Identification of Gingko biloba flavonol metabolites after oral administration to humans

Pharmacological activities and effective substances of the component-based Chinese medicine of Ginkgo biloba leaves based on serum pharmacochemistry, metabonomics and network pharmacology

As a potential drug candidate for the treatment of hypertension and complications, it is speculated that the component-based Chinese medicine of Ginkgo biloba leaves (GBCCM) which mainly composed of flavonoid aglycones (FAs) and terpene lactones (TLs) may have different pharmacological effects at different doses or ratios. Taking the normal mice as the study object, metabonomics was conducted by giving different doses of GBCCM. Based on the components of GBCCM absorbed into the blood, the network pharmacological prediction was carried out. By integrating the results of metabonomics and network pharmacology, predict the possible pharmacological effects of GBCCM and conduct experimental verification. It was found that eight of the 19 compounds in GBCCM could be absorbed into the blood. GBCCM mainly affected the signal pathways of unsaturated fatty acid, pyruvate, bile acid, melanin and stem cells. It was speculated that GBCCM might have activities such as lowering blood pressure, regulating stem cell proliferation and melanogenesis. By establishing the models of mushroom tyrosinase, rat bone marrow mesenchymal stem cells (BMSCs) and spontaneously hypertensive rats (SHRs), we found that FAs and TLs showed synergistic effect in hypertension and tyrosinase models, and the optimal ratio was 3:2 (4.4 mg/kg) and 1:1 (0.4 mg/ml), respectively. As effective substances, FAs significantly promoted the proliferation of rat BMSCs on the third and fifth days at the concentration of 0.2 μg/ml (p < 0.05). GBCCM showed a variety of pharmacological effects at different doses and ratios, which provided an important reference for the druggability of GBCCM.

Active Compounds with Medicinal Potential Found in Maxillariinae Benth. (Orchidaceae Juss.) Representatives-A Review

Orchids are widely used in traditional medicine for the treatment of a whole range of different health conditions, and representatives of the Neotropical subtribe Maxillariinae are not an exception. They are utilized, for instance, for their spasmolytic and anti-inflammatory activities. In this work, we analyze the literature concerning the chemical composition of the plant extracts and secretions of this subtribe's representatives published between 1991 and 2022. Maxillariinae is one of the biggest taxa within the orchid family; however, to date, only 19 species have been investigated in this regard and, as we report, they produce 62 semiochemicals of medical potential. The presented review is the first summary of biologically active compounds found in Maxillariinae.

Metabolism of phenolics in coffee and plant-based foods by canonical pathways: an assessment of the role of fatty acid β-oxidation to generate biologically-active and -inactive intermediates

ω-Phenyl-alkenoic acids are abundant in coffee, fruits, and vegetables. Along with ω-phenyl-alkanoic acids, they are produced from numerous dietary (poly)phenols and aromatic amino acids in vivo. This review addresses how phenyl-ring substitution and flux modulates their gut microbiota and endogenous β-oxidation. 3',5'-Dihydroxy-derivatives (from alkyl-resorcinols, flavanols, proanthocyanidins), and 4'-hydroxy-phenolic acids (from tyrosine, p-coumaric acid, naringenin) are β-oxidation substrates yielding benzoic acids. In contrast, 3',4',5'-tri-substituted-derivatives, 3',4'-dihydroxy-derivatives and 3'-methoxy-4'-hydroxy-derivatives (from coffee, tea, cereals, many fruits and vegetables) are poor β-oxidation substrates with metabolism diverted via gut microbiota dehydroxylation, phenylvalerolactone formation and phase-2 conjugation, possibly a strategy to conserve limited pools of coenzyme A. 4'-Methoxy-derivatives (citrus fruits) or 3',4'-dimethoxy-derivatives (coffee) are susceptible to hepatic "reverse" hydrogenation suggesting incompatibility with enoyl-CoA-hydratase. Gut microbiota-produced 3'-hydroxy-4'-methoxy-derivatives (citrus fruits) and 3'-hydroxy-derivatives (numerous (poly)phenols) are excreted as the phenyl-hydracrylic acid β-oxidation intermediate suggesting incompatibility with hydroxy-acyl-CoA dehydrogenase, albeit with considerable inter-individual variation. Further investigation is required to explain inter-individual variation, factors determining the amino acid to which C6-C3 and C6-C1 metabolites are conjugated, the precise role(s) of l-carnitine, whether glycine might be limiting, and whether phenolic acid-modulation of β-oxidation explains how phenolic acids affect key metabolic conditions, such as fatty liver, carbohydrate metabolism and insulin resistance.

Study on Integrated Pharmacokinetics of the Component-Based Chinese Medicine of Ginkgo biloba Leaves Based on Nanocrystalline Solid Dispersion Technology

Background

To improve the dissolution and bioavailability of the component-based Chinese medicine of Ginkgo biloba leaves (GBCCM), a novel nanocrystalline solid dispersion of GBCCM (GBCCM NC-SD) was first prepared.

Methods

GBCCM mainly containing high pure flavonoid aglycones (FAs) and terpenoid lactones (TLs) was used as the model drug. PVP K30 and SDS were used as solubilizers, combined stabilizers and carriers, and GBCCM NC-SD was prepared by high-pressure homogenization combined with freeze-dryer. Morphology and crystal characteristic of GBCCM NC-SD were analyzed. The dissolution and bioavailability evaluation were performed to investigate the feasibility of GBCCM NC-SD by in vitro dissolution and in vivo integrated pharmacokinetic models.

