Inhibition of mitochondrial respiration and production of toxic oxygen radicals by flavonoids. A structure-activity study

Substituent Effects in the Free Radical Reactions of Silybin: Radiation-induced Oxidation of the Flavonoid at Neutral pH

Silybin dihemisuccinate sodium salt, a flavonoid used in human therapy of liver dysfunction, has an inhibitory effect in vivo on radiation-induced deactivation of enzymes and peroxidation of membrane lipids in rat liver microsomes. The reactivity of silybin and its phenolic OH groups towards free radicals (OH, N3., (SCN)2.-, Cl3CO2.) in aqueous solution was studied by pulse radiolysis. Absorption spectra for the phenoxyl-type radicals were assigned using structurally similar models. The one-electron reduction potential for silybin at pH 7 (E07 = 0.76 V), determined using the p-methoxy-phenoxyl/phenolate redox couple as reference standard (E07 = 0.72 V, Lind et al. 1990), is related to the 3'-methoxy-4'-OH structure, the exclusive target for one-electron oxidation at pH 7, while the 7-OH and 5-OH groups are prevented from oxidation by 4-keto substitution and intramolecular H-bonding, respectively. The free radical reactivity of silybin compares favourably with poly-OH-substituted flavonoids; however, the latter compounds have been reported to generate potentially toxic oxygen species at a biologically relevant pH.

Baicalein induces proliferation inhibition in B16F10 melanoma cells by generating reactive oxygen species via 12-lipoxygenase

In a previous study, we demonstrated that baicalein induces hydroxyl radical formation in human platelets but the mechanisms are unclear. Herein, we show, using an electron spin resonance technique, that baicalein also induces hydroxyl radical formation in B16F10 melanoma cells in a dose-dependent manner. Baicalein produced superoxide anions in the presence of an iron chelator and superoxide dismutase (SOD) inhibitor. We suggest that superoxide anions produced by baicalein were promptly converted to hydroxyl radicals through SOD and the Fenton reaction in B16F10 melanoma cells. According to Western blotting results, the 12-LOX protein was expressed in B16F10 melanoma cells, but baicalein had no effect on 12-LOX expression. Decreases in 12-LOX protein expression and hydroxyl radical signals occurred in a 12-LOX small interfering RNA knockdown protein group compared with the baicalein control. In the MTT assay, we also found that baicalein caused a reduction in cellular viability, which was reversed by the addition of ROS scavengers. On the basis of these data, we conclude that ROS formation catalyzed by 12-LOX is one possible mechanism of growth inhibition by baicalein in B16F10 melanoma cells.

Restoration of energy metabolism in leukemic mice treated by a siddha drug--Semecarpus anacardium Linn. nut milk extract

Chronic myeloid leukemia (CML) is a clonal disorder characterized by proliferation of hematopoietic cells that possess the BCR-ABL fusion gene resulting in the production of a 210 kDa chimeric tyrosine kinase protein. CML, when left untreated, progresses to a blast phase during which the disease turns aggressive and shows poor response to known treatment regimens. We have studied a Siddha herbal agent, Semecarpus anacardium Linn. nut milk extract (SA) for its antileukemic activity and its effect on the changes in energy metabolism in leukemic mice. Leukemia was induced in BALB/c mice by tail vein injection of BCR-ABL(+) 12B1 murine leukemia cell line. This resulted in an aggressive leukemia, similar to CML in blast crisis, myeloid subtype, confirmed by histopathological study and RT-PCR for the p210 mRNA in the peripheral blood, spleen and liver. Leukemia-bearing mice showed a significant increase in lipid peroxides, glycolytic enzymes, a decrease in gluconeogenic enzymes and significant decrease in the activities of TCA cycle and respiratory chain enzymes as compared to control animals. SA treatment was compared with standard drug imatinib mesylate. SA administration to leukemic animals resulted in clearance of the leukemic cells from the bone marrow and internal organs on histopathological examination and this was confirmed by RT-PCR for the p210 mRNA. Treatment with SA significantly reversed the changes seen in the levels of the lipid peroxides, the glycolytic enzymes, the gluconeogenic enzymes and the mitochondrial enzymes. These effects are probably due to the flavonoids, polyphenols and other compounds present in SA which result in total regression of leukemia and correction of the alterations in energy metabolism. Study of animals treated with SA alone did not reveal any adverse effects. On the basis of the observed results, SA can be considered as a readily accessible, promising and novel antileukemic chemotherapeutic agent.

trans-Resveratrol induces apoptosis in human breast cancer cells MCF-7 by the activation of MAP kinases pathways

Polyphenols represent a large class of plant-derived molecules with a general chemical structure that act as potent free radical scavengers. They have long been recognized to possess several therapeutic activities ranging from anti-thrombotic to antioxidant. Moreover, the capability of polyphenols to act as reducing or oxidizing molecules depends on the presence of environmental metals and on the concentrations used. In this work we demonstrated that the stilbene trans-resveratrol was able to commit human breast cancer MCF-7 cells to apoptosis. Mainly, we evidenced a pivotal role of the mitochondria in this phenomenon as cytochrome c release into the cytosol was found after the treatment. We further showed that trans-resveratrol was able to affect cellular redox state. In particular, it induced an early production of ROS and lipid oxidation, and only later compromised the GSH/GSSG ratio. This mode of action was mirrored by a temporally different activation of JNK and p38(MAPK), with the former rapidly induced and the latter weakly activated at long intervals. The results obtained demonstrate a pro-apoptotic activity for trans-resveratrol, and suggest a preferential activation of different classes of MAP kinases in response to different oxidative stimuli (ROS versus GSH/GSSG alteration).

