Influence of diabetes on plasma pharmacokinetics and brain bioavailability of grape polyphenols and their phase II metabolites in the Zucker diabetic fatty rat.

SCOPE: The effect of diabetes on the pharmacokinetics, bioavailability and brain distribution of grape polyphenols and select metabolites was studied in the Zucker diabetic fatty (ZDF) rat model. METHODS AND RESULTS: (ZDF) rats and their lean controls (LN) were dosed with a Standardized Grape Polyphenol (SGP) Mixture consisting of grape seed extract, Concord grape juice and resveratrol (RES) by oral gavage for 10 days. An 8-h pharmacokinetic study was performed. After 24 h, a second dose of SGP was administered and 1 h later animals were sacrificed and brain tissue was harvested. Plasma, urine, and brain tissue were analyzed for grape polyphenols. ZDF rats exhibited significantly diminished Cmax for all catechin, epicatechin, quercetin and resveratrol conjugated metabolites. Bioavailability was significantly lower in ZDF rats for methylated flavan-3-ol, RES, and quercetin metabolites. Significantly lower levels of metabolites of RES, quercetin, and flavan-3-ols were found in brains of ZDF rats. There was no significant difference between ZDF and LN in anthocyanins in plasma and no anthocyanins were detectable in brain extracts. ZDF rats showed significantly higher urinary excretion for all polyphenols. CONCLUSION: Diabetes may alter the overall bioavailability of some polyphenols in plasma and brain in part due to higher urinary clearance.

Metabonomic analysis of quercetin against the toxicity of acrylamide in rat urine.

This research aims to determine whether quercetin has protective effects against the toxicity of acrylamide (AA) using metabonomic technology. Randomly, the rats were assigned into a control group, AA treatment group, quercetin treatment group and quercetin plus AA treatment group. Quercetin and AA were administered to rats daily via gavage and drinking water for 16 weeks, respectively. To detect the metabonomic profiles of urine, ultra-performance liquid chromatography/mass spectrometry was used. A total of 15 metabolites, including biomarkers of AA exposure (GAMA, AAMA, and iso-AAMA) and quercetin exposure (quercetin and isorhamnetin), were identified. In comparison with the control group, the intensities of GAMA, AAMA, iso-AAMA, 1-salicylate glucuronide, vinylacetylglycine, PE(20:1(11Z)/14:0), 7-ketodeoxycholic acid, cysteic acid, p-cresol sulfate, and l-cysteine in the AA-treated group were statistically significantly increased (p < 0.01), and the intensities of 2-indolecarboxylic acid, 3-acetamidobutanal, and kynurenic acid in the AA-treated group were statistically significantly decreased (p < 0.01). The above-mentioned metabolites were significantly ameliorated in the quercetin (50 mg per kg bw) plus AA-treated group compared with the AA-treated group (p < 0.01 or p < 0.05). However, the intensities of these metabolites in the quercetin (50 mg per kg bw) plus AA-treated groups were still significantly different from those of the control group (p < 0.01 or p < 0.05). The above results suggest that quercetin has a partial protective effect on AA-induced toxicity. The protective effects include regulation of fatty acid metabolism and amino acid metabolism and enhancing the antioxidant defense system.

Urinary Excretion of Select Dietary Polyphenol Metabolites Is Associated with a Lower Risk of Type 2 Diabetes in Proximate but Not Remote Follow-Up in a Prospective Investigation in 2 Cohorts of US Women.

