Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Physiologically based kinetic modelling based prediction of oral systemic bioavailability of flavonoids, their metabolites, and their biological effects
    Boonpawa, Rungnapa - \ 2017
    Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): Arjen Punt. - Wageningen : Wageningen University - ISBN 9789463430371 - 180
    flavonoids - bioavailability - modeling - metabolites - quercetin - physiology - hesperidin - flavonoïden - biologische beschikbaarheid - modelleren - metabolieten - quercetine - fysiologie - hesperidine

    Flavonoids, abundantly present in fruits and vegetables, have been reported to exert various positive health effects based on in vitro bioassays. However, effects detected in in vitro models cannot be directly correlated to human health as most in vitro studies have been performed using flavonoid aglycones at high concentration ignoring extensive metabolism of flavonoids in the human body. To better understand positive health effects of flavonoids in humans, it is of importance to gain insight in at which form and concentration flavonoids are present in the systemic circulation after consumption. This insight can be obtained using physiologically based kinetic (PBK) computer modeling. The results obtained show that PBK modeling provides a useful additional research tool for studies on the fate of flavonoids in the human body and can reveal at what oral dose levels of flavonoids in vitro positive health effects can be expected to occur in vivo, presenting opportunities that are not easily provided by other methods.

    Dietary epicatechnin and quercetin in cardiovascular health and disease
    Dower, J.I. - \ 2016
    Wageningen University. Promotor(en): Daan Kromhout; Marianne Geleijnse, co-promotor(en): Peter Hollman. - Wageningen : Wageningen University - ISBN 9789462577862 - 164
    cardiovascular disorders - cardiovascular diseases - epicatechin - quercetin - epidemiological surveys - genome analysis - chocolate - hart- en vaatstoornissen - hart- en vaatziekten - epicatechine - quercetine - epidemiologische onderzoeken - genoomanalyse - chocolade

    Epidemiological studies showed that the consumption of flavonoid-rich foods such as cocoa and tea is associated with a lower risk of cardiovascular disease (CVD). Randomised controlled trials (RCTs) showed that cocoa and tea improved markers of cardiometabolic health including blood pressure, endothelial function, insulin resistance, arterial stiffness and inflammation.

    Cocoa is particularly rich in the flavan-3-ol epicatechin and tea is the main dietary source of epicatechin and of the major flavonol quercetin. However, evidence on the individual roles of epicatechin and quercetin in the health effects of cocoa and tea is still scarce. Therefore, we estimated the strength of the association between epicatechin intake and CVD mortality in a prospective cohort study. Furthermore, we also investigated the effects of epicatechin and quercetin on markers of cardiometabolic health and gene expression, by means of two RCTs.

    In Chapter 2, the association between epicatechin intake and CVD mortality was studied using data from the Zutphen Elderly Study, a cohort of 744 elderly Dutch men. During 25 years of follow-up, 329 men died from CVD and 148 from coronary heart disease (CHD). Results from this study showed that men in the highest tertile of epicatechin intake had a 38% lower risk of CHD mortality compared to men in the lowest tertile. For men with prevalent CVD, the risk of CVD mortality was 46% lower for men in the highest tertile of intake, compared to men in the lowest tertile. This is the first epidemiological study to have investigated the association between epicatechin intake and CVD mortality. Hence, more and larger cohort studies are required to confirm this association, possibly with a focus on populations with a high risk of CVD.

    In Chapter 3, the chronic effects of pure epicatechin and quercetin on markers of cardiometabolic health were investigated by means of a RCT. Thirty-seven apparently healthy men and women aged 40–80 years consumed (-)-epicatechin (100 mg/d), quercetin-3-glucoside (160 mg/d), or placebo capsules for 4 weeks, in random order. Markers of cardiometabolic health were measured before and after each 4-week intervention. The results of this study showed that epicatechin improved insulin resistance and had a borderline significant effect on endothelial function. This suggests that epicatechin contributes to the cardioprotective effects of cocoa and tea, however, larger long-term RCTs are required to confirm these effects. Pure quercetin supplementation did not affect any of these markers of cardiometabolic health.

    Using data from the same study, we investigated the effects of supplementation of pure epicatechin and quercetin on a comprehensive set of biomarkers of endothelial dysfunction and inflammation (Chapter 4). With the exception of sE-selectin (a biomarker of endothelial dysfunction), epicatechin supplementation did not beneficially influence any of the biomarkers, suggesting a lack of evidence for a role of epicatechin in inflammation. Quercetin also lowered sE-selectin as well as the inflammatory biomarker IL-1β and the overall z-score for inflammation. This suggests that quercetin may contribute to the cardioprotective effects of tea by reducing inflammation and possibly by improving endothelial function.

    In the same study, the effects of pure epicatechin supplementation on whole genome gene expression profiles of circulating immune cells were also assessed (Chapter 5). Pure epicatechin supplementation modestly reduced gene expression related to inflammation signalling routes in circulating immune cells – routes which are known to play a role in cardiovascular health. However, there was no evidence that epicatechin affected pathways related to insulin resistance or endothelial function.

    To directly compare the acute effects of pure epicatechin and epicatechin from dark chocolate on vascular function, we carried out an acute RCT in 20 apparently healthy men aged 40-80 years (Chapter 6). On three separate occasions, subjects consumed: 1) 70g dark chocolate (150 mg epicatechin) with two placebo capsules; 2) two pure epicatechin capsules (100 mg epicatechin) with 75g white chocolate and 3) two placebo capsules with 75g white chocolate (0 mg epicatechin). Endothelial function and arterial stiffness were measured before and two hours after each intervention. To determine epicatechin bioavailability, epicatechin metabolites were measured in blood samples taken at repeated intervals over a period of 8 hours. There was no significant difference in improvement in endothelial function or arterial stiffness between pure epicatechin and dark chocolate. There was also no difference in bioavailability of pure epicatechin and epicatechin from dark chocolate, when standardised per 100 mg of epicatechin. This suggests that epicatechin may contribute to the vascular effects of cocoa and that the bioavailability of pure epicatechin and epicatechin from dark chocolate is similar.

    In the general discussion, the main findings of this thesis were first summarised. Methodological considerations related to cohort studies, such as the assessment of flavonoid intake and the possibility of residual confounding were also discussed. Issues related to the relevance of cardiometabolic markers in RCTs and the effect of cocoa flavan-3-ol bioavailability were addressed. Finally, suggestions for future research were put forward.

    In conclusion, the results of this thesis suggest that epicatechin contributes to the cardioprotective effects of cocoa and tea. Epicatechin intake was inversely related to CHD mortality in elderly men, and to CVD mortality in men with prevalent CVD. The cardioprotective effects of epicatechin are likely mediated through improvements in insulin resistance and possibly endothelial function. In contrast, quercetin is unlikely to play a major role in the cardioprotective effects of tea. Results for quercetin from cohort studies are inconclusive, and based on the results of our chronic RCT, quercetin did not affect vascular function or insulin resistance, but may help to lower inflammation. Evidence of the role that individual flavonoids play in the aetiology of CVD is still limited. More studies with pure flavonoids are required to elucidate their role.

