Visualizing loss of heterozygosity in living mouse cells and tissues

Chronic exposure to oxidative stress especially to highly reactive hydroxyl radicals (HO*) could damage biomolecules, particularly DNA, that in turn would accelerate onset of degenerative diseases. In the present study a few standard phytochemicals (vitamin C, gallic acid, catechin, apigenin, naringenin and naringin) and plant extracts (Hippophae rhamnoides kernel (HRK), Syzygium cumini kernel (SCK) and Punica granatum pericarp (PGP)) were evaluated for their potential to protect/damage DNA in Fenton's system using in vitro models. The results indicated a significant DNA protective effect for naringin and PGP whereas other phytochemicals/extracts showed DNA damaging effect similar to or more than that of control value. The phytochemicals/extracts were also evaluated for their antioxidant and iron chelation properties. In general, the phytochemicals/extracts with high antioxidant activity but without iron chelation capacity failed to protect DNA in Fenton's system, suggesting that iron chelation was an essential requirement for the phytochemicals studied here to retard HO* generation by Fenton's reaction. This was demonstrated by the high iron chelation capacity of naringin and PGP (83.67% and 68.67% respectively) and their DNA protective effect. Commonly consumed phytochemicals such as vitamin C and gallic acid with their high reducing power and at higher physiological concentration, could regenerate free iron for Fenton's reaction leading to DNA damage as shown here.     

An analytical survey of the polyphenols of seeds of varieties of grape (Vitis vinifera) cultivated in Greece: implications for exploitation as a source of value-added phytochemicals

Seed samples from 12 white and 25 red international and Hellenic native grape varieties (Vitis vinifera) were screened for their polyphenolic composition. The polyphenols determined were mainly of low molecular weight, including gallic acid, catechin, epicatechin, epicatechin gallate, epigallocatechin, epigallocatechin gallate and the procyanidins B1 and B2. Average values of total content for white and red varieties (376 and 388 mg/100 g seeds, respectively) were very similar. Comparable results were observed with respect to the individual polyphenol content with seeds from red varieties being, in general, slightly richer. The predominant flavanol monomer in white and red varieties was catechin (which accounted for 50.5 and 49.3%, respectively, of the total content), whilst gallic acid and epigallocatechin were the constituents showing the lowest content, respectively. The data obtained are discussed with regard to the exploitation of grape seeds as a low-cost source of value-added phytochemicals.     

Evaluation of in vitro antioxidant activity of Indian bay leaf, Cinnamomum tamala (Buch. -Ham.) T. Nees & Eberm using rat brain synaptosomes as model system

The study investigated the perturbation of oxidant-antioxidant balance in brain synaptosomes of diabetic rats and determined the antioxidant and free radical-scavenging property of the Indian bay leaf. Brain synaptosomes were isolated from control and streptozotocin-induced diabetic animals and oxidative stress parameters were assayed. A methanolic extract of bay leaf (BLE) was tested for the polyphenolic content and antioxidant activity by in vitro assays. A significant increase in the levels of lipids and lipid peroxidation products and a decline in antioxidant potential were observed in diabetic rat brain synaptosomes. The total polyphenolic content of BLE was found to be 6.7 mg gallic acid equivalents (GAE)/100g. BLE displayed scavenging activity against superoxide and hydroxyl radicals in a concentration-dependent manner. Further, BLE showed inhibition of Fe(2+)-ascorbate induced lipid peroxidation in both control and diabetic rat brain synaptosomes. Maximum inhibition of lipid peroxidation, radical scavenging action and reducing power of BLE were observed at a concentration of 220 microg GAE. These effects of BLE in vitro were comparable with that of butylated hydroxyl toluene (BHT), a synthetic antioxidant. It can be concluded that synaptosomes from diabetic rats are susceptible to oxidative damage and the positive effects of bay leaf in vitro, could be attributed to the presence of antioxidant phytochemicals.     