Antioxidants and polyunsaturated fatty acids in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). Oligodendrocyte damage and subsequent axonal demyelination is a hallmark of this disease. Different pathomechanisms, for example, immune-mediated inflammation, oxidative stress and excitotoxicity, are involved in the immunopathology of MS. The risk of developing MS is associated with increased dietary intake of saturated fatty acids. Polyunsaturated fatty acid (PUFA) and antioxidant deficiencies along with decreased cellular antioxidant defence mechanisms have been observed in MS patients. Furthermore, antioxidant and PUFA treatment in experimental allergic encephalomyelitis, an animal model of MS, decreased the clinical signs of disease. Low-molecular-weight antioxidants may support cellular antioxidant defences in various ways, including radical scavenging, interfering with gene transcription, protein expression, enzyme activity and by metal chelation. PUFAs may not only exert immunosuppressive actions through their incorporation in immune cells but also may affect cell function within the CNS. Both dietary antioxidants and PUFAs have the potential to diminish disease symptoms by targeting specific pathomechanisms and supporting recovery in MS.

Inhibition of iNOS gene expression by quercetin is mediated by the inhibition of IkappaB kinase, nuclear factor-kappa B and STAT1, and depends on heme oxygenase-1 induction in mouse BV-2 microglia

In the present study, experiments were performed to explore the action of quercetin, the most widely distributed flavonoids, and its major metabolite, quercetin-3'-sulfate, on lipopolysaccharide (LPS)- and interferon-gamma (IFN-gamma)-induced nitric oxide (NO) production in BV-2 microglia. Quercetin could suppress LPS- and IFN-gamma-induced NO production and inducible nitric oxide synthase (iNOS) gene transcription, while quercetin-3'-sulfate had no effect. LPS-induced IkappaB kinase (IKK), nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1) activation, and IFN-gamma-induced NF-kappaB, signal transducer and activator of transcription-1 (STAT1) and interferon regulatory factor-1 (IRF-1) activation were reduced by quercetin. Moreover quercetin was able to induce heme oxygenase-1 expression. To address the involvement of heme oxygenase-1 induction in iNOS inhibition, heme oxygenase-1 antisense oligodeoxynucleotide was used. Quercetin-mediated inhibition of NO production and iNOS protein expression were partially reversed by heme oxygenase-1 antisense oligodeoxynucleotide, but was mimicked by hemin, a heme oxygenase-1 inducer. The involvement of signal pathways in quercetin-induced heme oxygenase-1 gene expression was associated with tyrosine kinase and mitogen-activated protein kinases activation. All these results suggest quercetin should provide therapeutic benefits for suppression of inflammatory-related neuronal injury in neurodegenerative diseases.

Low concentrations of flavonoids are protective in rat H4IIE cells whereas high concentrations cause DNA damage and apoptosis

Dietary flavonoids possess a wide spectrum of biochemical and pharmacological actions and are assumed to protect human health. These actions, however, can be antagonistic, and some health claims are mutually exclusive. The antiapoptotic actions of flavonoids may protect against neurodegenerative diseases, whereas their proapoptotic actions could be used for cancer chemotherapy. This study was undertaken to determine whether a cytoprotective dose range of flavonoids could be differentiated from a cytotoxic dose range. Seven structurally related flavonoids were tested for their ability to protect H4IIE rat hepatoma cells against H(2)O(2)-induced damage on the one hand and to induce cellular damage on their own on the other hand. All flavonoids proved to be good antioxidants in a cell-free assay. However, their pharmacologic activity did not correlate with in vitro antioxidant potential but rather with cellular uptake. For quercetin and fisetin, which were readily taken up into the cells, protective effects against H(2)O(2)-induced cytotoxicity, DNA strand breaks, and apoptosis were detected at concentrations as low as 10-25 micromol/L. On the other hand, these flavonoids induced cytotoxicity, DNA strand breaks, oligonucleosomal DNA fragmentation, and caspase activation at concentrations between 50 and 250 micromol/L. Published data on quercetin pharmacokinetics in humans suggest that a dietary supplement of 1-2 g of quercetin may result in plasma concentrations between 10 and 50 micromol/L. Our data suggest that cytoprotective concentrations of some flavonoids are lower by a factor of 5-10 than their DNA-damaging and proapoptotic concentrations.

Estrogen, mitochondria, and growth of cancer and non-cancer cells

In this review, we discuss estrogen actions on mitochondrial function and the possible implications on cell growth. Mitochondria are important targets of estrogen action. Therefore, an in-depth analysis of interaction between estrogen and mitochondria; and mitochondrial signaling to nucleus are pertinent to the development of new therapy strategies for the treatment of estrogen-dependent diseases related to mitochondrial disorders, including cancer.

Doxorubicin hepatotoxicity and hepatic free radical metabolism in rats. The effects of vitamin E and catechin

Doxorubicin (DXR) is an anthracycline antibiotic, broadly used in tumor therapy. In the present study we investigated whether vitamin E and catechin can reduce the toxic effects of doxorubicin. Vitamin E (200 IU/kg/week), catechin (200 mg/kg/week), doxorubicin (5 mg/kg/week), doxorubicin+vitamin E (200 IU/kg/week), doxorubicin+catechin (200 mg/kg/week) combinations were given to rats weighing 210-230 g (n=6/group). Changes in major enzymes participating in free radical metabolism superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GSHPx), catalase (CAT) and malondialdehyde (MDA) were evaluated in the livers of all animals. Superoxide dismutase and catalase activity increased in the doxorubicin-treated group compared to control (P<0.05). Glutathione peroxidase levels increased in the catechin+doxorubicin-treated group (P<0.05) and reached maximum concentrations in the doxorubicin-treated group compared to control (P<0.01). Malondialdehyde levels increased in the doxorubicin-treated group compared to control and all-treated groups (P<0.05). Malondialdehyde, glutathione peroxidase and catalase activities were decreased in the vitamin E+doxorubicin- and catechin+doxorubicin-treated group compared to doxorubicin-treated group (P<0.05). All enzymes activities showed no statistical differences in the not mentioned groups above (P>0.05). Electron microscopic studies supported biochemical findings. We conclude that vitamin E and catechin significantly reduce doxorubicin-induced hepatotoxicity in rats.

