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PubMed2005

Flavonoids in baby spinach (Spinacia oleracea L.): changes during plant growth and storage.

The variation in flavonoid concentration and composition was investigated in baby spinach (Spinacia oleracea L.) cv. Emilia sown on three occasions, each harvested at three growth stages at 6-day intervals. After harvest, leaves were stored in polypropylene bags at 2 or 10 degrees C. Flavonoids were analyzed by reversed phase HPLC. Twelve flavonoid peaks were detected. The main flavonoid, making up on average 43% of the total flavonoid concentration, was identified as 5,3',4'-trihydroxy-3-methoxy-6:7-methylenedioxyflavone-4'-glucuronide. Four other flavonoids each contributed 7-12% of the total flavonoid content. Total flavonoid content was relatively stable during normal retail storage conditions, although some of the individual flavonoid compounds showed considerable variation. The youngest plants had the highest flavonoid concentration, indicating that by harvesting the baby spinach a few days earlier than the current commercial stage of harvest, the flavonoid concentration in the product may be increased and the content of potentially health-promoting compounds enhanced.

Flavonoids↗
PubMed2006

Is reversal of endothelial dysfunction by tea related to flavonoid metabolism?

Dietary flavonoids can improve endothelial function, but the response varies between individuals. Wide variability is also seen in flavonoid O-methylation, a major pathway of flavonoid metabolism. The O-methylation of flavonoids could alter activity, and thus influence any effect on endothelial function. The objective of the current analysis was to investigate whether variability in the endothelial function response to ingestion of tea, a rich source of flavonoids, is related to the degree of O-methylation of flavonoids. This relationship was investigated in two studies in which endothelium-dependent flow-mediated dilatation (FMD) of the brachial artery was assessed and urinary 4-O-methylgallic acid (4OMGA) excretion was used as a marker of the O-methylation of tea-derived flavonoids. In the first study, amongst participants consuming five cups of tea per day for 4 weeks, the degree of increase in 4OMGA excretion was inversely associated with the change in FMD responses (r -078, P=0.008). In the second study, there was a significant difference in the FMD responses to acute ingestion of three cups of tea between individuals with a low ( median) 4OMGA response (1.94 (sem 0.79) % and -0.25 (sem 0.53) %, respectively; P=0.03). That is, any improvement in FMD following ingestion of tea may be enhanced in individuals who O-methylate less of the absorbed flavonoids. The present results are consistent with the suggestion that differences in flavonoid metabolism may influence their effect on endothelial function. Thus, differences in flavonoid metabolism could be related to the level of benefit of dietary flavonoids on the risk of CVD.

Brachial Artery↗
PubMed1993

Intake of potentially anticarcinogenic flavonoids and their determinants in adults in The Netherlands.

Flavonoids are strong antioxidants that occur naturally in foods and can inhibit carcinogenesis in rodents. Accurate data on population-wide intakes of flavonoids are not available. Here, using data of the Dutch National Food Consumption Survey 1987-1988, we report the intake of the potentially anticarcinogenic flavonoids quercetin, kaempferol, myricetin, apigenin, and luteolin among 4,112 adults. The flavonoid content of vegetables, fruits, and beverages was determined by high-performance liquid chromatography. In all subjects, average intake of all flavonoids combined was 23 mg/day. The most important flavonoid was the flavonol quercetin (mean intake 16 mg/day). The most important sources of flavonoids were tea (48% of total intake), onions (29%), and apples (7%). Flavonoid intake did not vary between seasons; it was not correlated with total energy intake (r = 0.001), and it was only weakly correlated with the intake of vitamin A (retinol equivalents, r = 0.14), dietary fiber (r = 0.21), and vitamin C (r = 0.26). Our use of new analytic technology suggests that in the past flavonoid intake has been overestimated fivefold. However, on a milligram-per-day basis, the intake of the antioxidant flavonoids still exceeded that of the antioxidants beta-carotene and vitamin E. Thus flavonoids represent an important source of antioxidants in the human diet.

Adult↗
PubMed1994

Dietary flavonoids and cancer risk in the Zutphen Elderly Study.

