Identification of isoquercitrin metabolites produced by human intestinal bacteria using UPLC-Q-TOF/MS

Phytochemical profiling, antiviral activities, molecular docking, and dynamic simulations of selected Ruellia species extracts

The antiviral properties of the flowering aerial extracts of Ruellia tuberosa and Ruellia patula were investigated through phytochemical profiling via LC-MS/MS and HPLC techniques. Qualitative LC-MS/MS analyses identified seventy-seven metabolites from both Ruellia species. R. tuberosa had the highest phenolic content (49.3%), whereas R. patula had the highest flavonoid content (57.8%). Additionally, quantitative HPLC investigations of the compounds identified by LC-MS/MS were performed using the available standard compounds. The main constituents in the R. tuberosa extract was found to be catechin (5321.63 µg/g), gallic acid (2878.71 µg/g), and ellagic acid (2530.79 µg/g), whereas the major compounds in the R. patula extract was found to be rutin (11,074.19 µg/g) and chlorogenic acid (3157.35 µg/g). Furthermore, the antiviral activities of both Ruellia species against HAdV-40, herpes simplex type 2 and H1N1 were evaluated. These findings demonstrated that R. tuberosa was more active than R. patula against all tested viruses, except for the HSV-2 virus, against which R. patula showed greater activity than R. tuberosa, with IC50 values of 20, 65, 22.59, and 13.13 µg/ml for R. tuberosa flowering aerial parts and 32.26, 11.66, and 23.03 µg/ml for R. patula flowering aerial parts, respectively for HAdV-40, herpes simplex type 2, and H1N1. Additionally, computational docking and molecular dynamics simulations were used to assess the molecular interactions between the bioactive compounds and specific viral targets. The combined findings from the in-vitro and in-silico experiments comprehensively evaluated the antiviral activities of both Ruellia species extracts.

The bioavailability, absorption, metabolism, and regulation of glucolipid metabolism disorders by quercetin and its important glycosides: A review

Quercetin and its glycosides (QG), vitally natural flavonoid, have been popular for health benefits. However, the absorption and metabolism affect their bioavailability, and the metabolic transformation alters their biological activities. This review systematically summarizes the bioavailability and pathways for the absorption and metabolism of quercetin/QG in vivo and in vitro, the biological activities and mechanism of quercetin/QG and their metabolites in treating glucolipid metabolism are discussed. After oral administration, quercetin/QG are mainly absorbed by the intestine, undergo phase II metabolism in the small intestine and liver to form conjugates and are metabolized into small phenolic acids by intestinal microbiota. Quercetin/QG and their metabolites exert beneficial effects on regulating glucolipid metabolism disorders, including improving insulin resistance, inhibiting lipogenesis, enhancing thermogenesis, modulating intestinal microbiota, relieving oxidative stress, and attenuating inflammation. This review enhances understanding of the mechanism of quercetin/QG regulate glucolipid metabolism and provides scientific support for the development of functional foods.

Comment on the "Eco-friendly and efficient extraction of polyphenols from Ligustrum robustum by deep eutectic solvent assisted ultrasound"

Qin et al. have proposed an ecological and efficient method of extraction polyphenols from the leaves of Ligustrum robustum using eutectic solvents, assisted by ultrasounds. The authors tested a number of solvents, optimized the extraction parameters and explored the extraction mechanism. According to the results of biological activity experiments of the prepared Ligustrum robustum leaves extracts, they seem promising for practical applications. The issue which is disputable is the identification of the phenolic compounds by using electrospray ionization mass spectrometry, as described in details in this comment.

Gut microbiome-mediated glucose and lipid metabolism mechanism of star apple leaf polyphenol-enriched fraction on metabolic syndrome in diabetic mice

BACKGROUND

Diabetes is a kind of metabolic syndrome (MetS) that seriously threatens human health globally. The leaf of star apple (Chrysophyllum cainito L.) is an incompletely explored folk medicine on diabetes. And, the effects and mechanisms on diabetes complicated glycolipid metabolism disorders are unknown till now.