The rutin/β-cyclodextrin interactions in fully aqueous solution: spectroscopic studies and biological assays

In the present work the feasibility of beta-cyclodextrin complexation was explored, as a tool for improving the aqueous solubility and antioxidant efficacy of rutin. By means of 1H NMR, UV-vis and circular dichroism spectroscopy the single aromatic ring of rutin was found to be inserted into the beta-cyclodextrin cavity to form a 1:1 inclusion complex. The effect of beta-cyclodextrin on the spectral features of rutin was quantitatively investigated, in fully aqueous medium, by holding the concentration of the guest constant and varying the host concentration. The associated binding constants were estimated to be 142+/-20 and 153+/-20 M(-1), respectively, on the basis of the observed UV-vis absorption and circular dichroism intensities. The antioxidant activity of rutin was also investigated, as affected by molecular encapsulation within beta-cyclodextrin (batophenanthroline test; comet assay; lipid peroxidation); the inclusion complex revealed improved antioxidant efficacy that may be in part explained by an increased solubility in the biological moiety.

Molecular cytotoxic mechanisms of anticancer hydroxychalcones

Chalcones are being considered as anticancer agents as they are natural compounds that are particularly cytotoxic towards K562 leukemia or melanoma cells. In this study, we have investigated phloretin, isoliquiritigenin, and 10 other hydroxylated chalcones for their cytotoxic mechanisms towards isolated rat hepatocytes. All hydroxychalcones partly depleted hepatocyte GSH and oxidized GSH to GSSG. These chalcones also caused a collapse of mitochondrial membrane potential and increased oxygen uptake. Furthermore, glycolytic or citric acid cycle substrates prevented cytotoxicity and mitochondrial membrane potential collapse. The highest pKa chalcones were the most effective at collapsing the mitochondrial membrane potential which suggests that the cytotoxic activity of hydroxychalcones are likely because of their ability to uncouple mitochondria.

Antioxidant, a pro-oxidant and cytotoxic effects of Achyrocline satureioides extracts

In this study we compared the antioxidant properties of five different extracts of different composition obtained from Achyrocline satureioides' inflorescences (Compositae), a widely used Brazilian folk medicinal herb. All of the extracts presented significant antioxidant potential identified by TRAP assay, which increased in the presence of human plasma. Characterization of the content of flavonoids in each extract showed that the FDP80 (ethanol 80%) and FFr (enriched flavonoid fraction) extracts contained a higher content of flavonoids. Cytotoxicity of the extracts as determined in Sertoli cell culture showed that FDP80 and FFr were highly toxic at most concentrations tested. The extracts induced a significant increase in lipid peroxidation levels in Sertoli cells. These results suggest that medicinal herb extracts that contain higher flavonoid concentrations and shows higher antioxidant protection in vitro might not always produce the greatest benefit.

Inhibitory effects of plant-derived flavonoids and phenolic acids on malonaldehyde formation from ethyl arachidonate

The antioxidant activities of naturally occurring plant compounds were measured in a lipid peroxidation system consisting of ethyl arachidonate and Fenton's reagent. Inhibitory effects of 24 plant-derived flavonoids and 5 phenolic acids on malonaldehyde (MA) formation from ethyl arachidonate were examined using gas chromatography (GC) with a nitrogen-phosphorus detector (NPD). Luteolin, which showed the strongest antioxidant activity, inhibited MA formation by 94% and 97% at the levels of 0.5 and 1.0 mM, respectively. The antioxidant activities of the flavones and flavonols decreased in the following order: luteolin > rhamnetin > fisetin > kaempferol > morin > quercetin. Among the flavanones tested, hesperitin, taxifolin, and naringenin exhibited appreciable antioxidant activities (61-84%) at the 1.0 mM level. The inhibitory effect of epigallocatechin gallate (82.5% at the 1.0 mM level) was the strongest among the flavan-3-ols tested. Ferulic acid had the most potent antioxidant activity (74.6% at the 1.0 mM level) of the phenolic acids tested.

Reduction of genistein clastogenicity in Chinese hamster V79 cells by daidzein and other flavonoids

A broad spectrum of health benefits has been ascribed to soy products. These products contain soy protein and relatively high levels of polyphenolic compounds known as flavonoids. While they are the most likely candidates for biological activity, flavonoids as a class, and of specific interest, genistein, are well known to be genotoxic due to their ability to "poison" cellular DNA topoisomerase II (topo II) resulting in stable chromosome breakage and mutation and raising questions about the long term health effects associated with chronic flavonoid exposure. Interestingly, some flavonoids, such as biochanin, galangin and daidzein, are catalytic topo II inhibitors (not poisons) and actually antagonize the clastogenicity of topo II poisons. It is shown in the present paper that flavonoids possessing catalytic topo II inhibitory activity, strongly antagonize the clastogenicity of genistein in Chinese hamster V79 cells. Importantly, one of these, daidzein, is a major constituent of marketed soy products. It is conjectured that the potential human clastogenic risk of soy products containing genistein might be mitigated or abolished due to the presence of daidzein or other flavonoids in those products.

