Free radical scavenging reactions and antioxidant activity of embelin: biochemical and pulse radiolytic studies

Embelin (from Embelia ribes) is a component of herbal drugs and possess wide range of medicinal properties. These properties may be, in part, due to scavenging of oxidizing free radicals. In this context, free radical scavenging reactions and antioxidant activity of embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone) have been studied. It has been found to scavenge DPPH radical and inhibit hydroxyl radical induced deoxyribose degradation. It has been also found to inhibit lipid peroxidation and restore impaired Mn-superoxide dismutase in rat liver mitochondria. Further, kinetics and mechanism of the reactions of embelin with hydroxyl, one-electron oxidizing, organo-haloperoxyl and thiyl radicals have been studied using nanosecond pulse radiolysis technique. Its redox potential has been also evaluated with cyclic voltammetry. These studies suggest that embelin can act as a competitive antioxidant in physiological conditions.     

Synthesis and antioxidant evaluation of novel silybin analogues

In this work, we evaluated the antioxidant properties of the eight novel silybin analogues for their capacity to scavenge free radicals including superoxide anion radicals and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals in vitro. Compound 7d demonstrated an excellent antioxidant effect in scavenging superoxide anion free radical with an IC₅₀ value of 26.5 μM, while the IC₅₀ of quercetin (the reference compound) was 38.1 μM. Compounds 7b, 7e, 7h showed certain scavenging activities for both types of free radicals.     

Synthesis and antioxidant evaluation of novel silybin analogues

In this work, we evaluated the antioxidant properties of the eight novel silybin analogues for their capacity to scavenge free radicals including superoxide anion radicals and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals in vitro. Compound 7d demonstrated an excellent antioxidant effect in scavenging superoxide anion free radical with an IC50 value of 26.5 microM, while the IC50 of quercetin (the reference compound) was 38.1 microM. Compounds 7b, 7e, 7h showed certain scavenging activities for both types of free radicals.     

Effect of silybin dihemisuccinate on the ethanol metabolizing systems of the rat liver

Silybin dihemisuccinate produces a decrease in the ethanol metabolic rate of rats. This effect is ascribed to an inhibition of the microsomal ethanol oxidizing system (MEOS). Alcohol dehydrogenase activity, catalase activity and NADPH cytochrome c reductase activity are not affected by the flavonoid. It is proposed that the inhibition of MEOS by silybin dihemisuccinate is related to its antioxidant properties, acting as a scavenger of the free radicals involved in ethanol metabolism by this enzymatic system. This observation may have therapeutical implications because microsomal lipid peroxidation induced by hydroxyl free radicals has been related to the etiology of hepatic alcoholic disease.     

Free radical scavenging reactions of sulfasalazine, 5-aminosalicylic acid and sulfapyridine: mechanistic aspects and antioxidant activity

Reactions of sulfasalazine (SAZ) and its metabolites, 5-aminosalicylic acid (5-ASA) and sulfapyridine (SP), with various oxidizing and reducing free radicals (hydroxyl, haloperoxyl, one-electron oxidizing, lipid peroxyl, glutathiyl, superoxide, tryptophanyl, etc.) have been studied to understand the mechanistic aspects of its action against free radicals produced during inflammation. Nanosecond pulse radiolysis technique coupled with transient spectrophotometry has been used for in situ generation of free radicals and to follow their reaction pathways. The transients produced in these reactions have been assigned and radical scavenging rate constants have been measured. In addition to scavenging of various primary and secondary free radicals by SAZ, 5-ASA and SP, 5-ASA has also been observed to efficiently scavenge radicals of biomolecules. 5-ASA has been found to be the active moiety of SAZ involved in the scavenging of oxidizing free radicals whereas reduction of SAZ produced molecular radical anion. The study suggests that free radical scavenging activity of 5-ASA may be a major path of pharmacological action of SAZ against inflammatory bowel diseases (IBD).     

