Chain-breaking Antioxidant Activity Research Articles

Oxidative stress in rat brain during experimental status epilepticus: effect of antioxidants.

Antioxidants have been proposed as a treatment for diseases of the central nervous system. However, few studies actually studied their effects in the brain. To test central actions of antioxidants, we used the lithium-pilocarpine (Li-Pilo) model of status epilepticus (SE) in the rat in which seizures are accompanied by significant oxidative stress. We used in vivo microdialysis to determine isoprostane levels during SE in real time and brain homogenates for other measures of oxidative stress. Six different antioxidants were tested in acute and preventive experiments (vitamin C, vitamin E, ebselen, resveratrol, n-tert-butyl-α-phenylnitrone and coenzyme Q10). None of the antioxidants had an effect when given acutely during SE. In contrast, when antioxidants were given for 3days prior to seizure induction, vitamins C and E reduced isoprostane formation by 58% and 65%, respectively. Pretreatment with the other antioxidants was ineffective. In brain homogenates prepared after 90min of seizures, SE decreased the ratio of reduced vs. oxidized glutathione (GSH/GSSG ratio) from 60.8 to 7.50 and caused a twofold increase of 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels and protein carbonyls. Pretreatment with vitamin C or vitamin E mitigated these effects and increased the GSH/GSSG ratio to 23.9 and 28.3, respectively. Again, the other antioxidants were not effective. We conclude that preventive treatment with vitamin C or vitamin E ameliorates seizure-induced oxidative damage in the brain. Several well-studied antioxidants were inactive, possibly due to limited brain permeability or a lack of chain-breaking antioxidant activity in hydrophilic compounds.

Reaction with ROO• and HOO• Radicals of Honokiol-Related Neolignan Antioxidants.

Honokiol is a natural bisphenol neolignan present in the bark of Magnolia officinalis, whose extracts have been employed in oriental medicine to treat several disorders, showing a variety of biological properties, including antitumor activity, potentially related to radical scavenging. Six bisphenol neolignans with structural motifs related to the natural bioactive honokiol were synthesized. Their chain-breaking antioxidant activity was evaluated in the presence of peroxyl (ROO•) and hydroperoxyl (HOO•) radicals by both experimental and computational methods. Depending on the number and position of the hydroxyl and alkyl groups present on the molecules, these derivatives are more or less effective than the reference natural compound. The rate constant of the reaction with ROO• radicals for compound 7 is two orders of magnitude greater than that of honokiol. Moreover, for compounds displaying quinonic oxidized forms, we demonstrate that the addition of 1,4 cyclohexadiene, able to generate HOO• radicals, restores their antioxidant activity, because of the reducing capability of the HOO• radicals. The antioxidant activity of the oxidized compounds in combination with 1,4-cyclohexadiene is, in some cases, greater than that found for the starting compounds towards the peroxyl radicals. This synergy can be applied to maximize the performances of these new bisphenol neolignans.

Modulation of the chain-breaking antioxidant activity of phenolic organochalcogens with various co-antioxidants at various pH values.

Phenolic organochalcogen chain-breaking antioxidants, i.e. 6-bromo-8 (hexadecyltellanyl)-3,3-dimethyl-1,5-dihydro-[1,3]dioxepino[5,6-c]pyridin-9-ol and 2-methyl-2,3-dihydrobenzo[b]selenophene-5-ol, have been investigated in a two-phase (chlorobenzene/water) lipid peroxidation model system as potent inhibitors of lipid peroxyl radicals with various co-antioxidants at various pH values. The pH has a significant effect on the chain-breaking antioxidant activities of phenolic organochalcogens. The key chain-breaking mechanism profile was attributed to the first oxygen atom transfer from the lipid peroxyl radicals to the Se/Te atom, followed by hydrogen atom transfer in a solvent cage from the nearby phenolic group to the resulting alkoxyl radical. Finally, regeneration of organochalcogen antioxidants could take place in the presence of aqueous-soluble co-antioxidants. Also, in the presence of aqueous soluble N-acetylcysteine at pH 1-7, both antioxidants behaved as very good inhibitors of lipid peroxyl radicals. The role of aqueous soluble mild co-antioxidants in the regeneration studies of organochalcogen antioxidants has been investigated in a two-phase lipid peroxidation model system. The importance of the phase transfer catalyst has been explored in the inhibition studies of selenium containing antioxidants using an Fe(II) source. The overall pH-dependent antioxidant activities of organochalcogens depend on their hydrogen atom transfer ability, relative stability, and distribution in the aqueous/lipid phase.