    The influence of phase II conjugation on the biological activity of flavonoids
    Beekmann, K. - \ 2016
    Wageningen University. Promotor(en): Ivonne Rietjens; Peter van Bladeren, co-promotor(en): L. Actis-Goretta. - Wageningen : Wageningen University - ISBN 9789462577640 - 171
    flavonoids - biological activity - in vitro - biosynthesis - peroxisomes - microarrays - daidzein - genistein - oestrogen receptors - isoflavones - quercetin - kaempferol - serine proteinases - threonine - flavonoïden - biologische activiteit - in vitro - biosynthese - peroxisomen - microarrays - daidzin - genisteïne - oestrogeenreceptoren - isoflavonen - quercetine - kaempferol - serine proteïnasen - threonine

    Flavonoid consumption is often correlated with a wide range of health effects, such as the prevention of cardiovascular diseases, neurodegenerative diseases, and diabetes. These effects are usually ascribed to the activity of the parent flavonoid aglycones, even though these forms of the flavonoids generally have a low systemic bioavailability. During uptake, flavonoids undergo phase II metabolism and are present in the systemic circulation nearly exclusively as conjugated metabolites. The aim of this thesis was to study the effect of conjugation on the biological activity of selected flavonoids towards different endpoints relevant for human health. To this end, conjugation with glucuronic acid was taken as the model type of conjugation because this modification is generally observed to be the most important metabolic conjugation reaction for flavonoids in man.

    A review of scientific literature published until early 2012 reveals that metabolic conjugation can affect the biological activity of flavonoids in different ways. Conjugation can increase, decrease, inverse or not affect the biological activity, depending on the flavonoid, the type and position of conjugation, the endpoint studied, and the assay system used. Based on the literature reviewed it is concluded that the effect of conjugation has to be studied on a case-by-case basis.

    As the research on the biological activity of biologically relevant flavonoid conjugates is often hampered by the generally low commercial availability and high prices of these conjugates, a simple and versatile method for the biosynthesis of metabolically relevant flavonoid conjugates is described. Using this method, relevant conjugates can be prepared from different flavonoid substrates in sufficient quantities for in vitro bioassays. Further, an efficient strategy for the identification of these flavonoid conjugates by LC-MS and 1H-NMR using MetIDB (Metabolite Identification Database), a publicly accessible database of predicted and experimental 1H-NMR spectra of flavonoids, is presented.

    To study the effect of conjugation on the biological activities of flavonoids, several different assay systems and endpoints were used to study the activity of different flavonoids and their conjugates. The effects of quercetin, kaempferol, and their main plasma conjugates quercetin-3-O-glucuronide and kaempferol-3-O-glucuronide (K-3G) on different endpoints related to peroxisome proliferator-activated receptor (PPAR)-γ were studied. PPAR-γ activation is reported to have positive health effects related to adipogenesis, insulin resistance and inflammation. The presented results show that the flavonoid aglycones increased PPAR-γ mediated gene expression in a stably transfected reporter gene cell line, and that glucuronidation diminished this effect. These observed increases in reporter gene expression were accompanied by increased PPAR-γ receptor-mRNA expression upon exposure to kaempferol, an effect that was also reduced by glucuronidation. Using the cell-free Microarray Assay for Real-time Coregulator-Nuclear receptor Interaction (MARCoNI) it was demonstrated that, unlike the known PPAR-γ agonist rosiglitazone, neither the flavonoid aglycones nor the conjugates are agonistic ligands of the PPAR-γ receptor. Supporting the hypothesis that the tested compounds have a different mode of action from normal LBD agonism, quercetin appeared to synergistically increase the effect of rosiglitazone in the reporter gene assay. The modes of action behind the observed effects remain to be elucidated and might include effects on protein kinase activities affecting expression of the PPAR-γ receptor, or posttranscriptional modifications of PPAR-γ.

    Another type of nuclear receptor known to be targeted by certain flavonoids are the estrogen receptor (ER)α- and ERβ. ERs are the main targets of estrogenic compounds, and upon their activation different transcriptional responses with opposite effects on cell proliferation and apoptosis are elicited; ERα activation stimulates cell proliferation, while ERβ activation causes apoptosis and reduces ERα mediated induction of cell proliferation. Using the MARCoNI assay, the intrinsic estrogenic effects of the two main dietary isoflavones daidzein and genistein, and their plasma conjugates daidzein-7-O-glucuronide and genistein-7-O-glucuronide on the ligand induced coregulator binding of ERα- and ERβ-LBD were studied and compared to the effect of the positive control 17β-estradiol (E2). The results show that the tested isoflavone compounds are less potent agonists of ERα- and ERβ-LBD than E2, although they modulate the LBD-coregulator interactions in a manner similar to E2. Genistein is shown to be a more potent agonist than daidzein for both receptor subtypes. While in the MARCoNI assay genistein had a strong preference for ERβ-LBD activation over ERα-LBD activation, daidzein had a slight preference for ERα-LBD activation over ERβ-LBD activation. Glucuronidation reduced the intrinsic agonistic activities of both daidzein and genistein to induce ERα-LBD and ERβ-LBD - coregulator interactions and increased their average half maximal effective concentrations (EC50s) by 8 to 4,400 times. The results presented further show that glucuronidation changed the preferential activation of genistein from ERβ-LBD to ERα-LBD and increased the preferential activation of daidzein for ERα-LBD; this is of special interest given that ERβ activation, which is counteracting the possible adverse effects of ERα activation, is considered one of the supposedly beneficial modes of action of isoflavones.

    Many flavonoids are reported to be inhibitors of protein kinases. To study the effect of conjugation on the inhibition of serine/threonine protein kinases by flavonoids, kaempferol and its main plasma conjugate K-3G were selected as model compounds. Protein kinases are involved in a wide range of physiological processes by controlling signaling cascades and regulating protein functions; modulation of their activities can have a wide range of biological effects. The inhibitory effects of kaempferol, K-3G, and the broad-specificity protein kinase inhibitor staurosporine on the phosphorylation activity of recombinant protein kinase A (PKA) and of a lysate prepared from the hepatocellular carcinoma cell line HepG2 were studied using a microarray platform that determines the phosphorylation of 141 putative serine/threonine phosphorylation sites derived from human proteins. The results reveal that glucuronidation reduces the intrinsic potency of kaempferol to inhibit the phosphorylation activity of PKA and HepG2 lysate on average about 16 and 3.5 times, respectively. It is shown that the inhibitory activity of K-3G in the experiments conducted was not caused by deconjugation to the aglycone. Furthermore, the results show that kaempferol and K-3G, unlike the broad-specificity protein kinase inhibitor staurosporine, did not appear to inhibit all protein kinases present in the HepG2 lysate to a similar extent, indicating that kaempferol selectively targets protein kinases, a characteristic that appeared not to be affected by glucuronidation. The fact that K-3G appeared to be only a few times less potent than kaempferol implies that K-3G does not necessarily need to be deconjugated to the aglycone to exert potential inhibitory effects on protein kinases.

