Interaction between flavonoids and alpha-tocopherol in human low density lipoprotein

Oxidative modification of low density lipoprotein (LDL) may play an important role in the development of atherosclerosis. Alpha-tocopherol functions as a major antioxidant in human LDL. The present study was to test whether four natural flavonoids (kempferol, morin, myricetin, and quercetin) would protect or regenerate alpha-tocopherol in human LDL. The oxidation of LDL incubated in sodium phosphate buffer (pH 7.4, 10 mM) was initiated by addition of either 5.0 mM CuSO(4) at 37 degrees C or 1.0 mM of 2,2'-azo-bis (2-amidinopropane) dihydrochloride (AAPH) at 40 degrees C. It was found that alpha-tocopherol was completely depleted within 1 hour. Under the same experimental conditions, all four flavonoids demonstrated a dose-dependent protecting activity to alpha-tocopherol in LDL at the concentration ranging from 1 to 20microM. All flavonoids showed a varying protective activity against depletion of alpha-tocopherol in LDL, with kempherol and morin being less effective than myricetin and quercetin. The addition of flavonoids to the incubation mixture after 5 minutes demonstrated a significant regeneration of alpha-tocopherol in human LDL. The protective activity of four flavonoids to LDL is related to the number and location of hydroxyl groups in the B ring as well as the stability in sodium phosphate buffer.     

Effect of benzopyrone derivatives on simultaneously induced croton oil ear oedema and carrageenin paw oedema in rats.

Carrageenin paw oedema and croton oil ear oedema induced simultaneously in rats are inhibited in a dose-dependent manner and to statistically significant degrees by lipoxygenase- and cyclooxygenase-blocker flavonoids (diosmin, fisetin, quercetin, myricetin, galangin, sophoricoside, hesperidin-methylchalcone, oligomeric procyanidin, anthocyanidins (delphinidin, pelargonidin], and the prostaglandin antagonist polyphloretin phosphate and di-4-phloretin phosphate. Outstanding anti-inflammatory effects are displayed by myricetin and delphinidin, which contain vicinal hydroxy groups in ring B. The results confirm the importance of hydroxy group substitution in ring B. The most effective of the examined substances proved to be the prostaglandin antagonist di-4-phloretin phosphate.     

Effects of plant-derived flavonoids and polyphenolic acids on the activity of mutagens from cooked food

The ability of 3 plant flavonoids (morin, myricetin and quercetin) and 4 polyphenolic acids (caffeic acid, chlorogenic acid, ellagic acid and ferulic acid) to inhibit the genotoxic effects of a number of cooked-food mutagens (IQ, MeIQ, MeIQx, Trp-P-1 and Trp-P-2), was investigated in a bacterial mutation assay using Salmonella typhimurium TA98 as indicator and hepatic S9 mixes from either SWR mice or Syrian hamster as metabolic activating systems. Although the polyphenolic acids failed to have an effect, the flavonoids generally inhibited IQ, MeIQ, MeIQx and Trp-P-1 induced mutagenesis in a dose-dependent manner, irrespective of the source of S9. This was not the case with Trp-P-2 where the flavonoids were only observed to inhibit when SWR mouse S9 but not Syrian hamster S9 was used. Of the 3 compounds, myricetin and quercetin were superior to morin in their inhibitory capacity.     

Hepatoprotection of quercetin against oxidative stress by induction of metallothionein expression through activating MAPK and PI3K pathways and enhancing Nrf2 DNA-binding activity

Flavonoids are natural phenolic substances widely found in fruit, vegetables, grains, and wine. Most of these compounds exert health-promoting effects seem to attribute to their antioxidant activity. Metallothioneins (MT) has been suggested to protect against acute heavy metal toxicity in the liver, and the proteins of MT can be induced by various stimuli including antioxidant. Measuring the induction of MT genes may provide an efficient approach to understand the chemopreventive mechanisms of flavonoids. The antioxidant activity of eight flavonoids was determined by TEAC and ORAC assays and their effects on MT protein were also measured. HepG2 cells were employed to explore the mechanisms underlying flavonoid-induced MT induction. Statistical analysis revealed a positive correlation between the antioxidant activity of flavonoids and MT expression. Quercetin-induced MT expression may function by activating the phosphorylation of JNK, p38 and PI3K/Akt as well as by enhancing Nrf2 DNA-binding activity. Moreover, quercetin exhibited a potential protective effect on t-BHP-caused injury in hepatocytes through the induction of MT. These results suggest that quercetin is a natural antioxidant in the diet and the consumption of foods that are rich in quercetin could be beneficial for the prevention of environmental oxidant-induced liver damage.     