PURPOSE

This study aimed to investigate the constituents of star apple leaf polyphenol enriched-fraction (SAP), and elucidate their treatment effects and mechanism on diabetes and accompanied other MetS.

METHODS

The components of SAP were tentatively identified by HPLC-Q-TOF-MS/MS. The antioxidant activity was determined by the scavenging of free radicals and hypoglycemic activities by inhibition of α-glucosidase in vitro. HepG2 cells were used for evaluating the alleviation effects of SAP on lipid accumulation. Streptozotocin and high-fat diet induced diabetic mice were grouped to evaluate the effects of different dosages of SAP. 16S rRNA was conducted to analysis gut microbiome-mediated glucose and lipid metabolism mechanism.

RESULTS

It showed that myricitrin was one of the main active constituents of SAP. SAP not only showed low IC50 on -glucosidase (24.427± 0.626 μg/mL), OH·(3.680± 0.054 μg/mL) and ABTS· (9.155±0.234 μg/mL), but significantly induced the lipid accumulation in HepG2 cells (p < 0.05). SAP at 200 mg/kg·day significantly decreased the blood glucose, insulin and oral glucose tolerance test value (p < 0.05). The insulin resistance indexes and oxidative stress were alleviated after administration. SAP not only attenuated hepatic lipid deposition, but also reversed the hepatic glycogen storage. 16S rRNA sequencing results revealed that the interaction between SAP and gut microbiota led to the positive regulation of beneficial bacteria including Akkermansia, Unspecified S24_7, Alistipes and Unspecified_Ruminococcaceae, which might be one of the mechanisms of SAP on MetS.

CONCLUSION

For the first time, this study explored the regulation effect of star apple leaf polyphenols on the hepatic glycolipid metabolism and studied the underlying mechanism from the view of gut microbiota. These findings indicated that SAP possesses great potential to serve as a complementary medicine for diabetes and associated MetS. It provided scientific evidence for folk complementary medicine on the treatment of diabetes-complicated multiple metabolic disorders.

UHPLC-Q-TOF-MS/MS Dereplication to Identify Chemical Constituents of Hedera helix Leaves in Vietnam

Hedera helix has been reported to contain a wide range of metabolites and produce many pharmacological effects. This research demonstrates the determination and evaluation of the phytochemical profiling of H. helix grown in central Vietnam. Methanolic extract of ivy had been analyzed by ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS/MS). MS, and MS/MS experiments were manipulated using both negative and positive ionization modes to provide molecular mass information and production spectra for the structural elucidation of compounds. A total of 46 compounds including 24 triterpene saponins and other compounds were successfully identified of which four established saponin structures have been reported for the first time. This study has provided a base for building a quality control of the raw materials according to the profile of triterpene saponins and assessment of pharmaceutical ingredients of H. helix planted in Vietnam.

Extensive metabolism of flavonoids relevant to their potential efficacy on Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder, the incidence of which is climbing with ever-growing aged population, but no cure is hitherto available. The epidemiological studies unveiled that chronic intake of flavonoids was negatively associated with AD risk. Flavonoids, a family of natural polyphenols widely distributed in human daily diets, were readily conjugated by phase II drug metabolizing enzymes after absorption in vivo, and glucuronidation could occur in 1 min following intravenous administration. Recently, as many as 191 metabolites were obtained after intragastric administration of a single flavonoid, indicating that other bioactive metabolites, besides conjugates, might be formed and account for the contradiction between efficacy of flavonoids in human or animal models and low systematic exposure of flavonoid glycosides or aglycones. In this review, metabolism of complete 68 flavonoid monomers potential for AD treatment, grouped in flavonoid O-glycosides, flavonoid aglycones, flavonoid C-glycosides, flavonoid dimers, flavonolignans and prenylated flavonoids according to their common structural elements, respectively, has been systematically retrospected, summarized and discussed, including their unequivocally identified metabolites, metabolic interconversions, metabolic locations, metabolic sites (regio- or stereo-selectivity), primarily involved metabolic enzymes or intestinal bacteria, and interspecies correlations or differences in metabolism, and their bioactive metabolites and the underlying mechanism to reverse AD pathology were also reviewed, providing whole perspective about advances on extensive metabolism of diverse potent flavonoids in vivo and in vitro up to date and aiming at elucidation of mechanism of actions of flavonoids on AD or other central nervous system (CNS) disorders.