樟芝发酵液和菌丝体提取物抗氧化性能研究

采用甲醇、乙醇、异丙醇对樟芝发酵液和菌丝体进行提取,对其不同提取物进行还原力,DPPH、羟基自由基、超氧自由基、过氧化氢清除能力,亚铁离子螯合能力等抗氧化能力的测定。比较发酵液提取物和菌丝体提取物的抗氧化效果,比较不同提取剂提取物的抗氧化效果。结果显示:(1)发酵液提取物还原力最高的为异丙醇提取物,亚铁离子螯合能力最强的为乙醇提取物;DPPH清除能力乙醇和异丙醇提取物最高都达到97.88%;羟基自由基清除能力最高的为乙醇提取物,达到84.22%;3种提取物的超氧自由基清除能力都较高,具有最高清除率的异丙醇提取物达到94.89%;过氧化氢清除能力最高的为乙醇提取物的97.53%。(2)菌丝体提取物还原力最高和亚铁离子螯合能力最强的均为乙醇提取物;DPPH清除能力最高的为乙醇提取物的89.95%;3种提取物的羟基自由基清除能力普遍偏低,最高的仅为异丙醇提取物的37.28%;超氧自由基清除能力则普遍较高,最高为甲醇提取物的90.05%;过氧化氢清除能力最高的为乙醇和异丙醇提取物,最高清除率均为95.06%。抗氧化性能的研究比较,为进一步开发利用樟芝提供了依据。     

Diaziquone as a potential agent for photoirradiation therapy: formation of the semiquinone and hydroxyl radicals by visible light

When diaziquone was irradiated with 500 nm visible light, hydroxyl free radicals as well as the diaziquone semiquinone were produced. The diaziquone semiquinone is a stable free radical that exhibits a characteristic 5-line electron spin resonance (ESR) spectrum. Since hydroxyl free radicals are short lived, and not observable by conventional ESR, the nitrone spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) was used to convert hydroxyl radicals into longer lived ESR detectable spin adducts. The formation of hydroxyl radicals was further confirmed by investigating reactions in which hydroxyl radical scavangers, sodium formate and dimethylsulfoxide, compete with the spin traps DMPO or POBN (alpha-(4-Pyridyl-1-oxide)-N- tert-butylnitrone) for hydroxyl free radicals. The products of these scavenging reactions were also trapped with DMPO or POBN. If drug free radicals and hydroxyl free radicals are important in the activity of quinone-containing antitumor agents, AZQ may have a potential in photoirradiation therapy or photodynamic therapy.     

Analysis of antioxidant metabolites by solvent extraction from sclerotia of Inonotus obliquus (Chaga)

Introduction – The sclerotia of Inonotus obliquus (Chaga) are effective therapeutic agents to treat several human malignant tumours and other diseases without unacceptable toxic side‐effects. Objective – To investigate solvent effects on metabolic profiles and antioxidant activities of extracts of Chaga. Methodology – Chaga was extracted by petroleum ether, chloroform, ethyl acetate, acetone, ethanol and water. Solvent effects on metabolites in the extracts were assayed by NMR‐based metabolomic analysis. Antioxidant activities were indicated as capacities for scavenging superoxide anion, DPPH and hydroxyl radicals. Results – Petroleum ether and chloroform extracts contained primarily lanostane‐type triterpenoids (LT), whereas the extracts of ethyl acetate, acetone and ethanol were characterised by the predominant presence of hispidin analogues and LT, and water extracts by polysaccharides and phenolic compounds. The ethyl acetate, acetone, ethanol and water extracts revealed remarkable potential for scavenging the tested radicals, while those of petroleum ether and chloroform did not. Polyphenols are the major contributors for quenching the tested free radicals, while in LT only compounds 16 , 17 and 22 participated in scavenging hydroxyl radicals. Conclusion – Polyphenols in Chaga are the principles for quenching free radicals while polysaccharides and a few LT compounds contribute partially in scavenging DPPH and hydroxyl radicals, respectively. NMR‐based metabolomic analysis is a useful method by which to correlate ¹H‐NMR spectra of Chaga extracts with their antioxidant activities, and this allows the prediction of potentials for scavenging free radicals by ¹H‐NMR spectroscopy. Copyright © 2011 John Wiley & Sons, Ltd.     

银耳碱提多糖的纯化、化学表征及其抗氧化作用的研究(英文)

研究银耳孢子发酵物中的多糖类化学成分,并探讨了分离得到的一个多糖组分的抗氧化活性。银耳孢子发酵粉用热水煮提除去水溶性组分后,再采用0.5 mol.L-1的氢氧化钠溶液提取,Sevage法除蛋白,用乙醇沉淀得到粗多糖。粗多糖经DEAE-32-纤维素和Sephadex G-200分离纯化得到分布均一的多糖TFBP-A。糖组成分析显示,TFBP-A单糖组成为:甘露糖:半乳糖:葡萄糖,摩尔比为90∶5∶5;HPGPC测定TFBP-A分子量为58962。TFBP-A的抗氧化活性实验显示:在H2O2引起的红细胞溶血试验中,以蒸馏水抑制率为0%计算,TFBP-A抑制率为78.6%;在超氧阴离子自由基的清除作用实验中,TFBP-A最高抑制率为53%;在清除羟基自由基实验中,TFBP-A的EC50为0.191 mg.mL-1。从银耳孢子发酵物中用碱液提取得到的多糖组分TFBP-A为酸性杂多糖,重均分子量为58962,且具有一定的抗氧化活性。     