Natural Chain-Breaking Antioxidants and Their Synthetic Analogs as Modulators of Oxidative Stress.

Oxidative stress is associated with the increased production of reactive oxygen species or with a significant decrease in the effectiveness of antioxidant enzymes and nonenzymatic defense. The penetration of oxygen and free radicals in the hydrophobic interior of biological membranes initiates radical disintegration of the hydrocarbon “tails” of the lipids. This process is known as “lipid peroxidation”, and the accumulation of the oxidation products as peroxides and the aldehydes and acids derived from them are often used as a measure of oxidative stress levels. In total, 40 phenolic antioxidants were selected for a comparative study and analysis of their chain-breaking antioxidant activity, and thus as modulators of oxidative stress. This included natural and natural-like ortho-methoxy and ortho-hydroxy phenols, nine of them newly synthesized. Applied experimental and theoretical methods (bulk lipid autoxidation, chemiluminescence, in silico methods such as density functional theory (DFT) and quantitative structure–activity relationship ((Q)SAR) modeling) were used to clarify their structure–activity relationship. Kinetics of non-inhibited and inhibited lipid oxidation in close connection with inhibitor transformation under oxidative stress is considered. Special attention has been paid to chemical reactions resulting in the initiation of free radicals, a key stage of oxidative stress. Effects of substituents in the side chains and in the phenolic ring of hydroxylated phenols and biphenols, and the concentration were discussed.

Approach to Determination a Structure – Antioxidant Activity Relationship of Selected Common Terpenoids Evaluated by ABTS•+ Radical Cation Assay

Data available in the literature indicated various biological activities of terpenes. One of the most frequently investigated activities is the ability to scavenge free radicals. To date, studies based on the DPPH• method indicated conjugated double bonds as moieties responsible for antioxidant activity of selected terpenes. In order to verify this theory, studies based on 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+) were performed. The spectrophotometric investigations explicitly revealed relatively high antioxidant activity of terpenes possessing conjugated double bonds in comparison with substances without this structural element. It has been shown that the chain-breaking antioxidant activity of terpenes strictly depends on π bonds. TEAC values and percentage scavenging of the free radicals revealed that the most promising antioxidants are α-terpinene, ocimene, pulegone and farnesene. In order to explain the reaction between terpenes and ABTS•+ free radical cation, a possible antioxidant mechanism has been proposed.

Protective effects of 4-methylcoumarins and related compounds as radical scavengers and chain-breaking antioxidants

The aim of this study is to determine, and to compare the protective effects of eight 4-methylcoumarins and four related compounds as radical scavengers and chain-breaking antioxidants. The main kinetic parameters of their radical scavenging activity (as % RSA, stoichiometry, n, and rate constants of reaction with DPPH radical, kRSA) and of chain breaking antioxidant activity (as antioxidant efficiency, PF and reactivity, ID), have been determined and discussed. The RSA study has been conducted at physiological temperature (37 °С) towards DPPH radical and the tested compounds are separated into three main groups: with strong activity (% RSA > 40%); with moderate activity (20% < % RSA > 40%) and with weak activity (% RSA < 20%). Chain-breaking antioxidant activities of the studied compounds have been evaluated during bulk phase lipid (triacylglycerols of sunflower oil, TGSO) autoxidation at 80 °C. All results obtained are compared with those for standard and known inhibitors of oxidation processes, e.g. caffeic and p-coumaric acids, α-tocopherol and butylated hydroxytoluene (BHT). On the basis of a comparative analysis with standard antioxidants, the differences in the radical scavenging and antioxidant abilities of the studied compounds have been discussed and reaction mechanisms proposed. All structures are optimized at UB3LYP/6-31 + G(d,p) level in gas phase and in acetone solution to study the solvation effects.

