An UHPLC-MS/MS method for simultaneous determination of quercetin 3-O-rutinoside, kaempferol 3-O-rutinoside, isorhamnetin 3-O-rutinoside, bilobalide and ligustrazine in rat plasma, and its application to pharmacokinetic study of Xingxiong injection.

The present study was designed to develop and validate a rapid, sensitive, and reliable ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) method for the simultaneous determination of five major active constituents in the traditional Chinese medicinal preparation Xingxiong injection (XXI) in rat plasma, including quercetin 3-O-rutinoside (QCR), kaempferol 3-O-rutinoside (KFR), isorhamnetin 3-O-rutinoside (ISR), bilobalide (BB), and ligustrazine (LGT). The plasma samples were pretreated by protein precipitation with acetonitrile. The chromatographic separation was achieved on a Waters Symmetry C18 analytical column (2.1 mm × 100 mm, 3.5 µm) with a mobile phase of 0.1% aqueous formic acid (A)-acetonitrile (B). Quantitation of the five bioactive constituents was achieved. Naringin was used as the internal standard (IS). All the calibration curves showed good linearity (r > 0.996) over the concentration range, with the lowest limit of quantification (LLOQ) between 2-18 ng·mL-1. The intra- and inter-day accuracy and precision of the analytes were both within acceptable limits. Moreover, satisfactory extraction recoveries (90.92%-104.03%) were obtained by protein precipitation. The validated method was successfully applied to a pharmacokinetic study of XXI in rats after intravenous administration at three doses. The pharmacokinetic parameters of the five compounds varied in a dose-dependent manner within the tested dosage range. The present study was the first report of pharmacokinetic study for XXI.

Simultaneous determination of three active components in rat plasma by UPLC-MS/MS: Application to pharmacokinetic study after oral administration of Herba Sarcandrae extract.

A rapid, specific and sensitive ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for determination of isofraxidin, rosmarinic acid and kaempferol-3-O-glucuronide in rat plasma using warfarin as an internal standard (IS). Separation was conducted on a Thermo Hypersil GOLD C18 column with linear gradient elution using methanol and water. Mass spectrometric detection was conducted using selected reaction monitoring (SRM) via an electrospray ionization (ESI) source. All analytes exhibited good linearity within their concentration ranges (r > 0.9990). The lower limits of quantitations of isofraxidin, rosmarinic acid, and kaempferol-3-O-glucuronide were 1.31, 0.67 and 0.92 ng/mL, respectively. Intra- and inter-day precisions of these investigated components exhibited an RSD within 11.7%, and the accuracy ranged from -12.5 to 15.0% at all QC levels. The developed method was successfully applied to a pharmacokinetic study of isofraxidin, rosmarinic acid, and kaempferol-3-O-glucuronide in rats after oral administration of Herba Sarcandrae Extract.

Pharmacokinetics of dietary kaempferol and its metabolite 4-hydroxyphenylacetic acid in rats.

SCOPE: Kaempferol is a major flavonoid in the human diet and in medicinal plants. The compound exerts anxiolytic activity when administered orally in mice, while no behavioural changes were observed upon intraperitoneal administration, or upon oral administration in gut sterilized animals. 4-Hydroxyphenylacetic acid (4-HPAA), which possesses anxiolytic effects when administered intraperitoneally, is a major intestinal metabolite of kaempferol. Pharmacokinetic properties of the compounds are currently not clear. METHODS AND RESULTS: UHPLC-MS/MS methods were validated to support pharmacokinetic studies of kaempferol and 4-HPAA in rats. Non-compartmental and compartmental analyses were performed. After intravenous administration, kaempferol followed a one-compartment model, with a rapid clearance (4.40-6.44l/h/kg) and an extremely short half-life of 2.93-3.79min. After oral gavage it was not possible to obtain full plasma concentration-time profiles of kaempferol. Pharmacokinetics of 4-HPAA was characterized by a two-compartment model, consisting of a quick distribution phase (half-life 3.04-6.20min) followed by a fast elimination phase (half-life 19.3-21.1min). CONCLUSION: Plasma exposure of kaempferol is limited by poor oral bioavailability and extensive metabolism. Both compounds are rapidly eliminated, so that effective concentrations at the site of action do not appear to be reached. At present, it is not clear how the anxiolytic-like effects reported for the compounds can be explained.

Pharmacokinetic evaluation of the interaction between oral kaempferol and ethanol in rats.

