linoleic-acid and 2-2--azobis(2-amidinopropane)

Lipid peroxidation is a common feature of many chemical and biological processes, and is governed by a complex kinetic scheme. A fundamental stage in kinetic investigations of lipid peroxidation is the accurate determination of the rate of peroxidation, which in many instances is heavily reliant on the method of finite differences. Such numerical approximations of the first derivative are commonly employed in commercially available software, despite suffering from considerable inaccuracy due to rounding and truncation errors. As a simple solution to this, we applied three empirical sigmoid functions (viz. the Prout-Tompkins, Richards & Gompertz functions) to data obtained from the AAPH-mediated peroxidation of aqueous linoleate liposomes in the presence of increasing concentrations of Trolox, evaluating the curve fitting parameters using the widely available Microsoft Excel Solver add-in. We have demonstrated that the five-parameter Richards' function provides an excellent model for this peroxidation, and when applied to the determination of fundamental rate constants, produces results in keeping with those available in the literature. Overall, we present a series of equations, derived from the Richards' function, which enables direct evaluation of the kinetic measures of peroxidation. This procedure has applicability not only to investigations of lipid peroxidation, but to any system exhibiting sigmoid kinetics.

Topics: Amidines; Chromans; Kinetics; Linoleic Acid; Lipid Peroxidation; Liposomes; Water

Cinnamoylphenethylamine (CNPA) derivatives including feruloylphenethylamine (FRPA), caffeoylphenethylamine (CFPA), cinnamoyltyramine (CNTA), feruloyltyramine (FRTA) and caffeoyltyramine (CFTA) were synthesized in order to investigate the influence of the number and position of hydroxyl group on Cu(2+)/glutathione (GSH) and 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH)-induced oxidation of DNA. The radical-scavenging properties of these CNPA derivatives were also evaluated by trapping 2,2'-azinobis(3-ethylbenzothiazoline-6-sulphonate) cationic radical (ABTS(+•)), 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH) and galvinoxyl radical. In addition, these CNPA derivatives were tested by linoleic acid (LH)-β-carotene-bleaching experiment. The chemical kinetic was employed to treat the results from AAPH-induced oxidation of DNA and gave the order of antioxidant ability as CFTA > CFPA > FRTA > FRPA. CFTA and CFPA also possessed high abilities to inhibit Cu²(+)/GSH-mediated degradation of DNA, whereas FRPA and FRTA can protect LH against the auto-oxidation efficiently. Finally, CFPA and FRPA exhibited high activity in trapping ABTS(+•), DPPH and galvinoxyl radicals. Therefore, the cinnamoyl group bearing ortho-dihydroxyl or hydroxyl with ortho-methoxyl benefited for CNPA derivatives to protect DNA, while hydroxyl in tyramine cannot enhance the radical-scavenging abilities of CNPA derivatives.

Topics: Amidines; Antioxidants; Benzhydryl Compounds; Benzothiazoles; beta Carotene; Biphenyl Compounds; Cinnamates; Copper; DNA; Free Radical Scavengers; Glutathione; Hydroxides; Linoleic Acid; Oxidation-Reduction; Phenethylamines; Picrates; Solutions; Structure-Activity Relationship; Sulfonic Acids

4-methyl-8-hydroxylpsoralen (MXan) and 4,9-dimethyl-8-hydroxylpsoralen (DMXan) were synthesized in order to clarify the effect of methyl on the antioxidant effectiveness of xanthotoxol (8-hydroxylpsoralen, Xan), which were assessed by bleaching beta-carotene in linoleic acid-Triton emulsion, by interacting with 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS+), 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH), and galvinoxyl radical, and by protecting DNA against the oxidation induced by Cu2+/glutathione (GSH) and 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH). Methyl attaching to xanthotoxol did not affect its ability to protect linoleic acid against autoxidation and to inhibit Cu2+/GSH-induced oxidation DNA, but decreased its ability to scavenge ABTS+ and DPPH, and to protect DNA against AAPH-induced oxidation. Therefore, methyl attenuated the antioxidant effectiveness of xanthotoxol in radical-induced oxidation of DNA.

Topics: Amidines; Copper; DNA; Free Radical Scavengers; Furocoumarins; Glutathione; Linoleic Acid; Methane; Oxidation-Reduction; Reactive Oxygen Species

Now it is recognized that DHA is oxidatively stable fatty acid compared with linoleic acid (LA) in emulsified system, although DHA is oxidatively unstable in a bulk system. In fact, an emulsified mixture of DHA and LA behaves as in a bulk system, namely the oxidative stability of DHA becomes lower than that of LA. Therefore, in this study, tridocosahexaenoate (DDD) and glycerol trilinoleate (LLL) were separately emulsified using TritonX-100 as an emulsifier and DDD emulsion was mixed with the oxidizing LLL emulsion using a water-soluble radical initiator, 2,2'-azobis(2-aminopropane) dihydrochloride. As a result, DHA suppressed the oxidation of LA, while DHA was not significantly oxidized. This suppression ability was examined using glycerol trieicosapentaenoate, glycerol trilinolenate, or glycerol trioleate instead of DDD and it was found that this activity was increased with the increasing number of double bonds in the structure. Furthermore, the same type of experiment was carried out using a lipid-soluble radical initiator, 2,2'-azobisisobutyronitrile and the similar result was obtained. These results indicated that a highly polyunsaturated fatty acid might act as an antioxidant in an emulsion system oxidized by an azo compound.

