Effect of lysophosphatidylcholine on the radiation-induced lipid peroxidation in liposomes

The effect of lysophosphatidylcholine (LPC) on the lipid peroxidation process (LPO) in liposomes of rat liver phosphatidylcholine initiated by irradiation of 137Cs source was studied. The formation of diene conjugates (DC) is shown to increase dramatically on incorporation of more than 10% LPC into liposomes. The dependence of DC proportion on the irradiation dose is practically linear in the range of 0 to 5 kGy. The DC concentration in the liposomes without LPC grows at least to dose of 3.3 kGy and is unchanged on further irradiation. The malonic dialdehide accumulation follows the similar dependence. The LPC effect is neutralized by the incorporation of cholesterol into liposomes. The product of free radical fragmentation of LPC, palmitoxyacetone, practically has no influence on the DC concentration. The reasons of LPC effect on the irradiation initiated LPO in liposomes is discussed.     

Effect of lipid composition of liposomes on their sensitivity to peroxidation

The effect of lipid composition of liposomes on peroxidation induced by ferrous ion and ascorbate was examined. Temperature affects the sensitivity of liposomes; the peroxidation rate was increased with increase of the incubation temperature. With liposomes consisting of 1-palmitoyl-2-arachidonyl phosphatidylcholine (substrate) and a peroxidation-insensitive lipid, 1-palmitoyl-2-oleoyl phosphatidylcholine, peroxidation was dependent on the density of the substrate. No appreciable peroxidation was observed with liposomes containing less than 10 mol% of the substrate at 37 degrees C. When 1 mol substrate was mixed with 9 mol dimyristoyl phosphatidylcholine, peroxidation occurred below 10 degrees C, but not above 20 degrees C. Above 20 degrees C, the substrates should be located homogeneously on the membranes, whereas they should be clustered below 10 degrees C, since the gel-liquid crystalline phase transition temperature of matrix membrane of dimyristoylphosphatidylcholine was 17-21 degrees C. Peroxidation of liposomes consisting of 1-palmitoyl-2-arachidonyl phosphatidylcholine was also suppressed by cholesterol. These findings indicate that the lateral distribution as well as the density of the substrate on membranes affects the sensitivity of the substrate to peroxidation. It was also found that alpha-tocopherol is preferentially located in the 1-palmitoyl-2-arachidonyl phosphatidylcholine-rich regions of membranes consisting of mixed phospholipids, and efficiently suppresses peroxidation of liposomal lipids.     

Rabbit liver microsomal lipid peroxidation. The effect of lipid on the rate of peroxidation

Rat and rabbit liver microsomes catalyze an NADPH-cytochrome P-450 reductase-dependent peroxidation of endogenous lipid in the presence of the chelate, ADP-Fe3+. Although liver microsomes from both species contain comparable levels of NADPH-cytochrome P-450 reductase and cytochrome P-450, the rate of lipid peroxidation (assayed by malondialdehyde and lipid hydroperoxide formation) catalyzed by rabbit liver microsomes is only about 40% of that catalyzed by rat liver microsomes. Microsomal lipid peroxidation was reconstituted with liposomes made from extracted microsomal lipid and purified protease-solubilized NADPH-cytochrome P-450 reductase from both rat and rabbit liver microsomes. The results demonstrated that the lower rates of lipid peroxidation catalyzed by rabbit liver microsomes could not be attributed to the specific activity of the reductase. Microsomal lipid from rabbit liver was found to be much less susceptible to lipid peroxidation. This was due to the lower polyunsaturated fatty acid content rather than the presence of antioxidants in rabbit liver microsomal lipid. Gas-liquid chromatographic analysis of fatty acids lost during microsomal lipid peroxidation revealed that the degree of fatty acid unsaturation correlated well with rates of lipid peroxidation.     

Effect of melittin on thermotropic lipid state transitions in phosphatidylcholine liposomes.

