme had a purple color (lambda max 545 nm) and contained 2 iron atoms per enzyme molecule. Among reductants, ascorbic acid and Fe2+ were the best activators, although their combined effect was not additive. Fe2+ and ascorbic acid both changed the purple enzyme into the same active form (lambda max 515 nm), giving almost the same kinetic constants for substrates and for inhibitors such as molybdate, phosphate and fluoride. However, low concentrations of Fe2+, from 0.01 mM to 1.0 mM, immediately and reversibly activated the enzyme, whereas high concentrations of ascorbic acid over 1 mM were required for maximal activation, which was slow and irreversible.     

Relationship between the action of reactive oxygen and nitrogen species on bilayer membranes and antioxidants

Membrane lipid peroxidation (LPO) induced by hydroxyl (*OH) and ascorbyl (*Asc) radicals and by peroxynitrite (ONOO-) was investigated in asolectin (ASO), egg phosphatidylcholine (PC) and PC/phosphatidic acid mixtures (PC:PA) liposomes and rat liver microsomes (MC). Enthalpy variation (DeltaH) of PC:PA at different molar ratios were obtained by differential scanning calorimetry. It was also evaluated the LPO inhibition by quercetin, melatonin and Vitamin B6. The oxidant effect power follows the order *OH approximately *Asc > ONOO- on PC and MC; whilst on ASO liposomes, it follows *Asc > *OH approximately ONOO-. Increasing amounts of PA in PC liposomes resulted in lower levels of LPO. The DeltaH values indicate a more ordered membrane arrangement as a function of PA amount. The results were discussed in order to provide a complete view involving the influence of membranes, oxidants and antioxidants intrinsic behavior on the LPO dynamics.     

Copper-induced peroxidation of liposomal palmitoyllinoleoylphosphatidylcholine (PLPC), effect of antioxidants and its dependence on the oxidative stress

In an attempt to deepen our understanding of the mechanisms responsible for lipoprotein peroxidation, we have studied the kinetics of copper-induced peroxidation of the polyunsaturated fatty acid residues in model membranes (small, unilamellar liposomes) composed of palmitoyllinoleoylphosphatidylcholine (PLPC). Liposomes were prepared by sonication and exposed to CuCl(2) in the absence or presence of naturally occurring reductants (ascorbic acid (AA) and/or alpha-tocopherol (Toc)) and/or a Cu(I) chelator (bathocuproinedisulfonic acid (BC) or neocuproine (NC)). The resultant oxidation process was monitored by recording the time-dependence of the absorbance at several wavelengths. The observed results reveal that copper-induced peroxidation of PLPC is very slow even at relatively high copper concentrations, but occurs rapidly in the presence of ascorbate, even at sub-micromolar copper concentrations. When added from an ethanolic solution, tocopherol had similar pro-oxidative effects, whereas when introduced into the liposomes by co-sonication tocopherol exhibited a marked antioxidative effect. Under the latter conditions, ascorbate inhibited peroxidation of the tocopherol-containing bilayers possibly by regeneration of tocopherol. Similarly, both ascorbate and tocopherol exhibit antioxidative potency when the PLPC liposomes are exposed to the high oxidative stress imposed by chelated copper, which is more redox-active than free copper. The biological significance of these results has yet to be evaluated.     

Selective sensitization of chemiluminescence resulted from lipid and oxygen radical reactions

Eu3+-tetracycline complex (EuT) increased the chemiluminescence (CL) intensity of linolenic acid micells (UFA-somes) oxidized with lipoxygenase and CL of the lecithin liposomes peroxidized with Fe2+ ions by 3 orders of magnitude. In the systems producing oxygen radicals (xanthine + xanthine oxidase and Fenton's reagent) EuT was ineffective. Luminol increased CL intensity up to 4 orders of magnitude in Fenton's reagent and by 2 orders of magnitude in xanthine oxidase reaction. The sensitization of CL in Fe2+-induced lipid peroxidation (LPO) of liposomes was by a factor 40, while in lipoxygenase reaction very low sensitization was observed. By means of cut-off light filter OS-12 (Soviet) having short wave-length transmittance limit at 560 nm it was possible to measure separately in the same sample the luminol-sensitized CL (maximal emission near 480 nm) and EuT-sensitized CL (maximum at 620 nm); these two CL components reflect, correspondingly, the production rate of oxygen- and lipid-free radicals. Mannitol, the OH radical scavenger, inhibited luminol-dependent component of CL in peroxidized liposomes and did not inhibited EuT sensitized CL in the same system. Apparently, hydroxyl radicals are produced in LPO reactions and responsible for the effect of CL sensitization by luminol, but are not involved in the chain LPO process.     