Topics: Amidines; Antioxidants; Docosahexaenoic Acids; Emulsions; Linoleic Acid; Octoxynol; Solubility; Triglycerides

In order to find new sources of natural antioxidants, the antioxidant potential of 70% methanolic extracts from the inflorescences and leaves of 16 species from the genus Sorbus s.s. was evaluated using two complementary in vitro test systems: the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical-scavenging assay and the AAPH [2,2¢-azobis-(2-amidinopropane)dihydrochloride]-induced linoleic acid (LA) peroxidation test. The radical-scavenging capacities of the extracts towards the DPPH radical were in the range of 0.25-0.86 millimolar Trolox® equivalents/g dry weight. They were significantly correlated (r=-0.8089, p<0.001) with the results of the LA-peroxidation test, indicating the Sorbus extracts to be universal antioxidants. Significant linear correlations were also found between the different antioxidant potentials and total phenolic contents as estimated by the Folin-Ciocalteu method and further verified by serial determinations of proanthocyanidins, chlorogenic acid isomers and flavonoids (çrêin the range of 0.71-0.95, p<0.001). Cluster analysis of the data matrix identified the ten samples (inflorescences of S. aucuparia, S. pohuashanensis, S. decora, S. koehneana, S. commixta, S. gracilis, and S. sitchensis, and the leaves of S. wilfordii, S. pogonopetala, and S. gracilis) exhibiting the highest antioxidant activity and total phenolic levels and therefore the greatest potential as effective sources for natural health products.

Topics: Amidines; Antioxidants; Linoleic Acid; Oxidation-Reduction; Plant Extracts; Plant Leaves; Sorbus; Species Specificity

Enhanced oxidative stress is implicated in the development of atherosclerosis in humans and animal models. F(2)-isoprostanes are formed in vivo via free radical peroxidation of arachidonic acid, and their quantification has allowed assessment of oxidative stress in vivo. F(2)-isoprostanes associate with lipids, although their distribution in human plasma lipoproteins is unknown. Our aim was to determine the distribution and levels of F(2)-isoprostanes in lipoproteins isolated from human plasma by ultracentrifugation and fast protein liquid chromatography (FPLC). F(2)-isoprostanes were significantly higher in HDL compared with LDL or VLDL after isolation by ultracentrifugation or FPLC. Furthermore, HDL3 particles contained elevated levels of F(2)-isoprostanes compared with HDL2. Platelet activating factor acetylhydrolase (PAF-AH), which hydrolyses esterified F(2)-isoprostanes from phospholipids, was predominantly associated with LDL. Reduced F(2)-isoprostanes in LDL may be related to higher PAF-AH activity in LDL. Paraoxonase 1 (PON-1) activity was associated with HDL2 and may be a contributing factor to the lower F(2)-isoprostanes in HDL2 compared with HDL3. Further studies are required to establish the implications of these findings on HDL function.

Topics: 1-Alkyl-2-acetylglycerophosphocholine Esterase; Amidines; Arachidonic Acid; Aryldialkylphosphatase; Atherosclerosis; Biological Transport, Active; Carrier Proteins; F2-Isoprostanes; Female; Humans; In Vitro Techniques; Linoleic Acid; Lipid Peroxides; Lipoproteins; Lipoproteins, HDL; Male; Oxidants

A polyacrylic acid (PAA)-protected platinum nanoparticle species (PAA-Pt) was prepared by alcohol reduction of hexachloroplatinate. The PAA-Pt nanoparticles were well dispersed and homogeneous in size with an average diameter of 2.0 +/- 0.4 nm (n = 200). We used electron spin resonance to quantify the residual peroxyl radical ([Formula: see text]) generated from 2,2-azobis (2-aminopropane) dihydrochloride (AAPH) by thermal decomposition in the presence of O(2) and a spectrophotometric method to quantify the residual 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. PAA-Pt scavenged these two radicals in a dose-dependent manner. Platinum was the functional component. PAA-Pt reduced the rate of oxygen consumption required for linoleic acid peroxidation initiated by [Formula: see text] generated from AAPH, indicating inhibition of the propagation of linolate peroxidation. A thiobarbituric acid test also revealed dose-dependent inhibition of the linolate peroxidation by PAA-Pt. Fifty micromolar platinum, as PAA-Pt, completely quenched 250 microM DPPH radical for 5 min. Even when twice diluted in half, the PAA-Pt still quenched 100% of the 250 microM DPPH radical. The scavenging activity of PAA-Pt is durable. These observations suggest that PAA-Pt is an efficient scavenger of free radicals.

