Quercetin and myricetin protect against hydrogen peroxide-induced DNA damage (strand breaks and oxidised pyrimidines) in human lymphocytes

Induction of apoptosis by quercetin: different response of human chronic myeloid (K562) and acute lymphoblastic (HSB-2) leukemia cells

This work shows that 25 microM quercetin caused a marked inhibition of K562 cells growth together with a mild cytotoxicity, while HSB-2 cells were practically unaffected. Moreover, quercetin induced caspase-3 and cytochrome c-dependent apoptosis almost exclusively in the former cell line. Exposure of K562 cells to quercetin caused also a significant increase of cells in G(2)/M phase that reached the maximum peak at 24 h (4-fold with respect to the basal value). The major sensitivity exhibited by K562 cells was only in part imputable to their higher glutathione content, as compared to HSB-2 cells, thus confirming previous reports describing the formation of intracellular quercetin-thiol toxic adducts in cells exposed to the flavonoid. In fact, after induction of intracellular glutathione increase we detected in both cell lines a significant rise of apoptotic cells, again more marked in K562 cells. By contrast, glutathione-depleted cells, failed to show a decrease of apoptosis in both cell lines, thus contradicting our previous findings and literature data. Since the yet unresolved question about the anti-oxidant or the pro-oxidant capacity of quercetin, we investigated which of these two properties worked in our experimental model. Interestingly, not only quercetin did not produce reactive oxygen species but also prevented their formation, as observed in cells exposed to the oxidizing agent ter-butylhydroperoxide, acting as an efficient oxygen radicals scavenger. This result indicates that quercetin exhibited, in these cell lines, anti-oxidant more than pro-oxidant ability.

Assessment of the Anti-Genotoxic, Anti-Proliferative, and Anti-Metastatic Potential of Crude Watercress Extract in Human Colon Cancer Cells

Although it is known to be a rich source of the putative anti-cancer chemicals isothiocyanates, watercress has not been extensively studied for its cancer preventing properties. The aim of this study was to investigate the potential chemoprotective effects of crude watercress extract toward three important stages in the carcinogenic process, namely initiation, proliferation, and metastasis (invasion) using established in vitro models. HT29 cells were used to investigate the protective effects of the extract on DNA damage and the cell cycle. The extract was not genotoxic but inhibited DNA damage induced by two of the three genotoxins used, namely hydrogen peroxide and fecal water, indicating the potential to inhibit initiation. It also caused an accumulation of cells in the S phase of the cell cycle indicating (possible) cell cycle delay at this stage. The extract was shown to significantly inhibit invasion of HT115 cells through matrigel. Component analysis was also carried out in an attempt to determine the major phytochemicals present in both watercress leaves and the crude extract. In conclusion, the watercress extract proved to be significantly protective against the three stages of the carcinogenesis process investigated.

Antioxidant activity of far-infrared radiated rice hull extracts on reactive oxygen species scavenging and oxidative DNA damage in human lymphocytes

The antioxidant activities of methanolic extracts of far-infrared irradiated rice hull (FRH) and non-irradiated intact rice hull (IRH) were determined. The antioxidant effects against reactive oxygen species (ROS) were evaluated by measuring scavenging activities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, superoxide, hydrogen peroxide (H2O2), and nitric oxide radical and capacity for chelating metals. Except for H2O2 scavenging activity, FRH showed higher scavenging activity than IRH; for example, the 50% inhibitory concentration (mg/mL) values for DPPH radical scavenging of FRH and IRH were 0.067 and 0.085, respectively, as compared with 0.362 and 0.012 for butylated hydroxytoluene and alpha-tocopherol, respectively. The effect of rice hull extract on DNA damage induced by H2O2 in human lymphocytes was also evaluated by comet assay. The protective effect of rice hull extract increased as its concentration increased from 12.5 to 50 microg/mL, as indicated by DNA strand breakage decreasing from 38% to 22% with FRH and from 49% to 28% with IRH as compared with H2O2-treated positive controls. When human lymphocytes were post-incubated with rice hull extract for 30 minutes after exposure to H2O2, the protective ability of the rice hulls remained unchanged. These results suggest that methanol extracts of rice hulls possess significant ROS scavenging and metal chelating activities and protective effect against oxidative DNA damage.

Formation and inhibition of genotoxic malonaldehyde from DNA oxidation controlled with EDTA

The attack of DNA by reactive oxygen species, such as hydroxyl radical, causes several types of damage, which subsequently promote diseases. Determination of oxidized products, such as malonaldehyde (MA), from DNA would provide theoretical and practical information on the mechanisms of DNA oxidation following DNA damage and this information could be used to prevent DNA damage caused by oxidation. In the present study, calf thymus DNA was oxidized by Fenton's reagent/EDTA with or without natural antioxidants-flavonoids and anthocyanins-and synthetic antioxidants, Trolox and 2H-pyrrole, 3,4-dihydro-2,2-dimethyl-, 1-oxide (DMPO). Amounts of MA formed, which was determined by gas chromatography, in oxidized DNA with the presence of antioxidants, ranged from 7.35+/-0.88 nmol/mg (2''-O-GIV) to 12.6+/-0.24 nmol/g (cyanidin). Except for cyanidin, all antioxidants tested inhibited MA formation. DMPO and Trolox inhibited MA formation by 12.4% and 27.3%, respectively from oxidized DNA. The decreasing order of inhibitory effect by the anthocyanins was callistephin (30.2%)>keracyanin (27.3%)>Pelargonindin (10.1%)>cyanidin (0%). The decreasing order of inhibitory effect by the flavonoids was 2''-O-GIV (42.7%)>catechin (8.8%)>quercetin (36.4%)>apigenin (34.4%). It is hypothesized that EDTA controlled formation of hydroxyl radicals via trapping Fe(II) ions reversibly.

In vitro testing for genotoxicity of violacein assessed by Comet and Micronucleus assays

Chromobacterium violaceum is a Gram (-) bacteria found in water samples and soils from tropical and subtropical regions of the world. Violacein, the major pigment produced by these bacteria, has been shown to have antibiotic, antitumoral and trypanocidal activities. In the present work, the genotoxicity of violacein was investigated in four different cell lines by using the alkaline Comet assay and in VERO cells using the Micronucleus test. In the alkaline Comet assay, violacein, when tested at concentrations ranging from 0.19 to 1.5 microM, did not induce a significant increase in DNA damage in HEp-2 and MA104 cells. However, violacein was positive for DNA damage in FRhK-4 cells and for both DNA damage and micronuclei in VERO cells, in a concentration-response relationship. The results of this study indicated that violacein is genotoxic in VERO and FRhK-4 cells. These findings contribute to a comprehensive evaluation of the pharmacological potential of violacein.

In vitro basal and metabolism-mediated cytotoxicity of flavonoids

The purpose of this study was to compare the basal cytotoxicity and metabolism-mediated cytotoxicity of kaempferol, quercetin and rutin. McCoy cells were exposed to various concentrations of the flavonols with and without the S9 system. The neutral red uptake assay was used to determine viability after 24 h at 35-37 degrees C. Dose-response curves were established for each flavonol in the presence and absence of external metabolizing systems. Kaempferol and quercetin were cytotoxic and provoked a dose-dependent decrease in cell viability, without the S9 system. The hepatic S9 microsomal fraction metabolized these compounds to less cytotoxic metabolites. In contrast, rutin at 500 microg/ml failed to produce any overt signs of toxicity in either assay.

Enhancement of radiation-induced oxidative stress and cytotoxicity in tumor cells by ellagic acid

BACKGROUND

Failure of treatment of cancer in clinic by radio/chemotherapy is generally attributed to tumor resistance. It is, therefore, important to develop strategies to increase the cytotoxicity of tumor cells by radiation in combination with new tumor selective cytotoxic agents. We describe the role of ellagic acid (EA) and gamma radiation on the oxidative stress and subsequent cytotoxicity of tumor cells in vitro as well as in vivo and their sparing effects on normal cells.

