Antioxidant action of ubiquinol homologues with different isoprenoid chain length in biomembranes

Ubiquinones (CoQn) are intrinsic lipid components of many membranes. Besides their role in electron-transfer reactions they may act as free radical scavengers, yet their antioxidant function has received relatively little study. The efficiency of ubiquinols of varying isoprenoid chain length (from Q0 to Q10) in preventing (Fe2+ + ascorbate)-dependent or (Fe2+ + NADPH)-dependent lipid peroxidation was investigated in rat liver microsomes and brain synaptosomes and mitochondria. Ubiquinols, the reduced forms of CoQn, possess much greater antioxidant activity than the oxidized ubiquinone forms. In homogenous solution the radical scavenging activity of ubiquinol homologues does not depend on the length of their isoprenoid chain. However in membranes ubiquinols with short isoprenoid chains (Q1-Q4) are much more potent inhibitors of lipid peroxidation than the longer chain homologues (Q5-Q10). It is found that: i) the inhibitory action, that is, antioxidant efficiency of short-chain ubiquinols decreases in order Q1 greater than Q2 greater than Q3 greater than Q4; ii) the antioxidant efficiency of long-chain ubiquinols is only slightly dependent on their concentrations in the order Q5 greater than Q6 greater than Q7 greater than Q8 greater than Q9 greater than Q10 and iii) the antioxidant efficiency of Q0 is markedly less than that of other homologues. Interaction of ubiquinols with oxygen radicals was followed by their effects on luminol-activated chemiluminescence. Ubiquinols Q1-Q4 at 0.1 mM completely inhibit the luminol-activated NADPH-dependent chemiluminescent response of microsomes, while homologues Q6-Q10 exert no effect. In contrast to ubiquinol Q10 (ubiquinone Q10) ubiquinone Q1 synergistically enhances NADPH-dependent regeneration of endogenous vitamin E in microsomes thus providing for higher antioxidant protection against lipid peroxidation. The differences in the antioxidant potency of ubiquinols in membranes are suggested to result from differences in partitioning into membranes, intramembrane mobility and non-uniform distribution of ubiquinols resulting in differing efficiency of interaction with oxygen and lipid radicals as well as different efficiency of ubiquinols in regeneration of endogenous vitamin E.     

Simultaneous determination of tocopherols,ubiquinols, and ubiquinones in blood,plasma, tissue homogenates,and subcellular fractions

A fast single-step lipid extraction procedure and high-performance liquid chromatography with in-line uv and electrochemical detection are used for the simultaneous quantitative determination of tocopherols, ubiquinols, and ubiquinones in blood, plasma, tissue homogenates, and subcellular fractions. The compounds of interest can be quantitatively extracted into hexane from a sodium dodecyl sulfate-treated aqueous homogenate after precipitation of protein by addition of an equal volume of ethanol. α-, γ-, and δ-Tocopherol, ubiquinol 9, ubiquinol 10, and ubiquinones 9 and 10 can be well separated on a reversed phase column. Ubiquinones are detected at 275 nm by the uv detector, and ubiquinols and tocopherols by the electrochemical detector in the oxidative mode. Quantitation is done by comparing chromatographic peak heights to those of a standard solution containing known amounts of tocopherols, ubiquinols 9 and 10, and ubiquinones 9 and 10, analyzed under identical conditions. The high sensitivity of the electrochemical detection allows operation at low potentials (+0.5 V) with low detector response, but high selectivity for the easily oxidizable tocopherols and ubiquinols and decreased baseline noise. The uv detection limits the overall sensitivity of the procedure to 2 pmol ubiquinone, corresponding to 0.1 μm ubiquinone in the lipid extract. The ranges of values obtained for rat and guinea pig tissues, for rat liver mitochondria, and for blood and plasma from rats and humans are given.     

