Pure dietary flavonoids quercetin and (-)-epicatechin augment nitric oxide products and reduce endothelin-1 acutely in healthy men

Epicatechin: endothelial function and blood pressure

Epidemiological studies indicate an inverse relationship between flavanol intake and the risk of cardiovascular disease. Potential mechanisms include their effects on endothelial function and hypertension. A number of studies have shown that flavanol-rich cocoa reduces blood pressure and endothelial dysfunction, whereas black tea may have opposite effects. These results highlight the importance of the different effects of the multitude of phytochemical constituents in these foods and the need for studying the individual flavanols. Epicatechin seems to be a major bioactive constituent of cocoa and other flavanol-rich foods and beverages. It has been shown to improve endothelial function in animals and humans. In salt-sensitive animal models of hypertension, epicatechin lowers blood pressure and the associated end-organ damage. Nitric oxide (NO) seems to play a key role in the protection of both hypertension and endothelial dysfunction.

Acute, quercetin-induced reductions in blood pressure in hypertensive individuals are not secondary to lower plasma angiotensin-converting enzyme activity or endothelin-1: nitric oxide

Quercetin (Q) reduces blood pressure (BP) in hypertensive individuals, but the mechanism is unknown. We hypothesized that acute Q aglycone administration reduces BP in hypertensive men by decreasing angiotensin-converting enzyme (ACE) activity and/or by lowering the ratio of circulating endothelin-1 (ET-1) to nitric oxide and that these alterations will improve endothelial function. Using a double-blind, placebo-controlled, crossover design Q or placebo (P) was administered to normotensive men (n = 5; 24 ± 3 years; 24 ± 4 kg/m(2)) and stage 1 hypertensive men (n = 12; 41 ± 12 years; 29 ± 5 kg/m(2)). As anticipated, ingesting 1095 mg Q did not affect BP in normotensive men but resulted in maximal plasma Q (2.3 ± 1.8 μmol/L) at approximately 10 hours, with Q returning to baseline concentrations (0.4 ± 0.08 μmol/L) by approximately 17 hours. Results from this study provided rationale for determining end-points of interest in stage 1 hypertensive men 10 hours after ingesting Q or P. In stage 1 hypertensive individuals, plasma Q increased(0.6 ± 0.4 vs. 0.05 ± 0.02 μmol/L), and mean BP decreased (103 ± 7 vs 108 ± 7 mm Hg; both P < .05) 10 hours after Q vs P, respectively. Plasma ACE activity (16 ± 10 vs 18 ± 10 U/L), ET-1 (1.6 ± 0.9 vs 1.6 ± 0.8 pg/ml), nitrites (57.0 ± 3.0 vs 56.7 ± 2.6 μmol/L), and brachial artery flow-mediated dilation (6.2 ± 2.9 vs. 6.3 ± 3.2%) were unaffected by Q. A single dose of Q aglycone reduces BP in hypertensive men through a mechanism that is independent of changes in ACE activity, ET-1, or nitric oxide bioavailability and without affecting vascular reactivity.

Effect of cocoa on blood pressure

BACKGROUND

High blood pressure is an important risk factor for cardiovascular disease attributing to about 50% of cardiovascular events worldwide and 37% of cardiovascular related deaths in Western populations. Epidemiological studies suggest that cocoa rich products reduce the risk of cardiovascular disease. Flavanols found in cocoa have been shown to increase the formation of endothelial nitric oxide which promotes vasodilation and therefore blood pressure reduction. Previous meta-analyses have shown that cocoa-rich foods may reduce blood pressure. Recently additional trials had conflicting results.

OBJECTIVES

To determine the effect of flavanol-rich chocolate or cocoa products on blood pressure in people with or without hypertension.

SEARCH METHODS

We searched the following electronic databases from inception to November 2011: Cochrane Hypertension Group Specialised Register, CENTRAL, MEDLINE and EMBASE. In addition we searched international trial registries, and the reference lists of review articles and included trials.

SELECTION CRITERIA

Randomised controlled trials (RCT) investigating the effects of chocolate or cocoa products on systolic and diastolic blood pressure in adults for a minimum of two weeks duration.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data and assessed the risk of bias in each trial in consultation with a third author. Random effects meta-analyses on all studies fitting the inclusion criteria were conducted using Review Manager version 5.1 and Stata version 12. Heterogeneity was explored by subgroup analyses and univariate meta-regression analysis of several variables including dosage of flavanol content (total or monomers) in chocolate or cocoa products, blinding, baseline blood pressure, theobromine content, sugar content, body-mass-index (BMI), duration and age.

MAIN RESULTS

Twenty studies met the inclusion criteria. Meta-analyses of the 20 studies involving 856 mainly healthy participants revealed a statistically significant blood pressure reducing effect of flavanol-rich cocoa products compared with control in short-term trials of 2-18 weeks duration: Mean difference SBP (95%CI): -2.77 (-4.72, -0.82) mm Hg, p=0.005, n=20; mean difference DBP (95%CI): - 2.20 (-3.46, -0.93) mm Hg, p=0.006, n=19 available for DBP.Trials provided participants with 30-1080 mg of flavanols (mean=545.5 mg) in 3.6-105 g of cocoa products per day in the active intervention group. In half of the trials (n=10) the active group consumed 500-750 mg of flavanols per day. The control group received either a flavanol-free product (n=12) or a low-flavanol containing cocoa powder (6.4 and 41 mg flavanols, n=8). Subgroup meta-analysis of trials with a flavanol-free control group revealed a significant blood pressure reducing effect, in contrast to trials using a low-flavanol product in the control group. This analysis may have been confounded by trial duration and the level of blinding of participants.Trial duration was short (mean 4.4 weeks, range 2-8 weeks, n=19, and one trial of 18 weeks). A significant blood pressure reducing effect was evident in trials of 2 weeks duration (n=9), but not in trials of >2 weeks duration (n=11). It is important to note that seven out of the nine trials (78%) of 2 weeks duration also had a flavanol-free control group. Therefore, subgroup analysis by duration might be confounded by flavanol dosage used in the control groups, and the level of blinding of participants.Adverse effects including gastrointestinal complaints and distaste of the trial product were reported by 5% of patients in the active cocoa intervention group and 1% of patients in the control groups.

AUTHORS' CONCLUSIONS

Flavanol-rich chocolate and cocoa products may have a small but statistically significant effect in lowering blood pressure by 2-3 mm Hg in the short term.Our findings are limited by the heterogeneity between trials, which was explored by univariate meta-regression and subgroup analyses. Subgroup meta-analysis of trials using a flavanol-free control group revealed a significant blood pressure reducing effect of cocoa, whereas analysis of trials using a low-flavanol control product did not. While it appears that shorter trials of 2 weeks duration were more effective, analysis may be confounded by type of control and unblinding of participants, as the majority of 2-week trials also used a flavanol-free control and unblinding of participants. Results of these and other subgroup analyses based on, for example, age of participants, should be interpreted with caution and need to be confirmed or refuted in trials using direct randomized comparison.Long-term trials investigating the effect of cocoa products are needed to determine whether or not blood pressure is reduced on a chronic basis by daily ingestion of cocoa. Furthermore, long-term trials investigating the effect of cocoa on clinical outcomes are also needed to assess whether cocoa has an effect on cardiovascular events and to assess potential adverse effects associated with chronic ingestion of cocoa products.