Pharmacokinetic comparison of quercetin, isoquercitrin, and quercetin-3-O-β-D-glucuronide in rats by HPLC-MS

Background

Quercetin (Qr), isoquercitrin (IQ), and quercetin-3-O-β-D-glucuronide (QG) are powerful phytochemicals that have been shown to exhibit disease prevention and health promotion properties. However, there may exist transformations between Qr, IQ, and QG in vivo. And the pharmacokinetic profiles of Qr, IQ, and QG have not been systematically compared. The pharmacokinetics study would be helpful to better understand the pharmacological actions of them.

Methods

Herein, we developed a reliable HPLC-MS method to compare the pharmacokinetics of Qr, IQ, and QG after separate (50 mg/kg) oral administration of them in rats, using puerarin as internal standard. The detection was performed using negative selected ion monitoring. This method was validated in terms of selectivity, linearity, precision, accuracy, extraction recovery, matrix effect, and stability; and shows reliabilities in monitoring the pharmacokinetic behaviors of these three compounds.

Results

Our results showed that after separate oral administration of Qr, IQ, and QG, all of the compounds could be detected in plasma. In addition, QG could be detected in the Qr group; Qr and QG could be measured in the IQ group; and Qr could be found in rat plasma after 1.5 h of QG administration. Moreover, the AUC_0−t of Qr in the; Qr group (2,590.5 ± 987.9 mg/L*min), IQ group (2,212.7 ± 914.1 mg/L*min), and QG group (3,505.7 ± 1,565.0 mg/L*min) was larger than the AUC_0−t of QG in the; Qr group (1,550.0 ± 454.2 mg/L*min), IQ group (669.3 ± 188.3 mg/L*min), and QG group (962.7 ± 602.3 mg/L*min). The AUC_0−t of IQ was the lowest among all groups.

Discussion

Quercetin, IQ, and QG can all be absorbed into plasma. A mutual transformation exists between Qr and QG, and IQ can be metabolized into Qr and QG in SD rats. These results would provide a meaningful basis for understanding the pharmacological actions of these three compounds.

Bioavailability of Quercetin in Humans with a Focus on Interindividual Variation

After consumption of plant-derived foods or beverages, dietary polyphenols such as quercetin are absorbed in the small intestine and metabolized by the body, or they are subject to catabolism by the gut microbiota followed by absorption of the resulting products by the colon. The resulting compounds are bioavailable, circulate in the blood as conjugates with glucuronide, methyl, or sulfate groups attached, and they are eventually excreted in the urine. In this review, the various conjugates from different intervention studies are summarized and discussed. In addition, the substantial variation between different individuals in the measured quercetin bioavailability parameters is assessed in detail by examining published human intervention studies where sources of quercetin have been consumed in the form of food, beverages, or supplements. It is apparent that most reported studies have examined quercetin and/or metabolites in urine and plasma from a relatively small number of volunteers. Despite this limitation, it is evident that there is less interindividual variation in metabolites which are derived from absorption in the small intestine compared to catabolites derived from the action of microbiota in the colon. There is also some evidence that a high absorber of intact quercetin conjugates could be a low absorber of microbiota-catalyzed phenolics, and vice versa. From the studies reported so far, the reasons or causes of the interindividual differences are not clear, but, based on the known metabolic pathways, it is predicted that dietary history, genetic polymorphisms, and variations in gut microbiota metabolism would play significant roles. In conclusion, quercetin bioavailability is subject to substantial variation between individuals, and further work is required to establish if this contributes to interindividual differences in biological responses.

