High-performance liquid chromatographic determination of quercetin in human plasma and urine utilizing solid-phase extraction and ultraviolet detection

Separation/determination of flavonoids and ascorbic acid in rat serum and excrement by capillary electrophoresis with electrochemical detection

A capillary electrophoresis with electrochemical detection was developed for the simultaneous determination of three flavonoids (naringenin, rutin, quercetin) and ascorbic acid. It was found that naringenin, rutin, quercetin and ascorbic acid were well separated within 5 min in borate buffer solution (pH 8.6, 24 mM). The detection limit was 1.0 microM for naringenin, 8.0 microM for rutin, 2.0 microM for ascorbic acid and 0.5 microM for quercetin. The protocol was successfully applied for the determination of the analytes in rat serum and excrement. Recovery results ranged from 90.9 to 108.6%.

Analysis of isoflavones and flavonoids in human urine by UHPLC

A rapid, ultra high-performance liquid chromatographic (UHPLC) method has been developed and validated for simultaneous identification and analysis of the isoflavones genistein, daidzein, glycitin, puerarin, and biochanin A, and the flavonoids (±)-catechin, (−)-epicatechin, rutin, hesperidin, neohesperidin, quercitrin, and hesperetin in human urine. Urine samples were incubated with β-glucuronidase/sulfatase. UHPLC was performed with a Hypersil Gold (50 × 2.1 mm, 1.9 μm) analytical column. Elution was with a gradient prepared from aqueous trifluoroacetic acid (0.05%) and acetonitrile. UV detection was performed at 254 and 280 nm. The calibration curves were indicative of good linearity (r² ≥ 0.9992) in the range of interest for each analyte. LODs ranged between 15.4 and 107.0 ng mL⁻¹ and 3.9 and 20.4 ng mL⁻¹ for flavonoids and isoflavones, respectively. Intra-day and inter-day precision (C.V., %) was less than 3.9% and 3.8%, respectively, and accuracy was between 0.03% and 5.0%. Recovery was 70.35–96.58%. The method is very rapid, simple, and reliable, and suitable for pharmacokinetic analysis. It can be routinely used for simultaneous determination of these five isoflavones and seven flavonoids in human urine. The method can also be applied to studies after administration of pharmaceutical preparations containing isoflavones and flavonoids to humans.

Determination of quercetin and resveratrol in whole blood--implications for bioavailability studies

Resveratrol (trans-3,4',5-trihydroxystilbene) and quercetin (3,3’,4’,5,7-pentahydroxyflavone) are two naturally occurring polyphenols with the potential to exert beneficial health effects. Since their low bioavailability is a major obstacle to biomedical applications, efforts are being made to improve their absorption and slow down phase II metabolism. An accurate evaluation of the corresponding levels in the bloodstream is important to assess delivery strategies, as well as to verify claims of efficacy based on in vitro results. In the present work we have optimized a simple method ensuring complete stabilization and extraction of resveratrol and quercetin from whole blood. The suitability of different protocols was evaluated by measuring the recovery of polyphenol and internal standard from spiked blood samples via HPLC/UV analysis. The optimized procedure ensured a satisfactory recovery of both internal standards and compounds. Comparing plasma and whole blood, up to 76% of the analyte, being associated with the cellular fraction, was unaccounted for when examining only plasma. This indicates the importance of analysing whole blood rather than plasma to avoid underestimating polyphenol absorption in bioavailability studies.