    The results obtained in the present thesis support the conclusion that glucuronidation of flavonoids does not necessarily abolish their activity and that flavonoid glucuronides may be biologically active themselves, albeit at higher concentrations than the parent aglycones. In line with the conclusions from the earlier literature review, an updated literature review on the effect of conjugation on the biological activity of flavonoids concludes that that the effect of conjugation on the biological activity of flavonoids depends on the type and position of conjugation, the endpoint studied and the assay system used. Based on the results described and the literature reviewed in this thesis, several recommendations and perspectives for future research are formulated. Several methodological considerations are formulated that need to be taken into account when studying the biological activity of flavonoids and their conjugates to avoid confounding results. Further, the relevance of the gut microbiome for flavonoid bioactivity is highlighted, and considerations regarding the pharmacokinetics and pharmacodynamics of flavonoids in vivo are formulated. Altogether, it can be concluded that circulating flavonoid conjugates may exert biological activities themselves, and that understanding these is a prerequisite to successfully elucidate the mechanisms of action behind the biological activities linked to flavonoid consumption.

    Unravelling mechanisms of dietary flavonoid-mediated health effects: effects on lipid metabolism and genotoxicity
    Hoek-van den Hil, E.F. - \ 2015
    Wageningen University. Promotor(en): Ivonne Rietjens; Jaap Keijer, co-promotor(en): Peter Hollman. - Wageningen : Wageningen University - ISBN 9789462573031 - 157
    flavanoïden - flavonoïden - vetzuren - quercetine - flavonolen - lichaamsgewicht - lipidenmetabolisme - hart- en vaatziekten - lever - vetweefsel - gezondheid - genotoxiciteit - voeding - muizen - flavanoids - flavonoids - fatty acids - quercetin - flavonols - body weight - lipid metabolism - cardiovascular diseases - liver - adipose tissue - health - genotoxicity - nutrition - mice


    Consumption of foods containing flavonoids is associated with a reduced risk of cardiovascular diseases (CVD), possibly by lipid-lowering effects. On the other hand, for one of these flavonoids, quercetin, also genotoxicity was shown especially in in vitro bioassays. Therefore, the first aim of this thesis was to identify mechanisms underlying potential beneficial health effects of flavonoids. The focus was on hepatic lipid metabolism and circulating lipids and a molecular and physiological approach was used. Secondly, we aimed to study the potential in vivo genotoxic effects of quercetin by transcriptome analyses in liver and small intestine, since these represent the tissues of first contact exposed to relatively high levels upon oral intake of flavonoids.

    Circulating lipids are important CVD-related risk markers, which are in general determined with commercially available enzyme-based assays. However, the usual enzyme in these assays, peroxidase, has previously been reported to be inhibited by flavonoids. Therefore, we have studied in chapter 2 whether these assays can adequately be used in flavonoid research. We observed that various flavonoid aglycones interfere with peroxidase used in triglycerides (TG) and free fatty acids (FFA) enzymatic assays, reporting incorrect lower TG and FFA levels than actually present. Furthermore, addition of metabolites such as isorhamnetin or quercetin-3-O-glucuronide, the major metabolite of quercetin in human and rat plasma, to murine serum also resulted in a significant reduction of the detected TG levels, while a trend was seen towards reduced FFA levels. It can be concluded that when applying these biochemical assays, vigilance is needed and alternative analytical methods assessing FFA or TG levels should preferably be applied for studying the biological effects of flavonoids on TG and FFA levels.

    In chapter 3 mechanistic and physiological effects of quercetin on hepatic lipid metabolism were studied. C57BL/6JOlaHsd male adult mice received a mild high-fat (30 en%) diet without or with supplementation of 0.33% (w/w) quercetin for 12 weeks. Gas chromatography and 1H-NMR were used to quantitatively measure serum lipid profiles. Whole genome microarray analysis of liver tissue was used to identify potential mechanisms underlying altered circulating lipid levels by quercetin supplementation. Body weight, energy intake and hepatic lipid accumulation did not differ significantly between the quercetin and the control group. In serum of quercetin-fed mice, TG levels were decreased by 14% (p<0.001) and total poly unsaturated fatty acids (PUFA) levels were increased by 13% (p<0.01). Levels of palmitic acid, oleic acid, and linoleic acid were all decreased by 9-15% (p<0.05) in quercetin-fed mice. Both palmitic acid and oleic acid can be oxidized by omega-oxidation. Gene expression profiling showed indeed that quercetin increased hepatic lipid metabolism, especially omega-oxidation. At the gene level, this was reflected by the up-regulation of cytochrome P450 (Cyp) 4a10, Cyp4a14, Cyp4a31 and Acyl-CoA thioesterase 3 (Acot3). Two relevant regulators, cytochrome P450 oxidoreductase (Por, rate limiting for cytochrome P450 activities) and the transcription factor constitutive androstane receptor (Car; official symbol Nr1i3) were also up- regulated in the quercetin-fed mice. We concluded that quercetin intake increased hepatic lipid omega-oxidation and lowered corresponding circulating lipid levels, which may contribute to potential beneficial effects of quercetin on CVD.

    Subsequently, in chapter 4 effects of quercetin supplementation were studied in mice given a high-fat (40 en%) background diet. The set-up of the experiment was the same as in chapter 3, with the exception of the background diet that was used, which was different in fat content and composition. This high-fat diet-induced body weight gain, and serum and hepatic lipid accumulation, which are all known risk factors for CVD. The aim of this study was to investigate the effects and underlying molecular mechanisms of the effects of the flavonoid quercetin on hepatic lipid metabolism in mice given this high-fat diet background. C57BL/6JOlaHsd male adult mice received the high-fat diet without or with supplementation of 0.33% (w/w) quercetin for 12 weeks. Body weight gain was 29% lower in quercetin fed mice versus control mice (p<0.01), while the energy intake was not significantly different. Quercetin supplementation lowered high-fat diet-induced hepatic lipid accumulation to 29% of the amount present in the control mice (p<0.01). 1H-NMR serum lipid profiling revealed that the supplementation also significantly lowered high-fat diet-induced increases in serum lipid levels. Global gene expression profiling of liver showed that cytochrome P450 2b (Cyp2b) genes, key target genes of the transcription factor Car, were down-regulated. However, the induction of omega-oxidation observed by quercetin supplementation to a mild high-fat (30en%) diet (chapter 3), was not observed this time with the high-fat (40en%) diet. Cumulatively, quercetin decreased high-fat diet-induced body weight gain, hepatic lipid accumulation and serum lipid levels. This was accompanied by regulation of cytochrome P450 2b genes in liver, which are considered to be under transcriptional control of CAR. The quercetin effects are likely dependent on the fat content and composition of the diet.

