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New flavonol glycosides and new xanthone from Polygala japonica.

Three new flavonol glycosides and a new xanthone were isolated from Polygala japonica HOUTT. with eight known compounds. Their structures were identified as 1,7-dihydroxy-3,4-dimethoxy-xanthone (1), kaempferol-7,4'-dimethyl ether (2), physcion (3), guazijinxanthone (4), rhamnetin (5), polygalin A (6), 3,5,7-trihydroxy-4'-methoxy-flavone-3-O-beta-d-galactopyranoside (7), 3,5,3'-trihydoxy-7,4'-dimethoxy-flavone-3-O-beta-d-galactopyranoside (8), 3,5,3',4'-tetrahydroxy-7-methoxy-flavone-3-O-beta-d-galactopyranoside (9), 3,5,3',4'-tetrahydroxy-7-methoxy-flavone-3-O-beta-d-glucopyranoside (10), polygalin B (11), polygalin C (12). Among them, compound 4 is a new xanthone, and 6, 11 and 12 are new flavonol glycosides. Compounds 1, 4, 7 and 8 were tested for cytotoxic activity with MTT assays on five human tumor cell lines, K562, A549, PC-3M, HCT-8 and SHG-44. Compound 4 showed cytotoxic activity against all the five cell lines.

Antineoplastic Agents, Phytogenic↗
PubMed2000

Inhibitory effect of flavonoids on low-density lipoprotein peroxidation catalyzed by mammalian 15-lipoxygenase.

Lipoxygenase-dependent low-density lipoprotein (LDL) oxidation is believed to be involved in atherogenesis. Inhibition of lipoxygenase-induced lipid peroxidation might, therefore, be an important mode to suppress the development of atherosclerosis. Because dietary antioxidants inhibit LDL oxidation in vitro and their intake is inversely associated with coronary heart diseases, we compared the inhibitory effect of three typical flavonoids-quercetin, epicatechin, and flavone-with alpha-tocopherol and ascorbic acid against human LDL oxidation catalyzed by mammalian 15-lipoxygenase. The oxidative modification of LDL was monitored by measurement of cholesteryl ester hydroperoxide (CE-OOH) formation and consumption of antioxidants by using HLPC. Quercetin and epicatechin were the strongest inhibitors of LDL oxidation catalyzed by 15-lipoxygenase; ascorbic acid was an effective inhibitor in the first 3 h of oxidation; and fivefold alpha-tocopherol-enriched LDL showed a partial inhibition of CE-OOH formation only after 4-6 h of incubation. Flavone had no effect. Quercetin, ascorbic acid, and alpha-tocopherol were consumed in the first 3 h of incubation. Consumption of LDL alpha-tocopherol was partially inhibited by ascorbic acid and quercetin, whereas epicatechin and flavone were without effect. These results emphasize the inhibitory effect of the flavonoids quercetin and epicatechin on 15-lipoxygenase-mediated LDL lipid peroxidation. At similar concentrations, they are stronger antioxidants than ascorbic acid, alpha-tocopherol, and flavone.

Animals↗
PubMed2004

Ascorbic acid suppresses drug-induced apoptosis in human colon cancer cells by scavenging mitochondrial superoxide anions.

Although a high alimentary intake of antioxidant vitamins such as ascorbic acid may play an important role in cancer prevention, a high level of antioxidants may have quite different effects at different stages of the transformation process. In cancer development, the resistance of cells to apoptosis is one of the most crucial steps. We have tested the effects of ascorbic acid on apoptosis in HT-29 human colon carcinoma cells when induced by two potent apoptosis inducers, the classical antitumor drug camptothecin or the flavonoid flavone. Apoptosis was assessed based on caspase-3-like activity, plasma membrane disintegration and finally nuclear fragmentation and chromatin condensation. Ascorbic acid dose-dependently inhibited the apoptotic response of cells to camptothecin and flavone. RT-PCR analysis and western blot analysis revealed that ascorbic acid specifically blocked the decrease of bcl-X(L) by camptothecin or flavone. An increased generation of mitochondrial O(2)(-.) precedes the down-regulation of bcl-X(L) by camptothecin and flavone and ascorbic acid at a concentration of 1 mM prevented the generation of this reactive oxygen species. In conclusion, ascorbic acid functions as a potent antioxidant in mitochondria of human colon cancer cells and thereby blocks drug-mediated apoptosis induction allowing cancer cells to become insensitive to chemotherapeutics.