Relationship between the composition of flavonoids and flower colors variation in tropical water lily (Nymphaea) cultivars

Water lily, the member of the Nymphaeaceae family, is the symbol of Buddhism and Brahmanism in India. Despite its limited researches on flower color variations and formation mechanism, water lily has background of blue flowers and displays an exceptionally wide diversity of flower colors from purple, red, blue to yellow, in nature. In this study, 34 flavonoids were identified among 35 tropical cultivars by high-performance liquid chromatography (HPLC) with photodiode array detection (DAD) and electrospray ionization mass spectrometry (ESI-MS). Among them, four anthocyanins: delphinidin 3-O-rhamnosyl-5-O-galactoside (Dp3Rh5Ga), delphinidin 3-O-(2"-O-galloyl-6"-O-oxalyl-rhamnoside) (Dp3galloyl-oxalylRh), delphinidin 3-O-(6"-O-acetyl-β-glucopyranoside) (Dp3acetylG) and cyanidin 3- O-(2"-O-galloyl-galactopyranoside)-5-O-rhamnoside (Cy3galloylGa5Rh), one chalcone: chalcononaringenin 2'-O-galactoside (Chal2'Ga) and twelve flavonols: myricetin 7-O-rhamnosyl-(1 → 2)-rhamnoside (My7RhRh), quercetin 7-O-galactosyl-(1 → 2)-rhamnoside (Qu7GaRh), quercetin 7-O-galactoside (Qu7Ga), kaempferol 7-O-galactosyl-(1 → 2)-rhamnoside (Km7GaRh), myricetin 3-O-galactoside (My3Ga), kaempferol 7-O-galloylgalactosyl-(1 → 2)-rhamnoside (Km7galloylGaRh), myricetin 3-O-galloylrhamnoside (My3galloylRh), kaempferol 3-O-galactoside (Km3Ga), isorhamnetin 7-O-galactoside (Is7Ga), isorhamnetin 7-O-xyloside (Is7Xy), kaempferol 3-O-(3"-acetylrhamnoside) (Km3-3"acetylRh) and quercetin 3-O-acetylgalactoside (Qu3acetylGa) were identified in the petals of tropic water lily for the first time. Meanwhile a multivariate analysis was used to explore the relationship between pigments and flower color. By comparing, the cultivars which were detected delphinidin 3-galactoside (Dp3Ga) presented amaranth, and detected delphinidin 3'-galactoside (Dp3'Ga) presented blue. However, the derivatives of delphinidin and cyanidin were more complicated in red group. No anthocyanins were detected within white and yellow group. At the same time a possible flavonoid biosynthesis pathway of tropical water lily was presumed putatively. These studies will help to elucidate the evolution mechanism on the formation of flower colors and provide theoretical basis for outcross breeding and developing health care products from this plant.     

Synthesis of flavonol 3-O-glycoside by UGT78D1

Glycosylation is an important method for the structural modification of various flavonols, resulting in the glycosides with increased solubility, stability and bioavailability compared with the corresponding aglycone. From the physiological point of view, glycosylation of plant flavonoids is of importance and interest. However, it is notoriously complicated that flavonols such as quercetin, kaempferol and myricetin, are glucosylated regioselectively at the specific position by chemical method. Compared to the chemical method, enzymatic synthesis present several advantages, such as mild reaction condition, high stereo or region selectivity, no protection/deprotection and high yield. UGT78D1 is a flavonol-specific glycosyltransferase, responsible for transferring rhamnose or glucose to the 3-OH position in vitro. In this study, the activity of UGT78D1 was tested against 28 flavonoids acceptors using UDP-glucose as donor nucleoside in vitro, and 5 acceptors, quercetin, myricetin, kaempferol, fisetin and isorhamnetin, were discovered to be glucosylated at 3-OH position. Herein, the small-scale 3-O-glucosylated quercetin, kaempferol and myricetin were synthesized by UGT78D1 and their chemical structures were confirmed by (1)H and (13)C nuclear magnetic resonance (NMR) and high resolution mass spectrometry (HRMS).     

