Effect of single-dose and short-term administration of quercetin on the pharmacokinetics of talinolol in humans – Implications for the evaluation of transporter-mediated flavonoid–drug interactions

Targeting CD73 with flavonoids inhibits cancer stem cells and increases lymphocyte infiltration in a triple-negative breast cancer mouse model

Introduction

Chemotherapy remains the mainstay treatment for triple-negative breast cancer (TNBC) due to the lack of specific targets. Given a modest response of immune checkpoint inhibitors in TNBC patients, improving immunotherapy is an urgent and crucial task in this field. CD73 has emerged as a novel immunotherapeutic target, given its elevated expression on tumor, stromal, and specific immune cells, and its established role in inhibiting anti-cancer immunity. CD73-generated adenosine suppresses immunity by attenuating tumor-infiltrating T- and NK-cell activation, while amplifying regulatory T cell activation. Chemotherapy often leads to increased CD73 expression and activity, further suppressing anti-tumor immunity. While debulking the tumor mass, chemotherapy also enriches heterogenous cancer stem cells (CSC), potentially leading to tumor relapse. Therefore, drugs targeting both CD73, and CSCs hold promise for enhancing chemotherapy efficacy, overcoming treatment resistance, and improving clinical outcomes. However, safe and effective inhibitors of CD73 have not been developed as of now.

Methods

We used in silico docking to screen compounds that may be repurposed for inhibiting CD73. The efficacy of these compounds was investigated through flow cytometry, RT-qPCR, CD73 activity, cell viability, tumorsphere formation, and other in vitro functional assays. For assessment of clinical translatability, TNBC patient-derived xenograft organotypic cultures were utilized. We also employed the ovalbumin-expressing AT3 TNBC mouse model to evaluate tumor-specific lymphocyte responses.

Results

We identified quercetin and luteolin, currently used as over-the-counter supplements, to have high in silico complementarity with CD73. When quercetin and luteolin were combined with the chemotherapeutic paclitaxel in a triple-drug regimen, we found an effective downregulation in paclitaxel-enhanced CD73 and CSC-promoting pathways YAP and Wnt. We found that CD73 expression was required for the maintenance of CD44highCD24low CSCs, and co-targeting CD73, YAP, and Wnt effectively suppressed the growth of human TNBC cell lines and patient-derived xenograft organotypic cultures. Furthermore, triple-drug combination inhibited paclitaxel-enriched CSCs and simultaneously improved lymphocyte infiltration in syngeneic TNBC mouse tumors.

Discussion

Conclusively, our findings elucidate the significance of CSCs in impairing anti-tumor immunity. The high efficacy of our triple-drug regimen in clinically relevant platforms not only underscores the importance for further mechanistic investigations but also paves the way for potential development of new, safe, and cost-effective therapeutic strategies for TNBC.

Influence of dietary bioactive compounds on the bioavailability and excretion of PFOA and its alternative HFPO-TA: Mechanism exploration

Oral ingestion is considered an important route of human exposure to perfluorooctanoic acid (PFOA) and its alternative hexafluoropropylene oxide trimer acid (HFPO-TA). Bioactive compounds are widely used as dietary supplements and food additives. However, little is known about the influence of dietary bioactive compounds on the bioavailability of PFOA and HFPO-TA. Here, three dietary bioactive compounds, β-carotene, quercetin and curcumin, were selected to study their influence on the relative bioavailability (RBA) of PFOA and HFPO-TA in soil using a mouse model. Compared to the control group (68.7 ± 6.27 %), quercetin and curcumin at medium and high doses (20 and 100 mg/kg/d) significantly (p < 0.05) decreased PFOA RBA to 55.2 ± 4.85-56.4 ± 4.57 % and 48.3 ± 5.49-48.6 ± 5.44 %, respectively. Mechanism study showed that medium- and high-dose quercetin as well as high-dose curcumin increased urinary excretion of PFOA by 33.6-35.6 % and 32.2 % through upregulating renal expression of multidrug resistance protein 2 (Mrp2) (1.52-1.63 folds) and Mrp4 (1.26-1.53 folds), thereby reducing PFOA accumulation. In PFOA-treated groups, quercetin at medium and high doses dramatically downregulated the hepatic expression of organic anion transport polypeptides (Oatp1a6, Oatp1b2), organic anion transport proteins (Oat1, Oat2), and fatty acid binding proteins (FABP4, FABP12), while curcumin at medium and high doses inhibited the hepatic expression of Oatp1a6, Oat1 and Oat2. These downregulated genes may reduce the transport of PFOA from blood to liver, and in turn decrease the PFOA RBA. However, β-carotene, quercetin and curcumin exhibited no significant effect on RBA and excretion of HFPO-TA (p > 0.05). This indicated the different absorption mechanisms between PFOA and HFPO-TA, and further research is warranted. This study provided a novel perspective for establishing environmentally friendly ways to reduce health hazards from per- and polyfluoroalkyl substances (PFASs).