Antioxidants↗
PubMed1996

Time course of induction of rat hepatic drug-metabolizing enzyme activities following dietary administration of flavonoids.

Effects of continuous feeding flavonoids (flavone, flavanone, and tangeretin) on drug-metabolizing enzymes in rat liver were investigated to ascertain how long feeding is required to reach maximal induction and to determine whether maximal induction is maintained for a long period of feeding. In the first experiment rats received a diet containing 10 mmol flavonoid/kg dry matter for 4, 8, 16, or 32 d. The second experiment was designed to examine the time course for induction during the first 4 d. The kinetics of induction depended on the chemical structure of the flavonoid and was different from one enzyme to another. Flavone increased P450 1A and P450 2B apoproteins and stimulated many enzyme activities. A significant increase of P450 1A1/2 proteins, ethoxyresorufin O-deethylase (EROD), and methoxyresorufin O-demethylase (MROD) activities occurred as early as 6 h after the first administration, and a gradual increase was observed up to 4 d of feeding. P450 2B1/2 proteins and pentoxyresorufin O-depentylase (PROD) activity were also increased but after a lag period when compared with P450 1A1/2 proteins. EROD and MROD activities declined after 4 d, whereas PROD activity remained steady during 32 d of flavone feeding. Glutathione transferase (GST) and p-nitrophenol UDP-glucuronosyl transferase (UGT) activities were also increased. The maximal induction was reached by 4 d of feeding for UGT and after a longer duration of feeding (16 d) for GST. Flavanone treatment induced mostly P450 2B1/2 proteins and PROD, GST, and UGT activites. After 4 d of feeding, P450 2B1/2 proteins and PROD activity declined whereas GST and UGT activities remained steady. Tangeretin treatment produced changes similar to flavone but of lesser magnitude and after a longer delay.

Animals↗
PubMed2002

Activation of bone sialoprotein gene transcription by flavonoids is mediated through an inverted CCAAT box in ROS 17/2.8 cells.

Bone sialoprotein (BSP) is a major noncollagenous protein of the mineralized bone extracellular matrix that has been implicated in the nucleation of hydroxyapatite. Recent studies have shown that BSP is also expressed by osteotropic cancers suggesting BSP might play a role in the pathogenesis of bone metastases. The present study investigates regulation of BSP transcription in rat osteosarcoma ROS 17/2.8 cells by flavonoids: genistein (an inhibitor of protein tyrosine kinases), daidzein (an inactive compound of genistein), flavone, and flavanone. Genistein, daidzein, and flavone (50 microM) increased steady state levels of BSP mRNA about 1.7-fold at 12 h. From transient transfection assays using various sized BSP promoter-luciferase constructs, genistein increased luciferase activities within 12 h. Constructs including the promoter sequence nucleotides (nts) -116 to -43 (pLUC3) were found to enhance transcriptional activity approximately 2.6-fold in ROS 17/2.8 cells treated with genistein (50 microM). Daidzein, flavone, and flavanone (50 microM) also increased luciferase activities. In contrast, the tyrosine kinase inhibitors, herbimycin A and lavendustin A, which do not have a flavonoid structure, did not stimulate BSP transcription. Transcriptional stimulation by genistein was almost completely abrogated in a construct that included 2 bp mutations in the inverted CCAAT box. A monoclonal antibody against NF-YA, a CCAAT box-binding transcription factor, inhibited formation of DNA-NF-Y protein complex in gel shift assays formed by nuclear extracts of ROS 17/2.8 cells. These data suggest that the inverted CCAAT box is required for flavonoid-induced BSP expression and that the stimulatory action is dependent on the flavone structure and does not involve an inhibitory action on protein tyrosine kinase.

Animals↗
PubMed1995

Heterogenous effects of natural flavonoids on monooxygenase activities in human and rat liver microsomes.

