Aluminium salts accelerate peroxidation of membrane lipids stimulated by iron salts

Aluminium salts do not themselves stimulate peroxidation of ox-brain phospholipid liposomes, but they greatly accelerate the peroxidation induced by iron(II) salts at acidic pH values. This effect of Al(III) is not seen at pH 7.4, perhaps because Al(III) salts form insoluble complexes at this pH in aqueous solution. Peroxidation of liposomes in the presence of Al(III) and Fe(II) salts is inhibited by the chelating agent desferrioxamine, and by EDTA and diethylenetriaminepentaacetic acid at concentrations greater than those of Fe(II) salt. Aluminium salts slightly stimulate the peroxidation of peroxide-depleted linolenic acid micelles, but they do not accelerate the peroxidation induced by addition of iron(II) salts to the micelles at acidic pH. Aluminium salts accelerate the peroxidation observed when human erythrocytes are treated with hydrogen peroxide at pH 7.4. Desferrioxamine decreases the peroxidation. We suggest that Al(III) ions produce an alteration in membrane structure that facilitates lipid peroxidation, and that the increased formation of fluorescent age pigments in the nervous system of patients exposed to toxic amounts of Al(III) may be related to this phenomenon. The ability of desferal to bind both iron (III) and aluminium(III) salts and to inhibit lipid peroxidation makes it an especially useful chelating agent in the treatment of 'aluminium overload'.     

NADPH-dependent electron transport chain in microsomes and lipid peroxidation catalyzed by metal ions.

Like iron ions copper ions are also able to stimulate the NADPH-dependent lipid peroxidation in rat liver microsomes. This effect is strongly dependent on the concentration of Cu2+ added. Initial concentrations of Cu2+ above 50 microM completely inhibit the formation of malonaldehyde. The activator and inhibitor functions may be interpreted by a simultaneous participation of Cu+ ions formed in the chain branching and termination reaction of the free radical lipid peroxidation process. Inhibition studies with pCMB and the His-reagent diethyl pyrocarbonate indicate an essential role of cysteine and histidine residues in the Cu+-NADPH-dependent lipid peroxidation process.     

Protein-phosphate complexes as an inhibitor of iron-induced lipid peroxidation

Effect of phosphate buffer (pH 6.2) alone or in the presence of bovine serum albumin and other proteins on iron (II)-induced lipid peroxidation was studied. Phosphate buffer alone and in the presence of bovine serum albumin was found to inhibit lipid peroxidation. The inhibition was higher when bovine serum albumin was also present. Other proteins also inhibited lipid peroxidation in the presence of phosphate. Inhibition by proteins in the presence of phosphate seems to be due to binding of iron with phosphate and with protein-phosphate complexes. Reversal in inhibition was observed with an increase in iron concentration in reaction mixture. Equilibrium dialysis showed more binding of iron to protein in the presence of phosphate than in the presence of chloride ions.     

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

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

Stimulation and inhibition of iron-dependent lipid peroxidation by desferrioxamine

Peroxidation of rat brain synaptosomes was assessed by the formation of thiobarbituric acid reactive products in either 50 mM potassium phosphate buffer (pH 7.4) or pH adjusted saline. In phosphate, addition of Fe2+ resulted in a dose-related increase in lipid peroxidation. In saline, stimulation of lipid peroxidation by Fe2+ was maximal at 30 uM, and was less at concentrations of 100 uM and above. Whereas desferrioxamine caused a dose-related inhibition of iron-dependent lipid peroxidation in phosphate, it stimulated lipid peroxidation with Fe2+ by as much as 7-fold in saline. The effects of desferrioxamine depended upon the oxidation state of iron, and the concentration of desferrioxamine and lipid. The results suggest that lipid and desferrioxamine compete for available iron. The data are consistent with the hypothesis that either phosphate or desferrioxamine may stimulate iron-dependent lipid peroxidation under certain circumstances by favoring formation of Fe2+/Fe3+ ratios.     