METHODS

Ehrlich ascites carcinoma (EAC)-transplanted Swiss mice were intraperitoneally injected with EA followed by radiation treatment of 2 Gy for 4 alternate days. Hela cells were used for in vitro studies. Reactive oxygen species (ROS) level was measured by spectrofluorimetric method by using 2, 7-dichlorodihydrofluoresceindiacetate (DCHFDA) fluorescent probe. Cytotoxicity was measured by Trypan blue dye exclusion test and mitochondrial potential was measured using Rhodamine 123 as a probe. Antioxidant enzymes were measured by spectrophotometric methods.

RESULTS

EA was found to generate ROS in tumor cells, which increased, by an order of magnitude when cells were treated with EA in combination with gamma radiation. The decrease in mitochondrial potential and the loss of cell viability were remarkably greater in tumor cells from mice treated with EA and radiation than alone treatment with either of them. Moreover, EA was found to protect against radiation-induced oxidative stress in splenic lymphocytes of tumor-transplanted mice. Measurement of antioxidant enzymes such as superoxide dismutase (SOD), catalase, glutathione peroxidase (GSH-Px) and glutathione reductase (GR) in tumor cells showed decrease after treatment with EA and radiation in vivo. Treatment of tumor bearing mice with EA and radiation showed significant decrease in animal's body weight suggesting reduced tumor burden.

CONCLUSION

Combined treatment of tumor with EA and radiation enhances oxidative stress and cytotoxicity in tumor cells. EA protects normal cells against radiation damage. This may offer potential therapeutic benefit, which warrants clinical study for application in cancer radiotherapy.

Antioxidant intervention as a route to cancer prevention

The notion of cancer prevention through antioxidant intervention arises from the fact that fruits and vegetables contain antioxidants and are linked to low cancer rates in those who consume them. Protection against DNA damage by plant food products can be demonstrated in vitro. However, particular care is needed when measuring the damage, since oxidation readily occurs during sample preparation, creating a serious artefact. In the case of DNA oxidation, estimates of background levels in human cells range over 3 orders of magnitude, depending on the method used. Using validated, reliable biomarker assays for DNA oxidation, it is possible to demonstrate a decrease in oxidative damage after supplementation with isolated antioxidants or whole plant foods in humans. In contrast, in several large-scale interventions with disease or death as the endpoint, supplementation with beta-carotene resulted in no effect or an increase in cancer incidence. It is certainly true that we do not yet fully understand the role of phytochemicals as antioxidants, or as modulators of other processes related to carcinogenesis and its prevention.

Radioprotection by plant products: present status and future prospects

The development of radioprotective agents has been the subject of intense research in view of their potential for use within a radiation environment, such as space exploration, radiotherapy and even nuclear war. However, no ideal, safe synthetic radioprotectors are available to date, so the search for alternative sources, including plants, has been on going for several decades. In Ayurveda, the traditional Indian system of medicine, several plants have been used to treat free radical-mediated ailments and, therefore, it is logical to expect that such plants may also render some protection against radiation damage. A systematic screening approach can provide leads to identifying potential new candidate drugs from plant sources, for mitigation of radiation injury. This article reviews some of the most promising plants, and their bioactive principles, that are widely used in traditional systems of medicine, and which have rendered significant radioprotection in both in vitro and in vivo model systems. Plants and their constituents with pharmacological activities that may be relevant to amelioration of radiation-mediated damage, including antiemetic, antiinflammatory, antioxidant, cell proliferative, wound healing and haemopoietic stimulatories are also discussed.

Effects of polyphenols from grape seeds on oxidative damage to cellular DNA

Grape seed polyphenols have been reported to exhibit a broad spectrum of biological properties. In this study, eleven phenolic phytochemicals from grape seeds were purified by gel chromatography and high performance liquid chromatography (HPLC). The antioxidant activities of five representative compounds with different structure type were assessed by the free radical-scavenging tests and the effects of the more potent phytochemicals on oxidative damage to DNA in mice spleen cells were investigated. Procyanidin B4, catechin, epicatechin and gallic acid reduced ferricyanide ion and scavenged the stable free radical, alpha, alpha-diphenyl-beta-picrylhydrazyl (DPPH) much more effectively than the known antioxidant vitamin ascorbic acid, while epicatechin lactone A, an oxidative derivative of epicatechin, did not reduce ferricyanide ion appreciably at concentrations used and was only about half as effective on free radical-scavenging as epicatechin. Mice spleen cells, when pre-incubated with relatively low concentration of procyanidin B4, catechin or gallic acid, were less susceptible to DNA damage induced by hydrogen peroxide (H2O2), as evaluated by the comet assay. In contrast, noticeable DNA damage was induced in mice spleen cells by incubating with higher concentration (150 microM) of catechin. Collectively, these data suggest that procyanidin B4, catechin, gallic acid were good antioxidants, at low concentration they could prevent oxidative damage to cellular DNA. But at higher concentration, these compounds may induce cellular DNA damage, taking catechin for example, which explained the irregularity of dose-effect relationship.

Fluorescence in situ hybridisation analysis of chromosomal aberrations in gastric tissue: the potential involvement of Helicobacter pylori

In this series of experiments, a novel protocol was developed whereby gastric cells were collected using endoscopic cytology brush techniques, and prepared, such that interphase fluorescence in situ hybridization (FISH) could be performed. In total, 80 distinct histological samples from 37 patients were studied using four chromosome probes (over 32,000 cells analysed). Studies have previously identified abnormalities of these four chromosomes in upper GI tumours. Using premalignant tissues, we aimed to determine how early in Correa's pathway to gastric cancer these chromosome abnormalities occurred. Aneuploidy of chromosomes 4, 8, 20 and 17(p53) was detected in histologically normal gastric mucosa, as well as in gastritis, intestinal metaplasia, dysplasia and cancer samples. The levels of aneuploidy increased as disease severity increased. Amplification of chromosome 4 and chromosome 20, and deletion of chromosome 17(p53) were the more common findings. Hence, a role for these abnormalities may exist in the initiation of, and the progression to, gastric cancer. Helicobacter pylori infection was determined in premalignant tissue using histological analysis and PCR technology. Detection rates were comparable. PCR was used to subtype H. pylori for CagA status. The amplification of chromosome 4 in gastric tissue was significantly more prevalent in H. pylori-positive patients (n=7) compared to H. pylori-negative patients (n=11), possibly reflecting a role for chromosome 4 amplification in H. pylori-induced gastric cancer. The more virulent CagA strain of H. pylori was associated with increased disease pathology and chromosomal abnormalities, although numbers were small (CagA+ n=3, CagA- n=4). Finally, in vitro work demonstrated that the aneuploidy induced in a human cell line after exposure to the reactive oxygen species (ROS) hydrogen peroxide was similar to that already shown in the gastric cancer pathway, and may further strengthen the hypothesis that H. pylori causes gastric cancer progression via an ROS-mediated mechanism.

Protection by quercetin and quercetin-rich fruit juice against induction of oxidative DNA damage and formation of BPDE-DNA adducts in human lymphocytes

Flavonoids are claimed to protect against cardiovascular disease, certain forms of cancer and ageing, possibly by preventing initial DNA damage. Therefore, we investigated the protective effects of the flavonoid quercetin against the formation of oxidative DNA damage and bulky DNA adducts in human lymphocytes, both in vitro and ex vivo. First, human lymphocytes were pre-incubated with various concentrations of quercetin, followed by incubation with hydrogen peroxide; protection against oxidative DNA damage was evaluated by use of the single-cell gel electrophoresis (Comet) assay. Second, quercetin-treated human lymphocytes were challenged by treatment with benzo(a)pyrene (B(a)P), and BPDE-DNA adduct formation was measured by (32)P-postlabelling. Third, in a pilot study, lymphocytes from female volunteers who consumed a quercetin-rich blueberry/apple juice mixture for four weeks, were treated ex vivo with an effective dose of H(2)O(2) and benzo(a)pyrene, respectively, at three different time points, i.e. before (t=0 weeks), during (t=2 weeks) and after (t=4 weeks) the intervention. Results in vitro: a significant dose-dependent protection by quercetin against both the formation of oxidative DNA damage (p<0.01) and of BPDE-DNA adducts (p<0.05) was observed. Results in vivo: four weeks of juice intervention led to a significant increase in the total antioxidant capacity of plasma, as reflected by the increase of the TEAC value from 773 microM trolox equivalent at t=0 to 855 microM at t=4 weeks (p=0.04) and an increase in plasma quercetin content from 5.0 to 10.6 nM (p=0.03). After intervention, the level of oxidative damage upon ex vivo exposure to H(2)O(2) was non-significantly (p=0.07) decreased by 41%, and the BPDE-DNA adduct level induced ex vivo was non-significantly decreased by 11%. The combination of our findings in vitro and ex vivo provides evidence that quercetin is able to protect against chemically induced DNA damage in human lymphocytes, which may underlie its suggested anticarcinogenic properties.

