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PubMed1996

Interaction of 5,7-dihydroxy-4'-methoxyflavone with a multisubunit protein, carmin: thermodynamics and kinetics of interaction.

Acacetin (5,7-dihydroxy-4'-methoxy flavone) is a flavone intrinsically present in the seeds of Carthamus tinctorius. Carmin is a multimeric, high molecular weight protein from the seeds of Carthamus tinctorius. The association constant of interaction of acacetin and carmin is maximum at 37.2 degrees C with a value of (3.96 +/- 0.61) x 10(4) M-1 as measured by fluorescence quenching. Acacetin has at least two binding sites on carmin. The interaction follows pseudo-first-order kinetics with a reaction rate constant of 3.4 +/- 0.4 s-1. The titration calorimetric data suggest that binding sites for acacetin and its structural analogue, biochanin A, are conserved. The interaction does not affect the association-dissociation equilibrium of the protein. Also, the binding does not induce any significant conformational changes in the protein as monitored by circular dichroic spectra. Biochanin A (5, 7-dihydroxy-4'-methoxyisoflavone), a structural analogue, interacts with carmin with an association constant of (9.33 +/- 1.44) x 10(4) M-1 at 36.9 degrees C. This indicates that the stereochemistry of the ligand plays an important role in the binding process of flavone to protein. Interaction studies of chemically modified lysyl and tryptophanyl groups separately, and lysyl and tryptophanyl groups sequentially, in the protein carmin with the ligands reveal the involvement of tryptophanyl residues in the binding process and show that it is predominantly an entropically driven hydrophobic interaction.

Flavones↗
PubMed2002

GABA(A)-receptor ligands of flavonoid structure.

This review describes the new research developments that have established the CNS-activity of some natural flavonoids. The properties of flavone, chrysin, apigenin and cirsiliol are described and a survey of the occurrence of ligands for the benzodiazepine binding site in the flavonoid field is attempted. Natural compounds, structurally related to flavonoids and with similar CNS-activities, are also included. A medicinal chemistry approach to improve the biochemical and pharmacological properties of the flavone nucleus is described alongside with the enumeration of the principal achievements obtained to date. Quantitative structure-activity relationships studies leading to the formulation of pharmacophore models presumably describing the characteristics of the flavone-binding site in the GABA(A)-receptor are summarized.

Animals↗
PubMed1993

Evidence for tangeretin O-demethylation by rat and human liver microsomes.

1. Tangeretin, a polymethoxylated flavone, was studied as a substrate for cytochrome P450-catalysed demethylation reactions by rat and human liver microsomes. Evidence has been presented for the production of formaldehyde in the presence of tangeretin and NAD(P)H. Kinetic studies showed a Km value for tangeretin of about 18 microM in both species. 2. The reaction was inhibited by CO, piperonyl butoxide, 7,8-benzoflavone, propyl gallate, aminobenzothiazole and metyrapone. 3. Rats pretreated with classical cytochrome P450 inducers (Aroclor 1254, 3-methylcholanthrene, phenobarbital, dexamethasone and ciprofibrate) or with flavonoids (flavone, flavanone, quercetin and tangeretin) resulted in increased microsomal demethylation of tangeretin after 3-methylcholanthrene and flavone only. Tangeretin did not enhance its own metabolism. 4. Tangeretin interacted with the oxidized form of cytochrome P450 to produce a reverse type I spectrum. 5. Results indicate that tangeretin is metabolized in liver microsomes by an O-demethylation reaction involving cytochrome P450.

Animals↗
PubMed2003

[Identification and evaluation of TCM shayuanzi].

OBJECTIVE: To understand the varieties of Shayuanzi on sale and establish the method for evaluating its quality. METHOD: 22 samples collected from all over the country were identified by TLC and the contents of total flavone in them were determined with UV. RESULT: All samples could be classified into three varieties, and they could be identified by TLC. The contents of total flavone in them were 0.3%-1.0%. CONCLUSION: Shayuanzi on sale mainly includes Astragalus complanatus, and there are A. adsuragen and A. sinicus as well. TLC is a better method for the identification of shayuanzi. The total flavone in A. complanatus is 0.33%-0.82%.

Astragalus Plant↗
PubMed2006

[Chemical constituents from roots of Ficus hirta].