Topics: Amidines; Biphenyl Compounds; Free Radical Scavengers; Linoleic Acid; Lipid Peroxidation; Metal Nanoparticles; Peroxides; Picrates; Platinum

The antioxidant activities of curcumin, its natural demethoxy derivatives (demethoxycurcumin, Dmc and bisdemethoxycurcumin, Bdmc) and metabolite hydrogenated derivatives (tetrahydrocurcumin, THC; hexahydrocurcumin, HHC; octahydrocurcumin; OHC) were comparatively studied using 2,2-diphenyl-1-picrylhydrazyl (DDPH) radical, 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) induced linoleic oxidation and AAPH induced red blood cell hemolysis assays. Hydrogenated derivatives of curcumin exhibited stronger DPPH scavenging activity compared to curcumin and a reference antioxidant, trolox. The scavenging activity significantly decreased in the order THC>HHC=OHC>trolox>curcumin>Dmc>>>Bdmc. Stronger antioxidant activities toward lipid peroxidation and red blood cell hemolysis were also demonstrated in the hydrogenated derivatives. By the model of AAPH induced linoleic oxidation, the stoichiometric number of peroxyl radical that can be trapped per molecule (n) of hydrogenated derivatives were 3.4, 3.8 and 3.1 for THC, HHC and OHC, respectively. The number (n) of curcumin and Dmc were 2.7 and 2.0, respectively, which are comparable to trolox, while it was 1.4 for Bdmc. The inhibition of AAPH induced red blood cell hemolysis significantly decreased in the order OHC>THC=HHC>trolox>curcumin=Dmc. Results in all models demonstrated the lower antioxidant activity of the demethoxy derivatives, suggesting the ortho-methoxyphenolic groups of curcumin are involved in antioxidant activities. On the other hand, hydrogenation at conjugated double bonds of the central seven carbon chain and beta diketone of curcumin to THC, HHC and OHC remarkably enhance antioxidant activity.

Topics: Amidines; Antioxidants; Biphenyl Compounds; Chromans; Curcumin; Diarylheptanoids; Erythrocyte Membrane; Free Radical Scavengers; Free Radicals; Hemolysis; Humans; Hydrogenation; In Vitro Techniques; Linoleic Acid; Lipid Peroxidation; Molecular Structure; Oxidants; Picrates; Structure-Activity Relationship; Time Factors

The enzymatic hydrolysates from pollen Cistus ladaniferus were digested and prepared using three kinds of enzymes (pepsin, trypsin, and papain) and the antioxidative properties were investigated. The yields, total phenolic contents, and protein contents of these hydrolysates were as follows: yields (about 21-45%), total phenolics (10.39-14.33 microg/mg sample powder), and proteins (129.62-137.35 microg/mg sample powder), respectively. The hydrolysates possessed strongly antioxidative and scavenging abilities against reactive oxygen species. The present studies revealed that hydrolysates from honeybee-collected pollen are of benefit not only to the materials of health food diets, but also to patients with various diseases such as cancer, cardiovascular diseases, and diabetes.

Topics: Amidines; Antioxidants; Biphenyl Compounds; Cistus; Electrophoresis, Polyacrylamide Gel; Hydrogen-Ion Concentration; Hydroxyl Radical; Indicators and Reagents; Linoleic Acid; Oxidants; Oxygen; Papain; Pepsin A; Phenol; Picrates; Pollen; Protein Hydrolysates; Reactive Oxygen Species; Superoxides; Time Factors; Trypsin

Instant coffees produced from the same green coffee beans were supplied from a company in different roasting degrees, light, medium, and dark. Melanoidins were obtained by ultrafiltration (10 kDa) and subsequent diafiltration. Pure melanoidins were isolated from melanoidins after overnight incubation in 2 M NaCl. The antioxidant activities of instant coffees, melanoidins, and pure melanoidins were tested using the conjugated diene formation from a 2,2'-azobis(2-amidinopropane) dihydrochloride-induced linoleic acid oxidation in an aqueous system. No significant differences were found between melanoidins and pure melanoidins with different roasting degrees. Therefore, the contribution of the pure melanoidin fraction to the total antioxidant activity of melanoidins was significantly lower. More than 50% of the antioxidant activity of melanoidins is due to low molecular weight compounds linked non-covalently to the melanoidin skeleton. A new concept of the overall antioxidant properties of food melanoidins is described, where chelating ability toward low molecular weight antioxidant compounds is connected to the stabilization of these compounds involved in the shelf life of the product.

Topics: Amidines; Antioxidants; Coffea; Coffee; Food Handling; Hot Temperature; Linoleic Acid; Polymers; Seeds; Solutions

Coelenterazine is a luciferin found in many marine bioluminescent organisms. This luciferin also possesses high antioxidant properties and an exceptional ability to protect cells exposed to oxidative stress. It has been suggested that coelenterazine's antioxidative mechanisms include the formation of an oxidation product, coelenteramine, also endowed with chain-breaking properties. In this work, coelenterazine analogs were shown to delay the onset of lipid peroxidation in a linoleate micellar solution exposed to free radical initiators. Their consumption was accompanied by the concomitant formation of coelenteramine. This was followed by a reduction in the peroxidation rate coinciding with the consumption of coelenterazine's oxidation product coelenteramine. The addition of coelenteramine to micelles reduced the propagation rate of the oxidative process. When coelenterazine analogs oxidizing into an inactive analog of coelenteramine were applied, the delaying effect but not the reduced peroxidation rate nor the consumption of the aminopyrazine was observed. These results demonstrate the role of the oxidation product coelenteramine in the chain-breaking properties of coelenterazine and analogs.