Centella asiatica - Phytochemistry and mechanisms of neuroprotection and cognitive enhancement

This review describes in detail the phytochemistry and neurological effects of the medicinal herb Centella asiatica (L.) Urban. C. asiatica is a small perennial plant that grows in moist, tropical and sub-tropical regions throughout the world. Phytochemicals identified from C. asiatica to date include isoprenoids (sesquiterpenes, plant sterols, pentacyclic triterpenoids and saponins) and phenylpropanoid derivatives (eugenol derivatives, caffeoylquinic acids, and flavonoids). Contemporary methods for fingerprinting and characterization of compounds in C. asiatica extracts include liquid chromatography and/or ion mobility spectrometry in conjunction with high-resolution mass spectrometry. Multiple studies in rodent models, and a limited number of human studies support C. asiatica's traditional reputation as a cognitive enhancer, as well as its anxiolytic and anticonvulsant effects. Neuroprotective effects of C.asiatica are seen in several in vitro models, for example against beta amyloid toxicity, and appear to be associated with increased mitochondrial activity, improved antioxidant status, and/or inhibition of the pro-inflammatory enzyme, phospholipase A2. Neurotropic effects of C. asiatica include increased dendritic arborization and synaptogenesis, and may be due to modulations of signal transduction pathways such as ERK1/2 and Akt. Many of these neurotropic and neuroprotective properties of C.asiatica have been associated with the triterpene compounds asiatic acid, asiaticoside and madecassoside. More recently, caffeoylquinic acids are emerging as a second important group of active compounds in C. asiatica, with the potential of enhancing the Nrf2-antioxidant response pathway. The absorption, distribution, metabolism and excretion of the triterpenes, caffeoylquinic acids and flavonoids found in C. asiatica have been studied in humans and animal models, and the compounds or their metabolites found in the brain. This review highlights the remarkable potential for C. asiatica extracts and derivatives to be used in the treatment of neurological conditions, and considers the further research needed to actualize this possibility.

Metabolic profile and underlying improved bio-activity of Fructus aurantii immaturus by human intestinal bacteria

Fructus aurantii immaturus (FAI) is the dried young fruit of Citrus aurantium L. or Citrus sinensis L. Osbeck.

In-vivo absorption of pinocembrin-7-O-β-D-glucoside in rats and its in-vitro biotransformation

Pinocembrin-7-O-β-D-glucoside (PCBG), a flavonoid isolated from Penthorum chinense Pursh., has significant liver-protecting effects. The pharmacokinetics of PCBG and its major metabolite pinocembrin (PCB) in rats were investigated in this study. A sensitive and accurate UPLC-MS/MS method was developed and validated for the simultaneous quantitative determination of PCBG and PCB in rat plasma after oral and intravenous administration of PCBG. After intravenous administration, PCBG was the main form in plasma. In contrast, after oral administration, the concentration of PCB was about 4-fold higher than that of PCBG, indicating that PCBG was metabolized to PCB. We also investigated the biotransformation of PCBG in vitro in order to understand whether the pH and the intestinal flora of gastrointestinal tract could affect the metabolism of PCBG. PCBG was incubated in rat plasma, liver homogenization, gastrointestial contents, liver microsomes (RLM) and hepatocytes in vitro. The data showed that PCB was quickly formed in the gastrointestinal incubation but PCBG was converted to PCB gradually in other incubations. The results indicated that the majority of PCBG was converted to its aglycone PCB in digestive system after oral administration, and PCB could be the active ingredient in the body.

