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At least 1,243 records · Page 69Linked to original sources
PubMed2003

Divergent evolution of flavonoid 2-oxoglutarate-dependent dioxygenases in parsley.

Flavone synthases (FNSs) catalyze the oxidation of flavanones to flavones, i.e. the formation of apigenin from (2S)-naringenin. While many plants express a microsomal-type FNS II, the soluble FNS I appears to be confined to a few species of the Apiaceae and was cloned recently from parsley plants. FNS I belongs to the Fe(II)/2-oxoglutarate-dependent dioxygenases characterized by short conserved sequence elements for cofactor binding, and its evolutionary context and mode of action are under investigation. Using a homology-based reverse transcription polymerase chain reaction approach, two additional flavonoid-specific dioxygenases were cloned from immature parsley leaflets, which were identified as flavanone 3beta-hydroxylase (FHT) and flavonol synthase (FLS) after expression in yeast cells. Sequence alignments revealed marginal differences among the parsley FNS I and FHT polypeptides of only 6%, while much less identity (about 29%) was observed with the parsley FLS. Analogous to FNS I, FLS oxidizes the flavonoid gamma-pyrone by introducing a C2, C3 double bond, and (2R,3S)-dihydrokaempferol (cis-dihydrokaempferol) was proposed recently as the most likely intermediate in both FNS I and FLS catalysis. Incubation of either FNS I or FLS with cis-dihydrokaempferol exclusively produced kaempferol and confirmed the assumption that flavonol formation occurs via hydroxylation at C3 followed by dehydratation. However, the lack of apigenin in these incubations ruled out cis-dihydrokaempferol as a free intermediate in FNS I catalysis. Furthermore, neither (+)-trans-dihydrokaempferol nor unnatural (-)-trans-dihydrokaempferol and 2-hydroxynaringenin served as a substrate for FNS I. Overall, the data suggest that FNS I has evolved uniquely in some Apiaceae as a paraphyletic gene from FHT, irrespective of the fact that FNS I and FLS catalyze equivalent desaturation reactions.

Amino Acid Sequence↗
PubMed1997

Transport of lucifer yellow CH into plant vacuoles--evidence for direct energization of a sulphonated substance and implications for the design of new molecular probes.

Contrasting observations exist which indicate that in plants the fluorescent dye lucifer yellow CH (LYCH) either can be used as a tracer for endocytosis or as a substrate for an anion transporter located at the vacuolar membrane. In addition, LYCH as a disulphonated substance may represent an analogue of sulphonated or sulfated natural compounds like some flavonoids. We performed uptake experiments with LYCH into isolated rye vacuoles and observed saturable (Km = 0.3-0.6 mM) vacuolar transport and accumulation of the dye against the concentration gradient only when MgATP was present. GTP and, to a low extent, UTP could substitute for ATP, while the non-hydrolysable ATP analogue AMP-PNP did not drive LYCH uptake. Vanadate and probenecid, the latter substance is known to inhibit organic anion transport at the liver canalicular membrane, both strongly decreased the vacuolar uptake of LYCH, while bafilomycin A1, a specific inhibitor of the vacuolar H+-ATPase, had no effect. Together with the fact that abolishment of the delta pH via CCCP had only a weak influence on LYCH accumulation, our results indicate that this compound is taken up into rye vacuoles by a directly energized process. Uptake of LYCH was strongly inhibited by other sulfated compounds including sulfobromophthalein and the flavones apigenin 7,4'-disulfate and luteolin 7,4'-disulfate arguing for the presence of a vacuolar transporter for structurally different sulphonated or sulfated compounds. Glucuronates like the rye-specific flavone luteolin 7-O-diglucuronide also strongly decreased uptake of the dye, whereas only a weak effect was observed in the presence of glutathione and a glutathione conjugate, suggesting that LYCH uptake is not mediated via the vacuolar glutathione conjugate pump.

ATP-Binding Cassette Transporters↗
PubMed1999

Synthesis and X-ray crystal structure of the calcium channel antagonist: dimethyl 1,4-dihydro-2,6-dimethyl-4-[4'-(4H-4-oxo-1-benzopyran-2-yl)phenyl]- 3,5-pyridine dicarboxylate.