We have examined the Raman scattering due to CH stretching vibrations, as well as to v(-C=C-) and v(=C-C=) of beta-carotene, of liposomes composed of phosphatidylcholine (egg, dimyristoyl, dipalmitoyl) +/- cholesterol, beta-carotene or melittin in the temperature range of -10 degrees C to 45 degrees C. (2) Plots vs. temperature of the intensities of the 2885 cm-1 and 2930 cm-1 CH stretching bands relative to the intensity of the thermally stable 2850 cm-1 band, i.e. the I2885/I2850 and I2930/I2850 ratios, reveal a sharp discontinuity in cholesterol-free phosphatidylcholine liposomes; this coincides with the gel leads to liquid-crystal transition temperature of the fatty acyl chains. In cholesterol/phosphatudylcholine liposomes the change in I2885/I2850 occurs over a very broad temperature range and I2930/I2850 remains stable. (3) I1527/I1158, i.e. the intensity of v(-C=C-) relative to that of v(=C-C-) in beta-carotene/phosphatidylcholine liposomes, changes discontinuously at the gel leads to liquid-crystal transition temperature. The values above the transition temperature approach those of the carotenoid in organic solution. (4) The transitions reported in I2885/I2850 for phosphatidylcholine/melittin liposomes (25-56; 1, M/M) are shifted to much higher temperatures than observed in phosphatidylcholine liposomes. In the case of dimyristoyl phosphatidylcholine/melittin the changes in I2930/I2850 also occurs at a higher temperature (28 degrees C) than without melittin (21 degrees C), but the temperature shift is less than the +13 degrees C observed for I2885/I2850. It appears that the apolar moiety of melittin organizes phospholipids adjacent to and more remote from the peptide moiety, to form complexes with an elevated lipid transition temperature. The effect of the peptide moiety is greater on the methylene segments (I2885/I2850) than on the methyl termini (I2930/I2850).     

Carboxymethylated glucan inhibits lipid peroxidation in liposomes

Protective capabilities were studied of carboxymethylated (1-->3)-beta-D-glucan from Saccharomyces cerevisiae cell wall against lipid peroxidation in phosphatidylcholine liposomes induced by OH radicals produced with Fenton's reagent (H2O2/Fe2+) and also by microwave radiation using absorption UV-VIS spectrophotometry. A significant decrease in the conjugated diene production, quantified as Klein oxidation index, was observed in the presence of a moderate amount of added glucan. Increase of the oxidation index was accompanied with enhanced carboxyfluorescein leakage as a result of liposome membrane destabilization. This process was markedly suppressed with glucan present in the liposome suspension. Therefore, glucan may be considered as a potent protector against microwave radiation-induced cell damage.     

Effect of cisplatin, carboplatin and stobadine on lipid peroxidation of kidney homogenate and phosphatidylcholine liposomes.

The effects of the nephrotoxic, anticancer agents cisplatin (CDDP) and carboplatin (CBDCA), and the free radical scavenger, stobadine, were investigated on lipid peroxidation (LPO) of rat kidney homogenates and phosphatidylcholine (PC) liposomes. Kidney homogenates were incubated in air at 37 degrees C for 6-48 h and lipid peroxidation was detected spectroscopically as absorbance (533 nm) of the thiobarbituric acid-malondialdehyde (TBA-MDA) complex. CDDP (0.3-10 mmol.l-1) increased LPO of the homogenate. CBDCA decreased the TBA-MDA absorbance, yet was found to interfere with MDA, TBA and/or with the TBA-MDA complex. Thus when CBDCA is involved, the TBA-MDA method for detection of LPO is not suitable. Stobadine (0.1 mmol.l-1 and 1 mmol.l-1) inhibited LPO either in the control homogenate and in the homogenate where peroxidation was increased by CDDP. The effect of CDDP and CBDCA on peroxidation of PC liposomes was monitored as oxygen consumption using a Clark-type oxygen electrode. CDDP increased but CBDCA decreased the rate of oxygen consumption during the peroxidation of liposomes induced by FeSO4. The results suggest that the effects of CDDP and CBDCA on LPO may be linked with their nephrotoxicity.     

Effect of radiomodifiers on lipid peroxidation and the structural-functional state of irradiated mitochondria

SH-Containing radioprotective agents, for instance, cysteine, cystamine, dithiothreitol, exert an antioxidant effect on gamma-radiation-induced lipid peroxidation in mitochondrial membranes and, concurrently, uncouple oxidation from phosphorylation. A radiosensitizer, N-ethylmaleimide, on the contrary, being a pro-oxidant of lipid peroxidation couples oxidation and phosphorylation. At the same time, changes in the lipid peroxidation system and in the energy production processes, observed after irradiation of a mitochondrion suspension containing modifiers, are accompanied by the increased destruction of mitochondrial membranes as compared to irradiated controls.     