BACKGROUND: Polyphenols are phytochemicals that possess antioxidant and anti-inflammatory properties and improve glucose metabolism in animal experiments, although data from prospective epidemiologic studies examining polyphenol intakes in relation to type 2 diabetes (T2D) risk are inconsistent. OBJECTIVES: We examined urinary excretion of select flavonoid and phenolic acid metabolites, as biomarkers of intake, in relation to T2D risk. METHODS: Eight polyphenol metabolites (naringenin, hesperetin, quercetin, isorhamnetin, catechin, epicatechin, caffeic acid, and ferulic acid) were quantified in spot urine samples by liquid chromatography/mass spectrometry among 1111 T2D case-control pairs selected from the Nurses' Health Study (NHS) and NHSII. RESULTS: Higher urinary excretion of hesperetin was associated with a lower T2D risk after multivariate adjustment: the OR comparing top vs. bottom quartiles was 0.68 (95% CI: 0.49, 0.96), although a linear trend was lacking (P = 0.30). The other measured polyphenols were not significantly associated with T2D risk after multivariate adjustment. However, during the early follow-up period [≤ 4.6 y (median) since urine sample collection], markers of flavanone intakes (naringenin and hesperetin) and flavonol intakes (quercetin and isorhamnetin) were significantly associated with a lower T2D risk. The ORs (95% CIs) comparing extreme quartiles were 0.61 (0.39, 0.98; P-trend: 0.03) for total flavanones and 0.55 (0.33, 0.92; P-trend: 0.04) for total flavonols (P-interaction with follow-up length: ≤ 0.04). An inverse association was also observed for caffeic acid during early follow-up only: the OR was 0.52 (95% CI: 0.32, 0.84; P-trend: 0.03). None of these markers was associated with T2D risk during later follow-up. Metabolites of flavan-3-ols and ferulic acid were not associated with T2D risk in either period. CONCLUSIONS: These results suggest that specific flavonoid subclasses, including flavanones and flavonols, as well as caffeic acid, are associated with a lower T2D risk in relatively short-term follow-up but not during longer follow-up. Substantial within-person variability of the metabolites in single spot urine samples may limit the ability to capture associations with long-term disease risk.

Comparison of the urinary excretion of quercetin glycosides from red onion and aglycone from dietary supplements in healthy subjects: a randomized, single-blinded, cross-over study.

Some intervention studies have shown that quercetin supplementation can regulate certain biomarkers, but it is not clear how the doses given relate to dietary quercetin (e.g. from onion). We conducted a two-period, two-sequence crossover study to compare the bioavailability of quercetin when administered in the form of a fresh red onion meal (naturally glycosylated quercetin) or dietary supplement (aglycone quercetin) under fasting conditions. Six healthy, non-smoking, adult males with BMI 22.7 ± 4.0 kg m(-2) and age 35.3 ± 12.3 y were grouped to take the two study meals in random order. In each of the 2 study periods, one serving of onion soup (made from 100 g fresh red onion, providing 156.3 ± 3.4 µmol (47 mg) quercetin) or a single dose of a quercetin dihydrate tablet (1800 ± 150 µmol (544 mg) of quercetin) were administered following 3 d washout. Urine samples were collected up to 24 h, and after enzyme deconjugation, quercetin was quantified by LC-MS. The 24 h urinary excretion of quercetin (1.69 ± 0.79 µmol) from red onion in soup was not significantly different to that (1.17 ± 0.44 µmol) for the quercetin supplement tablet (P = 0.065, paired t-test). This means that, in practice, 166 mg of quercetin supplement would be comparable to about 10 mg of quercetin aglycone equivalents from onion. These data allow intervention studies on quercetin giving either food or supplements to be more effectively compared.

A novel solid fluorescence method for the fast determination of quercetin in biological samples based on the quercetin-Al(III) complex imprinted polymer.

In this work, a novel solid fluorescence method was proposed and applied to the fast determination of quercetin in urine and onion skin samples by using metal coordination imprinted polymer membrane, which was regarded as a recognition element. The quercetin-Al(III) imprinted polymer was immobilized in the microporous polypropylene fiber membrane via consecutive in situ polymerization. The CIP membrane had the porous, loose and layer upon layer structure. The CIP membrane was characterized by electron microscope photographs, infrared spectra, thermogravimetric analysis and solvent-resistant investigation. The extraction conditions including extraction solvent, extraction time, desorption solvent were optimized. Compared with MIP and NIP membrane, CIP membrane had been proved to be peculiar selective for quercetin even in presence of the structurally similar compounds such as kaempferol, rutin, naringenin and alpinetin. The CIP membrane was characteristic of high selectivity, stable and sensitive response to quercetin in polar environment. Under the optimum condition, there was a linear relationship between the state fluorescent response and the concentration of quercetin. The linear calibration range was over 0.02 mg L(-1)-0.80 mg L(-1) with a detection limit of 5 µg L(-1). The method was characteristic of flexible and good repeatability with relative standard deviation (RSD) of 4.1%. The proposed method was also successfully applied for the determination of quercetin in urine and onion skin samples without complicated pretreatment. The recoveries were 84.0-112.4% and RSDs varied from 1.5% to 6.8%. The results obtained by the proposed method agreed well with those obtained by HPLC method.

The effective method for investigation meridian tropism theory in rats.