Procyanidin B2 has anti- and pro-oxidant effects on metal-mediated DNA damage

Procyanidin B2 (epicatechin-(4beta-8)-epicatechin), which is present in grape seeds, apples, and cacao beans, has antioxidant properties. We investigated the mechanism of preventive action of procyanidin B2 against oxidative DNA damage in human cultured cells and isolated DNA. Procyanidin B2 inhibited the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in the human leukemia cell line HL-60 treated with an H2O2-generating system. In contrast, a high concentration of procyanidin B2 increased the formation of 8-oxodG in HL-60 cells. Experiments with calf thymus DNA also revealed that procyanidin B2 decreased 8-oxodG formation by Fe(II)/H2O2, whereas procyanidin B2 induced DNA damage in the presence of Cu(II), and H2O2 extensively enhanced it. An electron spin resonance spin trapping study utilizing 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO) demonstrated that procyanidin B2 decreased the signal of M4PO-OH from H2O2 and Fe(II), whereas procyanidin B2 enhanced the signal from H2O2 and Cu(II). As an antioxidant mechanism, UV-visible spectroscopy showed that procyanidin B2 chelated Fe(II) at equivalent concentrations. As a pro-oxidant property, we examined DNA damage induced by procyanidin B2, using 32P-labeled DNA fragments obtained from genes relevant to human cancer. Our results raise the possibility that procyanidin B2 exerts both antioxidant and pro-oxidant properties by interacting with H2O2 and metal ions.     

Isolation and Identification of the Phenols of Paul's Scarlet Rose Stems and Stem-Derived Suspension Cultures

The phenols of Paul's Scarlet rose stems and stem-derived cell cultures have been analyzed using C₁₈-reversed-phase high performance liquid chromatography.

Rose stems were found to contain gallic acid, (+)catechin, (−)epicatechin, the dimers (−)epicatechin-(+)catechin and (+)catechin-(+)catechin, a polymeric procyanidin, ferulic acid, and several gallotannins. In contrast, a cell suspension of Paul's Scarlet rose which has been maintained in culture for over 25 years contained only low levels of gallic acid and (−)epicatechin-(+)catechin. The phenol content of a second rose cell line which was started from the same initial isolate in 1957, but which was maintained in a laboratory other than our own was quantitatively and qualitatively similar to the cell line kept in our laboratory for the last 20 years. A third cell line which we started 6 months ago contained a wide variety of phenols, most of which were in common with those of rose stems.

Selective subculturing of smaller cell clumps of our oldest cell line failed to enhance either the quantities or the diversity of phenols which accumulated in these cultured cells. Possible reasons for the failure of selective subculturing to enhance phenol levels in this long-established cell line are discussed.

     

Procyanidins protect Fao cells against hydrogen peroxide-induced oxidative stress

In this paper, we evaluate the extent to which flavonoids in red wine (catechin, epicatechin, quercetin and procyanidins) protect against hydrogen peroxide-induced oxidative stress in Fao cells. When cells were exposed to H(2)O(2), malondialdehyde (MDA) levels, oxidized glutathione (GSSG) levels and lactate dehydrogenase (LDH) release increased, indicating membrane damage and oxidative stress. All the flavonoids studied, and in particular epicatechin and quercetin, protected the plasma membrane. Only procyanidins lowered MDA levels and LDH leakage, maintained a higher reduced/oxidized glutathione ratio, and increased catalase/superoxide dismutase and glutathione peroxidase/superoxide dismutase ratios, and glutathione reductase and glutathione transferase activities. These results show that the procyanidin mixture has a greater antioxidant effect than the individual flavonoids studied, probably due to its oligomer content and/or the additive/synergistic effect of its compounds. This suggests that the mixture of flavonoids found in wine has a greater effect than individual phenols, which may explain many of the healthy effects attributed to wine.     

Effects of dietary antioxidants on human DNA ex vivo

The protective effect of fruits and vegetables against cancer is well established. It is believed that this effect is mediated by antioxidants and decreased oxidative damage to DNA. However, the identity of the antioxidant(s) responsible is not clear. Moreover, a potentially damaging pro-oxidant effect of some antioxidants has been reported. In this study the ex vivo effects of several dietary antioxidants, including quercetin, various catechins, ascorbic acid and alpha-tocopherol, were investigated, at concentrations up to 200 microM, using the single cell gel electrophoresis (comet) assay for DNA damage. Lymphocytes from three healthy subjects were pre-incubated with these antioxidants, and the comet assay was performed on treated, untreated, challenged and unchallenged cells in parallel, oxidant challenge being induced by 5 min exposure to hydrogen peroxide (final concentrations H2O2: 30, 45, or 60 microM). Results using this ex vivo cellular assay showed protection by some antioxidants (quercetin, caffeic acid), no effect by some (catechin, epicatechin, catechin gallate, epicatechin gallate) and an apparently damaging effect by others (epigallocatechin, epigallocatechin gallate). Damage may have been caused by production of H2O2 from these polyphenolics. Neither ascorbic acid nor alpha-tocopherol protected or damaged DNA. Further study of the role of quercetin and caffeic acid in DNA protection is needed.     