Effect of liposomes on lipid peroxidation and total phospholipids in rabbit ischemic spinal cord model

The effect of spinal cord ischemia (induced by abdominal aorta ligation for 20 minutes) on lipid peroxidation and TPL composition was investigated and discussed in our previous articles. It is known, that partially reduced species of oxygen can be formed under aerobic conditions. For that reason, the effect of ligation release for 60 minutes was observed in experimental animals treated with the selected liposomes. Administration of CP, (CP+SA) and (CP+Chol) liposomes applied 30 minutes before 20 minutes ischemia revealed an ameliorating effect on in vivo and in vitro Fe-dependent peroxidation manifested by TBA-RS accumulation. Combined use of (CP+SA) liposomes with lipophylic form of stobadine (DP 1031) was not more effective. Application of CP liposomes directly before the ligation release slightly increased the antiradical capacity in spinal cord homogenates comparing with not-treated animals. Accumulation of TBA-RS was accompanied by TPL degradation during recirculation period but values of TPL after liposomal treatment were unaffected.     

Phosphorescent analysis of lipid peroxidation products in liposomes]

It was found that lipid peroxidation products incorporated into liposomes prepared from oxidized preparations of bovine heart phosphatidylcholine and the total lipid fraction of human erythrocyte membranes are able to phosphoresce at room temperature was studied. The temperature dependences of kinetic and spectral parameters of phosphorescence were measured. It is shown that mechanism of phosphorescence quenching of lipid chromophores has a dynamic nature. It is proposed to use endogenic molecules of the lipid peroxidation products capable of phosphorescence as intrinsic phosphorescence probes for studying the slow molecular dynamics of lipids in artificial and biological membranes in a millisecond range.     

Effect of melanins on lipid peroxidation

Effects of melanins obtained from cultured Cladosporium cladosporidae fungi and Alpha grape on Fe(2+)-induced, Fe(2+)-ascorbate-induced, and NADPH-induced lipid peroxidation in rat liver, brain, and eye were studied. Melanins were shown to inhibit the accumulation of lipid peroxidation products in vitro. The inhibitory effects of melanins were not due to direct interactions of these pigments with superoxide anion (O2). However, melanins may interact with other free radicals. Melanins were demonstrated to have the ability to oxidize NADPH, which is probably one of the mechanisms of their antioxidant effects.     

The role of iron in ferritin- and haemosiderin-mediated lipid peroxidation in liposomes.

Ferritin and haemosiderin were shown, by the measurement of malondialdehyde production and loss of polyunsaturated fatty acids, to stimulate lipid peroxidation in liposomes. At pH 7.4 ascorbate was additionally required to achieve peroxidation; however, peroxidation occurred at pH 4.5 in the presence of iron-proteins alone. The damage was completely inhibited by the incorporation of chain-breaking antioxidants (alpha-tocopherol and butylated hydroxytoluene) into the liposomes. Metal chelators (desferrioxamine and EDTA) also completely inhibited lipid peroxidation. These and further results indicate that, at pH 4.5, even in the absence of a reducing agent, iron is released from haemosiderin and can mediate oxidative damage to a lipid membrane.     

Effect of neutrophils on the state of lipid peroxidation in the erythrocytes and its physiological significance

Theoretical grounds of the existence (in the organism) of physiological process of the neutrophil granulocyte-erythrocyte interaction are presented. This process underlies damage and destruction of old erythrocytes. A conclusion is made concerning the peroxide mechanism of this interaction. This process possibly takes place under physiological conditions and becomes more pronounced after splenectomy .     

Effect of cryopreservation on lipid peroxidation in chick cornea.

A mechanism suggested to cause injury to the preserved organs in vitro is the generation of oxygen free radicals either during preservation or after transplantation due to reperfusion. Methods to suppress generation of oxygen free radicals may lead to improved methods of organ preservation. In this study, increase in the levels of lipid peroxidation in chick cornea after cryopreservation is reported. Addition of fetal bovine serum (FBS) in cryopreservation medium was found to prevent lipid peroxidation. Addition of FBS was also found to be protective towards corneal viability during cryopreservation.     

Effect of cisplatin on lipid peroxidation in blood platelets.

Cisplatin (cis-diamminedichloroplatinum II) at the concentrations of 2-20 micrograms induces non-enzymatic peroxidation of pig platelet lipids. At low concentration (0.1 microgram) it inhibits the enzymatic thrombin-stimulated transformation of platelet endogenous arachidonic acid. This drug also reduces the activities of platelet enzymes: superoxide dismutase and glutathione peroxidase.     