    In chapter 5 we investigated whether flavonoids from other flavonoid subclasses can exert the same effects as we observed for quercetin. Effects of quercetin, hesperetin, epicatechin, apigenin and anthocyanins, in C57BL/6JOlaHsd male adult mice fed a high-fat diet for 12 weeks were compared, relative to a normal-fat diet. High-fat diet-induced body weight gain was significantly lowered by all flavonoids (17-29%), but most by quercetin. Quercetin significantly lowered high-fat diet-induced hepatic lipid accumulation (by 71%). High-fat diet-induced increases of mesenteric adipose tissue weight and serum leptin levels were significantly lowered by quercetin, hesperetin, and anthocyanins. Adipocyte cell size and adipose tissue inflammation were not affected.

    The effects on body weight and adiposity could not be explained by individual significant differences in energy intake, energy expenditure, nor by differences in activity. Lipid metabolism was not changed as measured by indirect calorimetry or expression of known lipid metabolic genes in liver and white adipose tissue. Hepatic expression of Cyp2b9 was strongly down-regulated by all flavonoids. Overall, all five flavonoids lowered parameters of high-fat diet-induced adiposity, with quercetin being most effective.

    Next to the beneficial health effects of flavonoids, the safety of flavonoids is under discussion, mainly because of potential genotoxic effects found for quercetin in vitro. Therefore, in chapter 6 the in vivo genotoxicity of this flavonoid was studied by transcriptome analyses in two tissues, small intestine and liver, where the highest exposure to quercetin is expected. This is especially of interest in view of high intake by widely available food supplements. Quercetin (0.33%) supplemented to a high-fat diet was administered to C57BL/6JOlaHsd male adult mice during 12 weeks. Serum alanine aminotransferase and aspartate aminotransferase levels revealed no indications for hepatotoxicity. General microarray pathway analysis of liver and small intestinal tissue samples showed no regulation of genotoxicity related pathways. In addition, analysis of DNA damage pathways in these tissues did also not point at genotoxicity. Furthermore, comparison with a published classifier set of transcripts for identifying genotoxic compounds did not reveal any similarities in the regulation of these classifier set by quercetin. Available microarray datasets of known genotoxic liver carcinogens, 2-acetylaminofluorene and aflatoxin B1 in mice were taken along as positive controls for comparison, and indeed showed genotoxic properties (regulation of genotoxic related genes) in the analyses. This transcriptomic analysis showed that supplementation with quercetin at ~350 mg/kg bw/day for 12 weeks did not induce genotoxicity in liver and small intestine.

    In conclusion, we have shown in vivo efficacy of flavonoids reflected by effects on metabolic health parameters, including hepatic lipid metabolism. These effects on hepatic lipid metabolism seemed to be related or influenced by the transcription factor CAR. The dietary contexts appeared to modify the health effects. The five studied flavonoids in general showed the same effects, with quercetin being the most effective. No genotoxicity of quercetin was found by transcriptome analyses in liver and small intestine. Overall, we have obtained indications for beneficial health effects of flavonoids in mice, which makes it interesting to study if these effects can be extrapolated to humans to further explore their potential as functional compounds of dietary flavonoid intake.

    In vivo relevance of in vitro detected estrogenic effects of food associated compounds
    Veld, M.G.R. ter - \ 2008
    Wageningen University. Promotor(en): Ivonne Rietjens; Tinka Murk. - [S.l.] : S.n. - ISBN 9789085852858 - 152
    oestrogene eigenschappen - weekmakers - voedselverpakking - ftalaten - quercetine - oestrogenic properties - plasticizers - food packaging - phthalates - quercetin
    The aim of the present thesis was to study the in vivo relevance of in vitro detected estrogenic effects of food associated compounds, with emphasis on prenatal exposure. The estrogenic potency of 21 food packaging-associated compounds was studied in ERα or ERβ transfected U2-OS (human osteoblasts devoid of endogenous estrogen receptors) cell lines. Six plasticizers and three anti-oxidants were slightly estrogenic in the ERα cells. BPA, NP, tris (2-ethylhexyl) trimellitate (TEHTM), propyl gallate and butylated hydroxy anisole (BHA) were estrogenic both in ERα and ERβ cells. These compounds appeared to be more estrogenic relative to estradiol (E2) in ERβ than in ERα cells. To study the in vivo relevance of these effects, in vivo biomarker-responses of BPA, NP, DEHA, DEHP, DIHP, p,p’-DDE and quercetin were studied in ER-Luc male mice. Of these seven compounds, BPA, DEHP and quercetin induced estrogenic effects after a single oral dosage at exposure levels 10-104 times higher than the established Tolerable Daily Intakes (TDI’s). It remains to be seen whether these margins are sufficiently high to allow the conclusion that these compounds are unlikely to represent a human health risk. As exposure to estrogenic compounds during developmental stages could be an important risk factor in developing hormone dependent cancers later in life, these seven compounds were studied in pregnant ER-Luc mice as well. After oral exposure of the mother animal the compounds were unable to significantly induce luc-activity in any of the tissues including fetuses. Unexpectedly however, NP, BPA and DIHP significantly lowered the placental luc-activity. The results indicate that at the current levels of exposure to food associated estrogenic compounds, direct estrogenic effects in the fetus are not expected. The mechanism and consequences of the significant luc-reduction in the placenta should be investigated to a further extent to elucidate its possible significance. Because of the absence of significant luc-induction in the fetuses, the fate and distribution of radioactively labeled E2, NP and p,p’-DDE were studied in pregnant C57black mice in order to investigate whether the compounds can actually reach the fetuses. E2 did not reach the fetus at a level above the detection limit, NP and p,p’-DDE levels were above the detection limit in fetuses exposed via the mother from GD8-16. Levels of E2 and NP detected in the placenta were significantly higher than those in the fetuses, up to five fold for E2 and three fold for NP, possibly due to prevention of transport of the compounds to the fetuses by placental binding proteins.
    Based on the findings of the present thesis it was concluded that in spite of the in vitro estrogenicity of various food-born estrogens, in vivo estrogenic effects are not likely expected as estrogenicity in vivo is shown at levels 10-104 fold higher than the TDI’s for humans and placental binding proteins may reduce fetal exposure. However, the estrogenic compounds were given as a single acute dose, whereas TDI values and also risks associated with dietary exposure can be expected to result from chronic combined exposure. Therefore, it remains to be seen whether the estimated margins are sufficiently high. Future experiments are therefore needed that focus on long term and combined exposure. Another factor that remains to be solved relates to the fact that only in in vitro assays the relative ability of compounds to differentially activate ERα or ERβ can be quantified.
    All together the results of the present thesis reveal that the extent at which in vitro estrogenic effects may result in in vivo estrogenicity may vary with the compound under study and should be evaluated on a case by case basis taking differences in absorption, distribution, metabolism and excretion, the intrinsic estrogenic potency of chemicals for either the ERα or ERβ and the differential levels of expression of these receptors in different tissues in vivo into account.

