Fecalase: a model for activation of dietary glycosides to mutagens by intestinal flora

Inter-individual variability in the metabolism of psychotropic drugs by the enzyme activities from the human gut microbiome

The interaction between marketed drugs and the gut microbiome is increasingly being recognized, and it is now known that enzymes produced by the bacteria in the human gut can degrade psychotropic drugs. However, the degree of inter-individual variation in their metabolism remains largely unknown. Here, we present a simple model for detecting individual drug-microbiome interaction using fecalase. We incubated fecalase prepared from freshly collected stool samples from healthy volunteers (n = 18) and incubated with nine selected psychotropic medications. We proved fecalase retained enzymatic activities and showed the degree of drug degradation differed significantly for different psychotropic drugs, and there was significant inter-individual variation in the metabolism of phenytoin, amitriptyline, and chlorpromazine with the inter-individual point difference between the strongest and weakest metabolizer of 85 %, 39 %, and 30 % respectively. These findings highlight the potential of fecalase as a model for studying personalized drug metabolism and underscore the importance of considering gut microbiome variability in pharmacological research.

Functional diversification of dietary plant small molecules by the gut microbiome

Plants are composed of diverse secondary metabolites (PSMs), which are widely associated with human health. Whether and how the gut microbiome mediates such impacts of PSMs is poorly understood. Here, we show that discrete dietary and medicinal phenolic glycosides, abundant health-associated PSMs, are utilized by distinct members of the human gut microbiome. Within the Bacteroides, the predominant gram-negative bacteria of the Western human gut, we reveal a specialized multi-enzyme system dedicated to the processing of distinct glycosides based on structural differences in phenolic moieties. This Bacteroides metabolic system liberates chemically distinct aglycones with diverse biological functions, such as colonization resistance against the gut pathogen Clostridioides difficile via anti-microbial activation of polydatin to the stilbene resveratrol and intestinal homeostasis via activation of salicin to the immunoregulatory aglycone saligenin. Together, our results demonstrate generation of biological diversity of phenolic aglycone "effector" functions by a distinct gut-microbiome-encoded PSM-processing system.

Exploring Drug Metabolism by the Gut Microbiota: Modes of Metabolism and Experimental Approaches

Increasing evidence uncovers the involvement of gut microbiota in the metabolism of numerous pharmaceutical drugs. The human gut microbiome harbors 10-100 trillion symbiotic gut microbial bacteria that use drugs as substrates for enzymatic processes to alter host metabolism. Thus, microbiota-mediated drug metabolism can change the conventional drug action course and cause inter-individual differences in efficacy and toxicity, making it vital for drug discovery and development. This review focuses on drug biotransformation pathways and discusses different models for evaluating the role of gut microbiota in drug metabolism. SIGNIFICANCE STATEMENT: This review emphasizes the importance of gut microbiota and different modes of drug metabolism mediated by them. It provides information on in vivo, in vitro, ex vivo, in silico and multi-omics approaches for identifying the role of gut microbiota in metabolism. Further, it highlights the significance of gut microbiota-mediated metabolism in the process of new drug discovery and development as a rationale for safe and efficacious drug therapy.

Guava (Psidium guajava L.): a glorious plant with cancer preventive and therapeutic potential

Guava (Psidium guajava L.) tree (Myrtaceae family) bears fruit rich in vitamins, fiber, and other nutrients. While native to Latin America, guava is grown in many tropical and subtropical regions across the globe where it has long been used in traditional medicine to treat a myriad of ailments. Guava has been shown to exhibit a number of biological and pharmacological activities, such as antioxidant, anti-inflammatory, immunomodulatory, antimicrobial, antidiabetic, and anticancer properties. Several parts of the plant, including the leaves, fruits, seeds, peels, pulp, bark, and oil, produce phytochemicals with medicinal properties. Emerging research has found that guava bioactive phytochemicals exert antitumorigenic effects against various human malignancies through multiple mechanisms. While there are numerous individual studies that document the anticancer effects of guava constituents, an up-to-date, comprehensive, and critical review of available research data has not been performed. Therefore, the purpose of this review is to present a complete analysis of the cancer preventive and anticancer therapeutic potential of guava-derived products and guava constituents, with a focus on the cellular and molecular mechanisms of action. The bioavailability, pharmacokinetics, and toxicity of guava as well as limitations, challenges, and future directions of research have also been discussed.

In vitro genotoxicity assessment of functional ingredients: DHA, rutin and α-tocopherol

The in vitro genotoxicity of three compounds widely used as functional ingredients, docosahexaenoic acid (DHA), rutin and α-tocopherol, was assessed. A miniaturized version of the Ames test in Salmonella typhimurium TA97a, TA98, TA100, TA102, and TA1535 strains (following the principles of OECD 471), and the in vitro micronucleus test in TK6 cells (OECD 487) were performed. This strategy is recommended by the European Food Safety Authority for the in vitro genotoxicity assessment of food and feed. In addition, this approach was complemented with the in vitro standard and enzyme-modified comet assay (S9-/S9+) using hOGG1, EndoIII and hAAG in order to assess potential premutagenic lesions in TK6 cells. Rutin showed an equivocal response in the in vitro micronucleus test and also was a potent Salmonella typhimurium revertant inductor in the Ames test. DHA showed equivocal results in the in vitro micronucleus test. In this regard, DHA and rutin seemed to interact with the DNA at a chromosomal level, but rutin is also capable of producing frameshift mutations. No genotoxicity was observed in cells treated with α-tocopherol. This article complements the evidence already available about the genotoxicity of these compounds. However, more studies are needed in order to elucidate the consequences of their use as functional ingredients in human health.

The gut microbiome influences the bioavailability of olanzapine in rats

Background

The role of the gut microbiome in the biotransformation of drugs has recently come under scrutiny. It remains unclear whether the gut microbiome directly influences the extent of drug absorbed after oral administration and thus potentially alters clinical pharmacokinetics.