Elucidation of (-)-epicatechin metabolites after ingestion of chocolate by healthy humans

After absorption in the gastrointestinal tract, (-)-epicatechin is extensively transformed into various conjugated metabolites. These metabolites, chemically different from the aglycone forms found in foods, are the compounds that reach the circulatory system and the target organs. Therefore, it is imperative to identify and quantify these circulating metabolites to investigate their roles in the biological effects associated with (-)-epicatechin intake. Using authentic synthetic standards of (-)-epicatechin sulfates, glucuronides, and O-methyl sulfates, a novel LC-MS/MS-MRM analytical methodology to quantify (-)-epicatechin metabolites in biological matrices was developed and validated. The optimized method was subsequently applied to the analysis of plasma and urine metabolites after consumption of dark chocolate, an (-)-epicatechin-rich food, by humans. (-)-Epicatechin-3'-β-d-glucuronide (C(max) 290 ± 49 nM), (-)-epicatechin 3'-sulfate (C(max) 233 ± 60 nM), and 3'-O-methyl epicatechin sulfates substituted in the 4', 5, and 7 positions were the most relevant (-)-epicatechin metabolites in plasma. When plasmatic metabolites were divided into their substituent groups, it was revealed that (-)-epicatechin glucuronides, sulfates, and O-methyl sulfates represented 33 ± 4, 28 ± 5, and 33 ± 4% of total metabolites (AUC(0-24)(h)), respectively, after dark chocolate consumption. Similar metabolites were found in urine samples collected over 24h. The total urine excretion of (-)-epicatechin was 20 ± 2% of the amount ingested. In conclusion, we describe the entire metabolite profile and its degree of elimination after administration of (-)-epicatechin-containing food. These results will help us understand more precisely the mechanisms and the main metabolites involved in the beneficial physiological effects of flavanols.

Epicatechin ingested via cocoa products reduces blood pressure in humans: a nonlinear regression model with a Bayesian approach

BACKGROUND

Four meta-analyses of randomized controlled trials (RCTs) based on the classical random-effects model showed that cocoa consumption can reduce systolic blood pressure (SBP) and diastolic blood pressure (DBP). Because epicatechin is suggested to be responsible for the treatment effect, changes in blood pressure should depend on the dose of ingested epicatechin, which may explain the between-study differences.

OBJECTIVE

The objective was to quantify the effect of epicatechin ingested via cocoa products on changes in SBP and DBP.

DESIGN

A nonlinear meta-regression model was chosen to investigate the impact of the epicatechin dose on changes in SBP and DBP. A Bayesian approach using Markov chain Monte Carlo methods was applied for an appropriate treatment of the nonlinearity.

RESULTS

Data from 16 RCTs on SBP and 15 RCTs on DBP were included. The dose of epicatechin ingested via cocoa products influenced the changes in SBP and DBP. The asymptotic limit for the reduction was estimated at -4.6 mm Hg (95% CI: -5.4, -3.9 mm Hg) for SBP and at -2.1 mm Hg (95% CI: -2.7, -1.6 mm Hg) for DBP. An intake of 25 mg epicatechin/d led to a mean reduction of -4.1 mm Hg (95% CI: -4.6, -3.6 mm Hg) in SBP and of -2.0 mm Hg (95% CI: -2.4, -1.5 mm Hg) in DBP.

CONCLUSIONS

Blood pressure reduction by consumption of cocoa products depends on the dose of ingested epicatechin, which explains most of the between-study differences in classical meta-analyses. Similar effects may be achieved by consumption of other foods that are also rich in epicatechin.

Safety evaluation of Evesse EPC, an apple polyphenol extract rich in flavan-3-ols

The safety of the apple polyphenol extract EvesseEPC, which is rich in flavan-3-ols, particularly epicatechin, was evaluated. Both in a bacterial reverse mutation test and a mouse lymphoma assay, EvesseEPC showed a positive response in vitro. In vivo studies (UDS test in hepatocytes, bone marrow micronucleus test and comet assay in intestinal cells) were all negative and hence Evesse EPC is considered not to have genotoxic properties in vivo. In a 90-day study in rats, EvesseEPC was administered at dietary levels of 0%, 1.25%, 2% and 3.25%. Body weights were decreased in the high-dose group in both sexes without effects on feed or water intake. In the high-dose group, thrombocytes (males) and creatinine (both sexes) were decreased, prothrombin time (males) was increased, and liver, kidneys and spleen weights were increased (males), without histological correlates. Diffuse acinar cell hypertrophy, observed in the parotid salivary glands in all treatment groups, was not considered as adverse and presumably reflected a local, reversible and adaptive response to direct contact with EvesseEPC. The NOAEL for EvesseEPC in rats was 2% in the diet, equivalent to an overall average intake of 1.3 and 1.5 g/kg body weight/day for males and females, respectively.

Structurally related (-)-epicatechin metabolites in humans: assessment using de novo chemically synthesized authentic standards

Accumulating data suggest that diets rich in flavanols and procyanidins are beneficial for human health. In this context, there has been a great interest in elucidating the systemic levels and metabolic profiles at which these compounds occur in humans. Although recent progress has been made, there still exist considerable differences and various disagreements with regard to the mammalian metabolites of these compounds, which in turn are largely a consequence of the lack of availability of authentic standards that would allow for the directed development and validation of expedient analytical methodologies. In this study, we developed a method for the analysis of structurally related flavanol metabolites using a wide range of authentic standards. Applying this method in the context of a human dietary intervention study using comprehensively characterized and standardized flavanol- and procyanidin-containing cocoa, we were able to identify the structurally related (-)-epicatechin metabolites (SREM) postprandially extant in the systemic circulation of humans. Our results demonstrate that (-)-epicatechin-3'-β-D-glucuronide, (-)-epicatechin-3'-sulfate, and a 3'-O-methyl-(-)-epicatechin-5/7-sulfate are the predominant SREM in humans and further confirm the relevance of the stereochemical configuration in the context of flavanol metabolism. In addition, we also identified plausible causes for the previously reported discrepancies regarding flavanol metabolism, consisting, to a significant extent, of interlaboratory differences in sample preparation (enzymatic treatment and sample conditioning for HPLC analysis) and detection systems. Thus, these findings may also aid in the establishment of consensus on this topic.

Natural polypill Xuezhikang: its clinical benefit and potential multicomponent synergistic mechanisms of action in cardiovascular disease and other chronic conditions

Polypill has been a hot issue since it was first advanced in 2003. This new concept immediately spurred a worldwide discussion. Xuezhikang is a partially purified extract of fermented red yeast rice (Monascus purpureus). It is composed of 13 kinds of natural statins, unsaturated fatty acids, ergosterol, amino acids, flavonoids, alkaloid, trace element, and other substances, and thus could be regarded as a natural lipid-lowering polypill. Interestingly, Xuezhikang in the China Coronary Secondary Prevention Study trial lowered lipid levels less as compared with provastatin in the Cholesterol and Recurrent Events trial, but seemed to gain more benefit in reducing the cardiovascular events and the risk of death from cancer. In recent years, Xuezhikang has been further demonstrated to have additional health benefits and thus raised great interest. This article reviews the clinical benefits of Xuezhikang and the potential multicomponent synergetic mechanism. The authors hold that polypill is anticipated to be a more effective and feasible way to treat complicated diseases.

Intake of dietary procyanidins does not contribute to the pool of circulating flavanols in humans

BACKGROUND

Accumulating data show a causal role for flavanols in the mediation of cardiovascular benefits associated with the consumption of flavanol- and procyanidin-containing foods. Evidence for a direct causal role for procyanidins in this context is far less profound due to the poor absorption of procyanidins. However, it has been proposed that procyanidins may break down in the gastrointestinal tract, resulting in monomeric flavanols, which contribute to the systemic flavanol pool. Verification or rejection of this supposition could significantly affect the interpretation of epidemiologic and dietary intervention data and the design of food-content databases.

OBJECTIVE

We assessed the respective contribution of flavanols and procyanidins to the systemic pool of flavanols and 5-(3,4-dihydroxyphenyl)-γ-valerolactone (γ-VL) in humans.

DESIGN

Test drinks that contained only flavanols (D1), procyanidins with a degree of polymerization that ranged from 2 to 10 (D2-10), or flavanols and procyanidins with a degree of polymerization that ranged from 2 to 10 (D1-10) were consumed by subjects (n = 12) according to a randomized, double-masked, crossover design. Plasma and urine samples were collected postprandially and analyzed.