    Biomarkers of quercetin-mediated modulation of colon carcinogenesis
    Dihal, A.A. - \ 2007
    Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): R.H. Stierum; Ruud Woutersen. - [S.l.] : S.n. - ISBN 9789085046783 - 240
    biochemische merkers - quercetine - colorectaal kanker - biochemical markers - quercetin - colorectal cancer
    Colorectal cancer (CRC) is hypothesized to be prevented by intake of fruits and vegetables that contain anti-carcinogenic compounds, including theflavonoidquercetinthat is found in apples and onions. In this thesis,quercetin'smechanisms of cancer-preventive action were studied both in vitro and in vivo . The in vitro experiments were performed using the human Caco-2 cell line as a model for CRC, andquercetinstabilized byascorbatein the culture medium. Unexpectedly,ascorbate-stabilizedquercetinshowed enhancement of cellular processes involved in CRC-development, including stimulated cell proliferation, reduced cell differentiation and enhancement of pathways that stimulate cell survival. Furthermore,transcriptomicsshowed thatquercetindownregulatedexpression of genes involved intumorsuppression and phase II metabolism, andupregulatedoncogenes. Comparison with Caco-2 cells exposed toquercetinin the absence ofascorbateshowed the opposite, i.e. anti-carcinogenic effects by thisflavonoid. This led to the hypothesis thatquercetin-induced reactive oxygen species that eradicatetumorcells were scavenged by vitamin C, causingtumorcell survival. Withoutascorbate, these reactive oxygen species may be responsible for anti-carcinogenic effects, pointing to beneficial effects of supposed adverse reactive intermediates.

    Subsequently, the CRC-modulating potency ofquercetinand its conjugaterutinwere investigated in a rat model for CRC.Quercetin, but not its conjugaterutindecreased thetumorincidence, which was associated with the blood plasma levels of this anti-oxidant, but not reflected by the putativepreneoplasticbiomarker lesions, designated aberrant crypt foci. The combination oftranscriptomicsand proteomics showed thatquercetininhibited the potentiallyoncogenicmitogen-activated proteinkinase(Mapk) pathway and enhanced expression oftumorsuppressor genes, cell cycle inhibitors, and genes involved inxenobioticmetabolism. In addition,quercetinaffected the energy production pathways, by increasing mitochondrial fatty acid degradation, and inhibitingglycolysis. This observation provided a new hypothesis pointing at another anti-carcinogenic mechanism forquercetin, based on an alteration in routes for energy metabolism, shifting them infavorof non-tumorlike pathways like mitochondrial fatty acid degradation at the cost of thetumor-likeglycolyticpathway for cellular energy supply.

    Overall, the studies presented in the present thesis provided new hypotheses for the mode of action ofquercetinas an anti-tumoragent, but it appeared that the actual dose needed to exert this beneficial effect amounted to about 60 - 100 times the already relatively high prescribed dose forquercetinsupplements. Therefore, it is concluded that health claims on the use ofquercetinas an anti-cancer agent need better scientific support.
    Towards functional effects of polyphenols : modulation of energy metabolism revealed
    Boer, V.C.J. de - \ 2007
    Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): Jaap Keijer; Peter Hollman. - [S.l.] : S.n. - ISBN 9789085046080 - 184
    quercetine - weefselverdeling - colorectaal kanker - energiemetabolisme - quercetin - tissue distribution - colorectal cancer - energy metabolism
    A diet rich in fruits and vegetables contains high levels of polyphenols (up to 1 gram per day). Epidemiological studies suggest that a high dietary intake of selected polyphenols can be protective against development of cardiovascular heart diseases in humans. In addition, mechanistic studies demonstrate that polyphenols possess beneficial properties ininvitro and animal model systems. Due to the possible beneficial health effects of polyphenols, they are currently being sold extensively as food supplements. However, the basis for most of the health claims attributed to polyphenols in food supplements is often very small. Our objective was to elucidate relevant mechanisms of action of selected polyphenols. We studied the tissue distribution and in vivo physiological effects of quercetin (a polyphenol abundant in the human diet) after chronic dietary exposure, followed by in vitro elucidation of possible biological mechanisms. We revealed lungs as novel tissue target of quercetin and demonstrated that dietary quercetin alters fatty acid catabolism pathways in rats. In addition, dietary quercetin lowered tumor incidence in the colon of rats in a model of colon carcinogenesis. Furthermore, a major in vivo metabolite of quercetin, quercetin 3-O-glucuronide, opposed the effect of quercetin aglycone on SIRT1 activation in vitro , whereas quercetin 3-O-glucuronide attenuated glucose utilization in cultured adipocytes in a similar fashion as quercetin aglycone. Although we used high dietary dosages of quercetin and further studies should elucidate physiological effects of a normal dietary intake of polyphenols, the experiments described in this thesis point to a possible beneficial effect of dietary polyphenols. However, as long as the molecular mechanisms in humans are unknown and the risk of increasing dietary intakes of polyphenols via food supplements is not thoroughly investigated, there is no scientific justification for supplementing the diet with large amounts of polyphenols. Nevertheless, our approach successfully identified modulation of energy metabolism by polyphenols as an important process involved in mediating the possible health effects associated with dietary polyphenol intake.
    Mechanisms of toxic action of the flavonoid quercetin and its phase II metabolites
    Woude, H. van der - \ 2006
    Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): Gerrit Alink. - Wageningen : Ponsen & Looijen - ISBN 9789085043492 - 229
    quercetine - werkwijze - metabolische detoxificatie - risicoschatting - quercetin - mode of action - metabolic detoxification - risk assessment
    During and after absorption in the intestine, quercetin is extensively metabolised by the phase II biotransformation system. Because the biological activity of flavonoids is dependent on the number and position of free hydroxyl groups, a first objective of this thesis was to investigate the consequences of phase II metabolism of quercetin for its biological activity. For this purpose, a set of analysis methods comprising HPLC-DAD, LC-MS and 1 H NMR proved to be a useful tool in the identification of the phase II metabolite pattern of quercetin in various biological systems. These studies showed that the 3'- and 4'-hydroxyl groups of quercetin, (catechol hydroxyl groups) were important targets for methylation, sulfation and glucuronidation. Methylation of a catechol hydroxyl group of quercetin proved to decrease the pH-dependent radical scavenging capacity of the compound, both by increasing its pK a for deprotonation and by decreasing its electron-donating properties. Methylation of a catechol hydroxyl group had a similar effect as replacement of the hydroxyl group by a hydrogen atom. Regarding the pro-oxidant properties of quercetin, methylation of a catechol hydroxyl group of quercetin did not eliminate the pro-oxidant chemistry of quercetin, reflected in the formation of covalent adducts with glutathione upon oxidation of quercetin by horseradish peroxidase. However, methylated quercetin proved to form only 42% of the level of DNA adducts in exposed cells as compared to a similar amount of unconjugated quercetin, indicating that methylation of quercetin attenuates also this biological reactivity towards DNA.