Results

After homogenizing for 30 cycles under the pressure of 650 bar and freeze-drying, GBCCM NC-SD with uniform quality would be obtained. The particle size, PDI and zeta potential were found to be 335.9 ± 32.8 nm, 0.29 ± 0.02 and −28.4 ± 0.7 mV respectively. Based on charged aerosol detector (CAD) technology, a new chromatographic method for simultaneous detection of eight components in GBCCM was developed. In vitro drug release study showed that the cumulative dissolution of FAs and TLs in GBCCM NC-SD increased from 12.77% to 52.92% (P < 0.01) and 90.91% to 99.21% (P < 0.05) respectively. In comparison with physical mixture of GBCCM and stabilizer (PM), the integrated pharmacokinetics AUC_0-t of FAs and TLs in GBCCM NC-SD were significantly increased (P < 0.05), and the T_1/2 of TLs was also significantly prolonged (P < 0.05).

Conclusion

This study demonstrated that novel GBCCM NC-SD was prepared using Polyvinylpyrrolidone K30 (PVP K30) and Sodium dodecyl sulfate (SDS) as a synergetic stabilizer and also provided a feasible way to improve the dissolution and oral bioavailability of poorly soluble candidate antihypertensive drugs.

Pharmacokinetic, Metabolism, and Metabolomic Strategies Provide Deep Insight Into the Underlying Mechanism of Ginkgo biloba Flavonoids in the Treatment of Cardiovascular Disease

Ginkgo biloba, known as the “living fossil,” has a long history of being used as botanical drug for treating cardiovascular diseases and the content of flavonoids as high as 24%. More than 110 different kinds of flavonoids and their derivatives have been separated from G. biloba, including flavones, flavonols, biflavonoids, catechins, and their glycosides, etc., all of which display the ability to dilate blood vessels, regulate blood lipids, and antagonize platelet activating factor, and protect against ischemic damage. At present, many types of preparations based on G. biloba extract or the bioactive flavonoids of it have been developed, which are mostly used for the treatment of cardiovascular diseases. We herein review recent progress in understanding the metabolic regulatory processes and gene regulation of cellular metabolism in cardiovascular diseases of G. biloba flavonoids. First, we present the cardioprotective flavonoids of G. biloba and their possible pharmacological mechanism. Then, it is the pharmacokinetic and liver and gut microbial metabolism pathways that enable the flavonoids to reach the target organ to exert effect that is analyzed. In the end, we review the possible endogenous pathways toward restoring lipid metabolism and energy metabolism as well as detail novel metabolomic methods for probing the cardioprotective effect of flavonoids of G. biloba.

Dilute-and-shoot-based direct nano-electrospray ionization tandem mass spectrometry as screening methodology for multivitamins in dietary supplement and human urine

INTRODUCTION

In recent years, analytical screening methods for simultaneous detection of multivitamins have gained substantial attention to ensure quality and public confidence in dietary supplements. Even so, few analytical methods have been proposed for simultaneous analysis of multivitamin constituents due to the large divergence in chemical characteristics.

OBJECTIVES

In the present study, the objective was to develop a simple and rapid direct nano-electrospray ionization-tandem mass spectrometry (DI-nano-ESI-MS/MS) method for targeted detection of water soluble vitamins, fat soluble vitamins, amino acids, royal jelly, ginkgo biloba, and ginseng in a dietary supplement. The applicability of dilute-and-shoot-based DI-nano-ESI-MS/MS to analyze the same tested compounds and their related metabolites in clinical samples was also examined.

METHODS

Intact urine mixed with the ionization solvent was loaded (4-μL aliquot) into a nanospray (NS) capillary of 1-μm tip diameter. The NS capillary was then fitted into an off-line ion source at a distance of 5 mm from MS aperture. The sample was directly injected by applying a voltage of 1.1 kV, producing a numerous of m/z peaks for analysis in mere minutes.

RESULTS

The DI-nano-ESI-MS/MS method successfully identified almost all dietary supplement components, as well as a plethora of component-related metabolites in clinical samples. In addition, a new merit of the proposed method for the detection of index marker and chemical contaminants as well as subspecies identification was investigated for further quality evaluation of the dietary supplement.

CONCLUSIONS

The previous findings illustrated that DI-nano-ESI-MS/MS approach can emerge as a powerful, high throughput, and promising analytical tool for screening and accurate detection of various pharmaceuticals and ingredient in dietary supplements as well as biological fluids.

Systemic exposure to Ginkgo biloba extract in male F344/NCrl rats: Relevance to humans

Ginkgo biloba extract (GBE) is a popular botanical dietary supplement used worldwide and the safety of use is a public health concern. While GBE is a complex mixture, the terpene trilactones and flavonol glycosides are believed to elicit the pharmacological and/or toxicological effects of GBE. In a National Toxicology Program (NTP) 2-year rodent bioassay with GBE, hepatotoxicity was observed in rodents (≥100 mg/kg in rats, ≥ 200 mg/kg in mice). Subsequently, questions arose about whether or not the GBE used in NTP studies was representative of other GBE products and how rodent doses are related to human doses. To address these, we generated systemic exposure data for terpene trilactones in male rats following oral administration of 30, 100, and 300 mg/kg GBE test article from the 2-year bioassay. Dose-normalized C_max and AUC_∞ for terpene trilactones from the current study were within 5-fold of published rodent studies using a standardized GBE preparation. Comparison of our rat systemic exposure data at 100 mg/kg GBE to published human data following ingestion of 240 mg GBE-containing product showed that the rat/human exposure multiple was 3-22, for terpene trilactones. These data demonstrate the relevance of NTP rodent toxicity data to humans.

