Physiologically relevant metabolites of quercetin have no effect on adhesion molecule or chemokine expression in human vascular smooth muscle cells

A critical examination of human data for the biological activity of quercetin and its phase-2 conjugates

This critical review examines evidence for beneficial effects of quercetin phase-2 conjugates from clinical intervention studies, volunteer feeding trials, and in vitro work. Plasma concentrations of quercetin-3-O-glucuronide (Q3G) and 3'-methylquercetin-3-O-glucuronide (3'MQ3G) after supplementation may produce beneficial effects in macrophages and endothelial cells, respectively, especially if endogenous deglucuronidation occurs, and lower blood uric acid concentration via quercetin-3'-O-sulfate (Q3'S). Unsupplemented diets produce much lower concentrations (<50 nmol/l) rarely investigated in vitro. At 10 nmol/l, Q3'S and Q3G stimulate or suppress, respectively, angiogenesis in endothelial cells. Statistically significant effects have been reported at 100 nmol/l in breast cancer cells (Q3G), primary neuron cultures (Q3G), lymphocytes (Q3G and3'MQ3G) and HUVECs (QG/QS mixture), but it is unclear whether these translate to a health benefit in vivo. More sensitive and more precise methods to measure clinically significant endpoints are required before a conclusion can be drawn regarding effects at normal dietary concentrations. Future requirements include better understanding of inter-individual and temporal variation in plasma quercetin phase-2 conjugates, their mechanisms of action including deglucuronidation and desulfation both in vitro and in vivo, tissue accumulation and washout, as well as potential for synergy or antagonism with other quercetin metabolites and metabolites of other dietary phytochemicals.

Citrus flavonoids and adhesion molecules: Potential role in the management of atherosclerosis

Atherosclerosis as a chronic inflammatory disorder is accompanied with oxidative stress which causes a high morbidity and mortality. Adhesion molecules, including intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), P-selectin, and E-selectin, are amongst the most important contributors in atherosclerosis. In such cases, dietary interventions with functional foods containing natural antioxidant and anti-inflammatory constituents are of a great interest. Citrus fruits are rich sources of flavonoids as natural pigments with potent antioxidant and anti-inflammatory activities. This study aims to review current evidence regarding the role of citrus flavonoids in the management of atherosclerosis with a focus on their effect on adhesion molecules. Electronic databases including PubMed, Scopus, and Web of Science were searched with the names of adhesion molecules and flavonoids from inception until January 2023. The included articles highly support the beneficial effects of citrus flavonoids in preclinical models of atherosclerosis. Quercetin, naringin and naringenin, hesperidin and hesperetin, nobiletin, rutin, luteolin, apigenin, and kaempferol are the most common flavonoids in citrus fruits which could modulate adhesion molecules including ICAM-1, VCAM-1, E-selectin, and P-selectin. Additionally, markers of chronic inflammation such as interleukins, tumor necrosis factor-α, nuclear factor-κB, and nitric oxide signaling, as well as oxidative stress markers like superoxide dismutase and glutathione were all normalized upon administration of citrus flavonoids. Conclusively, this review confirms the modulatory role of flavonoids on adhesion molecules in atherosclerosis based on the preclinical evaluations. Thus, citrus fruits can be further studied in atherosclerotic patients regarding their activity in reducing adhesion molecules.

Potential Role of Quercetin Glycosides as Anti-Atherosclerotic Food-Derived Factors for Human Health

Quercetin is a monomeric polyphenol of plant origin that belongs to the flavonol-type flavonoid subclass. Extensive studies using cultured cells and experimental model animals have demonstrated the anti-atherosclerotic effects of dietary quercetin in relation to the prevention of cardiovascular disease (CVD). As quercetin is exclusively present in plant-based foods in the form of glycosides, this review focuses on the bioavailability and bioefficacy of quercetin glycosides in relation to vascular health effects. Some glucose-bound glycosides are absorbed from the small intestine after glucuronide/sulfate conjugation. Both conjugated metabolites and deconjugated quercetin aglycones formed by plasma β-glucuronidase activity act as food-derived anti-atherogenic factors by exerting antioxidant, anti-inflammatory, and plasma low-density lipoprotein cholesterol-lowering effects. However, most quercetin glycosides reach the large intestine, where they are subject to gut microbiota-dependent catabolism resulting in deglycosylated aglycone and chain-scission products. These catabolites also affect vascular health after transfer into the circulation. Furthermore, quercetin glycosides may improve gut microbiota profiles. A variety of human cohort studies and intervention studies support the idea that the intake of quercetin glycoside-rich plant foods such as onion helps to prevent CVD. Thus, quercetin glycoside-rich foods offer potential benefits in terms of cardiovascular health and possible clinical applications.

