Peroxidation of liposomal palmitoyllinoleoylphosphatidylcholine (PLPC), effects of surface charge on the oxidizability and on the potency of antioxidants (original) (raw)
Related papers
Chemistry and Physics of Lipids, 2002
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 a-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. : S 0 0 0 9 -3 0 8 4 ( 0 1 ) 0 0 2 0 8 -0 O. Bittner et al. / Chemistry and Physics of Lipids 114 (2002) 81-98 82
Chemistry and Physics of Lipids, 2007
Copper-induced peroxidation of liposomal palmitoyllinoleoyl-phosphatidylcholine (PLPC) is inhibited by ␣-tocopherol at micromolar concentrations. In our previous study we found that when the liposomes contain phosphatidylserine (PS), nanomolar concentrations of Toc were sufficient to inhibit peroxidation. In an attempt to gain understanding of the origin of this extreme antioxidative potency, we tested the antioxidative potency of 36 additional antioxidants and the dependence of their potency on the presence of PS in the liposomes. The results of these studies reveal that only 11 of the tested antioxidants possess similar antioxidative potency to that of Toc. These include trolox, butylated hydroxytoluene (BHT), curcumin, nordihydroguaiaretic acid (NDGA), diethylstilbestrol (DES), 2 of the 13 tested flavonoids (luteolin and 7,3 ,4 -trihydroxyflavone; T-414), ␣-naphthol, 1,5-, 1,6-and 1,7-dihydroxynaphthalenes (DHNs). Propyl gallate (PG), methyl syringate, rosmarinic acid, resveratrol, other flavonoids, as well as -naphthol, 1,2-, 1,3-, 1,4-, 2,3-, 2,6-, and 2,7-DHNs were either moderately antioxidative or pro-oxidative. For liposomes made of PLPC (250 M) and PS (25 M) the "lag" preceding copper-induced peroxidation (5 M copper) was doubled upon addition of 30-130 nM of the "super-active" antioxidants.
Copper-induced lipid peroxidation in liposomes, micelles, and LDL: Which is the role of vitamin E?
Free Radical Biology and Medicine, 1995
Liposomes, containing phospholipid hydroperoxides, are peroxidised in the presence of Cu ÷÷. Peroxidation starts after a period of resistance to oxidation, which is abolished by the shift of lipid organisation from bilayer to micellar dispersion. Independently from ongoing peroxidation, vitamin E in liposomes also reacts with Cu ++, and it is consumed. The evidence that phospholipid hydroperoxides induce an acceleration of vitamin E consumption rate and that the consumption of vitamin E and phospholipid hydroperoxides are stoichiometric indicates that, in liposomes, the rate-limiting reaction is the interaction between radicals generated by copper from vitamin E and phospholipid hydroperoxides. In micelles, on the other hand, vitamin E is directly oxidised by copper at a much faster rate; thus, the concerted consumption of phospholipid hydroperoxides does not take place. Moreover, in micelles challenged with Cu ++, vitamin E plays a pro-oxidant effect (M. Maiorino et al. FEBS Lens., 330(2): 174-176;. In LDL, incubation with Cu ÷+ promotes vitamin E consumption at a fast rate, as in micelles, but not the concerted disappearance of lipid hydroperoxides, as in liposomes. However, the direct vitamin E oxidation by Cu ++, observed in micelles and liposomes, does not lead to a pro-oxidant effect in LDL. The kinetics of peroxidation, indeed, is identical in native and vitamin E-depleted LDL. These results argue against an involvement of vitamin E, both as antioxidant or pro-oxidant in LDL challenged with Cu ++, and suggest that other factors, besides antioxidant content, must be relevant in determining LDL oxidative resistance.
Journal of Food Science, 2002
ABSTRACT: Cholesterol oxidation products (COPs) are present in biological tissues and in foods. The inhibitory effect of antioxidants, such as tocopherols, on COPs formation has been only partially investigated. The antioxidant effect of dl alpha-, dl beta-, dl gamma-, and dl-delta tocopherol on the metal-induced oxidation of phosphatidylcholine (PC): cholesterol liposomes was assayed. Formation during liposome oxidation of six different COPs was monitored by gas chromatography. dl alpha-, and dl gamma-tocopherol show good inhibitory effect against PC-fatty acid oxidation and also on COPs formation. dl delta-Tocopherol is less effective than the alpha-and gamma-homologous, beta-tocopherol being unable to prevent PC and cholesterol oxidation. dl alpha-, and dl gamma-Tocopherol are more effective to prevent the oxidation of the lateral chain of cholesterol molecule. At the highest tocopherol concentration assayed, dl alpha-tocopherol shows prooxidant effect, enhancing liposomal oxidation and COPs formation. It is concluded that the tocopherols assayed can inhibit cholesterol oxidation but to a different degree.