OBJECTIVE: To study the chemical constituents from the roots of Ficus hirta. METHOD: Compounds were isolated by chromatographic techniques on silica gel and HP-20 resin columns. Their structures were elucidated by chemical and spectroscopic methods. RESULT: Ten compounds were identified as beta-sitosterol (1), stigmasterol (2), psoralene (3), 3beta-hydroxy-stigmast-5-en-7-one (4), 5-hydroxy-4', 6, 7, 8-tetramethoxy flavone (5), 4', 5, 6, 7, 8-pentamethoxy flavone (6), 4', 5, 7-trihydroxy-flavone (7), 3beta-acetoxy-beta-amyrin (8), 3beta-acetoxy-alpha-amyrin (9) and hesperidin (10). CONCLUSION: The compounds 4, 5, 6 were obtained from this genus for the first time, and all the compounds were obtained from this plant for the first time.

Ficus↗
PubMed2006

[Chemical constituents of C-glycosylflavones from Mimosa pudica].

AIM: To study chemical constituents of Mimosa pudica of Hainan province. METHODS: The constituents were separated and purified by column chromatography with macroporous adsorption resin Diaion HP-20, Sephadex LH-20, Toyopearl HW-40, MCI Gel CHP-20, RP-18 and normal phase silica gel. Their structures were identified on the basis of physical and spectral data. RESULTS: Four compounds were isolated and identified as: 7, 8, 3', 4'-tetrahydroxyl-6-C-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranosyl flavone (I); 5, 7, 4'-trihydroxyl-8-C-[alpha-L-rhamnopyranosyl-( --> 2)]-beta-D-glucopyranosyl flavone (II); 5, 7, 3', 4'-tetrahydroxyl-6-C-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranosyl flavone (III); catcher (IV). CONCLUSION: Compound I is a new compound and componuds II - IV were isolated from this plant for the first time.

Disaccharides↗
PubMed2003

Antioxidant activity of Egyptian Eucalyptus camaldulensis var. brevirostris leaf extracts.

Leaves from Eucalvptus camaldulensis var. brevirostris trees, planted in the Nile delta in Egypt, were examined for the antioxidant activity of their nonvolatile compounds. The extracts obtained by ethanol digestion and by supercritical fluid extraction (SFE; CO2 with 15% ethanol) showed the most promising antioxidative activities. In order to identify the most active compounds, both extracts were subjected to a semipreparative reversed-phase HPLC separation, the main fractions were collected, tested for antioxidative activity and analysed by different chromatographical and spectroscopical methods for identification of the most relevant compounds. Gallic and ellagic acid were found to be the prevailing antioxidants in the ethanolic extract. The main two compounds of the SFE extract with antioxidative activity revealed to be flavones. To a high degree of probability they were identified as 5-hydroxy-7,4'-dimethoxy flavone and 5-hydroxy-7,4'-dimethoxy-8-methyl flavone, respectively. The extracts obtained by ethanoldigestion were dried and administered to rats for toxicity evaluation (up to 3 g/kg body weight). No mortality was observed which indicates a very low lethality of the tested extract.

Animals↗
PubMed2003

Nitric oxide suppresses apoptosis in human colon cancer cells by scavenging mitochondrial superoxide anions.

In cells lacking a functional p53 tumor suppressor protein, the endogenous free radical nitric oxide (NO) appears to inhibit apoptosis, and thereby promotes growth of cancer cells. In order to elucidate the underlying mechanisms on a molecular basis, we used HT-29 human colon carcinoma cells, carrying a p53 loss-of-function mutation, and examined the effects of NO on apoptosis when induced either by the flavonoid flavone or by the chemotherapeutic drug camptothecin (CPT), which is able to scavenge NO by superoxide anion production. Caspase-3 activation as well as nuclear fragmentation, both indicative of apoptosis, were dose dependently inhibited by the NO-liberating agents sodium nitroprusside (SNP) or S-nitroso-N-acetyl-D,L-penicillamine (SNAP) when apoptosis was initiated by flavone with only minor effects on apoptosis when initiated by camptothecin. The transcript levels of 9 apoptosis-related genes were assessed and NO liberation was shown to completely and specifically prevent the flavone-induced but not camptothecin-induced decrease in bcl-X(L) mRNA levels. These results were also confirmed at the protein level. The effects of NO on the mitochondrial apoptosis pathway were further evidenced by the scavenging of superoxide anions as produced in mitochondria of cells undergoing apoptosis. Scavenging of mitochondrial superoxide anions by NO prevents the downregulation of bcl-X(L), the depolarization of the mitochondrial membrane potential, the cytochrome c release and finally the activation of caspase-3. In conclusion, NO effectively inhibits apoptosis by scavenging superoxide anions generated in the mitochondria of p53 mutant cells and thereby prevents the downregulation of the antiapoptotic factor bcl-X(L), which controls the mitochondrial apoptosis pathway.

