Dietary flavonols: chemistry, food content, and metabolism

Bioactive Compounds and Antioxidant Capacity of Exotic Fruits and Commercial Frozen Pulps from Brazil

The objective of this work was to characterize exotic fruits (cambuci, araça-boi, camu-camu, jaracatia, araça) and commercial frozen pulps (araça, cambuci, umbu, coquinho, pana, native passion fruit, cagaita) from Brazil in relation to their bioactive compounds contents and antioxidant capacity. Camu-camu (Myrciaria dubia) presented the highest vitamin C and total phenolics contents (397 and 1797 mg/100 gf.w., respectively) and the highest DPPH• scavenging capacity. Coquinho (Butia capitata) also showed a significant vitamin C content (43 mg/100 gf.w.). Among the commercial frozen pulps, cagaita presented the higher DPPH scavenging activity and inhibition of β-carotene bleaching. A good correlation between total phenols and DPPH scavenging activity was found for fruits (r = 0.997) and commercial frozen pulps (r = 0.738). However, no correlation was found for total phenols and inhibition of β-carotene bleaching. Quercetin and kaempferol derivatives were the main flavonoids present in all samples and cyanidin derivatives were detected only in camu-camu. Camu-camu and araça (Psidium guineensis) showed the highest total ellagic acid contents (48 and 63.5 mg/100 gf.w.). All commercial frozen pulps presented lower contents of bioactive compounds and antioxidant capacity than their respective fruits. According to our results, camu-camu and araça might be sources of bioactive compounds.

Simultaneous extraction of epimedin A, B, C and icariin from Herba Epimedii by ultrasonic technique

An ultrasonic-assisted extraction (UAE) procedure of epimedin A, epimedin B, epimedin C and icariin from Herba Epimedii was developed. The effects of ethanol concentration, ratio of liquid to solid, UAE time, extraction temperature and number of extraction cycles on the extraction yields of the four flavonoids from Herba Epimedii were investigated. The optimal UAE condition was found using orthogonal test: 50% (v/v) ethanol solution, liquid:solid ratio of 30 ml/g, ultrasonication duration 30 min, extraction temperature 50 degrees C and three extraction cycles. The UAE method showed a high reproducibility. Epimedin A, B, C and icariin in the crude extract exhibited photodegradation under ultraviolet irradiation. This UAE method was shown to be highly efficient compared with the conventional Soxhlet extraction and boiling extraction. The effect of ultrasound on cell destruction was examined by scanning electron microscopy. The contents of epimedin A, B, C and icariin in the leaves of 20 Epimedium species were determined using high-performance liquid chromatographic method following UAE method.

Deconjugation and degradation of flavonol glycosides by pig cecal microbiota characterized by Fluorescence in situ hybridization (FISH)

As the bioavailability of flavonoids is influenced by intestinal metabolism, we have investigated the microbial deconjugation and degradation of several flavonols and flavonol glycosides using the pig cecum in vitro model system developed in our group. For this model system the microbiota was directly isolated from the cecal lumen of freshly slaughtered pigs. The characterization of the cecal microbiota by fluorescence in situ hybridization (FISH) with 16S rRNA-based oligonucleotide probes confirmed the suitability of the model system for studying intestinal metabolism by the human microbiota. We have investigated the microbial degradation of quercetin-3-O-beta-d-rutinoside 1, quercetin-3-O-beta-d-glucopyranoside 2, quercetin-4'-O-beta-d-glucopyranoside 3, quercetin-3-O-beta-d-galactopyranoside 4, quercetin-3- O-beta-d-rhamnopyranoside 5, quercetin-3- O-[alpha-l-dirhamnopyranosyl-(1-->2)-(1-->6)-beta-d-glucopyranoside 6, kaempferol-3-O-[alpha-l-dirhamnopyranosyl-(1-->2)-(1-->6)-beta-d-glucopyranoside 7, apigenin 8, apigenin-8- C-glucoside (vitexin) 9, and feruloyl-O-beta-d-glucopyranoside 10 (100 microM), representing flavonoids with different aglycones, sugar moieties, and types of glycosidic bonds. The degradation rate was monitored using HPLC-DAD. The flavonol O-glycosides under study were almost completely metabolized by the intestinal microbiota within 20 min and 4 h depending on the sugar moiety and the type of glycosidic bond. The degradation rates of the quercetin monoglycosides showed a clear dependency on the hydroxyl pattern of the sugar moiety. The degradation of 2 with all hydroxyl groups of the glucose in the equatorial position was the fastest. The intestinal metabolism of di- and trisaccharides was much slower compared to the monoglycosides. The structure of the aglycone has not much influence on the intestinal metabolism; however, the type of glycosidic bond ( C- or O-glycoside) has substantial influence on the degradation rate. The liberated aglycones were completely metabolized within 8 h. Phenolic compounds such as 3,4-dihydroxyphenylacetic acid 12, 4-hydroxyphenylacetic acid 13, and phloroglucinol 18 were detected by GC-MS as main degradation products.

Antigenotoxic effects of quercetin, rutin and ursolic acid on HepG2 cells: evaluation by the comet assay

In the present study, the chemoprotective effects of quercetin, rutin and ursolic acid on tert-butyl hydroperoxide (t-BHP)-induced DNA damage in a human hepatoma cell line (HepG2) were investigated by the comet assay. To determine whether protection was due to direct chemical interactions alone or to cellular-mediated responses three different types of treatments were used: simultaneous incubation of cells with individual test compounds and the toxicant; pre-treatment with test compound before addition of the toxicant followed or not by a recovery period. The expression of Hsp70 was quantified by Western blotting to test the involvement of heat shock proteins in the cellular responses to the test compounds. In addition, effects on proliferation were evaluated by the MTT assay. The results show that quercetin and ursolic acid prevented DNA damage and had antiproliferative properties in HepG2 cells suggesting an anticarcinogenic potential for these compounds. The protective effects of quercetin against t-BHP-induced DNA damage seem to be due to both direct effects on t-BHP toxicity and to cellularly mediated indirect effects which reflect the potentiation of the cellular antioxidant defenses. Ursolic acid seems to exert effects only through cellularly mediated mechanisms since it was not protective in simultaneous incubation. Quercetin and ursolic acid also showed to increase the rate of DNA repair. Rutin did not have effects at any level. These results, obtained with liver cells, emphasize and confirm the chemopreventive potential of quercetin and ursolic acid, which may help explain the lower cancer incidence in human population with high dietary intakes of fruits and vegetables. These results also demonstrate that Hsp70 is not involved in the observed effects in HepG2.