The in vitro effects of nine flavonoids on different monooxygenase activities from human and rat liver were investigated. Flavonoids belonging to different chemical classes [flavones (chrysin, tangeretin, flavone, 5,6-benzoflavone, 7,8-benzoflavone), flavonols (quercetin), and flavanones (pinocembrin, eriodictyol, flavanone)] were chosen. Ethoxyresorufin O-deethylase (EROD) and benzyloxyresorufin O-debenzylase (BROD) were selected as marker activities of P450 isoenzymes involved in carcinogen activation. Human EROD activity was inhibited by all flavonoids. Flavonoids without hydroxyl groups were more effective than those with hydroxyl groups. Flavonoids with an unsaturated flavone nucleus were more inhibitory than the corresponding saturated analogues. Similar structure-activity relationships were found in microsomes from methylcholanthrene-treated rats. The effects of flavonoids on human BROD activity were quite different from those observed on EROD activity. Nonhydroxylated flavones were effective activators. Hydroxylated flavonoids showed a biphasic effect, being activators at low concentrations and inhibitors at higher concentrations. The effects of flavonoids on BROD activity were rather similar in man and control rats.

Adult↗
PubMed1983

5,8-dihydroxyflavone (primetin) the contact sensitizer of Primula mistassinica Michaux.

5,8-Dihydroxyflavone (primetin) has been shown to be the sensitizer in Primula mistassinica Michaux and probably the source of allergic contact dermatitis in four milkers. Its sensitizing properties as determined in guinea-pigs, are strong. As far as is known this is the first experimental demonstration of the sensitizing potency of a flavone. Presumably the flavone, with its uncommon 5,8-arrangement of hydroxy groups, is oxidized in the skin to the corresponding quinone (primetinquinone). Quinone was prepared from primetin and used for experimental sensitization of guinea-pigs. It also revealed strong sensitizing properties. Cross-reactions were obtained not only with the synthetic quinone in the flavone-sensitive animals but also with primetin in primetinquinone-sensitive guinea-pigs. Preliminary sensitization tests with other flavones have demonstrated that the whole group of flavonoid components should be taken into consideration as potential sensitizers.

Allergens↗
PubMed1991

Effects of synthetic and naturally occurring flavonoids on benzo[a]pyrene metabolism by hepatic microsomes prepared from rats treated with cytochrome P-450 inducers.

Activity-directed fractionation of Trifolium pratense resulted in isolation of the isoflavone biochanin A, a potent inhibitor of metabolic activation of the carcinogen benzo[a]pyrene (B[a]P) in cells in culture. To determine the structural features required for maximal inhibition of cytochrome P-450 mediated metabolism of B[a]P, the inhibitory potencies of 23 flavonoids on metabolism of B[a]P to water-soluble derivatives were examined in liver S-9 homogenate from rats induced with Aroclor 1254. Flavones were much more efficient inhibitors than their corresponding isoflavone or flavanone analogs. Most flavonols were as effective inhibitors as their flavone analogs with the exception of kaempferide. Flavones with two hydroxyl or two methoxyl groups at positions 5 and 7 were the most active. Although all eight flavonoids tested effectively inhibited B[a]P metabolism by beta-naphthoflavone-induced microsomes, none were very effective inhibitors of B[a]P metabolism by phenobarbitol-induced microsomes, and only three were effective inhibitors of B[a]P metabolism by microsomes from non-induced rats. These results indicate that flavones or flavonols that contain free 5- and 7-hydroxyls are potent inhibitors of P-450 induced by beta-naphthoflavone (P-450IA1 and/or P-450IA2) and may potentially be useful as chemopreventive agents against hydrocarbon-induced carcinogenesis.

Animals↗
PubMed1990

Aromatase inhibition by flavonoids.

Several synthetic flavones were found to inhibit the aromatization of androstenedione to estrone catalyzed by human placental microsomes. Twenty-one compounds were tested and the IC50 of the most active were: flavone, 10 microM; 7-hydroxyflavone, 0.5 microM; 7,4'-dihydroxyflavone, 2.0 microM; flavanone, 8.0 microM; and 4'-hydroxyflavanone, 10 microM. Most of the others had IC50 values ranging from 80 to greater than 200 microM. These findings show that 4'-hydroxylation results in either no change or very little change in IC50 for flavanone, isoflavone and isoflavanone as well as other ring A hydroxylated flavones. Derivatives of flavone with a hydroxyl substituent at position 5, 6 and 7 were also screened. 7-Hydroxyflavone (11) was the most effective competitive inhibitor (IC50 = 0.5 microM) with an apparent Ki value of 0.25 microM. Compound 11 also induced a change in the absorption spectrum of the aromatase cytochrome P-450 which is indicative of substrate displacement. The relative binding affinities of the flavonoid analogs were determined and only ring A adn ring B dihydroxylated analogs were found to bind to the estrogen receptor.