Lipid peroxidation in rat liver microsomes. II. Response of hydroperoxide formation to iron concentration

When rat liver microsomes were incubated with NADPH, the major products were hydroperoxides which increased with time indicating that endogenous iron content is able to promote lipid peroxidation. The addition of either 5 microM Fe2+ or Fe3+ ions strongly enhanced the hydroperoxide formation rate. However, due to the hydroperoxide breakdown, hydroperoxide concentration decreased with time in this case. Higher ferrous or ferric iron concentration did not change the situation much, in that both hydroperoxide breakdown and formation were similar to those when NADPH only was present in the incubation medium. After lipid peroxidation, analysis of fatty acids indicated that the highest amount of peroxidized PUFA occurred in the presence of 5 microM of either Fe2+ or Fe3+. This analysis also showed that after 8 min incubation with low iron concentration, PUFA depletion was about 77% of that observed after 20 min, whereas without any iron addition or in the presence of 30 microM of either Fe3+, PUFA decrease was only about 37% of that observed after 20 min. As far as the optimum Fe2+/Fe3+ ratio required to promote the initiation of microsomal lipid peroxidation in rat liver is concerned, the highest hydroperoxide formation was observed with a ratio ranging from 0.5 to 2. These results indicate that microsomal lipid peroxidation induced by endogenous iron is speeded up by the addition of low concentrations of either Fe2+ or Fe3+ ions, probably because free radicals generated by hydroperoxide breakdown catalyze the propagation process. In experimental conditions unfavourable to hydroperoxide breakdown the principal process is that of the initiation of lipid peroxidation.     

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.     

Comparison of iron-catalyzed DNA and lipid oxidation

Lipid and DNA oxidation catalyzed by iron(II) were compared in HEPES and phosphate buffers. Lipid peroxidation was examined in a sensitive liposome system constructed with a fluorescent probe that allowed us to examine the effects of both low and high iron concentrations. With liposomes made from synthetic 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine or from rat liver microsomal lipid, lipid peroxidation increased with iron concentration up to the range of 10--20 microM iron(II), but then rates decreased with further increases in iron concentration. This may be due to the limited amount of lipid peroxides available in liposomes for oxidation of iron(II) to generate equimolar iron(III), which is thought to be important for the initation of lipid peroxidation. Addition of hydrogen peroxide to incubations with 1--10 microM iron(II) decreased rates of lipid peroxidation, whereas addition of hydrogen peroxide to incubations with higher iron concentrations increased rates of lipid peroxidation. Thus, in this liposome system, sufficient peroxide from either within the lipid or from exogenous sources must be present to generate equimolar iron(II) and iron(III). With iron-catalyzed DNA oxidation, hydrogen peroxide always stimulated product formation. Phosphate buffer, which chelates iron but still allows for generation of hydroxyl radicals, inhibited lipid peroxidation but not DNA oxidation. HEPES buffer, which scavenges hydroxyl radicals, inhibited DNA oxidation, whereas lipid peroxidation was unaffected since presumably iron(II) and iron(III) were still available for reaction with liposomes in HEPES buffer.     

Antioxidant and prooxidant action of nitric oxide donors and metabolites

Different nitric oxide donors and metabolites proved to have similar effects on the peroxidation in rat myocardium homogenate. PAPA-NONOate (synthetic nitric oxide donor), S-nitrosoglutathione, nitrite, and nitroxyl anion caused dose-dependent inhibition of the formation of malonic dialdehyde, a secondary product of lipid peroxidation. Dextran-bound dinitrosyl iron complexes and PAPA-NONOate were the most efficient inhibitors of lipid peroxidation. S-Nitrosoglutathione also inhibited the decline in coenzymes Q₉ and Q₁₀. Low-molecular-weight dinitrosyl iron complexes with cysteine accelerated lipid peroxidation, which could be caused by the release of iron ions upon their destruction. The antioxidant effect of nitric oxide donors appears to be due to the reduction of hemoprotein ferryl forms and the reaction of nitric oxide with lipid radicals.     

Ferritin and haemosiderin in free radical generation, lipid peroxidation and protein damage

Iron storage proteins, ferritin and haemosiderin, release iron to a range of chelators and reducing agents, including citrate, acetate and ascorbate. Released iron promotes both hydroxyl radical formation in the presence of hydrogen peroxide and lipid peroxidation in liposomes. Ferritin protein is modified in such reactions, both by free radical cleavage and addition reactions with aldehyde products of lipid peroxidation.     

