LC-MS metabolic study on quercetin and taxifolin galloyl esters using human hepatocytes as toxicity and biotransformation in vitro cell model

Quercetin: A Potential Polydynamic Drug

The study of natural products as potential drug leads has gained tremendous research interest. Quercetin is one of those natural products. It belongs to the family of flavonoids and, more specifically, flavonols. This review summarizes the beneficial pharmaceutical effects of quercetin, such as its anti-cancer, anti-inflammatory, and antimicrobial properties, which are some of the quercetin effects described in this review. Nevertheless, quercetin shows poor bioavailability and low solubility. For this reason, its encapsulation in macromolecules increases its bioavailability and therefore pharmaceutical efficiency. In this review, a brief description of the different forms of encapsulation of quercetin are described, and new ones are proposed. The beneficial effects of applying new pharmaceutical forms of nanotechnology are outlined.

Novel aspects of taxifolin pharmacokinetics: Dose proportionality, cumulative effect, metabolism, microemulsion dosage forms

Taxifolin (TFL) is a small drug molecule with a broad therapeutic potential limited by its poor aqueous solubility and excessive metabolism. Despite comprehensive research, some aspects of the TFL pharmacokinetics, e.g., dose proportionality and possible cumulative effect, remain unexplored. In the current study, we have tried to fill this gap. Our results revealed that the TFL pharmacokinetics in rats had nonlinear character in the dose range of 10-50 mg/kg after its single oral administration (AUC). For Cmax, the data are ambiguous: linearity was confirmed via the equivalence criterion and was disproved using the power model approach. Also, the cumulative drug effect was observed on the 4th day after its multiple-dose oral administration (25 mg/kg; compared to the 1st day). Interestingly, biologically active TFL metabolites such as aromadendrin and luteolin were putatively found in plasma samples, although they were previously detected only in feces. In addition, oil-in-water and water-in-oil microemulsions were fabricated to design novel drug delivery systems. These carrier dosage forms did not improve the TFL bioavailability but significantly affected its metabolism. To support pharmacokinetic studies, the bioanalytical liquid chromatography-tandem mass spectrometry method was developed and validated in the concentration range of 1-1000 ng/mL using candesartan as an internal standard. Liquid-liquid extraction with methyl tert-butyl ether was used to isolate the analytes from plasma followed by evaporation and reconstitution of the residues in acetonitrile. Thus, the present findings broaden our understanding of the TFL behavior in vivo and provide novel ideas and reference directions for its continued use in medical practice.

Gut microbial metabolites of dietary polyphenols and their potential role in human health and diseases

Polyphenols contribute as one of the largest groups of compounds among all the phytochemicals. Common sources of dietary polyphenols are vegetables, fruits, berries, cereals, whole grains, etc. Owing to their original form, they are difficult to get absorbed. Dietary polyphenols after undergoing gut microbial metabolism form bioaccessible and effective metabolites. Polyphenols and derived metabolites are all together a diversified group of compounds exhibiting pharmacological activities against cardiovascular, cancer, oxidative stress, inflammatory, and bacterial diseases. The formed metabolites are sometimes even more bioavailable and efficacious than the parent polyphenols. Studies on gut microbial metabolism of dietary polyphenols have introduced new approach for the use of polyphenol-rich food in the form of supplementary diet. This review provides insights on various aspects including classification of polyphenols, gut microbiota-mediated metabolism of polyphenols, chemistry of polyphenol metabolism, and pharmacological actions of gut microbial metabolites of polyphenols. It also suggests the use of polyphenols from marine source for the microbial metabolism studies. Till date, gut microbial metabolism of polyphenols from terrestrial sources is extensively studied as compared to marine polyphenols. Marine ecosystem is a profound but partially explored source of phytoconstituents. Among them, edible seaweeds contain high concentration of polyphenols, especially phlorotannins. Hence, microbial metabolism studies of seaweeds can unravel the pharmacological potential of marine polyphenol-derived metabolites.

