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Flavonoids from shoots and roots of Trifolium repens (white clover) grown in presence or absence of the arbuscular mycorrhizal fungus Glomus intraradices.

White clover (Trifolium repens) plants were grown in the presence or absence of the arbuscular mycorrhizal fungus Glomus intraradices. Flavones, 4',5,6,7,8-pentahydroxy-3-methoxyflavone and 5,6,7,8-tetrahydroxy-3-methoxyflavone, as well as two flavones 3,7-dihydroxy-4'-methoxyflavone and 5,6,7,8-tetrahydroxy-4'-methoxyflavone never previously reported in plants, were isolated. The known 3,5,6,7,8-pentahydroxy-4'-methoxyflavone, 2',3',4',5',6'-pentahydroxy-chalcone, 6-hydroxykaempferol, 4',5,6,7,8-pentahydroxyflavone and 3,4'-dimethoxykaempferol were also obtained. Analysis of extracts obtained from roots and shoots revealed that the compositions of the flavonoid mixtures varied with growing conditions. Quercetin, acacetin and rhamnetin accumulated in roots of inoculated plants, whereas they were not detected in non-inoculated plants.

Flavones↗

Elemanolide sesquiterpenes and eudesmane sesquiterpene glycosides from Centaurea hierapolitana.

Two elemanolide sesquiterpenes and two eudesmane-type sesquiterpene glycosides named hierapolitanins A-D, were isolated, together with five known compounds, two flavones; hispidulin and jaceosidin, a flavon-C-glycoside, shaftoside, a flavonol glycoside, kaempferol-3-O-rutinoside and a neolignan, dehydrodiconiferyl alcohol from the aerial parts of Centaurea hierapolitana Boiss. (Asteraceae). Structure elucidations were based on spectroscopic evidence.

Centaurea↗

Effects of simple aromatic compounds and flavonoids on Ca2+ fluxes in rat pituitary GH(4)C(1) cells.

The biological activity of phenolic compounds from plants is well documented in vitro, but little is known about the possible effect of simple aromatic compounds and flavonoids on voltage-operated Ca2+ channels (VOCCs). In pituitary cells, several intracellular pathways may regulate the activity of VOCCs. In this study, we investigated the effect of nine phenylpropanes and metanes, and 20 flavonoids on high K(+)-induced 45Ca2+ entry in clonal rat pituitary GH(4)C(1) cells. At the highest dose tested (20 microg/ml), flavone (a flavone) inhibited 45Ca2+ entry by 63.5%, naringenin (a flavanone) by 56.3% and genistein (an isoflavone) by 54.6%. The phenylmetane derivative octyl gallate was the most potent compound tested, with an IC(50) value of 15.0 microg/ml. The IC(50) value for the reference compound verapamil hydrochloride was 3.0 microg/ml. In sharp contrast to the above, the flavonols quercetin and morin potentiated 45Ca2+ entry. At 20 microg/ml, quercetin increased 45Ca2+ entry by 54.1% and morin by 48.0%. Quercetin increased the cellular cAMP content in a concentration-dependent manner. H 89, an inhibitor of protein kinase A, inhibited the effect of quercetin on 45Ca2+ entry. The results thus suggest that the effect of quercetin is the result of a protein kinase A-mediated activation of VOCCs. Quercetin induced a rapid and marked increase in both the transient (143.1+/-4.2%) and delayed (198.8+/-10.0%) Ca2+ currents, measured by the whole cell patch clamp technique. The onset of the inhibitory effect of octyl gallate was slow, but resulted in an almost complete inhibition of both Ca2+ currents.

Animals↗

Absorption, metabolism and health effects of dietary flavonoids in man.