Quercetin's effect on cycling efficiency and substrate utilization

Previous evidence suggests that quercetin supplementation increases performance in humans. We examined the effects of 3 weeks of quercetin supplementation on fuel utilization, gross efficiency (GE), and perceived effort during 3 h of cycling over 3 successive days. Forty cyclists were randomized into quercetin and placebo groups and tested for maximal oxygen consumption (53.2 +/- 1.2 and 54.7 +/- 1.1 mL.kg(-1).min(-1)). For 3 weeks following maximal oxygen consumption testing, subjects supplemented either 1000 mg.day(-1) quercetin or placebo during normal training. Following supplementation, subjects cycled at 57% maximum power for 3 h, on 3 successive days, using their own bicycles fitted to CompuTrainer Pro Model trainers (RacerMate, Seattle, Wash.). Metabolic measurements were taken every 30 min for each 3-h ride. Muscle biopsies obtained from the vastus lateralis immediately pre-exercise and postexercise on days 1 and 3 were analyzed for muscle glycogen content. Power output remained constant for all 3 exercise trials, but significant decreases over time were measured for GE, cadence, respiratory exchange ratio, blood glucose, and muscle glycogen. Significant increases were measured for heart rate and volume of oxygen consumption over time. No quercetin treatment effect was observed for any of the outcome measures in this study. These data indicate that GE is reduced during an exhausting 3-h bout of exercise. However, quercetin did not significantly affect any outcomes in these already well-trained subjects.

Incorporation of quercetin in lipid microparticles: effect on photo- and chemical-stability

Lipid microparticles loaded with the flavonoid, quercetin were developed in order to enhance its stability in topical formulations. The microparticles were produced using tristearin as the lipid material and phosphatidylcholine as the emulsifier. The obtained lipoparticles were characterized by release studies, scanning electron microscopy and powder X-ray diffractometry. The quercetin loading was 12.1% (w/w). Free or microencapsulated quercetin was introduced in a model cream formulation (oil-in-water emulsion) and irradiated with a solar simulator. The extent of photodegradation was measured by high-performance liquid chromatography. The light-induced decomposition of quercetin in the cream vehicle was markedly decreased by incorporation into the lipid microparticles (the extent of degradation was 23.1+/-3.6% for non-encapsulated quercetin compared to 11.9+/-2.5% for the quercetin-loaded microparticles) and this photostabilization effect was maintained over time. Moreover, the chemical instability of quercetin, during 3-month storage of the formulations at room temperature and in the dark, was almost completely suppressed by the lipid microparticle system. Therefore incorporation of quercetin in lipoparticles represents an effective strategy to enhance its stability in dermatological products.

Quercetin's influence on exercise-induced changes in plasma cytokines and muscle and leukocyte cytokine mRNA

Trained male cyclists ( n = 40) ingested quercetin (Q; n = 20) (1,000 mg/day) or placebo (P; n = 20) supplements under randomized, double-blinded methods for 3 wk before and during a 3-day period in which subjects cycled for 3 h/day at ∼57% maximal work rate. Blood samples were collected before and after each exercise session and assayed for plasma IL-6, IL-10, IL-1ra, IL-8, TNF-α, and monocyte chemoattractant protein 1, and leukocyte IL-10, IL-8, and IL-1ra mRNA. Muscle biopsies were obtained before and after the first and third exercise sessions and assayed for NF-κB and cyclooxygenase-2 (COX-2), IL-6, IL-8, IL-1β, and TNF-α mRNA. Postexercise increases in plasma cytokines did not differ between groups, but the pattern of change over the 3-day exercise period tended to be lower in Q vs. P for IL-8 and TNF-α ( P = 0.094 for both). mRNA increased significantly postexercise for each cytokine measured in blood leukocyte and muscle samples. Leukocyte IL-8 and IL-10 mRNA were significantly reduced in Q vs. P (interaction effects, P = 0.019 and 0.012, respectively) with no other leukocyte or muscle mRNA group differences. Muscle NF-κB did not increase postexercise and did not differ between Q and P. Muscle COX-2 mRNA increased significantly postexercise but did not differ between Q and P. In summary, 1 g/day quercetin supplementation by trained cyclists over a 24-day period diminished postexercise expression of leukocyte IL-8 and IL-10 mRNA, indicating that elevated plasma quercetin levels exerted some effects within the blood compartment. Quercetin did not, however, influence any of the muscle measures, including NF-κB content, cytokine mRNA, or COX-2 mRNA expression across a 3-day intensified exercise period.