Stepwise sequential analysis of stable multiradicals formation in polyphenolic myricetin active OH groups throughout the antioxidant process to scavenge free radicals

Five galvinoxyl radicals (G) reduction by one polyphenolic myricetin (Myc, 3,3′,4′,5,5′,7-Hexahydroxyflavone) molecule-using EPR method-demonstrated that each Myc should donate at least five H atoms resulted in multiradicals Myc5 (5 G + 1Myc → 5 GH + 1 Myc5). The process that five H atoms donation occurs from different OH sites of Myc lead to appearing of five unpaired valence electrons of Myc5 via two possible different mechanisms. First; concerted five H atoms donation from five different OH groups that directly results in Myc5 radicals (Myc → Myc5). Second; the step-wise radical formation in five different OH groups of Myc (Myc → Myc → Myc2 → Myc3 → Myc4 → Myc5). Computational DFT method was used to analyze all the six different OH groups of Myc which involved in free radical reactions for the purposes of clarification the stable multiradicals Myc5 formation mechanism. The fast semi-empirical combined quantum method, AM1/DFT, as well as full DFT geometry optimization approaches of B3LYP functional DFT/DFT with different basis sets of 6-31G (d), 6-311 + G (d,p) and 6-311 + G (2d,2p) confirmed the stepwise H atom abstraction trend on the main three hydroxyl sites as 4′-O → 4′-O3-O → 4′-O3-O-7O both in the gas and water phase. Spin delocalization over the entire Myc, adding the co-planarity, contributed to the stabilization of respective radical species. The excellent stability of Myc radicals should give an effective chain-breaking antioxidant activity for Myc in biological environment which is expected to have far fewer side effects. These findings may be useful to elucidate the radical scavenging mechanism of other flavonoids regarding to design novel antioxidants.

Chain-breaking antioxidant activity of hydroxylated and methoxylated magnolol derivatives: the role of H-bonds.

Chemical modification of magnolol, an uncommon dimeric neolignan contained in Magnolia genus trees, provides a unique array of polyphenols having interesting biological activity potentially related to radical scavenging. The chain-breaking antioxidant activity of four new hydroxylated and methoxylated magnolol derivatives was explored by experimental and computational methods. The measurement of the rate constant of the reaction with ROO˙ radicals (kinh) in an apolar solvent showed that the introduction of hydroxyl groups ortho to the phenolic OH in magnolol increased the kinh value, being 2.4 × 105 M-1 s-1 and 3.3 × 105 M-1 s-1 for the mono and the dihydroxy derivatives respectively (kinh of magnolol is 6.1 × 104 M-1 s-1). The di-methoxylated derivative is less reactive than magnolol (kinh = 1.1 × 104 M-1 s-1), while the insertion of both hydroxyl and methoxyl groups showed no effect (6.0 × 104 M-1 s-1). Infrared spectroscopy and theoretical calculations allowed a rationalization of these results and pointed out the crucial role of intramolecular H-bonds. We also show that a correct estimation of the rate constant of the reaction with ROO˙ radicals, by using BDE(OH) calculations, requires that the geometry of the radical is as close as possible to that of the parent phenol.

Model studies on the antioxidant activity of common terpenoid constituents of essential oils by means of the 2,2-diphenyl-1-picrylhydrazyl method.

The research aims to indicate which of the structural elements of monoterpenes are responsible for their antioxidant activity. The activity was determined spectrophotometrically with the use of the DPPH(•) assay. It has been shown that π bonds are responsible for the chain-breaking antioxidant activity of monoterpenes. It has been proved, for the first time, that blocking of conjugated double bonds leads to a decrease of the antioxidant activity of monoterpenes. A probable reaction mechanism between monoterpenes and DPPH(•) has been proposed. It has been indicated that the antioxidant activity of monoterpenes strongly depends on the polarity of solvent used in the experiments. The presented results may stimulate additional research in the field of terpenoid antioxidants.

Pyridoxine-derived organoselenium compounds with glutathione peroxidase-like and chain-breaking antioxidant activity.

One of the vitamin B6 vitamers, pyridoxine, was modified to incorporate selenium in various oxidation states in place of the methyl group in position 2. Such compounds were conveniently accessed by treatment of bis-4,5-(carboethoxy)-2-iodo-3-pyridinol with disodium diselenide and LiAlH4 -reduction. After work-up, selone 7 was isolated in good yield as an air-stable crystalline material. Hydrogen bonding to the neighboring hydroxyl group, as revealed by the short intramolecular Se⋅⋅⋅H distance in the crystal structure is likely to provide extra stabilization to the compound. Computational studies showed that selone 7 is more stable than the corresponding selenol tautomer by 12.2 kcal mol(-1) . Hydrogen peroxide oxidation of the selone 7 afforded diselenide 12, and, on further oxidation, seleninic acid 13. Treatment of the seleninic acid with thiophenol provided an isolable selenosulfide 14. The glutathione peroxidase-like properties of the pyridoxine-derived compounds were assessed by using the coupled reductase method. Seleninic acid 13 was found to be twofold more active than ebselen. The chain-breaking capacity of the pyridoxine compounds were studied in a water/chlorobenzene membrane model containing linoleic acid as an oxidizable substrate and N-acetylcysteine as a thiol reducing agent. Diselenide 15 could match α-tocopherol when it comes to reactivity towards peroxyl radicals and inhibition time.