Animals↗
PubMed2006

Synthesis of phospholipase A2 inhibitory biflavonoids.

A series of C-C biflavones was designed to investigate the relationship between structural array of different flavone-flavone subunit linkage and the inhibitory activity against phospholipase A2 (PLA2). Among six classes of C-C biflavones designed, four classes of C-C biflavones, which have flavone-flavone subunit linkages at A ring-A ring, A ring-B ring, B ring-B ring, and B ring-C ring, were synthesized. The synthetic biflavones exhibited somewhat different inhibitory activities against sPLA2-IIA. Among them, the biflavone a having a C-C 4'-4' linkage showed comparable inhibitory activity with that of the natural biflavonoid, ochnaflavone, and 7-fold stronger activity than that of amentoflavone. Further chemical modification is being carried out in order to obtain the chemically optimized biflavonoids.

Biflavonoids↗
PubMed2005

Assessment of estrogenic activity of flavonoids from Mediterranean plants using an in vitro short-term test.

Six isoflavones, daidzein (4',7,-dihydroxyisoflavone), genistein (4',5,7-trihydroxyisoflavone), genistin (genistein 7-O-beta-D-glucopyranoside), isoprunetin (4',7-dihydroxy, 5-metoxyisoflavone), isoprunetin 7-O-beta-D-glucopyranoside, isoprunetin 4',7-di-O-beta-D-glucopyranoside and four flavones, luteolin (3',4',5,7-tetrahydroxyflavone), luteolin 7-O-beta-D-glucopyranoside, luteolin 4'-O-beta-D-glucopyranoside, licoflavone C (4',5,7-trihydroxy,8-isoprenylflavone) were purified from Mediterranean plants (Genista morisii and Genista ephedroides) and their estrogenic activity was assessed by a yeast reporter gene assay (Saccharomyces cerevisiae RMY326 ER-ERE). Licoflavone C showed a powerful estrogenic activity at 10(-7) M (0.0338 microg/ml) and it was 47.45% than 10(-8) M 17beta-estradiol (0.00272 microg/ml). The estrogenicity of this flavone was found to be comparable to the activity showed by genistein at 10(-6) M (0.27 microg/ml). This study points out that a glucose substituent in flavones and isoflavones modulates the hormone-like activity in a different way. Isoflavone aglycones showed a more estrogenic activity than the corresponding glucosides. Conversely, the glucosidation made estrogenic the flavone luteolin and the position of substitution differently influenced the estrogenic activity of compounds.

Estradiol↗
PubMed2003

Chemical profiling of Ocimum americanum using external flavonoids.

A HPLC survey was undertaken of the external flavonoids in 111 herbarium specimens of Ocimum americanum L. (O. canum Sims), which were largely collected from their natural habitats throughout Africa and Asia. The purpose of this study was to establish the flavonoid profiles of this species over the full range of its geographic distribution in order to use these for authentication purposes. Six different external flavonoid chemotypes were found. The major chemotype, present in circa 80% of the specimens of both var. americanum and var. pilosum collected throughout the distribution area of the species, was characterised by very high levels of nevadensin, slightly lower levels of salvigenin and much lower levels of up to 15 other external flavones. Of the remaining five chemotypes, two were found in var. americanum and three in var. pilosum. All specimens belonging to these chemotypes were collected in South or East Africa and represented by only a few specimens. These samples contained much smaller levels of flavones than present in the major chemotype of O. americanum and all lacked nevadensin. Xanthomicrol, a compound absent from the main chemotype, was the dominant flavone in two of the minor chemotypes. The external flavonoid profiles found in the six chemotypes of O. americanum were compared with those of O. x citriodorum (11 herbarium specimens studied) and seven other closely related species of Ocimum. The main nevadensin/salvigenin pattern present in O. americanum was also found in O. x citriodorum, O. basilicum and some specimens of O. minimum, but there were strong quantitative differences in external flavonoids among these taxa. The other chemotypes of O. americanum showed some similarities in their external flavone profiles to those found in the closely related East African species O. fischeri, O. forskolei, O. kenyense and O. kilimandscharicum, which occur in the same geographic areas. This suggests that the uncommon chemotypes of O. americanum may have originated by an exchange of genes with other Ocimum species, e.g. by introgressive hybridisation. Despite some similarities in profiles, chemical differences were also found among the species, so that it should be possible to authenticate a large proportion of leaf samples of O. americanum on the basis of external flavonoid profiles.

