Effect of plasma metabolites of (+)-catechin and quercetin on monocyte adhesion to human aortic endothelial cells

Structural Similarities and Overlapping Activities among Dihydroflavonol 4-Reductase, Flavanone 4-Reductase, and Anthocyanidin Reductase Offer Metabolic Flexibility in the Flavonoid Pathway

Flavonoids are potent antioxidants that play a role in defense against pathogens, UV-radiation, and the detoxification of reactive oxygen species. Dihydroflavonol 4-reductase (DFR) and flavanone 4-reductase (FNR) reduce dihydroflavonols and flavanones, respectively, using NAD(P)H to produce flavan-(3)-4-(di)ols in flavonoid biosynthesis. Anthocyanidin reductase (ANR) reduces anthocyanidins to flavan-3-ols. In addition to their sequences, the 3D structures of recombinant DFR, FNR and ANR from sorghum and switchgrass showed a high level of similarity. The catalytic mechanism, substrate-specificity and key residues of three reductases were deduced from crystal structures, site-directed mutagenesis, molecular docking, kinetics, and thermodynamic ana-lyses. Although DFR displayed its highest activity against dihydroflavonols, it also showed activity against flavanones and anthocyanidins. It was inhibited by the flavonol quercetin and high concentrations of dihydroflavonols/flavonones. SbFNR1 and SbFNR2 did not show any activity against dihydroflavonols. However, SbFNR1 displayed activity against flavanones and ANR activity against two anthocyanidins, cyanidin and pelargonidin. Therefore, SbFNR1 and SbFNR2 could be specific ANR isozymes without delphinidin activity. Sorghum has high concentrations of 3-deoxyanthocyanidins in vivo, supporting the observed high activity of SbDFR against flavonols. Mining of expression data indicated substantial induction of these three reductase genes in both switchgrass and sorghum in response to biotic stress. Key signature sequences for proper DFR/ANR classification are proposed and could form the basis for future metabolic engineering of flavonoid metabolism.

Revisiting the Oxidation of Flavonoids: Loss, Conservation or Enhancement of Their Antioxidant Properties

Flavonoids display a broad range of health-promoting bioactivities. Among these, their capacity to act as antioxidants has remained most prominent. The canonical reactive oxygen species (ROS)-scavenging mode of the antioxidant action of flavonoids relies on the high susceptibility of their phenolic moieties to undergo oxidation. As a consequence, upon reaction with ROS, the antioxidant capacity of flavonoids is severely compromised. Other phenol-compromising reactions, such as those involved in the biotransformation of flavonoids, can also markedly affect their antioxidant properties. In recent years, however, increasing evidence has indicated that, at least for some flavonoids, the oxidation of such residues can in fact markedly enhance their original antioxidant properties. In such apparent paradoxical cases, the antioxidant activity arises from the pro-oxidant and/or electrophilic character of some of their oxidation-derived metabolites and is exerted by activating the Nrf2–Keap1 pathway, which upregulates the cell’s endogenous antioxidant capacity, and/or, by preventing the activation of the pro-oxidant and pro-inflammatory NF-κB pathway. This review focuses on the effects that the oxidative and/or non-oxidative modification of the phenolic groups of flavonoids may have on the ability of the resulting metabolites to promote direct and/or indirect antioxidant actions. Considering the case of a metabolite resulting from the oxidation of quercetin, we offer a comprehensive description of the evidence that increasingly supports the concept that, in the case of certain flavonoids, the oxidation of phenolics emerges as a mechanism that markedly amplifies their original antioxidant properties. An overlooked topic of great phytomedicine potential is thus unraveled.

Contribution of Biotransformations Carried Out by the Microbiota, Drug-Metabolizing Enzymes, and Transport Proteins to the Biological Activities of Phytochemicals Found in the Diet

The consumption of dietary phytochemicals has been associated with several health benefits and relevant biological activities. It is postulated that biotransformations of these compounds regulated by the microbiota, Phase I/II reactions, transport proteins, and deconjugating enzymes contribute not only to their metabolic clearance but also, in some cases, to their bioactivation. A number of factors (age, genetics, sex, physiopathological conditions, and the interplay with other dietary phytochemicals) modulating metabolic activities are important sources and contributors to the interindividual variability observed in clinical studies evaluating the biological activities of phytochemicals. In this review, we discuss all the processes that can affect the bioaccessibility and beneficial effects of these bioactive compounds. Herein, we argue that the role of these factors must be further studied to correctly understand and predict the effects observed following the intake of phytochemicals. This is, in particular, with regard to in vitro investigations, which have shown great inconsistency with preclinical and clinical studies. The complexity of in vivo metabolic activity and biotransformation should therefore be considered in the interpretation of results in vitro and their translation to human physiopathology.

Flavocoxid Ameliorates Aortic Calcification Induced by Hypervitaminosis D3 and Nicotine in Rats Via Targeting TNF-α, IL-1β, iNOS, and Osteogenic Runx2

PURPOSE

This research was designed to investigate the effects and mechanisms of flavocoxid (FCX) on vascular calcification (VC) in rats.