Apoptosis↗
PubMed1987

Clovers secrete specific phenolic compounds which either stimulate or repress nod gene expression in Rhizobium trifolii.

Rhizobium trifolii mutants containing Escherichia coli lac gene fusions to specific nodulation (nod) genes were used to characterise phenolic compounds secreted from the roots of white clover (Trifolium repens) plants. These compounds either had stimulatory or inhibitory effects upon the induction of the nod genes. The stimulatory compounds were hydroxylated flavones and the most active compound was 7,4'-dihydroxyflavone. The inhibitory compounds present in white clover root exudates were umbelliferone (a coumarin) and formononetin (an isoflavone). Transcriptional activation of nod gene promoters in response to short exposures (3 h) of 7,4'-dihydroxyflavone was growth phase dependent; cells in early log phase were highly responsive to flavone additions in vitro and nod gene induction could be detected within 20 min of exposure at 5 x 10 M. Cells in other growth phases were generally unresponsive. A 10-fold molar excess of umbelliferone to 7,4'-dihydroxyflavone resulted in complete inhibition of nod gene induction. Some commercially-obtained flavones were found to have weak stimulatory activity but could also inhibit nod gene induction by more effective stimulatory compounds. Strong stimulatory and inhibitory compounds all possessed a 7-hydroxy moiety and showed other structural similarities. This suggested that there was one binding site for these compounds. Because the response to these compounds was rapid, we propose that these phenolics act at the bacterial membrane or that an active uptake system is involved.

Journal Article↗
PubMed1997

Catalytic properties of NAD(P)H:quinone oxidoreductase-2 (NQO2), a dihydronicotinamide riboside dependent oxidoreductase.

Human NAD(P)H:quinone acceptor oxidoreductase-2 (NQO2) has been prepared using an Escherichia coli expression method. NQO2 is thought to be an isoform of DT-diaphorase (EC 1.6.99.2) [also referred to as NAD(P)H:quinone acceptor oxidoreductase] because there is a 49% identity between their amino acid sequences. The present investigation has revealed that like DT-diaphorase, NQO2 is a dimer enzyme with one FAD prosthetic group per subunit. Interestingly, NQO2 uses dihydronicotinamide riboside (NRH) rather than NAD(P)H as an electron donor. It catalyzes a two-electron reduction of quinones and oxidation-reduction dyes. One-electron acceptors, such as potassium ferricyanide, cannot be reduced by NQO2. This enzyme also catalyzes a four-electron reduction, using methyl red as the electron acceptor. The NRH-methyl red reductase activity of NQO2 is 11 times the NADH-methyl red reductase activity of DT-diaphorase. In addition, through a four-electron reduction reaction, NQO2 can catalyze nitroreduction of cytotoxic compound CB 1954 [5-(aziridin-1-yl)-2,4-dinitrobenzamide]. NQO2 is 3000 times more effective than DT-diaphorase in the reduction of CB 1954. Therefore, NQO2 is a NRH-dependent oxidoreductase which catalyzes two- and four-electron reduction reactions. NQO2 is resistant to typical inhibitors of DT-diaphorase, such as dicumarol, Cibacron blue, and phenindone. Flavones are inhibitors of NQO2. However, structural requirements of flavones for the inhibition of NQO2 are different from those for DT-diaphorase. The most potent flavone inhibitor tested so far is quercetin (3,5,7,3',4'-. 6pentahydroxyflavone). It has been found that quercetin is a competitive inhibitor with respect to NRH (Ki = 21 nM). NQO2 is 43 amino acids shorter than DT-diaphorase, and it has been suggested that the carboxyl terminus of DT-diaphorase plays a role in substrate binding (S. Chen et al., Protein Sci. 3, 51-57, 1994). In order to understand better the basis of catalytic differences between NQO2 and DT-diaphorase, a human NQO2 with 43 amino acids from the carboxyl terminus of human DT-diaphorase (i.e., hNQO2-hDT43) has been prepared. hNQO2-hDT43 still uses NRH as an electron donor. In addition, the chimeric enzyme is inhibited by quercetin but not dicumarol. These results suggest that additional region(s) in these enzymes is involved in differentiating NRH from NAD(P)H.