This present work describes an effective new method for study traditional Chinese medicine (TCM) on meridian tropism (MT) theory, which plays an essential role in clinical selection of TCM according to syndromes and strengthens the therapeutic effects. The new thread included material basis foundation and its tissue distribution study. Xiheliu, the most popular TCM on heart tropism, was investigated by simple and accurate high performance liquid chromatography (HPLC) method. The analysis of plasma after oral administration the total flavonoid of Xiheliu (TFX) exhibited that tamarixetin and kaempferide had the highest concentration and approximately the highest level within 25 min. The mixture of them could last accelerating the urine excretion more than 7 h after a single dose and could not cause the disorder of ion in rats, which was observed in diuretic activity experiment. In view of the reported biological activities was consistent with the effects of Xiheliu, tamarixetin and kaempferide were likely to be the material basis of it. Tissue distribution study showed that the highest level of analytes was in heart, lung, kidney and liver, and most tissues reached maximum level at 30 min post-dose. Since liver was the most important blood-supply tissue, the result of this experiment was in accordance with the MT record of Xiheliu and confirmed that tamarixetin and kaempferide was the material bases of it on MT. This is the first report for the illumination of material basis and the mechanism of Xiheliu on MT by analysis the record of Xiheliu in Compendium of Materia Medica and experimental study.

Identification of glutathione-related quercetin metabolites in humans.

The glutathionylation of quercetin was investigated in murine hepatic suspensions, in the absence of chemically or enzymatically induced oxidative stress, and in human urine after the consumption of 200 g of cooked onions ( approximately 74 mg of quercetin). In murine hepatic suspensions, 22 metabolites, including glucuronide, sulfate, and glutathione conjugates of quercetin, were identified by LC/ESI-MS/MS. In total, eight glutathione conjugates were identified in these suspension, including three isomeric forms of monoglutathionyl quercetin, two isomers of monoglutathionyl quercetin glucuronide, and three isomers of glutathionyl methyl quercetin. Quinone forms of glutathionyl quercetin and glutathionyl methyl quercetin were also apparent in mass spectra. In humans, several glutathione-related metabolites of quercetin were identified in urine as mercapturic acids of common hydroxyphenylacetic acids generated by the microbial degredation of quercetin in the gut. These include mercaptic acids of dihydroxytoluene, dihydroxybenzaldehyde, dihydroxyphenylacetic acid, dihydroxycinnamic acid, and dihydroxyphenylpropionic acid. Our results suggest that glutathionylation of quercetin occurs in both murine hepatic suspensions and humans and indicate that under certain conditions, quercetin intermediates require inactivation through conjugation with glutathione.

Urinary and plasma levels of resveratrol and quercetin in humans, mice, and rats after ingestion of pure compounds and grape juice.

The present study investigates the bioavailability of resveratrol and quercetin in humans, mice, and rats after oral ingestion of grape juice preparations or pure aglycones. Oral administration of resveratrol and quercetin to humans yielded detectable levels of resveratrol, quercetin, and their derivatives in the plasma and urine. Urinary levels of resveratrol, quercetin, and their metabolites were observed in human subjects receiving 600 and 1200 mL of grape juice, whereas quercetin metabolites were identified in urine samples even after receiving 200 mL of grape juice. The cumulative amounts of resveratrol and quercetin excreted in the urine of mice receiving concentrated grape juice for 4 days were 2.3 and 0.7% of the ingested doses, respectively. After i.g. administration of resveratrol to rats (2 mg/kg), up to 1.2 microM resveratrol was observed in the plasma. The study demonstrates that the glycoside forms of resveratrol and quercetin in grape juice are absorbed to a lesser extent than the aglycones.

Effect of diets based on foods from conventional versus organic production on intake and excretion of flavonoids and markers of antioxidative defense in humans.

Different food production methods may result in differences in the content of secondary metabolites such as polyphenolic compounds. The present study compared conventionally (CPD) and organically produced (OPD) diets in a human crossover intervention study (n = 16) with respect to the intake and excretion of five selected flavonoids and effect on markers of oxidative defense. The urinary excretion of quercetin and kaempferol was higher after 22 days of intake of the OPD when compared to the CPD (P < 0.05). The excretions of flavonoids in urine as a percentage of intake (0.6-4%) were similar after both interventions. Most markers of antioxidative defense did not differ between the diets, but intake of OPD resulted in an increased protein oxidation and a decreased total plasma antioxidant capacity compared to baseline (P < 0.05). Some varietal difference was seen in the study, and because selection of more resistant varieties is of central importance to organic farming, it cannot be excluded that the observed effects originate from these differences. The food production method affected the content of the major flavonoid, quercetin, in foods and also affected urinary flavonoids and markers of oxidation in humans.