In Vivo Lipid Peroxidation in Rat Brain Following Intracortical Fe2+ Injection

Cerebral contusion, cortical laceration, intracerebral hematoma formation, and hemorrhagic cortical infarction cause extravasation of red blood cells, followed by hemolysis, decompartmentalization of iron, formation and deposition of hemosiderin, and an increased incidence of epilepsy. In this experiment, 10 microliter of an aqueous solution containing 100 mmol/L FeCl2, 100 mmol/L CoCl2, or 0.9% (wt/vol) NaCl were injected at a depth of 1.8 mm into rat isocortex. The rate of formation of fluorescent compounds was measured in chloroform-methanol extracts of isocortical homogenates. Significant increases in the quantity of fluorescent products of lipid peroxidation were found 120 min after the injection of 100 mmol/L FeCl2. Cobaltous chloride and saline injection had no effect on the levels of fluorescent products found in the cortical homogenates. Although the intracortical deposition of aqueous solutions containing CoCl2 or FeCl2 in rodent cortex causes acute epileptiform discharges, the epileptogenic effect of CoCl2 is transient, while the injection of iron salts causes persistent seizures. Since CoCl2 injection failed to cause formation of lipid peroxidation products while the isocortical injection of iron caused significant increase in fluorescence within the injected hemisphere, we suggest that the occurrence of iron-induced lipid peroxidation may be of importance in initiation of recurrent seizures in the rat.     

A survey of chemicals inducing lipid peroxidation in biological systems

A great number of drugs and chemicals are reviewed which have been shown to stimulate lipid peroxidation in any biological system. The underlying mechanisms, as far as known, are also dealt with. Lipid peroxidation induced by iron ions, organic hydroperoxides, halogenated hydrocarbons, redox cycling drugs, glutathione depleting chemicals, ethanol, heavy metals, ozone, nitrogen dioxide and a number of miscellaneous compounds, e.g. hydrazines, pesticides, antibiotics, are mentioned. It is shown that lipid peroxidation is stimulated by many of these compounds. However, quantitative estimates cannot be given yet and it is still impossible to judge the biological relevance of chemical-induced lipid peroxidation.     

The measurement of malondialdehyde in peroxidised ox-brain phospholipid liposomes

The preparation of ox-brain phospholipid liposomes and their peroxidation using different catalysts have been described in detail. The degree of peroxidation is related to the formation of thiobarbituric acid (TBA)-reacting compounds and expressed as malondialdehyde (MDA). As confirmatory data, fluorescent MDA-phospholipid complexes were measured in parallel. Close agreement between the polar TBA-reactive compounds and the nonpolar fluorescent compounds confirmed the usefulness of the simple TBA test as a measure of peroxidative activity in pure lipid liposomes. Relative differences in the catalytic activity of ascorbic acid and cupric ions when assayed by the two methods are discussed.     

Inhibition of lipid peroxidation by calcium ions and their protection of steroid hydroxylase activity from peroxidative damage

Lipid peroxidation of adrenocortical mitochondria and microsomes was greatly stimulated by addition of 1.0 mM or less ferric ions. In the presence of NADPH-yielding system, the formation of corticosterone from endogeneous cholesterol and exogeneous deoxycorticosterone was inhibited as the concentrations of iron increased. Of interest is the fact that 0.5 mM ferric ion-mediated lipid peroxidation was completely abroagated upon addition of 2 mM calcium ions. Accordingly, protected from the peroxidative damage.     

Lipid peroxidation initiated by superoxide-dependent hydroxyl radicals using complexed iron and hydrogen peroxide

Iron salts stimulate lipid peroxidation by decomposing lipid peroxides to produce alkoxyl and peroxyl radicals which initiate further oxidation. In aqueous solution ferrous salts produce OH. radicals, a reactive species able to abstract hydrogen atoms from unsaturated fatty acids, and so can initiate lipid peroxidation. When iron salts are added to lipids, containing variable amounts of lipid peroxide, the former reaction is favoured and OH. radicals contribute little to the observed rate of peroxidation. When iron is complexed with EDTA, however, lipid peroxide decomposition is prevented, but the complex reacts with hydrogen peroxide to form OH. radicals which are seen to initiate lipid peroxidation. Superoxide radicals appear to play an important part in reducing the iron complex.     