Antioxidant properties of minocycline: neuroprotection in an oxidative stress assay and direct radical-scavenging activity

Minocycline is neuroprotective in animal models of a number of acute CNS injuries and neurodegenerative diseases. While anti-inflammatory and anti-apoptotic effects of minocycline have been characterized, the molecular basis for the neuroprotective effects of minocycline remains unclear. We report here that minocycline and a number of antioxidant compounds protect mixed neuronal cultures in an oxidative stress assay. To evaluate the role of minocycline's direct antioxidant properties in neuroprotection, we determined potencies for minocycline, other tetracycline antibiotics, and reference antioxidant compounds using a panel of in vitro radical scavenging assays. Data from in vitro rat brain homogenate lipid peroxidation and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays show that minocycline, in contrast to tetracycline, is an effective antioxidant with radical scavenging potency similar to vitamin E. Our findings suggest that the direct antioxidant activity of minocycline may contribute to its neuroprotective effects in some cell-based assays and animal models of neuronal injury.     

Structural aspects of antioxidant activity of substituted pyridoindoles

Stobadine and its two structural analogues, dehydrostobadine and N-acetylated stobadine were used to examine how structural alteration in the close proximity of the indolic nitrogen would influence the antioxidant activity of the substituted pyridoindoles. The compounds were tested for their efficiency to scavenge stable free radicals of alpha,alpha'-diphenyl-beta-picrylhydrazyl as well as for their ability to prevent 2,2'-azobis-(2-amidinopropane)hydrochloride induced peroxidation of dioleoyl phosphatidylcholine liposomes. The results proved that the substituted pyridoindoles can act as potent scavengers of peroxyl radicals both in aqueous and lipid phases, the antioxidant activity being comparable with that of Trolox. Structural changes in the proximity of the indolic nitrogen were found crucial for the radical scavenging efficiency: aromatisation of the pyridoindole skeleton in dehydrostobadine lowered the antioxidant activity, while acetylation of the indolic nitrogen completely abolished the ability to scavenge peroxyl radicals. The results are in agreement with the notion that the antioxidant activity of stobadine and of the related pyridoindoles may be mediated via the indolic nitrogen centre. When stobadine and Trolox were present simultaneously in liposomal incubations, Trolox spared stobadine in a dose-dependent manner; a direct interaction of Trolox with stobadinyl radical appears to be a plausible explanation with possible consequences for the antioxidant capacity of stobadine under in vivo conditions, where re-cycling of stobadine by vitamin E might occur.     

Vitamin E: action, metabolism and perspectives

Natural vitamin E includes four tocopherols and four tocotrienols. RRR-alpha-tocopherol is the most abundant form in nature and has the highest biological activity. Although vitamin E is the main lipid-soluble antioxidant in the body, not all its properties can be assigned to this action. As antioxidant, vitamin E acts in cell membranes where prevents the propagation of free radical reactions, although it has been also shown to have pro-oxidant activity. Non-radical oxidation products are formed by the reaction between alpha-tocopheryl radical and other free radicals, which are conjugated to glucuronic acid and excreted through the bile or urine. Vitamin E is transported in plasma lipoproteins. After its intestinal absorption vitamin E is packaged into chylomicrons, which along the lymphatic pathway are secreted into the systemic circulation. By the action of lipoprotein lipase (LPL), part of the tocopherols transported in chylomicrons are taken up by extrahepatic tissues, and the remnant chylomicrons transport the remaining tocopherols to the liver. Here, by the action of the "alpha-tocopherol transfer protein", a major proportion of alpha-tocopherol is incorporated into nascent very low density lipoproteins (VLDL), whereas the excess of alpha-tocopherol plus the other forms of vitamin E are excreted in bile. Once secreted into the circulation, VLDL are converted into IDL and LDL by the action of LPL, and the excess of surface components, including alpha-tocopherol, are transferred to HDL. Besides the LPL action, the delivery of alpha-tocopherol to tissues takes place by the uptake of lipoproteins by different tissues throughout their corresponding receptors. Although we have already a substantial information on the action, effects and metabolism of vitamin E, there are still several questions open. The most intriguing is its interaction with other antioxidants that may explain how foods containing small amounts of vitamin E provide greater benefits than larger doses of vitamin E alone.     