Main flavonoids in the root of Scutellaria baicalensis cultivated in Europe and their comparative antiradical properties

The content of the main flavonoids in the root of Scutellaria baicalensis Georgi cultivated in Central Europe was evaluated using the new simple RP-HPLC method with gradient of acetonitrile in mobile phase. The main components of the roots were baicalin (8.12% of dry root mass) and wogonin glucuronide (2.52%). The content of flavonoids was comparable with the content in plants cultivated in natural localities. Five main flavonoids were evaluated for their scavenging ability with DPPH radical-generating system and due to limited solubility only two flavonoids were investigated for their ability to scavenge hydroxyl radical by the aromatic hydroxylation method. The total extract was also tested in both the experimental arrangements. In experiments with DPPH, only baicalin and baicalein displayed a significant scavenging effect, while the production of OH radicals generated by UV photolysis of H(2)O(2) was considerable decreased in the presence of baicalin and wogonin glucuronide. After comparison with results obtained for the total extract, it was concluded, that the scavenging activity of the extract against DPPH is mainly derived from baicalin. On the other hand, baicalin, wogonin glucuronide and probably other flavonoids participate in scavenging OH radical.

Interaction of genistein with the mitochondrial electron transport chain results in opening of the membrane transition pore

Genistein, a natural isoflavone present in soybeans, is a potent agent in the prophylaxis and treatment of cancer. Addition of genistein to isolated rat liver mitochondria (RLM) induces swelling, loss of membrane potential and release of accumulated Ca2+. These changes are Ca2+-dependent and are prevented by cyclosporin A (CsA) and bongkrekic acid (BKA), two classical inhibitors of the mitochondrial permeability transition (MPT). Induction of the MPT by genistein is accompanied by oxidation of thiol groups and pyridine nucleotides. The reducing agent dithioerythritol and the alkylating agent N-ethylmaleimide (NEM) completely prevent the opening of the transition pore, thereby emphasizing that the effect of the isoflavone correlates with the mitochondrial redox state. Further analyses showed that genistein induces the MPT by the generation of reactive oxygen species (ROS) due to its interaction with the respiratory chain at the level of mitochondrial complex III.

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.

Protective role of antioxidant vitamin E and catechin on idarubicin-induced cardiotoxicity in rats

Idarubicin is an anthracycline antibiotic extensively used in acute leukemia. In the present study we investigated whether vitamin E and catechin can reduce the toxic effects of idarubicin. Vitamin E (200 IU kg(-1) week(-1)), catechin (200 mg kg(-1) week(-1)), idarubicin (5 mg kg(-1) week(-1)), idarubicin + vitamin E (200 IU kg(-1) week(-1)), and idarubicin + catechin (200 mg kg(-1) week(-1)) combinations were given to male Sprague-Dawley rats weighing 210 to 230 g (N = 6/group). Idarubicin-treated animals exhibited a decrease in body and heart weight, a decrease in myocardial contractility, and changes in ECG parameters (P<0.01). Catechin + idarubicin- and vitamin E + idarubicin-treated groups exhibited similar alterations, but changes were attenuated in comparison to those in cardiac muscle of idarubicin-treated rats (P<0.05). Superoxide dismutase and catalase activity was reduced in the idarubicin-treated group (P<0.05). Glutathione peroxidase levels were decreased in the idarubicin-treated group (P<0.05) and reached maximum concentrations in the catechin- and catechin + idarubicin-treated groups compared to control (P<0.01). Malondialdehyde activity was decreased in the catechin + idarubicin-treated groups compared to control and increased in the other groups, reaching maximum concentrations in the vitamin E-treated group (P<0.01). In electron microscopy studies, swelling of the mitochondria and dilatation of the sarcoplasmic reticulum of myocytes were observed in the idarubicin-treated groups. In groups that were given idarubicin + vitamin E and idarubicin + catechin, the only morphological change was a weak dilatation of the sarcoplasmic reticulum. We conclude that catechin and vitamin E significantly reduce idarubicin-induced cardiotoxicity in rats.

Flavonoid antioxidants: chemistry, metabolism and structure-activity relationships

Flavonoids are a class of secondary plant phenolics with significant antioxidant and chelating properties. In the human diet, they are most concentrated in fruits, vegetables, wines, teas and cocoa. Their cardioprotective effects stem from the ability to inhibit lipid peroxidation, chelate redox-active metals, and attenuate other processes involving reactive oxygen species. Flavonoids occur in foods primarily as glycosides and polymers that are degraded to variable extents in the digestive tract. Although metabolism of these compounds remains elusive, enteric absorption occurs sufficiently to reduce plasma indices of oxidant status. The propensity of a flavonoid to inhibit free-radical mediated events is governed by its chemical structure. Since these compounds are based on the flavan nucleus, the number, positions, and types of substitutions influence radical scavenging and chelating activity. The diversity and multiple mechanisms of flavonoid action, together with the numerous methods of initiation, detection and measurement of oxidative processes in vitro and in vivo offer plausible explanations for existing discrepancies in structure-activity relationships. Despite some inconsistent lines of evidence, several structure-activity relationships are well established in vitro. Multiple hydroxyl groups confer upon the molecule substantial antioxidant, chelating and prooxidant activity. Methoxy groups introduce unfavorable steric effects and increase lipophilicity and membrane partitioning. A double bond and carbonyl function in the heterocycle or polymerization of the nuclear structure increases activity by affording a more stable flavonoid radical through conjugation and electron delocalization. Further investigation of the metabolism of these phytochemicals is justified to extend structure-activity relationships (SAR) to preventive and therapeutic nutritional strategies.