Induction Effects of Apigenin, Luteolin and Vinpocetin on Neutral Endopeptidase (NEP) and Angiotensin-Converting Enzyme Activity (ACE) of SK-N-SH Cells

The long-term effects of a number of flavonoids (such as apigenin, luteolin and amentoflavone) and vinpocetine on the neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE) were investigated. It was shown that apigenin, luteolin and vinpocetin are able to induce the activity of both NEP and ACE associated with the inhibition of the proliferation of the neuroblastoma cell line SK-N-SH. Amentoflavone has no effect on either NEP or ACE activity. An additional enhancement of cellular NEP activity could be detected after the treatment of the cells with a combination of both arabinosylcytosine and either apigenin or luteolin. This effect supports the assumption that apigenin and luteolin influence directly the gene expression of NEP. Taking into account the significant role of NEP and ACE in the degradation of amyloid beta peptides, the induction of both enzymes by long-term treatment with apigenin, luteolin and vinpocetine may have a beneficial effect regarding the prevention of the formation of amyloid plaques and the effect of these substances may be discussed as neuroprotective.

Urinary excretion of ginkgolide terpene lactones following acute consumption of Ginkgo biloba extract

Urinary biomarkers of plant food supplement (PFS) exposure/intake represent an accurate, objective tool for determining PFS consumption in humans with applications ranging from epidemiology to subject compliance in clinical trials. Ginkgo biloba remains one of the worlds most popular PFS, yet few studies have investigated the uptake and metabolism of its primary unique bioactives: the terpene lactones. To this end, we conducted a dual-dose, acute crossover intervention using G. biloba supplements in healthy participants (n = 12). Pooled 24-H urine samples were analyzed by triple quadrupole LC-MS-MS. We observed that bilobalide and ginkgolides A and B were passed into urine intact and in a dose-dependent manner. Low levels of intact ginkgolides C and J were also excreted. To our knowledge, this is the first study to report intact ginkgolide J in urine following oral consumption of ginkgo supplements and is also the first to account for excreted terpene lactones as a proportion of dose.

Effects of Ginkgo biloba extract on the embryo-fetal development in Wistar rats

BACKGROUND

Ginkgo biloba extract (GBE) is an herbal medicine used for treating neurodegenerative diseases, cerebrovascular insufficiency, peripheral arterial occlusive disease, and also vestibular disturbance. Some components of GBE have presented estrogenic effects and, in a previous study, high dosages of GBE caused intra-uterine growth retardation in fetuses of Wistar rats treated during the fetogenesis period.

METHODS

Pregnant Wistar rats were treated, through gavage, with different dosages of aqueous GBE (3.5, 7.0, and 14.0 mg/Kg/day), during the tubal transit and implantation period. Rats were killed on the 15th day of pregnancy and the following parameters were evaluated: clinical symptoms of maternal toxicity; maternal body weight; feed and water intake; maternal liver, kidney, and ovary weights; number of corpora lutea; implants per group ratio; pre- and post-implantation loss per group ratio; live fetuses mean; dead fetuses percentage; fetus and placenta weight per offspring ratio; and fetal external malformation.

RESULTS

No significant alteration was found for both the maternal and embryonic parameters evaluated.

CONCLUSIONS

The GBE treatment in pregnant Wistar rats, during the tubal transit and implantation period, caused no toxic effect on the maternal organism and did not induce embryonic death, growth retardation, and/or fetal malformations.

Does Ginkgo biloba reduce the risk of cardiovascular events?

BACKGROUND

Cardiovascular disease (CVD) was a preplanned secondary outcome of the Ginkgo Evaluation of Memory Study. The trial previously reported that Ginkgo biloba had no effect on the primary outcome, incident dementia.

METHODS AND RESULTS

The double-blind trial randomly assigned 3069 participants over 75 years of age to 120 mg of G biloba EGb 761 twice daily or placebo. Mean follow-up was 6.1 years. The identification and classification of CVD was based on methods used in the Cardiovascular Health Study. Differences in time to event between G biloba and placebo were evaluated using Cox proportional hazards regression adjusted for age and sex. There were 355 deaths in the study, 87 due to coronary heart disease with no differences between G biloba and placebo. There were no differences in incident myocardial infarction (n=164), angina pectoris (n=207), or stroke (151) between G biloba and placebo. There were 24 hemorrhagic strokes, 16 on G biloba and 8 on placebo (not significant). There were only 35 peripheral vascular disease events, 12 (0.8%) on G biloba and 23 (1.5%) on placebo (P=0.04, exact test). Most of the peripheral vascular disease cases had either vascular surgery or amputation.

CONCLUSIONS

There was no evidence that G biloba reduced total or CVD mortality or CVD events. There were more peripheral vascular disease events in the placebo arm. G biloba cannot be recommended for preventing CVD. Further clinical trials of peripheral vascular disease outcomes might be indicated.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00010803.

Postnatal development of pups from nursing rats treated with Gingko biloba

The Gingko biloba extract is contraindicated during pregnancy and lactation due to the lack of information about its effects on these reproductive phases. Previous studies have shown that G. biloba extract contains components with estrogenic and antiestrogenic activities, thus nursing dams treated with the extract of this plant could show reduction in milk production, resulting in malnutrition and poor development of pups. This work analyzes the postnatal development of pups, whose mothers were treated with G. biloba extract during the lactation period. Nursing Wistar rats received 3.5 mg/kg/day of G. biloba aqueous extract, corresponding to the highest human dose. Clinical signs of maternal toxicity were evaluated. The growth rate, viability, survival during treatment and lactation indices of the pups were calculated. The physical, motor and sensorial development of the pups was also evaluated. No maternal signs of toxicity were observed. As there were no biological differences between control and G. biloba treated pups, it is possible to assume that, in this experimental design, the administration of G. biloba aqueous extract to nursing rats during the lactation period seems to be devoid of toxic effect to mothers and to the physical, motor and sensory development of the pups.