Effects of phenol-depleted and phenol-rich diets on blood markers of oxidative stress, and urinary excretion of quercetin and kaempferol in healthy volunteers.

OBJECTIVE: Epidemiological studies have suggested beneficial effects of dietary polyphenols in reducing the risk of chronic diseases. This study was performed to investigate the effects of polyphenol-depleted and polyphenol-rich diets on blood oxidative stress markers and urinary excretions of major phenols. METHODS: Nineteen healthy female non-smokers 19 to 21 years of age took part in the study, which consisted of two dietary intervention periods separated by three days. Experimental diets were composed of common foods selected to comply with low contents of polyphenols for phenol-depleted intervention and high contents of polyphenols for phenol-rich diets. Blood and urine samples were collected on day 0, 3 and 6 of each intervention. Duplicate portions of foods provided to the subjects were also collected. Blood oxidative stress markers included plasma antioxidant vitamins, erythrocyte superoxide dismutase (SOD) activity and lymphocyte DNA damage. Urinary excretions of major phenols were measured to affirm bioavailability of dietary phenols. RESULTS: Plasma alpha-tocopherol and beta-carotene concentrations were slightly decreased on day 3 and 6 of the phenol-depleted dietary intervention period, although no change was observed with phenol-rich diets. The erythrocyte SOD activity was also slightly decreased during phenol-depleted dietary intervention. However, at day 6 of the phenol-rich intervention, the activity of SOD was significantly increased by 41%. Tail moment and tail length of lymphocyte DNA as markers of DNA damage were higher on day 6 of phenol-depleted intervention, although only tail moment showed a statistical significance. The average intakes of quercetin and kaempferol during the phenol-rich intervention were 21 mg/day and 9 mg/day, respectively. The average urinary excretion rates during phenol-rich intervention were 2.06% for quercetin and 0.46% for kaempferol. There were positive correlations between erythrocyte SOD activity and urinary concentration of quercetin or kaempferol. CONCLUSIONS: These results suggest that polyphenol-rich diets may decrease the risk of chronic diseases by reducing oxidative stress.

Polyphenols from alcoholic apple cider are absorbed, metabolized and excreted by humans.

We determined the uptake and excretion of low doses of polyphenols in six subjects who each consumed 1.1 L of an alcoholic cider beverage. Over a 24-h period, no phloretin was detected in plasma (detection limit = 0.036 micromol/L), but 21 +/- 5% of the dose (4.8 mg) was excreted in the urine. In contrast, from a low dose of 1.6-mg quercetin equivalents, no quercetin was found in urine or plasma, but 3'-methyl quercetin was detected in plasma [C(max) (maximum concentration) = 0.14 +/- 0.19 micromol/L; range: 0 to 0.44 micromol/L]. No flavanol monomers (dose of free (+)-catechin and (-)-epicatechin = 3.5 mg) were detected in urine or plasma (detection limit: 0.01 micromol/L). Caffeic acid (total dose including esters = 11 mg) was detected only in plasma within 2 h, with C(max) = 0.43 +/- 0.3 micromol/L (range: 0.18 to 0.84 micromol/L). An almost 3-fold increase in hippuric acid was detected in 24-h urine (74 +/- 29 micromol/L; range: 38-116 micromol/L), compared with a prestudy value of 19 +/- 9 micromol/L. These data show that polyphenols are taken up from cider, that phloretin is excreted in the urine and suggest that low doses of quercetin are extensively methylated in humans.

Ultrasensitive assay for three polyphenols (catechin, quercetin and resveratrol) and their conjugates in biological fluids utilizing gas chromatography with mass selective detection.