Oxidative DNA damage: biological significance and methods of analysis

All forms of aerobic life are subjected constantly to oxidant pressure from molecular oxygen and also reactive oxygen species (ROS), produced during the biochemical utilization of O2 and prooxidant stimulation of O2 metabolism. ROS are thought to influence the development of human cancer and more than 50 other human diseases. To prevent oxidative DNA damage (protection) or to reverse damage, thereby preventing mutagenesis and cancer (repair), the aerobic cell possesses antioxidant defense systems and DNA repair mechanisms. During the last 20 years, many analytical techniques have been developed to monitor oxidative DNA base damage. High-performance liquid chromatography-electrochemical detection and gas chromatography-mass spectrometry are the two pioneering contributions to the field. Currently, the arsenal of methods available include the promising high-performance liquid chromatography-tandem mass spectrometry technique, capillary electrophoresis, 32P-postlabeling, fluorescence postlabeling, 3H-postlabeling, antibody-base immunoassays, and assays involving the use of DNA repair glycosylases such as the comet assay, the alkaline elution assay, and the alkaline unwinding method. Recently, the use of liquid chromatography-mass spectrometry has been introduced for the measurement of a number of modified nucleosides in oxidatively damaged DNA. The bulk of available chromatographic methods aimed at measuring individual DNA base lesions require either chemical hydrolysis or enzymatic digestion of oxidized DNA, following extraction from cells or tissues. The effect of experimental conditions (DNA isolation, hydrolysis, and/or derivatization) on the levels of oxidatively modified bases in DNA is enormous and has been studied intensively in the last 10 years.

Radioprotective effects of 2-imino-3-[(chromone-2-yl)carbonyl] thiazolidines against gamma-irradiation in mice

A series of 2-imino-3-[(chromone-2-yl) carbonyl]thiazolidines substituted at the C-5 and/or C-7 positions of a chromone ring were synthesized. The in vivo toxicity and radioprotective efficacy of these agents were evaluated in male NMRI mice against cobalt-60 gamma-rays. The LD50 values as determined by a Probit analysis, were 659, 1216 and 790 mg/kg for compounds, 2, 3 and 4, respectively. For studying radioprotective effects, one half of the toxic LD50 values were used, namely 330, 605 and 395 mg/kg for compounds 2, 3 and 4, respectively. The dose reduced factor (DRF) was determined by dividing the LD50/30 values obtained from the radiation survival curve in the presence of a radioprotective agent by the LD50/30 value obtained from a control radiation survival curve. A compound with a hydroxyl group substituent at the C-5 position afforded better radioprotective activity than those without this substituent. The radioprotective effect of chromone having a hydroxyl group at only the C-7 position was similar to that of the unsubstituted chromone. The most active compound has hydroxyl groups at the C-5 and C-7 positions of the chromone ring; it had a DRF of 1.48.

Genotoxic and anti-genotoxic properties of Calendula officinalis extracts in rat liver cell cultures treated with diethylnitrosamine

Calendula officinalis flower extracts are used to cure inflammatory and infectious diseases, for wound healing and even cancer with partial objective evidence of its therapeutic properties or toxic effects, many of which can be attributed to the presence of flavonols. We studied whether C. officinalis extracts induce unscheduled DNA synthesis (UDS) in rat liver cell cultures, and if these extracts can reverse diethylnitrosamine (DEN)-induced UDS. Four different flower extracts were prepared: aqueous (AE), aqueous-ethanol (AEE), ethanol (EE) and chloroform (CE). AE and AEE were evaporated to 6.72 and 4.54 mg of solid material per ml, respectively and final ethanol concentration in AEE was 0.8%. EE and CE were dried and resuspended in dimethyl sulfoxide (DMSO) to 19.2 and 10 mg of solid material per ml. Ethanol residue of EE was 0.34%. In the UDS assay in liver cell cultures, DEN at 1.25 microM produced a maximal increase of 40% (3)H-thymidine ((3)HdTT) incorporation, and both, AE and AEE showed complete reversion of the DEN effect at around 50 ng/ml and between 0.4 to 16 ng/ml, respectively. In the absence of DEN, these two polar extracts induced UDS at concentrations of 25 microg for AE and 3.7 microg/ml for AEE to 100 microg/ml in rat liver cell cultures. Concentrations producing genotoxic damage were three orders of magnitude above concentrations that conferred total protection against the DEN effect. Thus, at the lower end, ng/ml concentrations of the two polar extracts AE and AEE conferred total protection against the DEN effect and at the higher end, g/ml concentrations produced genotoxic effects. These results justify the study of C. officinalis flower extracts to obtain products with biological activity and to define their genotoxic or chemopreventive properties.

The in vitro antioxidative activity of some traditional Zulu medicinal plants

Methanol extracts prepared separately from the roots, stems and leaves of four traditional Zulu medicinal plants (Rhoicissus digitata, R. rhomboidea, R. tomentosa and R. tridentata) were tested for their antioxidant activity. The extracts of R. rhomboidea and R. tridentata inhibited the activities of the 1, 1'-diphenyl-2-picryhydrazyl free radical, xanthine oxidase, and also prevented production of thiobarbituric acid reactive substances and free radical mediated DNA sugar damage. The extracts had a strong chelating effect on Fe(2+) ions. R. digitata and R. tomentosa extracts, however, possessed some prooxidative properties at high concentrations. In view of these results, it is apparent that the antioxidative activity of these Zulu medicinal plants plays an important role in the healing of the various diseases that they are used for.

Evaluation of the clastogenic, DNA intercalative, and topoisomerase II-interactive properties of bioflavonoids in Chinese hamster V79 cells

Bioflavonoids are naturally occurring polyphenols with intriguing and varied therapeutic and chemoprotective activities generally ascribed to their antioxidant properties. However, many flavonoids have also been shown to be genotoxic in a variety of prokaryotic, eukaryotic, and in vivo systems. The mechanistic basis for this genotoxicity has not been fully elucidated, although structure-activity relationship studies have identified requisite flavonoid structural features. We utilized Chinese hamster V79 cells to evaluate the relationships between DNA intercalation ability, topoisomerase II interactions, reactive oxygen species (ROS) generation, and clastogenicity in a series of 14 bioflavonoids. Five of the flavonoids examined, luteolin, quercetin, genistein, apigenin, and acacetin, were strongly clastogenic. This clastogenicity was shown to require DNA intercalation (with the exception of genistein) and was substantially reduced by catalytic inhibitors of DNA topoisomerase II. The transition metals Cu(II) and Mn(II) formed chelates with and/or modified the structure and biological activity of some flavonoids but no consistent relationship could be demonstrated between metal reactivity and clastogenicity. There was no clear association between generation of ROS and clastogenicity. The data presented herein are consistent with a model in which the genotoxicity of most flavonoids arises via DNA intercalation and topo II poisoning, likely mediated through metabolism to flavonoid quinones. Interestingly, other flavonoids such as myricetin, daidzein, baicalein, fisetin, and galangin were catalytic topo II inhibitors, rather than poisons. These studies further validate the use of cell-based approaches for detecting drug/topo II interactions and raise interesting questions relating to biological and chemical mechanisms of flavonoids.