Topics: Amidines; Antioxidants; Free Radicals; Imidazoles; Linoleic Acid; Lipid Metabolism; Lipid Peroxidation; Micelles; Molecular Structure; Nitriles; Oxidation-Reduction; Pyrazines; Structure-Activity Relationship; Time Factors

The rate of accumulation of conjugated dienes of polyunsaturated fatty acids was measured during free-radical oxidation of linoleic acid (18:2n-6, LA), alpha-linolenic acid (18:3n-3, alpha-LNA), and gamma-linolenic acid (18:3n-6, gamma-LNA) initiated by 2,2;-azo-bis-(2-amidinopropane) hydrochloride in aqueous micellar solutions of sodium dodecyl sulfate and sodium cholate. It was shown that, unlike homogeneous solutions, the oxidative stability of PUFAs in aqueous dispersions increased with an increase in the extent of unsaturation. The rate of LA oxidation was more than tenfold greater than that of alpha- and gamma-LNA. The antioxidant activity of beta-carotene, in contrast to homogeneous solutions, in both micellar systems studied depended on the degree of PUFA unsaturation. We found that 5 micro M beta-carotene effectively inhibited the LA oxidation (almost by 90%), whereas the oxidation of alpha-LNA and gamma-LNA was not inhibited by beta-carotene even at much greater concentration (30 micro M). The paradoxical discrepancy between the extent of unsaturation and the PUFA oxidation rate, as well as a decrease in the efficiency of beta-carotene-dependent inhibition of oxidation of more polyunsaturated fatty acids in reactions conducted in aqueous dispersions is consistent with the model according to which the peroxyl radicals of LA and fatty acids with the double-bond number greater than two exhibit different polarity.

Topics: Amidines; Antioxidants; beta Carotene; Free Radicals; Kinetics; Linoleic Acid; Linolenic Acids; Micelles; Oxidation-Reduction; Sodium Cholate; Sodium Dodecyl Sulfate; Solutions; Water

Of three different solvents (acetone, ethanol, and methanol) mixed with water and acetic acid, the acetone/water/acetic acid mixture (70:28:2, v/v) proved to be best for extracting dark-chocolate procyanidins. High-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-MS-ESI) was further used to identify oligomers found in the extract. After HPLC fraction collection, the reduction power of flavanoid fractions was measured in the AAPH [2,2'-azobis(2-amidinopropane)dihydrochloride] assay, where oxidation of linoleic acid is induced in an aqueous dispersion. Even expressed in relative monomeric efficiency units, the oxidation-inhibiting power of polymerized oligomers is much stronger than that of monomers. A comparison with 10 usual antioxidants indicated that oligomers with three or more (epi)catechin units are by far the most efficient.

Topics: Acetic Acid; Acetone; Amidines; Antioxidants; Biflavonoids; Cacao; Catechin; Chromatography, High Pressure Liquid; Ethanol; Flavonols; Linoleic Acid; Methanol; Plant Extracts; Proanthocyanidins; Solvents; Spectrometry, Mass, Electrospray Ionization; Water

Identification of reliable biomarkers for oxidative stress for the prediction of the early development of pathological conditions is essential. The detection of biomarkers for oxidative stress such as degradation products of polyunsaturated fatty acid (PUFA), oxysterols, and oxidized proteins, as indicators of oxidative stress are in use, but suffers from insufficient specificity, accuracy and reliability. The overall aim of the present study was to develop new markers which will not only provide information about the presence and level of oxidative stress in biological systems but also on the type of reactive oxygen species (ROS) involved and their metabolic consequences. In the first stage of the study, we compared the level and type of oxidized products formed when different ROS were applied onto three major biomolecules, i.e. cholesterol, linoleic acid (LH) and tyrosine, representing sterols, PUFA and protein, when each compounds was exposed alone or in a mixture to the ROS [copper ions, 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH) and hypochlorous acid (HOCl)]. It was found that different types of oxidants resulted in the formation of different types of oxidation products. Furthermore, oxidation pattern differs when the substrates (cholesterol, PUFA or amino acid) were present alone or in a mixture. As biological systems such as lipoproteins and cell membranes are composed of the above studied molecules, the need for simultaneous detection of the major oxidized products is requires for better characterization of the oxidative stress outcome.

Topics: Amidines; Biomarkers; Cholesterol; Hypochlorous Acid; Linoleic Acid; Oxidants; Oxidation-Reduction; Reactive Oxygen Species; Tyrosine

Three tests of increasing complexity were used to assess the antioxidant activity of five synthetic gallic esters of sucrose bearing 3, 6, 7, or 8 galloyl units. In addition, two of these compounds had 1 or 2 hydrocarbon (C10-C12) acyl chains. Reaction with the DPPH radical led to the evaluation of the number of radicals trapped per galloyl unit n (3-4), as well as the apparent second-order rate constant for H atom donation k (1200-1500/M/s). These results indicated similar contribution and reactivity of all the galloyl units. Inhibition of the AAPH-initiated peroxidation of linoleic acid in a micellar medium confirmed the additive contribution of the galloyl units, whereas the presence of the hydrocarbon acyl chains had no influence. These results suggest an inhibition of initiation at high antioxidant levels and an underlying prooxidant effect of the galloyl radicals at low concentrations. Finally, LDL peroxidation was inhibited in proportion to the number of galloyl units, in agreement with the preceding tests.