Flavonoids are polyphenolic antioxidants naturally present in vegetable foods. Some flavonoids, such as quercetin, inhibit carcinogenesis in rodents, but their effect in humans is unknown. We measured the flavonoids quercetin, kaempferol, myricetin, apigenin, and luteolin in foods and assessed flavonoid intake in 1985 by dietary history in 738 men aged 65-84 years without a history of cancer, who were then followed for five years. Mean flavonoid intake was 25.9 mg/day. The major sources of flavonoid intake were tea at 61% and vegetables and fruits (mainly onions, kale, endive, and apples) at 38%. Between 1985 and 1990, 75 men developed cancer (all sites) and 34 men died from cancer. Flavonoid intake in 1985 was not associated with incidence of all-cause cancer (p for trend = 0.54) or with mortality from all-cause cancer (p for trend = 0.51). Flavonoid intake was also not associated with risk of cancers of the alimentary and respiratory tract (p for trend = 0.92). Adjustment for age, body mass index, smoking, physical activity, and vitamin C, vitamin E, beta-carotene, and dietary fiber intake did not change the relative risks. A high intake of flavonoids from vegetables and fruits only was inversely associated with risk of cancer of the alimentary and respiratory tract (relative risk of highest vs. lowest tertile = 0.51, 95% confidence interval 0.25-1.05); these results suggest the presence of other nonvitamin components with anticarcinogenic potential in these foods. We conclude that intake of flavonoids, mainly from tea, apples, and onions, does not predict a reduced risk of all-cause cancer or of cancer of the alimentary and respiratory tract in elderly men. The effect of flavonoids on risk of cancer at specific sites needs further investigation in prospective cohort studies.

Aged↗
PubMed2006

Perception and modification of plant flavonoid signals by rhizosphere microorganisms.

Flavonoids are a diverse class of polyphenolic compounds that are produced as a result of plant secondary metabolism. They are known to play a multifunctional role in rhizospheric plant-microbe and plant-plant communication. Most familiar is their function as a signal in initiation of the legume-rhizobia symbiosis, but, flavonoids may also be signals in the establishment of arbuscular mycorrhizal symbiosis and are known agents in plant defence and in allelopathic interactions. Flavonoid perception by, and impact on, their microbial targets (e.g. rhizobia, plant pathogens) is relatively well characterized. However, potential impacts on 'non-target' rhizosphere inhabitants ('non-target' is used to distinguish those microorganisms not conventionally known as targets) have not been thoroughly investigated. Thus, this review first summarizes the conventional roles of flavonoids as nod gene inducers, phytoalexins and allelochemicals before exploring questions concerning 'non-target' impacts. We hypothesize that flavonoids act to shape rhizosphere microbial community structure because they represent a potential source of carbon and toxicity and that they impact on rhizosphere function, for example, by accelerating the biodegradation of xenobiotics. We also examine the reverse question, 'how do rhizosphere microbial communities impact on flavonoid signals?' The presence of microorganisms undoubtedly influences the quality and quantity of flavonoids present in the rhizosphere, both through modification of root exudation patterns and microbial catabolism of exudates. Microbial alteration and attenuation of flavonoid signals may have ecological consequences for below-ground plant-microbe and plant-plant interaction. We have a lack of knowledge concerning the composition, concentration and bioavailability of flavonoids actually experienced by microbes in an intact rhizosphere, but this may be addressed through advances in microspectroscopic and biosensor techniques. Through the use of plant mutants defective in flavonoid biosynthesis, we may also start to address the question of the significance of flavonoids in shaping rhizosphere community structure and function.

Biosensing Techniques↗
PubMed2003

Effects of the flavonoids biochanin A, morin, phloretin, and silymarin on P-glycoprotein-mediated transport.

Flavonoids are constituents of fruits, vegetables, and plant-derived beverages, as well as components in herbal-containing dietary supplements. The objective of this investigation was to characterize the effect of flavonoids on P-glycoprotein (P-gp)-mediated cellular efflux and to determine the molecular mechanism(s) of the flavonoid-drug interaction. Studies were conducted in the sensitive and multidrug resistant human breast cancer cell lines MCF-7 and MDA435/LCC6 and examined the effects of the flavonoids biochanin A, morin, phloretin, and silymarin on daunomycin (DNM) accumulation and doxorubicin cytotoxicity. The potential mechanism(s) involved in the interaction was evaluated by determining flavonoid effects on 1) P-gp ATPase activity, 2) [(3)H]azidopine photoaffinity labeling of P-gp, and 3) cellular P-gp levels. The flavonoids increased [(3)H]DNM accumulation in P-gp positive cells, but not P-gp negative cells, and these effects were both flavonoid concentration- and P-gp expression level-dependent. Biochanin A and silymarin potentiated doxorubicin cytotoxicity in P-gp positive cells. Biochanin A and phloretin stimulated, whereas morin and silymarin inhibited P-gp ATPase activity, confirming that these flavonoids interact with P-gp. Morin and silymarin significantly inhibited [(3)H]azidopine photoaffinity labeling of P-gp, suggesting a direct interaction with P-gp substrate binding. A 24-h preincubation with all flavonoids, followed by flavonoid removal, did not alter cellular P-gp level in P-gp positive cells. In conclusion, biochanin A, morin, phloretin, and silymarin all inhibited P-gp-mediated cellular efflux and the mechanism of the interaction involved, at least in part, a direct interaction. The findings of this study indicate a potential for significant flavonoid-drug interactions with P-gp substrates.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2003

