Structure prerequisite for antioxidant activity of silybin in different biochemical systems in vitro.

Structural analogues (flavanone: 2-4 and flavone: 5 and 6, respectively) of silybin (1a) were synthesized and tested for inhibitory activity on O(2)(-) release and PKC translocation in PMA-stimulated neutrophils as well as xanthine oxidase activity in order to identify the molecular structures responsible for the antioxidant property of silybin. Concerning the prevention of hem-mediated oxidative modification of LDL by silybin, the hydroxyl radical scavenging activity of its structural analogues was also determined. We demonstrated that the basic skeleton of 1a (4) is responsible for its inhibitory activity on O(2)(-) release in PMA-stimulated neutrophils via inhibition of PKC translocation, since introduction of a double bound and hydroxyl groups at C-5 and C-7 position (5 and 6) did not result in further increase in inhibition of O(2)(-) release. It has been shown that the presence of the phenolic hydroxyl group at C-5 and C-7 of 1a is essential for the inhibition of xanthine oxidase activity. Moreover, introduction of a double bond into the C-ring of 2 and 3, resulting in flavone derivatives (5 and 6), markedly enhanced the antioxidant effect in all the tested systems. Finally, silybin (1a) and its flavon derivatives (5 and 6) directly scavenged hydroxyl radicals as well. On the basis of these results it might be concluded that different moiety of silybin is responsible for inhibition of overproduction of O(2)(-) in stimulated neutrophils, xanthine oxidase activity, and for prevention of hem-mediated oxidative modification of LDL.     

Significance of melatonin in antioxidative defense system: reactions and products

Melatonin is a potent endogenous free radical scavenger, actions that are independent of its many receptor-mediated effects. In the last several years, hundreds of publications have confirmed that melatonin is a broad-spectrum antioxidant. Melatonin has been reported to scavenge hydrogen peroxide (H(2)O(2)), hydroxyl radical (HO(.)), nitric oxide (NO(.)), peroxynitrite anion (ONOO(-)), hypochlorous acid (HOCl), singlet oxygen ((1)O(2)), superoxide anion (O(2)(-).) and peroxyl radical (LOO(.)), although the validity of its ability to scavenge O(2)(-). and LOO(.) is debatable. Regardless of the radicals scavenged, melatonin prevents oxidative damage at the level of cells, tissues, organs and organisms. The antioxidative mechanisms of melatonin seem different from classical antioxidants such as vitamin C, vitamin E and glutathione. As electron donors, classical antioxidants undergo redox cycling; thus, they have the potential to promote oxidation as well as prevent it. Melatonin, as an electron-rich molecule, may interact with free radicals via an additive reaction to form several stable end-products which are excreted in the urine. Melatonin does not undergo redox cycling and, thus, does not promote oxidation as shown under a variety of experimental conditions. From this point of view, melatonin can be considered a suicidal or terminal antioxidant which distinguishes it from the opportunistic antioxidants. Interestingly, the ability of melatonin to scavenge free radicals is not in a ratio of mole to mole. Indeed, one melatonin molecule scavenges two HO. Also, its secondary and tertiary metabolites, for example, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine, N-acetyl-5-methoxykynuramine and 6-hydroxymelatonin, which are believed to be generated when melatonin interacts with free radicals, are also regarded as effective free radical scavengers. The continuous free radical scavenging potential of the original molecule (melatonin) and its metabolites may be defined as a scavenging cascade reaction. Melatonin also synergizes with vitamin C, vitamin E and glutathione in the scavenging of free radicals. Melatonin has been detected in vegetables, fruits and a variety of herbs. In some plants, especially in flowers and seeds (the reproductive organs which are most vulnerable to oxidative insults), melatonin concentrations are several orders of magnitude higher than measured in the blood of vertebrates. Melatonin in plants not only provides an alternative exogenous source of melatonin for herbivores but also suggests that melatonin may be an important antioxidant in plants which protects them from a hostile environment that includes extreme heat, cold and pollution, all of which generate free radicals.     