Organically fertilized onions (Allium cepa L.): effects of the fertilizer placement method on quercetin content and soil nitrogen dynamics

Field-cured onions cv. Hyskin ( Allium cepa L.) supplied with organic nitrogen fertilizer were studied. The fertilizer was applied by broadcasting and harrowing, broadcasting and rotary cultivation, or placement between rows. Nitrogen dynamics were monitored throughout the growing season by soil sampling. Variation in quercetin content in the onion scales was analyzed by HPLC. The organically fertilized onions were compared with inorganically fertilized onions grown in the same field. Inoculation with arbuscular mycorrhizal fungi (AMF) in the row at sowing or during commercial transplant production was tested but did not significantly affect mycorrhizal root colonization levels in the field. Onions that received no fertilizer at all or that had fertilizer placed between rows had better establishment, probably due to more favorable soil nitrogen concentrations for seedling emergence. Broadcast application led to higher nitrogen concentration in the root zone, resulting in fewer but larger individual onions. Quercetin levels were not significantly altered as a result of nitrogen fertilizer source (inorganic or organic), application method, or mycorrhizal inoculation. However, variation between years was significant, with quercetin levels in 2004 almost twice as high as those in 2005.

What is Xenohormesis?

Polyphenols such as resveratrol and quercetin, which are produced by stressed plants, activate sirtuin enzymes and extend the lifespan of fungi and animals, ostensibly by mimicking the beneficial effects of caloric restriction. This observation raises an interesting question: Why should foreign molecules that are non-nutritive and seemingly unrelated to any endogenous molecule modulate the same biochemical pathways that mediate the response to an energy deficit? A possible explanation is that the sirtuin enzymes have evolved to respond to plant stress molecules as indicators of an impending deterioration of the environment. This idea has become known as the Xenohormesis Hypothesis, the name stemming from a combination of the prefix xeno-(for stranger) with hormesis (a protective response induced by mild stress). Here we review the evidence for xenohormesis in a broader context, taking into account the diverse spectrum of phytochemicals to which animals are exposed. We also consider alternative hypotheses that may explain some of the beneficial effects of plant-based foods. We suggest that xenohormesis, defined as an adaptive response in the physiology of an organism to molecular cues that are neither nutritive nor direct stressors, most likely occurs at some level. Whether this can fully or partially account for the beneficial effects of resveratrol and other phytochemicals remains to be seen. However, there is already sufficient cause to re-evaluate the relationship between complex organisms, including humans and their food.

The flavonoid silibinin decreases glucose-6-phosphate hydrolysis in perfused rat hepatocytes by an inhibitory effect on glucose-6-phosphatase

BACKGROUND/AIMS

The flavonoid silibinin has been reported to be beneficial in several hepatic disorders. Recent evidence also suggests that silibinin could be beneficial in the treatment of type 2 diabetes, owing to its anti-hyperglycemic properties. However, the mechanism(s) underlying these metabolic effects remains unknown.

METHODS

The effects of silibinin on liver gluconeogenesis were studied by titrating hepatocytes from starved rats with sub-saturating concentrations of various exogenous substrates in a perifusion system. Hepatocytes from fed rats were also used to investigate glycogenolysis from endogenous glycogen. The effect of silibinin on glucose-6-phosphatase kinetics was determined in intact and permeabilized rat liver microsomes.

RESULTS

Silibinin induced a dose-dependent inhibition of gluconeogenesis associated with a potent decrease in glucose-6-phosphate hydrolysis. This effect was demonstrated whatever the gluconeogenic substrates used, i.e. dihydroxyacetone, lactate/pyruvate, glycerol and fructose. In addition, silibinin decreased the glucagon-induced stimulation of both gluconeogenesis and glycogenolysis, this being associated with a reduction of glucose-6-phosphate hydrolysis. Silibinin inhibits glucose-6-phosphatase in rat liver microsomes in a concentration-dependent manner that could explain the decrease in glucose-6-phosphate hydrolysis seen in intact cells.

CONCLUSION

The inhibitory effect of silibinin on both hepatic glucose-6-phosphatase and gluconeogenesis suggests that its use may be interesting in treatment of type 2 diabetes.

QSAR modeling of antiradical and antioxidant activities of flavonoids using electrotopological state (E-State) atom parameters

In the present paper QSAR modeling using electrotopological state atom (E-state) parameters has been attempted to determine the antiradical and the antioxidant activities of flavonoids in two model systems reported by Burda et al. (2001). The antiradical property of a methanolic solution of 1, 1-diphenyl-2-picrylhydrazyl (DPPH) and the antioxidant activity of flavonoids in a β-carotenelinoleic acid were the two model systems studied. Different statistical tools used in this communication are stepwise regression analysis, multiple linear regressions with factor analysis as the preprocessing step for variable selection (FA-MLR) and partial least squares analysis (PLS). In both the activities the best equation is obtained from stepwise regression analysis, considering, both equation statistics and predictive ability (antiradical activity: R 2 = 0.927, Q2 = 0.871 and antioxidant activity: R 2 = 0.901, Q2 = 0.841).