METHODS

Vitamin D₃ and nicotine were administered to Wistar rats, which then received FCX (VC-FCX group) or its vehicle (VC group) for 4 weeks. Control and FCX groups served as controls. Systolic (SBP) and diastolic (DBP) blood pressures, heart rate (HR), and left ventricular weight (LVW)/BW were measured. Serum concentrations of calcium, phosphate, creatinine, uric acid, and alkaline phosphatase were determined. Moreover, aortic calcium content and aortic expression of runt-related transcription factor (Runx2), osteopontin (OPN), Il-1β, α-smooth muscle actin (α-SMA), matrix metalloproteinase-9 (MMP-9), inducible nitric oxide synthase (iNOS), and tumor necrosis factor-α (TNF-α) were assessed. Oxidative status in aortic homogenates was investigated.

RESULTS

Compared to untreated VC rats, FCX treatment prevented body weight loss, reduced aortic calcium deposition, restored normal values of SBP, DBP, and HR, and attenuated LV hypertrophy. FCX also improved renal function and ameliorated serum levels of phosphorus, calcium, and ALP in rats with VC. FCX abolished aortic lipid peroxidation in VC rats. Moreover, VC-FCX rats showed marked reductions in aortic levels of Il-1β and osteogenic marker (Runx2) and attenuated aortic expression of TNF-α, iNOS, and MMP-9 proteins compared to untreated VC rats. The expression of the smooth muscle lineage marker α-SMA was greatly enhanced in aortas from VC rats upon FCX treatment.

CONCLUSION

These findings demonstrate FCX ability to attenuate VDN-induced aortic calcinosis in rats, suggesting its potential for preventing arteiocalcinosis in diabetic patients and those with chronic kidney disease.

Microbiota metabolites modulate the T helper 17 to regulatory T cell (Th17/Treg) imbalance promoting resilience to stress-induced anxiety- and depressive-like behaviors

Chronic stress disrupts immune homeostasis while gut microbiota-derived metabolites attenuate inflammation, thus promoting resilience to stress-induced immune and behavioral abnormalities. There are both peripheral and brain region-specific maladaptations of the immune response to chronic stress that produce interrelated mechanistic considerations required for the design of novel therapeutic strategies for prevention of stress-induced psychological impairment. This study shows that a combination of probiotics and polyphenol-rich prebiotics, a synbiotic, attenuates the chronic-stress induced inflammatory responses in the ileum and the prefrontal cortex promoting resilience to the consequent depressive- and anxiety-like behaviors in male mice. Pharmacokinetic studies revealed that this effect may be attributed to specific synbiotic-produced metabolites including 4-hydroxyphenylpropionic, 4-hydroxyphenylacetic acid and caffeic acid. Using a model of chronic unpredictable stress, behavioral abnormalities were associated to strong immune cell activation and recruitment in the ileum while inflammasome pathways were implicated in the prefrontal cortex and hippocampus. Chronic stress also upregulated the ratio of activated proinflammatory T helper 17 (Th17) to regulatory T cells (Treg) in the liver and ileum and it was predicted with ingenuity pathway analysis that the aryl hydrocarbon receptor (AHR) could be driving the synbiotic's effect on the ileum's inflammatory response to stress. Synbiotic treatment indiscriminately attenuated the stress-induced immune and behavioral aberrations in both the ileum and the brain while in a gut-immune co-culture model, the synbiotic-specific metabolites promoted anti-inflammatory activity through the AHR. Overall, this study characterizes a novel synbiotic treatment for chronic-stress induced behavioral impairments while defining a putative mechanism of gut-microbiota host interaction for modulating the peripheral and brain immune systems.

The effect of quercetin on endothelial cells is modified by heterocellular interactions

Single cell-type models are useful for determining mechanisms, but in vivo, cell-cell interactions are important, and neighbouring cells can impact endothelial cell function. Quercetin can attenuate endothelial dysfunction by modulating vascular tone and reducing inflammation. We determined the effect of quercetin on a co-culture between Human Umbilical Vein Endothelial Cells (HUVEC) and human HepG2 hepatic cells or human LHCN-M2 muscle cells. Heme oxygenase-1 (HO-1) mRNA and protein were decreased, pyruvate dehydrogenase kinase (PDK) 4 and glucose transporter (GLUT) 3 mRNA increased, and GLUT1 protein decreased in HUVEC when cultured with HepG2. GLUT transporters, but not the other targets, were similarly regulated in co-culture with muscle cells. Some but not all of the effects were mediated by lactate and transforming growth factor β1. Quercetin added apically to the endothelial cells upregulated HO-1 and downregulated PDK4 both in monoculture and in co-culture, but the total PDK4 levels were higher in the presence of HepG2 cells. In the absence of general permeability changes, glucose transport across the endothelial monolayer was elevated in the presence of HepG2 cells, however this effect was moderated by quercetin applied on the apical side of the endothelial cells. At lower glucose concentration, apical quercetin also promoted glucose uptake in HepG2 cells. Co-culturing HUVEC with the HepG2 cells showed capacity to modulate quercetin-elicited changes in endothelial gene transcription and glucose transport.

Characterising absorption and health-related properties of phytochemicals extracted from Malaysian palm fruit biomass after oil extraction

After oil extraction, palm fruit biomass contains abundant water-soluble phytochemicals (PCs) with proven bioactivity in regulating oxidative stress and inflammation (OSI).