The synthesis of the title compound via the Hantzsch method from 4'-flavone carboxaldehyde is described, and its molecular structure was determined by X-ray crystallography. The 1,4-dihydropyridine (1,4-DHP) ring adopts a boat conformation. The phenyl ring of the flavone is not exactly perpendicular to the DHP ring. Calcium antagonistic activity of this compound was evaluated in vitro by using BaCl2-stimulated rat ileum.

Animals↗
PubMed2000

Spectrophotometric and coulometric detection in the high-performance liquid chromatography of flavonoids and optimization of sample treatment for the determination of quercetin in orange juice.

The capabilities of spectrophotometric and electrochemical detection techniques were investigated for the high-performance liquid chromatographic determination of flavonoids. Liquid chromatographic analyses were performed on eleven compounds belonging to three different classes of flavonoids: flavanone glycosides, flavone and flavonol aglycones. Separation of all compounds examined was carried out under reversed-phase conditions on a C18 narrow-bore column for UV detection, whereas for electrochemical detection, a C18 standard-bore column was used. UV analyses were carried out at 280 nm for flavanones and at 265 nm for flavones and flavonols, whereas controlled-potential coulometric measurements were performed using a porous graphite electrode. Analytical performances of the methods were compared in terms of linearity, limits of detection (LODs) and precision. Linearity over two orders of magnitude and LODs at low-ppm levels (0.06-1 mg/l) were demonstrated for all techniques considered. Instrumental precision in terms of relative standard deviation was found to be between 0 and 5% for the liquid chromatography (LC)-UV system and between 0.6 and 10% for the LC-electrochemical detection (ED) system. The methods developed were applied to the analysis of flavanones and flavonols in a real sample, such as an extract of orange juice. Even though quercetin glycoside is mostly present in orange juice as rutin, other different glycosides of this flavonol could be present; on this basis, the hydrolysis of all glycosides to aglycone allows one to obtain more accurate data on the flavonol concentration in orange juice. To avoid sample degradation and to increase extraction efficiency, quercetin hydrolysis was optimized using a central composite design to investigate the effects of acid concentration and hydrolysis time on extraction recovery.

Beverages↗
PubMed1999

The effects of flavonoids on human phenolsulphotransferases: potential in drug metabolism and chemoprevention.

Flavonoids are frequently found in fruits and vegetables, and are currently under investigation as potential chemopreventive agents. The present study reports the inhibitory effects of six flavonoids, quercetin, genistein, daidzein, equol, (+)-catechin and flavone, on sulphation of p-nitrophenol, a model substrate for the P-form of PST (thermostable, TS) and dopamine, a model substrate for the M-form of PST (thermolabile, TL). Kinetic studies of the PST activity and the inhibitory effects of flavonoids on the P-form of PST activity (using Hanes-Wolf and Dixon plots) show low Km and Ki values. Quercetin was found to be the most potent inhibitor and flavone was the least active inhibitor among the flavonoids. Kinetic analysis showed that the inhibition was non-competitive and Ki values were determined for each flavonoid. These observations suggest the potential for clinically important pharmacological and toxicological interactions by flavonoids.

Anticarcinogenic Agents↗
PubMed2001

Acylated apigenin glycosides from alfalfa (Medicago sativa L.) var. Artal.

Three flavones, including 4'-O-[2'-O-E-feruloyl-O-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]apigenin, 7-O-beta-D-glucuronopyranosyl-4'-O-[2'-O-E-feruloyl-O-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]apigenin and 7-O-beta-D-glucuronopyranosyl-4'-O-[2'-O-p-E-coumaroyl-O-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]apigenin have been identified in alfalfa var. Artal. The known flavone 7-O-[2-O-E-feruloyl-[beta-D-glucuronopyranosyl(1-->3)]-O-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucurono-pyranoside] apigenin was also isolated. The structures of these compounds were deduced on the basis of their spectral data.

Acylation↗
PubMed2002

Dinklagins A, B and C: three prenylated flavonoids and other constituents from the twigs of Dorstenia dinklagei.

