Effect of dietary flavonoids on pathways involved in drug metabolism

Antiviral Flavonoids: A Natural Scaffold with Prospects as Phytomedicines against SARS-CoV2

Flavonoids are vital candidates to fight against a wide range of pathogenic microbial infections. Due to their therapeutic potential, many flavonoids from the herbs of traditional medicine systems are now being evaluated as lead compounds to develop potential antimicrobial hits. The emergence of SARS-CoV-2 caused one of the deadliest pandemics that has ever been known to mankind. To date, more than 600 million confirmed cases of SARS-CoV2 infection have been reported worldwide. Situations are worse due to the unavailability of therapeutics to combat the viral disease. Thus, there is an urgent need to develop drugs against SARS-CoV2 and its emerging variants. Here, we have carried out a detailed mechanistic analysis of the antiviral efficacy of flavonoids in terms of their potential targets and structural feature required for exerting their antiviral activity. A catalog of various promising flavonoid compounds has been shown to elicit inhibitory effects against SARS-CoV and MERS-CoV proteases. However, they act in the high-micromolar regime. Thus a proper leadoptimization against the various proteases of SARS-CoV2 can lead to high-affinity SARS-CoV2 protease inhibitors. To enable lead optimization, a quantitative structure-activity relationship (QSAR) analysis has been developed for the flavonoids that have shown antiviral activity against viral proteases of SARS-CoV and MERS-CoV. High sequence similarities between coronavirus proteases enable the applicability of the developed QSAR to SARS-CoV2 proteases inhibitor screening. The detailed mechanistic analysis of the antiviral flavonoids and the developed QSAR models is a step forward toward the development of flavonoid-based therapeutics or supplements to fight against COVID-19.

The intestinal mucosal barrier - A key player in rheumatoid arthritis?

Rheumatoid arthritis (RA) is a recurrent chronic autoimmune disease, which is not only difficult to treat, but also has a great adverse impact on the physical and mental health of patients. The intestinal mucosa barrier has some relationship with RA and it consists of mechanical barrier, chemical barrier, immune barrier, and microflora barrier. It is a dynamic system that contributes to the stability of the intestinal environment by regulating the absorption of relevant substances from the lumen into the circulation, while limiting the passage of harmful substances. This article summarizes the connection between the intestinal mucosa barrier and RA, and proposes the role of relevant Chinese medicines on RA from the point of improving barriers, to provide new perspectives on the pathogenesis and therapeutic strategies of RA.

Evaluation of two different Cannabis sativa L. extracts as antioxidant and neuroprotective agents

Cannabis sativa L. is a plant that contains numerous chemically active compounds including cannabinoids such as trans-Δ-9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), and flavone derivatives, such as luteolin-7-O-glucuronide and apigenin glucuronide. In particular, the polar fraction of hemp including many phenolic compounds has been overlooked when compared with the more lipophilic fraction containing cannabinoids. Therefore, the aim of this study was to assess two extracts of industrial hemp (C. sativa) of different polarity (aqueous and hexane) by evaluating their antioxidant profile and their neuroprotective potential on pharmacological targets in the central nervous system (CNS). Several assays on in vitro antioxidant capacity (DPPH, superoxide radical, FRAP, ORAC), as well as inhibition of physiological enzymes such as acetylcholinesterase (AChE) and monoaminooxidase A (MAO-A) were carried out in order to find out how these extracts may be helpful to prevent neurodegenerative disorders. Neuro-2a cell line was selected to test the cytotoxic and neuroprotective potential of these extracts. Both extracts showed striking antioxidant capacity in the FRAP and ORAC assays, particularly the hexane extract, and interesting results for the DPPH and superoxide radical uptake assays, with the aqueous extract standing out especially in the latter. In enzyme inhibition assays, the aqueous extract showed AChE and MAO-A inhibitory activity, while the hexane extract only reached IC₅₀ value for AChE inhibitory bioassay. Neuro-2a assays demonstrated that polyphenolic extract was not cytotoxic and exhibited cytoprotective properties against hydrogen peroxide and antioxidant response decreasing reactive oxygen species (ROS) production. These extracts could be a source of compounds with potential benefit on human health, especially related to neurodegenerative disorders.

On the Development of a Cutaneous Flavonoid Delivery System: Advances and Limitations

Flavonoids are one of the vital classes of natural polyphenolic compounds abundantly found in plants. Due to their wide range of therapeutic properties, which include antioxidant, anti-inflammatory, photoprotective, and depigmentation effects, flavonoids have been demonstrated to be promising agents in the treatment of several skin disorders. However, their lipophilic nature and poor water solubility invariably lead to limited oral bioavailability. In addition, they are rapidly degraded and metabolized in the human body, hindering their potential contribution to the prevention and treatment of many disorders. Thus, to overcome these challenges, several cutaneous delivery systems have been extensively studied. Topical drug delivery besides offering an alternative administration route also ensures a sustained release of the active compound at the desired site of action. Incorporation into lipid or polymer-based nanoparticles appears to be a highly effective approach for cutaneous delivery of flavonoids with good encapsulation potential and reduced toxicity. This review focuses on currently available formulations used to administer either topically or systemically different classes of flavonoids in the skin, highlighting their potential application as therapeutic and preventive agents.

Flavonoids Alleviate Peripheral Neuropathy Induced by Anticancer Drugs

Simple Summary

Chemotherapy-induced peripheral neuropathy (CIPN) is a debilitating condition that severely reduces the quality of life of a considerable proportion of cancer patients. There is no cure for CIPN to date. Here, we explore the potential of flavonoids as pharmacological agents in combating CIPN. Flavonoids alleviate CIPN by reducing oxidative stress, inflammation, and neuronal damage, among other mechanisms. Future research should evaluate the efficacy and side effects of flavonoids in human models of CIPN.