This study was aimed at investigating the effect of ethanol on oral bioavailability of kaempferol in rats, namely, at disclosing their possible interaction. Kaempferol (100 or 250 mg kg-1 bm) was administered to the rats by oral gavage with or without ethanol (600 mg kg-1 bm) co-administration. Intravenous administration (10 and 25 mg kg-1 bm) of kaempferol was used to determine the bioavailability. The concentration of kaempferol in plasma was estimated by ultra high performance liquid chromatography. During coadministration, a significant increase of the area under the plasma concentration-time curve as well as the peak concentration were observed, along with a dramatic decrease in total body clearance. Consequently, the bioavailability of kaempferol in oral control groups was 3.1 % (100 mg kg-1 bm) and 2.1 % (250 mg kg-1 bm). The first was increased by 4.3 % and the other by 2.8 % during ethanol co-administration. Increased permeability of cell membrane and ethanolkaempferol interactions on CYP450 enzymes may enhance the oral bioavailability of kaempferol in rats.

Production, Characterization and Evaluation of Kaempferol Nanosuspension for Improving Oral Bioavailability.

CONTEXT: Kaempferol has a large particle size and poor water solubility, leading to poor oral bioavailability. The present work aimed to develop a kaempferol nanosuspension (KNS) to improve pharmacokinetics and absolute bioavailability. METHODS: A nanosuspension was prepared using high pressure homogenization (HPH) techniques. The physico-chemical properties of the kaempferol nanosuspension (KNS) were characterized using photon correlation spectroscopy (PCS), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and x-ray diffractometry (XRD). A reversephase high performance liquid chromatography (RP-HPLC) method for the analysis of the drug in rat plasma was developed and validated as per ICH guidelines. In vivo pharmacokinetic parameters of oral pure kaempferol solution, oral kaempferol nanosuspension and intravenous pure kaempferol were assessed in rats. RESULTS AND DISCUSSION: The kaempferol nanosuspension had a greatly reduced particle size (426.3 ± 5.8 nm), compared to that of pure kaempferol (1737 ± 129 nm). The nanosuspension was stable under refrigerated conditions. No changes in physico-chemical characteristics were observed. In comparison to pure kaempferol, kaempferol nanosuspension exhibited a significantly (P<0.05) increased in Cmax and AUC(0-∞) following oral administration and a significant improvement in absolute bioavailability (38.17%) compared with 13.03% for pure kaempferol. CONCLUSION: These results demonstrate enhanced oral bioavailability of kaempferol when formulated as a nanosuspension.

Sensitive determination of kaempferol using carbon dots as a fluorescence probe.

In this study, a new sensitive and convenient method for the determination of kaempferol (Kae) based on the fluorescence quenching of fluorescent carbon dots (C-dots) was developed. The C-dots were prepared by simply mixing acetic acid, water and diphosphorus pentoxide. This green synthesis approach proceeds rapidly and gives large quantities of C-dots. The fluorescence of the C-dots decreased obviously with the increase of Kae concentration. The effect of other interfering substances on the fluorescence intensity of C-dots showed low interference. Under the optimum conditions, a linear correlation was established between fluorescence intensity ratio Fo/F and the concentration of Kae in the range of 3.5-49 µM with a detection limit (S/N=3) of 38.4 nM. The proposed method has been successfully applied to determination of Kae in xindakang tablets and human serum samples with recovery in the range of 94.6-109.0%. The C-dots could be a promising fluorescence probe for the detection of Kae owing to its low-cost production, easy operation, low cytotoxicity, and excellent biocompatibility.

HPLC Plasma Assay of a Novel Anti-MRSA Compound, Kaempferol-3-O-Alpha-L-(2",3"-di-p-coumaroyl)rhamnoside, from Sycamore Leaves.