RESULTS

The ingestion of D1-10 resulted in the systemic presence of flavanols (plasma concentration: 863 ± 77 nmol/L), γ-VLs (24-h urine: 93 ± 18 μmol), and minute concentrations of procyanidin B2. With correction for small residual amounts of flavanols present in D2-10, only negligible concentrations of circulating flavanols were detected after ingestion of the drink, whereas the intake of D1 resulted in circulating flavanol concentrations similar to those detected after D1-10 consumption.

CONCLUSIONS

These outcomes show that dietary procyanidins do not contribute to the systemic pool of flavanols in humans. Thus, these data reject the notion that procyanidins, through their breakdown into flavanols and subsequent absorption, causally modulate vascular function.

Evidence for a protective effect of polyphenols-containing foods on cardiovascular health: an update for clinicians

Growing evidence suggests that polyphenols could be serious candidates to explain the protective effects of plant-derived foods and beverages. Based on current studies, a general consensus has been achieved to sustain the hypothesis that the specific intake of foods and beverages containing relatively high concentrations of flavonoids may play a meaningful role in reducing cardiovascular disease (CVD) risk through an improvement in vascular function and a modulation of inflammation. This review aims at providing an update on the effects of the consumption of polyphenols-rich foods on intermediate clinical markers of CVD in humans, namely cholesterolemia, blood pressure, endothelial function and platelet function. To date, on the basis of clinical studies, the demonstration is particularly convincing for flavonoids from cocoa-derived products and to a lesser extent for those of tea. While additional studies in this area are clearly needed, incorporating plant foods that are rich in flavanols in the diet of healthy individuals could help to reduce CVD risk. For flavonoids from fruits such as berries, pomegranate, grapes or citrus fruits and those from beverages such as red wine or coffee, the evidence is so far inconclusive. This is primarily due to the limited number and the weakness of experimental designs of the studies performed with these dietary sources. Future long-term well-designed investigations with polyphenols-rich foods but also with isolated phenolic compounds would provide valuable information to establish public health recommendations on polyphenols, taking into account both the nature of the compounds and the optimal dose, for cardiovascular health protection.

Endothelium/nitric oxide mechanism mediates vasorelaxation and counteracts vasoconstriction induced by low concentration of flavanols

PURPOSE

At relatively low concentrations, flavanols induce inconsistent effects on isolated arterial tone, sometimes explained as being due to a structure-activity relationship. The aim of our study was to investigate the effects of two flavanols at different doses on arterial functional state.

METHODS

The effects of two catechins, (-)-epigallocatechin-3-gallate (EGCG) and (-)-epicatechin (EP), on rat-isolated aorta tone were investigated on resting tension and on precontracted preparations, both in the presence and in the absence of endothelium.

RESULTS

At resting tension, endothelium-intact preparations, EGCG and EP (0.01-10 μM), induced a slight concentration-dependent, non-significant contraction. On endothelium-denuded preparations, both EGCG and EP induced a concentration-dependent contraction (significance at 0.1 and 1 μM concentrations of the two compounds, respectively). In phenylephrine (PE) (1 μM) precontracted, endothelium-intact preparations, EGCG and EP (0.01-10 μM), induced a concentration-dependent vasorelaxation, reaching significance at 1 μM concentration of both agonists. On endothelium-denuded preparations, EGCG and EP did not significantly affect PE (0.3 μM)-induced tone. In endothelium-intact precontracted preparations, Nω nitro-L-arginine (L-NNA), a nitric oxide synthase (NOS) activity inhibitor, abolished the vasorelaxant effect of EGCG and EP (0.01-10 μM). At high concentrations, EGCG and EP (100 μM) elicited a marked relaxation. This was significantly larger in the presence than in the absence of endothelium or in the presence of L-NNA.

CONCLUSIONS

Our findings highlight the important role played by an endothelium/NO-mechanism in the regulation of basal tone and in both mediating vasorelaxation and counteracting vasoconstriction induced by low concentrations of flavanols in rat thoracic aorta.

Inorganic nitrate ingestion improves vascular compliance but does not alter flow-mediated dilatation in healthy volunteers

Ingestion of inorganic nitrate elevates blood and tissue levels of nitrite via bioconversion in the entero-salivary circulation. Nitrite is converted to NO in the circulation, and it is this phenomenon that is thought to underlie the beneficial effects of inorganic nitrate in humans. Our previous studies have demonstrated that oral ingestion of inorganic nitrate decreases blood pressure and inhibits the transient endothelial dysfunction caused by ischaemia–reperfusion injury in healthy volunteers. However, whether inorganic nitrate might improve endothelial function per se in the absence of a pathogenic stimulus and whether this might contribute to the blood pressure lowering effects is yet unknown. We conducted a randomised, double-blind, crossover study in 14 healthy volunteers to determine the effects of oral inorganic nitrate (8 mmol KNO₃) vs. placebo (8 mmol KCl) on endothelial function, measured by flow-mediated dilatation (FMD) of the brachial artery, prior to and 3 h following capsule ingestion. In addition, blood pressure (BP) was measured and aortic pulse wave velocity (aPWV) determined. Finally, blood, saliva and urine samples were collected for chemiluminescence analysis of [nitrite] and [nitrate] prior to and 3 h following interventions. Inorganic nitrate supplementation had no effect on endothelial function in healthy volunteers (6.9 ± 1.1% pre- to 7.1 ± 1.1% post-KNO₃). Despite this, there was a significant elevation of plasma [nitrite] (0.4 ± 0.1 μM pre- to 0.7 ± 0.2 μM post-KNO₃, p < 0.001). In addition these changes in [nitrite] were associated with a decrease in systolic BP (116.9 ± 3.8 mm Hg pre- vs. 112.1 ± 3.4 mm Hg post-KNO₃, p < 0.05) and aPWV (6.5 ± 0.1 m/s pre- to 6.2 ± 0.1 post-KNO₃, p < 0.01). In contrast KCl capsules had no effect on any of the parameters measured. These findings demonstrate that although inorganic nitrate ingestion does not alter endothelial function per se, it does appear to improve blood flow, in combination with a reduction in blood pressure. It is likely that these changes are due to the intra-vascular production of NO.

Therapeutic potential of quercetin to decrease blood pressure: review of efficacy and mechanisms

Epidemiological studies beginning in the 1990s have reported that intake of quercetin, a polyphenolic flavonoid found in a wide variety of plant-based foods, such as apples, onions, berries, and red wine, is inversely related to cardiovascular disease. More recent work using hypertensive animals and humans (>140 mm Hg systolic and >90 mm Hg diastolic) indicates a decrease in blood pressure after quercetin supplementation. A number of proposed mechanisms may be responsible for the observed blood pressure decrease such as antioxidant effects, inhibition of angiotensin-converting enzyme activity, and improved endothelium-dependent and -independent function. The majority of these mechanisms have been identified using animal models treated with quercetin, and relatively few have been corroborated in human studies. The purpose of this review is to examine the evidence supporting the role of quercetin as a potential therapeutic agent and the mechanisms by which quercetin might exert its blood pressure-lowering effect.