Type 2 Diabetes mellitus alters the cargo of (poly)phenol metabolome and the oxidative status in circulating lipoproteins

The incidence of diabetes on the worldwide population has tripled in the past 5 decades. While drug-based therapies are valuable strategies to treat and ease the socio-economic burden of diabetes, nutritional strategies offer valuable alternatives to prevent and manage diabetes onset and contribute to the sustainability of health budgets. Whilst, intervention studies have shown that (poly)phenol-rich diets improve fasting glucose levels and other blood parameters, very little is known about the distribution of ingested polyphenols in circulation and the impact of diabetes on its cargo. In this study we investigate the impact of type 2 diabetes on the cargo of plasma (poly)phenols. Our results show that phenolic compounds are heterogeneously distributed in circulation though mainly transported by lipoprotein populations. We also found that diabetes has a marked effect on the phenolic content transported by VLDL resulting in the decrease in the content of flavonoids and consequently a decrease in the antioxidant capacity. In addition to the reduced bioavailability of (poly)phenol metabolites and increase of oxidative status in LDL and HDL populations in diabetes, cell-based assays show that sub-micromolar amounts of microbial (poly)phenol metabolites are able to counteract the pro-inflammatory status in glucose-challenged endothelial cells. Our findings highlight the relevance of triglyceride-rich lipoproteins in the transport and delivery of bioactive plant-based compounds to the endothelium in T2DM supporting the adoption of nutritional guidelines as an alternative strategy to drug-based therapeutic approaches.

Persicaria minor (Huds.) Opiz Prevents In Vitro Atherogenesis by Attenuating Tumor Necrosis Factor-α-Induced Monocyte Adhesion to Human Umbilical Vein Endothelial Cells

Persicaria minor (Huds.) Opiz is an herb with anti-inflammatory, antioxidant, and anti-atherosclerosis effects. Nevertheless, the mechanism underlying its anti-atherosclerosis effect is poorly comprehended. This in vitro study assessed the protective effects of standardized aqueous extract of P. minor leaves (PM) on tumor necrosis factor-α (TNF-α)-induced monocyte adhesion to human umbilical vein endothelial cells (HUVEC), which is one of the pivotal early steps in atherogenesis. The results showed that PM decreased the mRNA and protein expression of cellular adhesion molecules, vascular adhesion molecule-1 and intercellular adhesion molecule-1, resulting in reduced adhesion of monocytes to HUVEC. Additionally, PM inhibited nuclear factor kappaB (NF-κB) activation as indicated by reduced NF-κB p65 levels in TNF-α-induced HUVEC. Overall, PM could prevent in vitro atherogenesis by inhibiting NF-κB activation and adhesion of monocytes to HUVEC. The effects of PM are probably mediated by its bioactive compound, quercetin-3-O-glucuronide. The findings may provide a rationale for the in vivo anti-atherosclerosis effect of PM, and support its potential use in atherosclerosis.

Focus on the high therapeutic potentials of quercetin and its derivatives

BACKGROUND

Polyphenols and particularly flavonoids are of constant interest to the scientific community. Flavonoids are investigated for their biological and pharmacological purposes, notably as antioxidant, anticancer, antiviral and for their anti-inflammatory activities. Certainly, one of the best-known flavonols recognized for its therapeutic and preventive properties, is quercetin. Despite its biological interest, quercetin suffer from some drawbacks, mainly related to its bioavailability. Hence, its synthetic or biosynthetic derivatives have been the subject of intensive research. The health-promoting biological activities of flavonols and derivatives mainly arise from their capacity to disrupt the host-pathogen interactions and/or to regulate host cellular functions including oxidative processes and immunological responses. In the age of coronavirus pandemic, the anti-inflammatory and antiviral potential of flavonols should be put forward to explore these substances for decreasing the viral load and inflammatory storm caused by the infection.

PURPOSE OF STUDY

The present review will decipher and discuss the antioxidant, anti-inflammatory and antiviral capacities of major flavonol with a focus on the molecular basis and structure-activity relationships.

STUDY DESIGN

Current study used a combination of quercetin derivatives, pathway, antioxidant, anti-inflammatory, antiviral activities as keywords to retrieve the literature. This study critically reviewed the current literature and presented the ability of natural analogs of quercetin having superior antioxidant, anti-inflammatory and antiviral effects than the original molecule.

RESULTS

This review allowed the identification of relevant key structure-activity relationship elements and highlight approaches on the mechanisms governing the antioxidant, antiviral and anti-inflammatory activities.

CONCLUSION

Through a critical analysis of the literature, flavonols and more precisely quercetin derivatives reviewed and found to act simultaneously on inflammation, virus and oxidative stress, three key factors that may lead to life threatening diseases.