Synergistic inhibition of oxidation in dispersed phosphatidylcholine liposomes by a combination of vitamin E and cysteine

Oxidations of soybean phosphatidylcholine liposomes in an aqueous dispersion initiated by free radicals generated initially either in the aqueous phase or in the lipid phase were efficiently suppressed by vitamin E in the membranes. Vitamin E was consumed linearly with time and, when the inhibition period was over the oxidation proceeded rapidly at a rate similar to that in the absence of vitamin E. L-Cysteine was also effective by itself in scavenging radicals in the aqueous region, but it was consumed more rapidly than vitamin E. On the other hand, cysteine could not scavenge the radicals efficiently in a lipid region. Nevertheless, when vitamin E was incorporated into liposomes, the addition of cysteine in the aqueous phase prolonged the inhibition period and it reduced the rate of decay of vitamin E markedly even when the radicals were generated initially in the lipid bilayer. Furthermore, it was found by an electron spin resonance study that chromanoxyl radical disappeared quite rapidly when it was mixed with cysteine and that the spin adduct of cysteine radical was observed in the presence of alpha-(4-pyridyl-N-oxide)-N-tert-butyl nitrone. It was concluded that L-cysteine located in an aqueous region could regenerate vitamin E by reacting with vitamin E radical formed in a lipid region and show a synergistic antioxidant effect, although its efficiency of vitamin E regeneration was lower than that by vitamin C.     

Antioxidant activity of mycosporine-like amino acids isolated from three red macroalgae and one marine lichen

Several standard in vitro assays were performed in order to determine the potential antioxidant capabilities of purified aqueous extracts of the mycosporine-like amino acids (MAAs), porphyra-334 plus shinorine (P-334 + SH), isolated from the red alga Porphyra rosengurttii, asterina-330 plus palythine (AS-330 + PNE), from the red alga Gelidium corneum, shinorine (SH), from the red alga Ahnfeltiopsis devoniensis, and mycosporine -glycine (M-Gly), isolated from the marine lichen Lichina pygmaea. The scavenging potential of hydrosoluble radicals (ABTS⁺ decolorization method), the antioxidant activity in lipid medium (β-carotene/ linoleate bleaching method) and the scavenging capacity of superoxide radicals (pyrogallol autooxidation assay) were evaluated. In terms of scavenging of hydrosoluble radicals, the antioxidant activity of all MAAs studied was dose-dependent and it increased with the alkalinity of the medium (pH 6 to 8.5). M-Gly presented the highest activity in all pH tested; at pH 8.5 its IC₅₀ was 8-fold that of L-ascorbic acid (L-ASC) followed by AS-330 + PNE while P-334 + SH and SH showed scarce activity of scavenging of hydrosoluble free radicals. AS-330 + PNE showed high activity for inhibition of β-carotene oxidation relative to vitamin E and superoxide radical scavenging whilst the activity of P-334 +SH and SH were moderate. According to these results, the potential of MAAs in photoprotection can be considered high due to a double function: (1) UV chemical screening with high efficiency for UVB and UVA regions of the solar spectrum, and (2) their antioxidant capacity.     

Interactions among antioxidants in health and disease: vitamin E and its redox cycle.

Probably most diseases at some point during their course involve free radical reactions in tissue injury. In some cases, free radical reactions may be involved in multiple sites and at different stages of a chronic disease. So, both acute and degenerative diseases are thought to involve free radical reactions in tissue injury. An overview will be given of the evidence for the occurrence of free radicals and the importance of antioxidant interventions, with particular reference to the lipophilic antioxidant vitamin E (tocopherols and tocotrienols).     