Oxidation of flavonoids which promote DNA degradation induced by bleomycin-Fe complex.

Sixteen flavonoids including quercetin and kaempferol and their relatives were examined for their ability to promote DNA degradation induced by the bleomycin (BLM)-Fe complex. Three hydroxyl groups in the flavonoidal nucleus were proposed as a crucial structural requirement for effectively promoting DNA degradation: 1). the C7-hydroxyl substitution in the A-ring; 2). the C4'-hydroxyl substitution in the B-ring; and 3). the C3-hydroxyl substitution in the C-ring. Flavonoids, which lack even one of these hydroxyl substitutions, showed remarkably diminished activity. There was a good correlation (r=0.920, p<0.001) between activity to promote DNA degradation and oxidizability, which was measured following the Fe(III)-induced oxidation of flavonoids themselves, among the 16 flavonoids. The oxidizability of flavonoids which have the crucial hydroxyl substitutions, was remarkably enhanced in the presence compared with the absence of BLM. On the other hand, the extent of oxidation of flavonoids lacking these substitutions was enhanced little or not at all by BLM. No correlation between the Fe(III)-reducing activity and DNA degradation-promoting activity was found among flavonoids satisfying the crucial structural requirements. Furthermore, the correlation between the extent of oxidation of flavonoids and the Fe(III)-reducing activity was not confirmed among these flavonoids. Therefore, it was suggested that Fe(III)-reducing activity was not the only factor determining DNA degradation-promoting activity in flavonoids having the three hydroxyl groups necessary for effectively promoting DNA degradation induced by BLM-Fe complex.

Animals↗
PubMed1997

Dietary flavonoid and cancer prevention: evidence and potential mechanism.

Dietary flavonoids represent a family of polyphenol compounds found in common food items derived from plants. Depending on structural features, flavonoids can be further subdivided into flavones, flavonols, isoflavones, flavanes, and flavanols. The biological activities of flavonoids are structure dependent and epidemiological studies support their role in human cancer prevention. Several flavonoids inhibit cancer development in animal models of chemical and UV carcinogenesis. However, at high dose some flavonoids themselves may also increase cancer incidence. Although flavonoids have been shown to inhibit cancer cell growth in vitro, the ability of flavonoids to limit cancer progression is limited in animal studies. A potential application is the possible synergisticaction of flavonoids with chemotherapy agents. Molecularly, flavonoids have antioxidant properties and can further enhance the antioxidant protein activities in cells and in animals. Isoflavones and some other flavonoids have weak affinity for the estrogen receptor. Neonatal exposure of animals to isoflavonoids affects the development of reproductive organs, an observation that opens the possibility of using isoflavonoids in the prevention of cancers of the reproductive system. Some growth-inhibiting flavonoids also bind to the low-affinity type II estrogen binding sites, but the biochemical identity of type II sites is unknown.

Animals↗
PubMed1999

Induction of apoptosis by apigenin and related flavonoids through cytochrome c release and activation of caspase-9 and caspase-3 in leukaemia HL-60 cells.