Flavonoids are polyphenolic compounds that occur ubiquitously in foods of plant origin. Over 4,000 different flavonoids have been described, and they are categorized into flavonols, flavones, catechins, flavanones, anthocyanidins and isoflavonoids. Flavonoids have a variety of biological effects in numerous mammalian cell systems, in vitro as well in vivo. Recently, much attention has been paid to their antioxidant properties and to their inhibitory role in various stages of tumour development in animal studies. Quercetin, the major representative of the flavonol subclass, is a strong antioxidant, and prevents oxidation of low density lipoproteins in vitro. Oxidized low density lipoproteins are atherogenic, and are considered to be a crucial intermediate in the formation of atherosclerotic plaques. This agrees with observations in epidemiological studies that the intake of flavonols and flavones was inversely associated with subsequent coronary heart disease. However, no effects of flavonols on cancer were found in these studies. The extent of absorption of flavonoids is an important unsolved problem in judging their many alleged health effects. Flavonoids present in foods were considered non-absorbable because they are bound to sugars as beta-glycosides. Only free flavonoids without a sugar molecule, the so-called aglycones, were thought to be able to pass through the gut wall. Hydrolysis only occurs in the colon by microorganisms, which at the same time degrade flavonoids. We performed a study to quantify absorption of various dietary forms of quercetin. To our surprise, the quercetin glycosides from onions were absorbed far better than the pure aglycone. Subsequent pharmacokinetic studies with dietary quercetin glycosides showed marked differences in absorption rate and bioavailability. Absorbed quercetin was eliminated only slowly from the blood. The metabolism of flavonoids has been studied frequently in various animals, but very few data in humans are available. Two major sites of flavonoid metabolism are the liver and the colonic flora. There is evidence for O-methylation, sulphation and glucuronidation of hydroxyl groups in the liver. Bacterial ring fission of flavonoids occurs in the colon. The subsequent degradation products, phenolic acids, can be absorbed and are found in urine of animals. Quantitative data on metabolism are scarce.

Absorption↗

Alfalfa (Medicago sativa L.) flavonoids. 2. Tricin and chrysoeriol glycosides from aerial parts.

Ten flavone glycosides have been isolated and identified in aerial parts of alfalfa. These included six tricin, one 3'-O-methyltricetin, and three chrysoeriol glycosides. Most of these compounds were acylated with ferulic, coumaric, or sinapic acids, and acylation occurred on the terminal glucuronic acid. Eight of these compounds, including 7-O-beta-D-glucuronopyranosyl-3'-O-methyltricetin, 7-O-beta-D-glucuronopyranosyl-4'-O-beta-D-glucuronopyranosidechrysoeriol, 7-O-[2'-O-feruloyl-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]chrysoeriol, 7-O-[2'-O-feruloyl-[beta-D-glucuronopyranosyl(1-->3)]-O-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]chrysoeriol, 7-O-[2'-O-sinapoyl-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]tricin, 7-O-[2'-O- feruloyl-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]tricin, 7-O-[2'-O-p-coumaroyl-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]tricin, and 7-O-[2'-O-feruloyl-[beta-D-glucuronopyranosyl(1-->3)]-O-beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]tricin, have not been reported previously in the plant kingdom. Two previously identified alfalfa flavones, 7-O-beta-D-glucuronopyranosidetricin and 7-O-[beta-D-glucuronopyranosyl(1-->2)-O-beta-D-glucuronopyranoside]tricin, were also isolated.

Carbohydrate Conformation↗

Syntheses of 5,6,7- and 5,7,8-trioxygenated 3',4'-dihydroxyflavones having alkoxy groups and their inhibitory activities against arachidonate 5-lipoxygenase.

Arachidonate 5-lipoxygenase plays a pivotal role in the biosynthesis of leukotrienes. Cirsiliol (3',4',5-trihydroxy-6,7-dimethoxyflavone), a selective inhibitor of the enzyme, was derivatized by introducing alkyl groups of various chain lengths at positions 5, 6, 7, and 8 of the A ring of the flavone skeleton. Modification of the positions 5 and 6 with an alkyl group of 5-10 carbons markedly decreased the IC50 values for 5-lipoxygenase inhibition to the order of 10 nM. As tested with 5- or 6-hexyloxy derivatives, a relatively selective inhibition of 5-lipoxygenase was shown. Inhibition of 12-lipoxygenase required much higher concentrations of these compounds, and cyclooxygenase was not inhibited. Modification of positions 7 and 8 did not increase the inhibitory effect of most flavone compounds.