Abstract

Purpose: This study aimed to assess the potential of flavonoids in combating CIPN. Methods: PubMed and Google Scholar were used, and studies that investigated flavonoids in models of CIPN and models of neuropathic pain similar to CIPN were included. Only studies investigating peripheral mechanisms of CIPN were used. Results: Flavonoids inhibit several essential mechanisms of CIPN, such as proinflammatory cytokine release, astrocyte and microglial activation, oxidative stress, neuronal damage and apoptosis, mitochondrial damage, ectopic discharge, and ion channel activation. They decreased the severity of certain CIPN symptoms, such as thermal hyperalgesia and mechanical, tactile, and cold allodynia. Conclusions: Flavonoids hold immense promise in treating CIPN; thus, future research should investigate their effects in humans. Specifically, precise pharmacological mechanisms and side effects need to be elucidated in human models before clinical benefits can be achieved.

Potential Herb-Drug Interactions in the Management of Age-Related Cognitive Dysfunction

Late-life mild cognitive impairment and dementia represent a significant burden on healthcare systems and a unique challenge to medicine due to the currently limited treatment options. Plant phytochemicals have been considered in alternative, or complementary, prevention and treatment strategies. Herbals are consumed as such, or as food supplements, whose consumption has recently increased. However, these products are not exempt from adverse effects and pharmacological interactions, presenting a special risk in aged, polymedicated individuals. Understanding pharmacokinetic and pharmacodynamic interactions is warranted to avoid undesirable adverse drug reactions, which may result in unwanted side-effects or therapeutic failure. The present study reviews the potential interactions between selected bioactive compounds (170) used by seniors for cognitive enhancement and representative drugs of 10 pharmacotherapeutic classes commonly prescribed to the middle-aged adults, often multimorbid and polymedicated, to anticipate and prevent risks arising from their co-administration. A literature review was conducted to identify mutual targets affected (inhibition/induction/substrate), the frequency of which was taken as a measure of potential interaction. Although a limited number of drugs were studied, from this work, interaction with other drugs affecting the same targets may be anticipated and prevented, constituting a valuable tool for healthcare professionals in clinical practice.

The Activation of Procarcinogens by CYP1A1/1B1 and Related Chemo-Preventive Agents: A Review

CYP1A1 and CYP1B1 are extrahepatic P450 family members involved in the metabolism of procarcinogens, such as PAHs, heterocyclic amines and halogen-containing organic compounds. CYP1A1/1B1 also participate in the metabolism of endogenous 17-β-estradiol, producing estradiol hydroquinones, which are the intermediates of carcinogenic semiquinones and quinones. CYP1A1 and CYP1B1 proteins share approximately half amino acid sequence identity but differ in crystal structures. As a result, CYP1A1 and CYP1B1 have different substrate specificity to chemical procarcinogens. This review will introduce the general molecular biology knowledge of CYP1A1/1B1 and the metabolic processes of procarcinogens regulated by these two enzymes. Over the last four decades, a variety of natural products and synthetic compounds which interact with CYP1A1/1B1 have been identified as effective chemo-preventive agents against chemical carcinogenesis. These compounds are mainly classified as indirect or direct CYP1A1/1B1 inhibitors based on their distinct mechanisms. Indirect CYP1A1/1B1 inhibitors generally impede the transcription and translation of CYP1A1/1B1 genes or interfere with the translocation of aryl hydrocarbon receptor (AHR) from the cytosolic domain to the nucleus. On the other hand, direct inhibitors inhibit the catalytic activities of CYP1A1/1B1. Based on the structural features, the indirect inhibitors can be categorized into the following groups: flavonoids, alkaloids and synthetic aromatics, whereas the direct inhibitors can be categorized into flavonoids, coumarins, stilbenes, sulfur containing isothiocyanates and synthetic aromatics. This review will summarize the in vitro and in vivo activities of these chemo-preventive agents, their working mechanisms, and related SARs. This will provide a better understanding of the molecular mechanism of CYP1 mediated carcinogenesis and will also give great implications for the discovery of novel chemo-preventive agents in the near future.

Inhibitory effects of polyphenols and their colonic metabolites on CYP2D6 enzyme using two different substrates

Polyphenolic compounds (including flavonoids, chalcones, phenolic acids, and furanocoumarins) represent a common part of our diet, but are also the active ingredients of several dietary supplements and/or medications. These compounds undergo extensive metabolism by human biotransformation enzymes and the microbial flora of the colon. CYP2D6 enzyme metabolizes approximately 25% of the drugs, some of which has narrow therapeutic window. Therefore, its inhibition can lead to the development of pharmacokinetic interactions and the disruption of drug therapy. In this study, the inhibitory effects of 17 plant-derived compounds and 19 colonic flavonoid metabolites on CYP2D6 were examined, employing two assays with different test substrates. The O-demethylation of dextromethorphan was tested employing CypExpress 2D6 kit coupled to HPLC analysis; while the O-demethylation of another CYP2D6 specific substrate (AMMC) was investigated in a plate reader assay with BioVision Fluorometric CYP2D6 kit. Interestingly, some compounds (e.g., bergamottin) inhibited both dextromethorphan and AMMC demethylation; however, certain substances proved to be inhibitors only in one of the assays applied. Our results demonstrate that some polyphenols and colonic metabolites are inhibitors of CYP2D6-catalyzed reactions. Nevertheless, the inhibitory effects showed strong substrate dependence.