    A second objective of this thesis was to obtain more insight into the possible toxic effects of quercetin by studying various mechanisms that might be relevant in the context of carcinogenesis. Quercetin appeared to have a biphasic effect on the proliferation of cancer cell lines expressing the estrogen receptor (ER). The stimulation of cancer cell proliferation was ER-dependent and appeared to occur at concentrations that are physiologically relevant in humans. With respect to the pro-oxidant activity of quercetin, peroxidase- and tyrosinase-type oxidative enzyme activity did not play a major role in the intracellular formation of covalent adducts of quercetin with DNA and protein, indicating that the formation of covalent adducts of quercetin with cellular macromolecules might also be relevant in cell types lacking oxidative enzyme activity. Furthermore, the covalent quercetin DNA adducts were of transient nature, which may either eliminate or attenuate the adverse effects of covalent DNA adduct formation. The studies presented in this thesis provided indications for the dualistic character of quercetin, regarding its role in the process of cancer development.
    Studies on the pro-oxidant chemistry of flavonoids
    Awad, H.M. - \ 2002
    Wageningen University. Promotor(en): I.M.C.M. Rietjens; P.J. van Bladeren; J. Vervoort. - S.l. : S.n. - ISBN 9789058085887 - 133
    flavonoïden - oxidatiemiddelen - antioxidanten - quercetine - structuuractiviteitsrelaties - hplc - kernmagnetische resonantiespectroscopie - massaspectrometrie - flavonoids - oxidants - antioxidants - quercetin - structure activity relationships - hplc - nuclear magnetic resonance spectroscopy - mass spectrometry

    There is currently much interest in the development of functional foods aiming at the prevention of the development of some diseases, for example cancer, by the introduction of selected natural substances at elevated levels into the diet. The rationale for this approach is based especially on epidemiological data that indicate that food items containing such chemicals may reduce the risk of these diseases in humans. Epidemiological studies indicate, for example, that diets rich in fruit and vegetables protect against a variety of diseases, including heart diseases and certain forms of cancer. However, identification of the actual ingredient in a specific diet responsible for the beneficial health effects remains an important bottleneck for translating observational epidemiology to development of a functional food ingredient. The protection against cancer afforded by fruit and vegetables has been attributed to antioxidant micronutrients such as vitamin C, beta-carotene and vitamin E, which may act at many sites, including the stomach, intestine, lung and bladder. However, present scientific attention is focusing as well on the significance of other minor dietary components, notably the flavonoids as protectants against disease. Flavonoids are widespread in nature and are found in considerable quantities in fruits, vegetables, seeds, peel and tubers. The average Western diet may provide up to 1 g of flavonoids per day. Numerous in vitro studies show that flavonoids are potent antioxidants and metal chelators. Their potential as anti-inflammatory, antiallergic and antiviral compounds has also attracted attention. These studies provide the basis for the present rapidly increasing interest for the use of flavonoids as functional food ingredients. As a result increased human exposure to flavonoids can be expected in the near future. In shops and at the internet, food and food supplements based on (iso)flavonoids as functional ingredients are marketed. This, although hard scientific data supporting the health claims as well as data allowing a balanced risk-benefit evaluation are lacking. For flavonoids increased future human exposure regimens induce the question on their pro-oxidant chemistry. There is considerable evidence that some flavonoids are mutagenic in both bacterial and mammalian experimental systems. A high incidence of gastric cancer in some human populations has been linked to consumption of wine containing potentially mutagenic flavonoids (Tamura et al. , Proc. Natl. Acad. Sci. USA. 77, 4961-4965, 1980, Hoey et al. , Am. J. Epidemiol., 113, 669-974, 1981). Relatively little is understood about either the toxicity or protection afforded by flavonoids in humans.

    Since flavonoid quinone/quinone methides have been suggested as the major metabolites responsible for the possible pro-oxidant toxicity and mutagenicity of flavonoids, characterisation of flavonoid quinone chemistry is of importance. However, little information is available on the structure and reactivity of these flavonoid oxidation products. Therefore, the objective of this thesis was to investigate the pro-oxidant chemistry of flavonoids and to perform structure activity studies on the chemical behaviour of 3',4'-dihydroxyflavonoids with special emphasis on the nature and reactivity of the quinone/quinone methide type metabolites formed. Using the GSH trapping method, HPLC, LC/MS, MALDI-TOF, 1H NMR, 13C NMR and quantum mechanical computer calculations the quinone/quinone methide chemistry of a series of 3',4'-dihydroxyflavonoids could be characterised.

    The results provide insight in structure-activity-relationships for the pro-oxidant chemistry of these electrophilic quinone/quinone methide flavonoid metabolites. The results obtained also reveal an unexpected pH-dependent electrophilic behaviour of B ring catechol flavonoids. Furthermore the results of this thesis also reveal, for the first time, evidence for the pro-oxidative chemistry of quercetin in a cellular in vitro model. The formation of these glutathionyl-flavonoid adducts provides evidence for the actual pro-oxidative formation of reactive quinone type metabolites from B ring catechol flavonoids in the selected cellular in vitro model using melanoma cells. Oxidation of the catechols to quinones and their isomeric quinone methides generates potent electrophiles that could alkylate DNA. Interestingly, the structural requirements essential for good antioxidant activity match the requirements essential for pro-oxidant action and quinone methide formation. Altogether, the pro-oxidant behaviour of flavonoids and their quinone/quinone methides are far from straight forward and need to be re-evaluated especially in the framework of the risk-benefit evaluation of the use of these flavonoids as functional food ingredients and/or food supplements.


    Er is momenteel veel interesse voor de ontwikkeling van functionele voedingsmiddelen (functional foods), met als doel het voorkomen van het ontstaan van ziekten zoals bijvoorbeeld kanker, via het in verhoogde mate introduceren van geselecteerde natuurlijke bestanddelen in het dieet. De basis voor deze aanpak wordt momenteel met name gevonden in epidemiologische studies die laten zien dat diëten rijk aan specifieke voedselcomponenten of ingrediënten de kans op bepaalde ziekten bij de mens verlagen. Zo geven epidemiologische studies bijvoorbeeld aan dat diëten die rijk zijn aan fruit en groenten beschermen tegen een aantal ziekten zoals hartziekten en bepaalde vormen van kanker. Echter, het identificeren van de belangrijke ingrediënten in het betreffende dieet die het gezondheidsbevorderende effect tot stand brengen is een knelpunt voor het vertalen van de resultaten uit de epidemiologie naar de ontwikkeling van een functioneel voedingsingrediënt.

    De bescherming tegen kanker door groenten en fruit is toegeschreven aan antioxidanten zoals vitamine C, beta-caroteen en vitamine E, die op vele plaatsen in het lichaam, zoals de maag, darmen, long en de blaas actief zijn. Wetenschappelijk wordt momenteel veel aandacht besteed aan het mogelijke belang van andere belangrijke dieet componenten, zoals flavonoïden, als beschermende ingrediënten tegen ziekte. Flavonoïden komen in de natuur veel voor, en worden met name in hoge concentraties gevonden in fruit, groenten, knollen en zaden. Het gemiddelde Westerse dieet bevat ongeveer 1 gram aan flavonoïden per dag.