The aim of this study was to investigate the mechanism of flavonoid-induced apoptosis in HL-60 leukaemic cells. Thus, the effect of structurally related flavonoids on cell viability, DNA fragmentation and caspase activity was assessed. Loss of membrane potential and reactive oxygen species generation were also monitored by flow cytometry. The structurally related flavonoids, such as apigenin, quercetin, myricetin, and kaempferol were able to induce apoptosis in human leukaemia HL-60 cells. Treatment with flavonoids (60 microM) caused a rapid induction of caspase-3 activity and stimulated proteolytic cleavage of poly-(ADP-ribose) polymerase (PARP). Furthermore, these flavonoids induced loss of mitochondrial transmembrane potential, elevation of reactive oxygen species (ROS) production, release of mitochondrial cytochrome c into the cytosol, and subsequent induction of procaspase-9 processing. The potency of these flavonoids on these features of apoptosis were in the order of: apigenin > quercetin > myricetin > kaempferol in HL-60 cells treated with 60 microM flavonoids. These results suggest that flavonoid-induced apoptosis is stimulated by the release of cytochrome c to the cytosol, by procaspase-9 processing, and through a caspase-3-dependent mechanism. The induction of apoptosis by flavonoids may be attributed to their cancer chemopreventive activity. Furthermore, the potency of flavonoids for inducing apoptosis may be dependent on the numbers of hydroxyl groups in the 2-phenyl group and on the absence of the 3-hydroxyl group. This provides new information on the structure-activity relationship of flavonoids.

Apigenin↗
PubMed2002

Flavonoids in human urine as biomarkers for intake of fruits and vegetables.

Flavonoids are polyphenolic compounds ubiquitously found in human diets. We have studied the association between urinary excretion of flavonoids and the intake of fruits and vegetables to evaluate the usefulness of flavonoids as a biomarker for fruit and vegetable intake. Levels of 12 dietary relevant flavonoids were determined by LC-MS in urine samples collected prior to an intervention study, when the subjects were on their habitual diet (n = 94), and after they had participated in an intervention study with diets either high or low in fruits, berries, and vegetables (n = 77). Both flavonoid glycosides and aglycones were included in the assay, but only the flavonoid aglycones were detectable. Thus, the flavonols quercetin, kaempferol, isorhamnetin, and tamarixetin, the dihydrochalcone phloretin, and the flavanones naringenin and hesperetin were quantified in the enzymatically hydrolyzed urine samples. The habitual intake of fruits and vegetables, determined by 3-day dietary records before the intervention study, correlated significantly with the total excretion of urinary flavonoids, with a coefficient of correlation of 0.35, P < 0.005 (n = 94). In addition, highly significant differences in the urinary excretion of all flavonoids were observed in the human intervention study between subjects on diets high or low in fruits, berries, and vegetables. Also, at the individual level a significant positive correlation between changes in fruit and vegetable intake and changes in urinary flavonoid excretion was observed. We conclude that urinary flavonoids may be useful as a new biomarker for fruit, berry, and vegetable intakes and may prove useful when the possible health protective effects of flavonoids are studied.

Adult↗
PubMedDate not supplied

The antitumor activities of flavonoids.

The flavonoids are polyphenolic compounds found as integral components of the human diet. They are universally present as constituents of flowering plants, particularly of food plants. The flavonoids are phenyl substituted chromones (benzopyran derivatives) consisting of a 15-carbon basic skeleton (C6-C3-C6), composed of a chroman (C6-C3) nucleus (the benzo ring A and the heterocyclic ring C), also shared by the tocopherols, with a phenyl (the aromatic ring B) substitution usually at the 2-position. Different substitutions can typically occur in the rings, A and B. Several plants and spices containing flavonoid derivatives have found application as disease preventive and therapeutic agents in traditional medicine in Asia for thousands of years. The selection of a particular food plant, plant tissue or herb for its potential health benefits appears to mirror its flavonoid composition. The much lower risk of colon, prostate and breast cancers in Asians, who consume more vegetables, fruits and tea than populations in the Western hemisphere do, raises the question of whether flavonoid components mediate the protective effects of diets rich in these foodstuffs by acting as natural chemopreventive and anticancer agents. An impressive body of information exists on the antitumor action of plantflavonoids. In vitro work has concentrated on the direct and indirect actions of flavonoids on tumor cells, and has found a variety of anticancer effects such as cell growth and kinase activity inhibition, apoptosis induction, suppression of the secretion of matrix metalloproteinases and of tumor invasive behavior. Furthermore, some studies have reported the impairment of in vivo angiogenesis by dietary flavonoids. Experimental animal studies indicate that certain dietary flavonoids possess antitumor activity. The hydroxylation pattern of the B ring of the flavones and flavonols, such as luteolin and quercetin, seems to critically influence their activities, especially the inhibition of protein kinase activity and antiproliferation. The different mechanisms underlying the potential anticancer action of plant flavonoids await further elucidation. Certain dietary flavonols and flavones targeting cell surface signal transduction enzymes, such as protein tyrosine and focal adhesion kinases, and the processes of angiogenesis appear to be promising candidates as anticancer agents. Further in vivo studies of these bioactive constituents is deemed necessary in order to develop flavonoid-based anticancer strategies. In view of the increasing interest in the association between dietary flavonoids and cancer initiation and progression, this important field is likely to witness expanded effort and to attract and stimulate further vigorous investigations.