Antioxidant Activity of Vitamin E and Trolox: Understanding of the Factors that Govern Lipid Peroxidation Studies In Vitro

Peroxidation of lipids is of significant interest owing to the evidence that peroxyl radicals and products of lipid peroxidation may be involved in the toxicity of compounds initiating a deteriorative reaction in the processing and storage of lipid-containing foods. In view of the significance of the antioxidant role of the dietary compound vitamin E and its water-soluble analogue Trolox in research of lipid-containing foods, it is desirable to determine more specifically how and where they operate its antioxidant activity in lipid membranes. In this study, unilamellar liposomes of phosphatidylcholine were used as membrane mimetic systems to estimate the antioxidant properties of vitamin E and Trolox and establish a relationship between their interactions with the membrane and their consequent antioxidant activity. Lipid peroxidation was initiated by the peroxyl radical (ROO^•) in lipid and aqueous media by the thermal decomposition of azocompounds and was assessed by the fluorescence intensity decay of the fluorescent probe diphenylhexatriene propionic acid. Results obtained showed that membrane lipoperoxidation is related not only to the scavenging characteristics of the compounds studied but also to their ability to interact with the lipid bilayers, and consequently liposomes provide additional information to that obtained currently from assays performed in aqueous buffer media.     

Free radical recycling and intramembrane mobility in the antioxidant properties of alpha-tocopherol and alpha-tocotrienol.

d-Alpha-tocopherol (2R,4'R,8'R-Alpha-tocopherol) and d-alpha-tocotrienol are two vitamin E constituents having the same aromatic chromanol "head" but differing in their hydrocarbon "tail": tocopherol with a saturated and toctrienol with an unsaturated isoprenoid chain. d-Alpha-tocopherol has the highest vitamin E activity, while d-alpha-tocotrienol manifests only about 30% of this activity. Since vitamin E is considered to be physiologically the most important lipid-soluble chain-breaking antioxidant of membranes, we studied alpha-tocotrienol as compared to alpha-tocopherol under conditions which are important for their antioxidant function. d-Alpha-tocotrienol possesses 40-60 times higher antioxidant activity against (Fe2+ + ascorbate)- and (Fe2+ + NADPH)-induced lipid peroxidation in rat liver microsomal membranes and 6.5 times better protection of cytochrome P-450 against oxidative damage than d-alpha-tocopherol. To clarify the mechanisms responsible for the much higher antioxidant potency of d-alpha-tocotrienol compared to d-alpha-tocopherol, ESR studies were performed of recycling efficiency of the chromanols from their chromanoxyl radicals. 1H-NMR measurements of lipid molecular mobility in liposomes containing chromanols, and fluorescence measurements which reveal the uniformity of distribution (clusterizations) of chromanols in the lipid bilayer. From the results, we concluded that this higher antioxidant potency of d-alpha-tocotrienol is due to the combined effects of three properties exhibited by d-alpha-tocotrienol as compared to d-alpha-tocopherol: (i) its higher recycling efficiency from chromanoxyl radicals, (ii) its more uniform distribution in membrane bilayer, and (iii) its stronger disordering of membrane lipids which makes interaction of chromanols with lipid radicals more efficient. The data presented show that there is a considerable discrepancy between the relative in vitro antioxidant activity of d-alpha-tocopherol and d-alpha-tocotrienol with the conventional bioassays of their vitamin activity.     

Antioxidant activities of estrogens against aqueous and lipophilic radicals; differences between phenol and catechol estrogens

Natural estrogens have much greater radical-scavenging antioxidant activity than has previously been demonstrated, with activities up to 2.5 times those of vitamin C and vitamin E. The biological significance of this finding remains to be elucidated. In this work the antioxidant activity of a range of estrogens (phenolic, catecholic and stilbene-derived) has been studied. The activity of these substances as hydrogen-donating scavengers of free radicals in an aqueous solution has been determined by monitoring their relative abilities to quench the chromogenic radical cation 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS*+). The results show that the order of reactivity in scavenging this radical in the aqueous phase is dependent on the precise estrogenic structure, with phenolic estrogens being more potent antioxidants than catecholestrogens or diethylstilbestrol. The ability of the same estrogens to scavenge lipid phase radicals has also been assessed, determined by the ex vivo enhancement of the resistance of low-density lipoprotein (LDL) to oxidation; the order of efficacy is different from that in the aqueous phase, with the phenolic estrogens estriol, estrone and 17beta-estradiol being less potent than 2-hydroxyestradiol, 4-hydroxyestradiol, or diethylstilbestrol. In this lipid-based system, phenolic estrogens were found to be unable to regenerate alpha-tocopherol from LDL subjected to oxidative stress, while at the same time 2- and 4-hydroxyestradiol significantly delayed alpha-tocopherol loss. These results indicate that the various estrogens are good scavengers of free radicals generated in both the aqueous and the lipophilic phases. The antioxidant activity of an estrogen depends not only on the hydrophilic or lipophilic nature of the scavenged radical, but also on the phenol and catechol structures of the estrogen compound.     