In vitro exposure to quercetin and genistein alters lipid peroxides and prevents the loss of glutathione in human progenitor mononuclear (U937) cells

The effects of flavonoids quercetin and genistein were investigated according to their potency to inhibit the oxidation of U937 cells via Fenton's pathway through the analysis of lipid peroxides and glutathione (GSH) levels. Human leukemia (U937) cells from the American Type Culture Collection were maintained at 37 degrees C for 24 h under 5% CO2 tension in RPMI-1640 medium containing 10% fetal bovine serum and 50 units ml(-1) each of penicillin and streptomycin. Cells were oxidized with iron 50 microM) or copper (50 microM) in H2O2 (0.01 mM) without or with a flavonoid sample (10 or 20 microM) for the lipid peroxidation studies. The GSH levels were measured (GSH Kit) before and after oxidation as above with different concentrations of flavonoids (0-40 microM). Lipid peroxide was measured by the thiobarbituric acid assay. Both quercetin and genistein at either the 10 or 20 microM level decreased lipid peroxidation significantly compared with their respective controls (P < 0.01). Lipid peroxides by Fe compared to the Cu-treated samples did not differ significantly from each other. However, the combination of flavonoids at the doses tested significantly (P < 0.001) decreased lipid peroxides, the effect being the same for both metal ions. The GSH levels increased significantly before exposure to the metal ions (for the different doses for the differences between the flavonoid samples and their respective untreated levels). For quercetin and genistein the increases in GSH above their untreated levels were 4.5, 8.3, 11.7 and 15 and 3.8, 7.9, 12.5 and 14.6 nmol 10(-6) cells, respectively, for the 5-40 microM levels tested for each flavonoid. Following the exposure to the metal ions, GSH levels remained almost the same for the different concentrations for each of the flavonoids tested but significantly above all of the controls and same for those of the untreated samples. The results indicate that both flavonoids inhibited lipid peroxides and the inhibition may be attributed to the prevention of loss of intracellular GSH levels in U937 cells.

Assays for oxidative stress and antioxidant status: applications to research into the biological effectiveness of polyphenols

Oxidative stress is a factor in many human diseases, as either cause or effect. A convenient biomarker of oxidative stress is the extent of oxidation of bases in DNA (although measures of lipid or protein oxidation may be equally informative). 8-Oxo-7,8-dihydroguanine or the corresponding nucleoside is most often measured, either chromatographically (gas chromatography-mass spectrometry, HPLC with electrochemical detection, or HPLC-tandem mass spectrometry) or enzymically, with the use of the enzyme formamidopyrimidine DNA glycosylase to convert 8-oxo-7,8-dihydroguanine to DNA breaks, which are detected with alkaline elution, alkaline unwinding, or the comet assay. Estimates of background levels of 8-oxo-7,8-dihydroguanine in normal human cells vary 1000-fold, depending on the technique used. Gas chromatography-mass spectrometry is particularly prone to oxidation of samples during derivatization, whereas HPLC suffers from this artifact to a lesser degree. In a recent interlaboratory study that measured the same samples of human cells, median values obtained with HPLC with electrochemical detection and with formamidopyrimidine DNA glycosylase differed by approximately 10-fold. There are still questions regarding the actual level of damage, but it is probably approximately one 8-oxo-7,8-dihydroguanine residue per 10(6) guanines. Assays for antioxidant protection against oxidative damage generally depend on measurements of decreases in a marker of oxidation. Potential dietary antioxidants can be screened with in vitro antioxidant assays or tested in cell culture systems. The best test, however, is in humans. The total antioxidant capacity of plasma is generally insensitive to dietary supplementation with antioxidants or antioxidant-rich foods. An increase in the resistance of lymphocyte DNA to oxidation in vitro is commonly seen, however, and a decrease in endogenous oxidation of DNA may be detected, especially after prolonged supplementation.

Dietary isothiocyanates inhibit Caco-2 cell proliferation and induce G2/M phase cell cycle arrest, DNA damage, and G2/M checkpoint activation

Benzyl isothiocyanate and phenethyl isothiocyanate, two aromatic phytochemicals present in substantial concentrations in edible vegetables of the genus Brassica, were investigated for their effects on Caco-2 cell proliferation. Benzyl and phenethyl isothiocyanate inhibited DNA synthesis, with 50% inhibitory concentrations of 5.1 and 2.4 micromol/L, respectively, and significantly increased the doubling times of Caco-2 cells from 32 h to 220 and 120 h, respectively. There was no adverse effect of either chemical on cell viability in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, but benzyl isothiocyanate and phenethyl isothiocyanate both caused an accumulation of cells in the G(2)/M phase of the cell cycle, which was maintained for at least 48 h in cells synchronized at prometaphase with nocodazole and subsequently treated with 10 micromol/L benzyl isothiocyanate or phenethyl isothiocyanate. Both benzyl and phenethyl isothiocyanate increased DNA strand breakage, increased phosphorylation of the G(2)/M checkpoint enforcer Chk2, and induced p21 expression. These results suggest that the antiproliferative effects of benzyl and phenethyl isothiocyanates toward Caco-2 cells are due at least in part to the activation of the G(2)/M DNA damage checkpoint, and that sustained G(2)/M phase cell cycle arrest in response to benzyl and phenethyl isothiocyanates may be maintained through upregulation of p21. This study indicates that some dietary isothiocyanates may exert an antiproliferative effect through activation of the G(2)/M DNA damage checkpoint.

Induction of apoptosis and necrosis in A549 cells by the cis-Pt(II) complex of 3-aminoflavone in comparison with cis-DDP

Non-small cell lung cancer (NSCLC) includes a group of tumors that respond poorly to drugs. cis-Diamminedichloroplatinum(II) (cis-DDP) toxicity still remains problematic, and not completely solved by the improvement of supportive care. Therefore, the cis-Pt(II) complex of 3-aminoflavone was selected from cis-DDP analogues with a more favourable toxic profile towards normal cells and at least similar or better anti-tumor activity in comparison with cis-DDP. The aim of this research is to compare the ability of the cis-Pt(II) complex of 3-aminoflavone and cis-DDP to induce apoptosis and necrosis in the human non-small cancer cell line A549. Trypan blue dye exclusion, fluorochrome staining (acridine orange/ethidium bromide double staining), MTT and TUNEL (TdT-mediated dUTP Nick-End Labeling) assays were used. The results obtained show that the cis-Pt(II) complex of 3-aminoflavone is more active in inducing apoptosis and necrosis and in decreasing viability in A549 cells than cis-DDP, which suggests that it could be a potential chemotherapeutic drug.

The modulating effects of quercetin and rutin on the mitomycin C induced DNA damage

The present study was carried out to investigate the modulating effects of the two flavonoids quercetin and rutin on the mutagenic anticancer drug mitomycin C by single cell gel electrophoresis (Comet assay) in human lymphocytes. Lymphocytes were incubated with different concentrations of quercetin and rutin, with or without mitomycin C, and DNA damage was evaluated. Concentrations of 0.03, 0.15, 0.3, 0.6, 1.5 and 3mM quercetin significantly reduced the DNA strand breakage induced by mitomycin C (P<0.001) but the highest concentration of 6mM quercetin did not show a protective effect. The frequency of damaged cells induced by mitomycin C was not changed at 0.02 mM, and also at the highest concentrations of 1.64 and 3.28 mM rutin. However, at concentrations of 0.08, 0.16, 0.33 and 0.82 mM rutin cells were protected from DNA damage. Thus, in human lymphocytes quercetin and rutin displayed protective effects on DNA damage induced by mitomycin C, in a concentration-dependent manner.