Amino Acid Sequence↗
PubMed1999

Activation of Cl- channel and Na+/K+/2Cl- cotransporter in renal epithelial A6 cells by flavonoids: genistein, daidzein, and apigenin.

The present study investigates regulation of Cl- channels and Na+/K+/2Cl- cotransporter in a renal epithelial cell line, A6, by flavones: genistein [an inhibitor of protein tyrosine kinases (PTK)], daidzein (an inactive compound of genistein), and apigenin [an inhibitor of mitogen-activated protein (MAP) kinase]. Genistein and daidzein activated Cl- channels. Genistein and apigenin had a stimulatory effect on the bumetanide-sensitive Na+/K+/2Cl- cotransporter. Other PTK inhibitors, tyrphostin A23, lavendustin A, and herbimycin A, which do not contain a structure flavone, had no stimulatory action on Cl- channels or the Na+/K+/2Cl- cotransporter. These observations conclude that (i) genistein activates a Cl- channel and the Na+/K+/2Cl- cotransporter; and (ii) the stimulatory action is not mediated through its inhibitory action on protein tyrosine kinase, but rather the structure of flavone itself plays a crucial role in stimulatory regulation of Cl- channels and Na+/K+/2Cl- cotransporter.

Animals↗
PubMed1999

Extract from Scutellaria baicalensis Georgi attenuates oxidant stress in cardiomyocytes.

Extract from Scutellaria baicalensis Georgi Attenuates Oxidant Stress in Cardiomyocytes. Journal of Molecular and Cellular Cardiology (1999) 31, 1885-1895. Scutellaria baicalensis Georgi is a Chinese herbal medicine used to treat allergic and inflammatory diseases. The medicinal effects of S. baicalensis root may result, in part, from its constituent flavones reported to have antioxidant properties. Since oxidants play multiple roles in cells, we tested whether S. baicalensis could confer protection in a cardiomyocyte model of ischemia and reperfusion. The intracellular fluorescent probes 2',7'-dichlorofluorescin diacetate (DCFH-DA, sensitive to H(2)O(2) and hydroxyl radicals) and dihydroethidium (DHE, sensitive to superoxide) were used to assess intracellular reactive oxygen species (ROS), and propidium iodide (PI) was used to assess viability in cultured embryonic cardiomyocytes. S. baicalensis extract (SbE) quickly attenuated levels of oxidants generated during transient hypoxia and during exposure to the mitochondrial site III inhibitor antimycin A, as measured by DCFH oxidation or by DHE oxidation. These attenuated oxidant levels were associated with improved survival and function. Cell death after ischemia/reperfusion decreased from 47+/-3 % in untreated to 26+/-2 % in S. baicalensis treated cells (P<0.001). After antimycin A exposure, S. baicalensis decreased cell death from 49+/-6 % in untreated to 23+/-4 % in treated cells. Return of contraction occurred in S. baicalensis-treated cells but was not observed in control cells. Other in vitro studies revealed that baicalein, a major flavone component of SbE can directly scavenge superoxide, hydrogen peroxide, and hydroxyl radicals. Collectively, these findings indicate that SbE and its constituent flavones such as baicalein can attenuate oxidant stress and protect cells from lethal oxidant damage in an ischemia-reperfusion model.

Animals↗
PubMed2003

Hepatoprotective activity of polyhydroxylated 2-styrylchromones against tert-butylhydroperoxide induced toxicity in freshly isolated rat hepatocytes.