Gurgem-7 toxicity assessment: Regulation of cell survival or death by traditional Mongolian prescription

Surgical treatments and chemotherapy are the most commonly used methods of colorectal cancer treatment (CRC), unfortunately, these therapies have many side effects. Moreover, despite advances in primary and adjuvant treatments, the survival time in CRC patients is still unsatisfactory. Treatment options for patients with CRC continue to advance and recent research has shown that colorectal cancer is sensitive to plant-derived substances. The use of natural compounds contained in herbal extracts for the treatment of colon cancer or as adjunctive therapy for CRC gives patients a wide range of treatment options. In this study, we evaluate the potential toxicity of the Mongolian preparation - Gurgem-7 composed of Crocus sativus, Veronica officinalis, Capsella bursa-pastoris, Arctostaphylos uva-ursi, Calendula officinalis, Gentiana lutea, and Terminalia chebula. Therefore, the aim of this study was to determine its biological activities, biochemical and molecular features in vitro and composition analysis by HPLC-ESI-QTOF-MS/MS platform. We identified 18 metabolites and 8 of them were quantified. Majority of the secondary metabolites belonged to the group of phenolic constituents with taxifolin, chlorogenic acids' family, hydroxysafflor yellow A and hydroxybenzoic acid as leading compounds. In turn, our in vitro results suggest that the preparation inhibits cell metabolic activity through oxidative stress, numerous DNA damage and cell cycle arrest. Simultaneously enzymatic and non-enzymatic cell protection mechanisms mediated by TP53/Keap1 and Nrf2/HO-1 pathways may be activated in a cell-specific manner in vitro. In conclusion, we provide preliminary molecular evidence of the toxic properties of Gurgem-7 preparation to Caco-2 and CT26. WT cells related to insufficient action of their repair and adaptive mechanisms to stress conditions.

Advances in biochemistry and the biotechnological production of taxifolin and its derivatives

Taxifolin (dihydroquercetin) and its derivatives are medicinally important flavanonols with a wide distribution in plants. These compounds have been isolated from various plants, such as milk thistle, onions, french maritime, and tamarind. In general, they are commercially generated in semisynthetic forms. Taxifolin and related compounds are biosynthesized via the phenylpropanoid pathway, and most of the biosynthetic steps have been functionally characterized. The knowledge gained through the detailed investigation of their biosynthesis has provided the foundation for the reconstruction of biosynthetic pathways. Plant- and microbial-based platforms are utilized for the expression of such pathways for generating taxifolin-related compounds, either by whole-cell biotransformation or through reconfiguration of the genetic circuits. In this review, we summarize recent advances in the biotechnological production of taxifolin and its derivatives.

Quercetin-Loaded Luminescent Hydroxyapatite Nanoparticles for Theranostic Application in Monolayer and Spheroid Cultures of Cervical Cancer Cell Line In Vitro

Nanoscale materials have been explored as better alternatives to conventional therapeutic agents in cancer theranostics in the recent period due to efficacy in overcoming biological, biomedical, and biophysical barriers. Analysis on the ability of copper nanocluster (CuNC)-doped hydroxyapatite nanoparticles (Cu-HXNPs) as suitable nanocarriers for anticell proliferative application was carried out. Having high adsorption capacity, the Cu-HXNPs could be loaded with the anticancer drug quercetin, which is a polyphenolic flavonoid compound, and were used as nanocarriers to be applied on HeLa (cancer cells) and HEK-293 (normal cells). The drug release profile was found to be pH-dependent, where maximum release of quercetin from quercetin-loaded Cu-HXNPs was observed in acidic pH as compared to physiological pH. The Cu-HXNPs could release quercetin, which could effectively decline proliferation of cancer cells via generation of reactive oxygen species. Moreover, the released quercetin significantly altered the cell cycle pattern and triggered the cells to undergo apoptosis. Additionally, the efficacy of Cu-HXNPs as a nanocarrier to release quercetin on 3D spheroids of HeLa had been checked, which demonstrated significant reduction in the viability of 3D spheroids. The luminescent CuNCs used for doping HXNPs endowed the nanocarrier with the imaging property, which was an excellent feature in confirming their uptake by the cells. Thus, the study suggested Cu-HXNPs to be a beneficial nanocarrier for both bioimaging and therapeutic purpose in the field of cancer theranostics.