Effect of natural phenolic acids on DNA oxidation in vitro

We examined the antioxidant activity of the following natural phenolic compounds present in food: 3-OH-benzoic acid (3-OH-BA); 4-OH-benzoic acid (4-OH-BA); 2,3-dihydroxybenzoic acid (2,3-diOH-BA); 3,4-dihydroxybenzoic acid (3,4-diOH-BA or protocatechuic acid); ferulic acid; caffeic acid; and 2-coumaric, 3-coumaric and 4-coumaric acids. We measured the inhibitory effect of these compounds on iron-dependent oxidative DNA damage in vitro [incubating herring sperm DNA with Fe(III)/GSH] or using cumene hydroperoxide (CumOOH) as a free-radical generating system; we also studied the interaction of these phenols with Fe(II) or Fe(III) spectrophotometrically. Among the tested compounds, 2,3-diOH-BA, 3,4-diOH-BA and caffeic acid interacted with Fe(II) and showed a potent inhibitory effect on iron-induced oxidative DNA damage. CumOOH-induced DNA oxidation was not modified by these compounds. On the contrary, 2-coumaric, 3-coumaric and 4-coumaric acids did not interact with iron but protected against oxidative DNA damage induced by Fe(III)/GSH and by CumOOH, indicating a direct free-radical scavenging activity of these compounds in both systems. The IC(50)+/-S.E.M. of the three coumaric acids against CumOOH-induced DNA oxidation was 44.2+/-2.0, 54.7+/-2.0 and 33.1+/-1.0 microM, respectively. On the contrary, 3-OH-BA and 4-OH-BA did not have scavenging activity and 3-OH-BA actually enhanced oxidative DNA damage. In conclusion, some natural phenolic acids, commonly present in food, have interesting protective activity against DNA oxidation in vitro and deserve further consideration as effective antioxidants in vivo.

Inhibition of nitric oxide synthase inhibitors and lipopolysaccharide induced inducible NOS and cyclooxygenase-2 gene expressions by rutin, quercetin, and quercetin pentaacetate in RAW 264.7 macrophages

Several natural flavonoids have been demonstrated to perform some beneficial biological activities, however, higher-effective concentrations and poor-absorptive efficacy in body of flavonoids blocked their practical applications. In the present study, we provided evidences to demonstrate that flavonoids rutin, quercetin, and its acetylated product quercetin pentaacetate were able to be used with nitric oxide synthase (NOS) inhibitors (N-nitro-L-arginine (NLA) or N-nitro-L-arginine methyl ester (L-NAME)) in treatment of lipopolysaccharide (LPS) induced nitric oxide (NO) and prostaglandin E2 (PGE2) productions, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) gene expressions in a mouse macrophage cell line (RAW 264.7). The results showed that rutin, quercetin, and quercetin pentaacetate-inhibited LPS-induced NO production in a concentration-dependent manner without obvious cytotoxic effect on cells by MTT assay using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide as an indicator. Decrease of NO production by flavonoids was consistent with the inhibition on LPS-induced iNOS gene expression by western blotting. However, these compounds were unable to block iNOS enzyme activity by direct and indirect measurement on iNOS enzyme activity. Quercetin pentaacetate showed the obvious inhibition on LPS-induced PGE2 production and COX-2 gene expression and the inhibition was not result of suppression on COX-2 enzyme activity. Previous study demonstrated that decrease of NO production by L-arginine analogs effectively stimulated LPS-induced iNOS gene expression, and proposed that stimulatory effects on iNOS protein by NOS inhibitors might be harmful in treating sepsis. In this study, NLA or L-NAME treatment stimulated significantly on LPS-induced iNOS (but not COX-2) protein in RAW 264.7 cells which was inhibited by these three compounds. Quercetin pentaacetate, but not quercetin and rutin, showed the strong inhibitory activity on PGE2 production and COX-2 protein expression in NLA/LPS or L-NAME/LPS co-treated RAW 264.7 cells. These results indicated that combinatorial treatment of L-arginine analogs and flavonoid derivates, such as quercetin pentaacetate, effectively inhibited LPS-induced NO and PGE2 productions, at the same time, inhibited enhanced expressions of iNOS and COX-2 genes.

Amine oxidase-like activity of polyphenols. Mechanism and properties

Polyphenols in several oxidation systems gained amine oxidase-like activity, probably due to the formation of the corresponding quinones. In the presence of Cu(II), o- and p-phenolic compounds exhibited amine oxidase-like activity, whereas only the o-phenolic compounds showed the activity in the presence of 1,1-diphenyl-2-picrylhydrazyl radical. The activity was determined by measuring the conversion of benzylamine to benzaldehyde by HPLC. Moreover, gallic acid, chlorogenic acid, and caffeic acid, which are plant polyphenols, converted the lysine residue of bovine serum albumin to alpha-amino-adipic semialdehyde residue, indicating lysyl oxidase-like activity. We also characterized the activity of pyrocatechol, hydroquinone, and pyrogallol in the presence of Cu(II). The oxidative deamination was accelerated at a higher pH, and required O2 and transition metal ions. Furthermore, EDTA markedly inhibited the reaction but not beta-aminopropionitrile, which is a specific inhibitor of lysyl oxidase. Catalase significantly inhibited the oxidation, implying the participation of hydroxyl radical in the reaction, but superoxide dismutase stimulated the oxidation, probably due to its radical formation activity. We discussed the mechanism of the oxidative deamination by polyphenols and the possible significance of the activity for biological systems.