Transporters in drug development: International transporter consortium update on emerging transporters of clinical importance

During its 4^th transporter workshop in 2021, the International Transporter Consortium (ITC) provided updates on emerging clinically relevant transporters for drug development. Previously highlighted and new transporters were considered based on up-to-date clinical evidence of their importance in drug-drug interactions and potential for altered drug efficacy and safety, including drug-nutrient interactions leading to nutrient deficiencies. For the first time, folate transport pathways (PCFT, RFC, and FRα) were examined in-depth as a potential mechanism of drug-induced folate deficiency and related toxicities (e.g., neural tube defects, megaloblastic anemia). However, routine toxicology studies conducted in support of drug development appear sufficient to flag such folate deficiency toxicities, while prospective prediction from in vitro folate metabolism and transport inhibition is not well enough established to inform drug development. Previous suggestion of retrospective study of intestinal OATP2B1 inhibition to explain unexpected decreases in drug exposure were updated. Furthermore, when the absorption of a new molecular entity is more rapid and extensive than can be explained by passive permeability, evaluation of OATP2B1 transport may be considered. Emerging research on hepatic and renal OAT2 is summarized, but current understanding of the importance of OAT2 was deemed insufficient to justify specific consideration for drug development. Hepatic, renal, and intestinal MRPs (MRP2, MRP3, MRP4) were revisited. MRPs may be considered when they are suspected to be the major determinant of drug disposition (e.g., direct glucuronide conjugates); MRP2 inhibition as a mechanistic explanation for drug-induced hyperbilirubinemia remains justified. There were no major changes in recommendations from previous ITC whitepapers.

United States Pharmacopeia comprehensive safety review of Styphnolobium japonicum flower and flower bud

The dried flower and flower bud of Styphnolobium japonicum (L.) Schott (Japanese Sophora flower and Japanese Sophora flower bud, respectively) have long been used as herbal medicines in Asia. Today, they are marketed as dietary supplements in the United States for their anti-oxidative properties and as a source of flavonoids, including rutin and quercetin. This review focused on the safety of S. japonicum flower and flower bud as dietary supplement ingredients. No serious adverse events or toxicity were reported in the clinical or experimental animal studies we reviewed. Although some studies indicated that rutin or quercetin may have potential for drug interactions, none were identified for S. japonicum flower or flower bud. S. japonicum flower and flower bud are not known to have been associated with serious health risks when appropriately consumed in dietary supplements and have been admitted to the U.S. Pharmacopeial Convention monograph development process. However, pregnant and breastfeeding women should seek the advice of a healthcare professional because no data are available on their use by these special populations.

Interaction Characterization of a Tyrosine Kinase Inhibitor Erlotinib with a Model Transport Protein in the Presence of Quercetin: A Drug-Protein and Drug-Drug Interaction Investigation Using Multi-Spectroscopic and Computational Approaches

The interaction between erlotinib (ERL) and bovine serum albumin (BSA) was studied in the presence of quercetin (QUR), a flavonoid with antioxidant properties. Ligands bind to the transport protein BSA resulting in competition between different ligands and displacing a bound ligand, resulting in higher plasma concentrations. Therefore, various spectroscopic experiments were conducted in addition to in silico studies to evaluate the interaction behavior of the BSA-ERL system in the presence and absence of QUR. The quenching curve and binding constants values suggest competition between QUR and ERL to bind to BSA. The binding constant for the BSA-ERL system decreased from 2.07 × 10⁴ to 0.02 × 10² in the presence of QUR. The interaction of ERL with BSA at Site II is ruled out based on the site marker studies. The suggested Site on BSA for interaction with ERL is Site I. Stability of the BSA-ERL system was established with molecular dynamic simulation studies for both Site I and Site III interaction. In addition, the analysis can significantly help evaluate the effect of various quercetin-containing foods and supplements during the ERL-treatment regimen. In vitro binding evaluation provides a cheaper alternative approach to investigate ligand-protein interaction before clinical studies.