Isolation and purification of ginkgo flavonol glycosides from Ginkgo biloba leaves by high-speed counter-current chromatography

A high-speed counter-current chromatography method was developed for the separation and purification of bioactive flavonol glycosides from a crude ethanol extract of Ginkgo biloba leaves. The separation was performed with a two-phase solvent system composed of n-hexane-butanol-ethyl acetate-methanol-0.5% acetic acid (1:0.5:3.5:1:4, v/v) and three pure compounds were eluted in high purities in a one-step separation. Their purities were determined by HPLC and identified by MS,(1)H-NMR, and(13)C-NMR.

A critical review of the data related to the safety of quercetin and lack of evidence of in vivo toxicity, including lack of genotoxic/carcinogenic properties

Quercetin is a naturally-occurring flavonol (a member of the flavonoid family of compounds) that has a long history of consumption as part of the normal human diet. Because a number of biological properties of quercetin may be beneficial to human health, interest in the addition of this flavonol to various traditional food products has been increasing. Prior to the use of quercetin in food applications that would increase intake beyond that from naturally-occurring levels of the flavonol in the typical Western diet, its safety needs to be established or confirmed. This review provides a critical examination of the scientific literature associated with the safety of quercetin. Results of numerous genotoxicity and mutagenicity, short- and long-term animal, and human studies are reviewed in the context of quercetin exposure in vivo. To reconcile results of in vitro studies, which consistently demonstrated quercetin-related mutagenicity to the absence of carcinogenicity in vivo, the mechanisms that lead to the apparent in vitro mutagenicity, and those that ensure absence of quercetin toxicity in vivo are discussed. The weight of the available evidence supports the safety of quercetin for addition to food.

On-line automatic SPE-CE coupling for the determination of biological markers in urine

Automatic SPE has been coupled on-line to CE by a transfer tube and the replenishment system of the CE instrument. The approach allows the target analytes (viz. creatinine, creatine, xanthine, hypoxanthine, uric acid, p-aminohippuric acid and ascorbic acid in urine samples) to be removed from the sample matrix, cleaned up, preconcentrated and injected into the capillary. The detection limits range between 0.14 and 4.50 microg/mL, the quantification limits between 0.45 and 15.0 microg/mL, and linear dynamic ranges - which include the reference healthy human values - from the quantification limits to 1332 microg/mL. The precision, expressed as RSD, ranges between 0.38 and 2.22% for repeatability and between 1.79 and 7.61% for within-laboratory reproducibility. The errors, expressed as RSD for all compounds, range between 0.20 and 6.90%. The time for automatic SPE and that necessary for the individual separation-detection of the target analytes are 13 and 12 min, respectively; the analysis frequency is 5 h(-1). The accuracy of the method and potential matrix effects were studied by using spiked samples and recoveries between 96.00 and 103.07 % were obtained. The proposed method was applied to samples from healthy young students.

A new capillary zone electrophoresis method for the analysis ofGinkgo biloba extracts andGinkgo biloba pharmaceutical products

Ginkgo biloba, traditional Chinese medicine is now generally accepted. Separation and determination of active components in G. biloba is important for the product quality control. Therefore, the development of an effective and reliable separation method is important. In this work, a new capillary electrophoretic (CZE) method for separation of the G. biloba leaf extracts components was developed and optimized by the use of experimental design and artificial neural network (ANN). Under best separation conditions, in gamma-CD-modified buffer, the separation was reached within 10 min (36 mM borate BGE, pH 9.2, 1 mM gamma-CD), while the hydrodynamic mode for sample injection (2 s) and UV detection at 270 nm were applied. The method developed was validated and applied for analysis of various extracts and G. biloba products.

How should we assess the effects of exposure to dietary polyphenols in vitro?

Human intervention studies have provided clear evidence that dietary polyphenols (eg, flavonoids--eg, flavonols--and isoflavones) are at least partly absorbed and that they have the potential to exert biological effects. Biological activity of polyphenols is often assessed by using cultured cells as tissue models; in almost all such studies, cells are treated with aglycones or polyphenol-rich extracts (derived from plants and foods), and data are reported at concentrations that elicited a response. There are 2 inherent flaws in such an approach. First, plasma and tissues are not exposed in vivo to polyphenols in these forms. Several human studies have identified the nature of polyphenol conjugates in vivo and have shown that dietary polyphenols undergo extensive modification during first-pass metabolism so that the forms reaching the blood and tissues are, in general, neither aglycones (except for green tea catechins) nor the same as the dietary source. Polyphenols are present as conjugates of glucuronate or sulfate, with or without methylation of the catechol functional group. As a consequence, the polyphenol conjugates are likely to possess different biological properties and distribution patterns within tissues and cells than do polyphenol aglycones. Although deconjugation can potentially occur in vivo to produce aglycone, it occurs only at certain sites. Second, the polyphenol concentrations tested should be of the same order as the maximum plasma concentrations attained after a polyphenol-rich meal, which are in the range of 0.1-10 micromol/L. For correct interpretation of results, future efforts to define biological activities of polyphenols must make use of the available data concerning bioavailability and metabolism in humans.

Enteric Disposition and Recycling of Flavonoids and Ginkgo Flavonoids

OBJECTIVE

The objective of this study was to determine the intestinal and microbial disposition of flavonoids and how these disposition processes affect their enteric recycling.

DESIGN

Studies were performed using a perfused rat intestinal model or using enrichment cultures and a pure isolate of Enterococcus avium (LY1).