Methods

In this study, we evaluated whether changes in the gut microbiota of male Sprague Dawley rats, as a result of either antibiotic or probiotic administration, influenced the oral bioavailability of two commonly prescribed antipsychotics, olanzapine and risperidone.

Findings

The bioavailability of olanzapine, was significantly increased (1.8-fold) in rats that had undergone antibiotic-induced depletion of gut microbiota, whereas the bioavailability of risperidone was unchanged. There was no direct effect of microbiota depletion on the expression of major CYP450 enzymes involved in the metabolism of either drug. However, the expression of UGT1A3 in the duodenum was significantly downregulated. The reduction in faecal enzymatic activity, observed during and after antibiotic administration, did not alter the ex vivo metabolism of olanzapine or risperidone. The relative abundance of Alistipes significantly correlated with the AUC of olanzapine but not risperidone.

Interpretation

Alistipes may play a role in the observed alterations in olanzapine pharmacokinetics. The gut microbiome might be an important variable determining the systemic bioavailability of orally administered olanzapine. Additional research exploring the potential implication of the gut microbiota on the clinical pharmacokinetics of olanzapine in humans is warranted.

Funding

This research is supported by APC Microbiome Ireland, a research centre funded by Science Foundation Ireland (SFI), through the Irish Government's National Development Plan (grant no. 12/RC/2273 P2) and by Nature Research-Yakult (The Global Grants for Gut Health; Ref No. 626891).

Impact of host and environmental factors on β-glucuronidase enzymatic activity: implications for gastrointestinal serotonin

The gastrointestinal tract houses a reservoir of bacterial-derived enzymes that can directly catalyze the metabolism of drugs, dietary elements and endogenous molecules. Both host and environmental factors may influence this enzymatic activity, with the potential to dictate the availability of the biologically-active form of endogenous molecules in the gut and influence inter-individual variation in drug metabolism. We aimed to investigate the influence of the microbiota, and the modulation of its composition, on fecal enzymatic activity. Intrinsic factors related to the host, including age, sex and genetic background, were also explored. Fecalase, a cell-free extract of feces, was prepared and used in a colorimetric-based assay to quantify enzymatic activity. To demonstrate the functional effects of fecal enzymatic activity, we examined β-glucuronidase-mediated cleavage of serotonin β-d-glucuronide (5-HT-GLU) and the resultant production of free 5-HT by HPLC. As expected, β-glucuronidase and β-glucosidase activity were absent in germ-free mice. Enzymatic activity was significantly influenced by mouse strain and animal species. Sex and age significantly altered metabolic activity with implications for free 5-HT. β-Glucuronidase and β-glucosidase activity remained at reduced levels for nearly two weeks after cessation of antibiotic administration. This effect on fecalase corresponded to significantly lower 5-HT levels as compared with incubation with pre-antibiotic fecalase from the same mice. Dietary targeting of the microbiota using prebiotics did not alter β-glucuronidase or β-glucosidase activity. Our data demonstrate that multiple factors influence the activity of bacterial-derived enzymes which may have potential clinical implications for drug metabolism and the deconjugation of host-produced glucuronides in the gut.NEW & NOTEWORTHY This article explores a comprehensive range of host and environmental factors that introduce variability in the expression of bacterial-derived metabolic enzymes. Our results demonstrate that altered β-glucuronidase activity has implications for the bioavailability of luminal serotonin. The experimental approach employed, fecalase, provides a mechanistic basis and translational platform to further delineate the functional outputs of altered metabolic activity, and the associated physiological effects of microbiota-targeted interventions on host response to drugs and host-produced glucuronides.

A personally guided tour on some of our data with the Ames assay-A tribute to Professor Bruce Ames

In contributing to this Special Issue of Mutation Research dedicated to Professor Bruce N. Ames in recognition of his 90^th birthday in December 2018, we intend to portray the importance not only of the Ames Salmonella/mammalian-microsome mutagenicity assay in some of our studies over the years, but also the importance of the insight that Bruce Ames brought to the field of genetic toxicology.

Gut Reactions: Breaking Down Xenobiotic-Microbiome Interactions

The microbiome plays a key role in health and disease, and there has been considerable interest in therapeutic targeting of the microbiome as well as mining this rich resource in drug discovery efforts. However, a growing body of evidence suggests that the gut microbiota can itself influence the actions of a range of xenobiotics, in both beneficial and potentially harmful ways. Traditionally, clinical studies evaluating the pharmacokinetics of new drugs have mostly ignored the important direct and indirect effects of the gut microbiome on drug metabolism and efficacy. Despite some important observations from xenobiotic metabolism in general, there is only an incomplete understanding of the scope of influence of the microbiome specifically on drug metabolism and absorption, and how this might influence systemic concentrations of parent compounds and toxic metabolites. The significance of both microbial metabolism of xenobiotics and the impact of the gut microbiome on host hepatic enzyme systems is nonetheless gaining traction and presents a further challenge in drug discovery efforts, with implications for improving treatment outcomes or counteracting adverse drug reactions. Microbial factors must now be considered when determining drug pharmacokinetics and the impact that an evolving and dynamic microbiome could have in this regard. In this review, we aim to integrate the contribution of the gut microbiome in health and disease to xenobiotic metabolism focusing on therapeutic interventions, pharmacological drug action, and chemical biotransformations that collectively will have implications for the future practice of precision medicine.

How to Determine the Role of the Microbiome in Drug Disposition

With a paradigm shift occurring in health care toward personalized and precision medicine, understanding the numerous environmental factors that impact drug disposition is of paramount importance. The highly diverse and variant nature of the human microbiome is now recognized as a factor driving interindividual variation in therapeutic outcomes. The purpose of this review is to provide a practical guide on methodology that can be applied to study the effects of microbes on the absorption, distribution, metabolism, and excretion of drugs. We also highlight recent examples of how these methods have been successfully applied to help build the basis for researching the intersection of the microbiome and pharmacology. Although in vitro and in vivo preclinical models are highlighted, these methods are also relevant in late-phase drug development or even as a part of routine after-market surveillance. These approaches will aid in filling major knowledge gaps for both current and upcoming therapeutics with the long-term goal of achieving a new type of knowledge-based medicine that integrates data on the host and the microbiome.