Hypoglycaemic and Antioxidant Properties of Acrocomia aculeata (Jacq.) Lodd Ex Mart. Extract Are Associated with Better Vascular Function of Type 2 Diabetic Rats

Oxidative stress is involved in the metabolic dysregulation of type 2 diabetes (DM2). Acrocomia aculeata (Aa) fruit pulp has been described for the treatment of several diseases, and recently we have proved that its leaves have phenolic compounds with a marked antioxidant effect. We aimed to assess whether they can improve metabolic, redox and vascular functions in DM2. Control Wistar (W-Ctrl) and non-obese type 2 diabetic Goto-Kakizaki (GK-Ctrl) rats were treated for 30 days with 200 mg.kg-1 aqueous extract of Aa (EA-Aa) (Wistar, W-EA-Aa/GK, GK-EA-Aa). EA-Aa was able to reduce fasting glycaemia and triglycerides of GK-EA-Aa by improving proteins related to glucose and lipid metabolism, such as GLUT-4, PPARγ, AMPK, and IR, when compared to GK-Ctrl. It also improved viability of 3T3-L1 pre-adipocytes exposed by H2O2. EA-Aa also increased the levels of catalase in the aorta and kidney, reduced oxidative stress and increased relaxation of the aorta in GK-treated rats in relation to GK-Ctrl, in addition to the protective effect against oxidative stress in HMVec-D cells. We proved the direct antioxidant potential of the chemical compounds of EA-Aa, the increase in antioxidant defences in a tissue-specific manner and hypoglycaemic properties, improving vascular function in type 2 diabetes. EA-Aa and its constituents may have a therapeutic potential for the treatment of DM2 complications.

(Poly)phenol-Rich Diets in the Management of Endothelial Dysfunction in Diabetes Mellitus: Biological Properties in Cultured Endothelial Cells

Processed and ready-to-eat foods become routinely consumed resulting in a sharp rise of sugar intake in people's daily diets. The inclusion of fresh fruits and vegetables rich in (poly)phenols has been encouraged by the World Health Organization (WHO) as part of the daily choices to ameliorate endothelial dysfunction and ease the socio-economic burden of diabetes. Research in Food, Nutrition, and Cell Metabolism areas is revealing that the health benefits of (poly)phenol-rich foods go beyond their antioxidant properties and are in fact key modulators of redox and glycaemia status, and inflammatory response contributing to improved endothelial function and vascular health in diabetes. Other beneficial aspects include appetite modulation, regulation of hydrolytic enzymes involved in sugar and lipid metabolism, and mediation of cell-cell aggregation events. This work overviews the current knowledge on the biological properties of ingested (poly)phenols in cultured endothelial cells with emphasis on the circulating (poly)phenols, providing support to (poly)phenol-rich diets as alternatives to drug-based therapies in the prevention, treatment, and management of diabetes. A critical evaluation on the caveats and challenges involve in current experimental cell-based designs and approaches adopted is also discussed.

Going "Green" in the Prevention and Management of Atherothrombotic Diseases: The Role of Dietary Polyphenols

During the 20th century processed and ready-to-eat foods became routinely consumed resulting in a sharp rise of fat, salt, and sugar intake in people's diets. Currently, the global incidence of obesity, raised blood lipids, hypertension, and diabetes in an increasingly aged population contributes to the rise of atherothrombotic events and cardiovascular diseases (CVD) mortality. Drug-based therapies are valuable strategies to tackle and help manage the socio-economic impact of atherothrombotic disorders though not without adverse side effects. The inclusion of fresh fruits and vegetables rich in flavonoids to human diets, as recommended by WHO offers a valuable nutritional strategy, alternative to drug-based therapies, to be explored in the prevention and management of atherothrombotic diseases at early stages. Though polyphenols are mostly associated to color and taste in foods, food flavonoids are emerging as modulators of cholesterol biosynthesis, appetite and food intake, blood pressure, platelet function, clot formation, and anti-inflammatory signaling, supporting the health-promoting effects of polyphenol-rich diets in mitigating the impact of risk factors in atherothrombotic disorders and CVD events. Here we overview the current knowledge on the effect of polyphenols particularly of flavonoid intake on the atherothrombotic risk factors and discuss the caveats and challenges involved with current experimental cell-based designs.

An Aligned Patterned Biomimetic Elastic Membrane Has a Potential as Vascular Tissue Engineering Material

Cardiovascular disease is the leading cause of death worldwide, with an annual mortality incidence predicted to rise to 23.3 million worldwide by 2030. Synthetic vascular grafts as an alternative to autologous vessels have shown satisfactory long-term results for replacement of large- and medium-diameter arteries, but have poor patency rates when applied to small-diameter vessels. Nanoparticles with low toxicity, contrasting agent properties, tailorable characteristics, targeted/stimuli- response delivery potential, and precise control over behavior (via external stimuli such as magnetic fields) have made possible their use for improving engineered tissues. Poly (styrene-block-butadiene-block-styrene) (SBS) is a kind of widely used thermoplastic elastomer with good mechanical properties and biocompatibility. Here, we synthesized anthracene-grafted SBS (SBS-An) by the method for the fabrication of a biomimetic elastic membrane with a switchable Janus structure, and formed the patterns on the surface of SBS-An under ultraviolet (UV) light irradiation. By irradiating the SBS-An film at different times (0, 10, 20, 30, 60, and 120 s), we obtained six well-ordered surface-patterned biomimetic elastic film with SBS-An at different heights in the thickness direction and the same distances of intervals (named sample-0, 10, 20, 30, 60, and 120 s). The structural effects of the SBS-An films on the adhesion and proliferation of human umbilical vein endothelial cells (HUVECs) were studied, and the possible mechanism was explored. When the HUVECs were cultured on the SBS-An films at different heights in the thickness direction, the sample-30 s with approximately 4 μm height significantly promoted adhesion of the HUVECs at the early stage and proliferation during the culture period compared with the samples of the lower (0, 10, and 20 s) and higher (60 and 120 s) heights. Consistent with this, the sample 30 s showed a higher stimulatory effect on the proliferation- and angiogenesis-related genes. These results suggest that SBS-An with appropriate height could efficiently control bioactivities of the biomimetic elastic membrane and might have great potential in vascular tissue engineering application.