RESULTS

In the rat intestine, aglycones, such as quercetin and apigenin, were as permeable (P*(eff) > or = 2) as compounds such as propranolol (100% absorption). However, a significant portion of the absorbed aglycones was conjugated and the metabolites were excreted into the lumen. Flavonoid glycosides, such as isoquercitrin and apigenin-7-O-glucoside, also had high apparent P*(eff) values (> or = 2) in the upper small intestine because of rapid hydrolysis. However, isoquercitrin was absorbed much slower (P*(eff) < or = 0.7, p < 0.05) when hydrolysis was absent or inhibited by 20 mmol gluconolactone. Absorption of other intact glycosides was similar to intact isoquercitrin and was much slower than the corresponding aglycones (P*(eff) < or = 0.7, p < 0.05). Intestinal bacteria, such as LY1, hydrolyzed the flavonoid glycosides used in the study. Excreted glycosidases were involved in the hydrolysis of glycosides because glycosides were poorly taken up by LY1. In conclusion, glycosidase-catalyzed hydrolysis is a critical first step in the intestinal and microbial disposition of flavonoid glycosides. Aglycones were not only rapidly absorbed, but also rapidly metabolized into phase II conjugates, which were then excreted back into the lumen. Therefore, intestinal and microbial glycosidases and intestinal phase II enzymes make a significant contribution to the disposition of flavonoids via the proposed enteric and enterohepatic recycling scheme.

Ginkgo biloba extracts and cancer: a research area in its infancy

Recent studies conducted with various molecular, cellular and whole animal models have revealed that leaf extracts of Ginkgo biloba may have anticancer (chemopreventive) properties that are related to their antioxidant, anti-angiogenic and gene-regulatory actions. The antioxidant and associated anti-lipoperoxidative effects of Ginkgo extracts appear to involve both their flavonoid and terpenoid constituents. The anti-angiogenic activity of the extracts may involve their antioxidant activity and their ability to inhibit both inducible and endothelial forms of nitric oxide synthase. With regard to gene expression, a Ginkgo extract and one of its terpenoid constituents, ginkgolide B, inhibited the proliferation of a highly aggressive human breast cancer cell line and xenografts of this cell line in nude mice. cDNA microarray analyses have shown that exposure of human breast cancer cells to a Ginkgo extract altered the expression of genes that are involved in the regulation of cell proliferation, cell differentiation or apoptosis, and that exposure of human bladder cancer cells to a Ginkgo extract produced an adaptive transcriptional response that augments antioxidant status and inhibits DNA damage. In humans, Ginkgo extracts inhibit the formation of radiation-induced (chromosome-damaging) clastogenic factors and ultraviolet light-induced oxidative stress - effects that may also be associated with anticancer activity. Flavonoid and terpenoid constituents of Ginkgo extracts may act in a complementary manner to inhibit several carcinogenesis-related processes, and therefore the total extracts may be required for producing optimal effects.

Microbial aromatic acid metabolites formed in the gut account for a major fraction of the polyphenols excreted in urine of rats fed red wine polyphenols

The health effects of dietary polyphenols might be explained by both intact compounds and their metabolites formed either in the tissues or in the colon by the microflora. The quantitative importance and biological activities of the microbial metabolites have seldom been examined in vivo. We measured the microbial metabolites formed in four groups of rats (n = 8) fed for 8 d a diet supplemented with 0.12 g/100 g catechin, 0.25 or 0.50 g/100 g red wine powder containing proanthocyanidins, phenolic acids, flavanols, anthocyanins and flavonols or an unsupplemented diet. Fourteen aromatic acid metabolites were assayed in urine collected for 24 h by an HPLC-electrospray ionization (ESI)-mass spectrometry (MS)-MS method. The three main metabolites formed from the catechin diet were 3-hydroxyphenylpropionic acid, 3-hydroxybenzoic acid and 3-hydroxyhippuric acid. Their total urinary excretion accounted for 4.7 g/100 g of the catechin ingested and that of intact catechins for 45.3 g/100 g. For wine polyphenols, the same microbial metabolites as observed for the catechin diet were identified in urine along with hippuric, p-coumaric, vanillic, 4-hydroxybenzoic and 3-hydroxyphenylacetic acids. All together, these aromatic acids accounted for 9.2 g/100 g of the total wine polyphenols ingested and intact catechins for only 1.2 g/100 g. The higher excretion of aromatic acids by rats fed wine polyphenols is likely due to their poor absorption in the proximal part of the gut. Some of the microbial metabolites still bear a reducing phenolic group and should also prevent oxidative stress in inner tissues. More attention should be given in the future to these microbial metabolites and their biological properties to help explain the health effects of polyphenols that are not easily absorbed through the gut barrier.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

Chemical analysis of Ginkgo biloba leaves and extracts

The chemical analysis and quality control of Ginkgo leaves and extracts is reviewed. Important constituents present in the medicinally used leaves are the terpene trilactones, i.e., ginkgolides A, B, C, J and bilobalide, many flavonol glycosides, biflavones, proanthocyanidins, alkylphenols, simple phenolic acids, 6-hydroxykynurenic acid, 4-O-methylpyridoxine and polyprenols. In the commercially important Ginkgo extracts some of these compound classes are no longer present. Many publications deal with the analysis of the unique terpene trilactones. They can be extracted with aqueous acetone or aqueous methanol but also supercritical fluid extraction is possible. Still somewhat problematic is their sample clean-up. Various procedures, not all of them validated, employing partitioning or SPE have been proposed. Some further development in this area can be foreseen. Separation and detection can be routinely carried out by HPLC with RI, ELSD or MS, or with GC-FID after silylation. TLC is another possibility. No quantitative procedure for flavonol glycosides has been published so far due their difficult separation and commercial unavailability. Fingerprint analysis by gradient RP-HPLC is possible. After acidic hydrolysis to the aglycones quercetin, kaempferol and isorhamnetin and separation by HPLC, quantitation is straightforward and yields by recalculation an estimation of the original total flavonol glycoside content. For biflavones, simple phenols, 6-hydroxykynurenic acid, 4-O-methylpyridoxine and polyprenols analytical procedures have been published but not all assays are yet ideal. Lately a there is a lot of interest in the analysis of the undesired alkylphenols and a few validated procedures have been published. The analysis of Ginkgo proanthocyanidins is still in its infancy and no reliable assays exist.