Gut microbiota-mediated pharmacokinetics of ginseng saponins

Orally administered ginsengs come in contact with the gut microbiota, and their hydrophilic constituents, such as ginsenosides, are metabolized to hydrophobic compounds by gastric juice and gut microbiota: protopanxadiol-type ginsenosides are mainly transformed into compound K and ginsenoside Rh2; protopanaxatriol-type ginsenosides to ginsenoside Rh1 and protopanaxatriol, and ocotillol-type ginsenosides to ocotillol. Although this metabolizing activity varies between individuals, the metabolism of ginsenosides to compound K by gut microbiota in individuals treated with ginseng is proportional to the area under the blood concentration curve for compound K in their blood samples. These metabolites such as compound K exhibit potent pharmacological effects, such as antitumor, anti-inflammatory, antidiabetic, antiallergic, and neuroprotective effects compared with the parent ginsenosides, such as Rb1, Rb2, and Re. Therefore, to monitor the potent pharmacological effects of ginseng, a novel probiotic fermentation technology has been developed to produce absorbable and bioactive metabolites. Based on these findings, it is concluded that gut microbiota play an important role in the pharmacological action of orally administered ginseng, and probiotics that can replace gut microbiota can be used in the development of beneficial and bioactive ginsengs.

Antiatherogenic Roles of Dietary Flavonoids Chrysin, Quercetin, and Luteolin

Cardiovascular diseases (CVDs) are the commonest cause of global mortality and morbidity. Atherosclerosis, the fundamental pathological manifestation of CVDs, is a complex process and is poorly managed both in terms of preventive and therapeutic intervention. Aberrant lipid metabolism and chronic inflammation play critical roles in the development of atherosclerosis. These processes can be targeted for effective management of the disease. Although managing lipid metabolism is in the forefront of current therapeutic approaches, controlling inflammation may also prove to be crucial for an efficient treatment regimen of the disease. Flavonoids, the plant-derived polyphenols, are known for their antiinflammatory properties. This review discusses the possible antiatherogenic role of 3 flavonoids, namely, chrysin, quercetin, and luteolin primarily known for their antiinflammatory properties.

Application of Bioactive Quercetin in Oncotherapy: From Nutrition to Nanomedicine

Phytochemicals as dietary constituents are being explored for their cancer preventive properties. Quercetin is a major constituent of various dietary products and recently its anti-cancer potential has been extensively explored, revealing its anti-proliferative effect on different cancer cell lines, both in vitro and in vivo. Quercetin is known to have modulatory effects on cell apoptosis, migration and growth via various signaling pathways. Though, quercetin possesses great medicinal value, its applications as a therapeutic drug are limited. Problems like low oral bioavailability and poor aqueous solubility make quercetin an unreliable candidate for therapeutic purposes. Additionally, the rapid gastrointestinal digestion of quercetin is also a major barrier for its clinical translation. Hence, to overcome these disadvantages quercetin-based nanoformulations are being considered in recent times. Nanoformulations of quercetin have shown promising results in its uptake by the epithelial system as well as enhanced delivery to the target site. Herein we have tried to summarize various methods utilized for nanofabrication of quercetin formulations and for stable and sustained delivery of quercetin. We have also highlighted the various desirable measures for its use as a promising onco-therapeutic agent.

Quercetin: A flavonol with multifaceted therapeutic applications?

Great interest is currently centered on the biologic activities of quercetin a polyphenol belonging to the class of flavonoids, natural products well known for their beneficial effects on health, long before their biochemical characterization. In particular, quercetin is categorized as a flavonol, one of the five subclasses of flavonoid compounds. Although flavonoids occur as either glycosides (with attached glycosyl groups) or as aglycones, most altogether of the dietary intake concerning quercetin is in the glycoside form. Following chewing, digestion, and absorption sugar moieties can be released from quercetin glycosides. Several organs contribute to quercetin metabolism, including the small intestine, the kidneys, the large intestine, and the liver, giving rise to glucuronidated, methylated, and sulfated forms of quercetin; moreover, free quercetin (such as aglycone) is also found in plasma. Quercetin is now largely utilized as a nutritional supplement and as a phytochemical remedy for a variety of diseases like diabetes/obesity and circulatory dysfunction, including inflammation as well as mood disorders. Owing to its basic chemical structure themost obvious feature of quercetin is its strong antioxidant activity which potentially enables it to quench free radicals from forming resonance-stabilized phenoxyl radicals. In this review the molecular, cellular, and functional bases of therapy will be emphasized taking strictly into account data appearing in the peer-reviewed literature and summarizing the main therapeutic applications of quercetin; furthermore, the drug metabolism and the main drug interaction as well as the potential toxicity will be also spotlighted.