Cytotoxicity and Antiproliferative Activities of Several Phenolic Compounds Against Three Melanocytes Cell Lines: Relationship Between Structure and Activity

Polyphenolic compounds are widely distributed in the vegetable kingdom and are therefore consumed regularly in the human diet. Epidemiological studies suggest that foods rich in polyphenolic compounds contribute to reducing the risk of cancer. The purpose of our work is to: 1) study the possible cytotoxicity and antiproliferative effects of 13 polyphenolic compounds on 3 cell lines of melanocytes, 2 of melanoma (B16F10 and SK-MEL-1), and 1 of nontransformed melanocytes (Melan-a); and 2) identify the possible relationship between the chemical structure of the tested compounds and their effect on cellular viability. The said polyphenolic compounds corresponded to 8 flavonoids with varying hydroxyl and methoxyl substituents, related structurally through the oxidation state of their flavonoid skeleton, a catechin polymer and 4 phenolic acids. The cytotoxic activity of all the studied compounds was modest or not apparent. The flavonoids luteolin, tangeretin, baicalein, quercetin, and myricetin, and gallic acid showed antiproliferative effects on the tested lines. Our results suggest that a correlation exists between the structural oxidation state and the position, number, and nature of substituents of the polyphenolic compounds studied and their antiproliferative effects.

DNA damage in healthy term neonate

BACKGROUND

The process of childbirth is accompanied by an increase in oxidative aggression.

AIM

To determine DNA damage and oxidative stress in healthy term neonates at birth.

DESIGN

A total of 34 healthy full-term neonates, 22 healthy adults and 20 samples of colostrum from mothers of full-term neonates were examined. The malondialdehyde (MDA), DNA damage, GSH/GSSG ratio and total antioxidant capacity (TAC) in mononuclear cells isolated from umbilical blood and adult peripheral blood were measured. Moreover, the TAC of colostrum was also measured. The protective activity of five natural polyphenols against H(2)O(2)-induced DNA damage in mononuclear cells of umbilical blood was studied.

RESULTS

A high level of DNA damage (p<0.001) accompanied with lower TAC (p<0.05) and GSH/GSSG ratio (p<0.001) and with higher level of MDA (p<0.001) in umbilical blood compared with those of healthy adult peripheral blood. The natural polyphenols, 7,8-dihydroxy-4-methyl coumarin, quercetin and resveratrol, are able to protect mononuclear cells of umbilical blood from oxidative attack. However, other two polyphenols, rutin and 7-hydroxy-4-methyl coumarin, do not. The TAC of colostrum is significantly higher than that of umbilical blood (p<0.001).

CONCLUSIONS

The DNA oxidative damage in mononuclear cells of umbilical blood as well as other indexes related to redox status provided evidence that a sudden increase in oxygenation exposes the neonate into oxidative stress. Colostrum with a significant high TAC is very important for health care in infants against the oxidative stress.

Flavonol glycosides from the aerial parts ofAceriphyllum rossii and their antioxidant activities

The methanol extract obtained from the aerial parts of Aceriphyllum rossii (Saxifragaceae) was fractionated into ethyl acetate (EtOAc), n-BuOH and H2O layers through solvent fractionation. Repeated silica gel column chromatography of EtOAc and n-BuOH layers afforded six flavonol glycosides. They were identified as kaempferol 3-O-beta-D-glucopyranoside (astragalin, 1), quercetin 3-O-beta-D-glucopyranoside (isoquercitrin, 2), kaempferol 3-O-alpha-L-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside (3), quercetin 3-O-alpha-L-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside (rutin, 4), kaempferol 3-O-[alpha-L-rhamnopyranosyl (1-->4)-alpha-L-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside] (5) and quercetin 3-O-[alpha-L-rhamnopyranosyl (1-->4)-alpha-L-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside] (6) on the basis of several spectral data. The antioxidant activity of the six compounds was investigated using two free radicals such as the ABTS free radical and superoxide anion radical. Compound 1 exhibited the highest antioxidant activity in the ABTS [2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)] radical scavenging method. 100 mg/L of compound 1 was equivalent to 72.1+/-1.4 mg/L of vitamin C, and those of compounds 3 and 5 were equivalent to 62.7+/-0.5 mg/L and 54.3+/-1.3 mg/L of vitamin C, respectively. And in the superoxide anion radical scavenging method, compound 5 exhibited the highest activity with an IC50 value of 17.6+/-0.3 microM. In addition, some physical and spectral data of the flavonoids were confirmed.

Inhibitory effect of Eucommia ulmoides Oliv. on oxidative DNA damage in lymphocytes induced by H2O2

This study used the alkaline single cell gel electrophoresis assay (comet assay) to investigate the effect of water extracts of roasted cortex and leaves from Du-zhong on DNA damage in lymphocytes induced by H(2)O(2). The results showed that the DNA damage in human lymphocytes increased with an increase in the concentration of H(2)O(2) (0-200 micro;M), but that the water extracts from Du-zhong (0-2 g l(-1)) only slightly affected DNA damage. The inhibitory effect of leaf extract on DNA damage induced by H(2)O(2) in lymphocytes was more significant (P<0.05) than that of roasted cortex. Leaf extract showed a rather significant inhibitory effect in a concentration-dependent manner. At a concentration of 2 g l(-1), the leaf extract inhibited 37.9% DNA oxidative damage in human lymphocytes. In order to elucidate the mechanism of the leaf extract suppression effect on DNA damage induced by H(2)O(2) in lymphocytes, an experiment was divided with six groups (A-F). Group A was used to evaluate the repair ability of the leaf extract for DNA damage; Group B was employed to determine the scavenging ability on H(2)O(2); and Group C was studied to assess the ability of leaf extract to increase the defense capability. Groups D-F were negative controls and blank. The results showed that group B had the best inhibitory effect. Also, leaf extract had significant ability to scavenge H(2)O(2) in an in vitro HRP-phenol red test. Thus, it appears that H(2)O(2) scavenging potency may be the major mechanism whereby leaf extract inhibits oxidative DNA damage induced by H(2)O(2).

Effect of quercetin and genistein on copper- and iron-induced lipid peroxidation in methyl linolenate

The single and combined effects of two abundant flavonoids, namely quercetin and genistein, were investigated according to their ability to inhibit the oxidation of methyl linolenate via Fenton's pathway. Antioxidative activity was determined by oxidizing methyl linolenate suspended in a buffer solution with either Fe2+ (50 microM) or Cu2+ (50 microM) and hydrogen peroxide (0.01 mM) without or with a flavonoid sample (10 or 20 microM). Lipid peroxidation products were measured by the thiobarbituric acid (TBA) assay and the amounts of thiobarbituric acid-reactive substances (TBARS) were calculated from a calibration curve using 1,1,3,3-tetraethoxypropane as the standard. Both quercetin and genistein at the 10 or 20 microM level decreased lipid peroxidation significantly compared with their respective controls. Of the two flavonoids tested, quercetin had a more marked effect on inhibiting lipid peroxides. Peroxidation products for the control samples were higher for the Fe2+-treated samples compared with the Cu2+ samples. Combination of both flavonoids at the same dose levels continued to decrease lipid peroxidation, the effect being the same for both metal ions. The data suggest that the combined flavonoids offered better protection than the single treatments and this may be attributed to the better radical scavenging or increased chelating capabilities of the combined over the single treatments. The differences in peroxide levels for the single treatment of quercetin compared with the genistein-treated samples may reflect the structural differences between these compounds in combating oxidative stress.