Effect of α-Tocopherol Succinate on Free Radical and Lipid Peroxidation Levels in BL6 Melanoma Cells

Numerous studies have proposed a radical or oxidant involvement in a number of degenerative diseases such as cancer. This has led to suggestions that the supplementation of antioxidants such as α-tocopherol (vitamin E) may function to reduce the growth of cancer. In this study, a nonmalignant Monkey kidney (LLCMK) and a malignant Murine melanoma (BL6-F10) cell line were supplemented with varying levels of α-Tocopherol acid succinate (vitamin E succinate) ranging from 1 to 10 μg/ml. BL6-F10 cells supplemented with 5, 7, and 10 μg/ml vitamin E succinate, showed significant decreases in cell proliferation, and this decrease was accompanied by a concomitant increase rather than a decrease in the levels of free radicals and lipid peroxidation. LLCMK cells supplemented with 1–10 μg/ml vitamin E succinate showed no significant increase or decrease in growth, while the levels of lipid peroxidation were shown to be insignificantly elevated at 5, 7, and 10 μg/ml vitamin E succinate. Free radical levels in LLCMK cells were significantly decreased at 1 μg/ml vitamin E succinate, while at 3, 5, 7, and 10 μg/ml supplementary vitamin E succinate, free radical levels increased compared to the 1 μg/ml group, but not compared to control cultures. These results suggest that the inhibitory effects of vitamin E succinate on BL6-F10 cell growth in vitro is not a consequence of its antioxidant properties, but may, in fact, be due to one or more of its other potential roles within the cells, such as the regulation of cellular enzyme activities involved in growth. © 1997 Elsevier Science Inc.     

Effect of vitamin supplementation on cytokine response and on muscle damage after strenuous exercise

The present double-blinded, placebo-controlled study investigated whether antioxidant vitamin supplementation was able to modulate the cytokine and lymphocyte responses after strenuous eccentric exercise. Furthermore, muscle enzyme release was examined to see whether antioxidant treatment could reduce muscle damage. Twenty male recreational runners randomly received either antioxidants (500 mg of vitamin C and 400 mg of vitamin E) or placebo for 14 days before and 7 days after a 5% downhill 90-min treadmill run at 75% .VO(2 max). Although the supplemented group differed significantly with regard to plasma vitamin concentration before and after exercise when compared with the placebo group, the two groups showed identical exercise-induced changes in cytokine, muscle enzyme, and lymphocyte subpopulations. The plasma level of interleukin (IL)-6 and IL-1 receptor antagonist increased 20- and 3-fold after exercise. The plasma level of creatine kinase was increased sixfold the day after exercise. The concentrations of CD4+ memory T cells, CD8+ memory and na?ve T cells, and natural killer cells increased at the end of exercise. The total lymphocyte concentration was below prevalues in the postexercise period. In conclusion, the present study does not support the idea that exercise-induced inflammatory responses are induced by free oxygen radicals.     

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.     

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.     

Recycling and antioxidant activity of tocopherol homologs of differing hydrocarbon chain lengths in liver microsomes

Tocopherols (vitamin E) function as inhibitors of lipid peroxidation in biomembranes by donating a hydrogen atom to the chain propagating lipid radicals, thus giving rise to chromanoxyl radicals of the antioxidant. We have shown that alpha-tocopherol homologs differing in the lengths of their hydrocarbon side chains (alpha-Cn) manifest strikingly different antioxidant potencies in membranes. The antioxidant activity of tocopherol homologs during (Fe2+ + ascorbate)- or (Fe2+ + NADPH)-induced lipid peroxidation in rat liver microsomes increased in the order alpha-tocopherol (alpha-C16) less than alpha-C11 less than alpha-C6 less than alpha-C1. Chromanoxyl radicals generated from alpha-tocopherol and its more polar homologs by an enzymatic oxidation system (lipoxygenase + linolenic acid) can be recycled in rat liver microsomes by NAD-PH-dependent electron transport or by ascorbate. The efficiency of recycling increased in the same order: alpha-tocopherol (alpha-C16) less than alpha-C11 less than alpha-C6 less than alpha-C1. Thus the high efficiency of regeneration of short-chain homologs of vitamin E may account for their high antioxidant potency.     