Animals↗
PubMed2006

Toxicological aspects of flavonoid interaction with biomacromolecules.

OBJECTIVES: Flavonoids are widely accepted as health promoting phytochemicals, however, some flavonoids show ability of direct interaction with DNA and/or enhance carcinogen activation into DNA modifying agents. Thus, their potential harmful effect on the human body should be examined in detail. METHODS: Direct interaction of flavonoids (quercetin, rutin) with DNA was examined using square wave voltammetry on carbon paste electrode. Induction effect of selected flavonoids on content of cytochrome P450 1A1, carcinogens activating enzyme, in colon and liver microsomal samples of animals exposed to flavonoids was determined by Western blotting, using anti-cytochrome P450 1A1 specific antibody. RESULTS: Of the natural flavonoids tested, induction of CYP1A1 was elicited by the typical citrus flavonoid naringenin in the colon, as well as by flavone in the liver. Moreover, synthetic beta-naphthoflavone and naturally occurring chrysin, quercetin and diosmin induced CYP1A1 in both tissues. The oxidation signals of guanine and adenine in the DNA molecule were decreased in the presence of flavonoids. CONCLUSIONS: Although flavonoids are often considered to be safe because of their "plant origin", ingestion of flavonoids should be taken with caution. Enhanced expression of CYP1A1 in colon tissue might be responsible for increasing incidence of colorectal carcinoma in humans. Electrochemistry can be used to study the interactions of flavonoids and DNA.

Adenine↗
PubMed2001

Flavonoid sequestration by the common blue butterfly Polyommatus icarus: quantitative intraspecific variation in relation to larval hostplant, sex and body size.

Common blue butterflies (Polyommatus icarus) sequester flavonoids from their larval food and store these pigments as part of their adult wing colouration. Insects were reared on 10 different diets to assess effects of host plants on variation in flavonoid sequestration in this moderately polyphagous butterfly. Rearing experiments revealed an unexpectedly large gradient in flavonoid richness, ranging from individuals with high flavonoid loads (reared on inflorescences of Medicago sativa, Trifolium repens, T. pratense) to butterflies which contained almost no such pigments (fed with foliage of M. sativa or Robinia pseudoacacia). Flavonoid sequestration was much more effective from natural hostplants than from experimentally offered diets which would not be accepted in the field. Female butterflies on average sequestered almost 60% more flavonoids than males. This sex difference was more pronounced on natural than on experimental diets. Flavonoid load was significantly and positively related to dry mass and forewing length as two important fitness correlates of butterflies. This correlation was particularly strong on experimental diets (i.e. under constraining conditions for development). On natural hostplants, in contrast, when butterflies generally were flavonoid-rich, no clear relationship between flavonoid load and size or mass emerged. Our analytical data are consistent with field results according to which females rich in UV-absorbing flavonoid wing pigments are more attractive to mate-searching males. In P. icarus, flavonoid richness might therefore increase visibility (by more effective sensory stimulation of the visual system), but could also confer information about the feeding history, and thus ontogenetically determined 'quality' of a potential mate.

Journal Article↗
PubMed2002

Alteration of foliar flavonoid chemistry induced by enhanced UV-B radiation in field-grown Pinus ponderosa, Quercus rubra and Pseudotsuga menziesii.