Effect of lipid physical state on the rate of peroxidation of liposomes
Free Radical Biology and Medicine, 1992
The effect of cholesterol on the rate ofperoxidation ofarachidonic acid and 1-palmitoyl-2-arachidonoyl phosphatidylcholine (PAPC) in dimyristoylphosphatidylcholine (DMPC) liposomes was examined above and below the phase transition temperature (Tin) of the lipid. The rate of peroxidation of arachidonic acid was more rapid below the phase transition temperature of the host lipid. At a temperature below the Tm (4°C), increasing concentrations of cholesterol reduced the rate of peroxidation of arachidonic acid as judged by the production of thiobarbituric acid reactive substances. Above Tm (37°C), cholesterol increased the rate of peroxidation of the fatty acid. Similarly, PAPC was peroxidized more rapidly at 4°C than at 37°C. However, cholesterol had little effect on the rate of peroxidation of PAPC at 4°C. The rate of peroxidation of arachidonic acid was related to the lipid bilayer fluidity as judged by fluorescence anisotropy measurements of diphenylhexatriene. The rate of peroxidation increased slowly with increasing rigidity of the probe environment when the bilayer was relatively fluid and more rapidly as the environment became more rigid. The increase in the rate ofperoxidation ofarachidonic acid in the less fluid host lipid was unrelated to differences in iron binding or to transfer of arachidonic acid to the aqueous phase. Decreasing the concentration of arachidonic acid in DMPC to <2 mole% dramatically decreased the rate of peroxidation at 4°C, suggesting that formation of clusters of fatty acids at 4°C is required for rapid peroxidation. These data support the hypothesis that an increase in the packing density of the acyl chains of peroxidizable lipids promotes lipid peroxidation in less fluid environments which favor phase separation.
Biochimica et Biophysica Acta (BBA) - General Subjects, 1984
The events accompanying the inhibitory effect of a-tocopherol and/or ascorbate on the peroxidation of soybean L-a-phosphatidylcholine liposomes, which are an accepted model of biological membranes, were investigated by electron paramagnetic resonance, optical and polarograpic methods. The presence of a-tocopherol radical in the concentration range I0-s-10-7 M was detected from its EPR spectrum during the peroxidation of liposomes, catalysed by the Fe3+-triethylenetatramine complex. The a-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 a-tocopherol itself. A kinetic rate constant of about 2-10 5 M-1 .s-1 was estimated from the reaction as it occurs under the adopted experimental conditions. The scavenging effect of a-tocopheroi on lipid peroxidation is maintained as long a ascorbic acid is present.
Lipid peroxidation and 4-hydroxy-2-nonenal formation by copper ion bound to amyloid-β peptide
Free Radical Biology and Medicine, 2007
The lipid peroxidation product 4-hydroxy-2-nonenal (HNE) is proposed to be a toxic factor in the pathogenesis of Alzheimer disease. The primary products of lipid peroxidation are phospholipid hydroperoxides, and degraded reactive aldehydes, such as HNE, are considered secondary peroxidation products. In this study, we investigated the role of amyloid-β peptide (Aβ) in the formation of phospholipid hydroperoxides and HNE by copper ion bound to Aβ. The Aβ 1-42 -Cu 2+ (1:1 molar ratio) complex showed an activity to form phospholipid hydroperoxides from a phospholipid, 1-palmitoyl-2-linoleoyl phosphatidylcholine, through Cu 2+ reduction in the presence of ascorbic acid. The phospholipid hydroperoxides were considered to be a racemic mixture of 9-hydroperoxide and 13-hydroperoxide of the linoleoyl residue. When Cu 2+ was bound to 2 molar equivalents of Aβ 1-42 (2 Aβ 1-42 -Cu 2+ ), lipid peroxidation was inhibited. HNE was generated from one of the phospholipid hydroperoxides, 1-palmitoyl-2-(13-hydroperoxy-cis-9, trans-11-octadecadienoyl) phosphatidylcholine (PLPC-OOH), by free Cu 2+ in the presence of ascorbic acid through Cu 2+ reduction and degradation of PLPC-OOH. HNE generation was markedly inhibited by equimolar concentrations of Aβ 1-40 (92%) and Aβ 1-42 (92%). However, Aβ 1-42 binding 2 or 3 molar equivalents of Cu 2+ (Aβ 1-42 -2Cu 2+ , Aβ 1-42 -3Cu 2+ ) acted as a prooxidant to form HNE from PLPC-OOH. These findings suggest that, at moderate concentrations of copper, Aβ acts primarily as an antioxidant to prevent Cu 2+ -catalyzed oxidation of biomolecules, but that, in the presence of excess copper, pro-oxidant complexes of Aβ with Cu 2+ are formed.