Radiation protection of HepG2 cells by Podophyllum hexandrum Royale

Radioprotection by an aqueous extract of Podophyllum hexandrum (RP-1) was investigated in HepG2 cells by evaluating colony forming efficacy (CFE), redox status of mitochondria, reactive oxygen species (ROS), generation of nitric oxide (NO), peroxidation of lipids and intracellular glutathione. Lower concentrations of RP-1 (0.1 and 1 microg/ml) rendered maximum radioprotection when administered 1 or 2 h before irradiation. Higher concentrations (5 and 10 microg/ml) however were less effective when administered 1 or 2 h before irradiation, but were more effective with increased time intervals (4 or 8 h) between RP-1 administration and irradiation. RP-1 pre-treatment also significantly inhibited radiation-induced MTT reduction in a concentration and time-dependent manner by decreasing gamma radiation-induced leakage of electrons from electron transport chain. Pre-irradiation administration of RP-1 significantly reduced both ROS and NO generation and enhanced glutathione levels, thereby inhibiting lipid peroxidation.

Quantitative structure toxicity relationships for phenols in isolated rat hepatocytes

Quantitative structure toxicity relationship (QSTR) equations were obtained to predict and describe the cytotoxicity of 31 phenols using logLD(50) as a concentration to induce 50% cytotoxicity of isolated rat hepatocytes in 2 h and logP as octanol/water partitioning: logLD(50) (microM)=-0.588(+/-0.059)logP+4.652(+/-0.153) (n=27, r(2)=0.801, s=0.261, P<1 x 10(-9)). Hydroquinone, catechol, 4-nitrophenol, and 2,4-dinitrophenol were outliers for this equation. When the ionization constant pK(a) was considered as a contributing factor a two-parameter QSTR equation was derived: logLD(50) (microM)=-0.595(+/-0.051)logP+0.197(+/-0.029)pK(a)+2.665(+/-0.281) (n=28, r(2)=0.859, s=0.218, P<1 x 10(-6)). Using sigma+, the Brown variation of the Hammet electronic constant, as a contributing parameter, the cytotoxicity of phenols towards hepatocytes were defined by logLD(50) (microM)=-0.594(+/-0.052)logP-0.552(+/-0.085)sigma+ +4.540(+/-0.132) (n=28, r(2)=0.853, s=0.223, P<1 x 10(-6)). Replacing sigma+ with the homolytic bond dissociation energy (BDE) for (X-PhOH+PhO.-->X-PhO.+PhOH) led to logLD(50) (microM)=-0.601(+/-0.066)logP-0.040(+/-0.018)BDE+4.611(+/-0.166) (n=23, r(2)=0.827, s=0.223, P<0.05). Hydroquinone, catechol and 2-nitrophenol were outliers for the above equations. Using redox potential and logP led to a new correlation: logLD(50) (microM)=-0.529(+/-0.135)logP+2.077(+/-0.892)E(p/2)+2.806(+/-0.592) (n=15, r(2)=0.561, s=0.383, P<0.05) with 4-nitrophenol as an outlier. Our findings indicate that phenols with higher lipophilicity, BDE, or sigma+ values or with lower pK(a) and redox potential were more toxic towards hepatocytes. We also showed that a collapse of hepatocyte mitochondrial membrane potential preceded the cytotoxicity of most phenols. Our study indicates that one or a combination of mechanisms; i.e. mitochondrial uncoupling, phenoxy radicals, or phenol metabolism to quinone methides and quinones, contribute to phenol cytotoxicity towards hepatocytes depending on the phenol chemical structure.

Evaluation of the redox properties and anti/pro-oxidant effects of selected flavonoids by means of a DNA-based electrochemical biosensor

Quercetin and rutin as well as catechin and epigallocatechin gallate were investigated, as widely distributed representatives of flavonols and flavanols, respectively, regarding their anti/pro-oxidant properties. The flavonoids are irreversibly oxidized at a dsDNA-modified screen-printed electrode within 0.368 to 0.449 V vs. SHE without binding to DNA. Using the DNA biosensor the detection scheme of a DNA prevention/degradation exploits the [Co(phen)(3)](3+) complex as an electrochemical DNA marker. Antioxidant activity of flavonoids was tested in a model cleavage mixture composed of 5 x 10(-7) mol L(-1) [Cu(phen)(2)](2+) as the catalyst, 1 x 10(-3) mol L(-1) ascorbic acid as the chemical reductant and atmospheric oxygen as the natural oxidant where reactive oxygen radicals are generated. The antioxidant activity increases with the concentration of flavonoids reaching a maximum where pro-oxidative behaviour becomes of importance. The pro-oxidant potency of flavonoids depends on the presence of atmospheric oxygen and follows the order quercetin>rutin>epigallocatechin gallate>catechin.

Mutagenicity, antioxidant potential, and antimutagenic activity against hydrogen peroxide of cashew (Anacardium occidentale) apple juice and cajuina

Fresh and processed cashew (Anacardium occidentale) apple juice (CAJ) are among the most popular drinks in Brazil. Besides their nutritional benefits, these juices have antibacterial and antitumor potential. The chemical constituents of both the fresh juice and the processed juice (cajuina) were analyzed and characterized as complex mixtures containing high concentrations of vitamin C, various carotenoids, phenolic compounds, and metals. In the present study, these beverages exhibited direct and rat liver S9-mediated mutagenicity in the Salmonella/microsome assay with strains TA97a, TA98, and TA100, which detect frameshifts and base pair substitution. No mutagenicity was observed with strain TA102, which detects oxidative and alkylating mutagens and active forms of oxygen. Both CAJ and cajuina showed antioxidant activity as determined by a total radical-trapping potential assay. To test whether this antioxidant potential might result in antimutagenesis, we used a variation of the Salmonella/microsome assay that included pre-, co-, and posttreatment of hydrogen peroxide-exposed Salmonella typhimurium strain TA102 with the juices. CAJ and cajuina protected strain TA102 against mutation by oxidative damage in co- and posttreatments. The antimutagenic effects during cotreatment with hydrogen peroxide may be due to scavenging free radicals and complexing extracellular mutagenic compounds. The protective effects in posttreatment may be due to stimulation of repair and/or reversion of DNA damage. The results indicate that CAJ and cajuina have mutagenic, radical-trapping, antimutagenic, and comutagenic activity and that these properties can be related to the chemical constituents of the juices.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

Iron-overload induces oxidative DNA damage in the human colon carcinoma cell line HT29 clone 19A

Dietary iron may contribute to colon cancer risk via production of reactive oxygen species (ROS). The aim of the study was to determine whether physiological ferric/ferrous iron induces oxidative DNA damage in human colon cells. Therefore, differentiated human colon tumour cells (HT29 clone 19A) were incubated with ferric-nitrilotriacetate (Fe-NTA) or with haemoglobin and DNA breaks and oxidised bases were determined by microgelelectrophoresis. The effects of Fe-NTA were measured with additional H(2)O(2) (75microM) and quercetin (25-100microM) treatment. Analytic detection of iron in cell cultures, treated with 250microM Fe-NTA for 15 min to 24h, showed that 48.02+/-5.14 to 68.31+/-2.11% were rapidly absorbed and then detectable in the cellular fraction. Fe-NTA (250-1000microM) induced DNA breaks and oxidised bases, which were enhanced by subsequent H(2)O(2) exposure. Simultaneous incubation of HT29 clone 19A cells with Fe-NTA and H(2)O(2) for 15 min, 37 degrees C did not change the effect of H(2)O(2) alone. The impact of Fe-NTA and H(2)O(2)-induced oxidative damage is reduced by the antioxidant quercetin (75-67% of H(2)O(2)-control). Haemoglobin was as effective as Fe-NTA in inducing DNA damage. From these results we can conclude that iron is taken up by human colon cells and participates in the induction of oxidative DNA damage. Thus, iron or its capacity to catalyse ROS-formation, is an important colon cancer risk factor. Inhibition of damage by quercetin reflects the potential of antioxidative compounds to influence this risk factor. Quantitative data on the genotoxic impact of ferrous iron (e.g. from red meat) relative to the concentrations of antioxidants (from plant foods) in the gut are now needed to determine the optimal balance of food intake that will reduce exposure to this type of colon cancer risk factor.