Proton-Coupled Electron-Transfer Mechanism for the Radical Scavenging Activity of Cardiovascular Drug Dipyridamole

Dipyridamole (DIP) is a well-known pharmaceutical drug used as a coronary vasodilator and anti-platelet agent in clinics for treating several cardiovascular diseases. Primarily, the therapeutic effects of the drug are attributed to its antioxidant potency. In this research, we aim to declare the unknown antioxidant mechanism of DIP as well as its potent chain-breaking antioxidant activity in polar aqueous medium inside the cells, using different experimental methods and theoretical quantum calculations. Data demonstrated the higher antioxidant capacity of DIP against ROS and free radicals in polar cell's interior. DIP is capable of generating long living and noninvasive DIP• radicals in oxidant condition that leads to an effective “chain-breaking antioxidant” activity. Quantum computational data indicated that DIP antioxidant has more favorable ionization potential than trolox which means DIP has higher antioxidant activity. Also, data showed that the direct hydrogen-transfer is not a favorable process to construct DIP• because of high barrier energy, though electron-transfer process can more easily to produce DIP•+ with the lowest barrier energy. Altogether, the electron donating potency of DIP to reduce ferric ion, having the low anodic oxidation peak potential, producing long lived stable DIP• radicals and protecting myoblast cells from oxidation, proposed the excellent “chain-breaking antioxidant” potency via electron-transfer mechanism of this vasodilator DIP drug in polar aqueous medium.

Olive oil supplemented with Coenzyme Q10: Effect on plasma and lipoprotein oxidative status

Olive oil consumption is associated with protective cardiovascular properties, including some beneficial modifications in lipoprotein profile and composition. Coenzyme Q(10) (CoQ(10)) exerts a protective effect on plasma lipoproteins. Aim of the study was to investigate whether extra virgin (EV) olive oil enriched with CoQ(10) affects CoQ(10) levels and oxidative status in plasma and in isolated lipoproteins. Twelve subjects were administered 20 mL olive oil per day for 2 weeks, followed by 2 weeks of olive oil enriched with 20 mg and 2 more weeks with 40 mg of CoQ(10). Plasma and isolated lipoproteins were collected in each phase of the study and subsequently analyzed to assess lipid profile, CoQ10 levels, ORAC assay, resistance of lipoproteins to peroxidation and paroxonase 1 activity. Plasma CoQ(10) levels significantly increased with the 20 mg (+73%) and 40 mg dose (+170%), while the percentage of oxidized CoQ(10) decreased. A significant inverse correlation was found in plasma between percentage of oxidized CoQ(10) and total antioxidant capacity. A lower susceptibility of LDL to peroxidation was also found. Finally, a positive correlation was observed between concentration of CoQ(10) in HDL and paraoxonase-1 activity. EV olive oil enriched with both doses of CoQ(10) significantly affects its bioavailability and plasma redox status. These changes are associated with a decreased susceptibility of plasma lipoproteins to peroxidation associated with a chain-breaking antioxidant activity of the formulation.