The activity of recombinant human neuroglobin as an antioxidant and free radical scavenger

Free radicals are by-products of metabolism and exist in a homeostasis between generation and scavenging in vivo. Excessive free radicals cause various diseases, including nervous system diseases. Neuroglobin (Ngb), a nervous system-specific oxygen-binding protein, has been suggested to be a potential free radical scavenger in the nervous system in vivo; however, its underlying mechanism remains unclear. In this study, we investigated the antioxidant potential and free radical scavenging properties of recombinant human Ngb (rhNgb) in vitro. Interestingly, we found that the rhNgb protein itself has a direct and distinct antioxidant capacity and can efficiently scavenge a variety of free radicals, including the [2,2'-azino-di-(3-ethyl-benzthiazoline-6-sulfonic acid)] (ABTS) cation, superoxide anion, hydrogen peroxide, and hydroxyl radical. The capacity of rhNgb to scavenge the superoxide anion and hydrogen peroxide was even comparable to that of vitamin C. In addition, rhNgb had Fe(2+) chelating activity but hemoglobin did not. In conclusion, our results indicated that the rhNgb protein itself has antioxidant and free radical scavenging activities, providing fundamental evidence for the neuroprotective function of Ngb. These data provide key information for the origin of the neuroprotective and physiological role of Ngb and will promote the treatment of reactive oxygen species (ROS)-related diseases using this novel oxygen-binding globin.     

Role of vitamin E as a lipid-soluble peroxyl radical scavenger: in vitro and in vivo evidence

Multiple reactive oxygen/nitrogen species induce oxidative stress. Mammals have evolved with an elaborate defense network against oxidative stress, in which multiple antioxidant compounds and enzymes with different functions exert their respective roles. Radical scavenging is one of the essential roles of antioxidants and vitamin E is the most abundant and important lipophilic radical-scavenging antioxidant in vivo. The kinetic data and physiological molar ratio of vitamin E to substrates show that the peroxyl radicals are the only radicals that vitamin E can scavenge to break chain propagation efficiently and that vitamin E is unable to act as a potent scavenger of hydroxyl, alkoxyl, nitrogen dioxide, and thiyl radicals in vivo. The preventive effect of vitamin E against the oxidation mediated by nonradical oxidants such as hypochlorite, singlet oxygen, ozone, and enzymes may be limited in vivo. The synergistic interaction of vitamin E and vitamin C is effective for enhancing the antioxidant capacity of vitamin E. The in vitro and in vivo evidence of the function of vitamin E as a peroxyl radical-scavenging antioxidant and inhibitor of lipid peroxidation is presented.     

Oxidative damage shifts from lipid peroxidation to thiol arylation by catechol-containing antioxidants

Catechol-containing antioxidants are able to protect against lipid peroxidation by nonenzymatic scavenging of free radicals with their catechol moiety. During their antioxidant activity, catechol oxidation products such as semiquinone radicals and quinones are formed. These oxidation products of 4-methylcatechol inactivate the GSH-dependent protection against lipid peroxidation and the calcium sequestration in liver microsomes. This effect is probably due to arylation by oxidation products of 4-methylcatechol of free thiol groups of the enzymes responsible for the GSH-dependent protection and calcium sequestration, i.e. the free radical reductase and calcium ATPase. It is concluded that a catechol-containing antioxidant might shift radical damage from lipid peroxidation to sulfhydryl arylation.     