Fluorescence quenching of dipyridamole associated to peroxyl radical scavenging: a versatile probe to measure the chain breaking antioxidant activity of biomolecules

Dypiridamole is a highly efficient chain breaking antioxidant (Iuliano et al., Free Radic. Biol. Med. 18 (1995) 239-247) with an aromatic ring system responsible for an intense absorption band in the 400-480-nm region and for an intense fluorescence. Dipyridamole fluorescence is quantitatively quenched upon reaction with peroxyl radicals. In the presence of a flux of peroxyl radicals generated by thermal dissociation of azo-initiators, dipyridamole fluorescence decays linearly, showing a first-order reaction with respect to peroxyl radicals, and zero-order with respect to dipyridamole. The pH optimum for the fluorescence quenching is in the 7-8 range, from pH 7 to 6, the decay of fluorescence rapidly decreases to became negligible below pH 5.5. Dipyridamole consumption is blocked in the presence of an added chain breaking antioxidant for a time that is proportional to the antioxidant concentration. This effect is shown for ascorbic acid, trolox, vitamin E, uric acid, and N, N'-diphenyl-p-phenylenediamine. The slope of the linear correlation relative to trolox allows calculation of the bimolecular rate constant for a given molecule and peroxyl radicals. Comparison of data obtained by the dipyridamole consumption are comparable to values obtained by the oxygen consumption method.     

Ferulic acid dehydrodimers from wheat bran: isolation,purification and antioxidant properties of 8-0-4-diferulic acid

Summary

Wheat bran contains several ester-linked dehydrodimers of ferulic acid, which were detected and quantified after sequential alkaline hydrolysis. The major dimers released were: trans-5-[(E)-2-carboxyvinyl]-2-(4-hydroxy-3-methoxy-phenyl)-7-methoxy-2,3-dihydrobenzofuran-3-carboxylic acid (5–8-BendiFA), (Z)-β-(4-[(E)-2-carboxyvinyl]-2-methoxy-phenoxy)-4-hydroxy-3-methoxycinnamic acid (8-O-4-diFA) and (E,E)-4,4′-dihydroxy-5,5′-dimethoxy-3,3′-bicinnamic acid (5–5-diFA). trans-7-hydroxy-1-(4-hydroxy-3methoxyphenyl)-6-methoxy-1,2-dihydro-naphthalene-2,3-dicarboxylic acid (8–8-diFA cyclic form) and 4,4′-dihydroxy-3,3′-dimethoxy-β,β'-bicinnamic acid (8–8-diFA non cyclic form) were not detected. One of the most abundant dimers, 8-O-4-diFA, was purified from de-starched wheat bran after alkaline hydrolysis and preparative HPLC. The resultant product was identical to the chemically synthesised 8-O-4-dimer by TLC and HPLC as confirmed by ¹H-NMR and mass spectrometry. The absorption maxima and absorption coefficients for the synthetic compound in ethanol were: λ_max: 323 nm, λ_min: 258 nm, ε_λmax (M^?1cm^?1): 24800 ± 2100 and ε₂₈₀ (M^?1cm^?1): 19700 ± 1100. The antioxidant properties of 8-O-4-diFA were assessed using: (a) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes and; (b) scavenging of the radical cation of 2,2′-azinobis (3-ethyl-benzothiazoline-6-sulphonate) (ABTS) relative to the water-soluble vitamin E analogue, Trolox C. The 8-O-4-diFA was a better antioxidant than ferulic acid in both lipid and aqueous phases. This is the first report of the antioxidant activity of a natural diferulate obtained from a plant.     