Comprehensive characterisation of phenolics from Nitraria sibirica leaf extracts by UHPLC-quadrupole-orbitrap- MS and evaluation of their anti-hypertensive activity

ETHNOPHARMACOLOGICAL RELEVANCE

For more than ten scores years, the leaves and fruits of Nitraria sibirica have been used as a natural remedy for indigestion, irregular manes, and hypertension in the Middle East and Central Asia, especially, are recommended for hypertension treatment in the northwest region, China.

AIM OF THE STUDY

we aimed to support the traditional usage of N. sibirica leaves as pharmaceuticals or dietary supplements in treatment of hypertension by investigating their chemical constituents and anti-hypertensive activity. 
 METHODS: We identified the chemical composition of N. sibirica leaves ethanolic purified extract (NSL-EPE) using UHPLC-quadrupole-orbitrap-MS, and quantified the main chemical constituents by an analytical method established and validated. We also evaluated anti-hypertensive activity of NSL-EPE using spontaneously hypertensive rats (SHR): blood pressure was measured weekly by non-invasive blood pressure (NIBP) measurements; hemodynamic parameters, biochemical and clinical chemistry variables in plasma, serum and kidney tissue were measured after 10 weeks of treatment with NSL-EPE as well.
 RESULTS: UHPLC-quadrupole-orbitrap-MS analysis identified 52 compounds, of which 40 compounds were reported for the first time in N. sibirica. 11 phenolic compounds further quantitatively analyzed, among which the most abundant compound was found to be clovin (8.8%). Systolic blood pressure decreased progressively from the second treatment week compared to that in non-treated SHRs. The plasma endothelin, aldosterone, angiotensin II levels were significantly increased, while the level of NO_X was significantly decreased; glutathione to oxidized glutathione ratio, superoxide dismutase and total catalase levels in the kidney tissue were markedly accelerated, while malondialdehyde level was significantly reduced in NSL-EPE treated SHRs. Moreover, the serum cholesterol, triglyceride, blood uria nitrogen and creatinine were attenuated in NSL-EPE treated SHRs (P < 0.05), but in sharp contrast to those values in the water-treated SHRs.

CONCLUSION

This study screened out leading compounds from N. sibirica and offered a new understanding of the antihypertensive properties of N. sibirica leaves, by which inhibit oxidative stress-induced endothelial dysfunction and improve lipid profiles.

Sulfated flavanones and dihydroflavonols from willow

Phytochemical profiling of a hybrid species of willow, Salix × alberti L. (S. integra Thunb. × Salix suchowensis W.C. Cheng ex G.Zhu) revealed four sulfated flavonoids, which were then isolated from young stem tissue. The structures of dihydroflavonols (flavanonols) taxifolin-7-sulfate (1) and dihydrokaempferol-7-sulfate (2) and flavanones, eridictyol-7-sulfate (3) and naringenin-7-sulfate (4) were elucidated through NMR spectroscopy and high-resolution mass spectrometry. The identified sulfated flavanones and dihydroflavonols have not been previously seen in plants, but the former have been partially characterised as metabolites in mammalian metabolism of dietary flavonoids. In addition to providing full spectroscopic characterisation of these metabolites for the first time, we also compared the in vitro antioxidant properties, via the DPPH radical scavenging assay, of the parent and sulfated flavanones, which showed that 7-sulfation of taxifolin and eriodictyol attenuates but does not remove anti-oxidant activity.