Evaluation of the genotoxic effect of rutin and quercetin by comet assay and micronucleus test

Flavonoids are phenolic compounds, naturally found in vegetables, tea and red wines. A recent study has demonstrated that the flavonoids rutin and quercetin show a protective role against the deleterious effects of free radicals in cirrhotic rats. Considering this finding and the controversial results concerning the mutagenicity of rutin and quercetin recorded in the literature, the capacity of these flavonoids to cause damage to the DNA was evaluated using the alkaline single-cell gel electrophoresis (SCG) and micronucleus test in the bone marrow of mice. The doses for both compounds were 2 x 2500, 2 x 1250 and 2 x 625 mg/kg. Micronucleus test showed that rutin caused no damage to the DNA of the mice bone marrow cells, and the SCG assay demonstrated an increase of damage only at the dose of 2 x 1250 mg/kg. But when the mice cells of the three quercetin doses were compared with the negative control, significantly higher damage was observed by SCG assay, although not proportional to the dose. The micronucleus test also demonstrated a significant increase of damage, but only at the 2 x 1250 mg/kg dose. Considering the results obtained in this study with very high doses, it is unlikely that the consumption of rutin and quercetin produces any clastogenic effects. Our results also indicated that SCG could profitably be used in drug genotoxicity evaluation protocols.

Antioxidants prevent the lymphocyte DNA damage induced by PMA-stimulated monocytes

Oxidative stress has been related to several degenerative diseases such as cancer and coronary heart disease. Reactive oxygen species can damage different cellular macromolecules, including DNA, which is directly responsible for mutation and carcinogenesis. In this study, monocytes that were activated by phorbol 12-myristate 13-acetate (PMA) were coincubated with lymphocytes, and the DNA damage was measured by single-cell gel electrophoresis (comet) assay. Stimulation of monocytes with PMA activates the "respiratory burst," which evokes DNA damage in lymphocytes. The extent of the damage is related to the concentration of monocytes and the exposure time. Exogenous addition of superoxide dismutase did not prevent the DNA damage, which suggests that superoxide ions are not directly responsible for the damage. Partial protection was observed when catalase was included (60% protection), which indicates that other reactive species, in addition to H2O2, are responsible for the damage. In this system, the protective activity of natural antioxidants at different concentrations was also investigated. After coincubation of PMA-activated monocytes with lymphocytes in the presence of each antioxidant for one hour at 37 degrees C, the lymphocyte DNA damage was determined. All the compounds protected the lymphocytes to a certain degree, with a maximum effect at different concentrations: 41% protection with 1 microM ascorbic acid, 55% protection with 40 microM alpha-tocopherol, 50% protection with 3 microM beta-carotene, and 56% protection with 5 microM quercetin. On the basis of these results, we maintain that this "ex vivo model," more closely related to physiological conditions, could be used to test the antioxidant activity of different compounds.

Sedanolide, a natural phthalide from celery seed oil: effect on hydrogen peroxide and tert-butyl hydroperoxide-induced toxicity in HepG2 and CaCo-2 human cell lines

Sedanolide is a natural compound occurring in edible umbelliferous plants. Celery seed oil, a significant source of sedanolide, is used as an herbal remedy to treat inflammatory-associated conditions such as gout and rheumatism. The objective of this study was to assess the potential protective properties of sedanolide against hydrogen peroxide (H(2)O(2))- and tert-butyl hydroperoxide (tBOOH)-induced toxicity in HepG2 and CaCo-2 cells. Viability of HepG2 and CaCo-2 cells was unaffected by a 24-h exposure to sedanolide (7-500 microM), however, when the cells were cultured in sedanolide-free medium for a further two cell cycles (72 h), a decrease in cell viability was observed for HepG2 cells previously exposed to 500 microM of the compound. Cells pretreated with sedanolide (100 microM for 24 h) and exposed to either H(2)O(2) or tBOOH did not exhibit statistically significant difference in viability from controls. A significant increase (p < 0.05) in DNA strand breaks, as measured by the comet assay, was observed in HepG2 but not CaCo-2 cells following a 24-h incubation with 500 microM sedanolide. Sedanolide did not modulate H(2)O(2)- and tBOOH-induced DNA damage. Sedanolide is relatively nontoxic to cells in culture, however, the protection it afforded against H(2)O(2)- and tBOOH-induced toxicity was not statistically significant.

Comparative quantitative structure toxicity relationships for flavonoids evaluated in isolated rat hepatocytes and HeLa tumor cells

Quantitative structure activity relationship (QSAR) equations were obtained to describe the cytotoxicity of 22 polyphenols using toxicity (logLD50) representing the concentration for 50% cell survival in 2 h for isolated rat hepatocytes, log P representing octanol/water partitioning, and/or E(p/2) representing redox potential. One- and two-parameter equations were derived for the quantitative structure toxicity relationships (QSTR) for polyphenol induced hepatocyte cytotoxicity: e.g. log C(hepatocyte) (microM)=-0.65(-0.08)log P+4.12(-0.15) (n=19, r(2)=0.80, s=0.33, P<1 x 10(-6)). One- and two-parameter QSAR equations were also derived to describe the inhibitory effects of 13 polyphenols on tumor cell growth when incubated with HeLa cells for 3 days: e.g. log C(tumor) (microM)=-0.34(+/-0.04)log P+2.40(+/-0.07) (n=11, r(2)=0.90, s=0.13, P<1 x 10(-5)). These findings point to lipophilicity as a major characteristic determining polyphenol cytotoxicity. The E(p/2) also played a significant role in polyphenol cytotoxicity towards both cell types: e.g. log C(hepatocyte) (microM)=-0.60(+/-0.06)log P+2.01(+/-0.43)E(p/2) (V)+3.86(+/-0.12) (n=9, r(2)=0.96, s=0.15, P<0.005). The involvement of log P and E(p/2) could be explained if polyphenol cytotoxicity involved the formation of radicals, which interacted with the mitochondrial inner membrane resulting in a disruption of the membrane potential.

Effects of dietary antioxidants on DNA damage in lysed cells using a modified comet assay procedure

A modified version of the comet assay was employed to investigate the effect in vitro of dietary antioxidants in the subcellular environment. Human lymphocytes were isolated, embedded in agarose gel, lysed in high ionic strength solution with Triton X-100, and then incubated for 30 min with antioxidants at different concentrations. Gels were washed, and the comet assay performed on cells stressed by 5 min incubation with 45 microM hydrogen peroxide and on unstressed cells in parallel. Results showed that alpha-tocopherol was protective against oxidant stress, whereas caffeic acid did not protect, and at high concentration (100 microM) caused increased DNA damage. Results for quercetin suggested a direct damaging effect, but this did not reach statistical significance. However, at low concentration (3.1 microM), quercetin appeared protective. Thus some dietary antioxidants that have been shown previously to have a protective effect in the 'standard', whole-cell, comet assay cause DNA damage in this lysed-cell version. The cell membrane may have an important role in limiting cellular access of these 'double-edged' antioxidants. Furthermore, the absolute concentration and the presence of complementary or synergistic intracellular antioxidants may delineate the type of action of a putative antioxidant. We suggest that, used in conjunction with the standard comet assay, this lysed-cell version is useful for assessing the effect of the cell membrane and intracellular systems on susceptibility of DNA to oxidative damage, and will help determine the mechanism of protection or damage by phytochemicals.

