Kinetics of the lipoperoxyl radical-scavenging activity of indicaxanthin in solution and unilamellar liposomes

The reaction of the phytochemical indicaxanthin with lipoperoxyl radicals generated in methyl linoleate methanol solution by 2,2'-azobis(2,4-dimethylvaleronitrile), and in aqueous soybean phosphatidylcholine unilamellar liposomes by 2,2'-azobis(2-amidinopropane)hydrochloride, was studied. The molecule acts as a chain-terminating lipoperoxyl radical scavenger in solution, with a calculated inhibition constant of 3.63 x 10(5) M(-1) s(-1), and a stoichiometric factor approaching 2. Indicaxanthin incorporated in liposomes prevented lipid oxidation, inducing clear-cut lag periods and decrease of the propagation rate. Both effects were concentration-dependent, but not linearly related to the phytochemical concentration. The consumption of indicaxanthin during liposome oxidation was remarkably delayed, the lower the concentration the longer the time-interval during which it remained in its native state. Indicaxanthin and alpha-tocopherol, simultaneously incorporated in liposomes, exhibited cooperative antioxidant effects and reciprocal protective interactions. The extent of synergism decreased at the increase of the ratio (indicaxanthin)/(alpha-tocopherol). A potential antioxidant mechanism of indicaxanthin is discussed in the context of the chemistry of the molecule, and of the possible reactivity of a short-lived intermediate.     

Cytoprotective effects of the antioxidant phytochemical indicaxanthin in β-thalassemia red blood cells

Antioxidant phytochemicals are investigated as novel treatments for supportive therapy in β-thalassemia. The dietary indicaxanthin was assessed for its protective effects on human β-thalassemic RBCs submitted in vitro to oxidative haemolysis by cumene hydroperoxide. Indicaxanthin at 1.0–10 μM enhanced the resistance to haemolysis dose-dependently. In addition, it prevented lipid and haemoglobin (Hb) oxidation, and retarded vitamin E and GSH depletion. After ex vivo spiking of blood from thalassemia patients with indicaxanthin, the phytochemical was recovered in the soluble cell compartment of the RBCs. A spectrophotometric study showed that indicaxanthin can reduce perferryl-Hb generated in solution from met-Hb and hydrogen peroxide (H₂O₂), more effectively than either Trolox or vitamin C.

Collectively our results demonstrate that indicaxanthin can be incorporated into the redox machinery of β-thalassemic RBC and defend the cell from oxidation, possibly interfering with perferryl-Hb, a reactive intermediate in the hydroperoxide-dependent Hb degradation. Opportunities of therapeutic interest for β-thalassemia may be considered.     

Cytoprotective effects of the antioxidant phytochemical indicaxanthin in beta-thalassemia red blood cells

Antioxidant phytochemicals are investigated as novel treatments for supportive therapy in β-thalassemia. The dietary indicaxanthin was assessed for its protective effects on human β-thalassemic RBCs submitted in vitro to oxidative haemolysis by cumene hydroperoxide. Indicaxanthin at 1.0-10 μM enhanced the resistance to haemolysis dose-dependently. In addition, it prevented lipid and haemoglobin (Hb) oxidation, and retarded vitamin E and GSH depletion. After ex vivo spiking of blood from thalassemia patients with indicaxanthin, the phytochemical was recovered in the soluble cell compartment of the RBCs. A spectrophotometric study showed that indicaxanthin can reduce perferryl-Hb generated in solution from met-Hb and hydrogen peroxide (H₂O₂), more effectively than either Trolox or vitamin C.

Collectively our results demonstrate that indicaxanthin can be incorporated into the redox machinery of β-thalassemic RBC and defend the cell from oxidation, possibly interfering with perferryl-Hb, a reactive intermediate in the hydroperoxide-dependent Hb degradation. Opportunities of therapeutic interest for β-thalassemia may be considered.     