A prospective study of dietary flavonoid intake and incidence of epithelial ovarian cancer

Flavonoids are antioxidant compounds found in plants, including fruits, vegetables and tea. No prior prospective studies have examined the association between intake of flavonoids in the flavonol and flavone subclasses and ovarian cancer risk. We analyzed the association between intake of 5 common dietary flavonoids and incidence of epithelial ovarian cancer among 66,940 women in the Nurses' Health Study. We calculated each participant's intake of myricetin, kaempferol, quercetin, luteolin and apigenin from dietary data collected at multiple time points, and used Cox proportional hazards regression to model the incidence rate ratio (RR) of ovarian cancer for each quintile of intake. Our analysis included 347 cases diagnosed between 1984 and 2002, and 950,347 person-years of follow-up. There was no clear association between total intake of the 5 flavonoids examined and incidence of ovarian cancer (RR = 0.75 for the highest versus lowest quintile, 95% confidence interval [CI] = 0.51-1.09). However, there was a significant 40% decrease in ovarian cancer incidence for the highest versus lowest quintile of kaempferol intake (RR = 0.60, 95% CI = 0.42-0.87; p-trend = 0.002), and a significant 34% decrease in incidence for the highest versus lowest quintile of luteolin intake (RR = 0.66, 95% CI = 0.49-0.91; p-trend = 0.01). There was evidence of an inverse association with consumption of tea (nonherbal) and broccoli, the primary contributors to kaempferol intake in our population. These data suggest that dietary intake of certain flavonoids may reduce ovarian cancer risk, although additional prospective studies are needed to further evaluate this association. If confirmed, these results would provide an important target for ovarian cancer prevention.

Estimation of daily human intake of food flavonoids

The daily intake of food flavonoids was determined using a semiquantitative food frequency questionnaire (FFQ) and a four day non consecutive food diary (4DFR) in a group of 45 female Flemish dietitians. The subjects were asked to report their food intake three times: day 1 using the FFQ (FFQ1); between day 2 and 13 using a four day non consecutive food diary (4DFR); and again the FFQ on day 14 (FFQ2). The total flavonoid intake in mg/day as estimated with the different methods were respectively (mean and SD) for FFQ1 166.0 +/- 146.6 mg/day; for 4DFR 203.0 +/- 243.2 mg/day; and for FFQ2 158.3 +/- 151.8 mg/day. There was a significant different estimate for the amount of flavan-3-ols, flavanones and flavones when comparing the two FFQs with the 4DFR. The two research methods classified 88% of the 45 dietitians in the same or in an adjacent quartile for total flavonoid intake. The findings of this study indicate that the developed FFQ seems to be a simple and reliable method to assign subjects in quartiles of flavonoid intake.

Flavonoid composition of Citrus juices

In the early nineties the presence of flavonoids in Citrus juices began to attract the attention of a number of researchers, as a result of their biological and physiological importance. This short review will explore two different aspects. The first part will focus on analytical techniques for the characterization of juices from different Citrus fruits regarding their flavonoid content (even if present in only trace amounts), concentrating on the most widely used methods (LC-MS and LC-MS-MS). The second part analyzes data reported in the literature regarding the composition of Citrus juices. The main components that have been detected so far are flavanone-O-glycosides and flavone-O- or -C-glycosides. The presence of such derivatives in various hand-squeezed and industrial juices is discussed, with special emphasis on their correlation to different species.

Food content, processing, absorption and metabolism of onion flavonoids

The question as to how far the development of chronic diseases in humans depends on diet still remains open. Simultaneously, epidemiological studies suggest the consumption of a flavonoids rich diet might decrease the risk of degenerative changes and certain diseases. The intake of this group of compounds as to quality and quantity depends on dietary habits and a widespread presence of quercetin in the diet makes this compound one of the key factors. Onion, one of the richest and most common quercetin sources, was particularly often studied in different aspects. Quercetin is present in onion mainly as glycosides, of which the distribution within the onion bulb changes in onion processing, and biological activities attracted a lot of attention. Especially antioxidative activity demonstrated in vitro was initially associated with most of the beneficial effects of quercetin on the human body. However, after ingestion quercetin undergoes extensive metabolism and microbial action resulting in its altered or degraded structure; therefore, most of the effects shown in in vitro experiments with the pure compound cannot be directly extrapolated to in vivo systems. Yet, this does not mean that quercetin simultaneously loses its positive impact on consumer health. Even after being metabolized it may still affect the redox balance by inducing antioxidative and detoxifying enzymes or compounds which may be involved in sustaining homeostasis.

Physicochemical study of floranol, its copper(II) and iron(III) complexes, and their inhibitory effect on LDL oxidation

The antioxidant activity of floranol (3,5,7,2'-tetrahydroxy-6-methoxy-8-prenylflavanone), a new flavonoid isolated from the roots of Dioclea grandiflora, was evaluated by the inhibition of human low-density lipoprotein (LDL) oxidation. Floranol increased its oxidation lag-phase significantly in a dose-dependent manner. As the antioxidant mechanism may involve metal coordination, we have undertaken a detailed study of floranol interactions with Cu(II) and Fe(III) by combination of UV-visible (UV-Vis) and mass spectrometries and cyclic voltammetry. The acidity constants of the ligand as well as the stability constants of the metal complexes were calculated. The pKa values of 6.58, 11.97 and 13.87 were determined and the following acidity order is proposed 7-OH>5-OH>2'-OH. The best fit between experimental and calculated spectra was obtained assuming the formation of two Cu(II) complexes: [CuL] logbeta=19.34+/-0.05 and [CuL(2)](2-) logbeta=26.4+/-0.10 and three Fe(III) complexes: [FeL(3)](3-) logbeta=44.72+/-0.09, [FeL(2)](-) logbeta=35.32+/-0.08 and [FeL](+) logbeta=19.51+/-0.04. In addition, copper and iron reduction is less favorable in the presence of floranol. These results indicate that floranol can efficiently bind Cu(II) and Fe(III) ions thus preventing their effect on LDL oxidation.