The influence of mycorrhizal colonization on growth in the greenhouse and on catechin, epicatechin and procyanidin in roots of Fagus sylvatica L.

 The influence of mycorrhizal colonization on beech (Fagus sylvatica L.) root tannin (procyanidin polymer) and its putative precursors catechin and epicatechin was investigated by high performance liquid chromatography. Seedlings planted in a sterile mixture of litter, compost, soil and sand were inoculated with brown beech ectomycorrhizas collected from a woodland (Lactarius subdulcis Bull ex Fr. ×  F. sylvatica). The seedlings were not fertilized during the first year of growth. Nonmycorrhizal control plants showed severe nutrient-deficiency symptoms on their leaves and grew less well than mycorrhizal plants. Mycorrhizal roots contained significantly less catechin, epicatechin and procyanidin polymer than nonmycorrhizal roots. In the second year of growth, the plants were fertilized and procyanidin formation in roots was investigated. None of the fertilized plants showed mineral-deficiency symptoms. Fertilized mycorrhizal roots consistently contained significantly less catechin and epicatechin than nonmycorrhizal controls, but procyanidin polymer content varied between replicate experiments. The possible function of catechin and epicatechin in ectomycorrhizal formation is discussed. Accepted: 11 July 1997     

金刺梨果实和叶中酚类、Vc含量及其抗氧化能力分析

为了解贵州金刺梨（Rosa sterilis D.Shi）果实和叶片中的活性成分及其抗氧化活性,以贵州普定县金刺梨种植基地的果实和叶片为试材,测定其活性成分含量及其抗氧化活性,并对各项指标进行相关性分析。结果显示：没食子酸、芦丁、槲皮素、儿茶素、鞣花酸、绿原酸、阿魏酸是供试金刺梨果实和叶片的主要酚类成分,金刺梨果实和叶片中活性组分差异显著（P<0.05）,果实中p-香豆酸、总黄酮和抗坏血酸的含量相对较高,而叶片中没食子酸、儿茶素、绿原酸、表儿茶素、阿魏酸、鞣花酸、芦丁、槲皮素和总酚含量均高于果实;金刺梨果实抗氧化活性值均显著高于叶片（P<0.05）;相关性分析发现：总黄酮对总还原力（TRPA）值的贡献极强,抗坏血酸对Fe³⁺还原抗氧化能力（FRAP）值贡献最强,槲皮素对ABTS值的贡献最强,说明金刺梨果实和叶片是一种具有较高开发价值的药食同源资源。     

Effects of epigallocatechin gallate and quercetin on oxidative damage to cellular DNA

Phenolic phytochemicals are thought to promote optimal health, partly via their antioxidant effects in protecting cellular components against free radicals. The aims of this study were to assess the free radical-scavenging activities of several common phenolic phytochemicals, and then, the effects of the most potent phenolic phytochemicals on oxidative damage to DNA in cultured cells. Epigallocatechin gallate (EGCG) scavenged the stable free radical, alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH), most effectively, while quercetin was about half as effective. Genistein, daidzein, hesperetin, and naringenin did not scavenge DPPH appreciably. Jurkat T-lymphocytes that were pre-incubated with relatively low concentrations of either EGCG or quercetin were less susceptible to DNA damage induced by either a reactive oxygen species or a reactive nitrogen species, as evaluated by the comet assay. More specifically, control cells had a comet score of only 17+/-5, indicating minimal DNA damage. Cells challenged with 25 microM hydrogen peroxide (H(2)O(2)) or 100 microM 3-morpholinosydnonimine (SIN-1, a peroxynitrite generator) had comet scores of 188+/-6 and 125+/-12, respectively, indicating extensive DNA damage. The H(2)O(2)-induced DNA damage was inhibited with 10 microM of either EGCG (comet score: 113+/-23) or quercetin (comet score: 82+/-7). Similarly, the SIN-1-mediated DNA damage was inhibited with 10 microM of either EGCG (comet score: 79+/-13) or quercetin (comet score: 72+/-17). In contrast, noticeable DNA damage was induced in Jurkat T-lymphocytes by incubating with 10-fold higher concentrations (i.e., 100 microM) of either EGCG (comet score: 56+/-17) or quercetin (comet score: 64+/-13) by themselves. Collectively, these data suggest that low concentrations of EGCG and quercetin scavenged free radicals, thereby inhibiting oxidative damage to cellular DNA. But, high concentrations of either EGCG or quercetin alone induced cellular DNA damage.     