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious pathogen that is resistant to current antibiotic therapy. Thus, there is an urgent need for novel antimicrobial agents that can effectively combat these new strains of drug-resistant "superbugs". Recently, fractionation of an extract from Platanus occidentalis (American sycamore) leaves produced an active kaempferol molecule, 3-O-alpha-L-(2",3"-di-p-coumaroyl)rhamnoside (KCR), in four isomeric forms; all four isomers exhibit potent anti-MRSA activity. In order to further the preclinical development of KCR as a new antibiotic class, we developed and validated a simple analytical method for assaying KCR plasma concentration. Because KCR will be developed as a new drug, although comprising four stereoisomers, the analytical method was devised to assay the total amount of all four isomers. In the present work, both a plasma processing procedure and an HPLC method have been developed and validated. Mouse plasma containing KCR was first treated with ethanol and then centrifuged. The supernatant was dried, suspended in ethanol, centrifuged, and the supernatant was injected into an HPLC system comprising a Waters C18, a mobile phase composing methanol, acetonitrile, and trifluoroacetic acid and monitored at 313 nm. The method was validated by parameters including a good linear correlation, a limit of quantification of 0.27 microg/mL, and high accuracy. In summary, this method allows a rapid analysis of KCR in the plasma samples for pharmacokinetics studies.

Bioavailability of the flavonol quercetin in neonatal calves after oral administration of quercetin aglycone or rutin.

Polyphenols, such as flavonoids, are secondary plant metabolites with potentially health-promoting properties. In newborn calves flavonoids may improve health status, but little is known about the systemically availability of flavonoids in calves to exert biological effects. The aim of this study was to investigate the oral bioavailability of the flavonol quercetin, applied either as quercetin aglycone (QA) or as its glucorhamnoside rutin (RU), in newborn dairy calves. Twenty-one male newborn German Holstein calves were fed equal amounts of colostrum and milk replacer according to body weight. On d 2 and 29 of life, 9 mg of quercetin equivalents/kg of body weight, either fed as QA or as RU, or no quercetin (control group) were fed together with the morning meal. Blood samples were taken before and 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 12, 24, and 48 h after feed intake. Quercetin and quercetin metabolites with an intact flavonol structure (isorhamnetin, tamarixetin, and kaempferol) were analyzed in blood plasma after treatment with glucuronidase or sulfatase by HPLC with fluorescence detection. Maximum individual plasma concentration was depicted from the concentration-time-curve on d 2 and 29, respectively. Additional blood samples were taken to measure basal plasma concentrations of total protein, albumin, urea, and lactate as well as pre- and postprandial plasma concentrations of glucose, nonesterified fatty acids, insulin, and cortisol. Plasma concentrations of quercetin and its metabolites were significantly higher on d 2 than on d 29 of life, and administration of QA resulted in higher plasma concentrations of quercetin and its metabolites than RU. The relative bioavailability of total flavonols (sum of quercetin and its metabolites isorhamnetin, tamarixetin, and kaempferol) from RU was 72.5% on d 2 and 49.6% on d 29 when compared with QA (100%). Calves fed QA reached maximum plasma concentrations of total flavonols much earlier than did RU-fed calves. Plasma metabolites and hormones were barely affected by QA and RU feeding in this experiment. Taken together, orally administrated QA resulted in a greater bioavailability of quercetin than RU on d 2 and 29, respectively, and quercetin bioavailability of quercetin and its metabolites differed markedly between calves aged 2 and 29 d.

Quercetin and its metabolites inhibit the membrane NADPH oxidase activity in vascular smooth muscle cells from normotensive and spontaneously hypertensive rats.

Quercetin, the most abundant dietary flavonol, exerts antioxidant effects reducing vascular superoxide (O2(-)) and improving endothelial function in animal models of cardiovascular disease. Herein we evaluated the effects of quercetin, and its plasma metabolites, on the nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase activity, the main source of O2(-) in the vessel wall, in vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). Quercetin and its metabolites isorhamnetin and kaempferol inhibited the NADPH-stimulated lucigenin-chemiluminescence signal in VSMCs from both strains. The inhibitory effect of quercetin-3-glucuronide increased after prolonged incubation and was inhibited in the presence of the ß-glucuronidase inhibitor saccharolactone. These effects were unrelated to their O2(-) scavenging properties, since they induced only a small inhibition of the rate of pyrogallol autoxidation at high concentrations. All bioflavonoids tested acted as non-competitive inhibitors with respect to NADPH. In conclusion, quercetin and its metabolites inhibit the NADPH oxidase activity in VSMCs reducing O2(-) generation more efficiently than their effect as O2(-) scavengers. The effect of quercetin-3-glucuronide was due to deconjugation and release of free quercetin. The effect is similar in VSMCs from normotensive and hypertensive animals.

[Determination of plasma concentration of quercetin, kaempferid and isorhamnetin in Hippophae rhamnoides extract by HPLC-MS/MS and pharmacokinetics in rats].