Recycling of vitamin E in human low density lipoproteins.

Oxidative modification of low density lipoproteins (LDL) and their unrestricted scavenger receptor-dependent uptake is believed to account for cholesterol deposition in macrophage-derived foam cells. It has been suggested that vitamin E that is transported by LDL plays a critical role in protecting against LDL oxidation. We hypothesize that the maintenance of sufficiently high vitamin E concentrations in LDL can be achieved by reducing its chromanoxyl radicals, i.e., by vitamin E recycling. In this study we demonstrate that: i) chromanoxyl radicals of endogenous vitamin E and of exogenously added alpha-tocotrienol, alpha-tocopherol or its synthetic homologue with a 6-carbon side-chain, chromanol-alpha-C6, can be directly generated in human LDL by ultraviolet (UV) light, or by interaction with peroxyl radicals produced either by an enzymic oxidation system (lipoxygenase + linolenic acid) or by an azo-initiator, 2,2'-azo-bis(2,4-dimethylvaleronitrile) (AMVN; ii) ascorbate can recycle endogenous vitamin E and exogenously added chromanols by direct reduction of chromanoxyl radicals in LDL; iii) dihydrolipoic acid is not efficient in direct reduction of chromanoxyl radicals but recycles vitamin E by synergistically interacting with ascorbate (reduces dehydroascorbate thus maintaining the steady-state concentration of ascorbate); and iv) beta-carotene is not active in vitamin E recycling but may itself be protected against oxidative destruction by the reductants of chromanoxyl radicals. We suggest that the recycling of vitamin E and other phenolic antioxidants by plasma reductants may be an important mechanism for the enhanced antioxidant protection of LDL.     

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.     

Quantitative measurement of the total, peroxyl radical-trapping antioxidant capability of human blood plasma by controlled peroxidation. The important contribution made by plasma proteins

Plasma obtained from fasted humans has been analysed for total radical-trapping antioxidant content by subjecting it to controlled peroxidation using the thermal decomposition of water-soluble azobis (2-amidinopropane hydrochloride) at 37 degrees C to produce peroxyl radicals at a known, steady rate. It is found that the total radical-trapping antioxidant content is rather similar for the 7 subjects that have been tested and, furthermore, it is 10-20-times larger than the effect attributable to vitamin E alone. Although it is shown that urate and ascorbate augment the contribution from vitamin E, their contributions (21-34 and 0-2%, respectively) still leave 57-73% of the total antioxidant content unaccounted for. Evidence is presented to show that this previously unrecognized large reserve of antioxidant capacity is attributable to the plasma proteins.     

Reactivity of ebselen and related selenoorganic compounds with 1,2-dichloroethane radical cations and halogenated peroxyl radicals

The reactivity of ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)one, and structurally related analogues was studied by pulse radiolysis. The rate constant for the reaction of ebselen with trichloromethylperoxyl radicals was determined to be 2.9 X 10(8) M-1 s-1, while its sulfur analogue, 2-phenyl-1,2-benzisothiazol-3(2H)one, was oxidized at much lower rates, k less than or equal to 10(7) M-1 s-1. Among several derivatives studied, the only other compound that exhibited a high rate constant was 2-(methylseleno)-benzoic acid-N-phenylamide. Oxidation of ebselen by other halogenated peroxyl radicals was also carried out and revealed a direct relationship between rate constant and the degree of halogenation of the oxidant. The transient radicals generated during oxidation of ebselen and the analogues were characterized by optical absorption and conductivity measurements and were attributed to one-electron-oxidized radical cations. The oxidation potentials were determined by cyclic voltammetry. Comparative evaluation of the in vitro behavior during microsomal lipid peroxidation revealed ebselen to be the most potent antioxidant of the compounds investigated, 2-(Methylseleno)-benzoic acid-N-phenylamide, despite its high rate constant for oxidation by halogenated peroxyl radicals, was found to be a poor antioxidant. The rate constant of oxidation of ebselen by trichloromethylperoxyl radicals is comparable to that of alpha-tocopherol under similar conditions, underscoring the potential pharmacological interest of ebselen as an antioxidant.     

