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PubMedDate not supplied

Inhibition of ethoxy- and pentoxy-resorufin dealkylases of rat liver by flavones and flavonols: structure-activity relationship.

The inhibitory effects of 17 flavones and flavonols on ethoxy- and pentoxy-resorufin dealkylases of rat liver were investigated. Several findings concerning the relationship between structure and activity can be pointed out. The presence or lack of hydroxyl groups on the flavane nucleus has no influence on the efficiency of inhibition. Flavone and quercetin result in the same degree of inhibition. For polyhydroxylated moleculse, the position of hydroxyl groups on A and B rings was an important factor. The more powerful inhibitors were the flavones having hydroxyl groups only on the A ring (e.g. chrysin) and the inhibitory effect was decreased by addition of hydroxyl substituents on the B group (e.g. quercetin). EROD activities were more responsive than PROD activities. Flavone and quercetin were competitive inhibitors of EROD activity whereas chrysin and morin were mixed type inhibitors. In the case of PROD activity, all four flavones were of the mixed type inhibitors.

Animals↗

PubMed2004

The flavones luteolin and apigenin inhibit in vitro antigen-specific proliferation and interferon-gamma production by murine and human autoimmune T cells.

Plant-derived flavonoids are inhibitors of various intracellular processes, notably phosphorylation pathways, and potential inhibitors of cellular autoimmunity. In this study, the inhibiting effects of various flavonoids on antigen-specific proliferation and interferon-gamma (IFN-gamma) production by human and murine autoreactive T cells were evaluated in vitro. T-cell responses were evaluated for the human autoantigen alpha B-crystallin, a candidate autoantigen in multiple sclerosis, and for the murine encephalitogen proteolipid protein peptide PLP (139-151). The flavones apigenin and luteolin were found to be strong inhibitors of both murine and human T-cell responses while fisitin, quercitin, morin and hesperitin, members of the subclasses of flavonoles and flavanones, were ineffective. Antigen-specific IFN-gamma production was reduced more effectively by flavones than T-cell proliferation, suggesting that the intracellular pathway for IFN-gamma production in T cells is particularly sensitive to flavone inhibition. These results indicate that flavones but not flavanoles or flavanones are effective inhibitors of the potentially pathogenic function of autoreactive T cells. The effects of flavones were the same for human and murine autoreactive T cells, stressing the usefulness of animal models of autoimmunity for further studies on the effects of flavonones on autoimmune diseases.

Animals↗

PubMed2001

The ABC-like vacuolar transporter for rye mesophyll flavone glucuronides is not species-specific.

In many cases, the vacuolar uptake of secondary metabolites has been demonstrated to be strictly specific for a given compound and plant species. While most plants contain glycosylated secondary substances, few cases are known where flavonoids may also carry negative charges, e.g. as glucuronide conjugates. Vacuolar transport of glucosylated phenylpropanoid derivatives has been shown to occur by proton substrate antiport mechanisms (Klein, M., Weissenböck. G., Dufaud, A., Gaillard, C., Kreuz, K., Martinoia, E., 1996. Different energization mechanisms drive the vacuolar uptake of a flavonoid glucoside and a herbicide glucoside. J. Biol. Chem. 271, 29,666-29,671). In contrast, flavone glucuronides appearing specifically in rye mesophyll vacuoles are taken up by direct energisation utilising MgATP, strongly arguing for the presence of an ATP-binding cassette (ABC) transporter belonging to the subfamily of multidrug resistance-associated proteins (MRP) on the rye vacuolar membrane (Klein, M., Martinoia, E., Hoffmann-Thoma, G., Weissenböck, G., 2000. A membrane-potential dependent, ubiquitous ABC-like transporter mediates the vacuolar uptake of rye flavone glucuronides regulation of glucturonide uptake by glutathione and its conjugates. Plant Journal 21, 289-304). MRPs are known to transport negatively charged organic anions. Results presented here suggest that the vacuolar directly energised MRP-like glucuronate pump for plant-specific flavone glucuronides is ubiquitously present in diverse plant species since rye flavone glucuronides are taken up into vacuoles isolated from the barley mesophyll or from the broccoli stalk parenchyma representing two species which do not synthesise glucuronidated secondary compounds. According to the transport characteristics and inhibition profile observed we propose the existence of a high-capacity, uncoupler-insensitive vacuolar ABC transporter for flavone glucuronides and possibly other negatively charged organic compounds -- plant-born or xenobiotic -- irrespective of the plant's capability to endogenously produce glucuronidated compounds.