Strong and Selective Inhibitory Effects of the Biflavonoid Selamariscina A against CYP2C8 and CYP2C9 Enzyme Activities in Human Liver Microsomes

Like flavonoids, biflavonoids, dimeric flavonoids, and polyphenolic plant secondary metabolites have antioxidant, antibacterial, antiviral, anti-inflammatory, and anti-cancer properties. However, there is limited data on their effects on cytochrome P450 (P450) and uridine 5'-diphosphoglucuronosyl transferase (UGT) enzyme activities. In this study we evaluate the inhibitory potential of five biflavonoids against nine P450 activities (P450s1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A) in human liver microsomes (HLMs) using cocktail incubation and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The most strongly inhibited P450 activity was CYP2C8-mediated amodiaquine N-dealkylation with IC50 ranges of 0.019~0.123 μM. In addition, the biflavonoids-selamariscina A, amentoflavone, robustaflavone, cupressuflavone, and taiwaniaflavone-noncompetitively inhibited CYP2C8 activity with respective K_i values of 0.018, 0.083, 0.084, 0.103, and 0.142 μM. As selamariscina A showed the strongest effects, we then evaluated it against six UGT isoforms, where it showed weaker inhibition (UGTs1A1, 1A3, 1A4, 1A6, 1A9, and 2B7, IC50 1.7 μM). Returning to the P450 activities, selamariscina A inhibited CYP2C9-mediated diclofenac hydroxylation and tolbutamide hydroxylation with respective K_i values of 0.032 and 0.065 μM in a competitive and noncompetitive manner. However, it only weakly inhibited CYP1A2, CYP2B6, and CYP3A with respective K_i values of 3.1, 7.9, and 4.5 μM. We conclude that selamariscina A has selective and strong inhibitory effects on the CYP2C8 and CYP2C9 isoforms. This information might be useful in predicting herb-drug interaction potential between biflavonoids and co-administered drugs mainly metabolized by CYP2C8 and CYP2C9. In addition, selamariscina A might be used as a strong CYP2C8 and CYP2C9 inhibitor in P450 reaction-phenotyping studies to identify drug-metabolizing enzymes responsible for the metabolism of new chemicals.

Testing the Pharmacokinetic Interactions of 24 Colonic Flavonoid Metabolites with Human Serum Albumin and Cytochrome P450 Enzymes

Flavonoids are abundant polyphenols in nature. They are extensively biotransformed in enterocytes and hepatocytes, where conjugated (methyl, sulfate, and glucuronide) metabolites are formed. However, bacterial microflora in the human intestines also metabolize flavonoids, resulting in the production of smaller phenolic fragments (e.g., hydroxybenzoic, hydroxyacetic and hydroxycinnamic acids, and hydroxybenzenes). Despite the fact that several colonic metabolites appear in the circulation at high concentrations, we have only limited information regarding their pharmacodynamic effects and pharmacokinetic interactions. Therefore, in this in vitro study, we investigated the interactions of 24 microbial flavonoid metabolites with human serum albumin and cytochrome P450 (CYP2C9, 2C19, and 3A4) enzymes. Our results demonstrated that some metabolites (e.g., 2,4-dihydroxyacetophenone, pyrogallol, O-desmethylangolensin, and 2-hydroxy-4-methoxybenzoic acid) form stable complexes with albumin. However, the compounds tested did not considerably displace Site I and II marker drugs from albumin. All CYP isoforms examined were significantly inhibited by O-desmethylangolensin; nevertheless, only its effect on CYP2C9 seems to be relevant. Furthermore, resorcinol and phloroglucinol showed strong inhibitory effects on CYP3A4. Our results demonstrate that, besides flavonoid aglycones and their conjugated derivatives, some colonic metabolites are also able to interact with proteins involved in the pharmacokinetics of drugs.

Safety Aspects of the Use of Quercetin as a Dietary Supplement

The flavonoid quercetin is frequently found in low amounts as a secondary plant metabolite in fruits and vegetables. Isolated quercetin is also marketed as a dietary supplement, mostly as the free quercetin aglycone, and frequently in daily doses of up to 1000 mg d^-1 exceeding usual dietary intake levels. The present review is dedicated to safety aspects of isolated quercetin used as single compound in dietary supplements. Among the numerous published human intervention studies, adverse effects following supplemental quercetin intake have been rarely reported and any such effects were mild in nature. Published adequate scientific data for safety assessment in regard to the long-term use (>12 weeks) of high supplemental quercetin doses (≥1000 mg) are currently not available. Based on animal studies involving oral quercetin application some possible critical safety aspects could be identified such as the potential of quercetin to enhance nephrotoxic effects in the predamaged kidney or to promote tumor development especially in estrogen-dependent cancer. Furthermore, animal and human studies with single time or short-term supplemental quercetin application revealed interactions between quercetin and certain drugs leading to altered drug bioavailability. Based on these results, some potential risk groups are discussed in the present review.

The effect of quercetin on the pharmacokinetics of chlorzoxazone, a CYP2E1 substrate, in healthy subjects

PURPOSE

Previous in vitro studies have demonstrated that quercetin inhibits CYP2E1 enzyme, but there are no available data to indicate that quercetin inhibits CYP2E1 enzyme in humans. The purpose of the present study was to assess the effect of quercetin on CYP2E1 enzyme activity in healthy subjects using chlorzoxazone (CHZ) as a CYP2E1 substrate.

METHODS

An open-label, two-period, sequential study was conducted in 12 healthy subjects. A single dose of CHZ 250 mg was given to subjects during control phase and after treatment phases. Quercetin at a dose of 500 mg was given to subjects twice daily for a period of 10 days. The blood samples were collected at predetermined time intervals after CHZ dosing and analyzed to determine the concentrations of CHZ and 6-hydroxychlorzoxazone (6-OHCHZ).

RESULTS

Treatment with quercetin significantly enhanced the maximum plasma concentration (C _max), area under the curve (AUC), and half-life (t _1/2) by 47.8, 69.3, and 36.4%, respectively, while significantly decreased the elimination rate constant (k _el) and apparent oral clearance (CL/F) of CHZ by 25.1 and 41.6%, respectively, in comparison with the control. On the other hand, C _max and AUC of 6-OHCHZ were decreased by 30.1 and 32.6%, respectively, after quercetin treatment when compared to control. In addition, geometric mean ratios and 90% confidence intervals for C _max and AUC of CHZ and 6-OHCHZ were both out of the no-effect boundaries of 0.80-1.25, which indicates a significant pharmacokinetic interaction present between CHZ and quercetin. Furthermore, treatment with quercetin significantly decreased the metabolic ratios of C _max and AUC by 57.1 and 60.1%, respectively, as compared to control suggesting that reduced formation of CHZ to 6-OHCHZ.