Flavonoid-rich apples and nitrate-rich spinach augment nitric oxide status and improve endothelial function in healthy men and women: a randomized controlled trial

Flavonoids and nitrates in fruits and vegetables may protect against cardiovascular disease. Dietary flavonoids and nitrates can augment nitric oxide status via distinct pathways, which may improve endothelial function and lower blood pressure. Recent studies suggest that the combination of flavonoids and nitrates can enhance nitric oxide production in the stomach. Their combined effect in the circulation is unclear. Here, our objective was to investigate the independent and additive effects of flavonoid-rich apples and nitrate-rich spinach on nitric oxide status, endothelial function, and blood pressure. A randomized, controlled, crossover trial with healthy men and women (n=30) was conducted. The acute effects of four energy-matched treatments (control, apple, spinach, and apple+spinach), administered in random order, were compared. Measurements included plasma nitric oxide status, assessed by measuring S-nitrosothiols+other nitrosylated species (RXNO) and nitrite, blood pressure, and endothelial function, measured as flow-mediated dilatation of the brachial artery. Results are means and 95% CI. Relative to control, all treatments resulted in higher RXNO (control, 33 nmol/L, 26, 42; apple, 51 nmol/L, 40, 65; spinach, 86 nmol/L, 68, 110; apple+spinach, 69 nmol/L, 54, 88; P<0.01) and higher nitrite (control, 35 nmol/L, 27, 46; apple, 69 nmol/L, 53, 90; spinach, 99 nmol/L, 76, 129; apple+spinach, 80 nmol/L, 61, 104; P<0.01). Compared to control, all treatments resulted in higher flow-mediated dilatation (P<0.05) and lower pulse pressure (P<0.05), and apple and spinach resulted in lower systolic blood pressure (P<0.05). No significant effect was observed on diastolic blood pressure. The combination of apple and spinach did not result in additive effects on nitric oxide status, endothelial function, or blood pressure. In conclusion, flavonoid-rich apples and nitrate-rich spinach can independently augment nitric oxide status, enhance endothelial function, and lower blood pressure acutely, outcomes that may benefit cardiovascular health.

Epicatechin lowers blood pressure, restores endothelial function, and decreases oxidative stress and endothelin-1 and NADPH oxidase activity in DOCA-salt hypertension

Flavanol-rich diets have been reported to exert beneficial effects in preventing cardiovascular diseases, such as hypertension. We studied the effects of chronic treatment with epicatechin on blood pressure, endothelial function, and oxidative status in deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Rats were treated for 5 weeks with (-)-epicatechin at 2 or 10 mg kg(-1)day(-1). The high dose of epicatechin prevented both the increase in systolic blood pressure and the proteinuria induced by DOCA-salt. Plasma endothelin-1 and malondialdehyde levels and urinary iso-prostaglandin F(2α) excretion were increased in animals of the DOCA-salt group and reduced by the epicatechin 10 mg kg(-1) treatment. Aortic superoxide levels were enhanced in the DOCA-salt group and abolished by both doses of epicatechin. However, only epicatechin at 10 mg kg(-1) reduced the rise in aortic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and p47(phox) and p22(phox) gene overexpression found in DOCA-salt animals. Epicatechin increased the transcription of nuclear factor-E2-related factor-2 (Nrf2) and Nrf2 target genes in aortas from control rats. Epicatechin also improved the impaired endothelium-dependent relaxation response to acetylcholine and increased the phosphorylation of both Akt and eNOS in aortic rings. In conclusion, epicatechin prevents hypertension, proteinuria, and vascular dysfunction. Epicatechin also induced a reduction in ET-1 release, systemic and vascular oxidative stress, and inhibition of NADPH oxidase activity.

Cardiovascular effects of flavanol-rich chocolate in patients with heart failure

AIMS

Flavanol-rich chocolate (FRC) is beneficial for vascular and platelet function by increasing nitric oxide bioavailability and decreasing oxidative stress. Congestive heart failure (CHF) is characterized by impaired endothelial and increased platelet reactivity. As statins are ineffective in CHF, alternative therapies are a clinical need. We therefore investigated whether FRC might improve cardiovascular function in patients with CHF.

METHODS AND RESULTS

Twenty patients with CHF were enrolled in a double-blind, randomized placebo-controlled trial, comparing the effect of commercially available FRC with cocoa-liquor-free control chocolate (CC) on endothelial and platelet function in the short term (2 h after ingestion of a chocolate bar) and long term (4 weeks, two chocolate bars/day). Endothelial function was assessed non-invasively by flow-mediated vasodilatation of the brachial artery. Flow-mediated vasodilatation significantly improved from 4.98 ± 1.95 to 5.98 ± 2.32% (P = 0.045 and 0.02 for between-group changes) 2h after intake of FRC to 6.86 ± 1.76% after 4 weeks of daily intake (P = 0.03 and 0.004 for between groups). No effect on endothelial-independent vasodilatation was observed. Platelet adhesion significantly decreased from 3.9 ± 1.3 to 3.0 ± 1.3% (P = 0.03 and 0.05 for between groups) 2 h after FRC, an effect that was not sustained at 2 and 4 weeks. Cocoa-liquor-free CC had no effect, either on endothelial function or on platelet function. Blood pressure and heart rate did not change in either group.

CONCLUSION

Flavanol-rich chocolate acutely improves vascular function in patients with CHF. A sustained effect was seen after daily consumption over a 4-week period, even after 12 h abstinence. These beneficial effects were paralleled by an inhibition of platelet function in the presence of FRC only.

Cocoa and chocolate in human health and disease

Cocoa contains more phenolic antioxidants than most foods. Flavonoids, including catechin, epicatechin, and procyanidins predominate in antioxidant activity. The tricyclic structure of the flavonoids determines antioxidant effects that scavenge reactive oxygen species, chelate Fe2+ and Cu+, inhibit enzymes, and upregulate antioxidant defenses. The epicatechin content of cocoa is primarily responsible for its favorable impact on vascular endothelium via its effect on both acute and chronic upregulation of nitric oxide production. Other cardiovascular effects are mediated through anti-inflammatory effects of cocoa polyphenols, and modulated through the activity of NF-κB. Antioxidant effects of cocoa may directly influence insulin resistance and, in turn, reduce risk for diabetes. Further, cocoa consumption may stimulate changes in redox-sensitive signaling pathways involved in gene expression and the immune response. Cocoa can protect nerves from injury and inflammation, protect the skin from oxidative damage from UV radiation in topical preparations, and have beneficial effects on satiety, cognitive function, and mood. As cocoa is predominantly consumed as energy-dense chocolate, potential detrimental effects of overconsumption exist, including increased risk of weight gain. Overall, research to date suggests that the benefits of moderate cocoa or dark chocolate consumption likely outweigh the risks.

Dietary flavonoids: Role of (-)-epicatechin and related procyanidins in cell signaling

Plant polyphenols are among the most abundant phytochemicals present in human diets. Increasing evidence supports the health-promoting effects of certain polyphenols, including flavonoids. This review discusses current knowledge of the capacity of monomeric flavanols, i.e., (-)-epicatechin and (+)-catechin, and their derived procyanidins to modulate cell signaling and the associations of these actions with better health. Flavanols and procyanidins can regulate cell signaling through different mechanisms of action. Monomers and dimeric procyanidins can be transported inside cells and directly interact and modulate the activity of signaling proteins and/or prevent oxidation. Larger and nonabsorbable procyanidins can regulate cell signaling by interacting with cell membrane proteins and lipids, inducing changes in membrane biophysics, and by modulating oxidant production. All these actions would be limited by the bioavailability of flavanols at the target tissue. The protection from cardiac and vascular disease and from cancer that is associated with a high consumption of fruit and vegetables could be in part explained by the capacity of flavanols and related procyanidins to modulate proinflammatory and oncogenic signals.

Effect of milk and brewing method on black tea catechin bioaccessibility

The aim of this study was to investigate whether milk reduces the bioaccessibility of tea catechins, which would compromise tea beneficial effects ascribed to polyphenols. Adding milk to black tea has been shown to lead to polyphenol-protein complexes. So far, data on the intestinal stability of polyphenol-protein complexes are scarce. English black tea (0.93 ± 0.06 mol/L total catechins) and Indian black tea (1.83 ± 0.08 mol/L catechins) were prepared with skimmed or full-fat milk and subjected to simulated gastric, small intestinal, and brush border digestion. Adding milk (5.6-40%) to tea results in a decrease of total catechin (TCAT) recovery. However, the bioaccessibilities of TCAT of tea with milk versus tea controls were comparable (p > 0.05). The type of milk did not influence TCAT recovery during all digestive stages (p > 0.05). Polyphenol-protein complexes are degraded during digestion. It is very unlikely that consumption of tea with or without milk will result in differences in catechin plasma concentration.