The metabolic fate of dietary polyphenols in humans

Dietary polyphenols are widely considered to contribute to health benefits in humans. However, little is yet known concerning their bioactive forms in vivo and the mechanisms by which they may contribute toward disease prevention. Although many studies are focusing on the bioavailability of polyphenols through studying their uptake and the excretion of their conjugated forms, few are emphasizing the occurrence of metabolites in vivo formed via degradation by the enzymes of colonic bacteria and subsequent absorption. The purpose of this research was to investigate the relationship between biomarkers of the colonic biotransformation of ingested dietary polyphenols and the absorbed conjugated polyphenols. The results show that the majority of the in vivo forms derive from cleavage products of the action of colonic bacterial enzymes and subsequent metabolism in the liver. Those include the glucuronides of 3-hydroxyphenylacetic, homovanillic, vanillic and isoferulic acid as well as 3-(3-methoxy-4-hydroxyphenyl)-propionic, 3-(3-hydroxyphenyl)-propionic acid, and 3-hydroxyhippuric acid. In contrast, intact conjugated polyphenols themselves, such as the glucuronides of quercetin, naringenin and ferulic, p-coumaric, and sinapic acid were detected at much lower levels. The results suggest that consideration should be given to the cleavage products as having a putative role as physiologically relevant bioactive components in vivo.

Pharmacokinetics and bioavailability of a Ginkgo biloba extract

The aim of the present study was to assess the bioavailability of the main active ingredient in Ginkgo biloba extract, ginkgolid B. The study also focused on the pharmacokinetics of two different dosage regimens for orally administered Gingko biloba extract, 80 mg once daily and 40 mg twice daily for 7 days. Twelve healthy volunteers took part in the study. They were randomly assigned to one of the two treatment groups: 40 mg twice daily or 80 mg once daily, with an interval of 21 days between cycles. Statistical analysis was used to assess the main pharmacokinetic parameters. The results show that a dosage of 40 mg twice daily (every 12 hrs) is accompanied by a significantly longer half-life (t1/2) and mean residence time (MRT) than a single 80 mg dose, even though the latter causes a higher concentration peak (Cmax). The maximum concentration time (Tmax) is 2.3 hrs after administration in both treatments.

Pharmacokinetics and bioavailability of herbal medicinal products

The use of herbs for treating various ailments dates back several centuries. Usually, herbal medicine has relied on tradition that may or may not be supported by empirical data. The belief that natural medicines are much safer than synthetic drugs has gained popularity in recent years and led to tremendous growth of phytopharmaceutical usage. Market driven information on natural products is widespread and has further fostered their use in daily life. In most countries there is no universal regulatory system that insures the safety and activity of phytopharmaceuticals. Evidence-based verification of the efficacy of HMPs (herbal medicinal products, botanicals) is still frequently lacking. However, in recent years, data on evaluation of the therapeutic and toxic activity of herbal medicinal products became available. The advances in analytical technology have led to discovery of many new active constituents and an ever-increasing list of putatively active constituents. Establishing the pharmacological basis for efficacy of HMPs is a constant challenge. Of particular interest is the question of bioavailability to assess to what degree and how fast compounds are absorbed after administration of HMPs. Of further interest is the elucidation of metabolic pathways (yielding potentially new active compounds), and the assessment of elimination routes and their kinetics. These data become an important issue to link data from pharmacological assays and clinical effects. Of interest are currently also interactions of herbal medicinal products with synthetically derived drug products. A better understanding of the pharmacokinetics and bioavailability of phytopharmaceuticals can also help in designing rational dosage regimens. In this review, pharmacokinetic and bioavailability studies that have been conducted for some of the more important or widely used phytopharmaceuticals are critically evaluated. Furthermore, various drug interactions are discussed which show that caution should be exercised when combining phytopharmaceuticals with chemically derived active pharmaceutical ingredients.

Dietary flavonols: chemistry, food content, and metabolism

The flavonols belong to a large group of compounds called flavonoids, which are diverse in their chemical structure and characteristics. Fruits, vegetables, and beverages such as tea and red wine are major sources of flavonols in the human diet. The daily consumption of flavonols is difficult to estimate because values depend on accurate assessment of feeding habits and flavonol content in foods. Food sources, dietary intakes, and bioavailability of flavonols are strongly influenced by variations in plant type and growth, season, light, degree of ripeness, food preparation, and processing, all of which are discussed. In the past few years, a number of studies on the absorption and metabolism of flavonols in humans have been published and the findings from these studies are reviewed. We do not discuss the health effects of flavonols.

Novel biomarkers of the metabolism of caffeic acid derivatives in vivo

The purpose of this study was to investigate biomarkers of the bioavailability and metabolism of hydroxycinnamate derivatives through the determination of the pharmacokinetics of their urinary elimination and identification of the metabolites excreted. Coffee was used as a rich source of caffeic acid derivatives and human supplementation was undertaken. The results show a highly significant increase in the excretion of ferulic, isoferulic, dihydroferulic acid (3-(4-hydroxy-3-methoxyphenyl)-propionic acid), and vanillic acid postsupplementation relative to the levels presupplementation. Thus, ferulic, isoferulic, and dihydroferulic acids are specific biomarkers for the bioavailability and metabolism of dietary caffeic acid esters. Isoferulic acid is a unique biomarker as it is not a dietary component, however, dihydroferulic acid may well derive from other flavonoids with a structurally related B-ring. 3-Hydroxyhippuric acid has also been identified as an indicator for bioavailability and metabolism of phenolic compounds, and shows a highly significant excretion increase postsupplementation. The results reveal isoferulic acid (and possibly dihydroferulic acid) as novel markers of caffeoyl quinic acid metabolism.