Effects of Watercress Containing Rutin and Rutin Alone on the Proliferation and Osteogenic Differentiation of Human Osteoblast-like MG-63 Cells

Most known osteoporosis medicines are effective for bone resorption, and so there is an increasing demand for medicines that stimulate bone formation. Watercress (N. officinale R. Br.) is widely used as a salad green and herbal remedy. This study analyzed a watercress extract using ultra-performance liquid chromatography/mass spectrometry, and identified a rutin as one of its major constituents. Osteogenic-related assays were used to compare the effects of watercress containing rutin (WCR) and rutin alone on the proliferation and differentiation of human osteoblast-like MG-63 cells. The reported data are expressed as percentages relative to the control value (medium alone; assigned as 100%). WCR increased cell proliferation to 125.0±4.0% (mean±SD), as assessed using a cell viability assay, and increased the activity of alkaline phosphatase, an early differentiation marker, to 222.3±33.8%. In addition, WCR increased the expression of collagen type I, another early differentiation marker, to 149.2±2.8%, and increased the degree of mineralization, a marker of the late process of differentiation, to 122.9±3.9%. Rutin alone also increased the activity of ALP (to 154.4±12.2%), the expression of collagen type I (to 126.6±6.2%), and the degree of mineralization (to 112.3±5.0%). Daidzein, which is reported to stimulate bone formation, was used as a positive control; the effects of WCR on proliferation and differentiation were significantly greater than those of daidzein. These results indicate that WCR and rutin can both induce bone formation via the differentiation of MG-63 cells. This is the first study demonstrating the effectiveness of either WCR or rutin as an osteoblast stimulant.

Role of intestinal microflora in xenobiotic-induced toxicity

In addition to its role in digestion of food in the gastrointestinal tract, the intestinal microflora is also capable of biotransforming numerous drugs. Likewise, the intestinal microflora may significantly modulate xenobiotic-induced toxicity by either activating or inactivating xenobiotics via metabolism. To date, most investigations of xenobiotic metabolism have focused not only on metabolism in host tissues, but the modulation of the pharmacological activity of drugs by the intestinal microflora. Despite its importance, the presumed role of intestinal microflora metabolism in xenobiotic-induced toxicity has been understudied. Therefore, it is appropriate to briefly review our current situation, and state which research in xenobiotic metabolism by intestinal microflora, particularly in the field of toxicology, is needed.

Pharmacology in health food: metabolism of quercetin in vivo and its protective effect against arteriosclerosis

Quercetin, a member of the bioflavonoids family, has been proposed to have anti-atherogenic, anti-inflammatory, and anti-hypertensive properties leading to the beneficial effects against cardiovascular diseases. It was recently demonstrated that quercetin 3-O-β-D-glucuronide (Q3GA) is one of the major quercetin conjugates in human plasma, in which the aglycone could not be detected. Although most of the in vitro pharmacological studies have been carried out using only the quercetin aglycone form, experiments using Q3GA would be important to discover the preventive mechanisms of cardiovascular diseases by quercetin in vivo. Therefore we examined the effects of the chemically synthesized Q3GA, as an in vivo form, on vascular smooth muscle cell (VSMC) disorders related to the progression of arteriosclerosis. Platelet-derived growth factor-induced cell migration and proliferation were inhibited by Q3GA in VSMCs. Q3GA attenuated angiotensin II-induced VSMC hypertrophy via its inhibitory effect on JNK and the AP-1 signaling pathway. Q3GA scavenged 1,1-diphenyl-2-picrylhydrazyl radical measured by the electron paramagnetic resonance method. In addition, immunohistochemical studies with monoclonal antibody 14A2 targeting the Q3GA demonstrated that the positive staining specifically accumulates in human atherosclerotic lesions, but not in the normal aorta. These findings suggest Q3GA would be an active metabolite of quercetin in plasma and may have preventative effects on arteriosclerosis relevant to VSMC disorders.

Dietary influences on mutagenesis--where is this field going?

Early studies on dietary mutagenesis were mostly observational, with large numbers of potential dietary mutagens being identified from every conceivable dietary source. These included known dietary carcinogens such as aflatoxin B1 and benzo[a]pyrene, and hitherto unrecognized dietary mutagens, such as the pyrolysis products formed during the heating of proteinaceous materials (heterocyclic amines). The 1993 evaluation of 2-amino-3-methyl-3H-imidazo(4,5-j)quinoline as a probable human carcinogen by the International Agency for Research on Cancer was a landmark, as this was done in the absence of specific human carcinogenicity data, and strongly influenced by mutagenicity test data. In the 21st century, the field has moved from the identification of more and more mutagens, to molecular epidemiologic approaches that not only show a mutagenic effect but also seek to link it to a dietary (or environmental) cause. Effects of diet in stimulating chronic inflammation may lead to reactive species and thereby mutation as a secondary consequence, while dietary deficiencies and nutrient imbalances may be strong sources of mutagenesis. Recognition of the roles of nutrients in cell signaling processes and control of microRNAs suggest major influences on gene expression, in the absence of permanent DNA changes. Genome-wide association studies have highlighted new pathways such as JAK/STAT signaling that profoundly influence genomic instability and responses to dietary mutagens. With improved methodologies for DNA sequencing and epigenetic changes, it is time to apply more sophisticated approaches to recognizing and proving the role of diet as a primary modulator of mutagenesis in humans.

Ulmosides A and B: flavonoid 6-C-glycosides from Ulmus wallichiana, stimulating osteoblast differentiation assessed by alkaline phosphatase

Chemical investigation of Ulmus wallichiana stem bark resulted in isolation and identification of three new compounds (2S,3S)-(+)-3',4',5,7-tetrahydroxydihydroflavonol-6-C-beta-D-glucopyranoside (1), (2S,3S)-(+)-4',5,7-trihydroxydihydroflavonol-6-C-beta-D-glucopyranoside (3) and 3-C-beta-D-glucopyranoside-2,4,6-trihydroxymethylbenzoate (8), together with five known flavonoid-6-C-glucosides (2, 4-7). Their structures were elucidated using 1D and 2D NMR spectroscopic analysis. The absolute stereochemistry in compounds 1 and 3 were established with the help of CD data analysis and comparison with the literature data analysis. All the isolated compounds (1-8) were assessed for promoting the osteoblast differentiation using primary culture of rat osteoblast as an in vitro system. Compounds 1-3 and 5 significantly increased osteoblast differentiation as assessed by alkaline phosphatase activity.