CONCLUSIONS

The results suggest that altered pharmacokinetics of CHZ might be attributed to quercetin-mediated inhibition of CYP2E1 enzyme. Further, the inhibition of CYP2E1 by quercetin may represent a novel therapeutic approach for minimizing the ethanol-induced CYP2E1 enzyme activity and results in reduced hepatotoxicity of ethanol.

Gamma irradiation of medicinally important plants and the enhancement of secondary metabolite production

PURPOSE

The profitable production of some important plant-based secondary metabolites (ginsenosides, saponins, camptothecin, shikonins etc.) in vitro by gamma irradiation is a current area of interest. We reviewed different types of secondary metabolites, their mode of synthesis and effect of γ-radiation on their yield for different plants, organs and in vitro cultures (callus, suspension, hairy root). Special effort has been made to review the biochemical mechanisms underlying the increase in secondary metabolites. A comparison of yield improvement with biotic and abiotic stresses was made.

RESULTS

Phenolic compounds increase with γ-irradiation in whole plants/plant parts; psoralen content in the common herb babchi (Psoralea corylifolia) was increased as high as 32-fold with γ-irradiation of seeds at 20 kGy. The capsaicinoids, a phenolic compound increased about 10% with 10 kGy in paprika (Capsicum annum L.). The in vitro studies show all the three types of secondary metabolites are reported to increase with γ-irradiation. Stevioside, total phenolic and flavonoids content were slightly increased in 15 Gy-treated callus cultures of stevia (Stevia rebaudiana Bert.). In terpenoids, total saponin and ginsenosides content were increased 1.4- and 1.8-fold, respectively, with 100 Gy for wild ginseng (Panax ginseng Meyer) hairy root cultures. In alkaloids, camptothecin yield increased as high as 20-fold with 20 Gy in callus cultures of ghanera (Nothapodytes foetida). Shikonins increased up to 4-fold with 16 Gy in suspension cultures of purple gromwell (Lithospermum erythrorhizon S.). The enzymes associated with secondary metabolite production were increased with γ-irradiation of 20 Gy; namely, phenylalanine ammonia-lyase (PAL) for phenolics, chalcone synthase (CHS) for flavonoids, squalene synthase (SS), squalene epoxidase (SE) and oxidosqualene cyclases (OSC) for ginsenosides and PHB (p-hydroxylbenzoic acid) geranyl transferase for shikonins.

CONCLUSIONS

An increase in secondary metabolites in response to various biotic and abiotic stresses is compared with ionizing radiation. A ∼5- to 20-fold increase is noted with ∼20 Gy irradiation dose. It increases the yield of secondary metabolites by enhancing the activity of certain key biosynthetic enzymes. Identification of the optimum dose is the important step in the large-scale production of secondary metabolites at industrial level.

Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans

Oxidative stress is the result of the imbalance between reactive oxygen species (ROS) formation and enzymatic and nonenzymatic antioxidants. Biomarkers of oxidative stress are relevant in the evaluation of the disease status and of the health-enhancing effects of antioxidants. We aim to discuss the major methodological bias of methods used for the evaluation of oxidative stress in humans. There is a lack of consensus concerning the validation, standardization, and reproducibility of methods for the measurement of the following: (1) ROS in leukocytes and platelets by flow cytometry, (2) markers based on ROS-induced modifications of lipids, DNA, and proteins, (3) enzymatic players of redox status, and (4) total antioxidant capacity of human body fluids. It has been suggested that the bias of each method could be overcome by using indexes of oxidative stress that include more than one marker. However, the choice of the markers considered in the global index should be dictated by the aim of the study and its design, as well as by the clinical relevance in the selected subjects. In conclusion, the clinical significance of biomarkers of oxidative stress in humans must come from a critical analysis of the markers that should give an overall index of redox status in particular conditions.

The role of metabolism (and the microbiome) in defining the clinical efficacy of dietary flavonoids

At a population level, there is growing evidence of the beneficial effects of dietary flavonoids on health. However, there is extensive heterogeneity in the response to increased intake, which is likely mediated via wide interindividual variability in flavonoid absorption and metabolism. Flavonoids are extensively metabolized by phase I and phase II metabolism (which occur predominantly in the gastrointestinal tract and liver) and colonic microbial metabolism. A number of factors, including age, sex, and genotype, may affect these metabolic processes. In addition, food composition and flavonoid source are likely to affect bioavailability, and emerging data suggest a critical role for the microbiome. This review will focus on the current knowledge for the main subclasses of flavonoids, including anthocyanins, flavonols, flavan-3-ols, and flavanones, for which there is growing evidence from prospective studies of beneficial effects on health. The identification of key factors that govern metabolism and an understanding of how the differential capacity to metabolize these bioactive compounds affect health outcomes will help establish how to optimize intakes of flavonoids for health benefits and in specific subgroups. We identify research areas that need to be addressed to further understand important determinants of flavonoid bioavailability and metabolism and to advance the knowledge base that is required to move toward the development of dietary guidelines and recommendations for flavonoids and flavonoid-rich foods.