The concentrations of three polyphenols ((+)-catechin, quercetin and trans-resveratrol) in blood serum, plasma and urine, as well as whole blood, have been measured after their oral and intragastric administration, respectively, to humans and rats. The method developed for this purpose utilized ethyl acetate extraction of 100 microl samples and their derivatization with bis(trimethylsilyl)trifluoroacetamide (BSTFA) followed by gas-chromatographic analysis on a DB-5 column followed by mass selective detection employing two target ions and one qualifier ion for each compound. Total run time was 17 min with excellent resolution and linearity. The limits of detection (LOD) and quantitation (LOQ) were an order of magnitude less than for any previously published method, being 0.01 microg/l and 0.1 microg/l, respectively, for all compounds. Recovery at 1 microg/l and 10 microg/l was >80% in all instances but one, and was >90% in 50%. Imprecision was acceptable at 0.25 and 1.0 microg/l, concentrations below the LOQ of previous methods. Aglycones released from conjugates after hydrolysis were easily measurable. Optimal conditions for hydrolysis were established. After oral administration of the three polyphenols to humans, their conjugates vastly exceeded the concentrations of the aglycones in both plasma and urine. Concentrations peaked within 0.5-1.0 h in plasma and within 8 h in urine. During the first 24 h, 5.1% of the (+)-catechin and 24.6% of the trans-resveratrol given were recovered in the urine (free plus conjugated). This method can be proposed as the method of choice to assay these polyphenols and their conjugates in biological fluids.

Estrogenic activity of flavonoids in mice. The importance of estrogen receptor distribution, metabolism and bioavailability.

The in vivo estrogenic potential of the flavonoids apigenin, kaempferol, genistein and equol was investigated in immature female mice. Genistein and equol, administered by gavage for 4 consecutive days [post-natal day (PND) 17-20, 100 mg/kg body weight], was found to significantly increase uterine weights and the overall uterine concentration of estrogen receptor alpha (ERalpha). In kaempferol- and equol-exposed mice the cytosolic ERalpha concentration was significantly increased as compared to the solvent control, which is speculated to result in an increased sensitivity of the uterus to subsequently encountered estrogens. Oral administration of equol, genistein, biochanin A and daidzein to 6-week-old female mice revealed a great variation in their systemic bioavailability. The urinary recovery of equol was thus over 90% of a single gavage administered dose, whereas the urinary recoveries of biochanin A, genistein and daidzein were 16, 11 and 3%, respectively. Most of the metabolites were either hydroxylated or dehydrogenated forms of the parent compounds. The in vitro estrogenic potency of some of the metabolites was greater than that of the parent compounds, whereas others were of similar or lower potency. Bioavailability, metabolism, the ability to alter ERalpha distribution in the uterus and the estrogenic potential of parent compound and metabolites may thus contribute to the differences in in vivo estrogenicity of dietary flavonoids.

[Polyphenolic antioxidants in fruit juice. Urinary excretion and effects on biological markers for antioxidative status]. / Polyfenoliske antioxidanter i frugtjuice. Udskillelse i urin samt indflydelse på biomarkører for antioxidativ status.

This intervention study was designed as cross-over (four women, one man) with three doses of black currant/apple (1:1) juice (750, 1000, and 1500 mL) for one week corresponding to an intake of 4.8, 6.4, and 9.6 mg quercetin per day. Urinary excretion of quercetin increased significantly with dose and with time. The fraction excreted in urine was constant 0.29-0.47%. Plasma quercetin did not change with juice intervention. Plasma ascorbate increased during intervention due to ascorbate from the juice. Total plasma malondialdehyde decreased with time during 1500 mL juice intervention. Plasma protein 2-adipic semialdehyde residues, increased with time and dose, and glutathione peroxidase increased with juice dose, whereas other selected markers of oxidative status did not change. These effects might be related to several components of the juice and cannot be attributed solely to its quercetin content.

In vitro glucuronidation of kaempferol and quercetin by human UGT-1A9 microsomes.

Flavonoids are important polyphenolic substances with widespread occurrence in plants and therefore in the human diet. Although considerable work has been done on the pharmacology of flavonoids, the understanding of their metabolism is still incomplete. In this work, the in vitro glucuronidation of the common dietary flavonoids quercetin and kaempferol by human UDP-glucuronosyltransferase microsomes (UGT-1A9) was investigated using HPLC and LC-MS. The two flavonoids were extensively metabolised by this enzyme with four monoglucuronides of quercetin and two of kaempferol being detected after incubation. The presence of a quercetin monoglucuronide in the urine of a volunteer after consumption of Ginkgo biloba tablets was demonstrated.

Solid-phase extraction and gas chromatography-mass spectrometry determination of kaempferol and quercetin in human urine after consumption of Ginkgo biloba tablets.