Food supplement vitamins, minerals, amino-acids, fatty acids, phenolic and alkaloid-based substances: An overview of their interaction with drugs

Food supplements are a widespread group of products ingested as a diet complement, whose consumption has recently skyrocketed due to the consumers' concern with their well-being. Among food supplements, vitamin- and mineral-based ones are the top sellers, and the demand of others, such as those containing polyphenols, is increasing. Owing to their alleged natural characteristics, consumers take the safety of food supplements for granted, and use them even when taking medicines. Thus, their potential interactions with drugs have been sparsely evaluated. This manuscript aims to bring forth an up-to-date overview of the most important knowledge involving the interactions between food supplements and drugs, relevant to be aware by nutritionists and other healthcare professionals. To this end, an extensive bibliographic review was conducted focusing on peer reviewed data from experimental in vivo evidence and clinical studies whenever major clinical interactions have been reported. Elder people and polymedicated or chronic patients are especially vulnerable to the therapeutic ineffectiveness and toxicity caused by these types of interactions. Drugs used to treat cardiovascular, autoimmune, nervous, and oncological diseases are commonly involved in important clinical interactions with food supplements, many with a narrow therapeutic margin.

Transporter-mediated drug-drug interactions: advancement in models, analytical tools, and regulatory perspective

Drug-drug interactions mediated by transporters are a serious clinical concern hence a tremendous amount of work has been done on the characterization of the transporter-mediated proteins in humans and animals. The underlying mechanism for the transporter-mediated drug-drug interaction is the induction or inhibition of the transporter which is involved in the cellular uptake and efflux of drugs. Transporter of the brain, liver, kidney, and intestine are major determinants that alter the absorption, distribution, metabolism, excretion profile of drugs, and considerably influence the pharmacokinetic profile of drugs. As a consequence, transporter proteins may affect the therapeutic activity and safety of drugs. However, mounting evidence suggests that many drugs change the activity and/or expression of the transporter protein. Accordingly, evaluation of drug interaction during the drug development process is an integral part of risk assessment and regulatory requirements. Therefore, this review will highlight the clinical significance of the transporter, their role in disease, possible cause underlying the drug-drug interactions using analytical tools, and update on the regulatory requirement. The recent in-silico approaches which emphasize the advancement in the discovery of drug-drug interactions are also highlighted in this review. Besides, we discuss several endogenous biomarkers that have shown to act as substrates for many transporters, which could be potent determinants to find the drug-drug interactions mediated by transporters. Transporter-mediated drug-drug interactions are taken into consideration in the drug approval process therefore we also provided the extrapolated decision trees from in-vitro to in-vivo, which may trigger the follow-up to clinical studies.

New insight into the role of isorhamnetin as a regulator of insulin signaling pathway in type 2 diabetes mellitus rat model: Molecular and computational approach

We intended to examine the molecular mechanism of action of isorhamnetin (IHN) to regulate the pathway of insulin signaling. Molecular analysis, immunofluorescence, and histopathological examination were used to assess the anti-hyperglycemic and insulin resistance lowering effects of IHN in streptozotocin /high fat diet-induced type 2 diabetes using Wistar rats. At the microscopic level, treatment with IHN resulted in the restoration of myofibrils uniform arrangement and adipose tissue normal architecture. At the molecular level, treatment with IHN at three different doses showed a significant decrease in m-TOR, IGF1-R & LncRNA-RP11-773H22.4. expression and it up-regulated the expression of AKT2 mRNA, miR-1, and miR-3163 in both skeletal muscle and adipose tissue. At the protein level, IHN treated group showed a discrete spread with a moderate faint expression of m-TOR in skeletal muscles as well as adipose tissues. We concluded that IHN could be used in the in ameliorating insulin resistance associated with type 2 diabetes mellitus.