Separation and determination of flavonoids in Lamiophlomis rotata by capillary electrophoresis using borate as electrolyte

A capillary electrophoresis method was developed for the simultaneous determination of five flavonoids such as luteolin-7-O-glucoside, isorhamnetin, apigenin, luteolin and quercetin in Lamiophlomis rotata (Benth.) Kudo. Optimal conditions were obtained at pH 9.0 with 30 mM borate as buffer containing 8% (v/v) acetonitrile, 20 kV as driving voltage and 210 nm as detection wavelength. The association constant K and the change in Gibbs free energy (DeltaG) of the interaction of flavonoids with borate anion ion (a typical ion-dipole or ion-induced dipole interaction) were calculated for the quantitative evaluation and characterization of the interaction. The described method was successfully applied for the rapid and efficient quality control by quantifying flavonoids in L. rotata. Repeatability tests showed that the R.S.D.s of both intra- and inter-day migration times and peak areas were less than 5%. The LOD of the five flavonoids was less than 3.75 mg/l. Recovery results ranged from 94.2% to 105.1%.

Molecular imprinting of natural flavonoid antioxidants: Application in solid-phase extraction for the sample pretreatment of natural products prior to HPLC analysis

As shown in the past years, SPE based on molecularly imprinted polymers (MIPs) may provide significant enhancement of selectivity in sample preparation and analyte preconcentration. The objective of this work was the fabrication of MIPs for the specific adsorption of rutin and quercetin. The two flavonoids were used as the template molecules for the preparation of MIP phases in a self-assembly (noncovalent) approach. The produced MIPs were validated with regard to the imprinting efficiency as media for LC and SPE. The retention behavior of several flavonoid compounds was studied using as stationary phases imprinted, control nonimprinted polymers, and commercial silica-based materials. MIPs were applied as materials for the selective SPE and preconcentration of the flavonoids from white and red wine, orange juice, and tea. The collected fractions were analyzed by high-pressure LC. MIP-SPE facilitated specific analyte isolation and effective sample clean-up. The results show that molecularly imprinted SPE can be a useful tool for the simple, selective, and cost-effective pretreatment of samples containing natural antioxidants.

Determination of St. John's wort flavonoid-metabolites in rat brain through high performance liquid chromatography coupled with fluorescence detection

Flavonoids with the quercetin structure are widely distributed throughout the plant kingdom. Some effects such as their anti-oxidative and radical scavenging capacities are broadly discussed in literature. Furthermore, some Hypericum flavonoids show activity in depression-relevant animal model assays. So far, only one study concerning the pharmacokinetic profile of Hypericum perforatum (St. John's wort, SJW) flavonoids has been reported, but no data concerning their bioavailability in the CNS is on-hand. Thus, we developed a method for the quantification of quercetin, tamarixetin and isorhamnetin, both metabolites of quercetin, in very low concentrations in the rat brain in order to investigate the ability of flavonoids to cross the blood-brain barrier. The brain samples for analysis were taken 4h after feeding an oral dose of an alcoholic SJW extract or pure isoquercitrin. We found the presence of quercetin and isorhamnetin/tamarixetin after feeding a SJW extract at 7 ng/g brain and 35 ng/g brain, respectively. In addition, we examined blood plasma taken from the same rats to correlate plasma and brain levels. The plasma levels were 350 ng/mL for quercetin and 1006 ng/mL for isorhamnetin/tamarixetin after intake of SJW extract.