Bioscience, Biotechnology, and Biochemistry, 2010
Unilamellar liposomes of phosphatidylcholines (PCs), 1-palmitoyl-2-linoleoyl-3-sn-PC (PLPC), 1-linoleoyl-2palmitoyl-3-sn-PC (LPPC), and a 1:1 mixture of 1,2dilinoleoyl-3-sn-PC and 1,2-dipalmitoyl-3-sn-PC (DLPC/ DPPC), were peroxidized by the addition of a watersoluble 2,2 0 -azobis(2-amidinopropane) dihydrochloride (AAPH) and of a lipid-soluble 2,2 0 -azobis(4-methoxy-2,4dimethylvaleronitrile) (MeOAMVN). LPPC liposomes showed the lowest oxidizability and kinetic chain-length values on AAPH-initiated peroxidation. On MeOAMVNinitiated peroxidation, PLPC liposomes with their lower peroxidation kinetic values were more stable than LPPC or DLPC/DPPC liposomes. The incorporation of cholesterol into the liposomes induced dose-dependent inhibition of PLPC and of LPPC peroxidation, while its effect was less important for the DLPC/DPPC liposomes. Our results indicate that the sn-position of unsaturated acyl chains and the cholesterol content are important modulating factors in the oxidizability of membrane phospholipids.
Antioxidant effect of copper(II) on photosensitized lipid peroxidation
Journal of Inorganic Biochemistry, 1995
Unilamellar liposomes (LH) of phosphatidylcholine (PC), dispersed in phosphate buffer at pH 7 (PB), underwent lipid peroxidation and lysis with release of entrapped glucose-6-phosphate when irradiated with UVA light in the presence of 2-(3-benzoylphenyl)propionic acid (ketoprofen, KPF) or 2-(6-methoxy-2-naphthyl)propionic acid (naproxen, NAP), which were used as photosensitizers. Lipid photoperoxidation and consequent lysis were reduced when copper(II), up to 5 p.M, was present in the irradiated samples. Suitable experiments were performed to evidence the species responsible for the lipid peroxidation, the copper effect on the drug photodegradation, and the mechanism of the copper antioxidant activity. The overall results suggest that the photoperoxidation was probably initiated by organic radicals obtained from the irradiation of KPF and NAP and the inhibition by copper could be attributed to its interaction with the peroxyl radicals of the drug and/or the liposomes, breaking the propagation of the radical chain.
Peroxidation of liposomal lipids
European Biophysics Journal, 2007
Free radicals, formed via different mechanisms, induce peroxidation of membrane lipids. This process is of great importance because it modifies the physical properties of the membranes, including its permeability to different solutes and the packing of lipids and proteins in the membranes, which in turn, influences the membranes' function. Accordingly, much research effort has been devoted to the understanding of the factors that govern peroxidation, including the composition and properties of the membranes and the inducer of peroxidation. In view of the complexity of biological membranes, much work was devoted to the latter issues in simplified model systems, mostly lipid vesicles (liposomes). Although peroxidation in model membranes may be very different from peroxidation in biological membranes, the results obtained in model membranes may be used to advance our understanding of issues that cannot be studied in biological membranes. Nonetheless, in spite of the relative simplicity of peroxidation of liposomal lipids, these reactions are still quite complex because they depend in a complex fashion on both the inducer of peroxidation and the composition and physical properties of the liposomes. This complexity is the most likely cause of the apparent contradictions of literature results. The main conclusion of this review is that most, if not all, of the published results (sometimes apparently contradictory) on the peroxidation of liposomal lipids can be understood on the basis of the physico-chemical properties of the liposomes. Specifically: (1) The kinetics of peroxidation induced by an ''external'' generator of free radicals (e.g. AAPH) is governed by the balance between the effects of membrane properties on the rate constants of propagation (k p ) and termination (k t ) of the free radical peroxidation in the relevant membrane domains, i.e. in those domains in which the oxidizable lipids reside. Both these rate constants depend similarly on the packing of lipids in the bilayer, but influence the overall rate in opposite directions.