REVIEW ON DIFFERENT METHODS TO ASSESS THE ANTIOXIDANT ACTIVITY OF SOME COMMON PLANTS OF INDIAN TRADITIONAL MEDICINE

A lot of medicinal plants, traditionally used for thousands of years, are present in a group of herbal preparations of the Indian traditional health care system (Ayurveda) named Rasayana proposed for their interesting antioxidant activities. Among the medicinal plants used in ayurvedic Rasayana for their therapeutic action, some of these have been throughly investigated. In the present paper seven plants (Emblica officinalis L., Curcuma longa L., Mangifera indica L., Momordica charantia L., Santalum album L., Swertia chirata Buch-Ham, Withania somnifera (L.) Dunal) are viewed for their historical, etymological, morphological, phytochemical and pharmacological aspects. The plants described contain antioxidant principles, that can explain and justify their use in traditional medicine in the past as well as the present. In order to identify the plants with antioxidant activity in Ayurveda, a formulation of some rasayanas with well defined antioxidant properties has been examinated. For this purpose, we have considered Sharma's work on the preparation MAK4, MAK5, MA631, MA 471, MA Raja's Cup, MA Student Rasayana, MA Ladies Rasayana. The different methods to assess the antioxidant total peroxyl radical-trapping parameter (TRAP), oxygen radical absorbance capacity (ORAC) and hydroxyl radical averting capacity (HORAC) methods. ORAC, TRAP and HORAC values well correlated with polyphenol content. A good correlation was found also between the methods for measuring antioxidant capacity. Nevertheless, ORAC has been found to be the most sensitive method to measure chain-breaking antioxidant activity. Although we have found a good correlation between TRAP, ORAC and HORAC, using more than one antioxidant assay is recommended for more detailed understanding the principles of antioxidant properties of samples. Some other assays are also there are discussed in the article

Antiradical and antioxidant activities of new bio-antioxidants

Antioxidants could be promising agents for management of oxidative stress-related diseases. New biologically active compounds, belonging to a rare class of natural lignans with antiangiogenic, antitumoral and DNA intercalating properties, have been recently synthesized. These compounds are benzo[kl]xanthene lignans (1,2) and dihydrobenzofuran neolignans (3,4). The radical scavenging and chain-breaking antioxidant activities of compounds 1–4 were studied by applying different methods: radical scavenging activity by DPPH rapid test, chain-breaking antioxidant activity and quantum chemical calculations. All studied compounds were found to be active as DPPH scavengers but reaction time with DPPH and compounds’ concentrations influenced deeply the evaluation. The highest values of radical scavenging activity (%RSAmax) and largest rate constants for reaction with DPPH were obtained for compounds 2 and 3. Comparison of %RSAmax with that of standard antioxidants DL-α-tocopherol (TOH), caffeic acid (CA) and butylated hydroxyl toluene (BHT) give the following new order of %RSA max: TOH (61.1%) > CA (58.6%) > 3 (36.3%) > 2 (28.1%) > 4 (6.7%) > 1 (3.6%) = BHT (3.6%). Chain-breaking antioxidant activities of individual compounds (0.1–1.0 mM) and of their equimolar binary mixtures (0.1 mM) with TOH were determined from the kinetic curves of lipid autoxidation at 80 °C. On the basis of a comparable kinetic analysis with standard antioxidants a new order of the antioxidant efficiency (i.e., protection factor, PF) of compounds 1–4 were obtained: 2 (7.2) ≥ TOH (7.0) ≥ CA (6.7) > 1 (3.1) > 3 (2.2) > ferulic acid FA (1.5) > 4 (0.6); and of the antioxidant reactivity (i.e. inhibition degree, ID): 2 (44.0) >> TOH (18.7) >> CA (9.3) >> 1 (8.4) > 3 (2.8) > FA (1.0) > 4 (0.9). The important role of the catecholic structure in these compounds, which is responsible for the high chain-breaking antioxidant activity, is discussed and a reaction mechanism is proposed. Higher oxidation stability of the lipid substrate was found in the presence of equimolar binary mixtures 2 + TOH, 3 + TOH and 4 + TOH. However, an actual synergism was only obtained for the binary mixtures with compounds 3 and 4. The geometries of compounds and all possible phenoxyl radicals were optimized using density functional theory. For description of the scavenging activity bond dissociation enthalpies (BDE), HOMO energies and spin densities were employed. The best correlation between theoretical and experimental data was obtained for compound 2, with the highest activity, and for compound 4 with the lowest activity. The BDE is the most important theoretical descriptor, which correlates with the experimentally obtained antioxidant activity of the studied benzo[kl]xanthene lignans and dihydrobenzofuran neolignans.