    Vele in vitro studies tonen aan dat flavonoïden goede antioxidanten en metaal chelatoren zijn. Daarnaast hebben ze anti-inflammatoire, anti-allergische en anti-virale eigenschappen die van belang worden geacht. Deze bevindingen verschaffen de basis voor de momenteel snel groeiende interesse om flavonoïden te gebruiken als functionele voedingsingrediënten. Als gevolg hiervan zou er in de nabije toekomst een toename in de opname van flavonoïden via het dieet verwacht kunnen worden. In winkels en via het internet worden voedingsmiddelen en voedingssupplementen gebaseerd op (iso)flavonoïden als functionele voedingsingrediënten verkocht. Dit, terwijl zowel de wetenschappelijke onderbouwing voor de gezondheidsclaims als gegevens die een gebalanceerde "risk-benefit" analyse mogelijk maken, nog ontbreken. In het geval van verhoogde toekomstige blootstelling van mensen aan flavonoïden worden voor de risk-benefit evaluatie vragen van belang rond hun mogelijk pro-oxidatieve chemisch gedrag. Er zijn aanwijzingen dat sommige flavonoïden mutageen zijn in zowel bacteriële als zoogdier in vitro test systemen. Een verhoogde mate aan maagkanker in bepaalde humane populaties is in verband gebracht met de consumptie van wijn met daarin mogelijk mutagene flavonoïden (Tamura et al. , Proc. Natl. Acad. Sci. USA. 77, 4961-4965, 1980, Hoey et al. , Am. J. Epidem., 113, 669-974, 1981). Alles samenvattend is er eigenlijk weinig bekend van de schadelijke maar ook van de gezondheidsbevorderende effecten van flavonoïden.

    Omdat flavonoid chinon/chinon methides genoemd zijn als de belangrijkste metabolieten die verantwoordelijk zouden zijn voor de mogelijke pro-oxidatieve toxiciteit en mutageniteit van flavonoïden, is karakterisering van deze pro-oxidant chemie van flavonoïden van belang. Echter er is weinig bekend over de structuur en de reactiviteit van deze flavonoid oxidatie producten. Daarom was het doel van deze studie de pro-oxidant chemie van flavonoïden te onderzoeken en een structuur-activiteits studie uit te voeren naar het chemische gedrag van 3',4'-dihydroxyflavonoïden. Daarbij werd speciale aandacht besteed aan de aard en reactiviteit van de gevormde chinon/chinon methide metabolieten. Met behulp van de GSH-trapping methode, HPLC, LC/MS, MALDI-TOF, 1H-NMR, 13C-NMR en kwantum-chemische computerberekeningen kon de chinon/chinon methide chemie van een serie 3',4'-dihydroxyflavonoiden gekarakteriseerd worden.

    De verkregen resultaten geven inzicht in de structuur-activteits relaties voor de pro-oxidatieve chemie van de electrofiele chinon /chinon methides metabolieten van de flavonoïden. De resultaten laten ook een onverwacht effect zien van de pH op het electrofiele gedrag van de B-ring catechol flavonoïden. Bovendien laten de resultaten van het proefschrift zien dat zelfs onder reducerende omstandigheden in een cellulair in vitro model (melanoma cellen) de pro-oxidatieve chemie van quercetine van belang kan zijn. Met name de vorming van glutathion-flavonoid conjugaten is een bewijs dat in het gekozen cellulaire model de pro-oxidatieve vorming van reactieve flavonoid chinon/ chinon methide metabolieten is opgetreden. Oxidatie van de catecholen naar chinonen en hun isomere chinon methides genereert electrofielen die DNA kunnen alkyleren. Van belang is dat de structurele randvoorwaarden die een flavonoid een goede antioxidant maken gelijk blijken te zijn aan de structurele kenmerken die essentieel zijn voor pro-oxidant gedrag en chinon methide vorming.

    Al met al is de pro-oxidant chemie van flavonoïden en van hun chinon /chinon methides verre van recht toe recht aan gebleken en zou de pro-oxidatieve chemie en de toxiciteit van de flavonoïden in het kader van hun gebruik als functional food ingredienten beter onderzocht en afgewogen moeten worden, rekening houdend met hun mogelijk gezondheidsbevorderende effecten.

    Bioavailability of flavonoids and cinnamic acids and their effect on plasma homosysteine in humans
    Olthof, M.R. - \ 2001
    Wageningen University. Promotor(en): M.B. Katan; P.C.H. Hollman. - S.l. : S.n. - ISBN 9789058084170 - 135
    flavonoïden - kaneelzuur - homocysteïne - bloedplasma - biologische beschikbaarheid - mens - quercetine - theaflavine - chlorogeenzuur - hart- en vaatziekten - flavonoids - cinnamic acid - homocysteine - blood plasma - bioavailability - man - quercetin - theaflavine - chlorogenic acid - cardiovascular diseases

    Dietary antioxidants might prevent oxidative damage to tissues and therefore protect against cardiovascular disease and cancer. Dietary phenols are strong antioxidants in vitro but their role in vivo is uncertain. Furthermore, there are only limited data on their bioavailability in humans. The aim of this thesis was to investigate whether bioavailability data on flavonoids and cinnamic acids support the hypothesis that they can affect health in humans . Because the group of phenols in foods is huge, we focussed our research on major phenols in foods; the flavonol quercetin, black tea phenols and chlorogenic acid (5-caffeoylquinic acid). We studied their bioavailability and effect on plasma homocysteine in humans, a potential risk factor for cardiovascular disease.

    The bioavailability of quercetin and chlorogenic acid depends upon their conjugated moieties. Hollman et al. found that the bioavailability of quercetin-3-rutinoside, a major flavonol in tea, was only 20% of that of quercetin-4'-glucoside. We found that transformation of quercetin-3-rutinoside into quercetin-3-glucoside will improve its bioavailability because the 3-glucoside had the same high bioavailability as the 4'-glucoside. Caffeic acid is a major phenol in coffee, but it is present as a conjugate with quinic acid, called chlorogenic acid. We found that the conjugation of caffeic acid with quinic acid hinders absorption in humans: absorption of chlorogenic acid was only 30% of that of its caffeic acid moiety.

    Furthermore, we found that chlorogenic acid, black tea solids and quercetin-3-rutinoside are extensively metabolized in the human body, mainly before they reach the circulation. Their metabolites have no, or less, antioxidant activity in vitro than their parent phenols. Therefore the role of dietary phenols as antioxidants in vivo might be less important than suggested by their in vitro antioxidant activity.