Intracellular flavonoids as electron donors for extracellular ferricyanide reduction in human erythrocytes.

Reduction of extracellular ferricyanide [Fe(CN)(6)](-3) to ferrocyanide by intact cells reflects the activity of a trans-plasma membrane oxidoreductase that, in human red blood cells, utilizes ascorbic acid as an electron donor. We herein report that the flavonoids quercetin and myricetin, while inhibiting dehydroascorbic acid uptake-and thus the erythrocyte ascorbic acid content-effectively stimulate the extracellular reduction of ferricyanide. Other flavonoids such as rutin, acacetin, apigenin, and genistein do not show the same effect. The notion that quercetin or myricetin may serve as an intracellular donor for a trans-plasma membrane oxidoreductase is supported by the following lines of evidence: (i) they afford direct reduction of ferricyanide; (ii) extracellular reduction of ferricyanide was not mediated by direct effects of the flavonoids released by the cells and was abolished by the sulphydryl reagent parachloromercuribenzenesulfonic acid (pCMBS); (iii) the intracellular concentrations of quercetin or myricetin well correlate with increases in ferricyanide reduction; (iv) the intracellular concentration of the flavonoids dramatically declines after ferricyanide exposure. Taken together, the results presented in this study demonstrate that myricetin and quercetin, which accumulate in large amounts in red blood cells, act as intracellular substrates of a pCMBS-sensitive trans-plasma membrane oxidoreductase. This may represent a novel mechanism whereby these flavonoids exert beneficial effects under oxidative stress conditions.     

Inhibitory effects of flavonoids on alternative respiration of plant mitochondria

Inhibitory effects of flavonoids on plant alternative respiration were investigated using isolated mitochondria of Vigna radiata seedlings. The antioxidant flavonoids quercetin and myricetin effectively inhibited alternative respiration. We suggest that radical scavenging activity is involved in the inhibitory mechanism.     

Quercetin abrogates IL-6/STAT3 signaling and inhibits glioblastoma cell line growth and migration

Evidence has suggested that STAT3 functions as an oncogene in gliomagenesis. As a consequence, changes in the inflammatory microenvironment are thought to promote tumor development. Regardless of its origin, cancer-related inflammation has many tumor-promoting effects, such as the promotion of cell cycle progression, cell proliferation, cell migration and cell survival. Given that IL-6, a major cancer-related inflammatory cytokine, regulates STAT3 activation and is upregulated in glioblastoma, we sought to investigate the inhibitory effects of the chemopreventive flavonoid quercetin on glioblastoma cell proliferation and migration triggered by IL-6, and to determine the underlying mechanisms of action. In this study, we show that quercetin is a potent inhibitor of the IL-6-induced STAT3 signaling pathway in T98G and U87 glioblastoma cells. Exposure to quercetin resulted in the reduction of GP130, JAK1 and STAT3 activation by IL-6, as well as a marked decrease of the proliferative and migratory properties of glioblastoma cells induced by IL-6. Interestingly, quercetin also modulated the expression of two target genes regulated by STAT3, i.e. cyclin D1 and matrix metalloproteinase-2 (MMP-2). Moreover, quercetin reduced the recruitment of STAT3 at the cyclin D1 promoter and inhibited Rb phosphorylation in the presence of IL-6. Overall, these results provide new insight into the role of quercetin as a blocker of the STAT3 activation pathway stimulated by IL-6, with a potential role in the prevention and treatment of glioblastoma.     

The phenolic compounds of Oenothera

24 species of Oenothera, representing 8 subgenera, were examined for their phenolics by TLC. Several phenolic acids, hydrolysable tannins, a quercetin-glucoside and galactosides of quercetin, kaempferol and myricetin were identified. In addition delphinidin and cyanidin were found.     