To establish an HPLC-MS/MS method for the analysis of quercetin, kaempferid and isorhamnetin in rats plasma and study its pharmamacokinetics after an intragastrical administration of Hippophae rhamnoides extracts. Five healthy male Sprague-Dawley (SD) rats were given single doses of H. rhamnoides extracts (quercetin 26.35 mg x kg(-1), kaempferid 4.040 mg x kg(-1), isorhamnetin 31.37 mg x kg(-1)), and then their orbital sinus blood samples were collected at different time points. The drug plasma concentration of the three flavonoids was determined by HPLC-MS/MS method. After that, the main pharmacokinetics parameters were calculated by using Kinetica 5. 0. 11 software. The methodological test showed that the linear concentration ranges of quercetin, kaempferid and isorhamnetin were 7.500-600.0 µg x L(-1) (R2 = 0.998 5), 1.000-80.00 µg x L(-1) (R2 = 0.998 5 ) and 10.00-800.0 µg x L(-1) (R2 = 0.998 0), respectively. The inner and inter-days precisions were both less than 14.0%. The plasma samples showed a good stability and consistency with the requirement of biological sample analysis after the samples were frozen once and placed at - 20 degrees C for 15 d and room temperature for 6 h and the treated analytes were placed at -20 degrees C for 24 h. For quercetin, the pharmacokinetic parameter t(½ß), AUC(0-∞), MRT(0.∞), C.(max) and T(max) were (113.3 ± 19.37) min, (12 542.14 ± 3 504.05) µg x h x L(-1), (119.6 ± 13.29) h, (164.6 ± 27.33) µg x L(-1) and (5.199 ± 0.840 3) h, respectively. For kaempferid, the pharmacokinetic parameters t(½ß), AUC(0-t), MRT(0-∞), C(max) and T(max) were (79.85 ± 17.15) min, (934.51 ± 94.59) µg x h x L(-1), (81.50 ± 13.75) h, (80.15 ± 14.24) µg x L(-1) and (3.827 ± 0.902 7) h, respectively. For isorhamnetin, the pharmacokinetic parameters t1,2,, AUC(0-t), MRT(0-∞), C(max) and T(max) were (118.3 ± 20.73) min, (26 067.77 ± 4 124.60) µg x h x L(-1), (129.0 ± 16.30) h, (269.6 ± 29.32) µg x L(-1) and (6.513 ± 1.450) h, respectively. The HPLC-MS/MS analysis method established in this study was proved to be sensitive and accurate and could be applied in the pharmacokinetic study of quercetin, kaempferid and isorhamnetin in rat plasma.

The antibacterial activity of phytochemically characterised fractions from Folium Syringae.

To identify the most active antimicrobial fraction of Folium Syringae, four common pathogens were used in an in vitro screening. The results indicated that the combination of the 30% and 60% ethanol fraction (FSC) obtained from the water extraction was the most active fraction with a minimal inhibitory concentration of 0.65 mg mL(-1). FSC was also found to be able to protect mice from a lethal infection of Staphylococcus aureus at clinical dosage (0.2 g kg(-1)) with a survival rate of 83.3%. The antibacterial activity of FSC was then tested using the serum pharmacology method which revealed that FSC exhibits a more long-lasting activity than the positive control (levofloxacin hydrochloride). The main components were confirmed to be iridoid glycosides and flavones by HPLC-MS analysis.

[HPLC-MS/MS for determination of astragalin in rat plasma and its pharmacokinetics].

OBJECTIVE: To develop a LC-MS/MS method for determination of astragalin in rat plasma and study its pharmacokinetics in rats. METHODS: The analytical column was packed with ZORBAX SB-C18, and the mobile phase was methanol-water containing 10 mmol/L ammonium acetate-formic acid (80:20:0.15, V/V/V). Quercetin was used as the internal standard (IS). Multiple reaction monitoring (MRM) mode was employed, and the transition of m/z was m/z 449.1→m/z 287.1 for astragalin, and m/z 301.1→m/z 151.1 for IS. RESULTS: A good liner relationship was obtained within the range of 1.00-1000 ng/ml (r(2)=0.9929), and the lower limit of quantification of astragalin was 1.00 ng/ml in rat plasma. The extraction recoveries were all above 93%. After oral administration of astragalin, the maximum plasma concentration of astragalin was 231.1∓67.3 ng/ml and the time to reach this value was 0.5∓0.1 h, with a half-life of 3.9∓1.3 h and an AUC of 782.6∓152.8 ng·h/ml. CONCLUSION: The method is highly sensitive, selective and rapid for determination of the concentration of astragalin in rat plasma to facilitates the study of its pharmacokinetics.