The influence of alpha-tocopherol and pyritinol on oxidative DNA damage and lipid peroxidation in human lymphocytes

Unscheduled DNA synthesis (UDS) and lipid peroxidation (LPO) were measured in human peripheral lymphocytes from healthy volunteers. These processes were induced by the catalytic system Fe2+-sodium ascorbate. The degree of induced LPO was measured spectrophotometrically by the thiobarbituric acid assay. UDS was detected by scintillometric measurement of the incorporation of 3H-thymidine into DNA. The protective action by fat-soluble vitamin E (D,L-alpha-tocopherol) and the artificial antioxidant pyritinol on UDS and LPO was also investigated. The system Fe2+ (2 mumole/l)-sodium ascorbate (30 mumole/l) increased the LPO level in healthy volunteers approximately 2.5 times and the incorporation of 3H-thymidine by 60-70%. alpha-Tocopherol (0.2 mmole/l) very efficiently suppressed LPO processes (p less than 0.01) and the oxidative damage of DNA measured as UDS was also significantly diminished (p less than 0.05). Pyritinol had no effect on LPO and UDS under our experimental conditions.     

Antioxidant mechanism of Mn(II) in phospholipid peroxidation.

Antioxidant action of Mn2+ on radical-mediated lipid peroxidation without added iron in microsomal lipid liposomes and on iron-supported lipid peroxidation in phospholipid liposomes or in microsomes was investigated. High concentrations of Mn2+ above 50 microM inhibited 2,2'-azobis (2-amidinopropane) (ABAP)-supported lipid peroxidation without added iron at the early stage, while upon prolonged incubation, malondialdehyde production was rather enhanced as compared with the control in the absence of Mn2+. However, in a lipid-soluble radical initiator, 2,2'-azobis (2,4-dimethyl-valeronitrile) (AMVN)-supported lipid peroxidation of methyl linoleate in methanol Mn2+ apparently did not scavenge lipid radicals and lipid peroxyl radicals, contrary to a previous report. At concentrations lower than 5 microM, Mn2+ competitively inhibited Fe(2+)-pyrophosphate-supported lipid peroxidation in liposomes consisting of phosphatidylcholine with arachidonic acid at the beta-position and phosphatidylserine dipalmitoyl, and reduced nicotinamide adenine dinucleotide phosphate (NADPH)-supported lipid peroxidation in the presence of iron complex in microsomes. Iron reduction responsible for lipid peroxidation in microsomes was not influenced by Mn2+.     

Intermembrane transport and antioxidant action of alpha-tocopherol in liposomes

Studies were made of the ability of alpha-tocopherol, incorporated into unilamellar liposomes from saturated or unsaturated phospholipids (donor liposomes) to inhibit the accumulation of lipid peroxidation (LPO) products in unilamellar liposomes from rat cerebral cortex lipids (acceptor liposomes) in the presence of LPO inducer (Fe + ascorbate). With the molar alpha-tocopherol: phospholipids rations from 1:1000 to 1:100 in donor liposomes, obtained through sonication of lipid dispersions, alpha-tocopherol was incorporated into both monolayers of liposomes and was distributed in monomeric form without forming clusters. Based on the dependencies of LPO inhibition on the alpha-tocopherol concentrations, we chose the ones that completely prevented the accumulation of LPO products in donor liposomes. Under these conditions LPO inhibition in mixtures of donor and acceptors liposomes was fully determined by the antioxidant effect of alpha-tocopherol in acceptor liposomes due to its intermembrane transfer. The efficiency of the "intermembrane" antioxidant action of alpha-tocopherol increased in the course of preincubation of donor and acceptor liposomes (up to 60 min) and this increase was more pronounced when the donor liposomes contained unsaturated phospholipids. Evidence was obtained that the intermembrane transfer of alpha-tocopherol did not result from the fusion of donor and acceptor liposomes during preincubation.