Effects of phenolics in Empire apples on hydrogen peroxide-induced inhibition of gap-junctional intercellular communication

The present study investigated antioxidant and antitumor-promoting activities of major phenolic phytochemicals of apples. The contents of each antioxidant in Empire apples was quantified and their contributions to total antioxidant activity of apples were determined using assay for inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced superoxide radical generation in cell culture model and expressed in vitamin C equivalent antioxidant capacity (VCEAC). The estimated contribution of major phenolics and vitamin C to total anitoxidant capacity of 100 g fresh Empire apples is as follows: quercetin (60.05 VCEAC) > chlorogenic acid (12.32) > phloretin (7.41) > procyanidin B2 (7.22) > vitamin C (6.61) > epicatechin (5.10) in superoxide radical scavenging assay. Recent reports suggest that the mechanism of carcinogenic process of hydrogen peroxide (H2O2) may be associated with the inhibition of gap-junctional intercellular communication (GJIC), which is involved in tumor promotion process. Apple extracts showed the protective effects against the inhibition of GJIC by H2O2 in a dose-dependent manner. Quercetin exerted the strongest protective effects among major antioxidants in apples on H2O2-induced inhibition of GJIC, following epicatechin, procyanidin B2, and vitamin C, while chlorogenic acid and phloretin had no effects. Our results indicate that cancer chemopreventive activity of apples is associated with the combined antioxidant capacity and antitumor-promoting activities of diverse antioxidants.     

Wheat sprout extract induces changes on 20S proteasomes functionality

Wheat sprouts contain a very high level of organic phosphates and a powerful cocktail of different molecules such as enzymes, reducing glycosides and polyphenols. The antioxidant properties of wheat sprouts have been widely documented and it has been shown that they are able to protect DNA against free-radicals mediated oxidative damage. Furthermore, we have recently reported on the effects of several polyphenols on 20S proteasomes, underlying the dual role of epigallocatechin-3-gallate as an antioxidant and a proteasome effector in cancer cells. The aim of this study was to investigate the effects of wheat sprout extracts on 20S proteasome functionality. Wheat sprout extracts have been analysed and characterized for their polyphenolic content using the Folin-Ciocalteau reagent and RP-HPLC technique. Comparing our data with a polyphenol standard mixture we identified five different polyphenols: gallic acid, epigallocatechin-3-gallate, epigallocatechin, epicatechin and catechin. The treatment of isolated 20S proteasomes with the extract induced a gradual inhibition of all the tested components, ChT-L, T-L, PGPH and BrAAP, in both the complexes. At low extract concentration a slight activation of the enzyme was evident only for the BrAAP component of the constitutive enzyme and the ChT-L activity of the immunoproteasome. beta-casein degradation rate decreased, particularly with the immunoproteasome. Human Colon adenocarcinoma (Caco) cells, stimulated with 12-O-tetradecanoylphorbol-13-acetate, showed activation of the 20S proteasome activities at short incubation times and an increase in intracellular oxidative proteins. Cells treatment with wheat sprout extract led to proteasome inhibition in unstimulated cells and attenuated the effects mediated by TPA. Finally, exposure to the extract affected the expression levels of pro-apoptotic proteins.     