Arachidonate Lipoxygenases↗

Inhibition of [3H]-LSD binding to 5-HT7 receptors by flavonoids from Scutellaria lateriflora.

The hot water and 70% ethanol extracts of dried mad-dog skullcap (Scutellaria lateriflora) both bound to the 5-HT(7) receptor, with 87.2 +/- 6.2% and 56.7 +/- 1.3% inhibition of [(3)H]-LSD binding to the receptor at 100 microg/mL, respectively. The on-line analysis of a 70% ethanol extract by HPLC-UV/MS resulted in the identification of five flavones (1-5). Fractionation of the ethanol extract resulted in the isolation of three flavone-glucuronides (6-8) and a flavanone-glucuronide (9), including one new compound, lateriflorin (5,6,-dihydroxy-7-glucuronyloxy-2'-methoxyflavone) (8). The structure of 8 was determined by NMR ((1)H NMR, (13)C NMR, and NOESY experiments) and MS analysis. From the results obtained in the testing of the pure compounds, it is evident that the activity on the 5-HT(7) receptor is at least partly due to the presence of flavonoids. Scutellarin and ikonnikoside I showed the highest inhibition of [(3)H]-LSD binding with IC(50) values of 63.4 and 135.1 microM, respectively.

Cells, Cultured↗

Antihyperglycemic activity and chemical constituents of Eysenhardtia platycarpa.

The methanolic extracts from branches (BEP) and leaves (LEP) of Eysenhardtia platycarpa significantly decreased the blood glucose levels in normal and streptozotocin (STZ)-induced diabetic rats. One new flavone, (1"R)-5,4',1"-trihydroxy-6,7-(3",3"-dimethylchroman)flavone (1), together with the known compounds 5,7-dihydroxy-6-methyl-8-prenylflavanone (3), 5,7-dihydroxy-8-methyl-6-prenylflavanone (4), 5,7-dihydroxy-6-prenylflavanone (5), 5,7-dihydroxy-8-prenylflavanone (6), 3-O-acetyloleanolic acid (7), oleanolic acid, 3beta-acetoxy-11alpha,12alpha-epoxy-oleanan-28,13beta-olide, lupeol, betulinic acid, beta-sitosterol, beta-sitosteryl beta-D-glucopyranoside, beta-sitosteryl palmitate, and 3-O-methyl-myo-inositol were isolated from BEP. Additionally, one new flavanone, (2S)-4'-O-methyl-6-methyl-8-prenylnaringenin (2), as well as the known compounds 3, 4, 6, 4'-O-methyl-8-prenylnaringenin (8), and 5-hydroxy-7-methoxy-8-prenylflavanone (9) were isolated from LEP. 3-O-Acetyloleanolic acid (7), identified as the major constituent of BEP, showed a significant decrease (31 mg/kg of body weight, P < 0.05) in the glucose level of STZ-induced diabetic rats. The obtained results correlate with the traditional use of this species.

Animals↗

Luteolin and luteolin-7-O-glucoside from dandelion flower suppress iNOS and COX-2 in RAW264.7 cells.

Both reactive oxygen- and nitrogen-derived reactive species play important roles in physiological and pathophysiological conditions. Flavones, luteolin and luteolin-7-O-glucoside along with a rich plant source of both flavones, namely dandelion (Taraxacum officinale) flower extract were studied for antioxidant activity in different in vitro model systems. In this current study, luteolin and luteolin-7-O-glucoside at concentrations lower than 20 microM, significantly (p < 0.05) suppressed the productions of nitric oxide and prostaglandin E2 (PGE2) in bacterial lipopolysaccharide activated-mouse macrophage RAW264.7 cells without introducing cytotoxicity. The inhibitory effects were further attributed to the suppression of both inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein expression, and not reduced enzymatic activity. Similar suppression for both inducible enzymes was also found with the presence of dandelion flower extract, specifically, the ethyl acetate fraction of dandelion flower extract which contained 10% luteolin and luteolin-7-O-glucoside.

Animals↗

Dietary flavonoids attenuate tumor necrosis factor alpha-induced adhesion molecule expression in human aortic endothelial cells. Structure-function relationships and activity after first pass metabolism.