Simultaneous determination of major components of Huangqi-Honghua extract in rat plasma using LC-MS/MS and application to a pharmacokinetic study

A sensitive and reliable LC-MS/MS method was developed and validated for simultaneous quantification of the major components of Huangqi-Honghua extact in rat plasma, including hydroxysafflor yellow A (HSYA), astragaloside IV (ASIV), calycosin-7-O-β-d-glucoside (CAG), calycosin, calycosin-3'-O-glucuronide (C-3'-G) and calycosin-3'-O-sulfate (C-3'-S). After extraction by protein precipitation with acetonitrile and methanol from plasma, the analytes were separated on a Hypersil BDS C₁₈ column by gradient elution with acetonitrile and 5 mM ammonium acetate. The detection was carried out on a triple quadrupole tandem mass spectrometer equipped with electrospray ionization source switched between negative and positive modes. HSYA was monitored in negative ionization mode from 0 to 4.9 min, and ASIV, CAG, calycosin, C-3'-G and C-3'-S were determined in positive ionization mode from 4.9 to 10 min. The lower limits of quantification of the analytes were 6.25 ng/mL for HSYA, 0.781 ng/mL for CAG and 1.56 ng/mL for ASIV and calycosin. The intra- and inter-assay precision (RSD) values were within 13.43%, and accuracy (RE) ranged from -8.75 to 9.92%. The validated method was then applied to the pharmacokinetic study of HSYA, ASIV, CAG, calycosin, C-3'-G and C-3'-S in rat after an oral administration of Huangqi-Honghua extract.

Nutritional Relevance of Flavonoids in Disease Prevention

Flavonoids are not essential nutrients in that their absence from the diet does not produce deficiency conditions in animals and man. However, many have important similarities to pharmacological agents used in the treatment of disease. Their role as dietary components in disease prevention is less clear. Many potentially anti-carcinogenic and anti-atherogenic effects observed in cell cultures will not be of nutritional relevance unless flavonoids gain access to appropriate cellular sites. The bioavailability of flavonoids will depend on numerous factors including molecular structure, the amount consumed, the food matrix, degree of bioconversion in the gut and tissues, the nutrient status of the host and genetic factors. Moreover, extensive and rapid intestinal and hepatic metabolism of flavonoids suggests that the body may treat them as xenobiotic and potentially toxic compounds requiring rapid elimination. Consequently, in addition to potential health benefits, possible adverse effects of flavonoids in the diet also need to be considered when assessing their roles in the prevention of degenerative diseases.

Kolaviron and selenium reduce hydrogen peroxide-induced alterations of the inflammatory response

The abilities of kolaviron and selenium (either separately or in combination) to prevent hydrogen peroxide-induced alterations in cell viability and activation were investigated. The cell line U937 was incubated with the antioxidants (i.e. kolaviron or selenium) for 24 h before exposure to hydrogen peroxide and cell viability was assessed via trypan blue dye exclusion assay. The U937 cells were also transformed to the macrophage form, incubated with the antioxidants before exposure to hydrogen peroxide. Subsequently, production of nitric oxide and pro-inflammatory cytokines were assessed as indices of macrophage activation. The myoblast cell line H9c2 was also incubated with Se and kolaviron for 24 h before exposure to hydrogen peroxide. Cell viability and generation of reactive oxygen species (ROS) were assessed via MTT and DCHF assays. The results revealed that hydrogen peroxide significantly reduced (p < 0.05) the viability of U937 cells which was ameliorated by kolaviron and selenium. Kolaviron and selenium also reduced hydrogen peroxide-induced secretion of nitric oxide, TNF-α, IL-1 and IL-6 by transformed U937 cells. Hydrogen peroxide also significantly reduced (p < 0.05) the viability of H9c2 cells which was significantly restored by kolaviron. Though selenium had no effect on the proliferation of H9c2 cells, co-treatment with kolaviron significantly reduced hydrogen peroxide-induced alterations. Both kolaviron and selenium also reduced hydrogen peroxide-mediated ROS production by H9c2 cells. In all cases, the combined action of kolaviron and selenium offered greater amelioration of the hydrogen peroxide-induced alterations than their separate effects (p < 0.05) but may not be synergistic or additive.

Signatures of anthocyanin metabolites identified in humans inhibit biomarkers of vascular inflammation in human endothelial cells

SCOPE

The physiological relevance of contemporary cell culture studies is often perplexing, given the use of unmetabolized phytochemicals at supraphysiological concentrations. We investigated the activity of physiologically relevant anthocyanin metabolite signatures, derived from a previous pharmacokinetics study of 500 mg 13 C5 -cyanidin-3-glucoside in eight healthy participants, on soluble vascular adhesion molecule-1 (VCAM-1) and interleukin-6 (IL-6) in human endothelial cells.