Liquid chromatography of natural pigments

The newest results in the application of various liquid chromatographic techniques for the analysis of natural pigments in pure state and in complicated matrices are compiled. The methods employed for the separation and quantitative determination of the different pigment classes (flavonoids, coumarins, chlorophylls, etc.) are described and critically evaluated. The future trends are briefly discussed.

Flavonoids as antioxidants

Flavonoids are phenolic substances isolated from a wide range of vascular plants, with over 8000 individual compounds known. They act in plants as antioxidants, antimicrobials, photoreceptors, visual attractors, feeding repellants, and for light screening. Many studies have suggested that flavonoids exhibit biological activities, including antiallergenic, antiviral, antiinflammatory, and vasodilating actions. However, most interest has been devoted to the antioxidant activity of flavonoids, which is due to their ability to reduce free radical formation and to scavenge free radicals. The capacity of flavonoids to act as antioxidants in vitro has been the subject of several studies in the past years, and important structure-activity relationships of the antioxidant activity have been established. The antioxidant efficacy of flavonoids in vivo is less documented, presumably because of the limited knowledge on their uptake in humans. Most ingested flavonoids are extensively degraded to various phenolic acids, some of which still possess a radical-scavenging ability. Both the absorbed flavonoids and their metabolites may display an in vivo antioxidant activity, which is evidenced experimentally by the increase of the plasma antioxidant status, the sparing effect on vitamin E of erythrocyte membranes and low-density lipoproteins, and the preservation of erythrocyte membrane polyunsaturated fatty acids. This review presents the current knowledge on structural aspects and in vitro antioxidant capacity of most common flavonoids as well as in vivo antioxidant activity and effects on endogenous antioxidants.

Absorption of ferulic acid from low-alcohol beer

Flavonoids and monophenolic compounds have been well-described over recent years for their properties as antioxidants and scavengers of reactive oxygen and nitrogen species. A number of epidemiological studies implicate a role for flavonoids in reducing the risk of coronary heart disease. In particular, the focus has been on flavonol-rich fruit and vegetables and flavonoid-rich beverages, especially tea and red wine. Mechanisms of protection are unclear since the absorption, distribution, metabolism and elimination of dietary phenolics have not yet been extensively investigated. Here we report the bioavailability of ferulic acid, 4-hydroxy-3-methoxy-cinnamic acid, the major hydroxycinnamate in beer. Studies of the pharmacokinetics of urinary excretion of ferulic acid from low alcohol beer consumption in humans have been undertaken. The results show that ferulic acid is absorbed with a peak time for maximal excretion of ca. 8 h and the mean cumulative amount excreted is 5.8 +/- 3.2 mg. These findings are consistent with the uptake of ferulic acid from dietary sources, such as tomatoes, and suggest that ferulic acid is more bioavailable than individual dietary flavonoids and phenolics so far studied.

Determination of apigenin in rat plasma by high-performance liquid chromatography

Apigenin (4',5,7-trihydroxyflavone, AP) belongs to a less-toxic and non-mutagenic flavone subclass of flavonoids, the biotransformation and metabolism of which have been little studied until now. Therefore, this study is focussed on the determination of AP in free form. AP was administered to rats via the i.p. route (25 mg kg(-1)) and then the blood was collected at 10, 15, 30 and 45 min after injection. Methanol was used for rat plasma deproteinization. The HPLC assay (mobile phase, 2% formic acid-acetonitrile-methanol, 40:35:25, v/v; flow-rate, 1 ml min(-1); UV detection at 349 nm) for AP determination was validated and used for the quantification of AP in rat plasma. The unknown concentration was calculated from the equation obtained by the least-squares regression analysis (y = 0.521x + 1.130, r2 = 0.998). The highest concentration of AP in plasma was found to be 30 min after injection. The concentration profile of AP obtained here may contribute to until known results about AP metabolism. They could be applied to other studies of AP or related flavonoids because of favourable effects on human health.

Urinary metabolites of flavonoids and hydroxycinnamic acids in humans after application of a crude extract from Equisetum arvense

Flavonoids and hydroxycinnamic acids are polyphenolic compounds present in our daily diet in form of tea and vegetables as well as in herbal remedies used in phytomedicine. A wide range of in-vitro activities, in particular their antioxidant properties, have been studied intensively. However, in-vivo-data on absorption, bioavailability and metabolism after oral intake are scarce and contradictory. In order to examine the metabolism and renal excretion of these compounds a standardized extract from horsetail (Equisetum arvense) was administered to 11 volunteers following a flavonoid-free diet for 8 d. 24 h urine samples were collected and analyzed by HPLC-DAD. The putative quercetin metabolites, 3,4-dihydroxyphenylacetic acid or 3,4-dihydroxytoluene could not be detected in urine in any sample. The endogenous amount of homovanillic acid, generally regarded as one of the main quercetin metabolites, was 4 +/- 1 mg/d and did not increase significantly. However, hippuric acid, the glycine conjugate of benzoic acid, increased twofold after drug intake. Thus, the degradation to benzoic acid derivatives rather than phenylacetic acid derivatives seems to be a predominant route of metabolism. The results of this pilot study give rise to additional, substantial pharmacokinetic investigations in humans.