ATP-Binding Cassette Transporters↗

PubMed2001

Distribution of 8-oxygenated leaf-surface flavones in the genus Ocimum.

Nine species of Ocimum (Lamiaceae) were surveyed for leaf-surface flavonoids by means of HPLC with diode array detection and atmospheric pressure chemical ionisation (APCI) mass spectrometry. The analysis revealed the presence of 23 different flavones, most of which were identified by comparing their UV and mass spectra with those of standards. Almost all taxa investigated contained flavones methoxylated in the 6- and 8-positions, such as nevadensin, xanthomicrol and gardenin B. The same taxa also produced flavones methoxylated in the 6-position but hydroxylated in the 8-position, including isothymusin (5,8,4'-trihydroxy-6,7-dimethoxyflavone), pedunculin (5,8-dihydroxy-6,7,4'-trimethoxyflavone) and a new flavone, 5,7,8-trihydroxy-6,4'-dimethoxyflavone, which was given the trivial name pilosin. This compound was isolated from O. americanum var. pilosum and also detected as a minor constituent in O. x citriodorum leaf extracts. Its molecular structure was elucidated by means of NMR spectroscopy. 8-Oxygenated flavones were absent only from O. lamiifolium. APCI mass spectrometry of the flavonoids revealed that the product ions formed by collision induced dissociation of the protonated molecule provided structural information about the substitution pattern of the A-ring. The chemotaxonomic and biogenetic implications of the results are discussed.

Flavonoids↗

PubMed2002

Flavones from Scutellaria baicalensis Georgi attenuate apoptosis and protein oxidation in neuronal cell lines.

The oxidative modification of proteins plays a major role in a number of human diseases including Alzheimer's disease (AD). Flavones in extracts of Scutellaria baicalensis (SbE) have been reported to have exceptional antioxidant properties. We examined the effects of SbE on neuronal cells exposed to oxidative stress. Neuronal HT-22 cells were exposed to low levels of H(2)O(2) generated from glucose oxidase (GO) under conditions that caused cell death in 24 h. The mechanism of cell death was shown to occur via apoptosis. Flavone extracts (50 microg/ml) protected cells and increased viability to 85+/-5% (P<0.001). The flavones also increased the content of Bcl-2 in the cell, resulted in its phosphorylation, and in contrast decreased the Bax levels. Furthermore, the oxidative-stress-induced protein carbonyl formation was reduced nearly two-fold when cells were pretreated with the flavone extract. Two-dimensional electrophoresis (2-DE) showed that less than 15% of the total visible proteins were oxidized and that the oxidation was specific for certain oxidation-sensitive proteins. These data support the idea that flavones in SbE can attenuate oxidant stress and protect cells from lethal oxidant damage.

Animals↗

PubMed1998

Evaluation of the mutagenicity and antimutagenicity of forty-two 3-substituted flavones in the Ames test.