Topics: Amidines; Biphenyl Compounds; Esters; Free Radical Scavengers; Free Radicals; Gallic Acid; Hydrolyzable Tannins; Linoleic Acid; Lipid Peroxidation; Lipoproteins, LDL; Oxidants; Picrates; Sucrose; Tannins

The antioxidant activity of caseins and casein-derived peptides was evaluated by using three free radical producing reactions-the lipoxygenase- and AAPH-catalyzed oxidation of linoleic acid and the hemoglobin-catalyzed oxidation of linoleic acid hydroperoxide. Caseins and casein-derived peptides were able to inhibit enzymatic and nonenzymatic lipid peroxidation, suggesting they were preferred targets for the free radical intermediates. The antioxidative feature was not lost with the dephosphorylation or the proteolysis of the proteins. The fractionation of the tryptic beta-casein digest yielded peptides with antioxidant activity. A structure-function relationship between the amino acid sequence and the antioxidant capacity and effectiveness is proposed. In addition, indirect evidence suggested that the trapping of free radicals by the proteins/peptides was accompanied by the oxidation of proteins/peptides, according to a sequence-specific mechanism.

Topics: Amidines; Amino Acid Sequence; Animals; Antioxidants; Caseins; Cattle; Glycine max; Hemoglobins; Hydrogen Peroxide; Iron Chelating Agents; Linoleic Acid; Lipoxygenase Inhibitors; Oxidation-Reduction; Peptide Fragments; Phosphorylation; Trypsin

The aim of this paper was to clarify whether the interaction of the lazaroid U-74389G with phospholipid membranes might be relevant as to its antioxidant activity. Thus we evaluated the "in vitro" antioxidant activity of U-74389G in two experimental models: 1) bleaching of the stable 1,1-diphenyl-2-picrylhydrazyl radical; 2) peroxidation, induced by the water-soluble radical initiator 2,2'-azobis(2-amidino-propane) hydrochloride, on mixed dipalmitoyl-phosphatidylcholine/linoleic acid unilamellar vesicles. Moreover, given that biophysical techniques may help in explaining the role of a drug in its interaction with the microenvironment of the model lipid membranes, we used a classical approach to investigate the U-74389G/model membrane interaction: the differential scanning calorimetry technique on dimyristoylphosphatidylcholine multilamellar and unilamellar vesicles and the Langmuir-Blodgett technique on dimyristoylphosphatidylcholine monolayers. The results evidenced the strong antioxidant activity of U-74389G (especially in a membranous system) and its capability to interact with and be transported across model membranes. Thus one can speculate that U-74389G can act as scavenger of chain-propagating lipid peroxyl radicals within the membranes and may be able to protect not only cell membranes, but also intracellular components against peroxidative attack. Furthermore, also if there is no certain proof that the effect on the lipid packing order may play a key role in its antioxidant activity, the fluidifying effect on phospholipid bilayers of U-74389G favourably complements its free radical scavenging characteristics.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Amidines; Antioxidants; Bepridil; Biphenyl Compounds; Calorimetry, Differential Scanning; Dexamethasone; Free Radical Scavengers; Free Radicals; In Vitro Techniques; Linoleic Acid; Lipid Bilayers; Lipid Peroxidation; Oxidation-Reduction; Picrates; Pregnatrienes

In a previous work [Chem. Phys. Lipids 2000 104, 49], we have derived the following rate law for the oxidation of lipids in compartmentalized systems: R(T)=(k(1)/k(t))(0.5) k(p) [In](0.5) c(0.5) [LH], where, R(T) is the total rate of oxidation, k(1) is the rate constant for the production of free radicals, k(t) and k(p) are the intra-particle rate constants for the termination and propagation sets, respectively, [In] is the concentration of a water-soluble initiator, c is the concentration of particles, and [LH] is the intra-particle concentration of oxidable lipid. In the present work, we have investigated on the applicability of the proposed kinetic rate law for a system where it takes place the oxidation of a reactive lipid incorporated into an inert matrix. With this purpose, we have measured the rate of oxidation of linoleic acid incorporated into dipalmitoylphosphatidylcholine vesicles initiated by the thermal decomposition of 2,2'-azobis(2-amidinopropane) dihydrochloride as a function of the initiator, particles, and intra-particle LH concentrations. The experimentally determined kinetic orders obtained were 0.54+/-0.02, 0.48+/-0.05 and 0.83+/-0.04 for the dependence of the oxidation rate with initiator, particles, and LH intra-particle concentrations, respectively, in agreement with those theoretically predicted. The lower value obtained for the kinetic order in LH is attributed to a change in k(t) with the increase in oxidable lipid intra-particle concentration. The main point to be emphazised from the results here obtained is that the kinetic rate law for the oxidation of lipids in compartmentalized systems can be significantly different than that observed when to the oxidation takes place in homogeneous solution.

Topics: 1,2-Dipalmitoylphosphatidylcholine; 2-Naphthylamine; Amidines; Fluorescent Dyes; Kinetics; Laurates; Linoleic Acid; Lipid Peroxidation; Liposomes; Models, Biological; Oxidants; Spectrometry, Fluorescence; Thermodynamics