Influence of antioxidant flavonoids quercetin and rutin on the in-vitro binding of neratinib to human serum albumin

This study was designed to examine the interaction of neratinib (NRB) with human serum albumin (HSA) in presence of flavonoids quercetin and rutin. Both quercetin and rutin can compete with NRB to bind to HSA and displace NRB from its binding site. The interaction mechanism was studied with several spectroscopic techniques and molecular docking. Static fluorescence quenching mechanism was observed on interaction of HSA with NRB. van der Waals force and hydrogen bond were involved in the HSA-NRB interaction as per the results of thermodynamic parameters. Further, the conformational changes were observed in the HSA on its interaction with NRB. Interaction of NRB with HSA in presence of quercetin and rutin resulted in changes in the binding constants of HSA-NRB suggesting some impact on the binding of NRB in the presence of flavonoids.

Inhibitory Effects of Quercetin and Its Main Methyl, Sulfate, and Glucuronic Acid Conjugates on Cytochrome P450 Enzymes, and on OATP, BCRP and MRP2 Transporters

Quercetin is a flavonoid, its glycosides and aglycone are found in significant amounts in several plants and dietary supplements. Because of the high presystemic biotransformation of quercetin, mainly its conjugates appear in circulation. As has been reported in previous studies, quercetin can interact with several proteins of pharmacokinetic importance. However, the interactions of its metabolites with biotransformation enzymes and drug transporters have barely been examined. In this study, the inhibitory effects of quercetin and its most relevant methyl, sulfate, and glucuronide metabolites were tested on cytochrome P450 (CYP) (2C19, 3A4, and 2D6) enzymes as well as on organic anion-transporting polypeptides (OATPs) (OATP1A2, OATP1B1, OATP1B3, and OATP2B1) and ATP (adenosine triphosphate) Binding Cassette (ABC) (BCRP and MRP2) transporters. Quercetin and its metabolites (quercetin-3'-sulfate, quercetin-3-glucuronide, isorhamnetin, and isorhamnetin-3-glucuronide) showed weak inhibitory effects on CYP2C19 and 3A4, while they did not affect CYP2D6 activity. Some of the flavonoids caused weak inhibition of OATP1A2 and MRP2. However, most of the compounds tested proved to be strong inhibitors of OATP1B1, OATP1B3, OATP2B1, and BCRP. Our data demonstrate that not only quercetin but some of its conjugates, can also interact with CYP enzymes and drug transporters. Therefore, high intake of quercetin may interfere with the pharmacokinetics of drugs.

Recent Advances of Natural Polyphenols Activators for Keap1-Nrf2 Signaling Pathway

The Keap1-Nrf2/ARE signaling pathway is an important defense system against exogenous and endogenous oxidative stress injury. The dysregulation of the signaling pathway is associated with many diseases, such as cancer, diabetes, and respiratory diseases. Over the years, a wide range of natural products has provided sufficient resources for the discovery of potential therapeutic drugs. Among them, polyphenols possess Nrf2 activation, not only inhibit the production of ROS, inhibit Keap1-Nrf2 protein-protein interaction, but also degrade Keap1 and regulate the Nrf2 related pathway. In fact, with the continuous improvement of natural polyphenols separation and purification technology and further studies on the Keap1-Nrf2 molecular mechanism, more and more natural polyphenols monomer components of Nrf2 activators have been gradually discovered. In this view, we summarize the research status of natural polyphenols that have been found with apparent Nrf2 activation and their action modes. On the whole, this review may guide the design of novel Keap1-Nrf2 activator.

Liquid chromatography-tandem mass spectrometry assay for the simultaneous determination of three major flavonoids and their glucuronidated metabolites in rats after oral administration of Artemisia annua L. extract at a therapeutic ultra-low dose

The traditional antimalarial herb Artemisia annua L., from which artemisinin is isolated, is widely used in endemic regions. It has been suggested that artemisinin activity can be enhanced by flavonoids in A. annua; however, how fast and how long the flavonoids are present in the body remains unknown. In the present study, a rapid and sensitive liquid chromatography with tandem mass spectrometry method was developed and validated for the simultaneous determination of three major flavonoids components, i.e. chrysosplenol D, chrysoplenetin, and artemetin and their glucuronidated metabolites in rats after oral administrations of A. annua extracts at a therapeutic ultra-low dose. The concentration of the intact form was determined directly, and the concentration of the glucuronidated form was assayed in the form of flavonoids aglycones, after treatment with β-glucuronidase/sulfatase. The method was linear in the range of 0.5-300.0 ng/mL for chrysoplenetin and artemetin, and 2-600 ng/mL for chrysosplenol D. All the validation data conformed to the acceptance requirements. The study revealed a significantly higher exposure of the flavonoid constituents in conjugated forms in rats, with only trace intact from. Multiple oral doses of A. annua extracts led to a decreased plasma concentration levels for three flavonoids.