The assessment of vascular function during dietary intervention trials in human subjects

The potential to reduce cardiovascular morbidity through dietary modification remains an area of intense clinical and scientific interest. Any putatively beneficial intervention should be tested within a randomised controlled trial which records appropriate endpoints, ideally incident CVD and death. However, the large sample sizes required for these endpoints and associated high costs mean that the majority of dietary intervention research is conducted over short periods among either healthy volunteers or those at only slightly increased risk, with investigators using a diverse range of surrogate measures to estimate arterial health in these studies. The present review identifies commonly employed techniques, discusses the relative merits of each and highlights emerging approaches.

Health effects of green tea catechins in overweight and obese men: a randomised controlled cross-over trial

Regular consumption of green tea may be cardioprotective. In the present study we investigated the health effects of dietary supplementation with green tea catechins and the potential modifying effect of the catechol-O-methyltransferase (COMT) Val/Met genotype. Subjects (sedentary males, aged 40-69 years, with BMI ≥ 28 and ≤ 38 kg/m(2)) were randomly assigned to consume decaffeinated green tea extract (DGT; 530 mg containing about 400 mg total catechins/capsule, twice daily) and placebo in a complete cross-over design. Ambulatory blood pressure and biomarkers of metabolic function (cholesterol, TAG, glucose and insulin) were measured at weeks 0 and 6. Although a marked increase in the concentration of plasma epigallocatechin gallate (EGCG), urinary epigallocatechin (EGC) and urinary 4'-O-methyl EGC was found after DGT treatment, no effect on blood pressure or biomarkers of metabolic function was observed. However, a period × treatment interaction (P < 0·05) was detected for body-weight change. Despite a similar increase in estimated energy intake during intervention period 1, body weight decreased by 0·64 (sd 2·2) kg and increased by 0·53 (sd 1·9) kg in the DGT and placebo groups, respectively (P = 0·025), suggesting a protective effect of green tea catechins on weight gain. Additionally, the COMT Val/Met genotype influenced urinary accumulation of EGC and 4'-O-methyl EGC (P < 0·01). Mean concentrations were lower in individuals homozygous for the high-activity G-allele, possibly reflecting increased metabolic flux and a more rapid conversion to downstream metabolic species, compared with individuals carrying at least one copy of the low-activity A-allele. Additional studies are needed to confirm these findings and further explore the modifying effect of genotype.

3',4'-Dihydroxyflavonol reduces superoxide and improves nitric oxide function in diabetic rat mesenteric arteries

Background

3',4'-Dihydroxyflavonol (DiOHF) is an effective antioxidant that acutely preserves nitric oxide (NO) activity in the presence of elevated reactive oxygen species (ROS). We hypothesized that DiOHF treatment (7 days, 1 mg/kg per day s.c.) would improve relaxation in mesenteric arteries from diabetic rats where endothelial dysfunction is associated with elevated oxidant stress.

Methodology/Principal Findings

In mesenteric arteries from diabetic rats there was an increase in ROS, measured by L-012 and 2',7'-dichlorodihydrofluorescein diacetate fluorescence. NADPH oxidase-derived superoxide levels, assayed by lucigenin chemiluminescence, were also significantly increased in diabetic mesenteric arteries (diabetes, 4892±946 counts/mg versus normal 2486±344 counts/mg, n = 7–10, p<0.01) associated with an increase in Nox2 expression but DiOHF (2094±300 counts/mg, n = 10, p<0.001) reversed that effect. Acetylcholine (ACh)-induced relaxation of mesenteric arteries was assessed using wire myography (pEC₅₀ = 7.94±0.13 n = 12). Diabetes significantly reduced the sensitivity to ACh and treatment with DiOHF prevented endothelial dysfunction (pEC₅₀, diabetic 6.86±0.12 versus diabetic+DiOHF, 7.49±0.13, n = 11, p<0.01). The contribution of NO versus endothelium-derived hyperpolarizing factor (EDHF) to ACh-induced relaxation was assessed by evaluating responses in the presence of TRAM-34+apamin+iberiotoxin or N-nitro-L-arginine+ODQ respectively. Diabetes impaired the contribution of both NO (maximum relaxation, R_max diabetic 24±7 versus normal, 68±10, n = 9–10, p<0.01) and EDHF (pEC₅₀, diabetic 6.63±0.15 versus normal, 7.14±0.12, n = 10–11, p<0.01) to endothelium-dependent relaxation. DiOHF treatment did not significantly affect the EDHF contribution but enhanced NO-mediated relaxation (R_max 69±6, n = 11, p<0.01). Western blotting demonstrated that diabetes also decreased expression and increased uncoupling of endothelial NO synthase (eNOS). Treatment of the diabetic rats with DiOHF significantly reduced vascular ROS and restored NO-mediated endothelium-dependent relaxation. Treatment of the diabetic rats with DiOHF also increased eNOS expression, both in total and as a dimer.

Conclusions/Significance

DiOHF improves NO activity in diabetes by reducing Nox2-dependent superoxide production and preventing eNOS uncoupling to improve endothelial function.

The biological relevance of direct antioxidant effects of polyphenols for cardiovascular health in humans is not established

Human studies provide evidence for beneficial effects of polyphenol-rich foods on cardiovascular health. The antioxidant activity of polyphenols potentially explains these effects, but is the antioxidant activity a reliable predictor for these effects? An International Life Sciences Institute Europe working group addressed this question and explored the potential of antioxidant claims for polyphenols in relation to cardiovascular health by using the so-called Process for the Assessment of Scientific Support for Claims on Foods project criteria. In this process, analytical aspects of polyphenols, their occurrence in foods, dietary intake, and bioavailability were reviewed. Human studies on polyphenols and cardiovascular health were reviewed together with methods for biomarkers of oxidative damage and total antioxidant capacity (TAC). In retrospective studies, F2-isoprostanes and oxidized LDL, the most reliable biomarkers of lipid peroxidation, and measures for TAC showed the expected differences between cardiovascular disease patients and healthy controls, but prospective studies are lacking, and a causal relationship between these biomarkers and cardiovascular health could not be established. Therefore, the physiological relevance of a potential change in these biomarkers is unclear. We found limited evidence that some types of polyphenol-rich products modify these biomarkers in humans. A direct antioxidant effect of polyphenols in vivo is questionable, however, because concentrations in blood are low compared with other antioxidants and extensive metabolism following ingestion lowers their antioxidant activity. Therefore, the biological relevance of direct antioxidant effects of polyphenols for cardiovascular health could not be established. Overall, although some polyphenol-rich foods exert beneficial effects on some biomarkers of cardiovascular health, there is no evidence that this is caused by improvements in antioxidant function biomarkers (oxidative damage or antioxidant capacity).