Kinetic and thermodynamic aspects of the chain-breaking antioxidant activity of ascorbic acid derivatives in non-aqueous media

Ascorbic acid (vit. C) is a cofactor whose reactivity toward peroxyl and other radical species has a key-role in its biological function. At physiological pH it is dissociated to the corresponding anion. Derivatives of ascorbic acid, like ascorbyl palmitate, are widely employed in food or in cosmetics and pharmaceuticals. While the aqueous chemistry of ascorbate has long been investigated, in non-aqueous media it is largely unexplored. In this work oxygen-uptake kinetics, EPR and computational methods were combined to study the reaction of peroxyl radicals with two lipid-soluble derivatives: ascorbyl palmitate and 5,6-isopropylidene-l-ascorbic acid in non-aqueous solvents. In acetonitrile at 303 K the undissociated AscH(2) form of the two derivatives trapped peroxyl radicals with k(inh) of (8.4 ± 1.0) × 10(4) M(-1) s(-1), with stoichiometric factor of ca. 1 and isotope effect k(H)/k(D) = 3.0 ± 0.6, while in the presence of bases the anionic AscH(-) form had k(inh) of (5.0 ± 3.3) × 10(7) M(-1) s(-1). Reactivity was also enhanced in the presence of acetic acid and the mechanism is discussed. The difference in reactivity between the AscH(2)/AscH(-) forms was paralleled by a difference in O-H bond dissociation enthalpy, which was determined by EPR equilibrations as 81.0 ± 0.4 and 72.2 ± 0.4 kcal mol(-1) respectively for AscH(2) and AscH(-) in tert-butanol at 298 K. Gas-phase calculations for the neutral/anionic forms were in good agreement yielding 80.1/69.0 kcal mol(-1) using B3LYP/6-31+g(d,p) and 79.0/67.8 kcal mol(-1) at CBS-QB3 level. EPR spectra of ascorbyl palmitate in tBuOH consisted of a doublet with HSC = 0.45 G centred at g = 2.0050 for the neutral radical AscH˙ and a doublet of triplets with HSCs of 1.85 G, 0.18 G and 0.16 G centred at g = 2.0054 for Asc˙(-) radical anion.

Structure–activity relationship of dihydroxy-4-methylcoumarins as powerful antioxidants: Correlation between experimental & theoretical data and synergistic effect

The chain-breaking antioxidant activities of eight coumarins [7-hydroxy-4-methylcoumarin ( 1), 5,7-dihydroxy-4-methylcoumarin ( 2), 6,7-dihydroxy-4-methylcoumarin ( 3), 6,7-dihydroxycoumarin ( 4), 7,8-dihydroxy-4-methylcoumarin ( 5), ethyl 2-(7,8-dihydroxy-4-methylcoumar-3-yl)-acetate ( 6), 7,8-diacetoxy-4-methylcoumarin ( 7) and ethyl 2-(7,8-diacetoxy-4-methylcoumar-3-yl)-acetate ( 8)] during bulk lipid autoxidation at 37 °C and 80 °C in concentrations of 0.01–1.0 mM and their radical scavenging activities at 25 °C using TLC–DPPH test have been studied and compared. It has been found that the o-dihydroxycoumarins 3– 6 demonstrated excellent activity as antioxidants and radical scavengers, much better than the m-dihydroxy analogue 2 and the monohydroxycoumarin 1. The substitution at the C-3 position did not have any effect either on the chain-breaking antioxidant activity or on the radical scavenging activity of the 7,8-dihydroxy- and 7,8-diacetoxy-4-methylcoumarins 6 and 8. The comparison with DL-α-tocopherol (TOH), caffeic acid (CA) and p-coumaric acid ( p-CumA) showed that antioxidant efficiency decreases in the following sequence: TOH > CA > 3 > 4 > 6 > 5 > 2 > 1 = 7 = 8 = p-CumA. Theoretical calculations and the “Lipinski’s Rule of Five” were used for explaining the structure–activity relationships and pharmacokinetic behavior. A higher TGSO oxidation stability was observed in the presence of equimolar (1:1) binary mixtures of coumarins with TOH ( 1 + TOH, 3 + TOH and 5 + TOH). However, the synergism (14%) was observed only for the binary mixture of 5 + TOH.