Dendritic antioxidants with pyrazole as the core: ability to scavenge radicals and to protect DNA

Chalcones with or without a para-hydroxyl group were condensed with phenylhydrazine-related compounds to form 1,3,5-triphenyl-1H-pyrazole (TPP), 4-(1,5-diphenyl-1H-pyrazol-3-yl)phenol (APP), 4-(1,3-diphenyl-1H-pyrazol-5-yl)phenol (BPP), and 4-(3,5-diphenyl-1H-pyrazol-1-yl)phenol (CPP), in which the phenyl group formed a dendritic structure with pyrazole as the core. Thus, the aim of this work was to explore the antioxidant capacities of TPP, APP, BPP, and CPP in trapping 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS^+?) and 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH) and in inhibiting Cu^2 +/glutathione (GSH)-, ^?OH-, and 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH)-induced oxidation of DNA. TPP can react with ABTS^+? and DPPH, indicating that the N atom in pyrazole possesses radical-scavenging ability. Moreover, APP, BPP, and CPP can trap 1.71, 1.81, and 1.58 radicals, respectively, in protecting DNA against AAPH-induced oxidation. Thus, the combination of pyrazole with a phenyl group exerted antioxidant ability although only one phenolic hydroxyl group was involved. However, these compounds showed weak protective effect against Cu^2 +/GSH-induced oxidation of DNA and even a pro-oxidant effect on ^?OH-induced oxidation of DNA.     

Betacyanins as phenol antioxidants. Chemistry and mechanistic aspects of the lipoperoxyl radical-scavenging activity in solution and liposomes

Reaction kinetics of betanin and its aglycone betanidin towards peroxyl radicals generated from the azo-initiated oxidation of methyl linoleate in methanol and of a heterogeneous aqueous/soybean phosphatidylcholine liposomal system were studied by monitoring formation of linoleic acid hydroperoxides and consumption of the pigments. Betanin was a weak retarder in methanol and an effective chain breaking antioxidant in the liposomal model, indicating that kinetic solvent effects and partition in lipid bilayers may affect its activity. Betanidin behaved as a chain terminating antioxidant in both models. Kinetic parameters characterizing peroxyl radical-scavenging activity showed that betanidin was more effective than betanin, in terms of both radical-scavenging rate constant and stoichiometric factor, with effectiveness of the same order as vitamin E under comparable conditions. Products identified by spectrophotometric and HPLC techniques indicated reaction of the glucose-substituted monophenol and ortho-diphenol moieties of betanin and betanidin, respectively, and suggested mechanisms of the antioxidant activity. Either betanin or betanidin incorporated in liposomes with α-tocopherol had additive effects, supporting partition of the pigments in the bilayer and lipoperoxyl radical reduction.     

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

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

Increased Resistance to Oxidation of Betalain-enriched Human Low Density Lipoproteins

Betalains are natural pigments recently considered as compounds with potential antioxidative properties. In this work, ex vivo plasma spiking of pure either betanin or indicaxanthin, followed by isolation of low density lipoprotein (LDL), and measurement of its resistance to copper-induced oxidation, has been used to research if these betalains can bind to LDL and prevent oxidation of LDL lipids. When pooled human plasma from 10 healthy volunteers was incubated in the presence of 25–100?μM either betanin or indicaxanthin, incorporation of both compounds in LDL was observed, with a maximum binding of 0.52±0.08, and 0.51±0.06?nmoles of indicaxanthin and betanin, respectively, per mg LDL protein. Indicaxanthin-enriched and betanin-enriched LDL were more resistant than homologous native LDL to copper-induced oxidation, as assessed by the elongation of the induction period. The incorporated indicaxanthin, however, appeared twice as effective as betanin in increasing the length of the lag phase, while both compounds did not affect the propagation rate. Both betalains were consumed during the inhibition period of lipid oxidation, and delayed consumption of LDL-beta carotene. Indicaxanthin, but not betanin, prevented vitamin E consumption at the beginning of LDL oxidation, and prolonged the time of its utilization. The resistance of LDL to oxidation when vitamin E and indicaxanthin acted separately in a sequence, was lower than that measured when they were allowed to act in combination, indicating some synergistic interaction between the two molecules. No prooxidant effect over a large concentration range of either betanin or indicaxanthin was observed, when either betalain was added to the LDL system undergoing a copper-induced oxidation.

These results show than indicaxanthin and betanin may bind to LDL, and are highly effective in preventing copper-induced lipid oxidation. Interaction with vitamin E appears to add a remarkable potential to indicaxanthin in the protection of LDL. Although molecular mechanisms remain uncompletely understood, various aspects of the action of betanin and indicaxanthin in preventing LDL lipid oxidation are discussed.     