Evaluation of antioxidant activity of <Emphasis Type="Italic">Melothria maderaspatana in vitro</Emphasis>

In this study, an aqueous extract of leaves from Melothria maderaspatana was tested for in vitro antioxidant activity. Free radical scavenging assays, such as hydroxyl radical, hydrogen peroxide, superoxide anion radical and 2,2-diphenyl-1-picryl hydrazyl (DPPH), 2,2’-azinobis-(3-ethyl-enzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, and reducing power assay, were studied. The extract effectively scavenged hydroxyl radical, hydrogen peroxide and superoxide anion radicals. It also scavenged DPPH and ABTS radicals. Furthermore, it was found to have reducing power. All concentrations of leaf extract exhibited free radical scavenging and antioxidant power, and the preventive effects were in a dose-dependent manner. The antioxidant activities of the above were compared to standard antioxidants such as butylated hydroxytoluene (BHT), ascorbic acid, and α-tocopherol. The results obtained in the present study indicate that the M. maderaspatana extract could be considered a potential source of natural antioxidant.     

Potential therapeutic antioxidants that combine the radical scavenging ability of myricetin and the lipophilic chain of vitamin E to effectively inhibit microsomal lipid peroxidation

The flavonol myricetin, reacts with oxygen-centred galvinoxyl radicals 28 times faster than d-alpha-tocopherol (vitamin E), the main lipid-soluble antioxidant in biological membranes. Moreover, each myricetin molecule reduces twice as many such radicals as vitamin E. However, myricetin fails to protect vitamin E-deficient microsomes from lipid peroxidation as assessed by the formation of thiobarbituric acid reactive substances (TBARS). Novel and potentially therapeutic antioxidants have been prepared that combine the radical-scavenging ability of a myricetin-like head group with a lipophilic chain similar to that of vitamin E. C(6)-C(12) alkyl chains are attached to the A-ring of either a 3,3',4',5'-tetrahydroxyflavone or a 3,2',4',5'-tetrahydroxyflavone head group to give lipophilic flavonoids (C log P = 4 to 10) that markedly inhibit iron-ADP catalysed oxidation of microsomal preparations. Orientation of the head group as well as total lipophilicity are important determinants of antioxidant efficacy. MM2 models indicate that our best straight chain 7-alkylflavonoids embed to the same depth in the membrane as vitamin E. The flavonoid head groups are prepared by aldol condensation followed by Algar-Flynn-Oyamada (AFO) oxidation or by Baker-Venkataraman rearrangement. The alkyl tails are introduced by Suzuki or Negishi palladium-catalysed cross-coupling or by cross-metathesis catalysed by first generation Grubbs catalyst, which tolerate phenolic hydroxyl and ketone groups.     

Kinetic study of the reaction of vitamin C with vitamin E radicals (tocopheroxyls) in solution

New stable vitamin E radicals (7-tert-butyl-5-isopropyltocopheroxyl (4), 5,7-diisopropyltocopheroxyl (5), 7-tert-butyl-5-methyltocopheroxyl (6), and 5,7-diethyltocopheroxyl (7] with two bulky alkyl substituents at ortho positions (C-5 and C-7) have been prepared, and the reaction rates of vitamin C (ascorbic acid (1) and 6-O-stearyl ascorbic acid (2] with these tocopheroxyl radicals in benzene/ethanol/water (2:1:0.1, v/v) solution have been determined spectrophotometrically, using a stopped-flow technique. The second-order rate constants, k2, obtained vary in the order of 10(3), and decrease dramatically in the order 7 greater than 6 greater than 5 greater than 4, as the size of two ortho-alkyl groups in tocopheroxyl increases. The result suggests that the effect of steric hindrance on the reaction rate is considerable. These reaction rates were compared with those of vitamin C with alpha-tocopheroxyl reported by Packer et al. (Nature 278 (1979) 737-738) and Scarpa et al. (Biochim. Biophys. Acta 801 (1984) 215-219).     