Effects of quercetin on the pharmacokinetics of losartan and its metabolite EXP3174 in rats

1. This study investigates the influence of quercetin on the pharmacokinetics of losartan and its metabolite EXP3174 in rats. 2. The pharmacokinetic profiles of losartan and EXP3174 of orally administered losartan (10 mg/kg) with or without pretreatment with quercetin (20 mg/kg/day for 7 days) were investigated. Additionally, Caco-2 cell transwell model and rat liver microsome incubation experiments were also conducted to investigate its potential mechanism. 3. The results showed that when the rats were pretreated with quercetin, the C_max (2.16 ± 0.40 vs. 1.33 ± 0.21 mg/L) and the AUC_(0-t) (13.89 ± 1.22 vs. 7.34 ± 0.75 mg·h/L) of losartan increased significantly (p < .05), and while the C_max (0.76 ± 0.09 vs. 1.14 ± 0.18 mg/L) of EXP3174 decreased significantly compared to the control (p < .05). The t_1/2 of losartan was prolonged from 3.27 ± 0.45 h to 4.74 ± 0.51 h (p < .05). The results also indicated that quercetin could increase losartan absorption rate by inhibiting the activity of P-gp and decrease its metabolic stability by inhibiting the activity of CYP450 enzyme. 4. These results indicated that the herb-drug interaction between quercetin and losartan might occur when they are co-administered in rats, quercetin could increase the systemic exposure of losartan and decrease the plasma concentration of EXP3174, possibly by inhibiting the activity of P-gp or CYP450 enzyme.

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.

Transporter-mediated natural product-drug interactions for the treatment of cardiovascular diseases

The growing use of natural products in cardiovascular (CV) patients has been greatly raising the concerns about potential natural product–CV drug interactions. Some of these may lead to unexpected cardiovascular adverse effects and it is, therefore, essential to identify or predict potential natural product–CV drug interactions, and to understand the underlying mechanisms. Drug transporters are important determinants for the pharmacokinetics of drugs and alterations of drug transport has been recognized as one of the major causes of natural product–drug interactions. In last two decades, many CV drugs (e.g., angiotensin II receptor blockers, beta-blockers and statins) have been identified to be substrates and inhibitors of the solute carrier (SLC) transporters and the ATP-binding cassette (ABC) transporters, which are two major transporter superfamilies. Meanwhile, in vitro and in vivo studies indicate that a growing number of natural products showed cardioprotective effects (e.g., gingko biloba, danshen and their active ingredients) are also substrates and inhibitors of drug transporters. Thus, to understand transporter-mediated natural product–CV drug interactions is important and some transporter-mediated interactions have already shown to have clinical relevance. In this review, we review the current knowledge on the role of ABC and SLC transporters in CV therapy, as well as transporter modulation by natural products used in CV diseases and their induced natural product–CV drug interactions through alterations of drug transport. We hope our review will aid in a comprehensive summary of transporter-mediated natural product–CV drug interactions and help public and physicians understand these type of interactions.

Effects of berberine on the pharmacokinetics of losartan and its metabolite EXP3174 in rats and its mechanism

CONTEXT

Losartan and berberine (BBR) are often simultaneously used for the treatment of senile diabetic nephropathy in clinics. However, the potential herb-drug interaction between losartan and BBR is unknown.

OBJECTIVE

This study investigates the influence of BBR on the pharmacokinetics of losartan and EXP3174, and investigates the effects of BBR on the metabolic stability of losartan.