(Anti)mutagenic and immunomodulatory properties of quercetin glycosides

BACKGROUND

Quercetin-3-O-β-D-glucopyranoside (isoquercitrin) and quercetin-3-O-rutinoside (rutin) are common components of a normal human diet and are increasingly used in food supplements. Here their effect on mutagenesis and immunity is shown.

RESULTS

The in vitro (anti)mutagenic potential was compared with that of quercetin using the Ames test in Salmonella typhimurium His(-) strains TA100, TA98 and TA102. Isoquercitrin only slightly increased the number of revertants, while rutin was totally non-mutagenic. On the other hand, all compounds displayed dose-dependent protective activity against H2O2 - and tert-butyl hydroperoxide-induced oxidative damage to the TA102 strain and at 75 µmol L(-1) inhibited H2O2/Fe(2+)-induced formation of the open circular and linear forms of the DNA plasmid pBSIISK(-). In mice, none of the flavonols (0.86 µmol day(-1), 34 days) induced harmful effects. In immunized animals, all compounds enhanced ex vivo B cell proliferation; quercetin stimulated lymphocyte basal proliferation and increased the number of IgM-producing lymphocytes. Rutin promoted NK cytotoxic activity, supported T cells and enhanced gut epithelium renewal. No effect on IgG-forming cells was found.

CONCLUSION

Isoquercitrin displayed negligible and rutin no mutagenicity, but both showed significant antimutagenic and DNA-protective effects against oxidative damage. In vivo, they supported the readiness of the immune system for specific humoral immune response.

Simultaneous determination and pharmacokinetic study of eight components in rat plasma by UHPLC-MS/MS after oral administration of Hypericum japonicum Thunb extract

A rapid and sensitive assay based on ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) was established and validated for the simultaneous determination of gallic acid, protocatechuic acid, vanillic acid, caffeic acid, epicatechin, isoquercitrin, vincetoxicoside B and quercetin in rat plasma using catechin and daidzein as the internal standards (IS). Plasma samples added internal standards were acidified with formic acid then pretreated by direct protein precipitation with acetonitrile. The separation of eight constituents was achieved on a C18 column with gradient elution using methanol and 0.2% acetic acid aqueous solution as the mobile phase and detected by multiple reaction monitoring using electrospray ionization source in the positive-negative ionization mode. The method was validated for sufficient specificity, precision, accuracy, and sensitivity over the concentration range of 10-6000 ng mL(-1) for gallic acid, 1.5-3000 ng mL(-1) for protocatechuic acid, 10-15000 ng mL(-1) for vanillic acid, 2-3600 ng mL(-1) for caffeic acid, 1.5-3600 ng mL(-1) for epicatechin, 4-6000 ng mL(-1) for isoquercitrin, 2-9000 ng mL(-1) for vincetoxicoside B, and 20-18000 ng mL(-1) for quercetin. The overall intra‑run precision and the inter‑run precision were showed in the range of 1.0-14.2% and 2.8-12.9%, respectively, and the accuracy was no more than 12.8%. This analytical method was successfully applied to investigate the pharmacokinetics of eight ingredients in rats after oral administration of Hypericum japonicum Thunb extract.

Studies on metabolism of total glucosides of paeony from Paeoniae Radix Alba in rats by UPLC-Q-TOF-MS/MS

Total glucosides of paeony are the active constituents of Paeoniae Radix Alba. In this study, a novel strategy was proposed to find more metabolites and the differences between paeoniflorin, albiflorin and total glucosides of paeony (TGP). This strategy was characterized as follows: firstly, the animals were divided into three groups (paeoniflorin, albiflorin and TGP) to identify the source of TGP metabolites from paeoniflorin or albiflorin; secondly, a generic information-dependent acquisition scan for the low-level metabolites was triggered by the multiple mass defect filter and dynamic background subtraction; thirdly, the metabolites were identified with a combination of data-processing methods including mass defect filtering, neutral loss filtering and product ion filtering; finally, a comparative study was used in the metabolism of paeoniflorin, albiflorin and TGP. Based on the strategy, 18 metabolites of TGP, 10 metabolites of paeoniflorin and 13 metabolites of albiflorin were identified respectively. The results indicated that the hydrolysis, conjugation reaction and oxidization were the major metabolic pathways, and the metabolic sites were the glycosidic linkage, the ester bond and the benzene ring. This study is first to explore the metabolism of TGP, and these findings enhance our understanding of the metabolism and the interactions of paeoniflrin and albiflorin in TGP.