Antiodidant activity of thiosulfinates derived from garlic

Abstract

Garlic extract significantly inhibited the oxidation of methyl linoleate in homogeneous acetonitrile solution, whereas the antioxidant effect of allicin-free garlic extract, prepared by removing allicin by prepared by removing allicin by preparative HPLC, was much lower than that of the garlic extract. These results suggest that the antioxidant properties are mostly attributed to the presence of allicin in the garlic extract. Allicin a major component of the thiosulfinates in garlic extract, was found to be effective for inhibiting methyl linoleate oxidation, but its efficiency was less than that of α-tocopherol. Next, the reactivity of allicin toward the peroxyl radical, which is a chain-propagating species, was investigated by direct ESR detection. The addition allicin to 2,2′-azobis(2,4-dimethylvaleronitrile)-peroxyl radical solution caused the signal intensity of the peroxyl radical to dose-dependently decrease, indicating that allicin is capable of scavenging the the peroxyl radical and acting as an antioxidant. Finally, we studied the structure–anioxidant activity relationship for thiosulfinates and suggested that the combination of the allyl group (–CH₂CH=CH₂) and the –S(O)S– group is necessary for the antioxidant action of thiosulfinates in the garlic extract. In addition, one of the two possible combinations, –S(O)S–CH₂CH=CH₂, was found to make a much larger contribution to the antioxidant activity of the thiosulfinates than the other, CH₂=CH–CH₂–S(O)S–.     

Spin-labelled lutein as a new antioxidant in protection against lipid peroxidation

A new potentially antioxidant compound, spin-labelled lutein (SL-lut), was synthesized and incorporated into egg yolk phosphatidylcholine (EYPC) liposome membrane. The approximate location of nitroxide free radical groups of SL-lut was determined based on electron paramagnetic resonance (EPR) spectra. Then the ability of SL-lut to protect EYPC liposomes against lipid peroxidation (LPO) was compared to the antioxidant effects of lutein and a nitroxide spin label 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy (3-CP). Two free radical generation systems were used—a thermal decomposition of 2,2′-azobis (2,4 dimethyl-valeronitrile) (AMVN) and a modified Fenton reaction using ferric-8-hydroxyquinoline (Fe(HQ)₃). Determination of the amount of thiobarbituric acid reactive species (TBARS) was used as a measure of LPO. SL-lut was the most powerful antioxidant, reducing LPO by about 6-times in AMVN-treated liposomes and 7-times in Fe(HQ)₃-treated liposomes. Lutein alone gave only a moderate protection in both systems, while 3-CP was as efficient as SL-lut in the presence of AMVN, but not efficient whatsoever in the presence of Fe(HQ)₃. The results suggest that a nitroxide part of SL-lut plays an important role in enhancing the antioxidant activity of lutein and makes SL-lut a powerful antioxidant efficient under different conditions.     

The antioxidant action of 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-α]pyrazin-3-one (MCLA), a chemiluminescence probe to detect superoxide anions

The antioxidant effect of 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-α]pyrazin-3-one (MCLA), a Cypridina luciferin analog that acts as a chemiluminescence probe to detect O^⋅−₂, was investigated. MCLA produced a lag in oxygen consumption induced by cumene hydroperoxide in microsomes or by 2,2′-azobis (2-amidinopropane) dihydrochloride in liposomes and disappeared during the duration of the lag. MCLA profoundly inhibited the propagation reaction in Fe²⁺-dependent lipid peroxidation in liposomes, and MCLA disappearance accompanied by suppression of oxygen consumption markedly occurred in liposomes susceptible to peroxidation. Thiobarbituric acid-reactive substances in all systems used were also suppressed by MCLA dose dependently. These results indicate that MCLA has an antioxidant property through scavenging free radicals.     

The influence of carotenoids on the oxidative stability and phase behaviour of plant polar lipids

Carotenoids and total neutral lipids from thylakoids of Nerium oleander were evaluated as antioxidants in liposomes prepared from soybean polar lipids. The extent of lipid oxidation was assessed from the formation of malondialdehyde and conjugated dienes after exposure of the liposomes to free radicals generated by ⁶⁰Co gamma radiolysis. The carotenoids incorporated into the bilayers were isolated from clones of oleander grown at 20° or 45°, growth conditions which are known to result in a difference in the thermal properties of the membrane lipids. The effect of carotenoids on the temperature of the phase transition of thylakoid polar lipids was also examined. The results showed that, in comparison with the effectiveness of a reference antioxidant, α-tocopherol, the carotenoids and total neutral lipids from thylakoids of oleander did not protect the soybean polar lipids from oxidation, nor did they influence the temperature of the phase transition of thylakoid polar lipids.     