MATERIALS AND METHODS

The pharmacokinetic profiles losartan and EXP3174 of orally administered losartan (10 mg/kg) with and without pretreatment with BBR (20 mg/kg) within 24 h were determined in Sprague-Dawley rats. The inhibitory effects of BBR on the metabolic stability of losartan were investigated using rat liver microsomes.

RESULTS

The C_max (1.26 ± 0.37 versus 1.96 ± 0.45 mg/L) and the AUC_(0-t) (8.25 ± 0.89 versus 12.70 ± 1.42 mg h/L) of losartan were significantly (p < 0.05) increased by BBR compared to the control, while the C_max (0.97 ± 0.15 versus 0.77 ± 0.06 mg/L) of EXP3174 was significantly decreased compared to the control (p < 0.05). The T_max of losartan was prolonged from 0.41 ± 0.12 to 0.52 ± 0.18 h, but the difference was not significant. However, the T_max of EXP3174 was decreased significantly (p < 0.05) from 8.14 ± 0.36 to 3.33 ± 0.28 h. The metabolic stability of losartan was increased from 37.4 to 59.6 min.

DISCUSSION AND CONCLUSION

We infer that BBR might increase the plasma concentration of losartan and decrease the concentration of EXP3174 through inhibiting the activity of CYP3A4 or CYP2C9.

Impact of quercetin‑induced changes in drug‑metabolizing enzyme and transporter expression on the pharmacokinetics of cyclosporine in rats

The aim of the present study was to evaluate whether quercetin (Que) modulates the mRNA and protein expression levels of drug-metabolizing enzymes (DMEs) and drug transporters (DTs) in the small intestine and liver, and thus modifies the pharmacokinetic profile of cyclosporine (CsA) in rats. This two-part study evaluated the pharmacokinetic profiles of CsA in the presence or absence of Que (experiment I) and the involvement of DMEs and DTs (experiment II). In experiment I, 24 rats received single-dose CsA (10 mg/kg) on day 1, single-dose Que (25, 50 and 100 mg/kg/day; eight rats in each group) on days 3–8, and concomitant CsA/Que on day 9. In experiment II, the mRNA and protein expression levels of cytochrome P (CYP)3A1, CYP3A2, UDP glucuronosyltransferase family 1 member A complex locus, organic anion-transporting polypeptide (OATP)2B1, OATP1B2, P-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2 in the small intestine and liver of rats were analyzed following oral administration of Que at 25, 50 and 100 mg/kg in the presence or absence of CsA (10 mg/kg) for seven consecutive days. Co-administration of Que (25,50 and 100 mg/kg) decreased the maximum serum concentration of CsA by 46, 50 and 47% in a dose-independent manner. In addition, the area under the curve to the last measurable concentration and area under the curve to infinite time were decreased, by 21 and 16%, 30 and 33%, and 33 and 34% (P<0.01), respectively. However, the mRNA and protein expression levels of the above-mentioned DMEs and DTs were inhibited by Que in a dose-dependent manner (P<0.01) to a similar extent in the small intestine and liver. It was demonstrated that Que was able to reduce the bioavailability of CsA following multiple concomitant doses in rats. Overlapping modulation of intestinal and hepatic DMEs and DTs, as well as the DME-DT interplay are potential explanations for these observations.

Efficacy of flavonoids in the management of high blood pressure

Plant compounds such as flavonoids have been reported to exert beneficial effects in cardiovascular disease, including hypertension. Information on the effects of isolated individual flavonoids for management of high blood pressure, however, is more limited. This review is focused on the flavonoids, as isolated outside of the food matrix, from the 5 main subgroups consumed in the Western diet (flavones, flavonols, flavanones, flavan-3-ols, and anthocyanins), along with their effects on hypertension, including the potential mechanisms for regulating blood pressure. Flavonoids from all 5 subgroups have been shown to attenuate a rise in or to reduce blood pressure during several pathological conditions (hypertension, metabolic syndrome, and diabetes mellitus). Flavones, flavonols, flavanones, and flavanols were able to modulate blood pressure by restoring endothelial function, either directly, by affecting nitric oxide levels, or indirectly, through other pathways. Quercetin had the most consistent blood pressure-lowering effect in animal and human studies, irrespective of dose, duration, or disease status. However, further research on the safety and efficacy of the flavonoids is required before any of them can be used by humans, presumably in supplement form, at the doses required for therapeutic benefit.