Flavonoids increase the intracellular glutathione level by transactivation of the gamma-glutamylcysteine synthetase catalytical subunit promoter

Fruits and vegetables protect against cancer by so far not well-characterized mechanisms. One likely explanation for this effect is that dietary plants contain substances able to control basic cellular processes such as the endogenous defense against oxidative stress. Oxidative stress is pivotal in many pathological processes and reduced oxidative stress is implicated in prevention of disease. Our results demonstrate that extract from onion and various flavonoids induce the cellular antioxidant system. Onion extract and quercetin were able to increase the intracellular concentration of glutathione by approximately 50%. Using a reporter construct where reporter expression is driven by the gamma-glutamylcysteine synthetase (GCS) heavy subunit (GCS(h)) promoter we show that onion extract, quercetin, kaempferol, and apigenin increased reporter gene activity, while a fourth flavonoid, myricetin and sugar conjugates of quercetin were unable to increase reporter expression. Quercetin was also able to induce a distal part of the GCS(h) promoter containing only two antioxidant-response/electrophile-response elements (ARE/EpRE). Our data strongly suggest that flavonoids are important in the regulation of the intracellular glutathione levels. This effect may be exerted in part through GCS gene regulation, and may also contribute to the disease-preventing effect of fruits and vegetables.     

Stable free radical scavenging and antiperoxidative properties of resveratrol compared in vitro with some other bioflavonoids

Stable free radical scavenging and antiperoxidative activities of resveratrol, a component of grapes and red wine, were evaluated and compared with some other known bioflavonoids (quercetin, catechin, kaempferol, myricetin, fisetin, ellagic acid and naringenin) widely present in the plant kingdom. Free radical scavenging activity was measured in an in vitro chemical system (DPPH assay), while for antiperoxidative activity, biological system comprising of hepatic and pulmonary homogenates was employed. Antiradical activity assay showed quercetin and myricetin to be stronger antiradical agents than resveratrol. Structure-activity study revealed that O-dihydroxy group on ring B of flavonoid plays a crucial role. A double bond at 2-3 position conjugated with a 4-oxo function and hydroxy groups at positions 3 and 5 also contribute towards antiradical activity of flavonoids. Resveratrol exhibited stronger antiradical activity than kaempferol and naringenin and was also more efficient than alpha-tocopherol, a known strong endogenous non-flavonoid antioxidant, used for comparison. In vitro antiperoxidative assay showed fisetin as the strongest and kaempferol as the weakest antioxidant. Resveratrol was found to be stronger antioxidant than catechin, myricetin, kaempferol and naringenin, but was weaker than quercetin, fisetin and alpha-tocopherol. Antiradical and antiperoxidative activities of resveratrol may explain its beneficial effects in disease states. Assays exhibited no direct correlation between antiradical and antiperoxidative activities of the phenolics.     

Potent anti-amyloidogenic and fibril-destabilizing effects of polyphenols in vitro: implications for the prevention and therapeutics of Alzheimer's disease

Cerebral deposition of amyloid beta-peptide (Abeta) in the brain is an invariant feature of Alzheimer's disease (AD). A consistent protective effect of wine consumption on AD has been documented by epidemiological studies. In the present study, we used fluorescence spectroscopy with thioflavin T and electron microscopy to examine the effects of wine-related polyphenols (myricetin, morin, quercetin, kaempferol (+)-catechin and (-)-epicatechin) on the formation, extension, and destabilization of beta-amyloid fibrils (fAbeta) at pH 7.5 at 37 degrees C in vitro. All examined polyphenols dose-dependently inhibited formation of fAbeta from fresh Abeta(1-40) and Abeta(1-42), as well as their extension. Moreover, these polyphenols dose-dependently destabilized preformed fAbetas. The overall activity of the molecules examined was in the order of: myricetin = morin = quercetin > kaempferol > (+)-catechin = (-)-epicatechin. The effective concentrations (EC50) of myricetin, morin and quercetin for the formation, extension and destabilization of fAbetas were in the order of 0.1-1 micro m. In cell culture experiments, myricetin-treated fAbeta were suggested to be less toxic than intact fAbeta, as demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. Although the mechanisms by which these polyphenols inhibit fAbeta formation from Abeta, and destabilize pre-formed fAbetain vitro are still unclear, polyphenols could be a key molecule for the development of preventives and therapeutics for AD.     