The reactions of nitric oxide ((.)NO) and alpha-tocopherol (alpha-TH) during membrane lipid oxidation were examined and compared with the pair alpha-TH/ascorbate. Nitric oxide serves as a more potent inhibitor of lipid peroxidation propagation reactions than alpha-TH and protects alpha-TH from oxidation. Mass spectrometry, oxygen and (.)NO consumption, conjugated diene analyses, and alpha-TH fluorescence determinations all demonstrated that (.)NO preferentially reacts with lipid radical species, with alpha-TH consumption not occurring until (.)NO concentrations fell below a critical level. In addition, alpha-TH and (.)NO cooperatively inhibit lipid peroxidation, exhibiting greater antioxidant capacity than the pair alpha-TH/ascorbate. Pulse radiolysis analysis showed no direct reaction between (.)NO and alpha-tocopheroxyl radical (alpha-T(.)), inferring that peroxyl radical termination reactions are the principal lipid-protective mechanism mediated by (.)NO. These observations support the concept that (.)NO is a potent chain breaking antioxidant toward peroxidizing lipids, due to facile radical-radical termination reactions with lipid radical species, thus preventing alpha-TH loss. The reduction of alpha-T(.) by ascorbate was a comparatively less efficient mechanism for preserving alpha-TH than (.)NO-mediated termination of peroxyl radicals, due to slower reaction kinetics and limited transfer of reducing equivalents from the aqueous phase. Thus, the high lipid/water partition coefficient of (.)NO, its capacity to diffuse and concentrate in lipophilic milieu, and a potent reactivity toward lipid radical species reveal how (.)NO can play a critical role in regulating membrane and lipoprotein lipid oxidation reactions.

Topics: Amidines; Antioxidants; Ascorbic Acid; Free Radicals; Linoleic Acid; Lipid Peroxidation; Nitric Oxide; Oxidation-Reduction; Vitamin E

This paper presents a simple, convenient method for determining the efficiency of antioxidants in aqueous systems. Production of conjugated diene hydroperoxide by oxidation of linoleic acid in an aqueous dispersion is monitored at 234 nm. 2, 2'-Azobis(2-amidinopropane) dihydrochloride is used as a free radical initiator. Among 12 antioxidants tested, phenolic compounds proved to be the most efficient, both kinetically and in terms of the inhibition time (T(inh)). Applied to wort, malt, and hops, the method confirmed a significant antioxidant activity in such products, especially hops. This assay can be used to follow oxidative changes throughout the brewing process and to understand the contribution of each raw material.

Topics: Amidines; Antioxidants; Beer; Edible Grain; Linoleic Acid; Oxidants; Oxidation-Reduction; Water

(E)-Retinoic acid (RA) was shown to stimulate the rate of 2,2'-azobis(2-amidinopropane) (AAPH)-initiated autoxidation of linoleic acid (18:2) in sodium dodecyl sulfate (SDS) micelles. RA-dependent stimulation of 18:2 autoxidation was characterized by enhanced rates of dioxygen uptake which were linear with retinoid concentration. In contrast, 5,6-epoxy-RA, a major oxidation product of RA, failed to affect the rate of dioxygen consumption at all concentrations tested. RA was also shown to stimulate peroxyl radical-dependent oxidation of styrene to the corresponding oxirane when styrene was included in the micellar system as a molecular probe. Furthermore, unequivocal evidence of RA-dependent stimulation of 18:2 autoxidation was obtained by relative quantitation of 13-hydroxy-(9Z, 11E)-octadecadienoic acid (13-HODE) plus 9-hydroxy-(10E,12Z)-octadecadienoic acid (9-HODE) production. In addition, enhanced carbon-centered radical formation was demonstrated in the presence of RA by EPR spectroscopy using alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN) as a spin trap. Analysis and quantitation of RA oxidation products indicated that RA was oxidized to one primary product, 5,6-epoxy-RA, which was identified on the basis of cochromatography with synthetic standard (in a reverse-phase HPLC system), electronic absorption spectroscopy, and positive chemical ionization mass spectrometry of the corresponding methyl ester. Other minor oxidation products were also detected but not characterized. In contrast, reaction mixtures devoid of 18:2 failed to demonstrate significant retinoid oxidation. Mechanisms are proposed to account for the prooxidant effects of RA in this system.

Topics: Amidines; Humans; Linoleic Acid; Lipid Peroxidation; Micelles; Mutagens; Oxidation-Reduction; Sodium Dodecyl Sulfate; Spin Trapping; Tretinoin

Induced erythrocyte membrane peroxidation (EMP) is considered as an accurate model of reperfusion injuries and as such was used to investigate protective effects of various drugs. EMP was induced by an azo initiator and monitored by oxygen uptake. Both hydrophilic (ascorbic acid) and lipophilic (alpha-tocopherol, probucol, nicanartine) chain-breaking antioxidants as well as ferriheme-bound drugs (deferoxamine, chloroquine) inhibited EMP. When antioxidants and ferriheme-bound drugs were combined, synergistic effects were observed. It is proposed that ferriheme compounds which catalyse peroxide induced lipid peroxidation were blocked by deferoxamine and/or chloroquine. So these drugs inhibited at least partly the membrane peroxidation process and added their effects to the ones of chain-breaking antioxidants.