Tocotrienols, the unsaturated forms of vitamin E, can function as antioxidants and lipid protectors in tobacco leaves

Vitamin E is a generic term for a group of lipid-soluble antioxidant compounds, the tocopherols and tocotrienols. While tocotrienols are considered as important vitamin E components in humans, with functions in health and disease, the protective functions of tocotrienols have never been investigated in plants, contrary to tocopherols. We took advantage of the strong accumulation of tocotrienols in leaves of double transgenic tobacco (Nicotiana tabacum) plants that coexpressed the yeast (Saccharomyces cerevisiae) prephenate dehydrogenase gene (PDH) and the Arabidopsis (Arabidopsis thaliana) hydroxyphenylpyruvate dioxygenase gene (HPPD) to study the antioxidant function of those compounds in vivo. In young leaves of wild-type and transgenic tobacco plants, the majority of vitamin E was stored in thylakoid membranes, while plastoglobules contained mainly delta-tocopherol, a very minor component of vitamin E in tobacco. However, the vitamin E composition of plastoglobules was observed to change substantially during leaf aging, with alpha-tocopherol becoming the major form. Tocotrienol accumulation in young transgenic HPPD-PDH leaves occurred without any significant perturbation of photosynthetic electron transport. Tocotrienols noticeably reinforced the tolerance of HPPD-PDH leaves to high light stress at chilling temperature, with photosystem II photoinhibition and lipid peroxidation being maintained at low levels relative to wild-type leaves. Very young leaves of wild-type tobacco plants turned yellow during chilling stress, because of the strongly reduced levels of chlorophylls and carotenoids, and this phenomenon was attenuated in transgenic HPPD-PDH plants. While sugars accumulated similarly in young wild-type and HPPD-PDH leaves exposed to chilling stress in high light, a substantial decrease in tocotrienols was observed in the transgenic leaves only, suggesting vitamin E consumption during oxygen radical scavenging. Our results demonstrate that tocotrienols can function in vivo as efficient antioxidants protecting membrane lipids from peroxidation.     

Effects of tocopheryl quinone on the heart: model experiments with xanthine oxidase, heart mitochondria, and isolated perfused rat hearts

It is generally accepted that the protection effect of biological tissues by vitamin E is due to its radical scavenging potency in membranes, thereby being transformed to a vitamin E radical. A deficiency of appropriate reductants, which recycle vitamin E radicals back to its antioxidative active form, causes an irreversible degradation of vitamin E leading to tocopheryl quinone (TQ). TQ-like compounds were shown to result from both vitamin E and corresponding hydrophilic analogues of this antioxidant in vitro. In vivo elevated concentrations of tocopheryl quinones were detected after oxidative stress and TQ supplementation as well. Quinones in general are known to be efficient one-electron donors and acceptors. Therefore the question arises whether TQ-like compounds can undergo redox-cycling in conjunction with redox-active enzymes in the heart, thereby producing harmful oxygen radicals, or whether these compounds exhibit antioxidant properties. In order to elucidate this question we focused our interest on the interaction of TQ and a corresponding short-chain homologue (TQ(0)) with xanthine oxidase and heart mitochondria. Furthermore, we tested the influence of TQ on the recovery of isolated perfused rat hearts after ischemia/reperfusion. Our experiments revealed that hydrophilic TQ(0) was univalently reduced by xanthine oxidase (XOD) yielding semiquinone radicals in the absence of oxygen. However, under aerobic conditions TQ(0) enhanced the O(2)(*)(-) radical output of XOD. In the mitochondrial respiratory chain TQ was shown to interact with high potential cytochrome b in the bc(1) complex specifically. In contrast to the system XOD/TQ(0), lipophilic TQ in submitochondrial particles decreased the O(2)(*)(-) radical release during regular respiration possibly due to its interaction with b-cytochromes in the mitochondrial respiratory chain. In isolated rat hearts perfused with liposomes containing lipophilic TQ, it was efficiently accumulated in the heart tissue. When hearts were subjected to conditions of ischemia/reperfusion, infusion of TQ prior to ischemia significantly improved the recovery of hemodynamic parameters. Our results demonstrate that TQ derivatives may induce pro-oxidative and antioxidative effects depending on the distribution of TQ derivatives in the heart tissue and the interacting redox system.     