2-Styrylchromones are a novel class of chromones, vinylogues of flavones (2-phenylchromones), which have recently been found in nature. The best described property of almost every group of flavones and other flavonoids, especially the hydroxylated derivatives, is their capacity to act as antioxidants. Indeed there is a widely accepted view that the positive health effects of flavones are due to their antioxidant activity. As oxidative stress is a main cause of liver toxicity induced by several hepatotoxicants, agents with the ability to protect the liver against reactive pro-oxidant species may be therapeutically useful. The present study evaluated the possible protective activity of six new synthetic polyhydroxylated 2-styrylchromone derivatives against the pro-oxidant hepatotoxicity exerted by tert-butylhydroperoxide ( t-BHP) in freshly isolated rat hepatocytes. The cells were preincubated with the 2-styrylchromones in the final concentrations of 3.125, 12.5, 25, 50, 100, and 200 microM for 5 min before treatment with 1.0 mM t-BHP for 30 min (throughout this incubation period the cells were exposed to both compounds). The well-known antioxidant 3-hydroxyflavone (quercetin) was used as positive control. At the end of the 30-min incubation period, aliquots of cells suspensions were taken for measurement of lactate dehydrogenase leakage, thiobarbituric acid reactive substances, reduced glutathione, and oxidized glutathione contents. The tested compounds exhibited in vitro protective activity against t-BHP induced hepatotoxicity (1.0 mM, 30 min). Three of the tested compounds, at the concentrations of 3.125, 12.5, 25, and 50 microM, prevented the t-BHP induced glutathione depletion, lipid peroxidation, and cell death in freshly isolated rat hepatocytes to a comparable potency with that of quercetin.

Animals↗
PubMed1999

Comparative analysis of the effects of flavonoids on proliferation, cytotoxicity, and apoptosis in human colon cancer cell lines.

Flavonoids are polyphenolic compounds that occur ubiquitously in foods of plant origin. Their proposed protective role in tumor development may prevail especially in the intestinal tract due to direct exposure of intestinal epithelia to these dietary ingredients. We have screened more than 30 flavonoids for their effects on cell proliferation and potential cytotoxicity in the human colon cancer cell lines Caco-2, displaying features of small intestinal epithelial cells, and HT-29, resembling colonic crypt cells. In addition, for selected compounds we assessed whether they induce apoptosis by determining caspase-3 activation. Studies on the dose dependent effects of the flavonoids showed antiproliferative activity of all compounds with EC50 values ranging between 39.7 +/- 2.3 microM (baicalein) and 203.6 +/- 15.5 microM (diosmin). In almost all cases, growth inhibition by the flavonoids occurred in the absence of cytotoxicity. There was no obvious structure-activity relationship in the antiproliferative effects either on basis of the subclasses (i.e., isoflavones, flavones, flavonols, flavonones) or with respect to kind or position of substituents within a class. In a subset of experiments we examined the antiproliferative activities of the most potent compound of each flavonoid subgroup in addition in LLC-PK1, a renal tubular cell line, and the human breast cancer cell line MCF-7. Out of four flavonols tested, three displayed almost equal antiproliferative activities in all cell lines but fisetin was less potent in MCF-7 cells. The flavanones bavachinin and flavanone inhibited growth of Caco-2 and HT-29 cells with lower EC50 values than that obtained in LLC-PK1 and MCF-7 cells. The lower susceptibility of LLC-PK1 and MCF-7 cells towards growth arrest was even more pronounced in the case of the flavone baicalein. Half maximal growth-inhibition in LLC-PK1 and MCF-7 required 2.5 and 6.6 fold higher concentrations than that needed in the intestinal cell lines. The flavonoids failed to affect apoptosis in LLC-PK1 and MCF-7, whereas baicalein and myricetin were able to induce apoptosis in HT-29 and Caco-2 cells. In conclusion, flavonoids of the flavone, flavonol, flavanone, and isoflavone classes possess antiproliferative effects in different cancer cell lines. The capability of flavonoids for growth inhibition and induction of apoptosis can not be predicted on the basis of their chemical composition and structure.

Apoptosis↗
PubMed1989

Inhibition of mouse liver sialidase by plant flavonoids.