Interspecies metabolic diversity of artocarpin in vitro mammalian liver microsomes

Artocarpin has shown anti-inflammation and anticancer activities. However, the metabolism differences among different species have not been reported. In this work, we used liver microsomes to explore the metabolic characteristics and possible metabolites of artocarpin among different species. The structures of six metabolites were characterized by LC-MS/MS, and hydroxylated artocarpin was the main metabolite. Enzyme kinetics and depletion studies of artocarpin among different species proved that artocarpin metabolism exhibited significant species differences; rats and monkeys showed a great metabolic ability to artocarpin, and minipigs showed the highest similarity to humans. The in vivo hepatic clearances of artocarpin in rats and humans were predicted that artocarpin was classified as a high-clearance drug in humans and rats. The glucuronidation assay of artocarpin in different liver microsomes also proved that artocarpin metabolism showed significant species difference. These findings will support further pharmacological or toxicological research on artocarpin.Abbreviations: UGT: UDP-glucuronosyltransferase; CYP: cytochrome P450; LC-MS/MS: liquid chromatography-tandem mass spectrometry; HPLC: high-performance liquid chromatography; HLMs: human liver microsomes; MLMs: monkey liver microsomes; RAMs: rabbit liver microsomes; RLMs: rat liver microsomes; DLMs: dog liver microsomes; PLMs: minipig liver microsomes; V_max: maximum velocity; K_m: Michaelis constant; CL_int: intrinsic clearance; CL_H: hepatic clearance; Q_H: hepatic blood flow.

Pyroglutamide-Based P2X7 Receptor Antagonists Targeting Inflammatory Bowel Disease

This report deals with the design, the synthesis, and the pharmacological evaluation of pyroglutamide-based P2X7 antagonists. A dozen were shown to possess improved properties, among which inhibition of YO-PRO-1/TO-PRO-3 uptake and IL1β release upon BzATP activation of the receptor and dampening signs of DSS-induced colitis on mice, in comparison with reference antagonist GSK1370319A. Docking study and biological evaluation of synthesized compounds has highlighted new SAR, and low toxicity profiles of pyroglutamides herein described are clues for the finding of a usable h-P2X7 antagonist drug. Such a drug would raise the hope for a cure to many P2X7-dependent pathologies, including inflammatory, neurological, and immune diseases.

HPLC-MS/MS determination of flavonoids in Gleditsiae Spina for its quality assessment

Gleditsiae Spina, the thorn of Gleditsia sinensis Lam., has been used as an anti-inflammatory, anti-tumor, and anti-bacterial traditional medicine for hundreds of years in China. This study used high-performance liquid chromatography and tandem mass spectrometry combined with chemometric methods to allow the fast and accurate identification and quantification of the flavonoids compounds in Gleditsiae Spina, and created reliable criteria for accurate identification of Gleditsiae Spina and its adulterants. This research provides good evidence for the classification and quality evaluation of Gleditsiae Spina. Firstly, eight flavonoids compounds were detected and identified on the basis of their mass spectra, fragment characteristics, and comparison with published data. Then the mass spectroscopic fragmentation pathways of these compounds were determined and, in addition rutin, isoquercitrin, and quercitrin were detected in Gleditsiae Spina for the first time. The quantification was performed on a triple quadrupole tandem mass spectrometer in multi-reaction monitoring mode, and the baseline separation of the eight bioactive flavonoids components was achieved within 13 min. Furthermore, the proposed method was successfully applied for simultaneous quantitative determination of the eight Gleditsiae Spina compounds and adulterants obtained from different sources in China. Then, we built a classification model which showed a high level of accuracy predicting 100% of the samples, correctly.