Promise of bitter melon (Momordica charantia) bioactives in cancer prevention and therapy

Recently, there is a paradigm shift that the whole food-derived components are not 'idle bystanders' but actively participate in modulating aberrant metabolic and signaling pathways in both healthy and diseased individuals. One such whole food from Cucurbitaceae family is 'bitter melon' (Momordica charantia, also called bitter gourd, balsam apple, etc.), which has gained an enormous attention in recent years as an alternative medicine in developed countries. The increased focus on bitter melon consumption could in part be due to several recent pre-clinical efficacy studies demonstrating bitter melon potential to target obesity/type II diabetes-associated metabolic aberrations as well as its pre-clinical anti-cancer efficacy against various malignancies. The bioassay-guided fractionations have also classified the bitter melon chemical constituents based on their anti-diabetic or cytotoxic effects. Thus, by definition, these bitter melon constituents are at cross roads on the bioactivity parameters; they either have selective efficacy for correcting metabolic aberrations or targeting cancer cells, or have beneficial effects in both conditions. However, given the vast, though dispersed, literature reports on the bioactivity and beneficial attributes of bitter melon constituents, a comprehensive review on the bitter melon components and the overlapping beneficial attributes is lacking; our review attempts to fulfill these unmet needs. Importantly, the recent realization that there are common risk factors associated with obesity/type II diabetes-associated metabolic aberrations and cancer, this timely review focuses on the dual efficacy of bitter melon against the risk factors associated with both diseases that could potentially impact the course of malignancy to advanced stages. Furthermore, this review also addresses a significant gap in our knowledge regarding the bitter melon drug-drug interactions which can be predicted from the available reports on bitter melon effects on metabolism enzymes and drug transporters. This has important implications, given that a large proportion of individuals, taking bitter melon based supplements/phytochemical extracts/food based home-remedies, are also likely to be taking conventional therapeutic drugs at the same time. Accordingly, the comprehensively reviewed information here could be prudently translated to the clinical implications associated with any potential concerns regarding bitter melon consumption by cancer patients.

Redox Control of Multidrug Resistance and Its Possible Modulation by Antioxidants

Clinical efficacy of anticancer chemotherapies is dramatically hampered by multidrug resistance (MDR) dependent on inherited traits, acquired defence against toxins, and adaptive mechanisms mounting in tumours. There is overwhelming evidence that molecular events leading to MDR are regulated by redox mechanisms. For example, chemotherapeutics which overrun the first obstacle of redox-regulated cellular uptake channels (MDR1, MDR2, and MDR3) induce a concerted action of phase I/II metabolic enzymes with a temporal redox-regulated axis. This results in rapid metabolic transformation and elimination of a toxin. This metabolic axis is tightly interconnected with the inducible Nrf2-linked pathway, a key switch-on mechanism for upregulation of endogenous antioxidant enzymes and detoxifying systems. As a result, chemotherapeutics and cytotoxic by-products of their metabolism (ROS, hydroperoxides, and aldehydes) are inactivated and MDR occurs. On the other hand, tumour cells are capable of mounting an adaptive antioxidant response against ROS produced by chemotherapeutics and host immune cells. The multiple redox-dependent mechanisms involved in MDR prompted suggesting redox-active drugs (antioxidants and prooxidants) or inhibitors of inducible antioxidant defence as a novel approach to diminish MDR. Pitfalls and progress in this direction are discussed.

Absorption and disposition of naringenin and quercetin after simultaneous administration via intestinal perfusion in mice

As common constituents of vegetables, naringenin and quercetin are ingested together; for a clearer understanding of their bioavailability it is insightful to study them together.

Only a minority of broad-range detoxification genes respond to a variety of phytotoxins in generalist Bemisia tabaci species

Generalist insect can utilize two different modes for regulating their detoxification genes, the constitutive mode and the induced mode. Here, we used the Bemisia tabaci sibling species MEAM1 and MED, as a model system for studying constitutive and induced detoxification resistance and their associated tradeoffs. B. tabaci adults were allowed to feed through membranes for 24 h on diet containing only sucrose or sucrose with various phytotoxins. Quantitative real-time PCR analyses of 18 detoxification genes, indicated that relatively few transcripts were changed in both the MEAM1 and MED species, in response to the addition of phytotoxins to the diet. Induced transcription of detoxification genes only in the MED species, in response to the presence of indole-3-carbinol in the insect’s diet, was correlated with maintenance of reproductive performance in comparison to significant reduction in performance of the MEAM1 species. Three genes, COE2, CYP6-like 5 and BtGST2, responded to more than one compound and were highly transcribed in the insect gut. Furthermore, functional assays showed that the BtGST2 gene encodes a protein capable of interacting with both flavonoids and glucosinolates. In conclusion, several detoxification genes were identified that could potentially be involved in the adaptation of B. tabaci to its host plants.

A combined strategy of mass fragmentation, post-column cobalt complexation and shift in ultraviolet absorption spectra to determine the uridine 5'-diphospho-glucuronosyltransferase metabolism profiling of flavones after oral administration of a flavone mixture in rats

The use of dietary flavones is becoming increasingly popular for their prevention of cancers, cardiovascular diseases, and other diseases. Despite many pharmacokinetic studies on flavone mixtures, the position(s) of glucuronidation sites on the flavone skeleton in vivo remain(s) uncertain because of the lack of a convenient method to differentiate the isomers in biological samples. Accordingly, this study aimed to develop a new strategy to identify the position of the mono-O-glucuronide of flavones in vivo and to simultaneously determine the parent agent and its major metabolites responsible for complex pharmacokinetic characteristics. The novel strategy involves accurate mass measurements of flavone glucuronides, their [Co(II) (flavone glucuronide-H) (4,7-diphenyl-1,10-phenanthroline)2](+) complexes generated via the post-column addition of CoBr2 and 4,7-diphenyl-1,10-phenanthroline, and their mass spectrometric fragmentation by UPLC-DAD-Q-TOF and the comparison of retention times with biosynthesized standards of different isomers that were identified by analyzing the shift in UV spectra compared with the spectra of their respective aglycones. We successfully generated a metabolite profiling of flavones in rat plasma after oral administration of a flavone mixture from Dracocephalum moldavica L., which was used here as the model to demonstrate the strategy. Twelve flavone glucuronides, which were glucuronidated derivatives of acacetin, apigenin, luteolin, diosmetin, chrysoeriol and cirsimaritin, were detected and identified. Glucuronidation of the flavone skeleton at the 3'-/7-position was more prevalent, however, luteolin 4'-glucuronide levels exceeded luteolin 7-glucuronide levels. Based on the UDP-glucuronosyltransferase (UGT) metabolism profiling of flavones in rat plasma, six main compounds (tilianin, acacetin 7-glucuronide, apigenin 7-glucuronide, luteolin 3'-glucuronide, acacetin, and apigenin) were selected as pharmacokinetic markers. Pharmacokinetic results indicated that their maximal concentrations in blood were obtained within 0.4h, except for the concentration of luteolin 3'-glucronide (approximately 9h). Rat exposure was practically non-linear under the studied dosages (200 to 400mg/kg).