Microbial hydrolysis of steviol glycosides

A review of the role of gut microbiota in the metabolism of the steviol glycosides, stevioside and rebaudioside A, indicates that they are not absorbed intact but undergo hydrolysis by the intestinal microflora to steviol. Steviol is not metabolized by the intestinal flora and is absorbed from the intestine. The rate of hydrolysis for stevioside is greater than for rebaudioside A. Recent studies using mass spectrometry have shown that steviol-16,17-epoxide is not a microbial metabolite of steviol glycosides. Bacteroides species are primarily responsible for hydrolysis via their beta-glucosidase activity. Fecal incubation studies with both human and animal mixed flora provide similar results, and this indicates that the rat is an appropriate model for studies on steviol glycosides. Given the similarity in the microbial metabolism of stevioside and rebaudioside A with the formation of steviol as the single hydrolysis product that is absorbed from the intestinal tract, the toxicological data on stevioside are relevant to the risk assessment of rebaudioside A.

Sequential glucosylation of a furofuran lignan, (+)-sesaminol, by Sesamum indicum UGT71A9 and UGT94D1 glucosyltransferases

(+)-Sesaminol 2-O-triglucoside is the most abundant water-soluble furofuran lignan in sesame seeds (Sesamum indicum) and is considered to be a beneficial compound for human health. The biosyntheses and physiological roles of lignan glycosides, however, remain elusive. Here we report the molecular identification and biochemical characterization of two Sesamum uridine diphosphate (UDP) glucose:lignan glucosyltransferases. Sesamum indicum UGT71A9 preferentially glucosylated at the 2-hydroxyl group of (+)-sesaminol, resulting in (+)-sesaminol 2-O-glucoside. Similarly, two UGT71A9 homologs from Sesamum radiatum (UGT71A10) and Sesamum alatum (UGT71A8) also showed (+)-sesaminol glucosylating activity, evidencing the functional conservation of (+)-sesaminol 2-O-glucosyltransferases in the Sesamum genus. In addition, S. indicum UGT94D1 specifically glucosylated at the 6'-hydroxyl group of the sugar moiety of (+)-sesaminol 2-O-glucoside but not at that of flavonoid glucosides. The gene expression patterns of UGT71A9 and UGT94D1 during seed development were correlated with the glucosylating activities toward (+)-sesaminol in planta, suggesting that the two lignan UDP-glycosyltransferases participate in the sequential glucosylation steps in the biosynthesis of (+)-sesaminol 2-O-triglucoside.

Mutagenicity of arbutin in mammalian cells after activation by human intestinal bacteria

Arbutin (hydroquinone-beta-D-glucopyranoside) is present in various food plants. Its aglycone, hydroquinone, is mutagenic and carcinogenic. We investigated whether hydroquinone may be released under conditions encountered in the human gastrointestinal tract. Arbutin was stable in artificial gastric juice. Fecal slurries from nine human subjects completely converted arbutin (2 mM) into hydroquinone. Four of nine representative human intestinal species investigated, namely Eubacterium ramulus, Enterococcus casseliflavus, Bacteroides distasonis, and Bifidobacterium adolescentis, deglycosylated arbutin at rates of 21.08, 16.62, 8.43 and 3.59 nmol x min(-1) x (mg protein)(-1), respectively. In contrast, homogenates from small intestinal mucosa and cytosolic fractions from colon mucosa deglycosylated arbutin at substantially lower rates: 0.50 and 0.09 nmol x min(-1) x (mg protein)(-1), respectively. Arbutin, unlike hydroquinone, did not induce gene mutations in Chinese hamster V79 cells in the absence of an activating system. However, in the presence of cytosolic fractions from E. ramulus or B. distasonis, arbutin was strongly mutagenic. Cytosolic fraction from Escherichia coli, showing no arbutin glycosidase activity, was not able to activate arbutin in this model system. The release of the proximate mutagen hydroquinone from arbutin by intestinal bacteria in the immediate vicinity of the colon mucosa may pose a potential risk.

Quercetin, a flavonoid, inhibits proliferation and increases osteogenic differentiation in human adipose stromal cells

Flavonoids, which have been detected in a variety of foods, have been repeatedly reported to affect bone metabolism. However, the effects of flavonoids on osteoblastogenesis remain a matter of some controversy. In this study, the effects of quercetin on the differentiation and proliferation of human adipose tissue-derived stromal cells (hADSC) were determined. Quercetin was found to increase osteogenic differentiation in a dose-dependent manner. Other flavonoids, chrysin and kaempferol, were also shown to increase the osteogenic differentiation of hADSC, but this stimulatory effect was weaker than that associated with quercetin. Quercetin pretreatment administered prior to the induction of differentiation also exerted stimulatory effects on the osteogenic differentiation of hADSC. RT-PCR and real time PCR analysis showed that quercetin treatment induced an increase in the expression of osteopontin, BMP2, alkaline phosphatase and Runx2. Quercetin inhibited the proliferation of hADSC, but did not affect their survival. The pretreatment of quercetin increased ERK phosphorylation during osteogenic differentiation, although it did not increase ERK activity in control culture condition. ICI182780, an specific estrogen receptor antagonist, failed to inhibit the effects of quercetin on osteogenic differentiation. Quercetin-pretreated hADSC showed better bone regenerating ability in skull defect model of nude mice than naive cells. Our findings indicate that quercetin enhances osteogenic differentiation via an independent mechanism from estrogen receptor (ER) activation, and prove useful for in vivo bone engineering, using human mesencymal stem cells (hMSC).

An onion variety has natural antithrombotic effect as assessed by thrombosis/thrombolysis models in rodents

INTRODUCTION

Prevention of arterial thrombotic diseases has a high priority in developed countries. As inappropriate diet has been shown to be an important risk factor for thrombotic events, regular antithrombotic diet may offer a convenient and effective way of prevention. The aim of the present study was to test onion extracts for antithrombotic effect and to identify the effective varieties in Allium cepa.