    Coffee consumption increases plasma homocysteine, a potential risk factor for cardiovascular disease. Chlorogenic acid from coffee is partly responsible for the homocysteine-raising effect of coffee, because we found that it increased plasma homocysteine. Black tea solids also raised plasma homocysteine, whereas quercetin-3-rutinoside did not. Furthermore, we found that glycination of metabolites of phenols in the body is not involved in the homocysteine-raising effect of phenols.

    In conclusion, chlorogenic acid, tea phenols and quercetin are available in the human body, but their effects on health are uncertain. Further research on bioavailability and health effects of dietary phenols is needed.

    Determinants of the absorption of the dietary flavonoid quercetin in man
    Hollman, P.C.H. - \ 1997
    Agricultural University. Promotor(en): J.G.A.J. Hautvast; M.B. Katan; O. Korver. - S.l. : Hollman - ISBN 9789054856917 - 187
    flavonen - quercetine - darmabsorptie - flavones - quercetin - intestinal absorption

    Oxidation of low density lipoprotein is hypothesised to play an important role in the development of cardiovascular disease. It might be prevented by dietary antioxidants. Quercetin is a dietary flavonoid antioxidant and its intake was inversely associated with cardiovascular disease in some studies. Absorption from the diet is a prerequisite for its potentially beneficial role. This thesis describes studies on the absorption and elimination kinetics of dietary quercetin in humans.

    To perform these absorption studies, we developed a postcolumn chelation technique for quercetin in HPLC with fluorescence detection using aluminum. Only flavonols that contain a free 3-hydroxyl and 4-keto oxygen binding site formed fluorescent complexes with Al 3+. This method improved detectability of quercetin 300 fold as compared to conventional UV detection.

    We studied the absorption of quercetin in healthy ileostomy subjects so as to avoid losses caused by colonic bacteria. Absorption of quercetin was 52 + 15% for quercetin glucosides found in onions, 17 + 15% for quercetin rutinoside a major quercetin glycoside of tea, and 24 + 9% for free quercetin aglycone.

    The time course of the plasma quercetin concentration was studied in normal subjects with an intact colon who ingested major dietary sources of quercetin, viz. fried onions containing glucose conjugates of quercetin, apples containing both glucose- and non-glucose quercetin glycosides, and of quercetin-3-rutinoside. Peak plasma levels of quercetin were reached <0.7 h after ingestion of the onions, 2.5 h after the apples, and 9 h after the rutinoside. Bioavailability of both quercetin from apples and of pure quercetin rutinoside was 30% relative to onions. Half-lives of elimination were independent of the quercetin source and were about 24 h.

    We confirmed that the sugar moiety of the glycoside is an important determinant of absorption in a study with volunteers who ingested solutions of pure quercetin-4'-glucoside and of pure quercetin-3-rutinoside.

    In conclusion, absorption of dietary quercetin glycosides can be appreciable and depends on the type of sugar moiety of the glycoside. We propose that the sodium-glucose cotransporter is involved in the absorption of quercetin-4'glucoside. Elimination of quercetin from the blood is slow. Repeated consumption of quercetin- containing foods therefore will lead to accumulation of quercetin in plasma.

    Absorptie- en dispositiekinetiek van quercetine- glycosiden bij de mens
    Hollman, P.C.H. ; Leeuwen, S.D. van; Gaag, M.S. van der; Mengelers, M.J.B. ; Trijp, J.M.P. van; Vries, J.H.M. de; Katan, M.B. - \ 1996
    Voeding 57 (1996)3. - ISSN 0042-7926 - p. 28 - 28.
    bloedstoornissen - hart- en vaatziekten - hart- en vaatstoornissen - chemische analyse - chemische samenstelling - chlorofyl - ziektepreventie - flavonen - flavonoïden - voedingsmiddelen - isoprenoïden - metabolisme - planten - porfyrinen - preventie - preventieve geneeskunde - quercetine - steroïden - vaatziekten - blood disorders - cardiovascular diseases - cardiovascular disorders - chemical analysis - chemical composition - chlorophyll - disease prevention - flavones - flavonoids - foods - isoprenoids - metabolism - plants - porphyrins - prevention - preventive medicine - quercetin - steroids - vascular diseases
    Flavonols and flavones in foods and their relation with cancer and coronary heart disease risk
    Hertog, M.G.L. - \ 1994
    Agricultural University. Promotor(en): J.G.A.J. Hautvast; D. Kromhout; M.B. Katan. - S.l. : Hertog - ISBN 9789054852247 - 151
    flavonen - flavonolen - flavonoïden - quercetine - hartziekten - carcinoom - neoplasma's - flavones - flavonols - flavonoids - quercetin - heart diseases - carcinoma - neoplasms
    Flavonoids are polyphenolic antioxidants occurring ubiquitously in vegetable foods. Flavonols and flavones inhibit chemically induced tumors in rodents. The flavonol quercetin also inhibits LDL oxidation and platelet aggregation in vitro . We therefore decided to investigate the relation between flavonoid intake and cancer and coronary heart disease risk in humans. The three flavonols quercetin, kaempferol, myricetin, and the two flavones luteolin and apigenin were selected because of their anticarcinogenic and antioxidant activities and because of their ubiquitous occurrence in foods. We first developed and validated a HPLC method for the quantitative determination of these flavonoids in foods. We then determined the flavonol and flavone content of 28 types of vegetables, 12 types of fruits and 9 types of beverages commonly consumed in The Netherlands. Quercetin was the main flavonoid and occurred in most fruits, beverages and in some vegetables. Mean intake of flavonols and flavones combined among Dutch adults was 23 mg/day, and main dietary sources of these flavonoids were tea (48 %), onions (38%), and apples (8 %). Mean flavonol and flavone intake of 805 men aged 65-84 years participating in the Zutphen Elderly Study 1985 was 26 mg/day. During five year followup period 75 men had a first diagnosis of cancer, of which 28 men had lung cancer. Thirty-four men died from all-cause cancer. Intake of flavonols and flavones in 1985 was not related to subsequent (lung) cancer morbidity ( P trend 0.54) and mortality ( P trend 0.51). Between 1985 and 1990 43 men died from coronary heart disease and 38 men had a first myocardial infarction. Intake of flavonols and flavones, expressed as tertiles of intake, was, independently from known risk- and confounding factors, inversely associated with mortality from coronary heart disease ( P trend 0.015) and incidence of a first myocardial infarction ( P trend 0.08). Average intake of flavonols and flavones in 16 cohorts participating in the Seven Countries Study around 1960 was also inversely related to mortality from coronary heart disease after 25 years of follow-up, but it was not related to cancer mortality. In multivariate regression analysis including saturated fat intake, flavonoid intake, and percentage of smokers as independent variables about 90 % of the total variance in coronary heart mortality was explained. Flavonol and flavone intake contributed about 9 % to the explained variance.

    We conclude that intake of flavonols and flavones may protect against coronary heart disease in humans, but that it does not seem to be an important determinant of cancer risk. However, more experimental, clinical, and epidemiological evidence is needed before firm conclusions on the health effects of these flavonoids can be drawn.

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