A rapid and sensitive liquid chromatography-tandem mass spectrometric method for determination of actinoside E in rat plasma and application to a pharmacokinetic study.

A highly sensitive liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed for the determination of actinoside E in rat plasma. The analytes were extracted by ethyl acetate and an analogue of actinoside F was used as the internal standard. The mobile phase consisted of methanol-water (50: 50, V/V) containing 0.1% formic acid was delivered at a flow rate of 0.3 mL·min(-1) to a Zorbax SB-C18 column (100 mm × 2.1 mm, 3.5 µm). The detection was performed by electrospray ionization mass spectrometry in the negative multiple reaction monitoring mode with a chromatograph run time of 3.0 min. Calibration curves of actinoside E were linear in the range of 0.5-2 500 ng·mL(-1). In this range, intra- and inter-day precision ranged from 1.7% to 7.5% and 2.0% to 8.9%, respectively. The accuracy ranged from 95.7% to 108.6%, and extraction recovery from 83.2% to 85.5%. This method was successfully applied to a pharmacokinetic study of actinoside E in rats after intravenous (5 mg·kg(-1)) and oral (100 mg·kg(-1)) administration, and the results showed that actinoside E was poorly absorbed with an absolute bioavailability being approximately 0.27%.

Pharmacokinetic study of major bioactive components in rats after oral administration of extract of Ilex hainanensis by high-performance liquid chromatography/electrospray ionization mass spectrometry.

Ilex hainanensis Merr. is commonly used as a folk remedy for treating hypertension, dyslipidemia and inflammation in Traditional Chinese Medicine (TCMs) and it also has great potential to treat non-alcoholic fatty liver disease (NAFLD). Chlorogenic acid, kaempferol-7-O-ß-d-glucoside, and ilexgenin A are three major bioactive components in I. hainanensis extract. In this study, a rapid, sensitive and convenient LC-MS method was developed for their simultaneous determination in the plasma of normal and NAFLD rats. The method was validated in terms of selectivity, linearity and sensitivity, and shows advantages in monitoring the pharmacokinetic behaviors of these three compounds. Results revealed the pharmacokinetic behaviors of chlorogenic acid, kaempferol-7-O-ß-d-glucoside, and ilexgenin A could be significantly changed in NAFLD rats after oral administration of I. hainanensis extract compared with normal rats. The areas under the plasma concentration-time curve (AUC) and maximum plasma concentration (Cmax) of the three analytes were greatly decreased and the plasma clearance (CL) for kaempferol-7-O-ß-d-glucoside, Ilexgenin A were greatly increased in NAFLD rats. Meanwhile, the mean residence time (MRT) of kaempferol-7-O-ß-d-glucoside and Ilexgenin A were increased in the NAFLD rats. This is the first report on the determination of the major bioactive components in rat plasma after oral administration of I. hainanensis extract. These results provided a meaningful basis for evaluating the clinical application of this medicine.

Influences of glucose on the dietary hydroxyflavonoid-plasma protein interaction.

The influence of glucose on the interaction between flavonoids and plasma proteins from healthy humans (HPPs) was investigated. Glucose affected the flavonoid-protein interactions depending upon their structures. Glucose significantly reduced the affinities of HPPs for 6-hydroxyflavone by 10.72 times, slightly weakened the affinities of HPPs for quercetin, 7-hydroxyflavone, and kaempferol, and hardly affected the affinities of HPPs for myricetin, chrysin, and 3,7-dihydroxyflavone on the first day. However, glucose obviously enhanced the affinities of HPPs for 3-hydroxyflavone, luteolin, and apigenin. Glucose significantly weakened the binding affinities of HPPs for chrysin, kaempferol, quercetin, and myricetin by 6.17, 7.94, 14.12, and 112.2 times, when kept at 37 °C under air conditions for 14 days, and the binding affinities of HPPs for 7-hydroxyflavone, luteolin, 3,7-dihydroxyflavone, 3-hydroxyflavone, and 6-hydroxyflavone were slightly decreased by 1.35-, 1.58-, 1.58-, 1.9-, and 2.4-fold. The binding affinity between apigenin and HPP was hardly influenced. Glucose weakened the binding affinities of HPPs for hydroxyflavonoids. The differences between log K(a)(absence) and log K(a)(presence) were bigger for the more lipophilic hydroxyflavonoids, and more lipophilic hydroxyflavonoids are easily affected by glucose, when kept at 37 °C under air conditions for 14 days. These flavonoids with lower hydrogen donor/acceptor numbers prefer to stably interact with HPPs in the presence of glucose. However, other flavonoids with high hydrogen donor/acceptor numbers (multi-hydroxyl flavonoids) were apt to reduce their affinities with HPPs in the presence of glucose.