Analysis of tea catechins in human plasma by high-performance liquid chromatography with solid-phase extraction

Accurate monitoring of tea catechins in biological samples might provide a means of better evaluation of their benefits. The aim of the present study was to develop a rapid method for extracting tea catechins from human plasma samples with a solid-phase extraction technique and to subsequently measure their concentrations using an HPLC system. A human plasma sample spiked with known concentrations of the analyte standards was passed through a Waters Oasis HLB cartridge. After repeated washing, tea catechins were eluted with 70% dimethylformamide containing 0.1% phosphoric acid, and the resulting eluate was injected into an HPLC system. Analytes were separated on a reverse-phase C18 column using an isocratic mobile phase and detected electrochemically. The coefficient of variation for inter- and intraday reproducibility was less than 5.0% and 6.4%, respectively. Linearity was established for the concentration range of 0.01-1.0 microM. The method was successfully applied to measure tea catechin concentrations in the plasma of two healthy subjects who received a single ingestion of a green tea beverage. The proposed method enables the rapid and accurate quantitation of plasma tea catechins and might prove useful for the evaluation of beneficial health effects of tea consumption.

Human NAD(P)H:quinone oxidoreductase inhibition by flavonoids in living cells

Procedures for assessing enzyme inhibition in living cells are an important tool in the study of the relevance of enzyme-catalyzed reactions and interactions in the human body. This paper presents the effects of flavonoids on NAD(P)H:quinone oxidoreductase 1 (NQO1) activity, by a newly developed method to measure NQO1 inhibition in intact cells. The principle of this method is based on the resorufin reductase activity of NQO1. The change in fluorescence in time was used to determine NQO1 activity in intact Chinese hamster ovary (CHO) cells genetically engineered to overexpress human NQO1. Applying this method to determine the inhibitory effects of reported in vitro NQO1 inhibitors (dicoumarol, 7,8-dihydroxyflavone, chrysin) showed that for all inhibitors tested, the IC50 in intact cells was at least 3 orders of magnitude higher than the IC50 in cell lysates. This result demonstrates that in vitro studies with purified NQO1 or with extracts from disrupted tissues are of limited value for obtaining insight into the situation in living cells. Possible factors underlying this discrepancy are being discussed. For the first time, we determined NQO1 inhibition by flavonoids in cells without disruption of the cells or addition of cofactors, enabling the assessment of enzymatic activity and the interaction of modulators of enzymatic activity in an intracellular situation.

Modulation of osteoclastogenesis in porcine bone marrow cultures by quercetin and rutin

Flavonols, in contrast to soybean isoflavones, are the most abundant phytoestrogens in western diets, being present in onions, beans, fruits, red wine, and tea. They may protect against atherosclerosis, inhibit certain cancer cell types, and reduce bone resorption. The most widely distributed flavonol is quercetin, which occurs mainly as its glycoside, rutin, but data are very scarce regarding the precise mechanism of action of these compounds on bone-resorbing cells at concentrations similar to those detected in human plasma. We have therefore investigated the effects of nanomolar concentrations of quercetin and rutin on the development and activity of osteoclasts in vitro compared with the effects of 17beta-estradiol. Nonadherent porcine bone marrow cells were cultured on dentine slices in the presence of 10 nM 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), with or without 10 nM quercetin, 10 nM rutin or 10 nM 17beta-estradiol for 11 days. Multinuclear TRAP+ cells that resorbed dentine (osteoclasts) developed in the presence of 1,25(OH)2D3, but their number was significantly reduced by quercetin, rutin, and 17beta-estradiol (P < 0.05). Like 17beta-estradiol, both flavonols also significantly reduced resorption (P<0.05) as assessed by the size of pits resorbed on dentine slices. Osteoclasts and osteoclast progenitors contained estrogen receptor alpha (ERalpha), ERbeta, and RANK proteins. Both flavonols increased nuclear ERbeta protein and decreased ERalpha protein of osteoclast progenitors. Moreover, rutin reduced RANK protein, whereas 17beta-oestradiol and quercetin promoted apoptosis by cleavage of caspase-8 and caspase-3. All the effects of flavonols were reversed by 1 microM ICI 182,780, an estrogen antagonist. Thus, the anti-resorbing properties of flavonols are mainly mediated by ER proteins through the inhibition of RANK protein or the activation of caspases.