METHODS AND RESULTS

Signatures of peak metabolites (previously identified at 1, 6, and 24 h post-bolus) were reproduced using pure standards and effects were investigated across concentrations ten-fold lower and higher than observed mean (<5 μM) serum levels. Tumor necrosis factor-α (TNF-α)-stimulated VCAM-1 was reduced in response to all treatments, with maximal effects observed for the 6 and 24 h profiles. Profiles tested at ten-fold below mean serum concentrations (0.19-0.44 μM) remained active. IL-6 was reduced in response to 1, 6, and 24 h profiles, with maximal effects observed for 6 h and 24 h profiles at concentrations above 2 μM. Protein responses were reflected by reductions in VCAM-1 and IL-6 mRNA, however there was no effect on phosphorylated NFκB-p65 expression.

CONCLUSION

Signatures of anthocyanin metabolites following dietary consumption reduce VCAM-1 and IL-6 production, providing evidence of physiologically relevant biological activity.

5-(3',4'-Dihydroxyphenyl-γ-valerolactone), a Major Microbial Metabolite of Proanthocyanidin, Attenuates THP-1 Monocyte-Endothelial Adhesion

Several metabolomics of polymeric flavan-3-ols have reported that proanthocyanidins are extensively metabolized by gut microbiota. 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone (DHPV) has been reported to be the major microbial metabolite of proanthocyanidins. We demonstrated that DHPV has stronger prevention effect on tumor necrosis factor (TNF)-α-stimulated adhesion of THP-1 human monocytic cells to human umbilical vein endothelial cells compared to its potential precursors such as procyanidin A1, A2, B1 and B2, (+)catechin, (−)epicatechin and its microbial metabolites such as 3-(3,4-dihydroxyphenyl)propionic acid and 2-(3,4-dihydroxyphenyl)acetic acid. Mechanism study showed that DHPV prevents THP-1 monocyte-endothelial cell adhesion by downregulating TNF-α-stimulated expressions of the two biomarkers of atherosclerosis such as vascular cell adhesion molecule-1 and monocyte chemotactic protein-1, activation of nuclear factor kappa B transcription and phosphorylation of I kappa-B kinase and IκBα. We suggested that DHPV has higher potentiality in prevention of atherosclerosis among the proanthocyanidin metabolites.

Physicochemical properties of dietary phytochemicals can predict their passive absorption in the human small intestine

A diet high in phytochemical-rich plant foods is associated with reducing the risk of chronic diseases such as cardiovascular and neurodegenerative diseases, obesity, diabetes and cancer. Oxidative stress and inflammation (OSI) is the common component underlying these chronic diseases. Whilst the positive health effects of phytochemicals and their metabolites have been demonstrated to regulate OSI, the timing and absorption for best effect is not well understood. We developed a model to predict the time to achieve maximal plasma concentration (Tmax) of phytochemicals in fruits and vegetables. We used a training dataset containing 67 dietary phytochemicals from 31 clinical studies to develop the model and validated the model using three independent datasets comprising a total of 108 dietary phytochemicals and 98 pharmaceutical compounds. The developed model based on dietary intake forms and the physicochemical properties lipophilicity and molecular mass accurately predicts Tmax of dietary phytochemicals and pharmaceutical compounds over a broad range of chemical classes. This is the first direct model to predict Tmax of dietary phytochemicals in the human body. The model informs the clinical dosing frequency for optimising uptake and sustained presence of dietary phytochemicals in circulation, to maximise their bio-efficacy for positively affect human health and managing OSI in chronic diseases.

(+)-Catechin prevents methylglyoxal-induced mitochondrial dysfunction and apoptosis in EA.hy926 cells

OBJECTIVE

To investigate whether (+)-catechin, a strong antioxidant, can prevent methylglyoxal (MGO)-induced cytotoxicity and its mechanism.

METHODS

Cytotoxicity, apoptosis, reactive oxygen species (ROS) generation, hydrogen peroxide (H₂O₂) formation, mitochondrial membrane potential (MMP) and mitochondrial morphology were measured in EA.hy926 cells.

RESULT

MGO (4 mM)-induced cytotoxicity was markedly inhibited by (+)-catechin (0.1-4 mM) in 24 h. 1 mM MGO-induced apoptotic cell death (44.7%) was significantly inhibited by 4 mM (+)-catechin (to 24.4%), 1 mM aminoguanidine (AG) (to 28.8%) or 4 mM N-acetylcysteine (NAC) (to 24.3%). (+)-Catechin (4 mM) or AG (4 mM) can inhibit the decrease of MMP induced by MGO (2-8 mM) in 3 h. (+)-Catechin (4 mM) or AG (4 mM) can inhibit MGO (4 mM)-induced mitochondrial swelling in 3 h. However, MGO (4 mM)-induced ROS and H₂O₂ generation was not prevented by (+)-catechin (4 mM).

CONCLUSIONS

(+)-Catechin prevents MGO-induced cytotoxicity in EA.Hy926 cells through inhibiting apoptosis and mitochondrial damage.