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

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

Liquid chromatography/electrospray ionization mass spectrometric characterization of flavonol glycosides in tomato extracts and human plasma

Flavonoids continue to attract wide attention as possible very useful agents for combating free radical pathologies, i.e. the pathological states associated with free radical overproduction. Commonly used methods for the analysis of plant flavonoids include high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). On the other hand, the soft-ionization approach based on electrospray ionization (ESI-MS) permits highly selective analysis of complex matrices. In this work, we examined firstly the ESI-MS behaviour of representative aglycones and glycosides of flavonols, flavones and isoflavones with the aim of suggesting a possible relationship between structure and mass spectra. Using HPLC coupled to a diode array detector (DAD) for on-line UV spectra acquisition, and in parallel to ESI-MS for mass spectra (LC/DAD-ESI-MS), we have developed methodology to observe flavonols directly in tomato puree extract. In this way, it has been possible to detect intact flavonol glycosides in tomato extracts and to characterize a flavonol trisaccharide. For the first time, using LC/ESI-MS, it has been possible to detect intact flavonol glycosides in plasma of healthy volunteers and to provide further evidence on the absorption of flavonoid glycosides after consumption of common vegetables like tomatoes.

Chromatographic separations of aromatic carboxylic acids

The purpose of this review is to present methods of chromatographic analysis of aromatic carboxylic acids. The separation, identification and quantitative analysis of aromatic carboxylic acids are necessary because of their importance as non-steroid antiphlogistic drugs, semi-products of biosynthesis of aromatic amino-acids in plants (phenolic acids), metabolites of numerous toxic substances, drugs and catecholamines. HPLC separation of ionic samples tends to be more complicated than separation of non-ionic compounds. The review describes the dependence of the retention of ionic solutes on pH and solvent composition as well as on the ionic strength of a mobile phase. The application of the ion-suppressing RP-HPLC method using organic modifiers (aqueous buffer solutions) as eluents in aromatic carboxylic acid analysis is also presented. In more difficult cases of analysis the addition of an ion-pairing reagent, such as the quaternary alkylammonium ion, is necessary to obtain satisfactory separations. Hypotheses of ion-pair formation in reversed-phase systems as well as the influence of various agents on the separation of ionic solutes in IP-RP systems are explained. Examples of the application of ion-pair liquid chromatography to the analysis of aromatic carboxylic acids have also been reviewed. The principles and application of ion-exchange chromatography to the purification, isolation and less frequently, to chromatographic analysis are discussed. Polar adsorbents and polar bonded stationary phases are also widely used in carboxylic acid separation in normal-phase systems, mainly by TLC, often coupled with densitometry. The review also shows examples of separation of chiral benzoic acids and their derivatives in LC systems. The possibilities of application of gas chromatography preceded by derivatisation or pyrolysis of acidic compounds and applications of GC-MS and Py-GC-MS coupled methods in identification and quantitation of aromatic carboxylic acids is also reviewed.

Luteolin-rich artichoke extract protects low density lipoprotein from oxidation in vitro

Flavonoids represent a diverse group of phytochemicals which possess the capacity to act as antioxidants in vitro. This study examined the free radical scavenging properties of a luteolin-rich artichoke extract and some of its pure flavonoid constituents by assessing their ability to prevent Cu2+-mediated LDL oxidation. Artichoke extract retarded LDL oxidation in a dose-dependent manner as measured by a prolongation of the lag phase to conjugated diene formation, a decrease in the rate of propagation and a sparing of endogenous LDL alpha-tocopherol during oxidation. The pure aglycone, luteolin (1 microM), demonstrated an efficacy similar to that of 20 microg/ml artichoke extract in inhibiting lipid peroxidation. Luteolin-7-O-glucoside, one of the glycosylated forms in the diet, also demonstrated a dose-dependent reduction of LDL oxidation that was less effective than that of luteolin. Studies of the copper-chelating properties of luteolin-7-O-glucoside and luteolin suggest a potential role for chelation in the antioxidative effects of artichoke extract. Overall, the results demonstrate that the antioxidant activity of the artichoke extract relates in part to its constituent flavonoids which act as hydrogen donors and metal ion chelators, and the effectiveness is further influenced by their partitioning between aqueous and lipophilic phases.

Urinary detection of hydroxycinnamates and flavonoids in humans after high dietary intake of fruit

The determination of the abilities of flavonoids, hydroxycinnamates and phenolics to scavenge free radicals in vitro suggests potent combined antioxidant activities of fruits, vegetables, beverages and grains. However, the key question of uptake in humans has only recently been approached consistently. The study described here demonstrates the uptake of hydroxycinnamates, for the first time, and other phenolic components, applying an HPLC method for their detection in the urine of subjects consuming levels of specific fruit equivalent to an approximate intake of 25 mg flavonol glycosides.

Catechin metabolites after intake of green tea infusions

Green tea contains relatively large amounts of catechins, that have been recognized to be efficient free-radical scavengers. In spite of a largely described antioxidant effect, the metabolic fate of catechins in humans has been scarcely studied. An infusion of green tea (about 400 mg of catechins) was given to healthy volunteers; plasma and urine samples were collected for 5 h and 2 days, respectively. Epigallocatechin gallate and epicatechin gallate were detected in plasma samples, reaching the maximum concentration (2 microM) at 2 h. Urine samples collected at 6-48 h contained detectable amounts of final catechin metabolites, including 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3-methoxy-4-hydroxy-hippuric acid and 3-methoxy-4-hydroxybenzoic acid (vanillic acid). The total content of these metabolites averaged 60 mg. The levels of free plasma catechins account only partly for the increased (approximately +20%) total radical-trapping antioxidant parameter (TRAP) detected after green tea intake. Catechin conjugates (glucuronide and sulphate) and metabolites may add further contribution and explain the measured TRAP increase.