Is a flavonoid-rich diet with steamer cooking safe during calcineurin inhibitors therapy?

WHAT IS KNOWN AND OBJECTIVE

Dietary therapy is recommended for decreasing the symptoms of the metabolic syndrome and the risk of type 2 diabetes and cardiovascular diseases in subjects on calcineurin inhibitors. However, food-drug interactions may occur particularly with patients on such immunosuppressive therapy. This article comments on the benefit/risk assessment of a flavonoid-rich diet and steam-cooking of such food during calcineurin inhibitors therapy.

COMMENT

Patients are commonly advised against consuming citrus fruits and juices, grape juice and green tea. High vegetable intake may however increase the risk of food-diet interactions by inhibiting drug metabolic enzymes and transporters. Vegetable glucosinolates are potential interactants and may lead to adverse effects of drugs with narrow therapeutic indices and in the presence of genetic polymorphism. Examples of food components with potential drug interactants include all members of the Brassicaceae family.

WHAT IS NEW AND CONCLUSION

The potential additive and synergistic effects of flavonoids with other molecules in interfering with drug bioavailability need to be taken into account. The risk is highest with drugs with a narrow therapeutic index and in subjects with genetic polymorphisms of proteins involved in the disposition of those drugs.

Rapid identification of traditional Chinese herbal medicine by direct analysis in real time (DART) mass spectrometry

Direct analysis in real time-mass spectrometry (DART-MS) was employed as a novel fast method to identify traditional Chinese herbal medicine (TCHM). In order to obtain high quality mass spectra, the ionization temperature was optimized for every kind of sample. With minimal or no sample pretreatment, major TCHM components, including alkaloids, flavonoids and some ginsenosides, were directly detected within several seconds, while thirteen ginsenosides need derivatization to get good mass spectra. Pseudoginsenoside F11, compound K, protopanaxatriol (PPT) and protopanaxadiol (PPD), for the first time were detected without derivatization. Among five of eight tested Chinese herbal medicines, Rhizoma Corydalis, Bulbus Fritillariae Thunbergii, Arecae Semen, Ramulus Uncariae Cum Uncis and Scutellariae Radix, were first time identified by DART-MS. In addition, the ionization mechanisms of major herbal components, alkaloids, flavonoids and ginsenosides, were discussed in detail. Our results demonstrated that DART-MS could provide a rapid, reliable and environmental friendly method for the rapid identification of TCHM, and may be applicable to other plants.

Interference of flavonoids with fluorescent intracellular probes: methodological implications in the evaluation of the oxidative burst by flow cytometry

The evaluation of oxidative burst is particularly relevant in many pathological and subclinical conditions. Flow cytometry provides quick and accurate measures of the reactive oxygen species production by leukocytes in most situations. However, spurious results, related to probes' efflux may be observed in several instances. Many factors affect the evaluation of the oxidative burst with fluorescent probes that require intracellular deacetylation and could be substrate of the multidrug resistance proteins (MDR). After discussing the implications of the efflux of fluorophores in the normalization strategies in flow cytometry assays, we have pointed out the possible interference of flavonoids with fluorescet probes' staining and signal. We have also reviewed the results from human intervention studies regarding the evaluation of oxidative burst with these probes. In vitro, at concentrations close to post-ingestion circulating levels, some flavonoids and their metabolites could interfere with probes' staining and fluorescence signal through different mechanisms, such as the inhibition of esterases, the modulation of the MDR-mediate efflux of probe and the inhibition of the oxidation of probe. These effects may explain the contrasting results obtained by human intervention studies. Finally, also inflammatory state or the use of drugs substrate of MDR proteins could affect the evaluation of the oxidative burst with intracellular probes.

Dietary flavonoids modulate CYP2C to improve drug oral bioavailability and their qualitative/quantitative structure-activity relationship

This study aims to improve the drug oral bioavailability by co-administration with flavonoid inhibitors of the CYP2C isozyme and to establish qualitative and quantitative (QSAR) structure-activity relationships (SAR) between flavonoids and CYP2C. A total of 40 naturally occurring flavonoids were screened in vitro for CYP2C inhibition. Enzyme activity was determined by measuring conversion of tolbutamide to 4-hydroxytolbutamide by rat liver microsomes. The percent inhibition and IC50 of each flavonoid were calculated and used to develop SAR and QSAR. The most effective flavonoid was orally co-administered in vivo with a cholesterol-reducing drug, fluvastatin, which is normally metabolized by CYP2C. The most potent CYP2C inhibitor identified in vitro was tamarixetin (IC50 = 1.4 μM). This flavonoid enhanced the oral bioavailability of fluvastatin in vivo, producing a >2-fold increase in the area under the concentration-time curve and in the peak plasma concentration. SAR analysis indicated that the presence of a 2,3-double bond in the C ring, hydroxylation at positions 5, 6, and 7, and glycosylation had important effects on flavonoid-CYP2C interactions. These findings should prove useful for predicting the inhibition of CYP2C activity by other untested flavonoid-like compounds. In the present study, tamarixetin significantly inhibited CYP2C activity in vitro and in vivo. Thus, the use of tamarixetin could improve the therapeutic efficacy of drugs with low bioavailability.