The mutagenic and antimutagenic activities of forty-two synthetic flavones were assessed by the Ames test. The tested flavones included twenty-three 3-nitroflavones, eighteen 3-aminoflavones and the 3-chloroflavone. The mutagenicity was evaluated with Salmonella typhimurium TA100 and YG1042 (an overproducing nitroreductase and O-acetyltransferase TA100 strain) with and without metabolic activation (S9 mix). The antimutagenicity of the non mutagenic derivatives was evaluated against 11 known reference mutagens. A total of 39 synthetic flavones were mutagenic. The mutagenic activities ranged from 0.1 rev/nmole (4'-chloro-6-methoxy-3-nitroflavone) to 6240 rev/nmole (4'-methoxy-3, 3'-diaminoflavone). Two differences were found between the 3-amino and the 3-nitroflavones: (i) the mutagenicity of the 3-aminoflavones required the presence of the metabolic activation; (ii) the 3-amino derivatives were more mutagenic than their 3-nitro counterparts. Increased mutagenicity, as assessed with strain YG1042, was limited to 17/39 derivatives. The mutagenic activity was induced by the presence of the double bond at the 2,3-position for conjugation of the lone-pair electron with the carbonyl group on the 'C' ring. This mutagenicity was modulated by substituents at the 2'-position. Additional mutagenicity was brought by the aminoaromatic and nitroaromatic group reduction by bacterial nitroreductases and by the S9 mix; it was modulated by different substituents on the aromatic rings of the flavones. Three flavones: 3-chloroflavone (1C), 4'-hydroxy-3-nitroflavone (23N) and 2',3-diaminoflavone (2A) showed antimutagenic properties. Compound 1C was efficient against benzo(a)pyrene (BaP), 2-aminofluorene (2AF), 2-aminoanthracene (2AA), 4-nitroquinoline-1-oxide (4NQO) and 1-methyl-3'-nitro-1-nitrosoguanidine (MNNG). Compound 23N inhibited the mutagenicity of BaP and MNNG. The antimutagenic activity of 2A was limited to MNNG.

Antimutagenic Agents↗

PubMed1999

Cloning and expression of flavone synthase II from Gerbera hybrids.

In Gerbera hybrids, flavone synthesis is controlled by the locus Fns. The responsible enzyme, flavone synthase II, belongs to the NADPH-dependent cytochrome P450 monooxygenases. From two different chemogenetic defined Gerbera lines with the dominant (fns +.) or recessive (fns fns) alleles at the locus Fns, a cytochrome P450 fragment (CypDDd7a) was isolated using a differential display technique with upstream primers based on the conserved heme-binding region of cytochrome P450 proteins. The full-length cDNA (CYP93B2) which contained the open-reading frame and part of the CypDDd7a sequence was isolated via 5'-RACE and end-to-end PCR with gene specific primers. Northern blot analysis of total RNA of Gerbera hybrids indicated that the CYP93B2 gene was only transcribed in lines with the dominant allele fns + and that the transcript levels during flower development are in agreement with the measured enzyme activity of FNS II and flavone accumulation. Microsomes from yeast cells expressing CYP93B2 catalysed the direct formation of [14C]-flavones from the respective [14C]-flavanones. Thus, CYP93B2 was shown to encode flavone synthase II. This is the first report of the isolation and expression of a functional FNS II cDNA clone from any species. The comparison of amino acid sequences revealed that CYP93B2 had 54% identity with the sequence of CYP93B1, which has recently been reported as a (2S)-flavanone 2-hydroxylase of Glycyrrhiza echinata L.

Amino Acid Sequence↗

PubMed2004

Glucosylation of phenolic compounds by Pharbitis nil hairy roots: I. Glucosylation of coumarin and flavone derivatives.

Hairy roots of medicinal morning glory (Pharbitis nil) showed potent glucosylation activity against umbelliferone and aesculetin, so the glucosylation activity against several phenolic compounds was tested. Some coumarin derivatives and flavone derivatives having phenolic hydroxyl groups were incubated with the hairy roots. The coumarin derivatives and flavone derivatives almost disappeared from the culture medium in half a day. In the case of the coumarin derivatives, a 7-hydroxyl group was easily glucosylated. A methyl group at C-8 somewhat decreased the glucosylation to a hydroxyl group at C-7 of the coumarin skeleton. The 4-hydroxy coumarin derivatives were changed to acetophenone-type glucosides by incubation with the hairy roots through decarboxylation. Several flavonol derivatives were tested for glucosylation by the hairy roots. 3-Hydroxy flavone, 3.6-dihydroxyflavone and 3,7-dihydroxyflavone were glucosylated to give 3-glucosylated derivatives. Of these, 3,6-dihydroxyflavone was highly glucosylated, but not 3-hydroxyflavone or 3,7-dihydroxyflavone to the same degree. In the case of the flavones, a 3-hydroxy group could be predominantly glucosylated, and hydroxyl groups on the A and B ring of the flavones affected glucosylation by the hairy roots.