Flavonoids have been suggested to exert human health benefits by anti-oxidant and anti-inflammatory mechanisms. In this study, we investigated whether and by what mechanisms dietary flavonoids inhibit expression of cellular adhesion molecules, which is relevant to inflammation and atherosclerosis. We found that the capacity of flavonoids to inhibit tumor necrosis factor alpha-induced adhesion molecule expression in human aortic endothelial cells was dependent on specific structural features of the flavonoids. The 5,7-dihydroxyl substitution of a flavonoid A-ring and 2,3-double bond and 4-keto group of the C-ring were the main structural requirements for inhibition of adhesion molecule expression. In striking contrast, hydroxyl substitutions of the B- and C-rings but not the A-ring were essential for antioxidant activity. Hence, only hydroxyl flavones, such as apigenin and chrysin, and flavonols, such as galangin, kaempferol, and quercetin, were able to inhibit endothelial adhesion molecule expression, whereas flavone, chromone, the flavanone, naringenin, and the flavanol, (-)-epicatechin, were ineffectual. At low concentrations, the active flavonoids significantly attenuated expression of E-selectin and intercellular adhesion molecule 1 but not vascular cell adhesion molecule 1. In addition, exposure of apigenin and kaempferol to cultured hepatocytes, mimicking first pass metabolism, greatly diminished the inhibitory effect of flavonoids on endothelial intercellular adhesion molecule 1 expression. We conclude that the effect of dietary flavonoids on endothelial adhesion molecule expression depends on their molecular structure, concentration, and metabolic transformation but not their antioxidant activity.

Anti-Inflammatory Agents↗

Oxidation and rearrangements of flavanones by mammalian cytochrome P450.

To clarify the metabolic pathways of flavanones in mammals, the metabolism of (+/-)-flavanone and (+/-)-4'-methoxyflavanone by rat liver microsomes and recombinant human P450s in which structural changes are readily identifiable were examined. The beta-nicotinamide adenine dinucleotide phosphate (NADPH)-dependent formation of flavone plus (+/-)-2,3-trans-flavanonol and of 4'-methoxyflavone plus (+/-)-2,3-trans-4'-methoxyflavanonol, respectively, by rat liver microsomes was observed. The same metabolites were generated by recombinant human P450s in addition to the formation of isoflavone from (+/-)-flavanone. The kinetic isotope effects in these reactions were examined using deuterated (+/-)-flavanone and (+/-)-4'-methoxyflavanone. There was a strong isotope effect in the production of flavanonols, but the isotope effect in the production of flavones was small. The results indicated that the P450-mediated conversion of (+/-)-flavanone and of (+/-)-4'-methoxyflavanone to the corresponding metabolites proceeded via abstraction of a hydrogen radical from the C-2- or C-3-position of the flavanone skeleton. The antioxidant properties of flavanone and its metabolites were examined by measuring superoxide-scavenging activity in a xanthine-xanthine oxidase-cytochrome c system. (+/-)-2,3-trans-Flavanonol had higher activity than that of other flavonoids. Flavanones are metabolized by mammalian P450s, providing important information relevant to the metabolism and pharmacological action of dietary flavanones.

Animals↗

Two new compounds from Glycyrrhiza glabra.

Two new flavonosides have been isolated from the roots of Glychirriza glabra and identified as 5,8-dihydroxy-flavone-7-O-beta-D-glucuronide, glychionide A, and 5-hydroxy-8-methoxyl-flavone-7-O-beta-D-glucuronide, glychionide B.

Flavones↗

Dietary modification of drug-metabolizing enzyme activities: dose-response effect of flavonoids.