Membrane stabilising effects of natural polyphenols and flavonoids from Sempervivum tectorum on hepatic microsomal mixed-function oxidase system in hyperlipidemic rats

The extensive role of the microsomal mixed-function oxidase (MFO) system in the oxidation of endo-and xenobiotics, in the detoxication, in the generation of reactive free radicals and in the decomposition of the end products of lipid peroxides is well documented in the literature. Steatotic liver is a very frequent damage with different etiology. Drug metabolising reactions are suppressed in fatty liver, in which pathologically increased production of reactive oxygen intermediates may lead to the peroxidation of microsomal membrane lipids and to the change of membrane bound enzyme activities because of overwhelmed protective mechanisms. The subnormal activity of the MFO system may diminish the non specific resistance of the organism. Therefore we have studied the effects of natural flavonoids and polyphenolic compounds on the mixed-function oxidases. Antioxidant, O(2)(-&z.rad;) and &z. rad;OH scavenger properties of Sempervivum tectorum extract (STF1) were proved by EPR spectroscopic and chemiluminometric techniques. Potential bioactive constituents were determined by chromatography (HPLC, TLC) and spectrometric (UV, UV-VIS) methods. In the present study we reflect on the membrane stabilising, antioxidant and lipid metabolism modifying effects of this extract. It was established that activities of NAD(P)H reductase and content of cytochrome P450 were normalised in liver microsomes of hyperlipidemic rats, if the animals were treated with STF1 (2 g/bwkg for 9 days in drinking water parallel with fat-rich diet feeding). Fatty acid composition, examined by HRGLC analysis, was changed beneficially. NADPH induced lipid peroxidation was also decreased in microsomes in in vivo and in vitro experiments. At the same time the STF1 had no significant influence on MFO system in normolipidemic animals and on cytochrome b5 concentration of microsome fractions of hyperlipidemic rats.

Potential health impacts of excessive flavonoid intake

Plant flavonoids are common dietary components that have many potent biological properties. Early studies of these compounds investigated their mutagenic and genotoxic activity in a number of in vitro assays. Recently, a renewed interest in flavonoids has been fueled by the antioxidant and estrogenic effects ascribed to them. This has led to their proposed use as anticarcinogens and cardioprotective agents, prompting a dramatic increase in their consumption as dietary supplements. Unfortunately, the potentially toxic effects of excessive flavonoid intake are largely ignored. At higher doses, flavonoids may act as mutagens, pro-oxidants that generate free radicals, and as inhibitors of key enzymes involved in hormone metabolism. Thus, in high doses, the adverse effects of flavonoids may outweigh their beneficial ones, and caution should be exercised in ingesting them at levels above that which would be obtained from a typical vegetarian diet. The unborn fetus may be especially at risk, since flavonoids readily cross the placenta. More research on the toxicological properties of flavonoids is warranted given their increasing levels of consumption.

Chemical features of flavonols affecting their genotoxicity. Potential implications in their use as therapeutical agents

Flavonls are natural compounds present in edible plants and possess several biological activities that can be useful in drug design. Conversely some of these compounds have been shown to be genotoxic to prokaryotic and eukaryotic cells. In this study we tried to establish the chemical features responsible for the genotoxicity of flavonols and to study the conditions that can modulate their genotoxicity namely pH, the presence of antioxidants and metabolism. We assessed the induction of revertants in Salmonella typhimurium TA98 and the induction of Chromosomal aberrations in V79 cells by eight different flavonols and one catechin in the presence and in the absence of metabolizing systems. We have also studied the generation of hydroxyl radical by these flavonoids using the deoxyribose degradation assay. The results obtained in this study suggest that flavonols having a free hydroxyl group at position 3 of the C ring, a free hydroxyl group at position 7 of the A ring and a B ring with a catechol or pyrogallol structure, or a structure that after metabolic activation is transformed into a catechol or a pyrogallol, are flavonols whose genotoxicity in eukaryotic cells depends on their autooxidation. These flavonols can autooxidize when the pH value is slightly alkaline, such as in the intestine, and therefore can induce genotoxicity in humans. Given the above mentioned considerations it is necessary to clarify the mechanisms and the conditions that mediate the biological effects of flavonols before considering them as therapeutical agents.

Inhibition of gastric H+, K(+)-ATPase by flavonoids: a structure-activity study

Gastric H+, K(+)-ATPase plays a pivotal role in the final step of gastric acid secretion. Over 80 flavonoids, including flavones, flavanones, isoflavones and anthocyanidins were examined for their in vitro effect on gastric H+, K(+)-ATPase and some were found to be inhibitors of this enzyme. Kinetic studies showed that the inhibition of H+, K(+)-ATPase by flavonoids was competitive with respect to ATP, and non-competitive with respect to K+. Structure-activity analysis revealed the following: (1) The inhibitory potency of flavonoids depends on the number of hydroxyl groups up to four per molecule and that above this, no marked enhancement is seen; (2) The hydroxylation pattern is an important determinant of inhibitory potency. Two adjacent hydroxyl groups (catechol-type), three adjacent hydroxyl groups (pyrogallol-type) or hydroxyl groups at C-3, C-5 and C-7 are a minimum requirement for high potency inhibition; (3) Protection of the hydroxyl group(s) by glycosylation or methylation decreases potency; (4) Saturation of the C-2-C-3 double bond results in a decrease in potency; and (5) A ketone at C-4 is not essential for inhibition.