A Combined LC-MS Metabolomics- and 16S rRNA Sequencing Platform to Assess Interactions between Herbal Medicinal Products and Human Gut Bacteria in Vitro: a Pilot Study on Willow Bark Extract

Herbal preparations are complex mixtures of natural products, many of which are able to reach the distal gut due to low oral bioavailability. There, they can influence the microbial communities, and can be metabolized into potentially absorbable bioactive compounds by the intestinal bacteria. This aspect has often been disregarded when searching for the active principles of medicinal plants and herbal medicinal products. The aim of this study was to establish an interdisciplinary platform to unravel interactions of herbal medicine and intestinal microbiota, using a combined LC-MS metabolomics and 16S rRNA microbiome sequencing approach. Willow bark extract (WBE), a herbal medicinal product with a long history of traditional use and a well-established anti-inflammatory activity, was incubated with human fecal suspension under anoxic conditions. Samples were taken after 0.5, 4, and 24 h of incubation. Microbiome analyses revealed that incubation with WBE had a marked effect on microbial community composition and functions. For example, the proportion of Bacteroides sp. was clearly enhanced when the fecal sample used in this study was incubated with WBE. LC-MS analysis showed that WBE constituents were readily metabolized by fecal bacteria. Numerous microbial metabolites could be annotated, allowing the construction of putative microbial degradation pathways for the main groups of WBE constituents. We suggest that studies of this type help to increase the knowledge on bioactive principles of medicinal plants, since gut microbial metabolites might have been underestimated as a source of bioactive compounds in the past.

Semisynthetic flavonoid 7-O-galloylquercetin activates Nrf2 and induces Nrf2-dependent gene expression in RAW264.7 and Hepa1c1c7 cells

The natural flavonoid quercetin is known to activate the transcription factor Nrf2, which regulates the expression of cytoprotective enzymes such as heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1). In this study, a novel semisynthetic flavonoid 7-O-galloylquercetin (or quercetin-7-gallate, 3) was prepared by direct galloylation of quercetin, and its effect on the Nrf2 pathway was examined. A luciferase reporter assay showed that 7-O-galloylquercetin, like quercetin, significantly activated transcription via the antioxidant response element in a stably transfected human AREc32 reporter cell line. In addition, 7-O-galloylquercetin caused the accumulation of Nrf2 and induced the expression of HO-1 at both the mRNA and protein levels in murine macrophage RAW264.7 cells. The induction of HO-1 by 7-O-galloylquercetin was significantly suppressed by N-acetyl-l-cysteine and SB203580, indicating the involvement of reactive oxygen species and p38 mitogen-activated protein kinase activity, respectively. HPLC/MS analyses also showed that 7-O-galloylquercetin was not degalloylated to quercetin, but it was conjugated with glucuronic acid and/or methylated in RAW264.7 cells. Furthermore, 7-O-galloylquercetin was found to increase the protein levels of Nrf2 and HO-1, and also the activity of NQO1 in murine hepatoma Hepa1c1c7 cells. Taken together, we conclude that 7-O-galloylquercetin increases Nrf2 activity and induces Nrf2-dependent gene expression in RAW264.7 and Hepa1c1c7 cells.

Detection of the designer benzodiazepine metizolam in urine and preliminary data on its metabolism

Designer benzodiazepines provide an attractive alternative to prescribed benzodiazepines for abuse purposes as they are readily available via the Internet without control. Metizolam was ordered via the Internet and a 2 mg blue tablet was orally administered to a 54-year-old man. Urine samples were collected over 6 days in polypropylene tubes. After liquid/liquid extraction at pH 9.5, metizolam was analyzed by ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) using a standard method devoted to benzodiazepines, and ions transitions, at m/z 328.9 > 275.0 and 328.9 > 300.0. Metizolam was detectable in hydrolyzed urine during the 46-h period, with concentrations always lower than 11 ng/mL. About 0.3% of the initial dose was excreted in urines as total unchanged metizolam during the first 24 h. The most relevant potential CYP- and UGT-dependent metabolites of metizolam were investigated in vitro using human liver microsome incubation and, subsequently, liquid chromatography coupled with quadrupole-time of flight mass spectrometry (UHPLC-Q-TOF-MS) analysis. Three mono-hydroxylated metabolites were produced including a hydroxylation compound at the 2-ethyl moiety of metizolam (M1) as quantitatively main metabolite, and a N-hydroxymetiazolam (M2). The structure of the third metabolite (M3) could not be elucidated because of a too low experimental production rate. Two authentic urine samples were analyzed using the same analytical method to search for metabolites of metizolam. M1, together with its glucuronide (M1-Glu), and M2 were observed in urine at the 8 h mark, whereas only M1 and M1-Glu were still detected in urine at 30 h post administration. Copyright © 2016 John Wiley & Sons, Ltd.