MATERIALS AND METHODS

A shear-induced platelet function test (haemostatometry) was used to screen for antithrombotic potential. Onion extracts showing significant antithrombotic activity in vitro were further assessed in vivo by using a laser-induced thrombosis test in mice.

RESULTS AND CONCLUSIONS

An onion variety, Toyohira, showed significant antithrombotic activity both in vitro and in vivo. Toyohira showed thrombolytic activity in addition to the antiplatelet effect. Superkitamomiji, 2935A, and K83211 showed only thrombolytic activity. Quercetin, the richest flavonoid in onion, was measured, but no correlation was found between quercetin content and antithrombotic activity. It is concluded that onion A. cepa can be classified into varieties with or without antithrombotic and thrombolytic effects. This should be taken into account in future population studies on the antithrombotic effects of vegetables.

Quercetin suppresses bone resorption by inhibiting the differentiation and activation of osteoclasts

Although quercetin has suppressed bone resorption in several animal studies, its target cells and the mechanism of its action related to bone resorption has not been fully elucidated. We investigated the effect of quercetin on the differentiation and activation of osteoclasts. We used cocultures of mouse spleen cells and ST2 cells, and cultures of osteoclast progenitor cells [M-CSF-dependent (MD) cells from mouse bone marrow and murine monocytic RAW 264 (RAW) cells]. Quercetin dose-dependently inhibited osteoclast-like (OCL) cell formation at 2-5 microM concentration in both the coculture and MD cell culture. Quercetin inhibited the increase of tartrate-resistant acid phosphatase (TRAP) activity of mononuclear preosteoclasts (pOCs) induced by receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL) in both MD and RAW cell cultures. Quercetin reversely induced the disruption of actin rings in OCLs. Quercetin also suppressed both pit formation induced by osteoclasts on dentine slices and PTH-stimulated (45)Ca release in mouse long bone cultures. These results suggest that osteoclast progenitors as well as mature osteoclasts, are quercetin's target cells in relation to bone resorption, and that quercetin's suppressive effect on bone resorption results from both its inhibitory effect on the differentiation of osteoclast progenitor cells into pOCs and from its disruptive effect on actin rings in mature osteoclasts.

Quercetin, a flavonoid, inhibits the proliferation, differentiation, and mineralization of osteoblasts in vitro

It is possible that the flavonoids that are found in many foods might have a protective effect against osteoclastic activity. However, little information is available about the effects of flavonoids on osteoblastogenesis. Therefore, we investigated the effects of quercetin, a flavonoid, on the metabolism of rat calvarial osteoblast-like cells (ROB cells) in culture. The proliferation of cells was markedly inhibited upon exposure of cells to quercetin at 5 x 10(-6) to 1 x 10(-5) M. Quercetin at 1 x 10(-5) M did not induce apoptosis in ROB cells but arrested cells at the G1 phase of the cell cycle. In addition, quercetin stimulated the expression of mRNA for p21(waf1/cip1), which inhibits the activity of cyclin-dependent kinases, and inhibited the phosphorylation of histone H1. Furthermore, after cells had ceased to proliferate, quercetin reduced the activity of alkaline phosphatase, the level of expression of mRNA for osteocalcin, the rate of deposition of Ca(2+), and the formation of mineralized nodules, all of which are markers of osteoblast differentiation. These findings indicate that quercetin inhibits the proliferation, differentiation, and mineralization of osteoblastic cells.

Identification of quercetin 3-O-beta-D-glucuronide as an antioxidative metabolite in rat plasma after oral administration of quercetin

The potential beneficial effect of dietary quercetin (3,3',4',5,7-pentahydroxyflavone) has attracted much attention in relation to the prevention of cardiovascular disease. It is generally recognized that dietary quercetin is subject to metabolic conversion resulting in conjugated forms during absorption and circulation. However, no quercetin conjugates have yet been identified from biological fluids or tissues. In the present study, we isolated and characterized two quercetin conjugates from the plasma of quercetin-administered rats. The blood plasma was collected from 26 rats 30 min after oral administration of quercetin (250 mg/kg body weight), concentrated, dissolved in 2% acetic acid aqueous solution (pH 2.65), and extracted with ethyl acetate. Two compounds (P2, P3) were obtained from the extract by repeated reversed-phase HPLC. On the other hand, two quercetin glucuronides were synthesized chemically and identified as quercetin 3-O-beta-D-glucuronide (Q3GA) and quercetin 4'-O-beta-D-glucuronide (Q4'GA), as determined from FABMS, 1H- and 13C-NMR, and HMBC data. The retention times of P2 and P3 in the HPLC chromatogram corresponded to those of Q3GA and Q4'GA, respectively. FABMS data demonstrated that P2 and P3 are quercetin monoglucuronides. 1H-NMR data for P2 were completely in agreement with those for Q3GA. P2 was therefore identified as Q3GA. This is, to our knowledge, the first evidence that Q3GA accumulates in vivo after oral administration of quercetin. Q3GA is likely to act as an effective antioxidant in blood plasma low-density lipoprotein, because this conjugated metabolite was found to possess a substantial antioxidant effect on copper ion-induced oxidation of human plasma low-density lipoprotein as well as 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activity.

Accumulation of quercetin conjugates in blood plasma after the short-term ingestion of onion by women

Quercetin is a typical flavonoid present mostly as glycosides in plant foods; it has attracted much attention for its potential beneficial effects in disease prevention. In this study, we examined human volunteers after the short-term ingestion of onion, a vegetable rich in quercetin glucosides. The subjects were served diets containing onion slices (quercetin equivalent: 67.6-93.6 mg/day) with meals for 1 wk. Quercetin was only found in glucuronidase-sulfatase-treated plasma, and its concentration after 10 h of fasting increased from 0.04 +/- 0.04 microM before the trial to 0.63 +/- 0.72 microM after the 1-wk trial. The quercetin content in low-density lipoprotein (LDL) after glucuronidase-sulfatase treatment corresponded to <1% of the alpha-tocopherol content. Human LDL isolated from the plasma after the trial showed little improvement of its resistance to copper ion-induced oxidation. It is therefore concluded that conjugated metabolites of quercetin accumulate exclusively in human blood plasma in the concentration range of 10(-7) approximately 10(-6) M after the short-term ingestion of vegetables rich in quercetin glucosides, although these metabolites are hardly incorporated into plasma LDL.