Topics: Adult; Amidines; Antioxidants; Ascorbic Acid; Chloroquine; Deferoxamine; Drug Synergism; Erythrocyte Membrane; Fatty Acids; Female; Hemin; Humans; Linoleic Acid; Lipid Peroxidation; Male; Membrane Lipids; Oxidation-Reduction; Oxygen Consumption; Oxyhemoglobins; Probucol; Pyridines; Reperfusion Injury; Vitamin E

Antioxidant or pro-oxidant properties of epinephrine (EPI) and isoprenaline (ISO) were studied in the absence and presence of Fe2+, Fe3+ and Cu2+ ions. EPI and ISO (>2 micromol/l) inhibited peroxidation of low density lipoprotein (LDL) induced by 2, 2'-azobis(2-amidino-propane) (AAPH). EPI had a similar inhibitory potency as ISO, but their potency was several times higher than the potency of alpha-tocopherol (alpha-TOC). When the LDL peroxidation was induced by 5 micromol/l CuSO4, EPI and ISO enhanced LDL peroxidation at low concentrations (10micromol/l) and decreased peroxidation at higher concentrations (30 micromol/l). The compounds had a similar tendency to inhibit the peroxidation of phosphatidylcholine liposomes. EPI (3-30 micromol/l) inhibited lipid peroxidation of phosphatidylcholine liposomes induced by 2 mmol/l of AAPH, but it was less effective and even increased the peroxidation, when the samples contained 2 mmol/l AAPH with 50 micromol/l FeSO4 or 2 mmol/l AAPH with 20 micromol/l FeCl3. Inhibition of lipid peroxidation by EPI was also observed when studying decreased oxygen consumption, when the peroxidation of linoleic acid was induced by lipoxidase. In conclusion, EPI and ISO reduced lipid peroxidation, but they exhibit pro-oxidant properties in the presence of Fe2+, Fe3+ or Cu2+ ions, depending on the catecholamine and ionic concentration.

Topics: Amidines; Antioxidants; Copper; Epinephrine; Free Radicals; Iron; Isoproterenol; Linoleic Acid; Lipid Peroxidation; Lipoproteins, LDL; Liposomes; Lipoxygenase; Oxidants; Oxygen; Phosphatidylcholines; Thiobarbituric Acid Reactive Substances; Vitamin E

Large unilamellar vesicles (LUVs) are generally accepted to be a suitable model for peroxidation studies. In the present report, dipalmitoylphosphatidylcholine (DPPC)/linoleic acid-mixed LUVs were employed as model membranes to verify the inhibitory effect of tocopherol (an efficient representative antioxidant) against 2,2'-azobis(2-amidinopropane)hydrochloride-induced peroxidation (evaluated by monitoring conjugated diene accumulation). In this model, the appropriate experimental conditions (particularly, liposome composition and peroxidation temperature) were selected following characterization of bilayer physical state, and not only by evaluation of peroxidation rate. Thus, the experiments described provide a routine screening procedure that would be appropriate for assessing the activity profile of novel free-radical scavengers.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Amidines; Antioxidants; Calorimetry, Differential Scanning; Free Radical Scavengers; Free Radicals; Linoleic Acid; Linoleic Acids; Lipid Bilayers; Lipid Peroxidation; Liposomes; Models, Chemical; Vitamin E

The aerobic oxidation kinetics of methyl eicosapentaenoate (20:5n-3) and methyl linoleate (18:2n-6) were compared in homogeneous chlorobenzene solution and in Triton X-100 aqueous micelles at 37 degrees C. The rate of disappearance of 20:5n-3 was two times faster than that of 18:2n-6 in chlorobenzene, while the former was five times slower than the latter in aqueous micelles. It was also observed that delta O2 = delta 18:2n-6 and delta O2 = 2 delta 20:5n-3 in aqueous micelles. In the oxidation of a 1:1 mixture of 20:5n-3 and 18:2n-6 in micelles, the rate of disappearance of 20:5n-3 was 3.6 times faster than that of 18:2n-6, and the rate of total substrate disappearance was reduced by a factor of 5 as compared with 18:2n-6 oxidation. These data suggest that the peroxyl radical derived from 20:5n-3 is more polar than that from 18:2n-6, and the former is likely to diffuse from the core to the micelle surface. This lowers the oxidizability for 20:5n-3 in aqueous micelles by enhancing the termination reaction rate for peroxyl radicals and by reducing the rate of propagation since there may be more 20:5n-3 peroxyl radicals at the surface than in the micelle core.

Topics: Amidines; Azo Compounds; Chlorobenzenes; Eicosapentaenoic Acid; Esters; Fatty Acids, Unsaturated; Kinetics; Linoleic Acid; Linoleic Acids; Micelles; Models, Chemical; Nitriles; Octoxynol; Oxidation-Reduction; Peroxides

Neopterin and its reduced form, 7,8 dihydroneopterin are pteridines released from macrophages and monocytes when stimulated with interferon gamma in vivo. The function of this response is unknown though there is an enormous amount of information available on the use of these compounds as clinical markers of monocyte/macrophage activation. We have found that in vitro 7,8-dihydroneopterin dramatically increases, in a dose dependent manner, the lag time of low density lipoprotein oxidation mediated by Cu++ ions or the peroxyl radical generator 2,2'-azobis (2-amidino propane) dihydrochloride (AAPH). 7,8-Dihydroneopterin also inhibits AAPH mediated oxidation of linoleate. The kinetic of the inhibition suggests that 7,8-dihydroneopterin is a potent chain breaking antioxidant which functions by scavenging lipid peroxyl radicals. No anti-oxidant activity was observed in any of the oxidation systems studied with the related compounds neopterin and pterin.