The detection of mutations induced in vitro in the human p53 gene by hydrogen peroxide with the restriction site mutation (RSM) assay

We have analysed five mutation hotspots within the p53 gene (codons 175, 213, 248, 249, and 282) for mutations induced by hydrogen peroxide (H(2)O(2)), employing the restriction site mutation (RSM) assay. In addition, four other restriction sites covering non-hotspot codons of exons 5-9 of the p53 gene (codons 126, 153/54, 189 and the 3' splice site of exon 9) were analysed by the RSM assay for H(2)O(2)-induced mutations. Two cell types were concurrently analysed in this study, i.e. primary fibroblast cells and a gastric cancer cell line. Using the RSM assay, H(2)O(2)-induced mutations were only detected in exon 7 of the p53 gene. This was true for both cell types. These mutations were mainly induced in the Msp I restriction site (codon 247/248) and were predominantly GC to AT transitions (71%). Hence these GC to AT mutations were presumably due to H(2)O(2) exposure, possibly implicating the 5OHdC adduct, which is known to induce C to T mutations upon misreplication. Importantly, this study demonstrates that the RSM methodology is capable of detecting rare oxidative mutations within the hotspot codons of the p53 tumour suppressor gene. Hence, this methodology may allow the detection of early p53 mutations in pre-malignant tissues.

Quercetin modifies reactive oxygen levels but exerts only partial protection against oxidative stress within HL-60 cells

Quercetin may contribute to the protection afforded by fruit- and vegetable-rich diets against diseases for which excess production of reactive oxygen species (ROS) has been implicated as a causal or contributory factor. We examine the effect of short term (90 min) quercetin (1-100 microM) exposure on the progress of menadione induced oxidative stress within HL-60 cells. 2',7'-dichlorofluorescein and rhodamine-123 fluorescence, resulting from oxidation of the ROS-sensitive dyes dichlorodihydrofluorescein and dihydrorhodamine-123 respectively, were utilised as indicators of general ROS levels. Ethidium fluorescence, resulting from oxidation of dihydroethidium, was used as a potentially more specific indicator of O(2)(-). Exposure to quercetin alone induced a decrease in DCF and rhodamine fluorescence. Conversely, ethidium fluorescence was enhanced by treatment with >or=40 microM quercetin. Incubation with 1-100 microM quercetin reduced the extent of menadione-induced increase in DCF and rhodamine fluorescence but the menadione-induced increase in ethidium fluorescence was further elevated for cells treated with >or=25 microM quercetin. Exposure to >or=10 microM quercetin abrogated menadione-induced DNA single-strand breaks but, paradoxically, quercetin exacerbated membrane damage and failed to enhance the viability of menadione-challenged cells. In conclusion, quercetin exerts only site-specific protection against oxidative stress.

Antioxidant effect of flavonoids after ascorbate/Fe2+-induced oxidative stress in cultured retinal cells11Abbreviations: BME, basal medium of Eagle; DCFH2, 2′,7′-dichlorodihydrofluorescein; LDH, lactate dehydrogenase; PC, partition coefficient; Rf, retardation factor; ROS, reactive oxygen species; TBA, thiobarbituric acid; and TBARS, thiobarbituric acid-reactive substances

In this study, we investigated the structure-activity relationship of four flavonoids, i.e. eriodictyol, luteolin, quercetin, and taxifolin, in cultured retinal cells after ascorbate/Fe(2+)-induced oxidative stress. The relative order of antioxidant efficacy, determined by the thiobarbituric acid method, was the following: eriodictyol > quercetin > luteolin > taxifolin. Upon preincubation, the flavonoids were also effective in reducing the extent of lipid peroxidation. Oxidative stress, determined by the changes in fluorescence of 2',7'-dichlorodihydrofluorescein, was also decreased in the presence of the flavonoids, showing the following order of antioxidant efficacy: eriodictyol > taxifolin approximately quercetin > luteolin. Ascorbate/Fe(2+)-induced oxidative stress or incubation in the presence of the flavonoids did not significantly affect the viability of retinal cells. We also evaluated the degree of membrane partition of the flavonoids. In this system, the results strongly suggest that the higher antioxidant activity of the flavonoids is not correlated with the presence of a double bond at C(2)-C(3) and/or a hydroxyl group at C(3) on the C ring, but rather may depend on the capacity to inhibit the production of reactive oxygen species to interact hydrophobically with membranes. Eriodictyol was shown to be the most efficient antioxidant in protecting against oxidative stress induced by ascorbate/Fe(2+) in the retinal cells.

Disparate effects of similar phenolic phytochemicals as inhibitors of oxidative damage to cellular DNA

Phenolic phytochemicals are natural plant substances whose cellular effects have not been completely determined. Nordihydroguaiaretic acid (NDGA) and curcumin are two phenolic phytochemicals with similar molecular structures, suggesting that they possess comparable chemical properties particularly in terms of antioxidant activity. To examine this possibility in a cellular system, this study evaluated the capacities of NDGA and curcumin to function as antioxidants in inhibiting oxidative damage to DNA. Jurkat T-lymphocytes were pre-incubated for 30 min with 0-25 microM of either NDGA or curcumin to allow for uptake. The phenolic phytochemical-treated cells were then oxidatively challenged with 25 microM hydrogen peroxide (H2O2). Afterwards, cells were subjected to alkaline micro-gel electrophoresis (i.e. comet assay) to assess the extent of single-strand breaks in DNA. In a concentration-dependent manner, NDGA inhibited H2O2-induced DNA damage, whereas curcumin did not. In fact, incubating Jurkat T-lymphocytes with curcumin alone actually induced DNA damage. This effect of curcumin on DNA did not appear to reflect the DNA fragmentation associated with apoptosis because there was no proteolytic cleavage of poly-(ADP-ribose)-polymerase, which is considered an early marker of apoptosis. Curcumin-induced damage to DNA was prevented by pre-treatment of the cells with the lipophilic antioxidant, alpha-tocopherol, suggesting that curcumin damaged DNA through oxygen radicals. Therefore, it is concluded that NDGA has antioxidant activity but curcumin has prooxidant activity in cultured cells based on their opposite effects on DNA.

Effect of phytoestrogen and antioxidant supplementation on oxidative DNA damage assessed using the comet assay

Antioxidant species may act in vivo to decrease oxidative damage to DNA, protein and lipids thus reducing the risk of coronary heart disease and cancer. Phytoestrogens are plant compounds which are a major component of traditional Asian diets and which may be protective against certain hormone-dependent cancers (breast and prostate) and against coronary heart disease. They may also be able to function as antioxidants, scavenging potentially harmful free radicals. In this study, the effects of the isoflavonoids (a class of phytoestrogen) genistein and equol on hydrogen peroxide-mediated DNA damage in human lymphocytes were determined using alkaline single-cell gel electrophoresis (the comet assay). Treatment with hydrogen peroxide significantly increased the levels of DNA strand breaks. Pre-treatment of the cells with both genistein and equol offered protection against this damage at concentrations within the physiological range. This protection was greater than that offered by addition of the known antioxidant vitamins ascorbic acid and alpha-tocopherol, or the compounds 17beta-oestradiol and Tamoxifen which have similar structures to isoflavonoids and are known to have weak antioxidant properties. These findings are consistent with the hypothesis that phytoestrogens can, under certain conditions, function as antioxidants and protect against oxidatively-induced DNA damage.

Protective effect of extracts of Mesona procumbens Hemsl. on DNA damage in human lymphocytes exposed to hydrogen peroxide and UV irradiation

In the present study, the protective effect of water extracts from Hsian-tsao (WEHT) on DNA damage in human lymphocytes induced by UV-C and/or H(2)O(2) was evaluated using single-cell electrophoresis (comet assay). No toxicity was found in WEHT towards human lymphocytes. WEHT did not cause DNA damage at lower concentrations of 0.05 and 0.1 mg/ml, while it did cause slight DNA damage at a concentration of 0.5-2.5 mg/ml when compared with the control group. When WEHT was mixed with H(2)O(2) for reaction, it exhibited a slight inhibitory effect on DNA damage induced by H(2)O(2). Moreover, when WEHT and lymphocytes were irradiated by UV-C and then incubated for 35 min, the DNA damage decreased with an increase of the concentration of WEHT. Thus, WEHT could reduce UV-C-induced DNA damage, and WEHT had a more protective effect on UV-C than on H(2)O(2)-induced DNA damage. The protective effect of WEHT on DNA damage might be due to the fact that it contains polyphenol compounds and/or other active components.