Esterification of Quercetin Increases Its Transport Across Human Caco-2 Cells

Plant polyphenols showed useful biochemical characteristics in vitro; however, the assessments of their clinical applications in vivo are restricted by their limited bioavailability due to their strong resistance to 1st-pass effects during absorption. In order to improve the bioavailability of quercetin (QU), the ester derivative of QU (3,3',4',5,7-pentahydroxy flavones, TAQU) was synthesized, followed by examining the oil-water partition coefficient as well as the transport mechanisms of QU and its ester derivative (TAQU) using human Caco-2 cells. The transport characteristics of QU and TAQU transport under different conditions (different concentrations, time, pH, temperature, tight junctions, and potential transporters) were systematically investigated. Results showed that QU had a lower permeability coefficient (2.82 × 10(-6) cm/s) for apical-to-basolateral (AP-BL) transport over 5 to 50 μM, whereas the transport rate for AP to BL flux of TAQU (5.23 × 10(-6) cm/s) was significantly greater than that of QU. Paracellular pathways were not involved during the transport of both QU and TAQU. QU was poorly absorbed by active transport, whereas TAQU was mostly absorbed by passive diffusion. Efflux transporters, P-glycoproteins, multidrug resistance proteins were proven to participate in the transport process of QU, but not in that of TAQU. These results suggested that improving the lipophicity of QU by esterification could increase the transport of QU across Caco-2 cells.

Flavonolignan 2,3-dehydroderivatives: Preparation, antiradical and cytoprotective activity

The protective constituents of silymarin, an extract from Silybum marianum fruits, have been extensively studied in terms of their antioxidant and hepatoprotective activities. Here, we explore the electron-donor properties of the major silymarin flavonolignans. Silybin (SB), silychristin (SCH), silydianin (SD) and their respective 2,3-dehydroderivatives (DHSB, DHSCH and DHSD) were oxidized electrochemically and their antiradical/antioxidant properties were investigated. Namely, Folin-Ciocalteau reduction, DPPH and ABTS(+) radical scavenging, inhibition of microsomal lipid peroxidation and cytoprotective effects against tert-butyl hydroperoxide-induced damage to a human hepatocellular carcinoma HepG2 cell line were evaluated. Due to the presence of the highly reactive C3-OH group and the C-2,3 double bond (ring C) allowing electron delocalization across the whole structure in the 2,3-dehydroderivatives, these compounds are much more easily oxidized than the corresponding flavonolignans SB, SCH and SD. This finding was unequivocally confirmed not only by experimental approaches, but also by density functional theory (DFT) calculations. The hierarchy in terms of ability to undergo electrochemical oxidation (DHSCH~DHSD>DHSB>>SCH/SD>SB) was consistent with their antiradical activities, mainly DPPH scavenging, as well as in vitro cytoprotection of HepG2 cells. The results are discussed in the context of the antioxidant vs. prooxidant activities of flavonolignans and molecular interactions in complex biological systems.

In vitro characterization of potential CYP- and UGT-derived metabolites of the psychoactive drug 25B-NBOMe using LC-high resolution MS