Review: Health Effects of Cocoa Flavonoids

Flavonoids are phenolic substances widely found in fruits and vegetables. Many epidemiological studies associate the ingestion of flavonoids with a reduced risk of cardiovascular disease and certain types of cancer. These effects are due to the physiological activity of flavonoids in the reduction of oxidative stress, inhibiting low-density lipoproteins (LDL) oxidation and platelet aggregation, acting as vasodilators in blood vessels, inhibiting the adherence of monocytes to the vascular endothelium, promoting fibrinolysis, acting as immunomodulators and anti-inflammatory agents and as inhibitors in the different phases of tumour process. Cocoa is an important source of polyphenols, which comprise 12-18% of its total weight on dry basis; the major phenolic compounds are epicatechin, proanthocyanidins and cate-chin. The levels of flavonoids contained are higher than the ones founds in apples, onions or wine, foods known for their high amount of phenolic compounds. Cocoa and cocoa products are important sources of flavonoids in our diet. In the Dutch population chocolate contributes up to 20% of the total flavonoid intake in adults, and in children the percentage is even higher. The bioavailability of these compounds depends on other food constituents, and their interaction with the food matrix. This article reviews current evidence on the health effects of cocoa flavonoids in our diet. The compiled data supports the premise that the consumption of cocoa flavonoids is beneficial to human health.

Quercetin attenuates atherosclerotic inflammation and adhesion molecule expression by modulating TLR-NF-κB signaling pathway

Adhesion molecules expressed by activated endothelial cells play key role in regulating leukocyte trafficking to sites of inflammation. The present study attempted to explore whether the polyphenolic flavonoid quercetin influence leukocyte endothelial attraction and the involvement of TLR-NF-κB signaling pathway in the expression of adhesion molecules involved in the early development of atherosclerosis. Quercetin at 25μM concentration significantly reduced the HUVEC expression of VCAM-1 and ICAM-1 evidently enhanced by oxLDL. In addition, quercetin significantly downregulated the mRNA expression of MCP-1 and alleviated the nuclear translocation of NF-κB p65 subunit in oxLDL induced HUVECs. Western blot and PCR analyses revealed that quercetin significantly attenuated the expression of both protein and mRNA expression of TLR2 and TLR4. Quercetin supplementation significantly decreased the inflammatory mediators like COX, 5-LOX, MPO, NOS, CRP and the mRNA expression of the cytokine; IL-6 in hypercholesterolemic diet (HCD) fed atherosclerotic rats. The results demonstrate that quercetin is effective to regulate the atherosclerotic inflammatory process by inhibiting oxLDL induced endothelial leukocyte adhesion by attenuating the TLR-NF-κB signaling pathway in endothelial cells and decrease the inflammatory process induced by HCD in rats. Therefore, quercetin acts as anti-inflammatory and anti-atherogenic agent, which may have implications for strategies attenuating endothelial dysfunction-related atherosclerosis.

Antibacterial structure-activity relationship studies of several tricyclic sulfur-containing flavonoids

A structure–activity relationship study concerning the antibacterial properties of several halogen-substituted tricyclic sulfur-containing flavonoids has been performed. The compounds have been synthesized by cyclocondensation of the corresponding 3-dithiocarbamic flavanones under acidic conditions. The influence of different halogen substituents on the antibacterial properties has been tested against Staphylococcus aureus and Escherichia coli. Amongst the N,N-dialkylamino-substituted flavonoids, those having an N,N-diethylamino moiety exhibited good to excellent antimicrobial properties against both pathogens. Fluorine-substituted flavonoids were found to be less active than those bearing other halogen atoms.

Effect of quercetin and its metabolite on caveolin-1 expression induced by oxidized LDL and lysophosphatidylcholine in endothelial cells

Oxidized low-density lipoprotein contributes to atherosclerotic plaque formation, and quercetin is expected to exert anti-atherosclerotic effects. We previously reported accumulation of conjugated quercetin metabolites in the aorta of rabbits fed high-cholesterol diets with quercetin glucosides, resulting in attenuation of lipid peroxidation and inhibition of lipid accumulation. Caveolin-1, a major structural protein of caveolae in vascular endothelial cells, plays a role in atherosclerosis development. Here we investigated effects of oxidized low-density lipoprotein, quercetin and its metabolite, quercetin 3-O-β-glucuronide, on caveolin-1 expression. Oxidized low-density lipoprotein significantly upregulated caveolin-1 mRNA expression. An oxidized low-density lipoprotein component, lysophosphatidylcholine, also induced expression of both caveolin-1 mRNA and protein. However, lysophosphatidylcholine did not affect the location of caveolin-1 proteins within caveolae structures. Co-treatment with quercetin or quercetin 3-O-β-glucuronide inhibited lysophosphatidylcholine-induced caveolin-1 expression. Quercetin and quercetin 3-O-β-glucuronide also suppressed expression of adhesion molecules induced by oxidized low-density lipoprotein and lysophosphatidylcholine. These results strongly suggest lysophosphatidylcholine derived from oxidized low-density lipoprotein contributes to atherosclerotic events by upregulating caveolin-1 expression, resulting in induction of adhesion molecules. Quercetin metabolites are likely to exert an anti-atherosclerotic effect by attenuating caveolin-1 expression in endothelial cells.

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.

Hydroxytyrosol and tyrosol sulfate metabolites protect against the oxidized cholesterol pro-oxidant effect in Caco-2 human enterocyte-like cells

Hydroxytyrosol and tyrosol sulfate metabolites counteract the oxidizing action of oxidized cholesterol in Caco-2 cells with an efficiency comparable to that of the parent compounds.

The relationship between phenolic compounds from diet and microbiota: impact on human health

The human intestinal tract is home to a complex microbial community called microbiota.