Increased resistance to oxidation of betalain-enriched human low density lipoproteins

Betalains are natural pigments recently considered as compounds with potential antioxidative properties. In this work, ex vivo plasma spiking of pure either betanin or indicaxanthin, followed by isolation of low density lipoprotein (LDL), and measurement of its resistance to copper-induced oxidation, has been used to research if these betalains can bind to LDL and prevent oxidation of LDL lipids. When pooled human plasma from 10 healthy volunteers was incubated in the presence of 25-100 μM either betanin or indicaxanthin, incorporation of both compounds in LDL was observed, with a maximum binding of 0.52±0.08, and 0.51±0.06 nmoles of indicaxanthin and betanin, respectively, per mg LDL protein. Indicaxanthin-enriched and betanin-enriched LDL were more resistant than homologous native LDL to copper-induced oxidation, as assessed by the elongation of the induction period. The incorporated indicaxanthin, however, appeared twice as effective as betanin in increasing the length of the lag phase, while both compounds did not affect the propagation rate. Both betalains were consumed during the inhibition period of lipid oxidation, and delayed consumption of LDL-beta carotene. Indicaxanthin, but not betanin, prevented vitamin E consumption at the beginning of LDL oxidation, and prolonged the time of its utilization. The resistance of LDL to oxidation when vitamin E and indicaxanthin acted separately in a sequence, was lower than that measured when they were allowed to act in combination, indicating some synergistic interaction between the two molecules. No prooxidant effect over a large concentration range of either betanin or indicaxanthin was observed, when either betalain was added to the LDL system undergoing a copper-induced oxidation.

These results show than indicaxanthin and betanin may bind to LDL, and are highly effective in preventing copper-induced lipid oxidation. Interaction with vitamin E appears to add a remarkable potential to indicaxanthin in the protection of LDL. Although molecular mechanisms remain uncompletely understood, various aspects of the action of betanin and indicaxanthin in preventing LDL lipid oxidation are discussed.     

Resveratrol inhibition of lipid peroxidation

To define the molecular mechanism(s) of resveratrol inhibition of lipid peroxidation we have utilized model systems that allow us to study the different reactions involved in this complex process. Resveratrol proved (a) to inhibit more efficiently than either Trolox or ascorbate the Fe²⁺ catalyzed lipid hydroperoxide-dependent peroxidation of sonicated phosphatidylcholine liposomes; (b) to be less effective than Trolox in inhibiting lipid peroxidation initiated by the water soluble AAPH peroxyl radicals; (c) when exogenously added to liposomes, to be more potent than α-tocopherol and Trolox, in the inhibition of peroxidation initiated by the lipid soluble AMVN peroxyl radicals; (d) when incorporated within liposomes, to be a less potent chain-breaking antioxidant than α-tocopherol; (e) to be a weaker antiradical than α-tocopherol in the reduction of the stable radical DPPH^·. Resveratrol reduced Fe³⁺ but its reduction rate was much slower than that observed in the presence of either ascorbate or Trolox. However, at the concentration inhibiting iron catalyzed lipid peroxidation, resveratrol did not significantly reduce Fe³⁺, contrary to ascorbate. In their complex, our data indicate that resveratrol inhibits lipid peroxidation mainly by scavenging lipid peroxyl radicals within the membrane, like α-tocopherol. Although it is less effective, its capacity of spontaneously entering the lipid environment confers on it great antioxidant potential.     

Generation of Probucol Radicals and Their Reduction by Ascorbate and Dihydrolipoic Acid in Human Low Density Lipoproteins

Probucol, 4.4′-[(1-methylethylidene)bis(thio)]bis-[2,6-bis(1.1-dimethyl)phenol], is a lipid regulating drug whose therapeutic potential depends on its antioxidant properties. Probucol and x-tocopherol were quantitatively compared in their ability to scavenge peroxyl radicals generatcd by the thermal decomposition of the lipid-soluble azo-initiator 2,2′-azo-bis(2,4-dimethyl-valeronitrile), AMVN, in dioleoylphos-phatidylcholine (DOPC) liposomes. Probucol showed 15-times lower peroxyl radical scavenging efficiency than x-tocopherol as measured by the effects on AMVN-induced luminol-dependent chemiluminescence. We suggest that probucol cannot protect x-tocopherol against its loss in the course of oxidation, although probucol is known to prevent lipid peroxidation in membranes and lipoproteins. In human low density lipoproteins (LDL) ESR signals of the probucol phenoxyl radical were detected upon incubation with lipoxygenase + linolenic acid or AMVN. Ascorbate was shown to reduce probucol radicals. Dihydro-lipoic acid alone was not able to reduce the probucol radical but in the presence of both ascorbate and dihydrolipoic acid a synergistic effect of a stepwise reduction was observed. This resulted from ascorbate-dependent reduction of probucol radicals and dihydrolipoic acid-dependent reduction of ascorbyl radicals. The oxidized form of dihydrolipoic acid, thioctic acid, did not affect probucol radicals either in the presence or in the absence of ascorbate.     