Coumarins↗

PubMedDate not supplied

Antioxidant profile of mono- and dihydroxylated flavone derivatives in free radical generating systems.

A number of free radical generating systems were used to investigate the antioxidant properties and structure-activity relationships of a series of monohydroxylated and dihydroxylated flavones. Ortho-dihydroxylated flavones showed the highest inhibitory activity on enzymic and non-enzymic microsomal lipid peroxidation as well as on peroxyl radical scavenging. Most flavones were weak scavengers of hydroxyl radical, while ortho-dihydroxylated flavones interacted with superoxide anion generated by an enzymic system or by human neutrophils. This series of compounds did not exert cytotoxic effects on these cells. Scavenging of superoxide and peroxyl radicals may determine the antioxidant properties of these active flavones.

Animals↗

PubMed2003

In vitro effects of flavone from leaves of Diospyros kaki on rat cardiac myocyte apoptosis induced by hypoxia-reoxygenation and advanced glycation end products.

OBJECTIVE: To investigate the effects of flavone extracted from the leaves of Diospyros kaki on the apoptosis of rat cardiac myocytes induced by hypoxia-reoxygenation and advanced glycation end products in vitro. METHODS: The cardiac myocytes were isolated from neonatal SD rats and cultured in vitro for 72 h. Apoptosis of the cultured cells was induced by hypoxia-reoxygenation and advanced glycation end products (AGEs) respectively, and the effects of flavone extracted from the leaves of Diospyros kaki on the cell apoptosis was observed by measuring the apoptotic rates using flow cytometry. RESULTS: Apoptosis of neonatal rat cardiac myocytes was induced by hypoxia-reoxygenation in a time-dependent manner (6.05% +/-0.46% vs 12.45% +/-1.66%, P< 0.05), and flavone treatment of the cells significantly lowered the apoptotic rates. AGEs alone also induced apoptosis of neonatal rat cardiac myocytes (11.03+/-0.39 vs 6.25+/-0.48, P< 0.05), which was inhibited by flavone (8.40+/-0.47 vs 11.03+/-0.39, P < 0.05). CONCLUSION: Flavone extracted from the leaves of Diospyros kaki can inhibit the apoptosis of in vitro cultured neonatal rat cardiac myocytes induced by hypoxia-reoxygenation and advanced glycation end products.

Animals↗

PubMed2003

[Ginkgo flavones in in vitro metabolism and its clinical application].

AIM: To develop a method for assaying Ginkgo flavones in rat hepatical microsome. METHODS: Quercetin, isorhamnetin and keampferol were added to microsome incubate and incubated for a given time then extracted with ether-acetone. After evaporated, the residue was reconstituted with 100 microL of phosphate buffer solution (pH 2.0)-tetrahydrofuran-methanol-isopropanol (60:15:10:20). An aliquot of 20 microL was injected into the HPLC system. According to the result of estimate by means of HPLC, the results of metabolism of Ginkgo flavones in different conditions was compared. RESULTS: The assay was linear over the rang of 0.2-8 mg.L-1 for Ginkgo flavones. The limit of quantification was 0.1 mg.L-1 (n = 3). The recoveries of three components of Ginkgo flavones were 99.9%-113.8% for quercetin (RSD < 0.8%), 100.8%-117.3% for isorhamnetin (RSD < 1.9%) and 100.7%-116.5% for keampferol (RSD < 1.03%, n = 5). CONCLUSION: The method is simple, fast and accurate. It can be used for investigation of the metabolism of Ginkgo flavones.