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.

Prooxidant toxicity of polyphenolic antioxidants to HL-60 cells: description of quantitative structure-activity relationships

Polyphenolic antioxidants exhibited a dose-dependent toxicity against human promyelocytic leukemia cells (HL-60). Their action was accompanied by malondialdehyde formation, and was partly prevented by desferrioxamine and the antioxidant N,N'-diphenyl-p-phenylene diamine. This points to a prooxidant character of their cytotoxicity. A quantitative structure-activity relationship (QSAR) has been obtained to describe the cytotoxicity of 13 polyphenolic antioxidants belonging to three different groups (flavonoids, derivatives of gallic and caffeic acid): log cL50 (microM) = (2.7829+/-0.2339)+(1.2734+/-0.4715) Ep/2 (V)-(0.3438+/-0.0582) log P (r2 = 0.8129), where cL50 represents the concentration for 50% cell survival, Ep/2 represents the voltammetric midpoint potential, and P represents the octanol/water partition coefficient. Analogous QSARs were obtained using enthalpies of single-electron oxidation of these compounds, obtained by quantum-mechanical calculations. These findings clearly point to two important characteristics determining polyphenol cytotoxicity, namely their ease of oxidation and their lipophilicity.

The effect of increased intakes of polyunsaturated fatty acids and vitamin E on DNA damage in human lymphocytes

The effect of increasing dietary intakes of polyunsaturated fatty acids (PUFAs) and vitamin E on indices of oxidative DNA damage was investigated. Twenty-one healthy male, nonsmokers aged 28.9 +/- 1.3 years participated in a free-living, split plot/change over trial in which half the volunteers consumed diets containing 5% PUFA as food energy for 4 wk and, after a 10 wk washout period, consumed a 15% PUFA diet for another 4 wk. The other volunteers followed an identical protocol, except that they consumed the 15% PUFA diet first. The diets were provided to volunteers either with or without an additional 80 mg dalpha-tocopherol acetate/day; otherwise total fat, carbohydrates, protein, and basal vitamin E contents remained unchanged. DNA damage induced by 200 microM H(2)O(2) in lymphocytes from volunteers as well as endogenous DNA damage in the form of oxidized pyrimidines, measured by alkaline single-cell gel electrophoresis (the comet assay), significantly decreased after consumption of the 5% PUFA diet (P<0.001 and P=0.01, respectively), but significantly increased after consumption of the 15% PUFA diet when alpha-tocopherol levels were in the range of 5-7 mg/day (P=0. 008 and P=0.03, respectively). These changes were abolished by an additional 80 mg dalpha-tocopherol/day. This study indicates that increasing dietary levels of PUFA to 15% may adversely affect some indices of DNA stability. However, increasing the dietary intake of vitamin E by 80 mg/day ameliorates the damaging effects of PUFA. -Jenkinson, A. McE., Collins, A. R., Duthie, S. J., Wahle, K. W. J., Duthie, G. G. The effect of increased intakes of polyunsaturated fatty acids and vitamin E on DNA damage in human lymphocytes.

Comet assay application in environmental monitoring: DNA damage in human leukocytes and plant cells in comparison with bacterial and yeast tests

Urban airborne particulate is a complex mixture of air pollutants, many of which have not been identified. However, short-term mutagenesis tests together with chemicophysical parameter analysis are able to better assess air quality and genotoxic load. The findings of continuous monitoring (January 1991-August 1998) of urban air genotoxicity of a Po Valley town (Italy) on Salmonella typhimurium and Saccharomyces cerevisiae are reported. During this period, various measures (catalytic devices, unleaded fuels, annual vehicle overhaul, etc.) to improve air-dispersed pollutant control were enforced. However, a continuous presence of genotoxic compounds is shown and more qualitative than quantitative changes are evident. We also demonstrate the ability of the Comet assay to detect DNA-damaging agents in airborne particulate samples. We applied the test to human leukocytes and, with major improvements, to plant cells (Allium cepa roots and epigean tissues of Impatiens balsamina). The first findings on human leukocytes confirm the sensitivity of this assay, its peculiarity and its applicability in assessing genotoxicity in environmental samples. The capability of plants to show the response of multicellular organisms to environmental pollutants largely counterbalances a probable lowering in sensitivity. Moreover, application of the Comet test to epigean tissues could be useful in estimating the bioavailability of and genotoxic damage by air pollutants, including volatile compounds (ozone, benzene, nitrogen oxides, etc.) to higher plants.

Glutathione and ascorbate are negatively correlated with oxidative DNA damage in human lymphocytes

Intracellular antioxidants, glutathione and ascorbate, and two molecular markers of oxidative DNA damage, 5-hydroxy-2'-deoxycytidine (5-OH-dCyd) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo), were measured in lymphocytes from 105 healthy volunteers. The analysis of 5-OH-dCyd and 8-oxo-dGuo was carried out by HPLC with electrochemical detection such that both compounds were detected on the same chromatography run. There was no significant difference in oxidative DNA damage when the extraction of DNA from cells using phenol was carried out under anaerobic conditions or in the presence of metal ion chelators. This indicates that auto-oxidation of DNA during sample preparation was minimal. Using the above methods, the average level of oxidative DNA damage in lymphocytes was 2.9 +/- 1.4 for 5-OH-dCyd and 4.5 +/- 1.8 for 8-oxo-dGuo lesions per 10(6) dGuo (n = 105). It is unlikely that artifactual oxidation contributed to the observed damage because the level of 5-OH-dCyd was comparable with that of 8-oxo-dGuo in lymphocyte DNA, whereas 8-oxo-dGuo outnumbers 5-OH-dCyd by a ratio of >5:1 when DNA is exposed to various oxidants, including ionizing radiation or Fenton reagents. Rather, the nearly equal levels of 5-OH-dCyd and 8-oxo-dGuo in cellular DNA implies that 8-oxo-dGuo may be more efficiently removed by DNA repair. Finally, and most importantly, the correlation of our endpoints revealed that the naturally occurring level of intracellular antioxidants was negatively correlated to the level of oxidative DNA damage with the strongest correlation observed for glutathione and 8-oxo-dGuo (r = -0.36; P < 0.001). These results strongly suggest that intracellular glutathione and ascorbate protect human lymphocytes against oxidative DNA damage.

Fate of the flavonoid quercetin in human cell lines: chemical instability and metabolism

Although cell cultures are increasingly being used as models for studying the biological actions of flavonoids, no information on the fate, such as uptake and metabolism, exists for these natural products in these models. This study examined the elimination of quercetin, one of the most abundant flavonoids, from the cultured human hepatocarcinoma cell line Hep G2 using [14C]-labelled compound with HPLC and LC/MS for structure characterization. These cells showed a 9.6-fold accumulation of quercetin and the formation of an O-methylated metabolite, isorhamnetin. However, a rapid elimination of quercetin, with no unchanged compound present beyond 8 h, was mainly due to oxidative degradation. The initial intermediate reaction appears to involve peroxidation, leading to a dioxetan, as evidenced by a 32-amu increase in the molecular ion by LC/MS. Subsequently, opening of the C-ring leads to the formation of carboxylic acids, the major one identified in this study as protocatechuic acid. A separate reaction results in a polymeric quercetin product which is highly retained on a reversed-phase C18 HPLC column. It is postulated that these degradative and metabolic changes contribute to the multiple biological actions reported for quercetin, using cell culture models. Interestingly, part of the degradative pathway could be inhibited by including nontoxic concentrations of EDTA in the cell culture medium.

Single cell gel electrophoresis assay: methodology and applications

The single cell gel electrophoresis or Comet assay is a sensitive, reliable, and rapid method for DNA double- and single-strand breaks, alkali-labile sites and delayed repair site detection, in eukaryotic individual cells. Given its overall characteristics, this method has been widely used over the past few years in several different areas. In this paper we review the studies published to date about the principles, the basic methodology with currently used variations. We also explore the applications of this assay in: genotoxicology, clinical area, DNA repair studies, environmental biomonitoring and human monitoring.