One of the main challenges posed by the emergence of new psychoactive substances is their identification in human biological samples. Trying to detect the parent drug could lead to false-negative results when the delay between consumption and sampling has been too long. The identification of their metabolites could then improve their detection window in biological matrices. Oxidative metabolism by cytochromes P450 and glucuronidation are two major detoxification pathways in humans. In order to characterize possible CYP- and UGT-dependent metabolites of the 2-(4-bromo-2,5-dimethoxy-phenyl)-N-[(2-methoxyphenyl)methyl]ethanamine (25B-NBOMe), a synthetic psychoactive drug, analyses of human liver microsome (HLM) incubates were performed using an ultra-high performance liquid chromatography system coupled with a quadrupole-time of flight mass spectrometry detector (UHPLC-Q-TOF/MS). On-line analyses were performed using a Waters OASIS HLB column (30 x 2.1 mm, 20 µm) for the automatic sample loading and a Waters ACQUITY HSS C18 column (150 x 2 mm, 1.8 µm) for the chromatographic separation. Twenty-one metabolites, consisting of 12 CYP-derived and 9 UGT-derived metabolites, were identified. O-Desmethyl metabolites were the most abundant compounds after the phase I process, which appears to be in accordance with data from previously published NBOMe-intoxication case reports. Although other important metabolic transformations, such as sulfation, acetylation, methylation or glutathione conjugation, were not studied and artefactual metabolites might have been produced during the HLM incubation process, the record of all the metabolite MS spectra in our library should enable us to characterize relevant metabolites of 25B-NBOMe and allow us to detect 25B-MBOMe users.

Systematic characterization and simultaneous quantification of the multiple components of Rhododendron dauricum based on high-performance liquid chromatography with quadrupole time-of-flight tandem mass spectrometry

Rhododendron dauricum L. has been used as a traditional Chinese medicine to treat cough and asthma and relieve phlegm and bronchitis. In this study, a reliable method based on high-performance liquid chromatography with diode array detection and quadrupole time-of-flight tandem mass spectrometry was established to systematically identify and quantify the components in this herb for the first time. A total of 33 compounds were identified, including 24 flavonoids, six phenolic acids, two coumarins and one terpene. Among them, poriolin (17), farrerol-7-O-β-d-glucopyranoside (20), and syzalterin (30) were isolated from this plant for the first time, and quercetin-3-β-d-(6-p-hydroxy benzoyl) galactoside (19), quercetin-3-β-d-(6-p-coumaroyl) galactoside (21), and myrciacetin (23) were identified from this genus for the first time. Fragmentation pathways of flavonoids also have been investigated by electrospray ionization mass spectrometry. Moreover, seven bioactive constituents, namely, gallic acid (1), scopoletin (6), dihydroquercetin (7), quercetin (22), kaempferol (25), 8-desmethyl farrerol (27), and farrerol (28), were simultaneously quantified. The developed method has been validated and applied to analyze ten samples of R. dauricum from Hebei Province successfully. The contents of the seven compounds have been detected and compared.

Sulfation modulates the cell uptake, antiradical activity and biological effects of flavonoids in vitro: An examination of quercetin, isoquercitrin and taxifolin

Quercetin 3'-O-sulfate is one of the main metabolites of the natural flavonoid quercetin in humans. This study was designed to prepare quercetin 3'-O-sulfate (1), isoquercitrin 4'-O-sulfate (2) and taxifolin 4'-O-sulfate (3) by the sulfation of quercetin, isoquercitrin (quercetin 3-O-glucoside) and taxifolin (2,3-dihydroquercetin) using the arylsulfate sulfotransferase from Desulfitobacterium hafniense, and to examine the effect of sulfation on selected biological properties of the flavonoids tested. We found that flavonoid sulfates 1-3 were weaker DPPH radical scavengers than the corresponding nonsulfated flavonoids, and that 1-3, unlike quercetin, did not induce the expression of either heme oxygenase-1 in RAW264.7 cells or cytochrome P450 1A1 in HepG2 cells. In both cell types, the cell uptake of compounds 1-3 was much lower than that of quercetin, but comparable to that of the glycoside isoquercitrin. Moreover, HPLC/MS metabolic profiling in HepG2 cells showed that flavonoid sulfates 1-3 were metabolized to a limited extent compared to the nonsulfated compounds. We conclude that sulfation of the tested flavonoids reduces their antiradical activity, and affects their cell uptake and biological activity in vitro.