Bioavailability study of a polyphenol-enriched extract from Hibiscus sabdariffa in rats and associated antioxidant status.

The aqueous extracts of Hibiscus sabdariffa have been commonly used in folk medicine. Nevertheless, the compounds or metabolites responsible for its healthy effects have not yet been identified. The major metabolites present in rat plasma after acute ingestion of a polyphenol-enriched Hibiscus sabdariffa extract were characterized and quantified in order to study their bioavailability. The antioxidant status of the plasma samples was also measured through several complementary antioxidant techniques. High-performance liquid chromatography coupled to time-of-flight mass spectrometry (HPLC-ESI-TOF-MS) was used for the bioavailability study. The antioxidant status was measured by ferric reducing ability of plasma method, thiobarbituric acid reactive substances assay, and superoxide dismutase activity assay. Seventeen polyphenols and metabolites have been detected and quantified. Eleven of these compounds were metabolites. Although phenolic acids were found in plasma without any modification in their structures, most flavonols were found as quercetin or kaempferol glucuronide conjugates. Flavonol glucuronide conjugates, which show longer half-life elimination values, are proposed to contribute to the observed lipid peroxidation inhibitory activity in the cellular membranes. By contrast, phenolic acids appear to exert their antioxidant activity through ferric ion reduction and superoxide scavenging at shorter times. We propose that flavonol-conjugated forms (quercetin and kaempferol) may be the compounds responsible for the observed antioxidant effects and contribute to the healthy effects of H. sabdariffa polyphenolic extract.

Inhibition of hepatic uptake transporters by flavonoids.

Members of the human SLC superfamily such as organic anion transporting polypeptide 1B1 (OATP1B1), OATP1B3, and organic cation transporter 1 (OCT1) are drug uptake transporters that are localised on the basolateral membrane of hepatocytes mediating the uptake of drugs such as atorvastatin and metformin into hepatocytes. Ingredients of food such as flavonoids influence the effects of drugs, e.g. by inhibition of drug transporters. Therefore, we investigated the impact of the Ginkgo biloba flavonoids apigenin, kaempferol, and quercetin, and the grapefruit flavonoids naringenin, naringin, and rutin on the OATP1B1, OATP1B3, and OCT1 transport activity. Transporter expressing HEK293 cell lines were used with [3H]sulfobromophthalein ([3H]BSP) as substrate for OATP1B1 and OATP1B3, [3H]atorvastatin as substrate for OATP1B1, and [3H]1-methyl-4-phenylpyridinium ([3H]MPP(+)) as substrate for OCT1. The G. biloba flavonoids showed a competitive inhibition of the OATP1B1- and OATP1B3-mediated [3H]BSP and the OATP1B1-mediated [3H]atorvastatin uptake. Quercetin was the most potent inhibitor of the OATP1B1- and OATP1B3-mediated [3H]BSP transport with K(i)-values of 8.8±0.8µM and 7.8±1.7µM, respectively. For the inhibition of the OATP1B1-mediated [3H]atorvastatin transport, apigenin was the most potent inhibitor with a K(i) value of 0.6±0.2µM. Among the grapefruit flavonoids, naringenin was the most potent inhibitor of the OATP1B1- and OATP1B3-mediated [3H]BSP transport with IC(50)-values of 81.6±1.1µM and 101.1±1.1µM, respectively. All investigated flavonoids showed no significant inhibition of the OCT1-mediated [3H]MPP(+) uptake. Taken together, these in vitro studies showed that the investigated flavonoids inhibit the OATP1B1- and OATP1B3-mediated drug transport, which could be a mechanism for food-drug interactions in humans.

[Study on determination and pharmacokinetics of metabolites from Folium Mori extract in rats].