Targeting Inflammation by Flavonoids: Novel Therapeutic Strategy for Metabolic Disorders

A balanced metabolic profile is essential for normal human physiological activities. Disproportions in nutrition give rise to imbalances in metabolism that are associated with aberrant immune function and an elevated risk for inflammatory-associated disorders. Inflammation is a complex process, and numerous mediators affect inflammation-mediated disorders. The available clinical modalities do not effectively address the underlying diseases but rather relieve the symptoms. Therefore, novel targeted agents have the potential to normalize the metabolic system and, thus, provide meaningful therapy to the underlying disorder. In this connection, polyphenols, the well-known and extensively studied phytochemical moieties, were evaluated for their effective role in the restoration of metabolism via various mechanistic signaling pathways. The various flavonoids that we observed in this comprehensive review interfere with the metabolic events that induce inflammation. The mechanisms via which the polyphenols, in particular flavonoids, act provide a promising treatment option for inflammatory disorders. However, detailed clinical studies of such molecules are required to decide their clinical fate.

Quercetin, but Not Epicatechin, Decreases Plasma Concentrations of Methylglyoxal in Adults in a Randomized, Double-Blind, Placebo-Controlled, Crossover Trial with Pure Flavonoids

Background

Methylglyoxal (MGO) is the most potent precursor of advanced glycation end products (AGEs). MGO and AGEs have been associated with diabetes, its complications, and other age-related diseases. Experimental studies have shown that the flavonoids quercetin and epicatechin are able to scavenge MGO and lower AGE formation.

Objective

Data on the effects of these flavonoids on MGO and AGE concentrations in humans are not yet available. We therefore investigated the effect of quercetin and epicatechin on the concentrations of MGO and AGEs in a post hoc analysis.

Methods

Thirty-seven apparently healthy, nonsmoking adults with a systolic blood pressure between 125 and 160 mm Hg at screening were included in a randomized, double-blind, placebo-controlled crossover trial. Participants ingested (-)-epicatechin (100 mg/d), quercetin 3-glucoside (160 mg/d), or placebo capsules for periods of 4 wk separated by 4-wk washout periods. Fasting blood samples were collected at the start and end of each intervention period. Liquid chromatography-tandem mass spectrometry was used to determine plasma concentrations of the dicarbonyl compounds MGO, glyoxal (GO), and 3-deoxyglucosone (3-DG) and free and protein-bound AGEs. Gene expression of glyoxalase 1 (GLO1), the enzyme involved in the degradation of MGO, was determined by either microarray or quantitative reverse transcriptase-polymerase chain reaction.

Results

The treatment effect (Δtreatment - Δplacebo) of quercetin on MGO was -40.2 nmol/L (95% CI: -73.6, -6.8 nmol/L; P = 0.019), a decrease of 11% from baseline values, whereas GO, 3-DG, and free and protein-bound AGEs did not change significantly. Epicatechin did not affect the concentrations of dicarbonyls and free and protein-bound AGEs. We did not find a significant change in expression of GLO1.

Conclusions

In apparently healthy (pre)hypertensive men and women, quercetin but not epicatechin decreased plasma MGO concentrations. Quercetin may potentially form a new treatment strategy for diseases in which MGO plays a pivotal role. This study was registered at clinicaltrials.gov as NCT01691404.

Food and Drug Interactions

Natural foods and vegetal supplements have recently become increasingly popular for their roles in medicine and as staple foods. This has, however, led to the increased risk of interaction between prescribed drugs and the bioactive ingredients contained in these foods. These interactions range from pharmacokinetic interactions (absorption, distribution, metabolism, and excretion influencing blood levels of drugs) to pharmacodynamic interactions (drug effects). In a quantitative respect, these interactions occur mainly during metabolism. In addition to the systemic metabolism that occurs mainly in the liver, recent studies have focused on the metabolism in the gastrointestinal tract endothelium before absorption. Inhibition of metabolism causes an increase in the blood levels of drugs and could have adverse reactions. The food-drug interactions causing increased blood levels of drugs may have beneficial or detrimental therapeutic effects depending on the intensity and predictability of these interactions. It is therefore important to understand the potential interactions between foods and drugs should and the specific outcomes of such interactions.