Protein Hydroperoxides are a Major Product of Low Density Lipoprotein Oxidation During Copper,Peroxyl Radical and Macrophage-mediated Oxidation

Damage to apoB100 on low density lipoprotein (LDL) has usually been described in terms of lipid aldehyde derivatisation or fragmentation. Using a modified FOX assay, protein hydroperoxides were found to form at relatively high concentrations on apoB100 during copper, 2,2′-azobis(amidinopropane) dihydrochloride (AAPH) generated peroxyl radical and cell-mediated LDL oxidation. Protein hydroperoxide formation was tightly coupled to lipid oxidation during both copper and AAPH-mediated oxidation. The protein hydroperoxide formation was inhibited by lipid soluble α-tocopherol and the water soluble antioxidant, 7,8-dihydroneopterin. Kinetic analysis of the inhibition strongly suggests protein hydroperoxides are formed by a lipid-derived radical generated in the lipid phase of the LDL particle during both copper and AAPH mediated oxidation. Macrophage-like THP-1 cells were found to generate significant protein hydroperoxides during cell-mediated LDL oxidation, suggesting protein hydroperoxides may form in vivo within atherosclerotic plaques. In contrast to protein hydroperoxide formation, the oxidation of tyrosine to protein bound 3,4-dihydroxyphenylalanine (PB-DOPA) or dityrosine was found to be a relatively minor reaction. Dityrosine formation was only observed on LDL in the presence of both copper and hydrogen peroxide. The PB-DOPA formation appeared to be independent of lipid peroxidation during copper oxidation but tightly associated during AAPH-mediated LDL oxidation.     

Isoorientin-6″-O-glucoside,a water-soluble antioxidant isolated from Gentiana arisanensis

The antioxidant activities of isoorientin-6″-O-glucoside were studied using various models. Isoorientin-6″-O-glucoside was more potent than Trolox, probucol and butylated hydroxytoluene (BHT) in reducing the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). It also scavenged superoxide anion, peroxyl and hydroxyl radicals that were generated by xanthine/xanthine oxidase, 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) and Fe³⁺–ascorbate–EDTA–H₂O₂ system, respectively. The IC₅₀ value, stoichiometry factor and second-order rate constant were 9.0 ± 0.8 μM, 1.8 ± 0.1 and 2.6 × 10¹⁰ M⁻¹ s⁻¹ for superoxide generation, peroxyl and hydroxyl radicals. However, isoorientin-6″-O-glucoside did not inhibit xanthine oxidase activity or scavenge hydrogen peroxide (H₂O₂), carbon radical or 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN)-derived peroxyl radical in hexane. Isoorientin-6″-O-glucoside inhibited Cu²⁺-induced oxidation of human low-density lipoprotein (LDL) as measured by fluorescence intensity, thiobarbituric acid-reactive substance formation and electrophoretic mobility. Since isoorientin-6″-O-glucoside did not possess pro-oxidant activity, it may be an effective water-soluble antioxidant that can prevent LDL against oxidation.     

Antioxidant activity of palm oil carotenes in peroxyl radical-mediatedperoxidation of phosphatidyl choline liposomes