Three prenylated flavonoids, dinklagins A, B and C identified, respectively, as (-)-6-(3,3-dimethylallyl)-7-hydroxy-6''', 6'''-dimethylchromeno-(4',3',2''',3''')-flavanone, (+)-5,4',5"xi-trihydroxy-6'',6''-dimethylchromano-(7,6,2'',3'')-flavone and (+)6-(2xi-hydroxy-3-methyl-3-butenyl)-5,7,4'-trihydroxyflavone were isolated from the twigs of Dorstenia dinklagei together with the known 6-prenylapigenin, 4-hydroxylonchocarpin, stipulin and 5,4'-dihydroxy-6'',6''-dimethylchromano-(7,6,2'',3'')-flavone. Their structures were determined on the basis of spectral data and by comparison with data reported in the literature and with authentic specimens for known compounds.

Chromatography↗
PubMed2002

Flavonoids from two Lonchocarpus species of the Yucatan Peninsula.

Leaves, stem bark and root of Lonchocarpus xuul and Lonchocarpus yucatanensis were studied separately. A chalcone, 2',4-dimethoxy-6'-hydroxylonchocarpin (), and the flavones 5,4'-dihydroxy-3'-methoxy-(6:7)-2,2-dimethylpyranoflavone (2) and 5,4'-dimethoxy-(6:7)-2,2-dimethylpyrano-flavone (3), together with the known carpachromene (4), were isolated from the leaves of both species. Similarly, the previously reported flavans xuulanin (5) and 3beta-methoxyxuulanin (6), together with the novel 3beta,4beta,5-trimethoxy-4'-hydroxy-(6:7)-2,2-dimethylpyranoflavan (7), 3-hydroxy-4,5-dimethoxy-(6:7)-2,2-dimethyl-pyranoflavan (8), and 3,4-dihydroxy-5-methoxy-(6:7)-2,2-dimethylpyranoflavan (10), were isolated from the stem bark and root of both species. Finally, the known 2',4'-dihydroxy-3'-(3-methylbut-2-enyl) chalcone (13) was obtained from the root of L. xuul only. The structures of the various metabolites were established by interpretation of their spectroscopic data.

Fabaceae↗
PubMed2003

A rationale for the shift in colour towards blue in transgenic carnation flowers expressing the flavonoid 3',5'-hydroxylase gene.

Recently marketed genetically modified violet carnations cv. Moondust and Moonshadow (Dianthus caryophyllus) produce a delphinidin type anthocyanin that native carnations cannot produce and this was achieved by heterologous flavonoid 3',5'-hydroxylase gene expression. Since wild type carnations lack a flavonoid 3',5'-hydroxylase gene, they cannot produce delphinidin, and instead accumulate pelargonidin or cyanidin type anthocyanins, such as pelargonidin or cyanidin 3,5-diglucoside-6"-O-4, 6"'-O-1-cyclic-malyl diester. On the other hand, the anthocyanins in the transgenic flowers were revealed to be delphinidin 3,5-diglucoside-6"-O-4, 6"'-O-1-cyclic-malyl diester (main pigment), delphinidin 3,5-diglucoside-6"-malyl ester, and delphinidin 3,5-diglucoside-6",6"'- dimalyl ester. These are delphinidin derivatives analogous to the natural carnation anthocyanins. This observation indicates that carnation anthocyanin biosynthetic enzymes are versatile enough to modify delphinidin. Additionally, the petals contained flavonol and flavone glycosides. Three of them were identified by spectroscopic methods to be kaempferol 3-(6"'-rhamnosyl-2"'-glucosyl-glucoside), kaempferol 3-(6"'-rhamnosyl-2"'-(6-malyl-glucosyl)-glucoside), and apigenin 6-C-glucosyl-7-O-glucoside-6"'-malyl ester. Among these flavonoids, the apigenin derivative exhibited the strongest co-pigment effect. When two equivalents of the apigenin derivative were added to 1 mM of the main pigment (delphinidin 3,5-diglucoside-6"-O-4,6"'-O-1-cyclic-malyl diester) dissolved in pH 5.0 buffer solution, the lambda(max) shifted to a wavelength 28 nm longer. The vacuolar pH of the Moonshadow flower was estimated to be around 5.5 by measuring the pH of petal. We conclude that the following reasons account for the bluish hue of the transgenic carnation flowers: (1). accumulation of the delphinidin type anthocyanins as a result of flavonoid 3',5'-hydroxylase gene expression, (2). the presence of the flavone derivative strong co-pigment, and (3). an estimated relatively high vacuolar pH of 5.5.