Effects of Dietary Antioxidants on Human DNA Ex Vivo

The protective effect of fruits and vegetables against cancer is well established. It is believed that this effect is mediated by antioxidants and decreased oxidative damage to DNA. However, the identity of the antioxidant(s) responsible is not clear. Moreover, a potentially damaging pro-oxidant effect of some antioxidants has been reported. In this study the ex vivo effects of several dietary antioxidants, including quercetin, various catechins, ascorbic acid and &#102 -tocopherol, were investigated, at concentrations up to 200 &#117 &#119 M, using the single cell gel electrophoresis (comet) assay for DNA damage. Lymphocytes from three healthy subjects were pre-incubated with these antioxidants, and the comet assay was performed on treated, untreated, challenged and unchallenged cells in parallel, oxidant challenge being induced by 5 &#117 min exposure to hydrogen peroxide (final concentrations H 2 O 2 : 30, 45, or 60 &#117 &#119 M). Results using this ex vivo cellular assay showed protection by some antioxidants (quercetin, caffeic acid), no effect by some (catechin, epicatechin, catechin gallate, epicatechin gallate) and an apparently damaging effect by others (epigallocatechin, epigallocatechin gallate). Damage may have been caused by production of H 2 O 2 from these polyphenolics. Neither ascorbic acid nor &#102 -tocopherol protected or damaged DNA. Further study of the role of quercetin and caffeic acid in DNA protection is needed.     

Study on the inhibitory effects of Korean medicinal plants and their main compounds on the 1,1-diphenyl-2-picrylhydrazyl radical

A 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-generating system was used to evaluate the antioxidant properties of Korean medicinal plants that have been used widely as folk medicines for several disorders, as well as compounds isolated from them. Among the Rosaceae, Rosa rugosa and Rosa davurica showed strong DPPH radical-scavenging activity. The most effective medicinal plant from families other than Rosaceae was Cedrela sinensis, followed in order by Nelumbo nucifera, Eucommia ulmoides, Zanthoxylum piperitum, Cudrania tricuspidata and Houttuynia cordata. These results serve as a good index of the free radical-scavenging activities of Korean medicinal plants. Furthermore, the polyphenols isolated from these plants, procyanidin B-3, (+)-catechin, gallic acid, methyl gallate, quercetin, quercetin-3-O-beta-D-glucoside, quercetin-3-O-beta-galactoside, quercetin-3-O-rutinose and kaempferol, exerted strong DPPH radical-scavenging activity. These results suggest that the Korean medicinal plants and the polyphenols isolated from them that exhibited effective radical-scavenging activity may be promising agents for scavenging free radicals and treating diseases associated with excess free radicals.     

Antioxidant properties of catechins and proanthocyanidins: Effect of polymerisation, galloylation and glycosylation

A range of catechins and oligomeric procyanidins was purified by high performance liquid chromatography (HPLC) from grape seed, apple skin, lentil and almond flesh. Catechins, galloylated epicatechin, glycosylated catechin, procyanidin dimers, galloylated dimers, trimer, and tetramer species were all identified, purified and quantified by HPLC, LC-MS and NMR. The antioxidant properties of these compounds were assessed using two methods: (a) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes; (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 (expressed as Trolox C equivalent antioxidant capacity, TEAC). Antioxidant activity in the lipid phase decreased with polymerisation in contrast with antioxidant action in the aqueous phase which increased from monomer to trimer and then decreased from trimer to tetramer. Galloylation of catechin and dimeric procyanidins decreased lipid phase and increased aqueous phase antioxidant activity. Glycosylation of catechin demonstrated decreased activity in both phases.     

Antioxidant properties of catechins and proanthocyanidins: Effect of polymerisation,galloylation and glycosylation

A range of catechins and oligomeric procyanidins was purified by high performance liquid chromatography (HPLC) from grape seed, apple skin, lentil and almond flesh. Catechins, galloylated epicatechin, glycosylated catechin, procyanidin dimers, galloylated dimers, trimer, and tetramer species were all identified, purified and quantified by HPLC, LC-MS and NMR. The antioxidant properties of these compounds were assessed using two methods: (a) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes; (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 (expressed as Trolox C equivalent antioxidant capacity, TEAC). Antioxidant activity in the lipid phase decreased with polymerisation in contrast with antioxidant action in the aqueous phase which increased from monomer to trimer and then decreased from trimer to tetramer. Galloylation of catechin and dimeric procyanidins decreased lipid phase and increased aqueous phase antioxidant activity. Glycosylation of catechin demonstrated decreased activity in both phases.     