Metabolism of flavone C-glucosides and p-coumaric acid from antioxidant of bamboo leaves (AOB) in rats

The metabolism of flavone C-glucosides and p-coumaric acid from antioxidant of bamboo leaves (AOB) in rats is discussed systematically in the present study. Following single oral administration of AOB, p-coumaric acid was detected in plasma but not in gastrointestinal tract extracts and faeces, and the corresponding absorption pharmacokinetic curve at different time points showed a prolonged elimination phase with p-coumaric acid being detected in the kidneys and excreted as its original form (1 x 80 (sd 0 x 24) % and 1 x 90 (sd 0 x 26) % at 12 and 24 h, respectively). However, the four flavone C-glucosides orientin, homoorientin, vitexin and isovitexin were poorly absorbed in the gastrointestinal tract. More than 50 % recovery of flavone C-glucosides was determined at 12 h and faeces containing these four analytes (21 x 23 (sd 1 x 92) %) were excreted at 24 h. These data suggested that the effective time these compounds were in the colon was long enough so that they could exert their antioxidant activity and scavenge free radicals. Besides the excretion of the original forms, moieties of the flavone C-glucosides were hydrolysed by deglycosylation and the opening of the heterocyclic C ring. Some small molecules such as phloroglucinol (PG), hydrocaffeic acid (HCA) and phloretic acid (PA) were detected and identified as metabolites of the flavone C-glucosides. In the present work, we compared the metabolic fate of flavone C-glucosides to that of flavone O-glucosides in rats, and evaluated the absorption, tissue distribution and excretion of flavone C-glucosides in AOB on their metabolism for the first time.

Synthetic chalcones, flavanones, and flavones as antitumoral agents: biological evaluation and structure-activity relationships

A series of synthetic chalcones, flavanones, and flavones has been synthesized and evaluated for antitumor activity against the human kidney carcinoma cells TK-10, human mammary adenocarcinoma cells MCF-7 (estrogen receptor-positive), and human colon adenocarcinoma cells HT-29. The most active series is the chalcone ones with the best results against TK-10 and HT-29 cells. Fourteen out of 53 analyzed compounds resulted very active against at least two of the studied tumoral cells. Alkaline single cell gel electrophoresis, comet assay, was performed as a study of the chromosomal aberrations promoted by the compounds on normal cells. Four active and two inactive chalcones were studied in the comet assay against normal human kidney cells (HK-2). A structure-activity relationship analysis of these compounds was performed and for 4- and 3,4-disubstituted derivatives a quantitative correlation was obtained in the case of anti-HT-29 activity.

Flavonoids inhibit the formation of the cross-linking AGE pentosidine in collagen incubated with glucose, according to their structure

BACKGROUND

Glycoxidation of collagens contributes to development of vascular complications in diabetes.

AIM OF THE STUDY

Since flavonoids are potent antioxidants present in vegetal foods, it was interesting to examine their effect on the formation of a cross-linking advanced glycation endproduct, pentosidine, in collagens.

METHODS

Collagen was incubated with glucose (250 mM), in the presence of different flavonoids. Pentosidine was measured by HPLC, hydroxyproline colorimetrically.

RESULTS

Monomeric flavonoids (25 and 250 microM) markedly reduced pentosidine/hydroxyproline values in a concentration- and structure-dependent manner. In decreasing order of their specific inhibitory activity, they rank as follows: myricetin > or = quercetin > rutin > (+)catechin > kaempferol. Thus 3'-OH or 4-oxo + Delta(2-3) increase the inhibitory activity; conjugation by Rha-Glc on 3-OH decreases it. Procyanidin oligomers from grape seed were more active than pine bark procyanidin oligomers: this may be related to the galloyl residues present in grape seed oligomers only. Procyanidin oligomers are known to be cleaved into monomers in the gastric milieu and monomeric flavonoids to be absorbed and recovered at micromolar concentrations (with a long plasmatic half-life) in extracellular fluids, in contact with collagens.

CONCLUSION

Flavonoids are very potent inhibitors of pentosidine formation in collagens. They are active at micromolar concentrations; these might be achieved in plasma of diabetic patients after oral intake of natural flavonoids.

DFT study of quercetin activated forms involved in antiradical, antioxidant, and prooxidant biological processes

Quercetin, one of the most representative flavonoid compounds, is involved in antiradical, antioxidant, and prooxidant biological processes. Despite a constant increase of knowledge on both positive and negative activities of quercetin, it is unclear which activated form (quinone, semiquinone, or deprotonated) actually plays a role in each of these processes. Structural, electronic, and energetic characteristics of quercetin, as well as the influence of a copper ion on all of these parameters, are studied by means of quantum chemical electronic structure calculations. Introduction of thermodynamic cycles together with the role of coreactive compounds, such as reactive oxygen species, gives a glimpse of the most probable reaction schemes. Such a theoretical approach provides another hint to clarify which reaction is likely to occur within the broad range of quercetin biological activities.

Cytochrome P450 1A1 expression and activity in Caco-2 cells: modulation by apple juice extract and certain apple polyphenols

Cytochrome P450 (CYP) 1A1 plays a role in drug metabolism of intestinal cells (e.g., by activating certain chemical carcinogens such as polycyclic aromatic hydrocarbons into carcinogenic metabolites). In the human colon carcinoma cell line Caco-2, we investigated the effects of a defined polyphenolic apple juice extract (AJE), the major principle flavonoid/dihydrochalkone constituents quercetin and phloretin, and the corresponding prototype glycosides rutin and phlorizin on CYP1A1 expression and activity. Incubations were carried out with or without the potent aryl hydrocarbon receptor agonist/CYP1A1 inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). AJE and quercetin acted as weak inducers of CYP1A1 mRNA and protein, and AJE, quercetin, and phlorizin led to a slight induction of CYP1A1-catalyzed 7-ethoxyresorufin O-deethylase (EROD) activity. However, AJE, quercetin, and phloretin were highly effective in suppressing CYP1A1 induction in co-incubations of the cells with 1 nM TCDD. The antagonistic effects were seen on the levels of mRNA, enzyme protein, and catalytic activity. In contrast, the related glycosides rutin and phlorizin were inactive as inducers or inhibitors. Inhibition of CYP1A1 induction was not related to general cytotoxicity, which could be completely abolished by the addition of ascorbic acid/alpha-tocopherol. AJE, quercetin, and phloretin also antagonized the TCDD-mediated induction of a reporter gene driven by a regulatory sequence of the human CYP1A1 gene promoter. Our findings suggest that apple juice extract can antagonize TCDD-mediated CYP1A1 induction by interfering with AhR-dependent gene transcription and by inhibiting the catalytic activity of CYP1A1. These effects may result in reduced metabolic activation of certain chemical carcinogens, in particular, under conditions of sustained AhR activation.