An update on the role of nutrigenomic modulations in mediating the cardiovascular protective effect of fruit polyphenols

Polyphenols are plant food microconstituents that are widely distributed in the human diet, with fruits and fruit-derived products as one of the main dietary sources. Epidemiological studies have shown an inverse relationship between the intake of different classes of polyphenols and the risk of myocardial infarction or cardiovascular disease (CVD) mortality. These compounds have been associated with the promotion of cardiovascular health as evidenced by clinical studies reporting beneficial effects of polyphenol-rich fruit consumption on intermediate markers of cardiovascular diseases. Additionally, animal and in vitro studies have indicated positive roles of polyphenols in preventing dysfunctions associated with the development of cardiovascular diseases. However, the mechanisms of action underlying their beneficial effects appear complex and are not fully understood. This review aims to provide an update on the nutrigenomic effects of different groups of polyphenols from fruits and especially focuses on their cardiovascular protective effects in cell and animal studies.

At the interface of antioxidant signalling and cellular function: Key polyphenol effects

The hypothesis that dietary (poly)phenols promote well‐being by improving chronic disease‐risk biomarkers, such as endothelial dysfunction, chronic inflammation and plasma uric acid, is the subject of intense current research, involving human interventions studies, animal models and in vitro mechanistic work. The original claim that benefits were due to the direct antioxidant properties of (poly)phenols has been mostly superseded by detailed mechanistic studies on specific molecular targets. Nevertheless, many proposed mechanisms in vivo and in vitro are due to modulation of oxidative processes, often involving binding to specific proteins and effects on cell signalling. We review the molecular mechanisms for 3 actions of (poly)phenols on oxidative processes where there is evidence in vivo from human intervention or animal studies. (1) Effects of (poly) phenols on pathways of chronic inflammation leading to prevention of some of the damaging effects associated with the metabolic syndrome. (2) Interaction of (poly)phenols with endothelial cells and smooth muscle cells, leading to effects on blood pressure and endothelial dysfunction, and consequent reduction in cardiovascular disease risk. (3) The inhibition of xanthine oxidoreductase leading to modulation of intracellular superoxide and plasma uric acid, a risk factor for developing type 2 diabetes.

Common Phenolic Metabolites of Flavonoids, but Not Their Unmetabolized Precursors, Reduce the Secretion of Vascular Cellular Adhesion Molecules by Human Endothelial Cells

BACKGROUND

Flavonoids have been implicated in the prevention of cardiovascular disease; however, their mechanisms of action have yet to be elucidated, possibly because most previous in vitro studies have used supraphysiological concentrations of unmetabolized flavonoids, overlooking their more bioavailable phenolic metabolites.

OBJECTIVE

We aimed to explore the effects of phenolic metabolites and their precursor flavonoids at physiologically achievable concentrations, in isolation and combination, on soluble vascular cellular adhesion molecule-1 (sVCAM-1).

METHOD

Fourteen phenolic acid metabolites and 6 flavonoids were screened at 1 μM for their relative effects on sVCAM-1 secretion by human umbilical vein endothelial cells stimulated with tumor necrosis factor alpha (TNF-α). The active metabolites were further studied for their response at different concentrations (0.01 μM-100 μM), structure-activity relationships, and effect on vascular cellular adhesion molecule (VCAM)-1 mRNA expression. In addition, the additive activity of the metabolites and flavonoids was investigated by screening 25 unique mixtures at cumulative equimolar concentrations of 1 μM.

RESULTS

Of the 20 compounds screened at 1 μM, inhibition of sVCAM-1 secretion was elicited by 4 phenolic metabolites, of which protocatechuic acid (PCA) was the most active (-17.2%, P = 0.05). Investigations into their responses at different concentrations showed that PCA significantly reduced sVCAM-1 15.2-36.5% between 1 and 100 μM, protocatechuic acid-3-sulfate and isovanillic acid reduced sVCAM-1 levels 12.2-54.7% between 10 and 100 μM, and protocatechuic acid-4-sulfate and isovanillic acid-3-glucuronide reduced sVCAM-1 secretion 27.6% and 42.8%, respectively, only at 100 μM. PCA demonstrated the strongest protein response and was therefore explored for its effect on VCAM-1 mRNA, where 78.4% inhibition was observed only after treatment with 100 μM PCA. Mixtures of the metabolites showed no activity toward sVCAM-1, suggesting no additive activity at 1 μM.

CONCLUSIONS

The present findings suggest that metabolism of flavonoids increases their vascular efficacy, resulting in a diversity of structures of varying bioactivity in human endothelial cells.

Natural products-friends or foes?

A trend in the general population has been observed in recent years regarding the orientation toward preventive measures in health; in this context the increased interest from the users and researchers concerning the active effect of food supplements on the health state and on longevity, is noticeable. All over the world, the consumption of natural foods and of vegetal supplements has increased spectacularly over the last 5-10 years. The decreased prevalence of cardio-vascular diseases associated with Mediterranean diet, as well as the French paradox convinced researchers to scientifically document the beneficial outcomes pointed out by traditional use of plants, and to try to develop supplements that would have the same positive effects as these noticed for diet components. The intense research dedicated to this topic revealed the fact that food supplements are linked to some problematic aspects, such as toxicological side effects when associated with classical synthetic drugs. The food supplement-drug interactions are submitted to complex issues regarding pharmacokinetic interactions leading to changes in absorption, distribution, metabolism and excretion processes with direct impact on effect and toxicological potential. The present review based on recent literature aims at discussing the food-drug interactions with direct impact on efficacy and toxicity of drugs.