The effect of zinc on iron-induced lipid peroxidation in different lipid systems including liposomes and micelles

The effect of zinc on FeSO4/ascorbic acid-induced lipid peroxidation was measured by the thiobarbituric acid assay in various lipid systems including small unilamellar liposomes prepared from egg phosphatidylcholine (EPC), ionic micelles prepared from arachidonic acid (C20:4), non-ionic monocomponent micelles prepared from EPC-derived, methylated fatty acids, and an eicosatetrene emulsion. With the exception of C20:4 micelles, zinc inhibited lipid peroxidation in each of the above systems in a similar dose-related fashion, with 0.5 mM zinc having maximal effect. Gas-chromatographic fatty acid analysis too indicated a protective effect of zinc against FeCl3-induced lipid peroxidation in soybean PC vesicles, which do not contain C20:4 moieties. These findings, in particular the inhibition of lipid peroxidation in eicosatetrene emulsion, suggest that the presence of uncharged polar head groups, or packing of lipid molecules into ordered self-assemblages (membranes and micelles) have no critical influence on the antioxidant effect of zinc. The results with Fe2+ are compatible with the concept that zinc interferes with the formation of Fe2+-oxygen-enoic complexes. This mechanism, however, cannot account for the inhibition by zinc of the Fe#+-induced lipid peroxidation, suggesting the involvement of other types of zinc effects in these systems.     

Kinetic evaluation of lipophilic inhibitors of lipid peroxidation in DLPC liposomes

The authors have developed a kinetic method that allows one to obtain relative reactivity constants for lipophilic antioxidants in free radical systems. Two experimental model systems were developed: (a) a methanolic solution using AMVN as the free radical initiator and linoleic acid as the substrate, and (b) a multilamellar vesicle system composed of dilinoleoylphosphatidylcholine and AAPH as the substrate and the initiator, respectively. The use of these two systems allows researchers not only to determine the intrinsic reactivity of a potential antioxidant, but also to evaluate its potency in a membranous system where the contribution of the physical properties of the antioxidant to the inhibition of lipid peroxidation is important. These results show that all antioxidants tested acted in these systems as free radical scavengers, and they validate the synergism between intrinsic scavenging ability and membrane affinity and/or membrane-modifying physical properties in the inhibition of lipid peroxidation.     

Relation of lipid peroxidation to loss of cations trapped in liposomes

Lipid peroxidation and alterations in cation loss have been induced in liposomes by ferrous ion, ascorbic acid, reduced and oxidized glutathione, and gamma radiation. Modifications of these effects by tocopherol and 2,6-di-tert-butyl-4-methylphenol (BHT) were studied when these antioxidants were either incorporated in the membrane or were added to already formed liposomes prior to the addition of the chemical agent or to irradiation. Lipid peroxidation, as indicated by the thiobarbituric acid test for malonic dialdehyde, did not correlate with alterations in cation loss. The largest amounts of lipid peroxidation induced by ascorbic acid and glutathione were associated with decreased cation loss. Inhibition of Fe(2+)- and radiation-induced lipid peroxidation by antioxidants did not inhibit the associated increase in cation loss. Tocopherol was a more effective antioxidant than BHT when it was incorporated in the membrane, whereas BHT was more effective when it was added to the liposomes after formation.     

Investigation of lipid peroxidation in liposomes induced by heavy ion irradiation

Lipid peroxidation induced by heavy ion irradiation was investigated in 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) liposomes. Lipid peroxidation was induced using accelerated heavy ions that exhibit linear energy transfer (LET) values between 30 and 15 000 keV/μm and doses up to 100 kGy. With increasing LET, the formation of lipid peroxidation products such as conjugated dienes, lipid hydroperoxides, and thiobarbituric acid-reactive substances decreased. When comparing differential absorption spectra and membrane fluidity following irradiation with heavy ions and x-rays (3 Gy/min), respectively, it is obvious that there are significant differences between the influences of densely and sparsely ionizing radiation on liposomal membranes. Indications for lipid fragmentation could be detected after heavy ion irradiation. Received: 6 March 1997 / Accepted in revised form: 31 March 1998     

Iron binding to microsomes and liposomes in relation to lipid peroxidation

The effects of ADP, ATP, citrate and EDTA on iron-dependent microsomal and liposomal lipid peroxidation, and on 59FeCl3 binding to the lipid membranes were measured. The aim was to test if initiation of lipid peroxidation is a site-specific mechanism requiring bound iron. In the absence of chelator, iron was bound to both membranes. EDTA and citrate removed the iron and inhibited peroxidation. ATP and ADP stimulated peroxidation, but whereas ADP allowed only half of the iron to remain bound, all was removed by ATP. Chelators, therefore, cannot be simply influencing a site-specific mechanism. Their effects must relate to the reactivities of the different iron chelates as initiators of lipid peroxidation.