Africa↗
PubMed2000

Leaf flavonoids as systematic characters in the genera Lavandula and Sabaudia.

A comprehensive survey of the leaf flavonoids of the genus Lavandula and the related Sabaudia group was carried out using two-dimensional paper chromatography and high-performance liquid chromatography. The flavonoid patterns obtained were found to be systematically informative at the infrageneric level. Three main groupings were identified: the first containing sections Lavandula, Dentata and Stoechas characterised by the accumulation of flavone 7-glycosides; the second containing sections Pterostoechas, Subnuda and Chaetostachys characterised by the accumulation of 8-hydroxylated flavone 7-and 8-glycosides; the third encompassing the Sabaudia group and accumulating both flavone and 8-hydroxylated flavone 7- glycosides. Such a grouping of taxa is congruent with data from other disciplines, although it is not recognised in any present classifications. The taxonomic and evolutionary implications of the flavonoid data are discussed.

Journal Article↗
PubMed2001

Flavonoids of Lavoisiera, Microlicia and Trembleya (Melastomataceae) and their taxonomic meaning.

Leaves of species of three closely related genera of Melastomataceae, Lavoisiera, Microlicia and Trembleya were analyzed for their flavonoid composition. A total of 116 compounds were obtained, comprising 69 flavonol and 47 flavone glycosides. The common occurrence of flavones, including 6-oxygenated derivatives, characterize Lavoisiera (which often yielded methoxylated flavonols and flavones). Flavonols predominate in species of Microlicia. The flavonoid patterns of Trembleya are rather confusing, some species being akin to Lavoisiera, others to Microlicia. UPGMA analysis using the flavonoid aglycones as characters and the samples analyzed as OTUs gives no complete resolution for the three genera, but provides clusters combining exclusively or preferentially species of either Lavoisiera and Microlicia. Species of Trembleya emerge from the phenogram interspersed among species of the other genera. The data suggest the recognition of Lavoisiera and Microlicia and the lumping of species of Trembleya with either of these genera. If greater flavone diversity is viewed as indicative of further evolutionary advancement, shrubby habits in Microliceae (Lavoisiera and Trembleya) should be regarded as derived from herbaceous ones (Microlicia).

Journal Article↗
PubMed2001

Common phytochemicals are ecdysteroid agonists and antagonists: a possible evolutionary link between vertebrate and invertebrate steroid hormones.

Many plant compounds are able to modulate growth and reproduction of herbivores by directly interacting with steroid hormone systems. In insects, several classes of phytochemicals, including the phytoestrogens, interfere with molting and reproduction. We investigated whether the anti-ecdysone activity may be due to interaction with the ecdysone receptor (EcR) using a reporter-gene assay and a cell differentiation assay of an ecdysone-responsive cell line, Cl.8+. We tested rutin (delays molt in insects); four flavones: luteolin and quercetin (metabolites of rutin), and apigenin and chrysin; and three non-flavones, coumestrol and genistein (both estrogenic) and tomatine (alters molt in insects). None of the phytochemicals tested were ecdysone agonists in the reporter-gene assay, but the flavones were able to significantly inhibit EcR-dependent gene transcription. In the Cl.8+ cells, quercetin and coumestrol were mixed agonists/antagonists, while genistein, tomatine and apigenin showed a synergistic effect with ecdysteroid in the reduction of cell growth. We suggest that the rutin effects on molting in insects are most likely due to the metabolites, luteolin or quercetin, while tomatine acts via a non-EcR pathway. Flavones not only interact with EcR and estrogen receptor (ER), but also signal nitrogen-fixing bacteria to form root nodules. The NodD protein which regulates this symbiosis has two ligand-binding domains similar to human ERalpha. The evolutionary significance of these findings are discussed.