MK571 inhibits phase-2 conjugation of flavonols by Caco-2/TC7 cells, but does not specifically inhibit their apical efflux

MK571 is a multidrug resistance protein-2 (ABCC2, Mrp2) inhibitor and has been widely used to demonstrate the role of Mrp2 in the cellular efflux of drugs, xenobiotics and their conjugates. Numerous reports have described modulation of Caco-2 cellular efflux and transport of flavonoids in the presence of MK571. Since flavonoids are efficiently conjugated by Caco-2/TC7 cells, we investigated the effects of MK571 on the efflux of flavonoid conjugates. The flavonol aglycones kaempferol, quercetin and galangin were efficiently taken up, conjugated and effluxed by Caco-2/TC7 cells. Apically-applied MK571 caused significant reductions in both the apical and basolateral efflux of flavonol conjugates from Caco-2/TC7 monolayers. MK571 did not significantly alter the apical:basolateral efflux ratio for flavonol conjugates, however, which is not consistent with MK571 specifically inhibiting only apical Mrp2. Since MK571 decreased the total amounts of conjugates formed, and increased cellular flavonol aglycone concentrations, we explored the possibility that MK571 also inhibits phase-2 conjugation of flavonols. MK571 dose-dependently inhibited the intracellular biosynthesis of all flavonol glucuronides and sulphates by Caco-2 cells. MK571 significantly inhibited phase-2 conjugation of kaempferol by cell-free extracts of Caco-2, and production of kaempferol-4′-O-glucuronide was competitively inhibited. These data show that MK571, in addition to inhibiting MRP2, is a potential inhibitor of enterocyte phase-2 conjugation.

Unravelling of the health effects of polyphenols is a complex puzzle complicated by metabolism

Plant metabolism creates complex mixtures of polyphenols in plant foods. Epidemiology and human trials reduced this complexity, by studying specific foods; subclasses of polyphenols; individual polyphenols, or total antioxidant capacity (TAC). This implies the following assumptions: (1) a limited number of potent polyphenols exists; (2) well-defined natural potent mixtures of polyphenols exist; (3) polyphenols share a common biological activity (e.g. antioxidant activity). To find potent polyphenols (1st assumption), in vitro screening has been widely applied, but most published results are of limited use because metabolism, changing biological activity profoundly, has frequently not been considered. The abundant anecdotal evidence for natural potent mixtures of polyphenols (2nd assumption) on the internet is very hard to verify. Additionally, cross-cultural studies have revealed the potency of e.g. cocoa. Polyphenols share the antioxidant phenolic group which inspired researchers to measure their antioxidant activity, thus greatly reducing complexity (3rd assumption). Unfortunately, the elegant antioxidant hypothesis has to be rejected, because poor absorption and extensive metabolism annihilate any contribution to the endogenous body antioxidants. In conclusion, the above assumptions are hard to verify, and no quick answers are to be expected. Future research should focus on structure-activity relations at nanomolar levels and explore metabolomics.

Human metabolic transformation of quercetin blocks its capacity to decrease endothelial nitric oxide synthase (eNOS) expression and endothelin-1 secretion by human endothelial cells

The major dietary flavonol quercetin, which has been shown to improve endothelial function and decrease blood pressure, is extensively metabolized during absorption. This study examined the relative abilities of quercetin and its human metabolites to modulate the expression of eNOS and ET-1, which are involved in regulating endothelial homeostasis. Quercetin aglycone significantly reduced both eNOS protein and gene expression in HUVEC, mirroring the effects of the pro-inflammatory cytokine TNFα. In the presence of TNFα the aglycone caused further reductions in eNOS, whereas the metabolites were without effect in either TNFα-stimulated or unstimulated cells. ET-1 expression was significantly reduced by quercetin in both TNFα-stimulated or unstimulated HUVECs. The metabolites had no effect on ET-1 expression with the exception of quercetin-3'-sulfate, which caused a moderate increase in TNFα-stimulated cells. These results suggest that metabolic transformation of quercetin prevents it from causing a potentially deleterious decrease in eNOS in endothelial cells.