Lipid peroxyl radical intermediates in the peroxidation of polyunsaturated fatty acids by lipoxygenase. Direct electron spin resonance investigations

Lipid peroxyl radicals resulting from the peroxidation of polyunsaturated fatty acids by soybean lipoxygenase were directly detected by the method of rapid mixing, continuous-flow electron spin resonance spectroscopy. When air-saturated borate buffer (pH 9.0) containing linoleic acid or arachidonate acid was mixed with lipoxygenase, fatty acid-derived peroxyl free radicals were readily detected; these radicals have a characteristic g-value of 2.014. An organic free radical (g = 2.004) was also detected; this may be the carbon-centered fatty acid free radical that is the precursor of the peroxyl free radical. The ESR spectrum of this species was not resolved, so the identification of this free radical was not possible. Fatty acids without at least two double bonds (e.g. stearic acid and oleic acid) did not give the corresponding peroxyl free radicals, suggesting that the formation of bisallylic carbon-centered radicals precedes peroxyl radical formation. The 3.8-G doublet feature of the fatty acid peroxyl spectrum was proven (by selective deuteration) to be a hyperfine coupling due to a gamma-hydrogen that originated as a vinylic hydrogen of arachidonate. Arachidonate peroxyl radical formation was shown to be dependent on the substrate, active lipoxygenase, and molecular oxygen. Antioxidants are known to protect polyunsaturated fatty acids from peroxidation by scavenging peroxyl radicals and thus breaking the free radical chain reaction. Therefore, the peroxyl signal intensity from micellar arachidonate solutions was monitored as a function of the antioxidant concentration. The reaction of the peroxyl free radical with Trolox C was shown to be 10 times slower than that with vitamin E. The vitamin E and Trolox C phenoxyl radicals that resulted from scavenging the peroxyl radical were also detected.     

Vitamin E: action, metabolism and perspectives

Natural vitamin E includes four tocopherols and four tocotrienols. RRR-α-tocopherol is the most abundant form in nature and has the highest biological activity. Although vitamin E is the main lipid-soluble antioxidant in the body, not all its properties can be assigned to this action. As antioxidant, vitamin E acts in cell membranes where prevents the propagation of free radical reactions, although it has been also shown to have pro-oxidant activity. Non-radical oxidation products are formed by the reaction between α-tocopheryl radical and other free radicals, which are conjugated to glucuronic acid and excreted through the bile or urine. Vitamin E is transported in plasma lipoproteins. After its intestinal absorption vitamin E is packaged into chylomicrons, which along the lymphatic pathway are secreted into the systemic circulation. By the action of lipoprotein lipase (LPL), part of the tocopherols transported in chylomicrons are taken up by extrahepatic tissues, and the remnant chylomicrons transport the remaining tocopherols to the liver. Here, by the action of the “α-tocopherol transfer protein”, a major proportion of α-tocopherol is incorporated into nascent very low density lipoproteins (VLDL), whereas the excess of α-tocopherol plus the other forms of vitamin E are excreted in bile. Once secreted into the circulation, VLDL are converted into IDL and LDL by the action of LPL, and the excess of surface components, including α-tocopherol, are transferred to HDL. Besides the LPL action, the delivery of α-tocopherol to tissues takes place by the uptake of lipoproteins by different tissues throughout their corresponding receptors. Although we have already a substantial information on the action, effects and metabolism of vitamin E, there are still several questions open. The most intriguing is its interaction with other antioxidants that may explain how foods containing small amounts of vitamin E provide greater benefits than larger doses of vitamin E alone.     

The action of a homologous series of ubiquinols on lipid peroxidation in brain mitochondrial and synaptosomal membranes

The effects of inhibition of ubiquinols and ubiquinones with various length of isoprenoid chain on the lipid peroxidation in membranes of brain mitochondria and synaptosomes were studied. The efficiency of inhibition effects of ubiquinols depends on the length of isoprenoid chain. Ubiquinols with shorter isoprenoid chains demonstrated more effective inhibition.