Epigallocatechin gallate increase the prostacyclin production of bovine aortic endothelial cells

We describe the effect of (-) epigallocatechin gallate (EGCg), one of catechins known in tea, on the prostacyclin (PGI) production by bovine aortic endothelial cells. The amounts of 6-keto-PGF(1alpha) and Delta(17)-6-keto-PGF(1alpha), stable metabolites of PGI(2) and PGI(3), released in culture medium were measured using gas chromatography/selected ion monitoring (GC/SIM). The prostacyclin production of endothelial cells was increased by EGCg in a dose- and time-dependent manner. The effect by EGCg was stronger than any other catechins (catechin, epicatechin, epigallocatechin, and epicatechin gallate). When endothelial cells incubated with EGCg and arachidonic acid (AA) or eicosapentaenoic acid (EPA), PGI(2), and PGI(3) production were increased greater than those incubated with AA or EPA alone. Furthermore, gallic acid, that also has a pyrogallol structure, increased PGI(2) production. These observations indicate that catechins increase the prostacyclin production and that the pyrogallol structure is significant to this function.     

Isolation and characterisation of procyanidins from Rumex obtusifolius

An acetone:water (7:3) extract obtained from the leaves of Rumex obtusifolius was fractionated into procyanidin oligomer and polymer fractions using a linear gradient and a simple step method on Sephadex LH-20. The chemical characteristics of the procyanidin fractions were studied by 13C-NMR spectroscopy, acid-catalysed degradation in the presence of benzyl mercaptan, matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS and electrospray ionisation (ESI) MS. The 13C-NMR showed that the polymer fraction consisted predominantly of procyanidin polymers, some with galloyl groups attached. The thiolysis reaction products indicated a mean degree of polymerisation (DP) of 4.3 for the step method, and a range of 2.3-8.2 mean DP for the gradient fractionation, with epicatechin as the most abundant flavan-3-ol extension unit, while the terminal units consisted of equal proportions of catechin, epicatechin and epicatechin gallate. Singly charged ions observed in MALDI-TOF/MS showed a range of oligomeric procyanidins and their polygalloyl derivatives. These species (in the range DP 2-7) were also observed by ESI/MS but the spectra were more complex due to overlapping multiply charged ions. Isolation of oligomers from the Sephadex LH-20 fraction by chromatography on polyamide and C18 yielded B1, B2, B3 and B7 dimers, an A-type trimer and a B2 3,3'-O-digallate.     

Cysteinyl-flavan-3-ol conjugates from grape procyanidins. Antioxidant and antiproliferative properties

New bio-based antioxidant compounds have been obtained by depolymerisation of grape polymeric flavanols in the presence of cysteine. Their preparation and purification, as well as their antiradical/antioxidant and antiproliferative properties are reported. 4beta-(S-cysteinyl)epicatechin 5, 4beta-(S-cysteinyl)catechin 6 and 4beta-(S-cysteinyl)epicatechin 3-O-gallate 7 were efficiently purified from the crude depolymerised mixture by cation-exchange chromatography and preparative reversed-phase chromatography. The new compounds were more efficient than the underivatised (-)-epicatechin 1 as scavengers of the 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH) and weak growth inhibitors of human colon carcinoma HT29 cells. The order of antiradical and antiproliferative efficiency was 7 >5 approximately 6 >1, the same for both assays.     

Potent antioxidant dendrimers lacking pro-oxidant activity

It is well known that antioxidants have protective effects against oxidative stress. Unfortunately, in the presence of transition metals, antioxidants, including polyphenols with potent antioxidant activities, may also exhibit pro-oxidant effects, which may irreversibly damage DNA. Therefore, antioxidants with strong free radical-scavenging abilities and devoid of pro-oxidant effects would be of immense biological importance. We report two antioxidant dendrimers with a surface rich in multiple phenolic hydroxyl groups, benzylic hydrogens, and electron-donating ring substituents that contribute to their potent free radical-quenching properties. To minimize their pro-oxidant effects, the dendrimers were designed with a metal-chelating tris(2-aminoethyl)amine (TREN) core. The dendritic antioxidants were prepared by attachment of six syringaldehyde or vanillin molecules to TREN by reductive amination. They exhibited potent radical-scavenging properties: 5 times stronger than quercetin and 15 times more potent than Trolox according to the 1,1-diphenyl-2-picrylhydrazyl assay. The antioxidant dendrimers also protected low-density lipoprotein, lysozyme, and DNA against 2,2'-azobis(2-amidinopropane) dihydrochloride-induced free radical damage. More importantly, unlike quercetin and Trolox, the two TREN antioxidant dendrimers did not damage DNA via their pro-oxidant effects when incubated with physiological amounts of copper ions. The dendrimers also showed no cytotoxicity toward Chinese hamster ovary cells.