Flavonoids (103 species) were tested for inhibitory activity against mouse liver sialidase using sodium p-nitrophenyl-N-acetyl-alpha-D-neuraminate (PNP-NeuAc) as substrate. Isoscutellarein-8-O-glucuronide from the leaf of Scutellaria baicalensis showed most potent activity (IC50, 40 microM), and this flavone appeared to be a non-competitive inhibitor of the enzyme. This flavone inhibited the lysosomal solubilized sialidase against PNP-NeuAc and sialyllactose effectively, but not microsomal enzyme against gangliosides and colominic acid, whereas, negligible or weak inhibitory activities were observed for influenza virus sialidase, beta-galactosidase, alpha-mannosidase, and alpha-glucosidase tested. These results indicate that this flavone may be useful to elucidate the function of the lysosomal solubilized sialidase.

Animals↗
PubMed1990

Structure-activity relationships of polymethoxyflavones and other flavonoids as inhibitors of non-enzymic lipid peroxidation.

Polymethoxylated flavones and C-glycosyl derivatives isolated from medicinal plants besides other flavonoid compounds were studied for their influence on lipid peroxidation induced by FeSO4+ cysteine in rat liver microsomes. A number of hydroxyflavones (e.g. luteolin); C-glycosyl-flavones (e.g. orientin); methoxyflavones (e.g. gardenin D) and flavonols (e.g. datiscetin), as well as the flavanol leucocyanidol and the biflavone amentoflavone behaved as inhibitors of non-enzymic lipid peroxidation. Structure-activity relationships were established and it was observed that the structural features for active polyhydroxylated compounds were different from those of polymethoxylated flavones, antiperoxidative flavonoids possessing a high lipophilicity.

Animals↗
PubMed1986

Comparison of the effects of various flavonoids on ethoxycoumarin deethylase activity of rat intestinal and hepatic microsomes.

Fifteen flavonoids were examined for their effects on the activity of 7-ethoxycoumarin O-deethylase in rat hepatic and intestinal microsomes. The effect depended on both the chemical structure of the flavonoid and the origin of the microsomes. Polyhydroxylated flavonoids with a C2-C3 double bond (flavones and flavonols) were more effective inhibitors of the enzyme in both hepatic and intestinal microsomes than were the reduced homologues (flavanonols, flavanones and flavan-3-ols). In contrast, flavones lacking hydroxyl substituents (e.g. 5,6-benzoflavone, 7,8-benzoflavone and flavone) increased ethoxycoumarin deethylase activity in liver microsomes although they had an inhibitory effect in intestinal microsomes.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1983

Some pharmacological, toxicological and phytochemical investigations on Centaurea phyllocephala.

Centaurea phyllocephala Boiss. has been used in folkloric medicine as an antidiabetic agent. Present investigations on various extracts of C. phyllocephala revealed that basal plasma glucose concentration and plasma glucose response to glucose load were either elevated or unchanged by the i.v. administration of these extracts in anaesthetized rats or by i.p. or oral administration of the extracts in conscious rats. The predominant effect of C. phyllocephala is the toxicity in rats and mice and this indicates the presence of some toxic or active compounds which merit phytochemical isolation. Further, C. phyllocephala extracts also caused either an initial brief hypotension followed by a delayed hypertension or produced no changes when injected i.v. in the rats. The hypotensive effect was inhibited by atropine whereas the hypertensive effect was prevented by phentolamine or guanethidine but not by hexamethonium. The alcoholic extract also induced an initial brief negative inotropic effect, followed by delayed prolonged positive inotropic and negative chronotropic effects on the spontaneous inotropic and negative chronotropic effects on the spontaneous contractions of the guinea pig right atrium. The initial depressing effect and the delayed positive inotropic effect were inhibited by pretreatment with atropine. The extract of C. phyllocephala also produced a contractile activity on guinea pig ileum strips and this could be prevented by atropine. No significant diuretic effect was produced by the extract. Phytochemical screening revealed that C. phyllocephala contains tertiary and quaternary alkaloids, sesquiterpene lactones, methylated flavones and their glycosides, as well as leuco- and proanthocyanidines. Further studies on sesquiterpene lactones and methylated flavones resulted in the isolation of lactones with alpha-methylene gamma-lactone and methylene side chain on the cyclopentyl ring as well as of four methylated flavones (hispidulin, nepetin, cirsiliol, jaceosidin) structurally closely related to the cytotoxic flavonoids of other Compositae plants.

Animals↗