Anthocyanins↗
PubMed2000

Copigmentation gives bluer flowers on transgenic torenia plants with the antisense dihydroflavonol-4-reductase gene.

When anthocyanins in plants make complexes with copigments such as flavones or flavonols (copigmentation), the visible absorption maximum of the flowers is shifted so that it becomes longer: that is, the flowers look bluer. In an earlier study, our group reported the modification of flower color in torenia (Torenia fournieri Lind.) by re-introduction of the dihydroflavonol-4-reductase (DFR) gene or the chalcone synthase (CHS) gene. Our initial observation of torenia transformants was that plants with the antisense DFR gene produced bluer flowers than plants with the antisense CHS gene. In the present study we found that inactivation of the DFR gene by genetic transformation caused the accumulation of flavones - possible copigments - and that the resulting copigmentation likely to make the torenia flowers bluer. This method could be applied to other plant species to produce bluer flowers.

Journal Article↗
PubMed2001

Effects of a water-soluble extract of rosemary and its purified component rosmarinic acid on xenobiotic-metabolizing enzymes in rat liver.

The effects of a water-soluble extract (WSE) of rosemary and its purified antioxidant rosmarinic acid (RA) on xenobiotic metabolizing enzymes (XME) were studied in rat liver after dietary administration. The modulation of phase I enzymes such as cytochrome P450 (CYP) 1A, 2B, 2E1, 3A, and phase II enzymes such as glutathione S-transferase (GST), quinone reductase (QR) and UDP-glucuronosyltransferase (UGT) was evaluated by measuring enzyme activities with specific substrates. Protein levels of CYPs and rGST A1/A2, A3/A5, M1, M2 and P1 were measured using antibodies in Western blots. Caffeic acid was also studied because it results from RA biotransformation in rat after oral administration. Male SPF Wistar rats received the different compounds at 0.5% (w/w) incorporated into their diet for 2 weeks. WSE, containing RA, flavones and monoterpenes enhanced CYP 1A1, 2B1/2, 2E1 and GST (especially rGST A3/A5, M1 and M2), QR and UGT. On the contrary, no modification of XME was observed in response to RA or CA (except for a slight increase of UGT activity after CA treatment). The induction of XME by WSE could be attributed to flavones, monoterpenes or an additive effect of all components.

Animals↗
PubMedDate not supplied

Inhibition of the mutagenicity of 2-nitrofluorene, 3-nitrofluoranthene and 1-nitropyrene by flavonoids, coumarins, quinones and other phenolic compounds.