OBJECTIVE: To establish a RP-HPLC method for simultaneous determination of total quercetin, kaempferol and isorhamnetin in rat plasma after oral administration of Folium Mori extract (FME). METHODS: After a single dose of FME (110 mg/kg) was taken, rat plasma samples were collected. The samples were hydrolyzed with hydrochloric acid (c=3.0 mol/L), the mixed solution was extracted with ether acetone mixture. The total quercetin, kaempferol and isorhamnetin in plasma samples were determined by HPLC, pharmacokinetic parameters were calculated by DAS 3.0 software. RESULTS: The method was linear over the concentration ranges of 0.0545-8.70, 0.0954-14.7 and 0.0545-8.55 µg/ml for quercetin, kaempferol and isorhamnetin, respectively (r=0.9979, 0.9993, 0.9981). The absolute recoveries were 85.3%-86.1%, 79.4%-86.7% and 62.8%-89.7%, respectively and the assay recoveries were all from 94.7% to 107%. The relative standard deviation (RSD) of intra-and inter-day were less than 9.5% and 9.8%, respectively. The main pharmacokinetic parameters were as follows: T(1/2z) was 92.7, 67.9 and 54.2 h; Tmax was 0.400, 0.400 and 3.87 h; AUC(0-∞) was 68.0, 67.5 and 32.8 mg/h/L; MRT(0-∞) was 128, 85.2 and 72.0 h for quercetin, kaempferol and isorhamnetin, respectively. CONCLUSION: The method established in this study is accurate, reliable and reproducible, and can be applied for determination of total quercetin, kaempferol and isorhamnetin in rat plasma after oral administration of FME; the pharmacokinetic studies showed that the distribution of drugs is rapid and elimination is very slow.

Determination of free and glucuronidated kaempferol in rat plasma by LC-MS/MS: application to pharmacokinetic study.

Flavanoid kaempferol is mainly present as glucuronides and sulfates in rat plasma, and small amounts of the intact aglycone are also detected. In the this study, a rapid, specific and sensitive liquid chromatography-electrospray ionization-tandem mass spectrometry method (HPLC-MS/MS) was developed and validated for determination of kaempferol and its major metabolite glucuronidated kaempferol in rat plasma. A liquid-liquid extraction with acetic ether was involved for the extraction of kaempferol and internal standard. Analytes were separated on a C18 column (150 mm x 2.1 mm, 4.5 microm, Waters Corp.) with isocratic elution at a flow-rate of 0.3 ml min(-1). The mobile phase was consisted of 0.5% formic acid and acetonitrile (50:50, v/v). The Quattro Premier HPLC-MS/MS was operated under the multiple reaction-monitoring mode (MRM) using the electrospray ionization technique. The method was validated according to the FDA guidelines for validation of bioanalytical method. The validated method was successfully applied to the study of the pharmacokinetics in rats after oral administration of kaempferol with different doses.

Plasma levels and distribution of flavonoids in rat brain after single and repeated doses of standardized Ginkgo biloba extract EGb 761®.

It is undisputed that terpene lactones and flavonoid glycosides of Ginkgo biloba are responsible for most of the extracts (e.g., EGb 761®) pharmacological actions. This investigation focused on the pharmacokinetic and the ability of the flavonoid constituents to cross the blood-brain barrier in rats, after single (600 mg/kg) or repeated (8 days, 100, or 600 mg/kg) oral administration of EGb 761®, and their distribution in different areas of the brain. For this purpose, we developed an HPLC-fluorescence method for the determination of the Ginkgo flavonoid metabolites (quercetin, kaempferol, and isorhamnetin derivatives) in the brain and plasma. A single dose of 600 mg/kg EGb 761® resulted in maximum plasma concentrations of 176, 341, and 183 ng/mL for quercetin, kaempferol, and isorhamnetin/tamarixetin, respectively and in maximum brain concentrations of 291 ng/g protein for kaempferol and 161 ng/g protein for isorhamnetin/tamarixetin. In comparison, the repeated administration of the same dose for 8 days led to an approximate 4.5-fold increase in the plasma concentration for quercetin, 11.5-fold increase for kaempferol, and 10-fold increase for isorhamnetin/tamarixetin. In the brain, an approximate 2-fold increase was observed for kaempferol and isorhamnetin/tamarixetin. About 90% of the determined flavonoids were distributed in the hippocampus, frontal cortex, striatum, and cerebellum, which together represent only 38% of the whole brain.