Flavonoids and colorectal cancer in Italy

Because of their several biological activities, flavonoids may have an important role in explaining the protective effects of vegetables, fruit, and, possibly, tea against cancer. The potential relation between flavonoids and colorectal cancer risk was investigated using data from a multicentric Italian case-control study, including 1,953 cases of colorectal cancers (1,225 colon cancers and 728 rectal cancers) and 4,154 hospital controls admitted for acute nonneoplastic diseases. We have applied recently published data on the composition of foods and beverages, in terms of six principal classes of flavonoids, on dietary information collected through a validated food-frequency questionnaire. Odds ratios (OR) were estimated by multiple logistic regression models, including terms for sex, age, study center, family history of colorectal cancer, education, alcohol consumption, body mass index, physical activity, and energy intake. A reduced risk of colorectal cancer was found for increasing intake of isoflavones (OR, 0.76, for the highest versus the lowest quintile, P(trend) = 0.001), anthocyanidins (OR, 0.67, P(trend) < 0.001), flavones (OR, 0.78, P(trend) = 0.004), and flavonols (OR, 0.64, P(trend) < 0.001). No significant association was found for flavan-3-ols (OR, 0.98), flavanones (OR, 0.96), and total flavonoids (OR, 0.97). The estimates did not substantially differ for colon and rectal cancers, as well as in strata of sex, age, and body mass index. The findings of this large study provide support for an inverse association of selected classes of flavonoids with colorectal cancer risk.

Flavonoid-mediated inhibition of intestinal ABC transporters may affect the oral bioavailability of drugs, food-borne toxic compounds and bioactive ingredients

The transcellular transport of ingested food ingredients across the intestinal epithelial barrier is an important factor determining bioavailability upon oral intake. This transcellular transport of many chemicals, food ingredients, drugs or toxic compounds over the intestinal epithelium can be highly dependent on the activity of membrane bound ATP binding cassette (ABC) transport proteins, able to export the compounds from the intestinal cells. The present review describes the ABC transporters involved in the efflux of bioactive compounds from the intestinal cells, either to the basolateral blood side, facilitating absorption, or back into the intestinal lumen, reducing bioavailability. The role of the ABC transporters in intestinal transcellular uptake also implies a role for inhibitors of these transporters in modulation of the bioavailability upon oral uptake. The present paper focuses on the role of flavonoids as important modulators or substrates of intestinal ABC transport proteins. Several examples of such an effect of flavonoids are presented. It can be concluded that flavonoid-mediated inhibition of ABC transporters may affect the bioavailability of drugs, bioactive food ingredients and/or food-borne toxic compounds upon oral uptake. All together it appears that the flavonoid-mediated interactions at the level of the intestinal ABC transport proteins may be an important mechanism for unexpected food-drug, food-toxin or food-food interactions. The overview also indicates that future studies should focus on i) in vivo validation of the flavonoid-mediated effects on bioavailability of drugs, toxins and beneficial bioactive food ingredients detected in in vitro models, and on ii) the role of flavonoid phase II metabolism in modulating the activity of the flavonoids to act as ABC transporter inhibitors and/or substrates.

Quercetin content in field-cured onions (Allium cepa L.): effects of cultivar, lifting time, and nitrogen fertilizer level

Variation in quercetin content was investigated in field-cured onions (Allium cepa L.) that had been supplied with different nitrogen fertilizer levels and lifted at different developmental stages. Quercetin content varied significantly between years and was well correlated to global radiation in August. Field curing generally resulted in significant increases in quercetin content compared to levels at lifting. Nitrogen fertilizer level did not affect quercetin content, suggesting that nitrogen leakage from soil may be minimized without effects on flavonol content. Lifting time had minor effects on quercetin content in field-cured onions. Cultivar differences in quercetin content were significant but not consistent in all years. Quercetin content increased significantly less in dark environments compared to field curing, but some quercetin synthesis occurred regardless of light. Field curing with or without foliage still attached did not affect quercetin content, suggesting that no transportation from the foliage to the scales occurred.

EFFECTS OF PRENYLATED ISOFLAVONES OSAJIN AND POMIFERIN IN PREMEDICATION ON HEART ISCHEMIA-REPERFUSION

The present 15 days study was undertaken to evaluate the cardioprotective potential of the prenylated isoflavones osajin and pomiferin isolated from the infructences of Maclura pomifera, Moraceae, against ischemia-reperfusion induced injury in rat hearts as a model of antioxidant-based composite therapy. The study was performed on isolated, modified Langendorff-perfused rat hearts and the ischemia of heart was induced by stopping coronary flow for 30 min followed by 60 min of reperfusion (14 ml min(-1)). The Wistar rats were divided into four groups. The first treatment group received osajin (5 mg/kg/day in 0.5% Avicel); the second treatment group received pomiferin (5 mg/kg/day in 0.5% Avicel); the placebo group received only 0.5 Avicel; the last was an untreated control group. Biochemical indicator of oxidative damage-lipid peroxidation product malondialdehyde, antioxidant enzymes - superoxide dismutase, glutathione peroxidase, total antioxidant activity in serum and myocardium were evaluated. The effect of osajin and pomiferin on cardiac function, left ventricular end-diastolic pressure, left ventricular pressure and peak positive +dP/dt ischemia and reperfusion, also was examined. The results demonstrate that osajin and pomiferin attenuates the myocardial dysfunction provoked by ischemiareperfusion. This was confirmed by an increase in both antioxidant enzyme values and total antioxidant activity. The cardioprotection provided by osajin and pomiferin treatment results from the suppression of oxidative stress and this correlates with improved ventricular function.