Topics: Adult; Amidines; Antioxidants; Biopterins; Copper; Dose-Response Relationship, Drug; Female; Humans; Linoleic Acid; Linoleic Acids; Lipoproteins, LDL; Macrophages; Male; Neopterin; Oxidation-Reduction; Pteridines; Pterins; Vitamin E

The formation of phospholipid hydroperoxides was monitored in human red blood cell (RBC) membranes that had been peroxidized with an azo initiator. Peroxidation of RBC membranes caused a profound decrease in the amount of polyunsaturated fatty acids and concomitantly hydroperoxides, as primary products of peroxidation, appeared in the phospholipids. Hydroperoxides were predominantly generated in choline glycerophospholipid (CGP), while the extent of formation of ethanolamine glycerophospholipid (EGP) hydroperoxides was low and their presence was transient. Hydroxy and hydroperoxy moieties in CGP were identified as 9-hydroxy and 13-hydroxy octadecanoic acid, derived from linoleic acid, by gas chromatography-mass spectrometric analysis. No consistent generation of hydroperoxide from arachidonic acid was evident in CGP. The CGP-hydroperoxide accounted for approximately 76% of linoleic acid consumed during peroxidation of RBC membranes. The prominent generation of phospholipid hydroperoxides was observed in the linoleic acid-rich membranes from rabbit RBC, indicating that the level of linoleic acid in phospholipids determines, in part, the extent of formation of phospholipid hydroperoxides. Aldehydic phospholipids, as secondary products of peroxidation, were detected in oxidized membranes. EGP was the most prominent aldehydic phospholipid, while negligible amounts of aldehydic CGP were formed. This study indicates that the process of oxidation of individual phospholipids clearly differs among phospholipids and depends on the structure of each.

Topics: Adult; Amidines; Chromatography, High Pressure Liquid; Erythrocyte Membrane; Fatty Acids, Unsaturated; Humans; Hydrogen Peroxide; Linoleic Acid; Linoleic Acids; Linoleic Acids, Conjugated; Lipid Peroxidation; Phosphatidylcholines; Phosphatidylethanolamines

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.

Topics: Amidines; Antioxidants; Azo Compounds; Chromans; Chromatography, High Pressure Liquid; Free Radical Scavengers; Free Radicals; Kinetics; Linoleic Acid; Linoleic Acids; Lipid Peroxidation; Liposomes; Mass Spectrometry; Nitriles; Phosphatidylcholines; Piperazines; Pregnatrienes

The activities of six phenylpropanoid glycosides as chain-breaking antioxidants have been studied for the autoxidation of linoleic acid in cetyl trimethylammonium bromide (CTAB) micelles at 37 degrees C. Verbascoside, isoverbascoside, echinacoside and pedicularioside A, which possess four phenolic hydroxyl groups, exhibited antioxidant activities, while cistanoside D possessing only two phenolic hydroxyl groups and permethyl verbascoside without phenolic hydroxyl group did not suppress the oxidation appreciably. The ratio of rate constants for inhibition and propagation kinh/kp and stoichiometric factor n were determined.

Topics: Amidines; Cetrimonium; Cetrimonium Compounds; Glucosides; Glycosides; Iridoid Glucosides; Iridoids; Kinetics; Linoleic Acid; Linoleic Acids; Lipid Peroxidation; Micelles; Oxidation-Reduction; Oxygen Consumption; Phenols; Plant Extracts; Plants, Medicinal

The role of oxygen derived free radicals or tissue lipid peroxides in the pathogenesis of chronic pancreatitis has not been established. To evaluate long-term effects of tissue lipid peroxides in the pathogenesis of chronic pancreatitis, we treated Wistar male rats with 2,2'-azo-bis-(2-amidino-propane) dihydrochloride (AAPH) and/or linoleic acid (LA) for 3 or 6 months. Rats were divided into eight groups. A: Saline-treated rats for 3 months as control, B: AAPH 40 mg/kgw intraperitoneally, twice a week for 3 months, C: LA 0.5 ml/kgw intraperitoneally, every other week for 3 months, D: AAPH and LA for 3 months, E: Saline-treated for 6 months, F: AAPH for 6 months, G: LA for 6 months, H: AAPH and LA for 6 months. The results were as follows: Lipid peroxide contents of the pancreas were elevated in groups: C, D, G and H. Histological examination revealed epithelial hyperplasia of large pancreatic ducts, vacuolization of ductal epithelium, intraepithelial neutrophilic infiltration, periductal mononuclear cell infiltration (ductulitis and peri-ductulitis), and sporadically in the lobules, destruction of acinar cells, neutrophilic infiltration and ductular proliferation in the same groups. These findings indicate that tissue damage was more severe in the pancreatic ducts than in the acinar cells, however no damage was seen in the endocrine pancreas. Vitamin E content of the pancreas was decreased in groups: B, C, D, F, G and H. Tissue glutathione peroxidase (GSH-Px) activity was increased in groups: D and H. Tissue catalase activity was increased in groups: D, G and H, but no change of superoxide dismutase (SOD) activity was seen in any of the groups. These results indicate that vitamin E may play the role of the main scavenger in the situation of a smaller dose of lipid peroxides, but when larger doses are administered, GSH-Px may play the main role as the scavenger in this experimental system.

Topics: Amidines; Animals; Chronic Disease; Free Radical Scavengers; Free Radicals; Glutathione Peroxidase; Linoleic Acid; Linoleic Acids; Lipid Peroxides; Male; Pancreas; Pancreatitis; Rats; Rats, Wistar