Bioactivity of phenolic acids: metabolites versus parent compounds: a review

Phenolic acids are present in our diet in different foods, for example mushrooms. Due to their bioactive properties, phenolic acids are extensively studied and there is evidence of their role in disease prevention. Nevertheless, in vivo, these compounds are metabolized and circulate in the organism as glucuronated, sulphated and methylated metabolites, displaying higher or lower bioactivities. To clarify the importance of the metabolism of phenolic acids, knowledge about the bioactivity of metabolites is extremely important. In this review, chemical features, biosynthesis and bioavailability of phenolic acids are discussed, as well as the chemical and enzymatic synthesis of their metabolites. Finally, metabolite bioactive properties are compared with that of the corresponding parental compounds.

The effect of green tea on blood pressure and lipid profile: a systematic review and meta-analysis of randomized clinical trials

INTRODUCTION

Many different dietary supplements are currently marketed for the management of hypertension, but the evidence for effectiveness is mixed. The aim of this systematic review was to evaluate the evidence for or against the effectiveness of green tea (Camellia sinensis) on blood pressure and lipid parameters.

METHODS AND RESULTS

Electronic searches were conducted in Medline, Embase, Amed, Cinahl and the Cochrane Library to identify relevant human randomized clinical trials (RCTs). Hand searches of bibliographies were also conducted. The reporting quality of included studies was assessed using a checklist adapted from the CONSORT Statement. Two reviewers independently determined eligibility, assessed the reporting quality of the included studies, and extracted the data. As many as 474 citations were identified and 20 RCTs comprising 1536 participants were included. There were variations in the designs of the RCTs. A meta-analysis revealed a significant reduction in systolic blood pressure favouring green tea (MD: -1.94 mmHg; 95% CI: -2.95 to -0.93; I(2) = 8%; p = 0.0002). Similar results were also observed for total cholesterol (MD: -0.13 mmol/l; 95% CI: -0.2 to -0.07; I(2) = 8%; p < 0.0001) and LDL cholesterol (MD: -0.19 mmol/l; 95% CI: -0.3 to -0.09; I(2) = 70%; p = 0.0004). Adverse events included rash, elevated blood pressure, and abdominal discomfort.

CONCLUSION

Green tea intake results in significant reductions in systolic blood pressure, total cholesterol, and LDL cholesterol. The effect size on systolic blood pressure is small, but the effects on total and LDL cholesterol appear moderate. Longer-term independent clinical trials evaluating the effects of green tea are warranted.

Effects of selected bioactive natural products on the vascular endothelium

The endothelium, a highly active structure, regulates vascular homeostasis through the release of numerous vasoactive factors that control vascular tone and vascular smooth cell proliferation. A larger number of medicinal plants and their isolated chemical constituents have been shown to beneficially affect the endothelium. For example, flavonoids in black tea, green tea, and concord grape cause a vasodilation possibly through their antioxidant properties. Allicin, a by-product of the enzyme alliinase, has been proposed to be the main active metabolite and responsible for most of the biological activities of garlic, including a dose-dependent dilation on the isolated coronaries. Thymoquinone, the principal phytochemical compound found in the volatile oil of the black seed, and the hawthorn extract have also been shown to improve aging-related impairment of endothelium-dependent relaxations in animal models. In this review, the effect of some of the natural products, including Camellia sinensis (black tea and green tea), Vitis labrusca (concord grape), Allium sativum (garlic), and Nigella sativa (black seed) and Crataegus ssp (hawthorn extract), is explored. The molecular mechanisms behind these potential therapeutic effects are also discussed.

Flavanol metabolites reduce monocyte adhesion to endothelial cells through modulation of expression of genes via p38-MAPK and p65-Nf-kB pathways

SCOPE

Consumption of flavanol-rich foods is associated with an improvement in endothelial function. However, the specific biologically active flavanol metabolites involved in this benefit, as well as their molecular mechanisms of action have not been identified. The aim of this work was to examine the effect of plasma flavanol metabolites on adhesion of monocytes to TNF-α-activated endothelial cells and identify potential underlying mechanisms.

METHODS AND RESULTS

4'-O-methyl(-)-epicatechin, 4'-O-methyl(-)-epicatechin-7-β-d-glucuronide, and (-)-epicatechin-4'-sulfate decreased the adhesion of monocytes to endothelial cells at physiologically relevant concentrations, from 0.2 to 1 μM. Transcriptomic studies showed that each of the flavanol metabolites affected the expression of different genes in endothelial cells. However, these genes are involved in the cellular processes that control adhesion and migration of monocytes to vascular endothelium, most notably those regulating cell adhesion, cell-cell junctions, focal adhesion, and cytoskeleton remodeling. Gene expression profiles obtained suggest lower monocyte recruitment, in agreement with results from cell adhesion assays. The nutrigenomic effect of metabolites seems to be mediated through their capacity to modulate phosphorylation of p65 and p38 cell-signaling proteins.

CONCLUSION

Our study provides findings into the molecular mechanisms by which plasma flavanol metabolites could be efficient to preserve vascular endothelium integrity in nutritionally relevant conditions.