α-Tocopherol is an effective Phase II enzyme inducer: protective effects on acrolein-induced oxidative stress and mitochondrial dysfunction in human retinal pigment epithelial cells

Vitamin E has long been identified as a major lipid-soluble chain-breaking antioxidant in mammals. α-Tocopherol is a vitamin E component and the major form in the human body. We propose that, besides its direct chain-breaking antioxidant activity, α-tocopherol may exert an indirect antioxidant activity by enhancing the cell's antioxidant system as a Phase II enzyme inducer. We investigated α-tocopherol's inducing effect on Phase II enzymes and its protective effect on acrolein-induced toxicity in a human retinal pigment epithelial (RPE) cell line, ARPE-19. Acrolein, a major component of cigarette smoke and also a product of lipid peroxidation, at 75 μmol/L over 24 h, caused significant loss of ARPE-19 cell viability, increased oxidative damage, decreased antioxidant defense, inactivation of the Keap1/Nrf2 pathway, and mitochondrial dysfunction. ARPE-19 cells have been used as a model of smoking- and age-related macular degeneration. Pretreatment with α-tocopherol activated the Keap1/Nrf2 pathway by increasing Nrf2 expression and inducing its translocation to the nucleus. Consequently, the expression and/or activity of the following Phase II enzymes increased: glutamate cysteine ligase, NAD(P)H:quinone oxidoreductase 1, heme-oxygenase 1, glutathione S-transferase and superoxide dismutase; total antioxidant capacity and glutathione also increased. This antioxidant defense enhancement protected ARPE-19 cells from an acrolein-induced decrease in cell viability, lowered reactive oxygen species and protein oxidation levels, and improved mitochondrial function. These results suggest that α-tocopherol protects ARPE-19 cells from acrolein-induced cellular toxicity, not only as a chain-breaking antioxidant, but also as a Phase II enzyme inducer.

Different methods for control and comparison of the antioxidant properties of vegetables

The present study investigates the antioxidant properties of selected vegetables, using the total peroxyl radical-trapping parameter (TRAP), oxygen radical absorbance capacity (ORAC) and hydroxyl radical averting capacity (HORAC) methods. ORAC, TRAP and HORAC values well correlated with polyphenol content. A good correlation was found also between the methods for measuring antioxidant capacity. Nevertheless, ORAC has been found to be the most sensitive method to measure chain-breaking antioxidant activity. Although we have found a good correlation between TRAP, ORAC and HORAC, using more than one antioxidant assay is recommended for more detailed understanding the principles of antioxidant properties of samples.

Chain-breaking antioxidant activity of reduced forms ofmitochondria-targeted quinones, a novel type of geroprotectors

The chain-breaking antioxidant activities of reduced form of novel type of geroprotectors, mitochondria-targeted quinones (QH(2)) have quantitatively been measured for the first time. To this end, the chain peroxidation of methyl linoleate (ML) in Triton micelles was used as a kinetic testing model. The studied QH(2) were lipophilic triphenylphosphonium cations conjugated by an aliphatic linker to an antioxidant, i.e. a ubiquinol moiety (MitoQH(2)) or plastoquinol moiety (SkQH(2)). The antioxidant activity was characterized by the rate constant k(1) for the reaction between QH(2) and the lipid peroxyl radical (LO(2) (.)) originated from ML: QH(2) + LO(2) (.) --> HQ(.) + LOOH. All the tested QH(2) displayed a pronounced antioxidant activity. The oxidized forms of the same compounds did not inhibit ML peroxidation. The value of k(1) for SkQH(2) far exceeded k(1) for MitoQH(2). For the biologically active geroprotectors SkQ1H(2), the k(1) value found to be as high as 2.2 x 10(5) M(-) (1)s(-) (1), whereas for MitoQH(2), it was 0.58 x 10(5) M(-) (1)s(-) (1). The kinetic behavior of QH(2) suggested that SkQ1H(2) can rather easily diffuse through lipid-water microheterogeneous systems.

Synthesis and antioxidant activity of [60]fullerene–flavonoid conjugates

Chalcone, flavone, and arylideneflavanone derivatives bearing one or two 3,5-di- tert-butyl-4-hydroxyphenyl groups were synthesized from 2′,4′-dihydroxyacetophenone and 3,5-di- tert-butyl-4-hydroxybenzaldehyde. These flavonoids were converted into the corresponding malonates and then reacted with C 60 to yield the title compounds. The O–H bond dissociation enthalpies (BDE) and the chain-breaking antioxidant activity of the flavonoid derivatives and the corresponding C 60 conjugates were evaluated. These results are consistent with the phenolic moiety being the main responsible for the reaction with peroxyl radicals, while the C 60 part of the molecule acts synergically by trapping alkyl radicals under reduced O 2 partial pressure. These novel C 60–flavonoid conjugates are therefore promising leads for broad-spectrum radical scavengers.