水杨酸酰化对胭脂萝卜天竺葵素稳定性和抗氧化活性的影响

为探究水杨酸作为酰化剂对胭脂萝卜天竺葵素的稳定性和抗氧化活性的影响,以保留率为指标,分析光、温度、金属离子、pH及氧化剂对酰化天竺葵素稳定性的影响,探究酰化天竺葵素对羟自由基、DPPH自由基和ABTS自由基的清除能力。结果表明:酰化天竺葵素对光、温度、Al3+、pH的稳定性显著提高,对Fe2+、Mg2+和Zn2+以及氧化剂H2O2的稳定性无显著差影响。酰化天竺葵素对羟自由基、DPPH自由基和ABTS自由基的清除能力与未酰化天竺葵素无显著差异。以上结果表明采用水杨酸酰化胭脂萝卜天竺葵素不影响其抗氧化活性,还能提高其对光照、温度、pH及铝离子的稳定性。     

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.     

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.     

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.     

Antioxidant effects of the VO(IV) hesperidin complex and its role in cancer chemoprevention

Vanadium compounds are known for a variety of pharmacological properties. Many of them display antitumoral and osteogenic effects in several cell lines. Free radicals induce the development of tumoral processes. Natural polyphenols such as flavonoids have antioxidant properties since they scavenge different free radicals. For these reasons it is interesting to investigate the effects of a new complex generated between the vanadyl(IV) cation and the flavonoid hesperidin. The complex has been synthesized and characterized by physicochemical methods. Spectroscopic analysis revealed a 1:1 stoichiometry of ligand:VO and coordination by deprotonated cis-hydroxyl groups to the disaccharide moiety of the ligand. The complex improves the superoxide dismutase (SOD)-like activity of the ligand, but the scavenging of other radicals tested does not change upon complexation. When tested on two tumoral cell lines in culture (one of them derived from a rat osteosarcoma UMR106 and the other from human colon adenocarcinoma Caco-2), the complex enhanced the antiproliferative effects of the free ligand, and this effect correlated with the morphological alterations toward apoptosis. Also, on the osteoblastic cell line the complex stimulated cell proliferation and collagen type I production at low concentrations. At higher doses the complex behaved as a cytotoxic compound for the osteoblasts.     

球孢白僵菌不同菌株清除自由基活性评价

选择不同来源的12株球孢白僵菌,分别测定菌丝体2种溶剂提取物在不同抗氧化模型中的抗氧化作用。结果表明,不同溶剂提取物对二苯基苦味酰基苯肼自由基(DPPH)和羟自由基(.OH)均有清除作用,但是清除自由基的活性不同,乙酸乙酯提取物对.OH的清除作用最为显著,活性较高,最高清除率达到71.54%。甲醇提取物活性均较低,30 min时甲醇提取物对DPPH和.OH清除率最高分别为36%和38.96%,12株白僵菌间的清除自由基活性有较大的差异。     

Antioxidant Activities of Aqueous Extract from Cultivated Fruit-bodies of Cordyceps militaris （L.） Link In Vitro

Biological antloxldants extracted from plants and fungi have potential abilities to scavenge free radicals and Inhibit lipid peroxldatlon, playing Important roles in preventing diseases, for example, cancer, and aging Induced by reactive oxygen species, which may cause oxidative damage to DNA, proteins and other macromolecules. The antloxldant potency of cultivated fruit-bodies of Cordyceps militarls （L.） Link was investigated In this study. Five established In vitro systems were employed, including the 1,1-dlphenyl-2- plcryldrazyl （DPPH） free radical scavenging, hydroxyl radical eliminating, iron chelating, Inhibition of Ilnolelc acid lipid peroxldatlon and reducing power. The aqueous extract from cultivated fruit-bodies was subjected to the test of amino acid, polysaccharlde and mannitol. Ascorblc acid （Vc）, butylated hydroxytoluene （BHT） and ethylenedlamlnetetraacetlc acid （EDTA） were used as positive controls for comparisons. Among the assays, the aqueous extract of C. mllltarls frult-bodles shows a significant scavenging effect on DPPH, eliminating the capability on hydroxyl radicals and the chelating effect on ferrous Iron. The extract also shows positive results of Inhibiting Ilnoleic acid lipid peroxldatlon and reducing power.     