Animals↗

PubMed2004

[Effects of flavone from leaves of Diospyros kaki on rat vascular smooth muscle cells proliferation stimulated by native low-density lipoprotein in vitro].

OBJECTIVE: To observe whether rat vascular smooth muscle cells (VSMCs) proliferation induced by native low-density lipoprotein (LDL) is affected by flavone from leaves of Diospyros kaki in vitro. METHODS: Rat aortic VSMCs were cultured in vitro and treated with LDL and flavone from leaves of Diospyros kaki, respectively, and were observed in comparison with the control group. The ratio of cell proliferation was determined by non-radioactive MTS/PES assay. RESULTS: Compared with control, flavone from leaves of Diospyros kaki can dose-dependently inhibit LDL-stimulated vascular smooth muscle cells proliferation (P < 0.05). CONCLUSIONS: The flavone from leaves of Diospyros kaki can inhibit proliferation of rat vascular smooth muscle cells exposed to high levels of native LDL. Flavone from leaves of Diospyros kaki may exert vascular protection by inhibiting vascular smooth muscle cell growth associated with hypercholesterolemia.

Animals↗

PubMed2006

[Study on the non-covalent interaction of 7-hydroxy flavone and its phosphate with DNA by fluorescence method].

The non-covalent interaction of 7-hydroxy flavone and its phosphate with DNA was studied using ethidium bromide (EB)as a probe. The result showed that both 7-hydroxy flavone and its phosphate could form non-covalent complexes, but the phosphorylated flavonoid showed higher binding affinity with DNA than 7-hydroflavone did. Experiments demonstrated that the higher the temperature, the lower the slop of quenching curve of DNA-EB in the presence of different amounts of 7-hydroxy flavone and its phosphate. It was confirmed that the combinations of DNA with 7-hydroxy flavone and its phosphate were a single static quenching process. According to the Stern-Volmer equation and Scatchard equation the quenching constants and the intrinsic binding constants of 7-hydroxy flavone and its phosphate were measured respectively, they were Kq1 = 601 L x mol(-1), Kq2 = 1381 L x mol(-1); K1 = 2.07 x 10(4) L x mol(-1) , K2 = 3.19 x 10(4) L x mol(-1) respectively.

Animals↗

PubMed1995

Interaction of flavones and their bromoacetyl derivatives with NAD(P)H:quinone acceptor oxidoreductase.

Flavones are a new type of inhibitor of NAD(P)H:quinone acceptor oxidoreductase (DT-diaphorase, EC 1.6.99.2). To further characterize the flavone binding site, three bromoacetyl derivatives of flavones, i.e., 7-bromoacetylflavone, 5-hydroxyl-7-bromoacetylflavone, and 7,8-dibromoacetylflavone, have been synthesized. These compounds have been found to be potent inhibitors that inactivate the rat quinone reductase in a time-dependent manner, suggesting that they can be used as affinity labels for the enzyme. Among the three bromoacetyl derivatives, 7,8-dibromoacetylflavone is the most potent inhibitor; however, its labeling of the quinone reductase is the least stable, so that the enzyme regains activity after a short incubation. In contrast, the inactivation of the quinone reductase by 5-hydroxyl-7-bromoacetylflavone is stable. Accordingly, this flavone derivative is the most suitable compound for labeling the flavone binding site of the enzyme. Electrospray mass spectrometry has been applied to demonstrate that 5-hydroxyl-7-bromoacetylflavone labels this enzyme in a stoichiometric manner.

Animals↗

PubMed1993

Structural and conformational studies on bio-active flavonoids. Crystal and molecular structure of a complex formed between 2',6'-dimethoxyflavone and orthophosphoric acid: a model for flavone-nucleotide interactions.