Cyclic dipeptides exhibit potency for scavenging radicals

Twenty kinds of cyclic dipeptides containing l-leucine were synthesized, and their antioxidant activity against ·OH and O(2)(·-) was investigated. Compounds possessing polar amino acid residues, such as Asp, Cys, Glu, Lys, Pro, Ser, and Trp, exhibited higher antioxidant activity against ·OH than vitamin E. However, only cyclo(l-Cys-l-Leu) scavenged O(2)(·-).     

Antioxidant properties of nitecapone (OR-462).

Nitecapone [3-(3,4-dihydroxy-5-nitrophenyl)methylene-2,4-pentanedione] [OR-462] is a catechol-O-methyltransferase inhibitor with gastroprotective properties. Recently, its antioxidant properties have been discovered: It scavenges peroxyl radicals (ROO.) and thus spares glutathione. Further examination of the properties of nitecapone demonstrated a remarkable ability of this compound to act as an antioxidant: (1) to scavenge ROO. in solution with a stoichiometry factor of 2; (2) to scavenge ROO. in membranes; (3) to inhibit lipid peroxidation; (4) to act as a competitive inhibitor for xanthine oxidase with Ki of 8.8 microM; (5) to scavenge O2- with a second order kinetic rate constant of 1.0 x 10(4) M-1 s-1; and (6) to scavenge HO.. Nitecapone also interacts with oxidation product of ascorbate to participate in recycling of vitamin E. Thus, nitecapone potentially is an effective therapeutic antioxidant, and the use of this compound in a combination with other antioxidants may be beneficial.     

New data on the genus Chrysotoxum Meigen (Diptera: Syrphidae) from North-East Turkey,Armenia, Azerbaijan and Iran including descriptions of three new species

New data and records of the genus Chrysotoxum Meigen, 1803 are reported, arising from taxonomic and faunistic examination of adult specimens collected from 1920 to 2011 from four northeastern provinces of Turkey (Erzurum, Bayburt, Kars, and Artvin), and from the neighboring countries of Armenia, Azerbaijan and Iran. Three new species are described: Chrysotoxum antennalis Vuji?, Nedeljkovi? &; Hayat sp. n., C. clausseni Vuji?, Nedeljkovi? &; Hayat sp. n. and C. persicum Vuji?, Nedeljkovi? &; Hayat sp. n. The first two are known only from northeastern Turkey, and the third also occurs in Armenia, Azerbaijan and Iran. These new species have in common an antenna with the basoflagellomere being shorter than the scape and pedicel together.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:4C264678-8E47-4DE0-AC7D-91DABC597BCD     

苦槛蓝叶的黄酮类成分及其荔枝霜疫霉抑制活性研究

为了解苦槛蓝(Myoporum bontioides)的化学成分,采用色谱分离法从叶中分离得到11个化合物,分别鉴定为：5,7,3’-三羟基-4’-甲氧基黄酮(1)、3,5,7,4’-四羟基-3’-甲氧基黄酮(2)、5,7,4’-三羟基-3’,5’-二甲氧基黄酮(3)、木犀草素(4)、山奈酚(5)、鼠李黄素(6)、5,7-二羟基二氢黄酮(7)、7,4’-二羟基二氢黄酮(8)、5,7,3’,4’-四羟基二氢黄酮(9)、5-O-乙酰基-3,7,3’,4’-四羟基二氢黄酮(10)和7-甲氧基香橙素(11)。除化合物4、7、11之外,其他化合物均为首次从苦槛蓝叶中分离得到。菌丝生长速率法测试表明化合物4、7～9和11对荔枝霜疫霉菌具有较好的抑菌活性。