Inhibitive effects of mulberry leaf-related extracts on cell adhesion and inflammatory response in human aortic endothelial cells

Effects of mulberry leaf-related extracts (MLREs) on hydrogen peroxide-induced DNA damage in human lymphocytes and on inflammatory signaling pathways in human aortic endothelial cells (HAECs) were studied. The tested MLREs were rich in flavonols, especially bombyx faces tea (BT) in quercetin and kaempferol. Polyphenols, flavonoids, and anthocyanidin also abounded in BT. The best trolox equivalent antioxidant capacity (TEAC) was generated from the acidic methanolic extracts of BT. Acidic methanolic and water extracts of mulberry leaf tea (MT), mulberry leaf (M), and BT significantly inhibited DNA oxidative damage to lymphocytes based on the comet assay as compared to the H2O2-treated group. TNF- α -induced monocyte-endothelial cell adhesion was significantly suppressed by MLREs. Additionally, nuclear factor kappa B (NF- κ B) expression was significantly reduced by BT and MT. Significant reductions were also observed in both NF- κ B and activator protein (AP)-1 DNA binding by MLREs. Significant increases in peroxisome proliferator-activated receptor (PPAR) α and γ DNA binding by MLREs were also detected in M and MT extracts, but no evidence for PPAR α DNA binding in 50  μ g/mL MT extract was found. Apparently, MLREs can provide distinct cytoprotective mechanisms that may contribute to its putative beneficial effects on suppressing endothelial responses to cytokines during inflammation.

Chlorophyll-related compounds inhibit cell adhesion and inflammation in human aortic cells

The objectives of this study were to investigate the effects of chlorophyll-related compounds (CRCs) and chlorophyll (Chl) a+b on inflammation in human aortic endothelial cells. Adhesion molecule expression and interleukin (IL)-8, nuclear factor (NF)-κB p65 protein, and NF-κB and activator protein (AP)-1 DNA binding were assessed. The effects of CRCs on inflammatory signaling pathways of signal transducers and activators of transcription 3 (STAT3) and mothers against decapentaplegic homolog 4, respectively induced by IL-6 and transforming growth factor (TGF)-β, in human aortic smooth muscle cells cultured in vitro were also investigated. HAECs were pretreated with 10 μM of CRCs, Chl a+b, and aspirin (Asp) for 18 h followed by tumor necrosis factor (TNF)-α (2 ng/mL) for 6 h, and U937 cell adhesion was determined. TNF-α-induced monocyte-endothelial cell adhesion was significantly inhibited by CRCs. Moreover, CRCs and Chl a+b significantly attenuated vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and IL-8 expressions. Treatments also significantly decreased in NF-κB expression, DNA binding, and AP-1 DNA binding by CRCs and Asp. Thus, CRCs exert anti-inflammatory effects through modulation of NF-κB and AP-1 signaling. Ten micromoles of CRCs and Asp upregulated the expression of mothers against decapentaplegic homolog 4 (Drosophila) (SMAD4) in the TGF-β receptor signaling pathway, and SMAD3/4 transcription activity was also increased. Ten micromoles of CRCs were able to potently inhibit STAT3-binding activity by repressing IL-6-induced STAT3 expression. Our results provide a potential mechanism that explains the anti-inflammatory activities of these CRCs.

Inhibitive effect of purple sweet potato leaf extract and its components on cell adhesion and inflammatory response in human aortic endothelial cells

This study investigated the effects of purple sweet potato leaf extract (PSPLE) and its components, cyanidin and quercetin, on human aortic endothelial cells (HAECs) during the inflammatory process. HAECs were pretreated with 100 μg/mL PSPLE or 10 μM quercetin, cyanidin or aspirin for 18 h followed by TNF-α (2 ng/mL) for 6 h, and U937 cell adhesion was determined. Adhesion molecule expression and CD40 were evaluated; NFκB p65 protein localization and DNA binding were assessed. PSPLE, aspirin, cyanidin and quercetin significantly inhibited TNF-α-induced monocyte-endothelial cell adhesion (p < 0.05). Cyanidin, quercetin and PSPLE also significantly attenuated VCAM-1, IL-8 and CD40 expression, and quercetin significantly attenuated ICAM-1 and E-selectin expression (p < 0.05). Significant reductions in NFκB expression and DNA binding by aspirin, cyanidin and quercetin were also observed in addition to decreased expression of ERK1, ERK2 and p38 MAPK (p < 0.05). Thus, PSPLE and its components, cyanidin and quercetin, have anti-inflammatory effects through modulation of NFκB and MAPK signaling. Further in vivo studies are necessary to explore the possible therapeutic effects of PSPLE on atherosclerosis.

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.