Chromatographic analyses of foliage from several tree species illustrate the species-specific effects of UV-B radiation on both quantity and composition of foliar flavonoids. Pinus ponderosa, Quercus rubra and Pseudotsuga menziesii were field-grown under modulated ambient (1x) and enhanced (2x) biologically effective UV-B radiation. Foliage was harvested seasonally over a 3-year period, extracted, purified and the flavonoid fraction applied to a mu Bondapak/C(18) column HPLC system sampling at 254 nm. Total flavonoid concentrations in Quercus rubra foliage were more than twice (leaf area basis) that of the other species; Pseudotsuga menziesii foliage had intermediate levels and P. ponderosa had the lowest concentrations of total flavonoids. No statistically significant UV-B radiation-induced effects were found in total foliar flavonoid concentrations for any species; however, concentrations of specific compounds within each species exhibited significant treatment effects. Higher (but statistically insignificant) levels of flavonoids were induced by UV-B irradiation in 1- and 2-year-old P. ponderosa foliage. Total flavonoid concentrations in 2-year-old needles increased by 50% (1x ambient UV-B radiation) or 70% (2x ambient UV-B radiation) from that of 1-year-old tissue. Foliar flavonoids of Q. rubra under enhanced UV-B radiation tended to shift from early-eluting compounds to less polar flavonoids eluting later. There were no clear patterns of UV-B radiation effects on 1-year-old P. menziesii foliage. However, 2-year-old tissue had slightly higher foliar flavonoids under the 2x UV-B radiation treatment compared to ambient levels. Results suggest that enhanced UV-B radiation will alter foliar flavonoid composition and concentrations in forest tree species, which could impact tissue protection, and ultimately, competition, herbivory or litter decomposition.

Flavins↗
PubMed2004

Characterization of the interglycosidic linkage in di-, tri-, tetra- and pentaglycosylated flavonoids and differentiation of positional isomers by liquid chromatography/electrospray ionization tandem mass spectrometry.

The LC/UV-DAD/ESI-MSn negative fragmentation mode of 23 O-glycosylated flavonoids with two, three, four and five hexoses was studied. The results show that it is possible to differentiate the (1-->2) and (1-->6) interglucosidic linkages and also to discern between the flavonoid isomers with two glucoses (sophorosides, gentiobiosides and X,Y-diglucosides), three glucoses (sophorotriosides and X-sophoroside-Y-glucoside) and four glucoses (X-sophorotriosides-Y-glucoside and X-sophoroside-Y-sophoroside). In the characterization of the (1-->2) and (1-->6) interglycosidic linkages, the Y1- (-162 u) and Z1- (-180 u) ions play a relevant role. In the first case ions with high relative abundance (13-79%) are found, whereas in the other cases they are in very low abundance or absent. X,Y-di-O-glucoside flavonoids can be differentiated from the O-diglucoside flavonoids by the presence of Y1- (base peak) and Y0- (approximately 30%) ions and the absence of Z1- ions. Regarding flavonoids glycosylated with three glucoses, X-sophoroside-Y-glucoside flavonoids show the Y7(0-) (-162 u) ion as the only peak in MS2 events whereas in sophorotrioside flavonoids various ions due to intermediate fragmentations are observed. These ions are characteristic of a (1-->2) interglucosidic linkage. In MS2 experiments on flavonoids with four glucoses (X-sophorotrioside-Y-glucoside and X-sophoroside-Y-sophoroside), the base peak indicated the total loss of the sugar moieties in position 7. In addition, the characterization of the type of interglycosidic linkage in flavonoids glycosylated with five sugars can be achieved. On the other hand, in tetra- and pentaglycosylated flavonoids, the ions that characterize the (1-->2) interglucosidic linkage formed by intermediate fragmentation of the oligosacharide residues (sophorosides and sophorotriosides) are found in much higher relative abundance in MS3 than in MS2 experiments, where they are almost not detected.

Chromatography, Liquid↗
PubMed2002

Fasting plasma concentrations of selected flavonoids as markers of their ordinary dietary intake.

BACKGROUND: Dietary flavonoids, especially flavonols, are discussed as potentially preventive agents in the etiology of diseases such as coronary heart disease, stroke, and cancer. However, their consideration in epidemiologic studies is hampered by difficulties in exposure assessment. AIM OF THE STUDY: By comparison with dietary intake estimates, fasting plasma flavonoid concentrations should be evaluated as possible biomarkers of the ordinary dietary intake. METHODS: 7-d dietary records were completed by 48 healthy female students. Flavonoid intake was estimated by means of available literature data on the flavonoid content of foods. Fasting plasma samples were taken at the end of the record period for flavonoid determination (HPLC). RESULTS: The mean intake estimates (7-d period) of quercetin, kaempferol, naringenin, and hesperetin amounted to 17.9, 4.7, 12.1, and 17.4 mg/d, respectively; the corresponding mean plasma concentrations were 22.9, 10.7, 8.2, and 22.2 nmol/l. For all four flavonoids significant correlations between 7d-intake results and fasting plasma concentrations (r = 0.30-0.46, p < 0.05) existed. As expected from the known short elimination half-life of some plasma flavonoids, distinctly higher correlation coefficients were found for the relationship between intake estimates for the last day before blood sampling and the fasting plasma concentrations (r = 0.42-0.64; p < 0.01). The intraindividual variation in fasting plasma flavonoid concentrations during ad libitum intake was found to be rather high (mean coefficient of variation between 82 and 91 %; n = 4). CONCLUSIONS: The flavonoid content in fasting plasma samples seems to be a suitable biomarker of short-term intake and a possible biomarker of the medium-term intake. Due to the high intraindividual variation the combined use of plasma flavonoid concentrations and dietary intake estimates may be the best choice in epidemiologic studies.