Anti-cancer potential of flavonoids: recent trends and future perspectives

Cancer is a major public health concern in both developed and developing countries. Several plant-derived anti-cancer agents including taxol, vinblastine, vincristine, the campothecin derivatives, topotecan, irinotecan and etoposide are in clinical use all over the world. Other promising anti-cancer agents include flavopiridol, roscovitine, combretastatin A-4, betulinic acid and silvestrol. From this list one can well imagine the predominance of polyphenols, flavonoids and their synthetic analogs in the treatment of ovarian, breast, cervical, pancreatic and prostate cancer. Flavonoids present in human diet comprise many polyphenolic secondary metabolites with broad-spectrum pharmacological activities including their potential role as anti-cancer agents. A positive correlation between flavonoids-rich diet (from vegetables and fruits) and lower risk of colon, prostate and breast cancers lead to a question that whether flavonoids mediate the protective effects as chemopreventive agents or can interact with different genes and proteins to play role in chemotherapy. The current review emphasizes onto the therapeutic potential of flavonoids and their synthetic analogs as anti-cancer agents by providing new insights into the factors, regulation and molecular mechanisms along with their significant protein interactions.

Treatment of chronic venous disease with flavonoids: recommendations for treatment and further studies

OBJECTIVES

A variety of studies have suggested that flavonoids are effective for the treatment of CVD. However, many questions remain about their mechanism of action and when, how, and for what signs and symptoms they should be used.

METHOD

A panel of experts in CVD met in Budapest, Hungary in December 2011 to discuss the current state of knowledge of CVD and the role of flavonoids in its treatment. The discussion was based on a literature search in the current databases. The goals of this paper are recommendations for further studies on the use of flavonoids in the treatment of CVD.

RESULTS

There is good evidence to recommend the use of flavonoids in the treatment of CVD. However, because of the poor quality of some older clinical trials, inadequate reporting, and insufficient information, much work is still needed to firmly establish their clinical efficacy and to determine when and how they should be employed. In particular, long-term randomized, placebo-controlled, double-blind studies are needed to establish the efficacy and safety of flavonoids. Additional studies are also needed to establish their mechanism of action, pharmacokinetics, toxicity, and cost-effectiveness.

CONCLUSIONS

Aside from good evidence for the use of flavonoids in CVD further studies are indicated to establish long term treatment in this indication.

Protective effects of kaempferol on isoniazid- and rifampicin-induced hepatotoxicity

Isoniazid (INH) and rifampicin (RIF) are the first-line drugs for antituberculosis (anti-TB) chemotherapy. The levels of serum transaminases [aspartate aminotransferase (AST) and alanine aminotransferase (ALT)] are abnormal in 27% of patients undergoing INH and RIF treatments and in 19% of patients undergoing treatment with INH alone. Cytochrome P450 2E1 (CYP2E1) metabolizes many toxic substrates, including ethanol, carbon tetrachloride, and INH, which ultimately results in liver injury. The objective of this study was to screen for CYP2E1 inhibitors in vitro and investigate whether the selected compound could prevent INH/RIF-induced hepatotoxicity in vivo. We screened 83 known compounds from food and herbal medicines as inhibitors of CYP2E1. The hepatotoxic dose of INH/RIF was 50/100 mg kg(-1) day(-1). Hepatotoxicity was assessed using galactose single-point (GSP) method (a quantitative measurement of liver function), histopathological examination of the liver, malondialdehyde (MDA) assay, and measurement of AST and ALT activities. Kaempferol inhibited CYP2E1 activity in mice by 0.31- to 0.48-fold (p < 0.005). Mice with INH/RIF-induced hepatotoxicity showed significantly abnormal serum levels of AST and ALT, and GSP value, and these values could be decreased by the administration of kaempferol (p < 0.005). Kaempferol significantly reduced the depletion of hepatic glutathione and prevented the increase in MDA formation in mice. Furthermore, kaempferol did not affect the anti-TB effects of INH/RIF. To our knowledge, this is the first report of kaempferol's utility as an adjuvant for preventing CYP2E1-mediated hepatotoxicity induced by drugs such as INH and RIF.

Identification of flavone glucuronide isomers by metal complexation and tandem mass spectrometry: regioselectivity of uridine 5'-diphosphate-glucuronosyltransferase isozymes in the biotransformation of flavones

Flavone glucuronide isomers of five flavones (chrysin, apigenin, luteolin, baicalein, and scutellarein) were differentiated by collision-induced dissociation of [Co(II) (flavone-H) (4,7-diphenyl-1,10-phenanthroline)(2)](+) complexes. The complexes were generated via postcolumn addition of a metal-ligand solution after separation of the glucuronide products generated upon incubation of each flavone with an array of uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT) isozymes. Elucidation of the glucuronide isomers allowed a systematic investigation of the regioselectivity of 12 human UGT isozymes, including 8 UGT1A and 4 UGT2B isozymes. Glucuronidation of the 7-OH position was the preferred site for all the flavones except for luteolin, which possessed adjacent hydroxyl groups on the B ring. For all flavones and UGT isozymes, glucuronidation of the 5-OH position was never observed. As confirmed by the metal complexation/MS/MS strategy, glucuronidation of the 6-OH position only occurred for baicalein and scutellarein when incubated with three of the UGT isozymes.

Phytochemical characterisation of green beans (Phaseolus vulgaris L.) by using high-performance liquid chromatography coupled with time-of-flight mass spectrometry

INTRODUCTION

Although green beans (Phaseolus vulgaris L.) constitute a major agro-industrial crop worldwide and involve many bean varieties, the phytochemical composition and how this fluctuates among varieties is not well known.

OBJECTIVE

The purpose of this work was to conduct a comprehensive characterisation of the phytochemical compounds found in three varieties of green bean.

METHODOLOGY

Hydromethanol extracts from green beans were analysed by high-performance liquid chromatography (HPLC) coupled with electrospray time-of-flight mass spectrometry (ESI-TOF-MS) in order to characterise phytochemical compounds from different varieties of P. vulgaris L. The compounds were characterised based on interpreting their mass spectrum provided by the TOF-MS as well as by comparison with information from the literature (some compounds have been described previously in Fabaceae).

RESULTS

In this work, 72 phytochemical compounds were tentatively characterised by HPLC-ESI-TOF-MS. These compounds were classified as, 10 phenolic acids, 59 flavonoids, two lignans and an iridoid. Notably, out of the 72 compounds, 54 are new and their isomers have been characterised for the first time in green beans.