Flavonoid glycosides in bergamot juice (Citrus bergamia Risso)

A comprehensive profile of flavonoids in bergamot juice was obtained by a single DAD-ESI-LC-MS-MS course. Eight flavonoids were found for the first time, five of these are C-glucosides (lucenin-2, stellarin-2, isovitexin, scoparin, and orientin 4'-methyl ether), and three are O-glycosides (rhoifolin 4'-O-glucoside, chrysoeriol 7-O-neohesperidoside-4'-O-glucoside, and chrysoeriol 7-O-neohesperidoside). A method is proposed to differentiate chrysoeriol and diosmetin derivatives, which are often indistinguishable by LC-MS-MS. In-depth knowledge of the flavonoid content is the starting point for bergamot juice exploitation in food industry applications.

In vitro antileukaemic activity of extracts from berry plant leaves against sensitive and multidrug resistant HL60 cells

The aim of the present study was to determine in vitro antileukaemic activity of extracts obtained from selected berry plant leaves (Fragaria x ananassa Duch. cv Elsanta, raspberry Rubus ideus L. cv Polana and blueberry Vaccinium corymbosum L. cv Bluecrop) against promyelocytic HL60 cell line and its multidrug resistant sublines exhibiting two different MDR phenotypes: HL60/VINC (overexpressing P-glycoprotein) and HL60/DOX (overexpressing MRP1 protein). It was found that the blueberry extract was the most efficient against sensitive HL60 cell line (about 2-fold more active than strawberry and raspberry extracts) but presented much lower activity towards resistant cells. In contrast, strawberry and raspberry extracts exhibited the high cytotoxic activity against sensitive leukaemia HL60 cell line as well as its MDR sublines. The values of resistance factor (RF) found for these extracts were very low lying in the range 0.32/2.0.

Effect of different flavonoids on collagen synthesis in human fibroblasts

In this study, we discovered that flavonoids belonging to the subclasses: (flavanone, flavone, and flavonol) display differential effects on the synthesis of collagen in human dermal fibroblasts. At 80 microg/ml flavonoids quercetin-3,3',4', 5,7-pentahydroxyflavone, 3-methyl quercetin, and 7-hydroxyflavone significantly decreased the total protein concentration which was a direct consequence of their cytotoxic effect, while naringenin exhibited no effect on total collagen and total protein concentration. Quercetin-3,3'4',7-tetramethyl ether, 4'-hydroxyflavanone, flavanone, and fisetin significantly decreased collagen concentration while morin, rutin, and chrysin increased collagen concentration without changing the overall protein concentration. The initial screening performed in this study enables the identification of compounds that exert significant effects on fibroblast function and show potential as starting material for pharmaceutical preparations targeted against various disorders centered around disturbed collagen metabolism.

An in vitro study of the protective effect of the flavonoid silydianin against reactive oxygen species

The inhibitory effect of silydianin, an active constituent of Silybium marianum, on the in vitro production and release of oxidative products has been examined. Polymorphonuclear neutrophils (PMNs) play a primary role in the initiation and propagation of inflammatory responses. Their apoptosis is a major mechanism associated with the resolution of inflammatory reactions. Neutrophils were assessed for caspase-3 activity, the rst step in the execution phase of apoptosis. When cells were cultured with 100 microM silydianin for 24 h, caspase-3 was activated. Induction of apoptosis by silydianin was accompanied by a decrease in luminol-enhanced chemiluminescence as well as superoxide radical (O2*-) release in freshly isolated cells and lipid peroxidation in mouse spleen microsomes. No significant effect of silydianin on PMN hydrogen peroxide production evaluated by a flow cytometric dichlorofluorescin oxidation assay was found. Such results indicate a possible antiinflammatory activity for silydianin, which regulates caspase-3 activation, affects cell membranes and acts as a free radical scavenger.

Influence of galangin on HL-60 cell proliferation and survival

The effect of galangin, a flavonol component of India root spice and the 'herbal' medicine propolis, on HL-60 human leukaemia cell survival is characterised. Galangin (1-100 microM) exerted an antiproliferative effect that, with dose and exposure longevity, was progressively associated with an elevated hypodiploid DNA content and expression of the active form of caspase-3, principally prior to membrane damage. At >or=50 microM, plasmamembrane phosphatidylserine exposure was observed. There was no evidence for intracellular oxidative stress as an orchestrator of cytotoxicity and significant phagocyte-like differentiation was not detected. We discuss whether such cytotoxicity will be therapeutically exploitable or contribute to cancer prevention within a pharmacological or dietary context.

Simultaneous quantification of CTN986 and its deglycosylation products in rat serum using liquid chromatography/tandem mass spectrometry

A quantitative method for the simultaneous determination of CTN986, a flavonol triglycoside, and its two deglycosylation products rutin and hirsutin in rat serum was developed and validated for the investigation of the pharmacokinetics of CTN986. Analytes were isolated from the serum samples (200 microL) prior to analysis by liquid chromatography/tandem mass spectrometry (LC/MS/MS) using C(18) solid-phase extraction, and were separated on a Zorbax C(8) reversed-phase column with an isocratic mobile phase consisting of methanol/isopropanol/water/formic acid (20:10:70:0.1, v/v/v/v). The protonated analytes generated in the positive ion mode were monitored through multiple reaction monitoring in an eletrospray ionization source. Calibration was performed by internal standardization with CTN987, a flavonoid structurally similar to CTN986, and regression curves were constructed ranging from 2 to 1000 ng/mL in 200 microL serum samples. The intra- and inter-day precision values were below 11% and accuracy was between -2.37 and 1.4% for all quality control samples. This quantitation method was successfully applied to pharmacokinetic studies of CTN986 in rats following oral and intravenous administration. Rutin and hirsutin were not detected in rat serum.