Effects of tea and coffee on cardiovascular disease risk

Tea and coffee have been associated with risk of cardiovascular disease (CVD), both positively and negatively. Epidemiological data suggest that black and green tea may reduce the risk of both coronary heart disease and stroke by between 10 and 20%. Experimental and clinical trial data generally indicate either neutral or beneficial effects on risk factors and pathways linked to the development of CVD. Controversy still exists regarding the effects of coffee, where there have been concerns regarding associations with hypercholesterolaemia, hypertension and myocardial infarction. However, long term moderate intake of coffee is not associated with detrimental effects in healthy individuals and may even protect against the risk of developing type 2 diabetes. The detrimental effects of coffee may be associated with the acute pressor effects, most likely due to caffeine at high daily intakes, and lipids from boiled coffee can contribute to raised serum cholesterol. Genetic polymorphisms in enzymes involved in uptake, metabolism and excretion of tea and coffee compounds are also associated with differential biological effects. Potential mechanisms by which tea and coffee phytochemicals can exert effects for CVD protection include the regulation of vascular tone through effects on endothelial function, improved glucose metabolism, increased reverse cholesterol transport and inhibition of foam cell formation, inhibition of oxidative stress, immunomodulation and effects on platelet function (adhesion and activation, aggregation and clotting). The phytochemical compounds in tea and coffee and their metabolites are suggested to influence protective endogenous pathways by modulation of gene-expression. It is not known exactly which compounds are responsible for the suggestive protective effects of tea and coffee. Although many biologically active compounds have been identified with known biological effects, tea and coffee contain many unidentified compounds with potential bioactivity.

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.

Bioavailability of wine-derived phenolic compounds in humans: a review

Phenolic compounds are produced in the seeds and skins of grapes, and are transferred into wine during the fermentation process. Phenolic compounds can also be imparted into wine from maturation and storage in oak wood barrels after fermentation. The consumption of wine, an alcoholic beverage, has been observed in epidemiological studies to reduce the risk of cardiovascular disease and certain cancers, as well as diabetes and dementia, in a J-shaped relationship between amount consumed and level of risk. The bioactivity of wine primarily observed in vitro and ex vivo, may result from wine's relatively high content of phenolic compounds, which is similar to that observed in fruits and vegetables; a Mediterranean fruit and vegetable rich-diet is also associated with a reduced risk of cardiovascular disease and cancers. If the wine-derived phenolic compounds or their active metabolites are not absorbed in sufficient amounts and in a readily available form for cells, however, then they are less likely to have any significant in vivo activity. This review considers and discusses the available data to date on the bioavailability of the different wine-derived phenolic compounds in humans.

Metabolism-based synthesis, biologic evaluation and SARs analysis of O-methylated analogs of quercetin as thrombin inhibitors

In blood, quercetin is mainly found in metabolized forms. In order to study the activities of these quercetin metabolites in cardiovascular disease, 17 methylquercetin derivatives were synthesized based on metabolism in vivo, their thrombin inhibition activity were evaluated through the analyzation of prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT) and fibrinogen (FIB). The results showed that 6 methylquercetin derivatives had stronger inhibitory activities than that of quercetin. Preliminary SARs analysis showed that hydroxyl groups at C-3' and C-4' position in the B-ring and hydroxyl group at C-3 position in the C-ring played key roles in the thrombin inhibitory activity. The findings of this study would provide information for the exploitation and utilization of quercetin as thrombin inhibitor for thrombotic disease treatment.

Synthesis of Glycosides of Glucuronic, Galacturonic and Mannuronic Acids: An Overview

Uronic acids are carbohydrates present in relevant biologically active compounds. Most of the latter are glycosides or oligosaccharides linked by their anomeric carbon, so their synthesis requires glycoside-bond formation. The activation of this anomeric center remains difficult due to the presence of the electron-withdrawing C-5 carboxylic group. Herein we present an overview of glucuronidation, mannuronidation and galacturonidation reactions, including syntheses of prodrugs, oligosaccharides and stereochemical aspects.

The bioactive agent ergothioneine, a key component of dietary mushrooms, inhibits monocyte binding to endothelial cells characteristic of early cardiovascular disease

Regular consumption of fruits and vegetables is strongly associated with a reduced risk of cardiovascular disease (CVD). This effect occurs, in part, because of the plethora of bioactive agents in foods and their subsequent function as antioxidants. Ergothioneine (ERT), a novel antioxidant, is present in edible mushrooms and is not synthesized, but is accumulated, by humans through diet. In this study, we tested whether ERT, a bioactive agent, could interrupt pro-inflammatory induction of adhesion molecule expression associated with atherogenesis. Human aortic endothelial cells (HAECs) were incubated with increasing concentrations of ERT (0.01-10.0 mM) overnight (16 hours) followed by incubation with medium alone or with the pro-inflammatory cytokine interleukin (IL)-1β (5 ng/mL) for 6 hours to induce expression of vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and endothelial-leukocyte adhesion molecule (ELAM-1 or E-selectin). ERT at 0.1-0.3 mM significantly (P < .05) reduced VCAM-1, ICAM-1, and E-selectin expression up to 41%. VCAM-1 was suppressed to the greatest extent followed by E-selectin and then ICAM-1. We next tested if binding of preloaded U937 human monocytes to HAECs would be inhibited. U937 binding to HAECs was significantly reduced in IL-1β-stimulated HAECs preincubated with 1 and 3 mM ERT. Unstimulated monolayers demonstrated marginal, but significant, reductions. ERT was not toxic to HAECs at any concentration used. These data provide evidence that ERT found in commonly consumed dietary mushrooms can protect against events observed in atherogenesis, suggesting increased dietary intake of edible mushrooms would be a prudent medicinal means of reducing CVD risk.