When 56 flavonoids, 32 coumarins, five naphthoquinones, 12 anthraquinones and five structurally-related compounds were tested for their antimutagenic potencies with respect to mutagenicities induced by 2-nitrofluorene (2-NF), 3-nitrofluoranthene (3-NFA) and 1-nitropyrene (1-NP) in Salmonella typhimurium TA98 distinct structure-activity relationships were detected. First, the tetracyclic nitroarenes 3-NFA and 1-NP were in general more effectively antagonized by potent antimutagenic flavonoids and coumarins than the tricyclic 2-NF, while there were only minor differences with quinones. Secondly, antimutagenicity of natural compounds of plant origin correlated with the aglyconic nature 10 of a total of 15 glycosides were inactive, four flavonoid glycosides exerted antimutagenicity but to a distinctly lower degree than the corresponding aglycones. Thirdly, within flavonoids, coumarins and anthraquinones positive correlations were found between antimutagenic potency and the polarity of a molecule with the existence of an optimum of activity within flavonols and anthraquinones. However, polarity seemed to be unimportant within the chalcone and naphthoquinone series. Among flavonoids, the parent compounds flavone and flavanone were inactive, but all flavones and many flavonoids with phenolic hydroxyl groups exerted antimutagenicity. Antimutagenic potency reached a maximum with the presence of four hydroxyl functions-luteolin, kaempferol-though the position of hydroxyls was also a determinant of antimutagenic potency. Methylation of phenolic hydroxyl groups, however, always reduced antimutagenicity. A carbonyl group at carbon 4 was essential for antimutagenicity: two catechins and anthocyanidins each were inactive. On the other hand, ring C of the flavane nucleus was not essential for antimutagenicity: chalcones and dihydrochalcones were potent antimutagens. Among coumarins, the parent compound showed antimutagenicity against 1-NP and 3-NFA, although dihydrocoumarin, methylcoumarins and compounds with bulky substituents were inactive. Otherwise, antimutagenic activity depended on the presence of polar hydroxyl, amino or carboxyl groups at carbons 3, 4 or 7 but was diminished by interactions of hydroxyl groups vicinal to carbon 7. Again, antimutagenic potencies were reduced by alkylation or acetylation. Among furanocoumarins xanthotoxin exerted strong and bergapten moderate antimutagenicity, while psoralen (except against 3-NFA), isopimpinellin and the furanochromanones visnagin and khellin were inactive. Among anthraquinones, the principles delineated here were valid again, resulting in potent antimutagenicity of most phenolic compounds and inactivity of anthraquinone itself. Among compounds structurally related to anthraquinones, anthrone, acridone and xanthone exerted antimutagenicity, anthrone being the most potent one, while thioxanthone and 9-fluorenone were inactive. All naphthoquinones were potent antimutagens irrespective of the presence of methyl or hydroxyl functions. Plumbagin, 2-methyl-5-hydroxynaphthoquinone, however, showed exceptional antimutagenicity.

Animals↗
PubMed2000

Inhibitory effect of flavonoids from citrus plants on Epstein-Barr virus activation and two-stage carcinogenesis of skin tumors.

To search for possible anti-tumor promoters, thirteen flavones (1-13) obtained from the peel of Citrus plants were examined for their inhibitory effects on the Epstein-Barr virus early antigen (EBV-EA) activation by a short-term in vitro assay. Of these flavones, 3,5,6,7,8,3',4'-heptamethoxyflavone (HPT) (13) exhibited significant inhibitory effects on the EBV-EA activation induced by the tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA). Further, compound 13 exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test.

Animals↗
PubMed2002

Baicalein and genistein display differential actions on estrogen receptor (ER) transactivation and apoptosis in MCF-7 cells.

Genistein is a soy isoflavone that has attracted much attention for its chemopreventive properties. Baicalein is a flavone found in Scutellaria species, and its structure is analogous to that of genistein. We examined the two flavones' antiestrogenicity by using a transient transfection model. Our results indicated that baicalein could suppress 17beta-estradiol-induced transactivation in cells expressing estrogen receptor alpha, whereas no antagonistic activity was seen in genistein. Cell death assay and flow cytometry analysis demonstrated that baicalein was a stronger apoptosis inducing agent than genistein. Considering all the criteria tested, baicalein could be a better chemopreventive agent than genistein.

Antineoplastic Agents↗
PubMed2001

Role of reactive oxygen intermediates in Japanese encephalitis virus infection in murine neuroblastoma cells.

Infection with Japanese encephalitis virus (JEV), a mosquito-borne, neurotropic flavivirus, may cause acute encephalitis in humans and induce severe cytopathic effects in various types of cultured cells. This study attempted to determine whether JEV infection induces free radical generation and whether oxidative stress contributes to virus-induced cell death in neuroblastoma cells. A rise in the intracellular level of free radicals indicated by the 2',7'-dichlorofluorescein fluorescence was observed in N18 cells following JEV infection. Cellular flavon-containing enzymes were involved in JEV-induced fluorescent change. Cells were moderately protected from JEV-induced death by diphenyleneiodonium, a flavon-containing enzyme inhibitor, whereas common antioxidants such as N-acetylcysteine, pyrrolidine dithiocarbamate, Tiron, and Trolox turned out to be ineffective. These results suggest that the direct antioxidant action is not helpful in prevention of JEV-induced neuronal cell death.