Flow Injection Determination of Xanthine Oxidase Inhibitory Activity and Its Application to Food Samples

The enzyme xanthine oxidase (XOD) has been recognized as a key enzyme causing oxidative injury to tissues by ischemia-reperfusion. For this reason, XOD inhibitor, which effectively suppresses this enzyme, plays an important role in the inhibition of many diseases related to reactive oxygen species (ROS). In order to screen XOD inhibitors rapidly and conveniently, a novel assay using flow injection analysis (FIA) was proposed in the present investigation. To optimize the practical FIA system, we studied the effect of the reagent concentrations and the flow condition on the enzymatic reaction, and then selected the optimum condition as follows: 200-mU/ml XOD concentration, 0.5-mM xanthine concentration, 0.5-ml/min flow rate, and 2-m mixing coil length. Under this condition, a typical XOD inhibitor quercetin was determined in the concentration range 0.1 - 1.5 mM at a sampling frequency of 10 samples/h. Using the optimized FIA method, we determined the XOD inhibitory activity of some food samples: onions, apples and teas, which are the high sources of flavonoids known as the potential XOD inhibitors. Among these samples, tea leaves showed the highest activity, the second was onions and the lowest was apples. Based on the result of the assay, not only quercetin, but also other components in investigated samples, contributed to the XOD inhibitory activity.

Potential role of flavonoids in the prevention of intestinal neoplasia: a review of their mode of action and their clinical perspectives

Intestinal neoplasia (adenomas and carcinomas) can possibly be prevented by a diet rich in vegetables and fruits, treatment with aspirin and other nonsteroidal antiinflammatory drugs, and early colonoscopic removal of adenomas. Ballast, fiber, and secondary plant products could play a major role in colon cancer prevention. Recently there has been much experimental work in vitro and in vivo about flavonoids as inducers of bioprevention. Flavonoids are secondary plant products with a wide variety of beneficial biological properties, and they possess anticarcinogenic, antimutagenic, and antioxidative modes of actions. Flavonoids are the main components of a healthy diet containing fruits and vegetables and are concentrated especially in tea, apples, and onions. We will focus this review on flavonoids which are derived from tea products such as proanthocyanidins (green tea) and flavons (camomille tea). Oral supplementation with bioflavonoids derived from tea could be used in humans to prevent growth of intestinal neoplasia such as adenomatous polyps of the colon. Flavonoids are a large group of natural compounds of which only a few have been used in animal models, cell cultures, and enzyme studies to inhibit mutagenic and carcinogenic events. Their clinical mode of action was evaluated by epidemiological studies, but no intervention studies in humans have been performed so far. In vitro flavonoids can bind electrophils, inactivate oxygen radicals, prevent lipid peroxidation, and inhibit DNA oxidation. In cell cultures they increase the rate of apoptosis, inhibit cell proliferation, and angiogenesis. In vivo they can induce the activities of protective enzymes (conjugating enzymes such as glutathione transferases and glucuronosyl transferases) of the intestine and the liver. In models of intestinal polyposis, flavonoids suppress polyp formation. Some epidemiological studies show a protective effect of flavonoids contained in fruits, vegetables, and tea. Flavonoid mixtures of tea origin supplied as nutritional supplements could be studied as a new way of bioprevention of intestinal neoplasia (colon adenomas and cancer). Therefore, a controlled, randomized clinical study should be performed to evaluate the efficacy of flavonoids.

Flavonols inhibit proinflammatory mediator release, intracellular calcium ion levels and protein kinase C theta phosphorylation in human mast cells

Mast cells participate in allergies, and also in immunity and inflammation by secreting proinflammatory cytokines. Flavonoids are naturally occurring polyphenolic plant compounds, one group of which -- the flavonols, inhibits histamine and some cytokine release from rodent basophils and mast cells. However, the effect of flavonols on proinflammatory mediator release and their possible mechanism of action in human mast cells is not well defined. Human umbilical cord blood-derived cultured mast cells (hCBMCs) grown in the presence of stem cell factor (SCF) and interleukin (IL)-6 were preincubated for 15 min with the flavonols quercetin, kaempferol, myricetin and morin (0.01, 0.1, 1, 10 or 100 microM), followed by activation with anti-IgE. Secretion was quantitated for IL-6, IL-8, tumor necrosis factor-alpha (TNF-alpha), histamine and tryptase levels. Release of IL-6, IL-8 and TNF-alpha was inhibited by 82-93% at 100 microM quercetin and kaempferol, and 31-70% by myricetin and morin. Tryptase release was inhibited by 79-96% at 100 microM quercetin, kampferol and myricetin, but only 39% by morin; histamine release was inhibited 52-77% by the first three flavonols, but only 28% by morin. These flavonols suppressed intracellular calcium ion elevations in a dose-response manner, with morin being the weakest; they also inhibited phosphorylation of the calcium-insensitive protein kinase C theta (PKC theta). Flavonol inhibition of IgE-mediated proinflammatory mediator release from hCBMCs may be due to inhibition of intracellular calcium influx and PKC theta signaling. Flavonols may therefore be suitable for the treatment of allergic and inflammatory diseases.

In vitro availability of kaempferol glycosides from cream formulations of methanolic extract of the leaves of Melilotus elegans

In Ethiopian traditional medicine, Melilotus elegans Salzm. ex Ser. (Leguminosae) is used for the treatment of haemorrhoids and lacerated wounds. In view of its wide spread use and proven anti-inflammatory activity, 80% methanolic extract of the leaves was formulated into creams. HPLC/UV and MS studies revealed the presence of flavonoids, of which kaempferol was the major aglycone. Quantitative estimation of kaempferol in the hydrolyzed extract as determined by HPLC/UV was found to be 16.3+/-0.93 microg/mg (n=6, range) of extract. The in vitro release profiles of kaempferol glycosides (quantified as kaempferol equivalent) from the cream formulations in a multilayer membrane system indicated that a lipophilic cream of the extract provides higher release of kaempferol glycosides than hydrophilic and amphiphilic ones. Over a study period of 4h, the lipophilic cream released 66+/-5.70% of kaempferol glycosides, while the hydrophilic and amphiphilic creams resulted in 55+/-2.77 and 38+/-2.30% release, respectively.