Chronic treatment with quercetin does not inhibit angiotensin-converting enzyme in vivo or in vitro

The precise mechanisms explaining the anti-hypertensive effects produced by quercetin are not fully known. Here, we tested the hypothesis that chronic quercetin treatment inhibits the angiotensin-converting enzyme (ACE). We examined whether quercetin treatment for 14 days reduces in vivo responses to angiotensin I or enhances the responses to bradykinin in anaesthetised rats. We measured the changes in systemic arterial pressure induced by angiotensin I in doses of 0.03-10 μg/kg, by angiotensin II in doses of 0.01-3 μg/kg, and to bradykinin in doses of 0.03-10 μg/kg in anaesthetised rats pre-treated with vehicle (controls), or daily quercetin 10 mg/kg intraperitoneally for 14 days, or a single i.v. dose of captopril 2 mg/kg. Plasma ACE activity was determined by a fluorometric method. Plasma quercetin concentrations were assessed by high performance liquid chromatography. Quercetin treatment induced no significant changes in the hypertensive responses to angiotensin I and angiotensin II, as well in the hypotensive responses to bradykinin (all p>0.05). Conversely, as expected, a single dose of captopril inhibited the hypertensive responses to angiotensin I and potentiated the bradykinin responses (all p<0.01), while no change was found in the vascular responses to angiotensin II (all p>0.05). In addition, although we found significant amounts of quercetin in plasma samples (mean=206 ng/mL), no significant differences were found in plasma ACE activity in rats treated with quercetin compared with those found in the control group (50±6 his-leu nmol/min/mL and 40±7 his-leu nmol/min/mL, respectively; p>0.05). These findings provide strong evidence indicating that quercetin does not inhibit ACE in vivo or in vitro and indicate that other mechanisms are probably involved in the antihypertensive and protective cardiovascular effects associated with quercetin.

Tea consumption enhances endothelial-dependent vasodilation; a meta-analysis

Background

Tea consumption is associated with a lower risk of cardiovascular disease including stroke. Direct effects of tea components on the vasculature, particularly the endothelium, may partly explain this association.

Objective

We performed a meta-analysis of controlled human intervention studies on the effect of tea on flow-mediated dilation (FMD) of the brachial artery, a measurement of endothelial function, which is suggested to be associated with cardiovascular risk.

Methods

Human intervention studies were identified by systematic search of the databases Medline, Embase, Chemical Abstracts and Biosis through March 2009 and by hand-searching related articles. Studies were selected based on predefined criteria: intervention with tea as the sole experimental variable, placebo-controlled design, and no missing data on FMD outcome or its variability. A random effects model was used to calculate the pooled overall effect on FMD due to the intake of tea. The impact of various subject and treatment characteristics was investigated in the presence of heterogeneity.

Results

In total, 9 studies from different research groups were included with 15 relevant study arms. The overall absolute increase in FMD of tea vs. placebo was 2.6% of the arterial diameter (95% CI: 1.8-3.3%; P-value <0.001) for a median daily dose of 500 mL of tea (2–3 cups). This is a relative increase of approximately 40% compared to the average FMD of 6.3% measured under placebo or baseline conditions. There was significant heterogeneity between studies (P-value <0.001) that might partly be explained by the cuff position either distal or proximal to the area of FMD measurement. No indication for publication bias was found.

Conclusion

Moderate consumption of tea substantially enhances endothelial-dependent vasodilation. This may provide a mechanistic explanation for the reduced risk of cardiovascular events and stroke observed among tea drinkers.

Direct evidence that (-)-epicatechin increases nitric oxide levels in human endothelial cells

BACKGROUND

The dietary flavanol (-)-epicatechin has been suggested to mediate its vasodilatory effect by increasing nitric oxide levels in endothelial cells.

AIM OF THE STUDY

To directly prove the formation of nitric oxide (NO) in human endothelial cells (HUVEC) in vitro by trapping NO to yield a fluorescent nitrosamine.

METHODS

HUVEC were treated with (-)-epicatechin; nitrite and NO formation were determined by reductive chemiluminescence detection and the NO-sensitive fluorophore 5-methoxy-2-(1H-naphthol[2,3-d]imidazol-2-yl)-phenol copper complex (MNIP-Cu), respectively. MNIP was synthesized in a rapid and convenient one-step microwave reaction. Endothelial nitric oxide synthase (eNOS) mRNA levels and mRNA stability were measured.

RESULTS

Incubation with (-)-epicatechin (0.3-10 μM) led to elevated NO levels in HUVEC measured via reductive chemiluminescence detection and visualized as the fluorescent NO derivative of MNIP. Expression of eNOS mRNA and mRNA stability were not affected by (-)-epicatechin treatment within the time frame studied.

CONCLUSION

(-)-Epicatechin augments the level of NO in endothelial cells, a process suggested to be responsible for the vasodilatory properties of the compound.

Habitual intake of flavonoid subclasses and incident hypertension in adults

BACKGROUND

Dietary flavonoids have beneficial effects on blood pressure in intervention settings, but there is limited information on habitual intake and risk of hypertension in population-based studies.

OBJECTIVE

We examined the association between habitual flavonoid intake and incident hypertension in a prospective study in men and women.

DESIGN

A total of 87,242 women from the Nurses' Health Study (NHS) II, 46,672 women from the NHS I, and 23,043 men from the Health Professionals Follow-Up Study (HPFS) participated in the study. Total flavonoid and subclass intakes were calculated from semiquantitative food-frequency questionnaires collected every 4 y by using an updated and extended US Department of Agriculture database.

RESULTS

During 14 y of follow-up, 29,018 cases of hypertension in women and 5629 cases of hypertension in men were reported. In pooled multivariate-adjusted analyses, participants in the highest quintile of anthocyanin intake (predominantly from blueberries and strawberries) had an 8% reduction in risk of hypertension [relative risk (RR): 0.92; 95% CI: 0.86, 0.98; P < 0.03] compared with that for participants in the lowest quintile of anthocyanin intake; the risk reduction was 12% (RR: 0.88; 95% CI: 0.84, 0.93; P < 0.001) in participants ≤60 y of age and 0.96 (0.91, 1.02) in participants >60 y of age (P for age interaction = 0.02). Although intakes of other subclasses were not associated with hypertension, pooled analyses for individual compounds suggested a 5% (95% CI: 0.91, 0.99; P = 0.005) reduction in risk for the highest compared with the lowest quintiles of intake of the flavone apigenin. In participants ≤60 y of age, a 6% (95% CI: 0.88, 0.97; P = 0.002) reduction in risk was observed for the flavan-3-ol catechin when the highest and the lowest quintiles were compared.

CONCLUSIONS

Anthocyanins and some flavone and flavan-3-ol compounds may contribute to the prevention of hypertension. These vasodilatory properties may result from specific structural similarities (including the B-ring hydroxylation and methyoxylation pattern).

The stereochemical configuration of flavanols influences the level and metabolism of flavanols in humans and their biological activity in vivo

Extensive epidemiological and clinical evidence associates diets high in flavanol-containing foods with cardiovascular health benefits in humans. Catechin and epicatechin, the most common flavanols in foods, are present in the diet in different enantiomeric forms. This study investigated the influence of the stereochemical configuration of flavanols on their absorption, metabolism, and biological activity. Healthy adult males were asked to consume equal amounts of the stereochemically pure flavanols (-)-epicatechin, (-)-catechin, (+)-catechin, and (+)-epicatechin (1.5mg/kg bw) in a well-defined cocoa-based, dairy-containing drink matrix, and flavanol levels were subsequently determined in plasma and 24-h urine. The results obtained show that the stereochemical configuration of flavanols has a profound influence on their uptake and metabolism in humans. In addition, we assessed the vasodilatory activity of each flavanol stereoisomer in vivo and found (-)-epicatechin to be the single stereoisomer capable of mediating a significant arterial dilation response. Importantly, this effect was independent of the classic antioxidant properties of flavanols. Overall, these results indicate that the proposed beneficial health effects associated with the consumption of flavanol-containing foods will significantly depend on the stereochemical configuration of the flavanols ingested.