Adult↗
PubMed1994

Modulation of adriamycin accumulation and efflux by flavonoids in HCT-15 colon cells. Activation of P-glycoprotein as a putative mechanism.

Since P-glycoprotein (P-gp) in normal tissues may serve as a cellular defense mechanism against naturally occurring xenobiotics, we considered whether physiologically active components of commonly ingested plant foods could influence P-gp function. To examine this possibility, a series of flavonoids commonly found in plant foods was tested for their ability to modulate [14C]Adriamycin ([14C]ADR) accumulation and efflux in P-gp-expressing HCT-15 colon cells. Many flavonoids, in the micromolar range, inhibited the accumulation of [14C]ADR. Detailed experiments utilizing flavonoids with the greatest activity in reducing [14C]ADR accumulation, i.e. galangin, kaempferol, and quercetin, revealed that the efflux of [14C]ADR is increased markedly in the presence of these compounds. Flavonoid-induced stimulation of efflux was rapid and was blocked by the multidrug-resistant (MDR) reversal agents verapamil, vinblastine, and quinidine. The magnitude of flavonoid-stimulated efflux in sodium butyrate-treated cells with a 4-fold induction of P-gp protein was similar to that in uninduced cells. [3H]Azidopine photoaffinity labeling of P-gp in crude membrane preparations revealed mild to no competition for binding by flavonoids possessing either activity or inactivity in reducing ADR accumulation. Although flavonoid hydrophobicity was found to be unrelated to flavonoid activity in altering [14C]ADR accumulation, certain structural features were associated with enhancement or diminution of activity. Finally, the significance of flavonoid-related reduction of [14C]ADR accumulation was underscored in cell growth studies, showing partial protection by quercetin against ADR-induced growth inhibition. It is concluded that certain naturally occurring plant flavonoids may acutely upregulate the apparent activity of P-gp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

In vitro effects of a flavonoid-rich extract on LDL oxidation.

Flavonoids are phenolic compounds of vegetable origin with antioxidant effects. The present study aimed to determine their properties as LDL antioxidants. LDL were incubated with increasing concentrations of flavonoids (0-16 micrograms/ml) and LDL oxidation was started by adding CuCl2 (2 microM) to the media. When flavonoids were present in the media, vitamin E consumption, the lag phase of conjugated diene formation, LDL electrophoretic mobility in agarose gels and the appearance of thiobarbituric acid reacting substances (TBARS) were delayed in a concentration-dependent manner. To determine whether flavonoids could terminate LDL oxidation once initiated, two sets of experiments were performed. In the first, LDL oxidation was initiated as described above. At 2 or 4 h of incubation, flavonoids were added (4 micrograms/ml) and their effect compared to samples where butylated hydroxytoluene or EDTA were added. At 5 h, in the LDL samples where flavonoids were added, the electrophoretic mobility and TBARS production were the same as those present in LDL samples incubated for the whole period in the absence of flavonoids. However, when either butylate hydroxytoluene or EDTA was added, as would be expected, the LDL oxidation process was completely arrested as shown by a reduction in the appearance of TBARS and a lower LDL electrophoretic mobility. In the second experiment, LDL oxidation was initiated as described above and at 0, 10 and 20 min, flavonoids were added (4 micrograms/ml). When vitamin E was still present in the LDL solution, the flavonoids were able to both increase the lag phase in the formation of conjugated dienes and to delay the consumption of vitamin E. The present results show that in vitro, flavonoids prevent LDL oxidation in a concentration-dependent manner, delaying the consumption of vitamin E, but they cannot terminate or delay LDL oxidation once vitamin E in LDL is consumed.

Antioxidants↗