Chromatographic, capillary electrophoretic and capillary electrochromatographic techniques in the analysis of flavonoids

An overview is presented of chromatographic methods currently in use to determine flavonoids, including free aglycones, their corresponding glycosides, one by one, and, in the presence of each other. As a basis of selection, the following approaches can be distinguished: critical evaluation of the preliminary steps (extraction/isolation and hydrolysis) as well as the separation, identification and quantitation of constituents both on the basic research level and/or subsequently to various work up procedures. Chromatographic techniques were discussed after extraction/isolation of various flavonoids from several natural matrices. Papers were classified and compared from analytical point of view, primarily on the chromatographic, secondly on the detection techniques applied.

Dietary flavonoids and cancer risk: evidence from human population studies

High dietary intake of fruits and vegetables is consistently associated with a reduced risk of common human cancers, including cancers of the lung, breast, prostate, and colon. It is unknown which bioactive compound or compounds in plant foods provide the chemoprotective effects. One class of compounds currently under investigation is flavonoids, a large group of compounds with similar structure, consisting of two phenolic benzene rings linked to a heterocyclic pyran or pyrone. Although there are numerous in vitro and animal model data suggesting that flavonoids influence important cellular and molecular mechanisms related to carcinogenesis, such as cell cycle control and apoptosis, there are limited data from human population studies. This article reviews data from four cohort studies and six case-control studies, which have examined associations of flavonoid intake with cancer risk. There is consistent evidence from these studies that flavonoids, especially quercetin, may reduce the risk of lung cancer. Further research using new dietary databases for food flavonoid content is needed to confirm these findings before specific public health recommendations about flavonoids can be formulated.

Degradation of neohesperidin dihydrochalcone by human intestinal bacteria

The degradation of neohesperidin dihydrochalcone by human intestinal microbiota was studied in vitro. Human fecal slurries converted neohesperidin dihydrochalcone anoxically to 3-(3-hydroxy-4-methoxyphenyl)propionic acid or 3-(3,4-dihydroxyphenyl)propionic acid. Two transient intermediates were identified as hesperetin dihydrochalcone 4'-beta-d-glucoside and hesperetin dihydrochalcone. These metabolites suggest that neohesperidin dihydrochalcone is first deglycosylated to hesperetin dihydrochalcone 4'-beta-d-glucoside and subsequently to the aglycon hesperetin dihydrochalcone. The latter is hydrolyzed to the corresponding 3-(3-hydroxy-4-methoxyphenyl)propionic acid and probably phloroglucinol. Eubacterium ramulus and Clostridium orbiscindens were not capable of converting neohesperidin dihydrochalcone. However, hesperetin dihydrochalcone 4'-beta-d-glucoside was converted by E. ramulus to hesperetin dihydrochalcone and further to 3-(3-hydroxy-4-methoxyphenyl)propionic acid, but not by C. orbiscindens. In contrast, hesperetin dihydrochalcone was cleaved to 3-(3-hydroxy-4-methoxyphenyl)propionic acid by both species. The latter reaction was shown to be catalyzed by the phloretin hydrolase from E. ramulus.

A nutritional intervention promoting the Mediterranean food pattern is associated with a decrease in circulating oxidized LDL particles in healthy women from the Québec City metropolitan area

The aim of the present study was to evaluate the effect of a nutritional intervention promoting the Mediterranean food pattern under free-living conditions on circulating oxidized LDL (ox-LDL) in a group of 71 healthy women from the Quebec City metropolitan area. The 12-wk nutritional intervention consisted of 2 courses on nutrition and 7 individual sessions with a dietitian. A score based on the 11 components of the Mediterranean pyramid was established to determine the women's adherence to the Mediterranean food pattern. Plasma ox-LDL concentrations were measured by a monoclonal antibody mAb-4E6-based competition ELISA. Among all women, plasma ox-LDL decreased by 11.3% after 12 wk of nutritional intervention (P < 0.0001) despite a lack of change in plasma LDL cholesterol (LDL-C). Also, an increase in the Mediterranean dietary score was significantly correlated with a decrease in ox-LDL concentrations (r = -0.30; P = 0.01). More specifically, increases in servings of fruits (r = -0.25; P < 0.05) and vegetables (r = -0.24; P < 0.05) were associated with decreases in ox-LDL concentrations. Changes in the food pattern in response to a nutritional intervention promoting the Mediterranean food pattern were accompanied by beneficial effects in circulating ox-LDL concentrations in healthy women.

The dietary flavonoids apigenin and (-)-epigallocatechin gallate enhance the positive modulation by diazepam of the activation by GABA of recombinant GABA(A) receptors

The dietary flavonoids apigenin, genistein and (-)-epigallocatechin gallate (EGCG) inhibited the activation by GABA (40 microM) of recombinant human alpha1beta2gamma2L GABA(A) receptors expressed in Xenopus laevis oocytes with IC(50) values of 8, 30 and 15 microM, respectively. Apigenin and genistein also acted as GABA antagonists at flumazenil-insensitive alpha1beta2 GABA(A) receptors, indicating that they were not acting as negative modulators through flumazenil-sensitive benzodiazepine sites on GABA(A) receptors. In addition to these GABA(A) antagonist effects, a novel second order modulatory action was found for apigenin and EGCG on the first order enhancement of GABA responses by diazepam. Apigenin (1 microM) and EGCG (0.1 microM) enhanced the modulatory action of diazepam (3 microM) on the activation by GABA (5 microM) of recombinant human alpha1beta2gamma2L GABA(A) receptors by up to 22% and 52%, respectively. This was not found with genistein, nor was it observed with enhancement by allopregnanolone or pentobarbitone.