Abstract

The antioxidant efficacy of α-carotene and comparison with β-carotene in multilamellar liposomes prepared from egg yolk phosphatidyl choline (EYPC) exposed to the lipid soluble 2,2′-azobis (2,4-dimethyl valeronitrile) (AMVN) was investigated. Lipid peroxidation was measured as thiobarbituric acid reacting substances (TBARS)at 532 nm or as hydroperoxide formation at 234 nm after separation of phosphatidyl choline hydroperoxide (PCOOH) by high-pressure liquid chromatography (HPLC). Lutein and zeaxanthin, the hydroxyl derivatives of α- and β-carotenes, and the chain breaking antioxidant α-tocopherol were also included in the study.AMVN being a lipid soluble, non polar azo initiator penetrates into the hydrophobic interior of the phospholipid bilayer, forming peroxyl radicals which peroxidate the phospholipid leading to PCOOH accumulation. All the carotenoids tested at 1 mol% relative to EYPC significantly suppressed the formation of PCOOH compared to control samples.In this system, α-carotene retarded PCOOH formation better than β-carotene. Similarly, lutein was a better antioxidant than is zeaxanthin. But lutein and zeaxanthin were more effective antioxidants than α- and β-carotenes, respectively. After 1 h of incubation of the carotenoid with AMVN, α-, β-carotene, lutein and zeaxanthin limited PCOOH formation by 77%, 68%, 85%and 82%, respectively, while α-tocopherol elicited 90%reduction.AMVN incubated with EYPC for 2 h induced the formation of TBARS compared to control (P <0.001). α-Carotene significantly suppressed the TBARS formation by 78% whilst β-carotene, lutein, zeaxanthin and α-tocopherol elicited 60%, 91%and 80% reductions, respectively. Increasing the concentration of the carotenoid >1 mol% to EYPC did not significantly increase protection of the membrane against free radical attack.Our findings suggest that α-carotene is a better antioxidant than is β-carotene in phosphatidyl choline vesicles. It may, therefore, be useful in limiting free radical mediated peroxidative damage against membrane phospholipids _{in vivo}.     

Betanin inhibits the myeloperoxidase/nitrite-induced oxidation of human low-density lipoproteins

Production of nitrogen dioxide by the activity of myeloperoxidase (MPO) in the presence of nitrite is now considered a key step in the pathophysiology of low-density lipoprotein (LDL) oxidation. This study shows that betanin, a phytochemical of the betalain class, inhibits the production of lipid hydroperoxides in human LDL submitted to a MPO/nitrite-induced oxidation. Kinetic measurements including time-course of particle oxidation and betanin consumption, either in the presence or in the absence of nitrite, suggest that the antioxidant effect is possibly the result of various actions. Betanin scavenges the initiator radical nitrogen dioxide and can also act as a lipoperoxyl radical-scavenger. In addition, unidentified oxidation product(s) of betanin by MPO/nitrite inhibit(s) the MPO/nitrite-induced LDL oxidation as effectively as the parent compound. In the light of betanin bioavailability and post-absorbtion distribution in humans, present findings may suggest favourable in vivo activity of this phytochemical.     

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

The events accompanying the inhibitory effect of α-tocopherol and/or ascorbate on the peroxidation of soybean L-α-phosphatidylcholine liposomes, which are an accepted model of biological membranes, were investigated by electron paramagnetic resonance, optical and polarograpic methods. The presence of α-tocopherol radical in the concentration range 10^?8–10^?7 M was detected from its EPR spectrum during the peroxidation of liposomes, catalysed by the Fe³⁺-triethylnetatramine complex. The α-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 α-tocopherol itself. A kinetic rate constant of about 2·10⁵ M^?·s^?1 was estimated from the reaction as it occurs under the adopted experimental conditions. The scavenging effect of α-tocopherol on lipid peroxidation is maintained as long a ascorbic acid is present.     

Synthesis and antioxidant activity of novel Mannich base of 1,3,4-oxadiazole derivatives possessing 1,4-benzodioxan

A new series of Mannich base of 1,3,4-oxadiazole derivatives possessing 1,4-benzodioxan (6a–6ae) were synthesized and characterized by ¹H NMR, ESI-MS and elemental analysis. The structure of 6b was further confirmed by single crystal X-ray diffraction. All these novel compounds were screened for their in vitro antioxidant activity employing 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH), 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS⁺) and ferric reducing antioxidant power (FRAP) scavenging assays. Due to the combination of 1,4-benzodioxan, 1,3,4-oxadiazoles and substituted phenyl ring, most of them exhibited nice antioxidant activities. In all of these three assays mentioned above, compounds 6f and 6e showed significant radical scavenging ability comparable to the commonly used antioxidants, BHT and Trolox. Seven compounds with representative substituents or activities were selected for further assays in chemical simulation biological systems—inhibition of microsomal lipid peroxidation (LPO) and protection against 2,2′-azobis (2-amidinopropane hydrochloride) (AAPH) induced DNA strand breakage, in which, 6f and 6e were demonstrated to be of the most potent antioxidant activities.