Role of quercetin in modulating rat cardiomyocyte gene expression profile

Despite extensive studies, the fundamental mechanisms responsible for the development and progression of cardiovascular diseases have not yet been fully elucidated. Recent experimental and clinical studies have suggested that reactive oxygen species play a major pathological role. Oxidative stress reduction induced by flavonoids has been regarded by many as the most likely mechanism in the protective effects of these compounds; however, there is an emerging view that flavonoids may also exert modulatory actions on protein kinase and lipid kinase signaling pathways. Quercetin, a major flavonoid present in the human diet, has been widely studied, and its biological properties are consistent with its protective role in the cardiovascular system. However, it remains unknown whether the cardioprotective effects of quercetin may also occur through the modulation of genes involved in cell survival. The main goal of this study was to examine the gene expression profiling of cultured rat primary cardiomyocytes treated with quercetin using DNA microarrays and to relate these data to functional effects. Results showed distinct temporal changes in gene expression induced by quercetin and a strong upregulation of phase 2 enzymes, highlighting quercetin ability to act also with an indirect antioxidant mechanism.     

Myricetin and quercetin methyl ethers from Haplopappus integerrimus var. Punctatus

Nine flavonoids including two new myricetin derivatives, myricetin 3′,4′-dimethyl ether and myricetin 3,3′, 4′-trimethyl ether, were obtained from Haplopappus integerrimus var. punctatus. The known compounds are quercetin 7,3′-dimethyl ether, querectin 3,3′-dimethyl ether, isorhamnetin, quercetin 3,7-dimethyl ether, quercetin 3-methyl ether, quercetin and quercetin 3-β-d-glucoside.     

Comparative mutagenesis of plant flavonoids in microbial systems.

The plant flavonoids quercetin (3,5,7,3',4'-pentahydroxyflavone), morin (3,5,7,2',4'-pentahydroxyflavone), kaempferol (3,5,7,4'-tetrahydroxyflavone), chrysin (5,7-dihydroxyflavone), fisetin (3,7,3',4'-tetrahydroxyflavone), myricetin (3,5,7,3',4',5'-hexahydroxyflavone), myricitrin (myricetin-3-rhamnoside), hesperetin (3',5,7-trihydroxy-4'-methoxyflavanone), quercitrin (quercetin-3-L-rhamnoside), rutin (quercetin-3-rhamnosylglucoside or quercetin-3-rutinoside), and hesperidin (hesperetin-7-rutinoside) have been assayed for mutagenicity in the Salmonella/microsomal activation system. Quercetin, morin, kaempferol, fisetin, myricetin, quercitrin and rutin were mutagenic in the histidine reversion system with the frameshift strain TA98. The flavonols quercetin and myricetin are mutagenic without metabolic activation, although more effective when a rat liver microsomal preparation (S-9) is included; all others require metabolic activation. Flavonoids are common constituents of higher plants, with extensive medical uses. In addition to pure compounds, we have examined crude extracts of tobacco (snuff) and extracts from commonly available nutritional supplements containing rutin. Mutagenic activity can be detected and is correlated with the flavonoid content.     

Suppression of TNFalpha-mediated NFkappaB activity by myricetin and other flavonoids through downregulating the activity of IKK in ECV304 cells.

Flavonoids are a group of naturally-occurring phenolic compounds in the plant kingdom, and many flavonoids are found with vascular protective properties. Nevertheless how the protective response is exerted by flavonoids is not well characterized. In view of the nuclear factor-kappaB (NFkappaB) may play a central role in the initiation of atherosclerosis, prevention of the activation of NFkappaB represents an important role in protecting vascular injury. In this study, the effects of flavonoids on NFkappaB/inhibitor-kappaB (IkappaB) system in ECV304 cells activated with tumor necrosis factor-alpha (TNFalpha) were examined. We investigated the inhibitory action of six flavonoids on IkappaB kinase (IKK) activity, an enzyme recently found to phosphorylate critical serine residues of IkappaB for degradation. Of six flavonoids tested, myricetin was found to strongly inhibit IKK kinase activity, and prevent the degradation of IkappaBalpha and IkappaBbeta in activated endothelial cells. Furthermore, myricetin was also found to inhibit NFkappaB activity correlated with suppression of monocyte adhesion to ECV304 cells. Therefore we conclude that flavonoids may be of therapeutic value for vascular disease through down regulation of NFkappaB/IkappaB system.