Animals↗
PubMed2003

Structural requirements of flavonoids for nitric oxide production inhibitory activity and mechanism of action.

To clarify the structure-activity relationships of flavonoids for nitric oxide (NO) production inhibitory activity, we examined the inhibitory effects of 73 flavonoids on NO production in lipopolysaccharide-activated mouse peritoneal macrophages. Among those flavonoids, apigenin (IC(50)=7.7 microM), diosmetin (8.9 microM), and tetra-O-methylluteolin (2.4 microM), and hexa-O-methylmyricetin (7.4 microM) were found to show potent inhibitory activity, and the results suggested the following structural requirements of flavonoids: (1) the activities of flavones were stronger than those of corresponding flavonols; (2) the glycoside moiety reduced the activity; (3) the activities of flavones were stronger than those of corresponding flavanones; (4) the flavones and flavonols having the 4'-hydroxyl group showed stronger activities than those lacking the hydroxyl group at the B ring and having the 3',4'-dihydroxyl group; (5) the flavonols having the 3',4'-dihydroxyl group (catechol type) showed stronger activities than those having the 3',4',5'-trihydroxyl group (pyrogallol type); (6) the 5-hydroxyl group tended to enhance the activity; (7) methylation of the 3-, 5-, or 4'-hydroxyl group enhanced the activity; (8) the activities of isoflavones were weaker than those of corresponding flavones; (9) methylation of the 3-hydroxyl group reduced the cytotoxicity. In addition, potent NO production inhibitors were found to inhibit induction of inducible nitric oxide synthase (iNOS) without iNOS enzymatic inhibitory activity.

Animals↗
PubMed2003

Benzoflavone activators of the cystic fibrosis transmembrane conductance regulator: towards a pharmacophore model for the nucleotide-binding domain.

Our previous screen of flavones and related heterocycles for the ability to activate the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel indicated that UCCF-029, a 7,8-benzoflavone, was a potent activator. In the present study, we describe the synthesis and evaluation, using cell-based assays, of a series of benzoflavone analogues to examine structure-activity relationships and to identify compounds having greater potency for activation of both wild type CFTR and a mutant CFTR (G551D-CFTR) that causes cystic fibrosis in some human subjects. Using UCCF-029 as a structural guide, a panel of 77 flavonoid analogues was prepared. Analysis of the panel in FRT cells indicated that benzannulation of the flavone A-ring at the 7,8-position greatly improved compound activity and potency for several flavonoids. Incorporation of a B-ring pyridyl nitrogen either at the 3- or 4-position also elevated CFTR activity, but the influence of this structural modification was not as uniform as the influence of benzannulation. The most potent new analogue, UCCF-339, activated wild-type CFTR with a K(d) of 1.7 microM, which is more active than the previous most potent flavonoid activator of CFTR, apigenin. Several compounds in the benzoflavone panel also activated G551D-CFTR, but none were as active as apigenin. Pharmacophore modeling suggests a common binding mode for the flavones and other known CFTR activators at one of the nucleotide-binding sites, allowing for the rational development of more potent flavone analogues.

Animals↗
PubMed2004

Identification of the astringent taste compounds in black tea infusions by combining instrumental analysis and human bioresponse.

Application of taste dilution analyses on freshly prepared black tea infusions revealed neither the high molecular weight thearubigen-like polyphenols nor the catechins and theaflavins, but a series of 14 flavon-3-ol glycosides as the main contributors to the astringent taste perceived upon black tea consumption. Among these glycosides, the apigenin-8-C-[alpha-l-rhamnopyranosyl-(1-->2)-O-beta-d-glucopyranoside] was identified for the first time in tea infusions. Depending on the structure, the flavon-3-ol glycosides were found to induce a velvety and mouth-coating sensation at very low threshold concentrations, which were far below those of catechins or theaflavins; for example, the threshold of 0.001 micromol/L found for quercetin-3-O-[alpha-l-rhamnopyranosyl-(1-->6)-O-beta-d-glucopyranoside] is 190000, or 16000 times below the threshold determined for epigallocatechin gallate or theaflavin, respectively. Moreover, structure/activity considerations revealed that, besides the type of flavon-3-ol aglycon, the type and the sequence of the individual monosaccharides in the glycosidic chain are key drivers for astringency perception of flavon-3-ol glycosides.

Biflavonoids↗