Dietary (poly)phenolics in human health: structures, bioavailability, and evidence of protective effects against chronic diseases

Human intervention trials have provided evidence for protective effects of various (poly)phenol-rich foods against chronic disease, including cardiovascular disease, neurodegeneration, and cancer. While there are considerable data suggesting benefits of (poly)phenol intake, conclusions regarding their preventive potential remain unresolved due to several limitations in existing studies. Bioactivity investigations using cell lines have made an extensive use of both (poly)phenolic aglycones and sugar conjugates, these being the typical forms that exist in planta, at concentrations in the low-μM-to-mM range. However, after ingestion, dietary (poly)phenolics appear in the circulatory system not as the parent compounds, but as phase II metabolites, and their presence in plasma after dietary intake rarely exceeds nM concentrations. Substantial quantities of both the parent compounds and their metabolites pass to the colon where they are degraded by the action of the local microbiota, giving rise principally to small phenolic acid and aromatic catabolites that are absorbed into the circulatory system. This comprehensive review describes the different groups of compounds that have been reported to be involved in human nutrition, their fate in the body as they pass through the gastrointestinal tract and are absorbed into the circulatory system, the evidence of their impact on human chronic diseases, and the possible mechanisms of action through which (poly)phenol metabolites and catabolites may exert these protective actions. It is concluded that better performed in vivo intervention and in vitro mechanistic studies are needed to fully understand how these molecules interact with human physiological and pathological processes.

Membranar effects exerted in vitro by polyphenols - quercetin, epigallocatechin gallate and curcumin - on HUVEC and Jurkat cells, relevant for diabetes mellitus

Polyphenols are largely studied for their beneficial action in various pathologies, but the correlation with their effects on cell membranes is still elusive. In the present study we assessed the effects exerted in vitro by quercetin, epigallocatechin gallate and curcumin on membrane fluidity and transmembrane potential of human umbilical vein endothelial cells and Jurkat T lymphoblasts, in experimental conditions mimicking diabetes mellitus, i.e. high glucose conditions or increased concentration of advanced glycation end products. Results showed that the investigated polyphenols had beneficial effects on cell membranes altered in diabetic conditions, by restoring transmembrane potential and by membrane "stiffening". Moreover, they limited the release of pro-inflammatory factors, like monocyte chemotactic protein-1. These effects were more obvious for cells exposed to advanced glycation end products specific for the late stages of diabetes. Apparently, the inhibitory action of polyphenols on lipid peroxidation was associated with a decrease of membrane fluidity. Concluding, our in vitro study highlighted the potential beneficial action of polyphenols mainly in the late stages of diabetes, exerted at the level of membrane fluidity and transmembrane potential, accompanied by an anti-inflammatory effect on endothelial and immune cells.

Ellagitannin metabolites, urolithin A glucuronide and its aglycone urolithin A, ameliorate TNF-α-induced inflammation and associated molecular markers in human aortic endothelial cells

SCOPE

Numerous in vitro and in vivo studies indicate that ellagitannins exhibit anti-inflammatory, anti-atherosclerotic and anti-angiogenic activity which support their potential preventive effect against cardiovascular diseases. Ellagitannins exhibit low bioavailability and are transformed in the gut to ellagic acid and its microbiota metabolites urolithin A (Uro-A) and urolithin B (Uro-B). Urolithins are found in plasma mostly as glucuronides at low μM concentrations. We investigated whether urolithin glucuronides and their aglycones exhibit vascular protective effects.

METHODS AND RESULTS

Human aortic endothelial cells were exposed to tumor necrosis factor alpha and to Uro-A glucuronide, Uro-B glucuronide or their corresponding aglycones at low μM concentrations to determine their effects on monocytes adhesion and endothelial cell migration. The levels of related adhesion cytokines and growth molecular markers were also measured. Uro-A glucuronide (∼5-15 μM) inhibited monocyte adhesion and endothelial cell migration in a significant manner. These effects were associated with a moderate but significant down-regulation of the levels of chemokine (C-C motif) ligand 2 (CCL2) and plasminogen activator inhibitor-1 (PAI-1). Uro-A inhibited endothelial cell migration and was able to decrease the expression of CCL2 and interleukin-8 (IL-8).

CONCLUSION

Our results suggest that these metabolites might be involved, at least in part, in the beneficial effects against cardiovascular diseases attributed to the consumption of ellagitannin-containing foods.

Quercetin and epigallocatechin gallate induce in vitro a dose-dependent stiffening and hyperpolarizing effect on the cell membrane of human mononuclear blood cells

The bioactivity of polyphenols is closely linked to their ability to interact with biological membranes. The study evaluates the in vitro effect of quercetin and epigallocatechin on the membrane anisotropy and transmembrane potential of peripheral blood mononuclear cells (PBMCs) isolated from 26 type 2 diabetes mellitus patients compared to 25 age matched controls. The in vitro assays were analyzed in correlation with the biochemical and inflammatory profile of the subjects and with insulin resistance parameters (HOMA-IR, plasma resistin) as well. For type 2 diabetes patients, the increase of HOMA-IR and resistin concentration was associated with a significant decrease of the PBMCs membrane anisotropy. The two tested polyphenols induced a dose-dependent hyperpolarizing effect and stiffening of the cell membranes for all tested subjects. Physiological levels of quercetin and epigallocatechin gallate had the tendency to normalize the PBMCs membrane anisotropy of the cells isolated from diabetes patients, bringing it to the level of cells isolated from normoglycemic ones. Epigallocatechin gallate induced higher effects compared to quercetin on the membranes isolated from subjects with higher cardiovascular risk. The decrease of membrane fluidity and the hyperpolarizing effect could explain the cardiovascular protective action of the tested compounds.