A method was developed for the quantification of the flavonoids quercetin and kaempferol in human urine using a solid-phase extraction procedure followed by gas chromatography-mass spectrometry. Deuterated internal standards of the analytes were spiked into the samples prior to extraction. The limit of detection of the method was ca. 10 pg on column and precision of the method for quantification in a sample of urine was +/-9.40% for kaempferol and +/-7.34% for quercetin (n = 6). The levels of quercetin and kaempferol found in urine samples were only a small fraction of the amount ingested. The treatment of urine samples with beta-glucuronidase markedly increased the levels of flavonoids detected, supporting the view that kaempferol and quercetin are eliminated in the urine as glucuronides.

Absorption and excretion of conjugated flavonols, including quercetin-4'-O-beta-glucoside and isorhamnetin-4'-O-beta-glucoside by human volunteers after the consumption of onions.

Flavonols are polyphenols found ubiquitously in plants and plant-products. Flavonols, particularly quercetin, are potent antioxidants in vitro and their intake has been associated inversely with the incidence of coronary heart disease. The aim of this study was to investigate the accumulation in plasma and excretion in urine of flavonol glucosides following ingestion of lightly fried onions. Five healthy volunteers followed a low-flavonoid diet for 3 days. On day 4, after an overnight fast, subjects were given 300 g of lightly fried yellow onions which contain conjugates of quercetin and isorhamnetin, including quercetin-3,4 '-diO-beta-glucoside, isorhamnetin-4'-O-beta-glucoside and quercetin-4'-O-beta-glucoside. Blood collection was carried out at 0 min, 0.5, 1.0, 1.5, 2, 3, 4, 5 and 24h after the supplement. In addition, subjects collected all their urine for 24h following the onion supplement. Isorhamnetin-4'-O-beta-glucoside and quercetin-4 '-O-beta-glucoside accumulated in plasma with maximum levels, defined as proportion of intake, of 10.7+/-2.6% and 0.13+/-0.03% respectively. The time of the quercetin-4'glucoside peak plasma concentration was 1.3+/-0.2 h after the ingestion of onions while a value of 1.8+/-0.7 h was obtained for isorhamnetin-4'-glucoside. Excretion in urine, as a proportion of intake, was 17.4+/-8.3% for isorhamnetin-4'-O-beta-glucoside and 0.2+/-0.1% for quercetin-4'-O-beta-glucoside. Possible reasons for the accumulation and excretion of isorhamnetin-4'-glucoside in proportionally much higher amounts than quercetin-4'-glucoside are discussed. It is concluded that flavonols are absorbed into the bloodstream as glucosides and minor structural differences affect markedly both the level of accumulation and the extent to which the conjugates are excreted.

Plasma concentrations and urinary excretion of the antioxidant flavonols quercetin and kaempferol as biomarkers for dietary intake.

Flavonols are antioxidants that may reduce the risk of heart disease. Two major flavonols in the diet are quercetin and kaempferol, and their main sources in The Netherlands are tea and onions. We investigated whether plasma concentrations and urinary excretion of quercetin and kaempferol in humans could be used as biomarkers of intake. We provided 15 subjects with strong black tea (1600 mL/d) or fried onions (129 g/d) for 3 d each in random order separated by a 4-d washout period. The tea provided 49 mg quercetin and 27 mg kaempferol daily and the onions provided 13 mg quercetin and no kaempferol. Flavonols from both foods were clearly absorbed. However, the excretion of unmodified quercetin was 0.5% of intake after tea and 1.1% after onions. Thus, the absorption of quercetin from tea was half of that from onions. The onion treatment was repeated 7-14 d later to estimate within-subject CVs as a measure of reproducibility when the same treatment is given twice. CVs for quercetin were 30% in plasma and 42% in urine. The magnitude of these variations relative to actual variations of approximately 60% between free-living subjects indicates that concentrations of quercetin in plasma and urine are applicable as biomarkers of its intake. We conclude that flavonols in plasma and urine reflect short-term flavonol intake and that they could be used as biomarkers to distinguish between high and low flavonol consumption in epidemiologic studies.

Analysis of flavonoids in tablets and urine by gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry.

A method was developed for the analysis and characterization of quercetin and kaempferol in urine following ingestion of Ginkgo biloba tablets. The method utilized gas chromatography/negative ion chemical ionization mass spectrometry of the trimethysilyl derivatives of the flavonoids. Limits of detection for these compounds using this method were ca. 20 pg on column. Liquid chromatography with electrospray mass spectrometry in the negative ion mode was utilized to characterize the complex mixture of glycosides present in the G. biloba tablets, the limit of detection with this technique was ca. 10 ng on column.