In order to investigate mechanisms of action of flavones at the molecular level, we have prepared a complex between a flavone and orthophosphoric acid which can be considered as a simplest model of interaction between a flavone and a more complex biological phosphate such as nucleotide, coenzyme or DNA. With orthophosphoric acid, the title flavone forms crystals which have 1:2 stoichiometry (C17H14O4.2H3PO4). This compound was found to be the 1:1 salt co-crystallized with the unionized molecular acid C17H15O4+.H2PO4-.H3PO4. The symmetry is monoclinic, space group P2(1)/n and unit cell dimensions a = 15.571(2), b = 7.369(1), c = 17.837(2) A, beta = 100.84(1) degrees. One molecule of phosphoric acid is present as a solvate molecule of crystallization, but the other is ionized and protonates the carbonyl oxygen, introducing conformational and bond distance changes in the flavone. The dihedral angle between the benzopyrone and phenyl rings is 47 degrees. Complexes with phosphate groups involve strong hydrogen bonds and are expected to play important roles in biomolecular structures.

Crystallography↗

PubMed2004

Studies on the flavones using liquid chromatography-electrospray ionization tandem mass spectrometry.

Fragmentation pathways of nine flavone compounds have been studied by using electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn). Analyzing the product ion spectra of flavonoids and aglycones, we observed some diagnostic neutral losses, such as CH3, H2O, residue of glucose and gluconic acid, which are very useful for the identification of the functional groups in the structures. Furthermore, specific retro Diels-Alder (RDA) fragments for flavones with different hydroxyl substitution have also been discussed. The information is helpful for the rapid identification of the location site of hydroxyl substitution on flavones. Fragmentation pathways of C-glycosidic flavonoid have also been discussed using ESI-MSn, demonstrating ions [M-H-60]-, [M-H-90]-, [M-H-120]- are characteristic ions of C-glycosidic flavonoid. According to the fragmentation mechanism of mass spectrometry and HPLC-MS data, the structures of seven flavones in Scutellaria baicalensis Georgi have been identified on-line without time-consuming isolation. The HPLC-ESI-MSn method for analyzing constituents in the Scutellaria baicalensis Georgi has been established.

Chromatography, High Pressure Liquid↗

PubMed2005

Identification and quantification of eight flavones in root and shoot tissues of the medicinal plant huang-qin (Scutellaria baicalensis Georgi) using high-performance liquid chromatography with diode array and mass spectrometric detection.

A method of analysis of eight flavones using high-performance liquid chromatography (HPLC)-diode array detection (DAD)-mass spectrometry (MS) in root and aerial tissues of the medicinal plant Scutellaria baicalensis was developed. The identity of the analytes was confirmed using retention time, UV-vis and mass spectral comparisons to commercial standards. Both UV-vis and mass spectral patterns were characterized for glycosylated flavones. Two additional flavone glycosides were tentatively identified as chrysin-7-glucuronide and wogonoside, but not quantified. Greenhouse and in vitro-grown tissues were analyzed with flavone concentrations ranges of 0.14-150 and 0.030-1.7 microg/mg for greenhouse root and shoot tissue, respectively, and 0.0068-6.4 and 0.082-1.5 microg/mg for in vitro-grown roots and shoots, respectively.

Calibration↗

PubMed2005

Lipophilic flavones of Primula veris L. from field cultivation and in vitro cultures.

Ten lipophilic flavones were isolated from the leaves of Primula veris from field cultivation - the newly described 3'-hydroxy-4',5'-dimethoxyflavone and 3'-methoxy-4',5'-methylenedioxyflavone, the previously known from chemical synthesis 3',4'-dimethoxyflavone, 2',5'-dimethoxyflavone, and also flavone, 2'-hydroxyflavone, 2'-methoxyflavone, 3'-methoxyflavone, 3',4',5'-trimethoxyflavone and 5,6,2',6'-tetramethoxyflavone (zapotin) which were previously known from plants. The same flavones were found in the leaves of P. veris obtained by in vitro propagation. The structural assignments were derived from (1)H NMR, (13)C NMR, EIMS and UV spectral data and the influence of B-ring oxygen substituents on the C-2, C-3 and H-3 NMR resonances in flavones unsubstituted in the A ring is taken into consideration.

Flavones↗