The induction of drug-metabolizing enzymes for different dietary flavonoids has been shown previously. The purpose of this study was to determine the threshold effect of these components. Rats were fed diets containing flavone, flavanone, or tangeretin at different levels (20, 50, 200, 500, and 200 ppm). Flavone induced ethoxyresorufin and pentoxyresorufin dealkylase activities at 500 ppm and arylhydrocarbon hydroxylase at 200 ppm. Epoxide hydrolase and glutathion transferase were increased at 200 ppm. UDP-glucuronyl transferases were enhanced at 20 ppm. Flavanone induced pentoxyresorufin dealkylase and arylhydrocarbon hydroxylase at the greatest level. In contrast, epoxide hydrolase and conjugating enzymes were increased at the lowest dose. Significant induction was seen only for ethoxyresorufin deethylase and UDP-glucuronyl transferase with diets containing 2000 ppm tangeretin. We conclude that the threshold effect depends on the chemical structure of the flavonoid and the enzyme activity. Low threshold doses for conjugating enzymes may be important for the anticarcinogenicity properties of these compounds.

Animals↗

Suppression of cell cycle progression by flavonoids: dependence on the aryl hydrocarbon receptor.

Some flavonoids are ligands of the aryl hydrocarbon receptor (AHR) and cause cell cycle arrest. The dependency of the cytostatic effects of five flavonoids (flavone, alpha-naphthoflavone, apigenin, 3'-methoxy-4'-nitroflavone and 2'-amino-3'-methoxyflavone) on a functional AHR was examined in AHR-containing rat hepatoma 5L cells and an AHR-deficient cell line (BP8) derived from the 5L line. The potent AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was cytostatic to the 5L line due to the induction of a G(1) arrest and dramatically elevated steady-state levels of CYP1A1 mRNA. TCDD affected neither the proliferation nor CYP1A1 mRNA contents of BP8 cells. With the exception of apigenin, the flavonoids under study induced G(1) arrest in both 5L and BP8 cells when used at concentrations at which they functioned as AHR agonists, but not antagonists. Apigenin-treated 5L and BP8 cultures primarily arrested in G(2)/M. The AHR-containing murine hepatoma cell line 1c1c7 arrested following exposure to AHR agonist concentrations of flavone and alpha-naphthoflavone, but not TCDD. Unlike the G(1) arrest observed in 5L cultures, the latter two flavonoids caused principally G(2)/M arrest in 1c1c7 cells. These studies demonstrate that the cytostatic activities of flavonoids do not require the AHR and the site of checkpoint arrest with a specific flavonoid can vary with cell type.

Animals↗

Acacetin inhibits cell growth and cell cycle progression, and induces apoptosis in human prostate cancer cells: structure-activity relationship with linarin and linarin acetate.

This study was carried out to assess the anticancer efficacy of linarin (LN), linarin acetate (LA) and acacetin (AC), the flavonoid compounds with the same flavone ring structure but different substitution, against human prostate cancer (PCA), LNCaP and DU145 cells. LN was isolated and purified from Chrysanthemum zawadskii; LA was chemically synthesized from LN, and AC obtained commercially. In each case, the cells were treated with these agents at 25-100 microM doses for 24-72 h. LN and LA showed moderate cell growth inhibition with different time kinetics as compared to AC. LN caused up to a 5-fold increase in cell death and LA enhanced cell death by up to 4-fold with the increase in treatment time in both cell lines. AC showed a time- as well as dose-dependent stronger cell growth inhibition (20-70%) accompanied by cell death as compared to LN and LA in both the cell lines. LN or LA did not show any profound effect on cell cycle arrest except for a moderate G1 arrest, whereas, AC showed a stronger G1 and/or G2-M arrest depending on the doses and treatment times. G1 arrest was associated with an increase in Cip1/p21 and a decrease in CDK2, CDK4 and CDK6 protein levels. G2-M arrest was associated with a decrease in Cdc25C, Cdc2/p34 and cyclin B1, which were more prominent in LNCaP compared to DU145 cells. LN, LA and AC induced cell death was associated with significant increase in apoptosis induction (up to 5-6-fold) accompanied by poly-(ADP-ribose) polymerase cleavage. Overall, AC showed more potent anticancer efficacy among these three flavonoids, which was diminished when its flavone ring was modified by disaccharide rhamnose substitution at C7 (LN) or acetylation of this substituted group (LA). These findings, for the first time, revealed the structural determinants in anticancer efficacy and mechanisms of these three flavonoids against human PCA cells.