Oxygen and nitrogen are pro-carcinogens. Damage to DNA by reactive oxygen, chlorine and nitrogen species: measurement, mechanism and the effects of nutrition

Humans are exposed to many carcinogens, but the most significant may be the reactive species derived from metabolism of oxygen and nitrogen. Nitric oxide seems unlikely to damage DNA directly, but nitrous acid produces deamination and peroxynitrite leads to both deamination and nitration. Scavenging of reactive nitrogen species generated in the stomach may be an important role of flavonoids, flavonoids and other plant-derived phenolic compounds. Different reactive oxygen species produce different patterns of damage to DNA bases, e.g., such patterns have been used to implicate hydroxyl radical as the ultimate agent in H(2)O(2)-induced DNA damage. Levels of steady-state DNA damage in vivo are consistent with the concept that such damage is a major contributor to the age-related development of cancer and so such damage can be used as a biomarker to study the effects of diet or dietary supplements on risk of cancer development, provided that reliable assays are available. Methodological questions addressed in this article include the validity of measuring 8-hydroxydeoxyguanosine (8OHdG) in cellular DNA or in urine as a biomarker of DNA damage, the extent of artifact formation during analysis of oxidative DNA damage by gas chromatography-mass spectrometry and the levels of oxidative damage in mitochondrial DNA.

Generation of hydrogen peroxide by "antioxidant" beverages and the effect of milk addition. Is cocoa the best beverage?

The ability of several beverages to generate hydrogen peroxide was demonstrated by direct measurement using the ferrous ion oxidation-xylenol orange (FOX) assay. Tea and coffee could generate H2O2 to achieve levels over 100 microM, but cocoa did not. Milk decreased net H2O2 production by beverages and showed some ability to remove H2O2 itself, apparently not because of catalase activity. Hence several of the beverages commonly drunk by humans show a complex mixture of anti- and pro-oxidant abilities.

Phytoestrogen intake and prostate cancer: a case-control study using a new database

In the last several years, attention has been focused on comparing the Western diet, which is rich in fat, protein, and refined carbohydrates, with the Asian diet, which is rich in phytoestrogens, as a possible explanation for the contrasting rates of clinically relevant prostate cancer. Phytoestrogens, plant-derived nutrients, include several isoflavones, flavonoids, lignans, phytosterols, and coumestans, some of which have been postulated as having anticarcinogenic properties. Using a new database, we examined the role of phytoestrogen intake and prostate cancer risk in 83 Caucasian cases and 107 controls. Controls reported consuming higher amounts of foods containing genistein, daidzein, and coumestrol and lower amounts of foods containing campesterol and stigmasterol. Multivariate analysis, after adjustment for age, family history of prostate cancer, alcohol consumption, and total calorie intake, showed an inverse association between coumestrol (p = 0.03) and daidzein (p = 0.07) and prostate cancer risk. Genistein, the most studied phytoestrogen, showed a slight protective effect (p = 0.26). However, a positive association was found between campesterol (p = 0.08) and stigmasterol (p = 0.03) and risk of prostate cancer. These results are suggestive of a possible relationship between phytoestrogen intake and prostate cancer risk. Larger comprehensive studies are needed to further refine the role of phytoestrogen intake in prostate cancer risk.

Antioxidant and pro-oxidant actions of flavonoids: effects on DNA damage induced by nitric oxide, peroxynitrite and nitroxyl anion

Antioxidant and pro-oxidant activities of flavonoids have been reported. We have studied the effects of 18 flavonoids and related phenolic compounds on DNA damage induced by nitric oxide (NO), peroxynitrite, and nitroxyl anion (NO-). Similarly to our previous findings with catecholamines and catechol-estrogens, DNA single-strand breakage was induced synergistically when pBR322 plasmid was incubated in the presence of an NO-releasing compound (diethylamine NONOate) and a flavonoid having an ortho-trihydroxyl group in either the B ring (e.g., epigallocatechin gallate) or the A ring (e.g., quercetagetin). Either NO or any of the above flavonoids alone did not induce strand breakage significantly. However, most of the tested flavonoids inhibited the peroxynitrite-mediated formation of 8-nitroguanine in calf-thymus DNA, measured by a new HPLC-electrochemical detection method, as well as the peroxynitrite-induced strand breakage. NO- generated from Angeli's salt caused DNA strand breakage, which was also inhibited by flavonoids but at only high concentrations. On the basis of these findings, we propose that NO- and/or peroxynitrite could be responsible for DNA strand breakage induced by NO and a flavonoid having an ortho-trihydroxyl group. Our results indicate that flavonoids have antioxidant properties, but some act as pro-oxidants in the presence of NO.

Can oxidative DNA damage be used as a biomarker of cancer risk in humans? Problems, resolutions and preliminary results from nutritional supplementation studies

Damage to DNA by oxygen radicals and other reactive oxygen/nitrogen/chlorine species occurs in vivo despite the presence of multiple antioxidant defence and repair systems. Such damage is thought to make a significant contribution to the age-related development of cancer. Modulation of oxidative DNA damage by diet thus constitutes a "biomarker" putatively predictive of the effect of diet on cancer incidence, provided that DNA damage can be accurately quantitated by validated methods. Current issues addressed in this article include the problems of artifactual DNA oxidation during isolation and analysis, the relative merits of different analytical methods, the advantages and disadvantages of relying on measurement of 8-hydroxydeoxyguanosine (8OHdG, 8-oxodG) as an index of oxidative DNA damage, and the limited data that are so far available on how diet can affect "steady-state" levels of oxidative DNA damage in humans. It appears that such damage can be modulated by vegetable intake, although the effects of vegetables may be mediated by components different from the "classical" antioxidants vitamin C, alpha-tocopherol and beta-carotene.