Anthocyanins in cardiovascular disease

Anthocyanins are a group of abundant and widely consumed flavonoid constituents that occur ubiquitously in the plant kingdom, providing the bright red-orange to blue-violet colors present in many fruit- and vegetable-based food products. Their intake has been estimated to be up to 9-fold higher than that of other dietary flavonoids. Anthocyanins have become increasingly important to the food industry as their use as natural alternatives to artificial colors has become widespread and knowledge of their health-promoting properties has become more evident. Epidemiological studies suggest that increased consumption of anthocyanins lowers the risk of cardiovascular disease (CVD), the most common cause of mortality among men and women. Anthocyanins frequently interact with other phytochemicals, exhibiting synergistic biological effects but making contributions from individual components difficult to decipher. Over the past 2 decades, many peer-reviewed publications have demonstrated that in addition to their noted in vitro antioxidant activity, anthocyanins may regulate different signaling pathways involved in the development of CVD. This review summarizes the latest developments on the bioavailability/bioactivity and CVD preventative activities of anthocyanins, including results from in vitro cell culture and in vivo animal model systems as related to their multiple proposed mechanisms of action. Limited yet promising data from epidemiological studies and human clinical trials are also presented. Future studies aimed at enhancing the absorption of anthocyanins and characterizing their metabolic and/or breakdown products are necessary to ultimately evaluate their use for protection/prevention against the development of CVD.

Hesperidin contributes to the vascular protective effects of orange juice: a randomized crossover study in healthy volunteers

BACKGROUND

Although numerous human studies have shown consistent effects of some polyphenol-rich foods on several intermediate markers for cardiovascular diseases, it is still unknown whether their action could be specifically related to polyphenols.

OBJECTIVE

We investigated the effect of orange juice and its major flavonoid, hesperidin, on microvascular reactivity, blood pressure, and cardiovascular risk biomarkers through both postprandial and chronic intervention studies.

DESIGN

Twenty-four healthy, overweight men (age 50-65 y) were included in a randomized, controlled, crossover study. Throughout the three 4-wk periods, volunteers daily consumed 500 mL orange juice, 500 mL control drink plus hesperidin (CDH), or 500 mL control drink plus placebo (CDP). All measurements and blood collections were performed in overnight-fasted subjects before and after the 4-wk treatment periods. The postprandial study was conducted at the beginning of each experimental period.

RESULTS

Diastolic blood pressure (DBP) was significantly lower after 4 wk consumption of orange juice or CDH than after consumption of CDP (P = 0.02), whereas microvascular endothelium-related reactivity was not significantly affected when measured after an overnight fast. However, both orange juice and CDH ingestion significantly improved postprandial microvascular endothelial reactivity compared with CDP (P < 0.05) when measured at the peak of plasma hesperetin concentration.

CONCLUSIONS

In healthy, middle-aged, moderately overweight men, orange juice decreases DBP when regularly consumed and postprandially increases endothelium-dependent microvascular reactivity. Our study suggests that hesperidin could be causally linked to the beneficial effect of orange juice. This trial is registered at clinicaltrials.gov as NCT00983086.

Cocoa flavanols: effects on vascular nitric oxide and blood pressure

Diets rich in fruits and vegetables have been associated with benefits for human health. Those effects have been partially ascribed to their content in flavonoids, compounds that are present in many edible plants and its derived foods. In humans, a significant number of studies has been developed analyzing the effect of foods and beverages rich in flavonoids on the presence and progression of risk factors associated to cardiovascular diseases, including hypertension. Cocoa derived products, rich in flavanols, have been thoroughly studied and demonstrated to be efficient improving endothelial function and decreasing blood pressure in humans and animals. However, the final chemical species and the mechanism/s responsible for these effects have not been completely defined. In this paper we present data supporting the hypothesis that flavanols could define superoxide anion production and then, establish optimal nitric oxide levels and blood pressure.

Modulation of endogenous antioxidant system by wine polyphenols in human disease

Numerous studies indicate that moderate red wine consumption is associated with a protective effect against all-cause mortality. Since oxidative stress constitutes a unifying mechanism of injury of many types of disease processes, it should be expected that polyphenolic antioxidants account for this beneficial effect. Nevertheless, beyond the well-known antioxidant properties of these compounds, they may exert several other protective mechanisms. Indeed, the overall protective effect of polyphenols is due to their large array of biological actions, such as free radical-scavenging, metal chelation, enzyme modulation, cell signalling pathways modulation and gene expression effects, among others. Wine possesses a variety of polyphenols, being resveratrol its most outstanding representative, due to its pleiotropic biological properties. The presence of ethanol in wine aids to polyphenol absorption, thereby contributing to their bioavailability. Before absorption, polyphenols must be hydrolyzed by intestinal enzymes or by colonic microflora. Then, they undergo intestinal and liver metabolism. There have been no reported polyphenol adverse effects derived from intakes currently associated with the normal diet. However, supplements for health-protection should be cautiously used as no level definition has been given to make sure the dose is safe. The role of oxidative stress and the beneficial effects of wine polyphenols against cardiovascular, cancer, diabetes, microbial, inflammatory, neurodegenerative and kidney diseases and ageing are reviewed. Future large scale randomized clinical trials should be conducted to fully establish the therapeutic use of each individual wine polyphenol against human disease.

The effects of a lupin-enriched diet on oxidative stress and factors influencing vascular function in overweight subjects

A diet enriched in lupin kernel flour can lower blood pressure, but mechanisms responsible are unclear. Lupin is a source of polyphenols, protein, and L-arginine, factors that may influence blood pressure via effects on oxidative stress and vascular function. Therefore, we aimed to determine the effects of a lupin-enriched diet on oxidative stress and factors influencing vascular function as potential mechanisms for demonstrated benefits on blood pressure. Overweight men and women (n = 88) were recruited to a 16-week parallel-design study. Participants were randomly assigned to replace 15%-20% of their usual daily energy intake with white bread (control) or lupin kernel flour-enriched bread (lupin). All measurements were taken at baseline and 16 weeks. At baseline, plasma F₂-isoprostanes and 20-hydroxyeicosatetraenoic acid (20-HETE) were positively associated with blood pressure, and plasma nitrite was negatively associated with blood pressure (p < 0.05). For lupin relative to control, the estimated differences in plasma F₂-isoprostanes (45 pmol/L; 95%CI: -68, 158), urinary F₂-isoprostanes (17 pmol/mmol creatinine; 95%CI: -43, 76), plasma 20-HETE (75 pmol/L; 95%CI: -91, 241), and plasma nitrite (-0.3 μmol/L; 95%CI: -1.1, 0.4) were not significant. Although regular consumption of lupin-enriched bread can lower blood pressure, these results do not support for the hypothesis that this is via effects on oxidative stress or vascular function.

Recommending flavanols and procyanidins for cardiovascular health: current knowledge and future needs

Data on the potential health benefits of dietary flavanols and procyanidins, especially in the context of cardiovascular health, are considerable and continue to accumulate. Significant progress has been made in flavanol analytics and the creation of phytonutrient-content food databases, and novel data emanated from epidemiological investigations as well as dietary intervention studies. However, a comprehensive understanding of the pharmacological properties of flavanols and procyanidins, including their precise mechanisms of action in vivo, and a conclusive, consensus-based accreditation of a causal relationship between intake and health benefits in the context of primary and secondary cardiovascular disease prevention is still outstanding. Thus, the objective of this review is to identify and discuss key questions and gaps that will need to be addressed in order to conclusively demonstrate whether or not dietary flavanols and procyanidins have a role in preventing, delaying the onset of, or treating cardiovascular diseases, and thus improving human life expectancy and quality of life.