CONCLUSION

The phytochemical composition of three different varieties of P. vulgaris L have been characterised using HPLC-ESI-TOF-MS. A total of 72 phytochemical compounds were characterised, 54 being reported in green beans for the first time. Among these were the main flavonoids detected. These results highlight the influence that variety can exert on the quality of phytochemicals. Given that new phytochemical compounds have been characterised, this study offers a useful approach for improving and updating the food-composition tables.

Influence of fatty acid patterns on the intestinal absorption pathway of quercetin in thoracic lymph duct-cannulated rats

Since it is known that dietary fats improve the bioavailability of the flavonol quercetin, we purposed to investigate whether this effect is due to increased lymphatic transport of quercetin. In rats with implanted catheters in the thoracic lymph duct, we administered quercetin into the duodenum with TAG emulsions containing either long-chain fatty acids (LCT) or medium-chain fatty acids (MCT). Controls received quercetin together with a glucose solution. LCT administration increased the lymphatic output of quercetin (19·1 (sem1·2) nmol/8 h) as well as the lymph-independent bioavailability of the flavonol, determined as area under the plasma concentration curve (1091 (sem142) μm× min). Compared with glucose administration, MCT neither increased the lymphatic output (12·3 (sem1·5) nmol/8 h) nor the bioavailability of quercetin (772 (sem99) μm× min) significantly (glucose group: 9·8 (sem1·5) nmol/8 h and 513 (sem55) μm× min, respectively). Because LCT are released within chylomicrons into the intestinal lymph while MCT are mainly released into the portal blood, we conclude from the present results that dietary fats that are mainly composed of LCT improve quercetin bioavailability by increasing its transport via the lymph, thereby circumventing hepatic first-pass metabolism of the flavonol. In addition, LCT could enhance quercetin absorption by improving its solubility in the intestinal tract.

Inhibition and induction of glutathione S-transferases by flavonoids: possible pharmacological and toxicological consequences

Many studies reviewed herein demonstrated the potency of some flavonoids to modulate the activity and/or expression of glutathione S-transferases (GSTs). Because GSTs play a crucial role in the detoxification of xenobiotics, their inhibition or induction may significantly affect metabolism and biological effects of many drugs, industrials, and environmental contaminants. The effect of flavonoids on GSTs strongly depends on flavonoid structure, concentration, period of administration, as well as on GST isoform and origin. Moreover, the results obtained in vitro are often contrary to the vivo results. Based on these facts, the revelation of important flavonoid-drug or flavonoid-pollutant interaction has been complicated. However, it should be borne in mind that ingestion of certain flavonoids in combination with drugs or pollutants (e.g., acetaminophen, simvastatin, cyclophosphamide, cisplatine, polycyclic aromatic hydrocarbons, chlorpyrifos, acrylamide, and isocyanates), which are GST substrates, could have significant pharmacological and toxicological consequences. Although reasonable consumptions of a flavonoids-rich diet (that may lead to GST induction) are mostly beneficial, the uncontrolled intake of high concentrations of certain flavonoids (e.g., quercetin and catechins) in dietary supplements (that may cause GST inhibition) may threaten human health.

Mutual interactions between flavonoids and enzymatic and transporter elements responsible for flavonoid disposition via phase II metabolic pathways

Flavonoids, existing mainly as glycosides in nature, have multiple "claimed" beneficial effects in humans. Flavonoids are extensively metabolized in enterocytes and hepatocytes by phase II enzymes such as UGTs and SULTs to form glucuronides and sulfates, respectively. These glucuronides and sulfates are subsequently excreted via ABC transporters (e.g., MRP2 or BCRP). Therefore, it is the interplay between phase II enzymes and efflux transporters that affects the disposition of flavonoids and leads to the low bioavailability of flavonoid aglycones. Flavonoids can also serve as chemical regulators that affect the activity or expression levels of phase II enzymes including UGTs, SULTs and GSTs, and transporters including P-gp, MRP2, BCRP, OATP and OAT. In general, flavonoids may exert the inhibitory or inductive effects on the phase II enzymes and transporters via multiple mechanisms that may involve different nuclear receptors. Since flavonoids may affect the metabolic pathways shared by many important clinical drugs, drug-flavonoid interaction is becoming an increasingly important concern. This review article focused on the disposition of flavonoids and effects of flavonoids on relevant enzymes (e.g. UGTs and SULTs) and transporters (e.g. MRP2 and BCRP) involved in the interplay between phase II enzymes and efflux transporters. The effects of flavonoids on other metabolic enzymes (e.g. GSTs) or transporters (e.g. P-gp, OATP and OAT) are also addressed but that is not the emphasis of this review.

A new herb-drug interaction of Polygonum cuspidatum, a resveratrol-rich nutraceutical, with carbamazepine in rats

Carbamazepine (CBZ), an antiepileptic with narrow therapeutic window, is a substrate of CYP 3A which metabolizes CBZ to carbamazepine-10,11-epoxide (CBZE), an active metabolite. This study investigated the acute and chronic effects of Polygonum cuspidatum (PC), a resveratrol-rich nutraceutical, on the pharmacokinetics of CBZ in rats and the underlying mechanisms. Rats were orally administered CBZ (200 mg/kg) alone and coadministered with a single dose and the 7th dose of PC (2 g/kg) in a crossover design. The concentrations of CBZ and CBZE in serum and various tissues were determined by HPLC method. The results showed that PC significantly increased the AUC(0-t) of CBZ and CBZE, whereas the formation rate of CBZE was decreased. Tissue analysis showed that the concentrations of CBZ and CBZE in brain, liver and kidney were significantly increased by PC. Cell studies indicated that the efflux function of MRP 2 was inhibited by the serum metabolites of PC. In conclusion, PC markedly increased the systemic exposure and brain concentration of CBZ and CBZE through inhibiting the activities of CYP 3A and MRP 2.