Inhibition of mammalian 15-lipoxygenase-dependent lipid peroxidation in low-density lipoprotein by quercetin and quercetin monoglucosides

Lipoxygenase is suggested to be involved in the early event of atherosclerosis by inducing plasma low-density lipoprotein (LDL) oxidation in the subendothelial space of the arterial wall. Since flavonoids such as quercetin are recognized as lipoxygenase inhibitors and they occur mainly in the glycoside form, we assessed the effect of quercetin and its glycosides (quercetin 3-O-beta-glucopyranoside, Q3G; quercetin 4'-O-beta-glucopyranoside, Q4'G; quercetin 7-O-beta-glucopyranoside, Q7G) on rabbit reticulocyte 15-lipoxygenase (15-LOX)-induced human LDL lipid peroxidation and compared it with the inhibition obtained by ascorbic acid and alpha-tocopherol, the main water-soluble and lipid-soluble antioxidants in blood plasma, respectively. Quercetin inhibited the formation of cholesteryl ester hydroperoxides (CE-OOH) and endogenous alpha-tocopherol consumption effectively throughout the incubation period of 6 h. Ascorbic acid exhibited an effective inhibition only in the initial stage and LDL preloaded with fivefold alpha-tocopherol did not affect the formation of CE-OOH compared with the native LDL. CE-OOH formation was inhibited by both quercetin and quercetin monoglucosides in a concentration-dependent manner. Quercetin, Q3G, and Q7G exhibited a higher inhibitory effect than Q4'G (IC50: 0.3-0.5 microM for quercetin, Q3G, and Q7G and 1.2 microM for Q4'G). While endogenous alpha-tocopherol was completely depleted after 2 h of LDL oxidation, quercetin, Q7G, and Q3G prevented the consumption of alpha-tocopherol. Quercetin and its monoglucosides were also exhausted during the LDL oxidation. These results indicate that quercetin glycosides as well as its aglycone are capable of inhibiting lipoxygenase-induced LDL oxidation more efficiently than ascorbic acid and alpha-tocopherol.

The effect of dietary flavonoids on DNA damage (strand breaks and oxidised pyrimdines) and growth in human cells

The effects of the flavonoids quercetin, myricetin and silymarin on DNA damage and cytotoxicity in human cells were investigated. DNA strand breaks and oxidised pyrimidines were determined using alkaline single cell gel electrophoresis (the comet assay). Inhibition of cell growth was also measured. Caco-2 (colon), HepG2 (liver), HeLa (epithelial) cells and normal human lymphocytes showed different, dose-dependent susceptibilities (in terms of strand breakage) to the various flavonoids, quercetin being the most damaging. This agreed well with the ability of the flavonoids to inhibit cell growth. None of the flavonoids induced DNA base oxidation above background levels. All of the flavonoids under investigation caused depletion of reduced glutathione, which, in the case of quercetin, occurred prior to cell death. Neither cytotoxicity nor genotoxicity was associated with the antioxidant enzyme capacity (glutathione, glutathione reductase, glutathione peroxidase and catalase) of the cells.

A partially purified beta-glucosidase from Bifidobacterium adolescentis converts cycasin to a mutagenic compound

beta-Glucosidase was extracted from sonicated Bifidobacterium adolescentis Int-57 and partially purified by Sepharose CL-6B gel-filtration and DEAE-cellulose ion-exchange chromatography. The partially purified enzyme was confirmed to convert cycasin to a mutagen in the Ames and SOS chromotests. beta-Glucosidase negative strains were unable to activate cycasin mutagenically.

Anticarcinogenic, hypocholesterolemic, and antagonistic activities of Lactobacillus acidophilus

Lactobacillus acidophilus is considered to possess health-promoting attributes. These include anticarcinogenic and hypocholesterolemic properties and antagonistic action against intestinal and food-born pathogens. L. acidophilus can also survive the hostile environment and establish in the complex ecosystem of the gastrointestinal tract. Therefore, the beneficial effects of ingesting L. acidophilus accrue over a longer period than those organisms that cannot colonize the gut. However, the exact mechanisms of these attributes are not known. Presumably, the anticarcinogenic activity may be attributed to production of compounds and/or conditions that inhibit the proliferation of tumor cells, suppression of microorganisms that convert procarcinogens to carcinogens, and degradation of carcinogens formed. They hypocholesterolemic effect is probably exerted by inhibition of 3-hydroxy-3-methylglutaryl CoA reductase, which is a rate-limiting enzyme in endogenous cholesterol biosynthesis in the body and by promoting the excretion of dietary cholesterol in feces as a result of coprecipitation in the presence of deconjugated bile acids in the intestine and/or adsorption by the organisms. The antagonistic effect against pathogens and other organisms is possibly mediated by competition for nutrients and adhesion sites, formation of metabolites such as organic acids, hydrogen peroxide, and production of antibiotic-like compounds and bacteriocins.

Sesaminol glucosides in sesame seeds

The structures of novel sesaminol glucosides isolated from sesame seed were determined to be sesaminol 2'-O-beta-D-glucopyranoside, sesaminol 2'-O-beta-D-glucopyranosyl (1-->2)-O-beta-D-glucopyranoside and sesaminol 2'-O- beta-D-glucopyranosyl (1-->2)-O-[beta-D-glucopyransyl (1-->6)] -beta-D-glucopyranoside.