Flavanols and cardiovascular disease prevention

Diet is a major lifestyle factor in the primary and secondary prevention of numerous chronic diseases, including myocardial infarction, stroke, and diabetes. Epidemiological studies suggest that the beneficial cardiovascular health effects of diets rich in fruits and vegetables are in part mediated by their flavonoid content, with particular benefits provided by one member of this family, the flavanols. This concept is supported by findings from small-scale intervention studies with surrogate endpoints including endothelium-dependent vasodilation, blood pressure, platelet function, and glucose tolerance. Mechanistically, short-term effects on endothelium-dependent vasodilation following the consumption of flavanol-rich foods, as well as purified flavanols, have been linked to an increased nitric oxide bioactivity in healthy humans, and those with increased cardiovascular risk. The critical biological target(s) for flavanols have yet to be identified and the extent to which these acute results are important in the context of long-term human health is unknown. While flavanols represent a promising class of food components with respect to their ability to lower cardiovascular risk the flavanol-rich foods used in many trials have been poorly defined with respect to their flavanol content and flavanol-isomer profile; several studies have lacked appropriate controls, and the long-term randomized controlled intervention trials with flavanol-rich foods are missing. Thus, while the literature regarding flavanols and vascular health is encouraging, more in-depth and well-controlled clinical and experimental studies are needed to better define the potential protective vascular effects of these nutrients and their therapeutic value in cardiovascular medicine.

Tea flavonoids and cardiovascular health

The two main types of tea are green and black. Both green and black teas are rich dietary sources of flavonoids. Available evidence suggests that regular tea consumption may reduce the risk of cardiovascular disease. The cardiovascular health benefits of drinking tea are thought to be largely due to flavonoids. Tea intake and intake of flavonoids found in tea have been associated with reduced risk of cardiovascular disease in cross-sectional and prospective population studies. Isolated flavonoids found in tea have also been consistently shown to inhibit the development of atherosclerosis in animal models. A number of possible pathways and mechanisms have been investigated. There is now consistent data indicating that tea and tea flavonoids can enhance nitric oxide status and improve endothelial function, which may be at least partly responsible for benefits on cardiovascular health. There is also evidence, although limited, to suggest benefits of green tea (flavonoids) on body weight and body fatness. Data supporting reduced oxidative damage, inflammation, platelet activation, blood pressure, and risk of type 2 diabetes with tea (flavonoids) remains inadequate to draw any conclusions.

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.

Using isoprostanes as biomarkers of oxidative stress: some rarely considered issues

The measurement of F2-isoprostanes by methods utilizing mass spectrometry is widely regarded as the best currently available biomarker of lipid peroxidation. F2-isoprostanes and their metabolites can be measured accurately in plasma, urine, and other body fluids using mass spectrometric techniques, and detailed protocols have been published in several papers. However, many clinical studies and intervention studies with diets or supplements, have employed single "spot" measurements of F2-isoprostanes on either plasma/serum or urine to estimate "oxidative stress." This review examines the validity of the common assumption that plasma and urinary F2-isoprostane measurements are equivalent. It identifies scenarios where they may not be and where "spot" measurements can be misleading, with examples from the literature. We also discuss the controversial issue of whether and how F2-isoprostane levels in plasma should be standardized against lipids, and, if so, which lipids to use.

Specific Dietary Polyphenols Attenuate Atherosclerosis in Apolipoprotein E–Knockout Mice by Alleviating Inflammation and Endothelial Dysfunction

Objective— Animal and clinical studies have suggested that polyphenols in fruits, red wine, and tea may delay the development of atherosclerosis through their antioxidant and anti-inflammatory properties. We investigated whether individual dietary polyphenols representing different polyphenolic classes, namely quercetin (flavonol), (−)-epicatechin (flavan-3-ol), theaflavin (dimeric catechin), sesamin (lignan), or chlorogenic acid (phenolic acid), reduce atherosclerotic lesion formation in the apolipoprotein E (ApoE) −/− gene–knockout mouse.

Methods and Results— Quercetin and theaflavin (64-mg/kg body mass daily) significantly attenuated atherosclerotic lesion size in the aortic sinus and thoracic aorta ( P <0.05 versus ApoE −/− control mice). Quercetin significantly reduced aortic F 2 -isoprostane, vascular superoxide, vascular leukotriene B 4 , and plasma-sP-selectin concentrations; and augmented vascular endothelial NO synthase activity, heme oxygenase-1 protein, and urinary nitrate excretion ( P <0.05 versus control ApoE −/− mice). Theaflavin showed similar, although less extensive, significant effects. Although (−)-epicatechin significantly reduced F 2 -isoprostane, superoxide, and endothelin-1 production ( P <0.05 versus control ApoE −/− mice), it had no significant effect on lesion size. Sesamin and chlorogenic acid treatments exerted no significant effects. Quercetin, but not (−)-epicatechin, significantly increased the expression of heme oxygenase-1 protein in lesions versus ApoE −/− controls.

Conclusion— Specific dietary polyphenols, in particular quercetin and theaflavin, may attenuate atherosclerosis in ApoE −/− gene–knockout mice by alleviating inflammation, improving NO bioavailability, and inducing heme oxygenase-1. These data suggest that the cardiovascular protection associated with diets rich in fruits, vegetables, and some beverages may in part be the result of flavonoids, such as quercetin.

Symposium on Plant Polyphenols: Nutrition, Health and Innovations, June 2009

Reported here is a summary of the proceedings of the Symposium on Plant Polyphenols: Nutrition, Health and Innovations, which was cosponsored by the Southeast Asia Region branch of the International Life Sciences Institute and the Nutrition Society of Malaysia in Kuala Lumpur, Malaysia, June 22-23, 2009. The symposium provided a timely update of research regarding the protective effects of polyphenols in chronic diseases, such as cardiovascular disease and cancer, as well as the development of innovative polyphenol-containing food products with enhanced nutritive and health properties. Presentations covered polyphenols from a wide range of food sources such as tea, coffee, nuts and seeds, cocoa and chocolate, soy, and Asian fruits, vegetables, and spices. The symposium was attended by a large and diverse group of nutritionists, dietitians, researchers and allied health professionals, as well as management, research and development, and marketing personnel from the food and beverage industry. Their enthusiastic participation was a testament to the increasing awareness and interest in polyphenols in the prevention and control of chronic diseases. Presented here are some of the highlights and important information from the symposium.

Dietary flavonol intake may lower stroke risk in men and women

Flavonols are strong antioxidants in plant foods and tea is a major dietary source. There is evidence from prospective cohort studies that tea and flavonols are inversely related to stroke incidence. We conducted a metaanalysis of prospective cohort studies to assess quantitatively the strength of the association between flavonol intake and stroke incidence. Prospective cohort studies with data from individuals free of cardiovascular diseases (CVD) or stroke at baseline were included in the metaanalysis. Persons were followed for between 6 and 28 y. Data from 6 cohorts involving 111,067 persons with at least 2155 nonfatal and fatal cases were pooled. A random effects model was used. In all studies included, adjustments were made for major CVD risk factors except for 2 that did not adjust for alcohol and energy intake. A high intake of flavonols compared with a low intake was inversely associated with nonfatal and fatal stroke with a pooled relative risk of 0.80 (95% CI: 0.65, 0.98). Visual inspection of Begg's funnel plot and Egger's test (P = 0.01) indicated potential publication bias. We conclude that flavonols may reduce stroke risk.

Quercetin: A Treatment for Hypertension?-A Review of Efficacy and Mechanisms

Quercetin is a polyphenolic flavonoid. Common sources in the diet are apples, onions, berries, and red wine. Epidemiological studies have found an inverse relationship between dietary quercetin intake and cardiovascular disease. This has led to in vitro, in vivo, and clinical research to determine the mechanism by which quercetin exerts cardio-protective effects. Recent studies have found a reduction in blood pressure when hypertensive (>140 mm Hg systolic and >90 mm Hg diastolic) animals and humans are supplemented with quercetin. Proposed mechanisms for the antihypertensive effect of quercetin include decreased oxidative stress, inhibition of angiotensin converting enzyme activity, improved endothelial function, direct action on the vascular smooth muscle, and/or modulation in cell signaling and gene expression. Although in vitro and in vivo evidence exists to support and refute each possibility, it is likely that quercetin influences multiple targets via a combination of known and as yet undiscovered mechanisms. The purpose of this review is to examine the mechanisms whereby quercetin might reduce blood pressure in hypertensive individuals.