Determination of metabolites of diosmetin-7-O-glucoside by a newly isolated Escherichia coli from human gut using UPLC-Q-TOF/MS

Different human intestinal bacteria were isolated and screened for their ability to transform diosmetin-7-O-glucoside. A Gram-negative anaerobic bacterium, strain 4, capable of metabolizing diosmetin-7-O-glucoside was newly isolated. Its 16S rRNA gene sequence displayed 99% similarity with that of Escherichia. Then strain 4 was identified as a species of the genus Escherichia and was named Escherichia sp. 4. Additionally, an ultraperformance liquid chromatography/quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF/MS) technique combined with Metabolynx software method was established to screen the metabolites of diosmetin-7-O-glucoside. Comparing the retention time and MS/MS spectrum, three metabolites were detected and tentatively identified. These metabolites were acquired by four proposed metabolic pathways including dehydroxylation, deglycosylation, methylation, and acetylation. Diosmetin-7-O-glucoside was mainly bioconverted to considerable amounts of diosmetin and minor amounts of acacetin by the majority of the isolated intestinal bacteria such as Escherichia sp. 4. Subsequently, several strains could degrade acacetin to produce methylated and acetylated acacetin. The metabolites and metabolic pathways of diosmetin-7-O-glucoside by human intestinal bacterium Escherichia sp. 4 were first investigated.

Simultaneous quantification of Akebia saponin D and its five metabolites in human intestinal bacteria using ultra-performance liquid chromatography triple quadrupole mass spectrometry

A rapid and sensitive ultra-performance liquid chromatography triple quadrupole mass spectrometry (UPLC-TQ/MS) method was developed for simultaneous quantification of Akebia saponin D (ASD) and its five metabolites in intestinal mixtures of bacteria from human feces. After protein precipitation, the analytes and internal standard (IS), glycyrrhetinic acid, were determined in selected ion recording (SIR) mode with negative ion ESI source. Chromatographic separation was carried out on an ACQUITY UPLC™ BEH C18 column (100mm×2.1mm, 1.7μm) using gradient elution. The mobile phase consisted of solvents A (acetonitrile) and B (0.1% aqueous formic acid) at the flow rate of 0.4mL/min. Each sample was chromatographed within 10.5min including equilibration time. The linearity ranged from 0.1 to 100μg/mL for ASD, and 2-1000ng/mL for five metabolites, Dipsacus saponin A (M1), HN-saponin F (M2), hederagenin-28-O-β-d-glucopyranoside (M3), Akebia saponin PA (M4), hederagenin (M5). The limits of detection (LOD) were 0.41, 0.59, 0.61, 0.55, 0.52 and 0.31ng/mL for ASD, M1, M2, M3, M4 and M5, respectively. The intra- and inter-day precision was all within 11.1% and accuracy ranged from -8.33% to 12.47%. The conversion rate of five metabolites was 41.21% in 24h. The method was validated and successfully applied to quantification of ASD and its five metabolites in human intestinal bacteria.

Interactions of pharmacokinetic profile of different parts from Ginkgo biloba extract in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts from Ginkgo biloba L. leaves confer their therapeutic effects through the synergistic actions of flavonoid and terpenoid components, but some non-flavonoid and non-terpenoid components also exist in this extract. In the study of this paper, an investigation was carried out to compare the pharmacokinetic parameters of fourteen compounds to clarify the influences of non-flavonoid and non-terpenoid fraction (WEF) on the pharmacokinetics profile of the flavonoid fraction (FF) and the terpene lactone fraction (TLF) from Ginkgo biloba extracts.