Pharmacokinetic studies of diosmin and diosmetin in perfused rat liver

1. The kinetics and metabolism of diosmin and diosmetin were investigated in the isolated perfused rat liver in order to assess the role of the liver. 2. Diosmetin and especially diosmin disappeared quickly from the perfusion medium. 3. Both flavonoids were rapidly metabolized and diosmetin was partly excreted in bile as the glucuronide and sulphate and diosmin was partly excreted in bile as such and as the glucuronide conjugate. 4. Diosmin and diosmetin did not appear to affect various parameters of liver function.

Inhibition of HIV-1 infectivity by zinc-ejecting aromatic C-nitroso compounds

Retroviral nucleocapsid and gag-precursor proteins from all known strains of retroviruses contain one or two copies of an invariant sequence, Cys-X2-Cys-X4-His-X4-Cys, that is populated with zinc in mature particles. Modification of cysteine or histidine residues results in defective packaging of genomic viral RNA and formation of non-infectious particles, making these structures potentially attractive targets for antiviral therapy. We recently reported that aromatic C-nitroso ligands of poly(ADP-ribose) polymerase preferentially destabilize one of the two (Cys-X2-Cys-X28-His-X2-Cys) zinc-fingers with concomitant loss of enzymatic activity, coincidental with selective cytocidal action of the C-nitroso substituted ligands on cancer cells. Based on the occurrence of (3Cys, 1His) zinc-binding sites in both retroviral nucleocapsid and gag proteins and in poly(ADP-ribose) polymerase, we reasoned that the C-nitroso compounds may also have antiretroviral effects. We show here that two such compounds, 3-nitrosobenzamide and 6-nitroso-1,2-benzopyrone, inhibit infection of human immunodeficiency virus HIV-1 in human lymphocytes and also eject zinc from isoalted HIV-1 nucleocapsid zinc fingers and from intact HIV-1 virions. Thus the design of zinc-ejecting agents that target retroviral zinc fingers represents a new approach to the chemotherapy of AIDS.

Mutagenicity of crude senna and senna glycosides in Salmonella typhimurium

The mutagenicity of senna glycosides and extracts of senna folium and senna fructus was investigated in the Salmonella typhimurium reversion assay. Senna glycosides were inactive in all strains, except for a slight, but significant increase in mutant frequency in TA102 in the absence and presence of liver microsomes. Extracts of senna fructus and senna folium demonstrated weak activity in TA97a, TA100 and TA102 in the presence of liver microsomes, and in TA97a and TA102 in the absence of liver microsomes. A strong increase in mutant frequency (3- to 5-fold above background frequency) was observed with all extracts in TA98 in the presence of liver microsomes. This activity increased further following enzymatic hydrolysis with hesperidinase of extracts of senna fructus from one source, and could be correlated to the release of the flavonol aglycones kaempferol and quercetin. The weak or lacking activity of anthraquinone aglycones in the tested strains of Salmonella typhimurium indicates that mutagenicity can not be attributed solely to the anthraquinone content of these plant materials. The chemical nature of other mutagenic components has not been elucidated.

Colon-specific delivery of dexamethasone from a glucoside prodrug in the guinea pig

Dexamethasone-beta-D-glucoside is a potential prodrug for colonic delivery of the antiinflammatory agent, dexamethasone. The ability of this prodrug to deliver dexamethasone selectively to the colon depends not only on its being slowly absorbed from the alimentary canal, but also on its having chemical and enzymatic stability in the stomach and small intestine. Once reaching the large bowel, it should be quantitatively hydrolyzed to release the active agent. The potential of dexamethasone-beta-D-glucoside for colon-specific delivery of dexamethasone is assessed by determining the rates of its hydrolysis down the alimentary canal of the guinea pig, an animal in which an inflammatory bowel disease model has been developed. The hydrolytic activity is examined in tissues and luminal contents of the stomach, proximal and distal segments of the small intestine, cecum, and colon. For the tissues, the greatest hydrolytic activity is in the proximal small intestine, while the stomach, cecum, and colon have only moderate activity. In contrast, the contents of the cecum and colon show greater activity than the contents of the small intestine and stomach. The luminal contents retained beta-glucosidase activity even after repeated centrifugation and resuspension in a buffer. The activity was unaffected by homogenization. These observations suggest that hydrolytic activity is associated with enzymes located on the surface of luminal cells. The movement and hydrolysis of dexamethasone-beta-D-glucoside down the gastrointestinal tract of the guinea pig are also examined. About 20 to 30% of an oral dose appears to reach the cecum. Here the prodrug is rapidly hydrolyzed to the active drug. From intravenous administration of the prodrug and drug, it is apparent that dexamethasone-beta-D-glucoside is poorly absorbed in the gastrointestinal tract (bioavailability, less than 1%). There is a ninefold selective advantage for delivery of dexamethasone in cecal tissues in the guinea pig under the conditions of this experiment. Thus, there is a potential for a decrease in the usual dose and a concomitant reduction in the systemic exposure to dexamethasone. Because humans have much less glucosidase activity in the small intestine, even greater site-selective delivery to the cecum and colon is expected.

Intestinal microflora: metabolism of drugs and carcinogens

The intestinal microflora are capable of performing a wide variety of metabolic transformations. The digestive tract can be exposed to orally ingested, bile excreted, or blood-borne exogenous and endogenous substances that can be converted by the intestinal flora into carcinogens, mutagens, cocarcinogens or tumor promoting agents. In addition, the intestinal microflora can metabolize a wide variety of pharmacological agents resulting in production of metabolites required for the physiological activity of these agents or conversely in the inactivation of these agents. This article reviews the current knowledge of the relationship between the intestinal microflora and the metabolic reactions leading to the transformation of drugs and the production of mutagenic or carcinogenic compounds. The composition and distribution of bacteria in the gastrointestinal tract is discussed and the type of reactions these bacteria perform is summarized. The conversion of specific substrates such as, rutin, digoxin, cycasin, azulfidine and cyclamate are discussed and the physiological implication of these conversions are presented.