Albumin bound nonesterified fatty acids inhibit in vitro lipid peroxidation

Individual nonesterified fatty acids were bound to albumin in vitro and these fatty acid albumin complexes were used to study their effect on lipid peroxidation in liver microsomes. Peroxidation was induced by various methods and malondialdehyde (MDA) was measured as an index of peroxidation. Among the fatty acids tested, albumin-bound monounsaturated fatty acids showed more inhibition of peroxidation as compared to other fatty acids. Increasing the concentration of iron in the peroxidizing system, partially reversed the inhibition by fatty acids. Moreover, albumin-bound fatty acid did not inhibit iron independent peroxidation. This suggests that, like nonesterified fatty acids, albumin-bound fatty acids inhibit peroxidation by chelating the iron. Albumin fatty acid complex, similar to the fatty acid composition present in the circulating albumin, also showed inhibition of peroxidation. These data indicate that nonesterified fatty acids even when bound to albumin are capable of inhibiting peroxidation and circulating albumin, which contains various fatty acids bound to it, may impart some antioxidant effect in addition to other plasma antioxidants.     

Ferritin and superoxide-dependent lipid peroxidation

Ferritin was found to promote the peroxidation of phospholipid liposomes, as evidenced by malondialdehyde formation, when incubated with xanthine oxidase, xanthine, and ADP. Activity was inhibited by superoxide dismutase but markedly stimulated by the addition of catalase. Xanthine oxidase-dependent iron release from ferritin, measured spectrophotometrically using the ferrous iron chelator 2,2'-dipyridyl, was also inhibited by superoxide dismutase, suggesting that superoxide can mediate the reductive release of iron from ferritin. Potassium superoxide in crown ether also promoted superoxide dismutase-inhibitable release of iron from ferritin. Catalase had little effect on the rate of iron release from ferritin; thus hydrogen peroxide appears to inhibit lipid peroxidation by preventing the formation of an initiating species rather than by inhibiting iron release from ferritin. EPR spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide was used to observe free radical production in this system. Addition of ferritin to the xanthine oxidase system resulted in loss of the superoxide spin trap adduct suggesting an interaction between superoxide and ferritin. The resultant spectrum was that of a hydroxyl radical spin trap adduct which was abolished by the addition of catalase. These data suggest that ferritin may function in vivo as a source of iron for promotion of superoxide-dependent lipid peroxidation. Stimulation of lipid peroxidation but inhibition of hydroxyl radical formation by catalase suggests that, in this system, initiation is not via an iron-catalyzed Haber-Weiss reaction.     

脂质过氧化引起的DNA损伤研究进展

脂质过氧化可以引起各种碱基损伤、DNA链断裂和各种荧光产物生成,并对DNA分子鸟嘌呤碱基具有选择性损伤.过渡金属离子可以明显加深脂质过氧化对DNA的损伤程度.多种抗氧化剂、活性氧自由基清除剂对脂质过氧化引起的DNA损伤有一定程度的保护作用.具有致突、致癌作用的8－羟基鸟嘌呤已经观察到．脂质过氧化的致突变、致癌变作用机制引起了人们的极大兴趣．     

Antiradical and antioxidant effect of arginine and its action on lipid peroxidation in hypoxia

Arginine (0.5 and 1 mu mol) decreased by 14-17% rates of superoxide anion formation in two systems: HADH-phenazine methosulfate and hydroxylamine autooxidation with nitrotetrazolium blue. These concentrations of arginine decreased by 40-50% formation of diene conjugates and Schiff bases in plasma when lipid peroxidation initiated by iron -ascorbate. Arginine administration before hypoxia decreased lipid peroxidation rate in plasma and liver microsomal membranes of rats.     

Lipid peroxidation in peribacteroid membranes from French-bean nodules

Enriched peribacteroid membranes were prepared from Phaseolus vulgaris nodules and, in the presence of metleghemoglobin and H₂O₂, membranal lipid peroxidation was observed. The initial rate of the reaction was low and increased with time. Ferrous leghemoglobin was unable to induce this peroxidation with H₂O₂. Thus, it appears that leghemoglobin (IV) is not the activated species involved in this process. Heme plays a role in this peroxidation and the hydroxyl radical is not an intermediate of the reaction. Lipid peroxidation in peribacteroid membranes was also observed in the presence of iron ions. A mixture of iron (III) and iron (II) produced a maximal peroxidation. Senescing nodule extracts were able to provoke membranal lipid peroxidation; they contained nonprotein-bound iron. Peribacteroid membranes were more sensitive than microsomes to peroxidation, as measured by malonaldehyde formation.