Flavonols and cardiovascular disease

Flavonols, and specially quercetin, are widely distributed in plants and are present in considerable amounts in fruits and vegetables. In addition to their anti-oxidant effect, flavonols interfere with a large number of biochemical signaling pathways and, therefore, physiological and pathological processes. There is solid evidence that, in vitro, quercetin and related flavonols exert endothelium-independent vasodilator effects, protective effect on nitric oxide and endothelial function under conditions of oxidative stress, platelet antiaggregant effects, inhibition of LDL oxidation, reduction of adhesion molecules and other inflammatory markers and prevention of neuronal oxidative and inflammatory damage. The metabolites of quercetin show partial protective effects on endothelial function and LDL oxidation. Quercetin produces undisputed antihypertensive and antiatherogenic effects, prevents endothelial dysfunction and protects the myocardium from ischemic damage. It has no clear effects on serum lipid profile and on insulin resistance. Human intervention trials with isolated flavonols demonstrate an antihypertensive effect. The meta-analysis of epidemiological studies show an inverse association between flavonol (together with flavone) intake and coronary heart disease and stroke. Therefore, although there is no solid proof yet, a substantial body of evidence suggests that quercetin may prevent the most common forms of cardiovascular disease contributing to the protective effects afforded by fruits and vegetables.

Polyphenols and aging

Age-associated changes within an individual are inherently complex and occur at multiple levels of organismal function. The overall decline in function of various tissues is known to play a key role in both aging and the complex etiology of certain age-associated diseases such as Alzheimer's disease (AD) and cancer. Continuing research highlights the dynamic capacity of polyphenols to protect against age-associated disorders through a variety of important mechanisms. Numerous lines of evidence suggest that dietary polyphenols such as resveratrol, (-)-epigallocatechin-3-gallate (EGCG), and curcumin have the capacity to mitigate age-associated cellular damage induced via metabolic production of reactive oxygen species (ROS). However, recently acquired evidence also demonstrates a likely role for these polyphenols as anticancer agents capable of preventing formation of new vasculature in neoplastic tissues. Polyphenols have also been shown to possess other anticancer properties such as specific cell-signaling actions that may stimulate the activity of the regulatory protein SIRT1. Additionally, polyphenolic compounds have demonstrated their inhibitory effects against chronic vascular inflammation associated with atherosclerosis. These increasingly well-documented results have begun to provide a basis for considering the use of polyphenols in the development of novel therapies for certain human diseases. And while the mechanisms by which these effects occur are yet to be fully understood, it is evident that further investigation may yield a potential use for polyphenols as pharmacological interventions against specific age-associated diseases.

Effect of quercetin and its metabolites isorhamnetin and quercetin-3-glucuronide on inflammatory gene expression: role of miR-155

In the present study the effect of quercetin and its major metabolites quercetin-3-glucuronide (Q3G) and isorhamnetin on inflammatory gene expression was determined in murine RAW264.7 macrophages stimulated with lipopolysaccharide. Quercetin and isorhamnetin but not Q3G significantly decreased mRNA and protein levels of tumor necrosis factor alpha. Furthermore a significant decrease in mRNA levels of interleukin 1β, interleukin 6, macrophage inflammatory protein 1α and inducible nitric oxide synthase was evident in response to the quercetin treatment. However Q3G did not affect inflammatory gene expression. Anti-inflammatory properties of quercetin and isorhamnetin were accompanied by an increase in heme oxygenase 1 protein levels, a downstream target of the transcription factor Nrf2, known to antagonize chronic inflammation. Furthermore, proinflammatory microRNA-155 was down-regulated by quercetin and isorhamnetin but not by Q3G. Finally, anti-inflammatory properties of quercetin were confirmed in vivo in mice fed quercetin-enriched diets (0.1 mg quercetin/g diet) over 6 weeks.

Impact of apolipoprotein E genotype and dietary quercetin on paraoxonase 1 status in apoE3 and apoE4 transgenic mice

OBJECTIVES

The aim of the present study was to determine hepatic paraoxonase 1 (PON1) status in response to apoE genotype and dietary quercetin supplementation in mice.

METHODS AND RESULTS

ApoE3 and apoE4 transgenic mice were fed semi-synthetic diets without (controls) and with quercetin (2 mg/g diet) for 6 weeks. Hepatic mRNA and protein levels of PON1 were significantly lower in apoE4 as compared to apoE3 mice. Feeding quercetin-enriched diets induced hepatic PON1 gene expression with a tendency for greater induction in apoE3 as compared to apoE4 mice. Furthermore, hepatic mRNA and protein levels of beta-glucuronidase and sulfatase, both enzymes centrally involved in the deconjugation of quercetin conjugates, were lower in apoE4 vs. apoE3 mice. PPARgamma (which partly controls PON1 gene expression) mRNA levels were lower in apoE4 vs. apoE3 mice.

CONCLUSION

We provide first evidence that PON1 is differentially regulated in response to apoE genotype.