Apoptosis↗

Swertisin dihydrate.

The title compound, 6-C-glucopyranosyl-7-O-methylapigenin dihydrate, C(22)H(22)O(10).2H(2)O, is a natural C-glucosylflavone. The flavone skeleton is almost planar, the dihedral angle between the pyran moiety and the 4-hydroxyphenyl ring being 9.8 (3) degrees. The basal plane of the pyranosyl ring of the glucose moiety is almost perpendicular to the benzopyran ring system. The flavone skeletons are stacked along the a axis, forming layers parallel to (001). Between these hydrophobic layers, the glucose groups and water molecules of crystallization are connected via O-H...O hydrogen bonds, forming hydrophilic layers.

Flavones↗

Expression of the cathelicidin LL-37 is modulated by short chain fatty acids in colonocytes: relevance of signalling pathways.

BACKGROUND AND AIMS: Short chain fatty acids (SCFA) exert profound effects on the colonic mucosa. In particular, SCFA modulate mucosal immune functions. The antimicrobial cathelicidin LL-37 is expressed by colon epithelial cells. In the present study the effect of SCFA on LL-37 expression was investigated. METHODS: LL-37 expression in vivo was assessed by immunohistochemistry. Real time quantitative reverse transcription-polymerase chain reaction was employed to determine LL-37 expression in colonocytes in vitro after treatment with various cytokines, SCFA, or flavone. LL-37 levels were correlated to cell differentiation which was determined by alkaline phosphatase (AP) activity. In addition, intracellular signalling pathways such as MEK-ERK (mitogen/extracellular signal protein kinase (MEK)/extracellular signal regulated protein kinase (ERK)) and p38/mitogen activated protein (MAP) kinase were explored. RESULTS: In vivo, LL-37 expression in healthy mucosa was restricted to differentiated epithelial cells in human colon and ileum. In colonocytes, increased LL-37 expression associated with cell differentiation was detected in vitro following treatment with butyrate, isobutyrate, propionate, and trichostatin A. Flavone induced LL-37 transcription but did not affect AP activity while cytokines had no effect. To dissect pathways mediating differentiation and LL-37 expression, specific inhibitors were applied. Inhibition of the protein kinase MEK enhanced butyrate induced AP activity while LL-37 expression in colon epithelial cells was blocked. In contrast, inhibition of p38/MAP kinase blocked cell differentiation without inhibiting LL-37 expression. CONCLUSIONS: Expression of the cathelicidin LL-37 in colonocytes and cellular differentiation are separately modulated by SCFA via distinct signalling pathways. These data may provide a rationale for dietary modulation of mucosal defence mechanisms.

Adult↗

Inhibition of prostaglandin production by a structurally-optimized flavonoid derivative, 2',4',7-trimethoxyflavone and cellular action mechanism.

Flavonoids possess anti-inflammatory activity in vitro and in vivo. In order to find the anti-inflammatory flavone derivatives having optimum chemical structures, various flavones were previously synthesized and evaluated for their inhibitory activity of prostaglandin E(2) (PGE(2)) production from lipopolysaccharide (LPS)-treated mouse macrophage cell line, RAW 264.7 cells. Through this screening procedure, 2',4',7-trimethoxyflavone (TMF) was selected for further pharmacological study. From the present investigation, it was found that TMF potently inhibited PGE(2) production from LPS-treated RAW cells with an IC(50) of 0.48 microM, compared to the IC(50) values of 0.07 and 1.09 microM for NS-398 and wogonin. TMF, however, did not inhibit cyclooxygenase-2 (COX-2) activity or COX-2 expression level. Instead, TMF was proved to be a phospholipase A(2) (PLA(2)) inhibitor. The IC(50) values of TMF against secretory PLA(2)-IIA (sPLA(2)-IIA) and cytosolic PLA(2) (cPLA(2)) were 70.5 and 70.4 microM, respectively. At doses of 10-250 microg/ear, TMF also showed in vivo anti-inflammatory activity by topical application against mouse croton oil-induced ear edema assay, suggesting a potential for new anti-inflammatory agent.

Animals↗