Animals↗
PubMed1999

Structure-activity relationship of cardiotonic flavonoids in guinea-pig papillary muscle.

Sixteen flavonoids were tested for a positive inotropic effect (PIE) on guinea-pig papillary muscle paced at 0.2 Hz in a Krebs-Henseleit solution at 30 degrees C. The structure-activity relationship was investigated by determining both the pD2 value and the intrinsic activity in the case of ten flavonols, three flavones, one flavanone and two catechins. Quercetin showed the most potent intrinsic activity, and produced the strongest inotropic responses among the 16 compounds. The relative order of potency of the tested flavonoids was quercetin > morin = kaempferol = HEPTA > luteolin = apigenin > natsudaidain = fisetin = galangin. Those that did not produce any PIE were 3-hydroxyflavone, flavone, glycosides of quercetin (rutin and hyperin), flavanones (naringenin) and catechins. With respect to the essential flavonoid nucleus for PIE development, the presence of a hydroxy group at C-4', an alpha, beta-unsaturated ketone on the C-ring and a reasonable lipophilic moiety in the molecule are required. Pharmacological analyses suggest that there is a common mechanism for the PIE and it is cyclic AMP dependent.

Animals↗
PubMed2000

LC-MS for the identification of oxygen heterocyclic compounds in citrus essential oils.

The oxygen heterocyclic compounds (coumarins, psoralens and polymethoxylated flavones) present in the nonvolatile residue of the essential oils of Mandarin, Sweet Orange, Bitter Orange, Bergamot and Grapefruit were analysed with an HPLC/API/MS system equipped with an APcI probe in positive mode. The use of hyphenated techniques, such as LC/MS provides a great information about the content and nature of constituents of natural complex matrices, such as essential oils. In this work, MS spectra were recorded at different voltages, to obtain structural information in addition to molecular weight information. The different response of the compounds identified has been also evaluated. The method allowed the confirmation of the identification of the main components of the fraction, previously reported for the different oils. MS characteristics of coumarins, psoralens and polymethoxylated flavones with different substitution patterns were determined on the basis of the response obtained with the APcI interface. Interface parameters were optimised to obtain a contemporaneous response for all the three classes of components.

Chromatography, High Pressure Liquid↗
PubMed2000

Antioxidant properties of di-tert-butylhydroxylated flavonoids.

Epidemiological evidence suggests an inverse relationship between dietary intake of flavonoids and cardiovascular risk. The biological activities of flavonoids are related to their antioxidative effects, but they also can be mutagenic, due to the prooxidant activity of the catechol pattern. To prevent these problems, we synthesized new flavonoids where one or two di-tert-butylhydroxyphenyl (DBHP) groups replaced catechol moiety at position 2 of the benzopyrane heterocycle. Two DBHP moieties can also be arranged in an arylidene structure or one DBHP fixed on a chalcone structure. Position 7 on the flavone and arylidene or position 4 on the chalcone was substituted by H, OCH(3), or OH. New structures were compared with quercetin and BHT in an LDL oxidation system induced by Cu(II) ions. Arylidenes and chalcones had the best activities (ED(50) = 0.86 and 0.21) compared with vitamin E, BHT, and quercetin (ED(50) = 10.0, 7. 4, and 2.3 microM). Activity towards stable free radical 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) was measured by log Z and ECR(50) parameters. Synthesized flavones proved to be poor DPPH radical scavengers, the activity increasing with the number of DBHP units. In contrast, arylidenes and chalcones were stronger DPPH radical scavengers (log Z > 3, 0.3 < ECR(50) < 2.12) than BHT (log Z = 0.75, ECR(50) = 12.56) or quercetin (log Z = 2.76, ECR(50) = 0.43). Unlike quercetin, synthesized compounds neither chelated nor reduced copper, proving that these new flavonoids had no prooxidant activity in vitro.

Amidines↗