Oxidised derivatives of silybin and their antiradical and antioxidant activity

Carboxylic acids derived from silybin (1) and 2,3-dehydrosilybin (2) with improved water solubility were prepared by selective oxidation of parent compounds and a new inexpensive method for preparation of 2,3-dehydrosilybin from silybin was developed and optimised. The antioxidative properties of the above-mentioned compounds and of side product 3a from oxidation of compound 1 were determined by cyclic voltammetry, free radical scavenging (DPPH, superoxide) assays, and by inhibition of in vitro generated liver microsomal lipid peroxidation. Dehydrogenation at C((2))-C((3)) in flavonolignans (silybin vs 2,3-dehydrosilybin; silybinic acid vs 2,3-dehydrosilybinic acid) strongly improved antioxidative properties (analogously as in flavonoids taxifolin vs quercetin). Thus, in antioxidative properties, dehydrosilybin was superior to silybin by one order, but its water solubility is too low for application in aqueous milieu. On the other hand, 2,3-dehydrosilybinic acid is a fairly soluble derivative with antilipoperoxidation and antiradical activities better than that of silybin.     

Antioxidant properties of the melatonin metabolite N1-acetyl-5-methoxykynuramine (AMK): scavenging of free radicals and prevention of protein destruction

Abstract

In numerous experimental systems, the neurohormone melatonin has been shown to protect against oxidative stress, an effect which appears to be the result of a combination of different actions. In this study, we have investigated the possible contribution to radical scavenging by substituted kynuramines formed from melatonin via pyrrole ring cleavage. N¹-Acetyl-5-methoxykynuramine (AMK), a metabolite deriving from melatonin by mechanisms involving free radicals, exhibits potent antioxidant properties exceeding those of its direct precursor N¹-acetyl-N²-formyl-5-methoxykynuramine (AFMK) and its analog N¹-acetylkynuramine (AK). Scavenging of hydroxyl radicals was demonstrated by competition with ABTS in a Fenton reaction system at pH 5 and by competition with DMSO in a hemin-catalyzed H₂O₂ system at pH 8. Under catalysis by hemin, oxidation of AMK was accompanied by the emission of chemiluminescence. AMK was a potent reductant of ABTS cation radicals, but, in the absence of catalysts, a poor scavenger of superoxide anions. In accordance with the latter observation, AMK was fairly stable in a pH 8 H₂O₂ system devoid of hemin. Contrary to AFMK, AMK was easily oxidized in a reaction mixture generating carbonate radicals. In an oxidative protein destruction assay based on peroxyl radical formation, AMK proved to be highly protective. No prooxidant properties of AMK were detected in a sensitive biological test system based on light emission by the bioluminescent dinoflagellate Lingulodinium polyedrum. AMK may contribute to the antioxidant properties of the indolic precursor melatonin.     

黄伞胞外多糖抗自由基作用的研究

目的:以乙醇沉淀的黄伞发酵浓缩液得到的胞外多糖为研究对象,检验其对自由基的清除作用。方法:采用电子顺磁共振(EPR)波谱仪检测黄伞胞外多糖清除羟自由基OH.和超氧阴离子自由基O2-.的作用。结果:在样品浓度均为100mg/mL的条件下,利用Fenton反应体系,黄伞胞外多糖对羟自由基OH.的清除率仅为38.5%;而利用次黄嘌呤-黄嘌呤氧化酶体系,黄伞胞外多糖对超氧阴离子自由基O2-.的清除率可达到80.6%。结论:黄伞胞外多糖在体外对自由基有一定的清除作用且其对超氧阴离子自由基O2-.的清除作用明显优于对羟自由基OH.的清除作用。     

大豆肽体外抗氧化活性研究

研究大豆肽的体外抗氧化的作用。采用邻二氮菲-Fe^2＋检测大豆肽对羟自由基（·OH）的清除作用,邻苯三酚检测大豆肽对超氧阴离子（·O2^-）的清除作用,用硫代巴比妥酸法测定小鼠肝匀浆丙二醛（MDA）的含量,用比色法测定小鼠红细胞溶血度,来研究大豆肽的抗氧化效果。结果表明：大豆肽可以清除·OH和·O2^-,抑制·OH所致的丙二醛的产生,减少H2O2所致的红细胞溶血,在2～15g／L内均具有明显的量效关系。表明大豆肽在体外具有明显的抗氧化效果。