MATERIALS AND METHODS

A selective and sensitive UPLC-MS/MS method was established to determine the plasma concentrations of the fourteen compounds to compare the pharmacokinetic parameters after orally administration of FF, TLF, FF-WEF, FF-TLF, TLF-WEF and FF-TLF-WEF with approximately the same dose. At different time points, the concentration of rutin (1), isoquercitrin (2), quercetin 3-O-[4-O-(-β-D-glucosyl)-α-L-rhamnoside] (3), ginkgolide C (4), bilobalide (5), quercitrin (6), ginkgolide B (7), ginkgolide A (8), luteolin (9), quercetin (10), apigenin (11), kaempferol (12), isorhamnetin (13), genkwanin (14) in rat plasma were determined and main pharmacokinetic parameters including T1/2, Tmax, Cmax and AUC were calculated using the DAS 3.2 software package. The statistical analysis was performed using the Student׳s t-test with P<0.05 as the level of significance.

RESULTS

FF and WEF had no effect on the pharmacokinetic behaviors and parameters of the four terpene lactones, but the pharmacokinetic profiles and parameters of flavonoids changed while co-administered with non-flavonoid components. It was found that Cmax and AUC of six flavonoid aglycones in group FF-WEF, FF-TLF and FF-TLF-WEF had varying degrees of reduction in comparison with group FF, especially in group FF-TLF-WEF. On the contrary, the values of Cmax, Tmax and AUC of four flavonoid glycosides in group FF-TLF-WEF were significantly increased compared with those in group FF.

CONCLUSIONS

These results indicate that non-flavonoid components in Ginkgo biloba extracts could increase the absorption and improve the bioavailability of flavonoid glycosides but decrease the absorption and reduce the bioavailability of flavonoid aglycones.

Isolation and identification of quercetin degrading bacteria from human fecal microbes

Quercetin has a wide range of biological properties. The gut microflora can often modulate its biological activity and their potential health effects. There still is a lack of information about gut bacteria involving in this process. The strains of gut microbes from human feces that can transform quercetin were isolated and identified by in vitro fermentation. The results showed that Escherichia coli, Stretococcus lutetiensis, Lactobacillus acidophilus, Weissella confusa, Enterococcus gilvus, Clostridium perfringens and Bacteroides fragilis have the various ability of degrading quercetin. Among them, C. perfringens and B. fragilis were discovered to have the strongest ability of degrading quercetin. Additionally, quercetin can't inhibit the growth of C. perfringens. In conclusion, many species of gut microbiota can degrade quercetin, but their ability are different.

A sensitive LC-MS/MS method for simultaneous determination of six flavonoids in rat plasma: application to a pharmacokinetic study of total flavonoids from mulberry leaves

A simple and sensitive LC-MS/MS method has been developed and validated for the determination of rutin, isoquercitrin, astragalin, quercetin, kaempferol and isorhamnetin in rat plasma using naringin as the internal standard (IS). The plasma samples were pretreated and extracted by liquid-liquid extraction. Chromatographic separation was accomplished on a C18 column with a 10 min gradient elution using acetonitrile and 0.1% formic acid aqueous solution as mobile phase at a flow rate of 0.3 mL min(-1). A tandem mass spectrometric detection was conducted using multiple reaction monitoring (MRM) via an electrospray ionization (ESI) source and operating in the negative ionization mode. The lower limit of quantitation (LLOQ) of each analyte was lower than 1 ng mL(-1). Intra-day and inter-day precisions were less than 11.9%. The relative errors of accuracy were in the range of -9.2% to 6.1%. The mean recoveries of flavonoids and IS were higher than 53.8%. The proposed method was further applied to investigate the pharmacokinetics of all analytes after a single oral administration of total flavonoids from mulberry leaves to rats.